US Patent 7105416 Method for controlling the top width of a trench

A method for controlling the top width of a trench. A conductive layer is formed on the trench over the substrate, forming an interlayer over a part thereof, above the conductive layer. A sacrifice layer is formed on the trench sidewall above the interlayer, and the interlayer is removed to expose the trench sidewall above the conductive layer and the sacrifice layer, such that the exposed trench sidewalls are oxidized. Thus, the sacrifice layer on the trench sidewall reduces the top width of the trench. In the oxidization process, silicon oxide is formed on the sacrifice layer and the exposed trench sidewall, such that upper width of the trench will is not increased during subsequent wet etching.