JP2002062638A - Mask blank, photomask, pattern forming method and method for producing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a halftone mask or a photomask having high transparency and high light resistance in photolithography using a short-wavelength light source. SOLUTION: A mask blank or a photomask is formed on a transparent substrate with a thin film comprising a monolayer or two or more layers, and one or more layers of the thin film are made of an aluminum compound. A compound containing a nitrogen atom besides an aluminum atom is used as the aluminum compound. A compound containing an oxygen atom besides aluminum and nitrogen atoms may be used as the aluminum compound. A compound containing a silicon atom besides aluminum, nitrogen and oxygen atoms may further be used as the aluminum compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a photomask used for lithography in LSI manufacture.
More specifically, the present invention relates to a mask blank or a photomask capable of improving the resolution of a pattern with respect to exposure light having a short wavelength after excimer laser exposure, and a pattern forming method using the same.

[0002]

2. Description of the Related Art As the degree of integration of a semiconductor integrated circuit increases and the line width of a pattern becomes finer, when a fine pattern is projected and exposed, light passing through a light transmitting portion of a mask in a close pattern. Are diffracted and interfere with each other, so that the light spills to the unexposed portion, the contrast of the optical image is reduced, and the transferred resist pattern is not separated and resolved. As a countermeasure against this problem, shortening the wavelength of the exposure light source and adoption of a phase shift mask are being studied.

The phase shift mask improves the resolution of a fine pattern by giving a phase difference of 180 degrees to the phase of projection light transmitted through a pattern adjacent to the mask. In other words, by providing a phase shift section on one side of the adjacent light transmission section, when transmitted light is diffracted and interferes with each other, the phase is inverted so that the light intensity at the boundary is weakened and the optical image contrast is improved. As a result, the transfer pattern is separated and resolved. Since this relationship is established before and after the focus, even if the focus is slightly shifted, the resolution is improved as compared with the conventional exposure method, and the focus latitude is improved.

[0004] The phase shift method described above is based on IBM's Leve.
It is proposed by Nson et al. and described in JP-A-58-173744 and, in principle, JP-B-62-50811.
When the pattern is formed of a light-shielding layer, a phase shift portion is provided on one side of the opening adjacent to the light-shielding pattern and the phase is inverted (Levenson-type phase shift mask, or Alternativ
e type phase shift mask). On the other hand, when the light-shielding layer is slightly translucent to be made a translucent layer and the phase of the transmitted light is inverted by the translucent film, a similar resolution improving effect is obtained. This is effective for improving the resolution of the pattern. A phase shift mask having such a translucent film (halftone film) is generally called a halftone type phase shift mask (or an attenuated type phase shift mask). (Hereinafter, a halftone type phase shift mask is abbreviated as a halftone mask.) The halftone mask is described in U.S. Pat. No. 4,890,309.

The halftone mask technique is not limited to a single-layer halftone mask formed by patterning a translucent film having a phase shift effect, but also to a layer made of a relatively light-shielding thin film. A two-layer type or a multi-layer type halftone mask developed from a two-layer type has been proposed, in which layers composed of thin films having high transparency are separately laminated to form a mask blank and then a mask pattern is formed. (Hereinafter, the two-layer type will be described as a representative of the multilayer type.)

Needless to say, in order to improve the resolution of a transfer pattern by using a halftone mask, both the phase difference of the halftone layer with respect to the air layer and the target value of the transmittance are required for both the single-layer type and the multilayer type. Need to achieve. In order to maximize the resolution improvement effect, the phase difference must be substantially 180 degrees. On the other hand, it is said that the transmittance is usually about 5 to 10%, which is the most effective in improving the resolution. Actual specifications slightly differ depending on the exposure conditions and the resist process on the wafer. Come.

As a photomask blank material, a Cr film is mainly used in conventional masks and Levenson type phase shift masks. At present, MoSi films are mainly used for halftone masks for KrF lithography.

[0008]

As the exposure wavelength becomes shorter, the following two problems occur in the halftone mask. The first problem is that the transparency of the thin film used for the halftone mask at the exposure wavelength is reduced. When the exposure wavelength is shortened, light absorption in the thin film increases, and a desired transmittance may not be obtained. The second point is that when the halftone mask is irradiated with exposure light for a long time, the halftone thin film is deteriorated by irradiation. When the exposure wavelength is shortened, the photon energy of the exposure light increases, so that deterioration due to irradiation appears more remarkably.

When light resistance to exposure light is insufficient when using a mask with a pattern, the light-shielding property of a conventional mask changes, and the transmittance and phase angle of a halftone mask change. . Therefore, every time these masks are used, there is a possibility that a change in an appropriate exposure amount, a decrease in dimensional accuracy, and a decrease in a focus margin may occur, or these may change during use. The tolerance is reduced and the pattern shape is deteriorated. This becomes a critical problem as the integration of semiconductor elements progresses and the pattern line width becomes finer. FIG. 3 shows a specific example. FIG. 3A shows a dimensional change (dashed line) and a focal depth change (solid line) of the projected image when the transmittance of the halftone phase shift mask changes. As the transmittance increases, the depth of focus increases, but the size decreases. The dimensions shown in the figure change slowly, but the effect is greater for finer dimensions. FIG. 3B shows the change in the depth of focus (solid line) and the amount of change in the best focus position (dashed line) when the phase change changes from the center reference point. In a halftone phase shift mask, as described above,
Changes in transmittance, and / or changes in phase difference will change the characteristics of the pattern transferred on the wafer,
This affects the yield of a semiconductor device manufacturing process that must be strictly controlled.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a mask blank or a photomask capable of improving the resolution of a pattern with respect to exposure light having a short wavelength after excimer laser exposure, and a photomask using the same. It is an object of the present invention to obtain a pattern forming method.

[0011]

According to a first aspect of the present invention, there is provided a mask blank in which a single layer or two or more thin films are formed on a transparent substrate. Among them, at least one layer is made of an aluminum compound.

The mask blank according to the invention of claim 2 is characterized in that the aluminum compound is a compound containing a nitrogen atom in addition to an aluminum atom.

[0013] The mask blank according to the invention of claim 3 is characterized in that the compound is a compound containing an oxygen atom in addition to an aluminum atom and a nitrogen atom.

A mask blank according to a fourth aspect of the present invention is characterized in that the compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom and an oxygen atom.

According to a fifth aspect of the present invention, in the mask blank, the thickness and the component ratio of the thin film of the aluminum compound, and the type and thickness of the other thin film of the two or more thin films are adjusted. , Substantially 180 for a given transmitted light
° and a desired transmittance.

The photomask according to the invention of claim 6 is:
In a photomask in which a single layer or two or more layers of thin films are patterned on a transparent substrate, at least one layer of the single layer or two or more layers of thin films is an aluminum compound.

The photomask according to the invention of claim 7 is:
The aluminum compound, in addition to the aluminum atom,
It is a compound containing a nitrogen atom.

The photomask according to the invention of claim 8 is:
The compound is a compound containing an oxygen atom in addition to an aluminum atom and a nitrogen atom.

According to a ninth aspect of the present invention, there is provided a photomask comprising:
The compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom, and an oxygen atom.

According to a tenth aspect of the present invention, in the photomask, the thickness and the component ratio of the aluminum compound thin film, and the type and thickness of the other thin film of the two or more thin films are adjusted. , Substantially 180 for a given transmitted light
° and a desired transmittance.

According to a eleventh aspect of the present invention, there is provided a pattern forming method including a step of exposing a desired pattern to a resist film using a photomask and a step of developing the resist film. It is characterized by using a photomask in which a single layer or a thin film of two or more layers composed of an aluminum compound is patterned.

In a twelfth aspect of the present invention, the pattern forming method is characterized in that the aluminum compound is a compound containing a nitrogen atom in addition to an aluminum atom.

The pattern forming method according to the invention of claim 13 is characterized in that the compound is a compound containing an oxygen atom in addition to an aluminum atom and a nitrogen atom.

A pattern forming method according to a fourteenth aspect is characterized in that the compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom and an oxygen atom.

According to a fifteenth aspect of the present invention, in the step of exposing a desired pattern on the resist film using the photomask, a wavelength of a light source used for the exposure is 200 nm or less and 10 nm or more. It is a feature.

According to a sixteenth aspect of the present invention, a method of manufacturing a semiconductor device includes a step of forming a pattern by any one of the above-described pattern forming methods.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the features of the present invention will be described. In the present invention, a compound containing aluminum and nitrogen is used as a mask blank for a halftone mask or a thin film material for a photo. In addition, a compound containing oxygen in addition to aluminum and nitrogen is used. Further, a compound containing silicon in addition to aluminum, nitrogen, and oxygen is used.

Next, the operation in such a configuration will be described. By using a compound containing aluminum and nitrogen as a thin film material of a mask blank of a halftone mask, transparency is increased even with a short-wavelength light source, and a high transmittance is obtained even when the exposure wavelength is 200 nm or less. . Since aluminum nitride has a high refractive index, the thickness required for inverting the phase can be reduced. Also, aluminum nitride is mechanically and chemically stable, so mask blanks using a compound containing aluminum and nitrogen have excellent chemical resistance,
Also excellent in irradiation resistance by exposure light source.

When a halftone mask is formed using a thin film of a compound containing aluminum and nitrogen, a sufficient transmittance for exposure light having a short wavelength can be obtained. Therefore, when the halftone mask is used to form a pattern by exposing with a short wavelength light source, the resolution is improved. Further, since the thin film is stable against exposure light exposure,
Even if this halftone mask is used for long-term exposure, the mask is not deteriorated, and the resist pattern can be stably transferred. These effects are obtained when the exposure wavelength is 200
It is most remarkable when it is less than nm.

When a thin film is formed using a compound containing oxygen in addition to aluminum and nitrogen, the transparency is further improved as compared with a case where no oxygen is contained. When a thin film is formed using a compound to which silicon is added in addition to aluminum, nitrogen, and oxygen, the transparency is further increased as compared with the case where silicon is not added. Hereinafter, specific embodiments will be described.

Embodiment 1 Al target and Ar
An AlN _x thin film having a thickness of 100 nm was deposited on a quartz substrate by reactive sputtering in which N ₂ was added. The optical constant of this thin film was measured with an ellipsometer, and the transmittance was measured with a spectrophotometer in the vacuum ultraviolet region. Wavelength 19
The refractive index at 3 nm is 2.42 and the attenuation coefficient is 0.0
It was 4. The transmittance at a wavelength of 193 nm is 6
0.5%. The phase difference between the air layer and the thin film is 18
The film thickness at which the angle reaches 0 ° can be estimated to be 55 nm. When the thin film was irradiated with an ArF excimer laser, no deterioration of the thin film was observed. It also has sufficient resistance to alkaline solutions and acids.

Therefore, if mask blanks made of the above materials are used, sufficient transparency as a halftone thin film material at an exposure wavelength of 193 nm can be obtained. Furthermore, if the above-mentioned thin film and a thin film for adjusting transmittance are used in combination, a halftone mask blank having a desired transmittance can be produced.

The thin film is effective not only for use as a halftone at an exposure wavelength of 193 nm, but also for exposure light of other wavelengths. In particular, 10n at 200nm or less
It has excellent transparency to exposure light having a wavelength of m or more.
The composition of the thin film is AlN _x , but may be a mixture with other atoms. As a method of making the thin film,
Although the reactive sputtering method is used, another film formation method such as a vacuum evaporation method may be used.

Embodiment 2 Al target and Ar
An AlO _x N _y thin film having a thickness of 100 nm was deposited on a quartz substrate by reactive sputtering in which O ₂ and N ₂ were added. The optical constant of this thin film was measured with an ellipsometer, and the transmittance was measured with a spectrophotometer in the vacuum ultraviolet region. The refractive index at a wavelength of 193 nm was 1.96, and the attenuation coefficient was 0.02. The transmittance at a wavelength of 193 nm was 75.4%. The thickness at which the phase difference between the air layer and the thin film becomes 180 ° can be estimated to be 82 nm. When the thin film was irradiated with an ArF excimer laser, no deterioration of the thin film was observed. It also has sufficient resistance to alkaline solutions and acids.

Therefore, if a mask blank made of the above material is used, sufficient transparency as a halftone thin film material at an exposure wavelength of 193 nm can be obtained. Furthermore, if the above-mentioned thin film and a thin film for adjusting transmittance are used in combination, a halftone mask blank having a desired transmittance can be produced.

The thin film is effective not only for use as a halftone at an exposure wavelength of 193 nm but also for exposure light of other wavelengths. In particular, 10n at 200nm or less
It has excellent transparency to exposure light having a wavelength of m or more.
The composition of the thin film is AlO _x N _y , but may be a mixture with other atoms. Although a reactive sputtering method is used as a method for forming the thin film, other film forming methods such as a vacuum evaporation method may be used.

Embodiment 3 A thin film of AlSi _x O _y N _z having a thickness of 100 was formed on a quartz substrate by reactive sputtering using Al and Si as targets and adding O ₂ and N ₂ to Ar.
Deposited in nm thickness. The optical constant of this thin film was measured with an ellipsometer, and the transmittance was measured with a spectrophotometer in the vacuum ultraviolet region. The refractive index at a wavelength of 193 nm is 1.89.
And the attenuation coefficient was 0.02. In addition, the wavelength 193n
The transmittance at m was 79.5%. The thickness at which the phase difference between the air layer and the thin film becomes 180 ° can be estimated to be 88 nm. When the thin film was irradiated with an ArF excimer laser, no deterioration of the thin film was observed. It also has sufficient resistance to alkaline solutions and acids. The transmittance at 157 nm is 30.5%,
Even F ₂ halftone excimer laser lithography is effective.

Therefore, if mask blanks made of the above materials are used, sufficient transparency as a halftone thin film material at an exposure wavelength of 193 nm can be obtained. Furthermore, if the above-mentioned thin film and a thin film for adjusting transmittance are used in combination, a halftone mask blank having a desired transmittance can be produced.

The above thin film has an exposure wavelength of 193 nm and a wavelength of 1 nm.
Not only for use as a halftone at 57 nm,
It is also effective for exposure light of other wavelengths. In particular, 200
It is excellent in transparency to exposure light having a wavelength of 10 nm or less and 10 nm or less. The composition of the thin film is AlSi _x O _y
Although it is N _z , it may be a mixture with other atoms. Although a reactive sputtering method is used as a method for forming the thin film, other film forming methods such as a vacuum evaporation method may be used.

Embodiment 4 FIG. A with Cr as the target
A Cr film having a thickness of 10 nm is deposited on a quartz substrate by reactive sputtering using r, and a thin film of AlN _x is formed to a thickness of 50 nm by reactive sputtering using Al as a target and adding N ₂ to Ar. Deposited to create halftone mask blanks. A desired pattern is formed on the halftone mask blanks by electron beam direct writing, and Al is formed by reactive ion etching.
The N _x film and Cr film is etched to create the halftone mask shown in FIG. The transmittance for exposure light of 193 nm was 6%, and the phase difference was 180 °.

Using the above mask, a resist pattern of 0.15 μm holes could be transferred with an ArF excimer laser exposure machine. With an aperture ratio NA of 0.60, σ 0.3
Exposure was performed under the following conditions. After irradiating the mask with 1 × 10 ⁸ pulses of ArF light, a resist pattern of 0.15 μm holes was transferred using an ArF excimer laser exposure machine.
The dimensional fluctuation was 1 nm or less, and a pattern could be formed stably.

Therefore, when a pattern is formed using a photomask using the above-described materials, a stable resist pattern can be transferred even if the mask is used for a long period of time. The photomask is used as a halftone mask for ArF exposure, by adjusting the thickness of the Cr film can be used in F ₂ exposure or other exposure wavelength. The photomask is used a two-layer structure of AlN _x film and the Cr film, in addition to Cr film may be a film, such as Al or W, or TA. Alternatively, a single layer film of only the AlN _x film may be used. Although a reactive sputtering method is used as a method for forming the thin film, other film forming methods such as a vacuum evaporation method may be used.

Embodiment 5 FIG. Al target and Ar
A thin film of AlO _x N _y is formed on a quartz substrate to a thickness of 80 n by reactive sputtering using a gas obtained by adding O ₂ and N ₂ to the substrate.
m to form a halftone mask blank. Next, a desired pattern with an electron beam direct writing formed on the halftone mask blank, the AlO _x N _y film by reactive ion etching and etched to create a halftone mask shown in FIG. Fifteen
The transmittance for exposure light of 7 nm is 5%, and the phase difference is 18%.
0 °.

Using the above mask, a resist pattern having a hole of 0.13 μm could be transferred by an F ₂ laser exposure machine. Exposure was performed with an aperture ratio NA of 0.60 and a condition of σ 0.3. After irradiating the mask with 1 × 10 ⁸ pulses of F ₂ laser light, a resist pattern of 0.13 μm holes was transferred with an F ₂ laser exposure machine. We were able to.

Therefore, when a pattern is formed using a photomask using the above-described materials, a stable resist pattern can be transferred even if the mask is used for a long period of time. The photomask was used as a halftone mask for F ₂ exposure, but the O and N of the AlO _x N _y film were used.
By adjusting the ratio, ArF exposure or other exposure wavelengths can be used. The photomask has a single-layer structure, but may have a multi-layer structure in combination with a film of Cr, Al, W, or Ta. Although a reactive sputtering method is used as a method for forming the thin film, other film forming methods such as a vacuum evaporation method may be used.

[0046]

As described above, according to the present invention,
By using a compound containing aluminum and nitrogen as the thin film material of the mask blank of the halftone mask, the transparency becomes high even for a short-wavelength light source. Particularly, when the exposure wavelength is 200 nm or less, sufficient transmittance is obtained. A halftone mask having the same can be easily created. Accordingly, a halftone mask of the present invention when applied to a lithography using short wavelength light source such as F ₂ lasers, it is possible to form a very fine resist pattern. In addition, compounds containing aluminum and nitrogen are stable against short-wavelength light irradiation. Even if a halftone mask using the compound is used for a long time in mass production, the halftone mask does not deteriorate and is always stable. It is possible to form a suitable resist pattern.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a photomask according to a fourth embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a photomask according to a fifth embodiment of the present invention.

FIG. 3 is a diagram for explaining a problem in a conventional photomask.

[Explanation of symbols]

101, 201 mask substrate, 102 Cr film, 103 AlN _x film, 202 AlO _x N _y film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/027 H01L 21/30 502P

Claims (16)

[Claims] 1. A mask blank in which a single layer or two or more thin films are formed on a transparent substrate, wherein at least one or more of the single layer or two or more thin films is an aluminum compound. Mask blanks. 2. The mask blank according to claim 1, wherein the aluminum compound is a compound containing a nitrogen atom in addition to the aluminum atom. 3. The mask blank according to claim 2, wherein the aluminum compound is a compound containing an oxygen atom in addition to an aluminum atom and a nitrogen atom. 4. The mask blank according to claim 3, wherein the aluminum compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom, and an oxygen atom. 5. Adjusting the thickness and component ratio of the thin film of the aluminum compound and the type and thickness of the other thin film of the two or more thin films to substantially reduce the predetermined transmitted light. The photomask blank according to any one of claims 1 to 4, wherein a phase difference of 180 ° is generated, and a desired transmittance is obtained. 6. A photomask in which a single layer or two or more layers of thin films are patterned on a transparent substrate, wherein at least one of the single layers or two or more layers of thin films is an aluminum compound. Photomask. 7. The photomask according to claim 6, wherein the aluminum compound is a compound containing a nitrogen atom in addition to the aluminum atom. 8. The photomask according to claim 7, wherein said aluminum compound is a compound containing oxygen atoms in addition to aluminum atoms and nitrogen atoms. 9. The photomask according to claim 8, wherein said aluminum compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom and an oxygen atom. 10. Adjusting the thickness and component ratio of the thin film of the aluminum compound, and the type and thickness of the other thin film of the two or more thin films to substantially reduce the predetermined transmitted light. The photomask according to any one of claims 6 to 9, wherein a phase difference of 180 ° is generated, and a desired transmittance is obtained. 11. A pattern forming method comprising: exposing a desired pattern on a resist film using a photomask; and developing the resist film.
A pattern forming method, comprising using a photomask in which a single layer or two or more thin films in which at least one layer is made of an aluminum compound is patterned. 12. The pattern forming method according to claim 11, wherein the aluminum compound is a compound containing a nitrogen atom in addition to the aluminum atom. 13. The pattern forming method according to claim 12, wherein the aluminum compound is a compound containing an oxygen atom in addition to an aluminum atom and a nitrogen atom. 14. The aluminum compound according to claim 13, wherein the aluminum compound is a compound containing a silicon atom in addition to an aluminum atom, a nitrogen atom and an oxygen atom.
The pattern forming method described in the above. 15. The method according to claim 11, wherein in the step of exposing a desired pattern on the resist film using the photomask, the wavelength of a light source used for the exposure is 200 nm or less and 10 nm or more. Or a pattern forming method. 16. A method for manufacturing a semiconductor device, comprising: forming a pattern by the pattern forming method according to claim 11. Description: