Impact of multi-product and -process manufacturing on run-to-run control

For the past few years, both academia and industry have increased research in run-to-run (RtR) or supervisory level control of semiconductor processes. Run-to-run control has been cited as a necessary and integral part of many current and future leading edge processes(10). Run-to-run control has been applied or proposed for common and critical fab processes such as Chemical Mechanical Polish (CNP) and lithography/etch line width control. Many traditional as well as advanced control techniques have been used in the formulation of run-to-run controllers (time series and statistical process control (SPC) -based, state space methods, simple P/PI/PID algorithms, model-based predictive control, etc). In addition, papers have been published that discuss some of the many issues involved in deploying a run-to-run controller(11). However, one important issue that affects deployment of run-to-run control has largely been ignored In many state-of-the-art fabs, especially those that manufacture microprocessors and other logic chips, costly fab tools are required to run more than one process for throughput and flexibility reasons. Furthermore, today's fabs frequently produce more that one type of chip. Both of these factors, multi-processing and -products, sometime lead to major difficulties in designing and deploying a run-to-run controller. This paper will focus on the issues involved in multi-product and -process run-to-run control, as well as compare and contrast some strategies that could be used to design a run-to-run control system under these circumstances.