Controlling the transport of special lots of semiconductor wafers between process stockers, eg for dust monitoring

摘要

Semiconductor wafers are processed in lots at different processing stations in sequence. To determine, for example, the amount of dust collected by such a lot in the transport between stations, special lots are designated which travel between the stations, but are not processed at the stations. Instead they are stored in the stockers or stores at the stations for periods of time corresponding to the processing times for the production lots. The special lots are removed from the stocker at the last station for measurement, eg of the dust collected. This give an indication of the dust present in the processing facility. The transport of the special lots is automated under the control of a carrying host computer which stores data on all the lots, the various routes or "carrying path patterns" between stockers that the lots can be directed to follow and the actual location of a lot at any one time. When a stocker receives a lot, a report is issued to the computer and a timer is set. When a predetermined period has elapsed equivalent to the processing time of a production lot, the computer determines the next stocker on the route from the stored patterns and sends an instruction to the current stocker for transporting the lot to the next stocker in the route.