Stress Development and Impurity Segregation during Oxidation of the Si(100) Surface
Daniel J. Cole,1
Mike C. Payne,1
Lucio Colombi Ciacchi2,3
1Theory of Condensed Matter Group, Cavendish Laboratory,
University of Cambridge, CB3 0HE, UK
2Fraunhofer Institut für Werkstoffmechanik, 79108 Freiburg, Germany
3Institut für Zuverlässigkeit von Bauteilen und Systemen,
University of Karlsruhe, 76131 Karlsruhe, Germany
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.
Surface Science 601, 4888 (2007)
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