JPH0712016B2 - Method for forming SiC film for X-ray lithography - Google Patents

Description

The present invention relates to a method for forming a SiC film for X-ray lithography, in which stress changes little even when irradiated with a high energy electron beam or a high energy beam such as synchrotron radiation. .

(Prior Art) With the miniaturization of pattern formats in semiconductor devices, X-ray lithography technology is regarded as the most promising future lithography technology. The important performance required for an X-ray transparent film of a mask (also referred to as a supporting film of an X-ray absorber, which is also referred to as a membrane or a film hereinafter) of a mask used for X-ray lithography is 1). It has a smooth surface, no scratches or pinholes, and practical strength.

2) Visible light transmittance required for 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) Withstand irradiation of high energy beams such as high energy electron beams and synchrotron radiation.

Etc.

Conventionally, BN, boron-doped Si, Si ₃ N ₄ , SiC, etc. have been proposed as materials for mask membranes for X-ray lithography, but among them, SiC has the highest Young's modulus, so it has the highest resistance to high energy beams. It is considered to be a material.

Normally, the CVD method is most often used as the method for forming this SiC film. However, since the CVD method forms a film while reacting and decomposing the source gas, elements other than the film components are easily incorporated into the film, and as a result, these elements act as impurities in the film, 1) Irradiation with a high-energy beam easily separates impurities in the film. Therefore, defects such as strain of the film, fluctuation of stress of the film, deterioration of mechanical strength of the film, and deterioration of optical transparency of the film occur.

2) Pinholes and nodules are easily generated on the surface of the film, and it is difficult to obtain a good membrane.

There is a problem such as.

(Problems to be Solved by the Invention) As another method of forming this SiC film, Japanese Patent Application No. 63-315768
There is a sputtering method described in. in this way,
Although there are advantages such as few impurities in the film and few pinholes and nodules, the formed SiC film is in an amorphous state and is susceptible to stress fluctuations when irradiated with an excessively high energy beam, resulting in strain. There is a problem that it is easy to do.

Therefore, the problem to be solved by the present invention is to provide SiC for X-ray lithography having excellent high energy beam resistance.
To get a membrane.

(Means for Solving the Problems) As a result of advancing the crystallographic analysis of the SiC film in order to solve the problems, the present inventors have found that a film having specific physical properties has high energy beam resistance. As a result of confirmation and search for the optimum film formation method for this film, after forming the SiC film by the sputter method in the state of compressive stress, annealing is performed, and the state of compressive stress is changed to the state of tensile stress. It was possible to obtain a membrane in which variations in stress were small even when irradiated with a beam, and the present invention was completed.

The gist of the present invention is that a target is made of SiC and a SiC film is formed on a substrate by a sputtering method in a state of compressive stress, and then an SiC film is annealed to obtain a state of tensile stress.
This is a method for forming a SiC film for line lithography.

Hereinafter, the present invention will be described in detail.

First, in order to obtain a good SiC film, the tensile stress of the SiC film
It is necessary to be 0.1 to 8.0 × 10 ⁹ dyne / cm ² . 0.1 x
If it is less than 10 ⁹ dyne / cm ² , the tensile stress is too small to form a film easily, and even if it is formed, wrinkles easily occur. On the contrary, even if it exceeds 8.0 × 10 ⁹ dyne / cm ² , the tensile stress is too large, so that the film is difficult to form, and even if it is formed, the film is likely to burst. The preferred range is 0.3-4.0 × 10 ⁹ dyne / cm
^{Is 2} .

Next, it is necessary that the SiC film contains crystalline SiC.
Amorphous SiC produced by normal sputtering method
The main cause that the film is irradiated with a high-energy beam and the internal stress fluctuates is that the irradiation heats the SiC film and raises the temperature, and as a result, the crystal structure of SiC changes in the direction of increasing crystallinity. It seems that the internal stress also changes. Therefore, in the present invention, the crystallinity is given in advance during the sputtering process to form a film, so that even if a high-energy beam is irradiated during use as a mask, the fluctuation of stress and the occurrence of strain are extremely reduced.

Further, as the condition of this crystallinity, the sharpness of the peak waveform of the (111) crystal plane of SiC at 2θ = 35.5 ° of the X-ray diffraction peak targeting copper of the SiC film can be mentioned. In order to reduce the fluctuation of SiC stress to a practical level by irradiation with a high energy beam, the line connecting the waveforms of 2θ = 30 ° and 2θ = 40 ° in the X-ray diffraction peak is used as the baseline, and the baseline from 2θ = 35.5 ° Peak height L ₁ and 2θ
= 33 The ratio of the peak height L ₂ from baseline in ° L ₁ / L ₂ is 1.
It is necessary to be 5 or more, more preferably 3.0 or more. If it is less than 1.5, the stress varies so much that it cannot be used.

Next, a film forming method which gives the above various characteristics will be described.

As a 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. As the gas used for the sputter, an inert gas such as argon or sequinone is used, but other gases such as helium and nitrogen may be mixed. The substrate is usually silicon. The target is
It may be one obtained by sintering SiC powder into a predetermined shape, but the purity is 99% or more, preferably 99.9% or more because it is desirable that impurities in the film after film formation are as small as possible. The power applied to the target is preferably 5 W / cm ² or more. It is advantageous that the higher the applied power, the higher the film formation rate.

The substrate temperature at the time of sputtering is set to less than 500 ° C. so that the subsequent annealing can be effectively performed. Substrate temperature is 500 ° C
In the above case, the formed SiC film has an insufficient increase in crystallinity even after the subsequent annealing treatment, and as a result, the stress is likely to change due to the irradiation of the high energy beam. Conversely, if the substrate temperature falls below 50 ° C, the substrate and Si
This is not preferable because the adhesion of the C film decreases, and the preferable substrate temperature is 150 to 300 ° C.

The sputter pressure is very important to finish the internal stress of the film to the desired compressive stress. First, the sputtering temperature and the internal stress after the annealing treatment is 0.1 to 8.0 × 10 ⁹ dyne / cm ² which is the most preferable range in consideration of the temperature and time conditions of the annealing treatment to be performed later. The sputter pressure is determined so that the tensile stress becomes. Normal,
When annealing is performed, the stress changes to the tensile stress side,
The fluctuation amount is larger as the annealing temperature is higher. Therefore, it is necessary to previously obtain the relationship between the sputtering pressure and the internal stress at several levels of the sputtering temperature, and further to obtain the relationship between the annealing treatment condition and the variation amount of the stress. The sputtering pressure that satisfies the above requirements is 0.2 to 50 × 10 ⁻³ Torr.

The annealing conditions are Si finished in an amorphous state.
In order to impart crystallinity to the C film, the annealing temperature needs to be 500 ° C. or higher, preferably 700 ° C. or higher. Further, the annealing time is required to be 2 hours or more for a sufficient annealing treatment, and preferably 4 to 8 hours.
As an index of the increase in the crystallinity of SiC after the annealing treatment, evaluation is made from the waveform of the X-ray diffraction peak described above.

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 measurement and evaluation methods of the physical properties of the obtained SiC film are as follows.

Measurement of X-ray diffraction It was measured using an X-ray diffraction measuring device for thin films (TFD manufactured by Rigaku). Incident angle (θ) = fixed at 2 °, target is Cu, power is 40kV × 40mA.

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

High energy beam resistance 1.0KJ / high energy electron beam of 15eV as high energy
cm ^{2 was} irradiated, and the amount of change in the stress of the film due to irradiation was measured, and used as a measure of high energy beam resistance.

Suitable for membrane formation An amorphous BN film (hereinafter referred to as a-BN film) of 1.0 μm is formed on the back surface of the sample substrate by plasma CVD method, and this film is KOH
It was used as a protective film for the etching solution. Set a donut-shaped mask plate made of stainless steel on the a-BN film and dry-etch it with CF ₄ gas to remove the exposed a-BN film and then use 30% KOH.
The silicon surface exposed at was eluted by wet etching and turned into 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.

Measurement of visible light transmittance Multi-photospectrometer MPS-5000 with membrane
The transmittance (%) at the wavelength of 633 nm was measured by (Shimadzu product name).

(Examples 1 to 6 and Comparative Examples 1 to 3) A disk-shaped SiC target having a diameter of 3 inches and a thickness of 5 mm was used on the cathode side by using a high-frequency magnetron sputtering device SPF-332H (trade name of Nichiden Anelva Co., Ltd.) ( Purity 99.9%) was set. The substrate has a diameter of 3 inches and a thickness of 600μ
Argon gas was caused to flow at a flow rate of 7 cc / min while being heated to 250 ° C. using a double-sided polished silicon wafer of m. After adjusting the pressure in the chamber to a predetermined pressure with a valve communicating with an exhaust system, sputtering was performed for 15 minutes at a power density of 10 W / cm ^{2 to form} a SiC film with a thickness of 1.0 μm.

Next, the obtained silicon substrate provided with the SiC film was annealed by the following method. First, it was set on a wafer jig made of synthetic quartz and allowed to stand in a high temperature furnace. The pressure in the furnace is 20
mmTorr, the temperature was raised at a rate of 10 ° C./minute, and after reaching a predetermined temperature, the temperature was maintained for a certain period of time and then cooled at a rate of 10 ° C./minute. The internal stress after annealing was measured to obtain a tensile stress of 0.1 to 8.0 × 10 ⁹ dyne / cm ² , which is the stress required for membrane formation. By performing the annealing treatment, the internal stresses were all changed in the direction of tensile stress. The results are shown in Table 1.

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

The waveform of X-ray diffraction is shown in FIG. From this waveform, 2θ
2θ = with the line connecting the waveforms of = 30 ° and 2θ = 40 ° as the baseline
The ratio L ₁ / L ₂ of the peak height L ₁ from the baseline at 35.5 ° and the peak height L ₂ from the baseline at 2θ = 33 ° was determined, and the results are shown in Table 2. Further, as a comparative example, the same measurement was performed when the annealing treatment was not performed and when the annealing temperature was less than 500 ° C., and the results are also shown in Table 2. As shown in Table 2, when annealed at 500 ° C. or higher, L ₁ / L ₂ was 1.5 or higher, and no significant change in internal stress was observed even when irradiated with a high energy electron beam.

(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 having crystallinity defined by a waveform of X-ray diffraction is obtained, which has a high energy resistance that has not been obtained conventionally. The excellent SiC film, which has a beam property, has very little change in stress, and has no pinholes or nodules, can be stably mass-produced without variation. Change Can be processed into a mask for X-ray lithography,
Very useful in industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows X-ray diffraction waveforms targeting copper for defining the crystallinity of the SiC films of Examples 1-6 and Comparative Examples 1-3.

Claims (6)

[Claims] 1. An X-ray lithography characterized by using a target made of SiC to form a SiC film on a substrate by a sputtering method under a state of compressive stress, and then annealing this to make a state of tensile stress. For forming SiC film for automobiles. 2. The method for forming a SiC film for X-ray lithography according to claim 1, wherein the substrate temperature is lower than 500 ° C. and the annealing temperature is 500 ° C. or higher. 3. The method for forming a SiC film for X-ray lithography according to claim 1, wherein the tensile stress is 0.1 to 8.0 × 10 ⁹ dyne / cm ² . 4. The method for forming a SiC film for X-ray lithography according to claim 1, wherein the sputtering pressure is 0.2 to 50 × 10 ⁻³ Torr. 5. The method for forming a SiC film for X-ray lithography according to claim 1, wherein the SiC film under tensile stress contains crystalline SiC. 6. The X-ray diffraction peak of the SiC film according to claim 1, which targets copper at 2θ = 30 ° and 2θ = 40.
With the line connecting the waveforms of ° as the baseline, the ratio L ₁ / L ₂ of the peak height L ₁ from the baseline at 2θ = 35.5 ° and the peak height L ₂ from the baseline at 2θ = 33 ° is 1.5 or more. A characteristic method for forming a SiC film for X-ray lithography.