US Patent 9673055 Method for quadruple frequency FinFETs with single-fin removal

A method of single-fin removal for quadruple density fins. A first double density pattern of first sidewall spacers is produced on a semiconductor substrate from first mandrels formed by a first mask using a minimum pitch. A second double density pattern of second sidewall spacers is produced on a layer disposed above the first double density pattern from second mandrels formed by a second mask with a the minimum pitch that is shifted relative to the first mask. A single sidewall spacer is removed from either the first or second double density pattern of first and second sidewall spacers. Sidewall image transfer processes allow the formation of quadruple density fins from which but a single fin is removed.