USRE46433E1 - Method and device for irradiating spots on a layer - Google Patents

Abstract

For irradiating a layer a radiation beam is directed and focussed to a spot on the layer, relative movement of the layer relative to the lens is caused so that, successively, different portions of the layer are irradiated and an interspace between a surface of the lens nearest to the layer is maintained. Furthermore, at least a portion of the interspace through which the radiation irradiates the spot on the layer is maintained filled with a liquid, the liquid being supplied via a supply conduit. At least a portion of the liquid fills up a recess through which the radiation irradiates the spot.

Description

The invention relates to a method of irradiating a layer according to the introductory portion of claim1 and to a device for irradiating a layer according to the introductory portion ofclaim9.

Such a method and such a device are known from WO-A-02/13194. According to this publication, the described method and device are used for the manufacturing of an optically scannable information carrier. In such a process, first a master mold is manufactured, and then, by means of the master mold or by means of a daughter mold manufactured by means of the master mold, the information carrier is manufactured by means of a replica process. For manufacturing the master mold, a modulated radiation beam which is directed and focussed to a scanning spot on a photosensitive layer carried by a substrate by means of an optical lens system and the substrate and the lens system are moved relatively to each other. An interspace between the photosensitive layer and a nearest surface of a lens system facing the photosensitive layer is maintained filled up with a liquid.

For moving the substrate relative to the lens system a table carrying the substrate can be rotated about an axis of rotation. By means of a displacement device, the lens system can be displaced with a radial directional component with respect to the axis of rotation of the table. A liquid supply means supplies the liquid into the interspace between the photosensitive layer and a nearest optical surface of the lens system.

A problem of this known method and device is that the immersion of the successive portions of the layer to be irradiated is quite easily disrupted, for instance because the liquid is entrained away from the area of the interspace through which the radiation directed to the radiation spot passes when the layer and the lens move too quickly relative to each other. The immersion can also be disrupted due to important changes in the direction of movement of the lens and the layer relative to each other. The stability of the liquid film between the layer to be irradiated and the nearest optical surface of the lens or lenses can be improved by making the distance between the layer to be irradiated and the nearest optical surface of the lens or lenses very small. However, this entails that the device and in particular the lens nearest to the layer to be irradiated can easily be damaged in the event of contact between the lens and the layer moving relative to each other.

Another method and device for directing a radiation beam to a spot on a photosensitive layer are disclosed in JP-A-10255319. In accordance with this method, a photosensitive layer is applied to a disc-shaped substrate made from glass. The table and the substrate are rotated about an axis of rotation extending perpendicularly to the substrate, and the lens system is displaced, at a comparatively low rate, in a radial direction with respect to the axis of rotation, so that the scanning spot of the radiation beam formed on the photosensitive layer follows a spiral-shaped track on the photosensitive layer. The radiation beam—in this known device a laser beam—is modulated such that a series of irradiated and non-irradiated elements is formed on the spiral-shaped track, which series correspond to a desired series of information elements on the information carrier to be manufactured. The photosensitive layer is subsequently developed, so that the irradiated elements are dissolved and a series of depressions are formed in the photosensitive layer. Next, a comparatively thin aluminum layer is sputtered onto the photosensitive layer, which aluminum layer is subsequently provided with a comparatively thick nickel layer by means of an electro deposition process. The nickel layer thus formed is subsequently removed from the substrate and forms the master mold to be manufactured, which is provided, in the manner described above, with a disc-shaped surface having a series of raised portions corresponding to the desired series of information elements on the information carrier to be manufactured. The master mold thus manufactured can suitably be used in the manufacture of the desired information carriers, however, in general, a number of copies, so-called daughter molds are made by means of the master mold in a replica process. These daughter moulds are used to manufacture the desired information carriers by means of a further replica process, generally an injection molding process. In this manner, the required number of master molds, which are comparatively expensive, is limited. Such a method of manufacturing an optically scannable information carrier, such as a CD or DVD, having pit-shaped information elements by means of a master mold or by means of a daughter mold manufactured by means of the master mold is commonly known and customary.

The interspace between the photosensitive layer and the lens of the lens system facing the photosensitive layer is filled with water. For this purpose, the known device is provided with an outflow opening, which is situated near the axis of rotation of the table. The water supplied via the outflow opening is spread, under the influence of centrifugal forces, substantially throughout the surface of the photosensitive layer, so that also the interspace is filled with water. Since water has a considerably larger optical refractive index than air, the provision of water in the interspace leads to a substantial increase of an angle which the rays originating from the radiation beam and the optical axis of the lens system include at the location of the scanning spot. As a result, the size of the spot formed by the radiation beam on the photosensitive layer is reduced considerably, so that a much larger number of irradiated and non-irradiated elements can be formed on the photosensitive layer, and the information carrier to be manufactured has a higher information density.

Another example of an application in which the gap between a lens and a surface to be irradiated is maintained filled with a liquid are optical imaging methods and apparatus, such as optical projection lithography, in which the spot formed by the radiation projected onto the surface forms an image or a partial image. Such a method and apparatus are described in international patent application WO99/49504.

A drawback of these methods and devices is that the liquid film formed in the interspace is not always reliably maintained fully and in homogenous condition during and after relative displacement of the lens and the surface parallel to the surface. As a result, faults develop in the photosensitive layer. In addition, variations in the condition of the liquid film caused by relative movements of the lens and the surface result in varying forces being exerted on the lens system. Since the lens system is suspended with a limited rigidity, the varying forces exerted by the liquid film cause undesirable vibrations of the lens system, which disturb the precision with which the image is projected onto the surface. Furthermore, a comparatively large quantity of liquid must be supplied to keep a liquid volume in place in the portion of the interspace through which the radiation passes. As a result, the known device must be provided with extensive measures to prevent undesirable contact between the liquid and other parts of the device.

