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Yield is also the most important factor in overall processing cost.
This article describes a yield improvement project undertaken by Tower Semiconductor, a foundry in Migdal Haemek, Israel, that produces several dozen different products, each with the relatively low volume of a few hundred wafers. With this complex product mix, the company needs a yield management program that operates effectively to ensure that high yield levels are consistently maintained. The ambitious goals of Tower's yield improvement effort included not only decreasing the defect densities of existing technologies within 6 months and bringing the foundry's die yield to a worldwide level based on an entitlement database, but also setting a yield improvement infrastructure in place for all future technologies. The following sections outline the systematic approach that was taken to meet these goals and describe how a yield management methodology was successfully modified to fit the fab's needs. This article also describes how the company's goals were successfully met.