JPH04236781A - Plasma cvd device - Google Patents

Abstract

PURPOSE:To obtain a plasma CVD device appropriate to form a thin film over large-area by forming a discharge electrode with a ladder planar coil consisting of several wires and supporting a substrate parallel to the electrode. CONSTITUTION:A discharge electrode 11 placed in a reaction vessel 1 is formed with the ladder-like planar coil consisting of several wires, and a substrate 10 is supported parallel to the electrode 11. A vacuum pump 9 is driven to evacuate the vessel 1, a gaseous reactant is supplied through an inlet pipe 7 to hold the vessel at a specified pressure, and a voltage is impressed on the electrode 11 from a high-frequency power source 14 to produce glow discharge plasma. Meanwhile, an AC voltage is impressed on a coil 5 enclosing the vessel 1 from an AC power source 6 to generate a magnetic field orthogonal to the discharge electric field of the electrode 11. Consequently, the electric field close to the electrode 11 is intensified and uniformized, and a large-area amorphous silicon thin film is formed on the substrate 10 at a high rate.

Description

[Detailed description of the invention]

0001

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

0002

[Prior Art] Plasma CVD has been conventionally used to produce large-area amorphous silicon thin films.
The configuration of the device will be explained with reference to FIG. This technical means is well known, as disclosed in, for example, Japanese Patent Application No. 106314/1982.

[0003] Inside 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 a low frequency power source 4 of, for example, 60H.
z commercial frequency power is supplied. Note that a DC power source or a high frequency power source can also be used as the power source. A coil 5 is wound around the reaction vessel 1 so as to surround it, and AC power is supplied from an AC power source 6 . A mixed gas of, for example, monosilane and argon is supplied into the reaction vessel 1 from a cylinder (not shown) through a reaction gas introduction pipe 7 . The gas in the reaction vessel 1 is exhausted by a vacuum pump 9 through an exhaust pipe 8. The substrate 10 is supported by appropriate means outside the discharge space formed by the electrodes 2 and 3 so as to be orthogonal to the planes of the electrodes 2 and 3.

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

Among the gases supplied from the reaction gas introduction tube 7, 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.

Charged particles such as argon ions are
, 3, a so-called E·B drift motion is caused by the Coulomb force F1 = qE due to the electric field E and the Lorentz force F2 = q(V·B) (here, V is the velocity of the charged particle). The charged particles fly in a direction perpendicular 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 Larm
It flies in an orbit. Therefore, charged particles such as argon ions rarely hit the substrate 10 directly.

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 the surface thereof. 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. Moreover, the magnetic field B
Since this is varied by the AC power source 6, it is possible to uniformly form an amorphous thin film on the surface of the substrate 10. Note that there is no problem in making the lengths of the electrodes 2 and 3 as long as the length of the reaction vessel 1 allows. It becomes possible to form a thin film.

[0008]

[Problems to be Solved by the Invention] In the above-mentioned conventional device, the discharge electric field E between the electrodes that generates glow discharge plasma is
By generating the magnetic field B in the direction orthogonal to the direction, it is possible to easily form a film over a large area. However, there are the following problems.

(i) When forming a film over a large area, it is necessary to use a long electrode. In order to generate stable plasma using a long electrode, it is easier to keep the frequency of the power source as low as possible, so it is easier to generate stable plasma using a long electrode.
A power source with a frequency of 100 Hz to several 100 Hz is used. However, under conditions where the frequency is low and the ion travel distance during a half cycle exceeds the electrode spacing, ions are emitted from the cathode by collision to maintain the plasma, just as in the case of DC discharge. Secondary electrons will play an essential role. Therefore, if a film is attached to the electrode to insulate it, discharge will not occur in that area. In this case, it is necessary to keep the electrode surface clean at all times. Therefore, complicated operations such as frequent replacement of electrodes and frequent cleaning are required, which is one of the causes of high costs.

(ii) In order to compensate for the drawback of (i) above, if a high frequency power source of 13.56 MHz is used as the plasma generation source, the secondary electrons emitted from the electrode are no longer essential for sustaining the discharge, and the secondary electrons emitted from the electrode are no longer essential. Even if an insulating material such as a film is present between the electrodes, a glow discharge is formed between the electrodes. However, when using long electrodes, most of the current is transferred to the surface (approximately 0.01 mm) due to the skin effect caused by high frequency.
, the electrical resistance increases. For example, if the length of the electrode is about 1 m or more, a potential distribution will appear on the electrode and uniform plasma will not be generated. If this is considered as a distributed constant circuit, it will be 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 compared to the impedance Z1, Z2, . . . , Zn of the discharge portion, a potential distribution appears within the electrode. Therefore, when using a high frequency power source, it is extremely difficult to form a film over a large area, and this has not been possible in practice to date.

(iii) In the methods (i) and (ii) above, when manufacturing an amorphous silicon thin film with a large area of 50 cm x 50 cm or more, the film thickness distribution is maintained within ±10% and the film formation rate is It was extremely difficult to maintain the rate at 0.1 nm/sec or higher.

0012

[Means for solving the problems] Plasma CVD of the present invention
The apparatus includes a reaction vessel, a means for introducing and discharging a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and a power source that supplies glow discharge power to the discharge electrode. In a plasma CVD apparatus that forms an amorphous thin film on the surface of a substrate placed in a reaction vessel, the discharge electrode is formed of a planar coil made of several wires arranged in a ladder shape, and is characterized in that it is supported in parallel with the discharge electrode.

In the present invention, the power supply for supplying glow discharge power to the discharge electrode is, for example, a 13.56 MH
It is preferable to use a high frequency power source of z.

In the present invention, it is preferable that the interval between adjacent wires of the ladder-like planar coil electrode is 50 mm or less. If this distance exceeds 50 mm, the thickness distribution of the amorphous silicon film formed on the substrate surface will be ±30 mm.
% or more, which is not preferable.

In the present invention, it is preferable that an impedance matching circuit consisting of a coil and a capacitor be installed between the power supply and the ladder-like planar coil electrode to supply power for plasma generation to the electrode. .

In the present invention, a coil that surrounds the discharge electrode and generates a magnetic field B in a direction perpendicular to the electric field E generated between the electrodes, and a power supply that supplies current for generating the magnetic field B to this coil are provided. It is preferable to install a magnetic field and oscillate the plasma using a magnetic field. However, it is not always necessary to oscillate the plasma using a magnetic field.

[0017]

[Function] In the present invention, instead of the conventional multiple parallel plate electrodes, a flat coil electrode made of several wires arranged in a ladder shape is installed in the reaction vessel as an electrode for plasma generation. The surrounding electric field becomes stronger and its intensity distribution becomes flat. For example, SiH as a reaction gas
4, SiH emission intensity distribution (wavelength 414n
m) has a uniform intensity. Therefore, the amorphous silicon film formed on the substrate surface has a substantially uniform film thickness distribution and can be formed at high speed. Therefore, the plasma CVD apparatus of the present invention is suitable for manufacturing large-area amorphous thin films.

[0018]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1] FIG. 1 is a sectional view showing the configuration of a plasma CVD apparatus according to an embodiment of the present invention. Note that the same members as in the conventional device (FIG. 9) are given the same numbers. A ladder-like planar coil electrode 11 for generating glow discharge plasma is disposed within the reaction vessel 1 . As shown in FIG. 2 (plan view) and FIG. 5 (cross-sectional view), this ladder-like planar coil electrode 11 has a structure in which several wire rods are assembled in a ladder shape perpendicularly to two wire rods. death,
The outer periphery has a rectangular shape. Power at a frequency of, for example, 13.56 MHz is supplied from a high-frequency power source 14 to power supply points 11a and 11b of the ladder-like planar coil electrode 11 via an impedance matching circuit 12. Note that the power supply point 11a of the ladder-like planar coil electrode 11
, 11b may be at the center of the wire as shown in FIG. 3, or at the four corners as shown in FIG. A coil 5 is provided around the reaction container 1, and AC power is supplied from an AC power source 6. Note that this power source may be a DC power source. In this embodiment, the coil 5 generates a magnetic field of 50 to 120 Gauss. A mixed gas of, for example, monosilane and argon is supplied into the reaction vessel 1 from a cylinder (not shown) through a reaction gas introduction pipe 7 . The gas in the reaction vessel 1 is exhausted by a vacuum pump 9 through an exhaust pipe 8. As shown in FIG. 6, the substrate 10 is placed parallel to the ladder-like planar coil electrode 11 and supported by a substrate holder (not shown).

Using this apparatus, a thin film is produced in the following manner. The inside of the reaction vessel 1 is evacuated by driving the vacuum pump 9. For example, a mixed gas of monosilane and argon is supplied through the reaction gas introduction pipe 7 at a flow rate of about 100 to 200 cc/min, and the pressure inside the reaction vessel 1 is adjusted to 0.05 to 0.0 cc/min.
When the voltage is maintained at 5 Torr and a voltage is applied from the high frequency power supply 14 to the ladder-shaped planar coil electrode 11 via the impedance matching circuit 12, glow discharge plasma is generated around the electrode 11. The light emitting state is measured at a wavelength of 414 nm.
When observed through an optical filter that allows only nearby light to pass through, it appears as shown in Figure 7. That is, the electrode 11 and the substrate 1
The luminescence intensity is almost uniform between 0 and 0. From this,
The amorphous silicon thin film attached to the surface of the substrate 10 is
It is assumed that the film thickness distribution becomes uniform.

The thickness distribution of the amorphous silicon thin film is as follows:
In addition to the flow rate and pressure of the reaction gas, the SiH4 concentration, and the electric power, it also depends on the distance between adjacent wires of the staggered planar coil electrode 11 (as shown in FIG. 6). Therefore, a film formation experiment was conducted under the following conditions.

[0022] Substrate material: glass, substrate area: 30 cm x
30 cm, reaction gas: 100% SiH4, reaction gas flow rate: 50 cc/min, reaction vessel pressure: 0.05 Torr,
High frequency power: 30W, the distance between adjacent wires of the ladder-like planar coil electrode 11 is 10 mm to 50 mm.
The range was set to . Then, a thin film having an average thickness of 500 nm was formed with and without applying a magnetic field. FIG. 8 shows the relationship between the distance between adjacent wire rods and the film thickness distribution.

As shown in FIG. 8, when no magnetic field is applied, a film thickness distribution of ±10% or less is obtained when the distance between the wires is 30 mm or less. On the other hand, when an alternating magnetic field of ±80 Gauss with a sine wave (frequency: 10 Hz) is applied, the film thickness distribution is better than when no magnetic field is applied. In other words, ±1 when the distance between the wires is 50 mm or less
A film thickness distribution of 0% or less was obtained.

In this example, a ladder-like planar coil electrode 11 shown in FIG. 2 is used as a discharge electrode, a 13.56 MHz high frequency power source is used as a plasma generation power source, and a magnetic field is applied in a direction perpendicular to the electric field. By this, 0.
It is possible to produce an amorphous silicon thin film with a large area and uniform thickness distribution at a high deposition rate of 3 to 0.5 nm/sec.

[Embodiment 2] FIG. 11 shows a ladder-like planar coil electrode 15 in Embodiment 2. This ladder-like planar coil electrode 15 has a structure in which wires are assembled in a hexagonal shape to form an outer peripheral part, and several wires are arranged in parallel inside the outer peripheral part. This ladder-like planar coil electrode 15
Power at a frequency of 13.56 MHz is supplied from a high frequency power source 14 to the power supply points 15a and 15b via an impedance matching circuit 12.

An amorphous silicon thin film was produced under the same conditions as in Example 1 using a plasma CVD apparatus equipped with this ladder-like planar coil electrode 15. As a result, as in Example 1, an amorphous silicon thin film with a uniform thickness distribution could be manufactured.

Although the shape of the outer periphery is hexagonal in FIG. 11, it has been confirmed that the same effect as in this embodiment can be obtained even if the outer periphery is triangular or octagonal.

