NachhaltigElektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
L. Larcher, F. Puglisi, L. Jiang, Jonas Weber, Günther Benstetter, P. Pavan, M. Lanza, Werner Frammelsberger
Understanding Current Instabilities in Conductive Atomic Force Microscopy
Materials, vol. 12, no. 3
2019
DOI: 10.3390/ma12030459
Abstract anzeigen
Conductive atomic force microscopy (CAFM) is one of the most powerful techniques in studying the electrical properties of various materials at the nanoscale. However, understanding current fluctuations within one study (due to degradation of the probe tips) and from one study to another (due to the use of probe tips with different characteristics), are still two major problems that may drive CAFM researchers to extract wrong conclusions. In this manuscript, these two issues are statistically analyzed by collecting experimental CAFM data and processing them using two different computational models. Our study indicates that: (i) before their complete degradation, CAFM tips show a stable state with degraded conductance, which is difficult to detect and it requires CAFM tip conductivity characterization before and after the CAFM experiments; and (ii) CAFM tips with low spring constants may unavoidably lead to the presence of a ~1.2 nm thick water film at the tip/sample junction, even if the maximum contact force allowed by the setup is applied. These two phenomena can easily drive CAFM users to overestimate the properties of the samples under test (e.g., oxide thickness). Our study can help researchers to better understand the current shifts that were observed during their CAFM experiments, as well as which probe tip to use and how it degrades. Ultimately, this work may contribute to enhancing the reliability of CAFM investigations.
NachhaltigElektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid Scanning (Article ID 6286595, 12 pages)
Scanning, pp. 1-12
2017
DOI: 10.1155/2017/6286595
Abstract anzeigen
For advanced atomic force microscopy (AFM) investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD) and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT) in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
Y. Ji, V. Igelsias, Alexander Hofer, M. Liu, D. Lewis, Y. Shi, S. Long, N. Jiebin, P. McIntyre, Günther Benstetter, A. Scheuermann, H. Fei, M. Lanza, Werner Frammelsberger
Characterization of the photocurrents generated by the laser of atomic force microscopes
Review of Scientific Instruments, vol. 87, no. 8
2016
DOI: 10.1063/1.4960597
Abstract anzeigen
The conductive atomic force microscope (CAFM) has become an essential tool for the nanoscale electronic characterization of many materials and devices. When studying photoactive samples, the laser used by the CAFM to detect the deflection of the cantilever can generate photocurrents that perturb the current signals collected, leading to unreliable characterization. In metal-coated semiconductor samples, this problem is further aggravated, and large currents above the nanometer range can be observed even without the application of any bias. Here we present the first characterization of the photocurrents introduced by the laser of the CAFM, and we quantify the amount of light arriving to the surface of the sample. The mechanisms for current collection when placing the CAFM tip on metal-coated photoactive samples are also analyzed in-depth. Finally, we successfully avoided the laser-induced perturbations using a two pass technique: the first scan collects the topography (laser ON) and the second collects the current (laser OFF). We also demonstrate that CAFMs without a laser (using a tuning fork for detecting the deflection of the tip) do not have this problem.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Nanoscale characterization of CH3-terminated Self-Assembled Monolayer on copper by advanced scanning probe microscopy techniques
Applied Surface Science, vol. 356, pp. 921-926
2015
DOI: 10.1016/j.apsusc.2015.08.182
Abstract anzeigen
In this study, we used Self-Assembled Monolayer (SAM) with CH3 end-group molecules to protect copper surfaces from oxidation and investigated at nanometer scale the integrity and temperature stability of the protective film. The films were characterized by dynamic Chemical Force Microscopy (dCFM), Torsional Resonance Tunneling Atomic Force Microscopy (TR-TUNA) and Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR).
We observed that temperature stress degraded local properties of our SAM films significantly, when compared to unstressed films. After temperature stress at 100 °C, tunneling current increased and hydrophobicity decreased substantially. In combination with the ATR-FTIR results we assigned local high current spots and local hydrophobic variations to cuprous oxide (Cu2O). After temperature stress at 150 °C, the measurements indicate a decomposition of the SAM film and a further oxidation of the copper surface. In addition, the results show that dynamic dCFM and TR-TUNA are appropriate tools to characterize SAM films structurally, chemically and electrically. Most important, in contrast to conventional contact mode Atomic Force Microscopy techniques, we did not observe any damage to the SAM film by dCFM and TR-TUNA measurements.
NachhaltigElektrotechnik und MedientechnikZeitschriftenartikel
M. Nafría, Tobias Berthold, Günther Benstetter, R. Rodríguez, Werner Frammelsberger
Nanoscale characterization of copper oxide films by Kelvin Probe Force Microscopy
Thin Solid Films, vol. 584, no. June 2015, pp. 310-315
2015
DOI: 10.1016/j.tsf.2015.01.071
Abstract anzeigen
In this work Peakforce Kelvin Probe Force Microscopy (PF-KPFM) at ambient environment is used to characterize both oxidation states of copper (Cu) surfaces, cupric oxide CuO and cuprous oxide Cu2O, with high lateral resolution. Characteristic values of the contact potential difference were obtained for the copper oxide states. By this means, PF-KPFM measurements enabled to distinguish between the different types of Cu oxide with nanometer resolution and to correlate the oxidation states to local topography features. It was even possible to identify single oxide grains on top of the Cu surface. As a result, PF-KPFM is able to address the needs for nanoscale characterization methods in semiconductor manufacturing or other related technologies where the local oxidation behavior of copper is a critical issue.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
R. Stamp, J. Kiely, Günther Benstetter, Werner Frammelsberger
C-AFM-based thickness determination of thin and ultra-thin SiO2 films by use of different conductive-coated probe tips
Applied Surface Science, vol. 253, no. 7, pp. 3615-3626
2007
Abstract anzeigen
The influence of the probe tip type on the electrical oxide thickness result was researched for four differently coated conductive tip types using SiO2 (oxide) films with optical thickness of 1.7–8.3 nm. For this purpose, conductive atomic force microscopy (C-AFM) was used to measure more than 7200 current–voltage (IV) curves. The electrical oxide thickness was determined on a statistical basis from the IV-curves using a recently published tunnelling model for C-AFM application. The model includes parameters associated with the probe tip types used. The evolution of the tip parameters is described in detail. For the theoretical tip parameters, measured and calculated IV-curves showed excellent agreement and the electrical oxide thickness versus the optical oxide thickness showed congruent behaviour, independent of the tip type. However, differences in the electrical oxide thickness were observed for the different tip types. The theoretical parameters were modified experimentally in order to reduce these differences. Theoretical and experimental tip parameters were compared and their effect on the differences in the electrical oxide thickness is discussed for the different tip types. Overall, it is shown that the proposed model provides a comprehensive framework for determining the electrical oxide thickness using C-AFM, for a wide range of oxide thicknesses and for differently coated conductive tips.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
M. Nafría, G. Jaschke, Edgar Lodermeier, Heiko Ranzinger, Günther Benstetter, M. Porti, M. Lanza, Werner Frammelsberger
Influence of the manufacturing process on the electrical properties of thin (< 4 nm) Hafnium based high-k stacks observed with CAFM
Microelectronics Reliability, vol. 47, no. 9, pp. 1424-1428
2007
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In this work, the dependence of the electrical characteristics of some thin (<4 nm) HfO2, HfSiO and HfO2/SiO2 stacks on their manufacturing process is studied at the nanoscale. Topography, current maps and current–voltage (I–V) characteristics have been collected by conductive atomic force microscope (CAFM), which show that their conductivity depends on some manufacturing parameters. Increasing the annealing temperature, physical thickness or Hafnium content makes the structure less conductive.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
R. Stamp, J. Kiely, Günther Benstetter, Werner Frammelsberger
Thickness determination of thin and ultra-thin SiO2 films by C-AFM IV-spectroscopy
Applied Surface Science, vol. 252, no. 6, pp. 2375-2388
2006
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Conductive atomic force microscopy was used to determine the electrical oxide thickness for five different silicon dioxide layers with thickness in the order of 1.6–5.04 nm. The electrical thickness results were compared with values determined by ellipsometry. A semi-analytical tunnelling current model with one single parameter set was used to superpose current/voltage curves in both the direct tunnelling and the Fowler–Nordheim tunnelling regime regions. The overall electrical oxide thickness was determined by statistical means from results of nearly 3000 IV-curves recorded for different conductive CoCr-coated tips. Good agreement between the shape of model and experimental data was achieved, widely independent of the oxide thickness. Compared with the ellipsometry value, the electrical thickness was larger by a value of 0.36 nm (22%) for the thinnest oxide and smaller by a value of 0.31 nm (6%) for the thickest oxide, while intermediate values yielded differences better than 0.15 nm (<<6%). The physical differences between the measurement techniques were shown to contribute to this observation. In addition, statistical deviations between single and multiple measurements using a single tip and using a number of different tips were analysed. The causes, for example, natural oxide thickness variations, tip wear, air humidity induced effects and contaminations, are evaluated and discussed. The method proposed was able to determine the electrical oxide thickness with a standard deviation in the order of ±±6–9%. The results suggest that for optimal results it is necessary to perform several repetitions of IV-measurements for one sample and, in addition, to employ more than one tip.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
