JP5114367B2 - Photomask manufacturing method and pattern transfer method using the photomask - Google Patents

Description

  The present invention relates to a photomask manufacturing method used for manufacturing LSIs, liquid crystal display devices (Liquid Crystal Display: hereinafter referred to as LCD), and the like, and a pattern transfer method using the photomask.

  Thin film transistor liquid crystal displays (hereinafter referred to as TFT-LCDs) are currently commercialized and increased in size due to the advantage that they are thinner and have lower power consumption than CRTs (cathode ray tubes). Is progressing rapidly. A TFT-LCD includes a TFT substrate having a structure in which TFTs are arranged in pixels arranged in a matrix, and a color filter in which red, green, and blue pixel patterns are arranged corresponding to each pixel. It has a schematic structure superimposed under the intervention of.

  In the manufacture of a TFT-LCD, a lithography process using a projection exposure technique is frequently used as in the manufacture of a semiconductor device such as an LSI. A photomask used as a mask when performing this projection exposure includes a light-transmitting part and a light-shielding part after preparing a photomask blank in which a light-shielding thin film is formed on a transparent substrate and patterning the thin film. An exposure transfer pattern is formed. Alternatively, as the light-shielding film, a film that transmits a part of the irradiation light is used, and in addition to the light-transmitting part and the light-shielding part, a semi-light-transmitting part is further provided.

  A pellicle is generally mounted on the pattern forming surface of the photomask. This is because, if there is a foreign substance on the pattern formation surface of this photomask, the shape of the foreign substance is transferred to the transfer target, for example, in the lithography process, affecting the pattern shape to be obtained and causing the defective product. It becomes. For the purpose of reducing such foreign matter on the pattern formation surface of the photomask, a pellicle is mounted on the pattern formation surface of the photomask.

  On the other hand, in the field of semiconductor device manufacturing masks, when the mask is used for a predetermined period, foreign matter that did not exist when the pellicle film was mounted may be generated on the pattern formation surface of the photomask.

  For such growth foreign matter on the photomask surface, for example, Patent Document 1 discloses an inspection method for inspecting growth foreign matter on a reticle, residual contaminants on the reticle, environmental substances in the use environment, UV exposure amount, and the like. Based on the above, a reticle management method for predicting the occurrence of growth foreign substances is described.

Patent Document 2 describes a method for suppressing foreign matter precipitation by removing a substance such as ammonia, which is a causative substance that forms a precipitate on a reticle, from the pellicle space. Specifically, it describes that a layer of phosphoric acid, activated carbon, or the like is applied to the inside of the pellicle in order to capture the precipitation factor substance present in the gas in the pellicle.
JP 2008-165104 A JP 2000-352812 A

  According to the invention described in Patent Document 1, it is possible to manage by judging or predicting the occurrence of a growth foreign substance and judging whether or not the reticle can be used, while reducing the occurrence of the growth foreign substance itself. I can't. Further, in the invention described in Patent Document 2, since ammonia is present in normal air, it is difficult to completely remove ammonia from the pellicle space.

  By the way, as described in the above prior art, in a mask for manufacturing a semiconductor device such as an LSI (so-called reticle), a tendency of pattern miniaturization is remarkable, and in order to resolve a fine pattern, KrF light, An extremely short wavelength light source such as ArF light is used. Since such short-wavelength irradiation light has large energy, foreign substances are likely to be generated by activating the material constituting the irradiated mask and reticle and causing a reaction.

  On the other hand, large masks used for manufacturing liquid crystal devices (TFTs, color filters, etc.) are not so prominent in pattern miniaturization as compared with those for semiconductor manufacturing, but have a large area and require a large amount of exposure light. Therefore, an exposure light source (including i-line, h-line, and g-line wavelengths) having a wavelength range of i-line to g-line is frequently used. Since such a light source is not as large in light energy as the above-mentioned light source, there is substantially no problem of inducing a chemical reaction on the mask surface to generate a foreign substance.

