JP3095565B2 - Plasma chemical vapor deposition equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma-enhanced chemical vapor deposition (plasma CVD) apparatus suitable for producing large-area thin films used for various electronic devices such as amorphous silicon solar cells, thin film semiconductors, and semiconductor protective films for optical sensors. .

[0002]

2. Description of the Related Art Conventionally, plasma CVD is used to produce a large-area amorphous silicon thin film.
The configuration of the device will be described with reference to FIG. This technical means is known as disclosed in, for example, Japanese Patent Application No. 61-106314.

In a reaction vessel 1, electrodes 2 and 3 for generating glow discharge plasma are arranged in parallel.
These electrodes 2 and 3 are connected to the low frequency power supply 4 by, for example, 60
Hz commercial frequency power is supplied. Note that a DC power supply or a high-frequency power supply can be used as the power supply. A coil 5 is wound around the reaction vessel 1 so as to surround it, and AC power is supplied from an AC power supply 6. A reaction gas introduction pipe 7 is provided in the reaction vessel 1 from a cylinder (not shown).
, A mixed gas of, for example, monosilane and argon is supplied. The gas in the reaction vessel 1 is exhausted by a vacuum pump 9 through an exhaust pipe 8. The substrate 10 has electrodes 2 and 3
Are supported by appropriate means outside the discharge space formed by the electrodes so as to be orthogonal to the surfaces of the electrodes 2 and 3.

[0004] Using this apparatus, a thin film is manufactured as follows. The inside of the reaction vessel 1 is evacuated by driving the vacuum pump 9. When a mixed gas of, for example, monosilane and argon is supplied through the reaction gas introduction pipe 7, the pressure in the reaction vessel 1 is maintained at 0.05 to 0.5 Torr, and a voltage is applied from the low frequency power supply 4 to the electrodes 2 and 3. Then, glow discharge plasma is generated. An AC voltage of, for example, 100 Hz is applied to the coil 5 to generate a magnetic field B in a direction orthogonal to an electric field E generated between the electrodes 2 and 3. The magnetic flux density in this magnetic field is 10
It may be about Gaussian.

[0005] Among the gases supplied from the reaction gas introduction pipe 7, a monosilane gas is decomposed by glow discharge plasma generated between the electrodes 2 and 3. As a result, radical Si is generated and adheres to the surface of the substrate 10 to form a thin film.

[0006] Charged particles such as argon ions are
Coulomb force F due to electric field E between 2 and 3 ₁= QE and low
Lenz force F_Two= Q (V · B) (where V is the charged particle
So-called EB drift motion
You. Charged particles are given initial velocity by EB drift
In the direction perpendicular to the electrodes 2 and 3
Flying toward 10. However, between the electrodes 2 and 3
In the discharge space where the influence of the electric field is small,
Larm by the cyclotron motion by the magnetic field B
or orbit and fly. Therefore,
It is unlikely that charged particles such as on will hit the substrate 10 directly.
No.

The electrically neutral radical Si is not affected by the magnetic field B, deviates from the trajectory of the charged particle group, reaches the substrate 10, and forms an amorphous thin film on its surface. Since the radical Si collides with the charged particles flying in the Larmor orbit, an amorphous thin film is formed not only in front of the electrodes 2 and 3 but also spread to the left or right. In addition, since the magnetic field B is changed by the AC power supply 6, it is possible to uniformly form an amorphous thin film on the surface of the substrate 10.
Note that there is no problem if the length of the electrodes 2 and 3 is as long as the length of the reaction vessel 1 allows, so that even if the substrate 10 is long, a uniform amorphous A thin film can be formed.

[0008]

In the above conventional apparatus, a magnetic field B is generated in a direction orthogonal to a discharge electric field E between electrodes for generating glow discharge plasma, so that a large area film can be easily formed. It is possible. However, there are the following problems.

