Like most of the other thin film deposition techniques, evaporation also takes place a high-vacuum atmosphere (10 -5~10 -9 Torr). As reactive sputtering involves chemical reactions, it is not classified as physical vapour deposition technique. For example, molybdenum oxide can be sputtered using a pure molybdenum target in combination with O 2 plasma. These reactive gasses can react with the target material to form compound materials on the sample. In reactive sputtering in addition to inert gasses such as argon, reactive gasses such as oxygen are used in the sputtering process.

The easiest way to grow more complex materials is to sputter various elements at the same time and/or using multi-element sputtering targets. Schematic of the sputtering process In addition to the sputtering of pure materials such as aluminium or silver there are also two types of sputtering processes which can be used to make binary, tertiary, or even more complex materials. To increase the sputter yield often a so-called magnetron sputtering process is used which uses magnetic fields to confine the plasma to the sputter yield.įig.1. This explains why this can only be used for conductive sputter targets because the material has to be sufficiently conductive to avoid accumulation of gaseous ions at the target. On the other hand, during DC sputtering the sputtering target is negatively charged throughout the process. Subsequently, the source atoms are accelerated towards the substrate resulting in thin film deposition.

Secondly, the target is positively charged, which causes the ejection of gas ions and source atoms due to reverse polarisation. Firstly, the target material is negatively charged which causes the polarisation of atoms the ionized Ar + ions are attracted to the target surface. There are two cycles in a RF sputtering process. DC discharges are usually preferred for electrically conductive materials, while an RF plasma is suitable for all materials including dielectric target materials. When the plasma energy is sufficiently high, the kinetic energy of the bombarding particles is much higher than conventional thermal energies resulting in material removal at the sputter target. By applying a direct-current (DC) or alternative-current excitation, a plasma is generated. The sputtering system consists of a high-vacuum chamber, a gas inlet (typically for an inert gas such as argon), a pump connection, a sputter target which is negatively charged (the cathode), and the sample which is positively charged (the anode). A schematic description of a sputtering system is shown in Figure 1. Sputtering involves a target or source material being bombarded by high energy particles, ejecting atoms of this material which are subsequently deposited onto a substrate to form thin film layers. Sputtering and evaporation are the two most common PVD methods used in PV manufacturing. Physical vapour deposition (PVD) is a variety of vacuum deposition techniques in which the material goes from a condensed phase to a vapour phase and then back to a thin film condensed phase.

Sputtering physical vapor deposition