USRE40774E1 - Positioning device with a vibration-free object table, and lithographic device provided with such a positioning device - Google Patents

Abstract

A positioning device with a drive unit with which an object table is displaceable over a guide which is fastened to a first frame thereof. A stationary part of the drive unit is fastened to a second frame thereof and dynamically isolated from the first frame while a reaction force of the object table arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame.

Description

BACKGROUND OF THE INVENTIONFIELD OF THE INVENTION

The invention relates to a positioning device with an object table and a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame.

The invention further relates to a lithographic device with a machine frame which, seen parallel to a vertical Z-direction, supports in that order a radiation source, a mask holder, a focusing system with a main axis directed parallel to the Z-direction, and a substrate holder which is displaceable perpendicularly to the Z-direction by means of a positioning device.

The invention also relates to a lithographic device with a machine frame which, seen parallel to a vertical Z-direction, supports in that order a radiation source, a mask holder which is displaceable perpendicularly to the Z-direction by means of a positioning device, a focusing system with a main axis directed parallel to the Z-direction, and a substrate holder which is displaceable perpendicularly to the Z-direction by means of a further positioning device.

A positioning device of the kind mentioned in the opening paragraph is known from U.S. Pat. No. 5,260,580. The known positioning device comprises an object table which is supported by and guided over a stationary base which in its turn is supported by a first frame. The known positioning device comprises a drive unit for displacing the object table over the stationary base. The drive unit has a first linear motor of which a stationary part is supported by the stationary base and a second linear motor of which a stationary part is supported by a second frame. The second frame is dynamically isolated from the first frame, so that mechanical forces and vibrations present in the second frame cannot be transmitted to the first frame. The object table of the known positioning device is displaceable during operation by means of the second linear motor into a position which lies close to a desired end position, whereupon it can be moved into the desired end position by the first linear motor. The displacement of the object table by the second linear motor is usually a comparatively great, speed-controlled displacement during which the second linear motor exerts a comparatively great driving force on the object table. The subsequent displacement of the object table by the first linear motor is a comparatively small, position-controlled displacement during which the first linear motor exerts a comparatively small driving force on the object table. Since the stationary part of the second linear motor is supported by the second frame which is dynamically isolated from the first frame, it is prevented that a comparatively great reaction force exerted by the object table on the second linear motor and arising from the driving force exerted by the second linear motor on the object table, as well as mechanical vibrations caused by the reaction force in the second frame are transmitted into the first frame, the stationary base, and the object table. The fact that the stationary base and the object table of the known positioning device thus remain free from the comparatively strong mechanical vibrations caused by the second linear motor means that the object table is displaceable into the desired end position in a quick and accurate manner by means of the first linear motor.

A disadvantage of the known positioning device is that the stationary part of the first linear motor is supported by the stationary base over which the object table is guided. As a result, a reaction force exerted by the object table on the first linear motor and arising from the driving force exerted by the first linear motor on the object table is transmitted into the stationary base and the first frame. The displacement of the object table by means of the first linear motor is comparatively small, it is true, so that the value of said reaction force is comparatively low, but said reaction force has a comparatively high frequency. The frequency of said reaction force is comparable to a material frequency which is characteristic of a usual frame, such as the first frame of the known positioning device, in particular if the displacement of the object table into the desired end position is to take place within a comparatively short time span. Under such circumstances the reaction force of the first linear motor will cause the first frame to resonate, whereby comparatively strong mechanical vibrations arise in the first frame, the stationary base, and the object table, which detract from the positioning accuracy of the first linear motor and lengthen the time required for reaching the desired end position.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a positioning device of the kind mentioned in the opening paragraph with which the above disadvantage is prevented as much as possible.

The invention is for this purpose characterized in that a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame. Since said reaction force can be transmitted exclusively into the second frame, mechanical vibrations are caused in the second frame only by the reaction force. Since the second frame is dynamically isolated from the first frame, the mechanical vibrations caused in the second frame by the reaction force are not transmitted into the first frame, so that the first frame, the guide, and the object table remain free from mechanical vibrations caused by said reaction force. It is prevented thereby that the first frame is brought into resonance by comparatively high-frequency components of said reaction force which arise when the object table is accurately brought into the desired end position by the drive unit. The fact that the first frame remains free from mechanical vibrations caused by the reaction force implies not only that the positioning accuracy and the time required for positioning are improved owing to the absence of mechanical vibrations in the first frame, but also that the required time is further reduced because comparatively high frequencies of the driving force are admissible during positioning of the object table into the desired end position.

A special embodiment of a positioning device according to the invention is characterized in that the object table is coupled to the stationary part of the drive unit exclusively by a Lorentz force of a magnet system and an electric coil system of the drive unit during operation. Since the object table is coupled to the stationary part of the drive unit exclusively by said Lorentz force, the object table is physically decoupled from the stationary part of the drive unit, i.e. there is no physical contact or physical coupling between the object table and the stationary part of the drive unit. In the present embodiment, said Lorentz force comprises the driving force exerted by the drive unit on the object table. Since the object table is physically decoupled from the stationary part of the drive unit, it is prevented that mechanical vibrations caused in the stationary part of the drive unit by the reaction force arising from the Lorentz force are transmitted via the drive unit to the object table and the first frame.

A further embodiment of a positioning device according to the invention is characterized in that the magnet system and the electric coil system belong to a first linear motor of the drive unit, which drive unit comprises a second linear motor with a stationary part fastened to the second frame and a movable part which is displaceable parallel to the X-direction over a guide of the stationary part, the magnet system of the first linear motor being fastened to the object table and the electric coil system of the first linear motor being fastened to the movable part of the second linear motor. In this further embodiment, the object table is displaceable into a position close to a desired end position over a comparatively great distance parallel to the X-direction by means of the second linear motor, the object table being held in a substantially constant position relative to the movable part of the second linear motor during this by means of a Lorentz force of the first linear motor suitable for this purpose. After this, the object table is displaceable by means of the first linear motor into the desired end position, the movable part of the second linear motor being in a constant position relative to the stationary part during this. Since the object table need be displaced over comparatively small distances only during its positioning into the end position by means of the first linear motor, the magnet system and the electric coil system of the first linear motor need have only comparatively small dimensions. A reaction force on the stationary part of the second linear motor arising from a driving force exerted by the second linear motor is directly transmitted into the second frame. A reaction force on the electric coil system of the first linear motor arising from a Lorentz force exerted by the first linear motor is transmitted into the second frame via the movable part, the guide, and the stationary part of the second linear motor.

A yet further embodiment of a positioning device according to the invention is characterized in that the drive unit comprises a third linear motor with a stationary part which is fastened to the movable part of the second linear motor, and with a movable part which is displaceable parallel to a Y-direction which is perpendicular to the X-direction over a guide of the stationary part of the third linear motor, the electric coil system of the first linear motor being fastened to the movable part of the third linear motor. In this embodiment of the positioning device, the object table is displaceable parallel to the X- and Y-directions, while the guide for the object table is, for example, a surface which extends parallel to the X-direction and the Y-direction. The object table can be displaced over comparatively great distances parallel to the X-direction and the Y-direction into a position close to a desired end position by means of the second and third linear motors, respectively, whereupon it can be positioned in the desired end position by means of the first linear motor. It can be achieved through a suitable design of the magnet system and electric coil system of the first linear motor that the object table is displaceable over comparatively small distances parallel to the X-direction and the Y-direction by means of the first linear motor. A reaction force on the stationary part of the second motor arising from a driving force exerted by the second linear motor is transmitted directly to the second frame, while a reaction force on the stationary part of the third motor arising from a driving force exerted by the third linear motor is transmitted to the second frame via the movable part, the guide, and the stationary part of the second linear motor. A reaction force on the electric coil system of the first linear motor arising from a Lorentz force exerted by the first linear motor is transmitted to the second frame via the movable parts, the guides, and the stationary parts of the third and second linear motors in that order.

A particular embodiment of a positioning device according to the invention is characterized in that the positioning device is provided with a force actuator system controlled by an electric control unit and exerting a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity. The object table rests on the guide of the first frame with a support force which is determined by the force of gravity acting on the object table. When the object table is displaced, a point of application of said support force on the guide is also displaced relative to the first frame. The use of said force actuator system prevents the first frame from vibrating or shaking as a result of comparatively great or quick displacements of the object table and said point of application relative to the first frame. The control unit controls the compensation force of the force actuator system as a function of the position of the object table relative to the first frame. Owing to said compensation force, the displaceable object table has a so-called virtual centre of gravity which has a constant position relative to the first frame. In this embodiment of the positioning device, therefore, the first frame is not only free from mechanical vibrations caused by reaction forces of the drive unit of the object table, but also remains free from mechanical vibrations caused by displacements of the actual centre of gravity of the object table relative to the first frame. The positioning accuracy of the positioning device and the time required for a displacement of the object table into a desired end position are further improved in this manner.

A further embodiment of a positioning device according to the invention is characterized in that the object table is displaceable parallel to a horizontal direction, while the force actuator system exerts the compensation force on the first frame parallel to a vertical direction. Since the force actuator system exerts the compensation force on the first frame parallel to the vertical direction, the force actuator system does not exert forces on the first frame in a drive direction of the object table, so that no additional measures are necessary for preventing mechanical vibrations in the first frame directed parallel to the drive direction in addition to the measures taken in relation to the reaction forces of the drive unit of the object table. Vertical vibrations of the first frame are prevented in that a value of the compensation force of the force actuator system is kept constant and in that exclusively the point of application of the compensation force on the first frame is displaced as a function of the position of the object table. The displacement of the point of application of the compensation force of the force actuator system is achieved, for example, through the use of a force actuator system with at least two separate force actuators wherein the compensation forces of the force actuators are individually controlled as a function of the position of the object table, a sum of the compensation forces of the separate force actuators being kept constant.

A still further embodiment of a positioning device according to the invention is characterized in that the object table is displaceable parallel to a horizontal X-direction and parallel to a horizontal Y-direction which is perpendicular to the X-direction, triangle and each exerting a compensation force on the first frame parallel to the vertical direction. The use of the force actuator system with the three force actuators mutually arranged in a triangle not only prevents mechanical vibrations of the first frame arising from a displacement of the object table parallel to the X-direction, but also prevents mechanical vibrations of the first frame arising from a displacement of the object table parallel to the Y-direction. The sum of the compensation forces of the individual force actuators is kept constant continually during operation, so that no vertical vibrations of the first frame are caused. The triangular arrangement of the force actuators in addition provides a particularly stable operation of the force actuator system.

A special embodiment of a positioning device according to the invention is characterized in that the force actuator system is integrated with a system of dynamic isolators by means of which the first frame is coupled to a base of the positioning device. The dynamic isolators are, for example, dampers with a comparatively low mechanical stiffness by means of which the first frame is dynamically isolated from said base. Owing to the comparatively low mechanical stiffness of the dampers, mechanical vibrations present in the base such as, for example, floor vibrations or vibrations of the second frame if the latter is fastened, for example, on the base, are not transmitted into the first frame. The integration of the force actuator system with the system of dynamic isolators provides a particularly compact and simple construction of the positioning device.

A further embodiment of a positioning device according to the invention is characterized in that the compensation force comprises exclusively a Lorentz force of a magnet system and an electric coil system of the force actuator system. The force actuator system comprises a part which is fastened to the first frame and a part which is fastened to a base of the positioning device. Since the compensation force of the force actuator system comprises exclusively a Lorentz force, said parts of the force actuator system are physically decoupled, i.e. there is no physical contact or physical coupling between said parts. It is prevented thereby that mechanical vibrations present in the base of the positioning device such as, for example, floor vibrations or vibrations of the second frame, if the latter is fastened, for example, on the base, are transmitted into the first frame and the object table via the force actuator system.

A lithographic device with a displaceable substrate holder of the kind mentioned in the opening paragraphs is known from EP-A-0 498 496. The known lithographic device is used in the manufacture of integrated semiconductor circuits by means of an optical lithographic process. The radiation source of the known lithographic device is a light source, while the focusing system is an optical lens system by means of which a partial pattern of an integrated semiconductor circuit, which pattern is present on a mask which can be placed on the mask holder of the lithographic device, is imaged on a reduced scale on a semiconductor substrate which can be placed on the substrate holder of the lithographic device. Such a semiconductor substrate comprises a large number of fields on which identical semiconductor circuits are provided. The individual fields of the semiconductor substrate are consecutively exposed for this purpose, the semiconductor substrate being in a constant position relative to the mask and the focusing system during the exposure of an individual field, while between two consecutive exposure steps a next field of the semiconductor substrate is brought into position relative to the focusing system by means of the positioning device of the substrate holder. This process is repeated a number of times, each time with a different mask with a different partial pattern, so that integrated semiconductor circuits of comparatively complicated structure can be manufactured. The structures of such integrated semiconductor circuits have detail dimensions which lie in the sub-micron range. The partial patterns present on the consecutive masks should accordingly be imaged on said fields of the semiconductor substrate with an accuracy relative to one another which lies in the sub-micron range. The semiconductor substrate should accordingly be positioned relative to the mask and the focusing system by means of the positioning device of the substrate holder with an accuracy also in the sub-micron range. To reduce the time required for the manufacture of the semiconductor circuits, moreover, the semiconductor substrate should be displaced with a comparatively high speed between two consecutive exposure steps and should be positioned relative to the mask and the focusing system with the desired accuracy.

According to the invention, the lithographic device with the displaceable substrate holder is characterized in that the positioning device of the substrate holder is a positioning device according to the invention, wherein the first frame of the positioning device of the substrate holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the substrate holder belongs to a force frame of the lithographic device which is dynamically isolated from the machine frame. Comparatively great reaction forces exerted by the substrate holder on the positioning device during comparatively quick displacements between two exposure steps are thus transmitted to the force frame of the lithographic device, so that the machine frame of the lithographic device, which supports the mask holder, the focusing system and the substrate holder, remains free from mechanical vibrations caused by said reaction forces in the force frame. The accuracy with which the substrate holder can be positioned relative to the mask holder and the focusing system, and the time required for positioning the substrate holder with the desired accuracy are thus not adversely affected by said mechanical vibrations.

A lithographic device with a displaceable substrate holder and a displaceable mask holder of the kind mentioned in the opening paragraphs is known from U.S. Pat. No. 5,194,893. In this known lithographic device, the semiconductor substrate under manufacture is not in a constant position relative to the mask and the focusing system during the exposure of a single field of the semiconductor substrate, but instead the semiconductor substrate and the mask are synchronously displaced relative to the focusing system parallel to an X-direction which is perpendicular to the Z-direction by means of the positioning device of the substrate holder and the positioning device of the mask holder, respectively, during exposure. In this manner the pattern present on the mask is scanned parallel to the X-direction and synchronously imaged on the semiconductor substrate. It is achieved thereby that a maximum surface area of the mask which can be imaged on the semiconductor substrate by means of the focusing system is limited to a lesser degree by a size of an aperture of the focusing system. Since the detail dimensions of the integrated semiconductor circuits to be manufactured lie in the sub-micron range, the semiconductor substrate and the mask should be displaced with an accuracy also in the sub-micron range relative to the focusing system during the exposure. To reduce the time required for the manufacture of the semiconductor circuits, the semiconductor substrate and the mask should in addition be displaced and positioned relative to one another with a comparatively high speed during exposure. Since the pattern present on the mask is imaged on a reduced scale on the semiconductor substrate, the speed with which and the distance over which the mask is displaced are greater than the speed with which and the distance over which the semiconductor substrate is displaced, the ratio between said speeds and the ratio between said distances both being equal to a reduction factor of the focusing system.

According to the invention, the lithographic device with the displaceable substrate holder and displaceable mask holder is characterized in that the positioning device of the mask holder is a positioning device according to the invention, wherein the first frame of the positioning device of the mask holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the mask holder belongs to a force frame of the lithographic device which is dynamically isolated from the machine frame.

A special embodiment of a lithographic device with a displaceable substrate holder according to the invention is characterized in that the mask holder is displaceable perpendicularly to the Z-direction by means of a positioning device according to the invention, wherein the first frame of the positioning device of the mask holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the mask holder belongs to the force frame of the lithographic device.

Comparatively great reaction forces exerted on the positioning device of the mask holder by the mask holder as a result of the comparatively high speeds and acceleration of the mask holder during the exposure of the semiconductor substrate are thus transmitted to the force frame of the lithographic device. The lithographic device's machine frame, which supports the mask holder, the focusing system, and the substrate holder, thus remains free from mechanical vibrations caused by said reaction forces in the force frame. The accuracy with which the substrate holder and the mask holder are displaceable relative to the focusing system during the exposure of the semiconductor substrate is accordingly not adversely affected by said mechanical vibrations.

A further embodiment of a lithographic device according to the invention is characterized in that the positioning devices of the substrate holder and the mask holder have a joint force actuator system which is controlled by an electric control unit and which exerts a compensation force on the machine frame of the lithographic device during operation which has a mechanical moment about a reference point of the machine frame of a value which is equal to a value of a sum of a mechanical moment of a force of gravity acting on the substrate holder about said reference point and a mechanical moment of a force of gravity acting on the mask holder about said reference point, and a direction which is opposed to a direction of said sum of mechanical moments. The use of the joint force actuator system prevents the machine frame of the lithographic device from vibrating or shaking as a result of the comparatively quick displacements of both the mask holder and the substrate holder relative to the machine frame during the exposure of the semiconductor substrate. The control unit controls the compensation force of the joint force actuator system as a function of the position of the mask holder and the position of the substrate holder relative to the machine frame. It is prevented thereby that the accuracy with which the mask holder and the substrate holder can be positioned relative to the focusing system during the exposure of the semiconductor substrate is adversely affected by mechanical vibrations caused by displacements of the centres of gravity of the mask holder and the substrate holder relative to the machine frame.

