WO2024099740A1 - Procédé et appareil de mesure de mise au point d'inspection - Google Patents

Procédé et appareil de mesure de mise au point d'inspection Download PDF

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Publication number
WO2024099740A1
WO2024099740A1 PCT/EP2023/079327 EP2023079327W WO2024099740A1 WO 2024099740 A1 WO2024099740 A1 WO 2024099740A1 EP 2023079327 W EP2023079327 W EP 2023079327W WO 2024099740 A1 WO2024099740 A1 WO 2024099740A1
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Prior art keywords
substrate
image plane
metrology system
spot
optical element
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PCT/EP2023/079327
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English (en)
Inventor
Raul Andres GUEVARA TORRES
Gregory Warren JENKINS
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Asml Netherlands B.V.
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Publication of WO2024099740A1 publication Critical patent/WO2024099740A1/fr

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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70605—Workpiece metrology
    • G03F7/706843—Metrology apparatus
    • G03F7/706851—Detection branch, e.g. detector arrangements, polarisation control, wavelength control or dark/bright field detection
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
    • G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
    • G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
    • G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
    • G03F9/7026—Focusing

Definitions

  • the present disclosure relates generally to metrology methods and tools for use in lithographic apparatuses and more particularly to methods and systems for identifying an in-focus condition in a microscope of an inspection tool.
  • a lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate.
  • a lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs).
  • a patterning device which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC.
  • This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation- sensitive material (resist) provided on the substrate.
  • a single substrate will contain a network of adjacent target portions that are successively patterned.
  • lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”- direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
  • an exposed substrate After imaging, it may be useful to inspect an exposed substrate to measure one or more properties such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. If an error is detected, an adjustment may be made to an exposure of one or more subsequent substrates. This may particularly useful, for example, if the inspection can be done soon and fast enough that another substrate of the same batch is still to be exposed. Also, an already exposed substrate may be stripped and reworked (to improve yield) or discarded, thereby avoiding performing an exposure on a substrate that is known to be faulty. In a case where only some target portions of a substrate are faulty, a further exposure may be performed only on those target portions which are good. Another possibility is to adapt a setting of a subsequent process step to compensate for the error, e.g., the time of a trim etch step can be adjusted to compensate for substrate-to-substrate CD variation resulting from the lithographic process step.
  • a method of measuring a focus position in a metrology system including introducing an optical element into a measurement arm of the metrology system, the optical element being configured and arranged to modify a point spread function at at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions, illuminating a substrate comprising features to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane, and controlling a focal position of the substrate on the basis of a first spot characteristic at the image plane at the first position to a second spot characteristic at the image plane at the second position.
  • the first spot characteristic is a first spot size
  • the second spot characteristic is a second spot size
  • controlling a focal position of the substrate includes changing a focal position of the substrate until the first spot size and the second spot size are equal.
  • the first spot characteristic is a first intensity
  • the second spot characteristic is a second intensity
  • controlling a focal position of the substrate comprises changing a focal position of the substrate until the first intensity and the second intensity are equal.
  • a method of measuring a focus position in a metrology system includes introducing an optical element into a measurement arm of the metrology system, the optical element being configured and arranged to modify a point spread function at at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions, illuminating a substrate comprising features to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane, an illumination pattern of the measurement beam having a plurality of separate sources, comparing a plurality of spot characteristics at the image plane at the first position to a second spot characteristic at the image plane at the second position, and changing a focal position of the substrate until the first spot characteristic and the second spot characteristic are equal.
  • a non-transitory computer program product comprising machine-readable instructions configured to cause a processor to cause performance of a method described herein.
  • Figure 1 schematically depicts an embodiment of a lithographic cell or cluster
  • Figure 2 schematically depicts an embodiment of a scatterometer for use as a metrology device
  • Figure 3 schematically depicts another embodiment of a scatterometer for use as a metrology device
  • Figure 4 depicts a composite metrology target formed on a substrate
  • Figure 5A is a schematic representation of a prior art metrology system and Figure 5B is a schematic representation of an embodiment
  • Figure 6 schematically illustrates an embodiment of a device for determining focus in accordance with an embodiment
  • Figure 7 is an example of a focus/defocus curve
  • Figure 8 is an example of an optical element in accordance with an embodiment
  • Figure 9 is a schematic of a pinhole source in accordance with an embodiment
  • Figure 10 illustrates point spread functions generated by pinhole sources
  • Figure 11 illustrates the effect of introducing a phase plate to modify the point spread functions of Figure 10.
  • Figures 12A and 12B illustrate a correspondence between defocus and intensity (12A) and between defocus and width (12B).
  • a lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to as a lithocell or lithocluster, which also includes apparatus to perform one or more pre- and post-exposure processes on a substrate.
  • a lithographic cell LC also sometimes referred to as a lithocell or lithocluster
  • apparatus to perform one or more pre- and post-exposure processes on a substrate Conventionally these include one or more spin coaters SC to deposit a resist layer, one or more developers DE to develop exposed resist, one or more chill plates CH and one or more bake plates BK.
  • a substrate handler, or robot, RO picks up a substrate from input/output ports I/O I , I/O2, moves it between the different process devices and delivers it to the loading bay LB of the lithographic apparatus.
  • track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithographic control unit LACU.
  • SCS supervisory control system
  • LACU lithographic control unit
  • an exposed substrate In order that the substrate that is exposed by the lithographic apparatus is exposed correctly and consistently, it is desirable to inspect an exposed substrate to measure one or more properties such as overlay error between subsequent layers, line thickness, critical dimension (CD), etc. If an error is detected, an adjustment may be made to an exposure of one or more subsequent substrates. This may particularly useful, for example, if the inspection can be done soon and fast enough that another substrate of the same batch is still to be exposed. Also, an already exposed substrate may be stripped and reworked (to improve yield) or discarded, thereby avoiding performing an exposure on a substrate that is known to be faulty. In a case where only some target portions of a substrate are faulty, a further exposure may be performed only on those target portions which are good. Another possibility is to adapt a setting of a subsequent process step to compensate for the error, e.g., the time of a trim etch step can be adjusted to compensate for substrate-to-substrate CD variation resulting from the lithographic process step.
  • a patterning device MA may be provided with a functional pattern (i.e. a pattern which will form part of an operational device).
  • the patterning device may be provided with a measurement pattern which does not form part of the functional pattern.
  • the measurement pattern may be, for example, located to one side of the functional pattern.
  • the measurement pattern may be used, for example, to measure alignment of the patterning device relative to the substrate table WT of the lithographic apparatus, or may be used to measure some other parameter (e.g., overlay).
  • the techniques described herein may be applied to such a measurement pattern.
  • wafer features and lithographic apparatus attributes may be used to update a design for the reticle to improve performance.
  • locations of metrology targets may be located in accordance with measured and/or simulated features of the wafer such that the effects of the wafer features and apparatus attributes are reduced.
  • similar features of the wafer and/or lithographic system may be used to update positions and/or orientations for the functional patterns.
  • An inspection apparatus is used to determine one or more properties of a substrate, and in particular, how one or more properties of different substrates or different layers of the same substrate vary from layer to layer and/or across a substrate.
  • the inspection apparatus may be integrated into the lithographic apparatus LA or the lithocell LC or may be a stand-alone device. To enable most rapid measurements, it is desirable that the inspection apparatus measure one or more properties in the exposed resist layer immediately after the exposure.
  • the latent image in the resist has a very low contrast - there is only a very small difference in refractive index between the part of the resist which has been exposed to radiation and that which has not - and not all inspection apparatus have sufficient sensitivity to make useful measurements of the latent image. Therefore measurements may be taken after the post-exposure bake step (PEB) which is customarily the first step carried out on an exposed substrate and increases the contrast between exposed and unexposed parts of the resist.
  • the image in the resist may be referred to as semi-latent.
  • Figure 2 depicts an embodiment of a scatterometer SMI. It comprises a broadband (white light) radiation projector 2 which projects radiation onto a substrate 6. The reflected radiation is passed to a spectrometer detector 4, which measures a spectrum 10 (i.e., a measurement of intensity as a function of wavelength) of the specular reflected radiation. From this data, the structure or profile giving rise to the detected spectrum may be reconstructed by processing unit PU, e.g., by Rigorous Coupled Wave Analysis and non-linear regression or by comparison with a library of simulated spectra as shown at the bottom of Figure 3.
  • processing unit PU e.g., by Rigorous Coupled Wave Analysis and non-linear regression or by comparison with a library of simulated spectra as shown at the bottom of Figure 3.
  • a scatterometer may be configured as a normal-incidence scatterometer or an oblique-incidence scatterometer.
  • FIG. 3 Another embodiment of a scatterometer SM2 is shown in Figure 3.
  • the radiation emitted by radiation source 2 is focused using lens system 12 through interference filter 13 and polarizer 17, reflected by partially reflective surface 16 and is focused onto substrate W via a microscope objective lens 15, which has a high numerical aperture (NA), desirably at least 0.9 or at least 0.95.
  • NA numerical aperture
  • An immersion scatterometer may even have a lens with a numerical aperture over 1.
  • the reflected radiation then transmits through partially reflective surface 16 into a detector 18 in order to have the scatter spectrum detected.
  • the detector may be located in the back-projected pupil plane 11, which is at the focal length of the lens 15, however the pupil plane may instead be re-imaged with auxiliary optics (not shown) onto the detector 18.
  • the pupil plane is the plane in which the radial position of radiation defines the angle of incidence and the angular position defines the azimuth angle of the radiation.
  • the detector is desirably a two-dimensional detector so that a two-dimensional angular scatter spectrum (i.e., a measurement of intensity as a function of angle of scatter) of the substrate target can be measured.
  • the detector 18 may be, for example, an array of CCD or CMOS sensors, and may have an integration time of, for example, 40 milliseconds per frame.
  • Non-specular radiation i.e., diffraction orders of magnitude ⁇ 1 or higher
  • specular radiation i.e., diffraction orders of magnitude ⁇ 1 or higher
  • a reference beam is often used, for example, to measure the intensity of the incident radiation. To do this, when the radiation beam is incident on the partially reflective surface 16 part of it is transmitted through the surface as a reference beam towards a reference mirror 14. The reference beam is then projected onto a different part of the same detector 18.
  • One or more interference filters 13 are available to select a wavelength of interest in the range of, say, 405 - 790 nm or even lower, such as 200 - 300 nm.
  • the interference filter(s) may be tunable rather than comprising a set of different filters.
  • a grating could be used instead of or in addition to one or more interference filters.
  • the detector 18 may measure the intensity of scattered radiation at a single wavelength (or narrow wavelength range), the intensity separately at multiple wavelengths or the intensity integrated over a wavelength range. Further, the detector may separately measure the intensity of transverse magnetic- (TM) and transverse electric- (TE) polarized radiation and/or the phase difference between the transverse magnetic- and transverse electric-polarized radiation.
  • TM transverse magnetic-
  • TE transverse electric-
  • a broadband radiation source 2 i.e., one with a wide range of radiation frequencies or wavelengths - and therefore of colors
  • the plurality of wavelengths in the broadband desirably each has a bandwidth of ⁇ w. and a spacing of at least 26/. (i.e., twice the wavelength bandwidth).
  • sources may be different portions of an extended radiation source which have been split using, e.g., fiber bundles. In this way, angle resolved scatter spectra may be measured at multiple wavelengths in parallel.
  • a 3-D spectrum (wavelength and two different angles) may be measured, which contains more information than a 2-D spectrum. This allows more information to be measured which increases metrology process robustness. This is described in more detail in U.S. Patent Application Publication No. US 2006-0066855, which document is hereby incorporated in its entirety by reference.
  • one or more properties of the substrate may be determined. This may be done, for example, by comparing the redirected beam with theoretical redirected beams calculated using a model of the substrate and searching for the model that gives the best fit between measured and calculated redirected beams.
  • a parameterized generic model is used and the parameters of the model, for example width, height and sidewall angle of the pattern, are varied until the best match is obtained.
  • a spectroscopic scatterometer directs a broadband radiation beam onto the substrate and measures the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range.
  • An angularly resolved scatterometer uses a monochromatic radiation beam and measures the intensity (or intensity ratio and phase difference in case of an ellipsometric configuration) of the scattered radiation as a function of angle.
  • measurement signals of different wavelengths may be measured separately and combined at an analysis stage.
  • Polarized radiation may be used to generate more than one spectrum from the same substrate.
  • a best match is typically found between the theoretical spectrum produced from a model of the substrate and the measured spectrum produced by the redirected beam as a function of either wavelength (spectroscopic scatterometer) or angle (angularly resolved scatterometer).
  • a first method is an iterative search method, where a first set of model parameters is used to calculate a first spectrum, a comparison being made with the measured spectrum. Then a second set of model parameters is selected, a second spectrum is calculated and a comparison of the second spectrum is made with the measured spectrum. These steps are repeated with the goal of finding the set of parameters that gives the best matching spectrum.
  • the information from the comparison is used to steer the selection of the subsequent set of parameters. This process is known as an iterative search technique.
  • the model with the set of parameters that gives the best match is considered to be the best description of the measured substrate.
  • a second method is to make a library of spectra, each spectrum corresponding to a specific set of model parameters.
  • the sets of model parameters are chosen to cover all or almost all possible variations of substrate properties.
  • the measured spectrum is compared to the spectra in the library.
  • the model with the set of parameters corresponding to the spectrum that gives the best match is considered to be the best description of the measured substrate. Interpolation techniques may be used to determine more accurately the best set of parameters in this library search technique.
  • the target on substrate W may be a grating which is printed such that after development, the bars are formed of solid resist lines.
  • the bars may alternatively be etched into the substrate.
  • the target pattern is chosen to be sensitive to a parameter of interest, such as focus, dose, overlay, chromatic aberration in the lithographic projection apparatus, etc., such that variation in the relevant parameter will manifest as variation in the printed target.
  • the target pattern may be sensitive to chromatic aberration in the lithographic projection apparatus, particularly the projection system PL, and illumination symmetry and the presence of such aberration will manifest itself in a variation in the printed target pattern. Accordingly, the scatterometry data of the printed target pattern is used to reconstruct the target pattern.
  • the parameters of the target pattern may be input to the reconstruction process, performed by a processing unit PU, from knowledge of the printing step and/or other scatterometry processes.
  • Lines in targets may be made up of sub-units, including near or sub-resolution features that together define lines of the gratings, such as are described in US Pat. No. 7,466,413.
  • a scatterometer While embodiments of a scatterometer have been described herein, other types of metrology apparatus may be used in an embodiment. For example, a dark field metrology apparatus such as described in U.S. Pat. No. 8,797,554, which is incorporated herein in its entirety by reference, may be used. Further, those other types of metrology apparatus may use a completely different technique than scatterometry.
  • Targets as described herein may be, for example, overlay targets designed for use in the Yieldstar stand-alone or integrated metrology tools, and/or alignment targets such as those typically used with TwinScan lithographic systems, both available from ASML of Veldhoven, NL.
  • metrology targets for use with such systems should be printed on the wafer with dimensions that meet the design specification for the particular microelectronic device to be imaged on that wafer.
  • the design rule and process compatibility requirement place stress on the selection of appropriate targets.
  • the targets themselves become more advanced, often requiring the use of resolution enhancement technology, such as phase-shift masks, and optical proximity correction the printability of the target within the process design rules becomes less certain.
  • proposed marks may be subject to testing in order to confirm their viability, both from a printability and a detectability standpoint.
  • good overlay mark detectability may be considered to be a combination of low total measurement uncertainty as well as a short move-acquire-move time, as slow acquisition is detrimental to total throughput for the production line.
  • Modern micro-diffraction-based-overlay targets may be on the order of 10 pm on a side, which provides an inherently lower detection signal compared to 40x160 pm 2 targets such as those used in the context of monitor wafers.
  • Figure 4 depicts a composite metrology target formed on a substrate according to known practice.
  • the composite target comprises four gratings 32, 33, 34, 35 positioned closely together so that they will all be within a measurement spot 31 formed by the illumination beam of the metrology apparatus.
  • the four targets thus are all simultaneously illuminated and simultaneously imaged on sensor 4, 18.
  • gratings 32, 33, 34, 35 are themselves composite gratings formed by overlying gratings that are patterned in different layers of the semiconductor device formed on substrate W.
  • Gratings 32, 33, 34, 35 may have differently biased overlay offsets in order to facilitate measurement of overlay between the layers in which the different parts of the composite gratings are formed.
  • Gratings 32, 33, 34, 35 may also differ in their orientation, as shown, so as to diffract incoming radiation in X and Y directions.
  • gratings 32 and 34 are X-direction gratings with biases of +d, -d, respectively. This means that grating 32 has its overlying components arranged so that if they were both printed exactly at their nominal locations, one of the components would be offset relative to the other by a distance d.
  • Grating 34 has its components arranged so that if perfectly printed there should be an offset of d, but in the opposite direction to the first grating and so on.
  • Gratings 33 and 35 may be Y-direction gratings with offsets +d and -d respectively.
  • gratings While four gratings are illustrated, another embodiment may include a larger matrix to obtain desired accuracy.
  • a 3 x 3 array of nine composite gratings may have biases -4d, -3d, -2d, -d, 0, +d, +2d, +3d, +4d. Separate images of these gratings can be identified in the image captured by sensor 4, 18.
  • FIG. 5A As will be appreciated, such a metrology device should itself be properly in focus to ensure that the measurements are accurate.
  • conventional systems schematically illustrated in Figure 5A, include several optical branches.
  • the substrate W is positioned in the field of view of microscope objective lens 15.
  • a first branch of the system includes the detector 18, and associated optics, together forming a detection branch 40 of the system, which may be, for example, a diffraction based optical detection branch.
  • the substrate W is illuminated by an illumination branch 42 that includes an illumination source 44.
  • An additional light source 46 provides focus measurement illumination in the focus branch 48
  • an alignment branch 50 includes an alignment camera 52 as well as its own light source, not shown.
  • Figure 5B schematically illustrates a metrology system in accordance with an embodiment in which modifications to the detection branch 40’ of the system allow for the focus branch 48 to be omitted entirely.
  • FIG 6 is a schematic illustration of an embodiment of a detection branch 40’ of the system.
  • a substrate W there is a substrate W, and a detector 18 at an image plane of the metrology optical system 70.
  • a quadrature wedge (quad wedge) 72 is included in the metrology optical system 70.
  • This element has the function of spatially separating diffraction orders received from the substrate at the image plane (detector 18). That is, due to the presence of the quad wedge, there will be four separate quadrants (only Qi and Q2 are noted in the figure) of the image projected onto the detector 18.
  • an optical element 74 is arranged in the metrology optical system 70 that is configured to have a first portion 76 that provides a positive defocus to the image in a first quadrant Qi (i.e., at a first position) and a second portion 78 that provides a negative defocus to the image in a second quadrant Q2 (i.e., at a second position).
  • Qi in a positive defocus condition. That is, the plane of best focus (shown as a peak in the focus signal) is located to the right of the image plane in the diagram.
  • Q2 is in a negative defocus condition where the plane of best focus (maximum magnitude, even though it is a minimum value) is located to the left of the image plane.
  • the optical element 74 is movable in and out of the metrology optical system 70, for example by an actuator. It may rotate into and out of the optical path, or be slidably actuatable into and out of the optical path, for example.
  • the optical element 74 may be a lens element that can be introduced at or near a pupil plane (or a conjugate plane thereof) of the metrology optical system 70. In an embodiment, it is a lens element as shown in Figure 8, that includes the first portion 76 and the second portion 78. As will be seen in this example, the same defocus is applied to two quadrants each, Qi and Q3 together, and Q2 and Q4 together.
  • This optical element 74 may be manufactured, for example, by bonding two lenses together, the resulting optical element 74 then being movable in and out of the optical path of the metrology optical system 70.
  • the optical element 74 is introduced into the measurement arm of the metrology system (i.e., metrology optical system 70).
  • the optical element is both configured and arranged at an appropriate position in the metrology optical system 70 to modify a point spread function thereof for at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions.
  • the substrate W is then illuminated to measure surface features thereon to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane.
  • a first spot size at the image plane at the first position (in the first quadrant) is compared to a second spot size at the image plane at the second position (in the second quadrant). If the spot sizes are not equal then a focal position of the substrate is changed until they are.
  • spot intensity at a measured point may be used, and equality of the measured intensities corresponds to a position of best focus.
  • the spot sizes or intensities may never be exactly equal, such that a selected degree of similarity can be specified for a particular substrate pattern.
  • This specified similarity can be expressed, for example, as a percentage, and may constitute a difference of between 0.001% and 0.1%, 1%, or as much as 10% or any ranges between these values. This is because the difference in spot characteristics varies significantly with the aperture of the objective 15, the spot size, and the magnification between the substrate and image plane.
  • the spot characteristics should be equal to within a system specification, which may vary depending on the particular substrate pattern to be measured.
  • a stop 80 having an array of pinholes 82 in it is used to create an array of light sources.
  • Each pinhole 82 acts as to approximate a point source at a given object field point.
  • Each point source corresponds to a respective point spread function 84 at the image plane (detector 18) as seen in Figure 11.
  • the point spread function at each point depends on the optical behavior of the optical system between the sources and the image plane.
  • a phase plate 86 ( Figure 11) is introduced into the optical system in order to modify the point spread functions at the image plane. For each of a number of sub-regions of the image plane, the phase plate introduces positive, negative, or no defocus. In the regions that experience positive or negative defocus, the point spread function will be reduced in peak intensity, and broadened compared to those regions with no defocus.
  • the phase plate can be a static optical element that is movable in and out of the optical path with, for example, a one degree of freedom mechatronic stage.
  • a transparent spatial light modulator (SLM) could be used for this purpose as well.
  • the phase plate 86 should be placed near an image plane of the metrology optical system 70. In this regard, it may be near an intermediate image plane, within the metrology optical system 70, or near the sensor image plane. As these image planes are conjugate, the phase plate 86 has the same effect at either position. The phase plate 86 may be placed on either side of the wedge 72.
  • phase plate 86 If the phase plate 86 is placed exactly at an image plane, than any optical defects such as surface scratches or debris will appear in the image at the sensor, which can reduce the S/N ratio of the measurement. If it is far from an image plane, and near to, for example, a pupil plane, then the phase shifts will not correspond well to a particular PSF and a particular pinhole. Generally, the maximum distance between the phase plate 86 and an image plane depends on the pinhole size and the distance between pinholes. With fewer spots and more space between spots, the phase plate may be placed further from the image plane.
  • phase plate 86 When the phase plate 86 is downstream of the wedge 72, there is an increase in magnification of the images of the spots. Furthermore, this position may allow for different defocus to be applied to light from a single spot as that spot is imaged into multiple quadrants.
  • the phase plate 86 itself can be embodied as a grid of subregions in a machined optical material, or as an SLM device.
  • the phase plate can be rotationally symmetric and manufactured with standard optical glasses or polymers.
  • the pinholes are generated using an illumination mode selection at a spot size selector of the optical system.
  • Contrast as discussed herein includes, for an aerial image, image log slope (ILS) and/or normalized image log slope (NILS) and, for resist, dose sensitivity and/or exposure latitude.
  • ILS image log slope
  • NILS normalized image log slope
  • optical process means adjusting a lithographic process parameter such that results and/or processes of lithography have a more desirable characteristic, such as higher accuracy of projection of a design layout on a substrate, a larger process window, etc.
  • An embodiment of the invention may take the form of a computer program containing one or more sequences of machine -readable instructions describing a method as disclosed herein, or a data storage medium (e.g. semiconductor memory, magnetic or optical disk) having such a computer program stored therein.
  • the machine readable instruction may be embodied in two or more computer programs.
  • the two or more computer programs may be stored on one or more different memories and/or data storage media.
  • This computer program may be included, for example, with or within the inspection apparatus and/or with or within the control unit LACU of Figure 1. Where an existing apparatus, for example of the type shown in Figures 2 and 3, is already in production and/or in use, an embodiment can be implemented by the provision of updated computer program products for causing a processor of the apparatus to perform a method as described herein.
  • Any controllers described herein may each or in combination be operable when the one or more computer programs are read by one or more computer processors located within at least one component of the inspection apparatus.
  • the controllers may each or in combination have any suitable configuration for receiving, processing, and sending signals.
  • One or more processors are configured to communicate with the at least one of the controllers.
  • each controller may include one or more processors for executing the computer programs that include machine -readable instructions for the methods described above.
  • the controllers may include data storage medium for storing such computer programs, and/or hardware to receive such medium. So the controller(s) may operate according the machine readable instructions of one or more computer programs.
  • a method of measuring a focus position in a metrology system comprises: introducing an optical element into a measurement arm of the metrology system, the optical element being configured and arranged to modify a point spread function at at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions; illuminating a substrate comprising features to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane; and controlling a focal position of the substrate on the basis of a first spot characteristic at the image plane at the first position to a second spot characteristic at the image plane at the second position.
  • optical element is a lens element introduced proximate a pupil plane of the metrology system, and where in the lens element has a first portion that causes the positive defocus at the first position and a second portion that causes the negative defocus at the second position.
  • the optical element is a phase plate that has a first portion that causes the positive defocus at the first position and a second portion that causes the negative defocus at the second position. 7. A method as in clause 6, wherein the phase plate is at a position proximate a pupil plane of the metrology system.
  • each aperture of the array of apertures corresponds to a respective position in the image plane of the metrology system.
  • the measurement arm of the metrology system comprises a dark-field microscopic camera measurement arm.
  • the optical element comprises an optical element selected from the group consisting of: a machined optical material, a spatial light modulator device, and a deformable mirror.
  • a method of measuring a focus position in a metrology system comprises: introducing an optical element into a measurement arm of the metrology system, the optical element being configured and arranged to modify a point spread function at at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions; illuminating a substrate comprising features to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane, an illumination pattern of the measurement beam having a plurality of separate sources; comparing a plurality of spot characteristics at the image plane at the first position to a second spot characteristic at the image plane at the second position; and changing a focal position of the substrate until the first spot characteristic and the second spot characteristic are equal.
  • a system for measuring a focus position in a metrology system comprises: an optical element movable into and out of a measurement arm of the metrology system, the optical element being configured and arranged to modify a point spread function at at least two different positions in an image plane of the metrology system by adding a positive defocus to a first position of the at least two different positions and a negative defocus to a second position of the at least two different positions; an illumination source, configured to illuminate a substrate comprising features to be measured by the metrology system with a measurement beam of radiation that passes from the substrate to the image plane; and a focal position controller, configured to control a focal position of the substrate on the basis of a first spot characteristic at the image plane at the first position to a second spot characteristic at the image plane at the second position.
  • first spot characteristic is a first spot size
  • second spot characteristic is a second spot size
  • the focal position controller is configured to change a focal position of the substrate until the first spot size and the second spot size are equal.
  • first spot characteristic is a first intensity
  • second spot characteristic is a second intensity
  • the focal position controller is configured to change a focal position of the substrate until the first intensity and the second intensity are equal.
  • optical element is a lens element movable into and out of a position proximate a pupil plane of the metrology system, and where in the lens element has a first portion that causes the positive defocus at the first position and a second portion that causes the negative defocus at the second position.
  • optical element is a phase plate that has a first portion that causes the positive defocus at the first position and a second portion that causes the negative defocus at the second position.
  • phase plate is movable into and out of a position proximate a pupil plane of the metrology system.
  • phase plate is movable into and out of a position proximate an image plane of the metrology system.
  • a topography in a patterning device defines the pattern created on a substrate.
  • the topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof.
  • the patterning device is moved out of the resist leaving a pattern in it after the resist is cured.
  • lithographic apparatus in the manufacture of ICs
  • the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc.
  • LCDs liquid-crystal displays
  • any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively.
  • the substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.
  • the patterning device described herein may be referred to as a lithographic patterning device.
  • the term “lithographic patterning device” may be interpreted as meaning a patterning device which is suitable for use in a lithographic apparatus.
  • UV radiation e.g. having a wavelength of or about 365, 355, 248, 193, 157 or 126 nm
  • EUV radiation e.g. having a wavelength in the range of 5-20 nm
  • particle beams such as ion beams or electron beams.
  • lens may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

Abstract

Des systèmes et des procédés de mesure de position de mise au point dans un système de métrologie comprennent les étapes consistant à introduire un élément optique dans un bras de mesure du système de métrologie, l'élément optique étant conçu et disposé pour modifier une fonction d'étalement de point d'au moins deux positions différentes dans un plan d'image du système de métrologie en ajoutant une défocalisation positive à une première position parmi lesdites positions différentes et une défocalisation négative à une seconde position parmi lesdites positions différentes, à éclairer un substrat comprenant des caractéristiques devant être mesurées par le système de métrologie avec un faisceau de rayonnement de mesure qui passe du substrat au plan d'image, et à commander une position focale du substrat sur la base d'une première taille de point au niveau du plan d'image au niveau de la première position pour la faire passer à une seconde taille de point au niveau du plan d'image au niveau de la seconde position.
PCT/EP2023/079327 2022-11-07 2023-10-20 Procédé et appareil de mesure de mise au point d'inspection WO2024099740A1 (fr)

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US7466413B2 (en) 2003-07-11 2008-12-16 Asml Netherlands B.V. Marker structure, mask pattern, alignment method and lithographic method and apparatus
US20060066855A1 (en) 2004-08-16 2006-03-30 Asml Netherlands B.V. Method and apparatus for angular-resolved spectroscopic lithography characterization
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