1. A method comprising: creating a plurality of sets of rankings of a plurality of input variables by executing a decision tree-based prediction model for a plurality of iterations using the plurality of input variables, the plurality of iterations corresponding to the plurality of sets of rankings, the plurality of input variables being based on data from at least one semiconductor manufacturing tool; generating overall variables contribution data using the rankings of the plurality of input variables; and identifying a plurality of key input variables from the plurality of input variables based on the overall variables contribution data.