JPH0719912B2 - Thin film semiconductor manufacturing equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to the production of a thin film semiconductor in which a single layer or a plurality of thin film semiconductor layers are formed on a substrate transported in a plasma atmosphere by chemical vapor decomposition. The present invention relates to an apparatus, and particularly to an apparatus for manufacturing a thin film semiconductor suitable for manufacturing an amorphous silicon solar cell.

<Prior Art> A method of manufacturing a semiconductor device by forming a single-layer or multiple-layer thin-film semiconductor layers on a substrate in a plasma atmosphere by chemical vapor decomposition (hereinafter referred to as CVD) is described in, for example, silane (Si
This is a well-known technique that is widely practiced as a method for producing an amorphous silicon solar cell by discharge decomposition of H ₄ ) gas. In such a manufacturing method, as one of the manufacturing methods suitable for efficiently forming a thin film semiconductor layer, that is, suitable for mass production, there is known a method of passing a substrate through a CVD plasma discharge atmosphere while continuously transferring the substrate.

This method is roughly classified into the following two types. One is
A completely separate and independent single chamber for plasma discharge and a reaction chamber consisting of multiple chambers are installed between the substrate loading chamber and the substrate loading chamber, and a single substrate is placed on a moving carriage. It is a load-lock system in which film formation is performed while sequentially moving each chamber. The other one is that the substrate itself is formed into a long roll as in JP-A-58-216475 and JP-A-59-34668, and a substrate passage is provided between the unwinding chamber and the winding chamber. This is a roll-to-roll system in which a reaction chamber consisting of a single chamber and, if necessary, a plurality of chambers, which are communicated with each other, is installed, and a film is formed on a continuously conveyed thin film substrate.

In the case of performing high-speed film formation in order to further increase the production efficiency in such a manufacturing method, the conventional technique is to increase the discharge power while supplying sufficient raw material gas to increase the concentration of active species in the plasma atmosphere. Has been. However, in such a method, the kinetic energy of the charged particles in the plasma atmosphere increases as the discharge power increases, so that the film formation surface is damaged by the collision of the charged particles. However, there is a drawback that the characteristics of the semiconductor device are adversely affected. When a semiconductor layer is formed on a substrate and another type of semiconductor layer is further formed on the semiconductor layer, specifically, after forming a p layer or an n layer in the production of an amorphous silicon solar cell on the substrate. This effect was significant when the i layer was formed on top of it.

In order to manufacture a high performance thin film semiconductor layer, particularly an amorphous silicon solar cell, it is preferable to change the composition and the amount of doping impurities in the thickness direction of the deposited film. To change the composition and the amount of doping impurities in the film thickness direction to form a film, use a single reaction chamber to switch the reaction gas for each layer formation, or connect multiple dedicated reaction chambers. A method is used in which the reaction gas is changed for each reaction chamber to form a film and the substrates are sequentially transferred. This is because the gas composition in the plasma atmosphere is spatially substantially uniform in a single reaction chamber, and gas atmospheres having different compositions cannot be appropriately distributed in the reaction chamber.

However, if it is possible to give a desired spatial distribution to the gas composition in a single reaction chamber by some method, the substrate is transferred through a region of different gas composition in a plasma atmosphere that constantly discharges in the single reaction chamber. It is possible to form multiple layers with different compositions and doping amounts all at once,
A simplification of the manufacturing process and equipment is realized.

Also, 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 by CVD, it is possible to give a desired spatial distribution to the composition of the reaction gas in a single reaction chamber. Because of this, the following drawbacks existed in the past. That is, in the roll-to-roll system, it is necessary to continuously supply the reaction gas having the same composition to each reaction chamber in order to continuously convey the flexible strip-shaped substrate in the steady discharge plasma to form a film. In order to form multiple layers with different compositions and dopings in a single run, the number of dedicated reaction chambers was indispensable.

Furthermore, in the roll-to-roll system having a plurality of reaction chambers, the reaction chambers are not completely separated and independent, but are connected by the passage of the substrate. For this reason, it is not possible to avoid mutual mixing of the reaction gases in the reaction chambers between the adjacent reaction chambers via the substrate passage. If this mutual mixing deteriorates the characteristics of the thin film semiconductor device to be produced, a unidirectional gas flow may be formed in the substrate passage between the reaction chambers, or JP-A-58-216475 and JP-A-58-216475. As disclosed in Japanese Patent Laid-Open No. 59-34668, a dedicated buffer chamber is provided between the reaction chambers to bleed or differentially exhaust gas to perform gas separation to the required extent. However, in such a conventional method, once the reaction gas in the adjacent reaction chamber that has penetrated beyond the gas separation mechanism diffuses throughout the reaction chamber and becomes uniform in the reaction chamber, the composition distribution in the thickness direction at the interface with the adjacent layer and impurities The controllability of the profile of the distribution, for example, the controllability such as a gentle graded junction or a sharp stepwise junction, was poor.

