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Research Papers: Radiative Heat Transfer

Sub-Beam Size Temperature Measurement of Heavily Doped Silicon Heater Using Two-Wavelength Thermoreflectance Microscopy

[+] Author and Article Information
Jinsung Rho

Department of Mechanical Engineering,
Korea Advanced Institute of
Science and Technology,
Daejeon 34141, South Korea

Bong Jae Lee

Department of Mechanical Engineering,
Korea Advanced Institute of
Science and Technology,
Daejeon 34141, South Korea
e-mail: bongjae.lee@kaist.ac.kr

1Corresponding author.

Presented at the 2016 5th Micro/Nanoscale Heat & Mass Transfer International Conference. Paper No. MNHMT2016-6475.Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 18, 2016; final manuscript received November 8, 2016; published online February 7, 2017. Assoc. Editor: Zhuomin Zhang.

J. Heat Transfer 139(5), 052703 (Feb 07, 2017) (8 pages) Paper No: HT-16-1399; doi: 10.1115/1.4035251 History: Received June 18, 2016; Revised November 08, 2016

This work describes a novel technique for simultaneously determining local temperature and thickness of a heavily doped Si heater having a submicron width by using two-wavelength thermoreflectance microscopy. The doped silicon line heater, whose thickness and width are, respectively, 480 nm and 900 nm, is fabricated by conventional microfabrication techniques on a fused silica wafer. The full width at half maximum (FWHM) of the focused laser beam is measured to be 2.00 μm and 2.28 μm for green (λ = 516 nm) and red (λ = 640 nm) lasers, respectively. Because the heater width is narrower than the focused laser beam size, the reflected beam contains background information (i.e., reflection from the fused silica substrate) in addition to the thermoreflectance signal from the doped silicon heater. With precise knowledge of the laser beam size, heater width, and exact location of the laser beam spot on the heater, one can quantitatively model the reflectance. In reality, however, due to the difficulty of aligning the laser beam with respect to the submicron-wide Si heater, precise determination of local temperature from thermoreflectance signal is not easily attained. In the present study, instead of aligning the laser beam to the center of the submicron silicon heater, the probe laser horizontally scans over a region of the heater. By taking into account the size of the focused laser beam and the width of the doped silicon heater, it is possible to determine the absolute temperature of a local region of the heater from the measured reflectance during the scanning, even though the width of the heater line is only 39% of the size of the laser beam.

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Figures

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Fig. 1

Schematic of the scanning two-wavelength thermoreflectance microscope

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Fig. 2

Optical images of the fabricated silicon line heaters: (a) microheater and (b) submicron-wide heater. Scanning electron microscope images of (c) microheater and (d) submicron-wide heater.

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Fig. 3

Characterization of two laser diodes: (a) wavelength and (b) focused beam size measured using the knife-edge method

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Fig. 4

The temperature-dependent reflectance of the 4.74 -μm-wide heater: (a) effect of the spectral bandwidth of lasers, (b) room-temperature fitting analysis for determination of the thickness, (c) comparison between the theoretical model and the measured reflectance at various temperature conditions, and (d) comparison of the fitted temperature from the thermoreflectance with the measured temperature in a furnace. The inset of (c) shows the focused laser beams on the microheater.

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Fig. 5

Illustration of laser beam scan for a sub-beam size Si heater: (a) variation of the measured reflectance with the 516-nm laser during the scanning motion of the stage, (b) positions of the laser beam and the heater when the measured reflectance increases as the stage moves, (c) positions of the laser beam and the heater when the reflectance reaches the maximum (perfect alignment), and (d) positions of the laser beam and the heater when the measured reflectance decreases as the stage moves further from the center

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Fig. 6

The temperature-dependent reflectance of the 900-nm-wide heater: (a) effect of the laser beam size relative to the heater width shown by the theoretical model, (b) room-temperature fitting analysis for determination of the thickness, (c) comparison between the theoretical model and the measured reflectance at various temperature conditions, and (d) comparison of the fitted temperature from the thermoreflectance with the measured temperature in a furnace

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Fig. 7

Local temperature with respect to the input power for two Si heaters. The inset shows the simulation domain constructed in ansys.

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