Hyun K. Jeon

Homogeneous reactive coupling of terminally functional polymers

The rates of nine melt coupling reactions were measured by reacting terminally functional polymer chains. The functional groups are carboxylic acid, oxazoline, epoxy, aromatic primary amine, aliphatic primary amine, hydroxyl and cyclic anhydride. The functional groups were attached to the end of polystyrene (PS) and poly(methyl methacrylate) (PMMA) chains with most experiments performed at molecular weights of about 25,000 g/mol and temperature of 180°C. Reactions were performed homogeneously by blending stoichiometric amounts of the same type of polymer containing complementary functional groups. Reaction rates were determined from the amount of coupled chains via gel permeation chromatography. The functional group pairs, in order of increasing reactivity, are acid/amine, hydroxyl/(anhydride or acid), aromatic amine/epoxy, aliphatic amine/epoxy, acid/oxazoline, acid/epoxy, aromatic amine/anhydride, aliphatic amine/anhydride. This is in general agreement with results for very dilute small molecule analogs. Some experiments performed at higher molecular weights gave similar results. Coupling between aliphatic amine terminal and cyclic anhydride terminal chains was found to be extremely fast; complete conversion occurred in <30 s. Dilution studies and comparison to theory indicate that this reaction was not diffusion controlled. Mixing and diffusion are rapid enough to bring every chain end in contact within 15 s.

Visualization of block copolymer distribution on a sheared drop

We have visualized a fluorescently-labeled poly(styrene-b-methylmethacrylate) (NBD-PS-b-PMMA) block copolymer on the surface of a polymethylmethacrylate (PMMA) drop in a polystyrene (PS) matrix. Confocal microscopy revealed that the block copolymer distributed uniformly on the drop surface before deformation. However, in shear flow the copolymer concentration was higher at the tips and edges of the drop. Visualization of drop deformation using a counter-rotating apparatus showed enhanced drop deformation for a drop with block copolymer resulting in larger area generation. Drops with block copolymer showed widening even for shear strains exceeding 10, in contrast to bare drops, which first widened and then shrank. These results agree qualitatively with the observed distribution of fluorescent block copolymer. Copolymer concentration is highest in the regions of high curvature, where lowering interfacial tension should be most effective in retarding drop retraction. Block copolymer on these highly curved surfaces is found to be very effective since the exact theory for zero interfacial tension by Cristini fits our drop widening results well.

Experimental study and modeling of nanofoams formation from single phase acrylic copolymers

Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 1016/cm3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.

High speed AFM studies of 193 nm immersion photoresists during TMAH development

In this paper we report on our studies of the dynamic process of resist development in real time. Using High Speed – Atomic Force Microscopy (HS-AFM) in dilute developer solution, changes in morphology and nanomechanical properties of patterned resist were monitored. The Bruker Dimension FastScan AFMTM was applied to analyze 193 nm acrylic-based immersion resists in developer. HS-AFM operated in Peak Force mapping mode allowed for concurrent measurements of image topography resist stiffness, adhesion to AFM probe and deformation during development. In our studies we focused on HS-AFM topography data as it readily revealed detailed information about initial resist morphology, followed by a resist swelling process and eventual dissolution of the exposed resist areas. HS-AFM showed potential for tracking and understanding development of patterned resist films and can be useful in evaluating the dissolution properties of different resist designs.

Chemical trimming overcoat: an enhancing composition and process for 193nm lithography

As the critical dimension of devices is approaching the resolution limit of 193nm photo lithography, multiple patterning processes have been developed to print smaller CD and pitch. Multiple patterning and other advanced lithographic processes often require the formation of isolated features such as lines or posts by direct lithographic printing. The formation of isolated features with an acceptable process window, however, can pose a challenge as a result of poor aerial image contrast at defocus. Herein we report a novel Chemical Trimming Overcoat (CTO) as an extra step after lithography that allows us to achieve smaller feature size and better process window.

Top-coatless 193nm positive-tone development immersion resist for logic application

In this paper, we summarize our development efforts for a top-coatless 193nm immersion positive tone development (PTD) contact hole (C/H) resist with improved litho and defect performances for logic application specifically with an advance node. The ultimate performance goal was to improve the depth of focus (DoF) margin, mask error enhancement factor (MEEF), critical dimension uniformity (CDU), contact edge roughness (CER), and defect performance. Also, the through pitch CD difference was supposed to be comparable to the previous control resist. Effects of polymer and PAG properties have been evaluated for this purpose. The material properties focused in the evaluation study were polymer activation energy (Ea), polymer solubility differentiated by polymerization process types, and diffusion length (DL) and acidity (pKa) of photoacid generator (PAG). Additionally, the impact of post exposure bake (PEB) temperature was investigated for process condition optimization. As a result of this study, a new resist formulation to satisfy all litho and defect performance was developed and production yield was further improved.