Influence of the dose assignment and fracturing type on patterns exposed by a variable shaped e-beam writer: simulation vs experiment

The result of electron beam lithography is influenced by many effects: forward and backward scattering, formation of secondary electrons, re-scattering of electrons, chemicals diffusion in the resist material, wafer stack, etc. To achieve high resolution all these effects should be taken into account. Commonly, the electron energy distribution in the exposed matter is described by the Point Spread Function (PSF). This is a simple approach which takes into account large portion of phenomena using few parameters. PSF function is a Gauss or multiple Gauss function, which is determined experimentally by the calibration procedure. Each resist material with corresponding stack is characterised by its own PSF, in case of double Gaussian, with the following parameters: α, β and η. In the current work the PSF parameters were systematically varied to study their influence on the dose assignment and resulting pattern. This gives a broader understanding of the correction mechanism using PSF. Furthermore, the resulting shape of the structure is influenced not only by the PSF parameters and dose assignment, but by the fracturing type as well. All these effects were studied using experimental and simulation approaches.