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.

100 keV electron backscattered range and coefficient for silicon

“…7,8 Monte Carlo simulations have been used to calculate the parameters 9 while many of the values used in PEC models are based on experimental data for electron energies from 20 keV up to 120 keV. [10][11][12][13][14] Forward scattered electrons change the shape and dose of the feature being written. These effects have been countered with both dose assignments through PEC and with shape adjustments, 5,6 similar to near-field optical lithography techniques.…”

The range and intensity of backscattered electrons for use in the creation of high fidelity electron beam lithography patterns

“…Electrons backscatter from the substrate and can return up to several micrometers away from the beam, adding unintended dose to the resist layer, distorting the pattern. Proximity effect correction (PEC) has been used to balance the dose from direct write and backscattered electrons [13][14][15][16]. The values used in PEC are not fully characterized in literature; therefore, currently, the creation of nanoscale patterns by electron beam lithography is performed iteratively without a robust way of transferring the basic theoretical understanding to a practical implementation.…”

“…Achieving an accurate dose is most important for nanometer features because small changes in dose can change the feature size by larger percentages of the total feature size than at the micrometer scale. Backscatter parameters have been measured experimentally for a few materials using different techniques [13][14][15][16] that rely on optical or scanning electron microscope pattern inspection, causing discrepancies in observed parameters of up to 50%.…”