Lateral P-I-N photodiode element with high quantum...

Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation

Reexamination Certificate

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C438S048000, C438S057000

Reexamination Certificate

active

06323054

ABSTRACT:

BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to methods used to fabricate semiconductor devices, and more specifically to a method used to fabricate a lateral N/P photodiode element for an image sensor cell.
(2) Description of Prior Art
Active pixel, or image sensor cells, are usually comprised with a photodiode element, used to collect photon energy for the cell. The efficiency, or sensitivity of the photon collector, or the photodiode element, usually comprised of a N/P diode, is directly related to the depletion region of this diode. The depletion region in turn is a function of the doping level of the components of the N/P photodiode element, as well as a function of the area of the photodiode. However trends to micro-miniaturization have resulted in decreasing space allotted for the image censor cell, and thus smaller area, less efficient photodiode elements have to used.
This invention will describe a novel method for fabricating a CMOS image sensor device, using a process sequence that can be simultaneously used to form other CMOS devices, used for logic and memory applications. This invention however will feature the formation of a lateral N/P photodiode element, exhibiting an increased depletion region, when compared to other lateral N/P photodiodes, fabricated without the use of the processes described in this invention. Prior art, such as Chen, in U.S. Pat No. 5,880,495, describes a method of fabricating a photodiode element for an image sensor cell, however that prior art does not teach the process needed to fabricate the lateral N/P photodiode element, described in this present invention, in which an increased depletion region, and thus increased photosensitivity, is realized via the placement of a lightly doped, or of an intrinsic region, at the interface between the N type, and P type regions of the lateral N/P photodiode element.
SUMMARY OF THE INVENTION
It is an object of this invention to fabricate an image sensor cell featuring a lateral N/P photodiode element.
It is another object of this invention to use the P well, and the N well regions, used for the simultaneously fabricated CMOS devices, as the components of the lateral N/P photodiode element of the image sensor cell.
It is still another object of this invention to form a lightly doped, or an intrinsic region, between the P well and N well components of the lateral N/P photodiode element, to increase the depletion region, and thus the photosensitivity of the lateral N/P photodiode element.
In accordance with the present invention a method of fabricating a lateral, P well—intrinsic—N well, (P-I-N), photodiode element, for an image sensor cell, featuring a lightly doped, or intrinsic region, located between the P well and N well components of the lateral photodiode element, is described. After forming shallow trench isolation regions in a P type semiconductor substrate, P well regions are formed for reset and transfer gate transistors, as well as for the P type component of the subsequent lateral P/N photodiode element. The N well, or N type component of the lateral N/P photodiode element is next formed, however placed between about 0.2 to 0.4 um, away from the adjacent P well region, resulting in a lateral P-I-N, photodiode element, in which I, of the P-I-N photodiode element, refers to the region between the P well and N well regions. This intentionally formed I region, or space between the P well and N well regions, allows an increase in the depletion region of the photodiode element to be realized.


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