JPH0697649B2 - Amorphous film semiconductor manufacturing method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to improvements in the production of amorphous film semiconductors, especially amorphous films for optical devices such as solar cells.

2. Description of the Related Art Conventionally, several types of methods including single crystal silicon have been studied as materials for forming optical semiconductor devices such as solar cells and optical sensors, but recently, the materials and energy used are low and economical. For this reason, amorphous silicon is attracting attention.

There are glow discharge method, sputtering method, thermal CVD method, etc. as the manufacturing method, but at present, glow discharge is performed in an atmosphere in which a raw material gas such as silane and hydrogen is introduced into a low vacuum chamber (reaction chamber) to generate plasma. The decomposition products of the gas that are generated and generated in this plasma (Si-H, Si, H,
The H _2, etc.), by a chemical reaction on the substrate surface such as glass, amorphous film (amorphous silicon ~a-Si: H) is deposited as, by glow discharge plasma CVD method, the characteristics, productivity, etc. This method is excellent in terms of and is practically used.

FIG. 4 is an example showing a cross section of a main part of a solar cell in which an amorphous silicon film is formed by the plasma CVD method. In the figure, reference numeral 1 is a glass substrate having a transparent electrode 2 such as indium tin oxide on one surface thereof, and p
An amorphous silicon film 3 composed of three layers 3a, i layer (intrinsic layer) 3b, n layer 3c is sequentially deposited, and a back surface electrode 4 of aluminum, chromium or the like is formed on the upper surface thereof by a vapor deposition method or the like. is there.
If necessary, the upper surface of the back electrode 4 is covered with an organic or inorganic insulating material (not shown). Light passes through the transparent electrode 2 from the glass surface and enters the amorphous silicon film 3 to generate electromotive force as indicated by an arrow in the figure.

The amorphous silicon film 3 is formed under the optimum conditions for improving the photoelectric conversion characteristics. Regarding the deposition thickness, the thickness of each pin layer is generally the same as in FIG. 1 for consumer solar cells used indoors and outdoors. In the case of the example, p layer is 50 ~ 200Å, i layer is 3000 ~ 10,
The 000Å, n layer is about 200 to 500Å. Laboratoryly, a single chamber plasma CVD apparatus can be used to sequentially switch the source gases to deposit each layer. But,
Because it is easily affected by the atmosphere of the previous process, and the productivity is low because it is a batch type plasma, it is a plasma for mass production.
As a CVD apparatus, there have been developed two or three methods in which each pin layer is sequentially deposited while moving the substrate by a transporting means that advances the substrate in an independent chamber for each pin layer.

FIG. 5 is a block diagram showing an outline of the first example (reference: IEICE technical report [electronic parts / materials]).
P23, CPM81-83). The illustrated one comprises five chambers 11-1 to 11-5, and the chambers are connected by a gate valve 12. Each gate valve is closed to make each chamber an independent chamber except when a substrate electrode 15 (described later) moves between the chambers. Each chamber has an exhaust pipe indicated by 18-1 to 18-5, which is connected to a vacuum pump to enable independent exhaust. The substrate electrode 15 shown in each chamber is
Substrate 1 with the surface provided with the transparent electrode 2 facing down (FIG. 4)
Is a metal holder (frame plate) that accommodates a predetermined number of cells and serves as one electrode for performing glow discharge. Between the chambers and in the chambers, there is provided a transporting means such as a roller or a chain for sequentially moving and moving the substrate electrode 15 from the chambers 11-1 to 11-5.

