Dr. Richard A. Lawson Profile

Dr. Richard A. Lawson

Research Engineer at Milliken & Co

SPIE Involvement:

Author

Publications (52)

SPIE Journal Paper | 27 October 2017

Effect of chemoepitaxial guiding underlayer design on the pattern quality and shape of aligned lamellae for fabrication of line-space patterns

Benjamin D. Nation, Andrew J. Peters, Richard A. Lawson, Peter J. Ludovice, Clifford L. Henderson

JM3, Vol. 16, Issue 04, 043502, (October 2017) https://doi.org/10.1117/12.10.1117/1.JMM.16.4.043502

KEYWORDS: Line edge roughness, Line width roughness, Optical lithography, Double patterning technology, Interfaces, Directed self assembly, Polymers, Polymerization, Etching, Chemical species

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SPIE Journal Paper | 10 May 2016 Open Access

Calculations of the free energy of dislocation defects in lamellae forming diblock copolymers using thermodynamic integration

Andrew Peters, Richard Lawson, Benjamin Nation, Peter Ludovice, Clifford Henderson

JM3, Vol. 15, Issue 02, 023505, (May 2016) https://doi.org/10.1117/12.10.1117/1.JMM.15.2.023505

KEYWORDS: Directed self assembly, Thermodynamics, Polymers, Interfaces, Computer simulations, Polymerization, Systems modeling, Binary data, Thin films, Semiconductors

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SPIE Journal Paper | 8 March 2016

Coarse-grained molecular dynamics modeling of the kinetics of lamellar block copolymer defect annealing

Andrew Peters, Richard Lawson, Benjamin Nation, Peter Ludovice, Clifford Henderson

JM3, Vol. 15, Issue 01, 013508, (March 2016) https://doi.org/10.1117/12.10.1117/1.JMM.15.1.013508

KEYWORDS: Directed self assembly, Thin films, Interfaces, Polymers, Annealing, Diffusion, Scattering, Computer simulations, Process control

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Proceedings Article | 20 March 2015 Paper

Optimizing performance in cross-linking negative-tone molecular resists

Richard Lawson, Hannah Narcross, Brandon Sharp, Jun Sung Chun, Mark Neisser, Laren Tolbert, Clifford Henderson

Proceedings Volume 9425, 94250A (2015) https://doi.org/10.1117/12.2086007

KEYWORDS: Silicon, Molecules, Optical lithography, Extreme ultraviolet, Standards development, Oxides, Glasses, Polymerization, Switches, Polymers

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Proceedings Article | 20 March 2015 Paper

Base developable negative tone molecular resist based on epoxide cross-linking

Brandon Sharp, Richard Lawson, Ashten Fralick, Hannah Narcross, Jun Sung Chun, Mark Neisser, Laren Tolbert, Clifford Henderson

Proceedings Volume 9425, 94251S (2015) https://doi.org/10.1117/12.2086039

KEYWORDS: Glasses, Standards development, Polymers, Polymerization, Molecules, Scanning electron microscopy, Photoresist developing, Semiconducting wafers, Silicon, Line edge roughness

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Proceedings Article | 20 March 2015 Paper

Effect of molecular resist structure on glass transition temperature and lithographic performance in epoxide functionalized negative tone resists

Hannah Narcross, Richard Lawson, Brandon Sharp, Jun Sung Chun, Mark Neisser, Laren Tolbert, Clifford Henderson

Proceedings Volume 9425, 94250C (2015) https://doi.org/10.1117/12.2086027

KEYWORDS: Glasses, Lithography, Polymerization, Polymers, Extreme ultraviolet lithography, Diffusion, Scanning electron microscopy, Extreme ultraviolet, Optical lithography, Light sources

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Proceedings Article | 19 March 2015 Paper

Coarse-grained molecular dynamics modeling of the kinetics of lamellar BCP defect annealing

Andrew Peters, Richard Lawson, Benjamin Nation, Peter Ludovice, Clifford Henderson

Proceedings Volume 9423, 94231Y (2015) https://doi.org/10.1117/12.2085518

KEYWORDS: Thin films, Polymers, Interfaces, Diffusion, Neodymium, Bridges, Annealing, Computer simulations, Process control, Directed self assembly

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Proceedings Article | 19 March 2015 Paper

Effect of chemoepitaxial guiding underlayer design on the pattern quality and shape of aligned lamellae for fabrication of line-space patterns

Benjamin Nation, Andrew Peters, Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 9423, 94231J (2015) https://doi.org/10.1117/12.2085526

KEYWORDS: Line edge roughness, Chemical analysis, Optical lithography, Polymers, Double patterning technology, Data modeling, Molecular self-assembly, Chemical species, Thin films, Directed self assembly

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Proceedings Article | 19 March 2015 Paper

Effect of χN and underlayer composition on self-assembly of thins films of block copolymers with energy asymmetric blocks

Richard Lawson, Andrew Peters, Benjamin Nation, Peter Ludovice, Clifford Henderson

Proceedings Volume 9423, 94231L (2015) https://doi.org/10.1117/12.2086047

KEYWORDS: Interfaces, Polymers, Thin films, Systems modeling, Molecular self-assembly, Computer simulations, Lithography, Physics, Visualization, Directed self assembly

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Proceedings Article | 19 March 2015 Paper

Investigating SEM metrology effects using a detailed SEM simulation and stochastic resist model

