Chemistry, microstructure, and electrical properties at interfaces between thin films of platinum and alpha (6H) silicon
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J.S. Bow, M.J. Kim, and R.W. Carpenter Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 (Received 23 November 1994; accepted 4 May 1995)
Thin films (4-1000 A) of Pt were deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type a (6H)-SiC(0001) substrates and examined in terms of chemistry, microstructure, and electrical properties. The as-deposited contacts were polycrystalline and showed excellent rectifying behavior with low ideality factors {n < 1.1) and leakage currents of 5 X 10" 8 A/cm 2 at - 1 0 V. The Schottky barrier height increased from 1.06 eV before annealing to 1.26 eV after successive 20 min anneals at 450, 550, 650, and 750 CC. In addition, the leakage currents decreased to 2 X 10~8 A/cm 2 at —10 V. Interfacial reactions were not observed at annealing temperatures below 750 °C; above this temperature, Pt2Si and C precipitates were identified in the reaction zone.
I. INTRODUCTION The high strength and extreme thermal and electronic properties of SiC coupled with the high melting point, high work function, and metallic properties of Pt have led to interest in the Pt/SiC system for both structural and electronic applications. Chou1 investigated Pt/SiC diffusion couples ( 1 - 2 mm thick) for ceramicreinforced metal composites. Similar to the results in the present study, both Pt silicides and free C were identified in the reaction zones after annealing at temperatures between 900 and 1000 °C. An extension of this work2 showed the presence of several silicides after annealing at 1100 °C «s 4 h. In contrast to the present research in which thin films (=£1000 A) were used, annealing the thick Pt/SiC samples at high temperatures resulted in the formation of alternating silicide and C layers. Significant differences in the product phases are often observed for annealed thick and thin films of Pt on SiC, particularly if the thin films are completely consumed. The interfacial chemistry and structure of ultrathin (s£8 A) films of Pt deposited on /3-SiC(001) were studied by Auger electron spectroscopy (AES) and low energy diffraction (LEED).3 The results indicated no chemical reaction after annealing for 10 s at 800-900 °C and silicide and graphite formation after annealing for 10 s at 1000 °C. Papanicolaou et al.4 studied the electrical characteristics of Pt on n-type /3-SiC annealed for 20 min at temperatures between 300 and 800 °C. The study showed that Pt was a good Schottky contact with a 2336 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 9, Sep 1995 Downloaded: 15 Mar 2015
high Schottky barrier (0.95-1.35 eV) throughout the annealing sequence. However, the reverse current densities were at least six orders of magnitude higher than those observed in the present study. The higher reverse currents are likely due to a higher defect density in the /3-SiC films than in the 6H-SiC substrates and/or the difference in surface preparation. High-voltage Pt Schottky barrier diodes have been fabricated on n-type 6H-SiC at 140 °C.5 The
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