AVS 50th International Symposium
    Electronic Materials and Devices Thursday Sessions
       Session EM-ThM

Paper EM-ThM7
Long and Short Term Thermal Stability of Gate Metallizations on GaN/AlGaN/GaN Heterostructures

Thursday, November 6, 2003, 10:20 am, Room 321/322

Session: Materials for Interconnects and Contacts to Semiconductors
Presenter: E.D. Readinger, Penn State University
Authors: E.D. Readinger, Penn State University
S.E. Mohney, Penn State University
R. Therrien, Nitronex Corp.
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The III-nitride family of semiconductors is expected to provide devices for a variety of high power/high temperature applications, but only a few reports have addressed the thermal stability of gate metallizations for high electron mobility transistors (HEMTs) designed for these applications. This study examines two different forms of thermal stability. First, high temperature rapid thermal processing (RTP) commonly used for ohmic contact formation is used to identify candidates for gate metallizations that could be deposited prior to the anneal of source and drain ohmic contacts. Second, long-term anneals at moderate temperatures to accelerate the aging of HEMTs have been performed. A GaN capped Al@sub 0.23@Ga@sub 0.77@N/GaN heterostructure was used; the metallizations Re, Pt, Au, Ni, Ni/Au, Ni/Ga/Ni and Co were tested; and current-voltage curves were evaluated. Aside from Au and Pt which begin degrading above 400°C, the contacts exhibited neither improvement nor degradation after annealing for 60 s at 600°C. All the metallization schemes degrade above 600°C; however, Re showed marked improvement at 800°C for 60 s, returning to the as-deposited condition. The same metals were evaluated for long times at 425°C and 550°C. Although the commonly used Ni/Au contacts did not provide the lowest reverse currents among the metals tested, they do provide great stability at either temperature for at least 4 weeks. Rhenium exhibits improvement with respect to reverse currents after long times at 425°C, whereas most other contacts either degrade or remain stable. Materials characterization of the contacts will also be presented.