Abstract: Described is a method to form isolation structures on a semiconductor substrate. This method begins with forming one or more trenches in the semiconductor substrate and depositing a first portion of a dielectric layer at a first rate by a High Density Plasma—Chemical Vapor Deposition into the trenches and onto the semiconductor substrate. This first deposition at least partially fills the trenches and may completely fill the trenches. Next, a second portion of the dielectric layer is deposited at a second rate by the High Density Plasma—Chemical Vapor Deposition over the semiconductor substrate to partially planarize the dielectric layer. This second deposition is preferably performed with a different flow rate of reaction gasses than the first deposition. Finally, a portion of the dielectric layer that was deposited at the second rate is removed by a CMP process, for example.