Effect of Oxide and Nitride Films on Strength of Silicon: A Study Using Controlled Small-Scale Flaws
Yeon-Gil G. Jung, Antonia Pajares, Brian R. Lawn
Strength properties of silicon substrates containing dense oxide and nitride surface films are investigated using nanoindentations to introduce small flaws of predetermined scale. The indentation flaws provide favored sites for failure in subsequent flexure loading, even in the subthreshold region for indentations without visible corner cracking, confirming that microflaws generated within the indentation zone act as effective crack sources in the substrate. Deposition of the oxide films increases the strength while the nitride films diminishes it, at any given indentation load. The strength shifts are attributed to the presence of residual compressive stress in the oxide, tensile stress in the nitride. A fracture mechanics formulation based on a previous analysis for monolithic substrates is here adapted to allow for a superposed crack closing or opening stress-intensity factor term associated with the residual stresses. This formulation accounts for the basic strength shifts, and enables evaluation of the magnitude of the residual stresses. The results usefully quantify the susceptibility of basic small-scale device materials to damage from small-scale contacts and impacts.
Journal of Materials Research
nanoindentation, silicon, strength, subthreshold flaws, thin films