A method for modeling usage of semiconductor test wafers comprises the steps
of:
calculating an individual demand for test wafers by each of a plurality of tools,
assigning respective ones of the plurality of tools to a plurality of levels based
on ability of each tool to use wafers that have been processed by another one of
the plurality of tools, assigning wafers made available by one of the plurality
of tools to at least two other ones of the plurality of tools in proportion to
the individual demands of each of the at least two other tools, and determining
a total demand for test wafers, based on the number of wafers assigned to each
of the plurality of tools in the lowest one of the plurality of levels.
