JPH02105463A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To acquire a solid-state image sensing device which prevents afterimage phenomenon and realizes a large signal by making an impurity concentration of an impurity diffusion region of a photosensitive section higher at a side adjacent to a vertical transfer register. CONSTITUTION:A photosensitive section incorporates an N<->-type impurity region 1 and an N-type impurity region 2, and an impurity concentration thereof is made so high in the region 2 adjacent to a vertical resistor side as not to allow a diffusion potential with a P<+>-type read gate 9 which is a transfer region from photosensitive sections 1, 2 to the vertical register 6 exceed about one V. Since an impurity concentration in an impurity diffusion region of a photosensitive section is higher at a side 2 adjacent to a vertical register, readout of accumulated charge can be made satisfactorily, thus, resulting in increase of the accumulated charge at a photosensitive section without developing afterimage which causes deterioration of picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device, and particularly to the structure of a photosensitive portion.

[Conventional technology]

Generally, a solid-state imaging device using a charge-coupled device has a photosensitive part that accumulates charge according to the amount of incident light, a vertical transfer register that transfers the charge accumulated in the photosensitive part in the vertical direction, and a horizontal transfer register that transfers the charge in the horizontal direction. It consists of a register and a charge detection section that detects transferred charges.

Figure 3 shows the conventional vertical overflow drain structure for CO
FIG. 3 is a cross-sectional view of a semiconductor chip showing a D solid-state imaging device.

The photosensitive section has an N- type impurity diffusion region 1 provided in the P well layer 7 as a photosensitive element region.

The impurity concentration distribution in the N- type impurity diffusion region 1 is two-dimensionally uniform.

FIGS. 4(a) and 4(b) are potential distribution diagrams for explaining the operation of this conventional example.

FIG. 5 is a voltage waveform diagram showing the voltage applied to the vertical transfer electrodes.

The operation of this solid-state imaging device is as shown in FIG. 4(a).
After a certain period of time (timing t2 in Figure 5), the charge Q accumulated in the photosensitive section (timing tl in Figure 5) is transferred to the vertical transfer register (Figure 4(b)) and then transferred to the horizontal register (not shown). ) is transferred to a charge detection section (not shown) and the signal is extracted. If the image is not completely transferred from the photosensitive section to the vertical transfer register, a phenomenon called afterimage will occur when the image is displayed on a TV screen, degrading the image quality. In order to prevent this afterimage from occurring, the PN junction in the photosensitive area is normally used in a depleted state. In order to create a state in which the photosensitive area is structurally depleted, the N of the photosensitive area is reduced so that the photosensitive area is depleted by the readout voltage.
The impurity concentration of the - type impurity diffusion region 1 is reduced. When the impurity concentration is reduced, the amount of charge accumulated in the photosensitive area becomes smaller.

[Problem to be solved by the invention]

In the conventional solid-state imaging device described above, the impurity concentration in the impurity diffusion region of the photosensitive section is reduced to suppress the afterimage phenomenon, so there is a drawback that the amount of charge and signal that can be accumulated in the photosensitive section are reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state imaging device that suppresses afterimage phenomena and can obtain a large signal.

[Means for Solving the Problems] The solid-state imaging device of the present invention includes a photosensitive section on a semiconductor substrate, a vertical register that transfers charges accumulated in the photosensitive section in the vertical direction, and a horizontal register that transfers the charges accumulated in the photosensitive section in the horizontal direction. In a solid-state imaging device that integrates a charge detection section that detects the transferred charges, the impurity concentration of the impurity diffusion region of the photosensitive section is higher on the side adjacent to the vertical transfer register. It's something.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor chip showing one embodiment of the present invention.

The impurity concentration in the part (2) where the photosensitive part includes the N-type impurity region 1 and the N-type impurity region 2 and is adjacent to the vertical register side is high; ) and the P+ type read gate 9, which is a transfer region, is made dense so that the diffusion potential does not exceed about 1V.

The operation from this photosensitive section to the vertical register is as follows.

When a read pulse at timing t2 in FIG. 5 is applied to the vertical transfer electrode 3, the charges accumulated in the photosensitive area move to the vertical transfer register. The situation is shown in Figure 2 (a).
, shown in (b).

As shown in FIG. 2(a), the potential at the photosensitive area becomes deeper on the vertical register side and has a step-like shape. Conventionally, Fig. 4(a)
In this example, it is as shown in Fig. 2(a).
It can be seen that the amount of charge that can be accumulated increases in the area shown by the grid-like shading. In addition, the potential distribution changes in a step-like manner from the photosensitive area to the vertical register, so that the accumulated signal charge is smoothly transferred to the vertical register. So there is no problem.

〔Effect of the invention〕

As explained above, in the present invention, since the impurity concentration of the impurity diffusion region of the photosensitive section is higher on the side adjacent to the vertical register, the accumulated charge can be read out sufficiently, and as a result, no afterimage is generated that deteriorates the image quality. It is possible to increase the charge accumulated in the photosensitive area. Therefore, the characteristics of the solid-state imaging device can be improved, resulting in improved image quality and yield.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a semiconductor chip showing the vicinity of a photosensitive part according to an embodiment of the present invention, and FIGS. 2(a) and 2(b) show the vicinity of the photosensitive part and vertical register of the present invention immediately before and during readout, respectively. A potential distribution diagram, FIG. 3 is a sectional view of a semiconductor chip showing the vicinity of a photosensitive part in a conventional example, and FIGS. 4(a) and (
b) is a potential distribution diagram immediately before and at the time of readout near the photosensitive part and vertical register of the conventional example, respectively;
The figure is a waveform diagram of the voltage applied to the vertical transfer electrodes. DESCRIPTION OF SYMBOLS 1... N-type impurity diffusion region, 2... N-type impurity diffusion region, 3... Vertical transfer electrode, 4... Insulating film, 5...
...P+ layer, 6...N- type transfer channel, 7...P
Well layer, 8...N-type semiconductor substrate. Attorney Atsushi Douchi Shin 1N-type T: Disdainful Core Truth 1 ori! ±2−+jf−6÷ 2 coral diagram! Zutomata

Claims (1)

[Claims] A photosensitive section, a vertical register that transfers the charge accumulated in the photosensitive section in the vertical direction, a horizontal register that transfers it horizontally, and a charge detection section that detects the transferred charge are integrated on a semiconductor substrate. In a solid-state imaging device made of
A solid-state imaging device characterized in that the impurity concentration of the impurity diffusion region of the photosensitive section is higher on the side adjacent to the vertical transfer register.