JPS63244731A - Plasma vapor growth device - Google Patents

Abstract

PURPOSE:To make it possible to let a composition and an impurity distribution have the desired depth profile in the single layer formed in the same reaction chamber by a method wherein the partition plates, with which reaction gas will be shut off, are arranged in the substrate conveying direction vertical to the surface of discharge electrodes leaving the prescribed intervals, plasmic atmosphere space is divided at least into a plurality of sections having no gas diffusion in the direction where the substrate is conveyed excluding the limited gap of a substrate passage and the like, and the thin film having the prescribed compositional distribution in the direction of film thickness is formed. CONSTITUTION:In the reaction chamber 2 where i-type amorphous silicon is formed, five partition plates 11, which partition the plasmic atmosphere space between the opposing discharge electrodes 6 and 7, are provided vertical to the surface of the electrodes in the direction where substrate are conveyed leaving the prescribed intervals and excluding the necessary passage and a gap 14 in such a manner that the whole cross section of the reaction chamber is shut off. Accordingly, the plasma space is divided into a plurality of sections within the surface of the electrodes, and in order to have the reaction gas fed from the gas introducing hole 15, provided at the downstream end in the substrate conveying direction of the reaction chamber, to reach the exhaust port 16 at the end of the upstream, it is necessary that the gas is made to flow passing through the gap 14 provided by the partition plates 11 without fail.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a plasma vapor phase growth apparatus for forming a thin film in a plasma atmosphere by chemical vapor phase decomposition (CVD), and is particularly suitable for manufacturing amorphous silicon solar cells. The present invention relates to a plasma vapor phase growth apparatus.

<Prior art> Plasma vapor phase growth equipment, which manufactures semiconductor devices by forming thin film semiconductor layers on substrates in a plasma atmosphere using chemical vapor phase decomposition, uses, for example, discharge decomposition of silane (SiH4) gas. This is a well-known technique that has been widely put into practical use as a method for manufacturing amorphous silicon solar cells. When forming multiple layers with different compositions and doping impurity bases using this method, you can use a single reaction chamber and switch the reaction gas for each layer, or connect multiple dedicated reaction chambers for the reaction. A method is used in which films are formed using different reaction gases in each chamber, and the substrates are sequentially transferred. This is because the gas composition in the plasma atmosphere is spatially almost uniform within a single reaction chamber, and gas atmospheres having different compositions cannot be appropriately distributed within the reaction chamber.

However, if it is possible to somehow create a desired spatial distribution of the gas composition within a single reaction chamber, then the substrate can be transferred through regions with different gas compositions in a plasma atmosphere that is constantly discharged within a single reaction chamber. By simply doing this, it is possible to form multiple layers with different compositions and doping amounts all at once.
Simplification of the manufacturing process and equipment is realized.

In addition, 1il was deposited on the substrate in a plasma atmosphere by CVD.
Even in the roll-to-roll method, which is one of the methods for forming a semiconductor layer, it is not possible to give the desired spatial distribution to the composition of the reaction gas in a single reaction chamber.
Conventionally, there have been the following drawbacks. In other words, in the roll-to-roll method, a flexible strip substrate is continuously conveyed in a steady discharge plasma to form a film, so it is necessary to continuously supply a reaction gas of the same composition to each reaction chamber. In order to consistently form multiple layers with different compositions and dopings, it was necessary to have as many dedicated reaction chambers as possible.

Furthermore, in a roll-to-roll system having a plurality of reaction chambers, the reaction chambers are not completely separated and independent, but are connected by passages in the substrate. Therefore, it is impossible to avoid mutual mixing of the reaction gases in the reaction chambers between adjacent reaction chambers via the substrate passage. If this mutual mixing deteriorates the characteristics of the thin film semiconductor device to be fabricated, a unidirectional gas flow may be formed in the substrate passage between the reaction chambers, or 59
As disclosed in Japanese Patent No. 34668, etc., a dedicated buffer chamber was provided between the reaction chambers, and oil or gas was differentially pumped out to perform gas separation to the extent necessary. However, in such conventional methods, once the reaction gas from the adjacent reaction chamber enters beyond these gas separation mechanisms, it diffuses throughout the reaction chamber and becomes uniform within the reaction chamber, resulting in the composition distribution in the film thickness direction at the interface with the adjacent layer and impurities. The controllability of the distribution profile, such as whether to make a gentle sloped joint or a sharp step joint, was poor.

<Purpose> The present invention has been made in view of the current situation, and is
By controlling the spatial distribution of the reactant gas within a single reaction chamber with respect to the plasma vapor phase growth apparatus of D, the drawbacks of the above-mentioned conventional techniques can be overcome and the composition and impurity distribution can be controlled even within a single layer formed within the same reaction chamber. Plasma vapor phase epitaxy equipment that makes it possible to provide the desired depth profile, especially roll and
In the two-roll method, the object is to provide a plasma vapor phase growth apparatus that can control the steepness of the interface with an adjacent semiconductor layer.

