JPH0232566A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To prevent any optical carrier from being produced in a barrier region in a partial region of a vertical charge transfer portion having a photoelectric conversion function and further prevent a signal from being deteriorated owing to diffusion of the optical carrier and so on by blocking said partial region which corresponds to a potential barrier of said vertical charge transfer portion. CONSTITUTION:An optical detector 10 of a solid-state image sensing device includes a photosensitive region 14 composed of a group of optical detector elements formed of photoelectric conversion elements arranged vertically, and a photosensitive transfer region 15 composed of photosensitive elements provided for each vertical line of the region 14. Pluralities of the regions 14 and 15 are vertically alternately arranged. The respective photosensitive elements posses a photoelectric conversion function and transfer signal charges by mutual transfer operation downwardly through CCD shift registers. The region 15 forms a self-scanning image sensing device having functions of photosensitive storage and transfer. A horizontal charge transfer section 11 is connected to a final end of the optical detector 10 through a transfer gate Tg for transferring horizontally the signal charge.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a solid-state image sensor, and more particularly to a solid-state image sensor with improved configurations of a light receiving section and a vertical charge transfer section.

(Prior Art) In recent years, electronic still cameras using solid-state image sensors have been announced. As a device that can be incorporated into this camera and function suitably, for example, the light-shielding film on the vertical charge transfer section of a conventional interline transfer type CCD is removed and a filter is placed, and the vertical charge transfer section also has a photoelectric conversion function. A solid-state imaging device has been proposed that can simultaneously improve resolution and sensitivity by having the following characteristics.

In the above device, since a light-shielding film is not provided on the vertical charge transfer path, signal charge transfer is performed by forming in advance a barrier region and a potential well portion with different potential well depths in the semiconductor layer under the transfer electrode. This is done by applying phase-shifted tarok pulses between vertically adjacent transfer elements to provide the potential gradient necessary for charge transfer.

(Problem to be Solved by the Invention) However, in the solid-state imaging device having the above configuration, since a light shielding film is not provided on the vertical charge transfer path, the photocarriers formed in the barrier region excluding the potential wells are exposed to the surrounding potential. It diffused into the wells and caused deterioration of color separation.

SUMMARY OF THE INVENTION An object of the present invention was to provide a solid-state image sensor that can perform color separation well and has excellent sensitivity and resolution, and is particularly suitable for use in electronic still cameras. be.

(Means and effects for solving the problem) That is, the above object of the present invention is to provide a photosensitive area formed by forming a plurality of light receiving elements having a photoelectric conversion function in a predetermined direction, and a transfer gate for each light receiving element. a potential barrier that separates adjacent photosensitive transfer elements from each other; This is achieved by a solid-state imaging device characterized in that a partial region of the photosensitive transfer element corresponding to 1 is shielded from light.

By blocking light from entering a part of the photosensitive transfer element corresponding to the potential barrier, generation of photocarriers in the barrier region corresponding to the potential barrier is eliminated, and deterioration of color separation can be prevented.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention,
This element outputs color image signals of three primary colors, RSG and B, in a frame sequential manner.

In the figure, the light receiving section 10 includes a photosensitive area 14 consisting of a group of light receiving elements formed by photoelectric conversion elements arranged vertically as shown by a dotted rectangle, and a photosensitive area 14 attached to each vertical column of the photosensitive area 14. It is formed of photosensitive transfer areas 15 made of photosensitive transfer elements, and a plurality of photosensitive areas 14 and photosensitive transfer areas 15 are provided alternately in the horizontal direction (in the horizontal direction in the figure).

On the surface of each light-receiving element in the photosensitive area 14, green and blue filters indicated by symbols R and B are arranged alternately in a vertical direction (a direction perpendicular to the horizontal direction).

The photosensitive transfer area 15, as shown by the dotted rectangle in the figure, consists of photosensitive transfer elements arranged in the vertical direction corresponding to each light receiving element of the photosensitive area 14, and each photosensitive transfer element has a photoelectric conversion function. It is formed of a CCD shift register which has a function of transferring signal charges downward by mutual transfer operation. That is,
The photosensitive transfer area 15 consists of a self-scanning imaging device with photosensitive storage and transfer functions.

On the surface of this photosensitive transfer region 15, red filters indicated by symbol R are arranged in a striped pattern.

