JPH0354858A - Solid-state image sensing element - Google Patents

Abstract

PURPOSE:To make overcharge of a charge transfer channel flow to elements for preventing blooming that becomes white stripes by forming a potential barrier between the charge transfer channel and a light-receiving element of an end-fire overflow construction. CONSTITUTION:Surplus light hv is incident on a charge transfer channel L to generate overcharge C, a potential barrier formed between the former and a light-receiving element Pd is lowered to make charge C to flow to the element Pd. Further, by making the element Pd of an end-fire overflow VOD construction, the overcharge C of the element Pd is made to flow to the depth direction of a substrate through a transistor Q1. Accordingly, even when overcharge is generated on the channel L, the charge does not overflow along the channel L so that blooming to become white stripes is prevented for performing good image sensing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a solid-state image sensor, and in particular to an IT (Inter Line) device in which a charge transfer path is also used as a photosensitive region.
The present invention relates to a device structure suitable for reducing blooming in a solid-state imaging device comprising a CCD (transfer) type CCD.

[Prior Art] FIG. 5 is a partially cutaway plan view showing the planar structure of an IT-type solid-state image sensor that was studied prior to the present invention.

The basic structure and operation will be explained below. Light-receiving elements composed of photodiodes Pdl, Pd2, etc. are arranged in a matrix, and between each photodiode Pd there is a A plurality of charge transfer channels LL, L2, L3... are formed, and each photodiode Pd and charge transfer channels L1, L2,...
Part excluding L3 (hatched area surrounded by dotted lines in the figure)
is the channel stop region.

On the other hand, a plurality of transfer electrodes G1, G2, G3... made of a polysilicon layer extending in the horizontal direction are provided on the upper surfaces of the charge transfer channels L1, L2, L3..., and four transfer electrodes are combined into one. Clock signals φl, φ2, φ3, and φ4 based on a four-phase drive system are applied as a set. That is, two transfer electrodes G1 and G2 are formed corresponding to the row in which the photodiodes Pdl are lined up, and
Two transfer electrodes G3 and G4 are formed corresponding to the row in which the photodiodes Pd2 are lined up, and other photodiodes and charge transfer channels (not shown) are similarly configured.

Photodiodes Pdl, Pd2... and charge transfer channels L1, L2, L3... are connected to enable charge transfer by transfer gates Tgl, Tg2...
Signal charges generated in the photodiodes Pdl, Pd2, . . . are transmitted to the charge transfer channels L1, I2, L3, . and charge transfer channels L1, L2, L3
Regarding..., clock signals φ1, φ2, φ3, φ4
Potential wells are formed in response to voltage changes, and signal charges are sequentially transferred in the direction of arrow Y.

The IT type image sensor having the above structure generally covers the upper portions of the charge transfer channels L1, L2, L3, . . . with a light shielding plate, and is used exclusively for charge transfer as described above. However, depending on the area required for the shape of the charge transfer channel L, the area in which a photodiode can be formed becomes small, and therefore the light receiving area becomes small. Therefore, an imaging device has been developed in which the charge transfer channel L can also be used as a light receiving section. According to this structure, the light-receiving surface becomes enlarged, and the same effect as when the degree of integration is improved can be obtained.

However, according to the inventor's study, the charge transfer channel L
It has been found that the following unique problems occur in conjunction with the reception of light.

[Problem B to be Solved by the Invention] That is, when excessive light in the form of a spot is incident on a certain position on the charge transfer channel, excessive charges are generated corresponding to the amount of the incident light. The excess charge causes blooming on the image, but at the same time, the excess charge overflows into the charge transfer channel, causing white streaks to appear on the image as if light were received in a band-like manner.

The present invention was made to solve the above problems, and its purpose is to utilize a charge transfer channel as a light receiving surface,
Moreover, it is an object of the present invention to provide a solid-state image sensor configured to prevent pluming that causes white sushi.

Means for Solving Problem E] The object of the present invention is to provide a charge transfer channel that generates signal charges in response to light reception, and a charge transfer channel that generates signal charges in response to light reception and removes excess charges in the depth direction of the substrate. V flowing to
O D (Vertical Over flowDr
ain) structure, i.e., between the substrate, the well laminated on it, and the light-receiving element having the VOD structure in which the charge flows to the substrate side by means of an impurity layer for the photodiode laminated on the substrate. This is achieved by creating a potential barrier that allows excess charge generated from the transfer channel to flow to the light receiving element.

