JP2002299662A - Semiconductor substrate and its manufacturing method, and solar cell and its manufacturing method - Google Patents

Abstract

(57) Abstract: Provided is a method for obtaining a semiconductor substrate or a solar cell which is simple, has excellent characteristics, and is excellent in yield. SOLUTION: After a polycrystalline substrate or a grain boundary in a semiconductor layer formed thereon is made porous by anodizing, the porous grain boundary is oxidized in an oxygen atmosphere to perform insulation treatment. As a result, it is inactivated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate and a method for manufacturing the same, and a solar cell and a method for manufacturing the same. More specifically, the present invention relates to a low-cost and high-performance semiconductor substrate and a method for manufacturing the same, and a solar cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art Solar cells have been widely studied as power sources that are system-connected to driving energy sources of various devices and commercial power.

It is desired that a solar cell can form an element on a low-cost substrate due to cost requirements. On the other hand, silicon is generally used as a semiconductor constituting a solar cell.
Among them, single crystal silicon is the most excellent from the viewpoint of efficiency of converting light energy into electromotive force, that is, photoelectric conversion efficiency. However, amorphous silicon is considered to be advantageous from the viewpoint of increasing the area and reducing the cost. Also,
In recent years, for the purpose of obtaining low cost like amorphous silicon and high energy conversion efficiency like single crystal,
The use of polycrystalline silicon is being considered.

[0004]

By the way, generally, impurities are easily segregated at the grain boundaries of polycrystals due to segregation during the production of polycrystals. For this reason, when a semiconductor layer is formed on a polycrystalline substrate, particularly inexpensive metal-grade silicon (impurity 10) is used.
(ppm or more), a polycrystalline substrate is produced, and a silicon layer is formed thereon by an epitaxial growth method or the like. In this case, impurities segregated at grain boundaries of the polycrystalline substrate are formed on the polycrystalline substrate. And may adversely affect the characteristics of devices formed thereafter (for example, H. Itoh, T. Saitoh, N. Nakamura, S. Matsubara,
T. Warabisako and T. Tokuyama, “Characterization of
Silicon Layers Epitaxially Grown on Metallurgical
-Grade Polycrystalline Substrates ”, Journal of Cr
ystal Growth 45 (1978) p.446).

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a semiconductor substrate capable of forming a low-cost, simple, and good device with good characteristics. In particular, using metal grade silicon,
It is an object of the present invention to provide a low-cost, high-performance semiconductor substrate and a method for manufacturing the same.

Another object of the present invention is to provide a high-performance semiconductor device, particularly a solar cell, which can be mass-produced using the above-mentioned semiconductor substrate.

[0007]

In other words, a semiconductor substrate of the present invention is a semiconductor substrate having a polycrystalline structure composed of a plurality of crystalline bodies, and is formed on a polycrystalline structure composed of a first crystalline body. A polycrystalline structure composed of a set of second crystalline bodies is stacked, and a semiconductor substrate characterized in that it has an impurity fixed layer at least in the vicinity of including the adjacent interface of the first crystalline body. is there.

Further, the method of manufacturing a semiconductor substrate according to the present invention
In a method of manufacturing a semiconductor substrate having a polycrystalline structure,
i) a step of anodizing at least the main surface of the polycrystalline substrate to form a porous layer on each of the surface and the grain boundary of the polycrystalline substrate, and ii) oxidizing the polycrystalline substrate to form the polycrystalline substrate. Converting the surface of the crystal substrate and the porous layer at the grain boundary into oxide films, respectively; iii) removing the oxide film formed on the surface of the polycrystalline substrate by etching;
v) forming a semiconductor layer on the polycrystalline substrate by inheriting the crystal orientation of the polycrystalline substrate by an epitaxial growth method.

A solar cell according to the present invention is a solar cell manufactured using the above-mentioned semiconductor substrate, and a method for manufacturing a solar cell according to the present invention is a method for manufacturing a solar cell manufactured using the above method. It is.

[0010]

According to the method of manufacturing a semiconductor substrate and a solar cell of the present invention, the polycrystalline (metal-grade silicon) substrate composed of the aggregate of the first crystal body is made porous / insulated so that the grain boundary portion is made porous. Since impurities at the grain boundaries are fixed (an impurity fixed layer is provided near the grain boundaries), it is possible to drastically reduce the incorporation of impurities into the semiconductor layer formed thereon.
A semiconductor substrate or a solar cell having excellent characteristics can be obtained with high yield.

Here, the “impurity fixed layer” in the present invention
The term “layer (region)” refers to a layer (region) in which impurities present in a grain boundary portion are passivated (passivated).

As an example of oxidizing a polycrystalline substrate by making the grain boundaries porous, a high-purity polycrystalline silicon substrate is disclosed in, for example, JP-A-61-40149.
The technology disclosed in this publication is summarized as follows.
Converting the P-type inversion region in the n-type polycrystalline silicon substrate, which has been inverted into a mold, into a porous silicon region by electric field etching from a surface to a position deeper than a position where a pn junction is formed;
This is a technique for manufacturing a semiconductor photoelectric conversion device in which at least a part of the porous silicon region is oxidized to form a silicon oxide film, and thereafter, a thin oxide film formed outside the porous silicon region is removed. Then, a method for manufacturing a semiconductor photoelectric conversion device in which a leak current of a solar cell is reduced by selectively oxidizing a crystal grain boundary portion of polycrystalline silicon to form an insulator.

However, the technique described in the publication has a problem to be further solved in order to obtain a low-cost and high-quality semiconductor substrate.

That is, in order to obtain a semiconductor substrate with lower cost, it is necessary to use silicon (low-purity silicon, for example, so-called metal-grade silicon) which is lower in cost than conventional (high-purity) polycrystalline silicon. . In that respect, it is not possible to sufficiently solve the problem simply by "selectively oxidizing a part of the crystal grain boundary of polycrystalline silicon to make it an insulator".

In other words, in the above-described method, the grain boundary to be made porous is limited to a part of the p-type part, and when this part is oxidized, the part of the pn junction formed in the polycrystalline substrate is oxidized. Although a certain effect is recognized in reducing the leakage current, if the degree of porosity or oxidation at the grain boundary is insufficient, impurities segregated at the grain boundary of the polycrystalline substrate are removed. It cannot be sufficiently immobilized (passivated). In particular, in the case of a low-purity polycrystalline substrate, impurities tend to accumulate at the grain boundary during the production of the substrate, and the amount thereof is much larger than that of so-called semiconductor-grade (grade) silicon. It is difficult to efficiently suppress the adverse effect (diffusion) of impurities on the semiconductor layer.

Japanese Patent Application Laid-Open No. 2000-22183 discloses a heat-resistant substrate, a polycrystalline semiconductor film formed on the heat-resistant substrate, and the polycrystalline semiconductor film electrically connected to the polycrystalline semiconductor film. A polycrystalline semiconductor element having a pair of electrodes for extracting an electromotive force generated by carriers generated in the polycrystalline semiconductor film when the film is irradiated with light,
In the polycrystalline semiconductor film, a plurality of semiconductor crystal grains are separated by an oxide or nitride grain boundary layer formed at a crystal grain boundary between the semiconductor crystal grains, and the average thickness of the grain boundary layer is 10%.
A technique relating to a polycrystalline semiconductor element having a thickness of from 300 nm to 300 nm and a method for manufacturing the semiconductor element is disclosed.

With such a configuration,
Even if impurities such as oxides are present at the crystal grain boundaries, a solar cell type polycrystalline semiconductor element having a high power generation efficiency can be obtained.

However, in the above-described technique, when a polycrystalline semiconductor film is formed, it is necessary to adjust a raw material in advance so as to contain an oxide or a nitride, and the thickness of the oxide or the nitride in the grain boundary layer is increased. To fix the impurities by
It is difficult to make the thickness more than μm, and this technique cannot be directly applied to a low-purity polycrystalline substrate as described above.

We have studied low-purity polycrystalline substrates made of so-called metal-grade silicon at the grain boundaries, in addition to the metallic elements of Fe, Cr, Cu, Mn, Ni, Mg, Ti and V, B, Al , P, there are many as such, also selectively be porous is enhanced by anodizing at any grain boundaries therefor, also B, Al, P, of even such as as is relatively small elements Is introduced into the grain boundary, and the porous layer can be similarly made porous. As a result, the above impurities are fixed near the grain boundary by the insulation treatment of the porous layer by oxidation or the like, and the crystal growth method As a result, a semiconductor layer having good characteristics can be formed, and the present invention has been completed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment As an example of an embodiment according to the present invention, a method for manufacturing a semiconductor substrate shown in FIG. 1 will be described with reference to FIG.

As shown in FIG. 2A, first, a silicon ingot is prepared by a usual casting method using metal-grade silicon as a raw material, and the resulting ingot is sliced with a wire saw to obtain a polycrystalline silicon substrate 201. At this time, Fe, B, Al, As, P, Cr, Cu, Mn, Ni,
Impurities such as Mg, Ti, and V segregate at the crystal grain boundaries 202.

