SILICON-CARBIDE EPITAXY IN A VERTICAL CVD REACTOR - EXPERIMENTAL RESULTS AND NUMERICAL PROCESS SIMULATION

In this paper an overview is given on the epitaxial growth of SiC in a vertical CVD reactor. Results concerning impurity incorporation and w ags to achieve background doping levels as low as 10(14) cm(-3) are di scussed. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced press ure, lead to good control of dopant incorporation over more than three orders of magnitude, and smooth surface morphology at growth rates hi gher than 5 mu m/h. Doping variations < +/-12% across 35 mm wafers can routinely be obtained. The quality of the epilayers is proven by elec trical brakdown fields as high as 2 x 10(6) V/cm at N-A - N-D = 5 x 10 (-15) cm(-3) achieved in both pn and Schottky diodes and an electron m obility higher than 700 cm(2)/Vs at 300 K (4H-SiC) estimated from the on-resistance of these test devices. Another important experimental bo undary condition. the influence of the gas composition at the end of t he epitaxial growth process on the surface properties of the epitaxial layer, is described. It will be shown that surfaces nearly resistant against oxidation can be generated in a hydrogen free atmosphere. As a second main topic of this paper, results of an elaborate numerical pr ocess simulation will be described including both fluid mechanical and chemical behavior. The influence of the main process parameters like total flow, chamber pressure, and rotation speed on the stability of t he flow was investigated. The results achieved am compared with experi mental observations showing excellent agreement. The experimental obse rvation of an irradiant layer in the gas phase in front of the wafer u nder typical process conditions is explained with the help of the nume rical model. The usefulness of this specific feature for the optimizat ion of process conditions is discussed.