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              Angstrom Sun Technologies Inc. designs and manufactures a series of cost-effective optical solutions for characterizing film thickness and optical properties (refractive index N and extinction coefficient K). Affordable, low cost, but advanced and high performance tools, including spectroscopic reflectometer, microspectrophotometer and ellipsometers, offer a way to  probe film stacks nondestructively and precisely. Please select products listed in left panel to review product's configurations and specifications. For technical aspects, please review publications and Q&A in Support section. You are also welcome to directly contact us or our sales representatives for questions and quotations.

Ellipsometer, Reflectometer and Microspectrophotometer

Difference between reflectometer and ellipsometer

        There are many techniques for characterizing materials, each having its own advantages and disadvantages and each being uniquely able to reveal material properties that other techniques can't access. Spectroscopic ellipsometry (SE) and spectroscopic reflectometry (SR) are optical techniques that are particularly flexible in that they can be used to determine the optical and physical properties of a wide variety of thin-film materials such as silicon oxide, nitride, silicon, even metal films. Their ability to do this without contact or damage to the material of interest has seen it become routinely used in R&D laboratories and within manufacturing facilities for monitoring thin film growth and deposition processes.

         In general, reflectometer is used to acquire reflection spectrum over a wavelength range. If there is film or coating on some kind of substrate, the film or coating thickness can also be figured out from the measured  reflection  spectrum. Ellipsometry measurement is performed at non normal incident angles. The two ellipsometry parameters, Psi and Del, give more information than reflectance itself. Therefore, more information can be accessible through ellipsometry technique, such as multiple layer analysis, dielectric constants calculation, surface or interface roughness, inhomogeneity behavior etc. Of course, those information is always derived from an optical model, which leads to some difficulties  to use this technique although it is much more powerful than reflectometry technique.

       Angstrom Sun Technologies Inc manufactures both ellipsometer and reflectometer tools. Besides ellipsometer and reflectometer hardware systems, the advanced analysis software is essential to extract the desired information as above-mentioned, such as thickness, roughness, alloy concentration and dielectric constants. TFProbe 3.0 and TFProbe 2.0 software from us offer powerful analysis functions for ellipsometry and photometry with simulation and data regression. Unique but configurable mode allows different users to access different level and suitable for both R&D and production quality control purpose.

Thickness Measurement Tools

        For thickness measurement, both techniques rely on modeling. In general, ellipsometry gives better accuracy than reflectometry in thin thickness range such as below micron level. For a typical ellipsometer configuration, the maximum thickness measurable is below 10 microns. However, reflectometer can measure up to hundreds microns of non absorbing thick coatings.

Measurable Thickness range for Thin Films or Thick Coatings in general

       These optical methods need to have light to penetrate through film and reflect back from film/substrate interface. Without meeting such condition, the film thickness can not be figured out because of lacking necessary phase information. One example is a sample with thick metal films on it. Because metal has high absorption in visible and Near infrared range, light only can penetrate metal film with a depth of less than 1000 Angstroms. For such film with a thickness above 1000 Angstroms, it is impossible to measure its thickness by reflectometry or ellipsometry although reflection spectrum can be obtained with reflectometer and optical properties for metal film can be obtained with ellipsometry. Roughly, the measurable thickness for various films can be estimated from penetration depth if knowing its extinction coefficient or absorption coefficients.

Some application examples with spectroscopic ellipsometer or reflectometer measurements

  • Optical constants (refractive index n and extinction coefficient k) for thin films, coatings and bulk substrate

  • Dielectric constants  (real part and imaginary part) for thin films, coatings or bulk materials

  • Accurate nondestructive thickness determination for multiple layer thin films or coatings

  • Alloy concentration determination for various thin films such as Ge in SiGe alloy, Al in AlGaN films

  • Band gap determination for GaN, SiC, AlN, AlGaN, etc.

  • Porosity measurement in low-K films from modeling with EMA model (effective media approximation)

  • Simultaneously determining composite film thickness and Second or third components volume fraction like Nano Au particles embedded in Y2O3 matrix

  • Physical thickness and optical properties for each layer in a multiple layer stack or periodic structure such as quantum well structure

  • Thickness and optical properties uniformity information through mapping site by site with advanced mapping profile setup

  • Inhomogeneous film analysis in physical density or alloy concentration

  • Optical properties for high-k films

  • Nondestructive measurement for electrical conductivity of metal films, metallic compounds (such as WN, TiN, TaN, etc.), doped semiconductor epi layers (thickness can be also determined at the same time), other compound oxides such as ITO films

  • Nondestructive measurement for doping concentration in doped semiconductors (active dopant! not total concentration as given by destructive SIMS analysis)

Microspectrophotometry (Micro-Photometry, Micro Spectrophotometry) is used to characterize optical properties of thin films, thick coatings over a micron region area, which is typically found useful in patterned device or tiny medical device fabrications such as measuring silicone lubricant thickness on needles etc. Microspectrophotometer is also called microreflectometer, micro-reflectometer, microspectrometer, microphotometer (Spectroscopic), microspectroscopic photometer etc. With unique design by Angstrom's professionals, user can enjoy digital imaging capability in Microspectrophotometers (MSP series) by live video, powerful digital editing, measurement tools for reflection, transmission, absorption spectra measurement. Data acquisition only takes milliseconds. TFProbe software allows user to set up heating stage or cooling stage for kinetic study in real time for optical property changes such as reflectance, transmittance, coating thickness, refractive index (optical constants) etc. Automatic mapping function is also available in various Microspectrophotometer models with motorized X-Y stage or Rho-Theta Stage and also motorized focus function using Joystick. Wavelength range usually is an important factor for user to consider. Angstrom's microspectrophotometer covers from deep-ultraviolet (DUV) to near-infrared (NIR) ranges. Which range should be considered will depend on several factors such as what are thickness ranges for thin film or thick coating, what is typical wavelength range of interest for reflectance or transmittance and so on.

Based on ellipsometry, reflectometry and microspectrophotometry, Angstrom Sun Technologies builds various tools from simple, low cost film thickness measurement station, to advanced automatic variable angle spectroscopic ellipsometer combined with digital imaging microspectrophotometer products. In addition, low cost, desktop style film thickness mapping system (spectroscopic reflectometer mapping system SRM) is also available for various sample sizes. Integrated in-line solutions for film thickness /coating thickness monitoring module provide fast and easy integration even with advanced Zone-rage model for interpreting specific film properties on patterned production wafers. Probing beam size ranges from focused micron area to large spot with 20mm in diameter.