Thermal uniformity and stress minimization during rapid thermal processes

The practical development and implementation of rapid thermal processes will significantly influence the semiconductor fabrication industry. With the capability to perform heat cycles quickly and with low thermal budgets, rapid thermal processors have the potential to supplant conventional thermal systems in the years to come. Currently, rapid thermal processors are unable to match the thermal process uniformity produced in conventional convective-based systems. Using a thermal model to approximate the heating characteristics of silicon wafers, it is possible to determine the effects of time-varying intensity profiles on a wafer during a rapid thermal process. Interpretation of this model shows idealized intensity profiles can maintain thermal uniformity at steady-state temperatures. During thermal transients a dynamic continuously changing profile is required to maintain thermal uniformity. As a predictive tool, this analysis can be used to determine and evaluate dynamic uniformity producing intensity profiles before thermal transients occur within a process. This approach can reduce the accumulation of error during high temperature steps not only by providing thermal uniformity at steady states, but by reducing the initial nonuniformities produced by transitions. This paper will review the wafer model, show the results of an idealized profile for steady-state and transient temperatures, and explain the dynamic profiles required for continuous uniformity.<
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