Richard Lawson, Clifford Henderson

Proceedings Volume 9424, 94240K (2015) https://doi.org/10.1117/12.2086051

KEYWORDS: Scanning electron microscopy, Line edge roughness, Line scan image sensors, 3D modeling, Metrology, Monte Carlo methods, Surface roughness, Scattering, 3D metrology, Stochastic processes

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SPIE Journal Paper | 20 August 2014

Simulation study of the effect of differences in block energy and density on the self-assembly of block copolymers

Richard Lawson, Andrew Peters, Benjamin Nation, Peter Ludovice, Clifford Henderson

JM3, Vol. 13, Issue 03, 031308, (August 2014) https://doi.org/10.1117/12.10.1117/1.JMM.13.3.031308

KEYWORDS: Interfaces, Polymers, Thin films, Computer simulations, Molecular self-assembly, Lithography, Physics, Picosecond phenomena, Manufacturing, Directed self assembly

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Proceedings Article | 28 March 2014 Paper

Simulation study of the effect of differences in block energy and density on the self-assembly of block copolymers

Richard Lawson, Andrew Peters, Benjamin Nation, Peter Ludovice, Clifford Henderson

Proceedings Volume 9049, 90490S (2014) https://doi.org/10.1117/12.2046603

KEYWORDS: Interfaces, Polymers, Thin films, Computer simulations, Lithography, Physics, Chemistry, Manufacturing, Photoresist materials, Directed self assembly

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Implementation of directed self-assembly (DSA) of block copolymers (BCPs) introduces a series of engineering challenges that have not been completely addressed in previous block copolymer and lithography studies. One of the required innovations for further DSA development and implementation is the accurate simulation of specific block copolymer chemistries and their interactions with interfaces. Many of the BCP simulation tools developed so far have limitations or difficulty in terms of matching many of the common issues found in experimental BCP systems such as polydispersity and different statistical segment lengths. One of the potentially most important issues is the fact that real BCPs often have block energy and/or density asymmetry, meaning that each block has a different homopolymer density and/or cohesive energy density (CED). A simulation of BCP behavior and DSA processes based on molecular dynamics (MD) of coarse-grained polymer chains has been developed that can independently parameterize and control the density and CED of each block to more accurately match the asymmetry found in experimental BCPs. This model was used to study the effect of block asymmetry on the order-disorder transition (ODT), domain scaling, and self-assembly of thin films of BCPs. BCPs whose blocks each have a different density show deviations from the mean-field ODT coexistence curve, exhibiting an order-disorder transition or co-existence curve that is asymmetric with shifts and tilts in the direction of majority highest density block. This impact of density and cohesive energy differences diblock copolymers on their phase behavior can explain some of the unexpected shapes found experimentally in BCP ODT curves. Asymmetry in the BCP block energy or density does not appear to have a significant effect on domain scaling behavior compared to the mean-field estimates. Self-assembly of thin films of BCPs with mismatches in CED shows significant deviations in the expected morphologies from ones simulated using equivalent densities and cohesive energy densities. The lowest CED block has a strong propensity to segregate to and “wet” the free interface at the top of the film because it has the lowest energy penalty for the loss of interactions with other chains at the free surface relative to the bulk. This gives rise to an effective “skinning” of the film by the lowest CED block for almost the entire potential range of underlayer compositions and film thicknesses. Such materials will be extremely difficult to successfully pattern transfer for a lithographically useful process because they will not form vertically aligned morphologies through the entire film thickness. This CED mismatch also gives rise to a large number of non-bulk morphologies and deviations from bulk behavior including changing vertical-to-horizontal morphologies through film depth, compression and expansion of domain sizes to match film thickness dimensions, and island and hole formation among others. Increasing the χN value can potentially suppress some of these non-idealities due to CED asymmetry, but the required χN to overcome these issues will differ from polymer to polymer depending on the magnitude of the CED asymmetry.

Proceedings Article | 28 March 2014 Paper

Effect of guiding layer topography on chemoepitaxially directed self-assembly of block copolymers for pattern density multiplication

Benjamin Nation, Andrew Peters, Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 9049, 90492K (2014) https://doi.org/10.1117/12.2046629

KEYWORDS: Polymers, Computer simulations, Chemical species, Process modeling, Molecular self-assembly, Chemical engineering, Optical alignment, Semiconductor manufacturing, Feature extraction, Directed self assembly

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Proceedings Article | 28 March 2014 Paper

Predicting process windows for pattern density multiplication using block copolymer directed self-assembly in conjunction with chemoepitaxial guiding layers

Benjamin Nation, Andrew Peters, Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 9049, 90491C (2014) https://doi.org/10.1117/12.2046626

KEYWORDS: Polymers, Chemical species, Molecular self-assembly, Statistical modeling, Lithography, Computer simulations, Chemical analysis, Optical lithography, Physics, Directed self assembly

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Proceedings Article | 28 March 2014 Paper

Understanding defects in DSA: calculation of free energies of block copolymer DSA systems via thermodynamic integration of a mesoscale block-copolymer model

Andrew Peters, Richard Lawson, Benjamin Nation, Peter Ludovice, Clifford Henderson

Proceedings Volume 9049, 90492E (2014) https://doi.org/10.1117/12.2046664

KEYWORDS: Polymers, Thermodynamics, Systems modeling, Monte Carlo methods, System integration, Molecular interactions, Semiconductors, Motion models, Polymerization, Directed self assembly

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Proceedings Article | 27 March 2014 Paper

Positive tone cross-linked resists based on photoacid inhibition of cross linking

