JPS5944770B2 - Cleaning method for plasma CVD reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning a reactor in the production of silicon carbide thin films by plasma CVD.

The purpose of this invention is to obtain a silicon carbide thin film with good reproducibility and excellent film quality by removing products deposited on the inner wall of a reactor during the production of silicon carbide thin films by plasma CVD method. .

When creating a thin film using the plasma CVD method, if one reactor is used repeatedly without a cleaning process, the product deposited on the inner wall of the reactor will gradually increase in thickness, and eventually It starts to peel off.

This phenomenon causes many pinholes in the obtained film, which has a serious adverse effect on the film quality. Further, the above-mentioned products change the impedance of the reactor, causing a deviation in the discharge conditions for obtaining plasma. A deviation in the impedance of the reactor has an unfavorable effect on the reproducibility of the obtained thin film. In this way, it is very important to remove the products deposited on the inner wall of the reactor and refresh the reactor both physically and electrically in the production of thin films by plasma CVD.

Regarding the method for cleaning the reactor used to manufacture silicon carbide thin films by plasma CVD method, we have found that low-temperature plasma chemical reaction using a mixed gas of O2 gas and CF4 gas is the most effective and is also superior in terms of work efficiency. Confirmed by experiment. The mixed gas of CF4 and O2 introduced into the reactor is dissociated by high frequency glow discharge as shown in equations (1) and (m). CF4→C・+4F・・・・・・・・・・
・ (1) O2 → 20・ ・・・・・・・・・・ (2)
The activated F and 0 react with the silicon carbide deposited on the inner wall as shown in equations (4) and (5).S
iC+4F・→SiF4+C... (3)
C+20・→C02・・・・・・・・・・・・ (4)
SiC+40.→SiO2+C02... (5) Next, a method for cleaning the reactor will be explained in detail. Reactor 1 shown in the figure
is sufficiently evacuated using exhaust equipment 2 such as an oil rotary pump.

O2 gas and CF are supplied to the reactor 1 from the cleaning gas supply device 4.
Introducing 4 gases, vacuum approximately 60 Pa, high frequency power 20 OW
generate plasma and clean the reactor. The equipment for generating plasma consists of a 13.56MH2 high frequency power source 5, a matching box 6, and an electrode T. Although the electrode □ is provided on the outside of the reactor 1 in the figure, it may be provided on the inside. Next, the present invention will be explained in more detail by showing specific examples.

The partial pressure of the gas introduced for cleaning is set using a flow meter. The flow rate measured in a system with a gauge pressure of 1 Kgf/cm2 is called SCCM (Standard CubicC).
Table 1 shows the numerical values converted into entimeterperminute (flow rate Cd/min, ) at 1 atm. When gas with a total flow rate of 100 SCCM is introduced into the reactor and exhausted by an oil rotary pump with a pumping speed of 5001/min, 1
A vacuum level of 75 pa is maintained.

The reactor can be almost completely cleaned by generating plasma by glow discharge for several hours with a high frequency power of 200 W under such gas conditions. Furthermore, by heating the reactor to 300°C, it is possible to shorten the time required for cleaning. In such a cleaning operation, the mixing ratio of 02 gas and CF4 gas significantly affects the cleanliness of the inner wall of the reactor after cleaning.

That is, black fine particles remain as a residue on the inner wall of the reactor after cleaning with a mixed gas containing 02 gas of 15v01% or less. From reaction formula (4), this seems to be undecomposed carbon due to insufficient 02 partial pressure. On the other hand, white fine particles remain as a residue on the inner wall of the reactor after cleaning with a mixed gas containing 02 gas of 25v01% or more. This is the reaction formula (SiO produced by 5 mm excess of 02
It seems to be 2. Furthermore, it has the disadvantage that it corrodes Daiflon (trade name of Daikin Industries, Ltd., trifluorochloroethylene polymer), which is one of the materials in contact with the gas. When a silicon carbide thin film is produced using a reactor with fine particles of carbon or SiO2 attached to the inner wall of the reactor, the silicon carbide thin film deposited on the inner wall of the reactor will be in a state where it is very easy to peel off, and the material peeled off during deposition will be adheres to the substrate, forming pinholes and impairing film quality. Particularly in downward deposition, the damage to the film quality is significant. Oxygen content 15~
When the reactor was cleaned by generating plasma with a mixed gas of 25v01%, there was almost no residue on the inner wall of the reactor, and a clean wall surface was obtained.

When a reactor that is almost completely refreshed in this way is used, there is very little deviation in the discharge conditions due to repeated discharges, and it is possible to produce silicon carbide with good reproducibility and a deviation in film quality with few pinholes. Furthermore, even if carbon fluorides other than CF4 are used, the optimal conditions for removing the silicon carbide thin film can be estimated to some extent by calculating the number of atoms of carbon, fluorine, and oxygen contained in the mixed gas. It seems possible.

Furthermore, the optimum conditions for removing silicon carbide deposited on the inner wall of the reactor without leaving any residue are also sufficiently applicable to microfabrication by patterning of silicon carbide thin films deposited on substrates.

[Brief explanation of the drawing]

The figure is a schematic diagram of a plasma CVD apparatus for producing a silicon carbide thin film, in which a gas system is installed for cleaning the reactor.

Claims (1)

[Claims] 1. In the pre-cleaning process of the reactor of the plasma CVD apparatus for producing a charcoal-fired silicon thin film, a mixed gas of O_2 gas and CF_4 gas was used as the reaction gas, and the mixing ratio of O_2 gas was in the range of 15 to 25 vol%. Characteristic cleaning method for plasma CVD reactor.