JP3241793B2 - Phase shift photomask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photomask used for manufacturing high-density integrated circuits such as LSIs and VLSIs, and more particularly to a phase shifter having a phase shift layer for forming a fine pattern with high precision. It relates to a shift photomask.

[0002]

2. Description of the Related Art Semiconductor integrated circuits such as ICs, LSIs, and VLSIs apply a resist on a substrate to be processed such as a Si wafer, expose a desired pattern by a stepper or the like, and then perform development and etching. It is manufactured by repeating a lithography process.

A photomask called a reticle used in such a lithography process tends to be required to have higher and higher precision in accordance with higher performance and higher integration of a semiconductor integrated circuit. DRA which is LSI
Taking M as an example, the dimensional deviation of a 5 × reticle for a 1M bit DRAM, that is, a reticle having a size 5 times the size of a pattern to be exposed, is an average ± 3σ (σ is a standard deviation). Also, an accuracy of 0.15 μm is required. Similarly, a quintuple reticle for a 4 Mbit DRAM has a dimensional accuracy of 0.1 to 0.15 μm,
5x reticle for bit DRAM is 0.05-0.1μm
Dimensional accuracy is required.

Furthermore, the line width of a device pattern formed using these reticles is 1 Mbit DRAM.
1.2 μm, 0.8 μm for 4 Mbit DRAM, 1 μm
A 6-Mbit DRAM is required to be further miniaturized to 0.6 μm, and various exposure methods are being studied to meet such a demand.

However, in the case of the next-generation device pattern of, for example, a 64-Mbit DRAM class, the resolution of a resist pattern is limited by the conventional stepper exposure method using a reticle.
No. 44, Japanese Patent Publication No. 62-59296, and the like, a reticle based on a new concept called a phase shift mask has been proposed. Phase shift lithography using this phase shift reticle is a technique for improving the resolution and contrast of a projected image by manipulating the phase of light passing through the reticle.

[0006] Phase shift lithography will be briefly described with reference to the drawings. FIG. 3 is a diagram showing the principle of the phase shift method,
FIG. 4 is a view showing a conventional method, and FIG. 3 (a) and FIG.
(A) is a cross-sectional view of the reticle, and (b) and (b) of FIG.
3 (c) and 4 (c) show the light amplitude on the wafer, and FIGS. 3 (d) and 4 (d) show the light intensity on the wafer, respectively. A substrate 2, a light shielding film 3, a phase shifter 3, and an incident light 4 are shown.

In the conventional method, as shown in FIG. 4A, a light-shielding film 2 made of chrome or the like is formed on a substrate 1 made of quartz glass or the like, and a light transmitting portion having a predetermined pattern is formed. However, in phase shift lithography, as shown in FIG. 3A, a phase shifter 3 composed of a transmission film for inverting the phase (a phase difference of 180 °) is provided on one of the adjacent light transmission portions on the reticle. Is provided.
Accordingly, in the conventional method, the amplitude of the light on the reticle is in phase as shown in FIG. 4B, and the amplitude of the light on the wafer is also in phase as shown in FIG. 4C. While the pattern on the wafer cannot be separated as shown in FIG. 4D, in phase shift lithography, the light transmitted through the phase shifter
As shown in FIG. 3B, since the phases are made opposite to each other between the adjacent patterns, the light intensity becomes zero at the boundary of the patterns, and the adjacent patterns are clearly separated as shown in FIG. 3D. be able to. As described above, in the phase shift lithography, a pattern that cannot be separated conventionally can be separated and the resolution can be improved.

Next, one of the manufacturing steps of the phase shift reticle
An example will be described with reference to the drawings. FIG. 5 is a cross-sectional view showing a manufacturing process of the phase shift reticle, in which 11 is a quartz substrate, 12 is a chromium film, 13 is a resist layer, 14 is ionizing radiation, 15 is a resist pattern, 16 is an etching gas plasma, Reference numeral 17 denotes a chromium pattern, 18 denotes an oxygen plasma, 19 denotes a transparent film, 20 denotes a resist layer, 21 denotes ionizing radiation, 22 denotes a resist pattern, 23 denotes an etching gas plasma, 24 denotes a phase shift pattern, and 25 denotes an oxygen plasma.

