Abstract: A method for forming an isolation structure on a semiconductor substrate includes opening a portion of a pad oxide layer overlying the substrate using a process gas including an etchant gas and a polymer-forming gas. A portion of the substrate exposed by the opening step is etched to form a trench having a first slope and a second slope. The first slope is greater than 45 degrees, and the second slope is less than 45 degrees. The trench is filled to form the isolation structure.

Abstract: A method for making a semiconductor device having a first active region and a second active region includes providing first and second isolation structures defining the first active region on a substrate. The first active region uses a first operational voltage, and the second active region uses a second operational voltage that is different from the first voltage. A nitride layer overlying the first and second active regions is formed. An oxide layer overlying the nitride layer is formed. A first portion of the oxide layer overlying the first active region is removed to expose a first portion of the nitride layer. The exposed first portion of the nitride layer is removed using a wet etch method while leaving a second portion of the nitride layer that is overlying the second active region intact.