JPH02161775A - Ccd type solid-state image pickup device - Google Patents

Abstract

PURPOSE:To eliminate a weak point associated with a blooming preventing measure so as to improve the quality of images of the title device by forming deep grooves in the surface of a substrate and forming overflow controlling electrodes in the grooves through an insulating substance. CONSTITUTION:A photodiode 2, CCD transferring section 3, and readout gate 4 are provided on a P-type impurity layer 1 formed on an N-type semiconductor substrate 6. In addition, an insulating film 10 is formed on the surface of the substrate 6 and a signal reading-out/transferring electrode 5 is provided on the film 10. A deep groove is formed into the substrate 6 through the impurity layer 1 adjacently to the photodiode 2 on the CCD non-transferring side and overflow controlling electrodes 8 are formed through the film 10. The overflow gate 7 of a P-type area exists between the photodiode 2 and groove. Moreover, a P<+> type impurity layer 9 is provided as a channel stopper to cover the transferring section 3 so that no signal charge leaks to the substrate 6 from the section 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a CCD type solid-state imaging device, and particularly to a structure designed to prevent blooming.

[Conventional technology]

CCD solid-state imaging devices generally include multiple photodiodes,
It consists of a signal readout and transfer section and an output circuit section. In such a solid-state imaging device, when a high-brightness subject is photographed, a phenomenon called blooming occurs in which charges generated in the photodiode unnecessarily overflow into the signal transfer section. As a countermeasure against blooming, various proposals have been made in the past. For example, FIG. 3 is a schematic cross-sectional view of a main part of a solid-state imaging device in which an overflow drain is provided next to a photodiode.

The right side of the figure is a signal readout and transfer section, and a buried type CCD transfer section 3 is formed on the right side of the photodiode 2 by an N-type impurity layer in a P-type semiconductor substrate 1'. A read gate 4 is located between the photodiode 2 and the CCD transfer section 3. By applying a voltage to the signal readout/transfer electrode 5 provided on the substrate surface via the insulating film 10 and controlling the potentials of the CCD transfer section 3 and the readout gate 4, the signal generated in the photodiode 2 and transferred is The charge is C
The data is transferred to the CD transfer section 3. As a blooming prevention measure,
A highly doped P-type overflow drain 6 is provided adjacent to the photodiode 2 on the left side of the figure.

An overflow gate 7 is formed between the overflow drain 6 and the photodiode 2, and the potential of the overflow gate 7 is controlled by an overflow control electrode 8 provided on the substrate surface via an insulating film 10. The potential of the overflow gate 7 is transferred to the signal readout/transfer electrode 5.
If the potential of the readout gate 4 is set to be deeper than the potential of the readout gate 4 set in Excluded by 6. In this way, blooming can be effectively controlled.

[Problem to be solved by the invention]

The conventional solid-state imaging device shown in Fig. 3 is effective as a countermeasure against blooming, but since an overflow gate and an overflow drain are provided on the substrate surface, the proportion of the area occupied by the photodiode is only the area of the overflow gate and overflow drain. Since this decreases, the sensitivity characteristics decrease accordingly.

FIG. 4 shows a solid-state imaging device proposed in view of the drawbacks listed in -. In this solid-state imaging device, a P-type impurity layer I is provided on an N-type semiconductor substrate 6 by diffusion. At this time, by utilizing the lateral diffusion of the P-type impurity, the lower part of the photodiode 2 is intentionally formed to have a shallower thickness.

Since this shallowly formed region is depleted, when an appropriate bias potential is applied to the N-type semiconductor substrate 6, excess charges generated by strong light are rejected by the N-type semiconductor substrate 6. Therefore, in this solid-state imaging device, there is no need to provide an overflow gate and an overflow drain on the substrate surface as shown in FIG. However, since the shallow P-type impurity layer at the bottom of the photodiode is controlled using lateral thermal diffusion, the degree of shallowness varies from device to device. (Lack occurs.) Therefore, when the amount of light exceeds a certain level, the amount of signal charge accumulated in the photodiode differs, resulting in output variations and a reduction in the dynamic range.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-quality solid-state imaging device that eliminates the drawbacks associated with the blooming measures described above.

[Means to solve the problem]

The CCD type solid-state imaging device of the present invention includes an impurity layer of an opposite conductivity type provided on a semiconductor substrate of a -conductivity type, a photodiode arranged on the impurity layer, and adjacent to the CCD non-transfer side of the photodiode, the impurity layer This structure has a structure in which a groove reaching deeper into the semiconductor substrate is formed, and an overflow control electrode is formed in the groove with an insulator interposed therebetween.

[Effect]

Since the electrode formed in the groove becomes an overflow control electrode, an overflow gate is formed between this electrode and the photodiode. By adjusting the potential of the overflow gate of this vertical structure, the excess charge of the photodiode does not flow to the CCD transfer section, but first overflows to this side and flows into the semiconductor substrate, thereby preventing blooming.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a main part of an embodiment of the present invention. A P-type impurity layer 1 is provided on an N-type semiconductor substrate 6, and a photodiode 2, a CCD transfer section 3, and a read gate 4 are provided on this P-type impurity layer 1. Further, an insulating film 10 is present on the surface of the semiconductor substrate, and a signal readout/transfer electrode 5 is provided on the insulating film 10J:.

A groove is formed on the non-transfer side of the CCD adjacent to the photodiode 2, and the bottom of this groove is deeper than the P-type impurity layer l.
It is formed until it enters the N-type semiconductor substrate 6. The overflow control electrode 8 is formed so as to be embedded in the groove with an insulating film 10 interposed therebetween. An overflow gate 7 in the PJN region exists between the photodiode 2 and the trench. Furthermore, in order to prevent signal charges from leaking from the CCD transfer section 3 to the N-type semiconductor substrate 6, a thick P layer is applied to cover the CCD transfer section 3.
A + type impurity layer 9 is provided as a channel stopper. In the solid-state imaging device shown in FIG. 1, when signal charges are being accumulated in the photodiode 2, a voltage is applied to the overflow control electrode 8 so that the potential of the overflow gate 7 is deeper than the potential of the readout gate 4. Then, as in FIG.
be ostracized by

In the present invention, there is no need to provide an overflow drain on the substrate surface, and the overflow gate 7 also utilizes the depth direction, so the area occupied by the overflow gate 7 on the substrate surface can be small, and the potential of the overflow gate 7 can be controlled with relatively little variation by the overflow control electrode 8, so there is little variation in the maximum amount of charge that can be stored in the photodiode 2.

FIG. 2 is a sectional view of a main part of another embodiment of the present invention. The difference between this embodiment and the previous embodiment is the overflow control. The reason is that tli8 is connected to the N-type semiconductor substrate 6 at the n-bottom 1.

In this embodiment, the overflow control electrode 8 and N
Although the type semiconductor substrates 6 are at the same potential, there is no problem with operation, and there is an advantage that wiring, input power supply, etc. are simplified.

〔Effect of the invention〕

As explained above, the solid-state imaging device with blooming countermeasures according to the present invention forms deep grooves on the surface of the substrate, and embeds overflow control electrodes in these grooves to transfer excessive signal charges generated by the photodiodes to the substrate. Since it can be excluded, the photodiode CCDCD
It has excellent characteristics in that it does not reduce the area occupied by the resonant image device, and the maximum implanted charge hardness of the photodiode does not vary.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the main part of a solid-state imaging device showing one embodiment of the present invention, Fig. 2 is a sectional view of the main part of the second embodiment, and Fig. 3 is a sectional view of the main part of the conventional bag. is a sectional view of a main part of another conventional device. l...P-type impurity layer, 2...photodiode,
3... CCD transfer section, 4... Read gate, 5
...Signal readout/transfer electrode. 6... N type conductor substrate, 7... Overflow gate, 8... Overflow control electrode. 9... Channel stopper (high concentration P-type impurity layer) 10... Insulating film. First cause patent applicant: NEC Corporation

Claims (1)

[Claims] An impurity layer of an opposite conductivity type is provided on a semiconductor substrate of one conductivity type, a photodiode is disposed in the impurity layer, and a groove is formed adjacent to the CCD non-transfer side of the photodiode and reaching deeper into the semiconductor substrate than the impurity layer. A CCD solid-state imaging device, characterized in that it has a structure in which an overflow control electrode is formed in the groove with an insulator interposed therebetween.