Please help, The photoresist thickness in semiconductor manufacturing has a mean of 10 micrometers

a standard deviation of 1 micrometer. Assume that the thickness is normally distributed and that the thicknesses of different wafers are independent.


Determine the number of wafers that needs to be measured such that the probability that the average thickness exceeds 11 micrometers is 0.01.

Anonymous -

P(X > 11) = 0.01

P[ z > (11-10) / (1/sqrt N) ] = 0.01

The z-value associated with a probability greater than 0.01 is z = 2.326, so let's set that equal to (11-10) / (1/sqrt N):

1 / (1/sqrt N) = sqrt(N) = 2.326

N = 5.41 or 6 rounding up to the next higher integer.

Hope that helped