  However, recently, even in the above-described large mask, if the photomask is used or stored for a predetermined period (for example, one year or more), foreign matter that does not exist when the pellicle is mounted is generated on the photomask pattern forming surface. It has been found that The size of the growing foreign matter is about 1 μm to 50 μm, and affects the pattern transfer accuracy of, for example, a TFT substrate and causes defective products. In particular, in the large-sized mask for manufacturing a liquid crystal display device (such as a rectangular mask having a side of 300 mm or more), the above-mentioned foreign matter was frequently generated. In addition, since there are some varieties having a period of use ranging from 2 to 3 years, the large mask has to be removed as a defect at a certain time even if the growth rate is slow. In order to remove such defects, it is necessary to remove the pellicle, clean it, inspect it, and then remount the pellicle. This is extremely inconvenient in terms of production efficiency.

  The growing foreign matter is generated on the surface on which the light shielding film containing mainly Cr is formed, and further grows with time starting from the edge of the light shielding film pattern. Furthermore, the inventors have found that the generation amount has a stronger correlation with the environment such as the storage place than the number of exposures. This is because there is a change in the usage environment and storage environment of photomasks recently, and various substances are included in the atmosphere where photomasks exist, or the concentration of specific substances in the atmosphere is higher than before. It is thought that this is because

  As described above, it has been clarified that the growth foreign matter which is an object of the present invention has completely different properties from the foreign matter generated in the conventional semiconductor manufacturing mask and is generated due to different causes. An object of this invention is to provide the manufacturing method of the photomask which reduces the growth foreign material on the photomask surface reliably in view of the said subject.

  According to the inventors' investigation, it has been found that this growth foreign substance is particularly likely to occur when the humidity is high. Further, it has been found that the growth foreign substances of the present invention are likely to occur in a light shielding film containing Cr and not a single composition film but a film having a laminated structure of layers having different compositions. Therefore, in order to achieve the above object, the present inventors analyzed this growth foreign substance component, investigated the generation source in detail, and conducted earnest research on the generation mechanism. As a result, it has been found that the growth foreign substance contains oxalic acid and further contains ammonia (including ions or salts). Furthermore, the occurrence of growth foreign matter does not show much correlation with the number of times the photomask is used in the exposure apparatus, but has a correlation with the elapsed time, and the amount generated depends on the place and environment where the photomask is used and stored. Because of the strong influence, it was predicted that environmental substances present in the use / storage environment of the photomask were involved in the generation of foreign matter. That is, it is caused by the fact that the environmental material of the photomask causes some reaction with the residue of the material used at the time of manufacturing the photomask or the material derived from the composition of the photomask itself (including pellicle). I found it.

  In addition, the above-mentioned growth foreign matter is unlikely to occur near the back surface or the periphery of the photomask, and is easy to form in the formed film pattern. Therefore, the light shielding film component (specifically, Cr is formed). Or the compound) was presumed to be involved in the reaction. In general, however, it is unlikely that metal Cr will react with other elements or ions in the storage state at room temperature.

On the other hand, a Cr-based light-shielding film (or antireflection film) formed by sputtering may have a relatively high activity and an ionized state (Cr ²⁺ , Cr ^3+, etc.) with a certain probability. It is conceivable that such a chemical species can be used as a starting point to promote a reaction with an environmental substance to generate or grow a foreign substance. Alternatively, it is conceivable that the metal Cr contained in the light shielding film promotes the generation of ionized Cr having higher activity by contact with an environmental substance.

  Further, since foreign matter generation often starts from the edge of the pattern, it can be easily assumed that the above active chromium is likely to be present in the pattern cross section by etching. Note that a light-shielding film (including Cr) is generally patterned on a large mask for manufacturing TFTs by wet etching. As the wet etchant, those mainly composed of ceric ammonium nitrate are often used.

Further, according to the study by the inventors, since a large amount of foreign matter was observed under high humidity (for example, 80% or more), ionized Cr was generated by contact with an environmental substance at high humidity, and / or It can be understood that foreign substances are easily generated.
As a result of further analysis, oxalic acid ionized to Cr ions (Cr ²⁺ , Cr ^3+, etc.) contained in the light-shielding film of the photomask is coordinated with the growth material, and ammonia is bonded thereto. Crystals grown as salts mainly composed of oxalic acid and ammonia were detected. In view of this, the present inventors have considered reducing the amount of ionized Cr contained in the light-shielding film or the like of the photomask or preventing the growth of foreign substances by suppressing the ionization of Cr.

  That is, the method for manufacturing a photomask according to the present invention is a method for manufacturing a photomask formed by patterning a thin film mainly composed of Cr formed on a light-transmitting substrate. A patterning process and a Cr ion reduction process for reducing the amount of ionized Cr contained in the patterned thin film or suppressing the ionization of Cr are performed.

In that case, the Cr ion reduction treatment includes treatment for irradiating the thin film with light having a wavelength of 200 nm or less and an intensity of 30 mW / cm ² or more, or heating the thin film at a temperature of 150 ° C. or more and 500 ° C. or less for 1 hour or more. It is preferable that the processing is included.
Such surface treatment is effective because it acts not only on the surface of the Cr-based thin film but also on the cross section of the pattern.

  Furthermore, the thin film may be a light-shielding film, an antireflection film, or a semi-transparent film, and the effect of the present invention is effective when the film is formed by a sputtering method or on a cross section patterned by wet etching. It is remarkable.

The effect of the thin film of the present invention is remarkable when it is formed by laminating a plurality of layers having different compositions. In such a case, if the humidity is high, the plurality of layers constitute a battery through the electrolyte solution, and thus ionization of the contained metal (here, Cr) is particularly likely to occur. Therefore, the surface treatment of the present invention is particularly effective at such times.
For example, the Cr ion reduction treatment of the present invention can form a substantially insulating oxide on the thin film, so that a plurality of layers are insulated and ionization is suppressed. Further, when the Cr ion reduction treatment of the present invention is applied to a plurality of layers containing Cr, they form the same oxide and no potential difference occurs, so that the ionization of Cr is suppressed. The treatment of the present invention works effectively by one or more of these effects.

In the present invention, the pattern is transferred to the resist film formed on the transfer object by irradiating the photomask obtained by the above manufacturing method with exposure light including wavelengths of i-line, h-line, and g-line. Also includes a transfer method.
The invention has a significant effect on the photomask used for such applications. In particular, it is possible to obtain an excellent photomask in which the generation of growth foreign substances is suppressed even by exposure and storage at high humidity.

  In the use / storage environment of a mask for manufacturing a liquid crystal display device, there are compounds used for etching and development, and the inclusion of the oxalate ions and ammonia ions cannot be completely prevented. Furthermore, recent progress in process and efficiency have caused these concentrations to exceed a predetermined amount. Even under such a production site environment, the generation of foreign matter generated in the mask pattern was remarkably delayed so that no inconvenience occurred.

  The photomask manufacturing method according to the present invention reduces the ionized Cr contained in the light shielding film containing Cr or the like of the photomask prior to mounting the pellicle, or suppresses the ionization of Cr. By carrying out the above, it is possible to reduce and suppress the reaction between Cr ions and environmental substances, which are the main factors for the generation of growth foreign substances, and to suppress the generation of growth foreign substances.

  Embodiments of the present invention will be described below with reference to the drawings, examples and the like. In addition, these figures, Examples, etc. and description illustrate the present invention, and do not limit the scope of the present invention. It goes without saying that other embodiments may belong to the category of the present invention as long as they match the gist of the present invention.

  1 and 2 are cross-sectional views showing respective steps of a photomask manufacturing method according to the present invention. The photomask manufacturing method according to the present invention includes at least (film formation process), (resist application process), (resist patterning process), (light-shielding film patterning process), (resist removal process), and (Cr ion reduction process). In addition, a pellicle is mounted on the pattern formation surface after manufacturing the photomask (pellicle mounting step). Hereinafter, each process will be described.

(Film formation process)
First, as shown in FIG. 1A, a light-shielding film 2 is formed on the main surface of a light-transmitting substrate 1 made of quartz glass or the like by means such as sputtering to produce a photomask blank. For example, chromium can be used as a sputtering target, and argon can be used as a sputtering gas. Furthermore, oxygen, nitrogen, carbon dioxide, or the like can be introduced into the sputtering gas at an appropriate flow rate.

In the present invention, a light shielding film having a particularly effective laminated structure is formed by laminating a plurality of layers having different compositions. The boundary may be clear or may be due to a composition gradient.
For example, in an in-line type sputtering apparatus, a layer made of CrO is laminated on a Cr layer, for example, by changing the type and amount of sputtering gas to be supplied in accordance with the transport of a substrate, which is a film formation target. can do. The upper layer side may function as an antireflection layer of the photomask.