Richard Lawson, Jun Sung Chun, Mark Neisser, Laren Tolbert, Clifford Henderson

Proceedings Volume 9051, 90510E (2014) https://doi.org/10.1117/12.2046619

KEYWORDS: Molecules, Polymerization, Optical lithography, Polymers, Glasses, Extreme ultraviolet lithography, Extreme ultraviolet, Deep ultraviolet, Switches, Photoresist materials

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Proceedings Article | 27 March 2014 Paper

Methods of controlling cross-linking in negative-tone resists

Richard Lawson, Jun Sung Chun, Mark Neisser, Laren Tolbert, Clifford Henderson

Proceedings Volume 9051, 90510Q (2014) https://doi.org/10.1117/12.2046616

KEYWORDS: Line edge roughness, Polymerization, Optical lithography, Extreme ultraviolet, Molecules, Deep ultraviolet, Polymers, Diffusion, Glasses, Control systems

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Negative tone resists based on cross-linking via epoxide/cationic polymerization have a variety of potential advantages over more traditional positive tone resists based on photoacid catalyzed deprotection including low outgassing, intrinsic diffusion control, and improved pattern collapse performance through the higher modulus provided by a cross-linked network. Based on the promising baseline performance achieved previously in simple negative tone systems composed only of an epoxide functionalized molecular glass and a photoacid generator, a series of different methods and additives that can be used to control the extent and rate of cross-linking in such systems have been developed and are reported here which allow for even further improvement in resist performance. Simple addition of base quencher, as is used in conventional chemically amplified resists, is ineffective in these systems because the patterning reaction mechanism is different. Any control method must work by modifying the extent and rate of cationic polymerization of epoxides. By adding molecules containing phenolic OH groups to such an epoxide resist, one can slow the extent of cross-linking due to introduction of an additional reaction pathway and often a concomitant increase in the resist resin glass transition temperature. Generalized additives similar to base quencher were also developed based on the addition of strong nucleophiles such as triphenylphosphine which act essentially as chain termination agents. This approach allows for improved resolution and LER in negative tone epoxide resist systems. A more superior additive was developed that can be described as a photodecomposable nucleophile (PDN). The unexposed PDN acts similarly to the strong nucleophile additives in that it terminates chain propagation. Upon exposure, the PDN can act like a chain transfer agent or an additional initiator, but no longer has the effect of completely terminating chain propagation. This approach allows for high levels of control in the nominally unexposed regions of the resist, but maintains high efficiency of cross-linking in the most highly exposed regions. One particular implementation of a PDN used in this study is the blending of a PAG (i.e. triphenylsulfonium triflate, TPS-Tf) with a more nucleophilic anion that plays the role of a PDN, with the common and highly effective, non-nucleophilic PAG that is conventionally used in epoxide photopolymerizations (i.e. triphenylsulfonium hexafluoroantimonate, TPS-SbF₆). Addition of only a few percent of TPS-Tf to a baseline epoxide resist formulation shows a 5-10 nm improvement in ultimate resolution and a reduction in LER to around 65% as compared to the baseline resist without the PDN additive while only incurring a moderate increase in imaging dose. By modulating the amount of the different polymerization control additives, the performance of a particular epoxide resist was improved from a resolution of greater than 30 nm half pitch and an LER of around 9 nm to a resolution of ~20 nm half pitch, with an LER of around 4 nm, and a sensitivity of 18 mJ/cm². By increasing the additive loading even further, the resolution was improved to ~18 nm half pitch, although with an increase in imaging dose to 39 mJ/cm2.

Proceedings Article | 10 April 2013 Paper

Postiive tone resists based on network deploymerization of molecular resists

Richard Lawson, Jing Cheng, Ameneh Cheshmehkani, Laren Tolbert, Clifford Henderson

Proceedings Volume 8682, 868221 (2013) https://doi.org/10.1117/12.2021141

KEYWORDS: Polymers, Deep ultraviolet, Electron beam lithography, Molecules, Line edge roughness, Chemically amplified resists, Capillaries, Lithography, Extreme ultraviolet lithography, Optical lithography

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Conventional chemically amplified resists have several issues that can potentially limit their capability for sub-40 nm imaging. One of the major issues at this size scale is that the mechanical strength of positive tone CARs limits the amount of stress they can withstand during development, rinse, and drying, thus leading to problems with pattern collapse due to the high capillary forces generated during drying. This problem is exasperated by the fact that linear polymers show dramatically reduced modulus at sub-50 nm features sizes. To improve on this problem, we have made a positive tone resist based on network depolymerization of molecular resists. The resist thermally cross-links after being spin cast into thin film form through reactions between vinyl ether groups and carboxylic acid groups. By cross-linking the resist to form a dense three dimensional polymer network, the mechanical strength of the resist is greatly improved compared to linear polymers. The network is depolymerized using an acid catalyzed reaction to create development contrast that allows for patterning of the resist via development in either aqueous base or organic solvent. One drawback of the current resist design is that the free carboxylic acids on the resist molecule appear to react in solution at room temperature with both the vinyl ether groups on adjacent molecules and with any added base quencher. These reactions cause reduced effectiveness of the base quencher and produce a noticeable resist shelf life problem. Despite these limitations, the material was used to compare the effect of development in aqueous base versus organic solvent. The resist formulated in this work showed a DUV sensitivity of 7 mJ/cm² and a contrast of 5.2 for development in either solvent or aqueous base. Under 100 keV e-beam imaging, the material showed 40 nm resolution for both development types. In standard 0.26 N TMAH, the dose-to-size was 84 μC/cm² with 3σ LER of 14.2 nm. Using methyl isobutyl ketone for organic solvent development, the dose-to-size was 104 μC/cm² with 3σ LER of 7.4 nm.

