1. Field of the Invention
The present invention relates to a back-side illumination sensor, and more particularly, to a back-side illumination sensor with a reduced area.
2. Description of the Prior Art
As the pixel size of a complementary metal-oxide-semiconductor image sensor (CMOS image sensor, CIS) grows smaller, the degradation resulting from certain factors such as quantum efficiency, cross-talk and so forth in a sensor array also becomes significant. Regarding a conventional image sensor such as a front-side illuminated sensor, a lens of each pixel sensor is fabricated on a front side of a substrate. Therefore, the incident light has to travel through dielectric layers between circuitry formed by metal layers to arrive at a photo diode otherwise it will be reflected or absorbed by metal or any other reflective material.
In order to enhance the compactness of an image sensor, a back-side illumination (BSI) image sensor is introduced. In a BSI image sensor, the incident light is projected from a back side of a substrate of the image sensor, and therefore the front side of the substrate can be reserved for circuitry of various functions. Please refer to
With the utilization of the BSI technology, there are more and more available areas on the front side of the substrate for building various functional circuits. To further exploit advantages of the BSI structure, however, more and more effort is dedicated to improve an area efficiency and compactness of a BSI image sensor.
It is therefore one of the objectives of the present invention to provide a back-side illumination image sensor with a more compact size to solve the above-mentioned problem.
According to one embodiment of the present invention, a back-side illumination (BSI) image sensor comprises at least one pixel area. The pixel area comprises a photo diode and a transfer transistor. The transfer transistor has a control electrode made of a gate poly and a gate oxide for receiving a control instruction, a first electrode coupled to the photo diode, and a second electrode, wherein an induced conduction channel of the transfer transistor partially surrounds a recessed space which is filled with the gate poly of the transfer transistor.
According to another embodiment of the present invention, a back-side illumination image sensor comprises at least one pixel area. The pixel area comprises a photo diode and a transfer transistor. The photo diode includes a first doped substrate and a second doped substrate. The transfer transistor has a control electrode made of a gate poly for receiving a control instruction, a first electrode coupled to the photo diode, and a second electrode, wherein the first doped substrate also serves as the first electrode of the transfer transistor.
According to yet another embodiment of the present invention, a back-side illumination image sensor comprises at least one pixel area. The pixel area comprises a photo diode and at least one transistor. The transistor has a control electrode made of a gate poly and a gate oxide for receiving a control instruction, a first electrode and a second electrode. An induced conduction channel of the transistor partially surrounds a recessed space which is filled with the gate poly and the gate oxide of the transistor.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
One concept of one embodiment of the present invention is to combine the N-doped layer NL of the photo diode 100 and the N-doped connection path 300. As can be seen from
Please refer to
In another embodiment of the present invention, the substrate of the pixel structure can also be trenched to implement the recessed space. Please refer to
Please note that the exemplary embodiments in
Moreover, the recessed space is not limited to be formed upon an isolation structure, and it may also be designed solely upon the substrate. For an illustration of this, please refer to
To summarize, exemplary embodiments of the present invention provide back-side illumination image sensors each having a more compact size. With the utilization of a recessed space during a manufacturing process, a conduction channel of a transistor can be formed askew or vertically (i.e., the conduction channel is not formed horizontally) when induced, leading to a smaller area occupied by the transistor within a pixel structure.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
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