Wafer-level bonding method for camera fabrication

A wafer-level method for fabricating a plurality of cameras includes modifying an image sensor wafer to reduce risk of the image sensor wafer warping, and bonding the image sensor wafer to a lens wafer to form a composite wafer that includes the plurality of cameras. A wafer-level method for fabricating a plurality of cameras includes bonding an image sensor wafer to a lens wafer, using a pressure sensitive adhesive, to form a composite wafer that includes the plurality of cameras.

BACKGROUND

The development of imaging systems manufactured with complementary metal-oxide-semiconductor (CMOS) technologies used to fabricate integrated circuits has made cameras ubiquitous in high-volume consumer products, such as cellular phones and automotive camera systems. In the CMOS manufacturing process, integrated circuits, such as image sensors, are fabricated on a substrate called a wafer. A large number of image sensors may be fabricated on a single wafer. Similarly, a large number of identical lenses may be fabricated on a single substrate, using a single molding tool to shape all lenses, to form a lens wafer. For production of cameras with imaging objectives composed of multiple lenses, one or more lens wafers are stacked to make a lens wafer composed of multiple identical lens stacks, each forming an imaging objective. The image sensor wafer is diced to make individual image sensors, and the lens wafer is diced to make individual lenses or lens stacks. Cameras are then fabricated by disposing an image sensor on each lens or lens stack.

SUMMARY

In an embodiment, a wafer-level method for fabricating a plurality of cameras includes modifying an image sensor wafer to reduce risk of the image sensor wafer warping, and bonding the image sensor wafer to a lens wafer to form a composite wafer that includes the plurality of cameras.

In an embodiment, a wafer-level method for fabricating a plurality of cameras includes bonding an image sensor wafer to a lens wafer, using a pressure sensitive adhesive, to form a composite wafer that includes the plurality of cameras.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1illustrates one exemplary wafer-level bonding method100for fabricating a plurality of cameras utilizing lens-to-image sensor bonding at the wafer-level. Wafer-level bonding method100thus produces a plurality of cameras using only a single alignment operation. A lens wafer110, which includes a plurality of lenses112, is bonded to an image sensor wafer120, which includes a plurality of image sensors122, to form a composite wafer130. Lens wafer110and image sensor wafer120are configured and aligned with respect to each other, such that each of at least a portion of image sensors112are aligned with a respective lens122to form a camera140. Accordingly, composite wafer130includes a plurality of cameras140, which may be singulated from composite wafer130by dicing composite wafer130. In an embodiment, each lens112of lens wafer110is a single lens. In another embodiment, each lens112of lens wafer110is a stack of several lenses. For example, lens wafer110may be formed by bonding together two or more individual lens wafers, each including lenses associated with a respective layer in the lens stack. For the purpose of the present disclosure, the term “lens” may refer to a single lens, a stack of lenses, a pin-hole aperture, a stack of pin-hole apertures, a Fresnel filter, or an imaging objective, optionally including elements that do not serve to affect focusing of incident light, such as wavelength filters, apertures, and substrates. Similarly, the term “lens wafer” may refer to a wafer including a plurality of lenses according to the above definition. Lens wafer110may include more of fewer lenses112than illustrated inFIG. 1, and lenses112may be arranged in a pattern different from that illustrated inFIG. 1, without departing from the scope hereof. Similarly, image sensor wafer120may include more or fewer image sensors122than illustrated inFIG. 1, and image sensors122may be arranged in a pattern different from that illustrated inFIG. 1, without departing from the scope hereof. For clarity of illustration, not all lenses112, image sensors122, and cameras140are labeled inFIG. 1.

Wafer-level bonding method100requires only a single alignment operation, namely that of image sensor wafer120with respect to lens wafer110. In contrast, fabrication of wafer-level cameras according to conventional methods, wherein lenses and image sensors are singulated before bonding, requires an independent alignment operation for each individual camera. Typically sized image sensor wafers and lens wafers may accommodate thousands of image sensors and lenses, respectively. Therefore, conventional methods typically require thousands of alignment operations to assemble the cameras associated with a typically sized pair of lens and image sensor wafers. The performance of wafer-level cameras relies on precise alignment between the lens stack and the image sensor, which is a demanding task when each camera must be aligned individually. In wafer-level bonding method100, all of the thousands of individual cameras are aligned in a single operation. Consequently, method100offers substantial benefit in terms of camera fabrication complexity and cost. Additionally, method100may offer improved performance characteristics of the cameras140, since a batch of cameras140produced from lens wafer110and image sensor wafer120generally will exhibit low camera-to-camera alignment variation.

