Transcript Defect Analysis in Thermal Nanoimprint Lithography

Defect Analysis in
Thermal Nanoimprint
Lithography
Yoshihiko Hirai, Satoshi Yoshida, and Nobuyuki Takagi
Journal of Vacuum Science & Technology B: Microelectronics
and Nanometer Structures, Vol. 21, No. 6, pp. 2765–2770,
November 2003
Presentation by Chris Hannemann
Overview
Thermal nanoimprint lithography process
 Step-by-step FEA stress/strain simulations
 Experiments/proposed process
improvements
 Conclusions

Thermal NIL
Thermoplastic polymer
heated above Tg
 Mold pressed and held
 Temperature dropped below
Tg to set polymer
 Polymer ‘released’ from mold

Fracture Issues
Fracture defects occur
during cooling (different
thermal expansion rates)
and mold release
 Increased friction force in
high aspect ratio features
increases rate of fracture

Hot Pressing Step
Polymer treated as
rubber elastic body
 Polymer
‘stretched’ into
cavity, though
stress spreads
easily due to
fluidity of polymer
above Tg

Cooling Step

Stress and strain
concentrations near
corner of feature
Release Step
Principal stress
distribution
during release
step
 Friction force
pulls polymer
upwards

Revised Processes
Conventional
Revised
Advanced
Conclusions
Simulations assert that stress
concentrations near corner of the pattern
are formed during the cooling process and
from pressure applied below Tg
 Releasing pressure below Tg and slowing
the cooling process help mitigate fracture
defects

Questions?