Annealing Effects of Schottky Contacts on the Characteristics of 4H-SiC Schottky Barrier Diodes
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ABSTRACT This paper reports on the relationship between the microstructure and the device performance of Pt/4H-SiC schottky barrier diodes ( SBDs ). The evolution of microstructure in the metal/SiC interfaces annealed at different temperatures was characterized using X-ray scattering techniques. The reverse characteristics of the devices were degraded with annealing temperatures. The maximum breakdown voltages of as-deposited devices and 850 IC annealed devices are 1300 V and 626 V, respectively. However, the forward characteristics of the devices were found out to improve with annealing temperatures. X-ray scattering analysis showed that Pt-silicides were formed by annealing performed at or higher than 650 1C. The formation of silicides was shown to increase the roughness of the Pt/SiC interface. It is believed that the forward characteristics of the SBDs be strongly dependent on the crystallity of silicides formed in the Pt/SiC interface
during the annealing process.
INTRODUCTION SiC has been given significant attention as a potential material for high-frequency, high-power, and high-temperature applications due to its unique electrical and thermal properties. These properties include a high electric field at breakdown (2 x 106 V/cm), a high electron velocity (2 x 10' cm/sec), a large band gap (2. 86 eV for 6H and 3.2 eV for 414), and a high thermal conductivity (4 W/K cm) [I]. In particular, the extremely high critical electric field of SiC makes it a prime candidate for high-voltage applications, such as high-power rectifiers. Rectifiers utilize
SBDs to suppress high-voltage transients induced on the power line during current switching [2]. For a negligible dissipation of power during the switching, the reverse current transient of the SBD must be suppressed, maintaining a high reverse voltage without breakdown. There have been a lot of reports on the design and the fabrication of a SiC SBD to achieve its theoretical breakdown voltage [3]. However, there are only a few reports found on the relationship between 141 Mat. Res. Soc. Symp. Proc. Vol. 572 ©1999 Materials Research Society
the microstructure and the device performance of 4H-SiC SBDs. In this study, we attempted to establish the relationship between the current-voltage characteristics of Pt/4H-SiC SBDs and the microstructure of the Pt/4H-SiC interface annealed at various temperatures. It was found out that the annealing conditions for the schottky contact have a significant impact on the device performance. The evolution of microstructure in the Pt/4H-SiC interface was characterized using X-ray scattering techniques.
EXPERIMENT Single crystal 4H-SiC wafer with a nitrogen doped (Nd -- 1.2 x 10' 6/cm 3) epi-layer with 10 jan thickness was used to fabricate the SBDs. The substrates were cleaned according to the standard chemical cleaning procedure. The processing details for the fabrication of 4H-SiC SBDs are found elsewhere [ Baliga ] except that Al shadow mask was employed as the shadow mask for the Boron implantation [4]. Pt schottky contact ( t=3
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