5-4-2 Growth of 3C-SiC on Large-Area (Silicon) Substrates
Despite the absence of SiC substrates, the potential benefits of SiC hostile-environment electronics nevertheless drove modest research efforts aimed at obtaining SiC in a manufacturable wafer form.Toward this end, the heteroepitaxial growth of single-crystal SiC layers on top of large-area siliconsubstrates was first carried out in 1983 , and subsequently by a great many others over the years using a variety of growth techniques. Primarily owing to large differences in lattice constant (~20% difference between SiC and Si) and thermal expansion coefficient (~8% difference), heteroepitaxy of SiC using silicon as a substrate always results in growth of 3C-SiC with a very high density of crystallographic structural defects such as stacking faults, microtwins, and inversion domain boundaries . Other largearea wafer materials besides silicon (such as sapphire, silicon-on-insulator, and TiC) have been employed as substrates for heteroepitaxial growth of SiC epilayers, but the resulting films have been of comparablypoor quality with high crystallographic defect densities. The most promising 3C-SiC-on-silicon approach to date that has achieved the lowest crystallographic defect density involves the use of undulant silicon substrates . However, even with this highly novel approach, dislocation densities remain very high compared to silicon and bulk hexagonal SiC wafers.
While some limited semiconductor electronic devices and circuits have been implemented in 3C-SiC grown on silicon, the performance of these electronics (as of this writing) can be summarized as severely limited by the high density of crystallographic defects to the degree that almost none of the operational benefits discussed in Section 5.3 has been viably realized. Among other problems, the crystal defects “leak” parasitic current across reverse-biased device junctions where current flow is not desired. Because excessive crystal defects lead to electrical device shortcomings, there are as yet no commercial electronics manufactured in 3C-SiC grown on large-area substrates. Thus, 3C-SiC grown on silicon presently has more potential as a mechanical material in microelectromechanical systems (MEMS) applications (Section 5.6.5) instead of being used purely as a semiconductor in traditional solid-state transistor electronics.