MARS2: An advanced femtosecond laser mask repair tool

Abstract

Femtosecond pulsed lasers offer fundamental advantages over other techniques for repairing lithographic masks. Since the femtosecond ablation process is non-thermal, the spatial resolution is not degraded by thermal diffusion and is therefore limited only by optical diffraction. In addition, metal splatter, gallium staining, reduced optical transmission, beam induced charging, quartz damage, and phase errors inherent in other repair methods are eliminated. A second generation femtosecond laser repair tool is described. The tool utilizes DUV optics which allow ∼100 nm mask features to be imaged. The laser beam is focused to a round, gaussian spot. This gaussian spot is scanned over the defect, thus allowing arbitrarily shaped repairs to be performed with a spatial resolution of ∼100 nm. Since the mask is not degraded in any way during the repair process, repairs can be performed iteratively by ablating small slices of the defect. Mask features can be trimmed to an RMS precision of ∼5 nm. The system is also highly automated: masks are loaded into the tool from a SMIF pod via a robot and the tool is controlled from a single screen operator interface. This new tool has been operating successfully in the IBM Burlington mask house since late 2001, and is currently IBM's primary repair tool for 248 and 193 nm chrome on glass and phase shift masks.