Effects of accelerating voltage and pattern size on electron scattering by electron-beam mask

Electron scattering by electron-beam (EB) masks has been studied by a Monte Carlo simulation to investigate the influence of increasing accelerating voltage, of decreasing pattern size, and of using a thinner mask for a practical engineering application. The simulation study has revealed that there are two different exiting angle distributions; whether the most frequent exiting angle depends on L/S size or not, These are named interfeature scattering and intrafeature scattering, respectively. In order to analyze the electron scattering phenomena, we investigated the electron transmittance and absorbance by normalizing the mask thickness, using a Grun range. As a result, the EB mask was found to be categorazible into four function categories defined by the normalized mask thickness. They are pure absorber, scattering absorber, absorbing scatterer, and pure scatterer. This classification gives us important information for engineering design of the EB mask and for column design. For the EB mask, whose normalized mask thickness is more than 0.2, the transmitted electrons are scattered enough not to contribute to imaging in the angular and the energy distributions and high contrast can be obtained with some optimization of the angular limiting aperture, When the normalized mask thickness is less than 0.2, the limiting angle of the aperture may need to be decreased due to high electron transmittance, but optimization for different pattern sizes is not necessary in the case of the intrafeature scattering. The combination of thinner mask and an appropriate limiting aperture seems to be feasible and promising for future EB cell projection lithography to achieve higher resolution. (C) 1997 American Vacuum Society.