Solid-state imaging device

Abstract

The photosensitive region includes a first impurity region and a second impurity region having a higher impurity concentration than the first impurity region. The photosensitive region has one end away from the transmission part in the second direction and the other end close to the transmission part in the second direction. The shape of the second impurity region in a top view is line symmetric with respect to the center line of the photosensitive region along the second direction. The width of the second impurity region in the first direction increases along the transmission direction from one end toward the other end. The increase rate of the width of the second impurity region in each interval into which the photosensitive region is divided in the second direction gradually increases in the transmission direction. n is an integer greater than 2.

Description

Technical Field

[0001] The present invention relates to a solid-state imaging device. Background Art

[0002] A known solid-state imaging device includes: a plurality of photoelectric conversion units arranged in a first direction; and a plurality of transmission units arranged in a second direction intersecting the first direction with corresponding photoelectric conversion units among the plurality of photoelectric conversion units (for example, see Patent Document 1). Each photoelectric conversion unit has a photosensitive region that generates charge in response to incident light. Each transmission unit transmits the charge generated in the corresponding photoelectric conversion unit.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-90906 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In the above-mentioned solid-state imaging device, for example, if the length of the photoelectric conversion unit in the second direction is large, the distance for transferring charges in the photoelectric conversion unit becomes large. In this case, the photoelectric conversion unit needs to transfer charges efficiently. In order to efficiently transfer charges, for example, impurities are additionally injected into the photoelectric conversion unit to change the impurity concentration of the photosensitive region. The photosensitive region of the above-mentioned solid-state imaging device has: a first impurity region, and a second impurity region having a higher impurity concentration than the first impurity region. The photosensitive region has: an end away from the transfer unit in the second direction, and the other end close to the transfer unit in the second direction. The direction from one end toward the other end is the transfer direction of the charge. The second impurity region has a trapezoidal shape whose width in the second direction gradually increases in the transfer direction. The second impurity region forms a potential gradient that gradually increases in the transfer direction in the photosensitive region.

[0008] Depending on the shape of the second impurity region, the potential gradient formed in the photosensitive region may change. Designers often determine the shape of the second impurity region based on their own feelings or experience. In this case, it is difficult for the second impurity region to form a sufficient potential gradient to efficiently transfer charges, so there is a concern that the charge transfer time will increase. Therefore, further improvement of the charge transfer efficiency is sought.

[0009] An object of one embodiment of the present invention is to provide a solid-state imaging device with improved charge transfer efficiency.

[0010] Technical means of solving problems

[0011] The present inventors have newly obtained the following insights. For example, when the second impurity region is in a trapezoidal shape, a portion with a small potential gradient is generated in the photosensitive region. As long as the shape of the second impurity region is a shape that is not easy to generate a portion with a small potential gradient, the charge transfer efficiency is improved. Based on the above insights, the present inventors have conducted in-depth research on the shape of the portion with a small potential gradient that is not easy to generate, and completed the present invention.

[0012] One embodiment of the present invention is a solid-state imaging device, which includes: a plurality of photoelectric conversion parts arranged in a first direction, and a plurality of transfer parts arranged in a second direction intersecting the first direction corresponding to the photoelectric conversion parts of the plurality of photoelectric conversion parts. The plurality of photoelectric conversion parts have a photosensitive region that generates charges according to incident light. The plurality of transfer parts transfer the charges generated in the corresponding photoelectric conversion parts. The photosensitive region includes a first impurity region and a second impurity region having a higher impurity concentration than the first impurity region. The photosensitive region has an end away from the transfer part in the second direction and another end close to the transfer part in the second direction. The second impurity region is set from one end or the vicinity of one end of the photosensitive region to the other end of the photosensitive region. The second impurity region has a shape that is line-symmetrical with respect to the center line of the photosensitive region along the second direction when viewed from above. The width of the second impurity region in the first direction increases along the transfer direction from one end to the other end. The increase rate of the width of the second impurity region in each interval into which the photosensitive region is divided into n in the second direction gradually increases in the transfer direction. n is an integer greater than 2.

[0013] In the above-mentioned method, the width of the second impurity region increases in the transmission direction. Therefore, a potential gradient is formed in the photosensitive region as the potential increases from one end to the other end. The second impurity region has a shape that is line-symmetrical with respect to the center line of the photosensitive region along the second direction when viewed from above. Therefore, in the photosensitive region, regardless of the position where the charge is generated, the charge is transmitted with the same efficiency. The increase rate of the width of the second impurity region in each interval divided into n parts in the second direction gradually increases in the transmission direction. In this case, the shape of the second impurity region is a shape in which a portion with a small potential gradient is not easily generated in the photosensitive region. The photoelectric conversion unit transmits the charge more efficiently. Therefore, the solid-state imaging device of the above-mentioned method improves the charge transfer efficiency.

[0014] In the above embodiment, the width of the second impurity region in each interval can also be set so that the potential difference of the photosensitive region in each adjacent interval is constant. In this case, the potential gradient of the photosensitive region is substantially constant. Therefore, the photoelectric conversion unit transfers charge more efficiently.