A horizontal charge transfer section 11 is connected to the terminal end of the light receiving section 10 via a transfer gate Tg, and the horizontal charge transfer section 11 is formed of a horizontal CCD shift register that transfers signal charges in the horizontal direction.

An output amplifier 12 is arranged at the output end of the horizontal CCD, and signal charges are read out from the output terminal 13 for each horizontal row.

FIG. 2 shows a planar structure of the light receiving section 10. As shown in FIG.

The area surrounded by the dotted line is a channel stopper 16 formed on the silicon substrate, and the light receiving element of the photosensitive area 14 is formed in the area surrounded by the channel stopper 16.

A channel stopper 1 is provided between adjacent photosensitive areas 140.
A photosensitive transfer area 15 surrounded by 6 is formed. That is, transfer electrodes 18 and 19 made of polysilicon layers extending in the horizontal direction are formed alternately in the vertical direction, and the channel portion corresponding to the lower part of the transfer electrodes 18 and 19 corresponds to the photosensitive transfer element.

Then, two-phase drive (φ
V1. φV2).

Further, the photosensitive transfer region 15 is a region on the transfer region corresponding to a potential barrier between adjacent transfer elements (a region indicated by crossed diagonal lines in the figure, however, for the sake of simplicity, some regions are The AI light-shielding film 17 is provided only in the area (indicated by diagonal lines). As described above, the R filter is arranged on the photosensitive transfer element (in this embodiment, the area corresponding to the transfer electrode 19) where the AI light-shielding film 17 is not provided.

The reason for placing the R color filter on the photosensitive transfer element is that the signal charge caused by long wavelength light leaks in and the photocarriers generated deep in the substrate are diffused, which has a large effect on other light receiving cells. It depends on things.

A transfer gate 22 is provided in a part of the channel stopper for separating the photosensitive region 14 and the photosensitive transfer region 15 to control the field shift of signal charges generated in each light receiving element.

Although not shown in the figure, the polysilicon layers serving as the transfer electrodes 18 and 19 are overlamped so that adjacent parts are not electrically conductive, and are overlamped so as not to overlap the light receiving element in the photosensitive area 14. It is opened to

FIG. 3 shows a vertical section through the photosensitive transfer region 15 of the element.

In this embodiment, since charge transfer is performed using two-phase clock pulses, the thickness of the gate oxide film 20 under the transfer electrodes 18 and 19 is made different as shown in the figure, even under the same gate voltage. It is provided in a structure in which the depth of the potential well is partially varied.

As a result, even under the same voltage, the surface potential under the thin gate oxide film is higher than the potential in the thicker part, forming a deep potential well.

In addition, the transfer electrode 1 that forms this deep potential well
As described above, filters are arranged on the light shielding film 9 except for the light shielding film 17.

Therefore, light that irradiates the device is incident through this transfer electrode 19, and photocarriers are accumulated in the potential well below this transfer electrode 19. On the other hand, since the light shielding film 17 is provided on the transfer electrode 18 which acts as a barrier region when a low voltage is applied, photocarriers are not generated in the barrier region.

Figure 4 shows the switching process of charge transfer. When the charge accumulated in one potential well (before switching) is transferred under the next electrode, a voltage is applied to this electrode to create a deeper potential well. (during switching). At this time, the potential under the AI light-shielding film acts as a potential barrier against the leftward movement of the accumulated charge, and the signal charge always moves to the right (after switching).

Next, a case will be described in which the operation of the solid-state image sensor having such a configuration is applied to an electronic still camera.

First, when a subject image is formed on the light-receiving section 10 by shutter exposure, blue and green color signal charges are generated in the light-receiving element in the photo-sensitive area 14, and red color signal charges are generated in the photo-sensitive transfer element in the photo-sensitive transfer area 15. Electric charge is generated. Note that during shutter exposure, the transfer gate 22 and the transfer gate Tg are closed. Therefore, predetermined color signal charges are accumulated in each light receiving element and photosensitive transfer element as a lump.

Next, the transfer gate Tg is turned on and opened, and a two-phase driving tarok pulse φVl+φ is applied to the transfer electrodes 18 and 19.
Apply V2. As a result, as mentioned in Figure 4,
The red color signal charges in the photosensitive transfer region 15 are sequentially vertically transferred downward and supplied to the horizontal charge transfer section 11 .

This red color signal charge sent to the horizontal charge transfer section 11 is
The data is transferred at high speed in the horizontal direction and read out from the output terminal 13 via the output amplifier 12.

When a portion of the signal charge is read out, the signal charge is again sent from the photosensitive transfer area 15 to the horizontal charge transfer section 11 and read out from the output terminal 13, and by repeating this control operation, the signal charge is generated in the light receiving section 10. A red image signal for one screen is obtained.

Next, the transfer gate Tg is closed, and the transfer gate 22 is opened to field shift the charges in the photosensitive region 14 to the photosensitive transfer region 15. At this time, since there are two color signal charges of blue and green in the photosensitive region 14, only the signal charges of one color are read out by changing the threshold values of the respective gate voltages.

The blue or green color signal charge transferred to the photosensitive transfer area 15 is
Like the red color signal charge, it is vertically transferred and read out from the output terminal 13. Then, when an image signal for one screen is obtained for the signal charge of this color, finally, the other color signal charge of the remaining photosensitive area is similarly field-shifted and output from the output terminal 13. As a result, image signals of the three primary colors are obtained in a frame-sequential manner.

In the above description, it has been described that the two color signal charges in the photosensitive area 14 are field-shifted separately by changing the gate voltage, but it is also possible to field-shift the two colors at the same time and distribute them externally. . Then, a frame image is formed from these three fields of image signals read out (thereby, a suitable color still image can be obtained).

In addition to the so-called step oxide film method, which changes the oxide film thickness, as described in the above embodiment, as a method of creating a gradient in the potential distribution under one electrode, the so-called ion implantation method, which changes the doping level at a predetermined location, can be used. It can also be formed.

FIG. 5 shows another embodiment of the invention.

That is, in this embodiment, the photosensitive transfer area is clock pulse φ
It shows the case of 4-phase drive by Vl ~ φV,
Clock pulse φV1. A light shielding film 27 is formed on the transfer electrode to which φV3 is applied.

FIG. 6 shows the potential profile of this solid-state image sensor.

Note that FIG. 5A is a simplified illustration of FIG.

That is, a light shielding film 27 is provided on the electrodes E+' and E3, and no photocarriers are generated in the barrier region under this electrode during exposure with the shutter open (see the same figure). And 1=1. Only the mass of charge accumulated in the potential well under the E2 electrode at tt6 is transferred to the well formed under the E4 electrode at tt6.

In the above embodiment, a non-interlaced method has been described, but for example, field signals of each color that are output sequentially are stored in two different memories for each row, and the outputs from each memory are superimposed. By this,
It is also possible to form interlaced signals.

(Effects of the Invention) As described above, according to the solid-state image sensor of the present invention,
In the vertical charge transfer section having a photoelectric conversion function, a part of the region corresponding to the potential barrier is shielded from light, so that photocarriers are not generated in the barrier region below this region. Therefore,
Signal deterioration due to such diffusion of optical carriers does not occur. Furthermore, since the vertical charge transfer section has a photoelectric conversion function as well as a charge transfer function, sensitivity and resolution can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the configuration of an embodiment of a solid-state image sensor according to the present invention, FIG. 4 is a diagram illustrating the switching process of the photosensitive transfer region of FIG. 3; FIG. 5 is a vertical sectional view showing another embodiment of the present invention; FIG. The figure is a diagram illustrating the potential profile of the element in FIG. 5. 10: Light receiving section 11: Horizontal charge transfer section 12: Output amplifier 13: Output terminal 14: Photosensitive area 15: Photosensitive transfer area 16: Channel stopper 17. 27: A + light shielding film 18. 19: Transfer electrode 22: Transfer gate 3rd Figure 4 (3 others) After switching

Claims (1)

[Claims] A photosensitive area is formed by forming a plurality of light receiving elements having a photoelectric conversion function in a predetermined direction, and each light receiving element is formed via a transfer gate and has a photoelectric conversion function individually, and is interconnected by a predetermined transfer drive control. The device includes a photosensitive transfer region made of a photosensitive transfer element that transfers signal charges, and is characterized in that a partial region of the photosensitive transfer element corresponding to a potential barrier separating adjacent photosensitive transfer elements from each other is shielded from light. Solid-state image sensor.