Sputtering is a thin-film manufacturing process widely used across many industries including semiconductor processing, precision optics, and surface finishing. Sputtered thin films have excellent uniformity, density and adhesion making them ideal for multiple applications.
Sputtering can be described in a number of ways: cathodic sputtering, diode sputtering, RF or DC sputtering, ion-beam sputtering, reactive sputtering – but all of these are essentially describing the same physical process.
The target (source) material and substrate (destination) are placed into a vacuum chamber and a voltage is applied between them so that the target is the cathode and the substrate is attached to the anode.
A plasma is created by ionizing a sputtering gas, usually an inert gas such as argon or xenon. Inert gases are typically employed as the sputtering gas because they tend not to react with the target material or combine with any process gases and because they produce higher sputtering and deposition rates due to their high molecular weight.
The sputtering process occurs when the target material is bombarded with the sputtering gas and the resulting energy transfer causes target particles to escape, travel and deposit on the substrate as a film.
For the sputtering process to produce an effective coating, a number of criteria must be met. First, ions of sufficient energy must be created and directed towards the surface of the target to eject atoms from the material. The interaction of the ions and the target are determined by the velocity and energy of the ions. Since ions are charged particles, electric and magnetic fields can control these parameters. The process begins when a stray electron near the cathode is accelerated towards the anode and collides with a neutral gas atom converting it to a positively charged ion.
Second, ejected atoms must be able to move freely towards the substrate with minimal resistance to their movement. This is why sputter coating is a vacuum process. At too low pressures, there aren’t enough collisions between atoms and electrons to sustain a plasma. At too high pressures, there are so many collisions that electrons do not have enough time to gather energy between collisions to be able to ionize the atoms.