[0015] In the above embodiment, each section may be a section obtained by dividing the light sensitive region into n equal parts in the second direction. In this case, n is an integer greater than or equal to 2.

[0016] In the above-mentioned embodiment, each section may be a section formed by dividing the light sensing area in such a manner that the width in the second direction gradually narrows in the transmission direction.

[0017] In the above aspect, in the section closest to the other end, the increase rate of the width of the second impurity region may be changed so as to increase closer to the other end.

[0018] Effects of the Invention

[0019] According to one aspect of the present invention, there is provided a solid-state imaging device having improved charge transfer efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A diagram showing a planar structure of a solid-state imaging device.

[0021] Figure 2 A diagram showing a cross-sectional structure of a solid-state imaging device.

[0022] Figure 3 This is a schematic diagram showing the light sensing area.

[0023] Figure 4 This is a diagram showing changes in potential formed in the solid-state imaging device.

[0024] Figure 5 It is a diagram for explaining the width of the second impurity region.

[0025] Figure 6 is a graph showing the potential of the light-sensing region for each notch width.

[0026] Figure 7 is a graph showing the width of the second impurity region at each equally divided point.

[0027] Figure 8 FIG. 4 is a diagram showing a simulation model of a photosensitive region including a second impurity region according to the present embodiment.

[0028] Fig. 9 It is a graph showing the electric potential of the light-sensitive area in three dimensions.

[0029] Fig.10 It is a graph showing the potential gradient in the transport direction.

[0030] Fig.11 is a schematic diagram showing the second impurity region in the reference example.

[0031] Fig.12 This is a graph comparing the potential gradient in the photosensitive region in the present embodiment and the reference example.

[0032] Fig.13 This is a graph comparing the measured values ​​of image lag corresponding to the transmission time in the present embodiment and the reference example.

[0033] Fig.14 is a schematic diagram showing a modification example of the second impurity region. DETAILED DESCRIPTION

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions are denoted by the same reference numerals, and repeated descriptions are omitted.

[0035] First, refer to Figure 1 to Figure 4 , the structure of the solid-state imaging device 1 according to the present embodiment will be described. Figure 1 A diagram showing a planar structure of a solid-state imaging device. Figure 2 A diagram showing a cross-sectional structure of a solid-state imaging device. Figure 2 Display along Figure 1 A cross-sectional structure of a solid-state imaging device taken along line II-II. Figure 3 This is a schematic diagram showing the light sensing area. Figure 4 This is a diagram showing changes in potential formed in the solid-state imaging device.

[0036] like Figure 1 As shown, the solid-state imaging device 1 includes a light receiving unit 3, a plurality of input gate units 4, a plurality of transfer units 7, and a shift register 9. The shift register 9 is a charge output unit. The solid-state imaging device 1 is, for example, an embedded CCD linear image sensor.

[0037] The light receiving portion 3 has a plurality of photoelectric conversion portions 5. The plurality of photoelectric conversion portions 5 are arranged in a first direction D1. The photoelectric conversion portion 5 is located between the input gate portion 4 and the transmission portion 7. The photoelectric conversion portion 5 is in the shape of a long rectangular strip whose length in the second direction D2 is approximately 1 to 500 times the length in the first direction D1. In the present embodiment, the first direction D1 is a direction along the relative direction of the two long sides of the photoelectric conversion portion 5. The first direction D1 includes two directions along the positive and negative directions of the Y axis. The second direction D2 is a direction along the relative direction of the two short sides of the photoelectric conversion portion 5. The second direction D2 includes two directions along the positive and negative directions of the X axis. The second direction D2 intersects with the first direction D1. The first direction D1 is orthogonal to the second direction D2.

[0038] Each photoelectric conversion unit 5 has a photosensitive region 6. The photosensitive region 6 generates charges according to incident light. The photosensitive region 6 is rectangular in shape defined by two long sides and two short sides when viewed from above. The plurality of photosensitive regions 6 are arranged in a first direction D1. The plurality of photosensitive regions 6 are arranged in an array in the one-dimensional direction with the first direction D1 as a one-dimensional direction. One photosensitive region 6 constitutes one pixel in the light receiving unit 3.

[0039] The light sensing region 6 includes a plurality of impurity regions with different impurity concentrations. Figure 3 As shown, the photosensitive region 6 includes: a pair of first impurity regions 11 and a second impurity region 12 . The impurity concentration of the second impurity region 12 is higher than that of the first impurity region 11 .

[0040] The photosensitive region 6 has: a pair of short sides 6a, a short side 6b, and a pair of long sides 6c, 6d. The photosensitive region 6 is defined by a pair of short sides 6a, a short side 6b and a pair of long sides 6c, 6d. In the photosensitive region 6, the second impurity region 12 is provided from the short side 6a to the short side 6b in the second direction D2. In the present embodiment, the second impurity region 12 is provided continuously from the short side 6a to the short side 6b. The short side 6a is one end away from the transfer portion 7 in the second direction D2. The short side 6b is the other end close to the transfer portion 7 in the second direction D2. The second impurity region 12 has one end and the other end. The second impurity region 12 is located between the pair of first impurity regions 11 in the first direction D1. The pair of short sides 6a and the short side 6b are opposite in the second direction D2. The second direction D2 is the direction in which the pair of short sides 6a and the short side 6b are opposite. The pair of long sides 6c and 6d are opposite in the first direction D1. The first direction D1 is the direction in which the pair of long sides 6c and 6d are opposite.

