Direct In Situ Observation of the Early‐Stage Disorder–Order Evolution of Perpendicular Lamellae in Thermally Annealed High‐χ Block Copolymer Thin Films

Abstract

feature sizes and high aspect ratios for pattern transfer can be obtained. [6][7][8] Typically, such BCP thin films are prepared by spin-coating a dilute BCP solution onto silicon (Si) substrates. However, these as-cast BCP thin films exhibit a locally segregated, disordered morphology. [9][10][11] Although perpendicular lamellar structures can be obtained by various annealing processes, high defectivity in the resultant thin films reduces the potential for industrial applications. Furthermore, although chemical and physical guides can be used to alleviate the thin film defectivity, [6,[12][13][14][15] BCP thin films that can meet the industrial requirements of 0.01 defects cm −2 have yet to be developed.The difficulty in obtaining defect-free BCP thin films can be attributed to a lack of understanding and experimental documentation in the early-stage evolution of ordered structures and defects in perpendicular lamellar thin films. Previous studies on the evolution of ordered structures in thin films have focused on the formation of parallel lamellae with island-hole structures, [16][17][18] and late-stage defect dynamics, [9,[19][20][21][22][23][24][25][26] particularly using low-χ or parallel cylinder-forming BCPs. Capturing the real time evolution of perpendicular lamellae in situ has been difficult as BCP selfassembly tends to occur in shorter time frames than most characterization equipment can analyze the thin films and the fact that parallel structures tend to form due to interfacial selectivity at the substrate and free surfaces. However, by utilizing newer technology such as high-speed atomic force microscopy (AFM) equipped with a heating unit for in situ characterization of the annealing process in a wide temperature window from room temperature to above the glass transition temperature (T g ) of the BCP, the self-assembly behavior of BCP thin films can be documented in real time and space. Additionally, although differences in the surface free energies (SFEs) between the BCP components tend to induce the preferential interfacial segregation of one block, by balancing the surface affinities of both blocks or introducing chemically modifying layers to tune the chemical affinities of the interfaces, the selective segregation of one block can be prevented, The evolution of well-ordered, sub-10 nm, perpendicular lamellae from a disordered state is documented directly using in situ atomic force microscopy, cross-sectional scanning electron microscopy, and grazing-incidence small angle X-ray scattering. Since block copolymer (BCP) self-assembly occurs on extremely fast time scales, directly imaging the growth of perpendicular lamellae remains challenging. The lack of understanding behind early-stage self-assembly and how metastable defects can affect the kinetic behavior near thermodynamic equilibrium prevents the realization of defect-free thin films. By characterizing the evolution of nanostructures using a high-χ, perpendicular lamella-forming BCP, poly(polyhedral oligomeric silsesquioxane)-blockpoly(2,2,2...

Correlating polymer structure, dynamics, and function with atomic force microscopy

“…High-speed imaging has been used to study the initial stages of microphase separation and lamellar formation from a spin-coated film. 113 It has also been applied to track the conversion of a metastable "stitched" morphology templated by a chemically patterned substrate (chemoepitaxy) to its final aligned geometry. 56,114 In these systems, scan rates are limited by the potential for sample damage of the heated polymer melts rather than the AFM imaging capabilities.…”

“…Recent advancements in HS‐AFM during thermal annealing have expanded the range of accessible BCP dynamics. High‐speed imaging has been used to study the initial stages of microphase separation and lamellar formation from a spin‐coated film 113 . It has also been applied to track the conversion of a metastable “stitched” morphology templated by a chemically patterned substrate (chemoepitaxy) to its final aligned geometry 56,114 .…”

Engineering block copolymer materials for patterning ultra-low dimensions

“…94 Moreover, the group of Hayakawa have also highlighted synthesis routes to F-containing BCPs 95 as well as their self-assembly behavior. 96,97 They reported on the synthesis of a novel Si-and F- Despite the long history of using fluorinated polymers in the semiconductor industry, 104,105 their use as BCP etch masks have not been well studied until now. In this section, we have shown the knowledge gained over the past 5 years and the feasibility of F-BCPs as excellent candidates for next-generation sub-10 nm lithography.…”

Direct Observation of the Surface Topography at High Temperature with SEM

“…Only few methods are reported for the direct observation of surface topographic modifications at the microscopic scale as a function of temperature. Among them, on can cite Atomic Force Microscopy, up to 500°C in ambient air and 750°C in vacuum (Broekmaat et al, 2008 ;Hobbs et al, 2009 ;Roobol et al, 2015 ;Chandra et al, 2019) or 3D profilometry up to 400°C (Li, 2015). They are generally limited to relatively low temperatures and / or to limited regions of interest.…”