Method and apparatus for bonding substrates

Abstract

A method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; bringing the first substrate into contact with a second substrate to provide a zone of contact between the first substrate and the second substrate along the first axis; and releasing the first substrate from the first bending force.

Description

METHOD AND APPARATUS FOR BONDING SUBSTRATESCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24210716.7 which was filed on 2024-Nov- 05 and of EP application 25161504.3 which was filed on 2025-Mar-04 and which is incorporated herein in its entirety by reference.TECHNICAL FIELD

[0002] The present disclosure relates to bonding substrates.BACKGROUND

[0003] In manufacturing processes of integrated circuits (ICs), multiple finished or unfinished ICs (e.g., whole wafers, diced wafers, partially diced wafers, chips, dies, etc.) may be placed in contact, stacked, bonded, joined, or otherwise coupled (e.g., to heterogeneous or homogeneous devices) at various points in the fabrication process. The integration of different substrates, circuits, or other patterned devices may rely upon joining of specific portions (for example, conductive contact elements) of multiple dies — where these specific portions which may be aligned in three-dimensional space to ensure functional connectivity. As the physical sizes of IC components continue to shrink, and their structures continue to become more complex, accuracy, minimization of distortion and variability, and throughput in coupling become more important. In the context of semiconductor manufacture, improvements in substrate placement and joining lead to improvements in IC manufacturing and integration abilities.SUMMARY

[0004] Two or more substrates may be bonded together (e.g. wafer-to-wafer bonding, or die-to- wafer bonding) to form composite devices. In some known techniques for bonding substrates together, two substrates are pressed together, and a zone of contact that is formed between the substrates is allowed to expand freely. The dynamics of the formation of the bond between the substrates may be determined, for example, by bending stress relaxation in the substrate(s), gas escaping from the interface between the substrates, and any structure of the substrate surface(s) (e.g. scribe lines that are intended for subsequent dicing). The inventors have observed that these factors can cause a bond front (i.e. the edge of the zone of contact) to propagate in a non-isotropic manner, where propagation in some directions is faster than in others. In some cases, this can result in distortion that is observable as a “bonding fingerprint” in post-bonding inspection of the bonded substrates, such as in measurements of overlay or other properties. In addition, in some existingtechniques for bonding substrates together, the alignment of the substrates can be very sensitive to mechanical disturbances (e.g. rotational forces) for a period of time until the bond between the substrates has sufficiently formed.

[0005] The present disclosure therefore provides methods and apparatuses that may address one or more of the above-described shortcomings.

[0006] Described herein is a method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; bringing the first substrate into a contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and releasing the first substrate from the first bending force.

[0007] Also described herein is an apparatus for bonding substrates, the apparatus being configured to: apply a first bending force to bend a first substrate along a first axis; bring the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and release the first substrate from the first bending force. For example, the apparatus may comprise a first clamp, and the apparatus may be configured to apply the first bending force using the first clamp.

[0008] Advantageously, bending the first substrate along an axis (rather than, e.g., substantially spherically), may mean that releasing the substrate results in a more isotropic (and therefore controlled) propagation of the bonding interface (e.g. the bond front described above) than existing techniques, resulting in improved alignment of the substrates (e.g. as observed in overlay measurements) and therefore improved performance and yield of manufactured devices. For example, the bond front may propagate in a direction (or directions) substantially perpendicularly to the first axis (e.g. cylindrically). Furthermore, the elongated zone of contact may enable quicker formation of a bond between the substrates that is strong against rotational forces (or other mechanical forces or disturbances), thereby increasing throughput of the bonding process.

[0009] In some examples, a second bending force may be applied to bend the second substrate along a second axis. It will be understood that the second axis is different from the first axis. For example, the first axis and the second axis may be perpendicular (or substantially perpendicular) to one another (in a common coordinate system, such as a coordinate system of the apparatus for bonding substrates described herein). Bringing the first substrate into contact with the second substrate to provide the elongated zone of contact may comprise: bringing the first substrate into contact with the second substrate while the first substrate is under the first bending force and the second substrate is under the second bending force to provide a point-shaped zone of contact between the first substrate and the second substrate; and releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form the elongated zone of contact.

[0010] For example, an example method for bonding substrates according to the present disclosuremay comprise: applying a first bending force to bend a first substrate along a first axis, applying a second bending force to bend a second substrate along a second axis, bringing the first substrate into contact with the second substrate to provide a point-shaped zone of contact between the first substrate and the second substrate; releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form the elongated zone of contact; and releasing the first substrate from the first bending force.

[0011] Another example of a method for bonding substrates according to the present disclosure may comprise: applying a first bending force to bend a first substrate along a first axis; applying a second bending force to bend a second substrate along a second axis; bringing the first substrate into contact with the second substrate to form a zone of contact between the first substrate and the second substrate; releasing the second substrate from the second bending force to induce propagation of a bond front along the first axis; and releasing the first substrate from the first bending force to induce propagation of the bond front along the second axis.

[0012] Bending, and successively releasing, both the first and second substrates may advantageously result in even more uniform propagation of the bond front across the interface between the substrates, thereby improving overlay performance.

[0013] In some examples of the apparatus for bonding substrates described herein, the apparatus may comprise a second clamp, and the apparatus may be configured to apply the second bending force using the second clamp.

[0014] In some examples, the second substrate may be released from the second bending force, and the first substrate may be released from the first bending force, alternately in a plurality of stages. By alternately releasing the second and first substrates, the bond front may propagate gradually (i.e. over the plurality of stages) along the second and first axes, respectively. For example, the second substrate may be partially released from the second bending force while the first substrate is held under the first bending force, and then the first substrate may be partially released from the first bending force, while the second substrate is held under the remainder of the second bending force, and the process may be repeated sequentially and progressively to release the bending forces over a plurality of stages. The progressive process may provide increased control over the bonding process, which may further improve isotropy.

[0015] In some examples, a third bending force may be applied to bend the first substrate along a second axis (e.g. the second axis described herein). For example, the third bending force may be applied before the first substrate is brought into contact with the second substrate. The third bending force may be substantially smaller than the first bending force. For example, the third bending force may be just sufficient to prevent the ends of the elongated zone of contact from forming at the very edges of the substrates before being formed closer to the center. The application of the third bending force may therefore prevent the formation of a sharp point at the edge of the substrates, which mayotherwise be subject to high stresses, potentially leading to fracture. It will be appreciated that the third bending force should still not lead to substantially spherical bending of the first substrate. In some examples, the third bending force may be applied only at the outer edge(s) of the first substrate. The method may further comprise releasing the first substrate from the third bending force.

[0016] In some examples, one of the first substrate and the second substrate is, or comprises, a die, and the other comprises a wafer.

[0017] In some examples, controlled propagation of the bond front may be achieved by rolling the first substrate onto the second substrate. For example, applying the first bending force may comprise holding the first substrate against a curved surface. Releasing the first substrate from the first bending force may comprise rolling the first substrate around an axis of the curved surface.

[0018] A further example of a method for bonding substrates according to the present disclosure may therefore comprise: holding a first substrate against a curved surface; bringing the first substrate into contact with a second substrate; and bonding the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.

[0019] A further example of an apparatus for bonding substrates according to the present disclosure may comprise: a first clamp, and a curved surface, wherein the first clamp is configured to hold a first substrate against the curved surface to bend the first substrate along a first axis. The apparatus may be configured to: bring the first substrate into contact with a second substrate, and bond the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.

[0020] A curvature of the curved surface around the first axis (i.e. to bend the first substrate by the first bending force) may be greater than a curvature of the curved surface around an axis perpendicular to the first axis (which may be the second axis, or parallel to the second axis).

[0021] Bringing the first substrate into contact with the second substrate may comprise bringing a distal part of the first substrate into contact with the second substrate.

[0022] Rolling the first substrate around the curved substrate may mean that the bond front propagates in an actively controlled manner, rather than relying on the free self-propagation of the bond front.

[0023] In some examples, movement of the second substrate (e.g. a wafer stage holding the second substrate) may take place at the same time as rolling the first substrate. For example, a small offset between the first substrate and the second substrate, and / or a small amount of relative motion, may induce a strain at the interface between the first and second substrates, which may in turn lead to local deformation, which may at least partially correct the distortion (bonding fingerprint).

[0024] For example, a relative position offset between the first substrate and the second substrate may be introduced while rolling the first substrate. In some examples, an amount of relative position offset may be varied over time while rolling the first substrate.

[0025] In some examples, the second substrate may be moved relative to the curved surface while rolling the first substrate. In some examples, an amount of movement of the second substrate may be varied over time while rolling the first substrate.

[0026] In some examples the curved surface may have a substantially cylindrical shape.

[0027] In some examples, the curved surface may have a substantially ellipsoidal shape.

[0028] In some examples, the curved surface may be shaped to provide a component of a compressive force in a direction perpendicular to a direction of the rolling, e.g. to compensate the distortion caused by the bonding process.

[0029] In some examples, applying the first bending force comprises holding the first substrate against a substantially wedge-shaped surface. For example, applying pressure along a tip of a substantially wedge-shaped surface may cause the elongated zone of contact to form.

[0030] In some examples, applying the first bending force may comprise holding the first substrate against a compliant surface. For example, the surface against which the first substrate is held (e.g. curved, or wedge-shaped surface) may be part of a structure comprising a compliant material such as foam. A compliant surface may help to ensure that the line of contact is formed in the correct orientation.

[0031] The surface against which the first substrate is held may be referred to as a bond head, and may form part of an apparatus for bonding substrates as described herein.

[0032] In some examples, a positioning correction may be applied to the first substrate to align the first substrate with the first axis. For example, the positioning correction may be applied based on one or more sensors, such as active force sensors.

[0033] In some examples, an electrical connection may be formed between the first substrate and the second substrate when the first and second substrate are brought (e.g. bonded) together. For example, each of the first and second substrates may be patterned with one or more conductive features such as metal lines or wires, and / or contact pads. Bringing the first and second substrates together by bonding may bring one or more lines, wires, or contact pads (or any appropriate conductive features) on the first substrate into contact with one or more lines, wires, or contact pads (or any appropriate conductive features) on the second substrate, thereby forming an electrical connection between the substrates.

[0034] In some examples, the first axis may be selected according to an alignment of patterned features on one or both of the substrates. For example, the first axis may be perpendicular to a wire (or line, or other metal feature) alignment on the first or second substrate. More generally, the first axis may be perpendicular to a conductive feature alignment on the first or second substrate. As an example, multiple substrates may be stacked on top of one another in a stack. The second substrate may correspond to the previous layer of the stack, and the first substrate may correspond to the next layer to be added to the stack. By causing the bond front to propagate outwards from the line ofcontact linearly along one axis (perpendicular to the wire alignment) the impact of the bond front propagation on the alignment between the features on one (e.g. the second) substate (e.g. wires) and features on another (e.g. the first) substrate (e.g. any electrical contacts) along that axis will be minimized. The axis along which the bond front propagates may therefore be selected according to the sensitivity of the features to their alignment along that axis.

[0035] In some examples, at least one of the first substrate and the second substrate may be tiltable (e.g. the wafer stage and / or the bond head may be tiltable).

[0036] In some examples, at least one of the first substrate and the second substrate may be tiltable (e.g. an apparatus described herein may comprise a tiltable wafer stage and / or a tiltable bond head). The second substrate may be on a tiltable wafer stage. For example, an apparatus described herein may comprise a tiltable wafer stage configured to hold the second substrate, and / or on which the second substrate can be placed during the bonding process. For example, the apparatus may comprise one or more servos configured to adjust a tilt angle of the wafer stage (e.g. with respect to six degrees of freedom of the wafer stage). A stiffness of the servo(s) may be adjusted. More generally, a tilting stiffness of the wafer stage may be adjustable. The first substrate may be on (e.g. held by, held against, etc.) a tiltable bond head. For example, an apparatus described herein may comprise a tiltable bond head (which may be configured to hold the first substrate, and / or on which the first substrate can be placed during the bonding process). For example, the apparatus may comprise one or more servos configured to adjust a tilt angle of the bond head (e.g. with respect to six degrees of freedom of the bond head). A stiffness of the servo(s) may be adjusted. More generally, a tilting stiffness of the bond head may be adjustable.

[0037] In some examples, the tilting stiffness of the second substrate, the first substrate, the wafer stage, and / or the bond head may be adjusted (e.g. reduced) during the bringing of the first substrate into contact with the second substrate. Reducing the tilting stiffness may advantageously allow selfcorrection of any parallelism errors between the first and second substrates while the first and second substrates are brought together.

[0038] In some examples, the tilting stiffness of the second substrate may be (e.g. may be adjusted or reduced to) about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least some of the time (i.e. for at least a period of time) during the bringing of the first substrate into contact with the second substrate. In some examples, the tilting stiffness of the first substrate may be (e.g. may be adjusted or reduced to) about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least some of the time (i.e. for at least a period of time) during the bringing of the first substrate into contact with the secondsubstrate. In some examples, the tilting stiffness of the wafer stage may be (e.g. may be adjusted or reduced to) about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least some of the time (i.e. for at least a period of time) during the bringing of the first substrate into contact with the second substrate. In some examples, the tilting stiffness of the bond head may be (e.g. may be adjusted or reduced to) about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least some of the time (i.e. for at least a period of time) during the bringing of the first substrate into contact with the second substrate. In some examples, the tilting stiffness may only be adjusted (e.g. reduced) when a height of the first substrate above the second substrate falls below a threshold height.

[0039] In some examples, the first substrate comprises a first wafer, and the second substrate comprises a second wafer.

[0040] As described herein, a die may be considered as a portion of a wafer that is produced by dicing, or otherwise dividing, a wafer.

[0041] In some examples, the method(s) and apparatus(es) described herein may comprise, or be configured for, directly bonding the first substrate to the second substrate. For example, the substrates may be bonded, or coupled, together by e.g. dielectric coupling, fusion, hybrid bonding, or another suitable process for bonding the first and second substrates directly. In some examples, the first substrate and the second substrate may be annealed after being brought into contact with one another. Annealing may comprise heat annealing, electrical annealing, electrostatic processes, van der Waals processes, or any other suitable process.

[0042] In some examples, the method(s) and apparatus(es) described herein may comprise, or be configured for, adhesively bonding the first substrate to the second substrate. For example, at least one of the first substrate and the second substrate may be provided with an adhesive layer.

[0043] In some examples, the first substrate may be bonded to the second substrate via an interface layer, such as SiC>2 or SiCN, or an organic interface layer. In some examples, in particular in cases where the first substrate is only to be temporarily bonded to the second substrate (e.g. where the second substrate is a carrier wafer), then an adhesion material referred to as a “temporary bonding material” (TBM) may be used as the interface layer.

[0044] Also described herein is a composite substrate manufactured according to the method(s) of the present disclosure.

[0045] A semiconductor device manufactured according to the method(s) of the present disclosure is also described.

[0046] In addition, a substrate bonding apparatus configured to perform the method(s) of thepresent disclosure is described.BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above aspects and other aspects and features will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.

[0048] Figs. 1(a) and 1(b) illustrate a typical bonding process flow, according to an embodiment.

[0049] Fig. 2 re-illustrates several operations of the process flow shown in Fig. 1, with an additional illustration of deformation associated with an elastic wave that may occur during the process flow, according to an embodiment.

[0050] Figs. 3(a) and 3(b) illustrate a typical bonding process metrology and inspection flow for controlling a bonding process like the one shown in Fig. 1 and 2, according to an embodiment.

[0051] Figs. 4(a) and 4(b) illustrate a new substrate coupling system, according to an embodiment.

[0052] Fig. 5 provides an enlarged view of a sensor of the system shown in Fig. 4 (in a top view), according to an embodiment.

[0053] Fig. 6 illustrates a new bonding process metrology and inspection flow for controlling a bonding process using the system shown in Fig. 4 (and Fig. 5), according to an embodiment.

[0054] Fig. 7 illustrates a substrate coupling method, according to an embodiment.

[0055] Fig. 8 schematically depicts a lithography apparatus, according to an embodiment.

[0056] Fig. 9 illustrates a schematic representation of holistic lithography, representing a cooperation between three technologies to optimize semiconductor processing, according to an embodiment.

[0057] Fig. 10 is a block diagram of an example computer system, according to an embodiment.

[0058] Fig. 11 illustrates a schematic representation of an apparatus for bonding substrates by rolling, according to an embodiment.

[0059] Fig. 12 illustrates a process for bonding substrates by rolling, according to an embodiment.

[0060] Fig. 13 illustrates a process for bonding substrates in which an offset between the substrates is introduced, according to an embodiment.

[0061] Fig. 14 illustrates a process for bonding substrates in which the amount of offset and / or relative movement between the substrates is varied during rolling, according to an embodiment.

[0062] Fig. 15 illustrates how the direction of an induced strain at the interface between substrates can be controlled by optimizing the shape of the curved surface used during bonding by rolling.

[0063] Fig. 16 illustrates a method for bonding substrates by rolling, according to an embodiment.

[0064] Fig. 17(a) illustrates a known technique for bonding substrates in which a top substrate is caused to bend in two directions, and Fig. 17(b) illustrates a technique for bonding substrates in which the top substrate is bent in one direction according to the present disclosure.

[0065] Fig. 18 illustrates an example of a substrate patterned with wires.

[0066] Fig. 19(a) is a plot showing a normalized pressure distribution when a first substrate is brought into contact with a parallel second substrate.

[0067] Fig. 19(b) is a plot showing a normalized pressure distribution when a first substrate is brought into contact with a second substrate when the second substrate is slightly tilted with respect to the first substrate.

[0068] Fig. 20 is a plot showing a relationship between a safer stage tilting stiffness and the distance between first and second substrates during the bringing of the first substrate into contact with the second substrate.DETAILED DESCRIPTION

[0069] Embodiments of the present disclosure are described in detail with reference to the drawings, which are provided as illustrative examples of the disclosure so as to enable those skilled in the art to practice the disclosure. Notably, the figures and examples below are not meant to limit the scope of the present disclosure to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the disclosure. Embodiments described as being implemented in software should not be limited thereto, but can include embodiments implemented in hardware, or combinations of software and hardware, and vice-versa, as will be apparent to those skilled in the art, unless otherwise specified herein. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the disclosure is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present disclosure encompasses present and future known equivalents to the known components referred to herein by way of illustration.

