JP2005239452A - Ga COMPOUND-DOPED POLYCRYSTALLINE SILICON AND METHOD OF MANUFACTURING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a Ga compound-doped polycrystalline silicon, in which the accuracy of the measurement and the workability of Ga doping are improved and to provide the Ga compound-doped polycrystalline silicon hardly causing photo-degradation and having high conversion efficiency stably. <P>SOLUTION: A polycrystalline silicon is grown by doping a Ga compound which is solid at a temperature higher than the ordinary temperature. As a result, the accuracy and workability in weighing are improved compared to that in a conventional one. When the Ga compound-doped polycrystalline silicon is used for a solar cell, photo-degradation is hardly caused and high conversion efficiency is stably provided. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a Ga compound-doped polycrystalline silicon useful as a solar cell material and a method for producing the same.

  Solar cell materials can be broadly classified into “crystalline silicon”, “amorphous silicon”, and “compound semiconductor”, and “crystalline silicon” includes “single crystal silicon” and “polycrystalline silicon”. Among them, “amorphous silicon” has low conversion cost but low conversion efficiency representing solar cell performance of 6 to 8 (%), while “compound semiconductor” has high conversion efficiency of 20 to 25 (%). However, the material cost is high and it is difficult to reduce the cost. Furthermore, “single crystal silicon” has a conversion efficiency of 15-20 (%), which is the second highest after compound semiconductors. In order to obtain a solar cell substrate, the Czochralski method (CZ method) or the floating zone method ( It is necessary to process the columnar crystal obtained by the FZ method into a square substrate, and the cost of the substrate due to the low material yield is a problem.

  Finally, “polycrystalline silicon”, the current mainstream manufacturing method is melting and unidirectional solidification of silicon in a square crucible such as quartz, and the resulting crystal is square and single crystal silicon. Since such processing is unnecessary, the substrate cost is low and the conversion efficiency is relatively high at 12 to 17 (%).

  However, the ratio of the substrate cost to the polycrystalline silicon solar cell is currently as high as about 40%, and further reduction of the substrate cost is required. In order to reduce the cost of a polycrystalline silicon solar cell, it is required to reduce the substrate cost while increasing its conversion efficiency to that of a single crystal silicon solar cell. Furthermore, in a crystalline silicon solar cell, when sunlight is irradiated, a phenomenon of a decrease in conversion efficiency accompanying a decrease in substrate lifetime occurs, and there is a problem that a stable solar cell cannot be obtained.

  When the crystalline silicon solar cell is irradiated with sunlight, the lifetime of the substrate is reduced, and the reason why the conversion efficiency is reduced due to photodegradation is that B (boron) and oxygen present in the substrate form a composite by light irradiation. It is thought that it becomes a carrier recombination center. At present, the P-type is the main type of crystalline silicon substrate for solar cells, and since B (boron) is usually doped, photodegradation occurs.

In order to solve such problems, a manufacturing method in which Ga (gallium) is doped instead of B (boron) as a P-type dopant has been proposed in Patent Document 1, which makes it difficult to cause photodegradation and is high. It is described that a polycrystalline silicon solar cell having conversion efficiency was obtained.
JP 2001-64007 A

  However, the melting point of Ga is as low as 30 ° C., and it is necessary to handle liquid Ga for weighing and dope operations. In the liquid, it is difficult not only to adjust the trace amount Ga concentration with high accuracy, but also to decrease workability.

  The present invention has been made in view of such problems, a Ga compound-doped polycrystalline silicon manufacturing method with improved Ga-doping measurement accuracy and workability, and a high conversion efficiency that hardly causes photodegradation. It aims at providing Ga compound dope polycrystalline silicon from which can be obtained stably.

The method for producing a Ga compound-doped polycrystalline silicon according to the present invention is to grow by doping a Ga compound that is solid at room temperature or higher. In the present invention, the Ga compound is Ga ₂ O ₃ (gallium oxide). In the present invention, crystals are grown so that the Ga concentration in the polycrystalline silicon is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ).

The Ga compound doped polycrystalline silicon according to the present invention is grown by doping a Ga compound that is solid at room temperature or higher. In the present invention, the Ga compound is Ga ₂ O ₃ (gallium oxide). In the present invention, crystals are grown so that the Ga concentration in the polycrystalline silicon is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ).

The Ga compound-doped polycrystalline silicon production method of the present invention uses a Ga compound that is solid at room temperature, so that it is much more accurate when weighed than conventional liquid metal Ga having a low melting point (30 ° C.). And workability can be improved. Furthermore, since it is a Ga compound, the dope weight is increased by increasing the formula weight as compared with the metal Ga simple substance, and an improvement in weighing accuracy is also obtained. Since Ga ₂ O ₃ (gallium oxide) is used as the Ga compound, it can be obtained with high purity and low cost. By performing crystal growth so that the Ga concentration is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ), the conversion efficiency of the battery cell can be stabilized.

