JP2002160998A - Quartz crucible and method for producing silicon crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quartz crucible by which, in producing a Ga-doped silicon crystal useful as a solar cell material, the production cost of the crystal can be remarkably reduced and Ga-doping into a silicon crystal is easily and accurately conducted, and provide a method for producing a silicon crystal using the crucible. SOLUTION: The quartz crucible is used for housing a raw material for crystal and has its inner wall part containing gallium(Ga). The method for producing a silicon crystal uses this quartz crucible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz crucible for accommodating a crystal raw material for growing a crystal, and to a method for producing a silicon crystal using the same. More specifically, the present invention relates to a quartz crucible for doping gallium (Ga) into a silicon crystal useful as a material for a solar cell, and to a method for manufacturing a silicon crystal using the same.

[0002]

2. Description of the Related Art Generally, a silicon crystal is grown by accommodating a crystal raw material in a quartz crucible. The grown silicon crystal is used in a wide variety of ways, and a silicon crystal doped with Ga is used, for example, for a solar cell substrate as an example. Hereinafter, the technical background when used for a solar cell substrate will be described.

[0003] Solar cells are broadly classified into two types, "silicon-based solar cells" and "compound semiconductor-based solar cells," based on the type of semiconductor material used in the power generation unit. Furthermore, silicon-based solar cells are classified into “crystalline silicon-based solar cells” and “amorphous (amorphous) silicon-based solar cells”, and crystalline silicon-based solar cells are referred to as “silicon single-crystal-based solar cells” and “silicon-rich solar cells”. Crystalline solar cell "
are categorized.

[0004] Focusing on conversion efficiency, which is the most important characteristic of a solar cell, compound semiconductor solar cells have recently reached the highest of these, at about 25%, and next, silicon single crystal solar cells have been around 20%. Followed by 5 to 1 for silicon polycrystalline solar cells and amorphous silicon solar cells.
It is about 5%. On the other hand, paying attention to material costs, silicon is the second most common element after oxygen on the earth, and is much cheaper than compound semiconductors. Therefore, silicon-based solar cells are most widely used.

[0005] Here, the "conversion efficiency" is a value indicating the "ratio of energy which can be converted into electric energy by the solar cell and taken out by the solar cell with respect to the energy of light incident on the solar cell". It refers to a value expressed as a percentage (%).

[0006] Recently, demand for solar cells is increasing as one of clean energy due to environmental problems.
The high energy cost compared to general commercial power is a hindrance to its widespread use. Therefore, while reducing the manufacturing cost of the substrate in order to reduce the cost of the silicon crystal solar cell, it is a major problem to further increase the conversion efficiency.

Next, a method of manufacturing a general silicon single crystal solar cell will be briefly described. First, in order to obtain a silicon wafer serving as a substrate of a solar cell, a Czochralski method (CZ method) or a floating zone melting method (FZ method) is used.
A cylindrical silicon single crystal ingot is made. further,
Slice this ingot and for example, thickness 300μm
A wafer (substrate) serving as a solar cell can be obtained by processing the wafer into a thin wafer and etching the wafer surface with a chemical solution to remove processing distortion on the surface. The wafer is subjected to an impurity (dopant) diffusion process to form a PN junction surface on one side of the wafer, and electrodes are attached on both sides. Finally, light energy loss due to light reflection on the incident surface of sunlight is reduced. A solar cell is completed by providing an anti-reflection film for the purpose.

In a solar cell, it is important to manufacture a solar cell having a larger area in order to obtain a larger current. As a method for obtaining a large-diameter silicon wafer which is a substrate material for manufacturing a large-area solar cell, a large-diameter silicon single crystal can be easily produced, and the strength of the produced single crystal is excellent. The CZ method is suitable. For this reason, the production of silicon single crystals for solar cells is mainly performed by the CZ method.

On the other hand, as a silicon wafer to be used as a substrate material of a silicon single crystal solar cell, a value of a substrate lifetime (LT) which is one of the characteristics is 10%.
If it is not longer than μs, it cannot be used as a solar cell substrate, and in order to obtain a solar cell with higher conversion efficiency, the LT of the substrate is required to be preferably 200 μs or more.

However, when a single crystal manufactured by the CZ method, which is the mainstream of the current single crystal manufacturing method, is irradiated with strong light when the solar cell is processed into a solar cell, the L of the solar cell substrate is reduced.
T decreases, and sufficient conversion efficiency cannot be obtained to cause light degradation, and improvement is also required in terms of solar cell performance.

When a solar cell is made using this CZ silicon single crystal, strong light is applied to the solar cell to produce LT.
It is known that the cause of the photodegradation due to the decrease is caused by boron (B) and oxygen existing in the single crystal substrate. Currently, the conductivity type of wafers used as solar cells is mainly P-type, and B is usually added to this P-type wafer as a dopant. Then, a single crystal rod as a material of the wafer is subjected to a CZ method including a magnetic field pulling method (MCZ method) for pulling up a silicon melt by applying a magnetic field.
It can be manufactured by Z method or FZ method,
In the FZ method or the MCZ method, since the manufacturing cost of a single crystal rod is higher than that of a normal CZ method, at present, it is manufactured exclusively by a normal CZ method that does not apply a magnetic field that can produce a single crystal at a relatively low cost. .

However, a high concentration of oxygen is present in the crystal produced by the CZ method, so that the LT characteristics are affected by B and oxygen in the P-type CZ silicon single crystal.
There is a problem that light degradation occurs.

In order to solve such a problem, the present applicant proposed in an earlier application to use Ga instead of B as a P-type dopant (Japanese Patent Application No. 11-26).
No. 4549 and Japanese Patent Application No. 2000-061435). By using Ga as a dopant in this way, it is possible to prevent a decrease in LT due to the influence of B and oxygen.

[0014]

However, although the effect of B and oxygen is eliminated by using Ga as a silicon crystal for a solar cell as a dopant, the silicon crystal is doped with Ga as described below. There is a problem that the handling is complicated and difficult when nurturing.

In general, an appropriate amount of dopant needs to be added to a melt in order to grow a silicon crystal. However, since the physicochemical properties of a pure dopant element are very different from the behavior in a melt, It is said that it is easier to handle a silicon lump in which a dopant is added in a high concentration in advance. Except in the case of heavily doped, ie, low resistivity crystals, the amount of doping normally required is small enough to be difficult to handle. For this purpose, high-concentration doping usually called a dopant adjuster
Prepare low-resistance silicon particles and lump pieces of about Ωcm in advance,
There is a method of adding a dopant to a silicon melt to perform a dopant. Particularly in the case of Ga, the melting point is 30 ° C.
It is difficult to handle because it is low, and rather than putting Ga directly into the crucible, grow a silicon crystal rod to which high concentration Ga is added in advance as described above, and crush this high concentration Ga-doped silicon crystal rod to make it. As a dopant, a predetermined amount of Ga is added to the silicon melt. According to such a method, handling becomes easy, Ga concentration can be easily adjusted with high accuracy, an accurate dopant concentration can be obtained, and work can be performed efficiently.

However, in order to prepare this Ga-doped dopant adjusting agent, it is necessary to grow a silicon crystal rod to which high-concentration Ga is added beforehand. Since it cannot be used, there is a problem that productivity is reduced and the cost of the crystal material is increased. Further, in this case, since the pulling machine is contaminated with a high concentration of dopant, there arises a problem that the resistance of the product does not reach a desired value at the next pulling of the product.

At present, a silicon wafer, which is a main material of a silicon single crystal solar cell mainly used, is:
This is the same as a silicon wafer used in a semiconductor device such as an integrated circuit (IC) and a memory. A semiconductor device is sold at a price of several hundred yen or more in a chip size of 1 cm 2 or less, and an integrated circuit is sold at a price of several thousand yen. Compared with semiconductor devices, it is said that the cost per unit area of a solar cell must be reduced by two to four orders of magnitude, and there is a large problem in cost.

The present invention has been made in view of the above problems, and a quartz crucible capable of easily and accurately doping a silicon crystal with a dopant and greatly reducing the manufacturing cost, and a silicon crucible using the quartz crucible. A main object is to provide a method for producing a crystal.

[0019]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and is a quartz crucible for accommodating a crystal raw material, wherein gallium (G) is provided on an inner wall portion of the quartz crucible.
It is characterized by containing (a) (claim 1).

When growing a Ga-doped silicon crystal,
Ga is contained in the inner wall of the quartz crucible by Ga, Ga oxide, Ga compound or the like. By using this crucible, the inner wall of the crucible in contact with the silicon melt is melted during the growth of the silicon crystal, Ga contained in the inner wall is dissolved in the silicon melt, and Ga as a dopant is removed. Will be supplied.

In this case, the quartz crucible has a double structure in which translucent quartz glass is used as an outer layer and transparent quartz glass is used as an inner layer, and Ga is contained in the transparent quartz glass portion as the inner layer. Preferred (claim 2).

