Chapter 4, Problem 40E

Plot the residuals from Exercise 4.36 against the firing temperatures. Is there any indication that variability in baked anode density depends on the firing temperature? What firing temperature would you recommend using?

4.36. Compare the mean etch uniformity values at each of the C₂F₆ flow rates from Exercise 4.33 with a scaled t distribution. Does this analysis indicate that there are differences in mean etch uniformity at the different flow rates? Which flows produce different results?

4.35. An article in Solid State Technology (May 1987) describes an experiment to determine the effect of C₂F₆ flow rate on etch uniformity on a silicon wafer used in integrated-circuit manufacturing. Three flow rates are tested, and the resulting uniformity (in percent) is observed for six test units at each flow rate. The data are shown in Table 4E.4.

1. (a) Does C₂F₆ flow rate affect etch uniformity? Answer this question by using an analysis of variance with α = 0.05.
2. (b) Construct a box plot of the etch uniformity data. Use this plot, together with the analysis of variance results, to determine which gas flow rate would be best in terms of etch uniformity (a small percentage is best).
3. (c) Plot the residuals versus predicted C₂F₆ flow. Interpret this plot.
4. (d) Does the normality assumption seem reasonable in this problem?

   TABLE 4E.4

   Uniformity Data for Exercise 4.35