Collimated magnetron sputter deposition

Abstract

A technique to deposit films compatible with lift-off patterning techniques and hole filling has been developed for large magnetron sputter deposition systems. This technique allows the patterned sputter deposition of Cu films, as well as other relevant metal or alloy systems, using conventional lift-off lithography techniques. To overcome the gas scattering effects which are prevalent in the normal range of magnetron operation and which would prohibit lift-off of a photoresist mask by coating the sides of the mask, a hollow cathode electron source has been implemented near the magnetron cathode which allows operation (i.e., sputtering) of the cathode at full power in the low 10 4 Torr range. At this pressure, the mean free path for the sputtered atoms greatly exceeds the typical cathode-to-sample throw distance of 5–7 cm. To overcome the broadness of the sputtering target and the cosine-like distribution of the emitted, sputtered atoms, an array of collimating tubes is placed just above the sample to restrict the depositing flux to normal incidence + 5°. Atoms whose trajectory is more than 5° from normal are deposited on the inner surfaces of the collimators. The collimators are water cooled and grounded, which significantly reduces the thermal load on the samples due to electron bombardment. The lift-off samples must be backed and moved behind the collimators so as to eliminate shadowing and nonuniformity effects. Measured deposition rates for Cu are several hundred angstroms per minute at 1.5 kW discharge power for a 15 cm diam magnetron at 10 4 Torr using a 4:1 aspect ratio collimator. No degradation of the lift-off mask is observed, and the resulting, patterned films have little if any debris from deposition on the sides of the mask structures. Hole filling at aspect ratios up to 3.0 has been observed. The technique scales to virtually any size cathode, and has been tested on manufacturing scale systems with cathode diameters up to 30 cm and at powers approaching 30 kW. © 1991 American Vacuum Society