A background dose proximity effect correction technique for scattering with angular limitation projection electron lithography implemented in hardware

Abstract

A background dose proximity effect correction procedure is proposed that utilizes the unique way image contrast is formed in scattering with angular limitation projection electron lithography (SCALPEL(R)). An electron beam is selectively scattered by a thin, high atomic number layer patterned on a membrane mask. Some of the scattered radiation, which is normally blocked at an aperture to form contrast at the wafer, is allowed to pass through the system optics. Nominally dark regions of the mask are therefore allowed to expose the resist on a wafer. However, because the scattered radiation enters the projection system at relatively large angles, it is subjected to system aberrations and is improperly focused at the wafer. This dispersed radiation mimics the natural long range backscatter exposure emanating from the intentionally exposed regions, and ideally results in a constant background exposure in the resist—similar to the GHOST background correction technique used in direct-write applications. However, unlike the direct-write correction, both the primary exposure and the correction exposure are achieved at the same time. Throughput is not reduced by the correction. Although the correction dose profile may not resemble the form of the long range backscatter energy deposition in the resist, the deviations of background exposure are small for mask patterns of practical interest, in comparison with the variation of uncorrected exposures of the same pattern.