An intrinsic stress scaling law for polycrystalline thin films prepared by ion beam sputtering

Abstract

The intrinsic stresses of Al, Ti, Fe, Ta, Mo, W, Ge, Si, AlN, TiN, and Si₃N₄ films prepared by ion beam sputtering were investigated at low T_d/T_m values. The intrinsic stress is compressive and its origin is explained in terms of the ion peening model. Knock‐on linear cascade theory of forward sputtering is applied to derive a simple scaling law with the film’s physical properties. The results show that the stress is directly proportional to the elastic energy/mole, given by the quantity Q=EM/(1−ν)D, where E is Young’s modulus, M the atomic mass, D the density, and ν Poisson’s ratio. Stress data taken from the literature for a variety of materials deposited by low‐pressure magnetron sputtering, and rf and ion beam sputtering also fit the correlation with Q. Furthermore, the model predicts a square‐root dependence on the incident ion energy, suggesting that the stress is momentum rather than energy driven.