Investigation of a Self-Aligned Cobalt Silicide Process for Ohmic Contacts to Silicon Carbide

Previous studies showed that cobalt silicide can form ohmic contacts to p-type 6H-SiC by directly reacting cobalt with 6H-SiC. Similar results can be achieved on 4H-SiC, given the similarities between the different silicon carbide polytypes. However, previous studies using multilayer deposition of silicon/cobalt on 4H-SiC gave ohmic contacts to n-type. In this study, we investigated the cobalt silicide/4H-SiC system to answer two research questions. Can cobalt contacts be self-aligned to contact holes to 4H-SiC? Are the self-aligned contacts ohmic to n-type, p-type, both or neither? Using x-ray diffraction, it was found that a mixture of silicides (Co2Si and CoSi) was reliably formed at 800 degrees C using rapid thermal processing. The cobalt silicide mixture becomes ohmic to epitaxially grown n-type (1x1019cm-3) if annealed at 1000 degrees C, while it shows rectifying properties to epitaxially grown p-type (1x1019cm-3) for all tested anneal temperatures in the range 800-1000 degrees C. The specific contact resistivity (C) to n-type was 4.3x10-4cm2. This work opens the possibility to investigate other self-aligned contacts to silicon carbide.