ECE_220A_Lecture-16_Nov_15_2011_slides

ECE_220A_Lecture-16_Nov_15_2011_slides - SEM

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SEM
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http://research.amnh.org/pbi/description/imaging.html
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electron microscope image of a fruit Fy’s compound eye http://arstechnica.com/science/news/2009/03/looking-at-the-worlds-tiniest-dumbbells.ars
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Feather
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http://commons.wikimedia.org/wiki/File:AFM_%28used%29_cantilever_in_Scanning_Electron_Microscope,_magnifcation_1000x.GIF
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Electron column EDS detector Sample entry Pumps Image EDS data secondary electron detector
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secondary electron <50 eV Backscattered electron >50 eV up to incident energy Interaction volume Electrons incident upon you sample
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secondary electron <50 eV Backscattered electron >50 eV up to incident energy Interaction volume Electrons incident upon you sample
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Topological Contrast
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Topological Contrast
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Backscattered electron yield vs Z Electron yield vs energy Secondary electrons are more surface sensitive
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Atomic Number Contrast: backscattered electron image
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SEM Optics The condenser lenses demagnify the objective (the image of the beam source- Flament) The objective lens focuses on the specimen as well as demagniFes
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Working Distance: Specimen to lens Specimen must be moved closer to be in focus
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Smaller beam diameter Beam Size
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Lens Aberrations Spherical aberration (d s ) (aperture- beam current, diffraction limit (d d ) minimum size) Chromatic aberration (d c ) (Energy spread of electron source) Actual Probe Size = (d p 2 + d s 2 + d d 2 + d c 2 ) 1/2
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Astigmatism Lenses are not perfectly symmetrical Additional controls to adjust astigmatism
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Important factors and tradeoffs
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5 keV 25 keV Increasing voltage results in Decrease in lens aberrations Increase in probe current Potentially increase charge-up and damage Increase beam penetration - decreasing surface sensitivity Au particles 30 kV 1 kV
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MBE Regrowth Ȼ Gap Near Gate Ȼ Source Resistance W / Cr / SiO 2 gate W / Cr / SiO 2 gate SEM SEM Shadowing by gate: No regrowth next to gate Gap region is depleted of electrons High source resistance because of electron depletion in the gap MBE growth by Dr. Mark Wistey, device fabrication and characterization by U. Singisetti W/Cr gate Mo+InGaAs Ti/Au Pad Gap in regrowth SiO 2 cap Prof. Rodwell’s group
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This note was uploaded on 01/16/2012 for the course ECE 220a taught by Professor Staff during the Spring '08 term at UCSB.

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ECE_220A_Lecture-16_Nov_15_2011_slides - SEM

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