JPH08127876A - Formation of film and film forming device - Google Patents

Abstract

PURPOSE: To provide a method for forming a film in which the formation of a film of high quality free from the incorporation of impurities and free from the generation of voids is enabled at a high speed and to provide a film forming device therefor. CONSTITUTION: The method for forming a film in which raw material fine powder is introduced to the inside of a plasma generating part 3 made of a quartz tube 4 and in which coils 5 applied with high frequency voltage are arranged around the same via a carrier gas constituted of an inert gas. Based on the energy of plasma in the plasma generating part 3 confined by a gas for cooling flowed around the same, the state of the raw material fine powder is formed into a molten one, which is jetted onto a substrate 12 set in an atmosphere of an inert gas, and film deposition is executed to the substrate 12, and the film forming device therefor are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film forming method for forming a film of silicon or the like for a solar cell at high speed.

[0002]

2. Description of the Related Art In recent years, the importance of solar cells that make effective use of natural energy has been recognized, and their development has been actively conducted. The basic requirement for solar cells is to produce large-area, high-quality silicon thin plates inexpensively and at high speed. However, in the current mainstream production of single crystal silicon from ingots, half of the raw material ingot is discarded as machining loss in the slicing process and polishing process when making thin plates, so-called wafers, resulting in very high cost. It is the actual situation.

Therefore, a search for a method for eliminating these losses has been actively conducted. This is a method of directly producing a silicon sheet from a melt, etc., there is no need for mechanical processing such as cutting expensive solid silicon, and it is possible to directly produce a thin plate with a required thickness. And the like.

Until now, EFG (FVWaid, Crystals: Grow
th, Properties, and Applications, Vol.5, edited by J.
G. Grabmaier, Springer Verlag, Berlin (1981) 149), S
-Web (R. Falckenberg, G. Hoyler, and G. Grabmaier, P
roc.19th IEEE Photovoltaic Specialists Conf., New O
rleans, USA (1987) 317), SSP (A.Eyer, N.Schilling
er, J.Reis, and A.Rauber, J.Cryst.Growth, 104 (1990) 11
9), plasma spraying method (Int'l PVSEC-7 (1992) 238), etc. have been developed. In particular, the plasma spraying method has characteristics that it can be formed at a high speed and that a polysilicon film having large crystal grains can be formed, and is particularly promising.

[0005]

FIG. 2 is a sectional view of the structure of an apparatus for explaining the plasma spraying method. Ar gas is introduced from the carrier gas supply unit 21 into the DC plasma generation unit 22.
The DC plasma generating unit 22 has an electrode unit 23 to which a negative voltage is applied.
A discharge is generated between the nozzle portion 24 to which a positive voltage is applied and a high temperature plasma portion 25 is formed. Powder is introduced from a powder feeder 26 containing high-purity (6N) silicon powder (powder size 50-150 μm) into the plasma part 25 generated from the DC plasma generation part 22, and is heated and softened. And made of glassy carbon, heater
It is deposited on the substrate 26 which has been heated by the section 27 to a high temperature of about 600 ° C.

As described above, there is an advantage that the polysilicon film can be formed on the substrate 26 at a high speed, but there is a problem in film quality. It is said that the cell efficiency when a solar cell is formed by using a polysilicon film formed by this plasma spraying method is about 5%, which is considerably lower than that using a conventional silicon wafer. This is because the metal material (Fe, Cr, etc.) that composes the electrode 23 and the nozzle portion 24 that form the plasma spraying electrode portion is mixed into silicon during film formation, which becomes an impurity and deteriorates the film quality. This is because. In addition, when microscopically observing the film structure, many voids were seen between the powders that were in close contact with each other, and it was observed that the powders were deformed and piled up, and the film structure was not continuous. . This is due to incomplete melting and is a cause of deterioration of film quality.

The present invention solves the above-mentioned problems, and provides a film forming method and a film forming apparatus capable of forming a high-quality film at a high speed without containing impurities and without generating voids. It is intended.

[0008]

According to the present invention, a raw material is introduced through a carrier gas made of an inert gas inside a plasma generating portion made of a quartz tube and around which a coil to which a high frequency voltage is applied is arranged. The fine powder is introduced, the fine powder of the raw material is melted based on the plasma energy in the plasma generating part, and is jetted onto the substrate placed in an inert gas atmosphere to deposit a film on the substrate. In particular, in the quartz tube, the introduction part side of the raw material fine powder reaching the plasma generation part is composed of at least two layers of tubes, and the raw material fine powder is introduced into the inner tube through the carrier gas, and the outer tube and the inner tube An inert gas for cooling is introduced between them to form a film.

In addition, a plasma generating portion composed of a quartz tube and a coil installed around the quartz tube to which a high frequency voltage is applied, and a quartz tube inside or inside a chamber which is hermetically connected from the outside. The quartz tube has a structure in which the substrate is placed in the inside of the quartz tube, and the introduction side of the raw material fine powder reaching the plasma generation portion is composed of at least two layers of tubes. Is introduced, and the inert gas from the cooling gas supply unit is introduced between the outer tube and the inner tube to form the film forming apparatus.

[0010]

The raw material fine powder is introduced into the plasma generating part through the carrier gas composed of the inert gas. In the plasma generation unit, a high frequency magnetic field is formed by an induction coil to which a high frequency voltage is applied, which is arranged around a quartz tube, and electrons and ions are accelerated by an electric field formed in proportion to the time change of the magnetic field. As a result, high-density plasma is generated in the quartz tube, which constitutes a plasma generating part.

Since the raw material material in the form of fine powder (raw material fine powder) has an active property based on a very large surface area,
When the raw material fine particles are introduced into the high density plasma, they are almost completely excited and melted and ejected onto the substrate to form a film on the substrate. Receiving the energy of the excited particles and the heat energy of the heated substrate, the film formed on the substrate becomes a high-quality polycrystalline state without voids. Particularly, by setting the particle size of the raw material fine powder to 50 μm or less, an effective melted and decomposed state based on the size of the surface area is obtained, and further improvement of the film quality is recognized.

Further, of the quartz tube, a raw material fine particle introduction portion side, that is, a side reaching the high density plasma forming portion is composed of a two-layer tube, and the raw material fine particle is introduced into the inner tube through a carrier gas. An inert gas for cooling is introduced between the outer tube and the inner tube. The inert gas from between the outer tube and the inner tube covers the outside of the high density plasma excited by the generated coil, trapping the plasma inside it. As a result, the high-density plasma does not come into direct contact with the quartz tube, and the contamination of the plasma with the heating of the quartz tube is eliminated.

As a result, in the conventional plasma spraying method, the material composing the electrode of plasma spraying is mixed in during film formation, which becomes impurities and deteriorates the film quality, and incomplete melting is caused. The present invention solves the problem that voids are generated based on the above.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 illustrates a method of forming a film according to the present invention by taking an example of forming a polysilicon film, and shows a schematic view of the structure of a film forming apparatus therefor.

Silicon fine particles having a particle size of 10 μm are supplied from the raw material supply section 1 to the plasma generation section 3 together with the Ar gas from the carrier gas introduction section 2. The plasma generating part 3 is composed of a quartz tube 4 and a coil part 5. The coil part 5 is arranged in a plane with several turns and is connected to an RF power source 6 so that a high frequency voltage can be applied. Of the quartz tube 4, the raw material fine particle introduction portion side 7, that is, the side reaching the high-density plasma forming portion 8 is composed of a two-layer tube, and silicon fine particles are contained in the inner tube 10 via a carrier gas made of Ar. Introduced the outer tube 9
Ar gas is introduced as a cooling inert gas from the cooling gas supply unit 11 between the inner tube 10 and the inner tube 10. The inert gas from between the outer tube 9 and the inner tube 10 covers the outside of the high density plasma generated in the plasma forming part 8 and confine the plasma inside thereof. As a result, the high-density plasma does not directly contact the quartz tubes 9 and 10, and contaminants due to heating of the quartz tubes are not mixed into the plasma.

The silicon fine powder supplied to the plasma generating portion 8 via the carrier gas was generated by the electric field formed by the time change of the high frequency magnetic field from the coil portion 5 which was applied with 500 W from the RF power source 6. While being heated and melted by the high-density plasma, it is accelerated at a high speed and sprayed onto the substrate 12. The substrate 12 is placed in a chamber 13 filled with an inert gas so that the polysilicon film formed on the substrate 12 does not contain oxygen O ₂ forming the quartz tube 4. The pressure inside the chamber 13 is atmospheric pressure. In addition, the substrate 12 is heated to 30
It is heated to 0 ° C and supplies heat energy for film formation. The deposition rate of polysilicon by this method is 10 μm / min, which indicates that high-speed deposition is possible.

Microscopically observing the polysilicon film formed by the above method of the present invention, crystal grain boundaries are formed, and there are almost no voids observed by the conventional plasma spraying method, and the density is high. The state is obtained. Further, due to the confinement of plasma by the inert gas between the outer tube 9 and the inner tube 10, no contamination from the quartz tube 4 (9, 10) is observed. A solar cell was formed using the polysilicon film formed by this film forming method, and the efficiency of the cell was measured. As a result, 14% was obtained, which was a characteristic far exceeding the conventional 5%.

In the embodiments of the present invention, the case where the raw material is silicon fine powder to form the polysilicon film is described, but the present invention is not limited to this, and SiO ₂ or Al ₂ O _{3 is used.}
Even if the fine powder of is used, high density and high quality SiO ₂ and Al ₂ O ₃ film formation can be realized and effective.

In the examples, the particle size of the silicon fine particles is 10 μm, but if it is 50 μm or less, a sufficient molten state can be obtained and a high quality film can be formed.

[0021]

As described above, according to the present invention, voids are not generated in the film due to the good melting state of the raw material fine powder, and the inclusion of impurities in the film by confining the plasma by the cooling gas. The present invention provides a film forming method and a film forming apparatus therefor that enables high quality film formation at high speed, and has an extremely high industrial value.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a film forming apparatus for explaining an embodiment based on the present invention.

FIG. 2 is a schematic configuration diagram of a plasma spray apparatus for explaining a conventional plasma spray method.

[Explanation of reference numerals] 1 raw material supply section 2 carrier gas introduction section 3 plasma generation section 4 quartz tube 5 coil section 6 RF power supply 7 raw material fine particle introduction section side 8 plasma formation section 9 inner tube 10 outer tube 11 cooling gas supply section 12 Substrate 13 Chamber 14 Heater part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masao Uchida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A raw material fine powder is introduced through a carrier gas made of an inert gas into a plasma generating portion, which is made of a quartz tube and around which a coil to which a high frequency voltage is applied is arranged, is introduced. A film forming method in which powder is melted based on plasma energy in a plasma generation unit and is ejected onto a substrate placed in an inert gas atmosphere to deposit a film on the substrate. 2. A quartz tube is provided with at least two layers of raw material fine powder on the side where the raw material fine powder is introduced to the plasma generation portion, and the raw material fine powder is introduced into the inner tube through a carrier gas, and the outer side The film forming method according to claim 1, wherein an inert gas for cooling is introduced between the tube and the inner tube. 3. The film forming method according to claim 1, wherein the raw material fine powder has a particle size of 50 μm or less. 4. A plasma generating part comprising a quartz tube and a coil installed around the quartz tube and to which a high frequency voltage is applied, and a quartz tube inside or inside a chamber which is hermetically connected from the outside. The quartz tube has a structure in which the substrate is placed in the inside of the quartz tube, and the introduction side of the raw material fine powder reaching the plasma generation portion is composed of at least two layers of tubes. Is introduced, and an inert gas from the cooling gas supply unit is introduced between the outer tube and the inner tube.