The applicant of the present invention has previously described a quartz crucible having a double structure, in which the inner surface of the crucible is made substantially bubble-free and the surface layer is made smooth, and the outer layer is made of translucent glass to control the diameter of bubbles and the density of bubbles. (Japanese Unexamined Patent Publication No. 6-92779)
Reference). By making the quartz crucible have a double structure, the crucible is less deformed even in operation at high temperature, and deterioration of the smoothness of the inner surface can be reduced. In the double-layer crucible, Ga,
Ga is contained in advance by a Ga oxide or a Ga compound. In this manner, when growing a Ga-doped silicon crystal, the crucible inner wall in contact with the silicon melt is melted, and Ga contained in the inner layer is dissolved into the silicon melt, and Ga as a dopant is removed. Is supplied to the silicon crystal accurately and stably. Further, by using the double-structure crucible, the life of the quartz crucible is extended, and the time for growing the silicon crystal is extended, so that long-term stable operation and improvement in productivity can be achieved.

In this case, a plurality of transparent quartz glass layers are provided on the inner layer side of the double-structure quartz crucible to form a multilayer structure.
A transparent quartz glass layer containing Ga and a transparent quartz glass layer containing no Ga can be alternately formed (claim 3).

As described above, by providing a plurality of transparent quartz glass layers on the inner layer side of the quartz crucible to form a multi-layer structure, deformation of the crucible and deterioration of the smoothness of the inner surface can be further reduced even in operation at a high temperature. Can be. Then, a layer in which Ga is contained in the inner transparent quartz glass layer in the multiplex structure by Ga, Ga oxide, Ga compound or the like (hereinafter referred to as G
An a-containing layer) and a layer not containing Ga (hereinafter, referred to as a Ga-free layer) are alternately formed. By doing so, when growing a Ga-doped silicon crystal, the crucible inner wall in contact with the silicon melt is melted and Ga
Ga is dissolved from the containing layer into the silicon melt, and Ga as a dopant is supplied. However, when the layer no longer melts, the Ga-free layer comes into contact with the melt, so the supply of Ga stops. A silicon crystal containing a predetermined amount of dopant is grown.

After the growth of one crystal is completed and the silicon crystal is taken out, the raw material crystal is replenished to the residual melt and melted by heating to form a silicon melt. , Ga is newly eluted from the Ga-containing layer,
The Ga dopant-containing silicon crystal can be grown again. In this method, a quartz crucible having a multiple structure according to the present invention is applied to a so-called multi-pulling method (sometimes referred to as a multiple pulling method or a recharge pulling method).
Silicon crystals can be repeatedly grown by the number of the containing layers. Further, with this configuration, the life of the quartz crucible is further extended, and the operation time for growing the silicon crystal is further extended, so that long-term stable operation and improvement in productivity can be achieved. In this case, Ga is contained also in the inner surface of the translucent quartz glass to form a multilayer crucible having a plurality of transparent quartz glass layers provided thereon, whereby the number of Ga-containing transparent quartz glass layers plus one. Crystal growth becomes possible. In the above paragraph [0024], needless to say, if Ga is contained in the inner surface of the translucent quartz glass, two crystals can be grown.

When the above-mentioned quartz crucible is used when growing the silicon polycrystal, Ga contained in the inner wall of the quartz crucible can be eluted into the silicon melt to dope the silicon polycrystal with Ga. In addition, when the silicon single crystal is grown, when the quartz crucible is used, Ga contained in the inner wall of the quartz crucible is eluted into the silicon melt, so that the silicon single crystal becomes Ga. Can be doped (claim 5).

When growing a Ga-doped silicon polycrystal or single crystal as described above, the crucible inner wall in contact with the silicon melt is melted and the Ga layer contained in the inner layer is melted.
Is dissolved in the silicon melt, Ga as a dopant is supplied to the silicon crystal, and a Ga-doped silicon polycrystal or single crystal can be obtained. At this time, polycrystal growth is preferably performed by the Bridgman method, and single crystal growth is preferably performed by the Czochralski method.

The Ga-doped silicon polycrystal thus obtained can be generally used at a lower cost than a single crystal, so that it can be used, for example, as a material for a silicon polycrystal solar cell. However, there is an advantage that the time required for manufacturing is short and the cost can be reduced, so that the cost for a solar cell can be reduced.

Further, the Ga-doped silicon single crystal obtained as described above becomes a material for a silicon single crystal solar cell, and has the advantage that the conversion efficiency is high, the conversion efficiency is not deteriorated by light, and stable production is possible. There is.

