Abstract

The high cost and complexity of commercial illumination systems envisioned for soft x-ray projection lithography (SXPL) will require that their minimum replacement period is likely to be 6-12 months. For a laser plasma soft x-ray source, this corresponds to approximately 10⁹ laser pulses. Given that a deposited film just 100 Å thick of a typical target element (Au, W, Ta, etc.) will reduce the reflectance of a multilayer mirror by an order of magnitude, it is clear that the contamination rate of condenser elements from plasma source debris must approach zero. In the present Sandia laser plasma source SXPL illumination systems, reflectance values of multilayer-coated plasma-facing optical elements are reduced by ~50% within 10⁶ laser pulses. Clearly, large improvements in target debris production and/or mitigation are needed.

© 1993 Optical Society of America