TW201741442A - An etching solution and a processed photomask thereby - Google Patents

Abstract

The purpose of the present disclosure is to provide an etching solution which precisely controls the light transmittance of a semitransparent part of a photomask in the process of manufacturing the photomask applied to lithography, a method of manufacturing a gradation mask by using the etching solution and the gradation mask manufactured by the method. The technical means provided by the present disclosure is an etching solution containing Diammonium Cerium (IV) Nitrate and Ammonium Cerium (IV) Sulfate.

Description

Etching solution and reticle processed by etching solution

The present invention relates to an etching solution for pattern processing of an optical film of a photomask and a photomask processed by the etching liquid.

In recent years, in the manufacture of a TFT (Thin Film Transistor) liquid crystal display device, a gradation mask is used in order to simplify the manufacturing steps. Although the conventional reticle is composed of a light transmitting portion and a light shielding portion, and the intensity of the exposure light transmitted through the hood is substantially two values of light shielding and light transmission, the gradation cover is made of a light transmitting portion and a semi-transparent portion. The portion and the light shielding portion are configured to change the intensity of the exposure light transmitted by the respective portions, and are three values of light shielding, semi-light transmission, and light transmission. The use of a halftone exposure is a step of using a gradation mask to perform a conventional plurality of reticle with a reticle.

As one of the manufacturing methods of the gradation cover, it is proposed to use a chromium compound as a light shielding film, and the semi-transmissive portion partially etches the light shielding film to reduce In the case of a small thickness, a predetermined light transmittance can be obtained (Patent Document 1). However, in the method of performing local etching as described above, since it is difficult to uniformly etch the semi-transmissive portion over the entire mask, it is proposed to use a two-layer structure in which a light-shielding film and a semi-transmissive film are formed and each is formed into a film. A method of photomask blank.

In order to form a gradation cover of three or more gradations, when a plurality of semi-transmissive films having a predetermined semi-light transmittance are separately prepared and sequentially etched, it is not only required to be set in accordance with a desired combination of light transmittances. The composition or film thickness of the plurality of semi-transmissive films and the complicated film forming step are also imposed, and it is also possible to form only a limitation in which the light transmittance is set in advance before film formation.

Further, since the light transmittance of the formed laminate is substantially determined by a single film constituting each of the laminates, the light transmittance cannot be finely adjusted. Further, since the interface between the semi-transmissive films of the layers generates light, the calculation of the light transmittance obtained as a result is performed in advance by a preliminary experiment or the like, and a burden of verification is generated.

Here, as a method of producing a step cover having a different light transmittance, a method of providing a film thickness difference of a molybdenum molybdenum (MoSix) film is disclosed (Patent Document 2). In the method, the film thickness is adjusted by the film reduction of the semi-transmissive film formed by MoSix so as to have a desired light transmittance, thereby making the light transmittance difference small and relative to the first semi-transmissive portion. And the second semi-transmissive portion forms a desired difference in light transmittance. Patent Document 2 describes MoSix, MoSiN, MoSiN, etc. In comparison, when the film thickness is adjusted by a chemical solution such as an alkali, it is more effective to perform fine adjustment. On the other hand, a chromium-based compound film which is widely used as a light-shielding film and a semi-transmissive film is thin, and in the surface treatment method using an acid or an alkali liquid disclosed in Patent Document 2, it is difficult to finely adjust. In addition to the film thickness, there is also a problem that the uniformity of the film thickness after etching is insufficient. Therefore, in order to determine the end point of the film-removing step, it is not easy to conform to the desired light transmittance.

(previous technical literature)

(Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. Hei 07-049410.

Patent Document 2: Japanese Laid-Open Patent Publication No. 2009-230126.

As described above, in the light transmittance adjustment of the semi-transmissive portion of the mask, even in the film-reducing step, it is desirable to accurately measure the light transmittance and accurately grasp the film-reduction time until reaching the target value, in particular In a display device represented by a liquid crystal display device or an organic EL (electroluminescence) display device, there is a demand for higher quality in terms of brightness, operation speed, power saving, resolution, and the like.

