KR20180038543A - A method for controlling a target expansion rate in an ultraviolet light source - Google Patents

Abstract

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

Description

A method for controlling a target expansion rate in an ultraviolet light source

This application is related to U.S. Patent Application No. 14 / 824,141, filed on August 12, 2015, entitled " TARGET EXPANSION RATE CONTROL IN AN EXTREME ULTRAVIOLET LIGHT SOURCE ", filed on August 12, 2015, U.S. Patent Application 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 for controlling the rate of expansion of a target material for a laser-generated plasma extreme ultraviolet light source.

Electromagnetic radiation containing extreme ultra-violet (EUV) light, for example, light having a wavelength of about 50 nm or less (often called soft x-ray) and having a wavelength of about 13 nm can cause extremely small features in the substrate, Lt; RTI ID = 0.0 > photolithography < / RTI >

The method of generating EUV light includes, but is not necessarily limited to, converting a material having an emission line in the EUV band in a plasma state, such as xenon, lithium or tin. In one such method, often referred to as a laser-generated plasma ("LPP"), the required plasma is applied to a target material in the form of a droplet, plate, tape, It can be generated by irradiating a light beam. For this process, the plasma is typically generated in a sealed vessel, e.g., a vacuum chamber, and monitored using various types of instrumentation.

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

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

The first radiation beam may be directed towards the target material by overlapping the target material with the area of the first radiation beam surrounding the confocal parameter. The confocal parameter may be greater than 1.5 mm.

One or more characteristics 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 position may coincide with the beam waist of the first radiation beam. The first radiation beam may be directed along a first beam axis and the position of the target material may be measured along a direction parallel to the first beam axis. The target position can be measured for the primary focus of the collector device that collects the emitted EUV light. The position of the target material can be measured by measuring the position of the target material along two or more non-parallel directions.

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

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

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

If it is determined that the characteristics of the first radiation beam should be adjusted: at least one of the energy content of the pulse of the first radiation beam and the area of the first radiation beam interacting with the target material can be adjusted. The energy content of the pulses 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 an average power in a pulse of the first radiation beam.

The first radiation beam may be directed toward the target material by directing a pulse of the first radiation toward the target material; The one or more characteristics may be measured by measuring one or more characteristics for each pulse of the first radiation; It may be determined whether the characteristics of the first radiation beam should be adjusted by determining whether the feature 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 that is transmitted from the first radiation beam to the target material while at least a portion of the emitted EUV radiation exposes the wafer.

The target material may be provided by providing droplets of the target material; The geometric distribution of the target material can be modified by deforming the droplet of the target material into a disk-shaped volume of molten metal. The droplet of the target material can be deformed into a disc-shaped volume according to the expansion rate.

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

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

The first radiation beam is directed toward the target material such that a portion of the target material can be converted to a plasma that emits EUV light and the less EUV radiation from the plasma converted from the target material than is emitted from the plasma converted from the modified target Light is emitted and the 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 deforming the shape of the target material into a modified target, including inflating the modified target along at least one axis in accordance with the inflation rate. The amount of radiation exposure delivered to the target material can be controlled by controlling the rate of expansion of the target material to the modified target.

The modified target may be inflated along the at least one axis, and such axis is not parallel to the optical axis of the second radiation beam.

One or more characteristics 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.

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

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

At least one characteristic associated with at least one of the target material and the modified target may be measured by measuring the energy of the first radiation beam that is directed toward the target material and the amount of radiation exposure delivered to the target material is determined based on the measured energy 1 < / RTI > radiation beam to the target material. The first radiation beam may be directed towards the target material by overlapping the target material with the area of the first radiation beam surrounding the confocal parameter and the confocal parameter may be less than or equal to 2 mm.

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

The amount of radiation exposure transmitted from the first radiation beam to the target material is determined by the energy of the first radiation beam immediately before the first radiation beam transmits energy to the target material; The location of the target material; And a region of the target material that interacts with the first radiation beam.

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

In another general aspect, an apparatus 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 a target material at an initial target position, the target material comprising a material that emits extreme ultra-violet (EUV) light when converted to a plasma; An optical source configured to generate a first radiation beam and a second radiation beam; Optical steering system. The optical steering system includes: directing a first radiation beam toward an initial target position to transmit energy to a target material to modify a geometric distribution of the target material to form a modified target, and directing at least a portion of the modified target with EUV light And direct the second beam of radiation toward the target position for conversion to an emitting plasma. The apparatus includes a measurement system for measuring at least one characteristic associated with at least one of a target material and a modified target relative to a 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 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 beam of radiation at an initial target position or near an initial target position and to focus a second beam of radiation at or near a target position.

The apparatus may comprise a beam conditioning system, wherein the beam conditioning system is coupled to an optical source and a control system, wherein the control system is operable to control the amount of energy transmitted to the target material by transmitting one or more signals to the beam conditioning system, Wherein the beam conditioning system is configured to maintain an 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 modulation system coupled to the first radiation beam and the pulse width modulation system is configured to adjust the pulse width of the pulses of the first radiation beam. The pulse width adjustment system may include an electro-optic modulator.

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

The beam conditioning system is configured to transmit one or more signals to an optical source to control the amount of energy directed to the target material by transmitting one or more signals to the beam conditioning system, And can be configured to control the amount of energy directed to the target material by tuning.

The optical source includes a first set of one or more optical amplifiers through which the first radiation beam passes; And a second set of one or more optical amplifiers through which the second beam of radiation 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 beam of radiation when the first beam of radiation is directed towards the initial target position, and the control system receives the measured energy from the measurement system and, based on the measured energy, And 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 comprises: providing a target material comprising a component that emits extreme ultra-violet (EUV) light when converted to a plasma; Directing a first beam of radiation toward a target material to transfer energy to the target material to modify a geometric distribution of the target material to form a modified target; Directing a second beam of radiation toward the modified target, the second beam of radiation converting at least a portion of the modified target into a plasma emitting EUV light; Controlling an amount of radiation exposure delivered to the target material from the first radiation beam to within a predetermined energy range; And stabilizing the power of the EUV light emitted from the plasma by controlling the amount of radiation exposure 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 may be directed by directing a first radiation beam through a first set of optical components comprising one or more optical amplifiers, and the second radiation beam may be directed by an optical component Lt; RTI ID = 0.0 > beam < / RTI > 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 the first set of one or more optical amplifiers and the second radiation beam may be directed by directing the second radiation beam through the second set of one or more optical amplifiers 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 deforming the droplet of the target material into a disk-shaped volume of molten metal having a substantially planar surface.

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 deforming the droplet of the target material into the mist-shaped volume of the molten metal particle.

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

The amount of radiation exposure delivered to the target material from the first radiation beam is determined by measuring at least one characteristic associated with at least one of the target material and the modified target relative to the first radiation beam; Can be controlled by maintaining the amount of radiation exposure delivered from the first radiation beam to the target material within a predetermined amount of radiation exposure based on the 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 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 maintaining the rate of inflation 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 the characteristics of the first radiation beam should be adjusted. The amount of radiation exposure delivered from the first radiation beam to the target material can be adjusted 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 interacting with the target material, Lt; / RTI > The energy content of the pulses of the first radiation beam is determined by the width of each pulse of the first radiation beam; The duration of each pulse of the first radiation beam; And the power of each pulse of the first radiation beam.

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

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

The geometric distribution of the target material may be modified by deforming the shape of the target material into a modified target, including inflating the modified target along at least one axis in accordance with the inflation 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 characteristics of the first radiation beam can be adjusted by adjusting the energy of the first radiation beam.

In another general aspect, an apparatus includes a chamber defining a first 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 a target material at an initial target position, the target material comprising a material that emits extreme ultra-violet (EUV) light when converted to a plasma; An optical source configured to generate a first radiation beam and a second radiation beam; Optical steering system. The optical steering system includes: directing a first radiation beam toward an initial target position to transmit energy to a target material to modify a geometric distribution of the target material to form a modified target, and directing at least a portion of the modified target with EUV light And direct the second beam of radiation toward the target position for conversion to an emitting plasma. The apparatus includes a target material delivery system, an optical source, and a control system coupled to the optical steering system, wherein the control system controls the amount of radiation emitted from the plasma by controlling the amount of radiation exposure delivered to the target material from the first radiation beam to within a predetermined radiation exposure dose range And to transmit one or more signals to the optical source to stabilize the power of the EUV light.

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

The apparatus may also include a beam conditioning system, wherein the beam conditioning system is coupled to an optical source and a control system, wherein the control system is operable to control one or more signals to be transmitted to the beam conditioning system, Wherein the beam conditioning system is configured to control an amount of radiation exposure delivered to the target material by adjusting one or more characteristics of the optical source.

Figure 1 is a cross-sectional view of a laser source including a first radiation beam directed to a target material and an optical source for generating a second radiation beam directed to a modified target to convert a portion of the modified target to a plasma emitting EUV light And is a block diagram of a plasma polarized ultraviolet light source.
Figure 2 is a schematic diagram illustrating a first radiation beam directed to a first target location and a second radiation beam directed to a second target location.
3A is a block diagram of an exemplary optical source used in the light source of FIG.
Figures 3b and 3c are block diagrams of an exemplary beam path coupler and an exemplary beam path splitter, respectively, that may be used in the optical source of Figure 1;
Figures 4A and 4B are block diagrams of an exemplary optical amplifier system that may be used in the optical source of Figure 3A.
Figure 5 is a block diagram of an exemplary optical amplifier system that may be used in the optical source of Figure 3A.
6 is a schematic diagram illustrating another embodiment of a first radiation beam directed to a first target location and a second radiation beam directed to a second target location.
Figures 7A and 7B are schematic diagrams illustrating an embodiment of a first radiation beam that is directed to a first target position.
Figures 8A-8C and 9A-9C show schematic diagrams of various embodiments of a measurement system for measuring at least one characteristic associated with any one or more of a target material, a modified target, and a first radiation beam.
Figure 10 is a block diagram of an exemplary control system of the light source of Figure 1;
11 is a flow diagram of an exemplary 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 rate of expansion ER of the modified target.
Figure 12 is a flow diagram of an exemplary 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 exemplary optical source for generating first and second radiation beams, an example for modifying the first and second radiation beams and focusing the first and second radiation beams to first and second target locations, respectively ≪ / RTI > FIG.

A technique for increasing the conversion efficiency of extreme ultraviolet (EUV) light generation is disclosed. Referring to Figure 1, the target material is deformed and geometrically expanded by interaction between the target material 120 and the first radiation beam 110 to form a modified target 121, as discussed in more detail below, . The geometric expansion rate of the modified target 121 is controlled in a manner that increases the amount of available EUV light 130 that is transformed from the plasma due to the interaction between the modified target 121 and the second radiation beam 115 do. The amount of EUV light 130 available is the amount of available EUV light 130 that can be utilized for use in the optics 145. Thus, 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 the EUV light 130.

Control of the geometric expansion rate of the modified target 121 enables control of the size or geometry of the modified target 121 when the modified target 121 interacts with the second radiation beam 115 . For example, adjustment of the geometric expansion rate of the modified target 121 adjusts the density of the modified target 121 when the modified target interacts with the second radiation beam 115; The density of the modified target 121 when the modified target interacts with the second radiation beam 115 affects the total amount of radiation absorbed by the modified target 121 and the extent to which such radiation is absorbed to be. As the density of the modified target 121 increases, the EUV light 130 will not be able to escape from the modified target 121 at a certain point and thus the amount of available EUV light 130 can be reduced. As another example, the adjustment of 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 total amount of available EUV light 130 that is generated can be increased or controlled by controlling the rate of expansion of the modified target 121. In particular, the size of the modified target 121 and its rate of expansion depend on the amount of radiant exposure applied to the target material 120 from the first radiation beam 110, which is measured by the first radiation beam 110 The amount of energy transferred to the region of the target material 120. [ The rate of expansion of the target 121 thus modified can be maintained or controlled by maintaining or controlling the amount of energy delivered to the target material 120 per unit area. The amount of energy delivered to the target material 120 depends on the energy of the first radiation beam 110 just prior to impacting the surface of the target material.

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

The rate of expansion of the modified target 121 is dependent, at least in part, on the amount of energy in the pulse of the first beam of radiation 110 struck by the target material 120. In a virtual reference design, it is assumed that the target material 120 is always the same size and is located in the waste of the focused first radiation beam 110. In practice, however, the target material 120 may have a small, but nearly constant, axial positional offset relative to the beam waist of the first radiation beam 110. One of the factors controlling the rate of expansion of the modified target 121, if all these factors are kept constant, is that the first radiation beam 110 for the pulses of the first radiation beam 110, which has a duration of several nanoseconds to 100 ns, Is the pulse energy of 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 to be. If the pulse of the first radiation beam 110 has a shorter duration, for example in units of picoseconds (ps), other factors can control the rate of expansion of the modified target 121, I will discuss it later.

An optical source 105 (also referred to as a drive source or drive laser) is used to drive a laser-generated plasma (LPP) extreme ultra-violet (EUV) light source 100, as shown in FIG. The optical source 105 produces a first radiation beam 110 provided at a first target position 111 and a second radiation beam 115 provided at a second target position 116. The second radiation beam 115 is incident on a second target position 116, The first and second radiation beams 110 and 115 may be pulsed amplified light beams.

The first target location 111 receives the target material 120, e.g., tin, from the target material supply system 125. The geometry of the target material 120 may be modified by modifying or altering (e.g., deforming) the shape of the target material 120 by transferring energy to the target material 120 due to interaction between the first radiation beam 110 and the target material 120. [ The target 121 is deformed. The target material 120 is generally oriented along the -X axis from the target material supply system 125 or in the direction of placing the target material 120 in the first target position 111. [ After the first radiation beam 110 transmits energy to the target material 120 and transforms it into a modified target 121, the modified target 121 is moved along another direction, e.g., a direction parallel to the Z direction It is possible to continue moving in the -X direction. As the modified target 121 moves from the first target position 111, its geometric distribution continues to be deformed until the modified target 121 reaches the second target position 116. At least a portion of the modified target 121 will emit EUV light or radiation 130 due to interaction between the modified target 121 and the second radiation beam 115 (at the second target position 116) And converted into a plasma 129. A light collector system (or light collector) 135 collects the EUV light 130 with the condensed EUV light 140 and directs it toward an optical device 145, such as a lithography tool. The first and second target positions 111 and 116 and the light collector 135 may be housed in a chamber 165 that provides a control environment suitable for the generation of the EUV light 140.

It is possible for a portion of the target material 120 to be converted to a plasma when the target material 120 interacts with the first radiation beam 110 so that such plasma can emit EUV radiation. It should be understood, however, that the dominant action on the target material 120 by the first radiation beam 110 is to modify or modify the geometric distribution of the target material 120, The characteristics of the beam 110 are selected and controlled.

The first radiation beam 110 and the second radiation beam 115 are each directed by the beam delivery system 150 toward the respective target locations 111, 116. The beam delivery system 150 includes an optical steering component 152 and a focus assembly 156 for focusing the first radiation beam 110 and the second radiation beam 115 into a first focus region and a second focus region, . The first and second focus regions may overlap the first target position 111 and the second target position 116, respectively. The optical component 152 may include optical elements, such as lenses and / or mirrors, that direct the beam of radiation 110, 115 by refraction and / or reflection. The beam delivery system 150 may also include an element that controls and / or moves the optical component 152. For example, the beam delivery system 150 may include an actuator that is controllable to move the optical element within the optical component 152.

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 region 210 in the first axial direction 212, ). ≪ / RTI > The first axial direction 212 extends along a plane defined by the X-Z axis. In this example, the first axial direction 212 is parallel or nearly parallel to the Z direction, but may be at an angle to the Z direction. In the absence of the target material 120, the first radiation beam 110 diverges as it propagates from the first focus region 210 in the first axial direction 212.

The focus assembly 156 focuses the second radiation beam 115 such that the diameter D2 of the second radiation beam 115 is at a minimum in the second focus area 215. [ The focus assembly thus allows the second radiation beam 115 to converge as it propagates in the second axial direction 217 toward the second focus area 215, Direction. The second axial direction 217 also extends along a plane defined by the X-Z axis, and in this example the second axial direction 217 is parallel or nearly parallel to the Z direction. In the absence of the modified target 121, the second radiation beam 115 diverges as it propagates from the second focus region 215 in the first axial direction 217.

As discussed below, the EUV light source 100 also includes one or more measurement systems 155, a control system 160, and a beam conditioning system 180. The control system 160 may include other components in the light source 100 such as a measurement system 155, a beam delivery system 150, a target material supply system 125, a beam conditioning system 180, and an optical source 105 . The measurement system 155 may measure one or more characteristics within the light source 100. For example, one or more of these characteristics may be characteristics associated with the target material 120 or the modified target 121 relative to the first radiation beam 110. In another example, the at least one characteristic may be the pulse energy of the first radiation beam 110 that is directed toward the target material 120. These examples will be described in more detail below. The control system 160 is configured to receive one or more measured characteristics from the measurement system and to control the manner in which the first radiation beam 110 interacts with the target material 120. For example, the control system 160 may be configured to maintain the amount of energy delivered to the target material 120 from the first radiation beam 110 within a predetermined energy range. As another example, the control system 160 may be configured to control the amount of energy directed from the first radiation beam 110 to the target material 120. The beam conditioning system 180 adjusts the components in the optical source 105 or these components in the optical source 105 to adjust the characteristics of the first radiation beam 110 (e.g., pulse width, pulse energy, Or average power in a pulse).

Referring to FIG. 3A, in a particular implementation, the optical source 105 includes a first optical amplifier system 300 comprising a series of one or more optical amplifiers through which a first radiation beam 110 passes, And a second optical amplifier system 305 comprising a series of one or more optical amplifiers through which the light beam 115 passes. One or more amplifiers from the first system 300 may be in the second system 305; Or one or more amplifiers in the second system 305 may be in 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 necessarily, the optical source 105 may include a first optical generator 310 generating a first pulsed optical beam 311 and a second optical generator 310 generating a second pulsed optical beam 316. [ And an optical generator 315. Each of the optical generators 310 and 315 may be, for example, a laser, a seed laser (e.g., a master oscillator), or a lamp. An exemplary optical generator that may be used as the optical generator 310, 315 is a Q-switch, radio frequency (RF) pumped, axial flow, carbon dioxide (CO ₂ ) oscillator, which may operate at a repetition rate of, for example, 100 kHz.

Each of the optical amplifiers in the optical amplifier system 300 and 305 includes a gain medium on a respective beam path and light beams 311 and 316 propagate from each of the optical generators 310 and 315 along this path . 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 amplifying the amplified light beam 110 forming the first radiation beam 110 or the second radiation beam 115 .

The wavelengths of the light beams 311 and 316 or the radiation beams 110 and 115 may be separate from each other so that when the radiation beams 110 and 115 are combined at any point within the optical source 105, When the radiation beams 110 and 115 are generated by a CO ₂ amplifier, the first radiation beam 110 may have a wavelength of 10.26 micrometers (占 퐉) or 10.207 占 퐉 and the second radiation beam 115 may have a wavelength of 10.59 Lt; RTI ID = 0.0 > um. ≪ / RTI > Such wavelengths are selected to facilitate separation of the two radiation beams 110, 115 using a dispersive optic or a dichroic mirror or beam splitter coating. (E.g., in a situation where some of the amplifiers in the optical amplifier system 300 are within the optical amplifier system 305), even though the two radiation beams 110,115 propagate together in the same amplifier chain , 115 may be traversed through the same amplifier, separate wavelengths may be used to adjust the relative gain between the two radiation beams 110, 115.

For example, the radiation beams 110 and 115 may be steered or focused into two distinct locations (e.g., first and second target locations 111 and 116, respectively) within the chamber 165 once separated. Particularly when the radiation beams 110 and 115 are separated the first radiation beam 110 also interacts with the first radiation beam 110 while traveling from the first target position 111 to the second target position 116 The modified target 121 may be inflated.

The optical source 105 may include a beam path coupler 325 which overlies the first radiation beam 110 and the second radiation beam 115 to provide a path between the optical source 105 and the beam delivery system 150 The radiation beams 110 and 115 are arranged on the same optical path with respect to at least a part of the distances of the radiation beams 110 and 115, respectively. An exemplary beam path coupler 325 is shown in Figure 3B. The beam path coupler 325 includes a pair of dichroic beam splitters 340 and 342 and a pair of mirrors 344 and 346. The dichroic beam splitter 340 allows the first radiation beam 110 to pass along a first path to the dichroic beam splitter 342. The dichroic beam splitter 340 reflects the second radiation beam 115 along a second path in which the second radiation beam 115 is reflected from the mirrors 344 and 346, The mirror redirects the second radiation beam 115 towards the dichroic beam splitter 342. The first radiation beam 110 passes freely through the dichroic beam splitter 342 onto 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 and 115 overlap on this output path.

The optical source 105 may include a beam path separator 326 that separates the first radiation beam 110 from the second radiation beam 115 so that the two radiation beams 110 and 115 And can be separately steered and focused within the chamber 165. An exemplary beam path separator 326 is shown in Figure 3c. The beam path separator 326 includes a pair of dichroic beamsplitters 350 and 352 and a pair of mirrors 354 and 356. The dichroic beam splitter 350 receives the overlapping pairs of the radiation beams 110 and 115 to reflect the second radiation beam 115 along the second path and to direct the first radiation beam 110 along the first path And directs it to the dichroic beam splitter 352. The first radiation beam 110 passes freely through the dichroic beam splitter 352 to follow the first path. The second radiation beam 115 is reflected from the mirrors 354 and 356 and returned to the dichroic beam splitter 352 where it is reflected on 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 to the 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.

4A and 4B, the optical amplifier system 300 or 305 includes a set of three optical amplifiers 401, 402, 403 and 406, 407, 408, respectively, 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 that includes CO ₂ and amplifies light at a wavelength of from about 9.1 to about 11.0 [mu] m, particularly about 10.6 [mu] m, can do. The optical amplifiers 401, 402, 403 may be operated with similar or different wavelengths. Amplifiers and lasers suitable for use in optical amplifier systems 300 and 305 may include pulsed laser devices, such as pulsed gas discharge CO ₂ amplifiers, which may be operated at relatively high power, for example, 10 kW or more , Operates at a high pulse repetition rate, e.g., 50 kHz or higher, and produces radiation at about 9.3 占 퐉 or about 10.6 占 퐉, for example, using DC or RF excitation. Exemplary optical amplifiers 401, 402, 403 or 406, 407, 408 may be used in conjunction with axial high power CO ₂ lasers using wear-free gas circulation and capacitive RF excitation, such as TruFlow CO, produced by TRUMPF, Inc. of Farmington, ₂ laser.

Additionally, although not required, one or more of the optical amplifier systems 300 and 305 may include a first amplifier, each operating as a pre-amplifier 411, 421. If pre-amplifiers 411, 421 are provided, this may be a diffusion cooled CO 2 laser system, such as the TruCoax CO ₂ laser produced by TRUMPF, Inc. of Farmington, Connecticut.

The optical amplifier system 300, 305 may include an optical element for directing and shaping each light beam 311, 316, which is not shown in Figures 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.

The optical source 105 may also include one or more optical elements for directing the light beams 311 and 316 through the optical source 105 (e.g., reflective optics such as mirrors, partially reflective and partially transmissive optics such as beam splitters, (E.g., refractive optics such as prism, prism or 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, , 407, and 408 may be within the optical amplifier system 300. 5, the amplifiers 402 and 403 correspond to the respective amplifiers 407 and 408, and the optical amplifier systems 300 and 305 correspond to the amplifiers 407 and 408 which are output from the amplifiers 401 and 406, respectively (E.g., beam path coupler 325) for coupling the two light beams into a single path through amplifiers 402/407 and amplifiers 403/408. Optical amplifier system 300 , 305), a first radiation beam (110) and a second radiation beam (115) are coupled together to form one or more characteristics of the first radiation beam (110) The change can cause a change in one or more characteristics of the second beam of radiation 115 and vice versa. Thus, the energy of the first beam of radiation 110, or energy delivered to the target material 120, It becomes much more important to control the energy of the light, etc. In addition, The amplifier system 300,305 also separates the two light beams 100,115 output from the amplifiers 403/408 and directs the two light beams 110,115 to their respective target positions 111,116. (E.g., a beam path separator 326) that allows the beam to pass through the beam splitter.

The target material 120 may be any material that includes a target material that emits EUV light when converted to a plasma. The target material 120 may be a target mixture comprising a target material and impurities such as non-target particles. The target material is a material that can be converted into a plasma state having an emission line in the EUV band. The target material may be, for example, liquid or molten metal droplets, a portion of a liquid stream, solid particles or clusters, solid particles contained within a liquid droplet, foam of a target material, or solid particles Lt; / RTI > The target material may be, for example, water, tin, lithium, xenon, or any material having an emission line in the EUV band when converted to a plasma state. For example, the target material may be pure tin (Sn); Tin compounds (e.g., SnBr _4, SnBr _2, SnH _4), tin alloy (e.g. tin gallium alloys, indium tin alloy, tin-indium-gallium alloy, or any combination of such an alloy) with elemental tin which can be used Lt; / RTI > Furthermore, in the absence of any impurities, the target material contains only the target material. The following discussion deals with a droplet example in which the target material 120 is made of a molten metal such as tin. However, the target material 120 may take other forms.

The molten target material is passed through the nozzle of the target material supply device 125 and the target material 120 is allowed to drift to the first target position 111, Can be provided. In certain embodiments, the target material may be forced to the first target position 111.

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

The material is ablated from the surface of the target material 120 (and the modified target 121) by interaction between the first radiation beam 110 and the target material 120, Is deformed into a modified target 121 having a shape different from the shape 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 is such that when the shape of the modified target 121 reaches the second target position 116, ). The modified target 121 may be an un-ionized material (a 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 the target material without voids or substantial gaps, a mist of micro- or nano-particles, or a cloud of atomic vapor. For example, as shown in FIG. 2, the modified target 121 may be molten metal 121 within a second target location 116 (which may be in microseconds (μs) Shaped piece of disk.

In addition, the interaction between the first radiation beam 110 and the target material 120 causes the material to be fluxed from the surface of the target material 120 (and the modified target 121) A force can be provided that allows the motor 121 to obtain a specific thrust or speed along the Z direction. The expansion of the modified target 121 in the X direction and the rate of acquisition in the Z direction are dependent on the energy of the first radiation beam 110, in particular the energy delivered to the target material 120 (i.e., the energy that the target material impinges) Lt; / RTI >

For example, for a given target material 120 size and a long pulse of the first radiation beam 110 (a long pulse that is a pulse with a duration of a few nanoseconds (ns) to 100 ns) And is linearly proportional to the energy per unit area (J / cm ² ) of the beam 110. This energy per unit area is also referred to as the radiation exposure dose or the radiation dose (fluence). The radiation exposure dose is the radiance of the surface of the target material 120 on which the surface of the target material 120 per unit area is radiated, or the time during which the target material 120 is irradiated.

As another example, the relationship between the rate of expansion and the energy of the first radiation beam 110 may be different for a given target material 120 size and for short pulses (pulses having a duration of less than several hundred picoseconds (ps) have. In such a 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, and the first radiation beam 110 acts like a shock wave. In this case, the rate of expansion is primarily dependent on the intensity I of the first radiation beam 110, which is such that the energy E of the first radiation beam 110 is greater than the energy of the first radiation < RTI ID = 0.0 > (Or I = E / (A?)) Divided by the spot size (cross-sectional area A) of the beam 110 and the pulse duration?. In the case of this picosecond pulse duration, the modified target 121 expands to form a mist.

Additionally, the angular orientation of the disk shape of the modified target 121 (angle with respect to the Z or X direction) depends on the position of the first radiation beam 110 when impinging on the target material 120. The first radiation beam 110 impinges on the target material 120 such that the first radiation beam 110 encircles the target material and the beam waist of the first radiation beam 110 impinges on the center of the target material 120 The modified shape of the target 121 is likely to be such that the long axis 230 is parallel to the X direction and the short axis 235 is aligned parallel to the Z direction.

The first radiation beam 110 is made up of pulses of radiation, each pulse having a duration. Likewise, the second radiation beam 115 consists of pulses of radiation, each pulse having a duration. The pulse duration can be represented by the full width at a predetermined rate (half value) of the maximum value, i. E. The pulse can be expressed in the amount of time having an intensity that is at least a predetermined percentage of the maximum intensity of such a pulse. However, other metrics may be used to determine the pulse duration. The pulse duration of the pulse in 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 占 퐉, 1-10.6 占 퐉, 10.59 占 퐉, or 10.26 占 퐉.

As discussed above, the rate of expansion 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. Thus, for a pulse of the first radiation beam 110 having a duration of about 60 ns and an energy of about 50 mJ, the actual amount of radiation exposure is dependent on how closely the first radiation beam 110 is in the first focus region 210 Depending on what is being focused. As a specific example, the amount of radiation exposure may be about 400-700 J / cm ² in the target material 120. However, the amount of radiation exposure is highly sensitive to the position of the target material 120 with respect to the first radiation beam 110.

The second radiation beam 115 may be referred to as a main beam and consists of pulses that are released at a predetermined 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 the EUV light 130. The pulse of the first radiation beam 110 and the pulse of the second radiation beam 115 are delayed by a predetermined delay time (e.g., 1-3 microseconds (μs), 1.3 μs, 1-2.7 μs, 3-4 μs Or any amount of time that allows the expansion of the modified target 121 to the disk shape of the required size shown in FIG. 2). Thus, the modified target 121 undergoes two-dimensional expansion as it expands and elongates on the X-Y plane.

The second beam of radiation 115 may be configured to slightly defocus when it collides with the modified target 121. This defocusing technique is shown in FIG. In this case, the second focus area 215 is at a different location from the long axis 230 of the modified target 121 along the Z direction; Further, the second focus area 215 is outside the second target position 116. [ In this technique, the second focus area 215 is disposed 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 it impinges on the modified target 121. Other defocus techniques are possible. For example, as shown in FIG. 6, the second focus region 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 impacting the modified target 121.

2, the rate at which the modified target 121 is expanded 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 . In the first target position 111, immediately after the first radiation beam 110 impacts the target material 120 at time T1, the modified target 121 has a dimension taken along the major axis 230 Length) S1. The modified target 121 has a dimension of S2 taken along the long axis 230 when the modified target 121 reaches the second target position 116 at time T2. The expansion rate is the difference in the dimensions (S2-S1) of the modified target 121 taken along the long axis 230 divided by the time difference (T2-T1) and is thus:

It is also possible that the modified target 121 is expanded along the major axis 230 but the modified target 121 is compressed or thinned along the minor axis 235.

In the two-stage approach discussed above, the modified target 121 is formed by interacting the target material 120 with the first radiation beam 110 and then the modified target 121 is irradiated with the second radiation beam 115 By interacting, the modified target 121 is converted into a plasma, which results in a conversion efficiency of about 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 in the light source 100 It is desirable to increase the efficiency of converting the light from the optical source 105 into the EUV radiation 130 since the generation of debris in the chamber housing the first and second target positions 111 and 116 may be increased. Increasing the conversion efficiency can help meet the requirements for high volume manufacturing tools while keeping optical source power requirements within acceptable limits. Various parameters affect the conversion efficiency, for example, the wavelength of the first radiation beam 110 and the second radiation beam 115, the pulse shape of the target material 120, and the radiation beams 110 and 115, Energy, power, and strength. The conversion efficiency is determined by the 2% bandwidth around the center wavelength of the reflectance curve of the (multi-layer) mirror used in the light collector system 135 and either or both of the light collector system 135 and the illumination and projection optics within the optics device 145, Can be defined as the value obtained by dividing the EUV energy generated by the EUV light 130 by the energy of the irradiation pulse of the second radiation beam 115. [ As an example, the center 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 the expansion rate of the modified target 121, among other parameters, to be within a range of acceptable values It becomes important to keep. The rate of expansion of the modified target 121 is maintained within a range of acceptable values by maintaining the amount of radiation exposure on the target material 120 from the first radiation beam 110. [ And the amount of radiation exposure may be maintained based on one or more measured characteristics associated with the target material 120 or the modified target 121 relative to the first radiation beam 110. The radiation exposure dose is the radiant energy received by the surface of the target material 120 per unit area. Therefore, if the area of the target material 120 is kept constant in a pulse unit, the radiation exposure dose can be estimated or approximated by the amount of energy directed toward the surface of the target material 120. [

There are other methods or techniques for keeping the rate of expansion of the modified target 121 within acceptable values. The method or technique used may depend on the particular characteristic associated with the first radiation beam 110. [ The conversion efficiency is also influenced by other parameters such as the size or thickness of the target material 120, the position of the target material 120 with respect to the first focus area 210, or the angle of the target material 120 with respect to the xy plane .

One characteristic that can 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 to the point at which the area of the cross section doubles along the propagation direction of the radiation beam. Referring to FIG. 2, for a radiation beam 110, the Rayleigh length is determined such that 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 is doubled The distance to the point.

7A, the confocal parameter of the first radiation beam 110 is so long that the beam waist D1 / 2 can easily surround the target material 120 to form 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 intercepting the first radiation beam 110 at position Ll is greater than the surface area of the target material 120 intercepting the first radiation beam 110 at location L2 It is within 20%. In the first scenario, the probability that the surface area of the target material 120 intercepting the first radiation beam 110 deviates from the mean value (as compared to the second scenario described below) is small. From the first radiation beam 110, The amount of radiation exposure and hence the rate of expansion can be maintained or controlled (e.g., without taking into account the surface area of the target material 120 exposed to the first radiation beam 110) by maintaining an amount of energy directed at the first radiation beam 120 .

As another example, as shown in FIG. 7B, the confocal parameter of the first radiation beam 110 is so short that the beam waist D1 / 2 does not encompass the target material 120, The surface area of the target material 120 interfering with the first radiation beam 110 deviates from the average value when the position deviates from the position L1 of the beam waist D1 / 2. For example, the surface area of the target material 120 intercepting the first radiation beam 110 at location Ll is less than the surface area of the target material 120 intercepting the first radiation beam 110 at location L2, It is 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 (as compared to the first scenario) ), The amount of radiation exposure and thus the rate of expansion can be maintained or controlled. In order to control the radiation exposure dose, the radiation energy of the first radiation beam 110 received by the surface of the target material 120 per unit area is controlled. Thus, it is important that the target material 120 controls energy in the area of the first radiation beam 110 striking the first radiation beam 110 and in the pulse of the first radiation beam 110. The area of the first radiation beam 110 through which the target material 120 strikes the first radiation beam 110 is correlated to the surface of the target material 120 intercepting the first radiation beam 110. Another factor that may affect the area of the first radiation beam 110 that the target material 120 strikes the first radiation beam 110 is that of the beam waist D1 / 2 of the first radiation beam 110 Size and position stability. The position of the target material 120 relative to the beam waist D1 / 2 can be controlled, for example, if the first radiation beam 110 has a constant size and position of the waist. The size and location of the first radiation beam 110 may vary due to, for example, thermal effects within the optical source 105. Generally, it is desirable to maintain a constant energy of the pulse in the first radiation beam 110 so that the target material 120 arrives in a known axial (Z direction) position relative to the beam waist D1 / It becomes important to control other aspects of the optical source 105. [

All of the described methods of maintaining or controlling the rate of expansion of the modified target 121 within an acceptable value range entail the use of a measurement system 155, as described below.

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

8B, an exemplary measurement system 855B measures the energy of the radiation 860 reflected from the target material 120 after the first radiation beam 110 has interacted with the target material 120. For example, do. Reflection of the radiation 860 from the target material 120 may be used to determine the position of the target material 120 relative to the actual position of the first radiation beam 110.

8C, an exemplary measurement system 855B may be disposed within the optical amplifier system 300 of the optical source 105. In an alternative embodiment, In this example, measurement system 855B may be arranged to measure the amount of energy in reflected radiation 860 that impinges on or reflects on one of the optical elements (e.g., thin film polarizers) in optical amplifier system 300. [ The amount of radiation 860 reflected from the target material 120 is proportional to the amount of energy delivered to the target material 120; Thus, 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 the reflected radiation 860 is correlated with the number of photons in the beam. Thus, the measurement system 855A or 855B can be said to measure the number of photons in each beam. Additionally, the measurement system 855B may measure the number of photons reflected from the target material 120 (which is a modified target upon collision with the first radiation beam 110) As a function of < / RTI >

The measurement system 855A or 855B may be a photoelectric sensor, for example, an array of photovoltaic cells (e.g., a 2x2 array or a 3x3 array). Photovoltaic cells have sensitivity to the wavelength of the light to be measured and have a bandwidth or a sufficient speed for the duration of the optical pulse to be measured.

In general, the measurement system 855A or 855B can measure the energy of the radiation beam 110 by measuring the spatially-integrated energy in a direction perpendicular to the propagation direction of the first radiation beam 110. [ Since the measurement of the energy of the beam can be done quickly, measurements can be performed on each pulse emitted from the first radiation beam 110, so that measurement and control can be done on a pulse-by-pulse basis.

The measurement system 855A, 855B may be a high speed photodetector, for example a photoelectric (PEM) detector suitable for long wavelength 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 pulses in the first radiation beam 110 can be determined by integrating the laser pulse signals measured by the measurement systems 855A and 855B.

9A, the measurement system 155 may be an exemplary measurement system 955A that measures the position Tpos of the target material 120 relative to the target position. The target position may be in the beam waist of the first radiation beam 110. The position of the target material 120 may be measured along a direction parallel to the beam axis of the first radiation beam 110 (e.g., the first axial direction 212).

9B, the measurement system 155 may be an exemplary measurement system 955B that measures the position Tpos of the target material 120 with respect to the primary focus 990 of the light collector 135. As shown in FIG. Such a measurement system 955B may be used to measure the position of the target material 120 relative to the conditioning system within the chamber 165 and the time at which the target material 120 / RTI > and / or a camera that reflects the reflected light.

9C, the measurement system 155 includes an exemplary measurement system 955C that measures the size of the modified target 121 before the modified target 121 interacts with the second radiation beam 115 ). For example, the measurement system 955C may include a modified target 121 before the modified target 121 collides with the second radiation beam 115 while the modified target 121 is within the second target position 116. For example, (Smt) of the substrate W. The measurement system 955C may also determine the orientation of the modified target 121. The measurement system 955C may utilize the shadow graph technique of a pulsed backlighting illuminator and a camera (e.g., a charge coupled device camera).

The measurement system 155 may comprise a set of measurement subsystems, each of which is designed to measure a particular characteristic at a different rate or sampling interval. Such a set of subsystems may 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.

The measurement system 155 includes a plurality of EUV sensors in the chamber 165 for detecting EUV energy emitted from the plasma generated by the modified target 121 after interacting with the second radiation beam 115 . By detecting the emitted EUV energy, information about 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.

The beam conditioning system 180 is utilized under the control of the control system 160 to control the amount of energy delivered to the target material 120 (the amount of radiation exposure). The amount of radiation exposure can be calculated as the energy of the first radiation beam 110 within the first radiation beam 110 if the area of the first radiation beam 110 at a location where the first radiation beam 110 interacts with the target material 120 can be assumed to be constant. By controlling the amount of the gas. The beam steering system 180 receives one or more signals from the control system 160. The beam conditioning system 180 may be used to control the amount of energy transmitted to the target material 120 to maintain the amount of energy delivered to the target material 120 And is configured to adjust one or more features. The beam conditioning system 180 may thus include one or more actuators that control the characteristics of the optical source 105 such that the characteristics of the mechanical, electrical, optical, electronic, or optical source 105 may be modified Or any suitable force device for < / RTI >

In certain embodiments, the beam conditioning system 180 includes a pulse width modulation system coupled to the first radiation beam 110. The pulse width adjustment system is configured to adjust the pulse width of the first radiation beam (110). In this embodiment, the pulse width modulation system may comprise an electro-optic modulator, such as a Forklitz cell. For example, a forkloc cell is arranged in a light generator 310, and the pulse transmitted by the forkloc cell (and thus the emission from the light generator 310) by opening the forklell cell for a shorter or longer period of time May be adjusted to be shorter or longer.

In yet another embodiment, the beam conditioning system 180 includes a pulsed power adjustment system coupled to the 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 embodiment, the pulse power adjustment system may comprise an acousto-optic modulator. The acousto-optic modulator can be arranged to change the power of the pulse diffracted from the acousto-optic modulator by changing the change of the RF signal applied to the piezoelectric transducer at the edge of the modulator.

In certain embodiments, the beam conditioning system 180 includes an energy conditioning system coupled to the first radiation beam 110. The energy adjustment system is configured to adjust the energy of the first radiation beam (110). For example, the energy conditioning system may be an electrical-variable attenuator (e.g., a PoCz cell or an external acousto-optic modulator that is varied between 0V and half-wave voltage).

The position or angle of the target material 120 with respect to the beam waist D1 / 2 is changed very heavily such that the beam adjustment system 180 is positioned in the first target position 111 Or to control the position or angle of the beam waist D1 / 2 relative to other locations within the chamber 165. Such an apparatus may be part of the focus assembly 156 and may be used to move beam waist along a Z direction or along a direction transverse to the Z direction (e.g., along a plane defined by the X and Y directions) have.

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

The target material delivery system 125 includes a target material delivery control system that is responsive to a signal from the control system 160 to cause an error in reaching the desired target position 111 of the droplet of the target material 120 For example, to modify the release point of the droplet when released by an internal delivery mechanism for calibration.

Control system 160 generally includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system 160 may also include one or more computer program products 1030 that are implemented as a type in a machine readable storage device to be executed by a programmable processor and one or more programmable processors 1025, . Further, each subcontroller, such as subcontroller 1000, 1005, 1010, 1015, may be implemented as a type in a machine-readable storage device to be executed by its appropriate input / output device, one or more programmable processors, One or more computer program products.

Each of the one or more programmable processors may execute a program of instructions to perform the required function by operating on the input data and generating an appropriate output. Generally, a processor receives instructions and data from a read-only memory and / or a random access memory. Storage devices suitable for implementing computer program instructions and data types include all types of non-volatile memory, including semiconductor memory devices such as, for example, EPROM, EEPROM, and flash memory devices; Magnetic disks such as internal hard disks and removable disks; Magnetic optical disc; And a CD-ROM disc. Any of these may be reinforced by a specially designed ASIC (Application Specific Integrated Circuit) or integrated into an ASIC.

For this purpose, the control system 160 includes an analysis program 1040 that receives measurement data from one or more measurement systems 155. In general, analysis program 1040 may be used to determine or modify the energy delivered to target material 120 from first radiation beam 110 or to determine how to modify or control the energy of first radiation beam 110 All analyzes are performed, and this analysis can be performed on a pulse-by-pulse basis if the measurement data is obtained in pulse units.

Referring to Figure 11, the light source 100 includes a procedure for improving the conversion efficiency of the light source 100 by maintaining or controlling the rate of expansion ER of the modified target 121 (under the control of the control system 160) (1100). The light source 100 provides a target material 120 (1105). For example, the target material supply system 125 may deliver the target material 120 (under the control of the control system 160) to the first target position 111. The target material supply system 125 can include its own drive system (coupled to the control system 160) and nozzles through which the target material is moved and the drive system moves to the first target position 111, Lt; RTI ID = 0.0 > nozzle < / RTI > to produce a stream of droplets directed towards the nozzle.

Next, the light source 100 irradiates the first radiation beam 110 to the target material 120 to transmit energy to the target material 120 to modify the geometric distribution of the target material 120 to form the modified target 121 120) (1110). In particular, the first radiation beam 110 is directed toward the target material 120 through the first set of one or more optical amplifiers 300. For example, the optical source 105 may be activated by the control system 160 to generate a first radiation beam 110 (in the form of a pulse), and the first radiation beam 110 may be activated And may be directed toward the target material 120 within the target location 111 as shown. The focal plane (in the beam waist D1 / 2) of the first radiation beam 110 may be configured to traverse the target location 111. Further, in certain embodiments, the focal plane may overlap the target material 120 or the edge portion of the target material 120 facing the first radiation beam 110. The first radiation beam 110 may be directed to the target material 120 by directing the first radiation beam 110 through the beam delivery system 150 and in the beam delivery system the radiation 110 may be directed A variety of optics can be used to modify the direction or shape or divergence of the radiation 110 so as to interact with the target material 120.

The first radiation beam 110 may be directed 1110 towards the target material 120 by overlapping the target material with the area of the first radiation beam surrounding the confocal parameter. In a particular embodiment, the confocal parameter of the first radiation beam 110 is so long that the beam waist D1 / 2 can easily surround the target material 120 and cause the target material 120 to intercept the first radiation beam 110, (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 (see Fig. 7A). For example, the confocal parameter of the first radiation beam 110 may be greater than 1.5 mm. In another alternative embodiment, because the confocal parameter of the first radiation beam 110 is so short that the beam waist D1 / 2 does not encompass the target material 120, 2), the surface area of the target material 120 interfering with the first radiation beam 110 is considerably deviated (see FIG. 7B). For example, the confocal parameter may be, for example, 2 mm or less.

The modified target 121 changes its shape from the shape of the target material 120 to the expanded shape immediately after being impacted by the first radiation beam 110 and this expanded shape is moved from the first target position 111 And is continuously deformed as it drifts toward the second target position 116. The modified target 121 may have a geometric distribution that varies from the shape of the target material to a disk-shaped volume of molten metal having a substantially planar surface (e.g., see FIGS. 1 and 2). The modified target 121 is deformed into a disk-shaped volume according to the expansion rate. The modified target 121 is deformed by inflating the modified target 121 along at least one axis in accordance with the inflation rate. For example, as shown in FIG. 2, the modified target 121 is inflated along at least the long axis 230, which is generally parallel to the X direction. The modified target 121 is inflated along at least one axis that is not parallel to the optical axis (i.e., the second axial direction 217) of the second radiation beam 115.

Although the first radiation beam 110 primarily interacts with the target material 120 by altering the shape of the target material 120, neither the first radiation beam 110 interacts with the target material 120 in any other way It is possible; For example, the first radiation beam 110 may convert a portion of the target material 120 into a plasma that emits EUV light. However, it may be desirable to remove more from the plasma generated from the target material 120 than from the plasma generated from the modified target 121 (due to subsequent interaction between the modified target 121 and the second radiation beam 115) The lesser 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 the modified target 121. [

The light source 100 directs the second radiation beam 115 toward the modified target 121 so that the second radiation beam converts at least a portion of the modified target 121 into a plasma 129 emitting EUV light (1115). In particular, the light source 100 directs the second radiation beam 115 towards the modified target 121 through the second set of one or more optical amplifiers 305. For example, the optical source 105 may be activated by the control system 160 to generate a second radiation beam 115 (in the form of a pulse) and the second radiation beam 115 may be activated by a control system 160 Toward the modified target 121 in the second target position 116 as shown in FIG. At least one of the optical amplifiers in the first set 300 may be in the second set 305 as in the example shown in Fig.

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

In a particular embodiment, the characteristic that can be measured (at 1120) is the energy of the first radiation beam 110. [ A characteristic that can be measured (at 1120) is a characteristic 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) Position, and this position can be determined in the direction of the longitudinal axis Z or in the direction transverse to the longitudinal direction (e.g., the XY plane).

The energy of the first radiation beam 110 can be measured by measuring the energy of the radiation 860 reflected from the optical reflective surface of the target material 120 (e.g., as shown in Figures 8b and 8c). The energy of the radiation 860 reflected from the optical reflective surface of the target material 120 can be measured by measuring the total intensity of the radiation 860 over four individual photovoltaic cells.

The total energy content of the retroreflected radiation 860 is determined by the relative position between the beam waist of the first radiation beam 110 and the target material 120 along the Z or Z direction (e.g., the XY plane) May be used in combination with other information about the first radiation beam 110 to determine the position of the first radiation beam. Alternatively, the total energy content of the retroreflected radiation 860 can be used (along with other information) to determine the relative position between the beam waist of the first radiation beam and the target material 120 along the Z direction.

The energy of the first radiation beam 110 may be measured by measuring the energy of the first radiation beam 110 that is directed toward the target material 120 (e.g., as shown in FIG. 8A). The energy of the first radiation beam 110 can be measured by measuring the energy spatially accumulated over a direction perpendicular to the propagation direction of the first radiation beam 110 (first axis direction 212).

A characteristic that can be measured (at 1120) is the orientation or orientation of the first radiation beam 110 as the first radiation beam 110 advances toward the target material 120 being). This information about the orientation can be used to determine the overlap error between the axis of the first beam of radiation 110 and the location of the target material 120.

As a specific implementation, the characteristic that can be measured (at 1120) is the location of the target material 120 relative to the target location. This target position may be in the beam waist D1 / 2 of the first radiation beam 110 along the Z direction. The position of the 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 the target material 120 may be measured along two or more non-parallel directions.

In a particular implementation, the characteristic that can 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 into a plasma.

As a specific implementation, the characteristic that can be measured (at 1120) corresponds to an estimate of the rate of expansion of the modified target.

In a particular embodiment, the characteristic that can be measured (at 1120) corresponds to the spatial property of the radiation 860 reflected from the optical reflective surface of the target material 120 (e.g., as shown in Figures 8b and 8c) . This information can be used to determine the relative position of the beam of target material 120 and the beam waist of the first radiation beam 110 (e.g. along the Z direction). This spatial characteristic can be determined or measured by using an astigmatism imaging system disposed in the path of the reflected radiation 860.

In a particular embodiment, the characteristic that can be measured (at 1120) corresponds to the angle at which the radiation 860 is directed with respect to the angle of the 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 alternative embodiment, the characteristic that can be measured (at 1120) corresponds to the spatial aspect of the modified target 121 that is 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 in a predetermined direction, for example, in a predetermined direction in the X-Y plane across the Z direction. This information about the angle of the modified target 121 may be used to determine the distance between the axis of the first beam of radiation 110 and the target material 120 along the direction transverse to the Z direction. As another example, the size or rate of expansion of the modified target 121 may be measured after a predetermined or predetermined time since the initial formation of the interaction between the target material 120 and the first radiation beam 110. This information about the size or the rate of expansion of the modified target 121 can be used to determine the size or rate of expansion of the first radiation beam 110 along the longitudinal axis (Z direction), if it is known that the energy of the first radiation beam 110 is constant. Can be used to determine the distance between the beam waist and the target material 120.

(At 1120) the characteristic can be measured 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 (array of four PEMs), the measurement rate may be as fast as a pulse unit.

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

In certain embodiments, 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 inflation of the modified target. In another alternative embodiment, the amount of radiation exposure delivered from the first radiation beam 110 to the target material 120 by determining whether the characteristics of the first radiation beam 110 should be adjusted based on the one or more measured characteristics (1125). Thus, if it is determined that the characteristics of the first radiation beam 110 should be adjusted, for example, the energy content of the pulses of the first radiation beam 110 may be adjusted, or the energy of the first radiation beam 110 at the location of the target material 120 The area of the first electrode 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 moment of the pulse of the first radiation beam 110 Power < / RTI > The area of the first radiation beam 110 interacting with the target material 120 is 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 .

In a particular embodiment, the one or more characteristics may be measured 1120 for each pulse of the first radiation beam 110. In this way, it is possible to determine whether the characteristic of the first radiation beam 110 should be adjusted for each pulse of the first radiation beam 110.

The amount of radiation exposure delivered from the first radiation beam 110 to the target material 120 is controlled such that at least a portion of the emitted and condensed EUV light 140 is subject to control of the amount of radiation exposure while exposing the wafer of the lithography tool. (E.g., within a range of acceptable radiation exposure dose).

The procedure 1100 further includes the steps of: condensing at least a portion of the EUV light 130 emitted from the plasma (using the light collector 135); And directing the focused EUV light 140 towards the wafer to expose the wafer to the EUV light 140.

As a specific implementation, the at least one measured characteristic (at 1120) includes the number of photons reflected from the modified target 121. The number of photons reflected from the modified target 121 may be measured as a function of the number of photons impacting the target material 120.

As discussed above, the procedure 1100 includes controlling the amount of radiation exposure in the target material 120 from the first radiation beam 110 based on one or more characteristics. For example, the radiation exposure dose can be controlled to be maintained within a predetermined range of radiation exposure (1125). The amount of radiant exposure is the amount of radiant energy transmitted to the target material 120 from the first radiation beam 110 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 the first radiation beam 110 or intercepts the first radiation beam 110 is controlled (or is maintained within an acceptable range), these factors of the radiation exposure dose The amount of radiation exposure in the target material 120 may be controlled or maintained 1125 by maintaining the energy of the first radiation beam 110 within an acceptable energy range. There are various ways to maintain the unit area of the surface of the target material 120 exposed to the first radiation beam 110 within an acceptable area range.

The amount of radiation exposure 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 measured characteristic at 1120) Can be controlled to remain within a certain level or acceptable value range despite the disturbing factor that can cause such energy to oscillate.

The amount of radiation exposure in the target material 120 from the first radiation beam 110 is greater than the amount of radiation exposure in the direction of the long axis of the target material 120 relative to the beam waist of the first radiation beam 110 (E.g., increase or decrease) the energy of the pulse of the first radiation beam 110 by feedback control using the measured characteristic (at 1120) to compensate for the error in the (Z direction) arrangement .

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

The target material 120 may be a droplet of the target material 120 generated from the target material supply system 125. In this way, the geometric distribution of the target material 120 can be modified into the modified target 121, and the modified target is transformed into a disk-shaped volume of molten metal having a substantially planar surface. The target material droplet is deformed to such a disc-shaped volume according to the expansion rate.

12, by a light source 100 to stabilize the EUV light energy produced by the plasma 129 formed from the interaction between the modified target 121 and the second radiation beam 115 (Under the control of the controller 160). As with the above-described procedure 1100, the light source 100 provides 1205 a target material 120; The light source 100 directs the first radiation beam 110 to the target material 120 to transfer energy to the target material 120 to modify the geometric distribution of the target material 120 to form the modified target 121 (1210); The light source 100 directs the first radiation beam 110 toward the modified target 121 so that the second radiation beam converts at least a portion of the modified target 121 into a plasma 129 emitting EUV light (1215). The light source 100 controls the amount of radiation exposure applied to the target material 120 from the first radiation beam 110 using procedure 1110 (1220).

The power or energy of the EUV light 130 is stabilized 1225 by controlling the amount of radiation exposure. The EUV energy (or power) produced by the plasma 129 depends on at least two functions, the first is the conversion efficiency CE and the second is the energy of the second radiation beam 115. The conversion efficiency is the ratio of the modified target 121 that is converted to the plasma 129 by the second radiation beam 115. The conversion efficiency depends on several variables, including the peak power of the second beam of radiation 115, the size of the modified target 121 when interacting with the second beam of radiation 115, 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, and the like. 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 distance from the first radiation beam 110 to the target material 120 It is possible to control the rate of expansion of the modified target 121 by controlling the amount of radiation exposure applied to the target 120 so that both of these factors can be controlled. In this way, the conversion efficiency can be stabilized or controlled 1220 by controlling the amount of radiation exposure, and the EUV energy generated by the plasma 129 is thereby stabilized 1225.

13, a first radiation beam 110 may be generated by a dedicated subsystem 1305A in an optical source 105 and a second radiation beam 115 may be generated by an optical source < RTI ID = 0.0 > Can be generated by a dedicated separate subsystem 1305B within the radiation source 105 so that the two radiation beams 110 and 115 are separated into two distinct paths reaching the first and second target locations 111 and 116, . In this manner, each of the radiation beams 110 and 115 travels through each subsystem of the beam delivery system 150 and thus travels through each of the separate optical steering components 1352A and 1352B and the focus assemblies 1356A and 1356B, .

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 gas gain medium such as is generated by a CO ₂ amplifier. Exemplary solid state gain media that may be used as subsystem 1305A include erbium doped fiber laser 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 the solid state gain medium may be about 1 占 퐉 (e.g., about 1.06 占 퐉), and the wavelength of the second radiation beam 115 using the gaseous medium may be about 10.6 Lt; / RTI >

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

Claims (33)

Providing a target material comprising a component that emits extreme ultra-violet (EUV) light when converted to a plasma;
Directing a first beam of radiation toward the target material to transfer energy to the target material to modify the geometric distribution of the target material to form a modified target;
Directing a second beam of radiation toward the modified target, the second beam of radiation converting at least a portion of the modified target into a plasma emitting EUV light;
Measuring at least one characteristic associated with at least one of the target material and the modified target relative to the first beam of radiation; And
Controlling an amount of radiation exposure delivered to the target material from the first radiation beam to within a predetermined energy range based on the one or more measured characteristics. The method according to claim 1,
Wherein measuring at least one characteristic associated with at least one of the target material and the modified target comprises measuring energy of the first radiation beam. 3. The method of claim 2,
Wherein measuring the energy of the first beam of radiation comprises: measuring energy of the first beam of radiation reflected from an optical reflective surface of the target material, or measuring energy of the first beam of radiation ≪ / RTI > 3. The method of claim 2,
Wherein measuring the energy of the first beam of radiation comprises measuring spatially integrated energy over a direction perpendicular to the propagation direction of the first beam of radiation. 5. The method of claim 4,
Wherein directing the first beam of radiation toward the target material comprises overlapping the target material with a region of the first beam of radiation surrounding the confocal parameter. The method according to claim 1,
Wherein measuring at least one characteristic associated with at least one of the target material and the modified target comprises measuring a position of the target material relative to a target position. The method according to claim 6,
Wherein the first beam of radiation 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. The method according to claim 6,
Wherein measuring the position of the target material comprises measuring a position of the target material along two or more non-parallel directions. The method according to claim 1,
Wherein measuring at least one characteristic associated with at least one of the target material and the modified target comprises:
Detecting the size of the modified target before the second beam of radiation transforms at least a portion of the modified target into a plasma; And
Estimating an expansion rate of the modified target
≪ / RTI > The method according to claim 1,
Wherein controlling the amount of radiation exposure delivered to the target material from the first radiation beam based on the one or more measured characteristics comprises controlling an inflation rate of the modified target. The method according to claim 1,
Wherein controlling the amount of radiation exposure delivered to the target material from the first radiation beam based on the one or more measured characteristics comprises determining whether the characteristic of the first radiation beam is to be adjusted based on the one or more measured characteristics The method comprising the steps of: 12. The method of claim 11,
Wherein at least one of an energy content of a pulse of the first radiation beam and a region of the first radiation beam interacting with the target material is adjusted when the characteristic of the first radiation beam is determined to be adjusted. 13. The method of claim 12,
Adjusting the energy content of the pulses of the first radiation beam comprises:
Adjusting a width of the pulse of the first radiation beam;
Adjusting the duration of the pulse of the first radiation beam; And
Adjusting the average power within the pulse of the first radiation beam
≪ / RTI > 12. The method of claim 11,
Wherein directing the first radiation beam toward the target material comprises directing a pulse of the first radiation toward the target material,
Wherein measuring the at least one characteristic comprises measuring the at least one characteristic for each pulse of the first radiation,
Wherein determining whether the feature of the first radiation beam should be adjusted comprises determining whether the feature should be adjusted for each pulse of the first radiation. The method according to claim 1,
Wherein providing the target material comprises providing a droplet of a target material,
Wherein modifying the geometric distribution of the target material comprises deforming the droplet of the target material into a disk-shaped volume of molten metal,
Wherein the droplet of the target material is deformed into the disc-shaped volume according to an expansion rate. The method according to claim 1,
Wherein directing the first radiation beam toward the target material further comprises converting a portion of the target material to a plasma that emits EUV light and converting the portion of the target material from the target material Wherein 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. The method according to claim 1,
Wherein modifying the geometric distribution of the target material comprises modifying the shape of the target material with the modified target, comprising inflating the modified target along at least one axis in accordance with the inflation rate,
Wherein controlling the amount of radiation exposure delivered to the target material comprises controlling the rate of expansion of the target material to the modified target. 18. The method of claim 17,
Wherein the modified target is inflated along the at least one axis that is not parallel to the optical axis of the second beam of radiation. The method according to claim 1,
Wherein measuring at least one characteristic associated with at least one of the target material and the modified target comprises measuring energy of the first beam of radiation that is directed toward the target material,
Wherein controlling the amount of radiation exposure delivered to the target material comprises adjusting the amount of energy directed from the first radiation beam to the target material based on the measured energy,
Wherein directing the first beam of radiation toward the target material comprises overlapping the target material with a region of the first beam of radiation surrounding the confocal parameter. 20. The method of claim 19,
Wherein adjusting the amount of energy directed to the target material from the first beam of radiation comprises adjusting a characteristic of the first beam of radiation. The method according to claim 1,
Wherein controlling the amount of radiation exposure delivered to the target material from the first radiation beam comprises:
Adjusting the energy of the first beam of radiation immediately before the first beam of radiation transmits the energy to the target material;
Adjusting the position of the target material; And
Adjusting the area of the target material interacting with the first radiation beam
≪ / RTI > A chamber defining a first 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 a target material to the initial target location, the target material including a material that emits extreme ultra-violet (EUV) light when converted to a plasma;
An optical source configured to generate the first radiation beam and the second radiation beam;
An optical steering system comprising:
Directing the first beam of radiation toward the initial target position to transfer 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 beam of radiation toward the target position to convert at least a portion of the modified target into a plasma emitting EUV light;
A measurement system for measuring at least one characteristic associated with at least one of the target material and the modified target relative to the first radiation beam; And
And a control system coupled to the target material delivery system, the optical source, the optical steering system and the measurement system, wherein the control system receives one or more measured characteristics from the measurement system, And to transmit the one or more signals to the optical source to control an amount of radiation exposure delivered to the target material from the first radiation beam based on the radiation dose. 23. The method of claim 22,
Wherein the optical steering system includes a focusing device configured to focus the first radiation beam at or near the initial target position and to focus the second radiation beam at or near the target position Device. 23. The method of claim 22,
The apparatus further comprises a beam adjustment system, wherein the beam adjustment system is connected to the optical source and to the control system, wherein the control system is operable to adjust the energy delivered to the target material by transmitting one or more signals to the beam adjustment system Wherein the beam conditioning system is configured to maintain an amount of energy delivered to the target material by adjusting one or more characteristics of the optical source. 25. The method of claim 24,
Wherein the beam adjustment system includes a pulse width adjustment system coupled to the first radiation beam and wherein the pulse width adjustment system is configured to adjust a pulse width of a pulse of the first radiation beam. 26. The method of claim 25,
Wherein the pulse width adjustment system comprises an electro-optic modulator. 25. The method of claim 24,
Wherein the beam conditioning system includes a pulse power adjustment system coupled to the first radiation beam and wherein the pulse power adjustment system is configured to adjust an average power within a pulse of the first radiation beam. 28. The method of claim 27,
Wherein the pulse power adjustment system comprises an acousto-optic modulator. 25. The method of claim 24,
Wherein the beam conditioning system is configured to transmit one or more signals to the optical source to control an amount of energy directed to the target material by transmitting one or more signals to the beam conditioning system, And to control the amount of energy directed to the target material by adjusting one or more characteristics of the source. 23. The method of claim 22,
The optical source comprising:
A first set of optical components comprising a first set of one or more optical amplifiers through which the first beam of radiation passes; And
And a second set of optical components comprising a second set of one or more optical amplifiers through which the second radiation beam passes. 31. The method of claim 30,
Wherein at least one of the optical amplifiers in the first set is in the second set. 31. The method of claim 30,
Wherein the first set of optical components is separate and separate from the second set of optical components. 31. The method of claim 30,
Wherein the measurement system measures the energy of the first radiation beam when the first radiation beam is directed toward the initial target position,
The control system receives the 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 . ≪ / RTI >

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