Answer Happy

Wet chemical etching is commonly used in semiconductor production to remove silicon from the backs of wafers before metalisation. The etch rate is a crucial aspect of this procedure. The effectiveness of two distinct etching solutions is being investigated. Ten randomly selected wafers have been etched in each solution and the observed rates (in mils/min) are as follows. Solution A 9.7 10.6 9.5 10.2 10.0 10.5 10.4 10.1 9.9 10.9 Solution B 10.4 10.4 10.5 10.3 10.7 10.8 10.9 11.0 10.3 11.0 Assume that the etch rates of both etching solutions are normally distributed with unknown means and variances. Further assume that both etching solutions have equal variances. (i) Construct a 95% confidence interval of the difference in mean etch rate for the two solutions. (ii) At the 5% significance level, test the null hypothesis that the difference between the mean etch rates of solution A and solution B is 0.1.