Patent ID: 7244661

Claim:
A method for forming a buried diffusion layer with reducing topography in a surface of a semiconductor substrate, comprising: providing a semiconductor substrate with a first conductivity type; forming a first dielectric layer on said semiconductor substrate; patterning said first dielectric layer to form a hard mask of said first dielectric layer on said semiconductor substrate; performing a thermal oxidation process to form field oxides on the exposed potions of said semiconductor substrate; removing said patterned first dielectric layer; forming a second dielectric layer on said field oxides and said semiconductor substrate; patterning said second dielectric layer to form a hard mask of said second dielectric layer; performing an isotropic etching process to etch the exposed portions of said field oxides and said semiconductor substrate; removing said patterned second dielectric layer and the underlying field oxides to form a plurality of trenches on the surface of said semiconductor substrate; and forming a buried diffusion layer with a second conductivity type opposite to the first conductivity type along surroundings of said trenches in said semiconductor substrate.