Outlook

In an approximation to zero order, the plasmas differ with respect to their discharge pressures [ion beam methods (IB) which can be operated down to 10^-4 Torr or 0.1 Pa to microwave operation which work even at atmospheric pressure] and operating frequencies [DC to MW operation (technical frequency: 2.45 GHz)]. Finer tuning leads to resonant methods (ECR and helicon) and non-resonant techniques (CCP and ICP). Concerning the type of etching, we discriminate between ion beam etching [(IBE), pressure below 10^-4 Torr], ion etching (at least one order of magnitude higher), and plasma etching (another order of magnitude higher). Resonant methods are operated in the intermediate range between ion beam etching and ion etching. For resonant methods, the etch rates are second to none, next in line is ICP which is superior to CCP. We can also make a distinction between etching reactors which are operated downstream (ECR, helicon, ICP, and IB) and others with a parallel-plate reactor (DC and LF, CCP).