Stephen Y. Chou

Imprint of sub-25 nm vias and trenches in polymers

A nanoimprint process that presses a mold into a thin thermoplastic polymer film on a substrate to create vias and trenches with a minimum size of 25 nm and a depth of 100 nm in the polymer has been demonstrated. Furthermore, the imprint process has been used as a lithography process to fabricate sub‐25 nm diameter metal dot arrays of a 100 nm period in a lift‐off process. It was found that the nanostructures imprinted in the polymers conform completely with the geometry of the mold. At present, the imprinted size is limited by the size of the mold being used; with a suitable mold, the imprint process should mold sub‐10 nm structures with a high aspect ratio in polymers. The nanoimprint process offers a low cost method for mass producing sub‐25 nm structures and has the potential to become a key nanolithography method for future manufacturing of integrated circuits and integrated optics.

Imprint Lithography with 25-Nanometer Resolution

A high-throughput lithographic method with 25-nanometer resolution and smooth vertical sidewalls is proposed and demonstrated. The technique uses compression molding to create a thickness contrast pattern in a thin resist film carried on a substrate, followed by anisotropic etching to transfer the pattern through the entire resist thickness. Metal patterns with a feature size of 25 nanometers and a period of 70 nanometers were fabricated with the use of resist templates created by imprint lithography in combination with a lift-off process. With further development, imprint lithography should allow fabrication of sub-10-nanometer structures and may become a commercially viable technique for manufacturing integrated circuits and other nanodevices.

Sub-10 nm imprint lithography and applications

Nanoimprint lithography (NIL) is a new lithography paradigm that is based on deformation of a resist by compression molding rather than altering its chemical structure by radiation, and is designed to fabricate nanostructures inexpensively with high throughput. In this paper, we present significant new developments in achieving holes and dots with 6 nm feature size, 40 nm period on silicon, and 10 nm feature size, 40 nm period on a Au substrate. Moreover, we present an application of NIL to the fabrication of nanoscale compact disks (NanoCDs) of 400 Gbits/in/sup 2/ data density.

Fabrication of 5nm linewidth and 14nm pitch features by nanoimprint lithography

We report advances in nanoimprint lithography, its application in nanogap metal contacts, and related fabrication yield. We have demonstrated 5nm linewidth and 14nm linepitch in resist using nanoimprint lithography at room temperature with a pressure less than 15psi. We fabricated gold contacts (for the application of single macromolecule devices) with 5nm separation by nanoimprint in resist and lift-off of metal. Finally, the uniformity and manufacturability of nanoimprint over a 4in. wafer were demonstrated.

Deterministic hydrodynamics : Taking blood apart

We show the fractionation of whole blood components and isolation of blood plasma with no dilution by using a continuous-flow deterministic array that separates blood components by their hydrodynamic size, independent of their mass. We use the technology we developed of deterministic arrays which separate white blood cells, red blood cells, and platelets from blood plasma at flow velocities of 1,000 μm/sec and volume rates up to 1 μl/min. We verified by flow cytometry that an array using focused injection removed 100% of the lymphocytes and monocytes from the main red blood cell and platelet stream. Using a second design, we demonstrated the separation of blood plasma from the blood cells (white, red, and platelets) with virtually no dilution of the plasma and no cellular contamination of the plasma.

Imprint lithography with sub-10 nm feature size and high throughput

Abstract Nanoimprint lithography, a high-throughput, low-cost, nonconventional lithographic method proposed and demonstrated recently, has been developed and investigated. Nanoimprint lithography has demonstrated 10 nm feature size, 40 nm pitch, vertical and smooth sidewalls, and nearly 90° corners. Further experimental study indicates that the ultimate resolution of nanoimprint lithography could be sub-10 nm, the imprint process is repeatable, and the mold is durable. In addition, uniformity over a 15 mm by 18 mm area was demonstrated and the uniformity area can be much larger if a better designed press is used. Nanoimprint lithography over a non-flat surface has also been achieved. Finally, nanoimprint lithography has been successfully used for fabricating nanoscale photodetectors, silicon quantum-dot, quantum-wire, and ring transistors.

Ultrafast and direct imprint of nanostructures in silicon

The fabrication of micrometre- and nanometre-scale devices in silicon typically involves lithography and etching. These processes are costly and tend to be either limited in their resolution or slow in their throughput. Recent work has demonstrated the possibility of patterning substrates on the nanometre scale by ‘imprinting’ or directed self-assembly, although an etching step is still required to generate the final structures. We have devised and here demonstrate a rapid technique for patterning nanostructures in silicon that does not require etching. In our technique—which we call ‘laser-assisted direct imprint’ (LADI)—a single excimer laser pulse melts a thin surface layer of silicon, and a mould is embossed into the resulting liquid layer. A variety of structures with resolution better than 10 nm have been imprinted into silicon using LADI, and the embossing time is less than 250 ns. The high resolution and speed of LADI, which we attribute to molten silicons low viscosity (one-third that of water), could open up a variety of applications and be extended to other materials and processing techniques.

Patterned magnetic nanostructures and quantized magnetic disks

Nanofabrication, offering unprecedented capabilities in the manipulation of material structures and properties, opens up new opportunities for engineering innovative magnetic materials and devices, developing ultra-high-density magnetic storage, and understanding micromagnetics. This paper reviews the recent advances in patterned magnetic nanostructures, a fast-emerging field, including (1) state-of-the-art technology for patterning of magnetic nanostructures as small as 10 nm; (2) engineering of unique magnetic properties (such as domain structures, domain switching, and magnetoresistance) by patterning and controlling the size, shape, spacing, orientation, and compositions of magnetic materials; (3) quantized magnetic disks-a new paradigm for ultra-high-density magnetic storage based on patterned single-domain elements that have demonstrated a storage density of 65 Gb/in/sup 2/ (nearly two orders of magnitude higher than that in current commercial magnetic disks) and a capability of 400 Gb/in/sup 2/; (4) novel magnetoresistance sensors based on unique properties of magnetic nanostructures; (5) other applications of nanoscale patterning in magnetics such as the quantification of magnetic force microscopy (MFM) and a new ultra-high-resolution MFM tip; and (6) sub-10-nm imprint lithography-a new low-cost, high-throughput technology for manufacturing magnetic nanostructures.

Single‐domain magnetic pillar array of 35 nm diameter and 65 Gbits/in.2 density for ultrahigh density quantum magnetic storage

Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a period of 100 nm were fabricated. The density of the pillar arrays is 65 Gbits/in.2—over two orders of magnitude greater than the state‐of‐the‐art magnetic storage density. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. Each pillar can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method. A quantum magnetic disk scheme that is based on uniformly embedding single‐domain magnetic structures in a nonmagnetic disk is proposed.

Lithographically induced self-assembly of periodic polymer micropillar arrays

We observed, and believe it to be the first time, the self-formation of periodic, supramolecular (micrometer scale) pillar arrays in a thin, single-homopolymer film melt, which was originally flat on a plate. The self-formation was induced by placing a second plate (called a mask) a distance above the polymer film. The pillars, formed by rising against the gravitational force and surface tension, bridge the two plates. The pillar height is equal to the plate-mask separation, which is two to seven times the film’s initial thickness. If the surface of the mask has a protruding pattern (e.g., a triangle or rectangle), the pillar array can be formed only under the protruding pattern with the edge of the array aligned to the boundary of the mask pattern. We also discuss a model and novel applications of lithographically induced self-assembly.