confocal microscopy of electron - electrical engineering · 2008. 3. 20. · confocal microscopy...
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Confocal Microscopy of Electronic Devices
James Saczuk
Consumer Optical Electronics
EE594
02/22/2000
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Introduction
! Review of confocal principles
! Why is CM used to examine electronics?
! Several methods of CM are used, what are they?
! What kind of data is gathered and what analysis
can be performed on it?
! What is new in the field of CM?
! Conclusions
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Confocal Microscopy Basics
! CM is used to produce high resolution, three
dimensional images of specimens of various
thickness.
! How does it work, what resolution can we
achieve?
More
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Confocal Microscopy Optics Patent Diagram
Minsky (US Patent 03013467)
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Design Rules for Target Resolution
! Confocal lateral resolution is related to the lateral
resolution of the objective lens, which is a
function of a NA, the confocal pinhole size and
the wavelength of the projected light by the
equation:
! As the pinhole size approaches ? , the resolution
improves by a factor of ?2.
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Why use C.M. to Characterize Electronics ?
! Non-intrusive, thus non-destructive.
! Provide a method to correlate electrical and
tomographical data.
! Viewing of switching events at the
materials level.
! Establish fault conditions with great
precision for failure analysis.
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Methods of Confocal Microscopy
! LASER Scanning
! Fluorescence Mapping
! Single and Multi-Photon Optical Beam Induced
Current Mapping
! Near Field OBIC Imaging
! Future Technologies
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LASER Scanning Confocal Microscopy
! LASER sources:
– Ar+ 488/514nm
– Solid State 523nm
– HeNe 633nm
! Source is selected based on the specimen’s
properties to be examined.
! Long pass filter in detector used to protect
operator.
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LASER Scanning C.M. Optical Schematic
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LASER Scanning C.M. System Diagram
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CM Scanning versus Wide Field Microscopy
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Simplified Scan of 2D Specimen with S.M.
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Data from 3D S.M. Compiled for Viewing
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LSCM Image of LEPSi Wafer
· 200x200µm field of view
· Imaged at 488nm, emission above 550nm
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Fluorescence Mapping
! Light source is selected to support fluorescence of
the material being observed, and/or the
fluorophore added to the sample.
! The use of ultrafast lasers, optical parametric
oscillators and optical parametric amplifiers
provide for fluorescence imaging without the
addition of dyes, stains or other fluorophores.
! Typically a mode locked Ti:Sapphire LASER is
used at IR wavelengths.
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Fluorescence Process
Photons excite the electrons of a
fluorophore to a higher energy level.
As these electrons descend to a low
level they emit photons of a shorter
wavelength than the excitation
Emission spectra and
excitation spectra for
common fluorescence
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Fluorescence Mapping Analysis
! Fluorophore Emission Table
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LSCM Fluorescence Image of LEPSi Wafer
Light-Emitting Porous
Silicon wafer excited
at 488 nm, emission
above 550 nm
7.5x7.5mm field of
view
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Optical Beam Induced Current
! Uses apparatus similar to conventional LSCM
! 1, 2 and 3 photon OBIC
! LASER sources are 633 and 1152nm HeNe
! New techniques use 120fs pulse, 80MHz
repetition rate, tunable, mode locked Ti:Sapphire
lasers (Spectra-Physics, Opal)
! Imaging through the substrate of electronic
devices allows examination for failure analysis
without possible damage from decapsulation.
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Optical Beam Induced Current Apparatus
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Optical Beam Induced Current Capabilities
! Very low power, 1-10mW @ the focal point
! Excellent response in highly doped
semiconductors where one photon absorption
occurs below the bandgap of Si due to excess
charge carriers.
! Long dwell time of the sample image, ~10µS,
compared to ~1nS for others.
! Out of focus background current eliminated as
compared to the one photon method
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Optical Beam Induced Current Samples
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Optical Beam Induced Current Samples
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Optical Beam Induced Current Samples
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Optical Beam Induced Current Samples
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Optical Beam Induced Current Samples
Vcc = 5 VDC
Vcc = 0 VDC
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Optical Beam Induced Current Samples
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Near Field OBIC Imaging
! Use a near field optical “probe” to sense and
excite the specimen
! Tapered optical fibers are used as the probes
! Resolution can approach 10nm
! A tunable Ar+ pumped Ti:Sapphire LASER is
used to provide optical excitation through the fiber
! A scanning microscopy method that has evolved
from LSCM OBIC
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Near Field OBIC Imaging
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Near Field OBIC Imaging
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The Near Future...
! Confocal imaging of transparent objects
! Second harmonic generation
– limited to crystals & structured media
! Third harmonic generation
– all materials generate 3rd harmonic light in the beam
waste when an excitation source (LASER) is tightly
focused at a point in the material
– requires ultrafast pulses with ?>1µm
– 3rd harmonic detection at 400nm for 1.2µm excitation
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Third Harmonic Generation
THG in a homogenous sample
shows the beam waste summing
to zero because the 3rd harmonics
on each side of the beam waste are
exactly out of phase
Out of phase beam waste occurs near the interface between
materials with different 3rd order susceptibilities or indices
of refraction. The interference patterns can be mapped to
produce a stereoscopic image of the specimen.
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Conclusions
! Confocal microscopy applications are developing
steadily with the availability of cheaper, more user
friendly, ultrafast laser systems.
! The technology and expertise to use these systems
for electronic component characterization and
failure analysis will be in demand as electronics
continue to proliferate in the consumer market.
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References
! http://glu.ls.utsa.edu/CLSM/chpt2.html dzf
! http://www.zeiss.com/micro/products/
! http://www.science.uwaterloo.ca/physics/research/confocal/scapp.html#sc
! http://photon.bu.edu/selim/papers/jqe-95/node1.html
! http://www.cs.ubc.ca/spider/ladic/overview.html
! http://www.chips.ibm.com:80/services/asg/capabilities/asweb07.html#obic