Creep behaviors of surface-modified silicon: A molecular dynamics study

摘要

The creep properties and deformation behaviors of monocrystalline silicon coated by an amorphous SiO2 film with diverse thickness are explored using nanoindentation via molecular dynamics simulation. It is found that the creep displacement grows sharply at the beginning and then steadily towards the end of holding, and the final creep displacement is significantly larger at higher peak load. For a given bilayer SiO2/Si composite, the stress exponent n decreases with increasing peak load, exhibiting an inverse indentation size effect (ISE). At the same peak load, n decreases slightly with the increasing SiO2 film thickness. Careful analysis suggests the densification of amorphous SiO2 with different thickness occurs under three peak load during loading. The extent plastic deformation of SiO2 occurring during loading, to which depends on the thickness of SiO2 film and peak load, alters the creep behaviors of composites. The creep result indicates that SiO2 film undergoes densification during holding, and there is an increased deformation amount for SiO2 film and underlying silicon substrate under higher peak load. The study may be helpful for materials removal during CMP process and microdevices design in MEMS.