Mechanically controlled stress engineered optical system and method

Abstract

A fast dynamic waveplate is described. The system and method exploits the stress birefringence that occurs within the plate when a force is applied to the side of the plate. The force is applied using a set of piezoelectric actuators that are symmetrically distributed along the side of the plate. The magnitude of the force is controllable using a control unit. The generated stress birefringence varies spatially across the plate. By carefully adjusting the force, the plate can be transformed into a waveplate with any retardance value determined by the force. Since the parameter that determines the birefringence is the force, a control unit can be used to apply a combination of different force values ​​at sub-millisecond speeds to achieve fast control of the birefringence value and orientation within the plate.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 298,006, filed January 10, 2022, the entire contents of which are incorporated by reference herein.

[0002] This description relates generally to mechanically controlled stress engineered optical systems and methods. [Background technology]

[0003] Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A patterning device (e.g. a mask) may contain or provide a pattern ("design layout") corresponding to an individual layer of the IC, which can be transferred onto a target portion (e.g. comprising one or more dies) on a substrate (e.g. a silicon wafer) that is coated with a layer of radiation-sensitive material ("resist"), such as by irradiating the target portion through the pattern on the patterning device. Typically, a single substrate will contain several adjacent target portions onto which the lithographic projection apparatus transfers the pattern, one at a time. In one type of lithographic projection apparatus, the pattern of the entire patterning device is transferred onto one target portion in one step. Such an apparatus is commonly referred to as a stepper. In another apparatus, commonly referred to as a step-and-scan apparatus, the projection beam scans the patterning device in a predetermined reference direction (the "scan" direction), while the substrate is moved synchronously parallel or anti-parallel to this reference direction. Different portions of the pattern on the patterning device are transferred progressively onto one target portion. Generally, a lithographic projection apparatus will have a demagnification ratio M (e.g. 4), so the speed F at which the substrate moves will be 1 / M times the speed at which the projection beam scans the patterning device. More information on lithographic devices as described herein can be gleaned, for example, from U.S. Patent No. 6,046,792, which is incorporated herein by reference.

[0004]

[0004] Before transferring the pattern from the patterning device to the substrate, the substrate may undergo various procedures such as priming, resist coating, and a soft bake. After exposure, the substrate may be subjected to other procedures ("post-exposure procedures") such as a post-exposure bake (PEB), development, a hard bake, and metrology / inspection of the transferred pattern. This sequence of procedures is used as a basis for manufacturing an individual layer of a device, e.g. an IC. The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, deposition, chemical-mechanical polishing, all of which are aimed at completing an individual layer of the device. If the device requires several layers, the entire procedure, or a variant thereof, is repeated for each layer. Eventually, a device will be present on each target portion on the substrate. These devices are then separated from one another by techniques such as dicing or sawing, so that the individual devices can be attached to a carrier or connected to pins.

[0005]

[0005] Thus, the manufacture of devices such as semiconductor devices typically involves processing a substrate (e.g., a semiconductor wafer) using multiple manufacturing processes to form various features and multiple layers of the device. Such layers and features are usually manufactured and processed using, for example, deposition, lithography, etch, deposition, chemical mechanical polishing, and ion implantation. Multiple devices may be manufactured into multiple dies on a substrate and then separated into individual devices. This device manufacturing process may be considered as a patterning process. A patterning process includes a patterning step, such as optical lithography and / or nanoimprint lithography, in which a patterning device is used in a lithography apparatus to transfer a pattern on the patterning device to a substrate, typically optionally accompanied by one or more associated pattern processing steps, such as developing a resist in a developer, baking the substrate using a bake tool, etching with the pattern using an etcher, deposition, etc.

[0006]

[0006] Lithography is a central process in the manufacture of devices such as ICs, where patterns formed on a substrate define the functional elements of devices such as microprocessors, memory chips, etc. Similar lithographic techniques are used in the formation of flat panel displays, micro-electromechanical systems (MEMS), and other devices.

[0007]

[0007] As semiconductor manufacturing processes continue to advance, the dimensions of functional elements are continually shrinking, while the number of functional elements, such as transistors, per device has been steadily increasing for decades, following a trend commonly referred to as "Moore's Law". In current technology, layers of devices are fabricated using lithographic projection apparatus that projects a design layout onto a substrate using illumination from a deep ultraviolet illumination source, producing individual functional elements with dimensions well below 100 nm, i.e., less than half the wavelength of radiation from the illumination source (e.g., a 193 nm illumination source).

[0008]

[0008] This process of printing features with dimensions smaller than the conventional resolution limit of the lithographic projection apparatus is commonly known as low k1 lithography, according to the resolution equation CD=k1×λ / NA, where λ is the wavelength of the radiation used (currently mostly 248 nm or 193 nm), NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension", i.e., the minimum feature size that is typically printed, and k1 is an empirical resolution factor. In general, the smaller k1 is, the more difficult it is to reproduce a pattern on a substrate that resembles the shape and dimensions planned by the designer to achieve a particular electrical functionality and performance. To overcome such difficulties, sophisticated fine-tuning steps are applied to the lithographic projection apparatus, the design layout, or the patterning device. These include, but are not limited to, optimization of NA and optical coherence settings, customized illumination schemes, the use of phase-shifting patterning devices, optical proximity correction (OPC, sometimes called "optical and process correction") in the design layout, or other methods commonly defined as "resolution enhancement techniques" (RET). Summary of the Invention

[0009]

[0009] The system and method exploits the stress birefringence that is generated inside a (e.g., glass or quartz) plate when a force is applied to the side of the plate. The force is applied using a set of piezoelectric actuators that are symmetrically distributed along the side of the plate. The actuators are electronically controlled. By carefully adjusting the applied force, the plate may be transformed into a waveplate with any retardance value determined by the force. Since the force determines the birefringence, combinations of different force values ​​may be applied electronically at sub-millisecond speeds to achieve high speed control of the birefringence value and orientation of the fast and / or slow axes in the plate (while the plate itself remains stationary), creating a fast dynamic waveplate.

[0010] According to an embodiment, a system configured to condition light for metrology is provided, the system comprising an optically transparent plate, one or more actuators configured to apply forces to the plate that create a stress pattern in the plate, and one or more processors configured to control the one or more actuators to apply forces that create the stress pattern to impart a particular polarization to light passing through the plate according to a desired metrology function.

[0011]

[0011] In some embodiments, the plate comprises a wave plate in response to a force being applied to the plate.

[0012]

[0012] In some embodiments, the plate comprises a transparent material, and in response to a force being applied to the plate to generate a stress pattern, the plate is configured to change light passing through the plate from a first polarization state to a second polarization state.

[0013]

[0013] In some embodiments, the applied force induces an orientation and retardance in the plate. The induced retardance and orientation are not uniform. Each varies across the plate. The central region of the plate is an area of ​​interest where the retardance and fast axis orientation are approximately uniform.

[0014] In some embodiments, the orientation is controlled by the location and / or distribution of forces applied to the plate by one or more actuators.

[0015] In some embodiments, the retardance is controlled by the amount of force applied to the plate by one or more actuators.

[0016] In some embodiments, the plate comprises glass or crystal.

[0017] In some embodiments, the one or more actuators are piezoelectric.

[0018] In some embodiments, the stress pattern includes birefringence.

[0019]

[0019] In some embodiments, the one or more processors are configured to individually control each of the one or more actuators such that the stress pattern within the plate is dynamically adjustable before, during, and / or after light passes through the plate.

[0020]

[0020] In some embodiments, dynamic tuning involves applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the birefringence of the plate at controlled speeds of less than a millisecond.

[0021]

[0021] In some embodiments, dynamic adjustment involves applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at controlled speeds of less than a millisecond.

[0022] In some embodiments, the one or more actuators are disposed on one or more edges of the plate.

[0023] In some embodiments, the one or more actuators include a plurality of actuators symmetrically distributed around one or more edges of the plate.

[0024] In some embodiments, the plate, the one or more actuators, and the one or more processors are configured such that light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers.

[0025]

[0025] In some embodiments, imparting a particular polarization to the light includes conditioning the light passing through the plate for metrology.

[0026]

[0026] In some embodiments, the system further includes a polarizer and a sensor configured to generate a metrology signal based on light received by the sensor after the light passes through the polarizer and the plate.

[0027]

[0027] In some embodiments, the sensor is included in a camera.

[0028]

[0028] In some embodiments, the system further comprises an imaging lens positioned between the plate and the sensor.

[0029] In some embodiments, the metrology signals include overlay signals associated with a semiconductor manufacturing process.

[0030] According to another embodiment, there is provided a method of conditioning light for metrology, the method including applying forces to an optically transparent plate using one or more actuators to create a stress pattern in the plate, and controlling, using one or more processors, the one or more actuators to apply the forces that create the stress pattern to impart a particular polarization to light passing through the plate according to a desired metrology function.

[0031]

[0031] According to another embodiment, there is provided a non-transitory computer readable medium having instructions thereon which, when executed by a computer, cause operations including applying a force to an optically transparent plate using one or more actuators to create a stress pattern in the plate, and controlling, using one or more processors, the one or more actuators to apply the force that creates the stress pattern to impart a particular polarization to light passing through the plate in accordance with a desired metrology function.

