JP2917371B2 - 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 more particularly, to a solid-state imaging device in which signal charges photoelectrically converted in a light receiving region are temporarily stored under a storage gate electrode. .

[Prior Art] FIG. 4 shows a plan view of this type of conventional solid-state imaging device.
In the figure, a region surrounded by a solid line C is an active region, and an element isolation region is provided outside the active region. In the figure, reference numeral 301 denotes a light receiving region which is an n-type diffusion region formed in a surface region of a p-type semiconductor substrate, and 302 denotes a light receiving region 3
A storage gate electrode 303 for temporarily storing the signal charges photoelectrically converted in 01, a transfer gate 303 for controlling the transfer of the signal charges stored under the storage gate electrode 302 to the charge transfer unit 304 The electrode 305 is an overflow control electrode for controlling the transfer of the electric charge under the storage gate electrode 302 to the overflow diffusion layer 306.

FIGS. 5 (a) and 5 (b) show the potential distribution on the semiconductor surface along the lines AA and BB in FIG. 4, respectively. When a voltage is not applied to the overflow control electrode 305, the potential under the electrode is at a position indicated by a solid line a in FIG. 5 (a). Equal to the potential under the electrodes, both under the electrodes are in an enhanced state.

Thus, when a high-luminance subject is imaged, the accumulated charge overflows from below the accumulation gate electrode 302. To prevent this charge from flowing into the charge transfer portion, an overflow control electrode is required. It is necessary to make the potential under 305 deeper than that under transfer gate electrode 303.

Therefore, in the conventional example, a voltage of 3 to 4 V is applied to the overflow control electrode 305 to deepen the potential here as shown by the broken line b in FIG.

Further, in the conventional solid-state imaging device, when unnecessary charge under the storage gate electrode is discharged before storing necessary signal charge under the storage gate electrode, a voltage of about 12 V is applied to the overflow control electrode 305. The electric charge was discharged to the overflow diffusion layer 306 by applying the voltage and setting the potential under the electrode as shown by a broken line c in FIG.

[Problems to be Solved by the Invention] In the above-described conventional solid-state imaging device, the overflow control electrode has a voltage of 3 to 4 V during normal imaging and a voltage of 12 V when unnecessary charges are discharged.
Since V and binary voltages must be applied, peripheral circuits are complicated and voltage control is difficult.

[Means for Solving the Problems] A solid-state imaging device according to the present invention includes a light-receiving region of a second conductivity type formed in a surface region of a semiconductor substrate of a first conductivity type; A storage gate electrode provided on a substrate for forming a potential well for storing photoelectric conversion charges generated in the light receiving region, and transferring the photoelectric conversion charges generated in the light receiving region to an output unit; A charge transfer unit, a second conductivity type overflow diffusion layer formed in a surface region of the semiconductor substrate, and a transfer gate electrode provided on the semiconductor substrate between the storage gate electrode and the charge transfer unit And an overflow control electrode provided on the semiconductor substrate between the storage gate electrode and the overflow diffusion layer. -The control electrode part is depletion type (normally on type) and the transfer gate part is enhancement type (normally off type). In no bias, the potential under the overflow control electrode is deeper than that under the transfer gate electrode It has been made to be.

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

FIG. 1 is a plan view showing an embodiment of the present invention. In this figure, the same parts as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals in the last two digits, so that duplicate explanations will be omitted.
5 parts are made depletion type.

FIGS. 2 (a) and 2 (b) show AA line and BB line in FIG.
The potential distribution on the semiconductor substrate surface along the line is shown. The signal charge photoelectrically converted in the light receiving region 101 is stored in a potential well below the storage gate electrode 102.
In addition, the overflow control electrode 105 has a large amount of photoelectrically converted charges, and excessive charges are transferred to the overflow diffusion layer 106.
0V is applied to make it flow into the device, and 9V is applied to discharge unnecessary charges before storing necessary signal charges. The overflow control electrode portion is previously ion-implanted with phosphorus and arsenic under the electrode so as to be in a depletion state, and is made n-type. In this manner, even if no voltage is applied to the overflow control electrode, as shown in FIG. 2, the potential becomes deeper by d than under the transfer gate electrode. It flows only into the layer and not into the charge transfer section.

As described above, according to the present embodiment, the function of the overflow control electrode can be completed by applying only one type of voltage to the overflow control electrode, so that the peripheral circuit can be simplified.

FIG. 3 is a plan view showing another embodiment of the present invention.
In the figure, the same parts as in the embodiment of FIG.
Reference numbers with common digits are assigned. The difference of this embodiment from the previous embodiment is that only half of the channel below the overflow control electrode 205 (the shaded portion in the figure) is of the depletion type. In this embodiment, the same effect as in the previous embodiment can be expected.

[Effects of the Invention] As described above, according to the present invention, the potential under the overflow control electrode at the time of no bias is made deeper than the potential under the transfer gate electrode. The excess diffusion under the storage gate electrode can be absorbed by the overflow diffusion layer without applying a voltage. Therefore, according to the present invention, since only one type of voltage needs to be applied to the overflow control electrode, signal control is simplified and peripheral circuits are simplified.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are lines AA and BB in FIG. 1, respectively.
FIG. 3 is a plan view showing another embodiment of the present invention, FIG. 4 is a plan view showing a conventional example, and FIGS. 5 (a) and 5 (b). 4 is a potential distribution diagram of the semiconductor surface along the line AA and the line BB in FIG. 4, respectively. 101, 201, 301 ... light receiving area, 102, 202, 302 ... storage gate electrode, 103, 203, 303 ... transfer gate electrode, 104, 204, 304 ... charge transfer section, 105, 205, 305 ...
Overflow control electrodes, 106, 206, 306... Overflow diffusion layers.

Claims (1)

(57) [Claims] A second conductive type light receiving region formed in a surface region of a first conductive type semiconductor substrate; and a light receiving region provided on the semiconductor substrate adjacent to the light receiving region. A storage gate electrode for forming a potential well for storing the converted photoelectric conversion charge, a charge transfer unit for transferring the photoelectric conversion charge generated in the light receiving region toward an output unit, and a surface transfer region in the semiconductor substrate. A second conductivity type overflow diffusion layer formed on the semiconductor substrate, a transfer gate electrode provided on the semiconductor substrate between the storage gate electrode and the charge transfer unit, the storage gate electrode and the overflow diffusion layer, Between the overflow control electrode and the overflow control electrode provided on the semiconductor substrate during a period when no voltage is applied to the overflow control electrode. The potential on the semiconductor substrate under the overflow control electrode is set to be deeper than the potential on the semiconductor substrate under the transfer gate electrode when no voltage is applied to the transfer gate electrode. Solid-state imaging device.