Overview

       Angstrom Sun Technologies Inc. designs and manufactures a series of optical tools 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 and international distributors for questions and quotations.

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.x and TFProbe 2.x 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 reflectometry and ellipsometery 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 30 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, 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. Theoretically, 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)