JP3562128B2 - Solid-state imaging device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solid-state imaging device, for example, applied to a CCD solid-state imaging device, and forms a barrier by injecting a P-type impurity into a vertical pixel isolation region between photosensor portions to form a barrier between adjacent pixels. Is effectively avoided, and the sensitivity is improved.
[0002]
[Prior art]
Conventionally, in a CCD solid-state imaging device, a pixel separation region formed between photosensor portions and an overflow barrier (OFB: OverFlow-Barrier) formed below the photosensor portion and the pixel separation region cause a gap between adjacent pixels. It is designed to effectively avoid mixing of stored charges.
[0003]
That is, FIG. 6 is a plan view showing this type of CCD solid-state imaging device. In the CCD solid-state imaging device 1, photosensor units 2 each composed of a photoelectric conversion unit are arranged in a matrix, and a vertical transfer register 3 is arranged between the photosensor units 2 that are continuous in the horizontal direction. A horizontal transfer register is disposed at the lower end of the horizontal transfer register. Here, the photosensor unit 2 photoelectrically converts the incident light to generate accumulated charges, and each vertical transfer register 3 reads out the accumulated charges of each photosensor unit 2 at, for example, one field cycle by a predetermined drive pulse. The stored charges read out are sequentially transferred to the horizontal transfer register. The horizontal transfer register sequentially transfers the accumulated charges transferred from the vertical transfer register 3 toward the output unit, and when the accumulated charges are transferred for one line, inputs the accumulated charges of the next one line from the vertical transfer register 3. The output unit outputs the accumulated charges sequentially transferred to the external signal processing circuit, so that the CCD solid-state imaging device 1 sequentially outputs the accumulated charges in a raster scan order.
[0004]
In the CCD solid-state imaging device 1 configured as described above, an N-type semiconductor substrate (N ⁻ ) is shown in FIG. A P ⁻ type region is formed in 10, whereby an overflow barrier 11 is previously formed on the entire N type semiconductor substrate 10. Further, in the CCD solid-state imaging device 1, a P ^- type region, an N-type region, and a P ⁺ -type region are sequentially formed. At this time, a P-type region and an N-type region are sequentially formed in the formation region of the vertical transfer register 3, thereby forming a channel for transferring accumulated charges in the vertical transfer register 3.
[0005]
Between the channel and the photosensor section 2 for sending charges to each channel is held in a narrow P ^- type region, whereby the accumulated charges in the photosensor section 2 are sent to the vertical transfer register 3 for reading. Gate 12 is formed. A P ⁺ -type region is formed between the channel and the photosensor portion 2 on the opposite side of the readout gate 12, whereby the P ⁺ -type region is allocated to the horizontal pixel separation region AH, The separation region AH prevents the movement of the accumulated charge between the channel and the photosensor portion 2 sandwiching the horizontal pixel separation region AH.
[0006]
Subsequently, in the CCD solid-state imaging device 1, after an insulating film 13 of silicon oxide is formed on the surface, a transfer electrode 14 for forming the vertical transfer register 3 is sequentially formed of polysilicon with an insulating layer interposed therebetween. Thus, the vertical transfer register 3 and the like are formed. Subsequently, in the CCD solid-state imaging device 1, after the photosensor portion 2 is formed by ion implantation, the light-shielding metal film 15 and the like are formed.
[0007]
With respect to such a horizontal structure, as shown in FIG. 8, the photo sensor unit 2 is a cross section taken along the line BB in the vertical direction. Between the two, a vertical pixel isolation region AV is formed while being held in a P ⁻ type region, thereby preventing mixing of accumulated charges between the vertically adjacent photosensor units 2. On the other hand, the overflow barrier 11 prevents mixing of accumulated charges between the vertically adjacent photosensor units 2 below the vertical pixel isolation region AV, whereas the overflow barrier 11 below the photosensor unit 2 does not. In this case, surplus accumulated charges are discharged.
[0008]
[Problems to be solved by the invention]
By the way, in this kind of CCD solid-state imaging device 1, a device having high sensitivity may be required, and as one method of improving this sensitivity, the area of the photosensor unit 2 is enlarged in the depth direction of the semiconductor substrate. There is a method. That is, if the area of the photosensor unit 2 is expanded in this manner, the sensitivity of the photosensor unit 2 can be increased on the longer wavelength side of the incident light, and the sensitivity can be increased as a whole.
