JPS603001B2 - Method for manufacturing ribbon-shaped silicon crystals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for easily and easily obtaining ribbon-shaped silicon crystals having a specific orientation.

As fossil fuel resources become increasingly depleted and prices soar, the use of solar energy becomes increasingly important. The idea of using solar cells as an energy moat has been around for a long time.
However, because it is more expensive than conventional power generation methods, its range of use has been limited until now, and its use as a general-purpose energy source remained a mere idea.
Whether solar cells can help save the energy crisis depends entirely on lowering costs. 0
In the case of silicon solar cells, it is important to note that approximately 30% of the price is due to the silicon used alone.

A prerequisite for the economical use of solar energy is a significant reduction in the cost of semiconductor materials, as well as a reduction in the costs required for processing them into solar cells. Silicon wafers, which are commonly used in solar cells, are obtained by carefully manufacturing single-crystal rods from high-purity silicon raw materials and cutting them into thin sheets with a diamond saw.

To increase the efficiency of solar cells, silicon single crystals must be as perfect as possible. That is, there should be no point defects, dislocation, twinning, stacking faults, or chemical impurities. Approximately half of the silicon single crystal rod carefully obtained in this way is lost as shoulders during cutting with a diamond saw. Although various proposals have been made to reduce the manufacturing cost of silicon solar cells, there is currently no satisfactory method. Tyco Laboratories (Tyco Laboratories)
EFG (Ed group DefinedFilmFedGro
The method uses capillarity to pull up ribbon-shaped single crystal silicon. Although this method has the advantage of not requiring wafer cutting and can use all of the obtained ribbon crystals, it still leaves complicated manufacturing conditions and operational methods due to the limitation of manufacturing single crystals. The use of polycrystalline silicon instead of single crystal is particularly advantageous from a cost standpoint. It is said that solar cells made of polycrystalline silicon usually have an efficiency of only about 1%, which is economically disadvantageous.
s) April 4, 1974, page 109). However, solar cells using polycrystalline silicon wafers, which do not have grain boundaries in the direction perpendicular to the wafer surface and have a structure in which oriented columnar microcrystals are assembled, have excellent photoelectric conversion efficiency. It has been reported [P. H. Huang et al., Applied Physics Letters,
Volume 25, November 1974, page 583 (P.
angeGI Applied Physics Le
ratiors, Vol. 25Novem is rl974, plaque 3
)reference〕. In this case, the oriented polycrystal is obtained by depositing silicon on an aluminum substrate heated to about 500 qo. This method is not necessarily suitable for mass production. The purpose of the present invention is to inexpensively produce polycrystalline silicon wafers that do not have grain boundaries in the direction perpendicular to the wafer surface and have a structure in which oriented columnar microcrystals are assembled and are suitable as substrate materials for solar cells. , and to provide a manufacturing method for mass production. In the present invention, a heat-resistant tube having an elongated orifice nozzle at the tip is opposed to a predetermined position on the inner surface of a rotating hollow drum that is set at a predetermined temperature and rotates at high speed, and the nozzle is moved along the inner wall at a constant speed in the drum axis direction. A ribbon-shaped silicon crystal is produced by simultaneously moving heated and melted silicon metal by jetting it at a predetermined flow rate from a nozzle, bringing the molten silicon metal into contact with the inner surface of the rotating drum, and solidifying it with a temperature gradient. shall be. The present invention will be explained below by way of examples using drawings.
do.

The drawings are diagrams showing an example of an apparatus used to implement the present invention. A heat-resistant tube 2 made of a heat-resistant material such as a quartz tube and having an elongated orifice nozzle 1 at its tip has a crucible 3 made of a heat-resistant material such as quartz on which raw material silicon is melted.
The nozzle is gradually and smoothly bent from the main body of the heat-resistant tube 2, and is gradually tapered toward the tip.
．． It has an ejection port with a length of 1 to 1 arc and a length of 2 to 4 arcs. Since the heat-resistant tube 2 having the nozzle 1 with an elongated orifice at the tip is used in this manner, the jet of molten silicon ejected from the heat-resistant tube 2 can be maintained as an uninterrupted, elongated steady stream.
Incidentally, the groove 3 is filled with a silicon melt 5 melted by a resistor heating device 4 or an inductive heating device 4. In addition, a high-purity inert gas such as Artagon gas is fed into the upper part of the crucible 3 through a connector 6, and this gas prevents oxidation of the silicon during heating and melting, and also controls the inflow pressure of the inert gas. For example, the amount of silicone liquid 5 spouted from the nozzle 1 is adjusted by adjusting it using a cock 8 provided on another connector 7. 0
The heat-resistant tube 2 and Lupo 3 system as a whole is driven by a drive device 9.
You can move up and down (in the direction of the arrow) by using

On the other hand, the rotating hollow drum 10 is rotated at high speed by a motor 11. In order to minimize the centrifugal force load due to rotation, the rotating hollow drum 10 is a hollow cylinder made of a metal that is lightweight and has good thermal conductivity, such as aluminum, and the inner surface of the drum is preferably coated with silicone brood liquid. It is lined with a material 12 that does not melt and preferably does not cause wetting of the silicon melt. Silicon nitride or graphite is preferably used as such a free material. Reference numeral 13 denotes a radiation heating device for heating the inner surface of the drum and maintaining it at a temperature suitable for oriented crystallization.

