JPH03174772A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain an excellent reproduced image by applying a specified bias voltage on a picture-element isolating electrode which is provided beneath a barrier film, and isolating the picture element through an inverted layer which is formed in the barrier layer between an optoelectronic transducer film and a signal-charge accumulating part. CONSTITUTION:Picture-element isolating electrodes 16 are arranged in an insulating film at the upper side of an element isolating region 11 on a semiconductor substrate 10 in a grid pattern so as to surround an accumulating diode 12 for one picture element, respectively. When a negative bias voltage is applied on the picture-element isolating electrode 16, an n<-> type amorphous silicon film 22 is inverted on the picture-element isolating electrode 16. The inverted layer is formed in the n<-> type amorphous silicon film 22 so as to surround the accumulating diode 12 for one picture element, respectively. Thus, the deterioration of the characteristic of an after image and the deterioration of the characteristic of picture-element isolation can be prevented, and the excellent regenerated image can be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a photoelectric conversion film in which a photoelectric conversion film is laminated on an accumulation region for accumulating signal charges and a CCD type signal charge readout/transfer section. Related to solid-state imaging devices.

(Prior Art) In recent years, solid-state imaging devices using CCDs have been used as imaging units in television cameras, electronic still cameras, and the like. Recently, in order to increase the light-receiving area for the purpose of improving sensitivity, a stacked solid-state device with a double-layered vertical structure in which a photoelectric conversion film is stacked on a solid-state image sensor chip that integrates a storage diode and a charge transfer section has been developed. Imaging devices have been developed.

FIG. 10 is a diagram showing a cross-sectional structure of one pixel in a stacked solid-state imaging device. In FIG. 10, a storage diode 2 made of an n-type impurity region is formed in a region surrounded by an element isolation region (p+ layer) in a p-type silicon substrate 1. A vertical CCD channel region made of an n-type impurity region is formed. Transfer gate electrodes 4a and 4b are stacked on top of the channel region 3 and are insulated from the surroundings by a first insulating film 5a. Extracting electrodes 6 are formed on the tops of 4a and 4b.

A second insulating film 5b for surface flattening is formed on the extraction electrode 6 and the insulating film 5a, and a pixel electrode 7 corresponding to each pixel is formed on this insulating film 5b. .

On this pixel electrode 7, for example, a-8i :H(i)
A photoelectric conversion film 8 made of (i-type amorphous hydrogenated silicon) is formed, and a transparent electrode 9 is formed on this photoelectric conversion film 8.

In such a structure, incident light received by the photoelectric conversion film 8 is converted into electron-hole pairs, and a predetermined bias potential applied between the transparent electrode 9 and the pixel electrode 7 causes the electrons to be transferred to the pixel electrode 7. The holes are guided to the transparent electrode 9 side. The electrons induced in the pixel electrode 7 are given to the storage diode 2 through the extraction electrode 6, and are stored in the storage diode 2 as signal charges. The accumulated signal charge is
After being transferred to the channel region 3 of the vertical CCD by the voltage applied to the transfer gate electrodes 4a and 4b, the signal is sequentially moved through this channel region 3 and transferred.

By the way, in this type of solid-state imaging device, of the electron-hole pairs generated in the photoelectric conversion film 8, electrons move toward the pixel electrode 7 side, and holes move toward the transparent electrode 9 side. At this time,
As shown by the dotted line in the energy band diagram of FIG. 11, holes may be injected into the photoelectric conversion film 8 from the pixel electrode 7, resulting in image defects. In order to prevent such a phenomenon, it is necessary to form a hole barrier layer that acts as a barrier against holes on the pixel electrode 7 side. As this barrier layer, for example, a-
8iC:H(i)H (i-type amorphous hydrogenated silicon carbide) or a-8i:H(n) film (n-type amorphous hydrogenated silicon) can be used.

The a-SiC:H(i) film effectively acts as a luharia layer for holes, and has the advantage that its high resistance causes little lateral signal charge diffusion and eliminates the need for pixel separation. ing.

