JPS6044970B2 - Plasma reaction equipment - Google Patents

Description

[Detailed Description of the Invention] The present invention enables soft start of plasma discharge to be performed with good reproducibility in a plasma reactor for implementing plasma vapor phase deposition (hereinafter referred to as PCVD) using glow or arc discharge. This invention relates to a plasma reaction device.

In the present invention, when performing PCVD, generally a substrate having a surface to be formed is placed in a PCVD apparatus, and a 1×10-
3 to 10-5 is evacuated to 0 torr, and then a reactive gas is introduced to bring the degree of vacuum therein to 0.05 to 3 torr.

Then, a predetermined output of electrical energy is applied to this reactive gas from the outside to a pair of electrodes to cause plasma discharge, and reaction products from this plasma-turned reactive gas are formed on the surface to be formed. be. However, when such an operation is actually performed, it does not turn out as such.

And when trying to give electrical energy at a predetermined output,
In particular, when trying to apply the electric energy at a low energy of 50 W or less, this plasma discharge does not occur. For this reason, when trying to apply a plasma output of 5 to 10 W, for example, it is necessary to increase the output to 20 to 30 W to start the discharge, discharge, and then reduce the output to 5 to 10 W. I didn't get it. Furthermore, when trying to give this high frequency output to a reactive gas, the tuning (
matching) is required.

However, this matching cannot find a tuning point unless a discharge is made or electrical energy is applied. For this reason, even in the case of an auto-matching type PCVD apparatus, a high output is applied once to cause discharge, two matching points are searched, and the supplied electrical energy is further lowered to a predetermined output.

This work was necessary. However, this work is PCVD
When thin first and second semiconductor layers are laminated on a transparent conductive film by a method and it is attempted to prevent impurities added to each of these semiconductor layers from being mixed into each other, this becomes a very serious problem.

This high energy sputters (damages) the surface to be formed, especially during the few seconds it takes to search for a matching point with a constant high power, and during the transient phenomenon at the moment when matching is achieved. Even the short range order of causes disorder. For this reason, the number of recombination centers at this interface increases, and when an attempt is made to make a PIN junction on a transparent conductive film using a semiconductor, the transparent conductive film and the P-type semiconductor layer mix, and the conductive film becomes conductive due to the P-type semiconductor layer. It loses its sexuality. Furthermore, when attempting to fabricate an I-type semiconductor layer, impurities such as boron in the P-type semiconductor are mixed into this I layer. In addition, after matching is achieved, a semiconductor layer is formed on the surface to be formed with high discharge energy during the time until the discharge output is lowered from 20 to 30 W to 5 to 10 W, and for this reason, for example, an I layer is formed. During this time, due to this output, the transparent conductive film was peeled off from the glass surface of the substrate, and in ITO (indium oxide tin alloy), oxygen was liberated and metal indium was precipitated, causing a clouding phenomenon.

The present invention has been made to eliminate such drawbacks, and the discharge of plasma CVD has a smell of 2 to 5 W! However, a coil or wiring for promoting discharge is provided between the pair of capacitive electrodes so that the discharge can be carried out without any problems.

Furthermore, regarding matching, when trying to perform PCVD at 5 to 10 W, first supply a low output power of 1 to 2 W, find the impedance in this reactive gas and perform matching, and then increase the output power to 5 to 10 W. It is characterized by the fact that a plasma reaction is carried out by adding .

The details will be explained below with reference to the drawings.

FIG. 1 shows the principle of operation of the invention.

Between the pair of capacitively coupled electrodes 3 and 4, the impedance and interelectrode resistance are set to 1 before discharge, R1 during discharge, and R
'', and when that time is a frequency such as 13.56 MHz (time constant is ω), where R>>R″, +JO)L is given by a matching circuit so as to cancel out this retactance component 1/jωc.

Then, the impedance component becomes only ZC=R and the resistance component. This state indicates a so-called matching (synchronization) state. However, even if this matching is achieved, it does not necessarily mean that a discharge will occur.

When discharge occurs, the resistance of this resistance component R becomes 11,100 or less due to the plasma formation of the reactive gas, and the electrical energy supply source 6 or 10 continues to supply energy to maintain the plasma. In addition, as is clear from this intermediate circuit, there is a resistance (1~
An auxiliary circuit 43 is shown by wiring (300Ω).

Since this circuit uses a voltage-driven capacitive glow discharge method, the voltage required for discharge must be applied between electrodes 3 and 4, and the resistance component R before discharge is sufficiently large, so the initial It is extremely difficult to generate a discharge with low electrical energy. For this reason, this drive circuit is provided with an auxiliary circuit mainly using an inductance component for current drive.

Then, the impedance of this auxiliary circuit is r + j (J)
Since r is a small value at L, a current flows through this auxiliary circuit, and as a result, an initial discharge can be caused in this auxiliary circuit with a low applied voltage. Then, this discharge plasma spreads, and the resistance component of the main circuit 44 becomes as low as R'', and strong kinetic energy is no longer imparted to the reactive gas at the start of the discharge.Furthermore, the generation of discharge in this main circuit reduces the resistance component to R''. It is important that the discharge in the circuit is stopped or made sufficiently small by its m〉l, ie l>Zs>l'', preferably l>>Zs>>l''.

It was found that by doing this, matching and plasma discharge can be achieved with low energy even in a capacitively coupled electrode structure.

Further, this auxiliary circuit 43 may be a single wire, or may have a coil structure wound several times to several hundred times. In this way, it was possible to sufficiently reduce the initial sputtering effect on the surface to be formed in the plasma vapor phase method, which is unprecedented in the conventional method without an auxiliary circuit.

Examples thereof will be described below with reference to the drawings.

Embodiment 1 FIG. 2 shows an outline of a plasma CVD apparatus having a cylindrical reactor according to the present invention.

In the drawing, a substrate 1 having a surface to be formed is inserted into a reactor 2, and the surface is arranged parallel to the electric field direction of a pair of capacitive coupling electrodes 3 and 4 having an electrode area of 5 to 50 cIt. is protected from damage by reactive gases.

Further, the electrodes 3, 4 have an electric energy supply source 6, and the substrate 1 is heated in a resistance heating furnace 7 to a temperature of 100 to 500°C. There is an impedance of 1.1'' between the electrodes 3 and 4, and the auxiliary circuit 5 connected between these two electrodes by a coil has an impedance of Z3L.The reactive gas is, for example, a non-single crystal semiconductor. When trying to produce a liquid, the inlet 8 leads to the outlet 9, the pressure regulating needle valve 18, the stop valve 19, and the rotary pump 10.

The reactive gas is introduced, for example, when a semiconductor having a PIN junction is to be manufactured, silane is supplied from 14 through a flow meter 16 and a valve 15.

In addition, a P-type impurity, such as TMG (trimethylgallium Ga(CH2)3), is added to 1 by hydrogen.
With the doping gas 13 diluted to 000 PPM,
Further, TMA (trimethylantimony Sb(CH2)3), which is a V-valent impurity, was diluted with hydrogen to 1000 PPM and supplied from 12. 11, hydrogen or helium as a carrier gas was supplied.

Thus, a reactive gas containing 0.1 to 1 mol % of gallium added to silicon is reacted onto a substrate having a transparent conductive film of ITOl tin oxide (with 2 to 10% of antimony oxide added), for example, glass substrate 1. This system was sufficiently evacuated to remove residual oxygen and then supplied to the furnace 2, and the pressure was set at 0.05 to 1 t0rr.

Thereafter, high frequency energy at a frequency of 0.1 to 100 MHz, for example 13.56 MHz, was supplied from 6 to the electrodes 3 and 4 to cause a plasma reaction.

A sequence of time charts for supplying this electrical energy is shown in FIG.

Figure 3A is a time chart when there is no auxiliary circuit. Supply of electrical energy 26 Searching for matching point 27 Matching state Moving transient state 28 Adjusting optimal output 30
PCVD is currently being performed at the optimum output.

In FIG. 3A, the difference between the incident power 23 and the reflected power 24 is the power applied to the reactive gas.

As is clear from the drawing, the initial state 31 is extremely high compared to the output 25 during PCVD, and the transient state 28, 3
Even in the case of 0, the surface to be formed was sputtered.
For this reason, this P-type semiconductor layer is placed on the conductive electrode at 50 to 15
It was impossible to manufacture the electrode uniformly at an extremely thin thickness of 0A without causing any damage to the electrode. FIG. 3B shows a case where the auxiliary circuit of the present invention shown in FIG. 2 for this purpose is added.

Since this auxiliary circuit was installed, the initial discharge was also 22W (4).
It has been found that this can be achieved with 3W, and therefore the surface on which it is formed is not damaged at all.

Furthermore, in this (B), the initial discharges 31 and 32 can be made the same or weaker than the main discharge 21 during PCVD, so the voltage required to start the discharge is small, and therefore the reactive gas is exposed to the substrate at the start of the discharge. There was no need to apply strong kinetic energy that could easily damage the product. This is because strong plasma is induced in the auxiliary circuit as shown in Figure 2, and by spreading this strong plasma toward the main electrodes, the voltage at the main electrodes 3 and 4 required to start the discharge is lowered. . In this way, a P-type semiconductor layer as shown in FIG. 2 was fabricated.

Thereafter, an I-type non-single-crystal silicon semiconductor layer and a P-type semiconductor layer were formed in this reactor or another reactor to a thickness of 0.3 to 0.6 μm using the same process. When the auxiliary circuit of the present invention is used, even when forming this I-type semiconductor layer,
There is no sputtering of the P-type semiconductor layer that constitutes the formation surface below it, and therefore, it is possible to extremely minimize the incorporation of valent impurities from this P-type semiconductor layer into the I-type semiconductor layer by autodoping. did it. In other words, if boron is used as the valence impurity in the conventional method, 1 to 3 017
There is an impurity of cm-3 mixed in, and when this is used in the method of the present invention, it becomes 2 to 5 x 1016c! I was able to lower it to n-3.

In addition, in the method of the present invention using gallium as the above-mentioned impurity with a valence of 2, since there is no suction effect due to hydrogen, it was possible to lower the concentration to 0.3 to 1×10 16 cm −3 . Furthermore, the present invention is further improved by forming the I-type semiconductor layer at such a low power, disposing the discharge electrode in the direction of the flow of the reactive gas, and arranging the surface to be formed in that direction as shown in the figure. It's enabled. This is because when the substrates are placed perpendicular to the electric field, the thickness of the film formed on each substrate becomes non-uniform, and because the reactive gas hits perpendicularly to the surface on which it is formed, sputtering occurs at the same time. That is, in the plasma reactor of the present invention, (1) the initial discharge is sufficiently low to eliminate the sputtering effect on the surface to be formed, and (2) an electric field is applied along the surface to be formed so that the reactive gas flows along the surface. However, it is ideal to have all of the following: eliminating the sputtering effect, and minimizing damage to the substrate during transient conditions by making the initial discharge lower than the main discharge and matching there. This is an important matter in creating an electrode-P-type semiconductor layer, a P-type semiconductor layer-1-type semiconductor layer, and an I-type semiconductor layer-N-type semiconductor layer, which have such interfaces.

As the reactive gas formed in the present invention, a non-single crystal semiconductor of silicon was used.

However, this is SiXC, which is made by mixing methane and silane.
It is also effective in the case of different materials such as l-π(0<x×1), Si3N4-π(a)<X<4) produced by the reaction of silane and ammonia, or a stack of different materials. It is also effective in the case where the material to be formed is an amorphous or semi-amorphous semiconductor having an order of 5 to 100 A, or a non-single crystal semiconductor which has a growth property and has a fiber structure on the surface on which it is formed.

The embodiment shown in FIG. 2 has only one cylindrical reactor. However, a plurality of these may be connected, for example, to form P, I, and N type semiconductor layers independently. In this case, the patent application to be filed by the inventor: Semiconductor device manufacturing equipment (
56-192292, 192293, S56.11.3
0). The present invention is directed to such plasma CVD.
Needless to say, the present invention can also be applied to devices as is. Embodiment 2 FIG. 4 shows another structure of the present invention.

In this reactor, reactive gas is discharged downward from an inlet 8 and a spout that serves as an electrode on the saw side, and a plasma discharge is created between the pair of electrodes 3 and 4. be. Heating of the substrate is accomplished by a heater 7 and an electrode 17 at another electrode 4 in the drawing. The auxiliary circuit 5 was in this case placed inside the reactor and had the same effect as when placed outside the reactor as in Example 1. High frequency energy is supplied to six pairs of electrodes 3 and 4. Discharge 9 of the reaction products is carried out by a rotary pump 10. In the present invention, the electrode 3 is covered with a ground 22 with a ceramic 27 in between to prevent parasitic discharge between the electrode and the stainless steel reactor. The substrate with the surface to be formed was in this case placed on the electrode 4 for heat conduction. If this heating is done by radiation method using infrared lamps, the heating can be done in parallel to and perpendicular to the flow of the reactor, as shown in FIG. In either case, by providing the auxiliary circuit 5 in this embodiment as well, the initial discharge can be made lower than the main discharge, and tuning for mismatching can also be performed in a low output state. Ta.

Therefore, damage caused by plasma discharge on the surface to be formed can be almost completely eliminated compared to the conventional method.

As is clear from the above explanation, in a capacitively coupled plasma reaction, when discharging is to be performed at a low output of 1 to 20 W, the present invention provides a power supply of 15 to 50 W to start the discharge.
This can be achieved by connecting two electrodes with electrical wiring using a conductive wire or a resistive conductive wire of 5 to 100 Ω without damaging the surface to be formed by generating a high discharge, and its industrial effects. The characteristics of the film formed by plasma CVD could be determined very easily compared to the size of the film.

[Brief explanation of drawings]

FIG. 1 shows an equivalent circuit for implementing the invention.

Claims (1)

[Scope of Claims] 1. A plasma reaction space having a cylindrical shape, means for heating the reaction space, a pair of discharge capacitive electrodes disposed in the reaction space, and a power source supplying electrical energy to the electrodes. and a substrate having a surface to be formed in the plasma reaction space, further comprising an auxiliary circuit connected or disposed between the pair of electrodes for lowering glow or arc discharge initiation output. A plasma reaction device characterized by: 2. In claim 1, the auxiliary circuit for lowering the discharge start output power has an inductance component,
The impedance of the auxiliary circuit is Zc>Zs>Zc′ However, Zc is the impedance between the electrodes before the start of discharge, and Z
A plasma reaction device characterized in that c' has an impedance relationship between the electrodes after the start of discharge. 3. The apparatus for plasma reaction according to claim 1, characterized in that the surface of the substrate having the surface to be formed in the plasma reaction space is arranged along the lines of electric force applied between the pair of capacitive electrodes.