The plurality of substrate electrodes 15 accommodating the above substrates are heated to 200 to 300 ° C. by the infrared heater 13 in the preheating chamber 11-1 and then p-layer deposition in which a doping gas of 0.05 to 0.3% diborane / silane is introduced. It is sent to the chamber 11-2 and then to the non-doped i-layer (intrinsic layer) deposition chamber 11-3 in which silane alone or a gas to which a diluent gas such as hydrogen or argon is added is introduced. .
N-layer deposition chamber with 1 to 1% doping gas introduced 1
1-4, cathode electrodes 16-2, 16-3, 16-4, respectively
, The conductor 17-2, 17-3, 17-4, the high frequency power source 19-2a, 19-3a, 19-4a independent for each chamber and a matching device 19-2b for adjusting the plasma state, 19-3b and 19-4b are connected, the plasma state is adjusted for each chamber, and glow discharge is performed for a predetermined time, so that non-contact electrodes each having a predetermined thickness are formed on the surface facing the cathode electrode. A crystalline silicon film 3 (FIG. 4) is deposited and formed. Then, it is sent to the take-out chamber 11-5 and taken out of the apparatus.

During this time, while opening and closing the gate valves 12 between the chambers, evacuation is performed, then each source gas is introduced, and then glow discharge is performed to perform each type of amorphous silicon film 3
Deposit. 14 of each chamber is a hot plate for heating each substrate to 200 to 300 ° C., and 19-2, 19-3, 19-4 are introduction pipes for introducing each source gas.

As described above, the thickness of the pin layer is different under the optimum conditions, and the difference between the p and n layers is within 4 to 5 times, but p, n
Since there is a difference of 10 to several tens of times between the i-layer and the i-layer, as can be seen from FIG. 5, the chamber 11-3 for depositing the i-layer (intrinsic layer)
Is longer, chambers 11-2, 11-4 for depositing p, n layers
The long and narrow cathode electrode 16-3, which is several times as large as that of the cathode electrode, is used as a counter electrode with several substrate electrodes to ensure a deposition time several times that of other chambers. In the cathode electrode, when the width-to-length ratio is increased, the glow discharge tends to be unstable or impossible, and the limit is about 3 to 4 times that of the cathode electrode in other chambers). Therefore, it is necessary to increase the deposition rate in order to balance with the deposited film thickness of other chambers. That is, in the apparatus of FIG. 5, the length of the cathode electrode 16-3 of the chamber 11-3 is made as long as possible while stabilizing the glow discharge, and the deposition rate is increased to shorten the deposition time. It can be said that this will increase the productivity of the device and greatly reduce the production cost. Therefore, it has been studied to increase the deposition rate by adjusting the flow rate of the raw material gas, the mixing ratio of the silane and a dilution gas such as hydrogen and argon, and increasing the power of the glow discharge. When it is set, the quality of the amorphous film as seen from the photoelectric characteristics tends to deteriorate. One of the major factors is
There is a deviation (unevenness depending on location) in the deposited film thickness (Reference: Nippon Vacuum Co., Ltd., ULVAC TECHNICAL JOURNAL No.19.P25).

FIG. 7 shows the width of the chamber 11-3 of the apparatus shown in FIG.
Three glass substrates (not shown) mounted and stored on the entire surface of the substrate electrode 15 having a length of 55 cm and a length of 65 cm are fed into the length direction, and the cathode electrode 16-3 having a width of 55 cm and a length of 200 cm is opposed to the cathode electrode 16-3. 3 shows a film thickness distribution in the length direction when glow discharge is carried out with a substrate electrode transport device (not shown) stopped and an i-layer film is deposited. In this case, the target of the deposited film thickness is 4500Å in all cases, and the result of the experiment conducted by changing the deposition rate is illustrated. A = 2.5Å / sec, B = 5Å / sec,
With C = 9Å / sec, each deposition condition was optimized, a deposition test was performed, and the i-layer film thickness of each part was measured. As a result, in the lateral direction of the cathode electrode, the relative thickness unevenness of the film thickness at each position at each point in the length direction is A,
Both B and C were ± 5% or less. However, when viewed in the length direction of the cathode electrode, as shown in FIG. 7, the thickness unevenness increases as the deposition rate increases, and A = ± 7 for the target of 4500Å.
5% (± 338Å), B = ± 20% (± 900Å), C = ± 30% (± 1
350Å).

Looking at the state of the deposited film, in the large part of the thickness,
Defects such as pinholes due to flakes and dust are scattered and the photoelectric characteristics are deteriorated, resulting in poor adhesion between the substrate surface and the amorphous film. In the chamber 11-3 shown in FIG. 5, the substrate electrode 15 is actually continuously advanced (leftward in the drawing).
Therefore, the deposited film thickness in the lengthwise direction is apparently averaged, but even under the conditions of B and C in FIG. 7, as can be seen from the graph, the deposition rate at both ends of the cathode electrode 16-13 is shown. Is abnormally large, and the amorphous film part deposited when the substrate electrode passes through this part tends to have a decrease in photoelectric characteristics due to pinholes, etc. and weak adhesion to the substrate surface. , Is a problem in mass production.

The apparatus shown in FIG. 6 is a block diagram showing the outline of another example. In the figure, the chamber for depositing the i layer is 21-5, 21-
Each of the substrate electrodes 25, which is a pair of two chambers of 6 and is sent by depositing a p-layer, is arranged to face the cathode electrodes 26-5 and 25-6 in a stationary state, and glow discharges to form an i-layer film. accumulate. In this method, each substrate electrode is glow-discharged, and as a result, the film thickness distribution is better than that of the i-layer film deposited in the chamber 11-3 of FIG. 5, and the length and width directions are within ± 10%. It was settled in. However, with this method, the entire system operates intermittently, and the chamber for depositing the p-layer and the n-layer is 21-
It requires two chambers, each of which is 3,21-4 and 21-7 and 21-8, and discharges in one chamber to deposit a film, and the other one waits for a time. Therefore, if the number of chambers for i-layer deposition is increased,
It is necessary to increase the number of chambers for the p and n layers, and there are problems in mass production, such as an increase in the size of the entire device, a high device cost, and a low operating rate of the device.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention As described above, using a source gas having a different composition and a plurality of chambers, a plurality of amorphous films are continuously formed on a substrate that moves between the chambers by a transfer means. When the glow discharge / plasma CVD method is applied using a chamber provided with a rectangular cathode electrode elongated in the direction of travel of the substrate electrode, the deposition rate can be reduced without deterioration of film quality and uneven film thickness. It was difficult to raise. Therefore, the present invention provides
It is an object of the present invention to improve the deposition rate with a uniform film thickness by improving the electrode structure for glow discharge.

Means for Solving the Problems According to the present invention, when a rectangular cathode electrode elongated in the traveling direction of a substrate electrode is provided in one chamber, it is divided into a plurality in the longitudinal direction, and each divided cathode electrode is divided into a plurality of cathode electrodes. In addition to a glow discharge device such as a matching device, an insulating separator is provided between each split cathode electrode and at both ends to separate the plasma for each split electrode and to divide the substrate electrode while continuously moving it. Then, the amorphous film is formed on the substrate surface of the substrate electrode by sequentially facing and passing through each cathode electrode surface.

Function As described above, the rectangular cathode electrode is divided into a plurality of pieces, and the glow discharge device is provided for each of the divided electrodes, and the separators are arranged between the divided electrodes and at both ends, so that the glow discharge occurs. Since the plasma can be separated and adjusted independently for each divided electrode, this has been a problem of the conventional mass production plasma CVD apparatus shown in FIG.
The film thickness distribution of the amorphous film, which occurs when the substrate electrode is opposed to the rectangular cathode electrode, and the deterioration of the film quality can be greatly reduced, and even if the deposition rate is high, the film is homogeneous on the substrate. Amorphous films of constant thickness can be deposited.

Example FIG. 1 is a block diagram showing an electrode structure of a chamber for depositing an i layer (non-doped layer) of an amorphous film deposition apparatus showing a specific example by the manufacturing method of the present invention.

In this apparatus, a p-layer is deposited in the chamber 31-2 and an n-layer is deposited in 31-4. As described above, in optical semiconductors such as solar cells, the p-layer and the n-layer have the same thickness as the i-layer. Since it is several tenths, it can be deposited in a short time of, for example, several tens of seconds to 2 minutes as compared with the deposition time of the i layer. Therefore, in the chamber for depositing the p and n layer films, deposition is usually performed using a short cathode electrode, and the deposited film thickness and film quality can be controlled within a range that does not cause a problem, and thus it is not necessary to improve the film.

