JP2000345342A - Method for producing high-purity isotope silicon crystal film - Google Patents

Abstract

(57) Abstract: ²⁸ Si, ²⁹ Si and a high purity of ³⁰ Si isotope silicon having a controlled composition, to allow the provision of good crystallinity of the crystalline film. SOLUTION: ²⁸ Si by plasma CVD using silicon fluoride having a changed silicon isotope ratio as a source gas,
A method for producing an isotope silicon crystal film in which a silicon isotope of ²⁹ Si or ³⁰ Si has a composition different from the natural isotope ratio, wherein the silicon fluoride gas, the rare gas and hydrogen are used for a plasma CVD reaction. A gas is supplied at a ratio of silicon fluoride gas / rare gas: 0.04 to 1 silicon fluoride gas / hydrogen gas: 0.04 to 1 and an unreacted silicon fluoride gas is circulated to the plasma CVD reaction. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity isotope silicon crystal film. More specifically, the invention of this application relates to a method for producing a high-purity isotope silicon crystal film useful as an electronic / electric material such as a semiconductor element in an electronic material, an electric material, and a chemical material, or a heat-resistant / high-temperature material. is there.

[0002]

2. Description of the Related Art Conventionally, silicon crystal films have been used for semiconductor elements, heat-resistant materials and the like.

[0003] Such a silicon crystal film is generally
Silane (SiH ₄ , Si ₂ H ₅ etc.) and silicon chloride (S
iCl ₄ , Si ₂ Cl ₅ etc.), chlorosilane (SiHC)
l ₃ , SiH ₂ Cl _2, etc.) as a raw material by various epitaxial methods such as a CVD method.

[0004] To date, in order to create a silicon crystal film with higher performance, optimization of raw material compounds,
Researches such as improvement of various epitaxial methods and optimization of various conditions in a manufacturing process have been advanced.

However, it cannot be denied that there is inevitably a limit in terms of improving the performance and functionality of the conventional silicon crystal film.

Accordingly, the inventors of the present application have focused on a stable isotope of silicon as a completely different viewpoint from the prior art, and attempted to create a new function and improve the performance of a silicon crystal film by controlling the stable isotope. That has been the challenge.

[0007] In response to such a problem,
The bright people²⁸Si,²⁹Si, and ³⁰Any of Si
Silicon isotopes having a composition that exceeds the natural isotope ratio
Isotope silicon crystal film by plasma
Isotopically characterized by being manufactured by CVD.
A method for manufacturing a con-crystal film was proposed (Journal of Surface
Analysis, Vol.4, No.2 (1998) -pp372-376).

According to this method, the conventional Si natural isotope ratio, ²⁸ Si: ²⁹ Si: ³⁰ Si = 92.23: 4.6.
It is possible to provide a silicon crystal film having a controlled Si isotope composition, which is essentially different from the silicon crystal film of 7: 3.10.

In this proposed method, the silicon isotope ratios of the raw materials ²⁰ Si, ²⁹ and ³⁰ Si are previously prepared so as to be different from the natural isotope ratio.

The details are as follows.

That is, Si ₂ F ₅ gas, which is a kind of silicon fluoride gas, has an infrared absorption spectrum due to asymmetric stretching vibration of Si—F bond in an infrared region of a wave number band of 1000 cm ⁻¹ .

The vibrational spectrum of Si—F is
So slightly different,²⁸Si,²⁹Si,³⁰Becomes Si
About 10 cm toward the lower wave number^-1Spelled out. On the other hand,
Usual CO_TwoGas laser is also 1000cm^-1In the obi
Has several oscillations. Therefore, CO_TwoGas laser
-Select an appropriate oscillation line from the oscillations of_TwoF _Five
By irradiating the gas,²⁹S-F,³⁰Vibration of SF
Can be excited.

And the following equation

[0014]

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Through the above reaction, Si containing ²⁹ Si and ³⁰ Si
₂ F ₅ (gas) is selectively SiF ₄ (gas) and SiF ₂
(Solid) and the isotope silicon is
It is concentrated in iF ₄ and SiF ₂ . On the other hand, unreacted isotope silicon is concentrated in the undecomposed gas.

The above-mentioned methods already proposed are significant as enabling the production of an unprecedented isotope silicon crystal film.

However, the subsequent studies by the inventor of the present application show that the isotope silicon crystal film having higher quality, that is, a higher purity (100% or almost 100%) can be obtained as a high-purity silicon crystal film without impurities. ) Had to be admitted that further creativity was necessary for efficient production.

[0018]

SUMMARY OF THE INVENTION The claimed invention is as to solve the problem as described above, the first, by a plasma CVD silicon fluoride with varying silicon isotope ratio as the raw material gas ²⁸ Si, ²⁹ Si, and ³⁰ S
i is a method for producing an isotope silicon crystal film having a composition in which any of the silicon isotopes is different from the natural isotope ratio,
In the plasma CVD reaction, the above-mentioned silicon fluoride gas, rare gas and hydrogen gas are mixed in a volume ratio of silicon fluoride gas / rare gas: 0.04 to 1 silicon fluoride gas / hydrogen gas: 0.04 to 1 And a method for producing a high-purity isotope silicon crystal film characterized by circulating unreacted silicon fluoride gas in a plasma CVD reaction.

Second, the invention of this application is characterized in that, prior to the plasma CVD reaction, only the rare gas is supplied to the plasma CVD reaction section in advance and plasma discharge is performed, wherein Provided is a method for manufacturing a silicon crystal film.

Thirdly, the invention of this application also provides a high-purity isotope silicon crystal film produced by the first or second method.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and embodiments thereof will be described below.

First, the isotope silicon crystal film aimed at by the production method of the present invention has a <I> natural Si isotope ratio of ²⁸ Si,
It is required that any of the silicon isotopes of ²⁹ Si and ³⁰ Si be present at a different ratio, and that the crystal is a <II> crystal film.

Further, in the method of the present invention, <III> the multi-elements from the silicon fluoride gas of which the isotope ratio is changed as the raw material and from the substrate or the inner wall of the apparatus of the plasma CVD reaction section, etc. High purity isotope silicon crystal film with minimal contamination, <IV> 100%
Another requirement is that an isotope silicon crystal film can be produced at a high yield with a reaction yield of almost 100%.

According to these requirements, for example, the high-purity isotope silicon crystal film provided by the present invention can improve the circuit integration of a semiconductor component. Generally, ²⁸
Si is a stable isotope occupying the majority, and a Si single crystal consisting of only ²⁸ Si has an increase in thermal conductivity due to reduction of isotope scattering. By using this property, a silicon semiconductor formed of silicon crystal film mainly made of ²⁸ Si, the can as compared with conventional Si natural isotopic silicon semiconductor, releasing heat generated by the power consumption more rapidly In a semiconductor component such as an LSI, the degree of circuit integration can be increased more than ever.

Further, the present invention enables the activation material to be derivatized. That, S mainly of ²⁹ Si and ³⁰ Si
Since the iC material is a less induced radioactive material as compared with the natural isotope SiC, the SiC material composed of the isotope silicon crystal film mainly composed of ²⁹ Si and ³⁰ Si according to the present invention is:
It becomes a less induced activation material.

Further, the present invention makes it possible to reduce the resistivity of a P-doped n-type silicon wafer. That is, by using the silicon crystal film with enhanced ³⁰ Si concentration of the present invention, are uniformly accurately P dope, it is possible to provide a large diameter n-type silicon wafer of low resistivity, the miniaturization of the semiconductor element Make it possible.

Of course, not only the above-described improvement in the degree of circuit integration of semiconductor components, low induction of the activating material, and low resistivity of the P-doped n-type silicon wafer, but various possibilities are opened up. It is.

For example, a silicon crystal film is widely used not only as a semiconductor element but also as a main constituent material of heat-resistant and high-temperature materials such as SiC and Si ₂ N _{4. The} composition ratio of Si isotope of the present invention is arbitrarily controlled. By using the isotope silicon crystal film, excellent characteristics such as nuclear properties and thermophysical properties are realized.

Further, in the present invention, ²⁹ Si
Has only one-half quantum spin among the three stable isotopes, so that it can be applied to materials in the field of nuclear magnetic resonance.

In the method of manufacturing an isotope silicon crystal film of the present invention as described above, the silicon isotope ratio of silicon fluoride as a source gas is changed in advance.

As a method for changing the isotope ratio, various methods including conventionally known methods, including the method proposed by the present inventors, may be used. As a commercially available gas substance, for example, an isotope-enriched raw material gas can be used. The isotope enrichment method is an electromagnetic method, a laser method, a plasma method, and the like. 2) The gas diffusion method,
There are a centrifugal separation method, a distillation method, a chemical exchange method, a gas diffusion method and the like.

In the method for producing a high-purity isotope silicon crystal film according to the present invention, a rare gas and a hydrogen gas together with a silicon fluoride gas having a changed silicon isotope ratio are used for a growth reaction by plasma CVD. To supply.

As a rare gas, argon (Ar), helium (He), or the like is used, and these rare gases are indispensable for producing a high-purity isotope silicon crystal film. The same applies to hydrogen gas. As for the supply amount to these plasma CVD reactions, as described above, as a volume ratio per unit time, <A> silicon fluoride gas / rare gas = 0.04 to 1 <B> silicon fluoride gas / Hydrogen gas = 0.04 to 1.

If the ratio of the rare gas exceeds 1 in the ratio <A>, the plasma is not stabilized, and the film forming efficiency is reduced. On the other hand, even when the ratio of <A> is less than 0.04 or when there is a large excess of a rare gas, it is difficult to efficiently form an isotope silicon crystal film. For this reason, a rare gas is used so that the ratio is as shown in <A>. When the ratio of the <B> exceeds 1,
In the following formula, a sufficient amount of hydrogen to reduce to metal Si cannot be secured.

On the other hand, if this ratio is smaller than 0.04, a crystalline film cannot be obtained.

[0036]

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The silicon fluoride gas may be of various types such as SiF ₄ and SiF _{6 as} long as the isotope ratio is changed so as to be different from the natural abundance ratio.

Further, in the manufacturing method of the present invention, the unreacted silicon fluoride gas is converted into a plasma CV
It needs to be recycled to the D reaction. This cyclic use is an indispensable condition for making an isotope silicon crystal film of high purity, good crystallinity, and a high reaction yield for efficient film formation.

This circulation is preferably carried out with the total amount of unreacted silicon fluoride or at least 70% by volume or more.

The ratio of the rare gas and the hydrogen gas is determined by the above <A>
By using the ratio of <B> and circulating and using unreacted silicon fluoride, the contamination of impurities is minimized, that is, to a level of 1 mass ppm or more as a whole, and a high-purity isotope silicon crystal film is obtained. Although it is not possible to determine the reason why the compound can be manufactured, it is presumed that the fact that the isotope ratio is changed is not a small factor.

In the present invention, it is also effective to introduce and supply a rare gas in advance and perform plasma discharge prior to the plasma CVD reaction. This contributes to the improvement of the purity of the high-purity isotope silicon crystal film, high yield, and high-efficiency film formation.

Various substrates such as Si and SiO ₂ may be used as the substrate in the plasma CVD reaction, and the temperature of the substrate is preferably in the range of 250 to 650 ° C. The total pressure of the plasma CVD reaction zone is preferably 6
The range is 6.7 to 700 Pa.

The plasma generating means may be a microwave, a high frequency excitation, or other various means.

In the case of microwave irradiation, more preferably, the output is in the range of 200 to 350 W, and the frequency is 1 to 3 G.
Hz range.

According to the invention of this application as described above,
A high-purity isotope silicon crystal film can be easily manufactured. That is, according to the method of the present invention using a silicon fluoride gas having a controlled silicon isotope composition, a high-purity isotope silicon crystal film is reduced to 100% or almost 100%.
Can be efficiently obtained with a yield of

Hereinafter, the present invention will be described in more detail with reference to examples.

[0047]

[Example] ²⁸ Si isotope-enriched fluorinated silane gas (Si ₂
F ₅ ), Ar gas, and H ₂ gas were used as source gases, and a ²⁸ Si isotope-enriched silicon crystal film was produced using the plasma CVD apparatus shown in FIG.

The ratio of the silicon isotope in the ²⁸ Si isotope-enriched silicon fluoride gas was measured by a quadrupole mass spectrometer, and as a result, ²⁸ Si: ²⁹ Si: ³⁰ Si = 98.02: 1.6.
1: 0.37, which is significantly different from the conventional Si natural isotope ratio of 92.23: 4.67: 3.10.

In the CVD apparatus shown in FIG. 1, the inside of the reaction tube was previously subjected to plasma discharge with Ar gas, and then the quartz tube was supplied at a supply rate of 10 sccm of Ar gas, 10 sccm of H ₂ gas, and ₂ sccm of the above-mentioned silane fluoride gas. It was introduced into a CVD reaction tube, and at the same time, a microwave having an output of 350 W was applied to decompose it into plasma, and an isotope silicon crystal film was deposited on a substrate SiO ₂ which was placed at a downstream region and was heated to 450 ° C.

The unreacted fluorinated silane was collected by a cold trap and circulated again into the plasma CVD reaction zone.

An isotopic silicon crystal film was obtained with a yield of 100%.

FIG. 2 shows the microstructure of the cross section of the prepared silicon thin film observed by using a scanning electron microscope, and a columnar structure growing in the normal direction of the thin film can be seen. This, combined with the result of the X-ray diffraction spectrum of FIG.
This shows that the thin film grows crystal in the columnar direction.

The spectrum and crystallinity of FIG. 3 will be further described. In the crystal, atoms are periodically arranged to form a spatial lattice, and the interval between the atoms is usually about 10 ^-10 m. When X-rays having the same wavelength or less are incident on the lattice, the crystal lattice acts as a diffraction grating,
The lines are scattered in a particular direction. If the incident angle of X-rays incident at a specific angle θ and the reflection angle are equal to a certain atomic plane created by a group of atoms in the crystal, the phases of the scattered waves are the same, and the waves are buffered and strengthen each other . In FIG. 3, the horizontal axis represents the angle of 2θ, which is the sum of the incident wave and the reflected wave of the X-ray irradiated on the thin film, and the vertical axis represents the relative intensity of the scattered wave. If the thin film shows crystallinity, a specific atomic plane (Si (11
The reflected waves from (1), Si (220), Si (311), etc.) are observed as sharp peaks because they have the same phase and reinforce each other. Conversely, when the thin film is non-crystalline, the phases of the reflected waves are completely different, so that only a flat signal can be obtained. Accordingly, a sharp diffraction wave is observed from each atomic plane in FIG. 3, which indicates that the thin film has a good crystallinity.

Table 1 below shows the results of chemical analysis of metal impurities in the obtained isotope silicon crystal film. All impurities were 1 ppm by mass or less, and it was confirmed that an extremely high-purity silicon film was obtained.

When the plasma discharge was not performed by the Ar bus in advance, an increase in the amount of impurities was confirmed.

[0056]

[Table 1]

[0057]

Effects of the Invention The present invention, as described above in detail, ²⁸ Si, ²⁹ Si and, in high purity isotopic silicon with a controlled composition of ³⁰ Si, and allows the provision of good crystallinity of the crystalline film For example, it is possible to improve the degree of circuit integration of a semiconductor component, reduce the induction of a radiation material, and reduce the resistivity of a P-doped n-type silicon wafer, and to create a silicon material with higher performance.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an experimental apparatus used in an embodiment of the present invention.

FIG. 2 is an electron microscope (SEM) photograph illustrating the microstructure of a cross section of a thin film obtained as an example.

FIG. 3 is an X-ray diffraction spectrum of a thin film obtained as an example.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA04 AA06 AA16 AA17 BA29 BB00 BB03 CA05 DA02 DA06 EA12 FA01 JA06 LA15 5F045 AA08 AA09 AB02 AC02 AC16 DP04 EG09

Claims (3)

[Claims] 1. A method according to claim 1, wherein said silicon isotope ratio is varied and said silicon fluoride is used as a raw material gas by plasma CVD to obtain ²⁸ Si,
A method for producing an isotope silicon crystal film in which a silicon isotope of ²⁹ Si or ³⁰ Si has a composition different from the natural isotope ratio, wherein the silicon fluoride gas, the rare gas and hydrogen are used for a plasma CVD reaction. A gas is supplied at a ratio of silicon fluoride gas / rare gas: 0.04 to 1 silicon fluoride gas / hydrogen gas: 0.04 to 1 and an unreacted silicon fluoride gas is circulated to the plasma CVD reaction. A method for producing a high-purity isotope silicon crystal film. 2. The method for producing a high-purity isotope silicon crystal film according to claim 1, wherein prior to the plasma CVD reaction, only a rare gas is supplied to the plasma CVD reaction section in advance to cause plasma discharge. 3. A high-purity isotope silicon crystal film produced by the method according to claim 1.