The State of the Art
Physical Vapor Transport (PVT)
High temperatures are key to the Physical Vapor Transport (PVT) process. The crucible containing the polycrystalline silicon carbide seed material is heated to over 2000°C, causing the material to sublimate directly from solid to vapor. This vapor then moves from the hotter area of the crucible to a cooler area where the seed crystal is placed. When the vaporized silicon carbide encounters this cooler seed, it solidifies and forms crystalline layers on the seed. This phase is crucial to the growth of high quality SiC crystals. Temperature control throughout this process is critical because it affects the sublimation rate, vapor transport, and crystal growth rate on the seed, which ultimately determines the quality and uniformity of the resulting silicon carbide crystal.
High Temperature Chemical Vapor Deposition (HTCVD)
The High Temperature Chemical Vapor Deposition (HTCVD) process, developed jointly by Linköping University and ABB, is an advanced method for bulk crystal growth of silicon carbide. Unlike the conventional Physical Vapor Transport (PVT) method, HTCVD uses gaseous precursors in conjunction with a carrier gas stream, allowing for a more controlled growth environment.
This advanced process unfolds in three critical steps. First, precursor gases are strategically injected into the central zone of the reactor. At this point, the extremely high temperatures within the chamber induce rapid decomposition of the precursors, starting within the injector itself. This central injection method is critical because the absence of nearby cold surfaces promotes homogeneous nucleation directly in the gas phase.
The second phase involves the sublimation of the particles formed in the gas phase. This takes place under the influence of the elevated process temperatures, which are essential for the phase change of the material.
The process culminates in the third stage where these sublimed species are condensed on the surface of the seed crystal. This final step is critical for the formation of high-quality silicon carbide crystals and marks the successful completion of the HTCVD process.
