JPH0227775A - Manufacture of solar cell - Google Patents

Abstract

PURPOSE:To form a uniform film without distribution of the thickness of a film by so providing an electric field regulating member as to concentrate an electric field at the center of the opening of a mask mounted between an electrode and a substrate, and making the electric field distribution of the opening of the mask uniform. CONSTITUTION:An i-type layer reaction chamber 2 in which partition plates 11 for shutting OFF reaction gas are disposed vertically at a predetermined interval on the face of a discharge electrode 9 in a substrate conveying direction to be divided into a plurality of zones containing no gas diffusion in the substrate conveying direction except a limited gap of a substrate passage in a plasma atmosphere and an i-type amorphous semiconductor layer is formed, and a fine crystallizing reaction chamber 3 in which a mask 30 is disposed between a substrate 17 and discharging electrodes, and a fine crystalline amorphous semiconductor layer provided with an electric field regulating member 32 for regulating the electric field distribution of the opening is formed in the opening are provided. Thus, the gas composition distribution in the substrate conveying direction is controlled by the position of the substrate conveying direction of a gas inlet 15 and a discharge port 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention involves transporting a substrate through a plasma atmosphere of a predetermined number of reaction chambers in which an amorphous semiconductor layer is formed by chemical vapor phase decomposition; The present invention relates to a solar cell manufacturing apparatus that sequentially forms amorphous semiconductor layers of a predetermined conductivity type to form a photovoltaic layer having a predetermined structure such as 010.

<Prior art> A plasma vapor deposition apparatus for manufacturing semiconductor devices by forming a thin film semiconductor layer on a substrate in a plasma atmosphere using chemical vapor decomposition (CVD) uses, for example, silane (SiH4).
) This is a well-known technique that has been widely put into practical use as a method for manufacturing amorphous silicon solar cells by discharging gas.

In such a manufacturing method, a method for efficiently forming an amorphous silicon thin film semiconductor layer is disclosed in Japanese Patent Application Laid-Open No. 58-2164.
It has been known from Japanese Patent No. 75, Special Publication No. 59-34668, etc. that amorphous silicon III can be continuously formed on a substrate transported by a roll-to-roll method using a known plasma CVO device. It is being

When creating an amorphous silicon solar cell using this method, multiple dedicated reaction chambers are required to form at least p, i, and n amorphous silicon or microcrystalline amorphous silicon in independent reaction chambers. A method is used in which the reaction chambers are connected to form a film using a different reaction gas in each reaction chamber, and the substrates are sequentially transferred.

This is because the gas composition in the plasma atmosphere is spatially substantially uniform within a single reaction chamber, and gas atmospheres having different compositions cannot be appropriately distributed within the reaction chamber.

By the way, in the roll-to-roll method in which flexible substrates of approximately C length are continuously conveyed between a plurality of reaction chambers, each reaction chamber is not completely separated and independent; connected. 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 amorphous silicon solar cell to be produced, a unidirectional gas flow may be formed in the substrate passage between the reaction chambers, or Japanese Patent Publication No. 5934
As disclosed in Japanese Patent No. 668, etc., a dedicated mm 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 has penetrated beyond these gas separation mechanisms, it is diffused throughout the reaction chamber and becomes uniform within the reaction chamber. The controllability of the composition distribution and impurity distribution profile in the film thickness direction at the interface with the film, such as whether to form a gentle sloped junction or a sharp stepped junction, was poor.

Furthermore, in improving the characteristics of amorphous silicon solar cells,
At least the sunlight incident IP layer or 0 layer is 100A
After IFi, the extremely thin microcrystalline silicon layer is uniformly f[
It has become known that it is necessary to

By the way, when depositing these microcrystalline silicon films by the roll-to-roll method described above, the +1#! In order to adjust the film quality and II thickness, a mask is generally provided.
The plasma 7m reaching the substrate surface is adjusted by its opening width to control the deposited film quality and II thickness. A mask is also used to form a predetermined pattern.

However, when a microcrystalline amorphous silicon film was formed using a plasma CVD apparatus in which a mask was installed between the substrate and the discharge electrode, microcrystalization occurred in the areas near the opening edges of the mask. However, the conductivity gradually decreased as it approached the center, and it was confirmed that the film remained amorphous and no microcrystallization occurred.

That is, it has been found that, due to mask installation, the quality of the film obtained changes significantly at the center of the mask opening, specifically, at the center of the substrate, and at the edges of the mask opening, that is, at both ends of the substrate.

