Anomalous single bit retention induced by asymmetric STI-corner-thinning for floating gate Flash memories

Data retention is a major issue that significantly affects the reliability of Flash memories. In this work, the method of P-Well-Inside stress with a low electric field was used to effectively detect the stress induced leakage current that caused single bit retention due to non-optimized process in NOR-type floating-gate Flash memories. Based on the electrical and physical failure analysis, the asymmetric corner thinning of Shallow-Trench-Isolation induced by the asymmetric cell implantation was identified as the origin of the retention failure. In consequence, the proposed method of P-Well-Inside stress provides a new and fast evaluation for data retention and process optimization.