CN108388078B

CN108388078B - Defect correction method for phase shift mask

Info

Publication number: CN108388078B
Application number: CN201810100694.4A
Authority: CN
Inventors: 齐藤隆史; 山田慎吾; 森山久美子
Original assignee: SK Electronics Co Ltd
Current assignee: SK Electronics Co Ltd
Priority date: 2017-02-02
Filing date: 2018-02-01
Publication date: 2021-05-18
Anticipated expiration: 2038-02-01
Also published as: CN108388078A; KR102077904B1; TW201841052A; JP2018124466A; JP6960741B2; TWI663469B

Abstract

The invention provides a defect correction method of a phase shift mask, which is characterized by comprising the following steps: a first step (S1) of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step (S2) of determining whether or not the size of the defect in the phase shift film is 1.0 [ mu ] m × 1.0 [ mu ] m or more; and a third step (P2) of depositing a light-shielding film on the defective portion when the determination result is "NO".

Description

Defect correction method for phase shift mask

Technical Field

The present invention relates to a method of correcting defects generated in a phase shift mask used in manufacturing a flat panel display device, and a photomask having defects corrected.

Background

A Phase Shift Mask (PSM) is a photomask in which resolution is improved by a phase shift effect. Generally, a phase shift film used in a phase shift mask is a semi-permeable film having a transmittance of about 1 to 10 [% ] and an effect of inverting (or shifting) a phase.

The following techniques have been established: in general, in the case of a so-called binary mask in which only a pattern of a light-shielding film is formed on a transparent glass substrate, a region including a defect is locally shaped and removed (trimming) by laser ablation (laser trimming), and the light-shielding film is locally deposited on a portion shaped and removed by the light-shielding film or a defective portion of the pattern (hereinafter, a defective portion of the pattern may be referred to as a white defect) by a photo CVD method or the like. The above-described technique enables correction according to the size and type of the defect with high positional accuracy.

Patent document 1 discloses a defect correction method for a phase shift photomask, which includes: in a defect correction method for a phase shift photomask having a light-shielding pattern and a phase shifter pattern, after patterning the light-shielding layer and the phase shift layer at predetermined positions, SiO is selectively deposited at missing portions of the phase shifter pattern by a photo CVD method using a laser beam₂And (3) a membrane. Patent document 2 discloses a defect correction method for a gray mask.

Documents of the prior art

Patent document

[ patent document 1 ] Japanese patent laid-open No. 2009-020312

[ patent document 2 ] Japanese patent laid-open No. 2008-216346

[ patent document 3 ] Japanese Kokai 2014-074827

Disclosure of Invention

Technical problem to be solved by the invention

However, the phase shift mask applied to the flat panel display device is a special film in controlling 2 parameters of transmittance and phase shift amount by film thickness, and is originally an irreplaceable film. In the experiments of the present inventors, after light-shielding films of the same size were deposited by the optical CVD method in order to correct the line break defect (2.0 μm × 4.0 μm) in the 2.0 μm wide line pattern shown in the optical reflection image of the photomask of fig. 10 (a), the line width in the correction portion was locally narrowed, that is, normal correction was not performed, as shown in the SEM image after exposure shown in fig. 10 (B). In other experiments in which the light-shielding film was replaced with a phase-shift film, the line width was further thinned. This indicates that the correction of the phase shift film is extremely difficult.

That is, even if the defective portion is accurately shaped and removed by laser ablation, it is extremely difficult to deposit a phase shift film having optical characteristics such that the phase difference and the transmittance are exactly the same as those of the surrounding films at the position with accurate positional accuracy.

This is mainly caused by the difference in the deposition methods of the phase shift film and the defect correction film. That is, this is because the retardation is controlled by the film thickness, but the phase shift film and the defect correction film are different in deposition method and strictly speaking, different in composition, and therefore the retardation is not necessarily the same even if the film thickness is the same.

In addition, when films having different optical characteristics are deposited on the defective portion of the pattern, a difference in the interference effect of light is generated between the surrounding phase shift film and the deposited film formed on the defective portion, and thus a pattern formation failure is likely to occur in the pattern formed by transfer exposure.

In view of the above problems, a main object of the present invention is to provide an optimum defect correction method according to the size and type of a defect.

