Mr. Wei-Ming Yeh Profile

Wei-Ming Yeh

at Georgia Institute of Technology

SPIE Involvement:

Author

Publications (14)

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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

Read Abstract +

Showing 5 of 14 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years