Patent Application
20110278692
1. Field of the Invention
The present invention relates to a solid-state image sensing device for use in a digital camera, or the like, and a method for manufacturing the same.
2. Description of the Background Art
In the field of solid-state image sensing packages, the pixel size has been reduced, and therefore techniques have been researched and developed for increasing the sensitivity.
A conventional solid-state image sensing package is obtained by mounting a solid-state image sensing element on a package, and then placing a glass plate above the image sensing surface in order to protect the image sensing surface and fixing the glass plate to the package. A package of this structure is called a hollow package, where there is air between the solid-state image sensing element and the glass.
With this structure, light entering the solid-state image sensing package is reflected at the upper and lower surfaces of the glass and the surface of the solid-state image sensing element, thus losing some of the incident light. This is because there is a large refractive index difference between the air, the glass and the microlens.
In view of this, a direct-attachment package as shown in
However, the structure of Japanese Laid-Open Patent Publication No. 2000-323692 has the following problem. The adhesive 105 is applied on the semiconductor chip 101b, and then the light transparent substrate 102 is placed thereon. Even if the light receiving portion 101a and the group of microlenses 103 are aligned with each other in advance, the light transparent substrate 102 slides out of alignment (see
Specifically, the liquid adhesive 105 is dropped on the surface of the semiconductor chip 101b, and then the light transparent substrate 102 is placed thereon in position. Before the placement of the light transparent substrate 102, the adhesive 105 is yet to spread across the entire surface of the semiconductor chip 101b. The adhesive 105 later spreads across the space between the semiconductor chip 101b and the light transparent substrate 102 due to the weight of the light transparent substrate 102 being placed thereon. At this point, the light transparent substrate 102 may move (slide) together with the spreading (flow) of the adhesive 105.
After the light transparent substrate 102 is attached, pads of the semiconductor chip 101b and terminals of a package 110 are connected to each other by way of wire bonding. If the position of the light transparent substrate 102 is misaligned toward the pads, the light transparent substrate 102 interferes with a capillary 122 of the bonding apparatus, as shown in
Therefore, it is an object of the present invention to provide a solid-state image sensing device of a direct-attachment structure in which a light transparent substrate and a semiconductor substrate are directly attached to each other with a light transparent adhesive therebetween, wherein the light transparent substrate is prevented from sliding out of alignment when the light transparent substrate is attached to a solid-state image sensing element with an adhesive.
In order to achieve the object set forth above, the present invention provides a solid-state image sensing device, in which a protruding portion is provided on a light receiving surface of an image sensing element, wherein the protruding portion is in contact with a light transparent substrate.
Specifically, a solid-state image sensing device of the present invention includes a solid-state image sensing element and a light transparent substrate, wherein: the solid-state image sensing element is provided with a light receiving portion, and a light receiving surface of the solid-state image sensing element includes an effective pixel section in a central area, and includes, outside the effective pixel section, an electrode pad portion and a protruding portion protruding from the light receiving surface; the solid-state image sensing element and the light transparent substrate are attached to each other by an adhesive applied on the effective pixel section; the adhesive includes a thermosetting or photosetting resin; and the light transparent substrate is placed on at least a portion of the protruding portion. The thermosetting or photosetting resin included in the adhesive may be a hardened resin.
With such a configuration, the light transparent substrate is in contact with the protruding portion, whereby it is possible to prevent the relative position of the light transparent substrate with respect to the effective pixel section of the light transparent substrate from being shifted.
It is preferred that the friction coefficient between the protruding portion and the light transparent substrate is 0.1 or more.
It is preferred that the protruding portion has an equal protruding height across an area over which the light transparent substrate lies on the protruding portion. This means that where there are a plurality of protruding portions on which the light transparent substrate lies, the protruding portions have an equal protruding height, and where the light transparent substrate lies on a continuously extending portion, the height is the same across the continuously extending portion.
In one embodiment of the invention, at least a portion of the protruding portion lies between the effective pixel section and the electrode pad portion.
In one embodiment of the invention, the protruding portion extends in a ridge shape along the electrode pad portion between the effective pixel section and the electrode pad portion.
In one embodiment of the invention, the light transparent substrate lies on a portion of the ridge-shaped protruding portion.
In one embodiment of the invention, at least two protruding portions extend adjacent to and in parallel to each other between the effective pixel section and the electrode pad portion.
In one embodiment of the invention, there are a plurality of protruding portions each extending in a ridge shape; there are at least a set of protruding portions extending adjacent to and in parallel to each other; one of the set of protruding portions that lies closer to an edge of the solid-state image sensing element has a greater protruding height than another one of the set of protruding portions.
