JP3137532B2 - Plasma CVD equipment - Google Patents

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 (Chemical Vapor Depositio) for forming an amorphous silicon solar cell, a thin film semiconductor, an optical sensor, a semiconductor protective film and an insulating film.
n, hereinafter referred to as CVD).

[0002]

2. Description of the Related Art The configuration 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. Hei 3-5329 (Japanese Unexamined Patent Publication No. Hei.
No. 1).

FIG. 6 is a cross-sectional view of a plasma CVD apparatus. A ladder-shaped planar coil electrode 11 (hereinafter referred to as a ladder electrode) for generating glow discharge plasma is disposed in a reaction vessel 1. As shown in the electrode plan view of FIG. 7, the ladder electrode 11 has a structure in which several wires are assembled in a ladder shape perpendicularly to two wires 11a and 11b and connected to each other. No. Returning to FIG. 6, the high frequency power (for example, 13.56 MHz) from the high frequency power supply 5 is supplied to the power supply points 11a and 11b of the ladder electrode 11.
o Frequency; hereinafter, referred to as RF power) is supplied via the impedance matching device 6.

[0004] In the reaction vessel 1, for example, a mixed gas of monosilane / hydrogen is supplied from a cylinder (not shown) via a reaction gas introduction pipe 12. The gas in the reaction vessel 1 is exhausted out of the reaction vessel 1 by a vacuum pump 8 through an exhaust pipe 7.

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

Using this apparatus, a thin film is prepared as follows. First, the inside of the reaction vessel 1 is evacuated by driving the vacuum pump 8. 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, When RF power is applied to the ladder electrode 11 through the
Glow discharge plasma is generated in the space between the electrode 1 and the reaction vessel 1 and around the electrode 11. The mixed gas is decomposed by the generated plasma, and an a-Si thin film is deposited 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 where RF = 50 W, the electromagnetic field intensity distribution is almost uniform.
In the high power range of = 100 W, the strong electromagnetic field is present on the electrode wires 11, whereas the intensity between the electrode wires 11 is weaker than 50 W. The density of the generated plasma is proportional to the electromagnetic field intensity. Therefore, when comparing RF = 50W and 100W,
In the vicinity of the electrode wires 11, the density of the plasma is higher at 100 W, whereas between the electrode wires 11, the power is higher at 50 W. In the conventional method, most of the raw material gas does not pass over the electrode wires 11 but is supplied through the space between the wires 11, so that the deposition rate is proportional to the plasma density between the electrode wires 11. As a result, as shown in the relationship diagram between the deposition rate and the RF power in FIG. 9, as the RF power is increased, the deposition rate is increased. Since the plasma density did not increase, the film formation rate was reduced even if the RF power was increased, and a higher film formation could not be performed any more.

(2) In order to compensate for the drawback of the above (1), as shown in the cross-sectional view of the plasma CVD apparatus in FIG. 10, the gas introduction pipe 12 is brought close to the ladder electrode 11, and the gas blowing holes 12a of the gas introduction pipe 12 are formed. The gas 13 blown out from the electrode wire 11
It has been improved so that it can be supplied to the vicinity. However, in this case, as shown in the cross-sectional view of the gas introduction pipe of FIG.
A thick SiNx film 14 is deposited on the gas introduction pipe 12 near the area 1 by the decomposed gas component, and closes the gas outlet 12a. The SiNx film 14 deposited around the gas blowing holes 12a becomes flakes 15 and blows off due to the force of the gas 13 to be blown out, and the flakes 15 adhere to the substrate 9 to cause minute damage to the thin film deposited on the substrate 9. And the film quality deteriorated even though the film formation rate was improved.

SUMMARY OF THE INVENTION The present invention aims at solving such problems by blowing out a reaction gas as close to the ladder electrode as possible to increase the plasma density by a high magnetic field strength on the electrode, thereby performing high-speed film formation and high quality film formation. It is intended to provide a plasma CVD apparatus capable of producing an amorphous thin film.

[0011]

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

That is, the present invention provides a reaction vessel, means for introducing and discharging a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and a glow discharge electrode provided in the discharge electrode. A plasma CVD apparatus having a power supply for supplying electric power and forming an amorphous thin film on a substrate surface provided in the reaction vessel so as to face the discharge electrode, wherein the discharge electrode comprises a plurality of hollow wires. A ladder-like planar shape made of, and a plurality of hollow wires are provided with gas blowout holes at positions on the back surface of the surface facing the substrate, and the gas blowout holes are maintained at the same gap as the gas blowout holes. There is provided a plasma CVD apparatus comprising a covering earth shield, a gas flowing into a cavity of the hollow wire material, and a gas introducing portion integrated with a discharge electrode by ejecting the gas from the blowing hole.

[0013]

According to the present invention, by such means, the reaction gas passes through the cavity of the hollow wire constituting the discharge electrode, flows out of the gas outlet, and keeps the inside of the reaction vessel at a predetermined pressure. Power is supplied from the power supply 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 disposed opposite to the discharge electrode. In the process of forming the thin film, the gas outlet is provided on the surface opposite to 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 outlet through the earth shield. The hollow wire is guided to a region 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 region.Therefore, the periphery of the gas outlet is not exposed to the plasma, so that a thin film is deposited around the outlet. Accordingly, a high-speed, high-quality film can be formed without flakes scattering and damaging the substrate surface.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a sectional view showing the configuration of a plasma CVD apparatus according to one 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 this hollow ladder electrode, and FIG. FIG. 5 is a cross-sectional view of a hollow ladder electrode, showing a state of gas supply and plasma, and FIG. 5 is a view showing a relationship between a film forming speed and an RF electrode.

Hereinafter, embodiments will be described in detail with reference to these drawings, in which the same members as those of the conventional apparatus (FIG. 6) are denoted by the same reference numerals. In the reaction vessel 1, an apprentice-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. This hollow ladder electrode 2 has two hollow wires 2 as shown in the plan view of FIG. 2 and the sectional view of FIG.
It has a structure in which several hollow wires are connected vertically to a and 2b and assembled in a ladder shape, and the outer peripheral portion has a square shape.

The dimensions of the ladder electrode depend 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 mm.
10 to 10 mm is preferred.

As shown in FIG. 3, an arc-shaped earth shield 3 is provided on a semi-circumferential portion of the hollow wire at a predetermined interval at a position on the back surface of the front surface of the hollow wire facing the substrate 9. Have been. The distance between the 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 pressure in the reaction vessel 1 during film formation. The hollow portions of the respective wires are in communication with each other, and the hollow wires are provided with a plurality of gas blowing holes 4 at positions facing the earth shield 3, and are in communication with the hollow portions of the hollow wires.
It is preferable that the diameter of the gas blowing holes 4 is 0.2 to 0.7 mm and the arrangement pitch of the holes is about 10 to 25 mm.

The power supply points 2a, 2b of the hollow ladder electrode 2
, Power of a frequency of, for example, 13.56 MHz is supplied from the high-frequency power supply 5 through the impedance matching unit 6. At the gas supply point 2C of the hollow ladder electrode 2, for example, a mixed gas of monosilane / hydrogen is supplied from a gas supply pipe (not shown) to the hollow portion of the hollow ladder electrode 2 via an electrically insulating hollow material. The gas is supplied and sent out of the gas outlet 4 into the reaction vessel 1.

The cross-sectional shape of the hollow wire constituting the hollow ladder electrode 2 may be elliptical or polygonal. In this case, the distance between the ground shield 3 and the surface of the hollow wire is constant. It is necessary to have the same shape of an ellipse or a polygon so that The gas in the reaction vessel 1 is exhaust gas 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 is supported by a substrate heater 10 by a substrate holder (not shown).

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

Although the plasma density is large near the electrode wire and becomes smaller as the distance increases, the gas 21 is always supplied to the region having the highest plasma density as shown in FIG.
The high-density plasma 20 is generated in this area, and no plasma is generated in the vicinity of the gas blowout holes 4, so that the gas blowout holes 4 are not exposed to the plasma, and no film is deposited. It is presumed that it will be possible. Therefore, a film forming experiment was performed under the following conditions.

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

As shown in FIG. 5, when the high-frequency power is increased, the film forming speed is increased.
A very high film formation rate of 4 angstroms / sec was obtained. At this time, when the defect density of the obtained film was measured by an electron pin resonance method, it was found to be 1.2 × 10 ¹⁵ / CC, indicating a high quality film.

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

[0026]

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

[Brief description of the drawings]

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

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

FIG. 3 is a detailed sectional view of the hollow ladder electrode in FIG. 1;

FIG. 4 is a sectional view of a hollow ladder electrode according to one 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, illustrating the relationship between the film forming speed 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 illustrating a relationship between a film forming speed and RF power of a conventional plasma CVD apparatus.

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction container 2 Hollow ladder electrode 3 Earth shield 4 Gas blowout hole 5 High frequency power supply 6 Matching device 7 Exhaust pipe 8 Vacuum pump 9 Substrate 20 High density plasma

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 16/50-16/517 C30B 25/00-25/22 H01L 21/205 INSPEC (DIALOG)

Claims (1)

(57) [Claims] 1. 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 supplying glow discharge power to the discharge electrode. A plasma CVD apparatus having a power supply and forming an amorphous thin film on a surface of a substrate disposed opposite to the discharge electrode in the reaction vessel, wherein the discharge electrode has a ladder shape formed of a plurality of hollow wires. A gas outlet is provided at a position that is a back surface of the surface of the plurality of hollow wires facing the substrate, and an earth shield that covers the outlet while keeping a gap with the gas outlet is formed. A plasma CVD apparatus, wherein a gas introduction part is integrated with a discharge electrode by flowing a gas into the cavity of the hollow wire and ejecting the gas from the outlet.