JP5935021B2 - Method for producing silicon crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon crystal for a solar cell, and more specifically, a method for producing FZ single crystal silicon for a solar cell, which is limited to the purpose of using a FZ method single crystal for a solar cell among silicon crystals. About.

As a raw material for producing an FZ single crystal used as a substrate for a silicon solar cell, a Siemens method polycrystalline silicon rod is generally used.
For this reason, needles, dendritic, coral, and lump-like polycrystalline silicon produced by an inexpensive zinc reduction method can be used as a raw material for FZ single crystal production at low cost, in large quantities, and less There is a demand for technology that produces electricity.

  Silicon polychloride, which is generally mass-produced by the zinc reduction method of silicon tetrachloride, becomes a lifetime killer in product polycrystals by selecting the number of rectification stages and conditions in particular when purifying silicon tetrachloride as a raw material. Trace amounts of Fe and Ni-based impurities can be stably and easily controlled to the order of “−11” order or less.

  When manufacturing FZ single crystal silicon specialized for solar cells, the rod-like polycrystal used as the raw material is made into a uniform rod-like shape in a shorter time than polycrystalline silicon such as needle-like, dendritic, coral, and massive. The basic technology of molding into a material is required.

  In the production of FZ single crystals for solar cells, polycrystalline silicon generally mass-produced by the zinc reduction method of silicon tetrachloride is in the shape of needles, dendrites, corals, lumps, etc. Since it does not become a raw material, it must be densely molded into a rod-like shape efficiently and in a short time as much as possible. This also makes it possible to reduce the amount of impurities that become a lifetime killer from the melt-contacted portion to two digits or less of CZ single crystal silicon that is generally used at present.

  In order to form polycrystalline silicon such as needles, dendrites, corals, and lumps into silicon rods in as short a time as possible in the rod-shaped molding that is the raw material for producing FZ single crystals for solar cells, [Figure- 1] As shown in FIG. 1, vacuuming is performed with a quartz tube inserted into a silicon melt or a SiC tube impregnated with high-purity silicon (inner diameter 10 mmΦ to 30 mmΦ), and the suction speed is adjusted by adjusting the degree of vacuum. By controlling, it was possible to reduce the liquid contact time to one-hundredth or less during the production of CZ single crystal.

Set the heat ray (nichrome wire etc) or high frequency coil on the upper part of liquid contact part of suction pipe (≒ 100mm ~ 200mm) and adjust the coagulation time in the suction pipe by applying the output while adjusting the output (100kHz ~ 1MHz). I can do it. As a result, it became possible to produce a silicon polycrystalline rod equivalent to the Siemens method, which is dense and has no cracks.
The adjustment of the solidification time varies depending on the melting crucible diameter and casting rod diameter according to experience, but is about 20 to 70 seconds, and the penetration of the lifetime killer from the sucked tube material can be ignored.

  It is possible to produce a dense polycrystalline rod of 10 to 30 mmΦ from molten silicon by a high speed (> 1 mm / Sec) CZ pulling method and use it as a raw material for FZ single crystal production for the purpose of the present invention. The contact time requires 10 times or more that of the present invention, and this increases the chance of contamination of lifetime killer impurities.

The raw material for manufacturing FZ single crystal silicon for solar is a rod-like silicon polycrystal having an appropriate inner diameter of 10 to 30 mm as shown in “Japanese Patent Application No. 2011-260954”.
On the normal technical line, a rapid CZ single crystal rod (10 to 30 mmφ) suitable for manufacturing a solar FZ single crystal can also be used as the raw material polycrystalline rod.
However, one of the natural energies that is likely to be comparable to nuclear power generation and petroleum-based thermal power generation in the near future is solar power generation, and silicon bulk that includes technologies that can be realized quantitatively and cost-effectively. There is no doubt that it is a solar cell.

