R. Jonckheere

Magnetization reversal in patterned ferromagnetic and exchange-biased nanostructures studied by neutron reflectivity (invited)

We have measured the off-specular polarized neutron reflectivity of periodic arrays of micron-sized rectangular polycrystalline ferromagnetic Co bars and exchange-biased Co∕CoO bars, which were prepared by a combination of electron-beam lithography and evaporation techniques. The intensity of the first-order off-specular neutron satellite reflection was monitored as function of the magnetic field parallel to the long edge of the bars, allowing analysis of the magnetization reversal process using the four spin-polarized scattering cross sections. The neutron data are compared with calculations based on a micromagnetic simulation. The influence of shape anisotropy on the reversal mechanism is demonstrated.

Zero‐dimensional states in submicron double‐barrier heterostructures laterally constricted by hydrogen plasma isolation

The lateral dimensions of resonant tunneling AlGaAs‐GaAs double barrier heterostructures have been restricted by hydrogen plasma exposure. Ohmic contacts to the submicron diodes have been made by solid phase epitaxial growth of Ge on GaAs. The current‐voltage characteristics show a fine structure splitting that is inversely proportional to the lateral size of the diode. The results are interpreted as resonant tunneling through zero‐dimensional states in the quantum box confined by the AlGaAs barriers and a harmonic lateral confining potential.

Guided vortex motion in superconductors with a square antidot array

We have measured the in-plane anisotropy of the vortex mobility in a thin Pb film with a square array of antidots. Τhe Lorentz force, acting on the vortices, was rotated by adding two perpendicular currents and keeping the amplitude of the net current constant. One set of voltage probes was used to detect the vortex motion. We show that the pinning landscape provided by the square antidot lattice influences the vortex motion in two different ways. First, the modulus of the vortex velocity becomes angular dependent with a lower mobility along the diagonals of the pinning array. Second, the vortex displacement is preferentially parallel to the principal axes of the underlying pinning lattice, giving rise to a misalignment between the vortex velocity and the applied Lorentz force. We show that this anisotropic vortex motion is temperature dependent and progressively fades out when approaching the normal state.

Flux phases and quantized pinning force in superconductor with a periodic lattice of pinning centres.

Flux phases have been studied in superconducting Pb/Ge multilayers with a square lattice of submicrometre holes. Sharp peaks in the magnetic-field dependence of the critical current have been observed at integer Hm and rational Hk/l matching fields. At integer fields an artificial flux line crystal is formed, consisting of a stable square lattice of single or multiple flux quanta trapped by the holes. The existence of such a crystal leads to the quantization of the pinning force. New rational flux lines patterns at H = Hk/l, qualitatively different from those previously seen in superconducting networks, have been identified.

Extreme ultraviolet lithography at IMEC: Shadowing compensation and flare mitigation strategy

The extreme ultraviolet lithography (EUVL) program at IMEC is aimed to tackle many unsolved critical issues of EUV lithography as the technology moves towards production, by focusing specifically on tool, resist, and mask projects. Here, the authors describe the structure of the IMEC EUVL program and the status of the EUV alpha demo tool. In particular, they discuss their proposed strategies for flare mitigation and shadowing effect correction. They demonstrate how it is possible to implement an effective rule-based flare mitigation strategy. In addition, they propose a relatively simple methodology to fully compensate for shadowing pattern placement error and critical dimension bias.

Thin film interference effects in phase shifting masks causing phase and transmittance errors

Phase shifting masks have proven their potential to enhance resolution and depth‐of‐focus in optical lithography. Nevertheless, many questions still have to be solved, before the phase shifting concept can be introduced in production lines. Controllable mask fabrication is a major concern. This article addresses the influence of physical material properties and process steps in the attempt to fabricate phase shifting masks with acceptable phase shift and transmittance. Spectrophotometer measurements and computer simulations showed the need of matched refractive indices for all transparent materials in the reticle. Second, the sensitivity of the lithographic performance to these shifter deviations was investigated by aerial image simulations. These predicted a high sensitivity to phase errors, especially for negative resists. Using a negative tone top surface imaging resist process and a positive tone wet developed resist, experiments confirmed these predictions. Special attention was paid in finding an ac...

Enhanced vortex pinning by a composite antidot lattice in a superconducting Pb film

The use of artificial defects is known to enhance the superconducting critical parameters of thin films. In the case of conventional superconductors, regular arrays of submicron holes (antidots) substantially increase the critical temperature

VORTEX CONFIGURATIONS IN A PB/CU MICRODOT WITH A 2 X 2 ANTIDOT CLUSTER

{T}_{c}(H)

Matching effects in Pb/Ge multilayers with the lattice of submicron holes

and critical current

Experimental validation of full-field extreme ultraviolet lithography flare and shadowing corrections

{I}_{c}(H)