JPH0430192B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a solid-state imaging device that combines a photoconductor and a charge transfer device or a photoconductor and a solid-state switching scanning device, and particularly relates to a solid-state imaging device that has improved afterimage characteristics. Regarding an image sensor.

[Prior art and its problems]

The development of solid-state image sensors has been remarkable, and in addition to monolithic solid-state image sensors that form a photoelectric conversion section and a scanning section on a Si substrate, there are also monolithic solid-state image sensors that form a photoelectric conversion section and a scanning section on a Si substrate.
So-called "two-story solid-state image sensors" have begun to appear, which have a scanning section such as a CCD or MOS, and overlay a photoelectric conversion section such as a photoconductive layer on top of the scanning section.

FIG. 1 is a cross-sectional view of one pixel of a solid-state imaging device that combines a photoconductor and a charge transfer device. P type Si
A vertical CCD 2 consisting of an n ⁺ buried channel CCD and a storage diode 3 which is also n ⁺ are formed on the substrate 1 . Above the vertical CCD 2 is a poly-Si electrode 4 that serves as a transfer gate electrode. Storage diode 3
After etching the first oxide film 5 including the thermal oxide film to expose the n ⁺ part of the storage diode, a first electrode 6 made of, for example, Al is formed in a predetermined shape. Thereafter, a second oxide film 7 is formed, and this film is further etched to expose a portion of the first electrode, and a second electrode 8 made of Al or the like is formed thereon in a predetermined shape. A photoconductor layer 9 such as a-Si is formed on top of this by sputtering or glow discharge, and a transparent conductive film 10 is further formed to obtain a solid-state image sensor having a scanning section and a photoelectric exchange section.

In addition, almost the same structure was disclosed in Japanese Patent Application Laid-Open No. 1983-1983, in which the electrode material is poly-Si for the first layer and molybdenum for the second layer.
It is described in Publication No. 32183.

In such a solid-state imaging device, among carriers photo-generated in the photoconductor layer 9 such as a-Si, holes are stored on the transparent conductive film 10 side, and electrons are stored on the storage diode 3 as signal charges. These accumulated signal charges are transferred to polySi after 1/60 seconds or 1/30 seconds.
A pulse applied to a part of the electrode 4 causes the signal to be transferred from the storage diode 3 to the vertical CCD 2 . Thereafter, the signal charge transferred to the vertical CCD enters a horizontal CCD register (not shown) and is read out as a signal output after horizontal transfer.

Although such solid-state imaging devices have the advantage of having a larger photosensitive area and better smear and blooming characteristics than conventional Si monolithic devices, they may have problems with image retention characteristics. Some of the causes of afterimages are due to delayed photoresponse of photoelectric conversion films such as a-Si, but the
This is because when signal charges are transferred to the CCD, not all charges are transferred and remain. It is known that image retention caused by incomplete transfer is a problem not only in the solid-state image sensor shown in Figure 1, but also in conventional interline transfer type solid-state image sensors corresponding to the scanning section. "Afterimage phenomenon of CCD image sensors" (Shinichi Teranishi et al., Technical Report of the Television Society Vol.4.No.41pp25-30) and "No.
ImageLag Photodiodes Strveture in the
Interline CCD Image Sensor” (Nobukaqu
Teranishi etal IEDM82 12.6).

In other words, an interline transfer type CCD having an N ⁺ P junction photodiode 11 similar to the storage diode configuration shown in FIG. 1 as shown in FIG. 2 is in an incomplete transfer mode and tends to cause afterimages. The P ⁺ NP ^- structure photodiode 12 shown in FIG. 3 achieves a completely depleted state and enters a complete transfer mode, making it possible to eliminate afterimages.

In the solid-state image sensor with the configuration shown in Figure 1, an N ⁺ P junction storage diode is configured, resulting in an incomplete transfer ^mode . The electrostatic capacitance of the film is added, which also causes a delay in afterimage formation. Therefore,
It is desirable that the storage diode in combination with the photoconductor layer has a configuration that allows perfect transfer, and it is desirable to use a storage diode with a P ⁺ NP ^- structure that can eliminate the above-mentioned afterimage. However, as shown in Figure 1, electrons flow into the N ⁺ P storage diode through the electrode 6, and in the P ⁺ NP ^- configuration, the P ⁺ region that contacts the electrode 6 is photoexcited. Electrons cannot cross the P ⁺ region and enter the N region, resulting in no operation.

[Object of the Invention] An object of the present invention is to provide a solid-state imaging device that combines a photoconductor and a solid-state switching element with less afterimage.

[Summary of the invention]

This invention provides a solid-state scanning section in which an inlet for carriers from a photoelectric conversion section such as a photoconductor is provided in a storage diode section of a solid-state switching element, and a solid-state scanning section is configured such that most of the storage diode is in a complete transfer state. It is an imaging device.

〔Effect of the invention〕

According to the present invention, a solid-state image sensor with less afterimage can be obtained, and it is possible to image a subject under low illumination. In addition, the photoelectric conversion layer is located on the top of the Si solid-state scanning section,
Since the incident light does not reach the Si substrate and is absorbed within the photoelectric conversion layer, it is possible to obtain a solid-state imaging device that reproduces high-quality images without signals due to smear and crosstalk caused by carriers that conventionally occur within the Si substrate. .

[Embodiments of the invention]

Embodiments of the present invention will be described using the drawings.

FIG. 4 shows an embodiment of the present invention. The structure is almost the same as that in FIG. 1 except for the storage diode section. As shown in the figure, the structure of the storage diode section 15 is as follows: an n region 13 is formed on the P ^- Si substrate 1;
Furthermore, a thin P ⁺ region 14 is formed on the surface. this
The P ⁺ region is not formed over the entire surface, but is formed with a portion left. Furthermore, a first electrode 6 made of Al or the like is formed into a predetermined shape so as to be in contact with the n region. The subsequent formation method is similar to that shown in FIG.

When the storage diode section is configured as shown in the embodiment, electrons among carriers generated in the photoconductive film 9 such as a-Si are captured by the second electrode 8 due to the electric field and passed through the first electrode 9. Then, it is transferred to the storage diode 15, but a part of the P ⁺ region 14 is cut off,
Since it serves as an inlet to the n-region 13, signal charges can be easily accumulated in the storage diode 15. Furthermore, incomplete transfer to the vertical CCD section, which is a concern in conventional N ⁺ P and N ^{+ P-} configurations, is reduced.
P ⁺ NP ^- storage diode part, satisfies the condition of incomplete transfer and improves the afterimage phenomenon.

In most areas of the storage diode, the potential when the diode is depleted should be at least about 300 mV higher than the potential of the transfer gate determined by ^the poly-Si electrode 4, so that the complete transfer mode is achieved.
The realm fulfills this role. Electrons, which are signal charges, flow in from the n region, and it is desirable that the contact with the electrode in this region be as small as possible. Although the P ⁺ NP ^- configuration deviates from the original meaning of a diode, since the NP ^- diode primarily functions, P ⁺ NP ^- will also be called a storage diode.

[Other Examples]

FIG. 5 shows another embodiment of the invention. As in the previous embodiment, the configuration of the storage diode 17 is different from the conventional example.

It is the same as the embodiment shown in Fig. 4 in that the P ^- NP ⁺ configuration is adopted so that most of the storage diode is in a complete transfer state, but the place where electrons, which are signal charges, flow is set as the n ⁺ region 16. This is an example in which a storage diode 17 is configured. Electrons flow from the Al first electrode 6 to the n region 13, and the presence of the n ⁺ region 16 provides good electrical contact with the electrode, allowing electrons to flow more easily. In the configuration of the illustrated embodiment, the n ⁺ region is formed after the p ⁺ region is formed over the entire surface of the storage diode. In the diagram
Although the depth of the n ⁺ region and the p ⁺ region are the same, the depth is not limited to this.

In the above embodiment, an example has been described in which the electrode into which signal charges flow is divided into a first electrode and a second electrode, but the present invention is not limited to this, and it goes without saying that a single electrode may be used. Also, the contact part of the electrode is n or
Although an example is shown in which the area is smaller than or equal to the n ⁺ area, the contact portion of the electrode may extend to the p ⁺ area. As long as it is in contact with the n or n ⁺ region, signal charges can flow through that part, so it does not matter if it contacts the p ⁺ region, which is difficult to inflow.

Further, in the embodiment, the carriers transferred as signal charges are explained as electrons, but it is clear that if the carriers are holes, all p-type and n-type should be reversed.

Furthermore, it goes without saying that the photoelectric conversion section may be of not only a photoconductive type but also a photovoltaic type.

In any case, the signal charge from the photoelectric conversion section is
The diode structure of the storage part that exists before being transferred to the CCD is not just a PN format, but a thin P ⁺ layer is placed so that the transfer is in complete transfer mode.
Most of the part is composed of the P ⁺ NP ^- type, and the part where the signal charge can flow into a part of the P ⁺ layer that realizes the perfect transfer mode, that is, the part where the signal charge can flow into the same conductivity type as the signal charge (n type for electrons, n type for holes). In this case, it is sufficient if there is a p-type) part.

Further, in the above embodiments, the Si substrate is of p type or p ^- type, but the storage diode or CCD may be formed in a structure in which p type is diffused into an n substrate, for example.

Furthermore, the present invention can be applied when manufacturing a solid-state scanning section using a semiconductor other than Si as a substrate.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a conventional solid-state image sensor consisting of a photoelectric conversion section and a solid-state scanning section, Fig. 2 is a cross-sectional view of a conventional solid-state image sensor, and Fig. 3 is a cross-sectional view of a solid-state image sensor with improved afterimage. FIG. 4 is a cross-sectional view of a solid-state imaging device comprising a photoelectric conversion section and a solid-state scanning section of the invention, and FIG. 5 is another embodiment of the solid-state imaging device of the invention. 1...p-type Si substrate, 2...vertical CCD, 3...
Storage diode, 4... Poly-Si electrode, 5... First oxide film, 6... First electrode, 7... Second oxide film, 8
... second electrode, 9 ... photoconductor layer, 10 ... transparent conductive film, 11 ... smoothing oxide film, 12 ... photoconductive film, 13 ... n region, 14 ... p ⁺ region, 15 …
...storage diode, 16...n ⁺ region, 17...
storage diode.

Claims (1)

[Claims] 1. In a solid-state imaging device having a photoelectric conversion section provided on a semiconductor substrate and a solid-state scanning section formed on the semiconductor substrate, the surface of a storage diode provided on the semiconductor substrate that accumulates signal charges from the photoelectric conversion section A part of the surface is formed of a layer of the same conductivity type as the signal charge, and most of the other surface is formed of a layer of the opposite conductivity type to the signal charge, and the electrical contact from the photoelectric conversion part is at least connected to the signal charge. a storage diode portion formed of a layer of the same conductivity type to facilitate the flow of signal charge into the storage diode, and whose surface is formed of a layer of conductivity type opposite to that of the signal charge;
A solid-state imaging device characterized in that it is configured to enable complete charge transfer to a readout section provided on a semiconductor substrate.