JP2509592B2 - Stacked solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a stacked solid-state imaging device configured by stacking a photoconductor film on a solid-state imaging device chip.

(Prior Art) A solid-state image pickup device having a two-story structure in which a photoconductor film is laminated on a solid-state image pickup element chip can widen the opening area of the photosensitive portion, and therefore has excellent characteristics of high sensitivity and low smear. Have. For this reason, this solid-state imaging device is regarded as a promising camera for various surveillance TVs and high-definition TVs. The photoelectric conversion unit of this type of solid-state imaging device has a structure in which a photoconductor film is laminated on an array of pixel electrodes, and a transparent electrode is formed on the entire surface of the photoconductor film with a light-transmitting material. Therefore, it is the area of the pixel electrode that determines the photosensitive area of each pixel. However, since the transparent electrode and the photoconductive film are formed on the entire surface so as to cover the array of pixel electrodes, a part of the charge carriers generated by the light incident on the outside of the array of pixel electrodes may be part of the pixel at the edge. The electric field in the photoconductive film spreading outward from the upper part of the electrode strikes and flows into the pixel electrode at the end. Therefore, the area of the photosensitive portion of the pixel at the end of the pixel array is substantially larger than that of the pixels in other portions. Considering this as an image, the edge of the image becomes bright.
In particular, when the illuminance of incident light is high, a large amount of charge carriers generated outside the array of pixel electrodes flow into the pixel electrodes of several pixels at the end of the pixel array, which causes blooming. Therefore, the output signals from several pixels at the end of the pixel array cannot be used as a video signal.

(Problems to be Solved by the Invention) As described above, in the conventional stacked-type solid-state imaging device, charge carriers generated outside the pixel array flow into the edge part of the pixel array, so There is a drawback that output signals from several pixels cannot be used as video signals. In view of the above points, an object of the present invention is to provide a stacked solid-state imaging device that effectively uses an output signal from a pixel at an end as a video signal.

[Structure of Invention]

(Means for Solving the Problems) The stacked solid-state imaging device according to the present invention is characterized in that the dummy electrode is formed adjacent to the pixel electrode of the pixel at the end of the pixel array on the imaging element chip. This dummy electrode, directly or through the drain portion formed on the semiconductor substrate,
A constant voltage is applied.

(Function) Since the photoconductive film and the transparent electrode cover the pixel electrodes on the array of pixel electrodes in the stacked type solid-state imaging device, the photosensitive area of the pixel at the end of the pixel array is larger than that of the pixel in other areas. Grows. By forming a dummy electrode adjacent to the pixel electrode of the pixel at this end and applying a voltage similar to the voltage applied to the pixel electrode to this dummy electrode, the photosensitive region of the pixel at this end is It is possible to eliminate the effect of substantially increasing. That is, when there is no dummy electrode, the light incident on the outside of the pixel array is absorbed and a part of the generated charge carriers flows into the pixel electrode of the pixel at the end of the pixel array. By applying an appropriate voltage between the transparent electrode and the transparent electrode, it is possible to prevent the charge carriers generated outside the pixel array from flowing into the dummy electrode and from flowing into the pixel electrode. Therefore, since unnecessary charge carriers do not flow into the pixel electrodes at the ends, the pixels at the ends can have the same constant photosensitivity as the pixels at other parts.

 In addition, blooming at the edge of the pixel array can be suppressed.

