JP2798225B2 - High frequency plasma CVD equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an a-Si thin film, SiN _x
(Silicon nitride) Chemical vapor deposition (Chemical Vapor De) for forming a semiconductor film such as a thin film or an insulating film.
The present invention relates to a high-frequency plasma CVD apparatus used for forming a position (hereinafter, referred to as CVD) type thin film.

[0002]

FIG. 7 shows a conventional parallel plate type RF plasma C.
It is a schematic structure figure showing a VD device. In the reaction vessel 16, a cathode electrode 11, an anode electrode 12 at a position facing the cathode electrode 11, and an earth shield 13 at a portion of the cathode electrode 11 not facing the anode electrode 12 are arranged. The cathode electrode 11 is hollow, and has a diameter of 0.1 to 0.5 mm at a portion facing the anode electrode 12.
Many holes are provided. A gas supply pipe 15 is connected to the cathode electrode 11. Further, a substrate 14 is provided on the anode electrode 12.

A case where an amorphous silicon thin film (hereinafter referred to as an a-Si thin film) is formed by this apparatus will be described. The inside of the reaction vessel 16 is evacuated to a predetermined degree of vacuum required for forming a thin film by a vacuum pump (not shown). A reaction gas such as SiH ₄ is supplied from the gas supply pipe 15 to the hollow portion of the cathode electrode 11,
It is emitted in the form of a shower from a small hole provided on the side, and is uniformly supplied to the surface of the substrate 14 provided on the anode electrode 12. Usually, this method is called the shower method,
It has the feature that gas can be supplied uniformly to a large-area substrate surface. 13.5 from high frequency power supply (not shown)
6 MHz high-frequency power is supplied to the cathode electrode 11 via an impedance matching device (not shown). Since the portion of the cathode electrode 11 not facing the anode electrode 12 is surrounded by the earth shield 13, no plasma is generated in this portion. That is, a glow discharge plasma is generated between the cathode electrode 11 and the anode electrode 12 by the above-described high frequency power. The reaction gas (SiH ₄ ) supplied in a shower from the hole of the cathode electrode 11 is dissociated by the plasma, and an a-Si thin film is deposited on the surface of the substrate 14.

[0004]

SUMMARY OF THE INVENTION For forming an a-Si thin film,
Is mainly SiH_FourThe parent molecule is decomposed by the plasma
Neutral radicals produced are involved. inside that
Also especially SiH_ThreeRadicals control film formation
Have been. However, the plasma contains SiH_ThreeOther than LA
Zical, eg SiH_Two, SiH, Si, etc. are generated in large numbers
doing. SiH_ThreeRadicals other than
SiH_FourCauses a secondary reaction with the parent molecule. This result
Result, for example, SiH_TwoIn the case of a radical, a reaction like
Accordingly, higher silane is generated. SiH_Two + SiH_Four = Si_TwoH₆  SiH_Two + Si_TwoH₆ = Si_ThreeH₈  SiH_Two + Si_ThreeH₈ = Si_FourH_Ten  SiH_Two + Si_n-1H_2n = Si_nH_{2n + 2} (1)

[0005] The higher order silane having a certain size in this way floats in the plasma. This higher order silane is negatively charged by electron attachment in plasma,
It is trapped in plasma with a positive potential and stays in the plasma for a long time. Further, film deposition occurs on the surface and the size gradually increases, and finally powder (powder) is generated in the plasma. The density [Si _n H _{2n + 2} ] of the higher order silane Si _n H _{2n + 2} is given by the following equation by a simple approximation and a rate equation. [Si _n H _{2n + 2} ] = K ｛ _Ne · V _th · σ · k ^-1 ｝ [SiH ₄ ] ⁿ (2)

Where K is a constant and _Ne is S in the plasma.
The density of electrons having the energy required to generate SiH ₂ radicals upon collision with iH ₄ , V _th is the thermal velocity of the electrons,
is the electron impact decomposition cross section of the SiH ₄ parent molecule, and k is SiH
₂ and the reaction rate of SiH ₄ parent molecule, [SiH ₄ ] is Si
H ₄ represents the parent molecular density. As is clear from this equation, the electron density N _e (ie, input power), or SiH
_It can be seen that when the pressure in step ₄ is slightly increased, powder is rapidly generated.

