Model-based control of a high-temperature crystal growth process

This paper describes a modeling and control approach for the thermal aspects of a high-temperature semiconductor crystal growth process. From a thermal perspective, each crystal growth cycle is composed of three distinct phases, heat up, growth, and cool down, each with specific control challenges and objectives. This paper focuses on the heat up and growth phases. A simulation model is first developed based on the induction furnace geometry and known material properties. This model is calibrated using the experimental process data by minimizing the weighted error between the predicted and actual temperature measurements. The two critical temperatures for the process are the temperature of the source material and the temperature of the crystal seed. For the heat up phase, the input profile is generated to rapidly ramp up the source and crystal temperature while avoiding damaging temperature spikes. In the crystal growth phase, the objective is to maintain the source temperature above sublimation while keeping the crystal temperature sufficiently low to allow condensation. These temperatures cannot be directly measured. Instead, an observer-based controller achieves the temperature control objective. Simulation results with FEM-in-the-loop validation are presented.