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Research Papers

Mechanics-Based Approach for Detection and Measurement of Particle Contamination in Proximity Nanofabrication Processes

[+] Author and Article Information
Shrawan Singhal

NASCENT Center,
The University of Texas at Austin,
10100 Burnet Road, Building 160,
Austin, TX 78758
e-mail: shrawan@austin.utexas.edu

Michelle A. Grigas

NASCENT Center,
The University of Texas at Austin,
10100 Burnet Road, Building 160,
Austin, TX 78758
e-mail: mgrigas@astro.as.utexas.edu

S. V. Sreenivasan

Department of Mechanical Engineering;
Department of Electrical
and Computer Engineering;
NASCENT Center,
The University of Texas at Austin,
10100 Burnet Road, Building 160,
Austin, TX 78758
e-mail: sv.sreeni@mail.utexas.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received March 13, 2016; final manuscript received May 24, 2016; published online July 1, 2016. Assoc. Editor: Nicholas Fang.

J. Micro Nano-Manuf 4(3), 031004 (Jul 01, 2016) (7 pages) Paper No: JMNM-16-1008; doi: 10.1115/1.4033742 History: Received March 13, 2016; Revised May 24, 2016

In spite of the great progress made toward addressing the challenge of particle contamination in nanomanufacturing, its deleterious effect on yield is still not negligible. This is particularly true for nanofabrication processes that involve close proximity or contact between two or more surfaces. One such process is Jet-and-Flash Imprint Lithography (J-FIL™), which involves the formation of a nanoscale liquid film between a patterned template and a substrate. In this process, the presence of any frontside particle taller than the liquid film thickness, which is typically sub-25 nm, can not only disrupt the continuity of this liquid film but also damage the expensive template upon contact. The detection of these particles has typically relied on the use of subwavelength optical techniques such as scatterometry that can suffer from low throughput for nanoscale particles. In this paper, a novel mechanics-based method has been proposed as an alternative to these techniques. It can provide a nearly 1000 × amplification of the particle size, thereby allowing for optical microscopy based detection. This technique has been supported by an experimentally validated multiphysics model which also allows for estimation of the loss in yield and potential contact-related template damage because of the particle encounter. Also, finer inspection of template damage needs to be carried out over a much smaller area, thereby increasing throughput of the overall process. This technique also has the potential for inline integration, thereby circumventing the need for separate tooling for subwavelength optical inspection of substrates.

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Figures

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Fig. 1

Illustration of the J-FIL™ process. Courtesy of Canon Nanotechnologies, Inc.

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Fig. 2

(Left) Example of the signature left behind from a particle event in the J-FIL™ process. The lost imprint area has been marked with a dashed circle. (Right) A zoomed in view of the particle encounter showing potentially damaged pieces from the template. Pictures courtesy of Molecular Imprints, Inc.

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Fig. 3

Illustration of geometry during particle encounter assuming an axisymmetric system centered around the particle center. The presence of a particle leads to the formation of a dry exclusion zone, where there is no fluid, with radius R1. The transition zone radius extends from the center of the particle to the edge of the affected area and is given as R2. It includes both the dry region as well as a wet region, where the fluid film thickness is not the same as the desired mean film thickness, h0. The particle height is given by hp.

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Fig. 4

Frequency distribution of 67 random particle events encountered in a class 10–100 cleanroom environment while carrying out the J-FIL™ process. The exclusion zone radius was measured using a calibrated optical microscope. The x-axis represents the upper limit for the interval in which the exclusion zone was placed. For example, the x-axis value of 200 represents 12 exclusion zone radii measured between 100 and 200 μm.

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Fig. 5

Comparison of model prediction against experimental data for the film thickness profile in the wet region of the geometry. The model took as inputs the exclusion zone radius and film thickness at the beginning of the wet region, both of which were measured on the profilometer.

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Fig. 6

Model estimated contact force and transition zone diameters for four particle events

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Fig. 7

Variation of transition zone with height of particle assuming that the particle is a rigid cone with a cone angle of 45 deg. The model also assumes that the deformation due to particle contact is 5 nm at the transition zone edge. This confirms the hypothesis that the transition zone can be much larger than the particle height and can also allow for easier measurement than the particle itself.

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