Concurrent Design of an RTP Chamber and Advanced Control System
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ABSTRACT A concurrent-engineering approach is applied to the development of an axisymmetric rapidthermal-processing (RTP) reactor and its associated temperature controller. Using a detailed finiteelement thermal model as a surrogate for actual hardware, we have developed and tested a multiinput multi-output (MIMO) controller. Closed-loop simulations are performed by linking the control algorithm with the finite-element code. Simulations show that good temperature uniformity is maintained on the wafer during both steady and transient conditions. A numerical study shows the effect of ramp rate, feedback gain, sensor placement, and wafer-emissivity patterns on system performance. INTRODUCTION Rapid thermal processing (RTP) is an emerging technology for some thermal manufacturing steps in integrated circuit fabrication process flows. The extent that existing methods (e.g., batch furnaces) will be displaced by single-wafer technology depends on the ability of RTP systems to accurately control wafer temperature during processing. The task of achieving uniform and repeatable temperature relies on design of the lamp housing and reaction chamber, the temperature control system, and the temperature sensors. For optimal performance, an integrated approach to equipment design, control-system design and sensor implementation is essential. Temperature control of RTP systems is a topic that has received considerable study over the past several years. Control strategies incorporating internal nonlinear physically based models [ 1,2] along with approaches using empirically derived linear models [3] have been demonstrated as feasible methods for meeting the performance requirements for single wafer processing. A common element in each of these approaches is that the control design relies upon experimental data obtained from the reactor to be controlled. By waiting until the reactor fabrication has been completed to begin control system design, the burden of achieving acceptable closed-loop behavior is placed entirely on the controller. The system closed-loop behavior, however, is dependent on both the hardware design and the controller design. It has been demonstrated that the design process for RTP control can proceed using detailed physically based models instead of hardware [4]. This eliminates the need for pre-existing hardware to begin controller development. By beginning the controller design while the reactor 347 Mat. Res. Soc. Symp. Proc. Vol. 389 0 1995 Materials Research Society
development is still in the conceptual stage, both control and hardware design parameters can be adjusted to optimize closed-loop performance. We have developed a nonlinear physically based finite-element thermal model of CVC Products' (CVC) RTP chamber that can be linked with arbitrary process control algorithms. This model has been applied to the concurrent development and optimization of both the hardware design and the advanced control system design for the CVC RTP chamber. A preliminary temperature controller was developed using system respo
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