JPH06349751A - Method and device for liquid growth - Google Patents

Abstract

PURPOSE:To continuously form crystals on substrates by supplying a solute to a solvent in a solvent reservoir and circulating the solvent containing the solute through a pipeline and, at the same time, bringing the substrates into contact with the solvent containing the solute at an opening provided at part of the pipeline. CONSTITUTION:Liquid growth is performed by using Sn as a solvent and Si as a solute in such a way that polycrystalline Si is placed on a raw material plate 104 and a (100) single-crystal Si wafer is placed on a slider 108 as a substrate so that the wafer 107 cannot come into contact with the Sn and an electric furnace and heater block 102 are respectively maintained at about 950 deg.C and 960 deg.C. After a sufficient time has elapsed, the wafer 107 is brought into contact with the Sn solvent containing the Si solute by moving the slider 108 and the wafer 107 is kept in the same state for about 30 minutes. Upon completing the growth, the wafer 107 is separated from the Sn solvent by again moving the slider 108. Therefore, crystals can be continuously grown with a simple constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid phase growth method and an apparatus therefor, and more particularly to a liquid phase growth method and an apparatus therefor capable of continuous growth and capable of mass production.

[0002]

2. Description of the Related Art Since the liquid phase epitaxy method is crystal growth from a quasi-equilibrium state, high quality crystals close to stoichiometric composition can be obtained.
In the field of compound semiconductors such as aAs, LEDs, laser diodes, etc. are produced as already established technologies.

Recently, liquid phase growth of Si has been attempted for the purpose of obtaining a thick film (for example, Japanese Patent Laid-Open No. 58-89874).
Applications to solar cells are being studied.

However, in the conventional liquid phase epitaxy method, in general, the solvent is cooled to a supersaturated state and the excess solute is deposited on the substrate. Therefore, when the temperature drops to some extent, the temperature is temporarily raised to the original temperature and the crystal growth is performed again. It becomes a cycle of doing. Therefore, there was a problem in mass productivity. In particular, in the case of Si for solar cells, which requires a relatively thick film, the range of decrease in temperature during growth was large, and there was considerable time loss until the temperature was returned to the original temperature.

For the purpose of improving this point and increasing mass productivity, a temperature difference method has been proposed which enables continuous growth by providing a temperature difference in the solvent or between the solvent and the substrate. That is, FIG.
As shown in, by providing a temperature difference within the range of the height of the solvent reservoir, the solute is transported from the raw material plate 205 on the upper surface of the solvent to the substrate 203 on the lower surface of the solvent 206 for growth. However, in this case, there is a problem that precise temperature control in a narrow range is required and the growth apparatus becomes expensive.

[0006]

The present invention has been completed as a result of earnest research by the present inventors in order to solve the above-mentioned problems in the prior art, and is a simple and mass-producible liquid phase growth method. The purpose is to provide the device.

[0007]

That is, the method of the present invention is to provide a solute to a solvent in a solvent reservoir, to circulate the solvent supplied with the solute through a pipe, and to provide a part of the pipe. There is a gist in a liquid phase growth method characterized in that a crystal is formed on a substrate by bringing the substrate into contact with a solvent supplied with a solute at the opening.

The apparatus of the present invention is a liquid phase growth apparatus in which a solute is dissolved in a solvent to precipitate crystals on a substrate, and a solvent reservoir for supplying the solute to the solvent and a solvent supplied with the solute are circulated. And a pipe, both ends of the pipe are connected to the side wall of the solvent reservoir, and an opening for contacting with a substrate is provided in the middle of the pipe. To do.

[0009]

In the method and apparatus of the present invention, as shown in FIG. 1, a solvent reservoir and a growth place are separately provided, and each is controlled to be constant at different temperatures, and the solvent is circulated by a pipe between them. By doing so, a temperature difference can be easily established between the solvent reservoir and the substrate. The operation of the present invention will be described in detail below based on experiments conducted by the present inventors.

