GLOBAL-SHUTTER IMAGE SENSOR

Abstract

A global shutter image sensor of a back-illuminated type includes a semiconductor substrate and pixels. Each pixel includes a photosensitive area, a storage area, a readout area and areas for transferring charges between these different areas. The image sensor includes, for each pixel, a protector extending at least partly into the substrate from the back of the substrate to ensure that the storage area is protected against back illumination.

Claims

1-11. (canceled)

12. A back-illuminated image sensor comprising: a semiconductor substrate; a plurality of pixels in said semiconductor substrate, each pixel comprising a photosensitive area, a storage area, a readout area, areas for transferring charges between said photosensitive, storage and readout areas, and a protector extending at least partly into said substrate from a back of said substrate and configured to protect said storage area against back illumination.

13. The back-illuminated image sensor according to claim 12, wherein each pixel further comprises spaced apart first and second insulated vertical electrodes which extend from a front of said substrate to at least partially delimit said storage area, said first electrode including a space corresponding to a first area for transferring charges between said photosensitive area and said storage area.

14. The back-illuminated image sensor according to claim 12, wherein said protector comprises a single capacitive insulation trench that extends from a back of said substrate toward said first and second insulated vertical electrodes to cover said storage area.

15. The back-illuminated image sensor according to claim 12, wherein said protector comprises: spaced apart first and second capacitive insulation trenches which extend into said substrate from a back of said substrate, respectively opposite said first and second vertical electrodes; and a screen extending on the back of said substrate between said spaced apart first and second capacitive insulation trenches to cover said storage area.

16. The back-illuminated image sensor according to claim 12, wherein said protector non-electrically contacts said first and second insulated vertical electrodes.

17. The back-illuminated image sensor according to claim 12, wherein said protector comprises: spaced apart first and second capacitive insulation trenches extending into said substrate from a back of said substrate to at least partially delimit said storage area and forming, in said storage area, spaced apart first and second insulated vertical electrodes; said first insulated vertical electrode including a space corresponding to a first area for transferring charges between said photosensitive area and said storage area; and said protector comprising a screen extending on the back of said substrate between said first and one second capacitive insulation trenches to cover said storage area.

18. The back-illuminated image sensor according to claim 17, wherein said first and second capacitive insulation trenches extend from the back of said substrate to the front of said substrate.

19. The back-illuminated image sensor according to claim 17, wherein said substrate comprises on the front thereof, for each pixel, spaced apart implanted areas; and wherein said first and second capacitive insulation trenches extend from the back of said substrate to said spaced apart implanted areas.

20. The back-illuminated image sensor according to claim 12, wherein said protector comprises metal.

21. The back-illuminated image sensor according to claim 12, further comprising a control circuit configured to apply control signals to said first and second insulated vertical electrodes.

22. The back-illuminated image sensor according to claim 12, wherein said semiconductor substrate and said plurality of pixels in said semiconductor are configured so that the back-illuminated image sensor is a back-illuminated global shutter image sensor.

23. A three-dimensional integrated structure comprising: a first electronic chip comprising a back-illuminated image sensor comprising a semiconductor substrate, a plurality of pixels in said semiconductor substrate, each pixel comprising a photosensitive area, a storage area, a readout area, areas for transferring charges between said photosensitive, storage and readout areas, and a protector extending at least partly into said substrate from a back of said substrate and configured to protect said storage area against back illumination; and a second electronic chip comprising a control circuit for applying control signals to said back-illuminated global shutter image sensor; said first and second chips joined together.

24. The three-dimensional integrated structure according to claim 23, wherein said first and second chips are joined together via hybrid bonding, with the hybrid bonding comprising at least one of metal-metal and insulator-insulator type bonding.

25. The three-dimensional integrated structure according to claim 23, wherein each pixel further comprises spaced apart first and second insulated vertical electrodes which extend from a front of said substrate to at least partially delimit said storage area, said first electrode including a space corresponding to a first area for transferring charges between said photosensitive area and said storage area.

26. The three-dimensional integrated structure according to claim 25, wherein said protector comprises a single capacitive insulation trench that extends from a back of said substrate toward said first and second insulated vertical electrodes to cover said storage area.

27. The three-dimensional integrated structure according to claim 25, wherein said protector comprises: spaced apart first and second capacitive insulation trenches which extend into said substrate from a back of said substrate, respectively opposite said first and second vertical electrodes; and a screen extending on the back of said substrate between said spaced apart first and second capacitive insulation trenches to cover said storage area.

28. The three-dimensional integrated structure according to claim 25, wherein said protector non-electrically contacts said first and second insulated vertical electrodes.

29. The three-dimensional integrated structure according to claim 23, wherein said protector comprises: spaced apart first and second capacitive insulation trenches extending into said substrate from a back of said substrate to at least partially delimit said storage area and forming, in said storage area, spaced apart first and second insulated vertical electrodes; said first insulated vertical electrode including a space corresponding to a first area for transferring charges between said photosensitive area and said storage area; and said protector comprising a screen extending on the back of said substrate between said first and one second capacitive insulation trenches to cover said storage area.

30. The three-dimensional integrated structure according to claim 29, wherein said first and second capacitive insulation trenches extend from the back of said substrate to the front of said substrate.

31. The three-dimensional integrated structure according to claim 29, wherein said substrate comprises on the front thereof, for each pixel, spaced apart implanted areas; and wherein said first and second capacitive insulation trenches extend from the back of said substrate to said spaced apart implanted areas.

32. A method for protecting an image sensor from back-illumination, the global shutter image sensor comprising a semiconductor substrate, a plurality of pixels in the semiconductor substrate, with each pixel comprising a photosensitive area, a storage area, a readout area, and areas for transferring charges between the photosensitive, storage and readout areas, the method comprising: forming a protector that extends at least partly into the substrate from a back of the substrate to protect the storage area against back illumination.

33. The method according to claim 32, wherein each pixel further comprises spaced apart first and second insulated vertical electrodes which extend from a front of the substrate to at least partially delimit the storage area, the first electrode including a space corresponding to a first area for transferring charges between the photosensitive area and the storage area.

34. The method according to claim 33, wherein forming the protector comprises forming a single capacitive insulation trench that extends from a back of the substrate toward the first and second insulated vertical electrodes to cover the storage area.

35. The method according to claim 33, wherein forming the protector comprises: forming spaced apart first and second capacitive insulation trenches which extend into the substrate from a back of the substrate, respectively opposite the first and second vertical electrodes; and forming a screen extending on the back of the substrate between the spaced apart first and second capacitive insulation trenches to cover the storage area.

36. The method according to claim 35, wherein the protector non-electrically contacts the first and second insulated vertical electrodes.

37. The method according to claim 32, wherein forming the protector comprises: forming spaced apart first and second capacitive insulation trenches extending into the substrate from a back of the substrate to at least partially delimit the storage area and forming, in the storage area, spaced apart first and second insulated vertical electrodes; the first insulated vertical electrode including a space corresponding to a first area for transferring charges between the photosensitive area and the storage area; and forming a screen extending on the back of the substrate between the first and one second capacitive insulation trenches to cover the storage area.

38. The method according to claim 37, wherein the first and second capacitive insulation trenches extend from the back of the substrate to the front of the substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other advantages and features of the invention will become apparent upon examining the detailed description of embodiments, which are in no way limiting, and the appended drawings, in which:

[0022] FIGS. 1 to 6 illustrate embodiments of the invention.

DETAILED DESCRIPTION

[0023] FIG. 1 is a cross-sectional representation of a global-illumination image sensor according to one embodiment. The image sensor CAP comprises a substrate 1 comprising a semiconductive region 100 with weak p-type doping.

[0024] The front FS of the substrate is surmounted (i.e., placed on top) by an interconnect region 2, commonly known to the person skilled in the art by the acronym BEOL (Back End Of Line). The interconnect region 2 is shown in part for the sake of simplification.

[0025] The substrate 1 furthermore comprises, on its back BS, an anti-reflective layer 3, surmounted by a layer 4 acting, as will be seen below, as a hardmask for the production of capacitive insulation trenches. The layer 4, for example, may be silicon nitride.

[0026] A pixel matrix has been produced in the substrate. Although the sensor comprises numerous pixels, only two identical and juxtaposed pixels P.sub.i and P.sub.i+1 have been shown here for the sake of simplification.

[0027] Each pixel comprises a photosensitive area 5 comprising the stack of the semiconductive region 100, a first region 6 with n-type doping and a layer 9 with p.sup.+-type doping, extending from the front of the substrate 1, forming a PNP photodiode. A storage area 8 is for storing charges, which is formed by the stack of the semiconductive region 100, of a second region 7 with n-type doping and of the layer 9. Each pixel also comprises a readout area 26, not shown in the sectional view of FIG. 1 but shown diagrammatically in FIG. 2.

[0028] FIG. 2 is a highly diagrammatic top view of an exemplary layout for a photodiode and a storage area. It should be noted that this is only an example and that any other layout is conceivable. A first space corresponding to a first transfer gate 11 is located between the photodiode and the storage area. A second space corresponding to a second transfer gate 23 is located between the storage area and the readout area.

[0029] The storage area 8 is delimited by a first insulated vertical electrode 10, a second insulated vertical electrode 12 and a third insulated vertical electrode 25 (not shown in FIG. 1 for the sake of simplification). Each of the electrodes 10, 12 and 25 extend into the substrate from its front.

[0030] In this example, the depths of the electrodes are greater than the depths of the first and second implanted regions 6 and 7. For example, the electrodes extend into the substrate to a depth of 4 micrometers. The photodiode 5 (photosensitive area) is, in this example, notably delimited by the first electrode 10 of the storage area of the pixel P.sub.i+1, and by the second electrode 12 of the pixel P.sub.i.

[0031] The first electrode 10 includes the space 11 which divides the first electrode 10 into two portions and which forms the first transfer gate. The third electrode 25 includes the space 23 which divides the third electrode 25 into two portions and which forms the second transfer gate.

[0032] The operation of such a sensor is briefly provided below. Initially, the substrate is fixed to a reference potential, for example, to ground, and the three electrodes 10, 12 and 25 to a potential below the reference potential. This causes an accumulation of holes along the walls of the electrodes, and thereby creates a potential barrier in the transfer area 11. The barrier blocks the exchanges of electrons between the photosensitive area 5 and the storage area 8. The barrier also creates a potential barrier in the transfer area 23 by blocking the exchanges of electrons between the storage area and the readout area. When the photodiode is illuminated, electron-hole pairs are photogenerated in the photodiode and the electrons are accumulated in the region 6.

[0033] Next, during a first transfer phase, the two portions of the first electrode 10 are polarized to the same first potential above the reference potential, for example, a potential of 2 volts. This causes the transfer of all of the accumulated electrons from the region 6 to the region 7 of the storage area 8, via the transfer gate 11. Once the transfer has been made, the first electrode 10 is once again polarized to the reference potential to keep the electrons in the region 7 of the storage area 8.

[0034] Then, during a second transfer phase, a second potential above the reference potential, for example, a potential of 2 volts, is applied to the two portions of the third electrode 25. This causes the transfer, via the transfer gate 23, of all of the stored electrons from the region 7 to the readout area 26. Here the value of the pixel will be read out by a readout circuit, which is not shown in the diagram for the sake of simplification.

[0035] In FIG. 1, the image sensor CAP is back illuminated. When the sensor is illuminated, the luminous flux FL therefore reaches the back BS of the substrate. Each storage area 8 should therefore be protected from the light to avoid unwanted signals as much as possible. Thus, in this example, each storage area 8 is protected from the light by protection means or protector MP.

[0036] In this embodiment, the protector MP for the pixel P.sub.i comprise a single capacitive insulation trench 13 which extends from the back of the substrate opposite the three electrodes 10, 12 and 25. This is to cover the storage areas and partially delimit the photodiodes 5 of the pixels P.sub.i and P.sub.i+1.

[0037] In this example, the walls of the capacitive insulation trenches 13 are covered by an insulating material 14, for example, silicon oxide. The trenches are filled with a metallic material 15, for example, copper.

[0038] It should be noted that not only does the capacitive insulation trench 13 totally cover the storage area 8, but it additionally touches the three electrodes 10, 12 and 25, yet without being in electrical contact therewith. This contact is made by the insulating material 14 of the capacitive insulation trench.

[0039] However, to avoid any risk of electrical contact during the production of the trenches, provision can be made to leave a space between the capacitive insulation trench 13 and the electrodes 10, 12 and 25. For example, a space of 0.4 micrometer may be left. The trench can, for example, extend into the substrate to a depth of 2 to 16 micrometers.

[0040] The capacitive insulation trench 13 is adapted to be polarized to a third potential below the reference potential, for example, 3 volts. This is notably to limit the dark current. The capacitive insulation trenches of the image sensor are passive, i.e., they do not act as transfer electrodes. However, they do form waveguides for infrared rays.

[0041] FIG. 3 illustrates an embodiment in which the protector MP for the pixel Pi comprises a first capacitive trench 16 extending from the back of the substrate 1 opposite the first electrode 10, a second capacitive insulation trench 17 extending from the back of the substrate 1 opposite the second electrode 12, and a third capacitive insulation trench, not shown in FIG. 3, extending from the back of the substrate 1 opposite the third insulated vertical electrode 25.

[0042] Each capacitive insulation trench extends into the substrate over a length of 2 to 16 micrometers and is in mechanical contact, without being in electrical contact, with the electrode facing it. Each capacitive insulation trench also comprises an insulating layer 14 of silicon oxide and a copper filling 15. Once again, it would be possible to leave a space on the order of 0.4 micrometers between each capacitive insulation trench and the electrode facing it.

[0043] The protector furthermore comprises an opaque screen 18, for example, metallic, which extends from the back of the substrate 1 to cover the storage area 8 completely. The screen 18 is in contact with the two capacitive insulation trenches 16 and 17, and with the third capacitive insulation trench.

[0044] The insulation trenches 16 and 17, the third insulation trench and the opaque screen may be produced during the same process step, for example, a process known as dual-damascene that is familiar to the person skilled in the art, and therefore comprises the same material. In this example, the trenches 16 and 17, as well as the opaque screen 18, comprise the same metal 15, such as copper, for example.

[0045] Once again, the capacitive insulation trenches 16 and 17 and the third capacitive insulation trench are adapted to be polarized to a potential below the reference potential, for example, 3 volts. This is notably in order to limit the dark current. Once again, the capacitive insulation trenches 16 and 17 form waveguides, notably for infrared rays.

[0046] FIG. 4 illustrates an embodiment in which the protector MP comprises the insulated vertical electrodes. In this embodiment, the protector MP for the pixel P.sub.i comprises a first capacitive trench 19, a second capacitive insulation trench 20, a third capacitive insulation trench, and an opaque protection screen 18.

[0047] The first capacitive trench 19 extends into the substrate from its back to its front. This is between the photosensitive area 5 and the storage area 8.

[0048] The second capacitive insulation trench 20 extends into the substrate from its back to its front. This is between the storage area 8 and the photosensitive area of the neighboring pixel.

[0049] The third capacitive insulation trench, not shown in FIG. 5, extends into the substrate from its back to its front, between the storage area 8 and the readout area 26. The three capacitive insulation trenches thereby delimit the storage area 8.

[0050] The opaque protection screen 18 extends on the back BS of the substrate between the two capacitive insulation trenches 19 and 20 to cover the storage area 8. The first capacitive insulation trench 19 includes a space in its lower part. This corresponds to the gate for transferring charges 11 between the photosensitive area 5 and the storage area 8.

[0051] The third capacitive insulation trench (not shown) also includes a space in its lower part. This corresponds to the gate for transferring charges 23 between the storage area 8 and the readout area 26. The first capacitive trench 19 and the third capacitive trench are active, i.e., they act as charge-transfer gates in their lower parts. The second capacitive insulation trench 20 is passive here.

[0052] According to another embodiment, illustrated in FIG. 5, the front of the substrate furthermore comprises localized implanted areas 24 located on both sides of each storage area 8. The capacitive insulation trenches each extend up to an implanted area 24. These implanted areas 24 can accommodate electronic components, for example, transistors.

[0053] To produce a sensor as described above, a semiconductor substrate is taken as the starting point. On its front the various implanted areas of the various pixels are produced, as well as the electrodes 10, 12 and 25 (FIGS. 1 and 3). Then the interconnect portion (BEOL) on the front of the substrate is produced.

[0054] Next, the substrate is turned over and the substrate is thinned from its back. Next, the protectors MP are produced by etching and filling with metal, according to one of the embodiments described previously and illustrated in FIGS. 1 to 5. In the case of FIGS. 4 and 5, the capacitive insulation trenches of the protectors MP also form the vertical electrodes.

[0055] FIG. 6 illustrates an embodiment in which an image sensor CAP according to the embodiment described previously and illustrated in FIG. 1 has been integrated in a three-dimensional integrated structure STR. The integrated structure STR comprises a first chip P1 comprising the sensor CAP, and a second chip P2 comprising a control logic circuit, for example.

[0056] The first chip P1 comprises a plurality of pixels P.sub.i, P.sub.i+1, P.sub.i+2, etc.. Each pixel comprises a photosensitive area 5 and a memory area 8 protected by the single capacitive insulation trench 13. The interconnect portion of the first chip P1 comprises first bonding pads BP1 which comprise copper and which extend from its front.

[0057] The second chip P2 comprises a semiconductor substrate 21, surmounted by an interconnect region 22. The interconnect region 22 of the second chip P2 comprises metal levels and vias which between them connect the various electronic components of the second chip P2, as well as bonding pads BP2 comprising copper located on its front.

[0058] The two chips P1 and P2 are joined to one another by hybrid bonding. The hybrid bonding may be metal-metal and insulator-insulator. The control circuit CC intended to control the sensor and notably to polarize the various electrodes is located in the substrate of the chip P2.

[0059] It would also be possible for the control circuit CC to be located partly in the chip P2 and partly in the chip P1, or even entirely in the chip P1. Similarly, the chip P2 could be a simple support, known to the person skilled in the art by the term interposer.

[0060] Although a three-dimensional integrated structure STR comprising an image sensor according to the embodiment described in FIG. 1 has been described, such a structure is compatible with the other embodiments described previously.

[0061] Furthermore, although capacitive insulation trenches comprising copper have been described, the embodiments described previously are compatible with any type of metal, notably tungsten. Tungsten can advantageously be used for filling trenches with a very large aspect ratio (i.e., the ratio of height to width).