Oxidation of nitrogen-implanted silicon: Comparison of nitrogen distribution and electrical properties of oxides formed by very low and medium energy N2+ implantation

Abstract

In a previous work [Skarlatos et al., J. Appl. Phys. 93, 1832 (2003)] we investigated the influence of implantation energy on oxide growth and defect formation in nitrogen-implanted silicon substrates. It was shown that as the implantation energy decreases from medium to very low values the oxide reduction decreases. This was attributed to nitrogen out-diffusion, which is more effective when nitrogen is placed closer to the silicon surface. On the other hand very low implantation energy avoids the formation of dislocation loops in the silicon substrate, a key point for modern devices performance. In this second part we compare the nitrogen distribution and electrical properties of ultrathin (25–30 Å) oxides grown under the same oxidation conditions on very low (3 keV) and medium (25 keV) energy nitrogen-implantated silicon. Nitrogen distribution measurements show that a lower content of nitrogen remains within the oxides formed using 3 keV energy as compared to the 25 keV case supporting the results of the first part of this work. So at very low implantation energy the same oxide thickness is obtained increasing the implantation dose. On the other hand oxides formed through very low energy implants show superior electrical properties in terms of surface states and leakage currents due to the lower damage induced in the silicon substrate.