Reconsider the photoresist experiment in Problem 8-25. Use the variance of the resist thickness at each test combination as the response variable. Is there any indication that a transformation is required?

Problem 8-25

A spin coater is used to apply photoresist to a bare silicon wafer. This operation usually occurs early in the semiconductor manufacturing process, and the average coating thickness and the variability in the coating thickness has an important impact on downstream manufacturing steps. Six variables are used in the experiment. The variables and their high and low levels are as follows:

Factor Low Level High Level Final spin speed 7350 m 6650 m Acceleration rate 5 3 5 c Volume of resist applied Time of spin 14 s 6 s Resist batch variation Batch 1 Batch 2 Exhaust pressure Cover off Cover on 20