JPS5950515A - Manufacture of semiconductor thin film - Google Patents

Abstract

PURPOSE:To melt a polycrystalline film to be recrystallized, and to contrive to enlarge the particle diameter when the semiconductor thin film deposited on a substrate is heated to be melted in a belt type, and to be cooled in one direction by a method wherein a seed crystal is set up as the nuclei of crystal growth. CONSTITUTION:Because the progressing direction of cooling is the direction shown with an arrow mark 10, the farther the part on a crystal face 6, which is the (111) face, is separated from the substrate 1, the lower the temperature is reduced, and the condition to generate the two-dimensional crystal nuclei 7 at the position shown in the figure can be set up. Moreover, because the crystal face 6 is the growth hard face, the condition that crystal growth is not generated along the isothermal face 9 can be also set up. It is favorable to set up the condition of the growth direction as to make the isothermal line drawn by the isothermal face 9 on the crystal face 6 to cut an arrow mark 8 at right angles. Because the two-dimensional nuclei 7 are formed naturally following after the same crystal axial direction with the precedingly crystallized region, the growth part thereof in the arrow mark 8 direction becomes to have the same crystal orientation as the preceding part, and one directional solidification can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a polycrystalline semiconductor t'fe film having a large grain size.

[Technical background of the invention and its problems] A sample of a polycrystalline semiconductor layer film with a semiconductor thickness of several tens of μm and a width of several tens to several hundreds of cJ or more can be produced at low cost and with good characteristics. If so, it can be expected to be used for solar cells. Research and development for this purpose has been actively carried out in the past, but the technology has remained incomplete as nothing with sufficient characteristics has been developed. The reason for this is that the substrate material used to form the polycrystalline thin film affects the crystallinity of the polycrystalline semiconductor layer, making it difficult to create a polycrystalline semiconductor layer with large grain sizes. Various improvements have been made. One of them is to form a solid phase semiconductor layer in the form of a film on a substrate from a gas phase, and then increase the crystal grain size of this layer by some means.

The first improvement method is the simplest and attempts to increase the grain size of the polycrystalline semiconductor/J film by simply inserting the sample into a heat treatment furnace. Generally, the grain size of the polycrystalline semiconductor layer deposited from the solid phase to the solid phase is about 1 μm, but if the heat treatment conditions are appropriate, this method can increase the grain size to several μm to 10 μm. However, this particle size is far from producing a good solar cell, and this improved method cannot advance the technology to the desired width.

The second improved method is to raise the heat treatment temperature to a sufficiently high temperature and raise the polycrystalline semiconductor layer to a temperature above its melting point, so that
The purpose is to increase the particle size by returning this to the same phase again.

The key to the success or failure of this method is whether the polycrystalline half-gate body layer maintains its thin film shape after the transition from the liquid phase to the solid phase. If the substrate material is inappropriate, the liquefied semi-coated bodies will cohere and solidify in a so-called ball shape, and the thin film will disappear. In order to avoid this drawback, the substrate material should be selected from a material such as carbon that has good resistance to erosion with the silicon melt. Although such a method improves the particle size to about several tens of microns, this is still insufficient to create a good diameter 4-sized pond.

The third improved method is to form a layer of metal or the like with a lower melting point than silicon on the substrate, form a polycrystalline semiconductor layer on top of this, and then
This is a method of processing similar to the second improved method. In this method, upon heating, the low melting point gold layer is first melted, and then the upper polycrystalline semiconductor layer is melted. During cooling, the direction is the opposite; first, the polycrystalline semiconductor layer becomes a solid 1 on the gold IXQ.
The metal layer then solidifies.Generally, the solidification of the part that is in contact with the liquid is longer than the solidification of the part that is in contact with the solid. The disadvantage of this modified p method is metallographic.For example, taking a silicon polycrystalline semiconductor layer as an example, the metal layer is selected from A A, Ti, etc. Upon heating, these will dissolve into the silicon,
On the other hand, silicon also dissolves in metal by heating and melting it. Although it depends on the heating temperature and layer thickness, both j- actually melt together to form one liquid j-.

When this is cooled, a layer of pure silicon initially precipitates on top of the liquid and develops into crystals with a fairly large grain size. What is finally obtained is a eutectic structure of silicon and gold deposited at the polycrystalline grain boundaries of silicon. Such a film layer is unsuitable for use as a material for other uses such as the sun. Even if a solar cell is actually produced, one with good characteristics cannot be produced due to current leakage from this grain boundary.

The fourth improvement method relates to the cooling method. In order to increase the crystal grain size, it is sufficient to adopt the idea of unidirectional solidification, and the CZ method and FZ method, which actually create single crystal ingots, are used.
The Bridgman Act, etc., are all based on this idea. In order to apply this idea to the case of producing a polycrystalline semiconductor thin film, a part of the semi-quartet layer is melted in a band shape, melted in a direction perpendicular to the band; the reconnaissance area is moved, and solidification is performed in one direction. The disadvantage of this method is that the unidirectionality is lost due to the presence of the substrate. That is, if a U-shaped solid is present on the substrate, crystal nuclei are likely to occur on the surface of the solid, and other crystals will develop from that portion, making it impossible to achieve the purpose of unidirectional solidification.

[Purpose of the Invention J The present invention addresses the above-mentioned drawbacks of the conventional technology, and in particular melts the polycrystalline RF4 present on the substrate and recrystallizes it by incorporating the idea of unidirectional solidification to form grains. The purpose is to provide a practical method for expanding the diameter.

[Summary of the invention]

The present invention is based on setting a seed crystal as a nucleus for crystal growth when semiconductor aluminum deposited on a substrate is heated and melted in a belt shape and cooled in one direction. Here, the term "band-like" refers to an elongated portion that is generally straight-shaped when the thin film is viewed from a direction perpendicular to the direction in which the surface extends. Further, the present invention is characterized in that the cooling isotherm when heating and melting the semiconductor thin film and cooling it is set in relation to the crystallographic orientation of the seed crystal. In order to facilitate understanding of the principle of the present invention, explanation will be given below according to FIG. 1. In FIG. 1, 1 is a substrate, and 2 is a CV I
) method, 3 is the part melted by heating, 4 is the part of the silicon polycrystalline film recrystallized by cooling, 5 is the seed crystal, and 6 is the crystal (
111) plane, 7 is the two-dimensional nucleus of the crystal generated on the (111) plane, arrow 8 is the direction of development of the two-dimensional nucleus 7, dotted line 9 is the cooling surface, arrow 10 is the direction in which cooling progresses, 1 is As is well known, the (111> axis direction of the silicon crystal, which is the tangential plane between the substrate 1 and the melting part 3, is the only growth direction of the crystal, and therefore, the (1,11) direction is perpendicular to this direction. The surface is likely to be formed as a smooth surface.This is due to (lii) <-
This is because the 211> direction is the direction in which crystals easily grow.

Therefore, it is preferable that the arrow 8 in FIG. 1 be selected in this direction. Figure 1 will be explained based on this basic understanding, since the direction of cooling is in the direction of arrow 10 (1
11) On the crystal plane 6, the farther it is from the substrate 1, the lower the temperature becomes, and conditions can be set so that the two-dimensional crystal nucleus 7 is generated at the position shown in the figure. Furthermore, since the crystal plane 6 is a female growth plane, it is possible to set the condition that the crystal growth does not follow the uniform wetting plane 9. The direction of its development is the <-211> direction of the arrow 8, but it is preferable to set the conditions so that the equimixture line drawn by the isowetting plane 9 on the crystal plane 6 and the arrow 8 are perpendicular to each other. For example, the equal wetting surface 9 is made to extend in the direction of the joint on the paper surface, and the direction of the arrow 8 is the paper +
rri direction etc. Since the two-dimensional nucleus 7 is naturally formed in the same crystal axis direction as the first crystallized area, the part where it develops in the direction of arrow 8 has the same crystal orientation as the preceding part. The purpose of unidirectional solidification is achieved. When the crystal planes 9 and the growth direction of the crystals have the above-mentioned relationship 1.14, there is little chance of nucleation on the surface 1 where the substrate 1 contacts the melted portion 3.

〔Effect of the invention〕

As is clear from the above explanation, it is only after introducing the means of the present invention that a sample of a polycrystalline semiconductor layer deposited on a substrate is melted and cooled with directionality in a direction parallel to the film surface to form T4 crystals. When solidifying, the generation of crystal nuclei on the substrate surface is suppressed and the effect of unidirectional solidification appears, and as a result, it becomes possible to enlarge the crystal grain size unprecedentedly.

[Embodiments of the invention]

An embodiment of the method according to the above principles of the invention will be described with reference to FIG. In Fig. 2, 21 is the thickness l IIUI
22 is a carbon substrate with a thickness of 3 by the CVI) method.
This is a polycrystalline silicon thin film formed to a thickness of 0 μm. The seed crystal 23 is cut into a thin plate from a single crystal silicon ingot. 4 directions are within the paper <
111> direction, and the direction perpendicular to this, which is also within the plane of the paper, extends in the <-211> direction. The seed crystal 23 is fixed on the holding plate 25. Reference numeral 26 denotes a stand for moving the board 21 to the east, and is driven in the direction of the arrow 27 by a mobile device 1 (not shown). 28 is a lower heater which is wider than the upper heater 29, and both heaters 2B, 2
Both 9 extend in the direction perpendicular to the plane of the paper, and have a length longer than the entire length of the substrate 21 in the direction perpendicular to the plane of the paper, and heat the front and back surfaces thereof in a band-like manner.

The entire structure is housed in a container (not shown) filled with argon gas.

During operation, the stand 26 is first placed to the left of the position shown in the figure, and the seed crystal 23 is heated by the heaters 2B and 29.
Melt the left end of.

Leave it in this state for a while, then move on! The IIIJ mechanism is activated to move the table 26 in the 27 directions of the arrow at a speed of 3 mm/min.
The polycrystalline thin film 22 is melted and cooled up to the left end. The silicon film produced by such an operation was a crystalline film containing methic crystals and having large grain sizes.

In the embodiment, a strip heater was used as a means for heating and melting the thin film, but the present invention can also be achieved by using heating and melting using a Lede beam, for example.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, and FIG. 2 is an explanatory diagram of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1. Substrate, 2.. Polycrystalline silicon film, 3.. Heating melting part, 4.. Recrystallized polycrystalline silicon film, 5..
Seed crystal, 6...(111) plane, 7...2-dimensional nucleus,
8... Two-dimensional nuclear development direction, 9... Cooling isotherm, 1o
...Cooling progress direction, 21...Carbon substrate, 22...
Polycrystalline silicon thin film, 23... Seed crystal, 24 ゛<
111> direction, 25... presser plate, 26... stand, 27
・°° movement direction, 28.29...Heater

Claims (2)

[Claims] (1) A semiconductor layer film is deposited on a substrate, a china crystal is placed on this thin film, the semiconductor thin film in the seed crystal part is heated and melted, and the melted part is moved while cooling and recrystallization 1. A semiconductor layer 1 which is characterized in that the cooling, etc.-wet surface of the heating melting part is inclined such that the temperature is lower in the direction perpendicular to the substrate surface in the direction farther from the substrate. How to make Han. (2) The method for manufacturing a semiconductor thin film according to claim 1, wherein the specified cooling isothermal surface is arranged so as to be in line with the female growth direction of the seed crystal and the surface that is straight. (31tiil) The direction of the isothermal line drawn by the cooling isothermal surface on the plane perpendicular to the direction of growth of the seed crystal is perpendicular to the direction of easy growth, which is in the plane perpendicular to the direction of growth of the seed crystal. A method for manufacturing a semiconductor thin film according to claim 1.