Ion energy effects on the intrinsic stress in B xN y layers deposited by ion-beam-assisted evaporation

Abstract

The intrinsic stress σ of boron nitride (B x N y ) films deposited at room temperature by ion-beam-assisted deposition has been investigated as a function of the atomic flux ratio and film composition for different N 2 + energy values ranging from 0.25 to 2 keV. The value of σ was evaluated by an interferometric Newton's rings method. The stress reverses and becomes compressive for an atomic flux ratio N:B less than 0.3 which is the lowest value we have examined. Two domains of composition can be emphasized following the stress behaviour as a function of the ion energy. The first domain is that of nitrogen-poor films where the absolute value of the stress decreases (from -2.4 to -0.45 GPa) when the energy is increased. The creation of vacancies in the deposit depth or an “ion annealing” effect is proposed to explain the corresponding stress behaviour which is correlated with density measurements. The second domain is that of nitrogen-rich films in which the compressive stress increases drastically to -4.8 GPa with the ion energy. In this domain, according to the ion peening model proposed by Windischmann, the stress varies in proportion to the nuclear stopping power of the deposited material.