Evolution and Accomplishments of VLSI Yield Management at IBM

The methods developed at IBM to manage and improve the yield of some of its newer FET semiconductor products are described. A number of visual inspection and electric monitoring techniques have evolved since discrete semiconductors were manufactured. The data obtained with these techniques are used in self-checking yield models to give the relative yields for all the yield components. The results are applied not only to day-to-day control of the manufacturing lines, but also in the long-range forecasting and planning of future semiconductor integrated circuit products. An example is given comparing the actual and planned yield of a 64K-bit random access memory chip as a function of time. The results show the yield enhancement that was obtained with redundant circuits and additionally with the use of partially functional products. Another example shows the decrease in fault levels over a span of more than ten years.