Jaehyun Park EE235 Student presentation / Mar 09, 2009.

Jaehyun Park

EE235 Student presentation / Mar 09, 2009

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

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

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

Experiments : AFM

• AFM Shows heights of features

• Accurately reproduces nanoscale features over multiple cycles

• Some distortions : surface roughness of molded PU

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

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

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)

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

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)

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

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

Supplements : Pt catalyst