Failure modes and reliability of dynamic RAMS

The reliability of silicon gate N-channel MOS dynamic RAMS is discussed in terms of the primary failure modes of these devices. Analysis of field data and accelerated lifetest results show the majority of failures to be due to oxide defects with smaller percentages of failures caused by contamination and/or masking defects. Specific attention in the paper is directed to oxide defect failures. The temperature and time dependence of these failures is examined and compared to actual device failure rates. Methods of screening defective oxides in actual RAMS are discussed. It is concluded that the weak temperature dependence of this specific failure mode necessitates over voltage stressing as a prescreen. Accelerated life-tests at high temperature and nominal voltages are relatively ineffective in screening these defects.