Nitrogen trifluoride (NF3) is frequently used as a source of fluorine in the electronics device manufacturing industry as a dry etchant during plasma assisted etching of silicon wafers, or during the plasma cleaning of chemical vapor deposition chambers. As a result of the electrochemical synthesis procedures in which carbon anodes are used in a fluorine-rich environment, NF3 product streams are frequently contaminated with ppm-amounts of carbon tetrafluoride (CF4). The electronics manufacturing industry, however, requires NF3 of exceptional purity, i.e. so-called VLSI-grade (very large scale integration) NF3, with CF4 concentrations of 20 ppm and below. Due to the close chemical and physical similarities of the two compounds, the removal of CF4 from NF3 has proven to be rather difficult, and current NF3 purification technologies are relatively inefficient. Although membrane gas separation has proven to be competitive in terms of operating costs and energy efficiency, its use for the purification of NF3 seems to have remained unexplored to date. In this study, the use of high free volume glassy perfluoropolymers of Teflon AF2400, Teflon AF1600, and Hyflon AD60 was therefore investigated. To be able to measure the pure and mixed gas permeabilities and selectivities of the solution-cast membranes towards NF3 and CF4, a custom built experimental setup was used, in which a newly developed gas chromatographic (GC) analysis method was implemented. Using divinylbenzene-styrene co-polymer stationary phases in the form of Super Q, a reliable quantification of mixtures of NF3 and CF4 were achieved without requiring additional fluorocarbon liquid stationary phases, as is commonly used in NF3 production environments. Furthermore, by implementing a dual-channel configuration it was possible to quantify a wide range of NF3 and CF4 concentrations. Using the newly developed technique, NF3 and CF4 concentrations of ca. 1 mol% and upwards could be quantified using a Thermal Conductivity Detector (TCD) on one channel, and NF3 and CF4 concentrations of between ca. 40 vppm and 4000 vppm could be measured using a Pulsed Discharge Helium Ionisation Detector (PDHID) on the second channel of the GC method. The glassy perfluoropolymer membranes of Teflon AF2400, Teflon AF1600, and Hyflon AD60 were prepared by a solution casting method, and it was found that annealing at sufficiently high temperatures (170 – 200 °C) ensured optimum permeability selectivity. In contrast, thermal analysis of the solution-cast Hyflon AD60 membranes that were heated to only 95 °C confirmed that the polymer matrix was significantly swollen due to a residual amount of the casting solvent. Consequently, considerably reduced selectivity and increased permeability of both NF3 and CF4 were observed for such solvent-swollen Hyflon AD60 membranes in comparison with the non-swollen membranes that were annealed at 170 °C. Nonetheless, the measured He/N2 permeability and permeability selectivity of all the membranes studied compared favourably with literature values, and selectively permeated NF3 rather than CF4 wherein the pure and mixed gas permeability selectivity displayed a clear dependence on the fractional free volume (FFV) of the polymer matrices. Thus, in accordance with the decreasing FFV of the perfluoropolymers in the order Teflon AF2400 > Teflon AF1600 > Hyflon AD60, the NF3 permeability decreased from 227 Barrer for Teflon AF2400, to 29 Barrer for Teflon AF1600, to 1.9 Barrer for Hyflon AD60. In contrast, the NF3/CF4 selectivity, α(NF3/CF4), increased inversely from 4.5 for Teflon AF2400, to 6.0 for Teflon AF1600, to the highest selectivity of 12 which was obtained using Hyflon AD60. To elucidate the mechanism of separation, the transport properties of NF3 and CF4 in Teflon AF2400 and Teflon AF1600 w.r.t. diffusion and solubility were studied using Molecular Dynamics (MD), Grand Canonical Monte Carlo (GCMC), and statistical thermodynamic techniques. The results indicated that NF3/CF4 diffusion selectivity (DNF3/DCF4) was favoured by the lower free volume of Teflon AF1600, whereas poor correlation was achieved between the GCMC calculated sorption isotherms of CF4 and the experimentally determined isotherms as reported in the literature. Consequently, the non-equilibrium lattice fluid (NELF) model, which more accurately described the sorption isotherms of CF4, was used to evaluate the solubility selectivity. It was found that by adjusting the NELF model interaction parameter, Ψ, favourable NF3/CF4 solubility selectivities (SNF3/SCF4) were predicted. Furthermore, by combining the solubility selectivity values with the diffusion selectivities calculated from the MD results, permeability selectivity predictions that correlated well with the experimentally determined values were obtained. Based on a semi-quantitative technological evaluation, it was concluded that although good NF3/CF4 mixed gas permeability selectivity was obtained with Hyflon AD60, further research into improving the NF3 solubility, and hence permeability will aid in the development of an efficient membrane gas separation process for the purification of NF3. / PhD (Chemistry),North-West University, Potchefstroom Campus, 2013.

Nitrogen trifluoride (NF3) is frequently used as a source of fluorine in the electronics device manufacturing industry as a dry etchant during plasma assisted etching of silicon wafers, or during the plasma cleaning of chemical vapor deposition chambers. As a result of the electrochemical synthesis procedures in which carbon anodes are used in a fluorine-rich environment, NF3 product streams are frequently contaminated with ppm-amounts of carbon tetrafluoride (CF4). The electronics manufacturing industry, however, requires NF3 of exceptional purity, i.e. so-called VLSI-grade (very large scale integration) NF3, with CF4 concentrations of 20 ppm and below. Due to the close chemical and physical similarities of the two compounds, the removal of CF4 from NF3 has proven to be rather difficult, and current NF3 purification technologies are relatively inefficient. Although membrane gas separation has proven to be competitive in terms of operating costs and energy efficiency, its use for the purification of NF3 seems to have remained unexplored to date. In this study, the use of high free volume glassy perfluoropolymers of Teflon AF2400, Teflon AF1600, and Hyflon AD60 was therefore investigated. To be able to measure the pure and mixed gas permeabilities and selectivities of the solution-cast membranes towards NF3 and CF4, a custom built experimental setup was used, in which a newly developed gas chromatographic (GC) analysis method was implemented. Using divinylbenzene-styrene co-polymer stationary phases in the form of Super Q, a reliable quantification of mixtures of NF3 and CF4 were achieved without requiring additional fluorocarbon liquid stationary phases, as is commonly used in NF3 production environments. Furthermore, by implementing a dual-channel configuration it was possible to quantify a wide range of NF3 and CF4 concentrations. Using the newly developed technique, NF3 and CF4 concentrations of ca. 1 mol% and upwards could be quantified using a Thermal Conductivity Detector (TCD) on one channel, and NF3 and CF4 concentrations of between ca. 40 vppm and 4000 vppm could be measured using a Pulsed Discharge Helium Ionisation Detector (PDHID) on the second channel of the GC method. The glassy perfluoropolymer membranes of Teflon AF2400, Teflon AF1600, and Hyflon AD60 were prepared by a solution casting method, and it was found that annealing at sufficiently high temperatures (170 – 200 °C) ensured optimum permeability selectivity. In contrast, thermal analysis of the solution-cast Hyflon AD60 membranes that were heated to only 95 °C confirmed that the polymer matrix was significantly swollen due to a residual amount of the casting solvent. Consequently, considerably reduced selectivity and increased permeability of both NF3 and CF4 were observed for such solvent-swollen Hyflon AD60 membranes in comparison with the non-swollen membranes that were annealed at 170 °C. Nonetheless, the measured He/N2 permeability and permeability selectivity of all the membranes studied compared favourably with literature values, and selectively permeated NF3 rather than CF4 wherein the pure and mixed gas permeability selectivity displayed a clear dependence on the fractional free volume (FFV) of the polymer matrices. Thus, in accordance with the decreasing FFV of the perfluoropolymers in the order Teflon AF2400 > Teflon AF1600 > Hyflon AD60, the NF3 permeability decreased from 227 Barrer for Teflon AF2400, to 29 Barrer for Teflon AF1600, to 1.9 Barrer for Hyflon AD60. In contrast, the NF3/CF4 selectivity, α(NF3/CF4), increased inversely from 4.5 for Teflon AF2400, to 6.0 for Teflon AF1600, to the highest selectivity of 12 which was obtained using Hyflon AD60. To elucidate the mechanism of separation, the transport properties of NF3 and CF4 in Teflon AF2400 and Teflon AF1600 w.r.t. diffusion and solubility were studied using Molecular Dynamics (MD), Grand Canonical Monte Carlo (GCMC), and statistical thermodynamic techniques. The results indicated that NF3/CF4 diffusion selectivity (DNF3/DCF4) was favoured by the lower free volume of Teflon AF1600, whereas poor correlation was achieved between the GCMC calculated sorption isotherms of CF4 and the experimentally determined isotherms as reported in the literature. Consequently, the non-equilibrium lattice fluid (NELF) model, which more accurately described the sorption isotherms of CF4, was used to evaluate the solubility selectivity. It was found that by adjusting the NELF model interaction parameter, Ψ, favourable NF3/CF4 solubility selectivities (SNF3/SCF4) were predicted. Furthermore, by combining the solubility selectivity values with the diffusion selectivities calculated from the MD results, permeability selectivity predictions that correlated well with the experimentally determined values were obtained. Based on a semi-quantitative technological evaluation, it was concluded that although good NF3/CF4 mixed gas permeability selectivity was obtained with Hyflon AD60, further research into improving the NF3 solubility, and hence permeability will aid in the development of an efficient membrane gas separation process for the purification of NF3. / PhD (Chemistry),North-West University, Potchefstroom Campus, 2013.

