<title>Real-time monitoring and control of plasma etching</title>

Abstract

Process control strategies have been developed for reactive ion etching of silicon and silicon dioxide in CFJO2 and CF/H2 plasmas. Four measured variables four manipulated variables and six performance variables were considered for both chemistries. Relative gain array analysis and singular value decomposition were used to select manipulated/process variable control loop pairings for feedback control and to evaluate potential difficulties in control system performance. Block relative gain analysis of multivariable interactions in the process indicated that single loop feedback control would be inadequate for control of both CF/H2 and CFJO2 etching which was subsequently verified by simulation. Multivariable control (partial decoupling) was much more effective in reducing dynamic fluctuations in the process variables. Closed loop simulations have demonstrated a quality of control sufficient for manufacturing purposes. Singular value decomposition was also used to determine which process variable (measured in real-time) correlated best with a given performance variable. Empirical input-output models developed by response surface methodology were used for the above analyses. For the CF/H2 system functions based on semi-theoretical reasoning of process variables were also investigated. For example the function of [F](DC Bias)25/[CF2] was found to be more indicative of process performance than the absolute values of these process variables. Unfortunately this work reveals the need for more real-time measurable process variables in order to achieve sufficient process performance.