In a method of forming a semiconductor device on a semiconductor substrate (100), a photoresist layer (102) is deposited on the semiconductor substrate; a window (106) is formed in the photoresist layer (102) by electron beam lithography; a conformal layer (108) is deposited on the photoresist layer (102) and in the window (106); and substantially all of the conformal layer (108) is selectively removed from the photoresist layer (102) and a bottom portion of the window to form dielectric sidewalls (110) in the window (106).