As described above, in order to efficiently produce a high-performance amorphous silicon solar cell using the roll-to-roll method, the above-mentioned problems must be solved.

<Objective of the Invention> The present invention was made in view of the current situation, and it is an object of the present invention to control the steepness of the interface with an adjacent semiconductor layer in the formation of one layer, and to provide a desired depth profile in composition and impurity distribution even within n layers. It is an object of the present invention to provide a solar cell manufacturing apparatus suitable for industrial use, which enables uniform film formation without distribution of film quality and thickness in the formation of a microcrystalline semiconductor layer.

<Structure of the invention> The above objects are achieved by the invention as follows.

That is, the present invention comprises a predetermined number of reaction chambers for forming a predetermined amorphous semiconductor film by chemical vapor phase decomposition, which are connected so that the substrate can be transported between the discharge electrodes, In a solar cell manufacturing apparatus, the photovoltaic layer is transported through each reaction chamber to form a photovoltaic layer having at least one microcrystallized amorphous semiconductor layer and an i-type amorphous semiconductor layer on the substrate. , partition plates for blocking reaction gas are arranged perpendicularly to the discharge electrode surface at predetermined intervals in the substrate transport direction,
an i-layer reaction chamber in which the i-type amorphous semiconductor layer is formed, and an i-layer reaction chamber in which the plasma atmosphere is divided into a plurality of zones in which gas is not diffused in the substrate transport direction except for limited gaps such as substrate passages; a microcrystallization reaction chamber for forming the microcrystallized amorphous semiconductor layer, in which a mask is disposed between the N pole and an electric field adjustment member is provided in the opening for adjusting the electric field distribution in the opening; This is a solar cell manufacturing apparatus characterized by comprising:

In the above-described present invention, the substrate is a long flexible strip substrate such as a synthetic resin film, an unwinding chamber and a winding chamber are connected before and after the connected reaction chamber, and the substrate is rolled. - With the configuration in which each amorphous semiconductor thin film is formed on a substrate while being transported by rolls, a solar cell manufacturing apparatus with high productivity particularly suitable for mass production can be obtained.

The present invention will be explained in detail below.

First, the i-layer reaction chamber of the present invention will be explained.

The configuration of the i-layer reaction chamber was obtained as follows.

In other words, we found that even if a partition plate that blocks gas is provided vertically between the discharge electrodes to partition the plasma atmosphere, the plasma discharge is not affected and stable film formation can be achieved. It was discovered that the gas composition distribution in the substrate transport direction can be controlled by the position of the gas inlet and exhaust port in the substrate transport direction by limiting the flow path of the reaction gas between each area of the atmosphere to the vicinity of the substrate surface. It is.

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, but it is preferably one that is free from plasma damage, such as stainless steel. 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 (1) Usually, the substrate transport path and 6
There is only a small gap between the 1B4fffi surface,
The other parts are completely blocked off, and a shape is selected in which there is no gas movement outside the above-mentioned interval. 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 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 exhaust port is similarly selected through experiments according to the profile in the thickness direction of the film to be formed. For example, if you want to change the composition within the film, you can create a composition distribution with an appropriate gradient 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. can be obtained.

Next, the microcrystallization reaction chamber, which is another requirement of the present invention, will be explained.

The microcrystallization reaction chamber was constructed as follows. In other words, when we investigated the cause of film quality change due to the mask mentioned above, we found that the electric field concentrates at the edge of the opening of the mask, and a local discharge occurs between the substrate and the edge of the mask, generating strong plasma. The cause was found to be that the electric field strength at the center of the substrate was weakened by

Therefore, in order to alleviate the electric field concentration at the edge of the mask opening, various methods have been used, such as rounding the etch periphery to a shape similar to that along an equipotential surface, moving the mask as close to the substrate as possible, and suppressing the applied power as much as possible. I tried it, but it didn't have a big effect. Then, they found that the above structure can be solved by providing an electric field adjustment member that concentrates the electric field in the center of the opening of the mask installed between the electrode and the substrate, and uniformizing the electric field distribution in the opening of the mask. This is what I came up with.

Therefore, the electric field adjusting member provided in the opening of the mask of the present invention is not particularly limited as long as it can uniformize the electric field distribution in the opening without impairing the function of the opening. A wire material is preferable since the electric field distribution can be effectively adjusted without any influence.

The arrangement of the wire rods is preferably selected experimentally depending on the size and shape of the opening, such as simple arrangement in the center of the opening, parallel arrangement at appropriate intervals, lattice arrangement, or even concentric arrangement. The material may be any material as long as it can concentrate the electric field in RFM and adjust the electric field distribution in the opening, but it is preferably a conductive material with good workability, and more preferably a conductive material with good workability. A metal with a small amount of film gas is preferable, and is selected from metal materials resistant to plasma such as stainless steel, tungsten, titanium, and molybdenum.

Note that in order to obtain a good microcrystalline amorphous semiconductor film, the power applied to the substrate surface must be at least 5 mW/d or more at any point, so in order to satisfy this condition, it is preferable to 0.5-21111. More preferably, it is desirable to construct the electric field adjusting member with a wire material (either a single wire or a stranded wire) having a diameter of about 1 to 1.5 #lI.

Further, the electric field strength can be freely adjusted by changing the distance between the electric field adjusting member and the substrate.

The shape of the discharge electrode to which the present invention can be applied is not only a parallel plate type and a parallel curved type using a can, but also the shape of the electric field adjustment member in non-parallel electrodes.

By changing the position, material, etc., the unequal electric field can be alleviated and applied.

The i-layer reaction chamber and the microcrystallization reaction chamber, which are the characteristics of the present invention, have been described above.

The present invention is equipped with these i-layer reaction chambers and microcrystallization reaction chambers, but in general, conventionally known reaction chambers may be used in these reaction chambers depending on the configuration of the photovoltaic layer of the solar cell to be manufactured. Needless to say, they must be combined.

In addition, the number of required reaction chambers, their arrangement, etc. are not particularly limited.
It is clear from the gist of the present invention that it should be determined by the photovoltaic layer of the solar cell to be manufactured and its formation method.

Further, the solar cell to which the present invention can be applied may have at least an i-type amorphous semiconductor layer and a microcrystalline semiconductor layer. Typical examples include a p-layer or a 0-layer of a piO structure made of an amorphous silicon semiconductor, or a structure in which both layers are microcrystalline layers, or a tandem structure of these. Also in the structure described above, it is preferable from the viewpoint of sunlight utilization efficiency that at least the p layer or the 0 layer on the light incidence side is a microcrystalline layer.

From the above points, preferred basic aspects of the present invention include:
A third layer forming an amorphous semiconductor layer of p-type or n-type conductivity.
A layer reaction chamber, an i-layer reaction chamber for forming an i-type amorphous semiconductor layer, and a microcrystallization reaction chamber for forming an amorphous semiconductor layer of a conductivity type opposite to that of the -th layer reaction chamber are arranged in the substrate transport direction. The seedlings were placed in this order, and the unrolled seedlings were placed in front of the reaction chamber in the first layer.
A device that connects a winding chamber after the microcrystallization reaction chamber and forms a film while continuously transporting a long strip substrate using a roll-to-roll method is the most efficient method in terms of productivity and stable continuous film formation. Preferable in terms of formation.

The details of the present invention will be described below.
The explanation will be based on an example applied to the production of an amorphous silicon solar cell with zero configuration.

<Example> FIG. 1 is a configuration diagram of the above embodiment.

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.

1. CVD plasma discharge forming amorphous silicon layer of type and microcrystallization n(0(μC)) type. i
Layer reaction chamber 2. The microcrystallization reaction chamber 3, the unwinding chamber 18, and the winding chamber 19 are connected by a buffer chamber 13 for gas isolation, which is exhausted to a predetermined gas pressure by an exhaust system (not shown), and the unwinding is carried out from the unwinding roll 20. Roll 1 plate 17 including 2 rolls.
p, i, n (μC) while transferring by two-roll method.
It has a structure in which layers are formed continuously. In addition, 4 to 9 in the figure
10 is a discharge electrode, and 10 in the figure is a high frequency power source that supplies high frequency power to each discharge electrode, specifically an RF main power source, and each reaction chamber 1.2.3 has a gas inlet 15 and an exhaust boat 16, respectively. A predetermined amorphous semiconductor film can be formed by a CVD method by introducing a predetermined gas.

By the way, the single-layer 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 in the substrate transport direction, excluding a necessary passage, is installed perpendicular to the electrode surface and covering 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 between the electrodes by the partition plate 11, and the reaction chamber 2
The reaction gas supplied from the gas inlet 15 provided at the downstream end in the substrate transport direction always flows through the gap 14 set by the partition plate 11 in order to reach the exhaust boat 16 at the upstream end.

Note that, as described above, the partition plate 11 is installed at a certain distance from both of the opposing discharge bridges so as to form a gap 14. This gap 14 is used as a path for the reaction gas, for electrode insulation with respect to the power electrode 147 shown below in the figure, and as a passage for the substrate 17 with respect to the ground electrode 6 shown above in the figure. In this example, three shoes were used. Although the object of the present invention is achieved regardless of 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 connected to ground.

Furthermore, the microcrystallization reaction chamber 3 for forming an n (μC) layer of microcrystalline amorphous silicon as a window layer of a solar cell has the following configuration according to the present invention. That is, as shown in FIG. 3, which shows a side cross section of the inside of the reaction chamber, 8 is grounded at the substrate side electrode. 17 is a polymer film substrate that moves in the direction of the arrow.

Reference numeral 30 denotes a mask for adjusting the deposited film thickness having an opening (30a), which is grounded in this example, but may be floating.

In addition, the size of the opening is 50 #lI L X in this example.
250#IIIW. The dotted line 31 is plasma. As mentioned above, 9.10 has a discharge electrode and its RF main power source, so the discharge frequency is 13.56 MH as well known.
It is z.

Using this apparatus, first, for comparison, an n-type microcrystalline amorphous silicon film was formed using a conventional mask shown in FIG. 4 in which an opening (30a) having the above-mentioned area was provided. (Hydrogen + silane + phosphine) mixed gas is used, and the discharge pressure is I
Torr, the substrate temperature is 160°C, and the applied power is 0.
05 Under the conditions of W/CIi, stop running the board and
It was formed in a stationary state for 0 minutes. As a result, the mask opening (
In the vicinity of the etched portion of 30a), the conductivity is approximately 58-CIl.
-1, which was observed to be microcrystalline, but the central part showed a fairly high value of 9 x 104S-1, confirming that it remained an amorphous film.

Next, as the electric field adjusting member 32 of the present invention shown in FIG.
Film formation was performed under the same conditions except for the applied power using a mask with a single wire in the width direction. Here, a stainless steel wire of 1 sIφ was used for the electric field adjustment member 32. The applied power is 0.01 to 0.04 W/C! I changed it to i.

FIG. 6 shows the conductivity at the center of the substrate formed under the above conditions. In this figure, the white circles are the measured values during light irradiation, and the black circles are the measured values in the dark. From these results, it is confirmed that complete microcrystalization occurs even in the center of the n-type amorphous silicon, and, It was confirmed that a microcrystalline amorphous silicon film with uniform characteristics was obtained over the entire opening (30a),
It was found that the desired characteristics could be improved.

Furthermore, the applied power is 1
It has also been confirmed that microcrystalization can be achieved sufficiently with a low power of 0.02 W/-2 or less, and it has also been found to be advantageous in terms of the production process. It was confirmed that the film thickness distribution, etc., were the same as those of conventional masks, and there were no problems at all.

On the other hand, in the roll-to-roll method of this example, normally the first layer forming adjacent p, n (μC) type amorphous silicon
828s and PH3 gas are slowly flowing from the layer reaction chamber 1 and microcrystallization reaction chamber 3 to the single layer reaction chamber 2 that forms one layer! A trace amount is mixed in via the i-chamber 13.

On the other hand, since the single-layer reaction chamber 2 has the above-mentioned configuration, the reaction gas in the single-layer reaction chamber 2 for forming i-type amorphous silicon is closer to the microcrystallization reaction chamber 3 for the n (μC) layer. The gas is introduced from the gas inlet 15 and flows toward the exhaust port 16 near the first layer reaction chamber 1 for the zero layer. Therefore, the above-mentioned effect can be obtained.

In order to confirm this point, in this example, 100
Using a substrate in which an aluminum layer and a stainless steel layer are sequentially laminated as a lower electrode layer on a μm-thick polyethylene terephthalate film, a mixed gas of BzHs and Si 14 diluted with hydrogen gas is introduced into the first reaction chamber 1 as in the conventional method. , 5IH4 gas in the single-layer reaction chamber 2, and hydrogen gas diluted PH3 and S! in the microcrystallization reaction chamber 3. Supply a mixed gas of H4, p.

A photovoltaic layer made of amorphous silicon having a laminated structure of n (μC) was formed and evaluated as follows. That is, the depth profile of boron (B) atoms in the photovoltaic layer was measured by secondary ion mass spectrometry (Si MS).

The results are shown in Figure 7! Indicated by A. For comparison, other conditions are the same, partition #f111 and electric field adjustment member 32
The same p, i formed in the case of conventional equipment without installing
, n stack type photovoltaic layer is shown in the figure by a broken line B.

In the case of the conventional device without the partition plate 11, the 8zH6 gas mixed in from the first layer reaction chamber 1 diffuses uniformly throughout the single layer reaction chamber 2, resulting in a concentration profile of B atoms in the layer 1 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, B at the interface between the p layer and the i layer
It can be seen that the atomic composition profile has a sharp cut, and the profile in one layer has a constant slope. This result is 1 by the partition plate 11.
By dividing the plasma space in the layer reaction chamber 2, the same
This shows that the composition of the reactant gas in the plasma atmosphere has a constant spatial distribution from the part near the microcrystallization reaction chamber 3 to the part near the first layer reaction chamber 1 even during the reaction period. In other words, this means that the present invention can realize the idle circulation distribution required for the reaction gas in reaction science, and that the present invention has an excellent effect of making it possible to control the film composition, which was previously impossible. It shows.

Next, ITO (l n
A transparent electric field consisting of diul Tin Oxide).

Collection electrodes made of AQ were stacked and their solar pond performance was investigated.

As a result, as shown in Table 1, when the case where the partition plate 11 was not installed in the single-layer reaction chamber 2 and the electric field adjustment member 32 was not installed in the microcrystallization reaction chamber was used as a comparative example, the present invention The solar cells created by applying this method showed improvements in short-circuit current and fill factor.

As a result, the conversion efficiency also showed a significant improvement, confirming the effectiveness of the present invention. The improvement in short-circuit current is thought to be due to a decrease in absorption due to complete microcrystallization of the microcrystalline n-layer, while the improvement in fill factor is thought to be due to an improvement in the distribution of boron atoms in one layer. It will be done.

Table 1 Comparison of solar cell performance

[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, Fig. 2 is a cross-sectional view taken along line A-A' in Fig. 1, and Fig. 3 is a side cross-section of a microcrystallization reaction chamber. figure. FIG. 4 is a plan view of a conventional mask, FIG. 5 is a plan view of an example mask, and FIG. 6 is the conductivity of the center of the mask of the microcrystalline amorphous silicon semiconductor layer obtained in the example. FIG. 7 is a graph showing the measurement results of the distribution of B (boron) atoms in the film thickness direction in the electromotive force layer of the solar cell obtained in the example. 1: 1st layer reaction chamber, 2: 1st layer reaction chamber. 3: Microcrystallization reaction chamber, 11: Partition plate. 13: buffer chamber, 17: substrate, 30: mask. 32: Electric field adjustment member patent applicant Teijin Co., Ltd. Tomi Z 11 33 Figure Nido O Chi Figure 4 βP sword low power (W/cmJ brilliance, m force゛5 no swamp r (pm)

Claims (1)

[Scope of Claims] 1. A predetermined number of reaction chambers for forming a predetermined amorphous semiconductor film by a chemical vapor phase decomposition method connected so that a substrate can be transported between the discharge electrodes; Manufacture of a solar cell in which a substrate is transported through each reaction chamber and a photovoltaic layer having at least one microcrystallized amorphous semiconductor layer and an i-type amorphous semiconductor layer is formed on the substrate. In the apparatus, partition plates for blocking reaction gas 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 kept free of gas in the substrate transport direction except for limited gaps such as substrate passages. A mask is disposed between the i-layer reaction chamber in which the i-type amorphous semiconductor layer is formed, which is divided into a plurality of diffusion-free regions, the substrate and the discharge electrode, and the electric field distribution in the opening is controlled at the opening. 1. A solar cell manufacturing apparatus comprising: a microcrystallization reaction chamber for forming the microcrystallized amorphous semiconductor layer provided with an electric field adjustment member for adjustment. 2. An unwinding chamber and a winding chamber are connected before and after the connected reaction chambers, and a long flexible strip substrate is rolled up.
2. The solar cell manufacturing apparatus according to claim 1, wherein the solar cell manufacturing apparatus is conveyed by a roll method. 3. A first layer reaction chamber forming a p-type or n-type amorphous semiconductor layer, the i-type reaction chamber, and the microcrystal forming an amorphous semiconductor layer having a conductivity type opposite to that of the first layer reaction chamber. 3. The solar cell manufacturing apparatus according to claim 1, wherein the reaction chambers are arranged in this order between the unwinding chamber and the winding chamber.