JPH05299680A - Plasma cvd method and its device - Google Patents

Abstract

PURPOSE:To provide a plasma CVD device which can form an amorphous silicon thin film of a large area at a high speed. CONSTITUTION:A reaction container 1, a means to introduce and evacuate reaction gas to and from the reaction container 1, discharge electrodes 2, 3 contained in the reaction container 1, a power supply 4 for supplying glow discharge power to the discharge electrodes 2, 3, two solenoid coils 5, 100 arranged to make magnetic field generated by each thereof cross at right angles to an electric field generated and an AC power supply 103 for supplying power for magnetic field generation to the solenoid coils 5, 100 are provided. An amorphous silicon thin film is formed on a substrate 10 supported to cross at right angles to an electric field generated by the discharge electrodes 2, 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma CVD method and a plasma CVD apparatus suitable for the production of large area thin films used in various electronic devices such as amorphous silicon solar cells, thin film transistors, optical sensors and semiconductor protective films.

[0002]

2. Description of the Related Art Conventionally, plasma CVD has been used to manufacture 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 the reaction vessel 1, electrodes 2 and 3 for generating glow discharge plasma are arranged in parallel.
These electrodes 2 and 3 are connected to, for example, 60H from the low frequency power source 4.
Power of the commercial frequency of z is supplied. 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 container 1 so as to surround the reaction container 1, and AC power is supplied from an AC power supply 6. A mixed gas of, for example, monosilane and hydrogen is supplied into the reaction container 1 from a cylinder (not shown) through a reaction gas introduction pipe 7. The gas in the reaction container 1 is exhausted by the vacuum pump 9 through the exhaust pipe 8. The substrate 10 is supported by an appropriate means outside the discharge space formed by the electrodes 2 and 3 so as to be orthogonal to the surfaces of the electrodes 2 and 3.

Using this apparatus, a thin film is manufactured as follows. The vacuum pump 9 is driven to exhaust the inside of the reaction container 1. A mixed gas of, for example, monosilane and hydrogen is supplied through the reaction gas introducing pipe 7 so that the pressure in the reaction vessel 1 is 0.0
Keep at 5 to 0.5 Torr, from low frequency power source 4 to electrode 2,
When a voltage is applied to 3, glow discharge plasma is generated. An alternating voltage of 10 Hz, for example, is applied to the coil 5 to generate a magnetic field B in a direction orthogonal to the electric field E generated between the electrodes 2 and 3. That is, the magnetic field B is generated in the direction orthogonal to the discharge electric field E between the electrodes for generating glow discharge plasma. Since the strength of this magnetic field B changes in a sine wave shape, its direction changes periodically. The magnetic flux density in this magnetic field may be about 50 to 100 Gauss.

The gas supplied from the reaction gas introducing pipe 7 is decomposed by glow discharge plasma generated between the electrodes 2 and 3. As a result, radicals Si are generated and adhere to the surface of the substrate 10 to form a thin film.

Charged particles such as hydrogen ions are generated by the electrodes 2, 3
Coulomb force F ₁ = qE and Lorentz force F ₂ = q (V · B) due to electric field E between (where V is the velocity of charged particles)
Causes a so-called EB drift motion. The charged particles jump out in a direction orthogonal to the electrodes 2 and 3 and fly toward the substrate 10 while being given an initial velocity by the E / B drift. However, in the discharge space where the influence of the electric field generated between the electrodes 2 and 3 is small, the magnetic field B generated by the coil 5 causes the cyclotron motion to fly along the Larmor trajectory. Therefore, charged particles such as hydrogen ions rarely hit the substrate 10 directly.

The electrically neutral radicals Si are not affected by the magnetic field B, deviate from the orbits of the charged particle group and reach the substrate 10, and form an amorphous thin film on the surface thereof. Since the radical Si collides with 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 in a left or right spread form. Moreover, since the magnetic field B is changed by the AC power source 6, it is possible to uniformly form an amorphous thin film on the surface of the substrate 10.
It should be noted that there is no problem if the lengths of the electrodes 2 and 3 are as long as the length of the reaction container 1 allows, so that even if the substrate 10 is long, a uniform amorphous surface is formed on the surface thereof. It becomes possible to form a thin film.

