Etch: Intlvac Ion Beam Mill Etcher
The Intlvac Nanoquest Research Ion Beam Milling System is a versatile R&D ion milling etching system. Ion milling is an etching process where a directional beam of heavy inert gas atoms (argon) is accelerated towards the substrate, using the kinetic energy of the heavy argon atoms to dislodge and sputter away material from the surface of the substrate. While some machines also incorporate reactive gases to speed up etching (reactive ion milling), this machine only uses argon, which is chemically inert. The ion beam is initially composed of positively charged argon ions which are accelerated out of the Kaufman ion source. However, the beam of ionized argon is mostly neutralized by electrons emitted from a neutralizer filament before it hits the substrate, to minimize high voltage damage to sensitive substrates.
The machine allows independent control of ion energy, ion current density, and incidence angle. The water-cooled, rotating, tiltable stage accommodates up to 4-inch (100mm) substrates. Rotation is helpful in achieving good uniformity. Tilt is used to control sidewall angle, to remove “fences” of redeposited metal from sidewalls, and to optimize etch efficiency.
Since the sputter rate of materials varies with surface temperature, it is important for repeatability and accuracy to keep the substrate at a consistent temperature. The chilled stage, along with a silver-impregnated silicone rubber “dry chuck” (heat-conductive gasket) helps to keep the substrate cool. For smaller chips which require longer etches, they are usually attached to a carrier wafer using heat-conductive silver paste. For quicker etches, Kapton tape can be used to mount chips to the carrier wafer.
While the ion source can be programmed for a wide variety of voltage, current, and gas flow parameters, we have settled on four basic “Approved Recipes” which are proven to be safe for the ion source. There are, however, ranges of certain variables within those four basic “Approved Recipes” to facilitate all conceivable etching goals. The chart of approved recipes is provided in a link below as well as posted on a laminated card near the tool. It is important to stick within the guidelines of the approved recipes to keep the ion source from self-destructing, and to achieve a good, smooth substrate surface quality after etching.
In order to become a qualified user of the Intlvac Ion Mill, you need to follow each of these steps in the order as listed here: