Formation and Characterization of Ohmic Contacts on Diamond
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FORMATION AND CHARACTERIZATION OF OHMIC CONTACTS ON DIAMOND V .VENKATESAN, D.M. MALTA, and K. DAS Kobe Steel USA Inc., Electronic Materials Research Triangle Park, N. C. 27709
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ABSTRACT Low resistance ohmic contacts have been fabricated on a naturally occurring lib diamond crystal and on polycrystalline diamond films by B ion-implantation and subsequent Ti/Au bilayer metallization. A high B by ion implantation, a postconcentration was obtained at the surface implant anneal and a subsequent chemical removal of the graphite layer. A bilayer metallization of Ti followed by Au, annealed at 8501C, yielded specific contact resistance values (as measured using a standard transmission line model (TLM) pattern) of the order of 10-5 aI cm 2 for chemical vapor deposition (CVD) grown polycrystalline films and the natural lib crystal. Specific contact resistance values have also been determined from circular TLM measurements on CVD films and the values compared to those from standard TLM measurements. These contacts were stable to a measurement temperature of -400 0 C and no degradation due to temperature cycling was observed. INTRODUCTION Semiconducting diamond is considered to be well-suited as a material for the fabrication of solid-state electronic devices for high-power and high-frequency applications and also for use in chemically reactive and high-radiation ambients [1-3]. Low resistance ohmic contacts are essential for proper operation of these devices [4]. A number of researchers have studied the formation of ohmic contacts primarily on natural lib crystals. Recently, Moazed et al. [5] in an excellent review have described the earlier work in this area and also included recent results obtained using carbide forming transition metals protected by a Au film. Hewett et al. [6] used Ti/Au contacts on homoepitaxial diamond films to obtain a low specific contact resistance (Pc) of 2 x 10-5 fI cm 2 . The films [6] were insitu doped to achieve a high B concentration (- 1020 cm- 3 ). Ohmic contacts have also been reported on high B concentration layers in diamond produced by high-dose ion-implantation [7-9]. In an earlier report, the present authors [9] reported the formation of low resistance ohmic contacts on polycrystalline and single crystal semiconducting diamond substrates through a combination of a high surface concentration of B (introduced by ion implantation) and Ti/Au metallization. The polycrystalline films studied [9] were deposited on SiAlON substrates and the films revealed a small grain size (1-2 Igm). Also, Mat. Res. Soc. Symp. Proc. Vol. 270. 01992 Materials Research Society
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the films [9] were B ion implanted with the substrates maintained at room temperature and 100°C. The latter condition yielded higher incorporation of B in the surface layer compared to the former. In the present study, similar contacts have been fabricated on polycrystalline films deposited on Si and a natural lib crystal. A substrate temperature of 200'C was employed during implantation of the films so
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