JP2007088118A - Solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state imaging device which is made thinner while improving the sensitivity of the solid state image sensing elements. <P>SOLUTION: The solid state imaging device comprises an imaging sensor 1 consisting of many solid state imaging elements of a silicon substrate, screen electrodes 3 with matrix arrangement and micro lenses 4, and a transparent cover 7 which is directly pasted together via a transparent adhesive layer 6. Here, the micro lens 4 consists of organic material whose refractive index is 1.5 to 1.6, and the transparent adhesive layer 6 consists of resin whose refractive index is 1.4 or less. Preferably, a fluoride resin is used. By this way, a light 8 from the outside is transmitted through the transparent cover and the transparent adhesive layer so that it may be condensed by the micro lenses 4, and then may be received by the image sensor 1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device configured by a wafer level package or a chip size package in which an adhesive layer of a transparent resin material having a low refractive index is interposed between a solid-state imaging device and a transparent cap.

  A conventional solid-state image pickup device is configured such that a solid-state image pickup device is housed in a hollow structure package such as ceramics, a light receiving portion having a microlens arranged at the center of the upper surface of the solid-state image pickup device, and an electrode pad arranged around the light receiving portion Has been. The microlens is useful for improving the sensitivity of the light receiving portion, and is usually formed of an organic material having a refractive index of 1.5 to 1.6. The electrode is wire bonded to the electrode pad of the solid-state image sensor and the ceramic package. Further, the solid-state imaging device is housed in a ceramic package, and a transparent cap such as glass is sealed on the upper surface of the package. In the conventional ceramics package, the microlens of the solid-state imaging device is in contact with the atmosphere, and since the refractive index of the atmosphere is 1.0, the microlens can collect light efficiently.

On the other hand, as shown in Patent Document 1, a microlens is provided on the upper surface of a solid-state imaging device of a CCD chip, which is a light receiving unit, and a transparent adhesive having a lower refractive index than that is filled between the transparent cap. The CCD chip and the transparent cap are fixed with a sufficient adhesion area without lowering the light receiving sensitivity of the CCD chip, and the outer periphery of the CCD chip is sealed with a highly moisture-resistant sealing material. Accordingly, a solid-state imaging device having a package structure excellent in moisture resistance in which the weak point of an adhesive that places importance on a low refractive index is reinforced has been proposed.
Japanese Patent Laid-Open No. 2003-100998

  In the hollow package using the above-mentioned ceramics, there is a problem that the total package height is increased because a hollow gap exists between the solid-state imaging device and the cover glass. In addition, a metal hermetic package in which the lead wire is glass-sealed or a thin ceramic package is used for such a package, but there is a problem that the volume increases and the number of assembly steps increases. There is also a packaging method in which an epoxy or acrylic transparent adhesive is bonded onto a solid-state image sensor. In this case, since the adhesive has a refractive index of 1.5 or more, the refractive index is the same as or larger than the refractive index of the microlens material, and the light collected by the microlens formed on the solid-state image sensor does not work well, and the solid-state image sensor There was a problem that the sensitivity of became worse.

  In the solid-state imaging device disclosed in Patent Document 1, the outer peripheral portion of the solid-state imaging element and the transparent cap must be surrounded by a highly moisture-resistant sealing material in order to improve the moisture resistance of the package. However, the overall size was increased. In addition, for electrical connection between the solid-state imaging device and the external circuit, a TAB lead is incorporated into the package, and the solid-state imaging device and the TAB are connected by wire bonding, which increases the volume of the entire package and reduces the number of assembly steps. There was a problem in cost such as increase. In particular, the thickness of the low refractive index adhesive filled between the solid-state imaging device and the transparent cap is required to obtain a high moisture resistance for the sealing material on the outer peripheral portion, which is a limitation in reducing the thickness. It was.

