JP3372384B2 - Plasma CVD equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical vapor deposition method for forming an amorphous silicon solar cell, a thin film semiconductor, an optical sensor, a semiconductor protective film insulating film, and the like.
The present invention relates to a high-frequency plasma CVD apparatus used for forming a thin film. 2. Description of the Related Art An example of the configuration of a plasma CVD apparatus conventionally used for producing a large-area a-Si thin film will be described with reference to FIGS. 8 and 9. FIG. This technical means is an apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 4-236681. FIG. 8 is a cross-sectional view of a plasma CVD apparatus. A ladder-like planar coil electrode (2) (hereinafter referred to as a ladder electrode) for generating glow discharge plasma is arranged in a reaction vessel (1). I have. As shown in the electrode plan view of FIG. 9, the ladder electrode (2) has a structure in which a plurality of wires are assembled in a ladder shape perpendicularly to two wires and connected, and the outer peripheral portion has a square shape. No. Power supply points (2a) and (2b) of the ladder electrode (2) are supplied from a high frequency power supply (7) to a high frequency power (RadioFreque) of, for example, 13.56 MHz.
ncy; hereinafter referred to as RF power) is supplied via the impedance matching unit (8). [0004] In the reaction vessel (1), for example, a mixed gas of monosilane and hydrogen is supplied from a cylinder (not shown) via a reaction gas supply pipe (6). The gas in the reaction vessel (1) is exhausted to the outside of the reaction vessel (1) by a vacuum pump (10) through an exhaust pipe (9). Substrate for depositing thin film (1
2) is installed in parallel with the ladder electrode (2), and is supported on the substrate heater (11) by a substrate holder (not shown). [0005] Using this apparatus, a thin film is produced as follows. First, the inside of the reaction vessel (1) is evacuated by driving the vacuum pump (10). Next, for example, 100 to 200 cc of a mixed gas of monosilane and hydrogen is passed through a reaction gas supply pipe (6).
/ Min at a flow rate of approx.
When the RF power is applied to the ladder electrode (2) from the high frequency power supply (7) through the impedance matching device (8) while maintaining the pressure at 0.5 to 1 Torr, the space between the ladder electrode (2) and the reaction vessel (1) and Glow discharge plasma is generated around the ladder electrode (2). The mixed gas is decomposed by the generated plasma, and an a-Si thin film is deposited on the substrate surface. [0006] The above-mentioned conventional device is as follows.
The use of the ladder electrode (2) enables high-speed, large-area uniform film formation as compared with a generally used parallel plate type electrode. However, there are the following problems. 1) FIG. 10 is a diagram of the electromagnetic field intensity distribution of a 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 range of 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 wire (2), but the intensity of the electromagnetic field between the electrode wires (2) is weaker than 50W. The density of the generated plasma is proportional to the electromagnetic field intensity. Therefore, when RF = 50 W is compared with 100 W, 100 W has a higher plasma density in the vicinity of the electrode wire (2), whereas 50 W is higher between the electrode wires (2). In the conventional method, most of the gas as a raw material does not pass over the electrode wires (2) but is supplied between the wires, so that the film formation rate is reduced by the plasma density between the electrode wires (2). Is proportional to As a result, as shown in the relationship diagram between the film forming speed and the RF power in FIG. 11, as the RF power is increased, the film forming speed initially increases, but from a certain RF power value, as described above. Since the plasma density between the electrodes does not increase,
Even if the RF power was increased, the film formation speed was reduced, and no further high-speed film formation was possible. 2) In the conventional method, as shown by the SiH emission intensity distribution between the reaction gas introduction pipe (6), the ladder electrode (2) and the substrate (12) in FIG. In the vicinity of the substrate downstream of the gas flow, the reaction expressed by the following formula proceeds, and powder is likely to be generated. The generated powder enters a thin film growing on the surface of the substrate (12). As a result, the film quality was degraded. [0010] SiH ₄ + e ^- _{(e) → SiH 2 + H 2 SiH} 2 + SiH 4 → Si 2 H 6 SiH 2 + Si 2 H 6 → Si 3 H 8 · · · SiH 2 + Si n-1 H 2n → Si n H _{2 (n + 1)} (powder) 3) In order to compensate for the drawbacks of the above 1) and 2), the present inventors formed a ladder electrode with a hollow wire as shown in FIG. In addition to supplying gas, an improvement has been made to suppress the generation of plasma in unnecessary parts by attaching an earth shield.
Patent application No. 28665. However, in this case, the structure of the earth shield and the hollow ladder electrode becomes complicated, and when the substrate is used for a long time, the substrate heater (11)
The earth shield (14) is thermally deformed by heat conduction from the hollow ladder electrode (13) and the earth shield (14).
There was a problem in long-term reliability, such as the occurrence of abnormal discharge such as arc discharge due to a change in the distance between the electrodes. In order to solve the above-mentioned conventional problems, the present inventor has set forth a reaction vessel, means for introducing and discharging a reaction gas into and from the reaction vessel, A ladder-shaped flat discharge electrode composed of a plurality of wires accommodated in the electrode, and a power supply for supplying glow discharge power to the discharge electrode, facing the discharge electrode in the reaction vessel. In a plasma CVD apparatus for forming an amorphous thin film on the surface of a substrate placed, a portion of the discharge electrode not facing the substrate is buried at an interval in an earth shield plate, and A gas outlet is opened on a surface facing the discharge electrode, and a reaction gas is supplied from the gas outlet through the gap between the discharge electrode and the earth shield plate into the reaction vessel. The present invention proposes a plasma CVD apparatus characterized by the following. According to the present invention, the portion of the discharge electrode not facing the substrate is embedded in the earth shield plate at an interval, and the portion of the discharge electrode facing the discharge electrode is separated from the substrate. A gas blowing hole is opened on the surface to be blown, and the reaction gas is supplied from the gas blowing hole into the reaction vessel through the gap between the discharge electrode and the earth shield plate. From the electrode through the gap between the discharge electrode and the earth shield plate to a portion of the discharge electrode facing the substrate where the electromagnetic field intensity is high, and high-density plasma is generated in this portion. In this way, discharge can be suppressed in the portion of the electrode not facing the substrate and the reaction gas can be supplied to the high-density plasma portion, so that generation of powder in the plasma can be suppressed, and high-speed film formation can be performed. A quality amorphous thin film can be formed. 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 showing a ladder electrode in FIG. 1, and FIG. 3 is a detailed section showing the relationship between the ladder electrode and an earth shield plate. FIG. In these figures, the same parts as those of the related art described with reference to FIGS. 8 and 9 are denoted by the same reference numerals to avoid redundancy, and detailed description is omitted. In the present embodiment, a ladder-shaped planar coil (2) (hereinafter referred to as a ladder electrode) constituted by assembling wires to generate glow discharge plasma is disposed in a reaction vessel (1). . The ladder electrode (2) used in this embodiment also has a structure in which a plurality of wires are connected vertically to two wires as shown in a plan view of FIG. The part has a square shape. The dimensions of the ladder electrode depend on the capacity of the reaction vessel (1), but the length of the wire is 100 to 1000 mm, and the distance between the wires is 1 mm.
