JPH07103460B2 - Method for producing composite film consisting of SiC and Si (3) N (4) and method for producing mask for X-ray lithography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention has excellent visible light transmittance, high energy beam irradiation resistance, chemical resistance, moisture resistance and smoothness, and is free from scratches and pinholes. The present invention relates to a method for manufacturing a SiC / Si ₃ N ₄ composite film and a method for manufacturing an X-ray lithography mask using the same as an X-ray transparent film.

(Prior Art) Important performance required for an X-ray transparent film (membrane) of a mask for X-ray lithography is (1) a material that can withstand irradiation of a light energy beam such as a high energy electron beam or synchrotron radiation. To be.

(2) It has a high visible light transmittance of 50% or more and can perform highly accurate alignment.

(3) It has good chemical resistance and moisture resistance and is not easily damaged in the etching process and cleaning process.

(4) The surface of the membrane is smooth and free from scratches and pinholes. Etc.

Conventionally, materials such as BN, Si ₃ N ₄ , and SiC have been proposed as materials for the X-ray transparent film of the mask for X-ray lithography, but each has advantages and disadvantages and satisfies all the above-mentioned performances. Things have not been obtained. For example, BN has a good visible light transmittance, but its high energy beam resistance and chemical resistance are insufficient, and Si ₃ N ₄ has insufficient chemical resistance and moisture resistance. It had a defect that the light transmittance was insufficient.

(Problems to be Solved by the Invention) The inventors of the present invention previously disclosed Japanese Patent Application No. 1-19277 and Japanese Patent Application No. 1-33.
In 39094, as a solution to these drawbacks, a binary composite film composed of SiC and Si ₃ N ₄ has excellent characteristics, and sputtering using a target composed of SiC and Si ₃ N ₄ Although a method of forming a film by the method was proposed, it was not sufficiently satisfactory in terms of high energy beam resistance. Further, in this method, in order to obtain a composite film having an arbitrary composition ratio of SiC and Si ₃ N ₄ , it was necessary to refer to targets having respective composition ratios. On the other hand, as another method, using a target made of silicon, CH ₄ , C ₂ H ₆ , C ₃ H ₈ , and CH _{2 are used.}
= CH ₂ , CH ₃ -CH = CH ₂ and other gases that become carbon sources, and N ₂ , N
There is a reactive sputtering method in which sputtering is performed in an entrained air flow of a gas that becomes a nitrogen source such as ₂ O and NH ₃ . However, in this method, when hydrogen and N ₂ O are used, oxygen is contained as an impurity in the formed film. If hydrogen or oxygen is present in the film, these hydrogen and oxygen may be released from the film by irradiation with a high-energy beam, resulting in disadvantages such as pinholes, distortion, and deterioration of transparency, and defects. It was Therefore, the problems to be solved by the present invention include a method of forming a composite film of SiC and Si ₃ N ₄ on a substrate, which solves such disadvantages and defects, and an excellent method of using this thin film as an X-ray transparent film. Another object is to obtain an X-ray lithography mask having high energy beam resistance.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have selected a material for an X-ray transparent film to be formed on a Si substrate, and a film forming condition for a membrane having various suitable physical properties. The present invention has been achieved as a result of intensive studies on the search for, and its gist is as follows.

A method for producing a composite thin film, which comprises using a target made of SiC and silicon (Si) to form a composite film made of SiC and Si ₃ N ₄ on a substrate by a sputtering method under an N ₂ gas stream. A first invention, a method for producing a composite thin film, characterized in that the obtained composite thin film has a molar ratio of SiC to Si ₃ N ₄ of 95: 5 to 30:70, and then the second invention. X thin film
A third invention is directed to a method of manufacturing an X-ray lithography mask used as a line-transmissive film. Hereinafter, the present invention will be described in detail.

First, as a thin film material for the X-ray transparent film, it was found that a binary composite film composed of SiC and Si ₃ N ₄ has superior performance in each physical property than the single component system, and the ratio of the components is 95% by mole. :Five
A range of ~ 30: 70 is good. When the SiC content exceeds 95, the visible light transmittance is as low as that of SiC alone.
If the amount is smaller, the chemical resistance will be unsatisfactory, equivalent to that of Si ₃ N ₄ alone, which is not preferable. Therefore, the preferable molar ratio is 80:20 to 40:60. The tensile stress of the produced thin film needs to be 1 × 10 ⁸ to 1 × 10 ¹⁰ dyne / cm ² ,
When it is 1 × 10 ⁸ dyne / cm ² or less, wrinkles are likely to occur when the membrane is formed, and when it is 1 × 10 ¹⁰ dyne / cm ² or more, the membrane is easily broken. 5 is a suitable tensile stress
× 10 ^{8 to} 5 × 10 ⁹ dyne / cm ² .

Next, a method for producing a SiC / Si ₃ N ₄ composite film will be described.

When the film is formed by the reactive sputtering method of the present invention, it is possible to drastically change the composition ratio of SiC and Si ₃ N ₄ by controlling the flow rate of N ₂ gas. Since it does not have oxygen, there is no trouble such as generation of pinholes, distortion and deterioration of transparency even when irradiated with a high energy beam.

As the reactive sputtering method adopted in the present invention, a commonly used conventional sputtering method is used, but it is preferable to use a magnetron sputtering method having a high film forming rate from the viewpoint of mass productivity.

The target, which is an essential requirement of the present invention, is SiC and silicon (S
The composition ratio is determined by conducting a preliminary test so that the molar ratio of SiC to Si in the composite film to be formed is 95: 5 to 30:70. This is because the composition ratio of SiC and Si ₃ N ₄ of the composite film obtained by using the target of the same composition ratio is completely the same, depending on the N ₂ gas flow rate, the sputtering temperature, the power applied to the sputtering, etc. Because it will not be. However, as a preset value, SiC
And Si should be in a molar ratio of 84:16 to 12:88. Examples of silicon that is a raw material of the target include silicon single crystal, polysilicon, and amorphous silicon. However, silicon single crystal that does not contain SiH and is easily available is preferable.

SiC having a purity of 99% or higher, preferably 99.9% or higher is desirable in order to obtain a high-purity composite thin film. In addition to these two components, a slight amount of B or Si ₃ N ₄ may be contained to the extent that the performance of the composite film is not impaired. This two-component target may be manufactured by uniformly mixing a predetermined amount of graphite and silicon, molding by hot pressing, and sintering, and by combining targets of each component individually, a normal pinhole type, a split type, etc. It may be one composite target that is called. A silicon wafer is usually used as the substrate. The temperature of the Si substrate is not particularly limited, but a range of 100 to 1,000 ° C. is preferable because the number of defects and pinholes in the generated film is small. When the power applied to the target is 5 W / cm ² or more, the stress of the obtained film becomes tensile stress, which is preferable. It is advantageous that the higher the applied power, the higher the film formation rate.

The gas used at the time of spattering is preferably N ₂ gas having a purity of 99% or more, preferably 99.9% or more, and it is desirable to carry an inert gas such as argon or xenon for the purpose of maintaining a stable plasma state. The sputter pressure is not particularly limited, but 1 × 10 ^-2 to 1 × 10 ^-1 torr is preferable. In addition,
Since the sputter pressure has a great influence on the stress value of the film after film formation, it is necessary to set the sputter pressure such that a predetermined tensile stress is obtained under the sputtering conditions including the composition of the target. Hereinafter, specific embodiments of the present invention will be described with reference to examples and comparative columns, but the present invention is not limited thereto. The methods for measuring and evaluating the physical properties of the obtained composite thin film are as follows.

(Measurement and evaluation method of physical properties of composite thin film) Film formation speed: After masking a part of the surface of a silicon substrate with a stainless plate and performing sputtering for a certain period of time,
The stainless mask was removed, and the level difference at the boundary between the non-film-formed surface and the film-formed surface was measured by Surfcoder SE-30C (trade name, manufactured by Kosaka Laboratory) to obtain the film thickness, and the film-forming speed was calculated.

Tensile stress: The stress value was calculated from the amount of change in warpage before and after film formation of a silicon wafer.

Visible light transmittance: After forming a film on the quartz substrate 3WAF525 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) for photomasks by the above-mentioned method, this quartz substrate was measured with a multi-photospectrometer MPS-5000 (trade name, manufactured by Shimadzu Corporation) at a wavelength of 633 nm. The transmittance was measured.
At this time, a quartz substrate on which no film was formed was used as a sample on the difference side.

High energy beam resistance: 10 KeV as high energy
Was irradiated with 500 MJ / cm ³ of high energy electron beam and the rate of stress change of the film due to irradiation was determined and used as a guide for high energy beam resistance.

Chemical resistance: It was immersed in 30% KOH hot water at 90 ° C for 24 hours, and the stress change rate after immersion was obtained to be used as a guideline for chemical resistance.

Moisture resistance: Immersed in hot water at 90 ° C. for 7 days, and the rate of change in stress after immersion was determined and used as a measure of moisture resistance.

