Atomic force microscopy and surface resistivity measurement were used for characterization of ultra-thin tungsten layers deposited on purified silicon with 200 nm thermic silicon dioxide substrate. Radio-frequency magnetron sputtering was used for tungsten deposition. © Research India Publications

Fořt, Tomáš

Kudělka, Josef

Křesálek, Vojtěch

Martínek, Tomáš

Navrátil, Milan

English

Institutional repository of Tomas Bata University Library

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 11 (2016) pp 7523-7525 © Research India Publications.  http://www.ripublication.com 7523 Characterization of ultra-thin tungsten layers   Tomas Martinek1, Josef Kudelka1, Milan Navratil1, Tomas Fort2  and  Vojtech Kresalek1 1Tomas Bata University in Zlin, Faculty of Applied Informatics, Department of Electronics and Measurement, Nad Stranemi 4511, 760 05 Zlin, Czech Republic. 2Institute of Scientific Instruments ASCR, Kralovopolska 147, 612 64 Brno, Czech Republic.   Abstract: Atomic force microscopy and surface resistivity measurement were used for characterization of ultra-thin tungsten layers deposited on purified silicon with 200 nm thermic silicon dioxide substrate. Radio-frequency magnetron sputtering was used for tungsten deposition.  Keywords: atomic force microscopy; surface resistivity; tungsten; ultra-thin film; nanocharacterization; metrology; nanocomposite.   INTRODUCTION Nanotechnologies are one of the most perspective science fields with possible impact in almost all part of human being and knowledge. One of their parts are ultra-thin layers. Ultra-thin layers can be defined as material, where one of dimensions is at nanoscale. Ultra-thin layers are very interesting area of physics with properties located between microphysical structures, where classic physics takes place, and nanophysical structures, where quantum physics is used. They are interesting from application point of view, because their properties can dramatically change according to the thickness, material or substrate used. These layers have great potential in industry, e.g. as a diffusion barrier in electrical components fabrication [1]. These layers are also used in semiconductors [2], photonics [3], optoelectronics [4], spintronics [5] or for improvement of mechanical properties and temperature stability of materials [6]. Characterization and diagnostics of ultra-thin layers can be done only by a limited number of methods which are able to follow the features of these structures approaching atomic resolution. In our case, atomic force microscopy was used. This method is one of the scanning probe microscopy methods capable of measuring both conductive and nonconductive materials, providing high resolution and three-dimensional comprehensive information about the measured sample. Ultra-thin layers deposition can be done in many ways by physical or chemical deposition methods [7-10]. In this paper, physical deposition method – radio-frequency magnetron sputtering was used for deposition of ultra-thin tungsten layers on purified silicon with 200 nm layer of thermic silicon dioxide.   DEPOSITION OF ULTRA-THIN LAYERS Ultra-thin tungsten layers were deposited in a sputtering unit using tungsten target with 99.95% in purity. The argon flux was regulated with high accuracy mass flow controller. The pressure was measured by Baratron membrane vacuum gauge. Argon deposition pressure was kept at 165 mPa. Layers were deposited by radio-frequencymagnetron discharge at power of 150 W and the distance between the target and the rotating substrate holder was 50 mm. The rotation speed was set on 2.73 rpm. Two depositions in order to determine the deposition rate werecarried out. We have deposited after 200 passages of the sample under the target 64.9 nm and 62.7 nm. Therefore after one passage approximately 0.3 nm tungsten layer was deposited. One up to six passages under the tungsten target were accomplished on substrates. All samples were cleaned and checked on laser confocal microscope Olympus LEXT OLS 3100.   EXPERIMENT No special sample preparation was used. Measurement was performed with Agilent Technologies 5420 AFM/SPM atomic force microscopy in ambient air at common laboratory conditions. AFM silicon probe AAC (size 225 x 38 µm, spring constant of 48 N/m, resonant frequency of 190 kHz and with tip radius less than 10 nm) were used. Measurement area of 4 µm x 4 µm was chosen for all analysed samples. Three different random locations of sample surface were chosen for measurement of AFM topography. Results were visualized using Gwyddion software [11]. Samples were marked as SiO20W0for substrate without tungsten (Figure 1), SiO20W3 for 0.3 nm tungsten layer (Figure 2), SiO20W6 for 0.6 nm layer (Figure 3), SiO20W9 for 0.9 nm layer (Figure 4), SiO21W2 for 1.2 nm layer (Figure 5), SiO21W5 for 1.5 nm layer (Figure 6) and SiO21W8 for 1.8 nm tungsten layer on purified silicon with 200 nm thermic silicon dioxide substrate (Figure 7). Figures 1-7 present topography maps of the measured samples. Continuous growth of ultra-thin layers can be seen in Figure 1 – 3. However; structures in Figure 3 are much bigger than expected especially when compared to Figure 4-5. It can be assumed, that growth of these ultra-thin layers is nonlinear. Surface resistivity (Figure 8) of these samples wasmeasured using digital multimeter Keysight 34461A. As can be seen in Figure 8, surface resistivity of SiO21W8 is approximately thousand times lower than in the case of SiO21W2 sample. Electrical percolation threshold is probablylocated around a thickness of 1.8 nm. However; analysis of layers beyond 1.8 nm would be needed.  International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 11 (2016) pp 7523-7525 © Research India Publications.  http://www.ripublication.com 7524   Figure 1: SiO20W0 topography    Figure 2: SiO20W3 topography    Figure 3: SiO20W6 topography   Figure 4: SiO20W9 topography    Figure 5: SiO21W2 topography    Figure 6: SiO21W5 topography International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 11 (2016) pp 7523-7525 © Research India Publications.  http://www.ripublication.com 7525   Figure 7: SiO21W8 topography    Figure 8: Surface resistivity measurement   CONCLUSION Nanoscale characterization of ultra-thin tungsten layers deposited by radio-frequency magnetron sputtering was presented using atomic force microscopy and surface resistivity measurement. This tool showed the potential for nanoscale characterization of ultra-thin layers, their growth and for control of sputtering process.   ACKNOWLEDGEMENT This project was performed with financial support by the Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme project No. LO1030 (MSMT-7778/2014) and with support by the Internal Grant Agency of Tomas Bata University under the project IGA/CebiaTech/2016/003 and by Ministry of Education, Youth and Sports of the Czech Republic (project LO1212). The research infrastructure was funded by Ministry of Education, Youth and Sports of the Czech Republic and European Commission (project CZ.1.05/2.1.00/01.0017) and by The Czech Academy of Sciences (project RVO:68081731).  REFERENCES  [1]  I. Fernandez, X. Borris and F. Pérez-Murano, Atomic force microscopy local oxidation of silicon nitride thin films for mask fabrication, Nanotechnology, vol 16, no. 11, pp. 2731–2737, Nov. 2005. [2]  N. Bornemann, N. H. Sauer, E. 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Characterization of ultra-thin tungsten layers

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Characterization of ultra-thin tungsten layers

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