Angstrom Sun Technologies Inc. specializes in the design and manufacturing of a range of optical tools specifically tailored for characterizing film thickness and optical properties such as refractive index (N) and extinction coefficient (K). Our product lineup includes affordable, low-cost yet advanced and high-performance tools, including spectroscopic reflectometers, microspectrophotometers, and ellipsometers. These tools provide a precise and nondestructive means of probing film stacks. To explore the configurations and specifications of our products, please select the desired items from the list in the left panel. For technical details, we encourage you to refer to the publications and Q&A section available in the Support area. Should you have any inquiries or require quotations, we warmly invite you to reach out to us directly or contact our sales representatives and international distributors.
Difference between reflectometry and ellipsometry
Ellipsometry: Ellipsometry measures changes in the polarization state of light upon reflection from a sample. It provides information about the complex optical properties of materials, including refractive index (N) and extinction coefficient (K). Ellipsometers typically operate by measuring the change in polarization state (ellipticity and angle of polarization) of the reflected light, which is sensitive to the thin film properties. By analyzing the measured data with mathematical models, ellipsometry can determine various parameters such as film thickness, surface roughness, and composition. Ellipsometry is highly precise and can be used for both transparent and opaque films. It is commonly employed in research, development, and quality control applications in fields like semiconductors, optics, thin-film coatings, and material science.
Reflectometry: Reflectometry, on the other hand, focuses on measuring the intensity of reflected light from a sample. It is primarily used to determine film thickness and multi-layer structures. Reflectometers work by analyzing the intensity of light reflected at different wavelengths or angles, providing information about the film thickness or the thickness of each layer in a multi-layer stack. Reflectometry is often simpler and more cost-effective compared to ellipsometry, making it suitable for applications where precise optical property characterization is not required. Reflectometers are commonly used in the field of thin film coatings, surface analysis, and quality control.
- Information obtained: Ellipsometry provides complex optical properties (N and K) in addition to film thickness, while reflectometry primarily focuses on film thickness measurements.
- Measurement principle: Ellipsometry measures changes in the polarization state of light, whereas reflectometry analyzes the intensity of reflected light.
- Precision: Ellipsometry is generally more precise and sensitive, allowing for detailed characterization of thin films, including transparent and opaque layers. Reflectometry provides simpler thickness measurements with relatively lower precision.
- Applications: Ellipsometry is widely used in research and development settings where precise optical property analysis is required. Reflectometry is often employed in industrial applications for rapid and cost-effective thickness measurements.
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)