Block Copolymer Micelle Nanolithography Roman Glass, Martin Moller and Joachim P Spatz University of Heidelberg IOP Nanotechnology (2003) Erika Parra EE235 4/18/2007

Motivation Market Trends Small features Sub-10nm clusters deposited Patterns 50nm to 250nm and greater Lower cost of tedious fabrication processes for conventional lithography Increase throughput (from e-beam) – parallel process Bottom line: bridge gap between traditional self-assembly and lithography

Process Overview Dip wafer (Si) into micelle solution Retrieve at 12mm/min Air-evaporate solvent Plasma (H2, Ar, or O2) removes polymer shell Results: Uniform Hexagonal 2, 5, 6, or 8nm Spherical PS(190)-b-P[2VP(Au0.2)](190) PS(500)-b-P[2VP(Au0.5)](270) PS(990)-b-P[2VP(Au0.5)](385) PS(1350)-b-P[2VP(Au0.5)](400) Side view TEM – treated wafer Au ~ HAuCl4

Diblock Copolymer Micelles Dendrite shaped macromolecule Corona is amphiphilic Micelle MW and shape controlled by initial monomer concentration Polymer corona with “neutralized” core (Au, Ag, AgOx, Pt, Pd, ZnOx, TiOx, Co, Ni, and FeOx) Nanodot “core” size is controlled by the amount of metal precursor salt PS P2VP Au PS blocks form a shell around the less solvable P2VP blocks to reduce energetically unfavorable interactions with the solvent In this paper: Water-in-oil micelle (toulene solvent) Polystyrene(x)-b-poly(2-vinylpyridine)(y) (PS(x)-b-P2VP(y)) Au core from chloroauric precursor (HAuCl4)

Cluster Pattern Characterization Low PDI MW tunes nanodot distance (max of 200 nm micelle) Low polydispersity permits regularity Higher MW decreased pattern quality and position precision (softness in shell)

Guided Self-Assembly (>250nm) Predefine topographies using photo or e-beam Spin-on concentrated micelle solution (capillary forces of evaporating solvent adheres them to sides) Micelles are pinned to the substrate by plasma (100W, 0.4mbar, 3min) Lift-off removes PR and micelles 2nd plasma treatment removes micelle polymer (100W, 0.4mbar, 20min) PS(1350)-b-P[2VP(Au0.5)](400) D = 8nm, L = 85nm

Cluster Aggregation Vary PR thickness Feature height (volume) defines cluster diameter Figure: e-beam 200nm features on 2um square lattice 800nm 500nm 75nm

Line Patterning Cylindrical micelle Formed if corona volume fraction < core PS(80)-b-P2VP(330) Length of several microns Substrate patterned with grooves & dipped in micelle solution 4nm line

Negative Patterning with E-beam Spin-on micelles Expose with e-beam (1KeV, 400-50,000 μC/cm2), 200um width Ultrasound bath + 30min plasma Electrons stabilize micelle on Si due to carbon species formed during exposure

Micelles on Electrically Insulating Films Glass substrate desired in biology E-beam requires conductive substrate Evaporate 5nm carbon layer

Mechanical Stability of Nano-Clusters Treated and unaffected by: Pirahna, acids, many bases, alcohols, ultrasonic water bath Hypothesis: edge formed by the substrate-cluster borderline is partly wetted by surface atoms during plasma treatment Thermal 800 C evaporated clusters but no migration occured

Conclusions Simple process for sub-10nm clusters and lines Block copolymer micelle size controls nano-cluster interspacing Micelle size controlled by monometer concentrations Micelles as masks for diamond field emitters F. Weigl et al. / Diamond & Related Materials 15 (2006)