EUV conversion efficiency of laser irradiated water droplets for lithography

Summary form only given. To provide lithographic tools for semiconductor industry which requires the continuing decrease of the smallest structures on computer chips, new technologies have to be investigated. A promising approach is the 13 nm extreme ultraviolet lithography (EUVL). In our case the 13 nm radiation results from the 4d/spl rarr/2p line in fivefold ionized oxygen (O/sup 5+/) emitted by a laser produced plasma. To strongly reduce the debris from the target, with respect to solid bulk targets (e.g.), we used 20 /spl mu/m diameter water droplets. With the right laser energy, we ionized the droplet completely to the desired ionization stage, without leaving behind water contaminating the optics nor overionized plasma. This result is useful in designing a EUV source meeting the high demands of the industry.