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Research Papers

Study on Microgratings Using Imaging, Spectroscopic, and Fourier Lens Scatterometry

[+] Author and Article Information
Jonas Skovlund Madsen

Danish Fundamental Metrology A/S,
Matematiktorvet 307,
Kongens Lyngby 2800, Denmark;
Center for Quantum Devices,
Niels Bohr Institute,
Universitetsparken 5,
Copenhagen 2100, Denmark
e-mail: jsm@dfm.dk

Poul Erik Hansen

Danish Fundamental Metrology A/S,
Matematiktorvet 307,
Kongens Lyngby 2800, Denmark
e-mail: peh@dfm.dk

Pierre Boher

Eldim S.A.,
1185 Rue d'Epron Ancienne,
Hérouville-Saint-Clair 14200, France
e-mail: pboher@eldim.fr

Deepak Dwarakanath

Image Metrology A/S,
Lyngsø Alle 3A,
Hørsholm 2970, Denmark
e-mail: ddw@imagemet.com

Jan Friis Jørgensen

Image Metrology A/S,
Lyngsø Alle 3A,
Hørsholm 2970, Denmark
e-mail: jfj@imagemet.com

Brian Bilenberg

NIL Technologies ApS,
Diplomvej 381,
Kongens Lyngby 2800, Denmark
e-mail: bb@Nilt.com

Jesper Nygård

Center for Quantum Devices,
Niels Bohr Institute,
Universitetsparken 5,
Copenhagen 2100, Denmark
e-mail: nygard@nbi.ku.dk

Morten Hannibal Madsen

Danish Fundamental Metrology A/S,
Matematiktorvet 307,
Kongens Lyngby 2800, Denmark
e-mail: mhm@dfm.dk

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received December 21, 2016; final manuscript received May 17, 2017; published online June 7, 2017. Assoc. Editor: Stefan Dimov.

J. Micro Nano-Manuf 5(3), 031005 (Jun 07, 2017) (7 pages) Paper No: JMNM-16-1073; doi: 10.1115/1.4036889 History: Received December 21, 2016; Revised May 17, 2017

With new fabrication methods for mass production of nanotextured samples, there is an increasing demand for new characterization methods. Conventional microscopes are either too slow and/or too sensitive to vibrations. Scatterometry is a good candidate for in-line measuring in an industrial environment as it is insensitive to vibrations and very fast. However, as common scatterometry techniques are nonimaging, it can be challenging for the operator to find the area of interest on a sample and to detect defects. We have therefore developed the technique imaging scatterometry, in which the user first has to select the area of interest after the data have been acquired. In addition, one is no longer limited to analyze areas equal to the spot size, and areas down to 3 μm × 3 μm can be analyzed. The special method Fourier lens scatterometry is capable of performing measurements on misaligned samples and is therefore suitable in a production line. We demonstrate characterization of one-dimensional and two-dimensional gratings from a single measurement using a Fourier lens scatterometer. In this paper, we present a comparison between spectroscopic scatterometry, the newly developed imaging scatterometry, and some state-of-the-art conventional characterization techniques, atomic force microscopy and confocal microscopy.

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Figures

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Fig. 1

Three-dimensional microscope images with corresponding profiles for a segment in the center of each image, for 3.3 μm one-dimensional (1D) silicon grating. (a) AFM, (b) confocal microscope, 150× objective, and (c) confocal microscope, 50× objective.

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Fig. 2

Experimental data and best fit for scatterometry data for a 1D grating with a pitch of 3.3 μm. (a) Spectrometer-based scatterometry. Best reconstruction for a height of (422 ± 4) nm and a width of (1230 ± 30) nm. (b) Imaging scatterometry. Best reconstruction for a height of (426 ± 6) nm and a width of (1240 ± 30) nm.

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Fig. 3

Sketch of the imaging scatterometer setup. The liquid filter and the charged-coupled device (CCD) camera can be interchanged with a fiber coupled spectrometer turning the setup into a spectroscopic scatterometer.

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Fig. 4

BRDF measurements obtained with the Fourier lens system at a wavelength of 550 nm: (a) 1D grating with a pitch of 4 μm and a height of around 500 nm and (b) quadratic 2D grating with a pitch of 2 μm. The different diffraction orders are indicated. The parasitic light arises from multiple reflections in the optics and is avoided in the data analysis.

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Fig. 5

Comparison of measurements results for ten 1D gratings of different heights. (a) Direct comparison of all the techniques compared individually. The name of the characterization method applies to graphs both horizontally and vertically. As a guide to the eye, a solid line is plotted to indicate when the two methods give the same result. Further away from this line indicates a deviation between the techniques. (b) Deviation of all measurements with respect to the AFM measurements plotted as a function of the heights found using AFM.

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Fig. 6

Difference between the heights estimated by the imaging scatterometer and by the AFM. The error bar indicate a combination of the 95% confidence interval limits for the imaging scatterometer and the k = 2 uncertainties of the AFM measurements found by treating the 95% confidence interval as an uncertainty and performing standard error propagation. The dashed line is plotted through zero to guide the eye. A clear offset is observed.

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Fig. 7

Experimental data and best fit for scatterometry data for a 1D grating with a pitch of 3.3 μm using a model with rounded top corners. (a) Sketch of the new model with rounded top corners. The rounding, r, is defined as the radius of the dashed circle while the height, h, and the width, w, are the same as in the rectangular model. (b) Spectrometer-based scatterometry, using a model with rounded corners. Best reconstruction is found for a height of (435 ± 4) nm and a rounding of (200 ± 20) nm. The chi-square found using rounded corners is: χ2 = 0.20, compared to χ2 = 0.55 for a rectangular model.

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Fig. 8

AFM Profile averaged from 250 lines. A rounding of the corner is observed and highlighted by the dashed line.

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Fig. 9

Experimental data obtaining using the Fourier lens scatterometer using a wavelength of 550 nm and best fitting models. Diffraction efficiencies are normalized with respect to the zeroth-order: (a) measurements on a 1D grating and (b) measurements on a 2D grating.

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