Spectroscopic Reflectometer and Film Thickness Measurement Tools

Spectroscopic Reflectometer SR100

Spectroscopic reflectometer (SR) series are relative low cost and easy to use tools. By measuring reflection spectra (at normal incidence in most cases), film properties can be modeled with capable TFProbe software. If quick, routine, daily measurements on known films or simple film stack are needed in a low budget case, then SR series are a good choice. Wavelength range coverage is highly application oriented. If spectra are only of interest, like monitoring antireflection (AR) or high reflection devices' performance, then wavelength range will be most important factor in selecting tools. For example, in telecommunication application, all bands (O bands: 1260-1360nm; E band in 1360-1460nm; S band in 1460-1530nm, C band in 1530 -1560nm, L band 1565-1625nm, U band in 1625 -1675nm) are in near infrared wavelength range. To evaluate components’ performance, like antireflection coating's behavior in laser cavity, it is necessary to have such wavelength range covered. In photovoltaic area, many newly developed function films/coating are absorbing in visible range, like Copper indium gallium (di)selenide (CIGS), it is only possible to measure their thickness in transparent wavelength range which is also in the NIR range. If user needs to determine films' thickness, the optical resolution of spectrometer will also be a factor to consider. We have broad configurations available and system can be customized to meet your specific applications.

TFProbe series spectroscopic reflectometer tools have many unique features, like long working distance, adjustable working distance, large stage size, selectable light source and adjustable light source intensity, etc. Various easy add-on features are also available, like transmission, curved surface measurement adaptor, multiple channel, large or small beam setups, and so on.

Although there are several brands of spectrometer and spectrophotometers available in market, Angstrom Sun Technologies Inc delivers our Spectroscopic reflectometer tools with advanced support. Since we also make advanced spectroscopic ellipsometer systems, we provide advanced modeling support with our advanced ellipsometer tools at no cost to our customers who need assistance when using reflectometer tools. There have been many cases that customers upgrade reflectometer to ellipsometer by trading in basic model tools to meet their advanced application needs.

We have developed several versions of software for spectroscopic reflectometers. TFProbe 2.4 works under both Windows 32-Bit and 64-bit OS window systems. A more advanced version TFProbe 3.3 has also TFProbe 2.4 module integrated into it. As such, we have a complete solution for user to consider based on window's OS, advanced functionality and how simple user interface, like scientific mode or simple operator mode.

Reflectometry Principle:

RSample = ISample / Io     

RReference = IReference / Io

RSample = RReferenceISample / IReference

With reflectometry, a reference or standard (known its reflection) must be used to calibrate light intensity Io. By acquiring signal (IReference) from this reference and known reflection (RReference), Light intensity Io under the same measurement condition can be obtained. By getting signal from sample, RSample is finally obtained. If the film thickness or its optical constants are needed, then a mathematic fitting algorithm is applied to obtain them via an assumed model (Layer Stack).

A 6 around 1 reflection probe is typically used in setup. 6 fibers deliver light beam on to sample and one reading fiber guides reflected signal to detector. With such configuration, reflectometer can be conveniently implemented in an in-situ or in-line applications.

  • Easy to set up
  • Easy to operate with Window based software
  • Advanced optics design for best system performance
  • Array based detector system to ensure fast measurement
  • Uniquely designed light source for better intensity stability
  • There are four ways to adjust light intensity:
    • Power output adjustment by knob from power supply
    • Insert a filter into filter slot at light output exit port
    • Beam size adjustment
    • Integration time adjustment in Detector from TFProbe software
  • Measure film thickness and Refractive Index up to 5 layers
  • Allow to acquire reflection, transmission and absorption spectra in milliseconds
  • Capable to be used for real time or in-line thickness, refractive index monitoring
  • System comes with comprehensive optical constants database and library
  • Advanced TFProbe Software allows user to use either NK table, dispersion or effective media approximation (EMA) for each individual film.
  • Upgradeable to MSP (Microspectrophotometer) system, SRM Mapping system, Multiple channel system, Large Spot for · direct measurement over patterned or featured structure
  • Apply to many different types of substrates with different thickness
  • Various accessories available for special configurations such as running measurement over the curve surface
  • 2D and 3D output graphics and user-friendly data management interface
System Configuration:








Detector Type

CCD or CMOS Array

CCD or CMOS Array

InGaAs Array

CCD or CMOS and InGaAs Array

CCD or CMOS and InGaAs Array

InGaAs Array

Wavelength Range (nm)

190 to 1100

370 to 1100




1000 – 2500

Wavelength Resolution

0.01 -3nm

0.01 -3nm

3 to 6nm

0.01 to 3nm

0.01 to 3nm

3 to 6nm

Measurable Thickness Range

5nm to 50 µm

20nm to 1000 µm

100nm to 300 µm

20nm to 200 µm

5nm to 200 µm

20nm to 300µm

Thickness Precision

< 1Å (1 sigma from 50 thickness readings for 1500Å Thermal SiO2 on Si Wafer)

Thickness Accuracy

better than 0.5% (comparing with ellipsometry results for Thermal Oxide sample by using the same optical constants)

