Controlling the spectral characteristics of an output light beam produced by a light source

Abstract

The system includes a light source including a plurality of optical oscillators, a spectroscopic analyzer, and a controller. Each optical oscillator is configured to generate a light beam. The controller is configured to determine, based on data from the spectroscopic analyzer, whether a spectral characteristic of the light beam of one of the optical oscillators differs from a spectral characteristic of the light beam of at least one other of the plurality of optical oscillators. If the spectral characteristic of the light beam of a first of the optical oscillators differs from the spectral characteristic of the light beam of one other of the optical oscillators, the controller is configured to adjust the spectral characteristic of the light beam of the first of the optical oscillators or the light beam of at least one other of the optical oscillators.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Application No. 62 / 932,250, filed on November 7, 2019, entitled CONTROLLING A SPECTRAL PROPERTY OF AN OUTPUT LIGHT BEAM PRODUCED BY AN OPTICAL SOURCE, which is hereby incorporated by reference in its entirety.

[0002]

[0002] The present disclosure relates to controlling a spectral property of an output light beam produced by a light source. The light source includes a plurality of optical oscillators, each of which can generate a deep ultraviolet (DUV) light beam.

Background Art

[0003]

[0003] Photolithography is a process of patterning a semiconductor circuit on a substrate such as a silicon wafer. A light source generates deep ultraviolet (DUV) light that is used to expose a photoresist on the wafer. The DUV light can include wavelengths, for example, from about 100 nanometers (nm) to about 400 nm. The light source is a laser source (e.g., an excimer laser) and the DUV light is often a pulsed laser beam. The DUV light from the light source interacts with a projection optical system, which projects the beam onto the photoresist on the silicon wafer through a mask. In this way, a layer of the chip design is patterned on the photoresist. The photoresist and the wafer are then etched and cleaned, and then the photolithography process is repeated.

Summary of the Invention

[0004]

[0004] In one aspect, the system includes a light source including a plurality of optical oscillators, a spectroscopic analyzer, and a controller. Each optical oscillator is configured to generate an optical beam. The controller is configured to determine, based on data from the spectroscopic analyzer, whether the spectroscopic characteristics of the optical beam of the first one of the optical oscillators are different from those of the optical beam of at least one other of the plurality of optical oscillators, and when the spectroscopic characteristics of the optical beam of the first one of the optical oscillators are different from those of the optical beam of at least one other of the plurality of optical oscillators, the controller is configured to adjust the spectroscopic characteristics of the optical beam of the first one of the optical oscillators or the spectroscopic characteristics of the optical beam of at least one other of the plurality of optical oscillators.

[0005]

[0005] The embodiment may include one or more of the following features.

[0006]

[0006] The spectroscopic characteristics may include a spectral bandwidth. The control system may be configured to determine whether the spectral bandwidth of the optical beam of the first one of the optical oscillators is different from that of the optical beam of at least one other of the plurality of optical oscillators by determining whether the spectral bandwidth of the optical beam of the first one of the optical oscillators is smaller than that of the optical beam of at least one other of the plurality of optical oscillators. When the spectral bandwidth of the optical beam of the first one of the optical oscillators is smaller than that of the optical beam of at least one other of the plurality of optical oscillators, the controller may increase the bandwidth of the optical beam of the first one of the optical oscillators.

[0007]

[0007] The system may also include a plurality of spectroscopic adjustment devices. Each optical oscillator may be associated with one of the plurality of spectroscopic adjustment devices, and the controller may be configured to control the spectroscopic adjustment device associated with any one of the optical oscillators, thereby adjusting the spectroscopic characteristics of the optical beam of any one of the optical oscillators.

[0008]

[0008] Each spectral adjustment system may include at least one optical element, and the controller may be configured to control the spectral adjustment device by operating an actuator coupled to the optical element of a particular spectral adjustment device so that the optical element moves. Moving the optical element can change the center wavelength of the light beam. The controller may further be configured to determine the amount of actuation. To actuate the optical element, the controller may provide an electrical signal to the optical element, the amount of actuation may be based on the electrical signal, and one or more characteristics of the electrical signal may be determined based on a difference. One or more characteristics of the electrical signal may include amplitude and / or frequency. The amount of actuation may be based on the number of optical pulses expected to interact with the spectral adjustment system over a period of time, and the amount of actuation may be the number of separate actuations performed over that period of time. The amount of actuation may be based on the difference between the spectral characteristics of the light beam of the first of the optical oscillators and the spectral characteristics of the light beam of at least one of the other optical oscillators.

[0009]

[0009] Each spectral adjustment device may include at least one refractive optical element.

[0010]

[0010] Each spectral adjustment device may include at least one prism.

[0011]

[0011] Each spectral adjustment device may include a reflective optical element.

[0012]

[0012] Each spectral adjustment device may include a plurality of prisms and an actuator coupled to one of the prisms, and the controller may be configured to control the actuator of each spectral adjustment assembly and thereby move one of the prisms to adjust the spectral characteristics of the light beam of any of the optical oscillators.

[0013]

[0013] Each optical oscillator may be configured to emit a pulsed light beam including a plurality of optical pulses.

[0014]

[0014] The controller may further be configured to determine the updated spectral characteristics of the optical beam of the first optical oscillator after adjusting the spectral characteristics, and to determine whether the updated spectral characteristics of the optical beam of the first optical oscillator are different from the spectral characteristics of the optical beam of any of the other optical oscillators.

[0015]

[0015] The plurality of optical oscillators may include only one first optical oscillator and one second optical oscillator such that the first of the optical oscillators is the first optical oscillator and the second optical oscillator is at least one other optical oscillator. The controller may be configured to determine whether the spectral characteristics of the optical beam of the first optical oscillator are different from the spectral characteristics of the second optical oscillator based on data from the spectroscopic analysis system, and to adjust the spectral characteristics of the optical beam of the first optical oscillator or the spectral characteristics of the optical beam of the second optical oscillator when the spectral bandwidth of the first optical oscillator is different from the spectral bandwidth of the second optical oscillator.

[0016]

[0016] The spectroscopic analysis system may include a plurality of spectroscopic analysis systems. Each spectroscopic analysis system may be configured to receive one optical beam of the optical oscillators, and each spectroscopic analysis system may be configured to measure the spectral characteristics associated with that one optical beam of the optical oscillators.

[0017]

[0017] Each optical oscillator may be configured to contain a gaseous gain medium. The gaseous gain medium may include krypton fluoride (KrF). When the spectral characteristics of the optical beam of the first of the optical oscillators are different from the spectral characteristics of the optical beam of at least one other of the optical oscillators, the controller may be configured to adjust the pressure and / or concentration of one or more gas components of the gaseous gain medium of the first of the optical oscillators to adjust the spectral characteristics of the optical beam of the first of the optical oscillators, or to adjust the pressure and / or concentration of one or more gas components of the gaseous gain medium of at least one other of the optical oscillators to adjust the spectral characteristics of at least one other of the optical oscillators.

[0018]

[0018] The system may include a beam combiner, which is configured to receive the optical beams of all the optical oscillators and direct those optical beams toward a DUV lithography scanner tool.

[0019]

[0019] In some embodiments, each optical oscillator is configured to generate a pulsed optical beam having a certain repetition rate, and the controller is configured to adjust the spectral characteristics of the optical beam of the first one of the optical oscillators or the second one of the optical oscillators at a certain adjustment rate, where the adjustment rate is at least one-tenth of the repetition rate.

[0020]

[0020] Another aspect relates to a method for controlling a deep ultraviolet (DUV) light source including N optical oscillators, where N is an integer greater than 1, and each optical oscillator is configured to generate its own optical beam. The method includes forming an output optical beam based on M optical beams generated by M respective ones of the N optical oscillators, where M is an integer greater than zero and less than or equal to N, accessing data related to the spectral characteristics of each of the M optical beams, comparing the spectral characteristics of each of the M optical beams to a reference, and based on the comparison, determining whether to control one of the N optical oscillators to thereby adjust the spectral characteristics of one of the N optical beams.

[0021]

[0021] Embodiments may include one or more of the following features.

[0022]

[0022] The spectral characteristics may include a spectral bandwidth.

[0023]

[0023] The reference may include the spectral characteristics of all of the M optical beams such that comparing the spectral characteristics of each of the M optical beams to the reference includes comparing the spectral characteristics of each of the M optical beams to all of the spectral characteristics of the other M optical beams.

[0024]

[0024] Comparing the spectral characteristics of each of the M optical beams with all of the spectral characteristics of the other M optical beams may include determining the differences between the spectral characteristics of each of the M optical beams and the spectral characteristics of each of the other M optical beams, and determining based on the comparison may include comparing each of the determined differences with a specification.

