JP2002137992A - Method of growing liquid phase and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of growing liquid phase able to improve a wettability of the melt and to grow well with good repeatability even for a substrate which can't get sufficient effect (i.e., repeatability and productive efficiency) by a conventional method. SOLUTION: The method of growing the liquid phase by which crystal layer is grown on the substrate soaked in the melt melting raw material of the crystal is made to supersaturate in a furnace keeping airtight from outside for growing liquid phase, is characterized in that prior to soaking the substrate into the melt, the substrate is plasma treated in a room inside of the furnace or a room able to communicate with the furnace keeping airtight from outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solar cell and an LED.
The present invention relates to a liquid phase growth method applied to the production of a semiconductor crystal used for a device such as a semiconductor device and an optical crystal such as lithium niobate, and a liquid phase growth apparatus suitable for implementing the method.

[0002]

2. Description of the Related Art Solar cells have come to be widely used for consumer use with increasing awareness of the environment. Single-crystal or polycrystalline silicon is mainly used for consumer solar cells. And now,
These crystals are cut out from a large ingot as wafers having a thickness of about 300 μm. However, in this method, a cutting allowance of about 200 μm is produced along with the cutting, so that the material use efficiency is poor. In order to further increase the production volume and reduce the price in the future, it is necessary to grow a crystal with a minimum thickness of several tens to 100 μm, which is required electrically and optically, and use it. Is desired.

[0003] As a method for growing such thin crystalline silicon, a vapor phase growth method in which a gas containing silicon is decomposed by the action of heat or plasma has been mainly studied. However, in mass production of solar cells, an apparatus capable of growing silicon at a rate of 1 μm / min or more on several tens to several hundreds of 4 to 5 inch square substrates in one batch is required. A vapor phase growth apparatus that can meet such specifications is not commercially available, and is considered difficult to realize.

[0004] As a method of growing a crystal, a method called a liquid phase growth method has been known for a long time.
It is used for manufacturing compound semiconductor crystals for LEDs and optical crystals for electro-optical elements. Recently, examples have been reported in which a crystalline silicon substrate, a ceramic substrate, or a silicon crystal film grown on a metal substrate is used for manufacturing a solar cell.

[0005] The liquid phase growth method means that a metal such as tin, indium or gallium or an oxide such as lithium acid or niobate is heated and melted, and if necessary, arsenic or silicon is further added thereto. Is a method of dissolving a material for constituting the crystal, adjusting the melt, bringing the melt into contact with the substrate, and supersaturating the melt by means such as cooling to precipitate the crystal on the substrate.

[0006] In this liquid phase growth method, since high quality crystals can be grown and less wasteful materials are used as compared with the vapor phase growth method, devices such as solar cells which are strongly required to be inexpensive, gallium and niobium are required. It is suitable for application to an electro-optical device using expensive raw materials such as.

However, in the liquid phase growth method, it is important to control the wettability of the substrate to the melt. An example of the case where the wettability of the substrate with respect to the melt is poor will be described with reference to FIG. 4. FIG.
FIG. 3 illustrates a situation where the substrate 401 was not spread over the entire surface of the substrate 401 due to poor wetting when flowing. Originally, a crystal layer should be grown on the entire surface of the substrate, but in this situation, the crystal layer has grown only in a wide range of the melt 402.

Further, in FIGS. 4B and 4C, even when the melt is spread over the entire surface of the substrate or when the entire substrate is immersed in the melt, the problem is caused by insufficient wettability of the substrate. Probable, anomalous cases are shown in cross-section.
Here, (b) is observed when the crystal is grown on a single crystal substrate, and pyramid-like projections having a uniform direction are grown, which are influenced by the orientation of the substrate crystal. (C)
Is often seen when a polycrystalline substrate or a substrate of a material different from the crystal to be grown is used, and amorphous crystal grains grow randomly.

Cases (b) and (c) are thought to occur due to the formation of a very thin impurity layer on the substrate surface or the change in the termination state of surface atoms. Since it is a change in the range of the atomic layer and it is not easy to clarify the substance analytically, it is difficult to clearly show the details.

[0010] In order to improve such a problem, a method of cleaning a substrate used for growth has been devised. For example, in the case of a semiconductor substrate such as silicon, treatment with a mixed solution of sulfuric acid and hydrogen peroxide followed by treatment with hydrofluoric acid has the effect of improving the spread of the melt on the substrate. However, since sufficient reproducibility cannot be obtained by this alone, annealing the substrate in a hydrogen atmosphere of 1000 ° C. or more before crystal growth is a pretreatment method of the substrate in the liquid phase growth method. Widely implemented.

However, even when these methods are carried out, abnormal growth cannot be prevented in some cases. Moreover, sulfuric acid or hydrofluoric acid cannot be used due to insufficient chemical resistance of the substrate, or high-temperature annealing in a hydrogen atmosphere cannot be performed due to insufficient heat resistance in some cases.

In addition, the effect of high-temperature annealing is often reduced unless the substrate is brought into contact with the melt immediately after the annealing without exposing the substrate to outside air. However, the temperature required for high-temperature annealing is generally higher than the temperature at which liquid phase growth is performed, and if high-temperature annealing is performed in the vicinity of the growth site, the temperature of the melt fluctuates and adversely affects liquid phase growth. May be seen. If the furnace for high temperature annealing is made independent of the furnace for liquid phase growth and the substrate is transported while maintaining airtightness, the above-mentioned problem can be solved, but a high-temperature heating source is prepared independently. Required, and the device becomes complicated.

[0013]

SUMMARY OF THE INVENTION Under such circumstances,
The inventor paid attention to the plasma treatment of the substrate surface. The plasma treatment has been used as a surface treatment method for a semiconductor substrate, as described in, for example, JP-A-6-163484. According to the study of the present inventors, the plasma treatment of the substrate is also effective in improving the wettability to the melt in the liquid phase growth method. In many cases, the effect is improved, and a lower cost substrate can be used.

However, until now, this plasma treatment has
There is no example used for improving the wettability of a substrate in liquid phase growth. The reason is considered as follows. That is, as in the case of high-temperature annealing in a hydrogen atmosphere, the effect of the plasma treatment rapidly decreases unless liquid phase growth is started without breaking airtightness after the treatment. However, while the plasma treatment is performed in an atmosphere of about 1 torr or less, the liquid phase growth method is performed at about the atmospheric pressure for the purpose of suppressing the evaporation of the liquid melt. Is difficult, and it is difficult to quickly shift to liquid phase growth after the plasma treatment. It is considered that such a situation is an obstacle to utilizing the plasma treatment for improving the wettability of the substrate in the liquid phase growth.

The inventor of the present invention has intensively studied to overcome this difficulty so that the effect of improving the wettability of the substrate by the plasma processing method can be maximized even in the liquid phase growth method. As a result, the present invention has been achieved with the following intent.

That is, the present invention improves the wettability of the melt even with respect to a substrate for which a sufficient effect (ie, reproducibility and production efficiency) has not been improved by the conventional method, and has good reproducibility and good reproducibility. It is a first object of the present invention to provide a liquid phase growth method capable of performing a proper growth.

A second object of the present invention is to improve the wettability, improve the reproducibility, and achieve good growth of a substrate having low chemical resistance and heat resistance without damaging the substrate. It is to provide a liquid phase growth method that can be used.

In order to achieve this object, the present invention uses a relatively simple apparatus to improve the wettability of the substrate without adversely affecting the melt, and to achieve good growth with good reproducibility. The purpose is to.

[0019]

In order to achieve the above object, according to the present invention, a substrate is immersed in a melt in which crystal raw materials are melted inside a liquid phase growth furnace which is kept airtight from the outside. In the liquid phase growth method in which the melt is supersaturated and a crystal layer is grown on the substrate, prior to immersion in the melt, the furnace is kept in a space inside the furnace or while maintaining airtightness from the outside. The substrate is subjected to plasma processing in a space that can communicate with the substrate.

In the present invention, at least a melt for dissolving the semiconductor raw material, a melt holding means,
Substrate transport means for transporting the substrate to a contact position with the melt, plasma generating means, a liquid phase growth furnace capable of accommodating them and maintaining airtightness from the outside, and a melt for controlling the temperature of the melt. And a temperature control means.

Further, in the present invention, at least a melt for dissolving the semiconductor raw material, a melt holding means,
A furnace for liquid phase growth capable of holding these and maintaining airtightness from the outside, a melt temperature control means for controlling the temperature of the melt, and a surface treatment chamber capable of communicating with the furnace while maintaining airtightness from the outside. A liquid phase growth apparatus comprising: a plasma generating means provided in the surface treatment chamber; and a substrate transport means for transporting a substrate from the surface treatment chamber to a contact position with a melt.

In this case, as a typical method of the liquid phase growth method, depending on the difference in the manner in which the substrate is brought into contact with the melt,
The slide boat method and the dip method are known. Also,
Depending on the difference in the method of controlling the temperature of the melt, there are a constant temperature method and a slow cooling method.

The inventor of the present invention has considered suitable methods for the slide boat method and the dip method. In other words, in the case of the slide boat method, it is combined with the constant temperature method suitable for continuous processing, and in the case of the dip method, it is combined with the slow cooling method that can easily increase the number of sheets per batch, but the reverse combination is also possible. is there.

As described above, the plasma processing of a semiconductor is performed by:
Conventionally, it has been performed in an atmosphere of about 1 torr or less,
It is known that by devising a discharge method, plasma can be generated even in an atmosphere having a high pressure of about atmospheric pressure, and can be used for processing various materials. For example, Japanese Patent Application Laid-Open No. 5-69417 discloses a technique in which one or both surfaces of a parallel plate electrode are covered with a dielectric plate to generate plasma in a range of 500 to 1500 torr and used for drying wood. There is a description.

Therefore, the present inventor has proposed that the plasma treatment under the atmospheric pressure is preferably combined with the slide boat method, and incorporates a device unique to the liquid phase growth method into the flow of the gas used to generate the plasma. It has been found that preferred results can be obtained from the above.

On the other hand, in order to increase the throughput by the dip method, it is necessary to increase the number of substrates to be fed per batch. In this case, as described in Japanese Patent Application Laid-Open No. 5-69417, it is difficult to perform the atmospheric pressure plasma treatment, and it is possible to communicate with the growth furnace, but if necessary, in a space where the pressure can be maintained independently. It is desirable to perform a plasma treatment. However, when the substrate is a metal or a low-resistance semiconductor, it tends to be difficult to generate a uniform discharge.

Therefore, the present inventor has proposed that even in such a case,
We have found a way to get good results. These will be sequentially described in the embodiments described below.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a slide boat type liquid phase growth apparatus to which the present invention is applied. Here, reference numeral 100 denotes a substrate susceptor, which is adjusted so that the substrate 101 is fitted into the counterbored portion and no step is formed on the surface. Generally, the slide boat type substrate susceptor 100 is made of a material having high heat resistance, such as carbon or quartz glass, which does not stick to or react with the melt. The use of a conductive material is preferred.

That is, the conductive substrate susceptor 100
When the substrate is used, the substrate can be similarly used whether it is a conductive material such as metal or semiconductor, or a dielectric such as ceramics. In particular, when a single-crystal substrate is used, a crystal layer grown thereon can be a single crystal that inherits the orientation of the substrate (epitaxial growth). Also, even if the substrate and the crystal grown on it are different,
There are cases where epitaxial growth is possible (heteroepitaxial growth), which is used in the manufacture of LEDs and the like. In the case of such growth, the present invention is also effective in improving the wettability of the substrate.

The boat 103 is a heat-resistant member having upper and lower openings, and is usually made of carbon.
Holds a melt 102 of a low melting point metal such as indium, gallium, tin, copper, aluminum and zinc. When the gas is not to be occluded, the surface of the boat 103 is preferably coated with silicon carbide. The bottom portion of the boat 103 has good rubbing with the surface of the substrate susceptor 100 and can slide without leaking the melt 102.

Hereinafter, the case of a constant temperature method will be described as a method of controlling the temperature of the melt. On the surface of the melt 102, crystals to be grown or flakes 104 of the constituent material are floated. That is, when silicon is grown, the melt may be indium, gallium, tin, or the like, and the silicon substrate may be flakes 104. When gallium arsenide is grown, the melt may be gallium and the arsenic block may be flakes 104.

Independent heaters 10 are provided above and below the boat.
6, 107 are provided. Heaters 106, 107
Is controlled such that the liquid level is higher than the bottom of the melt 102. Then, at the liquid level of the melt 102,
The constituent material of the crystal melts into the melt from the flakes 104, but on the other hand, in the vicinity of the surface of the substrate 101, it becomes supersaturated, and the crystal layer 105 grows. In the constant temperature method, as long as the flakes 104 remain, the temperature of each part may be kept constant, and the growth can be performed continuously.

In this case, the substrate susceptor 100 may continuously move to the right or may intermittently move to the right every time the crystal layer 105 having a desired thickness grows on the surface of the substrate 101. Good. With this movement, the substrate 101 sequentially comes out from the right end of the boat. Further, the substrate susceptor 100 and the boat 103 are kept airtight from the outside air by the growth furnace 113. However, the inside is around atmospheric pressure, especially
When maintaining the positive pressure, the substrate susceptor 100 and the growth furnace 1
A small leak to the outside from the sliding portion with the thirteen does not often cause a practical problem.

Reference numeral 108 denotes a counter electrode for performing a plasma process. As described above, since the liquid phase growth is performed in an atmosphere around the atmospheric pressure, it is desirable that the plasma is also generated under the same pressure. For this purpose, the surface of the counter electrode 108 is covered with a dielectric layer 109, and the counter electrode 108 is
An AC electric field of about z to about 100 MHz is applied. The dielectric used is selected from materials such as silicon nitride, silicon oxide, and tantalum oxide depending on the type of gas used to generate the plasma.

The distance between the substrate 101 and the counter electrode 108 is kept as narrow as possible within a range of about 1 cm to 100 μm.
By such a method, even under a high pressure of about atmospheric pressure,
Plasma is generated, and plasma processing can be performed inside the growth furnace, and the process can proceed to growth as it is, thereby increasing the effect of the plasma processing.

The gas used for the plasma processing includes hydrogen,
Use of an inert gas such as helium or argon, a gas of a compound containing fluorine such as fluorine, tetrafluoromethane, or sulfur hexafluoride, a gas of a compound containing chlorine such as hydrochloric acid or tetrachlorosilane, or a mixed gas thereof it can. These gases are exhausted from the gas exhaust pipe 112 while being introduced into the growth furnace through the gas introduction pipe 111, and the internal pressure is maintained at a desired value.

