No abstract

The range of polishing-induced subsurface damage remaining in a commercially available production grade 4H-SiC (0001) epi-ready substrate was evaluated by the observation from the (-1100) cleavage plane using two kinds of highly strain-sensitive characterization methods. Firstly, the analysis using electron backscattered diffraction (EBSD) with a submicron spatial resolution was conducted on the exposed cross sectional plane. Then, for the further quantitative evaluation excluding the influence of roughness or contamination of the cleavage plane, a synchrotron X-ray micro-diffraction experiment was carried out. The range of the subsurface damage evaluated in those experiments was ensured by confirming none of additional strain inserted at the cleavage, as compared with the damage-free substrate prepared by high temperature thermal etching. As a result, the depth of the residual strained region below polishing-induced scratches at the surface was estimated to be in the range of a few microns, which is much deeper than the previously reported value of 100 nm by cross-sectional transmission electron microscopy. It suggests a potential of EBSD for the conventional tool to characterize even a small amount of strain in SiC single crystal.

Mechanism of surface roughening caused by the polishing induced subsurface damage on 4o off-cut 4H-SiC (0001) substrate during thermal etching, CVD epitaxial growth, and the subsequent high temperature annealing was investigated in the wide temperature range of 1000-1800°C. Different from the previous study based on a macroscopic characterization by optical microscopy, microscopic characterization based on a scanning electron microscopy (SEM) was employed in this study. By utilizing the SEM operated under various conditions, disordered step arrangements as well as stacking faults and dislocations were imaged. The obtained results revealed that the SFs cause the fluctuation in the step kinetics, resulting in the step bunching formation during the thermal process.

As a new post-implantation activation annealing of Silicon Carbide (SiC), we propose the Si-vapor ambient anneal using Tantalum Carbide / metal Tantalum composite materials (TaC/Ta). In this technique, semi-closed TaC/Ta container which can supply Si-vapor ambient is used, and Si vapor compensates thermal desorption Si atoms from the SiC surface above 1500°C and can maintain the original surface morphology by controlling a process temperature and Ar back pressure. Therefore the Si-vapor ambient anneal is able to simplify the process of conventional activation anneal methods using refractory cap-layers for protecting SiC surface from thermal damage of Si-atom desorption. Experiments were performed under Ar 1.3kPa at 1600/1700°C for 5min optimized conditions in a 6inch TaC/Ta container, and the Al+ ion-implanted 4H-SiC properties after annealing were characterized by atomic force microscopy (AFM), Rutherford Back-scattering Spectrometry (RBS) channeling method, and four-point probe method. According to evaluation, there was no roughening of SiC surface from AFM topographic images and recovery of crystallinity at the ion-implanted layer was equivalent to by the conventional cap-layer method from RBS channeling measurement. The sheet resistance of 12kΩ/ at 1700°C equal to the typical Al+ ion implanted p-type SiC is confirmed by four-point probe method.