Simultaneous real-time study of initial hillocking and changes in overall stress in evaporated Al films during heating

Abstract

Optical quality Al films were evaporated by an electron beam onto Si wafers in an ultrahigh vacuum system. The as-deposited samples were radiative heated at a rate of 3 °C/s in air environment. During heating, measurements of initial hillocking and changes in overall film stress were performed simultaneously and in real time as a function of time and temperature with a specially designed optical instrument. The physical principles of this instrument are based on laser beam deflection caused by film stress induced wafer bending and partial integrated light scattering from surface roughening. The experimental results show how the initial hillocking is accompanied by changes in the overall stress and yield a very good correlation between the onset of hillock formation and the maximum change in overall stress.