Proceedings Article | 5 April 2013 Paper

PS-b-PAA as a high X polymer for directed self-assembly: a study of solvent and thermal annealing processes for PS-b-PAA

Jing Cheng, Richard Lawson, Wei-Ming Yeh, Nathan Jarnagin, Laren Tolbert, Clifford Henderson

Proceedings Volume 8680, 86801V (2013) https://doi.org/10.1117/12.2021414

KEYWORDS: Annealing, Polymers, Scanning electron microscopy, Picosecond phenomena, Silicon, Semiconducting wafers, Etching, Polymerization, Solids, Directed self assembly

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Proceedings Article | 5 April 2013 Paper

Tuning domain size of block copolymers for directed self assembly using polymer blending: molecular dynamics simulation studies

Richard Lawson, Andrew Peters, Peter Ludovice, Clifford Henderson

Proceedings Volume 8680, 86801Z (2013) https://doi.org/10.1117/12.2021442

KEYWORDS: Polymers, Critical dimension metrology, Molecular self-assembly, Lithography, Interfaces, Image segmentation, Directed self assembly, Polymerization, Computer simulations, Silver

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A 10% batch-to-batch variation in molecular weight for a low polydispersity block copolymer (BCP) used for DSA lithography could result in more than a 6% change in critical dimension (CD). Therefore, there is a strong motivation and need to develop and understand methods for fine-tuning the domain size of DSA BCPs to meet the CD and pitch specifications that will be required for practical implementation of DSA processes. This study investigates two methods of fine-tuning the domain size of a specific batch of BCP through blending of the BCP with another polymer, either 1. a set of similar homopolymers (HPs) or 2. a similar BCP of different molecular weight. Each method was investigated and compared using a coarse grained molecular dynamics simulation. For BCP-HP blends, the domain size increases as the amount of HP increases because the HPs tend to slightly swell the BCP domains. A design heuristic was developed for guiding the determination of how much HP to add to obtain a desired pitch. For blends of different molecular weight BCPs, two different scaling regimes were identified; one regime is majority large chains and the other regime is majority small chains. Based on the simulation results, the domain scaling can be mapped across the full range of blends by simply measuring three points: the pure small chain domain size, the pure large chain domain size, and a 50/50 blend of the small and large chains. Comparing the two different blending methodologies, BCP blending with other BCPs is a more versatile approach because it can be used to either increase or decrease the domain size of a base BCP while HP blending can only increase the domain size. HP blending is also potentially problematic because the HPs tends to aggregate in the middle of each block’s half domain which can have a significant effect on CD uniformity due to the strong effect of local variations in the concentration of the HP and local variations in HP conformation. The use of BCP blends with other BCPs should be more favorable from a CD uniformity perspective because this approach is much less susceptible to initial local fluctuations than HP blends because all BCPs go to the A-B interface. The coarse grained molecular dynamics simulation is well suited for comparisons such as this and can produce design rules that are needed for experimental implementation of polymer blending with BCPs to tune domain size.

Proceedings Article | 5 April 2013 Paper

PS-b-PHEMA: synthesis, characterization, and processing of a high X polymer for directed self-assembly lithography

Jing Cheng, Richard Lawson, Wei-Ming Yeh, Nathan Jarnagin, Laren Tolbert, Clifford Henderson

Proceedings Volume 8680, 86801W (2013) https://doi.org/10.1117/12.2021417

KEYWORDS: Polymers, Annealing, Lithography, FT-IR spectroscopy, Optical lithography, Etching, Magnesium, Solids, Polymerization, Directed self assembly

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Proceedings Article | 5 April 2013 Paper

PS-b-PHOST as a high X block copolymers for directed self assembly: optimization of underlayer and solvent anneal processes

Nathan Jarnagin, Wei-Ming Yeh, Jing Cheng, Andrew Peters, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 8680, 86801X (2013) https://doi.org/10.1117/12.2021420

KEYWORDS: Polymers, Annealing, Polymerization, Scanning electron microscopy, Picosecond phenomena, Thin films, Nitrogen, Directed self assembly, Polymer thin films, Glasses

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Proceedings Article | 5 April 2013 Paper

Coarse grained molecular dynamics model of block copolymer directed self-assembly

Richard Lawson, Andrew Peters, Peter Ludovice, Clifford Henderson

Proceedings Volume 8680, 86801Y (2013) https://doi.org/10.1117/12.2021439

KEYWORDS: Polymers, Molecular self-assembly, Polymerization, Lithography, Interfaces, Computer simulations, Systems modeling, Graphics processing units, Molecular interactions, Directed self assembly

