Abstract An automated crystal pulling system utilizes a digital computer to control a Czochralski crystal puller. Crystal pull rate, crystal spin rate, crucible lift rate and crucible spin rate are monitored with tachometers, and the monitored signals are applied to controllers to control the respective motors and provide independent closed control loops, with each controller having a set point signal input from the computer. A sensor detects the output level of the radio frequency generator (induction heater) and applies a signal to a generator controller having a set point input from the computer, providing closed loop temperature control. A temperature control algorithm receives an input from a melt temperature sensor and calculates the set point to the generator controller. A diameter control algorithm receives an input from a crystal diameter sensor and calculates the set point to the crystal pull motor controller. A melt level control algorithm claculates the set point to the crucible lift motor controller to provide a constant melt level. An adaptive control algorithm adjusts melt temperature, via the temperature control algorithm, as required to maintain average pull rate within imposed limits. Crystal specifications are input to the computer via a card reader. Operators are required only to load the charge, read in the specification card, grow the crystal stem, initialize various procedures, and remove the crystal ingot and clean and reload the puller.
In a system for pulling single crystal ingots of predetermined diameter profile from a melt of material including a crystal puller of the type having heater means, means for pulling the crystal ingot from said melt as said crystal solidifies, means controlling the pull rate of said means for pulling, crystal diameter sensor means, pull rate sensor means, and melt temperature sensor means, the combination comprising: a. means responsive to change in the output of said crystal diameter sensor means to cause said means controlling the pull rate to change the pull rate of said crystal pulling means; and b. means responsive to said melt temperature sensor, said pull rate sensor, and said crystal diameter sensor to change the power input level to said heater means thereby to adjust said melt temperature and maintain the crystal pull rate within predetermined limits during the growth of said crystal ingots of predetermined diameter profile.
Claim 2
Dependent Claim
152 words
In a system for pulling single crystal ingots of predetermined diameter profile from a melt of material including a crystal puller of the type having heater means, means for pulling the crystal ingot from said melt as said crystal solidifies, means controlling the pull rate of said means for pulling, crystal diameter sensor means, pull rate sensor means, and melt temperature sensor means, the combination comprising: a. means responsive to change in the output of said crystal diameter sensor means to cause said means controlling the pull rate to change the pull rate of said crystal pulling means; and b. means responsive to said melt temperature sensor, said pull rate sensor, and said crystal diameter sensor to change the power input level to said heater means thereby to adjust said melt temperature and maintain the crystal pull rate within predetermined limits during the growth of said crystal ingots of predetermined diameter profile.
Claim 3
Dependent Claim
34 words
The combination defined in claim 1 wherein said last-named means includes means determining the average pull rate of said crystal pulling means and means maintaining the average pull rate at a previously determined value.