Materials Science Forum Vols. 821-823

Abstract: Elimination of basal plane dislocations (BPDs) in epitaxial 4H-SiC is demonstrated via a novel pulsed annealing technique in a moderate N₂ overpressure of 0.55 MPa. BPD removal in 15 µm thick epitaxial 4H-SiC was confirmed using ultraviolet photoluminescence (UVPL) imaging before and after the annealing process. The samples were capped with a carbon cap, introduced into the annealing chamber, and brought up to a base temperature (T_BASE) of around 1550 °C for the pulsed anneal. The multicycle rapid thermal anneal (MRTA) was then performed in the T_BASE:T_MAX range, where T_MAX = 1875 °C was the peak temperature reached by the annealing cycles. Post-anneal surface quality and carrier lifetime were characterized by atomic force microscopy and time-resolved photoluminescence decay.

Abstract: A peculiar surface defect on a silicon carbide (SiC) epitaxial wafer, found to be associated a basal plane dislocation (BPD), was studied using a low energy scanning electron microscope (LESEM), and a novel method we are calling multi directional scanning transmission electron microscopy (MD-STEM). We have confirmed that an etch pit with double cores neighboring a peculiar surface defect is derived from the extended BPD. The BPD consisted of two partial dislocations with a stacking fault width of about 100 nm. Observation of only one viewing direction in a previous study missed the extended dislocation but through the use of the MD-STEM method in the current study, the dislocation has been confirmed to be extended into a stacking fault.

Abstract: A mirror projection electron microscopy (MPJ), non destructive, high spatial resolution and high throughput method, is useful for defect inspection in silicon carbide (SiC) wafer. Previously, it was demonstrate that three type of typical dislocations in 4H-SiC, threading screw dislocation (TSD), threading edge dislocation (TED) and basal plane dislocations (BPD) can be identified in MPJ image. Origin of the contrast of dislocations in MPJ image was revealed by observation of the same wafer at as-grown and after CMP processing. Streak of TSD spot is due to surface morphology, and the contrast of BPD isn’t due to surface morphology but due to charging on dislocation line.

Abstract: We observed fine surface morphology of silicon carbide wafers using a low energy scanning electron microscope (LESEM). Typical kinds of surface defects were observed by LESEM. After low temperature KOH treatment, it is confirmed that positions of etch pits are the same positions of these defects. Correlation between LESEM imaging and cross-sectional scanning transmission electron microscopy (STEM) of the same defects reveals threading dislocations and basal plane dislocations at the core of the defects.

Abstract: In this study, we investigated the annealing temperature dependence of dislocation extension in an ion-implanted region of a 4H-silicon carbide (SiC) C-face epitaxial layer, revealing that a high temperature annealing led to dislocation formation. We also investigated the current-voltage (I-V) characteristics of a 4H-SiC PIN diode with and without these extended dislocations. We demonstrated that the forward biased I-V characteristics of samples with extended interfacial dislocations have a kink at lower current regions.

Abstract: Dislocation behavior during homo-epitaxy of 4H-SiC on offcut substrates by Chemical Vapor Deposition (CVD) has been studied using Synchrotron X-ray Topography and KOH etching. Studies carried out before and after epilayer growth have revealed that, in some cases, short, edge oriented segments of basal plane dislocation (BPD) inside the substrate can be drawn towards the interface producing screw oriented segments intersecting the growth surface. In other cases, BPD half-loops attached to the substrate surface are forced to glide into the epilayer producing similar screw oriented surface intersections. It is shown that the initial motion of the short edge oriented BPD segments that are drawn from the substrate into the epilayer is caused by thermal stress resulting from radial temperature gradients experienced by the wafer whilst in the epi-chamber. This same stress also causes the initial glide of the surface half-loop into the epilayer and through the advancing epilayer surface. These mobile BPD segments provide screw oriented segments that pierce the advancing epilayer surface that initially replicate as the crystal grows. Once critical thickness is reached, according to the Mathews-Blakeslee model, these screw segments glide sideways under the action of the mismatch stress leaving IDs and HLAs in their wake.

Abstract: This work reports on description and application of a new Photoluminescence (PL) Imaging technique for in-grown stacking fault (SF) characterization and identification on 4H-SiC epilayers. The purpose of this technique is to make a spectroscopic picture from a collection of PL imaging picture taken at different output wavelengths in order to both display the shape and an approximation of the maximum PL intensity wavelength at room temperature (RT) of the characterized SF. This is why we called this technique “PL Imaging Spectroscopy”. Five types of SFs have been observed and compared to PL spectra collected at RT and 10K.

Abstract: We have investigated the effect of thermal oxidation on stacking faults (SFs) in 4H-SiC epilayers using photoluminescence imaging. We found that a comb-shaped dislocation array was deformed by thermal oxidation and that SFs were formed on both sides of the comb-shaped dislocation array by a laser irradiation. Transmission electron microscopy has been performed in the comb-shaped dislocation array to observe the stacking pattern of SF near the dislocation. As a result, the SF turned out to be a single Shockley SF (1SSF). We also found that line-shaped faults perpendicular to the off-cut direction were formed during oxidation and were stretched with oxidation time. Moreover, triangle-shaped SFs were formed/expanded from the line-shaped faults by a laser irradiation. The characteristics of these line-shaped faults were discussed.

Abstract: Simple models for Shockley-type stacking-fault formations during 4H-SiC epitaxial growth are proposed. The model consists of the accidentally-faulted mis-stacking and the Shockley single-gliding events. At first, the mis-stacking event caused by imperfect step-flow growth is considered. Then the single-gliding event is followed to make more stable stacking sequences. Simple single-gliding is considered rather than complicated double, triple, or quadruple Shockley gliding. All possible mis-stacking and single-gliding events are considered. All of the reported Shockley-type SFs are derived without excess and deficiency from the proposed models.

Abstract: Recently, a new Micro-Raman technique has been used to detect extended defects in 4H-SiC homoepitaxy. The method is based on the local increase of free carriers in undoped epitaxies (n < 10¹⁶ at/cm^-3) produced by a high power laser. The Longitudinal optical Raman mode (LO) is coupled with the electronic plasma generated by the laser pumping; such a Raman signal is sensitive to crystallographic defects that lead to trapping (or dispersion) of the free carriers which results in a loss of coupling. The monitoring of the LOPC allows determining the spatial morphology of extended defects. The results show that the detection of defects via the induced-LOPC (i-LOPC) is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0,7eV thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Also, the i-LOPC method shows the connection between the carrier concentration and the carrier lifetime for undoped film, obtaining meaningful information related to electrical properties of the film, and demonstrating that this technique is a fast, reliable and powerful method to characterize most of crystallographic defects (extended and point-like defects) in the semiconductor field.