Is BPSG an effective sodium barrier? A WLR success story

This paper details a significant Burn-In (bake recoverable) product failure which was linked to mobile ion contamination even when the process utilized BPSG as a pre-metal dielectric. Making the assumption that the BPSG would be an effective sodium barrier, one of National's foundries implemented process changes subsequent to the metal-1 masking step assuming that these changes would not introduce significant mobile ion contamination. However, the process-on-record was already showing sporadic operational life failures. A Wafer Level Reliability (WLR) test was implemented, calibrated and a correlation made to the burn-in failures at 48 hrs. Using this WLR test a calculation was made as to the level of mobile sodium that would cause burn-in failures at an extrapolated lifetime necessary to exceed the customer's product life requirement. The use of phosphorus in the dielectric as a gettering agent is also discussed. Moreover, details of the correlation and calibration of the WLR test are covered.