Characterization of scraper-shaped defects on 4H-SiC epitaxial film surfaces

Abstract

We have found undiscovered defects on a 4H-SiC epitaxial layer, the shape of which resembles a scraper in images taken by confocal differential interference contrast optical microscopy. The surface morphological structure and formation mechanism of the scraper-shaped defects were investigated by atomic force microscopy and grazing incidence monochromatic synchrotron X-ray topography, respectively. The scraper-shaped defects were surface morphological defects consisting of surface asperity and were caused by the migration of interfacial dislocations. The evaluation of the thermal oxide reliability of metal–oxide–semiconductor capacitors fabricated on these defects was performed by time-dependent dielectric breakdown measurement. The degradation of thermal oxide occurred only on the downstream line of the scraper-shaped defects. The thickness of the oxide layer on these defects was also investigated using cross-sectional transmission electron microscopy.

Analysis of Dislocation Structures in 4H‐SiC by Synchrotron X‐Ray Topography

“…It is also reported that step‐bunching is induced during epitaxy film growth on the trace of movement of the interfacial dislocation terminal end on the surface associated with epitaxy film growth shown in Fig. (a), and surface unevenness appears and becomes more apparent as the epitaxy film grows . It is further found that all these uneven structures on the epi‐wafer surface cause dielectric breakdowns of the MOS capacitors .…”

“…It is further found that all these uneven structures on the epi-wafer surface cause dielectric breakdowns of the MOS capacitors [38,39]. Utilization of Berg-Barrett X-ray topography, TEM, SEM, AFM, and optical microscope allowed us to understand the relationship between "various uneven structures on the epitaxy film surface" and "lattice defects in the epitaxy film resulting in unevenness" [38][39][40][41]. Pits at the dislocation position were regarded as one of the significant factors of the MOS structure dielectric breakdowns on the 8°-off substrate.…”

Defect Inspection Techniques in SiC

“…Sako et al show that a surface defect with a scraper-shaped surface profile on the SiC epitaxial layer has been observed using CDIC. [56]. Kitabatake et al establish the integrated evaluation platform using CDIC to inspect surface defects on the SiC wafers and the epitaxial films [57,58].…”

Investigation of giant step bunching in 4H-SiC homoepitaxial growth: Proposal of cluster effect model

“…The cause of the breakdown is reported to be variations in gate oxide thickness arising from the surface morphology of 4H-SiC epilayers grown on the (0001) face (Si-face), such as giant steps that are several unit cells in height and pits. [3][4][5][6][7] In particular, the giant steps markedly decrease the reliability of the gate oxide.…”