[0070] Although specific reference may be made in this text to the manufacture of ICs, it should be explicitly understood that the description herein has many other possible applications. For example, it may be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid-crystal display panels, thin-film magnetic heads, etc. The skilled person will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” in this text should be considered as interchangeable with the more general terms “substrate” and “target portion”, respectively. The term “wafer” may be used generally to refer to alarge unit of manufacture (which may be the largest unit of manufacture), while the term “die” may be used to refer to a smaller unit of manufacture which may correspond to a lithography pattern, a portion of a lithography pattern, multiple lithography patterns, etc. A “die” may correspond to a portion of “wafer” -that is a “die” may be produced by dicing or otherwise dividing a “wafer”. The term “die” should be considered as interchangeable with the term chip, chiplet, or other terms for IC divisions. In some cases, a wafer to which a die is bonded may be referred to as an acceptor. A patterning device (for example, a lithography device) can comprise, or can form, one or more patterns, which may correspond to one or more dies. The patterns can be generated utilizing CAD (computer- aided design) programs, based on a pattern or design layout, this process often being referred to as EDA (electronic design automation). As used throughout this application “or”, unless indicated otherwise, takes a non-exclusive meaning, e.g., encompassing both “and” and “or”.

[0071] The bonding, or coupling, of substrates (including wafers and dies) is an important step in the manufacture of semiconductor integrated circuits (ICs), and other composite devices. Bonding techniques may include dielectric coupling, fusion, hybrid bonding, etc. In some cases, substrates may be temporarily bonded together, for example a die may be temporarily bonded to a carrier wafer. In some examples, substrates may be temporarily (or permanently) bonded together using an adhesive material. In an example manufacturing process, a center pin may be used to push one substrate towards another to initiate a bonding process.

[0072] Substrates (e.g. wafers and / or dies) forming a composite device, such as an IC, may be patterned as described herein. It may be the case that a pattern on the first substrate must be correctly aligned with a pattern on the second substrate, for example to provide an electrical contact between one or more patterned elements on the substrates, and / or to ensure electrical isolation of one or more patterned elements on the substrates. The lateral positioning between the substrates (referred to as overlay) must be within certain tolerances. For example, an intradie overlay fingerprint may comprise the following components: translation, rotation, magnification (or “scaling”), and higher order residual. A typical value for an intradie fingerprint for a 7 mm die of 50 pm thickness may be around 300 nm. This may be broken down into values for translation, rotation, magnification, and residue of around 200 nm, 20 nm, 150 nm, and 20 nm respectively. The components of translation and rotation can be corrected using the bonding tool. As electrical contacts between substrates become smaller, the overlay parameter becomes more critical. While a magnification correction may be applied to keep the overlay parameter within the required tolerance, for example as part of a control loop in a holistic lithographic process as described herein, it may be preferable to minimize the amount of correction that is required by reducing the magnitude of the overlay.

[0073] Fig. 1 schematically illustrates an example of an existing process for bonding a first substrate 102 (e.g. a die or a wafer) to a second substrate 104 (e.g. a wafer). Fig. 1(a) illustrates a side view of the process, while Fig. 1(b) illustrates a top view.

[0074] In a first step (i), the first substrate 102 is bent substantially uniformly, e.g. in an approximately spherical manner, such that a zone of contact 106(i) that is formed at the vertex point of the spherical deformation when the first substrate 102 is brought into contact with the second substrate 104. In a second step (ii), the edge of the zone of contact 106(ii) (which may be referred to as a bond front) propagates outwardly from the initial zone of contact 106(i) as the first substrate 102 is released. The expansion of the zone of contact 106(h) may be defined by the stress relaxation in the first substrate 102, the displacement of gas between the first substrate 102 and the second substrate 104, the initial curvature of the substrate(s) before bonding, and / or any structure of one or both substrate(s) 102, 104, such as scribe lines, and the inventors have observed that bond front may therefore propagate non-isotropically.

[0075] In overlay measurements of the bonded substrates, a “fingerprint” can be observed. Fig. 2 illustrates an example of an overlay map showing an overlay fingerprint, resulting from a rectangular pattern in the bond front caused by scribe lines. The overlay fingerprint is highly dependent on the shape, and other properties, of the substrates. As technological advances cause ICs, and other manufactured devices, to continue to get smaller, sensitivity to variations in overlay (i.e. alignment between the bonded substrates, and other layers) increases, which can negatively affect device yields.

[0076] In addition, because the bond formed by the bonding process illustrated in Fig. 1 originates at a small (point, or near-point) interface, the substrates 102, 104 remain vulnerable to rotational forces and other mechanical disturbances for a period of time that may be longer than the total interaction time between any bonding tool or apparatus and the substrates 102, 104. Thus, either the throughput needs to be reduced to reduce the risk of disturbing the bonded substrates 102, 104 (i.e. delaying the time between performing the bonding process and applying an acceleration to (i.e. moving) the wafer stage, or wafer table, on which the substrates 102, 104 may be situated), or an acceleration must be applied to the bonded substrates 102, 104 before the bond is fully formed, which may increase the likelihood of the disturbances and so reduce yield.

[0077] Fig. 3 schematically illustrates an example of a process for bonding a first substrate 202 (e.g. a die or a wafer) to a second substrate 204 (e.g. a wafer) according to the present disclosure. Fig. 3(a) illustrates a side view of the process, while Fig. 3(b) illustrates a top view.

[0078] As shown in the example illustrated in Fig. 3, at (i), rather than being bent substantially spherically, the first substrate 202 is bent (by a bending force) by a substantially different amount of curvature in one direction or along one axis (e.g. along the X axis as illustrated in Fig. 3) compared to any other direction or axis (e.g. the Y axis). Thus, when the first substrate 202 is brought into contact with a second substrate 204, an elongated (e.g. substantially line-shaped) zone of contact 206(i) is formed between the first substrate 202 and the second substrate 204. When the first substrate 202 is released, as shown in Fig. 3 at (ii), the zone of contact 206(h) expands (i.e. the bond front propagates) largely perpendicularly to the axis along which the first substrate 202 was bent. In some examples, thebond front may propagate cylindrically. The elongated zone of contact 206(i) provides improved strength against rotational forces, and ensures that the position of the first substrate 202 on the second substrate is secured more quickly (i.e. the zone of contact 206(h) more quickly covers a substantial area of the bonded substrates), so that the substrates 202, 204 can be released and / or accelerated more quickly with minimal risk of disturbance. Because at least two of the edges of the first substrate 202 and / or the second substrate 204 remain free, or open, at least during the formation of the elongated zone of contact 206(i), gas is able to escape from the interface between the substrates 202, 204 and the bond can form in a controlled fashion. For example, the open edges of the substrate(s) 202, 204 may help to reduce flow resistance and speed up the propagation of the bond front, at least during the formation of the elongated zone of contact 206(i), which may contribute to the formed bond becoming more quickly resistant to acceleration (e.g. of a wafer stage or wafer table).

[0079] It will be understood that the arrows in Figs. 1 and 3 correspond to the relative amount of curvature in the bending of the first substrate 102, 202. In Fig. 1, the first substrate 102 is bent by a substantially similar amount in both the X and Y directions, while in Fig. 3 the first substrate 202 is mostly bent in one direction (the X direction). As shown in Fig. 3(b), there may still be a small amount of bending in the Y direction.

[0080] Two or more substrates that are bonded together may be referred to as a composite substrate. Two or more substrates that are bonded together may form at least part of a semiconductor device (e.g. a semiconductor device may comprise a composite substrate manufactured according to the present disclosure).

[0081] Fig. 4 schematically illustrates a further example of a process for bonding a first substrate 402 (e.g. a die or a wafer) to a second substrate 404 (e.g. a wafer). Fig. 4(a) illustrates a side view of the process, while Fig. 4(b) illustrates a top view with the first substrate 402 omitted for clarity. As shown in Fig. 4, at (i), the first substrate 402 is bent (by a first bending force) along a first axis (e.g. the X axis) and the second substrate 404 is bent (by a second bending force) along a second axis (e.g. the Y axis), the second axis being different from the first axis (e.g. the axes may be substantially orthogonal). When the first substrate 402 and the second substrate 404 are brought into contact, a zone of contact 406(i) is formed at the point where the first substrate 402 and the second substrate 404 meet, and this zone of contact 406(i) may be substantially point-shaped. At (ii), the second substrate 404 is released (as shown by the arrows at (ii) in Fig. 4(a)), and the zone of contact 406(h) expands (i.e. the bond front propagates) along the first axis (as shown by the arrows at (ii) in Fig. 4(b)). This results in an elongated (e.g. substantially line-shaped) zone of contact 406(h) between the first substrate 402 and the second substrate 404, similar to the elongated zone of contact 206(i) of Fig. 3. At (iii), the first substrate 402 is released (as shown by the arrows at (iii) in Fig. 4(a)), and the zone of contact 406(iii) expands along the second axis (as shown by the arrows at (iii) in Fig. 4(b)).

[0082] The process illustrated in Fig. 4 may be particularly advantageous in improving theuniformity of the bond between the substrates by enabling improved control over the propagation of the bond front(s).

[0083] In some examples, the releasing of the second substrate and the first substrate may take place over a plurality of stages, in which, for example, the second substrate may be partially released, followed by a partial release of the first substrate, followed by a further partial release of the second substrate, and so on until the bond front has propagated fully in all directions. An example in which the substrates are released in a plurality of stages is shown in Fig. 5 (where again the first substrate is omitted for clarity). At (i) in Fig. 5, the second substrate 504 is partially released in a first stage so that the zone of contact 506(i) expands along the first axis (e.g. the X axis). At (ii), the first substrate is partially released in a first stage so that the zone of contact 506(ii) expands along the second axis (e.g. the Y axis). At (iii), the second substrate 504 is partially released in a second stage so that the zone of contact 506(iii) again expands along the first axis. At (iv), the first substrate is partially released in a second stage so that the zone of contact 506(iv) again expands along the second axis. In Fig. 5, the zone of contact 506(iv) is shown to cover the whole of the second substrate 504 (i.e. such that both substrates are fully bonded together to form a composite substrate) after the second substrate 504 and the first substrate are each released over two stages, respectively. However, it will be appreciated that the substrates may be released over any suitable number of stages according to the requirements of the process and the resultant composite substrate.

[0084] In some examples, bending one or both of the first substrate 202, 402 and the second substrate 204, 404, 504 may comprise using one or more clamps (not shown) to apply the required bending force(s). For example, the clamp(s) may form part of an apparatus for bonding substrates.

[0085] It will be understood that the coordinate system (X, Y, and Z) illustrated in Figs. 1, 3, 4, and 5 is merely an example. For example, a coordinate system may be defined with respect to an apparatus for bonding substrates.

[0086] Returning to Fig. 3, in some cases, bending the first substrate 202 along the first axis may mean that the ends of the elongated zone of contact 206(i) form, together with the edge of the substrate 202, a sharp point. If the placement of the first substrate 202 is not perfectly aligned with the plane of the second substrate 204, then the first point of contact between the substrates may be sharp, and therefore subject to high stresses, potentially leading to fracture. Therefore, in some examples, a third bending force (not shown) may be applied to bend the first substrate 202 just enough such that the elongated zone of contact 206(i) does not reach the edges of the substrate before forming closer to the center of the substrates 202, 204. For example, the third bending force may be applied to the first substrate 202 at the outer edges of the first substrate, or along a central axis (e.g. the Y axis illustrated in Fig. 3) perpendicular to the direction of propagation of the bond front that forms the elongated zone of contact 206(i). The small amount of bending provided by the third bending force may therefore reduce the risk of fracture described above. It will be understood that the third bending force shouldbe substantially smaller than the first bending force so that the first substrate 202 remains bent by a substantially different amount of curvature in one direction (or axis) compared to any other direction (or axis) as described herein. The first substrate 202 is released from the third bending force, e.g. after the elongated zone of contact 206(i) has (mostly) been formed, so that propagation of the bond front to form the elongated zone of contact continues to the edge(s) of the substrate(s).

[0087] Fig. 6 illustrates a block diagram of an example of a method 600 for bonding substrates according to the present disclosure.

[0088] The method 600 comprises, in a step S602, applying a first bending force to bend a first substrate along a first axis. As described herein, the first bending force may be applied to a first substrate 202, 402 as illustrated in Fig. 2 or Fig. 4, where the second substrate 204, 404 may be bent along a second axis (e.g. orthogonal to the first axis) (as shown in Fig. 4 and described herein), or may be substantially flat (i.e. not bent) (as shown in Fig. 2 and described herein). As described herein, the first substrate 202, 404 may be e.g. a wafer or a die.

[0089] In a step S604, the method 600 comprises bringing the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis. As described herein and illustrated in Fig. 4, in some examples, the elongated zone of contact may be provided by bringing the first substrate 402 (the first substrate being bent along the first axis) into contact with the second substrate 404 (the second substrate being bent along the second axis by a second bending force) to provide a point-shaped zone of contact 406(i), and then releasing the second substrate (from the second bending force) to cause the point-shaped zone of contact 406(i) to expand along the first axis to form the elongated zone of contact 406(h). In other examples, as described herein and illustrated in Fig. 2, the elongated zone of contact 206(i) is provided by bringing the bent first substrate 202 into contact with a substantially flat second substrate 204.

[0090] In a step S606, the method 600 comprises releasing the first substrate from the first bending force. As described herein, when the first substrate is released from the first bending force, the zone of contact is thereby caused to expand along the second axis (i.e. substantially orthogonally to the direction along which the first substrate was bent).

[0091] Fig. 7 illustrates a block diagram of a further example of a method 700 for bonding substrates according to the present disclosure.

[0092] The method 700 comprises, in a step S702, applying a first bending force to bend a first substrate along a first axis.

[0093] The method 700 comprises, in a step S704, applying a second bending force to bend a second substrate along a second axis.

[0094] As described herein, and illustrated in Fig. 4, the second axis may be substantially orthogonal to the first axis.

[0095] The method 700 comprises, in a step S706, bringing the first substrate into contact with the second substrate to form a zone of contact between the first substrate and the second substrate, for example the zone of contact 406(i) between the first substrate 402 and the second substrate 404 illustrated in Fig. 4.

[0096] The method 700 comprises, in a step S708, releasing the second substrate from the second bending force to induce propagation of a bond front (i.e. expansion of the zone of contact 406(h) as shown in Fig. 4(b)) along the first axis.

[0097] The method 700 comprises, in a step S710, releasing the first substrate from the first bending force to induce propagation of the bond front (i.e. expansion of the zone of contact 406(iii) as shown in Fig. 4(b)) along the second axis.

[0098] As described herein, in some examples, the first bending force and / or the second bending force may be gradually (and alternately) released in a plurality of stages as described herein and illustrated in Fig. 5, thereby causing the zone of contact to expand (i.e. the bond front to propagate) across the interface between the substrates 402, 404, 504 in stages in a controlled manner.

[0099] As described herein, in some examples, one or both of the first bending force and the second bending force may be applied using one or more clamps. For example, an apparatus for bonding substrates may be configured to perform one or both of the methods illustrated in Figs. 6 and 7 and described herein. An apparatus for bonding substrates may comprise at least one of a first clamp configured to apply the first bending force, and a second clamp configured to apply the second bending force.

[0100] Some further advantages of causing the bond front to propagate along one axis will now be described with reference to Figs. 17 and 18. Fig. 17(a) illustrates a known technique for bonding substrates, in which the top (e.g. first) substrate 1704a is caused to bend in two directions (e.g. X and Y) by the forming of a point-shaped zone of contact 1706a as described herein, and allowing the bond front to propagate outwards (e.g. radially) from the zone of contact 1706a. The point-shaped zone of contact 1706a may be formed e.g. using an apparatus having a pin-shaped member 1715a against which the substrate 1704a, or a bond head, may be held. Fig. 17(b) illustrates an example of a technique for bonding substrates according to the present disclosure, in which the substrate 1704b is instead held against a wedge-shaped surface (i.e. the apparatus may comprise a wedge-shaped member 1715b) to form a line-shaped zone of contact 1706b as described herein. The technique illustrated in Fig. 17(b) causes the bond front to propagate outwards from the line-shaped zone of contact 1706b, along an axis perpendicular to the line-shaped zone of contact 1706b. As described herein, a cylindrical surface may be used instead of, or in addition to, a wedge-shaped surface to achieve the line-shaped zone of contact 1706b. More generally as described herein, the substrate(s) may be held against a surface having a radius of curvature in one direction that is different from a radius of curvature in another (e.g. perpendicular) direction.

[0101] Fig. 18 illustrates an example of a patterned substrate 1850. The patterned substrate 1850 may correspond to any of the first and / or second substrates described herein. In an example, the patterned substrate 1850 is a bottom (i.e. second) substrate in a stack to which a top (i.e. first) substrate is being bonded. The patterned substrate 1850 is patterned with one or more metal wires 1857, or lines (or more generally conductive features). For example, the wires 1857 may be arranged in a Manhattan routing layout. The substrate 1850 may be one substrate in a stack of substrates, and each substrate in the stack may be patterned with wires 1857. For example, the wires 1857 may be in alternating orientations in X and Y in the stack. As described above, a top (i.e. first) substrate may be bonded to the bottom (second) substrate 1850. The top substrate may be patterned with features including a small electrical contact 1853, or contact pad. The electrical contact 1853 of the top substrate is shown in Fig. 18, positioned with respect to the bottom substrate 1850, while the rest of the top substrate (and any other patterning of the top substrate such as wires) has been omitted for clarity. An line-shaped zone of contact 1806 (exaggerated for clarity) between the substrates is also shown in Fig. 18. The line-shaped zone of contact 1806 in Fig. 18 may correspond to e.g. the lineshaped zone of contact 1706b illustrated in Fig. 17(b). As shown in Fig. 18, the line-shaped zone of contact 1806 is formed along a first (e.g. X) axis, meaning that the bond front will propagate along a second (e.g. Y) axis perpendicular to the first axis. The alignment of the electrical contact 1853 with the wires 1857 is significantly less sensitive along the second (Y) axis than along the first (X) axis. Any translation or magnification along the first (X) axis may be corrected e.g. by a magnification correction (for example as part of a control loop in a holistic lithographic process as described herein with respect to Figs. 8-10). By relaxing the overlay parameter in at least one direction, improved placement accuracy (e.g. within 100 nm) may be achieved while maintaining high throughput.

[0102] In some examples, as described herein, the surface (e.g. bond head of the apparatus) used to bend the substrate(s) may have a higher degree of curvature in the direction of bond front propagation than in the direction alone the zone of contact (e.g. an ellipsoidal bond head). This may ensure that the bond head can be lowered at a high speed allowing air to escape along the curvature along the lineshaped zone of contact. In some examples, the bond head may comprise a compliant material (e.g. foam). An ellipsoidal and / or compliant bond head may help to ensure that the line-shaped zone of contact is formed along the desired axis, as the alignment of the patterned features on the bonded substrates may be very sensitive to any misalignment of the zone of contact at the start of the bonding process. In some examples, a positioning correction may be applied to align the substrate(s) with the axis along which the zone of contact is formed. For example, one or more sensors (e.g. active force sensors) may be used to determine an alignment of the substrate(s). For example, an overlay (magnification, or scaling) fingerprint between two or more bonded substrates may be obtained, and may be fed back to the bonding apparatus to determine any misalignment between the substrate(s) and the axis of the line-shaped zone of contact.

[0103] In some cases, initiating a line of contact as described herein can be difficult due to parallelism errors between the first and second substrates (e.g. the first and second substrates may not be exactly parallel to one another as they are brought together). Fig. 19(a) is a plot showing a normalized pressure distribution between a first and second substrate when a first substrate (e.g. die) with a parabolic shape (e.g. bent along the X axis as shown in Fig. 19(a)) is brought into contact with a second substrate to form a line elongated zone of contact. In some examples, an apparatus for bonding substrates as described herein may comprise a wafer stage, and the second substrate (i.e. acceptor) may be situated on the wafer stage during the bonding process. The wafer stage may be tiltable. For example, a position (e.g. tilt angle, rotation, etc.) of the wafer stage in six degrees of freedom may be controllable e.g. via one or more servo motors and a controller connected to the motor(s). While the example described in relation to Figs. 19(b) and 20 refer to a tiltable wafer stage, it will be understood that an apparatus as described herein may alternatively or additionally comprise a tiltable bond head, and similar principles as described in relation to a tiltable wafer stage would apply to a tiltable bond head. More generally, any suitable means may be used to make one or both of the second substrate and the first substrate tiltable during the bonding process, and for a tilting stiffness of one or both of the second substrate and the first substrate to be adjustable.

[0104] Fig. 19(b) shows how the pressure distribution changes when the wafer stage is slightly tilted about the Y axis (i.e. the axis perpendicular to the line of contact) in the direction of the arrow. As is clear from Fig. 19(b), the pressure is no longer evenly distributed along the line of contact due to the tilt.

[0105] An apparatus for bonding substrates may comprise, or be connected to, a proportional controller with an adjustable setpoint. A system following a setpoint with a proportional controller can be thought of as a perfectly controlled reference connected to the system by a spring, where the spring stiffness is the proportional gain (kp) of the controller. Typically, controllers are designed such that kpis as large as possible so that external disturbances to the system cause small errors between the reference and the system.

[0106] A stiffness of the servo motor(s) (and therefore a tilting stiffness of the wafer stage) may be adjustable. For example, it may be desirable to adjust the stiffness so that the wafer stage effectively becomes floating to enable self-correction of any parallelism errors between the substrates. As is clear from Fig. 19(b), when the wafer stage is slightly tilted in the Y direction (along the dashed line), the pressure disturbance when the first substrate is brought towards the second substrate creates a moment about the dashed line that opposes the tilt direction. A reaction moment, Mr, can be approximated for small tilt angles, 0.Mr« kr9where kris the tilting stiffness of the wafer stage. Fig. 20 is a graph showing the relationship between the tilting stiffness and the distance between the centers of the substrates (“center height”), including the contribution of other forces such as air pressure.

[0107] If 0Ois considered to be an initial parallelism error, and 0enis considered to be the servo error, the moment balance is / fp^err ^r (^0 ^err) and the angle between the first substrate and the second substrate (e.g. between an acceptor and a die) is s = s0- eerrwhich results in

[0108] For example, the to reduce the parallelism error between the first and second substrates from 1 mrad to 1 prad as the first substrate becomes close to the second substrate, kpwould need to be of the order 0.1 Nm / rad.

[0109] In some examples, the tilting stiffness of the wafer stage may be (e.g. may be adjusted or reduced to) about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least some of the time (i.e. for at least a period of time) during the bringing of the first substrate into contact with the second substrate. For example, the tilting stiffness may be reduced when the first substrate reaches a certain position relative to the second substrate to allow for correction of the parallelism error, and then the tilting stiffness may be raised again for a subsequent stage in the bonding process. In some examples, the tilting stiffness may be adjusted (e.g. reduced) when a height of the first substrate above the second substrate falls below a threshold height. In some examples, the tilting stiffness may be reduced in the direction in which the alignment (i.e. overlay) between the substrates is less sensitive as described herein.

[0110] Fig. 11 illustrates an example of an apparatus 1100 for bonding substrates according to the present disclosure. The apparatus 1100 illustrated in Fig. 11 may be particularly suitable for bonding substrates together by rolling. The apparatus 1100 comprises a wafer stage 1114 (also referred to as asubstrate table), and a drum 1112 having a curved surface 1115.

[0111] As shown in Fig. 11, the first substrate 1102 is held against the curved surface 1115, e.g. by one or more clamps, and thereby bent along at least one axis (i.e. the first axis described herein). The second substrate 1104 is shown in Fig. 11 as being held flat on the wafer stage 1114, however it will be understood that in some examples the second substrate 1104 may be bent in accordance with one or more of the examples described herein.

[0112] Fig. 12 illustrates an example of a process for bonding the first substrate 1102 to the second substrate 1104 by rolling, e.g. using the apparatus 1100. As shown in Fig. 12, at (i), the first substrate 1102 is brought into contact with the second substrate 1104 (e.g. by bringing the drum 1112 towards the wafer stage 1114). In some examples, the curved surface 1115 may have substantially cylindrical or ellipsoidal shape (e.g. a curvature of the curved surface around the first axis, i.e. curvature in the rolling direction, may be greater than a curvature of the curved surface around an axis perpendicular to the first axis). Therefore, bringing the first substrate 1102 into contact with the second substrate 1104 may provide an elongated zone of contact between the first substrate 1102 and the second substrate 1104. Preferably, as shown in Fig. 12(i), a distal part of the first substrate 1102 is initially brought into contact with the second substrate 1104. At (ii), the first substrate 1102 is rolled around an axis of the curved surface of the drum (shown by the circular arrow), until the first substrate 1102 is bonded with the second substrate 1104 at (iii).

[0113] In some examples, movement of the drum may be controllable in six degrees of freedom, such that additional control over the application of pressure across the substrate surface(s) can be achieved. In some examples, the curved surface may be shaped (and the drum may be controlled) such that the initial zone of contact between the first substrate 1102 and the second substrate 1104 is substantially point-shaped rather than elongated. The six degree of freedom control of the drum movement may therefore enable further control of expansion of the zone of contact across the interface between the substrates.

[0114] In some cases, movement of the drum may create more pressure than the “free release” pressure of prior art methods, such as illustrated in Fig. 1. In some cases, movement of the drum may also enable control of the speed of expansion of the zone of contact, in particular when the bonding is performed under vacuum.

[0115] In some examples, it may be advantageous to introduce an offset between the first substrate 1102 (the drum) and the second substrate 1104 (the wafer stage). Fig. 13 illustrates a modified version of the process illustrated in Fig. 12. Introducing a (small) offset between the drum and the second substrate 1104 (e.g. of the order of nm), shown by the large arrows in Fig. 13 (ii) a local strain at the interface between the first substrate 1102 and the second substrate 1104 may be induced, shown by the small arrows in Fig. 13(ii) and (iii), which may in turn lead to a (local) deformation. The induced strain can be optimized in the direction(s) of rolling to counteract the strain and resulting deformationfrom the bonding process itself.

[0116] In some examples, the amount of deformation can be controlled dynamically over the course of the bonding process by changing the amount of offset between the first and second substrates. As shown in Fig. 14, by making the offset and / or the relative movement between the first and second substrates (i.e. between the drum and the wafer stage) time -dependent, a positiondependent strain can be introduced at the interface.

[0117] Distortion can be further compensated by optimizing the shape of the curved surface of the drum. In Fig. 15(a), the compressive force caused by rolling the first substrate around a substantially cylindrical curved surface is illustrated. The shaded region of Fig. 15(a) indicates a part of the interface between the first substrate and the second substrate where the first substrate is already in contact with the second substrate, while in the unshaded area the substrates are not yet in contact. Rolling the curved surface along the roll direction 1501a causes contact forces (shown by the arrows 1503a) to be predominantly in the direction of rolling. In contrast, Fig. 15(b) illustrates a case in which the curved surface is shaped to provide a component of a compressive force in a direction perpendicular to the rolling direction 1501b. In the case of Fig. 15(b), the contact forces 1503b “squeeze” the substrates in the center, causing an additional force perpendicular to the rolling direction to be induced. It will be understood that there may also be an expanding force in any hollow (e.g. concave) areas of the curved surface. By optimizing the shape of the curved surface, the resultant controlled strain between the first substrate and the second substrate can be optimized to counteract the distortion.

[0118] Fig. 16 illustrates a block diagram of an additional example of a method 1600 for bonding substrates according to the present disclosure.

[0119] The method 1600 comprises, in a step 1602, holding a first substrate against a first curved surface. As described herein, holding the first substrate against the curved surface may correspond to applying the first bending force. The curved surface may be a curved surface of a drum, as illustrated in Fig. 11.

[0120] In a step SI 604, the method 1600 comprises bringing the first substrate into contact with a second substrate. As illustrated in Fig. 11, the second substrate may be held on a wafer stage or substrate table. In some examples, a distal part of the first substrate may be brought into contact with the second substrate.

[0121] In a step SI 606, the method 1600 comprises bonding the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.

[0122] In some examples, the method(s) and apparatus(es) described herein may comprise, or be configured for, directly bonding the first substrate to the second substrate. For example, the substrates may be bonded, or coupled, together by e.g. dielectric coupling, fusion, hybrid bonding, or another suitable process for bonding the first and second substrates directly. In some examples, the firstsubstrate and the second substrate may be annealed after being brought into contact with one another. Annealing may comprise heat annealing, electrical annealing, electrostatic processes, van der Waals processes, or any other suitable process.

[0123] In some examples, the method(s) and apparatus(es) described herein may comprise, or be configured for, adhesively bonding the first substrate to the second substrate. For example, at least one of the first substrate and the second substrate may be provided with an adhesive layer.

[0124] In some examples, the first substrate may be bonded to the second substrate via an interface layer, such as SiC>2 or SiCN, or an organic interface layer. In some examples, in particular in cases where the first substrate is only to be temporarily bonded to the second substrate (e.g. where the second substrate is a carrier wafer), then an adhesion material referred to as a “temporary bonding material” (TBM) may be used as the interface layer. Examples of suitable TBMs include the WaferBOND® and BrewerBOND® material suites from Brewer Science.

[0125] In some examples, one or more portions of the method 600, the method 700, or the method 1600 may be implemented in and / or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and / or other mechanisms for electronically processing information). The processing devices may be or be included in a computer system such as a desktop computer, a laptop computer, a smartphone, a server, and / or other computing devices, for example. The one or more processing devices may include one or more devices executing some or all of the steps of method 600, method 700, or method 1600 in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured through hardware, firmware, and / or software to be specifically designed for execution of one or more of the operations of method 600, method 700, or method 1600.

[0126] Fig. 8 schematically depicts an embodiment of a lithographic apparatus LA. Lithography may be performed prior to and / or after substrate (e.g., wafer) coupling (e.g., bonding) as described herein, for example. Fig. 8 shows a generic transmissive lithography apparatus. It should be noted that reflective or other variations on the system are possible, as are ‘one-stage’ machines. The apparatus LA 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 dice and often referred to as fields) of thesubstrate W. For example, the substrate W may correspond to one or more of the first substrate 202, 402, described herein, the second substrate 204, 404, 504 described herein, and / or a composite substrate as described herein. The projection system is supported on a reference frame RF. As depicted, the apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the apparatus may be of a reflective type (e.g. employing a programmable mirror array, or employing a reflective mask).

[0127] The illuminator IL receives a beam of radiation from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising for example suitable directing mirrors and / or a beam expander. In other cases, the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

[0128] The illuminator IL may alter the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution is non-zero within an annular region in a pupil plane of the illuminator IL. Additionally or alternatively, the illuminator IL may be operable to limit the distribution of the beam in the pupil plane such that the intensity distribution is non-zero in a plurality of equally spaced sectors in the pupil plane. The intensity distribution of the radiation beam in a pupil plane of the illuminator IL may be referred to as an illumination mode.

[0129] 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 (commonly referred to as o-outer and o-inncr. respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be operable to vary the angular distribution of the beam. For example, the illuminator may be operable to alter the number, and angular extent, of sectors in the pupil plane wherein the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes may be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multi-pole distribution such as, for example, a dipole, quadrupole or hexapole distribution. A desired illumination mode may be obtained, e.g., by inserting an optic which provides that illumination mode into the illuminator IL or using a spatial light modulator.

[0130] 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 ofdifferent polarization modes may allow greater contrast to be achieved in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary across a pupil plane of the illuminator IL. The polarization direction of radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be chosen in dependence on the illumination mode. For multi-pole illumination modes, the polarization of each pole of the radiation beam may be generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the radiation may be linearly polarized in a direction that is substantially perpendicular to a line that bisects the two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as X-polarized and Y-polarized states. For a quadrupole illumination mode, the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode the radiation in the sector of each pole may be linearly polarized in a direction that is substantially perpendicular to a line that bisects that sector. This polarization mode may be referred to as TE polarization.

[0131] In addition, the illuminator IL generally comprises various other components, such as an integrator IN and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation. Thus, the illuminator provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross section.

[0132] 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. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”

[0133] A patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phaseshift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam, which isreflected by the mirror matrix.

[0134] 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). To achieve this, the adjustment mechanism may be operable to manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system wherein its optical axis extends in the z direction. The adjustment mechanism may be operable to do any combination of the following: displace one or more optical elements; tilt one or more optical elements; and / or deform one or more optical elements. Displacement of an optical element may be in any direction (x, y, z, or a combination thereof). Tilting of an optical element is typically out of a plane perpendicular to the optical axis, by rotating about an axis in the x and / or y directions although a rotation about the z axis may be used for a non-rotationally symmetric aspherical optical element. Deformation of an optical element may include a low frequency shape (e.g. astigmatic) and / or a high frequency shape (e.g. free form aspheres). Deformation of an optical element may be performed for example by using one or more actuators to exert force on one or more sides of the optical element and / or by using one or more heating elements to heat one or more selected regions of the optical element. In general, it may not be possible to adjust the projection system PS to correct for apodization (transmission variation across the pupil plane). The transmission map of a projection system PS may be used when designing a patterning device (e.g., mask) MA for the lithography apparatus LA. Using a computational lithography technique, the patterning device MA may be designed to at least partially correct for apodization.

[0135] 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.

[0136] In operation of the lithographic apparatus LA, 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 positiondifferent target portions C in the path of the radiation beam B. Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in Fig. 4) 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 dice.

[0137] The substrate (e.g. the first substrate, second substrate, or composite substrate as described herein) may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of photosensitive resist (‘photoresist’) to a substrate and develops the exposed photoresist) 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.

[0138] Fig. 9 depicts a schematic representation of holistic lithography, representing a cooperation between three technologies to optimize semiconductor processing, which may be performed prior to and / or after substrate (e.g., wafer) coupling (e.g., bonding) as described herein. Typically, the patterning process in a lithographic apparatus LA is one of the most critical steps in the processing which requires high accuracy of dimensioning and placement of structures on the substrate. To ensure this high accuracy, three systems (in this example) may be combined in a so called “holistic” control environment as schematically depicted in Fig. 9. One of these systems is the lithographic apparatus LA which is (virtually) connected to a metrology apparatus (e.g., a metrology tool) MTa (a second system), and to a computer system CS (a third system). A “holistic” environment may be configured to optimize the cooperation between these three systems to enhance the overall process window and provide tight control loops to ensure that the patterning performed by the lithographic apparatus LA stays within a process window. The process window defines a range of process parameters (e.g. dose, focus, overlay) within which a specific processing process yields a defined result (e.g. a functional semiconductor device) - typically within which the process parameters in the lithographic process or patterning process are allowed to vary.

[0139] The computer system CS may use a design layout to be patterned to predict which resolution enhancement techniques to use and to perform computational lithography simulations and calculations to determine which mask layout and lithographic apparatus settings achieve the largest overall process window of the patterning process (depicted in Fig. 9 by the double arrow in the first scale SCI). Typically, the resolution enhancement techniques are arranged to match the patterning possibilities of the lithographic apparatus LA. The computer system CS may also be used to detect where within the process window the lithographic apparatus LA is currently operating (e.g. using input from the metrology tool MTa) to predict whether defects may be present due to e.g. sub-optimal processing (depicted in Fig. 9 by the arrow pointing “0” in the second scale SC2).

[0140] The metrology apparatus (tool) MTa may provide input to the computer system CS to enable accurate simulations and predictions, and may provide feedback to the lithographic apparatus LA to identify possible drifts, e.g. in a calibration status of the lithographic apparatus LA (depicted in Fig. 9 by the multiple arrows in the third scale SC3).

[0141] In lithographic processes, it is desirable to make frequent measurements of the structures created, e.g., for process control and verification. Tools to make such measurements include metrology tool (apparatus) MTa. Different types of metrology tools MTa for making such measurements are known, including scanning electron microscopes or various forms of scatterometer metrology tools MTa. Scatterometers are inspection instruments that allow measurements of the parameters of a lithographic process by having a sensor in the pupil or a conjugate plane with the pupil of the objective of the scatterometer, these measurements are usually referred as pupil-based measurements, or by having the sensor in the image plane or a plane conjugate with the image plane, in which case the measurements are usually referred as image or field-based measurements.

[0142] It is often desirable to be able to computationally determine how a patterning process would produce a desired pattern on a substrate. Computational determination may comprise simulation, for example. Simulations may be provided for one or more parts of the processing process. For example, it is desirable to be able to simulate the lithography process of transferring the patterning device pattern onto a resist layer of a substrate as well as the yielded pattern in that resist layer after development of the resist, simulate metrology operations such as the determination of overlay, and / or perform other simulations. The objective of a simulation may be to accurately predict, for example, metrology metrics (e.g., overlay, a critical dimension, a reconstruction of a three dimensional profile of features of a substrate, a dose or focus of a lithography apparatus at a moment when the features of the substrate were printed with the lithography apparatus, etc.), processing process parameters (e.g., edge placements, aerial image intensity slopes, sub-resolution assist features (SRAFs), etc.), and / or other information which can then be used to determine whether an intended or target design has been achieved.

[0143] Fig. 10 is a diagram of an example computer system CS that may be used for one or moreof the operations described herein (e.g., one or more of the operations of method 600, method 700, or method 1600 shown in Figs. 6, 7, and 16, and / or other operations). Computer system CS may be included in and / or be similar to and / or the same as the controller described above (e.g., computer system CS may form some or all of the controller described above). Computer system CS includes a bus BS or other communication mechanism for communicating information, and a processor PRO (or multiple processors) coupled with bus BS for processing information. Computer system CS also includes a main memory MM, such as a random access memory (RAM) or other dynamic storage device, coupled to bus BS for storing information and instructions to be executed by processor PRO. Main memory MM also may be used for storing temporary variables or other intermediate information during execution of instructions 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.

[0144] Computer system CS may be coupled via bus BS to a display DS, such as a flat panel or touch panel display or a cathode ray tube (CRT) for displaying information to a computer user or observer. 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.

[0145] In some embodiments, all or some of one or more operations 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 included in main memory MM causes processor PRO to perform the process steps (operations) 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 some embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, the description herein is not limited to any specific combination of hardware circuitry and software.

[0146] The term “computer-readable medium” or “machine-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, andtransmission 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 operations described herein. Transitory computer-readable media can include a carrier wave or other propagating electromagnetic signal, for example.

[0147] 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.

[0148] 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.

[0149] 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) may use electrical, electromagnetic, or optical signals that carry digitaldata 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.

[0150] 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 CL One such downloaded application may provide all or part of a method described herein, for example. The received code may be executed by processor PRO as it is received, and / or stored in storage device SD, or other nonvolatile storage for later execution. In this manner, computer system CS may obtain application code in the form of a carrier wave.

[0151] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses. 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 method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; bringing the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and releasing the first substrate from the first bending force.2. A method according to clause 1, further comprising: applying a second bending force to bend the second substrate along a second axis; wherein bringing the first substrate into contact with the second substrate to provide the elongated zone of contact comprises: bringing the first substrate into contact with the second substrate while the first substrate is under the first bending force and the second substrate is under the second bending force to provide a pointshaped zone of contact between the first substrate and the second substrate; and releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form the elongated zone of contact.3. A method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; applying a second bending force to bend a second substrate along a second axis; bringing the first substrate into contact with the second substrate to provide a point-shaped zone of contact between the first substrate and the second substrate; releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form an elongated zone of contact; andreleasing the first substrate from the first bending force.4. A method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; applying a second bending force to bend a second substrate along a second axis; bringing the first substrate into contact with the second substrate to form a zone of contact between the first substrate and the second substrate; releasing the second substrate from the second bending force to induce propagation of a bond front along the first axis; and releasing the first substrate from the first bonding force to induce propagation of the bond front along the second axis.5. A method according to any one of clauses 2 to 4, comprising alternately releasing the second substrate from the second bending force and the first substrate from the first bending force in a plurality of stages.6. A method according to any one of clauses 1 to 5, comprising applying a third bending force to bend the first substrate along a second axis, the third bending force being substantially smaller than the first bending force; and wherein the method further comprises releasing the first substrate from the third bending force.7. A method according to any one of clauses 2 to 6, wherein the second axis is substantially perpendicular to the first axis.8. A method according to any one of clauses 1 to 7, wherein the first substrate comprises a die, and wherein the second substrate comprises a wafer.9. A method according to any one of clauses 1 to 7, wherein the first substrate comprises a first wafer, and wherein the second substrate comprises a second wafer.10. A method according to any one of clauses 1 to 9, comprising using a first clamp to apply the first bending force.11. A method according to any one of clauses 1 to 10, comprising using a second clamp to apply the second bending force.12. A method according to any one of clauses 1 to 11, the method being configured for directly bonding the first substrate to the second substrate.13. A method according to any one of clauses 1 to 11, wherein at least one of the first substrate and the second substrate is provided with an adhesive layer.14. A method according to clause 13, wherein the adhesive layer comprises an interface layer.15. A method according to clause 14, wherein the interface layer is an organic interface layer.16. A method according to any one of clauses 1 to 15, wherein applying the first bending force comprises holding the first substrate against a curved surface.17. A method according to clause 16, wherein a curvature of the curved surface around the first axis is greater than a curvature of the curved surface around an axis perpendicular to the first axis.18. A method according to clause 16 or clause 17, wherein releasing the first substrate from the first bending force comprises rolling the first substrate around an axis of the curved surface.19. A method according to clause 18, comprising introducing a relative position offset between the first substrate and the second substrate while rolling the first substrate.20. A method according to clause 19, comprising varying an amount of relative position offset over time while rolling the first substrate.21. A method according to any one of clauses 18 to 20, comprising moving the second substrate relative to the curved surface while rolling the first substrate.22. A method according to clause 21, comprising varying an amount of movement of the second substrate over time while rolling the first substrate.23. A method according to any one of clauses 16 to 22, wherein the curved surface has a substantially cylindrical shape.24. A method according to any one of clauses 16 to 23, wherein the curved surface has a substantially ellipsoidal shape.25. A method according to any one of clauses 1 to 24, wherein applying the first bending force comprises holding the first substrate against a substantially wedge-shaped surface.26. A method according to any one of clauses 1 to 25, wherein applying the first bending force comprises holding the first substrate against a compliant surface.27. A method according to any one of clauses 1 to 26, comprising applying a positioning correction to the first substrate to align the first substrate with the first axis.28. A method according to any one of clauses 1 to 27, comprising forming an electrical connection between the first substrate and the second substrate.29. A method according to any one of clauses 1 to 28, wherein the first axis is perpendicular to a conductive feature alignment direction on the second substrate.30. A method for bonding substrates, the method comprising: holding a first substrate against a curved surface; bringing the first substrate into contact with a second substrate; and bonding the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.31. A method according to clause 30, wherein bringing the first substrate into contact with the second substrate comprising bringing a distal part of the first substrate into contact with the second substrate.32. A method according to clause 30 or 31, wherein a curvature of the curved surface around the first axis is greater than a curvature of the curved surface around an axis perpendicular to the first axis.33. A method according to any one of clauses 30 to 32 comprising introducing a relative position offset between the first substrate and the second substrate while rolling the first substrate.34. A method according to clause 33, comprising varying an amount of relative position offset over time while rolling the first substrate.35. A method according to any one of clauses 30 to 34, comprising moving the second substrate relative to the curved surface while rolling the first substrate.36. A method according to clause 35, comprising varying an amount of movement of the second substrate over time while rolling the first substrate.37. A method according to any one of clauses 30 to 36, wherein the curved surface has a substantially cylindrical shape.38. A method according to any one of clauses 30 to 37, wherein the curved surface is shaped to provide a component of a compressive force in a direction perpendicular to a direction of the rolling.39. A method according to any one of clauses 1 to 38, wherein at least one of the first substrate and the second substrate is tiltable, and wherein the method further comprises adjusting a tilting stiffness of one or both of the first substrate and the second substrate during the bringing of the first substrate into contact with the second substrate.40. A method according to any one of clauses 1 to 38, wherein at least one of the first substrate and the second substrate is tiltable, and wherein the method further comprises reducing a tilting stiffness of one or both of the first substrate and the second substrate during the bringing of the first substrate into contact with the second substrate.41. A method according to clause 39 or clause 40, wherein the tilting stiffness of one or both of the first substrate or the second substrate is about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least a period of time during the bringing of the first substrate into contact with the second substrate.42. A method according to any one of clauses 1 to 41, wherein the second substrate is on a tiltable wafer stage, and wherein the method further comprises adjusting a tilting stiffness of the wafer stage during the bringing of the first substrate into contact with the second substrate.43. A method according to any one of clauses 1 to 41, wherein the second substrate is on a tiltable wafer stage, and wherein the method further comprises reducing a tilting stiffness of the wafer stage during the bringing of the first substrate into contact with the second substrate.44. A method according to clause 42 or clause 43, wherein the tilting stiffness of the wafer stage is about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad orless, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least a period of time during the bringing of the first substrate into contact with the second substrate.45. A method according to any one of clauses 1 to 44, wherein the first substrate is on a tiltable bond head during the bringing of the first substrate into contact with the second substrate, and wherein the method further comprises adjusting a tilting stiffness of the bond head during the bringing of the first substrate into contact with the second substrate.46. A method according to any one of clauses 1 to 44, wherein the first substrate is on a tiltable bond head during the bringing of the first substrate into contact with the second substrate, and wherein the method further comprises reducing a tilting stiffness of the bond head during the bringing of the first substrate into contact with the second substrate.47. A method according to clause 45 or clause 46, wherein the tilting stiffness of the bond head is about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less, for at least a period of time during the bringing of the first substrate into contact with the second substrate.48. A composite substrate manufactured by a method according to any one of clauses 1 to 47.49. A semiconductor device manufactured by a method according to any one of clauses 1 to 47.50. A semiconductor device comprising a composite substrate according to clause 48.51. An apparatus configured to perform the method of any one of clauses 1 to 47.52. An apparatus for bonding substrates, the apparatus being configured to: apply a first bending force to bend a first substrate along a first axis; bring the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and release the first substrate from the first bending force.53. An apparatus according to clause 52, the apparatus being further configured to: apply a second bending force to bend the second substrate along a second axis; wherein bringing the first substrate into contact with the second substrate to provide the elongated zone of contact comprises: bringing the first substrate into contact with the second substrate while the first substrate is under the first bending force and the second substrate is under the second bending force to provide a pointshaped zone of contact between the first substrate and the second substrate; and releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form the elongated zone of contact.54. An apparatus for bonding substrates, the apparatus being configured to: apply a first bending force to bend a first substrate along a first axis; apply a second bending force to bend a second substrate along a second axis;bring the first substrate into contact with the second substrate to provide a point-shaped zone of contact between the first substrate and the second substrate; release the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form an elongated zone of contact; and release the first substrate from the first bending force.55. An apparatus for bonding substrates, the apparatus being configured to: apply a first bending force to bend a first substrate along a first axis; apply a second bending force to bend a second substrate along a second axis; bring the first substrate into contact with the second substrate to form a zone of contact between the first substrate and the second substrate; release the second substrate from the second bending force to induce propagation of a bond front along the first axis; and release the first substrate from the first bonding force to induce propagation of the bond front along the second axis.56. An apparatus according to any one of clauses 53 to 55, configured to release alternately the second substrate from the second bending force and the first substrate from the first bending force in a plurality of stages.57. An apparatus according to any one of clauses 52 to 56, configured to apply a third bending force to bend the first substrate along a second axis, the third bending force being substantially smaller than the first bending force; and wherein the method further comprises releasing the first substrate from the third bending force.58. An apparatus according to any one of clauses 53 to 57, wherein the second axis is substantially perpendicular to the first axis.59. An apparatus according to any one of clauses 52 to 58, wherein the first substrate comprises a die, and wherein the second substrate comprises a wafer.60. An apparatus according to any one of clauses 52 to 58, wherein the first substrate comprises a first wafer, and wherein the second substrate comprises a second wafer.61. An apparatus according to any one of clauses 52 to 60, comprising a first clamp, the first clamp being configured to apply the first bending force.62. An apparatus according to clause 61, comprising a curved surface, wherein the clamp is configured to hold the first substrate against the curved surface.63. An apparatus according to clause 62, configured to bond the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.64. An apparatus according to any one of clauses 52 to 63, comprising a second clamp, the second clamp being configured to apply the second bending force.65. An apparatus according to any one of clauses 62 to 64, configured to apply the first bending force by holding the first substrate against a substantially wedge-shaped surface.66. An apparatus according to any one of clauses 52 to 65, configured to apply the first bending force by holding the first substrate against a substantially compliant surface.67. An apparatus according to any one of clauses 52 to 66, configured to apply a positioning correction to the first substrate to align the first substrate with the first axis.68. An apparatus according to any one of clauses 52 to 67, configured to form an electrical connection between the first substrate and the second substrate.69. An apparatus according to any one of clauses 52 to 68, wherein the first axis is perpendicular to a conductive feature alignment direction on the second substrate.70. An apparatus according to any one of clauses 52 to 69, configured for directly bonding the first substrate to the second substrate.71. An apparatus according to any one of clauses 52 to 69, wherein at least one of the first substrate and the second substrate is provided with an adhesive layer.72. An apparatus according to clause 71, wherein the adhesive layer comprises an interface layer.73. An apparatus according to clause 72, wherein the interface layer is an organic interface layer.74. An apparatus for bonding substrates, the apparatus comprising: a first clamp; and a curved surface; wherein the first clamp is configured to hold a first substrate against the curved surface to bend the first substrate along a first axis; wherein the apparatus is configured to: bring the first substrate into contact with a second substrate; and bond the first substrate to the second substrate by rolling the first substrate around an axis of the curved surface.75. An apparatus according to any one of clauses 62, 63, or 74, wherein the curved surface has a substantially cylindrical shape.76. An apparatus according to any one of clauses 62, 63, or 74, wherein the curved surface has a substantially ellipsoidal shape.77. An apparatus according to any one of clauses 62, 63, or 74, wherein the curved surface is shaped to provide a component of a compressive force in a direction perpendicular to a direction of the rolling.78. An apparatus according to any one of clauses 62, 63, or 74-77, wherein a curvature of the curved surface around the first axis is greater than a curvature of the curved surface around an axis perpendicular to the first axis.79. An apparatus according to any one of clauses 52 to 78, configured to bring a distal part of the first substrate into contact with the second substrate.80. An apparatus according to any one of clauses 52 to 79, configured to introduce a relative position offset between the first substrate and the second substrate while rolling the first substrate.81. An apparatus according to clause 80, configured to vary an amount of relative position offset over time while rolling the first substrate.82. An apparatus according to any one of clauses 52 to 81, configured to move the second substrate relative to the curved surface while rolling the first substrate.83. An apparatus according to clause 82, configured to vary an amount of movement of the second substrate over time while rolling the first substrate.84. An apparatus according to any one of clauses 52 to 83, comprising a tiltable wafer stage configured to hold the second substrate, wherein the apparatus is configured to adjust a tilting stiffness of the wafer stage during the bringing of the first substrate into contact with the second substrate.85. An apparatus according to any one of clauses 52 to 83, comprising a tiltable wafer stage configured to hold the second substrate, wherein the apparatus is configured to reduce a tilting stiffness of the wafer stage during the bringing of the first substrate into contact with the second substrate.86. An apparatus according to clause 84 or clause 85, wherein the apparatus is configured such that the tilting stiffness of the wafer stage is about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less for at least a period of time during the bringing of the first substrate into contact with the second substrate.87. An apparatus according to any one of clauses 52 to 86, comprising a tiltable bond head, wherein the apparatus is configured to adjust a tilting stiffness of the bond head during the brining of the first substrate into contact with the second substrate.88. An apparatus according to any one of clauses 52 to 86, comprising a tiltable bond head, wherein the apparatus is configured to reduce a tilting stiffness of the bond head during the bringing of the first substrate into contact with the second substrate.89. An apparatus according to clause 87 or clause 88, wherein the apparatus is configured such that the tilting stiffness of the bond head is about 1 Nm / rad or less, about 0.9 Nm / rad or less, about 0.8 Nm / rad or less, about 0.7 Nm / rad or less, about 0.6 Nm / rad or less, about 0.5 Nm / rad or less, about 0.4 Nm / rad or less, about 0.3 Nm / rad or less, about 0.2 Nm / rad or less, or about 0.1 Nm / rad or less for at least a period of time during the bringing of the first substrate into contact with the second substrate.

[0152] 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

1. CLAIMS1. A method for bonding substrates, the method comprising: applying a first bending force to bend a first substrate along a first axis; bringing the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and releasing the first substrate from the first bending force.

2. A method according to claim 1, further comprising: applying a second bending force to bend the second substrate along a second axis; wherein bringing the first substrate into contact with the second substrate to provide the elongated zone of contact comprises: bringing the first substrate into contact with the second substrate while the first substrate is under the first bending force and the second substrate is under the second bending force to provide a point-shaped zone of contact between the first substrate and the second substrate; and releasing the second substrate from the second bending force to cause the zone of contact to expand along the first axis to form the elongated zone of contact.

3. A method according to claim 2, comprising alternately releasing the second substrate from the second bending force and the first substrate from the first bending force in a plurality of stages.

4. A method according to claim 1, comprising applying a third bending force to bend the first substrate along a second axis, the third bending force being substantially smaller than the first bending force; and wherein the method further comprises releasing the first substrate from the third bending force.

5. A method according to any of claims 2 to 4, wherein the second axis is substantially perpendicular to the first axis.

6. A method according to any one of the preceding claims, wherein the first substrate is a die, and wherein the second substrate comprises a wafer.

7. A method according to any one of claims 1 to 5, wherein the first substrate comprises a first wafer, and wherein the second substrate comprises a second wafer.

8. A method according to any one of the preceding claims, the method being configured for directly bonding the first substrate to the second substrate.

9. A method according to any one of claims 1 to 7, wherein at least one of the first substrate and the second substrate is provided with an adhesive layer.

10. A method according to claim 9, wherein the adhesive layer comprises an organic interface layer.

11. A method according to any one of the preceding claims, wherein applying the first bending force comprises holding the first substrate against a curved surface.

12. A method according to claim 11, wherein releasing the first substrate from the first bending force comprises rolling the first substrate around an axis of the curved surface.

13. A method according to any one of the preceding claims, wherein applying the first bending force comprises holding the first substrate against a substantially wedge-shaped surface.

14. A method according to any one of the preceding claims, wherein applying the first bending force comprises holding the first substrate against a compliant surface.

15. An apparatus for bonding substrates, the apparatus being configured to: apply a first bending force to bend a first substrate along a first axis; bring the first substrate into contact with a second substrate to provide an elongated zone of contact between the first substrate and the second substrate along the first axis; and release the first substrate from the first bending force.

Images