Process for recess-free planarization of shallow trench isolation

Abstract

An improved and new process for fabricating planarized isolation trenches, wherein sharp corners at the top periphery of the trench are eliminated and erosion of insulating material at the edges of isolation trenches is suppressed, has been developed. The process uses a two layer mask to etch the isolation trench, followed by an isotropic etch to recess the first layer of the mask. An oxide liner is formed in the trench and across the exposed edge of the trench resulting in rounding the corners of the trench. Then, a second isotropic etch is used to recess the edge of the second mask layer, so that its opening now is beyond the edge of the trench. An oxide layer is conformally deposited over all exposed surfaces and fills the trench. After CMP to planarize the oxide layer, the remaining oxide fills the trench and, also, extends a small distance beyond the edge of the trench and serves to protect edge of the trench during subsequent etching.