Image pickup module with improved flatness of image sensor and via electrodes

An image pickup module includes a cover member, an image pickup device chip including photodiodes, a fixing member which is arranged around the image pickup device chip and which connects the cover member and the image pickup device chip together, a rewiring substrate arranged on the side opposite to the cover member of the image pickup device chip, connection members for connecting the image pickup device chip with the rewiring substrate, and a space surrounded by the cover member, the image pickup device chip, and the fixing member. The image pickup device chip includes a semiconductor substrate. The semiconductor substrate includes through-hole electrodes penetrating the substrate. When an area corresponding to the fixing member in the orthogonal projection of the image pickup module with respect to the cover module is defined as a fixed area, the through-hole electrodes and the connection members are arranged in the fixed area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup module and a camera.

2. Description of the Related Art

A conventional image pickup apparatus includes a WL-CSP (wafer level chip size package) in which a semiconductor substrate including an image pickup device and through-hole electrodes is bonded to a light transmissive support substrate via an adhesive having an opening on the image pickup device. Japanese Patent Laid-Open No. 2009-158863 discloses an image pickup module in which a semiconductor substrate is directly mounted on a mounting substrate via solder balls. The solder balls are formed on a large area in a second main surface of the semiconductor substrate opposite to a first main surface of the semiconductor substrate on which an image pickup device is formed. Here, the inventors found the problem described below. The thickness of a semiconductor substrate of an image pickup device chip including through-hole electrodes is thinner than the thickness of a semiconductor substrate of an image pickup device chip using wire bonding so as to improve throughput and reliability of a manufacturing process of the through-hole electrodes, so the rigidity of the semiconductor substrate is low. When connecting an image pickup device chip with a mounting substrate by soldering, the melted solder starts solidifying from a portion where the temperature falls below the melting point of the solder. Therefore, in the image pickup device chip which has been cooled to a room temperature, there is a difference of contraction between a portion where the solder attaches and a portion where no solder attaches. Thus, in Japanese Patent Laid-Open No. 2009-158863, when an image pickup device is connected with a mounting substrate via solder balls arranged below a hollow portion, concaves and convexes are formed in the image pickup device chip according to positions of solders, so the flatness of a light receiving surface decreases. Therefore, there is a problem that image quality degrades.

To solve the above problem, if the thickness of the semiconductor substrate of the image pickup device chip is increased simply, the flatness of the light receiving surface is improved because the rigidity increases. However, the through-hole electrodes become difficult to be formed.

The present invention is to solve the problem of such a conventional configuration, and the present invention provides an image pickup module and a camera in which the light receiving surface of the image pickup device chip including through-hole electrodes has a good flatness and which can obtain a high quality image.

SUMMARY OF THE INVENTION

The present invention provides an image pickup module including a cover member, an image pickup device chip including a photodiode, a fixing member arranged around the image pickup device chip and configured to connect the cover member and the image pickup device chip together, a rewiring substrate arranged on the side opposite to the cover member of the image pickup device chip, a connection member configured to connect the image pickup device chip with the rewiring substrate, and a space surrounded by the cover member, the image pickup device chip, and the fixing member. The image pickup device chip includes a semiconductor substrate. The semiconductor substrate includes a through-hole electrode penetrating a first main surface on the side of the cover member and a second main surface on the side opposite to the first main surface. When an area corresponding to the fixing member in the orthogonal projection of the image pickup module with respect to the cover module is defined as a fixed area, the through-hole electrode and the connection member are arranged in the fixed area.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference toFIGS. 1A to 7.

First Embodiment

FIGS. 1A and 1Bare diagrams showing an image pickup module of a first embodiment.FIG. 1Ais a transparent plan view.FIG. 1Bis a cross-sectional view taken along line IB-IB inFIG. 1A.

The image pickup module includes a cover member1, an image pickup device chip2, a fixing member3disposed between the cover member1and the image pickup device chip2, and a rewiring substrate4electrically connected to the image pickup device chip2. The image pickup device chip2has through-hole electrodes6around an image pickup area5including a plurality of photodiodes.

