Correlation of Stress in Silicon Carbide Crystal and Frequency Shift in Micro-Raman Spectroscopy

Abstract

The correlation of stress in Silicon Carbide (SiC) crystal and frequency shift in micro- Raman spectroscopy was determined by an experimental method. We applied uniaxial stress to 4H- and 6H-SiC single crystal square bar specimen shaped with (0001) and (11-20) faces by four point bending test, under measuring the frequency shift in micro-Raman spectroscopy. The results revealed that the linearity coefficients between stress and Raman shift were -1.96 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (0001) face, -2.08 cm-1/GPa for FTO(2/4)E2 on 4H-SiC (11-20) face and -2.70 cm-1/GPa for FTO(2/6)E2 on 6H-SiC (0001) face. Determination of these coefficients has made it possible to evaluate the residual stress in SiC crystal quantitatively by micro-Raman spectroscopy. We evaluated the residual stress in SiC substrate that was grown in our laboratory by utilizing the results obtained in this study. The result of estimation indicated that the SiC substrate with a diameter of 6 inch remained residual stress as low as ±15 MPa.

Impact of Mechanical Stress and Nitrogen Doping on the Defect Distribution in the Initial Stage of the 4H-SiC PVT Growth Process

“…While the latter one exhibits an asymmetrical shape, its peak position can be used for an approximation of the present nitrogen doping [ 36 , 37 ]. Furthermore, Sugiyama et al and Batten et al reported a FTA peak position shift of −1.96 cm −1 per GPa of present stress, where a downshift corresponds to tensile stress and vice versa [ 38 , 39 ]. This relationship was utilized to approximate the stress between the seed and the grown crystal in a relative manner.…”

Polytype switching identification in 4H-SiC single crystal grown by PVT

“…Using the Raman line frequency shift (0.43cm −1 for 6H and 0.12 cm −1 for 4H) and the Raman stress coefficient (taken from Ref. [32]), the stress in the test sample of SiC wafer is also calculated in 4H (region-1) and 6H-SiC (region-2). It is found that both the regions are compressively stressed with stress value ~ −61 MPa and −159 MPa, respectively.…”

“…FLO (m/n) and FLA(m/n) modes. The zone-folded modes are designated by the reduced wave vector; a folded mode corresponds to a phonon mode at a reduced wave vector in the Brillouin zone for SiC polytypes [30,32,33]. Figure 6b shows the Raman spectra of three different regions of the wafer using UV (266 nm) laser excitation source [low penetration depth (d~1/2α) where α is the absorption coefficient].…”

Stress-controlled zero-field spin splitting in silicon carbide

“…2). Figures 2(a) and (c) show three Raman peaks associated with the E 2 TO, E 2 TO and A 1 TO, and E 1 TO phonon modes in 6H-SiC 31,32 at a distance of 20 µm and exactly at the heterointerface, respectively. We extract the spectral positions of these peaks from their maxima averaged by 4 points within 1 µm along the perpendicular direction to the scanning axis with an accuracy of 0.2 cm −1 .…”