Apparatus for forming semiconductor crystals of essentially uniform diameter

In an apparatus for forming a single semiconductor crystal by pulling said crystal attached to a seed crystal from a melt volume and comprising a crucible formed of a dielectric material containing said melt volume, support means for said crucible, heating means, load-bearing rod means for holding said seed crystal and for imparting translational motion to said crystal attached to said seed crystal, and variable-speed motor means to drive said load-bearing rod means, the improvement comprising means to monitor and control the diameter of said crystal as it is formed, said means comprising crucible assembly circuit means to provide an electrical current through said seed crystal, crystal, melt volume and crucible thereby to generate a measured signal, said crucible serving as a variable resistance, the value of which varies with the level of said melt volume in it;

• means to provide a reference signal representative of a predetermined crystal diameter and formation rate;
• comparator means to determine the difference between said measured signal and said reference signal and to generate an operational signal which is a function of said difference;
• and means to transmit said operational signal to either said heating means or to said variable-speed motor means whereby the temperature of said molten mass or the rate of said translational motion is varied to maintain the diameter of said crystal essentially uniform throughout its formation.