Department of Electrical Engineering and Computer Sciences

University of California, Berkeley, CA 94720-1770 USA

Nanoimprint Lithography

Peter Matheu

EE 235 – “Nanoscale Fabrication”

Professor Connie Chang-Hasnain

April 14, 2008

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 2

Outline

Introduction to Nanoimprint Lithography (NIL)PromiseUV curing for NIL

Motivation for workCross-bar circuits

Single layer resist NILIssues

Best line patterns with NIL

G. Y. Jung, et al, App. Phys. A, 81, 2005.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 3

Nanoimprint Lithography - Basics

By using a patterned mold, or a shallow 3D pattern, we can transfer a pattern with dimensions below traditional optical lithographic limits.

Can be used in either a lift-off or etch mask pattern transfer method.

For smallest features sizes the resist is cured to the substrate using UV light

G. Y. Jung, et al, Nano Letters, 6, 2006.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 4

Capillary Action

Capillary forces spread the resist throughout the mold

By engineering the surface energies of the mold and the substrate, very little resist is left between the edge of the mold and the substrate.

G. Y. Jung, et al, Nano Letters, 4, 2004.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 5

Capillary Forces at Work

Of course, the capillary forces take time to reach a uniform resist thickness. ~30min.

G. Y. Jung, et al, Nano Letters, 4, 2004.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 6

Single Layer Resist NIL

The single layer recipe for:RigidityReleaseViscosityUV response

G. Y. Jung, et al, App. Phys. A, 81, 2005.G. Y. Jung, et al, Nano Letters, 4, 2004.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 7

Issues with a Single Layer Resist

Goal: Avoid etch mask simplicity NIL challenge no undercut with a mold Lift-off desire an undercut for resist Issue rabbit ears

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 8

Process for 17nm ½ pitch

SNAP transfer method:1. Selectively etch a superlattice2. Shadow (tilted) evaporation3. Transfer to sacrificial layer4. Transfer to underlying layers/substrate

Uniform pressure for the NIL process is accomplished by employing optically patterned disks in the vicinity of the NIL template.

G. Y. Jung, et al, Nano Letters, 6, 2006.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 9

A. The nanoimprint mold from the SNAP process

B. Transferred pattern in resist

C. Pattern in resist transferred to form metal nanowires

G. Y. Jung, et al, Nano Letters, 6, 2006.

EE 235 ‘Nanoscale Fabrication’ Peter Matheu 10

Conclusion

Motivation for further workA molecular monolayer of switching ‘material’A 34x34 cross-bar structure at 50nm ½ pitch10Gbit/cm2

At 17nm ½ pitch (with 15nm wide lines) ~100Gbit/cm2