Texas Instruments Corporation

David E Witter

Mohendra S Bawa

Jules D Levine

Graydon B Larrabee

Eva A Ziem

Liquid silicon is deposited on a high surface area column of silicon nitride particles, by hydrogen decomposition of trichlorosilane. This is accomplished in an environment heated to a temperature in excess of the melting point of silicon. After deposition, the liquid silicon flows by gravity to a collection point. Preferably a liquid transfer system moves the silicon directly to a crystal pulling operation. The liquid transfer to immediate pulling conserves energy and allows for continual withdrawal of melt from the reactor. The immediate pulling provides additional purification and the crystal thus pulled is preferably used as feedstock for a final crystal pulling operation.

Deposition of silicon at temperatures above its melting point

In one embodiment of the present invention, silicon spheres are fabricated by applying a slurry of metallurgical grade silicon, or other suitable material, on the surface of a substrate capable of maintaining integrity beyond the melting point of silicon. The layer of metallurgical grade silicon is then patterned to provide regions of metallurgical grade silicon of uniform size. The substrate and metallurgical grade silicon are then heated beyond the melting point of silicon. The metallurgical grade silicon then beads to the surface as relatively pure silicon and forms silicon spheres due to the high cohesion of silicon. The structure is then cooled below the melting point of silicon and the silicon spheres then crystallize. The silicon spheres are then removed from the surface of the substrate and are further processed using techniques disclosed in copending U.S. patent application Ser. Nos. 647,551 and 647,578 to further purify the crystalline silicon spheres.

Process for producing crystalline silicon spheres

The disclosure relates to a method for producing single crystal silicon from a polycrystalline silicon melt wherein dopants such as oxygen and nitrogen are uniformly distributed in the crystal both along the crystal axis and radially therefrom. This is accomplished by identifying the correct species in the melt and above the melt and determining the thermochemical equilibrium between the two chemical species which lead to a change of the composition of the silicon single crystal during the entire growth process. This approach effectively circumvents the segregation coefficient during the growth process through the control of the concentration of the dopants in the melt.

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Richardson, TX, United States of America

David E Witter