HK1211743B - Wafer-level bonding method for camera fabrication - Google Patents

Abstract

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.

Description

Wafer level bonding method for manufacturing camera

Background

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

Disclosure of Invention

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

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

Drawings

Fig. 1 illustrates a wafer level bonding method for manufacturing multiple cameras using wafer level lens to image sensor bonding according to one embodiment.

Fig. 2 illustrates a wafer level bonding method for manufacturing a camera according to an embodiment.

Fig. 3 illustrates a method of modifying an image sensor wafer to reduce the risk of warping the image sensor wafer, according to one embodiment.

Fig. 4A and 4B are top and side cross-sectional views, respectively, of an image sensor wafer having one or more stress relaxation trenches, according to one embodiment.

Fig. 5 illustrates a wafer level bonding method for manufacturing a camera using a pressure sensitive adhesive to bond an image sensor wafer to a lens wafer, according to one embodiment.

Fig. 6 illustrates an image sensor and a passivation layer encapsulating solder bumps of the image sensor according to an embodiment.

FIG. 7 depicts one embodiment of the method of FIG. 5, wherein a pressure sensitive adhesive is applied to the lens wafer prior to bonding the lens wafer to the image sensor wafer, and the method includes the step of reducing entrapment of air bubbles in the pressure sensitive adhesive, in accordance with one embodiment.

Fig. 8 illustrates a method for optically aligning an image sensor wafer and a wafer lens according to one embodiment.

Fig. 9A and 9B are schematic diagrams of the method of fig. 8 according to one embodiment.

FIG. 10 illustrates a camera made according to one embodiment of the method of FIG. 2, according to one embodiment.

Detailed Description

FIG. 1 illustrates an exemplary wafer level bonding method 100 for manufacturing multiple cameras using wafer level lens to image sensor bonding. The wafer level bonding method 100 thus produces a plurality of cameras that use only a single alignment operation. Lens wafer 110, which includes a plurality of lenses 112, is bonded to image sensor wafer 120, which includes a plurality of image sensors 122, to form composite wafer 130. The lens wafer 110 and the image sensor wafer 120 are arranged and aligned relative to each other such that at least a portion of each image sensor 112 is aligned with a corresponding lens 122 to form a camera 140. Thus, composite wafer 130 includes a plurality of cameras 140 that may be singulated from composite wafer 130 by dicing composite wafer 130. In one embodiment, each lens 112 of the lens wafer 110 is a singlet lens. In another embodiment, each lens 112 of the lens wafer 110 is a stack of multiple lenses. For example, lens wafer 110 may be formed by bonding two or more separate lens wafers together, each lens wafer including associated lenses in a respective layer in a lens stack. For the purposes of this description, the term "lens" may refer to a single lens, a lens stack, a pinhole aperture stack, a fresnel filter, or an imaging objective lens, optionally including elements that do not contribute to focusing incident light, such as wavelength filters, apertures, and substrates. Similarly, the term "lens wafer" may refer to one wafer comprising a plurality of lenses according to the above definition. The lens wafer 110 may include more or fewer lenses 112 than shown in fig. 1, and the lenses 112 may be arranged in a different pattern than shown in fig. 1 without departing from the scope of the invention. Likewise, the image sensor wafer 120 may include more or fewer image sensors 122 than shown in fig. 1, and the image sensors 122 may be arranged in a different pattern than shown in fig. 1 without departing from the scope of the present invention. For clarity, not all of the lens 112, image sensor 122, and camera 140 are labeled in FIG. 1.

The wafer level bonding method 100 requires only a single alignment operation, i.e., an alignment operation on the image sensor wafer 120 relative to the lens wafer 110. On the other hand, according to the conventional method, the manufacture of wafer-level cameras in which both the lens and the image sensor are singulated prior to bonding requires a separate alignment operation for each individual camera. A typical size image sensor wafer and lens wafer can accommodate thousands of image sensors and lenses, respectively. Thus, conventional methods typically require thousands of alignment operations to assemble the cameras associated with the typical size lens and image sensor wafer sets. The performance of wafer level cameras relies on precise alignment between the lens stack and the image sensor, which becomes a difficult task when each camera must be individually aligned. Whereas in the wafer level bonding method 100, all thousands of individual cameras are aligned in a single operation. Thus, the method 100 provides substantial benefits in terms of the complexity and cost of camera manufacturing. Furthermore, the method 100 may provide improved performance characteristics of the cameras 140, as a batch of cameras 140 produced from the lens wafer 110 and the image sensor wafer 120 will typically exhibit a low degree of camera-to-camera alignment deviation.

