Transcript Air bubble formation and dissolution in dispensing

Air bubble formation and dissolution
in dispensing nanoimprint
lithography
Xiaogan Liang, Hua Tan, Zengli Fu, and Stephen Y Chou
Nanotechnology, 17 Jan 2007
William Casper-Ortiz
Mechanical Engineering Dept.
UC Berkeley
Significance
•Nanoimprint lithography is a proven technique with
high throughput for patterning nano-structures
•Dispensing NIL are low cost and easy to implement
techniques that are attractive for mass production
•More research is needed in order to improve its
performance and determine its true potential for mass
production .
Introduction
Dispensing based NIL
•Room temperature
•Low imprint pressure
•Requires no vacuum
But…how good is it
removing the air bubbles?
How can bubble removal
be enhanced?
Experimental Study
Experimental
Nanonex NX-3000
Apparatus Step-and-repeat NIL tool
Resist NXR-2051(µ=4mPa s)
Mould 1in2 imprint area
Inject nozzle 100-800pl
•Vary mold features and pressure
•Collect data on bubble diameter, resist area and moldsubstrate gap size
Experimental Study
Pinning
•Spreading edge is pinned by a structural feature
•Size typically on the same order as pattern dimension !
•Bubbles < 100µm easily absorbed by the resist
> 300µm are still present after 1hr
Experimental Study
Encircling
•Multiple droplets reduce imprint force and increase speed
•Air is trapped as droplets merge
•Initial size depends on droplet separation
•Broad size distribution 100µm-mm
Theoretical Study
Theoretical Model
Molecular diffusion theory
Diffusion equation
Henry’s Law for BC’s
Hydrodynamics
Navier Stokes equation
Continuity equation
Theoretical Study
Effects of initial air bubble size
•Strong dependence
• > 100µm  >10s
Effects of imprint pressure
P
PB
nR
dissolution
Three regions
1. Boyle’s Law dominates
2. Constant pressure
3. Sizable Laplace pressure
Theoretical Study
Effects of air solubility
•Exponential decay
•Key parameter
Effects of resist viscosity
•1% difference 4-20mPa.s
•No important effect
•Viscous stress is 2 OM
smaller than PB
Theoretical Study
Effects of resist residual layer thickness
•Once the mold comes into close proximity to the substrate,
Pn contribution to PB is reduced.
Dissolution time increases
Conclusions
•Dissolution time can be significantly reduced by:
decreasing initial bubble size, applying higher imprinting
pressures, and/or increasing the resist’s Henry law
constant.
•Resist viscosity does not play an important role
•Near zero residual layer thickness slows bubble
shrinkage
•Key conclusion: Air absorption time might be to long for
the dispensing NIL at or near atmosphere to have the
necessary throughput for mass manufacturing