1. Air bubble formation and dissolution in dispensing nanoimprint lithography Xiaogan Liang, Hua Tan, Zengli Fu, and Stephen Y Chou William Casper-Ortiz Mechanical Engineering Dept. UC Berkeley Nanotechnology, 17 Jan 2007

2. 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.

3. 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?

4. Experimental Study Experimental Vary mold features and pressure Collect data on bubble diameter, resist area and mold- substrate gap size Nanonex NX-3000 Resist  NXR-2051(µ=4mPa s) Apparatus  Step-and-repeat NIL tool Mould  1in 2 imprint area Inject nozzle  100-800pl

5. Pinning Spreading edge is pinned by a structural feature > 300µm are still present after 1hr Bubbles < 100µm easily absorbed by the resist Size typically on the same order as pattern dimension ! Experimental Study

6. Encircling Air is trapped as droplets merge Multiple droplets reduce imprint force and increase speed Broad size distribution 100µm-mm Initial size depends on droplet separation Experimental Study

7. Theoretical Study Theoretical Model Molecular diffusion theoryHydrodynamics Navier Stokes equation Continuity equation Diffusion equation Henry’s Law for BC’s

8. Effects of initial air bubble sizeEffects of imprint pressure Strong dependence > 100µm  >10s P 1.Boyle’s Law dominates nRnR PBPB dissolution Three regions 2.Constant pressure 3.Sizable Laplace pressure Theoretical Study

9. Effects of air solubility Effects of resist viscosity Exponential decay Key parameter No important effect 1% difference 4-20mPa.s Viscous stress is 2 OM smaller than P B Theoretical Study

10. Effects of resist residual layer thickness Once the mold comes into close proximity to the substrate, P n contribution to P B is reduced. Dissolution time increases Theoretical Study

11. 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