JP2001135810A - Solid-state image pick-up element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image pick-up element which ensures an electric charge amount handled at a terminal part of a horizontal transfer part, while holds upper and lower electric fields, thereby increasing a squeezing effect in an output part. SOLUTION: In a structure from a horizontal transfer part 2 to an output part 3 of a solid-state image pick-up element, there are provided a plurality of barrier steps 81a, 81b; 82a, 82b for reducing a transfer width, in a part from a terminal part 23 to an output part of a horizontal transfer part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a solid-state imaging device. More specifically, the present invention relates to a solid-state imaging device in which the structure of the solid-state imaging device from the horizontal transfer unit to the output unit is changed, thereby reducing the electric field in the vertical direction of the horizontal transfer unit and securing the amount of charge handled at the terminal end. Is provided.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a conventional solid-state imaging device.
The general structure of a CCD solid-state imaging device is schematically shown.
As shown in FIG. 3, the CCD solid-state imaging device includes an imaging unit 1, a horizontal transfer unit 2, and an output unit 3. The imaging unit 1 includes a light receiving unit 4 for performing photoelectric conversion, a read gate 5 for reading signal charges from the light receiving unit 4, and a unit cell 7 including a vertical CCD 6 for vertically transferring the read signal charges, in a planar matrix. It is configured by arranging many.

The horizontal transfer section 2 is enlarged and schematically shown in FIG.
Shown in In the horizontal transfer section 2, an N region is formed in a P-type substrate or a P-type well to form a pattern 21 which is used as a transfer section (transfer path). Further, after an interlayer insulating film is formed, a transfer electrode 22 (for example, Formed of polysilicon), and an interlayer insulating film, a light-shielding film, and a protective film are further formed thereon. The pattern 21 of the horizontal transfer unit 2, that is, the pattern of the N region, is the end portion 23 of the horizontal transfer unit near its end.
Has a potential structure in which the transfer width is reduced toward the output unit 3. That is, by injecting a P-type impurity into the hatched portions in FIG. 4 (designated by reference numerals 9a and 9b), the potential of the portions is made shallow, and the P-type impurity region (the hatched portion) is horizontal. Barriers 8a and 8b are formed between the transfer unit 2 and the pattern 21 (pattern in the N region), whereby the transfer path is tapered toward the output unit 3. Specifically, in the example of FIG. 4, as shown in the figure, the portion toward the output unit 3 has a pentagonal shape that tapers. In the present specification, a region for forming the potential barriers 8a and 8b by the introduction of impurities or the like (regions indicated by oblique lines) is hereinafter referred to as a "barrier formation region".
In addition, a drain is provided below the horizontal transfer unit 2 to discard unnecessary charges.

As described above, in the vicinity of the terminal end 23 of the horizontal transfer section 2, P-type impurities are implanted up and down in a pattern as shown by hatched portions in FIG. 4 to form barrier formation regions 9a and 9b. This is for the purpose of efficiently collecting the signal charges transferred toward the terminal end, that is, from the right side of FIG. The transfer direction is indicated by reference numeral 24. The potential structure of such a configuration is as shown in FIG. 5 (this figure shows the potential in the XX′-Y′-Y section of FIG. 4). That is, the charge transfer region is denoted by the symbol I.
The potential of the barrier forming regions 9a and 9b formed by implanting the P-type impurities is shallow, and the barriers 8a and 9b are located between the portions corresponding to the transfer portion pattern 21 (deep portions). 8b are formed. At II, the unwanted charge indicates a discarded area.

In this case, if the amount of P-type impurities injected above and below the horizontal transfer section 2 is increased, the effect of collecting signal charges at the output section 3 increases, but the amount of charges handled at the terminal section decreases, and overflow occurs. Unnecessary charges formed at the subsequent stage or below the horizontal transfer unit 2 of the signal charges are spilled to the discard region II.

On the other hand, if the amount of the P-type impurities is too small, the effect of narrowing down to the output section 3 is reduced.
Further, when the amount of the P-type impurity is reduced, the signal charges at the terminal end or the lower end may be mixed with the signal charges transferred from the subsequent stage before being transferred to the output unit. That is,
If the amount of the P-type impurity is small, the electric field in the vertical direction becomes small, so that a part of the signal charges in the preceding stage (the signal charges transferred from the upper and lower ends of the horizontal transfer unit) are transferred from the subsequent stage. A problem of mixing with signal charges occurs.

For the above reasons, the amount of the P-type impurities to be implanted above and below the horizontal transfer section 2 is generally set to a value that does not cause these problems. Eventually, it is desired to increase the effect of narrowing down the output unit 3, but this causes a problem such as a decrease in the amount of charge handled at the terminal end. On the other hand, if the problem is avoided, the narrowing down to the output unit 3 is performed. It is difficult with the prior art to meet both of these conflicting demands, with reduced effectiveness and other problems.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and reduces the effect of narrowing the output section by maintaining the upper and lower electric fields while securing the amount of charge handled at the end of the horizontal transfer section. It is an object of the present invention to provide a solid-state imaging device capable of effectively preventing a transfer failure at an end of a horizontal transfer unit.

[0009]

According to the present invention, in a structure from a horizontal transfer section to an output section of a solid-state imaging device, a transfer width is reduced to a portion from a horizontal transfer section to an output section at a terminal end of the horizontal transfer section. A solid-state image sensor, wherein a plurality of barriers are provided.

According to the present invention, a plurality of (two or more) barriers for reducing the transfer width are provided at the end of the horizontal transfer unit from the horizontal transfer unit to the output unit.
The amount of charges handled at the end of the horizontal transfer unit can be ensured without weakening the electric field in the vertical direction of the horizontal transfer unit.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below, and specific examples thereof will be described with reference to the drawings. However, needless to say, the present invention is not limited to the embodiments described below.

According to the present invention, in a structure from a horizontal transfer portion to an output portion of a solid-state imaging device, a plurality of barriers for reducing a transfer width are provided at a portion from the horizontal transfer portion to the output portion at the end of the horizontal transfer portion. Although a step is provided, the barrier for reducing the transfer width is formed by forming a barrier formation region of a conductivity type (for example, P type) opposite to a conductivity type (for example, N type) constituting the horizontal transfer portion. be able to.

In this case, the barrier formation region is formed by introducing impurities giving a conductivity type (for example, P type) opposite to a conductivity type (for example, N type) constituting the horizontal transfer portion in a plurality of different patterns. By doing so, the barrier can be provided in a plurality of stages.

Embodiment 1 Hereinafter, preferred specific embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIG. FIG. 1 schematically shows a CCD solid-state imaging device to which the present invention is applied, and corresponds to FIG.
The same reference numerals as those in FIG. 4 indicate similar components. FIG. 2 also shows a potential profile of a CCD solid-state imaging device to which the present invention is applied, which corresponds to FIG. 5 for explaining the prior art, and the same reference numerals as those in FIG. 4 indicate the same components. .

Embodiment 1 Referring to FIG. FIG. 1 shows the above-mentioned prior art improved by applying the present invention, and shows a dummy pit portion of the horizontal transfer efficiency improvement pattern. In this embodiment, the Ps formed above and below the horizontal transfer unit 2
The pattern of the mold region is changed so that the barrier is formed in multiple steps.
It is formed by injecting P-type impurities in a plurality of different patterns. The example of FIG. 1 is a case of two stages, but may be more.

That is, in the present embodiment, the first barrier formation region 9
2a of the second barrier formation regions 91a and 9b.
The seed region is formed by changing the form of impurity implantation. Thus, the barriers are first barriers 81a and 81a.
b and second barriers 82a and 82b. Here, the second barrier formation regions 92a and 92b are formed of P-type regions by ion implantation similar to the above-described conventional pattern, and the first barrier formation regions 91a and 91b are
It is formed by performing ion implantation twice.

The potential structure in this case is as shown in FIG. 2 (this diagram is XX′-X ″-in FIG. 1).
The potential in the Y ″ -Y′-Y section is shown). That is, the first barrier 81, which is a potential barrier formed by the first barrier formation regions 91a and 91b.
a, 81b and second barriers 82a, 82b, which are potential barriers formed by the second barrier formation regions 92a, 92b.
A two-stage barrier with the transfer pattern 82b is formed between the barrier and the portion corresponding to the transfer portion pattern 21 (deep portion).

The other components shown in FIGS. 1 and 2 are the same as those in the prior art described above.

According to this embodiment, by providing a plurality of barriers (described in the present embodiment as two stages), (1) the electric field in the vertical direction at the terminal end 23 of the horizontal transfer unit 2 is strengthened, The charge transfer in the direction can be improved. (2) It is possible to increase the amount of charge handled at the terminal end 23 of the horizontal transfer unit 2. It is now possible to satisfy both requirements.

[0020]

As described above, according to the present invention, the amount of charge handled at the end of the horizontal transfer portion is ensured,
Maintain the upper and lower electric fields to increase the aperture effect of the output section,
As a result, a solid-state imaging device capable of effectively preventing a transfer failure at the end of the horizontal transfer unit can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing a potential profile according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a general schematic configuration of a CCD solid-state imaging device.

FIG. 4 is a diagram illustrating a configuration of a conventional technique.

FIG. 5 is a diagram showing a potential profile according to the related art.

[Explanation of symbols]

I: imaging unit, 2: horizontal transfer unit, 3: output unit, 81a, 81b: first barrier, 82a, 82b
... second barrier, 91a, 91b ... first barrier formation region, 92a, 92b ... second barrier formation region.

Claims (3)

[Claims] In a structure from a horizontal transfer section to an output section of a solid-state imaging device, a plurality of barriers for reducing a transfer width are provided in a portion from a horizontal transfer section to an output section at a terminal end of the horizontal transfer section. A solid-state imaging device. 2. The barrier according to claim 1, wherein the barrier for reducing the transfer width is formed by forming a barrier forming region with a conductivity type opposite to a conductivity type forming the horizontal transfer portion. The solid-state imaging device according to any one of the preceding claims. 3. The barrier formation region is formed by introducing impurities having a conductivity type opposite to the conductivity type constituting the horizontal transfer portion in a plurality of different patterns, thereby providing a plurality of barriers. The solid-state imaging device according to claim 1, wherein: