Nanoscale Nanoscale Imaging of Semiconductor and Imaging of - - PDF document

9/28/2005

• M. Selim Ünlü - Boston University

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1 LEOS DL Talk – 1 2005

Nanoscale Nanoscale Imaging of Semiconductor and Imaging of Semiconductor and Biological Systems Biological Systems

• M. Selim Ünlü

Boston University

Electrical Engineering Physics Biomedical Engineering Photonics Center / CNN

www.bu.edu/OCN

2 LEOS DL Talk – 1 2005

Outline Outline

• Nano-Optics – Aperture NSOM
• Earlier results (brief)
• Solid Immersion Lens Microscopy
• Numerical Aperture Increasing Lens (NAIL)
• Applications in IC imaging, thermal microscopy
• Quantum Dot Spectroscopy
• Spectral Self-interference Microscopy
• Preliminary results on lipid bilayers
• DNA conformation studies

9/28/2005

• M. Selim Ünlü - Boston University

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3 LEOS DL Talk – 1 2005

Mo Motivat tivation

• n: Resolution

Resolution Limitation Limitation in in Optics Optics

01 #

2 sin NA w f f n = = α

# 4 NA 2 f n spotsize π λ π λ = ≈

2w20 2w10

f

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Aperture Near-Field Microscopy Aperture Near-Field Microscopy

Resolution limited by Resolution limited by a an and d d

Synge 1928

• concept, scanning

1970’s RF metal plate a d Light or RF 100 X

9/28/2005

• M. Selim Ünlü - Boston University

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9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

Aperture NSOM

Imaging of PBG, Waveguide Devices and Lasers

6 LEOS DL Talk – 1 2005

Wavegui Waveguide Experimental Setup e Experimental Setup

• 4 -3 -2 -1 0

1 2 3 4 x (microns) 2.0 1.0 0.0

• 1.0
• 2.0
• 3.0

y (microns)

Refractive index

2.0 1.0 0.0

• 1.0
• 2.0
• 3.0

y (microns)

• 4 -3 -2 -1 0

1 2 3 4 x (microns)

• ptical field

9/28/2005

• M. Selim Ünlü - Boston University

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7 LEOS DL Talk – 1 2005

Optical fiber with wedged lens and AR coating Optical fiber with wedged lens and AR coating 980 nm GRINSCH LD 980 nm GRINSCH LD

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Laser Diode Facet under 40X microscope Laser Diode Facet under 40X microscope

NSOM Probe

pointing away from viewing direction

Laser Diode

AR-facet pointing towards viewing direction

9/28/2005

• M. Selim Ünlü - Boston University

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9 LEOS DL Talk – 1 2005

Lat Latera ral Beam Shift l Beam Shifts in in t the Near- e Near-Field ield a and Po d Poin inting in ng in the the Far-Field du Far-Field due to M e to Mode de Be Beating ating

⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × + + + + − − × ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ ⎥ ⎦ ⎤ ⎢ ⎣ ⎡ =

− 1 2 2 , ,

tan ) 1 ( ) ( 2 exp ) ( 2 ) ( 2 ) ( ) , , ( z z m l j z R y x jk jkz z w y G z w x G z w w A z y x U

m l m l m l

PTL Dec 2000

10 LEOS DL Talk – 1 2005

Outline Outline

• Nano-Optics – Aperture NSOM
• Earlier results (brief)
• Solid Immersion Lens Microscopy
• Numerical Aperture Increasing Lens (NAIL)
• Applications in IC imaging, thermal microscopy
• Quantum Dot Spectroscopy
• Spectral Self-interference Microscopy
• Preliminary results on lipid bilayers
• DNA conformation studies

9/28/2005

• M. Selim Ünlü - Boston University

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11 LEOS DL Talk – 1 2005

Throughput vs. spot size Throughput vs. spot size

SIL with GaP

Q Wu, G.D. Feke, R.D. Grober and L.P. Ghislain, Appl. Phys. Lett. 75, 4064 (1999)

1.0 0.5 0.4 0.15 0.10 Spot size in units of wavelength SIL 1 10-1 10-2 10-3 10-4 10-5 10-6 10-7

Near-field fiber tips

Diffraction limit in air GaP Glass Sapphire Si

Throughput

12 LEOS DL Talk – 1 2005

Solid Immersion Lens Techniques Solid Immersion Lens Techniques Surface microscopy Surface microscopy

Standard Solid Immersion Lens Super - SIL

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• M. Selim Ünlü - Boston University

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Subsurface microscopy Subsurface microscopy Object is already “immersed” Object is already “immersed”

Standard

• il Immersion

Standard subsurface Numerical Aperture Increasing Lens (NAIL)

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Need for Backside Imaging for ICs Need for Backside Imaging for ICs

Opaque metal above buried devices often make imaging through the substrate preferable

Stephen Ippolito, PhD May 2004

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• M. Selim Ünlü - Boston University

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15 LEOS DL Talk – 1 2005

Si IC failure analysis – Si IC failure analysis – resolution (?) esolution (?)

