Future developments for 1:1 projection photolithography

This paper reviews the application of 1 : 1 projection photolithography to present-day and future VLSI design rules. It now appears possible to extend 1 : 1 exposure techniques down to the realm 1.0-2.0- µm working features. To achieve this goal, exposure instruments must be designed to provide higher resolution, better uniformity of illumination, tighter overlay characteristics, and strict control over environmental factors. At the same time, an adequate depth of focus must be retained to accommodate real-world wafers. This paper demonstrates how control of partial coherence along with the possibility of lower exposure wavelengths (2400-3200 Å) makes 1:1 projection printing a realizable cost-effective solution for fabrication of VLSI for many years to come.