JPH0327569A - Solid-state image-pickup device - Google Patents

Abstract

PURPOSE:To increase the amount of charge to be accumulated and improve sensitivity of a image-pickup device by reducing the channel width directly below a gate electrode as compared with that directly below an overflow control electrode. CONSTITUTION:A gate electrode 4 and an overflow control electrode 8 are formed in one piece and a width W2 formed below the electrode 8 is made longer than a channel width W1 below the electrode 4. The same voltage is applied to both the electrode 4 and 8 and the depth phi4 of a potential well directly below the electrode 4 is made slightly shallower than that phi8 of the potential well directly below the electrode 8. Thus, when there are many changes produced due to photo-electric conversion, the overflown charge directly below an accumulated gate electrode passes through the potential well directly below the electrode 8 into an overflow drain region 9, thus restricting blooming positively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device of a type in which photoelectric conversion charges generated in a light-receiving region are temporarily stored under a storage gate electrode.

[Prior Art] FIG. 3 is a plan view of a conventional solid-state image sensor of this kind, and FIGS. 4(a) and 4(b) are IV in FIG. 3, respectively.
It is a sectional view taken along the a-IVa' line and the IVb-IVb' line.

As shown in FIGS. 3 and 4, in the conventional image sensor, an N-type light-receiving region 2 is provided in a P-type semiconductor substrate 1, and an insulating film 3 is provided on the semiconductor substrate adjacent to this light-receiving region. A gate electrode 4a is provided via the gate electrode 4a, and a storage gate electrode 5 and a transfer gate electrode @6 are provided sequentially in the charge transfer direction following this electrode. A charge transfer section 7 (the transfer gate electrode is not shown) is provided at the tip of the transfer gate electrode 6 . Further, an overflow control electrode fi8a is provided adjacent to the storage gate electrode 5 in a direction perpendicular to the charge transfer direction, and an N-type overflow drain region 9 is formed in the semiconductor substrate 1 beyond that. In FIG. 3, the region indicated by the solid line A is the active region, but this region is surrounded by a P+ type channel stopper or a LOCOS oxide film (both not shown) and is separated from other regions. .

FIGS. 4(a) and 4(a) of this conventional solid-state image sensor
The potential distribution on the surface of the semiconductor substrate along the cross-section in b) is shown in FIGS. 5(a) and 5(b), respectively. The charges photoelectrically converted in the light receiving region 2 are stored directly under the storage gate electrode 5 through a potential well with a depth φ41 directly under the gate electrode 4a. Normally, the charge directly under the storage gate electrode is sent to the charge transfer section 7 via the transfer gate electrode 6 (the potential under the electrode 6 when the transfer gate electrode is performing a charge transfer operation is shown in FIG. 5(a)). (indicated by a dotted line), the charge is then transferred within the charge transfer section toward the output section along the direction of the arrow. However, when the amount of photoelectrically converted charge is large and cannot be held under the storage gate electrode, the overflowing charge passes through a potential well with a depth of φ8a directly under the overflow control electrode 8a to the overflow drain region 9. Flow into.

This operation prevents a malfunction called blooming due to overflow of accumulated charges.

[Problems to be Solved by the Invention] In a solid-state imaging device, in order to suppress blooming, the depth of the potential well directly below the gate electrode 4a is set to φ4.
However, in conventional solid-state imaging devices, in order to completely suppress blooming, the potential well depth φ88 directly below the overflow control electrode 8a must be made deeper, taking into account manufacturing variations. The difference in depth of the wells is made to be sufficiently large. Therefore, in the conventional solid-state image sensor, the amount of photoelectric conversion charge that can be stored under the storage gate electrode is reduced, resulting in a decrease in sensitivity. Further, in the conventional example, the gate electrode and the overflow control electrode require wiring from separate power sources, which makes the wiring complicated and requires space for laying the wiring.

[Means for Solving the Problems] The solid-state imaging device according to the present invention is of a type in which photoelectric conversion charges generated in a light receiving region are temporarily accumulated under an accumulation gate electrode and sent to a charge transfer section by operating a transfer gate electrode. A gate electrode is provided between the light-receiving region and the storage gate electrode to control the charge passing under it, and a gate electrode is provided near the storage gate electrode to absorb the charge overflowing from under this electrode. An overflow drain is provided, and an overflow control electrode is provided between the overflow drain and the storage gate electrode.