Embodiments of the wafer level bonding method 100 discussed below include specific steps associated with overcoming the challenges of bonding the image sensor wafer 120 and the lens wafer 110, including: (a) preventing warping of the image sensor wafer 120, which may adversely affect the alignment of the image sensor wafer 120 to the lens wafer 110, (b) obtaining an optical path through the adhesive layer for bonding the image sensor wafer 120 to the lens wafer 110, and (c) preventing cracking of the image sensor wafer 120 when bonded to the lens wafer 110.

Fig. 2 depicts an exemplary wafer level bonding method 200 for manufacturing a camera. The wafer level bonding method 200 is one embodiment of the wafer level bonding method 100 (fig. 1). In step 210, the method 200 receives an image sensor wafer, such as the image sensor wafer 120 of fig. 1. In step 220, the method 200 receives a lens wafer, such as the lens wafer 110 of FIG. 1. In step 230, the image sensor wafer and the lens wafer received in steps 210 and 220, respectively, are aligned with respect to each other. For example, the image sensor wafer 120 (fig. 1) is aligned with the lens wafer 110 (fig. 1) such that at least a portion of each individual lens 112 on the lens wafer 110 is aligned with a corresponding image sensor 122 on the image sensor wafer 120. Alignment may be performed using optical or mechanical referencing methods, or a combination thereof. In step 240, the image sensor wafer is bonded to the lens wafer to form a composite wafer. Because at least a portion of the lenses on each lens wafer are aligned with corresponding image sensors on the image sensor wafer in step 240, the composite wafer includes cameras, where each camera includes a lens and an image sensor on the lens and image sensor wafers, respectively. For example, the image sensor wafer 120 (fig. 1) is bonded to the lens wafer 110 (fig. 1) such that the resulting composite wafer 130 (fig. 1) includes a plurality of cameras 140 (fig. 1). In one embodiment, the bonding is accomplished using an optically clear adhesive, such as epoxy, Ultraviolet (UV) curable epoxy, thermal cured epoxy, dry film, or pressure sensitive adhesive, such that the alignment in step 230 may be performed optically through the adhesive between the image sensor wafer and the lens wafer. In another embodiment, step 230 utilizes other bonding methods known in the art, such as direct bonding, annealing, or plasma activated bonding.

In one embodiment, method 200 further includes one or both of steps 212 and 214 performed after step 210 and before step 230. In step 212, the image sensor wafer received in step 210 is modified to reduce the risk of warping of the image sensor wafer. Warping may adversely affect the alignment action performed at step 230. Thus, step 212 is used to improve the alignment characteristics achieved in step 230. Step 212 may include reducing the risk of warping by at least partially relieving stress in the image sensor wafer, such as applying stress-relieving cuts to the image sensor wafer. In one example, the stress in image sensor wafer 120 (fig. 1) is at least partially relieved before image sensor wafer 120 is aligned with lens wafer 110 (fig. 1). In step 214, the image sensor wafer received in step 210, and optionally modified in step 212, is modified in step 240 of bonding with a lens wafer to reduce the risk of cracking the image sensor wafer. For example, the image sensor wafer 120 (fig. 1) is modified in the bonding with the lens wafer 110 (fig. 1) to reduce the risk of the image sensor wafer cracking. Step 214 may be advantageously included in one embodiment of the method 200, wherein step 240 includes applying mechanical pressure to the image sensor wafer. Image sensor wafers are typically more fragile than a single image sensor. In one embodiment of the method 200 including step 212, the modification made in step 212 may increase the vulnerability of the wafer at the image sensor. Step 214 is used to prepare the image sensor wafer for bonding so that the image sensor wafer does not crack during step 240. In one example, the image sensor wafer is modified to avoid or reduce the importance of local pressure points associated with non-planarity of the surface of the image sensor wafer away from the lens wafer in step 240. The non-planarity may result from, for example, solder bump on an image sensor wafer. In another example, the image sensor wafer is reinforced by a reinforcing support structure mounted thereon. Step 214 may be performed after step 230 and before step 240 without departing from the scope of the present invention.

