Patent ID: 8105901

Claim:
A method comprising: depositing an undoped silicon layer on a primary layer; depositing a cap layer on said undoped silicon layer; patterning a photoresist layer on said cap layer, said photoresist layer having openings; patterning said undoped silicon layer into silicon mandrels by removing portions of said undoped silicon layer and corresponding portions of said cap layer exposed by said openings in said photoresist layer; removing said photoresist layer to leave said silicon mandrels standing on said primary layer and cap layer mandrels on said silicon mandrels; incorporating impurities into sidewalls of said silicon mandrels in a process that leaves sidewall portions of said silicon mandrels doped with impurities and that leaves central portions of at least some of said silicon mandrels undoped, said central portions of said silicon mandrels being between said sidewall portions of said silicon mandrels, within individual silicon mandrels; removing said cap layer mandrels to leave said silicon mandrels standing on said primary layer; performing a selective material removal process to remove said central portions of said silicon mandrels and to leave said sidewall portions of said silicon mandrels standing on said primary layer; patterning at least said primary layer using said sidewall portions of said silicon mandrels as a patterning mask; and removing said sidewall portions of said silicon mandrels to leave at least said primary layer patterned.