[Embodiment 3] FIG. 12 shows a ladder-like planar coil electrode 16 in Embodiment 3. This ladder-like planar coil electrode 16 has a structure in which a wire is processed into a circular shape to form an outer peripheral part, and several wires are arranged in parallel inside the outer peripheral part. This ladder-like planar coil electrode 16
Power at a frequency of 13.56 MHz is supplied from a high-frequency power source 14 to the power supply points 16a and 16b via an impedance matching circuit 12.

An amorphous silicon thin film was produced under the same conditions as in Example 1 using a plasma CVD apparatus equipped with this ladder-like planar coil electrode 16. As a result, as in Example 1, an amorphous silicon thin film with a uniform thickness distribution could be manufactured.

[Embodiment 4] FIG. 13 shows a ladder-like planar coil electrode 17 in Embodiment 4. This ladder-like planar coil electrode 17 has a ladder-like structure in which several wires are assembled in a lattice shape, and the outer periphery thereof has a rectangular shape. Power supply points 17a and 17b of this ladder-like planar coil electrode 17 are connected to a high frequency power source 14 and 13.
Power at a frequency of 56 MHz is supplied through an impedance matching circuit 12.

An amorphous silicon thin film was produced under the same conditions as in Example 1 using a plasma CVD apparatus equipped with this ladder-like planar coil electrode 17. As a result, as in Example 1, an amorphous silicon thin film with a uniform thickness distribution could be manufactured.

In FIG. 13, the shape of the outer periphery is a square, but it has been confirmed that the same effect as in this embodiment can be obtained even if the outer periphery has a shape other than a polygon or a circle.

[0033]

Effects of the Invention As described in detail above, according to the present invention, by using a ladder-like planar coil electrode as the discharge electrode, the electric field strength near the electrode becomes stronger and more uniform. It is possible to produce large-area amorphous silicon thin films. Therefore, it has great industrial value in the fields of manufacturing amorphous silicon solar cells, thin film semiconductors, optical sensors, semiconductor protective films, etc.

[Brief explanation of the drawing]

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 plan view of a ladder-like planar coil electrode used in the plasma CVD apparatus of Example 1 of the present invention.

FIG. 3 is a plan view of a ladder-like planar coil electrode according to a modification of the present invention.

FIG. 4 is a plan view of a ladder-like planar coil electrode according to another modification of the present invention.

[Fig. 5] Cross-sectional view taken along line V-V in Fig. 2, Fig. 3, or Fig. 4

[
FIG. 6 is an explanatory diagram showing the arrangement of electrodes and substrates in the plasma CVD apparatus of Example 1 of the present invention

FIG. 7 is an explanatory diagram showing the SiH emission intensity distribution near the electrode in an example of the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the distance between adjacent wires of a ladder-like planar coil electrode and the film thickness distribution of amorphous silicon.

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

FIG. 10 is a diagram illustrating the drawbacks of a conventional plasma CVD apparatus.

FIG. 11 is a plan view of a ladder-like planar coil electrode used in the plasma CVD apparatus of Example 2 of the present invention.

FIG. 12 is a plan view of a ladder-like planar coil electrode used in the plasma CVD apparatus of Example 3 of the present invention.

FIG. 13 is a plan view of a ladder-like planar coil electrode used in the plasma CVD apparatus of Example 4 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Reaction container, 5... Coil, 6... AC power supply, 7... Reaction gas introduction pipe, 8... Exhaust pipe, 9... Vacuum pump, 10... Substrate,
DESCRIPTION OF SYMBOLS 11... Ladder-shaped planar coil electrode, 12... Impedance matching circuit, 14... High frequency power supply, 15, 16, 1
7...Ladder-shaped planar coil electrode.

Claims (1)

[Claims] 1. A reaction vessel, means for introducing and discharging a reaction gas into the reaction vessel, a discharge electrode housed in the reaction vessel, and supplying glow discharge power to the discharge electrode. In a plasma CVD apparatus that has a power supply and forms an amorphous thin film on the surface of a substrate placed in a reaction vessel, the above-mentioned discharge electrode is formed by a ladder-like planar coil made of several wires, and the above-mentioned A plasma CVD apparatus characterized in that a substrate is supported in parallel with the discharge electrode.