VUV Broad-Band absorption spectroscopy in downstream plasma soft-etch reactor

The patterning of nanometer scale features in complex stacks of ultrathin layers is a challenging plasma process.Plasma induced damage is a serious issue when dealing with ultrathin layers and adverse topography.As a result, there is a regain of interest for remote(downstream)etching reactors,in which the wafer is etched in the absence of ion bombardment by radicals only.However,downstream systems have been poorly characterized and are typically using complex plasma chemistry at relatively high pressure(≥1Torr). In this work we used VUV Broad Band absorption spectroscopy, described in[1],with a VUV CCD camera to detect closed shell molecules(NF3,NH3,HF..)in downstream NF3/H2 and NF3/NH3 plasmas,which are used to etch selectively Si,Si3N4 and SiO2. We focus on the production and loss mechanisms of HF, which seems to be the main etching agent,and discuss the impact of the plasma operating conditions on the HF density.Further,we show that due to the high sensitivity of the VUVAS,it is possible to monitor in real time the radical densities(NF3, NH3, HF),which is useful to understand their production and loss kinetics and also to provide an endpoint technique adapted to these reactors.in which the currently used optical emission for this purpose is not present. [1] G.Cunge et al,2011