|M.Sc Student||Dassau Eyal|
|Subject||Feedback Control of Rapid Thermal Processing (RTP)|
|Department||Department of Chemical Engineering||Supervisor||Professor Daniel Lewin|
In the past few years, Rapid Thermal
Processes (RTP) have gained acceptance as mainstream technology for semi-conductor
manufacturing. In RTP, the main control problem is that of temperature. In work
carried out in cooperation with Steag CVD Systems, we developed algorithms for
steady state and dynamic temperature uniformity, designed to ensure uniform
temperature in RTP equipment. The steady-state algorithm involves the reverse
engineering of the required power distribution, given a history of past
distributions and the resulting temperature profile. The algorithm for dynamic
temperature uniformity involves the development of a first-principles model of
the RTP chamber and wafer, its calibration using experimental data, and the use
of the model to develop a controller. Two distinct solutions are
presented in this work:
The first one involves the uniformity algorithm and an IMC-tuned PI controller. It utilizes the uniformity algorithm to set distinct zone ratios for the process region and for the ramp stage, with set point tracking achieved by the PI controller that brings the wafer center point to the set point temperature. By using different zone ratios, the overall temperature uniformity is kept at ± 2 ºC of the set point.
The second solution involves non-linear model predictive control (NMPC) based on genetic programming (GP). The strength of this approach is that the same set of tuning parameters can control the RTP system at a range of operating temperature set points with a very short rise time to the set point and a uniform temperature profile. Although we have experienced overshoot, it has been observed only for a few seconds and the set point was maintained accurately.
The two approaches have great potential for resolving real engineering problems associated with RTP. Together, they provide a RTP control package that represents the state-of-the-art.