Part of the Oxford Instruments Group

alpha300 Semiconductor Edition

Large-area wafer inspection for the semiconductor industry

The alpha300 Semiconductor Edition is a high-end confocal Raman microscope specifically configured for the chemical imaging of semiconducting materials. It helps researchers accelerate the characterization of crystal quality, strain and doping in their semiconductor samples and wafers.

The microscope’s extended-range scanning stage enables the inspection of up to 12 inch (300 mm) wafers and the acquisition of large-area Raman images. It is equipped with active vibration damping and active focus stabilization to compensate for topographic variation during measurements over large areas or long acquisition times. All microscope components are fully automated, permitting remote-control and the implementation of standard measurement procedures.

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Key features

  • Industry-leading confocal Raman microscope for high speed, sensitivity and resolution – simultaneously
  • Scientific-grade, wavelength-optimized spectrometer for high signal sensitivity and spectral resolution
  • Large-area scanning (300 x 350 mm) for wafer inspection
  • Active focus stabilization for large-area measurements (TrueSurface)
  • Active vibration damping
  • Extensive automation for remote-control and recurring measurement workflows
  • Software for advanced data post-processing
Raman image of defects in graphene
High-resolution Raman image of CVD-grown graphene, color coded according to the D-band intensity, which depends on the defect density in the carbon lattice.

Large-area wafer inspection

Monitoring the quality of wafers is critically important for the semiconductor industry. In order to establish the homogeneity of the material and reveal areas of strain or inhomogeneous doping, the entire area of a wafer must be investigated.

In this example, the complete surface of a 150 mm (6 inch) silicon carbide (SiC) wafer was imaged with Raman microscopy using a 532 nm laser for excitation. The analysis showed that the doping concentration was not homogeneous over the full area. The microscope‘s highly sensitive UHTS 600 spectrometer was able to detect peak shifts below 0.01 cm-1 and could thus reveal stress fields within the wafer.

To obtain a sharp Raman image of the entire wafer, actively keeping the surface in focus was crucial. TrueSurface recorded the wafer’s topography simultaneously with the Raman data and compensated for height variations.

Additionally, a depth scan through an epitaxially overgrown SiC wafer was recorded to visualize the distribution of the different layers.

Sample courtesy of the Fraunhofer Institute for Integrated Systems and Device Technology IISB, Erlangen, Germany.

Raman image of entire 6 inch SiC wafer
Confocal Raman image of a 150 mm SiC wafer. TrueComponent Analysis identified two spectra, which mainly differed in the doping-sensitive A1 peak (ca. 990 cm-1). The image reveals an oval region (blue) with a different doping concentration than the bulk wafer area (red).
Raman spectra identified in the 150 mm SiC wafer
Raman spectra of the two components identified in the 150 mm SiC wafer by TrueComponent Analysis.
Raman depth scan of an epitaxially overgrown SiC wafer
Raman depth scan of an epitaxially overgrown SiC wafer, showing a thin interface layer (blue) between the wafer substrate (green) and epitaxial layer (red).
Raman image of entire 6 inch SiC wafer
Confocal Raman image of a 150 mm SiC wafer, color coded for the position of the stress-sensitive E2 peak (776 cm-1). The image reveals a small, presumably stress-induced peak shift from the wafer’s center toward its edge.
Topography of 6 inch SiC wafer
Topography of a 150 mm SiC wafer with height variations of up to 40 µm.


  • Research-grade alpha300 Raman microscope
  • White-light illumination for sample overview
  • 300 x 350 mm scanning stage
  • Wafer chuck, optionally with vacuum pump
  • TrueSurface for active focus stabilization and topographic Raman imaging
  • Active vibration damping
  • Fully automated microscope control with AutoBeam Technology
  • Various laser wavelengths available
  • Highly sensitive, on-axis, lens-based, excitation wavelength-optimized UHTS spectrometer featuring thermoelectrically-cooled, scientific-grade spectroscopic CCD camera
  • Data acquisition and post-processing with latest WITec Software Suite
  • Workflow manager for streamlining recurring experimental tasks
  • DCOM interface for design and control of individual measurement procedures with LabVIEW, Python, C# and others programming tools
alpha300 Semiconductor Edition – Confocal Raman imaging microscope for wafer inspection
alpha300 Semiconductor Edition – Confocal Raman imaging microscope for wafer inspection

Benefits of Raman imaging in semiconductor research

Confocal Raman imaging is a powerful tool for research and quality control in the semiconductor industry, as it can nondestructively acquire detailed, spatially-resolved chemical information about conventional materials such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN) and gallium arsenide (GaAs) as well as novel 2D materials such as graphene, perovskite, molybdenum disulfide (MoS2), tungsten diselenide (WSe2) and other transition metal dichalcogenides (TMDs) and heterostructures. Raman images visualize the spatial distributions of different materials, as well as material properties such crystallinity, strain, stress or doping. Depth scans can be used to investigate material distribution on substrates and characterize interface layers, and 3D Raman images can be generated to depict inclusions in a sample.

Topographic Raman imaging

Topographic Raman image of micro-structured silicon
Topographic Raman image of micro-structured silicon (blue) with fluorescent impurities (pink). Chemical and profilometric information were recorded simultaneously by TrueSurface technology and overlaid. The maximum height variation was 9 µm.

2D materials analysis

Bright-field image of WSe2
Raman image of WSe2
Photoluminescence image of WSe2
Characterization of a WSe2 flake. A: bright-field image. B: high-resolution Raman image (102,400 spectra acquired in about 17 minutes), distinguishing single-layer (red), bi-layer (green), and multi-layer (blue) areas. C: photoluminescence image with visible grain boundary (white arrow).
Raman spectrum of MoS2
Representative Raman spectrum of CVD-grown mono-layer MoS2 on a Si/SiO2 substrate.
Raman image of MoS2
Raman image of mono-layer MoS2 color coded for shifts of the Raman E2g band, visualizing areas of strain and doping.


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Related Applications

Materials ScienceNano-Carbon & 2D MaterialsSemiconductors & Photovoltaics