Ultraviolet light pulse generation

Abstract

To modify some of the characteristics of the light pulses generated by an extreme ultraviolet light source. [Solution] An extreme ultraviolet (EUV) light pulse is formed by illuminating a semiconductor material of a modulation system with a first light beam having a first wavelength, applying a voltage to the semiconductor material for a certain duration that is sufficient to modify the refractive index of the semiconductor material so that the polarization state of a light beam having a second wavelength passing through the semiconductor material is modified and passes through at least one polarization-based optical element of the modulation system, and passing the semiconductor material through a second light beam having a second wavelength for the duration thereof to form a light pulse.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Application No. 15 / 469,267, filed on Mar. 24, 2017, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present disclosure relates to the generation of optical pulses of an extreme ultraviolet light source.

Background Art

[0003]

[0003] In a photolithography process, electromagnetic radiation including extreme ultraviolet (EUV) light, for example light having a wavelength of about 50 nm or less (sometimes referred to as soft X - rays) such as light having a wavelength of about 13 nm, can be used to create very small features on a substrate, such as a silicon wafer.

[0004]

[0004] Methods of generating EUV light include, but are not necessarily limited to, converting a material having an element with emission lines in the EUV region in a plasma state, such as xenon, lithium, or tin. In one such method, often called laser - produced plasma (“LPP”), the required plasma can be generated by irradiating a target material, which can take the form of, for example, droplets, plates, tapes, streams, or clusters of the material, with an amplified light beam, which can be referred to as a drive laser. For this process, the plasma is generally generated within a sealed container, such as a vacuum chamber, and monitored using various types of metrology (measurement) equipment.

Summary of the Invention

[0005]

[0005] In a general embodiment, a method for forming an optical pulse from an extreme ultraviolet (EUV) light source includes illuminating a semiconductor material of a modulation system with a first light beam having a first wavelength; applying a voltage to the semiconductor material for a certain duration sufficient to modify the refractive index of the semiconductor material so that the polarization state of a light beam having a second wavelength passing through the semiconductor material is modified to pass through at least one polarization-based optical element of the modulation system; and passing the semiconductor material through a second light beam having a second wavelength for the duration thereof to form an optical pulse. The formed optical pulse includes a first portion and a second portion, the first portion and the second portion being temporally continuous, the first portion occurring before the second portion, and one or more features of the first portion of the formed optical pulse being modified by illuminating the semiconductor material of the modulation system with the first light beam.

[0006]

[0006] The implementation may include one or more of the following features: One or more features of the first part of the light pulse may include one or more of the average intensity, maximum intensity, and duration. The formed pulse may be capable of propagating toward the target region, and the first part of the formed pulse may have a maximum intensity smaller than the maximum intensity of the second part of the formed pulse. The maximum intensity of the second part may be sufficient to convert the target material of the target in the target region into a plasma emitting EUV light.

[0007]

[0007] The second wavelength may be at least three times the magnitude of the first wavelength.

[0008]

[0008] The semiconductor material may also be associated with spectral transmission characteristics, which include a transmission region and an absorption edge wavelength, where the absorption edge wavelength is the lowest wavelength in the transmission region, the first wavelength is between the absorption edge wavelength and the second wavelength, and the second wavelength may be a wavelength within the transmission region. The second wavelength is not greater than 3.5 times the first wavelength.

[0009]

[0009] The semiconductor material may be associated with a bandgap energy, which is the energy difference between the valence band and the conduction band of the semiconductor material, and the photon energy of the first wavelength may be less than the bandgap energy. The semiconductor material may contain defects, which generate deep-level traps having energy levels between the valence band and the conduction band, and the photon energy of the first wavelength may be equal to or greater than the energy difference between at least one energy level of the deep-level trap and the conduction band or between at least one energy level of the deep-level trap and the valence band.

[0010]

[0010] The second wavelength may include 10.6 μm, and the semiconductor material may be one of zinc cadmium telluride (CdZnTe), cadmium telluride (CdTe), zinc telluride (ZnTe), and gallium arsenide (GaAs). The first wavelength may be a wavelength of 0.75 microns (μm) to 3.5 μm, and the second wavelength may include a wavelength of 9 μm to 11 μm.

[0011]

[0011] The first and second light beams may follow the same spatial path through the semiconductor material. The first and second light beams may be within the semiconductor material at the same time.

[0012]

[0012] The characteristics of the first light beam may be adjusted to adjust one or more of the characteristics of the first portion of the light pulse. Adjusting the characteristics of the first light beam may include increasing the intensity of the first light beam to reduce the maximum or average intensity of the first portion of the light pulse.

[0013]

[0013] In another general embodiment, an extreme ultraviolet (EUV) light source system includes a modulation system including a semiconductor material having one or more types of defects and whose refractive index changes in response to the application of a voltage, and a first light source configured to generate a first light beam having the first wavelength, such that when the semiconductor material is illuminated with light having the first wavelength, the leakage current of the semiconductor material increases. A control system coupled to a modulation system, The system includes a control system configured to apply a voltage to a semiconductor material while a second light beam having a second wavelength propagates through the semiconductor material to form a light pulse from the second light beam, the light pulse being configured to convert at least some of the target material into a plasma emitting EUV light.

[0014]

[0016] The implementation may include one or more of the following characteristics: The pulse may include a first part and a second part, the first and second parts being temporally continuous, and the first part occurring before the second part.

[0015]

[0017] The modulation system may also include at least one polarization-based optical element. The semiconductor material may be quartz. The second light beam may be a continuous light beam. The defect type may include one or more of the following: precipitates, inclusions, twins, and slip planes.

[0016]

[0018] The second light source may include a pulsed light source, and the control system may be coupled to the modulation system and the second light source, and the control system may be configured to control the second light source to emit pulses of light. The control system may also be configured to control the second light source to guide the pulses of the second light beam toward the semiconductor material while a voltage is applied to the semiconductor material and while the first light beam is guided toward the semiconductor material. At least one pulse of the first light beam and the second light beam may be simultaneously within the semiconductor material.

[0017]

[0019] The control system may also be configured to control a first light source, thereby controlling one or more characteristics of a first portion of the light pulse. These one or more characteristics may include one or more of the average intensity, maximum intensity, and duration. The control system may also be configured to control the intensity of the first portion of the pulse by controlling the first light source.

[0018]

[0020] The EUV light source system may also include a light beam delivery system between the first light source and the semiconductor material, the light beam delivery system being configured to guide the first light beam to a specific location on the semiconductor material.

[0019]

[0021] In another general embodiment, a method for modifying acoustic effects in an electro-optic modulator includes applying a voltage to a semiconductor of the electro-optic modulator for a first period of time, thereby generating an acoustic effect in the semiconductor, including a vibrating sound wave; and illuminating the semiconductor with a seed light beam having a wavelength having a photon energy smaller than the bandgap energy of the semiconductor, thereby modifying one or more of the amplitude and frequency of the sound wave.

[0020]

[0022] The implementation may include one or more of the following features: A continuous wave light beam may be guided toward the semiconductor of the electro-optic modulator. Here, the first quantity of the continuous wave light beam passes through the electro-optic modulator in a first polarization state for a first period of time when a voltage is applied to the semiconductor. The second quantity of the continuous wave light beam changes when no voltage is applied to the semiconductor and acoustic effects exist within the semiconductor, as the light beam passes through the electro-optic modulator at times other than the first period, illuminating the semiconductor with the seed light beam.

[0021]

[0024] The pulses of the pulsed light beam may be directed towards the electro-optic modulator. The first amount of light in the pulse passes through the semiconductor for a first period when a voltage is applied to the semiconductor, and the second amount of light in the pulse passes through the semiconductor when no voltage is applied to the semiconductor at times other than the first period. Here, the second amount of light changes when the semiconductor is illuminated with a seed light beam.

[0022]

[0025] Any implementation of the technologies described above may include an EUV light source, a system, a method, a process, a device, or an apparatus. Details of one or more implementations are described in the accompanying drawings and the following description. Other features will be apparent from the description and drawings, and from the claims.

Brief Description of the Drawings

[0023] [Figure 1]

[0026] FIG. 1 is a block diagram of an example of an extreme ultraviolet (EUV) lithography system including an EUV light source. [Figure 2A]

[0027] FIG. 2 is a block diagram of a modulation module used in the EUV light source of FIG. 1. [Figure 2B]

[0028] FIG. 3 is a diagram of an optical pulse. [Figure 3A]

[0029] FIG. 4 is a plot of light leakage of the modulation module of FIG. 2A and two pulses formed by the modulator of FIG. 2A. [Figure 3B]

[0030] FIG. 5 is an example of a timing diagram of an application to a modulation module for generating the pulse shown in FIG. 3A. [Figure 4A]

[0031] FIG. 6 is an example of an energy diagram of a semiconductor of the modulation module of FIG. 2A. [Figure 4B]

[0032] FIG. 7 is an example of a spectral transmission characteristic of a semiconductor of the modulation module of FIG. 2A. [Figure 5A]

[0033] FIG. 8 is a plot of two optical pulses that can be generated by the modulation module of FIG. 2A. [Figure 5B]

[0034] FIG. 9 is an example of a timing diagram of an application to a modulation module for generating the pulse shown in FIG. 5A. [Figure 6]

[0035] FIG. 10 is a flowchart of an example of a process for forming an optical pulse. [Figure 7]

[0036] FIG. 11 is an example of experimental results. [Figure 8]

[0036] FIG. 11 is an example of experimental results. [Figure 9]

[0036] FIG. 11 is an example of experimental results. [Figure 10]

[0036] An example of experimental results. [Figure 11]

[0037] This is a perspective view of a pulse generation system that may be used in the EUV light source shown in Figure 1. [Figure 12]

[0037] This is a perspective view of a pulse generation system that may be used in the EUV light source shown in Figure 1. [Figure 13A]

[0038] This is a block diagram of an example of an EUV light source. [Figure 13B]

[0038] This is a block diagram of an example of an EUV light source. [Modes for carrying out the invention]

[0024]

[0039] This paper describes techniques for forming light pulses in extreme ultraviolet (EUV) light sources. Electro-optic modulators used to form light pulses release trapped charges within their semiconductors when illuminated by a seed light beam. These charges are trapped due to defects in the semiconductor, and the trapped charges increase light leakage from the modulator. This light leakage introduces additional or unwanted light (spurious light) into the pulse formed by the modulator. Some of this unwanted light forms a "pedestal" at the beginning of the formed pulse. By releasing the trapped charges, light leakage can be reduced and / or controlled, and the pedestal can also be reduced and / or controlled.

[0025]

[0040] 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 an EUV light source 101, which provides EUV light 196 to a lithography apparatus 195. The lithography apparatus 195 exposes a wafer (e.g., a silicon wafer) with the EUV light 196 to form electronic features on the wafer. The EUV light 196 is emitted from a plasma formed by irradiating a target material of target 118 with an optical pulse 107. The target material is any material that emits EUV light in a plasma state (e.g., tin).

[0026]

[0041] The EUV light source 101 includes a pulse generation system 104 that generates pulses 107. The pulse generation system 104 includes a light source 105, which may be, for example, a pulsed (e.g., Q-switched) laser or a continuous-wave carbon dioxide (CO2) laser. The light source 105 generates a light beam 106. This light beam may be a pulse train of light or a continuous light beam. The light source 105 emits the light beam 106 toward a modulation module 120 which includes a semiconductor 122.

[0027]

[0042] The modulation module 120 is an electro-optic modulator that modulates the incident light beam based on the electro-optic effect. The electro-optic effect represents a change in the refractive index of a material (semiconductor 122) caused by the application of a direct current (DC) electric field or a low-frequency electric field. The modulation module 120 is controlled by the control system 175 to form a pulse 107 from the light beam 106 or from a pulse of light from the light beam 106. The pulse 107 propagates along the path 111 toward the vacuum vessel 180 housing the target 118. The pulse 107 and the target 118 interact in the target region 115 within the vacuum vessel 180, and this interaction converts at least some of the target material of the target 118 into a plasma that emits EUV light 196.

[0028]

[0043] The EUV light source 101 also includes a seed light source 110. The seed light source 110 emits a seed light beam 114 that illuminates the semiconductor 122. The semiconductor 122 contains defects that can trap charges. The seed light beam 114 has a wavelength related to sufficient photon energy to excite the trapped charges, which can move the trapped charges into the conduction band of the semiconductor 122, thereby increasing the conductivity of the semiconductor 122. By removing or reducing the trapped charges, as will be described in more detail below with respect to Figures 2 to 12, the ability of the modulation module 120 to form pulses 107 is improved.

[0029]

[0044] The control system 175 exchanges data and / or information with the pulse generation system 104 and / or any of its components via the communication interface 176. For example, in some implementations, the control system 175 may provide trigger signals for operating the modulation module 120 and / or the light source 105. The control system 175 includes an electronic processor 177, an electronic storage device 178, and an input / output (I / O) interface 179. The electronic processor 177 comprises one or more processors suitable for executing computer programs, such as general-purpose or dedicated microprocessors, and one or more processors of any type of digital computer. Generally, the electronic processor receives instructions and data from read-only memory, random access memory, or both. The electronic processor 177 may be any type of electronic processor.

[0030]

[0045] The electronic storage device 178 may be a volatile memory such as RAM, or it may be a non-volatile memory. In some implementations, the electronic storage device 178 includes non-volatile and volatile parts or components. The electronic storage device 178 may store data and information used in the operation of the control system 175 and / or components of the control system 175.

[0031]

[0046] Furthermore, the electronic memory device 178 can store, presumably as a computer program, instructions that cause the processor 177 to communicate with the components of the control system 175, the modulation module 120, and / or the light source 105 during execution. For example, in an implementation where the light source 105 is a pulse light source, the instruction may be an instruction to generate a signal in the electronic processor 177, which in turn causes the light source 105 to emit light pulses.

[0032]

[0047] The I / O interface 179 is any type of electronic interface that enables the control system 175 to receive and / or provide data and signals to an automated process operating on an operator, a modulation module 120, and / or a light source 105, and / or other electronic equipment. For example, the I / O interface 179 may include one or more of a visual display, a keyboard, and a communication interface.

[0033]

[0048] Figure 2A is a block diagram of the modulation module 120. The modulation module 120 includes a semiconductor 122, which is positioned between electrodes 123a and 123b. Electrodes 123a and 123b can be controlled to form an electric field between them. For example, the control system 175 may hold electrode 123a at a higher voltage than electrode 123b, thereby creating an electric field or potential difference (V) across the semiconductor 122.

[0034]

[0049] The modulation module 120 also includes one or more polarization-based optical elements 124. In the example in Figure 2A, only one polarization-based optical element 124 is shown. However, in other implementations, additional polarization-based optical elements 124 may be included. For example, a second polarization-based optical element 124 may be located on the side of the modulation module 120 that receives the light beam 106.

[0035]

[0050] A polarization-based optical element 124 is any optical element that interacts with light based on the polarization state of that light. For example, a polarization-based optical element 124 may be a linear polarizer that transmits horizontally polarized light and blocks vertically polarized light, or vice versa. A polarization-based optical element 124 may be a polarizing beam splitter that transmits horizontally polarized light and reflects vertically polarized light. A polarization-based optical element 124 may be an optical element that absorbs all light except light having a specific polarization state. In some implementations, a polarization-based optical element 124 may include a quarter-wave plate. At least one polarization-based optical element 124 is positioned to receive light passing through the semiconductor 122 and to guide light of a certain polarization state onto the beam path 111.

[0036]

[0051] The semiconductor 122 can be any material that transmits one or more wavelengths of the light beam 106. Furthermore, the semiconductor 122 exhibits anisotropy that can be modified by applying a controllable external force (such as a potential difference (V)). Controlling the anisotropy allows for control of the refractive index of various polarization components of the light propagating through the semiconductor 122. In the case of a configuration in which the light beam 106 contains light with a wavelength of 10.6 microns (μm), the semiconductor 122 may be, for example, zinc cadmium telluride (CdZnTe or CZT), cadmium telluride (CdTe), zinc telluride (ZnTe), and / or gallium arsenide (GaAs). Other materials may be used for other wavelengths. For example, semiconductor 122 may be monopotassium phosphate (KDP), ammonium dihydrogen phosphate (ADP), quartz, cuprous chloride (CuCl), zinc sulfide (ZnS), zinc selenide (ZnSe), lithium niobate (LiNbO3), gallium phosphide (GaP), lithium tantalate (LiTaO3), or barium titanate (BaTiO3). Other materials that transmit one or more wavelengths of the light beam 106 and exhibit birefringence in response to the application of an external force may also be used.

[0037]

[0052] The polarization state of light passing through semiconductor 122 can be controlled by controlling the potential difference (V) between electrodes 123a and 123b. Under ideal operation, the modulation module 120 emits light only when the potential difference V applied to semiconductor 122 matches the polarization state of light passing through semiconductor 122 to that of the polarization-based optical element 124. For example, if the polarization-based optical element 124 is a linear polarizer positioned to transmit horizontally polarized light along the beam path 111, and the light beam 106 is vertically polarized upon initial incidence to semiconductor 122, then pulse 107 is formed only when the potential difference V applied to semiconductor 122 changes the polarization state of the light beam 106 so that the light beam 106 is horizontally polarized.

[0038]

[0053] However, in actual operation, the modulation module 120 also emits unwanted light (light leakage). This light leakage is present throughout the operation of the modulation module 120, allowing additional amounts of light to pass through the modulation module 120, including when light should not pass through it. For example, this additional light brings an additional or surplus amount to the beginning of pulse 107, and this additional light forms the pedestal portion.

[0039]

[0054] Referring also to Figure 2B, a diagram of pulse 107 with pedestal 125 is shown. Figure 2B shows the intensity of pulse 107 as a function of time. Pedestal 125 occurs within the window labeled 121. Also, pedestal 125 occurs earlier in time than the rest of pulse 107. The portion of pulse 107 that does not include pedestal 125 is referred to as the main portion 168. Both pedestal 125 and the main portion 168 are parts of pulse 107, and pedestal 125 is temporally connected to the main portion 168.

[0040]

[0055] The average and maximum intensity and light energy of the pedestal 125 are lower than those of the main portion 168. The main portion 168 has sufficient intensity or energy to convert at least some of the target material of the target 118 into a plasma emitting EUV light. The pedestal 125 does not have as much energy and would not have enough energy to convert the target material into a plasma. However, the light from the pedestal 125 may reflect off the target 118, evaporating the material from the surface of the target 118 and / or removing part of the target 118.

[0041]

[0056] The pedestal 125 is generated before the main portion 168 and reaches the target 118 before the main portion 168. The pedestal 125 may interfere with plasma formation by altering the target 118 before the main portion 168 reaches the target 118, and / or cause undesirable reflections that propagate back along the path 111. Therefore, it is desirable to control the amount of light in the pedestal 125. It is also possible to modify, control, reduce, or eliminate one or more characteristics of the pedestal 125 by illuminating the semiconductor 122 with a seed light beam 114. For example, the average amount and / or maximum amount of light in the pedestal 125 can be reduced.

[0042]

[0057] Figure 3A shows a plot of optical leakage of the optical modulator as a function of time, without the benefit of irradiation by the seed light beam 114. The example shown in Figure 3A is described with respect to the modulation module 120 and semiconductor 122. Pulses 307_1 and 307_2 (Figure 3A) are generated by applying a potential difference to the semiconductor 122 of the modulation module 120 (Figure 3B). Optical leakage is the percentage of light incident on the modulation module 120 that passes through the modulation module 120 even when no potential difference is applied to the semiconductor 122.

[0043]

[0058] In the example shown in Figure 3A, a continuous wave light beam is incident on semiconductor 122. See also Figure 3B, which shows timing diagram 300B. Timing diagram 300B is an example of the voltage applied to semiconductor 122 during the period shown in Figure 3A. When a potential difference V is applied to semiconductor 122 and the polarization of the light emitted from semiconductor 122 matches the polarization-based optical element 124, a relatively high percentage of incident light passes through the modulation module 120. Pulses 307_1 and 307_2 are formed from the light passing through the modulation module 120 while the potential difference V is applied to semiconductor 122.

[0044]

[0059] Timing diagram 300B shows four periods 333 to 336. Period 333 includes time (t=0) to time (t=t2). During this period 333, the potential difference V is not applied to the semiconductor 122. Period 334 begins at time (t=t2) and ends at time (t=t3). During this period 334, the potential difference V is applied to the semiconductor 122, and pulse 307_1 is formed. Period 335 begins at time (t=t3) and ends at time (t=t5). During this period 335, the potential difference V is not applied to the semiconductor 122. The potential difference V is again applied to the semiconductor 122 during period 336 (starting at t=t5 and ending at t=t6), and pulse 307_2 is formed.

[0045]

[0060] The duration of periods 333 to 336 is determined by the characteristics of the modulation module 120 and the operating parameters of the EUV light source 101. For example, the rise time of the modulation module 120 (the time it takes for the semiconductor 122 to respond to the applied potential difference) can determine the minimum duration of periods 334 and 336. The desired duration of pulses 307_1 and 307_2 can also determine the duration of periods 334 and 336. In some implementations, periods 334 and 336 may be, for example, 50 to 300 nanoseconds (ns), 50 to 1000 ns, or 50 to 100 ns. Period 335 may be, for example, 20,000 ns. An example in Figure 3A shows two pulses 307_1 and 307_2. However, further pulses may be formed by applying the potential difference V again at a later time. For example, pulses may be generated at 50 kHz by applying the potential difference V to the semiconductor 122 every 20,000 ns.

[0046]

[0061] In addition to pulses 307_1 and 307_2, unwanted light (e.g., light leakage) is emitted from the modulation module 120 at other times due to defects in semiconductor 122 and other effects. The light leakage has several components, all of which are types of light leakage, namely static leakage 328, acoustic leakage 329, and dynamic leakage offset (DLO) 330. Static light leakage 328 exists regardless of whether a potential difference V is applied or not. Acoustic leakage 329 and DLO 330 are caused by the application of a potential difference V. Acoustic leakage 329 and DLO 330 together can be considered as dynamic light leakage.

[0047]

[0062] Static light leakage 328 is the percentage of incident light passing through the modulation module 120, regardless of whether a potential difference V is applied to the semiconductor 122. In the example in Figure 3B, line 327 shows the static light leakage 328 as a function of time.

[0048]

[0063] Dynamic light leakage also includes acoustic leakage 329. The application of a potential difference V affects the piezoelectric properties of semiconductor 122 and generates sound waves that propagate through semiconductor 122. The sound waves persist after the potential difference V is removed. The presence of sound waves in semiconductor 122 changes the refractive index of semiconductor 122, which may result in unintended transmission of light through the modulation module 120 during period 335. The portion or percentage of incident light emitted as acoustic leakage 329 fluctuates over time between minimum acoustic leakage 326 and peak acoustic leakage 329p. Acoustic leakage 329 is also attenuated over period 335 (the amount of acoustic leakage decreases from the peak 329p with each subsequent fluctuation that occurs during period 335). The characteristics of the attenuation depend on the properties of the semiconductor, and the fluctuations will not be completely attenuated until the potential difference V is next applied. For example, the fluctuations may not be completely attenuated until about 100 μs after the application of the potential difference V, and period 335 may be, for example, about 20 μs. Therefore, the oscillation may still exist in the semiconductor 122 when the potential difference V is applied again.

[0049]

[0064] Dynamic light leakage also includes DLO330. DLO330 is thought to be mainly caused by the presence of trapped charges (e.g., electrons) in defects in semiconductor 122. The trapped charges create an electric field within semiconductor 122, preventing the applied potential difference V from being uniform throughout semiconductor 122.

[0050]

[0065] Thus, during periods 334 and 336, a potential difference V is applied to the semiconductor to form pulses 307_1 and 307_2. However, due to the presence of light leakage, pulses 307_1 and 307_2 will contain light from an unwanted light source. For example, pulses 307_1 and 307_2 each contain pedestal portions 325a and 325b, respectively. Pedestal portions 325a and 325b occur before the remainder of each pulse 307_1 and 307_2. In the example in Figure 3A, pedestal portions 325a and 325b are shown as the percentage of average total light leakage transmission within a 400 nanosecond (ns) window. The windows are labeled 321a and 321b. Window 321a is from time = t1 to time = t2, and window 321b is from time = t4 to time = t5. The pedestal portions 325a and 325b occur when the potential difference V is not applied to the semiconductor 122.

[0051]

[0066] In the example in Figure 3A, DLO 330 is the largest component of total optical leakage, and most of the pedestal portions 325a and 325b can be eliminated by reducing or eliminating DLO 330. For example, DLO 330 may account for 33% to 66% of the total optical leakage. In one example, the total optical leakage is 0.3%, static leakage 328 is 0.07%, acoustic leakage 329 is 0.07%, and DLO 330 accounts for 0.16%. However, other examples may have different parameters. For example, CZT (which can be used as semiconductor 122) would have 2% DLO. In another example, the optical leakage in a modulation module using CdTe as semiconductor 122 would have a relatively small DLO component and a more dominant acoustic component. In these implementations, reducing the acoustic component of optical leakage has a greater impact on reducing or eliminating the pedestal portion. As described with respect to Figures 4A and 4B, the DLO 330 and acoustic leakage 329 are reduced by illuminating the semiconductor 122 with the seed light beam 114.

[0052]

[0067] Referring to Figure 4A, a diagram of the band structure 440 (energy vs. carrier momentum) of semiconductor 122 is shown. The band structure 440 represents the range of energy that electrons can possess in semiconductor 122. Semiconductor 122 has a band gap energy (Eg) 441, which is the energy difference (in electron volts, i.e., eV) between the conduction band 442 and the valence band 443. An electron (e.g., electron 445) can move from the valence band 443 to the conduction band 442 once it has gained enough energy to move into the conduction band 442. Electrons will gain energy by absorbing sound (heat) or photons (light). Electrons in the conduction band 442 flow as electric current.

[0053]

[0068] The semiconductor 122 contains defects such as precipitates, inclusions, twins, and / or slip planes. Defects act as places where charges (e.g., electrons 446) are trapped. In the example in Figure 4A, a deep-level trap 444 is formed from a defect. The deep-level trap 444 is associated with the trap gap energy 447, which is the energy difference between the deep-level trap 444 and the conduction band 442. The trap gap energy 447 is smaller than the band gap energy 441.

[0054]

[0069] Referring also to Figure 4B, the spectral transmission characteristics 450 of semiconductor 122 are shown. The spectral transmission characteristics 450 are expressed as a function of the wavelength of incident light in terms of transmission percentage. In the spectral transmission characteristics 450, the lowest wavelength (i.e., the shortest wavelength) is on the far left of the horizontal axis, and the wavelength increases (i.e., becomes longer) as the x-axis increases to the right.

[0055]

[0070] The spectral transmission characteristics 450 include a transmission region 452, an electron absorption region 451, and an absorption edge 453. The absorption edge 453 is the interface or boundary between the transmission region 452 and the electron absorption region 451. The wavelength of the absorption edge 453 has a photon energy corresponding to the bandgap energy 441. A photon with wavelength (λ) has a photon energy (E) determined by equation 1.

number

[0056]

[0073] The semiconductor 122 may be CdZnTe. In this example, the transmission region 452 is approximately 0.8 microns (μm) to 20 μm, and the absorption edge is approximately 730 nanometers (nm). For light with wavelengths in the transmission region, approximately 60% of the incident light is transmitted. In another example, the semiconductor 122 is CdTe. In this example, the transmission region 452 is approximately 0.9 μm to 20 μm, and the absorption edge is approximately 861 nanometers (nm). For light with wavelengths in the transmission region, approximately 65% ​​of the incident light is transmitted. Light with wavelengths in the electron absorption region 451 has a photon energy greater than the bandgap energy 441. Such photons are easily absorbed by the semiconductor 122.

[0057]

[0074] The light beam 106 used to form pulse 107 has a wavelength in the transmission region 452 and is therefore transmitted through the semiconductor 122. The light beam 114 used to illuminate the semiconductor 122 may have a broad spectrum and may have many wavelengths (and thus many different photon energies), including wavelengths with photon energies smaller than the bandgap energy 441. Light with wavelengths greater than the absorption edge 453 (or with photon energies smaller than the bandgap energy 441) can travel through the semiconductor 122 and excite charges trapped in deep-level traps formed by defects, such as the electron 446 in trap 444 in Figure 4A. The photons of light beam 114 transfer energy to the trapped charges, and the energy transferred will be sufficient to move the trapped charges into the conduction band 442, where the charges flow as an electric current. For example, these photons may increase the thermal energy of the trapped charges so that the charges can move into the conduction band 442. Additionally or alternatively, such photons may provide energy to charges accumulated in the valence band 443, causing these charges to move to the trap 444. Other photons from beam 114 may further excite these charges, causing them to move from the trap 444 to the conduction band 442 and flow as an electric current.

[0058]

[0075] In this way, by illuminating the semiconductor 122 with the light beam 114, trapped charges (such as electrons 446 in Figure 4A) are released, and these charges are excited and move to the conduction band 442. Also, by illuminating the semiconductor 122 with the light beam 114, the amount of electrons in the valence band 443 that move to the conduction band 442 may increase. Once in the conduction band 442, the charges flow as an electric current, thereby increasing conductivity and decreasing the resistivity of the semiconductor 122. As conductivity increases, DLO 330 decreases. Furthermore, by removing or reducing trapped charges, the electric field within the semiconductor 122 becomes more uniform when a potential difference V is applied. In addition, by illuminating the semiconductor 122 with the seed light beam 114, acoustic leakage 329 will also be reduced, and the acoustic properties of the semiconductor 122 will be modified. For example, one or more of the frequency and amplitude of the acoustic effect (or acoustic leakage) may change. Therefore, by illuminating the semiconductor 122 with the seed light beam 114, light leakage is reduced, and the amount of light in the pedestal portions 325a and 325b is reduced.

[0059]

[0076] Figures 3A and 3B show an example where the optical beam 106 is a continuous wave optical beam. However, in some implementations, the optical beam 106 is a pulsed optical beam containing a time-separated train of light pulses, synchronized with the potential V applied to the crystal. The modulation module 120 may be used to form an optical pulse from any of the pulses of the pulsed optical beam. Figures 5A and 5B relate to an optical pulse 507 formed from the light pulses.

[0060]

[0077] In implementations where the light beam 106 is a pulsed light beam, the control system 175 (Figures 1 and 2A) can provide a trigger to the light source 105 so that a pulse of light is emitted while a potential difference is applied to the semiconductor 122. For example, the light source 105 may be a Q-switched CO2 laser controlled to emit pulses upon receiving a trigger from the control system 175. In some implementations, the light source 105 periodically emits pulses without receiving a trigger from the control system 175.

[0061]

[0078] Figure 5A is a plot of light transmitted by the optical modulator 120 as a function of time. The vertical axis of Figure 5A is on a logarithmic scale. Figure 5B is a plot of voltage applied to semiconductor 122 during the period shown in Figure 5A. The optical pulse 507 is formed by applying a potential difference V to semiconductor 122 while all or part of the pulse of the optical beam 106 propagates through semiconductor 122. By applying a potential difference to semiconductor 122 while the pulse propagates through semiconductor 122, the polarization of the pulse can be changed so that the polarization-based optical element 124 (Figure 2A) directs the light emitted from semiconductor 122 onto the beam path 111 (Figure 2A).

[0062]

[0079] In the examples in Figures 5A and 5B, the potential difference V is applied to the semiconductor 122 for a period 537 that begins at time t=t8 and ends at time t=t9. The potential difference V is not applied at other times shown in Figure 5B. When the potential difference V is applied at time t=t8, the refractive index of the semiconductor 122 changes instantaneously so that the polarization of the light passing through the semiconductor 122 matches the polarization-based optical element 124 as it exits the optical modulator 120. Between times t7 and t8, light from pulses of the light beam 106 passes through the modulation module 120 due to light leakage, forming the pedestal portion 525. Light leakage may include DLO 330 and / or acoustic leakage 329 caused by sound waves formed in the semiconductor during the previous application of the potential difference V. By illuminating the semiconductor 122 with a seed light beam 114, the maximum or average amount of light in the pedestal 525 can be altered, reduced, or eliminated. In the example in Figure 5A, window 521 represents the portion of pulse 507 at pedestal 525.

[0063]

[0080] Referring to Figure 6, a flowchart of process 600 is shown. Process 600 is an example of a process that generates optical pulses, such as optical pulse 107 (Figures 1 and 2B), used in the EUV light source 101 in Figure 1 or any other EUV light source. Process 600 may be used to control or modify one or more characteristics of the pedestal portion of the optical pulse. For example, process 600 may be used to reduce the average or maximum intensity of the pedestal portion of the generated optical pulse. Process 600 is described in relation to the EUV light source 101 and modulation module 120 in Figure 1 (Figures 1 and 2A).

[0064]

[0081] The semiconductor 122 of the modulation module 120 is illuminated with a first light beam having a first wavelength (610). The first light beam may be a seed light beam 114. The first wavelength is any wavelength that can release charges trapped in the semiconductor 122. Defects in the semiconductor 122 can act as places where charges are trapped, such as deep-level traps 444 (Figure 4A). Trapped charges result in lower conductivity and higher resistivity compared to an ideal version of the semiconductor 122 without defects and trapped charges. Traps formed by defects have a bandgap energy smaller than the bandgap energy 441 of the semiconductor 122. Therefore, trapped charges can be released from defect traps by exciting the charges with light having a wavelength associated with a photon energy smaller than the bandgap energy 441.

[0065]

[0082] For example, semiconductor 122 may be CZT having a bandgap energy corresponding to a wavelength of 730 nm, or CdTe having a bandgap energy corresponding to a wavelength of 861 nm. In these examples, seed light source 110 may be any light source that generates near-infrared (NIR) light including light with wavelengths having photon energies smaller than the bandgap energy of semiconductor 122. NIR light includes wavelengths from 750 nm to 3.5 microns (μm). For example, a diode laser having a peak wavelength of 905.7 nm and a full width at half maximum (FWHM) of 1 nm, or a light-emitting diode having a peak wavelength of 873 nm and an FWHM of 70 nm, can be used as seed light source 110. In another example, seed light beam 114 may include one or more wavelengths from 838 nm to 988 nm. The first wavelength may be associated with a photon energy larger than the trapgap energy 447. As mentioned above, the trapgap energy 447 is smaller than the bandgap energy 441.

[0066]

[0083] A voltage is applied to the semiconductor 122 for a certain duration (620). During this duration, a light pulse (such as a light pulse 107) is formed by passing a second light beam having a second wavelength through the semiconductor (630). The second light beam may be, for example, the light beam 106 in Figure 1. The light beam 106 may be a continuous wave or a beam containing one or more light pulses.

[0067]

[0084] The second light beam includes at least one wavelength having a photon energy far below the band gap 441 of semiconductor 122. Therefore, the second light beam is transmitted through the semiconductor and used to form pulse 107. Light beam 106 includes one or more wavelengths different from the first wavelength. Light beam 106 may include wavelengths not exceeding 3.5 times the peak wavelength of the first light beam. In some implementations, light beam 106 includes wavelengths not exceeding 10 times the peak wavelength of seed light beam 114. Following the above examples, semiconductor 122 may be CZT with a band gap of 730 nm or CdTe with a band gap of 861 nm. In these examples, the second light beam may be generated by a CO2 laser and may include one or more wavelengths between 8 μm and 15 μm or one or more wavelengths between 9 μm and 11 μm. The light beams 106 and 114 can propagate simultaneously through the semiconductor 122. Furthermore, the light beams 106 and 114 can follow the same path through the semiconductor 122. The effect of irradiating the semiconductor 122 with the seed light beam 114 may persist even after the seed light beam 114 no longer illuminates the semiconductor 122. For example, electrical properties (such as leakage current and resistivity) will become more stable (with less variation over time) after illumination with the seed light beam 114.

[0068]

[0085] By illuminating semiconductor 122 with seed light beam 114, the charge trapped in semiconductor 122 is released, increasing the conductivity of semiconductor 122 and reducing light leakage from the modulation module 120. Reducing light leakage also reduces the amount of light in the pedestal portion of pulse 107. Figures 7 to 10 show the experimental results obtained by illuminating semiconductor 122 with seed light beam 114.

[0069]

[0086] Figure 7 includes current-voltage (IV) plots 701 and 702, which show the measured current (microamperes) versus the voltage (kilovolts) applied to semiconductor 122 when there is no irradiation by the seed light beam 114 (IV plot 701) and when there is irradiation by the seed light beam 114 (IV plot 702). In the example in Figure 7, a CZT was used as semiconductor 122. The applied voltage varied from 0V to 5000V (5kV) using a DC power supply. A 2 megaohm (MΩ) sampling resistor was connected to semiconductor 122, and the leakage current was measured with the high-voltage probe of the 2MΩ resistor. The leakage current was first measured without illuminating semiconductor 122. This measured current is included in plot 701. An NIR source was used as the seed light source 110. The leakage current was measured while semiconductor 122 was illuminated by the seed light beam 114. This measured leakage current is included in plot figure 702.

[0070]

[0087] As shown in Figure 7, illuminating semiconductor 122 with seed light beam 114 increased the leakage current at all applied voltages greater than zero. The increase in leakage current indicates that trapped charges were released by irradiation with seed light beam 114. This increase in leakage current due to illumination with the seed laser beam can also be considered an increase in the photoconductivity of the semiconductor.

[0071]

[0088] Figure 8 includes plot 800 of total light leakage (%) as a function of resistivity (in ohm-centimeters) of semiconductor 122 (at 1 kV-DC). In plot 800, semiconductor 122 was CZT. A seed light beam 114 illuminated semiconductor 122 while data was being acquired. The seed light beam 114 was an NIR beam. The beam intensity was also increased from zero to a maximum of 1 microwatt (μW) during data acquisition and coupled to the semiconductor. As shown, the total light leakage decreases as the resistivity of semiconductor 122 decreases and the intensity of the seed light beam 114 increases. Since resistivity is inversely proportional to conductivity, plot 800 shows that light leakage decreases with increasing conductivity and increasing intensity of the seed light beam 114. The increase in conductivity corresponds to the release of trapped charges through excitation by the seed light beam 114. Plot 800 also shows that different light leakage can be obtained by varying the intensity of the seed light beam 114. Therefore, by changing the intensity of the seed light beam 114, it is possible to reduce the amount of light leakage, as well as control or change the amount of light leakage (and consequently the amount of light on the pedestal of pulse 107).

[0072]

[0089] Figure 9 shows experimentally measured light leakage as a function of time. Plot 901 shows light leakage when semiconductor 122 is not illuminated by seed light beam 114, and plot 902 shows light leakage when semiconductor 122 is illuminated by seed light beam 114. In the example in Figure 9, light beam 106 was a continuous wave light beam generated by a CO2 laser. Seed light beam 114 was a continuous wave NIR light beam. Pulses 907_1 and 907_2 were formed using modulation module 120.

[0073]

[0090] As shown by comparing plots 901 and 902 in Figure 9, illuminating semiconductor 122 with seed light beam 114 reduces light leakage. In this particular example, the maximum light leakage in the pedestal region 921 decreases from approximately 1.1% (without seed light beam 114) to approximately 0.05% (with seed light beam). Light leakage occurring between pulses 907_1 and 907_2 (including leakage components due to acoustic leakage) also decreases from a maximum of approximately 1.4% (without seed light beam 114) to a maximum of approximately 0.3% (with seed light beam 114). Considering only acoustic leakage excluding DLO, the difference between the highest and lowest values ​​is approximately 0.6% without illumination and approximately 0.2% with illumination. Therefore, in this example, illuminating semiconductor 122 with seed light beam reduced acoustic leakage by approximately one-third. In other examples, further reductions in acoustic leakage (e.g., to one-sixth) may be achieved. Illuminating the semiconductor 122 with the seed light beam 114 does not eliminate or substantially alter the static leakage shown as line 927 in Figure 9.

[0074]

[0091] Figure 10 shows pulses 1007_a and 1007_b as measured sensor voltage versus time. Pulse 1007_a was formed by the optical modulator 120 without illuminating the semiconductor 122 with the seed light beam 114. Pulse 1007_b was formed by the optical modulator 120 while illuminating the semiconductor 122 with the seed light beam 114. In the example in Figure 10, the light beam 106 was a pulsed light beam generated by a CO2 laser. Although pulses 1007_a and 1007_b were formed from separate pulses of the pulsed light beam, they are shown on the same time scale for comparison. The light passing through the modulation module 120 was measured by a sensor that generates a voltage in response to the detection of light. The voltage generated by the sensor was measured over time and used to create the plot shown in Figure 10.

[0075]

[0092] 1007_a and 1007_b each have pedestal portions 1025a and 1025b that occur over a time window 1021. In this example, the maximum voltage measured by the sensor for pedestal 1025a was approximately 0.8 millivolts (mV). The maximum voltage measured by the sensor for pedestal 1025b was less than approximately 0.1 mV. Thus, illuminating the semiconductor 122 with the seed light beam 114 reduced the amount of light on the pedestal. The maximum voltage measured by the sensor for the pedestal portion of pulses generated while the semiconductor 122 is illuminated may be 1 / 10 to 1 / 20 of the voltage measured for the pedestal portion of pulses generated while the semiconductor 122 is not illuminated by the seed light beam. For example, during the first 1-2 hours of use of the system using the modulation module 120, the semiconductor 122 is heated from its initial unheated state by the application of the light beam 106 and a potential difference V. The reduction in the pedestal portion will be approximately 20 times when semiconductor 122 is unheated. As semiconductor 122 is heated by the application of the light beam 106 and potential difference V, the reduction in the pedestal portion will be approximately 10 times.

[0076]

[0093] The data shown in Figures 8 to 10 were measured using the same voltage sensor, a PEM sensor available from Boston Electronics, but this data was normalized to the peak intensity of the generated pulses.

[0077]

[0094] Figures 11 and 12 show perspective views of pulse generation systems 1104 (Figure 11) and 1204 (Figure 12). Pulse generation systems 1104 and 1204 are examples of implementations of pulse generation system 104 and can be used in the EUV light source 101 (Figure 1).

[0078]

[0095] In the pulse generation system 1104, the light beam 106 and the seed light beam 114 are coupled by a dichroic optical element 1161. The dichroic optical element 1161 can be any optical element that interacts with the light based on its wavelength. For example, the dichroic optical element 1161 may be a dichroic mirror that transmits a first wavelength (the wavelength of the light beam 106) and reflects a second wavelength (the wavelength of the seed light beam 114).

[0079]

[0096] After interacting with the dichroic optical element 1161, the light beam 106 and the seed light beam 114 interact with the semiconductor 122 of the optical modulator 120 (Figures 1 and 2A). The light beam 106 and the seed light beam 114 follow the same path through the semiconductor 122. Furthermore, the light beam 106 and the seed light beam 114 can propagate through the semiconductor 122 simultaneously. By applying a potential difference V to the semiconductor 122, a portion of the light beam 106 is extracted, forming a pulse 107. A portion of the seed light beam 114 can also pass through the optical modulator 120.

[0080]

[0097] In the pulse generation system 1204, the light beam 106 is incident on the semiconductor 122 at side 1262, and the seed light beam 114 is incident on the semiconductor 122 at side 1263. Sides 1262 and 1263 are different sides, and the seed light beam 114 and the light beam 106 propagate through the semiconductor 122 in different directions. In the implementation shown in Figure 12, the seed light beam 114 is diffused or split so that the seed light beam 114 illuminates more than one portion of the semiconductor simultaneously. The seed light beam 114 may be diffused by a diffuser element (not shown), such as a polytetrafluoroethylene (PTFE) diffuser. The diffuser element is placed between the seed light source 110 and the semiconductor 122.

[0081]

[0098] Referring to Figure 13A, the LPP EUV light source 1300 is shown. Pulse generation systems 104, 1104, and 1204 may be part of an EUV light source such as light source 1300. Pulse generation systems 104, 1104, and 1204 are not shown in Figure 13A. However, pulse generation systems 104, 1104, and 1204 may be located within light source 1300, for example, as part of a beam transmission system 1320. In these implementations, light source 105 of systems 104, 1104, and 1204 is part of the drive laser 1315, and the control system 175 may be part of the master controller 1355, one of the components of the master controller 1355, or implemented as a separate control system.

[0082]

[0099] The LPP EUV light source 1300 is formed by irradiating a target mixture 1314 located in a target region 1305 with an amplified light beam 1310 that travels along a beam path toward the target mixture 1314. The target material of the target 118 may be the target mixture 1314 or may contain the target mixture 1314. The target region 1305 is located inside the vacuum chamber 1330 1307. When the amplified light beam 1310 strikes the target mixture 1314, the target material within the target mixture 1314 is converted into a plasma state having elements that emit lines in the EUV region. The generated plasma has certain characteristics, which depend on the composition of the target material within the target material 1314. These characteristics may include the wavelength of the EUV light generated by the plasma and the type and amount of debris emitted from the plasma.

[0083] [000100] The light source 1300 also includes a target material delivery system 1325 for delivering, controlling, and guiding target material 1314 in the form of liquid droplets, liquid streams, solid particles or clusters, solid particles contained in liquid droplets, or solid particles contained in liquid streams. The target mixture 1314 includes target material such as water, tin, lithium, xenon, or any material that emits lines in the EUV region when converted to a plasma state. For example, elemental tin can be used as pure tin (Sn), as tin compounds such as SnBr4, SnBr2, SnH4, or as tin alloys such as tin-gallium alloys, tin-indium alloys, or tin-indium-gallium alloys, or any combination of these alloys. The target mixture 1314 may also include impurities such as non-target particles. Therefore, in the absence of impurities, the target mixture 1314 consists only of target material. The target mixture 1314 is delivered by the target material delivery system 1325 to the interior 1307 of the chamber 1330 and the target region 1305.

[0084] [000101] The light source 1300 includes a drive laser system 1315, which generates an amplified light beam 1310 by a gain medium or a population inversion in the medium of the laser system 1315. The light source 1300 includes a beam delivery system between the laser system 1315 and the target region 1305, which includes a beam transmission system 1320 and a focus assembly 1322. The beam transmission system 1320 receives the amplified light beam 1310 from the laser system 1315, guides and modifies the amplified light beam 1310 as needed, and outputs the amplified light beam 1310 to the focus assembly 1322. The focus assembly 1322 receives the amplified light beam 1310 and focuses the beam 1310 onto the target region 1305.

[0085] [000102] In some implementations, the laser system 1315 may comprise one or more optical amplifiers, lasers, and / or lamps to provide one or more main pulses and optionally one or more prepulses. Each optical amplifier includes a gain medium capable of optically amplifying a desired wavelength with high gain, an excitation source, and internal optical components. The optical amplifier may or may not have other feedback devices that form a laser mirror or laser cavity. Thus, even in the absence of a laser cavity, the laser system 1315 generates an amplified optical beam 1310 by population inversion in the gain medium of the laser amplifier. Furthermore, if the laser system 1315 has a laser cavity to provide sufficient feedback to the laser system 1315, it may generate an amplified optical beam 1310 which is a coherent laser beam. The term “amplified optical beam” includes one or more of the following: light from the laser system 1315 that is merely amplified and not necessarily a coherent laser oscillation, and light from the laser system 1315 that is both amplified and a coherent laser oscillation.

[0086] [000103] The optical amplifier of the laser system 1315 may be filled with a CO2-containing gas as a gain medium and can amplify light with wavelengths of about 9100 to about 11000 nm, particularly light with a wavelength of about 10600 nm, with a gain of 800 times or more. Amplifiers and lasers suitable for use in the laser system 1315 may include pulsed laser devices, such as pulsed gas discharge CO2 laser devices, which generate radiation of about 9300 nm or about 10600 nm by DC excitation or RF excitation, and operate at relatively high power, for example, 10 kW or more and at a high pulse repetition rate, for example, 40 kHz or more. The pulse repetition rate may be, for example, 50 kHz. The optical amplifier of the laser system 1315 may also include a cooling system, such as water, which can be used when operating the laser system 1315 at higher power.

[0087] [000104] Figure 13B shows a block diagram of the drive laser system 1380. The drive laser system 1380 may be used as part of the drive laser system 1315 of the light source 1300. The drive laser system 1380 includes three (or more) power amplifiers 1381, 1382, and 1383. Any or all of the power amplifiers 1381, 1382, and 1383 may include internal optical elements (not shown).

[0088] [000105] Light 1384 exits the power amplifier 1381 through the output window 1385 and is reflected by the curved mirror 1386. After reflection, light 1384 passes through the spatial filter 1387, is reflected by the curved mirror 1388, and enters the power amplifier 1382 through the input window 1389. Light 1384 is amplified and redirected in the power amplifier 1382 and exits the power amplifier 1382 as light 1391 through the output window 1390. Light 1391 is guided towards the amplifier 1383 by the folding mirror 1392 and enters the amplifier 1383 through the input window 1393. Amplifier 1383 amplifies light 1391 and guides it so that it exits the amplifier 1383 as output beam 1395 through the output window 1394. The folding mirror 1396 directs the output beam 1395 upward (outside the plane of the paper) towards the beam transmission system 1320 (Figure 13A).

[0089] [000106] Referring again to Figure 13B, the spatial filter 1387 defines an aperture 1397, which may be, for example, a circle having a diameter of about 2.2 mm to 3 mm. The curved mirrors 1386 and 1388 may be, for example, off-axis parabolic mirrors having focal lengths of about 1.7 m and 2.3 m, respectively. The spatial filter 1387 may be positioned so that the aperture 1397 coincides with the focus of the drive laser system 1380.

[0090] [000107] Referring again to Figure 13A, the light source 1300 includes a focusing mirror 1335 having an aperture 1340 that allows the amplified light beam 1310 to pass through and reach the target region 1305. The focusing mirror 1335 may be, for example, an ellipsoidal mirror and has a first focal point at the target region 1305 and a second focal point (also called an intermediate focal point) at an intermediate position 1345 through which the EUV light can be output from the light source 1300 and input to, for example, an integrated circuit lithography tool (not shown). The light source 1300 may also include a hollow conical shroud 1350 (e.g., a gas cone) with open ends. This shroud tapers from the focusing mirror 1335 toward the target region 1305, allowing the amplified light beam 1310 to reach the target region 1305 while reducing the amount of plasma-generated debris entering the focal assembly 1322 and / or beam transmission system 1320. For this purpose, a gas flow directed towards the target region 1305 may be provided within the shroud.

[0091] [000108] The light source 1300 may also include a master controller 1355 connected to a droplet position detection feedback system 1356, a laser control system 1357, and a beam control system 1358. The light source 1300 may include one or more target or droplet imagers 1360, which provide an output representing, for example, the position of a droplet relative to a target region 1305, and provide this output to the droplet position detection feedback system 1356. The droplet position detection feedback system can calculate, for example, the position and trajectory of a droplet, from which a droplet position error can be calculated for each droplet or on average. The droplet position detection feedback system 1356 thus provides the droplet position error as input to the master controller 1355. Therefore, the master controller 1355 provides correction signals for the position, direction, and timing of the laser to a laser control system 1357 and / or a beam control system 1358, which can be used, for example, to control a laser timing circuit, thereby controlling the position and shaping of the amplified light beam of the beam transmission system 1320 and changing the location and / or focusing power of the beam focus within the chamber 1330.

[0092] [000109] The target material delivery system 1325 is equipped with a target material delivery control system 1326, which is operable in response to signals from the master controller 1355 to correct, for example, the release point of droplets released by the target material supply device 1327 and to correct errors in the droplets arriving at the desired target region 1305.

[0093] [000110] Furthermore, the light source 1300 may include light source detectors 1365 and 1370. These light source detectors measure one or more EUV optical parameters, including but not limited to pulse energy, energy distribution as a function of wavelength, energy within a specific band of wavelength, energy outside a specific band of wavelength, and angular distribution of EUV intensity and / or average power. Light source detector 1365 generates a feedback signal used by master controller 1355. The feedback signal represents errors in parameters such as laser pulse timing and focus, so as to properly block droplets at the right place and time for effective and efficient EUV light generation.

[0094] [000111] The light source 1300 may also include a guide laser 1375, which can be used to align various parts of the light source 1300 or to assist in guiding the amplified light beam 1310 to the target region 1305. In connection with the guide laser 1375, the light source 1300 includes a metronome system 1324, which is installed in the focus assembly 1322 and samples a portion of the light from the guide laser 1375 and the amplified light beam 1310. In other configurations, the metronome system 1324 is installed in the beam transmission system 1320. The metronome system 1324 may also include optical elements that sample or redirect a subset of the light. Such optical elements are made from any material that can withstand the power of the guide laser beam and the amplified light beam 1310. The beam analysis system is formed from the metronome system 1324 and the master controller 1355. This is because the master controller 1355 analyzes the light sampled from the guide laser 1375 and uses this information to adjust the components in the focus assembly 1322 via the beam control system 1358.

[0095] [000112] In summary, the light source 1300 generates an amplified light beam 1310, which is guided along a beam path to irradiate the target mixture 1314 in the target region 1305, converting the target material in the mixture 1314 into a plasma that emits light in the EUV region. The amplified light beam 1310 operates at a specific wavelength (also referred to as the drive laser wavelength) determined based on the design and characteristics of the laser system 1315. Alternatively, the amplified light beam 1310 may be a laser beam if the target material provides sufficient feedback to the laser system 1315 to generate coherent laser light, or if the drive laser system 1315 includes suitable optical feedback to form a laser cavity.

[0096] [000113] Other implementations are described in the claims. Other aspects of the present invention are described in the following numbered clauses.

[0097] Clause 1. A method for forming light pulses from an extreme ultraviolet (EUV) light source, Illuminating the semiconductor material of the modulation system with a first light beam having a first wavelength, Applying a voltage to a semiconductor material for a certain duration sufficient to modify the refractive index of the semiconductor material, such that the polarization state of a light beam having a second wavelength passing through the semiconductor material is modified and passes through at least one polarization-based optical element of the modulation system, For the duration of the process, a second light beam having a second wavelength is passed through a semiconductor material to form an optical pulse. Equipped with, The formed light pulse comprises a first part and a second part, the first part and the second part being continuous in time, the first part occurring before the second part, A method in which one or more features of a first portion of a formed optical pulse are modified by illuminating a semiconductor material of a modulation system with a first light beam.

[0098] Clause 2. The method of Clause 1, wherein one or more features of the first portion of the light pulse are one or more of average intensity, maximum intensity, and duration.

[0099] Clause 3. The method of Clause 1, further comprising enabling the formed pulse to propagate toward a target region, wherein the first portion of the formed pulse has a maximum intensity less than the maximum intensity of the second portion of the formed pulse.

[0100] Clause 4. The method of Clause 3, wherein the maximum intensity of the second part is sufficient to convert the target material of the target region into a plasma emitting EUV light.

[0101] Clause 5. Semiconductor materials are related to spectral transmission properties, which comprise a transmission region and an absorption edge wavelength, where the absorption edge wavelength is the lowest wavelength in the transmission region. The first wavelength lies between the absorption edge wavelength and the second wavelength. The second wavelength is a wavelength within the transmission region, according to the method of clause 1.

[0102] Clause 6. Semiconductor materials are related to bandgap energy, which is the energy difference between the valence band and the conduction band of a semiconductor material, and the photon energy of the first wavelength is less than the bandgap energy, according to the method of Clause 1.

[0103] Clause 7. The semiconductor material is provided with a defect which generates a deep-level trap having an energy level between the valence band and the conduction band, and the photon energy of the first wavelength is equal to or greater than the energy difference between at least one energy level of the deep-level trap and the conduction band or between at least one energy level of the deep-level trap and the valence band, in the manner of Clause 6.

[0104] Clause 8. The method of Clause 1, wherein the second wavelength is 10.6 μm, and the semiconductor material is one of zinc cadmium telluride (CdZnTe), cadmium telluride (CdTe), zinc telluride (ZnTe), and gallium arsenide (GaAs).

[0105] Clause 9. The method of Clause 1, wherein the first wavelength comprises wavelengths from 0.75 microns (μm) to 3.5 μm, and the second wavelength comprises wavelengths from 9 μm to 11 μm.

[0106] Clause 10. The method of Clause 1, wherein the first and second light beams follow the same spatial path through the semiconductor material.

[0107] Clause 11. The method of Clause 10, wherein the first and second light beams are simultaneously located within the semiconductor material.

[0108] Clause 12. The method of Clause 1, further comprising adjusting the characteristics of a first light beam to adjust one or more characteristics of a first portion of a light pulse.

[0109] Clause 13. The method of Clause 12, comprising adjusting the characteristics of a first light beam to increase the intensity of the first light beam and reduce the maximum or average intensity of a first portion of a light pulse.

[0110] Clause 14. An extreme ultraviolet (EUV) light source system, A modulation system comprising a semiconductor material having one or more types of defects and whose refractive index changes in response to the application of a voltage, When a semiconductor material is illuminated with light having a first wavelength, the leakage current of the semiconductor material increases. A first light source is configured to generate a first light beam having a first wavelength, A control system coupled to a modulation system, A control system is configured to apply a voltage to a semiconductor material while a second light beam having a second wavelength propagates through the semiconductor material to form a light pulse from the second light beam, the light pulse being configured to convert at least some of the target material into a plasma emitting EUV light. A system that includes this.

[0111] Clause 15. The system of Clause 14, wherein the pulse comprises a first part and a second part, the first part and the second part being temporally continuous, and the first part occurring before the second part.

[0112] Clause 16. The second light source comprises a pulsed light source, The control system is coupled to the modulation system and the second light source. The system of Clause 14 is configured to control a second light source to emit pulses of light.

[0113] Clause 17. The system of Clause 16, wherein at least one pulse of the first light beam and the second light beam is simultaneously located within a semiconductor material.

[0114] Clause 18. The system of Clause 15, further configured to control a first light source, thereby controlling one or more characteristics of a first portion of a light pulse.

[0115] Clause 19. A system of Clause 18 in which one or more features of the first part comprises one or more of the average intensity, maximum intensity, and duration.

[0116] Clause 20. The control system of Clause 19 is configured to control the intensity of a first portion of a pulse by controlling a first light source.

[0117] Clause 21. The system of Clause 14, wherein the second light beam is a continuous light beam.

[0118] Article 22. A method for modifying acoustic effects in an electro-optic modulator, During the first period, a voltage is applied to the semiconductor of the electro-optic modulator, and the application of the voltage generates an acoustic effect in the semiconductor, including vibrational sound waves. This involves illuminating a semiconductor with a seed light beam having a wavelength with a photon energy smaller than the semiconductor's bandgap energy, thereby correcting one or more of the amplitude and frequency of the sound wave. A method that includes [a certain feature].

[0119] Clause 23. Further comprising guiding a continuous wave light beam toward the semiconductor of an electro-optic modulator, A first quantity of continuous wave light beam passes through an electro-optic modulator in a first polarization state for a first period of time when a voltage is applied to the semiconductor. The second quantity of the continuous wave light beam passes through the electro-optic modulator at a time other than the first period, when no voltage is applied to the semiconductor and acoustic effects exist within the semiconductor. The method of Clause 22, wherein the amount of a second light beam passing through an electro-optic modulator is changed by illuminating a semiconductor with a seed light beam.

[0120] Clause 24. Further comprising guiding the pulses of a pulsed light beam toward an electro-optic modulator, wherein a first amount of pulsed light passes through the semiconductor for a first period when a voltage is applied to the semiconductor, and a second amount of pulsed light passes through the semiconductor when no voltage is applied to the semiconductor at a time other than the first period. The method of clause 22, wherein a semiconductor is illuminated with a seed light beam, thereby changing a second amount of light.

Claims

1. A method for forming light pulses from an extreme ultraviolet (EUV) light source, Illuminating the semiconductor material of the modulation system with a first light beam having a first wavelength, Applying a voltage to the semiconductor material for a certain duration sufficient to modify the refractive index of the semiconductor material, such that the polarization state of a light beam having a second wavelength passing through the semiconductor material is modified and passes through at least one polarization-based optical element of the modulation system, During the duration, a light pulse is formed by passing the semiconductor material through a second light beam having the second wavelength. Equipped with, The formed light pulse comprises a first portion and a second portion, the first portion and the second portion being continuous in time, and the first portion occurring before the second portion. A method in which one or more features of a first portion of the formed light pulse are modified by illuminating the semiconductor material of the modulation system with the first light beam.

2. The method of claim 1, wherein the one or more features of the first portion of the light pulse include one or more of average intensity, maximum intensity, and duration.

3. The method of claim 1, further comprising enabling the formed pulse to propagate toward a target region, wherein the first portion of the formed pulse has a maximum intensity less than the maximum intensity of the second portion of the formed pulse.

4. The method of claim 3, wherein the maximum intensity of the second portion is sufficient to convert the target material of the target region into a plasma that emits EUV light.

5. The semiconductor material is related to spectral transmission properties, wherein the spectral transmission properties comprise a transmission region and an absorption edge wavelength, and the absorption edge wavelength is the lowest wavelength in the transmission region. The first wavelength lies between the absorption edge wavelength and the second wavelength. The method according to claim 1, wherein the second wavelength is a wavelength within the transmission region.

6. The method according to claim 1, wherein the semiconductor material is related to the band gap energy, the band gap energy is the energy difference between the valence band and the conduction band of the semiconductor material, and the photon energy of the first wavelength is smaller than the band gap energy.

7. The method of claim 6, wherein the semiconductor material has defects, the defects generate deep-level traps having energy levels between the valence band and the conduction band, and the photon energy of the first wavelength is equal to or greater than the energy difference between at least one energy level of the deep-level trap and the conduction band or between at least one energy level of the deep-level trap and the valence band.

8. The method of claim 1, wherein the second wavelength is 10.6 μm, and the semiconductor material comprises one of zinc cadmium telluride (CdZnTe), cadmium telluride (CdTe), zinc telluride (ZnTe), and gallium arsenide (GaAs).

9. The method according to claim 1, wherein the first wavelength comprises a wavelength of 0.75 microns (μm) to 3.5 μm, and the second wavelength comprises a wavelength of 9 μm to 11 μm.

10. The method according to claim 1, wherein the first light beam and the second light beam follow the same spatial path through the semiconductor material.

11. The method of claim 10, wherein the first light beam and the second light beam are simultaneously located within the semiconductor material.

12. The method of claim 1, further comprising adjusting the characteristics of the first light beam to adjust one or more of the features of the first portion of the light pulse.

13. The method of claim 12, wherein adjusting the characteristics of the first light beam is to increase the intensity of the first light beam and reduce the maximum or average intensity of the first portion of the light pulse.

14. An extreme ultraviolet (EUV) light source system, A modulation system comprising a semiconductor material having one or more types of defects and whose refractive index changes in response to the application of a voltage, When the semiconductor material is illuminated with light having a first wavelength, the leakage current of the semiconductor material increases. A first light source is configured to generate a first light beam having the first wavelength. A control system coupled to the modulation system, A control system is configured to apply a voltage to a semiconductor material while a second light beam having a second wavelength propagates through the semiconductor material to form a light pulse from the second light beam, the light pulse being configured to convert at least some target material into a plasma emitting EUV light. A system that includes this.

15. The system of claim 14, wherein the pulse comprises a first portion and a second portion, the first portion and the second portion being temporally continuous, and the first portion occurring before the second portion.

16. The second light source comprises a pulse light source, The control system is coupled to the modulation system and the second light source, The system according to claim 14, wherein the control system is configured to control the second light source to emit pulses of light.

17. The system according to claim 16, wherein at least one pulse of the first light beam and the second light beam is simultaneously located within the semiconductor material.

18. The system according to claim 15, wherein the control system is further configured to control the first light source, thereby controlling one or more features of the first portion of the light pulse.

19. The system of claim 18, wherein one or more features of the first part comprises one or more of average intensity, maximum intensity, and duration.

20. The system according to claim 19, wherein the control system is configured to control the intensity of a first portion of the pulse by controlling the first light source.

21. The system according to claim 14, wherein the second light beam comprises a continuous light beam.

22. A method for correcting acoustic effects in an electro-optic modulator, During the first period, a voltage is applied to the semiconductor of the electro-optic modulator, and the application of the voltage generates an acoustic effect including vibrational sound waves in the semiconductor. The semiconductor is illuminated with a seed light beam having a wavelength with a photon energy smaller than the bandgap energy of the semiconductor, thereby correcting one or more of the amplitude and frequency of the sound wave. A method that includes [a certain feature].

23. The continuous wave light beam is further guided toward the semiconductor of the electro-optic modulator, The first amount of the continuous wave light beam passes through the electro-optic modulator in a first polarization state for a first period of time when the voltage is applied to the semiconductor. The second amount of the continuous wave light beam passes through the electro-optic modulator at a time other than the first period when the voltage is not applied to the semiconductor and the acoustic effect is present within the semiconductor. The method of claim 22, wherein the amount of the second light beam passing through the electro-optic modulator is changed by illuminating the semiconductor with the seed light beam.

24. The invention further comprises guiding the pulses of a pulsed light beam toward the electro-optic modulator, wherein a first amount of the pulsed light passes through the semiconductor for a first period when the voltage is applied to the semiconductor, and a second amount of the pulsed light passes through the semiconductor at times other than the first period when the voltage is not applied to the semiconductor. The method of claim 22, wherein the amount of the second light changes by illuminating the semiconductor with the seed light beam.

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