UK-based sputtering technology firm Plasma Quest has a prototype system that could dramatically increase sputtering deposition rates and cut down-time.

Sputtering is used to deposit a wide variety of materials onto surfaces - including magnetic layers on hard drives as well as multi-layer coatings on photonics and optical communication components. “Globally, it’s a massive business,” Plasma Quest founder Professor Mike Thwaites told Electronics Weekly.

A limitation of existing systems is that targets, the source of coating material, are flat discs only 100-200mm in diameter. This limits the rate at which atoms can be ejected towards the object to be coated, and therefore the coating rate, as well as the life of the target.

In Thwaites’ new ‘linear’ system, the target is a massive bar 600mm long by 75mm diameter. “Tests indicate we should be able to deposit in excess of 1µm per minute for both reactive and ferromagnetic sputtering,” said Thwaites, “sufficient for roll-to-roll deposition.”

In the linear system, an argon plasma is generated by an RF antenna coil and a magnetic field outside the main chamber.

Guided by the launch magnet which confines it away from the walls, the plasma then drifts into and down the length of the deposition chamber.

Under the combined action of the launch magnet, the target magnet and the target’s -600V ion-acceleration potential, an even hail of Argon (Ar+) ions are accelerated into the target where they knock off coating atoms.

These atoms then drift ballistically and coat substrates in both the top and bottom of the chamber. The whole system can also be orientated vertically.

Plasma Quest sells and commissions sputtering systems as well as licensing firms to build their own. Managing director Barry Holton will not discuss customers or sales, except to say: “One US company bought a dozen systems and have ordered another nine, latterly with licence to build their own.”

Sputtering

The process involves generating Ar+ ions in a plasma, then accelerating these into the 'target' - a block of the material to be deposited. Atoms of the target are knocked off and ballistically travel to the object to be coated - the 'substrate'.

In conventional sputtering machines, the argon plasma is generated over the surface of the target. For electromagnetic reasons, most plasma is generated in a torus - resulting in uneven target erosion.

"Only 30 per cent of the target is actually used before it wears out," said Thwaites.

Plasma Quest's main intellectual property is in the remote generation of plasma in a quartz tube in the side of the main reaction chamber. "We get a target utilisation of 90 per cent," claimed Thwaites.

Plasma Quest