Optimization of post N2 treatment & USG cap layer to improve tungsten peeling defects for deep sub-micron device yield improvement

Integration issue of W-plug peeling from fluorinated silica glass (FSG) in deep sub-micron IMD application was investigated in this study. Tungsten would peel off immediately during post CMP N₂ treatment in-situ running with USG cap layer deposition after W-plug deposition. Separating or optimizing post-CMP N₂ treatment and cap layer would solve this peeling issue. The key points of peeling were the bias power of N₂ treatment and initial USG cap temperature in the HDP-CVD chamber. TOF-SIMS analysis revealed that higher bias power and longer treatment time lead to more fluorine distribution on the USG cap layer surface, which may cause non-Si-F bonding fluorine to react with subsequent Ti/TiN/W metal layer. FTIR spectra also showed that low bias power, adding an extra cooling step before substantial in-situ cap layer deposition or ex-situ cap would increase fluorine stability in FSG/USG interface.