JP4919220B2 - Gray tone mask - Google Patents

Description

  The present invention relates to a gray-tone mask manufacturing method, a gray-tone mask, and a gray-tone mask blank used for manufacturing a liquid crystal display (hereinafter referred to as LCD).

Conventionally, methods for reducing the number of photomasks required for manufacturing have been proposed in the field of LCDs. That is, a thin film transistor liquid crystal display (hereinafter referred to as TFT-LCD) is currently being commercialized rapidly due to its advantage of being thin and low in power consumption compared to a CRT (cathode ray tube). Progressing. 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 TFT-LCD, the number of manufacturing processes is large, and the TFT substrate alone is manufactured using 5 to 6 photomasks. Under such circumstances, a method of manufacturing a TFT substrate using four photomasks has been proposed (for example, Non-Patent Document 1 below).
In this method, the number of masks to be used is reduced by using a photomask (hereinafter referred to as a gray tone mask) having a light shielding portion, a light transmitting portion, and a semi-light transmitting portion (gray tone portion).

3 and 4 (FIG. 4 is a continuation of the manufacturing process of FIG. 3) show an example of a manufacturing process of a TFT substrate using a gray-tone mask.
A metal film for a gate electrode is formed on the glass substrate 1, and the gate electrode 2 is formed by a photolithography process using a photomask. Thereafter, a gate insulating film 3, a first semiconductor film 4 (a-Si), a second semiconductor film 5 (N ⁺ a-Si), a source / drain metal film 6, and a positive photoresist film 7 are formed (FIG. FIG. 3 (1)). Next, the positive photoresist film 7 is exposed and developed using the gray tone mask 10 having the light shielding portion 11, the light transmitting portion 12, and the semi-light transmitting portion 13, thereby developing the TFT channel portion and the source / drain forming region. Then, the first resist pattern 7a is formed so as to cover the data line formation region and to make the channel portion formation region thinner than the source / drain formation region (FIG. 3B). Next, using the first resist pattern 7a as a mask, the source / drain metal film 6 and the second and first semiconductor films 5 and 4 are etched (FIG. 3C). Next, the thin resist film in the channel portion formation region is removed by ashing with oxygen to form a second resist pattern 7b (FIG. 4A). Thereafter, using the second resist pattern 7b as a mask, the source / drain metal film 6 is etched to form the source / drains 6a and 6b, and then the second semiconductor film 5 is etched (FIG. 4 (2)). The remaining second resist pattern 7b is peeled off (FIG. 4 (3)).

  As a gray-tone mask used here, one having a structure in which a semi-translucent portion is formed in a fine pattern is known. For example, as shown in FIG. 5, the light-shielding portions 11a and 11b corresponding to the source / drain, the translucent portion 12, and the semi-transparent portion (gray tone portion) 13 corresponding to the channel portion are provided. The light part 13 is an area where a light shielding pattern 13a composed of a fine pattern below the resolution limit of an LCD exposure machine using a gray tone mask is formed. Both the light shielding portions 11a and 11b and the light shielding pattern 13a are usually formed from films of the same thickness made of the same material such as chromium or a chromium compound. The resolution limit of an LCD exposure machine that uses a gray-tone mask is about 3 μm for a stepper type exposure machine and about 4 μm for a mirror projection type exposure machine. For this reason, for example, in FIG. 5, the space width of the transmission part 13b in the semi-transmission part 13 is set to less than 3 μm, and the line width of the light shielding pattern 13a is set to less than 3 μm which is less than the resolution limit of the exposure machine.

  However, the above-mentioned fine pattern type semi-transmission part is a line-and-space type design for the gray tone part, specifically, a fine pattern for providing an intermediate halftone effect between the light-shielding part and the light-transmission part. There is a choice between a dot (halftone dot) type or another pattern, and in the case of the line and space type, how much the line width is to be set, and the part through which light is transmitted is blocked. The design had to be made in consideration of many things, such as what should be done with the ratio of the parts to be measured and how much the overall transmittance should be designed. Also in mask manufacturing, management of the center value of the line width and management of line width variation within the mask and extremely difficult production techniques have been required.

  Therefore, it has been conventionally proposed to use a semi-transmissive half-tone film (semi-transmissive film) for a portion to be subjected to half-tone exposure. By using this halftone film, halftone exposure can be performed while reducing the exposure amount of the halftone portion. By changing to a halftone film, it is only necessary to consider how much the overall transmittance is necessary in the design, and it is possible to produce a mask only by selecting the film type of the halftone film and the film thickness. It becomes possible. Therefore, in mask manufacturing, it is only necessary to control the film thickness of the halftone film, and management is relatively easy. Further, since a halftone film can be easily patterned by a photolithography process, even a complicated pattern shape is possible.