The solid-state image sensor of the present invention is characterized by:
The gate electrode and the overflow control electrode are electrically connected, and the channel width under the gate electrode is shorter than that under the overflow control electrode.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view showing one embodiment of the present invention, and FIG.
) is a sectional view taken along the line nn', and in these figures, the same reference numbers are given to the parts common to the conventional example shown in FIGS. 3 and 4, so duplicate explanations will be omitted. Omitted. In this embodiment, the gate electrode 4 and the overflow control electrode fi8 are integrated, and the width w2 of the channel formed under the overflow M# electrode 8 is made longer than the width w1 of the channel under the gate electrode 4. There are 5 6.

FIG. 2(b) shows the potential distribution on the surface of the semiconductor substrate along the cross section of FIG. 2(a).

The same voltage is applied to the gate electrode 4 and the overflow control electrode 8, but since the channel width Wl directly under the gate electrode is shorter than the channel width W2 directly under the overflow control electrode 8, the gate electrode 4 and the overflow control electrode 8 are applied with the same voltage. The depth φ4 of the potential well directly below the electrode 4 is slightly shallower than the depth φ8 of the potential well directly below the overflow control electrode 8. Therefore, when there is a large amount of photoelectrically converted charge, the overflowing charge directly below the storage gate electrode 5 flows into the overflow drain region 9 through the potential well directly below the overflow control electrode 8. Therefore, blooming can be reliably suppressed. In this way, by making a difference in the channel width directly under both electrodes, it is possible to precisely control the difference in potential under both electrodes, so it is necessary to take a margin like when making a difference in potential by the difference in voltage applied to both electrodes. Therefore, the amount of charge that can be stored under the storage gate electrode 4 can be increased.

Furthermore, in the solid-state imaging device manufactured in this manner, the same voltage can be applied to the gate electrode 4 and the overflow control electrode 8, so that the number of wiring lines can be reduced by one.

In addition, although the above embodiment used a P-type semiconductor substrate, this can be changed to one using an N-type semiconductor substrate. Furthermore, each element may be formed in a P (or N) type well region using an N type (or P type) semiconductor substrate.

[Effects of the Invention] As explained above, in the present invention, the channel width directly under the gate electrode is made shorter than that directly under the overflow control electrode, so according to the present invention, overflow control is performed using the narrow channel effect. The depth of the potential well under the electrode can be made deeper than that under the gate electrode, and the potential difference can be precisely controlled. Therefore, according to the present invention, there is no need to provide a margin for the voltage applied to each electrode as in the conventional example, and it is possible to increase the amount of charge that can be stored under the storage gate electrode and improve the sensitivity of the image sensor. can. Further, according to the present invention, since only one type of voltage is required to be applied to both electrodes, one voltage generation circuit and one power supply wiring can be omitted, and the circuit and wiring can be simplified.

5... Storage gate electrode, 6... Transfer gate electrode, 7... Charge transfer section, 8, 8
a... Overflow control electrode, 9... Overflow train region.

Claims (1)

[Claims] a light-receiving region of a second conductivity type formed on the surface of a semiconductor substrate of a first conductivity type; a gate electrode provided on the surface of the semiconductor substrate adjacent to the light-receiving region with an insulating film interposed therebetween; and adjacent to the gate electrode. a storage gate electrode that forms a potential well for storing photoelectrically converted charges generated in the light-receiving region and passed under the gate electrode; and a storage gate electrode that is provided adjacent to one side of the storage gate electrode. a transfer gate electrode that controls the transfer of photoelectric conversion charges accumulated under the storage gate electrode to the charge transfer section; an overflow control electrode provided adjacent to the other side of the storage gate electrode; and the overflow control electrode. and a second conductivity type overflow drain region formed on the surface of the semiconductor substrate adjacent to the semiconductor substrate, wherein the gate electrode and the overflow control electrode are electrically connected, and the overflow control electrode is electrically connected to the overflow control electrode. A solid-state imaging device characterized in that the width of the channel under the electrode is longer than that under the gate electrode.