JPS58134582A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To avoid blooming due to overflow of charges with a simple construction, by forming an overflow drain consisting of an impurity dope layer as a semiconductor substrate so as to surround each unit picture element. CONSTITUTION:The overflow drain 16 is formed on the surface of a p type substrate 5b, for example, so that the width is narrower than a width L of a picture element separation region 17 and the impurity doped layer having opposite conduction type (n type) as the substrate 5b with W in width around its center is formed. The layer is formed so as to surround a unit picture element 1 and an inverted voltage is applied to the substrate 5b. Thus, a well is formed beneath the overflow drain 16 and the charge plane in it is lowered for the potential, even if charge in the well beneath the picture element overflows, the charge flows in the well beneath the overflow drain, and is not invaded to the well beneath the adjacent picture elements, then no blooming takes place.

Description

Detailed Description of the Invention f3-) Technical Field of the Invention The present invention relates to a charge injection device (hereinafter abbreviated as "C") as a solid-state imaging device, particularly to "C" which does not cause pluming.

(To) Technical background In recent years, with the remarkable progress in semiconductor manufacturing technology, it has become easier to manufacture -dimensional or two-dimensional C. A pixel 1 consisting of a pair of electrodes gX and 2Y, to which voltages of about several volts and about ten-odd volts are applied, respectively, is two-dimensionally arranged on a dead and dead conductive substrate covered with an insulating film. Charges 4 within the semiconductor substrate generated from optical excitation of the imaging light projected onto the light receiving surface 60 are first accumulated in a potential well (hereinafter simply abbreviated as well) 811 directly below the electrode 2Y.

If the wells directly below the electrode 2Y connected to the Y bus are then erased all at once by voltage manipulation from the vertical shift register 20, the charge 4 will be transferred all at once to the well 3a directly below the electrode 2X. , the state at this time can be seen in the pixel group in the 8th row in FIG. At the moment this charge 4 is transferred, an image charge is generated on the electrode 2x.

The image electric bridge is X bus line X and electronic switch 11°111
8 and i4 to the output terminal of the charge amplifier 7. Here, 10 is a horizontal shift register, 9 is a reset switch, x1 to X4 . Yl to Y4 indicate the X bus line X group and the Y bus line Y group, respectively.

When the imaging of one frame from C is completed, the electronic switch 8
By closing 1 to S4, the well 8a to which the charge generated by the photoexcitation has been transferred is made to disappear.In this way, the charge is injected into the substrate and disappears, so that it is ready for the next frame of imaging. In the newly created well, charges are again accumulated due to photoexcitation.

(C) Prior art and problems The structure and operation of the CHD are summarized above. In the conventional solid-state imaging device, or CID, with this structure, if strong light is concentrated on one spot on the light-receiving surface, The wells directly under the electrodes 2X and 2Y in the pixel at that location are overflowing with charge, and before the charges flowing out of that well are completely eliminated, they flow into the wells directly below the surrounding pixels, causing so-called pluming. There was a drawback that it occurred.

In order to avoid this (as shown in FIG. 2(a), by using an epitaxy layer 5a and a substrate 6 of an n type, for example, a p-type epitaxia μ layer 5a and an n-type substrate 6 are separated in the opposite direction shown as E). Alternatively, as shown in Fig. 2 (to), a reverse voltage E is also applied between K and, for example, the n-type impurity dope 1 layer (buried layer) 8 buried in the p-type substrate bb. In this way, even if a phenomenon occurs where charges overflow into the well directly below one pixel, the overflowing charges will be reduced to the voltage E.
Due to the electric field generated by the lateral force shown in FIG. There will be no flow into other wells that are not flailed, and therefore there is a risk of micro-pming occurring. However, in FIGS. 8(f) and (to), 17 is a pixel separation region.

Figure 8 shows the above-mentioned Ebitaki Vya! When a substrate is used, even if charge overflow occurs in the well U directly below the pixel a where light is strongly incident, the well Zl)K directly below the adjacent pixel will not be charged.
The same thing can be said for K from C in Fig. 2 (6), which has a buried layer 8.
However, Figure 2 (to), @ and 15a in Figure 8
is electrode 1! Insulating film directly under X, 2Y, 15b is fee μ
It is a hard insulating film.

However, although the above-mentioned methods are very effective, the first problem is that the Ebitaxia/I/Rieva is expensive.

A second drawback is that forming the buried layer is extremely complicated.

A) Purpose of the present invention The present invention has been made in view of the above-mentioned conventional drawbacks, and is based on C, which can eliminate μm leakage due to charge overflow by a simple method without using an epitaxial wafer or a buried layer substrate. It is intended to provide the structure of a solid-state imaging device.

(e) Structure and object of the invention According to the present invention, a light-receiving surface is formed on the entire surface of a semiconductor substrate, and a plurality of unit pixels are formed on the light-receiving surface.

This is achieved by providing a solid-state imaging device characterized in that an overflow drain made of an impurity-doped layer of a conductivity type opposite to that of the substrate is formed to surround each unit pixel to prevent pluming. .

(f) Embodiments of the Invention Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, as shown in FIG.
6) is a plan view of the solid-state imaging device, that is, CID, according to the present invention, and FIG.

The main surface on the side where 2Y is disposed is the light-receiving surface.

In FIG. 4) and (to), 16 has a width W (W<L) on the surface of the p-type substrate 5b, which is narrower than the radius of the pixel isolation region 17 and near the center thereof, and has conductivity opposite to that of the substrate 5b. This is an overflow drain made to constitute an n-type (n-type) impurity doped layer, and this is shown in Figure 4 @
It is formed so as to surround each unit pixel l as shown in FIG.
) A reverse voltage is applied to K.

If this is done, wells like 21a and 21b in FIG. 4(C) will be created directly below the overflow drain 16, and the charge surface 2ga, in therein will be pulled down, so for example, the wells shown in FIG. 8 will be created. Even if the charge in the well Za directly under the pixel a overflows, the overflow charge will be transferred to the well 21a immediately below the overflow drain surrounding the pixel a as shown in FIG. 21b, and the inflowing charge is easily discharged, so it does not get mixed up in the well formed directly under the pixel adjacent to the right side or the pixel (not shown) adjacent to the left side. , thus eliminating the risk of pluming.

By the way, the reason for setting the condition W(L) is as follows.
If the width of the overflow drain 16 is made almost equal to the radius (t or the width of the element isolation region 17) of the field insulating film 151), each well directly under each adjacent pixel will instead be made to have a width directly under the overflow drain 16. This is because the wells 21a, 21N) are connected to each other, which is even more inconvenient than the layer before the overflow drain was provided.

Note that each of the X bus line X and the Y bus line Y drawn in the plan view of FIG. The disadvantage that the voltage supplied from the shift register to the busbar does not affect the effectiveness of the overflow drain 16 does not occur, and this overflow drain 1
6 can be easily formed by ion implantation or impurity diffusion, so manufacturing a CHD with such a structure is extremely easy, and there is no need to use an expensive Evita core wafer like the conventional CHD. Otherwise, there is no need to go through a complicated process such as forming a buried layer, and therefore the device can be manufactured at low cost. FIG. 6 is a cross-sectional view showing the structure of a CID that is a modified embodiment of the present invention. , an element isolation region @26 is embedded in the insulating film of the pixel isolation region 17.

These electrodes are connected to each other in a KW- manner, and the polarity of the pressure E is -E, which is the opposite of that in FIG. 4, so that a predetermined voltage VF can be applied between these electrodes and the substrate 15b.

The reason for adopting such a structure is to avoid forming a channel in the portion shown as G excluding the overflow drain in the pixel isolation region 17 in the neutralization shown in FIG.

However, in general, in a so-called MIS structure composed of the electrode 25, the insulating film 15a, and the substrate 5b, the so-called flat band voltage VFR is rounded to the predetermined voltage V.
'F may often be a value near zero.

If you look at it from another perspective, this pixel separation electrode also serves the purpose of shielding light.

(2) Effects of the Invention As described above in detail, the solid-state imaging device of the present invention has a simple structure, and has a relatively reliable puking prevention effect. It can be expected to have many useful effects.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the general configuration of a solid-state imaging device, that is, C, and Figures 2 (a) and (b) are conventional CID
Figure 8 is a cross-sectional view showing the structure of Figure 2(a).
Taking 1 as an example, a diagram showing how overflowing charges flow toward the substrate, FIG. A diagram showing a cross section, FIG. 4 (Q) is a diagram showing potential wells generated in each part drawn in FIG. 4 (F), and FIG. . In the drawings, 1 Halll element, 2X, 2'lK pole, 6
b indicates a substrate, 15b indicates a field insulating film defining the element isolation region 17, and 16 indicates an overflow drain.

Claims (1)

[Claims] In a configuration in which a light-receiving surface is formed on the entire surface of a semiconductor substrate, and a plurality of unit pixels are formed on the light-receiving surface, an impurity tope of a conductivity type opposite to that of the substrate is used to prevent pluming. A solid-state imaging device characterized in that an overflow drain consisting of layers is formed in a respectful manner around each unit pixel.