PRESENT AND FUTURE-TRENDS IN MICROLITHOGRAPHY

Some of the trends are well known and are desirable: features are shrinking and field sizes are expanding. At least one other trend is well known and is undesirable: wafer exposure tools are becoming very expensive. Other trends are less clear; throughput and overlay precision are improving but not dramatically. The failure of sub-optical technologies, notably X-ray lithography (XRL), to displace optical lithography is well publicized but at the same time the ability to push optical lithography to feature sizes smaller than the exposing wavelength is becoming tougher; phase-shifting masks and associated approaches (''wavefront engineering'') may be the saviour or may be the ''last gasp'' of optical lithography. How much further down lithographic technology will be pushed for IC manufacturing may well be set by factors unrelated to the physics of the lithographic process. Such factors include overlay capability, cost effectiveness and the electrical performance of circuit and systems with very small dimensions.