It is an object of this invention to reliably maintain the portion of the interspace between the optical surface nearest to the layer to be irradiated and that layer, through which portion the radiation passes, filled with liquid throughout a larger range of relative velocities and directions of relative displacement of the optical element and the layer.

It is another object of the invention to reduce the risk of damage due to unintentional contact between the optical element and the layer to be irradiated.

According to the invention, these objects are achieved by providing a method according to claim1. Also according to the invention, a device according toclaim9 is provided for carrying out a method according to claim1.

By providing that at least a portion of the liquid fills up a recess of which an internal surface bounds the portion of the interspace through which the radiation irradiates the spot, the interspace through which the radiation irradiates the spot can be maintained filled up with liquid with improved stability. Furthermore, a given stability of the liquid volume between the at least one optical element and the layer, can be achieved while maintaining a larger distance between the nearest optical surface and the layer to be irradiated, so that the risk of unintentional contact between the optical element and the layer is reduced.

That the method and the device are less sensitive to the velocity and direction of displacement of the optical element and the layer relative to each other and variations therein, is not only advantageous in the manufacturing of optical information carriers or molds therefor, but also in other applications, such as optical projection imaging, and more in particular in for instance wafer steppers and wafer scanners for optical projection lithography, for example for the production of semiconductor devices in which the direction of movement of the optical element relative to the layer is varied substantially when the wafer is stepped relative to the optical element to bring the optical element into a new position opposite the wafer for projecting the reticle onto a new spot on the wafer or for unrolling (scanning) the projected image of the reticle (mask) over a next area on the wafer. The spot is then formed either by the area of projection of the reticle onto the wafer or by the moving area of projection of a running, usually slit shaped, window portion of the reticle obtained by or as if scanning along the reticle in accordance with movement of the wafer relative to the optical element.

Particular embodiments of the invention are set forth in the dependent claims.

Other objects, features and effects as well as details of this invention appear from the detailed description of a preferred form of the invention.

FIG. 1 is a schematic side view of an example of a device for directing radiation to a spot on a layer;

FIG. 2 is a schematic, cross-sectional view of a distal end portion of a first example of an optical system for a device as shown inFIG. 1, of a layer to which the radiation is directed and of a liquid flow maintained in operation;

FIG. 3 is a schematic, bottom view along the line III-III inFIG. 2

FIG. 4 is a schematic, cross-sectional view of a distal end portion of a second example of an optical system for a device as shown inFIG. 1, of a layer to which the radiation is directed and of a liquid flow maintained in operation;

FIG. 5 is a schematic, bottom view along the line V-V inFIG. 4;

FIG. 6 is a schematic, cross-sectional view of a distal end portion of a third example of an optical system for a device as shown in.FIG. 1, of a layer to which the radiation is directed and of a liquid flow maintained in operation;

FIG. 7 is a schematic, bottom view along the line VII-VII inFIG. 2;

FIG. 8 is a schematic, bottom view of a distal end portion of a fourth example of a optical system for a device as shown inFIG. 1; and

FIG. 9 is a schematic top plan view representation of a wafer stepper/scanner for optical lithography.

In the manufacture of an optically scannable information carrier, such as a CD or a DVD, a disc-shaped substrate3 of glass (seeFIG. 1) carrying a thinphotosensitive layer5 on one of its two sides is irradiated by means of amodulated radiation beam7, for instance a DUV laser beam with a wavelength of approximately 260 nm. To irradiate thephotosensitive layer5, use is made of an example25 of a device in accordance with the invention, which device is described hereinafter with reference toFIGS. 1-3. Theradiation beam7 is focused to ascanning spot11 on thephotosensitive layer5 by an optical system, according to the present example alens system9 including a plurality of lenses. Thelens system9 includes anobjective lens55, which is secured in alens holder57. Thelens system9 further includes a mostdistal lens59, which is the one of the optical elements of thelens system9 that is located nearest to thelayer5 when in operation. Aninterspace53 is maintained between thelayer5 that is irradiated and the one of the lenses of thelens system9 that is located nearest to thelayer5. The optical elements may also include other items than lenses, such as filters, shields, diffraction gratings or mirrors.

Thelayer5 and thelens system9 are displaced with respect to each other, so that themodulated radiation beam7 on thephotosensitive layer5 successively irradiates a series of spaced apart irradiated portions of thelayer5 and does not irradiate portions of thelayer5 in-between the irradiated portions. The irradiatedphotosensitive layer5 is subsequently developed by means of a developing liquid, which dissolves theirradiated elements13 and leaves thenon-irradiated elements15 on thesubstrate3. It is also possible to provide that the irradiated portions are left while the non-irradiated portions are dissolved. In both cases, a series of pits or bumps, which corresponds to the desired series of pit-shaped information elements on the information carrier, are formed in thephotosensitive layer5. Thephotosensitive layer5 is subsequently covered with a comparatively thin layer of for instance nickel by means of a sputtering process. Subsequently, this thin layer is covered with a comparatively thick nickel layer in an electro deposition process. In the nickel layer, which is eventually removed from thesubstrate3, the pattern of pits formed in thephotosensitive layer5 leaves a corresponding pattern that is a negative of the-pattern to be formed in the information carrier to be manufactured, i.e. the master mold comprises a series of raised portions, which correspond to the series of pit-shaped elements formed in thephotosensitive layer5 and to the desired series of pit-shaped information elements on the information carrier. The master mold is thus rendered suitable for use as a mold in an injection-molding machine for injection molding the desired information carriers. Generally, however, a copy of the master mold is used as the mold for injection molding instead of the master mold, which copy of the master mold is commonly referred to as daughter mold, which is manufactured by means of the master mold using a customary replica process which is known per se.

