Effect of capping layer on hillock formation in thin Al films

The effect of capping layers oil hillock fort-nation has been studied in pure aluminum films. For this purpose, different capping materials (Ti, Mo, SiO2) of various thicknesses (from 200 angstrom to 1000 angstrom) were deposited on an Al/glass substrate. The density, diameter and height of hillocks were analyzed after annealing for 400 min at 280 degrees C. As the thickness of the capping layer increases, the hillock density, diameter and height decreases. The total volume of hillocks per unit area of the film decreases while both the thickness and the biaxial modulus of the capping layers increases. Using a spherical cap model of the bulge test, a simple equation which can predict the total volume of hillocks per unit area of the film is suggested. The comparison shows excellent agreement between the modeled and experimental profiles.