JPH10172793A - Plasma generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To light plasma without arranging a lighting means in a vacuum vessel by providing a magnetic field generator to generate a magnetic field in the direction orthogonal to an electric field impressed between electrodes in a plasma generating region and an exciting pulse voltage generator to supply a pulse voltage to the magnetic field generator. SOLUTION: Mixed gas of monosilane and hydrogen is supplied by passing through a reaction gas introducing tube, and pressure in a vacuum vessel 1 is kept at 0.05 to 0.5Torr, and a voltage is impressed on electrodes from a high frequency power source. At the same time, a pulse voltage having a pulse width of about one second is impressed to solenoid coils 14a and 14b from an exciting pulse voltage generator 15, and magnetic force corresponding to the gas pressure is generated in a discharge region. Electron density in the early stage of discharge is increased, and glow discharge plasma is lighted and maintained between the electrodes by an electric field by a high frequency power source. In this way, a radical is generated in the plasma, and a uniform amorphous thin film can be formed on the reverse of a base board. Therefore, the vacuum vessel can be adjusted without being opened to the atmosphere, and damage to a based board can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma generator used for a plasma ion source, a plasma sputtering apparatus, etc., and more particularly, to an amorphous silicon solar cell,
The present invention relates to a plasma generation device used as a plasma chemical vapor deposition device (plasma CVD device) applied to the production of large-area thin films used for various electronic devices such as thin film transistors, optical sensors, and semiconductor protective films.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration diagram of a conventional plasma generator. FIG. 6 shows a configuration diagram of a conventional plasma CVD apparatus applied to manufacture a large-area amorphous silicon thin film.

[0003] First, the plasma generator of FIG. 5 will be described. In the vacuum vessel 1, an electrode 2 for generating glow discharge plasma and a ground electrode 3 are arranged to face each other. The electrode 2 is connected to the
Power having a frequency of 3.56 MHz is supplied via the impedance matching circuit 5, the first high-frequency cable 6, and the power introduction terminal 7. The ground electrode 3 is connected to the ground 9 via the vacuum vessel 1 and the second high-frequency cable 8. The ground terminal of the impedance matching circuit 5 is connected to the vacuum vessel 1 by a third high-frequency cable 10.

A predetermined gas is supplied into the vacuum vessel 1 from a cylinder (not shown) having a flow meter through a gas pipe 11, and the gas in the vacuum vessel 1 is passed through an exhaust pipe 12 to a vacuum pump (not shown). Exhausted by A trigger electrode 17 connected to a high-voltage pulse power supply 18 is provided inside the vacuum vessel 1.
Is arranged. Also, the plasma extraction mesh electrode 19 transfers the generated ions to another plasma processing chamber 20.
This is an electrode for drawing out.

[0005] This plasma generator is operated as follows. First, the inside of the vacuum vessel 1 is evacuated. afterwards,
For example, a mixed gas of monosilane and hydrogen is supplied through the reaction gas introduction pipe 11, and the pressure in the vacuum vessel 1 is reduced to 0.05.
~ 0.5 Torr, and from the high frequency power supply 4 to the electrodes 2,3
Voltage. In this state, the high-voltage pulse power supply 18
By applying a high voltage pulse to the trigger electrode 17, the electron density at the initial stage of the discharge is increased, and the glow discharge plasma is turned on and maintained between the electrodes 2 and 3 by the electric field applied by the high frequency power supply 4. When the trigger electrode 17 is not used, the plasma is turned on by increasing the voltage applied from the high frequency power supply 4 sufficiently.

Next, the plasma CVD apparatus shown in FIG. 6 will be described. The configuration of the discharge section of this plasma CVD apparatus is almost the same as that of FIG. That is, in the vacuum vessel 1, the electrode 2 for generating glow discharge plasma and the ground electrode 3 are arranged to face each other. Power of a frequency of, for example, 13.56 MHz is supplied to the electrode 2 from the high-frequency power supply 4 via the impedance matching circuit 5, the first high-frequency cable 6, and the power introduction terminal 7. The ground electrode 3 is connected to the ground 9 via the vacuum vessel 1 and the second high-frequency cable 8. The ground terminal of the impedance matching circuit 5 is connected to the vacuum vessel 1 by a third high-frequency cable 10.

A predetermined gas is supplied into the vacuum vessel 1 from a cylinder (not shown) having a flow meter through a gas pipe 11, and the gas in the vacuum vessel 1 is passed through an exhaust pipe 12 to a vacuum pump (not shown). Exhausted by The substrate 13 is arranged in parallel with the electrodes 2 and 3, that is, orthogonal to the electric field between the electrodes 2 and 3.

