Mark W. Hart

Nanoscale patterning of magnetic islands by imprint lithography using a flexible mold

A nanomolding process for producing 55-nm-diameter magnetic islands over 3-cm-wide areas is described. A master pattern of SiO2 pillars is used to form a polymeric mold, which is in turn used to mold a photopolymer resist film. This latter film is used as a resist for etching SiO2, yielding a pattern of pillars. Finally, an 11-nm-CoPt multilayer is deposited. Magnetic force microscopy reveals that the film on top of each pillar is a magnetically isolated single domain that switches independently.

Magnetic and recording properties of Co/Pd islands on prepatterned substrates

Magnetically isolated single domain islands with perpendicular anisotropy have been prepared by depositing Co/Pd multilayer films on prepatterned sub-50 nm SiO2/Si islands. The island arrays were fabricated by both direct write electron beam lithography and nanoimprinting. Nanoimprinting allows the creation of large area, 4 mm×4 mm, samples appropriate for characterization by conventional measurement techniques. Magnetic force microscopy and vibrating sample magnetometry showed that the reversal behavior of the patterned islands is quite different from that of the continuous films with a large increase in both switching field and switching field distribution. Recording on island arrays with a periodicity of 100 nm, produced from prepatterned substrates, was demonstrated using a quasistatic tester.

Patterning ∼20nm half-pitch lines on silicon using a self-assembled organosilicate etch mask

Lines of ∼20nm half-pitch were generated on silicon surface using a self-assembled organosilicate nanostructure. A mixture of a poly(styrene-b-ethylene oxide) (PS-b-PEO) with an organosilicate precursor that is selectively miscible with PEO was used to create lamellar phase whose orientation was controlled perpendicular to the surface by tuning the surface energy of substrates. Thermal cross-linking of the organosilicate precursor followed by thermal decomposition of the PS-b-PEO leaves a robust organosilicate line pattern of sublithographic length scales on the surface. Line patterns on silicon substrate were created by transferring this self-assembled pattern into the underlying silicon substrate using anisotropic plasma etching.

5.2: High Performance Electrophoretic Displays

Electrophoretic (EP) displays have been proposed as a route to “paper-like” displays. A high performance EP display designed by IBM will be described along with aspects of electrode design, display characteristics, particle selection, and particle stabilization.

Vinyl ether resist system for UV-cured nanoimprint lithography

Cationic curing of vinyl ethers for step-and-flash nanoimprint lithography is described. Photochemical acid generators for use in the vinyl ether formulation were carefully selected on the basis of their solubility in neat lipophilic vinyl ether. Our favorite acid generators include diphenyltolylsulfonium triflate, CGI261, CGI1905, CGI1906, and CGI1907. The CGI1900 series is sensitive to i-line irradiation while the former two can be sensitized to 365 nm radiation by adding 9-anthracenemethanol. Phenothiazine is also an effective i-line sensitizer of the sulfonium salt. A major problem associated with the vinyl ether curing material is poor storage stability and the formulation rapidly solidifies at room temperature. However, it has been found that anthracenemethanol can stabilize the sulfonium salt and CGI formulations against the aging. Phenothiazine extends the shelf life of the sulfonium salt system but violently reacts with the CGI PAGs. Volatility of the vinyl ethers was measured by thermogravimetric analysis at room temperature. Photochemical curing of the formulations was investigated by FT-IR and also by differential scanning calorimetry (DSC) equipped with a UV lamp. The photo-DSC analysis was particularly useful in ascertaining the cure kinetics and the efficacy of the sensitization. Preliminary imprint experiments successfully printed 50 nm dense features.

Self-aligned self-assembled organosilicate line patterns of ~20nm half-pitch from block-copolymer mediated self assembly

We report the formation of robust organosilicate line patterns of ~20nm half-pitch on surfaces from the self-assembled lamellar phase of a diblock copolymer of polystyrene and poly(ethylene oxide), PS-b-PEO, and an oligomeric organosilicate precursor mixtures. We could control the orientation and alignment of microdomains of this hybrid to the same degree of the thin films of organic block copolymers. By controlling the surface energy of substrates using dense organosilicate, the perpendicular orientation of lamellae to the surface was achieved. Topographic prepatterns were generated by E-beam lithography and used for alignment of the line patterns from lamellar phase. Upon removing the organic component (i.e. PS-b-PEO) by thermal treatment, the organosilicate microdomains remain as periodic line patterns with global alignment on surfaces. This method gives well-aligned silicon-containing line patterns with sublithographic length scales on surface. The self-assembled organosilicate line patterns were successfully transferred into underlying silicon substrate using anisotropic plasma etching.

Space-based, multi-wavelength solid-state lasers for NASA's Cloud Aerosol Transport System for International Space Station (CATS-ISS)

Fibertek has designed and is building two space-based lasers for NASA’s CATS-ISS mission. This space-based lidar system requires lasers capable of provide 4-5 kHz output at 1064 nm, 532 nm and 355 nm with each wavelength having ~2-2.5 mJ pulse energy. The lasers will be based on the ISS for a mission lasting up to 3 years.

Magnetic recording on patterned media

The storage density of conventional thin film recording media, where each bit is comprised of several hundred grains, is limited by superparmagnetism, since thermal excitation of the magnetization may degrade recorded information. Patterned magnetic media where magnetic bits are recorded on pre-defined, single-domain islands is one of the proposed approaches for extending magnetic storage densities beyond the limit set by thermal decay for conventional media. In this paper we discuss writing and reading from single domain magnetic islands with a conventional recording head, compare the performance to unpatterned media, and present a possible manufacturable approach to achieving run-scale patterning over disk sized areas.

Controlling linewidth roughness in step and flash imprint lithography

Despite the remarkable progress made in extending optical lithography to deep sub-wavelength imaging, the limit for the technology seems imminent. At 22nm half pitch design rules, neither very high NA tools (NA 1.6), nor techniques such as double patterning are likely to be sufficient. One of the key challenges in patterning features with these dimensions is the ability to minimize feature roughness while maintaining reasonable process throughput. This limitation is particularly challenging for electron and photon based NGL technologies, where fast chemically amplified resists are used to define the patterned images. Control of linewidth roughness (LWR) is critical, since it adversely affects device speed and timing in CMOS circuits. Imprint lithography has been included on the ITRS Lithography Roadmap at the 32 and 22 nm nodes. This technology has been shown to be an effective method for replication of nanometer-scale structures from a template (imprint mask). As a high fidelity replication process, the resolution of imprint lithography is determined by the ability to create a master template having the required dimensions. Although the imprint process itself adds no additional linewidth roughness to the patterning process, the burden of minimizing LWR falls to the template fabrication process. Non chemically amplified resists, such as ZEP520A, are not nearly as sensitive but have excellent resolution and can produce features with very low LWR. The purpose of this paper is to characterize LWR for the entire imprint lithography process, from template fabrication to the final patterned substrate. Three experiments were performed documenting LWR in the template, imprint, and after pattern transfer. On average, LWR was extremely low (less than 3nm, 3σ), and independent of the processing step and feature size.

Impact of curing kinetics and materials properties on imprint characteristics of resists for UV nano-imprint lithography

UV curable resist formulations for nanoimprint must satisfy criteria for cure rate, volatility, viscosity, cohesion of the cured material and release from the template in addition to being successfully imprintable. We describe an investigation of the properties of a series of formulations comprising polyhedral oligomeric silsesquioxane and selected diluents as candidates for imprintable dielectrics. Although all have low viscosity and volatility and are successfully imprinted, significant variations in cure rate, mechanical and adhesion properties with resist composition are found. The trends observed are not all predictable from the literature, indicating that formulation optimization for this application requires a focus on the fundamentals of both materials and processes.