Advanced modeling of planarization processes for integrated circuit fabrication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 215-225).Planarization processes are a key enabling technology for continued performance and density improvements in integrated circuits (ICs). Dielectric material planarization is widely used in front-end-of-line (FEOL) processing for device isolation and in back-end-of-line (BEOL) processing for interconnection. This thesis studies the physical mechanisms and variations in the planarization using chemical mechanical polishing (CMP). The major achievement and contribution of this work is a systematic methodology to physically model and characterize the non-uniformities in the CMP process. To characterize polishing mechanisms at different length scales, physical CMP models are developed in three levels: wafer-level, die-level and particle-level. The wafer-level model investigates the CMP tool effects on wafer-level pressure non-uniformity. The die-level model is developed to study chip-scale non-uniformity induced by layout pattern density dependence and CMP pad properties. The particle-level model focuses on the contact mechanism between pad asperities and the wafer. Two model integration approaches are proposed to connect wafer-level and particle-level models to the die-level model, so that CMP system impacts on die-level uniformity and feature size dependence are considered. The models are applied to characterize and simulate CMP processes by fitting polishing experiment data and extracting physical model parameters. A series of physical measurement approaches are developed to characterize CMP pad properties and verify physical model assumptions. Pad asperity modulus and characteristic asperity height are measured by nanoindentation and microprofilometry, respectively. Pad aging effect is investigated by comparing physical measurement results at different pad usage stages. Results show that in-situ conditioning keeps pad surface properties consistent to perform polishing up to 16 hours, even in the face of substantial pad wear during extended polishing. The CMP mechanisms identified from modeling and physical characterization are applied to explore an alternative polishing process, referred to as pad-in-a-bottle (PIB). A critical challenge related to applied pressure using pad-in-a-bottle polishing is predicted.by Wei Fan.Ph.D

PRECISION POLISHING DYNAMICS: THE INFLUENCE OF PROCESS VIBRATIONS ON POLISHING RESULTS

The optical pitch polishing process has been used over 300 years to obtain high quality optical surface finish with little subsurface damage. A pitch tool consists of a metal platen coated with a layer of polishing pitch whereby pitch is a highly viscoelastic material. In polishing the workpiece is rubbed against the tool while abrasive slurry is supplied in between them. During polishing the workpiece is subjected to process vibrations, whereby be these vibrations are generated by the machine itself due to moving parts, or that are transmitted from the shop floor through the machine to the workpiece. To date, little is available in the public domain regarding the role of process induced vibrations on polishing outcomes. This research investigates such vibrations, how they transfer through the pitch layer on the tool, and ultimately how they affect the material removal rates and surface finishes obtainable on fused silica workpieces. Fundamental understandings with respect to the process vibration will reduce the heuristic nature of pitch polishing and generate deterministic polishing outcomes. Key findings include the following. The pitch selection has little influence on the magnitude or range of process vibrations transmitted through the tool to the workpiece in the 1 Hz to 16 kHz range. Within the same frequency bandwidth the recorded process vibrations are in the range of 0.2 to 10 nm and the main factors found to affect their magnitude include; the polishing machine itself, process speeds, and the use of passive damping materials in the tool construction. Material removal rates and surface finishes obtained on fused silica workpieces were found to be sensitive to the extent of the process vibrations. Up to 30% changes in the material removal rates were observed with increasing vibrational magnitudes. The higher level vibrations were also found to have a negative impact on the finishes obtained in the lower spatial domains. Additional testing on a specifically made test-bed demonstrated a linear correlation between the material removal rates and the vibrational power input. This relationship was further explored by adding external vibrational sources to an existing machine, and as expected the increased vibrational power resulted in 80% higher material removal rates. The results from this experimental work facilitated Dr. Keanini’s development of a vibrational based material removal model. Additional polishing tests combined with surface topography analysis of both hard and soft pitch tools demonstrated the robustness of the proposed model to accommodate the influence of different pitch grades. The summary in general is that in pitch polishing the process vibrations are important to monitor and control for process optimization

