Back-illuminated type imaging device and fabrication method thereof

Abstract

Light is illuminated from a back-surface side of a silicon substrate 4. A back-illuminated type imaging device 100 reads out, from a front-surface side of the silicon substrate 4, charges that are generated in the silicon substrate 4 in response to the illuminated light, so as to perform imaging. The back-illuminated type imaging device 100 includes pad portions 17 formed on the back surface of the semiconductor substrate 4, and a plurality of pillars 9 that are formed in the semiconductor substrate 4, are made of a conductive material and electrically connect wiring portions 12 formed on the front surface of the semiconductor substrate 4 and the pad portions 17 to each other.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is based upon and claims the benefit of priority from the Japanese Patent Application No. 2007-157460 filed on Jun. 14, 2007, the entire contents of which are incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Technical Field[0003]The invention relates to a back-illuminated type imaging device in which light is illuminated from a back-surface side of a semiconductor substrate and charges that are generated in the semiconductor substrate in response to the light are read from a front-surface side of the semiconductor substrate to perform imaging.[0004]2. Description of the Related Art[0005]The following back-illuminated type imaging device has been proposed. That is, light is illuminated from a back-surface side of a semiconductor substrate. The back-illuminated type imaging device stores charges that are generated in the semiconductor substrate in response to the light, into charge storage areas formed o...

AI Technical Summary

Benefits of technology

The invention provides a back-illuminated type imaging device that can prevent an increase in fabrication cost and resistance between pads and wirings even if pad openings are formed on the light incidence side. The device includes a semiconductor substrate with a pad portion and a wiring portion formed on the front surface of the substrate. A plurality of pillars made of conductive material are formed in the semiconductor substrate and connect the wiring portion and the pad portion. The pillars can be arranged two-dimensionally and may have a maximum width of 2 μm or less in length. The device also includes an alignment mark formed by a pattern of pillars that is used to align components on the front-surface side of the substrate with components on the back-surface side. The device can be fabricated using a method that includes forming first through holes in a plane area, filling the holes with conductive material to form pillars, and then forming a wiring portion and a pad portion on the back surface of the substrate.

Problems solved by technology

For this reason, if the pad opening is formed on the front-surface side of the semiconductor substrate in the back-illuminated type imaging device, it becomes necessary to drastically change or modify the test equipments, which may increase the fabrication cost.

However, such a method has the following problems.

That is, if the through hole is formed before the color filter or the microlens are formed on the back-surface side, a material for the color filter or the microlens may be left in the through hole and cannot be removed in subsequent steps.

Or, since the substrate on which the material is to be deposited has a large step formed thereon, the thickness of the deposited material is not even, which may cause a fixed pattern noise that appears as oblique lines in an image.

Moreover, even if the through hole is formed after the color filter or the microlens is formed, it is necessary to remove a photoresist that defines the through hole without causing any harm to the color filter or the microlens, which is very troublesome.

In particular, as described above, in the semiconductor substrate having a thickness of 10 μm, the above problems may become conspicuous, and it becomes more difficult to perform such a removal work.

Such a process step cannot be said to be practical as a semiconductor fabrication process.

However, in such a case, there arises a problem that the resistance of the conductive material filled in the trench may increase, which may affect the device characteristics.

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