[0008]

In the above-mentioned conventional apparatus, a large-area film can be easily formed by generating a magnetic field B in a direction orthogonal to a discharge electric field E between electrodes for generating glow discharge plasma. I am trying. However, there are the following problems.

(1) When forming a large-area film, it is necessary to use long electrodes. In order to generate stable plasma using a long electrode, the frequency of the power source is preferably as low as possible.
A power source of several 100 Hz is used. However, under the condition that the frequency becomes low and the ion migration distance during the half cycle exceeds the electrode interval, as in the case of DC discharge,
Secondary electrons emitted from the cathode due to ion collision play an essential role in maintaining the plasma. Therefore, if a film is attached to the electrodes and insulated, no electric discharge will occur at that portion. In this case, it is necessary to keep the electrode surface clean at all times. Therefore, complicated work such as frequent replacement of electrodes or frequent cleaning is required, which is one of the factors of high cost.

(2) If a high frequency power source of 13.56 MHz is used for the plasma generation source in order to make up for the drawback of (1), the secondary electrons emitted from the electrode for sustaining the discharge are not essential, and the secondary electrons on the electrode are eliminated. Even if an insulator such as a film is present in the electrode, glow discharge is formed between the electrodes. However, when a long electrode is used, most of the current flows on the surface (about 0.01 mm) due to the skin effect due to the high frequency, so that the electric resistance increases. For example, when the length of the electrode is about 1 m or more, a potential distribution appears on the electrode and uniform plasma is not generated. Considering this with a distributed constant circuit, it becomes as shown in FIG. In FIG. 10, x indicates the distance in the length direction of the electrode. That is, when the resistance R per unit length of the electrode becomes so large that it cannot be ignored as compared with the impedances Z ₁ , Z ₂ , ..., Z _n of the discharge part, a potential distribution appears in the electrode. Therefore, when a high frequency power supply is used, it is very difficult to form a large area film, which has not been practically achieved so far.

(3) In the above methods (1) and (2), as shown in FIG. 11, a modulating magnetic field whose magnetic field strength changes sinusoidally is applied to plasma. In this case, as compared with the case where the strength of the magnetic field is constant, the effect of increasing the plasma density by the magnetic field and improving the film formation rate based on it is not so great. For example, when depositing amorphous silicon, it was difficult to maintain the deposition rate at 1 to 2 angstrom / sec or more.

[0012]

Means for Solving the Problems Plasma CVD of the present invention
The method is a method of forming an amorphous thin film using glow discharge plasma, which is characterized by applying a magnetic field rotating at a constant angular velocity in a plane orthogonal to an electric field applied during discharge.

In the present invention, in order to rotate the magnetic field at a constant angular velocity, for example, two solenoid coils are
A means of arranging each of the generated magnetic fields so as to be orthogonal to the electric field generated by the discharge electrode and orthogonal to each other is used.

The plasma CVD apparatus of the present invention includes a reaction vessel, a means for introducing and exhausting a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and a discharge electrode for glow discharge. A power supply for supplying electric power, two solenoid coils arranged so that the respective magnetic fields generated are orthogonal to the electric field generated by the discharge electrodes, and the electric power for generating the magnetic field is supplied to these solenoid coils. An amorphous thin film is formed on a substrate having an alternating current power supply for supplying and being orthogonal to an electric field generated by the discharge electrode. In the present invention, each of the two solenoid coils is supplied with a phase-controlled sinusoidal current output from, for example, a phase variable two-output oscillator.

[0015]

In the present invention, the synthetic magnetic field B by the two solenoid coils is applied in the direction orthogonal to the electric field E of the plasma generating discharge electrode. If the phase of the sinusoidal current supplied from the phase variable dual output oscillator to the two solenoid coils is properly controlled, this composite magnetic field B will have a constant angular velocity ω.
It rotates at, and its strength is a constant value independent of time. As a result, the plasma between the electrodes has a force F that rotates at an angular velocity ω.
Receive (EB drift). That is, the plasma is swung in all directions in the plane orthogonal to the discharge electric field E.
Therefore, the plasma density is averaged temporally and spatially, and the film formation area can be greatly increased. Further, the film formation rate can be improved by the plasma confinement effect by the magnetic field.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of a plasma CVD apparatus according to an embodiment of the present invention. The same members as those in FIG. 9 of the conventional example are designated by the same reference numerals.

In the reaction vessel 1, electrodes 2 and 3 for generating glow discharge plasma are arranged in parallel.
For the electrode 2, from the high frequency power source 4, for example, 13.56 MHz
Power of the frequency of the impedance matching circuit 104
And the power supply terminal 105. Electrode 3
Is connected to the ground 107 via the reaction vessel 1 and the high-frequency cable 106. The ground side terminal of the impedance matching circuit 104 is the high frequency cable 1
08, it is connected to the reaction container 1. The substrate 10 is set by a substrate holder (not shown) so as to be parallel to the electrodes 2 and 3, that is, orthogonal to the electric field generated by the electrodes 2 and 3. Monosilane, for example, is supplied into the reaction vessel 1 from a cylinder (not shown) through the reaction gas introduction pipe 7. The gas in the reaction vessel 1 is exhausted by a vacuum pump (not shown) through the exhaust pipe 8. The pressure inside the reaction container 1 is measured by a pressure gauge 109.

Further, the first solenoid coil 5 and the second solenoid coil 100 are arranged around the reaction vessel 1. As shown in FIG. 2, the first solenoid coil 5 and the second solenoid coil 100 are arranged so that the magnetic fields B ₁ and B ₂ respectively generated by the first solenoid coil 5 and the second solenoid coil 100 are orthogonal to the electric fields generated by the electrodes 2 and 3 and are also orthogonal to each other. It is arranged. The positions of the reaction container 1, the first solenoid coil 5 and the second solenoid coil 100 are set in the relationship as shown in FIG. The first solenoid coil 5 and the second solenoid coil 100 are supplied with sinusoidal waveform power from the phase variable two-output oscillator 103 via the first power amplifier 101 and the second power amplifier 102, respectively. The phase variable dual output oscillator 103 can output two sine wave signals with their relative phases arbitrarily set. The signal is observed with an oscilloscope (not shown).

Using the above apparatus, for example, an amorphous silicon thin film is manufactured as follows. The inside of the reaction vessel 1 is evacuated by driving the vacuum pump. Monosilane, for example, is supplied at a flow rate of about 50 to 100 cc / min through the reaction gas introducing pipe 7, and the pressure in the reaction vessel 1 is set to 0.05 to 0.
Keep at 5 Torr. When a voltage is applied to the electrodes 2 and 3 from the high frequency power source 4 via the impedance matching circuit 104, the power introduction terminal 105, etc., glow discharge plasma is generated between the electrodes.

On the other hand, as shown in FIGS. 4 (b) and 4 (c),
For example, a sine wave power having a frequency of 10 Hz with a phase shifted by 90 ° is supplied from the phase variable dual output oscillator 103 to the first and second solenoid coils 5 and 100 via the first and second power amplifiers 101 and 102, respectively. Apply. At this time, a combined magnetic field B of the magnetic fields B ₁ and B ₂ is generated by the first and second solenoid coils 5 and 100, as shown in FIG. As shown in FIG. 5, this combined magnetic field B has a constant angular velocity 2 in the direction orthogonal to the electric field E between the electrodes 2 and 3.
It is applied to the glow discharge plasma while rotating at 0π (radian / sec). As a result, as shown in FIG. 6, the glow discharge plasma receives a force (E / B drift) that rotates at a constant angular velocity. Therefore, electrodes 2 and 3
The plasma between and is swung in a direction parallel to the electrode 2 and in all directions. The strength of the synthetic magnetic field B is 40 to 10
About 0 gauss is enough.

The film thickness distribution and film forming rate of the amorphous silicon thin film depend on the flow rate and pressure of the reaction gas, the electric power supplied between the electrodes, the strength of the synthetic magnetic field applied to the glow discharge plasma, and the like. Therefore, an amorphous silicon thin film was formed under the following conditions. Ie 1 diameter
A 000 mm electrode and a glass substrate were used. As the reaction gas, 100% monosilane gas was supplied at a flow rate of 100 cc / min, and the pressure inside the reaction vessel was set to 0.5 Torr. A high frequency power of 200 W was applied between the electrodes 2 and 3. The strength of the synthetic magnetic field B applied by the solenoid coils 5 and 100 was set to 0, 20, 40, 60, 80, and 100 gauss.

FIG. 7 shows the film thickness distribution of the obtained amorphous silicon thin film. From FIG. 7, as compared with the case where no magnetic field is applied, when the strength of the composite magnetic field B is 40 and 80 Gauss, the film thickness is uniform over a wide area.

FIG. 8 shows the relationship between the strength of the magnetic field and the film formation rate of the obtained amorphous silicon thin film. From FIG. 8, in the method of the present invention, compared to the case where no magnetic field is applied,
It can be seen that the film formation rate can be significantly improved by applying a synthetic magnetic field. Further, in the conventional method, the effect of improving the deposition rate is small even if the strength of the magnetic field is increased.

[0024]

As described in detail above, according to the present invention, a large area amorphous thin film is formed by applying a synthetic magnetic field to the glow discharge plasma that rotates at a constant angular velocity in a plane orthogonal to the discharge electric field. High speed film formation. Therefore, the industrial value in the manufacturing field of amorphous silicon solar cells, thin film transistors, optoelectronic devices, etc. is extremely large.

[Brief description of drawings]

FIG. 1 is a sectional view showing the configuration of a plasma CVD apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of two solenoid coils used in the plasma CVD apparatus.

FIG. 3 is a plan view showing a positional relationship between a reaction container of the plasma CVD apparatus and two solenoid coils.

FIG. 4A is a diagram illustrating a combined magnetic field generated by two solenoid coils, and FIGS. 4B and 4C are diagrams illustrating magnetic fields generated by the respective solenoid coils.

FIG. 5 is a diagram illustrating rotation of a synthetic magnetic field by two solenoid coils.

FIG. 6 is a diagram for explaining rotation of EB drift generated by interaction between a synthetic magnetic field and a discharge electric field.

FIG. 7 is a characteristic diagram showing a film thickness distribution of an amorphous silicon thin film obtained by the device of the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the film formation rate of an amorphous silicon thin film obtained by the apparatus of the present invention and the magnetic field strength.

FIG. 9 is a sectional view showing the configuration of a conventional plasma CVD apparatus.

FIG. 10 is an explanatory view showing a defect of the conventional plasma CVD apparatus.

FIG. 11 is a diagram illustrating a magnetic field applied in a conventional plasma CVD apparatus.

[Explanation of symbols]

1 ... Reactor container 2, 3 ... Electrode, 4 ... High frequency power source, 5, 1
00 ... Solenoid coil, 10 ... Substrate, 101, 102
... amplifier, 103 ... a phase variable two-output oscillator.

Claims (3)

[Claims] 1. A method for forming an amorphous thin film using glow discharge plasma, which comprises applying a magnetic field rotating at a constant angular velocity in a plane orthogonal to an electric field applied during discharge. Law. 2. The magnetic field is rotated at a constant angular velocity by arranging the two solenoid coils so that the magnetic fields generated by the two solenoid coils are orthogonal to the electric field generated by the discharge electrode and are orthogonal to each other. The plasma CVD method according to claim 1. 3. A reaction vessel, a means for introducing and exhausting a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and a power supply for supplying glow discharge power to the discharge electrode. , Two solenoid coils arranged so that the respective magnetic fields generated are orthogonal to the electric field generated by the discharge electrode and also orthogonal to each other, and an AC power supply for supplying electric power for generating a magnetic field to these solenoid coils. A plasma CVD apparatus having an amorphous thin film formed on a substrate supported so as to be orthogonal to an electric field generated by the discharge electrode.