Analysis of Energy-Efficient Multi-Heater Thermal Control for Semiconductor Vertical Furnaces
Fast, precise, and energy-efficient temperature control is essential for semiconductor vertical furnaces. In conventional configurations, a heater installed outside the process tube, referred to as the Main Heater, is relatively far from the temperature sensors near the wafers, resulting in slow thermal response and high energy consumption. To improve heat-transfer efficiency, this paper employs a heater installed inside the process tube, referred to as the Inside Heater, which is located close to the temperature sensors. However, since both the Main Heater and the Inside Heater act as heating actuators, their control inputs must be appropriately allocated while coordinating them with the Cooler. To address this issue, this paper proposes a three-actuator temperature control method based on virtual integrated heater-cooler control. The output of a single PID controller is separated by filters, assigning low-frequency heating components mainly to the Main Heater and high-frequency components to the Inside Heater. Switching logic is used to satisfy unilateral input constraints, i.e. the actuator inputs are constrained to be nonnegative, and suppress simultaneous heating and cooling. Experiments on a semiconductor vertical furnace show that the proposed method reduced energy consumption by 23.7% for a 390-400°C command compared with a Main Heater and Cooler method. These results demonstrate that the proposed filter-based task allocation efficiently utilizes the fast, low-power Inside Heater while retaining the heating capability of the Main Heater.