1. Nanoimprint Lithography
Steven Glenn
Ward Johnson
Advisor: Prof. Dale Ewbank
Department of Microelectronic Engineering, RIT
NSF REU grant # ECCS
Hello, my name is Steven Glenn. Welcome to my presentation

2. Outline Introduction Factors affecting Nanoimprinting Process Steps
Results and Analysis
Conclusion and Future Work
Acknowledgements

3. Nanoimprint Lithography
Low cost, high resolution, large area patterning process
Does not require an expensive optical system
Allows for patterning down to the sub-100nm regime
Molecular Imprints’ Imprio 250 offers sub-50 nm half pitch resolution.
Captured using Wyco NT1100

4. Goal
To achieve lines and spaces from a 10 µm pitch relief mask in a cross-linked imprint resist.

5. Imprint Resist .274 grams ethylene glycol diacrylate (30%)
.343 grams isobornyl acrylate (37.5%)
.274 grams butyl acrylate (30%)
.035 grams Irgacure 651 (2.5%)
-EGD - Cross-linking monomer for mechanical stability
-IBA - Matrix polymer (high Tg)
-BA - Reactive diluent low viscosity (low Tg)
-I651 - Photo-initiator (solid powder)
-Added in this order at 10µL increments
-Requires oxygen-free environment to allow cross-linking to occur
-Percentage by weight using microbalance

6. Factors Oxygen Inhibition Controlled Pressure Release Agent
Prevents cross-linking process from occurring fully and completely causing exposed resist to remain fluid.
Controlled Pressure
Due to the need for an non-oxygen environment and controlled pressure, a trade-off would have to be decided upon.
Release Agent
If not reliable, can cause either most of the resist to stick to mask or your resist to be damaged.
Glove Bag Light Transmission
Glove Bag needs to be flat against mask. The further the glove bag is from the mask, the less irradiance the mask sees.
Controlled Pressure
-While the SMFL has a tool (Karl Suss MA150) that can apply the a certain pressure, open environment in which the tool exists makes this option improbable

7. Process Steps

8. Preparation
-Glove bag filled with nitrogen and allowed to leak until almost flat.
-Wafer and mask cleaned with acetone and isopropyl alcohol.
-Wafer treated with HMDS Prime.
-One 2-µL drop is applied to wafer.
-Resist applied when still cool to keep resist standing on wafer.

9. Nitrogen Environment
-Mask and wafer are placed in glove bag and opening is shut.
-Glove bag is filled with Nitrogen and all gas and openings are closed.
-Wafer and mask sit in glove bag for 10 minutes.
-Mask is placed on top of wafer.
-Glove bag is mostly-deflated after time has elapsed.

10. Exposure & Separation
-Mostly-deflated glove bag is placed under i-line (365nm) head.
-The imprint resist is exposed at 150mJ/cm2.
-The glove bag is moved to a hood where the wafer and mask are removed from the bag.
-Using a vacuum, the wafer is held in place and the mask is removed by hand.

11. Resist Removal Branson Asher Acetone and Isopropyl Alcohol
One to two hard ashes necessary to completely remove resist
Acetone and Isopropyl Alcohol
Targeting the edges of the resist causes it to peal up making it easier to remove with compressed air or a chemical wipe
-Applies to both mask and wafer

12. Examination & Results
The wafer is checked for resist or lack thereof from the separation.
The resist is examined using:
Leica Microscope
Wyko NT1100 Optical Profiler
Amray Surface Electron Microscope (SEM)
Amray SEM
Source:
(SMFL, Rochester Institute of Technology)

13. Oxygen Inhibition
2µL resist drop exposed in Nitrogen-Oxygen Environment
2µL resist exposed in Nitrogen Environment

14. Varying Resist Thickness
Closer to edge of resist
Closer to center of resist

15. Varying Pressure

16. Release Agent
.28 grams of (heptadecafluoro-1,1,2,2-tetrahydrodecyl)dimethylchlorosilane (0.2%)
grams RER 600 (PGMEA) (99.8%)
-Resist stuck to mask more often with release agent than without
-140 grams of solution needed to completely cover mask.

17. Conclusion
Nanoimprint Lithography has shown itself to be a low-cost alternative to optical lithography. The total cost for materials was under $1000.
With the lack of the proper equipment, getting a uniform resist coating with controlled pressure and nitrogen was unattainable.
This exploration is successful nevertheless because we have achieved what we sought from the beginning—to imprint lines and spaces in a cross-linked resist.

18. Future Work Smaller Lines and Spaces Larger Line Aspect Ratio in Mask
Better Release Agent
Pattern Transfer
Controlled Pressure
Spin-on Resist Application

19. Acknowledgements
Prof. Dale Ewbank (Department of Microelectronics, RIT)
Ward Johnson (Department of Microelectronics, RIT)
SMFL Staff
Thomas Grimsley
Sean O’Brien
Dr. Alan Raisanen
Dr. Thomas Smith (Department of Chemistry, RIT)
Nitin Nampalli (Department of Microelectronics, RIT)
University of Texas at Austin
Dr. Grant C. Willson (Department of Chemical Engineering)
Frank Palmieri (Department of Chemical Engineering)
National Science Foundation (NSF REU grant # ECCS )
CIBA Specialty Chemicals
Dr. Eugene Sitzmann

20. References
"Imprio 250 Nano-Imprint Lithography Systems." Molecular Imprints Aug <

22. Chemical Structures Butyl acrylate Isobornyl acrylate Irgacure 651
Source: (Sigma-Aldrich)
Source: (Sigma-Aldrich)
Irgacure 651
Source: (CIBA Specialty Chemicals)
Ethylene glycol diacrylate
Source: (Sigma-Aldrich)