Plasma etching is a critical step in the fabrication of all semiconductor based devices including Memory, Logic, RF, Power, MEMS and Optoelectronics chip-sets. Time based etching is prone to unplanned variations in layer thicknesses, layer composition and/or etch rate variations caused by Etch chamber conditioning. End-point detection is key to controlling Plasma Etches because it precisely defines the point at which the etching must stop.  This eliminates the risks of under-etching (which would require wafer re-work) or over-etching, which can easily lead to excessive CD loss, sidewall pitting, stop layer loss and throughput deficiencies.