I. Kostic

MgB2 superconducting thin films on Si and Al2O3 substrates

Thin films of MgB2 superconductor were prepared by three different procedures on sapphire and silicon substrates. Boron thin films, ex-situ annealed in magnesium vapour, resulted in textured polycrystalline films with crystal dimensions below about 1000 nm, onset critical temperature Tcon near 39 K and width of phase transition about 1 K. Both, ex-situ and in-situ annealed co-deposited boron and magnesium thin films on sapphire and silicon substrates give smooth nanocrystalline films. DC properties of nanocrystalline MgB2 films co-deposited on silicon substrate reached Tcon = 33 K and zero resistance Tco = 27 K, the highest values received until now on Si substrates. In addition, microwave analyses prove the existence of superconducting parts of the film below 39 K. This result confirms the possibility to synthesise nanocrystalline superconducting MgB2 thin films on silicon substrate with critical temperature near 39 K, prepared by vacuum co-deposition of boron and magnesium films.Abstract Thin films of the superconductor MgB 2 were prepared by three different procedures on sapphire and silicon substrates. Boron thin films, ex situ annealed in magnesium vapour, resulted in textured polycrystalline films with crystal dimensions below about 1 μm, onset critical temperature T c on near 39 K and width of phase transition ΔT ⩽1 K. Both, ex situ and in situ annealed co-deposited boron and magnesium thin films on sapphire and silicon substrates give smooth nanocrystalline films. DC properties of nanocrystalline MgB 2 films co-deposited on silicon substrate reached T c on =33 K and zero resistance T c0 =27 K, the highest values received until now on Si substrates. In addition, microwave analyses prove the existence of unconnected superconducting parts of the film below 39 K. This result confirms the possibility to synthesize nanocrystalline superconducting MgB 2 thin films on silicon substrate with critical temperature near 39 K, prepared by vacuum co-deposition of boron and magnesium films.

Scanning proximal probes for parallel imaging and lithography

Scanning proximity probes are uniquely powerful tools for analysis, manipulation, and bottom-up synthesis. A massively parallel cantilever-probe platform is demonstrated. 128 self-sensing and self-actuated proximal probes are discussed. Readout based on piezoresistive sensors and bending control based on bimorph dc/ac actuations are described in detail.

Conformal AZ5214-E resist deposition on patterned (1?0?0) InP substrates

A draping technique was studied to deposit thin, visco-elastic AZ5214-E resist layers from a water surface over planar and patterned substrates. A visco-elastic AZ5214-E layer forms on the water surface when a drop of AZ5214-E makes contact with it. The drop spreads out within a fraction of a second because of a large positive difference in surface tension between water and AZ5214-E. The spreading mechanism lies in the ability of PGMEA (AZ5214-E liquid constituent) to form hydrogen bonds with water. We brought AZ5214-E drops to make contact with water at 20 ± 0.1 °C via adhesive forces to form AZ5214-E layers on the water surface of (1) circular and (2) square shapes. In case (1), the layers, formed from drops of V = 3 µl, had thickness t ≈ c ⋅ 4V/πΦ−2 for Φ c ⋅ 4V/πΦ−2 for larger Φ. In case (2), the layers had t ≈ a + bV for V between 7 and 12 µl on square-shaped water surfaces of constant area A = 34.5 mm × 34.5 mm. All layers exhibited microscopic waviness with an average thickness uniformity u ~ 91%, and submicron waviness with a root-mean-square roughness σ ~ 12 nm and a lateral correlation length ξ ~ 32 µm. AZ5214-E sheets coated conformally high mesa objects with sharp convex and concave edges: 61 µm high ridges confined to ~35°-inclined facets and 9 µm high ridges confined to negatively sloped facets. The draping technique can be used to deposit conformal AZ5214-E layers over non-planar substrates for non-planar device processing.

