A blanket layer of silicon can be added to a silicon substrate by a CVD process to achieve changes in the properties, like resistivity, type and defect density. This CVD process is called epi (or epitaxial) deposition. The thickness monitoring of the epi layer is part of the production process of making the epi wafers. This monitoring is executed on a sample basis, or only to confirm that the epi reactor is set up properly.


Semilab can offer non-contact optical solution for Epi thickness monitoring, depending on infrared reflection techniques.

Figure 1. Epi deposition




Semilab FTIR-based reflection techniques are both capable to apply the interferogram subtraction method and also the model-based approach by the advanced and versatile SEA analysis software. The model-based method not only takes into account the thickness of the layer, but the determination of the refractive index is also possible with it.

Figure 2. FTIR-based reflection technique


Figure 3. Optical path


The measurement of the sample in reflection mode is realized in the IR wavelength range.

Interference fringes are observed in the reflectivity spectrum.

Angle of incidence: 36°

The stable detector operates at room temperature (no need for maintenance, low cost of ownership).

The evaluation is performed either by direct inversion method (for thick epi layers), or by optical modeling (for thin < 2 µm epi or for complex stacks)

Figure 4. Si epi layer on Si wafer, IR reflectometry mode 

Figure 5. Measurement examples

For 100 nm epi thickness, the profile changes from being thinner in the center of the wafer to have more of a doughnut shape.



  • Non-contact and non-destructive optical measurements
  • Applicable for single- and multilayer structures - thickness measurement of each individual layer
  • Applicable materials: Si, SiC, SOI, SiGe, III - V
  • Optional measuring method: direct or optical modeling


Product Line


The system has a strong modular and versatile design to meet the needs of a high reliability, high throughput epi thickness measurement.
State-of-the-art automation
Fast mapping stage
Joystick for easy sample movement control (for manual measurement point setting)



The EIR-2500 is a unique automated epi thickness measurement tool with infared spectroscopic reflectometer for high throughput epi thickness measurement. Fully compliant to the relevant SEMI / CE standards. The EIR product line is based on smart, reliable electronics, which improves tool uptime and decreases maintenance needs.

Features and System specifications:

  • Wafer size: up to 300 mm
  • Loadport: Single or dual casette loadport
  • Fast mapping stage
  • Capable of handling the IR reflectance measurement head (for epi thickness)
  • Capable of handling additional measurement heads (for example Spectroscopic Ellipsometer, 4PP)
  • Measurement modes:
    • Interferogram mode:
      • Measures interferograms, which are analyzed using direct inversion method.
      • For fast measurements of thick epi layers and simple film stacks.
    • Reflectance mode:
      • Measures reflectance. Interference fringes are observed in the reflectance spectra, which are analyzed using optical modeling of the filmstack.
      • For thin (< 2 μm) epi, or for complex stacks with multi-layers or gradient profiles.

Software Highlights:

  • Semilab Automation Manager (SAM) to fully control the measurement cycle
  • Recipe-based operation, based on SEMI recommendations
  • Compliant with SECS/GEM, SECSII/GEM and CIM host communication standards (CMS, E87, STS and so on)
  • Smart evaluation of measurement interferograms:
    • Interferogram substraction as standard analysis method
    • Complex optical model for better precision in case of thin layers by reflection spectrum modeling
    • Cepstrum method

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