Investigation of Ultra-thin Gate Oxides Prepared by Anodization with Tensile Stress in Tilted Cathode Anodization System
Date Issued
2006
Date
2006
Author(s)
Li, Tsung-Hung
DOI
en-US
Abstract
A simple technique to improve the quality and reliability of SiO2 as ultra-thin gate dielectrics by bending the silicon wafer during oxidation is proposed; this technique is based on the concept that the oxide grown on enlarged silicon lattice may have better property because of reduced lattice mismatch. In this work, the oxidation was carried out in a novel tilted cathode anodization system. During anodization process, mechanical tensile stress was applied to the silicon wafer, and released after gate oxide formation.
Anodization is an alternative way to directly grow SiO2 on silicon substrate; due to its superiority over thermal oxidation in the control of thickness of ultra-thin gate oxide as well as that it can be held at room temperature, we considered that anodization is the most suitable oxidation process to demonstrate the effect of the applied tensile stress. The tilted cathode anodization system, a unique modification proposed in this work, is capable of growing oxides with gradual oxide thickness and thus helpful to the evaluation of gate oxides with different thicknesses on one single wafer. In addition to avoiding many process variations, the tilted cathode anodization system makes it possible to estimate the trend of characteristics of ultra-thin gate oxides with the growth kinetics investigated in this work.
From the investigation of ultra-thin gate oxides prepared by anodization with tensile stress, the flat-band voltage of the sample grown with applied tensile stress is found to shift more positively than that without and the mechanism of OH－ incorporation is proposed. The experimental result shows that the leakage current is significantly reduced and the reliability is much improved for ultra-thin oxides prepared by tensile-stress oxidation.
Subjects
超薄閘極氧化層
陽極氧化
外加機械張力
Ultra-thin Gate Oxides
Anodization
Applied Tensile Stress
Type
thesis
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