  If the Ga compound-doped polycrystalline silicon of the present invention is used as a solar cell material, it is possible to prevent the occurrence of a decrease in the substrate lifetime due to the oxygen and the carrier recombination center caused by the complex due to the light irradiation generated in the B doping, and the photodegradation This makes it possible to manufacture a solar cell in which high conversion efficiency is stably obtained.

Hereinafter, embodiments of the present invention will be described in detail. First, FIG. 1 shows a configuration example of a polycrystalline silicon manufacturing apparatus using a unidirectional solidification method used in the present invention. The polycrystalline silicon manufacturing apparatus includes a furnace chamber 1, a quartz crucible 2 for melting and crystal growth of raw material silicon in the center of the chamber 1, and the quartz crucible 2 accommodated therein and the quartz crucible 2 is damaged. A carbon crucible 3 that plays a role in preventing silicon leakage in the case of carbon dioxide, a carbon heater 4 for melting raw material silicon in the quartz crucible 2, a carbon heat insulating material 5 for preventing the radiant heat from the heater 4 from escaping to the outside, It has a carbon base 6 that holds the carbon crucible 3 and a crucible support shaft 7 that supports the carbon base 6 and that can move up and down and is water-cooled. An exhaust port 8 and a gas supply port 9 are formed in the chamber 1. The chamber 1 is evacuated from the exhaust port 8, and an inert gas such as Ar gas is purged and flowed into the chamber 1 from the gas supply port 9. Let The inner surface of the quartz crucible 2 is coated and baked with a Si ₃ N ₄ release agent. This release agent coating / baking is intended to suppress the reaction between the polycrystalline silicon generated in the quartz crucible 2 and the quartz crucible so that the polycrystalline silicon ingot can be easily taken out from the quartz crucible 2. .

Next, a method for producing polycrystalline silicon using the above apparatus will be described. First, raw material silicon and a Ga compound as a dopant are placed in the quartz crucible 2, the inside of the furnace (chamber 1) is evacuated, and Ar gas is injected. Thereafter, the quartz crucible 2 is heated by the heater 4 to dissolve the raw material silicon. In addition, as a Ga compound, the accuracy and workability | operativity at the time of weighing can be improved remarkably rather than 30 degreeC and low melting point liquid metal Ga by using a Ga compound which is solid at normal temperature or more. Furthermore, if Ga ₂ O ₃ (gallium oxide) is used as the Ga compound, it is easy to obtain with high purity and low cost.

  Next, when the raw material silicon is melted, the quartz crucible 2 is pulled down from the heating region formed by the heater 4 at a speed of 0.1 to 1 (mm / min) to be cooled and solidified, whereby columnar polycrystals are formed in the quartz crucible 2. Silicon is grown. When the molten silicon in the quartz crucible 2 is completely crystallized to the upper part, the temperature in the furnace starts to drop and is cooled to a temperature at which the polycrystalline silicon ingot can be taken out.

Examples of the present invention will be specifically described below, but the present invention is not limited to these. A polycrystalline silicon manufacturing apparatus as shown in FIG. 1 is used, and ₄ kg of raw silicon and 0.26 g of Ga ₂ O ₃ dopant are added in a quartz crucible 2 having an inner surface coated with a Si ₃ N ₄ release agent (Ga is 0.26 g of 70%) is set, and after melting the raw material silicon and Ga ₂ O dopant by the heater 4, the quartz crucible 2 is pulled down from the heating region at a rate of 0.2 (mm / min) to be cooled and solidified. Columnar polycrystalline silicon was grown. The silicon substrate is cut out from the central portion of the polycrystalline silicon ingot thus obtained in parallel with the crystal direction in which the columnar crystals are developed, and after processing distortion on the surface is removed by acid etching, the resistivity and lifetime of the substrate are removed. Measurements were made. The resistivity of the Ga compound-doped polycrystalline silicon substrate according to the present invention is shown in FIG. 2, and its lifetime is shown in FIG.

Next, a comparative example using conventional liquid Ga is shown.
Using the polycrystalline silicon manufacturing apparatus as shown in Comparative Example 1, the raw material silicon 4Kg and metal Ga dopant 0.18g in Si ₃ N ₄ release agent in the coated quartz crucible 2 to the inner surface The raw material silicon and the metal Ga dopant are dissolved by the heater 4. Thereafter, the quartz crucible 2 was pulled down from the heating region at a rate of 0.2 (mm / min) to be cooled and solidified to grow columnar polycrystalline silicon. The silicon substrate is cut out from the central portion of the polycrystalline silicon ingot thus obtained in parallel with the crystal direction in which the columnar crystals are developed, and after processing distortion on the surface is removed by acid etching, the resistivity and lifetime of the substrate are removed. Measurements were made. The resistivity of a silicon substrate produced using liquid Ga is shown in FIG. 4, and its lifetime is shown in FIG.