Next, one surface of the polycrystalline silicon substrate 201 is anodized in, for example, an HF solution to make the surface and the grain boundary portion of the polycrystalline silicon substrate 201 porous. At this time, B, Al, As, and P are previously thermally diffused into the surface of the polycrystalline silicon substrate 201 as necessary.
It may be selectively introduced into the grain boundary portion 202 by ion implantation or by being mixed during substrate formation.
By doing so, the current is concentrated on the grain boundary portion 202 during the anodization, the formation of the grain boundary portion selectively proceeds, and the grain boundary portion can be efficiently made porous.

After the formation, the polycrystalline silicon substrate 201
Is placed in, for example, an oxidation furnace and thermally oxidized to form a porous layer 203 and a porous grain boundary 204 formed on the surface of the polycrystalline silicon substrate 201 into a silicon oxide layer 205, respectively.
And an oxide grain boundary 206.

The silicon oxide layer 205 formed on the surface of the polycrystalline silicon substrate 201 is removed by etching with an HF solution or the like, and a polycrystal having a layer in which impurities at the grain boundaries are fixed (impurity fixed layer). Polycrystalline silicon substrate 2 having a silicon layer (polycrystalline structure composed of a set of first crystalline bodies)
07 is obtained. Further, a silicon layer (polycrystalline structure composed of a collection of second crystals) 208 is formed on the polycrystalline silicon substrate by an epitaxial growth method or the like, and a semiconductor substrate 209 is manufactured.

The low-purity polycrystalline substrate used in the present invention is prepared by melting / solidifying a metal-grade silicon (silica reduced by coke) having a purity of about 90 to 99.99% by a casting method. An ingot formed and processed into a wafer through a slicing step is preferably used. The size of the crystal grain size of the polycrystalline substrate is not particularly limited, but practically a range of 200 μm to 1 cm is easily used.

In the anodization method for forming the porous material used in the present invention, for example, an HF solution is used. When the HF concentration is 10% or more, the porous material can be formed. The formation of porous silicon by anodization requires holes for the anodic reaction, and therefore, it is said that porosification is performed mainly with p-type silicon having holes (T. Unagami, J. Electroche
m.Soc., vol. 127, 476 (1980)).

However, on the other hand, there is a report that low-resistance n-type silicon can be made porous (RP Holmstrom an).
d JYChi, Appl. Phys. Lett., vol. 42, 386 (1983)),
Regardless of whether it is p-type or n-type, it can be made porous with low resistance silicon. As the amount of current flowing at the time of anodization is appropriately determined by a porous layer thickness or polycrystalline grain boundaries state of the which is HF concentration and desired, approximately several mA / cm ² ~
A range of several tens mA / cm ² is appropriate. The thickness of the porous layer formed at the grain boundary portion is such that it functions more efficiently as an impurity fixed layer that is subsequently converted by oxidation treatment or the like.
In addition, from the viewpoint that the power generation efficiency is not significantly affected when the solar cell element is used, it is desirable that the ratio is determined to be 10% or less with respect to the entire surface of the base when viewed from above the base. Although it depends on the amount of impurities to be formed and the size of the crystal grain size of the polycrystalline substrate, specifically, it is preferably 500 nm or more and 10 μm or less from the grain boundary interface, more preferably 1 μm or more and 10 μm or less. Good to be.

By adding alcohol such as ethyl alcohol to the HF solution, bubbles of the reaction gas generated during anodization can be removed from the reaction surface without instantaneous stirring, and porous silicon can be formed uniformly and efficiently. can do. The amount of the alcohol to be added is appropriately determined depending on the HF concentration, the desired thickness of the porous layer, or the state of the polycrystalline grain boundary, and it is necessary to particularly determine the amount of the alcohol so that the HF concentration does not become too low.

In the present invention, before the porous layer is converted into the impurity fixed layer by an oxidation treatment or the like, heat treatment is performed in an inert gas such as an argon or nitrogen atmosphere to getter impurities around the porous layer. By action, it can be further incorporated into the porous layer. This is similarly effective not only in the grain boundary part but also in the porous layer formed on the surface of the polycrystalline substrate during anodization, and by further reducing impurities near the surface of the polycrystalline substrate by the gettering action, The influence on the formation of the semiconductor layer can be minimized.
The heat treatment conditions for gettering depend on the impurity concentration (concentration in crystal grains and grain boundaries) contained in the polycrystalline substrate, but the temperature is in the range of 900 ° C. to 1250 ° C. and the time is 30 minutes. A range from minutes to 5 hours is preferably used.

In the present invention, the concentration of the impurities segregated in the impurity fixed layer is preferably in the range of 10 ¹⁶ cm ^{−3 to} 10 ²⁰ cm ⁻³ . If it is more than 10 ²⁰ cm ^-3 , electrical characteristics may be adversely affected in a semiconductor device. There is no particular lower limit (smaller is preferred), but if it is 10 ¹⁶ cm ⁻³ or less, it is necessary to increase the purity of the raw material of the polycrystalline substrate, which may increase the cost.

In the present invention, the impurity-immobilized layer is not particularly limited, but may be an oxide layer, a nitride layer, or a carbonized layer. In particular, the oxide layer is preferable in performing a post-processing (selective) etching process. In the case of forming a nitride layer, it can be formed by performing heat treatment in an ammonia atmosphere or exposing the porous layer to nitrogen plasma.
In the case of forming a carbonized layer, it can be formed by implanting carbon ions into the substrate surface by ion implantation and performing heat treatment or performing heat treatment in an atmosphere containing a small amount of carbon monoxide.

The content of oxygen, nitrogen and carbon contained in the impurity-immobilized layer of the present invention is as follows when the polycrystalline substrate is silicon and the amount of silicon in the impurity-immobilized layer is 1. 0.01 to 3.5 and 0.01 respectively
-2.5, 0.01-3.0. Outside of these ranges, the layer may not function sufficiently as an impurity fixing layer.

In the present invention, as a means for forming the impurity-immobilized layer, a method of oxidizing a porous layer can be mentioned, such as a thermal oxidation method or a chemical oxidation method. Examples of the thermal oxidation method include pyro oxidation, dry oxidation, and rapid heating oxidation method. As a method of chemically oxidizing, a method using a heated hydrogen peroxide solution, or an oxidizing agent such as nitric acid, ammonium nitrate, ammonium perchlorate, ammonium chlorite and the like can be used.

In the present invention, a thermal CVD method, an LPCV
There are a D method, a sputtering method, a plasma CVD method, a photo CVD method, a liquid phase growth method and the like. For example, thermal CVD, LPCV
As a source gas used in the case of a vapor phase growth method such as a D method, a plasma CVD method, or a photo CVD method, for example, in the case of forming a silicon layer, SiH ₂ Cl ₂ , SiCl ₄ , S
iHCl ₃ , SiH ₄ , Si ₂ H ₆ , SiH ₂ F ₂ , Si ₂ F ₆
And the like, and halogenated silanes.

Further, hydrogen (H ₂₎ is added for the purpose of obtaining a reducing atmosphere to promote as the carrier gas or crystal growth in addition to the source gas. The ratio of the amount of the source gas to the amount of hydrogen is appropriately determined as desired depending on the forming method, the type of the source gas, and the forming conditions, but is preferably 1:10 or more and 1: 1000 or less (introduction flow ratio). Preferably, the ratio is from 1:20 to 1: 800.

When liquid phase growth is used, H ₂ or N ₂
Epitaxial growth is performed by dissolving silicon in a solvent such as Ga, In, Sb, Bi, or Sn in an atmosphere and gradually cooling the solvent or by providing a temperature difference in the solvent.

The temperature and pressure in the epitaxial growth method used in the present invention vary depending on the forming method and the kind of the raw material (gas) to be used, but the temperature is, for example, the case where silicon is grown by a normal thermal CVD method. The temperature is suitably in the range of 800 ° C. to 1250 ° C., more preferably in the range of 850 ° C. to 1200 ° C. In the case of the liquid phase growth method, the temperature is preferably controlled to 600 ° C. or higher and 1050 ° C. or lower when silicon is grown using Sn or In as a solvent, depending on the type of the solvent. In a low-temperature process such as a plasma CVD method, the temperature is preferably 200 ° C. or more and 600 ° C. or less, more preferably 200 ° C. or more and 500 ° C. or less.

Similarly, the pressure is about 1 Pa to 10 ⁵
Pa is appropriate, and more preferably 10 Pa to 10 ⁵
The range of Pa is desirable.

In the solar cell of the present invention, the surface of the semiconductor layer can be subjected to texture processing for the purpose of reducing the reflection loss of incident light. In the case of silicon, hydrazine or NaO
This is performed using H, KOH, or the like. The height of the pyramid of the texture to be formed is suitably in the range of several μm to several tens μm.

[0040]

Hereinafter, the formation of a desired semiconductor substrate by carrying out the method of the present invention will be described in more detail, but the present invention is not limited to these examples.

Example 1 In this example, a semiconductor substrate in which a grain boundary portion in a polycrystalline silicon wafer made of metal-grade silicon was insulated and a silicon layer was formed thereon by the process shown in FIG. Here is where you get

A silicon ingot was manufactured from a metal grade silicon having a purity of 98% by a casting method using induction heating. The resulting ingot was sliced with a wire saw to obtain a 150 mm square, 350 μm thick polycrystalline silicon wafer 201 (FIG. 2A). At this time, the F contained in the metal-grade silicon when the ingot is made
e, B, Al, As, P, Cr, Cu, Mn, Ni, M
Impurities such as g, Ti, and V segregate at the crystal grain boundaries 202.
Table 1 shows the results of the average impurity analysis near the grain boundary.

[0043]

[Table 1]

Further, when the crystal grain boundaries were revealed by etching, the crystal grain size of the obtained polycrystalline silicon wafer was expanded from several mm to several cm.

The polycrystalline silicon wafer 201 was converted to HF + C
Anodization was performed in a ₂ H ₅ OH solution under the conditions shown in Table 2 to form a porous layer 203 on the wafer and a porous grain boundary 204 on the grain boundary.
Was formed (FIG. 2B).

[0046]

[Table 2]

A polycrystalline silicon wafer 20 is placed in a dry oxidation furnace.
1 and oxidized at 1100 ° C. in an oxygen atmosphere to form a porous layer 203 and a porous grain boundary 204 formed on the surface of the polycrystalline silicon wafer 201, respectively.
A silicon oxide layer 205 and an oxide grain boundary 206 were formed (FIG. 2C).

The silicon oxide layer 205 formed on the surface of the polycrystalline silicon wafer 201 was removed by etching with a 10% HF solution to obtain a polycrystalline silicon substrate 207 having insulated grain boundaries (FIG. 2). (D)).

Next, on the surface of the polycrystalline silicon substrate 207, I
Epitaxial growth was performed by a slider type liquid phase growth apparatus using n as a solvent under the formation conditions shown in Table 3 to make the thickness of the silicon layer 208 30 μm. At this time, a very small amount of B (0.1 ppm to the amount of dissolved silicon)
~ Several ppm) to add p to the grown silicon layer 208.
^{-On the} mold

[0050]

[Table 3] (FIG. 2E). The obtained silicon layer inherited the crystal orientation and grain size of the underlying polycrystalline silicon wafer 201.

Thus, a semiconductor substrate 209 having a semiconductor silicon layer was obtained.

(Embodiment 2) In this embodiment, in the same manner as in Embodiment 1, a grain boundary portion in a polycrystalline silicon wafer made of metal-grade silicon is insulated by a process shown in FIG. This shows how to obtain a semiconductor substrate on which a silicon layer is formed.

A silicon ingot was produced from a metal grade silicon having a purity of 98% by a casting method using induction heating. The resulting ingot was sliced with a wire saw to obtain a 125 mm square, 350 μm thick polycrystalline silicon wafer 201 (FIG. 2A). At this time, the F contained in the metal-grade silicon when the ingot is made
e, B, Al, As, P, Cr, Cu, Mn, Ni, M
Impurities such as g, Ti, and V segregate at the crystal grain boundaries 202.

When the crystal grain boundaries were revealed by etching, the crystal grain size of the obtained polycrystalline silicon wafer was expanded from several mm to several cm.

BC on the surface of the polycrystalline silicon wafer 201
B was thermally diffused at a temperature of 1200 ° C. using l ₃ as a thermal diffusion source to form ap ⁺ layer, and a diffusion layer of about 3 μm was obtained (FIG. 2A: not shown). At this time, B
Accelerated diffusion occurred almost to the vicinity of the back surface of the wafer.

Next, the surface of the polycrystalline silicon wafer 201 was anodized in an HF + C ₂ H ₅ OH solution under the conditions shown in Table 4 to form a porous layer 205 on the wafer and a porous particle on the grain boundary. A field 206 was formed (FIG. 2B).

[0057]

[Table 4]

A polycrystalline silicon wafer 2 was placed in a rapid heating oxidation furnace.
01, and oxidized at 1200 ° C. in an oxygen atmosphere to form a porous layer 203 and a porous grain boundary 204 on the surface of the polycrystalline silicon wafer 201, respectively.
A silicon oxide layer 205 and an oxide grain boundary 206 were formed (FIG. 2C).

The silicon oxide layer 205 formed on the surface of the polycrystalline silicon wafer 201 is removed by etching with a 10% HF solution to obtain a polycrystalline silicon substrate 207 having insulated grain boundaries (FIG. 2). (D)).

Epitaxial growth was carried out on a polycrystalline silicon substrate 207 under the conditions shown in Table 5 using a conventional thermal CVD apparatus to form a silicon layer 208 (about 30 μm thick).

[0061]

[Table 5] At this time, the amount of B ₂ H ₆ was reduced to 0. Several ppm to several pp
m and the growth silicon layer is made p ^- type (FIG. 2).
(E)). The obtained silicon layer inherited the crystal orientation and grain size of the underlying polycrystalline silicon wafer 401.

Thus, a semiconductor substrate 209 having a semiconductor silicon layer was obtained.

Example 3 In this example, after the grain boundaries in a polycrystalline silicon wafer made of metal-grade silicon were made porous by the process shown in FIG. 2, gettering of impurities was performed. This shows that a semiconductor substrate is obtained by forming an insulating layer on the insulating layer by oxidation treatment to form a silicon layer thereon.

In the same manner as in Example 2, a silicon ingot was produced from metal-grade silicon having a purity of 95% as a raw material by a casting method using induction heating. Slice the resulting ingot with a wire saw, 125mm square,
A polycrystalline silicon wafer 201 having a thickness of 350 μm was obtained (FIG. 2A). At this time, Fe, B, Al, As, P, Cr,
Impurities such as Cu, Mn, Ni, Mg, Ti, and V segregate at the crystal grain boundaries 202.

When the crystal grain boundaries were revealed by etching, the crystal grain size of the obtained polycrystalline silicon wafer was expanded from several mm to several cm.

The PO on the surface of the polycrystalline silicon wafer 201
P was thermally diffused at a temperature of 1200 ° C. using Cl ₃ as a thermal diffusion source to form an n ⁺ layer, and a diffusion layer of about 3 μm was obtained (FIG. 2A: not shown). At this time, accelerated diffusion of P occurred in the grain boundary portion 202, and reached almost near the back surface of the wafer.

The polycrystalline silicon wafer 201 is converted to HF + C ₂
Anodization was performed in an H ₅ OH solution under the conditions shown in Table 2 to form a porous layer 203 on the wafer and a porous grain boundary 204 on the grain boundary.
Was formed (FIG. 2B).

Next, the polycrystalline silicon wafer 201 was placed in a heat treatment furnace and heat-treated at 1150 ° C. for 2 hours in an argon atmosphere to getter localized impurities in the porous portion and its periphery (FIG. 2). (B): not shown).

Further, the polycrystalline silicon wafer 201 is put into a dry oxidation furnace, and oxidized at 1100 ° C. in an oxygen atmosphere to form the porous layer 203 and the porous particles formed on the surface of the polycrystalline silicon wafer 201. The boundaries 204 were made into a silicon oxide layer 205 and an oxide grain boundary 206, respectively, to fix gettered impurities (FIG. 2).
(C)).

The silicon oxide layer 205 formed on the surface of the polycrystalline silicon wafer 201 was removed by etching with a 10% HF solution to obtain a polycrystalline silicon substrate 207 having insulated grain boundaries (FIG. 2). (D)).

Next, on the surface of the polycrystalline silicon substrate 207, I
Epitaxial growth was performed by a slider type liquid phase growth apparatus using n as a solvent under the formation conditions shown in Table 3 to make the thickness of the silicon layer 208 30 μm. At this time, a very small amount of B (0.1 ppm to the amount of dissolved silicon)
~ Several ppm) to add p to the grown silicon layer 208.
^- and the mold (FIG. 2 (e)). The obtained silicon layer inherited the crystal orientation and grain size of the underlying polycrystalline silicon wafer 201.

Thus, a semiconductor substrate 207 having a semiconductor silicon layer was obtained.

(Embodiment 4) In this embodiment, a polycrystalline solar cell will be described using the semiconductor substrate manufactured in Embodiment 3.

On the surface of the semiconductor substrate produced in Example 3,
Thermal diffusion of P was performed at a temperature of 900 ° C. using POCl ₃ as a diffusion source to form an n ⁺ layer. The junction depth is 0.5μ
m.

The dead layer on the surface of the formed n ⁺ layer was removed by etching. As a result, a junction depth having an appropriate surface concentration of about 0.2 μm was formed.

On the n ⁺ layer, a current collecting electrode (Cr (0.
02 μm) / Ag (1 μm) / Cr (0.004 μm)
m)) / Transparent electrode (ITO (0.085 μm)) was formed by vacuum evaporation. Al was deposited on the back surface of the sheet substrate to form a back electrode.

For comparison, a polycrystalline semiconductor substrate was prepared in the same manner as in Example 3 except that the steps of making the grain boundaries porous, gettering, and insulating were not performed in Example 3, and A solar cell was manufactured by the same process.

For these crystalline solar cells, AM1.
The IV characteristics under 5 (100 mW / cm ² ) light irradiation were measured. As a result, when the cell area was 2 cm ² and the grain boundaries were insulated, the open voltage was 0.63 V and the short-circuit photocurrent was 30 mA /
cm ^2, a fill factor 0.77, the conversion efficiency 14.6%
On the other hand, when the grain boundary is not insulated, the open circuit voltage is 0.5
7 V, short-circuit photocurrent 29 mA / cm ² , fill factor 0.76
And the conversion efficiency was 12.6%.

From the results of this example, it was found that a crystalline solar cell having good characteristics can be formed by using a polycrystalline semiconductor substrate having an insulated grain boundary.

In the above-described example, a solar cell is described. However, the present invention can be applied to, for example, an external driving element of a liquid crystal display device.

Further, in the above-described embodiment, a silicon substrate is shown. However, other than silicon, for example, a substrate of a compound semiconductor such as GaAs can be manufactured.

[0082]

As described above, according to the present invention, it is possible to provide a semiconductor substrate on which a device having good characteristics can be formed and a method for manufacturing the same. Batteries can now be offered to the market. Hereinafter, the effects of each claim will be described.

(Claim 1) Since impurities at the grain boundary are fixed, the contamination of the semiconductor layer formed thereon with impurities is drastically reduced. The characteristics of the semiconductor layer formed thereon are improved.

(Claim 2) The cost can be reduced by using metal-grade silicon.

(Claim 3) Even when the impurities are segregated, the impurities can be fixed (passivated) at the crystal grain boundaries, and the diffusion of the impurities into the semiconductor layer can be efficiently suppressed. can do. That is, when the impurities are segregated, the effect of the present invention appears more remarkably.

(Claim 4) In the case of a semiconductor device, the electric characteristics become better.

(Claim 5) Porosity can be promoted by selective anodic oxidation at any grain boundary.

(Claim 6) The function as the impurity fixed layer becomes more efficient.

(Claim 7) When a solar cell element is used, power generation efficiency is improved.

(Claim 8) Even in the case of a polycrystalline layer grown epitaxially, impurities segregated at the grain boundary are not mixed.

(Claim 9) In the case of an oxide film, a nitride film, and a carbide film, the effect of fixing impurities in the impurity fixing layer is excellent. The case of an oxide film is even better.

(Claim 10) It is possible to manufacture a semiconductor substrate having a semiconductor layer in which impurities in a grain boundary portion are fixed, and contamination of impurities into a semiconductor layer formed thereon is drastically reduced.

(Claim 11) The cost can be reduced by using metal-grade silicon.

(Claim 12) In the case of a semiconductor device, the electrical characteristics become better.

(Claim 13) Porosity is promoted by selective anodic oxidation or the like at any grain boundary.

(Claim 14) General silicon can be used as a semiconductor.

(Claim 15) The presence of a large amount of B, Al, P, As promotes selective porosity at any grain boundary, but even if these are preliminarily segregated with impurities. Since it can be made porous as in the case where it is originally contained, it is effective to introduce B, Al, P, and As when it is small.

(Claim 16) Impurities can be effectively introduced into grain boundaries by thermal diffusion.

(Claim 17) By further reducing impurities near the surface of the polycrystalline substrate by gettering, the influence on the subsequent formation of the semiconductor layer can be minimized.

(Claim 18) A semiconductor substrate, such as a solar cell, in which devices can be easily manufactured can be manufactured.

(Claim 19) By using a polycrystalline semiconductor substrate in which impurities are fixed and grain boundaries are insulated, a solar cell having good characteristics can be provided.

(Claim 20) By using a polycrystalline semiconductor substrate in which impurities are fixed and grain boundaries are insulated, a solar cell having good characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a semiconductor substrate of the present invention.

FIG. 2 is a diagram illustrating a method for manufacturing a semiconductor substrate according to the present invention.

[Explanation of symbols]

 101, 201 Polycrystalline substrate 202 Crystal grain boundary 203 Porous layer 204 Porous grain boundary 205 Insulating layer 103, 208 Semiconductor layer 102, 206 Insulating grain boundary 207 Polycrystalline substrate with grain boundary insulated 209 Semiconductor layer Polycrystalline substrate having

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shunichi Ishihara 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroshi Sato 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo F term in reference (reference) 5F051 AA03 CB05 CB12 CB21 CB29 CB30 GA04 GA13 GA15 GA20

Claims (20)

[Claims] 1. A semiconductor substrate having a polycrystal structure composed of a set of a plurality of crystals, wherein the polycrystal structure comprises a set of a second crystal on a polycrystal structure formed of a first set of crystals. Wherein the first crystal body has an impurity fixed layer at least in the vicinity including its adjacent interface. 2. The semiconductor substrate according to claim 1, wherein the polycrystalline structure composed of the first crystalline body is manufactured using metal-grade silicon as a raw material. 3. The semiconductor substrate according to claim 2, wherein impurities are segregated in the impurity fixed layer. 4. The semiconductor substrate according to claim 3, wherein the concentration of the impurities segregated in the impurity fixed layer is in a range of 10 ¹⁶ cm ^{−3 to} 10 ²⁰ cm ⁻³ . 5. The method according to claim 1, wherein the impurities are B, P, Al, As, and F.
5. The device according to claim 3, wherein the material is at least one of e, Cr, Cu, Mn, Ni, Mg, Ti, and V.
4. The semiconductor substrate according to claim 1. 6. The semiconductor substrate according to claim 1, wherein the vicinity including the adjacent interface of the first crystal body is within a range of 500 nm or more and 10 μm or less from the interface. 7. The ratio of the area of the impurity fixed layer region to the entire surface of the substrate is 1 when the surface of the substrate is viewed from above.
The semiconductor substrate according to claim 1, wherein the content is 0% or less. 8. The method according to claim 1, wherein the polycrystalline structure composed of the set of the second crystals is formed on the polycrystalline structure composed of the set of the first crystals by an epitaxial growth method. The semiconductor substrate according to any one of claims 1 to 7. 9. The semiconductor substrate according to claim 1, wherein said impurity fixed layer is made of silicon oxide, silicon nitride, or silicon carbide. 10. A method of manufacturing a semiconductor substrate having a polycrystalline structure, wherein: i) anodizing at least a main surface of the polycrystalline substrate to form a porous layer on the surface of the polycrystalline substrate and on a crystal grain boundary portion, respectively. Forming; ii) oxidizing, nitriding or carbonizing the polycrystalline substrate to change the surface of the polycrystalline substrate and the porous layer at the grain boundary to an oxide film, a nitride film or a carbonized film, respectively; iii. ) A step of etching away an oxide film, a nitride film or a carbide film formed on the surface of the polycrystalline substrate; and iv) inheriting the crystal orientation of the polycrystalline substrate on the polycrystalline substrate by an epitaxial growth method. Forming a semiconductor layer. 11. The method according to claim 10, wherein the polycrystalline substrate is produced using metal-grade silicon as a raw material. 12. The semiconductor substrate according to claim 10, wherein impurities are present at a concentration in a range of 10 ¹⁶ cm ^{−3 to} 10 ²⁰ cm ⁻³ in a crystal grain boundary portion of the polycrystalline substrate. Manufacturing method. 13. The method according to claim 1, wherein the impurities are B, P, Al, As, F
13. The method according to claim 12, comprising at least one of e, Cr, Cu, Mn, Ni, Mg, Ti, and V. 14. The method according to claim 10, wherein the semiconductor layer is silicon. 15. Before the step i), at least one impurity selected from the group consisting of B, P, Al and As is introduced into the surface of the polycrystalline substrate, and the impurity is previously introduced into the grain boundary portion. 2. The method according to claim 1, further comprising the step of segregating.
15. The method of manufacturing a semiconductor substrate according to any one of 0 to 14. 16. The method according to claim 15, wherein the impurity is introduced by thermal diffusion. 17. The method according to claim 1, further comprising a step of heat-treating the polycrystalline substrate at a temperature of 900 ° C. to 1250 ° C. to promote gettering treatment in the porous layer between the steps i) and ii). 17. The method of manufacturing a semiconductor substrate according to claim 10, wherein: 18. The method according to claim 10, wherein a semiconductor junction is formed on a surface of the semiconductor layer after the step (iv). 19. A solar cell manufactured using the semiconductor substrate according to claim 1. Description: 20. A method for manufacturing a solar cell manufactured by using the method according to claim 10.