Recent advances in electron optical systems which allow reduction of electron beam voltage while maintaining sufficiently small spot size and high current density have opened new possibilities for electron beam lithography. The main advantage of low beam energy lithography is a reduction of backscattered electrons and, consequently, the reduction of problems associated with proximity effects. The other advantages of this technique are reduction in the dose required to modify a resist and minimization of substrate damage caused by energetic electrons. Proper electron energy must be chosen at which the beam deposits its energy mainly within the resist film with minimal penetration into the substrate. Monte Carlo simulation programs have been used widely to predict the scattering interactions and thus the area of proximity effects. Rutherford cross section for angle scattering and Bethe energy loss have been commonly used in Monte Carlo modeling. However, low energy lithography (<5keV) requires a more accurate approach based on Mott cross sections for scattering and a more precise formula for energy loss replacing the Bethe law which is invalid below 1 keV energy.
Processes and time-scales of energy loss of low-energy electrons (<5 eV) in liquid water