JPH01295458A - Laminated type solid-state image sensing device - Google Patents

Abstract

PURPOSE:To prevent the increase in capacitance of a picture element electrode due to the addition of a light shielding layer, by providing a separated structure for the light shielding layer. CONSTITUTION:Four light shielding layers 19 each having the same cross shape are separated at the four sides of each picture element electrode 21. The four light shielding layers 19 as one unit surround one picture element electrode 21. when the light shielding layers 19 are separated in this way, the capacitance of the picture element electrode 21 is not increased even if the light shielding layer 19 is inserted between the picture element electrode 21 and a substrate. Thus, the increase in capacitive afterimage lague to the addition of the shielding layers 19 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention (Industrial Field of Application) The present invention relates to a stacked solid-state imaging device configured by stacking a photoconductor film on a solid-state imaging device chip, and in particular, The present invention relates to a stacked solid-state imaging device in which a light shield layer is provided between electrodes.

(Prior art) A solid-state imaging device with a two-story structure in which a leading conductor film is laminated on a solid-state image sensor chip photoelectrically converts incident light with a photoconductor film, and the resulting signal charge is used to image the underlying material. The signal is transferred using an element chip (for example, a CCD element), amplified, and extracted as a signal. This stacked solid-state imaging device has an excellent property of high sensitivity because the aperture area of the photosensitive section can be widened. Therefore, it is seen as promising for use in cameras such as various surveillance televisions and high-definition televisions.

The photoconductor film has a structure in which the upper part is a transparent electrode and the lower part is sandwiched between pixel electrodes made of a metal thin film that reflects visible light. The pixel electrodes are separated for each pixel, and by using a high-resistance semiconductor thin film such as hydrogenated amorphous silicon as the photoconductor film, no special structure is required for pixel separation. This pixel electrode thus defines each pixel. Incident light passes through the transparent electrode and is absorbed by the photoconductor film. This generates electron-hole pairs, and the holes are transported to the transparent electrode and the electrons are transported to the pixel electrode by the voltage applied between the upper and lower electrodes.

Then, the electrons that have reached the pixel electrode are transferred as signal charges by the underlying CCD element.

A portion of the light incident on the leading electric film is not absorbed, passes between each pixel electrode, enters the base CCD element, and is absorbed there and generated electrons mix with the signal charge and become noise. Noise caused by such light leakage is called smear. In order to suppress this leakage of light, it is effective to provide a light shield layer made of a metal thin film or the like that reflects visible light between the pixel electrode and the substrate.

However, when a light shield layer is provided, a problem of afterimage occurs in addition to smear. An afterimage is a phenomenon that remains for a long time even after the image itself disappears, and is explained as follows. That is, the transfer of signal charges from the storage diode section to the CCD element is an incomplete transfer called an incomplete transfer mode, and this transfer becomes more defective as the capacitance of the storage diode section is larger. This transfer failure causes an afterimage, and this afterimage is called a capacitive afterimage because it depends on capacitance. When a light shield layer is provided, a capacitance is formed between the light shield layer and the pixel electrode.

The storage diode and the pixel electrode are electrically connected by metal wiring or the like, and the capacitance of the pixel electrode also affects capacitive afterimages in the same way as the storage diode. Therefore, if the electrostatic capacitance of the pixel electrode is increased by forming a light shield layer between the pixel electrode and the substrate, the capacitive afterimage becomes larger.

(Problem to be Solved by the Invention) In this way, in conventional stacked solid-state imaging devices, if a light shield layer is formed between the pixel electrode and the substrate to prevent smear, which is noise caused by light leakage, the pixel electrode There is a problem in that the capacitance increases and the capacitive afterimage becomes large.

The present invention has been made in consideration of the above circumstances, and its purpose is to prevent the increase in capacitive afterimages caused by providing a light shield layer, reduce smear and reduce capacitive afterimages. An object of the present invention is to provide a stacked solid-state imaging device that can measure the following.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to prevent an increase in the capacitance of the pixel electrode due to the addition of the light shield layer by providing the light shield layer with a separate structure. be.

That is, the present invention provides a solid-state imaging chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top, and a In a solid-state imaging device including a stacked photoconductor film and a light shield layer formed between a pixel electrode and a semiconductor substrate so as to close a gap between the pixel electrodes, the first shield layer is placed between the pixel electrodes. It is not formed so as to cover the entire surface of the gap, but to separate a part of it.

(Function) According to the present invention, the light shield layer is not formed so as to be connected to the entire surface so as to cover all the gaps between the pixel electrodes, but to be formed so as to be partially separated. The increase in capacitance of the pixel electrode due to the addition of the light shield layer can be made extremely small. Therefore, it is possible to prevent smearing with the light shield layer without increasing capacitive afterimage caused by an increase in the capacitance of the pixel electrode. Note that by forming the optical shield layer into a separated structure, incident light will enter the substrate side at the separated portion, but this will hardly be a problem if the separation width is made sufficiently narrow.

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

1 and 2 are for explaining the schematic configuration of a stacked CCD imaging device according to an embodiment of the present invention, respectively, and FIG. 1 is a plan view showing the arrangement relationship of the pixel electrode and the front shield layer. , FIG. 2 is a sectional view showing the element structure. Second
In the figure, 11 is a p+ type Si substrate, and this substrate 1
An interline transfer type CCD image sensor chip 1 is constructed using a wafer on which a p-well 12 is formed. That is, storage diodes 13 for storing signal charges are formed in a matrix on the surface of the p-well 12.
A vertical CCD 14 consisting of an n+ type buried channel CCD is formed adjacent to the column of storage diodes 13.

15 is a p+ type layer as a channel stopper;
As a result, sets of storage diode arrays and vertical CCDs which are separated and have similar configurations are repeatedly arranged.

16. 162 is a transfer gate electrode of the vertical CCD 14, a part of which also serves as a charge transfer gate electrode from the storage diode 13 to the CCD channel. An interlayer insulating film 18. is formed on the substrate on which the transfer gate electrodes 161.162 are formed.
．． 18□, and a light shield layer 19 is formed thereon. The substrate on which the shield layer 19 has been previously formed is covered with an interlayer insulating film 20, and an extraction electrode 17 connected to the storage diode 13 is formed and planarized. First interlayer insulating film 18. For example, S by CVD
The second interlayer insulating film 18° and the third interlayer insulating film 20 are BPSG films formed by thermal CVD.

To obtain this structure, first the polycrystalline silicon film electrode 17.
is placed on each storage diode 13, a BPSG film is deposited as a second interlayer insulating film 18□ and melted to flatten the substrate surface.
The SG film is etched to expose the surface of the polycrystalline silicon electrode 17□. After that, a Mo silicide film is deposited on the entire surface using a sputtering method, and etched using a reactive ion etching method to form a predetermined shape.
A light shield layer 19 and a Mo silicide electrode 17□ are formed. After the optical shield layer 19 and the Mo silicide electrode 172 are formed, a B
A PSG membrane is encapsulated.

After melting this and flattening the substrate surface, the BPSG film is etched using a reactive ion etching method to expose the Mo silicide electrode 17□. Here, the polycrystalline silicon electrode 171 and the Mo silicide electrode 17□ constitute an extraction electrode 17 that electrically connects the storage diode 13 and the pixel electrode 21.

CCD image sensor chip 1 with a flattened surface in this way
A pixel electrode 21 connected to each extraction electrode 17 is formed thereon. The pixel electrode 21 is formed into a predetermined shape by depositing a conductive film such as a Mo silicide film over the entire surface by sputtering and then etching by reactive ion etching.

The photoconductor film 2 is an i-type a-3 film as a hole injection blocking layer.
IC: It (hydrogenated amorphous silicon carbide) film 22, a high-resistance a-
8l: p-type a- which becomes II film 23 and electron injection blocking layer
It consists of a three-layer structure of 8iC:II film 24. These films are formed by glow discharge decomposition of a gas containing SiH4 gas as a main component. The a-8iC:TL film 22 has a dark conductivity σD~10-"/Ω■ and a thickness of about 100. High resistance a-8i:I (the film 23 has a dark conductivity σD~10"/Ω■ and a thickness of about 100.
The thickness is sufficient for photoelectric conversion with the 0-+2/Ω mark.

The thickness of the p-type a-8 IC:H film 24 is approximately 200. Further, on the photoconductor film 2, an ITO electrode 25, for example, is formed as a transparent electrode.

A plan view of the stacked CCD imaging device formed in this manner is shown in FIG. In FIG. 1, other structures are omitted to clearly show the relationship between the arrangement of the pixel electrode 21 and the light shield layer 19. For comparison, conventional laminated type C
FIG. 6 shows the arrangement of the pixel electrode 21 and the light shield layer 19 of the CD imaging device. As can be seen by comparing FIG. 1 and FIG. 6, in the conventional example, the light shield layer 19 is formed to cover all the gaps between the pixel electrodes 21 and to be connected to the entire surface of the CCD chip. In contrast, in this embodiment, each pixel electrode 21 is separated by four sides, and four units of the same cross-shaped light shield layer 19 surround one pixel electrode 21. By separating the light shield layer 19 in this way, even if the light shield layer 19 is inserted between the pixel electrode 21 and the substrate, the capacitance of the pixel electrode 21 does not increase, so that capacitive afterimages are prevented. It never gets bigger.

In the structure of the light shield layer 19 of this embodiment, the pixel electrode 21
The reason for this will be described in detail below.

FIG. 3(a) shows the capacitance associated with the pixel electrode 21° storage diode 13 and extraction electrode 17 of one pixel in a conventional example using a simple equivalent circuit. Terminal a in Figure 3(a) is 1
Pixel electrode 21 of the pixel. This corresponds to the storage diode 13 and extraction electrode 17 portion. The capacitance QC8 is the capacitance between the pixel electrode 21 and the transparent electrode 25 that sandwich the photoconductor film 2, the extraction electrode 17, the storage diode 13, and the polycrystalline silicon electrode 16. ．． 16□ and the sum of the capacitance of the storage diode 13.

The terminals correspond to the optical shield layer 19. Therefore, the capacitance C
1 is a pixel electrode 21 of one pixel. This is the capacitance between the storage diode 13 and the extraction electrode 17 and the optical shield layer 19. Considering the arrangement in Figures 1 and 2, this capacitance f
f1c is the pixel electrode 21 of one pixel and the light shield layer 19
It can be thought of as the capacitance between The capacitance C2 is the transfer gate electrode 161°1 adjacent to the pixel electrode 21 of one pixel.
6□ represents the capacitance between the optical shield layer 19. The capacitance Q C3 is the other transfer gate electrode 16
It represents the capacitance between 1.16□ and the optical shield layer 19. Therefore, when comparing the magnitudes of capacitance C2 and capacitance i1 C3, it becomes C3)C2. Also,
C,>C,.

Therefore, the capacitance associated with terminal a is, and since c,>C,,C2, it becomes Co10.

FIG. 3(b) shows the pixel electrode 21 of one pixel in the case of this embodiment. The capacitance associated with the storage diode 13 and the extraction electrode 17 is shown by a simple equivalent circuit. Figure 3 (
It is approximately the same as a), and the same symbol is attached and detailed explanation is omitted. The difference from the third (a) is that the light shield layer 19 is separated by the four sides of each pixel electrode 21, so the polycrystalline silicon layer 161 that is not adjacent to the pixel electrode 21 of one pixel.
There is no electrostatic capacitance between 16□ and its pixel electrode 21. Therefore, 03 in FIG. 3(a) is not present in FIG. 3(b).

As a result, the capacitance associated with the pixel electrode 21° storage diode 13 and extraction electrode 17 of one pixel in this embodiment is as follows. Considering the arrangement of FIG. 2, the size of capacitance QC2 is the same or smaller than capacitance CI. Assuming that they are the same, the capacitance associated with terminal a is C8+C1
/2, which is smaller by C1/2 than the conventional example. C1・C2/(C+ + C2) is light shield layer 1
Pixel electrode 21 and transfer gate electrode 161 without 9.
It is equal to the capacitance between 162 and 162. Therefore, in this embodiment, although the optical shield layer 19 is inserted, the pixel electrode 21,
The capacitance associated with storage diode 13 and extraction electrode 17 does not increase.

Next, the reason why the capacitance associated with terminal a contributes to capacitive afterimage will be described. In FIG. 2, incident light is photoelectrically converted by the photoconductor film 2, and the generated electrons are stored in the storage diode 13. The accumulated electrons are transferred to the transfer gate electrode 16 during a period in which a positive voltage, for example, 7V pulse voltage called field shift, is applied to the substrate 11.
Transferred to D14. During this period, the potential of the storage diode 13 is determined by the voltage of the transfer gate electrode 161. In the case of 7v, it is approximately 5.6v. That is, electrons are transferred from the storage diode 13 to the vertical CCD 14 until the potential of the storage diode 13, which has decreased due to the accumulation of electrons, is returned to the potential determined by the field shift. Capacitive afterimage is caused by defective transfer of electrons from the storage diode 13 to the vertical CCD 14.

This transfer failure is explained in the literature (Teranishi et al.: TV Technical Report, 4, 41.
ED-557pp, 25-30. (Feb. 1981)
), S without stacking photoconductor films.
This also occurs in the case of a normal CCD imaging device in which a photodiode is formed as a photoelectric conversion section in a T-substrate.

This occurs because the photodiode section is not completely depleted during the field shift period.

In the case of a leading conductor film stacked solid-state imaging device, a storage diode 13 is formed by contacting an extraction electrode with a photo diode of the CCD imaging device. Since the electrodes are in contact, the storage diode 13 is never completely depleted, and in the case of a stacked CCD device, an afterimage due to empty space always exists. A transfer failure that causes a capacitive afterimage occurs when the difference between the potential of the storage diode 13 and the potential defined by the field shift is 30 mV or less. When electrons are accumulated in the storage diode 13, the potential decreases, and the electrons are transferred to the vertical CCD 14 by the field shift, increasing toward the potential specified by the field shift, and the potential specified by the field shift is increased. When the potential of the diode 13 approaches 30 mV or less, a transfer failure from the storage diode 13 to the vertical CCD 14 occurs. When transferring a certain amount of electrons from the storage diode 13 to the vertical CCD 14, the change in potential of the storage diode 13 is determined by the capacitance of the storage diode 13. If this capacitance is large, the change in the potential of the storage diode 13 will be small, and thus the capacitive afterimage will be large.

The storage diode 13 is connected to the extraction electrode 17 and the pixel electrode 21
3, the capacitance that determines the change in potential of storage diode 13 is the capacitance associated with terminal a in FIG. Therefore, the smaller this capacitance is, the more the capacitive afterimage is reduced. In the photoconductor film laminated CCD imaging device of this embodiment, despite the insertion of a light shield layer, this capacitance is not increased, so that capacitive afterimages do not become large.

As described above, in the stacked CCD imaging device of this embodiment, capacitive afterimage does not increase even though the optical shield layer 19 is inserted between the pixel electrode 21 and the substrate 1. Furthermore, since the optical shield layer 19 is provided, smear, which is noise caused by light leaking into the vertical CCD 14, is reduced. Note that, unlike the conventional example, the light shield layer 19 of this example does not cover the entire pixel gap, but some pixel gaps are open, so there is more smear than in the conventional example. Become. However, even in this embodiment, the opening of the pixel gap can be reduced to about 1/10 compared to the case without the light shield layer 19.
In principle, smear can be reduced to 1/10 compared to the case without it.

FIGS. 4 and 5 are plan views for explaining the schematic configuration of other embodiments of the present invention, respectively, showing an example of arrangement of pixel electrodes and a light shield layer.

Note that the same parts as in FIG. 1 are given the same symbols, and detailed explanation thereof will be omitted. This embodiment differs from the previously described embodiments in the shape of the optical shield layer 19. In FIG. 4, the structure is such that the first shield layer 19 is separated at the ends of the four sides of each pixel.

With this structure as well, the same effects as in the previous embodiment can be obtained. The optical shield layer 19 in the embodiment of FIG.
One unit of the light shield layer 19 is formed by connecting two units of the light shield layer 19 in the illustrated embodiment. In this embodiment, since the opening of the light shield layer 19 at the pixel gap is smaller, the smear reduction effect is greater than in the embodiment shown in FIG. 1 described above.

Note that the present invention is not limited to each of the embodiments described above. For example, the light shield layer is M.

It is not limited to silicide (W, Cr, other metals or their silicides, etc. can be used.
Figure 1 shows the separated shape of the optical shield layer.

The capacitance is not limited to those shown in FIGS. 4 and 5, and can be separated into an appropriate shape as long as the capacitance ff1C3 described above can be ignored (for example, smaller than C2). 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, since the first shield layer has a separate structure, the increase in capacitance of the pixel electrode due to the addition of the light shield layer can be extremely minimized, and therefore, smearing can be minimized. This makes it possible to prevent capacitive afterimages and reduce capacitive afterimages.

[Brief explanation of the drawing]

1 and 2 are for explaining the schematic configuration of a stacked CCD imaging device according to an embodiment of the present invention, respectively. FIG. 1 is a plan view, FIG. 2 is a sectional view, and FIG. 3 is a cross-sectional view. An equivalent circuit diagram schematically showing the state of capacitance in one pixel of the embodiment and the conventional example, FIGS. 4 and 5 are plan views showing the schematic configuration of other embodiments, and FIG. 6 is the conventional example. Laminated type C
1 is a plan view showing a schematic configuration of a CD imaging device. 1... CCD image sensor chip, 2... Photoconductor film,
11...p+ type St substrate, 12...p well, 13
...Storage diode, 14...Vertical CCD. 15... Channel stopper, 161, 162... Transfer gate electrode, 17... Leading electrode, 171...n
+ type packed crystal silicon electrode 17□...MO silicide electrode, 181, 18□, 20... interlayer insulating film, 19.
...Light shield layer, 20... Interlayer insulating film, 21...
Pixel electrode, 22...i type a-3iC:II film, 23.
・High resistance a-3i: If film, 24-p type a-8iC:
It film, 25,-ITO film. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) A solid-state image sensor chip in which a signal charge storage diode and a signal charge readout section are arranged and formed on a semiconductor substrate, and a pixel electrode electrically connected to the storage diode is formed on the top, and a layer is stacked on this chip. In the solid-state imaging device, the solid-state imaging device includes a photoconductor film and a light shield layer formed between a pixel electrode and a semiconductor substrate so as to close a gap between the pixel electrodes, wherein the light shield layer has a separate structure. A stacked solid-state imaging device featuring: (2) Claim 1, wherein the light shield layer is separated from each other on four sides of each pixel electrode.
The stacked solid-state imaging device described above. (3) The stacked solid-state imaging device according to claim 1, wherein the light shield layer is arranged between pixel electrodes arranged in a matrix, and each of the light shield layers has a cross shape.