Linus A. Fetter

Small‐area high‐current‐density Josephson junctions

Josephson junctions with areas of ∼10−9 cm2 and current densities of 105 A/cm2 are described. The junctions were patterned using a combination of optical lithography and oblique evaporation techniques. The junction width is limited by the lithographic resolution to about 1 μm. The junction length is determined essentially by the base‐electrode film thickness and can be as small as 1000 A. The moderate (∼10 Ω) normal resistances of these junctions combined with their short intrinsic RC times gives them potential for application in nonlatching Josephson logic and in quasiparticle mm‐wave mixers.

Mask technologies for soft-x-ray projection lithography at 13 nm.

We describe a variety of technologies for patterning transmissive and reflective soft x-ray projectionlithography masks containing features as small as 0.1 µm. The transmission masks fabricated for use at 13 nm are of one type, a Ge-absorbing layer patterned on a boron-doped Si membrane. Reflective masks were patterned by various methods that included absorbing layers formed on top of multilayer reflectors, multilayer-reflector-coating removal by reactive ion etching, and ion damage of multilayer regions by ion implantation. For the first time, we believe, a process for absorber repair that does not significantly damage the reflectance of the multilayer coating on the reflection mask is demonstrated.

Development of a laboratory extreme-ultraviolet lithography tool

The development of a laboratory EUV lithography tool based on a laser plasma source, a 10x Schwarzschild camera, and a magnetically levitated wafer stage is presented. Interferometric measurements of the camera aberrations are incorporated into physical-optics simulations to estimate the EUV imaging performance of the camera. Experimental results demonstrate the successful matching of five multilayer reflecting surfaces, coated to specification for a wide range of figure and incidence angle requirements. High-resolution, 10x-reduction images of a reflection mask are shown.

Mark topography for alignment and registration in projection electron lithography

We have studied two mark geometries for possible use in a projection e-beam lithography system using SCALPEL (scattering with angular limitation in projection electron lithography). These are V-grooves and vertically etched geometries, pedestals or trenches. We report results of measurements of backscattered electron (BSE) contrast form topographic marks of varying size and as a function of energy up to 100 kV. The marks were fabricated on silicon wafers. The measurements were taken both in a scanning electron microscope and in an experimental SCALPEL machine operating in focused probe mode. The V-grooves ranged from 1.0 to 30 micrometers wide. The vertical etched features ranged from 2 to 30 micrometers wide and 0.6 and 50 micrometers depth. The results depended not only on the feature width and depth, but also on whether the features were isolated or in line and space patterns. Using a BSE ratio of 1.05 as a criterion for acceptable contrast from an alignment mark, V-grooves and vertical etched features had acceptable contrast with exception of the smallest and shallowest features for both geometries.

OBSERVING ONE INTERFACE TRAP: LATTICE VERSUS ELECTRON TEMPERATURE

Ensemble averages of electron trapping at Si-SiO2 interfaces have long been studied in large devices containing many traps [1]. Now, with advanced microfabrication techniques, it is possible to make MOS transistors small enough to observe individual electron traps [2]. Here we describe some of the kinetics of electron capture and emission from a single trap.

Nonmetallic localization and interaction in one-dimensional (0.1 μm) Si MOSFETs

Abstract We have fabricated Si MOSFETs having parallel arrays of narrow (0.1 μm) conducting channels. We observe a divergent, nonmetallic decrease of conductance below 30 K that is in excellent quantitative agreement with the one-dimensional version of the combined theories for weak localization and interaction effects. We also observe structure in the conductance as a function of gate voltage that we attribute to random variations of the density of states, rather than the regular variations expected for simple one-dimensional quantization.

Nonlatching Josephson interferometer made with small‐area junctions

A 1:2:1 Josephson interferometer has been fabricated with small‐area, high–current‐density tunnel junctions. The short intrinsic RC times of these junctions result in device I‐V characteristics with reduced hysteresis suitable for use in nonlatching logic circuits. The control current for this interferometer was fed directly, and asymmetrically, into the base electrode. Critical current versus control current measurements indicate that this device has a current gain greater than unity. The interferometer described represents an exploratory study of circuit design incorporating low‐hysteresis junctions.

Characterization of the alignment system on a laboratory extreme ltraviolet lithography tool

A laboratory extreme ultraviolet ltihography tool (EUVL) has been assembled at Sandia National Laboratories. Its major components include a Schwarzschild camera with 0.1 micrometers resolution integrated with a laser plasma source and a magnetically levitated stage. Other subsystems are a grazing-incidence optical system to maintain focus, and a through-the- lens Moire alignment system for overlay. This exposure tool is being used to study integration issues for EUVL. Experiments have been performed to characterize the alignment systems performance. The measured sensitivity of the alignment system is 25 nm 3(sigma) .

Printability of substrate and absorber defects on extreme ultraviolet lithographic masks

This paper reports results from a study of defect printability for extreme ultraviolet lithographic masks (EUVL). Imaging experiments were preformed with an EUVL mask containing programmed defects. The mask contained defects of different sizes and locations with respect to the absorber patterns. Since an EUVL mask consists of absorber layer patterned above a multilayer-coated substrate, both substrate defects, located below the reflective coating, and absorber defects, located above the reflective coating, were included on the programmed defect mask. The absorber layer was patterned using a process previously described by Tennant et al. Imaging was performed using a 10X Schwarzschild camera operating at 13.4 nm with a numerical aperture of 0.08, corresponding to a Rayleigh resolution of 0.1 micrometers . This system has an effective exposure field of 0.4 mm diameter. Both positive-tone and negative-tone resists were used. Measurements of the defect-induced linewidth variations on the printed resist lines were performed with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Results show that substrate defects are more printable compared to defects of the same sizes located above the reflective coating. In addition, defects located in the center of a clear region in lines-and- space pattern are more printable compared to those located nearer to the absorber lines.

Electron-beam and x-ray lithographic characteristics of the optical resist ARCH

The multi-component, positive acting, chemically amplified deep-UV ((lambda) equals 248 nm) resist ARCH, has been evaluated for use in proximity x-ray and electron-beam lithography. Characterization of the x-ray lithographic response of ARCH resist using a pulsed laser point source ((lambda) equals 1.4 nm) proximity print stepper resulted in a process producing sub-0.20 micrometers features at a dose of 22 mJ/cm2. A time delay study was conducted in the helium environment of the x-ray exposure tool and the results indicate that a > 30 min delay period after exposure produced no change in the resist image profile. Electron- beam exposures using a JEOL JBX 5D-II tool operating at 50 KeV delineated patterns below 0.10 micrometers on silicon. The measured exposure sensitivity was in the range of 8-16 (mu) C/cm2. Time delay experiments performed in the vacuum environment of the e-beam exposure tool over a 15 hr. time period resulted in no line size variation. These results suggest that ARCH resist represents a common material platform for the various advanced lithography programs currently under investigation for fabrication of circuits having Advanced Lithography AL 51 1995-02-19|1995-02-24 SPIEs 1995 Symposium on Microlithography ML95 171399 Santa Clara, CA, United States Electron-Beam, X-Ray, EUV, and Ion-Beam Submicrometer Lithographies for Manufacturing V 2437 Process Control in X-Ray Lithography 1