Hironori Ikezawa

High-order aberration control during exposure for leading-edge lithography projection optics

High throughput with high resolution imaging has been key to the development of leading-edge microlithography. However, management of thermal aberrations due to lens heating during exposure has become critical for simultaneous achievement of high throughput and high resolution. Thermal aberrations cause CD drift and overlay error, and these errors lead directly to edge placement errors (EPE). Management and control of high order thermal aberrations is a critical requirement. In this paper, we will show practical performance of the lens heating with dipole and other typical illumination conditions for finer patterning. We confirm that our new control system can reduce the high-order aberrations and enable critical-dimension uniformity CDU during the exposure.

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.