[0025]

[0025] The reference may include a predetermined value of the spectral characteristic, and comparing the spectral characteristic of each of the M optical beams with the reference includes comparing the spectral characteristic of each of the M optical beams with the predetermined value. The predetermined value may include a maximum spectral bandwidth, and the spectral characteristic of each of the M optical beams may be compared with the maximum spectral bandwidth by determining the difference between the spectral characteristic of the optical beam and the maximum spectral bandwidth. Determining based on the comparison may include comparing the determined difference with a range of a predetermined allowable difference, and for those of the M optical beams having a determined difference outside the range of the predetermined allowable difference, one aspect of each of the optical oscillators may be controlled. Controlling one aspect of each of the optical oscillators may include operating a dispersive optical element.

[0026]

[0026] The output optical beam can be based on the M optical beams in the first period and can also be based on the L optical beams in the second period. L is an integer greater than or equal to 1 and less than or equal to N. And the criterion may include the spectral characteristics of each of the L optical beams, and comparing the spectral characteristics of each of the M optical beams with the criterion may include comparing the spectral characteristics of each of the M optical beams with the spectral characteristics of each of the L optical beams. L may be 1, M may be 1, N may be 2, the L beams may be the first beam generated by the first of the N optical oscillators, the M optical beams may be the second beam generated by the second of the N optical oscillators, comparing the spectral characteristics of the first optical beam and the spectral characteristics of the second optical beam may include determining whether the spectral bandwidth of the second optical beam is smaller than the spectral bandwidth of the first optical beam, and when the spectral bandwidth of the second optical beam is smaller than the spectral bandwidth of the first optical beam, controlling the prism of the second of the N optical oscillators so that the spectral bandwidth of the second optical beam is increased.

[0027]

[0027] L may be 1, M may be 1, and N may be 2. The L beams may be the first beams generated by the first of the N optical oscillators. The M optical beams may be the second beams generated by the second of the N optical oscillators. Comparing the spectral characteristics of the first optical beam and the spectral characteristics of the second optical beam may include determining whether the spectral bandwidth of the first optical beam is smaller than the spectral bandwidth of the second optical beam, and when the spectral bandwidth of the first optical beam is smaller than the spectral bandwidth of the second optical beam, controlling the prism of the first of the N optical oscillators so that the spectral bandwidth of the first optical beam is increased. The method may further include determining an adjustment amount to the prism of the second of the N optical oscillators based on the difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam. To control the prism of the second of the N optical oscillators, a time-varying signal may be applied to an actuator physically connected to the prism, and the amplitude of the time-varying signal is related to the difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam.

[0028]

[0028] In another aspect, a control system for a deep ultraviolet (DUV) light source controls a first set of N optical oscillators to generate a first set of optical beams during a first period such that the output optical beam generated by the DUV light source during the first period includes the first set of optical beams. The second set of N optical oscillators and the first set of N optical oscillators do not include the same one or more optical oscillators among the N optical oscillators. During a second period, the second set of N optical oscillators is controlled to generate a second set of optical beams such that the output optical beam generated by the DUV light source during the second period includes the second set of optical beams. At least one spectral adjustment device among the N optical oscillators is configured to be controlled to increase the uniformity of the spectral characteristics of the N optical beams.

[0029]

[0029] The embodiments may include one or more of the following features.

[0030]

[0030] The beam splitting adjustment device can be controlled before the second period. One or more of the beam splitting adjustment devices of the N optical oscillators in the second set can be controlled to adjust one or more of the beam splitting characteristics of the respective optical beams in the second set.

[0031]

[0031] In some embodiments, each optical oscillator is configured to generate its respective pulsed optical beam at a certain repetition rate, and the control system is configured to control at least one of the beam splitting adjustment devices of the N optical oscillators at an adjustment rate of one-tenth or more of the repetition rate.

[0032]

[0032] Any of the embodiments of the technologies described above and in this specification may include a process, an apparatus, a control system, instructions stored in a non-transitory machine-readable computer medium, and / or a method. Details of one or more embodiments are described in the accompanying drawings and the following description. Other features will become apparent from the description and the drawings, as well as from the claims.

Brief Description of the Drawings

[0033]

Figure 1

[0033] It is a block diagram of an example of a light source system.

Figure 2A

[0034] It is a block diagram of another example of a light source system.

Figure 2B

[0035] It is an example of a spectroscopic analyzer used in the light source system of FIG. 2A.

Figure 2C

[0036] It is an example of a spectral bandwidth represented by energy density as a function of wavelength.

Figure 3A

[0037] It is a block diagram of an example of a spectroscopic analyzer.

Figure 3B

[0038] It is an example of the rotation of a prism about an axis for changing the incident angle of an optical beam in a spectroscopic analyzer.

Figure 4

[0039] A flowchart of an example of a process for increasing the uniformity of the spectral characteristics of an output optical beam in a light source system.

Figure 5

[0040] A flowchart of an example of a process for adjusting one aspect of one or more optical oscillators in a light source system.

DETAILED DESCRIPTION OF THE INVENTION

[0034]

[0041] Referring to FIG. 1, a block diagram of system 100 is shown. The system includes a light source 110 and a control system 150. The light source 110 provides an output optical beam 111 to a common optical element 138. The common optical element 138 can be, for example, a beam combiner (such as beam combiner 218 in FIG. 2A) or a lithography tool (such as scanner device 280 in FIG. 2A).

[0035]

[0042] The light source 110 includes N optical oscillators 112-1 to 112-N, where N is an integer greater than 1. Each optical oscillator 112-1 to 112-N is configured to generate a respective optical beam 116-1 to 116-N. Depending on the requirements of the application using the system 100, one, two or more, or all of the optical beams 116-1 to 116-N can contribute to the output optical beam 111 at any given time. The one or more of the optical beams 116-1 to 116-N that contribute to the output optical beam 111 change over time. For example, in some embodiments, the control system 150 controls the light source 110 to cycle through the optical oscillators 112-1 to 112-N such that only one of the optical oscillators 112-1 to 112-N outputs its respective optical beam 116-1 to 116-N to the output optical beam 111 at a particular time.

[0036]

[0043] The light source 110 also includes a spectroscopic analyzer 198, which is configured to detect light and generate data related to the spectroscopic characteristics of the detected light. The spectroscopic characteristics can be, for example, the spectral bandwidth or the central wavelength. The spectroscopic analyzer 198 is configured to detect any one of the light beams 116-1 to 116-N. The spectroscopic analyzer 198 is shown as a single element in the example of FIG. 1. However, in some embodiments, the light source 110 includes N spectroscopic analyzers, and each of the optical oscillators 112-1 to 112-N (as in the embodiment of FIG. 2A) has an associated spectroscopic analyzer.

[0037]

[0044] Due to differences in the components, operations, and / or structures of the optical oscillators 112-1 to 112-N, one or more spectroscopic characteristics (e.g., spectral bandwidth) may differ among the various light beams 116-1 to 116-N. Since one or more of the light beams 116-1 to 116-N contributing to the output light beam 111 change over time, when the control system 150 switches from generating the output light beam 111 with a particular one or more of the optical oscillators 112-1 to 112-N to generating the light output beam 111 with another one or more of the optical oscillators 112-1 to 112-N, the spectroscopic characteristics of the output light beam 111 can change.

[0038]

[0045] On the other hand, the control system 150 analyzes the data from the spectroscopic analyzer 198 and controls one or more of the optical oscillators 112-1 to 112-N to control the spectroscopic characteristics of the respective optical beams 116-1 to 116-N. Therefore, the control system 150 can reduce or eliminate the discrepancies in the spectroscopic characteristics of the various optical beams 116-1 to 116-N. In this way, the spectroscopic characteristics of the output optical beam 111 received over time at the common optical element 138 will be more uniform or consistent even if one or more of the optical oscillators 112-1 to 112-N that generate the light contributing to the output optical beam 111 change over time. The control system 150 can also be used to perform other adjustments to the light source 110. For example, in some embodiments, the control system 150 controls or adjusts an optical element or other component of any of the optical oscillators 112-1 to 112-N that generates an optical beam having spectroscopic characteristics that do not meet the specifications.

[0039]

[0046] Before describing various embodiments and examples of the control system 150 in detail, with respect to FIGS. 2A and 2B, an overview of one possible embodiment of the light source 210 is presented.

[0040]

[0047] Referring to FIGS. 2A and 2B, the system 200 includes a light source 210 that provides an exposure beam (or output optical beam) 211 to a scanner device 280. The control system 250 is coupled to the light source 210 and various components associated with the light source 210. The data link 254 is any type of wireless and / or wired medium that carries data and information as, for example, electrical or optical signals. The light source 210 and the control system 250 are embodiments of the light source 110 and the control system 150 (FIG. 1), respectively.

[0041]

[0048] The light source 210 includes optical oscillators 212-1 to 212-N. However, N is an integer greater than 1. Each optical oscillator 212-1 to 212-N generates a respective optical beam 216-1 to 216-N. Details of the optical oscillator 212-1 will be described later. The other N-1 optical oscillators of the light source 210 include the same or similar characteristics.

[0042]

[0049] The optical oscillator 212-1 includes a discharge chamber 215-1 that surrounds a cathode 213-1a and an anode 213-1b. The discharge chamber 215-1 also contains a gaseous gain medium 214-1. A potential difference between the cathode 213-1a and the anode 213-1b forms an electric field in the gaseous gain medium 214-1. The potential difference can be generated by controlling a voltage source 297 to apply a voltage to the cathode 213-1a and / or the anode 213-1b. The electric field provides sufficient energy to the gain medium 214-1 to cause an inversion distribution and to enable the generation of pulses of light via stimulated emission. By repeatedly creating such a potential difference, a train of pulses is formed that is emitted as an optical beam 216-1. The repetition rate of the pulsed optical beam 216-1 is determined by the rate at which the voltage is applied to the electrodes 213-1a and 213-1b.

[0043]

[0050] The gain medium 214-1 is pumped by the application of a voltage to the electrodes 213-1a and 213-1b. The pulse duration and repetition rate of the pulsed optical beam 216-1 are determined by the duration and repetition rate of the application of the voltage to the electrodes 213-1a and 213-1b. The repetition rate of the pulses can range, for example, from about 500 to 6,000 Hz. In some embodiments, the repetition rate may be greater than 6,000 Hz, for example 12,000 Hz or more. Each pulse emitted from the optical oscillator 212-1 can have, for example, a pulse energy of approximately 1 millijoule (mJ).

[0044]

[0051] The gaseous gain medium 214-1 can be any gas suitable for generating an optical beam with the wavelength, energy, and bandwidth required for the application. The gaseous gain medium 214-1 may contain more than one type of gas, and various gases are referred to as gas components. In the case of an excimer light source, the gaseous gain medium 214-1 may contain a noble gas (rare gas) such as argon or krypton, or a halogen such as fluorine or chlorine. In an embodiment where the halogen is the gain medium, the gain medium also contains a trace amount of xenon in addition to a buffer gas such as helium.

[0045]

[0052] The gaseous gain medium 214-1 can be a gain medium that emits light in the deep ultraviolet (DUV) region. The DUV light can include wavelengths, for example, from about 100 nanometers (nm) to about 400 nm. Specific examples of the gaseous gain medium 214-1 include argon fluoride (ArF) that emits light with a wavelength of about 193 nm, krypton fluoride (KrF) that emits light with a wavelength of about 248 nm, or xenon chloride (XeCl) that emits light with a wavelength of about 351 nm.

[0046]

[0053] A resonator is formed between the spectral adjustment device 295-1 on one side of the discharge chamber 215-1 and the output coupler 296-1 on the second side of the discharge chamber 215-1. The spectral adjustment device 295-1 may include diffractive optical elements for finely adjusting the spectral output of the discharge chamber 215-1, such as a grating and / or a prism. The diffractive optical element can be reflective or refractive. In some embodiments, the spectral adjustment device 295-1 includes a plurality of diffractive optical elements. For example, the spectral adjustment device 295-1 may include four prisms, some of which are configured to control the central wavelength of the optical beam 216-1, and others of which are configured to control the spectral bandwidth of the optical beam 216-1.

[0047]

[0054] Referring also to FIG. 3A, a block diagram of the spectral adjustment device 395-1 is shown. The spectral adjustment device 395-1 can be used as any one or each of the spectral adjustment devices 295-1 to 295-N. The spectral adjustment device 395-1 includes a set of optical features or components 321, 322, 323, 324, 325 arranged to optically interact with the optical beam 216-1. The control system 250 is connected to one or more actuation systems 321A, 322A, 323A, 324A, 325A physically connected to the respective optical components 321, 322, 323, 324, 325. The actuation systems 321A, 322A, 323A, 324A, 325A may include a shaft (such as the shaft 326A), which rotates the component connected to the shaft about an axis parallel to the shaft. The actuation systems 321A, 322A, 323A, 324A, 325A also include electronic devices and mechanical devices such as motors and electronic interfaces for communication with the control system 250 and for receiving power, for example.

[0048]

[0055] The optical component 321 is a dispersive optical element, such as a grating or a prism. In the example of FIG. 3A, the optical component 321 is a reflective grating including a diffraction surface 302. The optical components 322, 323, 324, and 325 are refractive optical elements and can be, for example, prisms. The optical components 322, 323, 324, and 325 form a beam expander 301 having an optical magnification OM365. The OM365 of the optical beam 216-1 passing through the beam expander 301 is the ratio of the width Wo of the optical beam 216-1 going out of the beam expander 301 to the width Wi of the optical beam 216-1 entering the beam expander 201.

[0049]

[0056] The surface 302 of the grating 321 is made of a material that reflects and diffracts the wavelength of the light beam 216-1. Each of the prisms 322, 323, 324, and 325 is a prism, and when the light beam 216-1 passes through the body of the prism, it acts to disperse and redirect this light beam. Each of the prisms 322, 323, 324, and 325 is made of a material that transmits the wavelength of the light beam 216-1. For example, if the light beam 216-1 is in the DUV region, the prisms 322, 323, 324, and 325 are made of a material (such as calcium fluoride) that transmits light in the DUV region.

[0050]

[0057] The prism 325 is located farthest from the grating 321, and the prism 322 is located closest to the grating 321. The light beam 216-1 enters the spectral adjustment device through the aperture 355, and then passes through the prism 325, the prism 324, the prism 323, and the prism 322 (in that order). Each time the beam 216-1 passes through the successive prisms 325, 324, 323, 322, the light beam 216-1 is optically expanded and redirected (refracted at an angle) towards the next optical component. After passing through the prisms 325, 324, 323, and 322, the light beam 216-1 is reflected by the surface 302. The light beam 216-1 then passes through the prism 322, the prism 323, the prism 324, and the prism 325 (in that order). Each time the light beam 216-1 passes through the successive prisms 322, 323, 324, 325, the light beam 216-1 is optically compressed as it progresses towards the aperture 355. After passing through the prisms 322, 323, 324, and 325, the light beam 216-1 exits the spectral adjustment device 395-1 through the aperture 355. After exiting the spectral adjustment device 395-1, the light beam 216-1 passes through the chamber 215-1, is reflected by the output coupler 296-1, and returns to the chamber 215-1 and the spectral adjustment device 395-1.

[0051]

[0058] The spectral characteristics of the optical beam 216-1 can be adjusted by changing the relative orientations of the optical components 321, 322, 323, 324, and / or 325. Referring to FIG. 3B, the rotation of the prism P (which may be any of the prisms 322, 323, 324, or 325) about an axis perpendicular to the plane of the paper changes the angle of incidence at which the optical beam 216-1 impinges on the incident surface H(P) of the rotated prism P. Also, the two local optical qualities of the optical beam 216-1 passing through the rotated prism P, namely the optical magnification OM(P) and the beam refraction angle δ(P), are functions of the angle of incidence of the optical beam 216-1 impinging on the incident surface H(P) of the rotated prism P. The optical magnification OM(P) of the optical beam 216-1 passing through the prism P is the ratio of the lateral width Wo(P) of the optical beam 110A emerging from the prism P to the lateral width Wi(P) of the optical beam 216-1 entering the prism P.

[0052]

[0059] A change in the local optical magnification OM(P) of the optical beam 216-1 in one or more of the prisms P within the beam expander 301 causes an overall change in the optical magnification OM365 of the optical beam 216-1 passing through the beam expander 301. And a change in the local beam refraction angle δ(P) through one or more of the prisms P within the beam expander 301 causes an overall change in the angle of incidence 362 (FIG. 3A) of the optical beam 110A on the surface 302 of the grating 321. The wavelength of the optical beam 216-1 can be adjusted by changing the angle of incidence 362 (FIG. 3A) at which the optical beam 216-1 impinges on the surface 302 of the grating 321. The spectral bandwidth of the optical beam 216-1 can be adjusted by changing the optical magnification 365 of the optical beam 216-1.

[0053]

[0060] Therefore, the spectral characteristics of the optical beam 216-1 can be changed or adjusted by controlling the orientations of the grating 321 and / or one or more of the prisms 322, 323, 324, 325 via their respective actuators 321A, 322A, 323A, 324A, 325A. Other embodiments of the spectral adjustment device are possible.

[0054]

[0061] Further, the spectral characteristics of the optical beams 216-1 to 216-N may be adjusted by other methods. For example, the spectral characteristics such as the spectral bandwidth of the optical beams 216-1 to 216-N can be adjusted by controlling the pressure and / or gas concentration of the gaseous gain media in the respective chambers 215-1 to 215-N. In an embodiment where the source 210 is an excimer light source, the spectral characteristics (e.g., spectral bandwidth) of the optical beams 216-1 to 216-N can be adjusted by controlling, for example, the pressure and / or concentration of fluorine, chlorine, argon, krypton, xenon, and / or helium in the respective chambers 215-1 to 215-N. The pressure and / or concentration of the gaseous gain media 214-1 to 214-N can be controlled by the gas supply system 290.

