JP4433860B2 - Method for manufacturing glass substrate, method for manufacturing photomask blanks, and method for manufacturing photomask - Google Patents

Description

  The present invention relates to a glass substrate for a photomask used for LSI manufacturing, and a photomask blank and a photomask using the glass substrate.

  Conventionally, a photomask used in an LSI manufacturing process uses a predetermined glass material, cuts sheet-like glass, or slices block-like glass, then chamfers the outer peripheral portion, A light shielding film made of a metal such as chromium oxide was formed on the surface of the glass substrate obtained by polishing, cleaning and inspection by sputtering or the like, and a photoresist was applied to expose a predetermined portion. Thereafter, unnecessary photoresist portions are etched, and then unnecessary light shielding film portions are removed by etching. On the other hand, photomasks using new techniques have been proposed as LSIs are highly integrated and patterns are miniaturized. For example, a technique for improving the resolution of a transfer pattern by giving a phase difference to projection light transmitted through an adjacent opening of a photomask has been proposed by Levenson et al. Of IBM Corporation. Is generally called a Levenson-type phase shift mask. There are two methods for forming the phase shifter portion: a shifter type for forming a transparent thin film pattern called a shifter, and a digging type for forming a digging in a synthetic quartz glass substrate.

  This digging-type Levenson-type shift mask is one in which a digging portion having a phase difference of transmitted light of 180 degrees is formed in one of the adjacent openings on the photomask. Such a dug portion is formed by anisotropic etching, for example.

  However, in this case, the amount of light transmitted through the digging portion is lower than the amount of light transmitted through the non-digging portion due to the influence of the side wall of the digging portion, and the dimensions of the transfer patterns corresponding to the digging portion and the non-digging portion respectively. Make a difference. In order to avoid this, it has been proposed to provide a sufficient undercut under the light shielding film in the digging portion. That is, when the position of the side wall of the digging portion is shifted to the light shielding portion side, the amount of light transmitted through the digging portion is substantially equal to the amount of light transmitted through the non-digging portion, and corresponds to the digging portion and the non-digging portion. The dimensional difference of the transfer pattern can be reduced.

  In order to form such a digging portion with an undercut, isotropic wet etching using hydrofluoric acid or the like is used. In this wet etching, a chemical solution having acidic or alkaline reactivity is used. Examples of such chemical solutions include, for example, various compounds containing fluorine ions, chemical solutions such as sulfuric acid, nitric acid, hydrochloric acid, sodium hydroxide, potassium hydroxide, etc., or a mixture thereof, or a surfactant or chelating agent mixed with them. The liquid is selected as appropriate according to the film to be etched and the glass material.

  The following Patent Document 1 also discloses a Levenson type phase shift mask using isotropic wet etching.

In the case of an inexpensive photomask, wet etching is generally used when removing unnecessary light-shielding film portions.
JP 2003-241360 A

  However, in the above prior art, when processing a substrate by isotropic wet etching, scratches and cracks (hereinafter referred to as latent scratches) that were not detected in the inspection process and existed on the substrate surface were detected. This has caused problems such as etch pits on the surface of the glass, film defects, dimensional anomalies in the grooves, and the like, resulting in a decrease in product yield.

  4 (a) to 4 (e) are explanatory views of a mechanism for causing the latent damage. FIG. 4A is a schematic partial cross-sectional view of the glass substrate 10 after the slicing process or the lapping process, and there are large and small scratches and cracks on the surface of the substrate. These scratches and cracks are removed by polishing the surface of the glass substrate 10 to the expected surface 12 indicated by a broken line in FIG. However, if the polishing of the substrate surface in the precision polishing process is insufficient, some of them only have a shallow depth, and some scratches and cracks remain on the surface of the glass substrate 10.

  FIG. 4C shows an example of scratches or cracks existing on the surface of the glass substrate 10 after the precision polishing step. In FIG.4 (c), the damage | wound or crack 14a is a damage | wound or crack resulting from the lapping process by which the opening part was filled and became a latent flaw by the plastic flow which arises on the surface of the glass substrate 10 at the precision polishing process. The flaw or crack 15a is a flaw or crack resulting from a lapping process in which the opening is open but the opening is narrow and difficult to detect and latent. The flaws or cracks 16a are flaws or cracks caused by a lapping process in which the opening is wide and easy to detect, so that it is difficult to cause a latent flaw. The flaw or crack 17a is a flaw or crack caused by a precision polishing process in which the opening is wide and easy to detect and is not easily latent. The scratches or cracks 18a are scratches or cracks resulting from the precision polishing process in which the openings are filled and become latent scratches due to plastic flow that occurs on the surface of the glass substrate 10 in the precision polishing process. Among the above, the scratches or cracks 16a and 17a can be detected by a subsequent inspection process after the precision polishing process, and the glass substrate 10 with the scratches or cracks can be removed from the manufacturing process. is there. Note that the reason for the lapping process or precision polishing process is that scratches or cracks are generated when huge particles are present in the polishing agent used for lapping or precision polishing, or when foreign substances are struck on the substrate surface when handling the substrate. It means a crack that has occurred. In addition, the surface of the glass substrate 10 may be damaged or cracked by an ultrasonic cleaner used in the above-described cleaning process, or a latent scratch that becomes apparent only after etching.

  The predicted surface 20 when the isotropic wet etching is performed on the surface of the glass substrate 10 as described above is shown by a broken line in FIG. FIG. 4 (e) shows the surface of the glass substrate 10 after isotropic wet etching. As shown in FIG. 4D and FIG. 4E, the opening or opening is narrowed by the isotropic wet etching, and the opening is enlarged by plastic flow. The plastic fluidized bed is also removed from the scratches or cracks that have been buried and become latent scratches, and all of them become apparent on the surface of the glass substrate 10. In FIG. 4 (e), scratches or cracks 14b are scratches or cracks resulting from the lapping process that has been manifested by removing the plastic fluidized layer by isotropic wet etching. The flaws or cracks 15b are flaws or cracks resulting from the wrapping process that has become obvious due to the opening being widened by isotropic wet etching. The flaw or crack 16b is a flaw or crack resulting from a lapping process in which the opening is further widened by isotropic wet etching. The scratch or crack 17b is a scratch or crack resulting from a precision polishing process in which the opening is further widened by isotropic wet etching. The flaws or cracks 18b are flaws or cracks resulting from a precise polishing process that has been manifested by removing the plastic fluidized layer by isotropic wet etching.

  As described above, the conventional techniques have various causes of latent scratches, and it is difficult to remove them.

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a glass substrate in which latent scratches do not occur due to isotropic wet etching, and a photomask blank and a photomask using the glass substrate. It is in.

In order to achieve the above object, the present invention is a method of manufacturing a glass substrate for obtaining a product by isotropic wet etching , and after a precision polishing step , a predetermined amount of surface layer is removed by anisotropic dry etching , It is characterized by removing latent scratches existing on the surface . The anisotropic etching is preferably performed by a gas cluster ion beam method.

Moreover, this invention is a manufacturing method of the photomask blanks using the glass substrate manufactured by the said glass substrate manufacturing method, and the photomask manufacturing method using the photomask blanks manufactured by this Features.

  Further, according to the present invention, in the photomask, a light shielding portion and an opening portion are alternately present on the substrate, and a recessed portion for inverting the phase of transmitted light passing through is provided in a part of the opening portion. The Levenson type phase shift mask is characterized in that an undercut is formed in the digging portion.

  According to the present invention, latent scratches existing on the surface layer of the glass substrate can be removed by anisotropic etching, and latent scratches can be prevented from becoming apparent even when isotropic wet etching is performed.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described with reference to the drawings.

  1A to 1E show a schematic partial cross-section of a glass substrate 10 for explaining the glass substrate manufacturing process according to the present invention, and the same elements as those in FIG. The code | symbol is attached | subjected. 1 (a), (b), and (c) are the same as FIGS. 4 (a), (b), and (c), and FIG. 1 (a) is the glass after the slicing process or lapping process. It is a typical fragmentary sectional view of the board | substrate 10, and a small and large crack and a crack exist in the substrate surface. Further, FIG. 1B shows an expected surface 12 of the glass substrate 10 after being polished by the precision polishing step, and FIG. 1C shows the glass substrate 10 after the precision polishing step. Examples of scratches or cracks 14a, 15a, 16a, 17a, 18a present on the surface are shown.

  In FIG. 1D, an expected surface 22 when a predetermined amount of the surface layer of the glass substrate 10 after the precision polishing step and the cleaning step is removed by anisotropic etching is indicated by a broken line. A characteristic point of the present invention is that after the precision polishing step, a predetermined amount of the surface layer of the glass substrate 10 is removed by anisotropic etching, and scratches or cracks 14a, 15a, 16a, 17a, 18a, etc. existing on the surface are removed. There is. Thereby, almost all latent scratches can be removed. Therefore, as shown in FIG. 1 (e), even if isotropic wet etching is performed in a subsequent process, it is possible to prevent the occurrence of scratches or cracks. For the glass substrate 10 according to the present embodiment, various glass materials such as soda lime glass, alumina silicate glass, borosilicate, and synthetic quartz glass can be used.

  Examples of the anisotropic etching include dry etching such as reactive ion beam etching and other ion beam etching, plasma etching, sputter etching, photoetching, and gas cluster ion beam method.

  Among these, reactive ion beam etching has a magnetic coil for generating a magnetic field, introduces a reactive gas as an etching gas into the reaction tube, and generates plasma by the reactive gas using electric power by microwaves. And irradiating the glass substrate as reactive gas ions to etch the surface of the glass substrate.

  FIG. 2 shows a schematic diagram of the configuration of an apparatus used for the gas cluster ion beam method. In FIG. 2, the apparatus forms a gas cluster by adiabatic expansion by ejecting a source gas supplied from a gas cylinder 24 from a nozzle 28 at a supersonic speed arranged in a vacuum chamber 26. The generated gas cluster passes through the skimmer 30, and the beam shape is adjusted and supplied to the ionization unit 32. In this ionization part 32, a gas cluster is ionized by the electron collision by a filament. The ionized gas cluster is accelerated by an electric field in the acceleration unit 34. The accelerated gas cluster ions are applied to the glass substrate 10 to which a high voltage is applied, and are broken by collision with the surface of the glass substrate 10. At that time, cutting in the horizontal direction in the figure is performed on the surface of the glass substrate 10. According to such a gas cluster ion beam method, the convex portions on the surface of the glass substrate 10 are mainly shaved, and flat ultra-precision polishing at an atomic size can be performed.

  As the source gas used in the gas cluster ion beam method, an inert gas, for example, argon, nitrogen gas, oxygen gas, etc., as well as carbon dioxide of a compound, etc., one or more gases as necessary are used. Can be used alone or in admixture.

  The glass substrate 10 according to the present embodiment described above can be processed into a photomask blank and a photomask obtained by isotropic wet etching. In addition, a stamper for manufacturing a resin substrate for information recording media, a high-temperature or low-temperature polysilicon display element, a glass information recording medium, and the like are also obtained by isotropic wet etching from the glass substrate 10 according to the present embodiment. Can do. In addition, Lab-on-a-chip (laboratory chip), DNA chip, etc., in which laboratory processes such as chemical reaction, cell culture, and separation / detection are integrated on a chip with fine grooves and depressions on a glass substrate Also, it can be obtained by isotropic wet etching from the glass substrate 10 according to the present embodiment.

  FIG. 3 shows a partial sectional view of an example of a Levenson type phase shift mask using the glass substrate according to the present embodiment. In FIG. 3, on the glass substrate 10, an engraved portion 40 for reversing the phase difference of transmitted light by 180 degrees is formed in adjacent openings 38 through a metal light-shielding film 36. Yes. An undercut 42 is formed under the light shielding film 36 in the dug 40. As a result, the amount of light transmitted through the opening 38 in which the digging portion 40 is formed is substantially equal to the amount of light transmitted through the opening 38 in which the digging portion 40 is not formed, and corresponds to each opening 38. The dimensional difference of the transfer pattern can be reduced.

  In order to form the dug 40 having the undercut 42, isotropic wet etching using hydrofluoric acid or the like is used. In the glass substrate 10 according to the present embodiment, as described above, latent scratches are removed by anisotropic etching such as a gas cluster ion beam method, so isotropic wet etching is performed for forming the dug 40. Even if it is used, it is possible to prevent the appearance of scratches and cracks, and it is possible to manufacture a high-quality Levenson type phase shift mask.

  In addition, since the damage | wound and crack of the surface of the glass substrate 10 generate | occur | produce in various processes and circumstances, the depth is also various. Therefore, in the present invention described above, the amount of removal of the surface of the glass substrate 10 by anisotropic etching is not specifically defined, and the amount of surface removal is appropriately set so that those scratches and cracks can be appropriately removed. decide.

  Examples of the present invention will be described below. In addition, this invention is not limited to a present Example.

  A synthetic quartz glass ingot manufactured by a known method was prepared, and this was cut into a plate shape of 153.0 mm in length, 153.0 mm in width, and 6.75 mm in thickness using an inner peripheral slicer. A synthetic quartz glass plate sample was prepared. Next, a chamfering process was performed on these plate samples using a commercially available NC chamfering machine using a 120 mesh diamond grindstone so that the outer dimensions were 152 mm and the chamfering width was 0.2 to 0.4 mm.

  Next, this plate material sample was used by using a slurry in which GC # 400 (trade name, manufactured by Fujimi Corporation) was suspended in filtered water as a polishing material using a 20B double lap machine manufactured by Speed Fam. And processed to a thickness of 6.63 mm.

  Furthermore, using another 20B double-sided lapping machine, using a slurry in which FO # 1000 (trade name, manufactured by Fujimi Corporation) is suspended in filtered water as a polishing material in an amount of 18 to 20% by mass, the thickness is 6.51 mm. Processed until. Thereafter, the outer periphery of 30 μm was polished using a slurry and buff mainly composed of cerium oxide, and the end surface was mirror-finished.

  Next, using a 20B double-side polish machine as a primary polish for these plate material samples, LP66 (trade name, manufactured by Rhodes) as a polishing cloth, and Mille 801A (trade name, manufactured by Mitsui Kinzoku Co., Ltd.) as an abrasive are 10 to 10. 50 μm was polished on both sides using a slurry in which 12% by mass was suspended.

  Further, the above plate material sample was polished using a 20B double-side polishing machine, and 10 μm was polished on both sides by using Seagull 7355 (trade name, manufactured by Toray Cortex Co., Ltd.) as a polishing cloth, and then finalized using colloidal silica using another polishing machine. Polishing was performed.

  Next, the plate material sample was washed with a multi-stage automatic washer in which the first tank was a hot solution of sulfuric acid and hydrogen peroxide and the third tank was a neutral surfactant solution, and then the surface for the photomask Using a defect inspection machine M1320 (trade name, manufactured by Lasertec Corporation), 30 synthetic quartz glass substrates were obtained in which the number and position information of defects having a size of 150 nm or more were grasped. After that, the 30 synthetic quartz glass substrates were divided into 2 groups of 15 so that the total number of defects was almost equal, and they were designated as group 1 and group 2, respectively.

  As a comparative example of the present invention, Group 1 was immersed in a 5% by weight hydrofluoric acid solution for 5 minutes, etched, washed with the above-described automatic washing machine, and similarly subjected to surface defect inspection. Thereafter, a defect map as a result of the surface defect inspection was collated before and after the hydrofluoric acid treatment, and a defect (scratch) judged to have newly occurred was detected. Of these disadvantages, four representative samples were sampled and the substrate was cleaved so as to cross the wound, and the cross section was observed with an SEM. .8 μm. Further, when the etching speed of the synthetic quartz glass substrate with a 5 wt% hydrofluoric acid solution was separately measured, it was about 0.1 μm when the immersion time was 5 minutes.

  As an example of the present invention, Group 2 removed 1 μm of the surface layer of the synthetic quartz glass substrate by a gas cluster ion beam method (using an apparatus manufactured by Epion, USA). Next, hydrofluoric acid etching similar to that in Group 1 was performed.

  Table 1 shows the number of detected defects before etching hydrofluoric acid and the number of detected defects after etching.

  The results shown in Table 1 are a comparison of the average values of 15 synthetic quartz glass substrates in each group. As can be seen from Table 1, the increase in the number of defects of the group 1 which is the comparative example is much larger than the group 2 which is the embodiment of the present invention. This shows that the present invention is effective in removing latent scratches.

It is a typical partial cross section of a glass substrate for demonstrating the manufacturing process of the glass substrate concerning this invention. It is the schematic of the structure of the apparatus used for a gas cluster ion beam method. It is a fragmentary sectional view of the example of the Levenson type phase shift mask using the glass substrate concerning the present invention. It is explanatory drawing of the mechanism in which a latent damage generate | occur | produces on the glass substrate surface.

Explanation of symbols

  10 Glass substrate, 12, 20, 22 Expected surface, 14a, 14b, 15a, 15b, 16a, 16b, 17a, 17b, 18a, 18b Scratch or crack, 24 Gas cylinder, 26 Vacuum chamber, 28 Nozzle, 30 Skimmer, 32 Ionization Part, 34 acceleration part, 36 light shielding film, 38 opening part, 40 digging part, 42 undercut.

Claims (5)

A method for producing a glass substrate for obtaining a product by isotropic wet etching, wherein a predetermined amount of a surface layer is removed by anisotropic dry etching after a precision polishing step to remove latent scratches existing on the surface. A method for producing a glass substrate. The method for manufacturing a glass substrate according to claim 1, wherein the anisotropic etching is performed by a gas cluster ion beam method . A method for producing blanks for photomasks, wherein a glass substrate produced by the method for producing a glass substrate according to claim 1 or 2 is used. Photomask manufacturing method, characterized by using a photomask blank manufactured by the method of claim 3, wherein the photomask blank. 5. The method of manufacturing a photomask according to claim 4, wherein the manufactured photomask has a light-shielding portion and an opening portion alternately and repeatedly on the substrate, and a phase of transmitted light passing through a portion of the opening portion. A photomask manufacturing method , characterized in that the photomask is a Levenson-type phase shift mask in which a digging portion for inverting the pit is provided and an undercut is formed in the digging portion.

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