<Purpose> The present invention has been made to solve the above-mentioned drawbacks of the prior art and to form a high-quality thin film semiconductor device at high speed. Means for forming a favorable interface by reducing plasma impact in one reaction chamber Another object of the present invention is to provide a thin-film semiconductor manufacturing apparatus having means for controlling the air distribution of the reaction gas in the reaction chamber and controlling the composition and impurity distribution in the thickness direction of the deposited film.

<Structure of Invention> The above-mentioned object is achieved by the present invention described below. That is, the present invention is a thin-film semiconductor manufacturing apparatus for forming a predetermined semiconductor layer on a substrate in a plasma atmosphere by chemical vapor decomposition while transferring the substrate, in a predetermined range on the substrate entry side of opposed discharge electrodes. A grid electrode consisting of a perforated plate that reduces the plasma impact is provided in the middle in parallel with the discharge electrode over at least the entire width of the substrate, and partition plates that block the reaction gas are perpendicular to the discharge electrode surface at predetermined intervals in the substrate transfer direction. Direction, and at least the plasma atmosphere is divided into a plurality of areas with no gas diffusion in the substrate transport direction except for a limited gap such as a substrate passage to form a thin film having a predetermined composition distribution in the film thickness direction. The thin film semiconductor manufacturing apparatus is characterized by having a reaction chamber configured as described above.

The present invention described above is made as follows.
That is, the present inventors have succeeded in continuous mass production of amorphous silicon solar cells of high quality, that is, high conversion efficiency of solar energy, in a continuous plasma CVD apparatus similar to that disclosed in JP-A-59-34668. As a result of studying, it was observed that when the discharge power was increased to increase the deposition rate in order to improve productivity, the conversion efficiency was lowered. It has been found that one of the causes is that impurities are mixed from the lower layer in the initial stage of forming the i layer, and the plasma impact of the lower layer in the early stage of film formation is caused. Then, as a result of various investigations on this countermeasure, by providing the lattice electrode only on the substrate entrance side between the discharge electrodes, the plasma energy can be effectively reduced only in the lattice electrode existing portion and its vicinity, and the plasma damage can be prevented, and It was found that high-speed film formation can be performed without being affected by the lattice electrode except for the lattice electrode portion.

In order to form a high-quality i-layer, the impurity concentration in the i-layer film, especially the thickness in the i-layer film having a very small amount of B atom concentration mixed in from the reaction chamber where the adjacent p-layer is deposited. We have found that the directional distribution is important. As a result of various investigations on the control means, it was found that even if a partition plate that vertically shields gas between discharge electrodes is provided to partition the plasma atmosphere, plasma discharge is not affected and stable film formation can be performed. The gas composition distribution in the substrate transfer direction depends on the position of the gas inlet and exhaust ports in the substrate transfer direction by limiting the flow path of the reaction gas between each area of the plasma atmosphere partitioned by the partition plate Found that you can control. The present invention has been made based on these findings.

The details of the present invention will be described below.

The grid electrode of the present invention is provided only on the substrate entry side of the discharge electrode.
The region to be provided is related to the semiconductor to be formed and the bias voltage applied to the lattice electrode, and it is necessary to experimentally determine it. However, considering the film formation rate, it is appropriately selected between the substrate entrance and half the discharge electrode. Is practical. A perforated plate having a large number of holes such as a mesh body and a comb shape is used as the shape of the grid electrode. The size of the hole is selected within the range where plasma can be confined within the range where the passage of active species is not blocked as much as possible. Actually, it is experimentally determined. Is practical.

Further, the partition plate of the present invention is not particularly limited as long as it can block gas and the material thereof is not particularly limited, and one which does not have plasma damage is preferable, and stainless steel or the like is used.
The partition plate is generally grounded together with the reaction chamber, but it may be floated or an appropriate bias voltage may be applied. The shape may be any as long as gas diffusion in the substrate transport direction can be ignored. Normally, a shape is selected in which only a minute gap is provided between the substrate transport path and the discharge electrode surface, and the other portions are completely cut off, and gas movement does not occur outside the gap. This is preferable in that the gas flow velocity in the gap becomes large and the prevention of gas diffusion becomes more complete. However, it goes without saying that when the gas flow path is limited by the arrangement of the members in the reaction chamber, the partition plate may be installed so as to block the gas flow path. The partition plate needs to have a slit serving as a gas flow path at least between the partition plate and the front surface of the substrate.

Further, the number of partition plates and their gaps are selected according to the profile of the film to be formed in the film thickness direction. This selection depends on the experiment.