The diameter of the wire is preferably 2 to 10 mm. The outer peripheral portion of the ladder electrode (2) may have another polygonal shape such as a triangle or a hexagon, or a shape such as a circle or an ellipse. Alternatively, a structure in which several ladder electrodes are arranged in a plane may be used. As shown in FIG. 3, a half of the wire constituting the ladder electrode (2), which is not opposed to the substrate (12), is embedded in the earth shield plate (3) at a constant interval. . This electrode (2) and earth shield plate (3)
Is preferably about 0.5 to 2 mm, and is equal to or less than the mean free path of electrons at the internal pressure of the reaction vessel (1) during film formation. This earth shield plate (3) is a part of a member constituting the gas mixer (4), and has a plurality of surfaces connected to the inside of the gas mixer (4) on a surface facing the wire constituting the ladder electrode (2). Each gas outlet (5) is open. The diameter of this gas outlet (5) is
Preferably, the hole pitch is 0.2 to 0.7 mm and the hole pitch is 10 to 25 mm. The power supply point (2a) of the ladder electrode (2),
(2b) includes, for example, 13.56 M from the high frequency power supply (7).
RF power of the frequency of Hz is an impedance matching device (8)
Is supplied via For example, a monosilane gas is supplied to the gas mixer (4) from a gas supply pipe (6), and the reaction vessel (1) passes through a gap between a ladder electrode (2) and an earth shield plate (3) from a gas blowing hole (5). Sent out within. The gas in the reaction vessel (1) is exhausted by a vacuum pump (10) through an exhaust pipe (9). A substrate (12) on which a thin film is to be formed is placed in parallel with the ladder electrode (2), and is supported by a substrate heater (11) by a substrate holder (not shown). Using this apparatus, a thin film is manufactured as follows. First, the inside of the reaction vessel (1) is evacuated by driving the vacuum pump (10). Next, for example, monosilane gas is supplied as a reaction gas from the gas supply pipe (6) to the gas mixer (4) at a flow rate of about 20 to 100 cc / min, and the ladder electrode (2) is grounded through the gas blowing hole (5). Shield plate (3)
And squirt into the gap. When the pressure in the reaction vessel (1) is maintained at about 0.03 to 0.2 Torr and high frequency power is applied to the ladder electrode (2) from the high frequency power supply (7) via the impedance matching device (8), the electrode (2) Glow discharge plasma is generated around the portion without the earth shield plate (3). The reaction gas is decomposed by this plasma, and an amorphous thin film is formed on the surface of the substrate (12) arranged opposite to the ladder electrode (2). Although the plasma density decreases as the distance increases in the vicinity of the electrode wire, in this embodiment, as shown in FIG. 4, the reaction gas (21) is always supplied to the region (20) having the highest plasma density. You. The high-density plasma is generated in this region (20), and is not generated in a portion of the electrode wire not facing the substrate, which is unnecessary for depositing a thin film on the substrate (12). Further, since the gas outlet (5) is not exposed to plasma and the film is not deposited, there is no film peeling due to the force of the gas protruding from the gas outlet, so that a high-quality thin film can be formed at high speed. Guessed. Therefore, a film forming experiment was performed under the following conditions. That is, non-alkali glass was used as the substrate material, the substrate area was 300 × 300 mm, the substrate temperature was 250 ° C, and the reaction gas was Si.
H ₄ , the flow rate was 70 cc / min, and the pressure in the reaction vessel was 30 mTo
rr, and the applied high frequency power is 20 W
From 200W to 200W. FIG. 5 shows the relationship between the deposition rate and the high-frequency power thus obtained, and FIG. 6 shows the relationship between the defect density in the film measured by the electron spin resonance method (hereinafter referred to as ESR) and the deposition rate. As shown in FIG. 5, when the high-frequency power is increased, the film-forming speed is increased.
/ Sec., A very high film formation rate was obtained. The defect density obtained at this time is 2.8 × 10 ¹⁵ as shown in FIG.
Pcs / cc, which proved to be a high quality film. Further, the defect density of the thin film manufactured under the condition that the high-frequency power was slightly lowered and the film formation rate was 10 ° / sec or less was determined by the ESR used in this example.
Is below the lower limit of measurement (1 × 10 ¹⁵ cells / cc), and it was found that the film was very high quality. As described above, in this embodiment, the ladder electrode (2) embedded in the earth shield plate (3) is used as the discharge electrode as shown in FIGS.