Membrane suitability: Plasma CV on the back surface of the substrate after film formation
Amorphous BN film (hereinafter a-BN film) is 1.0 by D method
A film having a thickness of μm was formed, and this film was used as a protective film for the KOH etching solution. Set a stainless donut-shaped mask plate on the a-BN film, dry-etch it with CF ₄ gas to remove the exposed a-BN film, and then wet-etch the exposed silicon surface with 30% KOH. It was eluted with to form a membrane.
As the suitability for membrane formation, when the finished membrane was recognized as smooth without any scratches or pinholes, the others were judged as good, and the others were judged as bad.

(Example 1) A high frequency magnetron sputtering device SPF-332H (trade name, manufactured by Nichiden Anelva Co., Ltd.) was used, and the purity was 9 on the cathode side.
400 parts by weight of 9.9% SiC powder and 840 silicon single crystal powder
A target having a diameter of 3 inches and a thickness of 5 mm obtained by uniformly mixing the parts by weight and sintering by hot pressing was set.

The target has a molar ratio of SiC to silicon of 1: 3.
Is.

Using a double-sided polished silicon wafer with a diameter of 3 inches and a thickness of 600 μm as a substrate, N ₂ in a state of being heated to 250 ° C.
Gas and argon gas at a flow rate of 10 cc / min and 5 cc / min, respectively, power density of 12 W / cm ² , reaction pressure of 5.0 × 10 ^-2 To
Sputtering was performed for a predetermined time under rr to prepare a thin film of SiC and Si ₃ N ₄ with a thickness of 1.0 μm.

As a result of performing elemental analysis by ESCA method on the obtained thin film,
Si49.2%, N255%, molar ratio of C25.3% next SiC and Si ₃ N ₄ is about 1: was found to be 1.

Next, the main physical properties of this film were measured by the methods described above. The film formation rate was 0.14 μm / min, and the tensile stress was 1.8 × 10 ⁹ dyne.
/ cm ² , visible light transmittance 73%, high energy beam resistance,
Both the chemical resistance and the humidity resistance were 1% or less, and the suitability for membrane formation was good.

(Examples 2 and 3 and Comparative Examples 1 and 2) Targets having various compositions were prepared by variously changing the mixing ratio of the SiC powder and the powder of silicon single crystal, and SiC and Si ₃ N were prepared in the same manner as in Example 1. The composite film of ₄ was prepared, the composition ratio was determined by ESCA, and each physical property was measured (Examples 2 and 3).

Further, as a comparative example, a target was similarly prepared for those having a molar ratio of SiC and Si ₃ N ₄ outside the composition range of the present invention.
A composite film of SiC and Si ₃ N ₄ was prepared in the same manner as in Example 1 and ES
The composition ratio was determined by CA and each physical property was measured (Comparative Examples 1 and 2). Table 1 shows the film composition, film forming conditions and film properties.

(Effects of the invention) From the results of Table 1, the thin film formed by the method of the present invention has a visible light transmittance of 50% or more, high energy beam resistance, chemical resistance, moisture resistance, and membrane formation. It can be seen that each proper performance is also excellent. On the other hand, from the results of Comparative Example, in the composition of the target, the SiC and Si ₃ N ₄ molar ratio is more than 95: 5 Then, the visible light transmittance becomes 30% or less, which is not suitable for practical use (Comparative Example 1). Moreover, since the molar ratio of SiC and Si ₃ N ₄ is 30:70, S
Even if the amount of i ₃ N ₄ increases, the chemical resistance and moisture resistance deteriorate, and it cannot be practically used (Comparative Example 2).

As described above, the production method of the present invention has extremely high performance as an X-ray lithography mask and is industrially useful.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // B32B 9/00 A 9349-4F

Claims (4)

[Claims] 1. A target made of SiC and silicon (Si) is used, and SiC is sputtered on a substrate by a sputtering method under N ₂ gas flow.
SiC, which comprises forming a composite membrane to consist Si ₃ N ₄
A Si ₃ N ₄ composite film manufacturing method of consisting of. In the composition according to claim 2 wherein said composite film, the molar ratio of SiC and Si ₃ N ₄ 95: 5-30: consisting of SiC and Si ₃ N ₄ according to claim 1, characterized in that the 70 Method for manufacturing composite membrane. 3. Obtained by the method according to claim 1 or 2.
A method of manufacturing a mask for X-ray lithography, which comprises using a composite film of SiC and Si ₃ N ₄ as an X-ray transparent film. 4. A method for manufacturing an X-ray lithography mask, wherein the X-ray transparent film according to claim 3 has a tensile stress of 1 × 10 ⁸ to 1 × 10 ¹⁰ dyne / cm ² .