JPS62262419A - Plasma cvd equipment - Google Patents

Abstract

PURPOSE:To perform decomposition of each material gas while preventing residues produced during decomposition of other material gas from being entrained into the forming film and to obtain a high-quality thin film, by providing and distributing several groups of hollow cathodes classified by material gases for which they are exclusively and independently used while providing anodes adjacent to the cathodes. CONSTITUTION:Hollow cathodes are divided into three rows of hollow cathodes exclusively for diborane 41, hollow cathodes exclusively for phosphine 42 and hollow cathodes exclusively for silane 43. Anodes 5 are arranged adjacent to the cathodes 41, 42 and 43. The cathodes 41, 42 and 43 and the anode 5 are connected to discharge power sources 61, 62 and 63 via changeover switches 71, 72 and 73. One of the switches 71, 72 and 73 is closed to supply the electrodes with electric power while the inside of a reaction furnace 1 is evacuated through an exhaust port 8. Thereby, the material gases supplied to the cathodes 41, 42 and 43 are decomposed by glow discharge plasma and plasma activated species are discharged from the respective cathodes 41, 42 and 43. In this manner decomposition of each material gas can be performed, while preventing residues produced by decomposition of other material gas from being entrained int eh forming film. Thus, a thin film having high quality can be obtained.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a plasma CVD apparatus for manufacturing thin film semiconductors such as amorphous semiconductors.

[Prior art and its problems]

Research and development of amorphous semiconductors has progressed rapidly in recent years, and the fields of application of amorphous semiconductors as materials for various electronic devices are expanding. Among them, amorphous silicon (hereinafter referred to as a-5
t) films are attracting attention as low-cost solar cells because they can be easily made into large-area films, and currently 40c
Trial production of solar cells using large-area substrates with dimensions of m x 120 cs is underway, and improvements are being made to make the in-plane film quality uniform. Plasma CVD equipment is currently widely used as a manufacturing equipment for this type of a-Si film for large-area solar cells. Figure 2 shows a typical example of its structure, in which the raw material gas is passed through the gas circuit system into the reactor 1, which is evacuated from the inlet 25.
The source gas is decomposed by glow discharge by causing discharge plasma to be generated between a pair of opposing discharge electrodes 21 and 22 by a high frequency power source 23 or a DC power source 24. As a result, the film forming substrate 2 is placed on the lower electrode 22 which has a built-in substrate heating heater 26 connected to a power source 27.
An a-5t film can be formed thereon. The unreacted gas is then exhausted from the exhaust port 8 through the vacuum pump. At that time, intrinsic (hereinafter referred to as i-type) a-3i
To form a film, silane (SiH*) is used as a raw material gas.
, Disilane (SixHa) gas, etc. are introduced, and diborane (Bil+) gas and phosphine (PHff) gas are introduced as dopant gases to form the p-type film-3i film and n-type film-5i film, respectively. Mix and introduce. FIG. 3 shows a typical structure example of a solar cell using this a-Si film. After a transparent electrode 31 is provided on an insulating transparent substrate 2 such as glass, a p-type film 2
．． i-shaped membrane 3. A-5tWi was deposited in the order of n-type film 4, and lastly, back metal electrode 35 was formed. Therefore, three types of a-3i films are formed in the plasma CVD apparatus. By the way, a serious problem when manufacturing this type of large-area size Mi-5i solar cell using a plasma CVD apparatus is that the a-5i film quality becomes non-uniform within the a-3i film surface and the film quality deteriorates. The first reason for this is that as the area becomes larger, the discharge electrode also becomes larger, so the discharge power density becomes uneven within the electrode surface, and the flow of raw material gas becomes uneven due to the larger size of the device. Accordingly, a −5
This is because the density of the constituent elements in the t-film varies within the plane. The second reason is that when forming three types of a-5i films in a single furnace, for example, after depositing the first p-type film-5i film, the discharge electrodes 22 and 23 of FIG. Discharge residue from the first layer generation is attached to the film, and when discharge plasma is generated between the electrodes 22 and 23 to generate the second layer, the discharge residue is sputtered and mixed into the film. This is because it affects the film quality of the second layer. In particular, as the area of solar cell substrates increases, the amount of discharge residue mixed into the film increases, and the amount of mixed discharge residue varies greatly within the plane.As a countermeasure, recently, p-type, i-type, A separate formation type plasma CVD apparatus has been developed in which reaction chambers for forming n-type structures are provided independently, and the film-forming substrate can be transported between the reaction chambers, thereby reducing the amount of contamination by the discharge residue mentioned above. However, this type of equipment not only requires a significant increase in manufacturing costs compared to the conventional equipment shown in Figure 2, but also
It has the disadvantage that maintenance becomes difficult. The third reason is that when forming p-type and n-type doped layers, as described above, at least two types of raw material gases are mixed and then decomposed by glow discharge, so each atom incorporated into the film, That is, this is because it is not possible to sufficiently control the amounts of silicon, hydrogen, and boron atoms in p-formation, and silicon, hydrogen, and phosphorus atoms in n-formation. Therefore, it is difficult to obtain a film with optimal film quality, and especially when manufacturing large-area solar cells, the mixed state of the raw material gases becomes non-uniform between the discharge electrodes, so that the formed a- The film quality of the 3t film is noticeably non-uniform.

[Purpose of the invention]

The present invention solves the above-mentioned problems and is a single-chamber reactor that is inexpensive to manufacture and easy to maintain, yet provides good film quality when thin film semiconductors of different properties are stacked.
An object of the present invention is to provide a plasma CVD apparatus with excellent in-plane uniformity.

[Key points of the invention]

The present invention is directed to a plasma CVD apparatus that applies a voltage between opposing T species arranged in a reactor to generate discharge plasma to decompose raw material gas and form a thin film semiconductor on a substrate on a substrate support. , one reactor has multiple pairs of gas inlet tubes and opposing discharge electrodes for one raw material gas each having a discharge electrode function, and is equipped with multiple groups connected to a power source via a switch. The introduction tubes are uniformly distributed and open toward the substrate support. As a result, for example, for each p-type, i-type, and n-type Ma-5i film, discharge plasma is generated only in the introduction tube dedicated to the raw material gas necessary for each film, and as a result, the shearing radicals are transferred to the substrate on the support. can be uniformly dispersed and flowed into other forms of a-
A-
5i film is formed.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention, (al is a side sectional view,
(b) is a plan view of the substrate surface, in which parts common to those in FIG. 2 are given the same reference numerals. With this apparatus, p-type, i-type, and n-type a-stills are formed on the same substrate.In the reactor 1, a substrate support 3 for supporting a substrate 2 is disposed in the upper part, and a substrate support 3 for supporting the substrate 2 is disposed in the lower part. A large number of hollow cathodes (hollow cathodes) that open toward the inside are arranged in a dispersed manner. As shown by different hatchings in the figure, the hollow cathodes have three rows of diborane-dedicated hollow cathodes 41. It is divided into a hollow cathode 42 exclusively for phosphine and a hollow cathode 43 exclusively for silane. An anode 5 is arranged adjacent to each hollow cathode 41, 42, 43. 0 reactor 1 in which each hollow cathode group and adjacent anode group are connected together to a power source s1.62.63 via a switch 71.72.73
By closing the switch and applying electrical energy while evacuating the interior through the exhaust port 8 through a vacuum pump, the raw material gas supplied to the hollow cathode is decomposed by the glow discharge plasma, and the plasma active species (radicals) are When forming the p-type a-5i film 32 shown in FIG. 3 as the first layer blown out from the hollow cathode on the substrate 2 on which the transparent conductive film 31 is attached, diborane gas is applied to the entire hollow cathode 41. Silane gas is supplied to all of the hollow cathodes 43, the changeover switches 71 and 73 are closed, and the hollow cathodes ff1
By applying discharge power adaptively between 41.43 and the anode 5, radicals are generated from the group of hollow cathodes 41 due to glow discharge decomposition of diborane gas, and radicals are generated from the group of hollow cathodes 43 due to glow discharge decomposition of silane gas. are blown out and mixed on the opposing substrate 2, depositing a p-type a-Si film on the substrate. At that time, diborane dedicated discharge power supply 6
By setting the '8B power for 1 and the silane-dedicated discharge power source 63 individually, the plasma conditions for both can be independently controlled, and the optimal PLI-5i
In addition to being able to form a film, a homogeneous film can be obtained on a substrate having a large surface area by arranging the hollow cathode group and the anode group in a dispersed manner as shown in FIG. Next, after forming the p-type a-5i film 32, the i-type a-Si film 33
In order to form a cathode, open the changeover switches 71 and 73, stop feeding the raw material gas, feed only the silane gas to the hollow cathode group 43 again, close the changeover switch 73, and set the discharge power of the discharge power source 63 to an appropriate level. By setting i-layer a -5tll! I can be formed with good quality and homogeneity. Furthermore, the n-layer a-Si film 33
In order to form a discharge voltage, phosphine gas and silane gas may be similarly introduced into each group of dedicated hollow cathodes 42.43, the selector switch 72.73 may be closed, and the power of each discharge power source 62.63 may be adjusted appropriately. . By configuring as described above, the uneven film quality of the a-Si film due to non-uniformity of the discharge power density within the surface of the discharge electrode and non-uniformity of the raw material gas flow, which has been a problem with the conventional method, can be avoided. can be significantly reduced. In addition, each hollow cathode uses only a single raw material gas, and the glow discharge plasma occurs inside the hollow cathode tube, and the electric field during discharge is generated only between the hollow cathode and the anode. As in the single-chamber reactor, the second layer a
-The first layer a- attached on the discharge electrode during the formation of the 5i film
Discharge residues from the formation of the 5i film are not sputtered and incorporated into the film, thereby preventing deterioration in film quality.In addition, each hollow cathode group and adjacent anode group are independently discharged. Since it is equipped with a power source, it is possible to control the discharge plasma by independently adjusting the discharge power and gas flow rate for each source gas.
-5i film can be formed over a large area. A plan view of the substrate surface of another embodiment of the present invention is shown in FIG.
When using a square substrate, hollow cathodes are arranged on lines parallel to the diagonal glands of the substrate, and 4 hollow cathodes dedicated to diborane are placed on each line.
1. Several sets of phosphine-dedicated hollow cathodes 42 and silane-dedicated hollow cathodes 43 are arranged. and,
An anode 5 is installed adjacent to each hollow cathode 41.42° 43, and by glow discharge decomposition of each raw material gas as described above, it is possible to form a uniform bilayer film on a large substrate. ing. Effects of the Invention According to the present invention, a plurality of hollow cathode groups and anodes adjacent to each group are provided for each raw material gas, and each hollow cathode group is provided with an independent power source for radiation. By configuring a plasma CVD apparatus that is connected via a switch, the decomposition of each raw material gas for film formation can be performed while preventing the incorporation of hl and electrolytic residues into the film during the decomposition of other raw material gases. High quality and uniform 11111
Since a film semiconductor can be produced and the discharge plasma generation conditions can be independently controlled for each raw material gas, a high-quality doped film can be formed.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention, (al is a side sectional view,
(b) is a plan view of the substrate surface, and Figure 2 is a conventional plasma CV
FIG. 3 is a cross-sectional view of a solar cell manufactured according to an embodiment of the present invention, and FIG. 4 is a plan view of a substrate surface of a different embodiment of the present invention. l: Reactor, 2: Substrate, 3: Substrate support, 41 hollow cathode exclusively for rainbow borane, 42: hollow cathode exclusively for phosphine,
43: Hollow cathode for use only, 5: Positive, 61, 62.
63: Dandendenkaki, 71.72.73 = Sui, Chi. ;ゝ、2. , -・ , 71 mouths 7Figure 1Figure 2Figure 3Figure 4

Claims (1)

[Claims] 1) In a method in which a voltage is applied between opposing electrodes arranged in a reactor to generate discharge plasma to decompose a source gas and form a thin film semiconductor on a substrate on a substrate support,
Consisting of multiple pairs of gas inlet tubes and opposing discharge electrodes for one raw material gas with a discharge electrode function in one reactor,
A plasma CVD apparatus comprising a plurality of groups connected to a power source via a switch, and gas introduction tubes of each group being uniformly distributed and opening toward a substrate support.