Metal-free Growth of Si/SiO_2 Nanowires by Annealing SiO_x (x < 2) Films Deposited by PECVD

摘要

A new metal catalysis-free method of fabricating Si or SiO_2 nanowires (NWs) compatible with Si CMOS technology was proposed by annealing SiO_x (x < 2) films deposited by plasma -enhanced chemical vapor deposition (PECVD). The effects of the Si content (x value) and thickness of SiO_x films, the annealing process and flowing gas ambient on the NW growth were studied in detail. The results indicated that the SiO_x film of a thickness below 300 nm with x value close to 1 was most favorable for NW growth upon annealing at 1000-1150°C in the flowing gas mixture of N_2 and H_2. NWs of 50-100nm in diameter and tens of micrometers in length were synthesized by this method. The formation mechanism was likely to be related to a new type of oxide assisted growth (OAG) mechanism, with Si nanoclusters in SiO_x films after phase separation serving as the nuclei for the growth of NWs in SiO_x films > 200nm, and SiO molecules from thin SiO_x film decomposition inducing the NW growth in films < 100nm. An effective preliminary method to control NW growth direction was also demonstrated by etching trenches in SiO_x films followed by annealing.