JPH04204735A - Photomask blank and its manufacture and photomask and its manufacture - Google Patents

Abstract

PURPOSE:To restrain surface undulation in the upper surface of a phase shift film by forming a flattened thin film on the main surface of a transparent substrate with a light-shielding film pattern formed on it and forming the phase shift film on this flattened thin film. CONSTITUTION:This flattened thin film 6 flattened on the upper surface is formed on the main surface of the transparent substrate 1 having the light- shielding film 2 formed on it, thus restraining the main surface of the film 6 from being reflected by the upper surface of the film 6, and accordingly, allowing the upper surface of the phase shift layer 8 formed on the upper surface of the film 6 to naturally have flatness similar to or higher than that of the upper surface of the film 6. Since the conditions of forming the layer 8 does not contain the flattening conditions when the layer 8 is formed, the thickness of the layer 8 can be easily and correctly selected by separating the layer 8 from the layer 6, thus permitting the phase shift effect to be restrained from lowering and high resolution to be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an original plate used in the exposure process of photolithography, which improves the resolution of pattern transfer by particularly utilizing the phase difference of exposure light. The present invention relates to a photomask and a method for using the same, a photomask blank that is a material for the photomask, and a method for manufacturing the same.

[Conventional technology]

Conventionally, as this type of photomask blank and its manufacturing method, as well as a photomask and its manufacturing method, those described in, for example, Japanese Patent Application Laid-Open No. 2-78216 are known. As shown in FIG. 5, the photomask blank described in this publication includes a light-shielding film portion 5 and a transmitting portion 4 formed from a light-shielding film on the main surface of a transparent substrate 1 using a known photolithography method. Light shielding film pattern 2 having
The phase shift film 3 formed by applying a coating silicon compound is sequentially formed as a seed layer. Also, as shown in FIG. 6, the photomask has a phase shift of the photomask blank described above! The phase shift film portion 18 is formed by selectively etching iI3 using a known photolithography method.

C Problems to be Solved by the Invention] However, according to the method for manufacturing a photomask blank shown as a conventional example, the main surface of the transparent substrate, which has become uneven due to the formation of a light-shielding film pattern, is used as the base surface. Since a phase shift film is formed, large surface undulations reflecting the uneven surface shape of the underlying surface are generated on the upper surface of the phase shift film. In other words, this surface waviness reflects the surface condition of the underlying surface, with valleys above the transparent portion and peaks above the continuous light film portion. In this way, when a photomask is manufactured using a photomask blank having a phase shift group having a rough and uneven upper surface, the light shielding film is formed in each phase shift film part due to the surface waviness of the phase shift film. The film thickness on both sides in the vicinity is thicker, and the film thickness in the central part is thinner, resulting in a difference in film thickness within the phase shift film portion. Therefore, when pattern transfer is performed using such a photomask, the phase shift! Due to the difference in M1 between portions Ii and Ii, there is a problem in that the phase shift effect that should originally be obtained is reduced and the resolution is lowered.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a photomask blank in which surface waviness on the upper surface of a phase shift film is suppressed, and a method for manufacturing the same.

Another object of the present invention is to provide a photomask and a method for manufacturing the same, which suppress film thickness differences within individual phase shift film portions and prevent a decrease in resolution due to a reduction in the phase shift effect. do.

[Means to solve the problem]

The first photomask blank of the present invention includes a transparent substrate,
A light shielding film pattern formed on the main surface of the transparent substrate and having a transmitting part and a light shielding film part, a flattening thin film covering at least the transmitting part on the transparent substrate, and a flattening thin film on the upper surface of the flattening thin film. and a phase shift film to be formed, and the upper surface of the flattening thin film has flatness imparted by being subjected to a flattening treatment.

Moreover, the second photomask blank of the present invention is
The maximum filtering wave WcM (reference length 2 μm) on the upper surface of the flattened thin film of the photomask blank is 0.05 μm.
It is characterized by having a flatness of m or less.

Furthermore, the third photomask blank of the present invention is characterized in that, in the first or second photomask blank, a transparent conductive film is provided between the flattening thin film and the phase shift layer.

Further, in the photomask of the present invention, in any of the first to third photomask blanks described above, a portion of the phase shift film located above the transmitting portion of the light shielding film pattern is selectively removed. It is characterized by

Further, in the method for manufacturing a photomask blank of the present invention, a light-shielding film is formed on the main surface of a transparent substrate, and the light-shielding film is selectively removed. a step of forming a light-shielding film pattern having a light-shielding film pattern, and covering at least a transmitting portion on the main surface of the transparent substrate with a transparent thin film, and then performing a flattening treatment on the upper surface of the transparent thin film to form a flattened thin film. and forming a phase shift group on the upper surface of the planarizing thin film.

Furthermore, the method for manufacturing a photomask of the present invention includes selectively removing the portion of the phase shift film located above the transparent portion of the light-shielding film pattern in the photomask blank obtained by the method for manufacturing a photomask blank described above. It is characterized by

Note that "transparent" in the structure of the present invention means transparent even to exposure light.

[For production]

In the first to third photomask blanks of the present invention, a flattened ga whose upper surface has flatness imparted by a flattening process is formed on the main surface of a transparent substrate on which a light shielding film pattern is formed. First, the main surface of the transparent substrate is prevented from being reflected on the upper surface of the planarizing thin film. Therefore, the upper surface of the phase shift layer formed on the upper surface of this flattened thin film naturally has a flatness equal to or higher than the flatness of the upper surface of the flattened 111M! I will do t@. In addition, by separating the planarization thin film and the phase shift layer, when forming the phase shift film, the planarization processing conditions are not added to the film formation conditions, so the film thickness of the phase shift film can be reduced. It can be selected easily and accurately.

In addition, as in the second photomask blank of the present invention, the flatness of the upper surface of the flattened thin film is determined by the filtering maximum undulation WcM (
By selecting the reference length (2 μm) to be 0.05 μm or less, it is possible to provide a photomask material that can significantly reduce the line width error of the transferred pattern.

Furthermore, like the third photomask blank of the present invention,
By interposing a transparent conductive film at the same time as the flattening thin film and the phase shift film, it is possible to prevent charge-up during electron beam lithography, which is a process for selectively removing the phase shift film. can. In addition, since the reflection of the surface condition of the main surface of the transparent substrate, which has become uneven due to the formation of the light-shielding film pattern, is alleviated by the transparent conductive film, the phase shift film formed on this transparent conductive film is extremely High flatness can be obtained.

Further, in the photomask of the present invention, in any of the first to third photomask blanks described above, a portion of the phase shift film located above the transmitting portion of the light shielding film pattern is selectively removed. Therefore, it is possible to suppress the film thickness difference within the region of each phase shift film portion formed to give a phase difference to the exposure light.

According to the method for manufacturing a photomask blank of the present invention, at least the transmitting portion of the light-shielding film pattern on the main surface of the transparent substrate is coated with a transparent thin film, and then the upper surface of the coated transparent thin film is flattened. Since the photomask blanks are subjected to the chemical treatment, the first to third photomask blanks of the present invention described above can be easily produced.

Further, according to the method for manufacturing a photomask of the present invention, in the photomask blank obtained by the method for manufacturing a photomask blank described above, the portion of the phase shift film located above the transparent part of the light shielding film pattern is selectively removed. Since the photomask of the present invention described above can be easily manufactured.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a photomask blank and a method for manufacturing the same, and a photomask and a method for manufacturing the same according to the present invention will be described with reference to the drawings.

First, embodiments of the photomask blank and photomask of the present invention will be described with reference to FIGS. 1 and 2.

@Figure 1 is a vertical cross-sectional view of the photomask blank of this example,
FIG. 2 is a longitudinal cross-sectional view of a photomask manufactured using the photomask blank shown in FIG. 1 as a material.

The photomask blank lO shown in FIG.
A light-shielding film pattern 2 formed on the main surface of the transparent substrate 1 and having a transmitting part 4 and a light-shielding film part 5; a flattening thin film 6 covering the light-shielding film pattern 2; It is composed of a transparent conductive film 7 and a phase shift film 8 which are sequentially laminated on #II6.

The transparent substrate 1 is made of quartz glass whose main surface is mirror-polished, and has an external dimension of 127 mm long, 127 mm wide, and 2.29 mm thick.

The light-shielding film pattern 2 is made by first forming a chromium film with a thickness of M1000 over the entire main surface of the transparent substrate 1, and then forming a predetermined pattern (line and space in this example) to be pattern-transferred. The chromium film is selectively removed according to the above procedure, thereby patterning the chromium film into a transmitting part 4 and a light-shielding film part 5.

The flattening thin film 6 was formed to flatten the main surface of the transparent substrate I, which had become uneven due to the formation of the light shielding film pattern 2, and had a thickness of 5vrsoo.

Consists of human silicon oxide film. This flattening is thin! ! The upper surface 6B of 6 has a flatness with a maximum filtering wave WcM (reference length 2 μm) of 0.03 μm by performing a flattening process to be described later. The reference length in all descriptions is 2 μm, and the reference length is omitted). That is, on the upper surface 6a of the flattened thin film 6,
Within the reference length of 2 μm, the maximum difference between the peaks and valleys of the surface waviness is 0.03 μm.

Transparent guidance! ! ! 17 is made of 5nOs:5blK, which is tin oxide containing 5% by weight of antimony, and its film thickness is 20%.
There are 0 people. Since this transparent conductive film 7 is formed using the upper surface 6a of the flattening thin film 1116 as a base, the flatness of the upper surface 7a of this transparent conductive film 7 is further improved, and the maximum filter wave Wc is 0.02~0.031J
m. The transparent conductive film 7 having the above-mentioned composition is not only electrically conductive but also resistant to the conditions of processing and nodding the phase shift film. Therefore, this transparent conductive film 1 is used for selectively removing the phase shift film 8.
- During the process of electron beam lithography, it becomes a path for charges and can prevent charge-up. Also, phase shift! It also functions as an etching stopper when selectively etching I8.

The phase shift aS is made of a silicon oxide film with a refractive index n=1.45, and the film thickness is selected to be 4055 people. This phase shift film 8 has a filtering maximum wave wcM of 0.02.
Since a transparent conductor having a flatness of ~0.03 μm is formed on the upper surface of the film 7a as a base, the flatness of the upper surface 8a is further improved, and the maximum filtering wave WcM is 0.01 μm.
m.

Next, referring to FIG. 2, a photomask 20 manufactured using the photomask blank 10 described above will be described.

This photomask 20 is obtained by selectively removing the phase shift film 8 of the photomask blank 100 described above according to a predetermined pattern. This predetermined pattern refers to a form in which a phase difference of exposure light occurs within the region of the transmitting portion 4 of the light shielding film pattern 2 or between the transmitting portions 4, 4 with the light shielding film portion 5 interposed therebetween. In this embodiment, the phase shift film portion 9 was formed on one side of the transmitting portions 4.4 located on both sides of the light shielding film portion 5. Therefore, the exposure light (i-line) that passes through the phase shift film portion 9 has a phase different by π from the exposure light that passes through the portion where the phase shift film 8 is removed. The film thickness difference between the individual phase shift film portions 9 is reduced to about 2-8% compared to the prior art. As mentioned above, the photomask 20 of this example was manufactured using the filter mask blank 10 in which the upper surface of the phase shift film 8 has the thickest filter wave W, =0.01 μm. Therefore, the difference in film thickness within each phase shift film portion 9 was significantly reduced, and the originally obtained phase shift effect could be brought out to the subordinate. In other words, this photomask 1
When pattern transfer was performed using 0.0, it was possible to form a pattern with a good profile of 0.3 μm, m radiation, and the line width error between the photomask and the transferred object was 1.
We were able to keep it within %.

Here, other aspects of each component in the photomask blank 10 and photomask 20 described above will be described.

First, flatten and thin! ! The material of 6 is not limited as long as it can transmit exposure light well, and for example, a film of Sin! formed by sputtering can be used. , resists such as PMMA, magnesium oxide, zirconium oxide, and fluorides such as lithium fluoride, magnesium fluoride, lanthanum fluoride, and aluminum fluoride, which have high i-line transmittance, can be suitably used. In addition, the flatness of the upper surface of the flattening thin film 6 was selected so that the thickest filtered undulation wcM was 0.03 μm, but if this surface undulation wcM was selected to be 0.05 μm or less, the transfer pattern Line width errors can be suppressed. More preferably, if the surface waviness WCM is selected to be 0°03 μm or less, the film thickness within each phase shift film portion can be made substantially uniform, so that a nearly perfect phase shift effect can be obtained. . In addition, in the above-described embodiment, the light-transmitting film pattern 2 is completely covered with the flattening thin film 6, but for example, the light-transmitting film pattern 2 and the flattening *
The film thickness may be selected to be substantially equal to that of the film 6, and the upper surface of the continuous light film portion 5 may be exposed.