However, since the a-8iC:H(i) film has a wide band gap, it also serves as a barrier layer against signal charges (electrons). For this reason, a delay occurs in the movement of signal charges, which deteriorates the afterimage characteristics.

On the other hand, the a-8t:H(n) film serves as a barrier layer for holes, but does not serve as a barrier layer for signal charges. However, since the resistance is low, signal charges tend to diffuse laterally, so pixel separation is required. In order to perform pixel separation, a-8t:H(i
) Before forming the film, a process for pixel separation such as separating the a-8i:H(n) film is required.

Therefore, a natural oxide film or a large number of interface states are formed between the photoelectric conversion film 8 and the a-8i diH(n) film as a barrier layer. Therefore, signal charges are trapped in this interface level, causing noise and image defects.

Furthermore, although silicide is generally used for the pixel electrode 7 and the extraction electrode 6, a natural oxide film is likely to be formed on the surface of this silicide, resulting in uneven oxide film resistance.
This caused the characteristics to deteriorate.

On the other hand, in the case of a stacked solid-state imaging device, since the capacitance of the photoelectric conversion film connected to the storage diode is large, there is a problem that the capacitive and quantitative afterimage characteristics are poor.

One way to reduce afterimages is to introduce bias light from the outside (Japanese Patent Application Laid-Open No. 1997-11101), but in this case it is difficult to uniformly irradiate the light onto the chip, and it is not possible to reliably reduce afterimages. . Furthermore, a new light source or the like is required, which complicates the configuration. There is also a method of injecting bias charges by installing a source section for charge injection and a gate for bias injection, but in this case, a bias charge injection section is newly required and there is a problem that the device area increases.

(Problem to be solved by the invention) As described above, in the conventional stacked solid-state imaging device,
When an a-8iC:H(i) film is used as a barrier layer to prevent injection of holes from the pixel electrode side to the photoelectric conversion film, this a-8LC:H(i) film also prevents signal charges from being injected. Since it becomes a barrier, it deteriorates the afterimage characteristics. Also,
When an a-8i:H(n) film is used as the barrier layer, a pixel separation process is required, which causes characteristic deterioration due to the natural oxide film and interface states formed during this process. Therefore, aSiC:H(i) film or a-8i:H
None of the (n) films could function as a barrier layer against holes without causing property deterioration.

Furthermore, in the conventional stacked solid-state imaging device, the capacitance of the photoelectric conversion film connected to the storage diode is large, which causes a problem of poor capacitive afterimage characteristics.

In the method of injecting bias light to reduce this afterimage, it is difficult to reliably reduce the afterimage, and the structure becomes complicated. Furthermore, if a portion for injecting bias charges is provided adjacent to the storage diode, there is a problem in that miniaturization and high integration of the device become difficult.

The present invention has been made in consideration of the above circumstances, and its purpose is to prevent the deterioration of the afterimage characteristics due to the formation of the barrier layer, and to prevent the deterioration of the characteristics due to the pixel separation process. An object of the present invention is to provide a stacked solid-state imaging device that can obtain good reproduced images.

Another object of the present invention is to provide a stacked solid-state imaging device that can sufficiently reduce capacitive afterimages even when using a photoelectric conversion film with a large capacity, and can obtain good reproduced images. There is a particular thing.

[Structure of the invention] (Means for solving the problem) In order to achieve the above object, the present invention (Claim 1) provides the first
a plurality of second conductivity type signal charge accumulation sections formed on a conductivity type semiconductor substrate; a signal charge transfer section formed on the semiconductor substrate for transferring signal charges accumulated in the signal charge accumulation sections;
In a stacked solid-state imaging device that receives incident light to generate signal charges, and includes a photoelectric conversion film formed on a signal charge storage section and a signal charge transfer section so as to be shared by a plurality of signal charge storage sections. A barrier film of a second conductivity type is formed under the photoelectric conversion film to act as a barrier against induction of carriers of a conductivity type opposite to the signal charges to the photoelectric conversion film, and an insulating film is provided under the barrier film. A pixel separation electrode to which a bias voltage is applied to form an inversion layer in the 0 barrier film is formed so as to surround each signal charge storage portion.