  As the translucent substrate 1, for example, a substrate having a thickness of about 5 mm to 15 mm can be used. As the light-shielding film 2, as described above, a film mainly composed of Cr such as Cr (chromium) or an oxide, nitride, or carbide of Cr is preferably used. Further, the light shielding film 2 may be a semi-translucent film that transmits a part of the exposure light. Further, when the light shielding film 2 is a laminate of a plurality of layers (for example, a plurality of light shielding films, a light shielding film, and an antireflection film). Or the light-shielding film and the semi-transmissive film) may be a semi-transmissive film and a light-shielding film, respectively.

(Resist application process)
Next, as illustrated in FIG. 1B, a resist material is applied on the light shielding film 2 formed on the translucent substrate 1 to form a resist film 3. As a method for applying the resist material, a method using a known apparatus such as a spin coater can be used.

(Resist patterning process)
Next, as shown in FIG. 1C, pattern drawing (selective exposure) is performed on the resist film 3 based on a desired pattern. This pattern drawing can be performed by, for example, a drawing machine using a laser or an electron beam. Thereafter, a known process such as development is performed to form a resist pattern 3a.

(Light-shielding film patterning process)
Next, as shown in FIG. 1D, the light shielding film pattern 2a is formed by etching the light shielding film 2 using the resist pattern 3a thus formed as a mask. Although there is no restriction | limiting in particular in the system of an etching process, For example, the well-known wet etching process method can be used. In particular, the present invention is remarkable for the growing foreign matter formed from the vicinity of the pattern cross section of the light shielding film, which is formed when the chromium light shielding film is etched with a wet etching solution containing cerium nitrate second ammonium as a main component. Has an effect.

(Resist removal process)
Next, by removing the resist pattern 3a by a known method, a light shielding film pattern 2a is formed on the translucent substrate 1 as shown in FIG.

(Cr ion reduction process)
Next, a process of reducing or suppressing the generation of Cr ions such as Cr ²⁺ and Cr ³⁺ contained in the light-shielding film pattern 2a containing Cr as a main component is performed. This is to prevent the growth of foreign substances. There are the following two methods.

(1) Light irradiation treatment Ultraviolet light having a wavelength of 200 nm or less (for example, an excimer UV lamp having a wavelength of 172 nm) is irradiated at an intensity of 30 mW / cm ² or more (for example, 40 mW / cm ² ). By performing this treatment, the ionized Cr generated in the film pattern containing Cr formed on the photomask is activated by the energy of the UV light, and oxygen is adsorbed to lower oxide of Cr (Cr ₂ O ₃ , Cr ₃ O _4, etc.), and the amount of Cr ions decreases. For this reason, the coordination of oxalic acid is suppressed and the generation of growth foreign substances is suppressed. If the wavelength of the light to be irradiated exceeds 200 nm, the activation efficiency of Cr contained in the film is lowered, so that the generation of Cr oxide may be insufficient. On the other hand, when the strength is less than 30 mW / cm ² , energy may be insufficient to activate Cr ions in the film.

(2) Heat treatment Heating is performed at a temperature of 150 ° C. to 500 ° C. (preferably 200 ° C. to 350 ° C.) for about 1 hour. By this heating, the oxidation of Cr on the surface and inside of the light-shielding film pattern 2a is accelerated, and Cr ions become lower oxides of Cr (Cr ₂ O ₃ , Cr ₃ O _4, etc.), and the amount of Cr ions decreases. . For this reason, the coordination of oxalic acid is suppressed, and the generation of growth foreign substances is suppressed. When the temperature is set to 150 ° C. or more, when the Cr in the film is activated, the pattern cross section can be sufficiently oxidized. Further, even if the temperature exceeds 500 ° C., the above effect is not enhanced, and it is appropriate that the temperature is 500 ° C. or lower.

  By performing either one or both of the above two methods, the generation of growth foreign substances can be reliably reduced in the photomask shown in FIG.

  In addition, the Cr ion reduction process by said method is effective when the film | membrane which has target Cr as a main component is formed by sputtering method. A film formed by the sputtering method has many structural gaps and can be easily oxidized. In particular, in the heat treatment, the inside can be oxidized and stabilized. In any method, since it acts on the cross section of the film pattern, the patterned Cr-containing film is processed. Even if the same process is performed on the photomask blank before patterning, a sufficient effect cannot be obtained.