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A model has been developed for the simulation of block copolymer (BCP) directed self-assembly (DSA) based on a coarse grained polymer model that anneals using molecular dynamics. The model uses graphics processing units (GPUs) to perform the calculations; this combined with the coarse graining means simulations times approach the speed of other more commonly used simulation techniques for BCPs. The model is unique in how it treats the pure phase blocks interactions with themselves (i.e. A-A and B-B interactions) and their interactions with each other. This allows for simulations that can potentially more accurately capture the differences between the properties of each block such as density and cohesive energy. The model is fully described and used to examine some of the issues that are unique to DSA lithographic applications of BCPs. We describe a method to calculate χ for the off-lattice MD system based on observation of the order-disorder transitions (ODT) for different degrees of polymerization N. The model is used to examine the transient, complex, non-classical morphologies that can occur through film thickness during a DSA process. During the phase separation process from a mixed initial state, the BCPs first locally phase separate to form small aggregate type structures. These aggregates then coalesce into larger features that approach the size of the equilibrium domain. These features then shift to match the guiding pattern on the underlayer followed by the slow elimination of defects. We also studied how the guiding patterns work in chemo-epitaxy DSA. The guiding patterns have a strong immediate effect on the BCP film nearest the interface and induce locally aligned self-assembly. Over time, this induced pattern tends to propagate up through the thickness of the film until the film is uniformly aligned to the guiding pattern. We also clearly see that the observed morphology at the top of the film gives no indication of the morphology through the depth, especially during the transient portions of the self-assembly process.

Proceedings Article | 26 March 2013 Paper

Effects of block copolymer polydispersity and xN on pattern line edge roughness and line width roughness from directed self-assembly of diblock copolymers

Andrew Peters, Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 8680, 868020 (2013) https://doi.org/10.1117/12.2021443

KEYWORDS: Line edge roughness, Polymers, Line width roughness, Inspection, Lithography, Neodymium, Polymerization, Edge roughness, Autoregressive models, Directed self assembly

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Proceedings Article | 16 April 2012 Paper

Investigation of high x block copolymers for directed self-asssembly: synthesis and characterization of PS-b-PHOST

Nathan Jarnagin, Jing Cheng, Andrew Peters, Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 8323, 832310 (2012) https://doi.org/10.1117/12.918081

KEYWORDS: Polymerization, Polymers, Optical lithography, Lithography, Scanning electron microscopy, Annealing, Molecular self-assembly, Directed self assembly, Glasses, FT-IR spectroscopy

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Proceedings Article | 16 April 2012 Paper

Detailed mesoscale dynamic simulation of block copolymer directed self-assembly processes: application of protracted colored noise dynamics

Andrew Peters, Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 8323, 83231T (2012) https://doi.org/10.1117/12.918077

KEYWORDS: Polymers, Computer simulations, Monte Carlo methods, Picosecond phenomena, Polymethylmethacrylate, Interfaces, Electron beam lithography, Stochastic processes, Lithography, Directed self assembly

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Proceedings Article | 16 April 2012 Paper

Directed self-assembly of poly(styrene)-block-poly(acrylic acid) copolymers for sub-20nm pitch patterning

Jing Cheng, Richard Lawson, Wei-Ming Yeh, Nathan Jarnagin, Andrew Peters, Laren Tolbert, Clifford Henderson

Proceedings Volume 8323, 83232R (2012) https://doi.org/10.1117/12.918073

KEYWORDS: Polymers, Optical lithography, Lithography, Etching, Polymerization, Plasma etching, Annealing, Solids, Plasma, Directed self assembly

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Directed self-assembly (DSA) of block copolymers is a promising technology for extending the patterning capability of current lithographic exposure tools. For example, production of sub-40 nm pitch features using 193nm exposure technologies is conceivably possible using DSA methods without relying on time consuming, challenging, and expensive multiple patterning schemes. Significant recent work has focused on demonstration of the ability to produce large areas of regular grating structures with low numbers of defects using self-assembly of poly(styrene)-b-poly(methyl methacrylate) copolymers (PS-b-PMMA). While these recent results are promising and have shown the ability to print pitches approaching 20 nm using DSA, the ability to advance to even smaller pitches will be dependent upon the ability to develop new block copolymers with higher χ values and the associated alignment and block removal processes required to achieve successful DSA with these new materials. This paper reports on work focused on identifying higher χ block copolymers and their associated DSA processes for sub-20 nm pitch patterning. In this work, DSA using polystyrene-b-polyacid materials has been explored. Specifically, it is shown that poly(styrene)-b-poly(acrylic acid) copolymers (PS-b-PAA) is one promising material for achieving substantially smaller pitch patterns than those possible with PS-b-PMMA while still utilizing simple hydrocarbon polymers. In fact, it is anticipated that much of the learning that has been done with the PS-b-PMMA system, such as development of highly selective plasma etch block removal procedures, can be directly leveraged or transferred to the PS-b-PAA system. Acetone vapor annealing of PS-b-PAA (M_w=16,000 g/mol with 50:50 mole ratio of PS:PAA) and its self-assembly into a lamellar morphology is demonstrated to generate a pattern pitch size (L₀) of 21 nm. The χ value for PS-b-PAA was estimated from fingerprint pattern pitch data to be approximately 0.18 which is roughly 4.5 times greater than the χ for PS-b-PMMA (_χPS-b-PMMA ~ 0.04).

