Programmable thermal processing module for semiconductor substrates

This paper proposes the use of multivariable control methods to design a thermal platform for processing semiconductor substrates (semiconductor wafers and/or quartz reticles for photomasks) that far exceeds conventional methods in performance and flexibility. A thermal processing module for lithography applications is presented and demonstrated. The module comprises numerous (49) small, disjoint, and independently controlled heating elements capable of precise substrate spatial temperature control. The module also has a low thermal mass that allows for rapid element temperature variation, and hence transient control of substrate temperature. In addition, the module integrates active baking and chilling in a single unit, eliminating the need for substrate transfer between separate baking and chilling units and the temperature control limitations associated with it. The module is compared to a current state-of-the-art commercial system and shown to provide a factor of two improvement in transient temperature uniformity control on a six in quartz reticle using "hand-tuned" control techniques. A linear-quadratic regulator (LQR) feedback controller is also demonstrated and shown to provide peak-to-peak reticle temperature uniformity that does not exceed 1.6°C throughout the transient bake.