(Pellicle mounting process)
Next, as shown in FIG. 2G, the pellicle 4 is mounted on the pattern forming surface of the photomask manufactured through the Cr ion reduction process by a known method. As the pellicle, a known pellicle composed of a pellicle film such as nitrocellulose or cellulose ester, a fluoropolymer type, or a cycloolefin type and a pellicle frame can be used.

  By the above method, ionized Cr in the light shielding film pattern 2a was reduced in the photomask. In addition, by the above method, Cr contained in the light shielding film pattern 2a can be prevented from being ionized upon contact with an environmental substance. For this reason, when the above photomask was visually examined for the occurrence of growth foreign substances when left in the same atmosphere together with a photomask that had undergone the same process except that the Cr ion reduction process was not performed, In the photomask of the invention, the generation of growth foreign substances was suppressed.

In addition, after leaving the photomask according to the manufacturing method of the present invention and the photomask not subjected to the processing of the present invention in the same atmosphere (in which oxalic acid exists), the Cr pattern surface is analyzed by TOF-SIMS. As a result, it was found that the spectral peak of the complex of oxalic acid and Cr (CrC ₂ O ₄ ⁻ , CrC ₂ O ₅ H ⁻ , etc.) was not substantially detected only for those subjected to the treatment of the present invention.

  In addition, this invention is not limited to the said embodiment, It can implement by changing suitably. For example, in the above-described embodiment, an example in which only the light-shielding film 2 is formed on the light-transmitting substrate 1 is shown. However, the present invention is not limited to this, and other films such as a semi-transmissive film and an antireflection film are formed. May be. In that case, by performing the (Cr ion reduction process) after all the films are formed and patterned, the same effect is obtained even when Cr is contained in the semi-transmissive film, the antireflection film, or the like. An effect is obtained.

  In addition, the material, size, processing procedure, and the like in the above-described embodiment are merely examples, and various modifications can be made within the range where the effects of the present invention are exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

Sectional drawing which shows the process of the photomask manufacturing method in embodiment of this invention. Sectional drawing which shows the process of the photomask manufacturing method in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Translucent substrate 2 Light shielding film 2a Light shielding film pattern 3 Resist film 3a Resist pattern 4 Pellicle

Claims (12)

A method of manufacturing a photomask formed by patterning a thin film containing Cr as a main component formed on a translucent substrate,
A photo comprising: patterning a predetermined pattern on the thin film; and performing a Cr ion reduction process for reducing the amount of ionized Cr contained in the patterned thin film or suppressing ionization of Cr. Mask manufacturing method. The photomask manufacturing method according to claim 1, wherein the Cr ion reduction treatment includes a treatment of irradiating the thin film with light having a wavelength of 200 nm or less and an intensity of 30 mW / cm ² or more.   The photomask manufacturing method according to claim 1, wherein the Cr ion reduction process includes a process of heating the thin film at a temperature of 150 ° C. or more and 500 ° C. or less for 1 hour or more.   The method for producing a photomask according to claim 1, wherein the thin film is a light shielding film, an antireflection film, or a translucent film.   The photomask manufacturing method according to claim 1, wherein the thin film is a film formed by a sputtering method.   6. The method of manufacturing a photomask according to claim 1, wherein the thin film has a cross section patterned by wet etching.   7. The method of manufacturing a photomask according to claim 1, wherein the thin film is formed by laminating a plurality of layers having different compositions.   8. The photomask manufacturing method according to claim 7, wherein the Cr ion reduction treatment forms a substantially insulating oxide on the thin film.   8. The method of manufacturing a photomask according to claim 7, wherein each of the thin films is formed by laminating layers containing Cr as a main component.   A pattern is formed on a resist film formed on a transfer object by irradiating the photomask produced by the manufacturing method according to claim 1 with exposure light including wavelengths of i-line, h-line, and g-line. A pattern transfer method, wherein:   The pattern transfer method according to claim 10, wherein the pattern is transferred in an atmosphere containing oxalate ions and ammonium ions. The pattern transfer method according to claim 10, wherein the pattern is transferred in an atmosphere having a humidity of 80% or more.

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