Embodiments of wafer-level bonding method100, discussed below, include certain steps associated with overcoming challenges of bonding image sensor wafer120to lens wafer110. These challenges include (a) preventing warping of image sensor wafer120, which may adversely affect the alignment of image sensor wafer120with respect to lens wafer110, (b) gaining optical access through an adhesive layer used to bond image sensor wafer120to lens wafer110, and (c) preventing breakage of image sensor wafer120during bonding to lens wafer110.

FIG. 2illustrates one exemplary wafer-level bonding method200for camera fabrication. Wafer-level bonding method200is an embodiment of wafer-level bonding method100(FIG. 1). In a step210, method200receives an image sensor wafer, such as image sensor wafer120ofFIG. 1. In a step220, method200receives a lens wafer, such as lens wafer110ofFIG. 1. In a step230, the image sensor wafer and lens wafer received in steps210and220, respectively are aligned with respect to each other. For example, image sensor wafer120(FIG. 1) is aligned to lens wafer110(FIG. 1) such that each of at least a portion of individual lenses112of lens wafer110are aligned with respective image sensors122of image sensor wafer120. The alignment may be performed using optical or mechanical referencing, or a combination thereof. In a step240the image sensor wafer is bonded to the lens wafer to form a composite wafer. Since, in step240, each of at least a portion of the lenses of the lens wafer are aligned with respective image sensors of the image sensor wafer, the composite wafer includes cameras, where each camera includes a lens and an image sensor of the lens and image sensor wafer, respectively. For example, image sensor wafer120(FIG. 1) is bonded to lens wafer110(FIG. 1), such that the resulting composite wafer130(FIG. 1) includes a plurality of cameras140(FIG. 1). In an embodiment, bonding is achieved using an optically clear adhesive, such as an epoxy, an ultraviolet (UV) curable epoxy, a thermally curable epoxy, a dry film, or a pressure sensitive adhesive, such that the alignment of step230may be performed optically with the adhesive located between the image sensor wafer and the lens wafer. In another embodiment, step230utilizes other bonding methods known in the art, such as direct bonding, annealing, or plasma activated bonding.

In an embodiment, method200further includes one or both of steps212and214performed after step210and before step230. In step212, the image sensor wafer received in step210is modified to risk of the image sensor wafer warping. Warping may adversely affect the alignment performed in step230. Hence, step212serves to improve the alignment properties achieved in step230. Step212may include reducing risk of warping by at least partially releasing stress in the image sensor wafer, for example by applying stress-relieving cuts to the image sensor wafer. In an example, stress in image sensor wafer120(FIG. 1) is at least partially released prior to aligning image sensor wafer120with lens wafer110(FIG. 1). In step214, the image sensor wafer received in step210, and optionally modified in step212, is modified to reduce risk of the image sensor wafer breaking during bonding to the lens wafer in step240. For example, image sensor wafer120(FIG. 1) is modified to reduce risk of breaking during bonding to lens wafer110(FIG. 1). Step214may be advantageously included in embodiments of method200, wherein step240includes applying mechanical pressure to the image sensor wafer. An image sensor wafer is generally more fragile than a single image sensor. In embodiments of method200that include step212, the modifications made in step212may increase the fragility of the image sensor wafer. Step214serves to prepare the image sensor wafer for bonding, such that the image sensor wafer does not break during step240. In one example, the image sensor wafer is modified to avoid or reduce the significance of local pressure points associated with non-flatness of the surface of the image sensor wafer that faces away from the lens wafer in step240. Non-flatness may be due to, for example, solder bumps on the image sensor wafer. In another example, the image sensor wafer is strengthened by mounting thereto a strengthening support structure. Step214may be performed after step230and before step240, without departing from the scope hereof.

In an embodiment, method200further includes a step250, performed subsequently to step240. In step250, the composite wafer formed in step240is diced to form the plurality of cameras. For example, composite wafer130(FIG. 1) is diced to form a plurality of cameras140(FIG. 1). Step250may include masking the composite wafer prior to dicing, and removing the mask after dicing.

In an embodiment, method200includes one or both of steps201and202for forming the image sensor wafer and the lens wafer, respectively. Steps201and202may be performed using methods known in the art.