[0032]

[0032] According to another embodiment, a system is provided that is configured to condition light for overlay measurements as part of a semiconductor manufacturing process. The system is configured to dynamically condition birefringence and / or orientation of an optical plate before, during, and / or after light passes through the plate. The dynamic conditioning includes applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the birefringence and / or orientation of the plate at a controlled rate of less than a millisecond. The system includes a plate. The plate includes a transparent material and is configured to change light passing through the plate from a first polarization state to a second polarization state in response to forces being applied to the plate by the different actuators. The system includes different actuators. The different actuators include a plurality of piezoelectric actuators that are symmetrically distributed around one or more edges of the plate. The plurality of piezoelectric actuators are configured to apply a birefringence and / or orientation generating force to the plate. The system includes one or more processors configured to individually control each of the plurality of actuators to apply a birefringence and / or orientation generating force to impart a particular polarization to light passing through the plate to change the light to the second polarization state. [Brief description of the drawings]

[0033]

[0033] The above aspects and other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

[0034] [Figure 1] 1 illustrates a lithographic apparatus according to an embodiment; [Diagram 2]

[0035] 1 illustrates a schematic representation of an embodiment of a lithographic cell or cluster according to an embodiment. [Diagram 3]

[0036] 1 illustrates a schematic diagram of an exemplary inspection system according to an embodiment. [Figure 4]

[0037] 1 illustrates a schematic diagram of additional details of an exemplary inspection system, according to an embodiment; [Diagram 5]

[0038] 1 illustrates a relationship between a radiation illumination spot of an inspection system and a metrology target in accordance with an embodiment. [Figure 6]

[0039] 4 illustrates a process for deriving multiple variables of interest based on measurement data according to one embodiment. [Figure 7]

[0040] 5 illustrates a system configured to condition light for metrology, which may form part of the system illustrated in FIGS. 3 and 4, according to an embodiment. [Figure 8]

[0041] 8 illustrates another embodiment of the system shown in FIG. 7, according to an embodiment. [Figure 9]

[0042] 13 shows the mapped stress distribution and orientation in a (stress engineered optical) plate resulting from forces applied by actuators coupled to the plate, according to an embodiment. [Figure 10]

[0043] 13 shows an image of another (stress-engineered optical) plate between two crossed polarizers while a force is applied to the plate by an actuator, according to an embodiment. [Figure 11]

[0044] 1 illustrates the polarization state of light after passing through a central portion (e.g., an aperture) of a stress-engineered optical plate, according to one embodiment. [Figure 12]

[0045] 1 illustrates a method for conditioning light for metrology according to an embodiment. [Figure 13]

[0046] FIG. 1 is a block diagram of an exemplary computer system, according to an embodiment. [Figure 14]

[0047] 2 is a schematic diagram of a lithographic projection apparatus similar to FIG. 1 according to an embodiment; [Figure 15]

[0048] FIG. 15 is a more detailed diagram of the device of FIG. 14, according to an embodiment. [Figure 16]

[0049] FIG. 16 is a more detailed diagram of a source collector module of the apparatus of FIGS. 14 and 15 according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035]

[0050] Stress engineered optics (SEOs) exist as fixed waveplates with fixed force points on the sides of the (usually glass) plate. No active control methods are implemented for such plates. Existing polarization control systems typically contain liquid crystals and can be rapidly adjusted by electronic controllability. However, the response time of these systems can be longer than a few milliseconds due to slow orientation of the crystals. Also, the polarization state of such systems often drifts over time. Traditional rotating polarizer / waveplate systems are slow to achieve control of the polarization angle, for example.

[0036]

[0051] Advantageously, the present system and method exploits the stress birefringence that is generated within a (glass or crystal) plate when a force is applied to the side of the plate. The force is applied using a set of actuators that are symmetrically distributed along the side of the plate. The magnitude of the force can be controlled electronically. The stress birefringence that is generated varies spatially across the plate. By carefully adjusting the force, the plate may be transformed into a waveplate with any retardance value determined by the force. Because the force determines the birefringence, combinations of different force values ​​can be applied electronically at sub-millisecond speeds to provide high speed control of the value of birefringence, as well as orientation of the fast and / or slow axes within the plate (while the plate itself remains stationary), creating fast dynamic waveplates.

[0037]

[0052] Briefly, the description herein generally relates to semiconductor device manufacturing and patterning processes. More specifically, the following paragraphs describe several components of semiconductor manufacturing systems and / or related systems. As described herein, these systems and methods may be used, for example, for overlay measurement or other operations in the manufacturing process of semiconductor devices.

[0038]

[0053] Although specific reference may be made herein to the measurement of overlay in semiconductor devices and the manufacture of integrated circuits (ICs), it should be understood that the description herein has many other possible applications. For example, it may be used to measure alignment and / or other parameters, and it may also be used in the manufacture of integrated optical systems such as magnetic domain memories, liquid crystal display panels, thin film magnetic heads, guidance and detection patterns. Those skilled in the art will understand that in the context of such alternative applications, the terms "reticle," "wafer," or "die" as used herein should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

[0039]

[0054] The term "projection optics" as used herein should be broadly interpreted to encompass various types of optical systems including, for example, refractive optics, reflective optics, apertures, and catadioptric optics. The term "projection optics" may also include components that collectively or alone operate according to any of these design types to direct, shape or control a projection beam of radiation. The term "projection optics" may include any optical component in a lithographic projection apparatus, regardless of where it is located on the optical path of the lithographic projection apparatus. Projection optics may include optical components for shaping, conditioning and / or projecting radiation from a radiation source before it passes through a patterning device, and / or optical components for shaping, conditioning and / or projecting radiation after it has passed through a patterning device. Generally, projection optics does not include a radiation source and a patterning device.

[0040]

[0055] Fig. 1 shows a schematic representation of an embodiment of a lithographic apparatus LA. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV, DUV or EUV radiation), a support structure (e.g. mask table) MT constructed to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, a substrate table (e.g. wafer table) WT (e.g. WTa, WTb or both) configured to hold a substrate (e.g. resist coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies, often referred to as a field) of the substrate W. The projection system is supported on a reference frame RF. As shown, the apparatus is of a transmissive type (e.g. using a transmissive mask). Alternatively, the apparatus may be of a reflective type (eg employing a programmable mirror array, or employing a reflective mask).

[0041]

[0056] The illuminator IL receives the radiation beam from the radiation source SO. The source and the lithographic apparatus may be separate, for example when the source is an excimer laser. In such cases the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL using a beam delivery system BD, for example comprising suitable directing mirrors and / or beam expanders. In other cases the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0042]

[0057] The illuminator IL may vary the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero in an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a number of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in the pupil plane of the illuminator IL may be referred to as the illumination mode.

[0043]

[0058] The illuminator IL may comprise an adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Typically, at least the outer and / or inner radial extent (typically referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator may be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to vary the number and angular extent of sectors in the pupil plane where the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, various illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multipole distribution, such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, for example, by inserting an optical component providing that illumination mode into the illuminator IL or by using a spatial light modulator.

[0044]

[0059] The illuminator IL may be operable to change the polarization of the beam and may be operable to adjust the polarization using the adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as the polarization mode. Using different polarization modes may result in greater contrast in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across the pupil plane of the illuminator IL. The polarization direction of the radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen depending on the illumination mode. In the case of a multipole illumination mode, the polarization of each pole of the radiation beam may be approximately perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, in the case of a dipole illumination mode, the radiation may be linearly polarized in a direction substantially perpendicular to a line that bisects two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as the X and Y polarization states. In a quadrupole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line that bisects the sector. This polarization mode may be referred to as XY polarization. Similarly, in a hexapole illumination mode, the radiation in each pole sector may be linearly polarized in a direction substantially perpendicular to a line that bisects the sector. This polarization mode may be referred to as TE polarization.

[0045]

[0060] The illuminator IL will generally also comprise various other components, such as an integrator IN and a condenser CO. An illumination system may comprise various optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping or controlling radiation.

[0046]

[0061] The illuminator thus provides a conditioned beam of radiation B having a desired uniformity and intensity distribution in its cross-section.

[0047]

[0062] The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be for example a frame or a table, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" herein may be considered as synonymous with the more general term "patterning device".

[0048]

[0063] The term "patterning device" as used herein should be interpreted broadly to refer to any device that can be used to impart a pattern to a target portion of a substrate. In an embodiment, a patterning device is any device that can be used to impart a radiation beam with a pattern in its cross-section to generate a pattern in the target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the pattern desired in the target portion of the substrate, for example if the pattern includes phase-shifting features or so-called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion of the device, such as an integrated circuit.

[0049]

[0064] A patterning device may be of a transmissive or reflective type. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid masks. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilting mirrors impart a pattern to the radiation beam which is reflected from the mirror matrix.

[0050]

[0065] The term "projection system" as used herein includes refractive optics, catadioptric, catadioptric, magnetic, electromagnetic and electrostatic optics, or any combination thereof, and should be interpreted broadly to encompass any type of projection system that is suitable with respect to the exposure radiation used or with respect to other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein may be considered as synonymous with the more general term "projection system".

[0051]

[0066] The projection system PS may comprise a number of optical (e.g., lens) elements and may further comprise an adjustment mechanism configured to adjust one or more of the optical elements to correct aberrations (phase changes across the pupil plane across the field). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements in the projection system PS in one or more different ways. The projection system may have a coordinate system whose optical axis extends in the z-direction. The adjustment mechanism may be operable to displace one or more optical elements, tilt one or more optical elements, and / or deform one or more optical elements in any combination. The displacement of the optical elements may be in any direction (x, y, z, or combinations thereof). The tilt of the optical elements is typically out of plane perpendicular to the optical axis by rotation about an axis in the x and / or y directions, although rotation about the z-axis may be used for non-rotationally symmetric aspheric optical elements. The deformation of the optical element may include a low frequency shape (e.g. astigmatism) and / or a high frequency shape (e.g. free form asphericity). The deformation of the optical element may be performed, for example, by exerting a force on one or more sides of the optical element using one or more actuators and / or by heating one or more selected regions of the optical element using one or more heating elements. In general, it may not be possible to adjust the projection system PS to correct the apodization (change in transmission at the pupil plane). A transmission map of the projection system PS may be used in designing a patterning device (e.g. mask) MA for the lithographic apparatus LA. Computational lithography techniques may be used to design the patterning device MA to at least partially correct the apodization.

[0052]

[0067] The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g. two or more substrate tables WTa, WTb, two or more patterning device tables, a substrate table WTa and a table WTb below the projection system that does not contain the substrate, e.g. dedicated to facilitating measurement and / or cleaning, etc.). In such a "multi-stage" machine, the additional tables may be used in parallel, or preparatory steps may be performed on one or more tables whilst the other one or more tables are used for exposure. For example, alignment measurements may be made using alignment sensors AS and / or level (height, tilt, etc.) measurements using level sensors LS.

[0053]

[0068] The lithographic apparatus may also be of a type in which at least a portion of the substrate is covered by a liquid having a relatively high refractive index, e.g. water, filling a space between the projection system and the substrate. An immersion liquid may also be applied to other spaces in the lithographic apparatus, for example between the patterning device and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used herein does not imply that a structure such as the substrate has to be immersed in liquid, but simply that a liquid is located between the projection system and the substrate during exposure.

[0054]

[0069] In operation of a lithographic apparatus, a radiation beam is conditioned and provided by an illumination system IL. The radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a support structure (e.g. mask table) MT, and is patterned by the patterning device. After traversing the patterning device MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. Using a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder, a 2D encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (not explicitly shown in FIG. 1 ) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during a scan. In general, movement of the support structure MT may be realized using a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. The patterning device MA and the substrate W may be aligned using the patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between the target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks may be located between the dies.

[0055]

[0070] The depicted apparatus may be used in at least one of the following modes: In step mode, the support structure MT and the substrate table WT are kept substantially stationary while a pattern imparted to the radiation beam is projected onto the target portion C in one go (i.e. a single static exposure), and the substrate table WT is moved in the X and / or Y direction so that a different target portion C can be exposed. In step mode, a maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in non-scan direction) of the target portion in a single dynamic exposure, whereas the length of the scanning motion determines the height (in scan direction) of the target portion. In another mode, the support structure MT is kept substantially stationary holding the programmable patterning device and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto the target portion C. In this mode, a pulsed radiation source is generally used and the programmable patterning device is updated as required after each movement of the substrate table WT, or between successive radiation pulses during a scan. This mode of operation can readily be applied to maskless lithography employing a programmable patterning device such as a programmable mirror array of the type mentioned above.

[0056]

[0071] Combinations and / or variations on the above described modes of use or entirely different modes of use may also be employed.

[0057]

[0072] Substrates referred to herein may be processed, before or after exposure, for example in a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist) or a metrology tool or an inspection tool. Where applicable, the disclosure herein may apply to these and other substrate processing tools. Furthermore, a substrate may be processed more than once, for example to produce a multi-layer IC, and thus the term substrate as used herein may also refer to a substrate that already includes multiple processed layers.

[0058]

[0073] The terms "radiation" and "beam" as used herein with respect to lithography encompass all types of electromagnetic radiation, including ultraviolet (UV) or deep ultraviolet (DUV) radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams such as ion beams and electron beams.

[0059]

[0074] Various patterns on or provided by a patterning device may have different process windows, i.e., a space of process variables within which the patterns are to be produced. Examples of pattern specifications related to potential systematic defects include checking necking, line pullback, thinning, CD, edge placement, overlap, resist top loss, resist undercut and / or bridging. The process window of a pattern on a patterning device or an area thereof may be obtained by merging (e.g., overlapping) the process windows of each of the individual patterns. The boundary of the process window of a group of patterns includes the boundaries of the process windows of several individual patterns. In other words, these individual patterns limit the process window of the group of patterns.

[0060]

[0075] As shown in FIG. 2, the lithographic apparatus LA may form part of a lithographic cell LC, sometimes called a lithocell or cluster, which also includes apparatus for performing pre-exposure and post-exposure processes on the substrate. Conventionally, these include one or more spin coaters SC for depositing one or more resist layers, one or more developers for developing the exposed resist, one or more chill plates CH and / or one or more bake plates BK. A substrate handler or robot RO picks up one or more substrates from input / output ports I / O1, I / O2, moves them between the different process apparatus and delivers them to a loading bay LB of the lithographic apparatus. These apparatuses are often collectively referred to as a track, and are under the control of a track control unit TCU, which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus via a lithography control unit LACU. The various apparatuses can thus be operated to maximize throughput and processing efficiency.

[0061]

[0076] To ensure that a substrate exposed by a lithographic apparatus is accurately and consistently exposed and / or to monitor a part of a patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., a photolithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties, such as alignment, overlay (e.g., between structures of overlapping layers, or between structures in the same layer, e.g., provided separately in that layer by a double patterning process), linewidth, critical dimension (CD), focus offset, material properties, etc. Thus, a manufacturing facility in which the lithocell LC is located typically also includes a metrology system that measures some or all of the substrates W (FIG. 1) processed in the lithocell, or other objects in the lithocell. The metrology system may be part of the lithocell LC, or may be part of the lithographic apparatus LA (e.g., alignment sensor AS (FIG. 1)).

[0062]

[0077] The one or more parameters measured may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical line width) of features formed in or on the patterned substrate, focus or focus error of an optical lithography step, dose or dose error of an optical lithography step, optical aberrations of an optical lithography step, etc. The measurements are often made on dedicated metrology targets provided on the substrate. The measurements may be made after resist development and before etching, after etching, after deposition, and / or at other times.

[0063]

[0078] There are various techniques, including the use of scanning electron microscopes, image-based metrology tools, and / or various specialized tools, for making measurements of structures formed in a patterning process. As discussed above, a fast and non-invasive form of specialized metrology tool is one that directs a beam of radiation onto a target on the substrate surface and measures properties of the scattered (diffracted / reflected) beam. By evaluating one or more properties of the radiation scattered by the substrate, one or more properties of the substrate can be determined. Traditionally, this is sometimes referred to as diffraction-based metrology. One application of this diffraction-based metrology is the measurement of overlay. For example, alignment can be measured by comparing portions of the diffraction spectrum (e.g., comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0064]

[0079] Thus, in a device manufacturing process (e.g., a patterning process or a lithography process), a substrate or other object may be subjected to various types of measurements during or after the process. The measurements may determine whether a particular substrate is defective, may establish adjustments of the process and the equipment used in the process (e.g., aligning two layers on a substrate or aligning a patterning device to a substrate), may measure the performance of the process and the equipment, or may be for other purposes. Examples of measurements include optical imaging (e.g., optical microscopes), non-imaging optical measurements (e.g., diffraction-based measurements such as ASML's YieldStar metrology tools, ASML's SMASH metrology systems), mechanical measurements (e.g., profiling with a stylus, atomic force microscope (AFM)), and / or non-optical imaging (e.g., scanning electron microscope (SEM)). The SMASH (SMart Alignment Sensor Hybrid) system, described in U.S. Pat. No. 6,961,116, the entirety of which is incorporated herein by reference, employs a self-referencing interferometer that produces two overlapping, relatively rotated images of an alignment marker, detects the intensity in the pupil plane where the Fourier transforms of the images are interfered, and extracts position information from the phase difference between the diffraction orders of the two images, which appears as an intensity change in the interfered orders.

[0065]

[0080] The metrology results may be provided directly or indirectly to a supervisory control system SCS. If errors are detected, adjustments may be made to the exposure of subsequent substrates (especially if inspection can be done soon enough and quickly enough to allow further exposure of one or more other substrates in the batch) and / or to subsequent exposures of the exposed substrate. Also, already exposed substrates may be stripped and reworked to improve yield, or may be discarded, thereby avoiding further processing of substrates known to be defective. If only some target portions of a substrate are defective, further exposures may be made only to those portions that meet specifications. Other manufacturing process adjustments are also possible.

[0066]

[0081] A metrology system may be used to determine one or more properties of a substrate structure, in particular how one or more properties vary for different substrate structures or how different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or lithocell LC, or may be a stand-alone device.

[0067]

[0082] To enable metrology, one or more targets are often specially provided on the substrate. The targets may include, for example, alignment marks and / or other targets. Typically, the targets are specially designed and may include periodic structures. For example, the target on the substrate may include one or more 1D periodic structures (e.g., geometric features such as gratings) that are printed such that, after development, the periodic structural features are formed with solid resist lines. As another example, the target may include one or more 2D periodic structures (e.g., gratings) that are printed such that, after development, the periodic structures are formed with solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., one or more layers on the substrate).

[0068]

[0083] In some embodiments, one of the parameters of interest in the patterning process is overlay. Overlay can be measured using dark-field scatterometry, where the zeroth order of diffraction (corresponding to specular reflection) is blocked and only higher orders are processed. Examples of dark-field metrology can be found in PCT Patent Application Publications WO2009 / 078708 and WO2009 / 106279, which are incorporated by reference in their entirety. Further developments of this technology are described in U.S. Patent Application Publications US2011-0027704, US2011-0043791 and US2012-0242970, which are incorporated by reference in their entirety. Diffraction-based overlay using dark-field detection of diffraction orders allows overlay measurements on smaller targets. These targets can be smaller than the illumination spot and can be surrounded by device product structures on the substrate. In some embodiments, multiple targets can be measured in one radiation capture.

[0069]

[0084] FIG. 3 shows an exemplary inspection system 10 that may be used to determine overlay and / or perform other metrology operations. It comprises a radiation source 2 that projects or illuminates radiation onto a substrate W (which may, for example, comprise an overlay target in general). The redirected radiation is passed to a sensor such as a spectrometer detector 4 and / or other sensors that measure the spectrum (intensity as a function of wavelength) of the specularly reflected and / or diffracted radiation, for example as shown in the graph on the left side of FIG. 3. The sensor may generate an overlay signal that conveys, for example, overlay data indicative of a characteristic of the reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by one or more processors PRO, a generalized example of which is shown in FIG. 3, or by other operations.

[0070]

[0085] Figure 4 shows further possible details of the inspection system 10 shown in Figure 3. As shown in Figure 4, radiation emitted by the radiation source 2 is collimated using a lens system 12, transmitted through an interference filter 13 and a polarizer 17, reflected by a partially reflective surface 16 and focused to a spot S on the substrate W via an objective lens 15 having a high numerical aperture (NA) (e.g. at least 0.9 or at least 0.95). Immersion inspection setups (which use a fluid with a relatively high refractive index such as water) may have a numerical aperture greater than 1.

[0071]

[0086] As with the lithographic apparatus LA of FIG. 1, one or more substrate tables (not shown in FIG. 4) may be provided for holding the substrate W during measurement operations. The one or more substrate tables may be similar or identical in shape to the substrate table WT (a or b) of FIG. 1. In examples where the inspection system 10 is integrated with a lithographic apparatus, they may be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate relative to the measurement optics. Various sensors and actuators are provided, for example, to obtain the position of a target portion of interest of the structure (e.g. an overlay target) and bring it into position under the objective lens. Typically, many measurements will be made at different locations across the substrate W relative to the target portion of the structure. The substrate support may move in the X and Y directions to obtain different targets, and in the Z direction to obtain the desired location of the target portion relative to the focal point of the optics. For example, when in reality the optics are substantially stationary (typically in the X and Y directions, but possibly also in the Z direction) and the substrate is moving, it is convenient to think of and describe the operation as if the objective lens was brought to different locations relative to the substrate. Provided that the relative positions of the substrate and the optics are correct, it in principle does not matter whether either, both, or some combination of the optics is moving: the rest of the optics is stationary and the substrate is moving (e.g. in X and Y directions, and optionally also in Z and / or tilt directions).

[0072]

[0087] The radiation redirected by the substrate W then passes through the partially reflective surface 16 to the detector 18 for spectrum detection. The detector 18 may be located at the back-projection focal plane 11 (i.e. at the focal length of the lens 15), or the plane 11 may be re-imaged onto the detector 18 with auxiliary optics (not shown). The detector may be a two-dimensional detector such that a two-dimensional angular scatter spectrum of the substrate target 30 may be measured. The detector 18 may be, for example, an array of CCD or CMOS sensors and may use, for example, an integration time of 40 milliseconds per frame. The detector 18 shown in FIG. 4 may be, for example, similar and / or the same as the detector 4 shown in FIG. 3.

[0073]

[0088] The reference beam may be used, for example, to measure the intensity of incident radiation. To do this, when a radiation beam is incident on the partially reflective surface 16, a portion of it is transmitted through the partially reflective surface 16 as a reference beam directed to the reference mirror 14. The reference beam is then projected onto a different portion of the same detector 18, or alternatively onto a different detector (not shown).

[0074]

[0089] One or more interference filters 13 are available to select the wavelengths of interest. The interference filters may be tunable rather than comprising a set of different filters. A grating may be used instead of an interference filter. An aperture stop or spatial light modulator (not shown) may be provided in the illumination path to control the range of angles of incidence of the radiation on the target.

[0075]

[0090] Detector 18 may measure the intensity of the redirected radiation at a single wavelength (or a narrow wavelength range), separately at multiple wavelengths, or integrated over a range of wavelengths, and / or otherwise measure the intensity of the transverse magnetically polarized radiation and the transverse electrically polarized radiation separately, and / or the phase difference between the transverse magnetically polarized radiation and the transverse electrically polarized radiation.

[0076]

[0091] The target 30 on the substrate W may be a 1D grating that is printed such that after development the bars are formed of solid resist lines. The target 30 may be a 2D grating that is printed such that after development the grating is formed of solid resist pillars or vias in the resist. The bars, pillars or vias may be etched into or on the substrate (e.g. in one or more layers on the substrate). The pattern (e.g. of the bars, pillars or vias) may be sensitive to process variations in the patterning process (optical aberrations of the lithographic projection apparatus (particularly the projection system PS), focus variations, dose variations, etc.) and may appear as variations in the printed grating. Measurement data of the printed grating may therefore be used to reconstruct the grating. One or more parameters of the 1-D grating, such as line width and / or shape, or one or more parameters of the 2-D grating, such as width or length or shape of the pillars or vias, may be input to the reconstruction process performed by the processor PRO from knowledge of the printing step and / or other inspection processes.

[0077]

[0092] In addition to measuring parameters by reconstruction, angle resolved scatterometry is useful for measuring asymmetry of features of the product and / or resist pattern. A particular application of asymmetry measurement is the measurement of overlay, where the target 30 includes one set of periodic features overlaid on another set. The concept of asymmetry measurement using the apparatus of FIG. 3 or FIG. 4 is described, for example, in U.S. Patent Application Publication No. US2006-066855, which is incorporated herein in its entirety. The positions of the diffraction orders in the diffraction spectrum of the target are determined by the periodicity of the target, but the asymmetry of the diffraction spectrum indicates the asymmetry of the individual features that make up the target. In the system of FIG. 4, where the detector 18 can be an image sensor, such asymmetry of the diffraction orders is directly manifested as an asymmetry of the pupil image recorded by the detector 18. This asymmetry can be measured by digital image processing using the processor PRO and can be calibrated against a known value of overlay, for example.

[0078]

[0093] FIG. 5 shows a plan view of a typical target 30 and the extent of the illumination spot S in the apparatus of FIG. 4. To obtain a diffraction spectrum without interference from surrounding structures, in some embodiments, the target 30 may be a periodic structure (e.g., a grating) that is larger than the width (e.g., diameter) of the illumination spot S. The width of the spot S may be smaller than the width and length of the target. The target may be "underfilled" by the illumination, and the diffraction signal may be substantially free of signals from product features outside the target itself, etc. The illumination apparatus 2, 12, 13, 17 (FIG. 4) may be configured to provide illumination of uniform intensity across the back focal plane of the lens 15. Alternatively, the illumination may be limited in the on-axis or off-axis direction, for example, by including an aperture in the illumination path.

[0079]

[0094] FIG. 6 illustrates in schematic form an exemplary process for determining values ​​of one or more variables of interest of a target 30 based on measurement data obtained using metrology. Radiation detected by detector 18 provides a measured radiation distribution 608 of the target 30. For a given target 30, a radiation distribution 612 can be calculated / simulated from a parameterized model 606 using, for example, a numerical Maxwell solver 610. The parameterized model 606 illustrates exemplary layers of various materials that make up and are associated with the target 30. The parameterized model 606 may include one or more variables for the features and layers of the target portion under consideration that may be varied and derived. As illustrated in FIG. 6, one or more of the variables may include thickness t of one or more layers, width w (e.g., CD) of one or more features, height h of one or more features, and / or sidewall angle α of one or more features. Although not shown, one or more of the variables may further include, but are not limited to, one or more refractive indices of the layers (e.g., real or complex refractive index, refractive index tensor, etc.), extinction coefficients of one or more layers, absorption of one or more layers, resist loss during development, footing of one or more features, and / or line edge roughness of one or more features. The initial values ​​of the variables may be expected values ​​of the target being measured. Then, at 612, the measured radiation distribution 608 is compared to the calculated radiation distribution 612 to identify differences between the two. If there are differences, the values ​​of one or more of the variables of the parameterized model 606 may be changed and a new calculated radiation distribution 612 may be calculated and compared to the measured radiation distribution 608, and this may be done until the measured radiation distribution 608 and the calculated radiation distribution 612 are sufficiently matched. At that point, the values ​​of the variables of the parameterized model 606 provide a good or best match with the geometry of the actual target 30. In an embodiment, if the difference between the measured radiation distribution 608 and the calculated radiation distribution 612 is within a tolerance threshold, the match is sufficient.

[0080]

[0095] 7 illustrates a system 700 configured to condition radiation, such as light, for metrology. System 700 may form part of system 10, for example, as described above with respect to FIGS. 3 and 4. System 700 may be, for example, a subsystem of system 10. In some embodiments, one or more components of system 700 may be similar and / or the same as one or more components of system 10. In some embodiments, one or more components of system 700 may replace, be used in conjunction with, and / or augment one or more components of system 10.

[0081]

[0096] The system 700 comprises an optically transparent plate 702, one or more actuators 704, one or more processors PRO, and / or other components. The plate 702, actuators 704, processor PRO, and / or other components collectively constitute a mechanically controlled, stress-engineered optical waveplate as described herein to provide fast, active polarization control. The system 700 exploits stress birefringence that occurs within the (e.g., glass or crystal, and / or other transparent) plate 702 when a force is applied to the side of the plate 702. The force is applied using actuators 704 that are distributed along the side of the plate 702. The magnitude of the force can be controlled using the processor PRO. The described (e.g., fast and dynamic) polarization control allows for good accuracy and / or robustness for overlay metrology (by way of example) by minimizing sensitivity to unwanted asymmetries in the patterned substrate (e.g., sidewall angle changes, floor tilt, etc.) and maximizing sensitivity to features relevant for overlay metrology. In some embodiments, system 700 may be configured to replace conventional rotating wave plates and / or other devices and may improve the speed of systems in which polarization orientation is changed in less than a millisecond (e.g., system 10 shown in FIG. 4 ).

[0082]

[0097] The processor PRO may be included in a computing system CS and may operate based on computer or machine-readable instructions MRI (e.g., as described below in connection with FIG. 13). One or more components of the system 700 may be in bidirectional communication with each other as shown in FIG. 7 and / or with one or more components of the system 10 as shown in FIGS. 3 and 4. The communication may be by transmitting electronic signals between the individual components, transmitting data between the individual components, transmitting values ​​between the individual components, and / or other communication. The components of the system 700 may communicate by wire or wirelessly over a network such as the Internet or the Internet in combination with various other networks such as a local area network, a cellular network, or a personal area network, an internal organizational network, and / or other networks.

[0083]

[0098] In some embodiments, as shown in FIG. 8, the system 700 also includes a polarizer 800, an imaging lens 802, a sensor 804, and / or other components. The sensor 804 is configured to generate a metrology signal based on the light 808 being received by the sensor 804 after passing through the polarizer 800 and the plate 702. In some embodiments, the sensor 804 is included in a camera and / or other device. In some embodiments, the sensor 804 is the same as or similar to the detector 4 shown in FIG. 3 and / or the detector 18 shown in FIG. 4. As shown in FIG. 8, the imaging lens 802 may be positioned between the plate 702 and the sensor 804. In some embodiments, the imaging lens 802 is the same as or similar to one of the lenses or lens systems shown in FIG. 4 and described above (although it may be additional examples thereof). In some embodiments, the polarizer 800 is the same as or similar to the polarizer 17 shown in FIG. 4 (although it may be additional examples thereof).

[0084]

[0099] Returning to FIG. 7, plate 702 comprises an optically transparent material. Plate 702 may be formed from any transparent material that has a stress optical coefficient. The stress optical coefficient is defined by the ratio of the stress in plate 702 to the birefringence. Birefringence is an optical property of a material. A material has an index of refraction that depends on the polarization and propagation direction of the light. Birefringence may be stress induced (e.g., by actuator 704) as described herein. In some embodiments, plate 702 comprises glass, crystal, and / or other optically transparent materials that exhibit these properties.

[0085]

[0100] Plate 702 may have a circular cross-sectional shape (e.g., as shown in FIG. 7), square, rectangular, and / or other cross-sectional shape. Plate 702 may have a particular thickness and / or other characteristics. The shape and / or dimensions of plate 702 may be determined by a user based on, for example, the material used for plate 702, the application for which plate 702 is used (e.g., measuring overlays), optical behavior requirements of plate 702, handling requirements of plate 702, and / or other factors.

[0086]

[0101] When one or more forces are applied to the plate 702, a stress pattern may be generated in the plate 702. The stress pattern may include and / or be associated with birefringence (e.g., as described above). In response to the application of one or more stresses, the plate 702 is configured to change light passing through the plate 702 from a first polarization state to a second polarization state. In some embodiments, the plate 702 is configured with one or more actuators 704 and one or more processors PRO such that the wavelength of the light passing through the plate 702 may range from about 300 nanometers to about 1.5 micrometers, and the plate 702 is configured to change such light from a first polarization state to a second polarization state. For example, the first polarization state may be vertical. The second polarization state may be horizontal. The transmission wavelength range of the light passing through the plate 702 is large compared to conventional systems because it depends on the material used for the plate 702 and the large aperture that can be generated by the birefringence and dynamically controlled by the plate 702. The aperture may be greater than 10 mm, for example. A larger wavelength range allows more flexibility in the design of the instrument, allowing measurements to be performed at many wavelengths, and ultimately improving accuracy.

[0087]

[0102] One or more actuators 704 are configured to apply a force to the plate 702 to generate a stress pattern and / or induce birefringence in the plate 702. The actuators 704 are disposed on one or more edges of the plate 702. The actuators may be coupled to one or more edges of the plate 702 by adhesives, clips, clamps, screws, collars, and / or other mechanisms. In some embodiments, the actuators are coupled to the plate 702 but are not actually attached to the plate 702. Instead, the actuators 704 are held in contact with the plate 702 by a restraining force ("preload") that maintains contact with the edge of the plate 702. In some embodiments, the actuators 704 include multiple actuators that are symmetrically distributed around one or more edges of the plate 702. In FIG. 7, eight different actuators 704 are symmetrically distributed around the edge of the plate 702 (e.g., in FIG. 7, the plate 702 has only one edge). This is not intended to be limiting. Other quantities and arrangements of the actuators 704 are also contemplated.

[0088]

[0103] The actuators 704 are configured to be electronically controlled. Each actuator 704 is configured to convert an electrical signal into a mechanical displacement or stress. The mechanical displacement is configured to apply a force to the plate 702 that induces a stress in the plate 702. Each actuator 704 includes a high-precision force application mechanism. Each actuator 704 can control small mechanical displacements at high speeds (e.g., less than 1 millisecond).

[0089]

[0104] In some embodiments, one or more of the actuators 704 are piezoelectric. Piezoelectric actuators operate based on the piezoelectric effect, which is the ability of some materials to generate mechanical stress in response to an electric charge. The piezoelectric actuators 704 are configured to convert an electrical signal (or electrical energy in general) into a mechanical displacement. The electrical signal may be transmitted, for example, by a processor PRO or a computer system CS. An example of the actuator 704 may be the Thorlabs model PA4HKW or other models of the PA series.

[0090]

[0105] In response to a force being applied to the plate 702, the plate 702 includes, for example, a wave plate. The wave plate is configured to change the polarization state of light passing through the wave plate. For example, the polarization state may change from a first state to a second state as described above. The force applied by the actuator 704 induces an orientation and retardance in the plate 702. The orientation is controlled by the location and / or distribution of the force applied to the plate 702 by the actuator 704. The retardance is controlled by the magnitude of the force applied to the plate 702 by the actuator 704. The retardance includes, for example, the difference in optical phase shift between two polarization directions of light passing through the plate 702. The induced retardance and orientation are not uniform. Each varies across the plate. The central region of the plate is the area of ​​interest where the retardance and fast axis orientation are approximately uniform.

[0091]

[0106] One or more processors PRO are configured to control the actuators 704. The processor PRO is configured to control the actuators 704 to apply forces that create a stress pattern for imparting a particular polarization to light passing through the plate 702. This may be done according to a desired metrology function. The desired metrology function may be, for example, measurement of overlay and / or other parameters. The forces are configured to create a stress pattern for imparting a particular polarization to light passing through the plate according to the desired metrology function. Imparting a particular polarization to light includes conditioning the light passing through the plate for metrology.

[0092]

[0107] The one or more processors PRO are configured to individually control each of the one or more actuators 704 such that a stress pattern in the plate 702 is dynamically adjustable before, during, and / or after light passes through the plate 702. In some embodiments, the dynamic tuning includes applying different force magnitude combinations to different actuators 704 around the periphery of the plate 702 to change the birefringence of the plate 702 at controlled speeds of less than a millisecond. In some embodiments, the dynamic tuning includes applying different force magnitude combinations to different actuators 704 around the periphery of the plate 702 to change the orientation of the plate 702 at controlled speeds of less than a millisecond.

[0093]

[0108] The induced stress birefringence varies spatially across the plate 702. By precisely controlling and adjusting the force applied by the actuator 704, the central region and / or other regions of the plate 702 can be converted into a waveplate with any retardance value determined by the force. Because the parameter that determines the birefringence is the force, the processor PRO can be used to apply a combination of different force values ​​at sub-millisecond speeds to achieve high speed control of the birefringence value and orientation. The system 700 controls the retardance and orientation at any speed at sub-millisecond speeds. Thus, the plate 702 functions as a high speed dynamic waveplate.

[0094]

[0109] The orientation may be, for example, a fast axis orientation. Due to the above stress distribution, the glass material of the plate 702 acts as a birefringent material, resulting in different refractive indices for different polarization states. The slow / fast axis are the vibration directions of the polarization states that exhibit higher / lower refractive indices.

[0095]

[0110] 9-11 illustrate various aspects of the system 700 described above.

[0096]

[0111] FIG. 9 illustrates a mapped stress pattern 900 and orientation 902 in a plate 904 resulting from a force applied by an actuator (e.g., actuator 704, etc.) coupled to the plate 904. The plate 904 may be similar and / or the same as plate 702 described above. In this example, the actuator is not visible. However, the approximate location 906 of the actuator is apparent from the stress pattern 900. The stress pattern 900 illustrates contours 908 of differential stress. The stress pattern 900 includes and / or is associated with birefringence (e.g., as described above) caused by the force applied by the actuator. The generated stress birefringence varies spatially throughout the plate 904. In response to one or more stresses being applied by the actuator, the plate 904 is configured to change light passing through the plate 904 from a first polarization state to a second polarization state. In some embodiments, the wavelength of light passing through the plate 904 may range from about 300 nanometers to about 1.5 micrometers, and the plate 904 is configured to change such light from a first polarization state to a second polarization state. Also shown is an aperture 910 formed by the stress pattern 900 (whose location shown in FIG. 9 is approximate and not limiting). The aperture may be, for example, greater than 10 mm. The area of ​​the aperture 910 corresponds to an area where the birefringence changes slowly (e.g., as indicated by the stress pattern 900 toward the center of the plate 904).

[0097]

[0112] Orientation 902 is the orientation of the slow axis. As described above, when a force is applied to plate 904 by an actuator, plate 904 forms a waveplate. The waveplate is configured to shift the phase between two perpendicularly polarized components of a light wave passing through plate 904 such that there is a phase difference between the different components after passing through plate 904. For light entering plate 904, the component traveling along the optical axis of plate 904 travels at one speed, while the component traveling along the perpendicular axis travels at a different speed. The slow axis of plate 904 is perpendicular to the optical axis of plate 904. Orientation 902 shows the orientation of individual portions 912 of the slow axis around plate 904 caused by birefringence. Note that the birefringence of plate 904 varies from point to point across the cross section, as does the orientation of the slow / fast axes. The region of interest that acts as a uniform waveplate is the central region (as shown and described herein).

[0098]

[0113] FIG. 10 shows an image 1001 of a plate 1003 (e.g., similar and / or the same as plates 702 or 904 shown in FIGS. 7 and 9, respectively) between two crossed polarizers while a force is applied to the plate 1003 by an actuator (e.g., actuator 704 described above). The color changes in image 1001 in FIG. 10 correspond to the changing stresses induced in the plate 1003 by the force from the actuator. In this example, the actuator is again not visible. However, location 1005 corresponding to the location of the actuator is evident. Note that an aperture has been formed, as indicated by the dark, unchanging color in the center of the image. Note also that the pattern shown in FIG. 10 (and FIG. 9) is dynamically adjustable as described herein, allowing the pattern to be changed in time intervals of less than one millisecond.

[0099]

[0114] FIG. 11 illustrates a polarization state of light after passing through a central portion (e.g., an aperture) of a stress-engineered optical plate (e.g., plates 702, 904, 1003, etc., as shown in other figures), according to an embodiment. In this example, the light has a particular orientation, wavelength, power, ellipticity, and / or other properties imparted by the plate. As noted above, in some embodiments, the dynamic tuning of the force applied to the plate includes applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the birefringence of the plate at a controlled rate of less than a millisecond. In some embodiments, the dynamic tuning includes applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at a controlled rate of less than a millisecond. This control can be configured such that the light passing through the plate has a particular property as shown in FIG. 11. Note that FIG. 11 illustrates an elliptical polarization state. However, it could instead be a perfectly circular or perfectly linear state, which are special cases of the elliptical state.

[0100]

[0115] FIG. 12 illustrates a method 1200 of conditioning light for metrology. In some embodiments, conditioning light for metrology is performed as part of a semiconductor device manufacturing process. In some embodiments, one or more operations of the method 1200 may be performed in or by, for example, the system 700 shown in FIG. 7 and / or the system 10 shown in FIGS. 3 and 4, a computer system (e.g., shown in FIGS. 7 and 13 and described below), and / or by other systems. In some embodiments, the method 1200 includes applying a force to an optically transparent plate (operation 1202) and controlling the application of the force to generate a stress pattern to impart a particular polarization to light passing through the plate according to a desired metrology function (operation 1204). The method 1200 is described in the context of overlay measurement, but this is not intended to be limiting. The method 1200 may be generally applied to a number of different processes.

[0101]

[0116] The operations of method 1200 presented below are intended to be illustrative. In some embodiments, method 1200 may be accomplished by one or more additional operations not described and / or without one or more of the operations discussed. For example, in some embodiments, method 1200 may include additional operations including determining adjustments to a semiconductor device manufacturing process. Additionally, the order in which operations of method 1200 are shown in FIG. 12 and described below is not intended to be limiting.

[0102]

[0117] In some embodiments, one or more portions of method 1200 may be implemented in and / or controlled by one or more processing devices (e.g., digital processors, analog processors, digital circuits designed to process information, analog circuits designed to process information, state machines, and / or other mechanisms for electronically processing information). The one or more processing devices may include one or more devices that perform some or all of the operations of method 1200 in response to instructions electronically stored on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed (e.g., see the discussion below regarding FIG. 13 ) to perform one or more of the operations of method 1200.

[0103]

[0118] In operation 1202, a force is applied to an optically transparent plate using one or more actuators to generate a stress pattern in the plate. The stress pattern includes birefringence. The plate includes a transparent material. For example, the plate includes glass or crystal. In response to the force being applied to the plate to generate the stress pattern, the plate is configured to change light passing through the plate from a first polarization state to a second polarization state. In some embodiments, the plate is configured with the one or more actuators and one or more processors such that the wavelength of light passing through the plate can range from about 300 nanometers to about 1.5 micrometers. The plate may be similar and / or the same as plate 702 described above.

[0104]

[0119] The one or more actuators are disposed on one or more edges of the plate. In some embodiments, the one or more actuators include a plurality of actuators symmetrically distributed around one or more edges of the plate. In some embodiments, the one or more actuators are piezoelectric. The actuators may be the same and / or similar to actuator 704, for example, as described above.

[0105]

[0120] In some embodiments, in response to a force being applied to the plate, the plate includes, for example, a wave plate. The force applied by the actuator induces an orientation and retardance in the plate. The orientation is controlled by the location and / or distribution of the force applied to the plate by one or more actuators. The retardance is controlled by the magnitude of the force applied to the plate by one or more actuators. The induced retardance and orientation are not uniform. Each varies across the plate. The central region of the plate is the area of ​​interest where the retardance and fast axis orientation are approximately uniform.

[0106]

[0121] In operation 1204, one or more processors similar and / or the same as the processor PRO described above may be used to control the one or more actuators to apply forces. The forces are configured to generate a stress pattern to impart a particular polarization to light passing through the plate according to a desired metrology function. Imparting a particular polarization to the light includes tailoring the light passing through the plate for metrology. The desired metrology function may be, for example, an overlay measurement. The one or more processors are configured to individually control each of the one or more actuators such that the stress pattern in the plate is dynamically adjustable before, during, and / or after the light passes through the plate. In some embodiments, the dynamic tuning includes applying a combination of different force magnitudes to different actuators around the plate to change the birefringence of the plate at a controlled rate of less than a millisecond. In some embodiments, the dynamic tuning includes applying a combination of different force magnitudes to different actuators around the plate to change the orientation of the plate at a controlled rate of less than a millisecond.

