Resistivity mapping of SiC wafers by quantified Raman spectroscopy.

Area of Science:

• Materials Science
• Semiconductor Physics
• Spectroscopy

Background:

• Accurate measurement of electrical resistivity is crucial for semiconductor characterization.
• Traditional methods may have limitations in spatial resolution or bulk property assessment.
• 4H-Silicon Carbide (4H-SiC) is a key material for high-power and high-frequency electronic devices.

Purpose of the Study:

• To develop and validate a Raman spectroscopy-based method for mapping electrical resistivity in 4H-SiC.
• To correlate Raman spectral features with free carrier concentration and predict bulk resistivity.
• To automate the resistivity mapping process for efficient semiconductor wafer analysis.

Main Methods:

• Utilized micro-Raman spectroscopy to analyze the longitudinal optical phonon-plasmon coupled (LOPC) mode in 4H-SiC.
• Intercalibrated Raman measurements with established eddy current measurements for bulk resistivity.
• Developed a multi-variable model using spectral data (position and line width of LOPC mode) calibrated with known resistivity samples.
• Automated data analysis and image generation using R-language scripts.

Main Results:

• Demonstrated a strong correlation between LOPC mode variations and free carrier concentration.
• Successfully predicted pointwise resistivity across a 6-inch 4H-SiC wafer with 92 data points.
• Generated false-color images visualizing the spatial distribution of resistivity along X, Y, and Z axes.
• Achieved automated analysis and mapping, streamlining the characterization workflow.

Conclusions:

• Micro-Raman spectroscopy, coupled with a calibrated multi-variable model, provides an effective non-contact method for resistivity mapping in 4H-SiC.
• The developed automated procedure enhances the efficiency and accuracy of semiconductor material characterization.
• This technique offers valuable insights into the bulk and surface resistivity variations critical for device performance.