Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas

Abstract

This article describes the initial discovery and development of new approaches to SiC homoepitaxial and heteroepitaxial growth. These approaches are based upon the previously unanticipated ability to effectively supress two-dimensional nucleation of 3C-SiC on large basal plane terraces that form between growth steps when epitaxy is carried out on 4H-and 6H-SiC nearly on-axis substrates. After subdividing the growth surface into mesa regions, pure stepflow homoeptixay with no terrace nucleation was then used to grow all existing surface steps off the edges of screw-dislocation-free mesas, leaving behind perfectly on-axis (0001) basal plane mesa surfaces completely free of atomic-scale steps.Step-free mesa surfaces as large as 0.4 mm x 0.4 mm were experimentally realized, with the yield and size of step-free mesas being initally limited by substrate screw dislocations. Continued epitaxial growth following step-free surface formation leads to the formation of thin lateral cantilevers that extend the step-free surface area from the top edge of the mesa sidewalls. By selecting a proper pre-growth mesa shape and crystallographic orientation, the rate of cantilever growth can be greatly enhanced in a web growth process that has been used to (1) enlarge step-free surface areas and (2) overgrow and laterally relocate micropipes and screw dislocations. A new growth process, named step-free surface heteroepitaxy, has been developed to achieve 3C-SiC films on 4H-and 6H-SiC substrate mesas completely free of double positioning boundary and stacking fault defects. The process is based upon the controlled terrace nucleation and lateral expansion of a single island of 3C-SiC across a step-free mesa surface. Experimental results indicate that substrateepilayer lattice mismatch is at least partially relieved parallel to the interface without dislocations that undesirably thread through the thickness of the epilayer. These results should enable realization of improved SiC homojunction and heterojunction devices. In addition, these experiments offer important insights into the nature of polytypism during SiC crystal growth.

Formation process of 3C-SiC on 6H-SiC (0001) by low-temperature solution growth in Si–Sc–C system

“…In the case of CVD, a low growth temperature is important for 3C-SiC nucleation on step-free 4H or 6H-SiC substrates, since using a lower growth temperature reduces the surface adatom mobility and thus increases the rate of 2D terrace nucleation that initiates 3C-SiC growth on (0001) basal plane surfaces [15]. For the VLS method, Soueidan et al [11] found that the key point is the occurrence of 3C islands nucleation, during the heating ramp, resulting from a transient dissolution-precipitation reaction.…”

“…Heteroepitaxial growth of 3C-SiC by CVD [15] and the VLS method [11] have been investigated. In the case of CVD, a low growth temperature is important for 3C-SiC nucleation on step-free 4H or 6H-SiC substrates, since using a lower growth temperature reduces the surface adatom mobility and thus increases the rate of 2D terrace nucleation that initiates 3C-SiC growth on (0001) basal plane surfaces [15].…”

Nucleation of 3C-SiC associated with threading edge dislocations during chemical vapor deposition

“…The epitaxial growth of 3C-SiC on hexagonal polytype SiC substrates (e.g. 4H-, 6H-SiC) was found to result in double positioning boundaries [4,8,12,13]. This is due to 3C-SiC islands nucleating simultaneously on multiple terraces on the substrate.…”

“…Since the emergence point of a screw dislocation serves as a source of steps, the growth on a mesa intersected by the screw dislocation results in the formation of distinct hexagonal hillocks of the same polytype as the substrate. Nucleation elsewhere on the same mesa may result in the intergrowth of 3C-SiC with the hexagonal polytype and appearance of stacking faults and double position boundaries [4]. Some mesas, however, are not intersected by screw dislocations.…”

“…3C-SiC has a higher inversion channel mobility making it a better candidate over 4H and 6H-SiC for metal oxide semiconductor field effect transistors [1,2]. 3C-SiC also exhibits lower density of states at the oxide-semiconductor interface [3] and compares favorably with 4H-SiC in terms of lower turn-on voltage [4]. Despite the increased interest in 3C-SiC, high quality films are difficult to grow [5][6][7][8][9][10].…”