Solid-state imaging element and method of manufacturing the same

Provided are a solid-state imaging element which can be simply manufactured and can control movement of electric charges in an accumulation region with a high degree of accuracy, and a method of manufacturing the same. A solid-state imaging element (1a) includes a substrate (11) having a first conductivity type; an accumulation region (12) having a second conductivity type and provided in the substrate (11); a read-out region (13) for receiving the transferred electric charges accumulated in the accumulation region (12); and a transfer section (14) for transferring the electric charges from the accumulation region (12) to the read-out region (13). An impurity concentration modulation region 121 having a locally high concentration of an impurity having the second conductivity type, or having a locally low concentration of an impurity having the first conductivity type is formed in a part of the accumulation region (12). An area of the impurity concentration modulation region (121) per unit distance with respect to the transfer section (14), or a density of the discretely provided impurity concentration modulation region (121) increases with decreasing distance to the transfer section (14).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application tiled under 35 USC 371 of PCT International Application No. PCT/JP2013/054316 with an International Filing Date of Feb. 21, 2013, which claims under 35 U.S.C. § 119(a) the benefit of Japanese Application No. 2012-037209, filed Feb. 23, 2012, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a solid-state imaging element typified by a CMOS (Complementary Metal Oxide Semiconductor) imaging sensor, a CCD (Charge Coupled Device) imaging sensor, or the like.

BACKGROUND ART

The solid-state imaging element such as the CCD imaging sensor or the CMOS imaging sensor is mounted on an imaging device such as a digital video camera or a digital still camera, and is mounted on various kinds of electronic devices each having an imaging function, such as a camera cell-phone, a scanner, a copying machine, and a fax machine.

The solid-state imaging element includes a photoelectric conversion unit such as a photodiode in a substrate to generate electric charges by photoelectrically converting light inputted to the substrate. The generated electric charges are accumulated in an accumulation region in the substrate, and are subsequently transferred to a read-out region in the substrate through a transfer section. Thus, based on the charges transferred to the read-out region, one signal composing an image is generated.

Recently, it has been required to make the solid-state imaging element highly sensitive. However, when the accumulation region increases in size so that the solid-state imaging element is made highly sensitive, there is a decrease in transfer speed of the electric charges through the transfer section, which causes a problem.

This problem will be described with reference toFIG. 21.FIG. 21is a view showing a conventional solid-state imaging element. In addition,FIG. 21 (a)is a plan view of one pixel in the solid-state imaging element,FIG. 21(b) is a cross-sectional view showing a cross-sectional surface taken along X-X inFIG. 21 (a). Furthermore,FIG. 21 (c)is a graph showing a potential in the cross-sectional surface taken along X-X inFIG. 21 (a).

As shown inFIGS. 21 (a) and (b), a solid-state imaging element100includes a substrate101, an accumulation region102formed in the substrate101, for accumulating electrons generated by a photoelectric conversion, a read-out region103formed in the substrate101, for receiving transferred electrons accumulated in the accumulation region102, a transfer section104for transferring the electrons from the accumulation region102to the read-out region103, and an insulating film105formed on a surface of the substrate101. The transfer section104serves as a gate electrode formed on the insulating film105and is formed between the accumulation region102and the read-out region103.

The substrate101has a P type (P-sub), the accumulation region102has an N type (N−), and the read-out region103has the N type (N+). In the solid-state imaging element100, an N-type high-concentration impurity region1021(impurity concentration modulation region) having an N type (N) is formed by separately implanting an N-type impurity into an implantation region106which is provided in the accumulation region102and which is provided adjacent to the transfer section104. Therefore, according to the solid-state imaging element100in the present example, a photodiode is composed of the substrate101and the accumulation region102, and the electrons are accumulated in the accumulation region102.

When a predetermined potential is applied to the transfer section104in this solid-state imaging element100, the potential in the substrate101just below the transfer section104is lowered, and the electrons accumulated in the accumulation region102are transferred to the read-out region103. At this time, when an area of the accumulation region102is large as descried above, some electrons are accumulated in a position far away from the transfer section104, in the accumulation region102. Thus, it takes a long time for the electrons to reach the transfer section104.

When the N-type high-concentration impurity region1021is provided in the accumulation region102, in the solid-state imaging element100, the electrons are accumulated in the accumulation region102. However, as shown inFIG. 21 (c), a potential in the N-type high-concentration impurity region1021is lower than that of a peripheral part due to the implantation of the N-type impurity, but the potential is flat. Therefore, movement of the electrons accumulated in the N-type high-concentration impurity region1021to the transfer section104is not particularly accelerated, and it takes a long time for the electrons to reach the transfer section104.

Thus, in the case where the electrons accumulated in the accumulation region102cannot be completely transferred to the read-out region103within a predetermined read-out period, the electrons remain in the accumulation region102, and these electrons are added to electrons to be generated by next photoelectric conversion, so that a residual image is generated in an obtained image, which is the problem.

Thus, for example, Patent Document 1 discloses a solid-state imaging element in which movement of the electrons to the transfer section is accelerated by inclining a potential in the accumulation region. This solid-state imaging element will be described with reference toFIG. 22.FIG. 22is a view showing a conventional solid-state imaging element. In addition,FIG. 22 (a)is a plan view of one pixel in the solid-state imaging element,FIG. 22 (b)is a cross-sectional view showing a cross-sectional surface taken along Y-Y inFIG. 22 (a). Furthermore,FIG. 22 (c)is a graph showing a potential in the cross-sectional surface taken along Y-Y inFIG. 22(a).

As shown inFIGS. 22 (a) and (b), a solid-state imaging element200includes a substrate201, accumulation regions2021to2024which are formed in the substrate201and which accumulate electrons generated by a photoelectric conversion, a read-out region203which are formed in the substrate201and which receives the transferred electrons accumulated in the accumulation regions2021to2024, a transfer section204for transferring the electrons from the accumulation region2024to the read-out region203, and an insulating film205formed on a surface of the substrate201. The transfer section204serves as a gate electrode formed on the insulating film205and is formed between the accumulation region2024and the read-out region203.

The substrate201has the P type (P-sub), the accumulation regions2021to2024have the N type, and the read-out region203has the N type (N+). Therefore, according to the solid-state imaging element200in the present example, a photodiode is formed of the substrate201and the accumulation regions2021to2024, and the electrons are accumulated in the accumulation regions2021to2024. The accumulation regions2021to2024are formed by sequentially implanting the N-type impurity to implantation regions2051to2054. In addition, the implantation regions2051to2054are close to the transfer section204, respectively, and the implantation regions2051,2052,2053, and2054are decreased in size in this order.

According to the solid-state imaging element200, a concentration (N---) of the N-type impurity in the accumulation region2021provided farthest from the transfer section204is lowest, a concentration (N--) of the N-type impurity in the accumulation region2022provided second farthest is second lowest, a concentration (N-) of the N-type impurity in the accumulation region2023provided third farthest is third lowest, and a concentration (N) of the N-type impurity in the accumulation region2024provided closest to the transfer section204is highest. Therefore, as shown inFIG. 22 (c), the potential in the accumulation regions2021to2024can be inclined so as to decrease with the decreasing distance to the transfer section204. Thus, it is possible to accelerate the movement of the electrons in the accumulation regions2021to2024to the transfer section204. Therefore, even when the area of the accumulation regions2021to2024increases, the electrons accumulated in the accumulation regions2021to2024can be immediately transferred to the read-out region203.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: JP 2000-236081 A

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, as shown inFIGS. 22 (a) and (b), according to the solid-state imaging element200disclosed in Patent Document 1, in order to form the accumulation regions2021to2024each having the different N-type impurity concentration, it is necessary to sequentially implant the N-type impurity to each of the implantation regions2051to2054with implantation conditions (such as a doze amount or implantation energy) different from each other. Furthermore, positioning needs to be performed each time the N-type impurity is implanted to each of the implantation regions2051to2054. This positioning is to be performed with a very high degree of accuracy; otherwise there is a large variation in characteristics of the manufactured solid-state imaging element200. Therefore, the solid-state imaging element200disclosed in Patent Document 1 has the problem that the manufacturing process is complicated and requires a high degree of accuracy.

In the solid-state imaging element200manufactured by implanting the N-type impurity several times, the concentrations of the N-type impurity in the accumulation regions2021to2024are inevitably controlled step by step, so that the potential in the accumulation regions2021to2024take a step-like shape (refer toFIG. 22 (c)). However, with the potential having this step-like shape, the movement of the electrons cannot be controlled with a high degree of accuracy, which is the problem.

Thus, an object of the present invention is to provide a solid-state imaging element which can be simply manufactured and which can control movement of electric charges in an accumulation region with a high degree of accuracy, and a method of manufacturing the same.

Means for Solving the Problem

To achieve the above object, the present invention provides a solid-state imaging element comprising: a substrate having a first conductivity type; an accumulation region having a second conductivity type opposite to the first conductivity type and provided in the substrate, for accumulating electric charges generated by a photoelectric conversion; a read-out region having the second conductivity type and provided in the substrate, for receiving the transferred electric charges accumulated in the accumulation region; and a transfer section formed above a region between the accumulation region and the read-out region in the substrate and provided for transferring the electric charges from the accumulation region to the read-out region, wherein an impurity concentration modulation region having a locally high concentration of an impurity having the second conductivity type, or having a locally low concentration of an impurity having the first conductivity type is formed in a part of the accumulation region, and an area of the impurity concentration modulation region per unit distance with respect to the transfer section, or a density of the discretely provided impurity concentration modulation regions increases with decreasing distance to the transfer section.

According to this solid-state imaging element, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section. Especially, the potential can be inclined only by adjusting the area per unit distance with respect to the transfer section or the density of the impurity concentration modulation regions (the implantation regions of the impurity having the first conductivity type or the second conductivity type in the accumulation region) formed in the accumulation region.

In addition, “the first conductivity type” and “the second conductivity type” are the P type and the N type. For example, when “the first conductivity type” is the P type, “the second conductivity type” is the N type. Meanwhile, when “the first conductivity type” is the N type, “the second conductivity type” is the P type. In addition, “the substrate having the first conductivity type” means that a section where an element structure in the substrate is formed has the first conductivity type, so that it includes not only a substrate having the first conductivity type as a whole, but also a substrate including a well having the first conductivity type (such as a substrate in which a well having the first conductivity type is formed by implanting an impurity having the first conductivity type into a substrate having the second conductivity type as a whole).

In addition, in the solid-state imaging element, preferably a width of the impurity concentration modulation region increases with the decreasing distance to the transfer section.

According to this solid-state imaging element, the area of the impurity concentration modulation region per unit distance with respect to the transfer section increases with the decreasing distance to the transfer section. Therefore, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably a width of the impurity concentration modulation region continuously increases with the decreasing distance to the transfer section. For example, preferably a width of the impurity concentration modulation region linearly or exponentially increases with the decreasing distance to the transfer section.

According to the solid-state imaging element, the potential in the accumulation region can be smoothly inclined. Therefore, the electric charges accumulated in the accumulation region can be smoothly moved to the transfer section.

In the solid-state imaging element, preferably a width of the impurity concentration modulation region discretely increases with the decreasing distance to the transfer section.

In addition, in the solid-state imaging element, preferably, the impurity concentration modulation region branches into two or more parts in a direction being away from the transfer section.

According to this solid-state imaging element, the potential can be inclined in a large range of the accumulation region. Therefore, it becomes possible to effectively accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, a plurality of the impurity concentration modulation regions extend in parallel to the direction being away from the transfer section.

According to this solid-state imaging element, the area (total area) per unit distance with respect to the transfer section or the density of the plurality of the impurity concentration modulation regions increases as a whole, so that the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, an interval between the adjacent impurity concentration modulation regions becomes narrow with the decreasing distance to a center of the transfer section among the impurity concentration modulation regions.

According to this solid-state imaging element, the density of the impurity concentration modulation regions increases with the decreasing distance to the transfer section. Therefore, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, a plurality of the impurity concentration modulation regions radially extend in the direction being away from the transfer section.

According to this solid-state imaging element, the density of the impurity concentration modulation regions increases with the decreasing distance to the transfer section. Therefore, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, a width of an outline region surrounded by an outline enclosing the plurality of the impurity concentration modulation regions increases with the decreasing distance to the transfer section.

According to this solid-state imaging element, the area (total area) of the plurality of the impurity concentration modulation regions per unit distance with respect to the transfer section increases as a whole with the decreasing distance to the transfer section. Therefore, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, the width of the outline region continuously increases with the decreasing distance to the transfer section. For example, preferably, the width of the outline region linearly or exponentially increases with the decreasing distance to the transfer section.

According to the solid-state imaging element, the potential in the accumulation region can be smoothly inclined. Therefore, the electric charges accumulated in the accumulation region can be smoothly moved to the transfer section.

In addition, in the solid-state imaging element, preferably, the width of the outline region discretely increases with the decreasing distance to the transfer section.

In addition, in the solid-state imaging element, preferably, the outline region branches into two or more parts in a direction being away from the transfer section.

According to this solid-state imaging element, the potential can be inclined in a large range of the accumulation region. Therefore, it becomes possible to effectively accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section.

In addition, in the solid-state imaging element, preferably, in the case where the concentration of the impurity having the second conductivity type is locally high in the impurity concentration modulation region, the concentration of the impurity having the second conductivity type is uniform in the impurity concentration modulation region, and in the case where the concentration of the impurity having the first conductivity type is locally low in the impurity concentration modulation region, the concentration of the impurity having the first conductivity type is uniform in the accumulation region other than the impurity concentration modulation region.

According to this solid-state imaging element, the whole impurity concentration modulation region can be formed by implanting the impurity having the first conductivity type or the impurity having the second conductivity type at one time. Therefore, the impurity concentration modulation region can be simply formed.

The present invention provides a method of manufacturing a solid-state imaging element comprising: a substrate having a first conductivity type; an accumulation region having a second conductivity type opposite to the first conductivity type and provided in the substrate, for accumulating electric charges generated by a photoelectric conversion; a read-out region having the second conductivity type and provided in the substrate, for receiving the transferred electric charges accumulated in the accumulation region; and a transfer section formed above a region between the accumulation region and the read-out region in the substrate and provided for transferring the electric charges from the accumulation region to the read-out region, wherein an impurity concentration modulation region having a locally high concentration of an impurity having the second conductivity type, or having a locally low concentration of an impurity having the first conductivity type is formed, by selectively implanting the impurity having the first conductivity type or the impurity having the second conductivity type, in a part of the accumulation region and an area of the impurity concentration modulation region per unit distance with respect to the transfer section, or a density of the discretely provided impurity concentration modulation regions increases with the decreasing distance to the transfer section.

According to the method of manufacturing this solid-state imaging element, the potential in the accumulation region can be inclined so as to accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section. Especially, the potential can be inclined only by adjusting the area per unit distance with respect to the transfer section or the density of the implantation regions of the impurity having the first conductivity type or the impurity having the second conductivity type in the accumulation region (the impurity concentration modulation regions formed in the accumulation region).

Effect of the Invention

According to the solid-state imaging element and the method of manufacturing the same having the above characteristics, it becomes possible to incline the potential in the accumulation region, and accelerate the movement of the electric charges accumulated in the accumulation region to the transfer section only by adjusting the area per unit distance with respect to the transfer section or the density of the impurity concentration modulation regions formed in the accumulation region (the implantation region of the impurity having the first conductivity type or the second conductivity type in the accumulation region). Therefore, this solid-state imaging element can be simply manufactured.

Furthermore, it is possible to steplessly adjust the area per unit distance with respect to the transfer section or the density of the impurity concentration modulation regions formed in the accumulation region (the implantation regions of the impurity having the first conductivity type or the second conductivity type in the accumulation region). Therefore, according to the solid-state imaging element and the method of manufacturing the same having the above characteristics, the potential in the accumulation region can be inclined in a desired manner, and the movement of the electric charges in the accumulation region can be controlled with a high degree of accuracy.

DESCRIPTION OF EMBODIMENT

Hereinafter, a solid-state imaging element according to each embodiment of the present invention will be described with reference to the drawings. In addition, the description will be given to a case where the solid-state imaging element according to each embodiment of the present invention is a CMOS imaging sensor in which an N-type accumulation region is formed in a p-type substrate, in order to embody the following description.

In addition, “P-type substrate” means a substrate in which a section where an element structure is formed has a P type, so that the P-type substrate is not limited to a substrate which has the P type as a whole, but includes a substrate having a P-type well (such as a substrate in which a P-type well is formed by implanting a P-type impurity into a substrate having an N type as a whole), as a matter of course. Here, it is to be noted that each view referred in the following description shows the substrate having the P type as a whole.

