Monika Brzeska

High-resolution actinic defect inspection for extreme ultraviolet lithography multilayer mask blanks by photoemission electron microscopy

We report on the development and first experimental results of a “at wavelength” full-field imaging technique for defect inspection of multilayer mask blanks for extreme ultraviolet (EUV) lithography. According to the International Semiconductor Roadmap by Sematech, less than 5×10−3 defects per cm2 should be present on such multilayer mask blank to enable mass production of microelectronics using EUV lithography, thus fast high-resolution methods for mask defect inspection and localization are needed. Our approach uses a photoemission electron microscope in a normal incidence illumination mode at 13 nm to image the photoelectron emission induced by the EUV wave field on the multilayer mask blank surface. We show that by these means, buried defects in the multilayer stack can be probed down to a lateral size of 50 nm.

Magnetic Tunneling Junctions — Materials, Geometry and Applications

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grunberg, the Giant MagnetoResistance by Fert and Grunberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying standard thin film system with special regard to complex interdiffusion properties. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co2MnSi, where we obtain up to 100% TMR at low temperature. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm2. The last part will give a short overview on field programmable logic circuits made from magnetic tunnelling cells, where we demonstrate the clocked operation of a programmed AND gate.

Molecular Detection with Magnetic Labels and Magnetoresistive Sensors

For future lab-on-a-chip devices, compact and inexpensive detection units are required that directly translate the abundance of certain biomolecules into an electronic signal. By detecting specifically bound magnetic labels with magnetoresistive sensors, a versatile platform can be designed that fulfils those requirements and even enables on-chip manipulation of biomolecules by suitable magnetic gradient fields. Here, we present sensitive recognition of different types of magnetic labels by magnetoresistive sensors based both on giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR). Hybridization experiments show that our prototype magnetoresistive biosensor can detect complex DNA with a length of one thousand base pairs down to a concentration of 24 pM. A direct comparison of our magnetoresistive and a standard fluorescent detection method clearly shows the advantage and competitiveness of our approach.

Impact of geometry and material stacking on the properties of magnetic tunnelling junctions

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grunberg, the Giant MagnetoResistance by Fert and Grunberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying thin film system with special regard to the ferromagnetic electrodes. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm2. The last part will give a short overview on applications beyond the use of the tunnelling elements as storage cells in MRAMs. This concerns mainly field programmable logic circuits, where we demonstrate the clocked operation of a programmed AND gate. The second ‘unconventional’ feature is the use as sensing elements in DNA or protein biochips, where molecules marked magnetically with commercial beads can be detected via the dipole stray field in a highly sensitive and relatively simple way.