Spectroscopic Ellipsometry [& Beyond?]

Ellipsometry is a non-destructive model-based metrology technique used to measure the optical properties and thicknesses of single layer and multilayer thin films.

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Non-contact optical spectroscopic ellipsometry operates by directing light at a sample of interest. Change in the reflected polarization of the light is then modeled to infer physical parameters of interest.

Ellipsometry measures the change in reflectance as a function of the polarization states s and p, which can be used to determine the optical properties and thickness of various films. The data collected consists of Ψ (the tangent of the amplitude differences of Rs and Rp) and Δ (the phase shift of Rs and Rp.)

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Single wavelength ellipsometry

This technique uses a monochromatic light source of a given wavelength, typically 632.8nm, which allows for a smaller spot and higher intensity, but only collects Ψ and Δ for that specific wavelength, which limits measurement capability.

Spectroscopic ellipsometry

This technique utilizes a broad band light source, e.g., 220nm to 950nm, and can measure Ψ and Δ throughout the entire spectra, allowing for a greater measurement capability.

Single angle ellipsometry

This technique uses a set angle, typically close to the Brewster angle of the sample (~70° for Silicon) to collect measurements. This method is sufficient in most cases.

Variable angle spectroscopic ellipsometry

This technique takes measurements at various angles (typically 2 or 3) which can help with...?

Imaging ellipsometry

This technique combines ellipsometry and optical microscopy, allowing for images/maps of measured values like thickness.

[Add something about filmtek tools doing whichever they do?]

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Ellipsometry is not a type of reflectometry; they are distinct techniques.

Both spectroscopic reflectometry and spectroscopic ellipsometry  operate by directing light at a sample of interest. However, reflectometry measures an intensity ratio of reflected light, whereas ellipsometry measures polarization changes of the reflected/transmitted light.

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Both ellipsometry and reflectometry can measure the refractive index, However, the most accurate method utilizes multi-angle reflectometry with Bruker’s [exclusive?] Differential Power Spectral Density (DPSD) technology. This technique and technology allow Refractive Index resolution down to 2x10^-5.

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Ellipsometry is ideal for the measurement of very thin films. Reflectometry techniques are better suited to measure thicker films.

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Typical ellipsometry has limited data to use for modeling, which can often diminish measurement accuracy by result in multiple solutions.

FilmTek tools combine ellipsometry with mutli-angle reflectometry, [increasing the size of the dataset used for modeling to deliver unparalleled measurement accuracy?]. Using FilmTek tools, thin film thickness accuracy is possible down to the sub-Angstrom level, and Refractive Index can be measured accurately down to 2x10^-5.

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Ellipsometry measurements are conducted using an ellipsometer. The components and configuration of an ellipsometry system can vary.

The Filmtek product line of spectroscopic ellipsometry systems includes the 2000 PAR-SE, 3000 PAR-SE, 4000 PAR-SE, and 6000 PAR-SE, each of which feature both ellipsometry and reflectometry capabilities. The 2000M and 2000M TSV feature microscopy and reflectometry.

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FilmTek’s product line typically uses a light source for both 0° and 70° incident angles. The 0° light travels down to the sample, reflects off the sample and then back up to a detector. The 70° light travels through a polarizer and a compensator before arriving at the sample, and the reflectance off the sample travels through a compensator and into a detector. This signal is used for both ellipsometry and reflectometry.

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Due to the incident angle of ellipsometry and the focus point of the beam, thicker films can be difficult to measure due to incoherence and refraction. Transparent substrates can also result in backside reflectance and/or in birefringence.

The additional reflectometry component allows FilmTek products to overcome a lot of these limitations.

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Any type of solid/semi-solid sample can be used with FilmTek tools, and the thickness ranges will change by sample due to differences in optical properties of various materials (i.e. pure metals like copper will become opaque at smaller thicknesses than materials like SiO2.)

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Yes.

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Yes.

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Yes.

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FilmTek tools can measure Refractive Index and Extinction Coefficient, film thicknesses for single layer or multilayer stacks, roughness, and crystallinity.

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Optical properties and thickness measurements of films like Si3N4, Photoresist, Poly Silicon, Al2O3, etc.

FilmTek tools can be found in a wide variety of industries, from medical devices to sensors to front end and backend semiconductor manufacturing. The tools are used in both R&D and in line production environments.
 

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For semiconductor fabrication, the Filmtek tools are generally used to measure optical properties and film thicknesses of single layers and multilayer stacks, especially for films like Si3N4 where the Refractive Index can vary greatly at different process tools and even across wafers. FilmTek products are found in both R&D and in line production environments.
 

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Medical devices typically use FilmTek tools for thicker films, phase change materials, and to measure optical properties.

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No setup required. The sample is either handloaded or loaded via robot, and the data is collected based on the recipe selected by the user.

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No preparation required. Sample can be measured as is.

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An NIR light source might be required for thicker films (>150um.)

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As film thickness increases, less reflectance will come from the layer or substrate below the film due to refraction and/or absorption. Film thickness is often measured as oscillations within the reflectance signal, and thicker films will have higher frequency oscillations.

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For very thin films, there is often little difference in the reflectance spectra as thickness changes, so measuring the change in polarization states via ellipsometry will provide a larger change in data, allowing for accurate measurements of thin films.

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After data is collected, a model can be created using each layer on the film stack down to the substrate (if a layer in the stack is opaque, that can be assumed to be the substrate in the model.) The optical properties of each layer can be varied. The model data can then be fit to the measurement data, adjusting the thickness and optical properties of each layer, as set by the user. Once the model is complete, it can be saved as a recipe and used automatically.

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The primary source of error in ellipsometry and reflectometry is an incorrect model, either utilizing an incorrect thickness range or using the wrong material and/or optical properties.

How do you identify common mistakes in ellipsometry data?

A poor fitting of simulated spectra to measured spectra typically results from a mistake in modeling.

How do you correct them?

By floating optical properties or adjusting thickness ranges, a poor model can be corrected to yield good results.

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Collecting ellipsometric data with FilmTek SE-model instruments is simple, efficient, and intuitive. Equipped with our proprietary FilmTek software and optimization algorithms and capable of complete automation, these systems minimize the operational downtime and high potential for human-caused error that are inherent to manual measurement calibration, data acquisition, and data analysis processes and, unlike comparable ellipsometers, requires no manual sample alignment.

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FilmTek 6000 PAR-SE is ideal for use in front-end semiconductor manufacturing applications.

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FilmTek 2000M TSV is ideal for use in advanced packaging applications.

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Both FilmTek 4000 Robotic and FilmTek 4000 Benchtop are optimized for use in silicon photonics applications.

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FilmTek 2000 PAR-SE is ideal for collecting production measurements of thin films and multi-layers on patterned device wafers for front- and back-end manufacturing..

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FilmTek 2000M is ideal for use in medical sensor and device development.

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FilmTek 2000 PAR-SE is ideal for use in the development and production of MEMs devices.

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FilmTek 2000, equipped with optional transmission spectrophotometry capabilties, is ideal for use determining the thickness and optical constants of thin absorbing films on transparent substrates.

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FilmTek 2000 PAR-SE is ideal for use characterizing new materials with a wide range of rapid, accurate, and reliable R&D measurement capabilities.

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FilmTek 2000 PAR-SE is ideal for independently and unambiguously determining film thickness, refractive index, and extinction coefficient for unknown and complex materials.

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