Online measurement of photochemical reaction rates in the VUV with a quartz microbalance: Cl2 and Cu

An experimental setup to directly monitor the rates of light induced dry etching reactions is presented. We use an etching cell kept inside an ultrahigh vacuum chamber which allows in situ sample preparation and the combination with a vacuum ultraviolet monochromator for synchrotron radiation. The sample material is evaporated on a polished quartz crystal which serves to monitor the reaction rates via the frequency changes. As a model system measurements for Cu samples are presented with Cl2 as etching gas and Ar as carrier gas. We distinguish between processes originating from gas phase excitation (non-selective) and from surface excitation (selective). In addition the dark reaction is separated.