A p-layer having a thickness of 120 Å is deposited on the substrate in the chamber 31-2 for depositing the p-layer, and then the substrate electrode 35 accommodating the substrate is sequentially fed into the chamber 31-3 by opening / closing the gate valve 32. Substrate electrode transfer device installed in the same chamber (described later)
Thus, it is continuously moved and advanced according to a predetermined deposition rate. A cathode electrode is provided in the lower part corresponding to the plurality of substrate electrodes, but in the present invention, as a result of various experimental studies, uniform plasma is generated and an amorphous film having a uniform and constant thickness is deposited on the substrate. In addition, based on the knowledge that it is effective to divide the cathode electrode and partition the divided electrodes by a separating means to separate and separate the plasma into a plurality of independent plasmas, and to stabilize them individually, as shown in the figure, The cathode electrode is divided in the lengthwise direction like 36a, 36b, 36c, and between the cathode electrodes, the moving substrate electrode 35 is not touched and the flow of gas such as silane is not hindered. A partition plate 38 is provided to partition the space, and high frequency power supplies 40a, 40b, 40c are prepared for each cathode electrode, and the glow discharge state can be individually adjusted via the matching devices 39a, 39b, 39c. is there. The other substrate electrode is grounded in common.

2a and 2b show an enlarged side view and an enlarged view taken at a right angle to the advancing direction of the central part 36b of the split cathode electrode provided in the chamber 31-3. The cathode electrode 36b is the cathode electrode plate 36b-1, the lead wire 37b, and the cathode electrode plate 3
6b-1 metal shield plate 36b-2 for stabilizing the discharge state of the periphery, composed of an insulating support 36b-3 for fixing the electrode plate, by the fixing plate 36b-4 of the shield plate 36b-2, It is fixed to the floor 45 of the chamber.

The substrate electrode 35 is not shown so that a predetermined number of substrates 35-1 can be accommodated, but a glass substrate or the like provided by patterning transparent electrodes on a stainless steel holder with window openings in a grid pattern is required. Depending on the pattern mask,
It is configured to be stored. This substrate electrode 35 is a drive roller
An electrode for glow discharge, which is moved forward at a predetermined constant speed by a substrate electrode transfer device 34 including a pressing roller 34a and a driving mechanism, and is held at a predetermined distance from the facing cathode electrodes 36a to 36b to 36c. And forms an amorphous film on the surface 35f facing the cathode electrode. A surface heater 33 is provided on the upper surface of the holder 35 of the electrode substrate, and the substrate 35-1 is heated to a constant temperature of 200 to 300 ° C. to secure the film quality of the amorphous silicon film and the adhesion to the substrate. is doing.

The divided cathode electrodes 36a, 36b, 36c are installed with a space between them, and the separators 38 are disposed between the electrodes and at both ends as shown in the figure, and are attached using a fixing jig 38a. The separator 38 is made of an insulating ceramic plate, a heat-resistant resin, or the like, which is heat-stable and has no reactivity with the source gas and does not generate gas. As described above, the separator 38 is sized so that the electrodes can be sufficiently partitioned as shown in the figure within a range that does not hinder the progress of the opposing substrate electrodes and the flow of the source gas.

Chamber 31-3 for depositing i-layer configured as described above
Is introduced by adjusting the flow rate of silane diluted with hydrogen to 20 to 50% with a mass flow meter to a predetermined flow rate from a gas introducing pipe 43 while exhausting with a vacuum pump connected to an exhaust pipe 41. The substrate electrode 35 having the p layer deposited in this chamber is replaced with the chamber 31
-Sequentially from 2 to the cathode electrode 36a, 36b, 36c and the first
While facing each other as shown in the figure, a high frequency current is applied from the high frequency power supplies 40a, 40b, 40c to cause glow discharge.

At this time, fine adjustment is performed by the matching devices 39a, 39b, 39c so that the plasmas 44a, 44b, 44c on the cathode electrodes 36a, 36b, 36c are in the same state. In the above description, one matching device 39 and one high frequency power source are used for one polarized cathode electrode, but a high capacity power source with a large output is used as the high frequency power source and a plurality of matching devices are used. It is also possible to connect the device and split cathode electrodes.

As described above, the deposition conditions examined by the conventional method shown in FIG. 5 were changed by changing the conditions such as the flow rate and concentration (ratio to the dilution gas) of the source gas, silane, and the high frequency power of glow discharge. Under the same conditions, an amorphous silicon i-layer deposition experiment was performed.

Deposition thickness target 4500Å Deposition rate The substrate electrodes 35 are stopped in a state of being lined up in the chamber 31-3 (transport stop).

Similar to the conventional example (Fig. 7), the cathode electrodes 36a, 36b, 36c
The thickness of the i-layer film in each portion corresponding to was measured, and the results are shown in FIG. As can be seen from the figure, the film thickness variation width for B'at a deposition rate of 5Å / sec is 6.7% (300Å), 9Å /
In the case of C'in seconds, it was 11% (500Å). Compared with B and C of the conventional example shown in FIG. 7 described above, the variation in film thickness is greatly improved and made uniform. In addition, the occurrence rate of defects such as pinholes that deteriorate the film quality due to the minimal generation of flakes and dust is less than that of the conventional example A, and the defective rate in photoelectric characteristics is B:
B'can be reduced to less than 1/20 and C: C 'can be reduced to less than 1/50.
In addition, the adhesion strength between the substrate surface and the deposited film is also improved, and the occurrence rate of adhesion failure is smaller than A in the conventional example.

In the above embodiment, one divided cathode electrode has a width of 55 cm and a length of 65 cm, and its dimensional ratio is 1: 1.18.
According to the result of another examination, it is preferable that the size ratio of the width and length of the cathode electrode 36b applicable to the present invention is 0.8 to 1.3 with the width being 1. If it deviates from this ratio, the variation width of the deposited film thickness distribution will be 15% or more,
It becomes a problem in practical use.

As shown in FIG. 3, in the chamber 31-3, the amorphous film i layer is deposited with the substrate electrode 35 stopped moving to improve the film thickness distribution, film quality, and film adhesion strength. After the confirmation, the carrier device 34 for the substrate electrode was driven under the conditions of B'and C ', and a solar cell was made as a prototype to examine the characteristics and appearance.
It was confirmed that the characteristics were equal to or higher than that of the conventional solar cell prepared at the deposition rate of the condition A shown in the figure, and the defective rate was equal to or lower than that.

The cathode electrode 16-3 of the chamber 11-3 shown in FIG.
The lead wire 17-3 for connecting the high-frequency power source is connected to the cathode electrode by branching the tip into two, and each matching wire 19-3b (total of 2 units) is connected to each of the branched lead wires. When adjusted, the balance of the i-layer film thickness at both ends in the electrode length direction (cathode electrode length 0 to 200 cm in FIG. 7) can be slightly corrected, but basically cannot be averaged. In addition, in FIG. 1 of the configuration of the present invention, when the separator 38 is not provided between the divided electrodes of the cathode electrodes 36a, 36b, 36c of the chamber 31-3, when glow discharge is performed,
The divided electrodes interfere with each other and the plasma state becomes unstable, so that the object of the present invention cannot be achieved.

In the above-mentioned embodiment, the substrate used is a substrate electrode in which a plurality of relatively small glass plates and the like are housed in a metal holder made of stainless steel or the like, but in the case of a large metal substrate, the substrate electrode may be used alone. . Also, if the gate valve 32 (FIG. 1) is replaced with a differential pressure exhaust valve, various substrates longer than the above substrates can be used. Further, although the substrate electrode and the cathode electrode are opposed to each other in the horizontal direction in the embodiment, they can be similarly applied to the case where they are opposed to each other vertically.

EFFECTS OF THE INVENTION As described above, the present invention divides a rectangular cathode electrode, which is arranged to face a substrate electrode which is continuously moved and advanced by a transfer means, into a plurality of pieces in the longitudinal direction, and arranges a separator plate. Since the plasma generated during glow discharge is separated and adjusted separately for each divided electrode unit, the influence of the installation conditions of the facing cathode electrode is significantly reduced, and the film thickness is uniform and the defect A very small amount of amorphous film can be formed on the main surface of the substrate, and the adhesion strength with the substrate surface can be stably improved. Further, since the substrate electrode or the substrate can be continuously fed, when manufacturing a semiconductor that requires an amorphous film having a relatively large film thickness, as described in the conventional example and the example, the entire device can be manufactured more than the conventional device. It is useful for the production of amorphous film semiconductors because it can be covered by increasing the deposition rate without increasing the length.

In addition, in the embodiment of the present invention, the example in which the i layer of the amorphous film of the pi-n3 layer is thickened is described, but the same applies to the case where p, n is thickened or either of the two layers is thickened. Can be adapted.

[Brief description of drawings]

FIG. 1 is a block diagram showing a longitudinal cross section of a main part showing an entire electrode structure in a chamber for depositing an i layer of an amorphous film deposition apparatus showing a specific example of the present invention, and FIG. An enlarged side view of the divided central electrode, FIG. 2b is an enlarged view taken at right angles to the direction of travel of the substrate electrode, and FIG. 3 is a diagram showing the film thickness distribution of an amorphous film deposited by the same device. FIG. 4 is a diagram showing a cross-sectional structure of an amorphous silicon solar cell which is a subject of the present invention, FIG. 5 is a block diagram showing a side surface of an amorphous film deposition apparatus of a first conventional example, and FIG. 6 is the same. FIG. 7 is a block diagram showing another conventional example, and FIG. 7 is a film thickness distribution diagram according to the position of the electrode of the amorphous film deposited by the apparatus of the first conventional example. 31-3 ... chamber for depositing i layer, 32 ... gate valve, 34 ... substrate electrode transfer device, 34a ... same pressing roller, 34b ... same driving roller, 35 ... substrate electrode, 35-1 …
… Substrate, 35f… Face of substrate electrode facing cathode electrode, 3
6a, 36b, 36c …… Divided cathode electrodes, 37a, 37b, 37c…
… Conductor of each cathode electrode, 38 …… Separator, 38a …… Separator fixing jig, 39a, 39b, 39c …… Matching device, 40a, 4
0b, 40c …… High frequency power supply, 41 …… Exhaust pipe connected to a vacuum pump, 44a, 44b, 44c …… Plasma for each split electrode unit.

Claims (2)

[Claims] 1. A raw material having a predetermined composition is used in each chamber by using a device in which a cathode electrode is provided in each chamber so as to face a substrate electrode 35 that continuously moves between a plurality of chambers by a transfer device. Gas is introduced, and then glow discharge is performed by a glow discharge device that is connected and adjusted between the substrate electrode and each cathode electrode, and the decomposition products in the generated plasma are transferred to the substrate 35- When depositing and forming a plurality of amorphous films on one layer, as a means for depositing a specific layer of the plurality of amorphous films thicker than other layers, the corresponding chamber (31-3) In the rectangular shape in which the cathode electrode inside is elongated in the traveling direction of the substrate electrode, the rectangular cathode electrode is divided into a plurality of pieces in the longitudinal direction, and the divided cathode electrodes 36a, 36b, 36c are arranged between and at both ends. Insulating separator 38 is provided to separate the plasma for each divided electrode, and while continuously moving the substrate electrode 35, each divided cathode electrode 36a connected to a glow discharge device such as a matching device, A method for producing an amorphous semiconductor, characterized in that one layer of an amorphous film is formed on the surface of the substrate 35-1 of the substrate electrode 35 by sequentially passing through the surfaces 36b, 36c. 2. When the cathode electrode is divided, the dimensional ratio of the width and length of one divided electrode is 0.8 to 1.3 with the width being 1 and the length is 0.8 to 1.3. Method for manufacturing crystalline semiconductor.