TY - GEN A1 - Rietig, Anja A1 - Acker, Jörg T1 - Development and validation of a new method for the precise and accurate determination of trace elements in silicon by ICP-OES in high silicon matrices T2 - Journal of Analytical Atomic Spectrometry N2 - A new method for the accurate and precise determination of impurities in silicon was developed and statistically validated. Particular attention was paid to the correct determination of the non-metals boron and phosphorus. Instead a time-consuming open vessel digestion under mild conditions, the dissolution of silicon took place in a microwave-assisted high-pressure system. The essential innovation of the presented method is the direct use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the commonly used, time-consuming method that requires the removal of silicon and acid matrix by volatilisation, which is the most critical step in the determination of boron; however, the ICP-OES measurement in such high silicon matrices requires an entirely new optimisation of the measuring conditions, including the careful selection of emission lines with respect to selectivity and, spectral and non-spectral inferences. For quantification of the impurities contents, the methods of matrix matching (MMC) and multiple standard addition (MSA) were used. After optimisation of the spike concentrations for MSA, the qualities of both methods were compared through a statistical analysis. For the metallic impurities Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zr and P, the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate boron, 9 silicon samples with different contents of boron from three interlaboratory comparisons were used. The new procedure allows for the determination of the impurities of 4N-silicon (12 elements). KW - impurities KW - inductively coupled plasma emission spectroscopy KW - silicon KW - microwave-assisted digestion KW - high silicon matrix KW - multiple standard addition KW - boron KW - phosphorus Y1 - 2017 UR - http://pubs.rsc.org/en/content/articlelanding/2017/ja/c6ja00241b#!divAbstract U6 - https://doi.org/10.1039/C6JA00241B VL - 32 IS - 2 SP - 322 EP - 333 ER - TY - GEN A1 - Spindler, Mario A1 - Herold, Steven A1 - Acker, Jörg A1 - Brachmann, Erik A1 - Oswald, Steffen A1 - Menzel, Siegfried A1 - Rane, Gerd T1 - Chemical etching of Tungsten thin films for high-temperature surface acoustic wave-based sensor devices T2 - Thin Solid Films N2 - Surface acoustic wave devices are widely used as wireless sensors in different application fields. Recent developments aimed to utilize those devices as temperature sensors even in the high temperature range (T > N 300 degrees C) and in harsh environmental conditions. Therefore, conventional materials, which are used for the substrate and for the interdigital transducer finger electrodes such as multilayers or alloys based on Al or Cu have to be exchanged by materials, which fulfill some important criteria regarding temperature related effects. Electron beam evaporation as a standard fabrication method is not well applicable for depositing high temperature stable electrode materials because of their very high melting points. Magnetron sputtering is an alternative deposition process but is also not applicable for lift-off structuring without any further improvement of the structuring process. Due to a relatively high Ar gas pressure of about 10(-1) Pa, the sidewalls of the photoresist line structures are also covered by the metallization, which subsequently prevents a successful lift-off process. In this study, we investigate the chemical etching of thin tungsten films as an intermediate step between magnetron sputtering deposition of thin tungsten finger electrodes and the lift-off process to remove sidewall covering for a successful patterning process of interdigital transducers. KW - SAW devices KW - Tungsten electrodes KW - Magnetron sputtering KW - Wet-chemical etching KW - Lift-off structuring Y1 - 2016 UR - http://www.sciencedirect.com/science/article/pii/S004060901630116X U6 - https://doi.org/10.1016/j.tsf.2016.04.035 VL - 612 SP - 322 EP - 326 ER - TY - GEN A1 - Acker, Jörg A1 - Bücker, Stefan A1 - Hoffmann, Volker T1 - Impact of the chemical form of different fluorine sources on the formation of AlF molecules in a C2H2/N2O flame T2 - Journal of Analytical Atomic Spectrometry N2 - The formation of diatomic AlF molecules was studied in a C2H2/N2O flame by means of a high-resolution continuum source flame absorption spectrometer using different fluorine containing compounds HF, H2SiF6, HBF4 and CF3COOH as fluorine sources. The fragmentation of these fluorine sources, as well the resulting impact on the AlF molecule formation, was derived from flame height distribution studies of the atomic and molecular species Al, AlO, Si, SiO, SiF, B and BF as a function of the fluorine concentration, the molar Al : F ratio and the burner gas composition. As a consequence, the used fluorine sources HF, H2SiF6, HBF4 and CF3COOH have been divided into two major groups. The first group of fluorine sources, covering HF, H2SiF6 and HBF4, decomposes during the drying of the aerosol under the formation of AlF3, which is the dominating species for the transport of aluminium into the flame. Its decomposition into AlF results in a high sensitivity of AlF molecular absorption at low flame observation heights. The second group of fluorine sources is exemplarily given by CF3COOH. In the upper parts of the flame the cleavage of the very stable C–F bond proceeds incompletely so that the sensitivity of the AlF molecular absorption is considerably lower than that for the other fluorine sources. In consequence, the AlF molecules are formed by the reaction between the fluorine atoms and the aluminium atoms, which are transported into the flame without the aid of fluorine, presumably via oxidic and/or carbidic species. The present investigations show that the sensitivity of the AlF molecular absorption and the pathway of AlF formation depend on the chemical form of the fluorine in the studied samples. KW - flame molecular absorption spectrometry KW - diatomic molecule KW - aluminum monofluoride KW - C2H2/N2O flame KW - hexafluorosilicic acid KW - tetrafluoro boric acid KW - trifluoro acetic acid KW - species fragmentation Y1 - 2016 UR - http://pubs.rsc.org/en/Content/ArticleLanding/2016/JA/C5JA00470E#!divAbstract U6 - https://doi.org/10.1039/C5JA00470E SN - 0267-9477 SN - 1364-5544 VL - 31 SP - 902 EP - 911 ER - TY - GEN A1 - Grafe, Hans-Joachim A1 - Löser, Wolfgang A1 - Schmitz, Steffen A1 - Sakaliyska, Miroslava A1 - Wurmehl, Sabine A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Acker, Jörg A1 - Rietig, Anja A1 - Ducke, Jana T1 - NMR investigation of boron impurities in refined metallurgical grade silicon T2 - Physica status solidi. A, Applications and Materials Science N2 - The nuclear magnetic resonance (NMR) method was applied for tracking boron impurities in the refining process of metallurgical grade (MG) silicon. From the NMR signal of the 11B isotope at an operating temperature 4.2 K, the boron concentration can be estimated down to the order of 110 wppm B. After melting and resolidification of MG-Si alloyed with Ca and Ti, a major fraction of B impurities remains in the Si solid solution as inferred from the characteristic NMR frequency. The alloying element Ti does not form substantial fractions of TiB2. Acid leaching of crushed powders of MG-Si alloyed with Ca and Ti can diminish the initial impurity content of B suggesting its accumulation in the grain boundary phases. KW - boron KW - impurity KW - intermetallic compounds KW - nuclear magnetic resonance KW - silicon KW - transition-metal diboride KW - Si-Al melt KW - removal KW - solidification Y1 - 2015 UR - http://onlinelibrary.wiley.com/doi/10.1002/pssa.201431908/full U6 - https://doi.org/10.1002/pssa.201431908 SN - 1862-6319 VL - 212 IS - 9 SP - 2031 EP - 2036 ER - TY - GEN A1 - Meinel, Birgit A1 - Koschwitz, Tim A1 - Blocks, Christian A1 - Acker, Jörg T1 - Comparison of diamond wire cut and silicon carbide slurry processed silicon wafer surfaces after acidic texturisation T2 - Materials Science in Semiconductor Processing N2 - Our work focuses on the acidic etching of silicon wafers, cut via diamond wire (DW) or silicon carbide slurry process (SP). The DW and SP as-cut wafer surface structures have a significant impact on the evolution of the two resultant and different etched morphologies. The time-dependent development of the surface morphology for mono- and multi-crystalline wafers is compared and analyzed via etch rates, reflectivity measurements and confocal microscopy. The as-cut structure of the differently sawn wafers defines a template where the etch attack preferentially occurs and predetermines the texturisation of the etched surface. Based on the experimental results it is possible to lower the reflectivity of the SP-sawn wafers by varying the acidic mixture. On the contrary, the DW-sawn wafers obtain only a small enlargement of the folded surface area during acidic texturisation and no influence of different acidic etch solutions on the reflectivity values was found. To create homogeneously texturized DW-sawn wafers of low reflectivity, an adaptation of the sawing process as well as the development of new etchants and new etch conditions is necessary. KW - Surface morphology KW - Confocal microscopy KW - Acidic etching KW - Texturisation KW - Diamond wire sawing KW - Slurry sawing KW - silicon KW - solar cell KW - chemical analysis Y1 - 2014 UR - http://www.sciencedirect.com/science/article/pii/S1369800114001875 U6 - https://doi.org/10.1016/j.mssp.2014.03.046 SN - 1369-8001 VL - 26 SP - 93 EP - 100 ER - TY - GEN A1 - Meinel, Birgit A1 - Koschwitz, Tim A1 - Heinemann, Robert A1 - Acker, Jörg T1 - The texturization process during horizontal acidic etching of multi-crystalline silicon wafers T2 - Materials Science in Semiconductor Processing N2 - Horizontal wet-chemical etching of silicon wafers in an HF/HNO3/H2SiF6 mixture is the most widely-used technique to texturize multi-crystalline silicon wafers for solar cell production. For the first time, the etch rates were determined separately for the upper and lower side during the horizontal texturization and the their different morphologies. The dependency of the surface morphology from the etch rate and etch depth is proven. Furthermore, the influence of the temperature and stirring rates on the morphological development for the upper and lower side of the wafer were examined. From temperature-dependent measurements, activation energies in the range from 17 kJ/mol to 40 kJ/mol on the upper side and from 23 kJ/mol to 40 kJ/mol on the lower side dependent from the etching time were determined. The observed results reveal a connection between the etch depth, the agitation of the etch solution, the morphology and the reflectivity of the separate wafer sides. KW - Acidic etching KW - Surface properties KW - Confocal microscopy KW - Reflectivity KW - Activation energy KW - silicon KW - HF/HNO3 mixture KW - solar cell Y1 - 2014 UR - http://www.sciencedirect.com/science/article/pii/S136980011400482X U6 - https://doi.org/10.1016/j.mssp.2014.08.047 SN - 1369-8001 VL - 26 SP - 695 EP - 703 ER - TY - GEN A1 - Acker, Jörg A1 - Bücker, Stefan A1 - Hoffmann, Volker T1 - The Formation of AlF Molecules and Al Atoms in a C2H2/N2O Flame Studied by Absorption and Emission Spectrometry of Molecules and Atoms T2 - Current Analytical Chemistry N2 - The absorption of the diatomic molecule AlF in the C2H2/N2O flame at 227.66 nm reveals an interesting feature. The calibration curve of the AlF absorption plotted against a rising concentration of hydrofluoric acid in solutions of constant aluminum content consists of two subsequent linear sections of different slopes. The bend position is reproducibly found at a molar fluorine-to-aluminum ratio of 3, calculated from the composition of the studied solutions. To explain this behavior, the most prominent aluminum flame species Al, AlF, and AlO were recorded as a function of the burner gas composition and flame observation height, using a high-resolution continuum source flame absorption spectrometer. As a result, the two-sectioned calibration curve is explained by two different pathways of AlF molecule formation: At a molar fluorine-to-aluminum ratio of below 3, aluminum is transported into the flame by two parallel pathways. One is the common pathway in absence of fluorine via the reduction of oxidic and/or carbidic species by the flame gases. The second pathway comprises the formation of gaseous AlF3 and its decomposition into AlF molecules and, subsequently, Al atoms. The fractionation of AlF3 releases Al atoms much faster than through the reduction of the oxidic and/or carbidic species. At molar fluorine-to-aluminum ratios of above 3, all aluminum is introduced to the flame via gaseous AlF3. A further increase of the hydrofluoric acid concentration increases the fluorine atom concentration in the flame, so that the AlF formation is determined by the recombination of aluminum and fluorine atoms. KW - AlF KW - AlF3 KW - AlO KW - diatomic molecule KW - high-resolution continuum source absorption spectrometry KW - molecular absorption spectrometry KW - molecular emission spectrometry KW - air-acetylene flame Y1 - 2014 SN - 1875-6727 SN - 1573-4110 VL - 10 IS - 3 SP - 418 EP - 425 ER - TY - GEN A1 - Bücker, Stefan A1 - Hoffmann, Volker A1 - Acker, Jörg T1 - Determination of Fluorine by Molecular Absorption Spectrometry of AlF Using a High-Resolution Continuum Source Spectrometer and a C2H2/N2O Flame T2 - Current Analytical Chemistry N2 - The molecular absorption of the diatomic AlF molecule in the C2H2/N2O flame was studied using a highresolution continuum source flame atomic absorption spectrometer. AlF has a structured absorption spectrum in the range of 227.30 nm and 227.80 nm. From this band system, the remarkably narrow absorption band at 227.66 nm proved to be the optimum for analytical purposes. The signal intensity was studied as a function of the C2H2 : N2O