A yet further embodiment of a lithographic device according to the invention is characterized in that the machine frame is placed on a base of the lithographic device, on which also the force frame is placed, by means of three dynamic isolators mutually arranged in a triangle, while the joint force actuator system comprises three separate force actuators which are each integrated with a corresponding one of the dynamic isolators. The dynamic isolators are, for example, dampers with a comparatively low mechanical stiffness by means of which the machine frame is dynamically isolated from said base. Owing to the comparatively low mechanical stiffness of the dampers, mechanical vibrations present in the base such as, for example, mechanical vibrations in the force frame caused by reaction forcers of the positioning devices of the mask holder and the substrate holder are not transmitted to the machine frame. The integration of the force actuator system with the system of dynamic isolators provides a particularly compact and simple construction of the lithographic device. The triangular arrangement of the isolators in addition provides a particularly stable support for the machine frame.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to the drawings, in which

FIG. 1 shows a lithographic device according to the invention,

FIG. 2 is a diagram of the lithographic device ofFIG. 1,

FIG. 3 shows a base and a substrate holder of the lithographic device ofFIG. 1,

FIG. 4 is a plan view of the base and the substrate holder of the lithographic device ofFIG. 3,

FIG. 5 is a plan view of a mask holder of the lithographic device ofFIG. 1,

FIG. 6 is a cross-section taken on the line VI—VI inFIG. 5,

FIG. 7 is a cross-section of a dynamic isolator of the lithographic device ofFIG. 1,

FIG. 8 is a cross-section taken on the line VIII—VIII inFIG. 7, and

FIG. 9 diagrammatically shows a force actuator system of the lithographic device of FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED

The lithographic device according to the invention shown inFIGS. 1 and 2 is used for the manufacture of integrated semiconductor circuits by an optical lithographic process. AsFIG. 2 shows diagrammatically, the lithographic device is consecutively provided, seen parallel to a vertical Z-direction, with asubstrate holder1, a focusing system3, amask holder5, and a radiation source7. The lithographic device shown inFIGS. 1 and 2 is an optical lithographic device in which the radiation source7 comprises a light source9, a diaphragm11, and mirrors13 and15. Thesubstrate holder1 comprises asupport surface17 which extends perpendicularly to the Z-direction and on which a semiconductor substrate19 can be placed, while it is displaceable relative to the focusing system3 parallel to an X-direction perpendicular to the Z-direction and parallel to a Y-direction which is perpendicular to the X-direction and the Z-direction by means of afirst positioning device21 of the lithographic device. The focusing system3 is an imaging or projection system and comprises a system of optical lenses23 with an opticalmain axis25 which is parallel to the Z-direction and an optical reduction factor which is, for example,4 or5. Themask holder5 comprises asupport surface27 which is perpendicular to the Z-direction and on which amask29 can be placed, while it is displaceable parallel to the X-direction relative to the focusing system3 by means of asecond positioning device31 of the lithographic device. Themask29 comprises a pattern or partial pattern of an integrated semiconductor circuit. During operation, alight beam33 originating from the light source9 is passed through themask29 via the diaphragm11 and themirrors13,15 and is focused on the semiconductor substrate19 by means of the lens system23, so that the pattern present on themask29 is imaged on a reduced scale on the semiconductor substrate19. The semiconductor substrate19 comprises a large number ofindividual fields35 on which identical semiconductor circuits are provided. For this purpose, thefields35 of the semiconductor substrate19 are consecutively exposed through themask29, anext field35 being positioned relative to the focusing system3 each time after the exposure of anindividual field35 in that thesubstrate holder1 is moved parallel to the X-direction or the Y-direction by means of thefirst positioning device21. This process is repeated a number of times, each time with a different mask, so that comparatively complicated integrated semiconductor circuits with a layered structure are manufactured.

AsFIG. 2 shows, the semiconductor substrate19 and themask29 are synchronously displaced relative to the focusing system3 parallel to the X-direction by the first and thesecond positioning device21,31 during the exposure of anindividual field35. The pattern present on themask29 is then scanned parallel to the X-direction and synchronously imaged on the semiconductor substrate19. In this way, as is clarified inFIG. 2, exclusively a maximum width B of themask29 directed parallel to the Y-direction which can be imaged on the semiconductor substrate19 by the focusing system3 is limited by a diameter D of anaperture37 of the focusing system3 diagrammatically depicted in FIG.2. An admissible length L of themask29 which can be imaged on the semiconductor substrate19 by the focusing system3 is greater than said diameter D. In this imaging method, which follows the so-called “step and scan” principle, a maximum surface area of themask29 which can be imaged on the semiconductor substrate19 by the focusing system3 is limited by the diameter D of theaperture37 of the focusing system3 to a lower degree than in a conventional imaging method which follows the so-called “step and repeat” principle, which is used, for example, in a lithographic device known from EP-A-0 498 496, where the mask and the semiconductor substrate are in fixed positions relative to the focusing system during exposure of the semiconductor substrate. Since the pattern present on themask29 is imaged on a reduced scale on the semiconductor substrate19, said length L and width B of themask29 are greater than a corresponding length L′ and width B′ of thefields35 on the semiconductor substrate19, a ratio between the lengths L and L′ and between the widths B and B′ being equal to the optical reduction factor of the focusing system3. As a result also, a ratio between a distance over which themask29 is displaced during exposure and a distance over which the semiconductor substrate19 is displaced during exposure, and a ratio between a speed with which themask29 is displaced during exposure and a speed with which the semiconductor substrate19 is displaced during exposure are both equal to the optical reduction factor of the focusing system3. In the lithographic device shown inFIG. 2, the directions in which the semiconductor substrate19 and themask29 are displaced during exposure are mutually opposed. It is noted that said directions may also be the same if the lithographic device comprises a different focusing system by which the mask pattern is not imaged in reverse.

The integrated semiconductor circuits to be manufactured with the lithographic device have a structure with detail dimensions in the sub-micron range. Since the semiconductor substrate19 is exposed consecutively through a number of different masks, the pattern present on the masks must be imaged on the semiconductor substrate19 relative to one another with an accuracy which is also in the sub-micron range, or even in the nanometer range. During exposure of the semiconductor substrate19, the semiconductor substrate19 and themask29 should accordingly be displaced relative to the focusing system3 with such an accuracy, so that comparatively high requirements are imposed on the positioning accuracy of the first and thesecond positioning device21,31.

AsFIG. 1 shows, the lithographic device has a base39 which can be placed on a horizontal floor surface. The base39 forms part of aforce frame41 to which further a vertical, comparativelystiff metal column43 belongs which is fastened to thebase39. The lithographic device further comprises amachine frame45 with a triangular, comparatively stiff metalmain plate47 which extends transversely to the opticalmain axis25 of the focusing system3 and is provided with a central light passage opening not visible in FIG.1. Themain plate47 has threecorner portions49 with which it rests on threedynamic isolators51 which are fastened on thebase49 and which will be described further below. Only twocorner portions49 of themain plate47 and twodynamic isolators51 are visible inFIG. 1, while all threedynamic isolators51 are visible inFIGS. 3 and 4. The focusing system3 is provided near a lower side with a mounting ring53 by means of which the focusing system3 is fastened to themain plate47. Themachine frame45 also comprises a vertical, comparativelystiff metal column55 fastened on themain plate47. Near an upper side of the focusing system3 there is furthermore asupport member57 for themask holder5, which member also belongs to themachine frame45, is fastened to thecolumn55 of themachine frame45, and will be explained further below. Also belonging to themachine frame45 are threevertical suspension plates59 fastened to a lower side of themain plate47 adjacent the threerespective corner portions49. Only twosuspension plates59 are partly visible inFIG. 1, while all threesuspension plates59 are visible inFIGS. 3 and 4. AsFIG. 4 shows, ahorizontal support plate61 for thesubstrate holder1 also belonging to themachine frame45 is fastened to the threesuspension plates59. Thesupport plate61 is not visible in FIG.1 and only partly visible in FIG.3.

It is apparent from the above that themachine frame45 supports the main components of the lithographic device, i.e. thesubstrate holder1, the focusing system3, and themask holder5 parallel to the vertical Z-direction. As will be further explained below, thedynamic isolators51 have a comparatively low mechanical stiffness. It is achieved thereby that mechanical vibrations present in the base39 such as, for example, floor vibrations are not transmitted into themachine frame45 via thedynamic isolators51. Thepositioning devices21,31 as a result have a positioning accuracy which is not adversely affected by the mechanical vibrations present in thebase39. The function of theforce frame41 will be explained in more detail further below.

