Epitaxy

The SiC Lab has two CVD reactors (Chemical Vapor Deposition) that were designed and built by researchers at USC. Epitaxial growth of SiC is the formation of a high quality low defect density layer on top of bulk material that may be of inadequate quality for devices. Epi growth is extremely important for SiC because CVD grown epilayers are capable of reducing or eliminating defects that have a large impact on device performance. Micropipes can be closed and basal plane dislocations can be transformed into elementary screw dislocations in moderately thick layers of approximately 20 microns. The future of SiC devices depends on high quality epi.

CVD of silicon carbide requires that gaseous precursors containing Si and C species are carried into a reactor using a carrier gas such as hydrogen. In the reactor, these gases break down into their constituent species and saturate at the surface of a wafer where is energetically favorable for them to bond to the crystalline lattice at the wafer surface. CVD is a very versatile and controllable technique in that dopant atoms such as nitrogen, aluminum, and boron my be introduced into the system in the form of additional gasses.

USC operates a CVD furnace daily and has well defined process conditions to create high quality epilayers, control doping concentration, and even reduce defect density. Another new system is able to achieve a wider range of growth conditions. This is the HTCVD or high temperature CVD system. The HTCVD growth mechanism differs from conventional CVD in that the precursor gases break down much sooner and transport of the species becomes similar to the PVT process that is used for bulk growth.

High quality epitaxial layers are grown on SiC substrate wafers using these systems. After the epi-growth process is complete, the wafers may then be used for device fabrication.

CVD System

The CVD system operates between 1000 and 1550°C and is most often used to grow films approximately 20 microns thick. This system is several years old and process conditions are well defined, therefore this system is used daily to produce high quality epi.