On the Dependence of Band Alignment of SiO₂/Si Stack on SiO₂ Thickness: Extrinsic Or Intrinsic?

Yonggui Xu,Kai Han,Xiaolei Wang,Jinjuan Xiang

doi:10.1109/access.2020.3020072

Yonggui Xu, Kai Han + Show 2 more

Open Access

https://doi.org/10.1109/access.2020.3020072

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Abstract

The dependence of band alignment of SiO 2 /Si stack on SiO 2 thickness is restudied. The band structure of SiO 2 /Si stack is investigated by time-dependent X-ray photoelectron spectroscopy (XPS) with and without electron-compensation technology. The binding energy difference ΔSi_2p between Si 2p core-levels of SiO 2 and Si, measured without electron-compensation, is found larger than that with electron-compensation, owning to the charging effect. And more severe charging effect induces larger ΔSi_2p. The ΔSi_2p measured with electron-compensation technology, however, is scarcely affected by the charging effect and thus accurate band alignment can be obtained. The band alignment of SiO 2 /Si stack is found to be SiO 2 thickness dependent. And this dependence is attributed to the gap states on the SiO 2 surface and their lower charge neutrality level than the Fermi level of Si substrate, resulting in electron transfer from Si to SiO 2 and electric potential distribution across the SiO 2 . As a result, the experimentally obtained dependence of ΔSi_2p on SiO 2 thickness with electron-compensation is intrinsic. The proposed explanation about the XPS results further confirms the feasibility of the gap state theory in demonstrating the band lineup of hetero-structures.

Highlights

Complete understanding of electronic structure and band alignment of SiO2/Si stack is rather essential because this structure is fundamental and ubiquitous in Si based metal-oxide-semiconductor field effect transistor (MOSFET) [1], [2]
The band alignment of SiO2/Si stack with different SiO2 thicknesses is investigated by X-ray photoelectron spectroscopy (XPS) with and without electroncompensation
It is found that the charging effect can affect the band lineup of SiO2/Si structure when electroncompensation technology is not employed

Summary

INTRODUCTION

Complete understanding of electronic structure and band alignment of SiO2/Si stack is rather essential because this structure is fundamental and ubiquitous in Si based metal-oxide-semiconductor field effect transistor (MOSFET) [1], [2]. In the past the dependence of band alignment of SiO2/Si structure on the SiO2 thickness was investigated by XPS without electron-compensation technique. Under such condition the charging effect occurs due to the insulator characteristic of the SiO2 film. The influence of the charging effect on the band structures of SiO2/Si stack with various SiO2 thicknesses is firstly evaluated by XPS with and without electron-compensation. The dependence of band alignment of SiO2/Si stack on the SiO2 thickness is not extrinsic (charging effect) but intrinsic (gap states on the SiO2 surface). The equivalent oxide thickness (EOT) and flatband voltage (VFB) are extracted from the C-V fitting with quantum effect correction

RESULTS AND DISCUSSION

ON THE GAP STATE THEORY ACCOUNTING FOR THE HETERO-STRUCTURE CONTACT

CONCLUSION