JP2007194513A - Manufacturing method for crystal semiconductor particle, and photovoltaic conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent photovoltaic conversion device which has superior electric characteristics by using crystal semiconductor particles manufactured by a manufacturing method for the crystal semiconductor particles, in which semiconductor particles of polycrystalline silicon can stably be crystallized with high efficiency, and crystal silicon particles having high crystallinity can be manufactured inexpensively. <P>SOLUTION: The photovoltaic conversion device uses the crystal semiconductor particles 406 manufactured by introducing a base plate 102 having semiconductor particles 101 containing oxygen, placed on its top surface in a heating furnace to heat and fuse the semiconductor particles 101, and then solidifying the fused semiconductor particles 101 upward from the side of the base plate 102. The crystal semiconductor particles 406 contain oxygen, and density gradients are formed in each of crystal semiconductor particle 406 from one pole 103 to an opposite pole 104. The photovoltaic conversion device with photoelectric conversion efficiency is constituted by using the crystal semiconductor particles 101. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing crystalline semiconductor particles particularly used in a photoelectric conversion device such as a solar cell, and a photoelectric conversion device using the crystalline semiconductor particles produced by the production method.

  Conventionally, photoelectric conversion devices have been developed in view of market needs such as efficiency in terms of performance, consideration of resource finiteness, or low manufacturing costs. As one of promising photoelectric conversion devices in the future market, there is a photoelectric conversion device using crystalline silicon particles used as a solar cell.

  As a raw material for producing crystalline silicon particles, for example, silicon fine particles generated as a result of pulverizing single crystal silicon, high-purity silicon vapor-phase synthesized by a fluidized bed method, or the like is used. In order to produce crystalline silicon particles from these raw materials, after separating the raw materials according to size or weight, they are melted in a container using infrared rays or high-frequency waves, and then freely dropped (for example, Patent Document 1 and Patents). Spheroidized by a method using high-frequency plasma (see, for example, Patent Document 3).

However, most of the crystalline silicon particles produced by these methods are polycrystalline. Since a polycrystal is an aggregate of microcrystals, grain boundaries exist between the microcrystals. This grain boundary deteriorates the electrical characteristics of a semiconductor device using a polycrystal. This is because the recombination centers of the carriers are gathered at the boundary of the grain boundary, and the lifetime of minority carriers is significantly reduced by the recombination caused thereby.
In the case of a semiconductor device such as a photoelectric conversion device in which the electrical characteristics are greatly improved with an increase in the lifetime of minority carriers, the presence of grain boundaries in the crystalline silicon particles used therein deteriorates the electrical characteristics. It becomes a big problem. In other words, if the crystalline silicon particles can be changed from a polycrystal to a single crystal, the electrical characteristics of the photoelectric conversion device can be remarkably improved.

In addition, since the grain boundaries in the polycrystalline body lower the mechanical strength of the crystalline silicon particles made of the polycrystalline body, the thermal history and thermal distortion of each process for manufacturing the photoelectric conversion device, or mechanical pressure, etc. There was also a problem that the crystalline silicon particles were easily destroyed.
Therefore, when producing a photoelectric conversion device using crystalline silicon particles, it is indispensable to produce crystalline silicon particles made of a polycrystal or a single crystal having excellent crystallinity and having no grain boundaries. Become.

  As a method for obtaining crystalline silicon particles composed of a polycrystalline or single crystalline material having excellent crystallinity, a silicon compound film such as a silicon oxide film is formed on the surface of polycrystalline silicon or amorphous silicon, A method is known in which silicon inside a silicon compound film is melted and then cooled and solidified to produce crystalline silicon particles made of a polycrystal or single crystal excellent in crystallinity (for example, Patent Document 4). See).

WO99 / 22048 pamphlet U.S. Pat. No. 4,188,177 JP-A-5-78115 U.S. Pat. No. 4,430,150

  However, the silicon compound film formed on the surface by heating silicon particles, specifically, when silicon is melted inside the silicon oxide film and then solidified, the CZ (Czochralski) method or Since there is no solidification starting point like a seed crystal used in a crystal growth method for growing a general bulk silicon single crystal such as the FZ (floating zone) method, solidification does not occur in one direction, and many nuclei are generated due to the generation of many nuclei. The problem is that crystallization occurs. The polycrystallization of the crystalline silicon particles causes various problems as described above, and causes a problem that the characteristics of a photoelectric conversion device using the crystalline silicon particles for a photoelectric conversion element are deteriorated.

In addition, if the base plate on which the silicon particles are installed contains heavy metal impurities such as iron and nickel, contamination of the heavy metal impurities becomes a problem. Since the heavy metal impurity atoms diffuse between the lattices having no chemical bond in silicon, the impurity atoms are diffused by sewing the gaps in the silicon lattice. Heavy metal impurity atoms form deep levels in silicon and act as recombination centers, causing an increase in leakage current and a decrease in lifetime, causing photodegradation.
That is, it is difficult to produce desired high-quality crystalline silicon particles by the conventional method for producing crystalline silicon particles, and a photoelectric conversion device having excellent electrical characteristics is produced using the obtained crystalline silicon particles. Therefore, there was a problem that it was unsuitable as a manufacturing method.

  An object of the present invention is to produce a crystalline semiconductor particle capable of stably crystallizing semiconductor particles such as polycrystalline silicon with high efficiency and producing crystalline silicon particles having high crystallinity at a low cost. Another object of the present invention is to provide a good photoelectric conversion device having excellent electrical characteristics using crystal semiconductor particles produced by the production method.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have produced a method for producing crystalline semiconductor particles having the following configuration, and an electrical device using crystalline semiconductor particles having high crystallinity by the production method. The inventors have found that a good photoelectric conversion device having excellent characteristics can be provided, and have completed the present invention.

That is, the method for producing crystalline semiconductor particles and the photoelectric conversion device in the present invention have the following configurations.
(1) A base plate on which semiconductor particles containing oxygen are placed on the upper surface is introduced into a heating furnace, the semiconductor particles are heated and melted, and then the molten semiconductor particles are moved upward from the base plate side. A method for producing crystalline semiconductor particles, characterized in that the crystalline semiconductor particles are solidified toward the surface.
(2) The semiconductor particles are silicon particles containing oxygen, and when the molten silicon particles are solidified upward from the base plate side, oxygen contained in the silicon particles is converted to oxygen contained in the silicon particles. The method for producing crystalline semiconductor particles according to (1), wherein a concentration gradient in which the concentration increases from the lower end toward the upper end is formed.
(3) A plurality of crystalline semiconductor particles exhibiting one conductivity type are disposed on a substrate, an insulating material is disposed between the crystalline semiconductor particles, and a semiconductor layer exhibiting a reverse conductivity type is disposed on the crystalline semiconductor particles. A photoelectric conversion device, wherein the crystalline semiconductor particles contain oxygen, and a concentration gradient is formed inside the crystalline semiconductor particles from one electrode to a pole facing the oxygen. Conversion device.
(4) The photoelectric conversion device according to (3), wherein the concentration gradient of oxygen in the crystalline semiconductor particles has a maximum concentration of 1.1 to 6 times a minimum concentration.
(5) The photoelectric conversion device according to (3) or (4), wherein the crystalline semiconductor particles are crystalline silicon particles.

  According to the above (1), after the base plate on which the semiconductor particles are placed on the upper surface is introduced into a heating furnace and the semiconductor particles are heated and melted, the molten semiconductor particles are moved upward from the base plate side. Crystal semiconductor particles are solidified toward the surface, so that the semiconductor particles are placed on the base plate and melted, and then the solidification starting point when solidifying and crystallizing is the contact between the semiconductor particles and the base plate Since it can be set to a portion and the crystallization can proceed from above to the upper part of the semiconductor particles, it becomes possible to gradually solidify the crystalline semiconductor particles in one direction, greatly increasing the crystallinity of the crystalline semiconductor particles. Can be improved.

  According to (2), the semiconductor particles are semiconductor particles containing oxygen, and are included in the semiconductor particles when the molten semiconductor particles are solidified upward from the base plate side. A concentration gradient is formed in oxygen such that the concentration increases from the lower end to the upper end of the semiconductor particles. As a result, precipitation of excess oxygen is promoted on the high concentration side of oxygen closer to the surface layer of the crystalline semiconductor particles in which the oxygen concentration gradient is formed in the crystalline semiconductor particles than on the low concentration side. Such metal impurities can be effectively diffused and precipitated in the precipitate of excess oxygen by the gettering effect. As a result, metal impurities such as iron and nickel can be removed closer to the surface layer on the high oxygen concentration side, and the crystallinity on the low oxygen concentration side and inside the crystalline semiconductor particles can be remarkably improved.

Further, according to (3), compared to the case where no oxygen concentration gradient is formed inside the crystalline semiconductor particles, a rapid change in the oxygen concentration in the semiconductor melt is less likely to occur, and twins in the solidification process of the semiconductor. And subgrains, increase in misfit dislocations caused by the difference in lattice constant from the semiconductor, etc. can be suppressed. improves. As a result, according to the photoelectric conversion device of the present invention, it is possible to form crystal semiconductor particles without defects or transition, so that carriers generated by the incidence of sunlight are not lost by being trapped by defects or transition, Therefore, more current can be collected, and as a result, excellent photoelectric conversion efficiency can be obtained.
In addition, since the high-quality crystalline semiconductor particles having excellent electrical characteristics used in the photoelectric conversion device of the present invention can be manufactured at low cost with high productivity, silicon materials and the like can be efficiently used for the photoelectric conversion device. Therefore, it is possible to improve the efficiency and reliability.

  According to the above (4), when the concentration gradient of oxygen in the crystalline semiconductor particles is 1.1 to 6 times the lowest concentration, the excess oxygen, carbon impurities and metal impurities are precipitated. It can be effectively generated in the semiconductor particle surface layer, and it can suppress the increase in crystal defects due to excess oxygen, difference in thermal expansion coefficient between impurities and semiconductor, and difference in oxygen concentration in crystal semiconductor particles. Deterioration can be prevented.

  As described above, according to the present invention, a large number of crystal semiconductor particles can be stably and efficiently crystallized, and crystal semiconductor particles having high crystallinity can be easily mass-produced. Thus, it is possible to provide a good photoelectric conversion device excellent in photoelectric conversion characteristics and a photovoltaic device using the photoelectric conversion device.

Hereinafter, the photoelectric conversion device of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a state of a base plate and semiconductor particles in an example of an embodiment of a method for producing crystalline semiconductor particles according to the present invention, and FIG. 2 shows an embodiment of the method for producing crystalline semiconductor particles according to the present invention. It is a longitudinal cross-sectional view which shows schematic structure of an example of a form. In FIGS. 1 and 2, 101 is a semiconductor particle or crystalline semiconductor particle (silicon particle or crystalline silicon particle), 102 is a base plate, and 201 is a heating furnace. Reference numeral 103 denotes a solidification starting point (one pole), 104 denotes the other pole, and 105 denotes an arrow indicating a solidification (crystallization) direction. Also, 202 is a heating element, 203 is a furnace material (heat insulating material), 204 is a gas supply means, 205 is a gas filter, 206 is a temperature measuring means such as a thermocouple, 207 is a bell jar, and 208 is a ceramic table.
In this embodiment, an example in which silicon is used as a semiconductor material will be described.

(Silicon particles)
First, semiconductor grade crystalline silicon is used as a semiconductor material, and this is melted in a container using infrared rays or a high frequency coil, and then the polycrystalline silicon is melted and dropped by a free fall as a granular melt. Silicon particles 101 are obtained.
The polycrystalline silicon particles 101 produced by the melt drop method are usually doped with a dopant in order to obtain a desired conductivity type and resistance value. As dopants for silicon, boron, aluminum, gallium, indium, phosphorus, arsenic, and antimony are used. However, boron or phosphorus is used because it has a large segregation coefficient for silicon and a small evaporation coefficient when silicon is melted. desirable. The dopant concentration is about 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ added to the silicon crystal material.
At the time when the silicon particles 101 are obtained by this melting and dropping method, the shape of the silicon particles 101 is a teardrop type, a streamline type, or a connected type in which a plurality of particles are connected in addition to a substantially spherical shape. . When a photoelectric conversion device is manufactured using the polycrystalline silicon particles 101 as it is, good photoelectric conversion characteristics cannot be obtained. This is due to metal impurities such as Fe, Cr, Ni, and Mo that are normally contained in the polycrystalline silicon particles 101 and due to the carrier recombination effect at the polycrystalline grain boundaries. In order to improve this, the polycrystalline silicon particles 101 are remelted in a temperature-controlled heating furnace by the method for producing crystalline semiconductor particles according to the present invention, and then the temperature is lowered, for example, in an oxygen / nitrogen atmosphere. Single crystal crystalline silicon particles 101 with a low content of impurities, which are produced by solidification, are used.
In the present invention, although the single crystal ratio of the crystalline silicon particles 101 can be ensured to be 90% or more, there are cases where grain boundaries exist in several percent of the crystalline silicon particles 101, and the crystalline silicon particles 101 having such a single crystal ratio. If so, it can be sufficiently used for a photoelectric conversion device.

In order to manufacture the single crystal crystalline silicon particles 101, first, a plurality of polycrystalline silicon particles 101 are placed side by side on the upper surface of the base plate 102. Here, “one layer” indicates a state in which one layer is arranged in the vertical direction and a large number of silicon particles 101 are arranged in the horizontal direction to form one layer. The placement of the silicon particles 101 on the base plate 102 is desirably performed by filling one layer. In addition, it is desirable that the silicon particles 101 are filled and placed so that there is no gap as much as possible, but the silicon particles 101 may be in contact with each other. In this case, one silicon particle 101 can be placed on the top surface of the base plate 102 for processing. The base plate 102 is preferably plate-shaped and may be stacked in a plurality of stages. For the material of the base plate 102, quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for suppressing the reaction with the silicon particles 101, but it has excellent heat resistance, durability, chemical resistance and cost. Quartz glass is preferred because it is cheap and easy to handle.
In addition, the base plate 102 is used as a solidification starting point when the silicon particles 101 are cooled and solidified after being melted. By placing a large number of silicon particles 101 on the upper surface of the base plate 102 in this way, the solidification starting point 103 can be set at the contact portion between each silicon particle 101 and the base plate 102. The solidification (crystallization) direction 105 can be set from the one pole 103 to the opposite pole 104 with one pole 103 as one pole, and solidify gradually (gradually) in one direction without using a seed crystal. Thus, single crystal silicon particles 101 can be obtained, and the crystallinity of the crystalline silicon particles 101 can be greatly improved by suppressing the generation of subgrains and the like. Basically, the silicon particles 101 are gradually solidified. However, for example, a process of making the temperature substantially constant during the solidification can be performed.

  Moreover, it is desirable that the surface roughness of the base plate 102 is an arithmetic average roughness (Ra) of 0.1 to 50 μm. That is, by forming irregularities on the surface of the base plate 102 in contact with the silicon particles 101, the generation of a plurality of solidification starting points 103 can be suppressed during crystallization, and the generation of subgrains can be suppressed, thereby greatly improving the crystallinity. Can be made. When the arithmetic average roughness (Ra) of the surface of the base plate 102 is smaller than 0.1 μm, the silicon particles 101 adjacent to each other are easily moved and brought into contact with each other at the time of melting the silicon, which is not desirable. Further, when the arithmetic average roughness (Ra) of the surface of the base plate 102 is larger than 50 μm, it becomes difficult to form a silicon oxynitride film in the vicinity of the contact portion, and the melting reaction also tends to become non-uniform, and cooling after melting. This is not desirable because the effect is increased and sub-grains are generated and the grains grow easily and become polycrystalline.

(Oxygen concentration gradient)
On the other hand, the silicon particles 101 according to the present invention contain oxygen. Therefore, as described above, when the molten silicon particles 101 are solidified upward from the base plate 102 side, oxygen contained in the silicon particles 101 is changed from the lower end to the upper end of the silicon particles 101. A concentration gradient with increasing concentration is formed. This is because the silicon particles 101 placed on the base plate 102 start to solidify from a small area contact portion with the base plate 102 and harden toward the upper pole. Due to the segregation phenomenon of impurities with respect to silicon, when the segregation coefficient with respect to silicon is smaller than 1, the concentration of impurities contained in the solid portion becomes smaller than that in the melt portion, and the impurity concentration in the melt portion gradually increases. As a result, a concentration gradient in which the impurity concentration increases from the lower end toward the upper end of the silicon particles 101 is formed.
Accordingly, in the crystalline silicon particles 101, precipitation of excess oxygen is promoted on the high concentration side of oxygen closer to the surface layer of the crystalline silicon particles 101 in which the oxygen concentration gradient is formed than on the low concentration side. Metal impurities such as nickel and nickel can be effectively diffused and precipitated in the precipitate of excess oxygen by the gettering effect. In the case of impurities such as carbon, carbon itself hardly diffuses due to substitutional elements present at the silicon site, but oxygen precipitation is promoted around the carbon, so segregation causes carbon impurities close to the surface layer. On the high concentration side, the gettering effect can be further enhanced. Therefore, metal impurities such as iron and nickel can be moved closer to the surface layer on the high oxygen concentration side, and the crystallinity inside the low oxygen concentration side and inside the crystalline silicon particles 101 can be remarkably improved.

  Further, compared to the case where no oxygen concentration gradient is formed inside the crystalline silicon particles 101, a rapid change in the oxygen concentration in the silicon melt is less likely to occur, and the generation of twins and subgrains during the solidification process of silicon It is possible to suppress an increase in misfit dislocations and the like resulting from a difference in lattice constant from silicon, and the crystallinity is improved, and cracks due to thermal strain and the like are less likely to occur, so that the mechanical strength is also improved. In addition, it is possible to suppress the compositional supercooling state caused by the increase in the concentration of the conductive dopant in the silicon melt due to the segregation phenomenon on the growth interface during the solidification process of silicon. There is no problem that the crystallinity is disturbed by the generation of the second phase in which silicon and the conductive dopant are not mixed. As a result, according to the photoelectric conversion device of the present invention, the crystalline silicon particles 101 having no defects or transitions can be formed, so that carriers generated by the incidence of sunlight are eliminated by being trapped by crystal defects or transitions. Therefore, more current can be collected, and as a result, excellent photoelectric conversion efficiency can be obtained.

  Further, when the oxygen concentration of the crystalline silicon particles 101 is low, oxygen precipitates, crystal defects due to grain boundaries and oxygen concentration, etc. can be reduced, and the crystallinity of the crystalline silicon particles 101 is improved and thermal strain is reduced. Therefore, mechanical strength can be improved. In addition, since generation of strain and oxygen-induced stacking fault (OSF) at the interface with silicon can be suppressed, generation of subgrains, twins, and the like in the vicinity of the surface of the crystalline silicon particle 101 can be suppressed. And crystallinity can be improved.

The oxygen content is preferably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ . When the oxygen content is less than 1 × 10 ¹⁴ atoms / cm ³ , the impurity gettering effect due to oxygen precipitation cannot be obtained sufficiently, and when it exceeds 1 × 10 ¹⁸ atoms / cm ³ , crystal defects due to excess oxygen Etc. are not preferable.
In addition, since the size of the semiconductor particles 101 including the silicon particles 101 is usually substantially spherical, the average particle diameter is preferably 1500 μm or less, and the shape is preferably close to a sphere. However, the shape of the semiconductor particles 101 is not limited to a spherical shape, and may be a cubic shape, a rectangular parallelepiped shape, or other irregular shapes. When the size of the semiconductor particle 101 exceeds 1500 μm, a predetermined silicon compound film formed on the surface of the silicon particle 101 becomes relatively thin, so that the semiconductor particle 101 at the time of melting of the internal silicon is obtained. It is difficult to keep the shape of the film stable, and it is also difficult to completely melt the silicon. If the melting is incomplete, subgrains are likely to occur, which is not desirable. On the other hand, when the size of the semiconductor particle 101 is as small as less than 30 μm in diameter, it is difficult to maintain the shape of the silicon particle 101 at the time of melting because the thickness of the silicon compound film on the surface becomes thin. It is not desirable because the silicon particles 101 arranged adjacent to each other are easily combined. Therefore, it is desirable that the size of the semiconductor particles 101 is 30 to 1500 μm, thereby suppressing the coalescence of the semiconductor particles 101, maintaining the shape of the semiconductor particles 101 stably, and generating no subgrains. Crystal silicon particles 101 having a good shape can be stably produced.

(heating furnace)
As the heating furnace 201, a resistance heating type or induction heating type heater used for ceramic firing or the like is suitable, but a resistance heating type atmosphere firing furnace is desirable from the standpoint of uniformity of furnace temperature and ease of use. That is, since only a temperature range up to about 1100 ° C. is used in the semiconductor process, a high-temperature oxidation furnace is required to raise the temperature to 1415 ° C. or higher, which is the melting point of silicon. On the other hand, a resistance heating type atmosphere firing furnace used for firing ceramics or the like in the same processing furnace is relatively easy to raise the temperature of 1500 ° C. or more, and a large-scale and mass-produced atmosphere firing furnace is also compared to a horizontal oxidation furnace. It can be obtained inexpensively.

