X-ray Characterization of PEALD versus PVD Tantalum Nitride Barrier Deposition and the Impact on Via Contact Resistance

Abstract

Plasma enhanced atomic layer deposition (PEALD) of TaN demonstrated the significant benefit of lowering via resistance in back-end-of-line (BEOL) dual damascene copper interconnects with a line width of 32 nm, although PEALD TaN possessed a much higher intrinsic resistivity, approximately 2000 μΩcm, compared to physical vapor deposition (PVD) of Ta-rich TaN with a value around 250 μΩcm. The mechanism of lowering via resistance was studied by X-ray characterization techniques such as X-ray fluorescence (XRF) and X-ray reflectivity (XRR). XRF analysis indicated the nucleation rate of PEALD TaN is higher on a metal surface compared to a dielectric surface. XRR analysis revealed a smoother and damage free surface between PEALD TaN and silicon oxide, while a rougher interface was formed between PVD TaN and silicon oxide. Via resistance reduction with PEALD TaN is suggested to be related to reduced physical damage at the via bottom.