KEYWORDS: Metrology, Manufacturing, Photomasks, Atomic force microscopy, 3D metrology, Lithography, Holography, Nanostructures, Control systems, Fabrication
Eliminating the need for multilayer alignment in nanoscale manufactured devices will streamline the lithography process and open up avenues for flexible substrate roll-to-roll (R2R) manufacturing. A system capable of single-exposure 3D holographic lithography with in-line metrology and real-time feedback will revolutionize micro and nano manufacturing. Work towards such developments are demonstrated to show promise in the field of nanopatterning.
Microscale selective laser sintering (μ-SLS) is a high throughput additive manufacturing (AM) technique developed at The University of Texas at Austin. It can fabricate high aspect ratio metal interconnect structures such as micro-pillar arrays for applications in semiconductor packaging. Additionally, as an AM process, μ-SLS aims to create complex 3D structures at a throughput that cannot be achieved by multi-step lithography processes.
This paper seeks to demonstrate the efficacy of a new approach for fast, in-line, and direct topography measurement of nano-scale structures and features on a flexible substrate, or web, in a roll-to-roll fashion. Nanofeatured products manufactured with R2R processes can be extremely cost competitive compared to more traditional, wafer-based solutions in addition to their unique and desirable mechanical properties. As such they are an area of immense research interest. But, despite the promise of these products for a plethora of applications, the leap from lab-scale prototypes to pilot- or volumescale manufacturing has proven extraordinarily difficult and expensive — with both required research and development investment and achievable process yield proving sizable barriers. A key capability gap in current art and roadblock on the path towards more widespread research and adoption of these R2R fabricated products is the lack of high-throughput, nanometer-scale metrology for process development, control, and yield enhancement. In this work a new type of extremely compact, tip-based microscope designed and fabricated with a micro-electro-mechanical system approach is applied to the challenge of direct topography measurement for roll-to-roll fabricated nanopatterns. A proof-of-concept tool with subsystems to regulate the flexible web, isolate and position the atomic force microscope, and measure features on the substrate, all coordinated by a real-time embedded control system is shown and step-and-scan measurement results were acquired. However, to genuinely meet this extent need for roll-to-roll metrology, a system capable of atomic force microscope scanning despite a continuous, non-zero web velocity must be developed to meet throughput requirements without degrading measurement quality and thus help to enable the next generation of R2R nanomanufacturing technology.
Effective measurement of fabricated structures is critical to the cost-effective production of modern electronics. However, traditional tip-based approaches are poorly suited to in-line inspection at current manufacturing speeds. We present the development of a large area inspection method to address throughput constraints due to the narrow field-of-view (FOV) inherent in conventional tip-based measurement. The proposed proof-of-concept system can perform simultaneous, noncontact inspection at multiple hotspots using single-chip atomic force microscopes (sc-AFMs) with nanometer-scale resolution. The tool has a throughput of ∼60 wafers / h for five-site measurement on a 4-in. wafer, corresponding to a nanometrology throughput of ∼66,000 μm2 / h. This methodology can be used to not only locate subwavelength “killer” defects but also to measure topography for in-line process control. Further, a postprocessing workflow is developed to stitch together adjacent scans measured in a serial fashion and expand the FOV of each individual sc-AFM such that total inspection area per cycle can be balanced with throughput to perform larger area inspection for uses such as defect root-cause analysis.
Nanoscale size effects give rise to near-field thermal considerations when heating nanoparticles under high laser power. We solve Maxwell’s equations in the frequency domain to analyze near-field thermal energy effects for three nanoparticle assemblies with different variances in particle sizes and show that heat dissipation generally decreases as the spread in nanoparticle sizes increases within the nanoparticle packing. For this study, log-normally distributed copper nanoparticle packings with a mean radius of 116 nm and three different standard deviations (12, 48, and 84 nm) were created by using a discrete element model in which a specified number of particles is generated. The nanoparticle packings in the simulation are created by randomly placing each nanoparticle into the packing domain with a random initial velocity and a position. The nanoparticles are then allowed to interact with each other under gravitational and weak van der Waals forces until they settle to form a stable packing configuration. A finite-difference frequency-domain analysis, which yields the electromagnetic field distribution, is then applied to the packing by solving Maxwell’s equations to obtain absorption, scattering, and extinction coefficients. This analysis is used to calculate the surface plasmon effects due to the electromagnetic coupling between the nanoparticles and the dielectric medium under the different distributions and show that different particle distributions can create different plasmonic effects in the packing domain, which results in nonlocal heat transport. Overall, this analysis helps to reveal how sintering quality can be enhanced by creating stronger laser–particle interactions for specific groups of nanoparticles.
Nanoscale size effects bring additional near-field thermal considerations when heating nanoparticles under
high laser power. Scanning electron micrographs of a typical copper nanoparticle powder bed reveal that the
nanoparticles are distributed log-normally with 116 nm mean radius and 48 nm standard deviation. In this paper, we
solve Maxwell’s equations in frequency domain to understand near-field thermal energy effects for different standard
deviations. Log-normally distributed copper nanoparticle packings which have 116 nm mean radius with 3 different
standard deviations (12, 48 and 84 nm) are created by using Discrete Element Model (DEM) in which certain number
of particles are generated, specifying a position and radius for each. The solid particles interacting with the
neighbouring particles are to be distributed randomly into the bed domain with an initial velocity and a boundary
condition, which creates the particle packing within a defined time range under gravitational and weak van der Waals
forces. Finite Difference Frequency Domain analysis, which yields the electromagnetic field distribution, is applied
by solving Maxwell's equations to obtain absorption, scattering and extinction coefficients. We show that different
particle distributions create different plasmonic effects in the bed domain which results in non-local heat transport.
We calculate the surface plasmon effect due to the electromagnetic coupling between the nanoparticles and the
dielectric medium under the different distributions. This analysis helps to reveal how sintering quality can be enhanced
by creating stronger laser-particle interactions for specific groups of nanoparticles.
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