JP2542902B2 - Solid-state imaging device - Google Patents

Description

The present invention relates to a CCD solid-state image sensor.

(B) Conventional technology A conventional frame transfer type CCD solid-state image sensor is a channel for CCD channel separation in order to discharge excess charges to the outside when excessive light is picked up by the light receiving section that performs photoelectric conversion. An overflow drain was formed in the stop region.

In such a conventional device, since the overflow drain needs to be formed in the channel stop region, the entire channel stop region is widened, the device area is increased, and the integration rate is lowered.

On the other hand, in order to avoid such a decrease in the integration rate, it has been proposed to form an overflow drain in the deep part of the light receiving part (Japanese Patent Publication No. 59-17581), but such a deep overflow drain is formed by a frame transfer type. When it was applied to the CCD solid-state image sensor of, there were the following inconveniences.

That is, a frame transfer type CCD solid-state imaging device has a plurality of CCD channel regions and a channel stop region for partitioning the channel regions arranged in parallel on the surface of the semiconductor substrate, and the above-mentioned CC through an insulating film on the semiconductor substrate.
Since a plurality of charge transfer electrodes that are orthogonal to the D channel region are arranged in parallel, if the width of the channel stop region is narrowed because there is no overflow drain in the CCD channel region, the charge on this channel stop region will be reduced. The potential barrier fluctuates due to the voltage applied to the transfer electrode, resulting in incomplete channel separation. Therefore, even if an overflow drain is provided under the CCD channel region, excess charges will eventually flow out to the adjacent CCD channel region, and blooming cannot be eliminated.

(C) Problems to be Solved by the Invention The present invention has been made to solve the above-mentioned drawbacks, and it is possible to improve the integration ratio of a frame transfer type CCD solid-state imaging device provided with an overflow drain under a CCD channel region. It is intended to improve and prevent blooming.

(D) Means for Solving the Problems In the solid-state imaging device of the present invention, a drain region for discharging excess charges is provided in the deep portion of the semiconductor substrate, and the electrode width of the charge transfer electrode on the channel stop region is set on the CCD channel region. The width is set smaller than the electrode width.

(E) Action According to the solid-state image sensor of the present invention, by providing the drain region for discharging excess charges in the deep portion of the semiconductor substrate, as compared with the solid-state image sensor having the drain region for discharging excess charges in the CCD channel region. Can reduce the channel separation width,
Since the influence of the voltage applied to the charge transfer electrodes on the channel stop region can be reduced, there is no obstacle to channel separation.

(F) Embodiment FIG. 1 shows an embodiment of the CCD solid-state image pickup device of the present invention, in which FIG. 1 (a) is a plan view and FIG. 1 (b) is same as FIG.
Is a cross-sectional view taken along line XX of FIG.

In these figures, (1) is a semiconductor substrate made of silicon, a P well region (14) is formed on an N type substrate (10), and a P ⁺ type channel stop region (1
2) and an N-type CCD channel region (11) are formed. Further, a shallow intrinsic light receiving region (13) is formed near the surface of the channel region (11). The N-type substrate (10) in the deep part of the substrate constitutes an overflow drain.

(2) is an insulating film made of a silicon oxide film formed on the semiconductor substrate (1).

(31) and (32) are charge transfer electrodes of the first and second layers made of polysilicon on the insulating film.
In 1), the electrode width extending orthogonally to the CCD channel is constant, but the width of the second layer electrode (32) is set to be large at the center of the region and small at both ends.

 (4) is a protective film made of a silicon nitride film.

The image pickup device having such a structure is of a frame transfer type.
The CCD image pickup device is characterized in that the electrode width of the second layer electrode (32) is narrowed on the channel stop region (12). In the case of this embodiment, the narrow part of the electrode extends up to 30% on both sides of the channel width, and the part where no electrode exists in this channel region (11) serves as a light receiving window. An intrinsic light receiving region (13) is formed in the channel region (11) at the light receiving window position by introducing an impurity of the opposite conductivity type, and the second layer electrode (32) at the center 40% of the channel width has a substantial charge. It forms a transfer path.

The image sensor as described above has a light receiving area (13) at the light receiving window position.
After photoelectric conversion is performed and the charges are accumulated in the channel region (11) position under the first or second layer electrodes (31) (32) in the high potential state, the first and first pulse drive potentials are applied. The channel region under the two-layer electrodes (31) (32) is transferred,
It is output to the outside as an image signal.

The potential state during charge accumulation in the light receiving region (13) is lower than the potential of the channel stop region (12) and higher than the potential of the channel region, as shown in FIG. 1 (c). Therefore, at this time, since there is no electrode on the channel stop region (12) adjacent to the light receiving region (13), its potential barrier is higher than the potential of the light receiving portion (3) and is in a stable state. Does not flow over the barrier to the adjacent light receiving portion (3), and the excess charges are surely discharged to the deep N-type substrate (10) which becomes the overflow drain.

FIG. 2 shows another embodiment of the image pickup device of the present invention. The difference between this embodiment and the embodiment of FIG.
The electrode width of the layer electrode (31) is also equal to the channel stop region (1
2) The narrow part (30) narrowed above is provided.

Therefore, according to the structure shown in FIG. 2, during the charge transfer in which the pulse drive potential is applied to the first and second layer electrodes (31) (32), the transfer charge is in the high potential state. , Or the channel stop region (12) under the second layer electrode (32)
It is possible to suppress the decrease of the potential barrier of. As a result, it is possible to prevent the charges from flowing out to the adjacent channel not only when the charges are accumulated but also when the charges are transferred.

(G) Effect of the Invention Since the solid-state imaging device of the present invention is provided with the drain region for discharging excess charges in the deep portion of the semiconductor substrate, compared to the solid-state imaging device having the drain region for discharging excess charges in the CCD channel region. As a result, not only can the channel separation width be reduced and the integration rate of the device can be improved, but also the influence of the voltage applied to the charge transfer electrode in the channel stop region can be reduced, so that channel separation can be reliably performed and the blooming phenomenon can be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a), (b), and (c) are a plan view, a cross-sectional view, and a potential diagram of an embodiment of a solid-state imaging device of the present invention, and FIG. It is a top view of other examples of an element. (10) …… N-type substrate, (11) …… Channel area, (1
2) …… Channel stop area, (13) …… Light receiving area, (2) …… Insulating film, (31) (32) …… Electrode, (30)
...... Narrow part.

Claims (1)

(57) [Claims] 1. A plurality of CCD channel regions and a channel stop region for partitioning the channel regions are arranged in parallel on the surface of a semiconductor substrate, and a plurality of CCD channel regions orthogonal to the CCD channel regions are provided on a semiconductor substrate via an insulating film. In a solid-state imaging device in which charge transfer electrodes are arranged in parallel, a drain region for discharging excess charges is provided deep in the semiconductor substrate, and the electrode width of the charge transfer electrodes on the channel stop region is smaller than that on the CCD channel region. A solid-state image sensor characterized by having been set.