[Effect] In other words, when there is excessive light incident on the charge transfer channel and correspondingly excessive charge is generated in the charge transfer channel, the potential barrier formed between the light receiving element and the charge transfer channel becomes larger than the separation barrier between the charge transfer channels. If it is formed low, the excess charge will flow to the light receiving element, and the light receiving element will also flow the excess charge in the depth direction of the substrate due to the OD structure, so the excess charge generated in the charge transfer channel will flow into the charge transfer channel. There is no overflow and no white spots appear on the image.

[Example] Hereinafter, an example of a solid-state image sensor to which the present invention is applied will be described with reference to FIGS. 1 to 4. 1 is an explanatory diagram showing the basic concept of the present invention, FIG. 2 is a sectional view showing the structure of a solid-state imaging device, FIG. 3 is a potential distribution diagram, and FIG. 4 is a layout diagram of an optical filter.

First, the basic concept of the present invention will be explained with reference to FIG. Figure 1 shows the charge transfer channel L and the light receiving element Pd.
This is a schematic diagram showing that when excessive light hν in the form of a spot is incident on a part of the charge transfer channel L, for example,
Excess charge C is generated depending on the amount of light.

When excess charge C is generated, the potential harrier between the charge transfer channel L and the light-receiving element Pd is simultaneously lowered as shown by the dotted line in FIG. Make it flow to Pd. As a result, the overflowing excess charge C is not transferred along the charge transfer channel L, and although a white bright spot corresponding to the spot-like light appears on the screen, no white sewage appears.

As described above, when excess charges C flow into the light receiving element Pd, the excess charges C overflow into the light receiving element l-Pd. At the same time, if a part of the spot-like light hν falls on the adjacent light-receiving element Pd,
The light receiving element Pd itself may generate signal charges.

At this time, if the incident light is excessive, the light receiving element Pd itself also generates excessive charges. Therefore, in order to flow this excess charge in the depth direction of the substrate and prevent pluming, a VOD (ffl type overflow structure) structure is provided in the light receiving element l-Pd, in other words, in association with the photodiode.

To explain the VOD structure simply, when excess charge is generated in the light-receiving element Pd, a transistor Q1 is formed as shown in FIG. It is something to be warned against. This kind of VOD
Depending on the structure, the excess charge C transferred from the charge transfer channel L to the photodetector element Pd, and the excess charge C transferred from the charge transfer channel L to the photodetector element Pd
Excess charge generated from the substrate itself is swept away in the depth direction of the substrate.

Next, the device structure of the solid-state image sensor will be described with reference to FIGS. 2 and 3.

FIG. 2 is a cross-sectional view of the main parts of the solid-state imaging device, where 1 indicates an n-substrate and 2 indicates a p-well layer. and,
an N layer 3 forming a charge transfer channel in the p-well layer 2;
N guarding the photodiode Pd (light receiving element)
+lli4 is formed, and the upper surfaces of these N layer 3 and N' layer 4 are covered with a silicon oxide film (SiOz) 5.

Further, on the surface of the silicon oxide film 5 and above the N layer 3, a polysilicon layer 6 forming a transfer electrode is laminated, and on the top of the polysilicon layer 6 and the top of the N layer 4, a light source, which will be described later, is formed. Filters 7 and 8 are formed. The polysilicon layer 6 and optical filters 7 and 8 are covered with a silicon oxide film 9. Incidentally, a metal wiring (not shown) is connected to the polysilicon layer 6, and the structure is such that charge transfer can be controlled by a clock signal.

Next, the effect of flowing excess charge C to the substrate (n substrate) will be explained.

Generation of excess charge C and injecting it into the n-substrate 1 is performed as follows. That is, light reception control of a solid-state image sensor is generally controlled by a mechanical structure. When the shutter opens, the light hν enters the N layer 3 constituting the charge transfer channel L and the N° layer 4 constituting the photodiode Pd, and the excess charge C generated in the N layer 3 is transferred to the N layer 3. The current flows to the N° layer 4 via the field shift transistor Q2 formed between the N° layer 4 and the N° layer 4.

This excess charge C is flowed to the n-substrate 1 via the VOD structure (structure forming the transistor Q1) formed between the N' layer 4 and the n-substrate 1.

The field shift transistor Q2 is NJi3
When an excess charge C is generated in the NN3, it is formed by a corresponding change in the potential distribution, and operates to flow the excess charge C from the NN3 to the N layer 4.

On the other hand, the N'' layer 4 is formed in a p-well layer with a low impurity concentration and a shallow junction, whereas the N'' layer 3 is formed in a p-well layer with a high impurity concentration and a deep junction. Vsub is applied between the N layer 3 and the n-substrate l' so that the p-well layer with a shallow junction is depleted. A transistor serving as a path for charge is not formed between them.

However, if the excess charge C generated in the N layer 3 is flowed into the N layer 4, and if excess charge is further generated in the N layer 4, the VOD structure causes the excess charge to flow to the N substrate l. .

That is, as the charge accumulation in the N layer 4 increases, the potential decreases,
A forward bias is applied between the junction and the shallow p-well N2, so that a transistor Ql is formed as shown in the figure, and the excess charge C flows to the n-substrate 1 via the transistor Q1. As a result, excess charge C does not overflow along the charge transfer channel L, and the occurrence of the white scum is prevented.

Next, the flow of excess charge C will be explained with respect to the potential distribution shown in FIG. 3.

When excess charge C overflows in the N layer 3, the field shift transistor Q2 operates and the barrier between it and the photodiode Pd is controlled to be low. As a result, the overflowing excess charge C flows into the N layer 4, and further V
Due to the OD operation, it flows to the p-well N2 and n-substrate 1, which have a low potential distribution. Therefore, the excess charge C will be poured into the substrate in the depth direction, and no distortion will appear in the projected image.

Incidentally, the solid-state image sensor having the above structure is often used for capturing color images. For this reason, optical filters (color filters) 7 and 8 are provided as shown in FIG. There are various arrangements of the optical filters 7 and 8, but for example, as shown in FIG.
...A red (R) optical filter 7 is arranged above, and green (G) and blue (B) optical filters 8 are arranged above each photodiode Pd.
Place. The polysilicon layer 6, which serves as a transfer electrode, has the property of absorbing short wavelength light, but since red has a long wavelength, light transmission through the polysilicon layer 6 is good, creating a charge transfer channel, in other words. The N layer 3 can improve the light receiving sensitivity.

Furthermore, the characteristics of the field shift transistor Q2,
In other words, the potential barrier when excess charge C is generated can be adjusted by changing the amount of impurity implantation.

[Effects of the Invention] As explained above, the solid-state image sensor according to the present invention has the following effects:
A charge transfer channel that generates a signal charge corresponding to light reception and a light receiving element having a VOD structure that generates a signal charge corresponding to light reception and causes excess charge to flow in the depth direction of the substrate. St is a potential barrier for flowing the excess charge to the light receiving element when the excess charge is generated.

Therefore, according to the solid-state imaging device, even if excess charge is generated in the charge transfer channel, the excess charge does not overflow along the charge transfer channel.

As a result, white spots due to excess charge do not appear in images photographed by this solid-state image sensor, blooming is also reduced, and it is possible to take good images.

[Brief explanation of drawings]

FIGS. 1 to 4 show an embodiment of a solid-state image sensor to which the present invention is applied. FIG. Figure 3 is a potential distribution diagram explaining the injection of excess charge, Figure 4 is a layout diagram of an optical filter, and Figure 5 is an example of a conventional solid-state image sensor. FIG. Symbol 1 in the figure: N substrate 2: P well layer 3: N layer forming a charge transfer channel 4: N' layer forming a photodiode 5, 9: Silicon oxide film 6: Polysilicon layer 7, 8 : Optical filter L: Charge transfer channel Pd: Photodiode Q1: Transistor Q2 for VOD operation: Field shift transistor h ν Two incident light. Figure 1 hv Figure 2 Figure 1 3 Snake Figure 4 Pd

Claims (1)

[Claims] A plurality of light receiving elements arranged in a matrix,
a charge transfer channel that is provided along the arrangement of the plurality of light receiving elements in a predetermined direction and sequentially transfers charges generated from the plurality of light receiving elements, and also generates and transfers charges corresponding to light reception; In a solid-state imaging device having a VOD structure for causing excess charges generated from a plurality of light receiving elements to flow in the depth direction of the substrate, the light receiving element is adjacent to a potential barrier for separating pixels in the charge transfer channel. and each barrier is formed such that a potential barrier separating the charge transfer channels is low, and when excess charge is generated from the charge transfer channel, the excess charge flows from the charge transfer channel to the light receiving element, and A solid-state image sensor configured to flow in the depth direction of the substrate using a VOD structure.