JPH09283449A - Plasma chemical vapor deposition system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent contamination by particles generated at the time of high- speed deposition of an amorphous silicon (a-Si) film in the case where a plasma chemical vapor deposition system is applied to manufacture of a semiconductor thin film, such as, an amorphous silicon photosensitive drum. SOLUTION: A cylindrical RF electrode 31, a cylindrical heater (earth electrode) 33 and a cylindrical substrate 32 are arranged in parallel in a reactor 30. An RF power is supplied between both electrodes 31, 33 by an RF generator 37 and an impedance matching unit 38. In addition, a pair of electromagnetic coils 1-a, 1-b are arranged on the axes of the electrodes 31, 33 from outside of the reactor 30, and a DC power is supplied from a DC power supply 2. A reaction gas is fed to the electrode 31 from a feed tube 34 and guided between both electrodes 31, 33 by a gas emission tube 35, thereby generating a glow discharge plasma. Thus, an a-Si thin film is formed on the surface of the substrate 32. Electrons and particles in the plasma rotate around the magnetic line of force, increasing collision with gas molecules. Also, since the generated particles are negatively charged, the particles rotate around the magnetic line of force and do not migrate to the substrate 32. Thus, contamination by particles on the surface of the substrate 32 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma chemical vapor deposition apparatus applied to the production of thin films used in various electronic devices such as amorphous silicon photosensitive drums, solar cells, photosensors and semiconductor protective films.

[0002]

2. Description of the Related Art Amorphous silicon (hereinafter a-Si)
Thin film and silicon nitride (hereinafter referred to as SiNx)
A plasma chemical vapor deposition apparatus (hereinafter referred to as a plasma CVD apparatus) which has been conventionally used for producing a thin film.
A typical example of the configuration will be described. The shape of the substrate on which the thin film is formed is usually of two types: flat plate and cylindrical. Here, plasma CVD for a cylindrical substrate is used.
The device is shown.

FIG. 5 is a block diagram of a plasma CVD apparatus used for manufacturing a conventional photosensitive drum. In the figure, in the reaction vessel 30, an outer cylindrical electrode, that is, a cylindrical high-frequency electrode 31, a cylindrical substrate 32, and an inner cylindrical electrode, that is, a cylindrical heater 33 that also serves as a ground electrode.
Are arranged in parallel with the substrate holder 36.

A gas discharge pipe 35 is attached to the high-frequency electrode 31, and a mixed gas of, for example, monosilane and hydrogen is supplied from a reaction gas supply device (not shown) through the introduction pipe 34, and the gas discharge pipe 35 is supplied. The high frequency electrode 3
The mixed gas is discharged into the space between 1 and the substrate 32.
The gas in the reaction container 30 is discharged through the exhaust pipe 39 and the vacuum pump 40 (not shown).

The high frequency electrode 31 is supplied to the high frequency electrode 31 from a high frequency power source 37 through an impedance matching device 38, for example, 13.5.
High-frequency power of 6 MHz is supplied. The heater 33 is
It is grounded together with the reaction container 30 and serves as a ground electrode. Therefore, glow discharge plasma is generated between the high frequency electrode 31 and the heater 33, that is, the substrate 32.

Using this device, a-
A Si-based thin film is manufactured. The inside of the reaction vessel 30 is evacuated by driving a vacuum pump (not shown). When a mixed gas of, for example, monosilane and hydrogen is supplied through the reaction gas introducing pipe 34 to maintain the pressure in the reaction container 30 at 0.5 to 2.0 Torr and a voltage is applied from the high frequency power supply 37 to the high frequency electrode 31, glow discharge occurs. Plasma is generated.

The mixed gas discharged from the reactive gas discharge pipe 35 is decomposed and dissociated into radicals containing Si such as SiH ₃ and SiH ₂ by glow discharge. as a result,
An a-Si based thin film is formed on the surface of the substrate 32.

