Anisotropic plasma etching methods were introduced into semiconductor manufacturing in the late 1970s. The notion of using reactive gas glow discharges to etch solid materials had been described much earlier but it was not until the mid 1970s that the anisotropic etching capabilities of plasma etching were recognized. At this time, it was understood that the requirements for anisotropic etching were both energetic ion bombardment of the surface being etched and an exothermic chemical reaction between the gas phase reactants and the surface that form a volatile reaction product. Early plasma etching systems were primarily capacitively coupled, single frequency diodes with either planar or cylindrical geometry. In order to achieve the desired etch rates, relatively high energy (0.5 to 1 keV) ion bombardment of the surface being etched was required. However this bombardment tended to reduce etch selectivities and increase wafer damage. Furthermore, the plasma potential in capacitively coupled systems can exceed 100 volts, resulting in high energy ion bombardment and sputtering of grounded surfaces; a possible source of wafer contamination. These issues were addressed by separating the plasma generation from the wafer bias. During the early 1980s, single frequency and dual frequency triodes were popular. Later in the 1980s, inductively coupled and wave-generated plasma sources were introduced. These sources allowed the generation of high density plasmas (10@super 11@ to 10@super 13@ electrons/cm@super 3@) which, when combined with a relatively low power capacitively coupled chuck, allowed high etch rates to be achieved with relatively low ion energies (50 - 200 eV). Today, each wafer is exposed to a plasma etching environment between 10 and 20 times during its manufacture and without the highly anisotropic etching provided by this critical process, high density IC manufacturing would not be possible.