US Patent 7524683 Method of monitoring a semiconductor manufacturing trend

A method of monitoring trends in semiconductor processes is provided. Lot values are assigned to each of a set of wafer lots prior to performing semiconductor processes. After at least some of the semiconductor processes, at least some of the wafer lots are tested to generate a set of test data. A degree of scrambling is calculated for the set of wafer lots already tested using the test data: calculating a current scrambling value by subtracting the lot value of a current wafer lot from a maximum lot value of the lot values assigned for the set of wafer lots to yield the current scrambling value; storing the current scrambling value into a set of scrambling values; and determining a current adjusted maximum scrambling value by multiplying a selected multiplier value with a current maximum scrambling value of the set of scrambling values for a selected number of wafer lots.