When a large area film is formed, it is necessary to use a long electrode as the electrode. In order to generate stable plasma using a long electrode, the frequency of the power source is preferably as low as possible.
A power supply of 00 Hz is used. However, under the condition that the frequency becomes low and the ion movement distance during the half cycle exceeds the electrode interval, as in the case of the DC discharge, the ions are emitted from the cathode by ion collision to maintain the plasma. Secondary electrons will play an essential role. Therefore, if a film adheres to the electrode and is insulated, no discharge occurs in that portion. In this case, it is necessary to keep the electrode surface clean at all times. Therefore, complicated operations such as frequent replacement and frequent cleaning of the electrodes are required, which is one of the factors of high cost.

If a high frequency power source of, for example, 13.56 MHz is used as a plasma source to compensate for the above-mentioned disadvantage, the secondary electrons emitted from the electrode for sustaining the discharge are not essential, and an insulating film such as a film is formed on the electrode. Even if an object exists, a glow discharge is formed between the electrodes. However, when a long electrode is used, most of the current flows on the surface (approximately 0.01 mm) due to the skin effect due to the high frequency, so that the electric resistance increases. For example, if the electrode length is about 1
When it is more than m, a potential distribution appears on the electrode and uniform plasma is not generated. Considering this with a distributed constant circuit, the result is as shown in FIG. In FIG. 9, x represents the distance in the length direction of the electrode. That is, the resistance R per unit length of the electrode is the impedance Z ₁ ,
Z _2, ..., and becomes larger as the non-negligible compared to the Z _n, potential distribution appears in the electrode. Therefore, when a high-frequency power supply is used, the film thickness is significantly different between the central portion of the substrate and the peripheral portion. For this reason, it is very difficult to form a large-area film, and it has not been practically possible to date.

In the above method, 50 cm × 50 cm
When manufacturing the above-described amorphous silicon thin film having a large area, it has been extremely difficult to maintain the film thickness distribution at ± 10% or less and maintain the film forming rate at 1 ° / sec or more.

[0012]

The present invention employs the following means to solve the above-mentioned problems.

[0013] That is, a reaction vessel, and the supply and discharge means of the reaction gas connected to the reaction vessel, a pair of electrodes provided in the reaction vessel, a substrate holder provided between the pair of electrodes, the pair squid in the electrode plasma chemical vapor deposition apparatus and a high frequency power supply for supplying high frequency power to the other with a flat plate-shaped electrode is one of the pair of electrodes
It becomes a plurality of elongated plate electrodes arranged in it like, the plurality of
The interval between the long plate electrodes is such that the high-frequency power and the reactive gas
Can be changed depending on the supply flow rate and pressure
A plasma chemical vapor deposition apparatus was used. Also the raft described above
The width of the plurality of long plate electrodes arranged in
A plasma chemical vapor deposition device smaller than the width between the electrodes
Was. Furthermore, the width of the long plate electrode is smaller than the width between the pair of electrodes.
A plurality of long plates as described above, arranged in a ragged shape
The distance between the long plates placed adjacent to the electrodes is the same
A plasma chemical vapor deposition device made larger than the width of the plate electrode
Was.

[0014]

In the above means, a substrate to be CVD is set on a substrate holder in a reaction vessel. Then, the interval between the plurality of long plate electrodes is optimally set in accordance with the type, flow rate, pressure and discharge power of the reaction gas. Then, a predetermined discharge is supplied from a high-frequency power source while the reaction gas is flowed at a predetermined flow rate with a predetermined vacuum inside the reaction vessel by a reaction gas supply / discharge means, and a glow discharge plasma is generated between the electrodes. Then, the reaction gas is excited, the CVD action is promoted, and a film is rapidly formed on the substrate.

In the above, since the high-frequency power supply is used for the glow discharge, the glow discharge is easily generated, and the insulator does not adhere to the electrodes. By optimizing the distance between the long plate electrodes, the electric field distribution and the flow of the reaction gas are made uniform, and uniform deposition can be obtained on a substrate having a large area.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS.