[0041] The second impurity region 12 is in a line-symmetric shape with respect to the center line G1 of the light sensing region 6 along the second direction D2 when viewed from above. The planar shape of the second impurity region 12 is line-symmetric with respect to the center line G1. The center line G1 is positioned in a manner such that it is parallel to a pair of long sides 6c and 6d of the light sensing region 6 and is at the same distance from each long side 6c and 6d. In this embodiment, "same" not only means that the values ​​are completely the same, but also means that the difference in values ​​is within the range of measurement error or a predetermined small difference. The planar shape of the second impurity region 12 is line-symmetric with respect to the center line G1, which means that when the second impurity region 12 is divided by the center line G1, the regions positioned with the center line G1 sandwiched therebetween are mirror-symmetric, and the area and number of the regions are the same. The center line G1 is the axis of mirror symmetry.

[0042] The width W of the second impurity region 12 in the first direction D1 increases from the short side 6a toward the short side 6b. Hereinafter, the width W in the first direction D1 is referred to as "width W". The width W increases monotonically in a narrow sense as it moves from the short side 6a toward the short side 6b. For a detailed description of the shape of the second impurity region 12, refer to Figure 5 Described below.

[0043] The second impurity region 12 is formed along the light sensing region 6 Figure 1The potential gradient increases in the positive direction of the X-axis. The potential gradient increases in the direction from the short side 6a to the short side 6b. This potential gradient transfers the charges generated in the photosensitive region 6 in the direction from the short side 6a to the short side 6b. The charges reaching the short side 6b are discharged from the photosensitive region 6. Hereinafter, the direction from the short side 6a to the short side 6b is referred to as the "transfer direction TD".

[0044] like Figure 1 As shown, one input gate portion 4 corresponds to one photosensitive region 6 (one photoelectric conversion unit 5). The input gate portion 4 is arranged close to the short side 6a of the corresponding photosensitive region 6. The input gate portion 4 is arranged in the second direction D2 with the corresponding photosensitive region 6 (photoelectric conversion unit 5) in a manner adjacent to the short side 6a of the corresponding photosensitive region 6. The input gate portion 4 applies a predetermined potential to the region of the photosensitive region 6 close to the short side 6a.

[0045] One transfer unit 7 corresponds to one photosensitive region 6 (one photoelectric conversion unit 5). The transfer unit 7 is arranged close to the short side 6b of the corresponding photosensitive region 6. The transfer unit 7 is arranged in the second direction D2 with the corresponding photosensitive region 6 (photoelectric conversion unit 5) in a manner adjacent to the short side 6b of the corresponding photosensitive region 6. The transfer unit 7 is located between the photosensitive region 6 and the shift register 9. The transfer unit 7 obtains the charge discharged from the photosensitive region 6 and transfers the obtained charge to the shift register 9.

[0046] The shift register 9 is configured so that each transfer unit 7 is located between each photosensitive region 6 and the shift register 9. The shift register 9 is configured close to the short side 6b of the photosensitive region 6. The shift register 9 is adjacent to the plurality of transfer units 7 in the second direction D2. The shift register 9 obtains the charge transferred from each transfer unit 7, transfers it in the negative direction of the Y axis, and sequentially outputs it to the amplifier A. The amplifier A converts the charge output from the shift register 9 into a voltage, and outputs the converted voltage as the output of the photosensitive region 6 to the outside of the solid-state imaging device 1.

[0047] Isolation regions are disposed between adjacent photosensitive regions 6 and between adjacent transmission parts 7. The isolation regions disposed between the photosensitive regions 6 electrically isolate the adjacent photosensitive regions 6. The isolation regions disposed between the transmission parts 7 electrically isolate the adjacent transmission parts 7.

[0048] The solid-state imaging device 1 includes a semiconductor substrate 10. A light receiving unit 3, a plurality of input gate units 4, a plurality of transfer units 7, and a shift register 9 are formed on the semiconductor substrate 10. In this embodiment, the semiconductor substrate 10 is a silicon substrate. Figure 2As shown, it includes a main body layer 10A that becomes a base of the semiconductor substrate 10, and surface layers 22 to 27. The surface layers 22 to 27 are arranged on one side of the main body layer 10A.

[0049] The main layer 10A is a p-type semiconductor layer. The surface layer 22 is an n++-type semiconductor layer. The surface layer 23 is an n-type semiconductor layer. The surface layer 24 is Figure 3 The surface layer 24 includes a p+ type conductor layer 24c. The n-type semiconductor layer 24a and the n+ type semiconductor layer 24b are formed on the main layer 10A. The p+ type conductor layer 24c is formed on the n-type semiconductor layer 24a and the n+ type semiconductor layer 24b. Figure 3 As shown, the n+ type semiconductor layer 24b is located between a pair of n-type semiconductor layers 24a in the first direction D1. The surface layer 25 is an n-type semiconductor layer. The surface layer 26 is an n-type semiconductor layer. The surface layer 27 is a p+ type semiconductor layer. The conductivity types of the p-type and n-type can also be replaced in a manner opposite to the above-mentioned conductivity types.