T. Lutz, Günther Benstetter, W. Bergbauer, Werner Frammelsberger
Kelvin Probe Force Microscopy – An appropriate tool for the electrical characterisation of LED heterostructures
Microelectronics Reliability, vol. 46, no. 9-11, pp. 1736-1740
2006
Abstract anzeigen
Light Emitting Diodes (LEDs) are commercially important devices in opto-semiconductor industry. The light emitting properties of LEDs degrade with time of operation and may lead to device failure. Even though the stability and reliability of LEDs are important topics, they are not well researched with AFM to date. This work demonstrates that Kelvin Probe Force Microscopy (KPFM) is an appropriate method to identify specific sites of increased degradation in a semiconductor heterostructure. Furthermore, the study shows that KPFM provides the metrological basis for further investigations with respect to the progress of degradation and its physical background. In this study, KPFM has been used to measure the potential gradient over cross-sectioned LED heterostructure in operation at different states of degradation. The results show significant differences between new and aged LEDs, markedly at specific layers of the LED heterostructure.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
D. Liu, Günther Benstetter, Werner Frammelsberger
Nanoscale electron field emissions from the bare, hydrogenated and graphite-like layer covered tetrahedral amorphous carbon films
Journal of Applied Physics, vol. 99, no. 4
2006
DOI: 10.1063/1.2171806
Abstract anzeigen
We have compared nanoscale electron field emissions from the bare, hydrogenated, and graphitelike-layer-covered tetrahedral amorphous carbon (ta-C) films. The electron field emission is investigated using a combination of atomic force microscopy (AFM)-based nanowear tests and conducting AFM, by simultaneously measuring the topography and the conductivity of the samples. The analysis of Fowler-Nordheim tunneling currents indicates the formation of filamentlike emission channels within ta-C films. The low-field emission from carbon films is primarily due to a field enhancement arising from conducting nanostructures inside the films. The implications of surface structures for electron field emission are discussed. Electrons are easily delocalized within sp2-bonded rings/chains at a film surface, which leads to an increase in the nanotip emission area. At identical emission currents of 60–80 pA, hydrogenated films are much more easily destroyed due to a relatively insulating surface structure. The results suggest that a very high emission site density, required for field-emission display applications, may be produced by locally modifying a film surface layer.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
B. Knoll, Günther Benstetter, Peter Breitschopf, Werner Frammelsberger
Intermittent contact scanning capacitance microscopy-A novel method for 2D doping profiling
Microelectronics Reliability, vol. 45, pp. 1568-1571
2005
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In the present study an improved method for 2D doping profiling of semiconductor device structures is presented. The method combines the capabilities of scanning capacitance microscopy (SCM) with the advantages of intermittent contact atomic force microscopy (IC-AFM) and is called intermittent contact scanning capacitance microscopy (IC-SCM). Compared with standard SCM, IC-SCM provides mechanically stable measurement conditions because tip wear is nearly eliminated. Furthermore, background signals without local information are suppressed by demodulating the SCM signal at higher harmonics of the tapping tip frequency. Both, reduced tip wear and higher harmonics demodulation yield improved spatial image resolution at less tip degradation compared with standard SCM.
Elektrotechnik und MedientechnikMaschinenbau und MechatronikZeitschriftenartikel
T. Schweinböck, J. Kiely, Günther Benstetter, R. Stamp, Werner Frammelsberger
Simplified tunnelling current calculation for MOS structures with ultra-thin oxides for Conductive Atomic Force Microscopy investigations
Materials Science & Engineering B, vol. 116, no. 2, pp. 168-174
2004
DOI: 10.1016/j.mseb.2004.09.027
Abstract anzeigen
As charge tunnelling through thin and ultra-thin silicon dioxide layers is regarded as the driving force for MOS device degradation the determination and characterisation of electrically week spots is of paramount importance for device reliability and failure analysis. Conductive atomic force microscopy (C-AFM) is able to address this issue with a spatial resolution smaller than the expected breakdown spot. For the determination of the electrically active oxide thickness in practice an easy to use model with sufficient accuracy and which is largely independent of the oxide thickness is required. In this work a simplified method is presented that meets these demands. The electrically active oxide thickness is determined by matching of C-AFM voltage–current curves and a tunnelling current model, which is based on an analytical tunnelling current approximation. The model holds for both the Fowler–Nordheim tunnelling and the direct tunnelling regime with one single tunnelling parameter set. The results show good agreement with macroscopic measurements for gate voltages larger than approximately 0.5–1 V, and with microscopic C-AFM measurements. For this reason arbitrary oxides in the DT and the FNT regime may be analysed with high lateral resolution by C-AFM, without the need of a preselection of the tunnelling regime to be addressed.
Version: 2.1.0