It is possible to produce a high-quality a-Si thin film having a high film forming rate of about 25 ° / sec and a defect density of 3 × 10 ¹⁵ / cc or less. In addition, since the gas mixer (4) and the earth shield plate (3) are integrated and there is no need to make the ladder electrode (2) hollow, the structure is simple and thermal deformation is suppressed. The cross section of the wire constituting the ladder electrode (2) of the above embodiment is circular, and has a structure in which a semicircular portion is buried in the earth shield plate (3) as shown in FIG. The shape of the buried portion may be a polygon such as a square as shown in FIG. Also, the shape of the portion protruding from the earth shield plate (3) may be polygonal as shown in FIG. Alternatively, they may be on the same plane without protruding from the earth shield plate (3) as shown in FIG. 7 (c). According to the present invention, the portion of the discharge electrode that does not face the substrate is embedded in the earth shield plate at an interval, and the outlet hole is opened on the surface of the earth shield plate that faces the discharge electrode. Since the reactant gas is supplied to the portion where the electromagnetic field strength is high near the discharge electrode by introducing the reactant gas, a high-quality amorphous thin film can be manufactured at high speed. Therefore, it has great industrial value in the fields of manufacturing amorphous silicon solar cells, thin film semiconductors, optical sensors, semiconductor protective films, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a plasma CV according to an embodiment of the present invention.
It is sectional drawing which shows the structure of D apparatus. FIG. 2 is a plan view showing a ladder electrode in FIG. FIG. 3 is a detailed sectional view showing a relationship between a ladder electrode and an earth shield plate in FIG. 1; FIG. 4 is a diagram showing gas supply and a plasma state in the embodiment. FIG. 5 is a diagram showing a relationship between a film forming speed and a high-frequency power in the above embodiment. FIG. 6 is a diagram showing a relationship between a defect density in a film and a film formation rate in the above embodiment. FIG. 7 is a cross-sectional view illustrating the relationship between a ladder electrode and an earth shield plate in another embodiment of the present invention. FIG. 8 is a sectional view showing an example of a configuration of a conventional plasma CVD apparatus. FIG. 9 is a plan view showing a ladder electrode in FIG. 8; FIG. 10 is a diagram showing an electromagnetic field intensity distribution of a conventional ladder electrode. FIG. 11 is a conceptual diagram showing a state of film deposition on a ladder electrode of a conventional plasma CVD apparatus. FIG. 12 is a diagram showing a SiH emission intensity distribution between a gas outlet and a substrate in a conventional plasma CVD apparatus. FIG. 13 is a sectional view showing another example of the configuration of the conventional plasma CVD apparatus. [Description of Signs] (1) Reaction vessel (2) Ladder electrode (3) Earth shield plate (4) Gas mixer (5) Gas outlet (6) Reaction gas supply pipe (7) High frequency power supply (8) Impedance matching (9) Gas exhaust pipe (10) Vacuum pump (11) Substrate heater (12) Substrate (13) Hollow ladder electrode (14) Earth shield (20) High density plasma area (21) Gas flow

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C23C 16/505 C30B 25/00 H01L 21/205 INSPEC (DIALOG) JICST file (JOIS)

Claims (1)

(57) [Claims 1] A reaction vessel, means for introducing and discharging a reaction gas into and from the reaction vessel, and a ladder-like shape comprising a plurality of wires accommodated in the reaction vessel. A flat-type discharge electrode and a power supply for supplying glow discharge power to the discharge electrode, and forming an amorphous thin film on the surface of the substrate placed opposite to the discharge electrode in the reaction vessel. In the plasma CVD apparatus, a portion of the discharge electrode not facing the substrate is embedded in the earth shield plate at an interval, and a gas blowing hole is formed on a surface of the earth shield plate facing the discharge electrode. A plasma CVD apparatus, wherein a reaction gas is supplied into the reaction vessel from the gas outlet through a gap between the discharge electrode and the earth shield plate.