JPH0544818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thin film forming apparatus using a photo-excited gas phase chemical reaction, and particularly to a thin film forming apparatus with excellent mass productivity and workability.

[Background of the invention]

One of the methods for forming thin films through gas-phase reactions is a method in which the reaction is activated by light energy (hereinafter referred to as "light").
CVD method) is known. Compared to reaction activation using thermal energy, plasma, etc., activation using light energy allows the reaction to occur at a lower temperature, and also enables stable thin film formation without damage from electromagnetism or accelerated charged particles, so it can be used over a wide range of applications. Applications are being considered. As light energy, laser light, mercury lamp, halogen lamp, deuterium lamp, etc. are known. Among these, mercury lamps are often used from the viewpoints of wavelength, intensity, irradiation area, ease of handling, etc. suitable for reaction activation. In particular, reactions that use the resonance line of a low-pressure mercury lamp as excitation light, add mercury vapor to the raw material, and utilize the sensitizing effect are efficient and are widely used.

Figure 1 shows a conventional thin film forming apparatus using the optical CVD method. The apparatus is roughly divided into three parts: a reaction system 10, a reaction gas supply system 20, and an exhaust system 30.

The reaction system 10 includes a reaction container 11, an excitation light source 13,
It consists of a substrate support stand 14 and its heating source 15. The reaction vessel 11 is equipped with a light entrance window 12 made of transparent quartz or the like that transmits excitation light. Film-forming substrates, such as silicon wafers 16, are arranged on a substrate support 14 in a reaction vessel 11, and excitation light is irradiated almost perpendicularly to the surface of the silicon wafers 16. As the heat source 15, a resistance heater, an infrared lamp, or the like is used.

The reaction gas supply system 20 contains monosilane (SiH ₄ ),
Raw material gases such as oxygen (O ₂ ), ammonia (NH ₃ ), nitrous oxide (N ₂ O), and phosphine (PH ₃ ) pass through the flow meter 21, while liquid raw materials such as hydrazine (N ₂ H ₄ ) pass through a carrier gas. is used to supply the reaction vessel 11. Further, mercury vapor as a sensitizer is supplied to the reaction vessel 11 by flowing a reaction gas or other carrier gas through a mercury evaporator 22 in a constant temperature bath.

The exhaust system 30 uses an exhaust device 31 such as a rotary pump or a booster pump to replace the gas in the reaction vessel 11 and adjust the pressure of the atmosphere during the reaction. Additionally, a device 32 for trapping and removing unreacted gases and reaction products is added.

The problem here is the following regarding the reaction system 10.

A film is also deposited on the inner surface of the excitation light entrance window 12 of the reaction vessel 11, resulting in poor excitation light transmittance. The rate of photochemical reaction, that is, the rate of film deposition, is proportional to the intensity of the excitation light, so if the transmittance of the excitation light decreases, the rate of film deposition will decrease, and furthermore, the reaction will stop, making it impossible to obtain the desired film thickness. .

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film forming apparatus that prevents the formation of an undesired film on the inner surface of a light entrance window of a reaction vessel, and thereby has good workability and mass productivity.

[Summary of the invention]

The present invention is characterized by a thin film forming apparatus that sprays an inert gas onto the inner surface of the light entrance window of a reaction vessel to prevent source gas contributing to film deposition from coming into contact with the inner surface of the light entrance window.

[Embodiments of the invention]

The present invention will be explained in detail below using examples.

FIG. 2 shows an embodiment of the device of the present invention, in which an inert gas supply nozzle that does not produce deposits is provided in the reaction vessel, and the inert gas is sprayed onto the inner surface of the light entrance window. . The same parts as in FIG. 1 are indicated by the same symbols. The reaction vessel 11 is made of stainless steel and has a circular box shape with a diameter of 200 mm and a height of 80 mm, and is provided with a light entrance window 12 made of transparent quartz, especially synthetic quartz that has good transmittance for short wavelength light such as vacuum ultraviolet light. There is. The substrate support stand 14 is made of aluminum and can be rotated from the outside in order to make the deposited film thickness uniform. The heat source 15 is a resistance heater equipped with a temperature regulator and can maintain the substrate 16 at a desired temperature. The excitation light source 13 is a low-pressure mercury lamp with a wavelength of 185 nm and
Emits a resonance line of 254nm. Although not shown in the drawings, the space between the lamp house and the light entrance window 12 of the reaction vessel 11 is replaced with nitrogen gas to prevent light absorption, particularly ozone generation.

The gas supply system is the same as shown in Fig. 1 with another gas supply nozzle 17 for supplying one or a mixture of inert rare gases such as hydrogen, halogens and their hydrides, nitrogen, argon, and helium. I made it possible. This additional gas supply nozzle consists of a stainless steel pipe with a diameter of 1/4 inch arranged in a ring shape near the inner surface of the light entrance window, and multiple gas injection holes with a diameter of 0.25 mm facing the light entrance window. There is.

The exhaust system used a rotary pump with an exhaust speed of 950/min and a mechanical booster pump with an exhaust speed of 100 m ³ /h.

Experimental Example 1 (Silicone film formation example) A mercury evaporator 22 (mercury vapor pressure 5×
10 ^-3 Torr) to the reaction vessel 11.
The film-forming substrate 16 was a silicon wafer with a diameter of 3 inches, and the substrate temperature was set at 200°C. Hydrogen was supplied at 400 ml/min to the inert gas nozzle 17 for preventing film deposition on the light entrance window. The pressure inside the reaction vessel 11 is 1.55 Torr. 2700~ for 20 minutes reaction
A film of 3200 Å was deposited, and the average film deposition rate was approximately 150 Å.
Å/min. If inert gas (hydrogen in this example) is not blown onto the inner surface of the light entrance window,
An amorphous silicon film is deposited on the inner surface of the light entrance window, and within a few minutes, the light entrance window becomes cloudy in brown color, blocking the passage of excitation light and preventing the reaction from proceeding.
It is not possible to obtain a film thickness greater than that.