In one embodiment, the method 200 further includes a step 250, which is performed after the step 240. In step 250, the composite wafer formed in step 240 is diced to form a plurality of cameras. For example, the composite wafer 130 (fig. 1) is diced to form a plurality of cameras 140 (fig. 1). Step 250 may include masking the composite wafer prior to dicing and removing the mask after dicing.

In one embodiment, method 200 includes one or two steps 201 and 202 for forming the image sensor wafer and the lens wafer, respectively. Steps 201 and 202 may be performed using methods known in the art.

Fig. 3 illustrates an exemplary method 300 for modifying an image sensor wafer to reduce the risk of warping the image sensor wafer. Method 300 is one embodiment of step 212 in method 200 (FIG. 2). In step 310, at least one stress relaxation trench is formed in the image sensor wafer at a portion that does not overlap the image sensor. For example, at least one stress relaxation trench is formed in the image sensor wafer 120 (fig. 1) at a portion that does not overlap with the image sensor 122 (fig. 1). In one embodiment, each of the at least one stress relaxation trench is formed by making a cut in an image sensor wafer, wherein the cut does not penetrate completely through the image sensor wafer. In another embodiment, at least a portion of the at least one stress relaxation trench is formed by making a cut in an image sensor wafer, wherein a small portion of the length of the cut penetrates the image sensor wafer.

In one embodiment, step 310 includes step 320, wherein at least one stress relaxation trench is formed that spans the planar width of the image sensor wafer in a first direction. For example, at least one stress relaxation trench is formed on image sensor wafer 120 (fig. 1) such that the stress relaxation trench spans the entire width of image sensor wafer 120 in a direction in the plane of image sensor wafer 120. In one embodiment, step 310 further includes a step 330 in which at least one stress relaxation trench is formed that spans the planar width of the image sensor wafer in a second direction different from the first direction. For example, at least one stress relaxation trench is formed on image sensor wafer 120 (fig. 1) such that the stress relaxation trench spans the entire width of image sensor wafer 120 in a direction in the plane of image sensor wafer 120 that is different from the direction used in step 320. The combination of steps 310 and 320 may provide stress relief to prevent or reduce warpage in any direction along the in-plane of the image sensor wafer.

Fig. 4A and 4B illustrate an exemplary image sensor wafer 400 having one or more stress relaxation trenches. According to method 300 (fig. 3), image sensor wafer 400 may be the result of modifying an image sensor wafer, such as image sensor wafer 120 (fig. 1). Fig. 4A and 4B show a top view and a side cross-sectional view, respectively, of an image sensor wafer 400. Fig. 4A and 4B are best viewed together. Image sensor wafer 400 includes a sensor layer 450 and a cover glass layer 460 disposed on the sensor layer 450. Image sensor wafer 400 includes a plurality of image sensors 122, each of which includes a bare image sensor 451 and a portion of a cover glass layer 460. The image sensor 122 is capable of forming an image from light received through the cover glass layer 460. For clarity of illustration, not all of the image sensor 122 and the bare image sensor 451 are labeled in fig. 4A and 4B.

Image sensor wafer 400 includes stress relaxation trenches 410. The stress relaxation trench 410 is located between two rows of the image sensor 122. The stress relaxation trench 410 penetrates completely through the sensor layer 450 and only a small portion of the cover glass layer 460 greater than zero and less than 1. Stress relaxation trenches 410 span the planar width of image sensor wafer 400 along direction 401. Optionally, image sensor wafer 400 includes an additional stress relaxation trench 420 that also spans the planar width of image sensor wafer 400 along direction 401. In one embodiment, image sensor wafer 400 includes one or more stress relaxation trenches 430 that span the planar width of image sensor wafer 400 in direction 402. Direction 402 is substantially perpendicular to direction 401.

Although the stress relaxation trenches 410, 420, and 430 shown in fig. 4A span the entire width of the image sensor wafer 400, they may span only a portion of the planar width of the image sensor wafer 400 without departing from the scope of the present invention. Likewise, image sensor wafer 400 may include more stress relaxation trenches than shown in fig. 4A and 4B and/or stress relaxation trenches arranged in a different manner than shown in fig. 4A and 4B without departing from the scope of the present invention.

Fig. 5 illustrates an exemplary wafer level bonding method 500 for manufacturing cameras that uses a pressure sensitive adhesive to bond an image sensor wafer, such as image sensor wafer 120 (fig. 1), to a lens wafer, such as lens wafer 110 (fig. 1). Method 500 is one embodiment of method 200 (fig. 2). In step 510, the method 500 performs step 210 and optionally performs one or both of steps 201 and 212 of the method 200 (fig. 2). If included in step 510, step 212 may be performed in accordance with method 300 (FIG. 3). In step 514, a protective layer is coated on the image sensor wafer, such as image sensor wafer 120 (fig. 1), such that the protective layer encapsulates at least a portion of the solder bumps of the image sensor wafer. Step 514 is one embodiment of step 214 (FIG. 2). In one embodiment, the protective layer is an ultraviolet light releasable tape.

Fig. 6 illustrates an exemplary image sensor 600 and a passivation layer encapsulating the solder bumps of the image sensor 600. Image sensor 600 illustrates one embodiment of step 514 of method 500 (fig. 5). The image sensor 600 includes a bare image sensor 451 (fig. 4), which in turn includes a solder bump 610 on a surface of the bare image sensor 451 opposite to a light receiving surface. The image sensor 600 further includes a passivation layer 620 encapsulating the solder bump 610. In one embodiment, the protective layer 620 has a thickness and buffer to redistribute local pressure that would otherwise be applied to only the solder bump excluding other portions of the image sensor wafer. For example, the protective layer may redistribute pressure from over the solder bump to portions of the image sensor wafer located between the solder bump. In another embodiment, the protective layer 620 has grooves matching the positions of the solder bump bumps, so that pressure applied to the protective layer 620 in a direction toward the bare image sensor 451 is applied only to a portion of the bare image sensor 451 that is located differently from the solder bump bumps 610. While fig. 6 illustrates only a single bare image sensor 451, the protective layer 620 may span a large portion of the image sensor wafer, including portions that do not include image sensors, without departing from the scope of the invention. For clarity, not all of the solder bumps 610 are labeled in fig. 6.

Referring again to FIG. 5, in step 520, the method 500 performs step 220 and optionally step 202 of the method 200 (FIG. 2). In step 530, the method 500 performs step 230 of the method 200 (fig. 2). In step 540, which is one embodiment of step 240 (fig. 2), a composite wafer is formed from the image sensor wafer bonded to the lens wafer using a pressure sensitive adhesive. For example, composite wafer 130 (fig. 1) is formed by bonding image sensor wafer 120 (fig. 1) to lens wafer 110 (fig. 1) using a pressure sensitive adhesive. Pressure sensitive adhesive based bonding requires the application of mechanical pressure to the image sensor wafer and the lens wafer with a pressure sensitive adhesive applied between them. The mechanical pressure presses the image sensor wafer, the pressure sensitive adhesive and the lens wafer together. The solder bumps on the image sensor wafer typically protrude from the surface of the image sensor wafer. If mechanical pressure is applied to the unprotected solder bump, there is a risk that the solder bump may crack and/or that local pressure transmitted by the solder bump to other portions of the image sensor wafer in contact with the solder bump may crack the image sensor wafer. The protective layer applied in step 514 has the function of reducing the risk of such cracking. In one embodiment, pressure is applied to only a portion of the image sensor wafer. In this embodiment, step 514 may cover the entire surface of the image sensor wafer facing away from the lens wafer or only a portion thereof with a protective layer.

In step 545, the protective layer covered in step is removed. In one embodiment, associated with the protective layer is an ultraviolet light releasable tape, the protective layer being removed by exposing the protective layer to ultraviolet light. In another embodiment, the protective layer is removed mechanically or chemically, or using a combination of mechanical, chemical and/or optical methods. Optionally, method 500 further includes step 550, which performs step 250 of method 200 (fig. 2). In an alternative embodiment, step 545, not shown in FIG. 5, is performed after step 550.

