Design for control: Temperature uniformity in rapid thermal processor

Abstract

It is well known that the design of the heating source imposes an inherent limitation on the performance of the rapid thermal processor (RTP). In this work, the similarities and differences between flat and angled reflectors are studied. Thediscontinuous characteristic of the angled reflector can be used to compensate for the edge heat loss of the thin wafer and, consequently, a better temperature uniformity can be achieved. A design procedure is proposed to place the lamp ring as well as the angle of the reflectors. For the control system design, the measurement selection criterion of Huang et al. is employed to find candidate measurement sets followed by a structured singular value criterion. Once the control structure is determined, multivariable temperature controllers are designed according to the internal model control (IMC) principle. From process insight, a fairly simple nonlinear compensation is also devised. Simulation results show that, while only half of the thermal budget is used, improved temperature uniformity can be obtained by using the proposed approach.