US20050178752A1 - Method and device for correcting pattern film on a semiconductor substrate - Google Patents

Abstract

In order to correct a white defect on a surface of a substrate, the substrate is held with the surface facing downward, laser light is upward irradiated at the defect on the surface in material gas, and as a result, the white defect is covered with film.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
• This application is a division of application Ser. No. 09/981,712, filed Oct. 19, 2001, now pending, and based on Japanese Patent Application No. 2000-320107, filed Oct. 19, 2000, by Yukio Morishige and Makoto Oomiya. This application claims only subject matter disclosed in the parent application and therefore presents no new matter.
BACKGROUND OF THE INVENTION
• This invention relates to correction of pattern on a semiconductor substrate and, particularly, on a semiconductor photo mask.
• A semiconductor photo mask is used for exposing a circuit pattern on a wafer in a manufacturing process of a semiconductor device, a liquid crystal display device, etc. A semiconductor photo mask is a transparent substrate on that a minute pattern film, which is an opaque film, is formed. When the pattern film is formed on the substrate, two types of defects may occur: a white defect or a clear defect at which a part of the pattern film is lost, and a black defect or an opaque defect at which the substrate is unnecessarily covered with film.
• For correcting white defects on a semiconductor photo mask, laser CVD (chemical vapor deposition) is available. According to laser CVD, laser light is irradiated at the white defects on the substrate in material gas including chromium. Laser light thermally resolves material gas around the white defects and as a result, film including chromium grows over the white defects.
• An example of conventional technique for correcting white defects on a semiconductor photo mask is Japanese Patent number (JP-B) 3036687 which is hereinafter referred to as first conventional technique. According to the first conventional technique, an optical system for laser irradiator/laser microscope, which includes laser light source and a unit for irradiation/observation, is arranged above the substrate set in material gas. The optical system downward irradiates laser light at white defects on the substrate. The optical system shapes laser light by its slit and projects a pattern on the substrate. As a result, the optical system corrects white defects precisely.
• On the other hand, black defects, namely unnecessary part of pattern film, is conventionally vaporized to correct a semiconductor photo mask by irradiating laser light on the part.
• Japanese Unexamined Patent Publication (JP-A) number H7-104459, namely 104459/1995 is titled “Method and apparatus for correcting defects on a photo mask”, which is hereinafter referred to as second conventional technique. According to the second conventional technique, first, pattern film is printed on one surface of transparent substrate. Next, the substrate is laid on the surface. Then, laser light is irradiated from the other surface through the substrate at black defects to vaporize the black defects. Since the former surface faces downward, particles generated when the black defects are vaporized drop down, and therefore, are not stuck on the former surface.
• According to the first conventional technique, laser light is irradiated down at white defects on a substrate to form the pattern film covering the white defects. Laser CVD generates particles from decomposed material gas. The particles in the air fall down and are struck again around the area at which laser light has been irradiated on the substrate. From the struck particles, CVD forms unnecessary film on the substrate. As a result, edge of the pattern film swells up on border of the mask pattern. Compared with the second conventional technique, the first conventional technique has less precision.
• According to the second conventional technique, on the other hand, the surface of the substrate on which laser light is irradiated faces downward, and consequently, most particles generated by laser light fall down. However, 0.1 μm or smaller particles often stick on the substrate again and cause a decline of transmittance around the area at which laser light has been irradiated. The decline of transmittance seriously affects the newest apparatus for correcting photo mask in 0.13 μm rule, which corresponds to 0.5 μm rule on its original photo mask.
SUMMARY OF THE INVENTION
• It is an object of the present invention to provide a method and a device for correcting defects of pattern film on a surface of a substrate in high accuracy.
• According to the present invention, the method comprises the steps of: holding the substrate with the surface facing downward; irradiating laser light upward at a white defect on the surface; blowing material gas for forming pattern film to the surface; and forming pattern film over the white defect.
• The method may further comprise the steps of: irradiating laser light upward at a black defect on the surface; and vaporizing unnecessary part of pattern film in order to correct the black defect.
