JP3177072B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device,
In particular, the present invention relates to a structure of a pixel portion in which a false signal called smear is reduced.

[0002]

2. Description of the Related Art FIG. 5 is a view showing an example of a conventional one-dimensional solid-state imaging device. FIG. 5A is a plan view thereof, wherein 1 is an optical signal storage area (photoelectric conversion unit). Reference numeral 2 denotes a read gate for reading the charge stored in the optical signal storage region 1 by an external clock signal, and 3 denotes a charge-coupled device (hereinafter referred to as CCD) for storing and transferring the read charge. 4) an amplifier for detecting and amplifying the electric charge transferred from the CCD 3, and 5 a light shielding film provided to prevent light from entering an unnecessary place (other than the optical signal storage area 1). And 5a is its opening window. 5 (b) and 5 (c) show A-A in FIG. 5 (a).
7A and 7B are diagrams showing cross sections taken along lines A ′ and BB ′ and their potentials. In these figures, reference numeral 6 denotes a p-type semiconductor substrate;
12 and 8 are n-type semiconductor layers provided on the semiconductor substrate 6;
Reference numeral 7 denotes a transfer gate of the CCD.

Next, the operation will be described. FIG. 6 is a diagram showing the movement of the potential in the cross section taken along the line AA ′ in FIG. 5 (a) during the operation. In FIG. Then, as shown in FIG. 6B, the charge is accumulated in the accumulation region 1. Subsequently, the gate 2 is opened by the clock pulse applied to the readout gate 2, and the electric charges accumulated so far are transferred to the CCD 3 to be in the state shown in FIG. Thereafter, the read gate 2 closes and returns to the state of FIG.

In the above operation, the opening window 5a of the light shielding film 5
Incident on the semiconductor layer 12 through the semiconductor layer 12
An electron-hole pair is generated therein. At this time, the charges 11 generated between two adjacent storage regions 1 in FIG.
Moves in all directions because the electric field at the location is weak 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 spurious signals called smear, and has a very bad influence upon imaging.

[0005]

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

The present invention has been made to solve the above problems, and has as its object to obtain a solid-state imaging device with less smear.

[0007] The solid-state imaging device according to the present invention has a separation area.
The predetermined part of the area is the surface part or inside the semiconductor substrate
Have been depleted, and the rows and columns constituting the photoelectric conversion unit have been depleted.
An overflow gate which is arranged in a row and reads out charges generated in the isolation region to an overflow drain is provided.

[0008]

In the present invention, since the depletion layer exists in the separation region separating each photoelectric conversion unit , the light is generated in the photoelectric conversion unit.
The generated charges are prevented from going in the direction of the CCD.

[0010]

[0011]

[Embodiment 1] Hereinafter, a solid-state imaging device according to a first embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same reference numerals as those in FIG.
FIG. 5A is a plan view thereof, in which reference numeral 9 denotes an isolation region having a depletion layer in a semiconductor layer for isolating the optical signal accumulation region 1, and the other configuration is the same as that of FIG. (a)
Is the same as FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. 2A and a diagram showing its potential. In the figure, reference numeral 21 denotes an n-type semiconductor layer formed on the p-type substrate 6; Reference numeral 22 denotes a p-type semiconductor layer formed shallowly 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, by optimizing the impurity concentration and the junction depth of each of the semiconductor layers 21 and 22, when reading out the electric charge stored in the storage region 1, the n-type semiconductor layer 2 of the optical signal storage region 1 is read out.
1 can be completely depleted. Also, FIG.
3A is a sectional view taken along the line BB ′ of FIG. 3A and a diagram showing its potential. In the figure, reference numeral 23 denotes an n-type semiconductor layer formed on the p-type substrate 6; It is a p-type semiconductor layer formed shallowly above.

In the above configuration, 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), when the potential of the separation unit 9 is 0 V or more, a potential distribution in which the potential of the storage unit 1 is deeper than the potential of the separation unit 9 can be realized. In addition, FIG.
FIG. 2 is a cross-sectional view taken along line CC ′ of FIG.

Next, the operation will be described. The light incident through the opening window 5a is transmitted to the optical signal accumulation region 1 and the separation region 9
To generate electron-hole pairs in the respective semiconductor layers.
In the case of this example, electrons of the generated electron-hole pairs become signal charges. The signal charges generated in the optical signal storage region 1 are stored in the region as it is. On the other hand, as shown in FIG.
Since there is a potential wall on the third side, it does not diffuse in this direction. As a result, this charge does not flow into the CCD 3 and smear is reduced accordingly. Further, as shown in FIG. 1D, the charges 11 generated in the separation region 9 diffuse and flow into the adjacent storage region 1 and become a part of the signal charges.

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 made of the p-type semiconductor layer 24 is provided, a depletion layer is generated between the respective optical signal accumulation regions 1 and CC
A barrier is formed for D3, and the charge generated in the isolation region 9 can be prevented from flowing into the CCD3.

Embodiment 2 FIG. Next, a solid-state imaging device according to a second embodiment of the present invention will be described with reference to the drawings. In FIG. 2A, reference numeral 31 denotes an overflow gate for reading out unnecessary charges accumulated in the isolation region 9, and 32 denotes an overflow drain for discharging unnecessary charges. 2 (b) and 2 (c) are AA 'and B of FIG. 2 (a).
FIG. 4 is a diagram showing a cross section taken along line −B ′ and a potential during the storage period, in which V PD is a potential value of the optical signal storage region 1 and V TG is an 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 constituting the optical signal accumulation region 1 and the isolation region 9 and the voltage applied to the overflow gate 31, the above potentials can be set so that VPD>VTG> VIL. it can.

Next, the operation will be described. In the charge accumulation period, as shown in FIGS. 2B and 2C, light enters through the opening window 5a, and charges are generated in the optical signal accumulation region 1 and the separation region 9, respectively. Signal storage area 1
Below, the electric charge is accumulated because the potential value VPD of the optical signal accumulation region 1 is larger than the potential value VTG of the overflow gate 31. On the other hand, below the isolation region 9, the charge 11 flows into the overflow drain 32 through the overflow gate 31 because the potential value VTG of the overflow gate 31 is larger than the potential VIL of the region 9. Therefore, the charges caused by the light incident on the separation region 9 are transferred to the optical signal storage region 1 adjacent thereto.
The ratio of inflow to the air becomes smaller. This means that the sensitivity distribution of one pixel has a steep rise, and the resolution is improved.

As described above, according to the second embodiment, the overflow gate 31 and the overflow drain 32 are provided in parallel with the pixels, and the potential value VTG of the overflow gate 31 is changed to the potential value VTG of the optical signal storage region 1.
Since the value is set to a value between the PD and the potential value VIL of the isolation region 9, it is possible to suppress the charge accumulated in the isolation region 9 from flowing into the optical signal accumulation region 1. Unnecessary charges flowing into the optical signal storage region 1 are reduced, and the resolution is improved.

Embodiment 3 FIG. Next, a solid-state imaging 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 accumulation region according to the present embodiment. Reference numeral 9a denotes an isolation region, which is composed of a region 91 having a shallow potential value and a region 92 having a deep potential value. Other configurations are the same as those of the second embodiment.

Next, the function and effect will be described. In this embodiment, the optical signal storage region 1 is located in the separation region 9a.
Since the region 91 having a low potential value is arranged in the vicinity, the potential is shallow at a position near the optical signal accumulation region 1 in the separation region 9a, in other words, a high barrier against the optical signal accumulation region 1. Is formed, so that the ratio of the charge caused by the light incident on the separation region portion 9a to flow into the optical signal accumulation region 1 adjacent thereto is further reduced as compared with the second embodiment.

Embodiment 4 FIG. Although the one-dimensional solid-state imaging device has been described in each of the above embodiments, it is needless to say that the present invention can be applied to a two-dimensional solid-state imaging device. FIG. 4 is a view 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.
It is. As shown in FIG. 4, in the two-dimensional solid-state imaging device,
The plurality of vertical transfer CCDs 42 are connected to the horizontal transfer CCDs 42, whereby the optical signals detected by the pixels arranged in a plane can be sequentially extracted to the outside.

In the above embodiment, the charge storage section and the
Although the separated region has a pnp type structure, it may have an np structure by optimizing the impurity concentration, and the same effect can be obtained.

As described above, according to the solid-state imaging device of the present invention, a predetermined one of the separation regions is replaced with a surface portion thereof.
Alternatively, the inside of the semiconductor substrate is depleted , and the charge generated in the separation region provided between the photoelectric conversion units is caused to flow out to the overflow drain before flowing into the photoelectric conversion unit, so that there is no smear, and There is an effect that a solid-state imaging device with high resolution can be obtained.

[0023]

[Brief description of the 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 imaging 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 in which the present invention is applied to a two-dimensional solid-state imaging device according to Embodiment 4 of the present invention.

FIG. 5 is a plan view of a conventional solid-state imaging device and a diagram showing potential levels during operation.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical signal accumulation region 2 read gate 3 charge-coupled device 4 amplifier 5 light shielding film 5 a light shielding window 6 p-type semiconductor substrate 7 CCD transfer gate 9, 9 a isolation region 91 region with low potential value 92 region with large potential value 8 n-type semiconductor Layer 12 n-type semiconductor layer

Claims (3)

(57) [Claims] 1. A plurality of photoelectric conversion units arranged in a straight line on a semiconductor substrate, and in the solid-state imaging device that includes a arranged isolation regions between adjacent photoelectric conversion unit, predetermined the separation region Those whose surface part or semi-conductive
A solid-state imaging device, comprising: a body substrate that is depleted; and an overflow gate that is arranged in parallel with a row constituting the photoelectric conversion unit and reads out charges generated in the isolation region to an overflow drain. 2. The solid-state imaging device according to claim 1, wherein a potential value of a region immediately below said overflow gate during a charge accumulation period is smaller than a potential value of said photoelectric conversion unit and larger than a potential value of said separation region. A solid-state imaging device characterized by being set. 3. The solid-state imaging device according to claim 1, wherein a potential value of the separation region is small near the photoelectric conversion unit.