A New Sublimation Etching for Reproducible Growth of Epitaxial Layers of SiC on SiC Substrate in a CVD Reactor
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A New Sublimation Etching for Reproducible Growth of Epitaxial Layers of SiC on SiC Substrate in a CVD Reactor Rongjun Wang, Ishwara Bhat and Paul Chow Rensselaer Polytechnic Institute, Troy, NY 12180-3590 Ph: 518-276-2786 Fax: 518-276-2433 Email: [email protected] ABSTRACT We have developed a new and simple method to etch SiC at relatively low temperature with very high rates. This method is particularly useful for cleaning the susceptor after growth. By employing this etching method to clean the susceptor prior to every growth run, we have greatly improved the reproducibility of SiC epitaxial growth and increased the lifetime of the susceptor. The method can also be used to etch SiC wafers at a very fast rate as an alternative to mechanical polishing. An etch rate of over 100µm/hr was obtained at 1600oC using this new method. The surfaces of the etched wafers were examined by atomic force microscope (AFM). Results of epitaxial growth using new etching method are presented. INTRODUCTION The material properties of SiC make it an interesting semiconductor for devices operating at high temperature, high power, and high frequencies [1]. To support the power device efforts at Rensselaer Polytechnic Institute, a CVD reactor was recently installed and SiC epitaxial growths have been carried out. Good quality epilayers have been obtained. However, the reproducibility of growth was affected by the status and history of the susceptors used. SiC deposited on the susceptor during each epitaxial growth run can be tens of micrometers. Heavily coated SiC will change the growth conditions from run to run. Removing it prior to each growth will make the growth more reproducible. It is well known that hydrogen can etch SiC at high temperature. Many groups [2-5] have used this method to clean the substrates for SiC epitaxial growth. It can effectively remove scratches on the commercially available SiC substrates. Atomically flat and clean surface can be achieved after well-optimized etching process. In principle, heating the susceptor in hydrogen can also etch SiC deposited on the susceptor. However, hydrogen etching is a very slow process [2]. The etch-rate is usually around 1-3 µm per hour at temperatures 15001600oC. To remove the thick SiC coating on the susceptor, several hours of heat treatment is usually needed. Etching at higher rate can be achieved at a higher temperature [6,7]. It was reported that the etch-rate could be as high as 30 µm per hour at 1800oC and at 20 torr [6]. But this method can not be used in most of the conventional CVD systems, which do not have the capability to reach such a high temperature. In addition, exposing the susceptor to such a high temperature will crack the original coating and reduce the lifetime of the susceptor. Using H2/HCl etching might be another way to increase the etch-rate [8]. However, gaseous HCl is highly corrosive, which limits its use in the CVD system. We have developed a new etching method which combines H2 etching and sublimation etching. This process can be performed in a CVD sys
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