[0009]
In this case, if the overflow barrier 11 is formed at a position deeper than the semiconductor surface, the area of the photosensor section 2 can be expanded in the depth direction of the semiconductor substrate. However, when the overflow barrier 11 is simply formed at a position deeper than the semiconductor surface, as shown in FIG. 7, the distance from the substrate surface to the overflow barrier 11 is increased in the vertical pixel isolation region AV, so that the P ⁻ type is formed. The impurity concentration is partially reduced in the region, and an N-type region 17 is formed in the P ^- type region. As a result, there is a problem that the vertical pixel isolation region AV is partially depleted, and it is not possible to completely prevent the accumulation of accumulated charges between the photosensor portions 2 that are continuous in the vertical direction.
[0010]
If it becomes impossible to prevent the accumulation of charge from being mixed between the photosensor units 2 as described above, for example, when a complementary color filter is attached to the CCD solid-state imaging device 1 and the CCD solid-state imaging device 1 is applied to a single-panel imaging device, the imaging result is reduced. The color purity of the resulting color signal decreases, and the color reproducibility of the imaging result deteriorates accordingly.
[0011]
The present invention has been made in view of the above points, and aims to propose a solid-state imaging device capable of improving sensitivity by effectively avoiding mixing of accumulated charges between vertically adjacent pixels. It is.
[0012]
[Means for Solving the Problems]
In order to solve such a problem, the present invention employs a configuration in which a P-type region is formed only below a vertical pixel separation region between photoelectric conversion units that are continuous in the vertical direction.
[0013]
By these means, partial depletion can be prevented in the vertical pixel isolation region formed by implanting the P-type impurity, even if the overflow barrier is formed at a deep position. As a result, it is possible to effectively avoid mixing of accumulated charges between adjacent pixels, and it is possible to improve sensitivity by forming an overflow barrier at a deep position.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
[0015]
FIG. 2 is a plan view showing a CCD solid-state imaging device according to the embodiment of the present invention in comparison with FIG. Here, as shown in FIG. 1 by taking a vertical cross section of the photosensor portion 2 and the vertical pixel isolation region AV along the line CC, the CCD solid-state imaging device 20 includes an N-type semiconductor substrate 10 in which an overflow barrier 11 is provided in advance. After the formation, a P ^- type region, an N-type region, and a P ⁺ -type region are sequentially formed, and a channel and the like of the vertical transfer register 3 are formed.
[0016]
In this formation process, in the CCD solid-state imaging device 20, the overflow barrier 11 is formed in a deeper portion on the substrate surface than in the conventional case, thereby increasing the depth of the photosensor unit 2 and improving the sensitivity accordingly. It has been done.
[0017]
In the CCD solid-state imaging device 20, a P-type impurity is implanted by ion implantation with relatively high energy, and a P-type region 21 for forming a barrier of accumulated charges is formed below the vertical pixel isolation region AV. The P-type region 21 does not protrude into the charge accumulation region 22 of the photosensor unit 2 in the vertical direction, and does not protrude into the adjacent vertical transfer register 3 in the horizontal direction (FIG. 2). Is formed by patterning. Further, in the depth direction, the formation position is selected in accordance with the formation position of the overflow barrier 11 in the depth direction so that the vertical pixel isolation region AV is not locally depleted.
[0018]
In the above configuration, the incident light that has entered each photosensor unit 2 is converted into accumulated charge by photoelectric conversion, accumulated in the charge accumulation region 22 of the photosensor unit 2, and surplus accumulated charge is further reduced by the overflow barrier 11 in the lower part. Is discharged through. In the CCD solid-state imaging device 20, since the overflow barrier 11 is formed at a position deeper than the substrate surface as compared with the related art, the photoelectric conversion efficiency of each photosensor unit 2 is increased on the long wavelength side, and the corresponding amount is increased. As a result, the incident light can be photoelectrically converted more efficiently, and the sensitivity is increased.
[0019]
At this time, in each of the photosensor units 2, the P-type region 21 is formed in the vertical pixel isolation region AV, so that the capacitance is increased by that amount, and the change in potential with respect to the accumulated charge amount is reduced. As a result, in the CCD solid-state imaging device 20, the dependence of the amount of accumulated charge stored in the charge accumulation region 22 on the amount of incident light when the amount of accumulated charge increases is reduced. In addition, the incident light amount that can be photoelectrically converted increases accordingly, and the dynamic range can be expanded correspondingly, or the maximum incident light amount of this type that is guaranteed to the user can be increased.