[0050] The "+" marked on the conductivity type indicates a high impurity concentration. The "-" marked on the conductivity type indicates a low impurity concentration. The low impurity concentration also includes a method in which a portion of the impurities of the conductivity type marked with "-" are compensated by impurities of the conductivity type opposite to the conductivity type marked with "-", so that the impurity concentration is set to a low level in appearance. The number of "+"s indicates the degree of impurity concentration of the conductivity type marked with "+", and the greater the number of "+", the higher the impurity concentration of the conductivity type marked with "+". N-type impurities are, for example, N, P, or As. P-type impurities are, for example, B or Al.

[0051] A pn junction is formed at the interface between the main layer 10A and the n-type semiconductor layer 24a and the n+-type semiconductor layer 24b. The n-type semiconductor layer 24a and the n+-type semiconductor layer 24b constitute a photosensitive region 6 that generates charges by the incidence of light. The n-type semiconductor layer 24a constitutes a first impurity region 11 in the photosensitive region 6. The shape of the first impurity region 11 corresponds to the shape of the n-type semiconductor layer 24a. The n+-type semiconductor layer 24b constitutes a second impurity region 12. The shape of the second impurity region 12 corresponds to the shape of the n+-type semiconductor layer 24b.

[0052] The concentration of n-type impurities in the n+-type semiconductor layer 24b is higher than the concentration of n-type impurities in the n-type semiconductor layer 24a. Figure 3As shown, the width W of the n+ type semiconductor layer 24b gradually increases in the transmission direction TD. In the region close to the short side 6a in the transmission direction TD, the width of the n+ type semiconductor layer 24b is small. In the case where the width of the n+ type semiconductor layer 24b is small, the influence of the edge electric field of the n-type semiconductor layer 24a located on both sides of the n+ type semiconductor layer 24b is large. Therefore, in the region close to the short side 6a in the transmission direction TD, the electric potential of the surface layer 24 is shallow. In the region close to the short side 6b in the transmission direction TD, the width of the n+ type semiconductor layer 24b is large. In the case where the width of the n+ type semiconductor layer 24b is large, the influence of the edge electric field of the n-type semiconductor layer 24a located on both sides of the n+ type semiconductor layer 24b is small. Therefore, in the region close to the short side 6b in the transmission direction TD, the electric potential of the surface layer 24 is deep. As a result, in the surface layer 24, as Figure 4 As shown in FIG. 1 , a potential gradient gradually increases in the transport direction TD. A potential gradient gradually increases in the transport direction TD is formed in the surface layer 24 .

[0053] A plurality of electrodes 41, 42, and 43 are arranged on the insulating layer 20. The electrode 41 is formed on a region of the insulating layer 20 corresponding to the surface layer 23. The electrode 41 is arranged on the surface layer 23 so that the insulating layer 20 is located between the electrode 41 and the surface layer 23. The electrode 41 and the surface layer 23 constitute the input gate portion 4. The driving circuit 101 applies a signal IG to the electrode 41. The potential of the surface layer 23 is determined according to the signal IG. The potential of the surface layer 23 is determined to be lower than the potential of the surface layer 24. Therefore, as Figure 4 As shown, the potential of the surface layer 23 is shallower than the potential of the surface layer 24 , that is, the potential of the light sensing region 6 . The driving circuit 101 is controlled by the control device 102 .

[0054] The electrode 42 is formed on the region of the insulating layer 20 corresponding to the surface layer 25. The electrode 42 is arranged on the surface layer 25 so that the insulating layer 20 is located between the electrode 42 and the surface layer 25. The electrode 42 and the surface layer 25 constitute the transmission unit 7. The driving circuit 101 applies a signal TG to the electrode 42. According to the signal TG, the potential of the surface layer 25 changes. The potential of the surface layer 25 is as follows: Figure 4 (a), the potential of the surface layer 24 is shallower, or as shown in Figure 4 As shown in (b), the potential of the surface layer 24 is deeper. By the change in the potential of the surface layer 25, the transfer unit 7 acquires the charge from the photosensitive region 6 and transmits the acquired charge to the shift register 9.

[0055] The electrode 43 is formed on the region of the insulating layer 20 corresponding to the surface layer 26. The electrode 43 is arranged on the surface layer 26 in such a manner that the insulating layer 20 is located between the electrode 43 and the surface layer 26. The electrode 43 and the surface layer 26 constitute the shift register 9. The driving circuit 101 applies a signal PH to the electrode 43. According to the signal PH, the potential of the surface layer 26 changes. The potential of the surface layer 26 is as follows: Figure 4 (a), the potential of the surface layer 24 is shallower, and the potential of the surface layer 25 is deeper, or as shown in Figure 4 As shown in (b), the potential of the surface layer 24 is deeper than that of the surface layer 25. The shift register 9 acquires the charge from the transfer unit 7 by the change in the potential of the surface layer 26. The shift register 9 sends the acquired charge to the amplifier A.

