Design Techniques for Lithography-Friendly Nanometer CMOS Integrated Circuits

The Integrated Circuits industry has been a major driver of the outstanding changes and improvements in the modern day technology and life style that we are observing in our day to day life. The continuous scaling of CMOS technology has been one of the major challenges and success stories. However, as the CMOS technology advances deeply into the deep sub-micron technology nodes, the whole industry (both manufacturing and design) is starting to face new challenges. One major challenge is the control of the variation in device parameters. Lithography variations result from the industry incapability to come up with new light sources with a smaller wavelength than ArF source (193 nm wavelength). In this research, we develop better understanding of the photo-lithography variations and their effect on how the design gets patterned. We investigate the state-of-the-art mask correction and design manipulation techniques. We are focusing in our study on the different Optical Proximity Correction (OPC) and design retargeting techniques to assess how we can improve both the functional and parametric yield. Our goal is to achieve a fast and accurate Model Based Re-Targeting (MBRT) technique that can achieve a better functional yield during manufacturing by establishing the techniques to produce more lithography-friendly targets. Moreover, it can be easily integrated into a fab's PDK (due to its relatively high speed) to feedback the exact final printing on wafer to the designers during the early design phase. In this thesis, we focus on two main topics. First is the development of a fast technique that can predict the final mask shape with reasonable accuracy. This is our proposed Model-based Initial Bias (MIB) methodology, in which we develop the full methodology for creating compact models that can predict the perturbation needed to get to an OPC initial condition that is much closer to the final solution. This is very useful in general in the OPC domain, where it can save almost 50% of the OPC runtime. We also use MIB in our proposed Model-Based Retargeting (MBRT) flow to accurately compute lithography hot-spots location and severity. Second, we develop the fast model-based retargeting methodology that is capable of fixing lithography hot spots and improving the functional yield. Moreover, in this methodology we introduce to the first time the concept of distributed retargeting. In distributed MBRT, not only the design portion that is suffering from the hot-spot is moving to get it fixed but also the surrounding designs and design fragments also contribute to the hot-spot fix. Our proposed model-based retargeting methodology also includes the multiple-patterning awareness as well as the electrical-connectivity-awareness (via-awareness). We used Mentor Graphics Calibre Litho-API c-based programing to develop all of the methodologies we explain in this thesis and tested it on 20nm and 10nm nodes

Resolution Enhancement Techniques (RET) for Immersion Lithography

Ph.DDOCTOR OF PHILOSOPH

High Efficiency Silicon Photonic Interconnects

Silicon photonic has provided an opportunity to enhance future processor speed by replacing copper interconnects with an on chip optical network. Although photonics are supposed to be efficient in terms of power consumption, speed, and bandwidth, the existing silicon photonic technologies involve problems limiting their efficiency. Examples of limitations to efficiency are transmission loss, coupling loss, modulation speed limited by electro-optical effect, large amount of energy required for thermal control of devices, and the bandwidth limit of existing optical routers. The objective of this dissertation is to investigate novel materials and methods to enhance the efficiency of silicon photonic devices. The first part of this dissertation covers the background, theory and design of on chip optical interconnects, specifically silicon photonic interconnects. The second part describes the work done to build a 300mm silicon photonic library, including its process flow, comprised of basic elements like electro-optical modulators, germanium detectors, Wavelength Division Multiplexing (WDM) interconnects, and a high efficiency grating coupler. The third part shows the works done to increase the efficiency of silicon photonic modulators, unitizing the χ(3) nonlinear effect of silicon nanocrystals to make DC Kerr effect electro-optical modulator, combining silicon with lithium niobate to make χ(2) electro-optical modulators on silicon, and increasing the efficiency of thermal control by incorporating micro-oven structures in electro-optical modulators. The fourth part introduces work done on dynamic optical interconnects including a broadband optical router, single photon level adiabatic wavelength conversion, and optical signal delay. The final part summarizes the work and talks about future development

Integrated Bragg gratings in silicon-on-insulator

Dans la littérature, les réseaux de Bragg intégrés sur silicium sont relativement simples par rapport à leurs contreparties fibrées. Cependant, la fabrication de réseaux plus élaborés permettrait d’améliorer la capacité de traitement du signal des circuits sur silicium. Cette thèse s’attarde donc aux difficultés encourues lors de la conception, de la fabrication et de la caractérisation de réseaux de Bragg sur silicium ayant une réponse spectrale élaborée. Tout d'abord, afin de caractériser la réponse spectrale complexe des réseaux, l’utilisation de filtrage temporel est proposée afin de supprimer les réflexions parasites. Cela a permis d’utiliser des algorithmes de reconstruction fournissant une caractérisation complète de ces structures. De plus, l’ajout d’un filtrage des hautes fréquences spatiales a permis de réduire considérablement le bruit des mesures. Par la suite, les principales sources de distorsions de la réponse spectrale des réseaux ont été identifiées, soit la rugosité des guides et la variation de leur épaisseur. L’impact de ces phénomènes a été étudié numériquement et analytiquement et, pour la première fois, la longueur de corrélation de ces sources de bruit a été caractérisée expérimentalement sur une longueur suffisante. Finalement, deux techniques permettant de diminuer l’impact de ces phénomènes ont été proposées, ce qui a permis de fabriquer les réseaux de Bragg sur silicium ayant la plus petite largeur de bande publiée à ce jour. Également, nous avons fait les premières démonstrations d’apodisation de réseaux de Bragg utilisant uniquement la phase de ces derniers (c.-à-d. apodisation en phase et par superposition). Contrairement aux techniques déjà proposées, ces dernières ont l'avantage de ne pas introduire de distorsions de l'indice effectif, ils sont plus robuste aux erreurs de fabrication et sont compatibles avec l’apodisation de réseaux à corrugations de très petites amplitudes. Finalement, afin d'augmenter la longueur des réseaux tout en gardant leur dimension compatible avec la taille des puces de silicium, les réseaux ont été courbés en forme de spirale compacte. Pour ce faire, la période des réseaux a été modifiée afin de compenser l'effet de la courbure sur l'indice effectif. Ainsi, nous avons démontré que des réseaux de 2 mm de long pouvaient être intégrés sur une surface de 200 µm x 190 µm sans ajout de dégradation spectrale et, surtout, sans restriction sur la structure du design. Ces résultats sont significatifs, car un contrôle précis de la phase et de l’amplitude des réseaux combinés avec la capacité de fabriquer de réseaux longs sont nécessaire afin de réaliser des filtres optiques intégrés avec des réponses spectrales élaborées. Ainsi, le travail présenté dans cette thèse ouvre la porte à de nouveaux designs à base de réseaux de Bragg.In the literature, integrated Bragg gratings in Silicon-on-Insulator are relatively simple compared to their fibre Bragg grating counterpart. However, elaborate gratings could improve the signal processing capability of the silicon platform. Thus, this thesis addresses the issues that prevent the design, the fabrication and the characterization of Bragg gratings having elaborate spectral response in the silicon platform. Firstly, in order to precisely characterize Bragg gratings complex spectral response, we proposed to suppress parasitic reflections using temporal filtering. The results obtained with measurement technique, when used with an integral layer peeling algorithm, allowed us to retrieve the amplitude and phase profiles of the grating thus providing a complete characterization of the structure. Moreover, the addition of a low-pass spatial filter allowed improving the characterization process by reducing the measurement noise. Secondly, the main sources of distortion of Bragg gratings spectral response have been identified to be the sidewall roughness and the wafer height fluctuation. An exhaustive study of the impact of these phenomena has been done both numerically and analytically. Furthermore, for the first time, the autocorrelation of these noise sources has been characterized experimentally on a sufficient length. Finally, improvements in the waveguide designs have reduced significantly these effects which allowed the fabrication of Bragg gratings in silicon with the smallest bandwidth published to date. Thirdly, the first demonstration of apodized Bragg gratings using only phase modulation of the structure has been done (i.e. phase apodisation and superposition apodisation). Unlike already published techniques, the later ones have the advantage to be robust to deep-UV lithography and fabrication errors. Furthermore, they do no introduce distortions into the grating phase profile and they are compatible with gratings having small recesses. Finally, in order to increase the grating length while keeping their dimension compatible with the silicon chip size, we proposed to bend them in a compact spiral shape. To do this properly, the curvature impact on the effective index has been modeled and compensated successfully by modifying the grating period. Thus, we have shown that 2 mm long gratings can be integrated on a surface of 200 µm x 190 µm without the addition of spectral degradation and without restrictions on the design structure. These results are of importance because longer grating structures with weaker coupling coefficients and a precise control both on its phase and amplitude are required in order to achieve integrated optical filters with elaborate spectral responses. Thus, we believe that the work presented in this thesis open the door to many new grating-based optical filter designs compatible with integrated optics technologies

Optical thin film measurement by interferometric fringe projection and fluorescence stimulated emission

The introduction of a new technique for metrology of thin liquid films to give both the profile of the exterior surface and information on the thickness of the film is the main focus of this research. The proposed approach is based on the use of fringe projection system with a narrow band laser illumination and a high concentration of fluorescent dye dissolved in the fluid in order to generate fluorescence emission from minimum thickness of the film (i.e. the top few microns). The method relies on calculation of an interference phase term and the modulation depth of the fringes created by means of a twin fibre configuration. The characterisation of candidate fluorescent dyes in terms of absorption, related to the depth of penetration of the incident light into the dye and their fluorescence emission efficiency is presented and their application in full field imaging experiments is evaluated. A strong focus of the technique proposed is its flexibility and versatility allowing its extension to phase stepping techniques applied to determine the (fringe) phase map from static and dynamic fluids. Some experiments are carried out using the best dye solution in terms of fluorescence emission and light depth penetration. On the basis of the phase-height relationship achieved during the calibration process, the proposed measurement system is applied for the shape measurement of some static fluids. The profile of the exterior surface of these fluids is investigated by means of phasestepping technique and the resolution of the measurements is estimated. Furthermore a flow rig set-up based on inclined system (gravity assisted) is presented in order to test the shape measurement system in presence of real liquid flows. Different liquid flow thicknesses are processed and analysed. Example data will be included from some fluid films of known geometry in order to validate the method

Reconfigurable Phase-Change Metasurface Absorbers for Optoelectronics Device Applications

This thesis is concerned with the design and development of dynamically reconfigurable optical metasurfaces. This reconfigurability is achieved by integrating chalcogenide phase-change materials with plasmonic resonator structures of the metal-insulator-metal type. Switching the phase-change material between its amorphous and crystalline states results in dramatic changes in its optical properties, with consequent dramatic changes in the resonant behaviour of the plasmonic metasurface with which it is integrated. Moreover, such changes are non-volatile, reversible and potentially very fast, in the order of nanoseconds. The first part of the thesis is dedicated to the design, fabrication and characterisation of metasurface devices working at telecommunications wavelengths, specifically at wavelengths corresponding to the C-band (1530 to 1565 nm), and that act as a form of perfect absorber when the phase-change layer (in this case Ge2Sb2Te5) is amorphous but reflect strongly when switched to the crystalline state. Such behaviour can be used, for example, to provide a form of optical amplitude modulator. Fabricated devices not only showed very good performance, including a large modulation depth of ~77% and an extinction ratio of ~20 dB, but also incorporated a number of practicable design features often overlooked in the literature, including a means for protecting the phase-change layer from environmental oxidation and, importantly, an electrically-driven in-situ switching capability. In the second part of the thesis a method, based on eigenmode analysis and critical coupling theory, is developed to allow for the design and fabrication of perfect absorber type devices in a simple and efficient way, while at the same time maintaining design control over the key performance characteristics of resonant frequency, reflection coefficient at resonance and quality factor. Validation of this new method was carried out via the design and fabrication of a family of absorbers with a range of ‘on-demand’ quality factors, all operating at the same resonant frequency and able to be fabricated simply and simultaneously on the same chip. The final part of the thesis is concerned with the design and development of a switchable phase-change metamaterial type absorber working in the visible part of the spectrum and with non-volatile colour generating capability. With the phase-change layer, here GeTe, in the crystalline phase, the absorber can be tuned to selectively absorb the red, green and blue spectral bands, so generating vivid cyan, magenta and yellow pixels. When the phase-change layer is switched into the amorphous phase, the resonant absorption is suppressed and a flat, pseudo-white reflectance results. This potentially opens up a route to the development of non-volatile, phase-change metamaterial colour displays and colour electronic signage.Engineering and Physical Sciences Research Council (EPSRC