An adaptor plate for allowing 200 mm SMIF pods carrying one or more semiconductor wafers to be used on an access port of a wafer processing station configured to accept a 300 mm SMIF pod. The adaptor plate has a substantially circular outer circumference conforming substantially in size and shape to the outer circumference of a conventional 300 mm SMIF pod, and a central opening conforming substantially in size and shape to a conventional rectangular 200 mm SMIF pod. The one or more semiconductor wafers are supported on pod door of the pod, and the semiconductor wafers and pod door are lowered through the central opening in the adaptor plate into the wafer processing station. With the adaptor plate supported on the access port, and a cover of the 200 mm SMIF pod supported around the central opening, the access port is entirely covered and entry of contaminants into the processing station through the access port is prevented.