Temperature dependence of soft breakdown and wear-out in sub-3 nm SiO/sub 2/ films

Abstract

A comprehensive time-dependent dielectric breakdown study was conducted on sub-3 nm Si02 films over a temperature range from 22 "C to 350 "C. Two breakdown modes were observed in current versus time characteristics and low voltage I-V curves depending on device area and stress voltage. Larger device areas and lower stress voltage produced higher occurrences of softhoisy breakdown events while smaller device areas and larger stress voltages produced hardedthermal breakdown events. Stress temperature did not affect the breakdown mode. The results indicate that both breakdown modes exhibit the same thermal acceleration if the first occurrence of current noise is used as a breakdown criteria for those devices exhibiting noisy breakdown. The observed strong dependence of the thermal activation energy on gate voltage may explain previous reports of increased temperature acceleration for ultra-thin films.

Ultrathin gate oxide reliability: physical models, statistics, and characterization

“…The study indicated that soft breakdown was not a pre-cursor to hard breakdown since the hard breakdown conduction spot usually appeared in a different spatial location. Consistent acceleration parameters were obtained if breakdown was defined as the first permanent change in the current versus time characteristic regardless if the change was a hard or soft (or noisy) breakdown [31], [79]. Fig.…”

“…was observed to decrease for increasing applied gate voltage or electric field [14], [22], [79] which was predicted by the Thermochemical model [14]. In some reports the was observed to change with temperature [80].…”

“…Later studies reported a non-Arrhenius temperature dependence for ultrathin oxides and a steeper temperature dependence compared to results from earlier studies for thicker oxides [25], [81]- [83]. A strong voltage dependence for temperature acceleration was reported in [79] and it was pointed out that the steeper temperature dependence observed for thinner oxides may be due to the lower voltages used to stress thinner oxides.…”

Physical and predictive models of ultrathin oxide reliability in CMOS devices and circuits

“…This view was not consistent with a later statistical analysis of data [176] showing that the distribution of breakdown times is independent of whether they are soft or hard, and that an HBD which occurs after an SBD is a random event uncorrelated with the first SBD spot. It was also shown that SBD and HBD follow similar area dependence [177] but the temperature dependence and voltage dependence were found to be different [178] or the same [179] in different laboratories. The similar light emission spectral characteristics of SBD and HBD [180] also support the idea that they are related phenomena, differing only in the size of the breakdown spot.…”

Oxide Wearout, Breakdown, and Reliability

“…Unfortunately, most authors do not differentiate between these measurements and do not specifically tell, or provide information to determine, which breakdown event is being described. When making time-dependent-dielectric-breakdown (TDDB) distribution or ramped breakdown voltage distribution measurements, if all the breakdowns are recorded, then the first and last measurement distributions are parallel [52,58,60,61,64,132,173,217]. Thus, the two breakdown events, the first partial discharge and the last dielectric breakdown are caused by the same physical phenomena [83,93,173].…”