0.1 μ scale lithography using a conventional electron beam system

Abstract

A commercial electron beam machine has been used in conjunction with high contrast resists to define patterns with dimensions close to the minimum beam diameter of 0.1 μ on a range of solid substrates. This has required a detailed knowledge of the beam-substrate interactions in order to control linewidth. The electron scattering profiles in thin resist layers have been experimentally determined for substrates of Si, GaAs, InP, and Au on Si, and for beam voltages between 10 and 50 kV. These experimental results have been correlated with empirical models of electron scattering. It has been found that the simple double Gaussian model is inadequate at these dimensions, and the addition of an exponential term is necessary to fit data adjacent to the primary beam. Exposures have been modeled using this three term approximation, and the resultant lithography predicted by taking account of resist contrast. Routine fabrication of asymmetric 0.46 μm period gratings on InGaAsP substrates, used in the manufacture of distributed feedback lasers, has been possible, while experimental nonperiodic structures of 0.1–0.2 μ dimensions have been made on Si and InP. The reduction of backscattering by a multilevel resist system on Si has been studied with planarizing layer thicknesses up to 2 μm, and beam voltages of 20 and 30 kV.