The molten silicon is extruded through a nozzle by high-purity argon gas (for example, purity 99999 to 99.99999%) to a predetermined temperature, for example, a temperature of 800 qo or less,
More preferably, when it reaches the inner wall of a drum which is kept at 100 qo to 400 qo and rotates at high speed, for example, about 1000 to 500 pm, the molten silicon is brought into strong contact with the inner surface of the drum due to centrifugal force, so that the molten silicon is rapidly cooled and A large temperature gradient occurs in the thickness direction. Under such conditions, solidified or popped silicon exhibits a columnar structure consisting of single crystal regions arranged in the thickness direction. When spouting the silicone liquid, by moving the nozzle in the vertical direction along the inner wall, the molten silicon is constantly jetted onto the new inner surface of the drum, and ribbon-shaped crystals are continuously formed in a helical pattern along the circumference of the inner wall of the drum. can get. To obtain specifically doped silicon crystals, suitable doping agents such as boron, aluminum, gallium, indium or arsenic, antimony or phosphorous are added in the quartz rubbo. Even when such a melt is solidified, the doping agent is extremely homogeneously distributed in the silicon crystal without a concentration gradient in the in-plane direction or in the axial direction. As mentioned above, the crystals obtained by the method of the present invention are polycrystalline, and therefore there is no need for complex and careful setting of conditions or operation methods as in the case of producing a single crystal, and it is extremely simple and easy to produce the desired crystal. can do.

Furthermore, although the ribbon-shaped silicon crystal of the present invention is a polycrystalline substance, it has a structure in which single column-shaped microcrystals are arranged in the thickness direction, so that the lifetime of minority carriers generated by light impact is long. . In other words, since there are no grain boundaries in the thickness direction of the wafer, minority carriers are not trapped or scattered by grain boundaries and are efficiently collected at the electrodes, resulting in excellent light conversion efficiency and solar cells. Suitable as a substrate material. Therefore, it satisfies the previous requirement of producing solar cells at a significantly low cost. An example of manufacturing a solar cell substrate using the apparatus shown in the drawings will be described below.

High purity polycrystalline silicon doped with 2×1 and 5 boron atoms was heated to 150 psi and melted in a stone hollyhock crucible.

Next, the drum heated to about 300 qo was heated to about 100 pm.
The silicon melt was spouted from a nozzle having a spout in the shape of 0.2 x 20 bars, and the nozzle was moved upward. In this way, middle 2 enemies, thickness 0
．． I got a kite bond wafer of 1 skin and 20 lengths.

This crystal showed a columnar structure consisting of single crystal regions oriented in the thickness direction. To fabricate the solar fin pond, the surface layer of this crystal thin plate was removed by etching.

The efficiency of a solar cell manufactured from this silicon crystal thin plate by a known method was 8 to 10%. This value is at least equivalent to that of single-crystal materials that have been widely used until now, and
The cost of this solar cell is extremely low.

[Brief explanation of the drawing]

The drawing is a side cross-sectional view of the apparatus used to practice the invention. 1...Nozzle, 2...Heat-resistant tube, 3...
... Crucible, 10... Rotating drum.

Claims (1)

[Claims] 1. A heat-resistant tube having an elongated orifice nozzle at its tip is opposed to a predetermined position on the inner surface of a rotating hollow drum that is set at a predetermined temperature and rotates at high speed, and the nozzle is inserted along the inner wall of the drum toward the drum shaft. The ribbon-shaped silicone metal is moved at a constant speed in the direction and at the same time heated and melted silicon metal is jetted from a nozzle at a predetermined flow rate, and the molten silicon metal is brought into contact with the inner surface of the rotating drum and solidified with a temperature gradient. Method of manufacturing silicon crystals. 2. The ribbon-shaped ribbon according to claim 1, characterized in that a rotating drum is used, the inner wall of which is lined with a material that does not melt into the silicon melt or cause wetting of the silicon melt. Method of manufacturing silicon crystals. 3. A method for producing a ribbon-shaped silicon crystal according to claim 2, characterized in that silicon nitride or graphite is used as a material that does not dissolve in the silicon melt and does not cause wetting of the silicon melt. . 4. The method for producing ribbon-shaped silicon crystals according to claim 1, 2, or 3, wherein the temperature of the rotating drum is 100 to 400°C.