FIG. 3illustrates one exemplary method300for modifying an image sensor wafer to reduce the risk of warping of the image sensor wafer. Method300is an embodiment of step212of method200(FIG. 2). In a step310, at least one stress-relieving trench is formed in a portion of the image sensor wafer that does not coincide with an image sensor. For example, at least one stress-relieving trench is formed in a portion of image sensor wafer120(FIG. 1) that does not coincide with an image sensor122(FIG. 1). In one embodiment, each of the at least one stress-relieving trench is formed by making a cut into the image sensor wafer, which does not fully penetrate the image sensor wafer. In another embodiment, at least a portion of the at least one stress-relieving trench is formed by making a cut into the image sensor wafer, where the cut penetrates the image sensor wafer for a fraction of the length of the stress-relieving trench.

In an embodiment, step310includes a step320, wherein at least one stress-relieving trench is formed, which spans the planar extent of the image sensor wafer in a first direction. For example, at least one stress-relieving trench is formed in image sensor wafer120(FIG. 1), such that the stress-relieving trench spans the full extent of image sensor wafer120along a direction in the plane of image sensor wafer120. In an embodiment, step310further includes a step330, wherein at least one stress-relieving trench is formed, which spans the planar extent of the image sensor wafer in a second direction that is different from the first direction. For example, at least one stress-relieving trench is formed in image sensor wafer120(FIG. 1), such that the stress-relieving trench spans the full extent of image sensor wafer120along a direction, different from the direction used in step320, in the plane of image sensor wafer120. The combination of step310and320may provide release of stress to prevent or reduce warping along any direction within the plane of the image sensor wafer.

FIGS. 4A and 4Billustrate one exemplary image sensor wafer400that has one or more stress-relieving trenches. Image sensor wafer400may be the outcome of modifying an image sensor wafer, such as image sensor wafer120(FIG. 1), according to method300(FIG. 3).FIGS. 4A and 4Bshow image sensor wafer400in top-plan view and cross-sectional side-view, respectively.FIGS. 4A and 4Bare best viewed together. Image sensor wafer400includes a sensor layer450and a cover-glass layer460disposed on sensor layer450. Image sensor wafer400includes a plurality of image sensors122, each including a bare image sensor451and a portion of cover-glass layer460. Image sensors122are capable of forming images from light received through cover-glass layer460. For clarity of illustration, not all image sensors122and bare image sensors451are labeled inFIGS. 4A and 4B.

Image sensor wafer400includes a stress-relieving trench410. Stress-relieving trench410is located in between two columns of images sensors122. Stress-relieving trench410fully penetrates sensor layer450while penetrating only a fraction, greater than zero and less than one, of cover glass layer460. Stress-relieving trench410spans the planar extent of image sensor wafer400along a direction401. Optionally, image sensor wafer400includes an additional stress-relieving trench420, which also spans the planar extent of image sensor wafer400along direction401. In an embodiment, image sensor wafer400includes one or more stress-relieving trenches430that span the planar extent of image sensor wafer400in a direction402. Direction402is substantially orthogonal to direction401.

Although illustrated inFIG. 4Aas spanning the full planar extent of image sensor wafer400, stress-relieving trenches410,420, and430may span only a portion of the planar extent of image sensor wafer400, without departing from the scope hereof. Likewise, image sensor wafer400may include more stress-relieving trenches and/or differently arranged stress-relieving trenches than illustrated inFIGS. 4A and 4B, without departing from the scope hereof.

FIG. 5illustrates one exemplary wafer-level bonding method500for camera fabrication, which utilizes a pressure sensitive adhesive for bonding an image sensor wafer, such as image sensor wafer120(FIG. 1), to a lens wafer such as lens wafer110(FIG. 1). Method500is an embodiment of method200(FIG. 2). In a step510, method500performs step210, and optionally one or both of steps201and212, of method200(FIG. 2). If included in step510, step212may be performed according to method300(FIG. 3). In a step514, a protective layer is applied to the image sensor wafer, for example image sensor wafer120(FIG. 1), such that the protective layer encapsulates at least a portion of the solder bumps of the image sensor wafer. Step514is an embodiment of step214(FIG. 2). In an embodiment, the protective layer is an ultra-violet-light releasable tape.

FIG. 6illustrates one exemplary image sensor600with a protective layer that encapsulates the solder bumps of image sensor600. Image sensor600illustrates one embodiment of step514of method500(FIG. 5). Image sensor600includes bare image sensor451(FIG. 4), which in turn includes solder bumps610on the surface opposite the light receiving surface of bare image sensor451. Image sensor600further includes a protective layer620that encapsulates solder bumps610. In one embodiment, protectively layer620has thickness and cushion to redistribute local pressure, otherwise applied exclusively to the solder bumps, to other portions of the image sensor wafer. For example, the protective layer may redistribute pressure from the solder bumps to portions of the image sensor wafer located between the solder bumps. In another embodiment, protective layer620has indentations that match the location of the solder bumps, such that pressure applied to protective layer620in the direction towards bare image sensor451is applied only to portions of bare image sensor451different from solder bumps610. WhileFIG. 6illustrates only a single bare image sensor451, protective layer620may span larger portions of an image sensor wafer, including portions that do not include an image sensor, without departing from the scope hereof. For clarity of illustration, not all solder bumps610are labeled inFIG. 6.

Referring once again toFIG. 5, in a step520, method500performs step220, and optionally step202, of method200(FIG. 2). In a step530, method500performs step230of method200(FIG. 2). In a step540, which is an embodiment of step240(FIG. 2), a composite wafer is formed by bonding the image sensor wafer to the lens wafer using a pressure sensitive adhesive. For example, composite wafer130(FIG. 1) is formed by bonding images sensor wafer120(FIG. 1) to lens wafer110(FIG. 1) using a pressure sensitive adhesive. Pressure sensitive adhesive based bonding requires application of mechanical pressure to the image sensor wafer and lens wafer, with the pressure sensitive adhesive disposed therebetween. The mechanical pressure presses together the image sensor wafer, the pressure sensitive adhesive, and the lens wafer. The solder bumps of the image sensor wafer generally protrude from the surface of the image sensor wafer. If mechanical pressure is applied to an unprotected solder bump, there is a risk that the solder bump may break and/or that the local pressure conveyed by the solder bump to other portions of the image sensor wafer in contact with the solder bump may cause a crack in the image sensor wafer. The protective layer applied in step514functions to reduce the risk of such breakage. In an embodiment, pressure is applied to only a portion of the image sensor wafer. In this embodiment, step514may apply a protective layer to the full surface of the image sensor wafer, facing away from the lens wafer, or only to a portion thereof.

In a step545, the protective layer applied in step514is removed. In one embodiment, associated with the protective layer being an ultra-violet-light releasable tape, the protective layer is removed by exposing the protective layer to ultra-violet light. In another embodiment, the protective layer is removed mechanically or chemically, or removed using a combination of mechanical, chemical, and/or optical methods. Optionally, method500further includes a step550of performing step250of method200(FIG. 2). In an alternate embodiment, not illustrated inFIG. 5, step545is performed after step550.

FIG. 7illustrates one exemplary wafer-level bonding method700for camera fabrication utilizing a pressure sensitive adhesive for bonding an image sensor wafer to a lens wafer. The pressure sensitive adhesive is applied to the lens wafer prior to bonding with the image sensor wafer. Method700includes steps to reduce trapping of air bubbles in and/or at the pressure sensitive adhesive, as well as optional steps for removing such bubbles. Method700is an embodiment of method500(FIG. 5). In a step710, method700performs steps510and514of method500(FIG. 5).

In a step710, method700performs steps510and514of method500(FIG. 5). In a step720, method700performs step520of method500(FIG. 5). Step720is followed by an optional step721, a step722, and an optional step723, performed sequentially. In optional step721, the lens wafer is pre-cleaned to prepare the lens wafer for application of pressure sensitive adhesive. For example, lens wafer110(FIG. 1) is cleaned using a solvent. In step722, a pressure sensitive adhesive is applied to the lens wafer. For example, a pressure sensitive adhesive is applied to lens wafer110(FIG. 1). In optional step726, the lens wafer is autoclaved, i.e., exposed to elevated temperature and pressure, to remove bubbles trapped at the interface between the pressure sensitive adhesive and the lens wafer, and/or to remove bubbles from the pressure sensitive adhesive. For example, lens wafer110(FIG. 1), with a pressure sensitive adhesive adhered thereto, is autoclaved.

