The effectiveness of the PVD TiN barrier layer during the CVD Tungsten (W) plug deposition process and the mechanism of volcano formation are investigated. The area density of volcanoes decreases with a thicker TiN barrier and/or with increased N-2 flow during TiN deposition. The size of the volcano increases with an increase in TIN barrier thickness. RTP temperature appears to dominate TiN barrier integrity. The 100% flow of N-2 during RTP is shown to improve the TiN barrier properties while fractional amounts of O-2 flow appear to have a negative effect. We characterize the volcano structure with SEM-EDX.