In FIG. 1 and FIG. 2, a reaction gas introduction pipe 7 is connected to one side of the reaction vessel 1. An exhaust pipe 8 having a vacuum pump is connected to the other side. At the center of the reaction vessel 1, a flat plate-shaped electrode 14 is disposed orthogonal to the gas flow. A power supply rod 15a perpendicular to the center of the flat electrode 14
Is attached at one end. A plurality of long plate electrodes 2-a to 2-d are arranged in a row facing the flat electrode 14 at a predetermined interval D. Each of the long plate electrodes 2-a to 2-d is
At the center, it is attached to the longitudinal member 15 so that the distance D can be changed.

From a 13.56 MHz high frequency power supply 13 through an impedance matching device 12, power supply lines 16, 1
7 is connected to the longitudinal member 15 and the power supply rod 15a. In the figure, reference numeral 11 denotes an introduction terminal.

In the vicinity of the flat electrode 14, a substrate 10 to be subjected to CVD is set in parallel with the electrode surface by a substrate holder (not shown).

As described above, high-frequency power is supplied from the high-frequency power supply 13 through the impedance matching unit 12 between the flat-plate electrode 14 and the plurality of long-plate electrodes 2-a to 2-d.

On the other hand, for example, monosilane is supplied into the reaction vessel 1 through a reaction gas introduction pipe 7 from a reaction gas supply device (not shown). The gas in the reaction vessel 1 is exhaust gas 8
And is discharged by the vacuum pump 9.

Using this apparatus, a thin film is manufactured as described below. The inside of the reaction vessel 1 is evacuated by driving the vacuum pump 9. For example, monosilane is supplied at a flow rate of about 100 cc / min through the reaction gas introduction pipe 7, and the pressure in the reaction vessel 1 is maintained at, for example, 0.5 Torr. Then, from the high frequency power supply 13 to the impedance matching unit 12 and the power supply line 1
6, 17, etc., a plurality of long plate electrodes 2-a, 2-
When power is supplied to b, 2-c, 2-d and the grounded flat electrode 14, a glow discharge plasma is generated between the electrodes. When glow discharge plasma is generated, the monosilane gas is decomposed, radical species are generated, and amorphous silicon (a-Si) is formed on the surface of the substrate 14.

At this time, depending on the size of the substrate 10 , the power, the flow rate of the reaction gas, and the pressure, a plurality of long plate electrodes 2-a,
By optimally adjusting the distance D between 2-b, 2-c, and 2-d, the flow of the reaction gas and the electric field are made uniform, and a film is rapidly and uniformly formed on the substrate 14 having a large area. Is done.

The size of the substrate 10 is preferably slightly shorter than that of the flat electrode 14 (FIG. 1, R = 20 to 50 mm). The outermost diameter of the long plate electrodes 2-a to 2-d is made substantially equal to the outer diameter of the flat electrode 14. The width of each long plate electrode is preferably smaller than the distance between the flat plate electrode 14 and the long plate electrode.

An experimental example according to this embodiment will be described below. (A) Substrate ・ Substrate material: glass ・ Substrate temperature: 200 ° C. ・ Substrate area: 20 cm × 20 cm (b) Reaction gas ・ Monosilane gas flow rate: 100 cc / min ・ Reaction vessel pressure: 0.05 to 0.15 Torr (c) Electrode・ Plate electrode: 40cm × 40cm ・ Distance between flat electrode and long plate electrode: 4cm ・ Length and width of long plate electrode: 40cm and 2cm, respectively ・ Distance between long plate electrodes: 0.5cm ~ 5 cm High-frequency power: 10 W to 100 W Frequency: 13.56 MHz The results of forming a film of amorphous silicon with the above configuration are shown in FIGS.

FIG. 3 is data showing the dependence of the thickness distribution of the formed a-Si film on the distance D between the long plate electrodes. Adjusting the distance between electrodes optimally results in a film thickness distribution of ± 5
%. The film thickness distribution ± 5%
In the film formation, the film formation rate was about 1 ° / sec.

FIGS. 4 to 6 show that the distance D between the long plate electrodes is 25 mm , 35 mm and 45 mm , respectively.
It is data showing the dependency of the thickness distribution of the formed a-Si film on the high frequency power. This shows that if the distance D between the long plate electrodes is adjusted to an optimum value according to the high frequency power used for forming the a-Si film, the film thickness distribution will be within ± 5%.
In the case of the film thickness distribution shown in FIG.
Å / sec.

In FIGS. 3 to 6, the existence of an optimum value in the film thickness distribution means that the flow of the reaction gas is controlled by the flat electrode 14 and the elongated plate electrodes 2-a to 2-a as shown in FIG. due to the non-uniformity between d and the excess or deficiency in the value of the high frequency power that causes the gas to decompose. That is, in FIG. 3, on the side longer than the long plate electrode distance D = 25 mm, the amount of the reaction gas is large, so that the central portion of the substrate where the power supply is large becomes thick.

On the side shorter than D = 25 mm, the central portion of the substrate becomes thin because the amount of reactive gas is insufficient at the central portion of the substrate.

In FIGS. 4 to 6, the center of the substrate becomes thinner due to the shortage of the reactive gas on the side larger than the power value corresponding to the optimum film thickness distribution, and the reactive gas on the side smaller than the above power value. Since the amount is large, the film thickness becomes large at the central portion of the substrate.

As is clear from the above experimental results, according to the apparatus of the present embodiment, in accordance with the use conditions,
In accordance with the flow rate and pressure of the reaction gas and the high-frequency power, the distance between the electrodes of the long plate can be set to an optimum value in advance, so that an a-Si film having a uniform film thickness distribution can be formed under a large area and high-speed film forming condition. It is possible.

[0032]

As described in detail above, the use of the plasma CVD apparatus of the present invention makes it possible to form a thin film uniformly and at high speed on a large-area substrate. Therefore, the industrial value in fields such as amorphous silicon solar cells, thin film transistors, optical sensors, and semiconductor protective films is remarkably large.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a plasma CVD apparatus according to one embodiment of the present invention.

FIG. 2 is a perspective view of a flat electrode and a plurality of long plate electrode portions of the embodiment.

FIG. 3 is an operation explanatory view of the embodiment.

FIG. 4 is an operation explanatory view of the embodiment.

FIG. 5 is an operation explanatory view of the embodiment.

FIG. 6 is an operation explanatory view of the embodiment.

FIG. 7 is an operation explanatory view of the embodiment.

FIG. 8 is a configuration diagram of a conventional example.

FIG. 9 is an operation explanatory view of the conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 reaction vessel 2-a to 2-d long plate electrode 7 reaction gas introduction pipe 9 vacuum pump 10 substrate 13 high frequency power supply 14 flat plate (ground) electrode 15a power supply rod

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Daiichi Furushiro 5-7-17-1 Fukahori-cho, Nagasaki-shi Mitsubishi Heavy Industries, Ltd. Nagasaki Research Laboratory (56) References JP-A-2-61078 (JP, A) JP-A-60-220935 (JP, A) JP-A-4-171944 (JP, A) JP-A-3-74663 (JP, U) JP-A-4-654 (JP, U) (58) Int.Cl. ⁷ , DB name) H01L 21/205 C23C 16/50

Claims (3)

(57) [Claims] And 1. A reaction vessel, and the supply and discharge means of the reaction gas connected to the reaction vessel, a pair of electrodes provided in the reaction vessel, a substrate holder provided between the pair of electrodes, the pair A high-frequency power supply for supplying high- frequency power to the electrodes, wherein one of the pair of electrodes is a plate-type electrode and the other is a raft.
Becomes a plurality of elongated plate electrodes arranged in, the plurality of elongated
The distance between the plate electrodes is such that the supply of the high-frequency power and the reaction gas is
A plasma chemical vapor deposition apparatus characterized in that the apparatus can be changed depending on a supply flow rate and a pressure . 2. A plurality of long plates arranged in a raft.
That the width of the electrode is smaller than the width between the pair of electrodes.
The plasma enhanced chemical vapor deposition apparatus according to claim 1, wherein: 3. A plurality of long plates arranged in a raft.
Elongate plate placed adjacent to the electrode
3. The electrode according to claim 2, wherein the width is larger than the width of the electrode.
Plasma chemical vapor deposition equipment.