Magnetic fields and ferromagnetic target materials are two crucial technical aspects for physical vapor deposition (PVD), particularly in coating techniques.
Definition of Ferromagnetic Materials
Ferromagnetic materials refer to those that can become magnetized under the influence of an external magnetic field, and retain their magnetism even after the external magnetic field is removed, a phenomenon known as spontaneous magnetization.
Types of Ferromagnetic Metals
Ferromagnetic metals mainly include the following:
| Iron: Pure iron has a soft, silvery-white metallic luster. The iron commonly found in everyday life usually contains impurities and appears black. Iron is a good magnetic conductor and can be easily magnetized, exhibiting strong magnetic properties.
| Cobalt: Cobalt is a lustrous silver-gray metal that is hard and brittle. It exhibits ferromagnetism and has physical properties similar to iron and nickel in hardness, tensile strength, machinability, and electrochemical behavior.
| Nickel: Nickel is a silver-white metal known for its good ductility, magnetism, and corrosion resistance. It does not oxidize easily in air and can resist corrosion from caustic alkalis.
Definition of Target Materials
Target Materials are key consumables in the Physical Vapor Deposition (PVD) process, primarily used to transfer target atoms or molecules to the surface of substrates (such as silicon wafers or glass) by means of high-energy ion bombardment, thereby forming nanometer-scale films with specific functions.
Effects of Magnetic Fields on Target Materials
| Constrained electron orbits: The distribution of the magnetic field determines the constrained orbits of electrons, leading to the strongest plasma in specific areas of the target material surface (such as the annular ‘running target’ area), with sputtering primarily concentrated in that region.
| Regulating sputter distribution: By adjusting the strength and distribution of the magnetic field, the distribution of the plasma on the target material surface can be controlled, thereby controlling the spatial distribution of sputtered atoms to ensure uniform film thickness and performance on the substrate.
| Magnetic shielding effect: Ferromagnetic target materials (such as iron, nickel, and cobalt) shield some of the magnetic field lines, resulting in a weakened actual magnetic field on the target surface, which can affect the efficiency. This is typically compensated by optimizing the target thickness or magnetic field design.
Methods to Enhance Magnetic Field
| Adopting a target system: Two target materials are placed facing each other in parallel, with the target surface perpendicular to the magnetic field lines. A closed magnetic circuit is formed by the magnetic fields on both sides, effectively confining the plasma between the two targets and significantly enhancing the magnetic field strength at the target surface, while requiring a lower thickness of the target materials.
| Optimizing target thickness: Reducing the thickness of ferromagnetic target materials to make them sufficiently thin helps to minimize the shielding effect (magnetic saturation) of the target on the magnetic field, allowing more magnetic flux to pass through the surface of the target material.
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