JP3501606B2 - Method for manufacturing semiconductor substrate and method for manufacturing solar cell - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing a semiconductor substrate and a method for manufacturing a solar cell. More specifically,
It is preferably used in a method for manufacturing a high-performance solar cell using a thin film crystal that can be formed on a low-cost substrate.

[0002]

2. Description of the Related Art Solar cells have been widely studied as a driving energy source for various devices and a power source for systematic connection with commercial power. Due to cost requirements, solar cells are desired to be able to form elements on low-priced substrates. On the other hand, silicon is generally used as a semiconductor constituting a solar cell. Among them, single crystal silicon is extremely excellent in terms of efficiency of converting light energy into electric power, that is, photoelectric conversion efficiency. On the other hand, amorphous silicon is advantageous from the viewpoints of large area and low cost. Further, in recent years, polycrystalline silicon has come to be used for the purpose of obtaining low cost as amorphous silicon and high energy conversion efficiency as single crystal.

However, according to the method conventionally used for such single crystal or polycrystalline silicon, a lump crystal is sliced to form a plate-shaped substrate, and therefore the thickness thereof is set to 0.
It is difficult to reduce the thickness to 3 mm or less, and the substrate generally has a thickness (20 μm to 50 μm) or more necessary for absorbing incident light, and the material has not been sufficiently utilized. Further, recently, a method of forming a silicon sheet by a spin method in which molten silicon droplets are poured into a mold has been proposed, but even then, the thickness is at least about 0.1 mm to 0.2 mm, and it is still sufficiently thin. is not. That is, there is room for cost reduction by further reducing the thickness of silicon.

Therefore, there has been proposed an attempt to achieve high energy conversion efficiency and cost reduction by separating (peeling) a thin film epitaxial layer grown on a single crystal silicon substrate from the substrate and using it in a solar cell ( Milnes, AGand F
eucht, DL, "Peeled Film Technology Solar Cells", I
EEE Photovoltaic Specialist Conference, p.338,197
Five). In this method, an intermediate layer of SiGe is inserted between a single crystal silicon substrate and a growth epitaxial layer, a silicon layer is (hetero) epitaxially grown on the intermediate layer, and then the intermediate layer is selectively melted to grow. Peel off the layers. However, generally, the heteroepitaxially grown layer has a different lattice constant from that of the substrate, so that defects are easily induced at the growth interface. Further, it is not advantageous in terms of process cost in that a material much more expensive than silicon such as germanium is used.

Further, in US Pat. No. 4,816,420, selective epitaxial growth is performed on a crystal substrate through a mask material, and a sheet-like crystal is formed by a method of growing the crystal in the lateral direction, and then separated from the substrate. By doing
It is disclosed that a thin crystalline solar cell can be obtained.
However, in this method, since the sheet-like crystals are mechanically peeled off by using cleavage, if the sheet-like crystals are larger than a certain size, they are easily damaged during the peeling. In particular, when increasing the area of a solar cell, the above method becomes difficult to put into practical use.

Further, in JP-A-6-45622,
After forming a porous silicon layer on the surface of a silicon wafer by anodization, peeling it off, fixing the peeled porous layer on a metal substrate, and then forming an epitaxial layer on the porous layer. Batteries have been shown to make. However, in this method, since the metal substrate is exposed to a high temperature process, there is a problem that impurities are easily mixed in the epitaxial layer and the characteristics are limited.
Also, as realized with amorphous silicon solar cells, if a thin semiconductor layer is formed on a flexible substrate, for example, a polymer film such as polyimide, it can be installed on a curved object. Although it is expected that the field will be expanded, it is difficult to use such a low heat resistant substrate because the process of the above-mentioned single crystal or polycrystalline silicon solar cell requires high temperature.

[0007]

By the way, Japanese Patent Laid-Open No. 8-2136
In No. 45 publication, a silicon wafer surface is formed by anodization.
The active layer of the solar cell is epitaxially formed on the formed porous silicon.
From a portion of the porous silicon layer that grows axially
It has been shown that the active layer can be stripped. Therefore expensive
Not only can single substrates be used repeatedly, but
Highly efficient solar cells can be formed on a flexible low heat-resistant substrate.
I was able to do it. However, according to Japanese Patent Laid-Open No. 8-213645
For example, the epitaxial growth of the active layer is performed by the CVD method.
ing. Dichlorosilane (SiH₂C
l₂) And trichlorosilane (SiHCl ₃) Etc.
And a large amount of hydrogen gas will be used.
20 to 50 μm thick by using large amount of expensive gas
Depositing a silicon film costs a lot of money
Amorphous silicon with a thickness of 0.5 to 1.0 μm
It is considerably disadvantageous in terms of cost.

In order to carry out epitaxial growth of silicon at low cost, the liquid phase growth method is advantageous rather than the method using gas such as CVD. In the liquid phase growth method, molten Sn,
Silicon particles are dissolved in a metal such as In, Cu, Al, etc., and a crystalline substrate is immersed in the solution, and then the solution is brought into a supersaturated state to grow silicon on the substrate. The liquid phase growth method uses inexpensive raw materials, and requires less waste of raw materials. Further, since the growth can be performed at a temperature considerably lower than the melting point of Si, such as 1000 ° C. or less, it is energy-friendly as compared with the spin method. However, when silicon is actually grown by the liquid phase epitaxy method, abnormal crystal grains develop, the grown thin film semiconductor layer cannot be peeled off well, and there are many cases in which it cannot withstand use as a solar cell. It's a reality. Therefore, it has been difficult to achieve both high performance as a single crystal or polycrystal and low cost like amorphous silicon.

Further, not only a single crystal silicon wafer but also a substrate (first substrate) for epitaxial growth is used.
High-quality polycrystalline silicon wafers can be used, but in order to avoid the influence of impurity diffusion from the substrate, it is necessary to have a high degree of purity so that elements can be formed on the substrate itself. Repeated use was required. However, when the number of times of repeated use increases, the anodization conditions change due to changes in the surface state of the crystal, etc., and thus there is a point that it is difficult to handle in production. (Object of the Invention) The present invention has been made in view of the above circumstances, and an object thereof is to provide a manufacturing method suitable for a method for manufacturing a semiconductor substrate having good characteristics, particularly a method for manufacturing a solar cell. To do.

Another object of the present invention is low heat resistance,
An object of the present invention is to provide a method for manufacturing a semiconductor base material which can be used in various ways by forming a thin film semiconductor layer on an inexpensive and flexible substrate. Another object of the present invention is to provide a method for producing a high-efficiency solar cell that can be used in various forms by forming a crystalline solar cell using a thin film semiconductor layer.

Still another object of the present invention is to separate an epitaxial layer formed on a crystal substrate into a semiconductor substrate and reuse the crystal substrate, and by using inexpensive raw materials, high performance and further low cost are achieved. Another object is to provide a semiconductor substrate. Another object of the present invention is to provide a solar cell which uses a semiconductor substrate as a solar cell, reuses a crystal substrate, and uses inexpensive raw materials to provide a solar cell with high performance and low cost.

[0012]

The present invention has been completed as a result of intensive studies conducted by the present inventors to solve the problems in the above-mentioned conventional techniques and achieve the above-mentioned objects. The present invention relates to a method for manufacturing a semiconductor substrate and a method for manufacturing a solar cell which are excellent in cost and inexpensive.

That is, the method for producing a semiconductor base material of the present invention is a method for producing a semiconductor base material, which comprises at least the following steps (a) to (d).

(A) A porous layer is formed on the surface of the first substrate.
Forming process (b) The elements that make up the semiconductor to be grown to a certain concentration
The surface temperature of the non-supersaturated solution
Is lower than the temperature at which the solution of the above concentration becomes saturated.
Dipping the porous layer to grow a semiconductor layer on the surface of the porous layer
Step (c) at least the porous layer and the semiconductor layer are shaped
A process for adhering the second base to the surface of the formed first base.
Degree (d) the said through the porous layer and the first substrate first
The second substrate is separated to separate the semiconductor layer from the first substrate.
The step of further peeling off and transferring to the second substrate, and the method for producing a semiconductor substrate of the present invention include at least the following steps.
Half characterized by having steps (a ') to (e')
It is a manufacturing method of a conductor substrate.

