Improvements to optical performance in diffractive elements used for off-axis illumination

ABSTRACT As photolithographic tools are pressed to print the ever shrinking features required in today’s devices, complex off-axis illumination is taking an ever increasing role in meeting this challenge. This, in turn, is driving tighter, more stringent requirements on the diffractive elements used in these illumi nation systems. Specifically, any imbalance in the poles of an off-axis illuminator will contribute to reductions in th e ultimate imaging performance of a lithographic tool and increased complexity in tool-to-tool matching. The article will focus on improvements to the manufacturing process that achieve substantially better pole balance. The modeling of the possible process contributors will be discussed. Challenges resulting from the manufacturing methodology will be shared. Finally, the improvement in manufacturing process performance will be reported by means of a pole balance capability index. Key words : Pole Balance, DOE, Diffractive Optical Element, Off-axis illumination