The Impact of Deep UV Lithography on Device Fabrication

At present the critical lithographic for advanced Silicon devices with design rules down to 0.35 micron, is performed predominantly with i-line wafer steppers operating at a wavelength of 365 nm. In the friture wafer steppers will remain the equipment of choice for production lithography but the operating wavelength will change to the Deep UV at 248 nm, when design rules move to 0.3 micron and below. The shorter Deep UV wavelength will provide the higher depth of focus needed for a practical process window. It is expected that Deep UV will be applied first by manufacturers of microprocessors and other random logic devices. The Memory producers have more possibilities to extend the life of i-line lithography down to 0.3 micron, by using phase shifting masks and off-axis illumination, because these methods lend themselves better to repetitive geometries. In this paper the new technical properties of the Deep UV wafer steppers will be discussed, including the impact for use in production and the cost effects. Both factors will influence the speed of introduction in the fab area.