Soft x-ray projection lithography
As the VLSI (very large scale integration) industry demands cameras that can produce images of ever greater resolution, lithographic technology has responded by developing lenses capable of diffraction limited imaging. When the need arose for sub-half micron features, the industry sought higher resolution by using shorter wavelengths, the near UV in the mercury i-line at 365 nm, and soon the deep UV using excimer lasers at 248 nm and, eventually, perhaps even 193 nm. However, as we increase resolution we decrease the depth of focus, and patterns produced by poorly focused imaging is a major source of defects in the final circuits.
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