JPS6151631B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to plasma gas phase reaction (hereinafter referred to as PCVD). This invention is a capacitively coupled type method, and when forming a film in a large area by PCVD, especially when the electrode area is large, or when using a capacitively coupled type glow discharge, the distance between the electrodes is 10 cm or more, for example, 30 to 30 cm. The aim is to perform glow discharge uniformly even when performed at a distance of 50 cm.

Generally, in the PCVD method, the effective space (film formation area) in which the substrate is placed and the film is formed is increased by 0.2
m ³ (electrode area 0.7m x 0.7m, electrode spacing 0.4m) or more, the glow discharge becomes extremely inhomogeneous, with locally strong discharge occurring together with weak homogeneous discharge, and further It is known that strong electrical discharges extending in the direction of the electrode randomly move at a speed of 0.1 to 3 m/min (referred to here as dancing), and that the spatter effect caused by this electrical discharge deteriorates the quality of the formed film. . The object of the present invention is to eliminate such fluctuations in localized strong discharge and to generate a homogeneous glow discharge.

In order to eliminate strong local discharge, this invention uses a plurality of needle-shaped electrodes instead of a pair of capacitively coupled electrodes on a flat surface, and by separating the needle-shaped electrodes from each other, This prevents the discharge from concentrating on the discharge of other electrodes. Furthermore, in order to prevent discharge from flying from one electrode to another, a floating grid (a mesh-like conductor that is electrically released from the electrodes, reactor, etc. to form an equipotential) is placed between the electrodes. It is characterized by the fact that it was established.

This invention is characterized in that, in the relationship between the nozzle, electrode, and grit of the reactive gas supply port, the structure in the vicinity of the electrode is simplified by using the nozzle in combination with a needle electrode or grit.

The present invention is characterized in that both of the pair of electrodes have a plurality of electrode structures, and furthermore, a film formation region is provided between the electrodes, thereby promoting uniformity of discharge.

Another feature of the present invention is that the grit is disposed laterally or rearward compared to the end of the needle-like electrode (the part closest to the film forming area) to prevent flakes from forming on the grit.

An overview of conventional PCVD is shown in Figure 1. In the parallel plate electrode type using the glow discharge method, the plate spacing is 1 to 7 cm, for example, 4 cm.
cm, making it easier to discharge.

FIG. 1 shows such a structure, in which a pair of electrodes 3 and 8 are successively provided in the reactor 2 by a 13.5 MHz high frequency power source 25 and 41, 42. Further, in the reaction system 24, the reactive gas is 2
6, 27, and 28, for example, hydrogen silane and doping gas (B ₂ H ₆ , PH _3, etc.) are introduced, respectively.
It consists of a flow meter 22 and a valve 23, which are supplied to the discharge region 45 from a nozzle (reactive gas supply port) 5. The substrate 1 is heated by a heater 46 and is provided on one electrode 8 .

With this structure, a reactive gas such as silane is decomposed to form a non-single crystal semiconductor on the formation surface of the substrate 1. After this reaction, the reaction product is 44
The gas is then discharged into the exhaust system 32 by the valves 14 and 15 and the vacuum pump 16. The inside of the reactor is maintained at 0.01 to 0.5 torr, for example 0.1 torr, by the needle valve 14, and by supplying electrical energy from 25, a glow discharge is generated in the effective space, and a reaction product, such as a non-single crystal silicon film, is transferred to the substrate 1. formed on top.

However, if the electrodes 3 and 8 are 50 cm or longer, this discharge will be extremely unstable, resulting in a locally strong (bright) discharge 4.
3 was observed, and the discharge running between these linear (band-shaped) electrodes was moving randomly on the electrodes at a speed of 5 to 50 cm/sec.

The area where this local strong discharge occurs has a high energy density more than 10 times compared to other homogeneous discharge areas, so the reaction products that react here have strong kinetic energy and cause spatter (damage) to the substrate surface. )
Resulting in. Therefore, the properties of the formed film are extremely poor. For example, when trying to make an amorphous solar cell using silicon, so-called granular polycrystals are mixed in, reducing the conversion efficiency by as much as 5%. The variation in 0 to 5% is large,
This was an extremely serious problem in practical terms.

Furthermore, it has been found that this localized strong discharge occurs more frequently when the electrodes are separated by 5 cm or more, for example, 10 to 50 cm, and the discharge becomes extremely unstable.

Furthermore, in order to prevent this strong local discharge, it is possible to use only one electrode 3 as a plurality of needle-shaped electrodes. However, in this case, the other electrode 8 is not possible in this conventional structure because the substrate is oriented flat on the electrode 8. For this reason, it has been found that it is insufficient to make only one of the electrodes in the pair needle-like. In order to prevent such non-uniformity of discharge, the present invention provides a plurality of needle electrodes on one electrode side and a plurality of needle electrodes on the reactive gas supply side, and also arranges floating grit between the needle electrodes. It is characterized by completely eliminating strong local discharges.

The present invention is characterized in that a plurality of needle-like electrodes are used for each of a pair of electrodes arranged so as to sandwich the film formation region, thereby completely preventing strong local discharge.

In order to prevent this localized strong discharge from "jumping" from electrode to electrode, the present invention makes the length of the needle electrodes 20 mm or more, and furthermore, the interval between them is 20 mm or more, preferably 30 to 30 mm.
It is characterized by being 50mm.

Therefore, when a solar cell has a PIN junction type and is made of silicon, 6 to 8%
It has the great feature of being able to be manufactured using a 60cm substrate and improving manufacturing yield from 30% to more than 80%.

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 FIG. 2 shows an outline of the PCVD apparatus of the present invention.

In the drawings, a substrate 1 having a surface to be formed on
are arranged in pairs on the quartz holder 19 with their back surfaces overlapping each other. Preliminary room 2 to reactor 2
9 through the door 21, and use the pump 31 to close the valve 3.
Open it to 0 and draw a vacuum. After sufficient evacuation to 10 ^-3 torr or less is performed, the gate valve 20 is opened and the substrate 1 holder 19 is placed as shown in the figure. In the reactor 2, the substrate 1 is exposed to infrared lamps 7 from above and below.
7' to 100-400°C, for example 250°C.

26,2 reactive gas in doping system 24
7, 28, and 29, it is supplied into the reactor 2 through the flow meter 22, the valve 23, and the supply port 10. The supply port serves as one electrode 3 of the pair of electrodes 3 and 8, and causes a capacitively coupled glow discharge with the other electrode 8. This pair of electrodes is covered with quartz hoods 33 and 34 on the outside to prevent parasitic discharge with the inner wall of the reactor 2. Electrical energy is supplied to the electrodes 3 and 8 via terminals 41 and 42 of a high frequency power source 25.

Furthermore, in FIG. 2, regarding the electrode and grit of the present invention, an electrode 3 for performing glow discharge plasma CVD using a capacitive coupling method is shown above and below.
8 are provided respectively.

The upper electrode 3 is composed of a plurality of needle-shaped electrodes 54 and a hollow conductor 55 that conducts electrical energy to the electrode 54, and this conductor 55 is electrically connected to 41 and is also configured to supply reactive gas. It is electrically separated from the mouth 10. Also, the reactive gas is passed through the hollow conductor 5.
5 and is supplied to the film forming area from the nozzle 5. The needle-shaped electrode (for example, made of stainless steel or copper plated with nickel) having this nozzle 5 has a length of 20 mm or more, preferably 30 to 70 mm, for example.
It was set to 40mm. If this length is too short, less than 15 mm,
It does not have the function of a discharge electrode and does not need to be too long and take up more space than necessary;
was within the practical range. Also, the spacing between each needle electrode is 20
mm or more, preferably 30 to 70 mm, for example 50 mm. Again, the practical range is 20 to 100 mm, and over 100 mm, there is a region between each electrode where there is no discharge.

Further, in the electrode system 50 on the reactive gas supply side, these needle-like electrodes are arranged in a matrix at intervals of 40 mm, and a net-like equipotential is formed in the middle part of the needle-like electrodes to prevent local discharge from spreading between the needle-like electrodes. I made grit so that it wouldn't be there. This is 40mm of stainless steel with a diameter of 0.5 to 1mm.
(The needle electrode end 54 is provided in the center of the gap). This grit was extremely effective in preventing the occurrence of local discharge, especially when the length of the needle electrode was 50 mm or less.