Means for solving the problems

The method for correcting defects of phase shift mask 1 of the present invention comprises the steps of: a first step of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step of determining whether or not the size of the defect portion on the phase shift film is 1.0. mu. m.times.1.0. mu.m or more; and a third step of depositing a light-shielding film filling the defective portion on the defective portion when the determination result is "no".

The method for correcting defects of the 2 nd phase shift mask of the present invention is characterized by comprising the steps of: a first step of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step of determining whether or not the size of the defect portion on the phase shift film is 1.0. mu. m.times.1.0. mu.m or more; and a third step of further judging whether or not the wire is broken when the judgment result of the second step is yes,

if the determination result in the third step is "no", the method includes the steps of:

a fourth step of stacking the light-shielding film in a rectangular shape so as to overlap with a pattern edge portion of the phase shift film adjacent to the defective portion; and

a fifth step of shaping and removing the light-shielding film around the defective portion into a rectangular shape so that one side of a pattern edge portion covering the non-broken side of the defective portion among the stacked light-shielding films is left and the other side is left at a position covering the defective portion,

the width of the overlap is set to 1.0 μm or less.

The method for correcting defects of a 3 rd phase shift mask of the present invention is characterized by comprising the steps of: a first step of measuring a position and a size of a white defect with respect to a photomask substrate having a pattern including the white defect formed of a phase shift film on a transparent substrate; a second step of judging whether or not the size of the defect on the phase shift film is 1.0. mu. m.times.1.0 μm or more; and a third step of further judging whether or not the wire is broken when the judgment result of the second step is yes,

if the determination result in the third step is yes, the method includes the steps of:

a fourth step of depositing a light-shielding film in a region that includes all of the defective portion and overlaps with an edge portion of the phase shift film adjacent to the defective portion; and

a fifth step of shaping and removing the light-shielding film so that an error of the pattern width with respect to a pattern width before correction is 0.1 [ mu ] m + -0.1 [ mu ] m,

the width of the overlap is set to 1.0 μm or less.

The defect correction method of the 1 st to 3 rd phase shift masks is based on a photomask in which a pattern of a phase shift film is directly formed on a transparent substrate, but the defect correction method of the present invention can be applied to an "edge-emphasized phase shift mask" (patent document 3) in which a pattern of a light-shielding film is formed on a transparent substrate and a phase shift film is deposited on the pattern of the light-shielding film, particularly on a pattern edge portion or the like.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to correct a defect even in a phase shift mask which is originally difficult to correct a defect.

Drawings

Fig. 1 is a flowchart showing steps of a defect correction method of a phase shift mask according to embodiment 1.

Fig. 2 is a plan view and a cross-sectional view of a phase shift mask illustrating a state in which a pinhole defect is formed according to embodiment 1.

Fig. 3 is a plan view and a cross-sectional view of a phase shift mask illustrating a state in which correction of a pinhole defect of embodiment 1 is completed.

Fig. 4 is a plan view and an enlarged plan view of the phase shift mask showing a state where a non-disconnection defect is formed according to embodiment 1.

Fig. 5 is a plan view and an enlarged plan view of a phase shift mask illustrating a state in which the correction of the non-disconnection defect of embodiment 1 is completed.

Fig. 6 is a plan view and an enlarged plan view of the phase shift mask showing a state in which a disconnection defect is formed according to embodiment 1.

Fig. 7 is an enlarged plan view of the phase shift mask showing a state in which the correction of the disconnection defect of embodiment 1 is completed.

Fig. 8 shows an optical reflection image of a phase shift mask and a pattern after exposure (pinhole defect: A, B, non-broken line defect: C, D) showing a state in which the correction of the defect of embodiment 1 is completed.

FIG. 9 is an optical reflected image of a phase shift mask showing the completion of correction of a disconnection defect in embodiment 1 (in the case of insufficient overlap: A, in the case of excessive overlap: B)

Fig. 10 shows an optical reflection image of a phase shift mask and an exposed pattern in the case where a disconnection defect is corrected by a conventional method.

