JP2013004581A - Solid state image pickup device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state image pickup device and a method of manufacturing the same with which a smear reduction effect can be obtained.SOLUTION: In a solid state image pickup device having plural photodiodes 7 formed in a matrix form within a semiconductor substrate, a vertical transfer area 9 formed between the photodiode of respective columns within the semiconductor substrate, and a channel stop area 5 formed between the photodiode 7 of each column and the vertical transfer area 9 adjacent thereto, each channel stop area contains impurities, and the maximum value of the impurity concentration is set at a position nearer to the vertical transfer area than the center between the photodiode 7 of each column and the adjacent vertical transfer area 9, and the impurity concentration monotonically decreases from the position of the maximum value of the impurity concentration to the photodiode of each column.

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly to a CCD solid-state imaging device used for an image sensor or the like and having a smear reducing effect and a manufacturing method thereof.

Conventionally, this type of solid-state imaging device has a photodiode as a photoelectric conversion element on a semiconductor substrate, a vertical transfer region (VCCD) for transferring signal charges generated in the photodiode in the vertical direction, and transfers in the vertical direction. A horizontal transfer region for transferring the signal charge in the horizontal direction and an amplifier for outputting the signal charge transferred in the horizontal direction to the outside.
FIG. 14 shows a horizontal section of a pixel portion of a conventional solid-state imaging device (see, for example, Patent Document 1). As shown in FIG. 14, a low-concentration p-type diffusion layer 2 is formed on an n-type semiconductor substrate 1, and a photodiode 7 and a VCCD 9 are formed in the low-concentration p-type diffusion layer 2. The photodiode 7 and the VCCD 9 are formed by ion-implanting high-concentration n-type impurities into the low-concentration p-type diffusion layer 2. A high concentration p-type diffusion layer 8 for forming a potential barrier is formed on the surface side of the photodiode 7 in the low concentration p-type diffusion layer 2. Further, a smear preventing p-type impurity diffusion layer (channel stop region) 14 having a width wider than that of the photodiode 7 including the photodiode 7 is formed around the photodiode 7.

  A gate insulating film 3 is formed on the semiconductor substrate 1, a polysilicon gate electrode 10 is formed on the gate insulating film 3, and an interlayer insulating film 11 is formed so as to cover the polysilicon gate electrode 10. Further, a metal light shielding film 12 that prevents light from entering a region other than the photodiode 7 is formed on the interlayer insulating film 11. The metal light shielding film 12 has an opening on the photodiode 7.

Next, the operation of a general CCD solid-state imaging device will be described.
First, when light is irradiated to the photodiode 7, electric charges are generated in the photodiode 7 by photoelectric conversion and accumulated in the photodiode 7. The accumulated charge is transferred to the VCCD 9 by a transfer signal applied to the polysilicon gate electrode 10.
However, at this time, charges are generated in regions other than the photodiode 7 due to irregular reflection of light, and this charge may flow into the VCCD 9 to cause a smear phenomenon in which an image blurs. The smear phenomenon appears as white vertical stripes on the image, particularly when very strong light such as sunlight is incident. This is usually a very small noise component of about 80 dB and about 1/1000 in terms of the number of electrons, but this greatly affects the performance of the solid-state imaging device.

  In the conventional solid-state imaging device described above, in order to prevent this smear phenomenon, the p-type impurity diffusion layer 14 for preventing smear having a width wider than that of the photodiode 7 including the photodiode 7 is formed. A potential barrier is formed in the periphery of the light source to prevent the charge generated in the region other than the photodiode 7 from flowing into the VCCD 9 to reduce the smear phenomenon.

JP-A-8-55976 (4th item, FIG. 3)

  However, it has been found that the smear reduction effect is insufficient even when the configuration of the conventional solid-state imaging device is used. In a conventional p-type impurity diffusion layer for preventing smear, there is a region having a small impurity concentration gradient (a flat region on the top of the potential barrier). In a region where the concentration gradient of impurities is small, charges are likely to diffuse isotropically, and some of the charges may be directed to the VCCD side. As a result, some charges flow into the VCCD and a smear phenomenon may remain.

