Semiconductor structures and methods for forming isolation between fin structures formed from a bulk silicon wafer are provided. A bulk silicon wafer is provided having one or more fin structures formed therefrom. Forming of the fin structures defines isolation trenches between the one or more fin structures. Each of the fin structures has vertical sidewalls. An oxide layer is deposited in the isolation trenches and on the vertical sidewalls using HDPCVD in about a 4:1 ratio or greater. The oxide layer is isotropically etched to remove the oxide layer from the vertical sidewalls and a portion of the oxide layer from the bottom of the isolation trenches. A substantially uniformly thick isolating oxide layer is formed on the bottom of the isolation trench to isolate the one or more fin structures and substantially reduce fin height variability.