Analysis of defect maps of large area VLSI ICs

Defect maps of 57 wafers containing large area VLSI ICs were analyzed in order to find a good match between the empirical distribution of defects and a theoretical model. The main result is that the commonly employed models, most notably, the large area clustering negative binomial distribution, do not provide a sufficiently good match for these large area ICs. Even the recently proposed medium size clustering model, although closer to the empirical distribution than other known distributions, is not good enough. To obtain a good match, either a combination of two theoretical distributions or a 'censoring' procedure (i.e. ignoring the worst chips) is necessary.<>