Further, the present invention (claims 3 and 4) provides signal charge storage sections of a second conductivity type formed one-dimensionally or two-dimensionally on a semiconductor substrate of a first conductivity type, and signal charge storage sections adjacent to these signal charge storage sections. A signal charge transfer section is provided on the semiconductor substrate to transfer the signal charges accumulated in the signal charge storage section, and a photoelectric transfer section is provided on the semiconductor substrate via an insulating film and receives incident light and generates signal charges. In a stacked solid-state imaging device equipped with a conversion film, the photoelectric conversion film is of the second conductivity type and brought into direct contact with the signal charge storage section. 1st between
A conductive type photoelectric conversion film is provided.

(Function) According to the present invention (claim 1), a pixel separation electrode is provided under the barrier layer (barrier film), and a predetermined bias voltage is applied to this pixel separation 1 electrode to separate each pixel in the barrier film. An inversion layer is formed to surround the pixel, and the inversion layer separates signal charges in each pixel. Therefore, a-3i:H(n
) Even if a film with low resistance is used, such as a film with low resistance, it is possible to prevent characteristic deterioration caused by the pixel separation process.

Further, according to the present invention (claims 3 and 4), since the second conductivity type photoelectric conversion film is brought into direct contact with the second conductivity type signal charge storage section, there is no need to use an extraction electrode, and the signal charge storage section is brought into direct contact with the signal charge storage section. The storage section can be completely depleted. Therefore, even if a photoelectric conversion film with a large capacity is used, capacitive afterimages can be sufficiently reduced, and dark current unevenness caused by the substrate interface can be reduced.

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

1 and 2 are for explaining the element structure of a stacked solid-state imaging device according to the first embodiment of the present invention. FIG. 1 is a cross-sectional view, and FIG. 2 is a plan view. be.

The structure shown in FIGS. 1 and 2 is characterized by the fact that the semiconductor substrate 1 is different from the conventional structure shown in FIG.
Pixel isolation electrodes 16 for pixel isolation are arranged in a lattice shape so as to surround each storage diode 12 for one pixel in the insulating film above the element isolation region 11 formed in the pixel isolation region 11. Pixel separation is performed by

In order to obtain such a structure, first, for example, a storage diode 12 made of an n-type impurity region and a channel region 1 of a vertical CCD are formed in a surface region of a p-type silicon substrate 20.
form 3. In addition, the p+
A type element isolation region 11 is formed.

Thereafter, a transfer gate electrode 1.4.1.5 made of, for example, polycrystalline silicon is laminated on the channel region 13 with the first insulating film 17a interposed therebetween.

Furthermore, after forming a second insulating film 17b for planarization on the transfer gate electrode 15, the pixel separation electrode 16 described above is arranged in a lattice shape using polycrystalline silicon, for example, on this second insulating film 17b. Then, a third insulating film 17C for planarization is formed to planarize the surface.

Next, the first to third insulating films 17 on the storage diode 12
a, 17b, and 17c are removed to form an opening, and a third insulating film 17 is formed from the upper surface of the storage diode 12 along the sidewall of the opening.
On c, an extraction electrode 21 made of silicide, for example, is formed.

Thereafter, an n-type amorphous silicon (a-8i:H(n)) film 22, which will serve as a hole barrier layer (barrier film), is formed over the entire surface so as to be bonded to the extraction electrode 21. Further, on this n″′ type amorphous silicon film 22, an i type amorphous silicon (a-8
The i:H(+) film 23 and the p-type amorphous silicon carbide (a-5iC:H(p)) film 24 are thinned and laminated. Finally, a transparent electrode film 2 made of, for example, an ITO film is placed on the amorphous silicon carbide film 24.
5 is laminated to obtain a structure as shown in FIGS. 1 and 2.

Such a structure is used with a negative bias voltage applied to the pixel separation electrode 16. Pixel separation electrode 1
When a negative bias voltage is applied to the pixel separation electrode 16
At the top, the n-type amorphous silicon film 22 is inverted.

This inversion layer is formed in the n-type amorphous silicon film 22 so that the pixel separation electrode 16 surrounds each storage diode 12 for one pixel as shown in FIG.

In this state, the signal charge generated in the i-type amorphous silicon film 23 in response to the incident light is guided to the n-type amorphous silicon film 22 by the electric field applied between the transparent electrode 25 and the substrate. be done. The signal charges induced in the amorphous silicon film 22 are prevented from moving beyond the inversion layer 5 formed in the amorphous silicon film 22 to the amorphous silicon film 22 on the adjacent pixel side. That is, the signal charges induced in the amorphous silicon film 22 can move only in the amorphous silicon film 22 inside the inversion layer with the boundary as the boundary.

Therefore, this essentially results in pixel separation.

The signal charges injected into the amorphous silicon film 22 are applied to the storage diode 12 via the extraction electrode 21 and accumulated therein, and the accumulated signal charges are transferred and read out in the same manner as in the prior art described above.

In this way, by applying a negative bias voltage to the pixel separation electrode 16, an inversion layer is formed in the hole barrier layer 22 so as to surround the storage diode 12 and partition one pixel. The layer prevents lateral diffusion of signal charges, allowing pixel separation. Therefore, a pixel electrode, which has conventionally provided substantial pixel separation for signal charges, is no longer necessary.

6. Furthermore, by using the n-type amorphous silicon film 22 as a hole barrier layer, the movement of signal charges from the photoelectric conversion film 23 to the storage diode 12 can be prevented, as shown in the energy band diagram of FIG. Therefore, injection of holes from the extraction electrode 21 side to the photoelectric conversion film 23 can be prevented. This prevents deterioration of the afterimage characteristics.Furthermore, since the pixel separation process and the pixel electrode formation process in the atmosphere before the formation of the photoelectric conversion film 23 are not necessary, the photoelectric conversion film 23 and A natural oxide film or interface state will not be formed between the hole barrier layer 22 and the hole barrier layer 22. As a result, signal charges are captured in the interface level, making it possible to suppress the occurrence of noise and image defects.

Therefore, since the injection of holes can be prevented without deteriorating the afterimage characteristics, image defects can be reduced and high-quality images can be reproduced.

FIG. 4 is a sectional view showing the element structure of a stacked solid-state imaging device according to a second embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the first embodiment described above as follows:
The extraction electrode 21 is omitted and the n-type amorphous silicon film 22 of the hole barrier layer is brought into direct contact with the storage diode 12. In this embodiment as well, it is possible to obtain the same effects as in the above-described embodiment, and since the step of forming the extraction electrode is not required, it is possible to simplify the manufacturing process.

5 and 6 are for explaining the element structure of a stacked solid-state imaging device according to a third embodiment of the present invention,
FIG. 5 is a plan view, and FIG. 6 is a sectional view taken along the line xx' in FIG. 5.

Storage diodes 62 made of n-type impurity regions are arranged in a matrix on a semiconductor substrate 60 made of p-type silicon or the like.
A plurality of - type vertical CCD channels 63 and p+ type element isolation regions 8 61 are formed in the column direction. CCD channel 6
Transfer electrodes 64 and 65 are stacked on top of the storage diode 62, and a portion of the transfer electrode 64 extends above the storage diode 62 to form a signal readout section 64a. Further, an insulating film 67 for planarization is deposited on the substrate 10, and within this insulating film 67, there are pixel separation electrodes 66 for separating charges in a photoelectric conversion film, which will be described later.
are arranged in a grid pattern corresponding to each storage diode 62.

A contact hole 68 is formed on the storage diode 62 of the insulating film 67, and a photoelectric conversion film 73, such as a damage-free n-type photo-CVD film (a-3i: H(n)
) is deposited, thereby directly contacting the storage diode 62 and the photoelectric conversion film 73. A transparent electrode 75 made of ITO or the like is formed on the photoelectric conversion film 73. In addition, the storage diode 2 and the photoelectric conversion film 7
Since a natural oxide film etc. may be formed at the interface of 3,
Before forming the photoelectric conversion film 739, a method is used in which the natural oxide film is removed using, for example, hydrogen radicals of hydrogen fluoride gas.

In such a configuration, light transmitted through the transparent electrode 75 is photoelectrically converted within the photoelectric conversion film 73, and is connected to each storage diode 6 by the pixel separation electrode 66 as in the previous embodiment.
The signal charge is separated into two and stored as signal charges. This signal charge is transferred to the CCD channel 63 through the charge readout section 64a.
will be transferred to. At this time, since the photoelectric conversion film 73, the storage diode 62, and the substrate 60 have an n--p structure, the storage diode 62 can be completely depleted, and afterimages can be reduced.

Here, in the conventional structure, the photoelectric conversion film and the storage diode are connected by an extraction electrode, so the storage diode must be n+ in order to have a good ohmic connection, and this prevents the storage diode from being completely depleted. It is. Note that the signal charges transferred to the vertical CCD channel 63 are transferred to a horizontal CCD channel (not shown), and are transferred and read out through this horizontal CCD channel.

FIG. 7 is a potential distribution diagram in a cross section taken along arrow xx' in FIG. 5, showing that afterimages are reduced by complete depletion.

Since the photoelectric conversion film and the storage diode part have an n--p structure, the storage diode region can be completely depleted. Potential φd when the storage diode is completely depleted
Since ep (potential of the storage diode) is lower than the subthreshold potential φth, all signal charges are transferred to the COD channel before reaching the subthreshold region. As a result, afterimages can be sufficiently reduced.

In this way, according to this embodiment, the photoelectric conversion film 73 is n
Using type a-8i: H(n), this photoelectric conversion film 7
3 is in direct contact with the storage diode 62, unlike the case where an extraction electrode is used, the storage diode 62 can be an n-layer, and the storage diode 62 can be completely depleted. For these two reasons, even if a photoelectric conversion film with a large capacity is used, capacitive afterimages can be sufficiently reduced.

In addition, with this structure, charges are not trapped at the interface of the storage diode 62, and dark unevenness and dark current can be sufficiently reduced due to the gr center at the interface. In addition, since pixel electrodes and extraction electrodes are not required, it is possible to prevent the formation of natural oxide films that accompany the formation of these electrodes, which has the advantage of eliminating factors that degrade characteristics and simplifying the manufacturing process. .

FIG. 8 is a sectional view showing the element structure of a fourth embodiment of the present invention. Note that the same parts as in FIG. 6 are given the same reference numerals, and detailed explanation thereof will be omitted.

This embodiment differs from the previous third embodiment in that a p-type photoelectric conversion film 76 is formed between a photoelectric conversion film 73 and an insulating film 67.

For example, the p-type photoelectric conversion film 76 may be formed as follows. That is, as shown in FIG. 9(a), the insulating film 67
After forming an insulating film 67 using BPSG and opening a contact hole 68 to form an n-type photoelectric conversion film 73, a p-type layer 76 is formed by diffusion of boron from the insulating film 67. In addition, Fig. 9 (b
), after forming the insulating film 67, p
It is also possible to form a type photoelectric conversion film 76, then selectively etch the photoelectric conversion film 76 on the storage diode portion, as shown in FIG. good.

With such a configuration, not only the storage diode 62 but also the photoelectric conversion film 73 can be completely depleted, and complete depletion can be achieved more reliably than in the previous embodiment, and capacitive afterimages can be sufficiently reduced. It becomes possible to do so.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the storage diode region is n-
There is no need to limit the layer to a p-type silicon substrate. In other words, a storage diode may be formed using an n-type photoelectric conversion film 3 and a p-type silicon substrate without forming an n-layer on the substrate. Alternatively, after laminating an n-type photoelectric conversion film on a p-type silicon substrate, an n- layer may be formed on the p-type silicon substrate by diffusing from the photoelectric conversion film by, for example, low-temperature annealing.

[Effects of the Invention] As detailed above, according to the present invention (claim 1), by applying a predetermined bias voltage to the pixel separation electrode provided under the barrier film, the photoelectric conversion film and the signal charge accumulation are separated. Pixel isolation is performed by an inversion layer formed in a barrier film provided between the two parts. Therefore, it is possible to suppress the injection of holes into the photoelectric conversion film without causing image defects. As a result, it is possible to realize a stacked solid-state imaging device that can prevent characteristic deterioration and provide good reproduced images.

Further, according to the present invention (claim 2), since the photoelectric conversion film of the conductivity type opposite to that of the substrate is brought into direct contact with the signal charge storage section, the signal charge storage section can be completely depleted. This makes it possible to reduce capacitive afterimages.

[Brief explanation of drawings]

FIG. 1 is for explaining the element structure of a stacked solid-state imaging device according to the first embodiment of the present invention. FIG. 1 is a sectional view, FIG. 2 is a plan view, and FIG. FIG. 4 is a diagram showing the relationship of band energy in the example.
FIGS. 5 and 6 are cross-sectional views showing the device structure of the third embodiment of the present invention, and FIG. 5 is a plan view, and FIG. 6 is a cross-sectional view. 7 is a diagram showing the relationship of potential distribution in the cross section taken along arrows x-x' in FIG. 5, FIG. 8 is a sectional view showing the element structure of the fourth embodiment of the present invention, and FIG. FIG. 8 is a cross-sectional view showing an example of the formation process of the structure, FIG. 10 is a cross-sectional view of the element structure in a conventional solid-state imaging device, and FIG. 11 is a diagram showing the relationship of band energy in the conventional device. 10.60...p type silicon substrate, 11.61...p'l type element isolation region, 5 2.62...n type storage diode, 3.63...CCD channel, 4.15, 64.65... Transfer electrode, 6.66...
Pixel separation electrode, 7.67... Insulating film, 1... Extraction electrode, 2... Hole barrier layer, 3.73... N-type photoelectric conversion film, 5.75... Transparent electrode, 6...p-type photoelectric conversion film.

Claims (4)

[Claims] (1) A plurality of second conductivity types formed on a semiconductor substrate of a first conductivity type.
a conductive type signal charge storage section; a signal charge transfer section formed on the semiconductor substrate and configured to transfer the signal charges accumulated in the signal charge storage section; a photoelectric conversion film formed on the charge storage section and the signal charge transfer section so as to be shared by the plurality of signal charge storage sections; A barrier film of a second conductivity type serves as a barrier to induction into the conversion film, and a barrier film is formed under the barrier film via an insulating film, and is formed in the barrier film so as to surround each of the signal charge storage portions. A solid-state imaging device comprising: a pixel separation electrode to which a bias voltage forming an inversion layer is applied. (2) A conductive film is formed between the barrier film and the signal charge storage section and guides the signal charges generated in the photoelectric conversion film to the signal charge storage section. The solid-state imaging device described. (3) a signal charge accumulation section of a second conductivity type formed one-dimensionally or two-dimensionally on a semiconductor substrate of a first conductivity type; and a signal charge accumulation section provided on the semiconductor substrate adjacent to the signal charge accumulation section; a signal charge transfer section that transfers the signal charges accumulated in the signal charge accumulation section; and a second conductivity type photoelectric conversion provided on the semiconductor substrate via an insulating film and directly connected to the signal charge accumulation section. A solid-state imaging device comprising a film. (4) a signal charge storage section of a second conductivity type formed one-dimensionally or two-dimensionally on a semiconductor substrate of a first conductivity type; and a signal charge storage section provided on the semiconductor substrate adjacent to the signal charge storage section; a signal charge transfer section that transfers the signal charges accumulated in the signal charge accumulation section; and a second conductivity type photoelectric conversion provided on the semiconductor substrate via an insulating film and directly connected to the signal charge accumulation section. A solid-state imaging device comprising: a film; and a first conductivity type photoelectric conversion film provided between the photoelectric conversion film and the insulating film.