STI stress-induced degradation of data retention time in DRAM and a new characterizing method for mechanical stress

The effect of mechanical stress induced by shallow trench isolation (STI) slope on the data retention characteristics of DRAM is investigated and a new electrical parameter for monitoring the mechanical stress is proposed. To maintain high and uniform retention time for the reliable operation of DRAM, the STI slope should not be vertical and should be kept below 86-degree. The new electrical parameter measures the current gain of the parasitic BJT in DRAM cell and shows a strong correlation with the retention time induced by the mechanical stress.