A heating element 202 is provided in the heating furnace 201. The heating element 202 is composed of a resistance heating type heater or the like, and the installation location may be either horizontal or vertical. The heat generating part is made of molybdenum disilicide or silicon carbide.
The furnace material 203 of the heating furnace 201 is made of an insulating material such as alumina or mullite, which is generally used in an atmosphere firing furnace.
It is desirable to have a cover inside the heating element 202 and the furnace material 203 in order to prevent contamination from materials such as metal impurities and debris contained therein. Suitable materials for the cover include, for example, quartz glass, aluminum oxide, single crystal sapphire, silicon carbide, mullite and the like.
The heating furnace 201 is provided with a gas supply means 204 for introducing a reactive gas or an atmospheric gas into the furnace. The gas supply means 204 is preferably provided with a gas filter 205. That is, by installing the gas filter 205, impurities contained in an argon atmosphere gas containing a reactive gas of oxygen gas and nitrogen gas can be effectively removed.
In order to detect the temperature in the heating furnace 201, a thermocouple is provided as the temperature measuring means 206. The thermocouple is preferably covered with an alumina cover.

Before heating in the atmosphere firing furnace, it is desirable to perform solution cleaning in advance by an RCA cleaning method in order to remove metal, foreign matter, and the like attached to the surface of the silicon particles 101. The RCA cleaning method is a cleaning method generally used in the manufacturing process of a semiconductor device as a standard cleaning process of a silicon wafer. In the first stage among the three stages, ammonium hydroxide and peroxide are used. The oxide film and the silicon surface are removed with an aqueous solution of hydrogen, the oxide film attached in the previous step is removed with an aqueous hydrogen fluoride solution in the second step, and hydrogen chloride and hydrogen peroxide are removed in the third step. A heavy oxide is removed with an aqueous solution to form a natural oxide film.
Further, in order to prevent contamination from the furnace material 203 and the heating element 202 in the heating furnace 201, a bell jar 207 that covers the silicon particles 101 placed on the base plate 102 is installed in the heating furnace 201. Is desirable. Quartz glass, mullite, aluminum oxide, silicon carbide, single crystal sapphire, etc. are suitable for the material of the bell jar 207, but quartz glass is preferred because of its excellent heat resistance, durability, chemical resistance and low cost. is there.
In addition, in order to prevent re-adhesion contamination of organic substances or the like on the surface of the silicon particles 101, it is desirable that the inside of the bell jar 207 is sufficiently replaced with an inert gas atmosphere. Argon, nitrogen, helium, and neon are suitable as the inert gas, but argon or nitrogen is preferred from the viewpoint of low cost and easy handling.

(Silicon compound coating)
In the process of heating the silicon particles 101 while introducing a reactive gas composed of oxygen gas and nitrogen gas in the heating furnace 201 and raising the temperature to a temperature higher than the melting point of silicon, A silicon compound film is formed.
As the silicon compound film formed on the surface of the silicon particles 101, a silicon oxide film or an oxynitride film is suitable, but the density of the film is high and the strength per unit film thickness is high, and silicon particles such as contaminants and impurities From the viewpoint that the diffusion blocking force into the inside of 101 is large, it is preferable that a silicon oxynitride film is formed. That is, by forming a silicon oxynitride film on the surface of the silicon particles 101, the density of oxygen precipitates near the surface of the silicon particles 101, crystal defects due to oxygen precipitates, and the like can be reduced, and a pn junction interface is formed. The crystallinity of silicon in the vicinity can be greatly improved.
In addition, since distortion at the interface between silicon oxynitride film and silicon and generation of oxygen-induced stacking faults (OSF) can be suppressed, subgrains, twins, etc. near the surface of the crystalline silicon particles 101 Occurrence can be suppressed and surface crystallinity can be improved. Also, by forming a silicon oxynitride film, it functions as an effective gettering layer that traps and immobilizes heavy metal impurities such as Fe and Ni due to surface contamination by gettering, and improves the crystal quality of the pn junction interface. Can be improved.

Further, it is desirable that the oxygen partial pressure and the nitrogen partial pressure of the atmosphere in the heating furnace 201 by the reactive gas when forming the oxynitride film on the surface of the silicon particle 101 are 1% or more, respectively. When the oxygen partial pressure or nitrogen partial pressure in the atmospheric gas is less than 1%, the formation of the oxynitride film formed on the surface of the silicon particles 101 that crystallize the inside becomes insufficient, and the silicon compound film is cracked. Is likely to occur.
In addition, each gas partial pressure in the atmospheric gas in the heating furnace 201 can be adjusted with each gas flow rate with respect to the total gas flow rate. Atmospheric gas is supplied from the gas supply means 204 into the bell jar 207 through the gas filter 205. If the apparatus for supplying gas to the gas supply means 204 has a mechanism capable of adjusting the gas pressure and gas concentration. Good.

(Method for producing crystalline silicon particles)
Next, a method for manufacturing the crystalline silicon particles 101 will be described.
The silicon particles 101 introduced into the heating furnace 201 are heated to a temperature higher than the melting point of the semiconductor material and higher than the melting point of silicon (1415 ° C.), preferably 1480 ° C. or lower. During this time, silicon melts inside the silicon compound film on the surface of the silicon particles 101. At this time, the silicon compound film formed on the surface of the silicon particles 101 can maintain the shape of the silicon particles 101 while melting the silicon inside. However, when the temperature of the silicon particles 101 is difficult to maintain stably, for example, in the case of the silicon particles 101, when the temperature is raised to a temperature exceeding 1480 ° C., when the silicon inside melts, It is difficult to keep the shape of the silicon particles 101 stable, so that the adjacent silicon particles 101 are likely to coalesce, and a fusion reaction between the silicon particles 101 and the base plate 102 is likely to occur. Further, it is preferable that the base plate 102 is placed densely packed in one layer. “Dense” means that there is no gap as much as possible, and the silicon particles 101 may be in contact with each other. The base plate 102 may be stacked in a plurality of stages. Furthermore, it is desirable to install the base plate 102 so as to cover the quartz plate bell 207.

Specifically, first, before the heating of the heating furnace 201 is performed, the furnace is vacuum-treated or the gas is sufficiently replaced with an inert gas argon atmosphere so that the furnace is filled with only the argon atmosphere. To do. This is because dangling bonds on the surface of the silicon particles 101 after RCA cleaning are unstable in bonding state.
Next, the temperature in the heating furnace 201 is raised to a temperature below the melting point of silicon while introducing a reactive gas of oxygen gas and nitrogen gas. This is because a silicon oxynitride film is formed on the surface of the silicon particle 101. It is desirable that the oxygen partial pressure in the atmosphere gas of the reactive gas is 1% or more and the nitrogen partial pressure is 4% or more. That is, when the oxygen partial pressure in the atmospheric gas is less than 1% and the nitrogen partial pressure is less than 4%, the silicon particles 101 are easily bonded to each other, which is not desirable. Further, when the oxygen partial pressure in the atmospheric gas is 20% or more or the nitrogen partial pressure is 80% or more, cracks are likely to occur in the oxynitride film formed on the surface of the silicon particles 101.

When forming the oxynitride film, the film is held for several minutes at a temperature of 1000 ° C. or higher and lower than the melting point of silicon. That is, a more uniform silicon oxynitride film can be formed by holding at a temperature of 1000 ° C. or higher for several minutes. In addition, the uniformity of the temperature distribution in the heating furnace 201 or the uniformity of the temperature distribution of the silicon particles 101 can be improved. The oxynitride film formed on the surface of the silicon particles 101 in the above state can sufficiently hold the silicon when it melts. However, holding at a temperature of 1000 ° C. or more for 120 minutes or more is not desirable because it promotes the diffusion of oxygen into the silicon.
When simultaneously forming a nitride film or an oxynitride film on the surfaces of the base plate 102 and the bell jar 207 in the manufacturing process of the crystalline silicon particles 101, after introducing an argon atmosphere gas containing nitrogen gas, An argon atmosphere gas containing nitrogen gas may be introduced to form a nitride film or an oxynitride film on the surfaces of the base plate 102 and the bell jar 207 and to form an oxynitride film on the surface of the silicon particles 101.

  More specifically, the temperature is raised to 1420 to 1440 ° C., and the temperature is maintained for about 2 to 15 minutes. During this time, the internal silicon begins to melt. However, holding at a temperature of 1450 ° C. or higher or for 30 minutes or more is not desirable because the oxynitride film is easily broken when silicon is melted, and as a result, the base plate 102 and the silicon particles 101 may be fused and solidified. Further, by introducing oxygen gas and nitrogen gas in the atmosphere gas, cracks in the oxynitride film at high temperatures can be corrected. Further, when silicon is melted, it tries to be spheroidized by surface tension. However, the oxynitride film can be sufficiently deformed within the above temperature range, and the silicon to be crystallized can be made to be nearly spherical.

Next, in order to cool the molten silicon in the oxynitride film wrapped with the oxynitride film, the temperature is lowered to a temperature of 1350 ° C. or higher and 1400 ° C. or lower. In order to further promote the crystallization of the silicon particles 101, it is desirable to maintain the temperature for about 10 minutes at a temperature of 1350 ° C. or higher and 1400 ° C. or lower. When the holding time is shorter than 10 minutes, subgrains and the like are easily generated and it is difficult to sufficiently crystallize.
In order to solidify the molten silicon inside the silicon compound coating (oxynitride coating), when solidifying by lowering to a temperature of about 1400 ° C. or less below the melting point, the solidification is performed by maintaining a relatively high temperature below the melting point. In this case, since the solidification progresses in one direction toward the opposing pole 104 with the contact portion on the base plate 102 as the solidification starting point (one pole) 103, the outer shell of the crystalline silicon particle 101 as in normal solidification. Therefore, when the inside solidifies and then the inside solidifies, it is possible to avoid the occurrence of polycrystallization by breaking through the solidified portion of the outer shell due to volume expansion of the melt remaining in the inside. It becomes a crystal | crystallization and can improve crystallinity significantly.
Here, it is desirable that the rate of temperature decrease be in the range of about 10 ° C. per second to about 0.1 ° C. per minute. When the temperature lowering rate is higher than 10 ° C. per second, it is not desirable because the temperature distribution in the heating furnace 201 or the base plate 102 is likely to be uneven due to a sudden temperature change. Further, when the temperature lowering rate is slower than 0.1 ° C. per minute, it is difficult to keep the shape of the silicon particles 101 being melted stably, and union formation between adjacent silicon particles 101 is easily promoted, which is not desirable.

  Next, thermal annealing is performed at a temperature of 1000 ° C. or higher for several hours. This is for the purpose of precipitating oxygen mixed and added oxygen into the silicon by thermal convection when the silicon is melted, or for improving the crystallinity of the crystalline silicon particles 101 after melting and solidification. If the temperature is lower than 600 ° C., thermal donors such as oxygen donors are generated, which is not desirable. When oxygen mixed in silicon and added oxygen are deposited in the thermal history of the subsequent process, they become stacking faults and the electrical characteristics are greatly deteriorated. Since the shrinkage and growth of oxygen precipitation nuclei depend on temperature, the precipitate size increases and the density decreases at higher temperatures. Thermal annealing is also effective as a method for improving the crystallinity of the crystalline silicon particles 101 after melting and solidification. That is, holding at a high temperature has the effect of rearranging atoms to reduce strain and defects in the crystal, and get metal impurities to oxygen precipitates by thermal diffusion. After annealing, the temperature is lowered to room temperature.

The partial pressure of oxygen gas and nitrogen gas in the atmosphere gas containing argon inert gas, oxygen gas and nitrogen gas in the furnace can be adjusted by the flow rates of oxygen gas and nitrogen gas with respect to the argon flow rate. Any mechanism having a mechanism capable of adjusting the pressure and the gas concentration may be used. The partial pressures of oxygen gas and nitrogen gas may be kept constant without changing from the formation of the oxynitride film to the cooling after annealing.
Since the nitride film or oxynitride film is formed on the surface of the bell jar 207 and the base plate 102 installed in the atmosphere firing furnace, the surface of the bell jar 207 and the base plate 102 can be densified, and impurities such as heavy metals are contaminated. As a result, the diffusion barrier property can be greatly improved.
Further, silicon particles 101 are placed in a bell jar 207 and a base plate 102 on which a nitride film or an oxynitride film is formed, and a silicon compound film is formed on the surface to melt the inner silicon, and then the temperature is lowered and solidified. Thus, the crystal silicon particles 101 can be prevented from being contaminated with metal impurities, and high quality, cost reduction, and mass productivity can be realized.

  In the case of the silicon particles 101, the thickness of the silicon compound film formed on the surface is preferably 0.1 μm or more in the above average particle diameter (30 to 1500 μm) range. If the thickness is as thin as less than 0.1 μm, it is not desirable because the silicon compound film on the surface is easily broken when the silicon inside is melted. Further, if the silicon compound film has a necessary strength with a thickness of 0.1 μm or more, the silicon inside tends to be spheroidized by surface tension when melted, whereas the silicon compound film is in the above temperature range. Is sufficiently deformable, the crystalline silicon particles 101 obtained by crystallizing the inside can be made into a shape close to a true sphere. On the other hand, when the thickness of the silicon compound film exceeds 50 μm, the silicon compound film is difficult to be deformed in the above temperature range, and the shape of the obtained crystalline silicon particles 101 is unlikely to be a shape close to a true sphere. Not desirable. Accordingly, in the case of the silicon particles 101, the thickness of the silicon compound film on the surface is preferably 0.1 to 50 μm with respect to the above average particle diameter range (30 to 1500 μm). Nearly good-shaped crystalline silicon particles 101 can be stably obtained, and by using the crystalline silicon particles 101 in a photoelectric conversion element, a photoelectric conversion device having excellent conversion efficiency can be obtained.

  The crystalline semiconductor particles 101 thus obtained may be subjected to surface treatment or the like as necessary. For example, for the crystalline silicon particles 101, in order to obtain high-purity crystalline silicon particles 101 with good crystallinity, a silicon compound film of 1 μm or more formed on the surface may be removed by etching with hydrofluoric acid. In addition, here, in order to remove the crystal surface strained layer having a high impurity concentration on the crystal surface of the crystal silicon particles 101, it is desirable to perform an etching process on the surface of the crystal silicon particles 101 with a thickness of 1 μm or more with hydrofluoric acid. .

  As described above, in the method for manufacturing crystalline silicon particles 101 according to the present invention, the quartz base plate 102 introduced into the atmosphere firing furnace is mounted in an atmosphere gas containing a reactive gas of oxygen gas and nitrogen gas. In the production of crystalline silicon particles 101 that heat silicon particles 101 placed on plate 102 to melt silicon, and then cool and solidify to crystallize, contact with base plate 102 on the surface of silicon particles 101 Due to the small number of points, high-quality crystalline silicon particles 101 can be produced even in an inexpensive atmosphere firing furnace, and crystalline silicon particles 101 used for photoelectric conversion devices can be produced at low cost with high productivity, and silicon materials can be used efficiently. It is possible to improve efficiency and reliability.

