TWI825198B - Extreme ultraviolet (euv) light source and apparatus for the same, apparatus for forming optical pulse, and method of adjusting property of optical pulse - Google Patents

Abstract

An apparatus for an extreme ultraviolet (EUV) light source includes an optical modulation system including an electro-optic material, the optical modulation system configured to receive a pulsed light beam that includes a plurality of pulses of light separated from each other in time; and a control system configured to control an electrical source such that a first electrical pulse is applied to the electro-optic material while a first pulse of light is incident on the electro-optic material, a second electrical pulse is applied to the electro- optic material while a second pulse of light is incident on the electro-optic modulator, and an intermediate electrical pulse is applied to the electro-optic material after the first pulse of light is incident on the electro-optic material and before the second pulse of light is incident on the electro-optic material.

Description

Extreme ultraviolet (EUV) light sources and equipment for EUV light sources, equipment for forming optical pulses and methods for adjusting the properties of optical pulses

The present invention relates to the control of optical modulators. For example, optical leakage in optical modulators can be controlled. The optical modulator may be part of an extreme ultraviolet (EUV) light source and/or lithography system.

Extreme ultraviolet ("EUV") light, for example, with a wavelength of 100 nanometers (nm) or less (sometimes also called soft x-rays) and includes wavelengths of, for example, 20 nm or less, between 5 nm and 20 nm, or Electromagnetic radiation of light between 13nm and 14nm can be used in photolithography processes to create very small features in a substrate (such as a silicon wafer) by initiating polymerization in the resist layer.

Methods used to generate EUV light include, but are not necessarily limited to, converting materials including elements such as xenon, lithium or tin into a plasma state using emission lines in the EUV range. In one such method, often referred to as laser-produced plasma ("LPP"), materials such as droplets, plates, strips, or The desired plasma is generated by targeting the material in the form of a stream or cluster. For this procedure, the plasma is typically generated in a sealed container, such as a vacuum chamber, and various types of metrology equipment are used to monitor the plasma.

In one general aspect, an apparatus for an extreme ultraviolet (EUV) light source includes An optical modulation system including an electro-optical material configured to receive a pulsed beam including a plurality of light pulses that are temporally separated from each other; and a control system configured To control a power supply, a first electric pulse is applied to the electro-optic material when a first light pulse is incident on the electro-optic material, and a second electric pulse is applied when a second light pulse is incident on the electro-optic modulator. A pulse is applied to the electro-optical material, and an intermediate electrical pulse is applied to the electro-optical material after the first light pulse is incident on the electro-optical material and before the second light pulse is incident on the electro-optical material.

Implementations may include one or more of the following features. The first electrical pulse applied to the electro-optical material can produce a physical effect in the electro-optical material, and the physical effect can be present in the electro-optical material when the intermediate electrical pulse is applied to the electro-optical material. The physical effects may include acoustic waves and/or mechanical strains traveling in the electro-optical material. Applying intermediate electrical pulses to the electro-optical material can reduce this physical effect.

The first light pulse and the second light pulse may be continuous light pulses in the pulse beam.

The control system can be configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse.

The electro-optical material may include a semiconductor.

The electro-optical material may include an insulator.

The electro-optical material may include an electro-optical crystal.

The device may also include at least one polarization-based optical element.

In another general aspect, an apparatus for forming optical pulses includes an optical modulation system including an electro-optical material, the optical modulation system configured to transmit light in an on state and Blocks light in an off state, and the optical modulation system is Configured to receive a pulsed beam, the pulsed beam including at least a first light pulse and a second light pulse that are temporally separated from each other. A control system may be coupled to a voltage source, the control system being configured to: by causing the voltage source to apply the first voltage pulse to the electro-optic modulator when the first light pulse is incident on the electro-optic modulator. the electro-optical modulator to generate a first shaped optical pulse, the first voltage pulse being configured to switch the electro-optical modulator into the on state; applying an intermediate voltage pulse to the electro-optical material; and by applying the third A second voltage pulse is applied to the electro-optical material after a voltage pulse and the intermediate voltage pulse and when the second optical pulse is incident on the electro-optical material to generate a second shaped optical pulse. The second voltage pulse is configured to switch the electro-optic modulator into the on state, and a property of the second shaped optical pulse is controlled by application of the intermediate voltage pulse to the electro-optic material.

Implementations may include one or more of the following features. The second shaped optical pulse may include a base portion and a main portion, and the property of the second shaped optical pulse may include a property of the base portion such that a property of the base portion is determined by the intermediate voltage pulse to control the application of the electro-optical material. The base portion and the main portion may be temporally continuous. The property of the base portion may be a temporal duration, a maximum intensity and/or an average intensity of the base portion.

The application of the intermediate voltage pulse to the electro-optical material may modify an amount of optical leakage light transmitted by the optical modulation system in the off state. The application of the intermediate voltage pulse to the electro-optical material may reduce the amount of optical leakage light transmitted by the optical modulation system in the off state.

In some implementations, the control system causes the first voltage pulse to be applied to the electro-optical material at a first time, and the control system causes the intermediate voltage pulse to be applied to the electro-optical material at a second time after the first time. material, the second time is time-divided from the first time from a delay time, and the control system is further configured to adjust the delay time to thereby control a property of the second shaped optical pulse.

The control system may also be configured to control an amplitude, a duration and/or a phase of the intermediate voltage pulse.

The control system may be further configured to receive an indication of a measured property of the base portion and adjust a property of the intermediate voltage pulse based on the received indication.

The control system may be further configured to receive an indication of an amount of extreme ultraviolet (EUV) light generated by a plasma and adjust a property of the intermediate voltage pulse based on the received indication of the amount of EUV light. . The control system configured to adjust a property of the intermediate voltage pulse may include the control system configured to adjust an amplitude of the intermediate voltage pulse, a time interval of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or or a second time, the second time being a time for applying the intermediate voltage pulse to the electro-optical material.

In another general aspect, a method of modulating a property of an optical pulse includes applying a first voltage pulse to an electro-optical material of an optical modulation system when light is incident on the optical modulation system. to form a first optical pulse; applying an intermediate voltage pulse to the electro-optical material after applying the first voltage pulse; and by following the first voltage pulse and the intermediate voltage pulse and after light is incident on the electro-optical material A second voltage pulse is applied to the electro-optical material to form a second optical pulse. A property of the optical pulse is adjusted based on the application of the intermediate voltage pulse.

Implementations may include one or more of the following features. The first optical pulse can be amplified to form an amplified first optical pulse; an indication of an amount of extreme ultraviolet (EUV) light emitted from a plasma can be received by causing the amplified first optical pulse The pulse is generated by interaction with the target material; and can be determined based on the received indication of the amount of EUV light emitted from the plasma. Determine at least one property of the intermediate voltage pulse. The at least one property of the intermediate voltage pulse may include a time delay after application of the first voltage pulse, and determining the at least one property of the intermediate voltage pulse may include based on the amount of EUV light emitted from the plasma. The time delay is determined based on the received indication. The at least one property of the intermediate voltage pulse may include an amplitude and/or a duration of the intermediate voltage pulse, and determining the at least one property of the intermediate voltage pulse may include determining the amplitude and/or the duration of the intermediate voltage pulse. time.

In some implementations, the second optical pulse includes a base portion and a main portion, and a property of the base portion is adjusted based on the application of the intermediate voltage pulse. The base portion may be temporally continuous with the main portion.

In another general aspect, an extreme ultraviolet (EUV) light source includes: a container; a target material supply device configured to be coupled to the container; an optical modulation system configured to position Receiving a pulsed beam, the optical modulation system includes an electro-optical material; and a control system coupled to a voltage source, the control system being configured to cause the voltage source to apply a plurality of shaped voltage pulses to the electro-optical material. material, each of the plurality of shaped voltage pulses is applied to the electro-optical material at a different time, and causing the voltage source to apply at least one intermediate voltage pulse to the electro-optical material, the at least one intermediate voltage pulse being at Between two of the plurality of shaped voltage pulses are applied to the electro-optical material.

Implementations may include one or more of the following features. The target material supply device may be configured to provide a plurality of target material droplets to a target zone in the container, the target material droplets arriving at the target zone at a target delivery rate, and the control system in a shaped The shaping voltage pulses are applied to the electro-optical material at a rate that depends on the target delivery rate.

The characteristics of the intermediate voltage pulse may include an amplitude and/or a phase, and the control The control system may be further configured to access an amplitude and/or a phase stored in association with the forming rate and cause the voltage source to generate the intermediate voltage pulse having the accessed amplitude and/or phase. The control system may be further configured to control a time delay between application of one of the shaping voltage pulses and one of the intermediate voltage pulses.

The EUV light source may also include an optical amplifier. Whenever a shaped voltage pulse is applied to the electro-optical material, an optical pulse can be formed; the shaped optical pulse can be amplified by the optical amplifier to form an amplified optical pulse; the control system can be further configured to couple to a metrology system , the metrology system configured to measure an amount of EUV light generated by a plasma in the container, the plasma being formed by irradiating the target material with shaped amplified optical pulses, the control system The control system can be configured to receive a quantitative measurement of EUV light from the metrology system; and the control system can be configured to modify one or more characteristics of the intermediate voltage pulse based on the quantitative measurement of EUV light. The one or more characteristics of the intermediate voltage pulse may include an amplitude of the intermediate voltage pulse, a duration of the intermediate voltage pulse, a phase of the intermediate voltage pulse, and/or a duration following application of a most recently shaped voltage pulse. delay time.

Implementations of any of the techniques described above may include EUV light sources, systems, methods, procedures, apparatus, or devices. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings and from the patent claims.

2: Extreme ultraviolet (EUV) radiation emitting plasma

3: Near normal incidence collector

20: EUV radiation beam

21: Radiation beam

22: Faceted field mirror device/system

24: Faceted pupil mirror device

26: Patterned beam/radiation beam

28: Reflective element

30: Reflective element

100:System

101:EUV light source

104: Optical pulse generation system

105:Light source

106:Beam

107: Modified Optical Pulse

108: Irradiated optical pulse/amplified optical pulse

111:Path

115:Target area

118:Target/Target Material

120:Modulator/System

122:Material

123:Power supply

124: Electric field

130:Optical amplifier

132: Gain medium

175:Control system

176: Communication interface

177: Electronic processor

178: Electronic storage

179:Input/output (I/O) interface

180: Vacuum chamber

182: Weights and Measures System

183: Communication link

184:Sensor

185: Optical sensing system

195:Lithography equipment

196: EUV light

197:Plasma

206: Optical pulse

207: Modified Optical Pulse

214:Voltage signal

220: Modulation system

221:Window

223:Voltage source

223a:Electrode

223b:Electrode

224: Optical components based on polarization

225: Base part

266:Leaking light

267:Part

268:Main part

306:Beam

306_1: First optical pulse

306_2: Second optical pulse

324:Electrical signal

325a_1: First voltage pulse

325a_2: Second voltage pulse

325b_1: Intermediate voltage pulse

330: Delay

331_1: time interval/duration

331_2: time interval/duration

332: Width/Duration

400:Program

410: Steps

420: Steps

430: Steps

500: Lithography equipment

601:Reservoir

602:Nozzle

620:Enclosed structure

621:pore

623:Laser

624:Laser energy

626: Droplet Generator

628:Fuel flow

630: interceptor

660: Radiation intensity

669:Filter

B: Amplitude/radiation beam

C: Target part

IF: virtual source point/intermediate focus

IL: lighting system

M1: Patterning device alignment mark

M2: Patterned device alignment mark

MA: Patterning device/reduction mask

MT: support structure

O: Directional optical axis

P1: Substrate alignment mark

P2: Substrate alignment mark

PM: first locator

PS:Projection system

PS1: Position sensor

PS2: Position sensor

PW: Second locator

SO: Source collector module

t1: time

t2: time

ta: time

tb: time

ti: time

W: substrate

WT: substrate table

Figure 1 is a block diagram of an example EUV lithography system.

Figure 2A is a block diagram of an example of a modulation system.

Figure 2B is an illustration of an example of optical pulses.

Figure 2C is an illustration of an example of a modified optical pulse formed from the optical pulse of Figure 2B.

Figure 3A is an illustration of an example of a beam changing over time.

Figure 3B is an illustration of an example of an electrical signal changing over time.

Figure 4 is a flowchart of an example of a procedure for controlling the properties of irradiating optical pulses.

Figures 5 and 6 are block diagrams of examples of lithography equipment.

Figure 7 is a block diagram of an example EUV light source.

Techniques for controlling optical leakage in electro-optical modulators are described. An electro-optical modulator is used to modulate the initial beam to form a modified optical pulse. Electro-optical modulators include electro-optical materials. An electrical signal (eg, a voltage pulse of finite duration) is applied to the electro-optical material to change the refractive index of the electro-optical material, such that the initial light beam is modulated and a modified optical pulse is formed. After applying the electrical signal, an intermediate electrical signal is applied to the electro-optical material. As discussed in more detail below, applying an intermediate electrical signal to the electro-optical material allows the optical leakage of the electro-optical modulator to be controlled. The intermediate electrical signal reduces, changes or controls the sound waves generated by the electrical signal. Controlling the acoustic wave also controls the amount of optical leakage of the electro-optical modulator, thereby allowing control of the characteristics or properties of the modified optical pulse that is subsequently shaped (or later shaped).

Referring to Figure 1, a block diagram of system 100 is shown. System 100 is an example of an EUV lithography system. System 100 includes EUV light source 101 that provides EUV light 196 to lithography equipment 195 . Lithography equipment 195 uses EUV light 196 to expose a wafer (eg, a silicon wafer) to form electronic features on the wafer. EUV light 196 is emitted from the plasma 197 formed by irradiating the target material in target 118 using irradiation optical pulses 108 . The target material is any material that emits EUV light in the plasma state (eg, tin).

EUV light source 101 includes an optical pulse generation system 104 that generates amplified optical pulses 108 from modified optical pulses 107 . Optical pulse generation system 104 includes a light source 105, which may be, for example, a pulsed (e.g., Q-switched) or continuous wave carbon dioxide ( _CO2 ) laser or a solid-state laser (e.g., Nd:YAG laser or erbium-doped fiber (Er: glass)laser). The light source 105 generates an optical beam 106 (or light beam 106), which may be a series of light pulses or a continuous beam. The light source 105 emits a light beam 106 onto a path 111 toward a modulation system 120 including an electro-optical material 122 . Electro-optical material 122 is on path 111 and beam 106 is incident on electro-optical material 122 .

The modulation system 120 is an electro-optical modulator that modulates the light beam 106 based on the electro-optical effect. The electro-optical effect describes the change in the refractive index of the electro-optical material 122 resulting from the application of a direct current (DC) or low-frequency electric field 124 generated by the power source 123. The power source 123 may be, for example, a voltage source, a function generator, or a power supply. Modulation system 120 modulates the phase, polarization, or amplitude of beam 106 to form pulse 107 by controlling the electro-optical effect in electro-optical material 122 when beam 106 is incident on electro-optical material 122 .

Electric field 124 can be used to control whether modulation system 120 transmits light. The electric field 124 can be used to control the electro-optical material 122 so that only a portion or portions of the light beam 106 passes through the electro-optical material 122 . In this manner, modulation system 120 forms pulse 107 from a portion of beam 106 .

Optical pulse generation system 104 also includes one or more optical amplifiers 130 , each of which includes gain medium 132 on path 111 . Gain medium 132 receives energy via the pump and provides energy to pulse 107 such that pulse 107 is amplified into amplified or irradiated optical pulse 108. The amount of amplification of pulse 107 is determined by the gains of amplifier 130 and gain medium 132. Gain is the increase or factor by which the energy supplied by amplifier 130 to the input beam is increased.

Pulse 108 propagates on path 111 toward vacuum vessel 180 housing target 118 . Pulse 108 interacts with target 118 at target zone 115 in vacuum vessel 180, and the The interaction converts at least some of the target material in target 118 into plasma 197 that emits EUV light 196 .

Applying electric field 124 to electro-optical material 122 generates acoustic waves in material 122 . The sound waves create a strain in material 122 that persists even after electric field 124 is no longer applied to material 122 and/or after the properties of electric field 124 change. The strain produced by the acoustic waves changes the refractive index of material 122 even during periods of time when the refractive index of material 122 is not expected to change. Such refractive index changes may cause optical leakage. Optical leakage is the light that passes through modulator 120 when modulation system 120 is in a state where light should not pass through modulation system 120 . As discussed below, electric field 124 includes a component (eg, a pulse) that is applied to material 122 to mitigate and/or control optical leakage by mitigating and/or controlling residual acoustic waves in material 122 .

EUV light source 101 also includes a metrology system 182 positioned relative to target area 115 . Metrology system 182 includes one or more sensors 184 configured to sense EUV light 196 . Metrology system 182 produces an indication of the amount of EUV light 196 in vacuum chamber 180 (eg, at target zone 115). Metrology system 182 provides data representing the measured amount of EUV light to control system 175 via communication link 183 .

In some implementations, metrology system 182 also includes optical sensing system 185 , which includes one or more optical sensors configured to measure properties of pulse 107 and/or amplified pulse 108 . Optical sensing system 185 may include one or more wavelengths capable of detecting pulse 107 and/or pulse 108 such that sensing system 185 can determine the properties of pulse 107 and/or amplified pulse 108 (e.g., the properties of the base portion properties) of any sensor. In the example of FIG. 1 , optical sensing system 185 is part of metrology system 182 , however, optical sensing system 185 may be separate from metrology system 182 . For example, optical sensing system 185 may be positioned to receive samples of optical pulses 107 between modulation system 120 and optical amplifier 130 . Optical sensing system 185 Data related to the measurement of optical pulses 107 and/or pulses 108 may also be provided to control system 175 . In some implementations, information from EUV sensor 184 and/or optical sensing system 185 is used by control system 175 to set and/or change parameters of electric field 124 .

In addition to receiving data from the weights and measures system 182 , the control system 175 also exchanges data and/or information with the pulse generation system 104 and/or any of the components of the pulse generation system 104 via the communication interface 176 . For example, in some implementations, the control system 175 may provide a trigger signal to operate the modulation system 120 and/or the light source 105 . In another example, the control system 175 may receive a measurement of the EUV light from the EUV sensor 184 for a number of interactions between instances of the irradiating optical pulse 108 and the target 118 to determine the electric field. Which of many possible settings of specific parameters or properties of 124 results in the production of the highest amount of EUV light. In yet another example, control system 175 provides data and/or information to power source 123 that generates electric field 124 . In this example, data provided by control system 175 determines various properties of electric field 124 such as amplitude and/or time delay between two pulses of electric field 124 .

The control system 175 includes an electronic processor 177 , an electronic storage 178 , and an input/output (I/O) interface 179 . Electronic processor 177 includes one or more processors suitable for executing computer programs, such as a general or special purpose microprocessor, and any one or more processors of any kind of digital computer. Typically, electronic processors receive instructions and data from read-only memory, random access memory, or both. Electronic processor 177 may be any type of electronic processor.

Electronic storage 178 may be volatile memory such as RAM, or non-volatile memory. In some implementations, electronic storage 178 includes non-volatile and volatile portions or components. Electronic storage 178 may store data and information used in the operation of control system 175 and/or components of control system 175 .

Electronic storage 178 may also store instructions, possibly as computer programs, which The instructions, when executed, cause the processor 177 to communicate with components in the control system 175 , the modulation system 120 , and/or the light source 105 . For example, in implementations where source 105 is a pulsed source, the instructions may be instructions that cause electronic processor 177 to generate a signal that causes light source 105 to emit optical pulses.

I/O interface 179 is any type of electronic interface that allows control system 175 to receive and/or provide data to an operator, modulation system 120 and/or light source 105 and/or an automated program running on another electronic device. signal. For example, I/O interface 179 may include one or more of a visual display, a keyboard, and a communication interface.

FIG. 2A is a block diagram of the modulation system 220. Modulation system 220 is an example of an implementation of modulation system 120 (FIG. 1). Modulation system 220 includes electro-optical material 122, which in the implementation shown in Figure 2A is positioned between electrodes 223a, 223b. Electrodes 223a, 223b can be controlled to form an electric field between electrodes 223a and 223b. For example, control system 175 may cause voltage source 223 to provide voltage signal 214 to electrode 223b such that electrode 223b is maintained at a different voltage than electrode 223a, thereby creating an electric field or potential difference (V) across electro-optical material 122.

Additionally, modulation system 220 may include more than one instance of electro-optical material 122. For example, modulation system 220 may include two electro-optical materials 122 , three electro-optical materials 122 , or any number suitable for application that may be placed on beam path 111 . Each instance of electro-optical material 122 also includes respective electrodes 223a, 223b that are controllable to apply an electric field to that electro-optical material 122. In implementations that include more than one instance of electro-optical material 122, the electric field applied to each electro-optical material 122 may be the same, or at least some of the electro-optical fields may be different. The electro-optical materials 122 may be controlled as a group by the control system 175 , or the various electric fields may be controlled individually by respective instances of the control system 175 .

Modulation system 220 also includes one or more polarization-based optical elements 224. exist In the example of Figure 2A, only one polarization-based optical element 224 is shown. However, in other implementations, additional polarization-based optical elements 224 may be included. For example, the second polarization-based optical element 224 may be on the side of the modulation system 220 that receives the beam 106 . Furthermore, while polarization-based optical element 224 is shown physically separate from electro-optical material 122, other implementations are possible. For example, polarization-based optical element 224 may be a film formed on electro-optical material 122 such that optical element 224 and electro-optical material 122 are in contact with each other.

Polarization-based optical element 224 is any optical element that interacts with light based on its polarization state. For example, polarization-based optical element 224 may be a linear polarizer that transmits horizontally polarized light and blocks vertically polarized light, or transmits vertically polarized light and blocks horizontally polarized light. Polarization-based optical element 224 may be a polarizing beam splitter that transmits horizontally polarized light and reflects vertically polarized light. Polarization-based optical element 224 may be an optical element that absorbs all light except light with a specific polarization state. In some implementations, polarization-based optical element 224 may include a quarter wave plate. At least one polarization-based optical element 224 is positioned to receive light passing through electro-optical material 122 and direct light having a certain polarization state onto beam path 111 .

As discussed above, although one electro-optical material 122 and one polarization-based optical element 224 are shown in Figure 2, either or more than one of these components may be in series with each other on the beam path 111 and included in the modulation system 120. For example, the modulation system may include three polarization-based optical elements 224 and two electro-optical materials 122 in series on the beam path 111 , with each of the electro-optical materials 122 in the three polarization-based optical elements 224 between the two.

Electro-optical material 122 may be any material that transmits one or more wavelengths of light beam 106 . For implementations in which beam 106 includes light with a wavelength of 10.6 micrometers (μm), material 122 may be, for example, cadmium zinc telluride (CdZnTe or CZT), cadmium telluride (CdTe), zinc telluride (ZnTe), and/or gallium arsenide (GaAs). Other materials can be used at other wavelengths. For example, the material 122 may be potassium monophosphate (KDP), ammonium dihydrogen phosphate (ADP), quartz, cuprous chloride (CuCl), zinc sulfide (ZnS), zinc selenide (ZnSe), lithium niobate ( LiNbO ₃ ), gallium phosphide (GaP), lithium tantalate (LiTaO ₃ ) or barium titanate (BaTiO ₃ ). Other materials that transmit one or more wavelengths of light beam 106 and exhibit birefringence in response to the application of an external force may also be used as material 122 . For example, quartz may be used as material 122 .

Electro-optical material 122 also exhibits anisotropy. In materials that exhibit anisotropy, the properties of the material, such as the refractive index, are not uniform in space. Accordingly, the properties of material 122 can be modified along one or more specific directions by applying a controllable external force, such as a potential difference (V). For example, the refractive index of different polarization components of light propagating through material 122 can be controlled by applying an external force. Therefore, the polarization state of the light passing through the material 122 can be controlled by controlling the potential difference (V) between the electrodes 223a, 223b.

Under ideal operation, modulation system 220 only transmits light when the potential difference V applied to material 122 causes the polarization state of light passing through material 122 to match the polarization condition of polarization-based optical element 224 . For example, if polarization-based optical element 224 is a linear polarizer positioned to transmit horizontally polarized light onto beam path 111 , and beam 106 is vertically polarized upon initial incidence on material 122 , then only when applied to The potential difference V of the material 122 changes the polarization state of the beam 106 such that the beam 106 forms a pulse 107 when it becomes horizontally polarized before interacting with the polarization-based optical element 224 .

Modulation system 220 is considered to be in an on state any time modulation system 220 is controlled to intentionally transmit light. For example, when the applied potential difference V causes the polarization state of beam 106 to match polarization-based optical element 224 , optical modulation system 220 is considered to be in an on state and pulse 107 is formed. When the applied potential difference V causes the deflection of the beam 106 to The optical modulation system 220 is in the off state when the optical state is expected to be orthogonal to the polarization-based optical element 224 . Under ideal conditions, when the optical modulation system 220 is in the off state, the light beam 106 does not pass through the modulation system 120 .

However, applying a potential difference V to material 122 causes sound waves to propagate in material 122 . These acoustic waves may continue after the potential difference V is removed from the material 122 . Additionally, the acoustic waves create strains in the material 122 that change the optical properties of the material 122 and allow incident light to pass through the modulation system 220 (as optical leakage) even when the potential difference V is not applied. Therefore, in practice, modulation system 220 may transmit stray light (optical leakage) even when the polarization conditions of polarization-based optical element 224 are such that light incident on material 122 should not pass through modulation system 220 . For example, when the optical leakage is present only before the formation of the irradiation optical pulse, the optical leakage forms a base portion on the irradiation optical pulse.

Referring also to FIGS. 2B and 2C , an illustration of an example of optical pulse 206 ( FIG. 2B ) and an example of modified optical pulse 207 ( FIG. 2C ) formed from optical pulse 206 is shown. Pulse 207 includes base portion 225 and main portion 268 . Figure 2B shows the intensity of pulse 206 as a function of time, and Figure 2C shows the intensity of pulse 207 as a function of time.

Pulse 206 has an approximately Gaussian time profile (intensity versus time). Pulse 206 interacts with modulation system 220 to form pulse 207. The control system 175 controls the modulation system 220 to select or extract a specific portion 267 of the pulse 206 . In the example of Figure 2B, at time t=ta, the modulation system 220 is set to transmit light, and at time t=tb, the modulation system 220 is set to block light. In other words, optical modulation system 220 is only intended to transmit light in portion 267 (which is the light in pulse 206 between time ta and time tb). For example, the control system 175 may control the modulation system 220 to transmit light at time ta by applying the voltage signal 214 so that the light passing through the electro-optical material 122 has a polarization that matches the polarization of the polarization-based optical element 224 . By removing the voltage signal No. 214 to control the modulation system 220 to stop transmitting light at time tb.

However, optical leakage may be transmitted by modulation system 220 at times before ta and/or at times after time tb due to acoustic waves in electro-optical material 122 (or other disturbances, such as unintended motion of polarization-based optical element 224 ). . In the example of Figure 2B, leakage light 266 is an optical leakage that occurs only before time ta. Leak light 266 passes through modulation module 120 only before portion 267 .

Referring to FIG. 2C , leaked light 266 forms base portion 225 . In the example shown, base portion 225 occurs during the window labeled 221 and occurs temporally earlier than the remainder of pulse 207 . The portion of optical pulse 207 that is not base portion 225 is referred to as main portion 268. Both base portion 225 and main portion 268 are part of optical pulse 207, and base portion 225 is temporally connected to main portion 268. In other words, there is no period of no light between the base portion 225 and the main portion 268.

The base portion 225 has a different time profile (intensity versus time) than the main portion 268 . For example, the average and maximum intensity and light energy of base portion 225 are less than the average and maximum intensity and light energy of main portion 268 . Additionally, the base portion 225 has a different shape than the main portion 268 . Additionally, the characteristics of the base portion 225 (eg, intensity, time profile, and/or duration) differ from the characteristics of the early portion of the pulse formed without any optical leakage.

