DSA (Directed Self-Assembly)

Notes

Heavily researched around 2010 to 2015 but never reached volume production because of defect density limits.

Overview

DSA (directed self-assembly) is a patterning technique in which a block copolymer, a polymer made of two chemically incompatible chains joined end to end, separates on its own into regular lines or dots a few nanometres apart, steered into place by a coarser guide pattern made with ordinary lithography. Because the pitch is set by the length of the polymer chains rather than by optics, it can multiply the density of a guide pattern or tidy up an imperfect one. After an early wave of interest around 2012, DSA is being studied again, mainly as a partner to EUV lithography rather than a replacement.

How it works

The most studied material is PS-b-PMMA, in which a polystyrene block and a poly(methyl methacrylate) block are bonded together. Like oil and vinegar, the two blocks try to separate, but because they are joined they can only form domains whose size depends on the chain lengths. With roughly equal blocks they form alternating sheets, which appear as lines and spaces, and other ratios give other shapes; imec notes that guide patterns can be lines or holes.

Two guiding approaches are common. In graphoepitaxy, the polymer fills trenches patterned by conventional lithography, typically two to five times wider than the final feature, and assembles along the walls when annealed. In chemoepitaxy, a flat surface carries stripes of differing surface chemistry that anchor one block and leave the rest to self-align. One block is then etched away and the other serves as a mask.

Defects have been the main obstacle. Imec work reported in 2014 showed defect density falling from 200 to 24 per square centimetre, but with a 2.5 hour anneal, far slower than a lithography step. Newer high-chi polymers separate more strongly and allow tighter pitches: imec reported 18 nm pitch lines in 2021 after a 60 second anneal on a production-style track. Current work focuses on using DSA to repair roughness and stochastic defects in EUV patterns, which Intel and imec have both described.

Examples

• Imec's 18 nm pitch line and space pattern made with a high-chi block copolymer from a 90 nm pitch 193 nm immersion guide pattern, announced in February 2021.
• Intel's DSA-enhanced EUV multi-patterning flow, which the company says reached an 18 nm final metal pitch.
• EUV resist rectification, in which a block copolymer laid over EUV-printed lines reduces their roughness and stochastic variation.
• Imec's chemoepitaxial process using a cross-linked polystyrene guide layer, studied for its defect sources.

Why it matters

DSA interests patterning and materials researchers, lithography process engineers and materials suppliers, because it offers a route to finer, smoother patterns without a more expensive exposure tool. Its promise is balanced against defect control, integration effort and design restrictions, since it suits regular, repeating layouts best.

In the chip lifecycle, DSA sits in process research and development: it is evaluated during pathfinding for future nodes and, if adopted, becomes part of the patterning modules defined before a process reaches production.

It matters most to: Advanced Node Pathfinding R&D Engineer, EUV Lithography Research Scientist, Lithography Process Engineer, Patterning and Resist Materials Researcher, Semiconductor Materials Scientist

Common confusions

Not the same as multiple patterning

Multiple patterning reaches tighter pitches with extra lithography, deposition and etch steps. DSA gets the finer pitch from polymer chemistry, though it still needs a lithographic guide.

Not the same as DSA in other fields

DSA can also mean digital subtraction angiography in medicine or the Digital Signature Algorithm in security. In chip patterning it means directed self-assembly.

Sources

1. Imec Demonstrates 18nm Pitch Line/Space Patterning With a High-Chi Directed Self-Assembly Process (press release, 25 February 2021) (opens in a new tab), imec, 2026-10-22
2. Directed Self-Assembly Gets Another Look (Gregory Haley, 17 August 2023) (opens in a new tab), Semiconductor Engineering, 2026-10-22
3. DSA Defects Continue Downward Trend (12 November 2014) (opens in a new tab), Semiconductor Engineering, 2026-10-22

Related terms

• Multiple patterning
• NIL
• Defect density

Where it appears on the Hub

Used on 4 pages of the Hub. In each group, the pages that mention it most come first.