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Abstract

A method of preventing dopant from diffusing into atmosphere in a BiCMOS process is disclosed. The BiCMOS process includes the steps of: depositing a first silicon oxide layer and a silicon nitride layer over surface of a silicon substrate; etching the silicon substrate to form a plurality of shallow trenches therein; depositing a second silicon oxide layer over surface of the silicon substrate and forming silicon oxide sidewalls over inner side faces of each of the plurality of shallow trenches; forming a heavily doped pseudo buried layer under a bottom of one of the plurality of shallow trenches by implanting a dopant with a high concentration; performing an annealing process to promote diffusion of the dopant contained in the pseudo buried layer, wherein the method includes growing, by thermal oxidation, a silicon oxide layer over a bottom of each of the plurality of shallow trenches during the annealing process.

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First Claim