A study on the effect of ultra-low electron temperature on the etching of MoS₂ layer

We investigated the effect of ultra-low electron temperature (ULET, electron temperature < 1 V) on MoS₂ layer etching_. Oxygen ULET (~0.6 V) plasma was generated by using a grid. When a negative voltage (-20 V) is applied to the grid, an electron beam is generated, and ionization occurs by the electron beam [1]. Since the electron produced from the ionization have low energy, ULET plasma can be generated. When MoS₂ was exposed to conventional plasma, which has 3.9 V of electron temperature (T_e) and has about 2x10⁸ cm^-3 of electron density during 60 sec, MoS₂ layers are fully etched. However, MoS₂ layers are less etched in the ULET plasma despite the same density and exposure time as the conventional plasma. It is because the sheath voltage is significantly lower at ULET plasma than that of the conventional plasma due to low T_e. The removal of MoS₂ layer is verified through Raman spectroscopy and T_e are obtained by measuring electron energy probability function (EEPF). It is expected that plasma induced damage caused by ion bombardment can be reduced because of much lower sheath voltage in the ULET plasma.