16

Two types of stigmatic NAILs

central NAIL D = R - X aplanatic NAIL D = R(1+1/n) - X

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Comparison of limitations

conventional

Light-gathering power

θa = sin-1 (1/n) NA = 1

Lateral spatial resolution

λ0 /2

Longitudinal spatial resolution

nλ0(1+cosθa) NAIL

Light-gathering power

θa= π/2 NA = n

Lateral spatial resolution

λ0 /2n

Longitudinal spatial resolution

λ0 /n

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10X with NAIL Boston University 100X objective Conventional State-of-the-art

10 µm

Qualitative Qualitative Comparison Comparison

Images are courtesy of Hamamatsu Photonics Hamamatsu µAMOS-200, IC Failure Analysis System 1.3 µm laser confocal scanning

• ptical microscope

5X, 10X, 20X, and 100X

• bjectives

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Hig High r resolution NIR inspection mic solution NIR inspection microsc

• scope

APL 2001

Optimized confocal microscope at λ=1.05µm

Resolution: 230 nm lateral 1.3 µm axial

20 LEOS DL Talk – 1 2005

Thermal Imaging on Al Wires Thermal Imaging on Al Wires

w/o NAIL w/ NAIL thermal

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LIVA image with NAIL @ 1064nm

Application Application: Failure Analysis : Failure Analysis

Overlay of LIVA and reflectivity using NAIL Reflectivity image @ 1340nm

Reflectivity image with NAIL @ 1340nm

Dave Vallett and Ted Levin (IBM Microelectronics Division - Burlington, VT)

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LIVA images at 1064nm

50X + AR 20X + NAIL 10 µm

9/28/2005

• M. Selim Ünlü - Boston University

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Commercial Commercial Product Product

Patent US 6,687,058 – Feb. 3,04

9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

QD Spectroscopy Resolution and stability

• Improvement in resolution
• Improvement in throughput
• Improvement in stability

NA D 2 λ ≈

) cos 1 ( θ − ∝ I d d M ′ =

Linecut

9/28/2005

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9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN NA=.12

~500µm

Quantify Collection Efficiency Increase

~max 8x

2nd

Use of Aplanatic NAIL

>100nm 500µm

NA = .6

InGaAsQ Ds GaAs

1st

λex = 840nm T = 8 K

How can we utilize this increase in colleciton efficiency??

26 LEOS DL Talk - 1 2005

Outline Outline

• Nano-Optics – Aperture NSOM
• Earlier results (brief)
• Solid Immersion Lens Microscopy
• Numerical Aperture Increasing Lens (NAIL)
• Applications in IC imaging, thermal microscopy
• Quantum Dot Spectroscopy
• Spectral Self-interference Microscopy
• Preliminary results on lipid bilayers
• DNA conformation studies

Lev Moiseev, Bio, PhD May 2003 Mehmet Dogan, Physics, PhD 2006

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9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

• 1898 O. Wiener discovers standing waves on top of silver mirror covered with

photosensitive material

• 1960’s K. Drexhage studies fluorescence lifetime of dyes on lipid multilayers.
• 1996 P. Fromherz shows fluorescence interferometry can determine the

height of buried emitters above mirror

Interference of Fluorescent Emission

9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

Monomolecular layers of fluorescent dyes on top of a stair- like lipid multilayers show dependence of fluorescent emission on the thickness of the lipid film

Fluorescence emission intensity Mirror Lipid multilayers with fluorescent dye on top

Interference of Fluorescent Emission

Drexhage et al, Prog. Optics, XII, p. 163, 1974

Mirror

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9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

Basic Reflectivity Model

RTE,TM

SiO2 spacer layer

d Fluorophore Reflected wave Direct wave

Si substrate

D

9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

From Spectrum to Axial Position

20 40 60 80 100 120 140 160 180 16000 16500 17000 17500 18000 18500 wave number (1/cm)

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 16000 16500 17000 17500 18000 18500 wave number (1/cm) Fluorescence (a.u.)

Axial Position with sub-nm accuracy

data model

Measured Spectrum Oscillatory Component Spectral Envelope

= x = x

9/28/2005

• M. Selim Ünlü - Boston University

16 Conformation of DNA immobilized on the surface

Large DNA microarray industry dependent on hybridization

• f complementary sequences for detection and monitoring of

gene expression

Efficiency of hybridization depends on conformation of

DNA molecules

No known techniques (AFM, SPR, etc) that can measure

extension of DNA above surface

Utilize spectral self-interference to get a more in-depth

picture of the structure and conformation of DNA molecules in an array

9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

DNA on surfaces

Distal and proximal labeled second strand hybridization

Optical density (nd) increases with hybridization 3’ labeled second strand 2-3 nm from surface 5’ labeled second strand 10-12 nm from surface

9/28/2005

• M. Selim Ünlü - Boston University

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9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

50-mer

2 nm 6 nm 4 nm 8 nm

Si Substrate Thick thermal oxide

10 nm

Conformational changes on second strand hybridization

9/28/2005 LEOS DL Talk – 1 www.bu.edu/OCN

Conclusions on Spectral Interference

• Spectral self-interference is a novel technique for

measuring the height of fluorescent molecules above a reflecting surface.

• A classical model of dipole emission that takes

polarization effects into account can be used to precisely describe the oscillatory spectral component of fluorophores.

• Self-interference of the emitted light was used to trace

the position of the fluorescent tag above the surface with sub-nanometer precision and thus determine the physical structure of the immobilized DNA.

• It was found that surface-bound ssDNA exists either in

random coils or more extended forms depending on constraints from nearby molecules. After hybridization of a second strand the DNA adopts the conformation of a molecular brush, protruding from the surface.