JPH07330488A - Plasma cvd apparatus - Google Patents

Abstract

PURPOSE:To produce thin films having high quality at a high speed with a plasma CVD apparatus used for thin film production of solar batteries, thin-film semiconductors, optical sensors, etc. CONSTITUTION:A ladder electrode 2 consisting of a hollow wire exists in a reaction vessel 1. The lower part of the hollow wire is provided with gas blow- off ports 4. The lower half peripheral surface of the hollow wire is provided with a grounding shield 3 covering these blow-off holes 4 by maintaining a specified spacing from the surface. Reactive gases are filled in the vessel 1 from the blow-off ports 4 of the ladder electrode 2. Glow discharge is generated when voltage is impressed to the electrode 2 via a matching device 6 from a high-frequency power source 5, by which plasma is formed atop the electrode and an amorphous thin film is formed on the surface of the substrate 9. The reactive gases flow in the part where the electromagnetic field intensity atop the electrode 2 is strong and the high-density plasma is generated. Depositing of the thin films in the blow-off holes is prevented by the grounding shield 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical vapor deposition method for forming amorphous silicon solar cells, thin film semiconductors, photosensors, semiconductor protective film insulating films, and the like.
n, hereinafter referred to as CVD) A high frequency plasma CVD apparatus used for thin film formation.

[0002]

2. Description of the Related Art The structure of a conventional plasma CVD apparatus for producing a large-area a-Si thin film will be described with reference to FIGS. This technical means
For example, Japanese Patent Application No. 3-5329 (JP-A-4-23678).
No. 1) and the like.

FIG. 6 is a sectional view of a plasma CVD apparatus. In the reaction vessel 1, a ladder-shaped planar coil electrode 11 (hereinafter referred to as a ladder electrode) for generating glow discharge plasma is arranged. As shown in the electrode plan view of FIG. 7, the ladder electrode 11 has a structure in which several wire rods are vertically assembled in a ladder shape with respect to the two wire rods 11a and 11b, and are connected to each other. I am doing it. Returning to FIG. 6, high-frequency power (Radi) of, for example, 13.56 MHz is supplied to the power supply points 11a and 11b of the ladder electrode 11 from the high-frequency power source 5.
Frequency (hereinafter referred to as RF power) is supplied through the impedance matching device 6.

A mixed gas of, for example, monosilane / hydrogen is supplied into the reaction vessel 1 from a cylinder (not shown) through a reaction gas introducing pipe 12. The gas in the reaction container 1 is exhausted to the outside of the reaction container 1 by the vacuum pump 8 through the exhaust pipe 7.

A substrate 9 on which a thin film is deposited is placed in parallel with a ladder electrode 11 and is supported on a substrate heater 10 by a substrate holder (not shown).

Using this apparatus, a thin film is manufactured as follows. First, the vacuum pump 8 is driven to exhaust the inside of the reaction vessel 1. For example, a mixed gas of monosilane / hydrogen is supplied at a flow rate of about 100 to 200 CC / min through the reaction gas introduction pipe 12, the pressure in the reaction vessel 1 is maintained at 0.5 to 1 Torr, and the high frequency power supply 5 and the impedance matching device 6 are connected. When RF power is applied to the ladder electrode 11 via the
Glow discharge plasma is generated in the space between the electrode 1 and the reaction vessel 1 and around the electrode 11. The generated plasma decomposes the mixed gas to deposit an a-Si thin film on the surface of the substrate 9.

[0007]

The above-mentioned conventional device is
The use of the ladder electrode 11 enables high-speed and large-area uniform film formation as compared with a generally used parallel plate type electrode. However, there are the following problems.

(1) FIG. 8 is a diagram of the electromagnetic field intensity distribution of the conventional ladder electrode, showing the electromagnetic field intensity at a position 5 mm from the ladder electrode. As shown in the figure, in the low power region of RF = 50 W, the electromagnetic field intensity distribution is almost uniform.
In the high power region of 100 W, the electromagnetic field is strong on the electrode wire 11, but the electromagnetic field strength between the electrode wires 11 is weaker than 50 W. The density of the generated plasma is proportional to the electromagnetic field strength. Therefore, when comparing RF = 50W and 100W,
In the vicinity of the electrode wire rods 11, 100 W has a higher plasma density, whereas between the electrode wire rods 11, 50 W has a higher plasma density. In the conventional method, most of the raw material gas is supplied not through the electrode wire 11 but through between the wire 11, so that the film formation rate is proportional to the plasma density between the electrode wires 11. As a result, when the RF power is increased as shown in the relationship diagram between the film formation rate and the RF power in FIG. 9, the film formation rate increases, but from a certain RF power value, as described above, Since the plasma density of No. 1 did not increase, the film formation rate decreased even if the RF power was increased, and further high speed film formation was not possible.

(2) In order to make up for the drawback of (1) above, the gas introducing pipe 12 is brought close to the ladder electrode 11 as shown in the sectional view of the plasma CVD apparatus of FIG. The gas 13 blown out from the electrode wire rod 11
Improvements have been made to supply to nearby areas. However, in this case, as shown in the cross-sectional view of the gas introduction pipe of FIG.
The SiNx film 14 thickly deposited by the decomposed gas component is deposited on the gas introduction pipe 12 near 1 to close the gas outlet 12a. The SiNx film 14 deposited around the gas blowout holes 12a blows off into flakes 15 due to the force of the gas 13 blowing, and the flakes 15 adhere to the substrate 9 to cause minute scratches on the thin film deposited on the substrate 9. And the film quality deteriorated even though the film formation rate was improved.

In order to solve the above problems, the present invention blows out a reaction gas as close to the ladder electrode as possible to increase the plasma density due to the high magnetic field strength on the electrode to perform high-speed film formation and high quality. The present invention provides a plasma CVD apparatus capable of producing the amorphous thin film.

[0011]

Therefore, according to the present invention, the substrate is arranged in the reaction vessel so as to face the discharge electrode, and glow discharge plasma is generated from the discharge electrode to form an amorphous thin plate on the substrate. In the plasma CVD apparatus, the discharge electrode is composed of a hollow wire, and a gas is caused to flow in the cavity of the hollow wire to blow out a reaction gas from the surface of the electrode wire. Is integrated into a plasma CVD apparatus.

That is, the present invention provides a reaction vessel, a means for introducing and discharging a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and a discharge electrode for glow discharge. In a plasma CVD apparatus having a power supply for supplying electric power and forming an amorphous thin film on the surface of a substrate installed facing the discharge electrode in the reaction vessel, the discharge electrode has a plurality of hollow wires. Is formed in a ladder-like planar shape, and a gas blowout hole is provided at a position that is the back surface of the surface of the plurality of hollow wires facing the substrate, and the same blowout hole is formed with a gap maintained between the gas blowout holes. A plasma CVD apparatus comprising a grounding shield for covering, wherein a gas is flown into the cavity of the hollow wire and ejected from the blowout hole to integrate a gas introduction portion with the discharge electrode.

[0013]

According to the present invention, by such means, the reaction gas passes through the cavity of the hollow wire which constitutes the discharge electrode and flows out from the gas blowout hole to make the inside of the reaction vessel have a predetermined pressure. Electric power is supplied from the power source to the discharge electrode to generate glow discharge plasma, and an amorphous thin film decomposed by the plasma is formed on the surface of the substrate arranged facing the discharge electrode. In the process of forming this thin film, the gas blow-out hole is provided on the back surface of the surface of the hollow wire facing the substrate and is covered with the earth shield, so that the reaction gas is guided from the blow-out hole by the earth shield. The hollow wire is guided to an area where the electromagnetic field strength is high in the upper part of the peripheral surface on the substrate side, and plasma is generated in this area, so the area around the gas outlet is not exposed to the plasma, so a thin film accumulates around the outlet. As a result, it is possible to form a high-speed, high-quality film without the flakes being scattered and scratching the surface of the substrate.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 is a sectional view showing the structure of a plasma CVD apparatus according to an embodiment of the present invention, FIG. 2 is a plan view of the hollow ladder electrode in FIG. 1, FIG. 3 is a detailed sectional view of the hollow ladder electrode, and FIG. FIG. 5 is a cross-sectional view of a hollow ladder electrode, showing a gas supply state and a plasma state, and FIG. 5 is a view showing a relationship between a film formation rate and an RF electrode.

Embodiments will be described in detail below with reference to these drawings. The same members as those in the conventional apparatus (FIG. 6) are designated by the same reference numerals. A disciple-shaped planar coil electrode 2 (hereinafter referred to as a hollow ladder electrode) using a cylindrical hollow wire for generating glow discharge plasma is arranged in the reaction vessel 1. This hollow ladder electrode 2 has two hollow wire rods 2 as shown in the plan view of FIG. 2 and the sectional view of FIG.
It has a structure in which several hollow wire rods are connected vertically to a and 2b and assembled in a ladder shape, and the outer peripheral portion has a quadrangular shape.

The size of this ladder electrode depends on the capacity of the reaction vessel, but the length of the hollow wire is 100 to 1000 mm, the distance between the hollow wires is 10 to 50 mm, and the diameter of the hollow wire is 3.
10 mm is preferable.

Further, as shown in FIG. 3, a circular arc-shaped earth shield 3 is provided in a semi-circular portion of the hollow wire material at a position which is the back surface of the surface of the hollow wire material facing the substrate 9 with a constant interval. Has been. The distance between this electrode and the earth shield 3 is preferably about 0.5 to 2 mm and is preferably equal to or less than the mean free path of electrons at the internal pressure of the reaction container 1 during film formation. The hollow portion of each wire is in communication with each other, and a plurality of gas blowout holes 4 are provided in the hollow wire at a position facing the earth shield 3 so as to communicate with the hollow portion of the hollow wire.
It is preferable that the diameter of the gas outlet holes 4 is 0.2 to 0.7 mm and the arrangement pitch of the holes is about 10 to 25 mm.

Power supply points 2a, 2b of the hollow ladder electrode 2
A high-frequency power source 5 supplies electric power having a frequency of 13.56 MHz, for example, through the impedance matching device 6. In addition, at a gas supply point 2C of the hollow ladder electrode 2, a gas supply pipe (not shown) introduces a mixed gas of, for example, monosilane / hydrogen into a hollow portion of the hollow ladder electrode 2 through an electrically insulating hollow material. It is supplied and sent out into the reaction container 1 through the gas blowout hole 4.

The hollow wire rod forming the hollow ladder electrode 2 may have an elliptical cross section or a polygonal cross section. In that case, the earth shield 3 has a constant distance from the hollow wire rod surface. Therefore, it is necessary to use the same elliptical shape or polygonal shape. Gas in the reaction vessel 1 is exhaust pipe 7
Through the vacuum pump 8.

A substrate 9 on which a thin film is to be formed is placed in parallel with the hollow ladder electrode 2 and supported by a substrate heater 10 by a substrate holder (not shown).

Using this apparatus, a thin film is prepared as follows. First, the vacuum pump 8 is driven to exhaust the inside of the reaction vessel 1. Gas supply point 2 from a gas supply pipe (not shown)
A mixed gas of, for example, monosilane / hydrogen is supplied from C through the hollow portion of the hollow ladder electrode 2 at a flow rate of about 100 to 200 CC / min, and the pressure in the reaction vessel 1 is set to 0.5 to 1 To.
When the RF power is applied to the hollow ladder electrode 2 from the high frequency power source 5 through the impedance matching device 6 while maintaining about rr,
As shown in FIG. 4, glow discharge plasma is generated around the portion of the electrode 2 where the earth shield 3 is absent.

The plasma density is large in the vicinity of the electrode wire and becomes smaller as the distance increases, but in the present invention, the gas 21 is always supplied to the region having the highest plasma density, as shown in FIG.
Since the high-density plasma 20 is generated in this region and no plasma is generated in the vicinity of the gas outlet 4, the gas outlet 4 is not exposed to the plasma and a film is not deposited, so that high quality and high speed film formation is possible. It is speculated that it will be possible. Therefore, a film forming experiment was conducted under the following conditions.

Substrate material: glass, substrate area: 300 mm x
300 mm, substrate temperature: 250 ° C., reaction gas and flow rate: S
iH ₄ = 30 CC / min, hydrogen = 120 CC / min, reaction vessel pressure: 1 Torr, and high frequency power applied was 20.
It was set in the range of W to 100W. FIG. 5 shows the relationship between the film formation rate and the high frequency power.

As shown in FIG. 5, when the high frequency power is increased, the film forming rate is increased, and the high frequency power of 100 W
A very high deposition rate of 4 Å / sec was obtained. At this time, the defect density of the obtained film was measured by the electron pin resonance method and found to be 1.2 × 10 ¹⁵ defects / CC, which proved to be a high quality film.

As described above, in this embodiment, by using the hollow ladder electrode 2 shown in FIGS. 2 and 3 as the discharge electrode, a high film formation rate of 10 to 15 angstrom / sec and high quality a -Si thin film can be produced.

[0026]

As described in detail above, according to the present invention, by using the electrode made of a hollow wire as the discharge electrode, the reaction gas is blown out from the blowout port of the hollow wire and Since the reaction gas is supplied to the portion having a strong electromagnetic field strength, a high quality amorphous thin film can be manufactured at high speed. Therefore, it has great industrial value in the manufacturing field of amorphous silicon solar cells, thin film semiconductors, optical sensors, semiconductor protective films, and the like.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a plasma CVD apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view of the hollow ladder electrode in FIG.

3 is a detailed cross-sectional view of the hollow ladder electrode in FIG.

FIG. 4 is a cross-sectional view of a hollow ladder electrode according to an embodiment of the present invention, showing a state of gas supply and plasma generation.

FIG. 5 is a diagram showing the effect of the present invention, showing the relationship between the film formation rate and the RF power.

FIG. 6 is a sectional view of a conventional plasma CVD apparatus.

FIG. 7 is a plan view of the conventional ladder electrode shown in FIG.

FIG. 8 is a diagram showing an electromagnetic field intensity distribution of a conventional ladder electrode.

FIG. 9 is a diagram showing a relationship between a film formation rate and RF power of a conventional plasma CVD apparatus.

FIG. 10 is a cross-sectional view of a conventional improved plasma CVD apparatus.

FIG. 11 is a conceptual diagram showing a situation of film deposition on a ladder electrode in a conventional plasma CVD apparatus.

[Explanation of symbols]

 1 Reaction Vessel 2 Hollow Ladder Electrode 3 Earth Shield 4 Gas Outlet 5 High Frequency Power 6 Matching Machine 7 Exhaust Pipe 8 Vacuum Pump 9 Substrate 20 High Density Plasma

Claims (1)

[Claims] 1. A reaction container, means for introducing and discharging a reaction gas into the reaction container, a discharge electrode housed in the reaction container, and glow discharge power supplied to the discharge electrode. In a plasma CVD apparatus having a power source and forming an amorphous thin film on the surface of a substrate installed in the reaction vessel so as to face the discharge electrode, the discharge electrode is a ladder formed of a plurality of hollow wires. Of the same number of hollow wire rods, the gas blow-out hole is provided at a position which is the back side of the surface facing the substrate of the plurality of hollow wire rods, and an earth shield which covers the blow-out hole while keeping a gap with the gas blow-out hole. A plasma CVD apparatus characterized in that a gas introduction part is integrated with a discharge electrode by causing a gas to flow into the cavity of the hollow wire and ejecting the gas from the blowout hole.