Defects, Contaminants, and Yield

There are defects and defects , and there are killer defects !! From the relatively innocuous to those that immediately disqualify an integrated circuit (IC) chip, this chapter is largely concerned with the nature of defects, their generation during processing, strategies used to minimize their influence, and how they adversely influence product yield. In Chapter 2 we described how a failure could be hastened by a damaged area. We will now negotiate the murky waters between an IC that fails at final test and one that passes but is doomed to early failure. The harmful effects of crystallographic, structural, compositional, or stoichiometric defects strongly depend on the nature of the material they inhabit. For example, metals are usually far more tolerant of point defects, dislocations, and grain boundaries (GB) than are semiconductors. Semiconductors must be free of dislocations and GBs, whereas metallizations contain these in relatively large densities with little ill effect. And, since the matrices of most ceramics and dielectrics used in microelectronics are already amorphous or fine grained, these same crystallographic defects usually affect properties only marginally, if at all.