In these devices, for example, by using a photosensitive resin such as an organic insulating film and forming a three-dimensional structure such as a contact hole, there may be The lithography of the reticle is used effectively. In particular, it is necessary to form an insulating film having a portion having a locally different height or a plurality of photosensitive spacers having different heights from each other, and the three-dimensional structure is complicated, and the need for a mask of three or more degrees is generated. In order to accurately form a three-dimensional structure, it is important to manage the light transmittance of the photomask used.

In particular, it is estimated that the gradation cover having a plurality of semi-transmissive portions having different exposure light transmittances, in addition to the light-transmitting portion and the light-shielding portion, can be advantageously used. In order to accurately form a plurality of semi-transmissive portions having light transmittances different from each other, it is important to control light transmittance. That is, if the respective light transmittances of the plurality of light transmitting portions cannot be formed correctly as designed values, satisfactory functions cannot be achieved in the final device such as a display device.

Therefore, the subject of the present invention is to solve the above problems, and to provide an etching solution having a low etching rate (ER) for finely adjusting a film thickness and achieving a uniform film thickness, and a step using the etching liquid. The method of manufacturing the mask.

In order to solve the above problems, the inventors have found in the research that diammonium nitrate (IV) or tetrakis(IV) sulfate etching solution can realize the film thickness of the optical film in the pattern processing step of the optical film of the photomask. Micro-adjustment and uniform film thickness. In addition, by combining ammonium diamine nitrate (IV) or tetrakis(IV) sulfate with acid, it was found that a film thickness of the optical film can be more highly adjusted. The film thickness was uniform and the results of further research were completed, and the present invention was completed.

That is, the present invention is as follows.

[1] An etching solution for patterning an optical film of a photomask, and for photolithography of the photomask having a degree of 3 or more, and containing diammonium nitrate (IV) or sulfuric acid Bismuth (IV) ammonium.

[2] The etching liquid according to [1], wherein the photomask has a first semi-transmissive portion and a second semi-transmissive portion having different exposure light transmittances.

[3] The etching solution according to [1] or [2], which further contains an acid.

[4] The etching liquid according to the above [3], wherein the acid is one or more selected from the group consisting of sulfuric acid, methanesulfonic acid, nitric acid, acetic acid, and perchloric acid.

[5] The etching liquid according to any one of [1] to [4] wherein the optical film contains a film of chromium and/or a chromium compound.

[6] The etching solution according to [5], wherein the chromium compound is one or two selected from the group consisting of chromium oxide, chromium nitride, chromium oxynitride, and chromium oxynitride carbide. the above.

[7] The etching liquid according to any one of [1] to [6] wherein the etching rate is 0.1 nm/min or more and 100.0 nm/min or less.

[8] The etching liquid according to any one of [1] to [6] wherein the etching rate is 0.1 nm/min or more and 5.0 nm/min or less.

[9] A method of manufacturing a gradation cover for manufacturing a gradation cover having a transfer pattern, wherein the transfer pattern has a plurality of regions having different exposure light transmittances; and the manufacturing method of the gradation cover is used as Any one of [1] to [8] The etchant described is patterned on the optical film.

[10] The method for producing a gradation cover according to [9], wherein the optical film before the pattern processing is a light shielding film and/or a semi-transmissive film.

[11] The method for producing a gradation cover according to [9] or [10], wherein the semi-transmissive region has an exposure light transmittance of 10% to 70% and a plurality of semi-transmissive portions different from each other, and At least 3 degrees.

[12] A gradation cover manufactured by the method for producing a gradation cover according to any one of [9] to [11].

In the production of a mask having an optical film which is thin and has a small thickness and which is difficult to be finely adjusted, the etching solution of the present invention has a chromium-based compound film which is widely used as a light-shielding film and a semi-transmissive film. In the manufacture of the reticle, the light transmittance of the semi-transmissive portion of the reticle can be accurately controlled in accordance with the complicated design of the desired device. In particular, the transmittance measurement can be performed in the step of forming the semi-transmissive portion, and the necessary additional etching time can be accurately grasped.

