JPH0580245B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for producing a solid product containing silicon as a main component using a laser. [Prior Art] In recent years, solid thin films have attracted attention as materials in the field of electronics, and silicon films are used in solar cells, semiconductor devices, integrated circuits, and the like. To manufacture such a film, there is a method in which decomposed products produced by photolysis or discharge decomposition of gas are attached to the surface. Laser CVD (Chemical Vapor CVD) uses laser light as the light source for photolysis.
Deposition). Conventionally, methods using SiH ₄ and Si ₂ H ₆ gases are known as methods for forming silicon films by carbon dioxide laser CVD. In particular, carbon dioxide laser using SiH ₄ gas, which is cheap and easy to obtain.
Research on the formation of silicon films using CVD methods is active. On the other hand, the present inventors have succeeded in performing isotope separation of silicon using a laser using a silicon compound (Japanese Patent Application No. 21577/1982). For example Si ₂ F ₆
When isotope separation is performed using a carbon dioxide laser, ²⁹ Si and ³⁰ Si are concentrated in the low-order silane _SiF4 . [Problems to be Solved by the Invention] However, the production of solid products or thin films using a laser using a compound having an Si--F bond has not been achieved to date. An object of the present invention is to provide a method for producing a silicon-based solid product and a silicon isotope-selective solid product by laser using a compound having a Si--F bond. [Means for solving the problem] For the past few years, we have been researching the separation and concentration of silicon isotopes using infrared multiphoton dissociation of gaseous silicon compounds. On the way,
We found that compounds with Si-F bonds undergo efficient infrared multiphoton dissociation using a CO ₂ TEA laser, giving both gaseous and solid products.
Particularly in the case of Si ₂ F ₆ , a large amount of solid products are produced, and the main component thereof is silicon. This could be a new method for manufacturing silicon films.
Another interesting point about Si ₂ F ₆ is that the isotope ratio in the silicon film can be changed by appropriately selecting the irradiation wavenumber of the CO ₂ TEA laser.
In other words, it is possible to produce a silicon film selectively enriched with ²⁸ Si, ²⁹ Si, or ³⁰ Si. The present invention was completed based on the above findings, and involves irradiating a gas atmosphere of a compound having Si-F bonds with a laser to cause a photodecomposition reaction, thereby obtaining a solid product mainly composed of silicon. It is characterized by this. [Operation] When a suitable compound is irradiated with laser light, whether in the gas or liquid phase, solid photodecomposition products may adhere to the inner wall of the reaction vessel. Laser CVD is an application of this method to the production of significant films.
One significant membrane is a silicone membrane. on the other hand,
In recent years, rapid advances in laser technology have led to the development of high-power lasers over a wide wavelength range, and CO ₂ lasers are well-known in the infrared range. In particular, the CO ₂ TEA laser emits pulsed laser light with extremely high fluence, and its use led to the discovery of a new photochemical phenomenon called infrared multiphoton dissociation. The excitation wavelength of the stretching vibration of the Si-F bond often overlaps with the wavelength region of the CO ₂ laser. and
Compounds such as SiF ₃ H _, SiF ₃ Cl, SiF ₃ Br, SiF ₃ CH ₃ and Si ₂ F ₆ can be
When irradiated with the appropriate fluence, infrared multiphoton dissociation occurs. At this time, it was also found that a white or colored solid product was produced simultaneously with the gaseous product represented by SiF ₄ . In particular, Si ₂ F ₆ easily undergoes infrared multiphoton dissociation even at low fluences and efficiently produces solid products. The above results can be directly applied to CVD. On the other hand, laser light has an extremely narrow wavelength spread, and if there is an isotopic shift in the absorption of molecules, isotope-selective photolysis can be performed at an appropriate wavelength. As a result, isotope-selective CVD will be achieved. In principle, this can be said to be possible regardless of infrared multiphoton dissociation based on vibrational excitation of molecules or ultraviolet/visible light dissociation based on electronic excitation. For example, Si ₂ F ₆ has a very strong absorption band at 985 cm ^-1 based on the stretching vibration of the Si--F bond. When irradiated with CO ₂ TEA laser light near this wave number, it decomposes efficiently and produces SiF ₄ as a gas product. At the same time, white or colored solids are also formed inside the reaction tube. Solids formed in areas that are strongly irradiated with laser light are brown, and solids that form in areas that are weakly irradiated are white. However, when this white solid was heated or further irradiated with CO ₂ laser light, it was observed that it changed from yellow to brown. The main component of such a colored solid is silicon, although fluorine remains.
Quantitative analysis of Si ₂ F ₆ shows that it disappears in the reaction.
55-60% of silicon _{in Si2F6 is} gaseous product _Si2F6
It was found that the remaining 45-40% was converted into solid product. It has already been clarified that when Si ₂ F ₆ is irradiated with CO ₂ TEA laser light at around 940 to 960 cm ^-1 , ²⁹ Si, ³⁰ Si, etc. are concentrated in the gaseous product SiF ₄ (Patent application 1986- No. 21577). ³⁰ The concentration of Si reaches about 50%. On the other hand, as a result of subsequent research, we found that ²⁹ Si and ³⁰ Si are also concentrated in solid materials. Generally, when irradiated with high wave number laser light, ²⁸ Si is present in the solid product, and 940 to 960
When irradiated with laser light near cm ^-1 , ²⁹ Si is concentrated in the solid product. In this way, isotope-selective CVD is realized. [Effects of the Invention] According to the present invention, a solid product containing silicon as a main component can be obtained by laser using a compound having an Si--F bond, and a silicon thin film can be created using this. It is also possible to create silicon isotope selective products and thin films. EXAMPLE The drawing is a schematic representation of the apparatus used to carry out the invention. Si ₂ F ₆ is supplied into the reaction vessel 1 from a cylinder 3 via a pressure flow regulator 2 . The fixing plate 4 is placed in the atmosphere where Si ₂ F ₆ exists, and the fixing plate 4 is heated by the heater 5 . The CO ₂ laser beam 6 is irradiated onto the fixing plate 4 through the infrared window 7.
is formed by germanium, NaCl, KBr, etc. Furthermore, a pressure flow regulator 8 is installed on the inner surface of this window 7.
Argon gas supplied from a cylinder 9 is blown through the window to prevent solid products from adhering to the window. Therefore, reaction vessel 1 contains cylinder 3.
Si ₂ F ₆ with a natural isotope composition filled in is injected with controlled pressure and flow rate, and then
Through a photochemical reaction induced by the CO ₂ laser beam 6, it flows out together with some reaction products and argon.
At this time, of the gases flowing out from the reaction vessel 1, all but argon are collected in a trap 10 cooled with liquid nitrogen. At this time, the trap 11 is closed. In the case of thermal decomposition of a solid sample attached to the fixing plate or the next step of laser photolysis of the solid sample, close the trap 10 and open the trap 11 to make the reaction vessel 1 sufficiently _{evacuated .} Each decomposition reaction was carried out without introducing argon, and the decomposition products were collected in the trap 11. In either case, the collected gas is mostly SiF ₄ .
Although it is a mixture of SiF ₄ and a small amount of Si ₂ F ₆ , its quantitative analysis can be performed by low-temperature distillation, gas chromatography, gas chromatobluff mass spectrometry,
Infrared absorption method and mass spectrometry were used. When the partial pressures of argon and Si ₂ F ₆ were adjusted to, for example, about 2 torr each and irradiated with pulsed light from a CO ₂ TEA laser, it was observed that a white or colored film was formed on the fixing plate. .
For example, P(12) in the 10.6 μm band of CO ₂ TEA laser.
The brown film produced when the line was irradiated with a fluence of 0.6 to 0.7 Jcm ^-2 and a repetition rate of 10 Hz.
The analysis results by ESCA are shown in Table 1. As is clear from this table, the main component of the film is silicon. Generally, the solid substance deposited on the fixing plate is white or pale yellow at first, but changes to dark brown as the irradiation continues. Also, the supply of Si ₂ F ₆ was stopped,
Similar changes were observed when the already attached solid material was further irradiated with the laser, or when the temperature of the fuser plate was simply increased.

[Table] When the reaction vessel was sufficiently degassed with a certain amount of film attached and then heated, the appearance of the film changed as described above, but at the same time it was observed that SiF ₄ was emitted from the film. The results of measuring the isotope ratio of the generated SiF ₄ are shown in Tables 2 and 3. The isotopic ratio of natural silicon is ²⁸ Si: ²⁹ Si: ³⁰ Si = 92.23%: 4.67
%: 3.10%. SiF ₄ generated from the film formed by irradiation with 10P(8) rays contains a relatively large amount of ^29Si ,
SiF ₄ generated from the film produced by irradiation with 10P(12) radiation contains 34% ³⁰ Si. By thermal decomposition of the membrane
Since isotope enrichment cannot be considered to occur in the process of SiF ₄ generation, it is concluded that each isotope was enriched in the film itself.

[Table] The main ion in SiF ₄ mass spectrometry is SiF ₃ ⁺ .

【table】 [Brief explanation of the drawing]

The drawing is a schematic representation of the apparatus used to carry out the invention. 1... Reaction container, 2, 8... Pressure flow regulator,
3, 9...Cylinder, 4...Fixing plate, 5...Heater, 6...CO ₂ laser light, 7...Infrared window, 1
0,11...trap.

Claims (1)

[Claims] 1. Using a laser characterized in that a laser is irradiated into a gas atmosphere of a compound having a Si-F bond to cause a photodecomposition reaction and to obtain a solid product mainly composed of silicon. A method for producing a solid product whose main component is silicon. 2 The compound having the Si-F bond is Si ₂ F ₆ ,
A method for producing a solid product mainly composed of silicon using a laser according to claim 1, characterized in that the product is SiF ₃ H, Si ₃ FCl, SiF ₃ Br, or SiF ₃ CH ₃ . 3. A method for producing a solid product containing silicon as a main component using a laser according to claim 1, wherein the laser is a carbon dioxide laser. 4. The method for producing a solid product mainly composed of silicon using a laser according to claim 1, wherein the solid product is a silicon isotope selective solid product.