Next, in the method for producing a silicon crystal according to the present invention, a quartz crucible containing gallium (Ga) in the inner wall is used as a quartz crucible for accommodating a crystal material when growing a silicon crystal. Further, Ga contained in the inner wall portion of the quartz crucible is eluted into the silicon melt to thereby dope the silicon crystal with Ga. In this case, the silicon crystal can be silicon single crystal or silicon polycrystal (claim 7).

As described above, when growing a Ga-doped silicon crystal, the crucible inner wall in contact with the silicon melt is melted, so that Ga contained in the inner layer is dissolved in the silicon melt and the dopant is removed. Is supplied, and Ga
A doped silicon crystal (polycrystal or single crystal) is obtained. According to this method, it is not necessary to grow a crystal for preparing a doping material in advance, so that the productivity of the crystal manufacturing apparatus can be improved, and the apparatus is not contaminated with a high concentration of dopant. The Ga-doped silicon crystal (polycrystal or single crystal) obtained in this manner becomes a material for a silicon crystal solar cell, and has the advantage of high conversion efficiency, stable production without optical degradation of conversion efficiency.

Hereinafter, the present invention will be described in detail.
The present invention is not limited to these. The present inventors have made intensive studies on how to add an additive that is difficult to handle, such as Ga, having a low melting point of 30 ° C. when growing a silicon crystal, so that it can be easily handled and added in a stable state. The present invention was completed as a result of repeated experiments and studies.

The silicon crystal to which such a difficult-to-handle dopant is added can be used, for example, as a solar cell substrate material, but can be mass-produced relatively easily. At the same time, the solar cell has high conversion efficiency and low cost. Also, a diligent study was made on how to obtain the substrate.

That is, conventionally, the dopant added when growing a silicon crystal is to grow a high-concentration silicon crystal once and then crush it to produce a dopant adjusting material.
This conditioning material was added to the silicon melt. In order to manufacture the dopant adjusting material, it is impossible to manufacture a silicon crystal product during this time, thereby lowering the productivity of the product. In addition, the crucible used here is expensive G
The loss of a caused by the remaining a caused an increase in the manufacturing cost. Further, as described above, the crystal manufacturing apparatus used for producing the dopant adjusting material is contaminated with an extremely high concentration of dopant. Therefore, there is a demerit that a normal crystal product cannot be manufactured unless the apparatus has been idled many times.

The present inventors have conceived from the viewpoint that the inclusion of Ga in the crucible inner wall can prevent a decrease in product productivity and an increase in manufacturing cost.
That is, the present inventors, when growing a silicon crystal,
It has been confirmed that by including a predetermined amount of Ga in the inner wall of the crucible, it is not necessary to prepare a dopant adjusting material in advance, and the handling becomes easy. As a result, the Ga-doped silicon crystal can be manufactured stably, and the yield can be increased, so that the manufacturing cost can be reduced.

Further, a solar cell having a stable and high conversion efficiency can be manufactured from such a silicon crystal without causing light degradation, and the power generation cost by the silicon crystal solar cell can be reduced. As a result, the contribution to solving the cost problem of silicon raw materials for solar cells has become significant.

As a silicon crystal wafer used as a substrate for a solar cell, a substrate having a low resistivity and a high LT is desired. However, the concentration of a dopant in the silicon crystal, for example, Ga, is 2 × 10 ^{17 to} 3 × 10 ¹⁴ atoms. / Cm ³ , or a resistivity of 20 Ω · cm to 0.1 Ω · cm. The concentration of Ga in the silicon crystal is 3 × 10 ¹⁴ a
toms / cm ³ or less, or the resistivity is 20Ω · cm
In the case described above, power is consumed by the internal resistance of the solar cell when the solar cell is used, and the conversion efficiency is reduced. Further, the concentration of Ga is 2 × 10 ¹⁷ atoms / c.
If the resistivity is not less than m ³ or the resistivity is not more than 0.1 Ω · cm, the LT (lifetime) of minority carriers is reduced due to Auger recombination inside the substrate, and the conversion efficiency is reduced.

The interstitial oxygen concentration in the silicon crystal is preferably not more than 16 ppma (JEIDA; standard of Japan Electronic Industry Development Association), and if it is not more than 15 ppma, it is formed by initial interstitial oxygen or heat treatment. It is more preferable because LT can be prevented from being deteriorated by oxygen precipitates.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto. In the quartz crucible of the present invention and the method of manufacturing a silicon crystal using the same, a configuration example and a pulling method of a single crystal pulling apparatus by a CZ method are disclosed in Japanese Patent Application No. 11-11089.
No. 264,549, and Japanese Patent Application No. 2000-0 for a configuration example and a manufacturing method of a polycrystalline manufacturing apparatus using the Bridgman method.
The content is basically the same as that described in Japanese Patent No. 61435, and a general method may be used. However, since the addition of the dopant is completely different, a description thereof will be given below.

Since the quartz crucible directly holds the raw material melt, its inner surface contacts the silicon melt and reacts with and melts the silicon melt, or heat generated by an external carbon heater is supplied to the silicon melt. It has the function of transferring heat to
As a quartz crucible having such a function, translucent quartz glass is suitable. This semi-transparent quartz crucible has advantages such as high strength and easy production of a large-sized crucible as compared with a transparent quartz crucible. Further, there is an advantage that the minute air bubbles contained in the translucent quartz crucible make the transfer of heat energy from the external heater to the inner surface of the crucible uniform, and as a result, the heat distribution becomes uniform. For these reasons, translucent quartz crucibles are widely used in practice. As a result, at the time of growing the silicon crystal, the raw silicon melt receives a constant heat history over the entire inner surface of the crucible, and the single crystal is pulled stably.

Next, an example of the method for manufacturing a quartz crucible of the present invention will be described. First, the raw material powder used is natural quartz,
A refined powder such as synthetic quartz is used. The powder is supplied into a rotating crucible mold, and after forming a layer to a predetermined thickness by centrifugal force, melting is started from the inside by means such as arc discharge. At this stage, translucent quartz glass is formed. At this time, gallium (Ga),
Gallium hydride (Ga ₂ H ₆ ), gallium oxide (Ga ₂
O, Ga ₂ O ₃ ) or gallium hydroxide (Ga (O
H) ₃ ) and the like are measured in a predetermined amount and included in the inner surface of the crucible.

Here, the elution rate of the vitreous portion of the quartz crucible into the silicon melt is mainly proportional to the relative speed of the melt in the portion in contact with the silicon melt and the temperature of the silicon melt. From 3.6 to 9.1.
nm / sec. If the layer containing Ga is made as thin as possible, for example, to have a thickness of about 0.1 to 15 μm, the thickness of the layer becomes 3 mm after the silicon melt comes into contact with the inner surface of the quartz crucible.
Since the elution of Ga is completed within 0 minutes, the elution of Ga is completed during the melting of the raw material, and thereafter, no Ga is supplied during the growth of the silicon crystal, so that a stable silicon crystal can be manufactured.

The transparent quartz glass layer on the inner surface of the crucible having a double structure of the translucent quartz glass according to the present invention may be formed by melting and integrating a desirable high quality quartz glass layer in a molded powder layer. , Can be integrally formed by additional melting of powder. The transparent layer thus formed has no trace of air bubbles, and therefore does not expand under reduced pressure during silicon crystal growth. In particular, the quartz powder is supplied into a rotary mold, and a preform of the outer wall quartz powder layer is formed on the mold wall by centrifugal force, and then the quartz powder is passed through a high-temperature gas atmosphere such as arc discharge to obtain a semi-molten state. By continuously adhering the powder to the inner surface of the outer wall quartz powder layer by the discharge energy to form a substantially bubble-free completely molten layer,
Since the outer wall quartz powder layer and the inner transparent layer adhere to each other by simultaneous melting, a bubble-free transparent quartz glass layer having a desired thickness is firmly formed on the translucent quartz glass layer. Here, the crucible is composed of a translucent quartz glass layer containing 20,000 or more bubbles having a diameter of 10 to 250 μm per 1 cm ^3, and a substantially bubble-free and integrally formed on the inner surface of this layer. The transparent quartz glass layer has a smooth surface.

When the transparent quartz glass layer is formed, for example, gallium (Ga), gallium hydride (Ga ₂ H ₆ ), gallium oxide (Ga ₂ O, Ga ₂
A predetermined amount of O ₃ ) or gallium hydroxide (Ga (OH) ₃ ) may be measured and added. In particular, when continuously adhering to the inner surface of the outer wall quartz powder layer, it is preferable to include a predetermined amount of Ga only at the bottom of the quartz crucible.

Also in this case, in consideration of the dissolution rate of the vitreous portion of the quartz crucible, the surface layer containing Ga in the transparent quartz glass portion of the inner layer of the crucible is made as thin as possible, for example, about 0.1 to 15 μm. Is preferred. Elution of Ga was completed in about 30 minutes after the silicon melt contacted the transparent quartz glass layer, and the remaining G not containing Ga was removed.
If the a-free layer is set to, for example, about 800 to 10,000 μm, Ga is not supplied during the growth of the silicon crystal, and a stable silicon crystal can be manufactured.

By using such a crucible having a double structure according to the present invention, the heat energy from the external heater can be uniformly transmitted to the entire inner surface of the crucible during the growth of the silicon crystal, and the inner surface of the crucible can be partially eroded. The occurrence of surface roughness is extremely small. For this reason, a higher crystallization rate can be maintained as compared with the conventional crucible. further,
If a crystalline quartz component is present in the translucent quartz glass layer, the heat resistance of the crucible can be significantly increased. In addition, it is possible to maintain a stable and high single crystallization ratio not only in crystal growth under atmospheric pressure but also in crystal growth under reduced pressure.

Further, in order to form the transparent glass layer on the inner layer side of the quartz crucible in the present invention into a multilayer structure, when the transparent quartz glass layer of the above-mentioned double structure crucible is formed, for example, the powder to be additionally melted is Gallium (Ga), gallium hydride (Ga ₂ H ₆ ), gallium oxide (Ga ₂ O, Ga ₂ O)
₃ ) Alternatively, gallium hydroxide (Ga (OH) ₃ ) or the like is weighed in a predetermined amount and added to fuse. Further, a powder to which Ga is not added is additionally fused, and this may be alternately performed to form a multilayer structure of a Ga-containing layer and a Ga-free layer.

By adopting such a structure, after the Ga layer on the inner surface is eluted, the transparent glass layer containing no Ga becomes the surface, so that the inner surface is not roughened during use and the smoothness of the inner surface is reduced. Maintained, the inner wall of the quartz crucible was kept in contact with the high-temperature silicon crystal melt to prevent erosion, peeling, and deterioration, greatly extending the life of the quartz crucible, and maintaining a high dislocation-free rate of the crystal. It is possible to provide a large-diameter quartz crucible that can grow a crystal in a state for a longer time.

By using such a quartz crucible of the present invention, the inner wall of the crucible in contact with the silicon melt is melted, and Ga is dissolved from the Ga-containing layer into the silicon melt to be a dopant. Since Ga is supplied, a Ga-doped silicon crystal can be stably grown with good reproducibility.

Here, also in the case where the transparent quartz glass portion of the inner layer of the crucible has a multilayer structure in consideration of the elution speed of the vitreous portion of the quartz crucible, the thickness of one Ga-containing layer is made as thin as possible. If the thickness is set to about 0.1 to 15 μm, 3 μm is required after the silicon melt contacts the transparent quartz glass layer.
Elution occurs within 0 minutes, and the Ga-free layer is removed, for example, from 60 to 660.
If it is set to about μm, Ga is not supplied during, for example, 5 to 20 hours during the growth of the silicon crystal, so that a stable silicon crystal can be manufactured. The thickness of the Ga-free layer and the growth time of the silicon crystal are not limited to the numerical values described here, and the elution rate of the Ga-free layer is determined in advance according to the growth conditions of the silicon crystal. That is good.

Then, by using this multilayer crucible,
By the multi-pulling method, silicon crystals can be repeatedly grown by the number of Ga-containing layers. That is, after the silicon crystal grown first is taken out, the raw material crystal is supplied to the silicon melt remaining in the crucible, and is heated and melted to obtain a silicon melt. At this time, a Ga
Is eluted, and then the crystal growth is started again, whereby the dopant-containing silicon crystal can be grown again. This can be repeated. In this case, Ga is also contained in the inner surface of the translucent glass to form a multilayer crucible having a plurality of transparent quartz glass layers provided thereon, whereby the number of Ga-containing transparent quartz glass layers plus one crystal Growth is possible. Incidentally, also in the double-structure quartz crucible having the translucent quartz glass layer as the outer layer and the Ga-containing transparent quartz glass layer as the inner layer, G
Needless to say, if a is contained, two crystals can be grown.

On the other hand, regarding the oxygen concentration in the silicon crystal, the rotation speed of the crucible, the growth speed of the silicon crystal,
The diameter of the silicon crystal can be controlled by appropriately adjusting the pressure and flow rate of the inert gas in the chamber, and by adjusting the temperature of the silicon melt and the growth rate of the silicon crystal.

In the quartz crucible, the portion of the inner wall containing Ga must be in contact with the silicon melt. Therefore, the inner wall below the maximum depth of the raw material melt contained in the quartz crucible is required. Preferably contains Ga. In addition, if Ga is contained in the inner wall at the bottom, a predetermined amount of Ga can be reliably supplied to the melt. Of course, Ga may be contained in the entire inner wall of the quartz crucible, but in this case, G
It is necessary to consider that the a layer does not contribute as a dopant.

The grown silicon crystal was sliced into wafers having a thickness of 2 to 3 mm from blocks each having an appropriate size, and LT was measured. When measuring LT, this sliced wafer was subjected to HF: HNO ₃ = 5.
%: Treated with a mixed acid of 95% to remove the slice damage layer on both sides by etching, and then perform cleaning. After that, the surface of the wafer is irradiated with AM (Air Mass) 1.5 under constant light for 30 hours. The natural oxide film on the surface is removed by HF, followed by chemical passivation (CP) treatment using a mixed solution of iodine and ethanol to reduce carrier recombination on the crystal surface, and the microwave-PCD method (photoconductivity) Degree decay method).

The wafer prepared from the silicon crystal prepared by the method of the present invention is sliced by a slicer using a slicer, processed into a wafer, chamfered, wrapped, etc., and further processed by etching. Manufactured by removing distortion.
Furthermore, a solar cell manufactured using this silicon crystal wafer uses the silicon crystal wafer,
Large 10 × 10 cm square (cell area 100 cm ² ) R
P-PERC (Random Pyramid-Pa
sivated Emitter and Rear
(Cell) type solar cell was fabricated, and its conversion efficiency was measured.

The conversion efficiency of the solar cell was measured at 25 ° C.
A solar cell is placed on a temperature-controlled measuring table, and a solar simulator using a halogen lamp as a light source.
The cell was irradiated with steady light under the conditions of 5, and the voltage and current that could be taken out of the cell were measured to calculate the conversion efficiency of the solar cell. The conversion efficiency according to the present invention refers to a value defined by the following equation, and is as follows. [Conversion efficiency] = [power that could be taken out per cell unit area] / [light energy irradiated per cell unit area] × 100 (%)

The resistivity was measured by cutting a predetermined sample from a single crystal and using the four-point probe method.

[0058]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto. (Embodiment 1) Here, the quartz crucible used is shown in FIG. The quartz crucible 1 having a diameter of 18 inches made entirely of translucent glass was manufactured by the method described above, and the thickness of the translucent quartz glass 5 was set to 15 mm. The translucent quartz glass 5
1cm ² per 2 bubbles with a diameter of 10~250μm during
Contains more than 0000, with a total of 3.62 at the bottom of the inner surface
6 g of Ga was included. Using this crucible, 40 kg of raw silicon is melted, and the diameter is 6 inches by CZ method.
A silicon single crystal having a crystal orientation <100> was grown. Table 1 shows the results for each measurement item.

[0059]

[Table 1]

EXAMPLE 2 FIG. 2 shows a quartz crucible used here. The double quartz crucible 2 having a diameter of 18 inches was manufactured by the method described above, and the thickness of the translucent quartz glass 5 was set to 15 mm. The translucent quartz glass 5 has a diameter of 1
2. A transparent quartz glass 4 containing at least 20,000 bubbles of 0 to 250 μm per 1 cm ² and having substantially no bubbles is formed on the entire inner surface of the crucible by 1 mm, and 3 mm is formed on the bottom of the inner surface of the transparent quartz glass. 626 g of Ga were included. Using this crucible, 40 kg of raw silicon was melted, and a silicon single crystal having a diameter of 6 inches and a crystal orientation of <100> was grown by the CZ method. Table 1 also shows the results of each measurement item.

(Embodiment 3) Here, a quartz crucible having a multilayer structure used is shown in FIG. Caliber 1 in the manner described above
An 8-inch quartz crucible 3 is manufactured, and a translucent quartz glass 5
Was 15 mm in thickness. 1 cm ² per bubbles semi diameter 10~250μm the transparent quartz glass 5 20,0
Four layers of substantially bubble-free transparent quartz glass 4 were formed on the inner surface of the crucible containing at least 00 pieces. Translucent quartz glass 5
A 250 μm Ga-free transparent quartz glass layer was integrally fused with the translucent quartz glass, and a 10 μm Ga
The transparent glass layer 6 was further integrally fused, and a Ga-free layer having a thickness of 250 μm and a Ga-containing layer having a thickness of 10 μm were further fused to finally form a two-layer four-layer structure. still,
Each Ga-containing layer contained 3.626 g of Ga at the bottom. Using the above crucible, 40 kg of raw silicon is melted, and the diameter is 6 inches and the crystal orientation is <100> by CZ method.
Was grown. Table 1 also shows the results of each measurement item.

As can be seen from Table 1, in Examples 1 to 3, the oxygen concentration in the silicon single crystal was 16 ppm or less.
The resistivity is about 0.9Ω · cm, and LT is 600 μs
It can be seen that the conversion efficiency of the photovoltaic cells is as high as about 20% and that no photodeterioration has occurred. In addition, although reproducibility was also investigated, it was confirmed that stable characteristics were exhibited.

As a result, it was found that a Ga-doped silicon crystal can be efficiently, stably and easily manufactured without preparing a dopant adjusting material in advance. Also,
Using this silicon crystal, a solar cell having a stable and high conversion efficiency without causing photodegradation can be produced, and the power generation cost of the silicon crystal solar cell can be reduced. As a result, the contribution to solving the cost problem of silicon raw materials for solar cells has become significant.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above description, a case was described in which a silicon single crystal to which Ga was added was mainly manufactured by the CZ method. However, the present invention is not limited to the case where the conversion efficiency is not as high as that of a silicon single crystal. It can be applied to crystals. That is, it is needless to say that the use of the quartz crucible according to the present invention is effective in reducing the cost of the silicon raw material even in the production of a polycrystal by the so-called Bridgman method.

For example, in the above embodiment,
The case of a quartz crucible having a diameter of 18 inches has been described with reference to the embodiments, but the present invention is not limited to this, and is applicable to the case of crystal growth using a crucible having a diameter of 24 to 30 inches or more. Needless to say, we can do it.

Further, the present invention can be applied to a so-called MCZ method for applying a horizontal magnetic field, a vertical magnetic field, a cusp magnetic field, and the like to a silicon melt.

[0068]

By manufacturing a silicon crystal using the quartz crucible of the present invention, Ga can be stably doped for easy handling, no metallic impurities or infusible substances are mixed, and a long time is obtained. This enables a stable operation and an improvement in productivity, and is a very industrially advantageous production method.
Further, the present invention can be used as a quartz crucible for growing a silicon crystal for producing a solar cell having a low manufacturing cost, and is capable of producing a solar cell with high light energy conversion efficiency and no light deterioration. Can be. Furthermore, while contributing to the increase in diameter and cost of silicon crystals,
Crystals having high crystal strength and excellent durability can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a quartz crucible used in Example 1 of the present invention.

FIG. 2 is a schematic sectional view of a quartz crucible used in Embodiment 2 of the present invention.

FIG. 3 is a schematic sectional view of a quartz crucible used in Embodiment 3 of the present invention.

[Explanation of symbols]

1: Quartz crucible, 2: Double-structure quartz crucible, 3: Multi-layer quartz crucible, 4: Transparent quartz glass, 5: Translucent quartz glass, 6: Ga-containing layer.

Claims (7)

[Claims] 1. A quartz crucible for accommodating a crystal raw material, wherein gallium (Ga) is contained in an inner wall portion of the quartz crucible. 2. The quartz crucible has a double structure in which translucent quartz glass is used as an outer layer and transparent quartz glass is used as an inner layer, and Ga is contained in the transparent quartz glass portion as the inner layer. The quartz crucible according to claim 1, characterized in that: 3. The quartz crucible according to claim 2, wherein
A plurality of transparent quartz glass layers are provided on the inner layer side to form a multilayer structure, and a transparent quartz glass layer containing Ga and a transparent quartz glass layer not containing Ga are alternately formed. . 4. When growing a silicon polycrystal, the quartz crucible according to any one of claims 1 to 3 is used, and Ga contained in the inner wall of the quartz crucible is converted into a silicon melt. Elution results in Ga
A method for producing polycrystalline silicon, characterized by doping. 5. When growing a silicon single crystal, the quartz crucible according to any one of claims 1 to 3 is used, and Ga contained in the inner wall of the quartz crucible is converted into a silicon melt. Elution results in Ga single crystal
And a method for producing a silicon single crystal. 6. When growing a silicon crystal, gallium (G) is applied to the inner wall as a quartz crucible for accommodating a crystal raw material.
A method for producing a silicon crystal, comprising using a quartz crucible containing a) and doping Ga into the silicon crystal by eluting Ga contained in the inner wall of the quartz crucible into a silicon melt. 7. The method according to claim 6, wherein the silicon crystal is a silicon single crystal or a silicon polycrystal.