  A conventionally proposed method for manufacturing a halftone film type gray tone mask is as follows. Here, an LCD substrate pattern 100 as shown in FIG. 6 will be described as an example. The pattern 100 includes a light-shielding part pattern 101 including patterns 101a and 101b, a semi-transparent part pattern 103 between the light-shielding part patterns 101a and 101b, and a translucent part pattern 102 formed around these patterns. Has been.

  First, a mask blank in which a semi-transparent film and a light-shielding film are sequentially formed on a transparent substrate is prepared, and a resist film is formed on the mask blank. Next, a pattern is drawn and developed to form a resist pattern in a region corresponding to the light shielding part pattern 101 and the semi-transparent part pattern 103 of the pattern 100. Next, by etching with an appropriate method, the light shielding film in the region corresponding to the light transmitting portion pattern 102 in which the resist pattern is not formed and the semi-light transmitting film in the lower layer are removed, and FIG. A pattern as shown is formed. That is, the light transmitting portion 202 is formed, and at the same time, the light shielding pattern 201 in the region corresponding to the light shielding portion and the semi-light transmitting portion of the pattern 100 is formed. After removing the remaining resist pattern, a resist film is formed again on the substrate, pattern drawing is performed, and development is performed, so that a resist pattern is formed in a region corresponding to the light shielding portion pattern 101 of the pattern 100 this time. Form. Next, only the light shielding film in the region of the semi-transparent portion where the resist pattern is not formed is removed by appropriate etching. As a result, a pattern corresponding to the pattern 100 is formed as shown in FIG. That is, a semi-transparent portion is formed by the semi-transparent film pattern 203, and simultaneously, light-shielding portion patterns 201a and 201b are formed.

  Further, in Patent Document 1 below, when only the light shielding film in the region of the semi-transparent portion is removed by etching in the second photolithography process, the film thickness of the lower semi-transparent film is prevented. It is disclosed that an etching stopper film is provided between a semi-transparent film and a light shielding film on a transparent substrate in a mask blank.

JP 2002-189281 A “Monthly FP Intelligence”, May 1999, p. 31-35

  However, according to such a conventional gray-tone mask manufacturing method, when the light shielding film and the semi-transparent film are made of, for example, the same material (for example, chromium and chromium compound), the light shielding film and the semi-transparent film are formed. Since the etching characteristics are approximate, it is difficult to determine the end point of etching when only the light-shielding film in the region of the semi-transparent portion is removed by etching in the second photolithography process described above. If the light-shielding film remains on the optical film and the etching is over, the semi-transparent film is reduced, and in any case, the desired semi-transparent property cannot be obtained. Therefore, it is necessary to select a combination of materials having different etching characteristics at least for the light shielding film and the semi-transparent film, and the range of material selection is limited. Further, even if a combination of materials having different etching characteristics is selected for the light-shielding film and the semi-transparent film as described above, it is not possible to completely prevent the above-described reduction of the semi-transparent film.

  In this case, as described in Patent Document 1, by providing an etching stopper film between the semi-transparent film and the light-shielding film on the transparent substrate in the mask blank to be used, the light-shielding film in the semi-transparent part region is provided. Even if etching is performed slightly overlying, it is possible to prevent the lower semi-transparent film from being reduced. However, the layer structure of the mask blank to be used is a three-layer structure of a semi-transparent film, an etching stopper film, and a light shielding film, and three stages of film formation are required, which imposes manufacturing costs. Further, since the entire film thickness is increased, the aspect ratio (ratio between the pattern dimension and the height) is large. As a result, there is a problem that the pattern shape and pattern accuracy of the light shielding portion are deteriorated and the etching time is increased. Further, when the remaining etching stopper film is removed after the light shielding film is etched, there is a problem that the underlying semi-transparent film is reduced. Even if the etching stopper film remains, any material that does not affect the transmissivity of the semi-transparent film can be left without being removed, but the material and thickness of the etching stopper film are limited. Is done.

As a gray-tone mask that can solve such a problem, the applicant of the present invention firstly formed a light-shielding portion from a light-shielding film provided on a transparent substrate and a semi-transparent film formed thereon. The light part proposed the gray tone mask formed from the semi-transparent film formed on the transparent substrate which exposed the area | region corresponding to a semi-transparent part (Japanese Patent Application No. 2004-65115).
This gray tone mask can be manufactured as follows (see FIG. 8).

First, on a transparent substrate 21 such as a glass substrate, a positive resist film for electron beam is formed on a mask blank 20 on which a light shielding film 22 using a material mainly composed of chromium (Cr) is formed. Then, a predetermined pattern is drawn and developed to form a resist pattern 23c (see FIGS. 8A and 8B). In the resist pattern 23c, the resist is removed in the region where the semi-transparent portion is formed (region B shown in FIG. 8), and the region where the light-shielding portion is formed (region A shown in FIG. 8) and the transparent portion. The resist remains in the region where the film is formed (region C shown in FIG. 8).
Next, using the formed resist pattern 23c as a mask, the light shielding film 22 is etched to form a light shielding film pattern 22b corresponding to the light shielding portion and the light transmitting portion (see FIG. 8C). In the region (B region) corresponding to the semi-translucent portion, the underlying transparent substrate 21 is exposed by the etching of the light shielding film 22. The remaining resist pattern 23c is removed using ashing with oxygen or concentrated sulfuric acid (see FIG. 8D).

Next, the semi-transparent film 24 is formed on the entire surface of the substrate having the light shielding film pattern 22b on the transparent substrate 21 obtained as described above (see FIG. 8E). As a result, in the region corresponding to the semi-transparent portion, the semi-transparent film 24 is directly formed on the exposed transparent substrate 21 to form the semi-transparent portion.
Next, the positive resist film is formed again on the entire surface, and the second drawing is performed. After drawing, this is developed to form a resist pattern 23d in which the resist is removed in the light transmitting portion (C region) and the resist remains in the light shielding portion and the semi-light transmitting portion (see FIG. 8F).

Next, using the formed resist pattern 23d as a mask, the semi-transparent film 24 and the light-shielding film 22b in the C region to be a translucent part are removed by etching. Thereby, the light shielding portion is defined as a light transmitting portion, and a light shielding portion (A region) and a light transmitting portion (C region) are formed (see FIG. 8G). The remaining resist pattern 23d is removed using oxygen ashing or the like (see FIG. 8H).
The gray tone mask 40 is completed as described above.
As described above, the semi-transparent portion is formed by directly forming the semi-transparent film on the transparent substrate in which the region corresponding to the semi-transparent portion is exposed. In this case, it is not necessary to remove only the upper light-shielding film by etching and expose the lower semi-transparent film. Therefore, both the light-shielding film and the semi-transparent film are formed of film materials having the same or similar etching characteristics. It is also possible to expand the range of choice of film material. Therefore, the etching stopper film provided between the conventional light-shielding film and the semi-transparent film is unnecessary, the entire film thickness can be reduced, and the aspect ratio can be reduced.

  However, when the above manufacturing method was actually carried out, there were the following problems. That is, when the etching characteristics of the film materials of the light-shielding film and the semi-transparent film are the same or similar, in the process of FIG. Etching of the light shielding film 22b can be performed at once or continuously with the same etching gas (dry etching) or the same etching liquid (wet etching), but actually, the upper semi-transparent film 24 is etched, Subsequently, while the lower light-shielding film 22b is being etched, side etching of the semi-transparent film (B region serving as the semi-translucent part) whose side surface is exposed proceeds (damage portion indicated by D in FIG. 10), As a result, there was a problem that the pattern shape of the semi-translucent portion was deteriorated.

  In order to prevent such side etching of the semi-transparent film, the region where the semi-transparent portion is formed is etched by the first etching and the translucent portion is formed by the second etching as described above. Instead of etching the region, the region where the translucent part and the light transmitting part are formed is etched by the first etching, and the region where the light transmitting part is formed is etched by the second etching. It is conceivable to manufacture a similar gray-tone mask by (see FIG. 9).

First, on a transparent substrate 21 such as a glass substrate, a positive resist film is formed on a mask blank 20 in which a light shielding film 22 using a material mainly composed of chromium (Cr), for example, is formed, and a predetermined pattern is formed. Drawing and development are performed to form a resist pattern 23a (see FIGS. 9A and 9B). The resist pattern 23a exposes a region for forming a semi-translucent portion (region B shown in FIG. 9) and a region for forming a light-transmitting portion (region C shown in FIG. 9) to form a light shielding portion. The resist remains only in the region to be formed (region A shown in FIG. 9).
Next, using the resist pattern 23a as a mask, the light shielding film 22 is etched to form a light shielding film pattern 22a corresponding to the light shielding portion (see FIG. 9C). In the translucent part and the region corresponding to the translucent part, the underlying transparent substrate 21 is exposed by the etching of the light shielding film 22. The remaining resist pattern 23a is removed using ashing with oxygen or concentrated sulfuric acid (see FIG. 9D).

Next, the semi-transparent film 24 is formed on the entire surface of the substrate having the light shielding film pattern 22a on the transparent substrate 21 obtained as described above (see FIG. 9E).
The positive resist film is again formed on the entire surface, and the second drawing is performed. After drawing, this is developed to expose the translucent part (C region) and form a resist pattern 23b in which the resist remains in the light-shielding part and the semi-translucent part (see FIG. 9F).
Next, using the formed resist pattern 23b as a mask, the semi-transparent film 24 in the C region to be a translucent part is removed by etching (see FIG. 9G). The remaining resist pattern 23b is removed using oxygen ashing or the like (see FIG. 9H).
The gray tone mask 30 is completed as described above.

When the method shown in FIG. 9 is used, only the semi-transparent film needs to be etched in the second etching, and the semi-transparent film and the light-shielding film are etched in the second etching as in the method shown in FIG. It is not necessary to etch both in turn.
However, when the method shown in FIG. 9 is used, if the etching characteristics of the light-shielding film and the semi-transparent film are the same or similar, the process of etching the semi-transparent film 24 in the region corresponding to the translucent part (FIG. 9). 9 (g)), in practice, side etching of the light shielding film 22a in which the adjacent cross section is exposed may progress, and the cross sectional shape may be deteriorated as indicated by D in FIG.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a halftone film type gray-tone mask having a good pattern shape and cross-sectional shape, and a method for manufacturing the same, by solving conventional problems.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) A method for manufacturing a gray-tone mask having a pattern composed of a light-shielding part, a light-transmitting part, and a semi-light-transmitting part, for forming a light-shielding part on a light-shielding film formed on a transparent substrate Forming a first resist pattern, etching the light shielding film using the first resist pattern as a mask to form a light shielding film pattern, and peeling off the remaining first resist pattern; and the light shielding film Forming a semi-transparent film on the pattern, forming a second resist pattern for forming a translucent portion thereon, and etching the semi-transparent film using the second resist pattern as a mask; Forming a semi-transparent film pattern and peeling off the remaining second resist pattern, and the material constituting the semi-transparent film is more suitable than the material constituting the light-shielding film. Translucency The relative etchant for etching a method for manufacturing a gray-tone mask, wherein the etching rate is great material.
(Structure 2) The structure 1 is characterized in that the light shielding film is made of a material containing chromium (Cr) as a main component, and the semi-transparent film is made of a material containing chromium (Cr) and nitrogen (N). It is a manufacturing method of the described gray-tone mask.
(Configuration 3) An etching selection ratio of the semi-transparent film to the light-shielding film with respect to the etching for forming the semi-transparent film pattern (semi-transparent film etching rate / light-shielding film etching rate) is 2 or more. It is a manufacturing method of the gray tone mask of the structure 1 or 2 characterized by the above.

(Configuration 4) The etching solution used for the etching for forming the semi-transparent film pattern and the etching solution used for the etching for forming the light-shielding film pattern have different concentrations in the same kind of etching solution. The method of manufacturing a gray-tone mask according to any one of Configurations 1 to 3, wherein:
(Configuration 5) A gray-tone mask obtained by using the method of manufacturing a gray-tone mask according to any one of configurations 1 to 4, and a light-shielding film pattern formed on a transparent substrate and formed thereon A semi-transparent film pattern, wherein the light-shielding part is formed by at least a light-shielding film of the light-shielding film pattern, and the semi-transparent part is formed on a substrate exposed part of the light-shielding film pattern of the semi-transparent film pattern A gray-tone mask characterized by being formed of a semi-transparent film.
(Configuration 6) A gray-tone mask blank for use in the method for manufacturing a gray-tone mask according to any one of Configurations 1 to 4, wherein the gray-tone mask blank is formed on a transparent substrate and on the light-shielding film pattern. A material having a higher etching rate than an etchant for etching the semi-transparent film than a material constituting the light-shielding film. It is a gray tone mask blank characterized by being.

  According to the first aspect of the present invention, a step of forming a first resist pattern for forming a light-shielding portion on the light-shielding film formed on the transparent substrate, and the first resist pattern as a mask Etching the light shielding film to form a light shielding film pattern, removing the remaining first resist pattern, forming a semi-translucent film on the light shielding film pattern, and forming a translucent portion thereon Forming the second resist pattern, etching the semi-transparent film using the second resist pattern as a mask to form a semi-transparent film pattern, and peeling the remaining second resist pattern The material constituting the semi-transparent film is more etched than the material constituting the light-shielding film with respect to the etchant for etching the semi-transparent film. Since the material has a high rate, it is possible to suppress the progress of side etching of the light shielding film whose cross section is exposed when etching the semi-transparent film, and as a result, not only the pattern shape in plan view but also the cross sectional shape is good. A gray tone mask can be obtained. Further, an LCD or the like manufactured using this gray tone mask has good characteristics and high reliability.

According to the invention of claim 2, the light shielding film is made of a material containing chromium (Cr) as a main component, and the semi-transparent film is made of a material containing chromium (Cr) and nitrogen (N). The light-transmitting film has a higher etching rate than the light-shielding film with respect to the etchant for etching the semi-light-transmitting film, and the side-etching of the light-shielding film whose cross section is exposed when the semi-light-transmitting film is etched. Progress can be suppressed, and a gray-tone mask having a good pattern shape and cross-sectional shape can be obtained.
According to the third aspect of the present invention, the etching selectivity of the semi-transparent film to the light-shielding film with respect to the etching at the time of forming the semi-transparent film pattern (semi-transparent film etching rate / light-shielding film etching rate) is 2. As described above, since the progress of side etching of the light-shielding film whose cross section is exposed during the etching of the semi-translucent film can be particularly preferably suppressed, a gray-tone mask having a good pattern shape and cross-sectional shape can be obtained. It is done.

  According to invention of Claim 4, the etching liquid used for the etching for forming the semi-translucent film pattern and the etching liquid used for the etching for forming the light-shielding film pattern are the same kind of etching liquid and have a concentration. By using different ones, it is possible to easily adjust the etching rates of the light shielding film and the semi-transparent film so that the etching controllability is favorable.

According to invention of Claim 5, the gray tone mask obtained by this invention has the light shielding film pattern formed on the transparent substrate, and the semi-transparent film pattern formed on it, The said light shielding part is The light-shielding film of at least the light-shielding film pattern is formed, and the semi-light-transmitting portion is formed of a semi-light-transmitting film formed on the substrate exposed portion of the light-shielding film pattern of the semi-light-transmissive film pattern, In addition to obtaining a good pattern shape and cross-sectional shape, when forming a semi-transparent part as in the past, only the upper light-shielding film is removed by etching to expose the lower semi-transparent film. This eliminates the need for the conventional etching stopper film provided between the light-shielding film and the semi-transparent film, reduces the overall film thickness, reduces the aspect ratio, and improves the overall pattern accuracy. The It can be above.
According to invention of Claim 6, it has a light shielding film pattern on a transparent substrate, and the semi-transparent film formed on this light-shielding film pattern, The material which comprises a semi-transparent film is a light shielding film. A gray-tone mask blank made of a material having an etching rate larger than that of the constituent material to etch the semi-transparent film, and can be suitably used in the method of manufacturing a gray-tone mask of the present invention.

Hereinafter, the present invention will be described with reference to embodiments.
The graytone mask manufacturing method of the present invention is a graytone mask manufacturing method having a pattern composed of a light-shielding portion, a light-transmitting portion, and a semi-light-transmitting portion, on a light-shielding film formed on a transparent substrate, Forming a first resist pattern for forming a light-shielding portion; etching the light-shielding film using the first resist pattern as a mask to form a light-shielding film pattern; and stripping the remaining first resist pattern Forming a translucent film on the light shielding film pattern, forming a second resist pattern for forming a translucent portion thereon, and using the second resist pattern as a mask Etching the semi-transparent film to form a semi-transparent film pattern, and peeling off the remaining second resist pattern. Specifically, the manufacturing method shown in FIG. 9 can be applied. Therefore, the present invention will be described again with reference to FIG.