  FIG. 2 which is the resistivity of the Ga compound doped polycrystalline silicon according to the present invention is compared with FIG. 4 which is the resistivity of the conventional liquid Ga doped polycrystalline silicon. In the resistivity (FIG. 2) of the silicon of the present invention, the region of 1.5 to 1.7 Ω-cm is almost all, whereas in the resistivity (FIG. 4) of silicon generated from the conventional one, 1. A 5-1.7 Ω-cm region and a 1.7-1.9 Ω-cm region are mixed. From these figures, it can be seen that the silicon of the present invention, in which most regions are uniform, has little variation in low efficiency. Therefore, if the Ga compound-doped polycrystalline silicon according to the present invention is used for a solar cell, photodegradation hardly occurs and high conversion efficiency can be stably obtained.

  FIG. 3 showing the lifetime of the Ga compound-doped polycrystalline silicon according to the present invention is compared with FIG. 5 showing the lifetime of the conventional liquid Ga-doped polycrystalline silicon. In the silicon of the present invention (FIG. 3), the region of 15-20 μS or more occupies most of the central portion between 19-104 mm on the horizontal axis and 16-100 mm on the vertical axis, whereas conventional silicon (FIG. 3). In 5), the region of 15-20 μS or more occupies only about half between 18-92 mm on the horizontal axis and 23-97 mm on the vertical axis. Furthermore, in the silicon according to the present invention (FIG. 3), many regions of 20-25 μS are scattered in a region between 31-99 mm on the horizontal axis and 18-97 mm on the vertical axis, whereas conventional silicon ( In FIG. 5), there are only three regions of 20-25 μS between 20-80 mm on the horizontal axis and 28-87 mm on the vertical axis. From this, it can be seen that the Ga compound-doped polycrystalline silicon according to the present invention has a longer lifetime than conventional silicon and is less susceptible to photodegradation.

  In the present invention, a Ga compound that is solid at room temperature is used as a P-type dopant for growing polycrystalline silicon. As a result, the accuracy and workability at the time of weighing can be remarkably improved as compared with the conventional case using liquid metal Ga having a low melting point of 30 ° C. In the present invention, since the Ga compound is used, the dope weight is increased by increasing the formula weight as compared with the metal Ga simple substance, and the weighing accuracy can be improved.

As Ga compounds, many organic and inorganic Ga compounds are conceivable. However, in organic Ga compounds, there is a risk that the lifetime of the substrate may be reduced due to contamination of C (carbon), which is a component element, into the polycrystalline silicon. , Its use is not preferred. Furthermore, as an inorganic Ga compound, there are many oxides, chlorides, sulfides, etc. Among them, there is a track record as an oxide single crystal material such as GGG, and Ga ₂ which is available with high purity and low cost. The use of O ₃ (gallium oxide) is preferred.

When the Ga concentration is smaller than 3 × 10 ¹⁵ (atoms / cm ³ ), the resistivity of the polycrystalline silicon substrate becomes too high, and the power loss due to the internal resistance in the case of a solar cell increases, resulting in a decrease in conversion efficiency. Occurs. On the other hand, even when the Ga concentration is higher than 2 × 10 ¹⁷ (atoms / cm ³ ), the conversion efficiency is reduced due to the reduction in the substrate lifetime due to Auger recombination inside the substrate. Therefore, it is preferable to carry out crystal growth so that the Ga concentration is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ) where the conversion efficiency of the solar battery cell is stable.

  If the Ga compound polycrystalline silicon according to the present invention is used as a solar cell material, it is possible to prevent the occurrence of reduction in substrate lifetime due to oxygen and the carrier recombination center caused by the complex due to the light irradiation generated in the B doping, and the photodegradation. This makes it possible to manufacture a solar cell in which high conversion efficiency is stably obtained.

It is a block diagram of the manufacturing apparatus for manufacturing Ga compound dope polycrystalline silicon which concerns on this invention. It is a characteristic view which shows the resistance ratio of Ga compound dope polycrystalline silicon concerning the present invention. It is a characteristic view which shows the lifetime of Ga compound dope polycrystalline silicon which concerns on this invention. It is a characteristic view which shows the resistance ratio of the conventional Ga polycrystalline silicon. It is a characteristic view which shows the lifetime of the conventional Ga polycrystalline silicon.

Explanation of symbols

1 Chamber 2 Quartz crucible 3 Carbon crucible 4 Carbon heater 5 Carbon insulation 6 Carbon base 7 Crucible support shaft

Claims (6)

  A method for producing polycrystalline silicon, comprising: doping a Ga compound that is solid at room temperature or higher to grow polycrystalline silicon. The method for producing a Ga compound-doped polycrystalline silicon according to claim 1, wherein Ga ₂ O ₃ (gallium oxide) is used as the Ga compound. 3. The Ga crystal according to claim 1, wherein the crystal is grown so that a Ga concentration in the polycrystalline silicon is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ). A method for producing compound-doped silicon.   A Ga compound-doped polycrystalline silicon grown by doping a Ga compound that is solid at room temperature or higher. The Ga compound-doped polycrystalline silicon according to claim 4, wherein the Ga compound is Ga ₂ O ₃ (gallium oxide). 6. The Ga according to claim 4, wherein the crystal is grown so that a Ga concentration in the polycrystalline silicon is 3 × 10 ¹⁵ (atoms / cm ³ ) to 2 × 10 ¹⁷ (atoms / cm ³ ). Compound doped silicon.

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