Plasma etching is essential to the fine-line pattern transfer in current semiconductor processes. The article “Ion BeamAssisted Etching of Aluminum with Chlorine” (J. of the Electrochem. Soc., 1985: 2010– 2012) gives the accompanying data (read from a graph) on chlorine flow (x, in SCCM) through a nozzle used in the etching mechanism and etch rate (y, in 100 A/min).

x 1.5 1.5 2.0 2.5 2.5 3.0 3.5 3.5 4.0 y 23.0 24.5 25.0 30.0 33.5 40.0 40.5 47.0 49.0 The summary statistics are

.

a. Does the simple linear regression model specify a useful relationship between chlorine flow and etch rate?

b. Estimate the true average change in etch rate associated with a 1-SCCM increase in flow rate using a 95% confidence interval, and interpret the interval.

c. Calculate a 95% CI for , the true average etch rate when flow Has this average been precisely estimated?

d. Calculate a 95% PI for a single future observation on etch rate to be made when . Is the prediction likely to be accurate?

e. Would the 95% CI and PI when be wider or narrower than the corresponding intervals of parts

(c) and (d)? Answer without actually computing the intervals.

f. Would you recommend calculating a 95% PI for a flow of 6.0? Explain.