Correction for surface charge induced beam displacement in large area sub-45 nm patterning with FIB lithography

Abstract

Focused Ion Beam (FIB) lithography not only can produce features on photoresist, it can also be used to manufacture mold for Nanoimprint. FIB provides fast results with a well focused minimum 7 nm diameter Ga₊ ion beam, and making mold for Nanoimprint with FIB immunes oneself from photoresist issues involved in sub-45 nm large area patterning. However, due to surface charge accumulation, large area patterning often results in displaced and overlapped patterns, similar to e-beam lithography. This displacement occurs in area as small as 5 µm², and is a function of beam dwell time and ion current dose. A small dwell time can lessen this displacement to certain degree if the pattern is small, but fails when the area to be pattern is large. In this paper we present a correct scheme in which the ion beam is check periodically against a pre-drilled mark for beam displacement, and made adjustment in beam control correspondently. In this manner, a large area (10 µm²) pattern of 50 nm squares is successfully demonstrated on a Si wafer.