Imprint Lithography Templates Research Articles

Hydrogen silsesquioxane for direct electron-beam patterning of step and flash imprint lithography templates

The feasibility of using hydrogen silsesquioxane (HSQ) to directly pattern the relief layer of step and flash imprint lithography (SFIL) templates has been successfully demonstrated. HSQ is a spin-coatable oxide, which is capable of high resolution electron-beam lithography. Negative acting and nonchemically amplified, HSQ has moderate electron-beam sensitivity and excellent processing latitude. In this novel approach, 6 ×6 × 0.25 in.3 quartz photomask substrates are coated with a 60 nm indium tin oxide (ITO) charge dissipation layer and directly electron-beam written using a 100 nm film of HSQ. Direct patterning of an oxide relief layer eliminates the problems of critical dimension control associated with both chromium and oxide etches, both required processes of previous template fabrication schemes. Resolution of isolated and semidense lines of 30 nm has been demonstrated on imprinted wafers using this type of template. During this evaluation, a failure of the release layer to provide a durable nonstick surface on ITO was discovered and investigated. This problem was successfully remedied by depositing a 5 nm oxide layer over the patterned ITO/HSQ template.

Characterization of and imprint results using indium tin oxide-based step and flash imprint lithography templates

As compared to quartz relief structures currently employed, indium tin oxide-based (ITO-based) step and flash imprint lithography templates offer advantages in terms of electron-beam writing, scanning electron microscope inspection, and pattern transfer. The material properties of the ITO have been completely characterized, and data is presented for resistivity, crystal structure, transmission, stress, surface roughness, adhesion, composition, and etch characteristics. For a 600 Å annealed ITO film, the resistivity is approximately 3.5×102 Ω/sq and the optical transmission 77% at 365 nm. The atomic film composition was found to be 31.5% In, 4.3% Sn, and 64.2% O by x-ray photoelectron spectroscopy. When contrasted with SiO2 films, temperature programmed desorption data suggests that hydroxyl groups on the ITO surface bind H2O less strongly but are more abundant. Ultimate verification of compatibility was obtained by imprinting features into an etch barrier layer using an ITO-based template. The fidelity of 20 nm isolated and semi-isolated features, the smallest features present on the template, was successfully reproduced via the imprinting process.

Prediction of fabrication distortions in step and flash imprint lithography templates

Step and flash imprint lithography (SFIL) is an alternative approach for printing sub-100 nm features that relies on chemical and mechanical techniques to transfer patterns. The imprint process requires no projection optics and is performed at room temperature with low imprint pressures to reduce thermal and mechanical template distortions. Because imprint lithographies are 1× pattern transfer processes that preclude magnification corrections, the minimization of template distortions during fabrication and imprinting is critical. The processes and materials used in the fabrication of SFIL templates are similar to those used in the manufacturing of optical masks. The various process steps have been simulated using finite element techniques in order to predict the resulting pattern distortions. Two proposed template fabrication schemes were modeled, the resulting pattern distortions compared, and the error sources were quantified.

High resolution templates for step and flash imprint lithography

Step and flash imprint lithography (SFIL) is an attractive method for printing sub-100 nm geometries. Relative to other imprinting processes SFIL has the advantage that the template is transparent, thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, minimizing magnification and distortion errors. The purpose of this work was to investigate alternative methods for defining high resolution SFIL templates and study the limits of the SFIL process. Two methods for fabricating templates were considered. The first method used a very thin (<20 nm) layer of Cr as a hard mask. The second fabrication scheme attempts to address some of the weaknesses associated with a solid glass substrate. Because there is no conductive layer on the final template, scanning electron microscopy (SEM) and defect inspection are compromised. By incorporating a conductive and transparent layer of indium tin oxide on the glass substrate, charging is suppressed during SEM inspection, and the transparent nature of the final template is not affected. Using ZEP-520 as the electron beam imaging resist, features as small as 20 nm were resolved on the templates. Features were also successfully imprinted using both types of templates.