AsFIGS. 1 and 5 show, themask holder5 comprises ablock63 on which saidsupport surface27 is present. Thesupport member57 for themask holder5 belonging to themachine frame45 comprises a central light passage opening64 visible in FIG.5 and two plane guides65 which extend parallel to the X-direction and which lie in a common plane which is perpendicular to the Z-direction. Theblock63 of the mask holder S is guided over the plane guides65 of thesupport member57 by means of an aerostatic bearing (not visible in the Figures) with freedoms of movement parallel to the X-direction and parallel to the Y-direction, and a freedom of rotation about an axis ofrotation67 of themask holder5 which is directed parallel to the Z-direction.

AsFIGS. 1 and 5 further show, thesecond positioning device31 by which themask holder5 is displaceable comprises a firstlinear motor69 and a secondlinear motor71. The secondlinear motor71, which is of a kind usual and known per se, comprises astationary part73 which is fastened to thecolumn43 of theforce frame41. Thestationary part73 comprises aguide75 which extends parallel to the X-direction and along which amovable part77 of the secondlinear motor71 is displaceable. Themovable part77 comprises aconnection arm79 which extends parallel to the Y-direction and to which anelectric coil holder81 of the firstlinear motor69 is fastened. A permanent-magnet holder83 of the firstlinear motor69 is fastened to theblock63 of themask holder5. The firstlinear motor69 is a kind known from EP-B-0 421 527. AsFIG. 5 shows, thecoil holder81 of the firstlinear motor69 comprises fourelectric coils85,87,89,91 which extend parallel to the Y-direction, and anelectric coil93 which extends parallel to the X-direction. Thecoils85,87,89,91,93 are diagrammatically indicated with broken lines in FIG.5. Themagnet holder83 comprises ten pairs of permanent magnets (95a,95b), (97a,97b), (99a,99b), (101a,101b), (103a,103b), (105a,105b), (107a,107b), (109a,109b), (111a,111b), (113a,113b), indicated with dash-dot lines in FIG.5. Theelectric coil85 and thepermanent magnets95a,95b,97a and97b belong to afirst X-motor115 of the firstlinear motor69, while thecoil87 and themagnets99a,99b,101a and101b belong to asecond X-motor117 of the firstlinear motor69, thecoil89 and themagnets103a,103b,105a and105b belong to a third X-motor119 of the firstlinear motor69, thecoil91 and themagnets107a,107b,109a and109b belong to afourth X-motor121 of the firstlinear motor69, and thecoil93 and themagnets111a,111b,113a and113b belong to a Y-motor123 of the firstlinear motor69.FIG. 6 is a cross-sectional view of the first X-motor115 and thesecond X-motor117. AsFIG. 6 shows, thecoil holder81 is arranged between afirst part125 of themagnet holder83 which comprises themagnets95a,97a,99a,101a,103a,105a,107a,109a,111a and113a, and asecond part127 of the magnet holder which comprises themagnets95b,97b,99b,101b,103b,105b,107b,109b,111b and113b. AsFIG. 6 further shows, themagnet pair95a,95b of the first X-motor115 and themagnet pair99a,99b of the second X-motor117 are magnetized parallel to a positive Z-direction, while themagnet pair97a,97b of the first X-motor115 and themagnet pair101a,101b of the second X-motor117 are magnetized parallel to an opposed, negative Z-direction. Thus also themagnet pair103a,103b of the third X-motor119, themagnet pair107a,107b of the fourth X-motor121, and themagnet pair111a,111b of the Y-motor123 are magnetized parallel to the positive Z-direction, whereas themagnet pair105a,105b of the third X-motor119, themagnet pair109a,109b of the fourth X-motor121, and themagnet pair113a,113b of the Y-motor123 are magnetized parallel to the negative Z-direction. AsFIG. 6 further shows, themagnets95a and97a of the first X-motor115 are interconnected by amagnetic closing yoke129, while themagnets95b and97b, themagnets99a and101a, and themagnets99b and101b are interconnected by means of amagnetic closing yoke131, amagnetic closing yoke133, and amagnetic closing yoke135, respectively. The third X-motor119, the fourth X-motor121, and the Y-motor123 are provided with similar magnetic closing yokes. When during operation an electric current flows through thecoils85,87,89,91 of theX-motors115,117,119,121, the magnets and coils of theX-motors115,117,119,121 mutually exert a Lorentz force directed parallel to the X-direction. If the electric currents through thecoils85,87,89,91 are of equal value and direction, themask holder5 is displaced parallel to the X-direction by said Lorentz force, whereas themask holder5 is rotated about the axis ofrotation67 if the electric currents through thecoils85,87 are of equal values as, but have a direction opposed to the electric currents through thecoils89,91. The magnets and the coil of the Y-motor123 mutually exert a Lorentz force directed parallel to the Y-direction as a result of an electric current through thecoil93 of the Y-motor123, whereby the mask holder is displaced parallel to the Y-direction.

During exposure of the semiconductor substrate19, themask holder5 should be displaced relative to the focusing system3 parallel to the X-direction over a comparatively great distance and with a high positioning accuracy. To achieve this, thecoil holder81 of the firstlinear motor69 is displaced parallel to the X-direction by means of the secondlinear motor71, a desired displacement of themask holder5 being approximately achieved by the secondlinear motor71, and themask holder5 being carried along relative to themovable part77 of the secondlinear motor71 by a suitable Lorentz force of theX-motors115,117,119,121 of the firstlinear motor69. Said desired displacement of themask holder5 relative to the focusing system3 is achieved in that the Lorentz force of theX-motors115,117,119,121 is controlled by means of a suitable position control system during the displacement of themask holder5. The position control system, which is not shown in any detail in the Figures, comprises, for example, a laser interferometer which is usual and known per se for measuring the position of themask holder5 relative to the focusing system3, whereby the desired positioning accuracy in the sub-micron or nanometer range is achieved. During the exposure of the semiconductor substrate19, the firstlinear motor69 not only controls the displacement of themask holder5 parallel to the X-direction, but it also controls a position of themask holder5 parallel to the Y-direction and an angle of rotation of themask holder5 about the axis ofrotation67. Since themask holder5 can also be positioned parallel to the Y-direction and rotated about the axis ofrotation67 by the firstlinear motor69, the displacement of themask holder5 has a parallelism relative to the X-direction which is determined by the positioning accuracy of the firstlinear motor69. Deviations from parallelism of theguide75 of the secondlinear motor71 relative to the X-direction can thus be compensated through displacements of themask holder5 parallel to the Y-direction. Since the desired displacement of themask holder5 need be achieved approximately only by the secondlinear motor71, and no particularly high requirements are imposed on the parallelism of theguide75 relative to the X-direction, a comparatively simple, conventional, one-dimensional linear motor can be used as the secondlinear motor71, by means of which themask holder5 is displaceable over comparatively large distances with a comparatively low accuracy. The desired accuracy of the displacement of themask holder5 is achieved in that themask holder5 is displaced over comparatively small distances relative to themovable part77 of the secondlinear motor71 by means of the firstlinear motor69. The firstlinear motor69 is of comparatively small dimensions because the distances over which themask holder5 is displaced relative to themovable part77 of the secondlinear motor71 are only small. Electrical resistance losses in the electric coils of the firstlinear motor69 are minimized thereby.

As was noted above, thestationary part73 of the secondlinear motor71 is fastened to theforce frame41 of the lithographic device. It is achieved thereby that a reaction force exerted by themovable part77 of the secondlinear motor71 on thestationary part73 and arising from a driving force of the secondlinear motor71 exerted on themovable part77 is transmitted into theforce frame41. Since furthermore thecoil holder81 of the firstlinear motor69 is fastened to themovable part77 of the secondlinear motor71, a reaction force exerted by themask holder5 on themovable part77 and arising from a Lorentz force of the firstlinear motor69 exerted on themask holder5 is also transmitted into theforce frame41 via themovable part77 and thestationary part73 of the secondlinear motor71. A reaction force exerted during operation by themask holder5 on thesecond positioning device31 and arising from a driving force exerted on themask holder5 by thesecond positioning device31 is thus introduced exclusively into theforce frame41. Said reaction force has a low-frequency component resulting from the comparatively great displacements of the secondlinear motor71 as well as a high-frequency component resulting from the comparatively small displacements carried out by the firstlinear motor69 in order to achieve the desired positioning accuracy. Since theforce frame41 is comparatively stiff and is placed on a solid base, the mechanical vibrations caused by the low-frequency component of the reaction force in theforce frame41 are negligibly small. The high-frequency component of the reaction force does have a small value, but it usually has a frequency which is comparable to a resonance frequency characteristic of a type of frame such as theforce frame41 used. As a result, the high-frequency component of the reaction force causes a non-negligible high-frequency mechanical vibration in theforce frame41. Theforce frame41 is dynamically isolated from themachine frame45, i.e. mechanical vibrations having a frequency above a certain threshold value, for example 10 Hz, present in theforce frame41 are not transmitted into themachine frame45, because the latter is coupled to theforce frame41 exclusively via the low-frequencydynamic isolators51. It is achieved thereby that the high-frequency mechanical vibrations caused in theforce frame41 by the reaction forces of thesecond positioning device31 are not transmitted into themachine frame45, similar to the floor vibrations mentioned above. Since the plane guides65 of thesupport member57 extend perpendicularly to the Z-direction, and the driving forces exerted by thesecond positioning device31 on themask holder5 are also directed perpendicularly to the Z-direction, said driving forces themselves do not cause any mechanical vibrations in themachine frame45 either. Furthermore, the mechanical vibrations present in theforce frame41 cannot be transmitted into themachine frame45 through thestationary part73 and themovable part77 of the secondlinear motor71 either because, as is apparent from the above, themask holder5 is coupled to themovable part77 of the secondlinear motor71 substantially exclusively by Lorentz forces of the magnet system and the electric coil system of the firstlinear motor69, and themask holder5 is physically decoupled from themovable part77 of the secondlinear motor71, apart from said Lorentz forces. So the above discussion shows that themachine frame45 remains substantially free from mechanical vibrations and deformation caused by the driving forces and reaction forces of thesecond positioning device31. The advantages thereof will be further discussed below.

AsFIGS. 3 and 4 show, thesubstrate holder1 comprises ablock137 on which saidsupport surface17 is present, and an aerostatically supportedfoot139 which is provided with an aerostatic bearing. Thesubstrate holder1 is guided over anupper surface141, which extends perpendicularly to the Z-direction, of agranite support143 provided on thesupport plate61 of themachine frame45 by means of the aerostatically supportedfoot139, and has freedom of displacement parallel to the X-direction and parallel to the Y-direction, and a freedom of rotation about an axis ofrotation145 of thesubstrate holder1 which is directed parallel to the Z-direction.

AsFIGS. 1,3 and4 further show, thepositioning device21 of thesubstrate holder1 comprises a firstlinear motor147, a secondlinear motor149, and a thirdlinear motor151. The secondlinear motor149 and the thirdlinear motor151 of thepositioning device21 are of a kind identical to the secondlinear motor71 of thepositioning device31. The secondlinear motor149 comprises astationary part153 fastened on anarm155 which is fastened to thebase39 belonging to theforce frame41. Thestationary part153 comprises aguide157 which extends parallel to the Y-direction and along which amovable part159 of the secondlinear motor149 is displaceable. Astationary part161 of the thirdlinear motor151 is arranged on themovable part159 of the secondlinear motor149 and is provided with aguide163 which extends parallel to the X-direction and along which amovable part165 of the thirdlinear motor151 is displaceable. As is visible inFIG. 4, themovable part165 of the thirdlinear motor151 comprises acoupling piece167 to which anelectric coil holder159 of the firstlinear motor147 is fastened. The firstlinear motor147 of thefirst positioning device21 is, as is the firstlinear motor69 of thesecond positioning device31, of a kind known from EP-B-0 421 527. Since the firstlinear motor69 of thesecond positioning device31 has been described above in detail, a detailed description of the firstlinear motor147 of thefirst positioning device21 is omitted here. It is sufficient to note that thesubstrate holder1 is coupled to themovable part165 of the thirdlinear motor151 exclusively by a Lorentz force perpendicular to the Z-direction during operation. A difference between the firstlinear motor147 of thefirst positioning device21 and the firstlinear motor69 of thesecond positioning device31 is, however, that the firstlinear motor147 of thefirst positioning device21 comprises X-motors and Y-motors of comparable power ratings, whereas the single Y-motor123 of the firstlinear motor69 of thesecond positioning device31 has a power rating which is relatively low compared with power ratings of theX-motors115,117,119,121. This means that thesubstrate holder1 can not only be taken along by the firstlinear motor147 parallel to the X-direction over comparatively large distances, but also parallel to the Y-direction. Furthermore, thesubstrate holder1 is rotatable about the axis ofrotation145 by means of the firstlinear motor147.

During exposure of the semiconductor substrate19, thesubstrate holder1 should be displaced relative to the focusing system3 parallel to the X-direction with a high positioning accuracy, while thesubstrate holder1 is to be displaced parallel to the X-direction or the Y-direction when anext field35 of the semiconductor substrate19 is brought into position relative to the focusing system3 for exposure. To displace thesubstrate holder1 parallel to the X-direction, thecoil holder169 of the firstlinear motor147 is displaced parallel to the X-direction by means of the thirdlinear motor151, a desired displacement of thesubstrate holder1 being approximately achieved by the thirdlinear motor151, and thesubstrate holder1 being taken along by a suitable Lorentz force of the firstlinear motor147 relative to themovable part165 of the thirdlinear motor151. In a similar manner, a desired displacement of thesubstrate holder1 parallel to the Y-direction is approximated in that thecoil holder169 is displaced parallel to the Y-direction by means of the secondlinear motor149, thesubstrate holder1 being taken along by a suitable Lorentz force of the firstlinear motor147 relative to themovable part165 of the thirdlinear motor151. Said desired displacement of thesubstrate holder1 parallel to the X-direction or Y-direction is achieved by means of the Lorentz force of the firstlinear motor147 which is controlled during the displacement of thesubstrate holder1 by means of the position control system of the lithographic device referred to above, with which a positioning accuracy in the sub-micron or even nanometer range is achieved. Since the desired displacement of thesubstrate holder1 need be achieved by approximation only by the secondlinear motor149 and the thirdlinear motor151, and accordingly no particularly high requirements are imposed on positioning accuracy of the second and thirdlinear motors149,151, the secondlinear motor149 and the thirdlinear motor151 are, as in the secondlinear motor71 of thesecond positioning device31, comparatively simple, conventional, one-dimensional linear motors by means of which thesubstrate holder1 is displaceable with a comparatively low accuracy over comparatively large distances parallel to the Y-direction and X-direction, respectively. The desired accuracy of the displacement of thesubstrate holder1 is achieved in that thesubstrate holder1 is displaced by the firstlinear motor147 over comparatively small distances relative to themovable part165 of the thirdlinear motor151.

Since thepositioning device21 of thesubstrate holder1 is of a kind similar to thepositioning device31 of themask holder5, and thestationary part153 of the secondlinear motor149 of thefirst positioning device21 is fastened to theforce frame41 of the lithographic device, as is thestationary part73 of the secondlinear motor71 of thesecond positioning device31, it is achieved that a reaction force exerted by thesubstrate holder1 on thefirst positioning device21 during operation and arising from a driving force exerted by thefirst positioning device21 on thesubstrate holder1 is exclusively transmitted into theforce frame41. This achieves that the reaction forces of thefirst positioning device21 as well as the reaction forces of thesecond positioning device31 cause mechanical vibrations in theforce frame41, which are not transmitted into themachine frame45. Since theupper surface141 of thegranite support143 over which thesubstrate holder1 is guided extends perpendicularly to the Z-direction, furthermore, the driving forces of thefirst positioning device21, which are also perpendicular to the Z-direction, themselves do not cause any mechanical vibrations in themachine frame45 either.

The pattern present on themask29 is imaged on the semiconductor substrate19 with said accuracy because themask29 and the semiconductor substrate19 are both displaceable with said accuracy relative to the focusing system3 parallel to the X-direction by means of thesecond positioning device31 and thefirst positioning device21, respectively, during the exposure of the semiconductor substrate19, and because themask29 and the semiconductor substrate19 can in addition be positioned parallel to the Y-direction and be rotated about the respective axes ofrotation67,145 with said accuracy. The accuracy with which said pattern is imaged on the semiconductor substrate19 is even better than the positioning accuracy of thepositioning device21,31 because themask holder5 is not only displaceable parallel to the X-direction, but is also displaceable parallel to the Y-direction and rotatable about the axis ofrotation67. A displacement of themask29 relative to the focusing system3 in fact results in a shift of the pattern image on the semiconductor substrate19 which is equal to a quotient of said displacement of themask29 and the optical reduction factor of the focusing system3. The pattern of themask29 can thus be imaged on the semiconductor substrate19 with an accuracy which is equal to a quotient of the positioning accuracy of thesecond positioning device31 and the reduction factor of the focusing system3.

FIGS. 7 and 8 show one of the threedynamic isolators51 in cross-section. Thedynamic isolator51 shown comprises a mountingplate171 to which thecorner portion49 of themain plate47 of themachine frame45 resting on thedynamic isolator51 is fastened. Thedynamic isolator51 further comprises ahousing173 which is fastened on thebase39 of theforce frame41. The mountingplate171 is connected via acoupling rod175 directed parallel to the Z-direction to anintermediate plate177 which is suspended in acylindrical tub181 by means of threeparallel tension rods179. Only onetension rod179 is visible inFIG. 7, while all threetension rods179 are visible in FIG.8. Thecylindrical tub181 is positioned concentrically in acylindrical chamber183 of thehousing173. Aspace185 present between thecylindrical tub181 and thecylindrical chamber183 forms part of apneumatic spring187 and is filled with compressed air through afeed valve189. Thespace185 is sealed by means of an annular,flexible rubber membrane191 which is fastened between afirst part193 and asecond part195 of thecylindrical tub181 and between afirst part197 and asecond part199 of thehousing173. Themachine frame45 and the components of the lithographic device supported by themachine frame45 are thus supported in a direction parallel to the Z-direction by the compressed air in thespaces185 of the threedynamic isolators51, thecylindrical tub181 and accordingly also themachine frame45 having a certain freedom of movement relative to thecylindrical chamber183 as a result of the flexibility of themembrane191. Thepneumatic spring187 has a stiffness such that a mass spring system formed by the pneumatic springs187 of the threedynamic isolators51 and by themachine frame45 and the components of the lithographic device supported by themachine frame45 has a comparatively low resonance frequency such as, for example, 3 Hz. Themachine frame45 is dynamically isolated thereby from theforce frame41 as regards mechanical vibrations having a frequency above a certain threshold value such as, for example, the 10 Hz mentioned earlier. AsFIG. 7 shows, thespace185 is connected to aside chamber203 of thepneumatic spring187 via anarrow passage201. Thenarrow passage201 acts as a damper by means of which periodic movements of thecylindrical tub181 relative to thecylindrical chamber183 are damped.

AsFIGS. 7 and 8 further show, eachdynamic isolator51 comprises aforce actuator205 which is integrated with thedynamic isolator51. Theforce actuator205 comprises anelectric coil holder207 which is fastened to aninner wall209 of thehousing173. AsFIG. 7 shows, thecoil holder207 comprises an electric coil211 which extends perpendicularly to the Z-direction and is indicated in the Figure with a broken line. Thecoil holder207 is arranged between twomagnetic yokes213 and215 which are fastened to the mountingplate171. Furthermore, a pair of permanent magnets (217,219), (221,223) is fastened to eachyoke213,215, the magnets (217,219), (221,223) of a pair being magnetized in opposite directions each time perpendicular to the plane of the electric coil211. When an electric current is passed through the coil211, the coil211 and the magnets (217,219,221,223) mutually exert a Lorentz force directed parallel to the Z-direction. The value of said Lorentz force is controlled by an electric controller of the lithographic device (not shown) in a manner which will be explained in more detail further below.

Theforce actuators205 integrated with thedynamic isolators51 form a force actuator system which is diagrammatically pictured in FIG.9.FIG. 9 further diagrammatically shows themachine frame45 and thesubstrates holder1 andmask holder5 which are displaceable relative to themachine frame45, as well as thebase39 and the threedynamic isolators51.FIG. 9 further shows a reference point P of themachine frame45 relative to which a centre of gravity G_Sof thesubstrate holder1 has an X-position X_Sand a Y-position Y_S, and a centre of gravity G_Mof themask holder5 has an X-position X_Mand a Y-position Y_M. It is noted that said centres of gravity G_Sand G_Mdenote the centre of gravity of the total displaceable mass of thesubstrate holder1 with the semiconductor substrate19 and that of themask holder5 with themask29, respectively. AsFIG. 9 further shows, the Lorentz forces F_L,1, F_L,2and F_L,3of the threeforce actuators205 have points of application on themachine frame45 with an X-position X_F,1, X_F,2and X_F,3and a Y-position Y_F,1, Y_F,2and Y_F,3relative to the reference point P. Since themachine frame45 support thesubstrate holder1 and themask holder5 parallel to the vertical Z-direction, thesubstrate holder1 and themask holder5 exert a support force F_Sand a support force F_M, respectively, on themachine frame45 having a value corresponding to a value of a force of gravity acting on thesubstrate holder1 and themask holder5. The support forces F_Sand F_Mhave points of application relative to themachine frame45 with an X-position and Y-position corresponding to the X-position and Y-position of the centres of gravity G_Sand G_Mof thesubstrate holder1 and themask holder5, respectively. If thesubstrate holder1 and themask holder5 are displaced relative to themachine frame45 during exposure of the semiconductor substrate19, the points of application of the support forces F_Sand F_Mof thesubstrate holder1 and themask holder5 are also displaced relative to themachine frame45. Said electric controller of the lithographic device controls the value of the Lorentz forces F_L,1, F_L,2and F_L,3such that a sum of mechanical moments of the Lorentz forces F_L,1, F_L,2and F_L,3about the reference point P of themachine frame45 has a value which is equal to and a direction which is opposed to a value and a direction, respectively, of a sum of mechanical moments of the support forces F_Sand F_Mof thesubstrate holder1 and themask holder5 about the reference point P:
F_L,1+F_L,2+F_L,3=F_S+F_M
F_L,1*X_F,1+F_L,2*X_F,2+F_L,3*X_F,3=F_S*X_S+F_M*X_M
F_L,1*Y_F,1+F_L,2*Y_F,2+F_L,3*Y_F,3=F_S*Y_S+F_M*Y_M
The controller which controls the Lorentz forces F_L,1, F_L,2and F_L,3comprises, for example, a feedforward control loop which is usual and known per se, where the controller receives information on the position X_S, Y_Sof thesubstrate holder1 and the position X_M, Y_Mof themask holder5 from an electric control unit (not shown) of the lithographic device which controls thesubstrate holder1 and themask holder5, the received information relating to the desired positions of thesubstrate holder1 and themask holder5. The controller may alternatively be provided with a feedback control loop which is usual and known per se, where the controller receives information on the position X_S, Y_Sof thesubstrate holder1 and the positions X_M, Y_Mof themask holder5 from said position control system of the lithographic device, the received information relating to the measured positions of thesubstrate holder1 and themask holder5. The controller may alternatively comprise a combination of said feedforward and feedback control loops. The Lorentz forces F_L,1, F_L,2and F_L,3of the force actuator system thus form a compensation force by means of which displacements of the centres of gravity G_Sand G_Mof thesubstrate holder1 and themask holder5 relative to themachine frame45 are compensated. Since the sum of the mechanical moments of the Lorentz forces F_L,1, F_L,2, F_L,3and the support forces F_S, F_Mabout the reference point P of themachine frame45 has a constant value and direction, thesubstrate holder1 and themask holder5 each have a so-called virtual centre of gravity which has a substantially constant position relative to themachine frame45. It is achieved thereby that themachine frame45 does not sense the displacements of the actual centres of gravity G_Sand G_Mof thesubstrate holder1 and themask holder5 during exposure of the semiconductor substrate19. Without the above force actuator system, a displacement of thesubstrate holder1 or themask holder5 would lead to an uncompensated change in the mechanical moment of the support forces F_Sor F_Mabout the reference point P, as a result of which themachine frame45 would perform a low-frequency shaking movement on thedynamic isolators51, or elastic deformations or mechanical vibrations could arise in themachine frame45.

The fact that the threeforce actuators205 are integrated with the threedynamic isolators51 results in a compact and simple construction of the force actuator system and the lithographic device. The triangular arrangement of thedynamic isolators51 in addition achieves a particularly stable operation of the force actuator system. Since the compensation force of the force actuator system comprises exclusively a Lorentz force, mechanical vibrations present in thebase39 and theforce frame41 are not transmitted to themachine frame45 through theforce actuators205.

