JP7538346B2 - Multifocal imaging with wide wavelength intervals - Google Patents

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Application No. 63/123,833, filed December 10, 2020, entitled MULTIFOCAL IMAGING WITH INCREASED WAVELENGTH SEPARATION, which is hereby incorporated by reference in its entirety.

[0002] The disclosed subject matter relates to a wavelength selection device for selecting multiple wavelengths of a single pulsed light beam to form multiple aerial images in a single lithographic exposure pass.

[0003] Photolithography is the process of patterning semiconductor circuits onto a substrate such as a silicon wafer. A photolithography light source provides deep ultraviolet (DUV) light (a DUV light beam) that is used to expose photoresist on the wafer. The DUV light beam for photolithography is generated by an excimer light source. The light source is a laser source, the output of which is often a pulsed laser beam. The DUV light beam passes through a beam delivery unit, a reticle or mask, and is then projected onto a prepared silicon wafer. In this way, the chip design is patterned onto the photoresist, which is then developed, etched, and washed, and the process repeats.

[0004] Typically, an excimer laser uses a combination of one or more noble gases, which may include argon, krypton, or xenon, and a reactive gas, which may include fluorine or chlorine. Excimer lasers can create excimers, quasi-molecules, under the proper conditions of electrical simulation (energy provided) and high pressure (of the gas mixture), where the excimers exist only in an excited state. The excited excimers produce amplified light in the DUV range. An excimer light source can use a single gas discharge chamber or multiple gas discharge chambers. The DUV light beam can have a wavelength in the DUV range, including, for example, wavelengths from about 100 nanometers (nm) to about 400 nm.

[0005] In some general aspects, a wavelength selection device is disposed relative to a pulsed light source that generates a pulsed light beam. The wavelength selection device includes a center wavelength selection optic configured to select at least one center wavelength of each pulse of the pulsed light beam according to an angle of incidence of the pulsed light beam, a tuning mechanism disposed along a path of the pulsed light beam to the center wavelength selection optic configured to optically interact with the pulsed light beam and select an angle of incidence of the pulsed light beam to the center wavelength selection optic, and a diffractive optical element that is passive and transparent and disposed along the path of the pulsed light beam where the pulsed light beam is fully expanded or at least mostly expanded. The diffractive optical element is configured to interact with the pulsed light beam and generate from the pulsed light beam a plurality of pulsed light sub-beams, each associated with a distinct wavelength and each associated with a distinct angle of incidence to the center wavelength selection optic such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength.

[0006] Implementations may include one or more of the following features. For example, the diffractive optical element may be a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating.

[0007] The tuning mechanism may include four refractive optical elements. Each refractive optical element may be a right-angle prism. The tuning mechanism may include four right-angle prisms, and a location where at least a majority of the pulsed light beam is expanded is in an optical path between a right-angle prism closest to the central wavelength selection optics and a right-angle prism second closest to the central wavelength selection optics. The tuning mechanism may include four right-angle prisms disposed along a path of the pulsed light beam to the diffractive optical element, and the pulsed light beam is completely expanded between the four right-angle prisms and the central wavelength selection optics.

[0008] The wavelength spacing between the individual wavelengths of the multiple pulsed light sub-beams may be greater than about 10 picometers (pm), about 30 pm, or about 45 pm. The central wavelength of each pulse of the pulsed light beam may be about 248 nanometers (nm) or about 193 nm. The wavelength spacing between the individual wavelengths of the multiple pulsed light sub-beams may depend on the periodic shape of the diffractive optical element.

[0009] The wavelength selection device may also include an actuator configured to adjust the position of the diffractive optical element relative to the path of the pulsed light beam, such that at times the diffractive optical element is at a position along the path of the pulsed light beam and at other times is not at a position along the path of the pulsed light beam, and the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam. The actuator may further be configured to adjust the angle of the diffractive optical element relative to the direction of the path of the pulsed light beam, thereby adjusting the individual angle of incidence of each generated pulsed light sub-beam to the central wavelength selection optics.

[0010] The multiple pulsed light sub-beams may include three or more pulsed light sub-beams.

[0011] The tuning mechanism and center wavelength selection optics may be arranged to interact with the pulsed light beam in a Littrow configuration. The center wavelength selection optics may be reflective optical elements.

[0012] An aerial image can be formed for each individual wavelength of the pulsed light beam.

[0013] The wavelength-selecting device may also include a control system and one or more actuators associated with the tuning mechanism. The control system may be configured to adjust the angle of incidence of the pulsed light beam to the central wavelength-selecting optics by adjusting a signal to the one or more actuators.

[0014] The diffractive optical element may be positioned perpendicular to a direction of propagation along a path of the pulsed light beam. The diffractive optical element may be configured to recombine the multiple pulsed light sub-beams from the central wavelength selection optics to form the pulsed light beam.

[0015] In another general aspect, an optical system includes a light source configured to generate a pulsed light beam that is directed along a path to a lithography exposure apparatus, a lithography exposure apparatus configured to interact with the pulsed light beam, and a wavelength selection device disposed relative to the light source. The wavelength selection device includes a center wavelength selection optic configured to select at least one center wavelength of each pulse of the pulsed light beam according to an angle of incidence of the pulsed light beam, a tuning mechanism disposed along the path of the pulsed light beam to the center wavelength selection optic, the tuning mechanism configured to optically interact with the pulsed light beam and select an angle of incidence of the pulsed light beam to the center wavelength selection optic, and a diffractive optical element that is passive and transparent and disposed along the path of the pulsed light beam where the pulsed light beam is fully expanded or at least mostly expanded. The diffractive optical element is configured to interact with the pulsed light beam and generate a plurality of spatially separated and temporally unseparated pulsed light sub-beams from the pulsed light beam. Each pulsed light sub-beam is associated with a distinct wavelength and a distinct angle of incidence on the central wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength.

[0016] Implementations may include one or more of the following features. For example, the diffractive optical element may be a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating.

[0017] The tuning mechanism may include four refractive optical elements. Each refractive optical element may be a right angle prism.

[0018] The wavelength spacing between the individual wavelengths of the multiple pulsed light sub-beams may be greater than about 10 picometers (pm), about 30 pm, or about 45 pm. The central wavelength of each pulse of the pulsed light beam may be about 248 nanometers (nm) or about 193 nm.

[0019] The wavelength selection device may comprise an actuator configured to adjust a position of the diffractive optical element relative to the path of the pulsed light beam such that the diffractive optical element is at a position along the path of the pulsed light beam at some times and is not at a position along the path of the pulsed light beam at other times, and the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam. The optical system may also comprise a control system configured to control the wavelength selection device to adjust the position of the diffractive optical element relative to the path of the pulsed light beam.

[0020] A lithographic exposure apparatus may include a mask arranged to interact with a pulsed light beam from a light source and a wafer holder configured to hold a wafer. A plurality of distinct aerial images may be formed on the wafer in the wafer holder, each distinct aerial image being based on a distinct wavelength of an associated pulsed light sub-beam passing through the mask along a propagation direction.

[0021] The optical system may include a control system and one or more actuators associated with the tuning mechanism. The control system may be configured to adjust the angle of incidence of the pulsed light beam to the central wavelength selection optics by adjusting a signal to the one or more actuators.

[0022] In another general aspect, a method of forming a plurality of aerial images with a single pulsed light beam is performed. The method includes generating a pulsed light beam along a path toward a wafer, selecting an angle of incidence of the pulsed light beam to a central wavelength selection optic to select at least one central wavelength of each pulse of the pulsed light beam by optically interacting the pulsed light beam with a tuning mechanism disposed along the path to the central wavelength selection optic of the pulsed light beam, splitting the pulsed light beam into a plurality of pulsed light sub-beams by interacting the pulsed light beam with a diffraction pattern disposed along the path of the pulsed light beam, generating a plurality of spatially separated, non-temporally separated pulsed light sub-beams from the pulsed light beam, each associated with a respective angle of incidence to the central wavelength selection optic such that each is associated with a corresponding one of the respective wavelengths separated by at least 10 picometers (pm), and forming a plurality of aerial images on the wafer with the single pulsed light beam, each formed based on a respective wavelength.

[0023] Implementations may include one or more of the following features. For example, the pulsed light beam may be interacted with the diffraction pattern by transmitting the pulsed light beam through a diffractive optical element.

[0024] Each individual angle of incidence onto the central wavelength selection optics associated with each pulsed light sub-beam may be determined by the periodic shape of the diffraction pattern.

[0025] The angle of incidence of the pulsed light beam onto the central wavelength selection optics may be selected by adjusting the angle of one or more of the refractive optical elements in the tuning mechanism.

[0026] The multiple pulsed light sub-beams may be generated from the pulsed light beam by adjusting a position of a diffraction pattern relative to a path of the pulsed light beam. Adjusting the position of the diffraction pattern may include controlling by moving a diffractive optical element that includes the diffraction pattern.

[0027] Multiple aerial images may be formed on the wafer by flattening the intensity profile of the pulsed light beam at the wafer.

[0028] The method may also include recombining the multiple pulsed light sub-beams leaving the central wavelength selection optic by interacting the pulsed light sub-beams with a diffraction pattern disposed along the path of the pulsed light beam, whereby the multiple pulsed light sub-beams are generated when the pulsed light beam traveling along the path to the central wavelength selection optic interacts with the diffraction pattern, and the multiple pulsed light sub-beams are recombined to form the pulsed light beam when the pulsed light sub-beam traveling along the path away from the central wavelength selection optic interacts with the diffraction pattern.

[0029] In another general aspect, a wavelength selection device is associated with a pulsed light source that generates a pulsed light beam. The wavelength selection device includes a center wavelength selection optic configured to select at least one center wavelength of each pulse of the pulsed light beam according to an angle of incidence of the pulsed light beam, a tuning mechanism disposed along a path of the pulsed light beam to the center wavelength selection optic, the tuning mechanism configured to optically interact with the pulsed light beam and select an angle of incidence of the pulsed light beam to the center wavelength selection optic, the tuning mechanism including four refractive optical elements, and a passive and transmissive diffractive optical element disposed along the path of the pulsed light beam at a location between the tuning mechanism and the center wavelength selection optic. The diffractive optical element is configured to interact with the pulsed light beam and generate a plurality of spatially separated and temporally unseparated pulsed light sub-beams from the pulsed light beam. Each pulsed light sub-beam is associated with a respective wavelength and associated with a respective angle of incidence to the center wavelength selection optic such that the optical spectrum of the pulsed light beam has a peak at each respective wavelength.

[0030] FIG. 1 is a block diagram of an optical system comprising a light source configured to generate a pulsed light beam, a lithographic exposure apparatus configured to interact with the pulsed light beam, and a wavelength selection apparatus configured to select a plurality of discrete central wavelengths of the pulsed light beam. FIG. 2 is a block diagram of an embodiment of the wavelength-selective device of FIG. 1 including a central wavelength selection optics, a tuning mechanism, and a diffractive optical element. [0032] FIG. 2B is a block diagram of the center wavelength selection optics of FIG. 2A and an embodiment of the diffractive optical element of FIG. 2A that is a phase grating. [0033] FIG. 2 is a graph of an example optical spectrum of the pulsed light beam of FIG. 1 having a peak at each respective central wavelength of the pulsed light beam. FIG. 2 is a block diagram of an embodiment of the lithographic exposure apparatus of FIG. 1 including a projection optical system configured to interact with a pulsed light beam from the light source of FIG. 1, a mask positioned to interact with the pulsed light beam, and a wafer holder configured to hold a wafer. FIG. 3B is a block diagram of an embodiment of the projection optical system of FIG. 3A including a slit, the mask of FIG. 3A, and a projection objective including a lens. [0036] FIG. 3C is a schematic diagram of the wafer of FIG. 3A including multiple aerial images at different planes along the z-axis of the wafer, each formed by the projection optical system of FIG. 3B in a single exposure pass. [0037] FIG. 2B is a block diagram of an embodiment of the wavelength selection device of FIG. 2A including an embodiment of a tuning mechanism having a set of optical components arranged to optically interact with a pulsed light beam, an embodiment of a diffractive optical element, and an embodiment of a center wavelength selection optics. [0038] FIG. 4B is a block diagram illustrating beam expansion and beam deflection angles by one of the optical components of the wavelength-selective device of FIG. [0039] FIG. 4B is a block diagram of the wavelength-selective device of FIG. 4A viewed from above along the Z-axis, where the Z direction is perpendicular to the path of travel of the light beam. [0040] FIG. 2B is a block diagram of another embodiment of the wavelength-selective device of FIG. 2A viewed from above along the Z-axis. FIG. 4B is a block diagram of a side view along the Y axis of the wavelength-selective device of FIG. 4A including an actuator configured to adjust the position of a diffractive optical element along the path of the pulsed light beam relative to the path of the pulsed light beam. [0042] FIG. 6B is a block diagram of a side view along the Y-axis of the wavelength-selective device of FIG. 4A with the actuator of FIG. 6A, where the diffractive optical element is outside the path of the pulsed light beam. [0043] FIG. 4B is a block diagram of a side view along the Z axis of the wavelength selection device of FIG. 4A including an actuator configured to adjust the angle of the diffractive optical element relative to the direction of the path of the pulsed light beam, and another actuator configured to adjust the angle of an optical component in the tuning mechanism, thereby adjusting the angle of incidence of the pulsed light beam to the central wavelength selection optics. [0044] FIG. 7B is a block diagram of a side view along the Z axis of the wavelength-selective device of FIG. 4A with the actuators of FIG. 7A positioned in respective adjusted positions. [0045] FIG. 3D is a flowchart of a procedure for forming the multiple aerial images of FIG. 3C with the single pulsed light beam of FIG. [0046] FIG. 2B is a block diagram of an example of an embodiment of the optical system of FIG. 1 including the wavelength-selective device of FIG. 2A. [0047] FIG. 4B is a block diagram of a top view along the Z-axis of the wavelength-selective device of FIG. 4A including an example of a diffractive optical element that is a blazed grating. [0048] FIG. 10B is a block diagram of the diffractive optical element of FIG. 10A, which is a blazed grating. [0049] FIG. 10C is a side view of the diffractive optical element of FIGS. 10A and 10B, with the Z axis being up and down along the page.

[0050] Referring to FIG. 1, an optical system 100 includes a light source 105, which is a pulsed light source configured to generate a light beam 102, a lithography exposure device 107 configured to interact with the pulsed light beam 102, and a wavelength selection device 110 disposed relative to the light source 105. The light beam 102 is directed along a path 104 to the lithography exposure device 107. The light beam 102 is a pulsed light beam that includes pulses of light that are separated from one another in time. The pulses of the light beam 102 are centered around a wavelength in the deep ultraviolet (DUV) range, for example, at a wavelength of 248 nanometers (nm) or 193 nm. The pulsed light beam 102 is used to pattern microelectronic features on a substrate or wafer contained in the lithography exposure device 107. The size of the microelectronic features patterned on the wafer depends on the wavelength of the pulsed light beam 102, with lower wavelengths resulting in smaller minimum feature sizes or critical dimensions. For example, if the wavelength of the pulsed light beam 102 is 248 nm or 193 nm, the minimum size of the microelectronic features may be, for example, 50 nm or less.

[0051] The wavelength selection device 110 is disposed at a first end of the light source 105 for interacting with the light beam 102 generated by the source of light 105. The light beam 102 is a beam generated at one end of a resonator within the light source 105. For example, the light beam 102 may be a seed beam generated by a master oscillator. The wavelength selection device 110 is configured to finely tune or adjust the spectral characteristics of the pulsed light beam 102, including the wavelength of the pulsed light beam 102.

[0052] Specifically, and also referring to FIG. 2A, the wavelength selection device 110 includes a tuning mechanism 112 and a center wavelength selection optic 116. The light beam 102 enters and exits the wavelength selection device 110 through an aperture 211. The center wavelength selection optic 116 is configured to select at least one center wavelength of each pulse of the pulse light beam 102 according to an angle of incidence at which the pulse light beam 102, directed along a path 104, interacts with the center wavelength selection optic 116. The center wavelength selection optic 116 may be a reflective optical element, such as, for example, a reflective grating. The tuning mechanism 112 is disposed along the path 104 of the pulse light beam 102 to the center wavelength selection optic 116. The tuning mechanism 112 is configured to optically interact with the pulse light beam 102 and select an angle of incidence of a central ray of the pulse light beam 102 to the center wavelength selection optic 116.

[0053] The wavelength selection device 110 is designed to generate a pulsed light beam 102 that can form multiple aerial images on a wafer in the lithography exposure apparatus 107, each at a different spatial location along the z-axis of the wafer, as discussed in more detail below. The location of the aerial images along the z-axis of the wafer depends at least in part on the wavelength of the light beam 102. Thus, by varying or otherwise controlling the wavelength of the light beam 102, the location of one or more aerial images within the wafer can be controlled. Furthermore, by providing pulses having different primary wavelengths of light during a single exposure pass, multiple aerial images, each at a different location along the z-axis of the wafer, can be formed in a single exposure pass without the need to move the components of the lithography exposure apparatus 107 and the wafer relative to one another along the z-axis of the wafer.

[0054] The wavelength of the pulsed light beam 102 may be adjusted using a tuning mechanism 112, which may comprise optical components such as reflective optical components including reflective prisms and right-angle prisms, configured to rotate at a repetition rate to alternate or dither the wavelength of the pulsed light beam 102 with each pulse or any integer number of pulses. For example, by rotating a right-angle prism in the tuning mechanism 112, a maximum wavelength spacing of 15 picometers (pm) can be achieved. However, wavelength spacing greater than this maximum wavelength spacing may be desired or required depending on the desired or required microelectronic features. Furthermore, there is a desire to generate multiple different wavelengths in the pulsed light beam 102 at a given time to simultaneously generate multiple aerial images in the wafer. To this end, the wavelength selection device 110 also comprises a diffractive optical element 114. The diffractive optical element 114 is configured to interact with the pulsed light beam 102 and generate multiple pulsed light sub-beams 221, 223, 225 from the pulsed light beam 102. Each pulsed light sub-beam 221, 223, 225 is associated with a corresponding individual central wavelength w1, w2, w3 (FIG. 2C). Using a diffractive optical element 114 disposed within the wavelength selection device 110 along the path of the light beam 102, the wavelength spacing 220s between the individual central wavelengths w1, w2, w3 of the multiple pulsed light sub-beams 221, 223, 225 can be greater than about 10 picometers (pm). For example, the wavelength spacing 220s can be about 30 pm or about 45 pm. The size of the wavelength spacing 220s depends on the characteristics of the diffractive optical element 114.

[0055] The diffractive optical element 114 is disposed along the path 104 of the pulsed light beam 102 at a location where the pulsed light beam 102 is fully expanded or at least mostly expanded. Advantages of this arrangement include that the optical peak power of the pulsed light beam 102 is less or smaller at the location along the path 104 where the beam is fully expanded (compared to other locations along the path 104). For example, in some embodiments shown in FIG. 2A, the diffractive optical element 114 is disposed along the path 104 between the tuning mechanism 112 and the central wavelength selection optics 116. In the example of FIG. 2A, the diffractive optical element 114 is disposed perpendicular to the propagation direction of the pulsed light beam 102 along the path 104. That is, the surface normal of the diffractive optical element 114 is parallel to the path 104. In other examples, the diffractive optical element 114 may be disposed such that the diffractive optical element 114 is not perpendicular to the propagation direction of the pulsed light beam 102. Specifically, the diffractive optical element 114 may be positioned such that its surface normal is within 10 degrees of the propagation direction of the pulsed light beam 102, for example.

[0056] The diffractive optical element 114 is passive and therefore acts passively on the light beam 102 in the sense that no additional energy is required for the diffractive optical element 114 to operate. The diffractive optical element 114 acts on the pulsed light beam 102 by splitting the pulsed light beam 102 into sub-beams 221, 223, 225 directed along distinct angles. The diffractive optical element 114 is also transparent to the pulsed light beam 102, which interacts with the diffractive optical element 114 by passing through it. In the example of FIG. 2A, the diffractive optical element 114 generates three pulsed light sub-beams 221, 223, 225, each directed along a distinct direction and angle. In other examples, the diffractive optical element 114 may generate two pulsed light sub-beams or four or more pulsed light sub-beams. Further, in the example of FIG. 2A, the diffractive optical element 114 is further configured to recombine the multiple pulsed light sub-beams 221, 223, 225 returning from the central wavelength selection optics 116 to form the pulsed light beam 102 that is directed along the path 104 to the lithography exposure device 107.

[0057] Each pulsed light sub-beam 221, 223, 225 travels along a corresponding path 222, 224, 226 to the center wavelength selection optics 116. Each pulsed light sub-beam 221, 223, 225 is associated with an individual angle of incidence 222A, 224A, 226A (indicated by the curved double-sided arrow) on the center wavelength selection optics 116 such that each pulsed light sub-beam 221, 223, 225 is associated with an individual center wavelength w1, w2, w3. The wavelength spacing 220s (FIG. 2C) between the individual center wavelengths w1, w2, w3 of the multiple pulsed light sub-beams 221, 223, 225 depends at least in part on the periodic spacing 114s between the periodic features of the diffractive optical element 114. Each of the pulsed light sub-beams 221, 223, 225 maintains its angular offset as it travels along its path. Furthermore, when the pulsed light beam 102 is angularly or translationally moved, this causes all of the sub-beams to angularly or translationally move in unison without changing the angular spacing between each of the pulsed light sub-beams 221, 223, 225 and without changing the wavelength spacing between each of the individual center wavelengths. However, in this situation, the center wavelengths w1, w2, w3 will shift by an amount determined by how much the pulsed light beam 102 is moved or translated.

[0058] In the example shown in FIG. 2B, the diffractive optical element 114 is a phase grating 214, such as a binary phase grating or a blazed phase grating, with periodic spacing 214s between periodic surface reliefs 214g. Light transmitted through the phase grating acquires a position-dependent phase change, which may also result from the surface relief or from a holographic (interference) pattern. A blazed phase grating has the advantage of 100% efficiency into the first order (m=−1). Furthermore, the blazed phase grating may be configured with two different blaze angles (one on each side), essentially splitting the light beam 102 into two sub-pulses (each with 50% energy), i.e., no energy contribution to higher modes. Also, the blazed phase grating 214 may be slid horizontally (e.g., in the XY plane shown in FIG. 5A) to shift more of the light beam 102 into one order or the other. This ability to control or shift the optical power between aerial images (and thus from one aerial image to another) helps optimize or improve multifocal imaging at the wafer. Phase gratings work by changing the refractive index of the medium, i.e., modulating the refractive index. Phase gratings are designed to work at different wavelengths by adjusting the thickness of the medium and the refractive index modulation. An example of a binary phase grating is the binary phase grating manufactured by HOLO/OR, Ness Ziona, Israel.

[0059] In other embodiments, the diffractive optical element 114 can be a diffractive beam splitter or diffraction grating having grooves for interacting with the pulsed light beam 102. An example of a one-dimensional diffractive beam splitter is the 1D beam splitter manufactured by HOLO/OR, Ness Ziona, Israel.

[0060] The optical spectrum 220 (FIG. 2C) of the pulsed light beam 102 has a peak at each individual central wavelength w1, w2, w3. The optical spectrum 220 contains information about how the optical energy or power of the light beam 102 is distributed among the various wavelengths (or frequencies). The diffractive optical element 114 (including both the diffractive beam splitter/grating and the phase grating 214) is affected by periodic variations in physical features. For example, diffractive beam splitters and gratings comprise grooves, whereas phase gratings may comprise periodic surface relief or interference patterns (e.g., as shown in FIG. 2B). In either case, the spacing 114s, 214s between these features determines the spacing between these individual central wavelengths w1, w2, w3. For example, the difference Δλ(pk2pk) between any two adjacent center wavelengths is directly proportional to the change in the incidence angle (ΔαL) of the sub-beam at the center wavelength selection optics 116 relative to the incidence angle of the pulsed light beam 102 (without the diffractive optical element 114). Furthermore, the change in the incidence angle (ΔαL) of the sub-beam depends on the feature spacing and the order of the sub-beam. Finally, the difference (Δλ(pk2pk)) is also proportional to the rate of change of the wavelength of the pulsed light beam 102 (without the diffractive optical element 114) relative to the incidence angle of the pulsed light beam 102 (without the diffractive optical element 114) at the center wavelength selection optics 116, dλ/dαL. Thus, the design of the diffractive optical element 114 determines the magnitude of the change in the incidence angle of each sub-beam at the center wavelength selection optics 116.

3A-3C, in some embodiments, the lithography exposure apparatus 107 includes a projection optical system 327 and a wafer holder 329 configured to hold a wafer 328. The projection optical system 327 includes a mask 336b positioned to interact with the pulsed light beam 102 from the light source 105. The lithography exposure apparatus 107 may be an immersion system or a dry system. The pulsed light beam 102 enters the lithography exposure apparatus 107 from an aperture 311 along a path 104 to interact with the mask 336b and the wafer 328 in the projection optical system 327. Microelectronic features are formed on the wafer 328, for example, by exposing a layer of a reflection-sensitive photoresist material on the wafer 328 to the pulsed light beam 102.

[0062] As shown in FIG. 3B, the projection optical system 327 includes a slit 336a, a mask 336b, and a projection objective including a lens 336c. The pulsed light beam 102 enters the projection optical system 327 and impinges on the slit 336a, and at least a portion of the pulsed light beam 102 passes through the slit 336a. In the example of FIGS. 3A-3C, the slit 336a is rectangular and shapes the pulsed light beam 102 into an elongated rectangular light beam. A pattern is formed on the mask 336b, and the pattern determines which portions of the shaped light beam are transmitted and which portions are blocked by the mask 336b. The design of the pattern is determined by the specific microelectronic circuit design to be formed on the wafer 328.

[0063] The shaped light beam interacts with mask 336b. The portion of the shaped light beam transmitted by mask 336b passes through (and may be focused by) projection lens 336c to expose wafer 328. The portion of the shaped light beam transmitted by mask 336b forms an aerial image in the xy plane of wafer 328. The aerial image is the intensity pattern formed by the light that reaches wafer 328 after interacting with mask 336b. The aerial image is at wafer 328 and extends generally in the xy plane.

[0064] Optical system 100 with wavelength selection device 110 can form multiple aerial images, each at a different spatial location along the z-axis within wafer 328, during a single exposure pass. In this example, projection optical system 327 forms three aerial images 331, 333, 335 at different planes along the z-axis of wafer 328 in a single exposure pass. Each of aerial images 331, 333, 335 is formed from light having a central wavelength different from the central wavelength of another one of aerial images 331, 333, 335. Specifically, each of aerial images 331, 333, 335 is formed from a corresponding one of pulsed light sub-beams 221, 223, 225, each having a corresponding respective central wavelength w1, w2, w3. Thus, one aerial image 331, 333, 335 is formed for each respective central wavelength w1, w2, w3 of pulsed light beam 102.

[0065] As explained above, the locations of the aerial images 331, 333, 335 along the z-axis depend on the characteristics of the projection optical system 327 (comprising the projection lens 336c and the mask 336b) and the wavelength of the pulsed light beam 102. In general, light passing through the mask 336b with a single central wavelength is focused to a focal plane by the projection lens 336c. The focal plane of the projection lens 336c is between the projection lens 336c and the wafer holder 329, and the location of the focal plane along the z-axis of the wafer 328 depends on the characteristics of the projection optical system 327 and the central wavelength of the pulsed light beam 102. Thus, by varying or controlling the central wavelength of the pulsed light beam 102, it is possible to control the locations of the aerial images 331, 333, 335. The aerial images 331, 333, 335 are formed from the pulsed light beams 102 with different central wavelengths w1, w2, w3. In this way, aerial images 331, 333, 335 are at different locations on wafer 328. Aerial images 331, 333 are separated from one another along the z-axis of wafer 328 by separation distance 330a, and aerial images 333, 335 are separated from one another along the z-axis by separation distance 330b. Separation distance 330a depends on the difference between the central wavelength w1 forming aerial image 331 of pulsed light beam 102 and the central wavelength w2 forming aerial image 333 of pulsed light beam 102. Separation distance 330b depends on the difference between the central wavelength w2 forming aerial image 333 of pulsed light beam 102 and the central wavelength w3 forming aerial image 335 of pulsed light beam 102.

[0066] The wafer holder 329 and the mask 336b (or other parts of the projection optical system 327) generally move relative to each other in the x, y, and z directions during scanning for normal performance correction and operation, which may be used, for example, to achieve basic leveling, correction of lens distortion, and to correct stage positioning errors. This relative motion is called incidental actuation motion. However, the system of FIG. 3A does not rely on relative motion of the wafer holder 329 and the projection optical system 327 to form the separation distances 330a, 330b. Instead, the separation distances 330a, 330b are formed by being able to control the primary central wavelengths w1, w2, w3 of the pulses passing through the mask 336b of the pulsed light beam 102 during an exposure pass. Thus, unlike some conventional systems, the separation distances 330a, 330b are not created solely by moving the projection optical system 327 and the wafer 328 relative to each other along the z direction. Furthermore, aerial images 331, 333, and 335 are all present on wafer 328 during the same exposure pass. In other words, optical system 100 does not require that aerial image 331 be formed in a first exposure pass and aerial images 333 and 335 be formed in subsequent exposure passes.

[0067] The light of the first aerial image 331 interacts with the wafer at plane 331a, the light of the second aerial image 333 interacts with the wafer at plane 333a, and the light of the third aerial image 335 interacts with the wafer at plane 335a. In some embodiments, the wafer has already been patterned at one or more previous levels, resulting in features at different topographical locations on the wafer, i.e., at different planes along the z-axis, such as planes 331a, 331b, and 331c. Such interactions can form electronic features or other physical features, such as apertures or holes, on the wafer 328. Because the aerial images 331, 333, and 335 are at different planes along the z-axis, the aerial images 331, 333, and 335 can be used to form three-dimensional features on the wafer 328 or can be used to form features at different topographical levels of the wafer. For example, aerial image 331 may be used to form a peripheral region, aerial image 333 may be used to form a channel at a different location along the z-axis than the peripheral region, and aerial image 335 may be used to form a recess at a different location along the z-axis than the peripheral region and the channel. In this manner, multiple individual aerial images 331, 333, 335 are formed on wafer 328, each individual aerial image 331, 333, 335 being based on the individual central wavelengths w1, w2, w3 of associated pulsed light sub-beams 221, 223, 225 passing through mask 336b along a propagation direction along path 104. In this manner, different wavelengths of light may be used to form patterns at different levels of the wafer topography. Thus, the techniques discussed herein may be used to form three-dimensional semiconductor components, such as three-dimensional NAND flash memory components.

[0068] Referring to FIG. 4A, an embodiment 410 of the wavelength selection device 110 includes an embodiment 412 of the tuning mechanism 112, an embodiment 414 of the diffractive optical element 114, and an embodiment 416 of the center wavelength selection optics 116 (FIG. 1). The tuning mechanism 412 includes a set of optical mechanisms or components 440a-440d arranged to optically interact with the pulsed light beam 102 along the path 104. Each of the optical components 440a-440d may be a refractive optical element, such as a right-angle prism. In the example of FIG. 4A, the tuning mechanism 412 includes four right-angle prisms 440a-440d. In other examples, the tuning mechanism 412 may include fewer or more than four optical components. Each of the right-angle prisms 440a-440d is arranged along the path 104 of the pulsed light beam 102 to the diffractive optical element 114. Each of the prisms 440a-440d is a transmissive prism that serves to disperse and redirect the pulsed light beam 102 as it passes through the body of the prism 440a-440d. Each of the prisms 440a-440d may be made of a material that allows transmission of the wavelength of the pulsed light beam 102 (e.g., calcium fluoride, etc.). In the example of FIG. 4A, the center wavelength selection optics 416 is a reflective grating designed to disperse and reflect the pulsed light beam 102, and therefore, the center wavelength selection optics 416 is made of a material suitable for interacting with the pulsed light beam 102 having a wavelength in the DUV range.

[0069] As shown in Figure 5A, the prisms 440a, 440b, 440c, 440d, the central wavelength selection optical system 416, and the diffractive optical element 414 are arranged along the XY plane so that the path of the light beam 102 passes through approximately the XY plane. From the diagram in Figure 5A, it can be seen that the prism 440a is located farthest from the central wavelength selection optical system 416, while the prism 440d is located closest to the central wavelength selection optical system 416. After the pulsed light beam 102 enters the wavelength selection device 410 through the aperture 411, it passes through the prisms 440a, 440b, 440c, and 440d in this order before impinging on the diffractive surface 416s of the central wavelength selection optical system 416. Each time the pulsed light beam 102 passes through a succession of prisms 440a-440d, the light beam 102 is optically expanded and redirected (refracted at an angle) toward the next optical component. Thus, in the example of FIG. 4A, the pulsed light beam 102 is fully expanded between the four right-angle prisms 440a-440d and the central wavelength selection optics 416. And the diffractive optical element 414 is located at this location. Because the pulsed light beam 102 is fully expanded in the diffractive optical element 414, the energy or power of the pulsed light beam 102 is more evenly distributed across the entire surface area of the diffractive optical element 414.

[0070] Referring to FIG. 5B, in one embodiment 510 of the wavelength selection device 410, the location where at least a majority of the pulsed light beam 102 is expanded may be in the optical path 104 between the right-angle prism 440d closest to the central wavelength selection optics 416 and the right-angle prism 440c next closest to the central wavelength selection optics 416. Thus, in these embodiments, the diffractive optical element 414 is disposed between the prisms 440d and 440c at the location where at least a majority of the pulsed light beam 102 is expanded.

[0071] Referring again to FIG. 4A, the diffractive optical element 414 interacts with the pulsed light beam 102 to generate a plurality of pulsed light sub-beams 221, 223, 225 (shown in FIG. 2A) that are directed along corresponding paths 222, 224, 226, respectively, to the center wavelength selection optics 416, each associated with a respective angle of incidence to the center wavelength selection optics 416. Thus, each of the pulsed light sub-beams 221, 223, 225 is associated with a respective center wavelength w1, w2, w3, and the optical spectrum 220 (FIG. 2C) of the pulsed light beam 102 has a peak at each respective center wavelength w1, w2, w3. The diffractive optical element 414 does not alter the optical magnification of each of the generated pulsed light sub-beams 440a-440d.

[0072] The pulsed light beam 102 is diffracted and reflected from the center wavelength selection optics 416 back through the diffractive optical element 414, prism 440d, prism 440c, prism 440b, and prism 440a, in that order, before passing through the aperture 411 as the pulsed light beam 102 exits the wavelength selection device 410. The diffractive optical element 414 recombines the three pulsed light sub-beams 221, 223, and 225 traveling from the center wavelength selection optics 416 to reform the pulsed light beam 102 before interacting with the tuning mechanism 412. With each passage from the center wavelength selection optics 416 through successive prisms 440a-440d of the tuning mechanism 412, the pulsed light beam 102 is optically compressed as it travels toward the aperture 411.

[0073] In the example of FIG. 4A, each of the prisms 440a-440d is wide enough across the pulsed light beam 102 to be contained within the surface through which the light beam 102 passes. Each prism 440a-440d optically expands the light beam 102 on its path from the aperture 411 to the center wavelength selection optics 416, and thus each prism 440a-440d increases in size successively from prism 440a to prism 440d. Thus, prism 440d is larger than prism 440c, which is larger than prism 440b, and prism 440a is the smallest prism.

[0074] Referring to FIG. 4B, as the prism P of the tuning mechanism 412 (which may be any one of the prisms 440a-440d) rotates, the angle of incidence at which the pulsed light beam 102 impinges on the entrance face H(P) of the rotated prism P changes. Furthermore, two local optical qualities, the optical magnification OM(P) and the beam refraction angle δ(P) of the light beam 102 passing through the rotated prism P, are functions of the angle of incidence of the light beam 102 impinging on the entrance face H(P) of the rotated prism P. The optical magnification OM(P) of the light beam 102 passing through the prism P is the ratio of the lateral width Wo(P) of the light beam 102 exiting the prism P to the lateral width Wi(P) of the light beam 102 entering the prism P.

[0075] A change in the local optical magnification OM(P) of the pulsed light beam 102 at one or more of the prisms P in the tuning mechanism 412 causes an overall change in the optical magnification OM 438 of the pulsed light beam 102 passing through the tuning mechanism 412. The optical magnification OM 438 of the light beam 102 passing through the tuning mechanism 412 is the ratio of the lateral width Wo of the light beam 102 exiting the tuning mechanism 412 to the lateral width Wi of the light beam 102 entering the tuning mechanism 412.

[0076] Also, a change in the local beam refraction angle δ(P) through one or more of the prisms P in the tuning mechanism causes an overall change in the angle of incidence of the pulsed light beam 102 at the surface 416s of the central wavelength selection optics 416. Thus, the angles of incidence of each of the pulsed light sub-beams 221, 223, 225 at the surface 416s also change with the rotation of one of these prisms. In this manner, the central wavelength of the pulsed light beam 102 may also be tuned by changing the angle of incidence at which the pulsed light beam 102 impinges on the diffractive surface 416s of the central wavelength selection optics 416.

[0077] In some embodiments, the center wavelength selection optics 416 is a high blaze angle echelle grating, and the pulsed light beam 102 incident on the center wavelength selection optics 416 will be reflected (diffracted) at any angle of incidence that satisfies the grating equation. Furthermore, when the center wavelength selection optics 416 is used such that the angle of incidence of the light beam 102 on the center wavelength selection optics 416 is equal to the angle of emergence of the light beam 102 from the center wavelength selection optics 416, the center wavelength selection optics 416 and the tuning mechanism 412 (prisms 440a-440d) are arranged to interact with the pulsed light beam 102 in a Littrow configuration, and the wavelength of the light beam 102 reflected from the center wavelength selection optics 416 is the Littrow wavelength. It may be assumed that the vertical divergence of the light beam 102 incident on the center wavelength selection optics 416 is close to zero. To reflect the nominal wavelength, the center wavelength selection optics 416 is aligned with the light beam 102 incident on the center wavelength selection optics 416 so that the nominal wavelength is reflected back through the tuning mechanism 412 (prisms 440a-440d) to be amplified in the optical system 100 (if the tuning mechanism 412 is used in the optical system 100). The Littrow wavelength can then be tuned across the gain bandwidth of the resonator in the optical system 100 by changing the angle of incidence of the pulsed light beam 102 on the center wavelength selection optics 416.

[0078] In some embodiments, the wavelength selection device 410 is in communication with a control system 450 via a data connection 452. The control system 450 comprises electronic circuitry in the form of any combination of firmware and software. Additionally, any one or more of the center wavelength selection optics 416, the diffractive optical element 414, and the prisms 440a-440d of the tuning mechanism 412 may be coupled to respective actuation systems including actuators associated with the tuning mechanism 412 and connected to the control module 450. In the example of FIG. 4A, the control module 450 is connected to actuation systems 414A, 441A including actuators physically coupled to the diffractive optical element 414 and the prism 440d, respectively. In other examples, two or more of the prisms 440a-440d may be coupled to respective actuation systems connected to the control module 450.

[0079] The control system 450 comprises an electronic processor, electronic storage, and input/output (I/O) interfaces. The electronic processor is one or more processors suitable for executing a computer program, such as a general purpose or special purpose microprocessor, and any processor of any type of digital computer. In general, the processor receives instructions and data from a read-only memory or a random access memory or both. The electronic processor may be any type of electronic processor. The electronic storage may be a volatile memory, such as a RAM, or a non-volatile memory. In some embodiments, the electronic storage may comprise both non-volatile and volatile portions or components. The electronic storage stores instructions, possibly computer programs, that, when executed, cause the processor to communicate with other components in the control system 450 or other components of the wavelength selection device 410. The I/O interface is any type of electronic interface that allows the control system 450 to receive and/or provide data and signals to other components of the wavelength selection device 410, an operator, and/or an automated process running on another electronic device. For example, the I/O interface may include one or more of a touch screen or a communication interface.

[0080] Each of the actuators of actuation systems 414A, 441A is a mechanical device for moving or controlling a corresponding optical component. The actuators receive energy from control system 450 and convert the energy into some motion that is imparted to the corresponding optical component. For example, the actuators may be any one of a force device and a rotation stage for rotating one or more of the prisms of the tuning mechanism. The actuators may include motors, such as stepper motors, valves, pressure control devices, piezoelectric devices, linear motors, hydraulic actuators, voice coils, etc.

6A and 6B, one or more actuators 614A of the actuation system 414A (FIG. 4A) may be configured to adjust the position of the diffractive optical element 414 relative to the path 104 of the pulsed light beam 102. Specifically, the position of the diffractive optical element 414 is adjusted by the actuator 614A along a Z-axis perpendicular to the path (which is in the XY plane) traveled by the light beam 102. The actuator 614A may move the diffractive optical element 414 such that at times the diffractive optical element 414 is in a position along the path 104 of the pulsed light beam 102 (FIG. 6A) and at other times it is not in a position along the path 104 of the pulsed light beam 102 (FIG. 6B). For example, the actuator 614A may include a linear motor, such as a linear stepper motor. The control system 450 may control the actuator 614A based on, for example, a preprogrammed recipe or user input.

[0082] The diffractive optical element 414 interacts with the pulsed light beam 102 only when the diffractive optical element 414 is in a position along the path 104 of the pulsed light beam 102 (FIG. 6A). Thus, when the diffractive optical element 414 is in a position along the path 104 of the pulsed light beam 102, multiple pulsed light sub-beams 221, 223, 225 are generated by the diffractive optical element 414 such that the pulsed light beam 102 has associated central wavelengths w1, w2, w3 to form multiple aerial images 331, 333, 335 at the wafer. When the diffractive optical element 414 is not in a position along the path 104 of the pulsed light beam 102 (FIG. 6B), the diffractive optical element 414 does not interact with the light beam 102, and the pulsed light beam 102 includes only the first central wavelength of light to form a single aerial image at the wafer 328.

7A and 7B, one or more actuators 714A of the actuation system 414A (FIG. 4A) may be configured to adjust the angle of the diffractive optical element 414 about the Z-axis, thereby rotating the surface normal of the diffractive optical element 414 relative to the direction of the path 104 of the pulsed light beam 102. The individual angles of incidence of each generated pulsed light sub-beam 221, 223, 225 onto the central wavelength selection optics 416 are also adjusted when the angle of the diffractive optical element 414 relative to the direction of the path 104 is adjusted.

[0084] In one example, the actuator 714A may be configured to correct the angle of the diffractive optical element 414 with respect to the direction of the path 104 of the pulsed light beam 102 when the diffractive optical element 414 is significantly (e.g., more than 10°) misaligned with the direction of the path 104 of the pulsed light beam 102. For example, vibrations or other mechanical disturbances within the wavelength selection device 410 may cause the diffractive optical element 414 to become misaligned, and the actuator 714A may correct these misalignments by adjusting the angle of the diffractive optical element 414 with respect to the direction of the path 104 of the pulsed light beam 102. In one example, the diffractive optical element 414 may be considered misaligned when the angle between the diffractive optical element 414 and the direction of the path 104 of the pulsed light beam 102 is not equal to 90 degrees or is not within a threshold range of about 90 degrees.

[0085] Additionally, one or more actuators 741A associated with the tuning mechanism 412 of the actuation system 441A (FIG. 4A) may be configured to adjust the angle of incidence of the pulsed light beam 102 on the center wavelength selection optics 416 by adjusting the signal to the one or more actuators 741A. Specifically, in this example, the prism 440d is physically coupled to an actuator 741A that rotates the prism 440d about the z-axis. The individual angles of incidence of each generated pulsed light sub-beam 221, 223, 225 on the center wavelength selection optics 416 are also adjusted when the angle of incidence of the pulsed light beam 102 on the center wavelength selection optics 416 is adjusted. In the example of FIGS. 7A and 7B, the control system 450 may control the actuators 741A and 714A based on, for example, a preprogrammed recipe or user input. Each of the actuators 714A, 741A may be a rotary motor, such as, for example, a rotary stepper motor.

8, a procedure 860 is performed to form multiple aerial images with a single pulsed light beam (such as pulsed light beam 102). Procedure 860 may be performed for optical system 100 (FIG. 1) including wavelength selection device 110 (FIGS. 2A-2C), light source 105, and lithography exposure device 107 (FIGS. 3A-3C) including wafer 328. Procedure 860 may also be performed for any one of wavelength selection device 410 (FIGS. 4A and 5A) and wavelength selection device 510 (FIG. 5B). Procedure 860 is described below for optical system 100.

[0087] Procedure 860 includes generating (861) a pulsed light beam 102 along a path toward a wafer. For example, the pulsed light beam 102 may be generated by a light source 105 and directed along a path 104 to a wafer 328 in a lithography exposure tool 107. In the example of FIG. 1, the pulsed light beam 102 is directed from the light source 105 (after the light beam 102 is generated by the light source 105) to interact with a wavelength selection device 110. The pulsed light beam 102 is then directed from the wavelength selection device 110 to the lithography exposure tool 107, which includes a wafer 328 on which an aerial image may be formed.

[0088] At least one central wavelength of each pulse of the pulsed light beam is selected (863) by selecting an angle of incidence of the pulsed light beam on a central wavelength selection optic (e.g., 116). To select at least one central wavelength of each pulse, the pulsed light beam 102 optically interacts with a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optic (863). For example, the angle of incidence of the pulsed light beam 102 on the central wavelength selection optic 116 may be selected by interacting the pulsed light beam 102 with a tuning mechanism 112 of a wavelength selection device 110 disposed along a path 104 of the pulsed light beam 102 to the central wavelength selection optic 116. In the optical system 100 of FIG. 1 (which may be a DUV system), the central wavelength of each pulse of the pulsed light beam 102 may be selected to be about 248 nanometers (nm) or 193 nm.

[0089] In some embodiments, the tuning mechanism 112 may be a tuning mechanism 412 (FIG. 4A) with optical elements 440a-440d (which are refractive right-angle prisms), and the angle of incidence of the pulsed light beam 102 on the center wavelength selection optics 416 may be selected (and varied) by changing or adjusting the placement of at least one of the optical elements 440a-440d of the tuning mechanism 412 relative to the path 104 of the pulsed light beam 102. In other words, the angle of incidence of the pulsed light beam 102 on the center wavelength selection optics 416 is selected by adjusting the angle of one or more of the refractive optical elements 440a-440d in the tuning mechanism 412. In this manner, the center wavelength of the pulsed light beam 102 is selected by adjusting the tuning mechanism 112 (or the tuning mechanism 412 in FIG. 4A) and having the pulsed light beam 102 interact with the tuning mechanism 112.

[0090] A plurality of spatially separated, non-temporally separated pulsed light sub-beams from the pulsed light beam are generated by splitting the pulsed light beam into a plurality of pulsed light sub-beams by interacting the pulsed light beam with a diffraction pattern disposed along the path of the pulsed light beam (865). Each pulsed light sub-beam is associated with a distinct angle of incidence on the central wavelength selection optics (865) such that each pulsed light sub-beam has a different wavelength, i.e., each pulsed light sub-beam is associated with a corresponding one of the distinct wavelengths separated by at least 10 picometers (pm). For example, a plurality of spatially separated, non-temporally separated pulsed light sub-beams 221, 223, 225 may be generated by splitting the pulsed light beam 102 into a plurality of pulsed light sub-beams 221, 223, 225. To split the pulsed light beam 102, the pulsed light beam 102 may interact with a diffraction pattern of a diffractive optical element 114 disposed along the path 104 of the pulsed light beam 102. In other words, the pulsed light beam 102 can interact with the diffraction pattern of the diffractive optical element 114 by transmitting the pulsed light beam 102 through the diffractive optical element 114.

[0091] Additionally, the multiple pulsed light sub-beams 221, 223, 225 may be generated from the pulsed light beam 102 by adjusting the position of the diffraction pattern relative to the path 104 of the pulsed light beam 102. For example, the position of the diffractive optical element 114 may be adjusted by translating and/or rotating the diffractive optical element 114, e.g., by controlling actuators 614A, 714A (FIGS. 6A-7B), which also adjusts the position of the diffraction pattern of the diffractive optical element 114 relative to the path 104 of the pulsed light beam 102. In other words, the position of the diffraction pattern may be adjusted by controlling the movement of the diffractive optical element 114 that includes the diffraction pattern.

[0092] Each of the generated pulsed light sub-beams 221, 223, 225 is associated with a respective angle of incidence 222A, 224A, 226A into the central wavelength selection optics 116 such that each pulsed light sub-beam 221, 223, 225 is associated with a corresponding one of the respective central wavelengths w1, w2, w3 that are separated by at least 10 pm. In particular, the wavelength spacing between the respective central wavelengths w1, w2, w3 of the plurality of pulsed light sub-beams 221, 223, 225 may be greater than about 10 picometers (pm), about 30 pm, or about 45 pm. Furthermore, each respective angle of incidence 222A, 224A, 226A into the central wavelength selection optics 116 associated with each pulsed light sub-beam 221, 223, 225, respectively, is determined by the groove spacing 114s of the diffraction pattern (contained within the diffractive optical element 114).

1, the multiple pulsed light sub-beams 221, 223, 225 leaving the center wavelength selection optic 116 are recombined by having the pulsed light sub-beams 221, 223, 225 interact with a diffraction pattern disposed along the path of the pulsed light beam 102. In this manner, the multiple pulsed light sub-beams 221, 223, 225 are generated as the pulsed light beam 102 interacts with the diffraction pattern while traveling along the path 104 to the center wavelength selection optic 116, and are recombined to form the pulsed light beam 102 as the pulsed light sub-beams 221, 223, 225 interact with the diffraction pattern while traveling along the path 104 away from the center wavelength selection optic 116. In the example of FIG. 1, the diffractive optical element 114 recombines the multiple pulsed light sub-beams 221, 223, 225 after the pulsed light sub-beams 221, 223, 225 interact with the central wavelength selection optics 116 to form a recombined pulsed light beam 102 that is directed along a path 104 to the wafer 328. Thus, the recombined pulsed light beam 102 having multiple distinct central wavelengths w1, w2, w3 may then be directed to interact with the lithography exposure apparatus 107 to form multiple aerial images 331, 333, 335 on the wafer 328.

[0094] A plurality of aerial images are formed on the wafer with the single pulsed light beam such that each aerial image is formed based on a distinct central wavelength (867). For example, the plurality of aerial images 331, 333, 335 are formed on the wafer 328 with the single pulsed light beam 102 such that the aerial images 331, 333, 335 are formed at different locations on the z-axis of the wafer, and each aerial image 331, 333, 335 is based on one of the distinct central wavelengths w1, w2, w3. Each of the plurality of aerial images 331, 333, 335 is formed in a single exposure pass with the single light beam 102 because the single pulsed light beam 102 interacts with the diffraction pattern to select the plurality of central wavelengths w1, w2, w3 of the recombined pulsed light beam 102. The intensity profile of the pulsed light beam 102 is flattened at the wafer 328 in the lithography exposure apparatus 107. The intensity is flattened at the wafer 328 due to the increasing number of sub-pulses, each with the same optical power. The more sub-pulses there are (each with a distinct central wavelength), the flatter the power distribution through focus at the wafer 328.

[0095] Thus, by interacting the pulsed light beam 102 with the diffraction pattern (or diffractive optical element 114), multiple aerial images 331, 333, 335 associated with distinct central wavelengths w1, w2, w3, respectively, are formed on the wafer 328 with a single pulsed light beam 102 and a single lithography exposure pass.

[0096] Referring to FIG. 9, a block diagram of an example of an embodiment 900 of the optical system 100 is shown. The optical system 100 is a photolithography system 900 with a light source 905 as the light source 105. The light source 905 generates a pulsed light beam 102 that is provided to a lithography exposure apparatus 107. The light source 905 can be, for example, an excimer light source that outputs the pulsed light beam 102 (which can be a laser beam). When the pulsed light beam 102 enters the lithography exposure apparatus 107, it is directed through a projection optical system 327 as discussed above with reference to FIGS. 3A-3C and projected onto a wafer 328. In this manner, after one or more microelectronic features are patterned into the photoresist on the wafer 328, the photoresist is developed and washed before a subsequent process step, and the process repeats. The photolithography system 900 also includes a control system 450 (FIG. 4A) that, in the example of FIG. 9, is connected to the components of the light source 905 (including the wavelength selection device 410) and the lithography exposure device 107 to control various operations of the system 900.

9, the light source 905 is a two-stage laser system with a master oscillator (MO) 970 that provides a seed light beam 902s to a power amplifier (PA) 972. The MO 970 and PA 972 may be considered subsystems of the light source 905 or systems that are part of the light source 905. The power amplifier 972 receives the seed light beam 902s from the master oscillator 970 and amplifies the seed light beam 902s to generate a pulsed light beam 102 for use in the lithography exposure tool 107. For example, the master oscillator 970 may provide a pulsed seed light beam with a seed pulse energy of about 1 millijoule (mJ) per pulse, which may be amplified by the power amplifier 972 to about 10-15 mJ.

[0098] The master oscillator 970 comprises a discharge chamber 971 having two elongated electrodes 974, a gain medium 976 which is a gas mixture confined within the discharge chamber 971, and a fan for circulating the gas mixture between the electrodes 974. A resonator is formed between a wavelength selection device 410 (FIG. 4A) on one side of the discharge chamber 971 and an optical output coupler 978 on a second side of the discharge chamber 971. The wavelength selection device 410 finely adjusts or tunes the spectral characteristics of the pulsed light beam 102, including the wavelength and bandwidth of the pulsed light beam 102, by tuning or adjusting the seed light beam 902s.

[0099] The master oscillator 970 may also include a line center analysis module 979 that receives the output light beam from the output coupler 978 and a beam combining optical system 980 that modifies the size or shape of the output light beam as needed to form the seed light beam 902s. The line center analysis module 979 is a measurement system that may be used to measure or monitor the wavelength and/or bandwidth of the seed light beam 902s. The line center analysis module 979 may be located elsewhere in the light source 905 or at the output of the light source 905.

[0100] The gas mixture used in the discharge chamber 971 may be any gas suitable for producing a light beam of the wavelength and bandwidth required for illumination. In the case of an excimer source, the gas mixture may include noble gases, e.g., argon and krypton, other than the buffer gases helium and/or neon, halogens, e.g., fluorine or chlorine, and traces of xenon. Specific examples of gas mixtures include argon fluoride (ArF), which emits light at a wavelength of about 193 nm, krypton fluoride (KrF), which emits light at a wavelength of about 248 nm, or xenon chloride (XeCl), which emits light at a wavelength of about 351 nm. The excimer gain medium (gas mixture) is excited with short (e.g., nanosecond) current pulses in a high-pressure discharge by application of a voltage to the elongated electrodes 974.

[0101] The power amplifier 972 receives the seed light beam 902s from the master oscillator 970 and includes a beam combining optical system 982 that directs the light beam 902s through a discharge chamber 973 to a beam rotation optical element 981 that modifies or changes the direction of the seed light beam 902s so that it is sent back into the discharge chamber 973 and through the beam combining optical system 982. The discharge chamber 973 includes a pair of elongated electrodes 975, a gain medium 977 that is a gas mixture, and a fan for circulating the gas mixture between the electrodes 975.

[0102] The output pulsed light beam 102 is directed through a bandwidth analysis module 983 where various parameters of the beam 102 (such as bandwidth and wavelength) may be measured. The output light beam 102 may also be directed through a beam preparation system 984. The beam preparation system 984 may include, for example, a pulse stretcher in which each of the pulses of the output light beam 102 is stretched in time, for example in an optical delay unit, to adjust the performance characteristics of the light beam impinging on the lithography exposure apparatus 107. The beam preparation system 984 may also include other components that may act on the light beam 102, such as reflective and/or refractive optical elements (such as lenses and mirrors), filters, and optical apertures (including automatic shutters).

[0103] The photolithography system 900 also includes a control system 450. In the embodiment shown in FIG. 9, the control system 450 is connected to various components of the light source 905. For example, the control system 450 can control the timing of when the light source 905 emits a light pulse or a burst of light pulses including one or more light pulses by sending one or more signals to the light source 905. The control system 450 is also connected to the lithography exposure apparatus 107. Thus, the control system 450 can also receive instructions and/or data from the lithography exposure apparatus 107. The lithography exposure apparatus 107 can include a dedicated controller (which can communicate with the control system 450) that can be used to control the exposure of the wafer 328 and thus how electronic features are printed on the wafer 328. In some embodiments, the lithography controller can control the scanning of the wafer 328 by controlling the movement of the slit 336a in the xy plane (FIG. 3B). The lithography exposure apparatus 107 may also include, for example, temperature control devices (such as air conditioning devices and/or heating devices) and/or power supplies for various electrical components that are controlled by the lithography controller. In some embodiments, the lithography controller is part of a control system 450, which may include two or more sub-control systems.

