kV E-beam Research Articles

Optimizing Josephson Junction Reproducibility in 30 kV E-Beam Lithography: An Analysis of Backscattered Electron Distribution.

This paper explores methods to enhance the reproducibility of Josephson junctions, which are crucial elements in superconducting quantum technologies, when employing the Dolan technique in 30 kV e-beam processes. The study explores the influence of dose distribution along the bridge area on reproducibility, addressing challenges related to fabrication sensitivity. Experimental methods include e-beam lithography, with electron trajectory simulations shedding light on the behavior of backscattered electrons. Wedescribe the fabrication of various Josephson junction geometries and analyze the correlation between the success rates of different lithography patterns and the simulated distribution of backscattered electrons. Our findings demonstrate a success rate of up to 96.3% for the double-resist 1-step low-energy e-beam lithography process. As a means of implementation strategy, we provide a geometric example that takes advantage of simulated stability regions to administer a controlled, uniform dose across the junction area, introducing novel features to overcome the difficulties associated with fabricating bridge-like structures.

Junction fabrication by shadow evaporation without a suspended bridge

We present a novel shadow evaporation technique for the realization of junctionsand capacitors. The design by e-beam lithography of strongly asymmetricundercuts on a bilayer resist enables in situ fabrication of junctions and capacitorswithout the use of the well-known suspended bridge (Dolan 1977 Appl. Phys.Lett. 31 337–9). The absence of bridges increases the mechanical robustnessof the resist mask as well as the accessible range of the junction size, from10 − 2 µm2 to more than104 µm2. We havefabricated Al/AlOx/Al Josephson junctions, phase qubit and capacitors using a 100 kV e-beam writer. Althoughthis high voltage enables a precise control of the undercut, implementation using aconventional 20 kV e-beam is also discussed. The phase qubit coherence times, extractedfrom spectroscopy resonance width, Rabi and Ramsey oscillation decays and energyrelaxation measurements, are longer than the ones obtained in our previous samplesrealized by standard techniques. These results demonstrate the high quality of the junctionobtained by this bridge-free technique.

Cathodoluminescent Properties of Sol-Gel Derived Gd<sub>2</sub>O<sub>3</sub>:Eu Thin-Film Phosphors on Sapphire Substrates

Gd 2 O 3 :Eu thin-film phosphors were fabricated on sapphire substrates using a simple Pechini-type sol-gel process. The films were annealed at various temperatures between 700 and 1200°C for 2 hours in air after deposition. The sol-gel process enabled the synthesis of efficient Gd 2 O 3 :Eu thin-film phosphors with good optical properties, high crystallinities and smooth morphologies and a thickness of 1.5 μm. The Gd 2 Ο 3 :Eu thin film annealed at 1200°C had a thickness of 1.5 μm and exhibited a CL luminance of-124 cd/m 2 and CIE coordinates of (0.64, 0.35) under 5 kV e-beam excitation at 10 μA. A significant improvement (by a factor of-10) was found in the aging characteristics of the Gd 2 O 3 :Eu thin-film phosphors under 5 kV CL excitation (an electron dose of 10 μA/cm 2 DC for 1100 min) compared to those of commercialized Y 2 O 3 :Eu powder phosphors.

Optical properties of sol–gel derived Y 2O 3:Eu 3+ thin-film phosphors for display applications

Y 2O 3:Eu 3+ thin-film phosphors were grown on sapphire substrates using a simple sol–gel process. The films were annealed at various temperatures between 700 and 1400 °C for 2 h in air after deposition. The optical properties, morphologies and crystallographic structures of the Y 2O 3:Eu 3+ thin films are characterized and discussed. The sol–gel process enabled the synthesis of efficient Y 2O 3:Eu 3+ thin-film phosphors with good optical properties, high crystallinities and smooth morphologies. The cathodoluminescence (CL) and photoluminescence properties of these Y 2O 3:Eu 3+ thin films depend principally on the film thickness and annealing temperature. The Y 2O 3:Eu 3+ thin film annealed at 1200 °C had a thickness of ∼ 1.7 μm and exhibited a CL luminance of ∼ 150 cd/m 2 and Commission International del'Eclairage coordinates of (0.64, 0.35) under 5 kV e-beam excitation at 5 μA/cm 2. A significant improvement (by a factor of about 2) was found in the aging characteristics of the Y 2O 3:Eu 3+ thin-film phosphors under 5 kV CL excitation compared to those of powder phosphors.

Electron-beam induced initial growth of platinum films using Pt(PF3)4

Using an organometallic precursor, tetrakis(trifluorophosphine)platinum [Pt(PF3)4], electron-beam induced deposition of Pt thin films on a Cr-coated Si(100) substrate was investigated. Based on Auger electron spectroscopy, the Pt content reached 60 at. % for a 3 kV e-beam flux of 2.1×10−2 A cm−2, a precursor pressure of 2×10−5 Torr, and a substrate temperature of 80 °C. As the flux ratio (e-beam/precursor) increased above the optimized value of 10, the rate shifted from control by the e-beam flux to the precursor flux. The phosphorus content was reduced by adding O2.

Chemically Amplified Resist Approaches for E-beam Lithography Mask Fabrication

AbstractThis paper describes stable, high sensitivity (5-10 μC/cm2 at 50 kV) e-beam resist systems utilizing chemical amplification suitable for mask fabrication for device generations below 100 nm. In particular, two resist systems with improved performance for mask fabrication developed in a joint program by Etec, IBM and Shipley will be described: a Si- doped version of the IBM KRS-XE resist (now commercially available) developed at IBM Research, and a new MANA resist developed at Shipley. Commercialization issues for mask e-beam resists also will be discussed.

1 kV resist technology for microcolumn-based electron-beam lithography

The objective of this article is to evaluate low-voltage electron-beam (e-beam) resists suitable for direct write on wafer and mask fabrication in the sub-100 nm regime. Low kV exposure provides the advantages of high sensitivity, reduced charging, and a lack of proximity and heating effects. However, a major concern is whether a low-voltage e-beam is capable of patterning sub-100 nm features in resist with a thickness substantially greater than the penetration range of the electrons. At 1–2 kV, the penetration range is between 30 and 100 nm, while typical resist thickness is >200 nm. In an effort to overcome this limitation, thin film layer techniques are evaluated for low kV e-beam exposure. Preliminary 1 kV results on two thin imaging schemes, the bilayer CARL process and top surface imaging with NTS-4 resist, are reported here. Important results achieved are high sensitivity (1–2 μC/cm2), high contrast (γ>10), high resolution (70 nm in ∼300 nm thick resist), good critical dimension (CD) linearity (range=7 nm, mean=8 nm), large exposure latitude (ΔCD/Δdose=0.5 nm/% change in dose), and absence of proximity effects.

Comparison of negative resists for 100 nm electron-beam direct write and mask making applications

A new negative tone, chemically amplified deep ultraviolet resist, Shipley UVN-2, and a negative electron-beam (e-beam) resist, Sumitomo NEB-22A5, have been investigated for use in direct write and mask fabrication applications. The Sumitomo NEB-22A5 material has shown superior high resolution capabilities with excellent exposure latitude for both isolated and line/space features. Line and space gratings and isolated lines of 100 nm were resolved in a 400 nm film of NEB-22 using a 40 kV e-beam exposure tool. UVN-2 resist has shown resolution down to 150 nm line/space features with excellent etch selectivity and postexposure bake critical dimension control. Both resists perform well with respect to delay stability before and after exposure. This article will discuss the process development of the two resists and compare the performance characteristics including resolution, exposure latitude, linearity, and etch selectivity in various chemistries. Effects relating to pre-exposure and postexposure bake delay will also be considered because of the susceptibility of many chemically amplified resists to contaminants in the air. Finally, the application of these resists for both direct write and advanced mask making applications will be discussed.

High-resolution lithography with a vacuum STM

The scanning tunneling microscope (STM) is demonstrated to be a useful low-energy e-beam lithographic tool and a valuable probe of resist materials. Lithography with a vacuum STM and a 10 nm 50 kV e-beam has been performed on identically prepared and processed films of a state-of-the-art high-resolution negative resist (SAL-601 from Shipley). On bulk substrates (Si and GaAs), resist films up to 50 nm thick have been patterned, developed and observed in a scanning electron microscope. A resist thickness of 50 nm is sufficient to withstand a reactive ion etch. On Si, the minimum feature size observed with the 50 kV e-beam was 95 nm. In contrast, the STM lithography defined features observed in the developed resist to have linewidths down to 23 nm. The variation of feature size with exposure dose, exposure voltage and resist thickness has been studied. The STM lithography has shown that SAL-601 is inherently capable of sub 25 nm resolution and that low voltage e-beam lithography can produce smaller minimum feature sizes than lithography with a 10 nm 50 kV e-beam.

Investigations of undeveloped e-beam resist with a scanning tunneling microscope

A scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used to observe the latent image written with a focussed 50 kV e-beam in a polydiacetylene negative resist. The ability to study the latent image in the undeveloped resist allows the resolution degradation caused by the exposure process to be separated from that occurring during the resist development step. The minimum linewidth observed in the resist is close to 80 nm in both the developed and undeveloped resist. This linewidth is significantly greater than that expected on the basis of the 50 kV e-beam probe size, electron scattering, and secondary electrons. The results indicate that the resolution degradation occurs during the exposure process rather than during post-exposure processing. This implies that swelling during development is not the critical problem it is with other negative resists. The quality and accuracy of the STM observations is discussed together with descriptions of related surface modifications created in situ with the STM.

50 nm line fabrication in 0.5 μm PMMA film on silicon substrates with a 20 kV e-beam

With an isopropyl alcohol (IPA) development, 50–100 nm lines are fabricated in 0.5 μm PMMA film on silicon substrates with a 20 kV e-beam. The slope of solubility rate in an IPA development is 10.2 at a high electron dose. A higher contrast and an improved resolution are obtained by using an IPA development.

E-Beam Spreading and Resulting Field Variations in CO2 Laser Plasmas

large optical cross sections using e-beam controlled discharges in CO2 and very recently6 with uv initiation of self-sustained discharges. Principal differences between these two methods are in the spatial variations of electron production for the e-beam and the difficulty in obtaining large optical aperture without arc development for the self-sustained discharge. This paper presents a closed form method for rapidly analyzing and predicting e-beam controlled discharges while accounting for the spatial variations of electron production. Predictions obtained from this method are compared to experimental measurements. The e-beam controlled discharge7'10 has been analyzed for CO2 gas mixtures at 1 atm pressure. Previous analytical methods required considerable computer time because they were based on Monte Carlo7'13 calculations for electron scattering to determine spatial source functions of electron energy disposition. Fixed sets of laser cavity configurations, gas compositions, and densities have been successfully modeled. A new and fast computational method for describing the spatial variations of electron energy disposition in e-beam controlled discharges has been developed. Primary electron range enhancement or de-enhancemen t effects are included, but backscattering and electron-runaway effects are neglected. Spatial variations in the resulting drift current density and applied field are easily determined using the streamtube continuity approximation.9 Experiments using a 10-1 discharge volume controlled by a 0.4 A/cm2, 175 kV ebeam were conducted to derive data for correlation. Experimental values of the effective recombination rate, the e