Furthermore, the substrate may be composed of material such as silicon. In this case, as the P-type impurity, boron may be used. In this case, as an N-type impurity, phosphor or zinc may be used. Furthermore, these impurities can be implanted into the substrate by a method such as ion implantation.

Prior to the description for the solid-state imaging element according to each embodiment of the present invention, a basic principle of the solid-state imaging element according to each embodiment of the present invention will be described with reference toFIGS. 1 and 2.FIG. 1is a schematic view showing a state in which the N-type impurity is implanted into a whole surface of the P-type substrate. In addition,FIG. 2is a schematic view showing a state in which the N-type impurity is implanted into one part of the surface of the P-type substrate.

As shown inFIGS. 1 and 2, when donors D serving as the N-type impurity are implanted into the P-type substrate having acceptors A, a depletion layer DL is formed of ionized acceptors AI and ionized donors DI, in the vicinity of a boundary of a region having diffused donors D.

Here, when the donors D are implanted into the whole surface of the substrate as shown inFIG. 1, the depletion layer DL spreads in a depth direction of the substrate (in a direction vertical to the surface of the substrate), and has a shape of a thin plate parallel to the planar direction (the direction parallel to the surface of the substrate). In addition, a thickness of the depletion layer DL and a position of the depletion layer DL in the depth direction are the same in the whole surface of the substrate. Therefore, in the case where the depletion layer DL shown inFIG. 1is formed, a flat potential is formed as shown inFIG. 21 (c).

Meanwhile, as shown inFIG. 2, when the donors D are implanted into the one part of the surface of the substrate restrictively, the depletion layer DL spreads in the planar direction as well as in the depth direction. Thus, when the region having the donors D is made larger compared with the state shown inFIG. 2, the depletion layer DL spreads deeper in the depth direction, and its state comes close to the state shown inFIG. 1. That is, by enlarging the region having the donors D, the depletion layer DL can be formed deeper, so that the potential can be lowered.

As for the solid-state imaging element according to each embodiment of the present invention, by using the fact that the potential is gradually lowered as the region having the donors D is gradually enlarged, an accumulation region is formed such that the potential is inclined so as to be lowered toward a transfer section, so that it becomes possible to accelerate movement of electrons accumulated in the accumulation region to the transfer section.

In addition,FIGS. 1 and 2exemplify the case where the N-type impurity is directly implanted into the P-type substrate to simplify the description, but even in the case where the N-type impurity is further implanted into an N-type region formed in the P-type substrate, the potential can be inclined based on the similar principle (first embodiment of the present invention which will be described below). On the other hand, even in the case where the P-type impurity is implanted into the N-type region formed in the P-type substrate, the potential can be inclined based on the same principle (second embodiment of the present invention which will be described below).

Hereinafter, solid-state imaging elements according to a first embodiment of the present invention will be described with reference to the drawings. First, a first example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 3.FIG. 3is a view showing the first example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 3 (a)is a plan view of one pixel in the solid-state imaging element,FIG. 3 (b)is a cross-sectional view showing a cross-sectional surface taken along Q-Q inFIG. 3 (a). Furthermore,FIG. 3 (c)is a graph showing a potential in the cross-sectional surface taken along Q-Q inFIG. 3(a).

As shown inFIGS. 3 (a) and (b), a solid-state imaging element1aincludes a substrate11, an accumulation region12formed in the substrate11, for accumulating electrons generated in the substrate11by a photoelectric conversion, a read-out region13formed in the substrate11, for receiving the transferred electrons accumulated in the accumulation region12, a transfer section14for transferring the electrons from the accumulation region12to the read-out region13, and an insulating film15formed on a surface of the substrate11. The transfer section14serves as a gate electrode formed on the insulating film15and is formed between the accumulation region12and the read-out region13.

The substrate11has the P type (P-sub), the accumulation region12has the N type (N−), and the read-out region13has the N type (N+). In the solid-state imaging element1a, an N-type impurity is separately implanted into an implantation region16aformed adjacent to the transfer section14in the accumulation region12, whereby an N-type high-concentration impurity region121(impurity concentration modulation region) having the N type (N) is formed. Therefore, according to the solid-state imaging element1ain the present example, a photodiode is composed of the substrate11and the accumulation region12, and the electrons are accumulated in the accumulation region12.

As shown inFIG. 3 (a), according to the solid-state imaging element1ain the present example, the implantation region16ahas a shape in which its width continuously and linearly increases with decreasing distance to the transfer section14. The N-type high-concentration impurity region121has the same shape as the implantation region16a.

Thus, when the accumulation region12is formed so as to have this N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14, as shown inFIG. 3 (c). Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1ain the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14.

When a predetermined potential is applied to the transfer section14in the solid-state imaging element1a, the potential in the substrate11just below the transfer section14is lowered, and the electrons accumulated in the accumulation region12are transferred to the read-out region13. At this time, since the potential in the accumulation region12is inclined as described above, the movement of the electrons accumulated in the accumulation region12to the transfer section14is accelerated. Therefore, even when the accumulation region12is large in size in the solid-state imaging element1a, the electrons accumulated in the accumulation region12can be immediately transferred to the read-out region13(within a predetermined read-out period), so that a residual image can be prevented from being generated in an obtained image.

Next, a second example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 4.FIG. 4is a view showing the second example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 4corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and they are the same other than that. Therefore, hereinafter, only an implantation region16bin the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 4, according to a solid-state imaging element1bin the present example, the implantation region16bhas a shape in which its width discretely increases with the decreasing distance to the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16b.

Thus, when the accumulation region12is formed so as to have the above N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, a third example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 5.FIG. 5is a view showing the third example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 5corresponds toFIG. 3showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16cin the present example will be described, and for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as a reference, and its description is omitted.

As shown inFIG. 5, according to a solid-state imaging element1cin the present example, the implantation region16chas a shape in which its width continuously and exponentially increases with the decreasing distance to the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16c.

Thus, when the accumulation region12is formed so as to have the above N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1cin the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14.

Next, a fourth example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 6.FIG. 6is a view showing the fourth example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 6corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16din the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 6, according to a solid-state imaging element1din the present example, the implantation region16dhas a shape in which the implantation region16dbranches into two parts in a direction being away from the transfer section14and a width of each branch continuously and lineally increases with the decreasing distance to the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16d.

Thus, when the accumulation region12is formed so as to have the above N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1din the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14. Furthermore, according to the solid-state imaging element1din the present example, the potential can be inclined in a large range of the accumulation region12. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, a fifth example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 7.FIG. 7is a view showing the fifth example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 7corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16ein the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 7, according to a solid-state imaging element1ein the present example, the implantation region16ehas a shape in which the implantation region16ebranches into two parts in the direction being away from the transfer section14and a width of each branch continuously and exponentially increases with the decreasing distance to the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16e.

Thus, when the accumulation region12is formed so as to have the above N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1ein the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14. Furthermore, according to the solid-state imaging element1ein the present example, the potential can be inclined in a large range of the accumulation region12. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, a sixth example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 8.FIG. 8is a view showing the sixth example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 8corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16fin the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as a reference, and its description is omitted.

As shown inFIG. 8, according to a solid-state imaging element if in the present example, the implantation region16fhas a shape in which the implantation region16fbranches into three parts in the direction being away from the transfer section14and a width of each branch continuously and lineally increases with the decreasing distance to the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16f.

Thus, when the accumulation region12is formed so as to have the above N-type high-concentration impurity region121, the potential in the accumulation region12can be inclined so as to be lowered with the decreasing distance to the transfer section14. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element if in the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14. Furthermore, according to the solid-state imaging element if in the present example, the potential can be inclined in a large range of the accumulation region12. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, a seventh example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 9.FIG. 9is a view showing the seventh example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 9corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16gin the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 9, according to a solid-state imaging element1gin the present example, a plurality of the implantation regions16ghave a shape in which bars extend in parallel to the direction being away from the transfer section14. In addition, as for the plurality of the implantation regions16g, an interval between the adjacent implantation regions16gbecomes narrow with the decreasing distance to a center of the transfer section14among the implantation regions16g. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16g. Furthermore,FIG. 9also shows an outline region17gsurrounded by an outline enclosing a plurality of the N-type high-concentration impurity regions121(implantation regions16g).

According to the solid-state imaging element1gin the present example, a width of the outline region17gcontinuously and exponentially increases with the decreasing distance to the transfer section14. Thus, an area (total area) of a plurality of the N-type high-concentration impurity regions121(implantation regions16g) per unit distance with respect to the transfer section14increases with the decreasing distance to the transfer section14, as a whole. As a result, the potential in the accumulation region12can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14. Therefore, according to the solid-state imaging element1gin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1gin the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14.

In addition, according to the solid-state imaging element1gin the present example, a density of the N-type high-concentration impurity regions121increases with the decreasing distance to the transfer section14. Thus, since the density of the N-type high-concentration impurity regions121increases with the decreasing distance to the transfer section14, the potential in the accumulation region12can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14. Therefore, according to the solid-state imaging element1gin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, an eighth example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 10.FIG. 10is a view showing the eighth example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 10corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16hin the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 10, according to a solid-state imaging element1hin the present example, a plurality of the implantation regions16hhave a shape in which bars extend in parallel to the direction being away from the transfer section14. In addition, an interval between the adjacent implantation regions16his equal. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16h. Furthermore,FIG. 10also shows an outline region17hsurrounded by an outline enclosing the plurality of the N-type high-concentration impurity regions121(implantation regions16h).

According to the solid-state imaging element1hin the present example, the outline region17hbranches into two parts in the direction being away from the transfer section14, and a width of each branch continuously and exponentially increases with the decreasing distance to the transfer section14. Thus, an area (total area) of the plurality of the N-type high-concentration impurity regions121(implantation regions16h) per unit distance with respect to the transfer section14increases with the decreasing distance to the transfer section14, as a whole. As a result, the potential in the accumulation region12can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14. Therefore, according to the solid-state imaging element1hin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Furthermore, according to the solid-state imaging element1hin the present example, the potential in the accumulation region12can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region12can be smoothly moved to the transfer section14. In addition, according to the solid-state imaging element1hin the present example, it becomes possible to incline the potential in a large range of the accumulation region12. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

Next, a ninth example of the solid-state imaging element according to the first embodiment of the present invention will be described with reference toFIG. 11.FIG. 11is a view showing the ninth example of the solid-state imaging element according to the first embodiment of the present invention. In addition,FIG. 11corresponds toFIG. 3 (a)showing the first example of the solid-state imaging element according to the first embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only an implantation region16iin the present example will be described, and as for the rest of it, the description in the first example of the first embodiment described above andFIG. 3is to be occasionally used as references, and its description is omitted.

As shown inFIG. 11, according to a solid-state imaging element1iin the present example, a plurality of the implantation regions16ihave a shape in which bars extend radially in the direction being away from the transfer section14. In addition, the N-type high-concentration impurity region121has the same shape as the implantation region16i. Furthermore,FIG. 11also shows an outline region17isurrounded by an outline enclosing the plurality of the N-type high-concentration impurity regions121(implantation regions16i).

According to the solid-state imaging element1iin the present example, a density of the N-type high-concentration impurity regions121increases with the decreasing distance to the transfer section14. Thus, since the density of the N-type high-concentration impurity regions121increases with the decreasing distance to the transfer section14, the potential in the accumulation region12can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14. Therefore, according to the solid-state imaging element1iin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14.

<Each example of the first embodiment>

As described above, as for the solid-state imaging elements1ato1iaccording to the first embodiment of the present invention, the area per unit distance with respect to the transfer section14or the density of the N-type high-concentration impurity regions121formed in the accumulation region12(the implantation regions16ato16iof the N-type impurity in the accumulation region12) is only adjusted so that the area or the density can increase with the decreasing distance to the transfer section14. As a result, the potential in the accumulation region12can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region12to the transfer section14. Therefore, the solid-state imaging elements1ato1iaccording to the first embodiment of the present invention can be simply manufactured.

Furthermore, it is possible to steplessly adjust the area per unit distance with respect to the transfer section14or the density of the N-type high-concentration impurity regions121formed in the accumulation region12(the implantation regions16ato16iof the N-type impurity in the accumulation region12). Therefore, as for the solid-state imaging elements1ato1iaccording to the first embodiment of the present invention, the potential in the accumulation region12can be inclined in a desired manner, and the movement of the electrons in the accumulation region12can be controlled with a high degree of accuracy.

In addition, as for the first example to the ninth example (FIGS. 3 to 11), each of the implantation regions16ato16imay be set so as to partially protrude outside the accumulation region12(outside an active region or onto an element isolation region, for example).

Furthermore, the description has been given to the case where the implantation regions16dto16fbranch into the two or three parts in the fourth example to the sixth example (FIGS. 6 to 8), but each of them may branch into four or more parts. Furthermore, the branched implantation region may have a shape in which its width discretely increases with the decreasing distance to the transfer section14(refer to the second example in the first embodiment shown inFIG. 4). In addition, the branched implantation region is not always required to have the same shape, and it may have a different shape.

Furthermore, each of the outline regions17gto17iin the seventh example to the ninth example (FIGS. 9 to 11) may employ any shape. For example, each of the outline regions17gto17imay have the same shape as the N-type high-concentration impurity region121(the implantation regions16ato16f) in the first example to the sixth example in the first embodiment (including the above-described variation). Furthermore, the description has been given to the case where each of the N-type high-concentration impurity regions121(the implantation regions16gto16i) has the bar shape, but it may have a shape other than the bar shape.

Hereinafter, solid-state imaging elements according to a second embodiment of the present invention will be described with reference to the drawings. First, a first example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 12.FIG. 12is a view showing the first example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 12 (a)is a plan view of one pixel in the solid-state imaging element,FIG. 12 (b)is a cross-sectional view showing a cross-sectional surface taken along R-R inFIG. 12 (a). Furthermore,FIG. 12 (c)is a graph showing a potential in the cross-sectional surface taken along R-R inFIG. 12 (a).

As shown inFIG. 12 (a)(b), a solid-state imaging element2aincludes a substrate21, an accumulation region22formed in the substrate21, for accumulating electrons generated by a photoelectric conversion, a read-out region23formed in the substrate21, for receiving the transferred electrons accumulated in the accumulation region22, a transfer section24for transferring the electrons from the accumulation region22to the read-out region23, and an insulating film25formed on a surface of the substrate21. The transfer section24serves as a gate electrode formed on the insulating film25and is formed between the accumulation region22and the read-out region23.

The substrate21has the P type (P-sub), the accumulation region22has the N type (N), and the read-out region23has the N type (N+). In addition, according to the solid-state imaging element2a, a P-type impurity is separately implanted into an implantation region262aexcept for a non-implantation region261a(a region corresponding to the implantation region16ain the first example of the first embodiment shown inFIG. 3) formed adjacent to the transfer section24in the accumulation region22so as to form a P-type low-concentration impurity region (an impurity concentration modulation region)221having the N type (N) in which the P-type impurity is not implanted, and a P-type high-concentration impurity region222having the P type (P+) in which the P-type impurity is implanted. Therefore, according to the solid-state imaging element2ain the present example, a buried photodiode is formed of the substrate21and the accumulation region22, and electrons are accumulated in the accumulation region22.

As shown inFIG. 12 (a), according to the solid-state imaging element2ain the present example, the non-implantation region261ahas a shape in which its width continuously and linearly increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261a. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262a.

Thus, when the accumulation region22is formed so as to have this P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24as shown inFIG. 12 (c). Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2ain the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24.

When a predetermined potential is applied to the transfer section24in this solid-state imaging element2a, a potential in the substrate21just below the transfer section24is lowered, and the electrons accumulated in the accumulation region22are transferred to the read-out region23. At this time, since the potential in the accumulation region22is inclined as described above, the movement of the electrons accumulated in the accumulation region22to the transfer section24is accelerated. Therefore, even when the accumulation region22is large in size in the solid-state imaging element2a, the electrons accumulated in the accumulation region22can be immediately transferred to the read-out region23(within a predetermined read-out period), so that a residual image can be prevented from being generated in an obtained image. Furthermore, according to the solid-state imaging element2ain the present example, the potential in the accumulation region22can be inclined at the same time as the buried photodiode is formed.

Next, a second example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 13.FIG. 13is a view showing the second example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 13corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in an implantation region and a non-implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261band an implantation region262bin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 13, according to the solid-state imaging element2bin the present example, the non-implantation region261b(the region corresponding to the implantation region16bin the second example of the first embodiment shown inFIG. 4) has a shape in which its width discretely increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261b. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262b.

Thus, when the accumulation region22is formed so as to have the above P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, a third example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 14.FIG. 14is a view showing the third example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 14corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261cand an implantation region262cin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 14, according to a solid-state imaging element2cin the present example, the non-implantation region261c(the region corresponding to the implantation region16cin the third example of the first embodiment shown inFIG. 5) has a shape in which its width continuously and exponentially increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261c. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262c.

Thus, when the accumulation region22is formed so as to have the above P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2cin the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24.

Next, a fourth example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 15.FIG. 15is a view showing the fourth example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 15corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261dand an implantation region262din the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 15, according to a solid-state imaging element2din the present example, the non-implantation region261d(the region corresponding to the implantation region16din the fourth example of the first embodiment shown inFIG. 6) has a shape in which the non-implantation region261dbranches into two parts in a direction being away from the transfer section24, and a width of each branch continuously and linearly increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261d. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262d.

Thus, when the accumulation region22is formed so as to have the above P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2din the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24. Furthermore, according to the solid-state imaging element2din the present example, the potential can be inclined in a large range of the accumulation region22. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, a fifth example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 16.FIG. 16is a view showing the fifth example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 16corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the second examples are the same other than that. Therefore, hereinafter, only a non-implantation region261eand an implantation region262ein the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 16, according to a solid-state imaging element2ein the present example, the non-implantation region261e(the region corresponding to the implantation region16ein the fifth example of the first embodiment shown inFIG. 7) has a shape in which the non-implantation region261ebranches into two parts in the direction being away from the transfer section24, and a width of each branch continuously and exponentially increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261e. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262e.

Thus, when the accumulation region22is formed so as to have the above P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2ein the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24. Furthermore, according to the solid-state imaging element2ein the present example, the potential can be inclined in a large range of the accumulation region22. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, a sixth example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 17.FIG. 17is a view showing the sixth example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 17corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261fand an implantation region262fin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 17, according to a solid-state imaging element2fin the present example, the non-implantation region261f(the region corresponding to the implantation region16fin the sixth example of the first embodiment shown inFIG. 8) has a shape in which the non-implantation region261fbranches into three parts in the direction being away from the transfer section24, and a width of each branch continuously and lineally increases with the decreasing distance to the transfer section24. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261f. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262f.

Thus, when the accumulation region22is formed so as to have the above P-type low-concentration impurity region221, the potential in the accumulation region22can be inclined so as to be lowered with the decreasing distance to the transfer section24. Therefore, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2fin the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24. Furthermore, according to the solid-state imaging element2fin the present example, the potential can be inclined in a large range of the accumulation region22. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, a seventh example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 18.FIG. 18is a view showing the seventh example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 18corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261gand an implantation region262gin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 18, according to a solid-state imaging element2gin the present example, a plurality of the non-implantation regions261g(the region corresponding to the implantation regions16gin the seventh example of the first embodiment shown inFIG. 9) has a shape in which bars extend in parallel to the direction being away from the transfer section24. Furthermore, as for the plurality of the non-implantation regions261g, an interval between the adjacent non-implantation regions261gbecomes narrow with the decreasing distance to a center of the transfer section24among the non-implantation regions261g. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261g. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262g. Furthermore,FIG. 18also shows an outline region27gsurrounded by an outline enclosing a plurality of the P-type low-concentration impurity regions221(non-implantation regions261g).

According to the solid-state imaging element2gin the present example, a width of the outline region27gcontinuously and exponentially increases with the decreasing distance to the transfer section24. Thus, an area (total area) of a plurality of the P-type low-concentration impurity regions221(non-implantation regions261g) per unit distance with respect to the transfer section24increases with the decreasing distance to the transfer section24, as a whole. As a result, the potential in the accumulation region22can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24. Therefore, according to the solid-state imaging element2gin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2gin the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24.

In addition, according to the solid-state imaging element2gin the present example, a density of the P-type low-concentration impurity regions221increases with the decreasing distance to the transfer section24. Thus, since the density of the P-type low-concentration impurity regions221increases with the decreasing distance to the transfer section24, the potential in the accumulation region22can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24. Therefore, according to the solid-state imaging element2gin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, an eighth example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 19.FIG. 19is a view showing the eighth example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 19corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261hand an implantation region262hin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 19, according to a solid-state imaging element2hin the present example, a plurality of the non-implantation regions261h(the region corresponding to the implantation region16hin the eighth example of the first embodiment shown inFIG. 10) have a shape in which bars extend in parallel to the direction being away from the transfer section24. In addition, an interval between the adjacent non-implantation regions261his equal. In addition, the P-type low-concentration impurity region221has the same shape as the non-implantation region261h. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262h. Furthermore,FIG. 19also shows an outline region27hsurrounded by an outline enclosing the plurality of the P-type low-concentration impurity regions221(non-implantation regions261h).

