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Control of the Uniformity of Thin Films Formed by an RF Plasma

IP.com Disclosure Number: IPCOM000046519D
Original Publication Date: 1983-Jul-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 39K

Publishing Venue

IBM

Related People

Broom, RF: AUTHOR [+3]

Abstract

The uniformity of thin films formed by RF plasmas depends directly on the uniformity of the plasma itself. In the case of planar structures, only the uniformity of the density and energy of the reactive particles are important. In addition, for nonplanar structures like edge devices the uniformity in the incident angles of the reactive species also influences the uniformity of the films. For example, in edge junction technology for cryogenic circuits, variations of the Josephson current density across chip and wafer are substantially larger than those observed in planar technology. This effect is very pronounced when junctions of different orientation (left and right) are on the same chip.

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Control of the Uniformity of Thin Films Formed by an RF Plasma

The uniformity of thin films formed by RF plasmas depends directly on the uniformity of the plasma itself. In the case of planar structures, only the uniformity of the density and energy of the reactive particles are important. In addition, for nonplanar structures like edge devices the uniformity in the incident angles of the reactive species also influences the uniformity of the films. For example, in edge junction technology for cryogenic circuits, variations of the Josephson current density across chip and wafer are substantially larger than those observed in planar technology. This effect is very pronounced when junctions of different orientation (left and right) are on the same chip. It has been found that this problem can be significantly reduced by applying a nonuniform magnetic field (providing a field gradient) or by using a modified cathode geometry during the formation of the tunnel barriers.

At low pressure, about 2 mTorr, the dark space between plasma and substrate is large and the majority of the ions arriving at the substrate do so at near-normal incidence. However, for edge junctions the inhomogeneities in the incident ion to substrate-surface direction have a severe effect, as illustrated in Figs. lA and 1B. Since the two junctions face in opposite directions, the difference in the effective edge angle for oxidation is 2C where C is the deviation of the mean angle of incidence of the ions from normal in a plane perpendicular to the length axes of the junctions. For instance, if C . 2, the difference in the Josephson current between "left" and "right" facing junctions is approximately 40% for Nb/Pb-alloy edge junctions, which corresponds to a 2% change of the barrier thickness.

The two measures proposed, namely, the use of magnetic-field gradients and the change in cathode geometry, affect the mean angle of incidence C of the reactive species. Assuming that the ions will be mainly accelerate...