Chemical vapor deposition (CVD) has been used to deposit films such as silicon, silicon oxide, silicon nitride, tungsten, silicide, copper and titanium nitride in the semiconductor industry. The reaction driving forces for CVD are typically temperature for thermal CVD, plasma ionization for plasma enhanced CVD, or atomic oxygen for ozone CVD. In the recent years, plasma enhanced CVD (PECVD) and ozone CVD have found extensive applications in the semiconductor industry, due to the higher deposition rate and lower deposition temperature. For example, PECVD and ozone CVD are used to deposit almost all dielectric films such as silicon oxide and silicon nitride on a wafer. The dielectric films on wafers serve as insulating layers between conducting metal layers and as passivation layer on top of semiconductor devices.