Alexander Thesen

Two-dimensional dopant profiling of ultrashallow junctions by electron holography

Electron holography using a transmission electron microscope equipped with a Moellenstedt biprism has emerged as a viable technique for creating two-dimensional voltage maps of semiconductor devices. We are presenting an introduction to this dopant profiling method. Practical details are given on sample preparation, instrumentational considerations, and data interpretation.

Holographic voltage profiling on 75 nm gate architecture CMOS devices

Voltage profiles of the source-drain region of a CMOS transistor with 75nm gate architecture taken from an off-the-shelf Intel PIII processor are presented. The sample preparation using a dual beam system is discussed as well as details of the electron optical setup of the microscope. Special attention is given to the analysis of the reconstructed holograms.

Soft electron beam etching for precision TEM sample preparation

Electron-beam-stimulated etching has been investigated as a clean, alternative method for nanoscale selective processing. Primarily fluorine-based precursors have been used to etch a variety of technologically relevant materials. Empirical data reveals that with decreasing the electron beam energy increases the material removal rate, however the effective beam width increases. Both of these observations are consistent with the fact that cross-sections for electron-gas scattering increases with decresaing beam energy. Monte Carlo models of the electron-gas and electron-solid interactions have been performed to better udnerstand the fundamentals of the process. Finally, specific application to soft transmission electron microscopy sample preparation is made.

Low-voltage-point source microscope for interferometry

Conventional scanning electron microscopes are now close to the limit of their performance for tasks such as the metrology of sub-micron design rule devices. In order to overcome these limits we have designed, and are presently testing, a low voltage point source microscope operated with a nanotip field emitter and without any electron optical lenses. The microscope is designed such that can be operated in the transmission mode as well as in a reflection mode. The ultra-sharp field emitter delivers emission currents of several nanoamps at energies less than 100 eV. The magnification of the object wave is achieved by placing the specimen in the divergent electron beam from the nanotip and observing the object wave using a microchannel plate (MCP) at a great distance from the sample. Images obtained that way are out of focus images. As no lenses are present a special procedure for scaling the magnification has been developed. Since electrons from a point source are highly coherent the out of focus images of the sample are interferograms. Electrons diffracted at an edge of the specimen cause Fresnel fringes in the image plane. An electrically charged holey carbon foil acts in the same way on the electrons as the Youngs double slit experiment and results in an interference pattern consisting of parallel fringes. A comparison between the transmission mode and the reflection mode shows great similarities with respect to the magnification and the interference pattern. An electron gun needed in the transmission mode is the most important difference between the two modes of operation. The experimental results at a reflection of 45 degrees are in good agreement with our simulation. Following our simulations a reflection angle of 90 degrees is most promising for easiest image interpretation.

Advances In Variable Pressure Imaging and Detection

The variable pressure scanning electron microscopy (VPSEM) has gained considerable interest since its commercial introduction more than 30 years ago [1]. Unlike a conventional SEM, which functions only in high vacuum, the VPSEM can be operated under a gas pressure in the specimen chamber. This permits observation of non-conductive samples without coating, as well as outgassing specimens, which are normally not compatible with high vacuum. However, due to the skirt effect [2] of the primary electron beam, resolution of a VPSEM is usually significantly reduced compared to a conventional SEM. Furthermore the VPSEM is also particularly troublesome for EDS applications, because additional X-ray signal is produced by the electron skirt. In this contribution we will introduce the newly developed VP implementation of next-generation Zeiss SEM, which features not only a very restricted skirt effect under high gas pressures, but also enables the detection of pure secondary electron (SE) signal using all Zeiss Gemini technology in-lens detectors.

The New Zeiss GeminiSEM 500 Meets the Needs of Challenging Biological Applications

Modern field emission scanning electron microscopy (FE-SEM) techniques are increasingly important for studying structural properties of cells and tissue. Typical applications include imaging of tissue by serial block face or array tomography methods (AT) [1,2]. In serial block face imaging a thin layer of the embedded sample is removed either mechanically or with a focused ion beam. Afterwards the fresh block face is imaged. In contrast for AT serial sections of the sample are produced in advance and mounted on a solid support (i.e. silicon wafer, glass). The individual sections are investigated in the FESEM afterwards. The imaging modes can vary from secondary electrons (SE) over back scattered electrons (BSE) detection to scanning transmission electron microscopy (STEM). Key performance parameters for biological imaging are optimum resolution and contrast, surface sensitivity, control of sample charging as well as the need of speeding up the data acquisition for high-throughput imaging.

Applications of energy dependent backscatter yield variations at low voltage

For imaging of nano-materials and composites it is often necessary to detect smallest compositional differences in these materials. Very often the nanostructure needs to be distinguishable from matrix or substrates in order to image it. The main advantage of material analysis at low Voltages is due to the reduced interaction volume of the primary beam. Benefit is here a higher resolution and the ability to gain surface sensitivity for better imaging conditions.