AVS 51st International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuM

Invited Paper EM-TuM3
Investigation of the Sources of Variations in the Electrical Characteristics of Ohmic and Rectifying Contacts

Tuesday, November 16, 2004, 9:00 am, Room 304B

Session: Contacts and Metallization
Presenter: L.M. Porter, Carnegie Mellon University
Authors: L.M. Porter, Carnegie Mellon University
F.A. Mohammad, Carnegie Mellon University
D.J. Ewing, Carnegie Mellon University
R.R. Ciechonski, Linköping University, Sweden
M. Syväjärvi, Linköping University, Sweden
R. Yakimova, Linköping University, Sweden
Correspondent: Click to Email
Ohmic and rectifying contacts are widely known to yield significant variations in electrical properties, such as the contact resistance or Schottky barrier height. Importantly, these variations exist among contacts on the same substrate and therefore among contacts processed identically. In this study we have investigated more than one hundred ohmic and rectifying contacts on the wide band gap semiconductor, silicon carbide. The statistical variations in contact resistance, Schottky barrier height, etc. were quantitatively compared. As described below, the data indicate that multi-phase contacts and/or intrinsic or growth-related defects provide important sources of variability. We further show that control over these phenomena result in substantial improvements in the contact behavior. Ohmic contacts on p-type (1 x 10@super 19@ cm@super -3@) 4H-SiC were fabricated using both Pt and Pt-Si contacts and the conventional Al-Ti metallization. The Pt-Si contact layers were selected and processed such that single-phase PtSi contacts were produced, whereas the annealed Pt and Al-Ti contacts produced several phases. The single-phase PtSi contacts consistently yielded low contact resistances (4.9 x 10@super -5@ ohm-cm@super 2@) with a narrow distribution (standard deviation = 1.28 x 10@super -5@). Although the Al-Ti contacts yield comparable average contact resistance, the distributions in values for the multi-phase contacts were substantially higher. Nickel Schottky contacts were also investigated and showed a range of behaviors. For example, the barrier heights ranged from 0.88 - 1.36 eV and displayed an inverse correlation with the measured deep-level defect concentrations. The preliminary data also indicates that deep-level concentrations above ~5 x 10@super 13@ cm@super -3@ result in multiple-barrier characteristics in the forward I-V data.