JPH101392A - Formation of crystalline silicon thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the formation which enables the reduction in cost of LPE (liquid phase epitaxy) through the use of an inexpensive substrate and yet, maximum utilization of the characteristics of LPE capable of obtaining a good quality crystal. SOLUTION: This formation is intended for forming a crystal silicon thin film 16b on the surface of a substrate 5 by LPE that comprises saturating a solvent with silicon at a high temp. to form a saturated solution and cooling this saturated solution to deposit silicon from the resulting supersaturated solution with silicon and to grow crystalline silicon. In the formation, a substrate 5 consisting of a material different from silicon is prepared and then, a silicon oxide film 15 is formed on the surface of the substrate 5 and thereafter, silicon crystal liquid phase epitaxial growth is performed on the silicon oxide film 15 by using a solvent to which aluminum is added, to form the objective crystal silicon thin film 16b on the substrate 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of forming a crystalline silicon thin film based on a liquid phase growth method.

[0002]

2. Description of the Related Art Conventionally, as a method of obtaining a crystalline thin film used as a semiconductor material, conventionally, a solute material is saturated at a high temperature in a solvent having a low melting point, and then the saturated solution is cooled to obtain a supersaturated solute material. Liquid phase growth method (Liquid Phase) to obtain crystalline thin film by depositing as crystals on a substrate
Epitaxy (hereinafter abbreviated as “LPE”) is well known. This LPE is performed using, for example, the following various LPE devices.

[0003] First, the LP of the tipping method (tilt method)
FIG. 5 shows an example of the E apparatus. In this apparatus, a metal solution (hereinafter, referred to as “melt”) 3 serving as a solvent and a raw material 4 serving as a solute are put into a melting tank 2 in a furnace core tube 1 inclined to one side, and the melt 3 is biased. The substrate 5 is mounted in the melting tank 2 on the opposite side from the above, and the raw material 4 is diffused into the melt 3 and saturated at a high temperature. Then, the furnace core tube 1 was tilted to the opposite side, and the melt 3 in which the solute was saturated was moved onto the substrate 5, and in that state, epitaxial growth was performed while lowering the temperature, and a crystal film having a predetermined thickness was obtained. At this point, the furnace core tube 1 is tilted again as before, and the substrate 5 on which the crystal film is formed is taken out. In addition, 6 is a thermocouple, and 7 is a clamp for holding the substrate 5. The inside of the furnace core tube 1 is in an atmosphere of high-purity hydrogen gas or the like.

[0004] In addition, a dipping type (immersion method) LP
FIG. 6 shows an example of the E apparatus. In this apparatus, a platinum crucible 10 containing a melt 3 is placed in a vertical furnace 8, a raw material 4 to be a solute is put therein and melted at a high temperature, and then the substrate 5 is lowered from above to melt the melt. 3 and the temperature is lowered in this state to perform epitaxial growth on the surface of the substrate 5. In addition, 6 is a thermocouple, 11 is an upper heater, and 12 is an alumina tube.

FIG. 7 shows an example of a slide boat type LPE apparatus. In this apparatus, a substrate 5 and a raw material 4 are fitted and held on a top surface of a base plate 13 at a predetermined interval, and a slider 1 holding a melt 3 in a through-hole 14a thereon.
The slider 14 is moved to the right so that the melt 3 comes in contact with the raw material 4, and the melt 3
After the raw material 4 is diffused and saturated, the melt 3
The slider 14 is moved to the left so as to make contact with the substrate 5 and the temperature is lowered to perform epitaxial growth on the surface of the substrate 5.

[0006] Since the above-mentioned LPE is a crystal growth from a quasi-equilibrium state between a solid phase and a liquid phase, a crystal with high purity and few defects and high integrity can be obtained. This is a major advantage of LPE that other methods do not have. For this reason, LPE is regarded as promising as a method for forming a crystalline silicon thin film used for semiconductor materials and solar cells.

[0007]

However, in the conventional LPE, a crystal film made of the same material as that of the substrate is generated. If a crystalline silicon thin film is to be produced by LPE, the substrate 5 is Expensive silicon wafers must be used. That is, LPE
When a material different from silicon, such as carbon or stainless steel, is used for the substrate when a crystalline silicon thin film is prepared by the method, liquid phase growth hardly occurs because the lattice constant is different between the silicon and the substrate, and crystals are generated. do not do. Further, even if a certain amount of crystal is generated, the growth is insufficient and a film is not formed on the substrate, and it is impossible to obtain a film-like silicon crystal. Therefore, L
In order to obtain a crystalline silicon thin film by PE, a silicon wafer must be used as a substrate without fail as described above. This results in raising the cost of LPE. In addition, a crystalline silicon thin film is formed on a silicon wafer substrate by LPE,
When it is used for semiconductors and solar cells, the problem is that no matter how good the crystal obtained by LPE is, if the silicon wafer of the substrate has many defects, the properties of the good crystal by LPE will be reduced accordingly. There is.

[0008] As described above, the conventional LPE is problematic in that the cost is high and the greatest advantage of obtaining high quality crystals is not fully utilized.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to reduce the cost of an LPE by using an inexpensive substrate and to obtain a high-quality crystal.
It is an object of the present invention to provide a method for forming a crystalline silicon thin film which can make the most of the characteristics of the above.

[0010]

In order to achieve the above object, a method of forming a crystalline silicon thin film according to the present invention comprises the steps of: saturating silicon in a solvent at a high temperature; and cooling the saturated solution to deposit supersaturated silicon. A method of forming a crystalline silicon thin film on a substrate surface by a liquid phase growth method for growing, comprising preparing a substrate made of a material different from silicon, forming a silicon oxide film on the surface of the substrate, and then depositing aluminum. The gist of the present invention is to form a crystalline silicon thin film on the substrate by growing a liquid phase on the silicon oxide film using the added solvent.

[0011]

Next, embodiments of the present invention will be described in detail.

According to the method of the present invention, a substrate made of a material different from silicon is prepared, a silicon oxide film is formed on the surface of the substrate, and then a solvent containing aluminum is used to form a film on the silicon oxide film. By performing liquid phase growth by LPE, a thin film of crystalline silicon is formed on the substrate.

As the material of the substrate, various materials different from silicon are used, and inorganic materials such as carbon and quartz,
Various materials can be used as long as they can withstand high temperatures during liquid phase growth and do not dissolve in a solvent (tin or aluminum), such as ceramic materials such as alumina, silicon carbide, zirconia, and silicon nitride. . Among these, carbon is preferred from the viewpoint that it can be obtained at low cost, and that it can withstand high temperatures and is conductive, so that it can be used as a back electrode during device fabrication.

As a method for forming a silicon oxide film,
For example, a sputtering method, a vacuum deposition method, an ion plating method, and various CVD (chemical vapor) methods.
Various methods such as a rdposition method and a sol-gel method are performed, and the method is not particularly limited. Among these, the sol-gel method is suitably used, particularly from the viewpoint that mass productivity is good and a relatively good film can be obtained at a low temperature.

The thickness of the silicon oxide film is preferably 1 to 100 μm, more preferably 1 to 50 μm,
Most preferably, it is formed in the range of 1 to 10 μm. 10
If the thickness exceeds 0 μm, the cost of forming the silicon oxide film is too high, and the silicon oxide remaining without reacting is present as an insulator and becomes a resistance.
If it is less than 1, the effect of the silicon oxide film cannot be sufficiently obtained, and the formation of the crystalline silicon thin film becomes insufficient.

The solvents used for LPE include tin,
Various low-melting metals such as gallium, indium, copper, arsenic, and antimony are used. Among them, crystalline silicon having good electrical properties is advantageous, and in view of low cost, particularly, And tin are preferred.

The amount of aluminum added to the solvent is preferably 5 to 20% by weight, and most preferably 5 to 10% by weight. That is, 2
If the content exceeds 0% by weight, the growth of the solute in the solvent becomes dominant. If the content is less than 5% by weight, the effect of the addition of aluminum cannot be sufficiently obtained, and the dissolved amount of the solute, that is, the precipitated amount decreases. That's why.

In the method of the present invention, as shown in FIG. 1, first, a silicon oxide film 15 is formed on the surface of the substrate 5 made of the above-mentioned different material, and then the substrate 5 on which the silicon oxide film 15 is formed is formed. An LPE growth film of crystalline silicon is formed on the surface by a predetermined method such as the above-described tipping method, dipping method, slide boat method, or the like.

When performing this LPE, as described above,
Since aluminum is added to the solvent, when the substrate 5 is immersed in the solvent, the silicon oxide film 15 formed on the surface of the substrate 5 reacts with aluminum in the solvent as shown in the following formula. As shown in FIG. 2, the silicon oxide film 1
Silicon 16 is deposited on 5.

[0020]

## EQU1 ## 3SiO ₂ + 2Al → 2Al ₂ O ₃ + 3Si

The deposited silicon 16 serves as a nucleus, and as shown in FIG. 3, crystalline silicon 16a grows in a liquid phase. As shown in FIG. 4, a crystalline silicon thin film 16b is formed on the surface of the substrate 5 soon. It is formed. Of course, the method and apparatus for performing the LPE are not limited to those described above, and various methods and apparatuses can be used.

According to the above-mentioned method, the silicon oxide film 15 is formed on the surface of the substrate 5 in advance, and liquid phase growth is performed by LPE. Of the crystalline silicon thin film 16b can be formed. Moreover, despite the fact that the substrate 5 is made of a dissimilar material, the crystal growth does not become insufficient as in the prior art, and dense film-like crystalline silicon with few defects can be obtained.

In the present invention, the crystalline silicon thin film 16b is formed on a substrate 5 made of a material different from silicon used for a semiconductor or a solar cell, and the obtained crystalline silicon thin film 16b is integrated with the substrate 5. Formed. Therefore, various characteristics can be added to the crystalline silicon thin film 16b by selecting the material of the substrate 5. For example, when a material having high mechanical strength, such as alumina, silicon carbide, or zirconia, is used as the substrate 5, the substrate 5 acts as a reinforcing material, so that the mechanical strength of the crystalline silicon thin film 16b can be improved. . When a conductive material such as carbon or molybdenum is used for the substrate 5, the substrate 5 itself can be used as an electrode. Alternatively, when a transparent body such as quartz, sapphire, or the like is used as the substrate 5, the substrate 5 itself can be used as a cover material for a solar cell. As described above, by appropriately selecting the material of the substrate 5 according to the purpose, new characteristics can be added to the crystalline silicon thin film 16b, and the multi-faceted use of the crystalline silicon thin film 16b can be achieved. it can.

[0024]

As described above, according to the method for forming a crystalline silicon thin film of the present invention, a silicon oxide film is formed on the surface of a substrate made of a material different from silicon.
LPE growth is performed using a solvent to which aluminum is added, whereby aluminum in the solvent is reacted with silicon oxide to deposit silicon on the substrate, and liquid phase growth is performed using the deposited silicon as a nucleus. It is.
According to this method, unlike the conventional method, an inexpensive material different from silicon can be used for the substrate instead of an expensive silicon wafer. Therefore, LPE can be performed at low cost, and the cost of semiconductors and solar cells can be reduced. Can be reduced. In addition, despite the use of a substrate made of a different material, the crystal can be sufficiently grown to form a dense film.

Further, since the formed product of the crystalline silicon thin film obtained by the present invention is a combination of a substrate of a different material and a crystalline silicon thin film formed by LPE, only a high-quality crystal formed by LPE is used for a semiconductor or solar cell. And the like, the characteristics of high quality crystals by LPE are not diminished, and the characteristics of LPE can be utilized to the maximum.

Next, an embodiment will be described.

[0027]

Example 1 As a substrate, on a 0.5 mm thick carbon (25 mm × 25 mm), a sol-gel method was used.
A silicon oxide film having a thickness of 50 μm was formed.

On the other hand, a tin solvent to which 10% by weight of aluminum was added was prepared, and silicon was saturated. The solubility of silicon in the saturated silicon-tin solution at 850 ° C. was about 2.5% by weight.

Then, the substrate on which the silicon oxide film was formed was immersed in an aluminum-added saturated silicon-tin solution heated and melted at about 850 ° C. by using a dipping type LPE apparatus shown in FIG. The temperature was lowered to 650 ° C. at a cooling rate of ° C./min to grow a crystalline silicon thin film on the substrate in the liquid phase.

The crystalline silicon thin film thus obtained had a crystal size of 50 to 100 μm and a thickness of about 50 to 100 μm. Moreover, the grown crystals grew in close contact with each other, forming a good quality film with almost no defects.

[0031]

Example 2 A 1 μm thick silicon oxide film was formed on a 0.5 mm thick carbon (25 mm × 25 mm) as a substrate by a sputtering method.

On the other hand, a tin solvent to which 5% by weight of aluminum was added was prepared, the silicon was saturated, and the substrate on which the silicon oxide film had been formed was subjected to a dipping type LPE apparatus shown in FIG. Immersed in an aluminum-added saturated silicon-tin solution heated and melted to 750 ° C.
The temperature was lowered to 550 ° C. at a cooling rate of 1 ° C./min to grow a crystalline silicon thin film on the substrate in a liquid phase.

The crystalline silicon thin film thus obtained had a crystal size of 50 to 100 μm and a thickness of about 50 to 100 μm. Moreover, the grown crystals grew in close contact with each other, forming a good quality film with almost no defects.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a method of the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of the method of the present invention.

FIG. 3 is an explanatory view showing an embodiment of the method of the present invention.

FIG. 4 is an explanatory diagram showing one embodiment of the method of the present invention.

FIG. 5 is an explanatory diagram illustrating an example of an LPE device.

FIG. 6 is an explanatory diagram showing a second example of the LPE device.

FIG. 7 is an explanatory diagram showing a third example of the LPE device.

[Explanation of symbols]

 5 Substrate 15 Silicon oxide film 16b Crystalline silicon thin film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Go Matsuda 2-6-6 Chikushinmachi, Sakai City, Osaka Inside Daido Hokusan Sakai Plant (72) Inventor Shigeki Ito 2-6 Chikushinmachi, Sakai City, Osaka Prefecture 40 Daido Hokusan Co., Ltd. Sakai Plant

Claims (4)

[Claims] 1. A method for forming a thin film of crystalline silicon on a substrate surface by a liquid phase growth method in which a solvent is saturated with silicon at a high temperature, and a saturated solution is cooled to deposit and grow supersaturated silicon. A substrate made of a material different from silicon is prepared, a silicon oxide film is formed on the surface of the substrate, and then liquid phase growth is performed on the silicon oxide film using a solvent to which aluminum is added. Forming a crystalline silicon thin film on the substrate. 2. The method according to claim 1, wherein tin is used as a solvent. 3. The method for forming a crystalline silicon thin film according to claim 1, wherein the amount of aluminum added is 5 to 20% by weight based on the total amount of the solvent. 4. The silicon oxide film has a thickness of 1 to 100 μm.
The method for forming a crystalline silicon thin film according to claim 1.