JP6744397B2 - Target expansion coefficient control in extreme ultraviolet light source - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is entitled “TARGET EXPANSION RATE CONTROL IN AN EXTREME ULTRAVIOLET LIGHT SOURCE” filed on Aug. 12, 2015, US Application No. 14/824,141, and “STABILLIZING LIGHT EUV”. Claims the benefit of US Application No. 14/824,147, filed August 12, 2015, entitled "AN EXTREME ULTRAVIOLET LIGHT SOURCE", both of which are incorporated herein by reference.

The disclosed subject matter relates to controlling the expansion coefficient of a target material of a laser produced plasma extreme ultraviolet light source.

Extreme ultraviolet (EUV) light, eg, electromagnetic radiation having a wavelength of about 50 nm or less (sometimes referred to as soft x-rays) and including light of a wavelength of about 13 nm, is used in a photolithography process to a substrate, such as It can be used to make very small features on silicon wafers.

The method of generating EUV light includes, but is not necessarily limited to, converting a material having an element having an emission line in the EUV region in a plasma state, such as xenon, lithium, or tin. In one such method, often referred to as laser-produced plasma (“LPP”), the required plasma is the target material in the form of, for example, droplets, plates, tapes, streams, or clusters of material. Can be generated by irradiating with an amplified light beam, which can be referred to as a drive laser. Because of this process, plasma is typically generated in a closed vessel, such as a vacuum chamber, and monitored using various types of metrology equipment.

In some general aspects, a method provides a target material including a component that emits extreme ultraviolet (EUV) light when converted into a plasma, a first radiation beam directed toward the target material. Second, inducing and delivering energy to a target material to modify a geometric distribution of the target material to form a modified target, and converting at least a portion of the modified target into a plasma that emits EUV light. Directing a beam of radiation toward the modified target, measuring one or more properties associated with one or more of the target material and the target modified with respect to the first beam of radiation; and Or controlling the amount of radiant exposure delivered from the plurality of measured first radiation beams to the target material within a predetermined energy range based on the characteristic.

Implementations may include one or more of the following features. For example, one or more properties associated with one or more of the target material and the modified target can be measured by measuring the energy of the first radiation beam. The energy of the first radiation beam can be measured by measuring the energy of the first radiation beam reflected from the light reflecting surface of the target material. The energy of the first radiation beam can be measured by measuring the energy of the first radiation beam directed towards the target material. The energy of the first radiation beam can be measured by measuring the spatially integrated energy across a direction perpendicular to the direction of propagation of the first radiation beam.

The first beam of radiation is steerable toward the target material by overlapping the target material with an area containing the confocal parameter of the first beam of radiation. The confocal parameter may be greater than 1.5 mm.

One or more properties associated with one or more of the target material and the modified target can be measured by measuring the position of the target material with respect to the target position. The target position may coincide with the beam waist of the first radiation beam. The first beam of radiation may be directed along the first beam axis and the position of the target material is measurable along a direction parallel to the first beam axis. The target position can be measured relative to the principal focus of the collector device that collects the emitted EUV light. The position of the target material may be measured by measuring the position of the target material along two or more non-parallel directions.

One or more characteristics associated with one or more of the target material and the modified target may include a property of the modified target prior to the second radiation beam converting at least a portion of the modified target into a plasma. It can be measured by detecting the size. One or more properties associated with one or more of the target material and the modified target can be measured by estimating the coefficient of expansion of the modified target.

The amount of radiation exposure delivered from the first beam of radiation to the target material is controllable by controlling the expansion rate of the modified target.

The amount of radiant exposure delivered from the first radiation beam to the target material is controlled by determining whether the characteristics of the first radiation beam should be adjusted based on one or more measured characteristics. It is possible. The determination that the characteristics of the first radiation beam should be adjusted may be made while one or more properties are being measured.

One of the energy content of the pulse of the first radiation beam and the area of the first radiation beam that interacts with the target material if it is determined that the characteristics of the first radiation beam should be adjusted. Or a plurality may be adjusted. The energy content of the pulse of the first radiation beam is one of the pulse width of the first radiation beam, the duration of the pulse of the first radiation beam, and the average power within the pulse of the first radiation beam, or It can be adjusted by adjusting a plurality.

The first beam of radiation may be directed towards the target material by directing a pulse of first radiation towards the target material. The one or more characteristics can be measured by measuring the one or more characteristics for each pulse of the first radiation. Whether the characteristic of the first radiation beam should be adjusted may be determined by determining whether the characteristic should be adjusted for each pulse of the first radiation.

The radiant exposure delivered from the first radiation beam to the target material is the radiant exposure delivered from the first radiation beam to the target material while at least a portion of the emitted EUV light is exposing the wafer. Can be controlled by controlling.

The target material can be provided by providing a droplet of target material. The geometric distribution of the target material may be modified by transforming droplets of the target material into a disc-shaped mass of molten metal. The droplets of target material can be transformed into a disk-like mass according to the expansion coefficient.

The method may also include collecting at least a portion of the emitted EUV light, and directing the collected EUV light toward the wafer to expose the wafer to the EUV light.

The one or more properties can be measured by measuring at least one property for each pulse of the first radiation beam directed toward the target material.

The first beam of radiation is emitted from the plasma converted from the target material such that a portion of the target material is converted into a plasma that emits EUV light and from the plasma converted from the target material. It may be directed towards the target material so that less EUV light is emitted, the main effect on the target material is to modify the geometric distribution of the target material to form a modified target. ..

The geometric distribution of the target material can be modified by transforming the shape of the target material into a modified target, which includes expanding the modified target along at least one axis according to a coefficient of expansion. The amount of radiant exposure delivered to the target material can be controlled by controlling the coefficient of expansion of the target material into the modified target.

The modified target may be expanded along at least one axis that is not parallel to the optical axis of the second radiation beam.

One or more properties associated with one or more of the target material and the modified target can be measured by measuring the number of photons reflected from the modified target. The number of photons reflected from the modified target can be measured by measuring the number of photons reflected from the modified target as a function of how many photons hit the target material.

The first beam of radiation may be directed towards the target material by directing a pulse of first radiation towards the target material. The second beam of radiation may be directed towards the modified target by directing a pulse of second radiation towards the modified target.

The first beam of radiation may be guided by directing the first beam of radiation through a first set of one or more optical amplifiers. The second beam of radiation may be directed by directing the second beam of radiation through a second set of one or more optical amplifiers. Here, at least one of the first set of optical amplifiers is in the second set.

One or more properties associated with one or more of the target material and the modified target can be measured by measuring the energy of the first radiation beam directed toward the target material. The amount of radiant exposure delivered to the target material is controllable by adjusting the amount of energy directed from the first radiation beam to the target material based on the measured energy. The first beam of radiation can be steered towards the target material by overlapping the target material with an area of the first beam of radiation that contains the confocal parameter. The confocal parameter may be 2 mm or less.

The amount of energy delivered from the first radiation beam to the target material is adjustable by adjusting the properties of the first radiation beam.

The amount of radiant exposure delivered from the first radiation beam to the target material is determined by the energy of the first radiation beam just before the first radiation beam delivers energy to the target material, the position of the target material, and It can be controlled by adjusting one or more of the first radiation beam and the area of the target material that interacts.

The first beam of radiation may be guided by directing the first beam of radiation through a first set of optical components including one or more first optical amplifiers. The second beam of radiation may be directed by directing the second beam of radiation through a second set of optical components including one or more second optical amplifiers. Here, the first set of optical components is different and separate from the second set of optical components.

In another general aspect, an apparatus includes a chamber defining an initial target location for receiving a first beam of radiation and a target location for receiving a second beam of radiation, and extreme ultraviolet radiation when converted to plasma. A target material delivery system configured to provide a target material including an (EUV) light emitting material to an initial target location and optics configured to generate a first beam of radiation and a second beam of radiation. A source and a light steering system. The light steering system directs a first beam of radiation toward an initial target location to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target, and , A second radiation beam directed toward the target location to convert at least a portion of the modified target into a plasma that emits EUV light. The apparatus comprises a measurement system for measuring one or more properties associated with one or more of the target material and the target modified with respect to the first radiation beam, a target material delivery system, an optical source, a light steering system, And a control system connected to the measurement system. The control system receives radiation from the measurement system and transmits one or more signals to the optical source to emit radiation from the first radiation beam to the target material. It is configured to control the amount of exposure based on the one or more measured characteristics.

Implementations may include one or more of the following features. For example, the light steering system may be configured to focus a first beam of radiation at or near an initial target location and a second beam of radiation configured to focus at or near a target location. A focusing device may be included.

The device may include a beam conditioning system. Here, the beam conditioning system is connected to an optical source and a control system, the control system sending one or more signals to the optical source and sending the one or more signals to the beam conditioning system. Configured to control the amount of energy delivered to the material, the beam conditioning system adjusts one or more features of the optical source, thereby maintaining the amount of energy delivered to the target material. Is configured to. The beam conditioning system may include a pulse width conditioning system coupled to the first radiation beam, the pulse width conditioning system configured to condition the pulse width of the first radiation beam. The pulse width adjustment system may include an electro-optic modulator.

The beam conditioning system may include a pulse power conditioning system coupled to the first radiation beam, the pulse power conditioning system configured to regulate the average power within the pulses of the first radiation beam. .. The pulse power conditioning system may include an acousto-optic modulator.

The beam conditioning system is configured to send one or more signals to the optical source to control the amount of energy induced in the target material by sending the one or more signals to the beam conditioning system. And the beam conditioning system is configured to tune one or more features of the optical source and thereby control the amount of energy induced into the target material.

The optical source may include a first set of one or more optical amplifiers through which the first beam of radiation passes, and a second set of one or more optical amplifiers through which the second beam of radiation passes. At least one of the first set of optical amplifiers is in the second set. The measurement system is capable of measuring the energy of the first radiation beam as it is directed toward the initial target location. The control system receives the measured energy from the measurement system and sends one or more signals to the optical source to measure the amount of energy induced from the first radiation beam to the target material. It may be configured to control based on the generated energy.

In some general aspects, a method provides a target material including a component that emits extreme ultraviolet (EUV) light when converted into a plasma, a first radiation beam directed toward the target material. Second, inducing and delivering energy to a target material to modify a geometric distribution of the target material to form a modified target, and converting at least a portion of the modified target into a plasma that emits EUV light. Directing a beam of radiation toward the modified target, controlling the radiant exposure delivered from the first beam of radiation to the target material within a predetermined radiant exposure, and the first beam of radiation. Stabilizing the power of the EUV light emitted from the plasma by controlling the radiant exposure delivered from the to the target material within a predetermined radiant exposure range.

Implementations may include one or more of the following features. For example, the first beam of radiation may be directed by directing the first beam of radiation through a first set of optical components including one or more first optical amplifiers. The second beam of radiation may be directed by directing the second beam of radiation through a second set of optical components including one or more second optical amplifiers. The first set of optical components may be different and separate from the second set of optical components.

The first beam of radiation may be guided by directing the first beam of radiation through a first set of one or more optical amplifiers. The second beam of radiation may be directed by directing the second beam of radiation through a second set of one or more optical amplifiers. Here, at least one of the first set of optical amplifiers is in the second set.

The target material can be provided by providing a droplet of target material. The geometric distribution of the target material can be modified by transforming droplets of the target material into a disk-shaped mass of molten metal having a generally flat surface.

The target material can be provided by providing a droplet of target material. The geometric distribution of the target material can be modified by transforming droplets of the target material into an atomized mass of molten metal particles.

The target material may be transformed into a target modified according to the expansion coefficient.

Radiative exposure delivered from the first beam of radiation to the target material measures one or more properties associated with one or more of the target material and the target modified with respect to the first beam of radiation, and , Controllable by maintaining the amount of radiant exposure delivered from the first radiation beam to the target material within a predetermined radiant exposure range based on one or more measured characteristics.

The radiative exposure delivered from the first beam of radiation to the target material may be controlled by estimating the expansion rate of the modified target. The radiation exposure delivered from the first beam of radiation to the target material may be controlled by maintaining a modified target expansion coefficient.

The radiative exposure delivered from the first radiation beam to the target material may be controlled by determining whether the characteristics of the first radiation beam should be adjusted. Radiation exposure delivered from the first radiation beam to the target material adjusts one or more of the energy content of each pulse of the first radiation beam and the area of the first radiation beam that interacts with the target material. Can be controlled by adjusting the characteristics of the first radiation beam. The energy content of each pulse of the first radiation beam is determined by the width of each pulse of the first radiation beam, the duration of each pulse of the first radiation beam, and the power of each pulse of the first radiation beam. It can be adjusted by adjusting one or more of them.

The EUV light power emitted from the plasma can be stabilized by stabilizing the EUV light power while at least a portion of the EUV light emitted from the plasma exposes the wafer.

The method may also include collecting at least a portion of the emitted EUV light, and directing the collected EUV light toward the wafer to expose the wafer to the EUV light.

The geometric distribution of the target material can be modified by transforming the shape of the target material into a modified target, which includes expanding the modified target along at least one axis according to a coefficient of expansion.

The radiative exposure delivered from the first radiation beam to the target material is controllable by adjusting the properties of the first radiation beam. The properties of the first radiation beam can be adjusted by adjusting the energy of the first radiation beam.

In another general aspect, an apparatus includes a chamber defining an initial target location for receiving a first beam of radiation and a target location for receiving a second beam of radiation, and extreme ultraviolet radiation when converted to plasma. A target material delivery system configured to provide a target material including an (EUV) light emitting material to an initial target location and optics configured to generate a first beam of radiation and a second beam of radiation. A source and a light steering system. The light steering system directs a first beam of radiation toward an initial target location to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target, and , A second radiation beam directed toward the target location to convert at least a portion of the modified target into a plasma that emits EUV light. The apparatus is connected to a target material delivery system, an optical source, and a light steering system, and emits one or more signals to the optical source to be emitted from the first beam of radiation to the target material. A control system configured to stabilize the power of the EUV light emitted from the plasma by controlling the amount of exposure within a predetermined radiant exposure range.

Implementations may include one or more of the following features. For example, the apparatus may also include a measurement system for measuring one or more properties associated with one or more of the target material and the target modified with respect to the first radiation beam, the control system including the measurement system. It is connected.

The device may also include a beam conditioning system. Here, the beam conditioning system is connected to an optical source and a control system, the control system sending one or more signals to the optical source and sending the one or more signals to the beam conditioning system. The beam conditioning system is configured to control the amount of radiant exposure delivered to the material and the beam conditioning system adjusts one or more features of the optical source, thereby delivering the amount of radiant exposure to the target material. Is configured to control.

An optical source for producing a first beam of radiation directed to the target material and a second beam of radiation directed to the modified target, a portion of the modified target into a plasma emitting EUV light. FIG. 7 is a block diagram of a laser-produced plasma extreme ultraviolet light source for conversion. FIG. 5 is a schematic diagram showing a first beam of radiation directed to a first target location and a second beam of radiation directed to a second target location. 2 is a block diagram of an exemplary optical source used in the light source of FIG. 1. FIG. 2 is a block diagram of an exemplary beam path combiner that may be used in the optical source of FIG. 2 is a block diagram of an exemplary beam path separator that may be used in the optical source of FIG. 3B is a block diagram of an exemplary optical amplifier system that may be used in the optical source of FIG. 3A. 3B is a block diagram of an exemplary optical amplifier system that may be used in the optical source of FIG. 3A. 3B is a block diagram of an exemplary optical amplifier system that may be used in the optical source of FIG. 3A. FIG. 6 is a schematic diagram illustrating another implementation of a first beam of radiation directed to a first target location and a second beam of radiation directed to a second target location. FIG. 6 is a schematic diagram illustrating an implementation of a first radiation beam directed to a first target location. FIG. 6 is a schematic diagram illustrating an implementation of a first radiation beam directed to a first target location. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. FIG. 6 is a schematic diagram of an implementation of a measurement system that measures at least one property associated with any one or more of a target material, a modified target, and a first radiation beam. 2 is a block diagram of an exemplary control system for the light source of FIG. 1. FIG. 6 is a flow chart of an exemplary procedure performed by a light source (under control of a control system) to increase the conversion efficiency of the light source by maintaining or controlling the modified target expansion coefficient (ER). 6 is a flow chart of an exemplary procedure performed by a light source to stabilize the power of EUV light emitted from a plasma by controlling the radiation exposure delivered from a first radiation beam to a target material. An exemplary optical source for producing first and second radiation beams and modifying the first and second radiation beams and combining the first and second radiation beams with first and second target locations, respectively. FIG. 6 is a block diagram with an exemplary beam delivery system for focusing.

Techniques for increasing the conversion efficiency of extreme ultraviolet (EUV) light generation are disclosed. Referring to FIG. 1, as described in more detail below, the interaction of the target material 120 and the first radiation beam 110 causes the target material to deform and geometrically expand, thereby resulting in a modified target 121. It is formed. The geometric expansion coefficient of the modified target 121 is such that it increases the amount of usable EUV light 130 converted from the plasma produced by the interaction of the modified target 121 and the second radiation beam 115. Controlled. The amount of EUV light 130 that can be used is the amount of EUV light 130 that is available for use in the optical device 145. Therefore, the amount of EUV light 130 that can be used may depend on various aspects, such as the bandwidth or center wavelength of the optical components used to utilize the EUV light 130.

Controlling the geometric expansion rate of the modified target 121 may include controlling the size or geometric aspect of the modified target 121 as the modified target 121 interacts with the second radiation beam 115. To enable. For example, adjusting the geometric expansion coefficient of the modified target 121 adjusts the density of the modified target 121 as it interacts with the second radiation beam 115. Because the density of the modified target 121 when the modified target 121 interacts with the second radiation beam 115 is the total amount of radiation absorbed by the modified target 121 and the amount of such radiation absorbed. This is because it affects the range. As the density of the modified target 121 increases, the EUV light 130 can no longer escape from the modified target 121, and thus the amount of usable EUV light 130 may decrease. As another example, adjusting the geometric expansion coefficient of the modified target 121 adjusts the surface area of the modified target 121 as it interacts with the second radiation beam 115. It

In this way, the total amount of usable EUV light 130 produced can be increased or controlled by controlling the expansion rate of the modified target 121. In particular, the size and expansion coefficient of the modified target 121 depends on the radiation exposure applied to the target material 120 from the first radiation beam 110. This radiative exposure is the amount of energy delivered by the first beam of radiation 110 to an area of the target material 120. Thus, the modified coefficient of expansion of the target 121 can be maintained or controlled by maintaining or controlling the amount of energy delivered to the target material 120 per unit area. The amount of energy delivered to the target material 120 depends on the energy of the first radiation beam 110 just prior to impinging on the surface of the target material.

The energy of the pulses of the first beam of radiation 110 can be determined by integrating the laser pulse signal measured by the fast photodetector. The detector may be a photoelectromagnetic (PEM) detector suitable for long wavelength infrared (LWIR) radiation, an InGaAs diode for measuring near infrared (IR) radiation, or a silicon diode for visible or near infrared radiation. May be

The expansion coefficient of the modified target 121 depends, at least in part, on the amount of energy of the pulses of the first radiation beam 110 intercepted by the target material 120. The hypothetical basic design assumes that the target material 120 is always the same size and is placed in the waist of the focused first radiation beam 110. However, in practice, the target material 120 may have a small but roughly constant axial position offset with respect to the beam waist of the first radiation beam 110. If all of these factors remain constant, one factor controlling the expansion rate of the modified target 121 is the first factor for the pulse of the first radiation beam having a duration of a few ns to 100 ns. The pulse energy of the radiation beam 110. Another factor that can control the expansion rate of the modified target 121 when the pulses of the first radiation beam 110 have a duration of 100 ns or less is the instantaneous peak power of the first radiation beam 110. is there. As described below, if the pulse of the first radiation beam 110 has a shorter duration, for example on the order of picoseconds (ps), other factors may control the expansion rate of the modified target 121.

As shown in FIG. 1, an optical source 105 (also referred to as a drive source or drive laser) is used to drive a laser produced plasma (LPP) extreme ultraviolet (EUV) light source 100. The optical source 105 produces a first beam of radiation 110 provided to a first target location 111 and a second beam of radiation 115 provided to a second target location 116. The first and second radiation beams 110, 115 may be pulsed amplified light beams.

First target location 111 receives target material 120, such as tin, from target material supply system 125. The geometric distribution of the target material 120 is modified and modified because the interaction of the first radiation beam 110 and the target material 120 delivers energy to the target material 120 to modify or change (eg, deform) its shape. It becomes the target 121. The target material 120 is generally guided from the target material supply system 125 along the -X direction, or along the direction in which the target material 120 is placed within the first target location 111. After the first beam of radiation 110 delivers energy to the target material 120 to transform it into a modified target 121, the modified target 121 moves along another direction, such as a direction parallel to the Z direction. In addition, you may continue moving along the -X direction. As the modified target 121 moves away from the first target location 111, the geometric distribution continues to deform until the modified target 121 reaches the second target location 116. Interaction of the second radiation beam 115 (at the second target location 116) with the modified target 121 transforms at least a portion of the modified target 121 into a plasma 129 that emits EUV light or radiation 130. To do. A light collector system (or light collector) 135 collects the EUV light 130 and directs it as collected EUV light 140 towards an optical device 145, such as a lithographic tool. The first and second target locations 111, 116 and the light collector 135 may be housed in a chamber 165 that provides a controlled environment suitable for the generation of EUV light 140.

Some of the target material 120 can be converted into a plasma when interacting with the first beam of radiation 110, and thus such plasma can emit EUV radiation. However, the property of the first radiation beam 110 is that the main effect of the first radiation beam 110 on the target material 120 is to deform or modify the geometric distribution of the target material 120 to form a modified target 121. Selected and controlled as is.

Each of the first beam of radiation 110 and the second beam of radiation 115 is directed by a beam delivery system 150 towards each target location 111, 116. The beam delivery system 150 may include an optical steering component 152 and a focus assembly 156 that focuses the first or second beam of radiation 110, 115 into first and second focus regions, respectively. The first and second focal areas may overlap the first target location 111 and the second target location 116, respectively. The optical component 152 may include optical elements such as lenses and/or mirrors that direct the radiation beams 110, 115 by refraction and/or reflection. Beam delivery system 150 may also include elements that control and/or move optical component 152. For example, beam delivery system 150 may include an actuator controllable to move an optical element within optical component 152.

Referring also to FIG. 2, the focus assembly 156 focuses the first beam of radiation 110 such that the diameter D1 of the first beam of radiation 110 is minimized in the first focal region 210. In other words, the focus assembly 156 focuses the first beam of radiation 110 as it propagates toward the first focal region 210 in a first axial direction 212, which is the general direction of propagation of the first beam of radiation 110. Let The first axial direction 212 extends along a plane defined by the XZ axis. The first axial direction 212 is parallel or substantially parallel to the Z direction in this example, but may be along an angle to Z. In the absence of the target material 120, the first beam of radiation 110 diverges as it propagates away from the first focal region 210 in the first axial direction 212.

The focus assembly 156 also focuses the second beam of radiation 115 such that the diameter D2 of the second beam of radiation 115 is minimized in the second focal region 215. Therefore, the focus assembly focuses the second beam of radiation 115 as it propagates toward the second focal region 215 in the second axial direction 217, which is the general direction of propagation of the second beam of radiation 115. The second axial direction 217 also extends along a plane defined by the XZ axis, and in this example, the second axial direction 217 is parallel or substantially parallel to the Z direction. In the absence of the modified target 121, the second beam of radiation 115 diverges as it propagates away from the second focal region 215 along the second axial direction 217.

The EUV light source 100 also includes one or more measurement systems 155, a control system 160, and a beam conditioning system 180, as described below. The control system 160 is connected to other components within the light source 100, such as, for example, the measurement system 155, the beam delivery system 150, the target material supply system 125, the beam conditioning system 180, and the optical source 105. The measurement system 155 can measure one or more properties within the light source 100. The one or more properties may be, for example, properties associated with target material 120 or target 121 modified with respect to first radiation beam 110. As another example, the one or more characteristics can be the pulse energy of the first radiation beam 110 directed toward the target material 120. These examples will be described in detail later. The control system 160 is configured to receive the one or more measured properties from the measurement system so that it can control how the first radiation beam 110 interacts with the target material 120. it can. For example, the control system 160 can be configured to maintain the amount of energy delivered from the first radiation beam 110 to the target material 120 within a predetermined energy range. As another example, the control system 160 may be configured to control the amount of energy that is directed from the first radiation beam 110 into the target material 120. The beam conditioning system 180 is a system that includes a component within the optical source 105 or a component that adjusts a component within the optical source 105, whereby the properties of the first radiation beam 110 (pulse width, pulse energy, moment within a pulse). Power, or average power within a pulse, etc.).

Referring to FIG. 3A, in some implementations the optical source 105 includes a series of one or more optical amplifiers through which a first beam of radiation 110 passes, and a series of one or more optical amplifiers. A second optical amplifier system 305 including a plurality of optical amplifiers and a second beam of radiation 115 passing therethrough. One or more amplifiers of the first system 300 may be in the second system 305. Alternatively, one or more amplifiers of the second system 305 may be present in the first system 300. Alternatively, the first optical amplifier system 300 may be completely separate from the second optical amplifier system 305.

Although not essential, the optical source 105 includes a first light generation device 310 that generates a first pulsed light beam 311 and a second light generation device 315 that generates a second pulsed light beam 316. May be included. Each of the light generators 310 and 315 may be, for example, a laser, a seed laser such as a master oscillator, or a lamp. Exemplary light generators that may be used as the light generators 310, 315 include, for example, a Q-switch oscillator operable at a repetition rate of 100 kHz, a radio frequency (RF) pumped oscillator, an axial flow. The oscillator is a carbon dioxide (CO ₂ ) oscillator.

The optical amplifiers in the optical amplifier systems 300 and 305 each include a gain medium on each beam path, and the light beams 311 and 316 from the light generators 310 and 315 propagate along the beam paths. When the gain medium of the optical amplifier is excited, the gain medium provides photons to the light beam and amplifies the light beams 311 and 316 to form a first radiation beam 110 or a second radiation beam 115. Generate a beam.

The wavelengths of the light beams 311 and 316 or the radiation beams 110 and 115 may be different from each other so that the radiation beams 110 and 115 can be separated from each other if they are combined at any point within the optical source 105. .. If the radiation beams 110, 115 are produced by a CO ₂ amplifier, the first radiation beam 110 may have a wavelength of 10.26 micrometers (μm) or 10.207 μm and the second radiation beam 115. May have a wavelength of 10.59 μm. The wavelengths are chosen to more easily allow the separation of the two radiation beams 110, 115 using dispersive optics or dichroic mirrors or beam splitter coatings. In situations where both radiation beams 110, 115 propagate together in the same amplifier chain (eg, where some of the amplifiers of optical amplifier system 300 are in optical amplifier system 305), the two radiation beams 110, 115 are the same amplifier. Even though they pass through, their relative gains can be adjusted using different wavelengths.

For example, the radiation beams 110, 115, once separated, can be steered or focused to two separate locations within the chamber 165, such as the first and second target locations 111, 116, respectively. In particular, the separation of the radiation beams 110, 115 expands as the modified target 121 progresses from the first target location 111 to the second target location 116 after interaction with the first radiation beam 110. It also makes it possible.

The optical source 105 superimposes the first radiation beam 110 and the second radiation beam 115 so that the radiation beams 110, 115 have the same optical path for at least some of the distances between the optical source 105 and the beam delivery system 150. A beam path combiner 325 located at An exemplary beampath combiner 325 is shown in Figure 3B. The beam path combiner 325 includes a pair of dichroic beam splitters 340 and 342 and a pair of mirrors 344 and 346. The dichroic beam splitter 340 passes the first radiation beam 110 along a first path to the dichroic beam splitter 342. The dichroic beam splitter 340 reflects the second beam of radiation 115 along a second path. In this second pass, the second beam of radiation 115 is reflected from the mirrors 344, 346, which redirects the second beam of radiation 115 towards the dichroic beam splitter 342. The first beam of radiation 110 is free to pass through the dichroic beam splitter 342 to reach the output path, while the second beam of radiation 115 is reflected from the dichroic beam splitter 342 to reach the output path. Both two radiation beams 110, 115 overlap on the output path.

The optical source 105 also includes a beam path separator that separates the first radiation beam 110 from the second radiation beam 115 such that the two radiation beams 110, 115 can be steered separately and focused in the chamber 165. 326 may be included. An exemplary beam path separator 326 is shown in Figure 3C. The beam path separator 326 includes a pair of dichroic beam splitters 350 and 352 and a pair of mirrors 354 and 356. The dichroic beam splitter 350 receives the superposed radiation beam pairs 110, 115, reflects the second radiation beam 115 along a second path, and directs the first radiation beam 110 along a first path. The light is transmitted toward the dichroic beam splitter 352. The first beam of radiation 110 is free to pass through the dichroic beam splitter 352 along a first path. The second beam of radiation 115 reflects from the mirrors 354, 356, returns to the dichroic beam splitter 352, and is reflected on a second path that is different from the first path.

Further, the first beam of radiation 110 may be configured to have a pulse energy that is less than the pulse energy of the second beam of radiation 115. This is because the first radiation beam 110 is used to modify the geometry of the target material 120, while the second radiation beam 115 is used to transform the modified target 121 into a plasma 129. is there. For example, the pulse energy of the first radiation beam 110 may be one fifth to one hundredth of the pulse energy of the second radiation beam 115.

In some implementations, the optical amplifier system 300 or 305 includes three sets of optical amplifiers 401, 402, 403 and 406, 407, 408, respectively, as shown in FIGS. 4A and 4B. Only one amplifier or more than three amplifiers may be used. In some implementations, each of the optical amplifiers 406, 407, 408 comprises a gain medium containing CO ₂ to provide light at wavelengths of about 9.1 to about 11.0 μm, especially about 10.6 μm, to more than 1000. It can be amplified with a large gain. Optical amplifiers 401, 402, 403 can be operated at similar or different wavelengths. Amplifiers and lasers suitable for use in the optical amplifier system 300, 305 produce radiation of about 9.3 μm or about 10.6 μm, eg, by DC or RF excitation, and relatively high power, eg, 10 kW or more and, eg, 50 kHZ. These may include pulsed laser devices, such as pulsed gas discharge CO ₂ amplifiers, operating at high pulse repetition rates. Exemplary optical amplifiers 401, 402, 403 or 406, 407, 408 are commercially available from TRUMPF Inc. of Farmington, Connecticut. Such as TruFlow CO ₂ produced by a axial flow high power CO2 laser with RF excitation of the wear-free gas circulation and capacitive.

Although not essential, one or more of the optical amplifier systems 300 and 305 may include a first amplifier that functions as the preamplifiers 411 and 421, respectively. Preamplifiers 411, 421, if present, are TRUMPF Inc. of Farmington, Connecticut. Such as TruCoax CO ₂ laser system manufactured by, it may be diffused cooling CO ₂ laser system.

The optical amplifier system 300, 305 may include optical elements not shown in FIGS. 4A and 4B to guide and shape each light beam 311 316. For example, the optical amplifier systems 300, 305 may include reflective optics such as mirrors, partially transmissive optics such as beam splitters or partially transmissive mirrors, and dichroic beam splitters.

The optical source 105 also includes an optical system 320, which includes one or more optical systems (eg, reflective optics such as mirrors, beam splitters, etc.) for guiding the light beams 311 and 316 through the optical source 105. A partially reflective and partially transmissive optical system, a refractive optical system such as a prism or a lens, a passive optical system, an active optical system, etc.).

Although the optical amplifiers 401, 402, 403 and 406, 407, 408 are shown as separate blocks, at least one of the amplifiers 401, 402, 403 is in the optical amplifier system 305, and the amplifiers 406, 407, 408 are At least one of them can be in the optical amplifier system 300. For example, as shown in FIG. 5, the amplifiers 402 and 403 correspond to the amplifiers 407 and 408, respectively, and the optical amplifier systems 300 and 305 combine the two light beams output from the amplifiers 401 and 406. It includes additional optics 500 (such as beampath combiner 325) to provide a single pass through amplifiers 402/407 and 403-408. In such a system, where at least some of the amplifiers and optics overlap between the optical amplifier systems 300, 305, the first beam of radiation 110 and the second beam of radiation 115 are of the first beam of radiation 110. The changes in one or more properties may be combined such that one or more properties in the second radiation beam 115 may be changed, and vice versa. Therefore, it becomes even more important to control the energy within the system, such as the energy of the first radiation beam 110 or the energy delivered to the target material 120. The optical amplifier system 300, 305 also provides two light beams 110, 15 output from the amplifier 403/408 to enable the two light beams 110, 115 to be directed to each target location 111, 116. Also included is an optical element 505 (such as beam path separator 326) for separating the beams.

Target material 120 can be any material, including target materials that emit EUV light when converted to plasma. The target material 120 may be a target mixture containing a target material and impurities such as non-target particles. The target material is a material that can be converted into a plasma state having a bright line in the EUV region. The target material can be, for example, a liquid or molten metal droplet, a portion of a liquid stream, a solid particle can be a cluster, a solid particle contained in a liquid droplet, a foam of a target material, or a portion of a liquid stream. It can be solid particles contained. The target material can be, for example, water, tin, lithium, xenon, or any material that has an emission line in the EUV region when converted to a plasma state. For example, the target material may be pure tin (Sn), a tin compound such as SnBr4, SnBr2, SnH4, or a tin alloy such as a tin-gallium alloy, a tin-indium alloy, or a tin-indium-gallium alloy, or a combination thereof. It may be elemental tin, which may be used as any combination of alloys. Further, in a situation where there are no impurities, the target material contains only the target substance. The following discussion presents an example where the target material 120 is a droplet composed of a molten metal such as tin. However, the target material 120 may take other forms.

The target material 120 may be provided to the first target location 111 by passing the molten target material through a nozzle of the target material supply device 125 and drifting the target material 120 to the first target location 111. In some implementations, the target material 120 may be guided to the first target location 111 by force.

The shape of the target material 120 is changed or modified (e.g., deformed) by irradiating the target material 120 with a pulse of radiation from the first radiation beam 110 before reaching the second target location 116.

The interaction of the first radiation beam 110 and the target material 120 removes material from the surface of the target material 120 (and the modified target 121), which removes the target material 120 and the shape of the target material 120. Provide a force to deform into a modified target 121 having a different shape. For example, the target material 120 may have a shape similar to a droplet, but the shape of the modified target 121 is closer to the shape of a disc (such as a pancake shape) when reaching the second target location 116. It transforms to become. The modified target 121 can be non-ionized material (non-plasma material) or minimally ionized material. The modified target 121 may be, for example, a disk of liquid or molten metal, a continuous segment of target material without voids or large gaps, a mist of microparticles or nanoparticles, or a cloud of atomic vapors. For example, as shown in FIG. 2, the modified target 121 expands and, after a time T2-T1 (which may be on the order of a few microseconds (μs)), of the molten metal within the second target location 116. It becomes a disk-shaped piece 121.

Also, the interaction between the first radiation beam 110 and the target material 120, which removes material from the surface of the target material 120 (and the modified target 121), causes the modified target 121 to undergo some propulsion along the Z direction. A force may be provided which may be force or velocity responsive. The expansion of the modified target 121 in the X direction and the resulting velocity in the Z direction is the energy of the first radiation beam 110 and, in particular, the energy delivered to (ie, intercepted by) the target material 120. Depends on.

For example, if the target material 120 has a constant size and the pulse of the first radiation beam 110 is long (a long pulse is a pulse having a duration of a few nanoseconds (ns) to 100 ns), The expansion rate is linearly proportional to the energy per unit area of the first radiation beam 110 (joule/cm ² ). Energy per unit area is also called radiant exposure or fluence. Radiation exposure is the radiant energy that the surface of the target material 120 receives per unit area, or is also the irradiation of the surface of the target material 120 integrated over the time that the target material 120 is irradiated.

As another example, if the target material 120 has a constant size and the pulse is short (having a duration of less than a few hundred picoseconds (ps)), the expansion rate and the first radiation beam 110 may be reduced. The relationship with energy can be different. In this regime, a short pulse length correlates with an increase in the intensity of the first radiation beam 110 that interacts with the target material 120, and the first radiation beam 110 acts like a shock wave. In this regime, the expansion coefficient depends primarily on the intensity I of the first radiation beam 110, which causes the energy E of the first radiation beam 110 to interact with the target material 120. It is equal to the spot size (cross-sectional area A) divided by the pulse length (τ). That is, I=E/(A·τ). In this ps pulse length regime, the modified target 121 expands to form a fog.

Also, the modified disc-shaped angular orientation of the target 121 (angle with respect to the Z or X direction) depends on the position of the first radiation beam 110 as it strikes the target material 120. Thus, if the first radiation beam 110 impinges on the target material 120 such that the first radiation beam 110 contains the target material and the beam waist of the first radiation beam 110 is centered on the target material 120. The modified target 121 disk shape is more likely to be aligned with the major axis 230 parallel to the X direction and the minor axis 235 parallel to the Z direction.

The first beam of radiation 110 comprises pulses of radiation, each pulse having a duration. Similarly, the second beam of radiation 115 comprises pulses of radiation, each pulse having a duration. The pulse length can be represented by the full width of a percentage value (eg, half-value) with respect to the maximum value, ie the amount of time the pulse has an intensity that is at least a percentage of the maximum intensity of the pulse. However, other metrics may be used to determine the pulse length. The pulse length of the pulses in the first radiation beam 110 can be, for example, 30 nanoseconds (ns), 60 ns, 130 ns, 50 to 250 ns, 10 to 200 picoseconds (ps), or less than 1 ns. The energy of the first radiation beam 110 can be, for example, 1 to 100 millijoules (mJ). The wavelength of the first radiation beam 110 may be, for example, 1.06 μm, 1 to 10.6 μm, 10.59 μm, or 10.26 μm.

As mentioned above, the expansion coefficient of the modified target 121 depends on the radiative exposure (energy per unit area) of the first radiation beam 110 that intercepts the target material 120. Thus, for a pulse of the first radiation beam 110 having a duration of about 60 ns and an energy of about 50 mJ, the actual radiant exposure will be how closely the first radiation beam 110 is focused on the first focal region 210. It depends on what is done. In some examples, the radiation exposure may be about 400 to 700 Joules/cm ² at the target material 120. However, the radiation exposure is very sensitive to the location of the target material 120 with respect to the first radiation beam 110.

The second beam of radiation 115, which may also be referred to as the main beam, consists of pulses released at a certain repetition rate. The second beam of radiation 115 has sufficient energy to convert the target material in the modified target 121 into a plasma that emits EUV light 130. The pulse of the first beam of radiation 110 and the pulse of the second beam of radiation 115 may be, for example, 1 to 3 microseconds (μs), 1.3 μs, 1 to 2.7 μs, 3 to 4 μs, or the modified target 121. Are separated in time by a delay time, such as any amount of time that allows them to expand into the desired sized disk shape. Therefore, the modified target 121 performs a two-dimensional expansion as the modified target 121 expands and extends in the XY plane.

The second beam of radiation 115 may be configured to slightly defocus upon impacting the modified target 121. Such a defocus scheme is shown in FIG. In this case, the second focal area 215 is at a different location along the Z direction than the major axis 230 of the modified target 121. Further, the second focal area 215 is outside the second target location 116. In this scheme, the second focal area 215 is located in front of the modified target 121 along the Z direction. That is, the second beam of radiation 115 comes to the focus (or beam waist) before it impinges on the modified target 121. Other defocus systems are possible. For example, as shown in FIG. 6, the second focal area 215 is located after the modified target 121 along the Z direction. In this way, the second beam of radiation 115 comes to the focus (or beam waist) after it hits the modified target 121.

Referring again to FIG. 2, the rate at which the modified target 121 expands as it moves (eg, drifts) from the first target location 111 to the second target location 116 may be referred to as the expansion rate (ER). .. At the first target location 111, the modified target 121 has a range (or length) S1 along the major axis 230 immediately after the target material 120 is impacted by the first radiation beam 110 at time T1. As the modified target 121 reaches the second target location 116 at time T2, the modified target 121 has a range (or length) S2 along the major axis 230. The expansion coefficient is the difference (S2-S1) in the range along the major axis 230 of the corrected target 121 divided by the time difference (T2-T1),

Becomes The modified target 121 expands along the major axis 230, but it is also possible for the modified target 121 to compress or thin along the minor axis 235.

The modified target 121 is formed by interacting the first radiation beam 110 with the target material 120, and the modified target 121 is then formed by interacting the modified target 121 with the second radiation beam 115. The two-step approach described above, which is converted to plasma, results in a conversion efficiency of about 3-4%. In general, it is desirable to increase the conversion of light from optical source 105 to EUV radiation 130. This is because if the conversion efficiency is too low, it may be necessary to increase the amount of power that the optical source 105 needs to deliver, which increases the cost of operating the optical source 105 and also in the light source 100. May increase the heat load on all components of the first and second target locations 111, 116, leading to increased debris formation in the chamber. Increasing conversion efficiency can help meet the requirements of mass production tools while keeping optical source power requirements within acceptable limits. Various parameters affect the conversion efficiency, such as the wavelengths of the first and second radiation beams 110, 115, the target material 120, and the shape of the pulse, energy, power, and intensity of the radiation beams 110, 115. The conversion efficiency is 2 around the center wavelength of the reflectance curve of the (multi-layer) mirror used by the EUV light 130 in the 2π steradian and light collector system 135 and/or the illumination and projection optics in the optical device 145. It may be defined as the EUV energy produced in the bandwidth of% divided by the energy of the irradiation pulse of the second radiation beam 115. In one example, the center wavelength of the reflectance curve is 13.5 nanometers (nm).

One way to increase, maintain, or optimize the conversion efficiency is to control or stabilize the energy of the EUV light 130, in order to do this, among other parameters, the expansion of the modified target 121. It is important to keep the rate within acceptable values. The modified expansion coefficient of the target 121 is maintained within an acceptable range by maintaining a radiative exposure from the first beam of radiation 110 to the target material 120. Radiation exposure may also be maintained based on one or more measured properties associated with target material 120 or target 121 modified with respect to first radiation beam 110. Radiation exposure is the radiant energy received by the surface of the target material 120 per unit area. Thus, radiative exposure can be estimated or approximated as the amount of energy induced towards the surface of target material 120 if the area of target material 120 remains constant from pulse to pulse.

There are various methods or techniques for maintaining the expansion coefficient of the modified target 121 within an acceptable range of values. The method or technique used may then depend on certain characteristics associated with the first radiation beam 110. The conversion efficiency is also affected by other parameters such as the size or thickness of the target material 120, the position of the target material 120 with respect to the first focal region 210, the angle of the target material 120 with respect to the xy plane.

One property that can affect how the radiation exposure is maintained is the confocal parameter of the first radiation beam 110. The confocal parameter of the radiation beam is twice the Rayleigh length of the radiation beam, and the Raleigh length is the distance along the propagation direction from the waist to where the cross-sectional area doubles. Referring to FIG. 2, with respect to the radiation beam 110, the Rayleigh length is in the propagation direction 212 of the first radiation beam 110 from the waist (D1/2) of this first beam to where the cross section is doubled. Along the distance.

For example, as shown in FIG. 7A, the confocal parameter of the first radiation beam 110 is long enough that the beam waist (D1/2) easily encompasses the target material 120 and is intercepted by the first radiation beam 110. The surface area of the target material 120 (measured over the X direction) remains relatively constant even if the position of the target material 120 deviates from the location of the beam waist D1/2. For example, the area of the surface of the target material 120 that is intercepted by the first beam of radiation 110 at location L1 is within 20% of the area of the surface of the target material 120 that is intercepted by the first beam of radiation 110 at location L2. .. In this first scenario, where the surface area of the target material 120 intercepted by the first radiation beam 110 is less likely to deviate from the average value (compared to the second scenario described below), the radiation exposure and thus the expansion coefficient is By maintaining the amount of energy induced from the first beam of radiation 110 to the target material 120 (without having to factor in the surface area of the target material 120 exposed by the first beam of radiation 110). It can be maintained or controlled.

As another example, as shown in FIG. 7B, the confocal parameter of the first radiation beam 110 is so short that the beam waist (D1/2) does not include the target material 120, and The surface area of the intercepted target material 120 deviates from the average value if the position of the target material 120 deviates from the location L1 of the beam waist D1/2. For example, the surface area of the target material 120 intercepted by the first radiation beam 110 at location L1 is significantly different from the surface area of the target material 120 intercepted by the first radiation beam 110 at location L2. In this second scenario, where the area of the surface of the target material 120 intercepted by the first beam of radiation 110 is more likely to deviate from the mean value (than in the first scenario), the radiative exposure and thus the expansion rate is reduced to the first value. Can be maintained or controlled by controlling the amount of energy delivered from the radiation beam 110 to the target material 120. To control the radiant exposure, the radiant energy of the first radiation beam 110 received by the surface of the target material 120 per unit area is controlled. Therefore, it is important to control the energy of the pulses of the first radiation beam 110 and the area of the first radiation beam 110 where the target material 120 intercepts the first radiation beam 110. The area of the first radiation beam 110 where the target material 120 intercepts the first radiation beam 110 correlates to the surface of the target material 120 intercepted by the first radiation beam 110. Another factor that may affect the area of the first radiation beam 110 where the target material 120 intercepts the first radiation beam 110 is the location and size of the beam waist D1/2 of the first radiation beam 110. Stability. For example, if the waist size and position of the first radiation beam 110 is constant, the location of the target material 120 can be controlled with respect to the beam waist D1/2. The waist size and position of the first beam of radiation 110 may change due to thermal effects in the optical source 105, for example. In general, maintaining the constant energy of the pulse in the first radiation beam 110 and controlling other aspects of the optical source 105, the target material 120 has a known axial direction (relative to beam waist D1/2). It is important to arrive at a position in the Z direction) without too much variation for that position.

All described methods for maintaining or controlling the expansion coefficient of the modified target 121 within an acceptable range of values employ the use of the measurement system 155. This will be described next.

Referring again to FIG. 1, the measurement system 155 measures at least one property associated with the target material 120, the modified target 121, and any one or more of the first radiation beam 110. For example, the measurement system 155 can measure the energy of the first radiation beam 110. As shown in FIG. 8A, the exemplary measurement system 855A measures the energy of the first radiation beam 110 that is directed at the target material 120.

As shown in FIG. 8B, the exemplary measurement system 855B measures the energy of radiation 860 reflected from the target material 120 after the first beam of radiation 110 interacts with the target material 120. The reflection of the radiation 860 from the target material 120 can be used to determine the location of the target material 120 with respect to the actual position of the first radiation beam 110.

In some implementations, the exemplary measurement system 855B may be located within the optical amplifier system 300 of the optical source 105, as shown in FIG. 8C. In this example, measurement system 855B is for measuring the amount of energy in reflected radiation 860 that impinges on or reflects one of the optical elements in optical amplifier system 300 (such as a thin film polarizer). Can be placed. The amount of radiation 860 reflected from the target material 120 is proportional to the amount of energy delivered to the target material 120. Therefore, by measuring the reflected radiation 860, the amount of energy delivered to the target material 120 can be controlled or maintained. Also, the amount of energy measured in either the first radiation beam 110 or the reflected radiation 860 correlates with the number of photons in the beam. Therefore, it can be said that the measurement system 855A or 855B measures the number of photons in each beam. In addition, the measurement system 855B determines the number of photons reflected from the target material 120 (which immediately becomes the modified target 121 when impacted by the first radiation beam 110), how many photons impinge on the target material 120. It can be thought of as measuring as a function of what is done.

The measurement system 855A or 855B may be a photoelectric sensor such as an array of photovoltaic cells (eg, a 2×2 array or a 3×3 array). The photovoltaic cell is sensitive to the wavelength of the light being measured and has sufficient velocity or bandwidth to suit the duration of the light pulse being measured.

