JP2015037096A - Solid-state imaging element and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an increase or a decrease in a dark current due to a deviation in alignment or dimension.SOLUTION: A solid-state imaging element includes: a photoelectric conversion unit in which a plurality of picture elements are two-dimensionally arranged on an imaging surface and a signal charge corresponding to the amount of incident light is accumulated in each of the plurality of picture elements; an active region in which a charge detection unit for detecting the signal charge and a transfer transistor for transferring the signal charge from the photoelectric conversion unit to the charge detection unit are disposed; an isolation region formed around the active region; and a guard layer which is disposed at a part of the periphery of the photoelectric conversion unit and formed at the boundary portion between the active region and the isolation region. A first end of the photoelectric conversion unit is connected to the transfer transistor and the guard layer is not formed at a part of the periphery of a second end of the photoelectric conversion unit facing the first end of the boundary portion.

Description

  The present invention relates to a solid-state imaging device and an imaging apparatus.

  In recent years, video cameras and electronic still cameras have been widely used. These cameras use an amplification type solid-state imaging device such as a CCD type or a CMOS type, and are manufactured through a general semiconductor process.

  The solid-state imaging device has a pixel region in which a plurality of pixels are arranged two-dimensionally and a peripheral circuit that outputs an optical signal from the pixel to the outside. Charges corresponding to incident light are accumulated in a photoelectric conversion unit (for example, a photodiode) disposed in each pixel, transferred to the charge detection unit by a transfer transistor, and then read out to the outside through a peripheral circuit.

  The solid-state imaging device desirably reads out an output corresponding to incident light, but it is known that a phenomenon occurs in which output occurs even without incident light. This phenomenon is generally called dark current. Since the dark current increases with the accumulation time, it becomes a problem particularly when, for example, long-time exposure is performed in night scene photography.

  The main cause of dark current is an inflow of electrons generated from dangling bonds of crystals existing at the interface (boundary) between the semiconductor and the insulator. For example, when an element isolation region which is an insulator is provided around the photoelectric conversion unit, the boundary between the photoelectric conversion unit and the element isolation region becomes a large dark current generation source. As a countermeasure against this dark current component, a technique is known in which a reverse conductivity type guard layer is provided near the boundary between the photoelectric conversion unit and the element isolation region to prevent the depletion layer of the photoelectric conversion unit from reaching the interface ( Patent Document 1).

  The guard layer is provided at the boundary between the photoelectric conversion unit and the element isolation region, and it is not necessary to form a guard layer in the vicinity of the transfer transistor in which the element isolation region is not formed on the outer periphery of the photoelectric conversion unit. Therefore, in patent document 1, the guard layer is not formed only around the transfer transistor in the outer periphery of the photoelectric conversion unit, and has an asymmetric shape. Hereinafter, the transfer direction is referred to as the Y-axis direction, and the direction orthogonal to the transfer direction is referred to as the X-axis direction.

JP 2012-44219 A

  In a solid-state imaging device, it is desired to have a design that is robust against alignment and dimensional deviation so that the device characteristics are uniform. For example, it is desired to have a design that is robust against alignment and dimensional deviations when the photoelectric conversion part and the guard layer are injected.

  The guard layer is provided so as to straddle the boundary between the photoelectric conversion unit and the element isolation region, but the dark current suppression capability according to the width from the boundary to the photoelectric conversion unit side of the entire guard layer width (A0). Changes. The width (referred to as A1) on the photoelectric conversion portion side from this boundary changes due to alignment and dimensional deviation at the time of guard layer injection. For example, when misalignment occurs in the Y-axis direction, the width A1 on the photoelectric conversion unit side from the boundary increases on one side in the Y-axis direction and the dark current decreases, but on the opposite side, the width on the photoelectric conversion unit side from the boundary. A1 decreases and dark current increases.

  When a guard layer is not formed around the transfer transistor and the guard layer has an asymmetric shape as in Patent Document 1, if the asymmetric shape causes alignment or dimensional deviation in the Y-axis direction, the width A1 The total amount of dark current flowing into the photoelectric conversion unit increases or decreases with the change. This increase / decrease in the total amount of dark current appears as variations in device characteristics.

In a solid-state imaging device according to one embodiment of the present invention, a plurality of pixels are two-dimensionally arranged on an imaging surface, a photoelectric conversion unit that accumulates signal charges corresponding to the amount of incident light in each of the plurality of pixels, and a signal charge is detected. Provided in an active region provided with a charge detection unit, a transfer transistor for transferring signal charges from the photoelectric conversion unit to the charge detection unit, a separation region formed around the active region, and a part around the photoelectric conversion unit And a guard layer formed at a boundary portion between the active region and the isolation region, the photoelectric conversion unit has a transfer transistor connected to the first end, and the guard layer has a first end of the boundary portion. It is characterized in that it is not formed in a part of the periphery of the second end of the photoelectric conversion portion opposite to.
The imaging device by another one aspect | mode of this invention is equipped with the solid-state image sensor as described in any one of Claims 1-8, It is characterized by the above-mentioned.

  According to the present invention, increase / decrease in dark current due to alignment or dimensional deviation can be suppressed.

1 is a schematic block diagram illustrating an electronic camera according to a first embodiment of the present invention. It is a schematic circuit diagram which shows the structure of a solid-state image sensor. It is a schematic circuit diagram of the pixel provided in a solid-state image sensor. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 1st Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the conventional solid-state image sensor. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 2nd Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 3rd Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 4th Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 5th Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 6th Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 7th Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 8th Embodiment of this invention. It is an enlarged pixel top view of the pixel provided in the solid-state image sensor which concerns on the 9th Embodiment of this invention. It is a schematic circuit diagram which shows the structure of a solid-state image sensor.

(First embodiment)
FIG. 1 is a schematic block diagram showing an electronic camera 1 according to the first embodiment of the present invention. A photographing lens 2 is attached to the electronic camera 1. The photographing lens 2 is driven by a lens control unit 2a for focus and diaphragm. In the image space of the photographing lens 2, an imaging surface of an image sensor 30 that is one of the components of the solid-state imaging device 3 is arranged.

  The solid-state imaging device 3 is driven by a drive signal output from the imaging control unit 4 and outputs a signal. A signal output from the solid-state imaging device 3 is processed through the signal processing unit 5 and the A / D conversion unit 6 and then temporarily stored in the memory 7.

  The memory 7 is connected to the bus 8. The bus 8 is also connected with a lens control unit 2a, an imaging control unit 4, a microprocessor 9, a focus calculation unit 10, a recording unit 11, an image compression unit 12, an image processing unit 13, and the like. Although not shown in the drawing, the imaging control unit 4 is configured by a timing generator or the like, and supplies a drive signal or the like to each unit of the solid-state imaging device 3. An operation unit 9 a such as a release button is connected to the microprocessor 9. A recording medium 11a is detachably attached to the recording unit 11 described above.

  FIG. 2 is a schematic circuit diagram showing a part of the configuration of the image sensor 30 mounted on the solid-state imaging device 3. The image sensor 30 is formed of a silicon substrate and is configured as a CMOS type image sensor. The image sensor 30 includes a plurality of pixels 20 that output electrical signals corresponding to the amount of incident light, and a peripheral circuit that outputs signals from the pixels 20. The plurality of pixels 20 are two-dimensionally arranged in the pixel region 31 of the image sensor 30.

  In FIG. 2, as a peripheral circuit for outputting a signal from the pixel 20, a vertical scanning circuit 21, a horizontal scanning circuit 22, drive signal lines 23 and 24 connected thereto, and a pixel 20 for each pixel column. And a vertical signal line 25 that receives an electrical signal from each pixel 20, a pixel current source 26 that is provided for each vertical signal line 25 and supplies a constant current to the vertical signal line 25, and is provided for each vertical signal line 25. A correlated double sampling circuit (CDS) 27, a horizontal signal line 28 for receiving a signal output from the correlated double sampling circuit 27, and an output amplifier 29 are shown.

  The vertical scanning circuit 21 and the horizontal scanning circuit 22 output drive signals based on a command from the imaging control unit 4 of the electronic camera 1. Each pixel 20 is driven by receiving a drive signal output from the vertical scanning circuit 21 from a predetermined drive signal line 23, and outputs a signal corresponding to incident light to the vertical signal line 25. There are a plurality of drive signals output from the vertical scanning circuit 21 and a plurality of drive signal lines 23 accordingly.

  The signal output from the pixel 20 is subjected to predetermined noise removal by the correlated double sampling circuit 27. A driving signal is output from the horizontal scanning circuit 22 via the driving signal line 24, and the signal is output to the outside via the horizontal signal line 28 and the output amplifier 29.

  The electrical signal output to the vertical signal line 25 is subjected to well-known correlated double sampling in the CDS circuit 27 arranged for each vertical signal line 25, and noise is removed. The CDS circuit 27 is operated by a drive signal input from the horizontal scanning circuit 22 via the drive signal line 24.

  The electric signal after the noise is removed and converted into a true image signal component is sequentially output from the vertical signal line 25 to the horizontal signal line 28 and output to the outside of the image sensor 30 via the output amplifier 29. Although not shown in FIG. 2, a reset unit that actually resets the horizontal signal line 28 is connected to the horizontal signal line 28, and every time a signal is output from the output amplifier 29 to the outside, the horizontal signal line 28. Is reset.

