Cylinder-forming Block Copolymers Research Articles

Contact Hole Shrinkage: Simulation Study of Resist Flow Process and Its Application to Block Copolymers.

For vertical interconnect access (VIA) in three-dimensional (3D) structure chips, including those with high bandwidth memory (HBM), shrinking contact holes (C/Hs) using the resist flow process (RFP) represents the most promising technology for low-k1 (where CD=k1λ/NA,CD is the critical dimension, λ is wavelength, and NA is the numerical aperture). This method offers a way to reduce dimensions without additional complex process steps and is independent of optical technologies. However, most empirical models are heuristic methods and use linear regression to predict the critical dimension of the reflowed structure but do not account for intermediate shapes. In this research, the resist flow process (RFP) was modeled using the evolution method, the finite-element method, machine learning, and deep learning under various reflow conditions to imitate experimental results. Deep learning and machine learning have proven to be useful for physical optimization problems without analytical solutions, particularly for regression and classification tasks. In this application, the self-assembly of cylinder-forming block copolymers (BCPs), confined in prepatterns of the resist reflow process (RFP) to produce small contact hole (C/H) dimensions, was described using the self-consistent field theory (SCFT). This research paves the way for the shrink modeling of the enhanced resist reflow process (RFP) for random contact holes (C/Hs) and the production of smaller contact holes.

Directed Self-Assembly of Cylinder-Forming Block Copolymers Using Pillar Topographic Patterns.

We conducted a computational study on the self-assembly behavior of cylinder-forming block copolymers, directed by a guide pattern of hexagonally or tetragonally arrayed pillars, using mesoscale density functional theory simulations. By adjusting the spacing (Lp) and diameter (D) of the pillars in relation to the intrinsic cylinder-to-cylinder distance (L2) of the cylinder-forming block copolymer, we investigated the efficiency of multiple-replicating cylinders, generated by the block copolymer, through the pillar-directed self-assembly process. The simulations demonstrated that at specific values of normalized parameters L˜2=L2/Lp and D˜=D/Lp coupled with suitable surface fields, triple and quadruple replications are achievable with a hexagonally arrayed pillar pattern, while only double replication is attainable with a tetragonally arrayed pillar pattern. This work, offering an extensive structure map encompassing a wide range of possible parameter spaces, including L˜2 and D˜, serves as a valuable guide for designing the contact hole patterning essential in nanoelectronics applications.

Chain Redistribution Stabilizes Coexistence Phases in Block Copolymer Blends.

The nanoscale morphologies of block copolymer (BCP) thin films are determined by chain architecture. Experimental studies of thin film blends of different BCP chain types have demonstrated that blending can stabilize new motifs, such as coexistence phases. Here, we deploy coarse-grained molecular dynamics (MD) simulations in order to better understand the self-assembly behavior of BCP blend thin films. We consider blends of lamella- and cylinder-forming BCP chains, studying their morphological makeup, the chain distribution within the morphology, and the underlying polymer chain conformations. Our simulations show that there are local concentration deviations at the scale of the morphological objects that dictate the local structure, and that BCP chains redistribute within the morphology so as to stabilize the structure. Underlying these effects are measurable distortions in the BCP chain conformations. The conformational freedom afforded by BCP blending stabilizes defects and allows coexistence phases to appear, while also leading to kinetic trapping effects. These results highlight the power of blending in designing the morphology that forms.

Droplet-like Defect Annihilation Mechanisms in Hexagonal Cylinder-Forming Block Copolymers.

The annihilation of typical individual defects in hexagonal cylinder-forming block copolymers is investigated using the self-consistent field theory (SCFT) in conjunction with the string method. Usually, defect removal in two-dimensional hexagonal patterns involves reorganizing the cylindrical domains. Unlike atoms in solid crystals, the self-assembled cylindrical domains of block copolymers are "soft". Thus, the kinetic motions of the cylindrical domains resemble liquid droplets. Dislocations in hexagonal patterns are eliminated via creating and removing cylindrical domains. Our results show that new cylindrical domains are created via either a nucleation-like process or a fission-like process, whereas excessive domains are eliminated via a fusion-like or evaporation-like process. For weakly segregated block copolymers, the nucleation-like and evaporation-like processes are preferred.

Universality and Specificity in the Self-Assembly of Cylinder-Forming Block Copolymers under Cylindrical Confinement

Universality and Specificity in the Self-Assembly of Cylinder-Forming Block Copolymers under Cylindrical Confinement

Order-to-Disorder Transition of Cylinder-Forming Block Copolymer Films Confined within Neutral Interfaces

We present the phase behavior of cylinder-forming block copolymer (BCP) films confined within neutral interfaces through theory and experiment. The Langevin field-theoretic simulation (L-FTS) is utilized to account for the compositional fluctuation effect on the order-to-disorder transition (ODT), and the ultraviolet divergence in the L-FTS result is eliminated by renormalization of the Flory–Huggins parameter χ, allowing accurate comparison of thickness-dependent (χN)ODT, where N is the polymerization index. The L-FTS is accelerated by utilizing a deep learning method, and we managed to achieve a 50–60% reduction in simulation time. The L-FTS results show that (χN)ODT decreases as the film thickness decreases at a very large value of the invariant polymerization index N̅, and BCPs undergo a phase transition from disordered to cylindrical phases through a spherical phase as predicted by the self-consistent field theory calculation. By performing the L-FTS at experimentally relevant low N̅, we show that the BCPs undergo a direct transition from disordered to cylindrical phases, and the (χN)ODT value of cylinder-forming BCPs confined within neutral interfaces increases as the film thickness decreases. To verify and complement the theoretical results, we investigate the ODT temperature (TODT) of cylinder-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films supported on a neutral mat of P(S-r-2VP) random copolymers using grazing-incidence small-angle X-ray scattering. Our film experiments with low-N̅ PS-b-P2VP confirm the direct transition from disordered to cylindrical phases and the decrease in TODT with decreasing thickness below the onset thickness above which the TODT levels off.

Controlled self-assembly of block copolymers in printed sub-20 nm cross-bar structures.

Directed self-assembly (DSA) of block copolymers (BCPs) has garnered much attention due to its excellent pattern resolution, simple process, and good compatibility with many other lithography methods for useful nanodevice applications. Here, we present a BCP-based multiple nanopatterning process to achieve three-dimensional (3D) pattern formation of metal/oxide hybrid nanostructures. We employed a self-assembled sub-20 nm SiOx line pattern as a master mold for nanotransfer printing (nTP) to generate a cross-bar array. By using the transfer-printed cross-bar structures as BCP-guiding templates, we can obtain well-ordered BCP microdomains in the distinct spaces of the nanotemplates through a confined BCP self-assembly process. We also demonstrate the morphological evolution of a cylinder-forming BCP by controlling the BCP film thickness, showing a clear morphological transition from cylinders to spheres in the designated nanospaces. Furthermore, we demonstrate how to control the number of BCP spheres within the cross-bar 3D pattern by adjusting the printing angle of the multiple nTP process to provide a suitable area for spontaneous BCP accommodation. This multiple-patterning-based approach is applicable to useful 3D nanofabrication of various devices with complex hybrid nanostructures.

Enhanced Reduction of Thermal Conductivity in Amorphous Silicon Nitride-Containing Phononic Crystals Fabricated Using Directed Self-Assembly of Block Copolymers.

Studies have demonstrated that the thermal conductivity (κ) of crystalline semiconductor materials can be reduced by phonon scattering in periodic nanostructures formed using templates fabricated from self-assembled block copolymers (BCPs). Compared to crystalline materials, the heat transport mechanisms in amorphous inorganic materials differ significantly and have been explored far less extensively. However, thermal management of amorphous inorganic solids is crucial for a broad range of semiconductor devices. Here we present the fabrication of freestanding amorphous silicon nitride (SiNx) membranes for studying κ in an amorphous solid. To form a periodic nanostructure, directed self-assembly of cylinder-forming BCPs is used to pattern in the SiNx highly ordered, hexagonally close packed nanopores with pitch and neck width down to 37.5 and 12 nm, respectively. The κ of the nanoporous SiNx membranes is 60% smaller than the classically predicted value based on just the membrane porosity. In comparison, holes with much larger neck widths and pitches patterned by e-beam lithography lead to only a slight reduction in κ, which is closer to the classical porosity-based prediction. These results demonstrate that κ of amorphous SiNx can be reduced by introducing periodic nanostructures that behave as a phononic crystal, where the relationship between the smallest dimension of the nanostructure and the length scale of the mean-free paths of the dominant, heat-carrying phonons is critical. Additionally, changing the orientation of the hexagonal array of nanopores relative to the primary direction of heat flow has a smaller impact on amorphous SiNx than was previously observed in silicon.

Manipulating the sequences of block copolymer patterns on corrugated substrates

This paper describes manipulating the sequences of cylinder-forming block copolymer patterns on corrugated substrates. Upon thermal annealing, the topographic corrugation of the substrate generates a spontaneous flow-field of the block copolymer and induces thickness-dependent microdomains. The corrugation gradient has some range of surface roughness characterized by its topographic parameters. When the substrate topography matches the dimensions of the intrinsic surface relief structures of the block copolymer, the surface roughening is suppressed by inverted terrace formation, and sequenced patterns of in-plane cylinders and nonbulk lamella phases are generated. As soon as the surface roughening forms on the corrugated substrate with a roughness parameter lower than that of the surface relief structures, the reverse sequences of the alternative microphase separated structures are developed. However, enhanced mobility of the block copolymer induced by solvent annealing suppresses the pattern sequencing and the in-plane cylinders with a relatively high degree of ordering generated over the entire surface of the corrugated substrate. This observation may further enable new approaches for manipulating the sequences of spatially registered hierarchical surface patterns of block copolymers.

Creating Aligned Nanopores by Magnetic Field Processing of Block Copolymer/Homopolymer Blends.

We describe the phase behavior of a cylinder-forming block copolymer(BCP)/homopolymer blend and the generation of aligned nanopores by a combination of magnetic field alignment and selective removal of the minority-block-miscible homopolymer. Alignment is achieved by cooling through the order-disorder transition temperature (Todt) in a 6 T field. The system is a blend of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) and poly(ethylene glycol) (PEG). PEG is miscible with P4VP and partitions preferentially into the cylindrical microdomains. Calorimetry and X-ray scattering show that Todt decreases linearly with PEG concentration until the onset of macrophase separation, inferred by PEG crystallization. Beyond this point, Todt is invariant with PEG content. Increasing PEG molar mass decreases the concentration at which macrophase separation is observed. Nanopore formation is confirmed by dye uptake experiments that show a clear dependence of dye uptake on PEG content before removal. We anticipate that this strategy can be extended to other BCP/homopolymer blends to produce nanoporous materials with reliable control of pore alignment and effective pore dimensions.

Orienting Cylinder-Forming Block Copolymer Thin Films: The Combined Effect of Substrate Corrugation and Its Surface Energy

We explore the relative stability of three possible orientations of cylinder-forming di-block copolymer on a sinusoidally corrugated substrate. The cylinders can be aligned either parallel to the substrate, with their long axis being oriented along or orthogonal to the corrugation trenches, or perpendicular to the substrate. Using self-consistent field theory, we investigate the influence of substrate roughness and surface preference on the phase transition between the three orientations. When the substrate preference, $u$, towards one of components is small, increasing the substrate roughness induces a phase transition from parallel to perpendicular cylindrical phase. However, when $u$ is large, the parallel orientation is more stable than the perpendicular one. Within this parallel phase, increasing the substrate roughness leads to a transition of cylinder orientation changing from being orthogonal to parallel to the trench long axis. Increasing the substrate preference leads to an opposite transition from parallel to orthogonal to the trenches. Furthermore, we predict that the perpendicular cylinder phase is easier to be obtained when the unidirectional corrugation is along the longer unit vector of the hexagonal packing than when it is along the shorter unit vector. Our results qualitatively agree with previous experiments, and contribute towards applications of the cylinder-forming block copolymer in nanotechnology.

