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46 PCB007 MAGAZINE I MARCH 2019 defined by SECS II, is generally the same for all equipment in that class. In one HP journal article [7] , the author re- ported the following. "To date, they have encountered batch, me- trology, serial, and material handling equip- ment…batch processing systems, such as dif- fusion furnaces, process wafers in large quan- tities (batches). The primary characteristic is that once a batch has started processing, no more wafers can be added until the process sequence has run to completion. PC-10 will download only one recipe to the batch sta- tion when the batch is tracked in, and no other batches will be allowed in until the first batch is done. Metrology systems are classified separate- ly because they provide certain measurement data to PC-10. PC-10 supports SECS II stream 6 messages, which handle the transfer of mea- surement data to the host system for this class of equipment. Examples are line width, film thickness, and defect measuring devices. Wa- fers passing through these stations are not pro- cessed but merely measured to determine the effectiveness or accuracy of previous process steps. Serial processing handles wafers one at a time. Wafers from one lot may enter the equipment for processing before the preced- ing lot has been completed. Photolithography wafer track systems are a prime example of serial equipment. To ensure that the proper recipe is executed for each lot, PC-10 must check to see if the recipe already executing is the proper recipe for the next lot. If not, it must download the new correct recipe at the proper time for beginning processing of the new lot. Material handling requires an entirely dif - ferent set of messages since material handling Figure 7: PC-10 process control and supervision, including recipe downloading. (Source: Sematech Generic Equipment Model)