Optimum condition to fabricate 5-10 nm SiO_2/Si structure using advanced nitric acid oxidation of Si method with Si source

摘要

A low temperature (≦120℃) fabrication method to form relatively thick SiO_2/Si structure with a Si source has been developed using the advanced nitric acid oxidation of Si (NAOS) method, and the formation mechanism has been investigated. -The reaction mechanism consists of direct oxidation of Si, dissolution of Si sources, and surface reaction of the dissolved Si species. The dissolved Si species is present in HNO_3 solutions as mono-silicic acid and reacts with oxidizing species formed by decomposition of HNO_3 on an ultrathin SiO_2 layer (i.e., 1.4 nm) produced by the direct oxidation of Si substrates with HNO_3 solutions. To achieve a uniform thickness of SiO_2 layer with a smooth surface, HNO_3 solutions with concentrations higher than 60 wt. % are needed because the dissolved Si species polymerizes in HNO_3 solutions when the concentration is below 60 wt. %, resulting in the formation of SiO_2 particles in HNO_3, which are deposited afterwards on the SiO_2 layer. In spite of the low temperature formation at 120 ℃, the electrical characteristics of the advanced NAOS SiO_2 layer formed with 68 wt. % HNO_3 and subsequent post-metallization anneal at 250 ℃ are nearly identical to those of thermal oxide formed at 900 ℃.