Solid-state imaging device and method for fabricating same

The present invention contains subject matter related to Japanese Patent Application JP 2005-000727 filed in the Japanese Patent Office on Jan. 5, 2005, the entire contents of which are incorporated herein by reference.

1. Field of the Invention

The present invention relates to a solid-state imaging device in which photoelectric conversion efficiency per unit pixel is improved and to a method for fabricating the solid-state imaging device.

2. Description of the Related Art

In solid-state imaging devices, photoelectric conversion efficiency per unit pixel has been improved by increasing the aperture ratio in the unit pixel or by increasing the light collection efficiency of microlenses.

Recently, in solid-state imaging devices, a further increase in the number of pixels has been taking place, resulting in a decrease in the area per unit pixel, and thus a further improvement in photoelectric conversion efficiency has been desired. Therefore, for example, in the case of a photodiode, in a PN junction structure, the impurity concentrations in the individual regions are increased, and thereby the photoelectric conversion efficiency is improved (refer to Kazuya Yonemoto, “CCD/CMOS imeji sensa no kiso to oyo (Basics and Application of CCD/CMOS Image Sensors)”, CQ Publishing Co., Ltd., pp. 92-94).

However, in the known solid-state imaging devices and fabrication methods therefor, if the impurity concentrations of impurity regions of photoelectric converting elements are increased excessively, defective pixels, such as white spots, occur frequently, resulting in problems.

It is desirable to provide a solid-state imaging device in which photoelectric conversion efficiency per unit pixel can be improved and a method for fabricating such a solid-state imaging device.

According to an embodiment of the present invention, a solid-state imaging device includes a plurality of pixels two-dimensionally arrayed in a well region disposed on a semiconductor substrate, each pixel including a photoelectric conversion section having a charge accumulation region which accumulates signal charge; an element isolation layer which is disposed on the surface of the well region along the peripheries of the individual charge accumulation regions and which electrically isolates the individual pixels from each other; and a diffusion layer which is disposed beneath the element isolation layer and which electrically isolates the individual pixels from each other, the diffusion layer having a smaller width than that of the element isolation layer, wherein each charge accumulation region is disposed so as to extend below the element isolation layer and be in contact with or in close proximity to the diffusion layer.

According to another embodiment of the present invention, in a method for fabricating a solid-state imaging device including a plurality of pixels two-dimensionally arrayed in a well region disposed on a semiconductor substrate, each pixel including a photoelectric conversion section having a charge accumulation region which accumulates signal charge, the method includes the steps of forming an element isolation layer on the surface of the well region, the element isolation layer electrically isolating the individual pixels from each other; forming a diffusion layer so as to surround the individual charge accumulation regions and electrically isolate the individual pixels from each other beneath the element isolation layer; and forming the photoelectric conversion section for each pixel in the well region with the photoelectric conversion sections being electrically isolated from each other by the element isolation layer and the diffusion layer. The photoelectric conversion section formation step includes the substeps of implanting ions of an impurity for forming each charge accumulation region in the well region; and thermally diffusing the impurity implanted in the well region by the ion implantation substep to form each charge accumulation region so that the charge accumulation region extends below the element isolation layer and is brought in contact with or in close proximity to the diffusion layer.

According to another embodiment of the present invention, in a method for fabricating a solid-state imaging device including a plurality of pixels two-dimensionally arrayed in a well region disposed on a semiconductor substrate, each pixel including a photoelectric conversion section having a charge accumulation region which accumulates signal charge, the method includes the steps of forming an element isolation layer on the surface of the well region, the element isolation layer electrically isolating the individual pixels from each other; forming a diffusion layer so as to surround the individual charge accumulation regions and electrically isolate the individual pixels from each other beneath the element isolation layer; and forming the photoelectric conversion section for each pixel in the well region with the photoelectric conversion sections being electrically isolated from each other by the element isolation layer and the diffusion layer. The photoelectric conversion section formation step includes the substeps of implanting first ions of an impurity for forming the charge accumulation region of each photoelectric conversion section in the well region; masking above the charge accumulation region after the first ion implantation substep; and implanting second ions of an impurity that is different from the impurity used in the first ion implantation substep through the element isolation layer in the periphery of each charge accumulation region after the masking substep to form a charge accumulation extension so as to be brought in contact with or in close proximity to the diffusion layer.

According to another embodiment of the present invention, in a method for fabricating a solid-state imaging device including a plurality of pixels two-dimensionally arrayed in a well region disposed on a semiconductor substrate, each pixel including a photoelectric conversion section having a charge accumulation region which accumulates signal charge, the method includes the steps of forming a diffusion layer so as to surround the individual charge accumulation regions and electrically isolate the individual pixels from each other; forming the photoelectric conversion section for each pixel in the well region with the photoelectric conversion sections being electrically isolated from each other by the diffusion layer, the photoelectric conversion section formation step including the substep of implanting ions of an impurity for forming each charge accumulation region in the well region so that the charge accumulation region is brought in contact with or in close proximity to the diffusion layer; and forming an element isolation layer on the surface of the well region after the ion implantation substep, the element isolation layer electrically isolating the individual pixels from each other with the diffusion layer being located therebeneath.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a substantial part of a solid-state imaging device and a fabrication process step therefor according to a first embodiment of the present invention;

FIG. 2 is a schematic sectional view illustrating a substantial part of the solid-state imaging device and a fabrication process step therefor according to the first embodiment of the present invention;

FIG. 3 is a schematic sectional view illustrating a substantial part of a solid-state imaging device and a fabrication process step therefor according to a second embodiment of the present invention;

FIG. 4 is a schematic sectional view illustrating a substantial part of the solid-state imaging device and a fabrication process step therefor according to the second embodiment of the present invention;

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Active solid-state devices (e.g., transistors, solid-state diodes)

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