Since the growth furnace has a high temperature, a considerable amount of gas is released from the inside thereof. However, oxygen and moisture adsorbed on the inner wall of the growth furnace 113 are baked in the furnace before the start of growth. , Can be reduced to a considerable extent. However, even if baking is performed, since the melt vapor is constantly generated from the high-temperature melt 102 during the growth, the substrate 101 before the plasma treatment is generated.
When this vapor comes into contact with the surface of the substrate, it condenses and covers the surface of the substrate, thereby hindering the plasma processing.

Therefore, the flow direction of the gas in the growth furnace 113 is aligned with the transfer direction of the substrate to prevent the vapor from the melt 102 from reaching the substrate surface before processing. Thereby, the effect of the plasma processing is enhanced.

FIG. 2 shows an example in which the present invention is applied to a dip type liquid phase growth apparatus. Here, reference numeral 200 denotes a substrate susceptor, which can hold a plurality of substrates at predetermined intervals. Although the substrate surface is held horizontally in FIG. 2, it may be held vertically or at a predetermined angle. From the viewpoint of liquid phase growth, a material such as a metal or a dielectric can be used as the substrate susceptor as long as it does not dissolve or react with the melt.

Incidentally, reference numeral 201 denotes a substrate made of a crystal material to be dissolved in the melt, and 201 'denotes a substrate for growth. Since the substrates are supported at the same position on the substrate susceptor 200, they cannot be distinguished from each other in FIG. In the dip method, the melt 202 is held in a crucible 203. Hereinafter, the case of the slow cooling method will be described as the melt temperature control method.

That is, the melt 202 is heated and melted by the heater 204, the crystal material is melted therein, and the substrate 2 is melted.
When 01 is immersed, the crystalline material dissolves to a saturation concentration. Thereafter, the substrate 201 is pulled up, and the growth substrate 20 is removed.
1 ′, the melt was gradually cooled, and when the melt reached a predetermined temperature while being supersaturated, the growth substrate 2 was cooled.
When 01 ′ is immersed in the melt, a crystal layer (not shown) grows on the substrate 201 ′.

These components are housed in the growth furnace 205 and are kept airtight from the outside.
In order to keep the inside of the growth furnace airtight when exchanging 201 ′, a load lock chamber 207 communicating with a gate valve 206 is provided. That is, the load lock chamber 207 is connected to the gate valve 206, and in a state in which the substrates 201 and 201 ′ supported by the substrate susceptor 200 are housed, the inside atmosphere is evacuated and replaced, and then the gate valve is opened, 201 'can be introduced into the growth furnace 205; In this structure, the growth furnace 205
Since the pressure in the load lock chamber 207 can be controlled independently of the internal pressure, the plasma processing can be performed at an arbitrary pressure.

On the other hand, since a plurality of substrates 201 (201 ') are supported at predetermined intervals, it is appropriate to generate a discharge by a method different from that of the first device.
In this case, a method according to the conductivity of the substrate can be adopted. In the case where the substrate is an insulating or high-resistance semiconductor substrate with a small amount of glass, ceramics, or the like, a method of generating one plasma 210 over a plurality of substrates as shown in FIG. I can take it. To generate such a plasma, for example, a coil 208 wrapping the entire substrate 201 (201 ′) is wound, and here, for example, 13.5
It is preferable to apply a high frequency voltage such as 6 MHz. Note that FIG.
Here, the coil 208 is wound from outside the load lock chamber.

In this method, the plasma does not strike the surface of the coil to cause contamination.
It must be made of a dielectric such as quartz glass. When the coil is provided inside the load lock chamber, the load lock chamber may be made of a conductive material such as metal. Further, for the substrate susceptor 200, a dielectric such as quartz glass or silicon nitride is preferably used.

In the case of this configuration, the plasma processing
In order to achieve a uniform effect on the entire surface of the substrate 201 (201 '), it is desirable to positively generate a gas flow between the substrates and supply a fresh gas also to the central portion of the substrate. Where 2
Reference numeral 11 denotes a gas introduction pipe which blows out gas from a plurality of openings provided on the side surface. On the other hand, this gas is exhausted by an exhaust pipe 212 having a similar structure provided at a position opposed to the substrate and sandwiching the substrate, and fresh gas flows over the entire surface of the plurality of substrates. When the substrate 201 (201 ′) is rotated at the same time, the effect of improving the wettability over the entire surface is further improved.

[0046]

(Embodiment 1) In this embodiment, a polycrystalline silicon is grown on a ceramic substrate by the method of the present invention to obtain a semiconductor for a solar cell. As a substrate, 10 × 10 cm square by tape casting, thickness: 0.6 mm
Mullite were used _{(3Al 2} 0 3 -2Si0 ₂₎ plates. Since mullite has a coefficient of thermal expansion close to that of silicon, mullite is characterized in that bending due to a difference in coefficient of thermal expansion when the temperature changes and peeling of the silicon polycrystalline film hardly occur. Also,
In order to conduct to the back side of polycrystal, by electroless plating method,
A nickel layer having a thickness of 10 μm was formed over the entire front and back surfaces of the mullite plate.

Using this substrate, a polycrystalline silicon layer was grown by the apparatus shown in FIG. Here, the substrate susceptor 100 made of carbon having a counterbore formed on the surface was advanced rightward at a speed of 4 mm / min. In addition, the growth furnace 113
Mullite substrate 1 with nickel plating in the hollow
01 was dropped. As the substrate susceptor 100 advances, the substrate enters the inside of the growth furnace 113, but since the depth of the counterbore is equal to the thickness of the substrate 101 and the surface heights are uniform, the growth furnace 113 and the substrate susceptor No leakage from the sliding part.

The substrate 101 eventually passes over the front surface of the counter electrode 108. While flowing a 1: 1 mixed gas of hydrogen and argon from the gas introduction pipe 111, the gas exhaust pipe 112
And the inside was maintained at 770 torr. In this state, between the counter electrode 108 and the substrate susceptor 100,
When a high frequency voltage of 13.56 MHz was applied, plasma was generated in a space of about 1 mm between the surface of the silicon nitride layer 109 on the surface of the counter electrode 108 and the substrate 101. Argon itself has a function of removing contamination on the substrate surface and improving wettability, and also has a function of facilitating maintenance of plasma.

Thereafter, the substrate 101 was brought into contact with the melt 102 in the boat 103. This melt was formed by dissolving silicon in indium from a p-type polycrystalline silicon substrate 104 floating on the surface of indium, and adjusting the outputs of heaters 106 and 107 to bring the bottom of the melt at 900 ° C. The vicinity of the surface is maintained at 950 ° C. Due to this temperature difference, silicon dissolves into indium from the polycrystalline substrate 104, precipitates on the surface of the substrate 101, and eventually,
The substrate on which the p-type crystal layer 105 having a thickness of 30 μm was grown on the surface came out from the right end of the growth furnace.

Using a spin coater, a phosphorus diffusing agent is applied to the surface of the p-type crystal layer 105, and the surface is thermally diffused with phosphorus.
Junction depth: An n ⁺ layer of about 0.2 μm was formed. Then
From the peripheral part of the substrate to the back surface, the n ⁺ layer was removed by etching, and a thin thermal oxide film of about 200 A was formed on the surface in an oxidation furnace to form a passivation layer. On this, a comb-shaped grid electrode was printed with silver ink and fired. By this baking, silver penetrates the thin oxide film,
The n ⁺ layer was contacted. Further, a silicon nitride film was deposited on the surface to form a solar cell as an antireflection film.

On the other hand, for comparison, a nickel-plated mullite substrate 101 was supplied in the same manner as described above, except that a predetermined gas was flowed, but no voltage was applied to the counter electrode 108 and no plasma was generated. Then, when an attempt was made to grow a polycrystalline silicon layer, the surface of the substrate showed
Amorphous crystal grains such as grow randomly,
Not only could the solar cell not be formed, but also about three hours after the start of growth, the sliding part of the boat 103 was worn by friction with the crystal grains, and the melt 102 began to leak, making it impossible to continue growth. Was.

Example 2 In this example, a liquid phase growth method was used.
The present invention is applied to a process in which a single crystal layer is repeatedly formed on a single crystal substrate, and the single crystal layer is peeled off to obtain a thin single crystal solar cell. The details of the manufacturing process of this solar cell are described in Japanese Patent Application Laid-Open No. 10-189924, and the outline thereof will be described with reference to FIG.
Here, reference numeral 501 denotes a 100 mm square p ⁺ type silicon wafer.

This wafer was immersed in a hydrofluoric acid solution diluted with ethanol, and anodized by applying a positive voltage. By this anodization, the surface of the substrate 501 has a thickness of 5
A μm porous layer 502 was formed. In the porous layer, fine pores intricately entangled are formed, but have a single crystallinity, on which epitaxial growth can be performed. Prior to this, the substrate was annealed at 1050 ° C. in a hydrogen annealing furnace independent of the liquid phase growth apparatus.
In this case, atoms on the surface of the porous layer are rearranged and micropores on the surface are sealed, which is advantageous for subsequent epitaxial growth.

Thereafter, the substrate 501 is taken out of the hydrogen annealing furnace into the atmosphere, and then set in a liquid-phase growth apparatus, and the liquid-phase growth method is performed on the porous layer 502 whose surface is rearranged.
A 30 μm thick p ⁻ -type layer 503 was grown. further,
In order to form a junction, an n ⁺ layer 504 having a thickness of 0.3 μm was formed by a thermal diffusion method. The details of the liquid phase growth will be described separately.

Next, a thermal oxide film 505 was formed on the surface of the n ⁺ layer 504 as a passivation layer. Further, as a surface-side electrode, a silver paste was printed in a comb-shaped pattern and then fired to form a grid electrode 506. By baking, the silver pattern penetrates through the thermal oxide film 505 and n
⁺ Contacted layer 504. After bonding the glass plate 508 with the adhesive 507 on the thus formed layer, the silicon substrate 501 is fixed, and a force is applied to the glass substrate 508 to form a porous layer in which micropores are formed and are brittle. A portion 502 is destroyed, and a portion above the p ⁻ type layer 503 is
Peeled off.

