These simple devices, which were the staple of the industry until the mid-90s, consist of two flat, circular electrodes, about 20 cm in diameter, separated by about 10 cm. The wafer to be processed is mounted onto the bottom plate and held firmly by a “chuck”, which includes connections for the helium coolant and for connecting to a bias oscillator, which we will discuss later. To produce the plasma, RF power may be applied to either or both plates. The sidewalls may be of an insulating material such as aluminum oxide, or a metal such as stainless steel, which can be grounded. For definiteness in what follows, we shall assume that the wafer-bearing plate is grounded and the upper plate oscillates at 13.56 MHz. Gas is fed into the vacuum chamber, and the RF field electric field causes the first few electrons (there are always a few from cosmic rays or whatever) to oscillate and gain enough energy to ionize atoms. The electrons thus freed will also gain energy and cause further ionizations . This electron avalanche quickly fills the chamber with plasma, whose density and temperature depend on ihe RF power applied and on the neutral pressure.
KeywordsPlasma Source Electron Flux Displacement Current Plasma Potential Capacitive Discharge
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