JPH02143560A - Laminar type solid-state image sensing device - Google Patents

Abstract

PURPOSE:To surely prevent light rays from leaking into an optical black region so as to obtain a laminar type solid-state image sensing device capable of obtaining a stable black signal without enlarging the black region by a method wherein a groove is provided around the optical black region of a photoconductive film, and an optical shield layer is formed on the side wall of the groove and the black region. CONSTITUTION:A p<+>-type well 12 is formed on an Si substrate 11, and a solid- state image sensing chip 10 is provided onto the well 12. In succession, a photoconductive film 23 is deposited on the chip 12, and furthermore a transparent electrode 24 of ITO or the like is formed on the film 23. An element isolating layer 1, an n<+>-channel 14, and an n<++>-type storage diode 15 are provided onto the surface of the well 12, and transfer gates 16 and 17 are formed thereon. Next, a first insulating film 18 of SiO2 or the like is formed, an then a contact hole is bored in the film 18 to form a pixel electrode wiring 21. Moreover, a second insulating film 19 formed of a BPSG film (boro-silicate glass) used for flattening is deposited, a contact hole is provided to the film 19, pixel electrodes 22 are built, and thus the solid-state image sensing chip 10 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a stacked solid-state imaging device, and particularly to a stacked solid-state imaging device with an improved optical black area.

(Prior art) A solid-state imaging device with a two-story structure (stacked solid-state imaging device) in which a photoconductive film is laminated on a solid-state imaging element chip has high sensitivity and It has the excellent feature of low smear. Therefore, this solid-state imaging device is seen as promising as a camera for various surveillance televisions, high-definition televisions, and the like. At present, amorphous material films are used as photoconductive films for stacked solid-state image devices.

For example, 5e-As-Te film, Zn5e-ZnCdT
e, a-3i: H film (hydrogenated amorphous silicon film), etc. Among these materials, the a-8l:H film is becoming the favorite because of its good properties, workability, and possibility of low-temperature formation.

Incidentally, in a solid-state imaging device, an optical black area of about 40 pixel columns is formed on one side of the periphery of an image area in order to define the black level of a color signal, that is, the dark current.

The structure of this optical black area needs to be the same structure as the photosensitive part of the image area to which light is irradiated. Further, as a characteristic required for the optical black region, it is desirable that the difference in dark current between bright and dark states of light be within 0.1%. For this reason, in the case of a CCD imaging device, i is laminated with a thickness of about 1 μm as a light shielding layer with a smooth layer interposed therebetween. It has been confirmed that if the shielding layer has a thickness of this level, the ratio of light leakage due to direct transmission is 10-6 or less, and there is no problem in practical use.

However, it is known that light leaks into the optical black area from sources other than direct transmission. This is due to the light waveguide effect between the overcoat layer and the storage diode, and approximately five pixel columns around the optical black area are affected. In order to define the dark current, the number of pixel columns required in the NTSC system is approximately 30, but as described above, in consideration of light leakage, approximately 40 pixel columns are formed.

In the case of a photoconductive film stacked solid-state imaging device, basically the same problems as in the case of the above-mentioned CCD imaging device occur. In particular, leakage of light into the optical black area due to the optical waveguide effect becomes a problem.

Light leakage is different between the CCD type and the laminated type.

The CCD type light propagates inside the light shield layer while being reflected between the light shield layer and the polysilicon gate electrode, and between the Si substrate and the polysilicon gate electrode. And it has the following characteristics.

- Since the light propagation medium is a 5in2 insulator, there is no wavelength dependence.

(2) Since light is reflected through the polysilicon gate electrodes arranged discretely in each pixel region, it is absorbed intensively at the edges of the optical black region. As a result, the number of pixel columns through which light leaks remains at about five pixel columns.

On the other hand, in the case of a laminated type, as shown in FIG. 5, pixel electrodes 51 are arranged on a flattened substrate 50 at intervals of 1 to 2 μm, and a photoconductive film 52 is formed on top of the pixel electrodes 51 with a thickness of about 3 μm. A transparent electrode 53 is further laminated thereon. The light shield layer 54 is laminated directly on the transparent electrode 53 in a flat structure.

Therefore, unlike the CCD type, it has the following characteristics.

■ Light leakage is wavelength dependent. This is because the light propagation medium is a photoconductive film such as a-8t:H.

■ Because the photoresist film is thick, the light waveguide effect is large, and the penetration distance of light in the red region, which has a small absorption coefficient, is large. That is, C.C.
Unlike the D type, the amount of light leaking in is small, but
The penetration distance is large and extends to about 10 pixel columns. The depth of this penetration also varies depending on the thickness of the laminated films. Therefore, in the case of the laminated type, the effective black area is smaller than in the CCD type, and there is a problem in obtaining a stable black signal.

(Problems to be Solved by the Invention) As described above, in the conventional stacked solid-state imaging device, even if a light shield layer is provided on the optical black area,
It has been difficult to prevent light from leaking into the optical black area due to the optical waveguide effect. For this reason, it was not possible to obtain a stable black signal, and it was necessary to further enlarge the optical black area.

The present invention has been made in consideration of the above circumstances, and its purpose is to reliably prevent light from leaking into the optical black area, without enlarging the optical black area. An object of the present invention is to provide a stacked solid-state imaging device that can obtain a stable black signal.

[Structure of the Invention (Means for Solving the Problems) The gist of the present invention is to form a light shield layer not only on the upper surface of the optical black region but also on the side surfaces of the optical black region so as to surround the optical black region. be.

That is, the present invention provides a solid-state image sensor in which a signal charge storage diode, a signal charge readout section, and a signal charge transfer section are formed on a semiconductor substrate, and a pixel electrode electrically connected to the signal charge storage diode is formed on the top. In a stacked solid-state imaging device comprising an element chip, a photoconductive film laminated on the chip, and a transparent electrode formed on the photoconductive film, a layer is formed around the optical black area of the photoconductive film. A groove surrounding the area is formed, and a light shield layer is provided on the sidewall of the groove and the optical black area.

(Function) According to the present invention, since the optical shield layer is also embedded in the groove surrounding the optical black area, it is possible to reliably prevent light from leaking into the optical black area due to the optical waveguide effect. be able to. Therefore, it is possible to always obtain a stable black signal without enlarging the optical black area.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a plan view showing a schematic structure of a stacked solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a view taken along arrow A-A in FIG.
FIG. In the figure, 11 is an SL board, and this board 1
1, a p+ type upper well 12 is formed. By forming a storage diode and a CCD channel (not shown) in this well 12, and further forming a transfer gate (not shown) on the well 12 and a pixel electrode 22 in the top layer,
A solid-state image sensor chip 10 is configured. A photoconductive film 23 is laminated on this chip 10, and a transparent electrode 2
4 is formed.

The configuration up to this point is the same as the conventional device, but the present device differs from the conventional device in the following points.

That is, a separation groove 31 is formed around one optical black area of the image area so as to surround the area. A light shield film 33 is formed within this groove 31 and on the optical black region with an insulating film 32 interposed therebetween.

Next, a method for manufacturing the solid-state imaging device having the above configuration will be described.

First, as shown in FIG. 3(a), p+
A mold upper well 12 is formed, and the solid-state image sensor chip 10 is formed on this well 12.

Subsequently, a photoconductive film 23 was deposited on the chip 10, and a transparent electrode 24 made of ITO or the like was further formed on the photoconductive film 23.

Here, the photoconductive film 23 is of the (a-8t:H) system, and 2
It has a three-layer structure of 3a, 23b, and 23c. 23a is i-type amorphous hydrogenated silicon carbide (a-8IC:H(
1)) with a thickness of 200 mm, 23b is an i-type amorphous hydrogenated silicon (a-8i:H(+)) with a thickness of 3 μm, and 23c is a p-type amorphous hydrogenated silicon carbide (a- 3iC:
H(p)) and the thickness is 200 people. Photoelectric conversion is a −
8l: performed in the tl(1) layer 23b.

Note that one pixel of the solid-state image sensor chip 10 is configured as shown in FIG. That is, as shown in Figure 4, well 1
2, an element isolation layer 13, an n-type channel (vertical CC
After forming a D channel) 14 and an n++ type storage diode 15, transfer gates 16 and 17 are formed thereon.

Here, a part of the transfer gate 16 becomes a signal readout gate. Next, after forming a first insulating film 18 of SiO2 or the like, a contact hole is made in this insulating film 18 and a pixel electrode wiring 21 is formed. Furthermore, a BPSG film for planarization (
Second insulating film 19 made of boron phosphorus silicate glass)
The solid-state image sensing device chip 10 is created by depositing a pixel electrode 22 by forming a contact hole in one of the insulating films.

In the configuration shown in FIG. 4, the light incident from the transparent electrode 24 is photoelectrically converted by the photoconductive film 23, thereby converting the light into electrons.
A hole pair is formed. Since the potential of the pixel electrode 22 electrically connected to the storage diode 15 is higher than that of the transparent electrode 24, electrons move toward the pixel electrode 22 and holes move toward the transparent electrode 24. Holes are transparent electrode 2
4 to an external circuit, the electrons are accumulated in a storage diode 15 connected to the pixel electrode 22, and the potential of the diode 15 is lowered. Signal charges (electrons) accumulated for a certain period of time are read out from the storage diode 15 to the vertical COD channel 14 when a signal charge readout pulse is applied to the signal charge readout gate 16 . In addition, vertical CC
The charges read and transferred to the D channel 14 are outputted via a horizontal COD channel (not shown).

Next, as shown in FIG. 3(b), a separation groove 31 is formed so as to include about 40 pixel columns around the periphery of the image area, thereby defining an optical area.

At this time, the image area and the optical area are not completely separated, but are provided with a portion where the ITO transparent electrode 24 is partially connected, as shown in FIG. This results in
Eliminates the need for a bonding pad in the optical black area. The groove 31 is deep enough to reach the underlying pixel electrode surface, completely separating the photosensitive portions. For etching, ITO
Plasma etching was performed using hydrochloric acid for the photosensitive area and CF 4 gas for the photosensitive area.

Next, as shown in FIG. 3(e), a light shield layer consisting of an insulating film and a metal film is deposited over the entire surface by magnetron sputtering. The insulating film 32 is an amorphous hydrogenated silicon nitride film, and the metal film (light shield film) 33 is a Mo film with a thickness of 0.3 μm.

The thickness was approximately 0.5 μm. The light transmittance of Mo at 0.5 μm is 10 −6 . The a-3l:N:H film was formed by sputtering an S1 target with a ternary gas of Ar, N2, and N2. The film formation temperature was 100°C in both cases. This temperature was determined in consideration of the above-mentioned desorption temperature range of hydrogen atoms from the amorphous material and the film adhesion force.

Next, the light shield layer (insulating film 32 and metal film 33) is etched around 2 to 3 pixels around the outer periphery of the groove.

image area to expose the image area. Etching of these two layers was also performed using CF4 gas. Various combinations of the insulating film and metal film materials described here are possible. For example, SiO2 is used as an insulating film, and C is used as a metal film material.
r, Ti, All.

W is possible. However, as a criterion for material selection, it is required that the spectral sensitivity does not change when the ITO film (transparent electrode 24) is etched. Therefore, a material having a high etching selectivity with respect to the ITO film is required. a-91
The :N:H film is the most suitable material because the etching selectivity of the ITO film is about 500 times that of the CF4 gas plasma. Mo was selected to simplify the etching process, and this material also has an extremely high etching rate with respect to CF4 gas plasma.

Further, the reason why the insulating film 32 is provided is as follows.

When the etched end face of the photosensitive portion comes into direct contact with the metal film 33 of the optical shield layer, a Schottky structure or ohmic contact is formed. As a result, charge is injected from the ITO film 24, which causes an increase in dark current, and the black level of the image area and the optical black area become different.

In this device manufactured in this manner, the light shield film 33 is embedded not only on the optical black area but also in the groove 31 surrounding the optical black area, so that the light shielding film 33 is not affected by the film thickness of the photosensitive area. This means that the optical waveguide effect can be completely blocked. That is, it is possible to reliably prevent light from leaking into the optical black area due to the optical waveguide effect, and it is possible to always obtain a stable black level output. Furthermore, since leakage of light into the optical area can be reliably prevented, there is no need to enlarge the optical black area, which has the advantage of reducing the chip area.

Note that the present invention is not limited to the embodiments described above. For example, the light shield film serving as the light shield layer does not necessarily have to be made of a metal material, but may be an insulating material made by adding a black pigment or the like to an organic film. In this case, the above-mentioned insulating film becomes unnecessary. Further, the groove surrounding the optical black area does not necessarily have to be partially interrupted, and may completely surround the area.

In this case, the transparent electrode on the optical black area and the transparent electrode on the image area may be connected using a bonding wire or the like. Further, it is certain that the depth of the groove reaches the pixel electrode surface, but a sufficient effect in reducing the optical waveguide effect can be obtained if the groove reaches a portion close to the pixel electrode surface.

In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, a light shield layer is formed not only on the top surface of the optical black region but also on the side surfaces of the optical black region so as to surround the optical black region. It is possible to reliably prevent light from leaking into the black area, and it is possible to always obtain a stable black signal without enlarging the optical black area.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a schematic configuration of a stacked solid-state imaging device according to an embodiment of the present invention, and FIG. 2 is a view taken along arrow A-A in FIG.
3 is a sectional view showing the manufacturing process of the above device, FIG. 4 is a sectional view showing an enlarged view of one pixel configuration of the above device, and FIG. 5 is a sectional view for explaining the problems of the conventional device. It is a diagram. 10... Solid-state image sensor chip, 22... Pixel electrode,
23 (23a, ~, 23c) - Photoconductive film, 24... Transparent electrode, 31... Separation groove, 32...
- Insulating film, 33...metal film (light shield film). Applicant - Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 2

Claims (2)

[Claims] (1) A solid-state image sensor chip in which a signal charge storage diode, a signal charge readout section, and a signal charge transfer section are formed on a semiconductor substrate, and a pixel electrode electrically connected to the signal charge storage diode is formed on the top. In a stacked solid-state imaging device comprising a photoconductive film stacked on the chip, and a transparent electrode formed on the photoconductive film, an optical black area is formed around the optical black area of the photoconductive film. 1. A stacked solid-state imaging device comprising: a surrounding groove formed therein; and a light shield layer provided on the sidewall of the groove and the optical black area. (2) The stacked solid-state imaging device according to claim 1, wherein the light shield layer has at least a two-layer structure, the photoconductive film side being an insulator, and the uppermost layer being a metal. 3) The groove is formed except for a part of the periphery of the optical black area, and the transparent electrode on the optical black area is electrically connected to the transparent electrode on the image area at the interrupted part of the groove. The stacked solid-state imaging device according to claim 1, characterized in that: