Image sensor and its manufacturing process

Abstract

Image sensor and method of manufacturing the same The present description relates to an image sensor (60) comprising a semiconductor substrate (10) comprising a first face (10s), a porous layer (30), made of an electrically insulating and porous material, on the first face (10s), crossed by openings (34), a color filter (40) in each opening (34), a first moisture-proof protective layer (32) covering the porous layer (30) outside the openings (34), and a second moisture-proof protective layer (38) covering the first protective layer (32) and the walls of each opening (34), between the porous layer (30) and the color filter (40) present in the opening (34). Figure for abstract: Fig. 16

Description

Title of the invention: Image sensor and its manufacturing method Technical field

[0001] The present description relates generally to the field of image sensors and methods of manufacturing image sensors. Prior art

[0002] An image sensor generally comprises a plurality of photodetectors, for example photodiodes, integrated in and on a semiconductor substrate.

[0003] The focus here is more particularly on image sensors whose photodetectors are surmounted by colored filters or infrared filters. Each colored filter makes it possible to filter, according to the wavelength, the radiation which reaches the photodetector surmounted by the colored filter. The image sensor may comprise walls surrounding the colored filters in order to reduce optical crosstalk between the photodetectors. The walls may be partly metallic. However, the walls tend to absorb some of the incident photons. This leads to a drop in the optical efficiency of the image sensor, and this is all the more marked as the dimensions of the photodetectors and the colored filters are reduced.

[0004] It would be desirable to improve at least in part certain aspects of the known methods of manufacturing an image sensor comprising colored filters surrounded by walls. Summary of the invention

[0005] One embodiment overcomes all or part of the drawbacks of image sensors comprising colored filters surrounded by known walls.

[0006] One embodiment provides an image sensor comprising: - a semiconductor substrate comprising a first face; - a porous layer, made of an electrically insulating and porous material, on the first face, crossed by openings; - a colored filter in each opening; - a first layer of moisture-proof protection covering the porous layer outside the openings; and - a second layer of moisture-proof protection covering the first layer of protection and the walls of each opening, between the porous layer and the colored filter present in the opening.

[0007] According to one embodiment, the volume porosity of the porous material is between 35% and 55%.

[0008] According to one embodiment, the porous layer comprises a through groove completely surrounding the openings, the second protective layer covering the groove walls.

[0009] According to one embodiment, the image sensor further comprises: - a plurality of photodetectors in and on the semiconductor substrate, the colored filters covering the photodetectors; - a plurality of microlenses covering the colored filters; and - a third protective layer on the plurality of microlenses and on the first and second protective layers around the plurality of microlenses.

[0010] According to one embodiment, the semiconductor substrate comprises a second face opposite the first face and at least one hole extending from the first face to the second face, the image sensor further comprising an electrically conductive pad comprising a first portion extending on the first face and a second portion covering the sides of the hole and delimiting a gap in the hole.

[0011] According to one embodiment, the image sensor further comprises a guard ring and the electrically conductive pad is part of the guard ring.

[0012] According to one embodiment, the thickness of the porous layer is between 400 nm and 900 nm.

[0013] An embodiment also provides a method of manufacturing an image sensor comprising the following steps: a) forming a porous layer, made of an electrically insulating and porous material, on a first face of a semiconductor substrate; b) forming a first moisture-proof protective layer covering the porous layer; (c) forming openings passing through the first protective layer and the porous layer; (d) forming a second moisture-proof protective layer covering the first layer and the walls of each opening; and e) forming a colored filter in each opening, the second protective layer being located between the porous layer and the colored filter present in the opening.

[0014] According to one embodiment, the method further comprises, in step c), the formation of a through groove in the porous layer completely surrounding the openings, the second protective layer further covering in step d) the walls of the groove.

[0015] According to one embodiment, the method further comprises the following steps: - before step a), the formation of a plurality of photodetectors in and on the semiconductor substrate, the color filters being formed in step e) covering the photodetectors; - forming a plurality of microlenses covering the colored filters; and - forming a third protective layer on the plurality of microlenses and on the first and second protective layers around the plurality of microlenses.

[0016] According to one embodiment, the semiconductor substrate comprises a second face opposite the first face, the method further comprising the formation, before step a), of a hole extending from the first face to the second face and of an electrically conductive pad comprising a first portion extending on the first face and a second portion covering the sides of the hole and delimiting a gap in the hole.

[0017] According to one embodiment, the method further comprises, before step a), the formation of a resin block in the gap, the porous layer covering the electrically conductive pad and the resin block, and, after step e), the successive etching of the first protective layer, the second protective layer, and the porous layer to expose the electrically conductive pad and the resin block, and the removal of the resin block.

[0018] According to one embodiment, the method further comprises forming a guard ring, the electrically conductive pad forming part of the guard ring. Brief description of the drawings

[0019] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0020] [Fig.l], [Fig.2], [Fig.3], [Fig.4], [Fig.5], [Fig.7], [Fig.8], [Fig.9], [Fig.10], [Fig.11], [Fig.12], [Fig.13], [Fig.14], [Fig.15], and [Fig.16] are partial and schematic sectional views of structures obtained at the end of successive steps of an embodiment of a method for manufacturing an image sensor and [Fig.6] is a partial and schematic top view of the structure of [Fig.5];

[0021] [Fig. 17] is a partial and schematic sectional view of another embodiment of an image sensor; and

[0022] [Fig. 18] is a partial, schematic sectional view of an example of an image sensor. Description of the embodiments

[0023] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0024] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the realization of the photodetectors of the image sensors described, as well as their control circuits, has not been detailed, the production of these elements being within the reach of the person skilled in the art from the indications of the present description.

[0025] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0026] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0027] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%. Furthermore, the terms "insulator" and "conductor" are considered here to mean "electrically insulating" and "electrically conductive" respectively.

[0028] An embodiment of a method for manufacturing an electronic circuit corresponding to an image sensor will now be described. In general, this embodiment of the manufacturing method can be implemented for any type of electronic circuit comprising colored filters. In the remainder of the description, the refractive index of a material corresponds to the refractive index of the material for the wavelength range of the radiation captured by the image sensor. Unless otherwise indicated, the refractive index is considered substantially constant over the wavelength range of the radiation captured by the image sensor, for example equal to the average of the refractive index over the wavelength range of the radiation captured by the image sensor.

[0029] Figures 1 to 16 illustrate, in a partial and schematic manner, structures obtained at the end of successive steps of an embodiment of a method for manufacturing an image sensor.

[0030] More particularly, [Fig.l] corresponds to a starting structure comprising a semiconductor substrate 10, for example a silicon substrate, in which photodetectors 12 have been previously formed, five photodetectors 12 being shown in dotted lines in [Fig.l]. By way of example, the photodetectors 12 are photodiodes, for example, adapted to capture infrared, visible and / or ultraviolet radiation. By way of example, the photodetectors 12 are photodetectors produced in CMOS technology (from the English "Complementary Metal Oxide Semi-conductor"). According to one embodiment lization, the photodetectors 12 are arranged in rows and columns, the pitch between adjacent photodetectors being between 30 nm and 2 pm.

[0031] The substrate 10 comprises an upper face 10s and a lower face 10i, opposite the upper face 10s. A portion of the upper face 10s is covered by an insulating layer 14, itself covered by an opaque screen 16. An insulating layer 18 covers the opaque screen 16 and the remainder of the upper face 10s around the opaque screen 16. The substrate 10 is covered, on the side of the lower face 10i, by an interconnection structure 19, comprising a stack of insulating layers between which conductive tracks, not shown, extend and through which conductive vias, not shown, extend. According to one embodiment, the substrate 10 has a thickness of between 3 μm and 10 μm. The opaque screen 16 is intended, in operation, to block the light radiation received by the structure to protect electronic components present in the substrate 10 other than the photodetectors 12. The opaque screen 16 may be metallic.The opaque screen 16 may have a single-layer or multi-layer structure. For example, the opaque screen 16 may comprise a tungsten (W) layer and / or a titanium (TiN) layer. According to one embodiment, the opaque screen 16 has a thickness of between 150 nm and 400 nm. The insulating layer 14 and the insulating layer 18 may each be made of silicon oxide (SiO2) or silicon nitride (SiN). Similarly, a stack of anti-reflective materials may compose this layer. According to one embodiment, the insulating layer 14 has a thickness of between 50 nm and 250 nm. According to one embodiment, the insulating layer 18 has a thickness of between 100 nm and 550 nm.

[0032] In this example, the substrate 10 is intended to be illuminated by the upper face 10s. The starting structure further comprises one or more contact recovery pads 20, a single contact recovery pad 20 being shown in [Fig. 1]. According to one embodiment, the contact recovery pad 20 is electrically insulated from the substrate 10 by the insulating layer 18. The pads 20 are arranged out of line with the photodetectors 12 so as not to mask the photodetectors 12. For example, in top view, the photodetectors 12 are located in a central region of the substrate 10, and the pads 20 are located opposite a peripheral region of the substrate 10. According to one embodiment, the opaque screen 16 covers the photodetectors 12 as well as a portion of the face 10s of the substrate 10 between the photodetectors 12 and the pads 20.

[0033] Each contact recovery pad 20 comprises a contact area 20c which extends into a recess 22 provided in the upper face 10s of the substrate 10. The contact area 20c of each pad 20 is intended to be connected to an external device, for example by means of an electrically conductive wire, for example a metal wire. The substrate 10 comprises, for each pad 20, a through opening 24 which extends from the upper face 10s to the lower face 10i. The opening 24 opens into the depression 22. According to one embodiment, the upper face 10s is flat outside the depressions 22 and the through openings 24. According to one embodiment, the opening 24 has a cross section, seen in a direction perpendicular to the face 10s, which is substantially constant. For example, the cross section of the opening 24 is square or rectangular, in particular inscribed in a rectangle whose short side varies from 2 pm to 15 pm and whose long side varies from 10 pm to 50 pm. The contact recovery pad 20 comprises a junction portion 20j which extends into the through opening 24. By way of example, the junction portion 20j of the contact recovery pad 20 is connected to one or more metallization levels of the interconnection structure 19 arranged on the side of the lower face 10i of the substrate 10 by an opening 25 in the insulating layer 18. By way of example, the contact recovery pads 20 are made of a metallic material, for example aluminum.The junction portion 20j covers the sides of the opening 24. However, the opening 24 is not completely filled by the junction portion 20j so that a gap 26 filled with air, and opening onto the outside, remains in the opening 24. By way of example, the junction portion 20j has a thickness, measured relative to the sides of the opening 24, which is between 100 nm and 2 pm, and is for example equal to approximately 1 pm. By way of example, the depth of the gap 26 is between 2.5 pm and 15 pm, and is for example equal to approximately 6 pm.

[0034] By way of example, the contact pads 20 may be used for exchanging signals with the image sensor and / or for supplying power to the image sensor. According to another example, one of the contact pads 20 may be part of a protective structure such as a seal ring, in which case the pad may extend over the entire periphery of the image sensor.

[0035] [Fig. 2] illustrates the structure obtained at the end of a step of forming a resin block 28 in the gap 26 of each contact recovery pad 20. According to one embodiment, this step of forming the resin block 28 is carried out using specific developable resins known to those skilled in the art under the name “BSI fill” resin.

[0036] [Fig. 3] illustrates the structure obtained at the end of a step of forming a layer 30 of a material with a low refractive index on the insulating layer 18 outside the contact pads 20 and on the contact pads 20. According to one embodiment, the refractive index of the material constituting the layer 30 is in the range of 0.5 to 1.35. According to one embodiment, the thickness of the layer 30 is between 400 nm and 900 nm. According to one embodiment, the layer 30 is made of a porous material and is called a porous layer hereinafter. The porosity of a material is equal to the proportion by volume of the pores in a given volume of the material comprising both the solid part and the pores. According to one embodiment, the porosity of the layer 30 is in the range of 35% to 55%, preferably 40% to 50%, for example equal to approximately 45%. According to one embodiment, the pore size is equal to approximately 5 nm. According to one embodiment, the pores of the layer 30 are filled with voids or a gas mixture. According to one embodiment, the layer 30 comprises as essential constituent material at least one compound from silicon or carbon. The porous layer 30 may correspond to a simple oxide or a mixed oxide of at least one of the aforementioned elements. Preferably, the porous layer 30 is made of silicon oxide obtained by annealing above 200°C.