[0055]

[0062] Referring again to FIG. 2B, the optical oscillator 212-1 also includes a spectroscopic analyzer 298-1. The spectroscopic analyzer 298-1 is a measurement system that can be used to measure or monitor the wavelength of the optical beam 216-1. In the example shown in FIG. 2, the spectroscopic analyzer 298-1 receives light from the output coupler 296-1. Other embodiments are possible. For example, the spectroscopic analyzer 298-1 may be between the output coupler 296-1 and the spectral adjustment device 295-1, or may be located in the scanner device 280.

[0056]

[0063] The spectroscopic analysis device 298-1 provides data to the control system 250, and the control system 250 determines a metric related to the spectroscopic characteristics of the optical beam 216-1 based on the data from the spectroscopic analysis device 298-1. For example, the control system 250 may determine the central wavelength and / or the spectral bandwidth based on the data measured by the spectroscopic analysis device 298-1. The spectroscopic characteristics may be directly measured by the device 298-1 or may be determined by the control system 250 based on the data from the spectroscopic analysis device 298-1. The central wavelength is the power-weighted average wavelength of the optical beam. The spectral bandwidth is a measure of the spread or distribution of wavelengths in the optical beam. FIG. 2C shows an example of the spectral bandwidth 230 represented as the energy density as a function of wavelength, and the central wavelength is labeled 231. The spectral bandwidth may be characterized by a quantity such as the full width at half maximum (FWHM) or the 95% integrated width (E95). The FWHM is the spectral region included at half of the maximum intensity. The E95 is the interval surrounding 95% of the total energy of the spectrum.

[0057]

[0064] Referring again to FIG. 2A, the light source 210 also includes a gas supply system 290 that is fluidly coupled to the interior of the discharge chamber 215-1 via a fluid conduit 289. The fluid conduit 289 is any conduit that can transport gas or other fluids without loss or with minimal loss of that fluid. For example, the fluid conduit 289 can be a pipe made of or coated with a material that does not react with one or more fluids transported in the fluid conduit 289. The gas supply system 290 includes a chamber 291 configured to contain and / or receive one or more gases used in the gain medium 214-1. The gas supply system 290 also includes devices (such as pumps, valves, and / or fluid switches) that enable the gas supply system 290 to remove gas from the discharge chamber 215-1 or inject gas into the chamber. The gas supply system 290 is coupled to the control system 250. The gas supply system 290 can be controlled by the control system 250, for example, to perform a refill procedure.

[0058]

[0065] The other N - 1 optical oscillators are similar to optical oscillator 212 - 1 and have similar or identical components and subsystems. For example, each of optical oscillators 212 - 1 to 212 - N includes electrodes such as electrodes 213 - 1a and 213 - 1b, a spectroscopic analyzer such as spectroscopic analyzer 298 - 1, and an output coupler such as output coupler 296 - 1. Also, voltage source 297 may be electrically connected to the electrodes of each of optical oscillators 212 - 1 to 212 - N, or voltage source 297 may be implemented as a voltage system including N individual voltage sources, with each of those voltage sources being electrically connected to the electrodes of one of the optical oscillators 212 - 1 to 212 - N.

[0059]

[0066] Light source 210 also includes beam control device 217 and beam combiner 218. Beam control device 217 is between the gaseous gain media of optical oscillators 212 - 1 to 212 - N and beam combiner 218. Beam control device 217 determines which of light beams 216 - 1 to 216 - N is incident on beam combiner 218. Beam combiner 218 forms exposure beam 211 from one or more light beams incident on beam combiner 218. For example, beam combiner 218 may redirect all the light beams incident thereon towards scanner device 280.

[0060]

[0067] In the illustrated example, beam control device 217 is represented as a single element. However, beam control device 217 may be implemented as a collection of individual beam control devices. For example, beam control device 217 may include a collection of N shutters, with one shutter associated with each of optical oscillators 212 - 1 to 212 - N. Each of the N shutters can be a mechanical shutter or an electro - optical shutter. Each of the N shutters has a first state that blocks the respective light beams 216 - 1 to 216 - N and a second state that transmits the respective light beams 216 - 1 to 216 - N.

[0061]

[0068] The light source 210 may include other components and systems. For example, the light source 210 may include a beam preparation system 299. The beam preparation system 299 may include a pulse stretcher (not shown), which expands each pulse that interacts with the pulse stretcher over time. The beam preparation system may also include other components that can act on light, such as, for example, reflective and / or refractive optical elements (such as lenses and mirrors), and / or filters. In the example shown, the beam preparation system 299 is located in the path of the exposure beam 211. However, the beam preparation system 299 may be installed in other locations within the photolithography system 200. Also, other embodiments are possible. For example, the light source 210 may include N instances of the beam preparation system 299, each of which is installed between the beam combiner 218 and one of the chambers 215-1 to 215-N and is positioned to interact with one of the light beams 216-1 to 216-N. In another example, the light source 210 may include an optical element (such as a mirror) that directs the light beams 216-1 to 216-N toward the beam combiner 218.

[0062]

[0069] The system 200 also includes a scanner device 280. The scanner device 280 exposes the wafer 282 with the shaped exposure light beam 211'. The shaped exposure light beam 211' is formed by passing the exposure beam 211 through a projection optical system 281. The scanner device 280 may be an immersion system or a dry system. The scanner device 280 includes a projection optical system 281 through which the exposure beam 211 passes before reaching the wafer 282, and a sensor system or a metrology system 270. The wafer 282 is held or received on a wafer holder 283. The scanner device 280 may also include, for example, a temperature control device (such as an air conditioning device and / or a heating device), and / or a power supply for various electrical components.

[0063]

[0070] The metrology system 270 includes a sensor 271. The sensor 271 can be configured to measure characteristics of the shaped exposure beam 211’, such as, for example, bandwidth, energy, pulse length, and / or wavelength. The sensor 271 can be, for example, a camera or other device capable of capturing an image of the shaped exposure beam 211’ on the wafer 282, or an energy detector capable of capturing data describing the amount of optical energy in the x-y plane on the wafer 282.

[0064]

[0071] In the embodiment shown in FIG. 2A, the metrology system 270 is not connected to the control system 250. However, in other embodiments, the metrology system 270 is connected to the control system 250. In these embodiments, the metrology system 270 provides data to the control system 250, and the control system 250 can issue commands to the metrology system 270.

[0065]

[0072] The control system 250 includes an electronic processing module 251, an electronic storage device 252, and an I / O interface 253. The electronic processing module 251 includes one or more processors suitable for the execution of a computer program, such as a general-purpose or special-purpose microprocessor, and any 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 (RAM), or both. The electronic processing module 251 can include any type of electronic processor. One or more electronic processors of the electronic processing module 251 execute instructions and access data stored in the electronic storage device 252. One or more electronic processors can also write data to the electronic storage device 252.

[0066]

[0073] The electronic memory device 252 may be a volatile memory such as a RAM, or may be a non-volatile memory. In some embodiments, the electronic memory device 252 includes non-volatile and volatile portions or components. The electronic memory device 252 may store data and information used in the operation of the control system 250. For example, the electronic memory device 252 may store the specification information of the optical beams 216-1 to 216-N. The specification information may include, for example, the target energy, wavelength, and / or spectral bandwidth of the optical beams 216-1 to 216-N. The specification information may also include the range or upper limit of the amount of allowable difference in the spectral characteristics of the optical beams 216-1 to 216-N. The electronic memory device 252 may also store instructions (e.g., in the form of a computer program) for controlling the spectral adjustment devices 295-1 to 295-N and for analyzing data from the spectral analysis devices 298-1 to 298-N.

[0067]

[0074] The electronic memory device 252 may also store instructions (e.g., in the form of a computer program) for causing the control system 250 to interact with other components and subsystems of the optical lithography system 200. For example, the instructions may be instructions for causing the electronic processing module 251 to provide command signals to the light source 210 and / or the beam control device 217 to change one or more of the optical oscillators 212-1 to 212-N that contribute to the exposure beam 211. The electronic memory device 252 may also store information received from the optical lithography system 200, the scanner device 280, and / or the light source 210.

[0068]

[0075] The I / O interface 253 is any type of interface that enables the control system 250 to exchange data and signals with an automated process operating on an operator, a light source 210, a scanner device 280, and / or another electronic device. For example, in an embodiment where rules or instructions stored in the electronic storage device 252 can be edited, the editing can be performed through the I / O interface 253. The I / O interface 253 can include one or more of a visual display device, a keyboard, and a communication interface such as a parallel port, a universal serial bus (USB) connection, and / or any type of network interface such as Ethernet. The I / O interface 253 can also enable contactless communication, for example, through an IEEE802.11, Bluetooth, or near field communication (NFC) connection.

[0069]

[0076] The control system 250 is connected to the light source 210 through a data connection 254. The data connection 254 may be a physical cable or other physical data conduit (such as a cable that supports the transmission of IEEE 802.3-based data), a wireless data connection (such as a data connection that provides data via IEEE 802.11 or Bluetooth), or a combination of wired and wireless data connections. The data provided via the data connection may be set through any type of protocol or format. The data connection 254 is connected to the light source 210 at a communication interface. The communication interface may be any type of interface capable of transmitting and receiving data. For example, the data interface may be an Ethernet interface, a serial port, a parallel port, or a USB connection. In some embodiments, the data interface enables data communication through a wireless data connection. For example, the data interface may be an IEEE 811.11 transceiver, Bluetooth, or an NFC connection. The control system 250 may be connected to the systems and / or components within the light source 210. For example, the control system 250 may be directly connected to each of the optical oscillators 212-1 through 212-N.

[0070]

[0077] Referring also to FIG. 2B, the projection optical system 281 includes a slit 284, a mask 285, and a projection objective system including a lens system 286. The lens system 286 includes one or more optical elements. The exposure beam 211 enters the scanner device 280 and impinges on the slit 284, and at least some of the output light beam 211 passes through the slit 284 to form an exposure beam 211' that is shaped. In the examples of FIGS. 2A and 2B, the slit 284 is rectangular and shapes the exposure beam 211 into an elongated rectangular light beam. This is the shaped exposure beam 211'. The mask 285 includes a pattern that determines which portions of the shaped light beam are transmitted by the mask 285 and which portions are blocked by the mask 285. On the wafer 282, microelectronic features are formed by exposing a layer of radiation-sensitive photoresist material on the wafer 282 with the exposure beam 211'. The design of the pattern on the mask is determined by the specific microelectronic circuit features desired.

[0071]

[0078] The control system 250 controls one or more aspects of the optical oscillators 212-1 to 212-N so as to control one or more spectral characteristics of each of the light beams 216-1 to 216-N. The control system 250 may adjust the light beams 216-1 to 216-N to have substantially the same spectral characteristics. For example, the control system 250 may determine, based on information from the spectral analysis devices 298-1 to 298-N, that the spectral bandwidth of the light beam 216-1 is smaller than the spectral bandwidths of the other N-1 light beams. In response, the control system 250 controls the characteristics of the spectral adjustment device 295-1 or the gain medium 214-1 to increase the spectral bandwidth of the light beam 216-1.

[0072]

[0079] Referring to FIG. 4, a flowchart of procedure 400 is shown. Procedure 400 may be implemented by control system 150 (FIG. 1) or control system 250 (FIG. 2A). In the following example, procedure 400 is implemented by control system 250 and by light source 210. As described above, optical system 210 includes N optical oscillators 212-1 through 212-N, each configured to generate a respective optical beam 216-1 through 216-N. At least one of optical beams 216-1 through 216-N contributes to output optical beam 211 at any given time.

[0073]

[0080] Including more than one optical oscillator in light source 210 improves the performance of light source 210 and system 200. For example, optical oscillators are typically taken out of operation for maintenance after a certain operating interval has elapsed. The operating interval can be a certain period or a predefined number of pulses. Optical oscillators cannot reliably generate their respective optical beams while maintenance is being performed. Since light source 210 includes more than one optical oscillator, one of the optical oscillators can be operated while one or more of the other optical oscillators are being maintained. Thus, by including N optical oscillators, the downtime of source 210 (and system 200) is reduced. Also, the total period during which source 210 can operate without any of the optical oscillators needing to be replaced is longer than the amount of time that a light source including only one set of optical oscillators can operate.

[0074]

[0081] Accordingly, with N optical oscillators, source 210 will have a shorter downtime and a longer overall operating life. One or more of the optical beams 216-1 through 216-N that contribute to the output optical beam 211 change over time. Without correction, each of the optical beams 216-1 through 216-N may have different values or amounts for the same spectral characteristics. Thus, if no correction is made, the spectral characteristics of the output optical beam 211 will also change over time as the output optical beam 211 is generated using optical beams from different ones or more of the optical oscillators 212-1 through 212-N. Procedure 400 is implemented to increase the uniformity of the spectral characteristics of the output optical beam 211 over time.

[0075]

[0082] During a first period, the optical lithography system 200 generates an output optical beam 211 from a first set of N optical oscillators 212-1 through 212-N (410). The first period may be the time it takes for each of the first set of optical oscillators to generate a particular number of pulses, such as thousands of pulses, or the first period may be a preset period. The first set may include one of the N optical oscillators 212-1 through 212-N, a plurality of the N optical oscillators, or all of the N optical oscillators. The control system 250 controls the optical system 210 such that only the optical beams from the first set of oscillators contribute to the output optical beam 211.

[0076]

[0083] For example, in some embodiments, all of the optical oscillators 212-1 to 212-N each generate their respective optical beams 216-1 to 216-N, and the control system 250 acts on the beam control device 217 to ensure that only the optical beams generated by the first set of optical oscillators contribute to the output optical beam 211. In this embodiment, the control system 250 acts on the beam control device 217 such that only the optical beam generated by one optical oscillator of the first set contributes to the output optical beam 211. For example, the beam control device 217 may include N shutters, each of which is associated with one of the N optical oscillators 212-1 to 212-N. In the first state, each shutter blocks its respective optical beam. In the second state, each shutter transmits its respective optical beam. In these embodiments, the control system 250 controls the shutters associated with each optical oscillator of the first set to be in the second state. The control system 250 sets the shutters associated with each optical oscillator that is not in the first set to the first state. Thus, the optical beams generated by the optical oscillators that are not in the first set do not reach the beam combiner 218 and do not contribute to the output optical beam 211.

[0077]

[0084] In other embodiments, the control system 250 causes each optical beam to be generated only by the first set of optical oscillators, while the optical oscillators that are not in the first set are in an OFF state where they do not generate optical beams. In these embodiments, the optical beams from the first set of optical oscillators reach the beam combiner 218. The optical beams from the optical oscillators that are not in the first set do not reach the beam combiner 218. Thus, during the first period, the output optical beam 211 includes only the contribution from the optical beams generated by the first set of optical oscillators.

[0078]

[0085] During the second period, the photolithography system 200 generates output light beams 211 from the second set of N optical oscillators 212-1 to 212-N (420). The second period occurs after the first period. The second period can be the time it takes for each of the second set of optical oscillators to generate a specific number of pulses, such as thousands of pulses, or a preset period. The first and second periods may be the same or different.

[0079]

[0086] The second set of optical oscillators can include one optical oscillator, a plurality but less than all of the N optical oscillators 212-1 to 212-N, or all of the N optical oscillators 212-1 to 212-N. However, the second set of N optical oscillators 212-1 to 212-N does not include the same one or more optical oscillators as the first set. For example, if the first set of optical oscillators includes all of the N optical oscillators 212-1 to 212-N, the second set includes fewer optical oscillators than all of the N optical oscillators 212-1 to 212-N. If the first set of optical oscillators includes one of the optical oscillators 212-1 to 212-N, the second set of optical oscillators may be only another one of the optical oscillators 212-1 to 212-N, or the second set of optical oscillators may be a plurality of optical oscillators that include or do not include the optical oscillator used in the first set.

[0080]

[0087] The control system 250 controls one or more of the spectral adjustment devices 295-1 to 295-N so as to increase the uniformity of the spectral characteristics of the output optical beam 211 over time (430). Continuing the above example where N is 2 and the light source 210 includes the optical oscillator 212-1 as the first set and the optical oscillator 212-2 as the second set, during the first period, only the optical beam 216-1 reaches the beam combiner 218. The optical beam 216-2 is generated but does not reach the beam combiner 218. The spectral bandwidth of the optical beam 216-2 is measured by the spectral analyzer 298-2, and data representing the spectral bandwidth of the optical beam 216-2 is provided to the control system 250. The control system 250 compares the spectral bandwidth of the optical beam 216-2 with the measured or known spectral bandwidth or specification of the optical beam 216-1. If the spectral bandwidth of the optical beam 216-2 is smaller than the spectral bandwidth of the optical beam 216-1 and / or smaller than the specification, the control system 250 controls the spectral adjustment device 295-2 to increase the spectral bandwidth of the second optical beam 216-2.

[0081]

[0088] For example, the spectral adjustment device 295-2 may be the spectral adjustment device 395-1 shown in FIG. 3. In this example, the control system 250 adjusts the spectral characteristics of the optical beam 216-2 by controlling the orientation of one or more of the grating 321 and / or the prisms 322, 323, 324, 325 (shown in FIG. 3) via their respective actuators 321A, 322A, 323A, 324A, 325A.

