JPH05343338A - Plasma cvd apparatus - Google Patents

Abstract

PURPOSE:To provide a high-frequency plasma CVD apparatus, in which the generation of powder and flakes can be suppressed and a good quality thin film can be uniformly formed on a substrate of large area. CONSTITUTION:A plurality of cathode electrodes 3a-3f are installed in one plane so as to face an anode electrode 4 in a reaction container 7, the side and rear faces of respective cathode electrodes 3a-3f are surrounded by an earth shield 5, a plurality of jets 8a-8c of reaction gas supply pipes 6a-6c are installed on the rear face side of the plurality of cathode electrodes 3a-3f and a plurality of air outlets 10a-10d are alternately arranged between the plurality of jets 8a-8c.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art FIG. 5 shows a conventional parallel plate type RF plasma C.
It is a schematic block diagram which shows a VD apparatus. In the reaction container 16, a cathode electrode 11, an anode electrode 12 at a position facing the cathode electrode 11, and a ground 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 the diameter facing the anode electrode 12 is 0.1 to 0.5 mm.
A large number of holes are provided. A gas supply pipe 15 is connected to the cathode electrode 11. Further, the substrate 14 is placed 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 by a vacuum pump (not shown) to a predetermined degree of vacuum required for thin film formation. 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 shape of a shower from minute holes provided on the side, and is uniformly supplied to the surface of the substrate 14 placed on the anode electrode 12. This method is usually called the shower method,
It has the feature that gas can be uniformly supplied to the surface of a large area substrate. 13.5 from a high frequency power source (not shown)
A high frequency power of 6 MHz is supplied to the cathode electrode 11 via an impedance matching device (not shown). Since the portion of the cathode electrode 11 which does not face the anode electrode 12 is surrounded by the earth shield 13, plasma is not generated in this portion. That is, glow discharge plasma is generated between the cathode electrode 11 and the anode electrode 12 by the high frequency power described above. The reaction gas (SiH ₄ ) supplied in a shower shape from the hole of the cathode electrode 11 is dissociated by plasma, and an a-Si thin film is deposited on the surface of the substrate 14.

[0004]

The film formation of an a-Si thin film mainly involves neutral radicals produced by the decomposition of SiH ₄ parent molecules by plasma. Among them, it is considered that the SiH ₃ radicals dominate the film formation. However, many radicals other than SiH ₃ , such as SiH ₂ , SiH, and Si, are generated in the plasma. Radicals other than SiH ₃ cause a secondary reaction with the SiH ₄ parent molecule, which is sufficiently present in the gas phase. As a result, for example, in the case of SiH ₂ radicals, higher order silane is generated according to the following reaction. _{SiH 2 + SiH 4 = Si 2} H 6 SiH 2 + Si 2 H 6 = Si 3 H 8 SiH 2 + Si 3 H 8 = Si 4 H 10 SiH 2 + Si n-1 H 2n = Si n H 2n + 2 (1)

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

Where K is a constant and N _e is S in the plasma.
Density of electrons having the energy necessary to collide with iH ₄ to generate SiH ₂ radicals, V _th is the thermal velocity of electrons,
σ 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
It represents the H ₄ parent molecule density. As is clear from this equation, the electron density N _e (that is, input power), or SiH
_It can be seen that when the pressure of ₄ is slightly increased, powder is rapidly generated.

In the conventional shower type apparatus, since the reaction gas is supplied from the minute holes provided in the cathode electrode 11, the SiH ₄ parent molecule density is high in the vicinity of the cathode electrode 11. Further, near the cathode electrode 11, the density of electrons that decompose the reaction gas is high. That is, the reaction gas is jetted at high speed and 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 container by adiabatic expansion. As shown by the 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 probability of powder generation. Furthermore, in the conventional apparatus, since a film having high internal stress is deposited around the reaction gas ejection port of the cathode electrode during film formation, the end portion of the deposited film is blown off by the gas ejected at high speed as shown in FIG. Becomes flake, which flies onto the substrate 14 and adheres thereto. The powder and flakes generated during the film formation are considered to be the cause of forming pinholes in the film deposited on the substrate 14. And, this has been a cause of lowering the yield of TFT liquid crystal displays using a-Si thin films and a-Si solar cells. Further, since the gas ejected at high speed and low temperature partially cools the surface of the substrate placed on the opposing electrode, the film quality becomes nonuniform even though the film thickness seems to be uniform.

