The Limits of Lamellae-Forming PS-b-PMMA Block Copolymers for Lithography

Abstract

We explore the lithographic limits of lamellae-forming PS-b-PMMA block copolymers by performing directed self-assembly and pattern transfer on a range of PS-b-PMMA materials having a full pitch from 27 to 18.5 nm. While directed self-assembly on chemical contrast patterns was successful with all the materials used in this study, clean removal of PMMA domains and subsequent pattern transfer could only be sustained down to 22 nm full pitch. We attribute this limitation to the width of the interface, which may represent more than half of the domain width for materials with a critical dimension below 10 nm. With the limit of pattern transfer for PS-b-PMMA set at ∼11 nm, we propose an integration scheme suitable for bit patterned media for densities above 1.6 Tdot/in(2), which require features below this limit. Directed self-assembly was carried out on chemical contrast patterns made by a rotary e-beam lithography system, and pattern transfer was carried out to demonstrate fabrication of large area (up to 25 mm-wide annular band of circular tracks) nanoimprint templates for bit patterned media. We also demonstrate compatibility with hard disk drive architecture by fabricating patterns with skewed radial lines with constant angular pitch and with servo patterns that are needed in hard disk drives to generate a radial positional error signal (PES).

Directional Self‐Assembly of Fluorinated Star Block Polymer Thin Films Using Mixed Solvent Vapor Annealing

“…The achievable lowest L 0 was obtained from ( χN ) c values (i.e., 10.5 for linear PMMA‐PS, 8 for star PMMA‐PS, 11.5 for linear PFMA‐PS, 9 for star PFMA‐PS) divided by the achievable N on the basis of calculated χ eff ‐ values for each polymer. The achievable L 0 of linear PMMA‐PS BP was estimated to be ~17.4 nm (we note that this value agrees with literature reports of a minimum PMMA‐PS L 0 of ~17.5 nm), and the achievable L 0 of the star PMMA‐PS BP was ~15 nm, equivalent to a half‐pitch feature size of ~7.5 nm (i.e., sub‐10 nm). The impact of star architecture was more obvious in the higher‐ χ polymers.…”

“…Because PS and PMMA blocks have similar surface energies at the free surface, simple thermal annealing can be employed to generate perpendicularly oriented nanostructures in thin films, provided that neutral substrates are used . However, the relatively low χ of PS‐PMMA limits the BP's ability to meet resolution requirements for future nanolithography . Thus, BPs with higher‐ χ have been developed with a goal of fabricating perpendicular domains with sub‐10 nm features .…”

“…[16][17][18][19] However, the relatively low χ of PS-PMMA limits the BP's ability to meet resolution requirements for future nanolithography. 20 Thus, BPs with higher-χ have been developed with a goal of fabricating perpendicular domains with sub-10 nm features. [21][22][23][24][25][26] One straightforward approach is to increase the incompatibility between the two polymer blocks by changing the monomers' chemical structures while maintaining the linear BP molecular architecture.…”

High-χ, Si-Containing Block Copolymers and Process Strategies for Directing Their Self-Assembly

“…While PS-b-PMMA is as close to a material standard as is possible in the wide-ranging DSA field, its relatively low Flory-Huggins interaction parameter, χ = 0.04, is a resolution-limiter. As L 0 of PS-b-PMMA is decreased to about 24 nm and lower, its microdomains start to mix at the molecular level and form patterns with poor chemical definition and unsatisfactory etch selectivity [3].…”

Orthogonally Spin-Coated Bilayer Films for Photochemical Immobilization and Patterning of Sub-10-Nanometer Polymer Monolayers

“…35,36 Spatial control of surface energy by grafted polymers is critical to controlling microdomain orientation and alignment over multiple length scales, which is a requirement of very specific potential end uses like surface plasmonics, 20,37,38 microprocessor transistors, 39 and hard-disk memory. 31,40 Due to processing considerations, poly(styrene-block-methyl methacrylate) (PS-b-PMMA) is a model material for block copolymer lithography, and it is produced commercially at pilot scale for this application. 41 Therefore, we chose PS homopolymer, PMMA homopolymer, and the copolymers thereof to study as overlayers immobilized by grafting to PSSMA.…”