(Photoelectric conversion device)
Next, FIG. 3 shows a longitudinal sectional view of an example of an embodiment of the photoelectric conversion device of the present invention. In FIG. 3, 406 is a crystalline silicon particle, 407 is a conductive substrate, 408 is a bonding layer between the crystalline silicon particle 406 and the conductive substrate 407, 409 is an insulating material, 410 is a semiconductor layer, 411 is a translucent conductor layer, Reference numeral 412 denotes an electrode.
In the photoelectric conversion device using the crystalline silicon particles 406 of the present invention, a plurality of first conductivity type, for example, p-type crystalline silicon particles 406 are formed on one main surface of the conductive substrate 407, in this example, the upper surface. For example, the insulating layer 408 is bonded to the conductive substrate 407 by the bonding layer 408, the insulating material 409 is interposed between adjacent ones of the crystalline silicon particles 406, and the upper portions of the crystalline silicon particles 406 are exposed from the insulating material 409. The second conductive type, for example, the n-type semiconductor layer 410 and the translucent conductor layer 411 are sequentially provided on the crystalline silicon particles 406. In addition, when using this photoelectric conversion apparatus as a solar cell, the electrode 412 is deposited and formed in a predetermined pattern shape on the translucent conductor layer 411, for example, a finger electrode and a bus bar electrode. .
In the photoelectric conversion device of the present invention, in such a configuration, the crystalline silicon particles 406 are produced by the above-described method for producing the crystalline semiconductor particles 101 of the present invention. A concentration gradient is formed from one electrode 103 to the opposite electrode 104 in oxygen in 406.
The photoelectric conversion device of the present invention uses a plurality of crystalline silicon particles 406, but the generated current is about 30 μA with one crystalline silicon particle 406, and 100,000 pieces are connected in parallel and used. In general, 10,000 to 1,000,000 crystalline silicon particles 406 are used because a current of about 3.0 A is obtained.

In the photoelectric conversion device of the present invention, the crystalline silicon particles 406 are doped with a dopant for making the first conductivity type, for example, a p-type dopant so as to have a desired resistance value. The p-type dopant includes boron, aluminum, gallium, and indium. However, it is desirable to use boron from the viewpoint of a large segregation coefficient with respect to silicon and a small evaporation coefficient when silicon is melted. Note that the crystalline silicon particles 406 may be doped with an n-type dopant. As the n-type dopant, phosphorus, arsenic or the like is desirable.
According to the photoelectric conversion device of the present invention, since the crystalline silicon particles 406 are produced by the method for producing crystalline semiconductor particles according to the present invention, the crystalline silicon containing no impurities and having good crystallinity. Since the particles 101 can be stably manufactured with high quality as the crystalline silicon particles 101 with high quality, the silicon material used for the photoelectric conversion device can be efficiently used, and the high-quality crystalline silicon particles 406 can be used. It is possible to improve the photoelectric conversion efficiency and reliability of the photoelectric conversion device. Accordingly, a photoelectric conversion device with excellent photoelectric conversion efficiency can be provided at a low cost.

Next, a method for producing crystalline silicon particles 406 in the photoelectric conversion device of the present invention will be described.
The silicon particles 101 used as a starting material for the crystalline silicon particles 406 are preferably doped with a p-type semiconductor impurity as the first conductivity type so as to have a desired resistance value. As described above, boron, aluminum, gallium or the like is desirable as the p-type dopant, and the addition amount is desirably 1 × 10 ¹⁴ to 1 × 10 ¹⁸ atoms / cm ³ .
Since the crystalline silicon particles 406 manufactured by the manufacturing method according to the present invention start from a small area on the base plate 102 and solidify from one pole 103 toward the opposite pole 104, the crystalline silicon particles 101 inside the crystalline silicon particle 101 are solidified. Due to the segregation effect between the conductive type (p-type) dopant and the solid and the melt, the concentration of the dopant amount in the remaining melt increases as the solidification progresses.

As described above, the obtained crystalline silicon particles 101 (406) start to solidify from the small area contact portion with the base plate 102 when the silicon particles 101 placed on the base plate 102 are directed toward the upper pole. Since it is solidified, oxygen in the crystalline silicon particle 101 (406) has a concentration gradient in which the concentration increases from the lower end to the upper end of the crystalline silicon particle 101.
In the concentration gradient of oxygen in the crystalline silicon particles 101 (406), the maximum concentration is 1.1 to 6.0 times, preferably 1.1 to 3.0 times, more preferably 1.1 to 1.5 times the minimum concentration. Is double. That is, in this range, a concentration gradient is formed in which the concentration of oxygen increases from one pole 103 in the crystalline silicon particle 406 to the other opposing pole 104, so that the crystalline silicon particle 101 is converted into a single crystal. The required solidification direction and solidification speed are satisfied, and single crystallization is achieved. That is, as compared with the case where it is not so, precipitation of excess oxygen, carbon impurities, and metal impurities can be effectively generated in the surface layer of the crystalline silicon particles 101, and the difference in thermal expansion coefficient between the excess oxygen and impurities and silicon and the crystal. The increase in generation of crystal defects due to the difference in oxygen concentration in the silicon particles 101 can be suppressed, and deterioration of crystallinity can be prevented.
When the maximum concentration is smaller than 1.1 times the minimum concentration, the segregation coefficient is closer to 1, and twins and subgrains are generated due to the growth rate being too fast. Further, when the maximum concentration is larger than 6 times the minimum concentration, it is not desirable because crystal defects due to the concentration difference are likely to occur. Therefore, since the photoelectric conversion device using the crystalline silicon particles 101 of the present invention has good crystallinity, current generated by light incidence can be collected efficiently, so that high photoelectric conversion efficiency can be obtained.
In order to adjust the magnitude of the oxygen concentration gradient, when the molten silicon inside the silicon compound coating of the silicon particles 101 is cooled to a temperature not higher than the melting point and solidified in the manufacturing method according to the present invention, the temperature drop The cooling rate may be changed by adjusting the speed. By adjusting the temperature lowering speed in this way, it is possible to obtain a concentration gradient in which the maximum concentration of oxygen is about eight times the minimum concentration.

  The example shown in FIG. 3 is a photoelectric conversion device manufactured using the crystalline silicon particles 406 obtained as described above. In order to obtain this photoelectric conversion device, first, the silicon compound film formed on the surface of the crystalline silicon particles 406 obtained by the manufacturing method according to the present invention is removed by etching with hydrofluoric acid. The thickness of the silicon compound film removed at this time is 1 μm or more in the radial direction. Further, in order to remove the interfacial strain between the silicon compound film and the crystalline silicon particles 406 and impurities such as p-type dopant and metal segregated on the surface of the crystalline silicon particles 406, the surface of the crystalline silicon particles 406 is removed with hydrofluoric acid or the like. Etching can be removed. The thickness of the surface layer of the crystalline silicon particles 406 removed at that time is desirably 100 μm or less in the radial direction.

  Next, in order to form the second conductivity type semiconductor layer 410, the crystalline silicon particles 406 are formed on the surface of the crystalline silicon particles 406 by a thermal diffusion method with low process cost prior to the bonding of the crystalline silicon particles 406 to the conductive substrate 407. May be. In this case, for example, group V P, As, Sb, group III B, Al, Ga, or the like is used as the second conductivity type dopant, and the crystalline silicon particles 406 are accommodated in a diffusion furnace made of quartz. The semiconductor layer 410 of the second conductivity type is formed on the surface of the crystalline silicon particles 406 by heating while introducing the dopant.