In the present invention, a mask blank 20 having a light shielding film 22 formed on a transparent substrate 21 is used (see FIG. 9A). In the present invention, the material of the light-shielding film 22 is chromium (Cr) alone, or one or two selected from chromium, nitrogen, carbon, fluorine, oxygen, etc. in consideration of etching characteristics and adhesion to the substrate. It may contain the above elements. Furthermore, it may be a laminated film of films having different compositions or a composition gradient film in which the composition is changed in the film thickness direction. In general, the light shielding film has an antireflection film such as chromium oxide on the front surface or the front surface. The film thickness of the light shielding film 22 is set to have a sufficient optical density with respect to exposure light when using a mask. For example, when the exposure light is i-line, the light-shielding film with an antireflection film is preferably about 80 to 110 nm.
As the transparent substrate 21, for example, a quartz substrate is used, but soda lime glass, non-alkali glass, or the like may be used. The size of the transparent substrate 21 varies depending on the purpose of use of the mask. For example, it is usually 4 to 8 inches square for LSI manufacturing, and a large substrate for LCD has a short side of 300 mm or more. 450 mm to 1400 mm × 1600 mm.

The mask blank 20 is obtained by forming the light shielding film 22 on the transparent substrate 21, and the film forming method is suitable for the film type such as vapor deposition, sputtering, CVD (chemical vapor deposition). The method may be selected as appropriate.
A positive resist film for laser drawing, for example, is formed on the entire surface of the mask blank 20, and a predetermined pattern is drawn and developed to form a region (B region in FIG. 9) and a light-transmitting portion. A region for forming a portion (region C in FIG. 9) is exposed, and a resist pattern 23a in which the resist remains only in a region for forming a light shielding portion (region A in FIG. 9) is formed (see FIG. 9B).

Next, using the resist pattern 23a as a mask, the light shielding film 22 is etched to form a light shielding film pattern 22a corresponding to the region where the light shielding portion is to be formed (see FIG. 9C). In the semitranslucent portion and the region corresponding to the translucent portion, the underlying transparent substrate 21 is exposed by the etching of the light shielding film 22. It is to be noted that wet etching is preferably used for etching the light shielding film 22 in terms of cost, particularly in manufacturing a photomask for manufacturing a large liquid crystal device. For the wet etching of the light shielding film 22, a ceric ammonium nitrate-based etching solution that is usually used for wet etching of a chromium-based thin film can be used.
The remaining resist pattern 23a is removed using ashing with oxygen or concentrated sulfuric acid (see FIG. 9D).

Next, the semi-transparent film 24 is formed on the entire surface of the substrate having the light shielding film pattern 22a on the transparent substrate 21 obtained as described above (see FIG. 9E). In the present invention, the material constituting the semi-transparent film 24 is etched with respect to an etchant (for example, an etchant for wet etching) for etching the semi-transparent film 24 rather than the material constituting the light shielding film 22. It is a material with a high rate. As a material for such a semi-transparent film 24, a material containing an additive element that increases (fastens) the etching rate with respect to the etching solution of chromium in chromium (Cr) is used for etching the semi-transparent film 24. It is preferable because the rate can be adjusted appropriately. Examples of the additive element that increases (fastens) the etching rate include nitrogen and oxygen (wherein oxygen may act to decrease (slow) the etching rate depending on the addition method). However, since the crystal grain of the film increases and the film stress increases when oxygen is included, it is more preferable to adjust the etching rate of the semi-translucent film by including nitrogen. In the case where a material containing chromium and nitrogen is used as the semi-transparent film, the ratio of chromium to nitrogen is preferably Cr: N = 50: 50 to 10:90 in atomic ratio.
Further, the semi-transparent film 24 is preferably a material that can be etched with the same kind of etchant as the light shielding film 22.

  As for the method for forming the semi-transparent film 24, as in the case of the light shielding film 22 described above, a method suitable for the film type, such as a vapor deposition method, a sputtering method, or a CVD (chemical vapor deposition) method, may be selected as appropriate. Good. Further, the film thickness of the semi-translucent film 24 is not particularly limited, but may be formed with an optimized film thickness so as to obtain a desired semi-translucency. In consideration of transmittance, etching characteristics, film-forming characteristics on the light-shielding film pattern, film stress, film thickness distribution, etc., the range of 30 to 250 mm is usually appropriate. The semi-transparent film 24 is a thin film, and, for example, semi-transmissivity with a transmissivity of about 20 to 60% is obtained when the transmissivity of the translucent part is 100% with respect to i-line (365 nm) of exposure light. In the case of forming a resist pattern with two kinds of film thickness, it is generally set to about 40 to 60%, but the transmittance of the semi-transparent film needs to be limited to this. Absent. The degree to which the translucency of the semi-translucent portion is set is a design problem depending on the purpose of use of the mask. The transmittance of the semi-transparent film 24 can be adjusted by the film thickness and composition (for example, nitrogen content).

Next, the positive resist film is formed again on the entire surface, and the second drawing is performed. After drawing, this is developed to expose the light transmitting portion (C region), and a resist pattern 23b in which the resist remains is formed in the light shielding portion and the semi-light transmitting portion (see FIG. 9F).
Next, using the formed resist pattern 23b as a mask, the semi-transparent film 24 in the C region to be a translucent part is removed by etching (see FIG. 9G). As for the etching of the semi-transparent film 24, it is preferable in terms of cost to use wet etching, particularly in manufacturing a photomask for manufacturing a large liquid crystal device. For wet etching of the semi-transparent film 24, a ceric ammonium nitrate-based etching solution that is usually used for wet etching of a chromium-based thin film can be used, as in the case of the light shielding film 22. In order to adjust the etching rate of the light-shielding film 22 and the semi-transparent film 24 so that the etching controllability is preferable, the same kind of etching solution having different concentrations may be used. . For example, when nitrogen is contained in chromium as the material of the semi-transparent film, if the etching solution for etching the light-shielding film is used in its concentration, the etching rate of the semi-transparent film is too fast and the etching controllability is high. Since it is bad, it is preferable to dilute the etching solution for the light shielding film as appropriate.

In the present invention, the etching selection ratio of the semi-transparent film 24 to the light-shielding film 22 relative to the etching of the semi-transparent film 24 (etching rate of the semi-transparent film 24 / etching rate of the light-shielding film 22) is 2 or more. Particularly preferred.
The remaining resist pattern 23b is removed using oxygen ashing or the like (see FIG. 9H).
The gray tone mask according to the present invention is completed as described above.

In the present invention, the material that constitutes the semi-transparent film is a material that has a higher etching rate than the material that constitutes the light-shielding film with respect to the etchant for etching the semi-transparent film. When etching the translucent film 24 in the corresponding region (C region) (FIG. 9G), it is possible to suppress the progress of side etching of the light shielding film 22a in which the cross section of the adjacent light shielding portion is exposed. As a result, a gray-tone mask having not only a pattern shape in plan view but also a good cross-sectional shape can be obtained.
In this embodiment, the case where a positive resist is used is exemplified, but a negative resist may be used. In this case, the process can be carried out in exactly the same manner as described above only by reversing the drawing data.

(Example)
Hereinafter, specific examples will be described.
A quartz substrate was used as the transparent substrate, and the size was 330 mm × 450 mm × 10 mm, which is a large substrate size for LCD.
The light-shielding film was made of chromium alone, and was formed by sputtering on a transparent substrate so as to obtain a sufficient light-shielding property against i-line (365 nm). The sputtering gas was Ar 100%.

The material of the semi-transparent film was a material containing chromium and nitrogen, and was formed by sputtering film formation on the substrate on which the light shielding film pattern was formed. At this time, the sputtering gas is a mixed gas of Ar and nitrogen (N ₂ ), and the mixing ratio (volume ratio) is Ar: N ₂ = 0: 100, 20:80, 40:60, The film thicknesses were set to 74 nm, 76 nm, and 78 nm, respectively, so that the transmittance at i-line, which is an example of the required characteristics of the Grayton mask, was in the range of 40 to 50%. As a result, a transmittance of about 43% was obtained for any semi-transparent film. Regarding the film composition, when the sputtering gas composition is Ar: N ₂ = 40: 60, Cr: N = about 40:60 (atomic% ratio), and when Ar: N ₂ = 20: 80, When Cr: N = about 20:80 (atomic% ratio) and Ar: N ₂ = 0: 100, Cr: N = about 10:90 (atomic% ratio) was obtained.
Using the above materials, a gray-tone mask was manufactured according to the manufacturing process shown in FIG. For etching the light shielding film, a ceric ammonium nitrate-based etching solution was used, and for etching the semi-transparent film, the same etching solution as that for the light shielding film was appropriately diluted with distilled water.

