Abstruct-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.

A first-principles approach to the modeling of a rapid thermal processing (RTP) system to obtain temperature uniformity is described. RTP systems are single wafer and typically have a hank of heating lamps which can he individually controlled. Temperature uniformity across a wafer is difficult to obtain in RTP systems. A temperature gradient exists outward from the center of the wafer due to cooling for a uniform heat flux density on the surface of the wafer from the lamps. Experiments have shown that the nonuniform temperature of a wafer in an RTP system can he counteracted by adjusting the relative power of the individual lamps which alters the heat flux density at the wafer. The model is comprised of two components. The first predicts a wafer's temperature profile given the individual lamp powers. The second determines the relative lamp power necessary to achieve uniform temperature over all but the outermost edge of the wafer (cooling at the edge is always present). The model has been verified experimentally by rapid thermal chemical vapor deposition (surfacelimited) of polycrystalline silicon with a prototype LEISK'" RTP system. The wafer temperature profile is inferred from the poly-Si thickness. Results showed a temperature uniformity of +1%, an average absolute temperature variation of 5.5"C, and a worst-case absolute temperature variation of 6 S " C for several wafers processed at different temperatures. A comparison at one temperature showed a 30°C variation when no optimization is used. computer Controller Optical fyrometer h Pressure water cooled Sensor Stainless Steel Tube Vlewpon 0 0 0 0 0 0 0 0 rn Thronle fl Rotary Exhaust

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' 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.

Adaptive extensions to a multibranch run-to-run controller for plasma etching Process reproducibility is a challenging problem in semiconductor manufacturing as the component size shrinks and the manufacturing complexity increases. This article proposes a new adaptive run-to-run controller for intermittent batch operations and applies it to a rapid thermal annealing ͑RTA͒ process at Advanced Micro Devices. The adaptive controller has a self-monitoring component and requires little process knowledge to set up. The success of the controller is demonstrated on an AST SHS 2800 RTA system. Improvement was made to reduce the first wafer effects and lot-to-lot variability due to disturbances.