The role of the atomic structure on the Si/SiO₂ interface strains

While Si-SiO₂ systems have been under an intensive academic and industrial research since invention of MOSFET in 1960, the underlying physics and chemistry of this interface are still not well understood at the atomic scale level. As the size of electronic devices shrinks into the nanoscale dimension, the importance of understanding the atomic scale structure of Si-SiO₂ interfaces grows. This understanding is very crucial to extend the life of complementary metal-oxide semiconductor (CMOS) technology. In this paper, we present results of a computational study on Si/SiO₂ interface for several modifications of a proposed interface model. The interface model is obtained by removing a (100) layer of Si atoms from the crystalline silicon. Leftover Si atoms on each side of the removed atoms are shifted perpendicularly to the interface to adjust their separation and oxygen atoms are inserted at such positions to preserve usual Si-O bond lengths and angles. The computations were carried out using first-principles density functional theory (DFT) in the local density approximation (LDA). Our calculations revealed the important role of the interface structure on the shear and tensile strains on the interface. The first layer tensile strain was found to increase significantly and linearly with the increase of the O-Si-O bond angle from 102° to 126°. The first layer shear strain was found to decrease slowly and linearly with the increasing the O-Si-O bond angle. On the other hand, the O-O distance along the interface was found to have nearly the opposite effect of the O-Si-O bond angle.