Proceedings Article | 20 March 2012 Paper

Application of aziridine reactive rinses in a post-development process to reduce photoresist pattern collapse

Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 8325, 83251Y (2012) https://doi.org/10.1117/12.928877

KEYWORDS: Chemistry, Nitrogen, Photoresist materials, Photoresist processing, Scanning electron microscopy, Capillaries, Electron beam lithography, Liquids, Industrial chemicals, X-rays

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One of the problems for lithographic processes at very small feature scales is pattern collapse caused by unbalanced capillary forces experienced by the photoresist patterns during the final deionized water rinse and drying process. The use of surfactants or super critical fluids to reduce collapse problems has been proposed and studied by many research groups. However, the patterns rinsed with low surface tension fluids appear in many cases to shrink or such treatments cause other feature deformations. Super critical fluid processing requires major changes to the ways in which current track systems operate and can result in swelling and deformation of the resist features as well. Instead of utilizing super critical fluids or adding surfactants to the rinse liquid, one general methodology we have pursued for alleviating such pattern collapse problems involves the actual strengthening of the resist feature itself during wet processing in the development and rinse cycle. One method we have investigated extensively is the use of post-development resist surface crosslinking reactions while the resist structures are still in their wet state, a process we term "reactive rinsing". Such reactive rinse processes have shown significant impact on improving resist pattern collapse. However, previous chemistries used for such reactive rinse processes have either: (1) been complex mixtures that potentially have long term stability problems (i.e. thus making their application in a fab environment more difficult) or (2) been specific to a certain resist types in that the chemistries react with only certain resist functional groups that may not be present in all resists of interest (e.g. some chemistries only work with phenolic resins such as those found in DUV or EUV resists). Therefore, the goal of this work has been to investigate other novel reactive rinse chemistries that are both more robust and which can function with different families of resist materials. Poly-functional aziridines offer one potential such family of compounds that could be the basis for a reactive rinse chemistry. Such aziridines are often used industrially in both aqueous and nonaqueous coatings, inks and adhesives to promote both physical and chemical properties and are known to react with carboxylic acid functional groups such as those commonly found in many 193 nm resists. The goal of this specific study was to determine if poly-functional aziridine chemistry could be used as a reactive rinse for preventing photoresist pattern collapse in 193nm type resists. Contact angle studies and x-ray photoelectron spectroscopy (XPS) were used to characterize the surface crosslinking reaction using aziridine treatments of model resists containing carboxylic acid functionality. Pattern collapse test structures were fabricated and analyzed using a PMMA/PMAA copolymer resist commonly employed for e-beam lithography. SEM studies of the resulting patterns confirm that use of multifunctional aziridine crosslinkers during a post-development process can significantly reduce pattern collapse and enable production of higher resolution features.

Proceedings Article | 20 March 2012 Paper

Resist surface crosslinking using amine-based reactive rinses to mitagate pattern collapse in thin film lithography

Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 8325, 83251X (2012) https://doi.org/10.1117/12.928876

KEYWORDS: Lithography, Capillaries, Photoresist processing, Scanning electron microscopy, Nitrogen, Deep ultraviolet, Thin films, Resistance, Chemistry, Semiconductors

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As the semiconductor industry continues to push to smaller critical dimensions, pattern collapse during lithographic processing caused by unbalanced capillary forces during the final rinse and drying process has become an important problem that can limit the practical resolution of a resist material to feature sizes larger than its intrinsic resolution limit. One of the primary modes of pattern collapse is via elastoplastic pattern deformation which is strongly related to the mechanical properties of the resist. One approach to mitigating such collapse problems is to enhance the mechanical properties of the resist features. Since such modification of resist physical properties for pattern collapse purposes is difficult to achieve through modified formulation of the resist itself (i.e. due to the complex set of requirements that a resist must satisfy and the complex set of physical and chemical phenomena that underlie the imaging processing itself), we have pursued an alternative strategy for improving the resist mechanical properties after features are developed in the film but before they are rinsed and dried. The family of techniques being developed in this work function through the use of aqueous compatible reactive rinse solutions that can be applied to developed resist features while they are wet during normal rinse processing on a track system. By applying these techniques during the rinse process, the resist features can be strengthened before they are subjected to significant capillary forces during the final drying step. In this work, the use of diamine compounds to reactively crosslink the surface of resists containing carboxylic acid groups through formation of amide bonds using carbodiimide chemistry has been explored. One advantage of this approach is that it is an aqueous process that should be easily compatible with high volume, track-based lithographic processes. Contact angle studies and x-ray photoelectron spectroscopy (XPS) were used to characterize the surface crosslinking reaction using such diamine surface rinse treatments. Pattern collapse test structures were fabricated and analyzed to measure the amount of mechanical property improvement imparted by such treatments. Application of such amine reactive rinses was found to clearly result in an improvement in the resistance of resists to pattern collapse as observed by SEM. A comparison of the critical stress at the point of pattern collapse as a function of resist feature size also clearly shows a significant improvement in mechanical resilience of resist samples processed with the reactive rinse treatment.

Proceedings Article | 16 April 2011 Paper

Developing directly photodefinable substrate guiding layers for block copolymer directed self-assembly (DSA) patterning

Jing Cheng, Richard Lawson, Wei-Ming Yeh, Laren Tolbert, Clifford Henderson

Proceedings Volume 7972, 79722I (2011) https://doi.org/10.1117/12.894702

KEYWORDS: Polymers, Lithography, Electron beam lithography, Annealing, Optical lithography, Polymethylmethacrylate, Coating, Scanning electron microscopy, Deep ultraviolet, Directed self assembly

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Directed self-assembly (DSA) of block copolymers has gained significant attention in recent years as a possible alternative for large area fabrication of future sub-30 nm lithographic patterns. To achieve this patterning, at least three critical pieces are needed: (1) a block copolymer with sufficient immiscibility of the two blocks to drive phase separation at the low molecular weights required to achieve such small phase domains, (2) a method for selectively removing one of the blocks after phase separation to achieve formation of a relief pattern, and (3) a method for producing the templated surfaces used to guide and register the phase separated patterns on the substrate of interest. Current methods for achieving the patterned substrate template, whether they are of chemoepitaxial or graphoepitaxial nature, are generally complex involving a large number of steps that are not easily applied to a variety of different substrate surfaces. For example, numerous substrates have been studied to provide neutral wettability to the styrene-methacrylate (PS-b- PMMA) block copolymers, such as random styrene-methacrylate copolymer films (PS-r-PMMA) or self-assembled monolayer (SAM) modified surfaces, which induce perpendicularly oriented morphologies for PS-b-PMMA self-assembly. In the case of chemical epitaxy processes, a layer of photoresist is generally then coated on such neutral substrate films and patterned to render commensurability to the periodicity of the PS-b-PMMA being used. The open (i.e. space) regions in the resist are then exposed to alter their chemistry, e.g. soft X-ray or oxygen plasma exposures have been used, to achieve hydrophilicity which should preferentially wet PMMA. Finally, the resist is stripped and the block copolymer is coated and assembled on the template surface. Obviously such multi-step processes would not be preferred if alternatives existed. As a step toward that goal of making DSA processes simpler, a photodefinable substrate film that can be used for PS-b-PMMA self-assembly has been developed in this work that is coated, exposed, and baked in a manner analogous to current optical photoresists. The polymer resin for this material is a form of protected poly(hydroxystyrene) that is cross-linkable. The new material is suitable for DSA processes using both solvent and thermal annealing methods. Results of PS-b-PMMA DSA on this new material will be discussed.

Proceedings Article | 16 April 2011 Paper

The effect of drying rate on pattern collapse performance in thin film lithography

Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 7972, 79721Y (2011) https://doi.org/10.1117/12.895114

KEYWORDS: Photoresist materials, Scanning electron microscopy, Capillaries, Electron beam lithography, Lithography, Semiconducting wafers, Nitrogen, Photoresist developing, Liquids, Thin films

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As the semiconductor industry continues to push the limits of the lithography processes used to fabricate integrated circuits, pattern collapse during development and drying can have a substantial impact on process viability. This pattern collapse in general is caused by unbalanced capillary forces present during the drying step of the lithographic process. Significant research has focused on developing methods to reduce such capillary forces and improve the pattern collapse of photoresists. However, it appears that relatively little attention has been paid to other process dependent factors which may also significantly impact such collapse behavior. For example, another potential factor which may affect pattern collapse is the length of time during which the resist features are actually stressed during drying. As such, processes which result in different drying rates may be expected to yield different levels of pattern collapse. In this work, e-beam lithography was used to generate high resolution line-space pair arrays which contain different size spaces between a pair of adjacent lines in a model chemically amplified resist. Such line pairs present an excellent tool for studying pattern collapse and quantifying the level of stress required to cause collapse and failure of resist features. After development and rinse, such pattern collapse test structures were dried using a variety of different processes possessing a variety of different drying rates, and the impact of these different drying methods on pattern collapse was quantified. It was indeed found that drying rate has a dramatic impact on pattern collapse, with spin drying techniques performing better than most other techniques. However, it was discovered that such spin drying methods also yield a significant pattern orientation dependence of the degree of pattern collapse. Such behavior is explained in terms of additional mechanical forces caused by the centrifugal forces exerted during spin drying methods.

Proceedings Article | 16 April 2011 Paper

A study of reactive adhesion promoters and their ability to mitigate pattern collapse in thin film lithography

Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 7972, 79721W (2011) https://doi.org/10.1117/12.894705

KEYWORDS: Head-mounted displays, Silicon, Electron beam lithography, Photoresist materials, Scanning electron microscopy, Lithography, Thin films, Capillaries, Ellipsometry, Standards development

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As integrated circuit fabrication continues to advance towards the 22 nm node and below, it has become clear that although line edge roughness and resolution are important, other issues such as pattern collapse must be addressed in order for technology to continue to progress. One of the primary modes of pattern collapse at small feature sizes is adhesion failure caused by loss of adhesion of the resist to the substrate during the drying process. The main forces which govern pattern collapse by adhesion failure are related to substrate/resist interactions. Significant research has been conducted to find methods for reducing capillary forces, such as use of surfactants in rinses, to reduce pattern collapse. However, the use of spin drying has also been observed to exhibit other collapse related effects that are not sensitive to such treatments. To this end, in this work a reactive adhesion promoter capable of covalently attaching to hydroxystyrene-based positive tone resist copolymers has been developed and demonstrated. A vinyl-ether-modified silane was prepared and effectively applied using a solution silanization reaction. A model hydroxystyrene-based positive tone resist was applied and subjected to post apply bake to cause reaction of the surface modifier with the photoresist to occur prior to patterning using e-beam lithography. Contact angle studies and ellipsometry were used to characterize the surface silanization reaction. Pattern collapse test structures were fabricated and analyzed after development and drying on the different surfaces to quantify the impact of the use of the covalent surface linker and compare it to more standard adhesion promoter processes such as those utilizing hexamethyldilazane (HMDS). The effect of soft bake condition on the performance of the reactive adhesion promoter has also been studied. Ultimately, the results of critical stress analysis and SEM studies of the resulting patterns confirm that use of surface priming agents that covalently attach the resist to the substrate can significantly enhance resist-substrate adhesion and dramatically reduce pattern collapse.

