Photomask manufacturing method and photomask blank

Abstract

SOLUTION: From a photomask blank having a transparent substrate, a first inorganic film containing silicon and not containing chromium, and a second inorganic film containing chromium and not containing silicon, and the first inorganic film and the second inorganic film in contact with each other, a resist film is formed in contact with the second inorganic film, and the second inorganic film and first inorganic film are etched together with a fluorine-based dry etching to form a pattern.EFFECT: According to the present invention, the adhesion of the resist film is ensured regardless of the film quality of the silicon-containing film, and the problem of resist residue, which is a problem in the silylation treatment for the silicon-containing film, is avoided, and without adding a new process, photomasks having less defect can be produced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a photomask used in manufacturing semiconductor integrated circuits and the like, and a photomask blank suitable for use in this method. [Background technology]

[0002] In recent years, in semiconductor processing, particularly with the increasing integration density of large-scale integrated circuits, there has been an increasing need for finer circuit patterns, and there has been an increasing demand for technology to make finer wiring patterns that make up circuits and finer contact hole patterns for wiring between layers that make up cells. Therefore, in the manufacture of photomasks on which circuit patterns are written, which are used in optical lithography to form these wiring patterns and contact hole patterns, technology that can write circuit patterns more finely and accurately is required in line with the above-mentioned miniaturization.

[0003] To form a more accurate photomask pattern on a photomask substrate, it is first necessary to form a high-precision resist pattern on a photomask blank. In current lithography, the circuit pattern to be drawn is significantly smaller than the wavelength of the light used. If a photomask pattern that is four times the circuit shape is used, the exact shape of the photomask pattern will not be transferred to the resist film due to effects such as light interference that occur during actual optical lithography. To mitigate these effects, the photomask pattern may need to be processed into a shape more complex than the actual circuit pattern (a shape that utilizes techniques such as OPC: Optical Proximity Correction). Therefore, even in the lithography technology used to obtain photomask patterns, even higher-precision processing methods are currently required.

[0004] In forming a photomask pattern, a resist film is typically formed on a photomask blank having a light-shielding film, a phase shift film, or the like on a transparent substrate, a pattern is drawn using an electron beam, and a resist pattern is obtained through development. The obtained resist pattern is then used as an etching mask to etch the light-shielding film, the phase shift film, or the like to form a light-shielding film pattern, a phase shift film pattern, or the like (photomask pattern). However, if an attempt is made to process a finer photomask pattern while maintaining the thickness of the resist film unchanged, the ratio of film thickness to pattern width, or the so-called aspect ratio, becomes high, degrading the shape of the resist pattern and resulting in poor pattern transfer and, in some cases, causing the resist pattern to collapse or peel off. Therefore, as the photomask pattern becomes finer, it is necessary to make the resist film thinner.

[0005] On the other hand, methods of using hard masks to reduce the load on resist patterns during dry etching have long been attempted. For example, Japanese Patent Laid-Open Publication No. 63-85553 (Patent Document 1) describes forming an SiO2 film on a MoSi2 film and using the SiO2 film pattern as an etching mask when dry etching the MoSi2 film using a chlorine-containing gas. Also, for example, Japanese Patent Laid-Open Publication No. 7-49558 (Patent Document 2) describes forming a chromium film as a light-shielding film on a phase shift film, forming an SiO2 film as a hard mask film on the chromium film, and using the SiO2 film pattern as a hard mask when etching the chromium film. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 63-85553 [Patent Document 2] Japanese Patent Application Publication No. 7-49558 Summary of the Invention [Problem to be solved by the invention]

[0007] As photomask patterns become finer, the adhesion between the resist film and the resist pattern becomes important. However, when a resist film is formed on the surface of a silicon-containing film, which is processed into a resist pattern, and this resist pattern is used as an etching mask to process the silicon-containing film, the adhesion between the silicon-containing film and the resist film is low, so when attempting to form a fine photomask pattern, there is a problem that the resist film peels off during the development process when forming the resist pattern from the resist film. In order to avoid this problem, it is known that a treatment of silylating the surface of the silicon-containing film with hexamethyldisilazane or the like is effective.

[0008] However, silylation treatment increases the hydrophobicity of the treated surface, making aqueous cleaning difficult. Therefore, when forming a resist pattern from a resist film, a large amount of resist residue remains during the post-development cleaning process, resulting in defects. On the other hand, one method for improving adhesion to the resist film from the silicon-containing film side is to adjust the surface composition of the silicon-containing film, such as an SiO2 film, to a composition that has good adhesion to the resist film. However, when trying to improve adhesion to the resist film without impairing the essential properties required of the silicon-containing film, such as optical properties and etching properties, changing the composition of the silicon-containing film offers limited flexibility. Furthermore, adjusting the surface composition of the silicon-containing film to consider adhesion to the resist film also leads to problems such as poor etching controllability and difficulty in imparting conductivity.

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a method for producing a photomask, and a photomask blank suitable for this method, which avoids problems with adhesion between a silicon-containing film and a resist film (such as collapse or peeling of the resist pattern) that arise when a resist film is formed on a silicon-containing film, without impairing the properties required of the photomask blank and the silicon-containing film provided on the photomask, and which suppresses the occurrence of defects due to resist residues during cleaning. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that, when a photomask is manufactured from a photomask blank having a transparent substrate and a first inorganic film that contains silicon but does not contain chromium, adhesion to a resist film can be ensured by forming a second inorganic film that contains chromium but does not contain silicon in contact with the first inorganic film; and further, by making the second inorganic film, which is a film that contains chromium but does not contain silicon, a film that can be etched by fluorine-based dry etching, specifically a film that has an etching rate that is 0.3 or more higher than the etching rate of the first inorganic film when etched by fluorine-based dry etching under the same conditions, a resist film can be formed in contact with the second inorganic film, a resist pattern can be formed from the resist film, and the second inorganic film and then the first inorganic film can be patterned by fluorine-based dry etching in this order, thereby avoiding the generation of resist residues that are a problem in silylation treatment of silicon-containing films and enabling the formation of a fine photomask pattern with high precision, which has led to the present invention.

