Broad band Ultraviolet (UV) radiation of spin coated PerHydroPoIySilazane (PHPS) films prior to steam anneal is shown to improve density of final SiO2 inside high aspect ratio ( 7:1) gap fill structure. Post-steam anneal wet etch rate improvements of up to 18% in blanket films and up to 26% in the ≥7:1 aspect ratio gap fill structure have been obtained for UV treated films relative to control (steam annealed only films). UV dose plays a critical role in determining the final film densification. However, PHPS film becomes moisture sensitive post-UV exposure. The UV treated films show instability in presence of moisture and react/self-convert into Si02. The rate of moisture absorption and conversion depend on the UV dose and the Q time between UV and steam anneal. Presence of moisture adversely impacts the final wet etch rate of the oxide. Careful choice of UV dose and implementation of Q time between UV and steam anneal are critical to get full entitlement from UV.