[0082]

[0089] One or more spectral characteristics of the optical beam 216-2 are adjusted before the second period begins. Thus, when the control system 250 acts on the beam control device 217 to enable the optical beam 216-2 to interact with the beam combiner 218, the spectral characteristics of the optical beam 216-2 have already been adjusted. In this way, the control system 250 reduces or eliminates sudden changes in the spectral characteristics of the output optical beam 211, thereby increasing the uniformity of the output optical beam 211 even if different ones of the optical oscillators 212-1 to 212-N are used during the first and second periods.

[0083]

[0090] The first and second periods are provided as an example. The control system 250 may continue to alternately use the first optical oscillator 212-1 and the second optical oscillator 212-2 over more than two periods. Also, the first set and the second set each having only one optical oscillator are provided as an example. The control system 250 may cyclically switch among more than two sets of N optical oscillators. For example, N may be 6. The control system 250 causes three of the six optical oscillators to reach the beam combiner 218 during the first period, causes the other three of the six optical oscillators to reach the beam combiner 218 during the second period, and causes any group of three other oscillators to reach the beam combiner 218 during the third period.

[0084]

[0091] Referring to FIG. 5, a flowchart of procedure 500 is shown. Procedure 500 can be implemented by control system 150 (FIG. 1) or control system 250 (FIG. 2A). In the following example, procedure 500 is implemented by control system 250 and by light source 210. Procedure 500 is used to adjust the spectral characteristics of one or more light beams 216-1 to 216-N. Light source 210 includes N optical oscillators 212-1 to 212-N. In the following discussion, the N optical oscillators include a first set of M optical oscillators 212-1 to 212-M and a second set of L optical oscillators 212-1 to 212-L. M and L are integers greater than zero and less than or equal to N. The first set and the second set do not include the same optical oscillator. The first set of M optical oscillators is used to generate output light beam 211 during a first period. The second set of L optical oscillators is used to generate output light beam 211 during a second period.

[0085]

[0092] Procedure 500 can be used to adjust the spectral characteristics of light beams 216-1 to 216-L and / or light beams 216-1 to 216-M such that the spectral characteristics of all light beams 216-1 to 216-N are more similar to each other or substantially the same or closer to the specification. For example, procedure 500 can be used to equalize the spectral bandwidths of all light beams 216-1 to 216-N to the maximum spectral bandwidth possible for the light output generated by each optical oscillator 212-1 to 212-N.

[0086]

[0093] During the first period, the output optical beam 211 is generated based on light from M out of the optical oscillators 212-1 to 212-M (510). Data related to the spectral characteristics of one or more of the M optical beams is accessed (520). For example, the accessed data can be data from the spectral analyzers 298-1 to 298-M. In some embodiments, the accessed data can be data from the spectral analyzers 298-1 to 298-M stored in the electronic storage device 252. The determined spectral characteristics of each of the M optical beams are compared with a reference (530). It is determined based on the comparison whether to control any one aspect of the N optical oscillators (540). When one aspect is controlled, the control system 250 adjusts one or more of the M optical oscillators to adjust the spectral characteristics of one or more of each of the M optical beams (550).

[0087]

[0094] Hereinafter, various embodiments will be described using an example in which N is 4, M is 2, and L is 2. The light source 210 includes four optical oscillators 212-1 to 212-4. The first set includes the optical oscillators 212-1 and 212-2. The second set includes the optical oscillators 212-3 and 212-4.

[0088]

[0095] In some embodiments, the reference is a predetermined value representing the maximum spectral bandwidth. In these embodiments, the reference is stored in the electronic memory device 252. The reference may be stored in the electronic memory device 252 when the optical system 210 is manufactured, or may be loaded into the electronic memory device 252 while the light source 210 is in the field. The spectral characteristics of each of the M optical beams 216-1 and 216-2 are determined based on data from the spectral analyzers 298-1 and 298-2, respectively, or are directly measured using the spectral analyzers 298-1 and 298-2. The spectral characteristics of each of the optical beams 216-1 and 216-2 are compared with the maximum spectral bandwidth. For example, the comparison may be performed by determining the difference between the maximum spectral bandwidth and the spectral characteristics of each of the optical beams 216-1 and 216-2. The determined difference may be compared with a threshold value. If the difference for the optical beam 216-1 is greater than the threshold value, the control system 250 activates the spectral adjustment device 295-1 to increase the spectral bandwidth of the optical beam 216-1. For example, the spectral adjustment device 295-1 may be implemented as shown in FIG. 3. To increase the spectral bandwidth of the optical beam 216-1, the control system 250 activates the prism 324 using the actuator 324A.

[0089]

[0096] One approach to increasing the spectral bandwidth of the optical beam 216-1 is to increase the divergence of the light impinging on the grating of the spectral adjustment device 295-1. Another approach is to rapidly vary the angle of incidence of the light impinging on the grating of the spectral adjustment device 295-1. This rapid variation can be effected, for example, as will be described later, by applying an appropriate time-varying signal to the actuator for the steering prism of the spectral adjustment device 295-1. The speed at which the spectral adjustment device 295-1 is adjusted may be, for example, at least one tenth of the repetition rate of the optical beam 216-1 such that the spectral adjustment device 295-1 is adjusted and thereby adjusts the spectral characteristics of the optical beam 216-1 every 10 pulses. For example, if the repetition rate of the optical beam 216-1 is 6,000 Hz, the spectral adjustment device 295-1 is adjusted at a speed of at least 600 Hz. In this example, the actuator for the steering prism used as described above will operate at a speed of at least 600 Hz. Other adjustment speeds may be used. For example, the spectral adjustment device 295-1 may be adjusted for each pulse generated by the optical oscillator 212-1 (i.e., pulse by pulse). In another example, the optical elements (such as the steering prism) of the spectral adjustment device 295-1 may be operated at a speed that adjusts the spectral characteristics of the optical beam 216-1 every 5 pulses.

[0090]

[0097] If the difference for the optical beam 216-1 is less than the threshold value, the control system 250 does not adjust the spectral bandwidth of the optical beam 216-1. A similar analysis is performed for the optical beam 216-2.

[0091]

[0098] The above example relates to the reference being a predefined value or target value such that the spectral characteristics of one or more of the optical beams 216-1 to 216-N are compared to the predetermined value. Other embodiments are possible. For example, the spectral characteristics of a first set of optical beams may be compared to the spectral characteristics of a second set of optical beams, or the spectral characteristics of one optical beam in the first set may be compared to the spectral characteristics of another optical beam in the first set.

[0092]

[0099] To provide a more specific example, the criterion may include values representing the spectral bandwidths of each of the optical beams 216-3 and 216-4. The spectral bandwidths of each of the optical beams 216-1 and 216-2 are compared with the spectral characteristics of the optical beam 216-3 and / or the optical beam 216-4. For example, the comparison may be performed by determining the difference in spectral bandwidth between the optical beams 216-1 and 216-3. If the spectral bandwidth of the optical beam 216-1 is smaller than the spectral bandwidth of the optical beam 216-3, the control system 250 actuates the spectral adjustment device 295-1 to increase the spectral bandwidth of the optical beam 216-1. If the spectral bandwidth of the optical beam 216-3 is smaller than the spectral bandwidth of the optical beam 216-1, the control system 250 actuates the spectral adjustment device 295-3 to increase the spectral bandwidth of the optical beam 216-3. For example, the spectral adjustment devices 295-1 to 295-4 may be implemented as shown in FIG. 3. In these embodiments, to increase the bandwidth of the optical beam 216-1, the control system 250 actuates the prism 324 by controlling the actuator 324A of the spectral adjustment device 295-1.

[0093]

[0100] Further, the control system 250 may determine the amount of operation of the prism 324 based on the difference between the spectral bandwidth of the optical beam 216-1 and the spectral bandwidth of the optical beam 216-3. For example, the actuator 324A may be a piezo actuator that changes its shape in response to the application of a voltage signal. The prism 324 moves when the piezo actuator changes its shape. The amount and direction of movement of the prism 324 are determined by the characteristics of the applied voltage signal. The prism 324 can be rapidly moved by applying a time-varying voltage signal. The amplitude of the applied voltage signal determines the displacement of the prism 324, and the frequency of the applied voltage signal determines how rapidly the prism 324 is displaced. The amplitude of the applied voltage signal is based on the magnitude of the difference, and the amplitude is larger when the difference is larger than when the difference is smaller. The time-varying signal can be, for example, a sine or substantially sine signal, a square wave, a triangular wave, or any other time-varying signal. This scenario is provided as an example. However, a similar analysis may be performed to compare the spectral characteristics of other of the optical beams. For example, the spectral characteristics of each of the optical beams 216-3 and 216-4 can be compared with and appropriately adjusted based on the spectral characteristics of the optical beams 216-1 and / or 216-2. Also, the spectral characteristics of the optical beam 216-1 can be compared with and appropriately adjusted based on the spectral characteristics of the optical beam 216-2.

[0094]

[0101] Other aspects of the present invention are described in the clauses numbered below. 1. A light source comprising a plurality of optical oscillators, each optical oscillator being configured to generate an optical beam, a spectroscopic analyzer, a controller, configured to determine, based on data from the spectroscopic analyzer, whether the spectral characteristics of the optical beam of the first one of the optical oscillators differ from the spectral characteristics of the optical beam of at least one other of the plurality of optical oscillators, When the spectral characteristics of the light beam of the first one of the optical oscillators are different from the spectral characteristics of the light beam of at least one other of the optical oscillators, a controller configured to adjust the spectral characteristics of the light beam of the first one of the optical oscillators or the spectral characteristics of the light beam of at least one other of the optical oscillators, A system comprising. 2. The system of clause 1, wherein the spectral characteristics include a spectral bandwidth. 3. The system of clause 2, wherein the control system is configured to determine whether the spectral bandwidth of the light beam of the first one of the optical oscillators is different from the spectral bandwidth of the light beam of at least one other of the optical oscillators, and the controller is configured to determine whether the spectral bandwidth of the light beam of the first one of the optical oscillators is smaller than the bandwidth of at least one other of the plurality of optical oscillators. 4. The system of clause 3, wherein when the spectral bandwidth of the light beam of the first one of the optical oscillators is smaller than the spectral bandwidth of the light beam of at least one other of the optical oscillators, the controller is configured to increase the bandwidth of the light beam of the first one of the optical oscillators. 5. The system of clause 1, further comprising a plurality of spectral adjustment devices, each optical oscillator being associated with one of the plurality of spectral adjustment devices, and the controller being configured to control the spectral adjustment device associated with any one of the optical oscillators, thereby adjusting the spectral characteristics of the light beam of any one of the optical oscillators. 6. The system of clause 1, wherein each spectral adjustment system comprises at least one optical element, and the controller is configured to control a particular spectral adjustment device by operating an actuator coupled to the optical element of the spectral adjustment device so that the optical element moves. 7. The system of clause 6, wherein moving the optical element changes the center wavelength of the light beam. 8. The system of clause 6, wherein the controller is further configured to determine the amount of operation. 9. To operate the optical element, the controller provides an electrical signal to the optical element, the amount of operation is based on the electrical signal, and one or more characteristics of the electrical signal are determined based on the difference, the system of clause 8. 10. One or more characteristics of the electrical signal comprise amplitude and / or frequency, the system of clause 9. 11. The amount of operation is based on the number of optical pulses expected to interact with the spectroscopic adjustment system over a period, and the amount of operation is the number of separate operations performed over the period, the system of clause 8. 12. The amount of operation is based on the difference between the spectroscopic characteristics of the optical beam of the first of the optical oscillators and the spectroscopic characteristics of the optical beam of at least one of the other optical oscillators, the system of clause 8. 13. Each spectroscopic adjustment device comprises at least one refractive optical element, the system of clause 1. 14. Each spectroscopic adjustment device comprises at least one prism, the system of clause 1. 15. Each spectroscopic adjustment device comprises a reflective optical element, the system of clause 1. 16. Each spectroscopic adjustment device comprises a plurality of prisms and an actuator coupled to one of the prisms, and the controller is configured to control the actuator of each spectroscopic adjustment assembly, thereby moving one of the prisms, to adjust the spectroscopic characteristics of the optical beam of any of the optical oscillators, the system of clause 1. 17. Each optical oscillator is configured to emit a pulsed optical beam comprising a plurality of optical pulses, the system of clause 1. 18. The controller is further configured to determine the updated spectroscopic characteristics of the optical beam of the first optical oscillator after adjusting the spectroscopic characteristics, and configured to determine whether the updated spectroscopic characteristics of the optical beam of the first optical oscillator differ from the spectroscopic characteristics of the optical beam of any of the other optical oscillators, the system of clause 1. 19. The plurality of optical oscillators includes only one first optical oscillator and one second optical oscillator, where the first of the optical oscillators is the first optical oscillator and the second optical oscillator is at least one other optical oscillator, and the controller is configured to determine whether the spectral characteristics of the optical beam of the first optical oscillator are different from those of the second optical oscillator based on data from the spectroscopic analysis system, and if the spectral bandwidth of the first optical oscillator is different from that of the second optical oscillator, adjust the spectral characteristics of the optical beam of the first optical oscillator or the spectral characteristics of the optical beam of the second optical oscillator, for the system of clause 1. 20. The spectroscopic analysis system includes a plurality of spectroscopic analysis systems, each spectroscopic analysis system being configured to receive one optical beam of the optical oscillators, and each spectroscopic analysis system being configured to measure the spectral characteristics associated with one optical beam of the optical oscillators, for the system of clause 1. 21. Each optical oscillator is configured to contain a gaseous gain medium, for the system of clause 1. 22. The gaseous gain medium comprises krypton fluoride (KrF), for the system of clause 21. 23. If the spectral characteristics of the optical beam of the first of the optical oscillators are different from those of the optical beam of at least one other of the optical oscillators, the controller is configured to adjust the pressure and / or concentration of one or more gas components of the gaseous gain medium of the first of the optical oscillators to adjust the spectral characteristics of the optical beam of the first of the optical oscillators, or to adjust the pressure and / or concentration of one or more gas components of the gaseous gain medium of at least one other of the optical oscillators to adjust the spectral characteristics of at least one other of the optical oscillators, for the system of clause 21. 24. Further comprising a beam combiner, the beam combiner being configured to receive all the optical beams of the optical oscillators and direct the optical beams towards a DUV lithography scanner tool, for the system of clause 1. 25. Each optical oscillator is configured to generate a pulsed optical beam having a certain repetition rate, and the controller is configured to adjust the spectral characteristics of the optical beam of the first one of the optical oscillators or the second one of the optical oscillators at a certain adjustment rate, where the adjustment rate is equal to or greater than one-tenth of the repetition rate. The system of clause 1. 26. A method for controlling a deep ultraviolet (DUV) light source comprising N optical oscillators, where N is an integer greater than 1, and each optical oscillator is configured to generate a respective optical beam. M is an integer greater than zero and less than or equal to N. Based on M optical beams generated by M respective ones of the N optical oscillators, forming an output optical beam. Accessing data related to the spectral characteristics of each of the M optical beams. Comparing the spectral characteristics of each of the M optical beams with a reference. Based on the comparison, determining whether to control one of the N optical oscillators, thereby adjusting the spectral characteristics of one of the N optical beams. A method comprising. 27. The method of clause 26, where the spectral characteristics include a spectral bandwidth. 28. The reference is such that comparing the spectral characteristics of each of the M optical beams with the reference comprises comparing the spectral characteristics of each of the M optical beams with the spectral characteristics of all of the other M optical beams. The method of clause 26, comprising all of the spectral characteristics of the M optical beams. 29. Comparing the spectral characteristics of each of the M optical beams with the spectral characteristics of all of the other M optical beams comprises determining the difference between the spectral characteristics of each of the M optical beams and the spectral characteristics of each of the other M optical beams. Determining based on the comparison comprises comparing each determined difference with a specification. The method of clause 26. 30. The reference has a predetermined value of the spectral characteristics, and comparing the spectral characteristics of each of the M optical beams with the reference comprises comparing the spectral characteristics of each of the M optical beams with the predetermined value. The method of clause 26. 31. The predetermined value has a maximum spectral bandwidth, and the spectral characteristics of each of the M optical beams are compared with the maximum spectral bandwidth by determining the difference between the spectral characteristics of the optical beam and the maximum spectral bandwidth, in accordance with the method of clause 30. 32. Determining based on the comparison comprises comparing the determined difference with a range of a predetermined allowable difference, and for those having a determined difference outside the range of the predetermined allowable difference among the M optical beams, one aspect of each of the optical oscillators is controlled, in accordance with the method of clause 31. 33. Controlling one aspect of each of the optical oscillators comprises operating a dispersive optical element, in accordance with the method of clause 32. 34. The output optical beam is based on the M optical beams in the first period and also based on the L optical beams in the second period, where L is an integer greater than or equal to 1 and less than or equal to N, The reference has the spectral characteristics of each of the L optical beams, and comparing the spectral characteristics of each of the M optical beams with the reference comprises comparing the spectral characteristics of each of the M optical beams with the spectral characteristics of each of the L optical beams, in accordance with the method of clause 26. 35. L is 1, M is 1, N is 2, the L optical beams are the first optical beam generated by the first one of the N optical oscillators, the M optical beams are the second optical beam generated by the second one of the N optical oscillators, Comparing the spectral characteristics of the first optical beam and the spectral characteristics of the second optical beam comprises determining whether the spectral bandwidth of the second optical beam is smaller than the spectral bandwidth of the first optical beam, and when the spectral bandwidth of the second optical beam is smaller than the spectral bandwidth of the first optical beam, controlling the prism of the second one of the N optical oscillators so that the spectral bandwidth of the second optical beam is increased, in accordance with the method of clause 34. 36. L is 1, M is 1, N is 2, the L optical beams are the first optical beam generated by the first one of the N optical oscillators, the M optical beams are the second optical beam generated by the second one of the N optical oscillators, Comparing the spectral characteristics of the first optical beam and the spectral characteristics of the second optical beam includes determining whether the spectral bandwidth of the first optical beam is smaller than the spectral bandwidth of the second optical beam, and when the spectral bandwidth of the first optical beam is smaller than the spectral bandwidth of the second optical beam, controlling the prism of the first one of the N optical oscillators so that the spectral bandwidth of the first optical beam is increased, the method of clause 34. 37. The method of clause 35, further comprising determining an adjustment amount to the prism of the second one of the N optical oscillators based on the difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam. 38. To control the prism of the second one of the N optical oscillators, a time-varying signal is applied to an actuator physically connected to the prism, and the amplitude of the time-varying signal is related to the difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam, the method of clause 37. 39. A control system for a deep ultraviolet (DUV) light source comprising N optical oscillators, where N is an integer greater than 1, each optical oscillator being configured to generate a respective optical beam, the control system controls the first set of N optical oscillators to generate the first set of optical beams during a first period such that the output optical beam generated by the DUV light source during the first period comprises the first set of optical beams, where the second set of N optical oscillators and the first set of N optical oscillators do not include the same one or more of the N optical oscillators, and controls the second set of N optical oscillators to generate the second set of optical beams during a second period such that the output optical beam generated by the DUV light source during the second period comprises the second set of optical beams, A control system configured to control at least one spectral adjustment device among the N optical oscillators so as to increase the uniformity of the spectral characteristics of the N optical beams. 40. The control system of clause 39, wherein the spectral adjustment device is controlled prior to the second period. 41. The control system of clause 40, wherein one or more beam splitting adjustment devices of the N optical oscillators of the second set of N optical oscillators are controlled to adjust one or more beam splitting characteristics of the respective second set of optical beams. 42. The control system of clause 39, wherein each optical oscillator is configured to generate its respective pulsed optical beam at a certain repetition rate, and the control system is configured to control at least one beam splitting adjustment device of the N optical oscillators at an adjustment rate that is 1 / 10 or more of the repetition rate.