  In view of the above problems, an object of the present invention is to provide a solid-state imaging device having a smear reduction effect that surpasses that of a conventional solid-state imaging device and a method for manufacturing the same.

  In order to solve the above-described problems, in the solid-state imaging device and the manufacturing method thereof according to the present invention, the impurity concentration distribution in the smear prevention p-type impurity diffusion layer (channel stop region) is the photodiode and the vertical transfer region adjacent thereto. (VCCD) has a maximum value closer to VCCD than the center of the photodiode and VCCD, and the impurity concentration is reduced from the position of the maximum value to the photodiode. Is larger than the range in which the impurity concentration decreases from the position of the maximum value to the VCCD.

  Specifically, the first solid-state imaging device of the present invention includes a plurality of photodiodes formed in a matrix in a semiconductor substrate and a vertical transfer region formed between the photodiodes in each column in the semiconductor substrate. And a channel stop region formed between each column of photodiodes in the semiconductor substrate and a vertical transfer region adjacent thereto, each channel stop region contains impurities, The maximum value of the impurity concentration is closer to the vertical transfer region than the center between the photodiode of the column and the adjacent vertical transfer region, and the impurity is directed from the position of the maximum value of the impurity concentration toward the photodiode of each column. The concentration decreases monotonously.

In the first solid-state imaging device of the present invention, the maximum value of the impurity concentration is 0. 0 from the photodiode side when the distance between the photodiode of each column and the vertical transfer region adjacent thereto is 1. Located in the range of 6 to 0.9.
In the first solid-state imaging device of the present invention, the impurity concentration gradient from the position of the maximum value of impurity concentration toward the vertical transfer region is such that the impurity concentration of the impurity concentration is directed from the position of the maximum value of impurity concentration toward the photodiode. Greater than the gradient.

In the first solid-state imaging device of the present invention, the maximum value of the impurity concentration is 2E17 to 4E17 / cm ³ .
The second solid-state imaging device of the present invention includes a plurality of photodiodes formed in a matrix form in a semiconductor substrate, a vertical transfer region formed between photodiodes in each column in the semiconductor substrate, A channel stop region formed between each column of photodiodes and a vertical transfer region adjacent thereto in the semiconductor substrate, each channel stop region including each column of photodiodes and a vertical transfer region adjacent thereto. The potential barrier has a maximum value closer to the vertical transfer region than the center between the potential barriers, and the potential barrier monotonously decreases from the position of the potential barrier maximum value toward the photodiode in each column.

In the second solid-state imaging device of the present invention, the maximum value of the potential barrier is 0. 0 from the photodiode side when the distance between the photodiodes in each column and the vertical transfer region adjacent thereto is 1. Located in the range of 6 to 0.9.
In the second solid-state imaging device of the present invention, the potential gradient from the position of the maximum potential barrier value toward the vertical transfer region is greater than the potential gradient from the position of the potential barrier maximum value toward the photodiode. large.

In the first and second solid-state imaging devices of the present invention, the semiconductor substrate is an n-type semiconductor substrate, each photodiode is formed of a p-type diffusion layer and an n-type diffusion layer, and each vertical transfer region is Each channel stop region is formed of a p-type diffusion layer.
The solid-state imaging device manufacturing method of the present invention includes a step (a) of forming a mask having an opening on a channel stop region forming region on a semiconductor substrate, and implanting impurity ions into the semiconductor substrate from the opening. A solid-state imaging device comprising: a step (b) of forming the channel stop region; and a step (c) of forming a photodiode and a vertical transfer region so as to sandwich the channel stop region in the semiconductor substrate. In step (b), the impurity ions are implanted at an angle of 5 ° to 25 ° toward the vertical transfer region with respect to the thickness direction of the semiconductor substrate.