In a step730, method700performs step530of method500(FIG. 5). After performing step730, method700performs steps741,742, and, optionally, step743. Steps741,742, and, optionally, step743, together form an embodiment of step540of method500(FIG. 5). In step741, the image sensor wafer is contacted to the pressure sensitive adhesive, which was applied to the lens wafer in step722. For example, image sensor wafer120(FIG. 1) is contacted to a pressure sensitive adhesive applied to lens wafer110(FIG. 1). In order to reduce trapping of air bubbles at the interface of the pressure sensitive adhesive and the image sensor wafer, the image sensor wafer is contacted to the pressure sensitive adhesive using a low mechanical pressure. The low mechanical pressure is sufficient for the image sensor wafer to be mechanically coupled with the pressure sensitive adhesive, but insufficient to fully bond the pressure sensitive adhesive with the image sensor wafer. Thus, at least a portion of the air located at the interface between the image sensor wafer and the pressure sensitive adhesive has one or more pathways coupling the air with the surrounding atmosphere. In a step742, the image sensor wafer and lens wafer, for example image sensor wafer120(FIG. 1) and lens wafer110(FIG. 1), are bonded together, using the pressure sensitive adhesive. This results in the formation of a composite wafer, such as composite wafer130(FIG. 1). Step742is performed under vacuum, or at least reduced pressure as compared with standard atmospheric pressure, and includes applying mechanical pressure to the image sensor wafer and the lens wafer to press together the image sensor wafer and the lens wafer. At least a portion of the air located at the interface of the pressure sensitive adhesive with the image sensor wafer, and optionally also at least a portion of any air located at the interface of the pressure sensitive adhesive with the lens wafer, is pumped away while the image sensor wafer is pressed against the lens wafer. Accordingly, the amount of air trapped at the interface between the pressure sensitive adhesive and the image sensor wafer, and optionally the lens wafer, is reduced.

In optional step743, the composite wafer is autoclaved to remove at least a portion of residual air bubbles from the pressure sensitive adhesive and interfaces between the pressure sensitive adhesive and the image sensor wafer and the lens wafer. For example, composite wafer130(FIG. 3) is autoclaved to remove residual air bubbles from the pressure sensitive adhesive applied in step722, the interface between this pressure sensitive adhesive and image sensor wafer120(FIG. 1), and the interface between this pressure sensitive adhesive and lens wafer110(FIG. 1).

FIG. 8illustrates one exemplary method800for optically aligning an image sensor wafer, such as image sensor wafer120(FIG. 1), with a lens wafer, such as lens wafer110(FIG. 1). Method800is an embodiment of step230of method200(FIG. 2). In a step810, an image sensor wafer is aligned with a lens wafer using optical access through the lens wafer to the image sensor wafer. For example, image sensor wafer120(FIG. 1) is aligned with lens wafer110(FIG. 1) using optical access through lens wafer110to image sensor wafer120. In an embodiment, step810includes a step820, wherein at least two reference marks on the lens wafer are aligned with at least two respective image sensors of the image sensor wafer. The alignment may be evaluated visually, aided by optical viewing instruments, or automatically by optical instruments.

FIGS. 9A and 9Billustrate, by example, step820for one exemplary pair of image sensor wafer and lens wafer.FIGS. 9A and 9Bare best viewed together.FIG. 9Ais a diagram901that shows, in perspective view, alignment of image sensor wafer120(FIG. 1) with respect to a lens wafer910. Lens wafer910is an embodiment of lens wafer110(FIG. 1), which includes two reference marks920in addition to a plurality of lenses112(FIG. 1). Reference marks920are located in portions of lens wafer910that coincide with respective optical access paths930through lens wafer910to image sensor wafer120. In one embodiment, reference marks920are lenses112. In another embodiment, references marks920are optically clear portions of lens wafer910, each including a feature, such as an aperture, for evaluating the position of reference mark920. WhileFIG. 9Billustrates reference marks920as being circulary, reference mark920may have other shape, such as square, rectangular, circular, or a cross, without departing from the scope hereof. In yet another embodiment, all of lens wafer910is optically clear, and reference marks920are features, for instance located on the surface of lens wafer910, for evaluating the positions of reference marks920. Two of image sensors122of image sensor wafer120function as reference marks940. In an embodiment, each reference mark940is the outline of the photosensitive surface of an image sensor122. In an embodiment, each reference mark940is the color filter of an image sensor122, where the color filter may an IR filter and/or a color filter array for providing color imaging functionality, such as a Bayer-type color filter array. Step820of method800(FIG. 8) aligns references marks920with corresponding reference marks940using optical access paths930. For clarity of illustration, not all lenses112and image sensors122are labeled inFIG. 9A. WhileFIG. 9Ashows reference marks940as coinciding with outermost located image sensors122, reference marks940may coincide with image sensors122located in interior portions of the array of image sensors122of image sensor wafer120, without departing from the scope hereof.

FIG. 9Bis a diagram902showing a top-plan view of one reference mark920aligned with one reference mark940.FIG. 9Bthus illustrates the view along one optical access path930. Using optical access path930, the position of reference mark920, projected onto the plane of image sensor wafer120, and reference mark940are centered at a common location950. The optical evaluation of the positioning of reference mark920relative to reference mark940may be aided by optical guides, provided by an optical viewing instrument, such as cross hairs960.

Returning toFIG. 8, an embodiment of step810includes a step830, wherein alignment is performed further utilizing optical access through an optically clear adhesive that is disposed between the image sensor wafer and the lens wafer. Step830is useful for implementation of method800into wafer-level bonding methods that apply an adhesive to one or both of the image sensor wafer and the lens wafer prior to alignment thereof, such as method700(FIG. 7). Step830assumes that the adhesive is optically clear, such that method800may be performed with the adhesive in place between the image sensor wafer and the lens wafer. Optically clear adhesives include certain types of pressure sensitive adhesives, dry films, and epoxy resins. Embodiments of method800that include step830may be advantageously implemented in methods500(FIG. 5) and700(FIG. 7) as steps530and730, respectively.

FIG. 10illustrates one exemplary camera1000fabricated according to method200(FIG. 2), with step250(FIG. 2) included. Camera1000is an embodiment of camera140(FIG. 1). Camera1000includes an image sensor portion1010of rectangular cuboidal shape, and a lens portion1020of rectangular cuboidal shape. In an embodiment, camera1000further includes an adhesive layer1030, of rectangular cuboidal shape, disposed between image sensor portion1010and lens portion1040. Image sensor portion1010is a portion of image sensor wafer120(FIG. 1), including an image sensor122(FIG. 1). Lens portion1020is a portion of lens wafer110(FIG. 1), including a lens112(FIG. 1). In certain embodiments, adhesive layer1030is a pressure sensitive adhesive.

Camera1010has a bottom surface1050, a top surface1060, and four side surfaces1070. For clarity of illustration, only one of the four side surfaces1070is labeled inFIG. 10. Each side surface1070includes a surface of lens portion1020, a surface of image sensor portion1010, and, optionally, a surface of adhesive layer1030. Camera1010is the product of step250of method200(FIG. 2). Accordingly, for each side surface1070, all portions of side surface1070are formed in the same dicing operation. Therefore, side surface1070is planar with no step associated with interfaces between image sensor portion1010, lens portion1020, and optional adhesive portion1030.

Methods disclosed herein may be practiced in conjunction with methods disclosed in U.S. Patent Application Ser. No. 14/270,281 Entitled “System And Method For Black Coating Of Camera Cubes At Wafer Level.

Combinations of Features

Features described above as well as those claimed below may be combined in various ways without departing from the scope hereof. For example, it will be appreciated that aspects of one wafer-level bonding method for camera fabrication, or associated camera, described herein may incorporate or swap features of another wafer-level bonding method for camera fabrication, or associated camera, described herein. The following examples illustrate possible, non-limiting combinations of embodiments described above. It should be clear that many other changes and modifications may be made to the methods and device herein without departing from the spirit and scope of this invention:

(A) A wafer-level method for fabricating a plurality of cameras may include modifying an image sensor wafer to reduce risk of the image sensor wafer warping.

(B) The wafer-level method denoted as (A) may further include bonding the image sensor wafer to a lens wafer to form a composite wafer that includes the plurality of cameras.

(C) In the wafer-level method denoted as (B), the step of bonding may include bonding the image sensor wafer to the lens wafer using a pressure sensitive adhesive.

(D) The wafer-level methods denoted as (B) and (C) may further include applying a protective layer to the image sensor wafer for reducing risk of the image sensor wafer breaking during the step of bonding

(E) In the wafer-level method denoted as (D), the protective layer may encapsulate solder bumps of the image sensor wafer.

(F) In the wafer-level methods denoted as (D) and (E), the protective layer may be an ultraviolet-light-releaseable tape.

