Influence of substrate temperature and deposition rate on structure of thick sputtered Cu coatings

Thick [1–10 mil (25.4–254.0 μm)] OFHC copper coatings were deposited on copper, tantalum, and stainless-steel substrates maintained at temperatures (T) in the 50 °–950 °C range, at rates of from 200 to 18 000 Å/min, using primarily hollow and also post-type cathode sputtering apparatuses at argon pressures of 1 and 30 mTorr. Coating structures were examined by preparing metallographic cross sections. Surface topographies and fracture cross sections were examined by scanning electron microscopy. Crystallographic orientations were determined by x-ray diffraction. No significant deposition rate influence was found on the low-temperature structure zones reported previously [J. A. Thornton, J. Vac. Sci. Technol. 11, 666 (1974)] or on the columnar nature of coatings formed at elevated T. Truly equiaxed grain structures were generally not observed with hollow cathodes. Annealing twins were found within the grains for T≳350 °C. Evidence of extensive recrystallization and grain growth was seen for T∠900 °C. Coatings deposited at low rates and T≳400 °C on Cu substrates exhibited epitaxial effects; those on dissimilar substrates showed evidence of agglomeration.