  In the method for manufacturing a solid-state imaging device according to the present invention, the impurity ions are implanted by two-step implantation with acceleration energies of 5 to 15 KeV and 45 to 55 KeV.

  As described above, according to the solid-state imaging device and the manufacturing method thereof of the present invention, the charge generated between the photodiode and the vertical transfer region (VCCD) adjacent thereto can be efficiently caused to flow into the photodiode side. Thus, it is possible to obtain a smear reduction effect that surpasses conventional solid-state imaging devices.

The figure which shows the layout of each structure in the solid-state imaging device of this embodiment. Sectional drawing of the horizontal direction of the pixel part in the solid-state imaging device of this embodiment The figure which showed the impurity profile of the channel stop area | region in the solid-state imaging device of this embodiment by the contour line The figure which shows the one-dimensional cross-sectional profile (y-y 'cross section of FIG. 3) containing the point P Process sectional drawing for demonstrating the manufacturing method of the solid-state imaging device of this embodiment Process sectional drawing for demonstrating the manufacturing method of the solid-state imaging device of this embodiment Process sectional drawing for demonstrating the manufacturing method of the solid-state imaging device of this embodiment Contour lines showing impurity profile of channel stop region in a conventional solid-state imaging device The figure which shows the one-dimensional cross-sectional profile (y-y 'cross section of FIG. 8: broken line) in the conventional solid-state imaging device, and the one-dimensional cross-sectional profile (y-y' cross section of FIG. 3: solid line) in the solid-state imaging device of this embodiment. Diagram showing potential distribution in channel stop region in conventional solid-state imaging device The figure which shows the potential distribution of the channel stop area | region in the solid-state imaging device of this embodiment FIG. 10 is a diagram showing each y-y ′ cross section (FIG. 10: broken line, FIG. 11: solid line) of the conventional potential distribution shown in FIG. 10 and the potential distribution of this embodiment shown in FIG. The figure which shows the fluctuation of the amount of smear when the position where the potential barrier becomes maximum in the channel stop region is shifted in the horizontal direction The figure which shows the cross section of the horizontal direction of the pixel part of the conventional solid-state imaging device

Hereinafter, a solid-state imaging device and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a layout of each component in the solid-state imaging device of the present embodiment.
Photodiodes 7 are formed in a matrix, and one vertical transfer region 9 is formed between the photodiodes 7 in each column. The vertical transfer area 9 is for transferring the video signal charge generated by the photodiode 7 in the vertical direction. The horizontal transfer area 15 is for transferring the video signal charge transferred in the vertical direction in the horizontal direction. The amplifier 16 outputs the video signal charge transferred in the horizontal direction to the outside.

  FIG. 2 is a cross-sectional view taken along the line x-x ′ in FIG. 1, showing a horizontal cross section of the pixel portion in the solid-state imaging device of the present embodiment. In the present embodiment, a read channel 13 for reading signal charges accumulated in the photodiode 7 to the vertical transfer region 9 (9a) is formed between the photodiode 7 and the vertical transfer region 9 (9a). . On the other hand, a channel stop region 5 is formed between the photodiode 7 and the vertical transfer region 9 (9b) to prevent the signal charges accumulated in the photodiode 7 from flowing into the vertical transfer region 9 (9b). Has been. Other configurations are the same as those in FIG.

FIG. 3 shows the impurity profile of the channel stop region 5 in the solid-state imaging device of the present embodiment by contour lines, and corresponds to the region surrounded by the broken line in FIG. The numerical value in the figure indicates the impurity concentration (unit: / cm ³ ), the donor concentration is indicated by plus, and the acceptor concentration is indicated by minus. The maximum impurity concentration is, for example, 2E17 to 4E17 / cm ³ , and the width of the channel stop region 5, that is, the channel stop region 5 and the vertical transfer region from the junction between the channel stop region 5 and the photodiode 7. The distance (aa ′) to the junction with 9 (9b) is, for example, 0.12 μm. However, it is not limited to this dimension.

