Building-in reliability: soft errors-a case study

A case is described for implementing building-in reliability. The case study deals with the phenomenon of soft-error rates in DRAMs. It is shown that the process begins with looking at output variables and then working backwards to identify the key input variables that affect the output variables. The authors demonstrate how monitoring the identified input variables leads to a stable process in manufacturing. In addition, they have identified a new source of alpha particles that contributes to the soft error rate of memory ICs, namely, the phosphoric acid used during wafer fabrication. The findings show that the raw materials used in wafer fabrication are at least as great a source of alpha particle emissivity as are packaging materials.<>