Research Papers

Design of Tool for Exfoliation of Monocrystalline Microscale Silicon Films

[+] Author and Article Information
Martin Ward

Department of Mechanical Engineering,
University of Texas at Austin,
204 East Dean Keeton Street,
Austin, TX 78712-1591
e-mail: mjward@utexas.edu

Michael Cullinan

Department of Mechanical Engineering,
University of Texas at Austin,
204 East Dean Keeton Street,
Austin, TX 78712-1591
e-mail: michael.cullinan@austin.utexas.edu

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO-AND NANO-MANUFACTURING. Manuscript received December 15, 2018; final manuscript received March 30, 2019; published online May 15, 2019. Editor: Nicholas Fang.

J. Micro Nano-Manuf 7(1), 011003 (May 15, 2019) (7 pages) Paper No: JMNM-18-1067; doi: 10.1115/1.4043420 History: Received December 15, 2018; Revised March 30, 2019

This paper presents the development of a prototype exfoliation tool and process for the fabrication of thin-film, single crystal silicon, which is a key material for creating high-performance flexible electronics. The process described in this paper is compatible with traditional wafer-based, complementary metal–oxide–semiconductor (CMOS) fabrication techniques, which enables high-performance devices fabricated using CMOS processes to be easily integrated into flexible electronic products like wearable or internet of things devices. The exfoliation method presented in this paper uses an electroplated nickel tensile layer and tension-controlled handle layer to propagate a crack across a wafer while controlling film thickness and reducing the surface roughness of the exfoliated devices as compared with previously reported exfoliation methods. Using this exfoliation tool, thin-film silicon samples are produced with a typical average surface roughness of 75 nm and a thickness that can be set anywhere between 5 μm and 35 μm by changing the exfoliation parameters.

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Fig. 1

Spontaneous exfoliation of a silicon thin film showing poor uniformity and surface finish

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Fig. 2

Image of the wedge-type exfoliation tool and diagram of the wedge mechanism. The wedge pries the crack open but does not reach the crack tip.

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Fig. 3

Controlled peeling concept diagram. Rollers move the tensioned handle film over the wafer to exfoliate the film.

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Fig. 4

Prototype controlled peeling tool CAD rendering

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Fig. 5

Prototype controlled peeling tool

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Fig. 6

Close-up of exfoliation process and silicon thin-film

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Fig. 7

(a) Sample test result at approximately 20 μm Si film thickness, (b) bend radius demonstration, and (c) sample film thickness map

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Fig. 8

Roughness comparison: (Top) White light interferometer measurements of each method and (bottom) photographs of each sample. Note regular ridges on the wedge tool sample and irregular ridges on the hand peeled sample.

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Fig. 9

Example wafer measurement and prediction profile demonstrating crack depth control with step change

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Fig. 10

Example wafer measurement and prediction profile targeting minimum thickness aided by metamodel prediction



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