FIG. 1 shows the etching rate of the semi-transparent film and the film thickness of 5 nm when the dilutions of 2%, 4%, 6%, and 9% are used as the semi-transparent film etching liquid, respectively. The relationship of the etching time in the case of 20 nm is plotted. In addition, the value shown in FIG. 1 is an average value in the semi-transparent film having the above three kinds of film compositions.
As shown in FIG. 1, the lower the etching solution concentration, the lower the etching rate. Therefore, the etching time can be extended within an appropriate range, and the etching time with good etching controllability (for example, 20 seconds to 2 minutes). The dilution concentration can be selected. Note that the etching selectivity between the semi-transparent film and the light-shielding film was not greatly affected by the dilution of the etching solution.

FIG. 2 shows the average etching selectivity between the semi-transparent film and the light-shielding film (the semi-transparent film etching rate (nm / sec) / the light-shielding film etching rate (nm / sec)) is plotted for each semi-transparent film composition (the horizontal axis indicates the sputtering gas composition).
From the result of FIG. 2, it can be seen that when the N ₂ in the sputtering gas used for forming the translucent film is 60 atomic% or more, the above etching selectivity can be 2 or more.
Further, when the cross-sectional shape of the gray-tone mask pattern obtained in this example was observed by cross-sectional TEM, a good cross-sectional shape was obtained.

Furthermore, FIG. 12 is a graph showing the result of measuring the transmittance spectrum of a chromium nitride film formed with a sputtering gas composition of Ar: N ₂ = 0: 100 in the above example. A graph showing the result of measuring the transmittance spectrum of a chromium oxide film capable of increasing the etching rate is also shown. From this graph, the chromium nitride film has less wavelength dependency of the transmittance than the chromium oxide film, and when using a broad light source (including g-line, h-line, i-line, etc.) used in LCD exposure apparatus However, it can be seen that exposure can be performed with a more uniform intensity reduction for each wavelength.

It is a figure which shows the relationship between the etching liquid concentration used for the etching of a semi-transparent film, the etching rate of a semi-transparent film, and the etching time in case the film thickness of a semi-transparent film is 5 nm and 20 nm. It is a figure which shows the relationship between the sputtering gas composition at the time of carrying out sputter film-forming of a semi-transparent film, and the etching selectivity with respect to the light shielding film of a semi-transparent film in the etching of a semi-transparent film. It is a schematic sectional drawing which shows the manufacturing process of the TFT substrate using a gray tone mask. It is a schematic sectional drawing which shows the manufacturing process (continuation of the manufacturing process of FIG. 3) of the TFT substrate using a gray tone mask. It is a figure which shows an example of the gray tone mask of a fine pattern type. It is a figure which shows an example of a gray tone mask pattern. It is a mask pattern top view for demonstrating the manufacturing method of the conventional gray tone mask. It is sectional drawing which shows an example of the manufacturing process of a gray tone mask. It is sectional drawing which shows the other example of the manufacturing process of a gray tone mask. It is sectional drawing for demonstrating the malfunction which arises in the manufacturing process of the gray tone mask shown in FIG. It is sectional drawing for demonstrating the malfunction which arises in the manufacturing process of the gray tone mask shown in FIG. It is a graph of the result of having measured the transmittance | permeability spectrum about the chromium nitride film | membrane and the chromium oxide film | membrane.

Explanation of symbols

21 transparent substrate 22 light shielding films 23a to 23d resist pattern 24 semi-transparent film 20 mask blank 10, 30, 40 gray tone mask 100 mask pattern 101 light-shielding part pattern 102 translucent part pattern 103 semi-transparent part pattern

Claims (2)

Shielding portion, a gray-tone mask TFT substrate manufacturing having a pattern of transparent portion and semitransparent portion, the channel portion formation region of the TFT substrate is thinner than the source drain forming regions, two kinds of thickness In a gray-tone mask for forming a resist pattern having
A light-shielding film pattern formed on the transparent substrate; and a semi-light-transmitting film pattern formed thereon; wherein the light-shielding part is formed by at least a light-shielding film of the light-shielding film pattern; , Formed by a semi-transparent film formed on a substrate exposed portion of the light-shielding film pattern of the semi-transparent film pattern,
The gray tone mask is exposed by an exposure apparatus having a light source including g-line, h-line, and i-line, and
The semi-transparent film contains chromium (Cr) and nitrogen (N), and has a transmittance change of 1.5% or less in an exposure wavelength region from i-line to g-line. The material constituting the semi-transparent film contains chromium (Cr) and nitrogen (N), Cr in an atomic ratio: N 50: 50-10: according to claim 1, characterized in that it is 90 Gray tone mask.

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