JPH11288889A - Thin-film deposition method through plasma cvd - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for depositing a thin film of uniform thickness through a plasma CVD method, so as to cover a conductive layer formed on an insulating board. SOLUTION: A thin-film deposition method is carried out through a plasma CVD method in a manner, where a first conductive thin film 5 is formed covering all the primary surface of an insulating board 3, isolating grooves 7 which are substantially rectilinear and parallel with each other are provided to the first thin film 5 so as to divide it into several regions, and when a second thin film is deposited through a CVD method to cover the first conductive thin film 5, the isolating grooves 7 are formed to have each provided with at least one non-groove region 7x of a prescribed length.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for depositing a second thin film by plasma CVD on a first conductive thin film formed on an insulating substrate.

[0002]

2. Description of the Related Art As an example of an apparatus manufactured by using a thin film deposition method by plasma CVD, there is an integrated thin film solar cell. Generally, in an integrated thin-film solar cell module, a first electrode layer, a semiconductor photoelectric conversion layer, and a second electrode layer sequentially stacked on a single relatively large insulating substrate form a plurality of photoelectric conversion cells. A structure in which the cells are separated by a plurality of substantially linear and parallel separation grooves, and the plurality of cells are electrically connected in series is adopted. Then, the semiconductor photoelectric conversion layer is generally deposited by plasma CVD. An example of a part of such an integrated thin-film solar cell module is shown in the schematic sectional view of FIG.

In the integrated thin-film solar cell module 20 shown in FIG. 2, a first electrode layer 5 made of a light-transmitting conductive thin film is formed on a light-transmitting insulating substrate 3 such as glass. This comprises a plurality of linear first
The plurality of first electrodes 5a, 5b, 5c are formed by the electrode separation grooves 7.
Are separated. On the first electrode layer 5, a thin film semiconductor photoelectric conversion layer 11 including a semiconductor junction such as a pin junction is deposited by plasma CVD, and the thin film semiconductor photoelectric conversion layer 11 includes a plurality of connection opening grooves 8 parallel to the first electrode separation groove 7. Is divided into a plurality of photoelectric conversion areas 11a, 11b, 11c.
On the photoelectric conversion layer 11, the second electrode layer 1 made of a suitable metal
5 are also formed, and the plurality of second electrodes 15a, 15a are also formed by a plurality of separation grooves 9 parallel to the first electrode separation grooves 7.
b, 15c.

In this way, a plurality of photoelectric conversion cells 17a, 17b, 17c are formed on one substrate 3 corresponding to the plurality of photoelectric conversion regions 11a, 11b, 11c. The first electrode 5b of any of the photoelectric conversion cells 17b is electrically connected to the second electrode 15a of the adjacent cell 17a via the connection groove 8. That is,
On the substrate 3, a plurality of photoelectric conversion cells 17a, 17b, 17
c are electrically connected in series and integrated.

FIG. 3 shows that the first electrode layer 5 on the substrate 3 is formed by a plurality of first electrode separation grooves 7 before the semiconductor layer 11 of the integrated type thin film solar cell module shown in FIG. FIG. 4 is a cross-sectional view showing a state where the electrodes 5a, 5b, and 5c are separated from each other. FIG. 4 is a top view corresponding to the state shown in FIG. As can be seen from FIGS. 3 and 4, the electrode separation groove 7 of the first electrode layer 5 is formed over substantially the entire length of the rectangular substrate 3 in the longitudinal direction. This is because the output of the solar cell module as a whole is increased by taking as much as possible the area of the photoelectric conversion cells in the substrate area and increasing the effective area for photovoltaic power generation. That is, by doing so, even if the intrinsic efficiency per unit area of the photoelectric conversion cells is the same, the output of the entire solar cell module can be improved.

[0006]

On the other hand, in such an integrated thin-film solar cell module 20, it is naturally necessary to increase the output per one substrate 3 as much as possible. The local thickness variation of the semiconductor thin film layer 11 that contributes to photovoltaic power generation must be minimized. For example, assuming an integrated thin-film solar cell module 20 in which 50 stages of photoelectric conversion cells are connected in series, the short-circuit photocurrent (I
_SC ) is 10% lower than that of the other 49-stage cells, but the value of I _SC actually flowing through the entire module 20 is lower by 10%. At this time, local film thickness variation of the semiconductor thin film layer 11 is directly
_It does not affect _SC , but it does have a close correlation. In addition, if there is a locally abnormally thin portion in the semiconductor thin film layer 11, a local short-circuit defect portion between the first electrode layer 5 and the second electrode layer 15 is likely to be formed. If this happens, the open-circuit voltage (V _OC ) and fill factor (FF) of the integrated thin-film solar cell module 20 will also decrease.

Here, in a thin film deposition method by glow discharge decomposition such as plasma CVD, local fluctuations in the film thickness are caused by local fluctuations in the distance between the high-frequency electrode and the ground electrode, and the film thickness. The distribution of the process gas concentration in the deposition surface, the distribution of the potential gradient in the film deposition surface due to the use of the insulating substrate, and the like can be considered.

For example, a conductor layer 5 having a relatively small conductivity, such as a light-transmitting conductive oxide layer formed on an insulating substrate 11, is separated by a separation groove 7 and separated from each other. When the semiconductor thin film 11 is deposited by plasma CVD so as to cover a plurality of island-shaped conductor regions, the local difference in the resistance value with respect to the ground electrode in the conductor layer 5 becomes considerably large, and the average resistance value increases. Occurs. Further, the substrate mounting jig having the same potential as the ground electrode and the substrate 3 are only in mechanical contact with each other at the periphery of the substrate where film deposition is not expected. There is a problem that an electrical connection state may fluctuate depending on accuracy or the like. Even when this problem is solved, when the conductor layer 5 having a low conductivity is used, there is a large difference in the resistance value between the peripheral portion and the central portion of the film deposition surface with respect to the ground potential portion. The difference becomes more pronounced as the substrate size increases. When the semiconductor thin film 11 is deposited on the conductor layer 5 having such a relatively small conductivity, particularly when the discharge state is unstable or when the discharge power is weak, local variation in the film thickness of the semiconductor layer 11 may occur. Will increase.

Under such circumstances, various methods have conventionally been employed to reduce local fluctuations in the film thickness of the semiconductor thin film 11 deposited on the insulating substrate 3 having a large area.

In the first method, the flatness between the substrate surface and the high-frequency electrode surface facing the substrate surface is ensured, and the distance between the substrate and the electrodes is adjusted so that both surfaces are exactly parallel. Thereby, local potential fluctuation between the substrate and the high-frequency electrode can be reduced, and local thickness fluctuation of the deposited thin film can be reduced. However, this method cannot cope with a temporal change such as deformation of the electrode over a long period of time, so that it is necessary to periodically correct the arrangement of the electrode.

As a second method, there is a method in which a method of introducing a process gas is devised so that the gas is uniformly supplied to the entire film deposition surface. As a general gas introduction method, there is a method in which a high-frequency electrode plate is hollow and a large number of minute opening holes are uniformly provided on a surface facing the substrate 3. Also,
There is also a method in which a plurality of baffle plates are arranged parallel to the electrode surface in the hollow interior of the high-frequency electrode up to their opening holes, thereby uniformly introducing gas toward the substrate surface. Furthermore, the gas introduction pipe is arranged symmetrically in the plane parallel to the substrate so that the conductance of the gas introduction pipe becomes equal, and the gas introduction opening is provided at an appropriate portion to uniformly distribute the gas. There is also a method to introduce.

Normally, the semiconductor thin film 11 is uniformly deposited by appropriately combining some of the above methods. However, as the insulating substrate 3 becomes larger and the film deposition area becomes larger, when the discharge state in the plasma CVD is unstable or the discharge power is small, the local film thickness variation of the semiconductor film 11 to be deposited becomes larger. Tends to be larger.

In view of the state of the prior art as described above, the present invention provides a method of forming a second thin film on an insulating substrate by plasma CVD so as to cover the first conductive thin film separated into a plurality of regions.
In the case of depositing by the method, the local thickness fluctuation of the second thin film, which is controlled mainly by only the parameters of the plasma CVD apparatus, is further suppressed by devising the structure on the substrate side. It is an object of the present invention to provide a method for depositing a second thin film having a very small thickness variation.