ratio, the aspiration flow, and the aluminum concentration added to the analytical solution to generate the AlF molecules in the flame. The AlF molecule formation is significantly affected by the bonding state of the fluorine source used. Compared to ionic bound fluorine, organic bound fluorine leads to a markedly less sensitive molecular absorbance of AlF. Furthermore, several ions, such as Na+, K+ and NH4+, and acids, such as HCl, CH3COOH, and HNO3, affect the AlF signal intensity severely. It has to be concluded that the determination of fluorine by AlF F MAS only leads to reliable analytical results in simple matrices. KW - AlF KW - fluorine determination KW - high resolution continuum source absorption spectrometry KW - molecular absorption spectrometry KW - non-spectral interference KW - diatomic molecule Y1 - 2014 SN - 1573-4110 SN - 1875-6727 VL - 10 IS - 3 SP - 426 EP - 434 ER - TY - CHAP A1 - Acker, Jörg A1 - Ducke, Jana A1 - Rietig, Anja A1 - Müller, Tim A1 - Eisert, Stefan A1 - Reichenbach, Birk A1 - Löser, Wolfgang ED - Oye, Harald A. ED - Brekken, Harald ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - Segregation, grain boundary milling, and chemical leaching for the refinement of metallurgical-grade silicon for photovoltaic application T2 - Silicon for the Chemical and Solar Industry XII, Trondheim, 2014 N2 - The present work describes a completely new approach to the solidification refinement of metallurgical-grade silicon. The new process comprises the following steps: (i) The first step involves adding auxiliary metals to the molten silicon in order to segregate the metallic and non-metallic impurities in the secondary phase after cooling. (ii) The melt is rapidly cooled in the cellular solidification regime. This generates a Si microstructure with a defined cell size in which all cell boundaries are surrounded by the secondary phase. Furthermore, the secondary phase should form an interconnected three-dimensional network. (iii) The solids are crushed by shockwaves using electrohydraulic fragmentation techniques. The shockwaves lead to preferential crushing at the interface between the silicon and the secondary phase. (iv) The secondary phases are fast and effectively removed by microwave-assisted high-pressure leaching that was newly developed for this process. The potential of the new refinement procedure is demonstrated with auxiliary metals Ca, Al, and Ti. This new procedure yields a significant decrease in phosphorous and metal impurities. KW - silicon KW - leaching KW - hydrometallurgy KW - solar cell KW - segregation KW - etching Y1 - 2014 SN - 978-82-997357-8-0 SP - 177 EP - 188 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER - TY - CHAP A1 - Rietig, Anja A1 - Acker, Jörg ED - Nygaard, Lars ED - Pachaly, Bernd ED - Page, Ingrid Gamst ED - Rong, Harry ED - Tangstad, Merete ED - Tveit, Halvard T1 - A new and fast method for determination of boron, phosphorus and other trace elements in metallurgical grade silicon T2 - Silicon for the Chemical and Solar Industry XIII, Kristiansand, 2016 N2 - A new method for accurate and precise determination of non-metallic and metallic impurities in silicon was developed and statistically validated. The first step is the fast dissolution of silicon in a microwave-assisted high pressure system to minimize a loss of phosphorus. The essential innovation is the use of the concentrated digestion solution for ICP-OES measurements. This approach avoids the common removal of the silicon and acid matrix by volatilization, which can cause considerable losses of boron. Finally, for the ICP-OES measurements in such high-silicon matrices the optimum measuring conditions were determined and a careful selection of emission lines with respect to selectivity, spectral and non-spectral inferences and matrix effects was performed. The method of matrix matched calibration (MMC) is used for quantification of the impurities’ contents. For Al, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zr and P the validation was performed against certified reference materials (IPT134, IPT135, NIST57b). To validate the determination of boron 9 silicon samples of different boron contents from three interlaboratory comparisons were used. The new procedure allows the determination of impurities of 4N-silicon (12 elements) with high precision and accuracy. KW - silicon KW - ICP-OES KW - impurity KW - chemical analysis KW - boron KW - phosphorus Y1 - 2016 UR - https://www.ntnu.no/trykk/publikasjoner/Silicon%20for%20the%20chemical%20and%20solar%20industry%20XIII/ SP - 95 EP - 106 PB - Department of Materials Science and Engineering, Norwegian University of Science and Technology CY - Trondheim ER -