XY方向精度的过程能力定义

Measurement offsets in both X and Y direction are assumed to be normal distributed and independent to each other: X<- N(u1,s1) and Y<- N(u2, s2) ; the mean and standard deviation of X and Y were stored in the scanner after each measurement. Specification for registration is R = sqrt(X^2 + Y^2) <= 75um, zero point for offset calculation is based on the two-alignment hole in the corner. The distribution of value R couldn’t be regarded as a normal distribution, which leads to that no common process capability index could be obtained.