In addition, since the fine adjustment can be made in this way, the type of the reticle base to be prepared can be limited. Although the desired plurality of devices require different gradations or different transmittance values, the reticle bases to be prepared may become various types and the delivery date and cost may cause problems, but if used According to the reticle manufactured by the present invention, the step of performing a plurality of reticle can be performed by one reticle. On the other hand, if the present invention is applied, the type of the reticle base that should be prepared in advance can be defined, and can be adjusted to a desired level in the step. The light transmittance is such that a wide variety of display devices can be provided with high productivity.

Fig. 1 is an explanatory view for explaining a first embodiment of a method of manufacturing a photomask according to the present invention.

2 is an explanatory view illustrating a method of manufacturing a step cover, which employs a laminate composed of a semi-transmissive film, an etching stopper film, and a light-shielding film as an optical film formed on a transparent substrate.

Fig. 3 is a graph showing the relationship between the etching liquid and the etching rate in which the sulfuric acid concentration in the case of diammonium nitrate (IV) or tetra-(IV) ammonium sulfate is 2.0% by mass.

Fig. 4 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of nitric acid is changed in the case of cerium (IV) nitrate or cerium (IV) ammonium sulfate in an amount of 2.0% by mass.

Fig. 5 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of methanesulfonic acid is changed in the case of cerium (IV) nitrate or cerium (IV) ammonium sulfate in an amount of 2.0% by mass.

Fig. 6 is a graph showing the relationship between the etching liquid and the etching rate for changing the concentration of cerium (IV) nitrate.

Fig. 7 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of diammonium nitrate (IV) nitrate and tetrakis(IV) ammonium sulfate is changed in the case of 40% by mass of sulfuric acid.

Fig. 8 is a view showing the formation of an oxide on the surface of a glass substrate by etching using an etching solution containing 2.0% by mass of cerium (IV) nitrate and 40% by mass of sulfuric acid. A graph showing the relationship between the processing time and the amount of film reduction in the case of evaluating the substrate c of chromium.

Hereinafter, embodiments of the present invention will be described in detail.

Fig. 1 is an explanatory view for explaining a first embodiment of a method of manufacturing a photomask according to the present invention.

Step 1: As shown in (a) of FIG. 1, a photomask substrate on which an optical film is formed on a transparent substrate and a first resist film is further formed on the surface is prepared. Here, the mask substrate is a reticle base, but a part of the mask substrate may be patterned as a mask substrate.

Further, the first resist film in the mask substrate may be formed directly on the surface of the optical film, and other films may be interposed between the first resist film and the optical film as long as the effects of the present invention are not impaired. The optical film may be a light-shielding film or a semi-transmissive film, or may have a function of shifting the phase of the exposure light by a predetermined amount (phase shift film). Further, an antireflection layer that suppresses reflection of light may be provided on the surface portion of the film. In addition, the optical film may also be a laminate of a plurality of films. For example, the case where the optical film is a light shielding film is exemplified in FIG.

The film formation method of an optical film can be performed using a conventional film formation means, such as a sputtering method.

The optical film material is not particularly limited. In the light-shielding film material, for example, a light-shielding film containing Cr (chromium) as a main component is exemplified. It is preferable to have an antireflection layer such as a Cr oxide on the surface portion.

Step 2: A drawing pattern (first drawing pattern) for forming a light transmitting portion is drawn using a drawing device. After the drawing, the first resist pattern is formed by the first development ((b) in Fig. 1). Here, since a positive type photoresist is used as a resist, the resist of the drawn portion can be removed.

Step 3: The first resist pattern formed in the step 1 is used as an etching mask, and the optical film (light-shielding film) is removed by etching ((c) in FIG. 1). Here, wet etching is performed using a conventional etching solution. Thereby, the light transmitting portion is defined (first patterning step).

Step 4: Peeling off the first resist pattern (resist film) ((d) in Fig. 1).

Step 5: Coating on the surface to form a new second resist film ((e) in Fig. 1).

Step 6: The drawing device is used again to draw the second drawing pattern and perform the second development. Thereby, the second resist film corresponding to the portion of the light transmitting portion and the portion corresponding to the semi-light transmitting portion is removed, and the second resist pattern in which a part of the surface of the transparent substrate and the optical film is exposed is formed (the one in FIG. 1 (f)).

Step 7: Using the second resist pattern as a mask, using the present invention The etching solution etches and reduces the film on the exposed portion of the optical film (second patterning step). Thereby, a semi-transmissive portion having a desired exposure light transmittance ((g) in Fig. 1) is formed.

The present invention relates to an etching solution for patterning an optical film of a photomask, and for photolithographic use of the photomask having a degree of 3 or more, and containing diammonium nitrate (IV) or tetrakis(IV) ammonium sulfate.

Here, an etching liquid etching composition for etching an optical film constituting a gradation cover, for example, for etching a chromium film or a chromium compound, the etching composition containing cerium (IV) nitrate or sulfuric acid Bismuth (IV) ammonium.

The etching solution may also contain an acid. The acid is not particularly limited, and examples thereof include sulfuric acid, methanesulfonic acid, nitric acid, acetic acid, and perchloric acid. From the viewpoints of the etching rate of the chromium film or the chromium compound film and the stability of the chemical solution, it is preferred. It is sulfuric acid, methanesulfonic acid, acetic acid and nitric acid, more preferably sulfuric acid, methanesulfonic acid and acetic acid, and particularly preferably sulfuric acid and methanesulfonic acid.

The content of the diammonium nitrate (IV) or the tetrakis(IV) ammonium sulfate used in the present invention varies depending on the type of the acid, the chromium film or the chromium compound film, and therefore is not particularly limited, but is When the composition of the etching liquid is 100% by mass, it is preferably from 0.1% by mass to 10% by mass, more preferably from 0.5% by mass to 8.0% by mass, still more preferably from 1.0% by mass to 6.0% by mass.

For a substrate having a layer (or a film) composed of a chromium or a chromium compound, the etching rate is preferably 0.1 nm/min or more and 100.0 nm/min or less in the thickness direction of the layer (or the film). More preferably, it is 0.1 nm/min or more and 10.0 nm/min or less, more preferably 0.1 nm/min or more and 5.0 nm/min or less, and most preferably 0.3 nm/min or more and 1.0 nm/min or less.

Those skilled in the art can appropriately perform the temperature and time during etching, the flow conditions of the etching liquid during immersion, and the shaking conditions of the substrate (including the conditions for spraying the etching liquid composition onto the substrate by shower). Preferably, it is preferably 20.0 ° C to 25.0 ° C for temperature. When the temperature is within the above range, Cr can be used at room temperature, and the temperature is stable and suitable. Further, for the immersion time, it is preferably from 30.0 seconds to 180.0 seconds. When the immersion time is within the above range, it is suitable from the viewpoint of easily obtaining in-plane uniformity in the apparatus processing and the amount of etching liquid necessary for the treatment.

The optical film refers to a semi-transmissive film, an etching stopper film, and a light-shielding film; the so-called pattern processing refers to pattern processing in the photomask manufacturing step.

Step 8: The second resist pattern is peeled off to complete a photomask having a three-step degree of a light transmitting portion, a light blocking portion, and a semi-light transmitting portion ((h) in FIG. 1).

In the method of manufacturing a reticle as shown in FIG. 2, a method of manufacturing a gradation cover is exemplified by applying a semi-transparent film, an etching stopper film, and a light shielding film. The laminate is formed as an optical film formed on a transparent substrate.

Step 1: Prepare a photomask substrate having a film formed of a semi-transparent film, an etching stopper film, and a light-shielding film on a transparent substrate and further forming a first resist film on the surface (in FIG. 2 (a)). The semi-transmissive film has a film having a predetermined exposure light transmittance for transmitting a part of the exposure light. In the embodiment, the exposure light transmittance is, for example, 50% to 60%.

Further, the light-shielding film and the etching-preventing film are composed of materials having etching resistance and etching resistance to each other (here, an etching liquid due to application of wet etching). Further, the semi-transmissive film and the etching stopper film are also composed of materials which are resistant to each other by an etchant. The light-shielding film and the semi-transmissive film system may have etching selectivity with each other, and may not have etching selectivity with each other. Therefore, here, the material of the light-shielding film and the semi-transmissive film contains Cr, and the etching characteristics are common.

Step 2: Using a drawing device, a drawing pattern (first drawing pattern) for forming a light transmitting portion is drawn. After the drawing, the first resist pattern is formed by the first development ((b) in Fig. 2).

Step 3: The first resist pattern formed in the step 2 is used as an etching mask, and the light shielding film is removed by etching ((c) in FIG. 2).

Step 4: Change the etchant for the etch stop film, etch and remove the etch The film is blocked ((d) in Fig. 2).

Step 5: The etchant is changed again, and the semi-transmissive film is removed by etching with an etchant for the semi-transparent film. Thereafter, the first resist pattern (first resist film) is peeled off ((e) in FIG. 2).

Step 6: A new second resist film was formed on the surface ((f) in Fig. 2).

Step 7: The drawing device is used again to draw the second drawing pattern and perform the second development. Thereby, the second resist film corresponding to the portion of the light transmitting portion and the portion corresponding to the semi-light transmitting portion (the first semi-light transmitting portion) is removed, and a part of the surface on which the transparent substrate and the light shielding film are formed is exposed. The second resist pattern ((g) in Fig. 2).

Step 8: The second resist pattern is used as a cover, and the exposed portion of the light shielding film is removed by etching. Further, the etchant is removed by etching to remove the etching stopper film ((h) in Fig. 2).

Step 9: Then, the etchant is changed, and the exposed semi-transmissive film is etched and thinned using the etching liquid of the present invention (second patterning step). Thereby, a semi-transmissive portion (first semi-transmissive portion) having a desired exposure light transmittance is formed ((i) in FIG. 2).

Step 10: peeling off the second resist pattern (second resist film) to complete the A three-step mask having a light transmitting portion, a light blocking portion, and a semi-light transmitting portion ((j) in Fig. 2).

In addition, in addition to the light-transmitting portion and the light-shielding portion, the transfer of the two types of semi-transmissive portions (the first semi-transmissive portion and the second semi-transmissive portion) having different exposure light transmittances is provided. In the case of the fourth-order mask of the pattern, the following steps can be further performed on the mask of (j) in Fig. 2 .

Step 11: A new third resist film ((k) in Fig. 2) was formed on the surface.

Step 12: Using a drawing device, drawing a drawing pattern (third drawing pattern) for forming an additional semi-transmissive portion (second half-transmissive portion), and performing a third development, thereby forming a third resist pattern ((l) in Fig. 2).

Step 13: The third resist pattern is used as a cover, and the light shielding film and the etching stopper film are removed by etching to form a second semi-transmissive portion ((m) in FIG. 2).

Step 14: peeling off the third resist pattern (third resist film) to complete the fourth-order mask having the light-transmitting portion, the light-shielding portion, the first semi-transmissive portion, and the second semi-transmissive portion (FIG. 2) (n)).

According to the above steps, the plurality of first semi-transmissive portions and the second semi-transmissive portions having different exposure light transmittances can be formed by a single semi-transmissive film.

Although the state of the present invention has been described above with reference to Figs. 1 to 2, the present invention is not limited to these states, and various aspects may be included as long as the effects of the invention are not impaired. Further, the steps in the above embodiments may be changed or other steps may be added as long as the effects of the present invention are not impaired.

In the description of the embodiments, the terms "first" and "second" are used to facilitate the steps of the steps, and if other steps are performed before or after these, they may be appropriately renamed. .

In all of these states, etching is preferably applied by wet etching. In particular, in a photomask for manufacturing a device, since it is necessary to produce a large-sized photomask substrate having a single side of 300 mm or more and various types of aspect ratios or areas, the effect of applying wet etching is large.

In addition, the reticle base of the optical film and the resist film formed on the transparent substrate may be used as a starting material, and some reticle intermediates which are patterned or subjected to other processing may also be used as a starting point. Applied for materials.

