JPS61229355A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To enable to prevent the smear charge generated in the deep part of the substrate from intruding into the scanning line by a method wherein an impurity region, which is used as the drain of the smear charge, is provided between the photo diode and the scanning line and is electrically connected to the substrate. CONSTITUTION:A P-type region 13 is formed in an N-type substrate 12 and the buried CCD is formed of a photo diode region 14, the transfer channel 15 of the buried CCD, a gate oxide film 16, a polycrystalline Si electrode 17, which functions both as the readout gate and transfer gate of the channel 15, and so forth in the region 13. Moreover, N-type drain regions 22 to be electrically connected with the substrate 12 are formed on the side of the substrate to the photo diode 14. By this way, a positive voltage to the region 13 is impressed on the substrate 12 and when the diode 14 is fully filled with signal charge by a strong incident light, the excess charge is prevented from being swept out in the substrate 12 via the regions 22 and the smear charge is prevented from intruding into the channel 15.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to solid-state imaging devices, and particularly to improving the smear characteristics thereof.

Conventional technology Figure 3 shows a vertical 0FD (0v
IL-C with FIOW Drain) structure
FIG. 2 is a schematic diagram showing a cross-sectional structure of a unit pixel of OD.

Here, 1 is an N-type substrate, 2 is a P shadow region (1), 3 is a P shadow region (2), 4 is a photodiode, 6 is a COD transfer region, 6 is a gate oxide film, 7 is a poly S1 electrode, 8 is a field oxide film, 9 is a channel stop, 1o is an interlayer insulating film, and 11 is a light shielding film. In the conventional example, the P shadow area of 2 (
1) has an appropriate impurity concentration and thickness so that when the photodiode 4 is full of signal charges, excess signal charges flow out through punch-through to the N substrate of 1. The P shadow region (2) of No. 3 has a higher impurity concentration and is thicker than the P shadow region (1) of No. 2. Therefore, the area immediately below the photodiode is depleted, excess signal charges can be extracted to the substrate side, and the area other than the photodiode is not depleted. Furthermore, the potential barrier in the P shadow region (2) is intended to prevent the long-wavelength incident light from reaching the deep part of the substrate and the generated signal charges from entering the transfer region. (For example, JP-A-57-55672, JP-A-68-125962, JP-A-58-
125976) However, when strong incident light is incident, a large amount of charge is generated deep in the substrate, and it is not possible to completely prevent this charge from flowing into the transfer region. In this way, when new charges enter the transfer area from the outside where normal signal charges are being transferred, a phenomenon called smear occurs, which appears as a weak white line on the image pickup screen.

Problems to be Solved by the Invention In such a conventional vertical OFD structure, the P shadow area (2)
It is not possible to completely prevent the penetration of smear charges generated deep into the substrate with a potential barrier of 0.1-0.
It is on the order of 0.01%.

The present invention has been made in view of these points, and an object of the present invention is to provide a novel structure for improving the smear characteristics of a solid-state imaging device.

Means for Solving the Problems In order to solve the above problems, the present invention provides an impurity region between the photodiode and the scanning fin that can serve as a drain for smear charges, and is electrically connected to the substrate. be.

Function: With the above-described configuration, the present invention prevents smear charges generated deep in the substrate due to the incidence of long-wavelength light from entering the scanning line by controlling the substrate potential. .

Embodiment A solid-state imaging device according to an embodiment of the present invention is shown in FIG. Here, boron ion implantation and S
A P shadow region 13 is formed by epitaxial growth of 1, and the following cans are formed in this P shadow region. 14
is a photodiode region made of an n-type impurity diffusion layer, 1
6 is a transfer channel of the buried CCD made of an n-type impurity diffusion layer, 16 is a gate oxide film, and 17 is a read gate and CC from the photodiode 14 to the COD transfer stage 16.
Poly S1 electrode that also serves as DCCD channel 15 transmission gate,
18 is a thick field oxide film, 19 is a channel stop, 2o is an interlayer insulating film formed of psCt, NSG, etc.
Reference numeral 21 denotes a light-shielding film formed of a thin film having a high light-shielding effect, such as Mulberry or Mo. Furthermore, an n-type drain region 22 made of an n-type impurity diffusion layer is formed on the base layer side around the photodiode 14 and is electrically connected to the n-type substrate 12 .

N-type drain region 22 and photodiode 14°CGD
Between channels A/15, photodiode 14
When is full of signal charges, CCD channel/l/1
There is no bunch through between the photodiode 14 and the photodiode 14.
The photodiode 14 and CCD
Channel 15, n-type drain 22. The impurity concentration of the P shadow region 13 and the mutual distance are optimally designed.

The operation will be briefly explained here. The embodiment shown in FIG.
-I Since it is a Cfl type two-dimensional solid-state imaging device, τV
The incident light that has been optically integrated according to the standard scanning method is accumulated in the photodiode 14, and by applying a readout pulse to the readout gate 17,
5, then vertically transferred, and taken out as an image signal to the outside via a horizontal scanning circuit. On the other hand, a positive voltage Vgub is applied to the N-type substrate 12 with respect to the P shadow region 13, and when the photodiode 14 is full of signal charges due to strong incident light, excess charges are transferred to the n-type drain 2.
Charges generated by long-wavelength light that are swept out to the N-type substrate 12 via the P-type substrate 12 or entered deep into the P-shadow region are prevented from entering the surrounding CCD channel 16 by carrier diffusion. Figure 2 shows the horizontal cross section 1- in Figure 1.
This shows the potential distribution on the I line. strong incident light 3o
The smear charge 32 generated around the photodiode 14 is absorbed by the high potential at the drain 220, as shown by the potential distribution of the curve 35.

Effects similar to those of the above embodiment can also be obtained by surrounding the light receiving section with an n-type drain even when the light receiving section is constituted by a MOS capacitor.

Effects of the Invention As described above, according to the present invention, by surrounding part or all of the 7-otodiode with an n-type drain, (1) light generated by long-wavelength light incident deep into the P-type substrate region; (2) Excess signal charges overflowing from the photodiode due to strong incident light can be swept out to the N substrate through the n-type drain.

As described above, smearing and pluming can be prevented, and the image quality of the captured screen can be significantly improved.

[Brief explanation of the drawing]

12...N-type substrate, 13...P shadow area, 14...photodiode, 16...
・COD channel, 22...n-type drain. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3θ Figure 3/N Kikan

Claims (1)

[Claims] A diode region of the same conductivity type as the first semiconductor substrate and a signal charge accumulated in the diode region are formed on a second semiconductor substrate of an opposite conductivity type formed on a first semiconductor substrate of one conductivity type. The diode region has a scanning line for scanning, a part or all of the periphery of the diode region is surrounded by a region of the same conductivity type as the first semiconductor substrate, and is in electrical contact with the first semiconductor substrate. A solid-state imaging device featuring: