KR20240015174A - Target expansion rate control in an extreme ultraviolet light source - Google Patents

Abstract

The method includes providing a target material comprising a component that emits extreme ultraviolet (EUV) light when converted to plasma; directing the first radiation beam toward the target material to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target; Directing a second radiation beam toward the modified target, the second radiation beam converting at least a portion of the modified target into a plasma that emits EUV light; measuring one or more characteristics associated with one or more of the target material and the modified target relative to the first radiation beam; and controlling the amount of radiation exposure delivered from the first radiation beam to the target material within a predetermined energy range based on the one or more measured characteristics.

Description

Method for controlling target expansion rate within an extreme ultraviolet light source {TARGET EXPANSION RATE CONTROL IN AN EXTREME ULTRAVIOLET LIGHT SOURCE}

This application is based on U.S. Patent Application No. 14/824,141, filed on August 12, 2015, and titled “TARGET EXPANSION RATE CONTROL IN AN EXTREME ULTRAVIOLET LIGHT SOURCE” Priority is claimed on U.S. patent application Ser. No. 14/824,147, entitled “STABILIZING EUV LIGHT POWER IN AN EXTREME ULTRAVIOLET LIGHT SOURCE,” the contents of both of which are incorporated herein by reference.

The present invention relates to a method of controlling the expansion rate of a target material for a laser generated plasma extreme ultraviolet light source.

Extreme ultraviolet (EUV) light, such as electromagnetic radiation with wavelengths below approximately 50 nm (often referred to as soft It can be used in a photolithography process to create.

Methods for generating EUV light include, but are not necessarily limited to, converting a material with an element having an emission line in the EUV band, such as xenon, lithium, or tin, in a plasma state. In one such method, often called laser-generated plasma (“LPP”), the required plasma is an amplified energy source, which may be referred to as a driving laser, on a target material, for example in the form of a droplet, plate, tape, stream or cluster of material. It can be created by irradiating a light beam. For these processes, plasma is typically generated in a sealed vessel, such as a vacuum chamber, and monitored using various types of metrology equipment.

According to some general aspects, the method includes: providing a target material comprising a component that emits extreme ultraviolet (EUV) light when converted to plasma; directing the first radiation beam toward the target material to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target; Directing a second radiation beam toward the modified target, the second radiation beam converting at least a portion of the modified target into a plasma that emits EUV light; measuring one or more characteristics associated with one or more of the target material and the modified target relative to the first radiation beam; and controlling the amount of radiation exposure delivered from the first radiation beam to the target material within a predetermined energy range based on the one or more measured characteristics.

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 an optically reflective 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 at the target material. The energy of the first radiation beam may be measured by measuring the spatially integrated energy over a direction perpendicular to the direction of propagation of the first radiation beam.

The first radiation beam may be directed toward the target material by overlapping the target material with an area of the first radiation beam surrounding the confocal parameters. Confocal parameters can be greater than 1.5 mm.

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

One or more properties associated with one or more of the target material and the modified target may be measured by detecting the size of the modified target before the second radiation beam converts at least a portion of the modified target to plasma. One or more properties associated with one or more of the target material and the modified target may be measured by estimating the expansion rate of the modified target.

The amount of radiation exposure delivered to the target material from the first radiation beam can be controlled by controlling the rate of expansion of the modified target.

The radiation exposure delivered from the first radiation beam to the target material may be controlled by determining whether a characteristic of the first radiation beam should be adjusted based on one or more measured characteristics. A determination that a characteristic of the first radiation beam should be adjusted may be made while one or more characteristics are being measured.

Once it is determined that the characteristics of the first radiation beam should be adjusted, one or more of the following may be adjusted: the energy content of the pulses of the first radiation beam and the area of the first radiation beam that interacts with the target material. The energy content of the pulse of the first radiation beam is determined by: the pulse width of the first radiation beam; the duration of the pulse of the first radiation beam; and the average power within a pulse of the first radiation beam.

The first radiation beam can be directed toward the target material by directing a pulse of first radiation toward the target material; One or more characteristics may be measured by measuring one or more characteristics for each pulse of first radiation; It is possible to determine whether a characteristic of the first radiation beam should be adjusted by determining whether the characteristic should be adjusted for each pulse of the first radiation.

The amount of radiation exposure delivered from the first radiation beam to the target material can be controlled by controlling the amount of radiation exposure delivered from the first radiation beam to the target material while at least a portion of the emitted EUV light exposes the wafer.

The target material can be provided by providing a droplet of the target material; The geometric distribution of the target material can be modified by transforming a droplet of the target material into a disk-shaped volume of molten metal. A droplet of target material can be transformed into a disk-shaped volume depending on its expansion rate.

The method also includes concentrating at least a portion of the emitted EUV light; and directing the focused EUV light toward the wafer to expose the wafer to the EUV light.

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 radiation beam may be directed toward the target material such that a portion of the target material is converted to a plasma that emits EUV light, with less EUV light emitted from the plasma converted from the target material than emitted from the plasma converted from the modified target. Light is emitted, and its dominant action 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 may be modified by modifying the shape of the target material into the modified target, including expanding the modified target along at least one axis according to an expansion rate. The amount of radiation exposure delivered to the target material can be controlled by controlling the rate of expansion of the target material into the modified target.

The modified target can be expanded along at least one axis, which axis 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 may 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 the number of photons impinging on the target material.

A first radiation beam may be directed toward a target material by directing a pulse of first radiation toward the target material, and a second radiation beam may be directed toward a modified target by directing a second pulse of radiation toward the modified target. It can be.

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

One or more properties associated with one or more of the target material and the modified target may be measured by measuring the energy of a first radiation beam directed toward the target material, and the amount of radiation exposure delivered to the target material may be determined based on the measured energy. 1 can be controlled by adjusting the amount of energy directed from the radiation beam to the target material. The first radiation beam may be directed toward the target material by overlapping the target material with an area of the first radiation beam surrounding the confocal parameter, which may be less than or equal to 2 mm.

The amount of energy directed to the target material from the first radiation beam can be adjusted by adjusting the properties of the first radiation beam.

The radiation exposure amount delivered from the first radiation beam to the target material may include: the energy of the first radiation beam immediately before the first radiation beam transfers energy to the target material; location of target material; and an area of the target material that interacts with the first radiation beam.

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

In another general aspect, the device includes: a chamber defining an initial target position for receiving a first radiation beam and a target position for receiving a second radiation beam; a target material delivery system configured to provide target material, including a material that emits extreme ultraviolet (EUV) light when converted to plasma, to an initial target location; an optical source configured to generate a first radiation beam and a second radiation beam; Includes optical steering system. The optical steering system: directs the first radiation beam toward the 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 directs at least a portion of the modified target with EUV light. and configured to direct the second radiation beam toward the target location for conversion into an emitting plasma. The apparatus includes a measurement system that measures one or more properties associated with one or more of the target material and the modified target relative to the first radiation beam; and a control system coupled to the target material delivery system, optical source, optical steering system, and measurement system. The control system is configured to receive one or more measured characteristics from the measurement system and to transmit one or more signals to the optical source to control the amount of radiation exposure delivered to the target material from the first radiation beam based on the one or more measured characteristics. .

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

The device may include a beam steering system, the beam steering system coupled to an optical source and a control system, the control system configured to control the amount of energy delivered to the target material by transmitting one or more signals to the beam steering system. Configured to transmit one or more signals to the source, the beam steering system is configured to maintain the amount of energy delivered to the target material by adjusting one or more characteristics of the optical source. The beam steering system may include a pulse width steering system coupled to the first radiation beam, the pulse width steering system configured to adjust a pulse width of a pulse of the first radiation beam. The pulse width adjustment system may include an electro-optical modulator.

The beam steering system may include a pulse power adjustment system coupled to the first radiation beam, the pulse power adjustment system configured to adjust an average power within a pulse of the first radiation beam. The pulse power regulation system may include an acousto-optic modulator.

The beam steering system is configured to transmit one or more signals to the optical source to control the amount of energy directed to the target material by transmitting one or more signals to the beam steering system, wherein the beam steering system controls one or more characteristics of the optical source. It can be configured to control the amount of energy directed to the target material by adjusting it.

The optical source includes: a first set of one or more optical amplifiers through which a first radiation beam passes; and a second set of one or more optical amplifiers through which the second radiation beam passes, wherein at least one of the optical amplifiers in the first set is in the second set. The measurement system may measure the energy of the first radiation beam when the first radiation beam is directed toward the initial target location, and the control system may receive the measured energy from the measurement system and determine the energy of the first radiation beam based on the measured energy. It may be configured to transmit one or more signals to the optical source to control the amount of energy directed from the beam to the target material.

According to some general aspects, the method includes: providing a target material comprising a component that emits extreme ultraviolet (EUV) light when converted to plasma; directing the first radiation beam toward the target material to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target; Directing a second radiation beam toward the modified target, the second radiation beam converting at least a portion of the modified target into a plasma that emits EUV light; controlling the amount of radiation exposure delivered from the first radiation beam to the target material within a predetermined energy range; and stabilizing the power of EUV light emitted from the plasma by controlling the radiation exposure amount delivered from the first radiation beam to the target material within a predetermined radiation exposure amount range.

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

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

The target material may be provided by providing a droplet of the target material, and the geometric distribution of the target material may be modified by transforming the droplet of the target material into a disk-shaped volume of molten metal with a substantially planar surface.

The target material may be provided by providing droplets of the target material, and the geometric distribution of the target material may be modified by transforming the droplets of the target material into a mist-like volume of molten metal particles.

The target material can be transformed into a modified target depending on the rate of expansion.

The radiation exposure delivered to the target material from the first radiation beam measures one or more properties associated with one or more of the target material and the modified target relative to the first radiation beam; The radiation dose delivered to the target material from the first radiation beam may be controlled by maintaining the radiation dose within a predetermined radiation dose range based on one or more measured characteristics.

The amount of radiation exposure delivered to the target material from the first radiation beam can be controlled by estimating the expansion rate of the modified target. The amount of radiation exposure delivered to the target material from the first radiation beam can be controlled by maintaining the rate of expansion of the modified target.

The amount of radiation exposure delivered to the target material from the first radiation beam can be controlled by determining whether characteristics of the first radiation beam should be adjusted. The radiation exposure delivered from the first radiation beam to the target material is determined by adjusting 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 to determine the characteristics of the first radiation beam. It can be controlled by adjusting . The energy content of the pulses of the first radiation beam may include: 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.

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

The method also includes concentrating at least a portion of the emitted EUV light; and directing the focused EUV light toward the wafer to expose the wafer to the EUV light.

The geometric distribution of the target material may be modified by modifying the shape of the target material into the modified target, including expanding the modified target along at least one axis according to an expansion rate.

The amount of radiation exposure delivered to the target material from the first radiation beam can be controlled by adjusting the characteristics 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, the device includes a chamber defining an initial target location for receiving a first radiation beam and a target location for receiving a second radiation beam; a target material delivery system configured to provide target material, including a material that emits extreme ultraviolet (EUV) light when converted to plasma, to an initial target location; an optical source configured to generate a first radiation beam and a second radiation beam; Includes optical steering system. The optical steering system: directs the first radiation beam toward the 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 directs at least a portion of the modified target with EUV light. and configured to direct the second radiation beam toward the target location for conversion into an emitting plasma. The apparatus includes a control system coupled to the target material delivery system, the optical source, and the optical steering system, wherein the control system controls the radiation exposure delivered to the target material from the first radiation beam to within a predetermined radiation exposure range to produce radiation emitted from the plasma. It is configured to transmit one or more signals to the optical source to stabilize the power of EUV light.

Implementations may include one or more of the following features. For example, the device may also include a measurement system that measures one or more properties associated with one or more of the target material and the modified target relative to the first radiation beam, and the control system is coupled to the measurement system.

The device may also include a beam steering system, the beam steering system coupled to an optical source and a control system, the control system configured to control the amount of radiation exposure delivered to the target material by transmitting one or more signals to the beam steering system. Configured to transmit one or more signals to the source, the beam steering system is configured to control the amount of radiation exposure delivered to the target material by adjusting one or more characteristics of the optical source.

1 shows a laser generator comprising an optical source that produces a first radiation beam directed to a target material and a second radiation beam directed to a modified target to convert a portion of the modified target into a plasma that emits EUV light. This is a block diagram of a plasma extreme ultraviolet light source.
Figure 2 is a schematic diagram showing a first radiation beam directed to a first target location and a second radiation beam directed to a second target location.
FIG. 3A is a block diagram of an example optical source used in the light source of FIG. 1.
3B and 3C are block diagrams of an example beam path combiner and an example beam path splitter, respectively, that may be used in the optical source of FIG. 1.
Figures 4A and 4B are block diagrams of example optical amplifier systems that may be used in the optical source of Figure 3A.
FIG. 5 is a block diagram of an example optical amplifier system that may be used in the optical source of FIG. 3A.
Figure 6 is a schematic diagram showing another embodiment of a first radiation beam directed to a first target location and a second radiation beam directed to a second target location.
7A and 7B are schematic diagrams showing an example implementation of a first radiation beam directed to a first target location.
Figures 8A-8C and 9A-9C represent schematic diagrams of various implementations of measurement systems that measure at least one characteristic associated with any one or more of a target material, a modified target, and a first radiation beam.
FIG. 10 is a block diagram of an exemplary control system for the light source of FIG. 1.
11 is a flow diagram of an example procedure performed by a light source (under the control of a control system) to improve the conversion efficiency of the light source by maintaining or controlling the expansion rate (ER) of the modified target.
FIG. 12 is a flow diagram of an example procedure performed by a light source to stabilize the power of EUV light emitted from the plasma by controlling the amount of radiation exposure delivered to the target material from the first radiation beam.
13 illustrates an example optical source generating first and second radiation beams, modifying the first and second radiation beams, and focusing the first and second radiation beams to first and second target locations, respectively. This is a block diagram of a typical beam delivery system.

A technique for increasing the conversion efficiency of extreme ultraviolet (EUV) light generation is disclosed. 1 , as discussed in more detail below, the interaction between target material 120 and first radiation beam 110 causes the target material to deform and expand geometrically to form modified target 121. I do it. The rate of geometric expansion of the modified target 121 is controlled in such a way as to increase the amount of available EUV light 130 that is converted from the plasma due to the interaction between the modified target 121 and the second radiation beam 115. do. The amount of available EUV light 130 is the amount of available EUV light 130 that can be utilized for use in optical device 145. Accordingly, the amount of EUV light 130 available may depend on aspects such as the bandwidth or center wavelength of the optical component used to utilize EUV light 130.

Control of the rate of geometric expansion of the modified target 121 allows control of the size or geometric aspect of the modified target 121 when the modified target 121 interacts with the second radiation beam 115. . For example, adjusting the geometric expansion rate of the modified target 121 adjusts the density of the modified target 121 as it interacts with the second radiation beam 115; This is because the density of the modified target 121 when it interacts with the second radiation beam 115 affects the total amount of radiation absorbed by the modified target 121 and the extent to which this radiation is absorbed. am. As the density of modified target 121 increases, at a certain point EUV light 130 will not be able to escape from modified target 121 and thus the amount of available EUV light 130 may decrease. As another example, adjusting the geometric expansion rate of the modified target 121 adjusts the surface area of the modified target 121 when the modified target interacts with the second radiation beam 115.

In this way, the overall amount of available EUV light 130 produced can be increased or controlled by controlling the expansion rate of the modified target 121. In particular, the size of the modified target 121 and its expansion rate depend on the radiation exposure dose applied to the target material 120 from the first radiation beam 110, which This is the amount of energy delivered to the area of the target material 120. The expansion rate of the target 121 modified in this way 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 immediately before impacting the surface of the target material.

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

The rate of expansion of the modified target 121 depends, at least in part, on the amount of energy in the pulse of the first radiation beam 110 that the target material 120 intercepts. In the hypothetical reference design, the target material 120 is assumed to always be the same size and located at the waist of the focused first radiation beam 110. However, in practice, the target material 120 may have a small but substantially constant axial position offset with respect to the beam waist of the first radiation beam 110. If all these factors are held constant, one factor that controls the expansion rate of the modified target 121 is the first radiation for pulses of the first radiation beam 110 having a duration of a few nanoseconds to 100 ns. This is the pulse energy of the beam 110. Another factor that can control the rate of expansion of the modified target 121 when the pulse of the first radiation beam 110 has a duration of 100 ns or less is the instantaneous peak power of the first radiation beam 110. am. Other factors may control the rate of expansion of the modified target 121 if the pulses of the first radiation beam 110 have a shorter duration, for example, in units of picoseconds (ps). This will be discussed later.

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

The first target location 111 receives target material 120, such as tin, from the target material supply system 125. Due to the interaction between the first radiation beam 110 and the target material 120, energy is transferred to the target material 120 and its shape is modified or changed (e.g., deformed), thereby modifying the geometric distribution of the target material 120. transformed into a target 121. Target material 120 is generally oriented from target material supply system 125 along the -X axis or along a direction that places target material 120 within first target location 111 . After the first radiation beam 110 transfers energy to the target material 120 and transforms it into a modified target 121, the modified target 121 moves along another direction, for example parallel to the Z direction. In addition to doing so, you can continue moving in the -X direction. As the modified target 121 moves from the first target position 111, its geometric distribution continues to deform until the modified target 121 reaches the second target position 116. The interaction between the modified target 121 (at the second target location 116) and the second radiation beam 115 causes at least a portion of the modified target 121 to emit EUV light or radiation 130. converted to plasma (129). A light collector system (or light collector) 135 focuses this EUV light 130 into focused EUV light 140 and directs it toward an optical device 145, such as a lithography tool. The first and second target locations 111 and 116 and the light collector 135 may be housed within a chamber 165 that provides a controlled environment suitable for generation of EUV light 140.

When the target material 120 interacts with the first radiation beam 110 it is possible that a portion of the target material 120 is converted into a plasma, such that this plasma can emit EUV radiation. However, the first radiation beam 110 may be used such that the dominant action on the target material 120 is to transform or modify the geometric distribution of the target material 120 to form a modified target 121. The characteristics of beam 110 are selected and controlled.

The first radiation beam 110 and the second radiation beam 115 are directed toward respective target locations 111 and 116 by the beam delivery system 150, respectively. The beam delivery system 150 includes an optical steering component 152 and a focus assembly 156 that focuses the first radiation beam 110 and the second radiation beam 115 to a first focal region and a second focal region, respectively. It can be included. The first and second focus areas may overlap the first target location 111 and the second target location 116, respectively. Optical component 152 may include optical elements, such as lenses and/or mirrors, that direct radiation beams 110, 115 by refraction and/or reflection. Beam delivery system 150 may also include elements that control and/or move optical components 152. For example, beam delivery system 150 may include controllable actuators to move optical elements within optical component 152.

Referring also to FIG. 2 , the focus assembly 156 focuses the first radiation beam 110 such that the diameter D1 of the first radiation beam 110 is minimized in the first focus area 210 . In other words, the focus assembly 156 causes the first radiation beam 110 to converge as it propagates toward the first focus area 210 in the first axial direction 212, which direction is the first radiation beam 110. ) is the normal propagation direction. The first axial direction 212 extends along the plane defined by the X-Z axis. In this example, the first axial direction 212 is parallel or substantially parallel to the Z direction, but may also be at an angle to the Z direction. In the absence of target material 120, the first radiation beam 110 becomes divergent as it propagates from the first focal area 210 in the first axial direction 212.

Additionally, the focus assembly 156 focuses the second radiation beam 115 such that the diameter D2 of the second radiation beam 115 is minimal in the second focus area 215. Accordingly, the focus assembly causes the second radiation beam 115 to converge as it propagates in the second axial direction 217 toward the second focal area 215, which direction is the normal direction of the second radiation beam 115. It is the direction of propagation. The second axial direction 217 also extends along the plane defined by the X-Z axis, 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 radiation beam 115 becomes divergent as it propagates from the second focal area 215 in the first axial direction 217 .

As discussed below, EUV light source 100 also includes one or more measurement system 155, control system 160, and beam steering system 180. Control system 160 controls other components within light source 100, such as measurement system 155, beam delivery system 150, target material supply system 125, beam steering system 180, and optical source 105. ) is connected to. Measurement system 155 may measure one or more characteristics within light source 100. For example, one or more of these properties may be properties associated with the target material 120 or the modified target 121 relative to the first radiation beam 110 . As another example, one or more characteristics may be the pulse energy of the first radiation beam 110 directed toward the target material 120. These examples will be described in more detail later. Control system 160 is configured to receive one or more measured properties from the measurement system to control how first radiation beam 110 interacts with target material 120. For example, control system 160 may be configured to maintain the amount of energy delivered from first radiation beam 110 to target material 120 within a predetermined energy range. As another example, control system 160 may be configured to control the amount of energy directed from first radiation beam 110 to target material 120. Beam steering system 180 adjusts components within optical source 105 , or such components within optical source 105 , to adjust the properties of first radiation beam 110 (e.g., pulse width, pulse energy, instantaneous power within a pulse, It is a system that includes components that control (or average power within a pulse).

3A , in a particular implementation, optical source 105 includes a first optical amplifier system 300 including a series of one or more optical amplifiers through which a first radiation beam 110 passes, and a second radiation beam. and a second optical amplifier system 305 comprising a series of one or more optical amplifiers through which 115 passes. One or more amplifiers from first system 300 may be in second system 305; Alternatively, one or more amplifiers in the second system 305 may be within the first system 300. Alternatively, the first optical amplifier system 300 may be completely separate from the second optical amplifier system 305.

Additionally, although not required, the optical source 105 may include a first light generator 310 that generates the first pulsed light beam 311 and a second light generator 310 that generates the second pulsed light beam 316. It may include a light generator 315. Light generators 310 and 315 may each be, for example, a laser, a seed laser (eg, a master oscillator), or a lamp. Exemplary light generators that may be used as light generators 310, 315 are Q-switched, radio frequency (RF) pumped, axial flow, carbon dioxide (CO ₂ ) oscillators, which may operate at a repetition rate of, for example, 100 kHz.

Each optical amplifier in the optical amplifier systems 300, 305 includes a gain medium on a respective beam path along which the light beams 311, 316 from the respective light generators 310, 315 propagate. . When the gain medium of the optical amplifier is excited, the gain medium provides photons to the light beam to amplify the light beams 311 and 316, thereby forming the amplified light beam to form a first radiation beam 110 or a second radiation beam 115. is created.

The wavelengths of the light beams 311 and 316 or the radiation beams 110 and 115 may be distinct so that the radiation beams 110 and 115 can be separated from each other when combined at any point within the optical source 105. When the radiation beams 110, 115 are generated 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. It may have a wavelength of ㎛. These wavelengths are selected to facilitate separation of the two radiation beams 110, 115 using dispersive optics or dichroic mirrors or beamsplitter coatings. In situations where the two radiation beams 110, 115 propagate together in the same amplifier chain (e.g., in situations where several of the amplifiers of optical amplifier system 300 are within optical amplifier system 305), although both radiation beams 110 , 115) may be used to adjust the relative gain between the two radiation beams 110, 115, even though they are traversing through the same amplifier.

For example, radiation beams 110 and 115 may be steered or focused to two distinct locations within chamber 165 once separated (e.g., first and second target locations 111 and 116, respectively). In particular, when the radiation beams 110 and 115 are separated, they also interact with the first radiation beam 110 while the first radiation beam 110 progresses from the first target location 111 to the second target location 116. After this, the modified target 121 can be expanded.

The optical source 105 may include a beam path combiner 325 that overlays the first radiation beam 110 and the second radiation beam 115 to couple the first radiation beam 110 and the second radiation beam 115 between the optical source 105 and the beam delivery system 150. The radiation beams 110 and 115 are disposed on the same optical path for at least part of the distance. An exemplary beam path combiner 325 is shown in FIG. 3B. Beam path combiner 325 includes a pair of dichroic beam splitters 340 and 342 and a pair of mirrors 344 and 346. Dichroic beam splitter 340 allows first radiation beam 110 to pass along a first path to dichroic beam splitter 342. The dichroic beam splitter 340 reflects the second radiation beam 115 along a second path, within which the second radiation beam 115 is reflected from the mirrors 344, 346, The mirror redirects the second radiation beam 115 toward the dichroic beam splitter 342. The first radiation beam 110 freely passes through the dichroic beam splitter 342 and reaches the output path, and the second radiation beam 115 is reflected from the dichroic beam splitter 342 onto the output path. , both the first and second radiation beams 110, 115 overlap on this output path.

Additionally, the optical source 105 may include a beam path splitter 326 that separates the first radiation beam 110 from the second radiation beam 115 such that the two radiation beams 110, 115 Can be steered and focused separately within chamber 165. An exemplary beam path splitter 326 is shown in FIG. 3C. Beam path splitter 326 includes a pair of dichroic beam splitters 350, 352 and a pair of mirrors 354, 356. Dichroic beam splitter 350 receives the overlapping pair of radiation beams 110, 115 and reflects the second radiation beam 115 along the second path and the first radiation beam 110 along the first path. It is transmitted and directed to the dichroic beam splitter (352). The first radiation beam 110 is free to pass through the dichroic beam splitter 352 and follows a first path. The second radiation beam 115 reflects from the mirrors 354 and 356 and returns to the dichroic beam splitter 352, where it is reflected onto a second path that is separate from the first path.

Additionally, the first radiation beam 110 may be configured to have a pulse energy that is less than the pulse energy of the second radiation beam 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 convert the modified target 121 into plasma 129. . For example, the pulse energy of the first radiation beam 110 may be 5 to 100 times smaller than the pulse energy of the second radiation beam 115.

In a particular implementation, as shown in FIGS. 4A and 4B, optical amplifier system 300 or 305 includes a set of three optical amplifiers 401, 402, 403 and 406, 407, 408, respectively, but one An optical amplifier or four or more optical amplifiers may be used. In certain embodiments, each optical amplifier 406, 407, 408 includes a gain medium comprising CO ₂ and is capable of amplifying light of a wavelength of about 9.1 to about 11.0 μm, particularly about 10.6 μm, with a gain of greater than 1000. can do. Optical amplifiers 401, 402, 403 may be operated at similar or different wavelengths. Amplifiers and lasers suitable for use in optical amplifier systems 300, 305 may include pulsed laser devices, such as pulsed gas discharge CO ₂ amplifiers, which can operate at relatively high powers, such as 10 kW or more. , operates at high pulse repetition rates, for example above 50 kHz, and produces radiation at about 9.3 μm or about 10.6 μm using, for example, DC or RF excitation. Exemplary optical amplifiers 401, 402, 403 or 406, 407, 408 are axial high power CO ₂ lasers that utilize wear-free gas circulation and capacitive RF excitation, such as the TruFlow CO 2 laser produced by TRUMPF, Farmington, CT. ₂ It's a laser.

Additionally, although not required, one or more optical amplifier systems 300 and 305 may include a first amplifier operating as a pre-amplifier 411 and 421, respectively. If a pre-amplifier 411, 421 is provided, it may be a diffusion cooled CO2 laser system, such as the TruCoax _CO2 laser produced by TRUMPF, Farmington, Connecticut.

Optical amplifier systems 300 and 305 may include optical elements for directing and shaping the respective light beams 311 and 316, which are not shown in FIGS. 4A and 4B. For example, optical amplifier systems 300 and 305 may include reflective optics such as mirrors, partially transmissive optics such as beam splitters or partially transmissive mirrors, and dichroic beam splitters.

Optical source 105 may also include one or more optics (e.g., reflective optics such as mirrors, partially reflective and partially transmissive optics such as beam splitters) for directing light beams 311, 316 through optical source 105. It includes an optical system 320 that may include refractive optics such as a glass, a prism, or a lens, passive optics, active optics, etc.).

Although optical amplifiers 401, 402, 403 and 406, 407, 408 are shown as separate blocks, at least one of amplifiers 401, 402, 403 may be within optical amplifier system 305, and amplifier 406 , 407, 408) may be within the optical amplifier system 300. For example, as shown in FIG. 5, the amplifiers 402 and 403 correspond to the respective amplifiers 407 and 408, and the optical amplifier systems 300 and 305 are configured to output the amplifiers 401 and 406. Additional optical elements 500 (e.g., beam path combiner 325) for combining two optical beams into a single path through amplifiers 402/407 and 403/408. Optical amplifier system 300 , 305), in which at least some of the amplifiers and optics overlap, the first radiation beam 110 and the second radiation beam 115 are coupled together to produce one or more characteristics of the first radiation beam 110. A change may cause a change in one or more properties of the second radiation beam 115, and vice versa, and thus the energy delivered to the target material 120 or the energy of the first radiation beam 110 within the system. It becomes even more important to control the energy of etc. Additionally, the optical amplifier systems 300 and 305 also separate the two light beams 100 and 115 output from the amplifiers 403/408 to form two light beams ( Includes an optical element 505 (e.g., beam path splitter 326) that allows 110, 115 to be directed to respective target locations 111, 116.

Target material 120 may be any material including a target material that emits 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 with an emission line in the EUV band. The target material may be, for example, a droplet of a liquid or molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained within a liquid droplet, a foam of the target material, or a solid particle contained within a portion of the liquid stream. It can be. The target material may be, for example, water, tin, lithium, xenon, or any material that has an emission line in the EUV band when converted to a plasma state. For example, target materials include pure tin (Sn); Elemental tin, which can be used as a tin compound (e.g., SnBr ₄ , SnBr ₂ , SnH ₄ ), a tin alloy (e.g., a tin gallium alloy, a tin indium alloy, a tin-indium-gallium alloy, or any combination of these alloys). It can be. Furthermore, in the absence of any impurities, the target material contains only the target material. The following discussion deals with an example where the target material 120 is a droplet made of molten metal such as tin. However, target material 120 may take other forms.

The target material 120 is moved to the first target location 111 by passing the molten target material through the nozzle of the target material supply device 125 and allowing the target material 120 to drift to the first target location 111. can be provided. In certain implementations, the target material may be forcibly directed to the first target location 111 .

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

The interaction between the first radiation beam 110 and the target material 120 causes ablation of material from the surface of the target material 120 (and the modified target 121 ), and this ablation causes the target material 120 ) is provided to transform the target material 120 into a modified target 121 having a shape different from that of the target material 120. For example, the target material 120 may have a shape similar to a droplet, but the shape of the modified target 121 may be such that when it reaches the second target location 116 its shape is that of a disk (e.g., a pancake shape). ) is transformed to get closer to The modified target 121 may be a non-ionized material (non-plasma material) or a 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 substantial gaps, a mist of micro or nanoparticles, or a cloud of atomic vapor. For example, as shown in FIG. 2 , the modified target 121 is able to contact the molten metal 121 within the second target location 116 after a time of approximately T2-T1 (which may be in microseconds (μs)). is expanded into a disk-shaped piece of

Additionally, the interaction between the first radiation beam 110 and the target material 120 causes material to be ablated from the surface of the target material 120 (and the modified target 121) and this ablation causes the modified target to (121) A force may be provided to achieve a specific thrust or velocity along the Z direction. The expansion of the modified target 121 in the depends on

For example, for a given target material 120 size and a long pulse of the first radiation beam 110 (long pulses having a duration of a few nanoseconds (ns) to 100 ns), the expansion rate is It is linearly proportional to the energy per unit area of the beam 110 (J/cm ² ). This energy per unit area is also called radiation exposure or radiation fluence. The radiation exposure amount is the radiant energy received by the surface of the target material 120 per unit area, or the irradiance of the surface of the target material 120 accumulated over the time that the target material 120 is irradiated.

As another example, for a given target material 120 size and short pulses (pulses with a duration of less than a few hundred picoseconds (ps)), the relationship between the expansion rate and the energy of the first radiation beam 110 may be different. there is. In this case a shorter pulse duration is correlated with an increase in the intensity of the first radiation beam 110 interacting with the target material 120, which acts like a shock wave. In this case, the expansion rate mainly depends on the intensity (I) of the first radiation beam 110, which intensity is determined by converting the energy (E) of the first radiation beam 110 to the first radiation interacting with the target material 120. It is equal to the spot size (cross-sectional area A) of the beam 110 divided by the pulse duration (τ) (or I=E/(Aτ)). In the case of this picosecond pulse duration, the modified target 121 expands to form mist.

Additionally, the angular orientation of the disk shape of the modified target 121 (angle relative to the Z or Accordingly, the first radiation beam 110 impinges on the target material 120 such that the first radiation beam 110 surrounds the target material and the beam waist of the first radiation beam 110 is centered on the target material 120. In the case of the disk shape of the modified target 121, there is a high possibility that the major axis 230 is parallel to the X direction and the minor axis 235 is aligned parallel to the Z direction.

The first radiation beam 110 consists of pulses of radiation, and each pulse may have a duration. Likewise, the second radiation beam 115 consists of pulses of radiation, each pulse having a duration. Pulse duration can be expressed in terms of full width at some fraction (half maximum) of the maximum, i.e. the amount of time a pulse has an intensity that is at least a fraction of the maximum intensity of this pulse. However, other metrics may be used to determine pulse duration. The pulse duration of the pulse within the first radiation beam 110 may be, for example, 30 nanoseconds (ns), 60 ns, 130 ns, 50-250 ns, 10-200 picoseconds (ps), or less than 1 ns. The energy of the first radiation beam 110 may be, for example, 1-100 millijoules (mJ). The wavelength of the first radiation beam 110 may be, for example, 1.06 μm, 1-10.6 μm, 10.59 μm, or 10.26 μm.

As seen above, the expansion rate of the modified target 121 depends on the radiation exposure dose (energy per unit area) of the first radiation beam 110 intercepted by the target material 120. Therefore, for a pulse of first radiation beam 110 with a duration of about 60 ns and an energy of about 50 mJ, the actual radiation exposure depends on how close the first radiation beam 110 is to the first focal area 210. It depends on how well it is focused. As a specific example, the radiation exposure dose may be about 400-700 J/cm ² at the target material 120. However, the radiation exposure dose is very sensitive to the position of the target material 120 relative to the first radiation beam 110.

The second radiation beam 115 may be referred to as the main beam and consists of pulses that are released at a certain repetition rate. The second radiation beam 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 radiation beam 110 and the pulse of the second radiation beam 115 are delayed in time by a predetermined delay time (e.g., 1-3 microseconds (μs), 1.3 μs, 1-2.7 μs, 3-4 μs or by any amount of time to allow expansion of the modified target 121 into the disk shape of the desired size shown in Figure 2). Accordingly, the modified target 121 undergoes two-dimensional expansion as it expands and elongates in the X-Y plane.

The second radiation beam 115 may be configured to be slightly defocused when impinging the modified target 121 . This defocusing technique is shown in Figure 2. In this case, the second focus area 215 is at a different position from the long axis 230 of the corrected target 121 along the Z direction; Furthermore, the second focus area 215 is outside the second target location 116 . In this technique, the second focus area 215 is placed in front of the modified target 121 along the Z direction. In other words, the second radiation beam 115 reaches focus (or beam waist) before impinging on the modified target 121. Other defocus techniques are also possible. For example, as shown in Figure 6, the second focus area 215 is disposed behind the modified target 121 along the Z direction. In this way, the second radiation beam 115 reaches focus (or beam waist) after impinging on the modified target 121.

Referring again to FIG. 2, the rate at which the modified target 121 expands while moving (e.g., drifting) from the first target position 111 to the second target position 116 may be referred to as the expansion rate (ER). . At the first target position 111, immediately after impact of the first radiation beam 110 on the target material 120 at time T1, the modified target 121 has dimensions taken along the major axis 230 (or length)(S1). When the modified target 121 reaches the second target position 116 at time T2, the modified target 121 has a dimension of S2 taken along the long axis 230. The expansion rate is the dimensional difference (S2-S1) of the modified target 121 taken along the long axis 230 divided by the time difference (T2-T1), and is therefore:

Although the modified target 121 is expanded along the major axis 230 , it is also possible for the modified target 121 to be compressed or thinned along the minor axis 235 .

In the two-stage approach discussed above, a modified target 121 is formed by interacting a first radiation beam 110 with a target material 120 and then interacting the modified target 121 with a second radiation beam 115. By allowing them to interact, the modified target 121 is converted to plasma, with this approach resulting in a conversion efficiency of approximately 3-4%. In general, if the conversion efficiency is too low, it may be necessary to increase the amount of power that the optical source 105 must deliver, which increases the cost of operating the optical source 105 and the heat load on all components within the light source 100. This may increase the generation of debris within the chamber housing the first and second target locations 111 and 116, so it is desirable to increase the efficiency of converting light from the optical source 105 into EUV radiation 130. Increasing conversion efficiency can help meet requirements for high-volume manufacturing tools while keeping optical source power requirements within acceptable limits. Various parameters affect the conversion efficiency, such as the wavelength of the first radiation beam 110 and the second radiation beam 115, the target material 120, and the pulse shape of the radiation beams 110, 115, These include energy, power, and intensity. The conversion efficiency is 2% bandwidth around the center wavelength of the reflectance curve of the (multilayer) mirror used for one or both of the light collector system 135 and the illumination and projection optics within the optics 145 and 2π steradians. , may be defined as the EUV energy generated by the EUV light 130 divided by the energy of the irradiation pulse of the second radiation beam 115. As an example, the central wavelength of the reflectance curve is 13.5 nm.

One way to increase, maintain or optimize the conversion efficiency is to control or stabilize the energy of the EUV light 130, which requires, among other parameters, the expansion rate of the modified target 121 to be within the range of acceptable values. It becomes important to maintain. The expansion rate of the modified target 121 is maintained within a range of acceptable values by maintaining the radiation exposure dose on the target material 120 from the first radiation beam 110. And the radiation exposure dose may be maintained based on one or more measured characteristics associated with the target material 120 or modified target 121 relative to the first radiation beam 110 . The radiation exposure amount is the radiation energy received by the surface of the target material 120 per unit area. Accordingly, if the area of the target material 120 is kept constant in pulse units, the radiation exposure amount can be estimated or approximated as the amount of energy directed toward the surface of the target material 120.

There are other methods or techniques to maintain the expansion rate of the modified target 121 within the range of acceptable values. The method or technique used may depend on the specific characteristics associated with the first radiation beam 110. The conversion efficiency can also be affected by other parameters, such as the size or thickness of the target material 120, the position of the target material 120 relative to the first focal area 210, or the angle of the target material 120 with respect to the x-y plane. You will receive it.

One characteristic that may affect how the radiation exposure dose 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 Rayleigh length is the distance from the waist along the propagation direction of the radiation beam to the point where the area of the cross section is doubled. 2, for a radiation beam 110, the Rayleigh length is equal to twice the cross-section of the first radiation beam from the waist (i.e. D1/2) along the propagation direction 212 of the first radiation beam 110. It is the distance to the point.

For example, as shown in FIG. 7A , the confocal parameter of the first radiation beam 110 is so long that the beam waist D1/2 easily surrounds the target material 120 to direct the first radiation beam 110. The area of the surface of the intercepted target material 120 (measured in the X direction) remains relatively constant even when the position of the target material 120 deviates from the position of the beam waist D1/2. For example, the surface area of the target material 120 that intercepts the first radiation beam 110 at location L1 is the surface area of the target material 120 that intercepts the first radiation beam 110 at location L2. It is within 20%. In the first scenario, there is a small probability that the surface area of the target material 120 intercepting the first radiation beam 110 deviates from the average value (compared to the second scenario described below); By maintaining the amount of energy directed at 120 (without having to take into account the surface area of the target material 120 exposed to the first radiation beam 110), the radiation exposure dose and thus the rate of expansion 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 cannot surround the target material 120, thereby preventing the beam waist D1/2 from surrounding the target material 120. When the position deviates from the position L1 of the beam waist D1/2, the surface area of the target material 120 intercepting the first radiation beam 110 deviates from the average value. For example, the surface area of the target material 120 that intercepts the first radiation beam 110 at location L1 is the surface area of the target material 120 that intercepts the first radiation beam 110 at location L2 and Quite different. In this second scenario, there is a high probability that the surface area of the target material 120 intercepting the first radiation beam 110 deviates from the average value (compared to the first scenario), and the surface area of the target material 120 intercepting the first radiation beam 110 is high. ) By controlling the amount of energy delivered to the radiation exposure dose and thus the expansion rate can be maintained or controlled. In order to control the radiation exposure amount, the radiation energy of the first radiation beam 110 received by the surface of the target material 120 per unit area is controlled. Accordingly, it is important to control the energy in the pulses of the first radiation beam 110 and the area of the first radiation beam 110 at which the target material 120 intercepts the first radiation beam 110 . The area of the first radiation beam 110 over which the target material 120 intercepts the first radiation beam 110 is correlated to the surface of the target material 120 across which the first radiation beam 110 is intercepted. Another factor that can affect the area of the first radiation beam 110 over which the target material 120 intercepts the first radiation beam 110 is that of the beam waist D1/2 of the first radiation beam 110. Stability of size and position. For example, if the waist size and position of the first radiation beam 110 are constant, the position of the target material 120 with respect to the beam waist D1/2 can be controlled. The waist size and position of the first radiation beam 110 may vary due to thermal effects within the optical source 105, for example. In general, a constant energy of the pulse is maintained within the first radiation beam 110 such that the target material 120 reaches a known axial (Z-direction) position with respect to the beam waist D1/2 without too much variation. Controlling different aspects of the optical source 105 becomes important.

All of the described methods of maintaining or controlling the rate of expansion of the modified target 121 within a range of acceptable values involve the use of the measurement system 155 described below.

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

As shown in FIG. 8B , example measurement system 855B measures the energy of radiation 860 reflected from target material 120 after first radiation beam 110 interacts with target material 120. do. Reflection of radiation 860 from target material 120 can be used to determine the position of target material 120 relative to the actual position of first radiation beam 110.

In a particular implementation, example measurement system 855B may be disposed within optical amplifier system 300 of optical source 105, as shown in FIG. 8C. Measurement system 855B in this example may be arranged to measure the amount of energy in reflected radiation 860 that strikes or reflects from one of the optical elements (e.g., thin film polarizer) within optical amplifier system 300. The amount of radiation 860 reflected from target material 120 is proportional to the amount of energy delivered to target material 120; Accordingly, by measuring the reflected radiation 860, the amount of energy delivered to the target material 120 can be controlled or maintained. Additionally, the amount of energy measured in the first radiation beam 110 or reflected radiation 860 is correlated to the number of photons in the beam. Accordingly, measurement system 855A or 855B can be said to measure the number of photons in each beam. Additionally, measurement system 855B calculates the number of photons reflected from target material 120 (which becomes a modified target upon impact with first radiation beam 110) to the number of photons impinging on target material 120. It can be considered to measure as a function of .

Measurement system 855A or 855B may be a photoelectric sensor, for example an array of photovoltaic cells (eg, a 2x2 array or a 3x3 array). The photocell has sensitivity to the wavelength of light to be measured and has a bandwidth or sufficient speed suitable for the duration of the light pulse to be measured.

Generally, measurement system 855A or 855B can measure the energy of radiation beam 110 by measuring the spatially integrated energy over a direction perpendicular to the direction of propagation of first radiation beam 110. Since the measurement of the energy of the beam can be made quickly, measurements can be performed for each pulse emitted from the first radiation beam 110, and thus measurement and control can be made on a pulse-by-pulse basis.

Measurement systems 855A, 855B may be high-speed photodetectors, such as photoelectromagnetic (PEM) detectors suitable for long-wave infrared (LWIR) radiation. The PEM detector may be a silicon diode for measuring near-infrared or visible radiation or an InGaAs diode for measuring near-infrared radiation. The energy of the pulse within the first radiation beam 110 may be determined by integrating the laser pulse signals measured by measurement systems 855A and 855B.

Referring to FIG. 9A , measurement system 155 may be an example measurement system 955A that measures the position (Tpos) of target material 120 relative to a target location. The target location may be at the beam waist of the first radiation beam 110. The position of target material 120 may be measured along a direction parallel to the beam axis of first radiation beam 110 (eg, first axial direction 212).

Referring to FIG. 9B , measurement system 155 may be an example measurement system 955B that measures the position (Tpos) of target material 120 relative to the primary focus 990 of light collector 135. This measurement system 955B is configured to measure the position of the target material 120 and the time of arrival of the target material 120 relative to the conditioning system within the chamber 165 as the target material 120 approaches. ) may include a laser and/or camera that reflects the light.

9C, measurement system 155 is an example measurement system 955C that measures the size of modified target 121 at a location before modified target 121 interacts with second radiation beam 115. ) can be. For example, the measurement system 955C may detect the modified target 121 while the modified target 121 is within the second target location 116 before the modified target 121 collides with the second radiation beam 115. ) can be configured to measure the size (Smt). Measurement system 955C may also determine the orientation of modified target 121. Measurement system 955C may utilize the shadowgraph technique of a pulsed backlighting illuminator and camera (eg, charge coupled device camera).

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

Measurement system 155 may include a plurality of EUV sensors within chamber 165 to detect EUV energy emitted from the plasma generated by modified target 121 after interacting with second radiation beam 115. You can. By detecting the emitted EUV energy, information regarding the angle of the modified target 121 or the transverse offset of the second beam with respect to the second radiation beam 115 can be obtained.

Beam steering system 180 is utilized under the control of control system 160 to enable control of the amount of energy (radiation exposure) delivered to target material 120. The radiation exposure dose is the energy within the first radiation beam 110 if it can be assumed that the area of the first radiation beam 110 is constant at the location where the first radiation beam 110 interacts with the target material 120. It can be controlled by controlling the amount of. Beam steering system 180 receives one or more signals from control system 160. Beam steering system 180 may be used to maintain the amount of energy delivered to target material 120 (i.e., radiation exposure) or to control the amount of energy directed to target material 120. It is configured to adjust one or more characteristics. Accordingly, beam steering system 180 may include one or more actuators that control characteristics of optical source 105, such as mechanical, electrical, optical, electronic, or other actuators to modify the characteristics of optical source 105. It may be any suitable force device for doing so.

In a particular implementation, beam steering system 180 includes a pulse width steering 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 adjustment system may include an electro-optical modulator, such as a Pockels cell. For example, a Pockels cell is arranged within the light generator 310 and opening such a Pockels cell for a shorter or longer period allows the pulses to be transmitted by the Pockels cell (and thus emitted from the light generator 310). pulse) can be adjusted to be shorter or longer.

In another implementation, beam steering system 180 includes a pulse power steering 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 adjustment system may include an acousto-optic modulator. The acousto-optic modulator may be arranged so that the power of the pulse diffracted from the acousto-optic modulator can be changed by changing the RF signal applied to the piezoelectric transducer at the edge of the modulator.

In certain implementations, beam steering system 180 includes an energy steering system coupled to first radiation beam 110 . The energy adjustment system is configured to adjust the energy of the first radiation beam 110. For example, the energy regulation system could be an electrically variable attenuator (eg, a Pockels cell varying between 0V and a half-wave voltage, or an external acousto-optic modulator).

In certain implementations, the position or angle of the target material 120 relative to the beam waist D1/2 is varied so significantly that the beam steering system 180 causes the first target position 111 in the steering system of the chamber 165. ) or with respect to other positions within the chamber 165. This device may be part of the focus assembly 156 and may be used to move the beam waist along the Z direction or along a direction transverse to the Z direction (e.g., along the plane defined by the X and Y directions). there is.

As discussed above, control system 160 analyzes information received from measurement system 155 and adjusts one or more characteristics of first radiation beam 110 to control and maintain the rate of expansion of modified target 121. Decide how to adjust. 10, control system 160 may include one or more sub-controllers 1000, 1005, 1010, 1015 that interface with other portions of light source 100, such as optical source 105. a sub-controller 1000 specifically configured for interfacing with (receiving information from and transmitting information to an optical source), a sub-controller 1005 specifically configured for interfacing with a measurement system 155, and interfacing with a beam delivery system 150. It may include a sub-controller 1010 configured to interface with the target material supply system 125, and a sub-controller 1015 configured to interface with the target material supply system 125. Light source 100 may include other components that may interface with control system 160, not shown in FIGS. 1 and 10. For example, light source 100 may include one or more targets or droplet imagers and a diagnostic system, such as a droplet position detection feedback system. The target imager provides, for example, an output indicative of the position of the droplet relative to a particular location (e.g., the primary focus 990 of the light collector 135) and provides this output to a droplet position detection feedback system, which feedback The system calculates, for example, the droplet position and trajectory, from which the droplet position error can be calculated on a per-droplet basis or on an average basis. In this way, the droplet position detection feedback system provides the droplet position error as an input to the sub-controller of the control system 160. Control system 160 may provide laser position, direction, and timing correction signals to a laser control system, e.g., within optical source 105, which may be used to control a laser timing circuit, for example, and/or a first A beam control system may be provided to control the position and shaping of the amplified light beam in the beam transport system to change the position and/or focal force of the focal plane of the radiation beam 110 or the second radiation beam 115.

Target material delivery system 125 includes a target material delivery control system, which is responsive to signals from control system 160 to correct for errors in the droplet of target material 120 reaching the desired target location 111. To correct, for example, it may operate to modify the release point of the droplet when released by an internal delivery mechanism.

Control system 160 generally includes one or more of digital electronic circuitry, computer hardware, firmware, and software. Control system 160 may also include appropriate input/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. It can be included. Furthermore, each sub-controller, such as sub-controllers 1000, 1005, 1010, and 1015, has its own appropriate input/output device, one or more programmable processors, and a storage device tangibly implemented in a machine-readable storage device for execution by the programmable processors. It may include one or more computer program products.

Each of these one or more programmable processors is capable of executing a program of instructions to perform the required function by operating on input data to produce appropriate output. A processor typically receives instructions and data from read-only memory and/or random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; Magnetic disks, such as internal hard disks and removable disks; magneto-optical disk; and CD-ROM disks. Any of these can be augmented by or integrated into a specially designed application specific integrated circuit (ASIC).

For this purpose, 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 is necessary to modify or control the energy delivered from the first radiation beam 110 to the target material 120 or to determine a method to modify or control the energy of the first radiation beam 110. All analysis is performed, and this analysis can be performed on a pulse-by-pulse basis if the measurement data is acquired on a pulse-by-pulse basis.

Referring to FIG. 11, the light source 100 performs a procedure for improving the conversion efficiency of the light source 100 by maintaining or controlling the expansion rate (ER) of the modified target 121 (under the control of the control system 160). (1100) is performed. Light source 100 provides target material 120 (1105). For example, target material supply system 125 may deliver target material 120 (under control of control system 160 ) to first target location 111 . The target material supply system 125 may include its own drive system (connected to the control system 160) and nozzles, through which the target material is moved, the drive system being positioned at the first target position 111. Control the amount of target material directed through the nozzle to create a stream of droplets directed toward the target.

Next, the light source 100 directs the first radiation beam 110 to the target material 120 to deliver energy to the target material 120 to modify the geometric distribution of the target material 120 to form the modified target 121. 120) and orient it towards (1110). In particular, the first radiation beam 110 is directed toward the target material 120 through a first set of one or more optical amplifiers 300. For example, the optical source 105 can be operated by the control system 160 to generate a first radiation beam 110 (in the form of pulses), where the first radiation beam 110 is shown in FIG. As such, it may be directed toward target material 120 within target location 111. The focal plane of the first radiation beam 110 (at beam waist D1/2) may be configured to intersect the target location 111. Furthermore, in certain embodiments, the focal plane may overlap the target material 120 or an edge portion of the target material 120 that faces the first radiation beam 110. The first radiation beam 110 may be directed to the target material 120, for example by directing the first radiation beam 110 through a beam delivery system 150, wherein the radiation 110 Various optics may be used to modify the direction or shape or divergence of radiation 110 so that it can interact with target material 120.

The first radiation beam 110 may be directed toward the target material 120 by overlapping the target material with an area of the first radiation beam surrounding the confocal parameters (1110). In certain embodiments, the confocal parameter of the first radiation beam 110 is so long that the beam waist D1/2 easily surrounds the target material 120 to intercept the first radiation beam 110. The area of the surface (measured in the For example, the confocal parameter of the first radiation beam 110 may be greater than 1.5 mm. In another embodiment, the confocal parameter of the first radiation beam 110 is so short that the beam waist D1/2 cannot surround the target material 120, so the position of the target material 120 is located at the beam waist D1/2. When deviating from the position L1 of 2), the surface area of the target material 120 that intercepts the first radiation beam 110 deviates significantly (see FIG. 7B). For example, the confocal parameter may be eg 2 mm or less.

The modified target 121 changes its shape from the shape of the target material 120 to an expanded shape immediately after impact by the first radiation beam 110, and this expanded shape is It continues to deform as it drifts toward the second target location 116. The modified target 121 may have a geometric distribution that is transformed from the shape of the target material to a disk-shaped volume of molten metal with a substantially planar surface (see, eg, FIGS. 1 and 2 ). The modified target 121 is transformed into a disk-shaped volume depending on the expansion rate. The modified target 121 is deformed by expanding the modified target 121 along at least one axis according to the expansion rate. For example, as shown in Figure 2, the modified target 121 is expanded along at least the long axis 230, which is 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 (i.e., the second axial direction 217).

Although the first radiation beam 110 primarily interacts with the target material 120 by changing the shape of the target material 120, the first radiation beam 110 may also interact with the target material 120 in other ways. possible; For example, the first radiation beam 110 may convert a portion of the target material 120 into plasma that emits EUV light. However, more radiation is emitted from the plasma generated from the target material 120 than is emitted from the plasma generated from the modified target 121 (due to subsequent interaction between the modified target 121 and the second radiation beam 115). Less EUV light is emitted and the dominant action on the target material 120 from the first radiation beam 110 is to modify the geometric distribution of the target material 120 to form a modified target 121 .

The light source 100 directs the second radiation beam 115 toward the modified target 121 such that the second radiation beam converts at least a portion of the modified target 121 into a plasma 129 that emits EUV light. becomes (1115). In particular, light source 100 directs a second radiation beam 115 toward modified target 121 through a second set of one or more optical amplifiers 305. For example, the optical source 105 can be operated by the control system 160 to generate a second radiation beam 115 (in the form of pulses), where the second radiation beam 115 is shown in FIG. As such, it may be directed towards the modified target 121 within the second target location 116. At least one of the optical amplifiers in the first set 300 may be in the second set 305, such as the example shown in FIG. 5.

Light source 100 measures 1120 one or more properties (e.g., energy) associated with one or more of target material 120 and modified target 121 relative to first radiation beam 110. For example, measurement system 155 measures these characteristics under the control of control system 160, and control system 160 receives measurement data from measurement system 155. Light source 100 controls the amount of radiation exposure from first radiation beam 110 to target material 120 based on one or more of these characteristics (1125). As discussed above, the radiation exposure dose is the amount of radiant energy delivered from the first radiation beam 110 to the target material 120 per unit area. In other words, this is the radiant energy received by the surface of the target material 120 per unit area.

In certain implementations, the characteristic that can be measured (at 1120) is the energy of the first radiation beam 110. In another general implementation, the properties that can be measured (at 1120) are the properties of the target material 120 relative to the position of the first radiation beam 110 (e.g., relative to the beam waist of the first radiation beam 110). It is a position, and this position can be determined in the longitudinal axis (Z) direction or in a direction transverse to the longitudinal axis direction (eg, X-Y plane).

The energy of the first radiation beam 110 can be measured by measuring the energy of radiation 860 reflected from an optically reflective surface of the target material 120 (e.g., as shown in FIGS. 8B and 8C). The energy of radiation 860 reflected from the optically reflective surface of target material 120 can be measured by measuring the total intensity of radiation 860 across four individual photocells.

The total energy content of the retroreflected radiation 860 is determined by determining the relative position between the beam waist of the first radiation beam 110 and the target material 120 along the Z direction or a direction transverse to the Z direction (e.g., the X-Y plane). It may be used in combination with other information about the first radiation beam 110 to make a decision. Alternatively, the total energy content of the retroreflected radiation 860 can be used (along with other information) to determine the relative position between the target material 120 and the beam waist of the first radiation beam along the Z direction.

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 (e.g., shown in FIG. 8A). The energy of the first radiation beam 110 may be measured by measuring the spatially integrated energy over a direction perpendicular to the direction of propagation of the first radiation beam 110 (first axial direction 212).

In certain implementations, the characteristic that can be measured (at 1120) is the orientation or direction of the first radiation beam 110 as it travels toward the target material 120 (shown in FIG. 8A being). This information about orientation can be used to determine the overlap error between the axis of the first radiation beam 110 and the position of the target material 120.

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

In certain implementations, the characteristic that may be measured (at 1120) is the size of the modified target before the second radiation beam converts at least a portion of the modified target to plasma.

In certain implementations, the measurable property (at 1120) corresponds to an estimate of the expansion rate of the modified target.

In certain implementations, the properties that can be measured (at 1120) correspond to the spatial properties of the radiation 860 reflected from the optically reflective surface of the target material 120 (e.g., shown in FIGS. 8B and 8C). . This information can be used to determine the relative position between the target material 120 and the beam waist of the first radiation beam 110 (eg, along the Z direction). These spatial characteristics can be determined or measured by using an astigmatism imaging system placed in the path of reflected radiation 860.

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

In another embodiment, the properties that can be measured (at 1120) correspond to the spatial aspect of the modified target 121 formed after the first radiation beam 110 interacts with the target material 120. For example, the angle of the modified target 121 may be measured relative to a direction, for example in the X-Y plane transverse to the Z direction. This information regarding the angle of the modified target 121 can be used to determine the distance between the axis of the first radiation beam 110 and the target material 120 along a direction transverse to the Z direction. As another example, the size or rate of expansion of the modified target 121 may be measured a predetermined or set time after it is first formed from the interaction between the target material 120 and the first radiation beam 110. This information about the size or expansion rate of the modified target 121 can be used to determine the size of the first radiation beam 110 along the longitudinal axis (Z direction), provided that the energy of the first radiation beam 110 is known to be constant. It can be used to determine the distance between the beam waist and target material 120.

Properties can be measured (at 1120) as quickly as for each pulse of the first radiation beam 110. For example, if the measurement system 155 includes a PEM or a quadcell (an array of four PEMs), the measurement speed can be as fast as pulse units.

On the other hand, for the measurement system 155 that is measuring properties such as size or expansion rate of the target material 120 or modified target 121, a camera may be used for this measurement system 155, but the camera is typically much slower, for example cameras can measure at rates of about 1 Hz to about 200 Hz.

In certain implementations, the amount of radiation exposure delivered from the first radiation beam 110 to the target material 120 may be controlled to control or maintain the rate of expansion of the modified target. In another embodiment, the amount of radiation exposure delivered from the first radiation beam 110 to the target material 120 is determined by determining whether a characteristic of the first radiation beam 110 should be adjusted based on one or more measured characteristics. Can be controlled (1125). Accordingly, 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 position of the first radiation beam 110 at the location of the target material 120 may be adjusted. The area of (110) can be adjusted. The energy content of the pulses of the first radiation beam 110 is determined by the pulse width of the first radiation beam 110, the pulse duration of the first radiation beam 110, and the average or instantaneous pulse of the first radiation beam 110. It can be adjusted by adjusting one or more of the powers. The area of the first radiation beam 110 that interacts with the target material 120 can be adjusted by adjusting the relative axial position (along the Z direction) between the beam waist of the first radiation beam 110 and the target material 120. You can.

In certain embodiments, the one or more characteristics may be measured for each pulse of the first radiation beam 110 (1120). In this way, for each pulse of the first radiation beam 110 it can be determined whether a characteristic of the first radiation beam 110 should be adjusted.

In certain embodiments, the radiation exposure delivered from the first radiation beam 110 to the target material 120 controls the radiation exposure while at least a portion of the emitted and focused EUV light 140 exposes the wafer of the lithography tool. This can be controlled (e.g., within a range of acceptable radiation exposure doses).

Procedure 1100 also includes collecting at least a portion of the EUV light 130 emitted from the plasma (using a light collector 135); and directing the focused EUV light 140 toward the wafer to expose the wafer to the EUV light 140.

In a particular implementation, the one or more measured characteristics (at 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 the number of photons striking the target material 120.

As discussed above, procedure 1100 includes controlling the amount of radiation exposure at target material 120 from first radiation beam 110 based on one or more characteristics. For example, the radiation exposure dose can be controlled to remain within a predetermined range of radiation exposure dose (1125). The radiation exposure dose is the amount of radiant energy delivered from the first radiation beam 110 to the target material 120 per unit area. In other words, this is the radiant energy received by the surface of the target material 120 per unit area. If the unit area of the surface of the target material 120 that is exposed to or intercepts the first radiation beam 110 is controlled (or maintained within an acceptable range), this factor in the radiation exposure dose is The radiation exposure dose at the target material 120 can be controlled or maintained 1125 by remaining relatively constant and maintaining the energy of the first radiation beam 110 within an acceptable energy range. There are various methods for maintaining the unit area of the surface of the target material 120 exposed to the first radiation beam 110 within an acceptable area range.

The radiation exposure dose at the target material 120 from the first radiation beam 110 (at 1125) is determined by the energy of the pulse of the first radiation beam 110 (by feedback control using the characteristics measured at 1120). This energy can be controlled to remain at a constant level or within a range of acceptable values despite disturbances that may cause it to fluctuate.

In another aspect, the radiation exposure dose at the target material 120 from the first radiation beam 110 (at 1125) is oriented along the longitudinal axis of the position of the target material 120 relative to the beam waist of the first radiation beam 110. The energy of the pulses of the first radiation beam 110 may be controlled to be adjusted (e.g., increased or decreased) by feedback control using the measured characteristics (at 1120) to compensate for errors in positioning (in the Z direction). .

First radiation beam 110 may be a pulsed radiation beam that causes pulses of light to be directed toward target material 120 (1110). Likewise, the second radiation beam 115 may be a pulsed radiation beam such that pulses of light are directed toward the modified target 121 (1115).

Target material 120 may be a droplet of target material 120 generated from target material supply system 125 . In this way, the geometric distribution of target material 120 can be modified into a modified target 121 which is transformed into a disk-shaped volume of molten metal with a substantially planar surface. The target material droplet is transformed into this disk-shaped volume depending on its expansion rate.

Referring to FIG. 12 , a control system is used by the light source 100 to stabilize the EUV light energy generated by the plasma 129 formed from the interaction between the modified target 121 and the second radiation beam 115. Procedure 1200 is performed (under the control of 160). Similar to the procedure 1100 discussed above, the light source 100 provides a target material 120 (1205); Light source 100 directs a first radiation beam 110 to target material 120 to deliver energy to target material 120 to modify the geometric distribution of target material 120 to form modified target 121. orienting toward (1210); The light source 100 directs the first radiation beam 110 toward the modified target 121 such that the second radiation beam converts at least a portion of the modified target 121 into a plasma 129 that emits EUV light. (1215). Light source 100 controls the amount of radiation exposure applied to target material 120 from first radiation beam 110 using procedure 1110 (1220).

The power or energy of EUV light 130 is stabilized by controlling the radiation exposure amount (1225). The EUV energy (or power) generated by the plasma 129 depends on at least two functions, the first being the conversion efficiency (CE) and the second being the energy of the second radiation beam 115. Conversion efficiency is the proportion of the modified target 121 that is converted to plasma 129 by the second radiation beam 115. The conversion efficiency depends on several variables, including the peak power of the second radiation beam 115, the size of the modified target 121 when interacting with the second radiation beam 115, and the modified target 121 for the required position. The location of the target 121, the cross-sectional area or size of the second radiation beam 115 at the moment of interaction with the modified target 121, etc. are included. 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 that the target material 120 is separated from the first radiation beam 110. By controlling the amount of radiation exposure applied to 120, the expansion rate of the modified target 121 can be controlled, thereby controlling these two factors. In this way, the conversion efficiency can be stabilized or controlled (1220) by controlling the radiation exposure dose, and the EUV energy produced by the plasma 129 is thereby stabilized (1225).

Referring also to FIG. 13 , in a particular implementation, the first radiation beam 110 may be generated by a dedicated subsystem 1305A within the optical source 105 and the second radiation beam 115 may be generated by the optical source 105. may be generated by dedicated separate subsystems 1305B within 105 so that the two radiation beams 110, 115 take two separate paths to the first and second target locations 111, 116, respectively. It follows. In this way, each radiation beam 110, 115 travels through a respective subsystem of beam delivery system 150 and thus a respective separate optical steering component 1352A, 1352B and focus assembly 1356A, 1356B. It proceeds through.

For example, subsystem 1305A may be a system based on a solid state gain medium, while subsystem 1305B may be a system based on a gaseous gain medium, such as that produced by a CO ₂ amplifier. Exemplary solid-state gain media that can be used with 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 separate from the wavelength of the second radiation beam 115. For example, the wavelength of the first radiation beam 110 using a solid-state gain medium may be about 1 μm (e.g., about 1.06 μm), and the wavelength of the second radiation beam 115 using a gaseous medium may be about 10.6 μm. It may be ㎛.

Other embodiments are also within the scope of the following claims.

Claims (33)

Providing a target material comprising a component that emits extreme ultraviolet (EUV) light when converted to plasma;
directing a first radiation beam toward the target material to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target;
Directing a second radiation beam toward the modified target, the second radiation beam converting at least a portion of the modified target into a plasma that emits EUV light;
measuring one or more characteristics associated with one or more of the target material and the modified target relative to the first radiation beam; and
Controlling the amount of radiation exposure delivered from the first radiation beam to the target material within a predetermined energy range based on one or more measured characteristics. According to paragraph 1,
Wherein measuring one or more properties associated with one or more of the target material and the modified target comprises measuring the energy of the first radiation beam. According to paragraph 2,
Measuring the energy of the first radiation beam may comprise: measuring the energy of the first radiation beam reflected from an optically reflective surface of the target material, or the energy of the first radiation beam directed toward the target material. A method comprising measuring. According to paragraph 2,
The method of claim 1, wherein measuring the energy of the first radiation beam comprises measuring spatially integrated energy over a direction perpendicular to the direction of propagation of the first radiation beam. According to paragraph 4,
Directing the first radiation beam toward the target material comprises overlapping the target material with an area of the first radiation beam encompassing a confocal parameter. According to paragraph 1,
The method of claim 1, wherein measuring 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 relative to a target location. According to clause 6,
The method of claim 1, wherein the first radiation beam is directed along a first beam axis and the position of the target material is measured along a direction parallel to the first beam axis. According to clause 6,
Wherein measuring the position of the target material includes measuring the position of the target material along two or more non-parallel directions. According to paragraph 1,
Measuring one or more properties associated with one or more of the target material and the modified target includes:
detecting the size of the modified target before the second radiation beam converts at least a portion of the modified target to plasma; and
Estimating the expansion speed of the modified target
Method, comprising one or more of: According to paragraph 1,
Wherein controlling the radiation exposure delivered to the target material from the first radiation beam based on the one or more measured characteristics includes controlling a rate of expansion of the modified target. According to paragraph 1,
Controlling the radiation exposure delivered from the first radiation beam to the target material based on the one or more measured characteristics may include whether a characteristic of the first radiation beam should be adjusted based on the one or more measured characteristics. A method comprising determining. According to clause 11,
When it is determined that a characteristic of the first radiation beam should be adjusted: adjusting one or more of the energy content of a pulse of the first radiation beam and the area of the first radiation beam that interacts with the target material. According to clause 12,
Adjusting the energy content of the pulses of the first radiation beam:
adjusting the width of the pulse of the first radiation beam;
adjusting the duration of pulses of the first radiation beam; and
adjusting the average power within a pulse of the first radiation beam
A method comprising one or more of the following: According to clause 11,
Directing the first radiation beam toward the target material includes directing a pulse of first radiation toward the target material,
Measuring the one or more characteristics includes measuring the one or more characteristics for each pulse of first radiation,
The method of claim 1 , wherein determining whether the characteristic of the first radiation beam should be adjusted comprises determining whether the characteristic should be adjusted for each pulse of first radiation. According to paragraph 1,
providing a target material includes providing a droplet of the target material,
Modifying the geometric distribution of the target material includes transforming the droplet of the target material into a disk-shaped volume of molten metal,
The method of claim 1, wherein the droplet of target material is transformed into the disk-shaped volume depending on its expansion rate. According to paragraph 1,
Directing the first radiation beam toward the target material also converts a portion of the target material into a plasma that emits EUV light, and converts more of the EUV light from the target material than is emitted from the plasma converted from the modified target. Less EUV light is emitted from the plasma, and the dominant action on the target material is to modify the geometric distribution of the target material to form the modified target. According to paragraph 1,
Modifying the geometric distribution of the target material includes transforming the shape of the target material into the modified target, including expanding the modified target along at least one axis according to an expansion rate,
Wherein controlling the radiation exposure dose delivered to the target material includes controlling the rate of expansion of the target material into the modified target. According to clause 17,
The method of claim 1, wherein the modified target is expanded along the at least one axis that is not parallel to the optical axis of the second radiation beam. According to paragraph 1,
Measuring one or more properties associated with one or more of the target material and the modified target includes measuring the energy of the first radiation beam directed toward the target material,
Controlling the amount of radiation exposure delivered to the target material includes adjusting the amount of energy directed to the target material from the first radiation beam based on the measured energy,
Directing the first radiation beam toward the target material comprises overlapping the target material with an area of the first radiation beam encompassing a confocal parameter. According to clause 19,
Wherein adjusting the amount of energy directed to the target material from the first radiation beam comprises adjusting a characteristic of the first radiation beam. According to paragraph 1,
Controlling the amount of radiation exposure delivered from the first radiation beam to the target material includes:
adjusting the energy of the first radiation beam immediately before the first radiation beam delivers the energy to the target material;
adjusting the position of the target material; and
adjusting the area of the target material that interacts with the first radiation beam
A method comprising one or more of the following: a chamber defining an initial target position for receiving the first radiation beam and a target position for receiving the second radiation beam;
a target material delivery system configured to provide 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 radiation beam and the second radiation beam;
As an optical steering system:
directing the first radiation beam toward the initial target location to deliver energy to the target material to modify the geometric distribution of the target material to form a modified target;
an optical steering system configured to direct the second radiation beam toward the target location to convert at least a portion of the modified target into a plasma that emits EUV light;
a measurement system that measures one or more properties associated with one or more of the target material and the modified target relative to the first radiation beam; and
a control system coupled to the target material delivery system, the optical source, the optical steering system, and the measurement system, the control system receiving one or more measured characteristics from the measurement system, the one or more measured characteristics and transmit one or more signals to the optical source to control the amount of radiation exposure delivered to the target material from the first radiation beam based on According to clause 22,
The optical steering system includes a focusing device configured to focus the first radiation beam at or near the initial target location and to focus the second radiation beam at or near the target location. device to do. According to clause 22,
The device further includes a beam steering system, the beam steering system coupled to the optical source and the control system, the control system being configured to adjust the energy delivered to the target material by transmitting one or more signals to the beam steering system. An apparatus configured to transmit one or more signals to the optical source to control the amount, and wherein the beam steering system is configured to maintain the amount of energy delivered to the target material by adjusting one or more characteristics of the optical source. According to clause 24,
The apparatus of claim 1, wherein the beam steering system includes a pulse width steering system coupled to the first radiation beam, and the pulse width steering system is configured to adjust a pulse width of a pulse of the first radiation beam. According to clause 25,
The apparatus of claim 1, wherein the pulse width adjustment system includes an electro-optical modulator. According to clause 24,
The apparatus of claim 1, wherein the beam steering system includes a pulse power adjustment system coupled to the first radiation beam, and the pulse power adjustment system is configured to adjust an average power within a pulse of the first radiation beam. According to clause 27,
The apparatus of claim 1, wherein the pulse power adjustment system includes an acousto-optic modulator. According to clause 24,
The beam steering system is configured to transmit one or more signals to the optical source to control the amount of energy directed to the target material by transmitting one or more signals to the beam steering system, wherein the beam steering system is configured to transmit one or more signals to the optical source to control the amount of energy directed to the target material. An apparatus configured to control the amount of energy directed to the target material by adjusting one or more characteristics of the source. According to clause 22,
The optical source is:
a first set of optical components including a first set of one or more optical amplifiers through which the first radiation beam passes; and
and a second set of optical components including a second set of one or more optical amplifiers through which the second radiation beam passes. According to clause 30,
At least one of the optical amplifiers in the first set is in the second set. According to clause 30,
wherein the first set of optical components are separate and distinct from the second set of optical components. According to clause 30,
the measurement system measures the energy of the first radiation beam when the first radiation beam is directed toward the initial target location,
The control system receives measured energy from the measurement system and transmits one or more signals to the optical source to control the amount of energy directed to the target material from the first radiation beam based on the measured energy. A device configured to: