Rapid Thermal Processor Modeling, Control, and Design for Temperature Uniformity

With the ability to perform heat cycles on a wafer quickly and within low thermal budgets, Rapid Thermal Processor (RTP) systems offer potential advantages over conventional furnaces. However, RTP’s have an inherent problem with wafer temperature uniformity which can cause process nonuniformity and wafer stress. In this work, a thermodynamic model of a wafer is used to form an understanding of the wafer heating problem. This model shows that an idealized heating flux density profile can maintain thermal uniformity at steady-state temperatures. This profile uniformly heats the wafer while counteracting the additional cooling at the wafer edge. However, this profile induces temperature nonuniformities during wafer temperature transients, such as overheating of the edge during temperature rises. Therefore, a dynamic flux-density profile is needed during temperature transients to ensure continuous temperature uniformity. The model is used to predict the steady-state and dynamic profiles required to process a wafer with complete temperature uniformity. The predicted profiles can be used to adapt an RTP chamber and control system to approach production of uniform wafers and also for the design of new systems. This paper will explain the theory of wafer heating, describe the dynamic profiles required for continuous uniformity, review the wafer model, show the result of an idealized profile for steady state and transients processing, and present a new control methodology to achieve uniform temperatures.