Modeling, control, and temperature measurement in rapid thermal processing

The concept of Rapid Thermal Processing (RTP) has many potential applications in microelectronics manufacturing, but the details of chamber design, temperature dynamics, process control, and temperature measurement remain active areas of research. An RTP test bed was custom designed and installed in the SEMATECH cleanroom so that research could be conducted experimentally in these areas. It was shown that a more uniform light flux distribution can be achieved by passing the light through a kaleidoscope before it reaches the wafer. The design of a reflective enclosure for the wafer can also significantly affect its temperature distribution during processing. A novel lamp design using a homogenized light source above the wafer and a ring of lamps located around the periphery of the wafer produces a multizone system that is much more controllable than other types of RTP chambers discussed in the literature.;The temperature dynamics in RTP can be derived analytically with a few simplifying assumptions. Parameters for this model can be estimated from experimental data taken on any RTP chamber. While the model is highly non-linear in the Laplace domain, a discrete time formulation yields a model with nearly constant parameters. The model can be used to design a control system for physical equipment, and a model-based controller was implemented on the SEMATECH test bed. The choice of controlled variables and the input-output scaling affected the conditioning of the system. The performance of a multi-loop gain-scheduled PID controller together with decoupling blocks was sufficient to meet the requirements of the Semiconductor Industry Association for 0.35 ;Temperature measurement for control purposes was performed with thermocouples embedded in a silicon wafer; alternative temperature measurement techniques were discussed. Experiments were conducted with a pyrometric technique which attempted to use the heat lamp "ripple" to measure the wafer reflectivity and to compensate the wafer radiance measurement for heat lamp interference. Experiments measuring the time constants of the heat lamp filament and the power circuit were performed. A calibration of the "ripple" pyrometer was possible at wafer temperatures above 650...