Reduction of incorporation of B, Al, Ti and N in 4H-SiC epitaxial-layer grown by chemical vapor deposition at higher gro
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Reduction of incorporation of B, Al, Ti and N in 4H-SiC epitaxial-layer grown by chemical vapor deposition at higher growth temperature
Mitsuhiro Kushibe, Koh Masahara, Kzutoshi. Kojima, Tshiyuki Ohno, Yuki Ishida, Tetsuo Takahashi, Johji Nishio, Takaya Suzuki, Tomoyuki Tanaka, Sadahumi Yoshida, Kazuo Arai Ultra-Low-Loss Power Device Technology Research Body 1-1-4 Umezono, Tsukuba, Ibaraki 305-8568, Japan $%675$&7
The influence of growth conditions and susceptor purity on the residual contamination in undoped 4H-SiC epitaxial layer grown at higher temperature such as 1600 is investigated. Residual N concentration is found to increase with growth temperature. Growth temperature dependence of residual N concentration is stronger than that of Al or B. The effect of degradation of SiC coating layer on the purity of the epitaxial layer is studied. SiC coating layer is degraded after very few repetition of growth-run. SIMS measurement reveals that the concentration of N, Al, B, Ti and V in epitaxial layer increases with the deterioration of SiC coating layer. Therefore, serious consideration on the effect of contamination from the susceptor graphite is required. By using various grades of graphite as susceptor, the dependence of the purity of epitaxial layer on the susceptor purity is studied. High concentration (1017 to 1018 cm-3) of N is found in graphite. Contamination of all types of impurities such as p-type impurities, transition metal impurities and N in graphite is found to affect the purity of epitaxial layers.
INTRODUCTION
The use of SiC as high voltage power devices has been recognized attractive for quite some time. However, advances in the industrialization of the devices is limited both by the quality of substrate and insufficiency of process technologies. Recently there has been a rapid progress in fabrication technology of 4H-SiC substrate and density of micro-pipes in commercially available substrates is decreased dramatically. In addition to the progress, reduction of both shallow and deep levels in epitaxial layer should be pursued more intensively in order to fully exploit the advantages of material. For the realization of high voltage devices, thick and pure epitaxial layer is required. Therefore requirement for realizing high growth rate in epitaxial growth is strong to industrialize the SiC high power devices. For obtaining higher growth rate, higher growth temperature is preferable [1]. Therefore technology of growing pure epitaxial layer at higher growth temperature should be developed. There are some reports that consider graphite susceptor as a source of the contamination of the epitaxial layer [2,3]. There has been, however, no precise study on the effect of the purity of the susceptor up to now curtailed by many types of imperfectness of SiC substrate other than impurities. Reduction of impurity has become one of the most urgent issues to be solved. One E3.9.1
of the technologies to reduce the effect of purity of graphite has been SiC coating. However, SiC coating is etched of
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