1. 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

2. Overview Thermal nanoimprint lithography process
Step-by-step FEA stress/strain simulations
Experiments/proposed process improvements
Conclusions

3. Thermal NIL Thermoplastic polymer heated above Tg
Mold pressed and held
Temperature dropped below Tg to set polymer
Polymer ‘released’ from mold

4. 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

5. Hot Pressing Step Polymer treated as rubber elastic body
Polymer ‘stretched’ into cavity, though stress spreads easily due to fluidity of polymer above Tg

6. Cooling Step
Stress and strain concentrations near corner of feature

7. Release Step Principal stress distribution during release step
Friction force pulls polymer upwards

8. Revised Processes
Conventional Revised Advanced

9. 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

10. Questions?