Edgar Voelkl

Patterned growth of individual and multiple vertically aligned carbon nanofibers

The results of studies of patterned growth of vertically aligned carbon nanofibers (VACNFs) prepared by plasma-enhanced chemical vapor deposition are reported. Nickel (Ni) dots of various diameters and Ni lines with variable widths and shapes were fabricated using electron beam lithography and evaporation, and served for catalytic growth of VACNFs whose structure was determined by high resolution transmission electron microscopy. It is found that upon plasma pre-etching and heating up to 600–700 °C, thin films of Ni break into droplets which initiate the growth of VACNFs. Above a critical dot size multiple droplets are formed, and consequently multiple VACNFs grow from a single evaporated dot. For dot sizes smaller than the critical size only one droplet is formed, resulting in a single VACNF. In the case of a patterned line, the growth mechanism is similar to that from a dot. VACNFs grow along the line, and above a critical linewidth multiple VACNFs are produced across the line. The mechanism of the form...

Shaping carbon nanostructures by controlling the synthesis process

The ability to control the nanoscale shape of nanostructures in a large-scale synthesis process is an essential and elusive goal of nanotechnology research. Here, we report significant progress toward that goal. We have developed a technique that enables controlled synthesis of nanoscale carbon structures with conical and cylinder-on-cone shapes and provides the capability to dynamically change the nanostructure shape during the synthesis process. In addition, we present a phenomenological model that explains the formation of these nanostructures and provides insight into methods for precisely engineering their shape. Since the growth process we report is highly deterministic in allowing large-scale synthesis of precisely engineered nanoscale components at defined locations, our approach provides an important tool for a practical nanotechnology.

Direct observation of potential distribution across Si/Si p-n junctions using off-axis electron holography

Off‐axis electron holography was used to observe the potential distribution across a 2×1018/cm3 p‐ and n‐doped Si/Si p‐n junction. With digital image recording and processing, and a novel method for thickness determination, we have successfully extracted two‐dimensional maps of the depletion region potential. For a defect‐free region, we measured relatively abrupt changes in potential in the range 1.0–1.5 V across lateral distances of 20–30 nm. Although influenced by instrumental and sample limitations, these values are reasonably consistent with expected Si junction parameters and thus establish the promise of this technique for measuring potential distributions across device junctions and interfaces.

Semiconductor wafer defect detection using digital holography

Defect inspection metrology is an integral part of the yield ramp and process monitoring phases of semiconductor manufacturing. High aspect ratio structures have been identified in the ITRS as critical structures where there are no known manufacturable solutions for defect detection. We present case studies of a new inspection technology based on digital holography that addresses this need. Digital holography records the amplitude and phase of the wavefront from the target object directly to a single image acquired by a CCD camera. Using deep ultraviolet laser illumination, digital holography is capable of resolving phase differences corresponding to height differences as small as several nanometers. Thus, the technology is well suited to the task of finding defects on semiconductor wafers. We present a study of several defect detection benchmark wafers, and compare the results of digital holographic inspection to other wafer inspection technologies. Specifically, digital holography allows improved defect detection on high aspect ratio features, such as improperly etched contacts. In addition, the phase information provided by digital holography allows us to visualize the topology of defects, and even generate three-dimensional images of the wafer surface comparable to scanning electron microscope (SEM) images. These results demonstrate the unique defect detection capabilities of digital holography.

Direct to digital holography for semiconductor wafer defect detection and review

A method for recording true holograms directly to a digital video medium in a single image has been invented. This technology makes the amplitude and phase for every pixel of the target object wave available. Since phase is proportional wavelength, this makes high-resolution metrology an implicit part of the holographic recording. Measurements of phase can be made to one hundredth or even one thousandth of a wavelength, so the technology is attractive for dining defects on semiconductor wafers, where feature sizes are now smaller than the wavelength of even deep UV light.

Direct To Digital Holography For High Aspect Ratio Inspection of Semiconductor Wafers

Direct to Digital Holography (DDH) has been developed as a semiconductor wafer inspection tool and in particular as a tool for seeing defects in high aspect ratio (HAR) structures on semiconductor wafers and also for seeing partial‐height defects. While the tool works very well for general wafer inspection, it has unusual capabilities for high aspect ratio inspection (HARI) and for detecting thin residual film defects (partial height defects). Inspection of HAR structures is rated as one of the highest unmet priorities of the member companies of International SEMATECH, and finding residual thin film defects (in some cases called “stringers”) is also a very difficult challenge. The capabilities that make DDH unusually sensitive include: 1) the capture of the whole wave—both the classical amplitude captured by traditional optical systems, and the phase of the wave, with phase potentially measured to ∼1/1000’th of a wavelength or ∼2 to 3 Angstroms for a deep ultra‐violet (DUV) laser; 2) heterodyne detection—...

Ultrastructural Telepathology: Remote EM Diagnostic via Internet

The digital revolution has given rise to new tools in different disciplines of science; much of this new knowledge has been assimilated into different telemedicine applications and also extends the boundaries of pathology, a diagnostic medical discipline. The tissue-based pathologic diagnosis is the gold standard for all subsequent medical procedures - especially surgery and tumour treatment - and electron microscopy, owing to its high-resolution, can provide significant data not discernible by light microscopy to render the correct diagnosis. In case of diagnostic difficulty remote experts can instantly examine pathologic samples directly using an ultrastructural telepathology system: the consulting “second opinion” expert is no longer constrained by problems inherent in preselected images. Growing Internet bandwidth and developing Grid technology foster such interactive telemicroscopy solutions enabling savings of time and resources in healthcare, research and distance teaching.