[0020]
Further, in the vertical pixel isolation region AV, since the P-type region 21 having a higher concentration than that of the related art is formed, even when the overflow barrier 11 is formed at a deep position, depletion is effectively avoided. Mixing of the accumulated charges between the vertically adjacent photosensor units 2 is effectively avoided. In addition, the formation position of the overflow barrier 11 can be freely selected as needed.
[0021]
According to the above configuration, the overflow barrier 11 is formed at a deep position, and the barrier is formed by injecting a P-type impurity into the vertical pixel isolation region AV. Can be effectively avoided and sensitivity can be improved.
[0022]
In the above embodiment, the case where the P-type region 21 is formed in the horizontal direction so as not to contact the adjacent vertical transfer register 3 has been described. However, the present invention is not limited to this. As shown in FIGS. 3 to 5, as shown in FIGS. 3 to 5, P-type regions of various sizes are formed within a range not protruding into the adjacent vertical transfer register 3 to obtain the same effect as in the above-described embodiment. Can be.
[0023]
【The invention's effect】
As described above, according to the present invention, a barrier is formed by injecting a P-type impurity only into a lower portion of a vertical pixel isolation region between vertically continuous photoelectric conversion portions, thereby forming an overflow barrier correspondingly on the substrate surface. Since it can be formed at a deeper position, the sensitivity can be improved, and the mixing of accumulated charges between vertically adjacent pixels can be effectively avoided.
[Brief description of the drawings]
FIG. 1 is a front view showing a CCD solid-state imaging device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of the CCD solid-state imaging device of FIG.
FIG. 3 is a front view showing a CCD solid-state imaging device in which a P-type region is formed on a vertical transfer register side.
FIG. 4 is a front view showing a CCD solid-state imaging device in which a P-type region is formed substantially near the center of a photosensor unit 2;
FIG. 5 is a front view showing a CCD solid-state imaging device in which a P-type region is formed on an adjacent vertical transfer register.
FIG. 6 is a plan view showing a conventional CCD solid-state imaging device.
7 is a cross-sectional view showing the CCD solid-state imaging device in FIG.
FIG. 8 is a cross-sectional view showing the CCD solid-state imaging device of FIG.
FIG. 9 is a cross-sectional view for describing a case where an overflow barrier is formed deeply.
[Explanation of symbols]
1, 20: CCD solid-state imaging device, 2: photo sensor unit, 3: vertical transfer register, 21: P-type region, AV: vertical pixel separation region

Claims (2)

A photoelectric conversion unit that is arranged in a matrix in the vertical and horizontal directions, photoelectrically converts incident light to generate accumulated charges, and includes an N-type region formed in a P ⁻ -type region ;
A P ^- type vertical transfer register unit disposed between the horizontally continuous photoelectric conversion units, receiving the stored charge from an adjacent photoelectric conversion unit, and sequentially transferring the stored charge in the vertical direction;
In a solid-state imaging device having a P ^- type overflow barrier disposed below the photoelectric conversion unit and the vertical transfer register unit,
The P ^- a mold region, the solid-state imaging device, characterized in that the formation of the P-type region only in the lower part of the vertical pixel isolation region between the photoelectric conversion portion continuous in the vertical direction. A photoelectric conversion unit that is arranged in a matrix in the vertical and horizontal directions, photoelectrically converts incident light to generate accumulated charges, and includes an N-type region formed in a P ⁻ -type region;
A P ^- type vertical transfer register unit disposed between the horizontally continuous photoelectric conversion units, receiving the stored charge from an adjacent photoelectric conversion unit, and sequentially transferring the stored charge in the vertical direction;
In a solid-state imaging device having a P ^- type overflow barrier disposed below the photoelectric conversion unit and the vertical transfer register unit,
In the lower part of the vertical pixel separation region between the photoelectric conversion units that are continuous in the vertical direction, in the vertical direction, so as not to jump out to the photoelectric conversion unit, in the horizontal direction, it jumps out to the adjacent vertical transfer register unit . A solid-state imaging device, wherein a P-type region is formed in a range not present.

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