Laser Endotaxy and PIN Diode Fabrication of Silicon Carbide
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0911-B10-07
Laser Endotaxy and PIN Diode Fabrication of Silicon Carbide Zhaoxu Tian1, Nathaniel R Quick2, and Aravinda Kar1 1 College of Optics and Photonics, University of Central Florida, 4000 Central Florida Blvd. Bldg. 53, Orlando, FL, 32816 2 AppliCote Associates, LLC, 1445 Dolgner Pl, Sanford, FL, 32771
ABSTRACT A laser solid phase diffusion technique has been utilized to fabricate endolayers in n-type 6HSiC substrates by carbon incorporation. X-ray energy dispersive spectrometry (XEDS) analysis showed that the thickness of endolayer is about 100 nm. High resolution transmission electron microscopy (HREM) images indicate that the laser endotaxy process maintains the crystalline integrity of the substrate without any amorphization. The resistivity of the endolayer was 1.1 ×105 Ω·cm and 9.4 ×104 Ω·cm after annealing at 1000°C for 10 min. These resistivities provide device isolation for many applications. The silicon carbide endolayer was doped with aluminum using a laser doping technique to create p-region on the top surface of the endolayer in order to fabricate PIN diodes. INTRODUCTION Pulsed laser induced-epitaxy (PLIE) has produced epilayers by transforming an amorphous or disorder layer on a crystalline substrate into a thin crystalline layer. PLIE is a two-step process, where a target layer is first deposited on a semiconductor substrate and then a pulsed laser induces melting and solidification cycles to transform the top layer into a thin crystalline layer [1-3]. This technique has not been reported for peritectic single crystalline silicon carbide [4]. This paper presents the fabrication of an endolayer in silicon carbide by a laser-induced solidphase diffusion (LISPD) technique. Carbon atoms are introduced into the top layer of an n-type SiC substrate to form a high resistance endolayer for various applications such as device isolation and high voltage blocking. The wafer is not melted in the LISPD method because this process is based on the solid-state diffusion for dopant atoms into the wafer. The carbon dopant precursor of choice is a gas such as methane. Both pyrolytic and photolytic decomposition of methane during laser irradiation yield carbon atoms that subsequently diffuse into the wafer. The endolayer is then laser doped with aluminum (p-type dopant) to form a PIN diode. EXPERIMENT An n-type 6H-SiC substrate with nitrogen dopant concentration of 5×1018 atoms/cm3 was used to fabricate endolayers and PIN diodes. An experimental set-up for laser endolayer fabrication and doping of the substrate can be found in [5]. A laser beam is directed to the substrate placed in a vacuum chamber, while an appropriate gas, i.e., methane (CH4) for endolayer fabrication and trimethylaluminum ((CH3)3Al) for aluminum doping of SiC, is passed through the chamber. KrF and ArF excimer lasers with the wavelengths of 248 and 193 nm and pulse duration of 25 ns and 20 ns respectively were used for endolayer fabrication. The laser pulse had a beam diameter of 2×2.5 mm2; the laser fluences were 1.5 J/cm2 and 1.0 J/cm2 on
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