JP2021152574A - Photomask blank, manufacturing method of photomask, and manufacturing method of display device - Google Patents

Abstract

To provide a photomask blank that can manufacture a photomask excellent in the accuracy of a light-shielding film pattern, and having optical characteristics for achieving high pattern accuracy upon transcription of a pattern due to light exposure.SOLUTION: A photomask blank to be used in making a photomask for manufacturing a display device includes a transparent substrate and a light-shielding film disposed on the transparent substrate. The photomask blank is such that: the light-shielding film comprises from the transparent substrate side, a first reflection suppressing layer, a light-shielding layer, and a second reflection suppressing layer; the first reflection suppressing layer comprises sequentially from the transparent substrate side, a first low chromium oxide layer having a relatively small ratio of oxygen to nitrogen, and a first high chromium oxide layer having a relatively large ratio of oxygen to nitrogen; and the second reflection suppressing layer comprises sequentially from the transparent substrate side, a second low chromium oxide layer having a relatively small ratio of oxygen to nitrogen, and a second high chromium oxide layer having a relatively large ratio of oxygen to nitrogen.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a photomask blank and a photomask, and a method for manufacturing a display device.

In display devices such as FPDs (Flat Panel Display) typified by LCDs (Liquid Crystal Display), high-definition and high-speed displays are rapidly advancing along with larger screens and wider viewing angles. One of the elements necessary for high-definition and high-speed display is the production of electronic circuit patterns such as fine elements and wiring with high dimensional accuracy. Photolithography is often used for patterning electronic circuits for display devices. Therefore, there is a need for a photomask for manufacturing a display device in which a fine and highly accurate pattern is formed.

Photomasks for manufacturing display devices are made from photomask blanks. The photomask blank is formed by providing a light-shielding film made of a material opaque to exposure light on a transparent substrate made of synthetic quartz glass or the like. For example, as shown in Patent Document 1, in a photomask blank or a photomask, the reflected light from the transferred object when the photomask is used to expose the panel of the transferred object is reflected on the surface of the photomask. Antireflection films are provided on both the front and back sides of the light-shielding film in order to prevent the light-shielding film from being re-reflected again. It has a film structure in which a film, an antireflection film, and an antireflection film are laminated. The photomask is produced by patterning each film constituting the photomask blank by wet etching or the like to form a predetermined light-shielding film pattern.

Korean Registered Patent No. 10-14731163

By the way, in a photomask blank, when a light-shielding film is patterned by etching to form a photomask, the light-shielding film pattern is required to have high accuracy. If the accuracy of the light-shielding film pattern is low, when the light-shielding film pattern is transferred to the transferred body using a photomask, the line width of the transfer pattern and the size of the hole pattern become non-uniform, and the light-shielding film pattern is formed on the transferred body. This is because the CD uniformity of the pattern is impaired.

Further, the photomask blank is also required to have a low reflectance on the surface of the light-shielding film so that a highly accurate transfer pattern can be transferred when the object to be transferred is exposed to the photomask. .. When the reflectance of the surface of the light-shielding film pattern formed on the photomask is high, the reflected light from the transferred object repeatedly reflects off the surface of the light-shielding film pattern of the photomask during the exposure process, so-called flare. May occur. Further, for example, the exposure light from the exposure device, the reflected light reflected on the back surface of the light-shielding film pattern of the photomask is reflected again by the optical system of the exposure device (transfer device), and is re-entered into the photomask. Therefore, so-called return light may occur. Due to these flares and return light, the pattern accuracy of the transfer pattern formed by using the photomask may be impaired.

Therefore, an object of the present invention is that a highly accurate light-shielding film pattern can be obtained when a light-shielding film in a photomask blank is patterned by etching to produce a photomask, and the photomask is used on a transferred object. It is an object of the present invention to provide a photomask blank having optical characteristics such that the pattern accuracy of an object to be transferred is improved when a transfer pattern is transferred.

(Structure 1)
A photomask blank used when manufacturing a photomask for manufacturing a display device.
A transparent substrate made of a material that is substantially transparent to the exposure light,
It has a light-shielding film provided on the transparent substrate and made of a material substantially opaque to the exposure light.
The light-shielding film includes a first reflection suppression layer, a light-shielding layer, and a second reflection suppression layer from the transparent substrate side.
The first antireflection layer contains chromium, oxygen, and nitrogen, and contains a first low chromium oxide layer in which the ratio of oxygen to nitrogen is relatively small, and chromium, oxygen, and nitrogen, and oxygen to nitrogen. A first highly chromium oxide layer having a relatively large proportion is provided in order from the transparent substrate side.
The second antireflection layer contains a second low chromium oxide layer containing chromium, oxygen and nitrogen, and the ratio of oxygen to nitrogen is relatively small, and chromium, oxygen and nitrogen, and oxygen to nitrogen. A second highly chromium oxide layer having a relatively large proportion is provided in order from the transparent substrate side.
At least the first reflection-suppressing layer so that the reflectance of the exposure light on the front surface and the back surface of the light-shielding film with respect to an exposure wavelength of 300 nm to 436 nm is 15% or less and the optical density is 3.0 or more. A photomask blank characterized in that the composition and film thickness of the light-shielding layer and the second reflection-suppressing layer are set.

(Structure 2)
The photomask blank according to configuration 1, wherein the light-shielding layer is formed of a chromium-based material having a chromium content of 97 atomic% or more and 100 atomic% or less.

(Structure 3)
The photomask blank according to configuration 1 or 2, wherein the ratio of oxygen to nitrogen in the second highly chromium oxide layer is 2.5 or more and 10 or less.

(Structure 4)
The photomask blank according to any one of configurations 1 to 3, wherein the ratio of oxygen to nitrogen in the first high chromium oxide layer is 2.5 or more and 10 or less.

(Structure 5)
The photomask blank according to any one of configurations 1 to 4, wherein the first reflection-suppressing layer contains carbon.

(Structure 6)
The photomask blank according to any one of configurations 1 to 5, wherein the second reflection-suppressing layer contains carbon.

(Structure 7)
The first reflection-suppressing layer has a chromium content of 25 atomic% or more and 75 atomic% or less, an oxygen content of 15 atomic% or more and 45 atomic% or less, and a nitrogen content of 2 atomic% or more and 30 atomic% or less. There,
The second antireflection layer has a chromium content of 25 atomic% or more and 75 atomic% or less, an oxygen content of 15 atomic% or more and 60 atomic% or less, and a nitrogen content of 2 atomic% or more and 30 atomic% or less. The photomask blank according to any one of configurations 1 to 6, wherein the photomask blank is provided.

(Structure 8)
The composition of the first reflection-suppressing layer and the second reflection-suppressing layer, respectively, changes continuously or stepwise along the film thickness direction in the content of at least one of oxygen and nitrogen. The photomask blank according to any one of configurations 1 to 7, wherein the photomask blank has a region.

(Structure 9)
Between the transparent substrate and the first reflection suppression layer, between the first reflection suppression layer and the light shielding layer, and between the light shielding layer and the second reflection suppression layer, the first reflection suppression layer, The photomask blank according to any one of configurations 1 to 8, wherein the light-shielding layer and the elements constituting the second reflection-suppressing layer have a composition-inclined region in which the composition is continuously inclined.

(Structure 10)
The photomask blank according to any one of configurations 1 to 9, wherein the in-plane uniformity of the reflectance of the surface of the light-shielding film with respect to the exposure wavelength of the exposure light is 3% or less.

(Structure 11)
The photomask blank according to any one of configurations 1 to 10, further comprising a semipermeable membrane having an optical density lower than the optical density of the light-shielding film between the transparent substrate and the light-shielding film. ..

(Structure 12)
The photomask blank according to any one of configurations 1 to 10, further comprising a phase shift film between the transparent substrate and the light-shielding film.

(Structure 13)
The step of preparing the photomask blank according to any one of configurations 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A method for producing a photomask, which comprises.

(Structure 14)
The step of preparing the photomask blank according to any one of configurations 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A step of forming the semipermeable membrane pattern on the transparent substrate by etching the semipermeable membrane using the light-shielding film pattern as a mask.
A method for producing a photomask, which comprises.

(Structure 15)
The step of preparing the photomask blank according to any one of configurations 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A step of forming the phase shift film pattern on the transparent substrate by etching the phase shift film using the light film pattern as a mask.
A method for producing a photomask, which comprises.

(Structure 16)
The photomask obtained by the method for producing a photomask described in any of the configurations 13 to 15 is placed on a mask stage of an exposure apparatus, and a light-shielding film pattern formed on the photomask, the semi-transmissive film. A method for manufacturing a display device, which comprises an exposure step of exposing and transferring a pattern, at least one light-shielding film pattern of the phase shift film pattern, to a resist formed on a display device substrate.

According to the present invention, a highly accurate light-shielding film pattern can be obtained when a light-shielding film in a photomask blank is patterned by etching to produce a photomask, and a transfer pattern is obtained for a transferred object using the photomask. A photomask blank capable of producing a photomask having optical characteristics such that the pattern accuracy of the object to be transferred is increased when the above is transferred can be obtained.

FIG. 1 is a cross-sectional view showing a schematic configuration of a photomask blank according to an embodiment of the present invention. FIG. 2 is a diagram showing the results of composition analysis in the film thickness direction in the photomask blank of Example 1. FIG. 3 is a diagram showing the reflectance spectra of the front and back surfaces of the photomask blank of Example 1. FIG. 4 is a diagram showing the results of composition analysis in the film thickness direction in the photomask blank of Reference Example 1. FIG. 5 is a diagram showing the reflectance spectra of the front and back surfaces of the photomask blank of Reference Example 1.

<Examination by the present inventors>
The present inventors have studied a photomask blank in which a light-shielding film is formed by laminating a first reflection-suppressing layer, a light-shielding layer, and a second reflection-suppressing layer in order from the transparent substrate side in order to improve the optical characteristics. However, it was confirmed that the transfer pattern transferred to the transfer target does not have high accuracy simply by reducing the reflectance of the front surface and the back surface of the light-shielding film in the photomask blank.

As a result of examining this factor, the reason why the transfer pattern accuracy of the transferred material is lowered is that the reflectances of the front and back surfaces of the light-shielding film of the photomask blank are non-uniform in the plane (the in-plane variation of the reflectance is uneven). Large) was found. In the light-shielding film, the first and second reflection-suppressing layers are oxidized in order to lower the reflectance, but the degree of oxidation tends to vary in the plane. Further, when the light-shielding layer is nitrided, the degree of nitriding tends to vary in the plane. The degree of oxidation of the first and second reflection-suppressing layers and the degree of nitriding of the light-shielding layer vary in the plane, so that the reflectances of the front and back surfaces of the light-shielding film become non-uniform in the plane.

Further, in order to lower the reflectance of the front surface and the back surface of the light-shielding film, the first reflection-suppressing layer and the second reflection-suppressing layer require stronger oxidation, but defects are likely to occur during film formation. ..

In the photomask, the reflectance of the front and back surfaces of the light-shielding film pattern becomes non-uniform in the plane (the in-plane variation of the reflectance becomes large), so that the light-shielding film pattern of the photomask is accurately transferred to the transferred object. This is not possible, and the CD uniformity of the transfer pattern of the obtained transfer material is impaired.

On the other hand, a factor that reduces the pattern accuracy of the light-shielding film pattern obtained when the light-shielding film of the photomask blank is etched is that the etching rates or etching times of the layers constituting the light-shielding film are not uniform. If the etching rate and etching time of each layer constituting the light-shielding film are significantly different, when the light-shielding film is etched to form a light-shielding film pattern, etching is particularly performed at a portion of the first reflection suppression layer on the transparent substrate side. The rest is likely to occur. When etching residue occurs, the cross-sectional shape of the light-shielding film pattern becomes difficult to be vertical, so that the line width of the light-shielding film pattern differs between the front side and the back surface side, and the accuracy of the light-shielding film pattern of the photomask becomes low. It ends up.

From the above, the present inventors have studied a method for making the reflectances of the front surface and the back surface of the light-shielding film in the photomask blank uniform in the plane. In general, the first reflection-suppressing layer and the second reflection-suppressing layer in the conventional photomask blank are generally composed of a single layer of a highly oxidizing layer. However, when the first reflection suppression layer and the second reflection suppression layer are composed of a single layer of a highly oxidizing layer, the degree of oxidation of the first reflection suppression layer and the second reflection suppression layer varies within the photomask blank surface. It became more prominent, and it was considered that it had a great influence on the in-plane variation of the reflectance on the front surface and the back surface of the light-shielding film. Further, it was considered that defects are likely to occur by making the first reflection suppression layer and the second reflection suppression layer highly oxidized.

Therefore, the present inventors have focused on the fact that the first and second reflection-suppressing layers are composed of a laminated structure of two layers having different degrees of oxidation, that is, a low-oxidation layer and a high-oxidation layer. .. As a result, the reflectances of the front surface and the back surface of the light-shielding film can be made more uniform in the photomask blank surface as compared with the case where the first and second reflection suppression layers are composed of only a single layer having only a highly oxidizing layer. , It was found that the defect of the light-shielding film can be reduced. Moreover, by forming the first reflection suppression layer with a low-oxidation layer and a high-oxidation layer in order from the transparent substrate side, the etching residue on the transparent substrate side of the first reflection suppression layer is suppressed, and as a result, the etching residue is suppressed. It was found that the cross-sectional shape of the light-shielding film pattern can be made good and a high-precision light-shielding film pattern can be obtained.

Further, from the viewpoint of making the reflectance of the front surface and the back surface of the light-shielding film more uniform in the photomask blank surface, it is necessary to make the light-shielding layer of the light-shielding film as close as possible to a metal film that is not oxidized or nitrided. It was found to be preferable. Until now, the light-shielding layer has been composed of a metal film (metal nitride film) containing nitrogen from the viewpoint of controlling the etching rate (etching time) of the light-shielding film. However, when nitrogen is contained in the light-shielding layer, the nitrogen content varies (non-uniformity) in the photomask blank surface. Further, since the first and second reflection-suppressing layers located above and below the light-shielding layer contain oxygen, the first and second reflection-suppressing layers also have variations in oxygen content within the photomask blank surface ( Non-uniformity) occurs. The variation (non-uniformity) in the photomask blank surface of the nitrogen content in the light-shielding layer and the variation in the photomask blank surface of the oxygen content in the first and second reflectance layers combine to form the surface of the light-shielding film. In-plane variation (non-uniformity) of the reflectance on the back surface becomes large. In order to reduce the in-plane variation in reflectance on the front and back surfaces of the light-shielding film, it is more effective to reduce the variation in nitrogen in the photomask blank surface contained in the light-shielding layer. By reducing the content of nitrogen contained (without adding nitrogen), the in-plane variation in reflectance on the front and back surfaces of the light-shielding film can be reduced.

The present invention has been made based on the above findings.

<One Embodiment of the present invention>
Hereinafter, an embodiment of the present invention will be described. The following embodiment is an embodiment of the present invention, and does not limit the present invention to the scope thereof. Further, in the drawings, the same or corresponding parts may be designated by the same reference numerals to simplify or omit the description. In addition, the numerical range represented by using "~" in the present specification means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

(1) Photomask Blank First, a photomask blank according to an embodiment of the present invention will be described. The photomask blank of the present embodiment is, for example, a single wavelength light selected from a wavelength band of 300 nm to 436 nm, or a plurality of wavelengths of light (for example, j-line (wavelength 313 nm), wavelength 334 nm, i-line (wavelength 365 nm)). , H line (405 nm), g line (wavelength 436 nm)), which is used when producing a photomask for manufacturing a display device that exposes composite light.

FIG. 1 is a cross-sectional view showing a schematic configuration of a photomask blank according to an embodiment of the present invention. The photomask blank 1 includes a transparent substrate 11 and a light-shielding film 12. Hereinafter, as a photomask blank according to an embodiment of the present invention, a binary type photomask blank in which the light-shielding film pattern (transfer pattern) of the photomask is a light-shielding film pattern will be described.

(Transparent board)
The transparent substrate 11 is not particularly limited as long as it is a substrate that is formed of a material that is substantially transparent to exposure light and has translucency. A substrate material having a transmittance of 85% or more, preferably 90% or more with respect to the exposure wavelength is used. Examples of the material for forming the transparent substrate 11 include synthetic quartz glass, soda lime glass, non-alkali glass, and low thermal expansion glass.

The size of the transparent substrate 11 is not particularly limited, and may be appropriately changed according to the size required for the photomask. For example, in the case of a photomask for manufacturing a display device, the transparent substrate 11 is a rectangular substrate having a short side length of 330 mm or more and 1620 mm or less. be able to. The transparent substrate 11 has, for example, a size of 330 mm × 450 mm, 390 mm × 610 mm, 500 mm × 750 mm, 520 mm × 610 mm, 520 mm × 800 mm, 800 × 920 mm, 850 mm × 1200 mm, 850 mm × 1400 mm, 1220 mm × 1400 mm, 1620 mm × 1780 mm. Etc. can be used. In particular, the length of the short side of the substrate is preferably 850 mm or more and 1620 mm or less. By using such a transparent substrate 11, a photomask for manufacturing a display device of G7 to G10 can be obtained.

(Shading film)
The light-shielding film 12 is formed of a material that is substantially opaque to exposure light, and is configured by laminating a first reflection suppression layer 13, a light-shielding layer 14, and a second reflection suppression layer 15 in this order from the transparent substrate 11 side. There is. In the present specification, of the two sides of the photomask blank 1, the surface on the light-shielding film 12 side is the front surface and the surface on the transparent substrate 11 side is the back surface.
Then, at least the first reflection suppression layer so that the reflectance of the exposure light on the front surface and the back surface of the light shielding film 12 with respect to the exposure wavelength of 300 nm to 436 nm is 15% or less and the optical density is 3.0 or more. 13, the composition of the light-shielding layer 14 and the second reflection suppression layer 15, and the film thickness are set. Further, at least the first low chromium oxide layer 13a in the first reflection suppression layer 13 and the first height so as to be 10% or less with respect to the representative wavelength of 365 nm to 436 nm of the exposure light from the back surface side of the light shielding film 12. The composition ratio and the film thickness of the chromium oxide layer 13b may be adjusted.

(First reflection suppression layer)
When the first reflection suppression layer 13 is provided on the surface of the light-shielding film 12 on the side close to the transparent substrate 11 of the light-shielding layer 14 and pattern transfer is performed using a photomask produced by using the photomask blank 1. It is arranged on the side close to the exposure apparatus (exposure light source). When the exposure process is performed using a photomask, the exposure light is irradiated from the transparent substrate 11 side (back surface side) of the photomask, and a pattern transfer image is formed on a resist film formed on a display device substrate which is a transfer target. It will be transferred. At this time, the reflected light reflected by the exposure light on the back surface side of the light-shielding film pattern is incident on the optical system of the exposure apparatus and is incident on the transparent substrate 11 side of the photomask again, so that the stray light of the light-shielding film pattern is emitted. This causes deterioration of the transfer pattern such as formation of a ghost image and an increase in the amount of flare. According to the first reflection suppression layer 13, when pattern transfer is performed using a photomask, reflection of exposure light on the back surface side of the light-shielding film 12 can be suppressed, so that deterioration of the transfer pattern can be suppressed and transfer characteristics can be suppressed. Can be improved.

As described above, in the present embodiment, the first reflection suppression layer 13 can reduce defects, lower the reflectance of the back surface of the light-shielding film 12, and make the reflectance uniform in the photomask blank surface. In order to improve the properties (to suppress in-plane variation of reflectance), the first low chromium oxide layer 13a with relatively little oxidation and the first high chromium oxide layer 13b with relatively high oxidation are sequentially arranged from the transparent substrate 11 side. It is constructed by stacking.

The first low chromium oxide layer 13a is formed so that the degree of oxidation is small.

Further, as will be described later, the first low chromium oxide layer 13a has a smaller ratio of oxygen (O) to nitrogen (N) than the first high chromium oxide layer 13b, that is, the content of N is higher. , The etching time can be shorter than that of the first high chromium oxide layer 13b. Therefore, when the photomask blank 1 is etched, the etching residue of the first low chromium oxide layer 13a can be prevented, and the cross-sectional shape of the light-shielding film pattern can be made closer to vertical.

Further, since the first low chromium oxide layer 13a has a low degree of oxidation and a high N content, even when the light-shielding film 12 is etched to form a fine light-shielding film pattern, the adhesion to the transparent substrate 11 is maintained. It can be secured and the film peeling of the light-shielding film pattern can be prevented.

The first high chromium oxide layer 13b has a high degree of oxidation so that the back surface reflectance of the light-shielding film 12 (the back surface reflectance of the first reflection suppression layer 13) has a predetermined characteristic.

(Shading layer)
The light-shielding layer 14 is provided between the first reflection suppression layer 13 and the second reflection suppression layer 15 in the light-shielding film 12. The light-shielding layer 14 has a function of adjusting the light-shielding film 12 so that it has an optical density so as to be substantially opaque to the exposure light. Here, substantially opaque to the exposure light means a light-shielding property having an optical density of 3.0 or more, and from the viewpoint of transfer characteristics, the optical density is preferably 4.0 or more, more preferably 4.5. The above is preferable.

(Second reflection suppression layer)
The second reflection suppression layer 15 is provided on the surface of the light-shielding film 12 on the side far from the transparent substrate 11 of the light-shielding layer 14. When a resist film is formed on the second reflection suppression layer 15 and a predetermined resist pattern is formed on the resist film by the drawing light (laser light) of a drawing device (for example, a laser drawing device), the light-shielding film 12 It has a function of suppressing the reflection of the drawing light on the surface side of the. Thereby, the CD uniformity of the resist pattern and the light-shielding film pattern formed based on the resist pattern can be enhanced. On the other hand, when the photomask is used, the second reflection suppression layer 15 is arranged on the transfer target side, and the light reflected by the transfer target is reflected again on the surface side of the light shielding film 12 of the photomask to be covered. Suppresses the return to the transcript. This suppresses the deterioration of the transfer pattern and contributes to the improvement of the transfer characteristics.

Like the first reflection suppression layer 13, the second reflection suppression layer 15 is composed of two chromium oxide layers having different degrees of oxidation. Specifically, the second reflection suppression layer 15 can reduce defects, lower the surface reflectance of the light-shielding film 12, and increase the uniformity of the surface reflectance in the photomask blank surface (in order to increase the uniformity of the surface reflectance in the photomask blank surface). (To suppress in-plane variation in surface reflectance), the second low chromium oxide layer 15a with relatively little oxidation and the second high chromium oxide layer 15b with relatively high oxidation are laminated in order from the light-shielding layer 14 side. Will be done.

Like the first low chromium oxide layer 13a, the second low chromium oxide layer 15a is formed so as to have a small degree of oxidation.

The second high chromium oxide layer 15b has a high degree of oxidation so that the surface reflectance of the light-shielding film 12 (the reflectance of the surface of the second reflection suppression layer 15) has a predetermined characteristic. Further, since the second high chromium oxide layer 15b has a high degree of oxidation, the chemical resistance to a cleaning solution such as an acid or an alkali used when cleaning a photomask blank or a photomask is improved, and the second high chromium oxide layer 15b is on. It also contributes to high adhesion to the resist film when the resist film is formed.

(Material for light-shielding film)
Subsequently, the material for forming each of the first reflection suppression layer 13, the light shielding layer 14, and the second reflection suppression layer in the light shielding film 12 will be described.

The materials of the first reflection suppression layer 13, the light shielding layer 14, and the second reflection suppression layer are not particularly limited as long as they can obtain the above-mentioned optical characteristics in the photomask blank 1, but the above-mentioned optical characteristics can be obtained. From the viewpoint of obtaining, it is preferable to use the following materials for each layer.

The first reflection suppression layer 13 is preferably composed of a chromium-based material containing chromium, oxygen, and nitrogen. Oxygen (O) mainly has a function of reducing the reflectance of the first reflection suppression layer 13. Nitrogen (N) mainly has a function of reducing the reflectance of the first reflection suppression layer 13 and increasing the etching rate of the first reflection suppression layer 13 to shorten the etching time. From the viewpoint of controlling the etching characteristics, the first reflection suppression layer 13 may further contain carbon (C) and fluorine (F), and it is particularly preferable to contain carbon (C). By containing C in the first reflection suppression layer 13, it becomes easy to match the etching rates of the first reflection suppression layer 13 and the light shielding layer 14, and the cross-sectional shape of the light shielding film pattern can be improved.

The first reflection suppression layer 13 is composed of a first low chromium oxide layer 13a and a first high chromium oxide layer 13b having different degrees of oxidation. The degree of oxidation indicates the ratio of oxygen to nitrogen (hereinafter, also referred to as O / N ratio), and the first low chromium oxide layer 13a is formed from a chromium-based material having a relatively small ratio of O to N, and is the first. The highly chromium oxide layer 13b is formed from a chromium-based material in which the ratio of O to N is relatively large.

The light-shielding layer 14 is made of a chrome-based material. The light-shielding layer 14 may contain O, N, C, F and the like in addition to chromium (Cr). From the viewpoint of making the front surface reflectance and the back surface reflectance of the light-shielding film 12 more uniform in the photomask blank surface, it is preferable that the light-shielding layer 14 is a chrome film that does not substantially contain O, N, and F. .. A chromium film that does not substantially contain O, N, and F for the light-shielding layer 14 indicates that it is not intentionally added, and excludes cases where it is unavoidably contained. More specifically, in a chromium film that does not substantially contain O, N, and F, the total content of these elements is 3 atomic% or less, and further, the total content of these elements is 2 atomic% or less. A certain chrome film. As described above, the light-shielding layer 14 cannot make the nitrogen content uniform in the plane, and the difference in refractive index between the first reflection suppressing layer 13 and the second reflection suppressing layer 15 is made excessive or too small. This may promote in-plane variation in the back surface reflectance and the front surface reflectance of the photomask blank 1. In this respect, by making the light-shielding layer 14 a chrome film that does not substantially contain O, N, and F, the front surface reflectance and the back surface reflectance of the light-shielding film 12 can be made more uniform in the photomask blank surface. ..

The second reflection suppression layer 15 is preferably composed of a chromium-based material containing chromium, oxygen, and nitrogen. In the second reflection suppression layer 15, oxygen (O) not only reduces the reflectance of the exposure light and the drawing light, but also improves the adhesion to the resist film, so that the oxygen (O) can be seen from the interface between the resist film and the light-shielding film 12. It has a function of suppressing side etching due to penetration of the etchant. Nitrogen (N) reduces the reflectance of the second reflection suppression layer 15 and increases the etching rate of the second reflection suppression layer 15 to shorten the etching time. From the viewpoint of controlling the etching characteristics, carbon (C) and fluorine (F) may be further contained, and carbon (C) is particularly preferable. By containing C in the second reflection suppression layer 15, the etching rates of the second reflection suppression layer 15 and the light shielding layer 14 can be easily matched, and the cross-sectional shape of the light shielding film pattern can be improved.

(Composition of light-shielding film)
Subsequently, the composition of each layer in the light-shielding film 12 will be specifically described. The content of each element described later is a value measured by X-ray photoelectron spectroscopy (XPS).

The chromium-based material forming the first low chromium oxide layer 13a contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 0.1 or more and less than 2.5. preferable. Further, the first low chromium oxide layer 13a contains chromium (Cr) in an amount of 25 to 95 atomic%, oxygen (O) in an amount of 5 to 45 atomic%, and nitrogen (N) in an amount of 2 to 35 atomic%. The ratio of O to N is preferably 0.1 or more and less than 2.5.
The chromium-based material forming the first high chromium oxide layer 13b contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is preferably 2.5 or more and 10 or less. Further, the first high chromium oxide layer 13b contains chromium (Cr) at a content of 30 to 95 atomic%, oxygen (O) at a content of 7 to 50 atomic%, and nitrogen (N) at a content of 2 to 25 atomic%. The ratio of O to N is preferably 2.5 or more and 10 or less.
The content of Cr contained in the first low chromium oxide layer 13a and the first high chromium oxide layer 13b is preferably lower than that of Cr contained in the light-shielding layer 14. Further, the total content of O and N contained in the first low chromium oxide layer 13a and the first high chromium oxide layer 13b is preferably 7 to 75 atomic%.

The chromium material forming the light-shielding layer 14 mainly contains Cr, and it is preferable that the amount of Cr is 97 atomic% or more and 100 atomic% or less. In addition to Cr, O, N, C, F and the like may be contained, and the total content of these is preferably 3 atomic% or less.

The chromium-based material forming the second low chromium oxide layer 15a contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is 0.1 or more and less than 2.5. preferable. Further, the second low chromium oxide layer 15a contains chromium (Cr) in an amount of 25 to 95 atomic%, oxygen (O) in an amount of 5 to 45 atomic%, and nitrogen (N) in an amount of 2 to 35 atomic%. The ratio of O to N is preferably 0.1 or more and less than 2.5.
The chromium-based material forming the second highly chromium oxide layer 15b contains chromium (Cr), oxygen (O), and nitrogen (N), and the ratio of O to N is preferably 2.5 or more and 10 or less. Further, the second highly chromium oxide layer 15b contains chromium (Cr) at a content of 30 to 70 atomic%, oxygen (O) at a content of 15 to 60 atomic%, and nitrogen (N) at a content of 2 to 30 atomic%. The ratio of O to N is preferably 2.5 to 10.
The content of Cr contained in the second low chromium oxide layer 15a and the second high chromium oxide layer 15b is preferably lower than that of Cr contained in the light-shielding layer 14. Further, the total content of O and N contained in the second low chromium oxide layer 15a and the second high chromium oxide layer 15b is preferably 7 to 75 atomic%.

The first reflection-suppressing layer 13 and the second reflection-suppressing layer 15 each have a region in which the content of at least one of O and N is continuously or stepwise changed in composition along the film thickness direction. Is preferable.

Further, the first reflection suppression is performed between the transparent substrate 11 and the first reflection suppression layer 13, between the first reflection suppression layer 13 and the light shielding layer 14, and between the light shielding layer 14 and the second reflection suppression layer 15. A composition gradient region in which the elements constituting the layer 13, the light shielding layer 14, and the second reflection suppression layer 15 are continuously gradient in composition may be formed.

(About film thickness)
In the light-shielding film 12, the thicknesses of the first reflection-suppressing layer 13, the light-shielding layer 14, and the second reflection-suppressing layer 15 are not particularly limited, and are appropriately adjusted according to the optical density and reflectance required for the light-shielding film 12. It is good to do it.

From the viewpoint of suppressing defects in the first reflection suppression layer 13 and reducing the back surface reflectance, the thickness of the first low chromium oxide layer 13a and the first high chromium oxide layer 13b is 10 nm or more, respectively. The thickness is preferably 35 nm or less, and the total thickness of the first reflection suppression layer 13 is preferably 20 nm or more and 70 nm or less. The thickness ratio of the first low chromium oxide layer 13a to the first high chromium oxide layer 13b is preferably 1st high chromium oxide layer: 1st low chromium oxide layer = 1: 7 to 1: 1, and more preferably. The first high chromium oxide layer: the first low chromium oxide layer = 1: 5 to 1: 2 is desirable.

The thickness of the light-shielding layer 14 can be appropriately changed according to the optical density required for the light-shielding film 12. For example, when the optical density is 3 or more, the thickness of the light-shielding layer 14 may be 50 nm to 200 nm.

The thickness of the second reflection suppression layer 15 is adjusted so that predetermined optical characteristics (surface reflectance) can be obtained with respect to the exposure light and the drawing light from the surface side of the light shielding film 12. Specifically, the second low chromium oxide layer in the second reflection suppression layer 15 is set to 10% or less with respect to the representative wavelength (for example, 365 nm to 436 nm) of the exposure light from the back surface side of the light shielding film 12. The film thicknesses of the 15a and the second highly chromium oxide layer 15b are adjusted. From the viewpoint of suppressing defects in the second reflection suppressing layer 15 and reducing the surface reflectance, the thickness of the second low chromium oxide layer 15a and the thickness of the second high chromium oxide layer 15b are respectively. The thickness is preferably 10 nm or more and 35 nm or less, and the total thickness of the second reflection suppression layer 15 is preferably 20 nm or more and 70 nm. The thickness ratio of the second low chromium oxide layer 15a to the second high chromium oxide layer 15b is preferably the second high chromium oxide layer: the second low chromium oxide layer = 1: 7 to 1: 1, and more preferably. 2nd high chromium oxide layer: 2nd low chromium oxide layer = 1: 5 to 1: 2 is desirable.

(Optical characteristics of photomask blank)
The photomask blank 1 has the following optical characteristics.

The reflectance spectrum of the surface of the light-shielding film 12 obtained when the surface of the light-shielding film 12 of the photomask blank 1 is irradiated with exposure light or drawing light is surface reflection at a representative wavelength in the range of an exposure wavelength of 300 nm to 436 nm. The rate is preferably 15% or less, more preferably 12% or less, still more preferably 10% or less. More preferably, the reflection spectrum on the surface of the light-shielding film 12 has a surface reflectance of preferably 15% or less, more preferably 12% or less, still more preferably 10% or less in the range of an exposure wavelength of 300 nm to 436 nm. Alternatively, the reflectance spectrum of the surface of the light-shielding film 12 has a surface reflectance of preferably 10% or less, more preferably 7.5% or less, still more preferably 5% at a representative wavelength in the exposure wavelength range of 365 nm to 436 nm. It is as follows. More preferably, the reflectance spectrum of the surface of the light-shielding film 12 has a surface reflectance of preferably 10% or less, more preferably 7.5% or less, still more preferably 5% or less in the range of the exposure wavelength of 365 nm to 436 nm. Is.
Further, the reflectance spectrum of the back surface of the light-shielding film 12 obtained when the back surface of the light-shielding film 12 of the photomask blank 1 is irradiated with exposure light is the backside reflectance at a representative wavelength in the range of an exposure wavelength of 300 nm to 436 nm. Is preferably 15% or less, more preferably 12% or less, still more preferably 10% or less. More preferably, the reflection spectrum on the back surface of the light-shielding film 12 has a back surface reflectance of preferably 15% or less, more preferably 12% or less, still more preferably 10% or less within an exposure wavelength range of 300 nm to 436 nm. Further, the reflectance spectrum of the back surface of the light-shielding film 12 has a back surface reflectance of preferably 10% or less, more preferably 7.5% or less, still more preferably 5% at a representative wavelength in the range of an exposure wavelength of 365 nm to 436 nm. It is as follows. More preferably, the reflection spectrum on the back surface of the light-shielding film 12 has a back surface reflectance of preferably 10% or less, more preferably 7.5% or less, still more preferably 5% or less within an exposure wavelength range of 365 nm to 436 nm. be.

Further, the reflectance of the front and back surfaces of the light-shielding film 12 of the photomask blank 1 has a small wavelength dependence in the range of the exposure wavelength of 300 nm to 436 nm or in the range of 365 nm to 436 nm. Wavelength dependence means that the reflectance changes depending on the exposure wavelength, and small wavelength dependence means that the difference between the maximum value and the minimum value of the reflectance is small, that is, the change in reflectance. Indicates that the amount (fluctuation range) is small. Specifically, the wavelength dependence of the reflectance of the front and back surfaces of the light-shielding film 12 is preferably 12% or less, more preferably 10% or less within the range of the exposure wavelength of 300 nm to 436 nm. Alternatively, the wavelength dependence of the reflectance of the front and back surfaces of the light-shielding film 12 is preferably 5% or less, more preferably 3% or less within the range of the exposure wavelength of 365 nm to 436 nm.

Further, in the photomask blank 1, the in-plane variation in the reflectance (front surface reflectance, back surface reflectance) on the front surface and the back surface of the light-shielding film 12 can be suppressed, and the in-plane uniformity of the reflectance on the front and back surfaces is increased. be able to.
Specifically, the surface reflectance of the light-shielding film 12 can be suppressed to 3% or less (range). The in-plane uniformity of the surface reflectance of the light-shielding film 12 was measured using a reflectance meter on the surface of the photomask blank 1 with respect to 11 × 11 = 121 points in the photomask blank surface excluding the peripheral portion 50 mm. Calculated based on the surface reflectance results.
Further, the back surface reflectance of the light-shielding film 12 can be suppressed to 5% or less (range). The in-plane uniformity of the back surface reflectance of the light-shielding film 12 is determined with respect to a dummy substrate (for example, a size of 6 inches × 6 inches) in which a plurality of sheets are spread in the surface of the photomask blank 1 instead of the photomask blank 1. The reflectance of the back surface of the light-shielding film 12 formed on the dummy substrate by forming the first reflection-suppressing layer 13, the light-shielding layer 14 and the second reflection-suppressing layer 15 constituting the light-shielding film 12 is determined by using a reflectance meter. It is calculated based on the result of the measured backside reflectance.
The in-plane uniformity of the reflectance means the difference between the maximum value and the minimum value of the reflectance at any plurality of points of the mask blank.

<Manufacturing method of photomask blank>
Subsequently, the method for manufacturing the above-mentioned photomask blank 1 will be described.

(Preparation process)
A transparent substrate 11 that is substantially transparent to the exposure light is prepared. The transparent substrate 11 may be subjected to arbitrary processing steps such as a grinding step and a polishing step as necessary so as to have a flat and smooth main surface. After polishing, it is advisable to perform cleaning to remove foreign matter and contamination on the surface of the transparent substrate 11. As the cleaning, for example, sulfuric acid, sulfuric acid hydrogen peroxide (SPM), ammonia, ammonia hydrogen peroxide (APM), OH radical cleaning water, ozone water, warm water and the like can be used.

(Step of forming the first reflection suppression layer)
Subsequently, the first reflection suppression layer 13 is formed on the transparent substrate 11. In the present embodiment, the first low chromium oxide layer 13a and the first high chromium oxide layer 13b are laminated in this order from the transparent substrate 11 side to form the first reflection suppression layer 13.

In the formation of the first reflection suppression layer 13, a film is formed by reactive sputtering using a sputtering target containing Cr, a reactive gas containing an oxygen-based gas and a nitrogen-based gas, and a sputtering gas containing a rare gas. I do. At this time, as the film forming condition, a flow rate at which the flow rate of the reactive gas contained in the sputtering gas is in the metal mode is selected.

In reactive sputtering, when a sputtering target is discharged while introducing a reactive gas such as an oxygen-based gas or a nitrogen-based gas, the state of the discharged plasma changes according to the flow rate of the reactive gas, and the state of the discharged plasma changes accordingly. The film formation rate changes. In the metal mode, by reducing the ratio of the reactive gas, the adhesion of the reactive gas to the surface of the sputtering target can be reduced and the film formation rate can be increased. Moreover, in the metal mode, since the supply amount of the reactive gas is small, for example, at least one of the oxygen content (O content) and the nitrogen content (N content) is higher than that of the membrane having a stoichiometric composition. It is possible to form a film having a low content of.

From the viewpoint of suppressing defects in the first reflection suppression layer 13, it is preferable to reduce the power applied to the sputtering target among the film forming conditions. When the applied power to the sputtering target is lowered, micro arcs and abnormal discharges at the sputtering target are suppressed in reactive sputtering in which an oxygen-based gas or a nitrogen-based gas is introduced, and defects of the first reflection suppression layer 13 are suppressed. Occurrence can be suppressed. As the conditions of the metal mode for forming the first reflection suppression layer 13, for example, the flow rate of the oxygen-based gas is 1 to 45 sccm, the flow rate of the nitrogen-based gas is 30 to 60 sccm, and the flow rate of the hydrocarbon-based gas is 1 to 1. It is preferable that the flow rate of the rare gas is 15 sccm and the flow rate of the rare gas is 20 to 100 sccm. The target applied power is preferably 1.0 to 6.0 kW.

The sputter target may be any one containing chromium, and for example, in addition to chromium, a chromium-based material such as chromium oxide, chromium nitride, or chromium nitride can be used. As the oxygen-based gas, for example, oxygen (O2), carbon dioxide (CO2), nitrogen oxide gas (N2O, NO, NO2) and the like can be used. As the nitrogen-based gas, nitrogen (N2) or the like can be used. As the rare gas, for example, helium gas, neon gas, argon gas, krypton gas, xenon gas and the like can also be used. In addition to the above-mentioned reactive gas, a hydrocarbon-based gas may be supplied, and for example, methane gas, butane gas, or the like can be used.

In the present embodiment, the flow rate of the reactive gas and the electric power applied to the sputtering target are set under conditions such that the metal mode is set, and the film formation process by the reactive sputtering is performed using the sputtering target containing Cr. As a result, first, the first low chromium oxide layer 13a having a relatively small ratio of O to N is formed on the transparent substrate 11, and the first height having a relatively large ratio of O to N is formed on the first low chromium oxide layer 13a. By forming the chromium oxide layer 13b, the first reflection suppression layer 13 is formed. The first low chromium oxide layer 13a is formed in a metal mode and with low power so that the O content is lower than that of the first high chromium oxide layer 13b. The first high chromium oxide layer 13b is formed in a metal mode and with low power so that the O content is higher than that of the first low chromium oxide layer 13a. The film forming conditions in the metal mode can be set with reference to, for example, Japanese Patent Application Laid-Open No. 2019-20712.

When switching from the first low chromium oxide layer 13a to the first high chromium oxide layer 13b, the type and flow rate of the reactive gas and the reactive gas are changed in order to change the O content and the N content. The ratio of oxygen-based gas and nitrogen-based gas in the above may be changed as appropriate. Further, the arrangement of the gas supply port, the gas supply method, and the like may be changed. In addition, the film formation time may be appropriately changed according to the thickness of each layer.

(Step of forming a light-shielding layer)
Subsequently, the light-shielding layer 14 is formed on the first reflection suppression layer 13. This formation is performed by sputtering using a sputtering target containing Cr and a sputtering gas containing a rare gas. At this time, as the film forming condition, a flow rate at which the flow rate of the reactive gas contained in the sputtering gas is in the metal mode is selected.

The sputter target may be one containing chromium. From the viewpoint of improving the in-plane uniformity of the reflectance of the front surface and the back surface of the light-shielding film 12, it is preferable to use a sputter target made of chrome. As the rare gas, for example, helium gas, neon gas, argon gas, krypton gas, xenon gas and the like can also be used. In addition to the noble gas, oxygen-based gas, nitrogen-based gas, and hydrocarbon-based gas may be supplied as long as the effects of the present invention are not deviated.

In the present embodiment, the flow rate of the reactive gas and the power applied to the sputtering target are set under conditions such that the metal mode is set, and sputtering is performed using the sputtering target containing Cr. As a result, a light-shielding layer 14 mainly containing Cr is formed on the first reflection suppression layer 13.

As the film forming condition of the light-shielding layer 14, for example, the flow rate of the rare gas may be 60 to 200 sccm. The target applied power is preferably 3.0 to 10.0 kW.

(Step of forming the second reflection suppression layer)
Subsequently, the second reflection suppression layer 15 is formed on the light shielding layer 14. In this formation, similarly to the first reflection suppression layer 13, the flow rate of the reactive gas and the applied power to the sputtering target are set under conditions such that the metal mode is set, and the sputtering target containing Cr is used for reactive sputtering. The film is formed by. As a result, a second low chromium oxide layer 15a having a relatively small ratio of O to N is formed on the light-shielding layer 14, and a second high chromium oxide having a relatively large ratio of O to N is formed on the second low chromium oxide layer 15a. By forming the layer 15b, the second reflection suppression layer 15 is formed. The second low chromium oxide layer 15a is formed in a metal mode and with low power so that the O content is lower than that of the second high chromium oxide layer 15b. The second high chromium oxide layer 15b is formed in a metal mode and with low power so that the O content is higher than that of the second low chromium oxide layer 15a.

As the conditions of the metal mode for forming the second reflection suppression layer 15, for example, the flow rate of the oxygen-based gas is 1 to 45 sccm, the flow rate of the nitrogen-based gas is 30 to 60 sccm, and the flow rate of the hydrocarbon-based gas is 1 to 1. It is preferable that the flow rate of the rare gas is 15 sccm and the flow rate of the rare gas is 20 to 100 sccm. The target applied power is preferably 1.0 to 6.0 kW.

When switching from the second low chromium oxide layer 15a to the first high chromium oxide layer 13b, the type and flow rate of the reactive gas and the oxygen system in the reactive gas are the same as in the first reflection suppression layer 13. It is advisable to change the ratio of gas and nitrogen-based gas as appropriate. Further, the arrangement of the gas supply port, the gas supply method, and the like may be changed.

From the above, the photomask blank 1 of the present embodiment is obtained.

The film formation of each layer in the light-shielding film 12 may be performed in-situ using an in-line sputtering apparatus. In the case of non-in-line type, it is necessary to take out the transparent substrate 11 from the apparatus after forming the film of each layer, and the transparent substrate 11 may be exposed to the atmosphere, and each layer may be surface-oxidized or surface-carbonized. As a result, the reflectance and etching rate of the light-shielding film 12 with respect to the exposure light may be changed. In this respect, in the case of the in-line type, since each layer can be continuously formed without taking the transparent substrate 11 out of the apparatus and exposing it to the atmosphere, it is possible to suppress the uptake of unintended elements into the light-shielding film 12. ..

Further, when the light-shielding film 12 is formed by using an in-line type sputtering apparatus, a composition-inclined region (composition gradient region) in which the composition of the first reflection-suppressing layer 13, the light-shielding layer 14, and the second reflection-suppressing layer 15 is continuously inclined. Since it has a transition layer), it is preferable because the cross section of the light-shielding film pattern formed by etching (particularly wet etching) using a photomask blank can be made smooth and close to vertical.

<Manufacturing method of photomask>
Subsequently, a method of manufacturing a photomask using the above-mentioned photomask blank 1 will be described.

(Resist film forming process)
First, a resist is applied on the second reflection suppression layer 15 of the light-shielding film 12 of the photomask blank 1 and dried to form a resist film. As the resist, it is necessary to select an appropriate resist according to the drawing apparatus to be used, but a positive type or negative type resist can be used.

(Resist pattern forming process)
Subsequently, a predetermined pattern is drawn on the resist film using a drawing device. Usually, a laser drawing device is used when producing a photomask for manufacturing a display device. After drawing, the resist film is developed and rinsed to form a predetermined resist pattern.

In the present embodiment, since the reflectance of the second reflection suppression layer 15 is set to be low, the reflection of the drawing light (laser light) can be reduced when the pattern is drawn on the resist film. As a result, a resist pattern with high pattern accuracy can be formed, and a light-shielding film pattern with high dimensional accuracy can be formed accordingly.

(Process of forming a light-shielding film pattern)
Subsequently, the light-shielding film pattern 12 is formed by etching the light-shielding film 12 using the resist pattern as a mask. Etching may be wet etching or dry etching. Usually, in a photomask for manufacturing a display device, wet etching is performed, and as an etching solution (etchant) used in the wet etching, for example, a chromium etching solution containing dicerium ammonium nitrate and perchloric acid is used. be able to.

In the present embodiment, the composition of each layer is adjusted so that the etching rates of the first reflection suppression layer 13, the light shielding layer 14, and the second reflection suppression layer 15 are the same in the thickness direction of the light shielding film 12, so that wet etching is performed. That is, the cross-sectional shape of the light-shielding film pattern can be brought close to perpendicular to the transparent substrate 11, and high CD uniformity can be obtained.

(Peeling process)
Subsequently, the resist pattern is peeled off to obtain a photomask in which a light-shielding film pattern (light-shielding film pattern) is formed on the transparent substrate 11.

From the above, the photomask according to the present embodiment can be obtained.

<Manufacturing method of display device>
Subsequently, a method of manufacturing a display device using the above-mentioned photomask will be described.

(Preparation process)
First, a substrate with a resist film having a resist film formed on the substrate of the display device is prepared. Subsequently, the photomask obtained by the above-mentioned manufacturing method is placed on the mask stage of the exposure apparatus via the projection optical system of the exposure apparatus so as to face the resist film of the substrate with the resist film.

(Exposure process (pattern transfer process))
Next, a resist exposure step is performed in which the photomask is irradiated with exposure light to transfer the pattern to the resist film formed on the substrate of the display device.
The exposure light is, for example, a single wavelength light (j line (wavelength 313 nm), wavelength 334 nm, i line (wavelength 365 nm), h line (wavelength 405 nm), g line (wavelength 436 nm) selected from the wavelength band of 300 nm to 436 nm. ) Etc.), or composite light containing multiple wavelengths of light (for example, j-line (wavelength 313 nm), wavelength 334 nm, i-line (wavelength 365 nm), h-line (405 nm), g-line (wavelength 436 nm)) is used. When a large photomask is used, it is preferable to use composite light as the exposure light from the viewpoint of the amount of light.
In the present embodiment, a display device (display panel) is manufactured by using a photomask in which the reflectances of the front and back surfaces of the light-shielding film pattern (light-shielding film pattern) are reduced and the in-plane uniformity of these reflectances is high. Therefore, a highly accurate transfer pattern can be formed.

<Effect of this embodiment>
According to this embodiment, one or more of the following effects are exhibited.

(A) In the photomask blank 1 of the present embodiment, in the light-shielding film 12, the first reflection-suppressing layer 13 is composed of the first low-chromium oxide layer 13a with relatively little oxidation and the first high-chromium oxide with relatively high oxidation. It is configured by laminating the layer 13b. As a result, defects in the first reflection suppression layer 13 can be reduced, and the reflectance of the back surface of the light-shielding film 12 can be lowered. Moreover, in the photomask blank 1, it is possible to suppress the in-plane variation of the back surface reflectance and improve the uniformity of the back surface reflectance.

(B) Further, the second reflection suppression layer 15 is formed by laminating a second low chromium oxide layer 15a having a relatively small amount of oxidation and a second high chromium oxide layer 15b having a relatively large amount of oxidation. As a result, defects in the second reflection suppression layer 15 can be reduced, and the reflectance of the surface of the light-shielding film 12 can be lowered. Moreover, in the photomask blank 1, the in-plane variation of the surface reflectance can be suppressed, and the uniformity of the surface reflectance can be improved.

(C) The first low chromium oxide layer 13a contains Cr at 25 to 95 atomic%, O at 5 to 45 atomic%, and N at 2 to 35 atomic%, respectively, and the ratio of O to N is 2. The content of the first highly chromium oxide layer 13b is less than 5, Cr is 30 to 95 atomic%, O is 7 to 50 atomic%, and N is 2 to 25 atomic%, respectively, and the ratio of O to N is It is preferably 2.5 to 10. The second low chromium oxide layer 15a contains Cr at 25 to 95 atomic%, O at 5 to 45 atomic%, and N at 2 to 35 atomic%, respectively, and the ratio of O to N is 2.5. The second highly chromium oxide layer 15b contains Cr at a content of 30 to 70 atomic%, O at a content of 15 to 60 atomic%, and N at a content of 2 to 30 atomic%, respectively, and the ratio of O to N is 2. It is preferably .5-10. By configuring each layer with such a composition, the reflectance of the front surface and the back surface of the light-shielding film 12 can be reduced (10% or less with respect to the representative wavelength of the exposure light), and defects can be reduced. Moreover, since the etching rates of the respective layers of the light-shielding film 12 can be made uniform, the cross-sectional shape of the light-shielding film pattern can be made closer to vertical.

(D) The composition of the first reflection suppression layer 13 and the second reflection suppression layer 15 changes continuously or stepwise along the film thickness direction in the content of at least one of O and N, respectively. It is preferable to have a region. By changing the composition of each of the first reflection suppression layer 13 and the second reflection suppression layer 15, the difference in etching rate within each layer can be reduced, and the cross-sectional shape of the light-shielding film pattern can be made closer to vertical.

The light-shielding layer 14 preferably has a chromium content of 97 atomic% to 100 atomic%. By forming the light-shielding layer 14 with chromium that does not substantially contain O, N, and F, it is possible to suppress in-plane composition variation due to the inclusion of O, N, and F. Thereby, the front surface reflectance and the back surface reflectance of the light-shielding film 12 can be made more uniform in the photomask blank surface.

(F) In the first reflection suppression layer 13, the ratio of O to N in the first high chromium oxide layer 13b is preferably 2.5 to 10. By configuring so as to have the above O / N ratio, the reflectance of the first reflection suppression layer 13 is lowered, and at the same time, it is combined with other layers (light-shielding layer: particularly, the chromium content is 97 to 100 atomic%). The difference in etching rate can be reduced.

(G) In the second reflection suppressing layer 15, the ratio of O to N in the second highly chromium oxide layer 15b is preferably 2.5 to 10. By configuring the O / N ratio to be as described above, the reflectance of the second reflection suppression layer 15 can be lowered. Further, the adhesion to the resist film formed on the surface of the second low chromium oxide layer 15a can be improved, and the cross-sectional shape of the light-shielding film pattern can be made more stable and close to vertical.

(H) It is preferable that at least one of the first reflection suppressing layer 13 and the second reflection suppressing layer 15 further contains C. As a result, the difference in etching rate between the first reflection suppression layer 13 and the second reflection suppression layer 15 and the light shielding layer 14 can be reduced. In particular, when the chromium content of the light-shielding layer 14 is 97 atomic% to 100 atomic%, the difference can be made smaller.

(I) By providing the light-shielding film 12 described above, the photomask blank 1 has both front and back reflectances of 15% or less in the exposure wavelength range of 300 nm to 436 nm, and the front surface reflectance and the back surface in the above wavelength range. It has optical characteristics such that the wavelength dependence of each reflectance is 12% or less. Further, the photomask blank 1 is provided with the above-mentioned light-shielding film 12, so that both the front and back reflectances in the exposure wavelength range of 365 nm to 436 nm are 10% or less, and the front surface reflectance and the back surface reflection in the above wavelength range are both. It has optical characteristics such that the wavelength dependence of each rate is 5% or less. According to such a photomask blank 1, when the light-shielding film 12 is irradiated with exposure light as a photomask, the light-shielding film 12 covers the entire wavelength band of the exposure wavelength of 300 nm to 436 nm or the entire wavelength band of the exposure wavelength of 365 nm to 436 nm. And since the reflection of the light on the back surface can be suppressed, the total amount of the reflected light on the front and back surfaces can be reduced. In particular, the wavelength dependence of the back surface reflectance of the light-shielding film 12 is set to 5% or less, and the back surface reflectance can be lowered on average over the entire wavelength range, so that the return light to the back surface of the photomask can be suppressed. As a result, it is possible to suppress a decrease in transfer pattern accuracy due to light reflection on the front and back surfaces of the photomask when manufacturing a display device using the photomask.

It is preferable that the back surface reflectance of the photomask blank 1 is smaller than the front surface reflectance in the entire range of the exposure wavelength range of 300 nm to 436 nm. Alternatively, it is preferable that the back surface reflectance of the photomask blank 1 is smaller than the front surface reflectance in the entire range of the exposure wavelength range of 365 nm to 436 nm. As a result, the reflection of the exposure light can be suppressed over a wide wavelength band, and the total amount of the reflection of the exposure light can be further reduced.

(K) It is preferable that the wavelength dependence of the back surface reflectance of the photomask blank 1 is smaller than the wavelength dependence of the surface reflectance in the range of the exposure wavelength range of 300 nm to 436 nm. Alternatively, it is preferable that the wavelength dependence of the back surface reflectance of the photomask blank 1 is smaller than the wavelength dependence of the surface reflectance in the entire range of the exposure wavelength range of 365 nm to 436 nm. That is, in the above wavelength range, it is preferable that the amount of change in the back surface reflectance is smaller than the amount of change in the front surface reflectance. As a result, the return light on the back surface of the photomask can be further suppressed, and the decrease in transfer pattern accuracy can be further reduced.

(L) According to the photomask blank 1, the surface reflectance on the surface side of the light-shielding film 12 is low. Therefore, when a resist film is provided on the light-shielding film 12 and a resist pattern is formed by a drawing / developing process, drawing light is used. It is possible to reduce the reflection on the surface of the light-shielding film 12. Thereby, the dimensional accuracy of the resist pattern can be improved, and the dimensional accuracy of the light-shielding film pattern of the photomask formed from the resist pattern can be improved. Specifically, the CD uniformity of the light-shielding film pattern can be improved, and a high-precision light-shielding film pattern of 75 nm or less can be formed.

(M) The photomask manufactured from the photomask blank 1 has a high-precision light-shielding film pattern, low reflectance on the front and back surfaces of the light-shielding film pattern, and high in-plane uniformity of reflectance. When transferring a pattern to a transfer body, high transfer characteristics can be obtained.

<Other embodiments>
Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment and can be appropriately modified without departing from the gist thereof.

In the above-described embodiment, the case where the light-shielding film 12 is directly provided on the transparent substrate 11 has been described, but the present invention is not limited to this. For example, a photomask blank in which a semipermeable membrane having an optical density lower than that of the light-shielding film 12 is provided between the transparent substrate 11 and the light-shielding film 12 may be used. Even in the photomask blank in which the semitransparent film and the light-shielding film 12 are formed on the transparent substrate 11, the back surface reflectance of the semitransparent film with respect to the exposure light is 15% or less within the range of the exposure wavelength of 300 nm to 436 nm. The surface reflectance of the light-shielding film is preferably 15% or less. Further, in the photomask blank in which the semitransparent film and the light-shielding film 12 are formed on the transparent substrate 11, the back surface reflectance of the semitransparent film with respect to the exposure light is 10% or less within the range of the exposure wavelength of 365 nm to 436 nm. The surface reflectance of the light-shielding film is preferably 10% or less. This photomask blank can be used as a photomask blank for a gray tone mask or a gradation mask, which has the effect of reducing the number of photomasks used in manufacturing a display device. The light-shielding film pattern in this gray tone mask or gradation mask is a semipermeable membrane pattern and / or a light-shielding film pattern.

Further, instead of the semi-transmissive film, a photomask blank in which a phase shift film for shifting the phase of transmitted light is provided between the transparent substrate 11 and the light-shielding film 12 may be used. Even in the photomask blank in which the phase shift film and the light shielding film 12 are formed on the transparent substrate 11, the back surface reflectance of the phase shift film with respect to the exposure light is 15% or less within the range of the exposure wavelength of 300 nm to 436 nm. The surface reflectance of the light-shielding film is preferably 15% or less. Further, in the photomask blank in which the phase shift film and the light shielding film 12 are formed on the transparent substrate 11, the back surface reflectance of the phase shift film with respect to the exposure light is 10% or less within the range of the exposure wavelength of 365 nm to 436 nm. The surface reflectance of the light-shielding film is preferably 10% or less. This photomask blank can be used as a phase shift mask having a high pattern resolution effect due to the phase shift effect. The light-shielding film pattern in this phase-shift mask is a phase-shift film pattern, a phase-shift film pattern, and a light-shielding film pattern.

As the semipermeable membrane and the phase shift film described above, a material having etching selectivity with respect to a chromium-based material which is a material constituting the light-shielding film 12 is suitable. As such a material, a metal silicide-based material containing molybdenum (Mo), zirconium (Zr), titanium (Ti), tantalum (Ta) and silicon (Si) can be used, and oxygen, nitrogen, Materials containing at least one of carbon and fluorine are suitable. For example, metal silicides such as MoSi, ZrSi, TiSi, TaSi, MoZrSi, MoTiSi, and MoTaSi, oxides of metal silicides, nitrides of metal silicides, oxynitrides of metal silicides, carbides of metal silicides, and oxidation of metal silicides. Carbide and metal nitride carbide nitride are suitable. The semipermeable membrane and the phase shift membrane may be a laminated film composed of the above-mentioned films mentioned as functional films.

Further, in the above-described embodiment, an etching mask film composed of the light-shielding film 12 and a material having etching selectivity may be formed on the light-shielding film 12.

Further, in the above-described embodiment, an etching stopper film made of a light-shielding film and a material having etching selectivity may be formed between the transparent substrate 11 and the light-shielding film 12. The etching mask film and the etching stopper film are made of a material having etching selectivity with respect to the chromium-based material which is the material constituting the light-shielding film 12. Examples of such materials include metal silicide-based materials containing molybdenum (Mo), zirconium (Zr), titanium (Ti), tantalum (Ta) and silicon (Si), Si, SiO, SiO2, SiON, Si3N4 and the like. Silicon-based materials can be mentioned.

Next, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples.

<Example 1>
In this embodiment, the first low chromium oxide layer and the first height are formed on a transparent substrate having a substrate size of 1220 mm × 1400 mm as shown in FIG. 1 by the procedure shown in the above-described embodiment using an in-line sputtering apparatus. A photomask blank having a light-shielding film was produced by laminating a chromium oxide layer, a light-shielding layer, a second low-chromium oxide layer, and a second high-chromium oxide layer in this order.

The film forming conditions of the first low chromium oxide layer and the second high chromium oxide layer are the first low chromium oxide layer in which the ratio of O to N is relatively small, and the first high oxidation in which the ratio of O to N is relatively large. The sputter target is a Cr sputter target so as to form a chromium layer, and the flow rate of the reactive gas is 1 to 45 sccm for the oxygen gas and 30 to 60 sccm for the nitrogen gas so as to be in the metal mode. The flow rate of the hydrogen-based gas was selected from the range of 1 to 15 sccm and the flow rate of the rare gas was selected from the range of 20 to 100 sccm, and the target applied power was set in the range of 1.0 to 6.0 kW.

As for the film forming conditions of the light-shielding layer, the sputtering target was a Cr sputtering target, the flow rate of the rare gas was set in the range of 60 to 200 sccm, and the target applied power was set in the range of 3.0 to 10.0 kW.

The film forming conditions of the second low chromium oxide layer and the second high chromium oxide layer are the second low chromium oxide layer in which the ratio of O to N is relatively small, and the second high oxidation in which the ratio of O to N is relatively large. The sputter target is a Cr sputter target so as to form a chromium layer, and the flow rate of the reactive gas is 1 to 45 sccm for the oxygen gas and 30 to 60 sccm for the nitrogen gas so as to be in the metal mode. The flow rate of the hydrogen-based gas was selected from the range of 1 to 15 sccm and the flow rate of the rare gas was selected from the range of 20 to 100 sccm, and the target applied power was set in the range of 1.0 to 6.0 kW.

When the composition of the obtained light-shielding film of the photomask blank in the film thickness direction was measured by X-ray photoelectron spectroscopy (XPS), it was confirmed that each layer of the light-shielding film had the composition distribution shown in FIG. FIG. 2 is a diagram showing the results of composition analysis in the film thickness direction in the photomask blank of Example 1, where the horizontal axis represents the film thickness and the vertical axis represents the element content [atomic%]. The film thickness represents the depth [nm] from the surface of the light-shielding film.

In FIG. 2, a region containing about 15 atomic% of carbon (C) near the surface of the light-shielding film is a surface natural oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) to nitrogen (N) is 2.5 or more to a depth of about 1.3 nm to about 14 nm is the second highly chromium oxide layer. .. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) to nitrogen (N) is less than 2.5 to a depth of about 15 nm to about 43 nm is the second low chromium oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 44 nm to about 66 nm is a transition layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer having a chromium (Cr) content of 97 atomic% or more to a depth of about 67 nm to about 156 nm is a light-shielding layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 157 nm to about 164 nm is a transition layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) to nitrogen (N) is 2.5 or more to a depth of about 165 nm to about 188 nm is the first high chromium oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) to nitrogen (N) is less than 2.5 to a depth of about 189 nm to a depth of 195 nm is the first low chromium oxide layer. The region where the ratio of oxygen (O) to silicon (Si) is about 2 is a transparent substrate, and the region between the transparent substrate and the first low chromium oxide layer is a transition layer.

As shown in FIG. 2, the first low chromium oxide layer is a CrCON film, Cr is 54.2 to 56.5 atomic%, N is 12.0 to 14.2 atomic%, and O is 14.8 to. 15.1 atomic%, C contains 2.7-4.3 atomic%. The ratio of O to N (O / N ratio) was 1.9 to 2.4.

The first chromium oxide layer is a CrCON film, Cr is 57.1 to 90.7 atomic%, N is 2.0 to 11.3 atomic%, O is 7.3 to 28.3 atomic%, and C. Contains 0-3.3 atomic%. The ratio of O to N (O / N ratio) was 2.5 to 3.6.

The light-shielding layer is a CrO film, containing 97.4 to 99.1 atomic% of Cr and 0.9 to 2.6 atomic% of O.

The second low chromium oxide layer is a CrCON film, Cr is 49.3 to 76.9 atomic%, N is 6.2 to 18.9 atomic%, O is 24.4 to 32.5 atomic%, and C. Contains 2.9-5.2 atomic%. The ratio of O to N (O / N ratio) was 1.3 to 2.4.

The second chromium oxide layer is a CrCON film, Cr is 42.3 to 49.0 atomic%, N is 8.7 to 12.4 atomic%, O is 35.3 to 44.8 atomic%, and C. Contains 2.2-4.2 atomic%. The ratio of O to N (O / N ratio) was 2.9 to 5.2.

(Evaluation of photomask blank)
The photomask blank of Example 1 was evaluated by the methods shown below for the optical density of the light-shielding film and the reflectance of the front and back surfaces of the light-shielding film.

When the optical density of the light-shielding film of the photomask blank of Example 1 was measured with a spectrophotometer (“SolidSpec-3700” manufactured by Shimadzu Corporation), the g-line (wavelength 436 nm), which is the wavelength band of the exposure light, was measured. It was 5.0 or higher. In addition, the reflectance of the front and back surfaces of the light-shielding film was measured with a spectrophotometer (“SolidSpec-3700” manufactured by Shimadzu Corporation). Specifically, the reflectance (front surface reflectance) of the light-shielding film on the second reflection suppression layer side and the reflectance (back surface reflectance) of the light-shielding film on the transparent substrate side were measured by a spectrophotometer, respectively. As a result, the reflectance spectrum as shown in FIG. 3 was obtained. FIG. 3 shows the reflectance spectra of the front and back surfaces of the photomask blank of Example 1, where the horizontal axis represents the wavelength [nm] and the vertical axis represents the reflectance [%].
As shown in FIG. 3, it was confirmed that the photomask blank of Example 1 can significantly reduce the reflectance with respect to light of a wide range of wavelengths. Specifically, at wavelengths of 300 nm to 436 nm, the surface reflectance of the light-shielding film is 15.0% or less (12.2% (wavelength 300 nm), 10.9 nm (wavelength 313 nm), 8.2% (wavelength 334 nm)). Surface reflectance of light-shielding film at 4.3% (wavelength 365 nm), 1.8% (wavelength 405 nm), 1.7% (wavelength 413 nm), 2.0% (wavelength 436 nm), wavelength 365 nm to 436 nm. Was 10.0% or less (4.3% (wavelength 365 nm), 1.8% (wavelength 405 nm), 1.7% (wavelength 413 nm), 2.0% (wavelength 436 nm)). The backside reflectance of the light-shielding film is 7.5% or less (7.4% (wavelength 300 nm), 6.2% (wavelength 313 nm)) and 3.9% (wavelength 313 nm) at wavelengths of 350 nm to 436 nm and 365 nm to 436 nm. The wavelength was 334 nm), 1.7% (wavelength 365 nm), 0.9% (wavelength 405 nm), and 2.1% (wavelength 436 nm).
Further, the dependence of the front surface reflectance of the light-shielding film in the range of the exposure wavelength of 300 nm to 436 nm was 10.6%, and the dependence of the back surface reflectance was 6.6%. Further, the dependence of the front surface reflectance of the light-shielding film in the range of the exposure wavelength of 365 nm to 436 nm was 2.7%, and the dependence of the back surface reflectance was as good as 1.3%.
In the wavelength band ranging from 300 nm to 500 nm, the wavelength (bottom peak wavelength) corresponding to the minimum value (bottom peak) of the front surface reflectance and the back surface reflectance is 436 nm for the front surface reflectance and 415.5 nm for the back surface reflectance. there were.

(Evaluation of light-shielding film pattern)
A light-shielding film pattern was formed on the transparent substrate using the photomask blank of Example 1. Specifically, a novolac-based positive resist film was formed on a light-shielding film on a transparent substrate, and then laser drawing (wavelength 413 nm) and development processing were performed to form a resist pattern. Then, the resist pattern was used as a mask and wet-etched with a chrome etching solution to form a light-shielding film pattern on the transparent substrate. The evaluation of the light-shielding film pattern was carried out by forming a 2.5 μm line-and-space pattern and observing the cross-sectional shape of the light-shielding film pattern with a scanning electron microscope (SEM). As a result, it was confirmed that the angle formed by the side surface of the light-shielding film pattern and the transparent substrate was 77 °. From this, it was confirmed that the cross-sectional shape of the light-shielding film pattern can be formed in a state close to vertical.

(In-plane uniformity of reflectance)
The in-plane uniformity of the surface reflectance of the light-shielding film of the obtained photomask blank was measured. As a result of calculating the in-plane uniformity of the surface reflectance based on the evaluation result of the surface reflectance measured with a reflectance meter for 11 × 11 = 121 points in the substrate surface excluding the peripheral portion 50 mm of the substrate. It was 2.0% (range). The backside reflectance was 3.5% (range) as a result of calculating the in-plane uniformity of the backside reflectance of the light-shielding film using the dummy substrate as described above.

As described in Example 1 above, the light-shielding film of the photomask blank is formed by laminating a first reflection-suppressing layer, a light-shielding layer, and a second reflection-suppressing layer from the transparent substrate side so that each layer has a predetermined composition. As a result, the cross-sectional shape of the light-shielding film pattern when patterned by wet etching could be formed vertically. Further, defects can be reduced by forming the first reflection suppression layer and the second reflection suppression layer from the transparent substrate side into a laminated structure of a low chromium oxide layer and a high chromium oxide layer, respectively, so that each layer has a predetermined composition. It was confirmed that the in-plane uniformity of the reflectance of the front surface and the back surface of the light-shielding film was high.

(Making a photomask)
Next, a photomask was prepared using the photomask blank of Example 1.
First, a novolak-based positive resist was formed on the light-shielding film of the photomask blank. Then, a predetermined resist pattern was formed by drawing a pattern of a circuit pattern for a TFT panel on this resist film using a laser drawing device, and further developing and rinsing (the minimum line width of the above-mentioned circuit pattern is 0.75 μm).
Then, using the resist pattern as a mask, the light-shielding film is patterned by wet etching using a chrome etching solution, and finally the resist pattern is peeled off with the resist stripping solution, and the light-shielding film pattern (light-shielding film pattern) is placed on the transparent substrate. Obtained a photomask in which was formed. This photomask is a transparent substrate in which the aperture ratio of the light-shielding film pattern (light-shielding film pattern) formed on the transparent substrate, that is, the light-shielding film pattern occupying the entire area of the photomask in which the light-shielding film pattern is formed is not formed. The exposure ratio was 45%.
When the light-shielding film pattern of this photomask was observed with a scanning electron microscope (SEM), the cross-sectional shape of the light-shielding film pattern was as good as 77 °. The CD uniformity of the light-shielding film pattern of this photomask was measured by "SIR8000" manufactured by Seiko Instruments Nanotechnology Inc. The CD uniformity was measured at 11 × 11 points in a 1100 mm × 1300 mm region excluding the peripheral region of the substrate. As a result, the CD uniformity was less than 60 nm, and the CD uniformity of the obtained photomask was good.

(Manufacturing of LCD panel)
The photomask produced in Example 1 is set on the mask stage of the exposure apparatus, and the transferred object on which the resist film is formed on the substrate for the display apparatus (TFT) is subjected to pattern exposure to prepare a TFT array. bottom. As the exposure light, composite light containing an i-line having a wavelength of 365 nm, an h-line having a wavelength of 405 nm, and a g-line having a wavelength of 436 nm was used.
A TFT-LCD panel was produced by combining the produced TFT array with a color filter, a polarizing plate, and a backlight. As a result, a TFT-LCD panel with no display unevenness was obtained. It is considered that this is because when pattern exposure is performed using a photomask, the reflection of light on the front and back surfaces can be suppressed, the total amount of reflected light can be reduced, and the in-plane uniformity of reflectance can be improved. Be done.

(Reference example 1)
In Reference Example 1, the first reflection-suppressing layer is a single chromium oxide layer, the second reflection-suppressing layer is a laminated structure of a high chromium oxide layer and a low chromium oxide layer from the transparent substrate side, and the light-shielding layer is CrON. A photomask blank was prepared in the same manner as in Example 1.

The film forming conditions of the first reflection suppression layer are that the sputter target is a Cr sputter target, the flow rate of the reactive gas is 5 to 45 sccm, and the flow rate of the nitrogen gas is 30 so as to be in the metal mode. The flow rate of the rare gas was selected from the range of 60 to 150 sccm, and the target applied power was set to the range of 2.0 to 6.0 kW.

As for the film forming conditions of the light-shielding layer, the sputter target is set as the Cr sputter target, and the flow rate of the reactive gas is in the range of 1 to 60 sccm for the nitrogen-based gas and 60 to 200 sccm for the rare gas so as to be in the metal mode. The target applied power was set in the range of 3.0 to 7.0 kW.

The film formation condition of the second reflection suppression layer is that the sputter target is a Cr sputter target, the flow rate of the reactive gas is 8 to 45 sccm, and the flow rate of the nitrogen gas is 30 so as to be in the metal mode. The flow rate of the rare gas was selected from the range of 60 to 150 sccm, and the target applied power was set to the range of 2.0 to 6.0 kW.

When the composition in the film thickness direction of the obtained light-shielding film of the photomask blank was measured by XPS in the same manner as in Example 1, it was confirmed that each layer of the light-shielding film had the composition distribution shown in FIG. FIG. 4 is a diagram showing the results of composition analysis in the film thickness direction in the photomask blank of Reference Example 1, in which the horizontal axis represents the film thickness and the vertical axis represents the element content [atomic%]. The film thickness represents the depth [nm] from the surface of the light-shielding film.

In FIG. 4, a region containing about 21 atomic% of carbon (C) near the surface of the light-shielding film is a surface natural oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) to nitrogen (N) is less than 2.5 to a depth of about 5 nm to a depth of about 15 nm is a low chromium oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer in which the ratio of oxygen (O) loved to nitrogen (N) is 2.5 or more to a depth of about 16 nm to a depth of about 34 nm is a highly chromium oxide layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 35 nm to a depth of about 89 nm is a transition layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 90 nm to about 208 nm is the light-shielding layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 209 nm to a depth of about 227 nm is a transition layer. The region from the surface of the light-shielding film excluding the surface natural oxide layer to a depth of about 228 nm to a depth of about 251 nm is the first reflection suppression layer. The region where the ratio of oxygen (O) to silicon (Si) is about 2 is a transparent substrate, and the region between the transparent substrate and the first reflection suppression layer is a transition layer.

As shown in FIG. 4, the first reflection suppression layer is a CrCON film, in which Cr is 51.4 to 57 atomic%, N is 13.5-18.2 atomic%, and O is 22.6 to 31.6. Atomic%, C contains 2.8 to 4.8 atomic%. The light-shielding layer is a CrON film, which contains 85.4 to 91.9 atomic% of Cr, 7.4 to 9.3 atomic% of N, and 0.5 to 6.0 atomic% of O. The second reflection suppression layer is composed of a high chromium oxide layer and a low chromium oxide layer. The chromium oxide layer is a CrCON film, Cr is 49.0 to 50.6 atomic%, N is 9.1 to 13.0 atomic%, O is 33.7 to 39.4 atomic%, and C is 2. Includes .2-2.9 atomic%. The low chromium oxide layer is a CrCON film, Cr is 50.0 to 51.1 atomic%, N is 13.5-14.1 atomic%, O is 31.8 to 33.4 atomic%, and C is 2. .Contains 5 to 3.5 atomic%.

(Evaluation of photomask blank)
When the optical density of the light-shielding film was measured for the photomask blank of Reference Example 1 in the same manner as in Example 1, it was 5.0 or more in the g-line (wavelength 436 nm), which is the wavelength range of the exposure light. Moreover, when the reflectance of the front and back surfaces of the light-shielding film was measured by a spectrophotometer, the reflectance spectrum as shown in FIG. 5 was obtained. FIG. 5 shows the reflectance spectra of the front and back surfaces of the photomask blank of Comparative Example 1, where the horizontal axis represents the wavelength [nm] and the vertical axis represents the reflectance [%]. As shown in FIG. 5, it was confirmed that the photomask blank of Reference Example 1 can significantly reduce the reflectance with respect to light of a wide range of wavelengths, as in Example 1. Specifically, at wavelengths of 300 nm to 436 nm, the surface reflectance of the light-shielding film is 15.0% or less (15.0% (wavelength 300 nm), 13.3% (wavelength 313 nm), 7.7% (wavelength 365 nm). ), 1.8% (wavelength 405 nm), 1.1% (wavelength 413 nm), 0.3% (wavelength 436 nm)), and at wavelengths 365 nm to 436 nm, the surface reflectance of the light-shielding film is 10.0% or less (). It was 7.7% (wavelength 365 nm), 1.8% (wavelength 405 nm), 1.1% (wavelength 413 nm), 0.3% (wavelength 436 nm)). Further, at wavelengths of 300 nm to 436 nm, the backside reflectance of the light-shielding film is 15.0% or less (12.2% (wavelength 300 nm), 10.4% (wavelength 313 nm), 6.2% (wavelength 365 nm), 4 At 7.7% (wavelength 405 nm), 4.8% (wavelength 436 nm), and wavelengths 365 nm to 436 nm, the backside reflectance of the light-shielding film is 7.5% or less (6.2% (wavelength 365 nm), 4.7. % (Wavelength 405 nm), 4.8% (Wavelength 436 nm)). The reflectance of the front and back surfaces of the light-shielding film can be reduced to 15% or less at a wavelength of 350 nm to 436 nm, or the reflectance of the front and back surfaces of the light-shielding film can be reduced to 10% or less at a wavelength of 365 nm to 436 nm. Was confirmed to be able to have a front surface reflectance of 0.3% and a back surface reflectance of 4.8%.

The in-plane uniformity of the surface reflectance of the light-shielding film of the obtained photomask blank was measured. As a result of calculating the in-plane uniformity of the surface reflectance based on the evaluation result of the surface reflectance measured with a reflectance meter for 11 × 11 = 121 points in the substrate surface excluding the peripheral portion 50 mm of the substrate. It was 3.9% (range). Further, the back surface reflectance exceeds 5.0% (range) as a result of calculating the in-plane uniformity of the back surface reflectance of the light-shielding film using the dummy substrate as described above, and the unevenness of the reflectance is visually observed. confirmed.

(Evaluation of light-shielding film pattern)
A light-shielding film pattern was formed on the photomask blank of the reference example in the same manner as in Example 1, and evaluation was performed. When the light-shielding film pattern was observed by SEM, it was confirmed that the cross-sectional shape of the light-shielding film pattern was inclined from the vertical and tapered. When the angle formed by the side surface of the light-shielding film pattern and the transparent substrate was measured, it was confirmed that the angle was 54 °.

Next, using the photomask blank of the reference example, a photomask was prepared in the same manner as in Example 1. As a result of measuring the CD uniformity of the light-shielding film pattern of the obtained photomask, it was 100 nm, which was a bad result. As described above, in the mask blank of the reference example, the reflectance of the front and back surfaces could be reduced, but a highly accurate mask pattern could not be formed.

1 Photomask blank 11 Transparent substrate 12 Light-shielding film 13 First reflection-suppressing layer 13a First low-chromium oxide layer 13b First high-chromium oxide layer 14 Light-shielding layer 15 Second reflection-suppressing layer 15a Second low-chromium oxide layer 15b Second height Chromium oxide layer

Claims (16)

A photomask blank used when manufacturing a photomask for manufacturing a display device.
A transparent substrate made of a material that is substantially transparent to the exposure light,
It has a light-shielding film provided on the transparent substrate and made of a material substantially opaque to the exposure light.
The light-shielding film includes a first reflection suppression layer, a light-shielding layer, and a second reflection suppression layer from the transparent substrate side.
The first antireflection layer contains chromium, oxygen, and nitrogen, and contains a first low chromium oxide layer in which the ratio of oxygen to nitrogen is relatively small, and chromium, oxygen, and nitrogen, and oxygen to nitrogen. A first highly chromium oxide layer having a relatively large proportion is provided in order from the transparent substrate side.
The second antireflection layer contains a second low chromium oxide layer containing chromium, oxygen and nitrogen, and the ratio of oxygen to nitrogen is relatively small, and chromium, oxygen and nitrogen, and oxygen to nitrogen. A second highly chromium oxide layer having a relatively large proportion is provided in order from the transparent substrate side.
At least the first reflection-suppressing layer so that the reflectance of the exposure light on the front surface and the back surface of the light-shielding film with respect to an exposure wavelength of 300 nm to 436 nm is 15% or less and the optical density is 3.0 or more. A photomask blank characterized in that the composition and film thickness of the light-shielding layer and the second reflection-suppressing layer are set. The photomask blank according to claim 1, wherein the light-shielding layer is formed of a chromium-based material having a chromium content of 97 atomic% or more and 100 atomic% or less. The photomask blank according to claim 1 or 2, wherein the ratio of oxygen to nitrogen in the second highly chromium oxide layer is 2.5 or more and 10 or less. The photomask blank according to any one of claims 1 to 3, wherein the ratio of oxygen to nitrogen in the first high chromium oxide layer is 2.5 or more and 10 or less. The photomask blank according to any one of claims 1 to 4, wherein the first reflection-suppressing layer contains carbon. The photomask blank according to any one of claims 1 to 5, wherein the second reflection-suppressing layer contains carbon. The first reflection-suppressing layer has a chromium content of 25 atomic% or more and 75 atomic% or less, an oxygen content of 15 atomic% or more and 45 atomic% or less, and a nitrogen content of 2 atomic% or more and 30 atomic% or less. There,
The second antireflection layer has a chromium content of 25 atomic% or more and 75 atomic% or less, an oxygen content of 15 atomic% or more and 60 atomic% or less, and a nitrogen content of 2 atomic% or more and 30 atomic% or less. The photomask blank according to any one of claims 1 to 6, wherein the photomask blank is provided. The composition of the first reflection-suppressing layer and the second reflection-suppressing layer changes continuously or stepwise along the film thickness direction in the content of at least one of oxygen and nitrogen, respectively. The photomask blank according to any one of claims 1 to 7, wherein the photomask blank has a region. Between the transparent substrate and the first reflection suppression layer, between the first reflection suppression layer and the light shielding layer, and between the light shielding layer and the second reflection suppression layer, the first reflection suppression layer, The photomask blank according to any one of claims 1 to 8, wherein the light-shielding layer and the elements constituting the second reflection suppression layer have a composition-inclined region in which the composition is continuously inclined. The photomask blank according to any one of claims 1 to 9, wherein the in-plane uniformity of the reflectance of the surface of the light-shielding film with respect to the exposure wavelength is 3% or less. The photomask according to any one of claims 1 to 10, further comprising a semipermeable membrane having an optical density lower than the optical density of the light-shielding film between the transparent substrate and the light-shielding film. blank. The photomask blank according to any one of claims 1 to 10, further comprising a phase shift film between the transparent substrate and the light-shielding film. The step of preparing the photomask blank according to any one of claims 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A method for producing a photomask, which comprises. The step of preparing the photomask blank according to any one of claims 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A step of forming the semipermeable membrane pattern on the transparent substrate by etching the semipermeable membrane using the light-shielding film pattern as a mask.
A method for producing a photomask, which comprises. The step of preparing the photomask blank according to any one of claims 1 to 12, and the step of preparing the photomask blank.
A step of forming a resist film on the light-shielding film and etching the light-shielding film using the resist pattern formed from the resist film as a mask to form a light-shielding film pattern on the transparent substrate.
A step of forming the phase shift film pattern on the transparent substrate by etching the phase shift film using the light film pattern as a mask.
A method for producing a photomask, which comprises. The photomask obtained by the method for producing a photomask according to any one of claims 13 to 15 is placed on a mask stage of an exposure apparatus, and a light-shielding film pattern formed on the photomask, the semi-transmissive light. A method for manufacturing a display device, which comprises an exposure step of exposing and transferring a film pattern and at least one light-shielding film pattern of the phase shift film pattern to a resist formed on a display device substrate.

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