What is Sputtering? PVD Magnetron Sputtering Systems

The verb “To Sputter” comes from the Latin word Sputare meaning to “To emit saliva with noise.” While the word sputtering sounds funny to those who associate it with stammering and speech impediments, in 1970 Peter J. Clarke changed the course of history when he developed the first “Sputter gun” that catapulted the semiconductor industry by enabling the accurate and reliable deposition of materials on an atomic level using a charged plasma stream of electrons and ions in a vacuum environment. 

The sputtering process begins when a substrate to be coated is placed in a vacuum chamber containing an inert gas – usually Argon – and a negative charge is applied to a target source material that will be deposited onto the substrate causing the plasma to glow. 

Free electrons flow from the negatively charged target source material in the plasma environment, colliding with the outer electronic shell of the Argon gas atoms driving these electrons off due to their like charge. The inert gas atoms become positively charged ions attracted to the negatively charged target material at a very high velocity that “Sputters off” atomic size particles from the target source material due to the momentum of the collisions. These particles cross the vacuum deposition chamber of the sputter coater and are deposited as a thin film of material on the surface of the substrate to be coated. 

Sputtering only takes place when the kinetic energy of the bombarding particles is extremely high, much higher than normal thermal energies in the “Fourth state of nature” plasma environment. This can allow a much more pure and precise thin film deposition on the atomic level than can be achieved by melting a source material with conventional thermal energies.

The number of atoms ejected or “Sputtered off” from the target or source material is called the sputter yield. The sputter yield varies and can be controlled by the energy and incident of angle of the bombarding ions, the relative masses of the ions and target atoms, and the surface binding energy of the target atoms. Several different methods of physical vapor deposition are widely used in sputter coaters, including ion beam and ion-assisted sputtering, reactive sputtering in an Oxygen gas environment, gas flow and magnetron sputtering.

What is Magnetron Sputtering?

Because ions are charged particles, magnetic fields can be used to control their velocity and behavior. John S. Chapin is credited with inventing the first planar magnetron sputtering source with a patent filed in 1974. While conventional diode sputtering can deposit extremely thin films down to the atomic scale, it tends to be slow and most effective with small substrates. The bombardment of the substrate can also create overheating or damage to the object to be coated.

Magnetron sputtering deposition uses magnets behind the negative cathode to trap electrons over the negatively charged target material so they are not free to bombard the substrate, allowing for faster deposition rates.

                                                         Diagram of the DC Magnetron Sputtering Process