JPH05167056A - Lamination-type solid-state image sensing device - Google Patents

Abstract

PURPOSE:To achieve the low after image, the low sticking and the high sensitivity of a lamination-type solid-state image sensing device by a method wherein a voltage which can cause an avalanche multiplication operation or the like can be applied to a photoconductive film in the lamination-type solid-state image sensing device wherein the photoconductive film has been laminated on a solid-state image sensing element chip. CONSTITUTION:A charge storage part 2 and a charge transfer part 3 are formed on a semiconductor substrate 1; a pixel electrode 13 which has been connected electrically to the charge storage part 2 via a second metal electrode 11 is formed; an electric-field relaxation layer 14 which is composed of a high- resistance body is formed in a region around the end part of the pixel electrode 13. A photoconductive film 15 is laminated on the pixel electrode 13 and the electric-field relaxation layer 14; a transparent electrode 16 is formed on it. Thereby, a lamination-type solid-state image sensing device is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated solid-state image pickup device having a photoconductive film laminated on a solid-state image pickup element chip.

[0002]

2. Description of the Related Art Generally, a CCD (Charge Coupled Devic
In the solid-state imaging device using e) or the like, since the photodiode unit that performs photoelectric conversion and the circuit unit that reads out the signal charges are arranged on the same plane of the silicon substrate,
The utilization rate of incident light is poor, and there is a limit to high sensitivity.

Therefore, a method of collecting light for each pixel by providing a convex minute lens on each photodiode constituting the photodiode section, or stacking a photoconductive film used in an image pickup tube on a solid-state image pickup element The method to do is proposed. In particular, in the method of stacking photoconductive films, since the photosensitive part is located at the top of the device, the utilization rate of ultraviolet rays, blue light, etc. can be increased, and the spectral sensitivity can be freely designed by selecting the laminated film material. The advantage that can be obtained is obtained.

An example of such a laminated solid-state image pickup device is one in which an a-Si: H (hydrogenated amorphous silicon) film is laminated on a CCD chip (Television Society National Conference Proceedings, 3-5, 1983). , Pp45-46), MOS
Laminated Se-As-Te (saticon) film on the image sensor (Technical Report of the Television Society of Japan, ED480, 1980, pp41-)
46), a on the AMI (Amplified MOS Imager) image sensor
-Se films laminated (Television Society National Conference Proceedings, 2-15, 1989, pp41-42) have been reported by academic societies, etc., and can improve light utilization efficiency to nearly 100%, smear and false It has been confirmed that the signal (pseudo signal) can be reduced.

However, in an image pickup tube, a photoconductive film is formed on a glass substrate having excellent smoothness and signal charges are continuously read out by an electron beam, whereas a stacked solid-state image pickup device is used. In the device, since the photoconductive film is laminated on the pixel electrode separated for each pixel, dark current increases due to unevenness and unevenness of the base,
There is a problem that image defects called white scratches are likely to occur.

Therefore, for flattening the underlayer, a method of burying an insulator in the gap between the pixel electrodes has already been proposed, for example, in Japanese Patent Application Laid-Open No. 1-295457. Next, a cross-sectional structure and a planar structure of a pixel portion of the solid-state imaging device disclosed in the above publication are partially omitted, and FIGS.
Shown in. In the figure, 101 is a pixel electrode, 102 is a pixel separation layer embedded in a gap between the pixel electrodes, and 103 is a pixel electrode 10
1 and the photoconductive film formed on the pixel separation layer 102, 104 is a transparent electrode provided on the photoconductive film 103, and 105 is Al for wiring.
An electrode, 106 is a signal charge storage portion formed on the semiconductor substrate 107, and 108 is an insulating film, and the base is flattened by the pixel separation layer 102 embedded between the pixel electrodes.

[0007]

In the structure disclosed in the above publication, the step between the pixel electrode and the pixel electrode gap can be reduced, but when the voltage applied to the photoconductive film is gradually increased, the center of the pixel electrode is reduced. An edge breakdown phenomenon occurs in which the dark current sharply increases in the peripheral area before the area. This is because the transparent electrode and the pixel electrode formed by sandwiching the photoconductive film are not completely parallel plates at infinity, but the pixel electrodes are separated and arranged in an island shape, and the accumulated signal charge amount is Due to non-uniformity such as different for each electrode, the intra-film electric field is higher in the photoconductive film on the peripheral region of the edge of the pixel electrode than on the photoconductive film directly above the central part of the pixel electrode. This is because the intensifying electric field concentration occurs. As a result, the maximum voltage that can be applied to the photoconductive film is limited, and there is a problem that the photoconductive afterimage and printing cannot be sufficiently improved.

In Japanese Patent Laid-Open No. 63-304551, there has already been proposed an avalanche multiplication operation in a photoconductive film of an image pickup tube. This avalanche multiplication operation is a normal photoconductive film operation. It requires an applied voltage significantly higher than the voltage. For example, in the case of an a-Se photoconductive film having a film thickness of 2 μm, the normal operating voltage is about 25 V, whereas when amplification of 10 times is performed by the avalanche multiplication operation, the applied voltage is about It requires 240V.

In the case of the flattened laminated solid-state image pickup device disclosed in Japanese Patent Laid-Open No. 1-295457, edge breakdown occurs when the photoconductive film is applied with a high electric field required for avalanche multiplication operation. As a trigger, many white spots are generated on the image, and eventually the transparent electrode and the pixel electrode are electrically short-circuited, and eventually the entire image sensor is destroyed.

The present invention has been made in order to solve the above-mentioned problems in the conventional stacked type solid-state image pickup device, and prevents the edge breakdown phenomenon occurring in the peripheral portion of the pixel electrode and provides a sufficiently high voltage photoconductive film. It is an object of the present invention to provide a high-sensitivity stacked solid-state imaging device which has a low afterimage, low image sticking, and which can be uniformly applied to the solid-state imaging device.

[0011]

In order to solve the above problems, the present invention provides a plurality of signal charge accumulating portions and a plurality of signal charge reading portions arranged on a semiconductor substrate, and each signal charge accumulating portion at the uppermost portion. A solid-state imaging device chip in which a pixel electrode electrically connected to the solid-state imaging device chip is formed, and a photoconductive film laminated on the solid-state imaging device chip, wherein an end portion of the pixel electrode is provided. The peripheral region is covered with an electric field relaxation layer made of a high resistance material, and the electric field relaxation layer is interposed between the peripheral region of the end portion of the pixel electrode and the photoconductive film.

In the laminated solid-state image pickup device having such a structure, since the electric field relaxation layer is provided on the peripheral area of the end portion of the pixel electrode, the electric field concentration in the peripheral area of the end portion of the pixel electrode is mitigated, and Even if a high voltage that can cause avalanche multiplication operation is applied to the conductive film, the dark current does not increase due to the local concentration of the electric field in the pixel electrode peripheral region, so that the photoconductive film is stable over the entire pixel electrode. The avalanche multiplication can be performed, and at the same time, the traveling property of the signal charge in the photoconductive film is enhanced, so that the afterimage and burn-in of the photoconductive property are reduced.

[0013]

EXAMPLES Next, examples will be described. Figure 1 (A)
FIG. 1 is a sectional view showing a schematic structure of a pixel portion of a first embodiment of a laminated solid-state imaging device according to the present invention, and FIG. 1 (B) is a plan view thereof. In this embodiment, the signal reading unit has M
In the figure, 1 is a p-type semiconductor substrate, and 2 and 3 are n-type MOSs formed on the semiconductor substrate 1.
⁺ Charge storage unit and charge transfer unit, 4 is a p ⁺ pixel separation region,
A field insulating film 5 is formed on the pixel isolation region 4. 6 is a gate insulating film, 7 is a MOS gate electrode,
Reference numeral 8 is a first insulating film, 9 is a first conductive film electrically connected to the charge transfer portion 3 through a contact hole formed in the first insulating film 8.
A metal electrode, 10 is a second insulating film, 11 is a second metal electrode which is electrically connected to the charge storage unit 2 through a contact hole provided in the second insulating film 10 and is provided independently for each pixel. is there. 12 is a third insulating film, and 13 is a second insulating film formed on the third insulating film.
A pixel electrode electrically connected to the metal electrode 11, 14 is an electric field relaxation layer formed of a trapezoidal high resistance body having a tapered surface in cross section, which is provided so as to cover the peripheral region of the end of the pixel electrode 13. Is a photoconductive film provided on the pixel electrode 13 and the electric field relaxation layer 14, and 16 is a transparent electrode formed on the photoconductive film 15.

Next, the manufacturing process of the laminated solid-state image pickup device of the first embodiment shown in FIG. 1 will be described with reference to FIG. First, as shown in FIG. 2A, a field insulating film 5 having ap ⁺ pixel isolation region 4 is formed in a region of the surface layer of the p-type semiconductor 1 excluding a portion corresponding to a transistor region. Next, after forming the gate insulating film 6, a MOS gate electrode 7 made of polycrystalline silicon or Mo is formed. Further, the charge storage portion 2 and the charge transfer portion 3 of the MOS are formed by the ion implantation method.

Then, as shown in FIG. 2B, after the first insulating film 8 is deposited on these, the charge transfer portion 3 is electrically connected to the charge transfer portion 3 through a contact hole formed in the first insulating film 8. The conductive first metal electrode 9 is formed. Further, after the second insulating film 10 is deposited on this, the second metal electrode 11 is electrically connected to the charge storage unit 2 through the contact hole provided in the second insulating film 10 to form the second metal electrode 11 independently for each pixel. Form. At this stage, unevenness of several μm occurs on the surface of the device. Therefore, in order to flatten the surface shape of the pixel electrode formed next, SOG (spin
The third insulating film 12 is formed by an on-glass method or the like, and the surface of the third insulating film 12 is removed by anisotropic or isotropic dry or wet etching to partially remove the second metal electrode 11. Expose.

Next, as shown in FIG. 2C, a pixel electrode 13 made of metal or the like is formed on these. At this time, the pixel electrode 13 is formed flat. Then, this pixel electrode 13
The fourth insulating film 17 is again formed on the above by an SOG method or the like using an inorganic or organic material to a film thickness of about 0.5 μm.
Further, a resist pattern 18 is formed so as to cover the peripheral portions of the pixel electrodes and the portions corresponding to the upper portions of the gaps between the pixel electrodes. Subsequently, as shown in FIG. 2D, a trapezoidal electric field relaxation layer having a tapered surface is formed by etching by an isotropic etching method such as wet or dry.
By forming 14 and removing the resist pattern 18, as shown in FIG. 2E, a MOS type solid-state imaging device chip having an electric field relaxation layer 14 in the peripheral region of the edge of the pixel electrode 13 is obtained. ..

Next, although not shown in FIG. 2, a photoconductive film 15 is laminated on this chip (see FIG. 1). As the photoconductive film 15, an As ₂ Se film having a film thickness of 1000 Å was used as an electron injection blocking enhancement layer.
₃ and a-Se having a film thickness of 2 μm as a photoelectric conversion layer are sequentially laminated by a cluster ion beam vapor deposition method, and then CeO ₂ having a film thickness of 160 Å is laminated as a hole injection blocking enhancement layer by a high vacuum vapor deposition method. Form. Finally, an ITO film having a film thickness of 500 Å is formed as the transparent electrode 16 by a sputtering method to complete the stacked solid-state imaging device.

FIG. 3 shows the output signal current (blue light irradiation at room temperature) of the device when the positive voltage applied to the transparent electrode is changed with respect to the stacked type solid-state image pickup device manufactured according to the above embodiment. FIG. 3 is a diagram showing changes in dark current, and also shows characteristics of a stacked solid-state imaging device by a conventional flattening method for comparison. In FIG. 3, curves a and b are the signal current and dark current of the solid-state imaging device according to the present invention, and curves a ′ and b ′ are the signal current and dark current of the conventional device.

As can be seen from FIG. 3, in the case of the laminated solid-state image pickup device according to the present invention, the dark current is suppressed to be extremely lower than that of the conventional device even if the applied voltage is increased. Therefore, a
Avalanche multiplication occurs in the photoconductive film made of −Se 24
A high voltage of 0 V can be applied, and the signal current at that time is about 10 times higher than that when 50 V is applied. Further, in the laminated solid-state image pickup device according to the present invention, there were few white scratches, and no image sticking or afterimage was observed.

4A and 4B are a partially omitted sectional view and a plan view showing a second embodiment of the present invention. In this embodiment, the electric field relaxation layer 24 having a tapered surface in which a concave portion is formed along the gap between the pixel electrodes is provided. In order to form the electric field relaxation layer 24 having such a structure, FIG. 2C in the manufacturing process of the first embodiment shown in FIG.
In the step shown in (1), after the flat pixel electrode 13 is formed, a SiO ₂ film which is a high resistance material is formed to a film thickness of 0.1 μm by the CVD method or the sputtering method. Next, a resist pattern is formed so as to cover only the peripheral portion of the pixel electrode, and the other portion is etched by the anisotropic or isotropic etching method.
Etching to expose the electric field relaxation layer having the above shape.
Forming 24. Then, as in the first embodiment, the photoconductive film is formed.
15 and the transparent electrode 16 are laminated to obtain a laminated solid-state imaging device.

In the laminated solid-state image pickup device according to this embodiment, as in the first embodiment, a high voltage can be applied to the photoconductive film, and high sensitivity and low dark current, low afterimage, and low image sticking can be obtained.

FIG. 5 and FIG. 6 are schematic cross sectional views showing the third and fourth embodiments with a part thereof omitted. The third embodiment shown in FIG. 5 uses the electric field relaxation layer 34 having a triangular cross section. To form the electric field relaxation layer 34 having such a shape,
It is formed by over-wetting the fourth insulating film 17 shown in FIG. 2C in the manufacturing process of the first embodiment shown in FIG. In the fourth embodiment shown in FIG. 6, a high resistance film is formed only on the end portion of the pixel electrode 13 to form an electric field relaxation layer 44.
When 44 is formed, the photoconductive film 15 is formed by laminating the substrate 1 and the oblique evaporation method.

As the constituent material of the electric field relaxation layer, the one using SiO ₂ is shown in the above-mentioned embodiment.
₂ , CeO ₂ , GeO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , WO ₃ , Mo
O ₃ , MgO, PbO, BeO, V ₂ O ₅ , NiO, Co ₂ O ₃ ,
A high resistance material containing SiC, Si ₃ N ₄ , As ₂ Se ₃ or the like as a main component and having a specific resistance equal to or higher than that of the photoconductive film can be used in the same manner. , 50
Å or more and 1 μm or less is desirable, and one having a tapered cross section is particularly suitable.

In the above embodiment, the MOS type image pickup element chip is used as the solid-state image pickup element chip and the a-Se film is used as the photoconductive film to be laminated. However, the solid-state image pickup element chip is a CCD or AMI. The present invention can be applied to a device using an element and the like, and as a photoconductive film, a-Si: H, a-Si: B: H, a- other than the a-Se film.
SiC: H or the like can also be used. Furthermore, the present invention can be applied not only to the two-dimensional solid-state image pickup device but also to the one-dimensional solid-state image pickup device, and the same effects can be obtained.

[0025]

As described above on the basis of the embodiments,
According to the present invention, since the electric field relaxation layer is provided on the peripheral region of the end portion of the pixel electrode, even if a high voltage is applied to the photoconductive film, it is possible to prevent the electric field from being locally concentrated in the peripheral region of the pixel electrode. Since a dark current does not increase, stable avalanche multiplication of the photoconductive film can be performed over the entire area of the pixel electrode, and a stacked solid-state imaging device with high sensitivity and reduced afterimage and image sticking can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view and a plan view showing a first embodiment of a laminated solid-state imaging device according to the present invention.

FIG. 2 is a diagram showing a manufacturing process of the first embodiment.

FIG. 3 is a diagram showing signal current and dark current characteristics with respect to applied voltage in the first example and the conventional example.

FIG. 4 is a schematic cross-sectional view and a plan view showing a second embodiment.

FIG. 5 is a schematic sectional view showing a third embodiment.

FIG. 6 is a schematic sectional view showing a fourth embodiment.

7A and 7B are a schematic cross-sectional view and a plan view showing a configuration example of a conventional flattened stacked solid-state imaging device.

[Explanation of symbols]

 1 p-type semiconductor substrate 2 charge storage part 3 charge transfer part 4 pixel separation region 5 field insulating film 6 gate insulating film 7 gate electrode 8 first insulating film 9 first metal electrode 10 second insulating film 11 second metal electrode 12 second 3 insulating film 13 pixel electrode 14 electric field relaxation layer 15 photoconductive film 16 transparent electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Matsuzawa 2-43-2 Hatagaya, Shibuya-ku, Tokyo Olympus Optical Co., Ltd. (72) Inventor Junichi Yamazaki 1-10-11 Kinuta, Setagaya-ku, Tokyo Broadcasting Technology Institute of Japan Broadcasting Corporation (72) Hirotaka Maruyama 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Laboratory of Japan Broadcasting Corporation (72) Inventor Kazunori Miyagawa 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Inside the Broadcasting Technology Research Institute of the Japan Broadcasting Corporation (72) Inventor Fumihiko Ando 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Broadcasting Technology Research Institute of the Japan Broadcasting Corporation (72) Inventor Kazuhisa Taketoshi Kinuta 1 Setagaya-ku, Tokyo 10-11, Japan Broadcasting Corporation Broadcasting Technology Research Institute

Claims (4)

[Claims] 1. A solid-state image sensor chip having a plurality of signal charge accumulating portions and a plurality of signal charge reading portions arranged on a semiconductor substrate, and a pixel electrode electrically connected to each signal charge accumulating portion formed on the uppermost portion. And a photoconductive film laminated on the solid-state imaging element chip, in a laminated solid-state imaging device, a peripheral region of an end portion of the pixel electrode is covered with an electric field relaxation layer formed of a high resistance, A stacked solid-state imaging device, characterized in that an electric field relaxation layer is interposed between an edge peripheral region and the photoconductive film. 2. The stacked solid-state image pickup device according to claim 1, wherein the electric field relaxation layer has a specific resistance equal to or higher than that of the photoconductive film, and a film thickness of 50 Å or more and 1 μm or less. 3. The stacked solid-state imaging device according to claim 1, wherein the electric field relaxation layer has a tapered cross section in the thickness direction. 4. The laminate according to claim 1, wherein the photoconductive film is configured so that a high voltage that can cause avalanche multiplication in the film can be applied. Type solid-state imaging device.