The measures discussed above, i.e. the direct introduction of the reaction forces of thepositioning devices21,31 exclusively into theforce frame41, the direct coupling of thesubstrate holder1 and themask holder5 to theforce frame41 exclusively by means of a Lorentz force, and the compensation force of theforce actuators205 have the result that themachine frame45 has a supporting function only. Substantially no forces act on themachine frame45 which change in value or direction. An exception is formed by, for example, the horizontal viscous frictional forces exerted by the aerostatic bearings of thesubstrate holder1 and themask holder5 on theupper surface141 of thegranite support143 and the plane guides65 of thesupport member57, respectively, during displacements of thesubstrate holder1 and themask holder5. Such frictional forces, however, are comparatively small and do not result in appreciable vibrations or deformations of themachine frame45. Since themachine frame45 remains free from mechanical vibrations and elastic deformations, the components of the lithographic device supported by themachine frame45 occupy particularly accurately defined positions relative to one another. In particular the facts that the position of thesubstrate holder1 relative to the focusing system3 and the position of themask holder5 relative to the focusing system3 are very accurately defined, and in addition that thesubstrate holder1 and themask holder5 can be very accurately positioned relative to the focusing system3 by means of thepositioning devices21,31, imply that the pattern of a semiconductor circuit present on themask29 can be imaged on the semiconductor substrate19 with an accuracy which lies in the sub-micron range. Since themachine frame45 and the focusing system3 remain free from mechanical vibrations and elastic deformations, moreover, the advantage is created that themachine frame45 can act as a reference frame for the position control system mentioned above of thesubstrate holder1 and themask holder5, where position sensors of said position control system such as, for example, optical elements and systems of said laser interferometer, can be mounted directly to themachine frame45. Mounting of said position sensors directly to themachine frame45 results in that the position occupied by said position sensors relative to thesubstrate holder1, the focusing system3, and themask holder5 is not influenced by mechanical vibrations and deformations, so that a particularly reliable and accurate measurement of the positions of thesubstrate holder1 and themask holder5 relative to the focusing system3 is obtained. Since also themask holder5 can not only be positioned parallel to the X-direction, but can also be positioned parallel to the Y-direction and rotated about the axis ofrotation67, whereby a particularly high accuracy of imaging the pattern of themask29 on the semiconductor substrate19 is achieved, as noted above, semiconductor substrates with detail dimensions in the sub-micron range can be manufactured by means of the lithographic device according to the invention.

A lithographic device according to the invention was described above with asubstrate holder1 which is displaceable by means of afirst positioning device21 according to the invention, and amask holder5 which is displaceable by means of asecond positioning device31 according to the invention. Thepositioning devices21,31 have a common first frame, i.e. themachine frame45 of the lithographic device, and a common second frame, i.e. theforce frame41 of the lithographic device. It is noted that thepositioning devices21,31 may alternatively each have a first and second frame of their own, a common first frame and each a second frame of their own, of a common second frame and each a first frame of their own.

It is further noted that the invention also covers lithographic devices which work by the “step and repeat” principle mentioned earlier. Thus, for example, a positioning device according to the invention can be used for the displacement of the substrate holder in the lithographic device which is known from EP-A-0 498 496 and in which exclusively the substrate holder is displaceable over comparatively large distances relative to the focusing system. Such a lithographic device covered by the invention is also obtained in that thesecond positioning device31 withmask holder5 is replaced in the lithographic device discussed in the description of the Figures by a conventional mask holder which is stationary relative to themachine frame45, such as the one known, for example, from EP-A0 498 496. The invention also covers lithographic devices which work by the “step and scan” principle mentioned above where the mask holder only is driven by a positioning device according to the invention, and the substrate holder is driven by a conventional positioning device such as the one known from, for example, EP-A-0 498 496. Such a construction is conceivable, for example, if the focusing system of the lithographic device has a comparatively great optical reduction factor, so that the displacements of the substrate holder are comparatively small in relation to the displacements of the mask holder, and the positioning device of the substrate holder causes comparatively small mechanical vibrations in the machine frame.

The lithographic device described above comprises a force actuator system which is common to thefirst positioning device21 and thesecond positioning device31 and which supplies a compensation force by which displacements of the centres of gravity of both thesubstrate holder1 and themask holder5 can be compensated. It is noted that a lithographic device according to the invention may alternatively be provided with two force actuator systems with which the displacements of the centres of gravity of thesubstrate holder1 and themask holder5 can be individually compensated. A lithographic device according to the invention may also comprise a single force actuator system with which exclusively displacements of the centre of gravity of the mask holder can be compensated. Such a construction is conceivable, for example, if the focusing system of the lithographic device has a comparatively great optical reduction factor, so that the displacements of the centre of gravity of the substrate holder are comparatively small relative to the displacements of the centre of gravity of the mask holder, and the displacements of the centre of gravity of the substrate holder cause comparatively small mechanical vibrations in the machine frame.

The lithographic device according to the invention as described above is used for exposing semiconductor substrates in the manufacture of integrated electronic semiconductor circuits. It is further noted that such a lithographic device may alternatively be used for the manufacture of other products having structures with detail dimensions in the sub-micron range, where mask patterns are imaged on a substrate by means of the lithographic device. Structures of integrated optical systems or conduction and detection patterns of magnetic domain memories, as well as structures of liquid crystal display patterns may be mentioned in this connection.

It is further noted that a positioning device according to the invention may be used not only in a lithographic device but also in other devices in which objects or substrates are to be positioned in an accurate manner. Examples are devices for analyzing or measuring objects of materials, where an object or material is to be positioned or displaced accurately relative to a measuring system or scanning system. Another application for a positioning device according to the invention is, for example, a precision machine tool by means of which workpieces, for example lenses, can be machined with accuracies in the sub-micron range. The positioning device according to the invention is used in this case for positioning the workpiece relative to a rotating tool, or for positioning a tool relative to a rotating workpiece.

Thefirst positioning device21 of the lithographic device described comprises a drive unit with a first linear motor which supplies exclusively a Lorentz force, and a conventional second and third linear motor, while thesecond positioning device31 of the lithographic device described comprises a drive unit with a first linear motor supplying exclusively a Lorentz force, and a single conventional second linear motor. It is finally noted that the invention also relates to positioning devices provided with different drive units. Examples are a positioning device which comprises only a single motor supplying exclusively a Lorentz force, with a magnet system of the motor fastened to the object table supported by the first frame and an electric coil system of the motor fastened to the second frame, and a positioning device which comprises only a single conventional motor, with a stationary part of the motor fastened to the second frame and a movable part of the motor fastened to the object table supported by the first frame.

Claims (44)

1. A positioning device with an object table and a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame.

2. A positioning device as claimed inclaim 1, wherein the object table is coupled to the stationary part of the drive unit exclusively by a Lorentz force of a magnet system and an electric coil system of the drive unit during operation.

3. A positioning device as claimed inclaim 2, wherein the magnet system and the electric coil system belong to a first linear motor of the drive unit, which drive unit comprises a second linear motor with a stationary part fastened to the second frame and a movable part which is displaceable parallel to the X-direction over a guide of the stationary part, the magnet system of the first linear motor being fastened to the object table and the electric coil system of the first linear motor being fastened to the movable part of the second linear motor.

4. A positioning device as claimed inclaim 3, A positioning device with an object table and a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame, wherein the object table is coupled to the stationary part of the drive unit exclusively by a Lorentz force of a magnet system and an electric coil system of the drive unit during operation, wherein the magnet system and the electric coil system belong to a first linear motor of the drive unit, which drive unit comprises a second linear motor with a stationary part fastened to the second frame and a movable part which is displaceable parallel to the X-direction over a guide of the stationary part, the magnet system of the first linear motor being fastened to the object table and the electric coil system of the first linear motor being fastened to the movable part of the second linear motor, andwherein the drive unit comprises a third linear motor with a stationary part which is fastened to the movable part of the second linear motor, and with a movable part which is displaceable parallel to a Y-direction which is perpendicular to the X-direction over a guide of the stationary part of the third linear motor, the electric coil system of the first linear motor being fastened to the movable part of the third linear motor.

5. A positioning device as claimed inclaim 1, wherein the positioning device is provided with a force actuator system controlled by an electric control unit and exerting a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

6. A positioning device as claimed inclaim 5, wherein object table is displaceable parallel to a horizontal direction, while the force actuator system exerts the compensation force on the first frame parallel to a vertical direction.

7. A positioning device as claimed inclaim 6, wherein the object table is displaceable parallel to a horizontal X-direction and parallel to a horizontal Y-direction which is perpendicular to the X-direction, while the force actuator system comprises three force actuators mutually arranged in a triangle and each exerting a compensation force on the first frame parallel to the vertical direction.

8. A positioning device as claimed inclaim 5, wherein the force actuator system is integrated with a system of dynamic isolators by means of which the first frame is coupled to a base of the positioning device.

9. A positioning device as claimed inclaim 5, wherein the compensation force comprises exclusively a Lorentz force of a magnet system and an electric coil system of the force actuator system.

10. A lithographic device with a machine frame which, seen parallel to a vertical Z-direction, supports in that order a radiation source, a mask holder, a focusing system with a main axis directed parallel to the Z-direction, and a substrate holder which is displaceable perpendicularly to the Z-direction by means of a positioning device, the positioning device of the substrate holder, including an object table and a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein the first frame of the positioning device of the substrate holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the substrate holder belongs to a force frame of the lithographic device which is dynamically isolated from the machine frame; and wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame.

11. A lithographic device with a machine frame which, seen parallel to a vertical Z-direction, supports in that order a radiation source, a mask holder which is displaceable perpendicularly to the Z-direction by means of a positioning device, a focusing system with a main axis directed parallel to the Z-direction, and a substrate holder which is displaceable perpendicularly to the Z-direction by means of a further positioning device, the positioning device of the mask holder including an object table and a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein the first frame of the positioning device of the mask holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the mask holder belongs to a force frame of the lithographic device which is dynamically isolated from the machine frame; and wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame.

12. A lithographic device as claimed inclaim 10, wherein the mask holder is displaceable perpendicular to the Z-direction by means of said positioning device as claimed in wherein the first frame of the positioning device of the mask holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the mask holder belongs to the force frame of the lithographic device.

13. A lithographic device as claimed inclaim 11, wherein the positioning devices of the substrate holder and the mask holder have a joint force actuator system which is controlled by an electric control unit and which exerts a compensation force on the machine frame of the lithographic device during operation which has a mechanical moment about a reference point of the machine frame of a value which is equal to a value of a sum of a mechanical moment of a force of gravity acting on the substrate holder about said reference point and a mechanical moment of a force of gravity acting on the mask holder about said reference point, and a direction which is opposed to a direction of said sum of mechanical moments.

14. A lithographic device as claimed inclaim 13, wherein the machine frame is placed on a base of the lithographic device, on which also the force frame is placed, by means of three dynamic isolators mutually arranged in a triangle, while the joint force actuator system comprises three separate force actuators which are each integrated with a corresponding one of the dynamic isolators.

15. A positioning device as claimed inclaim 2, wherein the positioning device is provided with a force actuator system controlled by an electric control unit and exerting a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

16. A positioning device as claimed inclaim 3, wherein the positioning device is provided with a force actuator system controlled by an electric control unit and exerting a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

17. A positioning device as claimed inclaim 4, wherein the positioning device is provided with a force actuator system controlled by an electric control unit and exerting a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

18. A positioning device as claimed inclaim 6, wherein the force actuator system is integrated with a system of dynamic isolators by means of which the first frame is coupled to a base of the positioning device.

19. A positioning device as claimed inclaim 7, wherein the force actuator system is integrated with a system of dynamic isolators by means of which the first frame is coupled to a base of the positioning device.

20. A positioning device as claimed inclaim 6, wherein the compensation force comprises exclusively a Lorentz force of a magnet system and an electric coil system of the force actuator system.

21. A positioning device as claimed inclaim 7, wherein the compensation force comprises exclusively a Lorentz force of a magnet system and an electric coil system of the force actuator system.

22. A positioning device as claimed inclaim 8, wherein the compensation force comprises exclusively a Lorentz force of a magnet system and an electric coil system of the force actuator system.

23. A lithographic device with a machine frame which, seen parallel to a vertical Z-direction, supports in that order a radiation source, a mask holder, a focusing system with a main axis directed parallel to the Z-direction, and a substrate holder which is displaceable perpendicularly to the Z-direction by means of a positioning device, the positioning device of the substrate holder, including a first object table and a first drive unit by which the first object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the first drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein the first frame of the positioning device of the substrate holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the substrate holder belongs to a force frame of the lithographic device which is dynamically isolated from the machine frame by a plurality of dynamic isolators, each dynamic isolator comprising a force actuator and a pneumatic spring; and wherein a reaction force exerted by the first object table on the first drive unit during operation and arising from a driving force exerted by the first drive unit on the first object table is transmittable exclusively into the second frame, and wherein the mask holder is displaceable perpendicularly to the Z-direction by means of a mask holder positioning device with a second object table and a second drive unit by which the second object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the mask holder positioning device while a stationary part of the second drive unit is fastened to a second frame of the mask holder positioning device which is dynamically isolated from the first frame thereof, wherein a reaction force exerted by the second object table on the second drive unit during operation and arising from a driving force exerted by the second drive unit on the second object table is transmittable exclusively into the second frame, wherein the first frame of the positioning device of the mask holder belongs to the machine frame of the lithographic device, while the second frame of the positioning device of the mask holder belongs to the force frame of the lithographic device.

24. A positioning device with:

an object table; and

a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame by a plurality of dynamic isolators, each dynamic isolator comprising a force actuator and a pneumatic spring, wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame.

25. A positioning device according toclaim 24, wherein the object table is a mask table for holding a mask.

26. A positioning device according toclaim 24, wherein the object table is a substrate holder for holding a substrate.

27. A positioning device according toclaim 24, wherein the drive unit comprises a first motor for moving the object table in a first direction and a second motor for moving the object table in a second, perpendicular, direction.

28. A positioning device according toclaim 24, wherein the drive unit comprises:

a pair of linear motors constructed and arranged to produce gross movements of the object table in a pair of mutually perpendicular directions; and

an actuator, constructed and arranged to produce fine movements of the object table in a pair of mutually perpendicular directions and in a rotational direction.

29. A positioning device according toclaim 28, wherein the pair of linear motors are constructed and arranged to produce gross movements of the object table in an X-direction and a Y-direction and the actuator is constructed and arranged to produce fine movements of the object table in the X-direction and the Y-direction and rotational movement about a Z-axis, perpendicular to the X and Y directions.

30. A positioning device according toclaim 24, wherein the dynamic isolators are controlled by an electronic control unit to exert a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

31. A positioning device according toclaim 30, wherein the electronic control unit controls the dynamic isolators in a feedforward control loop based on position control information from a position control system.

32. A positioning device as recited inclaim 30, wherein the electronic control unit controls the dynamic isolators in a feedback control loop based on measured position information from an interferometric measuring system.

33. A positioning device as recited inclaim 30, wherein the electronic control unit controls the dynamic isolators based on a combination of position control information from a position control system of the positioning device and on measured position information from an interferometric measuring system.

34. A positioning device with:

an object table; and

a drive unit by which the object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame, wherein a reaction force exerted by the object table on the drive unit during operation and arising from a driving force exerted by the drive unit on the object table is transmittable exclusively into the second frame,

wherein the second frame comprises a base portion and a vertical column, and the base portion supports the first frame, and

wherein the vertical column is mounted to the base portion independently of the first frame, and

wherein the object table is a mask table for holding a mask and the stationary part of the drive unit is fastened to the vertical column.

35. A positioning device according toclaim 34, wherein the drive unit comprises a first motor for moving the object table in a first direction and a second motor for moving the object table in a second, perpendicular, direction.

36. A positioning device according toclaim 34, wherein the drive unit comprises:

a pair of linear motors constructed and arranged to produce gross movements of the object table in a pair of mutually perpendicular directions; and

an actuator, constructed and arranged to produce fine movements of the object table in a pair of mutually perpendicular directions and in a rotational direction.

37. A positioning device according toclaim 36, wherein the pair of linear motors are constructed and arranged to produce gross movements of the object table in an X-direction and a Y-direction and the actuator is constructed and arranged to produce fine movements of the object table in the X-direction and the Y-direction and rotational movement about a Z-axis, perpendicular to the X and Y directions.

38. A positioning device according toclaim 34, wherein the first frame is dynamically isolated from the second frame by a plurality of dynamic isolators, each dynamic isolator comprising a force actuator and a pneumatic spring cooperating to reduce transmission of vibrations between the machine frame and the reference frame.

39. A positioning device according toclaim 38, wherein the dynamic isolators are controlled by an electronic control unit to exert a compensation force on the first frame during operation, which compensation force has a mechanical moment about a reference point of the first frame having a value equal to a value of a mechanical moment of a force of gravity acting on the object table about said reference point and a direction which is opposed to a direction of the mechanical moment of said force of gravity.

40. A positioning device according toclaim 39, wherein the electronic control unit controls the dynamic isolators in a feedforward control loop based on position control information from a position control system.

41. A positioning device as recited inclaim 39, wherein the electronic control unit controls the dynamic isolators in a feedback control loop based on measured position information from an interferometric measuring system.

42. A positioning device as recited inclaim 39, wherein the electronic control unit controls the dynamic isolators based on a combination of position control information from a position control system of the positioning device and on measured position information from an interferometric measuring system.

43. A positioning device as recited inclaim 34 further comprising a substrate table constructed and arranged to hold a substrate in a position such that a pattern on the mask may be imaged onto the substrate.

44. A positioning device with:

a first object table, and a first drive unit by which the first object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the first drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame by a plurality of dynamic isolators, each dynamic isolator comprising a force actuator and a pneumatic spring, wherein a reaction force exerted by the first object table on the first drive unit during operation and arising from a driving force exerted by the first drive unit on the first object table is transmittable exclusively into the second frame; and a second object table, and a second drive unit by which the second object table is displaceable over a guide parallel to at least an X-direction, which guide is fastened to a first frame of the positioning device while a stationary part of the second drive unit is fastened to a second frame of the positioning device which is dynamically isolated from the first frame and wherein a reaction force exerted by the second object table on the second drive unit during operation and arising from a driving force exerted by the second drive unit on the second object table is transmittable exclusively into the second frame.

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