[0107]

[0122] In some embodiments, method 1200 also includes irradiating a target in the patterned substrate (e.g., target 30 shown in FIGS. 3 and 4) with radiation. The radiation includes light and / or other radiation. The target may include one or more structures in the patterned substrate capable of providing a diffraction signal. The target may be included in a layer of the substrate, for example, in a semiconductor device structure. In some embodiments, the features include geometric features, such as 1D or 2D features, and / or other geometric features. As some non-limiting examples, the features may include gratings, lines, edges, a series of fine pitch lines and / or edges, and / or other features.

[0108]

[0123] The radiation may have a target wavelength and / or wavelength range, a target intensity, and / or other characteristics. The target wavelength and / or wavelength range, the target intensity, etc. may be input and / or selected by a user, determined by a system (e.g., system 10 shown in FIGS. 3 and 4 and / or system 700 shown in FIG. 7) based on previous overlay measurements, and / or determined in other ways. In some embodiments, the radiation includes light and / or other radiation. In some embodiments, the light includes visible light, infrared light, near infrared light, and / or other light. In some embodiments, the radiation may be any radiation suitable for interferometry.

[0109]

[0124] The radiation may be generated by a radiation source (e.g., projector 2 shown in FIGS. 3 and 4 and described above). In some embodiments, the radiation may be directed by the radiation source onto a target, a sub-portion of the target (e.g., less than the entire target), multiple targets, and / or otherwise onto a substrate. In some embodiments, the radiation may be directed by the radiation source onto the target in a time-varying manner. For example, the radiation may be rastered across the target (e.g., by moving the target under the radiation) such that different portions of the target are illuminated at different times. As another example, the properties of the radiation (e.g., wavelength, intensity, etc.) may be varied. This may create a time-varying data envelope, or window, for analysis. The data envelope may facilitate analysis of individual sub-portions of the target, comparison of one portion of the target to another portion and / or other targets (e.g., in other layers), and / or other analysis.

[0110]

[0125] In some embodiments, the method 1200 includes detecting reflected radiation from the target. Detecting the reflected radiation includes detecting one or more phase and / or amplitude (intensity) shifts of the reflected radiation from one or more geometric features of the target. The one or more phase and / or amplitude shifts correspond to one or more dimensions of the target. For example, the phase and / or amplitude of the reflected radiation from one side of the target is different relative to the phase and / or amplitude of the reflected radiation from another side of the target.

[0111]

[0126] Detecting one or more phase and / or amplitude (intensity) shifts of the reflected radiation from the target includes measuring local phase shifts (e.g., local phase delta) and / or amplitude variations corresponding to different portions of the target. For example, reflected radiation from a particular area of ​​the target may include a sinusoidal waveform having a particular phase and / or amplitude. Reflected radiation from a different area of ​​the target (or a target in a different layer) may also include a sinusoidal waveform, but with a different phase and / or amplitude. Detecting the reflected radiation also includes measuring the phase and / or amplitude differences of the reflected radiation of different diffraction orders. Detecting one or more local phase and / or amplitude shifts may be performed using, for example, the Hilbert transform and / or other techniques. Interferometry and / or other operations may be used to measure the phase and / or amplitude differences of the reflected radiation of different diffraction orders.

[0112]

[0127] In some embodiments, the method 1200 includes generating a metrology signal based on the detected reflected radiation from the target. The metrology signal is generated by a sensor (such as detector 18 in FIG. 14, a camera in FIG. 8, and / or other sensor) based on light received by the sensor after the light passes through a polarizer (see, e.g., FIGS. 4 and 8) and a plate. The metrology signal includes measurement information about the target. For example, the metrology signal may be an overlay signal that includes overlay measurement information, and / or other metrology signals. The measurement information (e.g., overlay values ​​and / or other information) may be determined using principles of interferometry and / or other principles.

[0113]

[0128] The metrology signal includes an electronic signal representative of and / or corresponding to radiation reflected from the target. The metrology signal may indicate, for example, an overlay value and / or other information associated with the target. Generating the metrology signal includes sensing the reflected radiation and converting the sensed reflected radiation into an electronic signal. In some embodiments, generating the metrology signal includes sensing different portions of the reflected radiation from different areas and / or different geometric shapes of the target and / or multiple targets and combining the different portions of the reflected radiation to form the metrology signal. This sensing and conversion may be performed by components similar and / or the same as the detector 4, detector 18, and / or processor PRO shown in Figures 3, 4, and 7, the camera shown in Figure 8, and / or other components.

[0114]

[0129] In some embodiments, generating the metrology signal may include directly measuring the dimensions and / or locations of the targets. For example, direct measurements of the dimensions and / or locations of the targets may be made using a scatterometer and / or other system. In some embodiments, the direct dimension and / or location measurements may be used in combination with and / or in place of the local phase and / or amplitude shifts described herein to determine overlay and / or other parameters. For example, output (e.g., relative) dimension and / or location measurements from a scatterometer system for various targets may be provided to a processor PRO (FIGS. 3, 4, 7) and / or other system components, and a metrology signal may be generated based at least in part on the output dimension measurements from the scatterometer system.

[0115]

[0130] In some embodiments, method 1200 includes determining an adjustment to a semiconductor device manufacturing process. In some embodiments, method 1200 includes determining one or more semiconductor device manufacturing process parameters. The one or more semiconductor device manufacturing process parameters may be determined based on one or more of the detected phase and / or amplitude variations, the overlay value indicated by the metrology signal, the dimensions determined by a scatterometer system, and / or other similar systems, and / or other information. The one or more parameters may include a parameter of the radiation (radiation used to determine the overlay), the overlay value, an alignment inspection position on a layer of a semiconductor device structure, a trajectory of a radiation beam across a target, and / or other parameters. In some embodiments, the process parameters may be broadly interpreted to include a stage position, a mask design, a metrology target design, a semiconductor device design, an intensity of radiation (e.g., used to expose a resist), an angle of incidence of radiation (e.g., used to expose a resist), a wavelength of radiation (e.g., used to expose a resist), a pupil size and / or shape, a resist material, and / or other parameters.

[0116]

[0131] In some embodiments, method 1200 includes determining process adjustments based on one or more determined semiconductor device manufacturing process parameters, adjusting semiconductor device manufacturing equipment based on the determined adjustments, and / or other operations. For example, if the determined overlay is not within a process tolerance, one or more manufacturing processes may produce an overlay that is out of tolerance, and the process parameters of one or more manufacturing processes may have drifted and / or changed so that the process no longer produces acceptable devices (e.g., an overlay measurement may exceed a threshold for acceptability). One or more new or adjusted process parameters may be determined based on the determination of the overlay. The new or adjusted process parameters may be configured to cause the manufacturing process to again produce acceptable devices. For example, the new or adjusted process parameters may be adjusted to bring a previously unacceptable overlay value back into the acceptable range. The new or adjusted process parameters may be compared to existing parameters of a given process. If there is a difference, the difference may be used, for example, to determine an adjustment to an apparatus used to manufacture the device (e.g., parameter "x" needs to be increased / decreased / changed to match the new or adjusted version of parameter "x" determined as part of method 1200). In some embodiments, method 1200 may include electronically adjusting the apparatus (e.g., based on the determined process parameters). Electronically adjusting the apparatus may include, for example, sending an electronic signal and / or other communication to the apparatus that effects a change in the apparatus. Electronic adjustment may include, for example, changing settings on the apparatus and / or other adjustments.

[0117]

[0132] FIG. 13 is a diagram of an exemplary computer system CS that may be used for one or more of the operations described herein. The computer system CS may be the same as or similar to the computer system shown in FIG. 7 and described above. The computer system CS comprises a bus BS or other communication mechanism for communicating information, and a processor PRO (or processors) coupled to the bus BS for processing information, similar and / or the same as the processor shown in FIG. 7 and described above. The computer system CS also comprises a main memory MM, such as a random access memory (RAM) or other dynamic storage device, for storing information and instructions executed by the processor PRO coupled to the bus BS. The main memory MM may also be used to store temporary variables or other intermediate information during execution of instructions by the processor PRO. The computer system CS further comprises a read only memory (ROM) ROM or other static storage device for storing static information and instructions for the processor PRO coupled to the bus BS. A storage device SD, such as a magnetic or optical disk, for storing information and instructions is provided and coupled to the bus BS.

[0118]

[0133] The computer system CS may be coupled via a bus BS to a display DS, such as a cathode ray tube (CRT) or flat panel or touch panel display, for displaying information to a computer user. Input devices ID, including alphanumeric and other keys, are coupled to the bus BS for communicating information and command selections to the processor PRO. Another type of user input device is a cursor control CC, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor PRO and for controlling cursor movement on the display DS. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), allowing the device to be located in a plane. Touch panel (screen) displays may also be used as input devices.

[0119]

[0134] In some embodiments, parts of one or more operations described herein may be performed by the computer system CS in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM. Such instructions may be read into the main memory MM from another computer-readable medium, such as a storage device SD. Execution of the sequences of instructions contained in the main memory MM causes the processor PRO to perform the process steps (operations) described herein. One or more processors of a multiprocessing device may also be used to execute the sequences of instructions contained in the main memory MM. In some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0120]

[0135] The term "computer-readable medium" or "machine-readable medium" as used herein refers to any medium that participates in providing instructions to a processor PRO for execution. Such media may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks, such as a storage device SD. Volatile media include dynamic memory, such as a main memory MM. Transmission media include coaxial cables, copper wires, and optical fibers (including the wires that comprise the bus BS). Transmission media may also take the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. The computer-readable medium may be a non-transitory computer-readable medium, such as a floppy disk, a flexible disk, a hard disk, a magnetic tape, any other magnetic medium, a CD-ROM, a DVD, any other optical medium, a punch card, a paper tape, any other physical medium with a pattern of holes, a RAM, a PROM, and an EPROM, a FLASH-EPROM, any other memory chip or cartridge. The non-transitory computer-readable medium may record instructions. The instructions, when executed by a computer, can perform any of the operations described herein. The transitory computer-readable medium may include, for example, a carrier wave or other propagating electromagnetic signal.

[0121]

[0136] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the processor PRO for execution. For example, the instructions may initially reside on a magnetic disk of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system CS may receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus BS may receive the data carried in the infrared signal and place the data on the bus BS. The bus BS carries the data to the main memory MM, from which the processor PRO retrieves and executes the instructions. The instructions received by the main memory MM may optionally be stored in a storage device SD before or after execution by the processor PRO.

[0122]

[0137] The computer system CS may also comprise a communication interface CI coupled to a bus BS. The communication interface CI provides a two-way data communication coupling to a network link NDL, which is connected to a local network LAN. For example, the communication interface CI may be an Integrated Services Digital Network (ISDN) card or a modem providing a data communication connection to a corresponding telephone line type. As another example, the communication interface CI may be a Local Area Network (LAN) card providing a data communication connection to a compatible LAN. A wireless link may also be implemented. In such implementations, the communication interface CI transmits and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0123]

[0138] The network link NDL typically provides data communication through one or more networks to other data devices. For example, the network link NDL may provide a connection to a host computer HC through a local network LAN. This may include data communication services provided through a World Wide Packet Data Communication Network (now commonly referred to as the "Internet" INT). The local network LAN (Internet) may use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks as well as the signals on the network data link NDL and through the communication interface CI that carry digital data to the computer system CS are exemplary forms of carrier waves transporting information.

[0124]

[0139] The computer system CS can send messages and receive data including program code through the network, the network data link NDL, and the communication interface CI. In the Internet example, the host computer HC may send a request code of an application program through the Internet INT, the network data link NDL, the local network LAN, and the communication interface CI. One such downloaded application may provide, for example, all or part of the methods described herein. The received code may be executed by the processor PRO when received and / or stored in the storage device SD or other non-volatile storage for later execution. The computer system CS may thus obtain the application code in the form of a carrier wave.

[0125]

[0140] Figure 14 shows a schematic diagram of an exemplary lithographic projection apparatus similar and / or the same as the apparatus shown in Figure 1 that may be used in conjunction with the techniques described herein. The apparatus 1000 comprises an illumination system IL for conditioning a radiation beam B. In this particular case, the illumination system also comprises a radiation source SO, a first object table (e.g., patterning device table) MT provided with a patterning device holder for holding a patterning device MA (e.g., a reticle) and connected to a first positioner PM (working in conjunction with a first position sensor PS1) for accurately positioning the patterning device, a second object table (substrate table) WT provided with a substrate holder for holding a substrate W (e.g., a resist-coated silicon wafer) and connected to a second positioner PW (working in conjunction with a second position sensor PS2) for accurately positioning the substrate, and a projection system ("lens") PS (e.g., a refractive, reflective or catadioptric optical system) for imaging an illuminated portion of the patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0126]

[0141] As depicted herein, the apparatus is of a transmissive type (i.e. has a transmissive patterning device). In general, however, the apparatus may be of a reflective type (e.g. has a reflective patterning device). The apparatus may employ other types of patterning device than a conventional mask; examples include a programmable mirror array or an LCD matrix.

[0127]

[0142] A radiation source SO (e.g. a mercury lamp or excimer laser, LPP (Laser Produced Plasma) EUV source) produces a beam of radiation. This beam is fed into an illumination system (illuminator) IL, either directly or after having traversed conditioning means, such as a beam expander Ex. The illuminator IL may comprise conditioning means for setting the outer and / or inner extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution of the beam. The illuminator IL will generally also comprise various other components, such as an integrator and a condenser. In this way, the beam B impinging on the patterning device MA has a desired uniformity and intensity distribution in its cross-section.

[0128]

[0143] It should be noted with regard to Figure 14 that the source SO can be within the housing of the lithographic projection apparatus (as is the case when the source SO is, for example, a mercury lamp), but it may also be remote from the lithographic projection apparatus and the radiation beam it generates can be directed into the apparatus (for example by means of suitable directing mirrors), this latter scenario being typical when the source SO is an excimer laser (for example based on KrF, ArF or F2 lasing).

[0129]

[0144] The beam B is then intercepted by the patterning device MA, which is held on a patterning device table MT. After traversing the patterning device MA, the beam B passes through a lens, which focuses the beam B onto a target portion C of the substrate W. Using the second positioning means (and interferometry means), the substrate table WT can be accurately moved to, for example, position different target portions C in the path of the beam B. Similarly, the first positioning means may be used to accurately position the patterning device MA with respect to the path of the beam B, for example after mechanical retrieval of the patterning device MA from a patterning device library or during a scan. Typically, movement of the object tables MT, WT will be realized with the aid of not explicitly stated long-stroke modules (coarse positioning) and short-stroke modules (fine positioning). However, in the case of a stepper (as opposed to a step-and-scan tool) the patterning device table MT may simply be connected to a short-stroke actuator, or may be fixed.

[0130]

[0145] The depicted tool (similar or the same as that shown in FIG. 1 ) can be used in two different modes. In step mode, the patterning device table MT is kept essentially stationary and the entire patterning device image is projected onto the target portion C in one movement (i.e. in a single "flash"). The substrate table WT is then shifted in the x and / or y direction so that a different target portion C can be irradiated with the beam B. In scan mode, essentially the same scenario applies, but a given target portion C is not exposed in a single "flash". Instead, the patterning device table MT is movable in a given direction (the so-called "scan direction", e.g. the y direction) with a speed v, such that the projection beam B scans the patterning device image while the substrate table WT is simultaneously moved in the same or opposite direction with a speed V=Mv, in which M is the magnification of the lens PL (typically M=¼ or ⅕). In this way, a relatively large target portion C can be exposed, without having to compromise on resolution.

[0131]

[0146] FIG. 15 shows the apparatus 1000 with the source collector module SO, the illumination system IL and the projection system PS in more detail. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained within the closed structure 220 of the source collector module SO. The EUV radiation emitting plasma 210 may be formed by a discharge produced plasma source. The EUV radiation may be generated by a gas or vapor, for example Xe gas, Li vapor or Sn vapor, in which a high temperature plasma 210 is created to emit radiation in the EUV range of the electromagnetic spectrum. The plasma 210 is created, for example, by an electric discharge that produces an at least partially ionized plasma. For example, a partial pressure of 10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may be required for efficient generation of radiation. In an embodiment, a plasma of excited tin (Sn) is provided to generate the EUV radiation.

[0132]

[0147] Radiation emitted by the plasma 210 passes from the source chamber 211 into the collector chamber 212 via an optional gas barrier or contamination trap 230 (sometimes called a contamination barrier or foil trap) located in or behind the opening of the source chamber 211. The contamination trap 230 may comprise a channel structure. The contamination trap 230 may also comprise a gas barrier or a combination of a gas barrier and a channel structure. The contamination trap 230 as further illustrated herein comprises at least a channel structure.

[0133]

[0148] The source chamber 211 may comprise a radiation collector CO, which may be a so-called grazing incidence collector. The radiation collector CO has an upstream radiation collector side 251 and a downstream radiation collector side 252. Radiation traversing the collector CO may be reflected off a grating spectral filter 240 and focused to a virtual source point IF along an optical axis indicated by line "O". The virtual source point IF is commonly referred to as an intermediate focus, and the source collector module is configured such that the intermediate focus IF is located at or near the opening 221 of the enclosure structure 220. The virtual source point IF is an image of the radiation emitting plasma 210.

[0134]

[0149] The radiation subsequently traverses an illumination system IL, which may comprise a faceted field mirror device 22 and a facetted pupil mirror device 24 configured to provide a desired angular distribution of the radiation beam 21 at the patterning device MA, and a desired uniformity of the radiation intensity at the patterning device MA. Upon reflection of the radiation beam 21 off the patterning device MA, held by a support structure MT, a patterned beam 26 is formed, which is imaged by the projection system PS via reflective elements 28, 330 onto a substrate W held by a substrate table WT.

[0135]

[0150] Generally, more elements than shown may be present in the illumination optics unit IL and projection system PS. A grating spectral filter 240 may optionally be present depending on the type of lithographic apparatus. Further, there may be more mirrors than shown, for example 1-6 additional reflective elements may be present in the projection system PS than shown in Figure 15.

[0136]

[0151] 15 is depicted as a nested collector with grazing incidence reflectors 253, 254 and 255 as just one example of a collector (or collector mirror). The grazing incidence reflectors 253, 254 and 255 are arranged axially symmetrically about the optical axis O, and this type of collector optic CO is sometimes used in combination with a discharge produced plasma source, often referred to as a DPP source.

[0137]

[0152] Alternatively, the source collector module SO may be part of an LPP radiation system as shown in Fig. 16. A laser LA is configured to impart laser energy to a fuel such as xenon (Xe), tin (Sn) or lithium (Li) to generate a highly ionized plasma 210 with an electron temperature of tens of eV. Energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma and collected by a near-normal incidence collector system CO and focused into an opening 221 in a confinement structure 220.

[0138]

[0153] The embodiments may be further described using the following clauses. 1. A system configured to condition light for metrology, the system comprising: an optically transparent plate; one or more actuators configured to apply forces to the plate that create a stress pattern in the plate; and one or more processors configured to control the one or more actuators that apply the forces that create the stress pattern to impart a particular polarization to light passing through the plate in accordance with a desired metrology function. 2. The system of clause 1, wherein the plate comprises a wave plate in response to a force being applied to the plate. 3. The system of clause 1 or 2, wherein the plate comprises a transparent material and is configured to change light passing through the plate from a first polarization state to a second polarization state in response to a force being applied to the plate to generate a stress pattern. 4. The system of any one of clauses 1 to 3, wherein an applied force induces orientation and retardance in the plate. 5. The system of any one of clauses 1 to 4, wherein the orientation is controlled by the location and / or distribution of forces applied to the plate by one or more actuators. 6. The system of any one of clauses 1 to 5, wherein the retardance is controlled by the magnitude of force applied to the plate by one or more actuators. 7. The system of any one of clauses 1 to 6, wherein the plate comprises glass or crystal. 8. The system of any one of clauses 1 to 7, wherein one or more of the actuators is piezoelectric. 9. The system of any one of clauses 1 to 8, wherein the stress pattern includes birefringence. 10. The system of any one of clauses 1 to 9, wherein the one or more processors are configured to individually control each of the one or more actuators such that the stress pattern within the plate is dynamically adjustable before, during, and / or after light passes through the plate. 11. The system of any one of clauses 1 to 10, wherein the dynamic tuning comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to vary the birefringence of the plate at controlled rates of less than a millisecond. 12. The system of any one of clauses 1 to 11, wherein the dynamic adjustment includes applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at a controlled rate of less than a millisecond. 13. The system of any one of clauses 1 to 12, wherein one or more actuators are disposed on one or more edges of the plate. 14. The system of any one of clauses 1 to 13, wherein the one or more actuators include a plurality of actuators symmetrically distributed around one or more edges of the plate. 15. The system of any one of clauses 1 to 14, wherein the plate, the one or more actuators, and the one or more processors are configured such that light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers. 16. The system of any one of clauses 1 to 15, wherein imparting a particular polarization to the light includes conditioning the light passing through the plate for metrology. 17. The system of any one of clauses 1 to 16, wherein the system further comprises a polarizer and a sensor, the sensor configured to generate a metrology signal based on light received by the sensor after the light has passed through the polarizer and the plate. 18. The system of any one of clauses 1 to 17, wherein the sensor is included in a camera. 19. The system of any one of clauses 1 to 18, further comprising an imaging lens positioned between the plate and the sensor. 20. The system of any one of clauses 1 to 19, wherein the metrology signals include overlay signals related to a semiconductor manufacturing process. 21. A method for conditioning light for metrology, the method including: applying forces to an optically transparent plate using one or more actuators that create a stress pattern in the plate; and controlling, using one or more processors, the one or more actuators to apply the forces that create the stress pattern to impart a particular polarization to light passing through the plate in accordance with a desired metrology function. 22. The method of clause 21, wherein the plate comprises a waveplate in response to a force being applied to the plate. 23. The method of clause 21 or 22, wherein the plate comprises a transparent material, and wherein the plate is configured to change light passing through the plate from a first polarization state to a second polarization state in response to a force being applied to the plate to generate a stress pattern. 24. The method of any one of clauses 21 to 23, wherein the applied force induces orientation and retardance in the plate. 25. The method of any one of clauses 21 to 24, wherein the orientation is controlled by the location and / or distribution of forces applied to the plate by one or more actuators. 26. The method of any one of clauses 21 to 25, wherein the retardance is controlled by the magnitude of force applied to the plate by one or more actuators. 27. The method of any one of clauses 21 to 26, wherein the plate comprises glass or crystal. 28. The method of any one of clauses 21 to 27, wherein one or more actuators are piezoelectric. 29. The method of any one of clauses 21 to 28, wherein the stress pattern includes birefringence. 30. The method of any one of clauses 21 to 29, wherein the one or more processors are configured to individually control each of the one or more actuators such that the stress pattern within the plate is dynamically adjustable before, during, and / or after light passes through the plate. 31. The method of any one of clauses 21 to 30, wherein the dynamic tuning comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to vary the birefringence of the plate at a controlled rate of less than a millisecond. 32. The method of any one of clauses 21 to 31, wherein the dynamic adjustment comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at a controlled rate of less than a millisecond. 33. The method of any one of clauses 21 to 32, wherein the one or more actuators are disposed on one or more edges of the plate. 34. The method of any one of clauses 21 to 33, wherein the one or more actuators include a plurality of actuators symmetrically distributed around one or more edges of the plate. 35. The method of any one of clauses 21 to 34, wherein the plate, the one or more actuators, and the one or more processors are configured such that light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers. 36. The method of any one of clauses 21 to 35, wherein imparting light with a particular polarization comprises conditioning light passing through a plate for metrology. 37. The method of any one of clauses 21 to 36, wherein the method further includes using a sensor to generate a metrology signal based on light received by the sensor after the light has passed through the polarizer and the plate. 38. The method of any one of clauses 21 to 37, wherein the sensor is included in a camera. 39. The method of any one of clauses 21 to 38, further comprising passing the light through an imaging lens positioned between the plate and the sensor. 40. The method of any one of clauses 21 to 39, wherein the metrology signals include overlay signals associated with a semiconductor manufacturing process. 41. A non-transitory computer readable medium having instructions thereon which, when executed by a computer, cause an operation including applying forces to an optically transparent plate using one or more actuators that create a stress pattern in the plate, and controlling, using one or more processors, the one or more actuators to apply the forces that create the stress pattern to impart a particular polarization to light passing through the plate in accordance with a desired metrology function. 42. The medium of clause 41, in which the plate comprises a wave plate in response to a force being applied to the plate. 43. The medium of clause 41 or 42, wherein the plate comprises a transparent material, and wherein in response to a force being applied to the plate to generate a stress pattern, the plate is configured to change light passing through the plate from a first polarization state to a second polarization state. 44. The medium of any one of clauses 41 to 43, wherein an applied force induces orientation and retardance in the plates. 45. The medium of any one of clauses 41 to 44, wherein the orientation is controlled by the location and / or distribution of forces applied to the plate by one or more actuators. 46. ​​The medium of any one of clauses 41 to 45, wherein the retardance is controlled by the magnitude of force applied to the plate by one or more actuators. 47. A medium according to any one of clauses 41 to 46, wherein the plate comprises glass or crystal. 48. The medium of any one of clauses 41 to 47, wherein one or more of the actuators is piezoelectric. 49. A medium according to any one of clauses 41 to 48, in which the stress pattern includes birefringence. 50. The medium of any one of clauses 41 to 49, wherein the one or more processors are configured with instructions to individually control each of the one or more actuators such that the stress pattern within the plate is dynamically adjustable before, during, and / or after light passes through the plate. 51. The medium of any one of clauses 41 to 50, wherein the dynamic tuning comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to vary the birefringence of the plate at a controlled rate of less than a millisecond. 52. The medium of any one of clauses 41 to 51, wherein the dynamic adjustment includes applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at a controlled rate of less than a millisecond. 53. The medium of any one of clauses 41 to 52, wherein one or more actuators are arranged on one or more edges of the plate. 54. The medium of any one of clauses 41 to 53, wherein the one or more actuators comprise a plurality of actuators symmetrically distributed around one or more edges of the plate. 55. The medium of any one of clauses 41 to 54, wherein the plate, the one or more actuators, and the one or more processors are configured such that light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers. 56. A medium according to any one of clauses 41 to 55, wherein imparting a particular polarization to light includes conditioning light passing through a plate for metrology. 57. The medium of any one of clauses 41 to 56, wherein the instructions further cause an operation including using the sensor to generate a metrology signal based on light received by the sensor after the light has passed through the polarizer and the plate. 58. The medium of any one of clauses 41 to 57, wherein the sensor is included in a camera. 59. The medium of any one of clauses 41 to 58, wherein the light also passes through an imaging lens positioned between the plate and the sensor. 60. The medium of any one of clauses 41 to 59, wherein the metrology signals include overlay signals related to a semiconductor manufacturing process. 61. A system configured to condition light for overlay measurements as part of a semiconductor manufacturing process, the system configured to dynamically condition birefringence and / or orientation of an optical plate before, during, and / or after light passes through the plate, the dynamic conditioning comprising applying a combination of different force magnitudes to different actuators around a periphery of the plate to change the birefringence and / or orientation of the plate at a controlled rate of less than a millisecond, the system comprising: a plate comprising a transparent material and configured to change light passing through the plate from a first polarization state to a second polarization state in response to forces being applied to the plate by the different actuators; the different actuators comprising a plurality of piezoelectric actuators symmetrically distributed around one or more edges of the plate and configured to apply birefringence and / or orientation generating forces to the plate; and one or more processors configured to individually control each of the plurality of actuators to apply the birefringence and / or orientation generating forces to impart a particular polarization to light passing through the plate to change the light to the second polarization state. 62. The system of clause 61, wherein the plate is characterized by an orientation and a retardance in response to a force being applied to the plate. 63. The system of clause 61 or 62, wherein the orientation is controlled by the location and / or distribution of forces applied to the waveplate by the multiple actuators, and the retardance is controlled by the magnitude of forces applied to the waveplate by the multiple actuators. 64. The system of any one of clauses 61 to 63, wherein the plate, the plurality of actuators, and the one or more processors are configured such that light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers. 65. The system of any one of clauses 61 to 64, wherein the system further comprises a polarizer and a sensor, the sensor configured to generate a metrology signal based on light received by the sensor after the light has passed through the polarizer and the plate, and the metrology signal comprises an overlay signal associated with a semiconductor manufacturing process.

[0139]

[0154] The concepts disclosed herein may be associated with any general imaging system for imaging sub-wavelength features, and may be particularly useful with new imaging techniques capable of producing ever-shorter wavelengths. New techniques already in use include EUV (Extreme Ultraviolet), DUV lithography capable of producing 193 nm wavelengths with ArF lasers, and even 157 nm wavelengths with Fluorine lasers. EUV lithography can also produce wavelengths in the range of 20-5 nm by using synchrotrons or by bombarding materials (either solids or plasmas) with high energy electrons to produce photons in this range.

[0140]

[0155] Although the concepts disclosed herein may be used for imaging onto substrates such as silicon wafers, it is to be understood that the disclosed concepts may be used with any type of lithographic imaging system, for example, those used for imaging onto substrates other than silicon wafers. Additionally, combinations and subcombinations of the disclosed elements may constitute separate embodiments.

[0141]

[0156] The above description is intended to be illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications can be made as described without departing from the scope of the claims set forth below.

Claims

1. 1. A system configured to condition light for metrology, the system comprising: an optically transparent plate; one or more actuators configured to apply a force to the plate that generates a stress pattern in the plate; and one or more processors configured to control the one or more actuators to apply the forces that create the stress pattern to impart a particular polarization to light passing through the plate according to a desired metrology function.

2. The system of claim 1 , wherein the plate comprises a wave plate in response to the force being applied to the plate.

3. 3. The system of claim 1 or 2, wherein the plate comprises a transparent material and is configured to change the light passing through the plate from a first polarization state to a second polarization state in response to the force being applied to the plate to create the stress pattern.

4. The system of claim 1 or 2, wherein the applied force induces an orientation and retardance in the plate.

5. The system of claim 4 , wherein the orientation is controlled by the location and / or distribution of forces applied to the plate by the one or more actuators.

6. The system of claim 4 , wherein the retardance is controlled by the magnitude of the force applied to the plate by the one or more actuators.

7. The system of claim 1 or 2, wherein the plate comprises glass or crystal.

8. The system of claim 1 or 2, wherein the one or more actuators are piezoelectric.

9. The system of claim 1 or 2, wherein the stress pattern comprises birefringence.

10. 3. The system of claim 1 or 2, wherein the one or more processors are configured to individually control each of the one or more actuators such that the stress pattern within the plate is dynamically adjustable before, during, and / or after the light passes through the plate.

11. 11. The system of claim 10, wherein dynamic tuning comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the birefringence of the plate at controlled speeds of less than a millisecond.

12. The system of claim 10 , wherein dynamic adjustment comprises applying a combination of different force magnitudes to different actuators around the periphery of the plate to change the orientation of the plate at a controlled rate of less than a millisecond.

13. The system of claim 1 or 2, wherein the one or more actuators are disposed on one or more edges of the plate.

14. The system of claim 1 or 2, wherein the one or more actuators comprise a plurality of actuators symmetrically distributed around one or more edges of the plate.

15. 3. The system of claim 1 or 2, wherein the plate, the one or more actuators, and the one or more processors are configured such that the light passing through the plate can have a wavelength ranging from about 300 nanometers to about 1.5 micrometers.

16. 3. The system of claim 1, wherein imparting a particular polarization to the light comprises conditioning the light passing through the plate for metrology.

17. 3. The system of claim 1 or 2, wherein the system further comprises a polarizer and a sensor, the sensor configured to generate a metrology signal based on light received by the sensor after the light passes through the polarizer and the plate.

18. The system of claim 17 , wherein the sensor is included in a camera.

19. 20. The system of claim 17, further comprising an imaging lens positioned between the plate and the sensor.

20. 20. The system of claim 17, wherein the metrology signals include overlay signals associated with a semiconductor manufacturing process.

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