Breakthrough in semiconductor patterning

The compound, which has been chemically engineered for reliable directed self-assembly (DSA), has demonstrated the ability to form perpendicular lamellar structures with a half-pitch width of less than 10 nanometres, surpassing the capabilities of conventional block copolymers.

Miniaturisation is a key driver of progress in modern electronics, enabling the remarkable increases in performance observed over recent decades. To sustain this trajectory, achieving finer circuit patterns on semiconductor chips – a critical component of all electronic devices – is essential. Some experts project that by 2037, the smallest distance between features on semiconductor devices, known as the 'half-pitch,' will need to shrink to just 8 nanometres to support the next generation of electronics. This highlights the urgent need for advancements in lithographic processes, the techniques used to create complex circuit patterns on semiconductor parts.

Creating such intricately detailed structures on materials poses significant challenges. One promising approach to overcome these challenges is directed self-assembly (DSA) using block copolymers (BCPs). BCPs are long chain-like molecules composed of two or more distinct polymer sections, or blocks. The DSA process harnesses the interactions between these different blocks, causing them to spontaneously and consistently organise into ordered structures and patterns. Although DSA is a powerful technique, producing features smaller than 10 nanometres – referred to as sub-10nm – remains a formidable challenge.

In a recent study published on 6th July 2024 in Nature Communications, researchers from Tokyo Tech and TOK have made significant strides in this area. Under the leadership of Professor Teruaki Hayakawa, the research team developed a novel BCP tailored to create extremely small line patterns on a substrate in the form of lamellar domains – structures composed of fine, alternating layers. These minuscule patterns could potentially pave the way for new, advanced semiconductor devices.

The innovative BCP was derived from polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), a well-known and extensively studied BCP for DSA. The researchers began by incorporating an appropriate amount of poly(glycidyl methacrylate) (PGMA) into the PS-b-PMMA, resulting in a compound known as PS-b-(PGMA-r-PMMA). They then modified the PGMA segment with various thiols to fine-tune the repulsive interactions between the different blocks in the polymer, creating a new material named PS-b-PGFM. The PS and PMMA segments also played a crucial role in controlling the molecule's affinity for air, which is important for the self-alignment process during DSA.

When applied as a thin film, the tailored BCP reliably self-assembled into exceptionally small nanometric lamellar structures, as confirmed by atomic force microscopy. Additionally, this new compound exhibited outstanding performance on a substrate with parallel polystyrene chemical guides.

"Thin-film aligned lamellar domains with a vertical orientation could be reliably and reproducibly obtained via directed self-assembly, yielding parallel line patterns that correspond to a half-pitch size of 7.6 nm," noted Hayakawa. He emphasised that this is one of the smallest half-pitch sizes ever reported worldwide for thin-film lamellar structures without the need for a top coating.

These findings hold significant potential for advancing semiconductor manufacturing technologies. "PS-b-PGFM BCPs are promising templates for use in lithography because they can produce fine patterns in DSA processes similar to those used for conventional PS-b-PMMA, with the potential to outperform them," Hayakawa explained. He also revealed that future studies would focus on optimising pattern-transfer processes using line patterns in PS-b-PGFM thin films as templates.

These advancements could bring us closer to a new era in electronics and artificial intelligence systems, where the miniaturisation of components will play a pivotal role in enhancing performance and enabling new applications. As research continues, the work being done by Tokyo Tech and TOK may well set the stage for the next generation of semiconductor devices, driving further innovation in the tech industry.