Imec demonstrates 18nm pitch line/space patterning using a high-chi directed self-assembly process

Top-down (left) and cross-sectional (right) REM images of an 18-nm line/space pattern after high-χ-DSA and subsequent etching into a target SiN layer.

This week, at the SPIE Advanced Lithography Conference 2021, imec, a globally leading research and innovation center for nanoelectronics and digital technologies, demonstrated for the first time the capability of Directed Self Assembly (DSA) to pattern lines/spaces with a pitch of only 18 nm, using a High-Chi-Block-Copolymer (High-χ BCP) based process under High-Volume Manufacturing (HVM) conditions. An optimized dry etch chemistry was used to successfully transfer the pattern into an underlying thick SiN layer — enabling additional defect inspection. These results confirm the potential of DSA as a complement to traditional top-down patterning for the industrial fabrication of sub-2nm technology nodes.

The further miniaturization of components will require the patterning of structures with critical dimensions below 20 nm. At these small sizes, traditional top-down lithography is increasingly challenged by issues related to the response of photoresist materials to light — such as stochastic defects during printing and line-edge/line-width roughness (LER/LWR). Since 2010, the industry has begun to explore alternative bottom-up patterning approaches, such as directed self-assembly (DSA), as a possible way to complement and extend photolithography-based patterning.

DSA utilizes the microphase separation of a block copolymer (BCP) to define a pattern. The pattern can be generated by tuning the composition and size of the polymer. The assembly can be further guided — directed — by using a pre-pattern of lines/spaces or holes. This leads to a final regular pattern at the nanometer scale with much closer spacing (30-5 nm) than the guiding template. In 2019, imec was able to generate a line/space pattern with a 28 nm pitch with low and stable defectivity (i.e., bridges and dislocations), based on the DSA of the PS-b-PMMA block copolymer.

Building on these insights, imec is now focusing on developing the DSA process towards sub-20nm pitch patterning using second-generation block copolymers, i.e., high-χ BCPs from imec's DSA material partners (Merck KGaA, Darmstadt, Brewer Science Inc., Nissan Chemical Corp., Tokyo Ohka Kogyo Co. Ltd.). The pattern was produced from a full-pitch 90 nm guiding pattern created via 193-immersion lithography. After 60 seconds of self-assembly of high-χ BCP on an HVM-compatible surface (SCREEN Semiconductor Solutions Co., Ltd.), no dislocations were detected in the best case on the 18 nm pitch L/S pattern. "The subsequent transfer of the high-aspect-ratio lines into the underlying material stack was very challenging," says Hyo Seon Suh, Team Leader of Exploratory Patterning Materials at imec. "As a first step, we etched a block of the BCP with an optimized dry etch process with selective etching. After opening the block, the other block was transferred into the underlying stacks, which served as a hard mask for further patterning of a SiN layer. A tailored dry etch chemistry, developed in close collaboration with Tokyo Electron Ltd., enabled the successful transfer of the 18 nm line/space pattern into a SiN layer deep enough for subsequent defect inspection, without significant line jitter or collapse." In the next phase, this patterned layer will be used to establish metrology for defect inspection and LER/LWR measurements.

"In recent years, DSA has generated great industrial interest, which has resulted in a valuable ecosystem of universities, metrology experts, material and equipment suppliers. Our DSA ecosystem has been key to the results we have achieved so far," says Steven Scheer, VP of Advanced Patterning Process and Materials at imec. "For the first time, we have demonstrated that DSA can go beyond a 20 nm pitch to produce lines and spaces. The process is scalable to smaller pitches by gradually increasing the χ value of the BCP. We believe this bottom-up approach can complement traditional top-down patterning methods or be used in combination with EUV lithography to pattern the most critical features of tomorrow's devices."