Electrical and Reliability Characteristics of LPRTO and ISSG Oxide as Tunnel dielectric in SONOS Applications - Yi-Ping Lin

As the device dimensions continue to scaling-down, the retention characteristics have been a concern for scaled SONOS nonvolatile memory devices due to the use of thinner tunnel oxides. Thinner oxides are more susceptible to process-induced damage than thicker oxides, which lead to higher leakage currents and lower data retention [1]. Many studies have shown that the interfacial stress-induced leakage current (SILC) is more severe for thinner oxide [1]. Eriguch et al. have determined the strained layer near SiO2/Si interface to be approximately 1nm [2] and verified that the increased compressive strain decreases time-to-break-down (t
_bd
). The interfacial stress is related to growth condition such as temperature and growth rate. Higher temperatures and lower oxidation rates allow faster stress relaxation and reduced disorder at the interface for better reliability [3]. It is known that ultrathin oxides (<; 1.5nm) are difficult to achieve by in-situ-steam generation (ISSG) process due to high oxidation rate. As the growth temperature of thermally grown ultrathin oxides is reduced for better control, many weak spots and pinholes lead to unreliable properties [4- 5]. It is believed that the defects in the oxide can significantly increase the gate leakage, which in turn reduces device performance [6- 7].