[0008] This plasma CVD apparatus is operated as follows. First, the inside of the vacuum vessel 1 is evacuated using a vacuum pump (not shown). Then, the reaction gas introduction pipe 11
, A mixed gas of monosilane and hydrogen is supplied, the pressure in the vacuum vessel 1 is maintained at 0.05 to 0.5 Torr, and a voltage is applied from the high frequency power supply 4 to the electrodes 2 and 3.
In this state, the trigger electrode 17 is
By applying a high voltage pulse to the electrodes, the electron density at the initial stage of the discharge is increased, and the glow discharge plasma is turned on and maintained between the electrodes 2 and 3 by the electric field applied by the high frequency power supply 4. When the trigger electrode 17 is not used, the plasma is turned on by increasing the voltage applied from the high frequency power supply 4 sufficiently. Thus, radicals are generated in the plasma, and a uniform amorphous thin film is formed on the surface of the substrate 13.

[0009]

In the conventional apparatus shown in FIGS. 5 and 6, when a high voltage pulse is applied to the trigger electrode 17 to turn on the plasma, the following problems occur. (1) Since the trigger electrode 17 needs to be mounted in the vacuum vessel 1, the trigger electrode 17 must be opened to the atmosphere for adjustment.
Setting is troublesome.

(2) Since the trigger electrode 17 is exposed in the vacuum vessel 1, it can be an impurity source particularly in a plasma CVD apparatus in which cleanness of the vacuum vessel 1 is required. on the other hand,
In the conventional apparatus shown in FIGS. 5 and 6, when a sufficiently high voltage is applied from the high-frequency power supply 4 to turn on the plasma without using the trigger electrode 17, the energy input at the beginning becomes large. This causes a problem that the substrate 13 serving as a base is damaged.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to turn on plasma without providing a lighting means serving as an impurity source in the vacuum vessel, adjust the plasma without opening the vacuum vessel to the atmosphere, and reduce the initial input energy. It is an object of the present invention to provide a plasma generating apparatus capable of preventing the substrate from being damaged by reduction.

[0012]

According to the present invention, there is provided a plasma generating apparatus comprising: a vacuum vessel; means for introducing and exhausting a raw material gas into the vacuum vessel; a ground electrode housed in the vacuum vessel; An electrode, in a plasma generator having a power supply for supplying glow discharge power to the plasma generation electrode, a magnetic field generator that generates a magnetic field in a direction orthogonal to an electric field applied between the electrodes in a plasma generation region; A plasma lighting means including an excitation pulse voltage generator for supplying a pulse voltage to the magnetic field generator is provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A plasma generator according to the present invention generates a magnetic field in a direction perpendicular to an electric field applied between electrodes in a plasma generation region, and supplies a pulse voltage to the magnetic field generator. A plasma lighting means having an excitation pulse voltage generator is provided. At the start of plasma generation, a magnetic field is instantaneously (pulsely) generated, and by utilizing the property of the movement of electrons wrapping around the lines of magnetic force, electrons are instantaneously captured in the plasma generation region to turn on the plasma. Like that.

At this time, if the following conditions (I) to (III) can be satisfied, the number of times of ionization can be increased, so that the effect of lowering the firing voltage can be obtained. (I) The capture radius of the charged particles due to the magnetic field (referred to as Larmor radius) is smaller than 1/2 of the distance between the electrodes.

(II) The collision frequency of electrons due to a magnetic field is higher than the collision frequency with neutral particles (gas) due to thermal motion of electrons. (III) Regarding the collision between electrons and neutral particles, between one collision and the next collision, electrons are sufficiently accelerated by the electric field and have sufficient energy to ionize the medium gas.

Hereinafter, the conditions (I) to (III) will be analyzed in more detail. In the following discussion, B: magnetic flux density (T), κ: Boltzmann constant = 1.6 × 10 ⁻¹⁹ (J /
eV), _Te : electron temperature (eV), _me : electron mass =
9.1 × 10 ⁻³¹ (kg), e: electronic charge = 1.6 × 1
0 ^-19 (C), d: distance between electrodes (m), N: density of neutral particles (gas) (m ^-3 ), σ: cross section of collision between electrons and neutral particles (m ² ), V _e : The electron thermal velocity (m / s).

First, the condition (I) will be examined. The electrons make a circular motion that receives the interaction force between the thermal motion of the electrons and the magnetic field as a centripetal force, so the Larmor radius R is expressed by the following equation.

[0018] _{R = m e V e / (} e · B) = m e (3κT
_e / _me ) ^1/2 / (eB) Therefore, the condition (I) is expressed by the following equation. m _e (3κT _e / m _e ) ^1/2 / (e · B) <d / 2 (3) As can be seen from the equation (3), it is desirable that the applied magnetic field be large. By rearranging this equation (3), the following equation (1) is derived.

B> 2 (3κT _e m _e ) ^1/2 / (ed) (1) Next, the condition (II) will be examined. The electron collision frequency f _ee is represented by the period of a circular motion due to a magnetic field.

F _ee = e · B / (2πm _e ) (4) On the other hand, the electron-neutral particle collision frequency f due to the thermal motion of electrons
_eg is described by the following equation using the particle density and the collision cross section equivalent to the pressure of the neutral particles.

[0021] _{f eg = V e (2)} 1/2 Nσ = (6κT e / m e) 1/2 Nσ (5) Therefore, the condition of (II) is represented by the following formula. By organizing _{e · B / (2πm e)} > (6κT e / m e) 1/2 Nσ this equation, the following equation (2) is derived.

[0022] B> 2 [pi As can be seen from ^{_{(6κT e m e) 1/2 Nσ}} / e (2) Equation (2), magnetic flux density and neutral density of the magnetic field to act is proportional. For example, in the case of a magnetic flux density of about 100 gauss that can be normally operated,
The upper limit of the gas pressure is about 100 mTorr.

Finally, it is difficult to generalize the condition (III) because it greatly differs depending on the type of gas and the arrangement of electrodes (electric field application method). Of the above conditions,
It can be seen that the conditions (I) and (II) are necessary conditions for lowering the firing voltage using a magnetic field. Then, by applying a magnetic field to the discharge under a low vacuum of about 100 mTorr or less, the discharge can be started and maintained without changing the energy input at the start of the discharge. That is, since the energy input at the start of the discharge can be reduced as compared with the case where no magnetic field is applied, damage to the substrate can be suppressed.

[0024]

Embodiments of the present invention will be described below. FIG. 1 is a structural view of a plasma CVD apparatus according to the present invention, and FIG. 2 is a plan view of the same figure. In the vacuum vessel 1, an electrode 2 for generating glow discharge plasma and a ground electrode 3 are arranged to face each other. Power of a frequency of, for example, 13.56 MHz is supplied to the electrode 2 from the high-frequency power supply 4 via the impedance matching circuit 5, the first high-frequency cable 6, and the power introduction terminal 7. The ground electrode 3 is connected to the ground 9 via the vacuum vessel 1 and the second high-frequency cable 8. The impedance matching circuit 5
Is connected to the vacuum vessel 1 by a third high-frequency cable 10. A predetermined gas is supplied into the vacuum vessel 1 from a cylinder (not shown) having a flow meter through a gas pipe 11, and the gas in the vacuum vessel 1 is exhausted by a vacuum pump (not shown) through an exhaust pipe 12. You. The substrate 13 is arranged in parallel with the electrodes 2 and 3, that is, orthogonal to the electric field between the electrodes 2 and 3.

As shown in FIGS. 1 and 2, a pair of finite length solenoid coils 14a for generating a magnetic field in a direction orthogonal to an electric field applied between the electrodes 2 and 3 are provided outside the vacuum vessel 1. , 14b, and an excitation pulse voltage generator 15 for supplying a pulse voltage to these coils 14a, 14b.

This plasma CVD apparatus is operated as follows. First, the inside of the vacuum vessel 1 is evacuated using a vacuum pump (not shown). Then, the reaction gas introduction pipe 11
, A mixed gas of monosilane and hydrogen is supplied, the pressure in the vacuum vessel 1 is maintained at 0.05 to 0.5 Torr, and a voltage is applied from the high frequency power supply 4 to the electrodes 2 and 3.
At the same time, a pulse voltage having a pulse width of about 1 second is applied to the coils 14a and 14b from the excitation pulse voltage generator 15 to generate a magnetic force (about 100 gauss) in the discharge region according to the gas pressure. As a result, the electron density at the initial stage of the discharge increases, and the glow discharge plasma 16 is turned on and maintained between the electrodes 2 and 3 by the electric field generated by the high frequency power supply 4. Thus, radicals are generated in the plasma, and a uniform amorphous thin film can be formed on the surface of the substrate 13.

As described above, the coils 14a and 14b and the excitation pulse voltage generator 15 provided outside the vacuum vessel 1 are provided.
Since plasma can be lit by the plasma lighting means provided with these, these plasma lighting means do not become an impurity source. Further, the plasma lighting means can be adjusted without opening the vacuum vessel 1 to the atmosphere. Moreover, in the plasma CVD apparatus of the present invention, the initial input energy can be reduced to prevent the substrate from being damaged. Specifically, an argon pressure of 50 mT
An experiment was conducted in which plasma was turned on under the conditions of orr (neutral particle density: 1.6 × 10 ²¹ cm ⁻³ ), the distance between electrodes: 40 mm, and the input power density: 0.01 W / cm ² . As a result, whereas the conventional device did not discharge without the use of the trigger electrode, the device of the present invention starts the discharge without using the trigger electrode by applying a magnetic field having a magnetic flux density of 100 Gauss. I was able to.

In particular, the plasma is lit using plasma lighting means such as the apparatus of the present invention, and the amorphous thin film is formed by applying a rotating magnetic field as disclosed in Japanese Patent Application No. 4-113336. By forming, a high-quality amorphous thin film can be formed at high speed.

In the above embodiment, the present invention is applied to the plasma C
Although the case where the present invention is applied to a VD apparatus has been described, the present invention can be generally applied to a plasma generator that generates high-frequency discharge plasma. A general plasma generator according to the present invention will be described with reference to FIGS. FIG.
The plasma generating apparatus shown in FIG. 4 has a magnetic field in the direction orthogonal to the electric field applied between the electrodes 2 and 3 outside the vacuum vessel 1 instead of the trigger electrode 17 and the high-voltage pulse power supply 18 in the apparatus shown in FIG. And a pair of finite length solenoid coils 14a, 14b,
4b is provided with a plasma lighting means provided with an excitation pulse voltage generator 15 for supplying a pulse voltage to 4b. Even with such a plasma generator, the same effects as in the case of the plasma CVD apparatus shown in FIGS. 1 and 2 can be obtained.

[0030]

As described above in detail, according to the present invention, plasma can be turned on without providing a lighting means serving as an impurity source in the vacuum vessel, adjustment can be made without opening the vacuum vessel to the atmosphere, and initial charging can be performed. It is possible to provide a plasma generator that can reduce energy and prevent damage to a substrate.

[Brief description of the drawings]

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

FIG. 2 is a plan view of FIG. 1;

FIG. 3 is a configuration diagram of a plasma generator according to an embodiment of the present invention.

FIG. 4 is a plan view of FIG. 3;

FIG. 5 is a configuration diagram of a conventional plasma generator.

FIG. 6 is a configuration diagram of a conventional plasma CVD apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vacuum container 2 ... Electrode for plasma generation 3 ... Ground electrode 4 ... High frequency power supply 5 ... Impedance matching circuit 6 ... 1st high frequency cable 7 ... Power introduction terminal 8 ... 2nd high frequency cable 9 ... Ground 10 ... 3rd high frequency Cable 11: Gas pipe 12: Exhaust pipe 13: Substrate 14a, 14b: Solenoid coil 15: Pulse voltage generator for excitation 16: Glow discharge plasma 19: Mesh electrode for extracting plasma 20: Plasma processing chamber

Claims (3)

[Claims] 1. A vacuum vessel, means for introducing and exhausting a source gas into the vacuum vessel, a ground electrode and a plasma generation electrode housed in the vacuum vessel, and a glow discharge electrode A plasma generator having a power supply for supplying power, a magnetic field generator for generating a magnetic field in a direction orthogonal to an electric field applied between the electrodes in a plasma generation region, and an excitation for supplying a pulse voltage to the magnetic field generator A plasma generator comprising a plasma lighting means having a pulse voltage generator. 2. A pulse voltage is supplied to the magnetic field generator from the excitation pulse voltage generator to generate a magnetic flux density that satisfies the following equations (1) and (2). The plasma generator according to claim 1, wherein plasma is turned on during the period. _{B> 2 (3κT e m e} ) 1/2 / (e · d) (1) B> 2π (6κT e m e) 1/2 Nσ / e (2) ( where, B: magnetic flux density (T) , Κ: Boltzmann constant =
1.6 × 10 ⁻¹⁹ (J / eV), _Te : electron temperature (e
V), _me : electron mass = 9.1 × 10 ⁻³¹ (kg),
e: electron charge = 1.6 × 10 ⁻¹⁹ (C), d: distance between electrodes (m), N: density of neutral particles (gas) (m ⁻³ ), σ: collision between electron and neutral particles Area (m ² ). ) 3. A plasma CVD apparatus for supporting a substrate so as to be orthogonal to an electric field applied between a plasma generating electrode and a ground electrode and forming an amorphous thin film on the substrate. The plasma generator according to claim 1.