Methods and apparatus for zone melting

Claim 1

IN A METHOD OF ZONE MELTING A ROD OF SEMICONDUCTOR MATERIAL IN WHICH THE ROD IS VERTICALLY SUPPORTED AT BOTH ENDS AND A TRANSVERSE MOLTEN ZONE IS FORMED IN SAID ROD INTERMEDIATE THE TWO ENDS THEREOF, SAID MOLTEN ZONE BEING CAUSED TO MOVE RELATIVE TO SAID ROD ALONG THE LONGITUDINAL AXIS THEREOF SO THAT IT IS BOUNDED AT ONE EXTREMITY BY A TRANSVERSE INTERFACE OF MELTING AND AT THE OTHER EXTREMITY BY A TRANSVERSE INTERFACE OF RESOLIDIFICATION, AND IN WHICH THE DIAMETER OF THE ROD BEING SOLIDIFIED FROM SAID MOLTEN ZONE IS CONTROLLED BY MOVEMENT RELATIVE TO EACH OTHER OF THE SOLID PORTIONS OF SAID ROD ON EITHER SIDE OF SAID MOLTEN ZONE, THE IMPROVEMENT WHICH COMPRISES CONTINUALLY DETECTING VARIATIONS IN THE DISTANCE BETWEEN AT LEAST ONE POINT ON SIAD INTERFACE OF RESOLIDIFICATION AND AN ARBITRARILY SELECTED REFERENCE PLANE PASSING TRANSVERSELY THROUGH THE LONGITUDINAL AXIS OF SAID ROD AND MOVING RELATIVE TO SAID ROD ALONG SAID LONGITUDINAL AXIS AT A UNIFORM RATE EQUAL TO THE MEAN RATE OF MOVEMENT OF SAID MOLTEN ZONE RELATIVE TO SAID ROD, AND MOVING THE SOLID PORTIONS OF SAID ROD ON EITHER SIDE OF SAID MOLTEN ZONE RELATIVE TO EACH OTHER IN RESPONSE TO CHANGES IN SAID DISTANCE TO THEREBY PRODUCE BY SOLIDIFICATION OF SAID MOLTEN ZONE.