A method (200) of fabricating a semiconductor device includes etching (205) a group of trenches in a semiconductor surface layer of a substrate. The group of trenches includes an outermost trench that has a first width and remaining trenches of the group of trenches have a second width that is less than the first width. The outermost trench is formed at an edge of the group of trenches. A dielectric liner is formed (210) in the group of trenches and the dielectric liner is etched (215) in an upper portion of the group of trenches to remove a partial thickness of the dielectric liner. A full thickness of the dielectric liner is maintained in a lower portion of the group of trenches. The group of trenches is filled (220) with a polysilicon layer.