JPH0719911B2 - Solar cell manufacturing equipment - Google Patents

Description

TECHNICAL FIELD The present invention conveys a substrate through the plasma atmosphere of a predetermined number of reaction chambers for forming an amorphous semiconductor layer by chemical vapor decomposition and deposits the substrate on the substrate. The present invention relates to a solar cell manufacturing apparatus in which an amorphous semiconductor layer of a predetermined conductivity type is sequentially formed to form a photovoltaic layer having a predetermined structure such as a pin.

<Prior Art> A plasma vapor phase growth apparatus for manufacturing a semiconductor device or the like by forming a thin film semiconductor layer or the like on a substrate in a plasma atmosphere by chemical vapor decomposition (CVD) is, for example, silane (SiH ₄ ) gas. This is a well-known technique that has been widely put into practical use as a method of manufacturing an amorphous silicon solar cell by discharge decomposition.

In such a manufacturing method, as a method for efficiently forming an amorphous silicon thin film semiconductor layer, rolls are formed by using a plasma CVD apparatus known in JP-A-58-216475 and JP-A-59-34668. It is known that an amorphous silicon thin film is continuously formed on a substrate to be conveyed by a two-roll method.

When an amorphous silicon solar cell is produced by this method, a plurality of dedicated reaction chambers are formed in order to form at least p, i, n amorphous silicon or microcrystallized amorphous silicon in independent reaction chambers. A method of connecting the substrates to form a film by changing the reaction gas for each reaction chamber and sequentially transferring the substrate is performed. 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.

By the way, in the roll-to-roll system in which a long flexible substrate is continuously transported between a plurality of reaction chambers, each reaction chamber is not completely separated and independent, but is connected by a substrate passage. Has been done. 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. When this mutual mixing deteriorates the characteristics of the amorphous silicon solar cell to be created, a unidirectional gas flow is formed in the substrate passage between the reaction chambers,
As disclosed in JP-A-58-216475 and JP-A-59-34668, a dedicated buffer chamber is provided between the reaction chambers to bleed or differentially evacuate the gas to the required extent. It was However, in such a conventional method, once the reaction gas in the adjacent reaction chamber which has penetrated beyond these gas separation mechanisms diffuses into the entire reaction chamber and becomes uniform in the reaction chamber, the adjacent layer effective for improving the characteristics of the amorphous silicon solar cell is obtained. The controllability of the profile of the composition distribution in the film thickness direction and the profile of the impurity distribution at the interface with and, for example, the controllability such as a gentle graded junction or a sharp stepwise junction was poor.

Furthermore, in improving the characteristics of the amorphous silicon solar cell,
It has been known that it is necessary to uniformly deposit an extremely thin microcrystalline silicon layer having a thickness of about 100 Å at least on the p-layer or the n-layer on the sunlight incident side. By the way, when these microcrystallized silicon thin films are deposited by the roll-to-roll method described above, a mask is generally provided to adjust the film quality and film thickness of the thin film, and the amount of plasma reaching the substrate surface is adjusted. The quality and thickness of the deposited film are controlled by adjusting the width of the opening. A mask is also used to form a predetermined pattern.

However, when a microcrystallized amorphous silicon film was formed using a plasma CVD apparatus in which a mask was placed between the substrate and the discharge electrode in this manner, microcrystallization occurred in the portion near the opening edge portion of the mask. However, it was confirmed that the electric conductivity gradually decreased as it approached the central part, and finally the amorphous film remained as it was and did not crystallize.

That is, it has been found that the quality of the obtained film changes greatly at the center of the mask opening, specifically, at the center of the substrate and at a portion close to the edge of the mask opening, that is, at both ends of the substrate due to the installation of the mask.

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

<Objects of the Invention> The present invention has been made in view of the above circumstances, and it is possible to control the interface sharpness with an adjacent semiconductor layer in forming an i layer and to have a desired depth profile in composition and impurity distribution even in the layer. In addition to the above, it is an object of the present invention to provide a solar cell manufacturing apparatus suitable for mass production, which enables uniform film formation without distribution of film thickness in forming a microcrystallized semiconductor layer.

<Structure of Invention> The above-mentioned object is achieved by the present invention described below. That is, the present invention is provided with a predetermined number of reaction chambers for forming a predetermined amorphous semiconductor film by a chemical vapor phase decomposition method connected so that the substrate can be conveyed through between the discharge electrodes. In a solar cell manufacturing apparatus, which is transported through each reaction chamber, and on which a photovoltaic layer having at least one layer of a microcrystalline amorphous semiconductor layer and an i-type amorphous semiconductor layer is formed on the substrate. , Partition plates for blocking the reaction gas are arranged at a predetermined interval in the substrate transport direction in a direction vertical to the discharge electrode surface, and at least the plasma atmosphere is provided for gas diffusion in the substrate transport direction except for a limited gap such as a substrate passage. An i-layer reaction chamber for forming the i-type amorphous semiconductor layer, which is partitioned into a plurality of areas,
A microcrystallization reaction chamber for forming the microcrystallized amorphous semiconductor layer in which a mask is arranged between a substrate and a discharge electrode and an electric field adjusting member for adjusting an electric field distribution in the opening is provided in the opening. And a solar cell manufacturing apparatus.

In the above-mentioned present invention, the substrate is a long flexible strip-shaped substrate such as a synthetic resin film, and the unwinding chamber and the 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 the substrate while being transported by rolls, a highly productive solar cell manufacturing apparatus suitable for mass production can be obtained.

The details of the present invention will be described below.

That is, it was found that even if a partition plate for vertically blocking gas is provided between discharge electrodes to partition the plasma atmosphere, stable discharge can be performed without affecting plasma discharge, and a plasma partitioned by a partition plate capable of blocking gas is formed. It was found that the gas composition distribution in the substrate transfer direction can be controlled by limiting the flow path of the reaction gas between each area of the atmosphere to the vicinity of the substrate surface etc. by the position of the gas introduction port and the exhaust port in the substrate transfer direction. Is.

It is considered that this is because the mutual diffusion of the gas in the substrate transport direction between the areas of the plasma atmosphere partitioned by the partition plate is limited, and the gas composition of each area becomes substantially independent.

Therefore, the partition plate of the present invention is not particularly limited as long as it can block gas, and the material is not particularly limited to plasma damage, and stainless steel or the like is used. The partition plate is generally grounded together with the reaction chamber, but it may be floating or an appropriate bias voltage may be applied. The shape thereof should be such that the diffusion of gas in the substrate transport direction can be ignored, and normally there is only a minute gap between the substrate transport path and the discharge electrode surface, and the other parts are completely blocked. A shape having no gas migration other than the above-mentioned interval is selected. 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, when it is desired to change the composition in the film, the respective reaction gas inlets are arranged at both ends of the reaction chamber in the substrate transport direction, and a common exhaust port is provided at one end of the reaction chamber to provide an appropriate gradient composition distribution. Can be obtained.

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

The structure of the microcrystallization reaction chamber is as follows. That is, when the cause of the change in film quality due to the above-mentioned mask was examined, electric field concentration occurred in the opening edge portion of the mask, local discharge occurred between the substrate and the mask opening edge portion, and strong plasma was generated. It was found that the electric field strength in the central part of the substrate was weakened by this.

Therefore, in order to alleviate the electric field concentration at the edge portion of the mask opening, various methods such as rounding the edge portion to a shape close to that along the equipotential surface, bringing the mask as close to the substrate as possible, and suppressing the applied power as much as possible are available. I examined it but could not get a big effect. Further, it has been found that the problem can be solved by providing an electric field adjusting member for concentrating an electric field in the central portion of the opening of the mask installed between the electrode and the substrate and making the electric field distribution in the opening of the mask uniform. It was thought of.

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 make the electric field distribution of the opening uniform within a range that does not impair the function of the opening. A linear material is preferable because it has no influence and the electric field distribution can be adjusted effectively. It is preferable to experimentally select the arrangement of the wire rods according to the size and shape of the openings, such as a simple central arrangement of the openings, a parallel arrangement with an appropriate interval, a lattice arrangement, or a concentric arrangement. The material is RF
Any substance can be used as long as it can concentrate the electric field in the discharge and adjust the electric field distribution in the opening. However, a conductive substance having good workability is preferable, and a metal that is less likely to be outgassed during discharge is preferable. It is preferably selected from metal materials having resistance 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 needs to be at least 5 mW / cm ² or more at any place, so that the diameter is preferably set to satisfy this condition. 0.5-2 mm, more preferably diameter 1
It is desirable to construct the electric field adjusting member with a wire material (single wire or stranded wire) of about 1.5 mm.

Further, the adjustment of the electric field strength can be freely adjusted by 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 limited to the parallel plate type, the parallel curved surface type using a can, and also for non-parallel electrodes, the unequal electric field can be obtained by changing the shape, position, material, etc. of the electric field adjusting member. Can be relaxed and applied.

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

The present invention comprises the i-layer reaction chamber and the microcrystallization reaction chamber, but as a whole, conventionally known reaction chambers are set in these reaction chambers depending on the configuration of the photovoltaic layer of the solar cell to be manufactured. It goes without saying that they are combined.
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 depending on the photovoltaic layer of the solar cell to be manufactured and the method for forming the photovoltaic layer.

Further, the structure of the solar cell to which the present invention can be applied may be one having at least an i-type amorphous semiconductor layer and a microcrystallized semiconductor layer. As a typical example, either a p-layer or an n-layer having a pin structure made of an amorphous silicon semiconductor, or both layers of which are microcrystallized layers, or a tandem structure thereof can be used. Also in this configuration, at least the p-layer or the n-layer on the light incident side is preferably a microcrystallized layer from the viewpoint of the utilization efficiency of sunlight.

From the above points, as a preferable basic aspect of the present invention,
A first-layer reaction chamber for forming an amorphous semiconductor layer having a p-type or n-type conductivity, an i-layer reaction chamber for forming an i-type amorphous semiconductor layer, and conductivity opposite to that of the first-layer reaction chamber The microcrystallizing reaction chamber for forming the amorphous semiconductor layer of the shape is arranged in this order in the substrate transport direction, and in particular, the unwinding chamber is provided in front of the first layer reaction chamber,
A continuous film that is stable in terms of productivity is a film that is formed by continuously transferring long strip-shaped substrates by a roll-to-roll method by connecting a winding chamber after a microcrystallization reaction chamber. It is preferable in terms of formation.

The details of the present invention will be described below with reference to a pin in which a microcrystallized n layer is arranged on the window side.
A description will be given based on an example applied to manufacture of an amorphous silicon solar cell having a structure.

<Embodiment> FIG. 1 is a block diagram of the above embodiment.

The basic structure is as described in the above-mentioned JP-A-58-216475,
First layer reaction chamber of CVD plasma discharge for forming p-type, i-type, and microcrystallized n (n (μc))-type amorphous silicon layers, which are the same as those disclosed in JP-A-59-34668. The 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 that is exhausted to a predetermined gas pressure by an exhaust system (not shown), The substrate 17 is transferred from the unwinding roll 20 to the winding roll 21 by a roll-to-roll method, and three layers of p, i, n (μc) are continuously formed. 4 to 9 in the figure are discharge electrodes, 10 in the figure is a high-frequency power source for supplying high-frequency power to each discharge electrode, specifically, an RF power source, and each reaction chamber 1, 2 and 3 is provided with a gas inlet 15 respectively. And an exhaust port 16 so that a predetermined gas can be introduced to form a predetermined amorphous semiconductor film by the CVD method.

By the way, i-layer reaction chamber 2 for forming i-type amorphous silicon
Has the following configuration according to the present invention. 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. Five 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 between the electrodes, and the reaction gas supplied from the gas introduction port 15 provided at the downstream end of the reaction chamber 2 in the substrate transport direction is exhausted at its upstream end. The partition plate must be 11 to reach 16
Flow through the gap 14 set in.

As described above, the partition plate 11 is installed so as to form the gap 14 with a slight distance from both of the discharge electrodes facing each other. This gap 14 serves as a passage for the reaction gas, and also serves as an electrode insulation for the lower power electrode 7 in the drawing, and a substrate 17 for the upper ground electrode 6 in the drawing.
The purpose of this passage is to set the width to 3 mm in this embodiment. 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 connected to the ground.

Further, the microcrystallization reaction chamber 3 for forming n (μc) layer of microcrystallized amorphous silicon as the window layer of the solar cell has the following configuration according to the present invention. That is, as shown in the side cross section of the reaction chamber in FIG. 3, 8 is grounded at the substrate side electrode. 17 is a polymer film substrate which moves and runs in the direction of the arrow. Reference numeral 30 is a mask for adjusting the deposited film thickness having an opening (30a), which is grounded in this example, but may be floating. The size of the opening is 50 mmL × 250 mmW in this example. The dotted line at 31 is plasma. 9,10 is as described above
The discharge electrode and its RF power supply, so the discharge frequency is 13.56 MHz, as is known. Using this device, first, for comparison, the opening (30a) shown in FIG.
An n-type microcrystallized amorphous silicon film was formed with a conventional mask provided with. Using a mixed gas of (hydrogen + silane + phosphine), the discharge pressure was 1 Torr, the substrate temperature was 160 ° C, and the applied power was 0.05 W / cm ² , and the substrate was stopped for 30 minutes to form a static state. . As a result, the mask opening (30
It was confirmed that the electric conductivity was about 5 S · cm ⁻¹ near the edge part of a) and was crystallized, but it was 9 × 10 ⁻⁴ S in the central part.
・ It was confirmed that the film remained as an amorphous film, showing a considerably high value of cm ^-1 .

Next, as shown in FIG. 5, as the electric field adjusting member 32 of the present invention, a mask having a wire rod provided in the width direction of the substrate 17 at the center of the opening (30a) in the transfer direction of the substrate 17 is used to apply the applied power. Except for this, the film formation was performed under the same conditions. Here, the electric field adjusting member 32
A 1 mmφ stainless wire was used for this. Applied power is 0.0
It was carried out by changing it to 1 to 0.04 W / cm ² .

FIG. 6 shows the conductivity of the central portion of the substrate formed under the above conditions. In this figure, the white circles are the measured values when the black circles were in the dark at the time of light irradiation, and from this result, it was confirmed that the n-type amorphous silicon was completely microcrystallized even in the central portion, and It was confirmed that a microcrystalline amorphous silicon film with uniform characteristics could be obtained over the entire opening (30a),
It was found that the desired characteristics could be improved.

In addition, the applied power is 1/100 of that of the conventional mask.
It was also confirmed that sufficient microcrystallization was achieved at a low power of 0.02 W / cm ² of 2 or less, and it was also found to be advantageous in the production process. It was confirmed that the film thickness distribution and the like were the same as those of the conventional mask, and that there was no problem at all.

On the other hand, in the roll-to-roll method of this example, i layer is usually formed from the first layer reaction chamber 1 and the microcrystallization reaction chamber 3 which form the adjacent p, n (μc) type amorphous silicon. A small amount of B ₂ H ₆ and PH ₃ gas is mixed into the layer reaction chamber 2 via the buffer chamber 13.

On the other hand, since the i-layer reaction chamber 2 is configured as described above, the reaction gas in the i-layer reaction chamber 2 for forming i-type amorphous silicon is near the microcrystallization reaction chamber 3 for the n (μc) layer. The gas is introduced from the gas introduction port 15 and flows toward the exhaust port 16 near the first layer reaction chamber 1 for the p layer. Therefore, the above-mentioned effect is obtained.

In order to confirm this point, in this example, a substrate in which an aluminum layer and a stainless layer were sequentially laminated as a lower electrode layer on a polyethylene terephthalate film having a thickness of 100 μm was used, and hydrogen was placed in the first reaction chamber 1 in the same manner as a known ordinary method. a mixed gas of B ₂ H ₆ and SiH ₄ gas diluted, the SiH ₄ gas into the i layer reaction chamber 2, supplying a mixed gas of PH ₃ and SiH ₄ gas diluted with a hydrogen gas in the microcrystalline reaction chamber 3, p A photovoltaic layer made of amorphous silicon having a laminated structure of i, n (μc) was formed and evaluated as follows. That is, the depth profile of the boron (B) atom in the photovoltaic layer is determined by secondary ion mass spectrometry (SiMS).
It was measured at. The result is shown by the solid line A in FIG. For comparison, other conditions are the same, the partition plate 11 and the electric field adjusting member.
The same p, i,
The analysis result of the n-stacked photovoltaic layer is shown by the broken line B in FIG.

In the case of the conventional apparatus without the partition plate 11, the first layer reaction chamber 1
As a result, the B ₂ H ₆ gas mixed from the above diffuses uniformly throughout the i-layer reaction chamber 2, and as a result, 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 off, and the profile in the i layer has a constant gradient. You know that you have. This result is shown by the partition plate 11 in the i-layer reaction chamber 2
By dividing the plasma space of the above, even in the same reaction chamber, a space in which the composition of the reaction gas in the plasma atmosphere is constant from the portion near the microcrystallization reaction chamber 3 to the portion near the first layer reaction chamber 1 It has a distribution. That is, it means that one embodiment of the present invention can realize the spatial distribution required for the reaction gas in the reaction chamber, and shows that the present invention has an excellent effect that the composition of the film can be controlled, which has been impossible in the past. There is.

Next, on the photovoltaic layer obtained above, ITO (Indium Tin
The solar cell performance was investigated by stacking a transparent electrode made of Oxide) and a collecting electrode made of Ag.

As a result, as shown in Table 1, the partition plate 11 was not installed in the i-layer reaction chamber 2 and the electric field adjusting member 32 was added to the microcrystallization reaction chamber.
When the case where the solar cell was not installed was used as a comparative example, the solar cell manufactured by applying the present invention showed improvement in short-circuit current and fill factor. As a result, the conversion efficiency was significantly improved, and the effectiveness of the present invention was confirmed. The improvement of short circuit current is
This is due to the decrease in absorption due to the complete microcrystallization of the microcrystallized n layer, while the improvement of the fill factor is considered to be due to the improved distribution of boron atoms in the i layer.

[Brief description of drawings]

FIG. 1 is an explanatory view of the structure of an amorphous silicon solar cell manufacturing apparatus according to an embodiment, FIG. 2 is a sectional view taken along the line AA ′ in FIG. 1, and FIG. 3 is a side sectional view of a microcrystallization reaction chamber. 4 and 5 are plan views of a mask of a conventional example, FIG. 5 is a plan view of a mask of an embodiment, and FIG.
FIG. 7 is a graph showing the measurement results of the conductivity of the central portion of the mask of the microcrystallized amorphous silicon semiconductor layer obtained in the Example,
The figure is a graph showing the measurement results of the film thickness direction distribution of B (boron) atoms in the electromotive force layers of the solar cells obtained in the examples. 1: 1st layer reaction chamber, 2: i layer reaction chamber, 3: microcrystallization reaction chamber, 11: partition plate, 13: buffer chamber, 17: substrate, 30: mask, 32: electric field adjusting member

Claims (3)

[Claims] 1. A substrate is provided with a predetermined number of reaction chambers for forming a predetermined amorphous semiconductor film by a chemical vapor decomposition method connected so that the substrate can be conveyed between discharge electrodes. In a manufacturing apparatus of a solar cell, which is transported through a reaction chamber and is configured 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 that block the reaction gas are arranged at a predetermined interval in the substrate transport direction in the direction perpendicular to the discharge electrode surface, and at least the plasma atmosphere does not diffuse in the substrate transport direction except for a limited gap such as a substrate passage. Divided into multiple areas,
A mask was disposed between the i-layer reaction chamber for forming the i-type amorphous semiconductor layer and the substrate and the discharge electrode, and an electric field adjusting member for adjusting the electric field distribution in the opening was provided in the opening. An apparatus for manufacturing a solar cell, comprising: a microcrystallization reaction chamber for forming the microcrystallized amorphous semiconductor layer. 2. An unwinding chamber and a winding chamber are connected to each other before and after the connected reaction chamber to convey a long flexible belt-shaped substrate in a roll-to-roll system. Claim 1
An apparatus for manufacturing a solar cell according to the item. 3. A first layer reaction chamber for forming a p-type or n-type amorphous semiconductor layer, the i-type reaction chamber, and an amorphous semiconductor layer having a conductivity type opposite to that of the first layer reaction chamber. The solar cell manufacturing apparatus according to claim 1, wherein the microcrystallization reaction chamber is arranged between the unwinding chamber and the winding chamber in this order.