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Air bubble formation and dissolution in dispensing nanoimprint lithography

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.

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Air bubble formation and dissolution in dispensing nanoimprint lithography

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  1. 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

  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. But…how goodis it removing the air bubbles? How can bubble removal be enhanced? Introduction Dispensing based NIL • Room temperature • Low imprint pressure • Requires no vacuum

  4. 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 mold-substrate gap size

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

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

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

  8. Effects of initial air bubble size Effects of imprint pressure P PB nR dissolution • Strong dependence • > 100µm  >10s Three regions • Boyle’s Law dominates • Constant pressure • Sizable Laplace pressure Theoretical Study

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

  10. 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

  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

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