First, as shown in FIG. 5A, a chromium film 12 is formed on a quartz substrate 11 which has been optically polished.
An ionizing radiation resist such as chloromethylated polystyrene is uniformly applied by a conventional method such as spin coating,
A heat drying process is performed to form a resist layer 13 having a thickness of about 0.1 to 2.0 μm. The heating and drying treatment is usually performed at ± 80 to 150 ° C., depending on the type of resist used.
Perform for about 20 to 60 minutes.

Next, as shown in FIG. 1B, a pattern is drawn on the resist layer 13 with an ionizing radiation 14 using an exposure device such as an electron beam drawing device according to a conventional method, and an organic solvent such as ethyl cellosolve or ester is drawn. After development with a developer as a main component, rinsing with alcohol is performed to form a resist pattern 15 as shown in FIG.

Next, heat treatment and descum treatment are performed as necessary to remove unnecessary resist such as resist dust and whiskers remaining on the edge portion of the resist pattern 15, and the like, as shown in FIG. As shown, the resist pattern 1
The chromium layer 12 is dry-etched with the etching gas plasma 16 to form a chromium pattern 17. It is obvious to those skilled in the art that the chromium pattern 17 may be formed by wet etching instead of dry etching by the etching gas plasma 16.

After etching as described above, the resist pattern 15, ie, the remaining resist is ashed and removed by oxygen plasma 18 as shown in FIG. Complete the mask. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 18.

Subsequently, the photomask is inspected, a pattern is corrected if necessary, and the photomask is washed. Then, as shown in FIG.
_A transparent film 19 made of ₂ or the like is formed. Next, FIG.
As shown in FIG. 2, an ionizing radiation resist layer 2 such as chloromethylated polystyrene is formed on the transparent film 19 in the same manner as described above.
0 is formed, and as shown in FIG.
Then, an alignment is performed according to a conventional method, a predetermined pattern is drawn by ionizing radiation 21 such as an electron beam exposure apparatus, developed and rinsed to form a resist pattern 22 as shown in FIG.

Next, if necessary, a heating process and a descum process are performed, and as shown in FIG. 1K, the transparent film 19 exposed from the opening of the resist pattern 22 is etched with an etching gas plasma. Dry etching is performed by using 23 to form a phase shifter pattern 24. Note that the phase shifter pattern 24 may be formed by wet etching instead of dry etching by the etching gas plasma 23.

Next, the remaining resist is ashed and removed by oxygen plasma 25 as shown in FIG. Through the above steps, a phase shift mask having the phase shifter 24 as shown in FIG.

In the above-described conventional method for manufacturing a phase shift reticle, the etching control in the depth direction of the transparent film 19 forming the phase shifter must be performed accurately. In particular, since the substrate 11 and the transparent film 19 are made of the same SiO ₂ -based material, if the etching is continued even after the etching of the transparent film 19 is completed,
Is also etched, and the phase shift amount of the phase shifter becomes larger than 180 °, making it difficult to transfer an accurate pattern.

Therefore, an etching stopper layer made of a metal fluoride such as MgF ₂ is provided between the transparent film and the substrate,
It is conceivable that the etching is automatically stopped by this layer (JP-A-4-34587). Metal fluorides such as MgF ₂ have high transparency in the ultraviolet region, high hardness, and excellent etching selectivity.

[0018]

However, in the case where such an etching stopper layer made of metal fluoride is formed by a sputtering method, if the metal fluoride is used as a target and the sputtering is performed, the composition of the formed film is actually reduced. Has a problem that the stoichiometric ratio deviates from the stoichiometric ratio and contains a large amount of metal, so that the transmittance is reduced to, for example, 60% or less. To prevent this, fluorine may be mixed with an inert gas of a sputtering gas and sputtering may be performed in the mixed gas. However, fluorine is not possible because it affects a sputtering apparatus.

The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an etching stopper layer having excellent etching selectivity, capable of stopping etching automatically and reliably, and having high hardness. Another object of the present invention is to provide a phase shift photomask using a film made of a material having excellent transparency.

[0020]

In view of the above problems, the present invention has been studied to develop a practical and accurate phase shift reticle phase shifter. As a result, oxygen is mixed with an inert gas as a sputtering gas. The metal fluorinated oxide film formed by being sputtered therein has excellent etching selectivity almost in the same manner as the metal fluoride, has good transparency in the ultraviolet region, and has high hardness. The present invention has been completed based on the findings.

That is, the phase shift photomask of the present invention comprises a phase shift photomask having a substrate and a phase shifter pattern made of a material containing silicon oxide as a main component and provided directly or directly on the surface thereof through a light-shielding pattern. In the mask, MgF _2-2x O _y , CaF _2-2x O _{y
y, LiF 2-2x O y, BaF} 2-2x O y, La 2 F 6-2x O
_It is provided with a film made of _y or Ce ₂ F _6-2x O _y , wherein x satisfies 0.1 to 0.5 and y satisfies 0 <y ≦ x.

[0022]

In the phase shift photomask of the present invention,
MgF _2-2x O _y , CaF _2-2x O _y , LiF
_{2-2x O y, BaF 2-2x O y} , La 2 F 6-2x O y or Ce
_Since a film made of ₂ F _6-2x O _y is provided, x satisfies 0.1 to 0.5, and y satisfies 0 <y ≦ x, when forming a phase shifter pattern by etching, MgF is used.
_{2-2x O y, CaF 2-2x O y} , LiF 2-2x O y, BaF
_{2-2x O y, La 2 F 6-2x} O y or _{Ce 2} F 6-2x O _y acts as an etching stopper layer, with a phase shifter transparent film can be surely etched, automatically etching Can be stopped, resulting in a higher quality phase shift photomask. Further, since the film has good transparency in an ultraviolet region, it is suitable for a phase shift photomask using ultraviolet light, and further, has high hardness,
The phase shift photomask produced in this way has little deterioration due to the environment and has a long life.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The phase shift photomask of the present invention is used as an etching stopper layer between a substrate and a transparent film for a phase shifter, as MgF _2-2x O _y , CaF _2-2x O _y , LiF _{2-2x.
O y, BaF 2-2x O y,} La 2 F 6-2x O y, Ce 2 F
In which characterized in that a film made of _6-2x O _y. Hereinafter, embodiments of the phase shift photomask of the present invention will be described while describing a method of manufacturing the phase shift photomask.

FIG. 1 is a cross-sectional view showing the steps of a method for manufacturing a photomask having a phase shift layer (phase shift photomask) according to the present invention. In FIG.
_{gF 2-2x O y, CaF 2-2x O} y, LiF 2-2x O y, Ba
An etching stopper layer made of F _2-2x O _y , La ₂ F _6-2x O _y or Ce ₂ F _6-2x O _y , 32 a light shielding layer, 33 a resist layer, 34 an ionizing radiation, 35 a resist pattern, 36 is an etching gas plasma, 37 is a light shielding pattern, 38 is an oxygen plasma, 39 is a transparent film, 40 is a resist layer, 41 is ionizing radiation, 42 is a resist pattern,
3 is a reactive ion, 44 is a phase shift pattern, and 45 is oxygen plasma.

First, as shown in FIG. 1A, a uniform etching stopper layer 31 having a thickness of 10 to 200 nm and a light shielding layer 32 having a thickness of 10 to 200 nm are sequentially formed on an optically polished substrate 30. And an ionizing radiation resist, such as chloromethylated polystyrene, is uniformly applied by a conventional method such as spin coating, and is subjected to a heat-drying treatment.
A resist layer 33 having a thickness of about 1 to 2.0 μm is formed. Here, considering that the phase shift mask is for a short wavelength such as an i-line or an excimer laser, quartz or high-purity synthetic quartz is desirable as the substrate 30, but other than that, low expansion glass, white plate, Blue plate (SL), MgF ₂ , Ca
It can be used F ₂ and the like. The etching stopper layer 31 is made of MgF _2-2x O _y , CaF _2-2x O _y , L
_{iF 2-2x O y, BaF 2-2x O} y, La 2 F 6-2x O y, C
It can be formed using the _{e 2} F 6-2x O _y. Here, x is desirably in the range of 0.1 to 0.5, and y is desirably in the range of y ≦ x. When argon is used as a sputtering gas, x and y in this range can be obtained by mixing 20% or less of oxygen. Can be

Further, the light-shielding layer 32 can be formed by forming a chromium thin film in a single layer or a multi-layer. Can be formed. The heating and drying of the resist is usually ± 80 to 150 ° C., depending on the type of the resist.
For about 20 to 60 minutes.

Next, as shown in FIG. 2B, a predetermined pattern is drawn on the resist layer 33 by an exposure device using ionizing radiation 34 such as an electron beam drawing device according to a conventional method. After developing with a developing solution containing an organic solvent as a main component, rinsing with an alcohol forms a resist pattern 35 as shown in FIG.

Next, if necessary, heat treatment and descum treatment are performed to remove unnecessary resist such as resist dust and whiskers remaining at the edge portion of the resist pattern 35, as shown in FIG. Then, the processed portion exposed from the opening of the resist pattern 35, that is, the light-shielding layer 32 is dry-etched by the etching gas plasma 36 to form the light-shielding pattern 37. Note that this light-shielding pattern 3
It is obvious to those skilled in the art that the formation of 7 may be performed by wet etching instead of dry etching by the etching gas plasma 36.

After etching as described above, the remaining resist 35 is ashed and removed by oxygen plasma 38 as shown in FIG.
A photomask in which an etching stopper layer 31 is formed on a substrate 30 and a predetermined light shielding pattern 37 is formed thereon is formed. Note that this process can be performed by solvent stripping instead of the incineration process using the oxygen plasma 38.

Subsequently, the photomask is inspected, and if necessary, the pattern is modified and washed, and then, as shown in FIG. 9G, evaporation is performed on the light-shielding pattern 37 by spin-on-glass (SOG). A transparent film 39 mainly composed of SiO ₂ is formed. The thickness d of the transparent film 39 is a value given by d = λ / 2 (n−1), where n is the refractive index of the material forming the transparent film 39 and λ is the exposure wavelength.
When SOG is used, the value of d is about 406 nm.

Next, as shown in FIG.
9, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied to form a resist layer 40 in the same manner as described above, and as shown in FIG. Alignment is performed, a predetermined pattern is drawn at a position where the phase is to be shifted by ionizing radiation 41 of an electron beam exposure device or the like, developed and rinsed with a predetermined developing solution, and the resist is exposed as shown in FIG. The pattern 42 is formed.

Subsequently, after performing a heat treatment and a descum treatment as necessary, the transparent film 39 exposed from the opening of the resist pattern 42 is exposed to CF as shown in FIG.
₄ , dry etching is performed by reactive ion etching using reactive ions 43 using C ₂ F ₆ , CHF ₃ + O ₂ and a mixed gas thereof to form a phase shift pattern 44.

At this time, in the conventional method, the etching reaches the substrate 30 and it is difficult to determine the end point of the etching, or the substrate 30 is also etched, and the phase shift amount of the phase shifter is larger than 180 °. However, there was a problem that it was difficult to transfer an accurate pattern, but in the present invention, etching resistance to the fluorine-based reactive ions is large,
MgF _2-2x O _y , CaF _2-2x O _y , L
_{iF 2-2x O y, BaF 2-2x O} y, La 2 F 6-2x O y, C
Since the _{e 2} F 6-2x O _y is used as an etching stopper layer 31, it is possible to reliably etch the transparent film 39, automatically etching can be stopped, the higher quality phase shift photo A mask can be created.

Next, as shown in FIG. 1 (l), the remaining resist is ashed and removed by oxygen plasma 45. As a result, a highly accurate phase shift photomask as shown in FIG. This process can be performed by solvent stripping instead of the ashing process using the oxygen plasma 45.

Now, such an etching stopper layer can be applied not only to the phase shift photomask of the phase shifter upper type as shown in FIG. 3 but also to the phase shifter lower type phase shift photomask. Part 1
As an example, a brief description will be given of a case where the etching stopper layer is applied to a self-alignment type phase shift photomask proposed by the present applicant in Japanese Patent Application No. 2-181795.

FIG. 2 is a cross-sectional view showing a process for manufacturing such a phase shift photomask.
51 _{MgF 2-2x O y, CaF 2-2x O} y, LiF 2-2x O
_y , BaF _2-2x O _y , La ₂ F _6-2x O _y or Ce ₂ F
An etching stopper layer made of _6-2x O _y, 52 is a transparent film, the light-shielding thin film 53, 54 is a resist layer, 55 is a resist pattern, the ionizing radiation 56, 57 is an etching gas plasma, the light shielding pattern 58, 59 Oxygen plasma, 60 indicates a resist layer, 61 indicates back exposure, 62 indicates reactive ions, 63 indicates a phase shifter pattern, and 64 indicates oxygen plasma.

First, as shown in FIG. 2A, a uniform etching stopper layer 51 having a thickness of 10 to 200 nm and an SiO film having a film thickness d = λ / 2 (n−1) are formed on an optically polished substrate 50. Transparent film 52 mainly composed of ₂ and 50 to 200 nm
Are sequentially formed to form a photomask blank.

Next, an ionizing radiation resist such as chloromethylated polystyrene is uniformly applied on the photomask blanks by a conventional method such as spin coating, and is subjected to a heat-drying treatment to have a thickness of about 0.1 to 2.0 μm. A resist layer 54 is formed.

Here, as the substrate 50, considering that the phase shift mask of the present invention is usually for a short wavelength such as i-line or excimer laser, quartz, high-purity quartz,
It is preferable to use MgF ₂ , CaF ₂ or the like. However, in the case of a longer wavelength, low expansion glass, white plate glass, blue plate glass, or the like may be used. The etching stopper layer 51 is made of MgF _2-2x O, as in the case of FIG.
_y , CaF _2-2x O _y , LiF _2-2x O _y , BaF
_{2-2x O y, La 2 F 6-2x} O y, is formed using a _{Ce 2} F 6-2x O _y. Here, x is 0.1 to 0.5, and y is y ≦
The range of x is desirable. The transparent film 52 is made of high-purity S
An iO ₂ film is preferable. As a coating method of this film, a sputtering method, a CVD method, or spin-on-glass coating (for example, siloxane is spin-coated and heated to form an SiO ₂ film) is employed. Further, the light-shielding layer 53 can be formed by forming a single-layer or multi-layer thin film of chromium, chromium nitride, chromium oxide, tungsten, molybdenum, molybdenum silicide, or the like.

The heating and drying treatment of the resist is usually carried out at 80 to 200 ° C. and 20 to 20 ° C., though it depends on the type of the resist.
Perform for about 60 minutes.

Next, as shown in FIG. 2B, a predetermined pattern is drawn on the resist layer 54 by an exposure device using ionizing radiation 56 such as an electron beam drawing device in accordance with a conventional method, and ethylcellosolve, ester or the like is drawn. After developing with a developing solution containing an organic solvent as a main component, rinsing with alcohol forms a resist pattern 55 as shown in FIG.

Next, if necessary, a heating process and a descum process are performed to remove unnecessary resist such as resist dust and whiskers remaining on the edge portion of the resist pattern 55 and the like, as shown in FIG. The portion to be processed exposed from the opening of the resist pattern 55, that is, the light shielding layer 53
Is dry-etched with an etching gas plasma 57 to form a light-shielding pattern 58 (FIG. 4D). In addition,
It is obvious to those skilled in the art that the formation of the light shielding pattern 58 may be performed by wet etching instead of dry etching by the etching gas plasma 57.

After etching as described above, the remaining resist 55 is ashed and removed by oxygen plasma 59 as shown in FIG.
An etching stopper layer 51 is formed on a substrate 50, a phase shift layer 52 is formed thereon, and a photomask on which a predetermined light shielding pattern 58 is formed is formed. Note that the removal of the remaining resist 55 can be performed by solvent stripping instead of the incineration by the oxygen plasma 59.

Subsequently, the photomask is inspected, if necessary, the pattern is modified, and after cleaning, the OFPR is placed on the light-shielding pattern 58 as shown in FIG.
A photoresist such as -800 is uniformly applied by a conventional method such as spin coating, and is subjected to a heat-drying treatment.
A resist layer 60 having a thickness of about 2 μm is formed.

Subsequently, the resist layer 60 is subjected to back exposure 61 from the glass substrate 50 side, developed with an alkaline aqueous solution containing tetramethylammonium hydroxide as a main component, rinsed with pure water, and A pattern with a resist pattern is formed.