• The method may further comprise the steps of: blowing oxygen gas to the surface; irradiating first laser light upward to unnecessary part of pattern film on the surface in order to oxidize the top layer of the part; irradiating second laser light upward to the oxidized top layer in order to peel the oxidized top layer off; and repeating the steps of irradiating first and second laser light in order to eliminate the unnecessary part of pattern film.
• The step of blowing may further blow purge gas, which prevents a window for conducting laser light from clouding, and carrier gas, which is included in CVD gas for carrying material gas; and the main component of the purge and carrier gases may be helium gas.
• The substrate may be sucked in order to be held at the step of holding.
• According to the present invention, the device comprises: a holder for holding the substrate with the surface facing downward; a laser irradiator for irradiating laser light upward at a white defect on the surface; a gas circulatory unit for providing and withdrawing gas including material gas; a gas window for blowing material gas on the surface and conducting laser light from the laser source through the gas window to the white defect in order to form pattern film over the white defect.
• The device may further comprise an optical unit for observing pattern film on the substrate. In this case, the substrate may be permeable to light and the device further may comprise a penetrating light source for irradiating light through the substrate to the lower surface of the substrate in order to illuminate with the lower surface. Moreover, the sucking unit may comprise a top cover permeable to light, and the penetrating light source may comprise a lens that is designed to compensate the distortion of the lens with reference to the total thickness of the cover and the substrate.
• According to the device, the laser irradiator may comprise first laser source for irradiating first laser light for vaporizing pattern film, and second laser source for irradiating second laser light for laser CVD. In this case, the first laser light is irradiated through the gas window at black defects in order to vaporize the black defects. The second laser light is irradiated through the gas window at white defects with material gas provided by the gas circulatory unit in order to form film over the white defects.
• According to the device, the gas circulatory unit may provide purge gas, which prevents a window for conducting laser light from clouding, and carrier gas, which is included in CVD gas for carrying material gas. Preferably, the main component of the purge and carrier gases is helium gas.
• The holder may suck the substrate in order to hold the substrate.
BRIEF DESCRIPTION OF THE DRAWING
• FIG. 1 shows a block diagram for use in describing a pattern-correcting device of the present invention;
• FIG. 2 shows a sectional view for use in describing thegas window6 of the present invention; and
• FIG. 3 shows a sectional view for use in describing the suckingunit9 of the present invention.
DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENTS1. First Embodiment
• Description will be made about an embodiment, a pattern-correcting device of the present invention. With reference toFIG. 1, first laser source (laser source1) provides laser light for vaporizing film, namely for correcting black defects and includes Nd:YVO4 laser which generates laser light in pulse width 0.8 ns, wavelength 355 nm andoscillation frequency 3 Hz. Second laser source (laser source2) provides laser light for laser CVD, namely for correcting white defects and includes Nd:YLF laser which generates laser light inpulse width 30 ns, wavelength 349 nm andoscillation frequency 7 Hz.
• A laser irradiator/microscopeoptical unit3 irradiates laser light generated by thelaser sources1 and2 to a lower surface of asubstrate16, which is permeable to light, and works as a microscope for observing a pattern on thesubstrate16. The laser irradiator/microscopeoptical unit3 is arranged under thesubstrate16 in order to irradiate laser light upward through agas window6 to the lower surface. Anobject lens4 condenses laser light irradiated from the laser irradiator/microscopeoptical unit3 and guides the laser light through thegas window6 to thesubstrate16.
• A gascirculatory unit5 is connected with thegas window6 through a pipe. The gascirculatory unit5 provides CVD and purge gases. Further, the gascirculatory unit5 withdraws and immunizes the gases exhausted from thegas window6. The CVD gas includes material and carrier gases. For example, the material gas is chromium carbonyl gas, the carrier and purge gases are helium gas or argon gas.
• Thegas window6 is arranged under thesubstrate16. Thegas window16 has a structure for covering the lower surface of thesubstrate16 and has a window for receiving laser light through theobject lens4 from the laser irradiator/microscopeoptical unit3. Thegas window6 is provided the CVD and purge gases from the gascirculatory unit5 through the pipe, and sprays on the lower surface of thesubstrate16 the CVD gas, which includes material gas for pattern film, and the purge gas, which prevents from clouding the window. Further, thegas window6 sucks the sprayed gas to exhaust it to the gascirculatory unit5.
