Institute of Solid State Electronics

A new approach using focused electron beam induced deposition (FEBID) to deposit catalyst particles is reported for the synthesis of single crystalline silicon nanowires (SiNWs) grown by low pressure chemical vapor deposition (LPCVD). The FEBID deposited gold dot arrays fabricated from an acac-Au(III)-Me2 precursor were investigated by AFM and EDX. The depositions were found to form a sharp tip and a surrounding halo and consist of only 10 at.% Au. However, SiNWs could be synthesized on the deposited catalyst using the vapor-liquid-solid (VLS) method with a mixture of 2% SiH4 in He at 520 °C. NW diameters from 30 nm up to 150 nm were fabricated and the dependency of the NW diameter on the FEBID deposition time was observed. TEM analysis of the SiNWs revealed a [110] growth direction independent of the NW diameter. This new method provides a maskless and resistless approach for generating catalyst templates for SiNW synthesis on arbitrary surfaces.

Currently there is an increasing demand for high-throughput methods to identify and to verify the potential of new drug candidates. Cell-based microelectronic biosensors might be powerful tools for rapid screening assays. However, reliable cultivation of cells is influenced by the material characteristics and the surface topography of the wafers serving as growth supports. In order to investigate the influence of micropatterned structures on cell viability, Caco-2 cells were seeded on silicon wafers featuring trench/ mesa patterns obtained by lithography and reactive ion etching. Besides determination of the cell growth pattern by electron microscopic inspection, the adherence of cells on different patterned silicon wafers and the formation of the tight junctional network was investigated. Microstructured trench/mesa patterns, especially their lateral distances, remarkably influenced the adhesion and proliferation behavior of Caco-2 cells. Lateral distances below the average cell diameter were easily overgrown by the cells, whereas dimensions above the average cell diameter increasingly limited cell proliferation. Notably increased cell growth was observed using trenches with a width of 10-20 lm and a trench depth of around 35 lm. All in all, the results of this study might improve the production of microstructured biosensors and open up new perspectives concerning the combination of biosensors and microfluidic systems.

We report on the growth of ZrO thin films on silicon wafers by metal-organic chemical vapor deposition from zirconiumtri-2 fluoroacetylacetonate at deposition temperatures between 350 and 550 8C. The evolution of surface roughness of the deposited films is thoroughly investigated. Relative roughness is found to be minimum at a deposition temperature of 450 8C and also essentially independent of film thickness. The attained values of relative roughness are shown to be competitive to advanced deposition methods such as atomic layer deposition. Chemical composition of the films is examined in dependence of deposition temperature and post-deposition annealing procedures. Experimental results indicate that optimum properties in regard to chemical composition are obtained after thermal treatment at 650 8C. The film composition is not significantly altered by annealing at higher temperatures. Also the ambient atmosphere during the annealing process is shown to be of minor influence. ᮊ

A new approach using focused electron beam induced deposition (FEBID) to deposit catalyst particles is reported for the synthesis of single crystalline silicon nanowires (SiNWs) grown by low pressure chemical vapor deposition (LPCVD). The FEBID deposited gold dot arrays fabricated from an acac-Au(III)-Me2 precursor were investigated by AFM and EDX. The depositions were found to form a sharp tip and a surrounding halo and consist of only 10 at.% Au. However, SiNWs could be synthesized on the deposited catalyst using the vapor-liquid-solid (VLS) method with a mixture of 2% SiH4 in He at 520 °C. NW diameters from 30 nm up to 150 nm were fabricated and the dependency of the NW diameter on the FEBID deposition time was observed. TEM analysis of the SiNWs revealed a [110] growth direction independent of the NW diameter. This new method provides a maskless and resistless approach for generating catalyst templates for SiNW synthesis on arbitrary surfaces.

Novel ion beam processing for microelectronic applications has been performed by doping silicon with a focused ion beam tool. A Ga + ion beam with a energy between 10 and 50 keV was used for p-doping of Si. The ion beam could be focused to an effective beam diameter in the sub-micron range with the smallest focus own below 10 nm. In contrast to conventional implantation with a broad ion beam where the doped area is assigned by a hardmask the implantation was achieved by scanning a focused ion beam over the designated implantation area. With this approach not only the hardmask becomes obsolete because of the electronic beam guidance. Moreover, different doses may be implanted on the same wafer. An additional feature is the inhomogeneous implantation in a pixel-array, where the distance between exposed pixels can be deliberately varied. Even single spots can be independently doped with the focused gallium beam. Due to lateral scattering of ions in the semiconductor the circular implantation area is larger than the beam diameter. With a variation of the pixel spacing we could intentionally obtain either a overlap or a separation of implantation spots. With a four-point method we have investigated the conductivity of the dot-array implanted area.

