Research Papers

A Coupled Electromagnetic and Thermal Model for Picosecond and Nanometer Scale Plasmonic Lithography Process

[+] Author and Article Information
Ion-Hong Chao

Mechanical and Aerospace Engineering Department,
University of California, Los Angeles,
Los Angeles, CA 90024
e-mail: dennischao@ucla.edu

Liang Pan

Mechanical Engineering Department,
Purdue University,
West Lafayette, IN 47907
e-mail: liangpan@purdue.edu

Cheng Sun

Mechanical Engineering Department,
Northwestern University,
Evanston, IL 60208
e-mail: c-sun@northwestern.edu

Xiang Zhang

Mechanical Engineering Department,
University of California, Berkeley,
Berkeley, CA 94709
e-mail: xzhang@me.berkeley.edu

Adrienne S. Lavine

Mechanical and Aerospace Engineering Department,
University of California, Los Angeles,
Los Angeles, CA 90024
e-mail: lavine@seas.ucla.edu

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received March 1, 2014; final manuscript received April 30, 2014; published online July 8, 2014. Editor: Jian Cao.

J. Micro Nano-Manuf 2(3), 031003 (Jul 08, 2014) (10 pages) Paper No: JMNM-14-1011; doi: 10.1115/1.4027589 History: Received March 01, 2014; Revised April 30, 2014

Plasmonic lithography may become a mainstream nanofabrication technique in the future. Experimental results show that feature size with 22 nm resolution can be achieved by plasmonic lithography. In the experiment, a plasmonic lens (PL) is used to focus the laser energy with resolution much higher than the diffraction limit and features are created in the thermally sensitive phase-change material (PCM) layer. The energy transport mechanisms are still not fully understood in the lithography process. In order to predict the lithography resolution and explore the energy transport mechanisms involved in the process, customized electromagnetic wave (EMW) and heat transfer (HT) models were developed in comsol. Parametric studies on both operating parameters and material properties were performed to optimize the lithography process. The parametric studies show that the lithography process can be improved by either reducing the thickness of the phase-change material layer or using a material with smaller real refractive index for that layer.

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Fig. 1

Diagram of plasmonic lithography. A UV laser is focused through an optical (prefocusing) lens and a plasmonic lens to create a nanoscale pattern on the phase-change material on the rotating disk.

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Fig. 2

Layer structure of plasmonic lithography. A plasmonic lens is fabricated on the chromium layer underneath the sapphire flying head. When laser energy is focused by the plasmonic lens, the phase-change patterns are created on the TeOx-based phase-change material.

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Fig. 3

Plasmonic lens geometry. A single plasmonic lens includes concentric ring grooves and center aperture. The rings help to focus the UV laser excited surface plasmons on the center aperture. When the electric field of the incident laser is oriented in the specific direction, strong electric field is generated across the narrow gap in the dog-bone-shaped center aperture to highly focus the laser energy.

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Fig. 4

Microscope image of plasmonic lithography pattern array. From top to bottom, pattern size increases as the laser power increases.

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Fig. 5

Inputs and outputs of electromagnetic wave and heat transfer models

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Fig. 6

Geometry, domains, and materials for electromagnetic wave and heat transfer models (not to scale)

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Fig. 7

Boundary conditions for electromagnetic wave model

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Fig. 8

Heat source distribution at the top surface of PCM layer. This heat source profile is captured when the laser pulse reaches its peak value. This figure shows the strong focusing effect of the PL.

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Fig. 9

Temperature distribution of PCM layer with isotherm at phase-change temperature. From top to bottom are the temperature distributions of PCM layer top surface (parallel to xy-plane) and PCM layer cross section (xz-plane) at the end of laser pulse.

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Fig. 10

Lithography feature radius as a function of laser focused spot diameter. Feature sizes are obtained by varying the objectively focused laser spot diameter with other numerical parameters unchanged.

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Fig. 11

Feature radius and depth as a function of operating parameter values (relative to base case)

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Fig. 12

Feature radius and depth as a function of PCM layer properties (relative to base case). In the legend, from top to bottom the PCM properties are the real and imaginary parts of the refractive index, thermal conductivity, and volumetric heat capacity.



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