Furthermore, in FIG. 2, in the electrode of the present invention, an upper electrode system 50 and a lower electrode system 51 are both provided as needle-shaped electrodes. Regarding the lower electrode, the electrode 8 has a needle shape with the same dimensions and shape as the electrode 3. However, as is clear from the drawing, in order to prevent unnecessary reaction products from clogging the holes after the reaction, the electrode 8 is a plate-shaped stainless steel plate with needle-shaped electrodes provided every 40 mm. -Multiple holes of ~5 mm are drilled, and unnecessary reaction products and carrier gas are removed from holes 9 to 6.
The air was allowed to enter the exhaust system 32 from the exhaust port 6 through the exhaust port 6.

By making both the upper and lower parts needle-shaped, the effective electrode area of the film formation area is 70 cm.
No strong local discharge was observed even when the electrode spacing was 50 cm.

In the embodiment in the drawings, the reactor has a height
800 mm, width 800 mm, and depth 1000 mm, and the effective space 45 as a film forming area consists of 20 20 cm x 60 cm substrates (10 sets) arranged 8 cm apart from each other.
This is the case of cm x 60cm.

In this way, even though the distance between the needle-shaped electrodes of a pair of electrodes is about 30 cm and the electrode area is as large as 65 cm, in the case where the needle-shaped electrodes are formed on both sides of the present invention, or when they are formed on one side. By providing this in combination with grit, it was possible to completely eliminate the localized strong discharge that was observed in the conventional example. In particular, strong local discharge is more likely to occur when the reactive gas tends to become a reactive solid such as silane than when hydrogen, argon, nitrogen, etc. are used. However, in the present invention, it was not observed at all in silane (SinH _2o+2o 1) at 0.05 to 0.2 torr and 30W. Therefore, the reactive gas is less silane than 26.
A carrier gas such as hydrogen is supplied from diborane 28 and phospin 29 from 7, and one P (100
Å) When a PIN junction of I (5000 Å) N (100 Å) is provided on a CTF (transparent conductive film) on a glass substrate,
It was impossible to achieve a conversion efficiency of 1% at 2060 cm using a conventional plasma CVD apparatus having the structure shown in FIG. On the other hand, in the plasma CVD apparatus of the present invention shown in Fig. 2, in a system in which 40 stages of 15 mm x 40 cm cells are connected in series to a 420 cm x 60 cm panel, the open circuit voltage is 30 V or more (30 to 35 V) and the short circuit current is 600 V.
More than mA (700~800mA) Efficiency 5% (5~6.5
%) or more could be obtained at AMI (100 mW/cm ² ). This was an epoch-making achievement considering that conventional voltages varied widely from 5 to 25 V, currents varied widely from 70 to 500 mA, and efficiency varied widely from 0.1 to 2%.

In this drawing, there is only one reactor, but this
The reactors that form the PIN junction are made independent, and are used as a reactor for a P-type semiconductor layer, a reactor for an I-type semiconductor layer, and a reactor for an N-type semiconductor layer, and they are connected to each other and touch the outside. For example, patent application No. 56-55608 (53-152887) filed by the present inventor.
S53.12.10 Division of application) is effective.
Further, in the present invention, as shown in FIG. 2, a pair of grits 12 and 13 are provided on each side of the positive electrode 8 and the negative electrode 3, respectively.

Although this grit is effective on only one side of the electrode, strong local discharge can be completely prevented by adding it to both sides to improve film quality.

In the embodiment of the present invention, a stainless steel tube (outer diameter 3 mm, inner diameter 2 mm) was used as the needle electrode. However, it is effective to further improve the uniformity of the discharge by providing a flat or spherical appendage at the end of the needle electrode (the part closest to the film forming area) within a range where strong local discharge does not occur. This further leads to a multi-electrode structure.

Embodiment 2 In FIG. 2, the nozzle 5 and the electrode 3 are made of the same material, and the nozzle hole 5 is provided in a tubular stainless steel needle electrode. Furthermore, regarding the relationship between the electrode 3, nozzle 5, and grit, it is possible to deform the upper electrode 50 and lower electrode 51 of the electrode, grit, etc. as shown in FIG. 3A in the PCVD apparatus shown in FIG. can.

In FIG. 3A, the electrode 3 is a conductor 55, and a stainless steel wire 54 (1 to 3 mm in diameter) is provided as a needle electrode 55, and a grit 12 is provided between the needle electrodes. The reactive gas is introduced into this grit (which has a tubular shape and consists of a doping system 24 reactor and an electrically free conductor) with a diameter of 0.5 to 1 mm.
is ejected from the nozzle 5 into the film forming area, and a plasma reaction occurs. The rest is the same as in Example 1. Mechanically, the structure of the electrode section 50 could be simplified. The same effects as in Example 1 could be achieved.

Example 3 FIG. 3B shows another embodiment of the invention.

As is clear from the drawings, both the upper electrode part 50 and the lower electrode part 51 are needle-shaped electrodes, and no grit, which causes flakes, is provided. The rest is the same as in Example 1.

In this way, compared to Examples 1 and 2,
The occurrence of flakes (snowflakes) has decreased. That is, the flakes adhere to the grit portion and fall, thereby adhering to the surface to be formed and easily creating pinholes, etc., but this could be prevented. However, at the same time, it is necessary to set the length of the needle electrode to 50 to 80 mm to eliminate strong local discharge, and the length between the needle electrodes must also be 50 to 80 mm.
The opening had to be as wide as the electrode length (mm), and the film growth rate was reduced to 1 Å/sec from 3 Å/sec in Example 1.

In the present invention, the production of a semiconductor film using silane has been described. However, as a semiconductor film, SiF ₂ SiF ₄
PCVD with Si, silane and methane by PCVD reaction
SixC _1-x (o<x<1) by silane and germane SixGe _1-x (0<x<1) Si ₃ N _4-x (0<x<1) by reaction with silane and ammonia The present invention is also effective when provided as a single crystal semiconductor.

Furthermore, the film to be formed may be made of insulators such as silicon oxide or silicon nitride. In addition, TMA (Al
Conductors such as metallic aluminum using (CH ₃ ) ₃ ), silicon-added aluminum using TMA and silane, tin oxide using SnCl ₄ and oxide gas, InCl ₃ , SnCl ₄ and oxide gas It goes without saying that a light-transmitting conductive film made of indium tin oxide or the like used may also be formed.

Furthermore, in the present invention, as is clearer from the embodiment shown in FIG.
Furthermore, the electric field of plasma CVD was made parallel to the surface to be formed. However, the electrode and grit of the present invention may be modified and applied as long as the directions of the substrate surface, reactive gas, and electric field are changed so that the reaction products do not sputter on the substrate surface.

As described above, in the case of large-area electrodes or electrodes separated by 10 cm or more, the voltage between the electrodes is
This is especially effective when the voltage exceeds 500V.
We believe that such floating grits are particularly effective in PCVD using voltage driven glow discharge methods.

[Brief explanation of the drawing]

Figure 1 shows the conventional plasma CVD method. Second
The figure shows a plasma CVD apparatus of the present invention. FIG. 3 specifically shows the electrode arrangement for the reactive gas.

Claims (1)

[Scope of Claims] 1. A reaction vessel maintained at a reduced pressure of 1 atmosphere or less, a supply system for supplying a reactive gas to the reaction vessel, an exhaust system for evacuating unnecessary reaction products or carrier gas, In a plasma vapor phase reactor comprising a film forming region in which a substrate having a surface to be formed is disposed between a supply system and an exhaust system, a pair of first and second film forming regions supply electrical energy to the reactive gas. One of the two electrodes, which is provided on the side that supplies the reactive gas, has a plurality of needle-like electrodes, and has conductivity between the needle-like electrodes, and is electrically connected to either electrode. A plasma gas phase reactor characterized in that a grid is disposed in which both are free. 2. The plasma vapor phase reactor according to claim 1, wherein the plurality of needle-like electrodes or grids have openings through which reactive gas is led out to the film forming region.