Proceedings Article | 16 April 2011 Paper

A comprehensive model and method for model parameterization for predicting pattern collapse behavior in photoresist nanostructures

Wei-Ming Yeh, Richard Lawson, Clifford Henderson

Proceedings Volume 7972, 79721X (2011) https://doi.org/10.1117/12.895112

KEYWORDS: Data modeling, Polymers, Polymer thin films, Photoresist materials, Capillaries, 3D modeling, Liquids, Thin films, Nanostructures, Electron beam lithography

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Proceedings Article | 2 April 2011 Paper

Development of realistic potentials for the simulation of directed self-assembly of PS-PMMA di-block copolymers

Richard Lawson, Peter Ludovice, Clifford Henderson

Proceedings Volume 7970, 79700N (2011) https://doi.org/10.1117/12.879578

KEYWORDS: Polymethylmethacrylate, Picosecond phenomena, Polymers, Lithography, Electron beam lithography, Directed self assembly, Double patterning technology, Device simulation, Computer simulations, Failure analysis

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Proceedings Article | 31 March 2010 Paper

Three-dimensional mesoscale model for the simulation of LER in photoresists

Richard Lawson, Clifford Henderson

Proceedings Volume 7639, 76392G (2010) https://doi.org/10.1117/12.848415

KEYWORDS: Line edge roughness, Monte Carlo methods, 3D modeling, Diffusion, Polymers, Photoresist materials, Nanoimprint lithography, Modulation, Physics, Photoresist processing

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Proceedings Article | 31 March 2010 Paper

The use of surface modifiers to mitigate pattern collapse in thin film lithography

David Noga, Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 7639, 76391H (2010) https://doi.org/10.1117/12.862008

KEYWORDS: Head-mounted displays, Photoresist materials, Electron beam lithography, Lithography, Silicon, Thin films, Molecules, Scanning electron microscopy, Standards development, Chemistry

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Proceedings Article | 31 March 2010 Paper

Thin film buckling as a method to explore the effect of reactive rinse treatments on the mechanical properties of resist thin films

Wei-Ming Yeh, David Noga, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 7639, 76391I (2010) https://doi.org/10.1117/12.862009

KEYWORDS: Polymer thin films, Thin films, Polymers, Crystals, Quartz, Semiconducting wafers, Silicon, Optical lithography, Chemistry, Silicon films

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Proceedings Article | 31 March 2010 Paper

Non-traditional resist designs using molecular resists: positive tone cross-linked and non-chemically amplified molecular resists

Richard Lawson, David Noga, Jing Cheng, Laren Tolbert, Clifford Henderson

Proceedings Volume 7639, 76392F (2010) https://doi.org/10.1117/12.848419

KEYWORDS: Electron beam lithography, Deep ultraviolet, Polymers, Line edge roughness, Molecules, Solids, Optical lithography, FT-IR spectroscopy, Image resolution, Lithography

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Proceedings Article | 30 March 2010 Paper

Methods to explore and prevent pattern collapse in thin film lithography

David Noga, Wei-Ming Yeh, Richard Lawson, Laren Tolbert, Clifford Henderson

Proceedings Volume 7639, 76392O (2010) https://doi.org/10.1117/12.848423

KEYWORDS: Photoresist materials, Lithography, Scanning electron microscopy, Photoresist processing, Chemistry, Capillaries, Liquids, Electron beam lithography, Thin films, Line edge roughness

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Proceedings Article | 26 March 2010 Paper

Aqueous and solvent developed negative-tone molecular resists

Richard Lawson, Jing Cheng, David Noga, Todd Younkin, Laren Tolbert, Clifford Henderson

Proceedings Volume 7639, 76390O (2010) https://doi.org/10.1117/12.848414

KEYWORDS: Molecules, Electron beam lithography, Deep ultraviolet, Line edge roughness, Polymers, Polymerization, Glasses, Dewetting, Optical lithography, Scanning electron microscopy

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SPIE Journal Paper | 1 January 2010

Mesoscale kinetic Monte Carlo simulations of molecular resists: effects of photoacid homogeneity on resolution, line-edge roughness, and sensitivity

Richard Lawson, Clifford Henderson

JM3, Vol. 9, Issue 01, 013016, (January 2010) https://doi.org/10.1117/12.10.1117/1.3358383

KEYWORDS: Line edge roughness, Diffusion, Monte Carlo methods, Optical spheres, Molecular aggregates, Performance modeling, Stochastic processes, Molecules, 3D modeling, Optical lithography

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SPIE Journal Paper | 1 January 2010

Single-component molecular resists containing bound photoacid generator functionality

Richard Lawson, Laren Tolbert, Clifford Henderson

JM3, Vol. 9, Issue 01, 013015, (January 2010) https://doi.org/10.1117/12.10.1117/1.3280258

KEYWORDS: Line edge roughness, Glasses, Diffusion, Electron beam lithography, Line width roughness, Molecules, Polymers, Photoresist materials, Silicon, Silicon films

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SPIE Journal Paper | 1 October 2009

Nonionic photoacid generator behavior under high-energy exposure sources

Richard Lawson, David Noga, Laren Tolbert, Clifford Henderson

JM3, Vol. 8, Issue 04, 043010, (October 2009) https://doi.org/10.1117/12.10.1117/1.3259205

KEYWORDS: Deep ultraviolet, Absorbance, Polymers, Energy efficiency, Photons, Electron beams, Spectroscopic ellipsometry, Extreme ultraviolet, Refractive index, Absorption

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