In other words, the present invention provides a plasma vapor deposition apparatus that forms a thin film on a substrate while transporting the substrate through a plasma atmosphere caused by chemical vapor decomposition between opposing discharge electrodes. , partition plates for blocking reaction gas are arranged perpendicularly to the discharge electrode surface at predetermined intervals in the substrate transport direction, and at least the plasma atmosphere is prevented from gas diffusion in the substrate transport direction except for limited gaps such as substrate passages. This plasma vapor phase epitaxy apparatus is characterized in that it forms a thin film having a predetermined composition distribution in the film thickness direction.

The present invention has found that even if the plasma atmosphere is partitioned by providing a partition plate that blocks gas vertically between the discharge electrodes, plasma discharge is not affected and stable film formation can be performed. We discovered that by restricting the flow path of the reactive gas between each area of the plasma atmosphere to the vicinity of the substrate surface, it is possible to control the gas composition distribution in the substrate transport direction by controlling the positions of the gas inlet and exhaust port in the substrate transport direction. It has been done.

The reason for this is believed to be that mutual diffusion of gas in the substrate transport direction between the zones of the plasma atmosphere divided by the partition plates is limited, and the gas compositions of each zone become substantially independent.

Therefore, the partition plate of the present invention may be made of any material as long as it can block gas, and its material is not particularly limited, but it is preferably one that is free from plasma damage, and stainless steel or the like is preferably used. Although the partition plate is generally grounded together with the reaction chamber, it may be floating or a suitable bias voltage may be applied thereto. The shape may be such that the diffusion of gas in the substrate transport direction can be ignored, and usually there is only a small gap between the substrate transport path and the discharge electrode surface, and other parts are completely blocked. , a shape is selected that does not allow gas movement outside the gap. This is preferable because the gas flow rate increases in the gap and gas diffusion is more completely prevented. However, if the gas flow path is limited due to the arrangement of members in the reaction chamber, it goes without saying that a partition plate may be installed to block the gas flow path. Note that the partition plate needs to have at least a slit between it and the front surface of the substrate to serve as a gas flow path.

Further, the number of partition plates and the gap between them are selected depending on the profile of the film to be formed in the film thickness direction. This selection is based on experimentation.

On the other hand, the arrangement of the reactant gas inlet and exhaust port is similarly selected through experiments according to the profile in the thickness direction of the film to be formed. For example, when forming a two-layer film, it is sufficient to sequentially arrange the inlets for each reaction gas at both ends of the reaction chamber and a common exhaust port in the middle, or to change the composition within the film with a single-layer film. If desired, a composition distribution with an appropriate gradient can be obtained by arranging the inlets for each reaction gas at both ends of the reaction chamber in the substrate transport direction and providing a common exhaust port at one end.

The present invention described above can be applied not only to forming a multilayer film in a single reaction chamber, but also to controlling the profile of a single layer in a structure in which a plurality of reaction chambers are connected, such as in JP-A-58-218475. It can also be applied to

In addition, the present invention is for forming a film while continuously conveying a flexible long substrate in a roll-to-roll manner, and it is possible to greatly simplify the equipment used to form a multilayer film in a single reaction chamber. It is especially effective because it features a continuous film forming apparatus that can control the profile of a single layer in a multilayer film, which was previously impossible.

Hereinafter, the details of the present invention will be explained using an example of a continuous manufacturing apparatus for amorphous silicon solar cells.

<Example> FIG. 1 is a block diagram of a continuous manufacturing apparatus for amorphous silicon solar cells according to the above example.

Its basic structure is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 58-216475.

Same as that disclosed in Japanese Patent Application Laid-open No. 59-34668, p.
Type.

II! for gas isolation of each reaction chamber 1.2.3 of the CVD plasma discharge forming the i-type and n-type amorphous silicon layers, the unwinding chamber 18, and the winding chamber 19! The configuration is such that three WIs, p, i, and n, are continuously formed while being connected in an i-chamber 13 and transferring the substrate 17 from an unwinding roll 20 to a winding roll 21 in a roll-to-roll manner. In addition, 4 in the figure
~9 is the discharge electrode, and 10 in the figure is each discharge electrode. ! This is a high-frequency power source that supplies high-frequency power to the electrodes.

Incidentally, the reaction chamber 2 for forming i-type amorphous silicon has the following configuration according to the present invention. A partition plate 11 that partitions the plasma atmosphere between the facing discharge electrodes 6 and 7 except for a passage necessary in the substrate transport direction is installed perpendicular to the electrode surface and covers the entire cross section of the reaction chamber excluding the gap 14 as shown in FIG. Five boards were installed at predetermined intervals in the transport direction of the board so as to block the board. Therefore, the plasma space is divided into a plurality of areas within the electrode plane by the partition plate 11, and the reaction gas supplied from the gas inlet 15 provided at the downstream end of the reaction chamber 2 in the substrate transport direction is exhausted from the upstream end. In order to reach the boat 16, the water always flows through the gap 14 set by the partition plate 11.

Note that, as described above, the partition plate 11 is spaced a certain distance apart from both of the opposing discharge electrodes so as to form a gap 14. This gap 14 is used as a passage for reactant gas, for electrical insulation from the power electrode, and as a passage for the substrate 17 from the ground electrode, and is 3 m in this embodiment. did. Gas partition plate 11
The material is an electrical conductor.

Although any nonconductor can achieve the purpose of the present invention, it is necessary that no impurities be released into the plasma atmosphere. In this example, it was made of stainless steel and electrically grounded.

Such multiple reaction chamber roll-to-roll CVD
A solar cell was formed by sequentially stacking p-, i-, and n-type amorphous silicon films on a thin strip-like long substrate made of 5iHa gas rolled up into a roll using a plasma vapor deposition apparatus.

As the substrate 17, 3,000 aluminum metals and 50 stainless steel alloys were laminated on a polyethylene terephthalate film with a thickness of 100 μm. ,
I and N type amorphous silicon layers were continuously formed in one run.

That is, the p- and n-type amorphous silicon layers are each S
! It is formed by doping H4 gas with diborane <82 H6 or phosphine (PH3), and its thickness is 200 ~
There are 300 people.

The i-type amorphous silicon layer had a thickness of about 5000 nm, and the reaction gas used was SiH4 gas not doped with any impurity gas.

By the way, in the roll-to-roll method of this example, normally,
a reaction chamber 1 forming adjacent p-type and n-type amorphous silicon;
A small amount of 828e and PH3 gas are mixed into the reaction chamber 2 forming one layer from the buffer chamber 13 through the buffer chamber 13.

By the way, since the reaction chamber 2 has the above-mentioned configuration, the reaction gas in the reaction chamber 2 for forming i-type amorphous silicon is n
The gas is introduced from the gas inlet 15 near the reaction chamber 3 for the layer and flows toward the exhaust port 16 near the reaction chamber 1 for the p layer. p, which was formed in this way:

The depth profile of boron (B) atoms was measured using secondary ion mass spectrometry (Si
The results measured by MS) are shown in Figure 3 at 1 mA. For comparison, the analysis results of the same p-, i-, and n-layered amorphous silicon film formed using a conventional apparatus without the partition plate 11 under the same conditions are shown in the figure by a broken line B. Ta.

In the case of a conventional device that does not have a partition plate 11, the adjacent reaction chamber 1
．． B2 Ha gas mixed in from 3 is in reaction chamber 2 for ill.
As a result of uniform diffusion throughout, the concentration profile of B atoms in the i-layer in the film thickness direction is flat. On the other hand, in the case of the embodiment in which the partition plate 11 is installed, the composition profile of B atoms at the interface between pm and the first layer has a steep cut, and the profile in the ill has a constant slope. I understand. This result is the partition plate 1
By dividing the plasma space of the i-reaction chamber 2 by 1, even within the same reaction area, the plasma atmosphere extends from the part near the reaction chamber 3 for the n-layer to the part near the reaction chamber 1 for the p-layer. shows that the composition of the reactant gas has a constant spatial distribution. This means that the present invention can realize the necessary spatial distribution of the reaction gas in the reaction chamber.
This shows that the present invention has an excellent effect of enabling film composition control, which was previously impossible.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of an apparatus for manufacturing an amorphous silicon solar cell according to an example, and FIG. 2 is a side sectional view taken along line A-A' in FIG. 1.
FIG. 3 is a graph showing the implementation results. 1.2.3: Reaction chamber 11: Partition plate 13: Buffer chamber
14: Gap 17: Board No. 31 long side 1.5 5 yen 2 (tom)

Claims (1)

[Scope of Claims] 1. In a plasma vapor deposition apparatus that forms a thin film on a substrate while transporting the substrate through a plasma atmosphere caused by chemical vapor decomposition between opposing discharge electrodes, Gas-blocking partition plates are arranged perpendicularly to the discharge electrode surface at predetermined intervals in the substrate transport direction, so that at least the plasma atmosphere can be divided into multiple spaces without gas diffusion in the substrate transport direction, except for limited gaps such as substrate passages. 1. A plasma vapor phase epitaxy apparatus characterized in that a thin film is formed by dividing the region into two regions and having a predetermined composition distribution in the film thickness direction. 2. The plasma vapor phase growth apparatus according to claim 1, wherein the partition plate is provided to block the entire cross section of the reaction chamber except for the gap. 3. The plasma vapor deposition according to claim 1 or 2, wherein a reaction gas exhaust port is provided at one end of the reaction chamber in the substrate transport direction, and a reaction gas inlet port is provided at the other end. Device. 4. The plasma vapor deposition apparatus according to any one of claims 1 to 3, wherein the substrate is a flexible elongated substrate and is transported by a roll-to-roll method. 5. The plasma vapor phase epitaxy apparatus according to any one of claims 1 to 4, wherein the thin film to be formed is an amorphous silicon thin film.