Description of the reference symbols

11 a transparent substrate; 12 phase shift film; d1 pinhole defect (white defect of 1.0 μm × 1.0 μm or less); d2 non-disconnection defect; d3 disconnection defect; the width of O (O1-O4) overlap; difference between Δ t and design value of pattern width

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the following embodiments are not to be construed as limiting the gist of the present invention. Note that the same or similar components are denoted by the same reference numerals, and description thereof may be omitted.

(embodiment 1)

Basic idea of the invention (modification of Single-layer PSM)

Fig. 1 is a flowchart showing the procedure of defect correction of the phase shift mask according to embodiment 1 of the present invention. The defect correction of the present invention refers to correction of white defects, unless specifically indicated. However, for convenience of explanation, the explanation will be given assuming that the phase shift mask is a pattern in which a single-layer phase shift film is formed on a transparent substrate, and a complicated phase shift film having a multilayer structure will be described in embodiment 2.

1. Correction of pinhole Defect (1 st correction method)

When a pinhole defect is corrected, first, the position and size of a defective portion of a target photomask substrate are measured by an inspection machine (step S1). Next, it is determined whether or not the size of the defect portion in the phase shift film is 1.0. mu. m.times.1.0. mu.m or more (step S2). If the determination result is no, that is, if the size of the defective portion is equal to or smaller than the predetermined value, in process 1(P1), a light-shielding film having substantially the same size is deposited above the defective portion so as to fill the defective portion by a means capable of positioning and forming a film by a photo-CVD method or the like.

Here, the determination result of step S2 being "no" means that the defective portion formed in the pattern formed by the phase shift film is a minute white defect called a so-called pinhole defect. In this case, although the influence on the exposure is slight originally, the shaping and removal (trimming) by the laser ablation treatment is performed around the periphery including the defect, which adversely affects the optical characteristics. Therefore, step P1 of depositing the light-shielding film directly on the defective portion is executed without trimming, and only the film formation residue is removed as necessary. As a result, although a minute white defect formed on a pattern formed by the phase shift film is covered with a light-shielding film having a large film thickness, if the size is such that the effect of interference is hardly affected, even if the light-shielding film is used instead and filled in a defective portion of the phase shift film, the exposure is hardly affected.

The removal of the film formation residue is not required for the correction of the pinhole defect. However, as described later, if it is "defect related to edge", a trimming process is required to match the surrounding edge.

The light-shielding film used here may be any film as long as it has an optical density of 3.0 or more, and a chromium film is preferable as an example, but is not limited thereto, and other materials may be used as long as the condition of the optical density is satisfied. In the case of selecting a light-shielding film to be formed locally in a region including a defective portion, it is preferable to appropriately select a material that does not easily leave residues when it is evaporated in the subsequent laser ablation treatment.

In addition, "hardly affects the exposure", the wavelength of the exposure light and the target line width should be discussed on the premise, and in the present invention, the exposure light composed of a mixture of g-line, h-line, i-line (ultraviolet light having a wavelength of 365[ nm ] to 436[ nm ]), or monochromatic light is basically assumed, and a pattern having a minimum line width of about 2 μm to 3 μm is assumed. On this premise, a pinhole defect having a size of 1.0 μm × 1.0 μm or less exceeds the resolution limit, and hence it can be said that "the exposure is not substantially affected". This is a common premise in the invention of the present application including the method of correcting defects of the 2 nd and 3 rd phase shift masks described later.

When it is confirmed that the film formation residue (coagulation of the phase shift film) is formed in an independent dot shape in the defect portion, the film formation residue is preferably shaped and removed by a known method such as laser ablation.

Fig. 2 (a) is an enlarged plan view showing a state where a pattern of the phase shift film 12 is formed on the transparent substrate 11 such as synthetic quartz glass. The phase shift film is a semi-permeable film having a typical transmittance of about 1 to 10 [% ] and an effect of inverting or shifting the phase, and the pattern shows a typical pattern of lines and spaces. However, the actual pattern is not necessarily such a pattern, and is not limited to a pattern of lines and spaces. Further, a pinhole defect d1 of 1.0. mu. m.times.1.0 μm or less was present in the pattern of the phase shift film 12.

