Macrophase Separation Using Block Copolymer Blends

Transcription

1 Macrophase Separation Using Block Copolymer Blends Rachel Philiph 1,2, Kameron Oser 1, Sam Nicaise 1, and Karl Berggren 1 1 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology 2 Department of Materials Engineering, Iowa State University

2 Outline Introduction to nanolithography o Photolithography o Electron beam lithography o Self-assembling polymers Purpose Experimental methods Initial results and problem solving Final results Future work

3 Nanolithography Top-down approaches: Photolithography most common for electronics o Low resolution (~50 nm) Electron beam lithography o o Mask Photoresist SiO 2 Very high resolution (~10 nm) Very expensive, time consuming Si SiO 2 UV Light Si Etching Si Stripping Si

4 Self assembling Polymers Bottom-up approach Separation of immiscible polymer chains Requires solvent or heat for mobility Example of a PS b PDMS BCP forming spheres Conceptual schematic of microphase separation

5 Self assembling Polymers Assembly may be directed Resolution comparable to electron beam (~10 nm) More information on one microchip o o Less time Lower cost SEM image demonstrating the effect of a template on self assembly Chandler, D. L. (2012, July 19). Research update: Chips with self assembling rectangles. MIT News.

6 Purpose BCP blends could result in macrophase separation Possible benefits of BCP blends o Better resolution than photolithography o Faster than electron beam lithography o Structures not otherwise possible Conceptual schematic of macrophase separation

7 Methods Selected BCPs with a common block o PS-b-PDMS/PDMS-b-PMMA o PS-b-PDMS/PDMS-b-P2VP o PS-b-PDMS/PS-b-PFS Thermal annealing o Vacuum oven Selective solvent annealing o Beaker method o Mass flow system

8 Initial Results Thermal annealing did not provide enough mobility After a few experiments, focused solely on solvent annealing 200 nm PS b PDMS/PS b PFS blend thermally annealed at 170 C

9 Initial Results De-wetting was a problem Solutions: o Surface treatment with the common block of the BCP blend o Mixing solvents to reduce vapor pressure 400 nm PS b PDMS/PDMS b PMMA blend annealed in acetone

10 Final Results Macrophase separation achieved with PS-b- PDMS/PS-b-PFS blend Annealed with chloroform, toluene, and heptane in mass flow system 200 nm

11 Further Studies Initial result seemed to have formed multiple layers of structures Film thickness was studied Thickness: 34 nm 39 nm 42 nm 200 nm

12 Further Studies Helium ion microscopy used to image cross section Verified single layer of structures 100 nm PS b PDMS/PS b PFS blend cross sectional image

13 Further Studies Annealing time affected the degree of macrophase separation Separation maximized around 12 hours Anneal Time: 2 hours 5 hours 12 hours 18 hours 500 nm

14 Film thickness Conclusions o Less than ~35 nm: no nanostructure formation o Greater than ~45 nm: two layers Solvent selection o Solvent to swell each block in the blend Annealing time o At 12 hours, significant macrophase separation o After 12 hours, separation slows

15 Future Work Chemical and physical templating o Direct placement and morphology of regions Explore macrophase separation with other BCP blends

16 Acknowlegements We would like to thank James Daley and Mark K. Mondol for their help with using the facilities. Sample fabrication was completed in the Caroline Ross labs at MIT. SEM imaging was done in the Nanostructures Laboratory at MIT and in the shared scanning electron beam lithography facility in the Research Laboratory of Electronics. This work was supported by the CMSE Research Experience for Undergraduates Program, as part of the MRSEC Program of the National Science Foundation under grant number DMR , and by the MIT Materials Processing Center

17 Questions