On the other hand, the disposition of the reaction gas inlet and exhaust port is also selected by experiment according to the profile in the film thickness direction to be similarly formed. For example, in the case of forming a two-layer film, the reaction gas inlets may be sequentially arranged at both ends of the reaction chamber, and the common exhaust ports may be sequentially arranged in the middle thereof. In addition, a single-layer film may change the composition in the film. If desired, the respective reaction gas inlets may be arranged at both ends of the reaction chamber in the substrate transport direction, and a common exhaust port may be provided at one end thereof to obtain an appropriate gradient composition distribution.

The present invention can be advantageously applied to the case where required semiconductor layers are continuously and sequentially formed on a long substrate. Above all, it is effective when a semiconductor layer is already formed on the substrate and a semiconductor layer of a different type from this is formed on the semiconductor layer. Furthermore, JP-A-58-
In the case where a plurality of reaction chambers are connected as in Japanese Patent No. 216475, it can be applied to control the profile of one layer. In particular, the present invention exerts a great effect in forming an amorphous silicon semiconductor layer, particularly in forming an i layer in continuous production of an amorphous silicon solar cell having a large problem as described above.

Hereinafter, the details of the present invention will be described by taking continuous production of amorphous silicon solar cells as an example.

<Embodiment> FIG. 1 is a configuration diagram of a continuous production apparatus for an amorphous silicon solar cell of the above embodiment, and FIG. 2 is a sectional view of a reaction chamber 2 thereof.

The basic structure is as described in the above-mentioned JP-A-58-216475,
No. 59-34668, which is the same as that disclosed in Japanese Patent Laid-Open No. 59-34668.
The reaction chambers 1, 2, 3 of the CVD plasma discharge forming the respective amorphous silicon layers of the mold and the unwinding chamber 18 and the winding chamber 19 are connected by the buffer chamber 13 for gas isolation, and the unwinding roll 20 The substrate 17 is transferred from the take-up roll 21 to the take-up roll 21 by a roll-to-roll method, and three layers of p, i, and n are continuously formed. In addition, 4-9 of a figure are discharge electrodes, 10 of a figure is a high frequency power supply which supplies high frequency electric power to each discharge electrode.

With such a reaction chamber separation type roll-to-roll type CVD plasma discharge device, a well-known predetermined raw material gas such as SiH ₄ gas is supplied to each reaction chamber 1, 2, 3 and rolled up on a long substrate. A p-type, i-type, and n-type amorphous silicon film were sequentially stacked to form a solar cell. In this example, as described above, in the reaction chamber 2 in which the i-type amorphous silicon layer that affects the characteristics of the solar cell is formed, the grid electrode 22 is installed between the opposing discharge electrodes 6 and 7. The grid electrode 22 is provided along the traveling direction of the flexible long substrate 17 so as to cover the first half 1/3 of the discharge electrodes 6 and 7. A predetermined bias potential is applied to the grid electrode 22 from a power source (not shown). The material of the grid electrode 22 is a metal mesh of stainless alloy, the roughness of the mesh is fine enough to confine the plasma, and coarse enough not to block the passage of active species, in this example a mesh of 20 mesh did. The grid electrode 22 is installed 25 mm away from the substrate 17 (distance between discharge electrodes is 50 mm), and is biased by a power source capable of setting a DC voltage to an appropriate value between +200 and -200V.

A partition plate 11 for partitioning a plasma atmosphere in the middle of the discharge electrodes 6 and 7 facing each other except a passage required in the substrate transport direction is perpendicular to the electrode surface and the entire cross section of the reaction chamber is formed except for a gap 14 as shown in FIG. Four pieces were installed at predetermined intervals in the substrate transfer direction so as to be cut off. Therefore, the partition plate 11 divides the plasma space into a plurality of areas within the electrode surface, 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 at its upstream end. In order to reach the port 16, it always flows through the gap 14 set by the partition plate 11.

As described above, the partition plate 11 is installed so as to form the gap 14 and is apart from the opposing discharge powers by a slight distance. This gap 14 is intended as a passage for the reaction gas, an electrical insulation for the power electrode, and a passage for the substrate 17 for the ground electrode.
In this embodiment, it is 3 mm. Although the material of the gas partition plate 11 is either electrically conductive or non-conductive, the object of the present invention is achieved, but it is necessary that impurities are not emitted into the plasma atmosphere. In this example, it was made of a stainless alloy and electrically grounded to earth.

In this example, as the substrate 17, 3000 Å of aluminum metal and 50 on the film on the polyethylene terephthalate with a thickness of 100 μm are used.
Å Stainless steel alloys are sequentially laminated and used, and
A p, i, n type amorphous silicon layer was continuously formed in one run in the same manner as in Japanese Patent Publication No. 34668. The p-type and n-type amorphous silicon films have a thickness of 200 to 300Å, and the i-type amorphous silicon layer has a thickness of 5000.
The discharge power, the substrate transfer speed, and the reaction gas pressure were controlled to be about Å.

By the way, in the roll-to-roll system of this example, normally,
The B ₂ H ₆ and PH ₃ gases are transferred from the adjacent reaction chambers 1 and 3 for forming p- and n-type amorphous silicon to the reaction chamber 2 for forming the i-layer.
A small amount is mixed in via.

By the way, since the reaction chamber 2 has the above-described structure, the reaction gas 2 in the reaction chamber 2 for forming i-type amorphous silicon is n
The gas is introduced from the gas introduction port 15 near the reaction chamber 3 for layers and flows toward the exhaust port 16 near the reaction chamber 1 for p layers, and diffusion of the above mixture is controlled as described later.

FIG. 3 shows the solar cell characteristics when a negative bias potential (−20 V) is applied to the grid electrode 22 and the high frequency power applied to the discharge electrodes 6 and 7 is changed to form the i-type amorphous silicon layer. The relationship between (conversion efficiency) and discharge power is shown by the solid line A. As a matter of course, the increase of the discharge power increases the deposition rate as shown in FIG. 3 at the same time, which corresponds to the high speed film formation. In the manufacturing method according to the present invention, as shown by the solid line A'in FIG. 3, the characteristics of the solar cell are hardly deteriorated even when the discharge power is increased.

On the other hand, regarding the characteristics of the solar cell formed in the same manner as the above apparatus except for the grid electrode 22, the characteristics of the solar cell deteriorated as the discharge power increased, as shown by the broken line B'in FIG.

Furthermore, the characteristics of the solar cell formed in exactly the same manner as the above-mentioned device except for the partition plate 11 with the grid electrode 22 installed are as shown by the chain line C'in FIG. The solar cell characteristics were lower than the solid line A'provided with the partition plate 11 in the region. As described above, the characteristics of the solar cell produced according to the present invention are improved, and the effectiveness of the present invention was confirmed.

On the other hand, the depth profile of the boron (B) atom in the p, i, n stacked type amorphous silicon film formed in this example was measured by the secondary ion mass spectrometry (SiMS) to obtain the fourth result.
The solid line A is shown in the figure. For comparison, other conditions are the same,
The analysis result of the same p, i, n laminated type amorphous silicon film formed by the conventional device without the partition plate 11 is shown by a broken line B.
Is shown in FIG.

In the case of the conventional device without the partition plate 11, the adjacent reaction chambers 1, 3
As a result, the B ₂ H ₆ gas mixed in from the inside uniformly diffuses throughout the reaction chamber 2 for the i-layer, so that 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 the p layer and the i layer is sharply cut, and
It can be seen that the profile in the i-layer has a constant slope. This result shows that by partitioning the plasma space of the i reaction chamber 2 by the partition plate 11, even in the same reaction chamber, from the portion closer to the reaction chamber 3 for the n layer to the portion closer to the reaction chamber 1 for the p layer. It is shown that the composition of the reaction gas in the plasma atmosphere has a constant spatial distribution.

[Brief description of drawings]

FIG. 1 is an explanatory view of the structure of an apparatus for manufacturing an amorphous silicon solar cell according to an embodiment, FIG. 2 is a sectional view of a partition plate 11 of a reaction chamber 2 shown in FIG. 1, and FIG. FIG. 4 is a graph showing characteristics of the solar cell, and FIG. 4 is a graph showing B atom distribution in the i layer in the example. 1,2,3: Reaction chamber, 11: Partition plate 13: Buffer chamber, 14: Gap 17: Substrate, 22: Lattice electrode

Claims (3)

[Claims] 1. In a thin-film semiconductor manufacturing apparatus for forming a predetermined semiconductor layer on a substrate in a plasma atmosphere by chemical vapor decomposition while transferring the substrate, a predetermined range on the substrate entry side of discharge electrodes facing each other. A grid electrode made of a perforated plate that reduces the plasma impact is provided in the middle of at least the entire width of the substrate in parallel with the discharge electrode, and partition plates for blocking reaction gas are provided on the discharge electrode surface at predetermined intervals in the substrate transport direction. A thin film having a predetermined composition distribution in the film thickness direction is formed by arranging in a vertical direction and partitioning at least the plasma atmosphere into a plurality of areas where there is no gas diffusion in the substrate transport direction except for a limited gap such as a substrate passage. An apparatus for producing a thin film semiconductor, which has a reaction chamber adapted to be formed. 2. The thin-film semiconductor manufacturing apparatus according to claim 1, wherein the partition plate is provided so as to block the entire cross section of the reaction chamber except the gap. 3. The thin-film semiconductor manufacturing apparatus according to claim 1, wherein the substrate is a flexible long substrate and is transported by a roll-to-roll method.