Currently there is an increasing demand for high-throughput methods to identify and to verify the potential of new drug candidates. Cell-based microelectronic biosensors might be powerful tools for rapid screening assays. However, reliable cultivation of cells is influenced by the material characteristics and the surface topography of the wafers serving as growth supports. In order to investigate the influence of micropatterned structures on cell viability, Caco-2 cells were seeded on silicon wafers featuring trench/ mesa patterns obtained by lithography and reactive ion etching. Besides determination of the cell growth pattern by electron microscopic inspection, the adherence of cells on different patterned silicon wafers and the formation of the tight junctional network was investigated. Microstructured trench/mesa patterns, especially their lateral distances, remarkably influenced the adhesion and proliferation behavior of Caco-2 cells. Lateral distances below the average cell diameter were easily overgrown by the cells, whereas dimensions above the average cell diameter increasingly limited cell proliferation. Notably increased cell growth was observed using trenches with a width of 10-20 lm and a trench depth of around 35 lm. All in all, the results of this study might improve the production of microstructured biosensors and open up new perspectives concerning the combination of biosensors and microfluidic systems.

The fabrication of nanostructured dielectrics of high purity produced by electron beam induced deposition (EBID) was investigated. Additionally, the process parameters were optimized towards high deposition rate. Silicon oxide was chosen as exemplary dielectric. The deposition was performed with an electron microscope with a self-designed nozzle system. An organo-silicon precursor was used to deposit silicon oxide. The increase of the oxygen content and the reduction of carbon contaminations of the depositions were preformed by adding molecular oxygen. Patterns of large areas as well as nm-scale arrays were fabricated. To optimize the deposition rate the correlation between beam parameters and deposition rate was studied. It has been shown that this direct-write method allows obtaining arbitrary structures with superior material quality.

We report on the growth of ZrO thin films on silicon wafers by metal-organic chemical vapor deposition from zirconiumtri-2 fluoroacetylacetonate at deposition temperatures between 350 and 550 8C. The evolution of surface roughness of the deposited films is thoroughly investigated. Relative roughness is found to be minimum at a deposition temperature of 450 8C and also essentially independent of film thickness. The attained values of relative roughness are shown to be competitive to advanced deposition methods such as atomic layer deposition. Chemical composition of the films is examined in dependence of deposition temperature and post-deposition annealing procedures. Experimental results indicate that optimum properties in regard to chemical composition are obtained after thermal treatment at 650 8C. The film composition is not significantly altered by annealing at higher temperatures. Also the ambient atmosphere during the annealing process is shown to be of minor influence. ᮊ

Novel ion beam processing for microelectronic applications has been performed by doping silicon with a focused ion beam tool. A Ga + ion beam with a energy between 10 and 50 keV was used for p-doping of Si. The ion beam could be focused to an effective beam diameter in the sub-micron range with the smallest focus own below 10 nm. In contrast to conventional implantation with a broad ion beam where the doped area is assigned by a hardmask the implantation was achieved by scanning a focused ion beam over the designated implantation area. With this approach not only the hardmask becomes obsolete because of the electronic beam guidance. Moreover, different doses may be implanted on the same wafer. An additional feature is the inhomogeneous implantation in a pixel-array, where the distance between exposed pixels can be deliberately varied. Even single spots can be independently doped with the focused gallium beam. Due to lateral scattering of ions in the semiconductor the circular implantation area is larger than the beam diameter. With a variation of the pixel spacing we could intentionally obtain either a overlap or a separation of implantation spots. With a four-point method we have investigated the conductivity of the dot-array implanted area.

The fabrication of nanostructured dielectrics of high purity produced by electron beam induced deposition (EBID) was investigated. Additionally, the process parameters were optimized towards high deposition rate. Silicon oxide was chosen as exemplary dielectric. The deposition was performed with an electron microscope with a self-designed nozzle system. An organo-silicon precursor was used to deposit silicon oxide. The increase of the oxygen content and the reduction of carbon contaminations of the depositions were preformed by adding molecular oxygen. Patterns of large areas as well as nm-scale arrays were fabricated. To optimize the deposition rate the correlation between beam parameters and deposition rate was studied. It has been shown that this direct-write method allows obtaining arbitrary structures with superior material quality.

