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Magnetrons are cornerstones of Physical Vapor Deposition (PVD). In a magnetron the kinetic energy of some heavy nonreactive ions, typically argon ions, are bombarding a solid target material.
The atoms from the target (conductive or dielectric), sputtered through momentum transfer of the bombarding ions, producing a vapor of neutral atoms, which are deposited on work pieces in the form of a thin film. This process can be conducted in a reactive environment as well, where generally a mixture of argon and reactive gases such as oxygen, nitrogen, etc, are used for applications where compound layers, such as oxide, nitride, etc. are deposited. For increased efficiency of reactive deposition process, the reactive components could also be introduced by a remote plasma source, such as remote PLUME series ICP source.
Magnetrons are classified based on the magnetic flux through the magnet’s surfaces. In balanced magnetrons, the magnets, i.e. central and peripherical magnets, generate the same magnetic flux through their respective magnets’ pole. In unbalanced magnetrons, the magnetic flux through the poles’ surface has different values. Unbalanced configuration can be of type-I where the central magnet generates a magnetic flux that is greater than the one generated by the peripherical magnet. In the unbalanced magnetrons of type-II, it is the opposite.
Balanced magnetrons generate a denser plasma density in comparison to the two other aforesaid configurations, but have a limited utilization rate of target, only about ~25 % of the target is sputtered. This configuration is an adequate choice for applications that use reactive gases and where compounds layers are desired. Unbalanced magnetrons have a greater target utilization that may reach values greater than 40 %. Unbalanced magnetrons of type-II are more frequently used since this configuration provides an ion flux that assists the thin film growth and helps controlling the microstructure of the deposited thin film.
Our water cooled magnetrons are available with balanced and unbalanced configuration. The design prevents direct contact between cooling water and the magnets. We also provide customized magnetrons such as planar rectangular magnetrons, cylindrical magnetrons or magnetrons with a client specified degree of unbalance with indirect or direct cooling.
A Magnetron combines the use of an electric (E) field, provided by a power supply that biases the target negatively (cathode), with a magnetic (B) confinement field for electrons, provided by an external magnetic circuit. As an example, for a circular target, a ring magnet and a magnet at center of the ring, having opposite polarity, is used to form the magnetic circuit. The magnetic field lines produced, have parallel and perpendicular components to the electric field at points, where the perpendicular component of B field is the highest, the Laurence Force, ExB, perpendicular to both E and B field, is also the highest. In such configuration, the random electrons confined in magnetic field, accelerate to high energies and by collision with neutral gas atoms, partially ionize the gas and form a donut shaped high density plasma. The ions produced, unlike electrons, because of their larger mass, practically are not confined in the magnetic field; therefor, they accelerate only by the electric field which is perpendicular to the target. The bombarding ions on the target result in sputtering of the atoms from the surface, because of momentum transfer of randomly moving of energetic particles implanted in target.