In-fab identification of silicon wafers with clean, laser marked barcodes

All AT&T MOS cleanrooms uniquely identify and track individual wafers in the manufacturing process. Recently, we have developed a new technique to put a laser marked barcode on the front surface of the wafer which adds no detectable particles. The mark itself is an adaptation of the SEMI T1 specification which is popularly referred to as BC412. Unlike the SEMI specification, our BC412 barcode is marked on the top of the wafer during the actual wafer fabrication process. Since the marking is done in the cleanroom, a clean marking technology is absolutely essential. Also the front side mark presents challenges to the barcode readers due to process related surface variations. This paper discusses the reasons for individual wafer tracking and reviews some of the benefits we have seen in practice. We compare the front side, clean barcode to other types of wafer identification techniques. We also discuss the marking technology required for clean marking and the reading technology necessary for front side BC412