JPS59119760A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To simplify the process and contrive to improve the yield by a method wherein an electrode buried vertically in a photoelectric conversion film on the following insulation film and an electrode for external voltage at a fixed distance therefrom are provided through the insulation film in the upper part of an accumulation diode at a solid-state scanning part. CONSTITUTION:An n<+> layer 221 constituting a buried channel vertical CCD and an n<+> layer 222 constituting the accumulation diode are provided on a P type Si substrate 21, and poly Si layers 231 and 232 for transfer gate electrodes are provided above the n<+> layer 221. The photoelectric conversion film 25 is provided on the oxide film 24, and a window is opened through the films 25 and 24 by reactive ion etching by applying a resist mask, which window is made to reach the n<+> layer 222. Ni electrolytic plating is performed by impressing a voltage on the substrate, and the resist mask is removed by forming the vertical electrode 26. An opposed electrode 27 is formed at the fixed position away form the electrode 26. This constitution simplifies the complicated electrode construction in the lower part of a convertional element and then improves the yield. Further, the stepwise difference of the surface whereon the photoelectric conversion film is provided is improved, and the defect of an image due to pin holes is also prevented because of the use of transverse directional conduction.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state image sensor, and more particularly, to a solid-state image sensor that combines a photoelectric conversion film and a solid-state switching scanning element such as a charge transfer element.

[Technical background of the invention and its problems]

Solid-state image sensors are smaller than conventional image pickup tubes.

It has the advantage of being a lightweight, highly reliable camera, and can obtain high-quality images with almost no afterimages.

However, conventional solid-state imaging devices are mainly formed on Sl wafers, and have the disadvantage that the usable sensitivity wavelength range is limited to the visible wavelength range.
They have drawbacks that are not found in image pickup tubes, such as the effective photosensitive area of the photodiode and the ineffective photosensitive area of the signal transfer section, resulting in decreased sensitivity and the tendency to generate false signals such as moiré. As a solid-state imaging device that eliminates these drawbacks, an element has been proposed that uses a conventional solid-state imaging device as it is as a scanning section and performs photoelectric conversion with a photoconductor film provided on top of the device.

FIG. 1 is a cross-sectional view of a pixel of an interline transfer type solid-state image sensor that combines a photoconductor film and a charge transfer element. An n+ layer 121 forming a channel vertical CCD buried in a P-type Si substrate 1 and an n+ layer 121 forming a storage diode.
Layer 122 is formed. On top of the n''N12., there are two layers of ISi electrodes 13g and 132 which will become dart electrodes for transfer.
There is. In the storage diode part, the first oxide film 14 including the thermal oxide film is etched to reduce the n of the storage diode.
After forming the + layer 122 portion to be exposed, for example, At
The first electrode 15 is formed into a predetermined shape. After this, a second oxide film 16 is formed, and this film is further etched to expose a part of the first electrode 15.
The second electrode 17 is formed into a predetermined shape. A photoconductor film 18 such as A-8T is formed on top of this by sputtering or glow discharge, and a transparent conductive film 19 is further formed to obtain a solid-state image sensor having a scanning section and a photoelectric conversion section.

In addition, an example in which the first and second electrodes were made of polySt and molybdenum, respectively, and had a similar structure was disclosed in JP-A-5
It is described in Publication No. 7-32183.

In such a solid-state image sensor, whereas conventionally only the storage diode part effectively worked as one pixel, at least the second electrode 17 performs effective photoelectric conversion as one pixel. This has the advantage of increased sensitivity.

Originally, the photoconductor film 19 could be formed on the first electrode 15, but in this case, the oxide film 14 and the polySt electrode 13
Because the surface unevenness level difference due to the thickness of 1,132 mm is about 2 to 4 μm, and the etching part has steep parts, the photoconductor film is not continuous with these level differences, resulting in image defects. In extreme cases, sensitivity may not be obtained and image output may be poor. In order to prevent this, as shown in the figure, a second electrode is used to form a photoconductive film on a surface as smooth as possible while eliminating the step difference.

However, even with this configuration, the level difference on the surface cannot be completely resolved, and image defects are likely to occur. In addition, the manufacturing process is complicated, and there is a risk of defects due to misalignment of parquet.

There have been various proposals for the electrode structure of the photoconductor film, and one of the present inventors has already proposed the structure of the electrode in JP-A-56-891.
As shown in Japanese Patent No. 74, there is a structure in which electrodes to be opposed to each other are provided on the same plane or light is guided. However, even in this element, there is a problem in how to take out the electrodes.

[Purpose of the invention]

This invention has a new electrode configuration that connects the solid-state scanning section and the photoelectric conversion section, and has a so-called lateral conduction type in which signal charges generated in the photoelectric conversion section are subjected to an electric field almost parallel to the photoelectric conversion film. The purpose of this invention is to provide a solid-state image sensor having an electrode configuration.

[Summary of the Invention] This invention provides an electrode structure for a photoelectric conversion film in which one electrode is a vertical electrode that is embedded almost perpendicularly into a charging conversion film on the upper part of the storage diode in the solid-state scanning section through an insulating film on the upper part of the storage diode. At the same time, the other electrode for applying an external voltage to the photoelectric conversion film is formed at a position separated by a predetermined distance from this electrode to face the photoelectric conversion film, thereby making it a lateral conduction type.

〔Effect of the invention〕

According to the present invention, the complicated electrode structure of the conventional lower electrode can be eliminated, the manufacturing process is simplified, and the yield rate is improved. Furthermore, the level difference on the surface on which the photoelectric conversion film is provided is improved, the quality of the photoelectric conversion film is improved, and since lateral conduction is used, image defects due to pinholes in the film can be prevented. Further, there is no need for a transparent conductive film made of a limited material, and there is greater freedom in material selection.

[Embodiments of the invention]

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

FIG. 2 is a sectional view showing one pixel portion of an incline transfer type solid-state sensor according to an embodiment of the present invention. n” constituting the embedded channel of the vertical iM CCD in the P-type Si substrate 21.
N22. and an n+ layer 22 constituting a storage diode
The basic structure of providing polyst electrodes 231 and 232 thereon is the same as that in FIG. The oxide film 24 serving as an insulating film is formed by a melting method or the like to reduce unevenness and level difference to form a smooth surface, and a photoconductor film 25 such as a-8t is formed on the entire surface. Then, a resist film is applied over the entire surface for four times, and after nodding, the resist film is used as a block film and, for example, RIE (Reacjive Ion Etching) is performed.
), the photoconductor film 25 and the oxide film 24 are etched to form a contact hole reaching the n+ layer 222 of the storage diode, and an applied voltage applied to the St substrate is applied to the contact hole to etch a layer of, for example, Ni. Electrolytic plating is performed to form a vertical electrode 26 up to the upper surface of the photoconductor film 2.5. Excess plating can be removed by peeling off the resist film.

Although the upper surface of the vertical electrode 26 is preferably flush with the upper surface of the photoconductive film 25, there is no major problem even if there is a difference in level. A counter electrode 27 is formed at a position separated from the vertical electrode 26 by a certain distance. Note that the counter electrode 27 may be formed beyond the vertical electrode 26.

The solid-state imaging device of this embodiment does not require the complicated electrode structure of the conventional device shown in FIG. 1, and has an extremely simple structure because the electrodes are taken out from the storage diode section to the top. The electrodes include a vertical electrode 26 and a counter electrode 27 arranged in a plane.

FIG. 3 shows the electrode arrangement seen from the top of this solid-state imaging device. A vertical electrode 2 is provided for each pixel region with respect to the photoconductor film 25.
6, around which a counter electrode 27 is formed in a grid pattern common to all pixels. Note that the shape of the vertical electrode is not limited to the square shown in the figure, but may be circular or polygonal, and the surrounding counter electrode may be not only a square lattice, but may also be hexagonal, hexagonal, or simply striped. In either case, charges generated in the photoconductor film travel laterally across the film. Note that in some parts of the film thickness direction, charges may travel diagonally, but this is defined as lateral conduction as a whole including these.

According to this embodiment, since the electrodes do not face each other in the vertical direction of the photoconductor film, there is no risk of electrical short circuits in the vertical direction of the film due to defects introduced during film formation, such as sedge rush or dust. Defects will disappear. Further, in the embodiment shown in FIG. 2, the entire surface on which the photoconductor film is formed is uniformly an oxide film. Therefore, there is no effect on the physical properties of the photoconductive film, such as differences in adhesions or chemical composition, due to differences in substrate surface materials, so that the photoconductor film can be formed with good uniformity, which has the advantage of improving image quality. In addition to vapor deposition,
CvD (Chemical Vapor Deposit)
tion) Law and MBB (Mo1ecular Be
amEpitaxy) method, etc., due to the mismatch in the lattice spacing between the substrate and the photoconductive film material, an amorphous layer, a layer with little periodicity, or a polycrystalline layer may be formed in the initial stage of formation.
Even in the case where a predetermined single crystal photoconductor film is formed from a portion of an appropriate film thickness, the advantage of the configuration shown in FIG. 2 is that electrical contact can be made to the predetermined portion of the photoconductor film. There is. That is, since light is incident from the top surface, light is absorbed in the photoconductor film with good periodicity in the upper part, and the disordered film in the lower part can be left unrelated to photoelectric conversion.

Note that if the photoconductor film to be formed is not affected by the underlying material, various modifications can be made to the method of forming the electrode. For example, in FIG. 2, when the oxide film 24 is formed, a vertical electrode is formed by plating or the like up to the upper surface of the oxide film 24, and then a photoconductor film 25 is formed on the entire surface of the photoconductor. Similarly, vertical electrodes may be formed on the film and connected to the vertical electrodes in the previously formed oxide film.

FIG. 4 shows another embodiment, in which a counter electrode 27 is formed on the oxide film 24 before forming the photoconductor film 25. This embodiment has the advantage that the counter electrode 27 does not cast a shadow when viewed from the incident light, and the effective sensitive area increases.

FIG. 5 shows an example in which counter electrodes 271 and 272 are formed above and below the photoconductor film 25.

Further, FIG. 6 shows an example of an element in which the counter electrode 27 is formed in the contact hole by plating or the like in the same way as the vertical electrode 26. A hole is made in the photoconductor film 25 above the storage diode [2] Since the hole can be made in the same way when forming the vertical electrode 26, there is an advantage that both electrodes can be formed in the same process. It is clear that the structure shown in Fig. 5 is also of a completely transverse conduction type.

Other car inventions include various modifications as described below. Smoothing of the oxide film is not limited to the melt method; for example, a resist is applied to the oxide film with steps so that a large amount of resist accumulates on the four parts. The material and etching conditions may be selected so that the etching speed of the resist film and the oxide film are approximately the same, and etching may be performed by the RIE method until the etched surface becomes a smooth surface on the oxide film. .

As in the example, smoothing the oxide film has the advantage of making subsequent formation of the photoconductor film and/or turning extremely easy, but the photoconductor film and resist film are less affected by steps. In such cases, there is no need to force smoothing. Although it is necessary in the vertical direction, smoothing is not particularly necessary in a transversely conductive type as in the present invention, and the process can be shortened without smoothing.

For electrodes to be vertically buried in the photoconductor film, holes in the resist film are formed in advance in the photoconductor film, and after the resist is removed, the photoconductor film is left in the protruding shape. It may be formed. In this case as well, a photoconductive film is formed above the vertical electrode, but lateral conduction is utilized between it and the counter electrode.

Although an oxide film such as 5IO2 is mainly used as an example of the insulating film, an N513N4 film or a composite layer thereof may also be used.

Although a-8tO has been described as an example of the material for the photoelectric conversion section, the material is not limited to this, and examples include Sb2S3.5e-As-Te, CdSe, and C, which are used as photoelectric conversion materials for image pickup tubes.
It is clear that dZnTe can be used, but InSb and Pb
Infrared photoelectric materials such as 5nTθ and CdMgTe can also be used. Furthermore, in addition to photoconductor films, photovoltaic films can also be used.

The vertical electrodes can be formed not only by the method described in the embodiments but also by electroless plating or ion brating, and if the contact hole is wide, it is also possible to fill it with solder or conductive paste. Alternatively, the filling may be performed using the CVD method.

In addition to those mentioned in the examples, electrode materials include Cu, Pb, and A.
4Zn, Ti, Mo, Au, Ag, Pt, At-
8t, In.

Various materials such as Sn can be used, as well as vapor deposition, Sufu 4 Tsuta and C.
It is clear that a poly-Si film can also be used in the VD method. In the example, an example of an interline transfer type CCD was shown as the scanning readout section of a solid-state image sensor, but the invention is not limited to this, and a MOS type with a storage diode or a CPD Of course, it can also be applied to shapes.

In the embodiment, a two-dimensional sensor has been described, but the present invention can also be applied to a -dimensional sensor. Furthermore, it is clear that the planar electrode arrangement on the photoconductor film is not limited to the embodiments, but may also be a zigzag arrangement or the like.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a solid-state imaging device having a conventional electrode structure, FIG. 2 is a sectional view showing an embodiment of the solid-state imaging device of the present invention, and FIG. 3 is a plan view showing an example of the electrode arrangement. FIG. 4 #FIGS. 5 and 6 are cross-sectional views showing other embodiments of the solid-state imaging device of the present invention. 21 ・P type 81 board, 221, 2-22-n”
1L2-3. , 232--po vsi'rtt pole,
24... Smoothing oxide film, 25... Photoconductor film, 26...
...Vertical electrode, 27 (271, 272)...Counter electrode. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 7 Figure 3 Figure 4

Claims (1)

[Claims] Storage diodes that store signal charges provided corresponding to a plurality of pixels arranged in a semiconductor substrate, and a scanning readout section that reads out the signal charges of each storage diode are integrated and formed on the semiconductor substrate, with an insulating film interposed thereon. In a solid-state image sensor in which photoelectric conversion films are laminated and one electrode provided for each pixel region is connected to the corresponding storage diode to form a photoelectric conversion section, the one electrode is connected to the photoelectric conversion layer through the insulating film. 1. A solid-state image pickup device, comprising a vertical electrode vertically embedded in a conversion film, and a second counter electrode for applying an external voltage to the photoelectric conversion film arranged at a predetermined distance from the vertical electrode.