Double-sided and single-sided polished 6H-SiC wafers with subsurface damage layer studied by Mueller matrix ellipsometry

Abstract

The complex optical constants and the subsurface damage layer of uniaxial doped 6H-SiC wafers are measured using Mueller matrix spectroscopic ellipsometry. A comparison is made between measurements on a single-sided polished wafer that can be treated as a semi-infinite substrate and on a double-sided polished wafer that is studied with the partial-wave theory. The refractive indices and extinction coefficients for ordinary and extraordinary directions are determined below the bandgap after point-by-point fitting of experimental Mueller matrices. The thickness of the subsurface damage layer caused by mechanical polishing and chemical mechanical polishing determined by ellipsometry is consistent with the result of transmission electron microscope. The ellipsometry results show that the analysis based on a double-sided polished wafer is more informative about the optical properties of 6H-SiC than that of the single-sided polished wafer as it renders information properties about the bulk properties of the material, for example, allowing the determination of the very weak absorption coefficient (k≈10−4) due to doping.

Identification of subsurface damage of 4H-SiC wafers by combining photo-chemical etching and molten-alkali etching

“…Both non-destructive and destructive approaches have been developed to study the nature of SSD in semiconductor wafers. Non-destructive approaches including X-ray diffraction, laser scattering and acoustic probing are promising options for the detection of the SSD, but they are incapable of detecting the thickness of the SSD, and its distance away from the surface [14,15] . The destructive approaches, such as taper-polishing, cross-sectional microscopy and chemical etching, are able to directly and accurately detect the SSD [16−21] .…”

Application of imaging ellipsometry and white light interference microscopy for detection of defects in epitaxially grown 4H–SiC layers

“…1. Ellipsometry has been widely used to study semiconductor materials and SiC in particular [17][18][19]. SiC is transparent in a visible spectral range below the bandgap.…”

Mueller Matrix Ellipsometric Characterization of Nanoscale Subsurface Damage of 4H-SiC Wafers: From Grinding to CMP

“…results, while no roughness layer is set for the CMP wafer. Based on the prior knowledge [17], the Cauchy parameters of the damage layer are initialed as follows: A is 2, B is 0.05 μm 2 , and the initial thicknesses of damage layers are set to 50 nm, 4 and 2 nm for rough grinding, fine grinding, and CMP wafers according to their processing techniques, respectively. By fitting the MMSE data, the damage layer thicknesses of rough grinding, fine grinding, and CMP wafers are obtained as 53.7 ± 0.9 nm, 4.6 ± 0.6 nm, and 2.4 ± 0.2 nm, respectively.…”

“…As a nondestructive strategy, the Mueller Matrix Spectroscopic Ellipsometry (MMSE) is commonly used to measure the thickness and refractive index of thin films and crystal with excellent accuracy [13,14]. Previously reported refractive ellipsometric characterizations in SiC wafers have been done [17] but were limited in single-sided polished wafer without backside reflection [15] or treated the damage layer as an SiO 2 film [16]. Our group [17] took double-sided polished n-type 6H-SiC wafer with backside reflection and the damage layer into account based on partial-wave coherence theory.…”

“…Previously reported refractive ellipsometric characterizations in SiC wafers have been done [17] but were limited in single-sided polished wafer without backside reflection [15] or treated the damage layer as an SiO 2 film [16]. Our group [17] took double-sided polished n-type 6H-SiC wafer with backside reflection and the damage layer into account based on partial-wave coherence theory. However, effectively assessing the damage layer in the rough stage of grinding or polishing was excluded.…”