Motorola Corporation

Lawrence D Mason

Donald R Clement

Carl A Helber

Joseph O Diehl

David R Veres

Carl A Germano

Apparatus for automatically controlling, by stationary optical means, the diameter of a crystal from seed to final taper in a Czochralski crystal pulling method is disclosed. The diameter control has a feed back loop including diameter sensing means which controls a motor for moving the pulled crystal up faster or slower. The diameter, at any value, is sensed by two closely adjacent photocells receiving radiation from spaced points on the solid-liquid interface and a voltage value corresponding to that diameter is developed. When a constant diameter is being maintained and the diameter increases, the magnitudes of the sensed radiation change and a difference signal voltage in one direction is generated causing the crystal pull rate to increase. When the diameter decreases the magnitudes of the sensed radiation change in the reverse and a difference signal voltage in the opposite direction is generated causing crystal pull rate to decrease. For causing the crystal to grow in diameter as desired an offset voltage according to a predetermined program is balanced against the photocell voltage error voltage of one pair of photocells and the resultant difference signal is used to control the pull speed so as to change the diameter accordingly. When the diameter has changed, for example, increased to a point where the liquid-solid interface has changed location sufficiently, the next set of photocells takes over to develop an error voltage. A further diameter related offset voltage is developed and balanced against the error voltage and the crystal is forced to continue to increase in diameter accordingly. The process continues until final diameter is reached.

Automatic crystal diameter control for growth of semiconductor crystals

A semiconductor crystal resistivity measuring station comprised of an enclosed automatically operated probe apparatus electrically connected to a remotely controlled power supply and an electronic computer for automatically executing precise electrical resistivity measurements, in consecutive increments along a single crystal length.

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Phoenix, AZ, United States of America

Lawrence D Mason