Abstract

A novel supervisory controller that incorporates both a procedural and a rule-based language and is capable of responding to asynchronous real-time sensor interrupts is presented. This supervisory controller has been used for automating the manual operations in GaAs crystal growth in a liquid-encapsulated-Czochralski- (LEC-) process-based puller from Cambridge Instruments (CI-358). The controller, referred to as the metacontroller (MC), executes plans to sequence the operations of crystal growth. Plans are structured English-like representations of scripts that operators follow to grow crystals. The metacontroller executes the plans by responding to asynchronous sensor data interrupts in realtime and issuing actuator commands to a real-time controller module. The notion of time is explicitly incorporated into the syntax of the language. The metacontroller has been successful in automating sections of the full crystal growth protocol for GaAs using the LEC apparatus. Two 4-in.-diameter boules have been grown from 8-kg charges using the system where plans have been implemented. Portions of the synthesis and meltback steps have been automated, and the seed-on step that requires the most manual operation is almost completely automated. >

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