The Photoelastic Constant of (0001) 4H Silicon Carbide Determined by Scanning Infrared Polariscopy

Abstract

The piezo‐optic coefficients (π11‐π12) and the photoelastic constant Cσ of on‐axis (0001) 4H silicon carbide at λ = 1.3 μm are determined to (−3.3 ± 0.5) × 10−13 and (−2.8 ± 0.4) × 10−12 Pa−1, respectively. The experiment is conducted using a scanning infrared depolarization imager (SIRD) that uses a rotational mode for wafer scanning equipped with a special calibration setup for diametrical loading of 150 mm diameter wafers. The loading force is varied by gradually setting the wafer rotation frequency. (π11–π12) and Cσ are determined by analyzing the dependence of the shear stress equivalent on the loading force in the wafer center. This calibration procedure is made difficult by the pronounced inhomogeneous defect distribution on the wafer under study. Furthermore, the unloaded wafer is characterized using the multipolarization analysis on the base of an eccentric measurement mode. The resulting map of the shear stress maximum τmax completed by the direction of the large principal stress component reveals that the outer wafer part is tensile stressed in circumferential direction like a ring with magnitudes up to 10 MPa.

Observation of in-plane shear stress fields in off-axis SiC wafers by birefringence imaging

“…Here we note that (B 2 À B 1 ) is nearly equal to ðB 0 2 À B 0 1 Þ and much larger than B 6 since the components of mn n are small for a long-range stress field of dislocations in an off-axis SiC wafer. Using the reported values (Wang et al, 2013;Herms et al, 2021), the estimated value of ðB 0 2 À B 0 1 Þ for 4H-SiC with = 4 corresponds to the value of B 6 with 6 = 84 MPa, which is much larger than the stress field of threading edge dislocations (TEDs) in 4H-SiC with an observation range of (<À1 MPa). Then, equation ( 12) is approximated as follows:…”