Next, as the transparent conductive film 7, a 5nO-:Sb film having both conductivity and etching stopper function was used, but for example, an ITO (tin oxide + indium oxide) film having only conductivity or a coating resistance S with
The above effects may be obtained by using iNx and 5iCx.

Further, when the above-mentioned ITO film is provided, this ITO film may be interposed between the transparent substrate and the light shielding film pattern. still,
This transparent conductive M7 is not an essential requirement; for example, 1/cyst with a charge-up prevention function may be used,
Phase shift M using accurate end point detection method of etching
When etching 8, use this transparent conductive! 17 may not be provided.

Moreover, in this embodiment, this transparent conductive film 7 is phase-shifted! 18 and the flattening thin film 6, the phase shift l! Although the effect of further improving the flatness of the upper surface of 8 was obtained, in order to obtain such an effect, a plurality of other thin films were interposed between the flattening thin film 6 and the phase shift film 8. Also good. For example, flattening thin! ITO with conductivity on 16! 1. By sequentially forming a SiN film having etching resistance and a phase shift film, the flatness of the upper surface 8a of the phase shift film 8 can be further improved.

In the present embodiment, the phase shift film portion 9 completely removes the phase shift portion M8 located on one side of the transmission portions 4, 4 located on both sides of the fast light film portion 5, but partially A predetermined phase difference may be generated by removing the phase difference. Further, the phase shift film portion 9 may be provided within a predetermined transmitting portion region and spaced apart from the backlight waist portion. Further, as the material for the phase shifter II8, in addition to silicon oxide, a resist such as silicon nitride or PMMA may be used.

Further, in this embodiment, the phase shift film 8 and the flattening thin film described above are made of the same material, but they may be made of different materials.

Next, a method for manufacturing the photomask blank 10 described above will be explained with reference to FIG. 3, which schematically shows the process.

(First step) A sputtering target made of chromium is sputtered on the main surface of the transparent substrate 1 in an argon gas atmosphere to form a chromium film with a thickness of 1000 mm. Next, this chromium film is selectively etched using a known photolithography method according to a predetermined pattern to be transferred.
As a result, the chromium film was formed into a light-transmitting film pattern 2 consisting of a transmitting part 4 and a continuous light film part 5 (see FIG. 3(a)).

(Second step) On the main surface of the transparent substrate 1 on which the light-transmitting film pattern 2 was formed in the first step, a coating liquid O for forming a SiO++-based coating is applied.
CD (manufactured by Tokyo Applied Chemical Industry Co., Ltd.) was coated using a spin code method, and then baked to a film thickness of 4.
A film 11 of 1 g of silicon oxide was formed (Fig. 3(b)
)reference). In addition, the silicon oxide formed in this way - $8
The flatness of the upper surface 11a of 11 is the maximum undulation W of filtering. −
It was 0.08 μm.

Next, the upper surface 11a of the silicon oxide film 11 is flattened to ensure that the surface condition of the main surface of the transparent substrate 1 on which the fast-light pattern 2 is formed is reflected on the upper surface 11a of the silicon oxide 1g8111. suppress. In this example, an etch-back method was adopted as the planarization process. This etchback method will be explained in detail below.

First, on the upper surface 11a of the silicon oxide film 11 formed earlier, a 5-ins coating coating solution was applied again by the spin code method, and then baked to give a film thickness of 3000.
! ! ! 2 was formed (see FIG. 3(C)). Incidentally, the surface waviness of the upper surface 12a of this treated film 12 was the maximum filtering waviness 'NcM=0.03 μm. Next, the silicon oxide film with the treated film 12 laminated thereon is subjected to reactive ion etching to form the upper surface 1 of the treated film 12.
Etched from 2a to 4000 layers, film thickness 30
A planarized thin film 6 of 0.00000000000000000000000000000000 thin film 6 was formed (see FIG. 3 (cl)). Through this flattening process, the surface waviness of the upper surface 6a of the flattened thin film 11E6 is such that the filtering maximum waviness Wl is 0.0.
8 μm to 0.03. improved to czm.