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

FIG. 1 is a sectional structure of a portion including two pixels at an end portion of a pixel array of a stacked solid-state imaging device according to an embodiment. p ⁺ type Si
The interline transfer CCD image pickup device chip 1 is constructed by using a wafer in which the p-well 12 is formed on the substrate 11. That is, the storage diodes 13 that store the signal charges are formed in a matrix and adjacent to the column of the storage diodes 13.
A vertical CCD 14 composed of an n ⁺ type buried channel CCD is formed. Reference numeral 15 denotes a p ⁺ -type layer as a channel stopper, which is separated and a set of storage diode rows and vertical CCDs having the same structure is repeatedly arranged. 16 _1, 16 ₂
Is a transfer gate electrode of the vertical CCD 14, and a part thereof also serves as a charge transfer gate electrode from the storage diode 13 to the CCD channel. The substrate on which the transfer gate electrodes 16 ₁ and 16 ₂ are formed is covered with the interlayer insulating films 18 ₁ and 18 ₂ and the polycrystalline silicon electrode 17 connected to the storage diode 13 is formed and flattened. There is. The first interlayer insulating film 18 ₁ is, for example, C
A second interlayer insulating film, which is a SiO ₂ film formed by the VD method
18 ₂ is, for example, a BPSG film formed by the plasma CVD method. In this structure, after forming an opening in the first interlayer insulating film 18 ₁ ,
After the polycrystalline silicon film electrode 17 is formed on each storage diode 13, the BPSG film 18 ₂ is deposited and melted, and the BPSG film is etched by the reactive ion etching method to form the surface of the polycrystalline silicon electrode 17. It is obtained by exposing.

CCD image sensor chip 1 with a flat surface in this way
A pixel electrode 19 and a dummy electrode 20 connected to each polycrystalline silicon electrode 17 are formed on the top. The dummy electrode is adjacent to the pixel electrode 19 at the end and extends in the vertical direction in parallel with the vertical CCD 14. The pixel electrode 19 and the dummy electrode 20 are formed into a predetermined shape by depositing Cr by about 1000Å by a sputtering method and etching by a reactive ion etching method. The distance a between the dummy electrode 20 and the pixel electrode 19 at the end is formed so that the distance b between the pixel electrodes 19 is equal.

Thus, the photoconductor film 2 is laminated on the chip substrate on which the pixel electrode 19 and the dummy electrode 20 are formed. The photoconductor film 2 is an i-type a-SiC: H as a hole injection blocking layer.
(Hydrogenated amorphous silicon carbide) film 21, mainly consisting of a high resistance a-Si: H film 22 that undergoes photoelectric conversion, and a p-type a-SiC: H film 23 that serves as an electron injection blocking layer. . These films are formed by the glow discharge decomposition method of a gas containing SiH ₄ gas as a main component. The a-SiC: H film 21 has a dark conductivity σ _D -10 ⁻¹⁴ (Ωcm) ⁻¹ at room temperature and a thickness of about 100 Å. The high-resistance a-Si: H film 22 has σ _D ˜10 ⁻¹² (Ωcm) ⁻¹ and has a sufficient thickness necessary for photoelectric conversion. To have sufficient photosensitivity to visible light, a film thickness of 0.5 μm or more is required.
The p-type a-SiC: H film 23 has a thickness of about 200Å. The transparent electrode 24 is formed on the photoconductive film 2 thus formed, for example, by ITO (Indium).
Tin Oxide). Although not shown in FIG. 1, the photoconductor film 2 and the transparent electrode 24 on the dummy electrode 20.
Is partially removed by etching, and a desired voltage is applied to the dummy electrode 20 from the outside through the exposed portion of the dummy electrode.

The optical sensitivity of the image pickup apparatus of this example was measured. CCD
The image sensor chip is a 200,000 pixel, 2/3 inch size. White light was made incident so that the illuminance on the light receiving surface of the image pickup device was 1.5 lux. The charge carriers photoelectrically converted in the photoconductor film 2 and stored in the storage diode 13 are transferred to the vertical CCD 14 by the read pulse voltage applied to the transfer gate 16 ₁ . Therefore, the potential of the pixel electrode 19 electrically connected to the storage diode 13 becomes equal to the potential of the read pulse voltage applied to the transfer gate 16 ₁ . This read pulse was measured at + 5V and the transparent electrode 24 was grounded. Therefore, the voltage applied between the pixel electrode 20 and the transparent electrode 24 is 5V. The following table shows the result of measurement of photosensitivity when a voltage of 5 V, which is equal to that of the pixel electrode 19, is applied to the dummy electrode 20. The result is that the output voltage V ₁ from the pixel at the edge is
It is shown by dividing by the signal voltage V ₂ of the 10th pixel.

In addition, the results in the case of the conventional stacked type solid-state imaging device having no dummy electrode are also shown for reference. This laminated solid-state imaging device has the same structure as that of the embodiment except that no dummy electrode is formed. It can be seen that in the conventional example having no dummy electrode, the signal voltage of the pixel at the end is higher than that of the other pixels. This is because the electrons generated by entering the area A outside the pixel electrode 19 at the end flow into the adjacent pixel electrode 19 at the end. In the case of the embodiment in which the dummy electrode is provided, the dummy electrode 20 and the transparent electrode
It is possible to prevent electrons generated in the region A from flowing into the dummy electrode 20 due to the vertical electric field between 24, and unnecessary electrons from flowing into the pixel electrode 19 at the end. Therefore, it can be seen that the output signal voltage of the pixel at the end portion becomes equal to that of the pixels at other portions. It was also confirmed that blooming at the edge of the pixel array was suppressed when strong light was incident.

As is clear from the above results, in the stacked solid-state imaging device in which the dummy electrode adjacent to the pixel at the end of the pixel array is formed, the output signal from the pixel at the end of the pixel array is effectively used as the video signal. I can do things.

FIG. 2 shows a laminated solid-state image pickup device according to another embodiment. The parts corresponding to those in FIG. 1 are designated by the same reference numerals as those in FIG. 1 and their detailed description is omitted. The difference from FIG. 1 is that the drain portion 26 of the n ⁺ type layer is formed in the p well of the Si wafer and the drain portion 26 is formed.
That is, the polycrystalline silicon electrode 25 electrically connected to the dummy electrode 20 is formed thereon. In this embodiment, the dummy electrode 20
The potential is controlled by the voltage applied to the drain portion 26 in the same manner as in FIG. 1, and the same effect as in the previous embodiment can be obtained.

Although the CCD image sensor is used in the embodiment, the MOS type or BB
The present invention can be similarly applied to a stacked solid-state imaging device in which a D-type imaging element chip is used as a charge transfer section and a photoconductor film is stacked on the charge transfer section.

〔The invention's effect〕

As described above, according to the present invention, the dummy electrode is provided adjacent to the pixel electrode of the pixel at the end of the pixel array, and the potential of this dummy electrode is controlled, so that even the pixel at the end has uniform photosensitivity. Thus, a stacked solid-state imaging device that effectively utilizes the output signals of the pixels at the end portions can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a laminated solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a diagram showing a laminated solid-state imaging device according to another embodiment. In the figure, 1 ... CCD image sensor chip, 2 ... photoconductor film, 11 ... p
⁺ Type Si substrate, 12 …… p well, 13 …… storage diode, 1
4 …… vertical CCD, 15 …… p ⁺ type layer, 16 ₁ , 16 ₂ …… transfer gate, 17 …… n ⁺ type polycrystalline silicon electrode, 18 ₁ , 18 ₂ …… interlayer insulating film, 19 …… pixel Electrode, 20 ... Dummy electrode, 21 ... i
Type a-SiC: H film, 22 …… i-type a-Si: H film, 23 …… p-type a-SiC: H film
Membrane, 24 ... Transparent electrode, 25 ... n ⁺ type polycrystalline silicon electrode,
26 …… n ⁺ type drain part, 27 …… incident light, a …… distance between the pixel electrode 19 and the dummy electrode 20 at the end, b …… each pixel electrode
Distance between 19, A ... area outside the pixel array.

Claims (3)

(57) [Claims] 1. A solid-state imaging device in which an array of signal charge storage diodes and an array of signal charge readout units are formed on a semiconductor substrate, and an array of pixel electrodes electrically connected to the signal charge storage diodes is formed on an uppermost portion. In a solid-state imaging device in which a photoconductor film is stacked as a photoelectric conversion unit on an element chip, a dummy electrode is formed adjacent to the pixel electrode at the end of the array of pixel electrodes, and the dummy electrode is generated in the photoconductor film. A stacked solid-state image pickup device, characterized in that, of the signal charges, the signal charges flowing into the dummy electrode are discharged. 2. A drain portion formed of a diffusion region is formed on the semiconductor substrate, and the drain portion is electrically connected to the dummy electrode.
The laminated solid-state imaging device according to the item. 3. The stacked type device according to claim 1, wherein the signal charge storage diode and the pixel electrode electrically connected to the signal charge storage diode are two-dimensionally arranged. Solid-state imaging device.