Sputtering is the preferred industrial thin film vacuum deposition technique, but it is also widely used in research laboratories. Sputtered films exhibit excellent, reproducibility, uniformity, density, purity and adhesion. It is possible to make oxides, nitrites, and other compounds of precise composition by reactive sputtering from metal targets [28, 30]. In dc sputtering, substrates are placed in the vacuum chamber, and it is evacuated to high vacuum before a low pressure (0.05–1 Pa) of the process gas, usually argon, is introduced. Sputtering
starts when a negative potential of a few hundred volts is applied to the target material to be deposited, causing a plasma or glow discharge. Positively charged Ar+ ions generated in the plasma collide with the negatively biased target. The momentum transfer ejects atomic-scale particles from the target, which traverse the chamber and are deposited as a thin film on the surface of the substrate. A magnetic field is usually created near the target surface bymeans of an arrangement of permanent magnets, known as a magnetron, in order to improve the ionization efficiency. Oxygen is mixed with the argon sputtering gas to produce oxides from metal targets. Alternatively, to make oxide or other insulating films directly, the radio-frequency method of rf sputtering is employed. Here the power supply commonly operates at 13.56 MHz. For part of the cycle, Ar ions bombard the target; for the rest of the cycle, electrons neutralize the build up of positive charge. Electrons also ionize the argon to create the plasma. Sputtering systems often have multiple targets, which permit the fabrication of complex thin film stacks used for
spin electronic applications. An argon pressure of 0.02 Pa is usually sufficient to maintain a radio-frequency discharge.