Miri Park

Large area dense nanoscale patterning of arbitrary surfaces

We demonstrate a large-area fabrication of hexagonally ordered metal dot arrays with an area density of ∼1011/cm2. We produced 20 nm dots with a 40 nm period by combining block copolymer nanolithography and a trilayer resist technique. A self-assembled spherical-phase block copolymer top layer spontaneously generated the pattern, acting as a template. The pattern was first transferred to a silicon nitride middle layer by reactive ion etch, producing holes. The nitride layer was then used as a mask to further etch into a polyimide bottom layer. The metal dots were produced by an electron beam evaporation followed by a lift-off process. Our method provides a viable route for highly dense nanoscale patterning of different materials on arbitrary surfaces.

Lithography with a mask of block copolymer microstructures

Dense, periodic arrays of holes and troughs have been fabricated in silicon, silicon nitride, and germanium. The holes are approximately 20 nanometers (nm) wide, 20 nm deep, spaced 40 nm apart, and uniformly patterned with 3×1012 holes on a three inch wafer. To access this length scale, self-assembling resists were synthesized to produce either a layer of hexagonally ordered polyisoprene (PI) spheres or parallel cylinders of polybutadiene (PB) in a polystyrene (PS) matrix. The PI spheres or PB cylinders were then degraded and removed with ozone to produce a PS mask for pattern transfer by fluorine-based reactive ion etching. A PS mask of spherical voids was used to fabricate a lattice of holes and a mask of cylindrical voids was used to produce parallel troughs. This technique accesses a length scale difficult to produce by conventional lithography and opens a route for the patterning of surfaces via self-assembly.

Layer by layer imaging of diblock copolymer films with a scanning electron microscope

Abstract We present a novel technique which allows for the investigation of block copolymer microstructures on various substrates and at different depths. Using a low voltage, high resolution scanning electron microscope (SEM), we examined the topography and underlying morphology of poly(styrene)—poly(butadiene) diblock copolymer films. The internal morphology of the film was exposed for SEM imaging by using a non-selective fluorine-based reactive ion etching (RIE) technique. By controlling the depth of the RIE etch we removed the surface layer of poly(butadiene) and exposed the microphase separated structure underneath for SEM imaging. After obtaining SEM images of this exposed layer, we subsequently removed this layer with further RIE to obtain SEM images of the layer underneath. By continuing this procedure, we can obtain images of the microstructures as a function of depth with a 4-nm lateral resolution and a 10-nm depth resolution.

Investigation of Diblock Copolymer thin film Morphology for Nanolithography

The microphase separated morphology of diblock copolymers can be used to generate well-ordered nanometer scale patterns over a large area. To achieve this goal, it is important to understand and control the behavior of diblock copolymer thin films on substrates, which can differ from the bulk behavior. We have investigated the morphologies and ordering in thin polystyrene-polybutadiene (PS-PB) diblock copolymer films on bare silicon and silicon nitride substrates, and also on polymethylmethacrylate (PMMA) coated substrates. The PS-PB copolymers are synthesized to form, in bulk, PB cylinders or spheres in a PS matrix. In thin films (10–60 nm thick), prepared by spin-coating, we observe that the morphology and ordering of the microdomains are affected by strong wetting constraints and a reduced chain mobility on the substrate. The thinnest self-assembled layer of the copolymer films shows no in-plane microphase separation on both types of substrates. The PS blocks wet the PMMA substrates whereas the PB blocks wet the bare substrates as well as the air interface. Hence, different film thicknesses are necessary on the two types of substrates to obtain a uniform film of the first self-assembled cylindrical or spherical microdomain layer. The first layer of the cylindrical copolymer can vary from cylindrical to spherical morphology with a few nanometer decrease in film thickness. In the case of spherical PS-PB diblock copolymer films, we observe that the ordering of the microdomains is improved in the films on the PMMA substrates, compared to those on the bare substrates. We also demonstrate a successful transfer of the microdomain patterns to silicon nitride substrates by a reactive ion etching technique.