An extreme ultraviolet (EUV) photolithography system generates EUV light by irradiating droplets with a laser. The system includes a droplet generator with a nozzle and a piezoelectric structure coupled to the nozzle. The generator outputs groups of droplets. A control system applies a voltage waveform to the piezoelectric structure while the nozzle outputs the group of droplets. The waveform causes the droplets of the group to have a spread of velocities that results in the droplets coalescing into a single droplet prior to being irradiated by the laser.

The present disclosure is directed to a modularized vessel droplet generator assembly (MGDVA) including a droplet generator assembly (DGA). Under a normal operation, the liquid fuel moves along an operation pathway extending through the DGA to eject or discharge the liquid fuel (e.g., liquid tin) from a nozzle of the DGA into a vacuum chamber. The liquid fuel in the vacuum chamber is then exposed to a laser generating an extreme ultra-violet (EUV) light. Under a service operation, the operation pathway is closed and a service pathway extending through the DGA is opened. A gas is introduced into the service pathway forming a gas-liquid interface between the gas and the liquid fuel. The gas-liquid interface is driven to an isolation valve directly adjacent to the DGA. In other words, the gas pushes back the liquid fuel to the isolation valve. Once the gas-liquid interface reaches the isolation valve, the isolation valve is closed isolating the DGA from the liquid fuel.

Impurities in a liquefied solid fuel utilized in a droplet generator of an extreme ultraviolet photolithography system are removed from vessels containing the liquefied solid fuel. Removal of the impurities increases the stability and predictability of droplet formation which positively impacts wafer yield and droplet generator lifetime.

An optical element (1)includes: a substrate (2), applied to the substrate (2), a multilayer system (3) which reflects EUV radiation (4), and applied to the multilayer system (3), a protective layer system (5) having an uppermost layer (5a). Nanoparticles (7) are embedded into the material of the uppermost layer (5a) of the protective layer system (5) which nanoparticles contain at least one metallic material. An EUV lithography system which includes at least one such optical element (1) designed as indicated above, and a method of forming nanoparticles (7) in the uppermost layer (5a) of the protective layer system (5) are also disclosed.

A method includes following steps. A photoresist-coated substrate is received to an extreme ultraviolet (EUV) tool. An EUV radiation is directed from a radiation source onto the photoresist-coated substrate, wherein the EUV radiation is generated by an excitation laser hitting a plurality of target droplets ejected from a first droplet generator. The first droplet generator is replaced with a second droplet generator at a temperature not lower than about 150° C.

An apparatus for removing a residue of an EUV light source vessel including an internal side surface having a curved surface is provided. The apparatus includes a frame portion configured to be disposed on a bottom surface of an EUV light source vessel and a head portion above the frame portion. The head portion is configured to be rotatably moved on a circular trajectory while maintaining a desired (and/or alternatively predetermined) distance from the curved surface of the EUV light source vessel. The head portion may have a heating member configured to emit heat toward the curved surface of the EUV light source vessel. The heating member may have a shape curved in an arc corresponding to a portion of the circular trajectory.

An extreme ultraviolet radiation source apparatus includes a chamber including at least a droplet generator, a nozzle of the droplet generator, and a dry ice blasting assembly. The droplet generator includes a reservoir for a molten metal, and the nozzle has a first end connected to the reservoir and a second opposing end where molten metal droplets emerge from the nozzle. The dry ice blasting assembly includes a blasting nozzle, a blasting air inlet and a blaster carbon dioxide (CO.sub.2) inlet. The blasting nozzle is disposed inside the chamber. The blasting nozzle is arranged to direct a pressurized air stream and dry ice particles at the nozzle of the droplet generator.

An EUV light source module includes an EUV vessel, a collector disposed in the EUV vessel, a droplet generator, a droplet catcher, and a droplet collecting system. The droplet generator is coupled to the EUV vessel and configured to provide a plurality of target droplets into the EUV vessel. The droplet catcher is coupled to the EUV vessel and configured to catch at least a target droplet from the EUV vessel. The droplet colleting system is coupled to the droplet catcher. The droplet collecting system includes a connecting port coupled to the droplet catcher, and a thermal insulating device surrounding the droplet catcher. The droplet generator and the droplet catcher are disposed at opposite locations in the EUV vessel.

A light source is provided capable of maintaining the temperature of a collector surface at or below a predetermined temperature. The light source in accordance with various embodiments of the present disclosure includes a processor, a droplet generator for generating a droplet to create extreme ultraviolet light, a collector for reflecting the extreme ultraviolet light into an intermediate focus point, a light generator for generating pre-pulse light and main pulse light, and a thermal image capture device for capturing a thermal image from a reflective surface of the collector.

An extreme ultraviolet light generation apparatus may include: a chamber in which extreme ultraviolet light is generated when a target is irradiated with a laser beam inside the chamber; a target supply part configured to supply the target into the chamber; and a target collector configured to collect the target which is supplied by the target supply part but is not irradiated with the laser beam in a collection container, by receiving the target on a receiving surface having a contact angle of equal to or smaller than 90 degrees with the target.