    Therefore, the present invention has been proposed to eliminate the above-described defects, and an adhesion formed between a microlens formed on a solid-state image sensor and a cover glass using a wafer level package or a chip size package. It is an object of the present invention to provide a new and improved solid-state imaging device having a thin layer. That is, the object of the present invention is to directly bond the transparent cover to the solid-state image sensor in order to reduce the total package height, and to improve the light condensing property of the solid-state image sensor and increase the photosensitivity. The present invention provides a solid-state imaging device having a low overall height and high photosensitivity characterized by using a low refractive index adhesive having a refractive index of 1.4 or less.

  According to the present invention, a wafer level package or chip in which a solid-state imaging device provided with a microlens on a light receiving surface and a transparent cover are directly bonded via a transparent low refractive index adhesive layer having a refractive index of 1.4 or less. A solid-state imaging device configured with a size package is provided. Here, a solid-state imaging device is disclosed, in which the microlens is formed of a material having a refractive index of 1.5 or more, and the adhesive layer is thinly formed to be about several μm. Specifically, it is a solid-state imaging device characterized in that a fluorine-based resin is used as the low refractive index adhesive layer and a transparent cover is formed of a chip size package having substantially the same dimensions as the solid-state imaging device. The wafer level package is a technique in which a semiconductor substrate is directly processed by etching or the like on a semiconductor substrate constituting an integrated circuit to form electrodes, solder balls or electrode bumps, and the substrate itself is used as a part of the package. Therefore, from a package in which a microlens is provided on a solid-state imaging device on a semiconductor substrate processed using this technique, and a transparent cover is directly bonded and sealed through a low refractive index transparent adhesive layer with a refractive index of 1.4 or less. A solid-state imaging device is provided. In other words, a microlens is disposed on the light-receiving surface of the semiconductor optical sensor formed on the front surface side of the silicon substrate, a contact electrode electrically connected to the semiconductor sensor through a conduction through hole is provided on the back surface, and a transparent cover is provided on the silicon substrate. A large number of solid-state imaging devices are formed by directly bonding the microlenses to the microlenses via a transparent adhesive layer having a refractive index of 1.4 or less, and the transparent cover is divided into chip size packages by dicing. And a solid-state image pickup device having a wafer level package, wherein the solid-state image pickup device and the solid-state image pickup device have substantially the same dimensions.

  In the solid-state imaging device of the present invention, since the transparent cover is directly bonded to the light-receiving surface of the solid-state imaging element through a microlens using a low refractive index adhesive layer, the condensing characteristic of the solid-state imaging element is improved. Achieving thinness by increasing photosensitivity and reducing overall height. Also, in the conventional wafer level package and chip size package, the semiconductor substrate and the glass are bonded with an epoxy or acrylic adhesive having a refractive index of 1.5 or more, so that a solid-state imaging with a microlens provided on the light receiving surface In the case of the element, the light was not collected by the microlens and the sensitivity of the solid-state image sensor was lowered. However, in the present invention, the microlens is directly bonded via an adhesive layer of a fluorine resin having a refractive index of 1.4 or less. Helps improve the light collection characteristics of the lens. Furthermore, since the package structure does not use a moisture-resistant sealing material on the outer periphery including the adhesive layer between the microlens and the transparent cover, the adhesive layer is made thinner and the structure is simplified, thereby increasing industrial value. .

  Specific embodiments of the solid-state imaging device according to the present invention will be described below. The solid-state imaging device of the present invention is a wafer level package or chip size package in which a transparent cover is directly bonded to a solid-state imaging device having a microlens on a light receiving surface through a transparent adhesive layer having a refractive index of 1.4 or less. Composed. Here, an optical material having a refractive index of 1.5 or more is used for the microlens, and a fluorine-based resin having a low refractive index is used for the transparent adhesive layer having a refractive index of 1.4 or less. The transparent cover and the solid-state image pickup device are a solid-state image pickup device comprising a wafer level package or a chip size package formed with substantially the same dimensions. Although various technically preferable limitations are given for explanation, the scope of the present invention is not limited to these embodiments unless otherwise specified to limit the present invention.

  FIG. 1 is a partially enlarged cross-sectional view showing a solid-state imaging device according to an embodiment of the present invention. In the solid-state imaging device, a photodiode image sensor 1 serving as a solid-state imaging device is formed on a silicon substrate 2 by using semiconductor technology, and a screen electrode 3 and a microlens 4 arranged in a matrix are formed thereon, and are transparently bonded. The transparent cover 7 is directly bonded through the layer 6. Here, the microlens 4 is made of an organic material having a refractive index of 1.5 to 1.6, and the transparent adhesive layer 6 is a fluorine-based resin having a refractive index of 1.4 or less. As a result, the light 8 from the outside passes through the transparent cover 7 and the transparent adhesive layer 6, is condensed by the microlens 4, and is received by the image sensor 1. That is, the screen electrodes 3 and the microlenses 4 are arranged in a matrix on the silicon substrate on which the image sensor 1 is located, and each form a rectangular light receiving portion. The microlens 4 is provided to increase the light receiving sensitivity of the light receiving unit. The microlens 4 is made of an organic material having a refractive index of 1.5 to 1.6. A lead member is formed on the silicon substrate 2 as a through-hole electrode in the substrate by applying semiconductor technology through a via hole, and a contact electrode 5 such as a solder bump or Au bump is provided on the outer surface. An electrical signal from the image sensor 1 of the solid-state imaging device is electrically connected to an external circuit through the contact electrode 5. On the other hand, the microlens 4 collects the external light beam 8 from the transparent cover 7 such as glass through the transparent adhesive layer 6 made of fluororesin and receives it by the image sensor 1. The received light signal is converted into an electrical signal and is derived to an external circuit.

  FIG. 2 is a perspective view showing an overview of the imaging apparatus, and shows a 3 to 5 mm square chip component in which the silicon substrate 2 and the transparent cover 7 are directly bonded together with the transparent adhesive layer 6 interposed therebetween. An image sensor of a semiconductor photodiode and a microlens are provided on the surface side of the inner surface of the silicon substrate 2. On the other hand, a large number of solder bumps of the contact electrode 5 electrically connected to the image sensor through conduction through holes are provided on the rear surface side of the outer surface. Here, the transparent cover 3 is directly bonded to the silicon substrate 2 via a transparent adhesive layer having a refractive index of 1.4 or less. In the manufacturing process, a plurality of unit unit solid-state image sensors are formed, then divided into chip size packages by dicing, and the transparent cover and the unit unit solid-state image sensor are made substantially the same size and are reduced in size and thickness. A solid-state imaging device of a wafer level package is disclosed.

3A to 3C show the manufacturing process of the solid-state imaging device of the present invention. FIG. 3A shows a bonding process of the silicon substrate 2 and the transparent cover 7, showing a state in which the transparent adhesive layer 6 is coated on one or both bonding surfaces, and is a state immediately before the bonding. Next, as shown in FIG. 3B, after bonding, a large number of solder bump contact electrodes 5 are provided on the outer surface of the silicon substrate 2. Next, a transparent cover 7 is directly attached to a silicon substrate 2 having a light receiving portion including a large number of solid-state imaging devices manufactured by a semiconductor technology with a transparent adhesive layer 6 having a refractive index of 1.4 or less interposed therebetween. After the solder bumps are formed on the outer surface, as shown in FIG. 3C, it is cut and divided along the dicing line 9 to complete an individual unit solid-state imaging device. In this case, in order to increase the adhesive strength of the transparent adhesive layer 6, an adhesion auxiliary material may be applied in advance. After the transparent substrate is bonded to the silicon substrate 2 provided with the light receiving portion including the solid-state image sensor on which the transparent adhesive layer 6 is applied, the transparent adhesive layer is cured to fix the image sensor in an airtight state. In FIG. 3B, the silicon substrate 2 to which the transparent cover 7 is bonded is provided with a contact electrode 5 for deriving an electric signal of the image sensor 1 using a semiconductor technique, but an Au bump may be used in addition to the solder bump. . The transparent cover and the silicon substrate combined by pasting are cut into a chip size by the dicer as described above to obtain a chip part of the solid-state imaging device shown in FIG. This chip component is housed in a ceramics package and completed as a solid-state imaging device.

  As described above, in order to obtain a sensitive imaging device by condensing light with a microlens, the light needs to be refracted on the surface of the microlens. The refraction of light is determined by the refractive index of the microlens material, the refractive index of the cover material on the top surface of the microlens, and the microlens shape. In order for light to be refracted by the convex microlens, the refractive index of the cover material on the top surface of the microlens needs to be smaller than the refractive index of the microlens material. In addition, since the refractive angle of light is proportional to the refractive index ratio of the microlens material and the cover material on the microlens, the smaller the refractive index of the cover material on the microlens, the more effective the microlens works. Become. Since the refractive index of the microlens on the light-receiving surface of the solid-state imaging device is usually 1.5 or more, the refractive index of the adhesive material to be bonded is less than 1.5 in order to function as a microlens. However, in consideration of the actual microlens shape, a transparent adhesive layer having a refractive index of 1.4 or less is used in the present invention. In the solid-state imaging device of the present invention, it is desirable to use a transparent adhesive material having a refractive index of 1.35 or less in order to improve the light collecting characteristics of the microlens.

  For the transparent adhesive layer 6 having a low refractive index of the present invention, a transparent resin material having a refractive index of 1.4 or less is used. For example, a fluorine-based resin adhesive layer is preferable, and the thickness of the adhesive layer is about several μm. As a result, it is possible to provide a solid-state imaging device with high overall sensitivity while reducing the overall height. Examples of the fluorine-based resin include polytetrafluoroethylene (PTFEP) having a refractive index of 1.34, perfluoroalkoxy (PFA) having a refractive index of 1.35, and polyvinyl fluoride (PVF) having a refractive index of 1.33 to 1.38. ) -Containing polyvinyl resin, or perfluoroethylenepropene copolymer (PFEP), chlorotrifluoroethylene (CTFE), or ethylene chlorotrifluoroethylene (ECTFE).

It is a principal part expanded sectional view of the solid-state imaging device which shows embodiment of this invention. It is a perspective schematic diagram which shows the cutting-out chip component of the solid-state imaging device shown in FIG. It is a schematic diagram which shows a part of chip component manufacturing process of the solid-state imaging device shown in FIG.

Explanation of symbols

1; image sensor (solid-state image sensor), 2; silicon substrate,
3; screen electrode, 4; microlens, 5; contact electrode,
6; low refractive index transparent adhesive layer, 7; transparent cover (transparent glass substrate)
8; Ray, 9; Dicing line

Claims (4)

  A solid-state image pickup device constituted by a wafer level package or a chip size package in which a transparent cover is directly bonded to a solid-state image pickup element provided with a microlens on a light receiving surface through a transparent adhesive layer having a refractive index of 1.4 or less.   The solid-state imaging device according to claim 1, wherein the microlens of the solid-state imaging element is formed of a material having a refractive index of 1.5 or more.   The solid-state imaging device according to claim 2, wherein the adhesive layer is made of a fluorine-based resin. A microlens is disposed on the light receiving surface of the semiconductor optical sensor formed on the front surface side of the silicon substrate, a contact electrode electrically connected to the semiconductor sensor by a conductive through hole is provided on the back surface, and a transparent cover is provided on the silicon substrate. A large number of solid-state imaging devices are formed by directly bonding to the microlens via a microlens and a transparent adhesive layer having a refractive index of 1.4 or less, and then divided into chip size packages by dicing, and the transparent cover and the solid are separated. A wafer level package solid-state image pickup device characterized in that the image pickup element has substantially the same dimensions.

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