Method of removing a polysilicon buffer using an etching selectivity solution

Abstract

A method of removing a polysilicon buffer in a method of forming a field oxide and an active area is disclosed herein that comprises the step of applying an etching selectivity solution to the polysilicon buffer to substantially remove the polysilicon buffer without substantially affecting the field oxide, a pad oxide, and the substrate. An etching selectivity solution is defined herein is a solution that has an etching rate for one material that is higher than for another material. In this case, the etching selectivity solution has an etching rate for polysilicon material that is higher than its etching rate for field oxide material. Accordingly, when the etching selectivity solution is applied to the polysilicon buffer, it will substantially etch off the polysilicon buffer without substantially affecting the field oxide. In the preferred embodiment, the etching selectivity solution comprises a mixture of HF and HNO,, or HF, HNO,and CH,COOH. The advantage of this method is that it reduces the likelihood of the formation of pits within the field oxide, pad oxide and the substrate. Consequently, the charge-to-breakdown voltage for the device is not degraded because of the absence of the pits. In addition, methods of forming a field oxide and an active area are disclosed herein that uses at least in part the disclosed method of removing a polysilicon buffer.