Jeffrey H. Baker

Template fabrication schemes for step and flash imprint lithography

Abstract 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. The purpose of this work is to investigate alternative processes for defining features on an SFIL template. The first method considered using a much thinner (

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 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, SEM and defect inspection are compromised. By incorporating a conductive and transparent layer of indium tin oxide (ITO) 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.

Characterization and Modeling of Metal/Double-Insulator/Metal Diodes for Millimeter Wave Wireless Receiver Applications

In this paper we present measurements, models, and circuit implementations for a new low cost, thin film, metal/double-insulator/metal (MIIM) based tunneling diode technology. The device technology uses two insulators to form a tunneling device with very high speed performance capability, and is potentially compatible with many substrate technologies. This technology can potentially reduce cost, size, and improve performance for applications associated with high-speed communications, automotive collision avoidance and navigation, and homeland security weapons detection. Measured results of DC, S-parameter, and responsivity measurements in the 60 GHz band will be presented, including unmatched responsivity at 60 GHz of over 1000 V/W at -20 dBm, which is competitive with detector diodes on GaAs or Sb-based materials. ADS-compatible non-linear models are developed and demonstrated, and an envelope detector design and results is presented.

Fabrication of multi-tiered structures on step and flash imprint lithography templates

Step and flash imprint lithography (SFIL) replicates patterns by using a transparent template with relief images etched into its surface. Recent work has examined alternative methods for template fabrication. One scheme incorporates a conductive and transparent layer of indium tin oxide (ITO) on the surface of the substrate. Features are defined on the templates by patterning a thin layer of PECVD oxide that is deposited on the ITO layer. A second method bypasses the oxide etch process by imaging a thin layer of hydrogen silsesquioxane (HSQ). By combining or iterating the two methods, it is possible to form multi-tiere, structures on a template. Two and three tier structures were fabricated on silicon wafers and templates. A two layer structure was fabricated on a quartz photoplate by patterning PECVD oxide and subsequently patterning a second tier using HSQ. The resulting relief structures were successfully replicated on wafers using SFIL.

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.

Spectroscopic ellipsometry measurements of thin metal films

Optical methods are used to determine the thickness of thin metal films, with emphasis on spectroscopic ellipsometry and transmission. We discuss the conditions where this is possible and how to determine the optical constants for the material. The determination of the thickness of each of two metals in a bimetallic stack is discussed. Finally, by measuring thickness with these methods and measuring weight gain, we determine the density of platinum deposited by evaporation and deposited by a simple sputter deposition method. Explicitly, one of the results is that the determined optical constants depend on the deposition method. This implies that, with only a few exceptions, one must determine the optical constants of the material of interest, and that it is inappropriate to use values from another source such as a handbook or from another investigator. The resulting optical constants in this work suggest that the microstructure of the platinum films from the two different methods will not be the same, and x-ray diffraction and sheet resistance measurements verify that this is the case. Specifically, the significantly lower extinction coefficient of the sputter-deposited films correlates with a higher sheet resistance.

New methods for fabricating step and Flash Imprint Lithography templates

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. The purpose of this work is to investigate alternative methods for defining features on an SFIL template. The first method used a much thinner (< 20 nm) layer of Cr as a hard mask. Thinner layers still suppress charging during e-beam exposure of the template, and have the advantage that CD losses encountered during the pattern transfer of the Cr are minimized. The second fabrication scheme addresses some of the weaknesses associated with a solid glass substrate. Because there is no conductive layer on the final template, 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 inspection, and the UV characteristics of the final template are not affected. Templates have been fabricated using the two methods described above. Features as small as 30 nm have been resolved on the templates. Sub-80 nm features were resolved on the first test wafer printed.

Effect of process parameters on the optical constants of thin metal films

In this study, we show that the optical constants of sputter-deposited chromium depend on the argon pressure used for the deposition. Higher argon pressure gives lower extinction coefficients. Sheet resistance measurements show that those materials with lower extinction coefficients also have lower conductivity. Whereas the argon pressure strongly affects the resulting optical constants of the film material, the choice of substrate material does not affect the resulting optical constants of the film.

Fabrication of a monolithically integrated multiple wavelength Fabry-Perot filter array using transparent etch stop layers for accurate wavelength determination

In this paper we describe a method of fabricating a Fabry-Perot filter array consisting of four distinct wavelengths using a stopping layer, which in turn is discriminately measured. Precise control of the oxide thickness is demonstrated by using reflectance to measure center wavelengths (CWL) between 645nm-822nm with full width half maximum (FWHM) values of 15 nm. These parameters are used to confirm good narrow band filter characteristics. The physical and chemical properties of an oxide layer converted from a silicon-carbon-nitride (SiCN) etch stop layer (ESL) is reported for both as-deposited and the resultant oxidized film. The filter array can be fabricated directly on top of silicon photo diodes, to form a complete multi-wavelength sensor system. Fabricating a multi-wavelength filter array using etch-stop layers can provide better thickness control and across wafer uniformity compared to a timed-etch approach.

Selective growth and electrical properties of single-walled carbon nanotubes

In this paper, we have studied selective area chemical vapor deposition (CVD) of single-walled carbon nanotubes (SWNTs) on substrates patterened with catalyst films consisting of an ultra-thin transition metal layer supported by an Al under-layer.