• Detail of thegas window6 is shown inFIG. 2. In order to distinctly show the structure of thegas window6, inFIG. 2, thegas window6 is distinctly separated from thesubstrate16. However, thegas window6 and thesubstrate16 are actually spaced about 0.5 mm.
• As shown inFIG. 2, thegas window6 is arranged under thesubstrate16. Thegas window6 has a cylindrical shape with a roughly conical cavity at the center of thegas window6. The bottom of thegas window6, namely the lower face of thegas window6 toward theobject lens4, has an opening larger than another opening on the upper face of thegas window6. The opening on the lower face is occupied by awindow20, which stops the gases but conducts laser light from the laser irradiator/microscopeoptical unit3 via theobject lens4.
• On the side of thegas window6, apurge gas nozzle21 and amaterial supply nozzle22 are embedded through the cavity. Thepurge gas nozzle21 is opened near thewindow20 in order to spout purge gas for preventing clouding thewindow20. Thematerial supply nozzle22 is opened near a laser-irradiatinghole25, which is opened on the upper face of thegas window6, in order to spout the CVD gas out to the cavity, which includes material and carrier gases and is provided from the gascirculatory unit5.
• Furthermore, the upper face of thegas window6 has around groove23 on a circumference centering at the laser-irradiatinghole25. The gas sprayed on thesubstrate16 is sucked from theround groove23 and is exhausted through asuction pipe24 to the gascirculatory unit5.
• Arrows shown inFIG. 2 denote directions to which gas around the upper face of thegas window6 flows. The purge gas first spouts out from thepurge gas nozzle21 to thewindow20, next rises through the laser-irradiatinghole25, then flows between thegas window6 and thesubstrate16 to theround groove23, and after that is exhausted through thesuction pipe24. The CVD gas first spouts out from thematerial supply nozzle22 through the laser-irradiatinghole25 to the lower surface of thesubstrate16, next flows between thegas window6 and thesubstrate16 to theround groove23, and then is exhausted through thesuction pipe24.
• Not only the purge and CVD gases, but also the air around thegas window6 is sucked through theround groove23. Consequently, the CVD and purge gases spouted through the laser-irradiatinghole25 are isolated from the air around thegas window6. As a result, the pattern-correcting device can steadily deposit pattern film on thesubstrate16 by laser CVD without a vacuum device.
• Laser light irradiated from the laser irradiator/microscopeoptical unit3 through theobject lens4 is conducted from thewindow20, passes through the cavity of thegas window6 and the laser-irradiatinghole25 and is irradiated on the lower surface of thesubstrate16.
• Turning again toFIG. 1, a penetratinglight source7 lights up the translucent/transparent substrate16 in order to observe minute pattern on thesubstrate16 by the laser irradiator/microscopeoptical unit3. The penetratinglight source7 is designed to have an optimized optic angle with reference to compensation for thickness of thesubstrate16 and atranslucent cover31 of a sucking unit9 (seeFIG. 3).
• The laser irradiator/microscopeoptical unit3, theobject lens4, thegas window4 and the penetratinglight source7 compose an optical system for observing minute pattern on thesubstrate16. The wavelength of the light for observing is 365 nm. In a observing mode, the penetratinglight source7, an observing light and a slit light are available for light source of the optical system. The slit light projects shape of irradiated laser light on thesubstrate16.
• AX-Y stage8 horizontally carries thesubstrate16 between the place of delivery on a handler14 (the place where thesubstrate16 is drawn in solid line inFIG. 1) and the place over thegas window6. TheX-Y stage8 is permeable to light in order that light from the penetratinglight source7 can penetrate theX-Y stage8.
• A suckingunit9 is fixed on theX-Y stage8 to adhere to and hold thesubstrate16. The following description shows detailed structure of the suckingunit9. As shown inFIG. 3, the suckingunit9 includes an suckingmount30 that has a square frame shape. A 3-mm thicknesstranslucent cover31 is embedded in the top of the frame of the suckingmount30.Female screws32 for fixing the suckingmount30 on theX-Y stage8 are embedded on the top of the suckingmount30. An o-ring groove33 is cut around the inside of the suckingmount30 under thetranslucent cover31. A rubbery o-ring34 is embedded in the o-ring groove33 in order to keep the space between the suckingunit9 and thesubstrate16 airtight.
• On the side of the suckingmount30, atube10 is inserted. As shown inFIG. 1, thetube10 is connected via apressure sensor11 with apump12. Thepump12 sucks out the air in the space between the suckingunit9 and thesubstrate16, and consequently, the suckingunit9 adheres to thesubstrate16.
