Monte Carlo simulation of the electron beam scattering under gas mixtures environment in an HPSEM at low energy

The effects of various gas environment used in high pressure SEM inside the specimen chamber were investigated using Monte Carlo simulation. In order to improve the signal to noise ratio for the electron detection, we suggest to use helium gas-based mixture. The Helium gas is well known to reduce the skirt effect due to its low elastic scattering cross-section. The addition of an ionizing gas such as hydrogen or nitrogen is proposed to increase the inelastic scattering cross section which is mainly responsible for the ionisation process taking place during the beam-gas interactions. For all the mixtures (except He-Argon), the main results show that the skirt is slightly modified with the increase of the pressure. For the BSE detection, the signal to noise can remain high and gives a good contrast in imaging. Moreover, the presence of an ionizing gas will favour the ionizing process which is very important in beam-based electron detection. In this case, an increase of the signal to noise ratio can be expected.