US Patent 11996308 Method for mapping wafers in a wafer carrier

The present disclosure relates to a method. The method includes generating a first beam of radiation toward a first slot of a workpiece carrier. The first beam of radiation has a first beam area that is greater than or equal to an area of an opening of the first slot. The method further includes measuring a reflected portion of the first beam of radiation that is reflected toward, and impinges on, a radiation sensor. The method further includes determining if the first slot of the workpiece carrier is holding a workpiece based on the measured reflected portion of the first beam of radiation.