Next, a large number of crystalline silicon particles 406 are arranged on the conductive substrate 407. Then, the crystalline silicon particles 406 are bonded to the conductive substrate 407 through the bonding layer 408 generated by heating the whole in a reducing atmosphere. The bonding layer 408 is, for example, an alloy of aluminum and silicon.
At this time, when the conductive substrate 407 is a metal substrate including at least aluminum on its surface, the crystalline silicon particles 406 can be bonded at a low temperature, and a light-weight and low-cost photoelectric conversion device can be provided. Further, by making the surface of the conductive substrate 407 rough, it is possible to make the reflection of incident light in the non-light-receiving region reaching the surface of the conductive substrate 407 random, and reflect the incident light obliquely. Incident light can be used effectively by allowing the module surface to be re-reflected and further photoelectrically converting this with the photoelectric conversion part of the crystalline silicon particles 406.

Next, an insulating material 409 is placed on the conductive substrate 407 so that the adjacent crystalline silicon particles 406 are adjacent to each other, and at least the top of these crystalline silicon particles 406 is formed from the insulating material 409. Place it exposed.
Here, the surface shape of the insulating material 409 between the adjacent crystalline silicon particles 406 is made concave so that the crystalline silicon particle 406 side is high, thereby covering the insulating material 409 and the top thereof. The difference in the refractive index from the sealing resin of the photoelectric conversion module applied in this manner can promote the irregular reflection of incident light on the crystalline silicon particles 406 in the non-light-receiving region where the crystalline silicon particles 406 as the photoelectric conversion material are not present. it can.

  Next, the translucent conductor layer 411 is formed over the semiconductor layer 410. Then, a silver paste or the like is applied in a predetermined pattern shape in order to extract desired power as a solar cell, thereby forming electrodes 412 such as grit electrodes or finger electrodes and bus bar electrodes. In this manner, by using the conductive substrate 407 as one electrode and the electrode 412 as the other electrode, a photoelectric conversion device as a solar cell can be obtained.

According to the photoelectric conversion device of the present invention as described above, a large number of crystalline silicon particles 406, each of which is single-crystallized without using a seed crystal, can be manufactured with high productivity, and a silicon material used for the photoelectric conversion device can be produced. The high-quality crystalline silicon particles 406 can be used efficiently and can improve the photoelectric conversion efficiency and the reliability of the photoelectric conversion device. A photoelectric conversion device with high photoelectric conversion efficiency and low cost can be obtained. Can be provided.
The photoelectric conversion device can be used as a power generation unit, and a photovoltaic power generation device configured to supply the generated power from the power generation unit to a load can be obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and the photoelectric conversion apparatus of this invention and its manufacturing method are demonstrated in detail, this invention is not limited only to a following example.

A specific example of the manufacturing method of the crystalline semiconductor particles 101 of the present invention and the photoelectric conversion device using the crystalline silicon particles 406 manufactured thereby will be described along the manufacturing steps.
As a pretreatment, a mixed gas of nitrogen and oxygen is introduced into an atmosphere firing furnace of a resistance heating heater and held at about 1000 ° C. for about 1 hour, and the silicon oxynitride film is formed on the surfaces of the quartz glass bell jar 207 and the base plate 102. Formed.
Next, ten thousand silica particles 101 having an average particle diameter of about 400 μm subjected to RCA cleaning are filled in one layer on a base plate 102 made of quartz glass, and a quartz glass bell jar 207 filled with an argon inert atmosphere gas is used. The entire silicon particle 101 was heated by a resistance heater. An argon atmosphere gas containing a reactive gas of oxygen gas and nitrogen gas was introduced into the bell jar 207 simultaneously with heating. A silicon oxynitride film is formed on the surface of the silicon particle 101 while raising the temperature from room temperature to about 1400 ° C., and the silicon inside the oxynitride film is melted at about 1420 ° C., which is equal to or higher than the melting point of silicon, for about 2 minutes. The mixture was cooled to 0 ° C. and solidified while maintaining the temperature for about 5 minutes. Thereafter, the temperature was lowered to about 1100 ° C., and annealing treatment was performed for about 3 hours. Finally, the temperature was lowered to room temperature to produce crystalline silicon particles 101.

Here, each partial pressure in the atmospheric gas was argon: oxygen: nitrogen = 10: 1: 4. The partial pressure was adjusted by the flow rates of oxygen gas and nitrogen gas with respect to the argon flow rate. Oxygen gas and nitrogen gas were kept flowing until the temperature was lowered after annealing while the partial pressure was kept constant throughout.
The crystalline silicon particles 101 prepared by forming a silicon oxynitride film on the surface of the bell jar 207 and the quartz glass base plate 102, and the crystalline silicon particles prepared without forming a silicon oxynitride film on the surface of the base plate 102 The metal impurity concentration analysis contained in 101 was performed using ICP-MS (inductively coupled plasma mass spectrometry) and atomic absorption analysis. As a result, the metal impurity concentration of the crystalline silicon particles 101 produced by forming the silicon oxynitride film on the surfaces of the bell jar 207 and the base plate 102 was prepared without forming the silicon oxynitride film on the surface of the base plate 102. Compared to the case, it was greatly reduced. Therefore, it was found that the silicon oxynitride film formed on the surface of the quartz glass base plate 102 sufficiently functions as a barrier for preventing metal impurity contamination including heavy metals.

Next, a large number of crystalline silicon particles 101 having a boron concentration of 1 × 10 ¹⁶ atoms / cm ³ and an average particle diameter of about 500 μm are placed on a base plate 102 made of quartz glass, and these are heated in a heating furnace. A reaction gas of oxygen gas and nitrogen gas was introduced from a gas supply means 204 into a bell jar 207 made of quartz glass installed in an atmosphere baking furnace filled with an argon inert gas atmosphere as 201, and heated. Then, after heating to 1450 ° C. above the melting point of silicon and holding for 5 minutes to melt the silicon inside the silicon oxynitride film on the surface, the solidification starting point (one pole) 103 is cooled while cooling at a predetermined temperature drop rate. And solidified toward the other pole 104. Thereafter, the temperature was further lowered to 1300 ° C., and thermal annealing was performed for 200 minutes while introducing an argon inert gas. After this thermal annealing, the temperature was lowered to near room temperature to produce crystalline silicon particles 101.

At this time, the partial pressure with respect to the total gas flow rates of the oxygen gas and the nitrogen gas in the heating furnace 201 when forming the silicon oxynitride film on the surface of the crystalline silicon particles 101 is 15% and 85%, respectively. The temperature drop rate was adjusted by measuring the temperature in the furnace with a thermocouple installed near the base plate 102 and controlling the input power to the heating element 202. .
Next, the silicon oxynitride film formed on the surface of the recovered crystalline silicon particles 101 is removed with hydrofluoric acid, and the surface of the crystalline silicon particles 101 is deepened with hydrofluoric acid to a predetermined thickness (20 μm). Etching was removed.
The crystalline silicon particles 101 are placed on a quartz boat, introduced into a quartz tube whose temperature is controlled at 900 ° C., POCl ₃ gas is bubbled with nitrogen and fed into the quartz tube, and crystallized in 30 minutes by a thermal diffusion method. An n-type semiconductor layer 410 having a thickness of about 1 μm was formed on the surface of the silicon particle 101 (406), and then the surface oxynitride film was removed with hydrofluoric acid.

