Temperature dependent retention characteristics of ion-beam modified SONOS memories

Abstract

In this work, we report on the structural and electrical properties of oxide–nitride–oxide (ONO) structures that were formed by low-energy silicon or nitrogen implantation into oxide–nitride stacks. In particular ON stacks (2.5nm/6nm) were formed on n-type Si substrates, further implanted with 1keV Si or N to a fluence of 1016 ions/cm2, and finally wet oxidized at 850°C for 15min. TEM imaging showed that the thickness of the blocking oxide layer, formed during wet oxidation, strongly depends on the implanted species. Charging characteristics revealed that Si implanted stacks can trap either electrons or holes resulting to a memory window as large as 8.5V. In turn N implanted stacks can trap only electrons with a corresponding memory window of 4V. Room-temperature charge retention measurements showed that the electron loss rate is faster in samples implanted with Si (∼0.32V/decade) compared to N-samples (∼0.1V/decade). The 10-year extrapolated memory windows were 1.7 and 2.5V for Si and N-implanted devices, respectively. Retention measurements within the temperature range of 25–150°C indicate that the Si implanted stacks exhibit a thermally activated retention, while N-samples showed a temperature independent behavior. These results are mainly attributed to the different nature of traps generated by ion implantation and wet oxidation processing.