In the conventional shower-type apparatus, the reactive gas is supplied from a minute hole provided in the cathode electrode 11, so that the SiH ₄ parent molecular density is high near the cathode electrode 11. In the vicinity of the cathode electrode 11, the density of electrons that decompose the reaction gas is high. That is, the reaction gas is spouted at a high speed and a high density from a minute hole formed in the cathode electrode to a region having the highest plasma density, and then diffused throughout the reaction vessel by adiabatic expansion. As shown in the above equation (2), powder is likely to be generated under the condition that the plasma density and the parent molecule density are high, so that the conventional apparatus has a structure with a high powder generation probability. Further, in the conventional apparatus, a film having a high internal stress is also deposited around the reaction gas outlet of the cathode electrode at the time of film formation. Therefore, as shown in FIG. 8, the end of the deposited film is blown off by the gas which is blown at a high speed. Flakes, which fly and adhere onto the substrate 14. The powder and flakes generated during the film formation are considered to cause pinholes in the film deposited on the substrate 14. And this has caused a decrease in the yield of a TFT liquid crystal display or an a-Si solar cell using an a-Si thin film. In addition, since the gas ejected at high speed and low temperature partially cools the surface of the substrate provided on the facing electrode, the film quality becomes uneven even though the film thickness appears to be uniform.

As described above, the conventional shower type apparatus has a structure that easily generates powder and flakes, and also causes nonuniform film quality, which causes a reduction in product yield. I was Therefore, in order to suppress the generation of powder and flakes and to make the film quality uniform, the diameter of the gas ejection port on the cathode electrode 11 is increased, and the reaction gas is reduced in speed and density at the ejection port. It is possible. However, when such a measure is adopted, abnormal discharge occurs at the ejection port, and the film quality is deteriorated as a whole, and there is a practical problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a high-frequency plasma CVD apparatus capable of suppressing generation of powder and flakes and capable of uniformly forming a thin film of good quality on a large-area substrate. The purpose is to provide.

[0010]

According to the present invention, there is provided a high-frequency plasma CVD apparatus comprising, in a reaction vessel, a cathode electrode; an earth shield surrounding side and back surfaces of the cathode electrode;
A heater-equipped anode electrode provided with a substrate provided opposite to the cathode electrode, and a reaction gas supply pipe, and supplying a high-frequency power to the cathode electrode from a high-frequency power supply via an impedance matching device; In a CVD apparatus that generates plasma in a reaction vessel,
A plurality of cathode electrodes are arranged in a plane, side and back surfaces of each cathode electrode are surrounded by an earth shield, and a plurality of outlets of a reaction gas supply pipe are arranged on the back surface side of the plurality of cathode electrodes. It is assumed that.

[0011]

In the device of the present invention, a plurality of cathode electrodes are arranged in a plane, and the side and back surfaces of each cathode electrode are surrounded by an earth shield, so that an extra discharge in a portion not facing the anode electrode can be obtained. Restrained. In addition, a plurality of outlets of the reaction gas supply pipe are arranged on the back side of the plurality of cathode electrodes, that is, in a region surrounded by the earth shield and where no plasma is generated, and the reaction gas is diffused from the gap between the cathode electrodes to react. The gas is made to diffuse uniformly throughout the container.

By adopting such a structure, no powder is generated because no plasma is generated at the outlet of the reaction gas, and no flake is generated because no film is deposited at this portion. Since the reaction gas is uniformly supplied into the plasma, a thin film having a uniform thickness and film quality can be formed on a large-area substrate surface.

[0013]

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

FIG. 1 shows a high-frequency plasma CVD according to the present invention.
It is a schematic structure figure of an apparatus. In FIG. 1, a plurality of cathode electrodes 3 are arranged in a plane in a reaction vessel 7, and an anode (ground) electrode 4 with a built-in heater is provided at a position facing each cathode electrode 3. An earth shield 5 is arranged so as to surround a portion not facing the electrode 4, that is, a side surface and a back surface. A plurality of gas outlets 8 of the gas supply pipe 6 are arranged on the back side of the cathode electrode 3. A substrate 9 is provided on the anode electrode 4. Further, an impedance matching device 2 and a high-frequency power source 1 are connected to each cathode electrode 3.

In this embodiment, as each cathode electrode 3,
A rectangular one as shown in FIG. 2 is used, and the cathode electrodes 3 adjacent to each other are arranged at regular intervals. The shape of each cathode electrode 3 may be square as shown in FIG. 3 or circular as shown in FIG. Of course, polygons such as hexagons can also be used.

The case where an a-Si thin film is formed by this apparatus will be described below. The inside of the reaction vessel 7 is evacuated to a predetermined degree of vacuum required for forming a thin film by a vacuum pump (not shown). After supplying a reaction gas such as SiH ₄ ,
13.56 MHz high frequency power is supplied from the high frequency power supply 1 to each cathode electrode 3 via the impedance matching device 2. As shown in FIG. 5, an electric field having a uniform central portion and a weak end portion is formed around one cathode electrode 3. Therefore, when a plurality of cathode electrodes 3 are arranged as shown in FIGS. 1 and 2, a uniform electric field is formed due to the superposition effect of the electric fields, as shown in FIG. It is possible to generate an excellent plasma. Further, since the side surface and the back surface of each cathode electrode 3 are surrounded by the earth shield 5, no plasma is generated in this portion. That is, glow discharge plasma is generated only between the cathode electrode 3 and the anode electrode 4.

The reaction gas is supplied from gas supply pipes 6 through a plurality of jet ports arranged on the back side of the plurality of cathode electrodes 3. Although the partial pressure of the gas is high in the vicinity of the jet port 8, the earth shield 5 is provided in this portion and no plasma is generated, so that no gas decomposition occurs and no powder is generated. Further, the reaction gas diffuses in the reaction vessel 7 and is transported to the plasma region through the gap between the cathode electrodes 3. In the plasma region, the reaction gas is sufficiently diffused and uniform, so that no powder is generated. Then, the reaction gas is dissociated by the plasma,
An a-Si thin film is deposited on the surface of the substrate 9.

An a-Si thin film was actually deposited on the substrate surface under the following conditions using the apparatus shown in FIG. The substrate 9 was placed on the anode electrode 4 and heated to 200 to 300C. After reducing the degree of vacuum of the reaction vessel 7 to about 10 ⁻⁸ Torr and sufficiently exhausting the internal impurity gas, a SiH ₄ gas is supplied from the reaction gas supply pipe 6 at a flow rate of 10 cc / min to supply the inside of the reaction vessel 7. The pressure was 5 × 10 ⁻² Torr.

In this state, high-frequency power was applied to deposit an a-Si thin film on the surface of the substrate 9. In this case,
A film formation rate of 6 angstroms / sec was obtained. In addition, the number of powders generated in the plasma during film formation was observed by the Mie scattering method. As a result, it was found that the generation of powder was suppressed to 1/100 or less as compared with the case where the above-described film forming speed was obtained using the conventional apparatus.
The apparatus of the present invention is not limited to the formation of an a-Si thin film,
It can be applied to the formation of various thin films such as a Si ₃ N ₄ thin film, a SiO ₂ thin film, and a diamond thin film.

[0020]

As described above in detail, the use of the high-frequency plasma CVD apparatus of the present invention makes it possible to suppress the generation of powder and flakes, and to uniformly form a thin film having few pinholes on a large-area substrate. As a result, the production yield of the liquid crystal display and the a-Si solar cell can be improved.

[Brief description of the drawings]

FIG. 1 is a high-frequency plasma CVD according to an embodiment of the present invention.
FIG. 1 is a schematic configuration diagram of an apparatus.

FIG. 2 is a plan view of a cathode electrode used in the high-frequency plasma CVD apparatus according to the embodiment of the present invention.

FIG. 3 is a plan view of another cathode electrode used in the high-frequency plasma CVD apparatus according to the present invention.

FIG. 4 is a plan view of still another cathode electrode used in the high-frequency plasma CVD apparatus according to the present invention.

FIG. 5 is an explanatory diagram showing the intensity of an electric field formed by one cathode electrode in the high-frequency plasma CVD apparatus according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing the intensity of an electric field formed by a plurality of cathode electrodes in the high-frequency plasma CVD apparatus according to the embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional high-frequency plasma CVD apparatus.

FIG. 8 is an explanatory view showing a state of flake generation at a gas outlet of a cathode electrode in a conventional high-frequency plasma CVD apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... High frequency power supply, 2 ... Impedance matching device, 3 ... Cathode electrode, 4 ... Anode electrode, 5 ... Earth shield, 6
... gas supply pipe, 7 ... reaction vessel, 8 ... spout, 9 ... substrate.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazuhiro Hasezaki 1-1, Akunouramachi, Nagasaki City, Nagasaki Prefecture Examiner, Nagasaki Research Laboratory, Mitsubishi Heavy Industries, Ltd. Yoichi Gotani (58) Field surveyed (Int. Cl. ⁶ , (DB name) C30B 1/00-35/00 B01J 19/08

Claims (1)

(57) [Claims] 1. A cathode electrode, an earth shield surrounding side and back surfaces of the cathode electrode in a reaction vessel,
A heater-equipped anode electrode provided with a substrate provided opposite to the cathode electrode, and a reaction gas supply pipe, and supplying a high-frequency power to the cathode electrode from a high-frequency power supply via an impedance matching device; In a CVD apparatus that generates plasma in a reaction vessel,
A plurality of cathode electrodes are arranged in a plane, side and back surfaces of each cathode electrode are surrounded by an earth shield, and a plurality of outlets of a reaction gas supply pipe are arranged on the back surface side of the plurality of cathode electrodes. High frequency plasma CVD
apparatus.