JPH0758307A - Solid state image pickup apparatus - Google Patents

Abstract

PURPOSE:To reduce smear generated due to inflow of charges generated between the photoelectric conversion regions into a CCD in a solid state image pickup apparatus. CONSTITUTION:An N-type semiconductor layer 23 and a P-type semiconductor layer 24 formed thereon are provided in an isolation region 9 which isolates an optical signal storage region 1 from an optical signal storage region 1 adjacent thereto in order to form a depletion layer. Thereby, charges are accumulated therein to control diffusion of chrges 11 generated in the isolating region 9 into the direction of the CCD 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device,
In particular, the present invention relates to the structure of a pixel portion called smear for reducing false signals.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing an example of a conventional one-dimensional solid-state image pickup device. FIG. 5 (a) is a plan view of the same, in which 1 is an optical signal storage region (photoelectric conversion section). Reference numeral 2 denotes a read gate for reading the charges accumulated in the optical signal accumulation region 1 in response to an external clock signal, and 3 denotes a charge-coupled device (hereinafter, CCD) for accumulating and transferring the read charges. 4 is an amplifier for detecting and amplifying charges transferred from the CCD 3, and 5 is a light-shielding film provided to prevent light from entering an unnecessary place (other than the optical signal storage region 1). Yes, 5a is the opening window. In addition, FIG. 5 (b) and FIG.
It is a figure which shows the cross section in A'and BB 'line, and its potential, In these figures, 6 is a p-type semiconductor substrate,
12, 8 are n-type semiconductor layers provided on the semiconductor substrate 6,
Reference numeral 7 is a CCD transfer gate.

Next, the operation will be described. FIG. 6 is a diagram showing the movement of the potential along the line AA ′ in FIG. 5 (a) during operation. When a certain time elapses after the light enters the storage region 1 in FIG. 6 (a). As shown in FIG. 6B, the charge is stored in the storage region 1. Then, the gate 2 is opened by the clock pulse applied to the read gate 2, and the electric charge accumulated so far is transferred to the CCD 3 to be in the state shown in FIG. 6 (c). After that, the read gate 2 is closed and the state shown in FIG.

In the above operation, the opening window 5a of the light shielding film 5
Light incident on the semiconductor layer 12 through the
In it, electron-hole pairs are generated. At this time, charge 11 generated between two adjacent storage regions 1 in FIG.
Moves in all directions because the electric field at that location is very small and the potential is shallow. Therefore, a part of the generated charge moves to the CCD 3 side and is added as a part of the signal charge. This phenomenon is one of the false signals called smear, and has an extremely bad influence upon image pickup.

[0005]

Since the conventional solid-state image pickup device is constructed as described above, there is a problem that there are many smears and a lot of image noise at the time of image pickup.

The present invention has been made to solve the above problems, and an object thereof is to obtain a solid-state image pickup device with less smear.

[0007]

In the solid-state image pickup device according to the present invention, the surface of a predetermined one of the separation regions for separating the photoelectric conversion portion is depleted.

Further, an overflow gate is provided to read out the charge accumulated in the depletion layer of the isolation region to the overflow drain.

[0009]

In the present invention, since the depletion layer is present in the isolation region that separates the photoelectric conversion units, the charges generated between the photoelectric conversion units are prevented from moving toward the CCD.

Further, since the charge generated in the separation region is made to flow into the overflow drain, the resolution is improved.

[0011]

EXAMPLES Example 1. Hereinafter, a solid-state imaging device according to a first embodiment of the present invention will be described with reference to the drawings. 1, the same reference numerals as those in FIG. 5 denote the same or corresponding parts, and
(a) is a plan view thereof, in which reference numeral 9 is an isolation region having a depletion layer in the semiconductor layer for isolating the optical signal storage region 1, and other configurations are the same as those of the conventional structure shown in FIG. (a)
Is the same as. Further, FIG. 2B is a cross-sectional view taken along the line AA ′ of FIG. 1A and a diagram showing its potential. In the drawing, 21 is an n-type semiconductor layer formed on the p-type substrate 6, A p-type semiconductor layer 22 is shallowly formed on the n-type semiconductor layer 21. These semiconductor layers 21 and 22 can be easily formed by an ion implantation technique of a normal semiconductor process.
Therefore, when the charges accumulated in the accumulation region 1 are read out by optimizing the impurity concentration and the junction depth of each of the semiconductor layers 21 and 22, the n-type semiconductor layer 2 of the optical signal accumulation region 1 is read.
1 can be completely depleted. Also, the same figure (c)
2A is a cross-sectional view taken along the line BB ′ in FIG. 3A and a diagram showing its potential. In the figure, 23 is an n-type semiconductor layer formed on the p-type substrate 6, 24 is an n-type semiconductor layer 23. It is a p-type semiconductor layer formed shallowly on the top.

In the above structure, the impurity concentration of the n-type semiconductor layer 21 is made higher than that of the n-type semiconductor layer 23, and the p-type semiconductor layers 22 and 24 are manufactured in the same step. As shown in (c), it is possible to realize a potential distribution in which the potential of the storage unit 1 becomes deeper than the potential of the separation unit 9 when the potential of the separation unit 9 is 0 V or higher. In addition, Figure (d) is the same as Figure (a).
FIG. 3 is a cross-sectional view taken along the line CC ′ of FIG.

Next, the operation will be described. The light that has entered through the opening window 5a receives the optical signal storage region 1 and the separation region 9
Electron-hole pairs are generated in each of the semiconductor layers.
In the case of this example, the electrons of the generated electron-hole pairs become the signal charges. The signal charges generated in the optical signal storage area 1 are stored in the area as they are. On the other hand, as shown in FIG. 1C, the charge 11 generated in the separation region 9 is
Since there is a potential wall on the 3 side, it does not diffuse in this direction, and as a result, this charge does not flow into the CCD 3 and smear is reduced accordingly. Further, as shown in FIG. 1D, the charge 11 generated in the separation region 9 diffuses and flows into the adjacent storage region 1 side and becomes a part of the signal charge.

As described above, according to the first embodiment, the n-type semiconductor layer 23, is formed on the surface of the substrate 6 between the adjacent optical signal storage regions 1.
Since the isolation region 9 formed of the p-type semiconductor layer 24 is provided, a depletion layer is generated between the optical signal storage regions 1 and CC
A barrier is formed to D3, and it is possible to prevent charges generated in the separation region 9 from flowing into the CCD3 side.

Example 2. Next, a solid-state image pickup device according to a second embodiment of the present invention will be described with reference to the drawings. In FIG. 2A, 31 is an overflow gate for reading unnecessary charges accumulated in the separation region 9, and 32 is an overflow drain for discharging unnecessary charges. 2 (b) and 2 (c) are AA ′ and B of FIG. 2 (a).
It is a figure which shows the cross section in a -B 'line, and the potential in the accumulation | storage period in the figure, VPD is the potential value of the optical signal storage area 1, VTG is the overflow gate 3.
The potential value of 1 and VIL indicate the potential of the separation region. By optimizing the impurity concentration of the semiconductor layer forming the optical signal storage region 1 and the isolation region 9 and the voltage applied to the overflow gate 31, the above potentials can be set to VPD>VTG> VIL. it can.

Next, the operation will be described. In the charge accumulation period, as shown in FIGS. 2 (b) and 2 (c), light enters through the opening window 5a, and the light accumulation region 1 and the separation region 9
In the lower part of the optical signal accumulating region 1, the electric charges are accumulated in the electric potential accumulating region 1 because the potential value VPD of the optical signal accumulating region 1 is larger than the potential value VTG of the overflow gate 31. On the other hand, below the isolation region 9, since the potential value VTG of the overflow gate 31 is larger than the potential VIL of the region 9, the charge 11 flows into the overflow drain 32 through the overflow gate 31. Therefore, the ratio of the electric charge due to the light incident on the separation region 9 flowing into the optical signal storage region 1 adjacent thereto becomes small. This means that the sensitivity distribution of one pixel will have a steep rise,
The resolution will be improved.

As described above, according to the second embodiment, the overflow gate 31 and the overflow drain 32 are provided in parallel with the pixel, and the potential value VTG of the overflow gate 31 is set to the potential value V of the optical signal storage region 1.
Since the value is set to be a value between PD and the potential value VIL of the separation region 9, it is possible to suppress the charge accumulated in the separation region 9 from flowing into the optical signal storage region 1, and thus the first embodiment described above. Compared with this, unnecessary charges flowing into the optical signal storage region 1 are reduced, and the resolution is improved.

Example 3. Next, a solid-state image pickup device according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a plan view of the optical signal storage region portion according to the present embodiment, and 9a indicates a separation region, which is composed of a region 91 having a shallow potential value and a region 92 having a deep potential value. The other structure is the same as that of the second embodiment.

Next, the function and effect will be described. In this embodiment, the optical signal storage area 1 is formed in the separation area 9a.
Since the region 91 having a low potential value is arranged in the vicinity, the potential becomes shallow in the separation region 9a at a position close to the optical signal storage region 1, in other words, a high barrier for the optical signal storage region 1. Therefore, the ratio of the charges due to the light incident on the separation region portion 9a into the optical signal storage region 1 adjacent thereto is smaller than that in the second embodiment.

Example 4. In addition, although the one-dimensional solid-state imaging device has been described in each of the above-described embodiments, it goes without saying that the present invention can be applied to a two-dimensional solid-state imaging device. FIG. 4 is a diagram showing an example of such a two-dimensional solid-state imaging device, in which 41 is a vertical transfer CCD and 42 is a horizontal transfer CCD.
Is. As shown in FIG. 4, in the two-dimensional solid-state imaging device,
A plurality of vertical transfer CCDs 42 are connected to the horizontal transfer CCDs 42, whereby optical signals detected by the pixels arranged in a plane can be sequentially taken out to the outside.

In the above embodiment, the charge storage section is set to p-
Although the np type structure is adopted, this may be an np structure by optimizing the impurity concentration, and the same effect can be obtained.

[0022]

As described above, according to the solid-state image pickup device of the present invention, since the isolation region having the depletion layer is provided between the photoelectric conversion units, the charge generated between the photoelectric conversion units is CCD.
It is possible to obtain a solid-state imaging device with less smear, because the solid-state imaging device is prevented from going in the direction of.

Further, since the charges generated in the separation region are read out to the overflow drain before flowing into the photoelectric conversion unit, there is an effect that a solid-state image pickup device with less smear and high resolution can be obtained. is there.

[Brief description of drawings]

FIG. 1 is a plan view of a solid-state imaging device according to a first embodiment of the present invention and a diagram showing potential levels during operation.

FIG. 2 is a plan view of a solid-state image pickup device according to a second embodiment of the present invention and a diagram showing potential levels during operation.

FIG. 3 is a partial plan view of a solid-state imaging device according to a third embodiment of the present invention, and a diagram showing potential levels during operation.

FIG. 4 is a plan view showing a solid-state imaging device to which the present invention is applied to a two-dimensional solid-state imaging device according to Embodiment 4 of the invention.

5A and 5B are a plan view of a conventional solid-state imaging device and a diagram showing a potential level during operation.

FIG. 6 is a diagram for explaining how smear is diffused in a conventional solid-state imaging device.

[Explanation of symbols]

 1 Optical Signal Storage Area 2 Readout Gate 3 Charge Coupled Device 4 Amplifier 5 Light-shielding Film 5a Light-shielding Window 6 p-type Semiconductor Substrate 7 CCD Transfer Gate 9, 9a Separation Area 91 Shallow Potential Area 92 Deep Potential Area 8 n-type Semiconductor Layer 12 n-type semiconductor layer

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[Procedure amendment]

[Submission date] November 16, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

A solid-state image pickup device according to the present invention is a solid-state image pickup device in which a surface portion of a predetermined one of isolation regions for separating photoelectric conversion portions or the inside of a semiconductor substrate is depleted.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Next, the operation will be described. In the charge accumulation period, as shown in FIGS. 2 (b) and 2 (c), light is incident through the opening window 5a, charges are generated in the optical signal accumulation region 1 and the separation region 9, respectively, and light is generated. Signal storage area 1
Below, the potential value VPD of the optical signal storage region 1 is larger than the potential value VTG of the overflow gate 31, so that charges are stored. On the other hand, below the isolation region 9, since the potential value VTG of the overflow gate 31 is larger than the potential VIL of the region 9, the charge 11 flows into the overflow drain 32 through the overflow gate 31. Therefore, the electric charge due to the light incident on the separation region 9 is applied to the optical signal storage region 1 adjacent thereto.
The rate of inflow into This means that the sensitivity distribution of one pixel has a steep rise, and the resolution is improved.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

In the above embodiment, the charge storage portion and the storage
Although the isolated region has a p-n-p type structure, it may have an n-p structure by optimizing the impurity concentration, and the same effect can be obtained.

Claims (5)

[Claims] 1. A solid-state imaging device comprising: a plurality of photoelectric conversion units linearly arranged on a semiconductor substrate; and a separation region arranged between adjacent photoelectric conversion units. Is a depleted surface part of the solid-state image pickup device. 2. The solid-state imaging device according to claim 1, further comprising an overflow gate that is arranged in parallel with a column forming the photoelectric conversion unit and reads out charges generated in the separation region to an overflow drain. Solid-state imaging device. 3. The solid-state imaging device according to claim 1, wherein the isolation region has a conductivity type different from that of the substrate, and has the same conductivity type as the photoelectric conversion unit, and a semiconductor layer of the first conductivity type. A solid-state imaging device, comprising: a second conductive type semiconductor layer formed on the semiconductor layer. 4. The solid-state imaging device according to claim 2, wherein a potential value of a region directly below the overflow gate during a charge accumulation period is smaller than a potential value of the photoelectric conversion unit and larger than a potential value of the separation region. A solid-state imaging device characterized by being set. 5. The solid-state imaging device according to claim 1, wherein the potential value of the depleted separation region is small in the vicinity of the photoelectric conversion unit.