(A ′) Porous layer on the surface of the first substrate
Step of forming (b ') Semi-growth under high temperature reducing atmosphere
Before dissolving in a solution in which the elements that make up the conductor are dissolved to a supersaturated state
Immerse the porous layer to form a semiconductor layer on the surface of the porous layer.
Lengthening step (c) At least the porous layer and the semiconductor layer are
The second substrate is adhered to the surface of the formed first substrate.
Step (d ') The first substrate and the
The second substrate is separated to separate the semiconductor layer from the first substrate.
Step (e ') of peeling from the body and transferring to the second substrate of the first substrate separated in the step (d')
After treating the surface, impurities are introduced to the surface by liquid phase epitaxy.
The deposited semiconductor layer is grown, and again the first step of the step (a ′) is performed.
The method of manufacturing a semiconductor substrate of the present invention includes at least the following steps :
Half characterized by having steps (a ″) to (e ″)
It is a manufacturing method of a conductor substrate. (A ") Step of forming a porous layer on the surface of the first substrate (b") Constant concentration of elements constituting the semiconductor to be grown
The surface temperature of the solution dissolved up to
Immersing the porous layer lower than the saturation temperature,
Step (c) of growing a semiconductor layer on the surface of the porous layer At least the porous layer and the semiconductor layer are
The second substrate is adhered to the surface of the formed first substrate.
Step (d ") The first substrate and the above-mentioned first substrate through the porous layer
The second substrate is separated to separate the semiconductor layer from the first substrate.
The step of peeling from the body and transferring to the second substrate (e ") of the first substrate separated in the step (d")
After treating the surface, impurities are introduced to the surface by liquid phase epitaxy.
The semiconductor layer that has been put in is grown, and the first step of the step (a ″) is performed again.
The step of charging the substrate as a substrate of the present invention uses the method for producing a semiconductor substrate of the present invention described above.

In the present invention, in particular, a liquid phase growth method , that is, a method of immersing the porous layer in a solution in which the elements constituting the semiconductor are dissolved and growing the thin film semiconductor layer on the surface thereof is further adopted. Precisely controlling the degree of supersaturation of the solution at least initially (immediately after immersing the porous layer), and further immersing the surface temperature of the porous layer below the temperature at which the solution becomes saturated and immersing in the solution, The feature is that a high-quality thin film semiconductor layer can be easily obtained, and peeling can be easily performed in the porous layer. Further, in order to compensate for the decrease in the thickness of the first substrate due to the formation and peeling of the porous layer, a crystal layer is grown on the surface of the first substrate by a liquid phase growth method to form the first substrate. While making effective use of
It is also possible to optimize the porous layer without being directly affected by the quality of the substrate.

The position of separation through the porous layer may be either in the porous layer, at the interface between the porous layer and the first substrate, or at the interface between the porous layer and the semiconductor layer. It is not necessary to remove the porosity on the side of the substrate on which no porosity remains after separation.

Further, in the present application, the treatment of the surface of the separated first substrate means a treatment of removing the residual porosity, but the surface flatness is insufficient after the residual porosity is further removed. If so, it also includes polishing, etching, or the like used in a normal semiconductor process, or treatment for flattening the surface such as heat treatment in an atmosphere containing hydrogen.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described by taking a solar cell as an example. The present invention relates to a manufacturing method for transferring a semiconductor layer onto a second substrate,
Since semiconductor elements such as transistors, diodes, and LEDs can be formed on the semiconductor layer, it is not particularly limited to the production of solar cells.

An example of the structure of the solar cell manufactured by the method of the present invention is shown in FIG. 1, and an example of the manufacturing process of the present invention is shown in FIG. 1 and 2, 105 and 20
5 is a low heat resistant substrate, 109 and 209 are back electrodes, 10
4, 204 are p ⁺ (n ⁺ ) layers, and 103 and 203 are active (p
^- (n ^-)) layer, 106, 206 n ⁺ (p ⁺⁾ layer, 107,2
Reference numeral 07 is a transparent conductive layer, and 108 and 208 are collector electrodes. Here, the n ⁺ (p ⁺ ) layers 106 and 206 and the active (p ⁻ (n
^- )) Layers 103 and 203 form a semiconductor junction and generate a photovoltaic force. Active (p ⁻ (n ⁻ )) layers 103 and 203 are main bodies that absorb sunlight and generate carriers, and in the case of silicon, 10
The thickness is increased to about 50 μm. On the other hand, the n ⁺ (p ⁺ ) layer 106,
The thickness of 206 is 1 μm or less. Further, the p ⁺ (n ⁺ ) layers 104 and 204 form a back surface field between the p ⁺ (n ⁺ ) layers and the electrodes 109 and 209 and have a function of preventing carrier recrystallization near the electrodes 109 and 209, but they are not essential. Further, a thickness of 1 μm or less sufficiently functions. here,
The n ⁺ (p ⁺ ) layers 106 and 206 and the active (p ⁻ (n ⁻ )) layer 10
3,203 and p ⁺ (n ⁺ ) layers 104 and 204 are represented by 1
06,206 if the n ^+, is 103,203 ^p -, 1
04 and 204 indicate p ^+, and 106 and 206
Is p ⁺ , 103 and 203 are n ⁻ , 104 and 204
Indicates that it is n ^+, and each combination has a function, but if the combination of 106 and 206 is n ⁺ , the collector electrode side is negative, and if the combination of 106 and 206 is p ⁺ , the collector electrode side is positive, The difference is that electromotive force is generated.

Next, based on FIG. 2, the process of the manufacturing method of the present invention will be described.
The outline will be described. Crystalline first substrate 201
For example, a single crystal semiconductor wafer is used. That
By thermal diffusion and ion implantation of impurities on the surface
Or at least the wafer surface
P on the surface⁺(Or n⁺) Layer is formed (Fig. 2
(A)). Next, the wafer surface on the side where impurities are introduced is HF
A porous layer 202 is formed by anodization in a solution (Fig.
2 (b)). Japanese Patent Application Laid-Open
As described in Japanese Patent Publication No. 7-302889, the formation current level
For example, to change from low level to high level on the way
In addition, the density of the porous layer should be changed beforehand.
By doing so, they are separated by the porous layer after epitaxial growth.
It can be controlled easily. Then said porous
On the layer by liquid phase growth method (p ^-(n^-)) As a layer
Epitaxially grow a single crystal semiconductor layer 203
It Then p as necessary⁺(n⁺) Layer of single crystal semiconductor layer 20
4 is epitaxially grown. Further back on it beforehand
The second substrate 205 on which the surface electrode 209 is formed is
⁺(n⁺) Fixed to layer 204 or p⁺(n⁺) Form layer 204
After making, p⁺(n⁺) Form back electrode 209 on layer 204
After the formation, the second base 205 is fixed (FIG. 2D).
~ (E)). Fixed second substrate 205 and first crystalline
A force is applied between the base material 201 and the substrate 201 to mechanically form the porous layer.
By separating the first and second single crystal semiconductor layers 203 and 204,
From the crystalline substrate 201 of No. 2 onto the second substrate 205.
(FIG. 2 (f)). After the transfer, on the surface of the single crystal semiconductor layer 203
The remaining porous layer 202a was removed by etching
After, n⁺(p⁺) Type semiconductor layer 206, transparent conductive layer 207 and
And a collector electrode 208 are formed to form a solar cell (FIG. 2).
(G) to (h)). First crystalline group after exfoliation
The body 201 has the porous layer 202b remaining on its surface.
First again by removing / processing by etching etc.
(FIG. 2 (a)).

Next, the features of the manufacturing method of the present invention will be described in detail.

First, with respect to the porous layer 202, an example in which silicon is used as the material of the crystalline first substrate 201 (that is, the porous layer is silicon) will be described. The mechanical strength of the porous layer 202 of silicon varies depending on the porosity, but is considered to be sufficiently weaker than that of bulk silicon. For example, if the porosity is 50%, it can be considered that the mechanical strength is less than half the bulk strength. If the second substrate 205 is adhered to the surface of the porous silicon layer 202, and if there is sufficient adhesive force between the second substrate 205 and the porous layer 202, the silicon wafer 2 on which the porous layer is formed 2
When a compressive, tensile, or shearing force is applied between 01 and the second substrate 205, the porous silicon layer 202 is destroyed. If the porosity is further increased, the porous layer 202 can be broken with a weaker force.

The silicon substrate can be made porous by an anodization method using an HF solution having a concentration of 10% or more. The amount of current to be passed during the anodization is appropriately determined depending on the HF concentration, the desired thickness of the porous layer, the surface state of the porous layer, etc., but is generally several mA / cm ² to several tens m.
A range of A / cm ² is suitable. Further, by adding an alcohol such as ethyl alcohol to the HF solution, the bubbles of the reaction product gas generated during the anodization can be removed from the reaction surface without instantaneous stirring, and the porous silicon can be formed uniformly and efficiently. You can The amount of alcohol to be added is appropriately determined depending on the HF concentration, the desired film thickness of the porous layer or the surface condition of the porous layer, and particularly HF
Careful decisions must be taken to ensure that the concentration is not too low. The density of single crystal silicon is 2.33 g / cm ³ , but the porous silicon layer has a HF solution concentration of 50 to 20%.
By changing the density to 1.1-0.6 g / cm
It can be changed in the range of ³ . Also, porosity can be changed by changing the anodizing current.
Increasing the current also increases porosity.

The formation of porous silicon by anodization requires holes for the anodic reaction, and therefore it is said that the p-type silicon in which holes are mainly present is used to make the porous (T. Unagami, J. Electrochem. Soc., Vol.127,476 (198
0)). However, on the other hand, there is also a report that low resistance n-type silicon is made porous (RP Holmstrom and JY
Chi, Appl. Phys. Lett., Vol. 42, 386 (1983)) and p-type n-type, low resistance silicon can be used for porosity. Also, depending on the conductivity type, it can be made porous selectively.
POS (Full Isolation by Porous Oxidized Silico)
n) Only the p layer can be made porous by performing anodization in a dark place as in the process.

The porous silicon obtained by anodizing the single crystal silicon has a thickness of several nm when observed by a transmission electron microscope.
Holes having a diameter of about the same are formed, and the density thereof is less than half that of single crystal silicon. Nevertheless, single crystallinity is maintained and it is possible to grow an epitaxial layer on porous silicon. In addition, since the porous layer has a large amount of voids formed inside, the surface area of the porous layer has increased dramatically compared to the volume, and as a result, the chemical etching rate is higher than that of a normal single crystal layer. Compared to,
Significantly increased speed. However, it is known that a good quality epitaxial layer can be obtained by annealing at 950-1100 ° C. in a hydrogen atmosphere prior to epitaxial growth. This is a high temperature reducing atmosphere, and the outermost surface of the porous layer is reconstructed. It is believed that this is because the surface was flattened (Nikkei Microdevice, July 1994, p. 76).

Even if polycrystalline silicon is used instead of single crystal silicon, a porous layer can be similarly obtained by anodization.
A crystalline silicon layer can be grown thereon (in this case, partial epitaxial growth corresponding to the crystal grain size of polycrystalline silicon is possible). Further details will be described in each example.

Next, a liquid phase epitaxy method for forming a thin film semiconductor layer will be described. FIG. 5 is a schematic phase diagram in the thermal equilibrium state of the solvent M and the solute S (for example, silicon) for explaining the liquid phase growth method in the manufacturing method of the present invention. Here, the horizontal axis 501 represents the average concentration of solute S in the solution, the left end represents the state of pure solvent, and the concentration of solute S increases toward the right. The vertical axis 502 represents the temperature of the solution, and the state of the solution is roughly divided into two regions with the curve 503 as the boundary.
In P in the region 504, the solute S is uniformly dissolved in the solvent M, and its concentration matches the concentration shown on the horizontal axis.
In the region 505, a part of the solute S is solidified and deposited. For example, in Q, the solid S and the solution having the concentration Dq coexist.
When a substrate made of a material that does not melt at this temperature is immersed in the solution of the state R0 on the curve 503, and the temperature of the solution is slowly lowered, the concentration of the solute S in the solution is along the curve 503, for example, It decreases to R1. Solute S corresponding to the concentration difference between R0 and R1 is deposited as a solid on the surface of the substrate.
In particular, when the substrate is crystalline, the solid S may also be a crystalline substance that inherits the crystallinity of the substrate, which is called epitaxial growth. Usually, the epitaxial growth is easiest when the material of the substrate and the solid S are the same, but even if they are heterogeneous, the epitaxial growth is possible (heteroepitaxial growth). Thus, the thin film semiconductor layer can be grown on the surface of the crystalline first substrate. In general, the solution is just saturated or slightly unsaturated, the substrate is dipped, and after some time elapses, the solution is adjusted to the saturated state to start crystal growth. It is considered that by doing so, impurities and defects on the surface of the substrate are removed by the effect of thermal equilibrium, and high-quality crystals are likely to grow. However, it was found that some problems occur when the liquid phase growth method is actually performed on the porous layer. Hereinafter, description will be made based on the experiments conducted by the present inventors.

Epitaxial growth is performed using silane (Si
H ₄ ), dichlorosilane (SlH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ) and other gases may be decomposed by the action of heat or plasma (CVD method), but other methods than the liquid phase growth method are also possible. Since the liquid phase epitaxy method is performed in a state in which it is in a state close to a thermal equilibrium state, it is easy to obtain a good quality thin film semiconductor layer, and the cost of raw materials required for deposition is low.

First, FIG. 8 shows an example of an apparatus for growing a semiconductor layer of a solar cell suitable for carrying out the present invention. This device is used in Experimental Examples 1 to 3 and Example 1.
As shown in FIG. 8, the entire device is roughly divided into three parts. The inside of 601 'can be kept secret by closing the opening / closing door 602' in the load lock chamber. Reference numeral 603 'is a nitrogen introduction line that can replace the internal atmosphere with nitrogen. Reference numeral 604 'is a hydrogen annealing tank, and the load lock chamber 6 is passed through the gate valve 605'.
The sample can be transferred to and from 01 '. Hydrogen annealing tank 6
Hydrogen can be introduced into 04 'through a hydrogen introduction line 606' while controlling the flow rate. Reference numeral 608 'denotes a heater, which is a substrate 616' placed inside the hydrogen annealing bath 604 '.
Can be heated. The substrate 616 'is a set in which two silicon wafers are attached back to back, and a plurality of sets are arranged in parallel with a holder with a constant interval. The substrate can be moved up and down through a gate valve by a transfer mechanism (not shown). Reference numeral 609 'denotes a liquid phase growth tank capable of transferring a sample between the hydrogen annealing tank 604' and a gate valve 610 '. Hydrogen is supplied to the liquid phase growth tank 609 'from a hydrogen introduction line 611', and the atmosphere during the liquid phase growth can be kept reducing. A carbon boat 614 'is heated by a heater 613', and an element constituting a semiconductor such as silicon and a dopant element as necessary are melted in a low melting point metal such as In inside.

(Experiment 1) A p-type silicon wafer having a porous layer formed on its surface by standard anodization was held at a surface temperature Tsurf = 1050 ° C. for 30 minutes in a hydrogen stream (after annealing) and then at 900 ° C. The temperature dropped. On the other hand, Tm = 900
Silicon was dissolved in a metal indium solvent at a temperature of ℃ until the concentration reached a saturated state. Thereafter, a p-type silicon wafer having a porous layer formed on its surface by standard anodization was immersed in this solvent at a surface temperature Tsurf = 900 ° C. and gradually cooled at a cooling rate of −1 ° C./minute. A silicon layer was deposited on the surface, but an uneven structure was seen on this surface, and a broken ring-shaped RHEED (Reflection H
igh Energy Electron Diffraction (reflective high energy electron diffraction) image was obtained, and it was found that the grown silicon was irregular polycrystal. And when I tried to peel off this film, there was a part that remained without peeling,
It could not be used as a solar cell. However, when dichlorosilane was used to grow on the porous layer under the same conditions by the thermal CVD method, a single crystal film having good smoothness was obtained. Further, the entire surface of this film could be peeled off neatly. On the other hand, when the same p-type silicon wafer was subjected to liquid phase growth under the same conditions without forming a porous layer, a good single crystal was obtained. That is, it was found that trying to grow a crystal from the liquid phase on the porous layer causes an inherent problem.

(Experiment 2) Silicon was dissolved in a metal indium solvent at 900 ° C. until just saturated. That is, the temperature Tsat at which the solution becomes saturated is 900 ° C.

After the temperature of this solvent was set to Tm in Table 1, the p-type silicon wafer having a porous layer formed on its surface by standard anodization was annealed in a hydrogen stream in the same manner as in Experiment 1. Then, the surface temperature was used as the temperature of the solvent (Tsurf = Tm), and the film was slowly cooled at a cooling rate of −1 ° C./min to deposit a thin film of silicon having a thickness of 20 μm. Accordingly, a difference was observed in the RHEED image and the peeling method.

[0034]

[Table 1] Tm RHEED image Peeling ───────────────────────────── 904 ° C .-- Pyramid-like non-uniform growth--902 ℃ --- Discontinuous film --- 900 ℃ Broken ring image Not peelable 898 ℃ Blurred spot image Almost peelable 896 ℃ Blurred spot image Almost peelable 894 ℃ spot image Complete peeling 892 ℃ spot image Complete peeling If it is possible to lower Tm below Tsat, silicon having a saturation concentration or more should be immediately precipitated as in Q in FIG. 5, but actually, supersaturated silicon may exist in the solution to some extent. However, the state of supersaturation is unstable,
The presence of solids, such as wafers, in the solution is believed to initiate deposition on the wafer from the solution near its surface.

Thus, it was found that the state of the thin film semiconductor was significantly improved by immersing the silicon wafer after the solution was supersaturated to some extent. Tsat and T
As a result of experimenting by changing m, the inventors found that Tsat
When the relationship of −Tm ≧ 5 ° is established, the crystallinity is particularly high,
It was concluded that a film that can be exfoliated well can grow. However, if the degree of supersaturation is significant, solute precipitation occurs immediately from the solution, and stable precipitation cannot be achieved.

The present inventors presume the reason why the above results are obtained as follows. In other words, in a microscopic view even when solute precipitation is occurring, solute atoms that precipitate and coexisting solute atoms coexist on the surface of the wafer, and deposition occurs when there are many net solute atoms that precipitate. It is thought to occur (this point is considered to be different from the CVD method in which almost unidirectional precipitation occurs from the gas phase with the chemical reaction of molecules and deposits). Therefore, if no net deposition occurs or the net deposition rate is low at the beginning of the growth, there will be a large number of dissolved atoms from the substrate, which will change the initial structure of the substrate over time. it is conceivable that.
In particular, since the porous layer has a large effective surface area and high reactivity, it is considered that the exchange of atoms with the solute in the solution frequently occurs, and the porous layer is likely to be significantly altered. For this reason, it is considered that the crystallinity is particularly impaired and the voids are filled so that the peeling in the later step becomes difficult.

Further, in the liquid phase growth method, it is said that good quality crystals cannot grow unless the solution is saturated at the initial stage of immersion of the substrate. Since defects are removed and impurities such as oxygen are also removed, it is considered that, due to the above circumstances, it is easier to obtain a good-quality crystal when supersaturated from the initial stage.

(Experiment 3) Silicon was dissolved in a metal indium solvent at 900 ° C. to a concentration at which it was just saturated. A p-type silicon wafer having a porous layer formed on its surface by standard anodization was annealed in a hydrogen stream and immersed in Tsurf as shown in Table 2, and then the solution was cooled at a cooling rate of -1 ° C / The film was gradually cooled by a minute, and thin film silicon having a thickness of 20 μm was deposited. The surface temperature of the substrate seems to coincide with the temperature Tm of the solvent shortly after immersion in the solution.

[0039]

[Table 2] Tsurf RHEED image Delamination ────────────────────────────── 904 ° C−−Pyramid-shaped non-uniform growth−− 902 ℃ Cut ring image Partially peelable 900 ℃ Cut ring image Cannot be peeled 898 ℃ Blurred spot image Almost peelable 896 ℃ Spot image Almost peelable 894 ℃ Spot image Complete peeling 892 ℃ Spot image Complete peeling The indium metal solvent is not supersaturated at the start of growth, but Tsurf <Tsat, preferably Tsat-Tsurf.
It is considered that the adverse effect on the porous layer could be substantially prevented by setting ≧ 5 °. Tsat until cooling starts
= Tm = 900 ° C.

Next, the formation of the bond will be described. In FIG. 1, the p ⁺ (n ⁺ ) layer 104 (for forming a back surface field) on the substrate 105 side and the n ⁺ (p ⁺ ) layer 106 on the light incident side are shown.
Can be grown by the liquid phase growth method separately from the active (p ⁻ (n ⁻ )) layer 103. For example, when Ga is used as a solvent, Ga dissolves in the silicon layer and can be doped as p ⁺ type. When Sb is used as a solvent, Sb dissolves in the silicon layer and can be doped as n ⁺ type. Further, when In is used as a solvent, In hardly dissolves in silicon, so Ga can be added to In to dope p-type. Similarly, As can be added to In to perform n-type doping.

The n ⁺ (p ⁺ ) layer 106 on the light incident side can be separately formed after the semiconductor thin film is peeled off as described above.
However, when a substrate having low heat resistance such as a resin film is used, it is necessary to adopt a deposition method capable of depositing at a low temperature such as plasma CVD. Further details will be described in each example.

Next, the crystalline first substrate and its reuse will be described with reference to FIG. As already mentioned, it is best to use a silicon wafer as the first substrate for growing thin film silicon crystals. In order to carry out anodization, a wafer whose bulk is p-type doped may be used, or only the surface may be p-type doped. A method such as thermal diffusion or ion implantation is used as the method. The p-layer is mainly made porous by the anodization, and thus the porous layer 2
It becomes 02.

The porous layer 202a remaining on the active layer 203 separated from the silicon crystal substrate is selectively removed. Further, the porous layer 202b remaining on the surface of the silicon crystal substrate from which the active layer 203 has been peeled off is also selectively removed for reuse. Ordinary silicon etching liquid, hydrofluoric acid which is a selective etching liquid for porous silicon, or a mixed liquid in which at least one of alcohol and hydrogen peroxide water is added to hydrofluoric acid, or buffered hydrofluoric acid or buffer Only the porous silicon can be subjected to the electroless wet chemical etching using at least one kind of a mixed solution obtained by adding at least one of alcohol and hydrogen peroxide to dehydrofluoric acid.

The thickness of the first substrate gradually decreases as the peeling process is repeated. In addition, the surface tends to have irregularities and defects. Due to these factors, the number of times of repeated use is limited, but the number of times an expensive silicon single crystal wafer can be used has a great influence on the cost. Several improvements are possible from this point of view. That is, it is possible to recover the thickness by performing epitaxial growth on the surface of the substrate having the reduced thickness. In that case, it is particularly advantageous to use a liquid phase growth method, which allows growth at a lower cost.

Further, this method has some merits from the viewpoint of cost reduction. That is, by doping this epitaxial layer with p-type during growth, the step of doping the surface with p-type becomes unnecessary. Further, even if a low-quality silicon wafer having an indefinite impurity concentration is used as the crystalline first substrate, the reproducibility of the anodization process is improved and the quality of the porous layer is stabilized. Further, the reproducibility of anodization can be further enhanced by performing no doping or depositing an epitaxial layer doped with a lower concentration prior to the step of doping the surface to p-type. Further, when the surface is roughened due to repeated use, the subsequent steps are greatly affected, but mechanical polishing can be used together if necessary.

Up to now, the description has been made on the assumption that the thin film semiconductor is a single crystal, but this is not essential. In the application as a solar cell, even if it is a polycrystal, it can be put into practical use if the crystal grain size is about 1 mm as a guide. Even if the crystalline first substrate is polycrystalline, epitaxial growth locally occurs within the range of each crystal grain, and a polycrystalline thin film semiconductor layer is obtained. Further details will be described in each example.

In the solar cell according to the present invention, a polymer film or the like is preferably used as the low heat resistant substrate material for transferring the thin film crystalline semiconductor layer, and a typical example thereof is a polyimide film. It is also possible to use a plastic plate made of glass or resin. In the solar cell according to the present invention, as a method of adhering the substrate and the thin film crystal semiconductor layer, a method of inserting a conductive metal paste such as a copper paste or a silver paste between the two and adhering them to each other, and firing and fixing them. Is preferably used. In this case, the metal such as copper or silver after firing also functions as a back electrode and a back reflection layer. Also, in the case of a substrate such as a polymer film, the softening point of the film substrate is measured while the substrate and the thin film crystal semiconductor layer are in close contact (in this case, the back electrode is formed in advance on the surface of the thin film crystal semiconductor layer). It is also possible to raise the temperature up to and fix the both. In the solar cell according to the present invention, the surface of the semiconductor layer can be textured for the purpose of reducing reflection loss of incident light. In the case of silicon, hydrazine, NaOH, KOH
And the like. The height of the textured pyramid is suitably in the range of several μm to several tens of μm.

[0048]

EXAMPLES Hereinafter, examples of the method of the present invention will be described in detail, but the gist of the present invention is as described above, and the present invention is not limited to the following examples. (Example 1) In this example, a method of transferring a single crystal silicon layer to a polyimide film by the process shown in FIG. 2 to form a solar cell will be described.

A silicon wafer 2 made of a single crystal having a thickness of 500 μm
The surface of 01 was thermally diffused with BCl ₃ as a thermal diffusion source at a temperature of 1200 ° C. to form a p ⁺ layer, and a diffusion layer of about 3 μm was obtained (FIG. 2A). Next, anodization is performed in the HF solution under the conditions shown in Table 3, and the porous silicon layer 2 is formed on the wafer.
No. 02 was formed (FIG. 2 (b)).

[0050]

[Table 3] Anodizing solution HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1 Current density 5 mA / cm ² → 30 mA / cm ² Chemical conversion time 2.5 min → (30 sec) → 0 sec Next, the slow cooling method is used. Liquid phase epitaxial growth of silicon was performed by the so-called method. First, metallic indium (In) was melted at 900 ° C. in a carbon boat in a hydrogen stream. While stirring the solution in this, melt the polycrystalline silicon wafer to saturate, then slowly raise the temperature of the solution to 894 ° C.
To a solution for growth. Next, the atmospheric temperature was adjusted, the temperature of the single crystal silicon wafer 201 on which the porous layer 202 was formed was set to 1030 ° C. in a hydrogen stream, and after annealing for 1 hour, the temperature was lowered and waited until it coincided with the temperature of the solution. In this state, the wafer having a porous layer formed on the surface thereof is immersed in a solution and gradually cooled at a cooling rate of -1.0 ° C / min, and a non-doped thin film silicon layer 203 having a thickness of 20 µm is formed on the porous layer 202. Was deposited and pulled out of the solution. Next, in a separately prepared carbon boat, metal indium (In) was melted at 900 ° C. to be saturated with Si, and 0.1 at% gallium (Ga) of Si was further melted to prepare a growth solution. Subsequently, a wafer having a non-doped thin film silicon layer formed therein was immersed therein, and a p ⁺ thin film silicon layer 204 having a thickness of 1 μm was deposited on the thin film silicon and pulled out from the solution.

