Materials Science Forum Vols. 778-780

Abstract: 4H-SiC epitaxial wafers were prepared for the investigation of epitaxial stacking faults (SFs), for the purpose of classification and add to the epitaxial specification by PL-imaging analysis. Black colored SFs detected in PL colored images were focused, and investigated. Black SFs in the PL images were classified for two species, ones were correspond to the triangular defects, and the others were similar to the known SFs. Triangular defects were the killer defects for the I-V properties and the other black defects were not affected the I-V properties. Most of PL spectrums of triangular defects had the 538nm peak, and showed the 3C properties. Black defects undetectable as the surface defects (SDs) had 460, 480nm peak, differed from the reported typical 1-4SSFs spectrum. It seemed that these defects differed from the thickness of stacking layer and PL peak, whether the defects led to detectable/undetectable as the SDs. Thick stacking layers generated the triangular defects, and thin ones generated the PL-black defects undetectable as the surface analysis. Consequently, the black defects undetectable as the surface analysis (detected only for the PL-imaging analysis) has no use for add to the specification at the moment.

Abstract: A new type of defects, vacant broken line defects, was found to occur in a-face grown crystals of 4H-Silicon Carbide. We characterized the vacant broken line defects by high voltage transmission electron microscope (HV-TEM). The HV-TEM image revealed that the edges of broken line defects were connected by a bundle of dislocations, which elongated to the growth direction on the basal plane. The analysis by gb method for determining Burgers vector indicated that the dislocations were not pure screw dislocations, but complex of screw and edge dislocations. The vacant broken line defect was considered to be a quasi-stable state of a bundle of basal plane dislocations in a-face growth, similar to a micropipe defect in c-face growth.

Abstract: Epitaxial layers grown on mechanically lapped 4H-SiC (0001) substrates were analyzed by using scanning ion microscopy (SIM), photoluminescence (PL) mapping and transmission electron microscopy (TEM). Even in the use of substrates with standard nitrogen concentration of 1.3 × 10¹⁹ cm^-3, double Shockley-type stacking faults were observed to be formed in the epitaxial layer from the interface between the epitaxial layer and the substrate without any external stresses. Surface damaged layer seems to cause the formation of not only 2SSFs but also threading edge dislocation (TED) half-loops during epitaxial growth.

Abstract: We report an investigation of the formation of triangular defects (TDs) in 4H–SiC expitaxial layers using Kelvin probe force microscopy (KPFM) and a nano-indenter. The results provide valuable information on the crystallographic structure, including the polytype nature of the TDs and surface potential profile. The TDs were also characterized using micro-Raman spectroscopy and high-resolution transmission electron microscopy. We found that the TDs were composed of a thick 3C-SiC band, as well as stacking faults (SFs) in the 4H-SiC epilayer.

Abstract: Surface roughening regions running like scratches are often observed locally after epitaxy film grown on a very flat 4H-SiC wafer surfaces. We investigated generation mechanism of such roughening surface by using X-ray topography and confocal optical microscopy. We found that lattice defects were often introduced during CMP at local regions, and those local regions cannot be recognized by optical microscopy, since very flat surface can be observed. By H₂ etching which is preprocess of epitaxy film growth, those lattice defects are almost etched off, but local rough surface consists of pits and step bunching regions appear like scratches, and those local pits and surface roughening regions grew up to step bunching during epitaxy film growth.

Abstract: A mirror electron microscopy (MPJ) was developed for defect inspection in silicon carbide (SiC) wafer as non destructive, high spatial resolution and high throughput method. Each of three type dislocations, threading screw dislocation (TSD), threading edge dislocation (TED) and basal plane dislocations (BPD) in 4H-SiC wafer were identified in MPJ image as a dark dot with different type of tailing. This new method provides high performance inspection of defects in SiC possible without specimen pre-treatment.

Abstract: This paper reviews some recent advances in the application of scanning probe microscopy (SPM) electrical characterization techniques to several critical surface and interface issues in SiC technology. High resolution carrier profiling capabilities in SiC of scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) were employed for several applications. These included two-dimensional (2D) imaging of doped regions in SiC devices (to be used as input for device simulations or as a feedback for device processing) and the quantitative evaluation of the electrically active profiles of P (or N) and Al implanted 4H-SiC after high temperature treatments. Furthermore, the electrical modification of the SiO₂/4H-SiC interface in MOS devices subjected to post-oxide-deposition treatments in NO or N₂O and POCl₃ have been investigated, providing quantitative information on the electrical activation of incorporated N or P in the few-nm-thick SiC interfacial region. The lateral homogeneity of metal/SiC interfaces was probed at nanoscale by conductive atomic force microscopy (CAFM), with a special emphasis given to the case of Schottky contacts on 3C-SiC, where the diode behaviour is strongly affected by the high density of electrically active defects in the substrate. Finally, CAFM has been employed to study the current transport in epitaxial graphene (EG) grown on 4H-SiC (0001), revealing the impact of the substrate morphology (terraces and steps or facets) on the local conductivity.

Abstract: This paper reports an EDMR (electrically detected magnetic resonance) observation on 4H-SiC(000-1) “C face” MOSFETs. We found a new strong EDMR signal in wet-oxidized C-face 4H-SiC MOSFETs, which originates from intrinsic interface defects on C-face SiC-SiO2 structures.

Abstract: We focused on the inability of the common high-low method to detect very fast interface states, and developed methods to evaluate such states (Cψ_S method). We have investigated correlation between the interface state density (D_IT) evaluated by the Cψ_S method and MOSFET performance, and found that the D_IT(Cψ_S) was well reflected in MOSFET performance. Very fast interface states which are generated by nitridation restricted the improvement of subthreshold slope and field-effect mobility.

Abstract: Constant-capacitance deep-level transient spectroscopy was carried out to characterize in detail interface states close to the conduction band edge in SiO₂/SiC structures. The measured results are summarized as follows: (1) The capture of electrons by the interface states proceeds logarithmically with time. (2) The emission of electrons accelerates slightly with increasing density of captured electrons. The oxide trap model explains the logarithmic change in capture with time but not the phenomenon of accelerated emissions. This prompted us to formulate a new model that replicates the logarithmic capture process with time. In this model, we postulated the electron density at the interface decreases exponentially as the trapped electron density increases owing to the interaction between the trapped electrons and the free electrons. In this case, the capture process is almost the same as with the oxide trap model except for the definition of parameters. Further, we do not need to take into account the delay of the emission process caused by tunneling. The phenomenon of accelerated emissions may be explained by interactions among captured electrons in this model.