(Experiment 1) Growth on stationary substrate As shown in FIG. 1, a solvent reservoir 105 made of carbon, and one side surface of the solvent reservoir 105, and a mid-growth substrate 107.
The flat pipe 103 made of carbon, which comes into contact with the slider 108 on which is mounted at the opening 109 and returns to the other side surface of the solvent reservoir 105, is arranged in the electric furnace 101. Surrounded by a block 102, the temperature can be controlled independently. The slider 108 is movable in the length direction, and the movement of the slider 108 starts / stops the growth on the substrate 107. As shown in FIG. 2, several carbon partition plates 302 are installed inside the solvent reservoir 301, and in combination with a raw material plate 303 serving as a lid of the solution reservoir, the same figure (b).
The solvent flow path is formed as described above. While the solvent is passing through this flow path, the solute is dissolved from the raw material plate 303 into the solvent and becomes saturated. The solvent discharged from the solvent reservoir 105 is in a supersaturated state due to the temperature of the electric furnace 101 which is set to a temperature lower than that of the solution reservoir 105 while circulating in the heat exchanger 104 formed of a flat pipe, and contacts the slider 108. Opening 109
At, a solute is deposited on the substrate 107 on the slider.

The solvent reservoir 105 and the flat pipe 103 are filled with Sn sufficiently purified in a hydrogen atmosphere as a solvent,
The solution reservoir is covered with the polycrystalline Si raw material plate 104, and the temperature inside the electric furnace is kept constant at 950 ° C. (100) single crystal Si substrate 1
07 was placed on the slider 108. The position of the slider is adjusted in advance, so that the Si substrate 107 is connected to the opening 109 of the flat pipe.
Heater block 10
2 so that the temperature of the solvent reservoir 105 is set to be 5 ° C. higher than the temperature in the surrounding electric furnace, and the solvent is stored in the rotor 10
6 was used to circulate.

After a sufficient time has passed, the slider 10
8 to move the Si substrate 107 to S in the opening 109.
The n-solvent was brought into contact with the n-solvent, and the solvent was circulated for 30 minutes. Then, the slider 108 was moved again to separate the Si substrate 107 from the Sn solvent and the growth was completed.

Observation of the surface of the grown Si substrate with an optical microscope and a scanning electron microscope revealed that it was very smooth, and the thickness of the grown Si layer was measured with a step meter and a scanning electron microscope. It was about 25 μm. The Si layer obtained by the backscattered electron diffraction method and the Raman spectroscopy method inherited the orientation of the underlying Si substrate (10
0) It was confirmed to be single crystal Si.

(Experiment 2) Continuous Growth on a Moving Substrate Based on the result of Experiment 1, continuous growth on a moving substrate was performed.
As shown in FIG. 4, an elongated (100) Si substrate 407 was placed on a slider 408, and Sn was circulated under the same conditions as in Experiment 1 to grow. The position of the slider is adjusted in advance so that the Si substrate 407 does not come into contact with the opening 409 of the flat pipe, and the heater block 402
Is set so that the temperature of the solvent reservoir 405 is higher by 5 ° C. than the temperature in the electric furnace around the solvent reservoir 405 and the solvent is stored in the rotor 406
Was used to circulate.

After a sufficient time has passed, the slider 40
8 was fed at a feed rate of 5 mm / min, and the Si substrate 407 was brought into contact with the Sn solvent in the opening 409 to grow crystals. The feeding of the slider 408 was stopped when the Si substrate 407 had completely passed through the opening 409, and the growth was completed.

When the surface of the grown Si substrate was observed with an optical microscope and a scanning electron microscope, the entire surface of the substrate was smooth, and the thickness of the grown Si layer was measured with a step meter and a scanning electron microscope. , About 5
was μm. Further, it was confirmed by reflection electron diffraction method and Raman spectroscopy that the obtained Si layer was (100) single crystal Si inheriting the orientation of the underlying Si substrate.

As described above, it has been shown that the liquid phase growth can be continuously performed by separately controlling the temperature by separately setting the solvent reservoir and the growth place and circulating the solvent through the pipe between them.

The present invention, which has been completed based on the experimental results described above, relates to the liquid phase growth method for performing continuous growth as described above. The feature of the present invention is that the temperature is controlled independently of the location of the solvent reservoir and the growth substrate, and the solvent is circulated through the pipe between them to maintain the temperature gradient as seen in the conventional continuous liquid phase growth method. It does not require precise temperature control.

High-purity carbon is mainly used as the material of the solvent reservoir and the slider for storing the solvent used in the present invention.

The solvent and solute used in the present invention may be any combination as long as they are used in the conventional liquid phase growth method. For example, when Si is used as the solute, the solvent is For example, Sn, Ga, In, S
b, Bi, etc. are used. Here, when Sn is used as the solvent, the obtained Si crystal is electrically neutral, and the conductivity type can be determined at a desired doping concentration by appropriately adding a desired impurity after or during the growth. .

In the method of the present invention, H ₂ or N ₂ is used as the atmosphere in which the solvent and the substrate are placed, and the pressure is preferably about 10 ^-2 Torr to 760 Torr, more preferably 10 ^-1 Torr to 760 Torr.
It is the range of r.

The solvent temperature in the method of the present invention depends on the kind of the solvent, but is 800 ° C. when Sn is used.
It is desirable that the temperature be controlled to 1100 ° C. or lower.

The present invention can be applied not only to homoepitaxial but also to heteroepitaxial.

The speed of the solvent in the pipe is 1 to
100 mm / min is preferable, and the moving speed of the slider is preferably 0 to 300 mm / min. Further, the temperature difference ΔT between the temperature in the solvent reservoir and the substrate temperature is ΔT = 3 to
50 ° C is preferred. If ΔT is too small, the solute may melt back from the surface of the substrate. On the other hand, if ΔT is too high, the growth rate may decrease, or crystal grains may precipitate in the solvent in the pipe before reaching the substrate. It may happen.

[0025]

EXAMPLES Hereinafter, the method of the present invention for growing a desired crystal will be described in more detail, but the present invention is not limited to these examples.

(Example 1) Si was produced by using the apparatus shown in FIG.
The epitaxial layer was grown. Sn as solvent and S as solute
Growth was performed using i. Polycrystalline Si on the raw material plate 104
Further, a (100) single crystal Si wafer 107 is placed on the slider 108 as a substrate, and the Si wafer is not touched with Sn in advance. The inside of the electric furnace is kept at 950 ° C. and the inside of the heater block 102 is kept constant at 960 ° C. I kept it. When a sufficient time has passed, the slider 108 is moved to move the Si wafer 1
07 was brought into contact with a Sn solvent supplied with Si, and left as it was for 30 minutes. After that, the slider 108 was moved again to separate the Si wafer 107 from Sn and the growth was completed.

When the thickness of the grown silicon layer was measured with a step meter and a scanning electron microscope, the thickness was about 40 μm. Further, it was confirmed by reflection electron diffraction method and Raman spectroscopy that the obtained silicon layer was (100) single crystal silicon inheriting the orientation of the underlying silicon substrate.

Example 2 Polycrystalline S was prepared in the same manner as in Experiment 2.
i was continuously grown. Polycrystalline Si formed by casting method is 20 mm wide, 200 mm long, 0.6 mm thick
The substrate was processed into a substrate, surface-polished, and then washed to obtain a substrate.

As shown in FIG. 3, a polycrystalline Si substrate 407 is placed on a slider 408, and S is formed under the same conditions as in the first embodiment.
Growth was carried out by circulating n solvent. The length of the opening provided in the flat pipe is 50 mm, and the circulation speed of the Sn solvent is 25 mm.
mm / min, the position of the slider was adjusted in advance to prevent the Si substrate 407 from coming into contact with the Sn solvent in the opening 409 of the flat pipe, and the electric furnace was kept at 950 ° C. and the heater block was kept at 960 ° C. I kept it.

After a sufficient time has passed, the slider 40
While feeding 8 at a feed rate of 10 mm / min, the polycrystalline Si substrate 407 was brought into contact with the Sn solvent in the opening 409 to perform crystal growth. All the polycrystalline Si substrate 407 has the opening 4
After passing 09, the feeding of the slider 408 was stopped and the growth was completed.

When the film thickness of the grown Si layer was measured by a step meter and a scanning electron microscope, it was found to be uniform over almost the entire surface and about 7 μm. In addition, the orientation of the grown Si layer is determined by ECP (Electron Channel
ng Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited.

(Example 3) In the same manner as in Example 2, polycrystalline Si was continuously grown. Polycrystalline Si formed by casting method is 20 mm wide, 200 mm long, 0.6 m thick
The substrate was processed into m, surface-polished, and then washed.

As shown in FIG. 3, a polycrystalline Si substrate 407 was placed on a slider 408, and Sn was circulated for growth. The length of the opening provided in the flat pipe is 100 m
m, the circulation rate of the Sn solvent is 40 mm / min, the position of the slider is adjusted in advance so that the Si substrate 407 does not come into contact with the Sn solvent at the opening 409 of the flat pipe, and the inside of the electric furnace is 950 ° C. 970 ℃ in the heater block
Kept constant.

After a sufficient time has passed, the slider 40
While feeding 8 at a feed rate of 20 mm / min, the polycrystalline Si substrate 407 was brought into contact with the Sn solvent in the opening 409 to perform crystal growth. All the polycrystalline Si substrate 407 has the opening 4
After passing 09, the feeding of the slider 408 was stopped and the growth was completed.

The thickness of the grown Si layer was measured by a step meter and a scanning electron microscope, and it was found to be uniform and about 18 μm over almost the entire surface. In addition, the orientation of the grown Si layer is determined by ECP (Electron Channel)
ing Pattern) method, it was found that the crystal orientation of each grain of the underlying polycrystalline Si substrate was inherited.

As described above, it was shown that the crystalline Si layer can be continuously grown on the polycrystalline substrate while feeding the substrate.

In the above-mentioned Embodiments 2 and 3, the case where the substrate placed on the slider is used is shown. For example, a web-like substrate having a Si layer adhered on its surface is brought into contact with an Sn solvent. It is also possible to perform continuous film formation by feeding the substrate in one direction by roll-to-roll.

Example 4 An n ⁺ p-type thin film crystal solar cell was produced by the continuous liquid phase epitaxy method of the present invention. First, in the same manner as in Example 1, a polycrystalline Si layer was grown on a p-type polycrystalline Si wafer (ρ = 0.01 Ω · cm) having a thickness of 500 μm by using the apparatus shown in FIG.

As a raw material plate, p-type polycrystalline Si (ρ = 2Ω ·
cm) was used to keep the polycrystalline Si wafer from coming into contact with the Sn solvent, and the temperature inside the electric furnace was kept constant at 950 ° C. and the temperature inside the heater block was kept constant at 960 ° C. When a sufficient time had passed, the slider was moved to bring the polycrystalline Si wafer into contact with the Sn solvent, and the state was left as it was for 40 minutes. After that, the slider was moved again to separate the substrate from Sn and the growth was completed.

The thickness of the grown Si layer was measured by a step meter and a scanning electron microscope, and it was about 50 μm. Next, thermal diffusion of P was performed on the surface of the grown Si layer using POCl ₃ as a diffusion source at a temperature of 900 ° C. to form an n ⁺ layer, and a junction depth of about 0.5 μm was obtained. N ⁺ formed
The dead layer on the layer surface was wet-oxidized and then removed by etching to obtain a junction depth having an appropriate surface concentration of about 0.2 μm.

Finally, EB (Electron Bean)
m) Current collector electrode (Ti / Pd / Ag (40 nm
/ 20 nm / 1 μm)) / ITO transparent conductive film (820n
m) was formed on the n ⁺ layer, and a back surface electrode (Al (1 μm)) was formed on the back surface of the substrate.

The thin-film polycrystalline Si solar cell thus obtained was measured for IV characteristics under AM1.5 (100 mW / cm ² ) light irradiation, and an open circuit voltage of 0.57 V was obtained at a cell area of 4 cm ^2. , Short circuit photocurrent 33.5m
A / cm ² and a fill factor of 0.72 were obtained, and an energy conversion efficiency of 13.7% was obtained.

As described above, according to the present invention, the temperature of the solvent reservoir and the growth substrate are controlled independently, and the solvent is circulated between them by a pipe, thereby eliminating the need for precise control as in the prior art. It was shown that crystal growth can be performed continuously.

[0044]

As described above, according to the present invention, it is possible to continuously grow crystals in a liquid phase method with a simple structure. INDUSTRIAL APPLICABILITY The present invention is most suitable as a mass production method for devices requiring crystal thickness, particularly solar cells.

[Brief description of drawings]

FIG. 1 is a schematic view of a continuous liquid phase growth apparatus used to carry out the method of the present invention.

FIG. 2 is a schematic diagram of a solvent reservoir used to carry out the method of the present invention.

FIG. 3 is a schematic view of a continuous liquid phase growth apparatus used for carrying out the method of the present invention.

FIG. 4 is a schematic view of a conventional continuous liquid phase growth apparatus.

[Explanation of symbols]

 101, 401 electric furnace, 111, 411 heat exchanger, 102, 402 heater block, 201 boat, 103, 403 circulation pipe, 104, 205, 303, 404 raw material plate, 105, 301, 405 solvent reservoir, 106, 406 rotor 107, 203, 407 Substrate, 108, 202, 204, 408 Slider, 110, 206, 410 Solvent.

Claims (17)

[Claims] 1. A solute is supplied to a solvent in a solvent reservoir, the solvent to which the solute is supplied is circulated through a pipe, and a substrate is provided at an opening provided in a part of the pipe,
A liquid phase epitaxy method which comprises forming crystals on a substrate by bringing a solute into contact with a solvent supplied thereto. 2. The liquid phase growth method according to claim 1, wherein the temperature of the solvent reservoir is set higher than that of the circulation pipe and the substrate in contact therewith. 3. The liquid phase growth method according to claim 1, wherein the solvent supplied with the solute is circulated by a solvent circulation rotor provided in a part of the inside of the pipe. 4. The growth is performed by disposing the substrate on a slider and bringing the solvent into contact with the substrate at an opening of the circulation pipe while moving the slider. 4. The liquid phase growth method according to any one of 3 above. 5. The substrate is a web-shaped continuous substrate,
2. The liquid phase growth method according to claim 1, wherein the continuous substrate is grown by bringing the solvent into contact with the continuous substrate at the opening of the circulation pipe while the continuous substrate is moving. 6. The liquid phase epitaxy method according to claim 1, wherein the temperature of the solvent reservoir and the temperature of the circulation pipe and the substrate in contact therewith are kept constant. 7. The liquid phase growth method according to claim 1, wherein the solvent is Sn. 8. The liquid phase epitaxy method according to claim 1, wherein the solute is Si. 9. A liquid phase growth apparatus for dissolving a solute in a solvent to precipitate crystals on a substrate, comprising a solvent reservoir for supplying the solute to the solvent and a pipe for circulating the solvent supplied with the solute. A liquid phase growth apparatus, characterized in that both ends of the pipe are connected to a side wall of the solvent reservoir, and an opening for making contact with a substrate is provided in the middle of the pipe. 10. The liquid phase growth apparatus according to claim 9, further comprising means for independently controlling the temperature of the solvent reservoir and the temperature of the circulation pipe and the substrate in contact therewith. 11. The liquid phase growth according to claim 10, wherein the solvent reservoir and the pipe are arranged in an electric furnace, and means for independently heating the solvent reservoir is provided around the solvent reservoir. apparatus. 12. The liquid phase growth apparatus according to claim 9, wherein a rotor for solvent circulation is provided in a part of the pipe. 13. The slider according to claim 9, further comprising a slider arranged so that the solvent and the substrate are in contact with each other at the opening of the pipe while holding and moving the substrate. The liquid phase growth apparatus according to claim 1. 14. The substrate is a web-like continuous substrate, and means is provided for moving the continuous substrate so that it can come into contact with the solvent at the opening of the pipe. 13. The liquid phase growth apparatus according to any one of 1 to 12. 15. A control means is provided to keep the temperature of the solvent reservoir and the temperature of the circulation pipe and the substrate in contact therewith constant.
4. The liquid phase growth apparatus according to any one of 4 above. 16. The liquid phase growth apparatus according to claim 9, wherein the solvent is Sn. 17. The liquid phase growth apparatus according to claim 9, wherein the solute is Si.