The conditions for the above-mentioned reactive ion etching are as follows.

・Gas pressure...2. OPa ・High frequency output...0, 32 W/em'
(Third step) A sputtering target made of tin oxide containing 5% by weight of antimony is sputtered onto the upper Ga surface of the planarized JII film 6 formed in the second step in an argon gas atmosphere to form a sputtering target of 5nO= ; Transparent conductive material made of Sb! !
7 (film thickness: 200 layers) was formed (see FIG. 3(e)).

Incidentally, the surface waviness of the upper surface 7a of the transparent groove [membrane 7] was the thickest filter waviness W-=0.02 to 0.08 am.

(Fourth step) The 5iOs-based coating forming coating liquid is again applied to the upper surface 7al of the transparent conductive film 7 obtained in the third step by a spin code method, and then baked to form a phase shift M8.
A photomask blank 10 was formed by forming a film (jl
(See diagram (f)). In addition, the upper surface 8 of the phase shift tE8
The surface waviness of a is the maximum filtering waviness Wc, = 0.01μ
It was m.

Next, a manufacturing method for manufacturing a photomask 20 using the photomask blank lO obtained by the above-described method for manufacturing a photomask blank will be described in the 40th article, which schematically shows the steps thereof! This will be explained with reference to I.

(First step) A positive resist l! is applied on the phase shift film 8 of the photomask blank 10 obtained by the method for manufacturing a photomask blank described above. 13 (thickness: 4,500 layers), and then electron beam is irradiated onto the portion 13a of the resist M]3 located above the selectively removed portion of the phase shift film to form a latent image on this portion 13a. (see Figure 4(a)). In addition, the above-mentioned positive resist! 113 was formed by dropping a novolak resist solution (manufactured by Hoechst Co., Ltd. +AZ-1350) onto the phase shift film 8 and spreading it over the entire surface by a spin code method.

(Second step) Portion 13 of the resist film 13 that became a latent image in the first step
After that, using the remaining resist film portion 13b as a mask, the phase shift film M8 is selectively removed by dry etching using plasma discharge to form the phase shift film portion 9. formed (
(See Figure 4(b)).

The development and rinsing treatment of the resist [113] described above involves dropping a rinsing solution consisting of an alkaline developer and IPA (isopropyl alcohol) onto the resist film sequentially at predetermined intervals, and then spinning both solutions. This was expanded using the code method.

In addition, the dry etching by plasma discharge mentioned above is
The etching was performed under the following etching conditions.

(Fourth step) Finally, the resist film portion 13b used as a mask for the phase shift film portion 9 in the third step is heated to a high temperature and brought into contact with concentrated sulfuric acid to dissolve it, thereby obtaining a photomask 20. (See Figure 4(e)).

According to the mask blank and photomask manufacturing methods of the present embodiment described above. Phase shift 1! i8(
High flatness (filtering maximum undulation Wc, =0.01 μm) could be easily imparted to the upper surface of the phase shift film portion 9). Furthermore, since the phase shift film 8 and the planarization thin film 6 are formed separately, when forming the phase shift film, the film formation conditions can be determined without considering the planarization conditions. The film thickness can be controlled accurately and easily.

Furthermore, since the transparent conductive film 7 made of SnO and Sb is disposed as the base of the phase shift film 8, the phase shift film 8 can be easily etched without using an accurate etching end point detection means.
can be selectively removed, and also can prevent charge-up when performing electron beam drawing on the resist [13]. Furthermore, since the flattened i11 crotch 6 was formed using a spin code method using a coating liquid for forming a SiO*-based coating, the surface waviness of the upper surface to be flattened is relatively reduced compared to a sputtering method or the like. Therefore, a simple flattening process is sufficient.

Next, other aspects of each component in the method for manufacturing a photomask blank and the method for manufacturing a photomask described above will be described.

First, an etch-back method was used as a flattening process when forming a flattened thin film, but in addition to silicon oxide, silicon-based electron beam resist and silicon-based photoresist were used as materials for the film processed in this etch-back method. Alternatively, a polystyrene resist, or a novolac resin resist may be used. In addition, when etching a silicon oxide film with 11 layers of treated films, etching was performed over 4,000 layers from the upper surface of the treated film. It may be sufficient to remove only the ridges of the surface undulations. or,
As the planarization treatment, in addition to the etch-back method, a known method used in a semiconductor manufacturing process, such as a chemical etching method, may be used. Alternatively, in addition to flattening by such etching, predetermined! When obtaining a flattened thin film with a thickness of l, the spin code method is used to deposit a transparent thin film in multiple depositions instead of one-time deposition.
Flatness may be imparted to the upper surface. Furthermore, the silicon oxide film was formed by applying a 5ins-based coating solution using a spin code method, but it is also possible to use a film-forming method such as sputtering using 5iO6 as a sputtering target, evaporation, or CVD. It's okay.

Further, in this embodiment, the flattening thin film and the phase shift film are formed by the same method, but they may be formed by different methods.

〔Effect of the invention〕

According to the photomask blank of the present invention, a flattened II film is formed on the main surface of a transparent substrate on which a fast-lighting film pattern is formed, and a phase shift film is formed on this flattened II film. , it is possible to suppress the surface condition of the main surface of the uneven transparent substrate from being reflected on the upper surface of the phase shift film. Therefore, it is possible to provide a photomask material having high flatness and a phase shift ha on the upper surface.

According to the photomask of the present invention, since the upper surface of the phase shift film in the photomask blank material has high flatness, the phase shift film is selectively etched to form individual phase shift layers. Differences in film thickness within the film portion are suppressed. Therefore, when pattern transfer is performed using the photomask of the present invention, high resolution can be obtained while suppressing deterioration of the phase shift effect.

According to each of the photomask blank and photomask manufacturing methods of the present invention, a transparent thin film is provided on both the transparent substrate and the phase shift film, and the upper surface of this transparent*g is flattened. , high flatness can be easily imparted to the upper surface of the phase shift film. In addition, since the planarization thin film and the phase shift film are formed separately, there is no need to consider planarization as a film formation condition when forming the phase shift film. can be controlled easily and accurately.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a photomask blank according to an embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of a photomask according to an embodiment of the present invention, and FIG. 3 is a vertical cross-sectional view of a photomask according to an embodiment of the present invention. FIG. 4 is a process diagram of a method for manufacturing a photomask according to an embodiment of the present invention, FIG. 5 is a vertical cross-sectional view of a conventional photomask blank, and FIG. 6 is a process diagram of a conventional photomask blank. FIG. ]...Transparent substrate, 2...Takkouno pattern, 4...
Transmissive part, 5... Light shielding waist part, 6... Flattening i1 [j!
, 7-...Transparent groove! ! 1,8--phase shift family, 9-
...Phase shift film part.

Claims (6)

[Claims] (1) a transparent substrate; a light-shielding film pattern formed on the main surface of the transparent substrate and having a transmitting portion and a light-shielding film portion;
A flattening thin film that at least covers the transparent portion on the transparent substrate, and a phase shift film formed on the upper surface of the flattening thin film, the upper surface of the flattening thin film being subjected to a flattening treatment. A photomask blank characterized by having flatness imparted by flattening. (2) The upper surface of the flattened thin film has the maximum filtering undulation W_C_
The photomask blank according to claim 1, characterized in that M (reference length 2 μm) has flatness of 0.05 μm or less. (3) The photomask blank according to claim (1) or (2), characterized in that a transparent conductive film is provided between the flattening thin film and the phase shift film. (4) In the photomask blank according to any one of claims (1), (2), and (3), a portion of the phase shift film located above the transmitting portion of the light shielding film pattern is selectively removed. A photomask characterized by: (5) forming a light-shielding film on the main surface of the transparent substrate and selectively removing the light-shielding film to form the light-shielding film into a light-shielding film pattern having a transmitting portion and a light-shielding film portion; a step of covering at least a transparent portion on the main surface of the transparent substrate with a transparent thin film, and then subjecting the upper surface of the transparent thin film to a flattening treatment to form a flattened thin film; and an upper surface of the flattened thin film. A method for producing a photomask blank, comprising: forming a phase shift film thereon. (6) In the photomask blank obtained by the method for manufacturing a photomask blank according to claim (5), a portion of the phase shift film located above the transmitting portion of the light shielding film pattern is selectively removed. A method for manufacturing a photomask.