Next, as shown in FIG. 2G, the portion to be processed exposed from the opening of the resist pattern, that is, the phase shift layer 52 is formed of CF ₄ , C ₂ F ₆ and CHF ₃ +.
Dry etching is performed by reactive ion etching using reactive ions 62 using O ₂ and a mixed gas thereof to form a phase shifter pattern 63 (FIG. 3H).

Subsequently, the substrate is treated with an etching solution containing ceric ammonium nitrate as a main component, and the light-shielding film 58 sandwiched between the phase shifter 63 and the resist 60 is side-etched. The amount of side etching depends on the type and size of the pattern, but is usually 0.1 to 0.5.
It is about μm.

After etching as described above, the remaining resist 60 is ashed and removed by oxygen plasma 64 as shown in FIG. 2I, and a self-aligned phase as shown in FIG. The shift mask is completed.

Also in this case, as in the case of FIG. 1, the etching resistance is high with respect to the fluorine-based reactive ions.
MgF _2-2x O _y , CaF _2-2x with excellent transparency and hardness
O _y , LiF _2-2x O _y , BaF _2-2x O _y , La ₂ F _6-2x
O _y , Ce ₂ F _6-2x O _y are etched to the stopper layer 51
Therefore, the transparent film 52 can be surely etched, and the etching can be stopped automatically, so that a higher quality phase shift photomask can be produced.

Although the phase shift photomask of the present invention has been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications can be made. Also,
The type of the phase shift photomask to which the etching stopper layer of the above-mentioned material can be applied is not limited to the above example, but can be applied to any conventionally known type, for example, a halftone phase shift photomask.

[0051]

As a photomask used for manufacturing a semiconductor integrated circuit, a photomask in which a light-shielding film such as a chromium film is patterned on a glass substrate such as quartz is used at present. In, the conventional exposure technology using a photomask is approaching its limit, and is shifting to a direction using a phase shift photomask.

The phase shift photomask according to the present invention
As described above, MgF _2-2x O _y , CaF
_{2-2x O y, LiF 2-2x O y} , BaF 2-2x O y, La 2 F
_6-2x O _y or consisting Ce ₂ F _6-2x O _y film is provided,
Since x satisfies 0.1 to 0.5 and y satisfies 0 <y ≦ x,
When creating a phase shifter pattern by etching,
MgF _2-2x O _y , CaF _2-2x O _y , LiF _2-2x O _y , B
aF _2-2x O _y , La ₂ F _6-2x O _y or Ce ₂ F _6-2x O _y
Acts as an etching stopper layer, and can reliably etch the phase shifter transparent film,
Since the etching can be stopped automatically, the phase difference can be guaranteed over the entire surface of the mask. Further, since the above film has good transparency in an ultraviolet region, it is suitable for a phase shift photomask using ultraviolet rays, and further has a high hardness. Less and longer life.

[Brief description of the drawings]

FIG. 1 is a sectional view showing steps of a method for manufacturing a phase shift photomask according to the present invention.

FIG. 2 is a cross-sectional view showing a step of manufacturing another phase shift photomask according to the present invention.

FIG. 3 is a diagram illustrating the principle of the phase shift method.

FIG. 4 is a diagram showing a conventional method.

FIG. 5 is a cross-sectional view showing a manufacturing process of a conventional phase shift photomask.

[Explanation of symbols]

 REFERENCE SIGNS LIST 30 substrate 31 etching stopper layer 32 light shielding layer 33 resist layer 34 ionizing radiation 35 resist pattern 36 etching gas plasma 37 light shielding pattern 38 oxygen plasma 39 transparent film 40 resist layer 41 ionizing radiation 42 resist pattern 43 reactive ions 44 phase shift pattern 45 oxygen plasma

Claims (1)

(57) [Claims] 1. A phase shift photomask having a phase shifter pattern composed of a silicon oxide provided or directly through the substrate and the light-shielding pattern on the surface of a material composed mainly, MgF the substrate surface _{2- 2x} O _y , Ca
F _2-2x O _y , LiF _2-2x O _y , BaF _2-2x O _y , La ₂
A film made of F _6-2x O _y or Ce ₂ F _6-2x O _y , wherein x satisfies 0.1 to 0.5, and y satisfies 0 < y ≦ x. Phase shift photomask.