The modified pulse 207 is amplified by amplifier 130 to form an amplified pulse 208 that propagates to target zone 115 . The amplified pulse 208 includes a base portion 225 and a main portion 268 , wherein each portion 225 , 268 of the amplified pulse 208 has an intensity greater than the corresponding portion of the modified pulse 207 . In the example of FIG. 2C , base portion 225 appears before main portion 268 and reaches target 118 before main portion 268 . In some implementations, the main The desired portion 268 has sufficient intensity or energy to convert at least some of the target material in the target 118 into a plasma that emits EUV light. Base portion 225 does not have as much energy as main portion 268 and may or may not have enough energy to convert the target material into a plasma. However, light in base portion 225 may reflect away from target 118, causing material to evaporate from the surface of target 118, and/or causing portions of target 118 to break. The base portion 225 may interfere with plasma formation by modifying the target 118 before the main portion 268 reaches the target 118 and/or causing undesirable reflections to propagate back onto the path 111 .

On the other hand, base portion 225 may adjust target 118 such that properties (eg, density, shape, and/or size) are more favorable for plasma generation. Therefore, it is necessary to control the amount of light in the base portion 225 by controlling the amount of optical leakage. Control system 175 controls the amount of optical leakage (in this example, leakage light 266) using an intermediate electrical signal applied to electro-optical material 122 prior to forming pulse 207.

Pulse 207 discussed with respect to FIGS. 2B and 2C is provided as an example of a modified optical pulse 207. Pulse 207 may have other forms. For example, leakage light 266 may occur before time ta, causing base portion 225 to separate from main portion 268 . In such implementations, there are periods of no light between base portion 225 and main portion 268. Additionally, leaked light 266 may occur after time tb such that base portion 225 appears after main portion 268 . In such implementations, base portion 225 arrives at target zone 115 after main portion 268 . In some implementations, leakage light 266 occurs before time ta and after time tb, such that base portion 225 is present on each side of main portion 268 .

Figure 3A is a plot of the intensity of light beam 306 over time. Figure 3B is a plot of the voltage of electrical signal 324 as a function of time. The same time scale is used in Figures 3A and 3B. Electrical signal 324 is generated by a function generator controlled by control system 175 and applied to the electro-optical Example of electrical signals for material 122 (Figures 1 and 2A). Electrical signal 324 is discussed with respect to modulation system 220 (FIG. 2A). Beam 306 is an example of a light beam (optical beam or light beam) that may be incident on electro-optical material 122 .

The beam 306 includes two initial optical light pulses: a first initial optical pulse 306_1 and a second initial optical pulse 306_2 incident on the material 122 . Before the second initial pulse 306_2 is incident on the material 122, the first initial optical pulse 306_1 is incident on the material 122. The first optical pulse 306_1 and the second optical pulse 306_2 are separate optical pulses separated in time from each other. Beam 306 may include optical pulses in addition to initial optical pulses 306_1 and 306_2.

Electrical signal 324 includes a first electrical pulse 325a_1 applied to material 122 starting at time t1 and a second electrical pulse 325a_2 applied to material 122 starting at time t2. The electrical pulses 325a_1 and 325a_2 are voltage pulses having an amplitude of A volt within limited time intervals 331_1 and 331_2 respectively. Therefore, application of electrical pulses 325a_1 and 325a_2 produces voltage A applied to material 122 within time intervals 331_1 and 331_2 respectively.

Voltage A is a voltage sufficient to place the modulation system 220 in an on state. Therefore, when electrical pulses 325a_1 and 325a_2 are applied to material 122, light incident on material 122 is transmitted through optical modulation system 220. After the electrical pulses 325a_1 and 325a_2 end, the modulation system 220 returns to the off state.

Time intervals 331_1 and 331_2 may be the same or different. In the implementation of FIG. 3B , the first electrical pulse 325a_1 and the second electrical pulse 325a_2 have the same voltage amplitude (A). However, in other implementations, the electrical pulses 325a_1 and 325a_2 have different voltage amplitudes, wherein both of the electrical pulses 325a_1 and 325a_2 have a voltage sufficient to transition the modulation system 220 to the on state.

Electrical signal 324 also includes an intermediate electrical pulse applied to material 122 at time ti 325b_1. Time ti occurs after time t1 and before time t2. The time separation delay time 330 between time ti and the end of the first electrical pulse 325a_1 occurs. Intermediate electrical pulse 325b_1 has amplitude B over time interval or width 332.

At time 0, the modulation system 220 is in the off state. Applying the first electrical pulse 325a_1 at time t1 transitions the modulation system 220 to the on state. At time t1, first optical pulse 306_1 is incident on material 122. The time interval of the first electrical pulse 325a_1 is shorter than the time interval of the first optical pulse 306_1. Therefore, only the portion of the first optical pulse 306_1 that is incident on the material 122 during the duration 331_1 passes through the material 122 . The portion of first optical pulse 306_1 that passes through the material forms a modified optical pulse (such as modified optical pulse 207 of Figure 2C). Applying first electrical pulse 325a_1 to material 122 generates acoustic waves in material 122 . The sound waves create strains and change the optical properties of material 122 . Even after the first electrical signal 325a_1 ends and no voltage is applied to the material 122, sound waves continue to propagate in the material 122. When the second optical pulse 306_2 is incident on the material 122 but before the second electrical signal 325a_2 is applied to the material 122, there may be an acoustic wave generated by applying the first electrical signal 325a_1. In such cases, light can pass through the modulation system 220 even if the modulation system 220 is in a closed state. This light is an optical leak and forms a basis for the optical pulses later formed by the modulation system 220.

Figure 4 is a flowchart of an example of a process 400 for controlling the properties of irradiating optical pulses. The irradiating optical pulse may include a base portion. Process 400 is discussed with respect to EUV light source 101 and control system 175 (FIG. 1), modulation system 220 (FIG. 2A), beam 306 (FIG. 3A), and electrical signal 324 (FIG. 3B). However, process 400 may be performed by other EUV light sources, other light beams, other electrical signals, and/or other electro-optical modulation systems.

A first modified optical pulse is formed using modulation system 220 (410). The first modified optical pulse is generated by causing the first optical pulse 306_1 to be incident on the material 122 at time t1 and First voltage pulse 325a_1 is applied to material 122 to form. At time t1, the first optical pulse 306_1 is incident on the material 122 and the modulation system 220 is in the on state. Therefore, the portion of the first optical pulse 306_1 starting at time t1 and ending at the duration 331_1 passes through the material 122 and becomes a first modified optical pulse. Additionally, applying the first voltage pulse 325a_1 causes sound waves to propagate in the material 122 . These sound waves are called first sound waves and may continue to propagate in the material 122 after the first voltage pulse 325a_1 has ended and the modulation system 220 is in the off state.

Intermediate voltage pulse 325b_1 is applied to material 122 (420). Applying intermediate voltage 325b_1 to material 122 also causes sound waves (referred to as second sound waves) to propagate in material 122 . The second sound wave interferes with the first sound wave. Constructive interference increases the amplitude of sound waves, and destructive interference decreases the amplitude of sound waves. The amplitude and/or duration 332 of the intermediate voltage pulse 325b_1 determines the amplitude of the second acoustic wave. Delay 330 determines the phase of the second sound wave relative to the first sound wave. Therefore, by controlling delay 330 and/or amplitude B, the nature of the interaction between the first sound wave and the second sound wave can be controlled. For example, when the second sound wave has the same amplitude and opposite phase as the first sound wave, the first sound wave and the second sound wave interfere such that the sound wave does not propagate in the material 122 after the intermediate electrical pulse 325b_1 is applied.

A second modified optical pulse is formed using modulation system 220 (430). The second modified optical pulse is formed after intermediate voltage pulse 325b_1 is applied to material 122 . The second optical pulse 306_2 is incident on material 122 . At time t2, a second voltage pulse 325a_2 is applied to the material 122, causing the modulation system 220 to transition to the on state. A portion of second optical pulse 306_2 starting at time t2 and lasting for time 331_2 is transmitted through material 122 .

As discussed above, the first sound wave and the second sound wave interfere, and the characteristics of the sound wave in material 122 depend on the nature of the interference. The sound waves create strains in the material 122 and change the refractive index of the material 122 , and these changes in the refractive index may allow light to be in the modulation system 220 When in the off state it passes through modulation system 220 as optical leakage. The intermediate voltage pulse 325b_1 is used to modify one or more properties of the second optical pulse 306_2 in a desired manner. For example, the intermediate voltage pulse 325b_1 may be used to modify the maximum or average intensity, duration, and/or time profile of the second optical pulse 306_2. In some implementations, intermediate voltage pulse 325b_1 is used to control and/or form the base portion.

For example, depending on the characteristics of the acoustic waves in the material 122, the second optical pulse 306_2 is incident on the material 122 before time t2 or the time after the voltage pulse 325a_2 is no longer applied (when the modulation system 220 is in the off state). Some of the light above may also be transmitted through the modulation system 220 as an optical leak to form a base portion on the second modified optical pulse. The strength, duration, and other properties of the base depend on the amount of optical leakage, which can be controlled by adjusting the acoustic waves in the material 122 . Sound waves in material 122 can be controlled, modulated, or mitigated by applying intermediate voltage pulses 325b_1 to material 122. Therefore, one or more properties of the base portion are controlled or adjusted by applying the intermediate voltage pulse 325b_1. Additionally, one or more properties of the main portion of optical pulse 306_2 may be controlled using intermediate voltage pulse 325b_1.

Intermediate voltage pulse 325b_1 may be used to otherwise control one or more properties of second optical pulse 306_2. For example, as discussed above, the base portion may be temporally separated from the main portion of the modified pulse. In such implementations, intermediate voltage pulse 325b_1 may be used to modify individual base portions and/or main portions.

Additionally, beam 306 may include additional optical pulses and electrical signal 324 may include additional voltage pulses. In some implementations, control system 175 receives an indication of the amount of EUV light produced by the interaction between the modified optical pulse and target material 118, as measured by EUV sensor 184 (FIG. 1). For example, tracking the amount of EUV light for two or more interactions as the properties of the intermediate voltage pulse change to determine the best settings for the intermediate voltage pulse. Measure. Delay 330 can be varied for each of several interactions to determine which delay 330 produces the most EUV light. In another example, the amplitude B of the intermediate voltage pulse 325b_1 is varied to determine the amplitude B that produces the most EUV light.

In some implementations, a lookup table or database correlating the optimal values of amplitude B, width 332 and/or delay 330 with the repetition rate of the pulses in beam 306 is stored on electronic storage 178 such that upon repetition of beam 306 If the rate changes, the amplitude and/or delay 330 may be changed.

Figures 5 and 6 relate to lithography equipment that may use modulation systems such as systems 120 and 22. Figure 5 is a block diagram of a lithography apparatus 500 including a source collector module SO. Lithography equipment 500 includes:

• An illumination system (illuminator) IL configured to modulate the radiation beam B (eg EUV radiation).

● A support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a reticle or a reticle) MA and connected to a first positioning configured to accurately position the patterning device Device PM;

● A substrate table (eg, a wafer table) WT configured to hold a substrate (eg, a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and

• A projection system (eg, reflective projection system) PS configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (eg, including one or more dies).

Illumination systems may include various types of optical components for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithography equipment, and other conditions, such as whether the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic, or other clamping techniques to hold the patterned device. The support structure may be, for example, a frame or a table, which may be fixed or moveable as required. The support structure may ensure that the patterning device is in a desired position relative to the projection system, for example.

The term "patterning device" should be interpreted broadly to mean any device that can be used to impart a pattern to a radiation beam in its cross-section so as to produce a pattern in a target portion of a substrate. The pattern imparted to the radiation beam may correspond to specific functional layers in a device, such as an integrated circuit, produced in the target portion.

The patterning device may be transmissive or reflective. Examples of patterning devices include photomasks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary, alternating phase shift, and attenuated phase shift, as well as various hybrid mask types. One example of a programmable mirror array uses a matrix configuration of small mirrors, each of which can be individually tilted to reflect an incident radiation beam in different directions. Tilted mirrors impart patterns to the radiation beam reflected by the mirror matrix.

Similar to the illumination system IL, the projection system PS may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types, suitable for the exposure radiation used or suitable for other factors such as the use of a vacuum. optical components, or any combination thereof. A vacuum may be required for EUV radiation because other gases can absorb too much radiation. Therefore, a vacuum environment can be provided to the entire beam path by virtue of the vacuum wall and the vacuum pump.

In the examples of Figures 5 and 6, the device is of the reflective type (for example, using a reflective mask). Lithography equipment may be of the type having two (dual stages) or more than two substrate stages (and/or two or more patterning device stages). In these "multi-stage" machines, it is possible to Additional stages are used in parallel, or preparatory steps can be performed on one or more stages while one or more other stages are used for exposure.

Referring to Figure 5, the illuminator IL receives a beam of extreme ultraviolet radiation from the source collector module SO. Methods used to generate EUV light include, but are not necessarily limited to, converting a material containing at least one element (such as xenon, lithium or tin) into a plasma state using one or more emission lines in the EUV range. In one such method, often referred to as laser-produced plasma (LPP), a fuel (such as a droplet, stream, or cluster of material having the desired line-emitting element) is produced by irradiating it with a laser beam. And produce the required plasma. The source collector module SO may be part of an EUV radiation system including a laser (not shown in Figure 5) for providing a laser beam that excites the fuel. The resulting plasma emits output radiation, such as EUV radiation, which is collected using a radiation collector disposed in the source collector module. For example, when a carbon dioxide ( _CO2 ) laser is used to provide the laser beam for fuel excitation, the laser and source collector module may be separate entities.

In these cases, the laser is not considered to form part of the lithography apparatus, and the radiation beam is delivered from the laser to the source collector module by means of a beam delivery system including, for example, suitable guide mirrors and/or beam expanders. In other cases, for example when the source is a discharge plasma EUV generator (often referred to as a DPP source), the source may be an integral part of the source collector module.

The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Typically, at least an outer radial extent and/or an inner radial extent (commonly referred to as σ outer and σ inner respectively) of the intensity distribution in the pupil plane of the illuminator can be adjusted. Additionally, the illuminator IL may include various other components, such as faceted field mirror devices and faceted pupil mirror devices. The illuminator IL can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross-section.

Radiation beam B is incident on a patterning device (eg, mask) MA held on a support structure (eg, mask table) MT and is patterned by the patterning device. in self pattern After reflection from the irradiation device (eg, reticle) MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. By means of the second positioner PW and the position sensor PS2 (for example an interference device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B middle. Similarly, the first positioner PM and another position sensor PS1 can be used to accurately position the patterning device (eg, mask) MA relative to the path of the radiation beam B. The patterning device (eg, photomask) MA and the substrate W may be aligned using the patterning device alignment marks M1, M2 and the substrate alignment marks P1, P2.

The device depicted can be used in at least one of the following modes:

1. In step mode, the support structure (eg, mask table) MT and substrate table WT remain substantially stationary (i.e., while the entire pattern imparted to the radiation beam is projected onto the target portion C at once , single static exposure). Next, the substrate table WT is displaced in the X and/or Y directions so that different target portions C can be exposed.

2. In scanning mode, the support structure (eg mask table) MT and substrate table WT are scanned simultaneously while projecting the pattern imparted to the radiation beam onto the target portion C (ie, a single dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (such as the mask table) MT can be determined by the magnification (reduction ratio) and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (eg, mask table) MT remains substantially stationary, thereby holding the programmable patterning device, while the pattern imparted to the radiation beam is projected onto the target portion C, and Move or scan the substrate stage WT. In this mode, a pulsed radiation source is typically employed, and the programmable patterning device is updated as needed after each movement of the substrate table WT or between sequential radiation pulses during scanning. This mode of operation can be readily applied to maskless microscopy using programmable patterning devices such as programmable mirror arrays of the type mentioned above. film.

Combinations and/or variations of the usage modes described above or completely different usage modes may also be employed.

Figure 6 shows in greater detail an implementation of a lithography apparatus 500 including a source collector module SO, an illumination system IL and a projection system PS. The source collector module SO is constructed and configured such that a vacuum environment can be maintained within the enclosure 620 of the source collector module SO. Systems IL and PS are likewise contained within their own vacuum environments. The LPP plasma source can be generated by laser to form EUV radiation emitting plasma 2. The function of the source collector module SO is to deliver the EUV radiation beam 20 from the plasma 2 such that the EUV radiation beam is focused into the virtual source point. The virtual source point is often referred to as the intermediate focus (IF), and the source collector module is configured such that the intermediate focus IF is located at or near aperture 621 in enclosure 620 . The virtual source point IF is the image of the radiation emitting plasma 2 .

From the aperture 621 at the intermediate focus IF, the radiation traverses the illumination system IL, which in this example includes a faceted field mirror device 22 and a faceted pupil mirror device 24. These devices form a so-called "fly's eye" illuminator configured to provide the desired angular distribution of the radiation beam 21 at the patterning device MA, and the intensity of the radiation at the patterning device MA (as shown by element 660 ) requires uniformity. After reflection of the beam 21 at the patterning device MA held by the support structure (mask stage) MT, a patterned beam 26 is formed and imaged by the projection system PS via the reflective elements 28, 30 onto the substrate stage. WT is held on the substrate W. To expose the target portion C on the substrate W, pulses of radiation are generated while the substrate table WT and the patterning device table MT perform synchronized movements to scan the pattern on the patterning device MA through the illumination aperture.

Each system IL and PS is configured within its own vacuum or near-vacuum environment, which is defined by an enclosure similar to enclosure 620 . More components than shown are available It often exists in lighting system IL and projection system PS. Additionally, there may be more mirrors than shown. For example, in addition to the reflective elements shown in FIG. 6 , there may be one to six additional reflective elements in the lighting system IL and/or the projection system PS.

Considering source collector module SO in more detail, a laser energy source including laser 623 is configured to deposit laser energy 624 into a fuel including a target material. The target material may be any material that emits EUV radiation in the plasma state, such as xenon (Xe), tin (Sn), or lithium (Li). Plasma 2 is a highly ionized plasma with an electron temperature of tens of electron volts (eV). Other fuel materials, such as terium (Tb) and gallium (Gd), can be used to generate higher energy EUV radiation. High energy radiation generated during de-excitation and recombination of this plasma is emitted from the plasma, collected by near normal incidence collector 3 and focused on aperture 621. The plasma 2 and the pore 621 are respectively located at the first focus and the second focus of the collector CO.

Although the collector 3 shown in Figure 6 is a single curved mirror, the collector can take other forms. For example, the collector may be a Schwarzschild collector with two radiation collection surfaces. In one embodiment, the collector may be a grazing incidence collector comprising a plurality of substantially cylindrical reflectors nested within each other.

To deliver a fuel such as liquid tin, a droplet generator 626 is disposed within the enclosure 620 and is configured to emit a high frequency stream 628 of droplets towards a desired location of the plasma 2 . Droplet generator 626 may be target forming device 216 and/or include an adhesive, such as adhesive 234 . In operation, laser energy 624 is delivered synchronized with operation of droplet generator 626 to deliver pulses of radiation to convert each fuel droplet into plasma 2 . The droplet delivery frequency may be several kilohertz, such as 50kHz. Practically, laser energy 624 may be delivered in at least two pulses: a pre-pulse of limited energy is delivered to the droplet to vaporize the fuel material into a small cloud before it reaches the plasma site, and then , deliver the main pulse of laser energy 624 to the desired location Cloud-like objects at the location to generate plasma 2. Interceptor 630 is provided on an opposite side of enclosure 620 to capture fuel that does not become plasma for whatever reason.

Droplet generator 626 includes a reservoir 601 containing fuel liquid (eg, molten tin), as well as a filter 669 and a nozzle 602. Nozzle 602 is configured to inject droplets of fuel liquid toward the location where plasma 2 is formed. Droplets of fuel liquid may be ejected from the nozzle 602 by a combination of pressure within the reservoir 601 and vibration applied to the nozzle by a piezoelectric actuator (not shown).

As those skilled in the art will appreciate, reference axes X, Y, and Z can be defined to measure and describe the geometry and behavior of the device, its various components, and the radiation beams 20, 21, 26. At each part of the equipment, local reference coordinate systems for the X, Y, and Z axes can be defined. In the example of Figure 6, the Z-axis is approximately coincident with the directional optical axis O at a given point in the system, and is approximately perpendicular to the plane of the patterning device (reticle) MA and perpendicular to the plane of the substrate W. In the source collector module, the X-axis generally coincides with the direction of fuel flow 628, and the Y-axis is orthogonal to the direction of fuel flow 628, as indicated on the page, as indicated in Figure 6. On the other hand, near the support structure MT holding the reticle MA, the X-axis is generally transverse to the scanning direction aligned with the Y-axis. For convenience, in this area of Figure 6, the X-axis is pointed out from the page, again as labeled. Such designations are conventional in the art and will be used herein for convenience. In principle, any reference coordinate system can be chosen to describe the device and its behavior.

Numerous additional components used in the operation of the source collector module and lithography apparatus 500 as a whole are present in typical apparatuses but are not illustrated here. These components include arrangements for reducing or mitigating the effects of contamination within the enclosed vacuum, for example, to prevent deposits of fuel material from damaging or impairing the performance of the collector 3 and other optical components. Other features that are present but not described in detail are all sensors, controllers, and actuators involved in controlling the various components and subsystems of lithography apparatus 500.

Referring to Figure 7, an implementation of an LPP EUV light source 700 is shown. The light source 700 can be used as the source collector module SO in the lithography apparatus 500. Additionally, optical pulse generation system 104 of FIG. 1 may be part of driving laser 715. Driving laser 715 can be used as laser 623 (Fig. 6).

LPP EUV light source 700 is formed by irradiating target mixture 714 at plasma formation location 705 with an amplified beam 710 that travels along a beam path toward target mixture 714 . The target materials discussed with respect to Figures 1, 2A, 2B, and 3 and the targets in stream 121 discussed with respect to Figure 1 may be or include target mixture 714. The plasma formation location 705 is within the interior 707 of the vacuum chamber 730. When the amplified beam 710 is illuminated on the target mixture 714, the target materials within the target mixture 714 are converted into a plasma state of elements having emission lines in the EUV range. The generated plasma has certain properties that depend on the composition of the target materials within the target mixture 714. Such characteristics may include the wavelength of EUV light produced by the plasma and the type and amount of debris released from the plasma.

The light source 700 also includes a supply system 725 that delivers, controls, and directs the target mixture in the form of droplets, streams, solid particles or clusters, solid particles contained within a droplet, or solid particles contained within a stream. 714. Target mixture 714 includes target materials such as water, tin, lithium, xenon, or any material that has an emission line in the EUV range when converted to a plasma state. For example, element tin can be used as pure tin (Sn); as tin compounds, such as SnBr ₄ , SnBr ₂ , SnH ₄ ; as tin alloys, such as tin-gallium alloy, tin-indium alloy, tin-indium- Gallium alloy or any combination of such alloys. Target mixture 714 may also include impurities such as non-target particles. Therefore, in the absence of impurities, target mixture 714 consists solely of the target material. Target mixture 714 is delivered by supply system 725 into interior 707 of chamber 730 and to plasma formation location 705.

The light source 700 includes a driving laser system 715 due to The particle population in one or more gain media of the laser system 715 is inverted to produce an amplified beam 710 . The light source 700 includes a beam delivery system between the laser system 715 and the plasma formation location 705 . The beam delivery system includes a beam delivery system 720 and a focusing assembly 722 . Beam delivery system 720 receives amplified beam 710 from laser system 715, steers and modifies amplified beam 710 as necessary, and outputs amplified beam 710 to focusing assembly 722. Focusing assembly 722 receives amplified beam 710 and focuses beam 710 to plasma formation location 705 .

In some implementations, laser system 715 may include one or more optical amplifiers, lasers, and/or lamps for providing one or more main pulses and, in some cases, one or more pre-pulses. In implementations that include one or more pre-pulses, an optical pulse generation system such as optical pulse generation system 104 may be placed in the path of one or more of the pre-pulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength with high gain, an excitation source, and internal optics. The optical amplifier may or may not have a laser mirror or other feedback device forming a laser cavity. Therefore, laser system 715 may produce amplified beam 710 due to population inversion in the gain medium of the laser amplifier even in the absence of a laser cavity. Additionally, laser system 715 may generate amplified beam 710 as a coherent laser beam in the presence of a laser cavity to provide sufficient feedback to laser system 715. The term "amplified light beam" encompasses one or more of the following: light from laser system 715 that is merely amplified but not necessarily coherent laser oscillations, and light from laser system 715 that is also coherent laser oscillation. emit oscillating light.

The optical amplifier in the laser system 715 may include a filling gas (including CO ₂ ) as a gain medium, and may amplify a gain of greater than or equal to 800 times at a wavelength between about 9100 nm and about 11000 nm, and particularly at about 10600 nm. Light. Suitable amplifiers and lasers for use in laser system 715 may include pulsed laser devices, such as pulsed gas discharge _CO2 laser devices that operate, for example, with relatively high _power ( DC or RF excitation operating at a high pulse repetition rate (eg, 10 kW or more) and a high pulse repetition rate (eg, 40 kHz or more) produces radiation at about 9300 nm or about 10600 nm. For example, the pulse repetition rate may be 50kHz. The optical amplifier in laser system 715 may also include a cooling system, such as water, that may be used when operating laser system 715 at higher powers.

Light source 700 includes a collector mirror 735 having an aperture 740 to allow amplified light beam 710 to pass through and reach plasma formation location 705 . Collector mirror 735 may be, for example, an ellipsoidal mirror having a primary focus at plasma formation location 705 and a secondary focus (also referred to as an intermediate focus) at intermediate location 745, where EUV light may be output from light source 700 and This may be input to, for example, an integrated circuit lithography tool (not shown). The light source 700 may also include an open-ended hollow conical shield 750 (e.g., a gas cone) that tapers from the collector mirror 735 toward the plasma formation location 705 to reduce entry into the focusing assembly 722 and/or the beam. The amount of plasma generated by the delivery system 720 simultaneously allows the amplified beam 710 to reach the plasma formation location 705 . For this purpose, an air flow may be provided in the shroud, which air flow is directed to the plasma formation location 705 .

The light source 700 may also include a main control controller 755 connected to the droplet position detection feedback system 756, the laser control system 757, and the beam control system 758. The light source 700 may include one or more targets or droplet imagers 760 that provide an output indicative of the position of the droplet, such as relative to the plasma formation location 705 and provide this output to the droplet. The droplet position detection feedback system 756 may, for example, calculate the droplet position and trajectory, and may calculate the droplet position error from the droplet position and trajectory on a droplet-by-drop basis or on average. Therefore, the droplet position detection feedback system 756 provides the droplet position error as an input to the main control controller 755 . Therefore, the main control controller 755 can provide laser position, direction and timing correction signals to, for example, a laser control system 757 that can be used, for example, to control a laser timing circuit and/or to a beam control system 758, which uses To control the amplified beam position and beam delivery system The shape of 720 is used to change the position and/or power of the beam focal spot in the chamber 730 .

Supply system 725 includes a target material delivery control system 726 operable to modify the release point of droplets as released by target material supply device 727 in response to a signal, for example, from master controller 755 to correct The error in the droplet reaching the desired plasma formation position 705. Target material supply equipment 727 includes target forming equipment using an adhesive (such as adhesive 234).

In addition, the light source 700 may include light source detectors 765 and 770 that measure one or more EUV light parameters, including but not limited to pulse energy, energy distribution that changes according to wavelength, and specific wavelength bands. energy within a specific wavelength band, energy outside a specific wavelength band, and the angular distribution of EUV intensity and/or average power. The light source detector 765 generates a feedback signal for use by the main controller 755 . The feedback signal may, for example, indicate errors in parameters such as timing and focus of the laser pulse to intercept the droplet properly at the right place and time for effective and efficient EUV light production.

The light source 700 may also include a guide laser 775 that may be used to align various segments of the light source 700 or assist in steering the amplified beam 710 to the plasma formation location 705. In conjunction with the guide laser 775, the light source 700 includes a metrology system 724 placed within the focusing assembly 722 to sample a portion of the light from the guide laser 775 and the amplified beam 710. In other implementations, the weights and measures system 724 is placed within the beam delivery system 720 . Metrology system 724 may include optical elements that sample or redirect a subset of light and are made of any material that can withstand the power of the guided laser beam and amplified beam 710. The beam analysis system is formed by the metrology system 724 and the master controller 755 because the master controller 755 analyzes the light sampled by the guided laser 775 and uses this information to adjust the focus assembly 722 via the beam control system 758 of components.

Thus, in summary, light source 700 generates an amplified beam 710 that is directed along the beam path to irradiate target mixture 714 at plasma formation location 705 to convert the target material within mixture 714 to emit EUV Plasma of light within range. Amplified beam 710 operates at a specific wavelength (which is also referred to as the drive laser wavelength) determined based on the design and properties of laser system 715 . Additionally, amplified beam 710 may be a laser when the target material provides sufficient feedback back into laser system 715 to produce coherent laser light or when driving laser system 715 includes suitable optical feedback to form a laser cavity. beam.

Implementation may be further described by the following items:

1. An apparatus for an extreme ultraviolet (EUV) light source, the apparatus comprising: an optical modulation system comprising an electro-optical material, the optical modulation system being configured to receive a pulsed beam contained in a plurality of light pulses that are temporally separated from each other; and a control system configured to control a power source such that a first electrical pulse is applied to the electro-optic material when a first light pulse is incident on the electro-optic modulator , applying a second electrical pulse to the electro-optical material when a second light pulse is incident on the electro-optical material, and after the first light pulse is incident on the electro-optical material and after the second light pulse is incident on the electro-optical material An intermediate electrical pulse is previously applied to the electro-optical material.

2. The apparatus of clause 1, wherein applying the first electrical pulse to the electro-optical material produces a physical effect in the electro-optical material, and when the intermediate electrical pulse is applied to the electro-optical material, the physical effect is present in in the electro-optical material.

3. The device of clause 2, wherein the physical effect includes acoustic waves and/or mechanical strains traveling in the electro-optical material.

4. The device of clause 2, wherein applying the intermediate electrical pulse to the electro-optical material reduces the physical effect.

5. The device of clause 1, wherein the first light pulse and the second light pulse are continuous light pulses in the pulse beam.

6. The apparatus of clause 1, wherein the control system is configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse.

7. The device of clause 1, wherein the electro-optical material includes a semiconductor.

8. The device of clause 1, wherein the electro-optical material includes an insulator.

9. The device of clause 1, wherein the electro-optical material includes an electro-optical crystal.

10. The apparatus of clause 1, further comprising at least one polarization-based optical element.

11. The device of clause 1, wherein the intermediate electrical pulse generates an acoustic interference that interferes with an acoustic interference generated by the first electrical pulse.

12. An apparatus for forming optical pulses, the apparatus comprising: an optical modulation system comprising an electro-optical material, the optical modulation system configured to transmit light in an on state and block light in an off state light, and the optical modulation system is configured to receive a pulse beam, the pulse beam includes at least a first light pulse and a second light pulse that are temporally separated from each other; and a control system coupled to a a voltage source, the control system configured to produce a first shape by causing the voltage source to apply the first voltage pulse to the electro-optic modulator when the first light pulse is incident on the electro-optic modulator Optical pulses, the first voltage pulse configured to switch the electro-optical modulator to the on state; applying an intermediate voltage pulse to the electro-optical material; and by applying the first voltage pulse and the intermediate voltage pulse A second voltage pulse is then applied to the electro-optic material to generate a second shaped optical pulse when the second optical pulse is incident on the electro-optic material, wherein the second voltage pulse is configured to modulate the electro-optic material. switch to this On state, and the properties of the second shaped optical pulse are controlled by the application of the intermediate voltage pulse to the electro-optical material.

13. The apparatus of clause 12, wherein the second shaped optical pulse includes a base portion and a main portion, and the property of the second shaped optical pulse includes a property of the base such that one of the base portion Properties are controlled by the application of the intermediate voltage pulse to the electro-optical material.

14. The equipment of clause 13, wherein the base part and the main part are temporally continuous.

15. The equipment of clause 13, wherein the property of the base portion includes a time interval, a maximum intensity and/or an average intensity of the base portion.

16. The apparatus of clause 12, wherein the application of the intermediate voltage pulse to the electro-optical material modifies an amount of optical leakage light transmitted by the optical modulation system in the off state.

17. The apparatus of clause 16, wherein the application of the intermediate voltage pulse to the electro-optical material reduces optical leakage light transmitted by the optical modulation system in the off state.

18. The apparatus of clause 12, wherein the control system causes the first voltage pulse to be applied to the electro-optical material at a first time, and the control system causes the intermediate voltage pulse to be applied to the electro-optical material at a second time after the first time. is applied to the electro-optical material, the second time is temporally separated from the first time by a delay time, and the control system is further configured to adjust the delay time to thereby control a property of the second shaped optical pulse .

19. The apparatus of clause 18, wherein the control system is further configured to control at least one of an amplitude, a duration and/or a phase of the intermediate voltage pulse.

20. The equipment of clause 13, wherein the control system is further configured to: An indication of a measured property of the base portion is received, and a property of the intermediate voltage pulse is adjusted based on the received indication.

21. The apparatus of clause 12, wherein the control system is further configured to: receive an indication of an amount of extreme ultraviolet (EUV) light generated by a plasma, and based on receipt of the amount of EUV light Indicates and adjusts one of the properties of the intermediate voltage pulse.

22. The equipment of clause 21, wherein the control system is configured to adjust a property of the intermediate voltage pulse including the control system is configured to adjust an amplitude of the intermediate voltage pulse, a time interval of the intermediate voltage pulse, A phase of the intermediate voltage pulse and/or a second time, the second time being a time for applying the intermediate voltage pulse to the electro-optical material.

23. A method of modulating a property of a base of an optical pulse, the method comprising: applying a first voltage pulse to an electro-optical component of an optical modulation system when light is incident on the optical modulation system. material to form a first optical pulse, the first optical pulse including a first base portion and a first main portion; applying an intermediate voltage pulse to the electro-optical material after applying the first voltage pulse; and by After the first voltage pulse and the intermediate voltage pulse and when light is incident on the electro-optical material, a second voltage pulse is applied to the electro-optical material to form a second optical pulse, wherein a property of the second base portion It is adjusted based on the application of this intermediate voltage pulse.

24. The method of clause 23, further comprising: amplifying the first optical pulse to form an amplified first optical pulse; receiving an indication of an amount of extreme ultraviolet (EUV) light emitted from a plasma that Plasma is generated by interacting the amplified first optical pulse with the target material; and At least one property of the intermediate voltage pulse is determined based on the received indication of the amount of EUV light emitted from the plasma.

25. The method of clause 24, wherein the at least one property of the intermediate voltage pulse includes a time delay after application of the first voltage pulse, and determining the at least one property of the intermediate voltage pulse includes based on The time delay is determined based on the received indication of the amount of EUV light emitted.

26. The method of clause 24, wherein the at least one property of the intermediate voltage pulse includes an amplitude and/or a duration of the intermediate voltage pulse, and determining the at least one property of the intermediate voltage pulse includes determining the intermediate voltage pulse. the amplitude and/or the duration.

27. The method of clause 23, wherein the second optical pulse includes a base portion and a main portion, and a property of the base portion is adjusted based on the application of the intermediate voltage pulse.

28. The method of clause 27, wherein the base portion is temporally continuous with the main portion.

29. An extreme ultraviolet (EUV) light source, comprising: a container; a target material supply device configured to be coupled to the container; an optical modulation system configured to receive a pulsed beam , the optical modulation system includes an electro-optical material; and a control system coupled to a voltage source, the control system being configured to: cause the voltage source to apply a plurality of shaped voltage pulses to the electro-optical material, the plurality of Each of the shaped voltage pulses is applied to the electro-optical material at a different time and causes the voltage source to apply at least one intermediate voltage pulse to the electro-optical material, the at least one intermediate voltage pulse being applied to the electro-optical material during the plurality of shaped voltage pulses. One of two consecutive shaped voltage pulses in the voltage pulse time is applied to the electro-optical material.

30. The EUV light source of clause 29, wherein the target material supply device is configured to provide a plurality of target material droplets to a target area in the container, the target material droplets arriving at the target area at a target delivery rate. target area, and the control system applies the shaping voltage pulses to the electro-optical material at a shaping rate that is dependent on the target delivery rate.

31. The EUV light source of clause 28, wherein the characteristics of the intermediate voltage pulse include an amplitude and/or a phase, and the control system is further configured to: access an amplitude stored in association with the forming rate and /or a phase, and causing the voltage source to generate the intermediate voltage pulse having the accessed amplitude and/or phase.

32. The EUV light source of clause 29, wherein the control system is further configured to control a time delay between application of one of the shaping voltage pulses and one of the intermediate voltage pulses.

33. The EUV light source of clause 29, further comprising an optical amplifier, and wherein each time a shaped voltage pulse is applied to the electro-optical material, an optical pulse is formed; the shaped optical pulse is amplified by the optical amplifier to form an amplified Optical pulses; the control system is further configured to be coupled to a metrology system configured to measure an amount of EUV light generated by a plasma in the container by using The formed amplified optical pulses are irradiated to the target material to form, the control system is configured to receive a quantitative measurement of EUV light from the metrology system; and the control system is configured to generate an optical signal based on the quantitative measurement of EUV light. One or more characteristics of the intermediate voltage pulse are modified.

34. The EUV light source of clause 33, wherein the one or more characteristics of the intermediate voltage pulse include an amplitude of the intermediate voltage pulse, a time interval of the intermediate voltage pulse, a phase of the intermediate voltage pulse and/or A delay time after the application of a most recently shaped voltage pulse.

Other implementations are within the scope of the patent application.

106:Beam

107: Modified Optical Pulse

108: Irradiated optical pulse/amplified optical pulse

111:Path

115:Target area

122:Material

130:Optical amplifier

175:Control system

176: Communication interface

177: Electronic processor

178: Electronic storage

179:Input/output (I/O) interface

214:Voltage signal

220: Modulation system

223:Voltage source

223a:Electrode

223b:Electrode

224: Optical components based on polarization

Claims (34)

A device for an extreme ultraviolet (EUV) light source, the device containing: and A control system configured to control a power supply such that a first electrical pulse is applied to the electro-optic material when a first light pulse is incident on the electro-optic modulator, and a second light pulse is incident on the electro-optic modulator. A second electrical pulse is applied to the electro-optical material when the material is incident on the electro-optical material, and an intermediate electrical pulse is applied to the electro-optical material after the first light pulse is incident on the electro-optical material and before the second light pulse is incident on the electro-optical material. The electro-optical material. The device of claim 1, wherein applying the first electrical pulse to the electro-optic material produces a physical effect in the electro-optic material, and when the intermediate electrical pulse is applied to the electro-optic material, the physical effect is present in the electro-optic material in the material. The device of claim 2, wherein the physical effect includes acoustic waves and/or mechanical strains traveling in the electro-optical material. The device of claim 2, wherein applying the intermediate electrical pulse to the electro-optical material reduces the physical effect. The device of claim 1, wherein the first light pulse and the second light pulse are continuous light pulses in the pulse beam. The apparatus of claim 1, wherein the control system is configured to control an amount of time between the first electrical pulse and the intermediate electrical pulse. The device of claim 1, wherein the electro-optical material includes a semiconductor. The device of claim 1, wherein the electro-optical material includes an insulator. The device of claim 1, wherein the electro-optic material includes an electro-optic crystal. The device of claim 1, further comprising at least one polarization-based optical element. The device of claim 1, wherein the intermediate electrical pulse generates an acoustic interference that interferes with an acoustic interference generated by the first electrical pulse. A device for forming optical pulses, the device comprising: An optical modulation system including an electro-optical material, the optical modulation system is configured to transmit light in an on state and block light in an off state, and the optical modulation system is configured to receive a pulse a light beam, the pulsed light beam comprising at least a first light pulse and a second light pulse that are temporally separated from each other; and A control system coupled to a voltage source, the control system configured to: A first shaped optical pulse is generated by causing the voltage source to apply the first voltage pulse to the electro-optic modulator when the first optical pulse is incident on the electro-optic modulator, the first voltage pulse being configured to switch the electro-optical modulator to the on state; applying an intermediate voltage pulse to the electro-optical material; and A second shaped optical pulse is generated by applying a second voltage pulse to the electro-optical material after applying the first voltage pulse and the intermediate voltage pulse and when the second optical pulse is incident on the electro-optical material, wherein The second voltage pulse is configured to switch the electro-optic modulator into the on state, and a property of the second shaped optical pulse is controlled by application of the intermediate voltage pulse to the electro-optic material. The apparatus of claim 12, wherein the second shaped optical pulse includes a base portion and a main portion, and the property of the second shaped optical pulse includes a property of the base portion such that a property of the base portion is Controlled by the application of the intermediate voltage pulse to the electro-optical material. The device of claim 13, wherein the base part and the main part are temporally continuous. The device of claim 13, wherein the property of the base portion includes a time interval, a maximum intensity and/or an average intensity of the base portion. The apparatus of claim 12, wherein the application of the intermediate voltage pulse to the electro-optical material modifies an amount of optical leakage light transmitted by the optical modulation system in the off state. The apparatus of claim 16, wherein the application of the intermediate voltage pulse to the electro-optical material reduces optical leakage light transmitted by the optical modulation system in the off state. Such as the equipment of request item 12, wherein the control system causes the first voltage pulse to be applied to the electro-optical material at a first time, the control system causes the intermediate voltage pulse to be applied to the electro-optical material at a second time after the first time, The second time is temporally separated from the first time by a delay time, and The control system is further configured to adjust the delay time to thereby control a property of the second shaped optical pulse. The device of claim 18, wherein the control system is further configured to control at least one of an amplitude, a time interval, and a phase of the intermediate voltage pulse. The equipment of claim 13, wherein the control system is further configured to: receiving an indication of a measured property of the base portion, and A property of the intermediate voltage pulse is adjusted based on the received indication. The equipment of claim 12, wherein the control system is further configured to: receives an indication of an amount of extreme ultraviolet (EUV) light produced by a plasma, and A property of the intermediate voltage pulse is adjusted based on the received indication of the amount of EUV light. The device of claim 21, wherein the control system is configured to adjust a property of the intermediate voltage pulse including: the control system is configured to adjust an amplitude of the intermediate voltage pulse, a time interval of the intermediate voltage pulse, the A phase of the intermediate voltage pulse and/or a second time, the second time being a time for applying the intermediate voltage pulse to the electro-optical material. A method of adjusting one of the properties of an optical pulse, the method comprising: Forming a first optical pulse by applying a first voltage pulse to an electro-optical material of an optical modulation system when light is incident on the optical modulation system; applying an intermediate voltage pulse to the electro-optical material after applying the first voltage pulse; and A second optical pulse is formed by applying a second voltage pulse to the electro-optical material after the first voltage pulse and the intermediate voltage pulse and when light is incident on the electro-optical material, wherein the second optical pulse A property is based on the application of the intermediate voltage pulse. For example, the method of request item 23 further includes: amplifying the first optical pulse to form an amplified first optical pulse; an indication of the amount of extreme ultraviolet (EUV) light received from a plasma generated by interaction of the amplified first optical pulse with a target material; and At least one property of the intermediate voltage pulse is determined based on the received indication of the amount of EUV light emitted from the plasma. The method of claim 24, wherein the at least one property of the intermediate voltage pulse includes a time delay after application of the first voltage pulse, and determining the at least one property of the intermediate voltage pulse includes based on emission from the plasma. The time delay is determined based on the received indication of the amount of EUV light. The method of claim 24, wherein the at least one property of the intermediate voltage pulse includes an amplitude and/or a duration of the intermediate voltage pulse, and determining the at least one property of the intermediate voltage pulse includes determining the property of the intermediate voltage pulse. amplitude and/or duration. The method of claim 23, wherein the second optical pulse includes a base portion and a main portion, and a property of the base portion is adjusted based on the application of the intermediate voltage pulse. The method of claim 27, wherein the base portion is temporally continuous with the main portion. An extreme ultraviolet (EUV) light source containing: a container; a target material supply device configured to be coupled to the container; an optical modulation system configured to receive a pulsed beam, the optical modulation system including an electro-optical material; and A control system coupled to a voltage source, the control system configured to: causing the voltage source to apply a plurality of shaped voltage pulses to the electro-optical material, each of the plurality of shaped voltage pulses being applied to the electro-optical material at a different time, and The voltage source is caused to apply at least one intermediate voltage pulse to the electro-optical material, the at least one intermediate voltage pulse being applied to the electro-optical material between two consecutive shaped voltage pulses of the plurality of shaped voltage pulses. The EUV light source of claim 29, wherein the target material supply device is configured to provide a plurality of target material droplets to a target area in the container, the target material droplets arriving at the target area at a target delivery rate , and the control system applies the forming voltage pulses to the electro-optical material at a forming rate that depends on the target delivery rate. The EUV light source of claim 29, wherein the characteristics of the intermediate voltage pulse include an amplitude and/or a phase, and The control system is further configured to: access an amplitude and/or a phase stored in association with the forming rate, and The voltage source is caused to generate the intermediate voltage pulse having the accessed amplitude and/or phase. The EUV light source of claim 29, wherein the control system is further configured to control a time delay between application of one of the shaping voltage pulses and one of the intermediate voltage pulses. The EUV light source of claim 29, further comprising an optical amplifier, and in forming an optical pulse each time a shaped voltage pulse is applied to the electro-optical material; Amplify the shaped optical pulse by the optical amplifier to form an amplified optical pulse; the control system is further configured to be coupled to a metrology system configured to measure an amount of EUV light generated by a plasma in the container, The plasma is formed by irradiating the target material with shaped amplified optical pulses, The control system is configured to receive quantitative measurements of EUV light from the metrology system; and The control system is configured to modify one or more characteristics of the intermediate voltage pulse based on the quantitative measurement of EUV light. The EUV light source of claim 33, wherein the one or more characteristics of the intermediate voltage pulse include an amplitude of the intermediate voltage pulse, a time interval of the intermediate voltage pulse, a phase of the intermediate voltage pulse and/or a nearest A delay time after the application of the shaping voltage pulse.