JPS634449B2 - - 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 method (hereinafter referred to as PCVD) using glow or arc discharge. This invention relates to a plasma reaction device.

When performing PCVD in the present invention, generally a substrate having a surface to be formed is placed in a PCVD apparatus, and the vacuum is once evacuated to 1×10 ^-3 to ^{10 -5} torr, and then the degree of vacuum in this is reduced to 0.05 to 10 -5 torr. Achieved by introducing reactive gas to 3torr. Then, electrical energy of a predetermined output is applied to this reactive gas from the outside through a pair of electrodes to cause plasma discharge, and a reaction product from this plasma-turned reactive gas is 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, especially when trying to give this electrical energy at a low energy of 50W 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, then reduce the output to 5 to 10 W. Nakatsuta.

Furthermore, when trying to apply this high frequency output to a reactive gas, matching is required between them. However, this matching cannot find a matching point unless a discharge is generated or electrical energy is applied.

For this reason, even in an automatic matching type PCVD device, after a high output is applied to cause discharge, a matching point is found, and the supplied electrical energy is further lowered to a predetermined output. This work was necessary.

However, this process is extremely difficult when laminating the first, second, etc. semiconductor layers thinly on a transparent conductive film using the PCVD method, and when trying to prevent the impurities added to each of these semiconductor layers from mixing with each other. It becomes a big obstacle. This high energy spatters (damages) the surface to be formed, especially during the few seconds it takes to find a matching point with a constant high power, and during the transient phenomenon at the moment when matching is achieved.
Even short range orders of ~100 Å lead to disorder. Therefore, the number of recombination centers at this interface increases, and the PIN is formed on the transparent conductive film by the semiconductor.
When attempting to form a junction, the transparent conductive film and the P-type semiconductor layer mix, and the conductivity of the conductive film is lost due to the P-type semiconductor layer. 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, the discharge output is increased to 20~
In the time it takes to reduce from 30W to 5 to 10W,
A semiconductor layer is formed on the surface to be formed using high discharge energy, and for example, during the production of an I layer, this output may cause the transparent conductive film to peel off from the glass surface of the substrate, or cause ITO (indium tin oxide alloy) to peel off from the glass surface of the substrate. ), oxygen was liberated and metal indium was precipitated, resulting in a clouding phenomenon.

The present invention has been made to eliminate such drawbacks, and has a capacitive electrode that forms a pair of coils or wiring for promoting discharge so that plasma CVD discharge can be carried out without any problem even at 2 to 5 W. This is a time period.

Furthermore, regarding matching, PCVD is 5~
When trying to perform the operation with 10W, first supply a low output of 1~2W, find the impedance in this reactive gas and perform matching, then 5~
It is characterized by the fact that it generates a plasma reaction by applying an output of 10W.

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 inter-electrode resistance are Zc, R,
Let Zc' and R' be during discharge, and let the frequency at that time be 13.56 MHz (time constant is ω). Zc = R + 1/jωc Zc' = R' + 1/jωC where R≫R' and this retactance component 1 ±jωL is given by a matching circuit so as to cancel /jωC. Then, the impedance component becomes Zc=R, which is only 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. Further, when a discharge occurs, the resistance of this resistance component R becomes 1/100 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.

As is clear from this intermediate circuit, an auxiliary circuit 43 is shown in parallel with the main circuit by a resistive (1 to 300 Ω) wiring made of a plasma discharge promoting coil or a thin nichrome wire. 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 Zs=
At r+jωL, since this r is a small value, 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,
The resistance component of the main circuit 44 is also low, R', and no strong kinetic energy is imparted to the reactive gas at the start of discharge. Furthermore, this discharge in the main circuit causes a discharge in the auxiliary circuit to occur.
It is important to stop or sufficiently reduce Zs≫Zc. That is, it is important to set Zc>Zs>Zc′, preferably Zc≫Zs≫Zc′.

It has been 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 spatter effect on the surface to be formed in the plasma vapor phase method, which has not been seen in the conventional method without an auxiliary circuit.

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

Example 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 thereof is arranged parallel to the electric field direction of a pair of capacitively coupled electrodes 3 and 4 having an electrode area of 5 to 500 cm2. Prevents surfaces from being damaged by reactive gases. Furthermore, this electrode 3,
4 has an electric energy supply power source 6, and the substrate 1 is heated to a temperature of 100 to 500° C. by a resistance heating furnace 7. There are impedances Zc and Zc' between the electrodes 3 and 4, and an auxiliary circuit 5 connecting these two electrodes with a coil has an impedance of _ZL .

For example, when a non-single crystal semiconductor is to be manufactured, the reactive gas flows from the inlet 8 to the outlet 9, and then to the pressure adjustment needle valve 18, stop valve 19, and rotary pump 10.

The reactive gas is introduced, for example, when a semiconductor having a PIN junction is to be manufactured, by supplying silane from 14 through a flow meter 16 and a valve 15. Also P
A valent impurity, such as TMG (trimethylgallium Ga(CH ₃ ) ₃ ), which is a mold impurity, is removed with hydrogen.
A doping gas 13 diluted to 1000 PPM was used, and TMA (trimethylantimony Sb (CH ₃ ) ₃ ), which is a V-valent impurity, was supplied from 12 with hydrogen diluted to 1000 PPM. 11, hydrogen or helium as a carrier gas was supplied.

In this way, a reactive gas containing 0.1 to 1 mol% of gallium added to silicon on a substrate having a transparent conductive film of ITO and tin oxide (with 2 to 10% of antimony oxide added), for example, a glass substrate 1, is heated in a reactor. This system was sufficiently evacuated to remove residual oxygen, and then the pressure was adjusted to 0.05 to 1 torr.

Thereafter, high frequency energy with 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 line of time charts for supplying this electrical energy is shown in FIG.

Figure 3A is a time chart when there is no auxiliary circuit. Supplying electrical energy 26 Finding the matching point 27 Matching state Moving transient state 28
Adjusting the optimal output 30 PCVD is being performed at the optimal output 31.

In this figure 3A, the incident output 23 reflected output 2
The difference of 4 is the power applied to the reactive gas. As is clear from the drawings, the initial state 31 was much higher than the output 25 during PCVD, and sputtering occurred on the surface to be formed even in the transient states 28 and 30. For this reason, it has been impossible to uniformly form this P-type semiconductor layer on the conductive electrode with an extremely thin thickness of 50 to 150 Å 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.

Because this auxiliary circuit is installed, the initial discharge can also be reduced by A.
It was found that this could be achieved with 3W rather than 22W, and therefore no damage was caused to the surface to be formed. 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 can damage the substrate at the start of the discharge. It did not provide strong kinetic energy that was easy to do.

This induces strong plasma in the auxiliary circuit as shown in Figure 2, and by spreading this strong plasma toward the main electrode, the main electrode 3, which is necessary for starting the discharge,
This is due to lowering the voltage at 4.

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 μm using the same process. When the auxiliary circuit of the present invention is used, even when forming this I-type semiconductor layer, P
Since the type semiconductor layer is not sputtered, it is possible to minimize the incorporation of impurities having a higher value than the P type semiconductor layer into the I type semiconductor layer due to autodoping.

In other words, if boron is used as the valence impurity in the conventional method, impurities of 1 to 3 x 10 ¹⁷ cm ^-3 are mixed in.
Using the method of the present invention, this could be reduced to 2 to 5×10 ¹⁶ cm ⁻³ . In addition, in the method of the present invention using gallium as the impurity with the above-mentioned value, since there is no suction effect due to hydrogen, 0.3~
It was possible to lower the temperature 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 the surface perpendicularly to the surface on which it is formed, sputtering occurs at the same time.

That is, in the plasma reaction apparatus of the present invention, the initial discharge is sufficiently low to eliminate the spatter effect on the surface to be formed, and an electric field is applied along the surface to be formed so that the reactive gas flows along the surface. The ideal interface is to have all of the following: eliminate the spatter effect, make the initial discharge lower than the main discharge, and perform matching there to reduce damage to the substrate during transient conditions. An electrode having a P-type semiconductor layer, P
type semiconductor layer - I type semiconductor layer further I type semiconductor layer -
This is an important matter for creating an N-type semiconductor layer.

As the reactive gas formed in the present invention, a non-single crystal semiconductor of silicon was used. However, this is produced by mixing methane and silane to produce SixC _1-x (0<x<1), and by reacting silane and ammonia to create Si ₃ N _4-x (0<x
<4) It is also effective in the case of different materials or lamination of different materials.

In addition, the material formed is amorphous or 5-
It is also effective for semi-amorphous semiconductors with regularity of 100 Å or non-single-crystal semiconductors that also have growth properties and have a fiber structure on the surface on which they are formed.

The embodiment of 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 filed by the inventor for semiconductor device manufacturing equipment (No. 56-192292, 192293)
S56.11.30). It goes without saying that the present invention can be applied to such a plasma CVD apparatus as is.

Example 2 FIG. 4 shows another structure of the present invention.

In this reactor, reactive gas is discharged downward from an inlet 8 through a spout that serves as one electrode, and a plasma discharge is created between the pair of electrodes 3 and 4. . 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 from 6 to a pair 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 sandwiched therebetween to prevent parasitic discharge from occurring between the electrode and the stainless steel reactor. The substrate having a surface to be formed is
In this case, it was 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 the tuning for mismatching can also be performed in a low output state. .

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, the present invention is capable of generating a high discharge of 15 to 50 W to start the discharge when attempting to generate a discharge at a low output of 1 to 20 W in a capacitively coupled plasma reaction. This can be achieved by simply connecting two electrodes with electrical wiring using a conductive wire or a resistive conductor of 5 to 100Ω without damaging the surface to be formed, and compared to the magnitude of its industrial effect. Extremely easy plasma
We were able to evaluate the characteristics of the film formed by CVD.

[Brief explanation of the drawing]

FIG. 1 shows an equivalent circuit for implementing the invention. Figure 2 shows plasma created using the present invention.
An overview of the CVD equipment is shown. FIG. 3 shows a time chart of high frequency discharge power in the conventional and inventive reactors. Figure 4 shows the plasma of the present invention.
Another example of the CVD apparatus is shown.

Claims (1)

[Claims] 1. A step of filling a plasma gas phase reactor with a reactive gas to a predetermined pressure, and supplying a capacitive discharge electrode with electrical energy lower than the electrical energy that causes the plasma vapor phase reaction to occur. 1. A plasma vapor phase reaction method comprising: a step of applying this electrical energy and tuning the impedance between the electrodes; and a step of supplying predetermined electrical energy for carrying out a plasma vapor phase reaction. 2. In claim 1, by supplying low electrical energy and performing matching,
A plasma vapor phase reaction method characterized by causing an auxiliary circuit section to perform plasma discharge.