Self-Alignment of Cylinder-Forming Silicon-Containing Block Copolymer Films

Well-ordered perpendicular cylinders of star-block copolymers (BCPs) composed of polystyrene and poly(dimethylsiloxane) blocks with high aspect ratio can be achieved by using a combination of architecture effect (entropy effect) and surface air plasma treatment (enthalpy effect). An interesting morphological evolution from disordered texture to hexagonally packed cylinders with perpendicular orientation has been observed, in which perpendicular cylinders are initiated at the top surface and bottom substrate of the thin film, followed by a self-alignment process, resulting in span-thru cylinders through the thin film. The self-alignment process is systematically examined by a combination of real space imaging using transmission electron microscopy, reciprocal space imaging using grazing incidence small-angle X-ray scattering, and three-dimensional tomography. The experimental results reveal a unique mechanism for the formation of highly ordered BCP thin films via surface-induced nucleation of perpendicular...

Curvature as a Guiding Field for Patterns in Thin Block Copolymer Films.

Experimental data on thin films of cylinder-forming block copolymers (BC)-free-standing BC membranes as well as supported BC films-strongly suggest that the local orientation of the BC patterns is coupled to the geometry in which the patterns are embedded. We analyze this phenomenon using general symmetry considerations and numerical self-consistent field studies of curved BC films in cylindrical geometry. The stability of the films against curvature-induced dewetting is also analyzed. In good agreement with experiments, we find that the BC cylinders tend to align along the direction of curvature at high curvatures. At low curvatures, we identify a transition from perpendicular to parallel alignment in supported films, which is absent in free-standing membranes. Hence both experiments and theory show that curvature can be used to manipulate and align BC patterns.

Rapid shear alignment of sub-10 nm cylinder-forming block copolymer films based on thermal expansion mismatch

Directed self-assembly of block copolymers (BCPs) provided by shear-stress can produce aligned sub-10 nm structures over large areas for applications in integrated circuits, next-generation data storage, and plasmonic structures. In this work, we present a fast, versatile BCP shear-alignment process based on coefficient of thermal expansion mismatch of the BCP film, a rigid top coat and a substrate. Monolayer and bilayer cylindrical microdomains of poly(styrene-b-dimethylsiloxane) aligned preferentially in-plane and orthogonal to naturally-forming or engineered cracks in the top coat film, allowing for orientation control over 1 cm2 substrates. Annealing temperatures, up to 275 °C, provided low-defect alignment up to 2 mm away from cracks for rapid (<1 min) annealing times. Finite-element simulations of the stress as a function of annealing time, annealing temperature, and distance from cracks showed that shear stress during the cooling phase of the thermal annealing was critical for the observed microdomain alignment.

Interplay of Template Constraints and Microphase Separation in Polymeric Nano-Objects Replicated from Novel Modulated and Interconnected Nanoporous Anodic Alumina

We report on a versatile strategy to fabricate shape-controlled polymeric nano-objects with an internal compartmentalized structure by replication from pore-diameter-modulated and interconnected nanoporous anodized aluminum oxide (AAO). The AAO with modulated pore diameters is synthesized in a refined temperature-modulated hard anodization (TMHA) approach, by alternating the flow rate of an air stream cooling the electrolyte. Through pore-widening of the templates with modulated pore diameters, a stable interconnected 3D network with transversal ellipsoidal holes is fabricated as a second template structure. From these unprecedented template structures exhibiting modulated pores and an intricate 3D network structure, shape-controlled polymeric nano-objects are replicated using the melt wetting method with polystyrene homopolymer (PS) and cylinder-forming block copolymer polystyrene-block-polydimethylsiloxane (PS298-b-PDMS195). The replicated nanostructures are separated into individual anisotropically sha...

The One-Pot Directed Assembly of Cylinder-Forming Block Copolymer on Adjacent Chemical Patterns for Bimodal Patterning.