[0095]

[0102] Other embodiments may be within the scope of the claims.

Claims

1. a light source comprising a plurality of optical oscillators, each optical oscillator configured to generate a light beam; A spectroscopic analyzer; A controller, configured to compare a difference between a spectral bandwidth of the light beam of a first one of the optical oscillators and a spectral bandwidth of the light beam of at least one other one of the plurality of optical oscillators to a threshold value based on data from the spectroscopic analysis device; a controller configured to adjust the spectral bandwidth of any of the optical oscillators to increase the uniformity of the spectral bandwidth when the difference is greater than the threshold, and to not adjust when the difference is less than the threshold; A system comprising:

2. 2. The system of claim 1, further comprising a plurality of spectral adjustment devices, each optical oscillator being associated with one of the plurality of spectral adjustment devices, and the controller configured to control the spectral adjustment device associated with any of the optical oscillators, thereby adjusting the spectral bandwidth of the optical beam of any of the optical oscillators.

3. 2. The system of claim 1 , wherein each spectral adjustment system comprises at least one optical element, and the controller is configured to control a particular spectral adjustment device by actuating an actuator coupled to the optical element of that spectral adjustment device to move that optical element.

4. The controller is further configured to determine an actuation amount; The system of claim 3 , wherein the amount of actuation is based on a number of light pulses expected to interact with the spectroscopic tuning system over a period of time, the amount of actuation being the number of separate acts performed over the period of time.

5. 3. The system of claim 2, wherein each spectral adjustment device comprises a plurality of prisms and an actuator coupled to one of the prisms, and the controller is configured to control the actuator of the respective spectral adjustment device to thereby move the one of the prisms and thereby adjust the spectral bandwidth of the light beam of any of the optical oscillators.

6. Each optical oscillator is configured to contain a gaseous gain medium; 2. The system of claim 1 , wherein if the spectroscopic bandwidth of the light beam of the first one of the optical oscillators differs from the spectroscopic bandwidth of the light beam of at least one other one of the optical oscillators, the controller is configured to adjust a pressure and / or concentration of one or more gas components of the gaseous gain medium of the first one of the optical oscillators to adjust the spectroscopic bandwidth of the light beam of the first one of the optical oscillators, or to adjust the pressure and / or concentration of one or more gas components of the gaseous gain medium of the at least one other one of the optical oscillators to adjust the spectroscopic bandwidth of the at least one other one of the optical oscillators.

7. 2. The system of claim 1 , wherein each optical oscillator is configured to generate a pulsed optical beam having a repetition rate, and wherein the controller is configured to adjust the spectral bandwidth of the optical beam of the first one of the optical oscillators or the at least one other one of the optical oscillators at an adjustment rate, the adjustment rate being equal to or greater than one tenth of the repetition rate.

8. a light source comprising a plurality of optical oscillators, each optical oscillator configured to generate a light beam; A spectroscopic analyzer; A controller, configured to compare a difference between a spectral bandwidth of the light beam of a first one of the optical oscillators and a spectral bandwidth of the light beam of at least one other one of the plurality of optical oscillators to a threshold value based on data from the spectroscopic analysis device; a controller configured to adjust the spectral bandwidth of any of the optical oscillators to increase the uniformity of the spectral bandwidth when the difference is greater than the threshold, and to not adjust when the difference is less than the threshold; Equipped with Each spectral adjustment device includes a plurality of prisms, a reflective optical element, and an actuator coupled to one of the prisms; the controller is configured to adjust the spectral bandwidth of the light beam of any of the optical oscillators by controlling the actuator of the respective spectral tuning device, thereby moving the one of the prisms. system.

9. 1. A method of controlling a deep ultraviolet (DUV) light source comprising N optical oscillators, N being an integer greater than 1, each optical oscillator configured to generate a respective light beam; forming an output light beam based on the M light beams generated by the M respective optical oscillators, where M is an integer greater than zero and less than N; accessing data relating to a spectral bandwidth of each of the M light beams; comparing a difference between a spectral bandwidth of each of the M light beams and a spectral bandwidth of each of the other M light beams with a threshold; Equipped with If the difference is greater than the threshold, adjusting the spectral bandwidth of any of the optical oscillators to increase the uniformity of the spectral bandwidth, and if the difference is less than the threshold, not adjusting the spectral bandwidth of any of the optical oscillators. method.

10. the output light beam is based on the M light beams of a first time period and based on L light beams of a second time period, where L is an integer greater than or equal to 1 and less than or equal to N; The method of claim 9 , wherein the comparing comprises comparing a difference between the spectral bandwidth of each of the M light beams and the spectral bandwidth of each of the L light beams to a threshold value.

11. L is 1, M is 1, and N is 2, the L optical beams being first optical beams generated by a first one of the N optical oscillators, and the M optical beams being second optical beams generated by a second one of the N optical oscillators; The method of claim 10 , wherein the comparing comprises comparing a difference between the spectral bandwidth of the second light beam and the spectral bandwidth of the first light beam to a threshold value.

12. 12. The method of claim 11, further comprising determining an adjustment to the prism of the second of the N optical oscillators based on a difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam.

13. 13. The method of claim 12, wherein a time-varying signal is applied to an actuator physically coupled to the prism to control the prism of the second of the N optical oscillators, the amplitude of the time-varying signal being related to the difference between the spectral bandwidth of the first optical beam and the spectral bandwidth of the second optical beam.

14. 1. A control system for a deep ultraviolet (DUV) light source comprising N optical oscillators, N being an integer greater than 1, each optical oscillator configured to generate a respective light beam, the control system comprising: controlling a first set of optical oscillators of the N optical oscillators to generate a first set of optical beams during a first time period, such that an output light beam generated by the DUV light source during the first time period comprises a first set of optical beams; controlling the second set of optical oscillators to generate the second set of optical beams during the second time period, such that the output light beam generated by the DUV light source during the second time period comprises the second set of optical beams, where a second set of optical oscillators of the N optical oscillators and the first set of optical oscillators do not include the same one or more optical oscillators of the N optical oscillators; a control system configured to compare a difference between a spectral bandwidth of the first set of the light beams and a spectral bandwidth of the second set of the light beams with a threshold, and if the difference is greater than the threshold, adjust the spectral bandwidth of at least one of the N optical oscillators to increase the uniformity of the spectral bandwidth of the N light beams, and not adjust the spectral bandwidth of at least one of the N optical oscillators, so as to increase the uniformity of the spectral bandwidth of the N light beams.

15. The control system of claim 14 , wherein the spectral adjustment device is controlled prior to the second period of time.

Images