[0011] Therefore, the present invention provides the following photomask manufacturing method and photomask blank. 1. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (A) forming a resist film in contact with the second inorganic film; (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising: 2. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, and a resist film, wherein the first inorganic film, the second inorganic film, and the resist film are formed in contact with each other in this order, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising: 3. The manufacturing method according to 1 or 2, characterized in that the fluorine-based dry etching in step (C) and the fluorine-based dry etching in step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in step (D). 4. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, the first inorganic film and the second inorganic film being formed in contact with each other, and the first inorganic film being formed on the transparent substrate directly or via one or more other inorganic films, (A) forming a resist film in contact with the second inorganic film; (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. Including, The fluorine-based dry etching in the step (C) and the fluorine-based dry etching in the step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in the step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in the step (D). A method for manufacturing a photomask, comprising: 5. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, a second inorganic film containing chromium but not containing silicon, and a resist film, wherein the first inorganic film, the second inorganic film, and the resist film are formed in contact with each other in this order, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. Including, The fluorine-based dry etching in the step (C) and the fluorine-based dry etching in the step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in the step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in the step (D). A method for manufacturing a photomask, comprising: 6. A manufacturing method according to any one of 1 to 5, characterized in that the steps (C) and (D) are carried out successively by fluorine-based dry etching. 7. The manufacturing method according to any one of 1 to 6, wherein the thickness of the second inorganic film is 1 nm or more and 10 nm or less. 8. A manufacturing method according to any one of 1 to 7, characterized in that the photomask blank has a third inorganic film formed as the other inorganic film, the third inorganic film containing chromium but not silicon, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film. 9. The manufacturing method according to 8, wherein the etching rate of the third inorganic film by fluorine-based dry etching in step (D) is less than 0.3 relative to the etching rate of the first inorganic film by fluorine-based dry etching in step (D). 10. A device comprising a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films. And, When etched under the same conditions by fluorine-based dry etching, the etching rate of the second inorganic film relative to the etching rate of the first inorganic film is 0.3 or more. R A photomask blank characterized by: 11 A photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, A photomask blank characterized in that, when etched by fluorine-based dry etching under the same conditions, the etching rate of the second inorganic film relative to the etching rate of the first inorganic film is 0.3 or more. 12 The photomask blank has a third inorganic film that contains chromium but does not contain silicon, and is formed as the other inorganic film, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film. or 11 Photomask blank as described. 13 When etched under the same conditions using fluorine-based dry etching, the etching rate of the third inorganic film relative to the etching rate of the first inorganic film is less than 0.3. 12 Photomask blank as described. 14. A photomask blank comprising a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, and the photomask blank comprises a third inorganic film which contains chromium but not containing silicon and is formed as the other inorganic film, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film, When etched under the same conditions by fluorine-based dry etching, the etching rate of the third inorganic film relative to the etching rate of the first inorganic film is less than 0.3. A photomask blank characterized by: 15 10 to 13, characterized in that the thickness of the second inorganic film is 1 nm or more and 10 nm or less. 14 1. The photomask blank according to any one of claims 1 to 9. 16. The photomask blank according to any one of 10 to 15, further comprising a resist film in contact with the second inorganic film on the side remote from the transparent substrate. The present invention also relates to the following photomask manufacturing method and photomask blank. [1]. A method for manufacturing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, the first inorganic film and the second inorganic film being formed in contact with each other, and the first inorganic film being formed on the transparent substrate directly or via one or more other inorganic films, (A) forming a resist film in contact with the second inorganic film; (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising: [2]. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, a second inorganic film containing chromium but not containing silicon, and a resist film, wherein the first inorganic film, the second inorganic film, and the resist film are formed in contact with each other in this order, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising: [3] The manufacturing method according to [1] or [2], wherein the steps (C) and (D) are carried out successively by fluorine-based dry etching. [4] The manufacturing method according to any one of [1] to [3], characterized in that the fluorine-based dry etching in step (C) and the fluorine-based dry etching in step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in step (D). [5] The manufacturing method according to any one of [1] to [4], wherein the chromium content of the second inorganic film is 25 atomic % or more and less than 40 atomic %. [6] The manufacturing method according to any one of [1] to [5], wherein the thickness of the second inorganic film is 1 nm or more and 10 nm or less. [7] The manufacturing method according to any one of [1] to [6], wherein the photomask blank has a third inorganic film formed as the other inorganic film, the third inorganic film containing chromium but not silicon, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film. [8]. The manufacturing method according to [7], wherein the etching rate of the third inorganic film by fluorine-based dry etching in step (D) is less than 0.3 relative to the etching rate of the first inorganic film by fluorine-based dry etching in step (D). [9] The manufacturing method according to [7] or [8], wherein the photomask blank has a fourth inorganic film formed as the other inorganic film, the fourth inorganic film containing silicon and not containing chromium, and the fourth inorganic film is formed in contact with the transparent substrate side of the third inorganic film.

[10] . The manufacturing method according to [9], wherein the first inorganic film is a hard mask film for the third inorganic film, the second inorganic film is a processing auxiliary film for the first inorganic film, the third inorganic film is a light-shielding film, and the fourth inorganic film is a phase shift film.

[11] A photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, A photomask blank characterized in that, when etched by fluorine-based dry etching under the same conditions, the etching rate of the second inorganic film relative to the etching rate of the first inorganic film is 0.3 or more.

[12] The photomask blank according to

[11] , wherein the chromium content of the second inorganic film is 25 atomic % or more and less than 40 atomic %.

[13] The photomask blank according to

[11] or

[12] , wherein the second inorganic film has a thickness of 1 nm or more and 10 nm or less.

[14] The photomask blank according to any one of

[11] to

[13] , characterized in that the photomask blank has a third inorganic film formed as the other inorganic film, the third inorganic film containing chromium but not silicon, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film.

[15] The photomask blank according to

[14] , wherein when etched under the same conditions using fluorine-based dry etching, the etching rate of the third inorganic film relative to the etching rate of the first inorganic film is less than 0.3.

[16] The photomask blank according to

[14] or

[15] , characterized in that the photomask blank has a fourth inorganic film formed as the other inorganic film, the fourth inorganic film containing silicon but not containing chromium, and the fourth inorganic film is formed in contact with the transparent substrate side of the third inorganic film.

[17] . The photomask blank according to

[16] , wherein the first inorganic film is a hard mask film of the third inorganic film, the second inorganic film is a processing auxiliary film of the first inorganic film, the third inorganic film is a light-shielding film, and the fourth inorganic film is a phase shift film.

[18] The photomask blank according to any one of

[11] to

[17] , further comprising a resist film in contact with the second inorganic film on the side facing away from the transparent substrate. [Effects of the Invention]

[0012] According to the present invention, by forming a resist film on a first inorganic film containing silicon but not containing chromium via a second inorganic film containing chromium but not containing silicon, adhesion of the resist film is ensured regardless of the film quality of the silicon-containing film.Furthermore, by making the second inorganic film, which is a film containing chromium but not containing silicon, a film that can be etched by fluorine-based dry etching, and patterning the second inorganic film and the first inorganic film in that order using fluorine-based dry etching, the problem of resist residues generated after development when forming a resist pattern from a resist film, which is a problem in silylation treatment of silicon-containing films, can be avoided, and a photomask with few defects can be produced without adding a new process.Furthermore, according to the present invention, the film quality (composition, physical properties, etc.) of the first inorganic film, which is a silicon-containing film, does not need to be considered for adhesion to the resist film, so there is a high degree of freedom in selecting the first inorganic film. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of a photomask blank of the present invention. [Figure 2]FIG. 2 is a cross-sectional view showing another example of the photomask blank of the present invention. [Figure 3] FIG. 2 is a cross-sectional view showing an example of a photomask blank of the present invention having a third inorganic film. [Figure 4] FIG. 3 is a cross-sectional view showing another example of a photomask blank of the present invention having a third inorganic film. [Figure 5] FIG. 2 is a cross-sectional view showing an example of a photomask blank of the present invention having a third inorganic film and a fourth inorganic film. [Figure 6] FIG. 3 is a cross-sectional view showing another example of a photomask blank of the present invention having a third inorganic film and a fourth inorganic film. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in more detail below. The photomask blank of the present invention comprises a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, with the first inorganic film and the second inorganic film being formed in contact with each other. The transparent substrate is not particularly limited as long as it is made of a material transparent to exposure light and undergoes minimal deformation during heat treatment in the manufacture of the photomask blank and photomask. An example is a quartz substrate. The first inorganic film may be formed directly on the transparent substrate, or may be formed on the transparent substrate via one or more other inorganic films (e.g., a third inorganic film, a fourth inorganic film, etc.). However, it is preferred that the first inorganic film be formed on the transparent substrate via another inorganic film. A resist film may be formed in contact with the side of the second inorganic film that is away from the transparent substrate.

[0015] Fig. 1 is a cross-sectional view showing an example of a photomask blank of the present invention. This photomask blank 10 has a transparent substrate 1 on which a first inorganic film 21 is formed in contact with the transparent substrate 1, and a second inorganic film 22 is formed in contact with the first inorganic film 21. Fig. 2 is a cross-sectional view showing another example of a photomask blank of the present invention. This photomask blank 11 has a transparent substrate 1 on which a first inorganic film 21 is formed in contact with the transparent substrate 1, a second inorganic film 22 is formed in contact with the first inorganic film 21, and a resist film 3 is formed in contact with the second inorganic film 22.

[0016] The first inorganic film is a film that is patterned using the pattern of the second inorganic film as an etching mask. The first inorganic film is a film that contains silicon but does not contain chromium, but is preferably composed of a material that is resistant to chlorine-based dry etching and can be removed by fluorine-based dry etching. The first inorganic film may contain a transition metal other than chromium in addition to silicon. In the present invention, typical examples of chlorine-based dry etching include dry etching using an etching gas containing chlorine and oxygen, such as a mixed gas of Cl gas and O gas, and typical examples of fluorine-based dry etching include dry etching using an etching gas containing fluorine, such as CF gas or SF gas.

[0017] The material constituting the first inorganic film is preferably a material containing silicon but not a transition metal, or a material containing silicon and a transition metal other than chromium (Me) but not chromium. The material for the film containing silicon but not a transition metal may be elemental silicon (Si) or a silicon compound containing silicon (Si) and one or more selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such materials include silicon (Si), silicon and oxygen (SiO), silicon and nitrogen (SiN), silicon, oxygen, and nitrogen (SiON), silicon and carbon (SiC), silicon, oxygen, and carbon (SiOC), silicon, nitrogen, and carbon (SiNC), and silicon, oxygen, nitrogen, and carbon (SiONC).

[0018] On the other hand, the film material containing a transition metal (Me) other than chromium and silicon but not containing chromium may be a transition metal (Me) silicon compound containing a transition metal (Me) and silicon (Si), or a transition metal (Me) silicon compound containing a transition metal (Me), silicon (Si), and one or more selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such a material include a material consisting of a transition metal and silicon (MeSi), a material consisting of a transition metal, silicon, and oxygen (MeSiO), a material consisting of a transition metal, silicon, and nitrogen (MeSiN), a material consisting of a transition metal, silicon, oxygen, and nitrogen (MeSiON), a material consisting of a transition metal, silicon, and carbon (MeSiC), a material consisting of a transition metal, silicon, oxygen, and carbon (MeSiOC), a material consisting of a transition metal, silicon, nitrogen, and carbon (MeSiNC), and a material consisting of a transition metal, silicon, oxygen, nitrogen, and carbon (MeSiONC).

[0019] Here, the transition metal (Me) other than chromium is preferably one or more selected from molybdenum (Mo), tungsten (W), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf), with molybdenum (Mo) being particularly preferred from the viewpoint of dry etching processability. Note that the material constituting the first inorganic film may contain hydrogen, etc.

[0020] Examples of the first inorganic film include optical films such as light-shielding films, anti-reflection films, and phase shift films such as halftone phase shift films, and hard mask films used as an etching mask for a transparent substrate or a third inorganic film described below.

[0021] The thickness of the first inorganic film is preferably 1 nm or more and 100 nm or less. When the first inorganic film is a light-shielding film, anti-reflection film, or phase shift film, when used as a photomask, the entire film remaining as a light-shielding pattern preferably has a thickness such that the optical density (OD) of the entire film is 2.5 or more, particularly 3 or more, relative to exposure light, for example, light with a wavelength of 250 nm or less, particularly light with a wavelength of 200 nm or less, such as an ArF excimer laser (wavelength 193 nm) or an F2 laser (wavelength 157 nm). Specifically, the thickness is preferably 40 nm or more and 100 nm or less. When the first inorganic film is a hard mask film, the thickness is preferably 1 nm or more, particularly 2 nm or more, and 30 nm or less, particularly 20 nm or less, and especially 10 nm or less.

