JPH0620156B2 - Solar cell manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Use of the Invention] The present invention relates to a solar cell manufacturing apparatus.
The present invention relates to a solar cell manufacturing apparatus by VD (Chemical Vapor Deposition).

[Prior art]

Since the conventional plasma CVD apparatus usually has an electrode structure as shown in FIG. 1 (a), the thin film formed on the opposing electrode may have different film quality. That is, a high voltage applying electrode 2 and a ground electrode 3 are arranged as two electrodes facing each other in the reaction vessel 1, and an alternating voltage is applied between them by an alternating voltage 4 to cause plasma discharge of a raw material gas to cause a substrate 5, Alternatively, it is deposited on 6. In this case, a vacuum container is usually installed.

Further, the electrode 2 is of a floating type at the time of direct current, and normally a negative self-bias voltage is generated. Therefore, the substrate 5
Since Nos. 6 and 6 differ in the quality and thickness of the deposited film due to the potential difference between the electrodes 2 and 3, it was not possible to deposit a thin film having good characteristics on both substrates at the same time. More recently, a plasma CVD apparatus having the structure shown in FIG. 1 (b) has been produced in order to improve the productivity and homogeneity. That is, the reaction vessel 7 is made of a quartz glass tube and the whole is heated uniformly from the outside. Further, the high voltage applying electrodes 81 to 84
By arranging a large number of and ground electrodes 91 to 94 alternately, mass productivity is improved. However, even in this case, the substrate 11 could be mounted on only one of the high voltage application electrodes 81 to 84 or the ground electrodes 91 to 94. High voltage application electrodes 81-84 and ground electrodes 91-94
When a substrate was bonded to each of them and an amorphous silicon film was formed using monosilane glass, the film thickness varied greatly depending on the electrodes as shown in Table 1, and it was not possible to form an equivalent thin film on all electrodes at the same time. Was clear.

[Object of the Invention] An object of the present invention is to provide a solar cell manufacturing apparatus by plasma CVD capable of forming a uniform thin film on all substrates by eliminating the difference in film quality due to the difference in electrode potential. Another object of the present invention is to provide a solar cell manufacturing apparatus capable of improving the film thickness uniformity of uniform thin films obtained on all substrates and improving the optical and electrical characteristics of smooth films.

[Outline of Invention]

In order to achieve the above object, the present invention makes all electrodes in a reaction vessel AC equivalent. For this purpose, the electrode structure and arrangement must be as symmetrical as possible. Further, the electrode inputs are such that the two electrodes are equipotential in terms of direct current and opposite in terms of alternating current.

Example of Invention

Reference Example A reference example related to the present invention will be shown with reference to FIG. A 10% hydrogen mixed gas of monosilane is introduced into the reaction vessel 12 made of quartz from the reaction gas supply system 13 and exhausted by the vacuum pump 14. The reaction vessel 12 is heated by 250 from the outside by a heater 15.
Heated to ° C. Electrodes A161, 16 in the reaction vessel 12
2,163 and electrodes B171,172,173 are introduced,
Wiring was performed as shown in the figure. The electrodes A and B had the same shape, and the electrode intervals were all the same. A glass plate was mounted as the substrate 18 on the electrode. Connect the wiring from both electrodes to the balanced matching box 19
An AC power supply 20 was connected to the box 19. AC power supply 2
A power source of 50 KHz was used for 0. Pour reaction gas to 1 Torr
Amorphous silicon was deposited at a power of 20 W for 10 minutes under the above pressure. The film thickness measured on the sample of the sample 18 at the position facing the direction of the reaction gas supply system is
Shown in the table.

Sample No. was set from 1 to 5 from the exhaust side toward the gas supply side. Although there was some variation between the samples, there was no difference between electrode A and electrode B. There was also no difference in the refractive index or the etching rate with the hydrofluoric acid / nitric acid-based etching solution. Further, when deposition was performed with a structure in which a capacitor 21 was inserted between the matching box 19 and the electrode, the uniformity of the film pressure at the electrode end was improved.

Example 1 A first example of the present invention will be described with reference to FIG. Illustration of the reaction device after the balance type matching box 21 is omitted because it is exactly the same as that of the reference example. In the reference example, the electrode portion was electrically floating, and the potential was not fixed, and there was little variation in film quality and film thickness within and between lots. In order to keep this potential constant, a positive or negative voltage was applied by the DC power source 22 or the ground potential 23 was set. In this state, amorphous silicon was deposited under the same conditions as in the reference example. Table 3 shows the results of measuring the film thickness distribution when grounded for the sample 18 on the four central electrodes 162, 163, 172.

The variation in film thickness is smaller than in the reference example, and the effect of making the potential constant by grounding is clear. Even when a positive or negative DC voltage was applied within 100 V, the variation in film thickness could be reduced as in the case of grounding. Further, when deposited under a negative bias, the uniformity of the film thickness at the electrode edge was improved, the etching rate by the hydrofluoric acid / nitric acid mixture was decreased, and the effect of improving the film quality was also observed.

Embodiment 2 A second embodiment of the present invention will be shown according to FIG. The parts of the reactor after the balance type matching box 24 are the same as those of the reference example, and are therefore omitted. As shown in Reference Example 1, all the electrodes have the same shape, but it is impossible to arrange all the electrodes completely symmetrically. Therefore, even though the balance type is used, the electrodes A161, 162, 16
A slight electric potential difference is unavoidable between the No. 3 and the electrodes B171, 172, 173. To compensate for this, a matching box 24 was used as shown in FIG. That is, for each of the two electrodes 161, 162, 163 and 171, 172, 173 a suitable DC
DC voltage was applied using the power supplies 25 and 26 to equalize the film thickness and film quality. As a result, sample 18 on all electrodes
As for the above, the variation in the film thickness of the deposited amorphous silicon could be within ± 5%.

Note that in the above examples, the deposition material is shown only for amorphous silicon, but of course, silicon nitride, silicon oxide, boron nitride, etc. of a film containing microcrystals or microcrystals
It goes without saying that the present apparatus can be used for any substance that can be formed by the plasma CVD reaction.

〔The invention's effect〕

According to the present invention, since the two electrodes are completely electrically equivalent except that the AC phases are opposite, a uniform thin film is formed even if the substrate is mounted on either of the two electrodes required for plasma discharge. it can.

Further, since there is no potential difference between the two electrodes, there is also an effect that there is no plasma damage caused by the potential difference between the electrodes, which is seen in a normal plasma CVD method.

[Brief description of drawings]

1 (a) and 1 (b) are schematic views showing a conventional plasma CVD apparatus, FIG. 2 is a view showing a reference example related to the present invention, and FIGS. 3 to 4 are different embodiments of the present invention. It is a figure which shows an example. 1, 7, 12, ... Reaction vessels, 2, 81, 82, 83,
84 ... High-voltage applying electrode, 3, 91, 92, 93, 94
...... Grounding electrode, 4, 10, 20, ...... AC power supply, 5,
6, 11, 18, ... Substrate, 13, ... Reaction gas supply system, 14, ... Vacuum pump, 15, ... Heater, 16
1, 162, 163, ... Electrode A, 171, 172, 1
73, ... Electrode B, 19, 21, 24, ... Matching box, 22, 25, 26 ... DC power supply, 23 ...
ground.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masatoshi Utaka Masatoshi Utaka 1-280, Higashi Koigokubo, Kokubunji, Tokyo Metropolitan Research Laboratories, Hitachi, Ltd. ) Reference JP-A-58-125821 (JP, A)

Claims (1)

[Claims] 1. A solar cell manufacturing apparatus using a plasma CVD method, comprising: a primary coil connected to a high-frequency power source, one end of which is grounded; and a secondary coil connected to a pair of plasma counter electrodes. , Which have substantially the same shape, AC voltages of opposite phases are applied, and the midpoint of the secondary coil is grounded or a DC external bias is applied to the midpoint or the midpoint is DC And a DC external bias is applied to each of the counter electrodes so as to be substantially equipotential in terms of DC, and a growth substrate is provided so as to correspond to each of the counter electrodes. Solar cell manufacturing equipment.