Pressure Dependence of Aluminum Doping in SiC Vapor Phase Epitaxy
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Pressure Dependence of Aluminum Doping in SiC Vapor Phase Epitaxy Adolf Schöner and Malin Gustafsson Acreo AB, Department for Industrial Nano- & Microtechnology Electrum 236, SE - 164 40 Kista, Sweden
Abstract The dependence of the aluminum incorporation on the total pressure in a hot wall vapor phase reactor for SiC homoepitaxial growth has been investigated. It was found that in the doping concentration range from 1·1017 cm-3 to 1·1019 cm-3 the incorporated aluminum concentration varies by the factor 3 to 4, when the reactor pressure is changed from 150 mbar to 250 mbar. Lower reactor pressure gives lower aluminum concentration. Periodically changing reactor pressure results in aluminum concentration periodically changing with depth in the epilayer. All results were measured electrically by capacitance-voltage measurements on nickel Schottky contacts. Additional experiments have been performed for n-type nitrogen doped SiC epilayers for comparison. The nitrogen doping concentration was found to be independent of the reactor pressure within the accuracy of the applied C-V measurements and the doping profile analysis method. Introduction The SiC technology has matured during the last years and SiC devices are since a few years commercially available. More and more applications are found where SiC devices can improve the system performance. Epitaxial growth is one of the processes, which contributed to a large extent to the development of high performance SiC devices. Nowadays, SiC device structures become more complex and epitaxial growth and re-growth processes on planar and non-planar surfaces are involved in the realization of complex device structures. One of the most important issues in homoepitaxial growth of SiC by vapor phase epitaxy (VPE) is the control of the dopant incorporation. Device structures consist often of several epilayers with different conductivity type and/or different doping concentrations. The transition between the different epilayers should be as abrupt as possible. Dopants from one layer should not be transferred into the next layer, especially not to layers with opposite conductivity type, where they act as compensation. In cases, where compensation does not play an important roll, the transition between two layers can be more gradually and a transition layer is formed. The dopant incorporation in SiC VPE growth can be controlled through the parameters dopant precursor flow, silicon precursor flow, carbon to silicon (C/Si) ratio in the gas phase, growth temperature, and reactor pressure. In this study we will report on the Al incorporation in hexagonal SiC polytypes (4H-SiC and 6H-SiC) in dependence on the pressure in the VPEreactor cell. Experimental Details The experiments on the pressure dependent Al incorporation were done in a VPE reactor of hot wall type equipped with substrate rotation [1]. Hydrogen was the carrier gas, silane and propane the growth precursors, and trimethylaluminum (TMAl) the precursor for Al doping. To compare
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the growth at different reactor p
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