JP2633240B2 - Solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device, and particularly to a CCD solid-state imaging device.

2. Description of the Related Art FIG. 2A is a plan view of a photoelectric conversion unit and a vertical CCD shift register unit of a conventional CCD solid-state imaging device. FIG. 21
Is a LOCOS oxide film used to form an element isolation region, and a threshold voltage of a read gate electrode for reading an optical signal charge from a photodiode 25 as a photoelectric conversion element to a vertical CCD shift register. A diffusion region for controlling a read gate threshold value by ion implantation for control, 23 is a first-layer polysilicon electrode, and 24 is a second-layer polysilicon electrode.

The flow of the optical signal is as follows. Photodiode
The electric charge generated and accumulated at 25 passes through a path 26 indicated by an arrow, and passes through a vertical CCD formed at the second-layer polysilicon electrode 24.
Moved to In this case, since the electrodes are to be carried upward in the plane of the paper, the charges move through the path 27 to below the gate formed by the first-layer polysilicon electrode 23. In FIG. 2A, the photodiode 25
The charge generated and accumulated in the lower photodiode moves upward through the paths 28 and 27.

Problems to be Solved by the Invention In the CCD type solid-state imaging device, at least the path 28,
The transfer efficiency (hereinafter referred to as the vertical transfer efficiency) of the charge transfer at 27 must be 96% or more throughout the vertical CCD. At that time, the cross-sectional shape of the vertical CCD channel has a great influence on the vertical transfer efficiency. 2 b and c show the second
FIG. 2 shows a schematic view of an AA ′ section and a BB ′ section of FIG. A-
Assuming that the effective width of the CCD channel in the A 'section (FIG. 2b) is a, the BB' section (FIG. 2c) is AA 'section because both sides are sandwiched by the LOCOS 29. The left side of the channel is cut by bird's beak of LOCOS, and the effective channel width of CCD becomes b. Considering the case where charge travels in path 28, signal charge is carried from channel width b to channel width a. In this case, since the data is transferred from a narrow place to a wide place, the loss is small. However, when the charge moves along the path 27, a
, The data is transferred to a narrow b, so that the loss is larger than that described above. Further, if two channel widths a and b are mixed under one CCD gate due to design or mask misalignment, transfer loss will be larger than in the case described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state imaging device which can solve the conventional disadvantages, prevent a decrease in transfer efficiency of a vertical CCD, and can cope with high density.

Means for Solving the Problems In the solid-state imaging device of the present invention, an element isolation region is not formed between a photoelectric conversion element and a buried channel, but a diffusion region for controlling a read gate threshold is formed. .

Operation With the above configuration, the transfer efficiency can be improved by making the effective cross-sectional shape of the vertical CCD channel the same in the device, and the element isolation between the photoelectric conversion element and the buried channel, which has conventionally existed Since no region is formed, it is possible to cope with high density.

Embodiment An embodiment of the present invention will be described with reference to FIG.

FIG. 1a is a plan view of a CCD type solid-state imaging device. 1 is a LOCOS oxide film for forming an element isolation region. The difference from the conventional one is that a photodiode 5 and a vertical CCD,
Alternatively, the photodiode 5 and the photodiode 5 '
Is to give due consideration to the distance. Therefore, the LOCOS on the read gate side in contact with the buried channel 10
The oxide film 1 is recessed toward the photodiode 5 from the end of the read gate threshold voltage control diffusion region 2 on the buried channel side. This has been a problem in the prior art. However, as shown in the schematic cross-sectional view taken along the line BB 'of FIG.
The buried channel 10 of D is also shown in FIG. 1b.
In the schematic cross-sectional view taken along the line AA 'of FIG. 1a, it is possible to obtain a shape having the same channel width as the buried channel 10 of the CCD in which the left side is a read gate.
As a result, factors that degrade the transfer efficiency of the vertical CCD are eliminated. In addition, since the improved channel width is unified to the wider one of the conventional example, the transfer efficiency is thereby increased, the amount of charges handled is increased, and the characteristics of a video camera using the same are also improved.

Further, the increase in the amount of handled charges described above means that, if the amount of handled charges is the same, a larger number of pixels can be realized, and it is easier to respond to higher performance.

Here, as in the conventional case, the direction of movement of the charge can be considered from the path 8 to the path 7 as shown in the figure, but if the channel width is the same everywhere as in the present invention, the opposite direction ( It is apparent that the transfer efficiency from the top to the bottom in FIG. 1 is the same as the transfer efficiency in the conventional direction, and the drive method can be flexibly supported.

Effect of the Invention As described above, according to the present invention, the transfer efficiency can be improved by making the effective cross-sectional shape of the vertical CCD channel the same in the device, and the space between the photoelectric conversion element and the buried channel can be improved. Does not have an element isolation region, which has existed in the prior art, so that it is possible to cope with a high density, and its practical effect is large.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a CCD solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a diagram for explaining a conventional CCD solid-state imaging device. 1,21 LOCOS oxide film, 2,22 Diffusion region for read gate threshold control, 3,23 First polysilicon gate electrode, 4,24 Second polysilicon gate electrode.

Claims (1)

(57) [Claims] 1. A plurality of photoelectric conversion elements provided on a surface of a semiconductor substrate, and signal charges provided in close proximity to the photoelectric conversion elements and stored in the photoelectric conversion elements are sequentially read by a read gate, and predetermined. A solid-state imaging device having a CCD shift register for transferring in a given direction,
The shift register includes a buried channel extending along a charge transfer direction, and a threshold control diffusion region of the read gate extends along the entire length of a side wall of the buried channel between the photoelectric conversion element and the buried channel. In the four sides of the photoelectric conversion element, an element isolation region is formed by selective oxidation adjacent to three other sides except one side in contact with the read gate threshold value control diffusion region. A solid-state imaging device, wherein an element isolation region formed by oxidation does not contact the buried channel on the side where the gate threshold value control diffusion region is formed.