CN113767336A

CN113767336A - Measuring device and method using mechanical filter

Info

Publication number: CN113767336A
Application number: CN202080031831.9A
Authority: CN
Inventors: P·A·麦肯齐; J·Q·奥德勒
Original assignee: ASML Holding NV
Current assignee: ASML Holding NV; ASML Netherlands BV
Priority date: 2019-04-29
Filing date: 2020-04-28
Publication date: 2021-12-07
Also published as: NL2025432A; KR20220004063A; TW202107210A; WO2020221709A1

Abstract

A metrology apparatus comprising: a diagnostic device configured to interact a diagnostic probe with a current target at a diagnostic region before the current target enters a target space; a detection device; and a control system in communication with the detection device. The detection device comprises: a light sensor having a field of view overlapping the diagnostic region and configured to sense light resulting from interaction between the diagnostic probe and a current target at the diagnostic region; and a mechanical filter between the diagnostic region and the light sensor. The mechanical filter includes a beam reducer and an optical mask defining an aperture positioned between the beam reducer and the light sensor. The control system is configured to estimate a property of the current target based on an output from the light sensor.

Description

Measuring device and method using mechanical filter

Cross Reference to Related Applications

This application claims priority from U.S. application No. 62/839,922 entitled METHOD APPARATUS AND METHOD USING MECHANICAL FILTER, filed on 29.4.2019, which is incorporated herein by reference in its entirety.

Technical Field

The disclosed subject matter relates to a metrology apparatus and method that uses a mechanical filter to distinguish between two types of light in an extreme ultraviolet light source.

Background

In semiconductor lithography (or photolithography), the fabrication of Integrated Circuits (ICs) involves performing various physical and chemical processes on a semiconductor (e.g., silicon) substrate (also referred to as a wafer). A lithographic exposure apparatus or scanner is a machine that applies a desired pattern onto a target portion of a substrate. The wafer is irradiated with a beam extending in an axial direction, and the wafer is fixed to the stage such that the wafer generally extends along a transverse plane substantially perpendicular to the axial direction. The light beam may have a wavelength in the Ultraviolet (UV) range, for example, from about 10 nanometers (nm) to about 400nm, and particularly in the deep UV (duv) range, from about 100nm to about 400nm, or in the Extreme Ultraviolet (EUV) range, less than about 100nm (or about 50nm or less, and including 13 nm). The beam propagates in an axial direction (orthogonal to a transverse plane along which the wafer extends).

Methods of generating EUV light include, but are not necessarily limited to, converting a material having an element (e.g., xenon, lithium, or tin) into an emission line in the EUV range in the plasma state. In one such method, commonly referred to as laser produced plasma ("LPP"), the desired plasma can be produced by irradiating the target material, for example, in the form of droplets, plates, ribbons, streams or clusters of material, with an amplified beam that can be referred to as a drive laser. For this process, plasma is typically generated in a sealed vessel (e.g., a vacuum chamber) and monitored using various types of metrology equipment.

Disclosure of Invention

In some general aspects, a metrology apparatus comprises: a diagnostic device configured to interact a diagnostic probe with a current target at a diagnostic region before the current target enters a target space; a detection device; and a control system in communication with the detection device. The detection device comprises: a light sensor having a field of view overlapping the diagnostic region and configured to sense light resulting from interaction between the diagnostic probe and a current target at the diagnostic region; and a mechanical filter between the diagnostic region and the light sensor. The mechanical filter includes a beam reducer and an optical mask defining an aperture positioned between the beam reducer and the light sensor. The control system is configured to estimate a property of the current target based on an output from the light sensor.

Implementations may include one or more of the following features. For example, the mechanical filter may be configured to angularly separate diagnostic light emitted from the diagnostic region from non-diagnostic light emitted from the target space. The diagnostic light may be generated by interaction between the current target and the diagnostic probe at the diagnostic region. The non-diagnostic light may include light emitted from a plasma generated by a previous target in the target space. The lateral extent of the aperture may be greater than or about the same as the lateral extent of the diagnostic light in the plane of the photomask, and the lateral extent of the photomask may be greater than or about the same as the lateral extent of the non-diagnostic light in the plane of the photomask. The optical mask may be positioned such that non-diagnostic light emitted from the target space is substantially blocked by the optical mask and diagnostic light substantially passes through the aperture.

The mechanical filter may comprise an optical collimator between the diagnostic region and the beam reducer. The beam reducer may be an afocal beam reducer and may be configured in combination with an optical collimator to project a finite object to infinity. The components of the optical collimator and the beam reducer closest to the optical collimator, which have a positive focal length, may be integrated into a single refractive element. The beam reducer may be configured to maintain a collimated state of the light.

The light sensor may include one or more of: photodiodes, phototransistors, photoresistors, photomultiplier tubes, multi-cell photo-receivers, quad-cell photo-receivers, and cameras.

The diagnostic probe may include at least one diagnostic light beam, and the light sensor is configured to sense diagnostic light resulting from interaction between the current target and the at least one diagnostic light beam. The diagnostic light may include a diagnostic light beam reflected from, scattered from, or blocked by the current target.

The detection means may comprise one or more of a spectral filter and a polarisation filter.

The diagnostic probe may include a first diagnostic beam and a second diagnostic beam, each configured to interact with the current target before the current target enters the target space, each interaction occurring at a different region and at a different time.

The beam reducer may comprise a refractive telescope, a reflective telescope or a catadioptric telescope. The refractive telescope may comprise: a positive focal length lens arrangement and a negative focal length lens arrangement separated by a sum of focal lengths of the positive focal length lens arrangement and the negative focal length lens arrangement; or a pair of positive focal length lens arrangements separated by the sum of the focal lengths of the pair of positive focal length lens arrangements.

The beam reducer may be configured to reduce the lateral dimension of the incident light by at least five times, at least ten times, at least twenty times, or about ten times.

The aperture may comprise a circular opening, an elliptical opening, a polygonal opening, or an elongated slit opening.

The detection device may be positioned outside of a chamber of an Extreme Ultraviolet (EUV) light source, the diagnostic region may be inside of the chamber, and the detection device may receive light through an optical window in a wall of the chamber. The distance between the diagnostic region and the optical window may be about 200-500 times the size of the distance between the diagnostic region and the target space.

The detection means may comprise a focusing lens at the output of the aperture, the focusing lens being configured to focus the sensed light onto the light sensor.

The apertures have a range of at least 2 millimeters (mm). The aperture may be positioned to receive the diagnostic light at a location where the diagnostic light is collimated or non-converging and non-diverging.

In another general aspect, a method of metrology, comprises: interacting a diagnostic probe with a current target at a diagnostic region before the current target enters a target space; collecting diagnostic light resulting from interaction between a diagnostic probe at a diagnostic region and a current target, the collecting further comprising collecting non-diagnostic light resulting from a target space; collimating the diagnostic light and the non-diagnostic light; angularly separating the diagnostic light and the non-diagnostic light from each other, including reducing the lateral extent of the diagnostic light and the non-diagnostic light; sensing the diagnostic light at a sensing region after the diagnostic light and the non-diagnostic light have been angularly separated, the sensing region being laterally offset from a non-sensing region traversed by the non-diagnostic light; and estimating a property of the current target based on the sensed diagnostic light.

Implementations may include one or more of the following features. For example, the diagnostic probe may interact with the current target at the diagnostic region by: interacting one or more diagnostic beams with a current target at a diagnostic region; and the diagnostic light may be collected by: one or more diagnostic light beams that have been reflected from, scattered from, or blocked by the present target at the diagnostic region are collected.

The metrology method may further include filtering the diagnostic light based on spectral properties of the diagnostic light and a polarization state of the diagnostic light.

The diagnostic region may be inside a hermetic chamber of an Extreme Ultraviolet (EUV) light source, and collecting the diagnostic light further comprises collecting the non-diagnostic light may comprise: diagnostic light comprising non-diagnostic light transmitted through an optical window in a wall of the chamber is received.

The lateral extent of the diagnostic light and the non-diagnostic light may be reduced by: the lateral extent of the diagnostic light and the non-diagnostic light is reduced by at least five times, at least ten times, at least twenty times, or about ten times.

The metrology method may further comprise blocking or redirecting non-diagnostic light at the non-sensing region. The lateral extent of the diagnostic light and the non-diagnostic light may be reduced by one or more of: refracted and reflected light.

The measurement method may further comprise focusing the diagnostic light on the sensing region.

The lateral extent of the diagnostic light and the non-diagnostic light may be reduced by: maintaining the collimated state of the diagnostic light and the non-diagnostic light.

The measuring method can further comprise the following steps: after the diagnostic light and the non-diagnostic light are separated at an angle to each other and before the diagnostic light is sensed, the diagnostic light is passed through an aperture of the optical mask, the aperture having an extent greater than an extent of the diagnostic light.

Drawings

FIG. 1 is a schematic view of a metrology device including a detection device having a mechanical filter for collecting diagnostic and non-diagnostic light generated within an environment, diagnostic light generated from a target in a diagnostic region, and non-diagnostic light generated from a target in a target space different from the diagnostic region;

FIG. 2A is a schematic diagram of an implementation of a mask that may be used in the mechanical filter of FIG. 1;

FIG. 2B is a schematic diagram of an implementation of a mask that may be used in the mechanical filter of FIG. 1;

fig. 3 is a schematic diagram of an implementation of the detection apparatus of fig. 1, including a beam reducer designed as a refractive galilean telescope.

FIG. 4 is a schematic diagram of an implementation of the detection apparatus of FIG. 1 including a beam reducer designed as a refractive Keplerian telescope;

FIG. 5 is a schematic diagram of an implementation of the metrology apparatus of FIG. 1 in which the detection apparatus includes one or more spectral filters and polarization filters.

FIG. 6A is a schematic and block diagram of an implementation of a diagnostic device that generates a single diagnostic beam;

FIG. 6B is a schematic and block diagram of an implementation of a diagnostic device that produces two diagnostic light beams from a single light source;

FIG. 6C is a schematic and block diagram of an implementation of a diagnostic device that produces two diagnostic light beams from respective light sources;

FIG. 7 is a schematic diagram of an implementation of the metrology device of FIG. 1 implemented in an Extreme Ultraviolet (EUV) light source;

FIG. 8 is a block diagram of an implementation of a control device of the metrology device of FIG. 1.

FIG. 9 is a schematic diagram of an implementation of a lithographic apparatus that receives EUV light output from the EUV light source of FIG. 7.

FIG. 10 is a flow chart of a process performed by the metrology device of FIG. 1 to estimate one or more attributes of a current target;

FIG. 11 is a schematic diagram of an implementation of the detection apparatus of FIG. 1 including a beam reducer designed as a refractive Galilean telescope, and in which the optical collimator and the positive focal length lens of the beam reducer are integrated into a single refractive element;

FIG. 12 is a schematic diagram of an implementation of the metrology apparatus of FIG. 1 in which a diagnostic probe provides backlighting to a target such that a shadow of the target is formed from the target occluding at least a portion of the diagnostic probe;

FIG. 13 is a schematic diagram of an implementation of the detection apparatus of FIG. 1 including a beam reducer designed to reflect off-axis telescopes;

FIG. 14 is a schematic diagram of an implementation of the detection apparatus of FIG. 1 including a beam reducer designed as a catadioptric off-axis telescope; and

FIG. 15 is a schematic diagram of an implementation of the metrology device of FIG. 1 in which the mechanical filter includes a mask that blocks diagnostic light while allowing non-diagnostic light to pass to the sensor.

The applicant notes that the figures may not be drawn to scale. For example, the distance between the optical elements in the schematic may be greater or less than that shown.

Detailed Description

Referring to FIG. 1, a metrology device 100 is configured to estimate one or more attributes of a current target 105c, which current target 105c travels along a trajectory TR toward a target space 110 within an environment 115. The metrology device 100 is configured to estimate at least one attribute of the current target 105c, such as speed (speed), position, velocity (velocity), direction, by analyzing light (referred to as diagnostic light 120) generated due to interaction between the one or more diagnostic probes 125 and the current target 105c before the current target 105c enters the target space 110. However, the non-diagnostic light 122 is generated simultaneously and in the same vicinity as the diagnostic light 120. The non-diagnostic light 122 may saturate the light sensor 130 within the metrology device 100 or may interfere with the operation of the light sensor 130 in the metrology device 100. Thus, the non-diagnostic light 122 may reduce the accuracy performed by the metrology device 100, causing errors in the estimated properties of the current target 105 c.

The metrology device 100 is able to more efficiently and accurately estimate the properties of the current target 105c because it is able to more efficiently distinguish between diagnostic light 120 and non-diagnostic light 122. To this end, the metrology device 100 includes a detection device 135, the detection device 135 including an optical sensor 130, and a mechanical filter 140 between a diagnostic region 145 (where the current target 105c interacts with the diagnostic probe 125) and the optical sensor 130. The mechanical filter 140 includes a beam reducer 150 and an opaque photomask 155, the photomask 155 defining a light transmissive aperture 160. An aperture 160 is positioned between the beam reducer 150 and the light sensor 130. To properly sense the diagnostic light 120, the light sensor 130 is positioned such that its field of view overlaps the diagnostic region 145. The metrology device 100 further includes a diagnostic device 165 and a control system 170, the diagnostic device 165 generating a diagnostic probe 125, the control system 170 communicating with the detection device 135. The control system 170 receives the output from the sensor 130 and performs an analysis on the output to estimate one or more properties of the current target 105 c.

The mechanical filter 140 includes an optical collimator 142, the optical collimator 142 forming respective collimated beams from the diagnostic light 120 and the non-diagnostic light 122, and then a beam reducer 150 optically reduces the size of these collimated beams to form the reduced-size collimated

beams

121, 123, respectively. The beam reducer 150 increases the angular separation between the images produced by the collimated diagnostic beam 121 and the collimated non-diagnostic beam 123. The non-diagnostic light 122 originates from a location outside of the location of the current target 105c (producing the diagnostic light 120). For example, the diagnostic light 120 originates from the diagnostic region 145, while the non-diagnostic light 122 originates from outside the diagnostic region 145, such as from the target space 110. Thus, the non-diagnostic light 122 enters the mechanical filter 140 at an angle that is slightly different from the angle at which the diagnostic light 120 enters the mechanical filter 140. This fact may be exploited in the design of the mechanical filter 140, and the mechanical filter 140 may further separate the images produced by the diagnostic light 120 and the non-diagnostic light 122 by increasing the angular separation between the respective collimated

light beams

121, 123. The increase in angular separation allows for greater differentiation between the two images at the aperture 160 after the beam has traveled the length of the optical path 152 between the beam reducer 150 and the mask 155. Thus, in this implementation, mask 155 is positioned such that aperture 160 allows diagnostic light beam 121 (formed from diagnostic light 120) to reach sensor 130, while mask 155 blocks non-diagnostic light beam 123 (formed from non-diagnostic light 122) from reaching sensor 130.

The optical collimators 142 form respective collimated beams for input to the beam reducer 150. The collimated beam is a beam with a beam divergence low enough that the beam radius does not change significantly over a medium propagation distance. In this case, the beam radius of each collimated beam output from the optical collimator 142 does not vary significantly over the distance extending to the sensor 130 without any additional beam shaping (and therefore without the beam reducer 150). For example, the beam radius of the collimated beam output from the optical collimator 142 varies by less than 1%, less than 5%, or less than 10% (without any intermediate optical elements) over the distance to the sensor 130 along the Z-direction. In some examples, the distance between the optical collimator 142 and the sensor 130 in the Z direction is on the order of one meter, but it may be shorter or longer, depending on the design of the beam reducer 150.

The beam reducer 150 is an afocal system (i.e., a system without a focal point), meaning that the beam reducer 150 does not produce a net convergence or divergence of the collimated beam input to the beam reducer 150. That is, the beam reducer 150 may be considered to have an infinite effective focal length to maintain or maintain the collimated state of the beam output from the optical collimator 142. This type of system may be created with a pair of optical elements where the distance d between the elements is equal to the sum of the focal lengths f1, f2 of each element (i.e., d ═ f1+ f 2). While an afocal system does not change the divergence of the collimated beam, it changes the width of the beam, increasing or decreasing its magnification. In general, the beam reducer 150 may reduce the lateral dimension (i.e., the dimension in the XsYs plane) of the collimated beam output from the optical collimator 142 by at least five times, at least ten times, or at least twenty times. In some implementations, the beam reducer 150 reduces the lateral dimension of the collimated beam by a factor of about 10 or about 20.

The beam reducer 150 may be, for example, a refractive telescope, a reflective telescope, or a catadioptric telescope.

The refractive telescope uses refractive optics (such as lenses or prisms) to form an image of the respective collimated beam at the plane of the mask 155. In some implementations, the refractive telescope is a galilean telescope that includes a positive focal length lens arrangement and a negative focal length lens arrangement separated by a sum of their focal lengths. In other implementations, the refractive telescope is a keplerian telescope that includes a pair of positive focal length lens arrangements separated by the sum of their focal lengths. Examples of refractive telescopes for use as the beam reducer 150 are discussed below with reference to fig. 3 and 4.

The reflective telescope includes a single curved mirror or combination of curved mirrors that reflect the collimated beam output from the optical collimator 142 and form a corresponding image at the plane of the mask 155. For example, in some implementations, the reflective telescope is a Gregorian (Gregorian), newton, or Cassegrain (and variants thereof) telescope. In other implementations, the reflective telescope is an off-axis design, such as Herschel (Herschelian) or Schiefspieger (which is a variation of Cassegrain). One example of a reflective telescope is shown and described with respect to FIG. 13.

A catadioptric telescope is a type of catadioptric telescope that combines refraction and reflection in one optical system, typically implementing lenses (i.e., diopters) and curved mirrors (i.e., refractive indices). For example, in some implementations, the catadioptric telescopes include Schmidt-Cassegrain (Schmidt-Cassegrain) telescopes and macsutov-Cassegrain (Maksutov-Cassegrain) telescopes. In other implementations, the catadioptric telescope is a catadioptric variant of a heschel telescope (which uses both lenses and mirrors), or an off-axis variant of a Stevick-Paul telescope. An example of a catadioptric telescope is shown and described with respect to FIG. 14.

The environment 115 may be a vacuum environment within a chamber of an Extreme Ultraviolet (EUV) light source, such as the EUV light source discussed below with reference to fig. 7. In some implementations, the detection device 135 is placed outside of the chamber of the EUV light source with the diagnostic region 145 inside of the chamber, and the detection device 135 receives the diagnostic light 120 and the non-diagnostic light 122 through optical windows in the walls of the chamber. The optical window is transparent to the wavelength of the diagnostic light 120. This will be discussed below with reference to fig. 7.

As discussed with reference to fig. 7, the EUV light source provides EUV light to an output device, which may be a lithographic device. EUV light is formed in the environment 115 by converting the target 105 into a plasma that emits EUV light when the target 105 reaches the target space 110, and the EUV light is collected and transmitted to the lithographic apparatus. The target 105 reaching the target space 110 is converted by interacting the target 105 with radiation pulses in the target space 110 that provide the target 105 with sufficient energy to convert them into plasma. A continuous stream of targets 106 (each generally designated 105) is directed from the target supply 175 along a trajectory TR toward the target space 110.

The trajectory TR extends along a direction that may be considered a target (or axis) direction that lies in a three-dimensional X, Y, Z coordinate system defined by the physical aspects of the environment 115. Accordingly, the X, Y, Z coordinate system may be defined by walls or points of a chamber defining the environment 115. The axial direction of each target 105 generally has a component parallel to the-X direction of the coordinate system of the environment 115. The axial direction of each target 105 may also have components in one or more of the Y and Z directions that are perpendicular to the-X direction. Furthermore, each target 105 released by target provisioning device 175 may have a slightly different actual trajectory, and the trajectory depends at least in part on the physical properties of environment 115 and at the time target 105 is released.

On the other hand, the detection device 135 defines a local three-dimensional Xs, Ys, Zs coordinate system, and this local coordinate system may be defined by the image plane of the sensor 130.

Each target 105 includes components that emit EUV light when converted to plasma. These targets 105 travel (e.g., ballistically) from the generation area (such as from the target supply 175) to the target space 110. Attributes of the current target 105c, such as speed (speed), position, speed (velocity), direction, arrival or motion, are estimated by the probe current target 105c as it travels along the trajectory TR with the diagnostic probe 165 generated by the diagnostic system 165, the diagnostic light 120 resulting from the interaction between the diagnostic probe 125 and the current target 105c is detected or sensed, and the detected diagnostic light 120 is analyzed.

As described above, non-diagnostic light 122 may also be present, and this non-diagnostic light 122 may interfere with accurate estimation of the properties of the current target 105 c. The non-diagnostic light 122 may include broadband optical radiation emitted by a plasma generated by one or more previous targets 105p entering the target space 110 prior to or simultaneously with the current target 105c interacting with the diagnostic probe 125. Further, the intensity of the non-diagnostic light 122 may be much greater than the intensity of the diagnostic light 120.

The non-diagnostic light 122 may include, for example, EUV light emitted from plasma of the previous target 105p, light having a wavelength range that overlaps with the wavelength of the diagnostic light 120, and/or light that is present and has a wavelength range that includes a wavelength range that may be detected by the sensor 130.

On the other hand, the diagnostic light 120 results from the interaction between the diagnostic probe 125 and the current target 105c, and the diagnostic light 120 has a spectral bandwidth that is much narrower than the spectral bandwidth 122 of the non-diagnostic light. For example, the spectral bandwidth of the diagnostic light 120 may be hundreds of times lower than the total spectral bandwidth of the non-diagnostic light 122. In some implementations, such as shown in fig. 6A-6C, the diagnostic light 120 is generated by a portion of the diagnostic probe 125 that is reflected or scattered from the current target 105C.

In general, the sensors 130 may include one or more of the following: photodiodes, phototransistors, photoresistors, and photomultiplier tubes. In other implementations, the sensor 130 includes one or more thermal detectors, such as a pyroelectric detector, a bolometer, or a calibrated charge-coupled device (CCD) or CMOS. In other implementations, the sensor 130 includes a multi-unit light receiver, a four-unit light receiver, or a camera.

As shown in the implementation of fig. 1, the optical mask 155 is positioned such that the collimated non-diagnostic light beam 123 (produced by the non-diagnostic light 122) is substantially or mostly blocked, while the collimated diagnostic light beam 121 substantially passes through the aperture 160. Another implementation is shown and discussed with respect to fig. 15, in which the collimated non-diagnostic light beam 123 is substantially passed through the aperture and the collimated diagnostic light beam 121 is substantially blocked by the aperture.

Referring to fig. 2A, in some implementations, mask 155 is a mask 255A defining an aperture 260A having a circular shape in the XsYs plane. In other implementations, such as shown in fig. 2B, the mask 155 is a mask 255B defining an aperture 260B having a slit shape that is not rotationally symmetric and has a greater extent in the Ys direction than in the Xs direction. The design of fig. 2B is useful in cases where the collimated diagnostic beam 121 is moved, oscillated, or perturbed so that its image plane moves in the Ys direction. The range in the Ys direction accommodates such fluctuations in the image plane of the collimated diagnostic beam 121. The mask 155 may be configured to define other shapes of the aperture 160 in the image plane (XsYs plane), such as an elliptical aperture and a polygonal opening.

To properly allow the collimated diagnostic beam 121 to pass through the sensor 130, the aperture 160 along the XsYs plane is at least as large as the lateral extent of the collimated diagnostic beam 121 in the XsYs plane. Furthermore, in order to properly block the collimated non-diagnostic light beam 123, the extent of the optical mask 155 along the XsYs plane should be at least as large as the lateral extent of the collimated non-diagnostic light beam 123 in the XsYs plane. This means, referring to fig. 2A, the extent 261A of the aperture 260A in the XsYs plane is as large as the lateral extent of the collimated diagnostic beam 121 in the XsYs plane, and the extent 256A of the mask 255A is large enough to block the full extent of the collimated non-diagnostic beam 123 in the XsYs plane. As another example, referring to fig. 2B, the shortest extent 261B of the aperture 260B in the XsYs plane is as large as the lateral extent of the collimated diagnostic beam 121 in the XsYs plane, and the extent 256B of the mask 255B is large enough to block the full extent of the collimated non-diagnostic beam 123 in the XsYs plane.

In some implementations, the extent 261A, 261B of the

respective apertures

260A, 260B in the XsYs plane is at least 2 millimeters (mm) or about 4 mm. The range of the collimated diagnostic beam 121 in the XsYs plane at the

aperture

260A or 260B is approximately 3 mm. In some implementations, the

extent

256A, 256B of the

respective masks

255A, 255B is greater than 3 mm.

Unlike spatial filters where light is focused at the mask aperture, in the mechanical filter 140, the light (diagnostic light beam 121) passing through the aperture 160 (e.g.,

aperture

260A or 260B) is collimated and therefore has a greater lateral extent than the light focused at the aperture of the spatial filter. Thus, the size of the aperture 160 (e.g.,

aperture

260A or 260B) in the XsYs plane may be much larger than the apertures used in the spatial filter to block the focused non-diagnostic light and pass the focused diagnostic light. Thus, unwanted particles, such as dirt in environment 115, have a much smaller effect on the performance of the pores 160, such as

pores

260A or 260B, than do these particles. For example, the size of the apertures 160 in the XsYs plane is on the order of millimeters and much larger than the size of the unwanted particles. On the other hand, the typical size of the apertures of a spatial filter may be a fraction of a millimeter (e.g., in the range of 100 μm), while the unwanted particles may have comparable sizes. Thus, interference between unwanted particles in the mechanical filter 140 and the collimated beam 121 is reduced when compared to a spatial filter.

In addition, because the tolerance for relative positioning between the collimated diagnostic beam 121 and the 4mm aperture 160 (or 260A, 260B) is on the order of 0.2-0.4mm, it is easier to direct the collimated diagnostic beam 121 through the aperture 160(260A, 260B). On the other hand, the tolerance for the relative positioning between the collimated diagnostic beam 121 and the 100 μm aperture of the spatial filter is on the order of 5-10 μm.

Referring to fig. 3, an implementation 335 of the detection apparatus 135 is shown. In this illustration, the coordinate system XsYsZs of detection device 335 is such that Ys is out of the page and Zs extends perpendicular to the imaging area of sensor 330. Detection device 335 includes an optical collimator 342 that produces a respective collimated beam for each of diagnostic light 120 and non-diagnostic light 122 for input to beam reducer 350. As described above, without the beam reducer 350, the beam radius of each collimated beam will not vary significantly from within the distance extending from the optical collimator 342 to the sensor 330. The optical collimator 342 in this example is a doublet lens (two

lenses

342a, 342 b). The focal length or radius of curvature of doublet 342 is selected such that the original curved wavefronts of diagnostic light 120 and non-diagnostic light 122 become flat or substantially flat at least a distance that extends the length of sensor 330.

In this implementation, the beam reducer 350 is designed as a Galileo-type refractive telescope. The beam reducer 350 optically reduces the size of the collimated beam output from the optical collimator 342 to form reduced-size collimated

beams

121, 123, respectively. The beam reducer 350 includes a positive focal length lens arrangement 351 (which may be a converging lens arrangement including one or more of a positive biconvex lens, a plano-convex lens, or a meniscus lens) positioned on the input side. The beam reducer 350 includes a negative focal length lens arrangement 353 (which may be a diverging lens arrangement including a concave lens) on the output side. Positive focal length lens arrangement 351 and negative focal length lens arrangement 353 are separated by the sum of their focal lengths. The converging lens arrangement 351 in this example is a compound lens (having a convex lens 351a and a concave lens 351b) which can help correct for distortions in the beam. The beam reducer 350 has no intermediate focus (no focus between the converging lens arrangement 351 and the diverging lens arrangement 353). Although not required, in this implementation, diverging lens arrangement 353 includes a secondary lens 354 between converging lens 351 and diverging lens 353. Secondary lens 354 may be used in conjunction with diverging lens arrangement 353 to collimate the light beam from positive focal length lens arrangement 351. Secondary lens 354 may be a positive focal length lens such as a meniscus lens (as shown), a biconvex lens, or a plano-convex lens. In general, the beam reducer 350 may reduce the lateral dimension (i.e., the dimension in the XsYs plane) of the collimated beam output by the optical collimator 342 by at least five times, at least ten times, or at least twenty times.

Beam reducer 350 outputs reduced collimated diagnostic beam 121 and reduced collimated non-diagnostic beam 123, and then travels the length of optical path 352 to mask 355. The longer the optical path 352, the greater the separation between the respective images from these

beams

121, 123 at the mask 355. In this implementation, mask 355 is placed such that aperture 360 allows diagnostic beam 121 (formed from diagnostic beam 120) to pass to sensor 330, while mask 355 blocks non-diagnostic beam 123 (formed from non-diagnostic light 122) from passing to sensor 330. The collimated diagnostic beam 121 that has passed through aperture 360 may be focused by a converging lens 357 onto the imaging area of sensor 330.

Referring to fig. 4, another implementation 435 of the detection apparatus 135 is shown. In this illustration, the coordinate system XsYsZs of the detection device 435 is aligned with the page. The detection device 435 includes an optical collimator 442 that produces, for each of the diagnostic light 120 and the non-diagnostic light 122, a respective collimated beam for input to a beam reducer 450 of the detection device 435. As described above, the beam radius of each collimated beam output from optical collimator 442 does not change significantly over the distance extending to sensor 430. The optical collimator 442 in this example is similar to the optical collimator 342 and includes a doublet (two

lenses

442a, 442 b). The focal length or radius of curvature of doublet 442 is selected such that the original curved wavefronts of diagnostic light 120 and non-diagnostic light 122 become flat or substantially flat at least a distance that extends the length of sensor 430.

In this implementation, the beam reducer 450 is designed as a Keplerian type refractive telescope. The beam reducer 450 optically reduces the size of the collimated beam output from the optical collimator 442 to form reduced-size collimated

beams

121, 123, respectively. The beam reducer 450 comprises an input positive focal length lens arrangement 451 (which may be a converging lens arrangement comprising one or more of a double convex lens, a plano-convex lens or a meniscus lens) at the input side. The beam reducer 450 includes an output positive focal length lens arrangement 453 (which may be a converging lens arrangement including one or more of a biconvex lens, a plano-convex lens, or a meniscus lens) at the output side. For example, positive focal length lens device 453 is shown in fig. 4 as an aspheric lens element. The positive focal length lens device 453 may be a compound lens group. The positive focal

length lens devices

451, 453 are separated by the sum of their focal lengths. The converging lens arrangement 451 in this example is a compound lens (with a convex lens 451a and a concave lens 451b) that can help correct for distortions in the beam. An intermediate focus IF (or intermediate focal plane IF) is between the input converging lens arrangement 451 and the output converging lens arrangement 453. In general, beam reducer 450 may reduce the lateral dimension (i.e., the dimension in the XsYs plane) of the collimated beam output by optical collimator 442 by at least five times, at least ten times, or at least twenty times. The extent of beam reducer 450 in the Zs direction is often greater than the extent of beam reducer 350 in the Zs direction, and thus the space requirements may determine which design of

beam reducer

350 or 450 is more appropriate. Furthermore, beam reducer 350 may be a more suitable design IF the power of diagnostic light 120 or non-diagnostic light 122 is too high to apply an intermediate focus IF (such as present in beam reducer 450).

The beam reducer 450 outputs a reduced collimated diagnostic beam 121 and a reduced collimated non-diagnostic beam 123, and then travels the length of the optical path 452 to the mask 455. The longer the light path 452, the greater the separation between the respective images from these

beams

121, 123 at the mask 455. In this implementation, the mask 455 is positioned such that the aperture 460 allows the diagnostic light beam 121 (formed by the diagnostic light 120) to pass to the sensor 430, while the mask 455 blocks the non-diagnostic light beam 123 (formed by the non-diagnostic light 122) from passing to the sensor 430. The collimated diagnostic light beam 121 that has passed through aperture 460 can be focused through a converging lens 457 onto the imaging area of sensor 430.

Referring to fig. 5, in other implementations, the detection device 135 is a detection device 535 that further includes one or more spectral filters 543 and polarization filters 544, which may be arranged in series or in parallel with the mechanical filter 140. The spectral filter 543 is an optical filter, such as a band-pass filter, that passes light in a specific wavelength range. The polarization filter 544 is an optical filter that passes light having a specific polarization. For example, the diagnostic light 120 may have a different polarization depending on the polarization of the diagnostic probe 125, while the non-diagnostic light 122 may be unpolarized. Accordingly, the polarization filter may select the polarization of the diagnostic light 120 to pass through.

Referring to fig. 6A, in some implementations, the diagnostic device 165 is designed as a diagnostic device 665A. As one or more diagnostic probes 125, the diagnostic device 665A generates a single probe light beam 625A from the light source 626A. The probe beam 625A is directed as a light curtain to traverse the trajectory TR at the location x, such that each of the targets 105 traverse the light curtain on their way to the target space 110. Light source 626A produces a single light beam 611A that is directed through one or more optical elements 627A (such as mirrors, lenses, apertures, and/or filters) that modify light beam 611A to form a single probe light beam 625A.

The light source 626A may be a solid state laser, such as a YAG laser, which may be a neodymium-doped YAG (Nd: YAG) laser operating at 1070nm and 50W power. In this example, when the current target 105c passes the probe light beam 625A at time t, at least some of the probe light beam 625A reflects or scatters from the current target 105c to form diagnostic light 620A, which diagnostic light 620A is detected by the detection device 135. The control system 170 uses information from the sensors 130 to estimate movement properties of the current target 105, which may be used to estimate the arrival time of the current target (which may be the current target 105c or a subsequent target) at the target space 110. This estimate may be used to adjust the characteristics of the radiation pulses directed to the target space 110 to ensure that the radiation pulses interact with the current target in the target space 110. The control system 170 may also rely on some assumptions about the path of the current target to perform calculations to estimate the arrival time of the current target at the target space 110.

Probe beam 625A can be a Gaussian beam, such that its transverse profile of light intensity can be described by a Gaussian function. The focal points or beam waists of probe beam 625A may be configured to overlap in the track TR or-X direction. In addition, optical element 627A may include refractive optics that ensure that the focal point (or beam waist) of probe beam 625A overlaps track TR.

Referring to fig. 6B, in some implementations, the diagnostic device 165 is designed as a diagnostic device 665B. The diagnostic device 665B generates two probe beams 625B _1 and 625B _2 as one or more diagnostic probes 125. Probe light beam 625B _1 is directed as a first light curtain across trajectory TR at a first location (e.g., location X1 along the X-axis) such that each of targets 105 passes through the first light curtain on its way to target space 110. The probe light beams 625B _2 are directed as second light curtains through the trajectory TR at a second location (e.g., location X2 along the X-axis) such that each of the targets 105 passes through the second light curtain on its way to the target space 110 and after having passed through the first light curtain. Probe beams 625B _1, 625B _2 are separated at track TR by a distance Δ d, which is equal to x2-x 1. The dual light curtain diagnostic device 665B can be used to determine not only the location and arrival information of the target 105 on its way to the target space 110 through the second light curtain, but also after having passed through the first light curtain. Probe beams 625B _1, 625B _2 are separated at track TR by a distance Δ d, which is equal to x2-x 1. The double screen diagnostic device 665B may be used to determine not only the location and arrival information of the target 105, but also the speed (speed) or velocity (velocity) of the target 105.

In some implementations, diagnostic device 665B includes a single light source 626B that generates a single light beam 611B and one or more optical elements 627B that receives the single light beam and splits light beam 611B into two probe light beams 625B _1, 625B _ 2. Furthermore, optical element 627B may include components for directing probe beams 625B _1, 625B _2 along trajectory TR to respective positions x1, x 2.

In some implementations, optical assembly 627B includes a beam splitter that splits a single light beam from single light source 626B into two probe light beams 625B _1, 625B _ 2. For example, the beam splitter may be a dielectric mirror, a beam splitter cube, or a polarizing beam splitter. One or more of optical components 627B may be reflective optics positioned to redirect either or both of probe light beams 625B _1, 625B _2 such that both probe light beams 625B _1, 625B _2 are directed toward track TR.

In other implementations, optical assembly 627B includes beam splitting optics (such as diffractive optics or binary phase diffraction gratings, birefringent crystals, intensity beam splitters, polarizing beam splitters, or dichroic beam splitters) and refractive optical elements (such as focusing lenses). Light beam 611B is directed through splitting optics that splits light beam 611B into two beams that travel in different directions and are directed through refractive optics to produce probe light beams 625B _1, 625B _ 2. Separation optics may separate beam 611B such that probe beams 625B _1, 625B _2 are separated by a set distance (e.g., 0.65mm in the X direction) at track TR. In this example, x2-x1 is 0.65 mm. Furthermore, refractive optics may ensure that the focal point (or beam waist) of each of probe beams 625B _1, 625B _2 overlaps track TR.

As shown in this example, probe beams 625B _1, 625B _2 are directed such that they intersect trajectory TR at different positions X1, X2, but typically intersect at substantially similar angles with respect to the X-axis. For example, probe beams 625B _1, 625B _2 are oriented at about 90 relative to the X-axis. In other implementations, separation optics and refractive optics may be used to adjust the angle at which probe beams 625B _1, 625B _2 are oriented relative to the X-axis such that they fan out toward track TR and intersect track TR at different and distinct angles. For example, probe beam 625B _1 can intersect track TR at about 90 with respect to the-X direction, while probe beam 625B _2 can intersect track TR at an angle less than 90 with respect to the-X direction.

Each of the probe light beams 625B _1, 625B _2 can be a gaussian light beam such that the lateral distribution of light intensity of each probe light beam 625B _1, 625B _2 can be described by a gaussian function. The focal point or beam waist of each probe beam 625B _1, 625B _2 can be configured to overlap in the track TR or-X direction.

The light source 626B may be a solid state laser, such as a YAG laser, which may be a neodymium-doped YAG (Nd: YAG) laser operating at 1070nm and 50W power. In this example, the current target 105c passes through the first probe light beam 625B _1 at time t1 (and position x1), and at least some of the probe light beam 625B _1 reflects or scatters from the current target 105c to form diagnostic light 620B _1, which is detected by the detection device 135 (via the mechanical filter 140). In addition, the current target 105c passes through the second probe light beam 625B _2 at time t2 (and position x2), and at least some of the probe light beam 625B _2 reflects or scatters from the current target 105c to form light 620B _2, which is detected by the detection device 135 (via the mechanical filter 140).

The separation Δ d between probe beams 625B _1, 625B _2 at trajectory TR can be adjusted or customized depending on the rate at which target 105 is released from target supply 175 and the size and material of target 105. For example, the separation Δ d may be less than the spacing between adjacent targets 105. As another example, the separation Δ d may be determined or set based on the spacing between adjacent targets 105 to provide greater accuracy in measurements performed based on the interaction between the probe beams 625B _1, 625B _2 and the current target 105 c. At some point, generally, the greater the separation Δ d, the higher the accuracy of the measurements performed. For example, the separation Δ d may be between about 250 μm and 800 μm.

The interaction between the probe beams 625B _1, 625B _2 and the current target 105c enables the control system 170 to determine a movement attribute, such as the velocity V of the current target 105c in the-X direction. The velocity V or trend of the varying velocity V on many targets 105 may also be determined. Changes in the movement properties of the current target 105c in the-X direction may also be determined using only the probe beams 625B _1, 625B _2 if some assumptions are made about the motion of the current target 105 c.

The wavelengths of the diagnostic probe 125 (e.g., probe beam 625A and probe beams 625B _1, 625B _2) produced by the diagnostic device 165 should be sufficiently different from the wavelengths of the radiation pulses directed into the target space 110 (for interaction with the target 105) to facilitate discrimination between the diagnostic light 120 and the non-diagnostic light 122. In some implementations, the wavelength of the probe beams 125, 625A, 625B _1, and 625B _2 is 532nm or 1550 nm.

In other implementations, such as shown in fig. 6C, instead of having a single light source, such as light source 626B, in diagnostic device 665C, diagnostic device 665C includes a pair of light sources 626C _1, 626C _2 (such as two lasers), each of which produces a light beam 611C _1, 611C _2, respectively. Each of light beams 611C _1, 611C _2 passes through a respective one or more optical elements 627C _1, 627C _2, which may change or adjust the properties of light beams 611C _1, 611C _ 2. The output of each of the one or more optical elements is a respective probe beam 625C _1, 625C _ 2. Optical assemblies 627C _1, 627C _2 may include assemblies for directing respective probe light beams 625C _1, 625C _2 to respective positions x1, x2 along trajectory TR. Examples of optical components 627C _1, 627C _1 are discussed above with reference to optical assembly 608B.

As described above, and with reference to fig. 7, in some implementations, the metrology device 100 is implemented as a metrology device 700 in an EUV light source 776 to measure one or more properties of the target 105. The EUV light source 776 includes a target supply 775 that produces a continuous stream 706 of targets (each generally designated 105) along a trajectory TR toward a target space 710 within a vacuum environment 715 defined by the chamber 716. The EUV light source 776 supplies EUV light 777, which has been generated by the interaction between the target 105 and a pulse 778 of radiation to an output device 779. As described above, the metrology device 700 measures and analyzes one or more movement attributes (such as speed, velocity, and acceleration) of the current target 105c as the current target 105c travels along the trajectory TR toward the target space 710. The trajectory TR extends along a direction that may be considered a target (or axial) direction that lies in a three-dimensional X, Y, Z coordinate system defined by the chamber 716. As described above, the axial direction of the target 105 generally has a component parallel to the-X direction of the coordinate system of the chamber 716. However, the axial direction of target 105 may also have a component along one or more of directions Y and Z that are perpendicular to the-X direction. Further, each target 105 released by the target-supply 775 may have a slightly different actual trajectory, and the trajectory depends on the physical properties of the target-supply 775 and the environment 715 within the chamber 716 at the time the target 105 is released.

The EUV light source 776 generally includes an EUV light collector 780, a light source 781, an actuation system 782 in communication with the light source 781, a control device 783 in communication with the control system 770 of the metrology device 700, and a target supply 775, light source 781 and actuation system 782.

The EUV light collector 780 collects as much EUV light 784 emitted from the plasma 785 as possible and redirects this EUV light 784 as collected EUV light 777 to an output device 779. The light collector 780 can be a reflective optical device, such as a curved mirror capable of reflecting light having an EUV wavelength (i.e., EUV light 784) to form produced EUV light 777.

Light source 781 produces one or more pulsed beams of radiation 778 and directs one or more pulses of radiation 778 to target space 710 generally along the Z direction (although pulsed beams of radiation 778 may be angled with respect to the Z direction). In the schematically represented fig. 7, a pulsed beam 778 of radiation is shown directed in the-Y direction. The optical source 781 includes one or more optical sources that generate radiation pulses 778, a beam delivery system that includes an optical steering assembly that changes the direction or angle of the radiation pulse beam 778, and a focusing assembly that focuses the radiation pulse beam 778 to the target space 710. Exemplary optical turning assemblies include optical elements, such as lenses and mirrors, that turn or direct pulsed beams of radiation 778 as needed by refraction or reflection. An actuation system 782 can be used to control or move various features of the beam delivery system and the optical components of the focusing assembly and to adjust aspects of the light source 781 from which the radiation pulses 778 are generated.

The light source 781 includes at least one gain medium and an energy source to excite the gain medium to produce the radiation pulse 778. The radiation pulses 778 constitute a plurality of light pulses separated in time from each other. In other implementations, the light beam output from the light source 781 may be a Continuous Wave (CW) light beam. The light source 781 may be or include, for example, a solid state laser (e.g., a Nd: YAG laser, erbium doped fiber (Er: glass) laser, or neodymium doped YAG (Nd: YAG) laser operating at 1070nm and 50W power).

An actuation system 782 is coupled to the assembly of light sources 781 and is also in communication with and under control of the control device 783. Actuation system 782 can modify or control the relative position between radiation pulse 778 and target 105 in target space 710. For example, actuation system 782 is configured to adjust one or more of a timing of release of radiation pulse 778 and a direction of travel of radiation pulse 778.

The target-offering device 775 is configured to release the stream (or streams 706) of targets 105 at a particular rate. The metrology device 700 takes this rate into account when determining the total amount of time required to perform the measurement and analysis of the moving property (or properties) of the current target 105c and to effect changes in other aspects or components of the EUV light source 776 based on the measurement and analysis. For example, the control system 170 may communicate the results of the measurement and analysis to the control device 783, and the control device 783 determines how to adjust one or more signals to the actuation system 782 to adjust one or more characteristics of the radiation pulse 778 directed to the target space 710.

Adjustment of one or more characteristics of radiation pulses 778 may improve the relative alignment between current target 105' and radiation pulses 778 in target space 710. The current target 105' is a target that has entered the target space 710 when the radiation pulse 778 (just adjusted) reaches the target space 710. The target space 710 is adjusted when the radiation pulse 778 (which was just adjusted) reaches the target space 710. Such adjustment of one or more characteristics of the radiation pulse 778 improves the interaction between the current target 105' and the radiation pulse 778 and increases the amount of EUV light 784 produced by such interaction. As shown in fig. 7, the previous target 105p has interacted with a previous radiation pulse (not shown) to produce a plasma 785 that emits non-diagnostic light 122 (in addition to EUV light 784).

In some implementations, the current target 105' is the current target 105 c. In these implementations, the adjustment of one or more properties of the radiation pulse 778 occurs within a relatively short time frame. The relatively short time frame means that one or more properties of radiation pulse 778 are adjusted during the time after the analysis of the movement properties of current target 105c is completed to the time current target 105c enters target space 710. Because one or more properties of radiation pulse 778 can be adjusted within a relatively short time frame, there is sufficient time to affect the interaction between current target 105c (whose motion properties have just been analyzed) and radiation pulse 778.

In other implementations, the current target 105' is another target, i.e., a target other than the current target 105c, and follows the current target 105c in time. In these implementations, the adjustment of one or more characteristics of the radiation pulse 778 occurs over a relatively long time frame, such that it is not feasible to affect the interaction between the current target 105c (whose motion properties have just been analyzed) and the radiation pulse 778. On the other hand, it is feasible to affect the interaction between another (or later) target and the radiation pulse 778. The relatively long time frame is a time frame greater than the time until the current target 105c enters the target space 710 after the analysis of the movement attributes of the current target 105c is completed. Depending on the relatively long time frame, another object may be adjacent to the current object 105 c. Alternatively, another target may be adjacent to an intermediate target adjacent to the current target 105 c. In these other implementations, it is assumed that another target (not the current target 105c) is traveling with a movement attribute that is sufficiently similar to the detected or estimated movement attribute of the current target 105 c.

Each target 105 (including previous target 105p and current target 105c, as well as all other targets produced by target supply 775 (or 175)) includes material that emits EUV light when converted to plasma. Each target 105 is at least partially or mostly converted to a plasma by interacting with a radiation pulse 778 generated by a light source 781 within the target space 710. Each target 105 produced by target supply 775 (or 1750) is a target mixture that includes a target material and optional impurities, such as non-target particles. The target material is a substance that can be converted into a plasma state, which has an emission line in the EUV range. The target 105 may be, for example, a droplet of liquid or molten metal, a portion of a liquid stream, a solid particle or cluster, a solid particle contained in a droplet, a foam of the target material, or a solid particle contained in a portion of a liquid stream. The target material may comprise, for example, water, tin, lithium, xenon, or any material having an emission line in the EUV range when converted to a plasma state. For example, the target material may be elemental tin, which may be used as pure tin (Sn); as the tin compound, such as SnBr4, SnBr2, SnH 4; as the tin alloy, such as tin-gallium alloy, tin-indium-gallium alloy, or any combination of these alloys. In the absence of impurities, each target 105 then comprises only the target material. The discussion provided herein is one example where each target 105 is a droplet made of a molten metal (such as tin). However, each target 105 generated by the target-providing device 775 (or 175) may take other forms.

The target 105 may be provided to the target space 710 by passing molten target material through a nozzle of the target supply 775 (or 175) and allowing the target 105 to drift into the target space 710 along the trajectory TR. In some implementations, the target 105 may be directed to the target space 710 by a force (in addition to or in spite of gravity). As described below, the current target 105' (which may be the current target 105c) interacting with the radiation pulse 778 may also have interacted with one or more previous radiation pulses. Alternatively, the current target 105' interacting with radiation pulse 778 may reach the target space 710 without interacting with any other radiation pulse.

In this implementation, the detection device 735 is located outside of the chamber 716, while the diagnostic region 745 is located inside the environment 715 of the chamber 716. The walls of the chamber 716 are provided with an optical window 736, which optical window 736 is transparent to the wavelength of the diagnostic light 120 and is able to withstand any pressure differences at the walls. Optical window 736 may be held in a mount and sealed in a wall to maintain pressure within environment 715. For example, the optical window 736 may be made of a crown glass having a relatively low refractive index and low dispersion, such as borosilicate glass (BK7 or N-BK7) or fused silica. The optical window 736 has a sufficiently large aperture to accommodate the range of diagnostic light 120. The distance between the diagnostic region 745 and the optical window may be in the order of a few hundred millimeters (or about 600-700mm) and the distance between the diagnostic region 745 and the target space 710 may be in the order of a few millimeters (or about 1-5 mm). Thus, the distance between the diagnostic region 745 and the optical window may be 200-500 times the distance between the diagnostic region 745 and the target space 710.

The control 783 is in communication with the control system 170, and also in communication with other components of the EUV light source 776 (such as the actuation system 782, the target supply 775, and the light source 781). Referring to fig. 8, an implementation 883 of the control device 783 is shown, and an implementation 870 of the control system 170 is shown. The control 883 includes a control system 870, but the control system 870 may be physically separate from the control 883 and still remain in communication. In addition, features or components of the control device 883 may be shared with the control system 870, including features not shown in fig. 8.

The control system 870 includes a signal processing module 871 configured to receive an output from the detection device 735 (or 135, 335, 435). The control system 870 includes a diagnostic control module 872 that communicates with the diagnostic device 765 (or 165). For example, the signal processing module 871 receives a signal from the sensor 130 within the detection device 735(135, 335, 435), where the signal is a voltage signal related to the current generated from the light detected at the sensor 130. In general, the signal processing module 871 analyzes the output from the sensor 730 and determines one or more movement attributes of the current target 105c based on the analysis. The diagnostic control module 872 controls operation of the diagnostic device 765. For example, the diagnostic control module 872 may provide signals to the diagnostic device 765 for adjusting one or more characteristics of the diagnostic device 765, and also for adjusting one or more characteristics of the diagnostic probe(s) 725.

The signal processing module 871 also determines whether adjustments to subsequent radiation pulses 778 output from the optical source 781 are needed based on the determination of the one or more movement properties of the current target 105 c. Also, if adjustments are needed, the signal processing module 871 sends appropriate signals to the light source actuation module 884, and the light source drive module 884 interfaces with the light source 781 or the actuation system 782. The light source actuation module 884 may be within the control device 883 (as shown in fig. 8) or it may be integrated within the control system 870.

The signal processing module 871 may include one or more field programmable hardware circuits, such as a Field Programmable Gate Array (FPGA). An FPGA is an integrated circuit that is designed to be configured by a customer or designer after manufacture. The field programmable hardware circuit may be dedicated hardware that receives one or more values of the time stamp, performs calculations on the received values, and uses one or more look-up tables to estimate the time of arrival of the current target 105' in the target space 710. In particular, the field programmable hardware circuit may be used to quickly perform calculations to effect adjustments to one or more characteristics of radiation pulse 778 in a relatively short time frame to effect adjustments to one or more characteristics of radiation pulse 778, which radiation pulse 778 interacts with current target 105c, the motion attributes of which have just been analyzed by signal processing module 871.

The control device 883 includes a target transfer module 885 configured to interface with the target provisioning device 775. Further, the control device 883 and the control system 870 may include other modules configured to interface with other components of the EUV light source 776 that are not shown.

The control system 870 typically includes or has access to one or more of: digital electronic circuitry, computer hardware, firmware, and software. For example, the control system 870 may have access to a memory 873, and the memory 873 may be a read-only memory and/or a random access memory. Storage devices suitable 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 a CD-ROM disk. The control system 870 may also include or interface with one or more input devices 874i (such as a keyboard, touch screen, microphone, mouse, handheld input device, etc.) and one or more output devices 874o (such as a speaker and monitor).

The control system 870 may also include or have access to one or more programmable processors and one or more computer program products tangibly embodied in a machine-readable storage device for execution by the programmable processors. The one or more programmable processors can each execute a program of instructions to perform desired functions by operating on input data and generating appropriate output. Generally, a processor receives instructions and data from the memory 873. Any of the above may be supplemented by, or incorporated in, specially-designed ASICs (application-specific integrated circuits).

Furthermore, any one or more of the modules may include their own digital electronic circuitry, computer hardware, firmware, and software, as well as dedicated memory, input and output devices, programmable processors, and computer program products. Likewise, any one or more of the modules may access and use the memory 873, the input devices 874i, the output devices 874o, the programmable processors, and the computer program products.

Although the control system 870 is shown as a separate and integral unit, each of its components and modules may be separate units. The control means 883 may comprise other components not shown in fig. 8, such as a dedicated memory, input/output devices, a processor and a computer program product.

Referring to FIG. 9, an implementation 979 of lithographic apparatus 779 is shown. The lithographic apparatus 979 exposes a substrate (which may be referred to as a wafer) W with an exposure beam B. The lithographic apparatus 979 comprises a plurality of reflective optical elements R1, R2, R3, a mask M and a slit S, all in a housing 10. The enclosure 10 is an enclosure, can, or other structure capable of supporting the reflective optical elements R1, R1, R2, mask M, and slits S, and also capable of maintaining a vacuum space within the enclosure 10.

EUV light 777 enters the housing 10 and is reflected by the optical element R1 through the slit S toward the mask M. The slit S partially defines the shape of the distributed light used to scan the substrate W in the photolithography process. The dose delivered to the substrate W or the number of photons delivered to the substrate W depends on the size of the slit S and the speed at which the slit S is scanned.

The mask M may also be referred to as a reticle or patterning device. The mask M includes a spatial pattern representing features to be formed in a photoresist on a substrate W. EUV light 777 interacts with mask M. The interaction between the EUV light 777 and the mask M causes a pattern of the mask M to be imparted onto the EUV light 777 to form an exposure beam B. The exposure beam B passes through the slit S and is guided to the substrate W by the optical elements R2 and R3. Interaction between the substrate W and the exposure beam B exposes the pattern of the mask M onto the substrate W, thereby forming photoresist features on the substrate W. The substrate W includes a plurality of portions 20 (e.g., grains). The area of each portion 20 in the Y-Z plane is less than the area of the entire substrate W in the Y-Z plane. Each portion 20 may be exposed by the exposure beam B to include a copy of the mask M such that each portion 20 includes electronic features indicated by the pattern on the mask M.

The lithographic device 979 may include a lithographic control system 30 in communication with a control 783 of the EUV light source 776.

Referring to fig. 10, a process 1090 is performed by metrology device 100 (or metrology device 700). The diagnostic probe 125 interacts with the current target 105c in the diagnostic region 145 before the current target 105c enters the target space 110 (1091). The diagnostic light 120 resulting from the interaction (1091) is collected and, at the same time, some unwanted non-diagnostic light 122 resulting from the target space 110 is also collected (1092). Such as the pupil at the entrance of the mechanical filter 140, the diagnostic light 120, and the non-diagnostic light 122. The diagnostic light 120 and the non-diagnostic light 122 are collimated (1093). The optical collimator 142 collimates the diagnostic light 120 and the non-diagnostic light 122 that have entered the mechanical filter 140. The collimated diagnostic light and the non-diagnostic light are angularly separated from each other (1094). The beam reducer 150 reduces the lateral extent (along the XsYs plane) of the collimated diagnostic and collimated non-diagnostic beams, and these reduced

beams

121, 123 respectively exit the beam reducer 150 and their angular separation increases as they travel along the optical path 152 toward the mask 155. The collimated diagnostic light beam 121 is sensed at a sensing region (e.g., sensor 130) in optical communication with an open image plane that is laterally displaced (in the XsYs plane) from a closed image plane that blocks the collimated non-diagnostic light beam 123 (1095). For example, sensor 130 senses collimated diagnostic light beam 121, sensor 130 is in optical communication with aperture 160 (the open image plane), and aperture 160 is laterally displaced from mask 155 in the XsYs plane, with collimated non-diagnostic light beam 123 impinging on mask 155. The properties of the current target 105c are estimated based on the sensed diagnostic light (1096). In particular, the control system 170 analyzes the output from the sensor 130 to estimate one or more movement attributes of the current target 105 c.

As discussed above with reference to fig. 6A-6C, the diagnostic probe 125 may be one or more probe beams directed to traverse the trajectory of the target 105. Thus, the interaction (1091) between the diagnostic probe 125 and the current target 105c may be between the probe beams and the current target 105 c. In some implementations, the collected (1092) diagnostic light 120 may be part of the probe beam 125 reflected or scattered from the current target 105 c. In other implementations, the collected (1092) diagnostic light 120 is light produced by the current target 105 c. In other implementations, the collected 1092 diagnostic light 120 is light blocked by the current target 105c (shown in fig. 12).

The effect of the non-diagnostic light 122 on the analysis of the output from the sensor 130 is reduced by blocking or redirecting the non-diagnostic light 122 with the mechanical filter 140 and thus preventing the non-diagnostic light 122 from impinging on the sensor 130, but instead being blocked by the mask 155. In addition, the collimated state of the collimated diagnostic beam and the collimated non-diagnostic beam output from the collimator 142 is maintained up to the plane of the mask 155, and the collimated diagnostic beam 121 is further focused onto the sensor 130 after passing through the aperture 160.

Referring to fig. 11, in other implementations, the components of the optical collimator 142 and the beam reducer 150 that have a positive focal length and are closest to the optical collimator 142 are integrated into a single refractive element 1142/1151. Such an integrated single refractive element 1142/1151 may be applied to a galilean type refractive telescope (such as shown in fig. 3 and 11) or a keplerian type refractive telescope, such as shown in fig. 4.

Referring to fig. 12, in other implementations, the diagnostic light 120 is generated from a portion of the diagnostic probe beam 1225 that is blocked by the current target 105 c. In this implementation of the metrology device 1200, the diagnostic probe 1225 provides backlighting of the current target 105 c. The sensor 130 is a two-dimensional (e.g., imaging) sensor 1230, such as a camera. Thus, when the current target 105c passes through the diagnostic probe 1225, the shadow of the target 105c is formed by the target 105c, occluding at least a portion of the diagnostic probe 1225, as shown in the inset of FIG. 12. This arrangement may be considered a shadow map arrangement. In such implementations, the sensor 1230 is disposed on an opposite side of the target trajectory TR from the side on which the diagnostic device 1265 is disposed. Sensor 1230 is a camera that captures a two-dimensional representation (which can be considered an image) of diagnostic light 1220. Thus, for example, the sensor 1230 comprises a two-dimensional array of thousands or millions of light spots (or pixels). Diagnostic light 1220 is directed onto the photosensitive region of each pixel where it is converted into electrons, which are collected as voltage signals, and an array of these signals forms a two-dimensional image. As described above, the non-diagnostic light 1222 is substantially blocked from reaching the sensor 1230.

Referring to fig. 13, in other implementations, the beam reducer 150 is designed as a reflected beam reducer 1350 that receives a collimated beam from an optical collimator, such as collimator 342. The reflected beam reducer 1350 includes a concave reflective element (curved mirror) 1351 that converges the beam to a convex reflective element (curved mirror) 1353 that collimates the light into a collimated diagnostic beam 121 and a collimated non-diagnostic beam 123, which collimated diagnostic beam 121 and collimated non-diagnostic beam 123 travel in different directions (or angles) along the optical path 1352 toward the mask 155.

Referring to fig. 14, in other implementations, beam reducer 150 is designed as a catadioptric (hybrid) beam reducer 1450 that receives collimated beams from an optical collimator, such as collimator 342. Hybrid beam reducer 1450 includes a planar reflective element (planar mirror) 1451a that directs the beam onto a curved reflective element (curved mirror) 1451b that converges the beam to an intermediate focus IF between curved mirror 1451b and a convex or converging refractive element (lens) 1453. Lens 1453 collimates the light into collimated diagnostic beam 121 and collimated non-diagnostic beam 123, which propagate in different directions (or angles) along the optical path toward mask 155.

Referring to FIG. 15, in other implementations, mask 155 is designed as a mask 1555 that defines an aperture 1560 that is aligned with the path of the collimated non-diagnostic beam 123, while mask 1555 is used to stop or prevent the collimated diagnostic beam 121 from passing through to the sensor 130. Such a design may be useful if necessary to analyze aspects related to the non-diagnostic light 122.

Other aspects of the invention are set forth in the following numbered clauses.

1. A metrology apparatus comprising:

a diagnostic device configured to interact a diagnostic probe with a current target at a diagnostic region before the current target enters a target space;

a detection device, comprising:

a light sensor having a field of view that overlaps the diagnostic region and configured to sense light resulting from the interaction between the diagnostic probe and the current target at the diagnostic region; and

a mechanical filter between the diagnostic region and the light sensor, the mechanical filter comprising a beam reducer and an optical mask defining an aperture positioned between the beam reducer and the light sensor; and

a control system in communication with the detection device and configured to estimate a property of the current target based on an output from the light sensor.

2. The metrology device of clause 1, wherein the mechanical filter is configured to angularly separate diagnostic light emitted from the diagnostic region from non-diagnostic light emitted from the target space, wherein the diagnostic light is generated by interaction between the current target at the diagnostic region and the diagnostic probe.

3. The metrology device of clause 2, wherein the non-diagnostic light comprises light emitted from a plasma generated by a previous target in the target space.

4. A metrology device according to clause 2, wherein the lateral extent of the aperture is about the same as or greater than the lateral extent of the diagnostic light in the plane of the optical mask, and the lateral extent of the optical mask is about the same as or greater than the lateral extent of the non-diagnostic light in the plane of the optical mask.

5. The metrology device of clause 2, wherein the optical mask is positioned such that the non-diagnostic light emitted from the target space is substantially blocked by the optical mask while the diagnostic light substantially passes through the aperture.

6. The metrology device of clause 1, wherein the mechanical filter comprises an optical collimator between the diagnostic region and the beam reducer.

7. The metrology apparatus of clause 6, wherein the beam reducer is an afocal beam reducer and is configured to project a finite object to infinity in combination with the optical collimator.

8. The metrology device of clause 6, wherein the optical collimator and the component of the beam reducer closest to the optical collimator having a positive focal length are integrated into a single refractive element.

9. The metrology device of clause 6, wherein the beam reducer is configured to maintain a collimated state of the light.

10. The metrology device of clause 1, wherein the light sensor comprises one or more of: photodiodes, phototransistors, photoresistors, photomultiplier tubes, multi-cell photo-receivers, quad-cell photo-receivers, and cameras.

11. The metrology device of clause 1, wherein the diagnostic probe comprises at least one diagnostic light beam, and the light sensor is configured to sense diagnostic light resulting from the interaction between the current target and the at least one diagnostic light beam.

12. The metrology device of clause 11, wherein the diagnostic light comprises the diagnostic light beam reflected from, scattered from, or blocked by the current target.

13. The metrology device of clause 1, wherein the detection device further comprises one or more of a spectral filter and a polarization filter.

14. The metrology device of clause 1, wherein the diagnostic probe comprises a first diagnostic beam and a second diagnostic beam, each configured to interact with the current target before the current target enters the target space, each interaction occurring at a different region and at a different time.

15. The metrology apparatus of clause 1, wherein the beam reducer comprises a refractive telescope, a reflective telescope, or a catadioptric telescope.

16. The metrology apparatus of clause 15, wherein the refractive telescope comprises:

a positive focal length lens arrangement and a negative focal length lens arrangement separated by a sum of focal lengths of the positive focal length lens arrangement and the negative focal length lens arrangement; or

A pair of positive focal length lens devices separated by the sum of the focal lengths of the pair of positive focal length lens devices.

17. The metrology apparatus of clause 1, wherein the beam reducer is configured to reduce the lateral dimension of incident light by at least five times, at least ten times, at least twenty times, or about ten times.

18. A metrology device as described in clause 1 wherein the aperture comprises a circular opening, an elliptical opening, a polygonal opening, or an elongated slit opening.

19. The metrology device of clause 1, wherein the detection device is positioned outside of a chamber of an Extreme Ultraviolet (EUV) light source, the diagnostic region is inside of the chamber, and the detection device receives light from the chamber through an optical window in a wall of the chamber.

20. The metrology device of clause 19, wherein the distance between the diagnostic region and the optical window is about 200-500 times the size of the distance between the diagnostic region and the target space.

21. A metrology device as in clause 1 wherein the detection device comprises a focusing lens at the output of the aperture, the focusing lens configured to focus the light sensed onto the photosensor.

22. A metrology device as described in clause 1 wherein the aperture has a range of at least 2 millimeters (mm).

23. The metrology device of clause 1, wherein the aperture is positioned to receive the diagnostic light at a location where the diagnostic light is collimated or non-converging and non-diverging.

24. A method of metrology, comprising:

interacting a diagnostic probe with a current target at a diagnostic region before the current target enters a target space;

collecting diagnostic light resulting from the interaction between the diagnostic probe and the current target at the diagnostic region, the collecting further comprising collecting non-diagnostic light resulting from the target space;

collimating the diagnostic light and the non-diagnostic light;

separating the diagnostic light and the non-diagnostic light at an angle to each other, including reducing a lateral extent of the diagnostic light and the non-diagnostic light;

sensing the diagnostic light at a sensing region laterally offset from a non-sensing region traversed by the non-diagnostic light after the diagnostic light and the non-diagnostic light have been angularly separated; and

estimating a property of the current target based on the sensed diagnostic light.

25. The metrology method of clause 24, wherein:

interacting the diagnostic probe with the current target at the diagnostic region comprises interacting one or more diagnostic beams with the current target at the diagnostic region; and

collecting diagnostic light includes collecting one or more diagnostic light beams that have been reflected from, scattered from, or blocked by the current target at the diagnostic region.

26. The metrology method of clause 24, further comprising filtering the diagnostic light based on one or more of: spectral properties of the diagnostic light and a polarization state of the diagnostic light.

27. The metrology method of clause 24, wherein the diagnostic region is inside a hermetic chamber of an Extreme Ultraviolet (EUV) light source, and collecting the diagnostic light further comprises collecting non-diagnostic light comprising: receiving the diagnostic light comprising the non-diagnostic light transmitted through an optical window in a wall of the chamber.

28. The metrology method of clause 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises reducing the lateral extent of the diagnostic light and the non-diagnostic light by at least five times, at least ten times, at least twenty times, or about ten times.

29. The metrology method of clause 24, further comprising blocking or redirecting the non-diagnostic light in a non-sensing region.

30. The metrology method of clause 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises one or more of: refracting and reflecting the light.

31. The metrology method of clause 24, further comprising focusing the diagnostic light at the sensing region.

32. The metrology method of clause 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises maintaining a collimated state of the diagnostic light and the non-diagnostic light.

33. The metrology method of clause 24, further comprising: passing the diagnostic light through an aperture of an optical mask after the diagnostic light and the non-diagnostic light are angularly separated from each other and before the diagnostic light is sensed, the aperture having an extent greater than an extent of the diagnostic light.

Other implementations are within the scope of the following claims.

Claims

1. A metrology apparatus comprising:

a detection device, comprising:

2. The metrology device of claim 1, wherein the mechanical filter is configured to angularly separate diagnostic light emitted from the diagnostic region from non-diagnostic light emitted from the target space, wherein the diagnostic light is generated by interaction between the current target at the diagnostic region and the diagnostic probe.

3. A metrology apparatus as claimed in claim 2 wherein non-diagnostic light comprises light emitted from a plasma generated from a previous target in the target space.

4. A metrology apparatus according to claim 2, wherein a lateral extent of the aperture is about the same as or greater than a lateral extent of the diagnostic light in a plane of the optical mask and a lateral extent of the optical mask is about the same as or greater than a lateral extent of the non-diagnostic light in the plane of the optical mask.

5. The metrology device of claim 2, wherein the optical mask is positioned such that the non-diagnostic light emitted from the target space is substantially blocked by the optical mask and the diagnostic light substantially passes through the aperture.

6. A metrology apparatus as claimed in claim 1 wherein the mechanical filter comprises an optical collimator between the diagnostic region and the beam reducer.

7. The metrology device of claim 6, wherein the beam reducer is an afocal beam reducer and is configured to project a finite object to infinity in conjunction with the optical collimator.

8. A metrology apparatus as claimed in claim 6 wherein the optical collimator and the part of the beam reducer closest to the optical collimator having a positive focal length are integrated into a single refractive element.

9. The metrology apparatus of claim 6, wherein the beam reducer is configured to maintain a collimated state of the light.

10. The metrology device of claim 1, wherein the light sensor comprises one or more of: photodiodes, phototransistors, photoresistors, photomultiplier tubes, multi-cell photo-receivers, quad-cell photo-receivers, and cameras.

11. The metrology device of claim 1, wherein the diagnostic probe comprises at least one diagnostic light beam, and the light sensor is configured to sense diagnostic light resulting from the interaction between the current target and the at least one diagnostic light beam.

12. The metrology device of claim 11, wherein the diagnostic light comprises the diagnostic light beam reflected from, scattered from, or blocked by the current target.

13. A metrology apparatus as claimed in claim 1 wherein the detection apparatus further comprises one or more of a spectral filter and a polarisation filter.

14. A metrology apparatus as claimed in claim 1 wherein the diagnostic probe comprises a first and second diagnostic beam, each configured to interact with the current target before the current target enters the target space, each interaction occurring at a different region and at a different time.

15. The metrology apparatus of claim 1, wherein the beam reducer comprises a refractive telescope, a reflective telescope, or a catadioptric telescope.

16. A metrology apparatus as claimed in claim 15 wherein the refractive telescope comprises:

17. A metrology apparatus as claimed in claim 1 wherein the beam reducer is configured to reduce the lateral dimension of incident light by at least five times, at least ten times, at least twenty times, or about ten times.

18. A measurement apparatus according to claim 1, wherein the aperture comprises a circular opening, an elliptical opening, a polygonal opening, or an elongated slit opening.

19. A metrology apparatus as claimed in claim 1 wherein the detection apparatus is positioned outside of a chamber of an Extreme Ultraviolet (EUV) light source, the diagnostic region is inside the chamber and the detection apparatus receives light from the chamber through an optical window in a wall of the chamber.

20. The metrology device of claim 19, wherein a distance between the diagnostic region and the optical window is about 200-500 times a magnitude of a distance between the diagnostic region and the target space.

21. A metrology apparatus as claimed in claim 1 wherein the detection means comprises a focusing lens at the output of the aperture, the focusing lens being configured to focus the light sensed onto the light sensor.

22. A metrology apparatus as claimed in claim 1 wherein the apertures have a range of at least 2 millimeters (mm).

23. A metrology apparatus as claimed in claim 1 wherein the aperture is positioned to receive the diagnostic light at a location where the diagnostic light is collimated or non-convergent and non-divergent.

24. A method of metrology, comprising:

collimating the diagnostic light and the non-diagnostic light;

25. A metrology method as claimed in claim 24, wherein:

interacting the diagnostic probe with the current target at the diagnostic region comprises interacting one or more diagnostic beams with the current target at the diagnostic region; and is

26. The metrology method of claim 24, further comprising filtering the diagnostic light based on one or more of: spectral properties of the diagnostic light and a polarization state of the diagnostic light.

27. A metrology method as claimed in claim 24 wherein the diagnostic region is inside a hermetic chamber of an Extreme Ultraviolet (EUV) light source and collecting the diagnostic light further comprises collecting non-diagnostic light comprising: receiving the diagnostic light comprising the non-diagnostic light transmitted through an optical window in a wall of the chamber.

28. The metrology method of claim 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises reducing the lateral extent of the diagnostic light and the non-diagnostic light by at least five times, at least ten times, at least twenty times, or approximately ten times.

29. A metrology method as claimed in claim 24 further comprising blocking or redirecting said non-diagnostic light at a non-sensing region.

30. The metrology method of claim 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises one or more of: refracting and reflecting the light.

31. A metrology method as claimed in claim 24 further comprising focusing the diagnostic light at the sensing region.

32. The metrology method of claim 24, wherein reducing the lateral extent of the diagnostic light and the non-diagnostic light comprises maintaining a collimated state of the diagnostic light and the non-diagnostic light.

33. A metrology method as recited in claim 24, further comprising: passing the diagnostic light through an aperture of an optical mask after the diagnostic light and the non-diagnostic light are angularly separated from each other and before the diagnostic light is sensed, the aperture having an extent greater than an extent of the diagnostic light.