US Patent 9625824 Extreme ultraviolet lithography collector contamination reduction

An extreme ultraviolet (EUV) radiation source module includes a target droplet generator, a first laser source, and a second laser source. The target droplet generator is configured to generate a plurality of target droplets. The first laser source is configured to generate a plurality of first laser pulses that heat the target droplets at respective excitation positions thereby generating a plurality of target plumes. At least one of the target droplets is heated at an excitation position different from that of other target droplets. The second laser source is configured to generate a plurality of second laser pulses that heat the target plumes thereby generating plasma emitting EUV radiation.