Spectral feature control apparatus

Abstract

To provide an apparatus for controlling a spectral feature.SOLUTION: A spectral feature selection apparatus includes a dispersive optical element arranged to interact with a pulsed light beam; three or more refractive optical elements arranged in a path of the pulsed light beam between the dispersive optical element and a pulsed optical source; and one or more actuation systems, each actuation system associated with a refractive optical element and configured to rotate the associated refractive optical element to thereby adjust a spectral feature of the pulsed light beam. At least one of the actuation systems is a rapid actuation system that includes a rapid actuator configured to rotate the associated refractive optical element about a rotation axis. The rapid actuator includes a rotary stepper motor having a rotation shaft that rotates about a shaft axis that is parallel with the rotation axis of the associated refractive optical element.SELECTED DRAWING: Figure 3A

Description

[Technical field]

[0001] The disclosed subject matter relates to an apparatus for controlling spectral features, such as bandwidth or wavelength, of a light beam output from a light source that provides light to a lithographic exposure apparatus. [Background technology]

[0002] In semiconductor lithography (or photolithography), the fabrication of integrated circuits (ICs) requires various physical and chemical processes to be performed on a semiconductor (e.g., silicon) substrate (also called a wafer). A photolithography exposure tool, or scanner, is a machine that applies a desired pattern to a target portion of the substrate. The wafer is generally aligned along the orthogonal X-axis of the scanner. L and Y L The wafer is fixed to the stage so that it extends along a plane defined by the Z direction of the scanner. The wafer is illuminated by a light beam having a wavelength in the deep ultraviolet (DUV) range. The light beam is aligned with the Z direction of the scanner. L The scanner moves along an axis that coincides with the Z direction. L The direction is horizontal X L -Y L perpendicular to the surface.

[0003] Precise knowledge of the spectral features or characteristics (e.g., bandwidth) of a light beam output from a light source such as a laser is important in many scientific and industrial applications. For example, precise knowledge of the light source bandwidth can be used to control the minimum feature size or critical dimension (CD) in deep ultraviolet (DUV) optical lithography. The critical dimension is the feature size that is printed on a semiconductor substrate (also called a wafer), and therefore the CD can require fine size control. In optical lithography, a substrate is illuminated by a light beam generated by a light source. Often, the light source is a laser source, and the light beam is a laser beam. Summary of the Invention

[0004] In some general aspects, an optical system is used in conjunction with a light source. The optical system includes a dispersive optical element, a plurality of refractive optical elements between the dispersive optical element and the light source, and a plurality of actuation systems, each associated with a refractive optical element. At least one of the actuation systems includes an actuator configured to rotate an associated refractive optical element 360 degrees about a rotation axis, the actuator comprising a rotating shaft configured to rotate about a shaft axis, the shaft axis being parallel to the rotation axis of the associated refractive optical element, and the shaft axis being devoid of a ground energy state.

[0005] In some general aspects, the spectral feature selection device is used with a pulsed light source that generates a pulsed light beam. The spectral feature selection device includes a dispersive optical element arranged to interact with the pulsed light beam, three or more refractive optical elements arranged in a path of the pulsed light beam between the dispersive optical element and the pulsed light source, one or more actuation systems, each actuation system associated with a refractive optical element and configured to adjust the spectral feature of the pulsed light beam by rotating the associated refractive optical element, and a control system connected to the one or more actuation systems. At least one of the actuation systems is a high-speed actuation system including a high-speed actuator configured to rotate the associated refractive optical element about a rotation axis. The high-speed actuator includes a rotary stepper motor having a rotation shaft that rotates about a shaft axis parallel to the rotation axis of the associated refractive optical element. The control system is configured to send a signal to the high-speed actuator to rotate the associated refractive optical element about its rotation axis by adjusting the rotation shaft of the rotary stepper motor.

[0006] Implementations may include one or more of the following features. For example, the fast actuator may be configured to rotate a refractive optical element furthest from the dispersive optical element. The pulsed light beam path may be located in an XY plane of the apparatus, and the rotation shaft of the rotary stepper motor may have an axis parallel to a Z axis of the apparatus, thereby rotating the associated refractive optical element about its axis of rotation parallel to the Z axis of the apparatus.

[0007] The fast actuation system may also include a secondary actuator physically coupled to the associated refractive optical element, the secondary actuator configured to rotate the associated refractive optical element about an axis that lies in the XY plane and that also lies in the plane of the hypotenuse of the associated refractive optical element.

[0008] The apparatus may include a position monitor that detects a position of a rotating shaft of a rotary stepper motor. A control system may be connected to the position monitor and configured to receive the detected position of the rotating shaft and adjust the rotating shaft if the received detected position is not within an acceptable position range. The position monitor may be an optical rotary encoder. The rotating shaft may be configured to rotate a refractive optical element associated with a high speed actuator about an offset axis from the axis of rotation.

[0009] The shaft axis may be configured to rotate approximately 360 degrees, thereby rotating an associated refractive optical element approximately 360 degrees.

[0010] A refractive optical element associated with the high speed actuator may be fixedly coupled to the shaft axis.

[0011] The control system may include a high speed controller connected to a rotary stepper motor, with adjustments of the rotating shaft being made by the high speed controller.

[0012] Rotation of the refractive optical element associated with the fast actuator may cause a change in the magnification of the pulsed light beam interacting with the dispersive optical element. The change in the magnification of the pulsed light beam may cause a change in the bandwidth of the pulsed light beam. A range of bandwidths due to rotation of the refractive optical element associated with the fast actuator may be at least 250 femtometers (fm). Rotation of the refractive optical element associated with the fast actuator for one unit of rotation of the rotating shaft may change the bandwidth of the pulsed light beam by an amount less than the resolution of a bandwidth measuring device that measures the bandwidth of the pulsed light beam.

[0013] The dispersive optical element may be a diffractive optical element arranged to interact with the pulsed light beam in a Littrow configuration such that the pulsed light beam diffracted from the diffractive optical element travels along the path of the pulsed light beam that was incident on the diffractive optical element.

[0014] The refractive optical elements may be right angle prisms through which the pulsed light beam is transmitted such that the pulsed light beam changes its optical magnification as it passes through each right angle prism. The right angle prism furthest from the dispersive optical element may have the smallest hypotenuse of the plurality of right angle prisms, and each successive right angle prism closer to the dispersive optical element may have a hypotenuse that is larger than or the same size as an adjacent right angle prism further from the dispersive optical element.

[0015] In another general aspect, a spectral feature selection device includes a dispersive optical element positioned to interact with a pulsed light beam generated by a pulsed light source. The spectral feature selection device includes a plurality of refractive optical elements positioned in a path of the pulsed light beam between the dispersive optical element and the pulsed light source, and a plurality of actuation systems. Each actuation system is associated with a refractive optical element and configured to adjust the spectral feature of the pulsed light beam by rotating the associated refractive optical element. At least one of the actuation systems includes a high-speed actuator including a rotary motor having a rotating shaft that rotates about a shaft axis perpendicular to a face of the device. The refractive optical element associated with the high-speed actuator is mounted to the high-speed actuator such that the refractive optical element rotates about an offset axis that is parallel to the shaft axis, offset from the center of gravity, and offset from the shaft axis.

[0016] Implementations may include one or more of the following features. For example, the fast actuator may rotate and linearly translate an associated refractive optical element about an offset axis. The fast actuator may include a lever arm including a first region mechanically linked to a rotating shaft at the location of the shaft axis and a second region offset from the shaft axis along a direction perpendicular to the shaft axis and located in the plane of the device such that the second region is not intersected by the shaft axis. The refractive optical element associated with the fast actuator is mechanically linked to the second region.

[0017] The apparatus may also include a control system connected to the multiple actuation systems and configured to send signals to each actuation system. The control system may be configured to rotate and translate a refractive optical element associated with the fast actuator to adjust the spectral features of the pulsed light beam by sending a signal to the fast actuator. The refractive optical element associated with the fast actuator may be configured to rotate 15 degrees about the offset axis and reach a stable equilibrium position within about 50 milliseconds or less.

[0018] The spectral feature may be one or more of a bandwidth and a wavelength of the pulsed light beam.The refractive optical element controlled by the fast actuator may be devoid of an anti-reflective coating.

[0019] In another general aspect, the spectral feature selection device includes a diffractive optical element arranged to interact with a pulsed light beam in a Littrow configuration, the pulsed light beam being generated by a light source. The spectral feature selection device also includes a set of four or more right angle prisms through which the pulsed light beam is transmitted such that as the pulsed light beam passes through each right angle prism, the pulsed light beam changes its optical magnification. The pulsed light beam travels along a beam path and has a lateral extent that intersects with the hypotenuse of each prism such that the lateral extent of the pulsed light beam is contained within each of the hypotenuses of each prism. The right angle prism closest to the diffractive optical element has a hypotenuse with the greatest length of the set. Each successive right angle prism further away from the diffractive optical element has a hypotenuse with a length equal to or less than the hypotenuse of an adjacent right angle prism closer to the diffractive optical element. The right angle prism closest to the diffractive optical element is arranged with its right angle positioned away from the diffractive optical element. The region between the right-angle prism furthest from the diffractive optical element and the diffractive optical element is free of any reflective optical elements. The spectral feature selection device also includes at least two actuation systems, each actuation system associated with a right-angle prism of the set and configured to adjust the spectral features of the pulsed light beam by rotating an associated right-angle prism relative to the pulsed light beam.

[0020] Implementations may include one or more of the following features. For example, a prism farthest from the diffractive optical element may be associated with an actuation system and may be movable, and a prism second closest to the diffractive optical element may be associated with an actuation system and may be movable. [Brief description of the drawings]

[0021] [Figure 1] 1 is a block diagram of a photolithography system that generates a pulsed light beam, the photolithography system including a spectral feature selection device for tailoring one or more spectral features of the pulsed light beam. [Diagram 2] 2 is a graph of an exemplary optical spectrum of a pulsed light beam produced by the photolithography system of FIG. 1. [Figure 3A] FIG. 2 is a block diagram of an exemplary spectral feature selection device that can be used in the photolithography system of FIG. 1. [Figure 3B] FIG. 3B is a block diagram illustrating the beam expansion magnification and beam deflection angle through one of the refractive optical elements of the spectral feature selection device of FIG. 3A. [Figure 4A] FIG. 2 is a block diagram of an exemplary spectral feature selection device that can be used in the photolithography system of FIG. 1. [Figure 4B] FIG. 4B is a side view of a portion of an exemplary beam expander of the spectral feature selection apparatus of FIG. 4A. [Figure 4C] FIG. 4C is a top view of a portion of the example beam expander of FIG. 4B illustrating adjustment of the beam expander. [Figure 5A] FIG. 2 is a block diagram of an exemplary spectral feature selection device that can be used in the photolithography system of FIG. 1. [Figure 5B] FIG. 5B is a side view of a portion of an exemplary beam expander of the spectral feature selection apparatus of FIG. 5A. [Figure 5C] FIG. 5C is a top view of a portion of the example beam expander of FIG. 5B illustrating adjustment of the beam expander. [Figure 6A] FIG. 2 is a block diagram of an exemplary spectral feature selection device that can be used in the photolithography system of FIG. 1. [Figure 6B] FIG. 6B is a side view of a portion of an exemplary beam expander of the spectral feature selection apparatus of FIG. 6A. [Figure 6C]FIG. 6B is a top view of a portion of the example beam expander of FIG. 6A. [Figure 6D] FIG. 6C is a side view of a portion of the example beam expander of FIG. 6B illustrating adjustment of the beam expander. [Figure 7] FIG. 2 is a block diagram of an exemplary spectral feature selection device that can be used in the photolithography system of FIG. 1. [Figure 8] FIG. 2 is a block diagram of an example light source of the photolithography system of FIG. 1. [Figure 9] FIG. 2 is a block diagram of an exemplary control system for the photolithography system of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1, photolithography system 100 includes an illumination system 150 that generates a pulsed light beam 110 having a wavelength that is nominally at a central wavelength and that is directed to a photolithography exposure tool or scanner 115. Pulsed light beam 110 is used to pattern microelectronic features on a substrate or wafer 120 contained in the scanner 115. Illumination system 150 includes a light source 105 that generates pulsed light beam 110 at a variable pulse repetition rate. Illumination system 150 includes a control system 185 that communicates with light source 105 and other features in illumination system 150. Illumination system 150 also communicates with scanner 115 to control the operation of illumination system 150 and aspects of pulsed light beam 110.

[0023] The light beam 110 is directed through a beam preparation system 112, which may include optical elements that modify the behavior of the light beam 110. For example, the beam preparation system 112 may include reflective and / or refractive optical elements, optical pulse stretching circuits, and optical apertures (including automatic shutters).

[0024] The pulses of the light beam 110 are centered at wavelengths in the deep ultraviolet (DUV) region, e.g., 248 nanometers (nm) or 193 nm. The size of the microelectronic features patterned on the wafer 120 depends on the wavelength of the pulsed light beam 110, with lower wavelengths resulting in smaller minimum feature sizes or critical dimensions. If the wavelength of the pulsed light beam 110 is 248 nm or 193 nm, the minimum size of the microelectronic features can be, e.g., 50 nm or less. The bandwidth used to analyze and control the pulsed light beam 110 may be the actual instantaneous bandwidth of the optical spectrum 200 (or emission spectrum) as shown in FIG. 2. The optical spectrum 200 contains information about how the optical energy or power of the light beam 110 is distributed across different wavelengths (or frequencies).

[0025] The illumination system 150 includes a spectral feature selection device 130. The spectral feature selection device 130 is disposed at a first end of the light source 105 to interact with a light beam 110A generated by the light source 105. The light beam 110A is a beam generated at one end of a resonator in the light source 105, and may be a seed beam generated by a master oscillator as described below. The spectral feature selection device 130 is configured to fine-tune the spectral characteristics of the pulsed light beam 110A by adjusting or regulating one or more spectral features (such as bandwidth or wavelength) of the pulsed light beam 110A.

[0026] 3A, the spectral feature selection device 130 includes a set of optical features or components 300, 305, 310, 315, 320 arranged to optically interact with the pulsed light beam 110A, and a control module 350 including electronics in the form of any combination of firmware and software. The control module 350 is connected to one or more actuation systems 300A, 305A, 310A, 315A, 320A that are physically coupled to each optical component 300, 305, 310, 315, 320. The optical components of the device 130 include a beam expander 301 consisting of a dispersive optical element 300, which may be a grating, and a set of refractive optical elements 305, 310, 315, 320, which may be prisms. Grating 300 may be a reflective grating designed to disperse and reflect light beam 110A, and accordingly, grating 300 is made from a material suitable for interacting with pulsed light beam 110A having a wavelength in the DUV region. Each of prisms 305, 310, 315, 320 is a transmissive prism that acts to disperse and redirect light beam 110A as it passes through the body of the prism. Each prism may be made from a material (e.g., calcium fluoride, etc.) that allows the transmission of the wavelength of light beam 110A.

[0027] Prism 320 is located furthest from grating 300, and prism 305 is located closest to grating 300. Pulsed light beam 110A enters device 130 through aperture 355 and then travels through prisms 320, 310, and 305, in that order, before impinging on diffractive surface 302 of grating 300. With each passage of beam 110A through successive prisms 320, 315, 310, and 305, light beam 110A is optically expanded and redirected (tilted and refracted) towards the next optical component. Light beam 110A is diffracted and reflected from grating 300 and travels back through prisms 305, 310, 315, and 320, in that order, before light beam 110A passes through aperture 355 as it exits device 130. With each successive passage through the prisms 305 , 310 , 315 , 320 from the grating 300 , the light beam 110 A is optically compressed as it travels towards the aperture 355 .

[0028] 3B, the rotation of a prism P (which may be any of prisms 305, 310, 315, or 320) of the beam expander 301 changes the incidence angle at which the light beam 110A strikes the entrance face H(P) of the rotating prism P. In addition, two local optical qualities, the optical magnification OM(P) and the beam refraction angle δ(P) of the light beam 110A passing through the rotating prism P, are functions of the incidence angle of the light beam 110A striking the entrance face H(P) of the rotating prism P. The optical magnification OM(P) of the light beam 110A passing through the prism P is the ratio of the lateral width Wo(P) of the light beam 110A exiting the prism P to the lateral width Wi(P) of the light beam 110A entering the prism P.

[0029] A change in the local optical magnification OM(P) of the light beam 110A at one or more of the prisms P in the beam expander 301 results in an overall change in the optical magnification OM 365 of the light beam 110A passing through the beam expander 301. The optical magnification OM 365 of the light beam 110A passing through the beam expander 301 is the ratio of the lateral width Wo of the light beam 110A exiting the beam expander 301 to the lateral width Wi of the light beam 110A entering the beam expander 301.

[0030] Additionally, a change in the local beam refraction angle δ(P) through one or more of the prisms P in the beam expander 301 results in an overall change in the angle of incidence 362 of the light beam 110 A at the face 302 of the grating 300 .

[0031] The wavelength of the light beam 110A can be adjusted by changing the angle of incidence 362 at which the light beam 110A impinges on the diffractive surface 302 of the grating 300. The bandwidth of the light beam 110A can be adjusted by changing the optical magnification 365 of the light beam 110.

[0032] 3A-7, the spectral feature selection device 130 is redesigned to provide faster adjustment of the bandwidth of the pulsed light beam 110 while the light beam 110 is scanned across the wafer 120 by the scanner 115. The spectral feature selection device 130 can be redesigned with one or more new actuation systems for more efficiently and faster rotation of one or more of the optical components 300, 305, 310, 315, 320.

[0033] For example, the spectral feature selection device 130 includes a novel actuation system 320A for more effectively and faster rotation of the prism 320. The novel actuation system 320A can be designed to increase the speed at which the prism 320 rotates. Specifically, the rotation axis of the prism 320 attached to the novel actuation system 320A is parallel to the rotatable motor shaft 322A of the novel actuation system 320A. In another implementation, the novel actuation system 320A can be designed to include an arm that is physically linked to the motor shaft 322A at one end and to the prism 320 at the other end to provide additional force to rotate the prism 320. In this way, the optical magnification OM of the light beam 110A is made sensitive to the rotation of the prism 320.

[0034] In some implementations, such as that shown in Figure 7, the prism 305 is inverted relative to the conventional design of the beam expander to provide faster adjustment of the bandwidth. In these cases, the change in bandwidth is relatively faster with a relatively smaller rotation of the prism 320 (when compared to the conventional design of the device 130). The change in optical magnification per unit rotation of the prism 320 is increased in the redesigned spectral feature selection device 130 compared to the conventional spectral feature selection device.

[0035] Apparatus 130 is designed to adjust the wavelength of light beam 110A generated within one or more resonators of light source 105 by adjusting the angle of incidence 362 at which light beam 110A impinges on diffractive surface 302 of grating 300. Specifically, this can be done by rotating one or more of prisms 305, 310, 315, 320 and grating 300, thereby adjusting the angle of incidence 362 of light beam 110A.

[0036] Additionally, the bandwidth of light beam 110A generated by light source 105 is adjusted by adjusting the optical magnification OM 365 of light beam 110A. Thus, the bandwidth of light beam 110A can be adjusted by rotating one or more of prisms 305, 310, 315, 320 (which changes the optical magnification 365 of light beam 110A).

[0037] Wavelength and bandwidth control are combined in this design since rotation of a particular prism P results in a change in both the local beam deflection angle δ(P) and the local optical magnification OM(P) at that prism P.

[0038] In addition, the bandwidth of light beam 110A is relatively sensitive to the rotation of prism 320 and relatively insensitive to the rotation of prism 305 because the change in the local optical magnification OM(320) of light beam 110A due to the rotation of prism 320 is multiplied by the product of the changes in the optical magnifications OM(315), OM(310), OM(305) of the other prisms 315, 310, and 305, respectively (because these prisms are between rotating prism 320 and grating 300, and light beam 110A must travel through these other prisms 315, 310, 305 after passing through prism 320). On the other hand, the wavelength of light beam 110A is relatively sensitive to the rotation of prism 305 and relatively insensitive to the rotation of prism 320.

[0039] For example, to change the wavelength without changing the bandwidth of light beam 110A, the angle of incidence 362 should be changed without changing the optical magnification 365, which can be achieved by rotating prism 305 a large amount and rotating prism 320 a small amount. To change the bandwidth without changing the wavelength, the optical magnification 365 should be changed without changing the angle of incidence 362, and this can be achieved by rotating prism 320 a large amount and rotating prism 305 a small amount.

[0040] The control module 350 is connected to one or more actuation systems 300A, 305A, 310A, 315A, 320A that are physically coupled to each optical component 300, 305, 310, 315, 320. Although an actuation system is shown for each optical component, some of the optical components of the device 130 may remain stationary or not be physically coupled to an actuation system. For example, in some implementations, the grating 300 may remain stationary and the prism 315 may remain stationary and not be physically coupled to an actuation system.

[0041] Each of the actuation systems 300A, 305A, 310A, 315A, 320A includes an actuator connected to a respective optical component. Adjustment of the optical component results in adjustment of a particular spectral feature (wavelength and / or bandwidth) of the light beam 110A. The control module 350 receives control signals from the control system 185, which include specific commands to operate or control one or more of the actuation systems. The actuation systems can be selected and designed to work together.

[0042] Each actuator of the actuation systems 300A, 305A, 310A, 315A, 320A is a mechanical device for moving or controlling a respective optical component. The actuators receive energy from the module 350 and convert the energy into some type of motion imparted to the respective optical component. For example, the actuation system may be one of a force device and a rotation stage for rotating one or more of the prisms of the beam expander. The actuation system may include, for example, a motor such as a stepper motor, a valve, a pressure control device, a piezoelectric device, a linear motor, a hydraulic actuator, a voice coil, etc.

[0043] Grating 300 may be a high blaze angle echelle grating, and a light beam 110A incident on grating 300 at an incidence angle 362 that satisfies a grating equation is reflected (diffracted). The grating equation provides a relationship between the spectral order of grating 300, the diffracted wavelength (wavelength of the diffracted beam), the incidence angle 362 of light beam 110A on grating 300, the exit angle of light beam 110A diffracted away from grating 300, the vertical divergence of light beam 110A incident on grating 300, and the groove spacing of the diffractive surface of grating 300. Also, if the grating 300 is used such that the angle of incidence 362 of the light beam 110A on the grating 300 is equal to the angle of emergence of the light beam 110A from the grating 300, then the grating 300 and the beam expander (prisms 305, 310, 315, 320) are arranged in a Littrow configuration, and the wavelength of the light beam 110A reflected from the grating 300 is the Littrow wavelength. It can be assumed that the vertical divergence of the light beam 110A incident on the grating 300 is approximately zero. To reflect a nominal wavelength, the grating 300 is aligned with respect to the light beam 110A incident on the grating 300 such that the nominal wavelength is reflected back through the beam expander (prisms 305, 310, 315, 320) and amplified by the light source 105. The Littrow wavelength can then be tuned across the gain bandwidth of the cavity in the light source 105 by varying the angle of incidence 362 of the light beam 110 A on the grating 300 .

[0044] Each of the prisms 305, 310, 315, 320 is wide enough transversely of the light beam 110A so that the light beam 110A is contained within the plane through which it passes. Each prism optically expands the light beam 110A on its path from the aperture 355 towards the grating 300, and thus each prism increases in size successively from prism 320 to prism 305. Thus, prism 305 is larger than prism 310, which is larger than prism 315, and prism 320 is the smallest prism.

[0045] The prism 320, which is the furthest from the grating 300 and is also the smallest in size, is mounted on an actuation system 320A (specifically, relative to a rotating shaft 322A that rotates the prism 320), and such rotation changes the optical magnification of the light beam 110A impinging on the grating 300, thereby modifying the bandwidth of the light beam 110A output from the device 130. The actuation system 320A is designed as a high-speed actuation system 320A, since it includes a rotary stepper motor that includes the rotating shaft 322A to which the prism 320 is fixed. The rotating shaft 322A rotates about its shaft axis, which is parallel to the rotation axis of the prism 320. Also, since the actuation system 320A includes a rotary stepper motor, it lacks mechanical memory and also lacks an energy ground state. Each location on rotatable shaft 322A is in the same energy state as each other location on rotatable shaft 322A, and rotatable shaft 322A lacks a preferred resting location of low potential energy.

[0046] The rotary stepper motor of the system 320A should be fast enough to move the rotating shaft 322A, and thus the prism 320, at high speed (meaning fast enough to allow adjustments to the spectral features of the light beam 110A within the required time frame). In some implementations, the rotary stepper motor of the system 320A is configured with an optical rotary encoder to provide feedback regarding the position of the rotating shaft 322A. The rotary stepper motor can also be controlled with a motor controller that is a high resolution position controller and uses a variable frequency drive control method. In one example, the rotary stepper motor of the system 320A is fast enough to move the rotating shaft 322A and the prism 320 15 degrees in less than 50 ms, and the accuracy of the optical rotary encoder can be less than 50 micro degrees (e.g., 15 degrees in 30 ms). One example of a variable frequency drive control method is vector motor control, where the stator current of the motor is controlled by two orthogonal components, namely the motor flux and torque. The optical rotary encoder may be an encoder that uses an optical scan incorporating a periodic structured measurement fiducial known as a scale that is applied to a glass or steel carrier substrate. In some examples, the optical rotary encoder is manufactured by HEIDENHAIN.

[0047] 4A and 4B, in a first implementation, a spectral feature selection device 430 is designed with a grating 400 and four prisms 405, 410, 415, 420. The grating 400 and the four prisms 405, 410, 415, 420 are configured to interact with the light beam 110A generated by the light source 105 after the light beam 110A passes through an aperture 455 of the device 430. The light beam 110A travels along a path in the XY plane of the device 430 from the aperture 455 through prism 420, prism 415, prism 410, prism 405, and then reflects off the grating 400 and returns through prisms 405, 410, 415, 420 before exiting the device through aperture 455.

[0048] Prisms 405, 410, 415, 420 are right angle prisms through which pulsed light beam 110A is transmitted such that pulsed light beam 110A changes its optical magnification as it passes through each right angle prism. Right angle prism 420 furthest from dispersing optical element 400 has the smallest hypotenuse of the plurality, and each successive right angle prism closer to dispersing optical element 400 has a hypotenuse that is larger than or the same size as the adjacent right angle prism further away from the dispersing optical element.

[0049] For example, prism 405 closest to grating 400 is also the largest in size, e.g., its hypotenuse has the largest extent of the four prisms 405, 410, 415, 420. Prism 420 furthest from grating 400 is also the smallest in size, e.g., its hypotenuse has the smallest extent of the four prisms 405, 410, 415, 420. It is possible for adjacent prisms to be the same size. However, because light beam 110A is optically expanded as it travels through prisms 420, 415, 410, and 405, and as a result, the lateral extent of light beam 110A expands as light beam 110A approaches grating 400, each prism closer to grating 400 should be at least the same size as or larger than its neighboring prism. The lateral extent of light beam 110A is the extent along a plane perpendicular to the propagation direction of light beam 110A, which is in the XY plane of device 430.

[0050] Prism 405 is physically coupled to an actuation system 405A that rotates prism 405 about an axis parallel to the Z axis of device 430, prism 410 is physically coupled to an actuation system 410A that rotates prism 410 about an axis parallel to the Z axis, and prism 420 is physically coupled to a high speed actuation system 420A. High speed actuation system 420A is configured to rotate prism 405 about an axis parallel to the Z axis of device 430.

[0051] The high-speed actuation system 420A includes a rotary stepper motor 421A having a rotating shaft 422A and a rotating plate 423A fixed to the rotating shaft 422A. The rotating shaft 422A and thus the rotating plate 423A rotate about a shaft axis AR that is parallel to the center of mass of the prism 420 (corresponding to the rotation axis AP) and also parallel to the Z-axis of the device 430. Although not required, the shaft axis AR of the prism 420 may coincide or be aligned with the center of mass of the prism 420 (the rotation axis AP) along the XY plane. In some implementations, the center of mass of the prism 420 (or the rotation axis AP) is offset from the shaft axis AR along the XY plane. By offsetting the shaft axis AR from the center of mass of the prism 420, the position of the light beam 110A can be adjusted to be at a specific location on the surface of the grating 400 whenever the prism 420 rotates.

[0052] By mounting the prism 420 on the rotating plate 423A, the prism 420 rotates directly about its rotation axis AP as the shaft 422A and the rotating plate 423A rotate about their shaft axis AR. In this way, faster rotation or control of the prism 420 is possible compared to systems using linear stepper motors with linearly translatable shafts (which are converted to rotational motion using flexure). Because the rotational steps of the shaft 422A (and plate 423A) directly correlate with the rotational steps of the prism 420 (without providing any linear motion), the rotary stepper motor 421A can rotate the prism 420 at a speed that allows faster adjustment of the spectral features (such as bandwidth) of the light beam 110A and thus the light beam 110. The rotary design of the stepper motor 421A provides a pure rotational motion to the mounted prism 420 without the linear or flexure motion found on conventional actuators for the prism 420. The use of rotating shaft 422A also allows prism 420 to rotate a full 360°, unlike conventional actuators that use a flexure design in addition to a linear stepper motor, where prism 420 can only rotate about an angle determined from the flexure. In some implementations, prism 420 can be rotated 15° to adjust the bandwidth of light beam 110A within an acceptable range. Although not required by current bandwidth range requirements, prism 420 can be rotated more than 15°.

[0053] In some implementations, the stepper motor 421A may be a direct drive stepper motor. A direct drive stepper motor is a conventional electromagnetic motor that uses built-in step motor functionality for position control. In other implementations, where higher resolution of motion may be required, the stepper motor 421A may use piezoelectric motor technology.

[0054] Stepper motor 421 A may be a rotation stage controlled with a motor controller that uses a variable frequency drive control method to provide high speed rotation of prism 420 .

[0055] As explained above, the advantage of using the rotary stepper motor 421A is that the rotation axis AP of the prism 420 is parallel to the rotating shaft 422A and also to the shaft axis AR, resulting in a faster rotation of the prism 420. Thus, for each unit rotation of the shaft 422A, the prism 420 rotates by an incremental unit, and the prism 420 rotates as fast as the rotating shaft 422A can rotate. In some implementations, to increase the stability of this configuration and to increase the stability of the prism 420, the high-speed actuation system 420A includes a position monitor 424A configured to detect the position of the rotating shaft 422A of the rotary stepper motor 421A. The error between the measured position of the rotating shaft 422A and the expected or target position of the rotating shaft 422A directly correlates to the error in the position of the prism 420, and as a result, this measurement can be used to determine the rotation error of the prism 420 (i.e., the difference between the actual rotation and the commanded rotation) and to correct for this error during operation.

[0056] The control module 350 is connected to the position monitor 424A to receive values ​​of the position of the rotatable shaft 422A, and the control module 350 can also access stored or current values ​​of the commanded position of the rotatable shaft 422A so that the control module 350 can perform calculations to determine the difference between the measured position of the rotatable shaft 422A and the commanded position of the rotatable shaft 422A, and also how to adjust the rotatable shaft 422A to reduce this error. For example, the control module 350 can determine the size and direction of rotation of the rotatable shaft 422A to offset the error. Alternatively, the control system 185 can perform this analysis.

[0057] The position monitor 424A may be a very high resolution optical rotary encoder built integrally with the rotating plate 423A. Optical rotary encoders use optical sensing techniques to rotate an internal code disk with opaque lines and patterns. For example, the plate 423A is rotated with a beam of light, such as a light emitting diode (hence the name rotary encoder), and indicia on the plate 423A act as a shutter to block and unblock the light. An internal photodiode detector senses the alternating light beam, and the encoder electronics convert the pattern into an electrical signal that is then transmitted to the control module 350 via the output of the encoder 424A.

[0058] In some implementations, control module 350 can be designed with a high-speed internal dedicated controller just for operating rotary stepper motor 421 A. For example, the high-speed internal dedicated controller can receive high-resolution position data from encoder 424A and send a signal directly to rotary stepper motor 421 A to adjust the position of shaft 422A, and thereby the position of prism 420.

[0059] 4C, the illumination system 150 changes spectral features such as the bandwidth of the light beam 110A under the control of the control system 185 that interfaces with the control module 350. For example, to control the bandwidth of the light beam 110A and the light beam 110 to be coarse and wide, the control module 350 sends a signal to the rotary stepper motor 421A of the fast actuation system 420A to rotate the rotating shaft 422A from a first angle θ1 (left side of FIG. 4C) to a second angle θ2 (here, Δθ=θ2-θ1) (right side of FIG. 4C). This angular change of the shaft 422A is then directly imparted to the plate 423A fixed to the shaft 422A, and thereby also to the prism 420 fixed to the plate 423A. Rotating the prism 420 from θ1 to θ2 causes a corresponding change in the optical magnification OM365 of the pulsed light beam 110A interacting with the grating 400 from OM1 to OM2, and this change in the optical magnification OM365 of the pulsed light beam 110A causes a change in the bandwidth of the pulsed light beam 110A (and light beam 110 as well). The range of bandwidths that can be achieved by rotating the prism 420 using this fast actuation system 420A can be wide and can be from about 100 femtometers (fm) to about 450 fm. The total achievable bandwidth range can be at least 250 fm.

[0060] Rotation of the prism 420 associated with the fast actuation system 420A by one unit of rotation of the rotating shaft 422A changes the bandwidth of the pulsed light beam 110A by an amount less than the resolution of a bandwidth measurement device (e.g., as part of the metrology system 170 described below) that measures the bandwidth of the pulsed light beam 110. The prism 420 can be rotated up to 15 degrees to achieve such a bandwidth change. In practice, the amount of rotation of the prism 420 is constrained only by the optical layout of the other components of the apparatus 430. For example, too much rotation may displace the light beam 110A an amount that is so large that the light beam 110A does not impinge on the next prism 415. In some implementations, the prism 420 can be rotated 15 degrees to adjust the bandwidth of the light beam 110A within an acceptable range without the risk of the light beam 110A throwing off any of the other prisms 405, 410, or 415. Although not required by current bandwidth range requirements, prism 420 can be rotated by more than 15 degrees.

[0061] 4A, the prism 410 can be attached to an actuation system 410A that rotates the prism 410, and such rotation of the prism 410 can provide fine control of the wavelength of the light beam 110A. The actuation system 410A can include a rotary stepper motor controlled using a piezoelectric motor. Piezoelectric motors work by utilizing the inverse piezoelectric effect, in which a material is subjected to acoustic or ultrasonic vibrations to produce linear or rotational motion.

[0062] In some implementations, the next prism 415, which is closer to the grating 400 and has a size greater than or equal to the size of the prism 420, can be fixed in space. The next prism 410, which is closer to the grating 400, has a size greater than or equal to the size of the prism 415.

[0063] The prism 405 closest to the grating 410 has a size greater than or equal to the size of the prism 410 (prism 405 is the largest prism of the beam expander). The prism 405 can be mounted to an actuation system 405A that rotates the prism 405, and such rotation of the prism 405 can provide coarse control of the wavelength of the light beam 110A. For example, the prism 405 can be rotated 1-2 degrees to adjust the wavelength of the light beam 110A (and therefore the light beam 110) from about 193.2 nanometers (nm) to about 193.5 nm. In some implementations, the actuation system 405A includes a mounting surface (such as plate 423A) to which the prism 405 is secured, and a rotary stepper motor that includes a motor shaft that rotates the mounting surface. The motor of the actuation system 405A can be a piezoelectric motor that is 50 times faster than a conventional linear stepper motor and flexure combination design. Similar to actuation system 420A, actuation system 405A may include an optical rotary encoder that provides angular position feedback to control system 185 or control module 350.

[0064] 5A and 5B, in another implementation of the spectral feature selection device 530, the high-speed actuation system 520A is designed to rotate (R) the prism 520 of the beam expander furthest from the grating 500 about the shaft axis AR.

[0065] The device 530 includes an extension arm 525A having a first region 540A mechanically linked to a rotating plate 523A at the location of the shaft axis AR. The extension arm 525A has a second region 545A offset from the shaft axis AR along a direction in the XY plane (and consequently along a direction perpendicular to the shaft axis AR) such that the second region 545A is not intersected by the shaft axis AR. The prism 520 is mechanically linked to the second region 545A.

[0066] Both the center of mass of the prism 520 (prism axis AP) and the shaft axis AR remain parallel to the Z-axis of the device 530, but the center of mass of the prism 520 is offset from the shaft axis AR. Rotation of the extension arm 525A around the shaft axis AR by an angle Δθ imparts a compound motion to the prism 520, namely a rotation R of the prism 520 around the shaft axis AR by an angle Δθ (see FIG. 5C) in the XY-plane, and a linear translation T of the prism 520 along a direction lying in the XY-plane of the device 530. In the example of FIG. 5C, the prism 520 is rotated (R) from a first angle θ1 to a second angle θ2, and translated (T) from a first position Pos1 in the XY-plane to a second position Pos2 in the XY-plane.

[0067] A linear translation T relative to the prism 520 thereby translates the light beam 110A along a direction parallel to the long axis 501 of the face 502 of the grating 500, which also lies along the XY plane of the device 530. By performing this translation of the light beam 110A, it is possible to control which areas or regions of the grating 500 are illuminated at the lower end of the range of possible optical magnifications OM. Also, the grating 500 and the grating's face 502 are non-uniform, i.e., some regions of the grating 500's face 502 impart different changes to the wavefront of the light beam 110A compared to other regions of the grating 500's face 502, and some regions of the face 502 impart more distortion to the wavefront of the light beam 110A compared to other regions of the face 502. The control system 185 (or control module 350) can control the fast actuation system 520A to adjust the linear translation T relative to the prism 520 and the translation of the light beam 110A along the long axis 501 to take advantage of non-uniformity in the surface 502 of the grating 500 and to illuminate a higher distortion region of the grating surface 502 near one end of the grating surface 502, thereby increasing the spectral bandwidth beyond what would be expected to be achieved by simply reducing the optical magnification.

[0068] In addition, the linear translation T relative to prism 520 also translates hypotenuse H (see FIG. 5C) of prism 520 during rotation of prism 520 relative to the location of light beam 110A. Thus, translation relative to hypotenuse H exposes new areas of hypotenuse H to light beam 110A during operation of device 530. Over the life of device 530, prism 520 is rotated from one end of its rotational range to the other and more areas are exposed to light beam 110A, which reduces the amount of damage inflicted on prism 520 by light beam 110A.

[0069] Similar to device 430, spectral feature selection device 530 also includes a grating 500, and the beam expander includes prisms 505, 510, 515 located along the path of light beam 110A between prism 520 and grating 500. Grating 500 and four prisms 505, 510, 515, 520 are configured to interact with light beam 110A generated by light source 105 after light beam 110A passes through aperture 555 of device 530. Light beam 110A travels along a path in the XY plane of device 530 from aperture 555 through prism 520, prism 515, prism 510, prism 505, and then reflects off grating 500 and passes back through the successive prisms 505, 510, 515, 520 before exiting device 530 through aperture 555.

[0070] 6A-6D, in another implementation, fast actuation system 620A is designed similar to fast actuation system 520A, but with an additional secondary actuator 660A. Secondary actuator 660A is physically coupled to the prism 620 furthest from grating 600. Secondary actuator 660A is configured to rotate prism 620 about axis AH, which lies in the XY plane and also lies in the plane of hypotenuse H of prism 620.

[0071] In some implementations, although not required, the secondary actuator 660A is controlled by the control module 350 (or control system 185). The secondary actuator 660A may be a manual screw and bend design that is not controlled by the control module 350 or control system 185. For example, the actuator 660A may be set before the system 620A is used, or can be changed manually periodically between uses of the system 620A.

[0072] Thus, the prism 620 can be rotated about an axis AH located in the XY plane to allow for greater control over where the light beam 110A enters the prism 620 and the hypotenuse H of the prism 620 to better maintain the path of the light beam 110A through each of the prisms 615, 610, 605 and the grating 600. Specifically, the rotation of the prism 620 about the axis AH allows the light beam 110A to be finer adjusted. For example, the prism 620 can be rotated about the axis AH to ensure that the retro-reflected (i.e., diffracted) light beam 110A from the grating 600 remains in the XY plane and is not displaced along the Z axis of the device 630 even if the prism 620 rotates about the AP or AR axis. Having this Z axis adjustment is beneficial when the AP or AR axis is not perfectly aligned with the Z axis. In addition, because extension arm 625A is a cantilever and can sag or move along the Z axis such that it can deflect about axis AH and counteract this deflection using secondary actuator 660A, it can be beneficial to rotate prism 620 about axis AH.

[0073] 7, in another implementation, a spectral feature selection device 730 is designed with a dispersive optical element (such as a grating) 700 and a beam expander including three or more refractive optical elements configured to optically expand the light beam 110A as it travels from the aperture 755 towards the grating 700. The beam expander in this example includes four right angle prisms 705, 710, 715, 720 through which the pulsed light beam 110A is transmitted such that the pulsed light beam 110A changes its optical magnification as it passes through each right angle prism, as described above. The prism 705 closest to the grating 700 has a hypotenuse 705H that has the longest length of any of the hypotenuses of the prisms of the beam expander. Each successive right angle prism farther from grating 700 than prism 705 has a hypotenuse 710H, 715H, 720H ​​that has a length less than or equal to the hypotenuse H of the adjacent right angle prism closer to grating 700.

[0074] The right-angle prism 705 closest to the grating 700 is positioned with its right angle α oriented away from the grating 700. This can be compared to the prism 405 of the device 430 of FIG. 4A, whose right angle is positioned toward or next to the grating 400. Also, there are no other optical elements in the region 707 between the right-angle prism 705 and the grating 700. There are no optical elements (such as reflective or refractive optical elements) between the prism 705 and the grating 700. Thus, the light beam 110A travels between the prism 705 and the grating 700 without passing through any other optical elements.

[0075] By thus flipping the prism 705 from the layout shown in FIG. 4A to that shown in FIG. 7, it is possible to obtain a larger change in the optical magnification 365 of the light beam 110A per unit of rotation of the prism 720, and as a result, allows for faster adjustment of the bandwidth of the light beam 110A (and the light beam 110). In this implementation, a wide range of optical magnifications is obtained by rotating the prisms 720 and 710 in conjunction with each other to adjust the bandwidth of the light beam 110A. Specifically, when the prisms 720 and 710 rotate in conjunction with each other, the optical magnification can be adjusted from a low of 13 times to a high of 75 times (which is a wider range than is possible in the layout of FIG. 4A). The layout of the device 730 provides the fastest way to adjust the bandwidth of the light beam 110A as the two prisms 720, 710 rotate in conjunction with each other. Apparatus 730 has a different overall configuration than apparatus 430 of FIG. 4A, and may require redesign or reconfiguration of other components of illumination system 150 (such as light source 105).

[0076] Other aspects of photolithography system 100 will now be described with reference to FIGS.

[0077] 1, the control system 185 is operatively connected to the pulsed light source 105 and the spectral feature selector 130. And, the scanner 115 includes a lithography controller 140 operatively connected to the control system 185 and components within the scanner 115.

[0078] The pulse repetition rate of the pulsed light beam 110 is the rate at which pulses of the light beam 110 are generated by the light source 105. Thus, for example, the repetition rate of the pulsed light beam 110 is 1 / Δt, where Δt is the time between pulses. The control system 185 is generally configured to control the repetition rate at which the pulsed light beam 110 is generated, including modifying the repetition rate of the pulsed light beam as it exposes the wafer 120 in the scanner 115.

[0079] In some implementations, the scanner 115 triggers the light source 105 (through communication between the controller 140 and the control system 185) to generate the pulsed light beam 110 such that the scanner 115 controls the repetition rate, spectral features such as bandwidth or wavelength, and / or dose through the controller 140 and the control system 185. For example, the controller 140 sends a signal to the control system 185 to maintain the repetition rate of the light beam 110 within a certain acceptable rate. The scanner 115 generally maintains a constant repetition rate for each pulse burst of the light beam 110. The pulse burst of the light beam 110 can correspond to an exposure field on the wafer 120. The exposure field is the area of ​​the wafer 120 that is exposed in one scan of an exposure slit or window in the scanner 115. The pulse burst may include, for example, a range of 10 to 500 pulses.

[0080] Critical dimension (CD) is the smallest feature size that can be printed on wafer 120 by system 100. CD is determined by the wavelength of light beam 110. To maintain uniform CD of microelectronic features printed on wafer 120 and on other wafers exposed by system 100, the central wavelength of light beam 110 should remain at the expected or target central wavelength or within a wavelength range about the target wavelength. Thus, in addition to maintaining the central wavelength at or within an acceptable wavelength range about the target central wavelength, it is desirable to maintain the bandwidth of light beam 110 (the wavelength range of light beam 110) within an acceptable bandwidth range.

[0081] To maintain the bandwidth of the light beam 110 within an acceptable range or to adjust the bandwidth of the light beam 110, the control system 185 is configured to determine an adjustment amount of the bandwidth of the pulsed light beam 110. Additionally, the control system 185 is configured to send a signal to the spectral feature selection device 130 to change the bandwidth of the pulsed light beam 110 by the determined adjustment amount by moving at least one optical component (e.g., prism 320) of the device 130 when the pulsed light beam 110 is exposing the wafer 120, thereby compensating for bandwidth variations caused by modifying the pulse repetition rate of the pulsed light beam 110.

[0082] The bandwidth of the pulsed light beam 110 can be changed between any two pulse bursts. Also, the time it takes for the bandwidth to change from a first value to a second value and to stabilize at the second value should be less than the time between the pulse bursts. For example, if the period between bursts is 50 milliseconds (ms), the total time to change the bandwidth from a first value to a second value and to stabilize at the second value should be less than 50 ms. The control system 185 and the spectral feature selection device 130 are designed to allow such fast bandwidth changes, as described in more detail below.

[0083] The controller 140 of the scanner 115 sends signals to the control system 185 to adjust or modify aspects (such as bandwidth or repetition rate) of the pulsed light beam 110 being scanned across the wafer 120. The signals sent to the control system 185 may cause the control system 185 to modify the electrical signals sent to the pulsed light source 105 or the electrical signals sent to the device 130. For example, if the pulsed light source 105 includes a gas laser amplifier, the electrical signals provide a pulsed current to electrodes in one or more gas discharge chambers of the pulsed light source 105.

[0084] Referring again to FIG. 1, the wafer 120 is placed on a wafer table connected to a positioner constructed to hold the wafer 120 and configured to precisely position the wafer 120 according to certain parameters and under the control of a controller 140.

[0085] Photolithography system 100 may also include a metrology system 170, which may include a subsystem that measures one or more spectral features (such as bandwidth or wavelength) of light beam 110. Due to various disturbances applied to photolithography system 100 during operation, the value of the spectral feature (such as bandwidth or wavelength) of light beam 110 at wafer 120 may not correspond or match the desired spectral feature (i.e., the spectral feature expected by scanner 115). Thus, the spectral feature (such as characteristic bandwidth) of light beam 110 is measured or estimated during operation by estimating a metric value from the optical spectrum, so that an operator or an automatic system (e.g., a feedback controller) can use the measured or estimated bandwidth to adjust the characteristics of light source 105 and adjust the optical spectrum of light beam 110. The subsystems of metrology system 170 measure the spectral feature (such as bandwidth and / or wavelength) of light beam 110 based on the optical spectrum.

[0086] The metrology system 170 receives a portion of the light beam 110 redirected from a beam splitting device disposed in a path between the light source 105 and the scanner 115. The beam splitting device directs a first portion or percentage of the light beam 110 into the metrology system 170 and directs a second portion or percentage of the light beam 110 towards the scanner 115. In some implementations, a majority of the light beam 110 is directed towards the scanner 115 in the second portion. For example, the beam splitting device directs a small portion (e.g., 1-2%) of the light beam 110 into the metrology system 170. The beam splitting device may be, for example, a beam splitter.

[0087] The scanner 115 includes an optical arrangement having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask can be moved along one or more directions, such as along the optical axis of the light beam 110 or in a plane perpendicular to the optical axis. The objective arrangement includes a projection lens and can cause an image transfer from the mask to a photoresist on the wafer 120. The illuminator system adjusts the angular range of the light beam 110 that impinges on the mask. The illuminator system also equalizes (uniforms) the intensity distribution of the light beam 110 across the mask.

[0088] Scanner 115 may include, among other features, a lithography controller 140, air conditioning devices, and power sources for various electrical components. In addition to controlling the repetition rate of the pulses of light beam 110 (discussed above), lithography controller 140 controls how layers are printed on wafer 120. Lithography controller 140 includes memory to store information such as process recipes, and may also store information regarding which repetition rates may be used or are preferred, as described more fully below.

[0089] The wafer 120 is illuminated by the light beam 110. A process program or recipe determines the length of exposure to the wafer 120, the mask used, and other factors that affect the exposure. During lithography, as explained above, multiple pulses of the light beam 110 illuminate the same area of ​​the wafer 120, thereby constituting an illumination dose. The number N of pulses of the light beam 110 that illuminate the same area may be called the exposure window or slit, and the size of the slit can be controlled by an exposure slit placed in front of the mask. In some implementations, the value of N is several tens of pulses, e.g., 10-100 pulses. In other implementations, the number N is more than 100 pulses, e.g., 100-500 pulses.

[0090] One or more of the mask, objective, and wafer 120 may be moved relative to one another during exposure to scan an exposure window across the exposure field, which is the area of ​​the wafer 120 that is exposed in one scan of an exposure slit or window.

[0091] Referring to FIG. 8, an exemplary light source 805 is a pulsed laser source that generates a pulsed laser beam as the light beam 110. The light source 805 is a two-stage laser system that includes a master oscillator (MO) 800 that provides a seed light beam 110A to a power amplifier (PA) 810. The master oscillator 800 typically includes a gain medium in which amplification occurs, and an optical feedback mechanism such as an optical resonator. The power amplifier 810 typically includes a gain medium in which amplification occurs when seeded with a seed laser beam from the master oscillator 800. If the power amplifier 810 is designed as a regenerative ring resonator, it is called a power ring amplifier (PRA), and in this case, sufficient optical feedback can be provided from the ring design. The spectral feature selection device 130 receives the light beam 110A from the master oscillator 800, allowing fine tuning of the spectral parameters, such as the center wavelength and bandwidth, of the light beam 110A at a relatively low output pulse energy. A power amplifier 810 receives the light beam 110A from the master oscillator 800 and amplifies the output to obtain the required power at the output for use in photolithography.

[0092] The master oscillator 800 includes a discharge chamber with two elongated electrodes, a laser gas that serves as the gain medium, and a fan to circulate the gas between the electrodes. A laser cavity is formed between a spectral feature selection device 130 on one side of the discharge chamber and an output coupler 815 on a second side of the discharge chamber to output a seed light beam 110A to a power amplifier 810.

[0093] Light source 805 may also include a line center analysis module (LAM) 820 that receives the output from output coupler 815, as well as one or more beam modifying optical systems 825 that modify the size and / or shape of the beam as needed. Line center analysis module 820 is an example of a type of measurement system within metrology system 170 that can be used to measure the wavelength (e.g., center wavelength) of the seed light beam.

[0094] The power amplifier 810 includes a power amplifier discharge chamber, and if it is a regenerative ring amplifier, the power amplifier also includes a beam reflector or beam redirecting device 830 that reflects the light beam back into the discharge chamber, thereby forming a circulation path. The power amplifier discharge chamber includes a pair of elongated electrodes, a laser gas that serves as a gain medium, and a fan to circulate the gas between the electrodes. The seed light beam 110A is amplified by repeated passes through the power amplifier 810. The beam modifying optical system 825 provides a way (e.g., a partially reflective mirror) to couple the seed light beam 110A and decouple part of the amplified radiation from the power amplifier to form the output light beam 110.

[0095] The laser gas used in the discharge chamber of master oscillator 800 and power amplifier 810 may be any gas suitable for producing a laser beam at about the required wavelength and bandwidth. For example, the laser gas may be argon fluoride (ArF), which emits at a wavelength of about 193 nm, or krypton fluoride (KrF), which emits at a wavelength of about 248 nm.

[0096] The line center analysis module 820 monitors the wavelength of the output (light beam 110A) of the master oscillator 800. The line center analysis module 820 may be located elsewhere within the light source 805, or it may be located at the output of the light source 805.

[0097] With reference to Figure 9, details regarding control system 185 relevant to aspects of the systems and methods described herein are provided. Control system 185 may include other features not shown in Figure 9. In general, control system 185 includes one or more of digital electronic circuitry, computer hardware, firmware, and software.

[0098] The control system 185 includes memory 900, which may be read-only memory and / or random access memory. Suitable storage devices for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, by way of example, semiconductor memory devices such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks. The control system 185 may also include one or more input devices 905 (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices 910 (such as a speaker or monitor).

[0099] The control system 185 includes one or more programmable processors 915 and one or more computer programs 920 tangibly embodied in a machine-readable storage device for execution by a programmable processor (such as processor 915). Each of the one or more programmable processors 915 is capable of executing programs of instructions to perform desired functions by processing input data and generating appropriate output. Generally, the processor 915 receives instructions and data from a memory 900. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits).

[0100] The control system 185 includes, among other components, a spectral feature analysis module 925, a lithography analysis module 930, a determination module 935, a light source operation module 950, a lithography operation module 955, and a beam preparation operation module 960. Each of these modules may be a set of computer programs executed by one or more processors, such as the processor 915. Additionally, any of the modules 925, 930, 935, 950, 955, 960 may have access to data stored in the memory 900.

[0101] The spectral feature analysis module 925 receives output from the metrology system 170. The lithography analysis module 930 receives information from the lithography controller 140 of the scanner 115. The decision module 935 receives output from the analysis modules (such as modules 925 and 930) and determines which one or more operation modules need to be activated based on the output from the analysis modules. The light source operation module 950 is connected to one or more of the light source 105 and the spectral feature selection device 130. The lithography operation module 955 is connected to the scanner 115, and specifically to the lithography controller 140. The beam preparation operation module 960 is connected to one or more components of the beam preparation system 112.

[0102] 9, the control system 185 can include other modules. Additionally, although the control system 185 is shown as a box in which all components appear to be co-located, the control system 185 can be comprised of components that are physically separate from one another. For example, the light source actuation module 950 can be physically co-located with the light source 105 or the spectral feature selection device 130.

[0103] In general, the control system 185 receives at least some information regarding the light beam 110 from the metrology system 170, and the spectral feature analysis module 925 performs analysis on the information to determine how to adjust one or more spectral features (e.g., bandwidth) of the light beam 110 provided to the scanner 115. Based on this determination, the control system 185 sends signals to the spectral feature selection device 130 and / or the light source 105 to control the operation of the light source 105 via the control module 350.

[0104] In general, the spectral feature analysis module 925 performs all of the analysis necessary to estimate one or more spectral features (e.g., wavelength and / or bandwidth) of the light beam 110. The output of the spectral feature analysis module 925 is an estimate of the spectral features.

[0105] The spectral feature analysis module 925 includes a comparison block connected to receive the estimated spectral features and also connected to receive the spectral feature target values. In general, the comparison block outputs a spectral feature error value representing the difference between the spectral feature target value and the estimated value. The decision module 935 receives the spectral feature error value and determines the best way to cause the correction of the system 100 to adjust the spectral features. Accordingly, the decision module 935 sends a signal to the light source actuation module 950, which determines how to adjust the spectral feature selection device 130 (or the light source 105) based on the spectral feature error value. The output of the light source actuation module 950 includes a set of actuator commands sent to the spectral feature selection device 130. For example, the light source actuation module 950 sends commands to the control module 350, which is connected to the actuation system in the device 330.

[0106] The control system 185 operates the light source 105 at a given repetition rate. More specifically, the scanner 115 sends trigger signals to the light source 105 on a pulse-by-pulse basis, and the time interval between these trigger signals may be arbitrary, but if the scanner 115 sends trigger signals at regular intervals, then the rate of these signals is the repetition rate. The repetition rate may be a rate requested by the scanner 115.

[0107] The repetition rate of the pulses generated by the power amplifier 810 is determined by the repetition rate at which the master oscillator 800 is controlled by the control system 185 under command from the controller 140 in the scanner 115. The repetition rate of the pulses output from the power amplifier 810 is the repetition rate seen by the scanner 115.

[0108] Prism 320 (or prisms 420, 520, 620, 720) can be used for coarse, broad, slow bandwidth control, whereas bandwidth can be controlled finely and narrowly, as well as faster, by controlling the timing difference between the activation of electrodes in MO 800 and PRA 810.

[0109] Other implementations are within the scope of the following claims.

[0110] For example, in other implementations, the prism 315 is attached to its own actuation system 315A that rotates the prism 315, and such rotation can be used to change the angle of incidence of the light beam 110A impinging on the grating 300 and provide fine control of the wavelength of the light beam 110A. The actuation system 315A may include a piezoelectric rotation stage as an actuator. In these other implementations, the prism 310 may be attached to an actuation system 310A that provides fine control of the bandwidth of the light beam 110A. Such an actuation system 310A may include a stepper motor rotation stage as an actuator.

Claims

1. 1. A spectral feature selection apparatus for a pulsed light source generating a pulsed light beam, comprising: a dispersive optical element interacting with the pulsed light beam; three or more refractive optical elements in a path of the pulsed light beam between the dispersive optical element and the pulsed light source; one or more actuation systems, each actuation system associated with a refractive optical element and configured to adjust the spectral features of the pulsed light beam by rotating the associated refractive optical element, at least one of the actuation systems being a high speed actuation system comprising a high speed actuator configured to rotate an associated refractive optical element about a rotation axis, the high speed actuator comprising a rotary stepper motor having a rotation shaft that rotates about a shaft axis parallel to the rotation axis of the associated refractive optical element; a control system connected to the one or more actuation systems, the control system being configured to send signals to the fast actuators to adjust the rotation shaft of the rotary stepper motor, thereby rotating the associated refractive optical element about its axis of rotation; An apparatus comprising:

2. The apparatus of claim 1 , wherein the fast actuator is configured to rotate the refractive optical element furthest from the dispersive optical element.

3. the pulsed light beam path is located in an XY plane of the device; The apparatus of claim 1 , wherein the rotary shaft of the rotary stepper motor has an axis that is parallel to a Z-axis of the apparatus, thereby rotating the associated refractive optical element about its axis of rotation that is parallel to the Z-axis of the apparatus.

4. the fast actuation system also includes a secondary actuator physically coupled to the associated refractive optical element; the secondary actuator is configured to rotate the associated refractive optical element about an axis; The apparatus of claim 1 , wherein the axis lies in the XY plane and also lies in the plane of a hypotenuse of the associated refractive optical element.

5. 10. The apparatus of claim 1, further comprising a position monitor that detects a position of the rotatable shaft of the rotary stepper motor.

6. 6. The apparatus of claim 5, wherein the control system is connected to the position monitor and configured to receive the detected position of the rotatable shaft and adjust the rotatable shaft if the received detected position is not within an acceptable position range.

7. The apparatus of claim 4 , wherein the position monitor is an optical rotary encoder.

8. The apparatus of claim 1 , wherein the rotating shaft is configured to rotate the refractive optical element associated with the high speed actuator about an offset axis that is offset from the axis of rotation.

9. The apparatus of claim 1 , wherein the shaft axis is configured to rotate approximately 360 degrees, thereby rotating the associated refractive optical element approximately 360 degrees.

10. The apparatus of claim 1 , wherein the refractive optical element associated with the fast actuator is fixedly coupled to the shaft axis.

11. the control system comprises a high speed controller coupled to the rotary stepper motor; The apparatus of claim 1 , wherein the adjustment of the rotating shaft is performed by the high speed controller.

12. 2. The apparatus of claim 1, wherein the rotation of the refractive optical element associated with the fast actuator causes a change in an expansion magnification of the pulsed light beam interacting with the dispersive optical element, the change in the expansion magnification of the pulsed light beam causing a change in a bandwidth of the pulsed light beam, a range of bandwidth due to the rotation of the refractive optical element associated with the fast actuator being at least 250 femtometers (fm).

13. 13. The apparatus of claim 12, wherein the rotation of the refractive optical element associated with the high-speed actuator for one unit of rotation of the rotatable shaft changes the bandwidth of the pulsed light beam by an amount less than a resolution of a bandwidth measuring device that measures the bandwidth of the pulsed light beam.

14. 2. The apparatus of claim 1, wherein the dispersive optical element is a diffractive optical element configured to interact with the pulsed light beam in a Littrow geometry such that a pulsed light beam diffracted from the diffractive optical element travels along a path of the pulsed light beam incident on the diffractive optical element.

15. the refractive optical elements are right-angle prisms, and the pulsed light beam is transmitted through the right-angle prisms such that the pulsed light beam changes its magnification as it passes through each right-angle prism; the right-angle prism farthest from the dispersion optical element has the smallest hypotenuse among the plurality of right-angle prisms; 2. The apparatus of claim 1, wherein each successive right angle prism closer to the dispersing optic has a hypotenuse that is larger than or the same size as the adjacent right angle prism further away from the dispersing optic.

16. 1. A spectral feature selection apparatus for a pulsed light source generating a pulsed light beam, the apparatus comprising: a dispersive optical element interacting with the pulsed light beam; a plurality of refractive optical elements in a path of the pulsed light beam between the dispersive optical element and the pulsed light source; a plurality of actuation systems, each actuation system associated with a refractive optical element and configured to adjust a spectral feature of the pulsed light beam by rotating the associated refractive optical element; At least one of the actuation systems comprises a high speed actuator including a rotary motor having a rotary shaft rotating about a shaft axis perpendicular to the plane of the device; the refractive optical element associated with the fast actuator is mounted to the fast actuator such that the refractive optical element rotates about an offset axis; The offset axis is parallel to the shaft axis, offset from the center of gravity, and offset from the shaft axis.

17. The apparatus of claim 16 , wherein the fast actuator rotates and linearly translates the associated refractive optical element about the offset axis.

18. The high speed actuator a first region mechanically linked to the rotating shaft at the shaft axis; a second region offset from the shaft axis along a direction perpendicular to the shaft axis and located in the plane of the device, such that the second region is not intersected by the shaft axis; and a lever arm having The apparatus of claim 16 , wherein the refractive optical element associated with the fast actuator is mechanically linked to the second region.

19. 17. The apparatus of claim 16, further comprising a control system connected to the plurality of actuation systems and configured to send a signal to each actuation system.

20. 20. The apparatus of claim 19, wherein the control system is configured to send a signal to the fast actuator to rotate and translate the refractive optical element associated with the fast actuator to adjust the spectral features of the pulsed light beam.

21. 21. The apparatus of claim 20, wherein the refractive optical element associated with the fast actuator is configured to rotate 15 degrees about the offset axis and reach a stable equilibrium position in about 50 milliseconds or less.

22. 17. The apparatus of claim 16, wherein the spectral features are one or more of a bandwidth and a wavelength of the pulsed light beam.

23. The apparatus of claim 16 , wherein the refractive optical element controlled by the fast actuator is devoid of an anti-reflective coating.

24. 1. A spectral feature selection device for a light source generating a light beam, comprising: a diffractive optical element interacting with the pulsed light beam in a Littrow configuration; A set of four or more right angle prisms, transmitting the pulsed light beam through a set of four or more right-angle prisms such that the pulsed light beam changes its magnification as the pulsed light beam passes through each right-angle prism; the pulsed light beam travels along a beam path and has a lateral extent that intersects with the hypotenuse of each prism such that the lateral extent of the pulsed light beam is contained within each of the hypotenuses of each prism; the right angle prism closest to the diffractive optical element has a hypotenuse with the longest length of the set; each successive right-angle prism further from the diffractive optical element has a hypotenuse having a length equal to or less than the hypotenuse of the adjacent right-angle prism closer to the diffractive optical element; the right angle prism closest to the diffractive optical element is positioned so that its right angle is away from the diffractive optical element; and a set of four or more right angle prisms, the region between the right angle prism farthest from the diffractive optical element and the diffractive optical element being free of any reflective optical element; at least two actuation systems, each actuation system associated with a right-angle prism of the set and configured to adjust spectral features of the pulsed light beam by rotating the associated right-angle prism relative to the pulsed light beam; An apparatus comprising:

25. the prism furthest from the diffractive optical element is associated with and movable by an actuation system; 25. The apparatus of claim 24, wherein the prism second closest to the diffractive optical element is associated with an actuation system and is movable.

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