Polyimide film 205 having a thickness of 50 μm
20 of copper paste 209 by screen printing on one side of
It was applied in a thickness of μm, and this surface was closely adhered to the surface of the above-mentioned wafer p ⁺ thin film silicon layer 204 and bonded. In this state, the copper paste was placed in an oven and baked at 300 ° C. for 20 minutes, and the polyimide film and the wafer were fixed to each other (FIG. 2E). With respect to the fixed polyimide film and the wafer, the surface on the non-bonded side of the wafer is fixed with a vacuum chuck (not shown), and a force is applied from one end of the polyimide film 205 to perform peeling, The silicon layers 203 and 204 were separated from the wafer 201 and transferred onto the polyimide film 205 (see FIG. 2).
(F)).

The residue (porous layer 202a) of the porous layer 202 remaining on the thin film silicon layer 203 peeled from the wafer 201 is selected with stirring with a mixed solution of hydrofluoric acid, hydrogen peroxide solution and pure water. Etched. The thin film silicon layer 203 was left without being etched, and only the residue of the porous layer 202 was completely removed. The non-porous silicon single crystal has an extremely low etching rate with respect to the above-mentioned etching solution, and the selection ratio with respect to the etching rate of the porous layer is 10 ⁵
The etching amount in the non-porous silicon layer (about several tens of liters) is practically negligible. As a result of cross-sectional observation with a transmission electron microscope, it was confirmed that new crystal defects were not introduced into the thin film silicon layer 203 and good crystallinity was maintained. After cleaning the surface of the thin film silicon layer 203 on the obtained polyimide film 205 by etching with a hydrofluoric acid / nitric acid-based etching solution,
On the thin film silicon layer 203, n-type microcrystalline silicon (μc-
The Si) layer 206 was deposited at 200Å (FIG. 2 (g)).
At this time, the dark conductivity of the μc-Si layer was ˜5 S / cm. In addition, S (Siemens) shows the reciprocal of ohm (Ω).

[0053]

[Table 4] Gas flow rate ratio SiH ₄ / H ₂ = 1 cc / 20 cc PH ₃ / SiH ₄ = 2.0 × 10 ⁻³ Substrate temperature 250 ° C. Pressure 0.5 Torr Discharge power 20 W Finally EB on the μc-Si layer (Electron Beam) ITO transparent conductive film (82 nm) / collecting electrode (Ti
/ Pd / Ag (400 nm / 200 nm / 1 μm) was formed into a solar cell (FIG. 2 (h)).

Regarding the thin film on polyimide single crystal silicon solar cell thus obtained, AM1.5 (100 m
When the IV characteristic under irradiation with W / cm ² ) was measured, a conversion efficiency of 14.6% was obtained.

Also, the porous layer remaining on the silicon wafer 201 after peeling was removed by etching in the same manner as described above, and a smooth surface was exposed (FIG. 2 (i)). By repeating the above steps using the thus obtained reclaimed wafer, a plurality of thin film single crystal solar cells having high quality semiconductor layers were obtained. (Example 2) In this example, a solar cell having the same structure as that of Example 1 is manufactured. A porous silicon layer 202 was formed on the surface of the single crystal silicon wafer 201 by the same method as in Example 1.

Next, liquid phase epitaxial growth of silicon was performed by a method called a temperature difference method. In this example, the internal structure of the liquid phase growth tank of the apparatus of FIG. 8 is different as shown in FIG. That is, as shown in FIG. 9, a Si wafer is attached to the inner wall on the right side of the carbon board 614 ′,
The balance between the heaters 613 'and 613 "is changed to adjust the temperature on the right side of the carbon board so that the solution becomes unsaturated and the silicon melts out, and the melted silicon diffuses to the left. , Here, since the temperature is low and the solution is supersaturated, silicon deposition will occur.

First, 9 in a carbon boat in a hydrogen stream.
Metal indium (In) was melted at 00 ° C. Then, the polycrystalline silicon wafer for dissolution was immersed in the molten indium, stuck on a part of the inner wall of the boat, and dissolved by stirring to make it saturated. Then slowly increase the temperature of the solution to 890
The temperature was lowered to ℃ and used as a growth solution. Next, after annealing in a hydrogen stream, the atmosphere temperature was adjusted and waited until the temperature of the single crystal silicon wafer 201 on which the porous layer 202 was formed matches the temperature of the solution. In this state, the wafer 201 having a porous layer formed on the surface is immersed in a solution, and the temperature of the wall surface of the boat to which the Si wafer is attached is adjusted while adjusting the temperature around the single crystal silicon wafer 201 so as not to change. Was 910 ° C. Then, unlike in Example 1, the temperature of the solution or the like was left unchanged and the non-doped thin film silicon layer 203 with a thickness of 20 μm was formed on the porous layer 202.
Was deposited and pulled out of the solution. In the temperature difference method, since the solution in the vicinity of the melting polycrystalline silicon wafer is unsaturated, the silicon is constantly melted from the surface of the wafer, so that it is not particularly necessary to cool the entire solution. Next, in a separately prepared carbon boat, metal indium (In) is melted at 900 ° C. to saturate with Si, and further 0.1% of Si is added.
After dissolving at% gallium (Ga), the temperature was lowered to 890 ° C. to obtain a growth solution. Subsequently, a wafer having a non-doped thin film silicon layer formed therein is dipped therein, and a p ⁺ thin film silicon layer 20 of 1 μm thickness is formed on the thin film silicon.
4 was deposited and pulled up from the solution. In this case, since the growth time was short, deposition could be performed almost constantly without slow cooling or using a silicon wafer for melting.

A thin film single crystal silicon solar cell was formed on a polyimide film by the same method as in Example 1 below. AM1.5 (100mW /
cm ²⁾ was measured for the I-V characteristic under light irradiation, to obtain a 15.4% conversion efficiency.

The porous layer remaining on the silicon wafer after peeling was also removed by etching in the same manner as described above, and a smooth surface was exposed (FIG. 2 (i)). By repeating the above steps using the thus obtained reclaimed wafer, a plurality of thin film single crystal solar cells having high quality semiconductor layers were obtained. (Example 3) Also in this example, a solar cell having the same structure as that of Example 1 is manufactured. A porous silicon layer 202 was formed on the surface of the single crystal silicon wafer 201 by the same method as in Example 1.

Next, liquid phase epitaxial growth of silicon was performed by a method called constant temperature method described in Japanese Patent Laid-Open No. 6-191987 by the present inventors. In addition, in this embodiment, FIG.
The internal structure of the liquid phase growth tank of the above apparatus is different as shown in FIG. That is, the substrate and the polycrystalline silicon wafer are arranged to face each other. Since the density of the silicon eluted from the polycrystalline silicon decreases, convection occurs and the silicon is transported to the substrate side and deposited on it. In order to effectively generate such convection, it is necessary to keep a large distance between the substrate and the polycrystalline silicon.

First, 9 in a carbon boat in a hydrogen stream.
Metal indium (In) was melted at 00 ° C. Then melt
Dissolve polycrystalline silicon wafer in molten indium
It was dipped, stuck to the bottom of the boat, dissolved and saturated. Next
And slowly lower the temperature of the solution to 894 ° C for growth.
It was a solution. Next, the porous layer 202 that has been annealed
The temperature of the single crystal silicon wafer 201 on which the
I waited until it matched the temperature. Porous on the surface in this state
The layer-formed wafer 201 is immersed in a solution to form a porous layer.
202 face is on the melting polycrystalline silicon wafer for 2 cm
They were opposed to each other with a distance kept between them. After this, unlike Example 1, the solution
Etc., without changing the temperature, and unlike Example 2
The porous layer 202 is left to stand so that there is no temperature difference in the liquid.
20 μm thick non-doped thin film silicon layer 20 on top of
3 was deposited and pulled out of the solution. In the constant temperature method, the
Si melted into the solution near the crystalline silicon wafer
When the density decreases, the surface of the porous silicon layer 202 is convected by convection.
Silicon is removed from the surface of the wafer by being carried away to the surface.
In particular, the entire solution needs to be cooled in order to constantly dissolve it
There is no. Hereinafter, a polyimide film was prepared in the same manner as in Example 1.
A thin film single crystal silicon solar cell was formed on the film. This
The solar cells of AM1.5 (100mW / c
m²) Measurement of IV characteristics under light irradiation
R, cell area 6 cm ²Open voltage 0.6V, short circuit photocurrent
35 mA / cm², Fill factor becomes 0.79, and energy
A conversion efficiency of 16.2% was obtained.

