Corner-rounded shallow trench isolation technology to reduce the stress-induced tunnel oxide leakage current for highly reliable flash memories

This paper describes the key technology to realize highly reliable flash memory cells, which have submicron Shallow Trench Isolation (STI). It has been clarified for the first time that the Stress-Induced Leakage Current (SILC) of the tunnel oxide on the rounded corners of the STI edges is about one order smaller than SILC of the flat oxide. Moreover, data retention characteristics of the flash memory cells with the rounded corners are drastically improved due to the reduction of SILC. Therefore, corner-rounded STI technology will surely become necessary for highly reliable quarter-micron flash memories and beyond.