Measuring film thickness

Determine film thickness of a few millimeters up to 10 nanometers non-destructively

Measuring coating thicknesses optically

Here the "right" coating thickness is important

The areas of application in which coating thicknesses and very thin coatings determine function or efficiency are numerous. In the manufacture of smart phones, technical or spectacle lenses, modern screens, car parts and paints, and hundreds of other products, layer thicknesses and thin coatings are of great importance.

But also in industries such as photovoltaics (thin film), medical technology, semiconductors, OLED and optics, self-supporting layers (e.g. films), single layers or multilayer systems play an important role.

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The right measuring method for each layer

Anti-reflective coatings (ARC), photoresist, hard coatings, transparent conductive oxides (TCO), tin-doped indium oxides (ITO), drug eluting films or even materials such as silicon that are not transparent in visible light can be reliably determined with different light sources, spot sizes and thickness measuring ranges thanks to the large selection of sensors.

Our experts use optical layer thickness sensors with interferometric and reflectometric methods, so that layer thicknesses of a few millimeters up to 10 nanometers can be determined non-destructively.

Thin Films

Ultra-thin transparent layers prevent scratches and minimize reflections. You all know such scratch-resistant coatings, whether on plastic surfaces or lenses. In addition to functional coatings, refinement layers as well as protective and insulating layers on microelectronics are becoming thinner and thinner, while the demands on quality and homogeneity are increasing. Layer thickness and thickness variation are often decisive for the functionality.

thin film thickness

Application example 1: Very thin films

As an option, a sensor can be used for the measurement of thin foils from 2 µm thickness upwards, which evaluates the interference of the light reflecting on the upper and lower side of the foil. A modified method also enables topography measurements for the characterization of the film surfaces. Both sensors can be combined in the MicroProf®. In addition, a reflectometer is used for the measurement of thin-film systems. With the FTR sensor, layer thicknesses from 10 nm can be determined with a resolution of 1 nm.

lens

Application example 2: Lens coatings

The determination of the thickness of optical coatings in the form of thin films, or even layer stacks, is also particularly relevant in modern measurement technology. Layer thicknesses down to a few nanometers are determined, with a resolution in the sub-nanometer range. Lens roughness can be determined down to the sub-nanometer range, and topography measurements of the sample surface can be performed. Further applications are defect inspection of lenses.

opaque copper layer

Application example 3: Determination of opaque layer via step height

The present layer system is located on a wafer and consists of an opaque silicon substrate, a transparent oxide layer on top and an opaque copper layer in a limited area on top. To determine the thickness of the copper layer, the topography sensor measures the thickness of the copper layer including the transparent oxide layer. Furthermore, the thickness of the transparent oxide layer is measured separately with a layer thickness sensor. By subtracting the oxide thickness from the previously determined total thickness, the desired step height of the copper layer is obtained.

Hybrid metrology

Due to the multi-sensor concept we pursue, it is possible to solve a measurement task with different sensors by carrying out one measurement for each sensor and combining the different results. We determine parameters with hybrid metrology that cannot be measured directly!

FTR sensor

The FTR thin-film sensor developed by FRT is based on spectrally resolved reflection measurement and a sophisticated evaluation software. The determination of the thickness of thin films with the FTR sensor is based on the superposition of partial waves that are reflected at the interfaces of the thin film.

The evaluation of this spectral interference pattern with FRT's own software provides the information about the thickness of the film with nanometer resolution. The results are recorded, evaluated and finally visualized. The FTR sensor also includes a comprehensive database with refractive and absorption index of a large number of semiconductors, oxides, glasses, metals, resists, etc., which can be easily supplemented by the user. For automated measurement (point measurement, line profile or 3D mapping) recipes can be compiled.

With the FTR sensor, high resolution, accuracy and repeatability in layer thickness determination are achieved.

Nanometers are so small that it is difficult to be aware of this "size". A nanometer to a meter is like the diameter of a 1-cent coin to that of the globe (Link: Hamburger Abendblatt)

Nowadays in most cases layer thicknesses in the lower nanometer range can be measured.

Layer thickness

3D-Visualization of Film Thickness

The devices of our MicroProf® series allow not only to perform punctual and profile film thickness measurements but furthermore features an innovative 3D-Mapping Mode that allows the homogeneity determination of the film thickness distribution on a larger sample area. Manufacturers of coated products such as solar cells, technical glas, blood glucose test strips, CD's and DVD's as well as semiconductor and MST products use 3D film thickness maps to quickly identify possible failure sources and new potentials for optimization in their coating processes.

Up to 100 million individual measuring points!

For the 3D visualisation, the coated surface is first scanned contact-free by means of a motorized x, y-table underneath the film thickness sensor. This process results in up to 100 million individual measuring points, which are automatically calculated with powerful hardware and software to a high-resolution 3D image of the entire coating. With a mouse click, information about the specific coating thickness at a given position can be retrieved, profiles can be recorded or the entire homogeneity of the coating can be evaluated.

Measuring film thickness with powerful technology

FRT offers the right surface measuring device for every layer: Whether laboratory, development, quality assurance or production - with the multi-sensor measuring devices from the MicroProf® series you can measure your coatings easily and contact-free. The determination of the film thickness can be combined with topography measurements and can also be fully automated.

Depending on your application, different sensors are used: For the determination of film thicknesses in the sub-micrometer range, from a few ten nanometers to several ten micrometers, as well as for the analysis of complex multilayer structures with high resolution, the FTR sensor was developed in-house. Depending on the requirements, the thin-film sensor is used in variants with different wavelength ranges, so that optimum measuring conditions are offered for different materials and film thickness. For small structures, the lateral resolution can be increased up to 5 µm.

The evaluation of the reflection spectra of the interferometric sensor is carried out by means of a powerful software developed with our film thickness experts: depending on the film thickness and layer system, both an evaluation by means of FFT (Fast Fourier Transformation) and a model-based fit based on the material data or a combination of both methods are used. This allows the analysis of very thin films in the nanometer range with high resolution and fast measurement results. An extensive database with refractive indices and absorption coefficients of a variety of materials such as glasses, semiconductors, oxides, plastics, etc. is included in the scope of delivery. In conjunction with our measuring systems, the FTR can be used to generate not only point measurements but also film thickness profiles and film thickness mappings with high lateral resolution. The sensor is also excellently suited for integration in inline control.

In addition, this sensor can also be used to analyze multi-layer systems with up to ten layers. Transparent substrates coated on both sides can also be modeled. It is also possible to characterize components in which the layer system is located between thicker materials, such as OLEDs that are encapsulated with glass on one side and have a metal electrode on the other.

If you have questions about an application, our experts will be happy to help you.

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