Precision Surface Processing and Software Modelling Using Shear-Thickening Polishing Slurries

Mid-spatial frequency surface error is a known manufacturing defect for aspherical and freeform precision surfaces. These surface ripples decrease imaging contrast and system signal-to-noise ratio. Existing sub-aperture polishing techniques are limited in their abilities to smooth mid-spatial frequency errors. Shear-thickening slurries have been hypothesised to reduce mid-spatial frequency errors on precision optical surfaces by increasing the viscosity at the tool-part interface. Currently, controlling the generation and mitigating existing mid-spatial frequency surface errors for aspherical and freeform surfaces requires extensive setup and the experience of seasoned workers. This thesis reports on the experimental trials of shear-thickening polishing slurries on glass surfaces. By incorporating shear-thickening slurries with the precessed bonnet technology, the aim is to enhance the ability of the precessions technology in mitigating mid-spatial frequency errors. The findings could facilitate a more streamlined manufacturing chain for precision optics for the versatile precessions technology from form correction and texture improvement, to MSF mitigation, without needing to rely on other polishing technologies. Such improvement on the existing bonnet polishing would provide a vital steppingstone towards building a fully autonomous manufacturing cell in a market of continual economic growth. The experiments in this thesis analysed the capabilities of two shear-thickening slurry systems: (1) polyethylene glycol with silica nanoparticle suspension, and (2) water and cornstarch suspension. Both slurry systems demonstrated the ability at mitigating existing surface ripples. Looking at power spectral density graphs, polyethylene glycol slurries reduced the power of the mid-spatial frequencies by ~50% and cornstarch suspension slurries by 60-90%. Experiments of a novel polishing approach are also reported in this thesis to rotate a precessed bonnet at a predetermined working distance above the workpiece surface. The rapidly rotating tool draws in the shear-thickening slurry through the gap to stiffen the fluid for polishing. This technique demonstrated material removal capabilities using cornstarch suspension slurries at a working distance of 1.0-1.5mm. The volumetric removal rate from this process is ~5% of that of contact bonnet polishing, so this aligns more as a finishing process. This polishing technique was given the term rheological bonnet finishing. The rheological properties of cornstarch suspension slurries were tested using a rheometer and modelled through CFD simulation. Using the empirical rheological data, polishing simulations of the rheological bonnet finishing process were modelled in Ansys to analyse the effects of various input parameters such as working distance, tool headspeed, precess angle, and slurry viscosity

Electro-kinetically enhanced nano-metric material removal

This project is a fundamental proof of concept to look at the feasibility of using field activated abrasive particles to achieve material removal on a substrate. There are a few different goals for this project. The first goal is to prove through visualization that particle movement can be influenced and controlled by changes in electric field. The second goal is to fundamentally prove that particles controlled by electric field can remove material from a substrate. Third, it should be shown that changes in electric field can control the amount of material being removed in a given amount of time. A mathematical model will be presented which predicts metallic material removal rates based on changes in electric field strength. In this project, a technique combining concepts from electrokinetics, electrochemical mechanical planarization, and contact mechanics is proposed, aiming at enhancing planarization performance. By introducing an AC electric field with a DC offset, we try to achieve not only a better control of metallic material removal but also more flexible manipulation of the dynamic behaviour of abrasive particles. The presence of electric field will lead to electrokinetic phenomena including electroosmotic flow of an electrolyte solution and electrophoretic motion of abrasive particles. As a result, we aim to improve both the mechanical performance of planarization that is largely determined by the polishing parameters (e.g. down pressure, rotation speed, pads, and types of abrasives) and the chemical performance of planarization that is governed by selective and collective reactions of different chemical ingrediants of the slurry with the sample surface. The aim is also to understand and improve the interactions of abrasive particles with the sample.M.S.Committee Chair: Danyluk, Steven; Committee Member: Butler, David; Committee Member: Hesketh, Peter; Committee Member: Yoda, Minam

Investigation of novel alumina nanoabrasive and the interactions with basic chemical components in copper chemical mechanical planarization (CMP) slurries

Chemical mechanical planarization (CMP) is an enabling process technology for IC fabrication to maintain global planarity across the wafer to satisfy lithographic depth of focus constraints. It also enables integration of materials that cannot be anisotropically etched, such as Cu. CMP utilizes nanoparticle abrasives in aqueous slurry to aid in planarization

Cytotoxicity of engineered nanoparticles used in industrial processing

Engineered nanoparticles (NPs) are now heavily used in industrial processing where they are eliminated as waste after use. This waste is a mix of used nanoparticles and process byproducts. While research continues to be done on the toxicity of NPs due to size and composition of pristine material, waste NPs from industrial processes are likely to have modified properties that impact their level of toxicity. These studies investigate this transformation in physicochemical properties that has not been adequately explored by examining waste from relevant high-volume chemical mechanical planarization (CMP) processes used by the semiconductor industry. New (pristine) polish slurries and generated waste samples from various key CMP processes are fully characterized for relevant physicochemical properties to determine any transformation of NPs due to processing. Additionally, high throughput in vitro microplate-based assays assess the toxicity, oxidative stress, and mode of cell death for nanoparticles in both pristine and waste slurries to highlight any differences in biological effects. A combination of darkfield microscopy and inductively coupled plasma optical emission spectroscopy (ICP-OES) indicate cellular uptake of slurry nanoparticles. The results of this study explore the type, magnitude, and biological effect of transformed nanoparticles in CMP waste. The results presented support nanoparticle transformation as an important facet to consider in the risk assessment for new materials

Nanoparticle Engineering for Chemical-Mechanical Planarization

Increasing reliance on electronic devices demands products with high performance and efficiency. Such devices can be realized through the advent of nanoparticle technology. This book explains the physicochemical properties of nanoparticles according to each step in the chemical mechanical planarization (CMP) process, including dielectric CMP, shallow trend isolation CMP, metal CMP, poly isolation CMP, and noble metal CMP. The authors provide a detailed guide to nanoparticle engineering of novel CMP slurry for next-generation nanoscale devices below the 60nm design rule. This comprehensive text also presents design techniques using polymeric additives to improve CMP performance

Study of toxicity and uptake of nanoparticles towards understanding biotic-abiotic interactions

With the rapid growth in nanotechnology and tremendous applications the engineered nanomaterials (ENs) offer, there is increase in usage of ENs which increases their likelihood of coming in contact with biological systems which include complex beings like humans and other relatively simpler organism like bacteria and other microorganisms. The interaction between the nanomaterials (NMs) and biological systems includes the formation of protein coronas, particle wrapping, intracellular uptake and bio catalytic processes which could have biocompatible or bio adverse outcomes. Understanding these interactions allows the development of predictive relationships between structure and activity that are mainly determined by NM properties such as size, shape, surface chemistry, aggregation, and surface functionality among many others. This understanding will also provide insight towards the design and development of benign nanomaterials. The overarching goal of this dissertation is to understand the influence of the physicochemical characteristics of the NMs and their influence on their uptake and toxicity when they interact with the biological systems (cells and organs). For this purpose, thoroughly characterized NMs will be exposed to a cellular model, A549 cells (alveolar lung epithelial cells), and a mice model (CD-1 mice) through inhalational administration. The effects of NMs on the in vitro and in vivo models will be evaluated by bio- and immuno-chemical methods to understand toxicity, and a combination of analytical spectroscopic and microscopic tools to study uptake. In vivo toxicity assessment will also be performed by using electrocardiogram (ECG) measurements as a tool to study the effects of inhalation of NMs on cardiac response in mice. Through in vivo studies, a novel non-invasive method, Reserve of Refractoriness (RoR), will be introduced as a tool to study cardiotoxicity

Tribochemical investigation of microelectronic materials

To achieve efficient planarization with reduced device dimensions in integrated circuits, a better understanding of the physics, chemistry, and the complex interplay involved in chemical mechanical planarization (CMP) is needed. The CMP process takes place at the interface of the pad and wafer in the presence of the fluid slurry medium. The hardness of Cu is significantly less than the slurry abrasive particles which are usually alumina or silica. It has been accepted that a surface layer can protect the Cu surface from scratching during CMP. Four competing mechanisms in materials removal have been reported: the chemical dissolution of Cu, the mechanical removal through slurry abrasives, the formation of thin layer of Cu oxide and the sweeping surface material by slurry flow. Despite the previous investigation of Cu removal, the electrochemical properties of Cu surface layer is yet to be understood. The motivation of this research was to understand the fundamental aspects of removal mechanisms in terms of electrochemical interactions, chemical dissolution, mechanical wear, and factors affecting planarization. Since one of the major requirements in CMP is to have a high surface finish, i.e., low surface roughness, optimization of the surface finish in reference to various parameters was emphasized. Three approaches were used in this research: in situ measurement of material removal, exploration of the electropotential activation and passivation at the copper surface and modeling of the synergistic electrochemical-mechanical interactions on the copper surface. In this research, copper polishing experiments were conducted using a table top tribometer. A potentiostat was coupled with this tribometer. This combination enabled the evaluation of important variables such as applied pressure, polishing speed, slurry chemistry, pH, materials, and applied DC potential. Experiments were designed to understand the combined and individual effect of electrochemical interactions as well as mechanical impact during polishing. Extensive surface characterization was performed with AFM, SEM, TEM and XPS. An innovative method for direct material removal measurement on the nanometer scale was developed and used. Experimental observations were compared with the theoretically calculated material removal rate values. The synergistic effect of all of the components of the process, which result in a better quality surface finish was quantitatively evaluated for the first time. Impressed potential during CMP proved to be a controlling parameter in the material removal mechanism. Using the experimental results, a model was developed, which provided a practical insight into the CMP process. The research is expected to help with electrochemical material removal in copper planarization with low-k dielectrics

Evaluation of chemical mechanical planarization (CMP) for the removal of surface defects in extreme ultraviolet lithography (EUVL) mask substrates

A modified CMP process was investigated and developed with the goal of removing surface defects (nanoscale depressions or `pits\u27) from quartz mask blank substrates. Initially, quartz glass wafers were evaluated to observe surface roughness and defect introduction due to low down-force CMP processing. Following analysis of quartz glass wafers subjected to such processing it was determined that a CMP-based processing for pit removal of maskblank substrates was potentially viable. Consequently, a specially-designed mask carrier for investigating and developing CMP-based defect removal from EUV maskblank substrates was mounted on a Strasbaugh 6DS-SP CMP laboratory tool. A series of experiments was performed in order to investigate CMP-based pit removal with respect to CMP polish parameters, slurry dilution ratio, and polish time. For these experiments, additional surface pitting defects were generated on a number of maskblank substrates for the purpose of investigating the ability of a modified CMP process in removing said defects. The defects were generated using an ozonated DI water solution in concert with SC1 in a megasonic targeted cleaning system. After each polishing experiment, the mask substrates were cleaned using a standard cleaning process before AFM analysis to quantitatively measure pit modification and removal. Based on topographic analysis of pit defects (pre- and post-CMP) it was determined that chemical mechanical planarization was an effective route for pit defect removal from EUV maskblank substrates. Furthermore, it was observed that plate-bowing effects linked to the backpressure being used to hold the mask substrate in the modified carrier resulted in a radial dependence in the pitting defect removal data. Modification of the backpressure profile was sufficient to substantially reduce radial dependence in the pit defect removal data. It is noted that removal of particles from the maskblank substrate surface introduced by the CMP process requires further optimization

Robotic polishing of large optical components

Lightweight space mirrors have been widely used in earth observation and astronomy applications. Many organizations and companies, such as NASA in America, ESA in Europe, SSTL in UK as well as CASC in China, have spent a lot of money and effort on researching new materials for larger size space mirrors to meet both the payload weight constraints of launch and the increased advanced manufacturing process demanded for higher observations quality. This project is aimed at robot neutral polishing of lapped, ground and polished optical substrates using an industrial FANUC robot system. The project focused on three main fields which were: robot polishing with polyurethane tool and cerium oxide, pitch polishing with pitch tool and cerium oxide, as well as polishing of a 400mm ULE component. The polishing process targets were to achieve: 1) a surface roughness (Ra) of 10 nm and a surface profile (Pt) of 6 µm and 2µm on lapped and ground substrates respectively with polyurethane based tools and 2) a surface roughness (Ra) of 2nm with a surface profile (Pt) unchanged on robot neutral polished substrates using pitch based tools. This thesis comprises four main sections: a literature review, an experimental implementation, metrology and analysis, and the final conclusions. The experiment results measured with the metrology equipment selected were analysed. Conclusions of the relationship between the polishing performance of a specific sample and the selected polishing tool, polishing slurry, tool pressure, polishing time and other parameters were drawn. Results obtained from robot neutral polishing were surface roughness (Ra) of 8-10nm and surface profile (Pt) of 6µm for 100mm square lapped and ground parts. The process scalability was demonstrated from robot neutral polishing in 45hours, a 400mm square ground component from a surface roughness (Ra) of 200nm to 10nm. There is additional work to be implemented in the future, such as the development of robot pitch polishing of robot neutral polished parts to achieve 2nm Ra

Particle Removal In Post Chemical-Mechanical Planarization (Cmp) Cleaning Process: Experimental And Modeling Studies

Proses pencucian pasca perataan secara mekanikal-kimia memainkan peranan penting dalam teknologi wafer kerana ia adalah salah satu objektif untuk menghasilkan permukaan yang berkualiti tinggi bagi dimensi yang halus. Kajian ini terdiri daripada eksperimen dan teori untuk menilai kecekapan penyingkiran zarah silikon dioksida (SiO2) daripada permukaan wafer silikon semasa proses pencucian pasca perataan secara mekanikal-kimia (CMP). Kapasiti penyingkiran zarah daripada permukaan wafer melalui cakera pencucian dikaji menggunakan air dinyah ion dan asid sitrik dengan kadar pengaliran (dari 200 ml/min hingga 400 ml/min), tekanan cakera pencucian(1psi, 2psi dan 3psi), dan kelajuan cakera pencucian (0rpm, 1rpm and 2rpm) yang berbeza. Kecekapan penyingkiran zarah dalam setiap kes dikaji menggunakan jumlah zarah yang diukur melalui mesin pembiasan laser (SP1 KLA Tencor). Kecekapan penyingkiran zarah didapati meningkat dengan peningkatan kadar pengaliran, tekanan cakera pencucian dan kelajuan cakera pencucian. The post chemical mechanical planarization (CMP) cleaning became very important in wafer technology as one of its objectives was to manufacture high quality surfaces of fine dimensions. This study comprises of an experimental as well as a theoretical study on particle removal efficiency mainly silicon dioxide (SiO2) particles from wafer surface after chemical mechanical planarization (CMP) cleaning. The particle removal capacity from wafer surface in buffing (cleaning) disk was studied using de-ionized water and citric acid at different flow rates (200 ml/min to 400 ml/min) buffing disc pressure (1psi, 2psi and 3psi) and relative buffing disc speeds setting (0rpm, 1rpm and 2rpm). The removal efficiency in each case was evaluated using a particle count based on measurements with a laser scattering equipment (SP1 KLA Tenor). Particle removal efficiency was found to be increased with flow rates, buffing disc pressure and buffing disc speeds