Two cylindrically symmetric and complementary sputtering geometries, the post and hollow cathodes, were used to deposit thick (∼25-μ) coatings of various metals (Mo, Cr, Ti, Fe, Cu, and Al-alloy) onto glass and metallic substrates at deposition rates of 1000–2000 Å/min under various conditions of substrate temperature, argon pressure, and plasma bombardment. Coating surface topographies and fracture cross sections were examined by scanning electron microscopy. Polished cross sections were examined metallographically. Crystallographic orientations were determined by x-ray diffraction. Microstructures were generally consistent with the three-zone model proposed by Movchan and Demchishin [Fiz. Metal. Metalloved. 28, 653 (1969)]. Three differences were noted: (1) at low argon pressures a broad zone 1–zone 2 transition zone consisting of densely packed fibrous grains was identified; (2) zone 2 columnar grains tended to be faceted at elevated temperatures, although facets were often replaced by smooth flat surfaces at higher temperatures; (3) zone 3 equiaxed grains were generally not observed at the deposition conditions investigated. Hollow cathode deposition accentuated those features of coating growth that relate to intergrain shading.
Magnetron sputtering sources can be defined as diode devices in which magnetic fields are used in concert with the cathode surface to form electron traps which are so configured that the E×B electron-drift currents close on themselves. Coaxial cylindrical magnetron sputtering sources in which post or hollow cathodes are operated in axial magnetic fields have been reported for a number of years. However, their performance is limited by end losses. A remarkable performance is achieved when the end losses are eliminated by proper shaping of the magnetic field or by using suitably placed electron-reflecting surfaces. High currents and sputtering rates can be obtained, nearly independent of voltage, even at low pressures. This characterizes what has been defined as the magnetron mode of operation. This paper reviews the basic principles that underly the operation of dc sputtering sources in the magnetron mode with particular emphasis on cylindrical magnetrons. The important attributes of these devices as sputtering sources are also reviewed.
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