[0037] According to one embodiment, the porous layer 30 is formed either by a spin coating method, known to those skilled in the art as spin coating, followed by annealing or deposition of low permittivity oxide. According to one embodiment, the method for manufacturing the porous layer 30 comprises the deposition of a solution on the structure of [Fig. 2], for example by a spin coating technique, the solution comprising a precursor of the constituent material of the porous layer 30, in particular a hydrolyzable compound such as a silicon halide or alkoxide, in at least one solvent, in particular aqueous and / or alcoholic. The method then comprises the condensation of the precursor to form the solid material of the porous layer 30 and the removal of the solvent.

[0038] [Fig. 4] illustrates the structure obtained at the end of a step of forming a protective layer 32 on the porous layer 30. According to one embodiment, the thickness of the protective layer 32 is between 20 nm and 50 nm. According to one embodiment, the protective layer 32 is made of silicon oxide deposited at low temperature, for example at 150°C.

[0039] [Fig. 5] illustrates the structure obtained at the end of a step of forming openings 34 and a groove 36 through the protective layer 32, the porous layer 30, the insulating layer 18, and the opaque screen 16 and a portion of the layer 14. [Fig. 6] is a top view of the structure of [Fig. 5].

[0040] The openings 34 are formed directly above the photodetectors 12. For example, the openings 34 are distributed in rows and columns in the center of the structure. According to one embodiment, the groove 36 completely surrounds all of the openings 34. The contact pads 20, shown schematically in dotted lines in [Fig. 6], are located around the groove 36. According to one embodiment, the aspect ratio of each opening 34, corresponding to the ratio between the height and the width of the opening 34 is between 0.6 and 1.2. For example, the cross-section of each opening 34, in a direction perpendicular to the face 10s, is square or rectangular, in particular inscribed in a rectangle whose short side varies from 0.5 pm to 2 pm and whose long side varies from 1 pm to 10 pm. According to one embodiment, the width of the groove 36 is between 1 μm and 20 μm.

[0041] Preferably, the openings 34 and the groove 36 are made simultaneously. According to one embodiment, the openings 34 and the groove 36 are made by reactive ion etching, also called RIE (acronym for Reactive Ion Etching). The presence of the protective layer 32 allows the implementation of photolithography steps which could not be implemented directly on the porous layer 30 due to its high porosity. Similarly, this protective layer 32 has the advantage of allowing possible rework steps of the wafers in the successive photolithography steps. An advantage of this embodiment is the simultaneous etching of the layers 30 and 32 without altering the integrity of the pad 20.

[0042] [Fig.7] illustrates the structure obtained at the end of a step of forming a protective layer 38 on the protective layer 32 outside the openings 34 and the groove 36 and in each opening 34 and in the groove 36, the protective layer 38 covering the side walls of each opening 34 and the groove 36 and the bottom of each opening 34 and the groove 36. According to one embodiment, the thickness of the protective layer 38 is between 5 nm and 60 nm. The protective layer 38 is moisture-proof. According to one embodiment, the protective layer 38 is made of silicon oxide or aluminum oxide. Since the groove 36 completely surrounds the openings 34 and the protective layer 38 covers the porous layer 30, the walls of the groove 36, and the walls of each opening 34, the protective layer 38 prevents moisture from reaching the portion of the porous layer 30 in which the openings 34 are formed.In the absence of the groove 36, the walls of which are covered with the protective layer 38, moisture could penetrate into the part of the porous layer 30 in which the openings 34 are formed, in particular from the edge of the porous layer 30, and the presence of moisture would cause an increase and / or non-uniformity of the refractive index of the carrier layer 30. Similarly, the presence of moisture can cause reliability problems with the optical sensors.

[0043] [Fig. 8] illustrates the structure obtained at the end of a step of forming colored filters 40 in the openings 34. The colored filters 40 may correspond to blocks of colored resin. Colored filters 40 of different colors may be present. According to one embodiment, the colored filters 40 of the same type are formed by depositing a layer of photosensitive colored resin over the entire structure and in particular in the openings 34, exposing the colored resin layer to radiation, and removing the parts of the resin layer exposed to the radiation in the case of a positive photosensitive resin or not exposed to the radiation in the case of a negative photosensitive resin, to keep the colored resin blocks in the desired openings 34. These steps are repeated for each type of 40 colored filters.

[0044] [Fig. 9] illustrates the structure obtained at the end of a step of forming a resin layer 42 on the protective layer 38 and on the color filters 40. The resin layer 42 in particular completely fills the groove 36. The resin layer 42 has, for example, a thickness of between 0.6 μm and 4 μm, for example of the order of 4 μm. The resin of the layer 42 is, for example, a crosslinked resin which cannot be dissolved in the usual liquid solvents for developing and / or etching resins. The resin of the layer 42 is, for example, a non-photosensitive resin. By way of example, the resin of the layer 42 is chosen so that it can be crosslinked, for example by ultraviolet rays or from a certain temperature, for example, of the order of 200°C. For example, the resin of layer 42 is chosen so that it can be etched using an oxygen-based physical plasma.For example, the resin of layer 42 comprises a polymer, for example of the acrylic type.

[0045] [Fig. 10] illustrates the structure obtained at the end of a step of forming an etching mask 44 on the upper face of the resin layer 42. The mask 44 comprises structures in the form of microlenses, intended to be transferred into the resin layer 42 during a subsequent etching step, so as to form microlenses in the layer 42.

[0046] By way of example, the mask 44 is formed from a layer of photosensitive resin. The resin of the mask 44 is for example first deposited full plate, on and in contact with the upper face of the layer 42. At this stage, the resin of the mask 44 has for example a substantially uniform thickness over the entire surface of the structure. The deposition of the resin of the mask 44 can be done by a spin coating technique or by any other suitable deposition technique. The resin layer of the mask 44 is then structured, for example by photolithography, so as to form, opposite the photodetectors 12, separate resin pads 46. In this example, an individual resin pad 46 is provided opposite each photodetector 12 of the sensor. A finishing annealing is then carried out, during which the resin pads 46 deform to take the form of microlenses. After finishing, the resin pads 46 are, for example, separated.The embodiments described are however not limited to this particular case. The pads 46 have for example a thickness less than the thickness of the layer 42.

[0047] [Fig. 11] illustrates the structure obtained at the end of a physical etching step of the layer 42 and the mask 44, leading to the transfer of the pattern of the mask 44 into an upper part of the layer 42. The etching is for example stopped when all the resin of the mask 44 has been consumed.

[0048] Thus, in the structure illustrated in [Fig.l 1], the layer 42 comprises micro- lenses 48 opposite the photodetectors 12. For example, the microlenses 48 have a height of between 0.5 pm and 3 pm. At this stage, the connection pads 20 remain covered by the resin of the layer 42.

[0049] [Fig. 12] illustrates a device obtained at the end of a step of forming a masking layer 50 of resin on the upper face of the layer 42.

[0050] By way of example, the layer 50 is first deposited full plate on the upper face of the layer 42, for example in contact with the upper face of the layer 42. The layer 50 is then removed, for example by photolithography, opposite the pads 20, so as to expose the portion of the resin layer 42 coating the pads 20. The resin of the layer 50 is, for example, a photosensitive resin. By way of example, the layer 50 has a thickness greater than the maximum thickness of the layer 42. By way of example, the layer 50 has a thickness of between 4 μm and 10 μm, for example of the order of 6 μm.

[0051] [Fig. 13] illustrates the structure obtained at the end of a step of etching layer 42 through layer 50. During this step, layer 50 is used as an etching mask.

[0052] More particularly, during this step, the part of the layer 42 not covered by the layer 50 is removed so as to reveal the protective layer 38. The protective layer 38 can act as an etching stop layer.

[0053] According to one embodiment, the etching implemented during this step is a totally chemical, and therefore isotropic, plasma etching (a process sometimes referred to by the English terms "dry-stripping" or "dry-ashing"). This chemical etching is based on the use of free radicals generated by remote plasmas. This etching technique is usually used to remove, recycle or strip, full plate, resin layers. This technique is also sometimes used to carry out, full plate, chemical treatments on the exposed materials. It is proposed here to use it, in an unusual way, to carry out a localized etching of the resin layer 42 through the mask formed by the resin layer 50. This technique has the advantage of being less aggressive than a physical etching, and does not generate polymer fibers or filaments on the sides of the layer 42.

[0054] According to another embodiment, the etching carried out during this step is plasma etching by ion bombardment, also called reactive dry etching or spray etching. Such etching results in material removal by bombardment.

[0055] The etching plasma preferably comprises dioxygen, dinitrogen and dihydrogen. The plasma used during this etching step has, for example, a different composition from the plasma used during the etching leading to the formation of the microlenses 48. During the aforementioned step, the layers 50 and 42 are consumed simultaneously.

[0056] The aforementioned etching is stopped when the protective layer 38 is revealed. At this stage, a part of the layer 50 remains on the surface of the layer 42, in particular on the microlenses 48. The resin layer 42 has a lateral flank 51 inclined (not vertical) relative to the face 10s.

[0057] [Fig. 14] illustrates a device obtained at the end of a step of removing the remaining part of the layer 50 so as to release the upper face of the microlenses 48. This removal step is for example carried out by wet etching using a solvent, using an etching solution making it possible to selectively etch the material of the layer 50 relative to the material of the layer 42.

[0058] [Fig. 15] illustrates the structure obtained at the end of a step of depositing a protective layer 52 made of an electrically insulating material on the surface of the device illustrated in [Fig. 14],

[0059] The layer 52 extends for example continuously over the entire upper surface of the device of [Fig. 14]. Thus, the layer 52 covers in particular the microlenses 48 of the layer 42 and on the protective layer 38 in particular on the pads 20. By way of example, the layer 52 is a moisture-proof layer and makes it possible to protect the layer 42 from moisture. The layer 52 is, for example, made of an oxide, for example silicon oxynitride (SiON). According to one embodiment, the layer 52 is of the same material as the layer 38.

[0060] For example, the protective layer 52 is deposited, by a conformal deposition method on the upper face of the device illustrated in [Fig. 14], for example by chemical vapor deposition, for example plasma-enhanced chemical vapor deposition (PECVD). The layer 52 has, for example, a thickness of between 50 nm and 500 nm, for example of the order of 200 nm. Advantageously, the method for forming the layer 52 is the same as that used for forming the layer 38.

[0061] [Fig. 16] illustrates the structure obtained at the end of a step of forming an opening 54 in the protective layers 52, 38, and 32 and in the porous layer 30 to expose the contact recovery pad 20 and possibly a step of removing the resin block 28 present in the gap 26. The image sensor 60 is thus obtained. According to one embodiment, the material composing the resin blocks 28 is the same as that composing the resin layer 42 and the method described previously for removing the resin layer 42 can also be implemented for removing the resin blocks 28.

[0062] The porous layer 30 forms walls 62 separating the color filters 40. The refractive index of the material making up the walls 62 is lower than the refractive index of the material making up the color filters 40. As a result, the walls 62 play the role of mirror for the light rays passing through the color filters 40. In particular, the absorption of light rays by the walls 62 is reduced compared to walls which would be made of metal. The walls 62 advantageously make it possible to reduce the optical crosstalk between the color filters 40 without causing undesirable absorption of light rays. Indeed, the absorption of photons causes a drop in the optical efficiency of the image sensor 60, and this is all the more marked as the dimensions of the photodetectors 12 and the color filters 40 are reduced.

[0063] The aspect ratio of the walls 62, corresponding to the ratio between the height and the width of the wall 62, is between 0.08 and 0.15. According to one embodiment, the height of the walls 62 is between 400 nm and 900 nm. According to one embodiment, the width of the walls 62 is between 50 nm and 150 nm.

[0064] [Fig. 17] is a sectional view of another embodiment of an image sensor 65. The image sensor 65 shown in [Fig. 17] comprises all of the elements of the image sensor 60 shown in [Fig. 16] with the difference that the opaque screen 16 is not formed on the part of the substrate 10 comprising the photodetectors 12 but only on the part of the substrate 10 between the photodetectors 12 and the contact pads 20. The present embodiment makes it possible to further reduce the absorption of light rays since the material composing the opaque screen 16 is not present at the base of the walls 62.

[0065] [Fig. 18] is a partial, schematic sectional view of an example of an image sensor 70 described for comparison. The image sensor 70 comprises all of the elements of the image sensor 60 shown in [Fig. 16] except that the porous layer 30 is not present and the walls 62 between the color filters 40 are formed by portions 72 of the layer used to form the opaque screen 16 and the insulating layer 18.

[0066] An advantage of the image sensor 60 over the sensor 70 is that the absorption of photons in the walls 62 is less significant for the image sensor 60, which results in an increase in the optical efficiency for the image sensor 60. Another advantage is that it is easier to make walls 62 for the image sensor 60 with a high aspect ratio.

[0067] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In the embodiments described above, the groove 36 is filled with the material comprising the microlenses 48. Alternatively, the groove 36 may be filled with another material, for example the colored resin used to make one of the color filters 40.

[0068] Finally, the practical implementation of the described embodiments and variants is at the scope of the person skilled in the art from the functional indications given above.

Claims

Claims

1. Image sensor (60; 65) comprising: - a semiconductor substrate (10) comprising a first face (10s); - a porous layer (30), made of an electrically insulating and porous material, on the first face (10s), crossed by openings (34); - a color filter (40) in each opening (34); - a first moisture-proof protective layer (32) covering the porous layer (30) outside the openings (34); and - a second moisture-proof protective layer (38) covering the first protective layer (32) and the walls of each opening (34), between the porous layer (30) and the color filter (40) present in the opening (34).

2. The image sensor of claim 1, wherein the volume porosity of the porous material is between 35% and 55%.

3. An image sensor according to claim 1 or 2, wherein the porous layer (30) comprises a through groove (36) completely surrounding the openings (34), the second protective layer (38) covering the walls of the groove (36).

4. An image sensor according to any one of claims 1 to 3, further comprising: - a plurality of photodetectors (12) in and on the semiconductor substrate (10), the color filters (40) covering the photodetectors (12); - a plurality of microlenses (48) covering the color filters (40); and - a third protective layer (52) on the plurality of microlenses (48) and on the first and second protective layers (32, 38) around the plurality of microlenses (48).

5. An image sensor according to any one of claims 1 to 4, wherein the semiconductor substrate (10) comprises a second face (10i) opposite the first face (10s) and at least one hole (24) extending from the first face (10s) to the second face (10i), the image sensor further comprising an electrically conductive pad (20) comprising a first portion (20c) extending over the first face (10s) and a second portion (20j) covering the sides of the hole (24) and delimiting a gap (26) in the hole (24).

6. The image sensor of claim 5, further comprising a guard ring and in which the electrically conductive pad (20) is part of the guard ring.

7. An image sensor according to any one of claims 1 to 6, wherein the thickness of the porous layer (30) is between 400 nm and 900 nm.

8. A method of manufacturing an image sensor (60; 65) comprising the following steps: a) forming a porous layer (30), made of an electrically insulating and porous material, on a first face (10s) of a semiconductor substrate (10); b) forming a first moisture-proof protective layer (32) covering the porous layer (30); c) forming openings (34) passing through the first protective layer (32) and the porous layer (30); d) forming a second moisture-proof protective layer (38) covering the first layer (32) and the walls of each opening (34); and e) forming a color filter (40) in each opening (34), the second protective layer (38) being located between the porous layer (30) and the color filter (40) present in the opening (34).

9. A method according to claim 8, further comprising, in step c), forming a through groove (36) in the porous layer (30) completely surrounding the openings (34), the second protective layer (38) in step d) further covering the walls of the groove (36).

10. The method of claim 8 or 9, further comprising the following steps: - before step a), forming a plurality of photodetectors (12) in and on the semiconductor substrate (10), the color filters (40) being formed in step e) covering the photodetectors (12); - forming a plurality of microlenses (48) covering the color filters (40); and - forming a third protective layer (52) on the plurality of microlenses (48) and on the first and second protective layers (32, 38) around the plurality of microlenses (48).

11. A method according to any one of claims 8 to 10, wherein the semiconductor substrate (10) comprises a second face (10i) opposite the first face (10s), the method further comprising: forming, before step a), a hole (24) extending from the first face (10s) to the second face (10i) and an electrically conductive pad (20) comprising a first portion (20c) extending over the first face (10s) and a second portion (20j) covering the sides of the hole (24) and delimiting a gap (26) in the hole (24).

12. The method of claim 11, further comprising, before step a), forming a resin block (28) in the gap (26), the porous layer (30) covering the electrically conductive pad (20) and the resin block (28), and, after step e), successively etching the first protective layer (32), the second protective layer (38), and the porous layer (30) to expose the electrically conductive pad (20) and the resin block (28), and removing the resin block (28).

13. The method of claim 11 or 12, further comprising forming a guard ring and wherein the electrically conductive pad (20) is part of the guard ring.

Images