The Materials Properties of a Nickel Based Composite Contact to n -Sic for Pulsed Power Switching
- PDF / 1,874,717 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 74 Downloads / 205 Views
THE MATERIALS PROPERTIES OF A NICKEL BASED COMPOSITE CONTACT TO n-SiC FOR PULSED POWER SWITCHING M. W. Cole*, P. C. Joshi*, F. Ren** , C. W. Hubbard*, M. C. Wood*, M. H. Ervin* *U.S. Army Research Laboratory, Aberdeen Proving Ground, MD 21005 **Department of Chemical Engineering, University of FL, Gainesville, FL 32611
ABSTRACT Novel Ni/WSi/Ti/Pt composite Ohmic contacts to n-SiC were investigated as a function of annealing temperatures up to 1000o C. The onset of Ohmic behavior occurred at annealing temperatures of 900˚C. Annealing at temperatures between 950 o and 1000o C yielded excellent Ohmic behavior. At these temperatures the contact-SiC interface was smooth, defect free and characterized by a narrow Ni2 Si reaction region. The annealed contacts possessed atomically smooth surface morphologies and exhibited minimal contact expansion. The residual carbon, resultant from SiC decomposition, was constrained by reaction with the WSi and Ti metallization layers forming carbide phases of W and Ti. The locations of the carbide phases were spatially distant from the metal semiconductor interface. Our results demonstrate that the Ni/WSi/Ti/Pt composite Ohmic contact maintains the desirable electrical properties associated with Ni contacts and possess excellent interfacial, compositional and surface properties which are required for reliable high power and high temperature device operation. INTRODUCTION Recently, wide bandgap semiconductors such as SiC have attracted much attention for high power, high temperature, high frequency, and high radiation tolerance device applications. It is the exceptional properties of SiC, such as, high breakdown field, large bandgap, high thermal conductivity and large electron saturation velocity, which are responsible for these device application interests [1-7]. It has been reported that most SiC based electronic devices which can not sustain a long term operation at an elevated temperature/power level, suffered deterioration of their metal/SiC contacts [6]. Thus, an important concern for realization of SiC devices is the formation of low resistance Ohmic contacts with good thermal, chemical, and mechanical stability. The development of such Ohmic contacts serves to insure enhanced device reliability under the influence of high power and high temperature in-service operational stress. To date, many metallizations, namely, Ni, Al/Ni/Al, Cr, Al, Au-Ta, TaSi2 , W, Ta, Ti, Ti/Au, TiSi2 , Co, Hf, and WSi have been investigated for Ohmic contacts to n-SiC [7, 8]. Ni Ohmic contacts have been suggested as superior candidates due to their reproducible low specific contact resistance, less than 5.0 x 10-6 ohms-cm 2 , and deemed the industry standard Ohmic contact to n-SiC [7, 911]. Fabrication of Ni Ohmic contacts requires a post deposition anneal at temperatures ranging from 950o to 1000˚C. This anneal causes the Ni to react with SiC to form Ni 2 Si and is responsible for achieving Ohmic behavior [7, 9-16]. However, the annealing process also causes undesirable features, namely, broadening of
Data Loading...
