Growth of Ti thin films on sapphire substrates
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Growth of Ti thin films on sapphire substrates S. Rao Peddada,a) I. M. Robertson, and H. K. Birnbaum Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois at Urbana –Champaign, Urbana, Illinois 61801 (Received 2 April 1996; accepted 14 April 1997)
Titanium thin films have been grown by electron-beam physical vapor deposition on the (0001) surface of sapphire (single crystal a –Al2 O3 ) substrates at growth temperatures ranging from 295 to 1223 K. Single phase a –Ti films grew at all growth temperatures, even at 1223 K which is above the a-b transition temperature of Ti. Crystal quality, as measured by the width of x-ray rocking curves, was found to improve, and the elastic strain to increase, as the growth temperature increased from 295 K to 1023 K. The epitaxial relationship between the Ti and sapphire was s0002dTi k s0006dAl2 O3 and f1120gTi k f1010gAl2 O3 . The extent of interdiffusion across the TiyAl2 O3 interface was observed to be small (,20 nm) at all growth temperatures.
I. INTRODUCTION
Metal/ceramic interfaces have been the focus of considerable study in the past decade due to their importance in microelectronic packaging and in the automotive and aerospace industries.1 For these applications it is important to understand the nature of the bonding across the interface, its strength, and the effect of external variables on the bond strength. Although thin film laminates of Ti and Al2 O3 find extensive use, little is known about the system. Previous studies have shown a strong interaction at the TiyAl2 O3 interface with no appreciable interfacial reaction zone being formed.2–7 In the present study the effects of substrate temperature on Ti thin film growth, crystal quality, and interface morphology are investigated. II. EXPERIMENTAL PROCEDURES A. Thin film growth
Titanium films were vapor deposited on the polished side of circular (12.5 mm diameter) sapphire substrates that had a basal plane orientation and were 630 mm thick. Film thickness and rate of deposition were determined using a quartz crystal thickness monitor. High-purity Ti was used as the source for thin film deposition. Prior to placing the Ti charge in the growth chamber, it was cleaned using aqua regia, then acetone and, finally, pure ethyl alcohol. The sapphire substrates were subjected to sequential cleaning in acetone, petroleum ether, and pure ethyl alcohol. After loading into the vacuum chamber, the substrates were annealed at 1373 K for about 15 min to thermally desorb surface contaminants and then cooled to the growth temperature. The pressure a)
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J. Mater. Res., Vol. 12, No. 7, Jul 1997
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in the chamber prior to film deposition was ,5 3 1028 Pa, and this increased to 1 3 1026 Pa at the start of evaporation. A shutter was initially interposed between the electron gun and the sub
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