Method for forming square-shouldered sidewall spacers and devices fabricated

Abstract

A method for forming sidewall spacers with square shoulders on polysilicon gates and the structure formed by the method are disclosed. In the method, a polysilicon gate is first formed on a silicon substrate wherein the gate has a silicon nitride pad on top. A conformal silicon nitride layer is then blanket deposited on top of the structure followed by the deposition of a silicon oxide layer on top of the conformal silicon nitride layer. The silicon oxide layer is then planarized until a top of the conformal silicon nitride layer is exposed. The conformal silicon nitride layer and the silicon nitride pad are then wet etched away to expose the polysilicon gate by using the silicon oxide layer as a mask. After a photoresist layer is coated and etched-back such that only a cavity formed by the silicon oxide layer, the polysilicon gate and the conformal silicon nitride layer is filled with the photoresist, the silicon oxide layer is wet etched away by an etchant such as HF. The square-shouldered sidewall spacers are then formed by first anisotropically etching the first silicon nitride layer not masked by the photoresist layer and then by a wet etching step to remove the photoresist layer.