BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.

Extreme ultraviolet lithography (EUVL) has been developed to perform high-resolution photolithography in semiconductor manufacturing. The EUVL employs scanners using light in the extreme ultraviolet (EUV) region, having a wavelength of about 1-100 nm. Some EUV scanners provide 4×reduction projection printing, similar to some optical scanners, except that the EUV scanners use reflective rather than refractive optics, i.e., mirrors instead of lenses. One type of EUV light source is laser-produced plasma (LPP). LPP technology produces EUV light by focusing a high-power laser beam onto small tin droplet targets to form highly ionized plasma that emits EUV radiation with a peak maximum emission at 13.5 nm. The EUV light is then collected by a LPP collector and reflected by optics towards a lithography target, e.g., a wafer. The collector is subjected to damage and degradation due to the impact of particles, ions, radiation, and most seriously, tin deposition.

