Nanomechanical characterization of BD (Low-K) thin films and Cu/BD multilayered stacks

Abstract

Samples were fabricated using different thin film deposition processes such as, PECVD, sputtering and electroplating. Present study focuses on mechanical characterization of BD (low-k, Black Diamond TM) thin films of six different thicknesses and various Cu/BD stacks with Ta & TaN barrier layers and SiC & SiN cap layers which are of interest in IC (integrated circuit) back end technology. Hardness (H) and elastic modulus (E) properties were obtained by conducting nanoindentation experiments with continuous stiffness (CSM) method. In addition adhesive/cohesive strength of the thin film samples were studied by nanoscratch technique and reported in terms of critical load (Lc). Both nanoindentation and nanoscratch tests were performed on Nano IndenterA? XP system with respective attachments. The hardness and elastic modulus values of BD thin films of various thicknesses (100-1200nm) are in the range of 2.02 to 1.66 GPa and 16.48 to 9.27 GPa respectively and critical loads (Lc) are in the range of 13.02 to 25.86 mN. The H & E of single dielectric stacks are found to be better than the dual dielectric stack but dual dielectric stacks exhibit higher Lc than single stacks. Presence of barrier layer (Ta or TaN) at the BD/substrate interface doubles the adhesion strength (Lc) when compared with BD film without barrier. For dual stacks, two critical loads (Lc1 & Lc2) were noticed during scratch testing. Mechanical behavior of multilayered Cu/BD stacks is somewhat complex when compared to other samples undertaken in this study. Stacks with higher mechanical properties show higher critical loads (Lc). Stacks with SiN cap layer have demonstrated higher mechanical properties than stacks with SiC cap layer. No significant delamination is observed between copper and barrier & cap layers and BD.