Optical Lithography - Thirty years and three orders of magnitude - The evolution of optical lithography tools

The evolution of optical lithography is traced back more than 30 years to its beginnings with contact printing. As the complexity of integrated circuits increased, the intolerance for defects drove the industry to projection printing. Projection printing was introduced in the early 1970's by imaging the full wafer at 1:1 magnification. The rapid increase in wafer sizes was accommodated by annular field scanning using 1:1 imaging mirror systems. Decreased linewidths and tighter overlay budgets combined with larger wafers created huge difficulties for the mask maker which weren't relieved until the introduction of reduction step-and-repeat printing of small blocks of chips in the late 1970's. Further demands for smaller linewidths and larger chips have driven optical lithography to shorter wavelengths and to scanning the chip in a step-and-scan printing mode. Future advancements in lithography will likely combine novel scanning techniques with further reductions in wavelength.