  Next, as shown in FIG. 3, an aluminum substrate having a size of 50 mm × 50 mm × thickness 0.3 mm is used as the conductive substrate 407, and crystalline silicon particles 406 are disposed on the upper surface in a close-packed manner, and then aluminum, silicon, The lower part of the crystalline silicon particles 406 was bonded to the conductive substrate 407 by heating in a reducing atmosphere furnace of nitrogen containing 5% by volume of hydrogen at 600 ° C. exceeding 577 ° C. which is the eutectic temperature of . At this time, a bonding layer 408 made of a eutectic of aluminum and silicon was formed in the portion where the crystalline silicon particles 406 were in contact with aluminum of the conductive substrate 407, and exhibited strong adhesive strength.

Further, from above, the upper portions of the crystalline silicon particles 406 are exposed to each other, and an insulating material 409 made of polyimide is applied and dried to form a conductive substrate 407 serving as a lower electrode, and a light-transmitting conductive layer serving as an upper electrode. 411 is electrically insulated and separated.
A translucent conductor layer 411 as an upper electrode film was formed on the entire surface with a thickness of about 100 nm by sputtering.
Finally, silver paste was patterned in a grid shape with a dispenser to form an electrode 412 composed of finger electrodes and bus bar electrodes. The silver paste pattern was fired at 500 ° C. in the atmosphere.

表１に示す通り、酸素濃度がほぼ均一であった本発明の範囲外の結晶シリコン粒子４０６で形成された光電変換装置（試料Ｎｏ．８，９）に比較して、本発明の範囲内で作製した結晶シリコン粒子４０６中の酸素に一方の極１０３から対向する極１０４に向かって濃度勾配が形成されている場合の光電変換装置（試料Ｎｏ.１〜７）においては、いずれも本発明の範囲外のものに比べて光電変換効率が高く良好な結果であった。また、結晶シリコン粒子４０６内部の酸素濃度の濃度比と光電変換効率の値から、本発明の範囲内における光電変換装置は、結晶シリコン粒子４０６内部の酸素濃度の濃度分布は最高濃度が最低濃度の１．１〜１．５倍の範囲にある場合において、特に光電変換効率が高く電気特性に優れているものとなっている。
なお、本発明は以上の実施の形態の例に限定されるものではなく、本発明の要旨を逸脱しない範囲で種々の変更を加えることは何ら差し支えない。 In the manufacture of the photoelectric conversion device described above, the initial concentration of oxygen and the temperature lowering rate were set to the values shown in Table 1, so that the concentration distribution of oxygen was changed, so that the sample No. 1 to 9 crystalline silicon particles 406 were produced, and a photoelectric conversion device was produced using them.
Sample No. obtained above. About the photoelectric conversion apparatus using the crystalline silicon particles 406 of 1-9, the photoelectric conversion efficiency (unit:%) which shows the electrical property of a photoelectric conversion apparatus was irradiated by irradiating the light of predetermined intensity and predetermined wavelength. The measurement of electrical characteristics was carried out by a method based on JIS C 8913 using a solar simulator (WACOM: WXS155S-10). The results are shown in Table 1.
Note that the oxygen concentration of the crystalline silicon particles 406 was subjected to cross-sectional analysis by SIMS (secondary ion mass spectrometry), and the measurement result (unit: atoms / cm ³ ) where the crystal silicon particle 406 settled to a constant concentration in a portion deeper than 1 μm from the outermost surface. )showed that. Here, the measurement result of the oxygen concentration is an average value of 10 crystalline silicon particles sampled for each sample.

As shown in Table 1, in comparison with the photoelectric conversion device (sample Nos. 8 and 9) formed of the crystalline silicon particles 406 outside the scope of the present invention in which the oxygen concentration was almost uniform, within the scope of the present invention. In the photoelectric conversion device (sample Nos. 1 to 7) in the case where a concentration gradient is formed from one electrode 103 to the opposite electrode 104 in the oxygen in the produced crystalline silicon particles 406, all of the present invention. The photoelectric conversion efficiency was high and good results compared to those outside the range. Further, from the concentration ratio of the oxygen concentration inside the crystalline silicon particle 406 and the value of the photoelectric conversion efficiency, the photoelectric conversion device within the scope of the present invention has the highest concentration in the concentration distribution of the oxygen concentration inside the crystalline silicon particle 406 as the lowest concentration. In the range of 1.1 to 1.5 times, the photoelectric conversion efficiency is particularly high and the electrical characteristics are excellent.
In addition, this invention is not limited to the example of the above embodiment, A various change may be added in the range which does not deviate from the summary of this invention.

It is a longitudinal cross-sectional view which shows the mode of the baseplate and semiconductor particle in an example of embodiment about the manufacturing method of the crystalline semiconductor particle which concerns on this invention. It is a longitudinal cross-sectional view which shows schematic structure of an example of embodiment of the manufacturing apparatus used for the manufacturing method of the crystalline semiconductor particle which concerns on this invention. It is a longitudinal cross-sectional view which shows an example of embodiment about the photoelectric conversion apparatus of this invention.

Explanation of symbols

101: Semiconductor particles or crystalline semiconductor particles (silicon particles or crystalline silicon particles)
102 ... Base plate 103 ... Starting point of solidification (one pole)
104 ... the other electrode 105 ... an arrow indicating the solidification (crystallization) direction 201 ... a heating furnace 202 ... a heating element 203 ... a furnace material (heat insulating material)
204 ... Gas supply means 205 ... Gas filter 206 ... Temperature measurement means 207 ... Belger 208 ... Base plate 406 ... Crystalline silicon particle 407 ... Conductive substrate 408 ... Joining Layer 409 ... Insulating material 410 ... Semiconductor layer 411 ... Translucent conductor layer 412 ... Electrode

Claims (5)

  On the top surface, a base plate on which semiconductor particles containing oxygen are placed is introduced into a heating furnace, and the semiconductor particles are heated and melted, and then the molten semiconductor particles are directed upward from the base plate side. A method for producing crystalline semiconductor particles, characterized by solidifying the crystalline semiconductor particles.   The semiconductor particles are silicon particles containing oxygen, and when the molten silicon particles are solidified upward from the base plate side, oxygen contained in the silicon particles is converted into oxygen contained in the silicon particles from the lower end to the upper end. 2. The method for producing crystalline semiconductor particles according to claim 1, wherein a concentration gradient is formed such that the concentration increases toward the surface.   A photoelectric conversion device in which a plurality of crystalline semiconductor particles exhibiting one conductivity type are provided on a substrate, an insulating material is provided between the crystalline semiconductor particles, and a semiconductor layer having a reverse conductivity type is provided on the crystalline semiconductor particles. In the photoelectric conversion device, the crystalline semiconductor particles contain oxygen, and a concentration gradient is formed in the crystalline semiconductor particles from one electrode to the opposite electrode to the oxygen.   4. The photoelectric conversion device according to claim 3, wherein the concentration gradient of oxygen in the crystalline semiconductor particles is such that the highest concentration is 1.1 to 6 times the lowest concentration. The photoelectric conversion device according to claim 3, wherein the crystalline semiconductor particles are crystalline silicon particles.

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