As described above, the conventional shower-type apparatus has a structure that easily produces powder and flakes, and causes non-uniformity of the film quality, which causes a reduction in product yield. Was there. Therefore, in order to suppress the generation of powders 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 made to have a low velocity and low density at the ejection port. It is possible. However, if such a measure is adopted, abnormal discharge occurs at the ejection port, and the film quality is deteriorated as a whole, which is a practical problem. Further, in the conventional method, when the substrate area increases, the film thickness in the central portion of the substrate becomes
The thickness may not be uniform as shown in FIG. 7 and may be thin as shown in FIG.

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

[0010]

Means for Solving the Problems Plasma CVD of the present invention
The apparatus has, in a reaction container, a cathode electrode, an earth shield that surrounds the side surface and the back surface of the cathode electrode, and an anode electrode with a built-in heater that faces the cathode electrode and on which a substrate is installed. A plasma CVD apparatus that has a supply pipe and a reaction gas exhaust pipe, and that generates high-frequency plasma in the reaction container by supplying high-frequency power from a high-frequency power source to the cathode electrode via an impedance matching device. A plurality of cathode electrodes are installed in a plane so as to face each other, the side surface and the back surface of each cathode electrode are surrounded by an earth shield, and a plurality of ejection ports of a reaction gas supply pipe are installed on the back surface side of the plurality of cathode electrodes. In addition, a plurality of exhaust ports are alternately arranged between the plurality of jet ports.

[0011]

In the device of the present invention, a plurality of cathode electrodes are arranged in a plane and the side surface and the back surface of each cathode electrode are surrounded by the earth shield, so that an extra discharge is generated in a portion not facing the anode electrode. It's suppressed. Further, a plurality of ejection ports of the reaction gas supply pipe are arranged on the back surface side of the plurality of cathode electrodes, that is, in a region surrounded by an earth shield and where plasma is not generated, and the reaction gas is diffused from the gap between the cathode electrodes, and By arranging a plurality of exhaust ports alternately between a plurality of jet ports, the gas is made to diffuse uniformly throughout the reaction vessel.

By adopting such a structure, plasma is not generated at the ejection port of the reaction gas, so that powder is not generated, and since film is not deposited at this portion, flakes are not generated. Since the reaction gas is evenly supplied into the plasma even in the central portion of the substrate, a thin film having a uniform thickness and film quality can be formed on the surface of the large-area substrate.

[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 block diagram of an apparatus. In FIG. 1, a plurality of cathode electrodes 3a, 3b, 3c, 3d, 3 are provided in a reaction vessel 7.
e and 3f are arranged in a plane, and each cathode electrode 3
An anode (ground) electrode with a built-in heater 4 is arranged at a position facing a to 3f, and a ground shield 5 is arranged so as to surround a portion of each cathode electrode 3a to 3f not facing the anode electrode 4, that is, a side surface and a back surface. Gas supply pipes 6a, 6b, 6 are provided on the back side of the cathode electrodes 3a to 3f.
A plurality of gas ejection ports 8a, 8b, 8c of c are arranged. Further, a plurality of gas exhaust ports 10a, 10b, 10c, 10d are arranged on the back surface side of the cathode electrodes 3a to 3f so as to be alternately arranged between the gas ejection ports 8a to 8c. The substrate 9 is placed on the anode electrode 4. An impedance matching device 2 and a high frequency power source 1 are connected to each of the cathode electrodes 3a to 3f. FIG. 2 is a plan view showing an arrangement state of the cathode electrodes 3a to 3f, the gas ejection ports 8a to 8c, and the gas exhaust ports 10a to 10d described above.

The case of forming an a-Si thin film with this apparatus will be described below. The inside of the reaction vessel 7 is evacuated by a vacuum pump (not shown) to a predetermined degree of vacuum required for thin film formation. After supplying a reaction gas such as SiH ₄ ,
13.56 MHz high frequency power from the high frequency power supply 1 is passed through the impedance matching device 2 to the cathode electrodes 3a to 3f.
Is supplied to. As shown in FIG. 3, the cathode electrodes 3a ...
Since the electric field strength around 3f shows a uniform distribution, it is possible to generate plasma with a uniform density. Further, since the side surfaces and the back surfaces of the cathode electrodes 3a to 3f are surrounded by the earth shield 5, plasma is not generated in this portion. That is, glow discharge plasma is generated only between the cathode electrodes 3 a to 3 f and the anode electrode 4.

The reaction gas is supplied from the gas supply pipes 6a to 6c through a plurality of ejection ports 8a to 8c arranged on the back side of the plurality of cathode electrodes 3a to 3f. Jet 8a ~
In the vicinity of 8c, the partial pressure of gas is high, but since the earth shield 5 is provided in this portion and plasma is not generated, gas decomposition does not occur and powder does not occur. Further, the reaction gas is supplied to the plurality of ejection ports 8a to 8c.
As a result, it is diffused between the cathode electrodes 3a to 3f and the anode electrode 4 to become plasma, and the exhaust port 10a located closest to the plasma.
It is discharged from 10d. 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 plasma, and an a-Si thin film is deposited on the surface of the substrate 9.

Actually, using the apparatus of FIG. 1, an a-Si thin film was deposited on the surface of the substrate under the following conditions. The substrate 9 was placed on the anode electrode 4 and heated to 200 to 300 ° C. After the vacuum degree of the reaction vessel 7 is reduced to about 10 ⁻⁸ Torr and the impurity gas inside is sufficiently exhausted, SiH ₄ gas is supplied from the reaction gas supply pipes 6 a to 6 c at a flow rate of 10 cc / min. The internal pressure is 5 × 10 ^-2 Torr
And

In such a state, high frequency power was applied to deposit an a-Si thin film on the surface of the substrate 9. In this case, 2
A film formation rate of 6 Å / 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 film forming rate was obtained using the conventional apparatus.
In addition, as shown in FIG. 4, a large-area substrate (500 mm ×
A uniform film thickness distribution was obtained even when the film was formed to a thickness of 500 mm.

[0019]

As described in detail above, when the high frequency plasma CVD apparatus of the present invention is used, the generation of powder and flakes can be suppressed, and the reaction gas can be uniformly diffused over the entire surface of the substrate. It is possible to uniformly form a thin film having good film quality with few pinholes and improve the manufacturing yield of liquid crystal displays and a-Si solar cells. Thus, it can be said that the present invention has a great industrial value.

[Brief description of drawings]

FIG. 1 is a high frequency plasma CVD according to an embodiment of the present invention.
The schematic block diagram of a device.

FIG. 2 is a high-frequency plasma CVD method according to an embodiment of the present invention.
FIG. 3 is a plan view showing the arrangement of a cathode electrode, a gas ejection port, and a gas exhaust port of the device.

FIG. 3 is a diagram showing the electric field strength formed by a plurality of cathode electrodes used in the high-frequency plasma CVD apparatus according to the present invention.

FIG. 4 is a diagram showing a film thickness distribution of amorphous silicon obtained in one example of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional high frequency plasma CVD apparatus.

FIG. 6 is an explanatory diagram showing a flake generation state at a gas ejection port of a cathode electrode in a conventional high frequency plasma CVD apparatus.

FIG. 7 is a diagram showing an example of a film thickness distribution of amorphous silicon obtained by a conventional high frequency plasma CVD apparatus.

FIG. 8 is a diagram showing another example of the film thickness distribution of amorphous silicon obtained by a conventional high-frequency plasma CVD apparatus.

[Explanation of symbols]

1 ... High frequency power source, 2 ... Impedance matching device, 3a-3
f ... Cathode electrode, 4 ... Anode electrode, 5 ... Earth shield, 6a-6c ... Gas supply pipe, 7 ... Reaction vessel, 8a ...
8c ... Gas ejection port, 9 ... Substrate, 10a-10d ... Gas exhaust port.

Claims (1)

[Claims] 1. A cathode electrode, an earth shield surrounding a side surface and a back surface of the cathode electrode in a reaction vessel,
It has an anode electrode with a built-in heater which is provided facing the cathode electrode and on which a substrate is installed, and also has a reaction gas supply pipe and a reaction gas exhaust pipe, and from the high frequency power source to the cathode electrode via an impedance matching device. In a plasma CVD apparatus that generates plasma in the reaction vessel by supplying high-frequency power, a plurality of cathode electrodes are installed in a plane so as to face the anode electrode, and the side surface and the back surface of each cathode electrode are grounded. It is characterized in that it is surrounded by a shield, a plurality of ejection ports of a reaction gas supply pipe are provided on the back side of the plurality of cathode electrodes, and a plurality of exhaust ports are alternately arranged between the plurality of ejection ports. And a plasma CVD apparatus.