The present application discloses a method for fabricating the semiconductor device. The method for fabricating the semiconductor device includes forming a first dielectric layer on a substrate; forming a feature opening to exposing the substrate; performing a pre-cleaning treatment including a pre-cleaning solution to the feature opening; performing a cleaning process to the feature opening; and forming a conductive feature in the feature opening. The pre-cleaning solution includes a chelating agent and a corrosion inhibitor.

Described examples include a method having steps of forming an isolation pad oxide layer on a substrate and forming and patterning a silicon nitride layer on the isolation pad oxide layer. The method also has steps of oxidizing portions of the substrate not covered by the silicon nitride layer to form a LOCOS layer and oxidizing the silicon nitride layer in an oxidizing ambient containing a chlorine source to form a silicon dioxide layer.

A method of fabricating an integrated circuit includes forming a first opening having a first width and a second opening having a second width in a first dielectric layer over a silicon substrate. The openings expose the silicon substrate and the exposed silicon substrate is oxidized to form first and second LOCOS structures having a first thickness. A polysilicon layer is formed over the silicon substrate, so that the polysilicon layer fills the first and second openings. A blanket etch of the polysilicon layer is performed to remove at least a portion of the polysilicon layer over the second LOCOS structure while leaving the first LOCOS structure protected by the polysilicon layer. The silicon substrate under the second LOCOS structure is further oxidized such that the second LOCOS structure has a second thickness greater than the first thickness.

An integrated circuit includes a gate electrode over a silicon substrate and a local oxidation of silicon (LOCOS) structure between the gate electrode and the silicon substrate. The LOCOS structure has bird's beak portions, peripheral portions between the bird's beak portions, and a central portion between the peripheral portions. The peripheral portions have a first thickness, and the central portion has a greater second thickness.