Fig. 2 (B) is a cross-sectional view taken at X-X along line (a) of fig. 2. It was found that the pinhole defect d1 having a diameter of L1 formed in the phase shift film 12 reached the transparent substrate 11. The inspection machine of the photomask optically determines the position and size of the defect. In general, in the case of inspecting a single-layer semi-permeable membrane, the result of the transmission illumination is preferentially judged. Even if a defect is identified in the reflected illumination, no correction is required as long as there is no transmission in the transmitted illumination. When it is judged by the transmitted illumination that the pinhole defect has a size of 1.0 μm × 1.0 μm or less, the light shielding film is locally deposited only in the portion by the optical CVD method, and the state shown in fig. 3 (a) and 3 (B) is obtained, and the defect correction is completed.

Even if the light-shielding film is formed in a part of the portion where the phase shift film is to be formed, since the size is not more than the resolution limit of the exposure machine, the defect is corrected compared to the case where the pinhole defect is left without almost any influence after the exposure.

Fig. 8 (a) shows an optical reflection image of a single-layer phase shift mask containing white defects (pinhole defects) having a size of 1.0 μm × 1.0 μm, and fig. 8 (B) shows an SEM image obtained by observing an exposed pattern on the mask after the above-described correction method is applied. By performing correction of the same size as the defect size using the light-shielding film without trimming, the pattern after exposure can be corrected to be substantially normal.

2. Correction of non-disconnection defect (2 nd correction method)

In the case where the non-disconnection defect is corrected, if the determination result in the step S2 is yes (the size is 1.0 μm × 1.0 μm or more), a step S3 of determining whether or not the disconnection is caused is further required. Here, it is practical to set the following judgment criteria for distinguishing "broken line" from "non-broken line".

Fig. 4 (a) shows a pattern of the defective portion d2 having the phase shift film on the line pattern. Fig. 4 (B) is an enlarged view of the periphery of the defect portion d2 surrounded by a single-dot chain line in fig. 4 (a). The defective portion d2 is larger than 1.0 μm × 1.0 μm in size, but is judged to be unbroken because the pattern width Lr at the thinnest portion of the pattern near the defective portion is 1 μm or more in excess of the pattern width Lo.

If the determination result in step S3 is "no" (i.e., not broken), the light-shielding film is stacked in the range of the rectangular region T so as to overlap the pattern edge portion of the phase shift film adjacent to the defective portion d2 (step P2-1). In this case, the overlap width O (O1, O2) is set to 1.0 μm or less.

Next, as shown in fig. 5, the light-shielding film around the defective portion is shaped and removed into a rectangular shape so that one side of the non-broken pattern edge portion covering the defective portion among the stacked light-shielding films is left and the other side is left until the light-shielding film covers the defective portion (step P2-2). This step is called trimming, and in fig. 4 (B), a region Z to be trimmed is shown by a broken line diagram. As shown in fig. 5 (B), the light-shielding film is shaped and removed into a rectangular shape so that the remaining portion R remains and includes a defective portion which is a white defect, whereby the defect correction is completed. In addition, it is of course necessary to avoid removing adjacent patterns during trimming.

In this way, when the target pattern is a pattern including a non-broken line defect, a reference for distinguishing "non-broken line" from "broken line" is set in advance. In the above example, when the size of the pattern width Lr (the distance from the edge of the pattern to the edge of the defective portion) other than the defective portion is 1 μm or less, it is determined that the non-broken portion remains as "broken line", and the "correction of broken line defect" described later is applied (the 3 rd correction method). The key point here is that even if there is a defect in the pattern having a defect size exceeding 1.0 μm × 1.0 μm, a light-shielding film having a transmittance of 0 is filled in order to repair the defect of the pattern of the phase shift film, since the pattern has a pattern width of at least 1 μm.

However, strictly speaking, the electrode pattern and the like cannot be said to be a line pattern, and therefore, the distinction between "broken line" and "non-broken line" is not necessarily appropriate in some cases, but the present correction method can be applied depending on the size of the defective portion and the remaining portion. That is, the present correction method can be applied as long as the pattern is left at 1 μm or more, since there is a defect portion having a defect size exceeding 1.0. mu. m × 1.0. mu.m.

Fig. 8 (C) shows an optical reflection image of a single-layer phase shift mask including white defects (non-disconnection defects) having a size of 2.0 μm × 2.0 μm, and fig. 8 (D) shows an SEM image obtained by observing an exposed pattern after the above correction method is applied to the mask. The line width can be corrected to be equal to the normal portion by forming a film so as to cover the defective portion and trimming only the left edge of the defective portion. In this way, for a non-broken line defect of the phase shift film, the defect can be corrected by trimming only one side where the pattern width is secured, instead of the defect portion, with the light-shielding film. When exposure was performed through the corrected photomask, a thinned portion of about 20nm was strictly observed, but the influence was slight and was of a level that did not become a problem in practical use.

3. Correction of disconnection defect (3 rd correction method)

When the judgment result of the step S2 is yes (the size is 1.0 μm × 1.0 μm or more) when the disconnection defect is corrected, a step S3 of judging whether or not the disconnection is caused is further required. Here, the criterion for determining whether "broken line" or "non-broken line" is the same as described above.

That is, it is naturally determined that the line is "broken" when the line is physically broken, and is also determined that the line is "broken" when the pattern width Lr other than the defective portion is smaller than a predetermined reference value (for example, 1 μm) with respect to the pattern width Lo when the line is not completely broken.

Fig. 6 (a) shows a pattern of the defective portion d3 having the phase shift film on the line pattern. Fig. 6 (B) is an enlarged view of the periphery of the defect portion d3 surrounded by a single-dot chain line in fig. 6 (a). The defective portion d3 exceeded 1.0. mu. m.times.1.0. mu.m and was broken. That is, the determination result of step S3 is yes (i.e., disconnection).

At this time, as shown in fig. 6 (B) and 7 (a), a light-shielding film is deposited in a region T which includes all of the defective portion d3 and overlaps with the pattern edge portion of the phase shift film adjacent to the defective portion (step P3-1). Trimming may also be performed before depositing the light-shielding film. At this time, as shown in the figure, the size of the overlapping width O (O3, O4) of the region T and the phase shift film at the end E of the defect portion is adjusted to 1.0 μm or less.

Next, as shown in fig. 7 (B), the remaining portion R is left, and the edge portions on both sides of the light-shielding film are shaped and removed into a rectangular shape, thereby completing defect correction. At this time, the removal is performed so that the residue is wider than the pattern width by the width Δ t. Since a large-area defective portion of the phase shift film such as a line break defect is replaced with the light-shielding film, the magnitude of the difference Δ t from the design value of the pattern width greatly affects the line width after exposure.

The error Δ t between the allowable value and the design value of the pattern width, which is experimentally found to be necessary for reducing the thinning or thickening of the pattern after exposure, is 0.1 ± 0.1 μm, that is, the difference from the original pattern size is preferably 0.0 μm to +0.2 μm.

Fig. 9 (a) shows an optical reflection image of a single layer of the phase shift mask containing white defects (disconnection defects) having a size of 2.0 μm × 4.0 μm. In this example, since the overlapping is insufficient, light leakage occurs from the gap, and the pattern becomes fine. Fig. 9 (B) shows an optical reflection image when the size of the overlap width O (O3, O4) is +0.4 μm in the phase shift mask including a single layer of white defects (disconnection defects) having a size of 2.0 μm × 4.0 μm. In this case, local line width thickening occurs.

Therefore, it is important to reliably perform the overlapping at the time of forming the light-shielding film and to reliably correct the line width to a predetermined range after the light-shielding film is formed.

4. Limits on defect correction

The defect that can be corrected by the light-shielding film is limited in size or in the location of the defect. Since the accuracy of the conventional laser ablation is about 0.1 μm and the line width is about 2 to 3 μm, if a defect of 10 μm × 10 μm or more exists, it is determined that NG is present, and the phase shift mask is newly manufactured.

(embodiment 2) application to edge-emphasized phase-shift mask

The correction method of the present invention can also be applied to a phase shift mask having a 2-layer structure (referred to as an "edge-emphasized phase shift mask" in the present specification) in which a light-shielding film pattern is provided on a transparent substrate and a phase shift film is deposited in a portion where the line width is likely to be reduced, such as a pattern edge portion.

