Development of ArF Immersion Stepper for Mass-Production Applications

Nikon Corporation (Head office: Chiyoda-ku, Tokyo; President: Teruo SHIMAMURA) is pleased to announce that in the later half of 2005 it will introduce to the market an ArF immersion stepper to be used in the mass-production of 60 nm devices. For the first time anywhere in the world, the N.A. of the projection lens for the tool is greater than or equal to 1.0 .

Semiconductor tool manufacturers have accelerated research and development to keep pace with increasingly better performing and denser semiconductor devices. In the lithography field, advancements are being made to develop next-generation exposure tools, with plans also put forward to use current leading-edge ArF exposure tools for lithography processes that support even greater device miniaturization. Many semiconductor manufacturers hold great expectations for ArF exposure using immersion technology, as it is a groundbreaking method in which high resolution is obtained while hardly changing any process.

Nikon started its own basic development for this technology in the 90s, and feasibility studies have been performed jointly with Tokyo Electron since June, 2003. As a result of these activities, no bottleneck obstructing the realization of ArF immersion exposure could be found. It was therefore decided to move to the development stage directed toward productization, and in December of last year a development schedule was announced.

• Immersion Lithography Product Introduction Schedule

After studying the great market reaction following the December announcement, Nikon decided to accelerate the development plan. The company will skip the initially scheduled N.A. 0.92 mass-production tool, and in the later half of 2005 begin to market a mass-production version that has an N.A. greater than or equal to 1.0 and is compatible with current steppers, having an exposure field of 26x33 mm and a 1/4 reduction ratio.

By being the world's first to develop and productize a projection optical system with a super high N.A. of 1.0 or more - which would be impossible using air - Nikon will be contributing to the development of the semiconductor industry by making further miniaturization of semiconductor devices possible, and simultaneously providing efficient facility investments for semiconductor manufacturers.

Product Overview

Previous Development Schedule

Immersion Lithography Technology

Stepper resolution is normally expressed as resolution = k (process coefficient) x λ (light source wavelength) /N.A. (numerical aperture: the brightness of the projection lens), where a shorter light source wavelength and a higher projection lens N.A. produce a higher resolution. N.A. is derived from N.A. = n x sinθ, where n is the refractive index of the medium through which the exposure light passes, and θ is the angle the exposure light forms. Normal exposure is processed in air, and in that case n = 1. In immersion lithography, by contrast, a liquid that has a refractive index that is greater than 1 is introduced between the projection lens and the wafer. In terms of the definition of the projection optics N.A., the n increases in the equation N.A. = n sinθ. With same angle of incidence, the minimum resolution can be reduced (improved) by a factor of 1/n (equivalent to an n-fold increase in lens N.A.). On the other hand, if it is the same N.A. as in a conventional model, because θ becomes small, the depth of focus can increase (improve) n-fold. In an immersion lithography exposure system using an ArF laser as the light source, ultrapure water with an index of refraction of 1.44 is introduced between the projection lens and the wafer. Although this method is used conventionally in microscopes, only in recent years has serious research started applications to immersion lithography tools.

Nikon started this development jointly with Tokyo Electron Limited (Head office: Minato-ku, Tokyo; President: Kiyoshi SATO) in June, 2003.

• Nikon and TEL Agree on Joint Development of Liquid Immersion Technology
• Tokyo Electron Limited