Systems, methods, and software for model-based combined alignment and overlay metrology

Abstract

Disclosed are methods, systems, and computer programs for improved metrology. One method of metrology includes obtaining first signals generated by a first sensor measuring an alignment (AL) mark on a substrate and obtaining second signals generated by a second sensor measuring an overlay (OVL) mark on the substrate. An OVL of the substrate is determined by using 5 combined information derived from the first signals and the second signals.

Description

SYSTEMS, METHODS, AND SOFTWARE FOR MODEL-BASED COMBINED ALIGNMENT AND OVERLAY METROLOGYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 651,578 which was filed on May 24, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The description herein relates generally to metrology of patterns produced by lithographic processes. More particularly, the disclosure includes apparatus, methods, and computer programs for determining the overlay of patterns using regression to obtain asymmetries in alignment (AL) and overlay (OVL) marks and optimizing the AL and OVL measurement method to reduce OVL error due to asymmetries.BACKGROUND

[0003] Integrated circuits as manufactured include a plurality of layers containing different patterns, each layer being generated using an exposure process. In order to ensure proper operation of the integrated circuit that is manufactured the layers consecutively exposed need to be properly aligned to each other. In order to realize this, substrates are typically provided with a plurality of so-called alignment marks (also referred to as alignment targets), whereby a position of the alignment marks is used to determine or estimate a position of a previously exposed pattern. As such, prior to the exposure of a subsequent layer, the position of alignment marks is determined and used to determine a position of the pattern that was previously exposed.

[0004] Typically, in order to determine the positions of such alignment marks, an alignment sensor is applied which may, for example, be configured to project a radiation beam onto an alignment mark or target and determine, based on a reflected radiation beam, a position of the alignment mark. Some alignment sensors can illuminate the alignment mark with light having multiple wavelengths, and / or polarizations. The signals received from the light reflected from the alignment mark can be dependent upon the wavelengths, and polarizations. As such, received signals can be compared to an expected result to determine not only the position of the alignment mark but also asymmetries that may be present in the alignment mark (as such asymmetries can introduce wavelength and / or polarization dependent variations in the received signals).

[0005] Ideally, the measured position of the alignment mark would correspond to the actual position of the mark. However, various causes may result in a deviation between the measured position and the actual position of the alignment mark. In particular, a deformation of the alignment mark may result in the mentioned deviation. Such a deformation may e.g. be caused by the processing of the substrate, for example etching, chemical mechanical polishing (CMP) or layer deposition leading tosub-optimal marker position determination. As a result, a layer may be projected or exposed on a position which is not in line, i.e. not aligned, with the previously exposed pattern, resulting in a so- called overlay error. Overlay sensors can utilize similar diffraction-based or scatterometry-based methods of measuring overlay marks on select wafers. Overlay sensors can measure several layers at once to determine the OVL, which can be corrected by adjusting the manufacturing process. Overlay sensors can use micro diffraction-based overlay (pDBO) for small areas and / or continuous-bias DBO (cDBO) for larger areas or those without dense features. Overlay metrology can be more timeconsuming than AL metrology and thus can be somewhat compensated by relying on fewer channels (analysis of reflected light wavelengths / polarizations) in order to improve throughput.

[0006] Asymmetry in marks can be caused by the wafer manufacturing process, so both AL marks and OVL marks can have asymmetries. The asymmetry in AL marks can cause alignment errors in the lithography process. The asymmetry in OVL marks can cause overlay metrology errors, which in turn can result in a wrong OVL correction when the OVL results are fed back to the lithography scanner for OVL correction. As such, the asymmetries on AL marks and OVL marks provide different mechanisms for causing OVL errors. While some model-based determinations of the effects of asymmetries on OVL have been performed, further improvements in accuracy are needed in view of the ever-increasing requirements for performing metrology on more compact IC components.SUMMARY

[0007] Disclosed are systems, methods, and computer programs for improved metrology as well as the incorporation of same into improved methods of semiconductor manufacturing. In one aspect, a method of metrology includes obtaining first signals generated by a first sensor measuring an alignment (AL) mark on a substrate; obtaining second signals generated by a second sensor measuring an overlay (OVL) mark on the substrate; and determining an OVL of the substrate by using combined information derived from the first signals and the second signals.

[0008] In some variations, the first signals can provide a more precise parameter measurement of the AL mark than the second signals measurement of the OVL mark. The first sensor can be a laserbased interferometer or an optical camera and the second sensor can be an optical camera or a scatterometer. The first sensor can acquire a greater number of signal channels per acquisition than the second sensor. A bottom grating of the OVL mark can be on the same process layer as the AL mark. A top grating of the OVL mark can have an additional asymmetric characteristic that is not present in the AL mark.

[0009] In some variations, the first signals can comprise symmetric AL signals indicative of symmetric characteristics of the AL mark and asymmetric AL signals indicative of asymmetric characteristics of the AL mark. A method can include inputting the first signals into an AL model configured to determine symmetric characteristics of the AL mark, the AL model further configured to use the first signals to determine a stack geometry of the AL mark by simulating a first sensorsignal response based on the stack geometry; and generating, with the AL model, AL stack parameters of the symmetric characteristics of the AL mark, and AL stack parameters of the asymmetric characteristics of the AL mark.

[0010] In some variations, the AL stack parameters comprise AL stack parameters. The AL stack parameters can include one or more of stack thickness, stack material refractive index, stack material extinction coefficient, floor tilt, pitch, and critical dimension, sidewall angle. The AL stack parameters can include a representation of one or more dominant asymmetries in the AL mark, a dominant asymmetry being one of a subset of asymmetries in the AL mark that are independent from each other and has the largest contribution to a misalignment measurement. A method can include performing a selection of wavelengths and polarizations from channels of the first sensor such that the dominant asymmetry has a reduced impact on the misalignment measurement.

[0011] In some variations, the second signals can include symmetric OVL signals indicative of symmetric characteristics of the OVL mark and asymmetric OVL signals indicative of asymmetric characteristics of the OVL mark. A method can include inputting the AL stack parameters of the symmetric characteristics of the AL mark and the AL stack parameters of the asymmetric characteristics of the AL mark into an OVL model. A method can also include inputting the second signals and symmetric characteristic into the OVL model configured to determine the symmetric characteristics of the OVL mark, the OVL model further configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and inputting AL mark’s asymmetric characteristic parameters; and outputting, from the OVL model, the OVL stack parameters of the asymmetric characteristics of the OVL mark.

[0012] In some variations, a method can include adjusting, based on predetermined rules, the AL stack parameters and / or the OVL stack parameters based on the sensitivities of the first signals and the second signals. The adjusting can include performing regression of the AL stack parameters by the AL model and performing regression of the OVL stack parameters by the OVL model according to the predetermined rules. The regression of the AL stack parameters can be performed with predetermined bounding ranges. A method can include adjusting the OVL stack parameters that the first signals and the second signals have a high sensitivity to determine the OVL of the OVL mark and to determine an OVL fingerprint (FP).

[0013] In some variations, when the first signals and the second signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters can be fed into the OVL model as a seed value and regressed by the OVL model. When the first signals and the second signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters can be fed into the OVL model and not regressed by the OVL model. When the first signals and the second signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters can be regressed by the OVL model. When the first signals and the second signals are notsensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters can be fixed in the OVL model.

[0014] In some variations, a method can include repeating the determination of the AL stack parameters and the OVL stack parameters for additional AL marks and OVL marks to generate a collection of accumulated parameters; and determining, from the accumulated parameters, one or more of a symmetric parameter consistency, an asymmetric parameter consistency, or a correlation of OVL FP. A method can include obtaining first calibration signals generated by the first sensor measuring a calibration AL mark on a calibration substrate; obtaining second calibration signals generated by the second sensor measuring a calibration OVL mark on the calibration substrate; and grouping stack parameters of the AL mark and OVL mark according to signal sensitivities to the stack parameters.

[0015] In some variations, a method can include determining the sensitivities by calculating the ratios of a first calibration signals and second calibration signals change to a stack parameter change. The sensitivities can be further determined by measuring a plurality of calibration AL marks and a plurality of calibration OVL marks.

[0016] In some variations, when the first calibration signals and the second calibration signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters can be fed into the OVL model as a seed value and will be regressed by an OVL model. When the first calibration signals and the second calibration signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters can be fed into the OVL model but will not be regressed by an OVL model. When the first calibration signals and the second calibration signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters can be regressed by an OVL model. When the first calibration signals and the second calibration signals are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters can be fixed in an OVL model.

