Method for enhancing field oxide thickness at field oxide perimeters

Abstract

A method for enhancing the thickness of a field oxide layer at perimeters of the field regions is presented. The use of a relatively thin pad oxide layer under a nitride layer reduces lateral encroachment of the field oxide layer into device active areas, but also results in undesirable elevational disparities in an upper surface of the field oxide layer near perimeters. Elevational disparities are created when the field oxide layer grows up and around vertical edges of remaining portions of the patterned nitride layer. An oxide deposition step followed by a directional etch process are used to fill in the elevational disparities, increasing the thickness of the field oxide layer at perimeters of the field regions. In a first embodiment, an oxide layer is deposited over the exposed surface following removal of remaining portions of the nitride layer over device active areas. In a second and third embodiment, oxide layer deposition and etch follow removal of substantially all of the remaining portions of the pad oxide layer and an upper portion of the field oxide layer as to expose the silicon substrate in device active areas. In the third embodiment, a sacrificial oxide layer is grown in and on device active areas prior to oxide layer deposition and etch.

Dependencies are inferred from the claim text.