JPH03196148A - Formation of sic film for x-ray lithography - Google Patents

Abstract

PURPOSE:To obtain the SiC film having excellent high energy beam resistance by forming the SiC film in the state of compressive stress on a substrate, then annealing the film into the state of tensile stress. CONSTITUTION:The SiC film is formed in the state of the compressive stress on the substrate by using a target consisting of SiC and by a sputtering method. This film is then annealed to the state of the tensile stress. Namely, the SiC film is required to contain crystalline SiC. The film is formed by previously imparting crystallinity to the film at the time of a sputtering treatment for the above-mentioned purpose, by which the fluctuation in the stress and the generation of strains are lessened even if the film is irradiated with a high- energy beam at the time of use of the film as a mask. The SiC film which has the tensile stress of a specified range and has the crystallinity regulated by the waveform of X-ray diffraction is obtd. in this way. The excellent SiC film which has the high energy beam resistance, is extremely little in the change in the stress and is free from pinholes and nodules is stably mass-produced without fluctuations.

Description

Detailed Description of the Invention (Industrial Field of Application) This invention relates to a method for forming a SiC film for X-ray lithography that exhibits little change in stress even when irradiated with high-energy beams such as high-energy electron beams and synchrotron radiation. .

(Prior Art) With the miniaturization of pattern formats in semiconductor devices, X-ray lithography technology is considered the most promising as a future lithography technology. The important performances required of the X-ray transparent membrane (in other words, it is also called the support membrane of the X-ray absorber, but hereafter referred to as membrane or membrane) of the mask used in X-ray lithography are as follows: 1) The surface must be smooth, free of scratches and pinholes, and have practical strength.

2) Must have visible light transmittance necessary for highly accurate alignment.

3) It has good chemical resistance and moisture resistance, and is not easily damaged by etching and cleaning processes.

4) To withstand irradiation with high-energy beams such as high-energy electron beams and synchrotron radiation.

etc.

Conventionally, materials for mask membranes for X-ray lithography include BN, boron-doped Si, 5isN4. SiC
Among them, SiC is considered to be the material with the best high energy beam resistance because it has a high Young's modulus.

Usually, the CVD method is most often used as a method for forming this SiC film. However, since the CVD method forms a film while involving reaction and decomposition of the raw material gas, elements other than the film components are likely to be incorporated into the film, and as a result, these elements act as impurities in the film. 1) Impurities in the film are easily removed by high-energy beam irradiation. As a result, defects such as distortion of the film, fluctuation of stress in the film, reduction in mechanical strength of the film, and reduction in optical transparency of the film occur.

2) Pinholes and nodules are likely to occur on the surface of the membrane, making it difficult to obtain a good membrane.

There are other problems.

(Problems to be Solved by the Invention) Another method for forming this SiC film is the patent application No. 63-3.
There is a sputtering method described in 15768.

This method has advantages such as fewer impurities and fewer pinholes and nodules in the film, but the SiC film formed is in an amorphous state and is prone to stress fluctuations when irradiated with an excessively high energy beam ( As a result, there is a problem in that distortion is likely to occur.

Therefore, the problem to be solved by the present invention is to create a Si material for X-ray lithography that has excellent high-energy beam resistance.
The objective is to obtain a C film.

(Means for Solving the Problems) In order to solve the problems, the present inventors conducted crystallographic analysis of SiC films, and as a result, they found that films with specific physical properties have high energy beam resistance. After confirming this and searching for the optimal method for forming this film, we found that S
After forming the iC film under compressive stress, annealing is performed,
By changing the compressive stress state to the tensile stress state,
It was possible to obtain a membrane with little stress fluctuation even when irradiated with a high-energy beam, and the present invention was completed.

The gist of the present invention is to form an SiC film in a compressive stress state on a substrate by sputtering using a target made of SiC, and then to anneal it to a tensile stress state. A method for forming a SiC film for lithography.

The present invention will be explained in detail below.

First, in order to obtain a good SiC film, the tensile stress of the SiC film should be 0.1 to 8. OX 10' dyne/crrf
It is necessary that 0.1 x 10@dyne
If it is less than 8.Ox 10' dyne/crrr, it is difficult to form a film because the tensile stress is too small (and even if it is formed, wrinkles are likely to occur.On the other hand, even if it exceeds 8.Ox 10' dyne/crrr, the tensile stress is too large) It is difficult to form a film, and even if it is formed, it is likely to rupture.The preferable range is 0.3.
~4.0×10′ dyne/crrr.

Next, it is necessary that the SiC film contains crystalline SiC. The main reason why internal stress fluctuates when an amorphous SiC film produced by normal sputtering is irradiated with a high-energy beam is that the irradiation heats the SiC film and increases its temperature, which changes the crystal structure of the SiC. Since the crystallinity changes in the direction of increasing, it is thought that the internal stress also changes. Therefore, in the present invention, by imparting crystallinity to the film beforehand during sputtering, even when irradiated with a high-energy beam when used as a mask, stress fluctuations and distortions are extremely reduced.

Further, as a condition for this crystallinity, there is a sharpness of the peak waveform of the SiC (ill) crystal plane at 2θ:35.5° of the X-ray diffraction peak of the SiC film.

In order to reduce stress fluctuations in SiC due to high-energy beam irradiation to a practical level, the baseline at 2θ = 35.5° is set at the X-ray diffraction peak using a line connecting the waveforms at 2θ = 30° and 2θ = 40°. The peak height Ll from the base line and the peak height L from the base line at 2θ=33°
The ratio /L of 2 is required to be 1.5 or more, more preferably 3.0 or more. If it is less than 1.5, the stress will fluctuate greatly and cannot be used.

Next, a film forming method that provides the above characteristics will be described.

The sputtering method employed in the present invention is a commonly used conventional sputtering method, but from the viewpoint of mass productivity, it is preferable to use a magnetron sputtering method, which has a high film formation rate. As the gas used for sputtering, an inert gas such as argon or sequinone is used, but other gases such as helium or nitrogen may be mixed.

The substrate is usually made of silicon. The target is SiC
The powder may be sintered into a predetermined shape, but the purity is 99% or more, preferably 99.9% or more, since it is desirable that the formed film contains as few impurities as possible. The power applied to the target is preferably 5 W/crtr or more. The higher the applied power, the higher the deposition rate, which is advantageous.

The substrate temperature during sputtering is kept below 500° C. so that subsequent annealing can be performed effectively.

The SiC film formed when the substrate temperature is 500°C or higher,
Even if the next step, annealing treatment, is performed, the increase in crystallinity is insufficient, and as a result, stress tends to fluctuate due to high-energy beam irradiation. Conversely, if the substrate temperature is 50
If the temperature is below ℃, the adhesion between the substrate and the SiC film will decrease, which is not desirable, and the preferred substrate temperature is 150 to 300℃.
It is.

Sputtering pressure is very important to achieve the desired compressive stress within the film. First, considering the sputtering temperature and the temperature and time conditions of the annealing treatment to be performed later, the internal stress after the annealing treatment is in the most preferable range for producing a SiC film, 0, 1 to 0 g, OX 10.
The sputtering pressure is determined so that the tensile stress is 'dyne/Cm'.Normally, when annealing is performed, the stress changes toward the tensile stress side, and the amount of variation becomes larger as the annealing temperature increases.Therefore, several levels of It is necessary to determine the relationship between the sputter pressure and internal stress under the sputter temperature, and also determine the relationship between the annealing treatment conditions and the amount of stress variation.The sputter pressure that satisfies the above requirements is 0.2
˜50×10” Torr.

The annealing treatment conditions were S, which was finished in an amorphous state.
In order to impart crystallinity to the iC film, the annealing temperature is 500℃.
It is necessary that the temperature is at least 700°C, preferably at least 700°C. Further, the annealing time is required to be 2 hours or more for sufficient annealing treatment, and preferably 4 to 8 hours. As a measure of the increase in crystallinity of SiC after the annealing treatment, evaluation is made from the waveform of the above-mentioned X-ray diffraction peak.

Hereinafter, specific embodiments of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

The physical properties of the obtained SiC film were measured and evaluated as follows.

(2) Measurement of X-ray diffraction Measurement was carried out using an X-ray diffraction measuring device for thin films (TFD manufactured by Rigaku). Incident angle (θ) = 2° fixed, target is Cu,
Power is 40kV x 40mA.

■Measurement of internal stress The stress value was calculated from the amount of change in warpage of the substrate before and after film formation, and between before and after annealing.

■High energy beam resistance 15 eV high energy electron beam is used as high energy.
．． OKJ/cm'' was irradiated, and the amount of change in stress in the film due to irradiation was measured, which was used as a measure of high energy beam resistance.

■ Amorphous B is applied to the back side of the substrate of the sample suitable for membrane formation using plasma CVD method.
A 1.0 μm thick N film (hereinafter referred to as a-BN film) was formed,
This film was used as a protective film for KOH etching solution.

A donut-shaped stainless steel mask plate was set on the a-BN film, and the exposed a-BN film was removed by dry etching with CF4 gas, and then the exposed silicon surface was wet etched with 30% KOH. It was eluted and membraned. As for suitability for membrane formation, the finished membrane was judged to be good if it was found to be smooth without scratches or pinholes, and bad otherwise.

■Visible light transmittance measurement membrane is multi-photospectrometer MPS-
Transmittance (%) at a wavelength of 633 nm was measured using 5000 (trade name, manufactured by Shimadzu Corporation).

(Examples 1 to 6, Comparative Examples 1 to 3) A disk-shaped SiC target with a diameter of 3 inches and a thickness of 5 mm was placed on the cathode side using a high-frequency magnetron sputtering device 5PF-332H model (trade name manufactured by Nikkei Anelva Co., Ltd.). (
Purity: 99.9%) was set. A double-sided polished silicon wafer with a diameter of 3 inches and a thickness of 600 μm was used as the substrate, and 7 cc of argon gas was heated to 250°C.
It was flowed at a flow rate of /min. After adjusting the pressure in the chamber to the specified level with the valve leading to the exhaust system, the power density is adjusted to ION/
Sputtering was carried out for 15 minutes with a film thickness of 1.0 cm.
A μm SiC film was fabricated.

Next, the obtained silicon substrate provided with the SiC film was annealed in the following manner. First, it was set in a wafer jig made of synthetic quartz and left in a high-temperature furnace. The pressure in the furnace was set to 20 mm Torr, and the temperature was raised at a rate of 10"C/min.
After reaching a predetermined temperature, it was maintained at that temperature for a certain period of time, and then cooled at a rate of lO"c/min. The internal stress after annealing was measured, and the stress required for membrane formation was 0,
A specimen with a tensile stress of 1 to 1 g, Ox 10"dyne/cm" was obtained. By performing the annealing treatment, the internal stress in all cases varied in the direction of the tensile stress. The results are shown in Table 1.

Next, the annealed samples of Examples 1 to 6 in Table 1 were measured for X-ray diffraction, high energy beam resistance, membrane formation suitability, and visible light transmittance of the obtained membranes. The results are shown in Table 2. The samples used to measure membrane suitability and membrane visible light transmittance were not subjected to high-energy irradiation treatment.

The waveform of X-ray diffraction is shown in FIG. From this waveform, 2θ
=30° and 2θ:2 with the line connecting the 40° waveform as the base line
Peak height Ll from the base line at θ=35.5° and 2
Comparison of peak height L2 from the base line at θ = 33 m,
/L, and the results are shown in Table 2. Further, as a comparative example, similar measurements were made without annealing treatment and at an annealing temperature of less than 500° C., and the results are also listed in Table 2. From Table 2, when annealing is performed at 500°C or higher, Ll/L! was 1.5 or more, and no significant change in internal stress was observed even after irradiation with high-energy electron beams.

(Effects of the Invention) According to the film forming method of the present invention, a SiC film having a tensile stress in a specific range and crystallinity defined by an X-ray diffraction waveform can be obtained, and has high energy resistance It has become possible to stably mass-produce excellent SiC films with beam properties, extremely little stress change, and no pinholes or nodules without variation. Furthermore, Table 1 shows the following materials that can be processed into masks for X-ray lithography.
It has extremely high utility value in industry.

[Brief explanation of drawings]

FIG. 1 shows X-ray diffraction waveforms for defining the crystallinity of the SiC films of Examples 1 to 6 and Comparative Examples 1 to 3.

Claims (1)

[Claims] 1. Using a target made of SiC, a SiC film is formed on a substrate under compressive stress by a sputtering method, and then this is annealed to create a state under tensile stress. A method for forming a SiC film for X-ray lithography. 2. The substrate temperature is less than 500℃ and the annealing temperature is 5.
The method for forming a SiC film for X-ray lithography according to claim 1, wherein the temperature is 00°C or higher. 3. Tensile stress is 0.1 to 8.0 x 10^9 dyne/c
The S for X-ray lithography according to claim 1, which is m^2
A method for forming an iC film. 4. Sputter pressure is 0.2~50×10^-^3To
Si for X-ray lithography according to claim 1, which is rr.
Method for forming C film. 5. The method for forming an SiC film for X-ray lithography according to claim 1, wherein the SiC film under tensile stress contains crystalline SiC. 6. In the X-ray diffraction peak of the SiC film according to claim 4, the peak height L_1 and 2θ from the base line at 2θ = 35.5° with the line connecting the waveforms of 2θ = 30° and 2θ = 40° as the base line. : Peak height L from the base line at 33°
A method for forming a SiC film for X-ray lithography, characterized in that the ratio L_1/L_2 of _2 is 1.5 or more.