[0017] In some variations, a method can include inputting the first signals into an AL model configured to determine symmetric characteristics of the calibration AL mark, the AL model further configured to use the first signals to determine a stack geometry of the calibration AL mark by simulating the first sensor signal response based on the stack geometry; and generating, with the AL model, calibration AL stack parameters of the symmetric characteristics of the AL mark and calibration AL stack parameters of the asymmetric characteristics of the AL mark.

[0018] In some variations, a method can include inputting the second calibration signals and the AL stack parameters of the symmetric characteristics of the calibration AL mark into an OVL model configured to determine the symmetric characteristics of the OVL mark the OVL model further configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and inputting AL mark’s asymmetriccharacteristic parameters; and outputting, from the OVL model, the OVL stack parameters of the asymmetric characteristics of the calibration OVL mark.

[0019] In some variations, a method can include co-optimizing the OVL stack parameters and the AL stack parameters that the first calibration signals and the second calibration signals are sensitive to based on the grouping, the co-optimization causing the OVL stack parameters and the AL stack parameters to meet one or more cost functions; and determining a bounding range of the of the OVL stack parameters.

[0020] In some variations, the co-optimization can include regressing the first calibration signals and the second calibration signals to cause the AL stack parameters and the OVL stack parameters to meet the one or more cost functions. Alignment position deviation values from the AL model can be utilized to build an OVL correction map utilized in the co-optimization.

[0021] In an interrelated aspect, a semiconductor device manufacturing method includes receiving a substrate with a photoresist layer; directing (EUV / DUV) radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate according to any one of the preceding claims.

[0022] In an interrelated aspect, a non-transitory computer readable medium having instructions recorded thereon for a lithographic process, the instructions when executed by a computer having at least one programmable processor can cause operations comprising the operations as in any of the above methods.

[0023] In an interrelated aspect, a system for use with a lithographic process can include at least one programmable processor; and a non-transitory computer readable medium having instructions recorded thereon, the instructions when executed by a computer having the at least one programmable processor cause operations as in any of the above methods.

[0024] In some variations, the first sensor or the second sensor is a diffraction-based sensor. The first sensor can be a laser-based interferometer or an optical camera. The second sensor can be an optical camera or a scatterometer.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principals associated with the disclosed implementations. In the drawings,

[0026] Figure 1 schematically depicts a lithography apparatus, according to an embodiment of the present disclosure.

[0027] Figure 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment of the present disclosure.

[0028] Figure 3A schematically depicts an example metrology system, according to an embodiment of the present disclosure.

[0029] Figure 3B schematically depicts an example metrology technique, according to an embodiment of the present disclosure.

[0030] Figure 4 schematically depicts comparing exemplary stacks of an AL mark and an OVL mark, according to an embodiment of the present disclosure.

[0031] Figure 5 schematically depicts examples of symmetrical and asymmetrical characteristics of a mark (AL or OVL) that can be characterized by the AL or OVL sensor measurement, according to an embodiment of the present disclosure.

[0032] Figure 6 schematically depicts a simplified combination of AL metrology and OVL metrology utilizing model simulation of stack signals from AL and OVL diagnostics, according to an embodiment of the present disclosure.

[0033] Figure 7 schematically depicts a process flow diagram of an exemplary method of utilizing combined model-based AL and OVL metrology in calibration phase and in application phase, according to an embodiment of the present disclosure.

[0034] Figure 8 schematically depicts a process flow diagram of an exemplary method of calibrating a model utilizing combined measurements of an AL mark and an OVL mark, according to an embodiment of the present disclosure.

[0035] Figure 9 schematically depicts a process flow diagram of an exemplary method of applying combined model-based AL and OVL metrology, according to an embodiment of the present disclosure.

[0036] Figure 10 is a block diagram of an example computer system, according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0037] In semiconductor device manufacturing, AL metrology is performed to precisely align the positioning of the wafer with respect to the reticle. OVL metrology is performed to determine the position shift between two patterning layers. AL metrology and OVL metrology may be obtained using optical sensors that have similar or different configurations and operate on similar or different principles. Optical metrology can include illuminating AL or OVL marks with light having a range of wavelengths and / or polarizations. This can include receiving light from multiple layers of the substrate at the same time (e.g., from an OVL mark). The scattered or diffracted light can be received by an AL or OVL sensor. The positions and intensities of the diffracted orders can be compared to an expected result to determine the AL or OVL.

[0038] By way of a brief introduction, the description below relates to semiconductor device manufacturing and patterning processes. The following paragraphs also describe several components of systems and / or methods for semiconductor device metrology. These systems and methods may beused for measuring overlay, alignment on wafers, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0039] Although specific reference may be made in this text to the measurement of overlay, alignment, or other parameters, and the manufacture of integrated circuits (ICs) for semiconductor devices, it should be understood that the description herein has many other applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, display panels, thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms "reticle," "wafer" or "die" in this text should be considered as interchangeable with the more general terms "mask," "substrate" and "target portion," respectively.

[0040] Figure 1 schematically depicts 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 radiation, DUV radiation, or EUV radiation); a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters; a substrate table (e.g. a wafer table) WT (e.g., WTa, WTb or both) configured to hold a substrate (e.g. a resist coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters; and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g. comprising one or more dies and often referred to as fields) of the substrate W. The projection system is supported on a reference frame RF.

[0041] The illuminator IL may comprise adjuster AD configured to adjust the (angular / spatial) intensity distribution of the beam. Generally, at least the outer and / or inner radial extent of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to alter the polarization of the beam and may be operable to adjust the polarization using adjuster AD. The polarization state of the radiation beam across a pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO.

[0042] 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 a frame or a table, for example, 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.

[0043] Any use of the terms "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device." The term "patterning device" used herein should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of the 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 create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern 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 a target portion of the device, such as an integrated circuit. A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels.

[0044] The term "projection system" (PS) should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for 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."

[0045] The projection system PS may comprise a plurality 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 for aberrations (phase variations across the pupil plane throughout the field). 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 without a substrate that is dedicated to, for example, facilitating measurement, and / or cleaning, etc.). In such "multiple stage" machines, the additional tables may be used in parallel, or preparatory steps may be conducted on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements using an alignment sensor AS and / or level (height, tilt, etc.) measurements using a level sensor LS may be made.

[0046] In operation of the lithographic apparatus, a radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g. to position different target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Figure 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. aftermechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a shortstroke 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. Patterning device MA and substrate W may be aligned using patterning device alignment marks Ml, M2 and substrate alignment marks Pl, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between 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.

[0047] Between processing steps, alignment sensor AS can be utilized to confirm that the wafer is properly aligned relative to the reticle. The alignment sensor AS can provide illumination (e.g., light of varying wavelengths and / or polarizations) to an alignment mark and the diffraction pattern of the reflected light may be captured and analyzed to determine the position of the alignment mark. Errors in alignment can then be corrected before processing continues. One example of an alignment sensor AS can be a dual self-referencing interferometer, as described in further detail herein.

[0048] Also, as part of a manufacturing process (i.e., in-line operation) or before / after / between processing steps (i.e., offline operation), additional metrology can occur utilizing an overlay sensor to determine errors in alignment between process layers - overlay. An overlay sensor can also be diffraction-based but may utilize different or additional wavelengths and polarizations of light to obtain measurements of reference marks (overlay marks) at different process layers in order to determine the overlay.

[0049] The substrate 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) or a metrology or 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 includes multiple processed layers.

[0050] The terms "radiation" and "beam" 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, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

[0051] The lithographic apparatus LA and radiation source SO described herein can be used in a method for manufacturing a semiconductor device. A semiconductor device manufacturing method comprises receiving a substrate W with a photoresist layer. The method further comprises directing aradiation beam from radiation source SO to transfer a pattern from a mask onto the photoresist layer. This could be achieved by a patterning device which is configured to form a patterned radiation beam, imparting the patterned radiation beam onto the photoresist layer. The method for manufacturing a semiconductor device further comprises the step of removing a portion of the photoresist layer to form the pattern over the substrate W.

[0052] The substrate W may be made of silicon or other semiconductor materials. Alternatively or additionally, the substrate W may include other semiconductor materials such as germanium (Ge) or carbon (C). In some embodiments, the semiconductor substrate is made of a compound semiconductor such as III-V compound semiconductors, II-V compound semiconductors, and / or any suitable integration of Group IV materials. In some embodiments, the substrate W may be a silicon-on- insulator (SOI) or a germanium-on-insulator (GOI) substrate.

[0053] The semiconductor device made from the substrate W may have various device elements. Examples of semiconductor device elements that are formed over the substrate W include transistors (e.g., planar or non-planar metal oxide semiconductor field effect transistors (MOSFET), bipolar junction transistors (BJT), high-voltage transistors, high-frequency transistors, etc.), diodes, CMOS image sensors, passive devices, and / or other applicable elements. Various processes may be performed to form the semiconductor device elements, such as deposition, etching, implantation, epitaxial growth, polishing, thermal treatment, and / or other suitable processes. In some embodiments, the substrate W is coated with a photoresist layer sensitive to the EUV light.

