JPH0334414A - X-ray mask material and x-ray mask - Google Patents

Abstract

PURPOSE:To restrain internal stress and improve fine workability by making an X-ray absorbing mask contain tantalum and nickel in the range of a specified atom number ratio (Ta/Ni). CONSTITUTION:X-ray mask material is constituted by forming in order an X-ray transmitting film and an X-ray absorbing film on a substrate. The X-ray absorbing film contains tantalum and nickel with an atom number ratio (Ta/Ni) of 3.0/7.0-5.0/5.0. The X-ray absorbing film containing tantalum and nickel can easily formed on a substrate at a low temperature by sputtering, and the internal stress of said film is small. When the atom number ratio is in the above range, the formed film is in the amorphous state or the fine crystal state having a grain diameter less than or equal to, e.g. 15nm, so that the film excellent in fine workability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an X-ray mask material and an X-ray mask used in X-ray lithography.

[Background Art] In the field of semiconductor industry, lithography technology is used as a technology for forming integrated circuits and the like consisting of fine patterns on silicon substrates and the like. This lithography technique
This is generally done as follows.

Exposure electromagnetic waves are irradiated onto a mask in which a button corresponding to the fine pattern of an integrated circuit or the like is formed using a metal or the like that has the function of absorbing exposure electromagnetic waves on a substrate that has the function of transmitting electromagnetic waves for exposure. As a result, the fine pattern of the mask is transferred to a resist coated on a silicon substrate or the like. Next, various steps such as etching, impurity implantation, and dielectric film fabrication are performed based on this resist pattern to form an integrated circuit or the like consisting of a fine pattern on a silicon substrate or the like.

Conventionally, a photolithography method has been used in which a fine pattern is transferred using visible light and ultraviolet light as electromagnetic waves for exposure. However, recently there has been a demand for technology to transfer smaller fine patterns that goes beyond the physical limits of visible and ultraviolet light, and in order to transfer such fine patterns, X-rays with shorter wavelengths have been Attempts have been made to use X-ray lithography as electromagnetic waves for exposure.

By the way, the X-ray mask material used in this X-ray lithography method consists of a substrate, a film with high X-ray transmittance formed on the substrate (hereinafter referred to as an "X-ray transparent film"), and an X-ray transparent film. It is composed of a film with a high X-ray absorption rate (hereinafter referred to as an X-ray absorption film) formed on top of the film. Generally, the X-ray transmitting film is an extremely thin film made of atoms with a small atomic number, and the X-ray absorbing film is an extremely thin film made of a metal or the like having a high X-ray absorption rate.

It goes without saying that the X-ray absorbing film must be made of a material with a high X-ray absorption rate, but it must also satisfy the following requirements. First, the internal stress is small. This is because, as mentioned above, the X-ray absorbing film is formed on an extremely thin X-ray transmitting film, so if the internal stress of the X-ray absorbing film is large, this internal stress will cause distortion in the X-ray mask. This is because pattern transfer accuracy cannot be ensured. Second, the film structure is suitable for forming fine patterns. In many cases, the required pattern size is 0.25 μm or less, and therefore the film structure must be in an amorphous state or a microcrystalline state so that a pattern of 0.25 μm or less can be formed.

Conventionally, materials used as X-ray absorbing films in X-ray mask materials include gold (Au), tantalum (Ta), tungsten (W), rhenium (Re), or materials composed of these metals and nonmetallic elements. Compounds such as tantalum nitride, tungsten nitride, tantalum oxide, tungsten oxide, etc.

[Problems to be Solved by the Invention] However, all of the above-mentioned conventional X-ray absorbing films have the following drawbacks.

First, since Au is soft, malleable, and ductile,
There was a drawback that the pattern dimensions inevitably changed over time. Furthermore, since Au is chemically inert, it is extremely difficult to process it by wet etching or dry etching, so it has the disadvantage that fine patterns cannot be directly formed. Therefore, in order to form a fine pattern on an Au film, a stencil pattern is formed in a resist or the like in advance, and Au is deposited within the stencil pattern using an electrolytic plating method.
A method of forming fine patterns using u was used. However, the electrolytic plating method has the drawback that precise internal stress control, which is most important for producing an X-ray absorbing film, cannot be obtained, and furthermore, because it is a solution reaction, the film is easily contaminated.

Next, for metals other than Au, such as Ta, W, and Re, sputtering is almost the only method for forming these films, but when deposited by sputtering, there are the drawbacks mentioned above. there were. When producing an X-ray absorbing film by sputtering, it is extremely difficult to precisely control internal stress. This is because it has been revealed that the internal stress of the film depends on the sputtering gas pressure, but this dependency is such that the internal stress changes sharply in response to minute changes in the gas pressure. Therefore, the gas pressure range for obtaining the desired small internal stress is limited to an extremely small range.

