In-situ x-ray photoemission (XPS) and ex-situ FTIR studies of nanoporous organosilicate glass (OSG) films point to the separate roles of radicals vs. VUV photons in the carbon abstraction. The studies indicate that reaction with O2 in presence of VUV photons (~123 nm) result in significant carbon abstraction within the bulk and that the kinetics of this process is diffusion-limited. In contrast, OSG exposed to atomic O (no VUV) results in Si-C bond scission and Si-O bond formation, but this process is self-limiting after formation of ~1 nm thick SiO2 surface layer that inhibits further diffusion. Therefore, the diffusion-dominated kinetics of carbon abstraction observed for OSG exposed to O2 plasma is definitively attributed to the diffusion of O2 down OSG nanopores, reacting at photo-activated sites, rather than to the diffusion of atomic O. Pretreatment of OSG by 900 eV Ar+ ion bombardment also results in formation of 1 nm thick SiO2-like surface overlayer that inhibits O2 diffusion, inhibiting VUV+O2 and O2 plasma-induced reactions, and that the effectiveness of this treatment increases with ion kinetic energy. On the contrary, organosilicate glass (OSG) films with backbone carbon (-Si-R-Si-) exhibit significantly enhanced resistance to carbon loss upon exposure to O2 plasma, radicals and VUV+O2 compared to films with terminal methyl groups (Si-CH3). Films incorporating backbone carbon chains (-Si-R-Si-) were deposited from 1,2 bis (triethoxysilyl) ethane (BTESE) precursor by ebeam or plasma cross-linking. The radical effects on BTESE film indicates negligible carbon loss or Si oxidation, combined with C-O bond formation, under conditions where OSG films with terminal methyl groups exhibit > 80% carbon loss within the surface region of the film. C-O bond formation is never observed for terminal CH3 groups. Further, backbone carbon (-Si-R-Si-) films exposed to VUV+O2 exhibit self-limiting, minimal net carbon loss. This indicates that plasma-induced Si-C bond rupture still occurs in the linking unit, but with a low probability of simultaneous rupture of both Si-C bonds required for abstraction of an in-line methylene bridging group. The data thus demonstrate that OSG films containing backbone carbon groups exhibit greatly reduced rates of carbon loss in the presence of O2 plasma, radicals or VUV+O2 compared to films with terminal carbon groups due to fundamentally different patterns of Si-C bond scission. The results demonstrate the potential of backbone carbon low-k films to resist plasma induced damage.

Nanoporous low-k dielectrics are used for integrated circuit interconnects to reduce the propagation delays, and cross talk noise between metal wires as an alternative material for SiO2. These materials, typically organosilicate glass (OSG) films, are exposed to oxygen plasmas during photoresist stripping and related processes which substantially damage the film by abstracting carbon, incorporating O and OH, eventually leading to significantly increased k values. Systematic studies have been performed to understand the oxygen plasma-induced damage mechanisms on different low-k OSG films of various porosity and pore interconnectedness. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and atomic force microscopy are used to understand the damage kinetics of O radicals, ultraviolet photons and charged species, and possible ways to control the carbon loss from the film. FTIR results demonstrate that O radical present in the plasma is primarily responsible for carbon abstraction and this is governed by diffusion mechanism involving interconnected film nanopores. The loss of carbon from the film can be controlled by closing the pore interconnections, He plasma pretreatment is an effective way to control the damage at longer exposure by closing the connections between the pores.

In the crystalline Si solar cell industry, there is a push to reduce module cost through a combination of thinner substrates and increased cell efficiency. Achieving solar cells with sub-100 µm substrates cost-effectively is a formidable task because such thin substrates impose stringent handling requirements and thermal budget due to their flexibility, ease of breakage, and low yield. Moreover, as the substrate thickness decreases the surface passivation quality dictates the performance of the cells. Crystalline Si heterojunction (HJ) solar cells based on hydrogenated amorphous silicon (a-Si:H) have attracted significant interest in recent years due to their excellent surface passivation properties, potential for high efficiency, low thermal budget and low cost. HJ cells with ultra-passivated surfaces showing > 700 mV open-circuit voltages (Voc) and > 20% conversion efficiency have been demonstrated. In these cells, it has been identified that high-quality a-Si:H films deposited by a low-damage plasma process is key to achieving such high cell performance. However, the options for low-damage plasma deposition process are limited. The main objectives of this work are to develop a low-plasma damage a-Si:H thin film deposition process based on remote plasma chemical vapor deposition (RPCVD) and to demonstrate high efficiency HJ solar cells on bulk substrates as well as on ultra-thin silicon and germanium substrates obtained by a novel, low-cost semiconductor-on-metal (SOM) technology. This manuscript presents a detailed description of the RPCVD system and the process leading to the realization of high quality a-Si:H thin films and high efficiency HJ solar cells. First, p-type a-Si:H thin films are developed and optimized, then HJ solar cells are subsequently fabricated on bulk and ultra-thin Si and Ge SOM substrates without intrinsic a-Si:H passivation. Single HJ cells on ~ 500 µm bulk Si and ~25 µm ultra-thin substrates exhibited conversion efficiencies of η = 16% (Voc = 615 mV, Jsc = 34 mA/cm2, and FF = 77%) and η = 11.2% (Voc = 605 mV, Jsc = 29.6 mA/cm2, and FF = 62.8%), respectively. The performance of the ~25 µm cell was further improved to η = 13.4% (Voc = 645 mV, Jsc = 31.4 mA/cm2, and FF = 66.2%) by implementing the dual HJ architecture without front side i-layer passivation. For single HJ cells based on Ge substrates, the results were η = 1.78 % (Voc = 148 mV, Jsc = 35.1 mA/cm2, and FF = 1.78%) on ~500 µm bulk Ge, compared to η =5.3% (Voc = 203 mV, Jsc = 44.7 mA/cm2, and FF = 5.28%) on ~ 50 µm Ge SOM substrates. Respectively, the results obtained on ultra-thin SOM substrates are among the highest reported in literature for based on comparable architecture and substrate thickness. In order to achieve improved cell performance, dual HJ cells with i-layer passivation of both surfaces were fabricated. First, optimized RPCVD-based i-layer films were developed by varying the deposition temperature and H2 dilution ratio (R). It was found that excellent surface passivation on planar substrates with as-deposited minority carrier lifetimes > 1 ms is achievable by using deposition temperature of 200 ºC and moderate dilution ratio 0.5 ≤ R ≤ 1, even without the more rigorous RCA pre-cleaning process typically used in literature for achieving comparable results. Subsequently, dual HJ solar cells with i-layer films were demonstrated on planar and textured bulk Si substrates showing improved conversion efficiencies of η = 17.3% (Voc = 664 mV, Jsc = 34.34 mA/cm2 and FF = 76%) and η = 19.4% (Voc = 643 mV, Jsc = 38.99 mA/cm2, and FF = 77.5%), respectively. / text

In multi-level Co/low-k based interconnect systems of ultralarge-scale integrated electronic devices the removal of plasma etch residues by common plasma cleaning processes has been shown to alter material properties like k-value and leakage current of the low-k dielectric. Besides the development of less damaging plasma processes their substitution by wet cleaning steps is in the focus of research and development. With further decreasing feature dimensions the development of wet cleaning processes has to include wetting issues like the non-wetting of small features due to the surface energy of the liquid or pattern collapse effects of low-k dielectric trenches due to high capillary forces This work at first focuses on the determination of the surface energetic character of common cleaning solutions for PERR and differently etched or ashed low-k dielectric surfaces by contact angle analysis, to outline which combinations of solid and liquid will be critical regarding their wetting behavior. Besides the determination of the wetting behavior the contact angle analysis turned out to be a fast and sensible analytic tool to understand the surface modifications introduced by different plasma processes and can help to understand the mechanisms of plasma damage of low-k dielectric surfaces. The analysis showed that especially polymerizing plasma etch processes produce a low-energetic low-k dielectric surface with a negligible polar energy contributions, which inhibits their wetting by high energetic water based cleaning solutions, which actually are favored by semiconductor manufacturers. The strategy to overcome these wetting issues followed in the present work is the reduction of the surface energy of the cleaning liquids by the application of surfactants. Several types of surfactants have been applied to the cleaning liquids and the compatibility of the surfactant solutions to BEOL materials like low-k dielectrics, copper and diffusion barriers as well as their dynamic behavior has been studied. The analysis showed that choosing the appropriate rinsing solution after the cleaning process is essential to ensure its compatibility to porous low-k dielectrics. Optical, electrical and structural data indicated that DIW rinse in most of the cases was not able to remove residual surfactant species within the material, while for an IPA rinse most of the residual surfactants have been removed. Considering the data received for compatibility to low-k materials, copper and barriers, the dynamic behavior of the surfactant solutions as well as influences of increased bath temperature and long term stability a general advice about surfactant selection and processing of surfactant aided solutions within BEOL is given. / In mehrlagigen Kupfer/low-k basierten Metallisierungssystemen hochintegrierter elektronischer Bauelemente kann die Entfernung von Residuen nach der Plasmastrukturierung des Dielektrikums mittels herkömmlicher Plasmareinigungsprozesse zur Schädigung der Isolatorschicht und damit zum Ansteigen der relativen Dielektrizitätszahl sowie der Leckströme führen. Neben der Entwicklung schädigungsarmer Plasmaprozesse stellt der Ersatz dieser Prozesse durch Nassreinigungsschritte zur Ätzresiduenentfernung eine vielversprechende Alternative dar. Mit stetig abnehmenden Strukturabmaßen ist bei der Entwicklung dieser Nassreinigungsprozesse neben der Materialkompatibilität auch das Benetzungsverhalten der Reinigungsflüssigkeit von entscheidender Bedeutung, da die Oberflächenenergie der Reinigungslösung das Eindringen dieser in kleinste Strukturen verhindern und es durch hohe Kapillarkräfte zum Kollaps von Grabenstrukturen im Dielektrikum kommen kann. In der vorliegenden Arbeit wurde zunächst mittels Kontaktwinkelanalyse die Oberflächenenergie verschieden prozessierter low-k Dielektrikaschichten sowie herkömmlicher Lösungen zur Entfernung von Ätzresiduen untersucht, um hinsichtlich ihres Benetzungsverhaltens besonders kritische Materialkombinationen aufzuzeigen. Neben der Bestimmung des Benetzungsverhaltens hat sich die Kontaktwinkelanalyse zur Oberflächenenergieberechnung als schnelle und empfindliche Methode zur Analyse der Auswirkung von Plasmaprozessen auf die Oberfläche von low-k Dielektrika erwiesen. Die Untersuchungen haben gezeigt, dass besonders polymerisierende Plasmaprozesse eine niederenergetische Oberfläche erzeugen, welche von den derzeit in der Halbleiterfertigung bevorzugten hochenergetischen wasserbasierten Reinigungslösungen nur schlecht benetzt wird. Um diesem Effekt entgegenzuwirken wurde in der vorliegenden Arbeit die Senkung der Oberflächenenergie der Reinigungslösungen durch Zugabe von Tensiden untersucht. Es wurden mehrere Tenside unterschiedlichen Typs den Reinigungsflüssigkeiten zugemischt und die Kompatibilität dieser Lösungen mit low-k Dielektrika, Kupferschichten und Diffusionsbarrieren untersucht sowie ihr dynamisches Verhalten analysiert. Dabei hat sich gezeigt, dass die Auswahl der geeigneten Spüllösung nach dem eigentlichen Reinigungsprozess von entscheidender Bedeutung ist. Optische, elektrische sowie strukturelle Daten deuten darauf hin, dass bei Verwendung einer Spülung mit deionisiertem Wasser in den meisten Fällen Tensidrückstände im porösen Dielektrikum verbleiben. Eine Spülung mit Isopropanol war hingegen in der Lage, einen Großteil dieser Tensidrückstände zu entfernen. Unter Einbeziehung der Daten zur Materialkompatibilität und dem dynamischen Verhalten der Tensidlösungen bei Raumtemperatur und erhöhter Badtemperatur sowie ihrer Langzeitstabilität konnte schließlich eine Prozessempfehlung für die Verwendung der benetzungsoptimierten Reinigungslösungen in der BEOL-Prozessierung gefunden werden.

In multi-level Co/low-k based interconnect systems of ultralarge-scale integrated electronic devices the removal of plasma etch residues by common plasma cleaning processes has been shown to alter material properties like k-value and leakage current of the low-k dielectric. Besides the development of less damaging plasma processes their substitution by wet cleaning steps is in the focus of research and development. With further decreasing feature dimensions the development of wet cleaning processes has to include wetting issues like the non-wetting of small features due to the surface energy of the liquid or pattern collapse effects of low-k dielectric trenches due to high capillary forces This work at first focuses on the determination of the surface energetic character of common cleaning solutions for PERR and differently etched or ashed low-k dielectric surfaces by contact angle analysis, to outline which combinations of solid and liquid will be critical regarding their wetting behavior. Besides the determination of the wetting behavior the contact angle analysis turned out to be a fast and sensible analytic tool to understand the surface modifications introduced by different plasma processes and can help to understand the mechanisms of plasma damage of low-k dielectric surfaces. The analysis showed that especially polymerizing plasma etch processes produce a low-energetic low-k dielectric surface with a negligible polar energy contributions, which inhibits their wetting by high energetic water based cleaning solutions, which actually are favored by semiconductor manufacturers. The strategy to overcome these wetting issues followed in the present work is the reduction of the surface energy of the cleaning liquids by the application of surfactants. Several types of surfactants have been applied to the cleaning liquids and the compatibility of the surfactant solutions to BEOL materials like low-k dielectrics, copper and diffusion barriers as well as their dynamic behavior has been studied. The analysis showed that choosing the appropriate rinsing solution after the cleaning process is essential to ensure its compatibility to porous low-k dielectrics. Optical, electrical and structural data indicated that DIW rinse in most of the cases was not able to remove residual surfactant species within the material, while for an IPA rinse most of the residual surfactants have been removed. Considering the data received for compatibility to low-k materials, copper and barriers, the dynamic behavior of the surfactant solutions as well as influences of increased bath temperature and long term stability a general advice about surfactant selection and processing of surfactant aided solutions within BEOL is given. / In mehrlagigen Kupfer/low-k basierten Metallisierungssystemen hochintegrierter elektronischer Bauelemente kann die Entfernung von Residuen nach der Plasmastrukturierung des Dielektrikums mittels herkömmlicher Plasmareinigungsprozesse zur Schädigung der Isolatorschicht und damit zum Ansteigen der relativen Dielektrizitätszahl sowie der Leckströme führen. Neben der Entwicklung schädigungsarmer Plasmaprozesse stellt der Ersatz dieser Prozesse durch Nassreinigungsschritte zur Ätzresiduenentfernung eine vielversprechende Alternative dar. Mit stetig abnehmenden Strukturabmaßen ist bei der Entwicklung dieser Nassreinigungsprozesse neben der Materialkompatibilität auch das Benetzungsverhalten der Reinigungsflüssigkeit von entscheidender Bedeutung, da die Oberflächenenergie der Reinigungslösung das Eindringen dieser in kleinste Strukturen verhindern und es durch hohe Kapillarkräfte zum Kollaps von Grabenstrukturen im Dielektrikum kommen kann. In der vorliegenden Arbeit wurde zunächst mittels Kontaktwinkelanalyse die Oberflächenenergie verschieden prozessierter low-k Dielektrikaschichten sowie herkömmlicher Lösungen zur Entfernung von Ätzresiduen untersucht, um hinsichtlich ihres Benetzungsverhaltens besonders kritische Materialkombinationen aufzuzeigen. Neben der Bestimmung des Benetzungsverhaltens hat sich die Kontaktwinkelanalyse zur Oberflächenenergieberechnung als schnelle und empfindliche Methode zur Analyse der Auswirkung von Plasmaprozessen auf die Oberfläche von low-k Dielektrika erwiesen. Die Untersuchungen haben gezeigt, dass besonders polymerisierende Plasmaprozesse eine niederenergetische Oberfläche erzeugen, welche von den derzeit in der Halbleiterfertigung bevorzugten hochenergetischen wasserbasierten Reinigungslösungen nur schlecht benetzt wird. Um diesem Effekt entgegenzuwirken wurde in der vorliegenden Arbeit die Senkung der Oberflächenenergie der Reinigungslösungen durch Zugabe von Tensiden untersucht. Es wurden mehrere Tenside unterschiedlichen Typs den Reinigungsflüssigkeiten zugemischt und die Kompatibilität dieser Lösungen mit low-k Dielektrika, Kupferschichten und Diffusionsbarrieren untersucht sowie ihr dynamisches Verhalten analysiert. Dabei hat sich gezeigt, dass die Auswahl der geeigneten Spüllösung nach dem eigentlichen Reinigungsprozess von entscheidender Bedeutung ist. Optische, elektrische sowie strukturelle Daten deuten darauf hin, dass bei Verwendung einer Spülung mit deionisiertem Wasser in den meisten Fällen Tensidrückstände im porösen Dielektrikum verbleiben. Eine Spülung mit Isopropanol war hingegen in der Lage, einen Großteil dieser Tensidrückstände zu entfernen. Unter Einbeziehung der Daten zur Materialkompatibilität und dem dynamischen Verhalten der Tensidlösungen bei Raumtemperatur und erhöhter Badtemperatur sowie ihrer Langzeitstabilität konnte schließlich eine Prozessempfehlung für die Verwendung der benetzungsoptimierten Reinigungslösungen in der BEOL-Prozessierung gefunden werden.