Elastic and thermo-elastic characterizations of thin resin films using colored picosecond acoustics and spectroscopic ellipsometry

Colored Picosecond Acoustics (CPA) and Spectroscopic Ellipsometry (SE) are combined to measure elastic and thermoelastic properties of polymer thin-film resins deposited on 300 mm wafers. Film thickness and refractive index are measured using SE. Sound velocity and thickness are measured using CPA from the refractive index. Comparing the two thicknesses allows checking consistency between both approaches. The same combination is then applied at various temperatures from 19° to 180°C. As the sample is heated, both thickness and sound velocity change. By monitoring these contributions separately, the Temperature Coefficient on sound Velocity (TCV) and the Coefficient on Thermal Expansion are deduced. The protocol is applied to five industrial samples made of different thin-film resins currently used by microelectronic industry. Young’s modulus varies from resin to resin by up to 20%. TCV is large on each resin and varies from one resin to another up to 57%.