Also, it remains on the silicon wafer after peeling.
The porous layer formed by etching is also etched as described above.
Were removed to obtain a smooth surface (FIG. 2 (i)). Thus
Repeat the above steps using the obtained recycled wafer
Enables thin film single crystal solar cells with high quality semiconductor layers to be
I got more than one. Example 4 In this example, Tsat = Tm = 900 ° C.
Surface temperature of single crystal silicon wafer 201 immersed in solution
By the same method as in Example 1 except that Tsurf was set to 890 ° C.
A thin film single crystal solar cell was produced. About this solar cell
AM1.5 (100 mW / cm²) I- under light irradiation
When the V characteristic was measured, the conversion efficiency was 16.2%.
Obtained. (Embodiment 5) In this embodiment, a non-doped thin film silicon layer is used.
The process up to the step of depositing 203 is the same as in the first embodiment.
Samples pulled up from solution up to 1200 ° C in hydrogen stream
The mixture was heated and left for 30 minutes, and the temperature was set to 900 ° C again. This heat
By the treatment, boron (B) in the p-type porous layer 202
Is thermally diffused into the non-doped thin film silicon layer 203, and p
⁺ The thin film silicon layer 206 is formed. Then another
Injected metal into a designated carbon boat at 900 ° C
(In) is melted and saturated with Si.
01 at% antimony (Sb) is melted for growth
It was a solution. Continuing into this, non-doped thin film silicon
Thin film silicon
On top of n with a thickness of 1 μm⁺ Deposit thin silicon layer 204
Then, it was pulled up from the solution. After this, the plasma CVD equipment
More n-type microcrystalline silicon (μc-Si) layer 206 is deposited
Performed in the same manner as in Example 1 except that the step of
Example 1 is a thin film single crystal solar with the order of the doped layers reversed.
A battery was made. AM1.5 for this solar cell
(100 mW / cm²) Regarding the IV characteristics under light irradiation
As a result, a conversion efficiency of 15.7% was obtained. (Embodiment 6) In this embodiment, as shown in FIG.
A single crystal silicon wafer 301 was prepared in the same manner as in Example 1.
A porous silicon layer 302 was formed on the surface. Next, hydrogen flow
Indium metal at 800 ℃ in a carbon boat inside
(In) was melted. Polycrystal while stirring the solution in this
Melt a silicon wafer to make it saturated, and
Growth by dissolving 0.02 at% antimony (Sb)
Solution. Then slowly raise the temperature of the solution to 794
The temperature was lowered to ℃ and used as a growth solution. Next, adjust the ambient temperature
And a single layer with the annealed porous layer 302 formed
Temperature of crystalline silicon wafer 301 matches the temperature of the solution
Waited until In this state, a wafer with a porous layer formed on the surface
Dip C into the melt and slowly cool at a cooling rate of -1.0 ° C / min.
On the porous layer 302 with a thickness of 0.5 μm.⁺ Type thin film
A silicon layer 306 was deposited and lifted from the solution. Below
In the same manner as in Example 1, a non-doped thin film layer having a thickness of 20 μm was used.
Recon layer 303, p with a thickness of 1 μm⁺ Type thin film silicon layer 3
04 was deposited. After that, the plasma CVD apparatus is used to
⁺ Process for depositing a microcrystalline silicon (μc-Si) layer 306
Example 1 was repeated in the same manner as Example 1 except that steps were omitted.
A thin film single crystal solar cell having the same order of the doped layers was produced.
AM1.5 (100 mW / cm
²) When measured for the IV characteristics under light irradiation,
A conversion efficiency of 16.4% was obtained. (Embodiment 7) In this embodiment, liquid phase is used instead of thermal diffusion.
The p layer formed by the growth method was anodized. First in a hydrogen stream
Metal indium (I
n) was melted. While stirring the solution in this,
The conwafer is melted to make it saturated and the Si.
Solution for growth by dissolving 1 at% gallium (Ga)
And In this state, the same temperature was applied to the 500 μm thick unit.
Immersing the crystalline silicon wafer 201 in the solution, cooling rate
The p-type semiconductor layer having a thickness of 3 μm is annealed at −1.0 ° C./min.
Formed. The following is a thin film having the same procedure and the same configuration as in Example 1.
A single crystal silicon solar cell was obtained.

The porous layer remaining on the silicon wafer 201 after peeling was also removed by etching in the same manner as described above, and a smooth surface was exposed (FIG. 2 (i)). Thereafter, a p-type semiconductor layer having a thickness of 3 μm was formed again by the liquid phase growth method described above, and a thin film single crystal silicon solar cell having the same structure was obtained again by the same procedure as in Example 1. In the same manner, a thin film single crystal solar cell having a larger number of high quality semiconductor layers was obtained using the same single crystal silicon wafer 201. By performing this step, the expensive single crystal silicon wafer 20
Not only was 1 effectively utilized, but the step of heat diffusion of B became unnecessary. (Embodiment 8) In this embodiment, instead of the single crystal silicon wafer, the thickness is 1000 μm and the grain size is mainly 0.3 to 3
A thin-film polycrystalline solar cell was obtained on a polyimide film in the same manner as in Example 1 except that a polycrystalline silicon wafer of about cm was used as the first substrate. In the solar cell thus obtained, up to the non-doped layer, the crystal orientation is taken over within the individual crystal grain regions of the used polycrystalline silicon wafer, and it is considered that epitaxial growth occurs locally. The thin film polycrystalline silicon solar cell was measured for IV characteristics under AM1.5 (100 mW / cm ² ) light irradiation, and the conversion efficiency was 13.5.
Earned%.

The porous layer remaining on the silicon wafer 201 after peeling was also removed by etching in the same manner as described above, and a smooth surface was exposed (FIG. 2 (i)). By using the thus obtained inexpensive reclaimed wafer and repeating the above steps, a plurality of thin film polycrystalline solar cells having high quality semiconductor layers were obtained. (Embodiment 9) In this embodiment, inexpensive nominal purity is 98.5%.
An ingot pulled up by the CZ (Czochralski) method was sliced to a thickness of 1 mm from the metal-grade silicon, and a polycrystalline silicon substrate prepared by mirror-polishing the surface was used as a first substrate. Metal-grade silicon is inexpensive crude silicon that is also used as a raw material for aluminum alloys, etc., and is much cheaper than general semiconductor silicon, but it contains high-concentration impurities and cannot be used in electronic devices as it is. Absent. Elemental analysis of the vicinity of the surface of the produced metal-grade silicon substrate revealed that the results of Table 5 show that the total concentration of impurities is more than 0.01% (the purity of Si is 99.99).
Was weak). The crystal grain size of this metal-grade silicon substrate was several mm to several cm (FIG. 2 (a)).

[0065]

[Table 5] Impurity concentration Ca 42ppm B 38ppm Al 22ppm Ni <5ppm Fe 10ppm Cr 0.6ppm Mn <0.2ppm Ti <1ppm This wafer was subjected to liquid phase epitaxy as described in Example 7 to obtain a thickness of 1 μm. A non-doped layer and a p layer having a thickness of 3 μm were formed in this order, and this p layer was anodized. As shown here, metal-grade silicon is often p-type, but the reproducibility of anodization tends to deteriorate because the degree of doping is uncertain. The reproducibility of anodization can be improved by forming the p layer controlled by the liquid phase growth method and anodizing this. Further, by inserting a non-doped layer between the polycrystalline silicon and the p layer formed by the liquid phase epitaxy method, the controllability of the depth of the anodization is improved. The following is Example 1
A thin film polycrystalline silicon solar cell having the same structure was obtained by the same procedure as described above.

The porous layer remaining on the silicon wafer 201 after peeling was also removed by etching in the same manner as described above, and a smooth surface was exposed (FIG. 2 (i)). Thereafter, a non-doped layer having a thickness of 1 μm and a p-layer having a thickness of 3 μm were formed again by the liquid phase growth method described above, and a thin film polycrystalline silicon solar cell having the same structure was obtained by the same procedure as in Example 1. The same procedure was repeated thereafter to obtain a thin-film polycrystalline solar cell having a large number of high-quality semiconductor layers using the same polycrystalline silicon wafer 201 of metal-grade silicon. By performing this step, the low-quality polycrystalline silicon wafer 201
Not only is it available, but the step of heat diffusion of B is no longer necessary. (Embodiment 10) In this embodiment, a method of transferring a compound semiconductor layer having the structure shown in FIG. 4 to an acrylic resin to form an ultra-high efficiency tandem solar cell will be described.

