Contact angle measurements for adhesion energy evaluation of silver and copper films on parylene-n and SiO2 substrates

Abstract

Copper and silver films are being considered for future multilevel interconnect systems. The reduction of feature size has also demanded the use of different low-dielectric materials (e.g., parylenes) in place of conventional silicon dioxide based layers. Adhesion of these materials with each other is a major hurdle in the reliable and durable performance of the devices. Contact angle measurements are used to measure adhesion energies of Cu and Ag layers on substrates of either SiO2 and Pa–n. Qualitative tape-test analysis indicates improved adhesion of these films with anneal and plasma treatment. Surface energy increase of parylene–n using oxygen plasma treatment is demonstrated using sessile water-drop method. The increase in adhesion for the Ag/Pa–n system is attributed to increased roughness and presence of carbonyl groups on the surface. The contact angle measurements are corrected to compensate for the effect of roughness. The adhesion energy for Ag/Pa–n system increases from 0.33 to 1.28 N/m with plasma treatment. Higher-surface energies of copper at room temperature attribute to higher-copper adhesion energy when compared to that of silver.