document: The number of experiments conducted was reduced by selecting the four most important parameters for variation, Table 1 while the remaining parameters were kept constant. The O2 flow rate (QO2) was keep constant at 99sccm, while the SF6 flow rate (QSF6) was varied between 0 and 20sccm. The pressure in the etch chamber was controlled to keep the gas density stable. Since the pressure has a pronounced effect on etch characteristics, the pressure (p) was varied between 20 and 40mTorr. It should be noted that the system was run in automatic pressure control mode, which continuously adjusts the throttle valve to keep a constant pressure during etch. The coil power (PC) was fixed at 1000W, while the bias power (PB) was varied between 0 and 30W. Finally, the substrate chuck temperature (T) was controlled between 10 and 50°C. This design resulted in a full factorial screening in four parameters, where three center points were used to check for quadratic curvature, where the quadratic term of a parameter is needed to generate a valid model. The total number of experiments in this setup is 19, which were processed for 20min each. The experiments in the design were carried out in random order.
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