Thesubstrate3 with thephotosensitive layer5 is placed on a table27 that is rotatable about an axis ofrotation29, which extends perpendicularly to the table27 and thesubstrate3. The table can be driven by means of afirst electromotor31. Thedevice25 further comprises aradiation source33, which, in the example shown, is a laser source, which is secured in a fixed position to aframe35 of thedevice25. It is observed that, as an alternative, the radiation may also be obtained from outside the device. Control over the radiation directed to thelayer5 can be achieved in many ways, for instance by controlling theradiation source33 and/or by controlling a shutter or radiation diverter (not shown) between theradiation source33 and thelayer5.

Theoptical lens system9 is secured onto afirst traveller37, which can be displaced radially (parallel to the X-direction in the drawings) relative to the axis ofrotation29, by means of afirst displacement structure39. For this purpose, thefirst displacement structure39 includes asecond electromotor41 by means of which thefirst traveller37 can be displaced over astraight guide43, which extends parallel to the X-direction and is fixed relative to theframe35.

Amirror45 in line with anoptical axis49 of thelens system9 is also secured to thefirst traveller37. In operation, theradiation beam7 generated by theradiation source33 follows a radiation beam path47 extending parallel to the X-direction, and theradiation beam7 is deflected by themirror45 in a direction parallel to theoptical axis49 of thelens system9. Thelens system9 can be displaced in the direction of itsoptical axis49 by means of afocus actuator51, over comparatively small distances with respect to thefirst traveller3, so that theradiation beam7 can be focused on thephotosensitive layer5. The table27 with thesubstrate5 is rotated about the axis ofrotation29 at a comparatively high speed by means of thefirst motor31, and thelens system9 is displaced parallel to the X-direction by means of thesecond motor41 at a comparatively low speed, so that thescanning spot11 where theradiation beam7 hits the layer follows a spiral-shaped track over thephotosensitive layer5, leaving a trail of irradiated and non-irradiated elements extending in accordance with this spiral-shaped track.

Thedevice25 can suitably be used to manufacture master molds having a comparatively high information density, i.e. by means of thedevice25, a comparatively large number of irradiated elements can be provided per unit area of thephotosensitive layer5. The attainable information density increases as thescanning spot11 is smaller. The size of thescanning spot11 is determined by the wavelength of theradiation beam7 and by the numerical aperture of thelens system9, the numerical aperture depending upon the optical refractive index of the medium present between thelens system9 and thephotosensitive layer5. Thescanning spot11 is smaller as the refractive index of the medium present between thelens system9 and thephotosensitive layer5 is larger. Liquids typically have a much larger optical refractive index than air and therefore the portion of theinterspace53 between thelens system9 and thephotosensitive layer5 through which thebeam7 extends is maintained filled with a liquid—according to this example water. In the present example, water is also particularly suitable because it is transparent to theDUV radiation beam7 used and it does not attack thephotosensitive layer5.

As shown inFIG. 1, thedevice25 according to the present example further includes aliquid removal structure77, which is provided with a pick-upmouth79. The pick-upmouth79 is secured onto asecond traveller81 of thedevice25, which can be displaced by means of a second displacement structure83 of thedevice25 in a radial direction with respect to the axis ofrotation29, according to the present example parallel to the X-direction, but another radial direction of displacement may be provided. For driving the displacement of thesecond traveller81, the second displacement device83 comprises athird electromotor85 connected to thesecond traveller81 for displacing the second traveller over astraight guide87, which is attached to theframe35 and extends in the directions of displacement of thesecond traveller81.

In operation, the pick-upmouth79 is displaced by means of thethird motor85. Thethird motor85 is controlled so that thelens system9 and the pick-upmouth79 are continuously situated at substantially equal distances R from the axis ofrotation29 of thesubstrate3. In this manner, the pick-upmouth79 is maintained in a position downstream from thelens system9 where irradiated portions of thelayer5 pass, so that the liquid supplied at the location of thelens system9 is entrained by therotating layer5 to the pick-upmouth79 where the liquid is subsequently picked-up from thephotosensitive layer5 by the pick-upmouth79. As the water is thus removed from thephotosensitive layer5 downstream from thelens system9, it is substantially precluded that water that has already been used finds its way back to theinterspace53, thereby disturbing the accurately dosed liquid flow in theinterspace53. In operation, the pick-upmouth79 is always at a distance R from the axis ofrotation29 which corresponds to the distance Rat which thelens system9 is situated from the axis ofrotation29, both the size and the capacity of the pick-upmouth79 need only to be comparatively small to remove liquid that has already been used.

FIGS. 2 and 3 show, in more detail, thelens system9, thesubstrate3 with thephotosensitive layer5, and theinterspace53 between the-photosensitive layer5 and thelens system9. Thelens59 nearest to thelayer5 has anoptical surface63 facing thesubstrate3. Thelenses55,59 are suspended in ahousing61, which includes aflat wall65, which faces thelayer5 and which substantially extends in an imaginary plane perpendicular to the optical axis of thelens59 nearest to thelayer5. Between thelens59 nearest to thelayer5 and thelayer5, apassage90 is provided in thewall65, which faces thelayer5. Thewall 65 containing thepassage90 and thesurface63 of thelens59 nearest to thelayer5 form arecess92, inclusive of thepassage 90, in the surface of thewall65 facing thespot11 to which theradiation7 is directed. Thesurface63 of thelens59 nearest to thelayer5 is part of the internal surface of therecess92 and bounds the portion of theinterspace53 through which theradiation7 irradiates thespot11. According to the present example, thesurface63 of thelens59 nearest to thelayer5 is flat, however, this surface may also be concave or convex.