Single crystal silicon wafer 40 having a thickness of 500 μm
Thermal diffusion of B was performed on the surface of 1 at a temperature of 1200 ° C. using BCl ₃ as a thermal diffusion source to form a p ⁺ layer, and a diffusion layer of about 3 μm was obtained. Next, anodization was performed in the HF solution under the conditions shown in Table 6 to form the porous silicon layer 402 on the wafer.

[0068]

[Table 6] Anodizing solution HF: H ₂ O: C ₂ H ₅ OH = 1: 1: 1 Current density 1 mA / cm ² → 5 mA / cm ² → 40 mA / cm ² Chemical conversion time 2 min → 2.5 min → (20 sec ) → 0 sec Next, liquid phase heteroepitaxial growth of a compound semiconductor was performed by a slow cooling method. First, metallic gallium (Ga) was melted at 810 ° C. in a carbon boat in a hydrogen stream. Next, arsenic (As) was dissolved in the molten indium until it became saturated. On the other hand, the porous silicon layer 402 was annealed in a hydrogen atmosphere at 1050 ° C. for 7 minutes and then cooled to 800 ° C. Next, the temperature of the solution was adjusted to 800 ° C., and the single crystal silicon wafer 4 having the porous silicon layer 402 formed therein was prepared.
01 was dipped and the temperature of the solution was slowly lowered at a rate of −0.1 ° C./min to grow an n ⁺ GaAs layer 403. Next (referred to as _{Al x Ga 1-x As.} ) Gallium solution n ⁺ transition layer in which the concentration of the contact of aluminum (Al) was dissolve slowly to the solution continued to grow Al changes gradually 404
Grew up. When x = 0.37 was reached, the contact of Al with the gallium solution was stopped, and the n-type Al _0.37 Ga _0.63 As layer 405 was grown while keeping the Al concentration constant. Next, A containing a p-type dopant prepared separately from A
In a Ga solution containing 1 and As at 800 ° C., n-type Al _{0.37
Immersing} the substrate on which the Ga _0.63 As layer 405 has been formed,
The solution was cooled at 0.1 ° C./min and p-type Al _0.37 Ga _0.63 A
The s layer 406 is grown and the amount of dopant is further increased to p
⁺ The growth of the Al _0.37 Ga _0.63 As layer 407. In the same procedure as above, p-type Al _0.37 Ga _0.63 As layer 408, n
⁺ -Type Al _x Ga _1-x As layer 409, n-type Al _0.37 Ga
_0.63 As layer 410, n ⁺ -type Al _0.9 Ga _0.1 As layer 41
1, n-type GaAs layer 412, p-type GaAs layer 413
Grew up.

The grown outermost p-type GaAs layer 413
After Pd / Au is formed on the above by EB vapor deposition, a copper paste is applied to one side of a 1 mm thick acrylic resin plate by screen printing to a thickness of 10 to 30 μm, and this side is applied to the p-type GaAs layer 413 of the wafer described above. It was stuck to the side and stuck together. In this state, the copper paste was placed in an oven at 300 ° C. for 20 minutes, and the polyimide film and the wafer were fixed to each other. With respect to the acrylic resin plate and the wafer that are stuck together, vacuum chuck fixing is performed on each of the non-bonded side surface of the wafer and the non-bonded side surface of the acrylic resin plate, and is perpendicular to the bonded surface. To the porous layer 40 by applying a uniform pulling force to each other.
It was destroyed at 2 and the growth layer was peeled from the wafer and transferred onto an acrylic resin plate (FIG. 3 (e)). The porous layer remaining on the n ⁺ type GaAs layer 403 separated from the silicon wafer was selectively etched at 110 ° C. with a mixed solution of ethylenediamine + pyrocatechol + pure water. n ⁺
The GaAs layer 403 of the mold remained without being etched, and only the porous layer was completely removed. Single-crystal GaAs has an extremely low etching rate with respect to the above-mentioned etching solution, and has a practically negligible film thickness reduction. As a result of cross-sectional observation with a transmission electron microscope, it was confirmed that new crystal defects were not introduced into the growth layer and good crystallinity was maintained.

Next, the n ⁺ type GaAs layer 40 which is the outermost surface layer
3 is left in a grid shape and the other portions are etched to obtain n ⁺
Type Al _x Ga _1-x As layer 404 is exposed, and the surface electrode (A
u / Ge / Ni / Au) is formed only on the grid-shaped n ⁺ GaAs layer 403 by EB vapor deposition and photolithography, and then TiO ₂ / MgO is used as an antireflection film.
Was deposited by a plasma CVD method to obtain a solar cell.

Regarding the thin film compound semiconductor solar cell on the acrylic resin plate thus obtained, AM1.5 (10
When the IV characteristics under irradiation with 0 mW / cm ² ) light were measured, a conversion efficiency of 23.8% was obtained. The porous layer remaining on the silicon wafer after peeling was removed by etching in the same manner as in Example 1 and Example 2 to form a smooth surface. By repeating the above steps using the thus obtained reclaimed wafer, a plurality of thin film compound semiconductor solar cells having high quality semiconductor layers were obtained. (Embodiment 11) In this embodiment, a stagger type field effect transistor using single crystal silicon is manufactured by the process shown in FIG.

Single crystal silicon wafer 60 having a thickness of 500 μm
Thermal diffusion of B was performed on the surface of 1 at a temperature of 1200 ° C. using BCl ₃ as a thermal diffusion source to form a p ⁺ layer, and a diffusion layer of about 3 μm was obtained. Then, in the same manner as in Example 1, the porous layer 60
2 was formed (FIG. 6 (b)). Next, liquid phase epitaxial growth of silicon was performed by the slow cooling method. That is, first, a saturated solution at 900 ° C. was prepared in a carbon boat in a hydrogen stream, arsenic (As) was further dissolved as an n-type dopant, and the temperature of the solution was slowly lowered to 894 ° C. to prepare a growth solution. Next, the atmospheric temperature is adjusted, and the single crystal silicon wafer 60 on which the porous layer 202 is formed in the hydrogen stream is formed.
After the temperature of 1 was set to 1030 ° C. and annealed for 1 hour, the temperature was lowered and waited until the temperature of the solution coincided. In this state, dip the wafer with the porous layer formed on the surface in the solution,
An n ⁺ type thin film silicon layer 603 having a thickness of 0.1 μm was deposited on the porous layer 602. Next, a saturated solution at 900 ° C. is prepared in another carbon boat, and the temperature of the solution is slowly lowered to 894 ° C., and the wafer having the n ⁺ -type thin film silicon layer 603 formed therein is dipped in the saturated solution to a thickness of 0. ．
A 3 μm p ⁻ type thin film silicon layer 604 was deposited. Next, a p ⁻ -type thin film silicon layer 60 is formed by heat treatment in steam.
0.1 μm on the surface side of No. 4 was oxidized to form a gate insulating film. An aluminum layer was deposited thereon by a sputtering method, and a gate electrode / gate wiring 606 was formed by a photolithography process. On top of this, the SiO ₂ film 60 by the sol-gel method is formed.
The glass substrate 608 was attached by the method shown in FIG.
(G)). Thereafter, the wafer 601 is peeled off and the porous layer 60
After removing the residue of No. 2 (FIG. 6 (i)), the n ⁺ -type thin film silicon layer 603 is formed by a photolithography process 60.
3 ′, 603 ″, and then a silicon nitride layer is further deposited thereon and patterned by a photolithography process as 609, and further an aluminum layer is deposited and patterned by a photolithography process, and a drain electrode is formed. A drain wiring 610 ′ and a source electrode / source wiring 610 ″ were formed.

In the transistor thus manufactured, since the p ⁻ layer is a single crystal and is thin, the gate voltage is turned on / of.
Due to f, an extremely high on / off ratio of drain current was obtained and a large drain current was obtained. Therefore, even if the area of the transistor is small, it has a large driving capability. In addition, since it is a stagger type, even though it uses a single crystal, it has a high degree of freedom in drain / gate wiring, similar to a transistor using amorphous silicon. When used when driving a liquid crystal matrix, it has high contrast, high speed operation, and high aperture. Ratio can be easily realized. (Embodiment 12) In this embodiment, G
Create an aAlAs LED. 500 μm thick single crystal p
Type GaAs wafer 701 was reported by P. Schmuki et al. (PS
chmuki, J.Fraser, CMVitus, MJ.Graham, HSIssacs
Table 7 with reference to J. Electrochem, Soc. 143 ('96) p3316)
Anodization was performed under the conditions described above to form a porous layer 702 (FIG. 7).
(B)).

[0074]

[Table 7]     Anodizing solution HCl: H₂SO_Four: NH_FourH₂PO_Four= 1: 1: 3     Applied voltage 300mV → 1000mA / cm²     Formation time 1min → 5sec Next, we will perform liquid phase heteroepitaxial growth of compound semiconductors.
It was. First, 810 in a carbon boat in a hydrogen stream.
Metallic gallium (Ga) was melted at ℃. Then thawed
Dissolve arsenic (As) in indium until it is saturated
It was Next, adjust the temperature of the solution to 800 ℃ and
Immerse the single crystal silicon wafer 701 on which the quality layer 702 is formed.
While soaking, the solution is contacted with aluminum (Al)
Gradually dissolves in the aluminum and continues to grow, and the Al concentration gradually changes.
Transition layer (Al_xGa_1-xIt is referred to as As. ) Complete 703
It was prolonged (FIG. 7 (c)). Note that the growth of the transition layer 703 is a surface.
The surface temperature was 800 ° C. and the immersion was performed. The slow cooling condition is −0.
1 ° C./min. Gariu at x = 0.37
Stop contacting Al with the aluminum solution to keep the Al concentration constant.
Al as a barrier layer_0.37Ga_0.63Form As layer 704
It was prolonged (FIG. 7 (d)). Next, prepared separately from this
Emitting layer Al using solution_0.5 Ga_0.5 Form As layer 705
It was prolonged (FIG. 7 (e)). Al again as a barrier layer_0.37G
a_0.63An As layer 706 was grown (FIG. 7 (f)). Then
SnO₂Glass 709 coated with transparent conductive layer 708
In₂O₃Of the sol = gel film 708 of FIG.
(G)), the wafer 701 was peeled off (FIG. 7 (h)). It
And glass 711 with copper paste layer 710,
Furthermore, the lead-out line 712 is SnO.₂Transparent conductive layer 708,
It was pulled out from the copper paste layer 710 (FIG. 7 (i)). It
Further, the side surface was sealed with resin 713 (FIG. 7 (j)). like this
As a result, a high-luminance surface-emitting red LED could be obtained. This
In particular, the copper paste layer 710 enables light emission particularly in the front surface.
Reflected on and SnO₂Transparent conductive layer 708 and In₂O₃
Sol = gel film 708 of glass 711 and Al _0.37Ga
_0.63Reflection loss due to a large difference in the refractive index of the As layer 706
The brightness is increased due to the reduction.

[0075]

As described above, according to the present invention,
A semiconductor layer such as a single crystal or a polycrystal having excellent crystallinity can be formed on the second substrate at low cost. In addition, a semiconductor layer can be formed on an inexpensive and flexible substrate to obtain a semiconductor base material that can be used in various ways.

Further, according to the present invention, a thin film crystal solar cell having a high conversion efficiency can be obtained on a low heat resistant substrate, and thus a high-quality solar cell with mass productivity can be provided to the market. .

Further, according to the present invention, a thin film crystal solar cell having good characteristics is formed by peeling it from a substrate, the substrate is regenerated and repeatedly used, and the material is effectively used. It has become possible to manufacture various solar cells.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a solar cell of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing a solar cell according to the present invention.

FIG. 3 is a diagram illustrating a method for manufacturing a solar cell according to the present invention.

4 is a schematic cross-sectional view showing the structure of a GaAs / AlGaAs thin film solar cell formed on a porous layer by the method for manufacturing a solar cell of the present invention shown in FIG.

FIG. 5 is a diagram for explaining the principle of the liquid phase growth method.

FIG. 6 is a diagram illustrating a method of manufacturing a stagger type field effect transistor.

FIG. 7 is a diagram illustrating a method of manufacturing a GaAlAs-based LED.

FIG. 8 is a diagram showing an example of a semiconductor layer growth apparatus of a solar cell suitable for implementing the present invention.

FIG. 9 is a diagram showing a part of an example of an apparatus for growing a semiconductor layer of a solar cell suitable for carrying out the present invention.

FIG. 10 is a diagram showing a part of an example of an apparatus for growing a semiconductor layer of a solar cell suitable for carrying out the present invention.

[Explanation of symbols]

201, 301, 401 Crystal substrates 202, 202a, 202b, 302, 302a, 30
2b, 402 porous layer 103, 203, 303 active layer 104, 204, 304 p ⁺ layer (or n ⁺ layer) 106, 206, 306 n ⁺ layer (or p ⁺ layer) 107, 207, 307 antireflection layer ( Transparent conductive layer) 108, 208, 308 Current collecting electrode 109, 209, 309 Back electrode 403 n ⁺ GaAs 404 n ⁺ Al _x Ga _1-x As 405 nAl _0.37 Ga _0.63 As 406 pAl _0.37 Ga _0.63 As 407 p ⁺ Al _x Ga _1-x As 408 pAl _0.37 Ga _0.63 As 409 n ⁺ Al _x Ga _1-x As 410 nAl _0.37 Ga _0.63 AS 411 n ⁺ Al _0.9 Ga _0.1 As 412 nGaAs 413 pGaAs 501 phase solute concentration 502 Curve 504 that divides regions of different states Region 505 where only uniform solution exists 505 Solution and solid solute Existence area

Front Page Continuation (72) Inventor Takao Yonehara 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP 5-283722 (JP, A) JP 5-217825 ( JP, A) JP 7-302889 (JP, A) JP 8-213645 (JP, A) JP 6-45622 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/208 H01L 21/76 H01L 27/12 H01L 31/04

Claims (9)

(57) [Claims] 1. A method of manufacturing a semiconductor substrate, which comprises at least the following steps (a) to (d). (A) Step of forming a porous layer on the surface of the first substrate (b) A non- supersaturated solution in which the elements constituting the semiconductor to be grown are dissolved to a certain concentration has a surface temperature of the solution having the above concentration. The step of growing the semiconductor layer on the surface of the porous layer by immersing the porous layer at a temperature lower than the saturation temperature (c) at least the surface of the porous layer and the first substrate on which the semiconductor layer is formed Then, the step of adhering the second substrate (d) The first substrate and the second substrate are separated via the porous layer, and the semiconductor layer is peeled off from the first substrate. Transferring to the second substrate 2. The first separated in the step (d) of claim 1.
The method for producing a semiconductor substrate, wherein the surface of the substrate is treated, and the substrate is charged again as the first substrate in the step (a). 3. At least the following steps (a) to (e):
A method for manufacturing a semiconductor substrate, which comprises: (A) Step of forming a porous layer on the surface of the first substrate (b) Semiconductor which is grown in a reducing atmosphere at high temperature
In a solution in which the elements constituting the body are dissolved to a supersaturated state,
Dipping the porous layer and growing a semiconductor layer on the surface of the porous layer
Step (c) at least the porous layer and the semiconductor layer are shaped
A process for adhering the second base to the surface of the formed first base.
Degree (d) the said through the porous layer and the first substrate first
The second substrate is separated to separate the semiconductor layer from the first substrate.
Step of further peeling and transferring to the second substrate (e) A semiconductor layer obtained by treating the surface of the first substrate separated in the step (d) and then introducing impurities into the surface by a liquid phase growth method. was grown, the step of introducing a first substrate again the step (a) 4. At least the following steps (a) to (e):
A method for manufacturing a semiconductor substrate, which comprises: (A) Step of forming a porous layer on the surface of the first substrate (b) The elements constituting the semiconductor to be grown are kept at a constant concentration.
The surface temperature of the solution dissolved by
Immerse the porous layer whose temperature is lower than the
The step of growing a semiconductor layer on the surface of the porous layer (c) At least the porous layer and the semiconductor layer are shaped.
A process for adhering the second base to the surface of the formed first base.
Degree (d) the said through the porous layer and the first substrate first
The second substrate is separated to separate the semiconductor layer from the first substrate.
Step of further peeling and transferring to the second substrate (e) Surface of the first substrate separated in the step (d)
After the treatment, the impurities were introduced into the surface by liquid phase epitaxy.
Growing the semiconductor layer, and again the first substrate in the step (a)
As a process 5. The method for producing a semiconductor substrate according to claim 3 , wherein prior to forming the semiconductor layer having the impurities introduced thereinto, a liquid phase is formed on the surface of the first substrate after the surface treatment. A method for manufacturing a semiconductor substrate, which comprises forming a semiconductor layer in which no impurities are introduced or a lower concentration of impurities is introduced by a growth method. 6. The method for manufacturing a semiconductor substrate according to claim 3 , wherein a semiconductor having a purity of 99.99% or less is used as the first base. A method of manufacturing a semiconductor substrate, comprising: 7. The method of manufacturing a semiconductor substrate according to claim 1, wherein the first base is crystalline. 8. The method for manufacturing a semiconductor substrate according to claim 1, wherein the first base is a silicon single crystal. 9. A method of manufacturing a solar cell, which is manufactured using the semiconductor layer transferred to the second substrate according to any one of claims 1 to 8.