[0054] As shown in Figure 2, the lithographic apparatus LA may form part of a lithographic cell LC, also sometimes referred to a lithocell or cluster, which also includes apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include one or more spin coaters SC to deposit one or more resist layers, one or more developers to develop 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 port VOl, I / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus. These apparatuses, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by the supervisory control system SCS, which also controls the lithographic apparatus via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0055] In order that a substrate that is exposed by the lithographic apparatus is exposed correctly and consistently and / or in order to monitor a part of the patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., an optical lithography step), it is desirable to inspect a substrate or other object to measure or determine one or more properties such as alignment, overlay (which can be, for example, between structures in overlying layers or between structures in a same layer that have been provided separately to the layer by, for example, a double patterning process), line thickness, critical dimension (CD), focus offset, a material property, etc.Accordingly, a manufacturing facility in which lithocell LC is located also typically includes a metrology system that measures some or all of the substrates W (Figure 1) that have been processed in the lithocell or other objects in the lithocell. The metrology system may be part of the lithocell LC, for example it may be part of the lithographic apparatus LA (such as alignment sensor AS (Figure 1)).

[0056] The one or more measured parameters may include, for example, alignment, overlay between successive layers formed in or on the patterned substrate, critical dimension (CD) (e.g., critical linewidth) of, for example, 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. This measurement is often performed on one or more dedicated metrology marks provided on the substrate. The measurement can be performed after-development of a resist but before etching, after-etching, after deposition, and / or at other times.

[0057] A fast and non-invasive form of specialized metrology tool is one in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered (diffracted / reflected) beam are measured. 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 may be termed diffraction-based metrology. Applications of this diffraction-based metrology include the measurement of overlay, alignment, etc. For example, overlay and / or alignment can be measured by comparing parts of the diffraction spectrum (for example, comparing different diffraction orders in the diffraction spectrum of a periodic grating).

[0058] Thus, in a device fabrication process (e.g., a patterning process or a lithography process), a substrate or other objects may be subjected to various types of measurement during or after the process. The measurement may determine whether a particular substrate is defective, may establish adjustments to the process and apparatuses used in the process (e.g., aligning two layers on the substrate or aligning the patterning device to the substrate), may measure the performance of the process and the apparatuses, or may be for other purposes.

[0059] Metrology results may be provided directly or indirectly to the supervisory control system SCS. If an error is detected, an adjustment may be made to exposure of a subsequent substrate (especially if the inspection can be done soon and fast enough that one or more other substrates of the batch are still to be exposed) and / or to subsequent exposure of the exposed substrate. Also, an already exposed substrate may be stripped and reworked to improve yield, or discarded, thereby avoiding performing further processing on a substrate known to be faulty. In a case where only some target portions of a substrate are faulty, further exposures may be performed only on those target portions which meet specifications. Other manufacturing process adjustments are contemplated.

[0060] A metrology system may be used to determine one or more properties of the substrate structure, and in particular, how one or more properties of different substrate structures vary, or different layers of the same substrate structure vary from layer to layer. The metrology system may be integrated into the lithographic apparatus LA or the lithocell LC, or may be a stand-alone device.

[0061] To enable such metrology, often one or more metrology marks (also referred to as metrology targets) are specifically provided on the substrate. Typically, the mark is specially designed and may comprise a periodic structure made of multiple layers. For example, the mark on a substrate may comprise one or more 1-D periodic structures (e.g., geometric features such as gratings), which are printed such that after development, the periodic structural features are formed of solid resist lines. As another example, the mark may comprise one or more 2-D periodic structures (e.g., contact holes), which are printed such that after development, the one or more periodic structures are formed of solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

[0062] Figure 3A depicts an example metrology (inspection) system 10 that may be used to detect overlay or alignment. It comprises a radiation or illumination source 2 which projects or otherwise irradiates radiation onto a substrate W (e.g., which may typically include a metrology mark). The redirected radiation is passed to a sensor such as a spectrometer detector 4 and / or other sensors, which measures a spectrum (intensity as a function of wavelength) of the specular reflected and / or diffracted radiation, as shown, e.g., in the graph on the left of Figure 3B. The sensor may generate a metrology signal conveying metrology data indicative of properties 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 Figure 3B, or by other operations.

[0063] As in the lithographic apparatus LA in Figure 1, one or more substrate tables (not shown in Figure 3A) may be provided to hold the substrate W during measurement operations. The one or more substrate tables may be similar or identical in form to the substrate table WT (WTa or WTb or both) of Figure 1. In an example where inspection system 10 is integrated with the lithographic apparatus, they may even be the same substrate table. Coarse and fine positioners may be provided and configured to accurately position the substrate in relation to a measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest of a structure (e.g., a metrology mark), and to bring it into position under an objective lens. Typically, many measurements will be made on mark of a structure at different locations across the substrate W. The substrate support can be moved in X and Y directions to acquire different targets, and in the Z direction to obtain a desired location of the mark relative to the focus of the optical system. It is convenient to describe operations as if the objective lens is being brought to different locations relative to the substrate, when, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but perhaps also in the Z direction) and the substrate moves. Provided the relative position of the substrate and the optical system is correct, it does not matter in principle which one of those is moving, or if both are moving, or a combination of a part of the optical system is moving (e.g., in the Z and / or tilt direction) with the remainder of the optical system being stationary and the substrate is moving (e.g., in the X and Y directions, but also optionally in the Z and / or tilt direction).

[0064] For typical metrology measurements, mark 30 on substrate W may be a 1-D grating, which is printed such that after development, the bars are formed of solid resist lines (e.g., which may be covered by a deposition layer), and / or other materials. Or mark 30 may be a 2-D grating, which is printed such that after development, the grating is formed of solid resist pillars, and / or other features in the resist.

[0065] The bars, pillars, vias, and / or other features may be etched into or on the substrate (e.g., into one or more layers on the substrate), deposited on a substrate, covered by a deposition layer, and / or have other properties. Mark 30 can be designed to be sensitive to changes in processing in the patterning process (e.g., optical aberration in the lithographic projection apparatus such as in the projection system, focus change, dose change, etc.) such that process variation manifests in variation in mark 30. In addition, other non-patterning process (such as CMP, etch, etc.) can also cause pattern variations (e.g., changes in thickness, CD, asymmetry variations) that mark 30 can be sensitive to. Accordingly, the measured data from mark 30 may be used to determine an adjustment for one or more of the manufacturing processes, and / or used as a basis for making the actual adjustment.

[0066] For example, the measured data from mark 30 may indicate overlay for a layer of a semiconductor device. The measured data from mark 30 may be used (e.g., by the one or more processors PRO and / or other processors) for determining one or more semiconductor device manufacturing process parameters based the overlay, and determining an adjustment for, or active correction by, a semiconductor device manufacturing apparatus based on the one or more determined semiconductor device manufacturing process parameters. In some embodiments, this may comprise a stage position adjustment, for example, or this may include determining an adjustment for a mask design, a metrology mark design, a semiconductor device design, an intensity of the radiation, an incident angle of the radiation, a wavelength of the radiation, a pupil size and / or shape, a resist material, and / or other process parameters.

[0067] As used herein, the term “layer” refers to a process layer, e.g., a region of the printed object (e.g., a semiconductor device or wafer) that was created with the patterning processes. Layers can be made of different materials or may be different regions that are processed (e.g., when performing an etch, the area with material removed may be considered one layer and the area below it without material removed may be considered another layer).

[0068] As used herein, the term “alignment” (AL) means the alignment of a substrate (e.g., a wafer) to be correctly positioned for subsequent metrology or for processing / exposure. Alignment measurements can be performed with an AL sensor that can utilize, for example, scattered light from the substrate. The position of the substrate can be encoded in the phase shift of the scattered light and used to determine alignment corrections.

[0069] As used herein, the term “overlay” (OVL) means a displacement between two layers. For example, two layers may be intended to have aligned centers (e.g., a top layer directly over a lower layer) but during manufacturing undesirably constructed with a shift between the two layers (e.g., anoffset (or overlay) in the X and / or Y directions). In some cases, the overlay may be intentional, for example to test or calibrate equipment designed to measure or reduce the overlay.

[0070] From the above, “alignment” refers to determining the position of a substrate and “overlay” refers to determining errors between substrate layers.

