Pressure resistance evaluation of an ultrathin SiNx membrane etched by a gas cluster ion beam

In this study, reactive etching of a SiNx free-standing membrane with a thickness of a few nanometers was performed using a gas cluster ion beam (GCIB) and the pressure resistance of the membrane with respect to its thickness was evaluated. The low-damage irradiation effect of a 7 keV GCIB in an acetylacetone (Hacac) atmosphere enabled the etching to retain its pressure resistance compared with that of 400 eV Ar+ beam irradiation. In a previous study, it was shown that irradiation of SiNx films with Ar plasma of several hundred eV causes defects in the bonding network of the Si–N bond and the network is easily oxidized. XPS measurements on SiNx films after GCIB etching with Hacac and Ar+ beam irradiation showed that the composition of the Si–O bond was smaller with GCIB irradiation compared to Ar+ beam irradiation. This indicates that GCIB etching with Hacac can suppress the formation of defects in the Si–N network, which reduces the degradation of the pressure resistance.