Reactive ion etchers are parallel plate, capacitively coupled plasma etchers wherein the substrate sits on the powered electrode. An RF power, in most cases at 13.56MHz, is applied to the powered electrode. The powered electrode area is typically smaller than the grounded electrode area. Gases that are fed into the chamber are ioized and produce a gaseous mixture of neutral and ionized species. The positively charged species accelerate toward the biased electrode where the substrate is placed and causes the etching of the substrate. It is also called ion assisted etching as neutrals also participate in the etching process.