AVS 50th International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA9
Investigations of Plasma Etching and Contact Processing on AlGaN Alloys Containing 0 to 50% Al

Tuesday, November 4, 2003, 4:40 pm, Room 321/322

Session: Compound Semiconductor Growth and Processing
Presenter: K.H.A. Bogart, Sandia National Laboratories
Authors: K.H.A. Bogart, Sandia National Laboratories
A.J. Fischer, Sandia National Laboratories
M.H. Crawford, Sandia National Laboratories
D.D. Koleske, Sandia National Laboratories
A.A. Allerman, Sandia National Laboratories
R.J. Shul, Sandia National Laboratories
D.E. Peebles, Sandia National Laboratories
I. Adesida, University of Illinois at Urbana Champaign
S. Jones, Sandia National Laboratories
D. Selvanathan, University of Illinois at Urbana Champaign
K.W. Fullmer, Sandia National Laboratories
F. Jalali, Sandia National Laboratories
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AlGaN alloys are suitable for a variety of light emitting devices including LEDs and laser diodes as well as electronic devices such as high electron mobility transistors. Deep UV (<300 nm) LEDs have important applications as UV light sources for chemical-biological sensors, non-line-of-sight optical communications, and UV curing. Optical performance near 300 nm requires Al stoichiometry of 0.25 to 0.5, or more. The difficulty of forming high-quality ohmic contacts to n-type AlGaN materials increases with increasing percent Al due to the difficulty in effectively doping high %Al AlGaN. We performed a series of experiments to study the effects of several contact processing steps on the resultant material and device characteristics for AlGaN alloys with the percent Al ranging from 0 to 50%. For example, during LED device processing, plasma etching of the p-type material and the active material is done in order to access the underlyingn-type material for contact formation. We determined the effect of percent Al in AlGaN alloys on the surface roughness, etching rates, and resist selectivity, as a function of plasma etch method (ICP vs. RIE) and etching parameters such as substrate bias voltage. We also varied the pre-metallization surface treatments using dry plasma etching and wet chemical (BOE and HCl) etching. We evaporated metal contacts of either TiAlNiAu or TiAlMoAu and determined metal adhesion and specific contact resistance as a function of percent Al (0 to 50%). Annealing studies were also performed on materials after the contact deposition. Surface analysis by XPS, performed before and after plasma etching showed striking stoichiometric differences between the as-grown alloy and the etched surface. The composition of the metal-AlGaN interface was also investigated by XPS. The results from all of these studies will be presented. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.