JPH01148793A - Method for horizontally drawing silicon cystal of ribbon shape - Google Patents

Abstract

PURPOSE: To obtain a ribbon-shaped silicon crystal, which is suitable for semiconductor device, especially for solar battery, etc., and has a surface excellent in flatness, by bringing a supporting body, which is composed of a meshlike fiber textile having a specified mesh inner width and is used for supporting and forming crystalline nuclei into contact with a silicon fused body and drawing the supporting body in the horizontal direction.

CONSTITUTION: The meshlike fiber textile 1, the mesh inner width of which adapts to maximum thickness 300 μ of a silicon ribbon crystal 7 to be drawn and is set to ≤2.0 mm when temp. gradient in the silicon fused body 2 is ≤25 K/cm and which has resistance to the fused silicon 2 and shows a high radiation coefficient, is used as the supporting body for supporting silicon ribbons and for forming crystalline nuclei. Then, the supporting body composed of the fiber textile 1 is brought into contact with the silicon fused body 2 held at melting temp. by a heater 4 put at a bottom surface area of a quartz vessel 3 and then is drawn in a drawing direction V while canceling radiation loss 5 by a reflector 6 and also by shielding, if necessary, to obtain the ribbon-shaped silicon crystal 7.

COPYRIGHT: (C)1989,JPO

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides support for supporting a support made of a reticulated fiber fabric that is resistant to molten silicon and exhibits a high radiation coefficient, and for forming crystal nuclei in a silicon melt. It relates to a method for producing ribbon-shaped silicon crystals by horizontally drawing them in contact with the silicon crystal.

[Prior Art] This kind of known silicone ribbon drawing method, called horizontal S-web method, has a high drawing speed (approximately l m /mi
n ) and low material consumption (ribbon thickness 300 μm or less), it is cost-effective and
Journal of Crystal Growth
Crystal Growth) J 79.1986
, pp. 572-577 and European Patent Application Publication No. 0170
It is described in detail in Publication No. 119.

Next, the principle of this technique will be explained with reference to FIG.

A carbon fiber network 1 proceeding in the drawing direction (2) is drawn against the surface of a silicon melt 2 placed in a quartz layer 3. The dimension of this tank 3 is such that its length is at least the contact length L=v,
t (v2 is the drawing speed, L is the residence time). The silicon melt 2 is kept at melting temperature by a heater 4 placed in the bottom area of the vessel 3. The radiation losses indicated by 5 are then canceled out by means of shielding and reflectors 6, if necessary. 7 is the completed silicon ribbon. 8 indicates the starting point of crystallization within the mesh 9 at the inner width of the mesh 1. Silk threads act as heat sinks due to their high radiation coefficients and induce crystallization if the temperature gradient GL in the melt is suitable. Coagulation begins at the molten part in direct contact with the silk thread and spreads horizontally and vertically. As the horizontal expansion progresses, the crystallized silicon surface acts as a heat sink. The radiation on this surface is also worse than that of the molten body. Because the solidification rate consists of a horizontal component and a vertical component, a wave called a boat structure is formed on the opposite side of the carbon fiber network of the drawn silicon ribbon, and its period corresponds to that of the network structure. The silicon layer formed on the underside of the mesh does not grow uniformly in the depth direction and is thicker under the fibers than in the portion of the melt surface not covered by fibers. According to the experimental results, support 1
The thinner the silicon layer 7 melted and crystallized above, the more severe the wave of the boat-shaped structure becomes.

The boat-shaped structure is a hindrance when processing the silicon ribbon 7 into a solar cell, especially if it is necessary to provide contacts thereto.

[Problems to be Solved by the Invention] The purpose of the present invention is to provide silicon with an extremely flat surface.
The purpose of the present invention is to provide ribbon manufacturing using a horizontal S-web method.

[Means to solve the problem]

This objective is achieved by the present invention as a support used in the horizontal S-web drawing process, the internal width of the mesh is compatible with the maximum thickness of the silicon ribbon to be drawn, 300 μm, and the temperature gradient in the silicon melt is below 25 K/cm. Time 2.
This is achieved by using a material set to 0 mm or less. It is advantageous to use fibers of graphite or graphitic quartz.

Various embodiments of this invention are described in claim 2 of the claims.
Shown below.

〔Example〕

This invention will be explained below with reference to Examples.

The occurrence of waviness W, defined as the difference between the thickest and thinnest parts of the silicon ribbon within one mesh inner diameter, and its height are related to the mesh design, the temperature gradient within the melt, and the thickness of the silicon layer. However, the influence of fiber diameter is small.

The waviness increases as the silicon layer becomes thicker (thicker layers grow more slowly than thinner layers). However, a thickness of 300 μm or more is not suitable for cost-effective solar cells.

The temperature gradient GL within the melt has a significant effect on the rapidity of growth. The larger the temperature gradient, the more heat will be directed to the formed silicon layer and the growth will be correspondingly slower. To ensure cost-effective continuous drawing of the silicone ribbon, the drawing speed must be kept at a minimum of 1 m/min.

This means making the temperature gradient as small as possible.

The relationship between the average thickness d of the soric ribbon and the waviness W is schematically shown in FIG. The characteristics of the carbon fiber network are expressed by the inner width of the mensch, and W=W(
d) is shown in the figure. As the curve shows, W =
After passing the maximum value at both l mm and 2 mm, it decreases in the direction of increasing 1. The highest point moves toward the smaller thickness and undulation as the inner width of the mensch decreases.

FIG. 3 shows the waviness W as a function of the inner width of the mesh for an average silicon ribbon thickness d=300 μm and a temperature gradient GL=15 K/el+ in the melt. It can be seen from the straight line in FIG. 3 that the waving decreases as the inner width of the mesh decreases, and becomes 10 μm or less when it is 1.3 rrrra or less. As shown by measurement points 1.2.3, experiments were conducted on the following three types of mesh patterns.

Mesh pattern 1: = 1.7 mm Mesh pattern 2: = 2.28 Mesh pattern 3: = 4.2 mm The flatness of the fiber fabric used on the outside of the mesh has a strong influence on the inner width of the mesh. The thread binding used to stabilize the fabric in the warp direction creates thickenings at the intersections of the fibers, which increases waviness. In one embodiment of the invention, therefore, a fiber fabric without thread binding is used, ie the warp and weft threads are simply linen-bonded. As a result, the threaded connections necessary for stabilizing the mesh are limited to the edges of the mesh that do not come into contact with the silicon melt during drawing.

[Brief explanation of the drawing]

Figure 1 is a drawing explaining the invention in detail, Figure 2 is the relationship between the waving W and the average thickness d of the silicon layer with the mesh inner width as a parameter, and Figure 3 is the relationship as a function of the mesh inner width. It shows the wavy W of. 1... Carbon fiber network 2... Silicon melt 3... Quartz tank 4... Heater 6... Reflector 7... Silicon ribbon 8... Crystallization starting point (611B) Representative Patent Attorney Tomimura Column -11, -'

Claims (1)

[Claims] 1) Support for silicon ribbon support and crystal nucleation (1)
) is used as a reticulated fiber fabric that is resistant to molten silicon (2) and exhibits a high radiation coefficient, and this support is horizontally (v) in contact with the surface of the silicon melt in the melting tank (3). In a process by horizontal drawing of ribbon-shaped silicon crystals (7) which are drawn and covered with a silicone layer, the inner width of the mesh of the reticulated fiber fabric used as support (1) forms the drawn silicon ribbon crystal (7). ) A horizontal drawing method for ribbon-shaped silicon crystals, characterized in that the temperature gradient in the silicon melt (2) is set to 20 mm or less when the temperature gradient in the silicon melt (2) is 25 K/cm or less in accordance with the maximum thickness of 300 μm. 2) Process according to claim 1, characterized in that a fiber fabric of graphite fibers or graphitic quartz fibers is used. 3) A fiber fabric with a mesh inner width of 1.7 mm is used,
3. A method as claimed in claim 1, characterized in that the temperature gradient within the silicon melt is maintained at 15 K/cm. 4) A fiber fabric with a mesh inner width of 1.3 mm is used,
3. A method as claimed in claim 1, characterized in that the temperature gradient within the silicon melt is maintained at 15 K/cm. 5) Process according to one of the preceding claims, characterized in that a fiber fabric is used in which the warp and weft threads are mutually located at the point of intersection by a simple linen bond. 6) A fiber fabric is used in which the outer edge, which is not wetted by the melt ratio, exhibits a thread bond extending in the warp direction at the intersection of the warp and weft yarns for stabilization in the warp direction. The method described in one of the above. 7) Process according to one of claims 1 to 6, characterized in that it is used for the production of ribbon-shaped silicon crystals for semiconductor devices, in particular solar cells.