Effect of W nucleation process on the adhesion of W/TiN/SiO2 structures for BEOL interconnects

초록

This study provides a direct and quantitative analysis of interfacial adhesion (Gc) in W/TiN/SiO2 structures, which are widely used as back-end-of-line (BEOL) interconnects in memory devices. Silane (SiH4) and diborane (B2H6), two representative reducing agents, are utilized to form a W nucleation layer, enabling the subsequent growth of a bulk CVD-W layer. While B2H6-W offers superior electrical performance with lower resistance compared to SiH4-W, its mechanical interfacial reliability remains unclear. The Gc of W/TiN/SiO2 stacks is quantitatively compared using four-point bending (FPB) tests. The results show that in both cases, the weakest interface is TiN/SiO2, with lower interfacial adhesion (5.60 +/- 0.45J/m2) when B2H6 is used for the nucleation process compared to SiH4 (6.96 +/- 0.07J/m2). This degradation is primarily attributed to the diffusion of boron (B), originating from the decomposition of B2H6, into the TiN-SiO2 interface which is thought to disrupt Ti-O bonding at the TiN-SiO2 interface. With increasing in B2H6 flow rate and soak time, the delamination interface shifts from the TiN-SiO2 interface to the W-TiN interface, accompanied by reduction in adhesion energy (2.72 +/- 0.18J/m2). This study provides valuable insights into selecting appropriate reducing agents and process conditions for W nucleation to ensure interfacial reliability.

키워드