  Here, a point P in FIG. 3 is a position where the impurity concentration of the channel stop region 5 becomes the maximum value at a depth (y-y ′) of 0.1 μm from the surface of the semiconductor substrate. The distance (P−a) between the photodiode 7 and the point P is longer than the distance (P−a ′) between the vertical transfer region 9 (9b) and the point P. That is, the position where the impurity concentration becomes the maximum value is closer to the vertical transfer region 9 (9b) than the center between the photodiode 7 and the vertical transfer region 9 (9b). For example, the ratio of the distance (P−a) to the distance (P−a ′) is 6: 4, and when the distance (a−a ′) is 1, the distance (P−a) is 0.6. It is. However, it is not limited to this ratio, and when the distance (a−a ′) is 1, the distance (P−a) may be in the range of 0.6 to 0.9.

  Furthermore, a one-dimensional cross-sectional profile including the point P (y-y 'cross-section in FIG. 3) is shown in FIG. Here, there is substantially no flat portion between a and a 'with a constant impurity concentration. That is, the impurity concentration monotonously decreases from the position where the impurity concentration becomes the maximum value toward the photodiode 7. Further, the impurity concentration monotonously decreases from the position where the impurity concentration is maximized toward the vertical transfer region 9 (9b). In contrast to the impurity concentration gradient, the impurity concentration gradient between P-a 'is larger than the impurity concentration gradient between Pa.

5 to 7 are process cross-sectional views for explaining the method for manufacturing the solid-state imaging device of the present embodiment.
First, as shown in FIG. 5A, the low concentration p-type diffusion layer 2 is formed on the n-type semiconductor substrate 1, and the gate insulating film 3 is formed on the low concentration p-type diffusion layer 2. Further, a photoresist 4 is formed on the gate insulating film 3, the photoresist 4 is patterned, and a region to be a channel stop region 5 later is opened. Here, for example, the film thickness of the photoresist 4 is 0.7 μm, and the resist opening width is 0.2 μm. Next, boron, which is a p-type impurity, is ion-implanted. Here, the ion implantation is inclined with respect to the thickness direction of the semiconductor substrate. The impurity profile at this time is shown in FIG. Here, when the film thickness of the photoresist 4 is 0.7 μm and the resist opening width is 0.2 μm, for example, ion implantation is performed in two steps, the acceleration energy at that time is 10 KeV and 50 KeV, and the implantation angle is What is necessary is just to make an angle of 5-25 degrees with respect to the thickness direction of a semiconductor substrate. However, the acceleration energy is not limited to this, and may be 5 to 20 KeV and 45 to 65 KeV. As a result, a channel stop region 5 is formed as shown in FIG.

  Next, as shown in FIG. 6A, the photodiode 7, the vertical transfer region 9, and the readout channel 13 are formed by ion implantation into the low concentration p-type diffusion layer 2. At this time, since the channel stop region 5 has already been formed by angle injection, the region sandwiched between the photodiode 7 and the vertical transfer region 9 is far from the photodiode 7, that is, close to the vertical transfer region 9. The maximum impurity concentration of the channel stop region 5 is located.

  Next, as shown in FIG. 6B, a polysilicon gate electrode 10 is formed, and further, as shown in FIG. 6C, an insulating film 21 is formed. Next, as shown in FIG. 7A, the insulating film 21 is selectively etched to open the photodiode 7. As a result, the insulating film 21 becomes the interlayer insulating film 11 covering the polysilicon gate electrode 10. Next, as shown in FIG. 7B, for example, a tungsten film 22 is formed. Next, as shown in FIG. 7C, the tungsten film 22 is selectively etched to open the photodiode 7. As a result, the tungsten film 22 becomes the metal light-shielding film 12 that shields light so that light does not enter the region other than the photodiode 7.