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Mit zunehmender Miniaturisierung mikroelektronischer Bauelemente steigen die Anforderungen an reproduzierbare qualitätskonforme Schichten. Um die zur Herstellung notwendigen ALD/PVD/CVD-Schichtabscheideanlagen in einen zuverlässigen Zustand zu versetzen, ist eine regelmäßige Kammerreinigung notwendig. Während des Abscheideprozesses werden nicht nur das Substrat, sondern auch die umliegenden Kammerteile beschichtet. Diese Schichten wachsen mit jedem Beschichtungszyklus weiter an. Der Stress zwischen Schicht und Kammerwand steigt beständig, und es besteht das Risiko das Teile abplatzen und auf die Waferoberfläche fallen und damit die Struktur unbrauchbar machen. Um das zu verhindern, muss die Kammerwand in einen regelmäßigen Zustand versetzt werden, in dem sichergestellt ist, daß keine Schichtreste abplatzen können. In der vorliegenden Arbeit wird ein neues Verfahren zur Trockenreinigung von ALD-Titannitrid Kammern vorgestellt. Dazu wurden TiN-Stücke (hergestellt im ALD, CVD, PVD-Verfahren) auf einem temperaturgeregelten Probenhalter platziert. Eine Argon/NF3 Gasmischung wurde in einer externen Plasmaquelle (RPS) zerlegt und in die Reaktionskammer geschleust. Die Ätzung wurde mit in-situ Reflexionsmessung beobachtet. Experimente mit Chlorzugabe wurden unternommen und ein starker Einfluss auf den Ätzmechanismus beobachtet. Die Ätzraten des TiN sind exponentiell abhängig von der Temperatur und proportional abhängig von der Verfügbarkeit atomaren Fluors. Dieses wird bei der Zerlegung von NF3 frei gesetzt und steht der Reaktion zur Verfügung. Die NF3-Zerlegung in Fluor und Stickstoff wurde mit Hilfe der Massenspektrometrie (QMS) untersucht, Zerlegungsgrade größer 96% wurden erreicht. Mit Hilfe dieser Messung kann der Einfluss der Kammerreinigung auf den Treibhausgasausstoß (GWP) bestimmt werden. Mit dem Ar/NF3-Verfahren können die GWP-Emissionen um 90% im Vergleich zur RIE-Ätzung mit SF6 reduziert werden. Mit Argon/Chlor-Plasmen konnte kein Titannitrid geätzt werden, da die physikalische Sputterkomponente fehlte. Durch Hinzufügen von Chlor zu einer Ar/NF3-Gasmischung konnte die Ätzrate um bis zu 270% im Bereich niedrige Temperaturen/niedriger Druck gesteigert werden. Bei höheren Temperaturen/höherem Druck fielen die Ar/NF3/Chlor Ätzraten allerdings deutlich hinter die des Ar/NF3 zurück. Die dazu führenden Effekte werden untersucht und ausgeführt. Die Nutzung von externen Plasmaquellen bietet eine vielversprechende Alternative um Abscheideanlagen von TiN-Rückständen reinigen zu können. Bei hohen Temperaturen werden deutlich höhere Ätzraten als bei anderen Schichten (SiN, SiO2, W) erreicht. Für Anwendungen im niedrigen Temperaturbereich erlaubt die Zugabe von Chlor interessante Anwendungsmöglichkeiten. / Demands on state of the art deposition technologies for semiconductor production focus on uniformity, repeatability and low defectivity. The chamber condition is a key parameter to achieve these high demands in chemical vapour deposition (CVD) processes and are even more critical to the atomic layer deposition processes (ALD). During the deposition process not only the wafer surface but other chamber parts as well are covered with a thin film. This film accumulates during the deposition cycles and is prone to fall off the walls and pollute the wafer surface. The chamber parts that are exposed to the deposition must be set back to a steady state so that no deposits fall off the walls. The chamber condition also changes uncontrolled with varying film condition on the wall. A new approach for cleaning of ALD-titanium nitride (TiN) deposition chambers was investigated. To determine etch rates TiN-samples (created by ALD, CVD and PVD) were placed on a temperature controlled sample holder. An argon/NF3 mixture was excited in an upstream remote plasma source (RPS) and then routed through the reaction chamber. No further plasma activation inside the reaction chamber was done. The etching was monitored by in-situ reflectometry and etch rates were calculated. The effect of chlorine addition was also studied and strong influence on etch rates was found. The etch rate of TiN is dependent exponentially on temperature and very low etch rates were achieved below 70◦C at a chamber pressure ranging from 20-300 Pa. It was found that this correlates very well with the vapour pressure of the reaction product TiF4. At temperatures of 300◦C etch rates up to 800 nm/min were achieved. The optimum pressure for etching was found at 100 Pa while the pressure effect was small. The etch rate was mainly dependent on the availability of activated fluorine to create TiF4 by the reaction 2 NF3 → N2 + 6 F* 2 TiN + 8 F* → 2 TiF4 + N2 The NF3 decomposition to nitrogen and fluorine was monitored by quadrupole mass spectrometry (QMS) and was found to be greater than 96%. This figure allows an estimation of the amount of Global warm potential (GWP) gas emmited by the process for environmental considerations. Using argon/NF3 or argon/fluorine mixtures in RPS devices reduces the GWP emissions by more than 90% compared to RIE plasma cleaning with SF6. No etching occurred by using argon/chlorine only mixtures as no physical etch component was involved in RPS etch. However adding chlorine to the argon/NF3 mixture accelerated the etching process. Chlorine addition to the argon/NF3 mixture increased the etch rates up to 270% in the low pressure/low temperature regime. At higher temperatures or higher pressures the etch rates dropped below the etch rates achieved solely with fluorine chemistry. It must be emphasized that there is no physical acceleration of the ionized molecules toward the etched sample in this remote plasma setup. The usage of a remote plasma offers an alternative way to remove residues from chambers running TiN deposition processes. At high temperatures the Ar/NF3 offers remarkably high etching rates for TiN compared to other films (silicon nitride, -oxide, tungsten) usually cleaned by remote plasma. For low temperature applications the chlorine enhancement offers an interesting alternative to accelerate the etch process.

Mit zunehmender Miniaturisierung mikroelektronischer Bauelemente steigen die Anforderungen an reproduzierbare qualitätskonforme Schichten. Um die zur Herstellung notwendigen ALD/PVD/CVD-Schichtabscheideanlagen in einen zuverlässigen Zustand zu versetzen, ist eine regelmäßige Kammerreinigung notwendig. Während des Abscheideprozesses werden nicht nur das Substrat, sondern auch die umliegenden Kammerteile beschichtet. Diese Schichten wachsen mit jedem Beschichtungszyklus weiter an. Der Stress zwischen Schicht und Kammerwand steigt beständig, und es besteht das Risiko das Teile abplatzen und auf die Waferoberfläche fallen und damit die Struktur unbrauchbar machen. Um das zu verhindern, muss die Kammerwand in einen regelmäßigen Zustand versetzt werden, in dem sichergestellt ist, daß keine Schichtreste abplatzen können. In der vorliegenden Arbeit wird ein neues Verfahren zur Trockenreinigung von ALD-Titannitrid Kammern vorgestellt. Dazu wurden TiN-Stücke (hergestellt im ALD, CVD, PVD-Verfahren) auf einem temperaturgeregelten Probenhalter platziert. Eine Argon/NF3 Gasmischung wurde in einer externen Plasmaquelle (RPS) zerlegt und in die Reaktionskammer geschleust. Die Ätzung wurde mit in-situ Reflexionsmessung beobachtet. Experimente mit Chlorzugabe wurden unternommen und ein starker Einfluss auf den Ätzmechanismus beobachtet. Die Ätzraten des TiN sind exponentiell abhängig von der Temperatur und proportional abhängig von der Verfügbarkeit atomaren Fluors. Dieses wird bei der Zerlegung von NF3 frei gesetzt und steht der Reaktion zur Verfügung. Die NF3-Zerlegung in Fluor und Stickstoff wurde mit Hilfe der Massenspektrometrie (QMS) untersucht, Zerlegungsgrade größer 96% wurden erreicht. Mit Hilfe dieser Messung kann der Einfluss der Kammerreinigung auf den Treibhausgasausstoß (GWP) bestimmt werden. Mit dem Ar/NF3-Verfahren können die GWP-Emissionen um 90% im Vergleich zur RIE-Ätzung mit SF6 reduziert werden. Mit Argon/Chlor-Plasmen konnte kein Titannitrid geätzt werden, da die physikalische Sputterkomponente fehlte. Durch