Air bubble formation and dissolution in dispensing nanoimprint

lithography

Xiaogan Liang, Hua Tan, Zengli Fu, and Stephen Y Chou

William Casper-OrtizMechanical Engineering Dept.

UC Berkeley

Nanotechnology, 17 Jan 2007

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

•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 1in2 imprint area

Inject nozzle 100-800pl

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

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

Theoretical Study

Theoretical Model

Molecular diffusion theory HydrodynamicsNavier Stokes equation

Continuity equation

Diffusion equation

Henry’s Law for BC’s

Effects of initial air bubble size Effects of imprint pressure

•Strong dependence• > 100µm >10s

P

1. Boyle’s Law dominates

nRPB dissolution

Three regions

2. Constant pressure3. Sizable Laplace pressure

Theoretical Study

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 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

Theoretical Study

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