The direct self-assembly of cylinder-forming poly(styrene-block-methyl-methacrylate) (PS-b-PMMA) block copolymer is successfully assembled into two orientations, according to the underlying guiding pattern in different areas. Lying-down and perpendicular cylinders are formed, respectively, depending on the design of chemical pattern: sparse line/space pattern or hexagonal dot array. The first chemical pattern composed of prepatterned cross-linked polystyrene (XPS) line/space structure has a period (LS ) equal to twice the intercylinder period of the block copolymer (L0 ). The PS-b-PMMA thin film on the prepared chemical template after thermal annealing forms a lying-down cylinder morphology when the width of the PS strips is less than the width of PS block in the PS-b-PMMA block copolymer. The morphology is only applicable at the discrete thickness of the PS-b-PMMA film. In addition to forming the lying-down cylinders directly on the XPS guiding pattern, the cylinder-forming block copolymer can also be assembled in a perpendicular way on the second guiding pattern (the hexagonal dot array). The block copolymer films are registered into two orientations in a single directed self-assembly process. The features of the assembled patterns are successfully transferred down to the silicon oxide substrate.

Nanolithography of cylinder forming block copolymers via DSA for semiconductor manufacturing

To realize the full benefit of directed self-assembly (DSA), it is necessary to understand the interplay between the target structures and the process parameters.

Integration of a templated directed self-assembly-based hole shrink in a short loop via chain

The use of directed self-assembly (DSA) of cylinder forming block copolymers (BCP) for contact hole shrink applications has gained increased attention due to the dimensions that can be achieved with this materials. Recent work has focused on engineering the dimensions and surface energy of the templates to obtain straight profiles of the cylinders assembled in them. However, the impact of process optimization on defect formation is measured using scanning electron microscopy before and after transferring the BCP features to a hardmask, which provides limited information about the presence of defects or three-dimensional morphologies in the polymer structures. To identify the presence of single defects in arrays of various densities and sizes, we use Kelvin and chain structures available in the IMEC 28-nm node via chain electrical test vehicle, Everest, in combination with templated DSA. We tuned the surface energy and dimensions of the templates with the use of random copolymers and through the exposure conditions, respectively. Finally, the contact holes obtained with templated DSA of BCP were subsequently transferred into a relevant stack to apply advanced metallization processes and, ultimately, validated electrically.

Process highlights to enhance directed self-assembly contact patterning performances

We focus on the directed self-assembly (DSA) for contact hole (CH) patterning application using polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymers (BCPs). By employing the DSA planarization process, we highlight the DSA advantages for CH shrink, repair, and multiplication, which are extremely needed to push forward the limits of currently used lithography. Meanwhile, we overcome the issue of pattern density-related defects that are encountered with the commonly used graphoepitaxy process flow. Our study also aims to evaluate the DSA performances as functions of material properties and process conditions by monitoring main key manufacturing process parameters: CD uniformity (CDU), placement error (PE), and defectivity [hole open yield (HOY)]. Concerning process, it is shown that the control of surface affinity and the optimization of self-assembly annealing conditions enable significant enhancement of CDU and PE. Regarding material properties, we show that the best BCP composition for CH patterning should be set at 70/30 of PS/PMMA total weight ratio. Moreover, it is found that increasing the PS homopolymer content from 0.2% to 1% has no impact on DSA performances. Using a C35 BCP (cylinder-forming BCP of natural period L0=35 nm), good DSA performances are achieved: CDU-3σ=1.2 nm, PE-3σ=1.2 nm, and HOY=100%. Finally, the stability of DSA process is also demonstrated through the process follow-up on both patterned and unpatterned surfaces over several weeks.

Shear-Aligned Block Copolymer Monolayers as Seeds To Control the Orientational Order in Cylinder-Forming Block Copolymer Thin Films

We study the dynamics of coarsening of a cylinder-forming block copolymer thin film deposited on a prepatterned substrate made of a well-ordered block copolymer monolayer. During thermal annealing the shear-aligned bottom layer drives extinction of the disclinations and promotes a strong orientational correlation, disturbed only by dislocations and undulations along the cylinders of the minority phase. The thin film bilayer system remains stable during annealing, in agreement with self-consistent field theory results that indicate that although the thickness of a stack of two monolayers is not at the optimum thickness condition, it is very close to equilibrium. Phase field simulations indicate that the bottom layer remains undisturbed during annealing and acts as a periodic external field that stabilizes the orientation of those domains that share its orientation. Misoriented cylinders are rapidly reorganized through an instability mechanism that drives the fragmentation of the cylinders. As annealing pro...