jaehyun park ee235 student presentation / mar 09, 2009
TRANSCRIPT
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Jaehyun Park
EE235 Student presentation / Mar 09, 2009
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Motivation
• Among NGL methods : use molds for imprinting features into thin polymer films
• Evaluation of resolution limits : most effectively done by using molds
• Difficult to fabricate structures of sub 5nm using conventional methods : resolution limit and non-uniformities
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Their solution
• Use SWNTs as templates – Features of SWNT (single-walled nanotube)
• Cylindrical cross-sections• Atomic scale uniformity• Chemical inertness• Ability to grow or deposit them in large quantities over
large areas : 0.5~5nm dia.,1~10 tubes/μm2
• Research on polymer characteristics with SWNT molds
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Fabrication process
• Master mold : – Grow SWNT using CVD on SiO2/Si
• Replicated mold : – Spin h-PDMS on cured PDMS– Casting & curing: Platinum catalyst us
ed to form 3D crosslinking
• Imprinting :– Spin low viscosity PU – Lightly press mold & cure under UV– Peel off
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Experiments : AFM
• AFM Shows heights of features
• Accurately reproduces nanoscale features over multiple cycles
• Some distortions : surface roughness of molded PU
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Experiments : TEM
• TEM shows widths of features• PAA used instead of PU• Imprinted structures similar to
master features• For widths below 3nm : difficult
to determine due to grain size of Pt/C (~1nm)
TEM : mold
TEM : master
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Experiments : AFM at sub 2nm scale
feature capability
> 2nm Reliable
1~2nm Partial capability, still possible to identify heights
< 1nm Little to no capability, significant loss of height
• defects appeared
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Polymer limits resolution
• Clues1. Beaks in molded feature occurs at the same p
osition2. Imprinted features with dissimilar polymers ha
ve similar surface roughness3. SiO2/Si has 0.19nm surface roughness
4. Distance between crosslinks of polymer (1nm for h-PDMS)
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Density of crosslinks
• Crosslink density : affects capability of defining small feature and retaining shape
• Attempts to increase in h-PDMS : failed due to stiction to mater mold
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Surface roughness
• Got 0.26nm RMS at 9k rpm of polymer spin
• Processing conditions : extremely important in achieving high-fidelity nanoimprint lithography in the 1-10nm regime.
• F. Hua, et. al., “Processing Dependent Behavior of Soft Imprint Lithography on the 1-10 nm Scale”, IEEE Trans. on Nanotechnology, 5, 301 (2006)
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Conclusion
• Simple method for evaluating resolution limits on imprinting polymers, as small as 2nm
• Resolution is determined by both polymer chemistry and process condition
• To enhance the resolution– Polymer having high crosslink density– Process to make smaller roughness
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Supplements : TEM
• TEM analysis for lateral dimension
• Sample prepared by metal shadowing technique
• PAA can replicate fine feature and is dissolvable by water
• Pt/C has fine grain• Carbon mechamically su
pport the thin film
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Supplements : Pt catalyst