The light-shielding film of the 1 st layer is the same as a normal binary mask when the pattern formation of the light-shielding film of the 1 st layer is completed, and therefore can be corrected by applying the conventional technique.

The defect correction method described in embodiment 1 can be applied to a white defect generated when the phase shift film of layer 2 is formed.

(other embodiments)

The correction of the white defect is performed as described in embodiments 1 and 2, and the correction of the "black defect" generated due to the foreign substance or the film thickness abnormality of the phase shift film may be performed by removing the corresponding portion by a known removal method such as laser ablation to artificially form the "white defect", and then applying the method for correcting the white defect according to the present invention to the size and portion of the white defect. The judgment criteria for the size and the portion of the white defect may be the same as those described in the present invention.

Industrial applicability

According to the present invention, defects of a phase shift mask, which have been difficult to correct in the past, can be corrected, and therefore, the present invention has a great industrial applicability.

Claims

1. A method for correcting a defect of a phase shift mask, comprising the steps of:

a first step (S1) of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step (S2) of determining whether or not the size of the defect in the phase shift film is 1.0 [ mu ] m × 1.0 [ mu ] m or more; and a third step (P1) of, when the determination result is "no", depositing a light-shielding film on the defective portion to fill the defective portion.

2. A method for correcting a defect of a phase shift mask, comprising the steps of:

a first step (S1) of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step (S2) of determining whether or not the size of the defect in the phase shift film is 1.0 [ mu ] m × 1.0 [ mu ] m or more; and a third step (S3) of, when the determination result of the second step is YES, further determining whether or not the wire is disconnected,

a fourth step (P2-1) of stacking light-shielding films in a rectangular shape so as to overlap with a pattern edge portion of the phase shift film adjacent to the defect portion, the width of the overlap being 1.0 [ mu ] m or less; and

and a fifth step (P2-2) of shaping and removing the light-shielding film around the defective portion into a rectangular shape so that one side of the pattern edge portion of the stacked light-shielding film covering the non-broken side of the defective portion is left and the other side is left to a position covering the defective portion.

3. A method for correcting a defect of a phase shift mask, comprising the steps of:

a first step (S1) of measuring the position and size of a defective portion on a photomask substrate having a pattern including the defective portion formed by a phase shift film on a transparent substrate; a second step (S2) of determining whether or not the defect size on the phase shift film is 1.0 [ mu ] m × 1.0 [ mu ] m or more; and a third step (S3) of, when the determination result of the second step is YES, further determining whether or not the wire is disconnected,

if the determination result of the third step (S3) is yes, the method includes the steps of:

a fourth step (P3-1) of depositing a light-shielding film in a region that includes the entire defective portion and overlaps with an edge portion of the phase shift film adjacent to the defective portion, the width of the overlap being 1.0 [ mu ] m or less; and

a fifth step (P3-2) of shaping and removing the light-shielding film so that the error of the pattern width with respect to the pattern width before correction is 0.1 [ mu ] m + -0.1 [ mu ] m.

4. A phase shift mask for a photomask having a pattern of a phase shift film formed on a transparent substrate,

the phase shift mask includes a defect correction film composed of a light shielding film on the pattern,

the defect correction film is filled in such a manner as to cover a defective portion of the pattern of the phase shift film,

when the size of the defective portion of the pattern is judged to be larger than 1.0 [ mu ] m × 1.0 [ mu ] m and the defective portion of the pattern is not broken, the overlapping width of the lower phase shift film and the upper defect correction film is controlled to be 1.0 [ mu ] m or less.

5. A phase shift mask for a photomask having a pattern of a phase shift film formed on a transparent substrate,

when the defective portion of the pattern is determined to be broken, the overlapping width of the phase shift film of the lower layer and the defect correction film of the upper layer in the defective portion is controlled to be 1.0 μm or less, and the difference between the width of the defect correction film deposited in the defective portion and the design value of the pattern width of the defective portion is controlled to be 0.1 μm ± 0.1 μm.

6. A phase shift mask for a photomask, in which a light shielding film pattern and a phase shift film pattern are formed in this order on a transparent substrate,

7. A phase shift mask for a photomask, in which a light shielding film pattern and a phase shift film pattern are formed in this order on a transparent substrate,