研究目的
To develop a method to determine the thickness of homoepitaxial high resistivity SiC layers grown on conducting SiC substrates using scanning confocal Raman spectroscopy (SCRS).
研究成果
The developed SCRS method effectively measures the thickness of homoepitaxial SiC layers with submicrometer lateral and vertical resolution. It is non-destructive, model-independent (except for ellipsometry comparison), and robust against errors. Verification with ellipsometry and SIMS shows consistent results, making it suitable for scientific and industrial applications in SiC and graphene-based devices.
研究不足
The SCRS method has lower and upper bounds for layer thickness measurements: layers under ~500 nm show only partial changes in FWHM, requiring extrapolation, and thick layers are limited by the microscope objective working distance (typically >100 μm). The method requires a transition in free carrier density between layer and substrate (nf ~5×10^16 to 1×10^18 cm^-3), and exact resistivity determination is hindered by leakage currents in underlying substrates.
1：Experimental Design and Method Selection:
The study employs scanning confocal Raman spectroscopy (SCRS) to measure the thickness of SiC layers by detecting the transition from LO phonon to coupled LO phonon-plasmon modes at the interface between high resistivity SiC:V layers and conductive SiC:N substrates. The top surface is labeled using epitaxial graphene growth and Rayleigh scattering (RS). Methods are compared with ellipsometry and SIMS for verification.
2：Sample Selection and Data Sources:
Samples include conducting 4H-SiC substrates (off-axis) from II-VI Inc., diced into
3：5 × 5 mm2 pieces. Semi-insulating SiC:
V samples are used as references. SiC:V layers are grown by Modified Physical Vapor Transport (MPVT) on SiC substrates with vanadium doping.
4：List of Experimental Equipment and Materials:
Equipment includes Witec Alpha 300 confocal Raman microscope, JA Woollam Co. RC2 ellipsometer, IONTOF SIMS5 instrument, Bruker DektakXT stylus surface profiler, and growth setup with graphite crucible, residual gas analyzer (PrismaPlus QME220), and polishing equipment. Materials include SiC powder, vanadium carbide (VC) powder, Ar-H2 forming gas, colloidal silica slurry, and epitaxial graphene growth precursors.
5：Experimental Procedures and Operational Workflow:
SiC:V layers are grown in MPVT setup with controlled temperature (1700-1800°C), pressure (170-190 mbar), and gas flow (12-24 SLPH). Growth times vary from 30 s to 15 min. Samples are polished using CMP. Graphene is grown on SiC:V layers for surface labeling. SCRS measurements involve depth scans with 532 nm laser, collecting 200 spectra over 0-20 μm range. Ellipsometry and SIMS are performed for thickness verification.
6：Data Analysis Methods:
Raman spectra are analyzed for FWHM of LO phonon modes, integrated intensities, and center of mass. Interface position is determined from FWHM transitions. Thickness is calculated using geometrical optics corrections. SIMS data provide vanadium concentration profiles, and ellipsometry data are analyzed for interference patterns to extract thickness.
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confocal Raman microscope
Alpha 300
Witec
Used for scanning confocal Raman spectroscopy (SCRS) to measure Raman spectra and determine layer thickness with high lateral and vertical resolution.
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ellipsometer
RC2
JA Woollam Co.
Used to measure layer thickness by analyzing interference patterns in reflectivity spectra for comparison with SCRS results.
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stylus surface profiler
DektakXT
Bruker
Used for depth calibration with high step-height repeatability.
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SIMS instrument
SIMS5
IONTOF
Used for Secondary Ion Mass Spectroscopy to verify vanadium doping and measure depth profiles for thickness calibration.
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residual gas analyzer
PrismaPlus QME220
Used to monitor the growth ambient during SiC layer growth.
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SiC substrate
4H off-axis
II-VI Inc.
Used as the base substrate for growing homoepitaxial SiC layers.
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