Techniques have been developed to produce ohmic contacts to naturally occurring boron doped semiconducting diamond. Thin films of Mo, Mo/Au, and Mo/Ni/Au deposited on diamond produced adherent ohmic contacts after annealing at 950 °C. A thermally activated solid state reaction which produces a refractory carbide precipitate at the original diamond/metal interface is the principal factor in affecting the properties of the contacts. The interface reaction has been characterized using Auger electron spectroscopy, scanning electron microscopy, x-ray diffraction, metallography, and I-V measurements.

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Natural semiconducting diamond samples (Class 11-b) were used to develop techniques for the production of reproducible lowresistivity ohmic contacts for diamond devices. Annealed tantalum/gold and titanium/gold deposits on { 100) polished diamond surfaces reduced the resistance by seven orders of magnitude relative to the as-received samples. The interfaces were characterized using metallography, scanning electron microscopy, and secondary ion mass spectrometry.

PblIc reporting burden 1Wr this collection of bIfornalelon is 401maled to avrage I hourf Per ANSPOM. APRI 2 1993 9 -07481 l')'J Approved for public release; distribution is unlimited. ABSTRACT (Awmun 200 waro)A processing technology has been developed to make ohmic contacts to naturally doped semiconducting diamond. The approach follows, as far as possible, conventional photolithographic techniques for metallization of semiconductors currently in use in the microelectronic industry.Ohmic contacts have been successfully made to naturally doped semiconducting diamond using evaporated thin films of molybdenum, molybdenum/gold, and molybenum/nickel/gold. The metal contacts form a tenacious bond with the diamond suibstrate after annealing. The time and the temperature of annealing also affects the type and the degree of conduction of the contacts.Characterization of the interface of the metal contacts to diamond using AFS, SIMS, BBS, XRD, SEM, and metallography clearly indicates that metal-carbide-precipitates nucleate and grow at the diamond/metal interface during annealing. It is concluded that the size and the areal density of the carbide precipitates at the interface are the principal factors that control the adhesion, and the mode and the degree of conductivity of the metal contacts.Sponsorship of this research by SDIO/JSI, ONR, and NOSC/JR is gratefully acknowledged. Published in

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