The cover member1is a portion through which incident light passes to the photodiodes, which are photo detectors of the image pickup device2, and has at least a light transmissive property. The cover member1having a light transmissive property is formed of a crystal, a glass, a resin, or the like. When the semiconductor substrate11used for the image pickup device2is made of silicon, the glass can be TEMPAX Float (registered trademark) by SCHOTT AG, PYREX (registered trademark) by Corning Incorporated, SW glass substrate by ASAHI GLASS CO., LTD. When the cover member1is a resin, optical plastic formed of a polycarbonate resin can also be used. The cover member formed of the resin or the glass can be used because the resin and the glass are materials having a linear expansion coefficient similar to that of silicon. A silicon substrate is mainly used for the semiconductor substrate11for forming the photodiodes of the image pickup device chip2. An adhesive for fixing the cover member1and the image pickup device chip2is used for the fixing member3. The fixing member3is formed on a surface of at least either one of the cover member and the image pickup device chip by, for example, patterning.

The cover member1and the image pickup device chip2are fixed (i.e. connected or attached) together by the fixing member3. A space7is formed by being surrounded by the cover member1, the image pickup device chip2, and the fixing member3. A wiring structure12, a first flattening film14, a color filter15, a second flattening film16are arranged on the semiconductor substrate of the image pickup device chip2, and further microlenses17are arranged on the semiconductor substrate. An insulating film20, an electroconductive film21, and an insulting member23are arranged below the semiconductor substrate11(on the side opposite to the light incident side). An oxide film, a nitride film, or the like is used for the insulating film20. Al, Cu, or the like is used for the electroconductive film21. A solder resist or the like is used for the insulting member23. The image pickup device chip2includes the through-hole electrodes6penetrating a first main surface on the side of the cover member, which is the light incident side of the semiconductor substrate11, and a second main surface on the side opposite to the first main surface. The through-hole electrode6is formed by a part of the electroconductive film21. The through-hole electrode6is electrically connected to a surface electrode13in the wiring structure. The image pickup device chip2has back surface electrodes22formed by a part of the electroconductive film21to connect to the rewiring substrate4. The rewiring substrate4has first connection terminals25arranged on a first main surface on the side of the image pickup device chip and second connection terminals26arranged on a second main surface opposite to the main surface. Further, the rewiring substrate4has electroconductive members not shown in the drawings, which connect the first connection terminals25with the second connection terminals26. The image pickup device chip2and the rewiring substrate4are electrically connected to each other by the back surface electrodes22of the image pickup device chip2and the first connection terminals25of the rewiring substrate4via connection members24. An anisotropic electroconductive member is used for the connection member24in the present embodiment. For example, an anisotropic electroconductive member such as ACP, ACF, or NCP can be used. Solder can be used as the connection member24.

Here, the rewiring substrate4will be described with reference toFIGS. 2A and 2B. The rewiring substrate4has a silicon substrate31, through-hole electrodes32formed in the silicon substrate, a wiring structure33on the silicon substrate, surface electrodes25on the first main surface, and back surface electrodes34on the second main surface. An electroconductive pattern for rewiring is formed in the rewiring structure33. By such a structure, the first connection terminals25, which are the surface electrodes25of the rewiring substrate4, are connected with the second connection terminals34, which are the back surface electrodes of the rewiring substrate4, to form a rewiring structure. A solder ball or the like is formed on the back surface electrode of the rewiring substrate4and used to connect to another mounting substrate not shown in the drawings. By using such a rewiring substrate, solder terminals can be formed in a matrix form on the second main surface of the rewiring substrate4, so a structure capable of connecting to many pins can be formed. The material of the rewiring substrate4is not particularly limited, and a ceramic laminated substrate, a multilayer epoxy substrate, a silicon substrate, or the like can be used. However, if the semiconductor substrate11and the rewiring substrate4are silicon substrates, they have the same linear expansion coefficient and warping can be prevented from occurring. In this case, even if a flexible substrate or a glass epoxy substrate is connected to the rewiring substrate4using a silicon substrate, a stress due to a difference between thermal shrinkage rates of the rewiring substrate4and the connected substrate is difficult to be transmitted to a light receiving surface of the image pickup device chip2, so a high flatness can be obtained.

