Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapo
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Influence of growth parameters on the nitrogen incorporation in 4H- and 6H-SiC epilayers grown by hot-wall chemical vapour deposition U. Forsberg, A. Henry, Ö. Danielsson, M.K. Linnarsson(1), and E. Janzén Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden Tel: +46 (0) 13 28 26 99, Fax: +46 (0) 14 23 37, email: [email protected] 1 Solid State Electronics, Royal Institute of Technology, SE-164 40 Kista, Sweden ABSTRACT We have investigated the nitrogen incorporation dependency on temperature, pressure, C/Si ratio and growth rate in a horizontal hot-wall CVD reactor. The incorporation mechanism for 4H- and 6H-SiC both for Si- and C-face material is presented. A comparison with previously published results in a cold-wall reactor is also made. 1 INTRODUCTION In SiC, nitrogen is the most important n-type dopant. The shallow nitrogen donors are assumed to substitute carbon atom in the lattice. When epitaxial structures for devices, like metal semiconductor field effect transistor (MESFET) [1] and PiN diodes are grown it is necessary to have a complete understanding of the nitrogen incorporation during different growth conditions. The chosen growth parameters are usually such that the SiC epilayer has as good morphology as possible but these growth parameters may not necessarily be the optimal parameters when a very thin highly doped cap layer is grown. A change in growth parameters may be necessary to obtain n-type doping above 1⋅1019 cm-3. Nitrogen incorporation on C-face material shows a different behavior compared to Si-face. To get a further understanding of the nitrogen incorporation in SiC, thermodynamical calculations have been performed in the H2-SiH4-C3H8-N2 system. 2 EXPERIMENTAL The reactor used in this work is a commercial hot-wall CVD reactor. The reactor has been modified “in house” to fulfill our demands on intentional nitrogen doping. The precursors were silane (5 % in H2, N60) and propane (5 % in H2, N60). Palladium diffused hydrogen was used as carrier gas. Nitrogen (N60) was used for n-type doping. The SiC coated graphite susceptor was inductively heated by an RF generator. The temperature was measured by a two-color pyrometer and was focused on a drilled hole at the backside of the susceptor, giving an approximation of a black body. Silicon melting was performed to calibrate the temperature inside the susceptor to an accuracy better than ± 6 °C. The base pressure in the reactor chamber before growth was always lower than 2⋅10-6 mbar. A hydrogen flow of 13 l/min was used in all growth runs. The growth runs were performed between 1500-1600 °C, 50-1000 mbar, a C/Si ratio between 1.5 and 5.0 and a growth rate between 2-5.5 µm⋅h-1. Commercially available substrates , 4H- and 6H-SiC, Si- and C-face were used. All samples were cleaned using TL1 (H2O, NH3, H2O2; 5:1:1), TL2 (H2O, HCL, H2O2; 5:1:1), and a final HF dip. Secondary ion mass spectrometry (SIMS) measurements were performed on all samples. An intentional doping with nitrogen was performed during all run
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