Effect of Nucleation-Stage Reducing Agents on Residual Stress in CVD Tungsten Thin Films

Abstract

As vias become narrower and deeper, to improve semiconductor performance, the demand for tungsten (W) with excellent step coverage is increasing. However, residual stress remains an important issue in the W thin film deposition process. This study investigated the residual stress of chemical vapor deposition (CVD) W thin films using two different reducing gases: diborane (B₂H₆) and silane (SiH₄). Residual stress was quantitatively evaluated using the Stoney equation based-on wafer curvature measurements. As a result, the SiH₄-W thin film exhibited higher residual stress than the B₂H₆-W film as the thin film thickness increased. It was found that the difference in residual stress depending on the reducing gas was mainly attributed to microstructural effects rather than impurity incorporation. In both cases, the intrinsic stress was dominant in the residual stress. The SiH₄-W thin film exhibited smaller grains compared to B₂H₆-W, resulting in higher tensile stress. In addition, fracture surface analysis using fracture mechanics tests revealed that the fracture surface crack patterns varied with the level of residual stress. The results of this study are expected to provide insights into optimizing W thin-film deposition and improving mechanical reliability for advanced semiconductor applications.