JPH0799159A - Manufacture of semiconductor - Google Patents

Abstract

PURPOSE:To provide a manufacture method of a semiconductor, in which the defect density in the bulk of a tetrahedral amorphous semiconductor by vapor growth is reduced at a low substrate temperature and which can enhance an electric characteristic when the amorphous semiconductor is applied to a solar cell or the like. CONSTITUTION:A mesh heating element is arranged inside a reaction container 1, the mesh heating element is heated while a semiconductor is being grown, and heat energy is given to a vapor phase. In addition, the mesh heating element is formed as a mesh electrode 7, and the mesh electrode 7 is heated while an electric current is being applied to the electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing method, and more particularly to a manufacturing method capable of obtaining an extremely excellent film quality at a low substrate temperature when growing a semiconductor on a substrate in a vapor phase.

[0002]

2. Description of the Related Art In recent years, a tetrahedral amorphous semiconductor such as hydrogenated amorphous silicon obtained by a plasma CVD method or the like can be easily made large in area and can be manufactured at low cost. Attention has been focused on its application to thin film transistors for liquid crystal displays and the like. However, these amorphous semiconductors have a defect density of about 10 ¹⁵ to 10 ¹⁶ defects / cm ³ in the bulk, which is several orders of magnitude higher than that of crystalline semiconductors. Becomes the recombination center, which is a major obstacle to improving the photoelectric conversion efficiency.

Recently, as has already been known, the substrate temperature has been increased to 40 by Gangrie et al. Of the Institute of Electronics Technology, Ministry of International Trade and Industry.
The defect density of hydrogenated amorphous silicon was reduced to 1 by increasing the film formation rate to about 10 times that of the conventional method while increasing the temperature to 0 ° C.
We have succeeded in reducing the number to ¹⁴ units / cm ³ .

[0004]

However, 400 ° C.
That is, the substrate temperature is not desirable in manufacturing the device, and may adversely affect the transparent conductive film particularly in the case of solar cells and liquid crystal displays. This greatly limits the application range of the tetrahedral amorphous semiconductor, and it is desired to achieve a low defect density at a low substrate temperature.

[0005]

The present invention has been made to solve the above problems, and reduces the defect density in the bulk of a tetrahedral amorphous semiconductor by vapor phase growth at a low substrate temperature. The present invention provides a method for manufacturing a semiconductor, which can improve electric characteristics when applied to a solar cell or the like. Vapor growth here means
Silane-based gas or mixed gas of
Such as chemical vapor deposition, which decomposes by either light or a combination of two or more of these to form a silicon-based amorphous semiconductor on a substrate, sputtering by silicon or a silicon-based compound, or reactive sputtering. There is physical vapor growth.

Regarding hydrogenated amorphous silicon among the tetrahedral amorphous semiconductors, the dangling bonds of silicon atoms, which are considered to be the defect density in the bulk, are the dangling bonds existing on the growth surface as they are. It is considered that it is taken into the bulk along with. Therefore, if the dangling bonds on the growth surface can be terminated, the bulk defect density can be reduced.

The mechanism of the film growth of this hydrogenated amorphous silicon is as follows: As the film growth process, the film-forming precursor in the vapor phase adheres to the growth surface, and the surface-covered hydrogen is extracted and returned to the vapor phase. It is proposed that the precursor deposited on the growth surface is a film deposition process in which the precursor diffuses on the growth surface and bonds with dangling bonds. Therefore, if the distance over which the precursor diffuses on the growth surface can be increased, more dangling bonds on the growth surface can be terminated. Normally, the diffusion distance of the film growth precursor depends on the temperature of the substrate and the surface hydrogen coverage, so that the diffusion coefficient increases as the substrate temperature increases, but at the same time the surface hydrogen coverage decreases and the diffusion distance increases. Has a local maximum. Therefore, regarding the defect density, which is generally considered to decrease as the diffusion distance increases, the substrate temperature is 200 to 25.
It takes a minimum value at 0 ° C, and its value is 10 ¹⁵ pieces / c
It is reported to be about m ³ . Recently, Gangrie et al. Of the Electrotechnical Laboratory have increased the defect temperature of hydrogenated amorphous silicon to 10 ¹⁴ / cm ³ by setting the substrate temperature to 400 ° C. and increasing the film growth rate to about 10 times that of the conventional method. Succeeded in This is because at the substrate temperature of 400 ° C., the diffusion distance of the film-forming precursor is shortened due to the large desorption of the surface-coated hydrogen, but the unbonded dangling bonds that have desorbed hydrogen are terminated at a film formation rate of 10 times. It is considered that this prevents the decrease in the diffusion distance of the film-forming precursor. As a result, it has become possible to manufacture a semiconductor film having a low defect density, which has not been obtained conventionally, at a substrate temperature of 400 ° C.

However, as described above, a substrate temperature of 400 ° C. is not practical in consideration of application to a device, and it is practically desirable to manufacture a semiconductor film having a low defect density at least around 200 ° C. The present applicants have earnestly studied this point and completed the present invention. The present invention has been made from such a viewpoint, and increases the diffusion distance of the film-forming precursor even at a low temperature of about 200 ° C., and terminates more dangling bonds on the growth surface to cause bulk defects. The density can be reduced. Then, by applying thermal energy to the vapor phase during film growth, the energy state of the precursor itself is raised, and the diffusion distance on the surface after these reach the growth surface is measured by the diffusion at the actual substrate temperature. It is characterized by increasing the distance rather than the distance.

The manufacturing method of the present invention is a method for manufacturing a semiconductor by vapor phase growth, in which a mesh heating element is arranged in a reaction vessel and the mesh heating element is heated during the growth of the semiconductor. The present invention also proposes that the mesh heating element is a mesh electrode, and the mesh electrode is heated by energization. And the substrate temperature is 1
00 to 250 ° C, the temperature of the mesh heating element is 100
A temperature of 400 ° C is suitable.

As the mesh heating element, in addition to the above mesh electrode, the mesh heating element may be a hollow pipe, and the heated high boiling point liquid may be circulated inside.
As the mesh heating element, a lattice-shaped or mesh-shaped one can be widely used so as not to disturb the plasma discharge and the gas flow in the reaction vessel.

Although the amorphous semiconductor obtained by the manufacturing method of the present invention has a reduced defect density, the amorphous silicon semiconductor refers to an amorphous semiconductor containing at least Si, and a-Si. And a-Si and microcrystalline Si, C,
Alloys with Sn, Ge, etc. are also included. As typical alloys, a-Si _1-xy Ge _x C _y : H (0 ≦ x, y ≦ 1) a-Si _1-xy Ge _{x Cy} : H: F (0 ≦ x, y ≦ 1) etc. The amorphous semiconductor of the present invention can be suitably used for a semiconductor device having a pin structure or a Schottky structure, for example.

[0012]

When a mesh heating element is placed in the reaction vessel and the mesh heating element is heated during the growth of the semiconductor to give heat energy to the gas phase, the energy state of the precursor itself increases as described above. As a result, the diffusion distance on the surface after reaching the growth surface becomes larger than the diffusion distance at the actual substrate temperature. And since the pressure in the reaction vessel is extremely low,
Heat conduction from the mesh heating element to the substrate is of little concern.

[0013]

EXAMPLES Next, the semiconductor manufacturing method of the present invention will be explained based on examples, but the present invention is not limited to these examples.

[0014]

[Table 1]

Corning code 7059 was obtained by glow discharge decomposition of pure monosilane gas under the conditions shown in Table 1.
Intrinsic hydrogenated amorphous silicon thin films were deposited to 1-2 μm on glass and crystalline silicon substrates. FIG. 1 shows a schematic structural diagram of a plasma CVD apparatus used for manufacturing a semiconductor thin film.
The apparatus shown in the drawing is a normal diode-type capacitively coupled plasma CVD apparatus, in which a mesh electrode 7 made of stainless steel is installed as a mesh heating element between the cathode electrode 3 and the anode electrode 5 in the reaction vessel 1. The distance between the cathode electrode 3 and the mesh electrode 7 is 40 mm, and the distance between the mesh electrode 7 and the anode electrode 5 is 20 mm. The mesh electrode 7 is a cathode electrode 3 and an anode electrode 5
Both electrodes are not grounded and are in a floating potential state. And it is connected to the heating power source 9 by an insulating transformer 11, and by adjusting the voltage with the sliderac 13,
The amount of current flowing through the mesh electrode 7 is controlled. Each substrate was fixed on the anode electrode 5 with a stainless jig with good adhesion. In preparation for film formation, the wall of the reaction container 1, the substrate, and the mesh electrode 7 are sufficiently heated to exhaust the adsorbed impurities as much as possible, and then the temperature is lowered to a predetermined temperature to reach 2 × 10 5.
^It was evacuated to a vacuum degree of about ^-8 Torr. This vacuum exhaust is exhausted from the high vacuum exhaust port 15 connected to the turbo molecular pump, and during the film formation, the reaction container is exhausted from the pressure adjusting exhaust port 17 connected to the mechanical booster pump and the rotary pump. The inside of 1 is kept at a constant pressure. Then, pure monosilane gas was introduced into the reaction vessel 1 as a raw material gas, a high frequency voltage of 13.56 MHz was applied between the cathode electrode 3 and the anode electrode 5 from the high frequency power source 19, and a film thickness of 1 to 2 μm was obtained according to the conditions in Table 1. Then, a hydrogenated amorphous silicon film was formed.

On the hydrogenated amorphous silicon film thus obtained, A1 coplanar electrodes were formed at intervals of 0.2 mm by a vacuum deposition method. And the stationary photocurrent method (C
The defect density in the semiconductor in these samples was quantified by a method called PM method). The temperature of the mesh electrode 7 is plotted on the horizontal axis and the defect density is plotted on the vertical axis in FIG.
Is shown in. The defect density when formed at a normal substrate temperature, that is, 250 ° C. is about 10 ¹⁵ defects / cm ³ as shown by the point at the left end of FIG. 2A, but the mesh electrode 7 was heated to 200 ° C. In this case, the number of defects is reduced to about 10 ¹⁴ / cm ³ by about one digit, and it is understood that the defect density in the film can be reduced by supplying the thermal energy to the gas phase. In addition, a value obtained by measuring a sample on a crystalline silicon substrate formed at the same time with an infrared spectroscope and quantifying the amount of hydrogen in the film from the infrared light absorption characteristics is shown in FIG. Considering that the amount of hydrogen in the film is almost constant regardless of the temperature of the mesh electrode 7 and there is a correlation between the substrate temperature and the amount of hydrogen, the substrate temperature is not significantly affected by the radiation from the heated mesh electrode 7. I know there isn't.

[0017]

As described above, according to the semiconductor manufacturing method of the present invention, it is possible to manufacture a semiconductor having a very low defect density at a low substrate temperature. Therefore, it can greatly contribute to the practical application of high-performance solar cells, thin film transistors, and the like.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a plasma CVD apparatus for realizing the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the mesh electrode temperature and the defect density diagram and the hydrogen content in the film of the hydrogenated amorphous silicon semiconductor obtained by the manufacturing method of the present invention, in which (a) is the mesh electrode temperature- Defect density correlation diagram, (b) Correlation diagram of mesh electrode temperature-film hydrogen content

[Explanation of symbols]

 1 Reaction Vessel 3 Cathode Electrode 5 Anode Electrode 7 Mesh Electrode 9 Heating Power Supply 11 Insulation Transformer 13 Slideac 15 High Vacuum Exhaust Port 17 Pressure Adjusting Exhaust Port 19 High Frequency Power Source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gautam Gangley 1-4 1-4 Umezono, Tsukuba-shi, Ibaraki Electronic Technology Research Center (72) Inventor Akihisa Matsuda 1-4 1-4 Umezono, Tsukuba-shi, Ibaraki Electronic technology Inside the research institute

Claims (2)

[Claims] 1. A method for producing a semiconductor by vapor phase growth, wherein a mesh heating element is arranged in a reaction vessel, and the mesh heating element is heated during the growth of the semiconductor to give heat energy to the vapor phase. Manufacturing method. 2. The mesh heating element is a mesh electrode,
The method for producing a semiconductor according to claim 1, wherein the mesh electrode is heated by energization to apply heat energy to a gas phase.