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Fig. 12 shows the DOE/Opt problem formulation for optimizing a gate oxidation process. The set up is analogous to that described in the previous section. The input table consists of six variables. There are two process parameters: time of gate oxidation (), and temperature of gate oxidation (). Associated with each of the process parameters are the mean and the standard deviation for the disturbances, denoted by the prefixes and . The means and the standard deviations for the disturbances, which are assumed to be independent and normally distributed, can be determined by tuning FABRICS to the fabrication line for which the process is to be optimized . In using DOE/Opt we have explicitly specified the means and standard deviations of the disturbances corresponding to and , and do not vary the standard deviations (i.e. they are fixed at their tuned values). The output table consists of five parameters. These correspond to the mean of the gate oxide thickness (), standard deviation of the gate oxide thickness (), signal-to-noise ratio of the gate oxide thickness () defined as the ratio of the mean to the standard deviation, mean of Monte Carlo parametric yield for the gate oxide thickness (), and the standard deviation of Monte Carlo parametric yield for the gate oxide thickness (). The standard deviation is used to determine the confidence interval on the yield based on the Monte Carlo sampling. Yield calculation is based on whether the resulting responses fall within a region of acceptability; the limits for the acceptability of the gate oxide thickness are specified using the DOE/Opt coefficients table.