According to the solid-state imaging element2hin the present example, the outline region27hbranches into two parts in the direction being away from the transfer section24, and a width of each branch continuously and exponentially increases with the decreasing distance to the transfer section24. Thus, an area (total area) of the plurality of the P-type low-concentration impurity regions221(the non-implantation regions261h) per unit distance with respect to the transfer section24increases with the decreasing distance to the transfer section24, as a whole. As a result, the potential in the accumulation region22can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24. Therefore, according to the solid-state imaging element2hin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Furthermore, according to the solid-state imaging element2hin the present example, the potential in the accumulation region22can be smoothly inclined. Therefore, the electrons accumulated in the accumulation region22can be smoothly moved to the transfer section24. In addition, according to the solid-state imaging element2hin the present example, the potential can be inclined in a large range of the accumulation region22. Therefore, it becomes possible to effectively accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

Next, a ninth example of the solid-state imaging element according to the second embodiment of the present invention will be described with reference toFIG. 20.FIG. 20is a view showing the ninth example of the solid-state imaging element according to the second embodiment of the present invention. In addition,FIG. 20corresponds toFIG. 12 (a)showing the first example of the solid-state imaging element according to the second embodiment of the present invention. Furthermore, the present example differs from the first example only in a non-implantation region and an implantation region, and the present and the first examples are the same other than that. Therefore, hereinafter, only a non-implantation region261iand an implantation region262iin the present example will be described, and as for the rest of it, the description in the first example of the second embodiment described above andFIG. 12is to be occasionally used as references, and its description is omitted.

As shown inFIG. 20, according to the solid-state imaging element2iin the present example, a plurality of the non-implantation regions261i(the regions corresponding to the implantation regions16iin the ninth example of the first embodiment shown inFIG. 11) have a shape in which bars extend radially in the direction being away from the transfer section24. Furthermore, the P-type low-concentration impurity region221has the same shape as the non-implantation region261i. On the other hand, the P-type high-concentration impurity region222has the same shape as the implantation region262i. Furthermore,FIG. 20also shows an outline region27isurrounded by an outline enclosing the plurality of the P-type low-concentration impurity regions221(non-implantation region261i).

According to the solid-state imaging element2iin the present example, a density of the P-type low-concentration impurity regions221increases with the decreasing distance to the transfer section24. Thus, since the density of the P-type low-concentration impurity regions221increases with the decreasing distance to the transfer section24, the potential in the accumulation region22can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24. Therefore, according to the solid-state imaging element2iin the present example, it becomes possible to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24.

<Each Example of the Second Embodiment>

As described above, as for the solid-state imaging elements2ato2iaccording to the second embodiment of the present invention, the area per unit distance with respect to the transfer section24or the density of the P-type low-concentration impurity regions221formed in the accumulation region22(the non-implantation regions261ato261iof the P-type impurity in the accumulation region22) is only adjusted so that the area or the density can increase with the decreasing distance to the transfer section24. As a result, the potential in the accumulation region22can be inclined so as to accelerate the movement of the electrons accumulated in the accumulation region22to the transfer section24. Therefore, the solid-state imaging elements2ato2iaccording to the second embodiment of the present invention can be simply manufactured.

Furthermore, it is possible to steplessly adjust the area per unit distance with respect to the transfer section24or the density of the P-type low-concentration impurity region221formed in the accumulation region22(the non-implantation regions261ato261iof the P-type impurity in the accumulation region22). Therefore, as for the solid-state imaging elements2ato2iaccording to the second embodiment of the present invention, the potential in the accumulation region22can be inclined in a desired manner, and the movement of the electrons in the accumulation region22can be controlled with a high degree of accuracy.

In addition, as for the first example to the ninth example (FIGS. 12 to 20), each of the implantation regions262ato262imay be set so as to partially protrude outside the accumulation region22(outside an active region or onto an element isolation region, for example).

Furthermore, the description has been given to the case where the non-implantation regions261dto261fbranch into the two or three parts in the fourth example to the sixth example (FIGS. 15 to 17), but each of them may branch into four or more parts. Furthermore, the branched non-implantation region may have a shape in which its width discretely increases with the decreasing distance to the transfer section24(refer to the second example in the second embodiment shown inFIG. 13). In addition, the branched non-implantation region is not always required to have the same shape, and it may have a different shape.

Furthermore, each of the outline regions27gto27iin the seventh example to the ninth example (FIGS. 18 to 20) may have any shape. For example, each of the outline regions27gto27imay have the same shape as the P-type low-concentration impurity regions221(the non-implantation regions261ato261f) in the first example to the sixth example in the second embodiment (including the above-described variation). Furthermore, the description has been given to the case where each of the shapes of the P-type low-concentration impurity regions221(the non-implantation regions261gto261i) has the bar shape, but it may have a shape other than the bar shape.

The description has been given to the case where the N-type accumulation regions12and22are formed in the P-type substrates11and21, respectively (in the case where the electrons are accumulated in the accumulation regions12and22), but the P type and the N type may be reversed. That is, a P-type accumulation region may be formed in an N-type substrate (holes are accumulated in the accumulation region). In this case, as for the solid-state imaging elements1ato1iaccording to the first embodiment of the present invention, a P-type high-concentration impurity region (impurity concentration modulation region) is formed by implanting the P-type impurity in the implantation region corresponding to each of the implantation regions16ato16i. In addition, in this case, as for the solid-state imaging elements2ato2iaccording to the second embodiment of the present invention, an N-type low-concentration impurity region (impurity concentration modulation region) and an N-type high-concentration impurity region are formed by implanting the N-type impurity in the implantation region corresponding to each of the implantation regions262ato262i.

While the description has been given to the CMOS imaging sensor as the solid-state imaging elements1ato1i, and2ato2iaccording to the embodiments of the present invention, the present invention is applicable to a solid-state imaging element other than the CMOS imaging sensor (such as a CCD imaging sensor).

INDUSTRIAL APPLICABILITY

The solid-state imaging element according to the present invention can be preferably used for a CMOS imaging sensor, a CCD imaging sensor, or the like which is mounted on any kind of electronic device having an imaging function.

DESCRIPTION OF SYMBOLS

1ato1iSolid-state imaging element

2ato2iSolid-state imaging element