Moreover, sputtering gas pressure was the only parameter that could control internal stress. Furthermore, films with low internal stress can only be obtained under conditions of high sputtering gas pressure.
The film obtained under these conditions has the disadvantage that it has a low density and contains impurities, resulting in a low X-ray absorption rate, and that the grain size is extremely large, making microfabrication impossible.

Next, compounds composed of metals and nonmetallic elements, specifically tantalum nitride, tungsten nitride, tantalum oxide,
A film of tungsten oxide or the like can be obtained by the same sputtering method as in the case of forming the single metal film. In this case, it is easy to obtain an excellent film structure for microfabrication, such as an amorphous state or a microcrystalline state, for these films, while maintaining this excellent film structure. The drawback is that a film with low stress cannot be easily obtained. In other words, when trying to obtain a film with low internal stress, microfabrication becomes impossible due to a phase transition that changes from an amorphous state to a crystalline state, or from a microcrystalline state to a crystalline state with larger grain size. There was a drawback. Furthermore, in terms of internal stress control and X-ray absorption rate, it had almost the same drawbacks as the single metal, and was extremely unsatisfactory as an X-ray absorbing film.

Therefore, a first object of the present invention is to provide an X-ray mask material having an X-ray absorbing film that eliminates the above-mentioned drawbacks, has low internal stress, and has excellent microfabricability.

A second object of the present invention is to provide an X-ray mask having an extremely fine pattern using an X-ray mask material obtained by a distant relative of the first object.

[Means for Solving the Problems] A first object of the present invention is to provide an X-ray mask material in which an X-ray transmitting film and an X-ray absorbing film are sequentially provided on a substrate, wherein the X-ray absorbing film is made of tantalum and nickel. , their atomic ratio (
Ta/Ni) is 3. 0/7°0~5. 015. 0
It is distantly related to X-ray mask materials that are characterized by containing the following.

The second object of the present invention is distantly related to an X-ray mask characterized in that it is obtained by finely patterning the X-ray absorbing film of the X-ray mask material.

The present invention will be explained in detail below.

The X-ray mask material of the present invention has an X-ray transmitting film and an X-ray absorbing film sequentially provided on a substrate. Here, as the substrate, a commonly used substrate such as a silicon substrate is used, and as the X-ray transparent film, a commonly used X-ray transparent film such as silicon nitride, boron nitride, silicon carbide, etc. is used. It will be done.

In the X-ray mask material of the present invention, the X-ray absorbing film has a novel configuration, in which tantalum and nickel are used in an atomic ratio (Ta/Ni) of 3. 0/7°0~5.015.
It is characterized in that it is contained within a range of 0.

In the X-ray mask material of the present invention, as the X-ray absorbing film,
The reason for choosing a film containing tantalum and nickel is
It is as shown below.

The first reason is that even when tantalum and nickel are used alone as an X-ray absorbing film, they have a practically sufficient X-ray absorption rate when synchrotron radiation is used as an X-ray source. .

The second reason is that an X-ray absorbing film containing tantalum and nickel can be easily formed on a substrate at a low temperature by sputtering. Therefore, unlike the CVD method, mask distortion due to heat does not occur. Furthermore, the sputtering method can form a film more easily than the electrolytic plating method or the CVD method, and has a higher deposition rate.

The third reason is that an X-ray absorption film containing tantalum and nickel, when formed by sputtering, has advantages such as low internal stress, high density and no impurities, and high X-ray absorption rate. That's true.

Regarding this internal stress, the present inventor has confirmed that the internal stress can be easily controlled by changing the power input to the sputter target under conditions of a small gas pressure, such as 2 Pa or less. In this case, controlling the input power is different from controlling the sputtering gas pressure and allows extremely precise control, so by accurately setting the input power, the internal stress of the resulting film can be almost completely zeroed. be able to. Furthermore, since the film is formed under conditions of low gas pressure, a film with high density and extremely few impurities can be obtained, and therefore, an X-ray absorbing film with sufficient X-ray absorption rate can be obtained.

In forming a film containing tantalum and nickel by sputtering, a target containing tantalum and nickel may be used as the target material.

Next, tantalum and nickel, which constitute the X-ray absorption film, are prepared with an atomic ratio (Ta/Ni) of 3.0/7.0 to 5.0.
015. The reason for limiting it to 0 is as shown below.

The first reason is that the atomic ratio (Ta/Ni) is 3°0/7.
When the amount of tantalum decreases and the amount of nickel increases, even if the crystalline state of the formed film is microcrystalline, the grain size will exceed, for example, 15no+, and the atomic ratio (Ta/Ni) will increase. 5. 015. exceeds 0,
Even if the amount of tantalum increases and the amount of nickel decreases, even if the crystalline state of the formed film is microcrystalline, the grain size will exceed, for example, 15 na+, and in either case,
For example, it is difficult to form fine patterns of 0.25 μm or less, but when the atomic ratio (Ta/Ni) is 3,
0/7. 0-5. 015. If it is in the range of 0, the formed film will be in an amorphous state or preferably in a microcrystalline state with a grain size of 15 nm or less, so for example, 0.2
This is because it enables the formation of fine patterns of 5 μm or less and has excellent fine processing properties.

The second reason is that the atomic ratio (Ta/Ni) is 3.0/7.0
or less than 5. If it exceeds 0.015.0, the crystal grains of the film are large and the top and wall surfaces of the formed pattern will not be smooth.
3. 0/7. This is because in the case of 0 to 5°015.0, the film is in an amorphous state or in a microcrystalline state with small crystal grains, so that the top surface and wall surface of the formed pattern will be smooth.

Although the X-ray absorbing film in the present invention contains tantalum and nickel, conventional processing techniques such as dry etching can be used as is.

According to the present invention, an X-ray mask having a fine pattern of, for example, 0.25 μm or less can be obtained by using an X-ray mask material having the above characteristics and finely patterning the X-ray absorbing film by a conventional method. can.

[Examples] Hereinafter, the present invention will be further explained with reference to Examples, but the present invention is not limited to these examples.

Example I 3, where the atomic ratio (Ta/Ni) of tantalum and nickel constituting the X-ray absorption film is within the limited range of the present invention,
0/7. An example in the case where it is 0 is shown below.

A 0.6 μm thick X-ray absorption film made of tantalum and nickel was formed on a 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate by RF (radio frequency) magnetron sputtering. An X-ray mask material was obtained. The sputter target contains tantalum and nickel in an atomic ratio (Ta/Ni) of 3. It is a sintered body containing the following elements at a ratio of 0/7.0. The sputtering gas was argon, and the argon flow rate was 51.0 cc/min. The sputtering conditions are
The rf power was 300 W (6.58 W/cm2), and the sputtering gas pressure was 60 Pa. The deposition starting temperature was room temperature. The X-ray absorbing film produced under the above conditions is E S
CA (Electron 5pectroscopy
For Chemical Analysis), it was confirmed that the film had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorbing film was in a microcrystalline state (crystal grain size: 10 nn), and its stress was below the measurement limit (1×10 dyn/cm 2 ).

Furthermore, the obtained film was extremely hard and resistant to scratches. Further, the density of the obtained film was determined by gravimetric method and was found to be 11.0 g/cm3.

It was also confirmed that the thermal stability of internal stress was sufficiently ensured. That is, even if annealing was performed in vacuum at 350° C. for 13 hours, the internal stress did not change.

Next, after cleaning the surface of the X-ray absorption film, a resist for electron beam irradiation was applied, and a resist pattern with a line width of 0.25 μm was formed using the electron beam. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, a pattern with a line width of 0.25 μm is
It was possible to form a line-absorbing film. The above reactive ion beam etching method was performed using sulfur hexafluoride (SFa) as an etching gas at a flow rate of 10 cc per minute, with an ion acceleration energy of 600 V, and an etching temperature of 15°C. It was confirmed that the etching rate was slightly lower than that of a single tantalum film, and that a practically sufficient etching rate could be obtained.

Finally, the central portion of the Si substrate was etched and removed by immersion in a saturated hydroxide (IJ) aqueous solution maintained at 90° C. to form an X-ray mask. Furthermore, the synchrotron radiation light was passed through a mask pattern to a PM with a thickness of 0.6 μm.
When exposed to MA (polymethyl methacrylate) resist, it had sufficient contrast and a line width of 0.25μ.
I was able to transfer all the turns of the resist. This confirmed the effectiveness of the X-ray absorbing membrane in the present invention.

Example 2 The atomic ratio of tantalum and nickel (Ta/Ni) constituting the X-ray absorption film is included in the limited range of the present invention4,
0/6. An example in the case where it is 0 is shown below.

A 0.6 μm thick X-ray absorption film made of tantalum and nickel was formed on a 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate by RF (radio frequency) magnetron sputtering. An X-ray mask material was obtained. The Sunoku/Sota target contains tantalum and nickel in an atomic ratio (Ta/Ni) of 4. 0/6. It is a sintered body containing 0%. The sputtering gas is argon.
The argon flow rate was 51.0 cc/min. Sputtering conditions are RF power 300W (6,58W/cm2)
.

The sputtering gas pressure was 1.65 Pa. The deposition starting temperature was room temperature. The X-ray absorbing film produced under the above conditions is E
S CA (Electron 5pectrosc
opy1'or Chemical Analysis
), it was confirmed that the film had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorbing film was in an amorphous state, and its stress was below the measurement limit (I x 108 dyn /Cm2).

Furthermore, the obtained film was extremely hard and resistant to scratches. Further, the density of the obtained film was determined by gravimetric method and was found to be 11.7z/cm3.

It was also confirmed that the thermal stability of internal stress was sufficiently ensured. That is, even when annealing was performed in vacuum at 350° C. for 3 hours, the internal stress did not change.

Next, after cleaning the surface of the X-ray absorbing film, a resist for electron beam irradiation was applied, and a resist pattern with a line width of 0.10 μm was formed using the electron beam. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, a pattern with a line width of 0.10 μm is
It was possible to form a line-absorbing film. The above reactive ion beam etching method was carried out using sulfur hexafluoride (SF6) as an etching gas at a flow rate of 10 cc per minute, ion acceleration energy of 600 V, and etching temperature of 15°C. It was confirmed that the etching rate was slightly lower than that of a single tantalum film, and that a practically sufficient etching rate could be obtained.

Finally, the central portion of the Si substrate was etched and removed by immersion in a saturated sodium hydroxide aqueous solution maintained at 90° C. to form an X-ray mask. Furthermore, synchrotron radiation was transmitted through a mask pattern to a PMM with a thickness of 0.6 μm.
When resist A was exposed, a resist pattern with sufficient contrast and a line width of 0.10 μm could be transferred. This confirmed the effectiveness of the X-ray absorbing membrane in the present invention.

Example 3 The atomic ratio (Ta/Ni) of dantal and nickel constituting the X-ray absorption film is included in the limited range of the present invention5,
015. An example in the case where it is 0 is shown below.

A 0.6 μm thick X-ray absorption film made of tantalum and nickel was formed on a 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate by RF (radio frequency) magnetron sputtering. An X-ray mask material was obtained. The sputter target is a sintered body containing tantalum and nickel in an atomic ratio (Ta/Ni) of 5.015.0. The sputtering gas was argon, and the argon flow rate was 51.0 cc/min. The sputtering conditions are r
The f power was 300 W (6.58 W/cm2), and the sputtering gas pressure was 1.55 Pa. The temperature at the start of the deposition was room temperature. The X-ray absorbing film produced under the above conditions is E S
CA (Electron Spectroscopy
According to f'or Chemical Analysis), it was confirmed that it had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorption film is
It was in a microcrystalline state (crystal grain size: 10 nm), and its stress was below the measurement limit (IXIOdyn/cm2).

Furthermore, the obtained film was extremely hard and resistant to scratches. Further, the density of the obtained film was determined by gravimetric method and was 12.5 g/cm3.

It was also confirmed that the thermal stability of internal stress was sufficiently ensured. That is, even when annealing was performed in vacuum at 350° C. for 3 hours, the internal stress did not change.

Next, after cleaning the surface of the X-ray absorption film, a resist for electron beam irradiation was applied, and a resist pattern with a line width of 0.25 μm was formed using the electron beam. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, a pattern with a line width of 0.25 μm is
It was possible to form a line-absorbing film. The above reactive ion beam etching method was carried out using sulfur hexafluoride (SFs) as an etching gas at a flow rate of 10 cc per minute, ion acceleration energy of 600 V, and etching temperature of 15°C. It was confirmed that the etching rate was slightly lower than that of a single tantalum film, and that a sufficient etching rate could be obtained in practice.

Finally, the center of the Si substrate is etched away by immersing it in a saturated sodium hydroxide aqueous solution maintained at 90°C.
An X-ray mask was formed. Furthermore, the synchrotron radiation light was passed through a mask pattern to a PMMA film with a thickness of 0.6 μm.
When the resist was exposed, it had sufficient contrast and a line width of 0. A pattern of 25 μm could be transferred. This confirmed the effectiveness of the X-ray absorbing membrane of the present invention.

Comparative Example I Comparison 11) 1 in which the X-ray absorption film was formed only from tantalum is shown below.

An X-ray film made of tantalum is placed on a 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate.
A radiation absorbing film was formed to a thickness of 0.6 μm by RF (high frequency) magnetron sputtering to obtain an X-ray mask material.

The sputter target is a sintered body containing only tantalum. The sputtering gas is argon, and the argon flow rate is 5/min.
It was 1.0CC. The sputtering conditions are RF power 29
0W (6,36W/cm2), sputtering gas pressure 3
It was ゜OPa. The temperature at the start of the deposition was room temperature.

The X-ray absorbing film produced under the above conditions was ESCA (Elec
tron 5pectroscopy f'or Ch
According to chemical analysis), it was confirmed that the film had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorption film has a columnar crystal state (
The diameter of the columnar crystals was 20 nm), and the stress was below the measurement limit (1×10 dyn/cm 2 ). After cleaning the surface of the X-ray absorption film, a resist for electron beam irradiation was applied, and a resist pattern with a line width of 0.25 μm was formed using the electron beam. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, the upper surface and wall surface of the formed pattern were not smooth, and a pattern with the desired line width of 0.25 μm could not be formed.

Comparative Example 2 The atomic ratio (Ta/Ni) of tantalum and nickel constituting the X-ray absorption film is not included in the limited range of the present invention2.
0/8. A comparative example where the value is 0 is shown below.

A 0.6 μm thick X-ray absorbing film made of tantalum and boron is formed on a 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate by RF (radio frequency) magnetron sputtering. An X-ray mask material was obtained. The sputter target is a sintered body containing tantalum and nickel in an atomic ratio (Ta/Ni) of 2.0/8.0. The sputtering gas was argon, and the argon flow rate was 51.0 cc/min. The sputtering conditions are
The rf power was 300 W (6.58 W/cm2), and the sputtering gas pressure was 40 Pa. The temperature at the start of the deposition was room temperature. The X-ray absorbing film produced under the above conditions is E S
CA (Electron 5pectroscope
According to yfor Chemical Analyses), it was confirmed that the film had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorption film was in a microcrystalline state (crystal grain size: 20 nm), and its stress was below the measurement limit (IXIOdyn/cm2). After cleaning the surface of the X-ray absorption film, a resist for electron beam irradiation was applied, and a resist pattern with a line width of 0.25 μm was formed using the electron beam. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, the upper surface and wall surface of the formed pattern were not smooth, and a pattern with the desired line width of 0.25 μm could not be formed.

Comparative Example 3 The atomic ratio (Ta/Ni) of tantalum and nickel constituting the X-ray absorption film is 6.0, which is not included in the limited range of the present invention.
/4.0 is shown below.

A 2 μm thick silicon nitride film (X-ray transparent film) formed on a 5i (100) substrate is coated with an X-ray absorbing film made of tantalum and nickel by RF (radio frequency) magnetron sputtering. An X-ray mask material was obtained by forming the film to a thickness of 6 μm. The sputter target contains tantalum and nickel in an atomic ratio (Ta/Ni) of 6. 0/4. It is a sintered body containing 0%. The sputtering gas was argon, and the argon flow rate was 51.0 cc/min. The sputtering conditions were RF power of 300 W (6.58 W/cm2) and sputtering gas pressure of 1.36 Pa. The temperature at the start of the deposition was room temperature. The X-ray absorbing film produced under the above conditions is E
S CA (Electron 5pectrosc
Opyf'or Chemical Ana! ys1s
), it was confirmed that the film had the same composition ratio as the target, that this composition ratio was almost constant in the depth direction of the film, and that it did not contain any impurities. This X-ray absorption film is in a microcrystalline state (crystal grain size 20 nm), and its stress is at the measurement limit (IXIOdyn/cm").
It was below. After cleaning the surface of the X-ray absorption film, a resist for electron beam irradiation is applied, and a line width of 0.2 is applied using an electron beam.
A resist pattern of 5 μm was formed. Furthermore, the resist pattern was transferred to the X-ray absorbing film by reactive ion beam etching. At this time, the upper surface and wall surface of the formed pattern were not smooth, and a pattern with the desired line width of 0.25 μm could not be formed.

[Effects of the Invention] As described above, according to the present invention, internal stress is small;
In addition, an X-ray mask material having an X-ray absorbing film with excellent microfabricability has been provided.

Furthermore, according to the present invention, using the above-mentioned X-ray mask material,
For example, an X-ray mask having an extremely fine pattern of 0.25 μm or less has been provided.

Claims (2)

[Claims] (1) In an X-ray mask material in which an X-ray transmitting film and an X-ray absorbing film are sequentially provided on a substrate, the X-ray absorbing film contains tantalum and nickel in an atomic ratio (Ta/Ni) of 3.
．． An X-ray mask material characterized in that the content is in a range of 0/7.0 to 5.0/5.0. (2) An X-ray mask characterized in that it is obtained by finely patterning the X-ray absorbing film of the X-ray mask material according to claim 1.