[0056] The surface layer 27 electrically separates the surface layers 22 to 26 from other parts of the semiconductor substrate 10. The above-mentioned isolation region can be formed by the surface layer 27. The electrodes 41 to 43 are, for example, polysilicon films. The insulating layer 20 is, for example, a silicon oxide film.

[0057] Next, refer to Figure 5 The shape of the second impurity region 12 will be described. Figure 5 It is a diagram for explaining the width of the second impurity region. Figure 5 (a) is a schematic diagram showing the light sensing area. Figure 5 In (a), the photosensitive region 6 having a length L in the second direction D2 is divided into n pieces in the second direction. n is an integer greater than or equal to 2. Figure 5 (a) represents the width W0, ..., Wk, ..., Wn of the second impurity region 12 in each section L1, ..., Lk, ..., Ln after the photosensitive region 6 is divided into n sections. k is an integer greater than or equal to 2 and less than or equal to n-1. The width W1, ..., Wk, ..., Wn of the second impurity region 12 is, for example, the width at the position closest to the short side 6b in each section L1, ..., Lk, ..., Ln. In this case, the width W1, ..., Wk, ..., Wn is the maximum width in each section L1, ..., Lk, ..., Ln. The width W0 is the minimum width in the section L1. The width W0 is the width of the second impurity region 12 at the end (short side 6a) most upstream in the transmission direction TD in the photosensitive region 6. The width W1, ..., Wk, ..., Wn is not limited to the maximum width in each section L1, ..., Lk, ..., Ln. For example, the widths W1, ..., Wk, ..., Wn may be the average values ​​of the widths in the respective sections L1, ..., Lk, ..., Ln. Figure 5 (b) is a graph showing the potential gradient of the photosensitive region 6 in each of the sections L1, ..., Lk, ..., Ln. Figure 5The horizontal axis of (b) represents the position [μm] in the photosensitive region 6 along the transport direction TD. Figure 5 The vertical axis of (b) represents the maximum potential [V] at each position.

[0058] In this embodiment, each section L1, ..., Lk, ..., Ln is a section that divides the light sensing area 6 into n equal parts in the second direction D2. Equal division means dividing into equal parts, but each section L1, ..., Lk, ..., Ln may not be divided into completely equal parts. For example, the width of each section L1, ..., Lk, ..., Ln in the second direction D2 may include a measurement error or a small difference within a preset range of ± several μm. Figure 5 As shown in (a), the increase rates ΔW1, ..., ΔWk, ... ΔWn (ΔWk = Wk-Wk-1) of the widths W1, ..., Wk, ..., Wn of the second impurity regions 12 gradually increase in the transmission direction TD. In each interval L1, ..., Lk, ..., Ln, the width W of the second impurity region 12 gradually increases from the upstream to the downstream in the transmission direction TD. In each interval L1, ..., Lk, ..., Ln, the width W of the second impurity region 12 increases monotonically in the transmission direction TD from the upstream end to the downstream end in the transmission direction TD. As shown in Figure 5 As shown in (b), the widths W1, ..., Wk, ..., Wn of the second impurity region 12 are set so that the potential differences ΔV1, ..., ΔVk, ..., ΔVn (ΔVk = Vk-Vk-1) between the adjacent sections L1, ..., Lk, ..., Ln are constant. Here, ΔV1 = V1-V0. V0 is the potential of the photosensitive region 6 at the position of the width W0.

[0059] Next, the process of determining the shape of the second impurity region 12 will be described.

[0060] First, the order of obtaining the widths W1, ..., Wk, ..., Wn of the second impurity region 12 is described. In the first order, the potential of the photosensitive region 6 is calculated for each predetermined notch width. When calculating this potential, a model of a solid-state imaging device having a second impurity region 12 with a constant notch width in the transmission direction TD is used. For each predetermined notch width, the maximum potential of the photosensitive region 6 is calculated. The notch width is, for example, a value in the range of 0.8 μm to 6.1 μm. The calculation results are displayed on Figure 6 . Figure 6 is a graph showing the potential of the light-sensing region for each notch width. Figure 6 The horizontal axis represents the notch width [μm]. Figure 6 The vertical axis represents the maximum potential [V] of the photosensitive region 6 corresponding to the notch width. Figure 6 The vertical axis indicates that the maximum potential increases as the direction goes up, and decreases as the direction goes down.

[0061] In the second order, Figure 6 In the graph of , the potential in the range corresponding to the notch width of 0.8 μm to 6.1 μm is divided into n equal parts. Figure 6 In the example shown, the potential is divided into 12 equal parts. Figure 6 The notch widths at each equally divided point (1, ...k, ...n) of the potential are read from the graph. The notch widths at each equally divided point are set as the widths W1, ..., Wk, ..., Wn of the second impurity region 12 corresponding to each equally divided point. Figure 6 In the example shown, width W1 is 0.9 μm, width W2 is 1.0 μm, width W3 is 1.1 μm, width W4 is 1.2 μm, width W5 is 1.35 μm, width W6 is 1.5 μm, width W7 is 1.7 μm, width W8 is 2.0 μm, width W9 is 2.4 μm, width W10 is 2.9 μm, width W11 is 3.9 μm, and width W12 is 6.1 μm.

[0062] According to the above sequence, the widths W1, ..., Wk, ..., Wn of the second impurity regions 12 are obtained so that the potential difference of the photosensitive regions 6 in the adjacent intervals is constant. The width W0 is set to the minimum value of the notch width. Figure 6 In the example shown, the width W0 is 0.8 μm.

[0063] Next, based on the obtained widths W0, W1, ..., Wk, ..., Wn of the second impurity regions 12, the shape of the second impurity regions 12 is determined. Figure 7 As shown in the graph of , the widths W0, W1, ..., Wk, ..., Wn of the second impurity region 12 are plotted corresponding to the equally divided points of n=0, 1, k, ...n. Figure 7 is a graph showing the width of the second impurity region at each equally divided point. Figure 7 : is a graph showing the widths W0, W1, ..., Wk, ..., Wn of the second impurity region 12 corresponding to the equally divided points. Figure 7 The horizontal axis represents the equal division points of n=0, 1, k, ... n. Figure 7 The vertical axis represents the position [μm] with the center of each width W0, W1, ..., Wk, ..., Wn as a reference. Figure 7 The vertical axis of may also be the boundary position between the second impurity region 12 and the first impurity region 11 .

[0064] The shape of the second impurity region 12 is determined by the above procedure. The shape of the second impurity region 12 is the same as that of the photoelectric conversion unit 5 regardless of its length in the transfer direction TD. Figure 7 The shapes shown in the diagram are similar.

[0065] Next, a simulation was performed to show that the shape of the second impurity region 12 is suitable for improving the charge transfer efficiency. The simulation results are shown in Figure 8 to Figure 10 . Figure 8 FIG. 4 is a diagram showing a simulation model of a photosensitive region including a second impurity region according to the present embodiment. Fig. 9 It is a graph showing the electric potential of the light-sensitive area in three dimensions. Fig. 9 The potentials shown are for use Figure 8 The simulation results of the electric potential of the light sensing area 6 of the model are shown. Fig. 9 In the case of , the positive x-axis is equivalent to the transmission direction TD. Fig. 9 In FIG. 1 , the y-axis direction corresponds to the width direction of the second impurity region 12 . Fig. 9 The vertical axis represents the maximum potential. Fig. 9 The vertical axis indicates that the maximum potential decreases as one moves upward, and increases as one moves downward. Fig. 9 The vertical axis indicates that the electric potential becomes shallower as you go up, and becomes deeper as you go down. Fig.10 It is a graph showing the potential gradient in the transport direction. Fig.10 is based on Fig. 9 The simulation results shown are graphs depicting the values ​​of the potential corresponding to the positions of the photosensitive regions 6 in the transport direction TD. Fig.10 The horizontal axis of represents the position [μm] of the photosensitive region 6 in the transmission direction TD. Fig.10 , the positive direction of the x-axis is the transmission direction TD. Fig.10 The vertical axis represents the maximum potential [V] of the photosensitive region 6 at each position. Fig.10 The vertical axis indicates that the maximum potential decreases as one moves upward, and increases as one moves downward.

[0066] like Fig.10 As shown, the potential gradient of the photosensitive region 6 is substantially constant over substantially the entire region along the transfer direction TD of the photosensitive region 6. The charges generated in the photosensitive region 6 are transferred along the potential gradient having a substantially constant slope. Therefore, the charges generated in the photosensitive region 6 are efficiently transferred.

[0067] Next, refer to Fig.11 and Fig.12 , compared with the reference example, it is shown that the shape of the second impurity region 12 of this embodiment is suitable for improving the charge transfer efficiency. Fig.11 is a schematic diagram showing the second impurity region in the reference example. Fig.11 In the reference example shown in (a), the increase rate of the width W of the second impurity region 50A is constant from the short side 6a to the end region EA close to the short side 6b. The increase rate of the width W in the end region EA is greater than the increase rate of the width W from the short side 6a to the end region EA. Fig.11In the reference example shown in (b), the increasing rate of the width W of the second impurity region 50B is constant from the short side 6 a to the short side 6 b .

[0068] Fig.12 This is a graph comparing the potential gradient in the photosensitive region in the present embodiment and the reference example. Fig.12 The characteristic 60a in FIG. 6 represents the potential gradient in the photosensitive region 6 including the second impurity region 12 of the above-mentioned embodiment, and is Fig.10 The characteristics shown correspond. Fig.12 The characteristic 60b in φ represents the potential gradient in the photosensitive region 6 including the second impurity region 50A. The characteristic 60b represents the potential gradient obtained from the simulation result of the potential of the photosensitive region 6 using the simulation model of the photosensitive region 6 including the second impurity region 50A. Fig.12 The characteristic 60c in φ represents the potential gradient in the photosensitive region 6 including the second impurity region 50B. The characteristic 60c represents the potential gradient obtained from the simulation result of the potential of the photosensitive region 6 using the simulation model of the photosensitive region 6 including the second impurity region 50B.