At present, the typical manufacturing method and product of semiconductor grade high-purity silicon are Siemens polycrystalline silicon, which accounts for about 95% of the world.
The current purity is generally referred to as “11-nine”, and the technology has been industrially established to the extent that other methods cannot be followed for high quality and mass productivity.
However, as shown in the previous section, in order for the silicon bulk solar cell to make a big leap forward in the near future, there is another possibility of a broader supply in terms of one-stage raw materials and a further cost improvement. Is required. This is a silicon bulk solar cell that is developed based on silicon polycrystals by the zinc reduction method that uses silicon tetrachloride as a raw material for further improvement of the power consumption unit related to production.

90% of solar cells that have made significant progress worldwide over the past few years are silicon bulk solar cells. Fortunately, silicon bulk solar cells that have been greatly improved during this period have their photoelectric conversion efficiency (P / N junction). In terms of general expression, the purity of the polycrystalline silicon used as the raw material is sufficient if the purity of the polycrystalline silicon used as the raw material is "6-nine" or higher. Even so, I have been continually pursuing the amount.
However, as the expectation of further power supply by solar cells increases, the demand of the global market has been strongly demanded to increase the energy conversion efficiency of the solar cells themselves.
For example, the solar conversion efficiency of current silicon bulk solar cells is the highest at 21% on a commercial basis module basis, and is reaching 24% in the next 2-3 years.
In this case, the polycrystal purity is “6-nine” → “8-nine”. As the purity increases, the conversion efficiency increases in terms of technology and industry. The commercial value of raw materials lacking in lot homogeneity such as reclaimed silicon has been remarkably lowered, and only so-called virgin silicon has entered an era in which it can be used as solar cell silicon.

  Instead of the Siemens method, which has been regarded as the world standard up to now, described in “0010”, the focus is on virgin polycrystals by the zinc reduction method, which is considered to be much lower in the cost of power consumption, silicon tetrachloride, etc. during production. The purity of the silicon polycrystalline material is “8-nine” → “10-nine” → “11-nine” and can be mass-produced.

However, the only drawback compared to the Siemens method of the zinc reduction method is that the shape of the product is needle-like, dendritic, coral-like, lump-like, etc., and as such is not a raw material for producing FZ single crystals.
The present invention is characterized in that this raw material is made into rod-like polycrystalline silicon equivalent to a product manufactured by the Siemens method, and contamination in the process is minimized, and mass production is possible at low cost.

Future solar cells must be able to compete in terms of nuclear power and fossil fuel energy and cost, and the development path has already been established for silicon bulk solar cells.
The process of photoelectric conversion efficiency 24% → 29% → 35% → 45% → 60% → 75% is already being steadily advanced by scholars and engineers related to solar cells in the world. Is on the base line.
In this case, 24% → 29% is likely to be achieved by the initial processing and technology on the CZ single crystal base line, but if the solar cell FZ single crystal can be produced at a cost close to that of the CZ single crystal, This will greatly contribute to the improvement of photoelectric conversion efficiency of solar cells in the future, and will probably become a favorite.

  The charged polycrystalline rod raw material for FZ single crystal production made by this method has one feature in electric heating or high-frequency heating control provided for slow cooling during casting, and subtle gradual control And enables effective production of cracked silicon casting rods.

  Silicon rod forming furnace   Silicon casting furnace

  This is shown in “Figure 2”.

Claims (3)

  Semiconductor grade transparent quartz or opaque quartz crucible is charged with acicular, dendritic, coral or massive high-purity polycrystalline silicon prepared by zinc reduction method, and the temperature is increased to 1420 ° C. or higher in an argon or helium atmosphere. A method of producing a silicon rod, which comprises rapidly melting and inserting a tube of the same material as the crucible having an inner diameter of 10 to 30 mmφ into the melt and sucking it up from the tip thereof in a vacuum.   Charge a semiconductor grade silicon carbide or silicon nitride crucible with acicular, dendritic, coral or lump high purity polycrystalline silicon made by the zinc reduction method to 1420 ° C or higher in an argon or helium atmosphere. A method of producing a silicon rod, which comprises rapidly melting and inserting a tube of the same material as the crucible having an inner diameter of 10 to 30 mmφ into the melt and sucking it up from the tip thereof in a vacuum.   The melting furnace has a continuous charge structure and is a silicon rod manufacturing method in which high-purity polycrystalline silicon raw material is charged, melted and sucked up as an integrated operation.