Procedure for in-situ determination of thermal gradients at the crystal growth front

A semiconductor crystal growth apparatus comprising:

• a crucible to hold melt;
• a crystal pull unit disposed to pull a crystal from the crucible at a pull speed;
• a diameter measurement system to provide a diameter signal indicative of diameter of the crystal;
• a control system to control the crystal pull unit, the control system including
• a memory to store data and instructions;
• and
• a processor responsive to the stored data and instructions, the processor operative to provide to the crystal pull unit a nominal pull speed signal superimposed with a periodic pull speed signal of predetermined frequency, the processor further operative to estimate temperature gradients in the crystal and the melt based in part on response to the superimposed periodic pull speed signal.

A semiconductor crystal growth apparatus comprising:

• a crucible to hold melt;
• a crystal pull unit disposed to pull a crystal from the crucible at a pull speed;
• a diameter control system to generate control signals for the crystal pull unit to cause the crystal pull unit modulate the pull speed at which the crystal is pulled from the crystal by superimposing a periodic pull speed on an average speed, the average speed including a target pull speed plus a corrective speed;
• and
• a temperature gradient estimation system to estimate temperature gradients in the semiconductor crystal and the melt based in part on response to the superimposed periodic pull speed.