In thecarrier61, aliquid supply67 has aport69 that opens into therecess92 directly adjacent thelens59 nearest to thelayer5. In operation, the portion of theinterspace53 through which theradiation7 irradiates thespot11 on thelayer5 is maintained filled withliquid91. To this end, the liquid91 is supplied via theport69 into a portion of theinterspace53 in therecess92 and through which theradiation7 irradiates thespot11. Via a most downstream outflow opening, formed by thepassage90 in thewall65 between thespot11 and thesurface63 of thelens59, the liquid91 is subsequently also fed to and fills up a portion of theinterspace53 between thewall65 and thelayer5. In therecess92, the liquid91 is, at least to an important extent, protected against being entrained from theinterspace53. Since, the liquid91 is less susceptible to being entrained away from the portion of theinterspace53 through which the radiation passes to thespot11, occurrence of the associated optical distortion caused by the portion of theinterspace53 through which the radiation passes not being completely filled with liquid is thus counteracted.

Moreover, the size of theinterspace53 measured parallel to the optical axis of thelenses55,59—and thus the distance between thelens59 and thelayer5—can be relatively large without causing the liquid to be entrained along with movement of thelayer5 too easily. In turn, this reduces the risk of damage to thelens59 nearest to thelayer5. Moreover, the allowable tolerances on the tilt of the lens can be larger without increasing the risk of thelens59 touching thelayer5.

Therecess92 may be positioned and of such dimensions, so that only a portion of the radiation passes through the recess. However, for a particularly effective protection ofliquid91 across the whole radiation beam, it is preferred that therecess92 has arim portion93 closest to thelayer5, which extends around theradiation7 irradiating thespot11. Accordingly, the portion of theinterspace53 in therecess92 in whichliquid91 is shielded from being entrained extends throughout the whole cross-section of theradiation beam7.

According to the present example, therecess92 is bounded by thepassage90 in thewall65 containing thepassage 90 between thespot11 and thelens59 nearest to thespot11, and by thesurface63 of thelens59. Thesurface63 of thelens59 nearest to thespot11 is thereby shield by thewall65, so that the risk of damage to thelens59 is virtually eliminated. Moreover, since thewall65 also shields the liquid91, thenearest lens59 does not need to be positioned very near to thelayer5 to effectively keep theinterspace53 between thelayer5 and thenearest lens59 filled with liquid. The distance between thewall65 and thelayer5 can be selected to be quite small so that a very effective capillary effect can be achieved for keeping a liquid film in place in the portion of theinterspace53 in the periphery of thepassage90, because inadvertent contact between thewall65 and thelayer5 has far less detrimental effects than contact between an optical surface such as a lens surface and thelayer5. Thewall65 is preferably made of or covered with a relatively soft material, such as plastic material, so that there is little risk of damage in the event of inadvertent contact between thewall65 and thelayer5.

The optimum working distance between thelayer5 and thewall65, i.e. the portion of the lens assembly nearest to thelayer5, is determined by two factors. On the one hand, the distance should be large enough to retain sufficient tolerance on the distance between thesubstrate3 and arrangement of thelenses55,59 and thehousing61. On the other hand, this distance should not be too large because this would require a too large liquid flow to maintain the immersed condition of the portion of theinterspace53 through which the radiation passes to thespot11. A presently preferred range for the smallest thickness of theinterspace53 is 3-1500 μm and more preferably 3-500 μm if the liquid is water, larger values for the smallest thickness of the interspace can be particularly advantageous if the liquid has a larger viscosity than water. Also the width of the outflow opening affects the upper end of the preferred range for the smallest thickness of the interspace, the smallest thickness of the interspace being preferably smaller than (100+ 1/20*W) μm in which W is the overall width of the outflow opening measured in a plane parallel to thelayer5.

Due to the presence of a recess facing thelayer5, the distance between thelayer5 and the nearest optical surface may be larger than approximately 10 μm, for instance larger than 15 m, 30 μm or even 100 μm, to increase the insensitivity to tolerances and to further reduce the risk of contact between the layer and an optical surface.

In thedevice25 according to the present example, theliquid supply structure67 communicates with thepassage90 for maintaining a liquid outflow via thepassage90.

Since the liquid91 flows out towards thelayer5 via thepassage90 in thewall65 between thelens59 and the layer S through which also theradiation7 passes to thespot11, the liquid91 is particularly effectively guided through theinterspace53 through which the radiation passes to thespot11. Moreover, since theradiation7 passes to thespot11 through theoutflow opening90 through which the liquid91 is directed, theradiation beam7 extends through the area through which the liquid91 flows out. This results in a very reliable full immersion of the portion of theinterspace53 through which the radiation passes to the spot during movement parallel to thelayer5 of thelens59 and thelayer5 relative to each other. Yet another advantage of causing the liquid to flow out via an opening through which also the radiation for irradiating the spot is passed is that a relatively high pressure can be maintained in the immersed area through which the radiation passes. This in turn reduces the risk of bubble formation, which may for instance be caused by gasses dissolved in the liquid under influence of an increase of temperature.

To avoid inclusion of air bubbles in the liquid and for reliably maintaining the filled condition of the portion of theinterspace53 through which theradiation7 passes to thespot11, liquid outflow via theoutflow opening90 is preferably such that a liquid volume between thewall65 and thelayer5 is maintained which includes a liquid volume upstream of the portion of theinterspace53 through which the radiation irradiates thespot11. Thus, a safety margin of liquid upstream (in a direction opposite to the direction of relative movement of thelayer5 in the area of the spot11) is formed which ensures that, variations in the distance over which liquid is urged in upstream direction do not cause a disruption of the completely filled condition of the portion of theinterspace53 intersected by theradiation7 passing to thespot11.

