Silicon ingot casting: heat exchanger method. Multi-wire slicing: fixed abrasive slicing technique. Phase III. Quarterly progress report No. 4, July 1-September 30, 1979

Abstract

This contract is for casting silicon ingots by the Heat Exchanger Method (HEM) and slicing by multi-wire Fixed Abrasive Slicing Technique (FAST). Significant advancements have been made in the area of crystal casting. It has been demonstrated that nearly single crystal ingots can be cast with a single HEM solidification of upgraded metallurgical grade silicon. The impurities were rejected to the last material to freeze-near the wall of the crucible. The resistivity of the silicon after directional solidification by HEM was 0.1 to 0.2 ..cap omega..-cm. Macroscopic impurities, presumably SiC, did not break down the solid-liquid interface and, in some cases, caused only localised twin formation. This material may be used for making solar cells directly. The HEM process has been scaled up to solidify 22 cm x 22 cm square cross-section ingots weighing up to 10.5 kg. The 22 cm square cross-section ingot is nearly all single crystal material. For silicon slicing using FAST significant progress has been made in demonstrating high throughput of the slicer and extended life of the wires. Cutting rates exceeded 1986 goals by more than 40%. This has been achieved with the combination of high speeds of the slicer and improvement in the blade.more » Emphasis in the area of blade development has been with impregnation using CSI technology of impregnating diamonds only in the cutting edge.« less