(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(AMAA AOU CAAATA
`
`(10) International Publication Number
`WO 2017/194289 Al
`
`= a
`
`WIPO! PCT
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`(43) International Publication Date
`16 November 2017 (16.11.2017)
`
`(51) International Patent Classification:
`GO03F 7/20 (2006.01)
`GO3F 9/00 (2006.01)
`GOLN 21/956 (2006.01)
`HOLL 21/66 (2006.01)
`
`(21) International Application Number:
`
`PCT/EP2017/059474
`
`(22) InternationalFiling Date:
`
`21 April 2017 (21.04.2017)
`
`English
`English
`
`(25) Filing Language:
`(26) Publication Language:
`.
`(30) Priority Data:
`EP
`12 May 2016 (12.05.2016)
`16169384.1
`12 September 2016 (12.09.2016) EP
`16188380.6
`29 March 2017 (29.03.2017)
`EP
`17163586.5
`(71) Applicant: ASML NETHERLANDSB.V.[NL/NL]; P.O.
`Box 324, 5500 AH Veldhoven (NL).
`
`(72) Inventors: CEKLI, Hakki, Ergun; P.O. Box 324, 5500
`AH Veldhoven (NL). ISHIBASHI, Masashi; P.O. Box
`324, 5500 AH Veldhoven (NL). VAN DE VEN, Wendy,
`Johanna, Martina; P.O. Box 324, 5500 AH Veldhoven
`(NL). ROELOEFS, Willem, Seine, Christian; P.O. Box
`324, 5500 AH Veldhoven (NL). MC NAMARA,Elliott,
`Gerard; P.O. Box 324, 5500 AH Veldhoven (NL). RAH-
`MAN, Rizvi; P.O. Box 324, 5500 AH Veldhoven (NL).
`KUPERS, Michiel; P.O. Box 324, 5500 AH Veldhoven
`(NL). SCHMITT-WEAVER,Emil, Peter; P.O. Box 324,
`5500 AH Veldhoven (NL). DELVIGNE, Erik, Henri,
`Adriaan; P.O. Box 324, 5500 AH Veldhoven (NL).
`
`(74) Agent: PETERS, John; P.O. Box 324, 5500 AH Veld-
`hoven (NL).
`(81) Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY, BZ,
`CA, CH, CL, CN, CO, CR, CU, CZ, DE, DJ, DK, DM, DO,
`
`(54) Title: METHOD OF OBTAINING MEASUREMENTS, APPARATUS FOR PERFORMING A PROCESS STEP AND
`METROLOGY APPARATUS
`
`
`
`[_ 606"
`., oS 4
`
`an
`
` 2
`
`
`Fig. 6
`
`(57) Abstract: Measurements are obtained fromlocations across a substrate (W') before or after performinga lithographic process step.
`Examples of such measurements include alignment measurements madeprior to applying a pattern to the substrate, and measurements of
`performance parameters such as overlay, after a pattern has been applied. A set of measurement locations (606, 606' or 606") is selected
`from amongall possible measurement locations (302). At least a subset of the selected measurementlocations are selected dynamically
`(202c), in response to measurements obtained using a preliminary selection (610) of measurement locations. Preliminary measurements
`of height can be used to select measurement locations for alignment. In another aspect of the disclosure, outlier measurements are
`detected based on supplementary data such as height measurements orhistoric data.
`
`[Continued on next page]
`
`
`
`
`
`wo2017/194299A.IIINININMIINANITATA0AA
`
`

`

`WO 2017/194289 A[IMUM CIMATMT! TAEAAUT
`
`DZ, EC, EE, EG, ES, FL, GB, GD, GE, GH, GM,GT, HN,
`HR, HU,ID, IL, IN, IR, IS, JP, KE, KG, KH, KN, KP, KR,
`KW, KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, MX, MY, MZ, NA, NG, NL NO, NZ, OM,
`PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW,SA, SC,
`SD, SL, SG, SK, SL, SM, ST, SV, SY, TIL TJ, TM, TN, TR,
`TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM,KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ,
`UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU,TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE,ES, FI, FR, GB, GR, HR, HU,IE, IS, IT, LT, LU, LV,
`MC,MK,MT, NL, NO,PL, PT, RO, RS, SE, SL SK, SM,
`TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW,
`KM,ML, MR, NE, SN, TD, TG).
`
`Published:
`
`— with international search report (Art. 21(3))
`
`

`

`WO 2017/194289
`
`PCT/EP2017/059474
`
`METHOD OF OBTAINING MEASUREMENTS, APPARATUS FOR
`PERFORMING A PROCESS STEP AND METROLOGY APPARATUS
`
`BACKGROUND
`
`CROSS-REFERENCE TO RELATED APPLICATIONS
`
`[0001]
`
`This application claims priority of EP application EP16169384 which wasfiled on
`
`May 12, 2016, EP application EP16188380 which was filed on September 12, 2016 and EP
`
`application EP17163586 which was filed on March 29, 2017 which are incorporated herein
`
`in its entirety by reference.
`
`Field of the Invention
`
`[0002]
`
`The present invention relates to methods of obtaining measurements from locations
`
`across one or more substrates. The invention can be applied for example in a lithographic
`
`apparatus, or in a metrology apparatus. The present invention further relates to methods of
`
`manufacturing devices using such lithographic apparatus, and to data processing apparatuses
`
`and computer program products for implementing parts of such a method.
`
`Background Art
`
`[0003]
`
`A lithographic apparatus is a machine that applies a desired pattern onto a substrate,
`
`usually onto a target portion of the substrate. A lithographic apparatus can be used, for
`
`example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device,
`
`which is alternatively referred to as a mask or a reticle, may be used to generate a circuit
`
`pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a
`
`target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon
`
`wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive
`
`material (resist) provided on the substrate. In general, a single substrate will contain a
`
`network of adjacent target portions that are successively patterned. Known lithographic
`
`apparatus include so-called steppers, in which each target portion is irradiated by exposing an
`
`entire pattern onto the target portion at one time, and so-called scanners, in which each target
`
`portion is irradiated by scanning the pattern through a radiation beam in a given direction
`
`(the
`
`“scanning”-direction) while
`
`synchronously scanning the
`
`substrate parallel
`
`or
`
`anti-parallel to this direction.
`
`[0004]
`
`A key performance parameter of the lithographic process is the overlay error. This
`
`error, often referred to simply as “overlay”, is the error in placing product features in the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`2
`
`PCT/EP2017/059474
`
`correct position relative to features formed in previous layers. As device structures become
`
`ever smaller, overlay specifications becomeever tighter.
`
`[0005]
`
`Within the lithographic apparatus, wafer alignment models are conventionally applied
`
`based on measurement of alignment marks provided on the substrate,
`
`the measurements
`
`being made as a preliminary step of every patterning operation. The alignment models
`
`nowadays include higher order models, to correct for non-linear distortions of the wafer. The
`
`alignment models may also be expanded to take into account other measurements and/or
`
`calculated effects such as thermal deformation during a patterning operation. However, the
`
`time available per wafer does not permit measurement of all the alignment marks, and a
`
`compromise between speed and accuracy inevitably has to be made.
`
`[0006]
`
`Currently the overlay crror is controlled and corrected by mcans of mcthods such as
`
`advanced process control (APC) described for example in US2012008127A1 and wafer
`
`alignment models described for example in US2013230797A1. The advancedprocess control
`
`techniques have been introduced in recent years and use measurements of metrology targets
`
`applied to substrates alongside the applied device pattern. The inspection apparatus may be
`
`separate from the lithographic apparatus, or integrated within it.
`
`[0007]
`
`While alignment models and advanced process control have brought great reductions
`
`in overlay, not all errors are corrected. Some of these errors may be uncorrectable noise, for
`
`example, but others are correctable using available techniques
`
`in theory, but not
`
`economically correctable in practice. For example, one can envisage yet higher order models,
`
`but these in turn would require a higher spatial density of position measurements. Again,
`
`even if there is a high spatial density of possible measurementlocations, to actually measure
`
`such a number of measurement
`
`locations would adversely affect
`
`throughput of the
`
`lithographic process of the metrology apparatus.
`
`[0008]
`
`Accordingly, it is common to define a measurement “recipe” that captures the most
`
`important features of a substrate, from the point of view of improving the key performance
`
`parameters, such as overlay. If it is known that a certain type of processing gives rise to a
`
`particular “fingerprint” in the distortions of the substrates that undcrgo that process, the sct of
`
`measurement locations can be selected to capture that fingerprint in a way that maximizes the
`
`chancecorrecting for it in the patterning step. A problem arises, however, in that the process
`
`fingerprints can vary quite widely even with a single lot of wafers. The set of measurement
`
`locations that gives good overlay performance for one wafer may not give good overlay
`
`performance for the next one. The same principles apply to the selection of measurement
`
`locations in a metrology application, on substrates that have already been subject to the
`
`lithographic process.
`
`[0009]
`
`Another problem that affects both alignment and metrology performance is that of
`
`anomalous samples or “outliers”.
`
`In the alignment data, an outlier may be a position
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`3
`
`PCT/EP2017/059474
`
`measurement influenced by a very localized cause such as contamination under the wafer.
`
`When this measurement is included in the alignment model, however, the influence of the
`
`anomalous measurement may spread, degrading overlay performance over and unduly wide
`
`area. Similarly, outliers in performance metrology may cause noise and degradation in
`
`advanced performancecontrol loops.
`
`SUMMARYOF THE INVENTION
`
`[0010]
`
`The present invention has the aim of improving relevance of measurement results
`
`(primarily relevance for performance of a lithographic process) without necessarily
`
`increasing the number of measurementlocations required to be measured.
`
`[0011]
`
`According to an aspect of the invention,
`
`there is provided a method of obtaining
`
`measurements from locations across a substrate before or after performing a lithographic
`
`process step, wherein a set of measurement locations is selected from among all possible
`
`measurement locations, and at each selected location a measurement ts made of a property of
`
`a structure on the substrate, wherein at least a subset of the selected measurement locations is
`
`selected dynamically at least partly in response to recognition of a fingerprint associated with
`
`measurements obtained using a preliminary selection of measurement locations.
`
`[0012]
`
`Dynamic selection of the set of measurement locations allows the locations that are
`
`most likely to be relevant for performance improvement to be selected on a per-substrate
`
`basis, without necessarily increasing the total number of measurements and measurement
`
`time. The performance penalty that might otherwise be expected to result from choosing a
`
`limited set of measurement locations can be reduced, even in the presence of process
`variation between substrates.
`
`[0013]
`
`The lithographic process step may be a patterning step performed in a lithographic
`
`apparatus, or it may be a chemical or physical processing step performed in another
`
`apparatus.
`
`[0014]
`
`The measurements made at the preliminary selection of measurementlocations and/or
`
`the measurements made at the selected sect of measurement locations may be made within the
`
`lithographic apparatus or other processing apparatus, or they may be made in a separate
`
`metrology apparatus.
`
`[0015]
`
`The measurements made at the preliminary selection of measurement locations may
`
`be of the type of measurement as the measurements obtained at
`
`the selected set of
`
`measurement locations, or a different type. The measurements made at
`
`the preliminary
`
`selection of measurement locations may made in the same apparatus as the measurements
`
`obtained at the selected set of measurement locations, or a different apparatus.
`
`[0016]
`
`In some examples disclosed herein, locations for alignment measurements (which
`
`measure positional deviations in the plane of the substrate) are dynamically selected based on
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`4
`
`PCT/EP2017/059474
`
`alignment measurements at preliminary locations. In other examples, locations for alignment
`
`measurements are dynamically selected based on height measurements
`
`(out-of-plane
`
`positional deviations).
`
`[0017]
`
`Examples of measurements made before a lithographic process
`
`step include
`
`alignment measurements made for positioning a pattern to be applied in a lithographic
`
`apparatus. Examples of measurements made aftcr a lithographic proccss step include
`
`measurements of performance parameter such as overlay.
`
`[0018]
`
`The invention further provides an apparatus for performing a process step in a
`
`lithographic process, the apparatus including a measurement system for making measurement
`
`of a substrate prior to performing said process step, the measurement system being arranged
`
`to obtain mceasurcments at a sclected sct of locations across the substrate using a method
`
`according to the invention as set forth above.
`
`[0019]
`
`The
`
`invention further provides
`
`a metrology apparatus
`
`arranged to obtain
`
`measurements of one or more properties of structures at a selected set of locations across a
`
`substrate using a method according to the invention as set forth above.
`
`[0020]
`
`The invention further provides a method of manufacturing devices including a
`
`lithographic process step, wherein, before or after performing said lithographic process step,
`
`measurements are obtained at a selected set of locations across a substrate by a method
`
`according to the invention as set forth above, and wherein the obtained measurements are
`
`used to adjust parameters of the lithographic process step for the processing of the substrate
`
`and/or further substrates.
`
`[0021]
`
`The invention in a further, independent aspect provides a method of determining a
`
`weighting factor for a measurement made at a measurement location on a substrate, the
`
`method comprising the stepsof:
`
`applying a quality test to the measurement, the quality test being basedat least partly
`
`on supplementary data associated with the measurementlocation; and
`
`determining the weighting factor based on a result of said quality test.
`
`[0022]
`
`The supplementary data in some cmbodiments compriscs statistical data based on
`
`previously processed substrates. The weighting factor can be exploited in various ways, for
`
`example to reduce the influence of outlier measurements on future processing.
`
`[0023]
`
`The apparatus and method of
`
`the invention can be implemented in some
`
`embodiments by modifying control software of existing apparatuses.
`
`[0024]
`
`The invention further provides a computer program product comprising machine-
`
`readable instructions for causing one or more processors to implement aspects of the method
`
`in the apparatus set forth above. The computer program product may comprise said machine
`
`readable instructions stored in a non-transitory storage medium.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`5
`
`PCT/EP2017/059474
`
`BRIEF DESCRIPTION OB'THE DRAWINGS
`
`[0025]
`
`Embodiments of the invention will now be described, by way of example only, with
`
`reference to the accompanying schematic drawings in which:
`
`Tigure | depicts a lithographic apparatus together with other apparatuses forming a production
`
`facility for semiconductor devices;
`
`Figure 2 illustrates schematically measurement and cxposure processes in the lithographic
`
`apparatus of Figure 1, according to knownpractice and modified in accordance with an
`
`embodimentof the present invention;
`
`Figure 3 shows(a) the distribution of measurement locations available for measurement on an
`
`example wafer and (b) an example set of measurementlocations, selected for measurement
`
`during high-volume manufacture;
`
`Figure 4 illustrates (a) an example of a process-induced fingerprint on a semiconductor wafer,
`
`and (b) variation of the fingerprint between wafers in a sample of wafers taken from severallots;
`
`Figure 5 illustrates deviation of performance parameters of the lithographic process, attributable
`
`to using the selected set of measurement locations, over the same sample of wafers shown in
`
`Figure 4 (b);
`
`Figure 6 illustrates a modified method for selecting a set of measurement locations dynamically
`
`for an individual substrate, according to a first embodiment of the present invention;
`
`Figure 7 illustrates deviation of performance parameters of the lithographic process, calculated to
`
`simulate the effect of selecting sets of measurement locations dynamically for each wafer over
`
`the same sample of wafers as Figure 5;
`
`Figure 8 illustrates the spatial distribution of deviation of performance(a) in the case of using the
`
`same selected measurementlocations and (b) using the dynamically selected sets of measurement
`
`locations;
`
`Figure 9 illustrates a method of metrology and process control in a second embodimentof the
`
`present invention;
`
`Figure 10 illustrates the problem of outliers in measurement data, for example alignmentdata in a
`
`real cxample;
`
`Figure 11 illustrates techniques for detecting outliers and reducing their influence in accordance
`
`with various embodiments of the second aspect of the present disclosure;
`
`T'igure 12 illustrates a principle of statistical analysis according to an example outlier detection
`
`method based on principal component analysis;
`
`Figure 13 illustrates detection of outliers using the principle of Figure 12 in the example of
`
`Figure 10;
`
`Figure 14 illustrates improved overlay performance on problem wafers, compared with the
`
`example of Figure 10(a);
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`6
`
`PCT/EP2017/059474
`
`Figure 15 illustrates a method of metrology and control in a third embodiment ofthe present
`
`invention, the method comprising (a) an offline process and (b) an inline process;
`
`Figure 16 illustrates height gradient maps and dynamic selection of measurement locationsin the
`
`method of Figure 15; and
`
`Figure 17 illustrates a method of metrology and control in a fourth embodimentof the present
`
`invention, the method comprising (a) an offline process and (b) an inline process.
`
`DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
`
`[0026]
`
`Before describing embodiments of the invention in detail, it is instructive to present
`
`an example environment
`
`in which embodiments of
`
`the present
`
`invention may be
`
`implemented.
`
`[0027]
`
`Figure 1 at 100 showsa lithographic apparatus LA as part of an industrial facility
`
`implementing a high-volume, lithographic manufacturing process. In the present example,
`
`the manufacturing process is adapted for the manufacture of for semiconductor products
`
`(integrated circuits) on substrates such as semiconductor wafers. The skilled person will
`
`appreciate that a wide variety of products can be manufactured by processing different types
`
`of substrates in variants of this process. The production of semiconductor products is used
`
`purely as an example which has great commercial significance today.
`
`[0028]
`
`Within the lithographic apparatus (or “litho tool” 100 for short), a measurement
`
`station MEAis shown at 102 and an exposure station EXP is shown at 104. A control unit
`
`LACUis shown at 106.
`
`In this example, each substrate visits the measurementstation and
`
`the exposure station to have a pattern applied. In an optical lithographic apparatus, for
`
`example, a projection system is used to transfer a product pattern from a patterning device
`
`MAonto the substrate using conditioned radiation and a projection system. This is done by
`
`forming an image ofthe pattern in a layer of radiation-sensitive resist material.
`
`[0029]
`
`The term “projection system” used herein should be broadly interpreted as
`
`encompassing any type of projection system, including refractive, reflective, catadioptric,
`
`magnetic, clectromagnetic and clectrostatic optical systems, or any combination thercof, 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. The patterning MA device may be a mask or
`
`reticle, which imparts a pattern to a radiation beam transmitted or reflected by the patterning
`
`device. Well-known modes of operation include a stepping mode and a scanning mode.Asis
`
`well known, the projection system may cooperate with support and positioning systems for
`
`the substrate and the patterning device in a variety of ways to apply a desired pattern to many
`
`target portions across a substrate. Programmable patterning devices may be used instead of
`
`reticles having a fixed pattern. The radiation for example may include electromagnetic
`
`radiation in the deep ultraviolet (DUV)or extreme ultraviolet (EUV) wavebands. The present
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`7
`
`PCT/EP2017/059474
`
`disclosure is also applicable to other types of lithographic process, for example imprint
`
`lithography and direct writing lithography, for example by electron beam.
`
`[0030]
`
`The lithographic apparatus control unit LACU controls all
`
`the movements and
`
`measurements of various actuators and sensors, causing the apparatus to receive substrates W
`
`and reticles MA and to implement the patterning operations. LACU also includes signal
`
`processing and data processing capacity to implement desired calculations relevant to the
`
`operation of the apparatus.
`
`In practice, control unit LACU will be realized as a system of
`
`many sub-units, each handling the real-time data acquisition, processing and control of a
`
`subsystem or component within the apparatus.
`
`[0031]
`
`Before the pattern is applied to a substrate at the exposure station EXP, the substrate
`
`is processed in at the measurement station MEA so that various preparatory steps may be
`
`carried out. The preparatory steps may include mapping the surface height of the substrate
`
`using a level sensor and measuring the position of alignment marks on the substrate using an
`
`alignment sensor. The alignment marks are arranged nominally in a regular grid pattern.
`
`However, due to inaccuracies in creating the marks and also due to deformations of the
`
`substrate that occur throughout
`
`its processing,
`
`the marks deviate from the ideal grid.
`
`Consequently,
`
`in addition to measuring position and orientation of the substrate,
`
`the
`
`alignment sensor in practice must measure in detail the positions of many marks across the
`
`substrate area, if the apparatus is to print product features at the correct locations with very
`
`high accuracy.
`
`[0032]
`
`The lithographic apparatus LA may beof a so-called dual stage type which has two
`
`substrate tables, each with a positioning system controlled by the control unit LACU. While
`
`one substrate on one substrate table is being exposed at the exposure station EXP, another
`substrate can be loaded onto the other substrate table at the measurement station MEAso that
`
`various preparatory steps may be carried out. The measurement of alignment marks is
`
`therefore very time-consuming and the provision of two substrate tables enables a substantial
`
`increase in the throughput of the apparatus.
`
`If the position sensor IF is not capable of
`
`measuring the position of the substrate table whilc it is at the mcasurcment station as well as
`
`at the exposure station, a second position sensor may be provided to enable the positions of
`
`the substrate table to be tracked at both stations. Alternatively, the measurement station and
`
`exposure station can be combined. lor example, it is known to have a single substrate table,
`
`to which a measurement stage is temporarily coupled during the pre-exposure measuring
`
`phase. The present disclosure is not limited to either type of system.
`
`[0033]
`
`Within the production facility, apparatus 100 forms part of a “litho cell” or “litho
`
`cluster” that contains also a coating apparatus 108 for applying photosensitive resist and
`
`other coatings to substrates W for patterning by the apparatus 100. At an output side of
`
`apparatus 100, a baking apparatus 110 and developing apparatus 112 are provided for
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`8
`
`PCT/EP2017/059474
`
`developing the exposed pattern into a physical resist pattern. Between all of these
`
`apparatuses,
`
`substrate handling systems
`
`take care of supporting the substrates and
`
`transferring them from one piece of apparatus to the next. These apparatuses, which are often
`
`collectively referred to as the “track”, are under the control of a track control unit which is
`
`itself controlled by a supervisory control system SCS, which also controls the lithographic
`
`apparatus via lithographic apparatus control unit LACU. Thus, the different apparatuses can
`
`be operated to maximize throughput and processing efficiency. Supervisory control system
`
`SCS receives recipe information R which provides in great detail a definition of the steps to
`
`be performedto create each patterned substrate.
`
`[0034]
`
`Oncethe pattern has been applied and developed in the litho cell, patterned substrates
`
`120 are transferred to other processing apparatuses suchasarc illustrated at 122, 124,126. A
`
`wide range of processing steps is
`
`implemented by various apparatuses in a typical
`
`manufacturing facility. For the sake of example, apparatus 122 in this embodiment is an
`
`etching station, and apparatus 124 performs a post-etch annealing step. Further physical
`
`and/or chemical processing steps are applied in further apparatuses, 126, etc.. Numerous
`
`types of operation can be required to make a real device, such as deposition of material,
`
`modification of surface material characteristics (oxidation, doping,
`
`ion implantation etc.),
`
`chemical-mechanical polishing (CMP), and so forth. ‘The apparatus 126 may, in practice,
`
`represent a series of different processing steps performed in one or more apparatuses.
`
`[0035]
`
`As is well known,
`
`the manufacture of semiconductor devices involves many
`
`repetitions of such processing, to build up device structures with appropriate materials and
`
`patterns, layer-by-layer on the substrate. Accordingly, substrates 130 arriving at the litho
`
`cluster may be newly prepared substrates, or they may be substrates that have been processed
`
`previously in this cluster or in another apparatus entirely. Similarly, depending on the
`
`required processing, substrates 132 on leaving apparatus 126 may be returned for a
`
`subsequent patterning operation in the samelitho cluster, they may be destined for patterning
`
`operations in a different cluster, or they may be finished products to be sent for dicing and
`
`packaging.
`
`[0036]
`
`Each layer of the product structure requires a different set of process steps, and the
`
`apparatuses 126 used at each layer may be completely different in type. Further, even where
`
`the processing steps to be applied by the apparatus 126 are nominally the same, in a large
`
`facility, there may be several supposedly identical machines working in parallel to perform
`
`the step 126 on different substrates. Small differences in set-up or faults between these
`
`machines can mean that they influence different substrates in different ways. Even steps that
`
`are relatively commonto each layer, such as etching (apparatus 122) may be implemented by
`
`several etching apparatuses that are nominally identical but working in parallel to maximize
`
`throughput.
`
`In practice, moreover, different layers require different etch processes, for
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`9
`
`PCT/EP2017/059474
`
`example chemical etches, plasma etches, according to the details of the material to be etched,
`
`and special requirements such as, for example, anisotropic etching.
`
`[0037]
`
`The previous and/or subsequent processes may be performed in other lithography
`
`apparatuses, as just mentioned, and may even be performed in different types of lithography
`
`apparatus. For example, some layers in the device manufacturing process which are very
`
`demanding in parametcrs such as resolution and overlay may be performed in a morc
`
`advanced lithography tool than other layers that are less demanding. Therefore some layers
`
`may be exposed in an immersion type lithography tool, while others are exposed in a ‘dry’
`
`tool. Some layers may be exposed in a tool working at DUV wavelengths, while others are
`
`exposed using EUV wavelength radiation.
`
`[0038]
`
`In order that the substrates that are exposed by the lithographic apparatus are exposed
`
`correctly and consistently, it is desirable to inspect exposed substrates to measure properties
`
`such as overlay errors between subsequent layers, line thicknesses, critical dimensions (CD),
`
`etc. Accordingly a manufacturing facility in which litho cell
`
`ILC is located also includes
`
`metrology system MET which receives some or all of the substrates W that have been
`
`processed in the litho cell. Metrology results are provided directly or indirectly to the
`
`supervisory control system (SCS) 138. If errors are detected, adjustments may be made to
`
`exposures of subsequent substrates, especially if the metrology can be done soon and fast
`
`enough that other substrates of the same batchare still to be exposed. Also, already exposed
`
`substrates may be stripped and reworked to improve yield, or discarded, thereby avoiding
`
`performing further processing on substrates that are known to be faulty. In a case where only
`
`some target portions of a substrate are faulty, further exposures can be performed only on
`
`those target portions which are good.
`
`[0039]
`
`Also shown in Figure 1 is a metrology apparatus 140 which is provided for making
`
`measurements of parameters of the products at desired stages in the manufacturing process.
`
`A common example of a metrology apparatus in a modern lithographic production facility is
`
`a
`
`scatterometer,
`
`for
`
`example
`
`an angle-resolved scatterometer or
`
`a
`
`spectroscopic
`
`scattcrometcr, and it may be applicd to measure propertics of the developed substrates at 120
`
`prior to etching in the apparatus 122. Using metrology apparatus 140, it may be determined,
`
`for example, that important performance parameters such as overlay or critical dimension
`
`(CD) do not meet specified accuracy requirements in the developed resist. Prior to the
`
`etching step, the opportunity exists to strip the developed resist and reprocess the substrates
`
`120 through the litho cluster. As is also well known, the metrology results 142 from the
`
`apparatus 140 can be used to maintain accurate performance of the patterning operations in
`
`the litho cluster, by supervisory control system SCS and/or control unit LACU 106 making
`
`small adjustments over time, thereby minimizing the risk of products being made out-of-
`
`specification, and requiring re-work. Of course, metrology apparatus 140 and/or other
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`

`

`WO 2017/194289
`
`2016PO00009WO
`
`10
`
`PCT/EP2017/059474
`
`metrology apparatuses (not shown) can be applied to measure properties of the processed
`
`substrates 132, 134, and incoming substrates 130.
`
`[0040]
`
`The present disclosure concerns the dynamic selection of measurement locations, in
`
`cases where the time available for a set of measurements does not permit measurementofall
`
`possible locations across the substrate. This dynamic selection can be applied in various
`
`operations in the manufacturing facility of Figure 1. For example,
`
`the techniques can be
`
`applied in the selection of measurement locations when measuring alignment marks on the
`
`substrates, as part of the patterning operation. Alternatively, or in addition,
`
`the dynamic
`
`selection of measurementlocations can be applied to the selection of metrology targets in the
`
`metrology apparatus 140. A detailed example will be described in the context of alignment,
`
`which can then be readily applicd in metrology apparatus 140, in a similar manner.
`
`Alignment process background
`
`[0041 ]
`
`Figure 2 illustrates the steps to expose target portions (e.g. dies) on a substrate W in
`
`the dual-stage type of lithographic apparatus, used in the example of Figure |. The process
`
`according to conventional practice will be described first. The present disclosure is not
`
`limited to dual-stage apparatus. The dynamic selection technique disclosed herein can be
`
`applied in any situation where time does not permit measurements of any type to be
`
`measuredat all possible measurement locations on every substrate.
`
`[0042]
`
`On the left hand side within a dotted box are steps performed at a measurement
`
`station MEA, while the right hand side shows steps performed at the exposure station EXP.
`
`From time to time, one of the s