As optical designs become more sophisticated and incorporate aspheric and free form surfaces, the need to specify limits on mid-spatial frequency manufacturing errors becomes more critical, particularly as we better understand the effects of these errors on image quality. While there already exist methods based on Fourier analysis to specify these errors in most commercial interferometry software, the method of calculation and the power spectral density (PSD) results remain obscure to many in the optical design and manufacturing field. We suggest that the structure functions (SF) contains the same information as in the Fourier based PSD but in a way that is much more transparent to analysis, interpretation and application as a specification. The units of measure are more familiar and the concept behind the analysis is simpler to understand. Further, the information contained in the structure function (or PSD) allows a complete specification of an optical surface from the finest measurable detail of roughness to the overall figure. We discuss the origin of the structure function in the field of astronomy to describe the effects of air turbulence on image quality, the simple mathematical definition of the structure function and its easy means of calculation and how its results should be scaled depending on the location of the optical surface in a system from pupil to image plane. Finally, we give an example of how to write a specification of an optical surface using the structure function.

A nanotecnologia não é mais um sonho, já faz parte da nossa realidade, do nosso dia a dia. É considerada, por muitos, a quinta Revolução Industrial, uma revolução tecnológica de grande abrangência, que poderá causar impactos talvez sem precedentes na história. A soma anual dos investimentos nesta nova tecnologia é de bilhões de dólares. Devido às inovações oriundas da nanotecnologia, os processos da manufatura e a medição de ultra-precisão vêm se desenvolvendo a cada dia. A nanotecnologia fez da usinagem de ultraprecisão com ferramenta de diamante uma grande aplicação na produção de itens de alto volume, tais como: disco de memória de computadores, lentes de contato, moldes de dentes, cilindros para impressão, espelhos metálicos. A alta integridade da superfície é requerida em todos os itens obtidos por este processo. Em conseqüência, é necessário um método de medição que seja o mais exato possível, isto é, que chegue a resultados o mais próximo possível do valor verdadeiro. Mas o que significa exatidão para uma análise ideal da superfície, uma vez que não existe referência para isso? Superfícies têm sido avaliadas por meio da medição da rugosidade, a qual consiste na determinação de um valor médio, de vários setores, dentro de valores limites preestabelecidos. A metrologia, através de seus métodos e princípios, é um importante instrumento para validar modelos e teorias. O conceito que \"uma vez testado, passa a ser aceito em qualquer lugar\". Daí a crescente necessidade de resultados de medições confiáveis que possam ser validados em qualquer lugar e a qualquer tempo. Assim, um caminho a ser seguido é o de se entenderem profundamente todos os métodos e princípios envolvidos nas operações de medição de rugosidade. E para que um método seja metrologicamente válido (ou aceitável), faz-se necessário realizarem-se comparações de diversas medições, de um mesmo mensurando, utilizando métodos diversos. Havendo discrepância nos resultados, é uma evidência de que as premissas e hipóteses levaram a acreditar que a teoria ou modelo adotado deve ser reavaliado. Este trabalho selecionou os três métodos mais utilizados na caracterização da integridade de superfícies técnicas obtida em torneamento de ultraprecisão com diamante, e descreveu uma metodologia para a avaliação da capabilidade do processo de controle de superfícies técnicas usinadas em torno de ultraprecisão. / Nanotechnology is no longer a dream. It is part of the real world. It is considered by many people as the fifth Industrial Revolution, a technological revolution of great impact in history. The world annual investment in this technology reaches billions of dollars. Due to innovations related to nanotechnology, ultraprecision manufacturing processes and metrology is developing steeply. Nanotechnology made single point diamond turning an important mass production process of, for instance, computer hard discs, contact lenses, moulds, printer cylinders, metallic mirrors, etc. High grade surface integrity is required of items produced by this process. As a consequence, it is necessary to use a measurement method which is most accurate as possible, i.e., resulting in a value as close as possible to the true. But what does true mean if there is no reference for that? Surfaces have been assessed by roughness measurements which determines a mean value of several sectors within pre-determined limits. Metrology, with its methods and principles, is an important instrument to validate models and theories. The concept, once tested, becomes accepted everywhere. Therefore the increasing necessity of reliable measurement results which may be validated anywhere and any time. Thus, it is essential a deep understanding of all methods and principles involved in roughness metrology operations. For a method to be metrologically accepted, it is necessary that it is compared with different methods. In the event of existing discrepancies, the premisses and hypotheses which fundamented the theory or model should be reassessed. Three of the most used methods have been selected to characterize the surface integrity of technical surfaces generated by diamond turning. A methodology to assess the capability of the process of control of those surfaces is proposed.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

A nanotecnologia não é mais um sonho, já faz parte da nossa realidade, do nosso dia a dia. É considerada, por muitos, a quinta Revolução Industrial, uma revolução tecnológica de grande abrangência, que poderá causar impactos talvez sem precedentes na história. A soma anual dos investimentos nesta nova tecnologia é de bilhões de dólares. Devido às inovações oriundas da nanotecnologia, os processos da manufatura e a medição de ultra-precisão vêm se desenvolvendo a cada dia. A nanotecnologia fez da usinagem de ultraprecisão com ferramenta de diamante uma grande aplicação na produção de itens de alto volume, tais como: disco de memória de computadores, lentes de contato, moldes de dentes, cilindros para impressão, espelhos metálicos. A alta integridade da superfície é requerida em todos os itens obtidos por este processo. Em conseqüência, é necessário um método de medição que seja o mais exato possível, isto é, que chegue a resultados o mais próximo possível do valor verdadeiro. Mas o que significa exatidão para uma análise ideal da superfície, uma vez que não existe referência para isso? Superfícies têm sido avaliadas por meio da medição da rugosidade, a qual consiste na determinação de um valor médio, de vários setores, dentro de valores limites preestabelecidos. A metrologia, através de seus métodos e princípios, é um importante instrumento para validar modelos e teorias. O conceito que \"uma vez testado, passa a ser aceito em qualquer lugar\". Daí a crescente necessidade de resultados de medições confiáveis que possam ser validados em qualquer lugar e a qualquer tempo. Assim, um caminho a ser seguido é o de se entenderem profundamente todos os métodos e princípios envolvidos nas operações de medição de rugosidade. E para que um método seja metrologicamente válido (ou aceitável), faz-se necessário realizarem-se comparações de diversas medições, de um mesmo mensurando, utilizando métodos diversos. Havendo discrepância nos resultados, é uma evidência de que as premissas e hipóteses levaram a acreditar que a teoria ou modelo adotado deve ser reavaliado. Este trabalho selecionou os três métodos mais utilizados na caracterização da integridade de superfícies técnicas obtida em torneamento de ultraprecisão com diamante, e descreveu uma metodologia para a avaliação da capabilidade do processo de controle de superfícies técnicas usinadas em torno de ultraprecisão. / Nanotechnology is no longer a dream. It is part of the real world. It is considered by many people as the fifth Industrial Revolution, a technological revolution of great impact in history. The world annual investment in this technology reaches billions of dollars. Due to innovations related to nanotechnology, ultraprecision manufacturing processes and metrology is developing steeply. Nanotechnology made single point diamond turning an important mass production process of, for instance, computer hard discs, contact lenses, moulds, printer cylinders, metallic mirrors, etc. High grade surface integrity is required of items produced by this process. As a consequence, it is necessary to use a measurement method which is most accurate as possible, i.e., resulting in a value as close as possible to the true. But what does true mean if there is no reference for that? Surfaces have been assessed by roughness measurements which determines a mean value of several sectors within pre-determined limits. Metrology, with its methods and principles, is an important instrument to validate models and theories. The concept, once tested, becomes accepted everywhere. Therefore the increasing necessity of reliable measurement results which may be validated anywhere and any time. Thus, it is essential a deep understanding of all methods and principles involved in roughness metrology operations. For a method to be metrologically accepted, it is necessary that it is compared with different methods. In the event of existing discrepancies, the premisses and hypotheses which fundamented the theory or model should be reassessed. Three of the most used methods have been selected to characterize the surface integrity of technical surfaces generated by diamond turning. A methodology to assess the capability of the process of control of those surfaces is proposed.

This thesis contains theoretical analysis of optimization methods of cutting conditions for current machining processes with focus on finishing turning. Further focus was put on influences of cutting conditions and other effects on requested quality and roughness of machined surface. The effect of part of these conditions was verified in experimental part. The influence of feed rate and depth of cut on surface roughness and geometrical accuracy was experimentally verified.

This thesis is titled "A Framework for Enhancing the Accuracy of Ultra Precision Machining." In this thesis unwanted relative tool / workpiece vibration is identified as a major contributor to workpiece inaccuracy. The phenomenon is studied via in situ vibrational measurements during cutting and also by the analysis of the workpiece surface metrology of ultra precision diamond face turned aluminum 6061-T6. The manifestation of vibrations in the feed and in-feed directions of the workpiece was studied over a broadband of disturbance frequencies. It is found that the waviness error measured on the cut workpiece surface was significantly larger than that caused by the feed marks during cutting. Thus it was established that unwanted relative tool / workpiece vibrations are the dominant source of surface finish error in ultra precision machining. By deriving representative equations in the polar coordinate system, it was found that the vibrational pattern repeats itself, leading to what are referred to in this thesis as surface finish lobes. The surface finish lobes describe the waviness or form error associated with a particular frequency of unwanted relative tool / workpiece vibration, given a particular feed rate and spindle speed. With the surface finish lobes, the study of vibrations is both simplified and made more systematic. Knowing a priori the wavelength range caused by relative tool / workpiece vibration also allows one to extract considerable vibration content information from a small white light interferometry field of view. It was demonstrated analytically that the error caused by relative tool / workpiece vibration is always distinct from the surface roughness caused by the feed rate. It was also shown that the relative tool / workpiece vibration-induced wavelength in the feed direction has a limited and repeating range. Additionally, multiple disturbance frequencies can produce the same error wavelength on the workpiece surface. Since the meaningful error wavelength range is finite given the size of the part and repeating, study then focussed on this small and manageable range of wavelengths. This range of wavelengths in turn encompasses a broadband range of possible disturbance frequencies, due to the repetition described by the surface finish lobes. Over this finite range of wavelengths, for different machining conditions, the magnitude of the waviness error resulting on the cut workpiece surface was compared with the actual relative tool / workpiece vibrational magnitude itself. It was found that several opportunities occur in ultra precision machining to mitigate the vibrational effect on the workpiece surface. The first opportunity depends only on the feed rate and spindle speed. Essentially, it is possible to force the wavelength resulting from an unwanted relative tool / workpiece vibration to a near infinite length, thus eliminating its effect in the workpiece feed direction. Further, for a given disturbance frequency, various speed and feed rate combinations are capable of producing this effect. However, this possibility exists only when a single, dominant and fixed disturbance frequency is present in the process. By considering the tool nose geometry, depth of cut, and vibrational amplitude over the surface finish lobe finite range, it was found that the cutting parameters exhibit an attenuating or filtering effect on vibrations. Thus, cutting parameters serve to mitigate the vibrational effect on the finished workpiece over certain wavelengths. The filter curves associated with various feed rates were compared. These filter curves describe the magnitude of error on the ultra precision face turned workpiece surface compared with the original unwanted tool / workpiece vibrational magnitude. It was demonstrated with experimental data that these filter curves are physically evident on the ultra precision diamond face turned workpiece surface. It was further shown that the surface roughness on the workpiece surface caused by the feed rate was reduced with relative tool / workpiece vibrations, and in some cases the feed mark wavelength was changed altogether. Mean arithmetic surface roughness curves were also constructed, and the filtering phenomenon was demonstrated over a broadband of disturbance frequencies. It is well established that a decrease in the feed rate reduces the surface roughness in machining. However, it was demonstrated that the improved surface finish observed with a slower feed rate in ultra precision diamond face turning was actually because it more effectively mitigated the vibrational effect on the workpiece surface over a broadband of disturbance frequencies. Experimental findings validated this observation. By only considering the effect of vibrations on the surface finish waviness error, it was shown that the workpiece diamond face turned with a feed rate of 2 {tm / rev has a mean arithmetic surface roughness, Ra , that was 43 per cent smaller than when a feed rate of 10 μm / rev was used. / Thesis / Doctor of Philosophy (PhD)

Das reaktiv gesteuerte Ionenstrahlätzen von optischen Aluminiumoberflächen bietet einen vielversprechenden Prozessansatz, um Formfehlerkorrektur, Glättung periodischer Drehstrukturen und die Reduzierung von Rauheitsmerkmalen im Ortsfrequenzbereich der Mikrorauheit in einer Technologie zu kombinieren. Diese Arbeit konzentriert sich auf die experimentelle Analyse der niederenergetischen Ionenbestrahlung von einkorn-diamantgedrehten, technischen Aluminiumlegierungen RSA Al6061 und RSA Al905. Die Ionenstrahlbearbeitung unter Verwendung der Prozessgase Sauerstoff und Stickstoff ermöglicht eine direkte Oberflächenformfehlerkorrektur bis zu 1 µm Bearbeitungstiefe unter Beibehaltung der Ausgangsrauheit. Die sich aus dem vorangegangenen Formgebungsverfahren, dem Einkorn-diamantdrehen, ergebende Drehmarkenstruktur schränkt allerdings häufig die Anwendbarkeit dieser Spiegeloberflächen im kurzwelligen Spektralbereich ein. Daher wurde im Rahmen dieser Arbeit ein zweistufiger Prozessablauf entwickelt, um eine weitere Verbesserung der Oberflächenrauheit zu erreichen. Durch die Ionenstrahl-Planarisierungstechnik unter Verwendung einer Opferschicht werden die im hohen Ortsfrequenzbereich liegenden Drehmarken erfolgreich um insgesamt 82 % reduziert. Eine Kombination mit anschließender, direkter Ionenstrahlglättung zur nachfolgenden Verbesserung der Mikrorauigkeit wird vorgestellt. Um die Prozessführung in einem industrietauglichen Rahmen zu etablieren, wurden die experimentellen Untersuchungen mit einer 13,56 MHz betriebenen Hochfrequenz-Ionenquelle durchgeführt, konnten aber auch erfolgreich auf eine Breitstrahl-Ionenquelle vom Typ Kaufman übertragen werden.:Bibliographische Beschreibung iv Danksagung vi Table of Contents viii 1 Introduction 1 2 Surface engineering with energetic ions 8 2.1 Ion target interactions during ion beam erosion 8 2.2 Ion beam finishing methods 10 2.2.1 Ion beam figuring 11 2.2.2 Ion beam planarization 12 2.2.3 Ion beam smoothing 14 3 Experimental set-up and analytical methods 15 3.1 Experimental set-up 15 3.2 Kaufman-type broad beam ion source 18 3.3 Materials 19 3.3.1 Aluminium alloy materials 19 3.3.2 Photoresist materials as planarization layer 21 3.4 Surface topography error regimes 22 3.5 Analytical Methods 23 3.5.1 Analysis of surface roughness 23 3.5.1.1 White light interferometry (WLI) 23 3.5.1.2 Atomic force microscopy (AFM) 25 3.5.1.3 Power spectral density (PSD) analysis 27 3.5.2 Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) 29 3.5.3 X-ray photoelectron spectroscopy (XPS) 31 3.5.4 Time of flight- secondary ion mass spectrometry (ToF-SIMS) 32 3.5.5 Reflectometry 34 3.5.6 Photoresist composition 35 3.5.6.1 Attenuated total reflection infrared spectroscopy (ATR-IR) 35 3.5.6.2 Thermogravimetric analysis (TGA) 36 3.5.6.3 Differential scanning calorimetry (DSC) 38 3.5.6.4 Gas chromatography coupled mass spectrometry (GC-MS) 39 4 Surface engineering by reactive ion beam etching 41 4.1 Reactive ion beam etching with nitrogen 41 4.1.1 Dependence of the aluminium alloy composition 42 4.1.2 Ion beam etching of Al905 44 4.2 Local smoothing by reactive ion beam etching 50 4.2.1 Local surface error slope dependent sputter erosion 51 4.2.2 RIBE O2 direct smoothing 56 4.2.2.1 Oxygen finishing at 1.5 keV 56 4.2.2.2 Oxygen finishing at 0.6 keV 62 4.3 Conclusions 66 5 Technological aspects on photoresist preparation for ion beam planarization 69 5.1 Selection of a suitable photoresist 69 5.2 Photoresist application steps 71 5.2.1 DUV exposure of the photoresist layer 72 5.2.2 Postbake: the influence of the amount of organic solvent 73 5.2.3 Postbake: the influence of the baking temperature 74 5.3 Influence of process gas composition 77 5.3.1 Influence on roughness evolution during ion beam irradiation of the photoresist layer 78 5.3.2 Dependency of the process gas on the selectivity 79 5.4 Influence of the ion energy on the selectivity 80 5.5 Ion beam irradiation of the photoresist layer with nitrogen at different material removal depths 81 5.6 Conclusions 82 6 Ion beam planarization of optical aluminium surfaces RSA Al6061 and RSA Al905 84 6.1 Photoresist application on SPDT aluminium alloys 84 6.2 Ion beam planarization 85 6.2.1 Iterative nitrogen processing of RSA Al905 86 6.2.2 Iterative nitrogen processing of RSA Al6061 90 6.3 Ion beam direct smoothing 93 6.3.1 RIBE O2 smoothing of RSA Al905 93 6.3.2 RIBE O2 smoothing of RSA Al6061 97 6.4 Conclusions 101 7 Process transfer to a Kaufman-type broad beam ion source 103 7.1 RIBE machining investigations on RSA Al905 103 7.2 Ion beam planarization of RSA Al6061 106 7.3 Ion beam incidence angle dependent sputtering 107 7.4 Conclusions 113 8 Summary 115 9 Conclusions and Outlook 123 A List of abbreviations 127 B Selected properties of photoresist materials 129 References 131 / Reactively driven ion beam etching of optical aluminium surfaces provides a promising process route to combine figure error correction, smoothing of periodically turning structures and roughness features situated in the microroughness regime within one technology. This thesis focuses on experimental analysis of low-energy ion beam irradiation on single-point diamond turned technical aluminium alloys RSA Al6061 and RSA Al905. Reactively driven ion beam machining using oxygen and nitrogen process gases enables the direct surface error correction up to 1 µm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Hence, during this work a two-step process route was developed to attain further improvement of the surface roughness. Within the ion beam planarization technique with the aid of a sacrificial layer, the turning marks situated in the high spatial frequency range are successfully reduced by overall 82 %. A combination with subsequently applied direct ion beam smoothing procedure to perform a subsequent improvement of the microroughness is presented. In order to establish the process control in an industrial framework, the experimental investigations were performed using a 13.56 MHz radio frequency ion source, but the developed process routes are also successfully transferred to a broad-beam Kaufman-type ion source.:Bibliographische Beschreibung iv Danksagung vi Table of Contents viii 1 Introduction 1 2 Surface engineering with energetic ions 8 2.1 Ion target interactions during ion beam erosion 8 2.2 Ion beam finishing methods 10 2.2.1 Ion beam figuring 11 2.2.2 Ion beam planarization 12 2.2.3 Ion beam smoothing 14 3 Experimental set-up and analytical methods 15 3.1 Experimental set-up 15 3.2 Kaufman-type broad beam ion source 18 3.3 Materials 19 3.3.1 Aluminium alloy materials 19 3.3.2 Photoresist materials as planarization layer 21 3.4 Surface topography error regimes 22 3.5 Analytical Methods 23 3.5.1 Analysis of surface roughness 23 3.5.1.1 White light interferometry (WLI) 23 3.5.1.2 Atomic force microscopy (AFM) 25 3.5.1.3 Power spectral density (PSD) analysis 27 3.5.2 Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) 29 3.5.3 X-ray photoelectron spectroscopy (XPS) 31 3.5.4 Time of flight- secondary ion mass spectrometry (ToF-SIMS) 32 3.5.5 Reflectometry 34 3.5.6 Photoresist composition 35 3.5.6.1 Attenuated total reflection infrared spectroscopy (ATR-IR) 35 3.5.6.2 Thermogravimetric analysis (TGA) 36 3.5.6.3 Differential scanning calorimetry (DSC) 38 3.5.6.4 Gas chromatography coupled mass spectrometry (GC-MS) 39 4 Surface engineering by reactive ion beam etching 41 4.1 Reactive ion beam etching with nitrogen 41 4.1.1 Dependence of the aluminium alloy composition 42 4.1.2 Ion beam etching of Al905 44 4.2 Local smoothing by reactive ion beam etching 50 4.2.1 Local surface error slope dependent sputter erosion 51 4.2.2 RIBE O2 direct smoothing 56 4.2.2.1 Oxygen finishing at 1.5 keV 56 4.2.2.2 Oxygen finishing at 0.6 keV 62 4.3 Conclusions 66 5 Technological aspects on photoresist preparation for ion beam planarization 69 5.1 Selection of a suitable photoresist 69 5.2 Photoresist application steps 71 5.2.1 DUV exposure of the photoresist layer 72 5.2.2 Postbake: the influence of the amount of organic solvent 73 5.2.3 Postbake: the influence of the baking temperature 74 5.3 Influence of process gas composition 77 5.3.1 Influence on roughness evolution during ion beam irradiation of the photoresist layer 78 5.3.2 Dependency of the process gas on the selectivity 79 5.4 Influence of the ion energy on the selectivity 80 5.5 Ion beam irradiation of the photoresist layer with nitrogen at different material removal depths 81 5.6 Conclusions 82 6 Ion beam planarization of optical aluminium surfaces RSA Al6061 and RSA Al905 84 6.1 Photoresist application on SPDT aluminium alloys 84 6.2 Ion beam planarization 85 6.2.1 Iterative nitrogen processing of RSA Al905 86 6.2.2 Iterative nitrogen processing of RSA Al6061 90 6.3 Ion beam direct smoothing 93 6.3.1 RIBE O2 smoothing of RSA Al905 93 6.3.2 RIBE O2 smoothing of RSA Al6061 97 6.4 Conclusions 101 7 Process transfer to a Kaufman-type broad beam ion source 103 7.1 RIBE machining investigations on RSA Al905 103 7.2 Ion beam planarization of RSA Al6061 106 7.3 Ion beam incidence angle dependent sputtering 107 7.4 Conclusions 113 8 Summary 115 9 Conclusions and Outlook 123 A List of abbreviations 127 B Selected properties of photoresist materials 129 References 131