  FIG. 3 is an equivalent circuit diagram of the pixel 20. As shown in FIG. 3, the pixel 20 includes a photodiode PD, a floating diffusion FD, a transfer transistor Ta, a source follower amplification transistor Tb, a reset transistor Tc, and a selection transistor Td.

  The transfer transistor Ta, the amplification transistor Tb, the reset transistor Tc, and the selection transistor Td are N-channel MOS transistors. Each transistor is turned on when its gate becomes H level (high level), and turned off when its gate becomes L level (low level). VDD is a power source.

  The photodiode PD generates and accumulates charges according to the amount of incident light. When the transfer transistor Ta is turned on, the charge accumulated in the photodiode PD is transferred to the floating diffusion FD.

  The floating diffusion FD converts the charge transferred through the transfer transistor Ta into a voltage. The voltage is applied to the gate of the amplification transistor Tb. The amplification transistor Tb generates and outputs an electrical signal corresponding to the voltage.

  The transfer transistor Ta is turned on / off by a drive signal φTG input to its gate. The drive signal φTG is output from the vertical scanning circuit 21 and applied to the gate of the transfer transistor Ta via the drive signal line 23.

  The selection transistor Td is turned on to electrically connect the pixel and the vertical signal line. The selection transistor Td outputs the electric signal generated by the amplification transistor Tb to the vertical signal line. The selection transistor Td is turned on / off by a drive signal φS input to its gate. The drive signal φS is output from the vertical scanning circuit 21 and applied to the gate of the selection transistor Td via the drive signal line 23.

  When the reset transistor Tc is turned on, the reset transistor Tc discharges the charge transferred to the floating diffusion FD and the gate of the amplification transistor Tb, and resets the reset transistor Tc. The reset transistor Tc is turned on / off by a drive signal φFDR input to its gate. The drive signal φFDR is output from the vertical scanning circuit 21 and applied to the gate of the reset transistor Tc via the drive signal line 23.

  The gates of the transfer transistors Ta arranged in the pixels 20 are commonly connected in the row direction. Similarly, the gates of the reset transistor Tc and the selection transistor Td are also commonly connected in the row direction. Then, the pixels 20 in the row direction are driven simultaneously. Accordingly, the pixels 20 arranged in the row direction simultaneously output electrical signals to the corresponding vertical signal lines 25.

  FIG. 4A is an enlarged pixel plan view of the pixel 20. In FIG. 4A, two pixels 20 arranged side by side on the imaging surface of the image sensor 30 are shown side by side. FIG. 4B is a Y0-Y0 cross-sectional view of FIG.

  The pixel 20 has an active region 41 surrounded by a thick line in FIG. Inside the active region 41, an N-type photodiode PD, an N-type floating diffusion FD, and a transfer transistor Ta that transfers charges from the photodiode PD to the floating diffusion FD in the Y-axis direction are provided.

  As shown in FIG. 4B, the image sensor 30 has an epitaxial layer formed on a semiconductor substrate, and a P-type well formed on the epitaxial layer. The photodiode PD is formed by injecting an N-type impurity into a P-type well. A P-type surface layer 42 is formed on the N-type photodiode PD. The P-type impurity concentration of the surface layer 42 is higher than that of the P-type well. The surface layer 42 prevents a dark current from flowing into the photodiode PD from a crystal dangling bond (tangling bond) existing on the semiconductor surface.

  As shown in FIGS. 4A and 4B, an isolation region 43 made of an oxide film is formed around the active region 41, and the plurality of pixels 20 are electrically isolated. In FIG. 4A, the boundary between the separation region 43 and the active region 41 is represented by a thick line. The isolation region 43 by the oxide film is an insulator, and the boundary between the isolation region 43 and the active region 41 may cause a dark current to flow into the photodiode PD.

  In order to suppress the dark current from flowing into the photodiode PD from the boundary between the isolation region 43 and the active region 41, a part of the boundary between the isolation region 43 and the active region 41 is located near the photodiode PD. Except for this, a P-type guard layer 44 is implanted.

  Of the boundary between the isolation region 43 and the active region 41, the guard layer 44 is not injected in the boundary near the photodiode PD, for example, in the vicinity of the transfer transistor Ta. In the vicinity of the transfer transistor Ta, the guard layer 44 is not implanted in order to prevent charge transfer failure.

  Further, the guard layer 44 is not injected into a part of the boundary between the isolation region 43 and the active region 41 in the vicinity of the second end 52 facing the first end 51 of the photodiode PD connected to the transfer transistor Ta. . The boundary portion where the guard layer 44 is not implanted near the second end 52 is provided at a position facing the connection portion where the photodiode PD is connected to the transfer transistor Ta at the first end 51.

  The ability of the guard layer 44 to suppress dark current increases as the width A1 of the guard layer 44 injected from the boundary between the isolation region 43 and the active region 41 toward the active region 41 increases. When the alignment is shifted in the Y-axis direction (transfer direction) when the guard layer 44 is implanted, the overall width A0 of the guard layer 44 does not change, but the guard layer 44 implanted from the boundary toward the active region 41 side. The width A1 varies.

  In the cross section Y1-Y1 shown in FIG. 4A, the guard layer 44 includes the boundary between the isolation region 43 and the active region 41 on the first end 51 side and the second end 52 side of the photodiode PD. Are provided at both boundaries. If the alignment is shifted by ΔA in the Y-axis direction when the guard layer 44 is implanted, the width A1 of the guard layer 44 on either the first end 51 side boundary or the second end 52 side boundary of the photodiode PD. Decreases by ΔA, and the width A1 of the other guard layer 44 increases by ΔA. In other words, when the alignment is shifted in the Y-axis direction when the guard layer 44 is injected, the dark current flowing from one of the boundary on the first end 51 side and the boundary on the second end 52 side of the photodiode PD is The dark current flowing from the other increases and decreases. That is, the total of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side in the cross section Y1-Y1 is the same as that when the guard layer 44 is injected. It does not change due to misalignment in the Y-axis direction.

  In the cross section Y2-Y2 shown in FIG. 4A, the guard layer 44 is not located on the boundary between the isolation region 43 and the active region 41 on the first end 51 side of the photodiode PD. It is provided at the boundary on the end 52 side. The dark current flowing from the boundary on the first end 51 side of the photodiode PD changes due to the misalignment in the Y-axis direction when the guard layer 44 is injected because the guard layer 44 is not present on the boundary on the first end 51 side. do not do. The dark current that flows from the boundary of the photodiode PD on the second end 52 side changes due to a misalignment in the Y-axis direction when the guard layer 44 is injected. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side in the cross section Y2-Y2 is the same as that when the guard layer 44 is injected. Changes due to misalignment in the Y-axis direction.

  In the cross section Y0-Y0, the boundary between the active region 41 and the isolation region 43 does not exist in the vicinity of the first end 51 of the photodiode PD. That is, in the cross section Y0-Y0, no dark current flows into the photodiode PD from the first end 51 side of the photodiode PD. Of the boundary between the isolation region 43 and the active region 41, the guard layer 44 is not provided at the boundary on the second end 52 side of the photodiode PD. That is, in the cross section Y0-Y0, the dark current flowing from the second end 52 side of the photodiode PD does not change due to the misalignment in the Y-axis direction. Therefore, the total dark current flowing into the photodiode PD in the cross section Y0-Y0 does not change due to the misalignment in the Y-axis direction when the guard layer 44 is injected.

  Conventionally, the guard layer 44 is implanted in the vicinity of the second end 52 as shown in the enlarged pixel plan view shown in FIG. That is, like the cross section Y3-Y3 in FIG. 5A, there is no portion where the guard layer 44 is not provided at the boundary on the second end 52 side of the photodiode PD.

  The cross section Y4-Y4 shown in FIG. 5A is the same as the cross section Y1-Y1 shown in FIG. The cross section Y5-Y5 is the same as the cross section Y2-Y2 shown in FIG. That is, when the alignment is shifted in the Y-axis direction when the guard layer 44 is injected, the sum of the dark current flowing from the boundary on the first end 51 side and the dark current flowing from the boundary on the second end 52 side is: The section Y4-Y4 does not change, and the section Y5-Y5 changes.

  A cross section Y3-Y3 of the conventional solid-state imaging device is different from the cross section Y0-Y0 of the image sensor 30 shown in FIG. 4A and is the same as the cross section Y2-Y2. That is, in the cross section Y3-Y3, when the alignment is shifted in the Y-axis direction when the guard layer 44 is injected, the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the second end 52 side The total of the dark current flowing from the boundary of the first and second currents changes due to the misalignment in the Y-axis direction when the guard layer 44 is injected.

  FIG. 5B is a Y3-Y3 cross-sectional view of FIG. 4B is different from FIG. 4B in that a P-type guard layer 44 is implanted between the isolation region 43 and the photodiode PD.

According to the image sensor 30 according to the first embodiment of the present invention shown in FIGS. 4A and 4B, compared with the conventional solid-state imaging device shown in FIGS. The following effects can be obtained.
In the image sensor 30 according to the first embodiment of the present invention, the guard layer 44 is not injected into a part in the vicinity of the second end 52, as shown in a cross section Y3-Y3 in FIG. When the guard layer 44 is injected, the number of locations where the total dark current changes due to the misalignment in the Y-axis direction can be reduced, and the change in the total amount of dark current due to the misalignment can be reduced.

(Second Embodiment)
FIG. 6A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the second embodiment of the present invention. In FIG. 6A, two pixels 20 arranged side by side on the imaging surface of the image sensor 30 are shown side by side. FIG. 6B is a sectional view taken along the line Y6-Y6 of FIG.

  Compared with the first embodiment, the pixel 20 of the image sensor 30 according to the second embodiment has a larger area where the guard layer 44 provided near the second end 52 is not implanted. Different. Specifically, the length B1 of the region where the guard layer 44 provided near the second end 52 is not implanted is the same as the length B0 of the region where the guard layer 44 provided near the transfer transistor Ta is not implanted. To do.

  By enlarging the region where the guard layer 44 provided in the vicinity of the second end 52 is not implanted, the guard layer 44 is provided only in the vicinity of the second end 52 as shown in the section Y2-Y2 of FIG. There are no parts. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is misalignment in the Y-axis direction when the guard layer 44 is injected. The part which changes with is gone.

  A cross section Y7-Y7 shown in FIG. 6A is the same as the cross section Y1-Y1 shown in FIG. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is the alignment in the Y-axis direction when the guard layer 44 is injected. It does not change due to deviation.

  In the cross section Y8-Y8 shown in FIG. 6A, the guard layer 44 has a boundary between the first end 51 side and the second end 52 side of the photodiode PD among the boundaries between the isolation region 43 and the active region 41. Not provided for both. Therefore, both the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side are caused by misalignment in the Y-axis direction when the guard layer 44 is injected. It does not change. Therefore, in the cross section Y8-Y8, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is the same as when the guard layer 44 is injected. It does not change due to misalignment in the Y-axis direction.

  The cross section Y6-Y6 shown in FIG. 6A is the same as the cross section Y0-Y0 shown in FIG. That is, no dark current flows from the first end 51 side of the photodiode PD, and the dark current flowing from the second end 52 side does not change due to misalignment in the Y-axis direction. Therefore, the total dark current flowing into the photodiode PD in the cross section Y6-Y6 does not change due to the misalignment in the Y-axis direction when the guard layer 44 is injected.

  Note that the magnitude of the dark current itself flowing into the photodiode PD from the boundary on the second end 52 side of the photodiode PD is larger than that in the region where the guard layer 44 is not injected, so that the image sensor 30 in the first embodiment. To increase. In the design stage of the image sensor 30, in consideration of both the total amount of dark current and the change in the total amount of dark current due to misalignment in the Y-axis direction when the guard layer 44 is injected, It is preferable to determine the length B1 of the region where the provided guard layer 44 is not implanted.

According to the image sensor 30 according to the second embodiment of the present invention shown in FIGS. 6 (a) and 6 (b), compared with the first embodiment shown in FIGS. 4 (a) and 4 (b). The following effects can be obtained.
In the image sensor 30 according to the second embodiment of the present invention, the region where the guard layer 44 provided in the vicinity of the second end 52 is not implanted is enlarged as compared with the first embodiment, so that FIG. As shown in the cross section Y2-Y2 of a), the number of locations where the total dark current changes due to misalignment in the Y-axis direction when the guard layer 44 is implanted is reduced, and the change in the total dark current due to the misalignment is further reduced. be able to.

(Third embodiment)
FIG. 7A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the third embodiment of the present invention. FIG. 7A shows two pixels 20 arranged side by side on the imaging surface of the image sensor 30. FIG. 7B is a cross-sectional view taken along the line Y9-Y9 in FIG.

  In each pixel 20 of the image sensor 30 according to the third embodiment, each active region 41 extends from a part on the second end 52 side of the photodiode PD to the floating diffusion FD of the pixel 20 adjacent to each pixel 20. There are different points. In other words, as apparent from FIG. 7A, in the image sensor 30 according to the third embodiment, the active regions 41 of the pixels 20 arranged side by side in the Y-axis direction are integrated. Hereinafter, the partial region 61 of the active region 41 extending from a part of the photodiode PD of each pixel 20 on the second end 52 side to the pixel 20 adjacent to each pixel 20 is referred to as a non-separation region 61.

  In FIG. 7A, the non-isolation region 61 is a part of a P-type well. The non-isolation region 61 extends from the position on the second end 52 facing the connecting portion between the photodiode PD provided at the first end 51 and the transfer transistor Ta toward the adjacent pixel.

  The non-separation region 61 physically connects the active regions 41 between the pixels 20 adjacent to each other in the Y-axis direction, but electrically separates the two pixels 20. Note that the performance of the non-isolation region 61 to electrically separate the two pixels 20 is inferior to an insulator such as the isolation region 43.

  Since the boundary between the second end 52 of the photodiode PD and the non-isolation region 61 is not the boundary between the active region 41 and the isolation region 43, the guard layer 44 is not provided.

  A cross section Y10-Y10 shown in FIG. 7A is the same as the cross section Y1-Y1 shown in FIG. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is the alignment in the Y-axis direction when the guard layer 44 is injected. It does not change due to deviation.

  The cross section Y11-Y11 is the same as the cross section Y2-Y2 shown in FIG. That is, in the cross section Y11-Y11, when the alignment is shifted in the Y-axis direction when the guard layer 44 is injected, the dark current flowing from the boundary on the first end 51 side and the dark current flowing from the boundary on the second end 52 side are included. The sum with the current varies.

  The cross section Y9-Y9 is different from the cross section Y0-Y0 of the image sensor 30 shown in FIG. 4A, and the active region 41 and the isolation region are provided at both the first end 51 and the second end 52 of the photodiode PD. No boundary with 43 exists. That is, no dark current flows into the photodiode PD in the cross section Y9-Y9.

  In the cross section Y12-Y12, dark current does not flow into the photodiode PD from the boundary on the first end 51 side of the photodiode PD, and dark current flowing from the second end 52 side of the photodiode PD does not align in the Y-axis direction. Changes due to deviation. Therefore, the total dark current flowing into the photodiode PD in the cross section Y12-Y12 changes due to the misalignment in the Y-axis direction when the guard layer 44 is injected.

According to the image sensor 30 according to the third embodiment of the present invention shown in FIGS. 7A and 7B, compared with the first embodiment shown in FIGS. 4A and 4B. The following effects can be obtained.
The image sensor 30 according to the third embodiment includes a non-separation region 61 extending from a position on the second end 52 facing the connection portion connected to the transfer transistor Ta toward an adjacent pixel. Since the image sensor 30 according to the third embodiment has the non-isolation region 61, the total amount of dark current flowing into the photodiode PD from the second end 52 side of the photodiode PD is larger than that in the first embodiment. Can be reduced.
Further, in the image sensor 30 according to the third embodiment, by preventing the guard layer 44 from being injected into the region where the non-separation region 61 is provided in the vicinity of the second end 52, as shown in FIG. As shown in the cross section Y3-Y3, it is possible to reduce the number of places where the total dark current changes due to misalignment in the Y-axis direction when the guard layer 44 is implanted, and to reduce the change in the total dark current due to the misalignment.

(Fourth embodiment)
FIG. 8A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the fourth embodiment of the present invention. FIG. 8A shows two pixels 20 arranged side by side on the imaging surface of the image sensor 30. FIG. 8B is a Y13-Y13 cross-sectional view of FIG.

  The pixel 20 of the image sensor 30 according to the fourth embodiment increases the length C1 of the non-separation region 61 as compared to the third embodiment. Specifically, the length C1 of the non-isolation region 61 is the same as the gate width W of the transfer transistor Ta.

  By extending the length C1 of the non-isolation region 61 to the gate width W of the transfer transistor Ta, the guard layer 44 is provided only in the vicinity of the second end 52 as in the cross section Y11-Y11 of FIG. Eliminate the place. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is misalignment in the Y-axis direction when the guard layer 44 is injected. The place which changes with is eliminated.

  A cross section Y14-Y14 shown in FIG. 8A is the same as the cross section Y1-Y1 shown in FIG. The section Y15-Y15 is the same as the section Y2-Y2 shown in FIG. That is, when the alignment is shifted in the Y-axis direction when the guard layer 44 is injected, the sum of the dark current flowing from the boundary on the first end 51 side and the dark current flowing from the boundary on the second end 52 side is: The cross section Y14-Y14 does not change, and the cross section Y15-Y15 changes.

  A cross section Y13-Y13 shown in FIG. 8A is the same as the cross section Y9-Y9 shown in FIG. That is, dark current does not flow into the photodiode PD in the cross section Y13-Y13.

  A cross section Y16-Y16 shown in FIG. 8A is different from the cross section Y12-Y12 shown in FIG. 7A, and is the same as the cross section Y9-Y9 shown in FIG. That is, dark current does not flow into the photodiode PD even in the cross section Y13-Y13.

According to the image sensor 30 according to the fourth embodiment of the present invention shown in FIGS. 8A and 8B, compared with the third embodiment shown in FIGS. 7A and 7B. The following effects can be obtained.
The image sensor 30 according to the fourth embodiment expands the length C1 of the non-separation region 61 as compared with the third embodiment, so that a guard layer as shown in a cross-section Y12-Y12 in FIG. It is possible to reduce the number of locations where the dark current flowing into the photodiode PD changes due to the misalignment in the Y-axis direction when implanting 44, and further reduce the change in the total amount of dark current due to the misalignment.

(Fifth embodiment)
FIG. 9A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the fifth embodiment of the present invention. In FIG. 9A, two pixels 20 arranged side by side on the imaging surface of the image sensor 30 are shown side by side. FIG. 9B is a sectional view taken along line Y17-Y17 in FIG.

  The fifth embodiment is a combination of the second embodiment and the fourth embodiment. That is, the fifth embodiment is different from the fourth embodiment in that the length B1 of the region where the guard layer 44 provided in the vicinity of the second end 52 of the photodiode PD is not implanted is set to the length of the transfer transistor Ta. This is the same as the length B0 of the region where the guard layer 44 provided in the vicinity is not implanted.

  A cross section Y18-Y18 shown in FIG. 9A is the same as the cross section Y1-Y1 shown in FIG. That is, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is the alignment in the Y-axis direction when the guard layer 44 is injected. It does not change due to deviation.

  In the cross section Y19-Y19 shown in FIG. 9A, the guard layer 44 is the boundary between the first end 51 side and the second end 52 side of the photodiode PD among the boundaries between the isolation region 43 and the active region 41. Not provided for both. Therefore, both the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side are caused by misalignment in the Y-axis direction when the guard layer 44 is injected. It does not change. Therefore, in the cross section Y19-Y19, the sum of the dark current flowing from the boundary on the first end 51 side of the photodiode PD and the dark current flowing from the boundary on the second end 52 side is the same as when the guard layer 44 is injected. It does not change due to misalignment in the Y-axis direction.

  The cross section Y17-Y17 and the cross section Y20-Y20 shown in FIG. 9A are the same as the cross section Y13-Y13 shown in FIG. That is, no dark current flows into the photodiode PD in the cross sections Y17-Y17 and Y20-Y20.

According to the image sensor 30 according to the fifth embodiment of the present invention shown in FIGS. 9A and 9B, as compared with the fourth embodiment shown in FIGS. 8A and 8B. The following effects can be obtained.
In the image sensor 30 according to the second embodiment of the present invention, an area where the guard layer 44 provided in the vicinity of the second end 52 is not implanted is enlarged as compared with the fourth embodiment, so that FIG. As in the cross section Y15-Y15 in a), the number of places where the total dark current changes due to the misalignment in the Y-axis direction when the guard layer 44 is implanted is reduced, and the change in the total dark current due to the misalignment is the fourth. This can be further reduced than in the embodiment.

(Sixth embodiment)
FIG. 10A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the sixth embodiment of the present invention. FIG. 10A shows two pixels 20 arranged side by side on the imaging surface of the image sensor 30. FIG. 10B is a Y21-Y21 cross-sectional view of FIG.

  In the pixel 20 of the image sensor 30 according to the sixth embodiment, a P-type impurity layer 62 is formed by injecting a P-type impurity into the non-isolation region 61. The P-type implantation layer 62 has a higher impurity concentration than the P-type well, and has a higher performance of electrically separating the two pixels 20 than the P-type well.

According to the image sensor 30 according to the sixth embodiment of the present invention shown in FIGS. 10A and 10B, the following operational effects can be obtained as compared with the third to fifth embodiments.
When the image sensor 30 is downsized or the pixel density is increased, it is conceivable to shorten the distance between the photodiode PD and the floating diffusion FD that face each other with the non-isolation region 61 interposed therebetween. If the distance between the photodiode PD and the floating diffusion FD, both of which are N-type conductivity, is shortened, the probability that an unexpected leakage current flows between the photodiode PD and the floating diffusion FD increases. Providing a P-type injection layer 62 having a higher impurity concentration than the P-type well in the non-isolation region 61 reduces the probability of occurrence of a leak current between the photodiode PD and the floating diffusion FD that face each other across the non-isolation region 61. can do.

(Seventh embodiment)
FIG. 11A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the seventh embodiment of the present invention. FIG. 11A shows two pixels 20 arranged side by side on the imaging surface of the image sensor 30. FIG.11 (b) is Y22-Y22 sectional drawing of Fig.11 (a).

  In the pixel 20 of the image sensor 30 according to the seventh embodiment, the surface layer 42 formed on the photodiode PD is extended to the non-separation region 61. The surface layer 42 on the non-isolation region 61 prevents inflow of dark current from the dangling bonds (tangling bonds) existing on the semiconductor surface of the non-isolation region 61 to the photodiode PD and sandwiches the non-isolation region 61 therebetween. Thus, the probability of occurrence of leakage current between the photodiode PD and the floating diffusion FD facing each other can be reduced.

(Eighth embodiment)
FIG. 12A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the eighth embodiment of the present invention. In FIG. 12A, two pixels 20 arranged side by side on the imaging surface of the image sensor 30 are shown side by side. FIG. 12B is a Y23-Y23 cross-sectional view of FIG.

  The eighth embodiment is a combination of the fifth embodiment and the sixth embodiment. That is, in the eighth embodiment, the P-type injection layer 62 is provided in the non-isolation region 61 of the fifth embodiment. By doing so, the change in the total amount of dark current due to the misalignment in the Y-axis direction when the guard layer 44 is injected can be reduced as in the fifth embodiment, and the non-separation region 61 can be reduced. As in the sixth embodiment, it is possible to reduce the probability of occurrence of leakage current between the photodiode PD facing each other and the floating diffusion FD.

(Ninth embodiment)
FIG. 13A is an enlarged pixel plan view of the pixel 20 of the image sensor 30 according to the ninth embodiment of the present invention. FIG. 13A shows two pixels 20 arranged side by side on the imaging surface of the image sensor 30. FIG.13 (b) is Y24-Y24 sectional drawing of Fig.13 (a).

  In the image sensor 30 according to the ninth embodiment, the shape of the photodiode PD in the fifth embodiment is symmetric (laterally symmetric) in the Y-axis direction, and the position of the photodiode PD in the active region 41. Has changed. Specifically, the X-axis dimension D1 from the boundary on the first end 51 side to the first end 51 of the photodiode PD and the X-axis dimension D2 from the boundary on the second end 52 side to the second end 52 are the same. A photodiode PD is provided at the position. By doing so, it is possible to reduce the change in the total amount of dark current due to the misalignment in the Y-axis direction when the photodiode PD is injected.

  The embodiment described above can be implemented with the following modifications.

(Modification 1)
In each of the above embodiments, the pixel 20 of the image sensor 30 includes the transfer transistor Ta, the amplification transistor Tb, the reset transistor Tc, and the selection transistor Td. However, one or a plurality of transistors may be shared among a plurality of pixels. FIG. 14 shows an equivalent circuit diagram in the case where the amplification transistor Tb, the reset transistor Tc, and the selection transistor Td are shared by two pixels.

(Modification 2)
In each of the above embodiments, the pixel 20 of the image sensor 30 has the floating diffusion FD. However, the floating diffusion FD may be shared by a plurality of pixels. For example, the transfer transistors Ta of two pixels may be disposed facing each other, a floating diffusion FD may be disposed between the two transfer transistors Ta, and the floating diffusion FD may be shared between the two pixels. .

  As long as the characteristics of the present invention are not impaired, the present invention is not limited to the above-described embodiments, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. .

1: electronic camera, 3: solid-state imaging device, 20: pixel, 30: image sensor, 31: non-separation region, 41: active region, 42: surface layer, 43: separation region, 44: guard layer, 51: first End 52: Second end 61: Non-isolation region 62: P-type injection layer

Claims (9)

A plurality of pixels are two-dimensionally arranged on the imaging surface,
For each of the plurality of pixels,
An active region provided with a photoelectric conversion unit that accumulates signal charges according to the amount of incident light, a charge detection unit that detects the signal charges, and a transfer transistor that transfers the signal charges from the photoelectric conversion unit to the charge detection unit When,
An isolation region formed around the active region;
A guard layer provided at a part of the periphery of the photoelectric conversion unit and formed at a boundary between the active region and the separation region;
The photoelectric conversion unit is connected to the transfer transistor at a first end,
The said guard layer is not formed in a part of periphery of the 2nd end of the said photoelectric conversion part facing the said 1st end among the said boundary parts, The solid-state image sensor characterized by the above-mentioned. The solid-state imaging device according to claim 1,
The length of the first end side where the guard layer is not formed in the periphery of the photoelectric conversion unit is equal to the length of the second end side where the guard layer is not formed. The solid-state imaging device according to claim 1 or 2,
The active region of each of the plurality of pixels has a non-separation region extending from a part of the second end of the pixel to the active region of a pixel adjacent to the pixel. . The solid-state imaging device according to claim 3,
A solid-state imaging device, wherein a width in a direction orthogonal to an extending direction and a depth direction of the non-isolation region is equal to a width of the photoelectric conversion unit and the transfer transistor. The solid-state imaging device according to claim 3 or 4,
The solid-state imaging device, wherein the non-isolation region has a separate injection layer of the same conductivity type as the guard layer. The solid-state imaging device according to claim 3 or 4,
The same conductivity type as the guard layer, further comprising a surface layer formed on the photoelectric conversion portion,
The surface layer is also formed on the non-separation region. The solid-state imaging device according to claim 3,
A solid-state imaging device, wherein a width of the non-isolation region in a direction perpendicular to the extending direction and the depth direction is equal to a width of a connection portion between the photoelectric conversion unit and the transfer transistor. The solid-state imaging device according to any one of claims 1 to 7,
The solid-state imaging device, wherein a distance from the first end to the boundary portion on the first end side is the same as a distance from the second end to the boundary portion on the second end side.   An imaging device comprising the solid-state imaging device according to claim 1.

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