terahertz non-invasive sub-surface nano-scanner
TRANSCRIPT
Terahertz non-invasive sub-surface nano-scanner
and 3D Imager
Anis Rahman*, and Aunik K Rahman
Applied Research & Photonics, Inc. 470 Friendship Road, Suite 10, Harrisburg, PA, 17111, USA
+1-717-623-8201, *[email protected]
CLEO Conference 2013 AF2J.4 Applied Optical Measurements in Fabrication
Processes and Products II Friday 14 June 2013
10:30 AM - 12:30 PM; Salon I & II (Marriott San Jose), CA, USA
Plan • Why terahertz sub-surface nano-
scanner
• Principle of non-destructive and non-invasive characterization
• Examples of sub-surface measurement and imaging
• Future work: In-vivo tomography
• Summary
Introduction • Terahertz is able to penetrate most non-metalic
objects sub-surface scanning
• It is non-ionizing allows, non-invasive probing
• Penetrates Sub-surface, interior of multi-layered composite
• Nano-scale diagnostics of semiconductor wafer, paint, coatings, etc.
• Biological applications: Early detection of Skin, Biological tissue, Dental
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Terahertz
terahertz gap
Raman/IR covers ~250 to 4000 cm-1 Bond, torsion
THz covers 0.1 THz to ~35 THz (from ~3 to 1200 cm-1) All kinds of resonances, Molecular backbone, intermolecular interaction
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Difference Frequency Generation U. Simon et al., 1993
Ref: U. Simon, C. E. Miller, C. C. Bradley, R. G. Hulet, R. F. Curl, and F. K. Tittel, “Difference-frequency generation in AgGaS2 by use of single-mode diode-laser pump sources,” OPTICS LETTERS Vol. 18, No. 13 / July 1, 1993, p 1062–1064.
12 THzfl1
l2 c(2) matl.
Setup of Simon et al., 1993
THz power as c(2)
Principle of detection • Concentration: Beer-Lambert’s Law: A(l, C) = εlC
• Layer thickness/uniformity/defect: R(l, ρ) = εlρ
A = absorbance
l = path length
C = concentration
ε = extinction coeff.
R = reflectance
ρ = density
Multilayer
• Concentration distribution
Principle (contd.)
𝜕𝐶
𝜕𝑥𝑎𝑛𝑎𝑙𝑦𝑡𝑒
=𝜕𝐶
𝜕𝑥𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒
−𝜕𝐶
𝜕𝑥𝑠𝑢𝑏𝑠𝑡+𝑎𝑛𝑎𝑙𝑦𝑡𝑒
drop
substrate
analyte
• Penetration/diffusion kinetics
Principle (contd.)
Kinetics of different analytes in to vitroskin
𝑱 = −𝑫 𝝏𝑪 𝝏𝒕
Application Example Coating penetration in to paint
Depth profile of over-coating (green) in to paint. Red curve (top) is the paint without coating and the bottom curve (blue) is the scan of coated paint. The difference is the profile of the coating. Left: Coating penetrated. Right: coating remained on the surface.
3D nano-scanner/Imager
Scan X, XY, or XYZ for profiling and/or reconstructed imaging Angular scan for conformal imaging
Console
Reproducibility
Reproducibility of the traces. Very slight mismatch is due to the course resolution of the stage. This will improve by installing a higher resolution stage.
Example
High resolution scan revealing periodic pattern from different segments of a wafer without any defect. The left and the right plots are from two different segments of a wafer.
Example: Non-destructive testing
X
Y
Z
Reconstructed thickness profile. The glaze/paint and porcelain layers have different reflected intensity; thus permitting precise thickness determination.
Reconstructive Imaging
Potential products
• THz Coherent Tomography
• Semiconductor diagnostics
• Skin/tissue imaging
• Dental imaging
• Early breast cancer detection Applied Research & Photonics -- Proprietary -- 02/01/2013
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Wafer reject
• Wafer reject is a big problem
• Current art is limited to “see” only surface
• Hidden defects in inside layers need to be revealed
• Nanometer size defects need to be identified and quantified
• Particulate inclusion, cracks, non-uniformity, etc.
3D Imaging
A wafer mounted on the scanner
Parameter modeling
Physical parameters of interest may be modeled and measured From the front-end operation
Isosurface
An isosurface is a surface of constant value in a three-dimensional volume. The isosurface separates regions less then the isovalue from regions greater than the isovalue. All points on the isosurface have the same value (the isovalue). Provides a means for finer inspection and comparison
Wafer inspection
Reflection and transmission
Simultaneous measurement: same length of time
Transmission Image
Transmission image video
Summary
• Terahertz 3D imaging is an effective technique for sub-surface defects inspection
• Almost all non-metals many be inspected – Semiconductors, paint, laminates, etc. – Skin, transdermal, and other biological tissue
• May be extended to medical imaging/tomography
• Both quantitative measurement and visual inspection