Next, a plan view layout of the image pickup module will be described with reference toFIG. 1A. The plan view layout is, for example, orthogonal projections of the constituent elements with respect to the cover member1. In the image pickup module, an area where the fixing member3is arranged is defined as a fixed area when seen from the light incident side. The fixed area is the outside of the inner circumference27of the fixing member3. An area including the image pickup area inside the inner circumference27of the fixing member3is defined as a device area. In the fixed area, electrode units such as the surface electrodes13, the through-hole electrodes6, and the connection members24are arranged in the fixed area. The semiconductor substrate11has an area having a first thickness and an area having a second thickness thinner than the first thickness. The through-hole electrodes6are provided in the area having the second thickness. A boundary at which the thickness of the semiconductor substrate11of the image pickup device chip2changes is arranged below the fixing member, that is, in a range of the fixed area when seen from the light incident side. The connection members24electrically connecting the image pickup device chip2with the rewiring substrate4are arranged in a range of the fixed area. Although the boundary at which the thickness changes may corresponds to the boundary of the fixed area in the orthogonal projection of the cover member1, the boundary at which the thickness changes is desired to be inside the fixed area. Although the inner edge of the connection member24may corresponds to the boundary of the fixed area in the orthogonal projection of the cover member1, the inner edge of the connection member24is desired to be arranged inside the fixed area. This structure will be described with reference toFIG. 3, which is an enlarged diagram of a portion III inFIG. 1B.

As shown inFIG. 3, the fixed area includes an area in which the semiconductor substrate has a first thickness T1and an area in which the semiconductor substrate has a second thickness T2thinner than the first thickness T1. As a method for thinning the thickness of the semiconductor substrate, at least either one of etching and grinding is used. The through-hole electrodes6and the connection members24are arranged in a range of the fixed area. The connection members24are arranged in the area having the first thickness T1and the through-hole electrodes6are arranged in the area having the second thickness T2. The area having the first thickness T1has high rigidity because the area is in the fixed area and is a portion where the thickness of the semiconductor substrate is large. Therefore, by arranging the connection members24in the area having the first thickness T1, which is a thicker portion of the semiconductor substrate11, it is possible to reduce the influence of stress applied to the semiconductor substrate11when the connection members24are formed. Since the area having the first thickness T1has high rigidity, a necessary pressure can be applied during a connection operation, and so electrically and mechanically stable connection can be achieved. Further, by arranging the through-hole electrodes6in the area having the second thickness T2, which is a thinner portion of the semiconductor substrate11, it is possible to easily form the through-hole electrodes6in the semiconductor substrate11. When electrical connection portions are provided in the area having the thickness T1under the adhesive, the rigidity increases because the area is below the fixing member and is a thicker portion of the silicon. Therefore, an appropriate pressure can be applied when the connection operation is performed, so that a stable connection can be made, and the yield rate and reliability can be improved. Further, since the connection members are not arranged below the space, that is, in a range of the device area, it is possible to reduce the influence of the stress applied to the semiconductor substrate due to contraction of the solder.

Therefore, in the image pickup module, a light receiving surface, which is the surface of the image pickup area, has a good flatness, and so a high quality image can be obtained.

Next, a modified example of the image pickup module inFIG. 1Bwill be described with reference toFIG. 4.

FIG. 4is a partial cross-sectional view corresponding to a portion IV inFIG. 1Bin the same manner as inFIG. 3.

A configuration of the image pickup module ofFIG. 4different from the configuration ofFIGS. 1B and 3is that the edge of the semiconductor substrate11outside the through-hole electrodes has the first thickness T1. Even if there are areas having the first thickness T1at both sides of the area having the second thickness T2in this way, the same effect can be obtained.

Next, a modified example of the image pickup module inFIG. 1B, which is different from the image pickup module inFIG. 3, will be described with reference toFIG. 5.

FIG. 5is a partial cross-sectional view corresponding to a portion V inFIG. 1Bin the same manner as inFIG. 3.

A configuration of the image pickup module ofFIG. 5different from the configuration ofFIGS. 1B and 3is that the connection members24are arranged from the area having the first thickness T1to the area having the second thickness T2. In this way, by enlarging the connection area of the connection members24, the yield rate and reliability can be further improved.

As described above, by the image pickup module described in the present embodiment, an image pickup module can be obtained in which the light receiving surface of the image pickup device chip including through-hole electrodes has a good flatness and which can obtain a high quality image.

In a conveyer type reflow furnace in which solder is formed, fixation timing of a plurality of solder balls when the solder balls come out from the furnace varies depending on the positions of the solder balls. However, the connection is performed in an area having high rigidity, so that the variation is reduced and high flatness of the light receiving surface is maintained.

Second Embodiment

FIGS. 6A and 6Bare cross-sectional views of an image pickup module of a second embodiment of the present disclosure.

A point different from the image pickup module inFIG. 1Bis that a bump electrode is arranged on the surface electrode of the rewiring substrate. The bump electrode is a gold bump or a solder bump, and arranged on the first connection terminal, which is the surface electrode of the rewiring substrate.

The bump electrode30and the back surface electrode22of the image pickup device chip2are connected to each other by an anisotropic electroconductive member in the same manner as in the first embodiment. When the bump electrode30is used, an electroconductive adhesive may be provided to each bump and connected.

By using the bump electrodes30, the connection between the image pickup device chip2and the rewiring substrate4becomes a plurality of point contacts, so the load during connection can be largely reduced and it is possible to further prevent the semiconductor substrate11from being deformed or cracked.

The differences betweenFIG. 6AandFIG. 6Bare the thickness of the fixing member3, that is, the size of the space7, and whether or not the cover member1is in contact with the microlenses17. The configuration ofFIG. 6Bhas further higher rigidity, so the light receiving surface has high flatness. These configurations can be applied to the configuration of the first embodiment.

Third Embodiment

Application to Digital Camera

FIG. 7is a block diagram in which the image pickup module described in the first and the second embodiments of the present invention is applied to a digital camera, which is an example of an image pickup system.

A configuration for bringing light in a solid-state image pickup device704includes a shutter701, an image pickup lens702, and an aperture703. The shutter701controls exposure of the solid-state image pickup device704, and the incident light is focused on the solid-state image pickup device704by the image pickup lens702. At this time, the light quantity is controlled by the aperture703.

A signal outputted from the solid-state image pickup device704according to the light brought in is processed in an image pickup signal processing circuit705and converted from an analog signal to a digital signal by an A/D converter706. The outputted digital signal is calculated by a signal processing unit707and picked-up image data is generated. The picked-up image data can be accumulated in a memory710mounted in the digital camera or transmitted to an external device such as a computer or a printer through an external I/F unit713according to setting of operation mode set by a user. The picked-up image data can also be recorded in a recording medium712that can be attached and detached to and from the digital camera through a recording medium control I/F unit711.

The solid-state image pickup device704, the image pickup signal processing circuit705, the A/D converter706, and the signal processing unit707are controlled by a timing generator708, and the entire system is controlled by an overall control/calculation unit709. The above system can also be formed on the same semiconductor substrate as that of the solid-state image pickup device704by the same process.

The embodiments described above can be properly combined or properly modified.

This application claims the benefit of Japanese Patent Application No. 2010-186464 filed Aug. 23, 2010, which is hereby incorporated by reference herein in its entirety.