Epitaxial Growth of SiC in a Vertical Multi-Wafer CVD System: Already Suited as Production Process?
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ABSTRACT Results about a new CVD system suited for epitaxial growth on six 2 inch SiC-wafers at a time are presented. Excellent gas flow stability is achieved for this new reactor type as shown by in- situ observations of the gas flow dynamics in the reactor chamber. These experimental results agree favorably with numerical process simulation results. The epitaxial layers grown in the multi-wafer system so far show a by an order of magnitude higher background impurity level (_• 1015 cm" 3) as reported previously for layers grown in single-wafer systems by the authors and other groups (< 1014 cm-3). On the other hand, the doping homogeneity achieved until today is very encouraging. The variation on a 2 inch wafer is less than ± 20% at about 1*1016 cm-3 . The wafer to wafer variation of the average doping value both within a run and from run to run is within 15 %. The reproducibility and uniformity of the layer thickness is even better (total thickness variation _< 5% on a 2 inch wafer). The surface of the epitaxial layers is very smooth with a typical growth step height of 0.5 nm (4H, 80 off orientation). First measurements on Schottky diodes build on these layers show low leakage current values indicating low point defect density in the epitaxial layers. INTRODUCTION In the last 10 years significant progress in SiC epitaxial growth took place. Advancements cover control, reproducibility and homogeneity of doping and thickness but also background doping. This was enabled by better understanding of the deposition process (step control [1], influence of graphite parts [2], site competition [3,4]) and by the development of commercially available epitaxial equipment [5,6,7], which allows accurate control of the relevant process parameters. Nevertheless the costs of the epitaxial process - apart from the still extremely high wafer prices - are a major drawback for a wide range commercialization of SiC devices. This would hold even in the case of zero micropipe density. A pragmatic way to achieve a substantial potential in cost reduction is the use of multiple-wafer instead of single-wafer processing. On the other hand, this leads to new challenges in direction of process control and homogeneity adjustment. Today there exist three major commercial suppliers for SiC epi systems, all using different basic setups. These companies are EPIGRESS in Sweden (hot wall tube reactor [6]), AIXTRON in Germany (planetary reactor with independent rotation of each wafer [5]) and EMCORE in New Jersey, USA (vertical cold wall reactor [7]). To the knowledge of the authors multi-wafer epitaxial processing of SiC is only reported either on AIXTRON ([8], seven 2" wafers) or on EMCORE ([9], six 2" wafers) systems.
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Mat. Res. Soc. Symp. Proc. Vol. 572 01999 Materials Research Society
In the following paper we shall describe how and how far we have been able to solve the difficulties of this technology and to report about growth results recently achieved with this tool. A comparison will be made with results formerly achieved with a single
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