Physics and technology of magnetron sputtering discharges

Abstract

Magnetron sputtering deposition has become the most widely used technique for deposition of both metallic and compound thin films and is utilized in numerous industrial applications. There has been a continuous development of the magnetron sputtering technology to improve target utilization, increase ionization of the sputtered species, increase deposition rates, and to minimize electrical instabilities such as arcs, as well as to reduce operating cost. The development from the direct current (dc) diode sputter tool to the magnetron sputtering discharge is discussed as well as the various magnetron sputtering discharge configurations. The magnetron sputtering discharge is either operated as a dc or radio frequency discharge, or it is driven by some other periodic waveforms depending on the application. This includes reactive magnetron sputtering which exhibits hysteresis and is often operated with an asymmetric bipolar mid-frequency pulsed waveform. Due to target poisoning the reactive sputter process is inherently unstable and exhibits a strongly non-linear response to variations in operating parameters. Ionized physical vapor deposition was initially achieved by adding a secondary discharge between the cathode target and the substrate and later by applying high power pulses to the cathode target. An overview is given of the operating parameters, the discharge properties and the plasma parameters including particle densities, discharge current composition, electron and ion energy distributions, deposition rate, and ionized flux fraction. The discharge maintenance is discussed including the electron heating processes, the creation and role of secondary electrons and Ohmic heating, and the sputter processes. Furthermore, the role and appearance of instabilities in the discharge operation is discussed.

Engineered ion-bombardment as a tool in thin film deposition

“…[37,38] Secondary electron emission occurs if 0.78 > 2 . The expression above yields ~0.18 for Ti target sputtered by Ar + ions and for most metals rarely exceed 0.2 [34].…”

“…At increased pressure, the collisions between the electrons and background gas are increased but at the same time the deposition rate suffer due to increased gas scattering of the sputtered atoms with the background gas. [34] In order to increase the deposition rate, a magnetic trap for the electrons can be introduced in front of the target. This increases the electron path length and makes it possible to operate the discharge at a lower pressure.…”

“…There is also a probability for the neutralized ion to be reflected especially if the target atoms have higher mass compared to the incoming ion. [5,11,14] Secondary electron emission also occurs but it should be noted that it depends more on the potential energy of the incident ion rather than its kinetic energy [34,37,38] An empirical expression for secondary electron emission yield ( ) is given as,…”

“…Figure 2.7. The energy distribution of sputtered Ti atoms according to the Sigmund-Thompson theory and the modified model from Stepanova-Dew (after Gudmundsson[34]). …”

Synthesis and Characterization of Cu2ZnSnS4 Thin Films Obtained by Combined Magnetron Sputtering and Pulsed Laser Deposition

“…High deposition rates and high-purity films can be achieved using MS [ 24 ]. However, some issues in MS are related to target poisoning by reactive gas and target cracking at high power [ 25 ]. Additionally, with a damaged target, the sputter rate can change significantly, and it can be difficult to control the quantity of the elements incorporated into the film [ 26 ].…”