• As shown inFIG. 3, the lower surface of thesubstrate16 corresponds to the lower surface of the suckingunit9 when the suckingunit9 adheres to thesubstrate16. This structure of the pattern-correcting device allows theX-Y stage8 to move without obstruction in a horizontal plane with keeping a minute space between thegas window6 and thesubstrate16. To keep the minute space allows gas between thegas window6 and thesubstrate16 to flow steadily. Therefore, this structure prevents turbulence of gas damaging formation of pattern film and causing a gas leak from the inside of thegas window6.
• Turning again toFIG. 1, an image-processingunit13 takes image of thesubstrate16 on thehandler14 in order to confirm whether thesubstrate16 is put on a stand of thehandler14 at a correct position.
• When thesubstrate16 is put on the stand of thehandler14, thehandler14 turns around to the place of delivery of thesubstrate16 to the suckingunit9. Then, thehandler14 lifts up the stand by its Z-axis mechanism in order that the suckingunit9 becomes available for adhering to thesubstrate16.
• After finishing correcting defects of a photo mask, the suckingunit9 releases thesubstrate16 and puts thesubstrate16 on the stand of thehandler14. Then, thehandler14 lowers the stand by the Z-axis mechanism and turns around to the place for taking out thesubstrate16 from the pattern-correcting device.
• Acontroller15 controls workings of the pattern-correcting device; thelaser sources1 and2, laser irradiator/microscopeoptical unit3, gascirculatory unit5, penetratinglight source7,X-Y stage8,pressure sensor11, pump12,handler14 and image-processingunit14.
• Description will be made about the working process of the pattern-correcting device of the present invention.
• (1) A photo-mask-examining device has previously detected white and black defects on a photo mask. The photo-mask-examining device acquires information about defects. Hereinafter, the data that represents the information about the defects is referred to as defect data. The defect data include data representing where and which defects are detected and are stored in thecontroller15 of the pattern-correcting device.
• First, an operator of the pattern-correcting device puts thesubstrate16 of a 6-inch photo mask on the stand of thehandler14. Thecontroller15 makes the image-processingunit13 recognize thesubstrate16 on the stand of thehandler14 in order to acquire information about positioning thesubstrate16 on the stand of thehandler14. The positioning information includes position of the center of thesubstrate16 and an angle that thesubstrate16 is set in X-Y plane. With reference to the positioning information, thecontroller15 directs thehandler14 to turn around the stand so as to suppress disagreement between the angle of thesubstrate16 and the angle of the suckingunit9 whensubstrate16 moves to the place for delivery to the suckingunit9. Simultaneously, thecontroller15 directs theX-Y stage8 to tune in its horizontal position exactly in order that thesubstrate16 is positioned just under the suckingunit9 when the stand of thehandler14 turns around to the place for delivery.
• Next, thecontroller15 directs thehandler14 to lift the Z-axis mechanism up to the predetermined position, and thepump12 to start to suck out the air in the suckingunit9. With reference to pressure measured by thepressure sensor11, thepump12 adjusts conductance of the suckingunit9 in order that the pressure inside the suckingunit9 becomes 0.3 atm. Further, thecontroller15 directs thehandler14 to lower the Z-axis mechanism to a ready position and to stand by.
• After the suckingunit9 adheres to thesubstrate16, thecontroller15 directs theX-Y stage8 to move thesubstrate16 to the position over thegas window6. On this situation, thecontroller15 directs the gascirculatory unit5 to provide purge gas and CVD gas to thegas window6. It is assumed that: each of the carrier gas included in the CVD gas and purge gas is argon gas; the material gas included in the CVD gas is chromium carbonyl gas; the flow rate of the CVD gas is 70-sccm; and the flow rate of the purge gas is 1500-sccm.
• With reference to the defects data previously stored in thecontroller15, thecontroller15 directs theX-Y stage8 to move thesubstrate16 so as to a white defect on thesubstrate16 is positioned right above the laser-irradiatinghole25 of thegas window6. The operator observes the white defect on thesubstrate16 by the laser irradiator/microscopeoptical unit3 with her/his own eyes to make sure, and next, exactly tunes in size, angle and position of a slit for irradiating laser of the laser irradiator/microscopeoptical unit3. Then, thelaser source2, which irradiates laser light for CVD, irradiates laser light 5 seconds at the white defect to form film. These processes are repeated for all of the white defects on thesubstrate16.
• When all of the white defects on thesubstrate16 are corrected, the operator stops providing CVD gas and only provides purge gas. Next, thecontroller15 directs theX-Y stage8 to move a black defect on thesubstrate16 just above the laser-irradiatinghole25 of thegas window6. The operator observes the black defect on thesubstrate16 by the laser irradiator/microscopeoptical unit3 with her/his own eyes to make sure, and next, exactly tunes in size, angle and position of a slit for irradiating laser of the laser irradiator/microscopeoptical unit3. Then, thelaser source1, which irradiates laser light for vaporizing film, irradiates two shots of laser light at the black defect to vaporize unnecessary part of pattern film. These processes are repeated for all of the black defects on thesubstrate16.
• After all of the black defects on thesubstrate16 are corrected, thecontroller15 stops providing purge gas and directs theX-Y stage8 to move the suckingunit9 over the stand of thehandler14. Then, thecontroller15 directs thehandler14 to lift its Z-axis mechanism up and the suckingunit9 to release thesubstrate16 in order to put on thesubstrate16 on the stand of thehandler14. Next, thecontroller15 directs thehandler14 to lower the Z-axis mechanism and turn around thesubstrate16 to the place where the operator can receive thesubstrate16. Finally, theoperator16 takes out thesubstrate16 from the pattern-correcting device.
• (2) Compared with a typical conventional technique, the pattern-correcting device is described below.
• Conventionally, a laser light source for forming film on a substrate is arranged over the substrate, and irradiates laser light downward to the substrate. It is assumed that a 5 μm×5 μm square of chromium film will be formed on a substrate under ideal processing condition according to this conventional technique. Argon gas is used for purge and CVD gas. In this case, though laser light is irradiated to a 5 μm×5 μm square on the substrate, it is probable that CVD size, which means size of film actually formed on the substrate, grows to about 5.4 μm×5.4 μm. Further, CVD size is fluctuant over 0.1 μm even under the same condition.
• On the other hand, it is assumed that the same square will be formed on a substrate under ideal processing condition according to the pattern-correcting device of the present invention. In this case, when laser light is irradiated to a 5 μm×5 μm square on the substrate, the CVD size grows to about 5.2 μm×5.2 μm. The fluctuation of CVD size is about 0.07/m. Moreover, when helium gas is used for purge and CVD gases instead of argon gas and light is irradiated to a 5 μm×5 u m square on the substrate, there is great improvement in both growth and fluctuation of the CVD size. In this case, the CVD size is 4.9 μm×4.9 μm and the fluctuation of the CVD size is 0.03 μm.
• Mean free path of particles in helium gas is about ten times longer than that in argon gas or the air. Consequently, particles are diffused more rapidly and widely in helium gas than in argon gas or the air. As a result, in helium gas, the particles caused by laser CVD leave from the substrate faster, and density of the particles near the substrate, which is possible to stick on the substrate again, is lower than in argon gas or the air. This effect is available even if one of purge and carrier gases is argon gas and the other is helium gas.
• Regardless of type of gas in which the substrate is arranged, as mentioned above, since laser light is irradiated upward on the lower surface of thesubstrate16, the particles caused by processes for correcting defects fall down. As a result, the probability that the particles stick on the substrate again reduces greatly.
• As shown inFIG. 2, purge gas at the top of thegas window6 becomes ascending current. The ascending current blows against thesubstrate16 and causes a boundary layer of gas flow under thesubstrate16. The boundary layer has a thickness several ten micron-meters. In the boundary layer, the particles fall down. On the other hand, under the boundary layer, the particles are caught in a radial current from the top center of thegas window6 to theround groove23.
• The thickness of the boundary layer depends on viscosity of gas, flatness of thesubstrate16, etc. Generally, the boundary layer is thicker in argon gas than in helium gas. However, since mean free path of particles in helium gas is longer than in argon gas, CVD size by laser CVD is tighter in helium gas than in argon gas.
• (3) Next, description will be made about working process of the suckingunit9.
• The suckingunit9 applies negative pressure to the upper surface of thesubstrate16, which is opposite to the lower surface for masking, in order to adhere to thesubstrate16. This method of holding is effective because: thesubstrate16 can be held as its lower surface for masking faces downward; and there is no obstacle between the lower surface of thesubstrate16 and thegas window6.
• The top of the suckingunit9 is covered with thetranslucent cover31. With reference to the total thickness of thetranslucent cover31 and thesubstrate16, compensation for distortion of the lens included in the penetratinglight source7 can be optimized, namely, optical distortion of light irradiated by the penetratinglight source7 can be compensated. Consequently, the optical system for illuminating, which includes the penetratinglight source7, thetranslucent cover31 and thesubstrate16, can be given a numerical aperture optimized for the numerical aperture of theobject lens4. As a result, the operator can observe pattern mask on thesubstrate16 as high-resolution image.
• Negative pressure that the suckingunit9 applies to thesubstrate16 may be selected according to the thickness of thesubstrate16. For example, when thesubstrate16 is 5 inch square and 2.3-mm thickness, the negative pressure may be low, such as 0.3 kg/cm2. This can prevent the negative pressure breaking thesubstrate16.
• The pattern-correcting device mentioned above stops providing CVD gas when eliminating unnecessary pattern film, namely when correcting black defects. However, effect of correcting black defects with providing CVD gas hardly seems to be different from effect of correcting black defects without providing CVD gas. Therefore, the pattern-correcting device does not have to stop providing CVD gas when correcting black defects. To stop providing CVD gas when correcting black defects allows the pattern-correcting device to save material gas consumption, and as a result, replacement of material gas can be delayed.
• Further, according to the pattern-correcting device mentioned above, the inclination of thesubstrate16 is not checked after the suckingunit9 adheres to thesubstrate16. However, the pattern-correcting device may include an interlock mechanism for checking the inclination of thesubstrate16 if necessary. The interlock mechanism, for example, includes sensors for measuring height of thesubstrate16.
• According to the pattern-correcting device mentioned above, the surface processed for correcting defects faces downward when the surface is held by the suckingunit9 in order to correct white defects on a photo mask by laser CVD. Consequently, the pattern-correcting device can prevent from sticking again particles caused by laser CVD on thesubstrate16. The difference between the area on thesubstrate16 irradiated by laser light and the area on thesubstrate16 covered with film is smaller. The fluctuation of the area covered with film is smaller. As a result, the pattern-correcting device can process photo mask with high accuracy.
• Further, the pattern-correcting device includes two laser sources. One of the laser sources irradiates laser light for vaporizing film. The other irradiates laser light for laser CVD. Consequently, a single one of the pattern-correcting device can execute by itself functions for correcting both white and black defects. Both of the laser sources irradiate laser light to the lower surface of the substrate. Consequently, particles both caused by laser CVD for correcting white defects and caused by vaporizing unnecessary film for correcting black defects fall down and do not stick again on the substrate. As a result, the pattern-correcting device can correct white and black defects on a photo mask in high accuracy.
• Further, helium gas may be available for the main component of purge gas and carrier gas and prevents particles caused by laser CVD from sticking again on thesubstrate16. According to helium gas, the pattern-correcting device can process pattern film on thesubstrate16 in higher accuracy.
• Further, in order to hold thesubstrate16, the suckingunit9 adheres to thesubstrate16 when correcting defects of pattern film on thesubstrate16. To adhere to thesubstrate16 allows thesubstrate16 facing downward when the suckingunit9 holds thesubstrate16.
• Further, compensation for distortion of the lens included in the penetratinglight source7 is optimized with reference to the total thickness of thetranslucent cover31 and thesubstrate16 for the numerical aperture of theobject lens4. As a result, the operator can observe pattern mask on thesubstrate16 as high-resolution image.
2. Second Embodiment
• The second embodiment is provided for improving a method of correcting black defects, which is unnecessary part of film, on a photo mask. The pattern-correcting device of the first embodiment mentioned above is applied for the following description of the second embodiment.
• According to the first embodiment, argon or helium gas is provided as purge gas. On the other hand, according to the second embodiment, oxygen gas is provided as purge gas and no CVD gas is provided. In this situation, thelaser source1 irradiates one shot of laser light to a black defect. The shot has twenty-five percent strength of laser light which is conventionally irradiated for eliminating a black defect. The shot eliminates chromium oxide film, which is formed on the top surface of chromium film as an AR court layer b (film preventive of reflection), about 200-angstrom in order to expose a layer lower than the AR court layer.
• Next, thelaser source2 irradiates laser light 0.5 second on thesubstrate16. This time, the strength of the laser light is less than strength for vaporizing chromium film in order that the top of the exposed chromium layer is oxidized and changes color. Then, thelaser source1 irradiates another laser shot on the exposed chromium layer. After that, the exposed chromium layer is peeled off and another chromium layer is newly exposed. After exposure and peeling of a chromium layer are repeated about ten times, chromium film of a black defect on thesubstrate16 is eliminated and a glass surface of thesubstrate16 appears.
• The second embodiment can eliminate black defects by laser light with twenty five percent lower strength than laser light used in conventional technique. Lower strength of laser light allows thesubstrate16 to be less damaged. According to conventional techniques for eliminating black defects, a quartz glass layer of thesubstrate16 is dug 300-angstrom depth on average under even an optimized condition. On the other hand, according to the second embodiment, the quartz glass layer is dug 50-angstrom depth.
• According to the second embodiment, the chromium film is oxidized and then is eliminated. Molecular weight of chromium oxide is larger than that of non-oxidized chromium. Therefore, the particles that the second embodiment produces when eliminating chromium film is easy to fall down, and as a result, hardly sticks again on thesubstrate16. Compared with conventional technique for eliminating black defects, the second embodiment can form film on thesubstrate16 whose edges are highly straight and have smooth walls. Further, when a5, m×5 μm square black defect on thesubstrate16 has been corrected according to conventional techniques, transmittance around the corrected black defects on thesubstrate16 declines about 1.5 percent. On the other hand, when the same black defect has been corrected according to the second embodiment, the transmittance drops only 1.0 percent or less.
• According to the present invention, the substrate is held with the surface facing downward and material gas for forming pattern film is blown on the surface. In this situation, laser light is irradiated upward at a white defect in order to form pattern film over the white defect. When the laser light is irradiated at the white defect, particles are generated. However, the particles fall down and do not stick again to the substrate. Consequently, the present invention can prevent pattern film from overgrowing and growing irregularly in size. As a result, according to the present invention, a photo mask is processed in high accuracy.
• Further, in order to correct a black defect on the substrate, laser light may be upward irradiated at the black defect to vaporize unnecessary part of pattern film. Though particles are generated in the air when the black defect is vaporized, the particles fall down and do not stick again to the substrate.
• In order to eliminate unnecessary part of pattern film, the present invention may repeatedly both oxidize the top layer of pattern film and peel the layer off. In this case, one layer peeled off at a time is so thin that the substrate is damaged less to eliminate unnecessary part of pattern film.
• Helium gas is available for purge and CVD gas of the pattern-correcting device of the present invention. When purge and CVD gas include helium gas as the main component, less particles stick again to the substrate.
• In order to hold the substrate, the present invention may suck the substrate. To suck the substrate is helpful to downward face the surface of the substrate on which defects are irradiated by laser light.
• The pattern-correcting device including the top cover and the lens allows its operator to observe the substrate with penetrating light in high resolution.
• While this invention has thus far been described in conjunction with a few embodiments thereof, it will be readily possible for those skilled in the art to put the this invention into various other manners.

Claims (5)

1. A method of correcting defects of pattern film on a surface of a substrate, comprising the steps of:

holding the substrate with the surface facing downward;

blowing material gas for forming pattern film to the surface; and

irradiating laser light upward at a white defect on the surface to form pattern film over the white defect.

2. The method claimed inclaim 1, further comprising the steps of:

irradiating laser light upward at a black defect on the surface; and

vaporizing unnecessary part of pattern film in order to correct the black defect.

3. The method claimed inclaim 1, further comprising the steps of:

blowing oxygen gas to the surface;

irradiating first laser light upward to unnecessary part of pattern film on the surface in order to oxidize the top layer of the part;

irradiating second laser light upward to the oxidized top layer in order to peel the oxidized top layer off; and

repeating the steps of irradiating first and second laser light in order to eliminate the unnecessary part of pattern film.

4. The method claimed in clam1, wherein:

the step of blowing further blows purge gas, which prevents a window for conducting laser light from clouding, and carrier gas, which is included in CVD gas for carrying material gas; and

the main component of the purge and carrier gases is helium gas.

5. The method claimed inclaim 1, wherein the substrate is sucked in order to be held at the step of holding.

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