  According to the present embodiment, the channel stop region 5 has an impurity concentration between the photodiode 7 and the vertical transfer region 9 (9b) close to the vertical transfer region 9 (9b) that is 60% or more away from the photodiode 7 side. Take the maximum value of. Therefore, a wide region where the impurity concentration monotonously decreases from the position where the impurity concentration reaches the maximum value to the photodiode 7 can be secured. Therefore, electric charges generated between the photodiode 7 and the vertical transfer region 9 are likely to flow into the photodiode 7, and a smear reduction effect that surpasses that of the conventional solid-state imaging device can be obtained.

FIG. 8 is a contour line showing the impurity profile of the channel stop region in the conventional solid-state imaging device. FIG. 9 shows a one-dimensional cross-sectional profile in the conventional solid-state imaging device (the yy ′ cross section in FIG. 8: a broken line) and the one-dimensional cross-sectional profile in the solid-state imaging device of the present embodiment (the yy ′ cross section in FIG. ).
In the prior art (broken line), there is a portion where the impurity concentration is flat between the photodiode 7 and the vertical transfer region 9 (9b), whereas in the present embodiment (solid line), the photodiode 7 and the vertical transfer region 9 (9b). ) And the portion where the impurity concentration is flat. In this embodiment, the distance (P−a) between the photodiode 7 and the point P is longer than the distance (P−a ′) between the vertical transfer region 9 (9b) and the point P. It can be seen that electrons easily flow into the photodiode 7 efficiently. As a specific example, the ratio of distance (P−a) to distance (P−a ′) is 6: 4.

  FIG. 10 shows the potential distribution of the channel stop region in the conventional solid-state imaging device, and FIG. 11 shows the potential distribution of the channel stop region in the solid-state imaging device of the present embodiment. The numerical values in FIG. 10 and FIG. 11 are electrostatic potential values (unit: V). Moreover, the broken line in FIG. 10 and FIG. 11 has shown the watershed where the potential barrier becomes the maximum. Here, the point P ′ indicates the maximum value of the potential barrier. FIG. 12 shows y-y ′ cross sections (FIG. 10: broken line, FIG. 11: solid line) of the conventional potential distribution shown in FIG. 10 and the potential distribution of the present embodiment shown in FIG. 11.

  Compared to the conventional potential (broken line), the watershed whose potential (solid line) is the maximum value of the potential barrier is closer to the vertical transfer region 9 (9b) side. That is, the position where the potential barrier becomes the maximum value is closer to the vertical transfer region 9 (9b) than the center of the photodiode 7 and the vertical transfer region 9 (9b). For example, the ratio between the distance A between the photodiode 7 and the point P 'and the distance B between the vertical transfer region 9 (9b) and the point P' is 6: 4. That is, when the distance between the photodiode 7 and the vertical transfer region 9 (9b) is 1, the distance A is 0.6. However, the ratio is not limited, and the distance A may be in the range of 0.6 to 0.9. As described above, since the position where the potential barrier becomes the maximum value is close to the vertical transfer region 9 (9b), the charge generated between the photodiode 7 and the vertical transfer region 9 (9b) easily flows into the photodiode 7. Thus, efficient smear reduction can be achieved.

FIG. 13 shows the variation of the smear amount when the position where the potential barrier in the channel stop region 5 is maximum is shifted in the horizontal direction. Here, the displacement of 0 nm from the center indicates a case where the maximum value of the potential barrier is at the center position between the photodiode 7 and the vertical transfer region 9 (9b).
As is apparent from FIG. 13, for example, when the position at which the potential barrier is maximum is shifted by 20 nm toward the vertical transfer region 9 (9b), the smear amount is -1.0 to -1.012 (about 1.5 dB). ). That is, it can be seen that smear is reduced by moving the position where the potential barrier of the channel stop region 5 becomes the maximum value to the vertical transfer region 9 (9b) side.

  In addition, the conductivity type of the semiconductor demonstrated in this embodiment is not limited to it, Even if each structure is made into a reverse conductivity type, it is materialized similarly.