Experimental Example 2 (Silicone film formation example (2)) 500 ml/min of a mixed gas of 5% monosilane and 95% nitrogen is supplied to the reaction vessel 11 through the mercury evaporator 22 as a reaction gas. The gas nozzle 17 for preventing film deposition on the light entrance window 12 is filled with 100 ml of hydrogen chloride.
Supply a mixed gas of 200ml/min and nitrogen at 200ml/min.
A quartz louver 18 is installed between the raw gas for film deposition on the substrate and the gas for preventing film deposition on the inner surface of the light incident window in order to prevent mixing and improve the efficiency of both.
(scale board) was installed. The plates of the louver 18 are 100 μm thick, 6 mm long, and 4 mm apart, and the set angle is perpendicular to the substrate surface, that is, parallel to the speed of excitation light, so as not to impede the irradiation of the excitation light and to reduce the conductance of both gases. . The exhaust gas was released to atmospheric pressure. Other reaction conditions were the same as in Experimental Example 1. After one hour of reaction, an amorphous silicon film of about 4000 Å was deposited. Average film deposition rate is 67Å/
min, which is inferior to Experimental Example 1 and the conventional example, but it has the advantage of being able to operate under atmospheric pressure and forming a thick film with no clouding of the light entrance window 12. Here, hydrogen chloride gas not only prevents direct contact between monosilane and the light entrance window, but also has the effect of etching the amorphous silicon that has undesirably deposited on the inner surface of the light entrance window, thereby preventing the light entrance window from fogging. It is extremely effective.

Experimental example 3 (Formation of silicon oxide film) 500 ml/min of a mixed gas of 5% monosilane and 95% nitrogen was passed through the mercury evaporator 22 as a raw material gas.
and nitrous oxide at 250 ml/min to the reaction vessel 11. Although the substrate 16 is not heated, the temperature is raised to 60 to 70° C. by irradiation with the mercury lamp 13. Nitrogen is supplied at 2000 ml/min as an inert gas to prevent film deposition on the inner surface of the light entrance window 12. The pressure inside the reaction vessel is atmospheric pressure. When forming a silicon oxide film, if pure silicon oxide is formed in the form of a film, clouding of the light entrance window will not occur, but if silicon chemotactic particles adhere, the incident light will be scattered and the intensity of the excitation light will be reduced. lower. This tendency is particularly strong in reactions where the film deposition rate is high under atmospheric pressure.
For this reason, it is effective to spray an inert gas that does not cause deposits on the inner surface of the light entrance window. A 1 μm silicon oxide film was formed in about 15 minutes of reaction.

Experimental example 4 (Formation of silicon nitride film) Silicon monosilane 8ml/min as raw material gas
and 72 ml/min of ammonia are supplied to the reaction vessel 11 through the mercury evaporator 22. Substrate 16 is 200℃
heated to. Helium is supplied at 300 ml/min as an inert gas to prevent deposition on the inner surface of the light entrance window 12. The pressure inside the reaction vessel is 3 to 4 Torr. A 30 minute reaction deposits a 2200-2700 Å film, with an average film deposition rate of about 70-90 Å/min. If an inert gas is not sprayed onto the inner surface of the light entrance window, the reaction will stop in about 15 minutes, making it difficult to obtain a film thickness of 1000 to 1500 Å or more.

The above has described in detail the formation of thin films of silicon and its compounds, but when dopants such as phosphorus and boron are further added to these, or other materials such as compound semiconductors, metals and their oxides, carbides,
The present invention can be similarly applied to the formation of thin films such as nitrides.

Inert gases that do not cause deposits on the inner surface of the light entrance window include not only gases such as nitrogen and argon whose light absorption cross section or extinction cross section hardly reacts;
A gas having the property of reacting with deposits and etching them, such as halogen or its hydride, can be used. Particularly in the latter case, a conductance control board such as a louver or a differential exhaust system is effective in order to reduce mixing with the source gas.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the formation of an undesired film and the adhesion of fine particles on the inner surface of the light entrance window of a reaction vessel in the optical CVD method, and it is possible to form a thick film with a high film deposition rate. For this reason, we were able to develop an optical CVD device with good workability and mass production.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional optical CVD apparatus, and FIG. 2 is a schematic diagram of an optical CVD apparatus according to the present invention. 11... Reaction container, 12... Light entrance window, 13...
... Excitation light source, 14 ... Substrate support stand, 15 ... Heating device, 16 ... Substrate, 17 ... Gas nozzle for preventing fogging of the light incidence window, 18 ... Louver.

Claims (1)

[Scope of Claims] 1. (a) A reaction vessel having a window through which light of a selected wavelength is incident; (b) A surface of the reaction vessel on which a substrate on which a thin film is to be formed is placed, facing the incident light. (c) heating means having a temperature control function for heating the substrate to a predetermined temperature; (d) means for guiding reaction gas into the reaction vessel; (e) means for guiding exhaust gas from the reaction vessel. (f) Means for blowing an inert gas onto the inner surface of a window of the reaction vessel through which light enters; (g) Means for blowing the gas onto a support in the reaction vessel. 1. A thin film forming apparatus using a photo-excited gas phase chemical reaction, comprising: a louver having a space substantially parallel to the direction in which light is incident;