[0008]

SUMMARY OF THE INVENTION Conventional plasma CVD
In the apparatus, when the film formation rate for forming the a-Si film is increased,
A large amount of powder is generated for the following reasons, which is a problem in manufacturing a photosensitive drum and the like. That is, in FIG. 5, the high frequency power supplied between the high frequency electrode 31 and the ground electrode 33 is 0.
When the film formation rate is set to a high speed of 5 to 20 Å / S and the pressure of the reaction gas is set to 1 to 1 KW and the pressure of the reaction gas is set to 0.2 to 2.0 Torr, powders such as polymers such as Si ₂ H ₆ and Si ₃ H ₈ are generated in the plasma. appear.

As a result, the quality of the a-Si film is remarkably deteriorated due to deterioration of photoconductivity and generation of pinholes, and it is difficult to put it into practical use for a photosensitive drum, a solar cell and the like. Therefore, it is very difficult to improve the film forming speed without deteriorating the film quality.

[0010]

The present invention provides the following means in order to solve such a problem.

A reaction container; a reaction gas discharge hole for supplying a reaction gas into the reaction container; a reaction gas discharge hole for discharging the reaction gas in the container; an inner cylindrical electrode installed in the reaction container; A pair of discharge cylindrical electrodes composed of outer cylindrical electrodes; a power supply for supplying electric power for glow discharge generation to the discharge cylindrical electrodes; and a cylindrical substrate arranged between the inner and outer cylindrical electrodes of the discharge cylindrical electrodes. A heater for heating; an electromagnetic coil having the same axis as the axis of the discharge cylindrical electrode and arranged outside the reaction container; and a direct current power source for supplying electric power to the electromagnetic coil, A plasma-enhanced chemical vapor deposition device, comprising forming a thin film of the reaction gas on a cylindrical substrate.

According to the present invention, in the above means, a predetermined amount of a reaction gas, for example, a mixed gas of monosilane and hydrogen is introduced into the reaction vessel and is supplied from the reaction gas discharge hole between the pair of discharge cylindrical electrodes. A cylindrical substrate is arranged close to the heater between the pair of electrodes, high frequency power is supplied from the power supply between the pair of electrodes, and direct current power is supplied to the electromagnetic coil from the direct current power supply. A magnetic field is generated by the coil. When a magnetic field is generated, glow discharge plasma is formed between the electrodes. Here, the pressure in the reaction vessel is, for example,
The magnetic field strength is set to 2.0 Torr or less and 40 to 100 Gauss.

In this case, the electrons and charged particles in the plasma cause a motion of rotating around a magnetic field, that is, a line of magnetic force. That is, the frequency of collision of electrons with the reaction gas molecules is remarkably increased, the plasma density is increased, and the film formation rate for forming the a-Si thin film formed on the surface of the cylindrical substrate is increased. In addition, powder generated in plasma, that is, Si ₂ H ₆ and S
Since a polymer such as i ₃ H ₈ is generally negatively charged, it causes a motion of rotating around this magnetic field line and is not transported toward the cylindrical substrate.

In this situation, as will be described with reference to FIG. 3 in an embodiment to be described later, the vicinity of the cylindrical substrate is irradiated with laser light, and the scattered light intensity from the powder floating in that portion is measured. As a result, at a pressure of 0.5 to 1 Torr, it can be seen from the fact that the scattered light intensity from the powder suddenly weakens when the magnetic field intensity is around 50 Gauss. That is, by applying a magnetic field at right angles to the electric field formed by a pair of cylindrical electrodes with an electromagnetic coil, the amount of powder transported to the vicinity of the surface of the cylindrical substrate is suppressed, and the powder is formed in the film during a-Si thin film formation. It suppresses the mixed powder.

[0015]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a configuration diagram of a plasma enhanced chemical vapor deposition apparatus according to an embodiment of the present invention. In FIG. 1, reference numerals 30 to 31 have the same configuration as the conventional example of FIG. 5, but will be described again. A cylindrical high frequency electrode 31, a cylindrical substrate 32, and a cylindrical heater 33 are arranged in parallel with a substrate holder 36 in the reaction container 30.

A gas discharge pipe 35 for discharging a reaction gas is attached to the high-frequency electrode 31, and a mixed gas of, for example, monosilane and hydrogen is supplied from a reaction gas supply device (not shown) through an introduction pipe 34 to supply the gas. The mixed gas is discharged from the discharge pipe 35 into the space between the high frequency electrode 31 and the substrate 32.

The gas in the reaction container 30 is exhausted through an exhaust pipe 39 and a vacuum pump 40 (not shown).

To the high frequency electrode 31, for example, 13.5 from a high frequency power source 37 through an impedance matching device 38.
High-frequency power of 6 MHz is supplied. The heater 33 is
It is grounded together with the reaction container 30 and serves as a ground electrode.
Therefore, between the high frequency electrode 31 and the heater 33,
That is, glow discharge plasma is generated with the substrate 32.

Outside the reaction container 30, a pair of electromagnetic coils 1-a and 1-b are arranged so that their respective axes coincide with the axes of the cylindrical heater 33 and the cylindrical high-frequency electrode 31. Is located in.

The output from the DC power source 2 is supplied to a pair of electromagnetic coils 1-a, 1-b, and the pair of coils 1-a, 1-b
1-b generates magnetic lines of force, that is, a magnetic field B, in the same direction as the axes of the heater 33 and the substrate 32. (Hereinafter, the letters B and E in magnetic field B and electric field E represent vectors).

FIG. 2 shows the relationship between the electric field E and the magnetic field B formed by the ground electrode 33 and the high frequency electrode 31 in the configuration of FIG. 1, (a) shows the state of the electric field on the horizontal plane of both electrodes,
(B) shows the relationship between the electric field and the magnetic field on the x, y, and z axes.

In FIGS. 2A and 2B, electrons and charged particles in the plasma generated in the ground electrode 33 and the high frequency electrode 31 due to the generation of the magnetic field B and the electric field E are respectively E
Receives xB drift. In addition, the electrons make Larmor orbital motion by the magnetic field B.

Due to these movements, the collision frequency of electrons with the reaction gas molecules is remarkably increased, and the plasma density is increased.
The film formation rate for forming the a-Si thin film is high. Furthermore, since the powder generated in plasma is generally negatively charged,
It moves like rotating around the magnetic field lines. That is,
The charged powder is promoted by the magnetic field B, and its movement toward the substrate 32 is suppressed.

FIG. 3 shows the results of investigation of the effect of suppressing the movement of such powder in the direction of the substrate 32. As a result of irradiating the vicinity of the cylindrical substrate 32 with laser light and measuring the scattered light intensity from the powder floating in that portion, the data as shown in FIG. 3 was obtained. According to the figure, pressure 0.5 ~
It was found that at 1 Torr, the scattered light intensity from the powder suddenly weakened when the magnetic field intensity was around 50 gauss.

That is, it was found that by applying a magnetic field B in the direction perpendicular to the electric field E formed by the pair of cylindrical electrodes 31, the amount of powder transported to the vicinity of the substrate surface is suppressed. . Therefore, such a plasma-enhanced chemical vapor deposition apparatus effectively acts to suppress powder mixed in the film during the formation of the a-Si thin film.

A specific example of manufacturing an amorphous silicon thin film in the above-described embodiment will be described. The inside of the reaction vessel 30 is evacuated by a vacuum pump (not shown). After the reaction container 30 is sufficiently evacuated, for example, 1 × 10 ⁻⁶
After reaching the pressure of 1 × 10 ⁻⁷ Torr, the reaction gas discharge pipe 35
From the above, for example, monosilane is supplied at a flow rate of about 100 to 150 cc / min, and the pressure in the reaction vessel 30 is set to 0.2 to 2.0.
Keep on Torr.

From the high frequency power source 37 to the high frequency electrode 31 via the impedance matching device 38, for example, 13.56 MH.
z High-frequency power of 200 W to 1000 W is supplied.

On the other hand, DC power is supplied from the DC power source 2 to the electromagnetic coils 1-a and 1-b to generate a magnetic field having a magnetic field strength of 10 to 100 gauss in the electromagnetic coils.

The film formation rate of the amorphous silicon thin film depends on the reaction gas flow rate, pressure, high frequency power and magnetic field strength. Therefore, an amorphous thin film was formed under the following conditions.

As reaction gas, 10% of 100% monosilane was used.
It is supplied at a flow rate of 0 cc / min and the pressure in the reaction vessel 30 is adjusted to 0.
It was set to 2 to 2.0 Torr. The high frequency power was 500 W and the strength of the magnetic field was 60 gauss. An example of the film formation result is shown in FIG.

According to this data, the pressure range 0.2-
At 2.0 Torr, since the refractive index is 3.2 or more, it is judged that the film is a good quality film free from the inclusion of powder. In the case of a-Si, if powder is mixed, the refractive index will be 3.2 or less,
According to the results shown in FIG. 4, the refractive index is 3.2 or more, indicating that no powder is mixed.

[0032]

As described above in detail, the present invention provides a reaction container, a reaction gas discharge hole in the reaction container, a reaction gas discharge hole, a pair of discharge cylindrical electrodes installed in the reaction container,
Power source for generating glow discharge in the discharge cylinder electrode, heater for heating the cylindrical substrate arranged between the electrodes, electromagnetic coil arranged to have the same axis as the discharge cylinder electrode, and direct current for supplying power to the electromagnetic coil Since it is configured to include a power supply, the following effects are achieved.

(1) A magnetic field B is added by an electromagnetic coil also in a direction parallel to the axis of the cylindrical discharge electrode to rotate E × B drift and negatively charged powder around the magnetic field B in the plasma. Since the movement was realized, the powder generated and growing in the plasma did not mix with the a-Si film on the substrate.

(2) As a result, a, which was conventionally regarded as difficult,
-Si film It became possible to prevent deterioration of film quality due to mixing of powder into the a-Si film during high-speed film formation. Therefore, the industrial value thereof in the manufacturing field of a-Si photosensitive drums, solar cells, photosensors, and the like is extremely large.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a plasma enhanced chemical vapor deposition apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an operation of the plasma enhanced chemical vapor deposition apparatus according to the embodiment of the present invention, in which (a) shows a state of an electric field in a horizontal plane of an electrode, and (b) shows x, y, z axes. The relationship between the electric field and the magnetic field is shown respectively.

FIG. 3 is a characteristic diagram of scattered light from powder obtained by the plasma chemical vapor deposition apparatus according to the embodiment of the present invention.

FIG. 4 is a characteristic diagram obtained by a plasma chemical vapor deposition apparatus according to an embodiment of the present invention, where (a) is a film forming rate, (b) is a refractive index, (c) is a photoconductivity, and (d) is ) Indicates dark conductivity, respectively.

FIG. 5 is a configuration diagram of a plasma chemical vapor deposition apparatus using a conventional cylindrical discharge electrode.

[Explanation of symbols]

 1-a, 1-b Electromagnetic coil 2 DC power supply 30 Reaction container 31 Cylindrical high frequency electrode 32 Cylindrical substrate 33 Cylindrical heater 34 Introducing pipe 35 Gas discharge pipe 36 Substrate holder 37 High frequency power supply 38 Impedance matching device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // H01L 31/04 H01L 31/04 V

Claims (1)

[Claims] 1. A reaction vessel; a reaction gas discharge hole for supplying a reaction gas into the reaction vessel; a reaction gas discharge hole for discharging the reaction gas in the vessel; an inner cylinder installed in the reaction vessel. A pair of discharge cylinder electrodes composed of an electrode and an outer cylinder electrode; a power supply for supplying glow discharge generation power to the discharge cylinder electrode; a cylinder arranged between the inner and outer cylinder electrodes of the discharge cylinder electrode A heater for heating the substrate; an electromagnetic coil having the same axis as the axis of the discharge cylindrical electrode and arranged outside the reaction container; and a direct current power source for supplying electric power to the electromagnetic coil. A plasma-enhanced chemical vapor deposition apparatus comprising: forming a thin film of the reaction gas on the cylindrical substrate.