PRECISION POLISHING DYNAMICS: THE INFLUENCE OF PROCESS VIBRATIONS ON POLISHING RESULTS

The optical pitch polishing process has been used over 300 years to obtain high quality optical surface finish with little subsurface damage. A pitch tool consists of a metal platen coated with a layer of polishing pitch whereby pitch is a highly viscoelastic material. In polishing the workpiece is rubbed against the tool while abrasive slurry is supplied in between them. During polishing the workpiece is subjected to process vibrations, whereby be these vibrations are generated by the machine itself due to moving parts, or that are transmitted from the shop floor through the machine to the workpiece. To date, little is available in the public domain regarding the role of process induced vibrations on polishing outcomes. This research investigates such vibrations, how they transfer through the pitch layer on the tool, and ultimately how they affect the material removal rates and surface finishes obtainable on fused silica workpieces. Fundamental understandings with respect to the process vibration will reduce the heuristic nature of pitch polishing and generate deterministic polishing outcomes. Key findings include the following. The pitch selection has little influence on the magnitude or range of process vibrations transmitted through the tool to the workpiece in the 1 Hz to 16 kHz range. Within the same frequency bandwidth the recorded process vibrations are in the range of 0.2 to 10 nm and the main factors found to affect their magnitude include; the polishing machine itself, process speeds, and the use of passive damping materials in the tool construction. Material removal rates and surface finishes obtained on fused silica workpieces were found to be sensitive to the extent of the process vibrations. Up to 30% changes in the material removal rates were observed with increasing vibrational magnitudes. The higher level vibrations were also found to have a negative impact on the finishes obtained in the lower spatial domains. Additional testing on a specifically made test-bed demonstrated a linear correlation between the material removal rates and the vibrational power input. This relationship was further explored by adding external vibrational sources to an existing machine, and as expected the increased vibrational power resulted in 80% higher material removal rates. The results from this experimental work facilitated Dr. Keanini’s development of a vibrational based material removal model. Additional polishing tests combined with surface topography analysis of both hard and soft pitch tools demonstrated the robustness of the proposed model to accommodate the influence of different pitch grades. The summary in general is that in pitch polishing the process vibrations are important to monitor and control for process optimization

Robotic processes to accelerate large optic fabrication

The manufacture of metre-scale optics for the next generation of extremely large telescopes (and many other applications) poses a number of unique challenges. For the primary mirror of the European Extremely Large Telescope, each of its 1.45 m segments will need to be completed with nanometre scale accuracy. This demands an unprecedented combination of hybrid fabricating technology to process nearly 1000 segments before the year 2024. One important aspect in improving the current state-of-the-art manufacturing developments is adding an efficient smoothing process that can achieve a faster, and less expensive, manufacturing process-chain. The current process to finish a prototype segment using CNC grinding and CNC polishing takes approximately 1-2 months, and a significant contributing factor in this is the excessive processing times needed to correct the local grinding marks. In this study, therefore, grolishing, an intermediate process between grinding and polishing, is adopted to smooth the part and reduce the overall manufacturing time. This PhD work serves to advance the development of effective robotic grolishing processes (RGP) by the following achievements: (1) to propose the specification and achieve the requirements; (2) to design tools and establish a mechanism for grolishing; (3) to investigate and propose experimental methods to reduce process times while still achieving high performance, reliability and quality surfaces; (4) to establish the RGP and demonstrate that this process can smooth the errors from grinding and provide superior surfaces for polishing to speed up the current process; (5) to develop prototype metrology systems and algorithms to measure grolished surfaces; and, (6) to investigate an innovative proposed method to control mid-spatial frequencies on complex surfaces by using rotating rigid tools. These novel achievements describe the newest fabrication technology, and anticipate the evolution of the process-chain for future high-quality imaging systems for use in astronomy, space-research and laser physics

Manufacturing Metrology

Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation

Modeling, Simulation, And Optimization Of Diamond Disc Pad Conditioning In Chemical Mechanical Polishing

Microfabrication (originally based on structuring the surface of silicon) remains the basic manufacturing technology of the semiconductor industry. The semiconductor business model has been driven by “Moore’s Law†which predicts that the number of transistors the industry would be able to place on a computer chip would double every two years

Aspheric geodesic lenses for an integrated optical spectrum analyser

Abstract available p. xiii-xi

Comparison of zinc oxide nanoparticle integration into non-woven fabrics using different functionalisation methods for prospective application as active facemasks

The development of advanced facemasks stands out as a paramount priority in enhancing healthcare preparedness. In this work, different polypropylene non-woven fabrics (NWF) were characterised regarding their structural, physicochemical and comfort-related properties. The selected NWF for the intermediate layer was functionalised with zinc oxide nanoparticles (ZnO NPs) 0.3 and 1.2wt% using three different methods: electrospinning, dip-pad-dry and exhaustion. After the confirmation of ZnO NP content and distribution within the textile fibres by morphological and chemical analysis, the samples were evaluated regarding their antimicrobial properties. The functionalised fabrics obtained via dip-pad-dry unveiled the most promising data, with 0.017 ± 0.013wt% ZnO NPs being mostly located at the fibre’s surface and capable of total eradication of Staphylococcus aureus and Escherichia coli colonies within the tested 24 h (ISO 22196 standard), as well as significantly contributing (**** p < 0.0001) to the growth inhibition of the bacteriophage MS2, a surrogate of the SARS-CoV-2 virus (ISO 18184 standard). A three-layered structure was assembled and thermoformed to obtain facemasks combining the previously chosen NWF, and its resulting antimicrobial capacity, filtration efficiency and breathability (NP EN ISO 149) were assessed. The developed three-layered and multiscaled fibrous structures with antimicrobial capacities hold immense potential as active individual protection facemasks.FCT -Fundação para a Ciência e a Tecnologia(LA/P/0029/2020)info:eu-repo/semantics/publishedVersio