Reflection Probe







Stage/Sample Holder

Black Anodized Aluminum Alloy with Easy Adjustment for sample height, 200mmx200mm size

Working Distance

~ 25mm (from Sample Surface)

Measurement Time

0.1 milliseconds to 10s, user definable

User Definable

Wavelength range, wavelength points, integration time, spectra average numbers, smooth factors


TFProbe 2.4 or TFProbe 3.3



Operating System

Both 32bit and 64 Bit, Win XP, 7, 8, 10

Computer Requirement

P3 above with minimum 150 MB space, 2GB RAM; CD-ROM; at least 2 USB ports

Power Input

World-wide, universal 110– 240 VAC /50-60Hz, 1.5 A

Light Source

Deuterium       + Tungsten Halogen

Tungsten Halogen

Tungsten Halogen

Tungsten Halogen

Deuterium + Tungsten Halogen

Tungsten Halogen

Light Source Intensity







Lifetime of Lamp(s)

4000 hrs.

10000 hrs.

10000 hrs.

10000 hrs.

4000 hrs.

10000 hrs.

 Note: system will be configured within above specified wavelength ranges per quote to meet specific applications.


Example Setups (SR300)                                                  Example Setups (SR500 with Dual Detectors):

  • Transmission Fixture for Transmission and Absorption Measurement (SRxxx-RT)


  • Micro spot for measuring small area down to 5 µm size (MSPxxx)


  • Large Spot


  • In-Situ Integration and Processing Monitoring


  • Multiple Channel for simultaneously measurement at multiple locations (SRxxx-X)

  • Mapping uniformity over 200- or 300-mm wafer (SRMxxx-200 /300)


  • Simple, low cost measurement stage is available (SRxxx-S)

  • Fixture to measure curved surfaces


  • Semiconductor fabrication (PR, Oxide, Nitride..)
  • Liquid crystal display (ITO, PR, Cell gap…..)
  • Forensics, Biological films and materials
  • Inks, Mineralogy, Pigments, Toners
  • Pharmaceuticals, Medical Devices
  • Optical coatings, TiO2, SiO2, Ta2O5…..
  • Semiconductor compounds
  • Functional films in MEMS/MOEMS
  • Amorphous, nano and crystalline Si
  • Solar Cell Films
Interface Example:

TFProbe 2.4 Interfaces:

  1. More than 300 NK Tables


  1. User Definable Measurement Parameters

  1.  Up to 5 Layers with NK table. Dispersion or Effective Media Mixture Model

  1. Advanced Levenberg-Marquardt Fitting with Search and scale Functions

  1. Fast Fourier Transfer (FFT) Method for thick films

TFProbe 3.3 Interfaces:

  • Work with Window based operating systems
  • User friendly and easy to use interface
  • Integrated all-in-one functions for Simulation, Hardware Configuration and Calibration, Data Acquisition, Regression and Graphics Presentation
  • Simulation on photometry and ellipsometry on spectroscopic, Variable Angle or combined parameters
  • Comprehensive Optical Constants database, over 300 sets of optical constants for various materials included
  • Unlimited layers in layer stack can be set up

  • Each Layer or film can be defined from NK table (Library database), dispersion, interface, surface roughness or composite mixture model (EMA, effective media approximation)
  • Capable to define inhomogeneous layer with linear, exponential, Gaussian etc profile
  • Various dispersion model available such as Cauchy, Sellmeier, Gaussian, Tauc-Lorentz, Drude IR, Exponential, model dielectric functions etc, plus user can add unlimited absorption bands into dispersion

  • Support Anisotropic layers with dispersion definition
  • EMA Model can be defined with 2 or 3 materials mixture with Bruggeman or Maxwell-Garnett, both component’s volume fraction and depolarization factors can be set as variable
  • Advanced regression control on single set or multiple sets data, incident angle, angle deviation, fitting range modification, backside reflection factors, weighted consideration on either ellipsometry parameters with Marquardt-Levenberg or Simplex algorithms
  • 2D and 3D graphic presentation

  • User level control with password protected levels
  • Support both CCD-based array or Scanning monochromator detecting system
  • Flexible recipe setup interface from simple measurement to one-click to results full recipe
  • Support and communicate with various type of CCD based array detector systems
  • Allow to acquire ellipsometry, reflection and transmission data if licensed
  • Allow for time series with fixed time step or continuous measurement which is suitable for real time monitoring and inline metrology applications
  • Advanced optical constants editor and mapping profile setup
  • Operating systems:  Win XP, Win Vista or Win 7(32Bit), Win 8(64bit), Win 10(64bit)
  • Functions: Simulation, Hardware Configuration and Calibration, Data Acquisition, and Regression
  • Application: Photometry and Ellipsometry
Application Examples:

Measured Reflection Spectra for optical Antireflection (AR) Coatings

Measured thicknesses for three layers Nitride-Oxide-Nitride on Glass

Measured Thickness for thick coating

Measured Reflection Spectrum and Thickness for Nano-crystalline Si




  • System configuration and Specifications subject to change without notice
  • Measurable thickness range and number of layers are Film property, surface quality and layer stack dependent
  • Customized system available for special applications
  • TFProbe is registered trademark of Angstrom Sun Technologies Inc.
  • Special configurations are available