A method for manufacturing a solid-state image sensing device of the present invention includes the steps of: providing a solid-state image sensing element provided with a light receiving portion; forming a protruding portion protruding from a light receiving surface of the solid-state image sensing element in at least a portion of a surrounding area around the light receiving portion; applying a liquid adhesive on the light receiving portion; placing a light transparent substrate on the adhesive so that the light transparent substrate contacts at least a portion of the protruding portion; and hardening the adhesive.
Solid-state image sensing devices according to preferred embodiments of the present invention will now be described with reference to the drawings.
The solid-state image sensing device of the present embodiment includes a solid-state image sensing element 1 provided with a light receiving portion, and a light transparent substrate 3 attached to the light receiving surface of the solid-state image sensing element 1 via a transparent adhesive 14. The solid-state image sensing element 1 is in a rectangular plate shape, and a rectangular effective pixel section 17 being a part of the light receiving portion is provided in a central area of the light receiving surface. On the light receiving surface of the solid-state image sensing element 1, a row of electrode pad portions 15 extends on the outer side of one side of the effective pixel section 17 and another row on the outer side of another, opposing side of the effective pixel section 17. Between the effective pixel section 17 and each row of the electrode pad portions 15, there is a ridge-shaped protruding portion 16 extending in parallel to the row of the electrode pad portions 15.
The effective pixel section 17 includes an image sensing portion of the solid-state image sensing element 1, and microlenses (on-chip microlenses) provided thereon.
The adhesive 14 is applied on the effective pixel section 17, and the light transparent substrate 3 is placed thereon. Two opposing sides of the rectangular light transparent substrate 3 lie on the protruding portions 16 and 16.
The solid-state image sensing device of the present embodiment is mounted on a package substrate 2, and the electrode pad portions 15 are electrically connected to lead terminals 5 exposed on the outside of the package substrate 2 via wires 4, thus forming a solid-state image sensing package.
The light transparent substrate 3 may be of an inorganic material (a borosilicate glass, a quartz glass, etc.), an organic material (an acrylic resin, a polycarbonate resin, an olefin resin, etc.), or a hybrid thereof.
Thus, it is required that the light transparent substrate 3 has a high visible light transmittance, can be processed into a flat (plate) shape, and can be bonded by the adhesive 14 to be described below. Where an organic material is used for the light transparent substrate 3, if the anti-shock property is poor, it is more preferred to use a hybrid material containing an inorganic material added as a filler. In this case, the transparent substrate 3 may become translucent substrate. The use of a borosilicate glass as the light transparent substrate 3 is more advantageous in view of the possibility of handling scratches, the anti-solvent property during manufacture, and the cost. The use of quartz as the light transparent substrate 3 is also more advantageous in view of the possibility of handling scratches, and the anti-solvent property during manufacture.
With the conventional hollow package, light entering the solid-state image sensing element is reflected at the upper and lower surfaces of the glass and the surface of the semiconductor substrate, thus losing some of the incident light. This is because of the large refractive index difference between the air, the glass and the microlenses.
In contrast, the solid-state image sensing device of the present embodiment has a structure in which the light transparent substrate 3 is directly attached to the light receiving portion with the adhesive 14 therebetween. Then, the portion corresponding to the air in a conventional structure is filled with the adhesive 14 being used for attaching the light transparent substrate 3, and the adhesive 14 has a greater refractive index than that of air. As a result, it is possible to reduce the refractive index difference between the light transparent substrate 3, the adhesive 14 and the solid-state image sensing element 1, thereby reducing the loss of light due to reflections.
Moreover, the protruding portions 16 are formed on the solid-state image sensing element 1 in order to prevent the light transparent substrate 3 from sliding when the light transparent substrate 3 is placed on the adhesive 14 applied on the solid-state image sensing element 1. The provision of the protruding portions 16 prevents the light transparent substrate 3 from sliding as follows.
Where only the liquid adhesive 14 is present between the light transparent substrate 3 and the solid-state image sensing element 1, with no protruding portions 16 therebetween, the adhesive 14 serves as a lubricant, and the friction between the light transparent substrate 3 and the solid-state image sensing element 1 is a fluid friction, whereby the friction resistance is equal to the viscosity resistance of the adhesive 14. In this state, the friction coefficient is less than 0.01 based on the Stribeck curve, and the light transparent substrate 3 slides easily even with a small horizontal force.
In the present embodiment, the light transparent substrate 3 is in contact with the solid protruding portions 16, and the friction therebetween is believed to be a dry friction or a boundary friction, whereby the friction coefficient is 0.1 or more based on the Stribeck curve, or 0.2 or more if the protruding portion 16 is formed by a resin material as shown below. Since there is a sufficient frictional force between the light transparent substrate 3 and the protruding portions 16, the light transparent substrate 3 will not slide even if there is some horizontal force acting on the light transparent substrate 3 during manufacture. If the light transparent substrate 3 can be attached and fixed to the solid-state image sensing element 1 while being aligned thereto, the microlens will not be misaligned, and it is possible to avoid a problem in the wire bonding step as shown in
The protruding portions 16 are formed by a resin, for example, and the resin material may be a common positive or negative photosensitive resin such as an acrylic resin, a styrene resin or a phenol novolak resin, or an organic resin such as a urethane resin, an epoxy resin or a styrene resin. The patterning process for forming the protruding portions 16 is performed by a photolithography when using a photosensitive resin, and by a liftoff process otherwise.
The main component of the light transparent adhesive 14 is a thermosetting or photosetting resin. Therefore, the adhesive 14 is a liquid upon application, but becomes a solid when a heat or light is applied thereto after the light transparent substrate 3 is placed thereon.
In the present embodiment, each protruding portion 16 is provided between the effective pixel section 17 and the electrode pad portions 15, with its width and height being precisely controlled to intended values. If the width of the protruding portion 16 is greater than the intended value, there will be a shorter distance between the protruding portion 16 and the effective pixel section 17 or the electrode pad portions 15, thereby resulting in shadows and color irregularities (an image defect). If the height of the protruding portion 16 varies, the flatness of the light transparent substrate 3 to be placed thereon will be poor (i.e., it will be slanted with respect to the plane of the effective pixel section 17), thereby resulting in an image defect such as moiré. Color irregularities refer to an image defect as follows. When light enters the effective pixel section 17 of the solid-state image sensing device from an oblique direction, the light is blocked by the protruding portion 16, and the portion of the image near the light-blocking protruding portion 16 appears darker, resulting in a brightness difference between such a portion and other portions, which is seen as irregularities.
In the present embodiment, since each protruding portion 16 is provided between the effective pixel section 17 and the electrode pad portions 15, with its width and height being precisely controlled to intended values, it is possible to prevent image defects such as color irregularities and moiré.
If the protruding portion 16 has a larger width than the intended value, the wire bonding strength is lowered, thus resulting in a defect where the wires 4 cannot be connected to the electrode pads. In the present embodiment, it is possible to prevent such a defect.
In view of the precision or the process of patterning, it is more preferred that a photosensitive resin (positive or negative) is used for the protruding portions 16. Then, the protruding portions 16 can be produced with precisely-controlled width and height. Thus, the light transparent substrate 3 can be attached to a predetermined position while being flat, and it is possible to prevent the weakening of the wire bonding without affecting the image quality (i.e., without moiré or color irregularities).
If the same resin as the photosensitive resin used in the diffusion step or the on-chip microlens formation step of
The material of the protruding portions 16 may be a material obtained by adding about 0% to about 80% of a spherical, fibrous or indeterminate-form filler made of a resin, a glass or quartz to a binder resin. By using a resin material containing a filler therein, it is possible to increase the mechanical strength of the protruding portions 16.
If the thickness of the resin material of the protruding portions 16 is about 1 to about 50 μm, a film of the resin material can be formed in a single rotation application process. For larger thicknesses, the rotation application can be performed a plurality of times. With rotation application, the upper surface of the semiconductor substrate and the upper surface of the obtained film can be made substantially parallel to each other. Particularly, where a photosensitive resin is used to form the protruding portions 16, a film is formed by that photosensitive resin, and a photolithography process is performed to harden the portions to be the protruding portions 16 while peeling off unnecessary portions. In such a case, an apparatus for manufacturing the solid-state image sensing element 1 can be used as it is, and the production can be done at low cost. For example, the speed of the rotation application is about 1000 rpm to about 3000 rpm, the prebake temperature is about 80° C. to about 100° C., the exposure time is about 100 ms to about 1000 ms, and the developer is an alkali developer or an organic developer. Then, the postbaking process is performed at a temperature of about 200° C. to about 220° C.
Where the protruding portion 16 is formed by a resin that can be etched, a film of the resin is formed, and a mask is formed thereon, which selectively covers portions to be the protruding portions and has openings in other portions. Then, an etching process is performed to remove unnecessary portions while selectively leaving the portions to be the protruding portions 16. In this case, there is a greater variety of choice of resin materials.
The solid-state image sensing device of the present embodiment is produced by a process flow as shown in
In the present embodiment, the protruding portions 16 are formed to a predetermined height, the light transparent substrate 3 is placed on the adhesive 14 applied on the effective pixel section 17, and the light transparent substrate 3 is pressed down until the light transparent substrate 3 is in contact with the upper surface of the protruding portions 16 so as to spread the adhesive 14, after which the adhesive 14 is hardened. Since the protruding portions 16 are higher than the light receiving surface of the solid-state image sensing element 1, the solid-state image sensing element 1 can be prevented from being damaged during the pressing process.
Since the thickness of the adhesive 14 influences the light transmittance property, it is very important to realize a thickness as intended. With the present configuration, the interval between the solid-state image sensing element 1 and the light transparent substrate 3, i.e., the thickness of the adhesive 14, can be defined by the height of the protruding portions 16. There are two protruding portions 16 and 16 provided so as to interpose the effective pixel section 17 therebetween, and the protruding portions 16 and 16 have an equal height from the light receiving surface. Thus, the light transparent adhesive 14 can be formed to an intended thickness.
In the present embodiment, since the light transparent substrate 3 is attached to a predetermined position in the presence of the protruding portions 16, it is possible to eliminate the incidence of unnecessary light on the effective pixel section 17 (particularly, light coming from an oblique direction). Moreover, by defining the height of the two protruding portions 16 and 16, the light transparent substrate 3 can be attached while being flat. Since the two protruding portions 16 and 16 have an equal height, the light receiving surface of the solid-state image sensing element 1 and the light transparent substrate 3 can easily be arranged parallel to each other by placing the light transparent substrate 3 on both of the two protruding portions 16 and 16.
While the light transparent substrate 3 is attached to the surface of the solid-state image sensing element 1 via the adhesive 14, the adhesive 14 has a larger refractive index than that of the air. Thus, it is possible to reduce the refractive index difference between the light transparent substrate 3, the adhesive 14 and the solid-state image sensing element 1, thereby reducing the loss of light due to reflections. As a result, it is possible to obtain an image with a high sensitivity (with reduced reflection loss) without affecting the image quality (i.e., without moiré or color irregularities).
Since the protruding portions 16 each extend between a row of electrode pads and the effective pixel section 17, the adhesive 14 is blocked by the protruding portions 16 serving as a dam and will not reach the electrode pad portions 15, whereby the electrical connection between the wires can the electrode pad portions 15 is reliably made by wire bonding.
When the adhesive 14 is hardened, the adhesive 14 penetrates between the light transparent substrate 3 and the protruding portions 16, thereby enhancing the adhesion strength therebetween.
Next, variations of the shape of the protruding portions 16 will be described.
The protruding portion 16, 16b, 16c or 16d is provided for the purpose of suppressing the sliding of the light transparent substrate 3 when the light transparent substrate 3 is attached, and the sliding of the light transparent substrate 3 can be controlled by changing the shape of the upper surface of the protruding portion 16, 16b, 16c or 16d, i.e., by changing the contact area between the light transparent substrate 3 and the protruding portion 16, 16b, 16c or 16d.
Where the upper surface of the protruding portion 16 or 16d is parallel to the light receiving surface, the sliding of the light transparent substrate 3 can be controlled also by changing the width of the upper surface. Because of the contact area between the light transparent substrate 3 and the protruding portion, the most preferred is the upper surface being parallel to the light receiving surface, the second most preferred is the upper surface being depressed, and the third most preferred is the upper surface being upwardly protruding.
Where the upper surface of the protruding portions is parallel to the light receiving surface (e.g., the protruding portion 16 or 16d), the distance between the lower surface of the light transparent substrate 3 and the light receiving surface is constant, irrespective of the position on the protruding portions 16 and 16d at which the light transparent substrate 3 lies. This provides a further advantage of a large alignment margin for placing the light transparent substrate 3. Moreover, if a load is applied from above the light transparent substrate 3 after the light transparent substrate 3 is attached, the load is applied entirely across the protruding portion 16 or 16d, whereby deformation is unlikely to occur.
Where the upper surface of the protruding portions is upwardly protruding (e.g., the protruding portion 16b), since the protruding portion 16b has no corners, it is possible to suppress the generation of chips due to chipping/shaving of the protruding portion 16b as the light transparent substrate 3 contacts the protruding portion 16b.
Where the upper surface of the protruding portions is depressed (e.g., the protruding portion 16c), the adhesive 14 permeates also into the gap between the light transparent substrate 3 and the protruding portion 16c during the attachment of the light transparent substrate 3, and the adhesive 14 can partly be pushed out of the protruding portion 16c. This varies the contact area between the light transparent substrate 3 and the protruding portion 16c, whereby it is possible to control the sliding of the light transparent substrate 3.
Where the protruding portions are tapered (into a trapezoidal shape) as shown in
A solid-state image sensing device of Embodiment 2 is the same as that of Embodiment 1, except for the protruding portions, which will now be described below.
In the present embodiment, the two protruding portions 26a and 26b formed along one side of the solid-state image sensing device have an equal height. In Variation 1 shown in
In the present embodiment, with the two protruding portions 26a and 26b having the same height, a portion of the adhesive 14 that is pushed over the first protruding portion 26b can be blocked by the second protruding portion 26a.
The arrangement where one of two adjacent protruding portions (the protruding portion 26a) has a different height from that of the other protruding portion 26c or 26d as in Variation 1 or 2 is advantageous in that the light transparent substrate 3 can first be placed at an oblique angle with respect to the horizontal plane with one side thereof lying on the protruding portion 26c on the side of the effective pixel section 17, and then be brought down to a horizontal position for attachment, as shown in
Where there are two (or more) protruding portions with their upper surfaces being parallel, it is possible to more reliably prevent a portion of the adhesive that is pushed over one protruding portion from reaching the pads, and the sliding of the light transparent substrate is more reliably blocked, whereby it is possible to increase the contact area between the light transparent substrate and the protruding portions. In other words, even if some adhesive is partly pushed over the first protruding portion, the amount of such adhesive is small, which will be reliably prevented by the second protruding portion from leaking to the outside. Where there are two protruding portions with the same upper portion width, the contact area with the light transparent substrate is doubled as compared with a case where there is only one protruding portion, thereby increasing the effect of preventing the sliding of the light transparent substrate.
Where there are two ridge-shaped protruding portions with different heights (e.g., the protruding portions 26a and 26c), the light transparent substrate 3 can first be placed on the adhesive 14 with one side of the light transparent substrate 3 lying on the protruding portion 26c on the side of the effective pixel section 17, as shown in
As described above, where there are a plurality (two) of protruding portions (e.g., the protruding portions 26a and 26b, 26c or 26d) formed along one side of the solid-state image sensing element 1, even if the adhesive 14 is pushed over the protruding portion 26b, 26c or 26d on the side of the effective pixel section 17 and leaks toward the electrode pad portions 15, the adhesive 14 can be prevented from reaching the electrode pad portions 15.
The particular embodiments set forth above are merely illustrative, and the present invention is not limited to those particular embodiments. For example,
In the embodiments above, electrode pad portions are formed along two sides of the solid-state image sensing element, and the protruding portions are accordingly formed along two sides of the solid-state image sensing element. Where electrode pad portions are formed along three or four sides of the solid-state image sensing element, the protruding portions may be formed accordingly. The position of the protruding portion is not limited to between the effective pixel section and the electrode pad portions, but may alternatively be along a side where the electrode pad portions are not formed outside the effective pixel section or may be further outside the electrode pad portions.
The shape of the protruding portion is not limited to a ridge shape, but may alternatively be a dotted shape or a string or strings of dots. The placement of the light transparent substrate on the protruding portions may be varied on the order of μm or more. Where the interval between the protruding portions is the same as the width of the light transparent substrate, the light transparent substrate being shifted may hang over a protruding portion. If the surrounding space is filled with an encapsulation resin, the encapsulation resin may not reach the corner between the protruding portion and a portion of the light transparent substrate hanging over the protruding portion, thus resulting in incomplete filling of an encapsulation resin. Where the interval between the protruding portions is sufficiently larger than the light transparent substrate, the light transparent substrate will not lie over a protruding portion even if the placement of the light transparent substrate is shifted by some μm, thus preventing an incomplete filling of an encapsulation resin.
The solid-state image sensing device of the present invention includes protruding portions provided on the light receiving surface of the image sensing element, and the light transparent substrate is placed on the protruding portions. Therefore, there is a frictional force between the protruding portions and the light transparent substrate. Thus, when the light transparent substrate is placed on a thermosetting or photosetting liquid adhesive, the light transparent substrate is prevented from sliding with the adhesive serving as a lubricant.
As described above, the solid-state image sensing device of the present invention, in which the light transparent substrate is placed with a high precision, is useful in applications such as digital cameras.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-259025 | Oct 2007 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12237890 | Sep 2008 | US |
| Child | 13192155 | US |