[0014]

According to the method of depositing a thin film by plasma CVD of the present invention, a conductive first thin film is formed so as to cover one entire main surface of an insulating substrate, and the first thin film is formed into a plurality of thin films. A method of forming a plurality of substantially linear and parallel separation grooves so as to separate into regions, and depositing a second thin film by plasma CVD so as to cover the first thin film, wherein the separation grooves are formed. Include at least one of the groove interrupted regions of a predetermined length.

According to such a thin film deposition method of the present invention, a conductive layer having a relatively small conductivity, such as a light-transmitting conductive oxide layer formed on an insulating substrate, is formed by a plurality of separation grooves. And when the second thin film is deposited by plasma CVD so as to cover the plurality of separated island-shaped conductor regions, the local resistance value variation and resistance value of the conductor layer with respect to the ground potential Is reduced, the plasma C
Even when the discharge state in VD is unstable or when the discharge power is small, local thickness fluctuation of the second thin film deposited on the conductor layer can be reduced.

[0016]

FIG. 1 is a schematic top view showing a conductive first thin film 5 formed on an insulating substrate 3 in order to explain one embodiment of the present invention. Have been. In FIG. 1, as in the case of FIG.
The electrode separation groove 7 of the first electrode layer 5 formed thereon is formed over substantially the entire area of the rectangular substrate 3 in the longitudinal direction. However, at the central portion in the longitudinal direction of the substrate 3, one groove interruption region 7 x is provided for each of the electrode separation grooves 7. The groove interruption region 7 in the transparent electrode layer 5
Regarding x, the number, position, and length of each separation groove are not particularly limited.

When a light-transmitting insulating substrate such as glass or transparent resin is used as the substrate 3, a light-transmitting oxide conductive material is usually used for the first electrode layer 5. However, the specific material for the first electrode layer 5 is not particularly limited, and can be appropriately selected from known conductive materials and used.

The material used for the second thin film formed on the first electrode layer 5 is not particularly limited as long as it can be deposited by plasma CVD. For example, when it is an amorphous silicon-based semiconductor material, in addition to amorphous silicon, hydrogenated amorphous silicon, hydrogenated amorphous silicon carbide, hydrogenated amorphous silicon nitride, carbon, germanium And an amorphous silicon alloy containing tin or the like. Further, by adding a p-type or n-type dopant element to these various semiconductor materials, a thin film of a material whose valence electrons are controlled can be deposited.

The second thin film is deposited by plasma CVD so as to cover the conductive thin film 5 on the insulating substrate 3 as shown in FIG. The conductive film 5 having a relatively small conductivity such as an object is separated by the separation groove 7, and the second thin film is formed by plasma CVD so as to cover the separated plurality of island-shaped conductive thin film regions.
, Local variations in resistance to ground potential and average resistance in the film deposition plane can be significantly reduced.

The connection between the substrate mounting jig having the same potential as the ground potential and the substrate 3 is made by contacting the four sides of the peripheral portion of the substrate 3, but as compared with the case of FIG. Since a current path exists through the electrode separation groove interruption region 7x in the central portion in the longitudinal direction, the local fluctuation of the resistance value and the average resistance value over the entire film deposition surface can be considerably reduced. As a result, when depositing the second thin film by plasma CVD so as to cover the first electrode layer 5, local potential fluctuation between the horizontal deposition surface and the high-frequency electrode surface can be considerably reduced, and accordingly, As a result, local fluctuations in the density of the generated film deposition precursor can be suppressed, and the second
Local variation in film thickness of the thin film can be reduced.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the embodiment of the present invention described with reference to FIG. 1, a second CVD method is used to cover a plurality of first thin film regions formed on an insulating substrate. Was deposited as an example.

First, a first electrode layer 5 is formed on a glass substrate 3 having a rectangular shape of 910 mm × 455 mm and a thickness of 4 mm.
A transparent oxide conductive thin film was formed by thermal CVD. The transparent electrode layer 5 is separated into a plurality of strip-shaped transparent electrode regions by irradiating the second harmonic of a YAG laser having a wavelength of 0.53 μm from the film surface side to form a plurality of separation grooves 7. Was done. Then, the substrate 3 and the transparent electrode layer 5
Was washed in pure water, and a second thin film layer was deposited on the transparent electrode layer 5 by plasma CVD.

In the transparent electrode layer 5 according to this embodiment, 51 separation grooves 7 having a length of 88 cm and a width of 50 μm are formed at a pitch of 0.9 cm, and an appropriate length is formed at the center of the separation grooves 7. A groove interruption region 7x was provided.

By changing the length of the groove interruption region 7x in the electrode separation groove 7 from 0.5 mm to 12 mm as described above,
The state of the change in the resistance value between the ground electrode and the surface of the transparent electrode layer 5 was examined. Table 1 shows that the resistance values depending on the positions a to e along the longitudinal center line represented by the dashed line on the substrate 3 as shown in FIG. The variation is shown.

[0025]

[Table 1]

The area resistance of the transparent electrode layer 5 is as follows:
It was about 10 to 12 Ω / □. Table 1 also shows, for reference, resistance values between the points a to e on the transparent electrode layer 5 and the ground electrode before the electrode separation groove 7 is formed. 18Ω, but in a state where the separation groove 7 is formed as in the conventional example shown in FIG. 4 (7x =
0 mm), the average value of the resistance is greatly increased to 168Ω. On the other hand, the interruption length 7x of the separation groove 7 is set to 0.5
mm, the average resistance is 101Ω,
It is reduced by about 40% as compared with the conventional method. Also, when 7x = 2 mm, the average resistance value is 93Ω, and 7x
= 12 mm, the average resistance is 87Ω, and the greater the groove interruption length 7x, the smaller the average resistance value.
Further, as the average resistance value decreases, the variation in each resistance value also decreases.

When an integrated thin-film solar cell module is formed on a substrate as shown in FIG.
For example, the module may be cut together with the substrate 3 so as to remove the groove interruption region 7x.

[0028]

As described above, according to the thin film deposition method of the present invention, the first thin film having relatively small conductivity such as the transparent conductive oxide formed on the insulating substrate is separated by the separation groove. When separating and depositing the second thin film by plasma CVD so as to cover the plurality of isolated island-shaped conductive regions, a local variation or an average of a resistance value with respect to a ground potential in a film deposition surface is obtained. Since the value can be considerably reduced, even when the discharge state in plasma CVD is unstable or the discharge power is weak, the second layer having a uniform film thickness distribution can be obtained.
Can be deposited. In particular, local variation in thickness of a thin film deposited on a large-area substrate can be significantly reduced, and the production yield of the thin film can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a schematic top view showing a conductive layer and a plurality of separation grooves formed on an insulating substrate according to an example of an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a part of the integrated thin-film solar cell module.

FIG. 3 is a schematic cross-sectional view showing a conductive layer and a plurality of separation grooves formed on an insulating substrate by a conventional method.

FIG. 4 is a schematic top view showing a state corresponding to FIG. 3;

[Explanation of symbols]

 Reference Signs List 3 Substrate such as glass 5 First electrode layer 7 First electrode separation groove 8 Connection groove 9 Second electrode separation groove 11 Semiconductor photoelectric conversion layer 15 Second electrode layer 17 Photoelectric conversion cell 20 Integrated thin-film solar cell module

Claims (4)

[Claims] 1. A first conductive thin film is formed so as to cover one entire main surface of an insulating substrate, and is substantially linear and parallel to each other so as to divide the first thin film into a plurality of regions. A method of forming a plurality of isolation trenches and depositing a second thin film by plasma CVD over the first thin film, wherein each of the isolation trenches includes at least one groove interrupted region of a predetermined length. Plasma CVD
Thin film deposition method. 2. The plasma CVD method according to claim 1, wherein the first thin film contains a light-transmitting conductive oxide.
Thin film deposition method. 3. The method according to claim 1, wherein the second thin film contains hydrogenated amorphous silicon or an alloy thereof.
3. The method for depositing a thin film by plasma CVD according to 1. 4. The plasma CV according to claim 1, wherein the second thin film contains polycrystalline silicon.
D. Thin film deposition method.