The application of secondary effects in high aspect ratio dry etching for the fabrication of MEMS

With increasing aspect ratio of etched features, secondary effects of plasma etching, such as RIE-lag or aspect ratio dependent etching (ARDE), become more important for etching processes for the fabrication of microelectromechanical systems (MEMS). Furthermore, the etching behavior, which is represented in the profile slope, sidewall surface quality and etching rate, depends not only on the aspect ratio of the etched trenches or features but also on their design and the pattern density. We discuss these effects and propose ways to use them in order to expand the variability of etching processes and to overcome their disadvantages.

Automatic VIS- near IR laser refractometer

This work presents a simple automatic VIS-IR laser refractometer, based on a critical-angle method. Its experimental error is smaller than 6×10−4 within the range of 1.32–1.47. Such precision of the refractometer is sufficient for the most industrial applications, for environmental protection, structural analysis, investigation of new materials, etc. Spectral refractive index measurements of different liquids are led and the calculated dispersion coefficients are reported.

Evaluation and fabrication of AFM array for ESA-Midas/Rosetta space mission

The MIDAS (Micro-Imaging Dust Analysis System) experiment is dedicated to the micro-textural and statistical analysis of cometary dust particles. The instrument is based on the technique of atomic force microscopy. The comparative simplicity and robustness of the technique lends itself to advanced space applications. The instrument is considered as essential for this mission since, for the first time, it has the capability of three-dimensional imaging of interplanetary and pristine cometary particles in the manometer to micrometer range. In this paper we describe our effort to evaluate and fabricate the AFM arrays for the ESA-Midas/Rosetta space mission.

Fabrication of a vector Hall sensor for magnetic microscopy

We have developed a micromachined Hall sensor for scanning the entire magnetic field vector whose active dimensions are an order of magnitude smaller (∼5 μm) than the smallest existing vector field sensor. It is realized by patterning three Hall probes on the tilted faces of epitaxy-overgrown GaAs-based pyramidal-shaped mesa structures. Data from these “tilted” Hall probes are used to reconstruct the full magnetic field vector.

Some peculiarities of resist-profile simulation for positive-tone chemically amplified resists in electron-beam lithography

In the present work, we numerically modeled the processes of exposure and development of the CAMP6 chemically amplified resist during electron-beam lithography. The radial distributions of the absorbed electron energy in the resist for a zero-width δ-function 30keV electron beam are obtained by Monte Carlo simulation. These distributions (discrete data) are approximated by an analytical function (sum of double Gaussian and an exponential function). The values of the parameters of the function are calculated using an original Monte Carlo technique, and their dependencies on the resist thickness (d=100, 200, 600, 1000, and 1500nm) at two resist depths are presented. Using these parameters’ values, we performed a computer simulation of the process of developing the resist taking into account its peculiarities due to the complicated mechanism of resist removal from soluble resist areas. We obtained profiles at various development times of a single 100nm line.

Reactive ion etching with end point detection of microstructured Mo/Si multilayers by optical emission spectroscopy

Abstract Reactive Ion Etching (RIE) of Mo/Si multilayers (MLs) with double layer thicknesses of about 10 nm and total layer thicknesses between 80 nm and 300 nm prepared by electron beam deposition onto Si or oxidized Si substrates was investigated in a fluorine based plasma. Patterns with line widths in the range of 200 nm to several microns produced by e-beam- and UV-lithography were transferred into the MLs. For this application it is necessary to stop the etching process just after the ML is totally removed. For end point detection optical emission spectroscopy was used. The plasma was analyzed by optical emission spectroscopy and a significant drop of the atomic fluorine concentration at the multilayer/substrate interface was observed. An algorithm was developed to stop the etching process at the end point. AFM and TEM measurements show that the ML is totally removed and an over-etching of less than 6 nm occurs.

Advanced patterning techniques for nanodevice fabrication

The key elements in the fabrication of future devices are lithography and pattern transfer. The continuous advances in miniaturization and increasing integration densities are a direct result of improved lithographic resolution and overlay accuracy. Electron beam direct write and e-beam projection lithography are potential candidates for the mass production of microelectronic devices with critical dimensions below 100 nm. To realize these nanometer patterns by this technology, the performance of exposure tools and resist materials should be increased. In this paper, the method of direct write e-beam lithography is demonstrated and critical issues are discussed.