JPH0587130B2 - - Google Patents

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 epitaxy 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 (SiH ₄ ) 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 amounts of doping impurities using this method, you can use a single reaction chamber and switch the reaction gas for each layer, or connect multiple dedicated reaction chambers. A method is used in which films are formed using different reaction gases in each reaction chamber, and the substrates are sequentially transferred. This is because within a single reactant, the gas composition in the plasma atmosphere is substantially uniform spatially, and gas atmospheres with 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 becomes possible to form multiple layers with different compositions and doping amounts at once, which simplifies the manufacturing process and equipment.

Furthermore, in the roll-to-roll method, which is one of the methods for forming a thin film semiconductor layer on a substrate in a plasma atmosphere using CVD, it is possible to create a desired spatial distribution in the composition of the reactant gas within a single reaction chamber. As a result, the following drawbacks have existed in the past. 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 form multiple layers with different compositions and dopings in one run, it was necessary to have as many dedicated reaction chambers as there were.

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 in the reaction space.
As disclosed in Publication No. 34668, etc., a dedicated buffer chamber was provided between the reaction chambers, and gas was separated to the extent necessary by extraction or differential exhaust. 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. Controllability of the distribution profile, for example, whether to use a gently sloped junction,
The controllability was such that it was possible to create a sharp staircase joint.

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

<Structure> That is, 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 phase 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. By limiting the flow path of the reactive gas between each zone of the plasma atmosphere to the vicinity of the substrate surface,
It has been discovered that the gas composition distribution in the substrate transport direction can be controlled by the positions of the gas inlet and exhaust port in the substrate transport direction.

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 any material as long as it can block gas, and its material is not particularly limited.
Among these, materials without plasma damage are preferred, and stainless steel or the like is 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 is sufficient as long as 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 the 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 Guy diffusion is more completely prevented. However, if the gas flow path is limited due to the arrangement of members within 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 outlet is similarly selected through experiments depending on the profile in the thickness direction of the film to be formed. For example, when forming a two-layer film, the inlets for each reaction gas should be placed at both ends of the reaction chamber.
All you have to do is place the common exhaust ports in the middle,
If it is desired to change the composition within the film, the inlet for each reaction gas may be placed at both ends of the reaction chamber in the substrate transport direction, and a common exhaust port may be provided at one end. A gradient compositional distribution can be obtained.

The present invention described above is applicable 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-58-216475. 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. The effects are especially great, such as enabling a continuous film forming apparatus that can control the profile of one 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 configuration is the same as that disclosed in the aforementioned Japanese Patent Application Laid-Open No. 58-216475 and Japanese Patent Application Laid-Open No. 59-34668,
The reaction chambers 1, 2, 3 of the CVD plasma discharge forming p-type, i-type, and n-type amorphous silicon layers, the unwinding chamber 18, and the winding chamber 19 are provided with a buffer chamber 13 for gas isolation. The structure is such that the three layers p, i, and n are continuously formed while the substrate 17 is connected and transferred from the unwinding roll 20 to the winding roll 21 in a roll-to-roll manner. Note that 4 to 9 in the figure are discharge electrodes, and 10 in the figure is a high frequency power source that supplies high frequency power to each discharge electrode.

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 opposing discharge electrodes 6 and 7, excluding a necessary passage in the substrate transport direction, is installed perpendicular to the electrode surface and with a gap 14 as shown in FIG.
Five substrates were installed at predetermined intervals in the direction of transport of the substrate so as to block the entire cross section of the reaction chamber except for the substrate.
Therefore, the plasma space is divided into a plurality of regions 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 directed to the upstream end. In order to reach the exhaust port 16, the air always flows through the gap 14 set in the partition plate 11.

Note that, as described above, the partition plate 11 is installed at a certain distance from both of the opposing discharge electrodes so as to form the gap 14. This gap 14 is intended to serve as a passage for the reactant gas, for electrical insulation from the power electrode, and as a passage for the substrate 17 from the ground electrode, and is 3 mm in this embodiment. Although the object of the present invention can be achieved whether the material of the gas partition plate 11 is electrically conductive or nonconductive, it is necessary that impurities are not released into the plasma atmosphere. In this example, it was made of stainless steel and electrically grounded.

In this multiple reaction chamber type roll-to-roll type CVD plasma vapor phase growth apparatus, p-, i-, and n-type amorphous silicon films are formed on a thin strip-shaped long substrate made of SiH ₄ gas as a raw material. A solar cell was formed by sequentially stacking layers.

As the substrate 17, aluminum metal of 3000 Å and stainless steel alloy of 50 Å were laminated on a polyethylene terephthalate film with a thickness of 100 μm, and
Specifically, p-, i-, and n-type amorphous silicon layers were continuously formed in one run using the same method as in the above-mentioned Japanese Patent Laid-Open No. 59-34668. That is, the p-type and n-type amorphous silicon layers are each formed by doping SiH ₄ gas with diborane (B ₂ H ₆ ) or phosphine (PH ₃ ), and have a thickness of 200 to 300 Å. The i-type amorphous silicon layer had a thickness of about 5000 Å, and the reaction gas used was SiH ₄ gas not doped with any impurity gas.

By the way, in the roll-to-roll method of this example, normally, reaction chambers 1 and 3, which form adjacent p-type and n-type amorphous silicon, and reaction chamber 2, which forms the i-layer,
A trace amount of B ₂ H ₆ and PH ₃ gas is mixed in through the buffer chamber 13 .

By the way, since the reaction chamber 2 has the above-mentioned configuration, the reaction gas is introduced from the gas inlet 15 near the reaction chamber 3 for the n-layer into the reaction chamber 2 for forming i-type amorphous silicon, and the reaction gas is introduced into the reaction chamber for the p-layer. It flows in the direction of the exhaust port 16 closer to the first one. Regarding the p, i, n laminated type amorphous silicon film formed in this way,
The depth profile of boron (B) atoms was measured using secondary ion mass distribution method (SIMS).
It is shown by a solid line A in the figure. For comparison, the broken line B shows the analysis results of the same p, i, n laminated type amorphous silicon film formed using a conventional device without the partition plate 11 under the same other conditions. Ta.

In the case of the conventional device without the partition plate 11, the B ₂ H ₆ gas mixed in from the adjacent reaction chambers 1 and 3 is uniformly diffused throughout the reaction chamber 2 for the i-layer, and as a result, the B in the i-layer is
The concentration profile of atoms 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 the p layer and the i layer has a steep cut, and the profile in the i layer has a uniform gradient. It can be seen that it has a slope. 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 chamber, the plasma atmosphere can be maintained from the part near the reaction chamber 3 for the n-layer to the part near the reaction chamber 1 for the p-layer. It shows that the composition of the reactant gas in the sample has a certain spatial distribution. In other words, this means that the present invention can realize the necessary spatial distribution of the reaction gas in the reaction chamber, and shows that the present invention has an excellent effect of enabling film composition control, which was previously impossible. There is.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of an apparatus for manufacturing an amorphous silicon solar cell according to an example, FIG. 2 is a side sectional view taken along line A-A' in FIG. 1, and FIG. 3 is a graph showing the results of the implementation. . 1, 2, 3...Reaction chamber, 11...Partition plate, 13
...Buffer chamber, 14...Gap, 17...Substrate.

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 generated by chemical vapor decomposition between opposing discharge electrodes, a reactive gas By disposing partition plates perpendicular to the discharge electrode surface at predetermined intervals in the substrate transport direction, at least the plasma atmosphere can be divided into multiple spaces in the substrate transport direction without gas diffusion, except for limited gaps such as substrate passages. A plasma vapor phase epitaxy apparatus characterized in that it forms a thin film divided into 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 apparatus 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. . 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.