Proximity effect in electron beam patterned x-ray masks

Abstract

Electron beam exposures of 30 nm Au/5 nm Cr/2.2 μm Si x-ray lithography mask structures were carried out at 25, 50, 75, and 100 keV to study the reduction in the proximity effect at higher beam voltages resulting from the loss of backscattered electrons out the backside of the masks. Surprisingly, the thin Au/Cr plating base was found to be the major source of backscattering over distances <1.0 μm. In addition, the plating base served to limit the decrease in the ratio of the backscattered to forward scattered exposure that resulted from increasing the beam voltage. These results indicate that simply increasing the beam voltage will not completely eliminate the proximity effect due to backscattering that arises during the electron beam patterning of x-ray masks.