Furthermore, the liquid91 flows out from the mostdownstream outflow opening90 over a cross-section larger than the largest cross section94 of the portion of theinterspace53 through which the radiation irradiates thespot11. This also contributes to the reliable immersion of theinterspace53 with the liquid91.

As can be seen inFIGS. 2 and 3, theoutflow opening90 has a total projected cross-sectional passage area in a plane parallel to thelayer5 of which, seen in a direction parallel to the optical axis of thelens system109, the centre is located inside the portion of theinterspace53 through which theradiation7 irradiates the spot.11. Accordingly, the average path along which liquid flows out is at least to a large extent centred relative to the portion of theinterspace53 through which radiation passes to thespot11. Accordingly, the direction of movement of thelayer5 and thelens arrangement9 relative to each other in the area of thespot11 can be varied substantially without disrupting complete immersion of the portion of theinterspace53 through which thespot11 is irradiated. Even if the direction of movement of thelayer5 is varied substantially, the trace ofliquid95 will still cover the entire portion of theinterspace53 through which the spot is irradiated. Nevertheless, areas of theoutflow opening90 around thebeam7 are located close to the beam, so that superfluous wetting of thelayer5 is limited.

According to the present example, the portion of theinterspace53 through which theradiation7 irradiates thespot11 is also centrally located relative to theoutflow opening90 to such an extent that thetrace95 ofliquid91 fed from theoutflow opening90 into theinterspace53 completely immerses the portion of theinterspace53 through which theradiation7 irradiates thespot11, not only while, in the position of thespot11, thelayer5 and the at least onelens system9 move relative to each other in the direction indicated by the arrow52 (which indicates the direction of movement of thelayer5 relative to the lens system9), but also while, in the position of thespot11, thelayer5 andlens system9 move relative to each other in opposite direction.

More specifically, because in the example shown inFIGS. 2 and 3 theradiation beam7 passes centrally through the cross-sectional area of theoutflow opening90, the liquid91 flowing into and out of theoutflow opening90 already immerses the portion of theinterspace53 through which theradiation7 irradiates thespot11.

The more the direction of movement of thelayer5 and thelens system9 parallel to thelayer5 in the area of thespot11 can be changed without disrupting the immersion of the portion94 of thearea53 through which the radiation passes, the more the device is suitable for applications in which thespot11 needs to move over the surface of the layer in widely varying directions, such as in imaging processes in which the spot is a two-dimensional image projected to thelayer5. In such applications, the advantage of a comparatively large refractive index between the lens system and the medium between the lens system and the irradiated surface is that the image can be projected with a higher resolution, which in turn allows further miniaturization and/or an improved reliability.

An example of such applications is optical projection lithography for the processing of wafers for the manufacture of semiconductor devices. An apparatus and a method for this purpose are schematically illustrated inFIG. 9. Wafer steppers and wafer scanners are commercially available. Accordingly, such methods and apparatus are not described in great detail, but primarily to provide an understanding of liquid immersion as proposed in the present application in the context of such optical imaging applications.

The projection lithography apparatus according toFIG. 9 includes awafer support12 and aprojector13 having alens assembly14 above thewafer support12. InFIG. 9, thewafer support12 carries awafer15 on which a plurality ofareas16 are intended to be irradiated by a beam projecting an image or partial image of a mask orreticle17 in ascanner18 operatively connected to theprojector13. The support table is moveable in X and Y direction alongspindles19,20 driven by spindle drives21,22. The spindle drives21,22 and thescanner18 are connected to acontrol unit23.

Usually one of two principles of operation are applied in optical lithography. In the so-called wafer stepper mode, the projector projects a complete image of the reticle onto one of theareas16 on thewafer15. When the required exposure time has been reached, the light beam is switched off or obscured and thewafer15 is moved by the spindle drives21,22 until anext area16 of the wafer is in the required position in front of thelens assembly14. Dependent on the relative positions of the exposed area and the next area to be exposed, this may involve relatively quick movement of thelens assembly14 along the surface of the wafer in widely varying directions. The size of the irradiated spot on the surface of the wafer in which the image of the reticle is projected is typically about 20×20 mm, but larger and smaller spots are conceivable.

In particular when it is desired to manufacture larger semiconductor units, it is advantageous to project the image in the other mode, generally referred to as the wafer scanner mode. In that mode, only a slit-shaped portion of the reticle is projected as a slit shaped spot having a length that is several (for instance four or more times) times larger than its width in anarea16 of the surface of thewafer15. A typical size for the spot is for instance about 30×5 mm). Then, thereticle17 to be scanned is moved along scanning window while thewafer support12 is synchronously moved relative to thelens assembly14 under control of thecontrol unit23 with a velocity adapted so that only the projection spot, but not the scanned partial image portions of thereticle17 that are projected on the wafer move relative to thewafer15. Thus, the image of thereticle17 is transferred to anarea16 of the wafer. The movement of thewafer15 relative to thelens assembly14 while a running window portion of the reticle is projected onto thewafer15 is usually carried out slowly and usually each time in the same direction. After the complete image of areticle17 has been projected onto thewafer15, thewafer15 is generally moved much more quickly relative to thelens assembly14 to bring a next area of thewafer15 where a next image of the or areticle17 is to be projected in front of thelens assembly14. This movement is carried out in widely varying directions dependent on the relative positions of the exposedarea16 of thewafer15 and thenext area16 of thewafer15 to be exposed. To be able to recommence radiating the surface of thewafer15 after the displacement of thewafer15 relative to the lens14 (i.e. also the lens or the lens and the wafer may be moved), it is advantageous if the liquid volume in the interspace between thelens14 and the surface of thewafer15 through which the radiation passes is immediately filled with liquid after completion of that movement, so that the space is reliably immersed before irradiation is recommenced.

Also for optical lithography, water can be used, for instance if the radiation is light of a wavelength of 193 nm. However in some circumstances other liquids may be more suitable.

FIGS. 4 and 5 show a distal end portion of a second example109 of a lens system for devices such as the devices shown inFIGS. 1 and 9. Thelens system109 according to this example includes ahousing161, alens159 nearest to thelayer5 on thesubstrate3. According to this example, therecess192 is bound by a concave portion of thesurface163 of thelens159 nearest to thespot11 on thelayer5 to which the beam ofradiation107 is directed. This allows to obtain the liquid retaining characteristics of a recess in combination with a relatively uniform flow pattern throughout theportion194 of theinterspace153 through whichradiation107 passes to thespot11. In particular, a uniform pattern of flow velocity gradients in theinterspace153 is obtained. In turn, the relatively uniform flow pattern is advantageous to avoid inducing vibrations and for obtaining a continuous uniform supply of fresh liquid and thereby a uniform, steady liquid temperature. These effects are both advantageous for avoiding optical disturbance of theradiation beam107.

InFIG. 5, the dotted circle designated byreference numeral194 indicates the largest cross section of the portion of theinterspace153 between thelens159 and thelayer5 through which theradiation beam107 passes.

For supplying liquid191 to theinterspace153 between thelens159 and thelayer5, aliquid supply conduit167 extends through thehousing161 and leads to anoutflow opening190. According to the present example, theoutflow opening190 has the form of a canal structure in asurface154 facing thelayer5. Thecanal structure190 is open towards thelayer5, for distributing supplied liquid191 longitudinally along thecanal190 and dispensing distributed liquid towards thelayer5. In operation, the liquid191 is distributed by thecanal structure190 longitudinally along that canal structure andliquid191 is dispensed from thecanal structure190 towards thelayer5. This results in a relatively wide,flat liquid trace195 and full immersion of theportion194 of theinterspace153 through which theradiation beam107 passes, even if the direction of movement of thelens system109 and thelayer5 relative to each other parallel to the plane of thelayer5 is changed substantially.

Thecanal190 can have various forms. In the embodiment shown inFIGS. 4 and 5, the canal is formed such that theoutflow opening190 is located outside theradiation beam107 and extends around theportion194 of theinterspace153 through which theradiation7 irradiates thespot11. Thecross196 indicates the centre, seen in a direction parallel to the optical axis of thelens system109, of the total cross-sectional passage area of theoutflow opening190. Also in this embodiment, seen in a direction parallel to the optical axis of thelens system109, the centre of the total cross-sectional passage area of theoutflow opening190 is located inside theportion194 of theinterspace153 through which theradiation107 irradiates thespot11. Furthermore, as in the embodiment discussed above, theportion194 of theinterspace153 through which theradiation107 irradiates thespot11 is centrally located relative to the cross-sectional area of theoutflow opening190 to such an extent that the direction of movement of thelens system9 and thelayer5, relative to each other and parallel to the plane of thelayer5, can be reversed without disrupting the full immersion of theportion194 of theinterspace153 through which theradiation beam107 passes.

Another feature theoutflow opening190 of the example shown inFIGS. 4 and 5 has in common with theoutflow opening90 shown inFIGS. 2 and 3 is that, seen in a direction parallel to the optical axis of thelens system109, it includes portions that are spaced about theportion194 of theinterspace153 through which theradiation beam107 irradiates thespot11, over such an angle that the trace ofliquid195 fed from theoutflow opening190 into theinterspace153 completely immerses theportion194 of the interspace through which the radiation irradiates thespot11 while, in the position of thespot11, thelayer5 and thelens system109 move relative to each other in directions parallel to thelayer5 that may be perpendicular to each other. The ability to keep theportion194 of the interspace through which the radiation passes immersed during movements of thelayer5 and thelens system109 relative to each other in directions perpendicular to each other is of particular advantage, because it allows to write an image onto thelayer5 while making movements in X- and Y-directions.

The liquid191 is preferably supplied at a pressure drop over the liquid between thecanal structure190 and the environment that is just sufficient to keep portion of theinterspace153 through which the radiation passes reliably immersed. Thus, the amount of water fed to the surface is kept to a minimum.

Furthermore, when the liquid191 is dispensed via a canal shapedoutflow opening190, the smallest thickness of the interspace153 (in this example the distance between thelayer5 and thesurface154 of the wall portion165) may be larger, without causing an undue risk of disrupting the immersion of theportion194 of the interspace through which the radiation passes.

The flow rate with which the liquid191 is supplied is preferably as follows: if theinterspace153 betweenlayer5 and the surface of thelens system109 nearest to thelayer5 has a smallest thickness H (measured perpendicular to the layer5), thelayer5 and the at least onelens159 are moved relative to each other at a velocity V, the liquid191 is supplied via anoutflow opening190 having a diameter D measured in a plane parallel to thelayer5, the flow rate is preferably equal to 0.5*β*H*(D+α*H)*V, where α is a constant between 1 and 10 and β is a constant between 1 and 3.

Thus, it can be reliably ensured that a laminar flow with an essentially linear velocity profile and preferably a homogeneous Couette flow is present in theinterspace153. Such a flow exerts a substantially constant force on thewall165 in which thecanal190 is provided and on theside163 of thelens159 nearest to thelayer5. As a result, the water present in theinterspace153 exerts substantially no variable liquid forces on thelens system109. Such varying liquid forces would lead to undesirable vibrations of thelens system109 and hence to focusing errors and positioning errors of theradiation beam107 on thephotosensitive layer5. The flow is preferably free of air inclusions, so that theradiation beam107 is not disturbed thereby.

InFIGS. 6 and 7, a third example of alens system209 for devices such as the devices shown inFIGS. 1 and 9 is shown. According to this example, theoutflow opening290 downstream of theliquid supply canal267 is also provided with a canal structure open towards the layer5 (i.e. in the direction in which thebeam207 is directed), but has a different, rectangular shape when seen in axial direction of thelens system209. An essentially rectangular shape is particularly advantageous for reliably immersing arectangular area294 of the interspace intersected by the radiation beam while maintaining a uniform liquid flow patter throughout the intersectedportion294 of the interspace, in particular if the movement of thelens system209 and thelayer5 relative to each other is in a direction perpendicular to one of the sides of therectangular canal structure290. Such circumstances typically occur in optical projection lithography.

As in the example shown inFIGS. 2 and 3, therecess292 is bounded by apassage295 in a wall265 perpendicular to the axis of thelens system9 and a surface of thelens259 nearest to thespot11 and the surface of thelens259 nearest to thespot11 also bounds theportion294 of theinterspace253 through which theradiation207 passes to the spot1. Accordingly, thelens259 is effectively protected against damage due to inadvertent contact between thelens system209 and thelayer5 on thesubstrate3. However, according to this example, thepassage295 is not an outflow opening via which liquid is dispensed.

Thelens system309 shown inFIG. 8 is provided with two mostdownstream outflow openings390,390′ and theportion394 of the interspace through which the radiation passes to the spot on the layer to be irradiated is located centrally relative to the outflow openings, so that theportion394 of the interspace through which the radiation passes is fully immersed in aliquid trace395 dispensed from a first one of theoutflow openings390 if the movement of the layer relative to thelens system309 in the area of the spot is in a first direction indicated with anarrow352 and fully immersed inliquid trace395′ dispensed from the other one of theoutflow openings390′ if the movement of the layer relative to thelens system309 in the area of the spot is in a second, opposite direction indicated with anarrow352′. If it is desired to ensure immersion during relative movement of thelens system309 and the layer in other directions parallel to the layer,outflow openings390 can be provided in other angular positions relative to theportion394 of the interspace through which the radiation is passed, the pressure drop and the flow rate can be increased to create wider liquid traces and/or the outflow openings can be of a different design, for instance slit shaped wherein the slit may for instance be straight or curved about the optical axis of thelens system309.

Also in thelens system309 according to this example, seen in a direction parallel to the optical axis of thelens system309, thecentre396 of the total cross-sectional passage area of theoutflow openings390,390′ is located inside theportion394 of the interspace353 through which the radiation passes to thespot11.

A particular advantage of having a plurality of outflow openings circumferentially spaced around theportion394 of the interspace through which the radiation passes to the spot on the layer to be irradiated is, that dependent of the direction of movement of the layer and thelens system309 relative to each other, liquid can be fed selectively from the outflow opening or openings upstream of the spot on the layer to be irradiated only. Thus, the flow rate of the liquid can be limited and the amount of liquid that needs to be picked up is reduced.

Claims (21)

The invention claimed is:

1. A method of irradiating a layer, the method including:

directing and focussing focusing a radiation beam to a spot on said layer by means of at least one optical element;

causing relative movement of the layer relative to said at least one optical element so that, successively, different portions of the layer are irradiated and an interspace between said layer and a surface of said at least one optical element nearest to said layer is maintained; and

maintaining said interspace through which said radiation irradiates said spot on said layer filled with a liquid, the liquid being supplied via a supply conduit;

characterized in that at least a portion of said interspace is bounded by a recess which is filled by at least a portion of said liquid, said radiation beam passing through said liquid in said recess when irradiating said spot, wherein said recess is bounded at least in part by a passage in a wall between said layer and a surface of said at least one optical element nearest to said layer and by said surface of said at least one optical element nearest to said layer, wherein a passage is formed in said wall as an opening from the recess, wherein said wall has a width-wise axis that extends through the body of the wall, the width-wise axis essentially extending perpendicular to an optical axis, through the interspace, of the radiation beam, wherein said wall has a major exterior surface contacting said liquid, the major exterior surface being essentially perpendicular to the optical axis, extending at least partly underneath said at least one optical element, being a bottom-most surface of the wall and spanning a width that is larger than a height of the wall, and wherein said radiation beam passing passes through said passage while at least a portion of the liquid is flowing out of said passage onto said layer.

2. The method as claimed inclaim 1, wherein the recess has a rim portion positioned between said surface of said at least one optical element nearest to said layer and said layer, closest to said layer and extending around said radiation beam irradiating said spot.

3. The method as claimed inclaim 1, wherein a liquid outflow from said recess via said passage is maintained.

4. A The method as claimed inclaim 1, wherein a smallest thickness of said interspace is maintained at a value selected from within the range of 3-1500 μm.

5. A The method as claimed inclaim 1, wherein said recess includes a concave portion of said surface of said at least one optical element nearest to said layer.

6. A The method as claimed inclaim 1, wherein the liquid flows out from at least one outflow opening in said recess in the form of at least one canal open towards said layer, said canal distributing supplied liquid longitudinally along said canal and dispensing distributed liquid towards said layer.

7. A method of irradiating a layer including:

directing and focusing a radiation beam to spot on said layer by means of at least one optical element;

causing relative movement of the layer relative to said at least one optical element so that, successively, different portions of the layer are irradiated and an interspace between a surface of said at least one optical element nearest to said layer is maintained; and

maintaining at least a portion of said interspace through which said radiation irradiates said spot on said layer filled with a liquid, the liquid being supplied via a supply conduit;

characterized in that at least a portion of said liquid fills up a recess through which said radiation irradiates said spot,

wherein said interspace between said layer and said surface of said at least one optical element nearest to said layer has a thickness H, the layer and the at least one optical element are moved relative to each other at a velocity V, the liquid is supplied via an outflow opening having a width W measured in a plane parallel to said layer and at a flow rate equal to 0.5*•*H*(W+•*H)*V 0.5*β*H*(W+α*H)*V, where • α is a constant between 1 and 10 and • β is a constant between 1 and 3.

8. A device for directing radiation to a layer, the device including:

at least one optical element for focussing a radiation originating beam from said a radiation source to a spot on said layer;

a displacement structure for causing relative movement of the layer relative to said at least one optical element so that, successively, different portions of the layer are irradiated and an interspace between said layer and a surface of said at least one optical element nearest to said spot is maintained; and

an outflow opening for supplying liquid to fill said interspace, in operation, said radiation irradiates said spot on said layer through said liquid,; and

characterized in that said device further comprises a recess having an internal surface bounding at least said a portion of said interspace through which said radiation irradiates said spot on said layer through said liquid, said outflow opening being formed in said recess, wherein said recess is being bounded at least in part by a passage in a wall between said spot and a surface of said at least one optical element nearest to said spot and by said surface of said at least one optical element nearest to said spot, a passage for liquid flow formed in said wall, wherein said wall has a width-wise axis that extends through the body of the wall, the width-wise axis essentially extending perpendicular to an optical axis, through the interspace, of the radiation beam, wherein said wall has a major exterior surface arranged to contact said liquid, the major exterior surface being essentially perpendicular to the optical axis, extending at least partly underneath said at least one optical element, being a bottom-most surface of the wall and spanning a width that is larger than a height of the wall, and wherein said outflow opening is formed in said recess above said passage and said passage forming said outflow opening is a further opening in the recess and is arranged to have the radiation beam pass therethrough onto said spot.

9. The device as claimed inclaim 8, wherein said recess has a rim portion closest to said layer extending around said portion of said interspace through which, in operation, said radiation irradiates said spot.

10. The device as claimed inclaim 8, wherein said device further comprises a liquid supply structure communicating with said recess for maintaining a liquid outflow via said passage.

11. The device as claimed inclaim 8, wherein said device is arranged for maintaining a smallest thickness of said interspace at a value selected from within the range of 3-1500 μm.

12. The device as claimed inclaim 8, wherein said recess includes a concave portion of said surface of said at least one optical element nearest to said spot.

13. The device claimed inclaim 8, wherein the at least one outflow opening is formed by at least one canal open towards said layer, for distributing supplied liquid longitudinally along said canal and dispensing distributed liquid towards said layer.

14. The method as claimed in claim 1, wherein said major surface of the wall is upward facing.

15. A device manufacturing method comprising:

forming a beam of radiation with an image of a mask or reticle; and

irradiating a layer with the image using the method as claimed in claim 1.

16. The device as claimed in claim 8, wherein said major surface of the wall is upward facing.

17. A lithography apparatus comprising:

a wafer support table configured to support a wafer to be irradiated;

a scanner configured to have a reticle or mask;

a drive, coupled to the wafer support table, configured to move the support table in X and Y directions;

a control unit configured to control the drive and the scanner; and

a device as claimed in claim 8.

18. A method comprising:

directing and focusing a radiation beam to a spot on a layer by means of at least one optical element;

causing relative movement of the layer relative to said at least one optical element so that, successively, different portions of the layer are irradiated and an interspace between said layer and a surface of said at least one optical element nearest to said layer is maintained; and

maintaining said interspace through which said radiation irradiates said spot on said layer filled with a liquid, the liquid being supplied via a supply conduit,

wherein at least a portion of said interspace is bounded by a recess which is filled by at least a portion of said liquid, said radiation beam passing throuqh said liquid in said recess when irradiating said spot, and wherein the boundary of said recess is formed at least in part by a wall between said layer and said surface of said at least one optical element nearest to said layer, wherein a passage for liquid flow is formed in said wall as an opening from the recess, wherein said wall has a width-wise axis that extends through the body of the wall, the width-wise axis essentially extending perpendicular to an optical axis, through the interspace, of the radiation beam, wherein said wall has a major exterior surface contacting said liquid, the maior exterior surface being essentially perpendicular to the optical axis, extending at least partly underneath said at least one optical element, being a bottom-most surface of the wall and spanning a width that is larger than a height of the wall, and wherein said radiation beam passes through said passage while at least a portion of the liquid is flowing out of said passage onto said layer.

19. A device manufacturing method comprising:

forming a beam of radiation with an image of a mask or reticle; and

irradiating a layer with the image using the method as claimed in claim 18.

20. A device comprising:

at least one optical element configured to focus a radiation beam from a radiation source to a spot on a layer;

a displacement structure configured to cause relative movement of the layer relative to said at least one optical element so that different portions of the layer are irradiated;

an outflow opening configured to supply liquid to fill an interspace between said layer and a surface of said at least one optical element nearest to said spot; and

a recess having an internal surface bounding at least a portion of said interspace through which said radiation irradiates said spot on said layer through said liquid, said recess being bounded at least in part by a wall between said layer and said surface of said at least one optical element nearest to said layer, a passage being formed in said wall, wherein said wall has a width-wise axis that extends through the body of the wall, the width-wise axis essentially extending perpendicular to an optical axis, through the interspace, of the radiation beam, wherein said wall has a major exterior surface arranged to contact said liquid, the major exterior surface being essentially perpendicular to the optical axis, extending at least partly underneath said at least one optical element, being a bottom-most surface of the wall and spanning a width that is larger than a height of the wall, and wherein said outflow opening is formed in said recess above said passage and said passage is a further opening in the recess and is arranged to have the radiation beam pass therethrough onto said spot.

21. A lithography apparatus comprising:

a wafer support table configured to support a wafer to be irradiated;

a scanner configured to have a reticle or mask;

a drive, coupled to the wafer support table, configured to move the support table in X and Y directions;

a control unit configured to control the drive and the scanner; and

a device as claimed in claim 20.

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