Stress Development and Impurity Segregation during Oxidation of the Si(100) Surface

TL;DR

This study uses first-principles simulations to analyze how phosphorus and boron impurities behave during silicon surface oxidation, revealing their tendency to stay at the interface and avoid bonding with oxygen, affecting surface properties.

Contribution

It provides new insights into impurity segregation and stability during silicon oxidation, highlighting the interface localization and bonding behavior of P and B impurities.

Findings

Impurities segregate to stable surface or subsurface sites in bare silicon.

Oxidation induces tensile surface stress and oxidized silicon species formation.

Dopants prefer to stay at the Si/SiOx interface, avoiding bonding with oxygen.

Abstract

We have studied the segregation of P and B impurities during oxidation of the Si(100) surface by means of combined static and dynamical first-principles simulations based on density functional theory. In the bare surface, dopants segregate to chemically stable surface sites or to locally compressed subsurface sites. Surface oxidation is accompanied by development of tensile surface stress up to 2.9 N/m at a coverage of 1.5 monolayers of oxygen and by formation of oxidised Si species with charges increasing approximately linearly with the number of neighbouring oxygen atoms. Substitutional P and B defects are energetically unstable within the native oxide layer, and are preferentially located at or beneath the Si/SiOx interface. Consistently, first-principles molecular dynamics simulations of native oxide formation on doped surfaces reveal that dopants avoid the formation of P-O and B-O bonds, suggesting a surface oxidation mechanism whereby impurities remain trapped at the Si/SiOx interface. This seems to preclude a direct influence of impurities on the surface electrostatics and, hence, on the interactions with an external environment.