Yusaku Uehara

Thermal aberration control for low-k1 lithography

For many years, we have used a lens aberration controller that works via positioning elements of the projection lens assembly. While this has worked well, its disadvantage is that controllable aberrations are only relatively low order components and not enough for the degree of compensation of thermal aberrations required by leading-edge lithography. We have developed two methods to overcome thermal aberrations specific to dipole illumination exposure. One scheme is process-dedicated aberration control by the conventional aberration controller. The other is aberration control system using infra-red irradiation. This system can compensate uniform astigmatism which is generated by asymmetric setting of illumination light sources, such as dipole illumination schemes. Theses two techniques allow us to increase productivity by reducing pattern imaging performance degradation due to thermal aberrations. These schemes are applicable not only to current systems but also to next generation very low k1 lithography systems with very high throughput.

Latest performance of ArF immersion scanner NSR-S630D for high-volume manufacturing for 7nm node

In order to achieve stable operation in cutting-edge semiconductor manufacturing, Nikon has developed NSR-S630D with extremely accurate overlay while maintaining throughput in various conditions resembling a real production environment. In addition, NSR-S630D has been equipped with enhanced capabilities to maintain long-term overlay stability and user interface improvement all due to our newly developed application software platform. In this paper, we describe the most recent S630D performance in various conditions similar to real productions. In a production environment, superior overlay accuracy with high dose conditions and high throughput are often required; therefore, we have performed several experiments with high dose conditions to demonstrate NSR’s thermal aberration capabilities in order to achieve world class overlay performance. Furthermore, we will introduce our new software that enables long term overlay performance.

Immersion and dry ArF scanners enabling 22nm HP production and beyond

Pattern shrinks using multiple patterning techniques will continue to the 22nm half pitch (HP) node and beyond. The cutting-edge Nikon NSR-S621D immersion lithography tool, which builds upon the technology advancements of the NSR-S620D [1], was developed to satisfy the aggressive requirements for the 22 nm HP node and subsequent generations. The key design challenge for the S621D was to deliver further improvements to product overlay performance and CD uniformity, while also providing increased productivity. Since many different products are made within an IC manufacturing facility, various wafer process-related issues, including the flatness or grid distortion of the processed wafers and exposure-induced heating had to be addressed. Upgrades and enhancements were made to the S620D hardware and software systems to enable the S621D to minimize these process-related effects and deliver the necessary scanner performance. To enable continued process technology advancements, in addition to pattern shrinks at the most critical layers, resolution for less critical layers must also be improved proportionally. As a result, increased demand for dry ArF instead of KrF scanners is expected for less critical layers, and dry ArF tools are already being employed for some of these applications. Further, multiple patterning techniques, such as sidewall double patterning, actually enable use of dry ArF instead of immersion scanners for some critical layers having relaxed pattern resolution requirements. However, in order for this to be successful, the ArF dry tool must deliver overlay performance that is comparable to the latest generation immersion systems. Understanding these factors, an ArF dry scanner that has excellent overlay performance could be used effectively for critical layers and markedly improve cost of ownership (CoO). Therefore, Nikon has developed the NSR-S320F, a new dry ArF scanner also built upon the proven S620D Streamlign platform. By incorporating the Streamlign innovations, sufficient overlay accuracy for critical layers, as well as maximized productivity can be achieved. Furthermore, CoO will be significantly improved, which is the vital benefit when comparing ArF dry vs. immersion scanners. In this paper / presentation the latest S621D and S320F performance data will be introduced.

An intelligent imaging system for ArF scanner

The k1 factor continues to be driven downwards, even beyond its theoretical limit 0.25, in order to enable the 32 nm feature generation and beyond. Due to the extremely small process-window that will be available for such extremely demanding imaging challenges, it is necessary that not only each unit contributing to the imaging system be driven to its ultimate performance capability, but also that the final integrated imaging system apply each of the different components in an optimum way with respect to one another, and maintain that optimum performance level and cooperation at all times. Components included in such an integrated imaging system include the projection lens, illumination optics, light source, in-situ metrology tooling, aberration control, and dose control. In this paper we are going to discuss the required functions of each component of the imaging system and how to optimally control each unit in cooperation with the others in order to achieve the goal of 32 nm patterning and beyond.

A hyper-NA projection lens for ArF immersion exposure tool

Resolution enhancement in ArF dry lithography is limited by the numerical aperture (NA), which cannot be extended past the physical limit of 1.0. Immersion lithography is proposed as a candidate to overcome this limitation as resolution can be enhanced with a hyper-NA immersion projection lens. In addition, depth of focus (DOF) can be extended owing to the small incident angle for marginal rays onto the image plane. Our development of immersion optics can be divided into three phases. First, the initial evaluation has successfully been conducted in the engineering evaluation tool (EET), in which the projection optics is converted from dry-use to wet-use while retaining the same NA, 0.85. Second, the projection optics with 1.07NA has been developed aiming at devices with 50-55nm half-pitch (hp) patterns. The optics, comprising only the refractive elements, is exclusively dedicated to immersion usage. Third, catadioptric optics with 1.3NA targeting at 45nm hp devices is intensively studied. This paper will focus on the second and the third phases of the development.

Immersion scanners enabling 10nm half-pitch production and beyond

Nikon’s new immersion scanner “NSR-S630D” has been developed to deliver enhanced product overlay and CD uniformity while improving productivity at 10 nm half pitch node and beyond. The NSR-S630D is equipped with various advanced technologies. Among them are the new reticle stage with encoder servo control and advanced reticle bending mechanism, new optics with enhanced correction knobs for thermal aberration control, and advanced thermally stable wafer stage; all of which are key components to providing the best scanner solution to meet the requirements for 10 nm half pitch node and beyond. In this paper, we describe the NSR-630D development concept and the latest performance data at factory. One of the key factors in improving overlay is shot distortion; in order to improve shot distortion, the NSR-S630D is equipped with a newly developed state-of-the-art projection lens. The overall overlay improvements have been made possible not only by minimizing lens distortion through advancements in lens manufacturing techniques, but also by reducing thermal distortion, which is especially important in actual device production. In addition, we have also added a new function for more effective reticle heating distortion compensation. In order to improve wafer grid performance, we newly designed a wafer table with enhanced thermal stability. We have also further improved the reticle bending system in order to minimize the field curvature induced by projection lens thermal aberration. The new features described above, in addition to the matured Streamlign platform, have enabled the NSR-S630D to deliver highest accuracy and stability.

An imaging system for extended ArF immersion lithography

The k1 factor continues to be driven downwards, even beyond its theoretical limit 0.25 in order to enable the 32 nm feature generation and beyond. Due to the extremely small process window that will be available for such extremely demanding imaging challenges, it is necessary that each unit contributing to the imaging system be driven to its ultimate performance capability. The units in such an integrated imaging system include the projection lens, illumination optics, in-situ metrology tooling, reticle stage control, and wafer stage control. In this paper we are going to discuss the required functions especially for projection lens and illumination system and how to optimally control each unit in cooperation with the others in order to achieve the goal of 32 nm patterning and beyond.