In €œOrthogonal Design for Process Optimization and Its Application to Plasma Etching€ (Solid State Technology, May 1987), G. Z. Yin and D. W. Jillie describe an experiment to determine the effect of C2F6 flow rate on the uniformity of the etch on a silicon wafer used in integrated circuit manufacturing. Three flow rates are used in the experiment, and the resulting uniformity (in percent) for six replicates is shown below.

(a) Does C2F6 flow rate affect etch uniformity? Construct box plots to compare the factor levels and perform the analysis of variance. Use a = 0.05.
(b) Do the residuals indicate any problems with the underlying assumptions?

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Observations 3 CF, Flow (SCCM) 5 2 4 125 2.7 2.6 4.6 3.2 4.6 3.0 3.8 4.9 3.6 4.2 4.2 160 5.0 2.9 3.5 200 3.4 4.1 4.6 5.1 2.