Abstract: The present invention provides a method and apparatus for classifying faults. The method includes accessing wafer state data associated with at least one wafer processed by at least one processing tool and sensor tool trace data associated with the at least one processing tool and determining that at least one fault occurred based upon at least one of the wafer state data and the sensor tool trace data. The method also includes selecting, in response to determining that the at least one fault occurred, a subset of a plurality of faults based upon at least one of the wafer state data and the sensor tool trace data and selecting at least one fault from the subset of the plurality of faults based upon at least one of the wafer state data and the sensor tool trace data.