  The solid-state imaging device and the manufacturing method thereof according to the present invention provide a smear reduction effect that surpasses that of a conventional solid-state imaging device, and are particularly useful in a CCD solid-state imaging device represented by an image sensor and a manufacturing method thereof.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Low concentration p-type diffusion layer 3 Gate insulating film 4 Photoresist 5 Channel stop region 7 Photodiode 8 High concentration p-type diffusion layer 9 Vertical transfer region (VCCD)
DESCRIPTION OF SYMBOLS 10 Polysilicon gate electrode 11 Interlayer insulating film 12 Metal light shielding film 13 Read channel 14 P-type impurity diffusion layer for smear prevention 15 Horizontal transfer region 16 Amplifier 21 Insulating film 22 Tungsten film

Claims (10)

A plurality of photodiodes formed in a matrix in a semiconductor substrate;
A vertical transfer region formed between each row of photodiodes in the semiconductor substrate;
In a solid-state imaging device including a channel stop region formed between each column of photodiodes in the semiconductor substrate and a vertical transfer region adjacent thereto.
Each channel stop region contains impurities, takes a maximum value of the impurity concentration closer to the vertical transfer region than the center between each column of photodiodes and the adjacent vertical transfer region, and the maximum value of the impurity concentration. A solid-state imaging device in which the impurity concentration monotonously decreases from a position toward a photodiode in each column.   The maximum value of the impurity concentration is located within a range of 0.6 to 0.9 from the photodiode side when a distance between the photodiodes of each column and a vertical transfer region adjacent thereto is 1. The solid-state imaging device described in 1.   The gradient of the impurity concentration from the position of the maximum value of the impurity concentration toward the vertical transfer region is larger than the gradient of the impurity concentration from the position of the maximum value of impurity concentration toward the photodiode. Solid-state imaging device. The solid-state imaging device according to claim 1, wherein the maximum value of the impurity concentration is 2E17 to 4E17 / cm ³ . A plurality of photodiodes formed in a matrix in a semiconductor substrate;
A vertical transfer region formed between each row of photodiodes in the semiconductor substrate;
A channel stop region formed between each column of photodiodes in the semiconductor substrate and a vertical transfer region adjacent thereto;
Each channel stop region takes the maximum value of the potential barrier closer to the vertical transfer region than the center between the photodiode of each column and the adjacent vertical transfer region, and from each position of the maximum value of the potential barrier, A solid-state imaging device in which the potential barrier monotonously decreases toward a photodiode.   6. The maximum value of the potential barrier is located in a range of 0.6 to 0.9 from the photodiode side when a distance between the photodiodes in each column and a vertical transfer region adjacent thereto is 1. The solid-state imaging device described in 1.   7. The solid-state imaging device according to claim 5, wherein a gradient of potential from the position of the maximum value of the potential barrier toward the vertical transfer region is larger than a gradient of potential of the potential from the position of the maximum value of the potential barrier toward the photodiode.   The semiconductor substrate is an n-type semiconductor substrate, each photodiode is formed by a p-type diffusion layer and an n-type diffusion layer, each vertical transfer region is formed by an n-type diffusion layer, and each channel stop region is a p-type diffusion layer. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is formed of layers. Forming a mask having an opening on a channel stop region formation region on a semiconductor substrate (a);
Step (b) of implanting impurity ions into the semiconductor substrate from the opening to form the channel stop region;
A step (c) of forming a photodiode and a vertical transfer region so as to sandwich the channel stop region in the semiconductor substrate,
In the step (b), the impurity ions are implanted at an angle of 5 ° to 25 ° toward the vertical transfer region with respect to the thickness direction of the semiconductor substrate.   The method of manufacturing a solid-state imaging device according to claim 9, wherein the impurity ions are implanted by two-step implantation with acceleration energy of 5 to 20 KeV and 45 to 65 KeV.

Images