Low voltage resist processes developed for MAPPER tool first exposures

The FP7 European project MAGIC [1] aims at designing a multi electron beam machine. In the frame of this project, LETI evaluates a multibeam tool from MAPPER lithography [2]. Each beam has an acceleration voltage of 5kV. A tool has been installed in LETI premises in July 2009. In order to prepare its evaluation, preliminary work was performed on Gaussian beam tools down to 5kV. It aimed at the determination of a stable and robust resist process allowing high resolution at 5kV. Then those results were used to characterize MAPPER tool performances. Meeting the requirements of high resolution and low roughness at low voltage, Dow Corningmolecular glass HSQ (hydrogen silsesquioxane) and MicroChem PMMA (polymethylmethacrylate) were used to test MAPPER tool as negative and positive tone resist references. We did exposures at beam acceleration voltages from 5 kV up to 100 kV. Different post application bake (PAB) temperatures were applied to resist. Several developer concentrations were also tested. The impact of those three parameters on contrast and resolution was checked. Resists chemical characterization was performed with FTIR (Fourier transform infra red) spectroscopy in order to understand the mechanisms leading to the observed variations of contrast and exposure dose as process parameters are changed. The main purpose of this work was to show that high resolution can be achieved at 5kV. First exposures performed with MAPER tool confirmed those results.