
Cluster Analysis Using the Negative Binomial Model
For a given product line, both random defect yield limits and systematic yield
limits can be extracted using cluster analysis [44]. Reorganization of wafer probe
maps grouping adjacent devices into cells containing 1, 2, 3, 4 (2 2), 6 (2 3),
and 9 (3 3) chips enables an analyst to emulate and calculate the percent yield for
dice with various area sizes. All chips of a given cell must pass all tests for a
grouped cell to pass and qualify for production. Using a least square method, the
six yield points obtained for the various areas are fitted to an equation representing
the defect distribution.