[0022] In the photomask blank of the present invention, the second inorganic film, which is a film containing chromium but not silicon, is a film that can be etched by fluorine-based dry etching. Fluorine-based dry etching is an etching method typically used to pattern silicon-containing films, particularly silicon-containing films not containing chromium, when producing a photomask from a photomask blank. However, by making the second inorganic film a film that can be etched by fluorine-based dry etching, the second inorganic film can be etched by fluorine-based dry etching, which is the etching method used for the first inorganic film, particularly in the same etching process as the etching method used for the first inorganic film. Specifically, the second inorganic film that can be etched by fluorine-based dry etching can be a film that, when etched by fluorine-based dry etching under the same conditions, has an etching rate that is 0.1 or more, preferably 0.3 or more, relative to the etching rate of the first inorganic film.

[0023] The second inorganic film can be considered a processing aid film for the first inorganic film. From the viewpoint of a processing aid film, the film thickness of the second inorganic film is preferably 1 nm or more, particularly 2 nm or more, and 10 nm or less, particularly 5 nm or less. By setting the film thickness of the second inorganic film within the above range, the second inorganic film can be patterned without increasing the film thickness of the resist film, which is preferable. Furthermore, from the viewpoint of efficient patterning by fluorine-based dry etching, the material constituting the second inorganic film is preferably a chromium compound. The chromium compound may be any chromium compound containing chromium (Cr) and one or more elements selected from oxygen (O), nitrogen (N), and carbon (C). Such materials include a material made of chromium and oxygen (CrO), a material made of chromium and nitrogen (CrN), a material made of chromium, oxygen and nitrogen (CrON), a material made of chromium and carbon (CrC), a material made of chromium, oxygen and carbon (CrOC), a material made of chromium, nitrogen and carbon (CrNC), and a material made of chromium, oxygen, nitrogen and carbon (CrONC).

[0024] In the case of a chromium compound that is the material of the second inorganic film, the chromium content is preferably 25 atomic % or more, particularly 30 atomic % or more, and less than 40 atomic %, particularly 39 atomic % or less. Furthermore, the oxygen content is preferably 0 atomic % or more, particularly 10 atomic % or more, and 70 atomic % or less, particularly 65 atomic % or less. The nitrogen content is preferably 0 atomic % or more, particularly 5 atomic % or more, and 60 atomic % or less, particularly 50 atomic % or less. The carbon content is preferably 0 atomic % or more, particularly 1 atomic % or more, and 30 atomic % or less, particularly 20 atomic % or less.

[0025] The sheet resistance of the second inorganic film is 1×10 4 By reducing the sheet resistance of the second inorganic film, the first inorganic film can be used as a high-resistance film such as SiO2 (for example, a film having a sheet resistance of 1×10 12 When the resistivity is Ω / □ or more, the second inorganic film can function as a conductive film.

[0026] A preferred example of a photomask blank in which a first inorganic film is formed on a transparent substrate via one or more other inorganic films is one in which the other inorganic film is a third inorganic film that contains chromium but does not contain silicon, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film. In this way, the third inorganic film functions as a hard mask that is resistant to fluorine-based dry etching of the first inorganic film, and the third inorganic film can be selectively peeled off from the first inorganic film.

[0027] Further, an example of a photomask blank in which a first inorganic film is formed on a transparent substrate via one or more other inorganic films includes a photomask blank having, as other inorganic films, a third inorganic film and a fourth inorganic film that contains silicon but does not contain chromium, the fourth inorganic film being formed in contact with the transparent substrate side of the third inorganic film. Even when the photomask blank has other inorganic films, a resist film may be formed in contact with the side of the second inorganic film that is remote from the transparent substrate.

[0028] Fig. 3 is a cross-sectional view showing an example of a photomask blank of the present invention having a third inorganic film. This photomask blank 12 has a transparent substrate 1 on which a third inorganic film 23 is formed in contact with the transparent substrate 1, a first inorganic film 21 is formed in contact with the third inorganic film 23, and a second inorganic film 22 is formed in contact with the first inorganic film 21, in this order. Fig. 4 is a cross-sectional view showing another example of a photomask blank of the present invention having a third inorganic film. This photomask blank 13 has a third inorganic film 23 formed in contact with the transparent substrate 1, a first inorganic film 21 formed in contact with the third inorganic film 23, a second inorganic film 22 formed in contact with the first inorganic film 21, and a resist film 3 formed in contact with the second inorganic film 22, in this order.

[0029] Fig. 5 is a cross-sectional view showing an example of a photomask blank of the present invention having a third inorganic film and a fourth inorganic film. This photomask blank 14 has a transparent substrate 1 on which a fourth inorganic film 24 is formed in contact with the transparent substrate 1, a third inorganic film 23 is formed in contact with the fourth inorganic film 24, a first inorganic film 21 is formed in contact with the third inorganic film 23, and a second inorganic film 22 is formed in contact with the first inorganic film 21, in this order. Fig. 6 is a cross-sectional view showing another example of a photomask blank of the present invention having a third inorganic film and a fourth inorganic film. This photomask blank 15 has a fourth inorganic film 24 formed in contact with the transparent substrate 1, a third inorganic film 23 is formed in contact with the fourth inorganic film 24, a first inorganic film 21 is formed in contact with the third inorganic film 23, a second inorganic film 22 is formed in contact with the first inorganic film 21, and a resist film 3 is formed in contact with the second inorganic film 22, in this order.

[0030] In the photomask blank of the present invention, the third inorganic film, which is a film containing chromium but not silicon, may be a film that can be etched by fluorine-based dry etching, but preferably has etching characteristics different from those of the first inorganic film or has high etching selectivity relative to the first inorganic film, and is preferably a film that cannot be etched by fluorine-based dry etching.Specifically, the third inorganic film that cannot be etched by fluorine-based dry etching is preferably a film whose etching rate relative to the etching rate of the first inorganic film is less than 0.3, particularly 0.1 or less, when etched by fluorine-based dry etching under the same conditions.

[0031] The material constituting the third inorganic film, which is a film containing chromium but not silicon, may be elemental chromium (Cr) or a chromium compound containing chromium (Cr) and one or more selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such materials include a material made of chromium and oxygen (CrO), a material made of chromium and nitrogen (CrN), a material made of chromium, oxygen, and nitrogen (CrON), a material made of chromium and carbon (CrC), a material made of chromium, oxygen, and carbon (CrOC), a material made of chromium, nitrogen, and carbon (CrNC), and a material made of chromium, oxygen, nitrogen, and carbon (CrONC).

[0032] In the case of a chromium compound that is the material of the third inorganic film, the chromium content is preferably 30 atomic % or more, particularly 35 atomic % or more, and 100 atomic % or less, particularly 80 atomic % or less. Furthermore, the oxygen content is preferably 0 atomic % or more, particularly 5 atomic % or more, and 70 atomic % or less, particularly 60 atomic % or less. The nitrogen content is preferably 0 atomic % or more, particularly 10 atomic % or more, and 60 atomic % or less, particularly 50 atomic % or less. The carbon content is preferably 0 atomic % or more, particularly 1 atomic % or more, and 40 atomic % or less, particularly 30 atomic % or less.

[0033] Examples of the third inorganic film include optical films such as light-shielding films, anti-reflection films, and phase shift films such as halftone phase shift films, etching stopper films for the first inorganic film, and hard mask films used as etching masks for the transparent substrate or the fourth inorganic film. When the third inorganic film is provided, for example, the third inorganic film can be a light-shielding film and the first inorganic film can be an anti-reflection film.

[0034] The thickness of the third inorganic film is preferably 1 nm or more and 100 nm or less. When the third inorganic film is a light-shielding film, an anti-reflection film, or a phase shift film, when used as a photomask, the entire film remaining as a light-shielding pattern preferably has a thickness such that the optical density (OD) of the entire film is 2.5 or more, particularly 3 or more, relative to exposure light, for example, light with a wavelength of 250 nm or less, particularly light with a wavelength of 200 nm or less, such as an ArF excimer laser (193 nm) or an F2 laser (wavelength 157 nm). Specifically, the thickness is preferably 40 nm or more and 100 nm or less. When the third inorganic film is an etching stopper film or a hard mask film, the thickness is preferably 1 nm or more, particularly 2 nm or more, and 30 nm or less, particularly 20 nm or less, and especially 10 nm or less.

[0035] In the photomask blank of the present invention, the fourth inorganic film, which is a film containing silicon but not containing chromium, preferably has etching characteristics different from those of the third inorganic film or has high etching selectivity relative to the third inorganic film, and is preferably made of a material that is resistant to chlorine-based dry etching and removable by fluorine-based dry etching. The fourth inorganic film may contain a transition metal other than chromium together with silicon.

[0036] The material constituting the fourth inorganic film is preferably a material containing silicon but not a transition metal, or a material containing a transition metal other than chromium (Me) and silicon but not chromium. Similar to the examples of the first inorganic film, the material for the film containing silicon but not a transition metal may be elemental silicon (Si) or a silicon compound containing silicon (Si) and one or more selected from oxygen (O), nitrogen (N), and carbon (C). Similarly to the examples of the first inorganic film, the material for the film containing a transition metal other than chromium (Me) and silicon but not chromium may be a transition metal (Me) silicon compound containing a transition metal (Me) and silicon (Si), or a transition metal (Me) silicon compound containing a transition metal (Me), silicon (Si), and one or more selected from oxygen (O), nitrogen (N), and carbon (C). The transition metal (Me) other than chromium may be the same as those exemplified for the first inorganic film, and molybdenum (Mo) is particularly preferred from the viewpoint of dry etching processability. The material constituting the fourth inorganic film may also contain hydrogen, etc.

[0037] Examples of the fourth inorganic film include optical films such as a light-shielding film, an anti-reflection film, and a phase shift film such as a halftone phase shift film, and an etching stopper film for the third inorganic film.

[0038] The thickness of the fourth inorganic film is preferably 1 nm or more and 100 nm or less. When the fourth inorganic film is a light-shielding film, an anti-reflection film, or a phase shift film, when used as a photomask, the film as a whole remaining as a light-shielding pattern preferably has a thickness such that the optical density (OD) of the film is 2.5 or more, particularly 3 or more, relative to exposure light, for example, light having a wavelength of 250 nm or less, particularly light having a wavelength of 200 nm or less, such as an ArF excimer laser (wavelength 193 nm) or an F2 laser (wavelength 157 nm), and specifically, is preferably 40 nm or more and 100 nm or less.

[0039] The first inorganic film, the second inorganic film, and other inorganic films (such as a third inorganic film and a fourth inorganic film) may each be composed of a single layer or multiple (two or more, usually four or less) layers, or may be films having a gradient composition. In the case of a multiple-layer structure, for example, the transparent substrate side may be formed of a material with a high oxygen or nitrogen content to improve adhesion or an antireflection layer (layer A), and the side away from the transparent substrate may be an antireflection layer (layer B), and the light-shielding film may be, from the transparent substrate side, a two-layer structure of layer A and a light-shielding layer, a two-layer structure of the light-shielding layer and layer B, or a three-layer structure of layer A, light-shielding layer, and layer B.

[0040] In the photomask blank of the present invention, an organic film such as a resist film may be formed in contact with the side of the second inorganic film that is away from the transparent substrate. The resist film may be an electron beam resist that is imaged with an electron beam or a photoresist that is imaged with light, with a chemically amplified resist being particularly preferred. The chemically amplified resist may be either positive or negative, and may, for example, contain a hydroxystyrene-based resin or a (meth)acrylic acid-based resin and an acid generator, with a crosslinker, a quencher, a surfactant, or the like added as needed. The thickness of the resist film can be appropriately set so as to obtain a photomask pattern with a good shape, but is preferably 50 nm or more, particularly 70 nm or more, and 200 nm or less, particularly 150 nm or less.

[0041] The photomask blank of the present invention may be a binary mask blank or a phase shift mask blank such as a halftone phase shift mask blank, from which phase shift masks such as binary masks and halftone phase shift masks are manufactured, respectively.

[0042] A suitable configuration of the inorganic film on the transparent substrate is, for example, a first inorganic film as a hard mask film of a third inorganic film, a second inorganic film as a processing auxiliary film for the first inorganic film, a light-shielding film, and a fourth inorganic film as a phase shift film. When the first inorganic film is a hard mask film of a third inorganic film, the processing accuracy of the first inorganic film as a hard mask film can be sufficiently maintained while improving the pattern transferability. In particular, for photomask blanks for forming fine patterns, such as photomask blanks for forming photomask patterns finer than 30 nm, using the first inorganic film as a hard mask film of a third inorganic film and the second inorganic film as a processing auxiliary film for the first inorganic film is particularly effective in forming photomask patterns with high accuracy. When the first inorganic film is a hard mask film, a material composed of silicon and oxygen (SiO) or a material composed of silicon, oxygen, and nitrogen (SiON) is particularly preferred as a material for the first inorganic film, as they have high etching resistance.

[0043] The formation of the inorganic film used in the photomask blank of the present invention is not particularly limited, but for example, when forming a film of a material consisting of silicon and oxygen, such as SiO2, it may be formed by CVD using a silicon-containing gas, such as monosilane, dichlorosilane, or trichlorosilane, but formation by a sputtering method is preferred because it has good controllability and makes it easy to form a film with predetermined properties. The sputtering method can be DC sputtering, RF sputtering, or the like, and is not particularly limited.

[0044] When forming a film containing silicon but not containing a transition metal as the first inorganic film, the fourth inorganic film, etc., a silicon target can be used as the sputtering target. When forming a film containing a transition metal other than chromium (Me) and silicon but not containing chromium as the first inorganic film, the fourth inorganic film, etc., a target containing a transition metal other than chromium (Me) and silicon can be used as the sputtering target. In this case, co-sputtering can be performed using a silicon target and a transition metal other than chromium (Me) target, using multiple targets containing the transition metal other than chromium (Me) and silicon but with different compositions (some or all of the constituent elements are different, or the constituent elements are the same but their concentrations are different), or using a silicon target or a transition metal other than chromium (Me) target and a target containing the transition metal other than chromium (Me) and silicon. On the other hand, when forming a film containing chromium but not containing silicon as the second inorganic film, the third inorganic film, etc., a chromium target can be used as the sputtering target.

[0045] The power input to the sputtering target can be set appropriately depending on the size of the sputtering target, cooling efficiency, ease of control of film formation, etc., and is usually 0.1 to 10 W / cm as the power per area of ​​the sputtering surface of the sputtering target. 2 This can be done as follows.

[0046] When forming a film of a material consisting only of silicon, only of silicon and a transition metal, or only of chromium, only a rare gas such as helium gas (He), neon gas (Ne), or argon gas (Ar) is used as the sputtering gas. On the other hand, when forming a film of a material containing oxygen, nitrogen, or carbon, reactive sputtering is preferred. The sputtering gases used are a rare gas such as helium gas (He), neon gas (Ne), or argon gas (Ar) and a reactive gas. For example, when forming a film of a material containing oxygen, oxygen gas (O gas) can be used as the reactive gas, and when forming a film of a material containing nitrogen, nitrogen gas (N gas) can be used as the reactive gas. When forming a film of a material containing both nitrogen and oxygen, oxygen gas (O gas) and nitrogen gas (N gas) can be used simultaneously as the reactive gas, or a nitrogen oxide gas such as nitric oxide gas (NO gas) or nitrogen dioxide gas (NO gas) can be used. When forming a film of a material containing carbon, a gas containing carbon such as methane gas (CH4), carbon monoxide gas (CO gas), or carbon dioxide gas (CO2 gas) may be used as the reactive gas.

[0047] The pressure during film formation may be appropriately set in consideration of film stress, chemical resistance, cleaning resistance, etc., and chemical resistance is improved by normally setting the pressure to 0.01 Pa or more, particularly 0.03 Pa or more, and 1 Pa or less, particularly 0.3 Pa or less. The flow rate of each gas may be appropriately set to obtain the desired composition, and is normally set to 0.1 to 100 sccm.

[0048] During the manufacturing process of the photomask blank, the transparent substrate or the transparent substrate and inorganic film may be subjected to a heat treatment. The heat treatment method may be infrared heating, resistance heating, or the like, and the treatment conditions are not particularly limited. The heat treatment may be carried out, for example, in an oxygen-containing gas atmosphere. The concentration of the oxygen-containing gas is not particularly limited, and in the case of oxygen gas (O gas), for example, it may be 1 to 100% by volume. The heat treatment temperature is preferably 200°C or higher, and particularly 400°C or higher. Furthermore, during the manufacturing process of the photomask blank, the inorganic film may be subjected to an ozone treatment, a plasma treatment, or the like, and the treatment conditions are not particularly limited. Either treatment may be carried out for the purpose of increasing the oxygen concentration in the surface portion of the inorganic film, and in this case, the treatment conditions may be appropriately adjusted to achieve a predetermined oxygen concentration. When forming an inorganic film by sputtering, it is also possible to increase the oxygen concentration on the surface of the inorganic film by adjusting the ratio of the rare gas in the sputtering gas to an oxygen-containing gas (oxidizing gas) such as oxygen gas (O2 gas), carbon monoxide gas (CO gas), or carbon dioxide gas (CO2 gas).

[0049] In the manufacturing process of a photomask blank, a cleaning treatment may be performed to remove particles present on the surface of the transparent substrate or inorganic film. Cleaning can be performed using one or both of ultrapure water and functional water, which is ultrapure water containing ozone gas, hydrogen gas, etc. Alternatively, after cleaning with ultrapure water containing a surfactant, further cleaning may be performed using one or both of ultrapure water and functional water. Cleaning can be performed while irradiating with ultrasonic waves as necessary, and UV light irradiation can also be combined.

[0050] When a resist film is formed on the photomask blank of the present invention, the method for applying the resist film is not particularly limited, and known methods can be applied.

[0051] A photomask can be manufactured from the photomask blank of the present invention. For example, when a resist film is not formed on the photomask blank, first, a resist film is formed in contact with the second inorganic film (step (A)). Next, the resist film is patterned to form a resist pattern (step (B)). Next, using the resist pattern as an etching mask, the second inorganic film is patterned by fluorine-based dry etching to form a pattern of the second inorganic film (step (C)). Next, using the pattern of the second inorganic film as an etching mask, the first inorganic film is patterned by fluorine-based dry etching to form a pattern of the first inorganic film (step (D)). When there are no other inorganic films (such as a third inorganic film or a fourth inorganic film) between the transparent substrate and the first inorganic film, the remaining resist pattern and the pattern of the second inorganic film can be further removed as necessary to obtain a photomask.

[0052] The dry etching of the second inorganic film containing chromium but not silicon in step (C) is performed using fluorine-based dry etching, rather than the chlorine-based dry etching typically performed on chromium-containing, silicon-free films when fabricating a photomask from a photomask blank. Therefore, steps (C) and (D) are both performed using fluorine-based dry etching, allowing steps (C) and (D) to be performed consecutively. To perform steps (C) and (D) using fluorine-based dry etching, it is effective to set the ratio of the etching rate of the second inorganic film by fluorine-based dry etching in step (C) to the etching rate of the first inorganic film by fluorine-based dry etching in step (D) to be 0.1 or greater, particularly 0.3 or greater. Furthermore, the fluorine-based dry etching in step (C) and the fluorine-based dry etching in step (D) are preferably performed under the same conditions.

[0053] If a third inorganic film is present between the transparent substrate and the first inorganic film, after step (D), a pattern of the third inorganic film can be formed by chlorine-based dry etching using the pattern of the first inorganic film as an etching mask, depending on the etching characteristics of the third inorganic film. If no other inorganic film (fourth inorganic film) is present between the transparent substrate and the third inorganic film, a photomask can be obtained by further removing the remaining resist pattern and the pattern of the second inorganic film as needed, and then removing the pattern of the first inorganic film as needed. In this case, a pattern can also be formed on the transparent substrate by fluorine-based dry etching using the pattern of the third inorganic film as an etching mask, depending on the etching characteristics of the transparent substrate.

[0054] If a third inorganic film and a fourth inorganic film are present between the transparent substrate and the first inorganic film, after step (D), a pattern of the third inorganic film can be formed by chlorine-based dry etching using the pattern of the first inorganic film as an etching mask, depending on the etching characteristics of the third inorganic film. Furthermore, a pattern of the fourth inorganic film can be formed by fluorine-based dry etching using the pattern of the third inorganic film as an etching mask, depending on the etching characteristics of the fourth inorganic film. Thereafter, if necessary, the remaining resist pattern and the pattern of the second inorganic film can be appropriately removed, and further, if necessary, the pattern of the first inorganic film can be removed to obtain a photomask blank. In this case, if necessary, a new resist pattern can be further formed, and part or all of the pattern of the third inorganic film can be etched and removed by chlorine-based dry etching.

[0055] From the viewpoint of etching selectivity relative to the first inorganic film, it is preferable that the etching rate of the third inorganic film by fluorine-based dry etching in step (D) is less than 0.3, particularly 0.1 or less, relative to the etching rate of the first inorganic film by fluorine-based dry etching in step (D).

[0056] The photomask of the present invention is particularly effective in photolithography for forming a pattern on a substrate to be processed with a half pitch of 50 nm or less, preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 10 nm or less, and is particularly effective in exposure to transfer a pattern to a photoresist film formed on the substrate to be processed with exposure light having a wavelength of 250 nm or less, particularly 200 nm or less, such as an ArF excimer laser (wavelength 193 nm) or an F2 laser (wavelength 157 nm).

[0057] In the pattern exposure method using the photomask of the present invention, a photomask manufactured from a photomask blank is used, and the photomask pattern is irradiated with exposure light to transfer the photomask pattern to a photoresist film formed on a substrate to be processed, which is the exposure target of the photomask pattern. The exposure light may be irradiated under dry conditions or immersion exposure, and the method is particularly suitable for exposing the photomask pattern to a wafer of 300 mm or more as the substrate to be processed by immersion exposure. [Example]

[0058] EXAMPLES The present invention will be specifically explained below by showing examples and comparative examples, but the present invention is not limited to the following examples.

[0059] [Example 1] A MoSiON film (75 nm thick) was sputtered onto a 152 mm square, approximately 6 mm thick quartz substrate as a phase shift film (fourth inorganic film). Argon, oxygen, and nitrogen gases were used as sputtering gases, and two types of targets, a MoSi2 target and a Si target, were used. The film was deposited while the quartz substrate was rotated at 30 rpm. The composition of this phase shift film was measured using ESCA (Electron Spectroscopy for Chemical Analysis) (XPS) with a Thermo Fisher Scientific K-Alpha (the same applies to the ESCA method below), revealing a Mo:Si:O:N atomic ratio of 1:4:1:4.

[0060] Next, a CrN layer (30 nm thick) and a CrON layer (20 nm thick) were formed on the quartz substrate side as a light-shielding film (third inorganic film) on the fourth inorganic film by sputtering. The sputtering gases used for the CrN layer were argon and nitrogen gases, and for the CrON layer were argon, oxygen, and nitrogen gases. A metal chromium target was used as the target, and the films were formed while the quartz substrate was rotated at 30 rpm. The composition of this light-shielding film was measured using the ESCA method, and the CrN layer had a Cr:N=9:1 (atomic ratio), and the CrON layer had a Cr:O:N=4:5:1 (atomic ratio).

[0061] Next, a SiO film (5 nm thick) was formed as a hard mask film (first inorganic film) on the third inorganic film by sputtering. Argon and oxygen gases were used as the sputtering gas, and a Si target was used as the target. The film was formed while rotating the quartz substrate at 30 rpm. The composition of this hard mask film was measured by ESCA, and was found to be Si:O = 1:2 (atomic ratio).

[0062] Next, a CrON film (5 nm thick) was formed on the first inorganic film as a processing aid film (second inorganic film) by sputtering. Argon, oxygen, and nitrogen gases were used as the sputtering gas, and a metal chromium target was used as the target. The film was formed while rotating the quartz substrate at 30 rpm. The composition of this processing aid film was measured by ESCA and found to be Cr:O:N = 37:51:12 (atomic ratio).

[0063] Next, a negative electron beam resist (manufactured by Shin-Etsu Chemical Co., Ltd.) was applied onto the second inorganic film to form a resist film (thickness: 100 nm), thereby obtaining a photomask blank (phase shift mask blank).

[0064] The resist film of the photomask blank obtained by this method was developed with tetramethylammonium hydroxide and rinsed with pure water. When this was inspected using a defect inspection system (Lasertec Corporation, MAGICS 2350), the number of defects detected that were 0.1 μm or larger in size was low, at 50 or less.

[0065] In addition, a pattern was written on the resist film of the photomask blank obtained by this method using an electron beam (EB) and developed with tetramethylammonium hydroxide to form a resist pattern. Next, using the resist pattern as an etching mask, the second inorganic film and the first inorganic film were sequentially etched by fluorine-based dry etching under the following conditions to form a pattern of the second inorganic film and a pattern of the first inorganic film. Next, using the pattern of the first inorganic film as an etching mask, the third inorganic film was etched by chlorine-based dry etching under the following conditions to form a pattern of the third inorganic film. At this stage, the remaining resist pattern was removed.

[0066] Next, using the pattern of the third inorganic film as an etching mask, the fourth inorganic film was etched by fluorine-based dry etching under the following conditions to form a pattern of the fourth inorganic film and remove the patterns of the second inorganic film and the first inorganic film. Next, a new resist film was formed on the quartz substrate and the pattern of the third inorganic film, forming a resist pattern in which the resist film remained outside the mask pattern formation area of ​​the photomask. Using the resist pattern as an etching mask, the third inorganic film within the mask pattern formation area was etched by chlorine-based dry etching under the following conditions to remove the third inorganic film. Finally, the remaining resist pattern was removed to obtain a photomask (phase shift mask).

[0067] <Fluorine-based dry etching conditions> RF1 (Bias RF Power Supply): RIE (Reactive Ion Etching), CW (Continuous Discharge), 54W RF2 (antenna high frequency power supply): ICP (inductively coupled plasma), CW (continuous discharge), 325W Pressure: 5mTorr (0.67Pa) SF6:18sccm O2: 45sccm

[0068] <Chlorine-based dry etching conditions> RF1 (Bias RF power supply): RIE (Reactive Ion Etching), Pulse, 700V RF2 (antenna high frequency power supply): ICP (inductively coupled plasma), CW (continuous discharge), 400W Pressure: 6mTorr (0.80Pa) Cl2: 185sccm O2: 55sccm He: 9.25 sccm

[0069] The ratio of the etching rate of the second inorganic film to the etching rate of the first inorganic film by the fluorine-based dry etching was 0.3, and the ratio of the etching rate of the third inorganic film to the etching rate of the first inorganic film was 0.2.

[0070] [Comparative Example 1] A photomask blank (phase shift mask blank) was obtained in the same manner as in Example 1, except that a second inorganic film was not formed on the first inorganic film, and a resist film was formed directly on the first inorganic film.

[0071] The resist film of the photomask blank obtained by this method was developed with tetramethylammonium hydroxide and rinsed with pure water. When this was inspected with a defect inspection system (Lasertec Corporation, MAGICS 2350), a large amount of resist residue remained, and the number of defects detected was an extremely large number of over 4,500, with a size of 0.1 μm or larger.

[0072] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0073] 1 Transparent substrate 21 First inorganic membrane 22 Second inorganic membrane 23 The third inorganic membrane 24 The fourth inorganic membrane 3. Resist film 10, 11, 12, 13, 14, 15 Photomask blanks

Claims

1. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (A) forming a resist film in contact with the second inorganic film; (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising:

2. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, and a resist film, wherein the first inorganic film, the second inorganic film, and the resist film are formed in contact with each other in this order, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. A method for manufacturing a photomask, comprising:

3. 3. The manufacturing method according to claim 1, wherein the fluorine-based dry etching in step (C) and the fluorine-based dry etching in step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in step (D).

4. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, the method comprising: (A) forming a resist film in contact with the second inorganic film; (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. Including, The fluorine-based dry etching in the step (C) and the fluorine-based dry etching in the step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in the step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in the step (D). A method for manufacturing a photomask, comprising:

5. A method for producing a photomask from a photomask blank having a transparent substrate, a first inorganic film containing silicon but not containing chromium, a second inorganic film containing chromium but not containing silicon, and a resist film, wherein the first inorganic film, the second inorganic film, and the resist film are formed in contact with each other in this order, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, (B) patterning the resist film to form a resist pattern; (C) patterning the second inorganic film by fluorine-based dry etching using the resist pattern as an etching mask to form a pattern of the second inorganic film; and (D) A step of patterning the first inorganic film by fluorine-based dry etching using the pattern of the second inorganic film as an etching mask to form a pattern of the first inorganic film. Including, The fluorine-based dry etching in the step (C) and the fluorine-based dry etching in the step (D) are performed under the same conditions, and the etching rate of the second inorganic film by the fluorine-based dry etching in the step (C) is 0.3 or more relative to the etching rate of the first inorganic film by the fluorine-based dry etching in the step (D). A method for manufacturing a photomask, comprising:

6. 6. The method according to claim 1, wherein steps (C) and (D) are carried out successively by fluorine-based dry etching.

7. 7. The method according to claim 1, wherein the second inorganic film has a thickness of 1 nm or more and 10 nm or less.

8. 8. The manufacturing method according to claim 1, wherein the photomask blank has a third inorganic film formed as the other inorganic film, the third inorganic film containing chromium but not silicon, and the third inorganic film is formed in contact with the transparent substrate side of the first inorganic film.

9. 9. The manufacturing method according to claim 8, wherein the etching rate of the third inorganic film by fluorine-based dry etching in step (D) is less than 0.3 relative to the etching rate of the first inorganic film by fluorine-based dry etching in step (D).

10. a transparent substrate; a first inorganic film containing silicon but not containing chromium; and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, the first inorganic film and the second inorganic film being formed in contact with each other, the first inorganic film being formed on the transparent substrate directly or via one or more other inorganic films; When etched under the same conditions by fluorine-based dry etching, the etching rate of the second inorganic film relative to the etching rate of the first inorganic film is 0.3 or more. A photomask blank characterized by:

11. A photomask blank comprising a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film containing chromium but not containing silicon, wherein the first inorganic film and the second inorganic film are formed in contact with each other, and the first inorganic film is formed on the transparent substrate directly or via one or more other inorganic films, A photomask blank characterized in that, when etched by fluorine-based dry etching under the same conditions, the etching rate of the second inorganic film relative to the etching rate of the first inorganic film is 0.3 or more.

12. 12. The photomask blank according to claim 10, further comprising a third inorganic film formed as the other inorganic film, the third inorganic film containing chromium but not silicon, the third inorganic film being formed in contact with the transparent substrate side of the first inorganic film.

13. 13. The photomask blank according to claim 12, wherein when etched by fluorine-based dry etching under the same conditions, the etching rate of the third inorganic film relative to the etching rate of the first inorganic film is less than 0.

3.

14. A photomask blank comprising a transparent substrate, a first inorganic film containing silicon but not containing chromium, and a second inorganic film which is a chromium compound containing chromium at a content of 25 atomic % or more but less than 40 atomic % and not containing silicon, the first inorganic film and the second inorganic film being formed in contact with each other, the first inorganic film being formed on the transparent substrate directly or via one or more other inorganic films, the photomask blank comprising a third inorganic film containing chromium but not containing silicon, the third inorganic film being formed as the other inorganic film, the third inorganic film being formed in contact with the transparent substrate side of the first inorganic film, When etched by fluorine-based dry etching under the same conditions, the etching rate of the third inorganic film relative to the etching rate of the first inorganic film is less than 0.

3. A photomask blank characterized by:

15. 15. The photomask blank according to claim 10, wherein the second inorganic film has a thickness of 1 nm or more and 10 nm or less.

16. 16. The photomask blank according to claim 10, further comprising a resist film in contact with the second inorganic film on a side thereof remote from the transparent substrate.

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