Growth of diamond films on copper
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Copper and diamond both have cubic crystal structures and similar lattice constants, making Cu an excellent candidate substrate for the heteroepitaxial growth of electronic device quality diamond. In this study a Cu substrate preparation method was developed to obtain large-area, free-standing polycrystalline diamond films. Concurrently, a statistically designed experiment was used to maximize the diamond film quality and resulted in (111) and (100) faceted films of quality comparable to or better than those grown on Si. The diamond films were analyzed by Raman spectroscopy, x-ray diffraction, and scanning electron microscopy.
I. INTRODUCTION Diamond has been cited as a potential semiconductor for electronic devices operating at high powers and frequencies, and under harsh conditions. This is because of its high thermal conductivity, radiation hardness, high breakdown voltage, and chemical inertness. 1 ^ In order to utilize diamond's exceptional properties in active electronic devices, methods must be developed to obtain nearly defect-free material at reasonable cost. The economical use of homeoepitaxial growth is hindered by expensive, defective, and small substrates. Heteroepitaxial growth has the potential to provide high quality material over useful areas at a practical substrate cost. For these reasons heteroepitaxial growth of diamond is an important area of research. Copper is a candidate substrate for heteroepitaxial growth of diamond because, like diamond, it has a cubic crystal structure, and its lattice mismatch with diamond is only 1.14% (Table I). Furthermore, Cu does not form a carbide which makes it an excellent candidate for the heteroepitaxial growth of diamond.5 However, Cu has a thermal expansion coefficient that is —11.8 times TABLE I. Selected properties of diamond and Cu. Property Crystal structure
ffa(X10~6/K) Lattice parameter (A) Melting point (°C)
Diamond Diamond cubic 1.5_4.8 (400-1200 K)b a = 3.567b
Cu Fee 17.7 (293-573 K)c a — 3.608d 1083 o c c
a
Coefficient of thermal expansion. Ref. 1, pp. 643, 650. C J. Crane and J. Winter, in Encyclopedia of Materials Science and Engineering, edited by M. B. Beaver (The MIT Press, Cambridge, MA, 1986), Vol. 2, p. 848. ''•Handbook of Chemistry and Physics, edited by D. R. Lide (CRC Press, b
Boca Raton, FL, 1990), pp. 12-18. J. Mater. Res., Vol. 9, No. 4, Apr 1994 http://journals.cambridge.org
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greater than that of diamond. Preliminary experiments in this lab have shown that the large mismatch in thermal expansion coefficients coupled with the abrupt interface between diamond and Cu6 results in very poor adhesion and catastrophic failure of the diamond films during postdeposition cooling.7 Denatale et al.8 noted that the poor adhesion of diamond films to various substrate materials was caused in part by thermal expansion mismatch between the diamond films and substrates. There have been several reports of growth of diamond particles and films on Cu in the literature.5'9"11 In this paper, we report on the results of an e
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