[0071] Embodiments of the present disclosure can utilize an AL sensor and an OVL sensor for improved metrology. An AL sensor can, for example, generally be an interferometer-based diagnostic or in some cases can be a dual self-referencing interferometer. A dual self-referencing interferometer can include an input light source (e.g., a multi-color light source) that can provide light through a collimating lens. Relay optics can then be used to project the exit pupil plane of the collimation lens to the input pupil plane of an objective that illuminates the wafer mark and collects a diffracted signal. Also, there can be a spot mirror to turn the input light to circular polarization and block zero-order diffracted signals from returning along the input path. Along the return path, there can be a color compensator that corrects aberrations (e.g., after MAR optics are removed). The diffracted light can then go to a dual self-referencing interferometer assembly and a phase optics assembly. The phase optics assembly can split sum and difference signals into two separate (dual) output channels. Each of the output channels can itself have a dual output lens assembly that project light from the phase optics assembly to output fibers.

[0072] OVL sensors can generally be similar to a diffraction-based AL sensor though, since they are typically used post-development, they can utilize a broader or more continuous spectrum of light for performing OVL metrology on a developed wafer. The particular wavelengths of light can be selected specifically for use at particular stack layers. However, this discussion is merely exemplary; it will be appreciated that the present disclosure is not limited to any specific type or configuration an AL or OVL sensor.

[0073] Model-based metrology, in general, can utilize a computer model that simulates the sensor responses to predict expected signals from a wafer (or mark) and then compare the modeled signals with actual measurements to estimate the alignment error or overlay. For model-based AL metrology, good performance can result from the large number of AL sensor signals (e.g., 24 channels) These signals help determine multiple stack parameters used for modeling signals from the stack and determining dominant asymmetrical characteristics of the mark with sufficient constraints. For model-based OVL metrology, the issue is the limited number of OVL sensor signals usable to perform OVL metrology during the actual manufacturing process. For example, an OVL sensor may be configured only to provide two channels per single wavelength on one OVL mark. This challenges model use due to an insufficient number of constraints. If only model-based AL metrology is implemented, it only enables providing feedback to the scanner to improve only AL results. But the OVL measurement will still suffer OVL error due to asymmetry features. This means that scanner control based on the feedback from OVL sensor can have reduced accuracy.

[0074] An AL model can be developed that utilizes stack information such as thickness or other geometry information and materials of the layers etc. and information about an AL mark design (e.g., a grating) to simulate how diffracted signals from an AL mark change based on variations in design, geometry, and offset (AL error) of the AL mark from its intended location. With diffracted signals from an actual measurement, the model can be utilized to determine what AL error would result in those measured signals and thus provide an estimate of the AL error. This AL error can then be fed back into the wafer position control mechanism of the lithography system to correct the wafer’ s position. An OVL model development and use can be similar, but can utilize diffracted light that can vary due to the relative position of layers in the wafer. For example, the diffraction pattern can vary from an ideal (or known) case when a shifting of a layer causes the structure of the mark at that layer to be different and thus the light diffracted from that layer is not the same as it would be without the layer shift. Again, while OVL model-based OVL metrology can be sufficient in offline operation, to maintain throughput during inline operation a reduced number of channels may be required. This can cause the OVL determination to be unacceptably inaccurate due to the reduced number of constraints available as model inputs.

[0075] The present disclosure provides various methods of combining model-based AL and OVL metrology to, among other things, improve AL sensor and OVL sensor measurement accuracy and robustness. As one example, signals from the AL sensor (and data derived therefrom) can be utilized to supplement the possibly more limited OVL signals (e.g., fewer channels) generated from the OVL sensor. The present disclosures embodiments include those where AL model output can be fed into an OVL model, with the AL model output providing additional data that can be used to improve the determination of OVL by the OVL model.

[0076] In some embodiments, the bottom gratings of AL marks and OVL marks are same and fabricated at the same time (and so may share the same stack with limited physical and geometrical variation). While the AL model can be used to determine alignment of the substrate (typically before lithography exposure), the OVL model can also reuse the AL measurements to improve determination of the OVL (typically after development).

[0077] Figure 4 depicts a diagram comparing exemplary stacks of AL mark 410 and OVL mark 420. As previously mentioned, it can be assumed that portions of AL mark 410 and OVL mark 420 are the same (or similar). Specifically, that the bottom grating of OVL mark 420 can be on the same process layer as AL mark 410. As shown in the Example of Figure 4, features of AL mark 410 at bottom grating 430 can be the same as the OVL mark 420 at bottom grating 430. Accordingly, the information derived from measuring AL mark 410 can be used to characterize the OVL mark 420. Thus, measurements of the AL mark 410 can be utilized as model input even when estimating features normally derived from OVL marks.

[0078] It will be appreciated that the present disclosure is not limited to any specific designs of AL marks and OVL marks. For example, in some embodiments, while the AL mark does not have a topgrating, there may be one in an OVL mark. There may be other differences as well between AL marks and OVL marks. For example, an OVL mark may have a reduced thickness (e.g., on top resist layer, while other layer thicknesses can be substantially the same - within process variations), than the AL mark (depicted in Figure 4 by the removal of the top layer in the OVL mark). This may be due to the OVL mark being printed after AL marks have been measured, and then the resist layer being exposed and developed. The resist layer thickness reduction (e.g., of 1-10 nm.) can be estimated based on knowledge of the manufacturing process. This process knowledge can therefore be utilized by the disclosed AL and OVL models to account for estimated changes in OVL mark stack characteristics relative to similar AL mark stack characteristics.

[0079] Figure 5 is a diagram showing examples of symmetrical and asymmetrical characteristics of a mark 500 (AL or OVL) that can be characterized by the AL or OVL sensor measurement.Characteristics of the marks can be classified as symmetrical or asymmetrical. The disclosed methods can utilize these two types of characteristics differently. For example, symmetrical characteristics can be utilized to tune symmetrical stack parameters (as described further herein) and asymmetrical characteristics can be utilized to find a dominant asymmetry, which can be used in selection of which wavelengths of light can be utilized to minimize the asymmetry’s impact on model output. As used herein, symmetrical characteristics are those that typically do not cause the AL position error or OVL error even if those stack parameter values change. These can include, for example, stack thickness 520, stack material refractive index, stack material extinction coefficient, etc. In contrast, asymmetrical characteristics are those that characterize aspects of the mark that typically cause AL position error and OVL error when those stack parameter values change . For example, floor tilt is asymmetrical characteristics. Such asymmetries can cause changes in the phase of diffracted light from the measurement location relative to what it would be were the asymmetry not present.

[0080] Whether a characteristic is symmetrical or asymmetrical can be based on whether the characteristic is mirrored relative to a centerline (e.g., of a mark or pattern). For example, a grating can have a left side wall angle and right side wall angle. If the left side wall angle is equal to the right side wall angle, the side wall angle characteristic is symmetrical. Otherwise, the side wall angle characteristic is asymmetrical. Physically, symmetrical characteristics will not cause errors in AL and OVL metrology, while asymmetrical characteristics can cause errors in AL and OVL metrology.

[0081] Examples of asymmetrical characteristics can include floor tilt, critical dimension imbalance, non-uniform etch depth, asymmetrical sidewall angle 530, etc. While some the characteristics (symmetric or asymmetric) can be the same in both AL and OVL marks, in some cases, the top grating of the OVL mark can have an additional measurable asymmetric characteristic that is not present in the AL mark. Examples of asymmetric characteristics can include a top grating floor tilt, top grating asymmetrical sidewall angle top grating CD imbalance, etc.

[0082] Figure 6 is a diagram of a simplified combination of AL metrology and OVL metrology utilizing model simulation of stack signals from AL and OVL diagnostics.

[0083] A first sensor can be implemented as part of a lithography system to measure AL marks and a second sensor can be part of a metrology system to measure the OVL marks. In some embodiments, a measurement of the AL mark can occur with first sensor 610. First sensor 610 can, for example, be a diffraction-based sensor to receive first signals 612 from an AL mark. Second sensor 620 can, for example, also be a diffraction-based sensor to receive second signals 614 from an OVL mark. In some embodiments, the two sensors may operate on different principles. In some embodiments, second sensor 620 can be an optical camera or a scatterometer.

[0084] Exemplary measurement devices for first sensor 610 or second sensor 620 can include, but are not limited to, an imaging reflectometer, a digital holographic microscope, an imaging spectroscopic reflectometer, a polarized spectroscopic imaging reflectometer, a scanning reflectometer system, a system with two or more reflectometers configured for parallel data acquisition, a system with two or more spectroscopic reflectometers configured for parallel data acquisition, a system with two or more polarized spectroscopic reflectometers configured for parallel data acquisition, a system with two or more polarized spectroscopic reflectometers configured for serial data acquisition without moving the wafer stage or moving any optical elements or the reflectometer stage, imaging spectrometers, imaging system with wavelength filter, imaging system with long-pass wavelength filter, imaging system with short-pass wavelength filter, imaging system without wavelength filter, interferometric imaging system, imaging ellipsometer, imaging spectroscopic ellipsometer, a scanning ellipsometer system, a system with two or more ellipsometers configured for parallel data acquisition, a system with two or more ellipsometers configured for serial data acquisition without moving the wafer stage or moving any optical elements or the ellipsometer stage, a Michelson interferometer, a Mach-Zehnder interferometer, a Sagnac interferometer, a dual self-referencing interferometer, a scanning angle of incidence system, and a scanning azimuth angle system. Furthermore, in general, measurement data collected by different measurement technologies and analyzed in accordance with the methods described herein may be collected from multiple tools, rather than one tool integrating multiple technologies.

[0085] Both first signals 612 and second signals 614 can include both symmetry signals and asymmetry signals. As explained further herein, the symmetrical signals can be used to derive (e.g., regress (or tune)) symmetrical stack parameters, while asymmetrical signals can be used to derive (e.g., regress (or tune)) asymmetric stack parameters.

[0086] Signals from first sensor 610, can be provided to model 630 that can simulate symmetries and asymmetries caused by process variations. The model can combine simulations of signals from first sensor 610 and second sensor 620 to improve the identification of asymmetries and for more accurate AL and OVL determination. As used herein, model 630 is understood to include an AL model 632 (which can determine an alignment error of the AL mark) and an OVL model 634 (which can determine an OVL based on analysis of the OVL mark). Input to the AL model can include signals from the polarized light from the AL mark. The AL model can be configured to determine symmetriccharacteristics associated with the AL mark, for example by using signals to determine a stack geometry of the AL mark by simulating a sensor signal response based on the stack geometry. Similarly, the OVL model (which can determine the OVL based on polarized light from an OVL mark) can be configured to determine asymmetric characteristics associated with the OVL mark, for example by using signals to determine a stack geometry of the OVL mark by simulating a sensor signal response based on the stack geometry.

[0087] Simulation can be performed to estimate the effects of asymmetries in alignment marks or overlay marks on determining alignment position deviation (APD) and / or overlay. Model 630 can receive input such as the model stack information (e.g., materials in the stack, their thicknesses, etc.). Input can also include process variations where asymmetries can be created in the stack characteristics of the stack (e.g., differences in the stack caused by material removal rates, development processes, etc.). Asymmetries can be parameterized by, for example, floor tilt, etch depth, dish depth, side wall angle, etc. Asymmetry in the stack can cause measurement errors. Because many metrology techniques utilize receiving and analyzing light, aberrations in optical components can also appear as substrate errors, and so optical component modeling can be simulation input.

[0088] Computational electromagnetic simulation can model emitted / reflected spectra from the substrate received by a simulated sensor and the subsequent sensor output. This can include accounting for the various wavelengths and polarizations of light that may be provided by the particular metrology device as the apparent errors can be a function of incident wavelength.

[0089] The simulation can then provide output, for example, apparent APD versus wavelength and polarizations of incident light, signal intensities that can reflect wafer quality (e.g., refractive index and absorption), and alignment key-performance indicators such as overlay. In some embodiments, dominant asymmetries can be identified after minimizing the difference between simulated AL signals and the AL sensor measured signals. OVL errors due to the asymmetric alignment mark can then be minimized by choosing a proper weighted wavelength method.

[0090] Figure 7 depicts a process flow diagram of an exemplary method of utilizing combined model-based AL and OVL metrology in calibration phase 710 and in application phase 720.

[0091] In calibration phase 710, a comparatively large number of AL and OVL signals from multiple wavelengths and polarizations can be used as the input to extract stack parameters and identify the dominate asymmetries. The parameter sensitivity to AL signals and OVL signals can be learned and the parameters can be grouped accordingly. The results from the calibration phase can guide the handling of the stack parameters in the application phase. The handling of the parameters in the application phase can thereby be based on which parameters are found to be sensitive to the input signals.

[0092] Embodiments of the disclosed processes can include model 630 receiving a comparatively large number of signals as input during calibration phase 710. For example, first calibration signals 712 (e.g., 12 wavelengths and two polarizations) and second calibration signals 714 (e.g., 15-30wavelengths, and 2-3 polarizations) can be acquired per mark and utilized to calibrate model 630, as described in further detail herein. Such a calibration can include model 630 determining groupings of stack parameters, determining rules for handling parameter regression based on signals from first sensor 610 and second sensor 620, etc. In application phase 720, with model 630 thus calibrated, first signals 612 and second signals 614 can be received from a substrate of interest and analyzed to output, for example, an OVL 730 of the substrate. Details of the various embodiments of these processes and sub-processes are further described herein. While it is contemplated that some embodiments may include a calibration phase, it is also contemplated that a calibration could have previously occurred and that use of the measurements and model could include application phase 720, without specifically performing operations related to calibration of model 630.

[0093] Figure 8 depicts a process flow diagram of an exemplary method of calibrating a model utilizing combined measurements of an AL mark and an OVL mark. In the calibration phase, the OVL / AL model can start with nominal stack parameters, and then find out the best estimated stack parameters by minimizing the difference between measured signal and model simulated signal. During this calibration phase, the stack parameter sensitivity (e.g., the ratio of signal change to stack parameter change) can also be found. The calibration phase thus can provide both the best estimated stack parameters and stack parameter sensitivity. Calibration of model 630 can include, at 810, obtaining first calibration signals 712 generated by first sensor 610 measuring a calibration AL mark (e.g., an AL mark used for purposes of calibration) on a calibration substrate (e.g., a substrate used for purposes of calibration). At 820, the method can also include obtaining second calibration signals 714 generated by the second sensor 620 measuring a calibration OVL mark on the calibration substrate. At 830, the method can include grouping stack parameters of the AL mark and OVL mark according to signal sensitivities to the stack parameters.

[0094] The signal sensitivities can be determined by, for example, calculating the ratios of the first calibration signals 712 and second calibration signals 714 change to the stack parameter change, e.g., through simulation. Comparing the signal sensitivity to their respective noise levels, we can determine which parameter has high sensitivity. For example, if the floor tilt parameter changes 0.1 degree, the first calibration signals 712 and second calibration signals 714 might change 5% and 2.5% respectively. Assuming first calibration signals 712 and second calibration signals 714 noise levels are 0.5% and 1% respectively, then both first calibration signals 712 and second calibration signals 714 have high sensitivity to the floor tilt parameter. In some embodiments, the sensitivities can be further determined by measuring multiple calibration AL marks and multiple calibration OVL marks. This can include measuring marks on one substrate or more than one substrate.

[0095] While Figure 8 provides a general representation of the overall calibration process, calibration phase 710 can be separated into three steps. In some embodiments, the steps include applying model 630 on first calibration signals 712 from an AL mark, applying model 630 on second signals from an OVL mark, and grouping the stack parameters based on the sensitivities to first calibration signals 712and second calibration signals 714), each of which are detailed further below. The resultant grouping allows stack information derived from AL signals from AL marks to be selectively used as input to the OVL model for determination of overlay in the OVL marks.

[0096] A first step in calibration phase 710 can include calibrating the AL model such that it can accurately correlate stack properties with the sensor response signals. It includes inputting first calibration signals 712 into an AL model 632 (e.g., first model) configured to determine symmetric characteristics of the calibration AL mark. The AL model 632 can be further configured to use first signals 612 to determine a stack geometry of the calibration AL mark by simulating the first sensor signal response based on the stack geometry. Particularly, given certain signals from the sensor, the AL model 632 can generate calibration AL stack parameters of the symmetric characteristics of the AL mark (e.g., stack thickness) as well as calibration AL stack parameters of the asymmetric characteristics of the AL mark (e.g., floor tilt, asymmetrical sidewall angle, etc.).

[0097] A second step in calibration phase 710 can include inputting second calibration signals 714 and the AL stack parameters of the symmetric characteristics of the calibration AL mark into OVL model 634 configured to determine the symmetric characteristics of the OVL mark. In some embodiments, the method can also include inputting calibration AL stack parameters of the asymmetric characteristics of the AL mark. The OVL model 634 can further be configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and with inputting the AL mark symmetric characteristics. The OVL model 634 can output the OVL stack parameters of the asymmetric characteristics of the calibration OVL mark.

[0098] A third step in calibration phase 710 can include co-optimizing the OVL stack parameters and the AL stack parameters that the first calibration signals and the second calibration signals are sensitive to based on the grouping (at 930). This co-optimization can cause the OVL stack parameters and the AL stack parameters to meet one or more cost functions that in turn determine a bounding range of the of the OVL stack parameters. Examples of these cost functions can include:1) consistency [symmetric AL stack parameters, symmetric OVL stack parameters],2) consistency [dominant asymmetric AL parameter, dominant asymmetric OVL parameter], and3) Correlation[OV residual(first calibration signals), OE(second calibration signals)].

[0099] In some embodiments, the co-optimization can include separately regressing the first calibration signals and the second calibration signals to cause the AL stack parameters and the OVL stack parameters to meet the cost function! s). For example, alignment position deviation values from the AL model 632 are utilized to build an OVL correction map utilized in the co-optimization.

[0100] Thus, during the calibration phase, because both the AL mark stack parameter’ s values and the OVL mark stack parameter’s values are known, their relationship to each other can be established and therefore bounding ranges can be determined. As one example, for bottom grating layerthickness, it could be determined that AL mark thickness is within ± 0.5nm of nearby OVL mark thickness and for the top resist layer thickness, it could be determined that AL mark thickness is 3-5 nm larger than OVL mark thickness. This can be used to generate constraints during the application phase, e.g., OVL mark bottom grating layer thickness is within + / -0.5nm of nearby AL mark bottom grating layer thickness, and OVL mark’s resist layer thickness is 3-5nm smaller than nearby AL mark’s resist layer thickness. Here“± 0.5nm” and “3-5nm” can be referred to as “predetermined bounding ranges.”

[0101] In some embodiments, part of calibration phase 710 can include grouping stack parameters according to associated response signal sensitivity and generating predetermined rules for how the measured stack parameters will be used in application phase 720. An example of a rule set can be one that covers four different combinations of whether the signals are sensitive to AL and / or OVL stack parameters.

[0102] In a first condition, when the first calibration signals 712 and the second calibration signals 714 are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters will be fed into the OVL model 634 as a seed value and will be regressed by OVL model 634.

[0103] In a second condition, when the first calibration signals 712 and the second calibration signals 714 are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters will be fed into OVL model 634 but will not be regressed by the OVL model 634.

[0104] In a third condition, when first calibration signals 712 and second calibration signals 714 are not sensitive to AL stack parameters and but are sensitive to OVL stack parameters, the OVL stack parameters will be regressed by OVL model 634.

[0105] In a fourth condition, when first calibration signals 712 and second calibration signals 714 are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in OVL model 634.

[0106] The above conditions can be utilized for processing output of model 630, which can include, for example, stack parameters, dominant asymmetries, OVL, and / or an OVL residual.

[0107] Figure 9 depicts a process flow diagram of an exemplary method of applying combined model-based AL and OVL metrology. At 910, the method can include obtaining first signals 612 generated by a first sensor 610 (e.g., an AL sensor) measuring an AL mark on a substrate. At 920, the method can include obtaining second signals 614 generated by a second sensor 620 (e.g., an OVL sensor) measuring an OVL mark on the substrate. At 930, the method can include determining an OVL of the substrate by using combined information derived from first signals 612 and second signals 614.

[0108] In some embodiments, first signals 612 can provide a more precise parameter measurement of the AL mark parameters than the second signals 614 measurement of the OVL mark parameters.During a calibration of model 630, first sensor 610 can be configured to acquire 12 wavelengths and two polarizations, whereas second sensor 620 can be configured to acquire between 15-30 wavelengths and 2-3 polarizations. In contrast, during an application of the model (e.g., in use during high volume wafer production), second sensor 620 can obtain data with a reduced number of channels (e.g., to improve speed), for example, by acquiring 1-2 wavelengths at a single polarization. In such embodiments, first sensor 610 can acquire a greater number of signal channels per acquisition than the second sensor 620. These additional channels can supplement second signals 614 input to model 630 to improve the ability of model 630 to calculate the OVL. Again, such operations are possible because first signals 612 and second signals 614 can be assumed to be measuring features that are the same in both AL marks and OVL marks, due to sharing a common stack.

[0109] In the application phase (e.g., with a calibrated model 630), first sensor 610 can acquire first signals 612, which may include symmetric AL signals indicative of symmetric characteristics of the AL mark as well as asymmetric AL signals indicative of asymmetric characteristics of the AL mark. The stack parameters result derived from the first signals 612 can then be utilized to supplement the stack parameter measurement using the second signals 614 (e.g., measuring an OVL mark) acquired during actual use such as when producing a wafer or otherwise printing to a substrate. As previously mentioned, the additional channels available from first signals 612 can provide additional data such as when second signals 614 (e.g., from an OVL sensor) have a reduced number of channels.

[0110] While Figure 9 provides a general representation of the overall application process, in some embodiments, application phase 720 can be separated into three steps (e.g., applying model 630 on first signals 612 from measuring an AL mark, applying model 630 on second signals 614 from measuring an OVL mark (including utilization at step 930 of first signals 612 to supplement OVL determination when second signals 614 have a reduced number of channels), and checking for consistency / correlation of measured stack parameters and OVL between different measurement sites), each of which are detailed further below.

[0111] The first step of the application phase can be similar to that described for the first step of the calibration phase. Thus, the method can also build on the framework of Figure 7 to include inputting first signals 612 into AL model 632, which can be configured to determine symmetric characteristics of the AL mark. AL model 632 can be further configured to use the first signals to determine a stack geometry of the AL mark by simulating a first sensor signal response based on the stack geometry. AL model 632 can generate AL stack parameters of the symmetric characteristics of the AL mark and AL stack parameters of the asymmetric characteristics of the AL mark.

[0112] AL stack parameters can include AL stack parameters (e.g., one or more of stack thickness, stack material refractive index, stack material extinction coefficient, floor tilt, pitch, and critical dimension, sidewall angle). The AL stack parameters can include a representation of one or more dominant asymmetries in the AL mark, a dominant asymmetry being one of a subset of asymmetriesin the AL mark that are independent from each other and has the largest contribution to a misalignment measurement.

[0113] In some embodiments, the method can include performing a selection of wavelengths and polarizations from channels of first sensor 610 such that the dominant asymmetries have a reduced impact on the misalignment measurement.

[0114] The second step in the application phase can include selectively feed-forward (or otherwise handle) certain parameters into OVL model 634. Second signals 614 (e.g., from second sensor 620 used for measuring an OVL mark) can include symmetric OVL signals indicative of symmetric characteristics of the OVL mark and asymmetric OVL signals indicative of asymmetric characteristics of the OVL mark. Accordingly, some operations can include inputting the AL stack parameters of the symmetric characteristics of the AL mark and the AL stack parameters of the asymmetric characteristics of the AL mark into OVL model 634.

[0115] In some embodiments, the method can include inputting second signals 614 and the AL stack parameters of the symmetric characteristics of the AL mark into an OVL model 634 configured to determine the symmetric characteristics of the OVL mark. OVL model 634 can be further configured to use second signals 614 to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and with inputting the AL mark asymmetric characteristics. OVL model 634 can output the OVL stack parameters of the asymmetric characteristics of the OVL mark.

[0116] In the application phase, the method can include selecting what AL stack parameters are used and / or adjusted (e.g., regressed) in the OVL modeling based on the sensitivity of the signals to the AL and OVL stack parameters. Recalling that the predetermined rules for how to utilize various parameters were determined in the calibration phase, based on those predetermined rules the following operations may occur.

[0117] As a first condition, the method can include, when first signals 612 and second signals 614 are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters can be fed into the OVL model and regressed by OVL model 634.

[0118] As a second condition, the method can include, when first signals 612 and second signals 614 are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters are fed forward into the OVL model and not regressed by OVL model 634.

[0119] As a third condition, the method can include, when determining whether first signals 612 and second signals 614 are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters are regressed by OVL model 634.

[0120] As a fourth condition, the method can include, when first signals 612 and second signals 614 are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in OVL model 634 (e.g., equivalently giving a regression weight of zero to both so effectively not regressed).

[0121] In some embodiments, the method can include adjusting, based on the predetermined rules, the AL stack parameters and / or the OVL stack parameters based on the sensitivities of first signals 612 and second signals 614. The adjusting can include performing regression of the AL stack parameters by AL model 632 and performing regression of the OVL stack parameters by OVL model 634 according to the predetermined rules. Based on which of the four parameter groupings was determined in the calibration phase, the following regression weights may be utilized. For the first grouping, equal non-zero weights can be given to the prior AL and instant OVL stack parameters. For the second grouping, the instant OVL stack parameters can be given a weight of zero (i.e., not regressed). For the third grouping, the prior AL stack parameters can be given a weight of zero. And for the fourth grouping, both prior AL and instant OVL stack parameters can be given a weight of zero.

[0122] The regression of the AL stack parameters can be performed with predetermined bounding ranges. The method can further include adjusting the OVL stack parameters that the first signals and the second signals have a high sensitivity to determine the OVL of the OVL mark and to determine an OVL fingerprint (FP).

[0123] In some embodiments, a third step in the application phase can include repeating the determination of the AL stack parameters and the OVL stack parameters for additional AL marks and OVL marks (on the same wafer or on different wafers) to generate a collection of accumulated parameters (e.g., those parameters utilized in the aforementioned cost functions). Then, from the accumulated parameters, the method can include determining one or more of a symmetric parameter consistency (between symmetric parameters measured by first sensor 610 and second sensor 620), an asymmetric parameter consistency (between asymmetric parameters measured by first sensor 610 and second sensor 620), or a correlation of OVL FP (between an OVL residual calculated based on measurements by first sensor 610 and an OVL calculated based on measurements from second sensor 620). If there are outliers in any of these, they can be reported for examination of the wafer or the production process.

[0124] In terms of consistency of symmetric parameters, in some embodiments, the OVL mark resist layer may have a slightly smaller thickness than the AL mark resist layer. For all other layers, both the OVL mark and the AL mark likely have a very similar thickness. OVL mark bottom CD and AL mark bottom CD likely have similar relationships to mask CD in various features, such as CD bias.

[0125] In terms of consistency of asymmetric parameters, in some embodiments, the OVL mark likely has the same asymmetry as the AL mark, especially bottom grating asymmetry. Due to the top resist grating layer, the OVL mark might have additional asymmetry.

[0126] In terms of the correlation between the OVL residual and the OVL, AL sensor reported alignment position deviation values can be taken from multiple locations to build an OVL correction map and apply them when printing the patterns, so the OVL wafer map (based on OVL sensor data) will be similar as AL OVL residual map (based on AL sensor data).

[0127] Figure 10 is a block diagram of an example computer system CS, according to an embodiment of the present disclosure.

[0128] Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processor) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor PRO. Computer system CS further includes a read only memory (ROM) ROM or other static storage device coupled to bus BS for storing static information and instructions for processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

[0129] Computer system CS may be coupled via 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. An input device ID, including alphanumeric and other keys, is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is cursor control CC, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor PRO and for controlling cursor movement on 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), that allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

[0130] According to one embodiment, portions of one or more methods described herein may be performed by computer system CS in response to processor PRO executing one or more sequences of one or more instructions contained in main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In an alternative embodiment, 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.

[0131] The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium 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 storage device SD. Volatile media include dynamic memory, such as main memory MM. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can alsotake the form of acoustic or light waves, such as those generated during radio frequency (RF) and infrared (IR) data communications. Computer-readable media can be non-transitory, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. Non- transitory computer readable media can have instructions recorded thereon. The instructions, when executed by a computer, can implement any of the features described herein. Transitory computer- readable media can include a carrier wave or other propagating electromagnetic signal.

[0132] Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to processor PRO for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can 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 bus BS can receive the data carried in the infrared signal and place the data on bus BS. Bus BS carries the data to main memory MM, from which processor PRO retrieves and executes the instructions. The instructions received by main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

[0133] Computer system CS may also include a communication interface CI coupled to bus BS. Communication interface CI provides a two-way data communication coupling to a network link NDL that is connected to a local network LAN. For example, communication interface CI may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, communication interface CI may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

[0134] Network link NDL typically provides data communication through one or more networks to other data devices. For example, network link NDL may provide a connection through local network LAN to a host computer HC. This can include data communication services provided through the worldwide packet data communication network, now commonly referred to as the “Internet” INT. Local network LAN (Internet) both use electrical, electromagnetic or optical signals that carry digital data streams. The signals through the various networks and the signals on network data link NDL and through communication interface CI, which carry the digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

[0135] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CL In the Internet example,host computer HC might transmit a requested code for an application program through Internet INT, network data link NDL, local network LAN and communication interface CI. One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0136] Embodiments of the present disclosure can be further described by the following clauses.1. A method of metrology comprising: obtaining first signals generated by a first sensor measuring an alignment (AL) mark on a substrate; obtaining second signals generated by a second sensor measuring an overlay (OVL) mark on the substrate; and determining an OVL of the substrate by using combined information derived from the first signals and the second signals.2. The method of clause 1, wherein the first signals provide a more precise parameter measurement of the AL mark than the second signals measurement of the OVL mark.3. The method of clause 2, wherein the first sensor is a laser-based interferometer or an optical camera.4. The method of clause 2, wherein the second sensor is an optical camera or a scatterometer.5. The method of clause 1, wherein the first sensor acquires a greater number of signal channels per acquisition than the second sensor.6. The method of clause 1, wherein a bottom grating of the OVL mark is on the same process layer as the AL mark.7. The method of clause 1, wherein a top grating of the OVL mark has an additional asymmetric characteristic that is not present in the AL mark.8. The method of clause 1, wherein the first signals comprise symmetric AL signals indicative of symmetric characteristics of the AL mark and asymmetric AL signals indicative of asymmetric characteristics of the AL mark.9. The method of clause 8, further comprising: inputting the first signals into an AL model configured to determine symmetric characteristics of the AL mark, the AL model further configured to use the first signals to determine a stack geometry of the AL mark by simulating a first sensor signal response based on the stack geometry; and generating, with the AL model, AL stack parameters of the symmetric characteristics of the AL mark, and AL stack parameters of the asymmetric characteristics of the AL mark.10. The method of clause 9, wherein the AL stack parameters comprise AL stack parameters.11. The method of clause 9, wherein the AL stack parameters include one or more of stack thickness, stack material refractive index, stack material extinction coefficient, floor tilt, pitch, and critical dimension, sidewall angle.12. The method of clause 9, wherein the AL stack parameters include a representation of one or more dominant asymmetries in the AL mark, a dominant asymmetry being one of a subset of asymmetries in the AL mark that are independent from each other and has the largest contribution to a misalignment measurement.13. The method of clause 12, further comprising performing a selection of wavelengths and polarizations from channels of the first sensor such that the dominant asymmetry has a reduced impact on the misalignment measurement.14. The method of clause 9, wherein the second signals comprise symmetric OVL signals indicative of symmetric characteristics of the OVL mark and asymmetric OVL signals indicative of asymmetric characteristics of the OVL mark.15. The method of clause 14, further comprising inputting the AL stack parameters of the symmetric characteristics of the AL mark and the AL stack parameters of the asymmetric characteristics of the AL mark into an OVL model.16. The method of clause 9, further comprising: inputting the second signals and symmetric characteristic into an OVL model configured to determine the symmetric characteristics of the OVL mark, the OVL model further configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and inputting AL mark’ s asymmetric characteristic parameters; and outputting, from the OVL model, the OVL stack parameters of the asymmetric characteristics of the OVL mark.17. The method of clause 16, further comprising adjusting, based on predetermined rules, the AL stack parameters and / or the OVL stack parameters based on the sensitivities of the first signals and the second signals.18. The method of clause 17, the adjusting comprising performing regression of the AL stack parameters by the AL model and performing regression of the OVL stack parameters by the OVL model according to the predetermined rules.19. The method of clause 18, wherein the regression of the AL stack parameters is performed with predetermined bounding ranges.20. The method of clause 18, further comprising adjusting the OVL stack parameters that the first signals and the second signals have a high sensitivity to determine the OVL of the OVL mark and to determine an OVL fingerprint (FP).21. The method of clause 17, further comprising, when the first signals and the second signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters are fed into the OVL model as a seed value and regressed by the OVL model.22. The method of clause 17, further comprising, when the first signals and the second signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters are fed into the OVL model and not regressed by the OVL model.23. The method of clause 17, further comprising, when the first signals and the second signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters are regressed by the OVL model.24. The method of clause 17, further comprising, when the first signals and the second signals are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in the OVL model.25. The method of clause 14, further comprising: repeating the determination of the AL stack parameters and the OVL stack parameters for additional AL marks and OVL marks to generate a collection of accumulated parameters; and determining, from the accumulated parameters, one or more of a symmetric parameter consistency, an asymmetric parameter consistency, or a correlation of OVL FP.26. The method of clause 1, further comprising: obtaining first calibration signals generated by the first sensor measuring a calibration AL mark on a calibration substrate; obtaining second calibration signals generated by the second sensor measuring a calibration OVL mark on the calibration substrate; and grouping stack parameters of the AL mark and OVL mark according to signal sensitivities to the stack parameters.27. The method of clause 26, further comprising determining the sensitivities by calculating ratios of a first calibration signals and second calibration signals change to a stack parameter change.28. The method of clause 27, wherein the sensitivities are further determined by measuring a plurality of calibration AL marks and a plurality of calibration OVL marks.29. The method of clause 26, wherein when the first calibration signals and the second calibration signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters will be fed into an OVL model as a seed value and will be regressed by the OVL model.30. The method of clause 26, wherein when the first calibration signals and the second calibration signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stackparameters that are common to OVL stack parameters will be fed into an OVL model but will not be regressed by the OVL model.31. The method of clause 26, wherein when the first calibration signals and the second calibration signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters will be regressed by an OVL model.32. The method of clause 26, wherein when the first calibration signals and the second calibration signals are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in an OVL model.33. The method of clause 26, further comprising inputting the first signals into an AL model configured to determine symmetric characteristics of the calibration AL mark, the AL model further configured to use the first signals to determine a stack geometry of the calibration AL mark by simulating a first sensor signal response based on the stack geometry; and generating, with the AL model, calibration AL stack parameters of the symmetric characteristics of the AL mark and calibration AL stack parameters of asymmetric characteristics of the AL mark.34. The method of clause 33, further comprising: inputting the second calibration signals and the AL stack parameters of the symmetric characteristics of the calibration AL mark into an OVL model configured to determine the symmetric characteristics of the OVL mark the OVL model further configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and inputting AL mark’s asymmetric characteristic parameters; and outputting, from the OVL model, the OVL stack parameters of the asymmetric characteristics of the calibration OVL mark.35. The method of clause 34, further comprising: co-optimizing the OVL stack parameters and the AL stack parameters that the first calibration signals and the second calibration signals are sensitive to based on the grouping, the co-optimization causing the OVL stack parameters and the AL stack parameters to meet one or more cost functions; and determining a bounding range of the of the OVL stack parameters.36. The method of clause 35, wherein the co-optimization includes regressing the first calibration signals and the second calibration signals to cause the AL stack parameters and the OVL stack parameters to meet the one or more cost functions.37. The method of clause 35, wherein alignment position deviation values from the AL model are utilized to build an OVL correction map utilized in the co-optimization.38. The method of Clause 1, wherein the method further comprises according to predetermined rules regarding stack parameter sensitivities to the first signals and the second signalsrespectively, selecting the first or second signals in regression to obtain a stack parameter of the OVL mark.39. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing (EUV / DUV) radiation from radiation source to transfer a pattern from a mask onto the photoresist layer; removing a portion of the photoresist layer to form the pattern over the substrate; and performing metrology on the substrate according to any one of the preceding clauses.40. A non-transitory computer readable medium having instructions recorded thereon for a lithographic process, the instructions when executed by a computer having at least one programmable processor cause operations comprising, the operations as in any of method clauses 1- 37.41. A system for use with a lithographic process, the system comprising: at least one programmable processor; and a non-transitory computer readable medium having instructions recorded thereon, the instructions when executed by a computer having the at least one programmable processor cause operations as in any of method clauses 1-38.42. The system of clause 41, wherein the first sensor or the second sensor is a diffractionbased sensor.43. The system of clause 1, wherein the first sensor is a laser-based interferometer or an optical camera.44. The system of clause 1, wherein the second sensor is an optical camera or a scatterometer.

[0137] The combinations and sub-combinations of the elements disclosed herein constitute separate embodiments and are provided as examples only. Also, the descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made as described without departing from the scope of the claims set out below.

Claims

CLAIMS1. A method of metrology comprising: obtaining first signals generated by a first sensor measuring an alignment (AL) mark on a substrate; obtaining second signals generated by a second sensor measuring an overlay (OVL) mark on the substrate; and determining an OVL of the substrate by using combined information derived from the first signals and the second signals, wherein the determining the OVL comprises, according to predetermined rules regarding stack parameter sensitivities to the first signals and the second signals respectively, selecting from the first or second signals to obtain a stack parameter of the OVL mark.

2. The method of claim 1, wherein the first sensor comprises one of a laser-based interferometer and an optical camera; wherein the second sensor comprises one of an optical camera, a scatterometer; and wherein a bottom grating of the OVL mark is on the same process layer as the AL mark, and wherein a top grating of the OVL mark has an additional asymmetric characteristic that is not present in the AL mark.

3. The method of claim 1, further comprising: inputting the first signals into an AL model configured to determine symmetric characteristics of the AL mark, the AL model further configured to use the first signals to determine a stack geometry of the AL mark by simulating a first sensor signal response based on the stack geometry; and generating, with the AL model, AL stack parameters of the symmetric characteristics of the AL mark, and AL stack parameters of the asymmetric characteristics of the AL mark, wherein the first signals comprise symmetric AL signals indicative of symmetric characteristics of the AL mark and asymmetric AL signals indicative of asymmetric characteristics of the AL mark, wherein the second signals comprise symmetric OVL signals indicative of symmetric characteristics of the OVL mark and asymmetric OVL signals indicative of asymmetric characteristics of the OVL mark, wherein the AL stack parameters include one or more of stack thickness, stack material refractive index, stack material extinction coefficient, floor tilt, pitch, and critical dimension, sidewall angle.

4. The method of claim 3,wherein the AL stack parameters include a representation of one or more dominant asymmetries in the AL mark, a dominant asymmetry being one of a subset of asymmetries in the AL mark that are independent from each other and has the largest contribution to a misalignment measurement, wherein the method further comprises performing a selection of wavelengths and polarizations from channels of the first sensor such that the dominant asymmetry has a reduced impact on the misalignment measurement.

5. The method of claim 3, further comprising: inputting the AL stack parameters of the symmetric characteristics of the AL mark and the AL stack parameters of the asymmetric characteristics of the AL mark into an OVL model; inputting the second signals and symmetric characteristic into an OVL model configured to determine the symmetric characteristics of the OVL mark, the OVL model further configured to use the second signals to determine a stack geometry of the OVL mark by simulating the second sensor signal response based on the stack geometry and inputting AL mark’ s asymmetric characteristic parameters; and outputting, from the OVL model, the OVL stack parameters of the asymmetric characteristics of the OVL mark.

6. The method of claim 5, further comprising adjusting, based on predetermined rules, the AL stack parameters and / or the OVL stack parameters based on the sensitivities of the first signals and the second signals.

7. The method of claim 6, wherein the adjusting comprises performing regression of the AL stack parameters by the AL model and performing regression of the OVL stack parameters by the OVL model according to the predetermined rules, further comprising adjusting the OVL stack parameters that the first signals and the second signals have a high sensitivity to determine the OVL of the OVL mark and to determine an OVL fingerprint (FP).

8. The method of claim 7, further comprising, when the first signals and the second signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters are fed into the OVL model as a seed value and regressed by the OVL model; when the first signals and the second signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters are fed into the OVL model and not regressed by the OVL model;when the first signals and the second signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters are regressed by the OVL model; and when the first signals and the second signals are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in the OVL model.

9. The method of claim 3, further comprising: repeating the determination of the AL stack parameters and the OVL stack parameters for additional AL marks and OVL marks to generate a collection of accumulated parameters; and determining, from the accumulated parameters, one or more of a symmetric parameter consistency, an asymmetric parameter consistency, or a correlation of OVL FP.

10. The method of claim 1, further comprising: obtaining first calibration signals generated by the first sensor measuring a calibration AL mark on a calibration substrate; obtaining second calibration signals generated by the second sensor measuring a calibration OVL mark on the calibration substrate; and grouping stack parameters of the AL mark and OVL mark according to signal sensitivities to the stack parameters.

11. The method of claim 10, further comprising determining the sensitivities by calculating ratios of a first calibration signals and second calibration signals change to a stack parameter change.

12. The method of claim 11, wherein when the first calibration signals and the second calibration signals are sensitive to both AL stack parameters and OVL stack parameters, the AL stack parameters that are common to OVL stack parameters will be fed into an OVL model as a seed value and will be regressed by the OVL model; when the first calibration signals and the second calibration signals are sensitive to AL stack parameters but not OVL stack parameters, the AL stack parameters that are common to OVL stack parameters will be fed into an OVL model but will not be regressed by the OVL model; wherein when the first calibration signals and the second calibration signals are not sensitive to AL stack parameters but are sensitive to OVL stack parameters, the OVL stack parameters will be regressed by an OVL model; and wherein when the first calibration signals and the second calibration signals are not sensitive to both the AL stack parameters and the OVL stack parameters, the AL stack parameters and the OVL stack parameters will be fixed in an OVL model.

13. The method of claim 11, further comprising: co-optimizing the OVL stack parameters and the AL stack parameters that the first calibration signals and the second calibration signals are sensitive to based on the grouping, the co-optimization causing the OVL stack parameters and the AL stack parameters to meet one or more cost functions.

14. The method of claim 11, further comprising: determining a bounding range of the of the OVL stack parameters for use in regression, wherein the co-optimization includes regressing the first calibration signals and the second calibration signals to cause the AL stack parameters and the OVL stack parameters to meet the one or more cost functions.

15. The method of claim 13, wherein alignment position deviation values from the AL model are utilized to build an OVL correction map utilized in the co-optimization.

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