The use of the photomask of the present invention is not particularly limited.

For example, it can also be applied to a PEP (Photo Engraving Process) which is useful as a gradation cover (the number of reticle used can be reduced when manufacturing a display device panel).

Further, it can be used as a structural material for forming a display device (by photosensitivity) A three-dimensional photomask made of a resin or the like is used. For example, the effect of the invention is remarkable since the photosensitive spacer of the liquid crystal display device or the insulating layer of the display device can be accurately performed with respect to the height control of a plurality of structural materials having different heights, respectively. It is particularly advantageous among masks of 4 steps or more.

Furthermore, the present invention includes a method of manufacturing a display device, the method of manufacturing the display device comprising the steps of: using a photomask manufactured according to any of the embodiments, and transferring the transfer pattern by an exposure device To the transferred body.

The material of the optical film used as the photomask of the present invention is exemplified as follows.

The material of the optical film used herein is not particularly limited, but a compound containing Cr as a main component can be preferably used. For example, an oxide, a nitride, a carbide, an oxynitride or a carbodiimide carbide of Cr can be used, and an oxide of Cr or an oxynitride can be preferably used. These materials may be used alone or in combination of two or more. The film thickness of the portion used as the light shielding portion is preferably such that a sufficient light blocking property (optical density OD ≧ 3, preferably OD ≧ 4) is obtained.

As the semi-transmissive film, the semi-transmissive film and the light-shielding film may have an etching selectivity or may not have an etching selectivity. Among them, without eclipse In the case of engraving selectivity (i.e., common etching characteristics), since a common etchant can be used, the efficiency in production is good.

Therefore, it is possible to select from the light-shielding film material exemplified above. Further, in the case of etching the film, it is more preferable that the film thickness is 50 Å to 2,000 Å in order to easily control the etching time until the light transmittance reaches the target.

Since the etching stopper film is desired to have etching selectivity to the light shielding film and the semi-transmissive film, compounds of Ta, Mo, W, and the like (for example, oxide, nitride, oxynitride or TaSi, MoSi, WSi ( A material selected from metal halides or these nitrides, oxynitrides, and the like.

[Examples]

The present invention will be more specifically described by the following examples and comparative examples, but the invention is not limited thereto, and various modifications can be made without departing from the spirit and scope of the invention.

An evaluation substrate a having oxidized chromium of 19 nm (light transmittance: 17%) and 15 nm (light transmittance: 35.5%) was formed on the surface of the glass substrate, and the etching liquid compositions shown in Tables 1 and 2 were respectively adjusted. Things. At this time, observation was made as to whether or not each of the etching compositions was crystallized.

Each evaluation substrate a was cut into 2.0 cm × 2.0 cm, and the film thickness of the chromium oxide film was measured using a fluorescent X-ray analyzer (ZSX100e) before the etching liquid was immersed.

Each of the evaluation substrates b was obtained by immersing in a glass vessel containing 80 ml of each etching liquid composition at 25 ° C for 15 seconds to 1800 seconds, rinsing with ultrapure water for 1 minute, and drying by a nitrogen stream.

For each evaluation substrate b, the amount of etching of the chromium oxide film was measured using a fluorescent X-ray analyzer, and the etching rate (E.R.) was calculated from the immersion time and the etching amount. The results of the presence or absence of precipitation of the crystal and the etching rate are shown in Tables 1 and 2 together with the composition of the etching solution composition and the concentration of the component.

In the case of using an acid of diammonium nitrate (IV) and any of perchloric acid, nitric acid, sulfuric acid, acetic acid, methanesulfonic acid, the intended etching rate can be obtained. On the other hand, when phosphoric acid is used as the acid, crystals are precipitated regardless of the concentration, and the etching rate cannot be measured.

In the case of using an acid of any of tetrakis(IV) ammonium sulfate and nitric acid, sulfuric acid, acetic acid, or methanesulfonic acid, the intended etching rate can be obtained. On the other hand, when perchloric acid and phosphoric acid were used as the acid, crystals were precipitated regardless of the concentration, and the etching rate could not be measured.

