Mark D. Morgan

Application of optical filters fabricated by masked ion beam lithography

Masked ion beam lithography (MIBL) was employed to fabricate optical filters as a critical component of an energy conversion system which utilizes semiconductor photovoltaics. This article will describe the operation and novel application of these devices and the MIBL pilot production line being facilitized. The conversion concept, thermophotovoltaics (TPV), when coupled with these MIBL produced bandpass filters, is capable of converting heat to electrical power with >20% conversion efficiency. The EDTEK TPV filter is based on a high density array of slotted antenna elements patterned into a single layer of thin gold film.

A proximity ion beam lithography process for high density nanostructures

Image contrast in proximity ion beam lithography is limited by scattered ions which enter the opaque regions of the mask and exit through the sidewalls of the mask windows. The scattering angles are widely distributed resulting in a ‘‘proximity effect’’ whose range is on the order of the mask‐to‐wafer gap. This problem becomes more severe with increasing pattern density and sets the resolution limit for high density patterns such as interdigital transducers. The only way to counteract this effect is to limit the ion range to a fraction of the mask thickness so that the scattered ions can be recaptured by adjacent sidewalls. This article explores the dependence of image contrast on resolution, pattern density, and beam energy in proximity ion beam lithography. Patterns with feature sizes in the range from 20 to 50 nm and 0.4 μm pitch have been printed with a linewidth change of only 3 nm for a 10% change in dose.

Reactive ion etching of silicon stencil masks in the presence of an axial magnetic field

A reactive ion etching (RIE) system with a magnetic field, mainly parallel to the dark space electric field on the etch electrode, is described. This axial‐field RIE system has been used with a molecular bromine (Br2) plasma to fabricate Si stencil masks for ion beam lithography. Silicon dioxide (SiO2) films were used as masking layers, and the etching process was optimized for smallest silicon wall angle at a constant Si/SiO2 selectivity of 50. The optimized process was used to fabricate 0.75–1.0‐μm‐thick Si masks with sub‐50 nm resolution. Over a thickness of 0.75 μm, change in linewidth was found to be less than 10 nm, corresponding to a wall angle of less than 0.2° or 3 mrad.

Radioisotope thermophotovoltaic power system utilizing the GaSb IR photovoltaic cell

Unique challenges to space power systems engineers are posed by the special requirements of lunar and planetary surface missions as well as deep space missions where solar photovoltaic conversion is not a viable option. An approach to these problems is the utilization of radioisotope decay to generate infrared (IR) power (heat) which is converted to useable electric power via the application of IR photovoltaic (PV) technology. This paper presents the progress status of an innovative concept for such a radioisotope thermophotovoltaic (RTPV) power system. Results for IR photovoltaic cell development indicate near theoretical PV performance can be obtained and computer simulation of these cells operating within an RTPV system yield an overall system efficiency of ∼13%. Neutron testing of the TPV cells have demonstrated an approximate 20% power reduction at the end of a 10 year mission lifetime. In addition, the results of a proprietary modification of the isotope heat source will be shown which is predicted ...

Rapid prototyping of infrared bandpass filters using aperture array lithography

We demonstrate the prototyping of infrared bandpass filters, which consist of cross-shaped openings in a thin gold film, using ion beam aperture array lithography. In the lithography process, a stencil mask containing a periodic array of square apertures is irradiated by a broad beam of helium ions. The ions that pass through the openings expose the resist on a substrate that is placed in close proximity and cross-shaped filter structures are printed by moving the stage underneath the substrate, thus allowing for rapid formation of periodic patterns. We have fabricated filter patterns with peak transmittance ranging from 53% to 67% at wavelengths between 1.2 and 1.3μm that exhibit high reflectance for longer wavelength radiation. The prototyping throughput for masks with 2μm pitch patterns was about 2cm2∕h. The spectral performance of the prototyped filters was measured. Large-area, second-generation masks with 667nm pitch had a lithography throughput of 300cm2∕h and were used to print filter patterns of ...