Since there is a residue of the porous layer on the back surface of the peeled p ^- type layer 503, the porous layer residue is removed by etching, and then the copper plate 5 nickel-plated with a conductive adhesive 509 is removed.
10 was pasted. On the other hand, since there was a residue of the porous layer on the surface of the remaining substrate, this was also removed by etching to recover the mirror surface.

The substrate 511 thus regenerated was the same as the initial state except that the thickness was slightly more than 5 μm, and thus the substrate 511 was returned to the beginning of the process and could be used repeatedly. In FIG. 5, the thickness of the porous layer 502 is
It should be noted that for the sake of explanation, the expression is extremely thick.

Next, the substrate 2 having a porous layer formed on the surface
At 01 ', a step of growing a single crystal silicon layer will be described in detail. The apparatus shown in FIG. 2 was used for this growth.
First, with the gate valve 206 closed, the growth reactor 20
Indium was melted in the crucible 203 while flowing nitrogen into the melt 5 to obtain a melt. Next, the load lock chamber 20
7 was moved to a substrate exchange position (not shown), and a p-type polycrystalline silicon substrate was set on the substrate susceptor 200 and stored in the load lock chamber 207.

In this state, the load lock chamber 207 was moved right above the gate valve 206. While the gate valve was kept closed, the load lock chamber 207 was evacuated and replaced with nitrogen. After evacuating and replacing with nitrogen twice, evacuating again, exhausting the gas from the gas exhaust pipe 212 while introducing pure hydrogen from the gas introduction pipe, and then 0.1 torr the inside.
r.

In this state, 13.56M is applied to the coil 208.
A high-frequency current of Hz was applied to generate plasma 210, and this state was maintained for 10 minutes while rotating the substrate 6 times per minute.
On the other hand, the gas flowing in the growth reactor was switched from nitrogen to hydrogen. Next, after the pressure in the load lock chamber was set to 770 torr, which is the same as that in the growth furnace 205, the gate valve was opened, the polycrystalline substrate 201 was immersed in the melt maintained at 950 ° C., and maintained for 60 minutes while rotating. Melted silicon inside.

Then, the substrate 201 is lifted from the melt, housed in the load lock chamber 207, and
06 was closed. After the inside of the load lock chamber 207 is evacuated and replaced with nitrogen, the load lock chamber 207 is moved to a substrate exchange position (not shown), the substrate 201 is removed, and the substrate 20 having a porous layer formed on the surface thereof is removed.
Replaced with 1 '.

The load lock chamber 207 is moved to a position immediately above the gate valve again, and the atmosphere is replaced and the plasma treatment is performed while flowing a mixed gas of hydrogen and argon, as in the case of the substrate 201. Open 206,
The substrate 201 'was waited for the same temperature as in the growth furnace. Thereafter, the electric furnace 204 is controlled and the melt is heated to 950 ° C.
At a rate of 0.5 ° C./min. Melt is 940 ° C
Then, the substrate 201 ′ was immersed in the melt, left as it was for 30 minutes, lifted up, and loaded in the load lock chamber 207.
, The gate valve was closed, and the inside was replaced with nitrogen. Then, the load lock chamber 207 was again moved to the substrate exchange position (not shown), and the entire substrate susceptor 200 was removed.

For comparison, hydrogen annealing was performed in an independent hydrogen annealing furnace, then taken out of the hydrogen annealing furnace into the atmosphere, and the plasma treatment was omitted in the liquid phase growth apparatus shown in FIG. Growth was performed in the same manner as in the example. Crystal grains as shown in FIG. 4 (b) were randomly grown on the substrate pulled up from the melt and could not be used in the solar cell manufacturing process. this is,
It is considered that even if hydrogen annealing was performed on the substrate in an independent hydrogen annealing furnace, the effect was lost because the substrate was taken out into the atmosphere before growth.

Further, for comparison, instead of the plasma treatment using hydrogen gas, the temperature of the growth furnace was increased to 1050 ° C. under a hydrogen gas flow in the growth furnace, and a hydrogen annealing treatment was performed. In this case, it took about one hour for the temperature of the melt to rise to 950 ° C. once. Thereafter, growth was carried out in the same manner as in this example. However, a large number of holes were found in the grown silicon layer in a worm-like manner. This is because the indium vapor condenses on the surface of the porous layer 502 during the time until the growth after the hydrogen annealing, and the once smoothed surface is corroded in a dotted manner. It is considered that was formed.

Thus, also in this example, the effect of the present invention was demonstrated.

Example 3 (a) Here, a case of forming a solar cell by growing a polycrystalline silicon layer on a nickel-plated steel plate will be described. First, the entire process will be described with reference to FIG. FIG.
(A) and (b) show a plan view and a cross-sectional view of a substrate 601 to be used. After three grooves 602 are formed at equal intervals in a 10 cm square steel plate, : 3 μm
Nickel plating. (B) When liquid phase growth was performed using this substrate, a polycrystalline silicon layer 603 was grown so as to avoid the grooves 602 (FIG. 7).
(A), (b)). The groove 602 has a steel plate 601
This has the effect of reducing the warpage of the substrate caused by the difference in the thermal expansion coefficient between the substrate and the silicon layer 603. That is, heat (wire) of silicon
Although the coefficient of expansion is 2.5 × 10 ⁶ deg ⁻¹ , the thermal (linear) expansion coefficient of a metal, for example, iron is generally 11.8 × 10 ⁶ deg ⁻¹ ,
Much larger. Therefore, when the substrate is cooled after the silicon layer 603 is grown at a high temperature, the contraction of the steel plate 601 is greater, and the substrate is curved convexly at the top. However, if the substrate has a groove, the entire substrate can be prevented from being greatly curved. In particular, the long side of the rectangle formed by the groove /
When the ratio of the short sides is 3 or more, the effect is large. (C) Thereafter, the polycrystalline silicon layer 603 is formed by thermal diffusion.
An n ⁺ layer 604 having a junction depth of 0.2 μm is formed on the surface of
Further, a peripheral portion was removed by etching, and a passivation layer (not shown) was formed by thermal oxidation. (D) Further, the substrate 601 was cut from the groove 602 to make four strips. (E) The strip was pasted on a glass substrate 605. (F) Further, the insulating layer 606 was formed by printing so as to cover the cross section at the right end of each strip. Then, a silver paste was printed thereon to form a grid electrode 607.
The grid electrode 607 contacts the strip substrate on the right and
The strips are connected in series. However, the strip at the right end is connected to a bar 608 of a nickel plate. Eventually, the left-hand strip substrate is at the + terminal 609, and the bar 608 is at the-terminal.
It becomes a terminal 610 (see FIG. 8).

Next, a plasma processing apparatus used in this embodiment will be described with reference to FIG. The growth furnace of this apparatus is the same as the apparatus shown in FIG. Here, reference numeral 307 denotes a load lock chamber, and reference numeral 300 denotes a substrate susceptor made of quartz glass. The substrate susceptor is configured such that two of the four pins supporting the substrate are electrically connected to the even-numbered substrate by molybdenum electrodes, as shown at 308. On the other hand, the remaining two substrates can make electrical contact with the odd-numbered substrates from the bottom.

Since the substrate of this embodiment is made of metal, a DC or AC / high-frequency voltage can be applied to the even-numbered substrate and the odd-numbered substrate by adopting such a structure.

Next, the step of growing the polycrystalline silicon layer 603 on the nickel-plated steel plate 601 will be described in detail (see FIGS. 6 and 7). First, the melt 202 was adjusted in exactly the same manner as in Example 2 (see FIG. 2). Next, the crystal material is melted at the substrate exchange position (not shown),
1 and the substrate 601 are exchanged, and this is
7 and moved to a position immediately above the gate valve 206. Here, first, the inside of the load lock chamber is evacuated and replaced with nitrogen twice, and after evacuating again, a 2: 1 mixed gas of sulfur hexafluoride and oxygen is allowed to flow through the gas introduction pipe 311. While the gas is exhausted from the gas exhaust pipe 312, the internal pressure is maintained at 0.1 torr, and the pins 308 and 309
When an AC voltage of 50 Hz was applied between the two, plasma was generated.

After 10 minutes of processing, the load lock chamber 307
The inside of the reactor is evacuated, and the flow of hydrogen is started.
Was opened, and the substrate 601 was introduced into the growth furnace. Meanwhile, 9
With respect to the melt 202 kept at 50 ° C, 0.5 ° C /
Then, cooling was started at a rate of 940 ° C., and when the temperature reached 940 ° C., the substrate 601 was immersed in the melt 202, and crystals were grown for 30 minutes.

Next, the substrate 601 is lifted from the melt 202, accommodated in the load lock chamber 307, the gate valve 206 is closed, the load lock chamber is replaced with nitrogen, and then moved to a substrate exchange position (not shown). Then, when the substrate on which the polycrystalline silicon layer 603 was grown was removed, as shown in FIG. 6B, no silicon layer had grown on the groove 602.

For comparison, the growth was attempted in exactly the same manner except that the plasma treatment of the substrate 601 was not performed. However, an amorphous crystal as shown in FIG. The grains grew randomly and could not be flowed into the solar cell manufacturing process.

[0073]

According to the present invention, in the liquid phase growth of the crystal layer, the wettability of various substrates to the melt can be improved, and the crystal layer can be grown with good reproducibility. Also, in order to improve the wettability, it is not necessary to expose the substrate to a temperature higher than that used for strong chemicals or liquid phase growth.
Not only semiconductors, but also substrates with low chemical resistance and heat resistance, such as ceramics and metals, and substrates with a coefficient of thermal expansion that is significantly different from the crystal layer grown on them can be used. It greatly contributes to the development. In addition, since the configuration of a necessary apparatus is simple, it can be easily applied to a large growth apparatus.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional side view showing an example of a liquid phase growth apparatus of a slide boat method to which the method of the present invention is applied.

FIG. 2 is a vertical sectional front view showing one example of a liquid phase growth apparatus of a dipping method to which the method of the present invention is applied.

FIG. 3 shows another example of the liquid-phase growth apparatus using the dip method described above.
It is a vertical front view partially showing an example (plasma generating means).

FIG. 4 is a diagram showing an example of abnormal growth when a substrate has poor wettability to a melt.

FIG. 5 is a diagram illustrating a process of repeatedly removing a crystal layer epitaxially grown on a single crystal substrate to obtain a large number of thin film single crystal layers.

FIG. 6 is a plan view and a side view of a metal plate used when growing a polycrystalline phase.

FIG. 7 is a process diagram showing a process of growing a polycrystalline layer on a metal substrate to obtain a solar cell connected in series.

FIG. 8 is a plan view of the completed solar cell.

[Explanation of symbols]

100, 200, 300 Substrate susceptor 101, 201, 401, 501, 601 Substrate 102, 202 Melt 103 Boat 203 Crucible 104 Substrate for melting 106, 107, 204 Heater 113, 205 Growth furnace 108 Counter electrode 208 Induction coil 206 Gate Valves 207, 307 Load lock chambers 111, 211, 311 Gas introduction pipes 112, 212, 312 Gas exhaust pipes 110, 210, 310 Plasma 402 Melt 403, 404 not spread on substrate Crystal grains abnormally grown 502 Porous layer 503 Single crystal layer 603 Polycrystalline layer 504, 604 n ⁺ layer 506, 607 Grid electrode 510 Back electrode

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shunichi Ishihara 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hirokazu Otori 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo Inside non-corporation (72) Inventor Ryuji Kondo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Keishi Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koichi Matsuda 3-30-2, Shimomaruko 3-chome, Ota-ku, Tokyo F-term ( Reference) 4G077 AA03 BA04 CG01 CG10 ED06 EE02 EG30 HA20 5F053 AA01 AA05 BB03 BB24 BB41 BB60 DD01 DD03 FF01 GG01 LL05 PP20 RR01 RR13 RR20

Claims (13)

[Claims] 1. A substrate is immersed in a melt in which crystal raw materials are melted in a furnace for liquid phase growth, which is kept airtight from the outside, and the melt is supersaturated to form a crystal layer on the substrate. In the liquid phase growth method for growing, prior to immersion in the melt, the substrate is subjected to plasma treatment in a space inside the furnace or in a space that can communicate with the furnace while keeping airtightness from the outside. Liquid phase growth method. 2. The temperature of a space in which the plasma processing is performed is:
2. The liquid phase growth method according to claim 1, wherein the temperature is equal to or lower than the temperature of the melt. 3. The liquid phase growth method according to claim 1, wherein the liquid phase growth method is a slide boat method. 4. The plasma processing includes applying an electric field or / and / or a predetermined gas flowing along a direction of transport of a substrate to a melt.
4. The liquid phase growth method according to claim 3, wherein the method is realized by applying a magnetic field. 5. The plasma processing according to claim 3, wherein the plasma processing is realized by passing the substrate through a region where plasma is generated when the substrate is transported toward the melt. Liquid phase growth method. 6. The plasma processing is realized by plasma generated between a substrate set on a conductive substrate support and a counter electrode having a dielectric layer formed on a surface thereof. The liquid phase growth method according to any one of claims 3 to 5. 7. The liquid phase growth method according to claim 1, wherein the liquid phase growth method is a dipping method. 8. The plasma processing includes flowing a predetermined gas along a gap between a plurality of substrates supported in parallel at a predetermined distance by an insulating support member, and applying an electric field and / or a magnetic field to the gas. 8. The liquid phase growth method according to claim 7, wherein the method is realized by applying the following. 9. The liquid phase growth method according to claim 7, wherein the plasma processing is realized by plasma generated by applying a potential difference between a plurality of conductive substrates. 10. The plasma processing apparatus according to claim 7, wherein the plasma processing is performed while rotating a plurality of substrates.
The liquid phase growth method according to any one of the above. 11. The plasma used in the plasma treatment is generated by applying an electric field and / or a magnetic field to a flow of a gas containing hydrogen and / or a halogen element. The liquid phase growth method according to any one of items 10 to 10. 12. At least a melt for melting a semiconductor raw material, a means for holding the melt, a substrate transport means for transporting a substrate to a contact position with the melt, a plasma generating means, and a housing for accommodating these. A liquid phase growth apparatus, comprising: a furnace for liquid phase growth capable of maintaining airtightness from the outside world; and a melt temperature control means for controlling the temperature of the melt. 13. A melt for melting a semiconductor raw material, a means for holding the melt, a furnace for liquid phase growth capable of containing the melt and maintaining airtightness from the outside, and a melt for controlling the temperature of the melt. Temperature control means, a surface treatment chamber capable of communicating with the furnace while maintaining airtightness from the outside world,
A liquid phase growth apparatus comprising: a plasma generating means provided in the surface processing chamber; and a substrate transporting means for transporting a substrate from the surface processing chamber to a contact position with the melt.