Fig. 7 illustrates an exemplary wafer level bonding method 700 for manufacturing cameras that utilizes pressure sensitive adhesives to bond an image sensor wafer to a lens wafer. The pressure sensitive adhesive is applied to the lens wafer prior to bonding the lens wafer to the image sensor wafer. Method 700 includes a step of reducing entrapment of air bubbles in the pressure sensitive adhesive and includes an optional step for removing such air bubbles. Method 700 is one embodiment of method 500 (fig. 5). In a step 710, the method 700 performs steps 510 and 514 of the method 500 (fig. 5).

In step 710, method 700 performs steps 510 and 514 of method 500 (FIG. 5). In step 720, method 700 performs step 520 of method 500 (FIG. 5). Step 720 is followed by optional step 721, step 722, and optional step 723, in that order. In optional step 721, the lens wafer is pre-cleaned to prepare the lens wafer for application of the pressure sensitive adhesive. For example, lens wafer 110 (fig. 1) is cleaned using a solvent. In step 722, a pressure sensitive adhesive is applied to the lens wafer. For example, a pressure sensitive adhesive is applied to the lens wafer 110 (FIG. 1). In optional step 726, the lens wafer is hot pressed, i.e., exposed to elevated temperature and pressure, to remove air bubbles trapped at the interface between the pressure sensitive adhesive and the lens wafer and/or to remove air bubbles from the pressure sensitive adhesive. For example, the lens wafer 110 (FIG. 1) having a pressure sensitive adhesive adhered thereto is hot pressed.

In step 730, method 700 performs step 530 of method 500 (FIG. 5). After performing step 730, method 700 performs steps 741, 742, and optionally step 743. Steps 741, 742, along with optional step 743, form one embodiment of step 540 of method 500 (FIG. 5). In step 741, the image sensor wafer is contacted with the pressure sensitive adhesive applied to the lens wafer in step 722. For example, image sensor wafer 120 (FIG. 1) is contacted with a pressure sensitive adhesive applied to lens wafer 110 (FIG. 1) in step 722. To reduce air bubbles trapped in the interface of the pressure sensitive adhesive and the image sensor wafer, the image sensor wafer is contacted with the pressure sensitive adhesive with low mechanical pressure. The low mechanical pressure is sufficient to mechanically attach the image sensor wafer to the pressure sensitive adhesive, but insufficient to adequately bond the pressure sensitive adhesive to the image sensor wafer. Thus, at least a portion of the air at the interface between the image sensor wafer and the pressure sensitive adhesive has one or more passageways connecting to the surrounding atmosphere. In step 742, the image sensor wafer and the lens wafer are bonded together using a pressure sensitive adhesive, such as image sensor wafer 120 (fig. 1) and lens wafer 110 (fig. 1). This results in the formation of a composite wafer, such as composite wafer 130 (fig. 1). Step 742 is performed under vacuum, or at least under reduced pressure compared to standard atmospheric pressure, and includes applying mechanical pressure to the image sensor wafer and the lens wafer to press the image sensor wafer and the lens wafer together. When the image sensor wafer is pressed against the lens wafer, at least a portion of the air at the interface of the image sensor wafer and the pressure sensitive adhesive and optionally at least a portion of any air at the interface with the lens wafer and the pressure sensitive adhesive is drawn away. Thus, the amount of air trapped at the interface between the pressure sensitive adhesive and the image sensor wafer, and optionally the interface between the pressure sensitive adhesive and the lens wafer, will be reduced.

In optional step 743, the composite wafer is hot pressed to remove at least a portion of residual bubbles from the pressure sensitive adhesive and the interface between the pressure sensitive adhesive and the image sensor wafer and the lens wafer. For example, composite wafer 130 (fig. 3) is hot pressed to remove residual air bubbles from the pressure sensitive adhesive applied at step 722, the interface between the pressure sensitive adhesive and image sensor wafer 120 (fig. 1), and the interface between the pressure sensitive adhesive and lens wafer 110 (fig. 1).

In step 745, method 700 performs step 545 of method 500 (FIG. 5). Optionally, method 700 further includes step 750 of performing step 550 of method 500 (fig. 5).

Fig. 8 illustrates an exemplary method 800 for optically aligning an image sensor wafer, such as image sensor wafer 120 (fig. 1), with a lens wafer, such as lens wafer 110 (fig. 1). Method 800 is one embodiment of step 230 of method 200 (FIG. 2). In step 810, the image sensor wafer is aligned using an optical path through the lens wafer to the image sensor wafer. For example, the image sensor wafer 120 (fig. 1) is aligned with the lens wafer 110 (fig. 1) using an optical path through the lens wafer 110 to the image sensor wafer 120. In one embodiment, step 810 includes step 820, wherein at least two reference marks on the lens wafer are aligned with at least two corresponding image sensors in the image sensor wafer. The alignment may be visually assessed, assisted by optical viewing instruments, or automatically assisted by optical instruments.

Fig. 9A and 9B illustrate by way of example a pair of an exemplary image sensor wafer and lens wafer of step 820. Fig. 9A and 9B are best viewed together. Fig. 9A is a diagram 901 showing a perspective view of image sensor wafer 120 (fig. 1) aligned relative to lens wafer 910. Lens wafer 910 is one embodiment of lens wafer 110 (fig. 1) and includes two reference marks 920 in addition to the plurality of lenses 112 (fig. 1). Reference mark 920 is located in lens wafer 910 at a portion that coincides with a respective optical path 930 through lens wafer 910 to image sensor wafer 120. In one embodiment, reference numeral 920 is a lens 112. In another embodiment, reference mark 920 is an optically transparent portion of lens wafer 910, each of which includes a feature, such as an aperture, for evaluating the position of reference mark 920. Fig. 9B illustrates a circular reference mark 920, and the reference mark 920 may have other shapes, such as a square, a rectangle, a circle, or a cross, without departing from the scope of the present invention. In yet another embodiment, all of lens wafer 910 is optically transparent, and reference mark 920 is characterized, for example, by being located on the surface of lens wafer 910 for evaluating the location of reference mark 920. Two of the image sensors 122 of the image sensor wafer 120 serve as reference marks 940. In one embodiment, each reference mark 940 is a contour of a photosensitive surface of the image sensor 122. In one embodiment of the profile of the photosensitive surface, each reference mark 940 is a color filter of the image sensor 122, wherein the color filter of the color filter may be an infrared filter and/or a color filter array for providing color imaging functionality, such as a bayer-type color filter array. Step 820 of method 800 (FIG. 8) aligns the reference marks 920 with the corresponding reference marks 940 using optical path 930. For clarity of illustration, not all of the lens 112 and image sensor 122 are labeled in fig. 9A. While fig. 9A shows that when the reference mark 940 is overlapped with the outermost image sensor 122, the reference mark 940 may be overlapped with the image sensor 122 located inside the array of image sensors 122 of the image sensor wafer 120 without departing from the scope of the present invention.

FIG. 9B shows a simplified top view 902 of the alignment of reference mark 920 with reference mark 940. Fig. 9B thus depicts a view along one optical path 930. The optical path 930 is used so that the positions of the reference marks 920 are projected onto the plane of the image sensor wafer 120 while the centers of the reference marks 940 are positioned at a common position 950. Optical assessment of the positioning of the reference mark 920 relative to the reference mark 940 may be aided by a light guide provided by an optical scope, such as a crosshair 960.

Returning to fig. 8, one embodiment of step 810 includes step 830, wherein the act of aligning is further performed with an optical path through an optically clear adhesive disposed between the image sensor wafer and the lens wafer. Step 830 is useful for implementing method 800 in a wafer level bonding method where an adhesive is applied to one or both sides of the image sensor wafer and the lens wafer prior to alignment as in method 700 (fig. 7). Step 830 assumes that the adhesive is optically clear so that method 800 can be performed on an image sensor wafer and a lens wafer with adhesive therebetween. Optically clear adhesives include certain types of pressure sensitive adhesives, dry films, and epoxies. Embodiments of method 800 including step 830 may be advantageously implemented in methods 500 (fig. 5) and 700 (fig. 7) as steps 530 and 730, respectively.

Fig. 10 depicts an exemplary camera 1000 made in accordance with method 200 (fig. 2) including step 250 (fig. 2). Camera 1000 is one embodiment of camera 140 (FIG. 1). The camera 1000 includes an image sensor portion 1010 of a rectangular cubic shape and a lens portion 1020 of a rectangular cubic shape. In one embodiment, the camera 1000 further includes an adhesive layer 1030 having a rectangular cubic shape disposed between the image sensor portion 1010 and the lens portion 1020. Image sensor portion 1010 is a portion of image sensor wafer 120 (fig. 1) that includes one image sensor 122 (fig. 1). The lens portion 1020 is a portion of the lens wafer 110 (fig. 1) that includes one lens 112 (fig. 1). In certain embodiments, the adhesive layer 1030 is a pressure sensitive adhesive.

The camera 1010 has a bottom surface 1050, a top surface 1060, and four side surfaces 1070. For clarity of illustration, only one of the four sides 1070 is labeled in fig. 10. Each side 1070 includes a surface of lens portion 1020, a surface of image sensor portion 1010, and optionally a surface of adhesive layer 1030. Camera 1010 is the product of step 250 of method 200 (fig. 2). Thus, for each side 1070, all portions of side 1070 are formed in the same cutting operation. Thus, side 1070 is flat without the step associated with the interface between image sensor portion 1010, lens portion 1020, and optional adhesive layer 1030.

The methods disclosed herein may be implemented in conjunction with the methods disclosed in U.S. patent application entitled "System And Method For Wafer Level Black Coating Of Camera cube" co-filed with attorney docket No. 554361.

Feature combination

The features mentioned above as well as in the following claims can be combined in various ways without departing from the scope of the invention. For example, it may be understood that one wafer level bonding method for manufacturing a camera or aspects associated with a camera described herein may be combined with or exchanged with another wafer level bonding method for manufacturing a camera or features associated with a camera described herein. The following examples illustrate possible, non-limiting combinations of the above embodiments. It will be understood that numerous other variations and modifications may be made to the methods and apparatus described herein without departing from the spirit and scope of the invention:

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

(B) The wafer level method of (a) may further comprise bonding the image sensor wafer to a lens wafer to form a composite wafer comprising a plurality of cameras.

(C) As in the wafer level method shown in (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 method as shown in (B) and (C) may further include covering a protective layer on the image sensor wafer to reduce the risk of cracking the image sensor wafer during the bonding step.

(E) As in the wafer level method shown in (D), the passivation layer may encapsulate the solder bumps of the image sensor wafer.

(F) As in the wafer level processes shown in (D) and (E), the protective layer may be an ultraviolet light releasable tape.

(G) The wafer level method as shown in (F) may further comprise removing the protective layer with ultraviolet light after the bonding step.

(H) The wafer level method of (B) through (G) may further include optically aligning the image sensor wafer and the lens wafer.

(I) As in the wafer level method of (H), the step of aligning may include aligning at least two alignment marks of the lens wafer with two of the plurality of image sensors via an optical path through the lens wafer.

(J) The wafer level process of (H) and (I) may further comprise applying an optically clear adhesive to the lens wafer.

(K) As in the wafer level method of (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) As in the wafer level processes shown in (J) and (K), the optically clear adhesive can be a pressure sensitive adhesive.

(M) in the wafer level method as shown in (a) through (L), the step of modifying the image sensor wafer to reduce the risk of warping may include relieving stress from the image sensor wafer.

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

(O) in the wafer level method as shown in (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 pressure includes applying at least one cut to a portion of the image sensor wafer that does not overlap an image sensor, wherein the at least one cut penetrates the sensor layer and forms a trench in the cover glass layer.

(P) in the wafer level method as shown in (O), the step of applying at least one kerf may comprise applying at least one kerf that traverses a planar width of the image sensor wafer along a first direction.

(Q) as in the wafer level method of (P), the step of applying at least one kerf may further comprise applying at least one kerf that spans a planar width of the image sensor wafer along a second direction, the second direction being different from the first direction.

(R) a wafer-level method for manufacturing a plurality of cameras may include bonding the image sensor wafer to a lens wafer using a pressure sensitive adhesive to form a composite wafer including a plurality of cameras.

(S) the wafer level method of (R) may further comprise modifying the image sensor wafer to reduce the risk of warping of the image sensor wafer.

(T) in the wafer level method as shown in (S), the step of modifying may include covering a protective layer on the image sensor wafer.

(U) as in the wafer level method of (T), the passivation layer may encapsulate the solder bumps of the image sensor wafer.

(V) as in the wafer level processes shown in (T) and (U), the protective layer may be an ultraviolet light releasable tape.

(W) the wafer level method of (V) may further comprise removing the protective layer with ultraviolet light after the bonding step.

(X) the wafer level process of (R) to (W) may further comprise coating a pressure sensitive adhesive on the lens wafer, wherein the pressure sensitive adhesive is optically clear.

(Y) the wafer level method of (X) may further comprise aligning the image sensor wafer and the lens wafer using an optical path through the lens wafer and the pressure sensitive adhesive.

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

(AA) as in the wafer level method shown in (R) to (Z), the step of bonding may include contacting the image sensor with the pressure sensitive adhesive and applying mechanical pressure to the image sensor wafer and the lens wafer under vacuum to form the composite wafer.

(AB) as in the wafer level method of (R) to (AA), the step of bonding may further include heat pressing the composite wafer to remove air bubbles from at least one of the pressure sensitive adhesive, an interface between the pressure sensitive adhesive and the image sensor wafer, and an interface between the pressure sensitive adhesive and the lens wafer.

(AC) as in the wafer-level method shown in (R) to (AB), the step of bonding may include cleaning a surface portion of the lens wafer on which the pressure-sensitive adhesive is applied in the step of applying the pressure-sensitive adhesive.

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

(AE) as in the wafer level method shown in (R) to (AC), the step of bonding may include hot pressing the lens wafer coated with the pressure sensitive adhesive to remove air bubbles from at least one of the pressure sensitive adhesive and an interface between the pressure sensitive adhesive and the lens wafer.

Changes may be made in the above described systems and methods without departing from the scope of the invention. It is intended, therefore, that the matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.

Claims (11)

1. A wafer-level method for manufacturing a plurality of cameras, comprising:

forming at least one stress-relieved cut in an image sensor wafer having a sensor layer using a plurality of image sensors and a cover glass layer disposed on the sensor layer to reduce a risk of warping of the image sensor wafer, the at least one stress-relieved cut passing through the sensor layer and forming a trench in the cover glass layer; and

the image sensor wafer is bonded to a lens wafer using a pressure sensitive adhesive to form a composite wafer comprising a plurality of cameras.

2. The wafer level method of claim 1, at least one notch is located at a portion of the image sensor wafer that does not overlap any of the image sensors.

3. The wafer level method of claim 1, the step of forming at least one cut comprising applying at least one first cut across a planar width of the image sensor wafer along a first direction.

4. The wafer level method of claim 3, the step of applying at least one notch further comprising applying at least one second notch that spans a planar width of the image sensor wafer along a second direction, the second direction being different from the first direction.

5. The wafer level method of claim 1, further comprising covering a protective layer on the image sensor wafer to reduce a risk of cracking the image sensor wafer during the bonding step, the protective layer encapsulating the solder bump of the image sensor wafer.

6. The wafer-level method of claim 5, wherein the protective layer is an ultraviolet light releasable tape, the wafer-level method further comprising removing the protective layer with ultraviolet light after the bonding step.

7. The wafer level method of claim 1, further comprising optically aligning the image sensor wafer and the lens wafer.

8. The wafer level method of claim 7, the step of aligning comprising aligning at least two alignment marks of the lens wafer with two image sensors of the image sensor wafer via an optical path through the lens wafer.

9. The wafer level method of claim 8, further comprising applying an optically clear adhesive to the lens wafer, the bonding step comprising bonding the image sensor wafer to the lens wafer using the optically clear adhesive, the aligning step being performed after the applying an optically clear adhesive and before the bonding step.

10. The wafer level method of claim 9, the optically clear adhesive being a pressure sensitive adhesive.

11. The wafer level method of claim 1, in the step of forming, a cover glass layer disposed on the sensor layer is in direct contact with the sensor layer.