A supercharged metal-ion generator( BERKELEY CA In the electronics indu...)

BERKELEY, CA In the electronics industry, thin metal films are deposited on silicon wafers with a sputter gun, which uses energetic ions atoms with a positive charge to knock the metal atoms off a target. Scientists at the U.S. Department of Energy's Lawrence Berkeley National Laboratory have now developed a powerful new kind of sputter process that can deposit high-quality metal films in complex, three-dimensional nanoscale patterns at a rate that by one important measure is orders of magnitude greater than typical systems.

Called "self-sputtering far above the runaway threshold," the new method "is an extraordinarily prolific generator of metal ions," says Andre Anders, a senior scientist in Berkeley Lab's Accelerator and Fusion Research Division, where he leads the Plasma Applications Group. Anders and his colleague Joakim Andersson, now at Uppsala University in Sweden, based their new method on the existing technique of High Power Impulse Magnetron Sputtering (HIPIMS).

Conventional DC (direct-current) sputtering accelerates ions in a plasma typically a noble gas like argon to erode atoms from the target. The magnetron design concentrates free electrons near the target in a strong magnetic field, increasing the collision rate between atoms and electrons to create more positive ions that can be accelerated toward the target. HIPIMS, invented in the late 1990s, improves this process further by encouraging self-sputtering, in which some of the metal atoms sputtered off the target are themselves ionized and return to the target to knock off still more atoms.

The great advantage of HIPIMS is to increase the ratio of metal ions to neutral atoms reaching the substrate, which makes for great improvements in coating quality. Even in HIPIMS, however, the discharge current in the circuit that powers the sputter gun is typically more than ten times greater than the current of positive ions that actually reaches the substrate.

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