Process independent integrated optics for wafer alignment sensors

Abstract

A system is disclosed for determining a focus or tilt of a target in an alignment sensor. The system includes two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors.

Description

PROCESS INDEPENDENT INTEGRATED OPTICS FOR WAFER ALIGNMENT SENSORSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 687,737 which was filed on August 27, 2024 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The description herein relates generally to alignment sensors for lithographic processes. More particularly, the disclosure includes apparatus, methods, and computer programs for determining focus and / or tilt of a target with an alignment sensor.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.

[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 causedby the processing of the substrate, for example etching, chemical mechanical polishing (CMP) or layer deposition leading to sub-optimal marker position determination.SUMMARY

[0006] In one aspect, a system for determining a focus or tilt of a target in an alignment sensor is disclosed. The system includes two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors.

[0007] In some embodiments, the output can be an alignment position deviation of the target. The two optical sensors can have a tilt-defocus sensitivity that is the same for the two optical sensors.

[0008] In some embodiments, the design features can cause the differing outputs with respect to both a focus and a tilt of the target. The design features can be deviations from a nominal design.

[0009] In some embodiments, the two optical sensors can be grating couplers. The design features can comprise fill ratios of the grating couplers that are different from each other or can comprise periodicities of grooves in the grating couplers, and the periodicities are different from each other.

[0010] In some embodiments, the two optical sensors have a substantively coplanar arrangement. The two optical sensors can be grating couplers that have different grating constructions with respect to symmetry about a grating coupler longitudinal axis.

[0011] In some embodiments, the two optical sensors can have a multi-layer arrangement where the two optical sensors are at least partially overlapping with respect to the light. The two optical sensors can be grating couplers that have the same grating constructions with respect to symmetry about a grating coupler longitudinal axis. There can be a third optical sensor and the three optical sensors comprise a top sensor designed for a positive defocus and a positive tilt, a middle sensor designed for no-tilt and no defocus, and a bottom sensor designed for a negative defocus and a negative tilt.

[0012] In an interrelated aspect, a method for determining a focus or a tilt of a target in an alignment sensor can include measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors. The method can also include determining the focus or the tilt of the target based on the two outputs and the design features.

[0013] In some embodiments, the method can include determining, based on the measured two outputs, a first difference between a first output of a first optical sensor and a second output of a second optical sensor.

[0014] In some embodiments, the alignment sensor can have a third optical sensor with a third output, with the method further comprising determining, based on the measured three outputs, a second difference between the third output of the third optical sensor and the second output of the second optical sensor.

[0015] In an interrelated aspect, a semiconductor device manufacturing method can include receiving a substrate with a photoresist layer, directing EUV or DUV radiation from a 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 determining a focus or a tilt of a target on a substrate with an alignment sensor. The method can further include measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors. The method can also include determining the focus or the tilt of the target based on the two outputs and the design features, and adjusting a manufacturing process for the pattern based on the focus or the tilt of the target.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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 principles associated with the disclosed implementations. In the drawings,Figure 1 schematically depicts a lithography apparatus, according to an embodiment of the present disclosure.Figure 2 schematically depicts an embodiment of a lithographic cell or cluster, according to an embodiment of the present disclosure.Figure 3A schematically depicts an example metrology system, according to an embodiment of the present disclosure.Figure 3B schematically depicts an example metrology technique, according to an embodiment of the present disclosure.Figure 3C depicts an example alignment sensor that includes at least two optical sensors for receiving diffracted light from a target, according to an embodiment of the present disclosure.Figure 4 depicts an example of the focus or tilt of a target being measured by optical sensors of the alignment sensor, according to an embodiment of the present disclosure.Figure 5 shows an example of an optical sensor being a grating coupler, according to an embodiment of the present disclosure.Figure 6 shows an example of optical sensors arranged to collect multiple wavelengths of diffracted light from a target, according to an embodiment of the present disclosure.Figure 7 shows an example of coplanar optical sensors for a single color and single polarization, according to an embodiment of the present disclosure.Figure 8 shows an example of multi-layer optical sensors, according to an embodiment of the present disclosure.Figure 9 shows an example of a method for determining a focus or tilt of a target in an alignment sensor, according to an embodiment of the present disclosure.Figure 10 is a block diagram of an example computer system, according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0017] In semiconductor device manufacturing, AL metrology is performed to precisely align the positioning of the wafer with respect to the reticle. Optical metrology can include illuminating AL marks with light having a range of wavelengths and / or polarizations. The scattered or diffracted light can be received by an AL sensor. The positions and intensities of the diffracted orders can be compared to an expected result to determine the AL.

[0018] 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 be used for measuring overlay, alignment on wafers, etc., in a semiconductor device manufacturing process, for example, or for other operations.

[0019] 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 beconsidered as interchangeable with the more general terms "mask," "substrate" and "target portion," respectively.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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 targetportion 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.

[0024] 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."

[0025] 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.

[0026] 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 theradiation 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. after mechanical 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 short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected to a short-stroke actuator only, or may be fixed. 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 a radiation 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.

[0032] 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.

[0033] 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.

[0034] 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 I / Ol, I / O2, movesthem 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.

[0035] 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)).

[0036] 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.

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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).

[0042] Figure 3 A 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 detector4 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.

[0043] 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).

[0044] 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.

[0045] 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 inprocessing 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.

[0046] 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 on the alignment of the substrate W, 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.

[0047] 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.

[0048] Embodiments of the present disclosure can utilize an AL 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 sumand 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.

[0049] Figure 3C depicts an example alignment sensor that includes at least two optical sensors for receiving diffracted light from a target. The simplified system depicted is similar to that of Figure 3A, with illumination source 2 providing light to substrate W having target T (e.g., an alignment mark). Diffracted light from target T can be received at a detector 4 that can include one or more optical sensors . The diffracted light can have different diffraction orders, which can be obtained by different detectors 4. For example, one detector 4 can receive +1 order diffracted light and another detector 4 can receive -1 order diffracted light. This light can be analyzed by the alignment sensor (e.g., via a processing system to convert electrical signals from detector 4 into a measurement of the diffracted light) to determine the position, tilt, focus, etc., of target T and thereby substrate W.

[0050] Figure 4 depicts an example of the focus or tilt of a target being measured by optical sensors of the alignment sensor. Alignment sensors can measure the X and Y position of target T. Defocus (Z) and / or tilt of the target T (e.g., away from a nominal position as shown in Figure 4 by the dashed outline) can cause a deviation or an error in the reading of the X and Y position measurement that determines the real APD. As such, the defocus and / or tilt causes the reported APD to be inaccurate.

[0051] Figure 4 also depicts some additional details of detectors 4. One or more of detectors 4 can include a number of optical sensors 410, which due to their arrangement, physical construction, etc. can be utilized to determine the tilt or focus of target T. The number and features of the optical sensors 410 can vary as disclosed herein, with the example of Figure 4 not implying any particular number, feature, or configuration of optical sensors 410 other than to indicate that there may be several distinct optical sensors 410 in one or more of detectors 4. More specific designs are disclosed herein according to various embodiments. As shown in the embodiment of Figure 4, there can be at least two optical sensors 410, each having design features that cause the two optical sensors 410 to have differing outputs with respect to the focus or the tilt of target T based on light sensed by the two optical sensors 410. While two optical sensors may be utilized, in some embodiments other numbers of optical sensors can be utilized, for example three, four, five, etc. In some embodiments, it can be useful (though not essential) for there to be at least three optical sensors 410, as three optical sensors can be utilized for determining both tilt and focus of the target, as explained below and depicted in several figures.

[0052] An optical sensor can have design features that can vary from optical sensor to optical sensor and that allow extracting the tilt and / or defocus of target T when used in combination. Ideally, the output of an optical sensor (alignment position) deviates by the target defocus and target tilt as:However, in practice, the APD (alignment position deviation) can be determined as:APD = (Az - Az (A0 - A0 .The constant ci is the tilt-defocus sensitivity and it is the characteristic of the sensor and so indicates the relationship between the focus, tilt, and the APD. DZ is the focus and Dq is the tilt, e.g., when scanned a horizontal direction. The other parameters (Azxand A6 ) depend on the optical sensor design, or design deviations due to fabrication / alignment error, but they are fixed parameters and can be extracted by calibration and measuring a reference mark. In some cases, the stack variation and mark asymmetry can also be translated into DZ and Dq, respectively, and the diffracted light may vary (e.g., in intensity) based on the wavelength of light used for measurement.

[0053] The tilt-defocus sensitivity ci can be considered essentially the same for similar optical sensors (e.g., sensors of essentially the same construction or principle of operation), but in some embodiments can be different for all three sensors. Accordingly, in a system where there are for example two optical sensors, they can have a tilt-defocus sensitivity that is the same. However, in various embodiments, the optical sensors can have design features that cause differing outputs with respect to a focus, a tilt, or both a focus and a tilt of the target. Such design features can be intentionally introduced into the optical sensors, can be deviations from a nominal design, etc. Examples of design errors for particular types of optical sensors are described further herein.

[0054] Given optical sensors with the same tilt-defocus sensitivity, this can allow determination of the focus and tilt of target T. For two optical sensors, the method below allows for determining one unknown (e.g., either focus or tilt). For the example of three optical sensors, this results in a system of equations that can be solved for both the unknown focus (DZ) and tilt (qy):Here, with N measured APDs (e.g., N = 3) that are different due toand qyN being different for each optical sensor, the differences between the equations can be utilized to determine the unknown focus and tilt (shown bolded below):While the left-hand side differences cannot be zero, the design features of the optical detectors should be selected such that the necessary above differences on the right-hand side can also be established. However, not all right-hand side differences are necessary. For example, were DZ2 = DZi , and qy2 = qys, then the above equations would still be solvable for focus and tilt. Accordingly, while some differences in the design of the optical sensors are needed, there is some flexibility in their designs as contemplated by the present disclosure. If the system is configured to extract only tilt or defocus, two sensors are sufficient.

[0055] Figure 5 shows an example of an optical sensor being a grating coupler. Grating coupler 510 can be a type of waveguide sensitive to diffracted light of a particular wavelength and / or polarization. Physically, grating coupler 510 can have a grating surface 520 (e.g., made of Si) with grooves 530 that can be used to couple the incoming light into a waveguide on the photonic chip. Grooves 530 can be periodic or can be on an apodised grating coupler in which the periodicity and filling factor of grating lines can be different. Grooves 530 can have parameters such as thickness (or height / depth of the grooves), a fill ratio (fraction of filling the groove structure, e.g., if the grooves have the same distance between them as their width then the fill ratio would be 0.5), a periodicity (distance before a groove repeats), etc. Beneath the grating surface can be a low index material layer 550 (e.g., made of SiCh). There may also be (not shown in Figure 5) a layer of low-index cladding over grating surface 520. The light can propagate down the waveguide and be directed into output portion 540. Output portion 540 can be connected to a fiber optic, or a lens, where the light can be directed to a detector suchas a photodetector. In some embodiments, the photodetector can be on the chip and capture the light directly. There are numerous ways to vary the design features that allow grating couplers to provide different outputs. One way to show this is to consider the case where the grating coupler would act as an emitter rather than a receiver. In the sense of being an emitter, the grating couplers can be designed such that they emit slightly different light (e.g., different emission angle, different beam sizes, etc.). Conversely, such design features (when the grating coupler is acting as a receiver) can result in differences in the light output from output portion 540 and hence measurable differences in signal at a detector. The above-mentioned periodicity, thickness, etching depth, placement on different layers (e.g., causing a physical change of the working distance) are other parameters of the grating coupler(s) that can be varied to cause the utilized differences. As one example of physical features that can cause such differences, the design features can include fill ratios of the grating couplers that are different from each other. Fill ratios can vary from, for example, 0.1 to 0.9, but in various embodiments the deviations between fill ratios of different grating couplers can be small, for example, 5%, 10%, 15%, etc. In some embodiments, the design features can include periodicities of grooves in the grating couplers, and the periodicities can be different from each other. Examples of changes in periodicity or thickness can include 1-5 nm in periodicity or less than one nanometer in thickness.

[0056] Figure 6 shows an example of optical sensors arranged to collect multiple wavelengths of diffracted light from a target. Examples of optical sensors can be found in U.S. 63 / 506,466, the contents of which are incorporated by reference. In some embodiments, a first group 610 of optical sensors 610a-d can be coupled together (e.g., via fiber optics 630) in an interferometric arrangement with a second group 620 of optical sensors 620a-d. Light from corresponding optical sensors in the two groups can thus combine to provide light to a detector with a total intensity (based on constructive or destructive interference between ± order signals):

[0057] In some embodiments, light having multiple wavelengths can be delivered to the target. Accordingly, to obtain the corresponding diffracted light from the target, the optical sensors can have differing designs and positions. This is depicted in Figure 6 by the four different optical sensors in each of the two groups 610 and 620, the four designs arranged to collect fourdifferent wavelengths of diffracted light. The optical sensors for a given wavelength can vary by size, grating pattern, etc.

[0058] Figure 7 shows an example of coplanar optical sensors for a single color and single polarization. The depicted example is similar to the example of Figure 6, with one group of three optical sensors shown in an expanded view. In the depicted example, there can be at least two optical sensors 710, 720 that have a substantively coplanar arrangement. By “coplanar,” this means that the grating surfaces (or the grating coupler as a whole) can be on or close to being in the same plane. An optional additional third coplanar optical sensor 730 is also depicted. As shown, any two optical sensors can be grating couplers that have different grating constructions with respect to symmetry about their grating coupler longitudinal axis. For example, first grating coupler 710 can have a symmetric grating pattern about its longitudinal axis 710a. Second grating coupler 720 can have a different and asymmetric grating pattern around its longitudinal axis 720a, with the asymmetry shown by some of the grooves not extending fully across the grating coupler. Third grating coupler 730 can be similar to second grating coupler but mirrored to have a corresponding mirrored asymmetry about its longitudinal axis 730a. Again, the grating design can be selected to optimize the particular grating coupler for a particular position, measuring a particular focus or tilt, etc.

[0059] Figure 8 shows an example of multi-layer optical sensors. The two (or three as in Figure 8) optical sensors (e.g., optical sensors 810, 820, 830) can have a multi-layer arrangement where the two (or three) optical sensors can be at least partially overlapping with respect to light 840 (e.g., diffracted from the target). In some embodiments, the optical sensors can be fully overlapping but in other embodiments the overlapping may only be partial. The optical sensors can optionally be surrounded by an SiCh layer 850 and may include an Si substrate layer 860. One advantageous technical benefit of the multi-layer configuration is that any two optical sensors can be grating couplers that have the same grating constructions with respect to symmetry about a grating coupler longitudinal axis. This can, for example, simplify manufacturing as essentially the same grating coupler designs can easily have the same ci as discussed above. In contrast, having grating couplers in a coplanar arrangement can cause ci to be slightly different for each grating coupler, introducing a nonlinear term:Even so, the nonlinear term is small (because Ci ~ Cj) and thus is small enough to be neglected, consistent with ci be considered the same, as discussed above. The multi-level design however, further facilitates avoiding or reducing this nonlinear term.

[0060] The present disclosure contemplates many combinations of optical sensors (e.g., grating couplers) in different arrangements in the same plane, being stacked into a multi-level configuration, etc. Again, the number of grating couplers can also be two, three, four, etc. depending on how many parameters are desired to be measured (e.g., focus, tilt, or focus and tilt). The differences in DZN and qyN can be reflected in a multi-layer arrangement in a variety of ways. However, as one example embodiment, there can be three optical sensors (as in Figure 8), where they can include a top sensor designed for a positive defocus (e.g., DZN > 0) and a positive tilt (e.g., qyx> 0), a middle sensor designed for no-tilt (e.g., DZN = 0) and no defocus (e.g., qyN = 0), and a bottom sensor designed for a negative defocus (e.g., DZN < 0) and a negative tilt (e.g., qyN< 0).

[0061] Figure 9 shows an example of a method for determining a focus or tilt of a target in an alignment sensor. The disclosed systems can be implanted as a method (e.g., a computer implemented method) to perform the functions described in various embodiments herein. As one example, a method for determining a focus or a tilt of a target in an alignment sensor can include, at 910, measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors. At 920, the focus or the tilt of the target can be determined based on the two outputs and the design features. While the method may stop here and rely on other ways of determining the unknown focus and / or tilt, when expressed as differences of equations the method can include, at 930, determining, based on the measured two outputs, a first difference between a first output of a first optical sensor and a second output of a second optical sensor. This method can be extended to measuring both focus and tilt by including a third optical sensor with a third output. The method can then include, at 940, determining, based on the measured three outputs, a second difference between the third output of the third optical sensor and the second output of the second optical sensor.

[0062] Figure 10 is a block diagram of an example computer system CS, according to an embodiment of the present disclosure.

[0063] 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 forstoring 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.

[0064] 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.

[0065] 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.

[0066] In the following, further features, characteristics, and exemplary technical solutions of the present disclosure will be described in terms of clauses that may be optionally claimed in any combination:1. A system for determining a focus or tilt of a target in an alignment sensor, the system comprising: two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors.The system of clause 1, wherein the output is an alignment position deviation of the target.3. The system of clause 1, wherein the two optical sensors have a tilt-defocus sensitivity that is the same for the two optical sensors.4. The system of clause 1, wherein the design features cause the differing outputs with respect to both a focus and a tilt of the target.5. The system of clause 1, wherein the design features are deviations from a nominal design.6. The system of clause 1, wherein the two optical sensors are grating couplers.7. The system of clause 6, wherein the design features comprise fill ratios of the grating couplers that are different from each other.8. The system of clause 6, wherein the design features comprise periodicities of grooves in the grating couplers, and the periodicities are different from each other.9. The system of clause 1, wherein the two optical sensors have a substantively coplanar arrangement.10. The system of clause 9, wherein the two optical sensors are grating couplers that have different grating constructions with respect to symmetry about a grating coupler longitudinal axis.11. The system of clause 1, wherein the two optical sensors have a multi-layer arrangement where the two optical sensors are at least partially overlapping with respect to the light.12. The system of clause 11, wherein the two optical sensors are grating couplers that have the same grating constructions with respect to symmetry about a grating coupler longitudinal axis.13. The system of clause 11, wherein there is a third optical sensor and the three optical sensors comprise: a top sensor designed for a positive defocus and a positive tilt; a middle sensor designed for no-tilt and no defocus; and a bottom sensor designed for a negative defocus and a negative tilt.14. A method for determining a focus or a tilt of a target in an alignment sensor, the method comprising: measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors; and determining the focus or the tilt of the target based on the two outputs and the design features.15. The method of clause 14, further comprising determining, based on the measured two outputs, a first difference between a first output of a first optical sensor and a second output of a second optical sensor.16. The method of clause 15, the alignment sensor having a third optical sensor with a third output, the method further comprising determining, based on the measured three outputs, a second difference between the third output of the third optical sensor and the second output of the second optical sensor.17. A semiconductor device manufacturing method comprising: receiving a substrate with a photoresist layer; directing EUV or DUV radiation from a 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 determining a focus or a tilt of a target on a substrate with an alignment sensor, the method further comprising: measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors; determining the focus or the tilt of the target based on the two outputs and the design features; and adjusting a manufacturing process for the pattern based on the focus or the tilt of the target.

[0067] 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 also take 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Computer system CS can send messages and receive data, including program code, through the network(s), network data link NDL, and communication interface CI. 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 non-volatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0072] 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 system for determining a focus or tilt of a target in an alignment sensor, the system comprising: two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors.

2. The system of claim 1, wherein the output is an alignment position deviation of the target.

3. The system of claim 1, wherein the two optical sensors have a tilt-defocus sensitivity that is the same for the two optical sensors.

4. The system of claim 1, wherein the design features cause the differing outputs with respect to both a focus and a tilt of the target.

5. The system of claim 1, wherein the design features are deviations from a nominal design.

6. The system of claim 1, wherein the two optical sensors are grating couplers.

7. The system of claim 6, wherein the design features comprise fill ratios of the grating couplers that are different from each other.

8. The system of claim 6, wherein the design features comprise periodicities of grooves in the grating couplers, and the periodicities are different from each other.

9. The system of claim 1, wherein the two optical sensors have a substantively coplanar arrangement.

10. The system of claim 9, wherein the two optical sensors are grating couplers that have different grating constructions with respect to symmetry about a grating coupler longitudinal axis.

11. The system of claim 1, wherein the two optical sensors have a multi-layer arrangement where the two optical sensors are at least partially overlapping with respect to the light.

12. The system of claim 11, wherein the two optical sensors are grating couplers that have the same grating constructions with respect to symmetry about a grating coupler longitudinal axis.

13. The system of claim 11, wherein there is a third optical sensor and the three optical sensors comprise: a top sensor designed for a positive defocus and a positive tilt; a middle sensor designed for no-tilt and no defocus; and a bottom sensor designed for a negative defocus and a negative tilt.

14. A method for determining a focus or a tilt of a target in an alignment sensor, the method comprising: measuring two outputs of two optical sensors, each having design features that cause the two optical sensors to have differing outputs with respect to the focus or the tilt of the target based on light sensed by the two optical sensors; and determining the focus or the tilt of the target based on the two outputs and the design features.

15. The method of claim 14, further comprising determining, based on the measured two outputs, a first difference between a first output of a first optical sensor and a second output of a second optical sensor.

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