Directed Self-Assembly and Pattern Transfer of Five Nanometer Block Copolymer Lamellae Austin P. Lane,† XiaoMin Yang,¶ Michael J. Maher,‡ Gregory Blachut,∇,† Yusuke Asano,‡ Yasunobu Someya,‡ Akhila Mallavarapu,§ Stephen M. Sirard,∇ Christopher J. Ellison,†,⊥ and C. Grant Willson*,‡,† †
McKetta Department of Chemical Engineering, ‡Department of Chemistry, and §Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712, United States ⊥ Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States ¶ Media Research Center, Seagate Technology, 47488 Kato Road, Fremont, California 94538, United States ∇ Lam Research Corporation, 4400 Cushing Parkway, Fremont, California 94538, United States S Supporting Information *
ABSTRACT: The directed self-assembly (DSA) and pattern transfer of poly(5-vinyl-1,3-benzodioxole-blockpentamethyldisilylstyrene) (PVBD-b-PDSS) is reported. Lamellae-forming PVBD-b-PDSS can form well resolved 5 nm (half-pitch) features in thin films with high etch selectivity. Reactive ion etching was used to selectively remove the PVBD block, and fingerprint patterns were subsequently transferred into an underlying chromium hard mask and carbon layer. DSA of the block copolymer (BCP) features resulted from orienting PVBD-b-PDSS on guidelines patterned by nanoimprint lithography. A density multiplication factor of 4× was achieved through a hybrid chemo-/grapho-epitaxy process. Cross-sectional scanning tunneling electron microscopy/electron energy loss spectroscopy (STEM/EELS) was used to analyze the BCP profile in the DSA samples. Wetting layers of parallel orientation were observed to form unless the bottom and top surface were neutralized with a surface treatment and top coat, respectively. KEYWORDS: directed self-assembly, block copolymer, lithography, bit-patterned media, nanopatterning, nanoimprint lithography surface with sparsely spaced guidelines.3,4 Orientation of BCP domains in the presence of these guidelines results in domains with long-range order and minimum resolution well beyond the capabilities of traditional photolithography. DSA provides the feature sizes required for many of the most demanding nextgeneration patterning applications, including fabrication of bitpatterned media (BPM)5−8 for hard disk drives as well as FinFETs9 and contact holes10,11 for microelectronics. The natural periodicity of a BCP (L0) is controlled primarily by two variables: the overall degree of polymerization (N) and the segment−segment interaction parameter (χ). To achieve the highest possible resolution features (i.e., smallest L0) while remaining ordered, the chemical structure of the BCP must be carefully designed to maximize the chemical incompatibility between blocks (i.e., high-χ, low-N). Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) is the most studied BCP
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mprovements in photolithography have enabled the patterning of the ever-smaller features found in microelectronic devices. The diminishing dimensions of these features are largely responsible for increased computing performance at lower cost. However, progress toward improving the resolution of photolithography has slowed as the technology has matured and reached its physical limitations. Single-pass 193 nm immersion lithography, which is the most advanced technology deployed for high volume semiconductor manufacturing (HVM), cannot scale below ∼40 nm half pitch. Driven by a relentless pursuit for higher resolution patterning tools, manufacturers of microelectronics devices are now exploring and employing a variety of multiple patterning techniques that provide access to features with dimensions below the 40 nm limit. One such method is block copolymer (BCP) lithography,1,2 which relies on BCP microphase separation into periodic nanostructures (e.g., lamellae) on length scales in the sub-10 nm regime. The directed self-assembly (DSA) of BCP films can be used to force BCP domains to adopt well-aligned structures suitable for lithography. This requires prepatterning the substrate © 2017 American Chemical Society
Received: April 18, 2017 Accepted: July 12, 2017 Published: July 12, 2017 7656
DOI: 10.1021/acsnano.7b02698 ACS Nano 2017, 11, 7656−7665
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Figure 1. Top-down and tilted view SEMs of (A) fully developed 5 nm wide domains on top of a Cr/SOC-coated silicon wafer and (B) transferred patterns after the Cl2/O2 etch process. An oxidizing RIE process was used to completely remove the PVBD block in panel A. The full height of the etch stack in panels A and B is approximately 26 nm. Scale bars = 100 nm.
system for lithography applications because thin films of this material can produce lamellae or cylinder morphologies that adopt an orientation perpendicular to the substrate upon thermal annealing.12−15 Although processing PS-b-PMMA is simple, it suffers from a low χ parameter, which limits its minimum lamellar L0 to ∼22 nm (half-pitch = ∼11 nm).16 Unfortunately, PS-b-PMMA will not be able to fulfill the resolution requirements for future manufacturing goals.6,16−18 Consequently, there is increasing demand for the development of “high-χ” BCPs that are capable of forming sub-10 nm patterns.19−24 In particular, sub-5 nm BCP features25−28 have garnered special interest because these dimensions surpass the resolution limit of known litho/multiple patterning processes operating at their technological and economic limits.29 For most patterning applications, the perpendicular lamellae are preferred over parallel cylinders because lamellae provide a uniform, through-film cross-section. This affords a larger process window for full BCP development and subsequent image transfer into the substrate.30 BCPs of different chemistries have been shown to reach the sub-10 nm threshold (as referenced previously), but some of these systems fail to satisfy two other properties that are highly desirable for processing: (1) intrinsic etch contrast between the component blocks to enable development/pattern transfer and (2) achievement of perpendicular orientation of the BCP features by thermal annealing. Work in our group has focused on designing BCPs with minimum feature sizes that scale into the sub-10 nm regime but also satisfy these other two prerequisites. These include BCPs that incorporate inorganic elements such as silicon20 and tin31 in one block that resist specific plasma etch chemistries and provide the etch contrast required to produce a robust high-aspect-ratio etch mask upon development.32,33 BCP orientation control by thermal annealing is desirable for applications in manufacturing because that process requires no new equipment and is generally fast (