Infrared (IR) absorption of molecules is enhanced , greatly (101-103 times) when they are adsorbed on or near vacuum-evaporated Ag or Au thin films. By using this surface Enhanced i$ absorption (SEIRA) phenomenon, we could obtained IR spectra of some organic molecules of a few picogram amount in good signal-to-noise ratios. Thus, the SEIRA spectroscopy is promising as a new trace analytical technique. General properties of SEIRA found in our experiments are summarized. An electromagnetic theory of this phenomenon is proposed. Key W surface enhanced infrared spectroscopy, trace analysis Optical properties of molecules are altered dramatically when they are adsorbed on or near some rough metal surfaces. Surface enhanced Raman scattering (SERS) [1] is the most prominent example. Similar surface enhanced

Anomalous absorption and the corresponding change in the optical band gap of a CO 2-laser-ablated Si-rich SiO 2 ͑SiO x ͒ film are studied. The optical band gap energy of as-grown nonstoichiometric SiO x is slightly reduced by increasing Si-Si bonds as compared to quartz. After rapid thermal annealing using a CO 2 laser, the dehydrogenation of SiO x film further increases the Si-Si bonding states and redshifts the optical band gap by 1 eV. Laser ablation is initiated at a laser intensity of Ͼ7.5 kW/ cm 2 , leaving numerous luminescent centers that are related to neutral oxygen vacancy defects, increasing the absorption coefficient and related optical band gap energy, and reducing the refractive index in partially annealed SiO x .

Nanolaminates of HfO 2 and SiO 2 were prepared using atomic layer deposition (ALD) methods. Successive exposure of substrates maintained at 120 or 160°C to nitrogen flows containing Hf(NO 3) 4 and (t BuO) 3 SiOH led to typical bilayer spacings of 2.1 nm, with the majority of each bilayer being SiO 2. The density of the SiO 2 layers (measured using X-ray reflectometry (XRR)) was slightly higher than expected for amorphous silica, suggesting that as much as 10 % HfO 2 was incorporated into the silica layers. Based on cross-sectional transmission electron microscopy (TEM) and XRR, oxidation of the silicon substrate was observed during its first exposure to Hf(NO 3) 4 , leading to a SiO 2 interfacial layer and the first HfO 2 layer. Combining the ALD of Hf(NO 3) 4 /(t BuO) 3 SiOH with ALD cycles involving Hf(NO 3) 4 and H 2 O allowed the systematic variation of the HfO 2 thickness within the nanolaminate structure. This provided an approach towards controlling the dielectric constant of the films. The dielectric constant was modeled by treating the nanolaminate as a stack of capacitors wired in series. The nanolaminate structure inhibited the crystallization of the HfO 2 in post-deposition annealing treatments. As the HfO 2 thickness decreased, the preference for the tetragonal HfO 2 phase increased.

During the last decades, focused electron beam induced deposition (FEBID) has become a successful approach for direct-write fabrication of nanodevices. Such a deposition technique relies on the precursor supply to the sample surface which is typically accomplished by a gas injection system using a tube-shaped injector nozzle. This precursor injection strategy implies a position-dependent concentration gradient on the surface, which affects the geometry and chemistry of the final nanodeposit. Although simulations already proposed the local distribution of nozzle-borne gas molecules impinging on the surface, this isolated step in the FEBID process has never been experimentally measured yet. This work experimentally investigates the local distribution of impinging gas molecules on the sample plane, isolating the direct impingement component from surface diffusion or precursor depletion by deposition. The experimental setup used in this work maps and quantifies the local impinging rate of argon gas over the sample plane. This setup simulates the identical conditions for a precursor molecule during FEBID. Argon gas was locally collected with a sniffer tube, which is directly connected to a residual gas analyzer for quantification. The measured distribution of impinging gas molecules showed a strong position dependence. Indeed, a 300-lm shift of the deposition area to a position further away from the impingement center spot resulted in a 50 % decrease in the precursor impinging rate on the surface area. With the same parameters, the precursor distribution was also simulated by a Monte Carlo software by Friedli and Utke and showed a good correlation between the empirical and the simulated precursor distribution. The results hereby presented underline the importance of controlling the local precursor flux conditions in order to obtain reproducible and comparable deposition results in FEBID.

Nanomagnet logic (NML) is a relatively new computation technology that uses arrays of shape-controlled nanomagnets to enable digital processing. Currently, conventional resist-based lithographic processes limit the design of NML circuitry to planar nanostructures with homogeneous thicknesses. Here, we demonstrate the focused electron beam induced deposition of Fe-based nanomaterial for magnetic inplane nanowires and out-of-plane nanopillars. Three-dimensional (3D) NML was achieved based on the magnetic coupling between nanowires and nanopillars in a 3D array. Additionally, the same Fe-based nanomaterial was used to produce tilt-corrected high-aspect-ratio probes for the accurate magnetic force microscopy (MFM) analysis of the fabricated 3D NML gate arrays. The interpretation of the MFM measurements was supported by magnetic simulations using the Object Oriented MicroMagnetic Framework. Introducing vertical out-of-plane nanopillars not only increases the packing density of 3D NML but also introduces an extra magnetic degree of freedom, offering a new approach to input/output and processing functionalities in nanomagnetic computing.