A technique that uses the tendency of block copolymers to form regular fine patterns on their own, aligning their position and orientation with guides made by lithography to create patterns finer than the resolution limit. Reducing defects to extremely low levels is the challenge for volume production.
Japanese name: 誘導自己組織化(DSA)
Directed self-assembly (DSA) appears in 3 practice questions across 1 topic, including Lithography.
Field: Lithography
A block copolymer joins chains (blocks) of two different polymers end to end. A typical example, PS-b-PMMA, consists of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The two blocks do not want to mix, but because they are joined they cannot separate far, so on annealing they spontaneously form stripes (lamellae) or cylinders with a period set by the molecular length. The period can be tuned by molecular weight and ranges from a few to several tens of nanometers.
Left alone, the pattern's orientation is random, so guides made by lithography set its position and direction. Graphoepitaxy confines the material in trenches, while chemoepitaxy patterns the surface chemistry in stripes. If the guide period is an integer multiple of the self-assembly period, the space between guides fills with finer stripes and the pattern pitch is multiplied. Cylinder patterns can also be used to make contact holes whose position and size variations are rectified.
The tendency of the two blocks to separate is expressed by the χ (chi) parameter; the larger χ, the finer the period that still separates cleanly. PS-b-PMMA has a low χ and a practical pitch limit of about 20 nm, so high-χ materials are being developed for finer pitches. The biggest problem for volume production is defects: dislocations and other defects where stripes shift must be reduced to the extremely low densities required in semiconductor manufacturing and verified by inspection.
In the 2020s, combining DSA with EUV lithography has drawn attention. In EUV, the small number of photons causes stochastic variation in line width and line-edge roughness. Using EUV patterns as guides for self-assembly is expected to snap them to the regular period set by the material and reduce that variation. imec, Intel and others have reported patterning results combining EUV and DSA since the early 2020s.
Answer: A. The molecular length (molecular weight) of the block copolymer
A block copolymer joins chains of two different polymers end to end. On annealing, the two blocks try to separate but, being joined, cannot separate far, so they form a pattern whose period is set by the molecular length. The period can be tuned by molecular weight, and how fine it can go depends on the χ parameter, which expresses how strongly the blocks separate. In directed self-assembly (DSA), guides made by lithography align the pattern's position and orientation.
Answer: C. Using EUV patterns as guides, the pattern is snapped to a regular period, reducing line-width and roughness variation caused by stochastic effects
In EUV lithography, few photons are used per exposure, so stochastic effects cause variation in line width and line-edge roughness. In directed self-assembly (DSA), the period of the block copolymer pattern is fixed by the material, so self-assembling on EUV-made guide patterns is expected to smooth out that variation. imec, Intel and others have reported results since the early 2020s, but reducing defects to extremely low levels is the challenge for volume production.
It means aligning the position and orientation of the block copolymer pattern with guides made by lithography, such as trenches or chemical patterns. Without guides, the pattern is regular but randomly oriented.
Mainly the molecular length (molecular weight) of the block copolymer. How small it can go depends on the χ parameter, which expresses how strongly the two blocks separate.
They are not only competitors but can be combined. Using EUV patterns as guides and refining them with DSA is being studied as a way to reduce line-width and roughness variation caused by EUV stochastics.
In directed self-assembly (DSA), guides made by lithography align the pattern's position and orientation.
In directed self-assembly (DSA), what mainly determines the…In directed self-assembly (DSA), the period of the block copolymer pattern is fixed by the material, so self-assembling on EUV-made guide patterns is expected to smooth out that variation.
What effect is expected when directed self-assembly (DSA) i…Directed self-assembly (DSA) uses lithographically defined guide patterns to control their position and orientation, creating features finer than the lithographic limit.
Which patterning technique uses the tendency of block copol…As an Amazon Associate I earn from qualifying purchases.
Annealing EUV lithography ArF excimer laser Bottom anti-reflective coating (BARC) Chemically amplified resist Depth of focus (DOF) DUV (deep ultraviolet) High-NA EUV Immersion lithography Line edge roughness (LER)