Fig. 3 is a graph showing the relationship between the etching liquid and the etching rate in which the sulfuric acid concentration in the case of cerium (IV) nitrate or cerium (IV) ammonium sulfate is 2.0% by mass. It was confirmed that as the sulfuric acid concentration is increased, the etching rate tends to decrease.

Fig. 4 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of nitric acid is changed in the case of 2.0% by mass of cerium (IV) nitrate or ammonium cerium (IV) sulfate. In the case of cerium (IV) nitrate dinitrate, it was confirmed that the etching rate tends to decrease as the concentration of nitric acid increases. On the other hand, in the case of ammonium tetrakis(IV) sulfate, when the concentration of nitric acid is within about 40%, the higher the concentration of nitric acid, the more the etching rate tends to increase; when the concentration of nitric acid is above 40% In the range of the above, it was confirmed that the larger the nitric acid concentration, the lower the etching rate.

Fig. 5 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of methanesulfonic acid is changed in the case of 2.0% by mass of cerium (IV) nitrate or ammonium cerium (IV) sulfate. It was confirmed that as the concentration of methanesulfonic acid is larger, the etching rate tends to decrease.

Fig. 6 is a graph showing the relationship between the etching liquid and the etching rate for changing the concentration of cerium (IV) nitrate. It was confirmed that as the concentration of cerium (IV) nitrate dinitrate is smaller, the etching rate tends to decrease.

Fig. 7 is a graph showing the relationship between the etching liquid and the etching rate in which the concentration of diammonium nitrate (IV) nitrate and tetrakis(IV) sulfate is changed in the case of 40% by mass of sulfuric acid. It was confirmed that the etching rate tends to increase as the concentration of cerium (IV) nitrate and cerium (IV) sulphate increases.

8 is a view showing a treatment time and a film reduction amount in the case where an evaluation substrate c in which chromium oxide is formed on the surface of a glass substrate is etched using an etching solution containing 2.0% by mass of cerium (IV) nitrate and 40% by mass of sulfuric acid. Diagram of the relationship. Since a linear film reduction occurs with respect to the treatment time, it can be confirmed that the light transmittance of the chromium oxide can be controlled by the treatment time.

Claims (12)

An etching solution for patterning an optical film of a photomask, and for photolithography of the photomask having a degree of 3 or more, and containing diammonium nitrate (IV) or tetrasulfate (IV) Ammonium. The etching liquid according to claim 1, wherein the photomask has a first semi-transmissive portion and a second semi-transmissive portion having different exposure light transmittances. The etching solution according to claim 1 or 2, which further contains an acid. The etchant according to claim 3, wherein the acid is one or more selected from the group consisting of sulfuric acid, methanesulfonic acid, nitric acid, acetic acid, and perchloric acid. The etching solution according to any one of claims 1 to 4, wherein the optical film contains a film of chromium and/or a chromium compound. The etching liquid according to claim 5, wherein the chromium compound is one or more selected from the group consisting of chromium oxide, chromium nitride, chromium oxynitride, and chromium oxynitride carbide. The etching solution according to any one of claims 1 to 6, wherein an etching rate is 0.1 nm/min or more and 100.0 nm/min or less. The etching solution according to any one of claims 1 to 6, wherein the etching rate is 0.1 nm/min or more and 5.0 nm/min or less. A method for manufacturing a gradation cover for manufacturing a gradation cover having a transfer pattern, wherein the transfer pattern has a plurality of regions having different exposure light transmittances; and the manufacturing method of the gradation cover is as claimed in claim 1 The etching liquid described in any one of 8 is used to pattern the optical film. The method of manufacturing the gradation cover according to claim 9, wherein the optical film before the pattern processing is a light shielding film and/or a semi-transmissive film. The method for manufacturing a gradation cover according to claim 9 or 10, wherein the semi-transmissive region has an exposure light transmittance of 10% to 70% and different from each other, and has at least 3 gradations. . A gradation cover manufactured by the method of manufacturing a gradation cover according to any one of claims 9 to 11.