[0069] like Fig.12 As shown, when the photosensitive region 6 includes the second impurity region 50A or the second impurity region 50B, the potential gradient decreases from the center to the terminal in the transfer direction TD of the photosensitive region 6. Specifically, a portion where the potential gradient decreases occurs at a position of 100μm to 200μm. In contrast, when the photosensitive region 6 includes the second impurity region 12 of the above-mentioned embodiment, a portion where the potential gradient decreases does not occur, and the potential gradient is approximately constant. In this embodiment, compared with the reference example, the photosensitive region 6 is less likely to produce a portion where the potential gradient decreases, and charges are efficiently transferred. Based on the above, it is understood that the shape of the second impurity region 12 of this embodiment is suitable for improving the charge transfer efficiency.

[0070] Fig.13 This is a graph comparing the measured values ​​of image lag corresponding to the transmission time in the present embodiment and the reference example. Fig.13 The horizontal axis represents the charge transfer time [μs] in the photosensitive region 6 . Fig.13 The vertical axis represents image hysteresis [%]. Image hysteresis is an afterimage caused by the fact that charges are not completely transferred from the photosensitive region 6 and remain in the photosensitive region 6. Fig.13, each characteristic 61a, 61b, and 61c represents the measured result of image hysteresis. Characteristic 61a represents the measured result of image hysteresis in the structure in which the photosensitive region 6 includes the second impurity region 12. Characteristic 61b represents the measured result of image hysteresis in the structure in which the photosensitive region 6 includes the second impurity region 50A. Characteristic 61c represents the measured result of image hysteresis in the structure in which the photosensitive region 6 includes the second impurity region 50B.

[0071] like Fig.13 As shown, the image lag is significantly reduced in the photosensitive region 6 including the second impurity region 12 of the present embodiment compared to the photosensitive region 6 including the second impurity regions 50A and 50B. Therefore, the actual measured values ​​also show that the present embodiment improves the charge transfer efficiency of the photosensitive region 6 compared to the reference example.

[0072] As described above, in the present embodiment, the width W of the second impurity region 12 increases in the transfer direction TD. Therefore, a potential gradient is formed in the photosensitive region 6 as the potential increases from the short side 6a toward the short side 6b. The second impurity region 12 has a shape that is line-symmetrical with respect to the center line G1 of the photosensitive region 6 when viewed from above. Therefore, in the photosensitive region 6, regardless of the position where the charge is generated, the charge is transferred with the same efficiency. The increase rates ΔW1, ..., ΔWk, ... ΔWn of the widths W1, ..., Wk, ..., Wn of the second impurity region 12 in each of the sections L1, ..., Lk, ..., Ln after the photosensitive region 6 is divided into n sections in the second direction D2 gradually increase in the transfer direction TD. In this case, the shape of the second impurity region 12 is a shape of a portion where a small potential gradient is not easily generated in the photosensitive region 6. Each photoelectric conversion unit 5 efficiently transfers the charge. Therefore, the solid-state imaging device 1 improves the charge transfer efficiency.

[0073] In the present embodiment, the widths W1, ..., Wk, ..., Wn of the second impurity regions 12 in each section L1, ..., Lk, ..., Ln are set so that the potential difference of the photosensitive regions 6 in the adjacent sections L1, ..., Lk, ..., Ln is constant. In this case, the potential gradient in the photosensitive regions 6 is substantially constant. Therefore, each photoelectric conversion unit 5 further transfers charges more efficiently. In the case where the photoelectric conversion unit 5 is in an elongated shape and the transfer distance in the photosensitive regions 6 is extended, it is more effective to make the potential gradient in the photosensitive regions 6 substantially constant.

[0074] As mentioned above, although embodiment of this invention was described, this invention is not necessarily limited to the said embodiment, Various changes are possible within the range which does not deviate from the summary.

[0075] For example, the shape of the second impurity region 12 is not limited to the shape shown in the above embodiment. Fig.14 It can be in various shapes. Fig.14 , showing a modification example of the second impurity region 12 , namely, a plurality of second impurity regions 12A to 12E. Fig.14 is a schematic diagram showing a modification example of the second impurity region. Fig.14 In FIG. 1 , the boundary positions of the respective sections into which the light sensing region 6 is divided are shown by two-dot chain lines.

[0076] In the above embodiment, the second impurity region 12 is disposed from the short side 6a to the short side 6b in the light sensing region 6. The second impurity region 12 may also be disposed not from the short side 6a in the light sensing region 6. For example, Fig.14 As shown in (a), the second impurity region 12A is provided from the vicinity of the short side 6a to the short side 6b. The vicinity of the short side 6a refers to, for example, a position away from the short side 6a to a degree that does not hinder the movement of charges. In this case, the vicinity of the short side 6a is a position about several μm away from the short side 6a. Fig.14 In (a), the vicinity of the short side 6a is a position closer to the short side 6b than the short side 6a in the section L1 closest to the short side 6a among the sections L1, ..., Lk, ..., Ln.

[0077] In the above embodiment, each section L1, ..., Lk, ..., Ln is a section that divides the light sensing area 6 into n equal parts, and the widths of each section L1, ..., Lk, ..., Ln in the second direction D2 are the same. The widths of each section L1, ..., Lk, ..., Ln in the second direction D2 may also be different. Fig.14 As shown in (b), each section divides the photosensitive region 6 so that the width in the second direction D2 gradually narrows in the transmission direction TD. In this case, the increase rate of the width of the second impurity region 12B in each section gradually increases in the transmission direction TD.

[0078] In the above embodiment, the width W of the second impurity region 12 increases in each interval L1, ..., Lk, ..., Ln. The width W of the second impurity region 12 may not increase in each interval L1, ..., Lk, ..., Ln. For example, Fig.14 As shown in (c), the width W of the second impurity region 12C does not increase within each section, but increases at the boundary position of each section. The outer shape of the second impurity region 12C within each section is a rectangle.

[0079] In the above embodiment, the second impurity region 12 is composed of one region. The second impurity region 12 may also be composed of a plurality of micro regions. Fig.14 As shown in (d), the second impurity region 12D is composed of a plurality of micro regions 12d in each section. Fig.14In (d), the outline of the region corresponding to the second impurity region 12D is shown by a dotted line.

[0080] In the interval Ln closest to the short side 6b among the intervals L1, ..., Lk, ..., Ln, the increase rate of the width Wn of the second impurity region 12 may also be changed so as to increase near the short side 6b. Fig.14 In (e), the light sensing area 6 is divided into three equal parts.

[0081] In the interval closest to the short side 6b among the intervals dividing the photosensitive region 6 into three equal parts, the increase rate of the width of the second impurity region 12E is not constant, but changes in a manner that increases near the short side 6b. The photosensitive region 6 may be divided into two equal parts, or may be divided into four equal parts or more. "Near the short side 6b" means, for example, that the interval closest to the short side 6b is closer to the short side 6b than the center line CL in the second direction D2.

[0082] Each photoelectric conversion unit 5 may not be in a strip shape. Each photoelectric conversion unit 5 may have a plurality of photosensitive regions 6. Each photoelectric conversion unit 5 may include a plurality of pixels. When the photoelectric conversion unit 5 has a plurality of photosensitive regions 6, since the potential gradient of each photosensitive region 6 is substantially constant, the solid-state imaging device 1 improves the charge transfer efficiency.

[0083] Industrial Applicability

[0084] The invention can be used for CCD linear image sensor.

[0085] Explanation of symbols

[0086] 1…solid-state imaging device, 5…photoelectric conversion unit, 6…photosensitive region, 6a…short side, 6b…short side, 7…transmission unit, 11…first impurity region, 12…second impurity region, D1…first direction, D2…second direction, TD…transmission direction, G1…center line, W…width.

Claims

1. A solid-state imaging device, wherein: have: A plurality of photoelectric conversion sections having photosensitive regions that generate charges according to incident light and arranged in a first direction; and a plurality of transfer sections arranged with corresponding photoelectric conversion sections among the plurality of photoelectric conversion sections in a second direction intersecting the first direction and transferring charges generated in the corresponding photoelectric conversion sections, Each of the plurality of photoelectric conversion units is composed of only one of the light sensing regions constituting one pixel. The photosensitive region includes a pair of first impurity regions of a first conductivity type, a second impurity region of the first conductivity type located between the pair of first impurity regions in the first direction in the same layer as the pair of first impurity regions and having an impurity concentration higher than that of the first impurity region, and a semiconductor layer of the second conductivity type located in a layer different from the first impurity region and the second impurity region and forming a pn junction with the first impurity region and the second impurity region, and has one end in the second direction close to the photoelectric conversion portion and one end away from the transmission portion in the second direction, and another end in the second direction close to the photoelectric conversion portion and another end in the second direction close to the transmission portion, The second impurity region is continuously provided from one end of the photosensitive region or the vicinity of the one end to the other end of the photosensitive region, and has a shape that is line-symmetrical with respect to a center line of the photosensitive region along the second direction when viewed from above. The width of the second impurity region in the first direction increases in the transmission direction from the one end toward the other end, and is smaller than the width of the photosensitive region in the first direction at the other end, The increase rate of the width of the second impurity region in each of the n sections into which the photosensitive region is divided in the second direction gradually increases in the transmission direction, and n is an integer greater than or equal to 2, The photoelectric conversion section has an elongated shape whose length in the second direction is larger than its length in the first direction.

2. The solid-state imaging device according to claim 1, wherein The width of the second impurity region in each of the sections is set so that a potential difference between the photosensitive regions in each of the adjacent sections becomes constant.

3. The solid-state imaging device according to claim 1 or 2, wherein: The sections are sections obtained by dividing the light sensing area into n equal parts in the second direction, and n is an integer greater than or equal to 2.

4. The solid-state imaging device according to claim 1 or 2, wherein: The sections are sections formed by dividing the light sensing area in such a manner that the width in the second direction gradually becomes narrower in the transmission direction.

5. The solid-state imaging device according to any one of claims 1 to 4, wherein: In the section closest to the other end, the increase rate of the width of the second impurity region changes so as to increase closer to the other end.

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