Laser Direct-Metallization of Silicon Carbide without Metal Deposition
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Laser Direct-Metallization of Silicon Carbide without Metal Deposition I.A. Salama , A. Kar and N.R. Quick1 Laser-Aided Manufacturing, Materials and Micro-Processing Laboratory (LAMMP) School of Optics/CREOL, University of Central Florida Orlando, FL 32816-2700, USA 1 AppliCote Associates, LLC, 894 Silverado Court Lake Mary, FL 32746, USA ABSTRACT Laser direct-write (LDW) is used for in-situ metallization in single crystal 4H- and 6H-SiC wafers without metal deposition. Nanosecond-pulsed Nd:YAG (λ= 1064 and 532 nm) and excimer (λ = 193, 248 and 351 nm) lasers are utilized to create metal-like conductive phases in both n-type and p-type SiC wafers. Frequency-doubled Nd:YAG irradiation( Ephoton < Eg) induces a carbon rich conductive phase due to thermal decomposition of SiC. However, pulsed excimer laser irradiation (Ephoton > Eg ) produces a Si- rich conductive phases due to carbon photo ablation. The Schottky barrier heights (SBH) between the laser-metallized layer and the original n-type SiC (ND =1018 cm-3) is determined to be 0.8 eV and 1.0 eV by the current-voltage and capacitance-voltage measurements at room temperature, respectively. Linear transmission line method pattern is directly fabricated in n-type doped (ND= 1018cm-3) SiC substrate by pulsed laser irradiation allowing to extract the specific contact resistance (rc) of the laser fabricated metal-like tracks (rc= 0.04-0.12 Ωcm2).The specific contact resistance is unchanged after annealing up to 3 hrs at 9500C. INTRODUCTION A barrier to SiC device fabrication is metallization and the control of the interfacial properties at the metal contacts. Interfacial properties include thickness uniformity, stability and reactivity at high temperatures (600-650°C), and most importantly, the Schottky barrier height (SBH-ΦB), which determines the electrical behavior of an ohmic or Schottky contact [1]. An ohmic contact, important for external connections to the device, requires low ΦB.; a high value of ΦB is needed for rectifying contact [2,3]. Most metals form a rectifying contact on SiC with low leakage current, low ideality factor, high break down voltage and SBHs in excess of 1 eV. Difficulty in forming ohmic contacts on SiC with low contact resistance may be overcome by heavy doping of the SiC and/or using an insulator interlayer to reduce the barrier height [4]. The contact metal can react with SiC to form carbides and/or silicides particularly after long-term exposure at the device operating temperature (400-600°C). In this study a laser-conversion process is demonstrated for contact fabrication in SiC; this is an in situ process that requires no additional metal deposition or post fabrication steps for metallization [5,6]. EXPERIMENTAL DETAILS 4H-SiC (single crystal low doped n-type 4H-SiC 0001 Si face with an epitaxial layer of 10µm and a donor concentration in the range of 8 ×1015 to 5 ×1018 cm-3) and 6H- SiC (single crystal , virgin, with (0001) Si-face semi insulating, V-doped samples are used in this study.
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