In general, the measurement system 855A or 855B can measure the energy of the radiation beam 110 by measuring the spatially integrated energy across a direction perpendicular to the direction of propagation of the first radiation beam 110. .. Since the measurement of the energy of the beam can be performed quickly, it is possible to make a measurement for each pulse emitted in the first radiation beam 110, and thus this measurement and control can be done on a pulse-by-pulse basis.

The measurement system 855A, 855B may be a fast photodetector, such as a photoelectromagnetic (PEM) detector suitable for long wavelength infrared (LWIR) radiation. The PEM detector can be a silicon diode for measuring near infrared or visible radiation or an InGaAs diode for measuring near infrared radiation. The energy of the pulses of the first radiation beam 110 may be determined by integrating the laser pulse signals measured by the measurement system 855A, 855B.

With reference to FIG. 9A, the measurement system 155 can be an exemplary measurement system 955A that measures the position Tpos of the target material 120 with respect to the target position. The target location may be at the beam waist of the first beam of radiation 110. The position of the target material 120 can be measured along a direction parallel to the beam axis of the first radiation beam 110 (such as the first axial direction 212).

With reference to FIG. 9B, the measurement system 155 can be an exemplary measurement system 955B that measures the position Tpos of the target material 120 with respect to the primary focus 990 of the light collector 135. Such a measurement system 955B may reflect a laser and/or a laser that reflects off the target material 120 as it approaches to measure the position of the target material 120 relative to the coordinate system within the chamber 165 and the arrival time of the target material 120. It may include a camera.

With reference to FIG. 9C, the measurement system 155 is an exemplary measurement system 955C that measures the size of the modified target 121 in a position before the modified target 121 interacts with the second beam of radiation 115. obtain. For example, the measurement system 955C may measure the size of the modified target 121 within the second target location 116 but before the modified target 121 is impinged by the second beam of radiation 115. It may be configured to measure Smt. The measurement system 955C may also determine the orientation of the modified target 121. The measurement system 955C may use the shadowgraph technology of a pulsed backlight illuminator and camera (such as a charge coupled device camera).

The measurement system 155 may include a set of measurement subsystems, each subsystem designed to measure a particular characteristic at a different rate or sampling interval. Such a set of subsystems may cooperate to provide a clear image of how the first radiation beam 110 interacts with the target material 120 to form a modified target 121. ..

The measurement system 155 includes a plurality of chambers 165 for detecting EUV energy emitted from the plasma produced by the modified target 121 after the modified target 121 interacts with the second radiation beam 115. The EUV sensor may be included. By detecting the emitted EUV energy it is possible to obtain information about the angle of the modified target 121 or the lateral offset of the second beam with respect to the second radiation beam 115.

The beam conditioning system 180 is used to enable control of the amount of energy delivered to the target material 120 (radiative exposure) under the control of the control system 160. Radiation exposure is the amount of energy in the first radiation beam 110 if the area of the first radiation beam 110 at the location where the first radiation beam 110 interacts with the target material 120 can be assumed to be constant. Can be controlled by controlling. Beam conditioning system 180 receives one or more signals from control system 160. The beam conditioning system 180 adjusts one or more features of the optical source 105 to maintain the amount of energy delivered to the target material 120 (ie, radiative exposure) or to the target material 120. It is configured to control the amount of energy delivered. Accordingly, the beam conditioning system 180 may include one or more actuators that control the characteristics of the optical source 105, which actuators may be mechanical force devices, electrical force devices, optical force devices, electromagnetic force devices, or It may be any suitable force device that modifies the characteristics of the optical source 105.

In some implementations, beam conditioning system 180 includes a pulse width conditioning system coupled to first radiation beam 110. The pulse width adjustment system is configured to adjust the pulse width of the first radiation beam 110. In this implementation, the pulse width conditioning system may include an electro-optic modulator, such as a Pockels cell. For example, a Pockels cell is placed within the light-generating device 310, and by opening this Pockels cell for a shorter or longer period of time, the pulse transmitted by the Pockels-cell (and thus the pulse emitted by the light-generating device 310) is It can be adjusted to be shorter or longer.

In other implementations, beam conditioning system 180 includes a pulse power conditioning system coupled to first radiation beam 110. The pulse power adjustment system is configured to adjust the power of each pulse of the first radiation beam 110, for example, by adjusting the average power within each pulse. In this implementation, the pulse power conditioning system may include an acousto-optic modulator. The acousto-optic modulator may be arranged such that the change in the RF signal applied to the piezoelectric transducer at the end of the modulator is modified, thereby changing the power of the pulse diffracted from the acousto-optic modulator. Good.

In some implementations, beam conditioning system 180 includes an energy conditioning system coupled to first radiation beam 110. The energy conditioning system is configured to condition the energy of the first radiation beam 110. For example, the energy conditioning system may be an electrically variable attenuator (Pockels cell or external acousto-optic modulator that varies between 0V and half-wave voltage).

In some implementations, the position or angle of the target material 120 with respect to the beam waist D1/2 varies significantly, so that the beam conditioning system 180 may move the chamber 165 within the chamber 165 relative to the first target location 111 or in the coordinate system of the chamber 165. Apparatus for controlling the location or angle of the beam waist D1/2 with respect to another location. The device may be part of the focus assembly 156 and moves the beam waist along the Z direction or along a direction transverse to the Z direction (eg, along a plane defined by the X and Y directions). Can be used to

As described above, the control system 160 analyzes the information received from the measurement system 155 to determine how to adjust one or more properties of the first radiation beam 110, thereby modifying the modified target. Control or maintain the expansion rate of 121. Referring to FIG. 10, the control system 160 interfaces with a measurement system 155, a sub-controller 1000 specifically configured to interface with (receive information from, and send information to, the optical source 105). Of a light source 100, such as a sub-controller 1005 specifically configured as such, a sub-controller 1010 configured to interface with the beam delivery system 150, and a sub-controller 1015 configured to interface with the target material supply system 125. It may include one or more sub-controllers 1000, 1005, 1010, 1015 that interface with other parts. Light source 100 may include other components not shown in FIGS. 1 and 10, but which may interface with control system 160. For example, light source 100 may include a droplet position detection feedback system and a diagnostic system such as one or more targets or droplet imagers. The target imager provides, for example, an output that indicates the position of the droplet relative to a particular position (such as the primary focus 990 of the light collector 135) and provides this output to the droplet position detection feedback system, which may, for example, be the droplet. The position error and the trajectory can be calculated, and the error of the position of the liquid drop can be calculated for each liquid drop or on the average. Thus, the drop position detection feedback system provides the drop position error as an input to the sub-controller of the control system 160. The control system 160 may amplify the laser position, orientation, and timing correction signals to, for example, a laser control system within the optical source 105, which may be used to control the laser timing circuit, and/or amplification of the beam delivery system, for example. A beam control system for controlling the position and shaping of the light beam is provided to change the focal plane location and/or focusing power of the first radiation beam 110 or the second radiation beam 115.

The target material delivery system 125 includes a target material delivery control system, which, in response to a signal from the control system 160, may, for example, release a droplet of target material 120 released by an internal delivery mechanism. It is operable to correct to compensate for the error of the droplet arriving at the desired target location 111.

Control system 160 generally includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system 160 includes suitable input and output devices 1020, one or more programmable processors 1025, and one or more computer program products 1030 tangibly embodied in a machine-readable storage device for execution by the programmable processors. May also be included. Also, each of the sub-controllers, such as sub-controllers 1000, 1005, 1010, 1015, has its own suitable input and output device, one or more programmable processors, and a machine-readable storage device for execution by the programmable processor. May include one or more computer program products tangibly embodied in.

One or more programmable processors may each execute a program of instructions to perform desired functions by operating on input data and producing appropriate outputs. Generally, a processor will receive instructions and data from a read-only memory and/or a random access memory. Suitable storage devices for tangibly embodying computer program instructions and data include any form of non-volatile memory, including, for example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices, internal hard disks, and It includes a magnetic disk such as a removable disk, a magneto-optical disk, and a CD-ROM disk. Any of the foregoing may be supplemented by, or incorporated into, a specially designed ASIC (Application Specific Integrated Circuit).

As such, control system 160 includes an analysis program 1040 that receives measurement data from one or more measurement systems 155. In general, the analysis program 1040 determines whether to modify or control the energy delivered from the first radiation beam 110 to the target material 120, or modifies the energy of the first radiation beam 110. It carries out all of the analysis necessary to control, and such analysis can be carried out on a pulse-by-pulse basis, provided that the measurement data is obtained on a pulse-by-pulse basis.

Referring to FIG. 11, the light source 100 (under the control of the control system 160) maintains or controls the expansion coefficient (ER) of the modified target 121, thereby increasing the conversion efficiency of the light source 100. Perform 1100. The light source 100 provides a target material 120 (1105). For example, target material supply system 125 (under control of control system 160) may deliver target material 120 to first target location 111. The target material supply system 125 may include a unique actuation system (connected to the control system 160) and a nozzle that delivers the target material, the actuation system controlling the amount of target material directed through the nozzle. To produce a stream of droplets that is directed towards the first target location 111.

The light source 100 then directs a first beam of radiation 110 toward the target material 120 to deliver energy to the target material 120 and modify the geometric distribution of the target material 120 to create a modified target 121. It is formed (1110). In particular, the first beam of radiation 110 is directed toward the target material 120 through the first set 300 of one or more optical amplifiers. For example, the optical source 105 may be actuated by the control system 160 to produce a first beam of radiation 110 (in the form of a pulse) that is directed toward the target material 120 within the target location 111 as shown in FIG. Can be guided to. The focal plane of the first beam of radiation 110 (at beam waist D1/2) may be configured to intersect the target location 111. Also, in some implementations, the focal plane may overlap the target material 120 or the end of the target material 120 opposite the first radiation beam 110. The first beam of radiation 110 may be directed (1110) to the target material 120, such as by directing the first beam of radiation 110 through the beam delivery system 150. In the beam delivery system, various optics may be used to modify the direction or shape or divergence of the radiation 110 so that the radiation 110 interacts with the target material 120.

The first beam of radiation 110 can be steered 1110 toward the target material 120 by overlapping the target material 120 with an area of the first beam of radiation 110 that contains confocal parameters. In some implementations, the confocal parameter of the first radiation beam 110 is long enough that the beam waist (D1/2) easily encompasses the target material 120 and the target intercepted by the first radiation beam 110. The area of the surface of material 120 (measured over the X direction) remains relatively constant even if the position of target material 120 deviates from the location of beam waist D1/2 (as shown in FIG. 7A). is there. For example, the confocal parameter of the first radiation beam 110 may be greater than 1.5 mm. In other implementations, the confocal parameters of the first radiation beam 110 are so short that the beam waist (D1/2) does not encompass the target material 120 and the target material 120 intercepted by the first radiation beam 110. The area of the surface deviates significantly if the position of the target material 120 deviates from the location L1 of the beam waist D1/2 (as shown in FIG. 7B). For example, the confocal parameter may be 2 mm or less as an example.

The modified target 121 changes shape from the shape of the target material 120 immediately after impact by the first radiation beam 110 to an expanded shape, which expanded shape is second away from the first target location 111. Continues to deform as it drifts toward the target location 116 of the. The modified target 121 may have a geometric distribution that transforms from the shape of the target material into a disc-shaped mass of molten metal having a substantially flat surface (such as that shown in FIGS. 1 and 2). The modified target 121 is transformed into a disk-shaped mass according to the expansion coefficient. The modified target 121 is transformed by expanding the modified target 121 along at least one axis with a coefficient of expansion. For example, as shown in FIG. 2, the modified target 121 is expanded along at least a major axis 230 generally parallel to the X direction. The modified target 121 is expanded along at least one axis that is not parallel to the optical axis of the second radiation beam 115, which is the second axial direction 217.

Although the first radiation beam 110 interacts with the target material 120 primarily by changing the shape of the target material 120, the first radiation beam 110 can interact with the target material 120 in other ways. is there. For example, the first beam of radiation 110 may convert a portion of the target material 120 into a plasma that emits EUV light. However, the plasma produced from the target material 120 emits less EUV light than the plasma produced from the modified target 121 (due to the subsequent interaction of the modified target 121 with the second radiation beam 115). The primary action of the first radiation beam from the 110 on the target material 120 is to modify the geometric distribution of the target material 120 to form a modified target 121.

The light source 100 directs a second beam of radiation toward the modified target 121 such that the second beam of radiation 115 converts at least a portion of the modified target 121 into a plasma 129 that emits EUV light. (1115). In particular, the light source 100 directs a second beam of radiation 115 through a second set of one or more optical amplifiers 305 toward a modified target 121. For example, the optical source 105 may be actuated by the control system 160 to produce a second beam of radiation 115 (in the form of a pulse), which is modified within the second target location 116 as shown in FIG. Can be directed towards the target 121. At least one optical amplifier of the first set 300 may be in the second set 305, as in the example shown in FIG.

The light source 100 measures (1120) one or more properties (eg, energy) associated with one or more of the target material 120 and the target 121 modified with respect to the first radiation beam 110. For example, the measurement system 155 measures the characteristic under the control of the control system 160, and the control system 160 receives the measurement data from the measurement system 155. The light source 100 controls the radiant exposure of the first radiation beam 110 at the target material 120 based on the one or more measured properties (1125). As mentioned above, radiant exposure is the amount of radiant energy delivered from the first beam of radiation 110 to the target material 120 per unit area. In other words, radiant exposure is the radiant energy that the surface of the target material 120 receives per unit area.

In some implementations, the measurable property (1120) is the energy of the first radiation beam 110. In another general implementation, the measurable property (1120) is the position of the target material 120 with respect to the position of the first radiation beam 110 (eg, with respect to the beam waist of the first radiation beam 110), Such positions may be determined in the longitudinal (Z) direction or in a direction transverse to the longitudinal direction (eg in the XY plane).

The energy of the first beam of radiation 110 can be measured by measuring the energy of the radiation 860 reflected from the light-reflecting surface of the target material 120 (as shown in FIGS. 8B and 8C). The energy of the radiation 860 reflected from the light-reflecting surface of the target material 120 can be measured by measuring the total intensity of the radiation 860 across four individual photovoltaic cells.

The total energy content of the back-reflected radiation 860, in combination with other information about the first beam of radiation 110, is targeted along either the Z direction or a direction transverse to the Z direction (such as the XY plane). It can be used to determine the relative position of the material 120 and the beam waist of the first radiation beam 110. Alternatively, the total energy content of the back-reflected radiation 860 is used (along with other information) to determine the relative position of the target material 120 and the beam waist of the first radiation beam along the Z direction. obtain.

The energy of the first radiation beam 110 can be measured by measuring the energy of the first radiation beam 110 directed toward the target material 120 (as shown in FIG. 8A). The energy of the first radiation beam 110 can be measured by measuring the spatially integrated energy across a direction perpendicular to the direction of propagation of the first radiation beam 110 (first axial direction 212). is there.

In some implementations, the measurable property (1120) is the pointing or direction in which the first beam of radiation 110 (as shown in FIG. 8A) travels toward the target material 120. Information about this pointing can be used to determine the registration error between the position of the target material 120 and the axis of the first radiation beam 110.

In some implementations, the measurable property (1120) is the position of the target material 120 with respect to the target position. The target position may be at the beam waist (D1/2) of the first radiation beam 110 along the Z direction. The position of the target material 120 can be measured along a direction parallel to the first axial direction 212. The target position can be measured with respect to the primary focus 990 of the light collector 135. The position of the target material 120 may be measured along two or more non-parallel directions.

In some implementations, the measurable property (1120) is the size of the modified target before the second radiation beam converts at least a portion of the modified target into a plasma.

In some implementations, the measurable characteristic (1120) corresponds to a modified target expansion coefficient estimate.

In some implementations, the measurable property (1120) corresponds to the spatial property of the radiation 860 reflected from the light-reflecting surface of the target material 120 (as shown in FIGS. 8B and 8C). Such information can be used to determine the relative position of the target material 120 (eg, along the Z direction) and the beam waist of the first radiation beam 110. This spatial property can be determined or measured by using an astigmatism imaging system placed in the path of the reflected radiation 860.

In some implementations, the measurable characteristic (1120) corresponds to the angle at which the radiation 860 is directed relative to the angle of the first beam of radiation 110. This measured angle can be used to determine the distance between the target material 120 and the beam axis of the first radiation beam 110 along a direction transverse to the Z direction.

In other implementations, the measurable property (1120) corresponds to a spatial view of the modified target 121 formed after the first beam of radiation 110 interacts with the target material 120. For example, the angle of the modified target 121 may be measured with respect to a direction, eg, a direction in the XY plane transverse to the Z direction. Such information about the angle of the modified target 121 can be used to determine the distance between the target material 120 and the axis of the first radiation beam 110 along a direction transverse to the Z direction. As another example, the size or expansion coefficient of the modified target 121 is predetermined or set after the modified target is first formed by the interaction of the target material 120 and the first radiation beam 110. May be measured after a certain amount of time. Such information about the size or expansion coefficient of the modified target 121 can be used to determine the target along the longitudinal direction (Z direction) if the energy of the first radiation beam 110 is known to be constant. It can be used to determine the distance between the material 120 and the beam waist of the first radiation beam 110.

The characteristic can be measured as fast (1120) as for each pulse of the first radiation beam 110. For example, if the measurement system 155 includes a PEM or a quad cell (4 PEMs deployed), the measurement rate can be as fast as pulse by pulse.

On the other hand, for the measurement system 155 measuring characteristics such as size or expansion coefficient of the target material 120 or the modified target 121, a camera can be used for the measurement system 155. Are generally much slower, for example a camera may measure at speeds of about 1 Hz to about 200 Hz.

In some implementations, the amount of radiant exposure delivered from the first radiation beam 110 to the target material 120 is controllable to thereby control or maintain a coefficient of expansion of the modified target (1125). ). In other implementations, the amount of radiation exposure delivered from the first radiation beam 110 to the target material 120 is adjusted based on one or more measured characteristics of the characteristics of the first radiation beam 110. It can be controlled (1125) by determining if it should. Thus, if it is determined that the characteristics of the first radiation beam 110 should be adjusted, for example, the energy content of the pulses of the first radiation beam 110 may be adjusted, or the target material 120. The area of the first radiation beam 110 at the position may be adjusted. The energy content of the pulses of the first radiation beam 110 is the pulse width of the first radiation beam 110, the pulse length of the first radiation beam 110, and the average or instantaneous power of the pulses of the first radiation beam 110. It is adjustable by adjusting one or more of them. The area of the first radiation beam 110 that interacts with the target material 120 adjusts the relative axial position (along the Z direction) of the target material 120 and the beam waist of the first radiation beam 110. Is adjustable by.

In some implementations, one or more properties can be measured (1120) for each pulse of the first beam of radiation 110. In this way, it can be determined whether the characteristics of the first radiation beam 110 should be adjusted for each pulse of the first radiation beam 110.

In some implementations, the radiation exposure delivered from the first beam of radiation 110 to the target material 120 is performed while at least a portion of the emitted and collected EUV light 140 is exposing a wafer of a lithographic tool. By controlling the radiant exposure, it is controllable (eg within the range of acceptable radiative exposure).

