The limitations of subhalf-micrometer optical lithography in depth of focus, field size, and overlay accuracy, are discussed. The existing depth of focus budget as well as those for the near and the ultimate future are given. The optical depth of focus is explored in the point of view of microlithographers and means to overcome the depth of focus limit are suggested. Field size requirement of projected IC products is compared with the capability of known and projected optical systems followed with a discussion on methods to overcome the field size limit. The configuration of imaging optics is characterized and discussed by 1X versus reduction systems, refractive versus catadioptric and reflective systems, step-and-repeat versus step-and-scan systems. Overlay accuracy is discussed in terms of off-axis versus through-the-lens alignment, bright-field versus dark-field, actinic versus nonactinic alignment, followed with an overlay budget outlining the specification of the contributors to alignment errors. If all speculations are fulfilled, it is feasible to consider 0.18 μm resolution with 0.07 μm overlay.