JPH1027896A - Solid-state image sensing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid-state image sensing device which is simple in structure, capable of effectively restraining blooming from occurring, and markedly improved in resolution. SOLUTION: P-type diffusion layers 14 (N) are formed in stripes on the primary surface of an N-type silicon substrate 10 through the intermediary of an element isolating film 12, a light transmitting insulating film 16 which is thin enough to induce a direct tunnel phenomenon is formed on the P-type diffusion layers 14 respectively, and light transmitting electrode layers 18 (M) are formed in stripes at a prescribed interval on the oxide films 16 and the element isolating film 12 so as to cross the P-type diffusion layers 14 at right angles. A negative drive voltage is applied to the diffusion layers 14. A depletion region 30 is formed in the diffusion layers 14 at their intersections with the electrode layers 18 or at their parts which confronts the electrode layers 18 respectively. When light rays enters the depletion region 30 through the electrode layer 18 and the oxide film 16, a certain number of charges (electron-hole) are induced in the depletion region 30 corresponding to the brightness of an incident light on the region 30. Electrons induced in the depletion region 30 are moved to the electrode layer 18 passing through the insulating film 16 due to a direct tunnel phenomenon and taken in as a sensed current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0010]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device for converting an optical image into a video signal.

[0020]

2. Description of the Related Art As a conventional representative solid-state imaging device, C
CD imaging devices and MOS imaging devices are well known.

As shown in FIG. 12, the CCD image pickup device
An insulating oxide film (SiO2) is formed on the surface of the P-type silicon substrate 100.
) 102, a number of electrodes 104 are arranged on the oxide film 102, and the surface (imaging surface) of the silicon substrate 100 is formed.
The charges e ⁻ generated in the photoelectric conversion units of the respective pixels provided in a matrix are sequentially applied to the respective electrodes 10 like a bucket brigade.
The optical image formed on the imaging surface is taken out as a video signal by transferring the light from the lower part of 4 to the lower part of the adjacent electrode 104.

In the MOS type image pickup device, as shown in FIG. 13, each pixel 106 includes a photosensitive element (photodiode) 1
08 and a MOS switching element 110. MO
The S switching element 110 is connected to two selection lines (metal wiring) of X (horizontal) and Y (vertical) orthogonal to each other. When the X-selection line and the Y-selection line are selected (activated) by a horizontal scanning circuit and a vertical scanning circuit (not shown), the electric charge induced by the incident light in the photosensitive element 108 is transmitted through the MOS transistor 110 to the X line. It is taken out on the selection line.

[0050]

However, CCDs
The image sensor requires a plurality of phases of pulses for transferring signal charges, high-precision timing control is required, the configuration of the scanning unit is complicated, and blooming is likely to occur. There's a problem. In addition, the MOS type image pickup device includes an MO
The provision of the S switching element 110 not only increases the number of manufacturing steps but also increases the pixel area and limits the resolution.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a new type of solid-state imaging device which has a simple structure, can effectively suppress blooming, and can greatly improve resolution. I do.

[0070]

In order to achieve the above object, a first solid-state imaging device according to the present invention comprises a semiconductor substrate of a first conductivity type and discretely arranged in a predetermined arrangement pattern on a main surface of the semiconductor substrate. A plurality of second conductivity type semiconductor regions provided on the semiconductor region, a light-transmitting insulating film having a small thickness provided on the semiconductor region, and a predetermined arrangement so as to intersect the semiconductor region in a matrix. A plurality of light-transmissive electrode layers discretely provided on the insulating film in a pattern; a driving unit for applying a predetermined driving voltage to each of the semiconductor regions in a predetermined scanning procedure; Activating each of the electrode layers, collecting charges induced by incident light in each of the semiconductor regions and guided to each of the corresponding electrode layers through the insulating film by a tunnel effect to generate a video signal. And output means for performing It was.

Further, in the second solid-state imaging device according to the present invention, in the first solid-state imaging device, an insulating oxide film for electrically isolating the semiconductor regions from each other is formed on the main surface of the semiconductor substrate. It was configured to be provided.

Further, according to the third solid-state image pickup device of the present invention, in the first or second solid-state image pickup device, a metal wire electrically connected in parallel with each of the electrode layers is provided on the electrode layer. The configuration is such that it is provided via an interlayer insulating film.

The fourth solid-state imaging device according to the present invention, in the first or second solid-state imaging device, wherein the semiconductor region is provided independently for each pixel, and a plurality of the semiconductor regions are provided for each predetermined set. A metal line electrically connected in common with the region is provided on the electrode layer via an interlayer insulating film.

[0110]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIGS. 1 and 2 show the structure of a solid-state image sensor according to an embodiment of the present invention. FIG. 1 is a plan view schematically showing a main part of the solid-state imaging device, and FIG. 2 is a partial cross-sectional perspective view showing the structure of a frame A in FIG.

In this solid-state imaging device, a plurality (N) of p-type diffusion layers 14 are formed in a stripe shape on the surface (main surface) of an n-type silicon substrate 10 with an element isolation film 12 interposed therebetween.
An ultra-thin light-transmitting insulating film 16 is provided on the p-type diffusion layer 14, and an oxide film 16
In addition, a plurality (M) of light-transmitting electrode layers 18 are provided in stripes at predetermined intervals on the element isolation film 12.

The element isolation film 12 may be, for example, a field oxide film formed by the LOCOS method. Insulating film 16
May be, for example, a silicon oxide film (SiO2) formed by thermal oxidation or CVD. Electrode layer 18 may be, for example, n-type polysilicon formed by CVD.

A negative bias voltage or drive voltage VG is applied to each diffusion layer 14 from the drive circuit 22 under the control of the vertical scanning circuit 20. In this embodiment, the vertical scanning circuit 2
0 and the driving circuit 22 constitute driving means.

In the diffusion layer 14, a depletion (depletion) region 30 is formed at a location that intersects or faces each electrode layer 18, as shown by a dotted line. When light enters each depletion region 30 through the electrode layer 18 and the oxide film 16, a number of charges (electrons-holes) corresponding to the brightness of the incident light are induced there.

The insulating film 16 is formed thin enough to cause a quantum mechanical direct tunnel phenomenon between the diffusion layer 14 and the electrode layer 18. For example, a thermal oxide film (SiO
When the insulating film 16 is formed in 2), a direct tunnel effect is obtained at a thickness of about 50 ° or less, and a practically sufficient direct tunnel effect is obtained at a thickness of about 30 ° or less.

The electrons that have moved from the depletion region 30 of the diffusion layer 14 to the electrode layer 18 by the direct tunnel effect in the insulating film 16 are taken into the horizontal scanning circuit 26 as a sensing current via the amplifier circuit 24 by a predetermined scanning control.
The horizontal scanning circuit 26 outputs the video signal VS. In this embodiment, the horizontal scanning circuit 26 constitutes an output unit.

As described above, in the solid-state imaging device of this embodiment, the pixel Q is formed at each intersection of the diffusion layer 14 and the electrode layer 18. Here, the principle of photoelectric conversion and photocharge extraction in each pixel Q will be described with reference to FIGS.

3 and 4, when light enters the depletion region 30 of the diffusion layer 14, an electron (e ⁻ ) -hole (h ⁺ ) pair is generated by the energy of the light. Among these carriers, electrons (e ⁻ ) pass through the ultra-thin oxide film 16 by the direct tunnel effect and move to the electrode layer 18 side. The holes (h ⁺ ) are sucked into the diffusion layer 14 side.

For example, as one model, oxide film 1
6, the thickness of the electrode layer 18 is 2 mm, the sheet resistance of the diffusion layer 14 is 10 to 15 Ωcm, and sufficiently strong (more than 10,000 arbitary units) light is incident, as shown in FIG. Such a characteristic of the driving voltage V-the sensing current I is obtained.

It should be noted that the driving voltage V
Is zero, that is, even if a bias voltage is not applied between the diffusion layer 14 and the electrode layer 18, slightly (about 1 × 10
^The sensing current I due to the direct tunneling effect ( ^-8 amps). However, this level of current is
Compared to a practically sufficient sensing current I (approximately 1 × 10 ⁻⁵ amperes) obtained when a normal driving voltage V (for example, 2 volts) is applied, it is much smaller.

[0230] Among the various conditions of the above model, the oxide film 1
When the thickness of the film 6 is increased, for example, to 65 °, a characteristic of the driving voltage V-the sensing current I as shown in FIG. 6 is obtained. The sensing current I in this case is due to the Fowler-Nordheim tunnel phenomenon. This is not the tunnel phenomenon used in this embodiment.

Next, the operation of the solid-state imaging device of this embodiment will be described.

In this solid-state imaging device, the vertical scanning circuit 20
, A drive voltage VG of, for example, -2 volts is applied from the drive circuit 22 to each diffusion layer 14 in one horizontal line cycle. Then, while the driving voltage VG is applied to each diffusion layer 14, the horizontal scanning circuit 26 sequentially (or at once) selects each electrode layer 18 via the amplifier circuit 24.

That is, first, the drive voltage VG is applied to the diffusion layer 14 in the first row for a predetermined time, and during this application period, the electrode layers 18 from the first column to the M-th column are sequentially (or simultaneously) selected. (Activation), one horizontal line (first
The horizontal scanning circuit 26 receives the sensing current or the video signal for the row). Next, the driving voltage V is applied to the diffusion layer 14 in the second row.
G is applied for a predetermined time, and during this application period, the electrode layers 18 from the first column to the M-th column are sequentially (or at once) activated to sense one horizontal line (for the second row). The current or the video signal is taken into the horizontal scanning circuit 26. This operation is sequentially repeated for the electrode layers 18 in the third to Nth rows, thereby performing one frame of raster scanning.

In the diffusion layer 14 to which the driving voltage VG is applied, in the depletion region 30 located at the intersection with the electrode layer 18 selected by the horizontal scanning circuit 26, the charge (electron-hole) depends on the amount of incident light. Pair) is induced, and electrons move through the ultra-thin insulating film 14 by the direct tunnel phenomenon to the electrode layer 18 side, and are taken into the horizontal scanning circuit 26 via the amplifier circuit 24 as a sensing current for one pixel therefrom. It is.

At this time, as the electrons move between the depletion region 30 and the electrode layer 18, the potential difference increases by the drive voltage (2
Bolt). In addition, some electrons caused by the direct tunnel phenomenon leak from the depletion region 30 in the other diffusion layer 14 (to which the driving voltage VG is not applied) to the selected electrode layer 18. However, FIG.
As described above, this leakage current is negligibly small compared to the normal sensing current.

In the solid-state imaging device of the present embodiment, in each pixel Q where the diffusion layer 14 and the electrode layer 18 intersect as described above, electrons excited by incident light in the depletion region 30 in the diffusion layer 14 Insulation film 14 due to direct tunnel phenomenon
And is directly taken into the electrode layer 18 by passing through. Unlike a CCD image sensor, there is no need to transfer charges by a bucket brigade. Therefore, the transfer electrode, the transfer clock, and the transfer control are unnecessary, and the configuration of the scanning unit is simplified. Further, unlike the MOS type image sensor, it is not necessary to provide a switching element for each pixel. Therefore, the pixel area is reduced, and the resolution can be greatly improved.

Further, in the solid-state imaging device of this embodiment, since the sense current is based on the direct tunnel phenomenon,
There is also an advantage that blooming is effectively suppressed.

The mechanism of the blooming suppressing effect will be described with reference to FIGS.

FIG. 7 shows an example of the relationship between the amount of incident light and the sensing current in each pixel Q of the solid-state imaging device of this embodiment. When the amount of incident light is not so large (10 arc
(Tari unit and below), the light quantity and the sensing current maintain a substantially proportional relationship. In this case, as shown in FIG.
The depletion region 30 expands on the fourth side, no inversion layer is generated at the boundary surface, and electrons generated in the depletion region 30 quickly move through the insulating film 14 to the electrode layer 18 by the direct tunnel phenomenon.

However, when the amount of incident light exceeds a certain value (10 arc units), the sensing current saturates.
In this state, as shown in FIG. 9, electrons (e ⁻ ) accumulate in the valence band on the surface of the diffusion layer 14, and an inversion layer is formed.
This inversion layer acts to suppress the direct tunnel phenomenon. As described above, the sensitivity to extremely strong incident light is reduced, and blooming is suppressed.

Even if light does not enter the pixel Q, some electron-hole pairs are generated in the depletion region 30 and a minute dark current flows. Such a dark current can be sufficiently reduced by a known technique, for example, by using an epitaxially formed wafer.

The structure and operation of the solid-state imaging device according to the above-described embodiment are examples of the present invention, and various modifications are possible.

For example, in the modification of FIG. 10, a metal wire (film) 32 made of, for example, aluminum is formed on each electrode layer 18.
Are electrically connected in parallel. Each metal line 32 is provided on the electrode layer 18 in parallel with each electrode layer 18 with an interlayer insulating film interposed therebetween, and is electrically connected to each electrode layer 18 through a through hole 34 at a position outside the region of the pixel Q. Is done. As described above, by connecting the metal lines 32 having a high conductivity to each of the electrode layers 18 in parallel, the resistance of each of the electrode layers 18 is greatly reduced, and the scanning time is reduced.

In the modification shown in FIG. 11, an independent (separated) diffusion layer 14 'is provided for each pixel, and the electrode layer 1
Are electrically connected to a metal line (film) 36 common to the diffusion layers 14 ′, 14 ′,. Each metal wire 36 is provided on the electrode layer 18 in a direction orthogonal to the electrode layer 18 with an interlayer insulating film interposed therebetween.
Are electrically connected to the diffusion layers 14 ', 14',. The drive voltage from the drive circuit is applied to the diffusion layers 14 ′, 14 ′,.
According to this configuration, since the diffusion layer 14 'of each pixel Q is separated, leakage of charges from each pixel Q to surrounding pixels Q is small, and blooming can be more effectively prevented. In addition, the metal line 36 has a function of efficiently drawing holes from each pixel Q, and charges (holes) between pixels in each column.
It also has the effect of suppressing blooming in order to prevent leakage of water.

Further, in the above embodiment, the depletion region 30 constituting the photoelectric conversion unit of each pixel Q is formed in the p-type diffusion layer 14, but it is also possible to use an n-type diffusion layer. However, in this case, a bias voltage or a driving voltage is applied in the reverse direction, that is, so that the diffusion layer 14 has a positive potential with respect to the electrode layer 18. Although the n-type silicon substrate is used in the above embodiment, a p-type silicon substrate may be used. Further, the material of the electrode layer 18 is not limited to polysilicon, and a transparent electrode such as ITO (indium / titanium / oxide) may be used. The insulating film 16 may be made of a material other than the SiO2 film, for example, a SiNx film. The configuration of the scanning unit, in particular, the configuration of the driving unit and the output unit is not limited to that of the above-described embodiment, and various circuit configurations are possible.

[0390]

As described above, according to the solid-state imaging device of the present invention, the semiconductor region discretely provided on the main surface of the semiconductor substrate and the thin film provided on the semiconductor region are provided. A pixel is composed of an insulating film and an electrode layer provided on the insulating film, and charges excited by incident light in a depletion region formed in the semiconductor region are transferred to the electrode layer through the insulating film by a tunnel phenomenon. Since the charge on the electrode layer is collected by a predetermined scanning procedure to obtain a video signal, simplification of the configuration, prevention of blooming, improvement of resolution, and the like can be easily realized.

[Brief description of the drawings]

FIG. 1 is a plan view schematically showing a configuration of a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional perspective view showing the structure of a frame A in FIG.

FIG. 3 is a schematic partial cross-sectional view for explaining the principle of photoelectric conversion and photocharge extraction in each pixel of the solid-state imaging device according to the embodiment.

FIG. 4 is an energy band diagram for explaining the principle of photoelectric conversion and photocharge extraction in each pixel of the solid-state imaging device according to the embodiment.

FIG. 5 is a diagram showing an example of a drive voltage-sense current characteristic for explaining the principle of photoelectric conversion and photocharge extraction in each pixel of the solid-state imaging device according to the embodiment.

FIG. 6 is a diagram showing a drive voltage-sense current characteristic as a reference example obtained when the thickness of the insulating film in each pixel of the solid-state imaging device according to the embodiment is increased by a predetermined value or more.

FIG. 7 is a diagram illustrating an example of a characteristic of a light quantity of incident light-a sensing current in each pixel of the solid-state imaging device according to the embodiment.

8 is an energy band diagram for explaining an operation in a proportional region of the characteristic curve of FIG. 7;

9 is an energy band diagram for explaining the operation of the characteristic curve of FIG. 7 in a saturation region.

FIG. 10 is a partial plan view showing a configuration of a main part according to a modification.

FIG. 11 is a partial plan view showing a configuration of a main part according to another modification.

FIG. 12 is a diagram schematically showing a configuration of a CCD image sensor.

FIG. 13 is a diagram schematically illustrating a configuration of a pixel of a MOS imaging device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 n-type silicon substrate 12 element isolation film 14 p-type diffusion region 16 insulating film 18 electrode layer 20 vertical scanning circuit 22 drive circuit 24 amplifier circuit 26 horizontal scanning circuit 30 depletion region 32 metal line 34 through hole 36 metal line 38 through hole

Claims (4)

[Claims] A first conductive type semiconductor substrate; a plurality of second conductive type semiconductor regions discretely provided in a predetermined arrangement pattern on a main surface of the semiconductor substrate; and a plurality of second conductive type semiconductor regions provided on the semiconductor region. A light-transmitting insulating film having a small thickness, a plurality of light-transmitting electrode layers discretely provided on the insulating film in a predetermined arrangement pattern so as to intersect the semiconductor region in a matrix, Driving means for applying a predetermined driving voltage to each of the semiconductor regions in a predetermined scanning procedure; and activating each of the electrode layers in a predetermined scanning procedure, and being induced by incident light in each of the semiconductor areas, and being tunneled. Output means for collecting charges guided to each corresponding electrode layer through the insulating film by an effect to generate a video signal. 2. The solid-state imaging device according to claim 1, wherein an insulating oxide film for electrically separating the adjacent semiconductor regions from each other is provided on a main surface of the semiconductor substrate. 3. The solid-state imaging device according to claim 1, wherein a metal line electrically connected in parallel with each of said electrode layers is provided on said electrode layers via an interlayer insulating film. element. 4. The semiconductor region is provided independently for each pixel, and a metal line electrically connected in common to a plurality of the semiconductor regions for each predetermined set is provided on the electrode layer via an interlayer insulating film. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is provided.