JPS61208868A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain a solid-state image pickup device having an overflow drain structure, by providing an overflow drain diode which is composed of a semiconductor thin film and a light-shielding electrode and is in/an electrically reverse junction with a storage diode of a semiconductor substrate. CONSTITUTION:When incident rays of light are weak, electrons of electron-hole couples generated in a photoconductive film 14 when the rays fall thereon are stored in a storage diode 2 by an electric field formed in the photoconductive film 14. As this state is enhanced, the level of energy in the N<+> layer of the storage diode 2 rises, and a diffusion potential VB of an overflow drain diode 9 diminishes. When surplus electrons are generated by the incidence of a strong light, on the other hand, the diffusion potential VB of the overflow drain diode 9 turns to be 0 naturally, and the surplus electrons are thrown away to the outside through the overflow drain diode 9. According to this constitution, a phenomenon of blooming can be controlled without the deterioration of the performance of the part of a solid-state switching scan element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a solid-state imaging device that combines a solid-state switching scanning element and a photoconductive film.

[Technical background of the invention and its problems]

A solid-state imaging device in which a photoconductive film is laminated uses a photoconductive film as a light-receiving element and has excellent characteristics of high sensitivity and low smear. For this reason, many TVs such as surveillance TV cameras
It can be used with the right camera and is being actively developed as a next-generation solid-state imaging device.

An example of this type of solid-state imaging device is one in which a photoconductive film and a transparent electrode are sequentially laminated on a semiconductor substrate having a charge transfer function, such as a CCD. That is, a pixel electrode connected to a diode region formed on the semiconductor substrate and separated for each pixel is provided on the semiconductor substrate. A photoconductive film is formed on this pixel electrode, and a transparent electrode is further provided on the photoconductive film. Note that in order to smooth the surface on which the photoconductive film is formed, an insulating layer may be formed on the uneven surface of the semiconductor substrate.

In this solid-state imaging device, when a bright subject is photographed, the charge generated in the photoconductive film becomes larger than the transfer capacity of the COD, and the charge accumulated in the CCD overflows from the vertical transfer circuit, causing a blooming phenomenon. Sometimes.

In order to suppress this pluming phenomenon, a horizontal or vertical overflow drain may be formed within the semiconductor substrate. However, in the case of a horizontal overflow drain, it is necessary to form an overflow control and an automatic gate 70-drain adjacent to each picture element, which reduces the area of storage diodes and transfer circuits, and improves the performance of the solid-state imaging device. will deteriorate. In addition, in the case of a vertical oat (-70- drain), it is formed three-dimensionally in the semiconductor substrate, for example, in a 2:P well structure, so scratches are likely to occur on the semiconductor substrate, and the resistance λ is also increased. The process is complex.

[Purpose of the invention]

The present invention has been made to solve these conventional drawbacks, and an object of the present invention is to provide a solid-state imaging device that is provided with an overflow drain structure at a position different from that of a solid-state switching scanning element.

[Summary of the invention]

That is, the present invention is constructed of a semiconductor thin film and a light-shielding electrode formed over the thin film, and is embedded in an insulating layer for smoothing the unevenness of the semiconductor substrate. The present invention is an optical four-electrode layer type solid-state imaging device characterized by having an overflow drain diode that is electrically reversely connected.

[Embodiments of the invention]

The details of the present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. This embodiment will now be described according to the manufacturing process.

First, a semiconductor substrate (1), for example, P+ on which a P well is formed.
On one side of the silicon substrate, there is a storage diode (2),
Vertical C0D (3
) are formed adjacent to each other, and this integrated structure is further separated from each other by a channel stop (4).

Then, an insulating film (7) for insulating the transfer electrodes (5), (6) is placed along with the transfer electrodes (5), (6) so that a part of the n-type region of the storage diode (2) is exposed. It is formed. In this way, a storage diode (2) and a scanning section are formed on the semiconductor substrate (1). A first electrode (8) made of, for example, An-81 is placed on the semiconductor substrate (1) so that a portion thereof contacts the n-type region of the storage diode (2).
) are formed separated from each other for each pixel. Next, on the first electrode (8) facing the storage diode (2),
As the overflow drain diode (9), for example, an amorphous 8%4(t) is used. A semiconductor thin film (91) made of ;, :H and having a thickness of about 0.5 μm and a light-shielding second electrode (92) made of, for example, Or are sequentially formed.

Of these, the semiconductor thin film (91) is formed from the first electrode (8) side to the n-type layer (911) and the n-type layer (9) using the glow discharge decomposition method.
The overflow drain diode (9) is electrically connected to the storage diode (2) via the first electrode (8). Here, the role of the n-type layer (911) is to connect the overflow drain diode (9) to the first electrode (8).
It is to make ohmic contact with 1 layer (912)
If not blocking the first electrode (8), the n-type layer (9
11) is not necessarily required. Further, the optical co-do gap value of the n-type layer (912) is about 1.20 e V, and the Pi layer (913) is for blocking injection of electrons from the second electrode (92). Furthermore, a second electrode (92)
The structure is such that a voltage can be applied depending on the external bias α value.

Next, an insulating layer made of polyimide, which is a heat-resistant organic material, is formed to smooth the surface of the 11i (8) and the overflow drain diode (9). is embedded inside the insulating layer (11). Then, avoid the overflow drain diode (9) and first electrode (8).
) A contact hole α2 is made on the insulating layer side to connect with
After forming the insulating layer αD, a third electrode (13) made of, for example, Affl-Si is formed at a predetermined interval on the insulating layer αD. It is electrically connected to the electrode (8).Then, on the third electrode (the second is a photoconductive film I, an amorphous 8i: HW (141)) and a P-type 8iC as an electron injection blocking layer. :H film (142) are sequentially formed with a thickness of about 3 μm and about 200λ, respectively, by the glow discharge public book method.Here, the diffusion potential of the photoconductive film I is about 1.
-OeV, which is larger than the extended to potential of the overflow drain diode (9), which is about 0.8 eV. Then [on the photoconductive film I (: is the light-transmitting fourth electrode (1
5 is formed, and a voltage can be applied to this by an external bias (lI19). In this way, a desired solid-state image sensor is obtained.

Figure 2 shows the transfer electrode (5), which transfers the charge accumulated in the storage diode (2) to the vertical COD (3), the overflow drain diode (9), and the third electrode (to) in this embodiment. FIG. 3 is a schematic diagram showing the positional relationship when viewed from the conductive film I side. As can be seen from the figure, the overflow drain diode (9) is formed separately along the transfer electrode (5), but this is because the overflow drain diode (9) is present between the first electrode (8). In this case, an overflow drain diode (
This is to prevent electrical leakage (9). Further, between adjacent overflow drain diodes (9), it is possible to create a connection structure in which the electric field is weakened in a region other than the picture element so that electrical leakage does not become a problem.

FIG. 3 is a diagram for explaining the pluming suppression operation mechanism of this embodiment.
FIG. 5B shows a case where the incident light is strong and excessive charges are generated. As shown in FIG. 3(, ), when light is incident, electron-hole pairs are generated in the photoconductive film I, but the electrons are transferred to the storage diode (2) due to the electric field formed in the photoconductive film I. is accumulated in And as this situation progresses,
The energy level of nJl of the storage diode (2) increases, and the diffusion potential vB of the overflow drain diode (9) decreases. Note that as long as the diffusion potential v1 does not become O, all of the electrons remain stored in the storage diode (2), and the stored electrons are sent to the vertical COD (3) by the action of the transfer electrode (5). On the other hand, when strong light is incident and excessive electrons are generated, the diffusion potential VB of the overflow drain diode (9) inevitably becomes O, as shown in Figure 3(b), and the excess electrons will be discarded to the outside through the overflow drain diode (9). Note that the amount of excess electrons that are discarded can be controlled arbitrarily because the diffusion potential VB of the overflow drain diode (9) can be freely adjusted by the action of the external bias (1). Since the amount of electrons transferred can be easily controlled so as not to exceed the vertical transfer capacity, the pluming phenomenon can be completely eliminated.

In this embodiment, the overflow drain structure is placed outside of the solid state switching scan element portion, without reducing the area of the storage diode as in the case of horizontal overflow drains, and without reducing the storage diode area as in the case of horizontal overflow drains. In addition, the slope 8/aI structure does not make it more likely to cause damage. In addition, in the case of horizontal or vertical overflow drains, the dimensions are on the order of several μm due to constraints within the substrate, but the overflow drain diode (9) of this embodiment has an arbitrary diode on the electrode (8). Since the shape can be reduced to a maximum size of about 10 μm, which corresponds to one pixel, design rules and manufacturing processes can be significantly relaxed.

Also in this example, the nW layer (911) has a thickness of 100×
Although the electrode is relatively thin and the resistance is extremely high, if electrical leakage occurs between the first electrodes (8) in the direction @ shown in FIG. 2 (C), the following can be done. In other words, the film and nHM that are the materials of the first electrode (8) and the layer (911) are connected to the semiconductor substrate (1).
After forming these layers continuously on top and etching them so as to separate each pixel, a 1-type layer (912) and a P-type layer (913) are formed in the same shape as shown in FIG. 1C-2. do.

In this structure, the shunn9 between adjacent 1u11 electrodes (8)
Since the layer (911) is not present, the aforementioned electrical leakage is not a problem at all.

In the embodiments so far, the structure of the overflow train diode (9) has been explained using an n -1-P base as an example, but as long as it is electrically reversely connected to the storage diode (2), for example, a Schottky diode can be used. Alternatively, it may be a heterostructure. In addition, the material of the overflow drain diode (9) is amorphous Sio,z
Geo, a: H is used, but if a diffusion potential is applied in advance by an external voltage, an amorphous material containing a halide or the like may also be used, and the first electrode (8
) etc. are made of polysilicon, for example, it may be made of other than amorphous semiconductor. 'Also, the overflow drain diode (9) may be formed on the first electrode (8) via an insulating layer, and connected to the first electrode (8) through a contact hole provided in this insulating layer. Furthermore, when the signal charges are mainly holes, it goes without saying that the polarities of the storage diode (2) and the overflow drain diode (9) may be reversed from those shown in FIG.

〔Effect of the invention〕

As explained above, the solid-state imaging device of the present invention has an overflow drain diode embedded in an insulating layer that smoothes unevenness on the surface of a semiconductor substrate, so that the performance of the solid-state switching scanning element can be improved. The blooming phenomenon can be suppressed without causing any deterioration.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing the positional relationship of the overflow drain diode, etc. of the embodiment shown in FIG. 1 when viewed from the photoconductive film side, and FIG. FIG. 1 is a diagram for explaining the blooming suppressing mechanism of the illustrated embodiment. (1)... Semiconductor substrate (8)... Third pole (9)... Overflow drain diode I...
・Insulating layer...Third electrode I...Photoconductive film a9...Fourth electrode Representative Patent attorney Kensuke Chika (and 1 other person) Figure 1 Figure 2 - ! Figure 8

Claims (3)

[Claims] (1) A semiconductor substrate on which a storage diode and a scanning section are formed, a first electrode formed on this semiconductor substrate to be separated from each other so that a part contacts the storage diode, a semiconductor thin film, and this semiconductor thin film. A light-shielding second layer formed on top
an overflow drain diode having a structure in which it has an electrode and is electrically reversely connected to the storage diode via the first electrode; an insulating layer smoothing over the first electrode and the overflow drain diode; are formed on the insulating layer at predetermined intervals, and the first
A solid body comprising: a third electrode connected to the electrode; a photoconductive film formed on the third electrode; and a transparent fourth electrode formed on the photoconductive film. Imaging device. (2) The solid-state imaging device according to claim 1, wherein the overflow drain diode has a structure to which a bias voltage can be applied from the outside. (3) The solid-state imaging device according to claim 1, wherein the semiconductor thin film is made of an amorphous material.