(G) The wafer-level method denoted as (F) may further include, after the step of bonding, removing the protective layer using ultraviolet light.

(H) The wafer-level methods denoted as (B) through (G) may further include aligning the image sensor wafer with the lens wafer using an optical method.

(I) In the wafer-level method denoted as (H), the step of aligning may include aligning, by optical access through the lens wafer, at least two alignment marks of the lens wafer with two image sensors of the image sensor wafer.

(J) The wafer-level methods denoted as (H) and (I) may further include applying an optically clear adhesive to the lens wafer.

(K) In the wafer-level method denoted as (J), the step of bonding may include bonding the image sensor wafer to the lens wafer using the optically clear adhesive, wherein the step of aligning is performed after the step of applying the optically clear adhesive and before the step of bonding.

(L) In the wafer-level methods denoted as (J) and (K), the optically clear adhesive may be a pressure sensitive adhesive.

(M) In the wafer-level methods denoted as (A) through (L), the step of modifying the image sensor wafer to reduce risk of warping may include relieving stress from the image sensor wafer.

(N) In the wafer-level method denoted as (M), the step of relieving stress may include applying thereto at least one cut to form a trench in the image sensor wafer.

(O) In the wafer-level methods denoted as (M) and (N), the image sensor wafer may include a sensor layer and a cover glass layer disposed on the sensor layer, and the step of relieving stress may include applying at least one cut to a portion of the image sensor wafer not overlapping with an image sensor, wherein the at least one cut penetrates the sensor layer and forms a trench in the cover glass.

(P) In the wafer-level method denoted as (O), the step of applying at least one cut may include applying at least one cut that spans the image sensor wafer along a first direction in the plane of the image sensor wafer.

(Q) In the wafer-level method denoted as (P), the step of applying at least one cut may further include applying at least one cut that spans the image sensor wafer along a second direction in the plane of the image sensor wafer, wherein the second direction is different from the first direction.

(R) A wafer-level method for fabricating a plurality of cameras may include bonding an image sensor wafer to a lens wafer, using a pressure sensitive adhesive, to form a composite wafer that includes the plurality of cameras.

(S) The wafer-level method denoted as (R) may further include modifying the image sensor wafer to reduce risk of the image sensor breaking during the step of bonding.

(T) In the wafer-level method denoted as (S), the step of modifying may include applying a protective layer to the image sensor wafer.

(U) In the wafer-level method denoted as (T), the protective layer may encapsulate solder bumps of the image sensor wafer.

(V) In the wafer-level methods denoted as (T) and (U), the protective layer may be an ultraviolet-light-releaseable tape.

(W) The wafer-level method denoted as (V) may further include, after the step of bonding, removing the protective layer using ultraviolet light.

(X) The wafer-level methods denoted as (R) through (W) may further include applying the pressure sensitive adhesive to the lens wafer, wherein the pressure sensitive adhesive is optically clear.

(Y) The wafer-level method denoted as (X) may further include aligning the image sensor wafer with the lens wafer, using optical access through the lens wafer and the pressure sensitive adhesive.

(Z) In the wafer-level method denoted as (Y), the step of aligning may include aligning, using the optical access through the lens wafer and the pressure sensitive adhesive, at least two alignment marks of the lens wafer with two of the plurality of image sensors.

(AA) In the wafer-level methods denoted as (R) through (Z), the step of bonding may include contacting the image sensor to the pressure sensitive adhesive, and applying mechanical pressure, under vacuum, to the image sensor wafer and lens wafer to form the composite wafer.

(AB) In the wafer-level methods denoted as (R) through (AA), the step of bonding may further include autoclaving the composite wafer to remove bubbles from at least one of the pressure sensitive adhesive, interface between the pressure sensitive adhesive and the image sensor wafer, and interface between the pressure sensitive adhesive and the lens wafer.

(AC) In the wafer-level methods denoted as (R) through (AB), the step of bonding may include cleaning surface portions of the lens wafer, to which the pressure sensitive adhesive is applied in the step of applying the pressure sensitive adhesive.

(AD) In the wafer-level methods denoted as (R) through (AC), the step of bonding may include rolling the pressure sensitive adhesive onto to the lens wafer.

(AE) In the wafer-level methods denoted as (R) through (AC), the step of bonding may include autoclaving the lens wafer with the pressure sensitive adhesive to remove bubbles from at least one of the pressure sensitive adhesive and interface between the pressure sensitive adhesive and the lens wafer.