Hinzufügen von Chlor zu einer Ar/NF3-Gasmischung konnte die Ätzrate um bis zu 270% im Bereich niedrige Temperaturen/niedriger Druck gesteigert werden. Bei höheren Temperaturen/höherem Druck fielen die Ar/NF3/Chlor Ätzraten allerdings deutlich hinter die des Ar/NF3 zurück. Die dazu führenden Effekte werden untersucht und ausgeführt. Die Nutzung von externen Plasmaquellen bietet eine vielversprechende Alternative um Abscheideanlagen von TiN-Rückständen reinigen zu können. Bei hohen Temperaturen werden deutlich höhere Ätzraten als bei anderen Schichten (SiN, SiO2, W) erreicht. Für Anwendungen im niedrigen Temperaturbereich erlaubt die Zugabe von Chlor interessante Anwendungsmöglichkeiten. / Demands on state of the art deposition technologies for semiconductor production focus on uniformity, repeatability and low defectivity. The chamber condition is a key parameter to achieve these high demands in chemical vapour deposition (CVD) processes and are even more critical to the atomic layer deposition processes (ALD). During the deposition process not only the wafer surface but other chamber parts as well are covered with a thin film. This film accumulates during the deposition cycles and is prone to fall off the walls and pollute the wafer surface. The chamber parts that are exposed to the deposition must be set back to a steady state so that no deposits fall off the walls. The chamber condition also changes uncontrolled with varying film condition on the wall. A new approach for cleaning of ALD-titanium nitride (TiN) deposition chambers was investigated. To determine etch rates TiN-samples (created by ALD, CVD and PVD) were placed on a temperature controlled sample holder. An argon/NF3 mixture was excited in an upstream remote plasma source (RPS) and then routed through the reaction chamber. No further plasma activation inside the reaction chamber was done. The etching was monitored by in-situ reflectometry and etch rates were calculated. The effect of chlorine addition was also studied and strong influence on etch rates was found. The etch rate of TiN is dependent exponentially on temperature and very low etch rates were achieved below 70◦C at a chamber pressure ranging from 20-300 Pa. It was found that this correlates very well with the vapour pressure of the reaction product TiF4. At temperatures of 300◦C etch rates up to 800 nm/min were achieved. The optimum pressure for etching was found at 100 Pa while the pressure effect was small. The etch rate was mainly dependent on the availability of activated fluorine to create TiF4 by the reaction 2 NF3 → N2 + 6 F* 2 TiN + 8 F* → 2 TiF4 + N2 The NF3 decomposition to nitrogen and fluorine was monitored by quadrupole mass spectrometry (QMS) and was found to be greater than 96%. This figure allows an estimation of the amount of Global warm potential (GWP) gas emmited by the process for environmental considerations. Using argon/NF3 or argon/fluorine mixtures in RPS devices reduces the GWP emissions by more than 90% compared to RIE plasma cleaning with SF6. No etching occurred by using argon/chlorine only mixtures as no physical etch component was involved in RPS etch. However adding chlorine to the argon/NF3 mixture accelerated the etching process. Chlorine addition to the argon/NF3 mixture increased the etch rates up to 270% in the low pressure/low temperature regime. At higher temperatures or higher pressures the etch rates dropped below the etch rates achieved solely with fluorine chemistry. It must be emphasized that there is no physical acceleration of the ionized molecules toward the etched sample in this remote plasma setup. The usage of a remote plasma offers an alternative way to remove residues from chambers running TiN deposition processes. At high temperatures the Ar/NF3 offers remarkably high etching rates for TiN compared to other films (silicon nitride, -oxide, tungsten) usually cleaned by remote plasma. For low temperature applications the chlorine enhancement offers an interesting alternative to accelerate the etch process.

NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.