The procedure 1100 collects at least a portion of the EUV light 130 emitted from the plasma (using a light collector 135) and directs the collected EUV light 140 toward the wafer to direct the EUV light 140 to the wafer. Can also be included.

In some implementations, the one or more measured properties (1120) include the number of photons reflected from the modified target 121. The number of photons reflected from the modified target 121 can be measured as a function of how many photons hit the target material 120.

As mentioned above, the procedure 1100 includes controlling (1125) the radiant exposure of the first radiation beam 110 at the target material 120 based on one or more characteristics. For example, the radiant exposure may be controlled 1125 to be maintained within a predetermined radiant exposure range. Radiation exposure is the amount of radiant energy delivered from the first beam of radiation 110 to the target material 120 per unit area. In other words, radiant exposure is the radiant energy that the surface of the target material 120 receives per unit area. If the unit area of the surface of the target material 120 that is exposed to or intercepted by the first beam of radiation 110 is controlled (or maintained within an acceptable range), this radiation exposure factor Remains relatively constant and controls or maintains the radiation exposure on the target material 120 by maintaining the energy of the first radiation beam 110 within an acceptable energy range (1125). ) Is possible. There are various techniques for maintaining the unit area of the surface of the target material 120 exposed to the first beam of radiation 110 within an acceptable area range. Next, these will be described.

Radiation exposure (1125) from the first beam of radiation 110 on the target material 120 results in (using the measured characteristic 1120, despite the disturbances in which the energy of the pulses of the first beam of radiation 110 can change the energy. Control to maintain a constant level or within an acceptable range of values.

In another aspect, the radiative exposure (1125) from the first beam of radiation 110 at the target material 120 is performed by feedback control of the energy of the pulses of the first beam of radiation 110 using the measured characteristic 1120. Can be controlled (eg, increased or decreased) to compensate for longitudinal (Z-direction) placement error of the position of the target material 120 with respect to the beam waist of the radiation beam 110.

The first beam of radiation 110 may be a pulsed beam of radiation such that pulses of light are directed towards the target material 120 (1110). Similarly, the second beam of radiation 115 may be a pulsed beam of radiation such that a pulse of light is directed towards the modified target 121 (1115).

The target material 120 may be droplets of the target material 120 generated from the target material supply system 125. Thus, the geometric distribution of the target material 120 may be modified to become the modified target 121, which is transformed into a disk-shaped mass of molten metal having a substantially flat surface. The droplets of the target material are transformed into a disk-shaped mass according to the expansion coefficient.

Referring to FIG. 12, the EUV light energy produced by the plasma 129 formed by the interaction of the modified target 121 and the second radiation beam 115 by the light source 100 (under control of the control system 160) is stabilized. The procedure 1200 for implementing is implemented. Similar to procedure 1100 above, the light source 100 provides the target material 120 (1205), and the light source 100 directs the first beam of radiation 110 toward the target material 120 to deliver energy to the target material 120, The geometric distribution of the target material 120 is modified to form a modified target 121 (1210) and the light source 100 directs at least a portion of the modified target 121 of the second radiation beam into a plasma 129 that emits EUV light. A second beam of radiation 115 is directed (1215) toward the modified target 121 for conversion. The light source 100 controls 1220 the radiant exposure applied to the target material 120 from the first beam of radiation 110 using procedure 1110.

The power or energy of the EUV light 130 is stabilized (1225) by controlling the radiant exposure. The EUV energy (or power) produced by the plasma 129 depends on at least two functions, the first of which is the conversion efficiency CE and the second is the energy of the second radiation beam 115. The conversion efficiency is the percentage value of the modified target 121 that is converted into plasma 129 by the second beam of radiation 115. The conversion efficiency is the peak power of the second radiation beam 115, the size of the modified target 121 when interacting with the second radiation beam 115, the position of the modified target 121 relative to the desired position, the modified It depends on several variables including the cross-sectional area or size of the second radiation beam 115 at the time it interacts with the target 121. The position of the modified target 121 and the size of the modified target 121 depend on how the target material 120 interacts with the first radiation beam 110, so By controlling the applied radiant exposure, it is possible to control the expansion coefficient of the modified target 121, and thus control these two factors. In this way, controlling the radiant exposure allows the conversion efficiency to be stabilized or controlled (1220) and thus the EUV energy produced by the plasma 129 to be stable (1225).

Referring also to FIG. 13, in some implementations, the first beam of radiation 110 may be generated by a dedicated subsystem 1305A within the optical source 105 and the second beam of radiation 115 within the optical source 105. As may be generated by a dedicated and separate subsystem 1305B, the radiation beams 110, 115 follow two separate paths on their way to each of the first and second target locations 111, 116. In this way, each of the radiation beams 110, 115 travels through a respective subsystem of the beam delivery system 150, and thus through respective separate optical steering components 1352A, 1352B and focus assemblies 1356A, 1356B.

For example, subsystem 1305A may be a solid gain medium based system, while subsystem 1305B may be a gas gain medium based system such as that produced by a CO ₂ amplifier. Exemplary solid gain media that may be used as subsystem 1305A include erbium-doped fiber lasers and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. In this example, the wavelength of the first radiation beam 110 may be different than the wavelength of the second radiation beam 115. For example, the wavelength of the first radiation beam 110 using a solid gain medium may be about 1 μm (eg, about 1.06 μm), and the wavelength of the second radiation beam 115 using a gas medium is about 10.6 μm. May be.

Other implementations are within the scope of the claims.

Claims (15)

Providing a target material that includes a component that emits extreme ultraviolet (EUV) light when converted to plasma.
Directing a first beam of radiation toward the target material to deliver energy to the target material to modify a geometric distribution of the target material to form a modified target;
Immediately after directing the first beam of radiation to the target material, a second beam of radiation that converts at least a portion of the modified target into a plasma that emits EUV light is directed toward the modified target. Leading to
Measuring one or more properties associated with the interaction between the first radiation beam and one or more of the target material and the modified target, and the target from the first radiation beam. Controlling the amount of radiant exposure delivered to the material within a predetermined energy range based on the one or more measured properties;
With
Method. And one or more of the target material and the corrected target, said first measuring the one or more characteristics associated with the interaction between the radiation beam, the energy of the first radiation beam The method of claim 1, comprising measuring. Measuring the energy of the first radiation beam may be measuring the energy of the first radiation beam reflected from a light reflecting surface of the target material, or may be directed towards the target material. The method of claim 2, comprising measuring the energy of the first beam of radiation that The measuring of the energy of the first beam of radiation comprises measuring spatially integrated energy across a direction perpendicular to a direction of propagation of the first beam of radiation. The described method. The method of claim 4, wherein directing the first beam of radiation toward the target material comprises overlapping the target material with an area containing confocal parameters of the first beam of radiation. .. The method of claim 1, wherein measuring the one or more characteristics associated with one or more of the target material and the modified target comprises measuring a position of the target material with respect to a target position. the method of. Measuring the one or more properties associated with one or more of the target material and the modified target comprises:
Detecting a size of the modified target before the second beam of radiation converts at least a portion of the modified target into a plasma; and estimating a coefficient of expansion of the modified target,
The method of claim 1, comprising one or more of: Controlling the amount of the radiation exposure delivered from the first beam of radiation to the target material based on the one or more measured characteristics comprises controlling a coefficient of expansion of the modified target. The method of claim 1, comprising. Controlling the amount of the radiation exposure delivered from the first radiation beam to the target material based on the one or more measured characteristics is characterized in that the first radiation beam is characterized by the one or more characteristics. The method of claim 1, comprising determining whether to adjust based on the measured characteristic of the. A chamber defining an initial target location for receiving the first beam of radiation and a target location for receiving the second beam of radiation;
A target material delivery system configured to provide a target material including a material that emits extreme ultraviolet (EUV) light when converted to plasma to the initial target location.
An optical source configured to generate the first beam of radiation and the second beam of radiation;
Directing the first beam of radiation toward the initial target location to deliver energy to the target material to modify a geometric distribution of the target material to form a modified target; and
Immediately after directing the first beam of radiation to the target material, a plasma that directs the second beam of radiation toward the target location to emit EUV light to at least a portion of the modified target. A light steering system configured to convert to
A measurement system for measuring one or more properties associated with an interaction between the target material and one or more of the modified targets and the first radiation beam ;
Connected to the target material delivery system, the optical source, the light steering system, and the measurement system to receive the one or more measured properties from the measurement system; and Configured to send a plurality of signals to the optical source to control the amount of radiant exposure delivered from the first beam of radiation to the target material based on the one or more measured properties. Control system,
A device comprising. The light steering system is configured to focus the first beam of radiation at or near the initial target location, and to focus the second beam of radiation at or near the target location. 11. The device of claim 10, comprising a focused device. A beam conditioning system is further provided, wherein the beam conditioning system is connected to the optical source and the control system, the control system transmitting one or more signals to the optical source to provide one or more signals. Configured to control the amount of energy delivered to the target material by transmitting to the beam conditioning system, the beam conditioning system adjusting one or more features of the optical source, 11. The apparatus of claim 10, configured to maintain the amount of energy delivered to the target material by. The beam conditioning system comprises a pulse width conditioning system coupled to the first radiation beam, the pulse width conditioning system configured to regulate a pulse width of a pulse of the first radiation beam. Item 13. The device according to item 12. The beam conditioning system comprises a pulse power conditioning system coupled to the first radiation beam, the pulse power conditioning system configured to regulate an average power within a pulse of the first radiation beam. The device according to claim 12. The optical source is
A first set of optical components including a first set of one or more optical amplifiers through which the first beam of radiation passes;
A second set of optical components including a second set of one or more optical amplifiers through which the second beam of radiation passes;
The apparatus of claim 10, comprising: