JPH0118575B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a silicon crystal film with excellent crystallinity.

Currently, semiconductor devices using silicon use wafers with a thickness of 200 μm, which are obtained by slicing and polishing a single crystal ingot made by the Czyochoralski method. However, in semiconductor devices, only the vicinity of the surface of the wafer is used, and most of it is wasted, which is one obstacle to reducing the cost of devices. Additionally, the thick silicon layer makes it difficult to separate elements, making it difficult to develop high-speed LSIs.

One solution is the SOS technology, in which a silicon thin film is epitaxially grown on sapphire crystal, but the cost of sapphire crystal is high and there is a problem in reducing the cost of the device.

In order to solve the above problems, attempts have been made to fabricate semiconductor devices by forming a transferred crystalline silicon film on an inexpensive substrate. However, with conventional methods, it has not been possible to obtain an element with sufficient performance due to the small crystal grain size of 0.1 to 10 μm. To improve performance, it is necessary to increase the grain size and reduce the recombination of minority carriers at the grain boundaries. Therefore, the polycrystalline film is heated near the melting point of silicon to grow crystal grains and eventually form a single crystal film. Attempts are being made to obtain However,
Grain growth does not proceed rapidly when heated below the melting point (CDOuwens and H. Heijigers, App. Phys.
Letters, Vol. 26, No. 10, 569 (1975)), and above the melting point, the silicon melt becomes spherical due to surface tension, making it impossible to obtain a film with uniform thickness.

In order to prevent polycrystalline silicon films from agglomerating due to surface tension during melting, the present invention provides a protective film on a silicon film provided on an insulating non-single crystal substrate such as alumina or a metal film formed on the substrate. It is characterized by providing the following. Conventionally, the method of improving crystallinity by adding a protective film to reduce surface tension was
Although known in InSb (HHWieder,
Solid State Communication, Vol.3, 159
(1965)) Nothing is known about Si.

The inventors have found that various oxide films for passivation of single-crystal silicon devices are suitable as protective films for recrystallization of polycrystalline silicon. For example, SiO ₂ , Al ₂ O ₃ , In ₂ O ₃ ,
_{SnO2 , Al2O3} - _{SiO2 , B2O3 - SiO2} , _{P2O5 , P2O5}
- Low-melting glasses containing SiO ₂ and PbO, as well as multi-component glasses containing various combinations of the above (e.g.
7059 glass) etc. are suitable. Among the various glass films mentioned above, B ₂ O ₃ -SiO ₂ -based and P ₂ O ₅ -SiO ₂ -based glasses can have thermal expansion coefficients that match those of Si by appropriately selecting the composition, and are stable during heating and cooling. Suitable as a crack-free protective film. Other examples of such glasses include PbO−B ₂ O ₃ −Al ₂ O ₃ −
SiO ₂ system, PbO−Al ₂ O ₃ −SiO ₂ system, PbO−B ₂ O ₃ −
ZnO−SiO ₂ system and PbO−B ₂ O ₃ −Al ₂ O ₃ −ZnO−
Examples include SiO ₂ glass. When the silicon film melts, the silicon contracts, and when it cools and solidifies, it shrinks by about 9%.
As it expands, a large stress is applied to the protective film. It is undesirable for the protective film to crack or peel due to such stress, and in order to prevent this, it is necessary to soften the protective film during melting or recrystallization of the silicon film in order to alleviate stress.

The various silicate glasses mentioned above generally soften near the melting point of Si and are suitable as a protective film. When this type of oxide film has a significantly low softening point, it generally tends to flow easily and the silicon surface tends to become uneven. In this case, this problem can be overcome by forming a two-layer film by depositing a hard film that does not soften on top of a softening oxide film. In addition, B ₂ O ₃ in the above glass film
_-SiO2 -based or _P2O5 - _SiO2- based silicate glass films are not only effective as _a protective film during recrystallization, but also effective for doping B or P impurities into the substrate crystal. Needless to say, it is effective.

Although the oxide film has been described above, other materials that have good wettability with silicon are also effective. Other materials with good wettability include nitrides such as BN, AIN, GaN, and Si ₂ N ₄ , carbides such as B ₄ C, Al ₄ C ₃ , and SiC, and carbon. These materials generally have better wettability than oxides, and carbon and carbides in particular wet silicon almost completely.

As the above-mentioned protective film forming method, normal film forming methods such as chemical vapor deposition, sputtering, electron beam evaporation, and glass welding can be used. Direct oxidation, nitridation, and carbonization of the silicon film surface are also effective.

The silicon film before recrystallization is usually a polycrystalline film, but it is also effective for amorphous films. Such an amorphous film is formed at a low temperature by a chemical vapor deposition method using silane gas, an electronic vapor deposition method, or the like. Further, as the silicon film, a multilayer consisting of a silicon film and another substance, or a silicon film containing another substance is also effective. Other materials include various metals and compounds such as aluminum, tin, titanium, zirconium, niobium, and platinum, and alloys of these materials with silicon have a lower melting point than silicon, making them advantageous as low-temperature recrystallization methods.

Hereinafter, the present invention will be explained in detail using Examples as well as Reference Examples.

Reference Example 1 After depositing a polycrystalline silicon film on an alumina substrate by chemical vapor deposition, an alumina film was deposited on the silicon film, heated above the melting point of silicon, cooled, and then recrystallized. A reference example will be explained below with reference to FIG.

First, an alumina plate 1 was ultrasonically cleaned in an organic solvent, then inserted into a high frequency heating furnace and heated to 1100°C, and trichlorosilane gas was flowed to form a 5 μm thick polycrystalline silicon layer 2. When the grain size of the polycrystalline layer was examined using a transmission electron microscope, the average grain size was about 1 μm.

Next, the sample was heated to 400° C. and an alumina film 3 having a thickness of 0.7 μm was deposited on the polycrystalline silicon layer 2 by oxidation of triisobutyaluminum gas.

This sample was heated at 1420° C. for 10 minutes in an oxygen gas atmosphere. As a result, the silicon film melted and recrystallized during cooling. The grain size of the recrystallized silicon film is 2 mm.
The value was an order of magnitude higher than the value before recrystallization.

Reference Example 2 After depositing a polycrystalline silicon film on an alumina substrate by chemical vapor deposition, a phosphosilicate glass film is deposited on the silicon and recrystallized by heating it above the melting point of silicon. Ta. This reference example will be explained below with reference to FIG.

First, an alumina plate 1 was ultrasonically cleaned in an effective solvent, then inserted into a high frequency heating furnace and heated to 1100°C, and trichlorosilane gas was flowed to form a 20 μm thick polycrystalline silicon film 2. When the grain size of the polycrystalline layer was examined using a transmission electron microscope, the average grain size was about 1 μm.

Next, the above sample was heated to 400℃ and PH ₃ −SiH ₄
5 mol% by chemical vapor deposition method using system gas.
A phosphosilicate glass film 3 containing P ₂ O ₅ was deposited on the 1 μm polycrystalline film 2 .

This sample was heated at 1420° C. for 10 minutes in an air atmosphere. As a result, the silicon film melted and recrystallized into dendrites during rapid cooling. The length of the dendrite crystal is about 1 cm, the width is about 1 mm, and the direct placement is 1μ before crystallization.
The particle size was much larger than that of m. If the silicon film is not coated with a phosphosilicate glass film, the silicon film will aggregate during melting and form a spherical shape, exposing the surface of the alumina substrate.

Reference Example 3 Polycrystalline silicon was deposited on an alumina substrate in the same manner as in Reference Example 1, and then heated in steam at 1000° C. for 1 hour to oxidize the surface. The thickness of the oxide film was approximately 0.5 μm.

This sample was heat treated in the same manner as in Reference Example 1 to obtain a recrystallized silicon film of the same level.

Reference Example 4 Polycrystalline silicon with a thickness of 50 μm was deposited on a carbon substrate in the same manner as in Reference Example 1.

This sample was heated to 1100°C, and a 1.0 μm thick silicon nitride film was deposited on the silicon surface by a reaction between silane gas and ammonia gas. Thereafter, low melting point glass powder was placed on the silicon nitride film and melted by heating to form a glass film with a thickness of 5 μm.

This was heated to 1420°C in an argon gas stream and then cooled to perform recrystallization. The crystallinity of the silicon film was similar to that of Reference Example 1.

Reference Example 5 After forming a polycrystalline silicon film on an alumina substrate, it was heated to about 1300° C. in an ammonia or nitrogen atmosphere to nitride the silicon surface.

Thereafter, a low melting point glass film was formed on the nitride film in the same manner as in Reference Example 4, and the same heat treatment was performed to obtain a recrystallized film of the same degree.

Reference Example 6 Polycrystalline silicon with a thickness of 50 μm was deposited on a carbon substrate in the same manner as in Reference Example 1.

This sample was heated to 1300°C and a silicon carbide film was deposited by a reaction between silicon and propane gas. Reference Example 4
It was heat treated in the same manner. As a result, reference example 1
A recrystallized film of similar quality was obtained.

Reference Example 7 A 50 μm thick polycrystalline silicon film was formed on a carbon substrate in the same manner as in Reference Example 1. A carbon film having a thickness of 0.5 μm was deposited on the surface of this silicon film by vacuum evaporation. This sample was heat treated in the same manner as in Reference Example 4 to obtain a recrystallized film having the same degree of crystallinity.

Reference Example 8 A 50 μm thick polycrystalline silicon film was formed on a carbon substrate in the same manner as in Reference Example 1. This sample was heated to 1350°C in a carbon-containing gas to carbonize the silicon surface.

This sample was heat-treated in the same manner as in Reference Example 4, and a recrystallized film close to the crystallinity obtained in Reference Example 1 could be obtained.

Example 1 After depositing metallic titanium on an alumina substrate, a polycrystalline silicon film was deposited, a double film of a borosilicate glass film and a silicon oxide film was deposited, and recrystallization was performed. below,
The present invention will be explained with reference to FIG.

First, the alumina substrate 11 was cleaned and inserted into a vacuum deposition apparatus. A titanium film 12 with a thickness of approximately 0.1 μm was formed on an alumina substrate 11 by electron beam evaporation, and a polycrystalline layer 13 with a thickness of 20 μm was further deposited in the same manner as in Reference Example 1.

Next, this sample was heated to 400℃ to form B ₂ H ₆ SiH ₂
The polycrystalline film 1 is formed by chemical vapor deposition using gas.
3, a borosilicate glass film 14 containing 17 mol% B ₂ O ₃ with a thickness of 0.8 μm is formed, and a silicon oxide film 15 is further formed on it.
0.2 μm was deposited. The SiO ₂ film 15 is provided to prevent the borosilicate glass film 14 from absorbing moisture and deteriorating, and to prevent the film 14 from softening and flowing.

This sample was heated in oxygen at 1380°C for 10 minutes to melt the silicon film, and then cooled at a rate of about 1°C/min to recrystallize the sample. The grain size of the recrystallized crystals is approximately
The grain size was 0.5 cm, which was significantly larger than before recrystallization.

Example 2 A 1 μm thick amorphous silicon film was deposited on an alumina substrate by electron beam evaporation, and a two-layer film similar to that in Example 1 was formed on the surface of the silicon film.

This sample was heat treated in the same manner as in Example 1,
A recrystallized film with comparable crystallinity was obtained.

Above, the present invention has been described for the case where a sample is uniformly heated and cooled, that is, for uniform recrystallization.
It is clear that the crystallinity of a silicon film can also be improved by combining the present invention with a method of recrystallization (recrystallization) or recrystallization during a temperature gradient.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a multilayer film showing a reference example, and FIG. 2 is a diagram for explaining an embodiment according to the present invention.

Claims (1)

[Claims] 1. After forming a first protective film on a polycrystalline silicon or amorphous silicon film formed on an insulating non-single crystal substrate, a step of forming a second protective film; The silicon film is heated to a temperature at which the first protective film is softened but not the second protective film, and the silicon film is recrystallized by liquid phase growth and the first protective film is softened. A method for producing a silicon crystal film, the method comprising the step of transitioning to a temperature at which the film is softened. 2. A step of forming a first protective film on a polycrystalline silicon film or an amorphous silicon film formed on a metal film provided on a substrate, and melting the silicon film and removing the first protective film. production of a silicon crystal film, comprising the step of heating the silicon film to a temperature at which it softens, and shifting the silicon film to a temperature at which the silicon film recrystallizes by liquid phase growth and at which the first protective film softens. Method. 3 After forming a first protective film on a polycrystalline silicon film or an amorphous silicon film formed on a metal film provided on a substrate, a step of forming a second protective film, and a process in which the silicon film is The silicon film is melted and heated to a temperature at which the second protective film does not soften but the first protective film softens, and the silicon film recrystallizes by liquid phase growth and the first protective film softens. 1. A method for producing a silicon crystal film, the method comprising the step of transitioning to a temperature of