A method includes ejecting initial droplets of a material using a nozzle. The method includes applying a pressure on the nozzle using an electromechanical element. The method includes controlling the applied pressure on the nozzle using an electrical signal generated by a waveform generator. The electrical signal includes a first periodic waveform and a second periodic waveform. The method includes coalescing the initial droplets to generate coalesced droplets based on the first and second periodic waveforms and drag. The method includes generating a detection signal, using a detector, corresponding to time intervals between crossings of coalesced droplets at the detector. The method includes determining at least first and second ones of the time intervals using a processor.

A method for generating an extreme ultraviolet (EUV) radiation includes simultaneously irradiating two or more target droplets with laser light in an EUV radiation source apparatus to produce EUV radiation and collecting and directing the EUV radiation produced from the two or more target droplet by an imaging mirror.

The stability of operations of an EUV light generating apparatus is improved. A droplet detector may include: a light source unit configured to emit illuminating light onto a droplet, which is output into a chamber and generate extreme ultraviolet light when irradiated with a laser beam; a light receiving unit configured to receive the illuminating light and to detect changes in light intensities; and a timing determining circuit configured to output a droplet detection signal that indicates that the droplet has been detected at a predetermined position within the chamber, based on a first timing at which the light intensity of the illuminating light decreases due to the droplet being irradiated therewith and a second timing at which the light intensity of the illuminating light increases.

A chamber device may include a chamber, and a target generation device assembled into the chamber and configured to supply a target material into the chamber, the target generation device including a tank configured to store the target material, a temperature variable device configured to vary temperature of the target material in the tank, and a nozzle section in which a nozzle hole configured to output the target material in a liquid form is formed, and the chamber device may further include a gas nozzle having an inlet port facing the nozzle section and configured to introduce gas into the chamber, a gas supply source configured to supply gas containing hydrogen to the gas nozzle to supply the gas containing the hydrogen to at least periphery of the nozzle section, and a moisture remover configured to remove moisture at least in the periphery of the nozzle section in the chamber.

A droplet accelerating assembly includes an acceleration chamber extending in a first direction parallel to an ejection direction of the droplet, the acceleration chamber having a first side connected to the droplet generator, a second side opposite the first side in the first direction, the second side including a discharge hole, and a fluid flow path, a pressure controller connected to the fluid flow path of the acceleration chamber, the pressure controller being configured to adjust an internal pressure of the acceleration chamber, an electrifier in the acceleration chamber, the electrifier being configured to electrify the droplet ejected by the droplet generator into an electrified droplet, and an accelerator in the acceleration chamber, the accelerator being configured to accelerate the electrified droplet.

A method for generating an extreme ultraviolet (EUV) radiation includes simultaneously irradiating two or more target droplets with laser light in an EUV radiation source apparatus to produce EUV radiation and collecting and directing the EUV radiation produced from the two or more target droplet by an imaging mirror.

An apparatus for monitoring a stream of droplets of target material for generating a radiation beam in a radiation source, wherein the apparatus comprises: a target material emitter for creating the stream of droplets of target material, wherein the target material emitter comprises a chamber configured for the target material to pass through before forming the stream of droplets; a first transducer configured to generate acoustic pressures in the chamber, and a second transducer configured to sense the acoustic pressures in the chamber.

A circulation mechanism includes a storage section, a supply pipe, a collection pipe, a circulation drive section, and a protective member. The storage section accommodates liquid metal. The supply pipe supplies the liquid metal accommodated in the storage section to a target mechanism. The collection pipe is communicated with the storage section and collects the liquid metal that has been drained away from the target mechanism into the storage section. The circulation drive section allows the liquid metal accommodated in the storage section to move to the supply pipe, and thus circulates the liquid metal to and from the target mechanism. The protective member is disposed to cover a portion of an inner wall of the collection pipe, the portion corresponding to a position at which the liquid metal flowing through the collection pipe collides with the liquid metal accommodated in the storage section.

A target droplet source for an extreme ultraviolet (EUV) source includes a droplet generator configured to generate target droplets of a given material. The droplet generator includes a nozzle configured to supply the target droplets in a space enclosed by a chamber. In some embodiments, a nozzle tube is arranged within the nozzle of the droplet generator, and the nozzle tube includes a structured nozzle pattern configured to provide an angular momentum to the target droplets.

A target substance replenishment device may include a first container containing a solid target substance, a first path through which the solid target substance supplied from the first container passes, a first supply switching device switching between a first state where supply of the solid target substance from the first container to the first path is suppressed and a second state where the supply of the solid target substance from the first container to the first path is allowed, a first valve connected to the first path, a second path which is connected to the first valve and through which the solid target substance having passed through the first valve passes, a first detector outputting a first detection signal indicating that the second path is clogged with the solid target substance, and a processor controlling the first supply switching device to the first state based on the first detection signal.