Scaling to the 7 nm node and beyond with multiple patterning is heavily dependent upon reducing overlay and increasing throughput under manufacturing conditions. These require thermal control capabilities in the scanner’s lens. At recent industry conferences, Nikon experts spotlighted hardware and software solutions that ensure optimal on-product performance and productivity using real-world exposure conditions.
Speaking at SPIE Advanced Lithography earlier this year, Satoshi Ishiyama, Chief Researcher for Nikon Corporation, reported that the NSR-S631E immersion scanner supports 7 nm node manufacturing by delivering enhanced image quality with on-product CD uniformity (CDU) below 0.7 nm and on-product overlay (OPO) below 2.5 nm. This is made possible through marked innovations in thermal aberration management. Ishiyama-san explained that scaling with multiple patterning necessitates on-going improvements in overlay, as well as increased throughput, and the use of negative tone processes (Figure 1A). This drives the need for projection optics that provide enhanced thermal aberration control capabilities.
Ishiyama-san shared data showing continuous reduction in projection lens distortion over several generations of immersion scanners (Figure 1B). S631E projection lens distortion was 0.7 nmPV, with earlier generation S630D and S620D scanners (both use the “D” generation lens design) showing 1.1 nmPV and 2.0 nmPV, respectively. The new S631E lens design also delivers lower projection lens wavefront levels (0.48 nmRMS compared to 0.91 nmRMS on the S620D), which was made possible through advances in lens tuning capabilities. These critical progressions play a role in enhancing lens performance under “cool” processing conditions.
Leading-edge Nikon immersion scanners use a catadioptric lens design to deliver a 1.35 numerical aperture, and the Quick Reflex deformable mirror enables aberration control that is constant across the field. The S631E employs the newly developed Quick Reflex II system, which is composed of MDDM and TAAAF, to enable high order wavefront control capabilities that are uniform across the field as well as across-field aberration control capabilities.
MDDM expands the number of control axes, enabling the S631E to better correct for high order thermal aberrations, which enhances image quality for on-product patterning (Figure 2). TAAAF then provides additional compensation for residual wavefront error and pattern dependencies to optimize overlay in manufacturing. Ishiyama-san shared data confirming that Z10 heating aberration is very well controlled using the S631E with TAAAF. He also showed a practical example evaluating CDU under heated conditions. This consisted of a flash memory application using dipole-Y, H polarized illumination for 41 nm 98.4 nm pitch and 100 nm 220 nm pitch features, and the intra-lot CD uniformity drift for those varied patterns was substantially reduced using the S631E (Figure 3A).
At the LithoVision symposium, Nikon Corporation 1st Development Section Manager, Kazuo Masaki, provided additional insight about other thermal control solutions that are essential in next-node lithography. Lens Master thermal aberration optimizer (ThAO) is application software that supports scanner lens controller parameter calculations. ThAO enables computational calculation and correction of lens heating aberrations without heat testing. Masaki-san showed a comparison of lens heating effects with Z5 coefficients reduced from 89 mλ to less than 10 mλ when Lens Master computational corrections were used. Masaki-san also highlighted the recently developed Reticle Expansion Optimizer (REO) function. This reticle expansion prediction system uses a reticle transmittance map to generate a heat map calculation and a reticle deformation calculation, which is applied automatically to the scanner recipe parameters for exposure (Figure 3B). REO effectively predicts and compensates for Mag-X, Mag-Y, and K17, K18 parameters to optimize on-product overlay performance.
The NSR-S631E delivers exceptional “cool” lens performance, and also minimizes thermal impacts across diverse illumination conditions to dramatically improve manufacturing capabilities. Evaluations under various extreme heat conditions have consistently demonstrated across lot Mean + 3σ overlay results below 2.3 nm (Figure 4A). Continued industry scaling requires steady performance improvements under aggressive real-world, manufacturing conditions. The S631E supports an extensive suite of hardware and software solutions (Figure 4B) that compensate for thermal aberrations and heating effects to optimize 7 nm node device patterning and productivity.