[0104] Additionally, the control system 450 can control various components of the wavelength selection device 410. For example, the control system 450 can control the positions of each of the prisms 440a-440d, the position of the diffractive optical element 414, and the position of the central wavelength selection optics 416.

10A-10C, an embodiment 1014 of the diffractive optical element 114 is shown. In this embodiment 1014, the diffractive optical element 114 is a blazed grating disposed between the prism 440d and the center wavelength selection optics 416. The periodic structures or features are linearly disposed along the Z axis such that the periodic structures are symmetric about a centerline 1014c parallel to the Z axis. As discussed above, when the blazed grating 1014 is moved along a direction Ds perpendicular to the direction in which the light beam 102 travels (and in the XY plane), the amount of light that becomes one sub-beam or the other, i.e., impinges on the selection optics 416, can be adjusted. In this way, the amount of optical power of one aerial image at the wafer can be changed relative to another aerial image. Multifocal imaging at the wafer can be controlled.

[0106] The embodiments may be further described using the following clauses: 1. A wavelength selection device for a pulsed light source generating a pulsed light beam, comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optics, the tuning mechanism optically interacting with the pulsed light beam to select an angle of incidence of the pulsed light beam to the central wavelength selection optics;
A wavelength selection device comprising: a diffractive optical element that is passive and transparent and is positioned along the path of the pulsed light beam at a location where at least a majority of the pulsed light beam is expanded, the diffractive optical element interacting with the pulsed light beam to generate from the pulsed light beam a plurality of pulsed light sub-beams, each associated with a distinct wavelength and each associated with a distinct angle of incidence on a central wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength.
2. The wavelength-selective device of clause 1, wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating.
3. The wavelength-selective device of claim 1, wherein the tuning mechanism comprises four refractive optical elements.
4. The wavelength-selective device of clause 3, wherein each refractive optical element is a right-angle prism.
5. The wavelength selection device of clause 1, wherein a wavelength spacing between individual wavelengths of the plurality of pulsed optical sub-beams is greater than about 10 picometers (pm), about 30 pm, or about 45 pm.
6. The wavelength selection device of clause 1, wherein a central wavelength of each pulse of the pulsed light beam is about 248 nanometers (nm) or about 193 nm.
7. The wavelength selection device of claim 1, wherein wavelength spacing between individual wavelengths of the plurality of pulsed light sub-beams depends on the periodic shape of the diffractive optical element.
8. The wavelength selection device of clause 1, wherein the tuning mechanism comprises four right-angle prisms arranged along a path of the pulsed light beam to the diffractive optical element, and the pulsed light beam is fully expanded between the four right-angle prisms and the central wavelength selection optics.
9. The wavelength selection device of clause 1, further comprising an actuator for adjusting the position of the diffractive optical element relative to the path of the pulsed light beam, such that the diffractive optical element is at a position along the path of the pulsed light beam at some times and is not at a position along the path of the pulsed light beam at other times, such that the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam.
10. The wavelength selection device of clause 9, wherein the actuator further adjusts an angle of the diffractive optical element relative to a direction of a path of the pulsed light beam, thereby adjusting an individual angle of incidence of each generated pulsed light sub-beam onto the central wavelength selection optics.
11. The wavelength-selective device of clause 1, wherein the plurality of pulsed optical sub-beams includes three or more pulsed optical sub-beams.
12. The wavelength selection device of claim 1, wherein the tuning mechanism and center wavelength selection optics are arranged to interact with the pulsed light beam in a Littrow configuration.
13. The wavelength selection device of claim 1, wherein the central wavelength selection optics is a reflective optical element.
14. The wavelength-selective device of claim 1, wherein an aerial image is formed for each individual wavelength of the pulsed light beam.
15. The wavelength selection device of clause 1, further comprising a control system and one or more actuators associated with the tuning mechanism, wherein the control system adjusts an angle of incidence of the pulsed light beam to the central wavelength selection optics by adjusting a signal to the one or more actuators.
16. The wavelength-selective device of claim 1, wherein the diffractive optical element is disposed perpendicular to a direction of propagation of the pulsed light beam along the path.
17. The wavelength selection device of claim 1, wherein the diffractive optical element further recombines the multiple pulsed light sub-beams from the central wavelength selection optics to form the pulsed light beam.
18. The wavelength selection device of clause 1, wherein the tuning mechanism comprises four right-angle prisms, and the location where at least a majority of the pulsed light beam is expanded is in the optical path between the right-angle prism closest to the central wavelength selection optics and the right-angle prism second closest to the central wavelength selection optics.
19. A light source generating a pulsed light beam that is directed along a path to a lithography exposure apparatus;
a lithography exposure apparatus that interacts with the pulsed light beam;
and a wavelength-selective device disposed relative to the light source, the wavelength-selective device comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optics, the tuning mechanism optically interacting with the pulsed light beam to select an angle of incidence of the pulsed light beam to the central wavelength selection optics;
an optical system comprising: a diffractive optical element that is passive and transparent and is positioned along the path of the pulsed light beam at a location where the pulsed light beam is completely or at least largely expanded, the diffractive optical element interacting with the pulsed light beam to generate a plurality of spatially separated, not temporally separated, pulsed light sub-beams from the pulsed light beam, each pulsed light sub-beam associated with a distinct wavelength and associated with a distinct angle of incidence on a central wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength;
20. The optical system of clause 19, wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating.
21. The optical system of clause 19, wherein the tuning mechanism comprises four refractive optical elements.
22. The optical system of clause 21, wherein each refractive optical element is a right-angle prism.
23. The optical system of clause 19, wherein a wavelength spacing between individual wavelengths of the plurality of pulsed light sub-beams is greater than about 10 picometers (pm), about 30 pm, or about 45 pm.
24. The optical system of clause 19, wherein a central wavelength of each pulse of the pulsed light beam is about 248 nanometers (nm) or about 193 nm.
25. The optical system of clause 19, wherein the wavelength selection device further comprises an actuator that adjusts a position of the diffractive optical element relative to the path of the pulsed light beam such that at times the diffractive optical element is at a position along the path of the pulsed light beam and at other times is not at a position along the path of the pulsed light beam, and the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam.
26. The optical system of clause 25, further comprising a control system that controls the wavelength selection device to adjust a position of the diffractive optical element relative to a path of the pulsed light beam.
27. The optical system of clause 19, wherein the lithographic exposure apparatus comprises a mask positioned to interact with the pulsed light beam from the light source, and a wafer holder to hold a wafer.
28. The optical system of clause 27, wherein a plurality of distinct aerial images are formed on a wafer in a wafer holder, each distinct aerial image being based on a distinct wavelength of an associated pulsed light sub-beam passing through the mask along a propagation direction.
29. The optical system of clause 19, further comprising a control system and one or more actuators associated with the tuning mechanism, wherein the control system adjusts an angle of incidence of the pulsed light beam to the central wavelength selection optics by adjusting a signal to the one or more actuators.
30. A method for forming multiple aerial images with a single pulsed light beam, comprising:
generating a pulsed light beam along a path toward the wafer;
selecting an angle of incidence of the pulsed light beam to a central wavelength selection optic to select at least one central wavelength of each pulse of the pulsed light beam by optically interacting the pulsed light beam with a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optic;
A method comprising: splitting a pulsed light beam into a plurality of pulsed light sub-beams by interacting the pulsed light beam with a diffraction pattern disposed along a path of the pulsed light beam; generating a plurality of spatially separated, non-temporally separated pulsed light sub-beams from the pulsed light beam, each of the pulsed light sub-beams being associated with a respective angle of incidence on a central wavelength selection optics such that each of the pulsed light sub-beams is associated with a corresponding one of the respective wavelengths separated by at least 10 picometers (pm); and forming a plurality of aerial images on a wafer with the single pulsed light beam, each of the aerial images being formed based on the respective wavelengths.
31. The method of clause 30, wherein interacting the pulsed light beam with the diffractive pattern comprises transmitting the pulsed light beam through a diffractive optical element.
32. The method of clause 30, wherein each individual angle of incidence onto the central wavelength selection optics associated with each pulsed light sub-beam is determined by a periodic shape of the diffraction pattern.
33. The method of clause 30, wherein selecting an angle of incidence of the pulsed light beam onto the central wavelength selection optics comprises adjusting one or more angles of refractive optical elements in a tuning mechanism.
34. The method of clause 30, wherein generating the plurality of pulsed light sub-beams from the pulsed light beam includes adjusting a position of the diffraction pattern relative to a path of the pulsed light beam.
35. The method of clause 34, wherein adjusting the position of the diffractive pattern comprises controlling by moving a diffractive optical element that includes the diffractive pattern.
36. The method of clause 30, wherein forming a plurality of aerial images on the wafer includes flattening an intensity profile of the pulsed light beam at the wafer.
37. The method of clause 30, further comprising recombining the multiple pulsed light sub-beams leaving the central wavelength selection optic by interacting the pulsed light sub-beams with a diffraction pattern disposed along the path of the pulsed light beam, whereby multiple pulsed light sub-beams are generated as the pulsed light beam interacts with the diffraction pattern as it travels along the path toward the central wavelength selection optic, and the multiple pulsed light sub-beams are recombined to form the pulsed light beam as the pulsed light sub-beams interact with the diffraction pattern as it travels along the path away from the central wavelength selection optic.
38. A wavelength selection device for a pulsed light source generating a pulsed light beam, comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optics, the tuning mechanism including four refractive optical elements that optically interact with the pulsed light beam to select an angle of incidence of the pulsed light beam to the central wavelength selection optics;
A wavelength selection device comprising: a passive, transmissive diffractive optical element disposed along a path of the pulsed light beam at a location between a tuning mechanism and a center wavelength selection optics, the diffractive optical element interacting with the pulsed light beam to generate a plurality of spatially separated, non-temporally separated pulsed light sub-beams therefrom, each pulsed light sub-beam being associated with a respective wavelength and associated with a respective angle of incidence on the center wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each respective wavelength.
39. The wavelength-selective device of clause 38, wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating.
40. The wavelength selection device of clause 38, wherein the tuning mechanism comprises four refractive optical elements.
41. The wavelength selection device of clause 38, wherein a wavelength spacing between individual wavelengths of the plurality of pulsed optical sub-beams is greater than about 10 picometers (pm), about 30 pm, or about 45 pm.

[0107] Other embodiments are within the scope of the claims.

Claims (33)

1. A wavelength selection device for a pulsed light source generating a pulsed light beam, comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along a path of the pulsed light beam to the center wavelength selection optics, the tuning mechanism optically interacting with the pulsed light beam to select the angle of incidence of the pulsed light beam to the center wavelength selection optics;
a diffractive optical element that is passive and transparent and positioned along the path of the pulsed light beam at a location where at least a majority of the pulsed light beam is expanded, the diffractive optical element interacting with the pulsed light beam to generate from the pulsed light beam a plurality of pulsed light sub-beams, each associated with a distinct wavelength and each associated with a distinct angle of incidence on the central wavelength selection optics, such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength; The wavelength selection device of claim 1, wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating. The wavelength selection device of claim 1, wherein the tuning mechanism comprises four refractive optical elements. The wavelength selection device of claim 3, wherein each refractive optical element is a right-angle prism. The wavelength selection device of claim 1, wherein the central wavelength of each pulse of the pulsed light beam is about 248 nanometers (nm) or about 193 nm. The wavelength selection device of claim 1, further comprising an actuator for adjusting the position of the diffractive optical element relative to the path of the pulsed light beam, such that the diffractive optical element is sometimes at a position along the path of the pulsed light beam and other times not at a position along the path of the pulsed light beam, and the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam. The wavelength selection device of claim 6, wherein the actuator further adjusts an angle of the diffractive optical element relative to a direction of the path of the pulsed light beam, thereby adjusting the individual angles of incidence of each generated pulsed light sub-beam to the central wavelength selection optical system. The wavelength selection device of claim 1, wherein the tuning mechanism and the central wavelength selection optics are arranged to interact with the pulsed light beam in a Littrow configuration. The wavelength selection device of claim 1, wherein the center wavelength selection optical system is a reflective optical element. The wavelength selection device of claim 1, further comprising a control system and one or more actuators associated with the tuning mechanism, the control system adjusting the angle of incidence of the pulsed light beam to the central wavelength selection optical system by adjusting a signal to the one or more actuators. The wavelength selection device of claim 1, wherein the diffractive optical element is disposed perpendicular to the direction of propagation of the pulsed light beam along the path. The wavelength selection device of claim 1, wherein the diffractive optical element further recombines the plurality of pulsed light sub-beams from the central wavelength selection optics to form the pulsed light beam. 2. The wavelength selection device of claim 1, wherein the tuning mechanism comprises four right-angle prisms, and the location where at least a majority of the pulsed light beam is expanded is in the path between the right-angle prism closest to the central wavelength selection optics and the right-angle prism second closest to the central wavelength selection optics. a light source generating a pulsed light beam that is directed along a path to a lithography exposure apparatus;
a lithography exposure tool that interacts with the pulsed light beam;
a wavelength-selective device disposed relative to the light source, the wavelength-selective device comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along the path of the pulsed light beam to the center wavelength selection optic, the tuning mechanism optically interacting with the pulsed light beam to select the angle of incidence of the pulsed light beam to the center wavelength selection optic;
an optical system comprising: a diffractive optical element that is passive and transparent and is positioned along the path of the pulsed light beam at a location where the pulsed light beam is completely or at least largely expanded, the diffractive optical element interacting with the pulsed light beam to generate a plurality of spatially separated, not temporally separated, pulsed light sub-beams from the pulsed light beam, each pulsed light sub-beam associated with a distinct wavelength and associated with a distinct angle of incidence on the central wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength; The optical system of claim 14 , wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating. The optical system of claim 14 , wherein the tuning mechanism comprises four refractive optical elements. 17. The optical system of claim 16 , wherein each refractive optical element is a right angle prism. 15. The optical system of claim 14 , wherein the central wavelength of each pulse of the pulsed light beam is about 248 nanometers (nm) or about 193 nm. 15. The optical system of claim 14, wherein the wavelength selection device further comprises an actuator that adjusts a position of the diffractive optical element relative to the path of the pulsed light beam such that the diffractive optical element is at a position along the path of the pulsed light beam at times and is not at a position along the path of the pulsed light beam at other times, and the diffractive optical element interacts with the pulsed light beam only when the diffractive optical element is at a position along the path of the pulsed light beam. 20. The optical system of claim 19 , further comprising a control system that controls the wavelength selection device to adjust the position of the diffractive optical element relative to the path of the pulsed light beam. The optical system of claim 14 , wherein the lithographic exposure apparatus comprises a mask positioned to interact with the pulsed light beam from the light source, and a wafer holder for holding a wafer. 22. The optical system of claim 21 , wherein a plurality of distinct aerial images are formed on the wafer in the wafer holder, each distinct aerial image being based on the distinct wavelength of the associated pulsed light sub-beam passing through the mask along a propagation direction. 15. The optical system of claim 14, further comprising a control system and one or more actuators associated with the tuning mechanism, the control system adjusting the angle of incidence of the pulsed light beam to the central wavelength selection optical system by adjusting a signal to the one or more actuators. 1. A method for forming multiple aerial images with a single pulsed light beam, comprising:
generating said pulsed light beam along a path toward a wafer;
selecting an angle of incidence of the pulsed light beam onto a central wavelength selection optic to select at least one central wavelength of each pulse of the pulsed light beam by optically interacting the pulsed light beam with a tuning mechanism disposed along a path of the pulsed light beam to the central wavelength selection optic;
generating from the pulsed light beam a plurality of spatially separated, non-temporally separated pulsed light sub-beams, each of the plurality of pulsed light sub-beams associated with a respective angle of incidence on the central wavelength selection optics such that each of the plurality of pulsed light sub-beams is associated with a corresponding one of a respective wavelength separated by at least 10 picometers (pm); and forming on the wafer with the single pulsed light beam a plurality of aerial images, each of the aerial images being formed based on a respective wavelength. 25. The method of claim 24 , wherein interacting the pulsed light beam with the diffractive pattern comprises transmitting the pulsed light beam through a diffractive optical element. 25. The method of claim 24 , wherein selecting the angle of incidence of the pulsed light beam to the central wavelength selection optics comprises adjusting one or more angles of a refractive optical element in the tuning mechanism. 25. The method of claim 24 , wherein generating the plurality of pulsed light sub-beams from the pulsed light beam comprises adjusting a position of the diffraction pattern relative to the path of the pulsed light beam. 28. The method of claim 27 , wherein adjusting the position of the diffractive pattern comprises controlling by moving a diffractive optical element that includes the diffractive pattern. 25. The method of claim 24, further comprising recombining the multiple pulsed light sub-beams leaving the central wavelength selection optic by interacting the pulsed light sub-beams with the diffraction pattern disposed along the path of the pulsed light beam, whereby the multiple pulsed light sub-beams are generated when the pulsed light beam interacts with the diffraction pattern as it travels along the path towards the central wavelength selection optic, and the multiple pulsed light sub-beams are recombined to form the pulsed light beam when the pulsed light sub-beams interact with the diffraction pattern as it travels along the path away from the central wavelength selection optic. 1. A wavelength selection device for a pulsed light source generating a pulsed light beam, comprising:
a central wavelength selection optical system for selecting at least one central wavelength of each pulse of the pulsed light beam in accordance with an angle of incidence of the pulsed light beam;
a tuning mechanism disposed along a path of the pulsed light beam to the center wavelength selection optics, the tuning mechanism comprising four refractive optical elements that optically interact with the pulsed light beam to select the angle of incidence of the pulsed light beam to the center wavelength selection optics;
a passive, transmissive diffractive optical element disposed along the path of the pulsed light beam at a location between the tuning mechanism and the center wavelength selection optics, the diffractive optical element interacting with the pulsed light beam to generate a plurality of spatially separated, non-temporally separated pulsed light sub-beams therefrom, each pulsed light sub-beam associated with a distinct wavelength and associated with a distinct angle of incidence on the center wavelength selection optics such that the optical spectrum of the pulsed light beam has a peak at each distinct wavelength. 31. The wavelength-selective device of claim 30 , wherein the diffractive optical element is a diffractive beam splitter, a diffraction grating, a phase grating, a binary phase grating, or a blazed phase grating. 31. The wavelength-selective device of claim 30 , wherein the tuning mechanism comprises four refractive optical elements. 31. The wavelength selection device of claim 30 , wherein a wavelength spacing between the individual wavelengths of the plurality of pulsed light sub-beams is greater than about 10 picometers (pm), about 30 pm, or about 45 pm.

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