Shock wave visualization for extreme ultraviolet plasma optimization

A method, comprising:

• ejecting a first metal droplet from a droplet generator of an extreme ultraviolet (EUV) light source;
• irradiating the first metal droplet with a laser beam to generate a plasma;
• generating a shock wave produced by the plasma in the EUV light source;
• irradiating the shock wave with a non-ionizing light;
• capturing one or more images of the shock wave by an image sensor;
• and
• adjusting one of or both of a first time delay between pulses generated by a source of the laser beam or a second time delay between metal droplets generated by the droplet generator to minimize an impact of the shock wave associated with the first metal droplet on a subsequent second metal droplet.

An extreme ultraviolet (EUV) lithography apparatus, comprising:

• an EUV light source;
• a metal droplet generator;
• a metal droplet catcher;
• a shock wave illumination module;
• a shock wave detection module;
• and
• a controller, coupled to the shock wave illumination module and the shock wave detection module, configured to:
• determine whether a shock wave is generated based on images captured by the shock wave detection module;
• determine shock wave parameters of the shock wave;
• and
• adjust one of or both of a first time delay between pulses generated by the EUV light source and a second time delay between metal droplets generated by the metal droplet generator to minimize an impact of the shock wave associated with a first metal droplet on a subsequent second metal droplet.