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Robust Measurement of Nano-structures in Milli-seconds!

InFoScat is an acronym for “Industrial Fourier Scatterometry", which is a Eurostars project (E8875) started in 2014. The partners for this project are Image Metrology A/S (Denmark), Danish National Metrology Institute - DFM A/S (Denmark) and ELDIM S.A. (France). The aim of the project is to create a fast tool for measuring critical dimensions of repeated micro and nanostructures and light emissive displays that is well suited for inline quality control in industrial production environment.  

Fourier scatterometer on robotic armFourier scatterometer on robotic arm

The project consists of a hardware and software part:

ELDIM is taking care of the hardware by developing a new unique Fourier lens optical system that will unlock the potential of scattered light characterization in production environment to give direct feedback to manufacturing processes like injection molding.

DFM is responsible for the development of software algorithms that can calculate the geometry of nanostructure based on the scattered light analysis.

Image Metrology is implementing the algorithms in a user-friendly software package. The software will be bundled to the Fourier lens system developed by ELDIM, but will also work together with existing spectroscopic scatterometry and spectroscopic ellipsometry systems.

 

 The InFoScat software is now available for beta testers who has applicable scatterometry or ellipsometry systems.

Main Features:

  • Measuring capabilities at nano-scale.

  • Fast and precise

  • Robust to sample vibrations.

  • Provides quality control and assurance capabilities. 

  • Can be used as a nano-structure design tool for meeting optical criteria
  • Applicable in industries for emissive devices (flat panels), semiconductors, structured colored plastic, self-cleaning surfaces, solar cells etc.

  • Patented technology - US patent 7,321,433 (2008).

  • The technique has been validated and compared with AFM Measurements

 InFoScat supports various optical characterization techniques:

 

Measuring Capabilities for various techniques

Scatterometry Measuring CapabilitiesScatterometry Measuring Capabilities

InFoScat supports the following measurements:

In current beta-version:

Thin film: Thickness.

1D Line structures: (known pitch and straight sidewalls)

Height, width, sidewall angles.

In development:

1D Line structures: (unknown pitch)

Pitch, Height, width and sidewall angles / complex sidewall form.

2D Structures:

Pitch, Height, width/length/radius, sidewall angles / complex sidewall form. 

Working Principle

InFoScat is governed by the principle of scatterometry. A periodic structure diffracts light into diffraction orders. Scatterometry is a characterization technique where the intensities of diffraction spots are used as a ‘fingerprint’ to describe the surface. One can also measure the wavelength dependent diffraction efficiencies. For the analysis an inverse modelling approach is used, where computer simulated model database is compared to the experimental data.

Scatterometry analysis consists of following steps as described in the figure below.

(A) A sample with unknown dimension to be characterized is placed in a combined microscope, and scatterometer.

(B) The reflected light is analyzed by a spectroscopic scatterometer.

(C) Simulation database generation - computer simulations of the diffraction efficiencies are stored in a database. Using a database approach makes the inverse modelling extremely fast. 

(D) Database comparison - the measured diffraction efficiencies are compared with the simulated data and the best match gives the dimensions of the structures of the sample.

 

InFoScat WorkflowInFoScat Workflow

 

 

 

Simulation Database Generation 

The InFoScat software uses stable algorithms based on rigorous coupled-wave analysis (RCWA) for solving Maxwell’s relations. The user has to specify possible ranges of representative geometric parameters, such as height, width and sidewall angle, to describe a given pattern. With RCWA a structure is divided into slabs and the electromagnetic fields at each boundary is matched.

 

Screen dump of the InFoScat software interface for generating the simulation database. Here a grating is described with possible ranges for height, width and slope angles. The applied optical technique is Spectroscopic Ellipsometry.Screen dump of the InFoScat software interface for generating the simulation database. Here a grating is described with possible ranges for height, width and slope angles. The applied optical technique is Spectroscopic Ellipsometry.

 

 

Deducing the Geometrical Dimensions

Using a pre-generated simulation database it is extremely fast (typically only a few milliseconds) to find the simulation fitting the measured spectrum best and thereby deduce the geometrical dimensions together with confidence intervals.  

 

Screen dump of the InFoScat software interface for simulation database comparison results. Here the result shows the estimated height, width and slope angles for every sample, along with 95% confidence interval ranges and statistics of measurements. The samples are measured using Spectroscopic Scatterometry optical technique.Screen dump of the InFoScat software interface for simulation database comparison results. Here the result shows the estimated height, width and slope angles for every sample, along with 95% confidence interval ranges and statistics of measurements. The samples are measured using Spectroscopic Scatterometry optical technique.

 

 

Optical Techniques

The InFoScat software will support several optical characterization techniques, which can be classified as:

 Illustrating optical techniques. Illustrating optical techniques.

 
Techniques Description Pros Cons

Spectroscopic Scatterometry (A)   

 

 

Normal incident spectroscopic scatterometry. 

The wavelength dependent diffraction 

efficiencies are measured for the

specular reflection.

  • Very robust to vibrations

  • Fast data acquisition

  • Easy alignment

  • Needs input for optical constants
  • Highest sensitivity for             structures with a pitch comparable to the wavelength

Angular Scatterometry (B)

 

 

With an angular scatterometry the diffraction 

intensities of diffraction orders are measured,

typically using a coherent light source.

 

  • Good for gratings with large pitch

  • Simultaneous pitch measurements

  • Challenging with 2D gratings

  • Highest sensitivity for pitches larger than the wavelength, tedious alignment

Spectroscopic Ellipsometry (C)

 

 

Spectroscopic ellipsometry measures the

wavelength dependent diffraction efficiency, 

at a specific angle of incident. 

 

  • Good for measuring very thin film thicknesses  (few nm)

  • The best solution for low pitch measurements.

  • Longer data acquisition time (minutes)

  • Alignment of polarizators has  to be controlled carefully

Fourier Lens Scatterometry (D)

 

 

Fourier Lens scatterometry uses specially

designed optical components for 

simultaneously measuring all diffraction 

orders with an azimuth angle up to 75 deg. 

By using color filters a wavelength dependent 

signal can also be measured.

  • Alignment free setup

  • Simultaneous pitch measurements

  • Ideal for 2D gratings

  • The most practical instrumentation for               diffractive structure.

  • Requires special optics,

  • Acquisition time for 1D         gratings is less than for 2D gratings (< 1 minute)

Try it out!

We are seeking beta testers! If you have Spectroscopic Scatterometry or Ellipsometry systems available and would like to expand its measurement capabilities by combining it with the InFoScat software please contact info@imagemet.com. We appreciate to hear about your motivation and would be pleased to receive your feedback.

Try it outTry it out

News

New Release

Image Metrology is proud to announce the release of InFoScat version 0.5.6 (Beta).

You can now also use the InFoScat software as a design tool for nano-structures meeting optical criteria within a selected wave length.

The new version features a Database Browser Functionality, which enables the user to browse through every entry of the database in order to:

  • Inspect how the structural properties influence the spectroscopic outcome

  • Compute average and peak values for the calculated spectra over range of wavelengths and sort by values

Do you want to try out the new feature? Send us a mail at  info@imagemet.com and become a Beta-tester!

References

Poul-Erik Hansen, Morten Hannibal Madsen, Joonas Lehtolahti and Lars Nielsen, "Traceable Mueller polarimetry and scatterometry for shape recosntruction of grating structures", Applied Surface Science (2017) (doi: 10.1016/j.apsusc.2017.02.091

 

Morten Hannibal Madsen, Pierre Boher, Poul-Erik Hansen and Jan Friis Jørgensen, "Alignment-free characterization of 2D gratings", Applied Optics, Vol. 55, No. 2, p. 317 (2016)  (doi: 10.1364/AO.55.000317)

 

Morten Hannibal Madsen, Poul-Erik Hansen, Maksim Zalkovskij, Mirza Karamehmedović, and Jørgen Garnæs, “Fast characterization of moving samples with nano-textured surfaces”, Optica 2, p. 301 (2015) (doi: 10.1364/OPTICA.2.000301)

 

Morten Hannibal Madsen, Poul-Erik Hansen, Brian Bilenberg and Mirza Karamehmedović, “Characterization of nano-textured samples in a production environment" euspen's 15th International *Conference & Exhibition, 2015

 

J. Garnaes, P.-E. Hansen, N. Agersnap, J. Holm, F. Borsetto, and A. Kuhle, “Profiles of a high-aspect-ratio grating determined by spectroscopic scatterometry and atomic-force microscopy,” Appl. Opt. 45, 3201–3212 (2006) (doi: 10.1364/AO.45.003201)

 

P. Boher, J. Petit, T. Leroux, J. Foucher, Y. Desieres, J. Hazart, and P. Chaton, “Optical Fourier transform scatterometry for LER and LWR metrology,” Proc. SPIE 5752, 192–203 (2005). (doi: 10.1117/12.594526)

 

InFoScat Papers

Partners

 

 

Industrial Fourier Scatterometer (InFoScat) is a Eurostars project (E8875). The partners for this project are ELDIM S.A. (France), Image Metrology A/S (Denmark) and DFM A/S (Denmark). 

 

 

 

ELDIM (www.eldim.fr) has been involved in optical metrology since 1991. 

ELDIM's market is mainly in the liquid crystal displays and the flat panel displays field and 80% of their turnover is made outside France. ELDIM's products are used for research and development needs as well as being included in production lines. The product line includes systems for viewing angle measurements, for imaging measurements and temporal measurements. 

Additional products for display driving and calibration purpose are also available.

 

 

Image Metrology A/S (www.imagemet.com) is a software company founded in 1998 and possess competences within image and data analysis software for microscopy.IM’s main product is the Scanning Probe Image Processor™ (SPIP™) originally designed for Scanning Probe Microscopy (SPM), for example AFM, but now also used together with other imaging techniques, such as Scanning Electron Microscopy (SEM) and optical microscopy. SPIP is widely used among academics and more than 800 papers with reference to SPIP™ has been published. IM has developed a number of unique image correction algorithms that corrects for systematic and stochastic artifacts typically found in high magnification microscopes.

 

DFM (www.dfm.dk) is the national metrology institute (NMI) in Denmark. DFM maintains several primary standards, including the meter and kilogram, for calibrations with the highest possible accuracy. DFM is participating in many national and international research projects (16 projects in 2013) of which, several includes optical characterization of nano-textured surfaces (4 projects in 2013). DFM is known for excellence in modeling, measurements and consultancy within the field of scatterometry. DFM has several homebuilt scatterometers and has developed algorithms for modeling scattering intensities; with many peer-reviewed papers published in recent years (complete list can be found in DFM's annual reports available here.

Contacts 

Image Metrology A/S

Lyngsø Alle, 3A,

DK- 2970, Hørsholm,

Denmark

 

Phone: +45 4692 3400

E-mail: sales@imagemet.com

Website: www.imagemet.com

Danish National Metrology Institute A/S

Kogle Alle 5, 

DK-2970, Hørsholm,

Denmark 

 

Phone: +45 7730 5800

E-Mailadministration@dfm.dk

Website: www.dfm.dk

ELDIM S.A.

1185 Rue d'Epron (Ancienne)

14200, Hérouville Saint Clair

Calvados, France

 

Phone: +33 (0)231 947600

E-Mail: sales@eldim.fr

Website: www.eldim.fr