Method for treating contact recovery pads

Abstract

Method for processing contact pads The present description relates to a method for manufacturing an electronic circuit comprising, in order, the formation of an opening (16) in a semiconductor substrate (10) comprising a first face (10s) and formation of at least one electrically conductive pad (13) comprising a first portion (13c) extending over the first face (10s) and a second portion (13j) covering the sides of the opening (16) and delimiting a gap (17) in the opening (16), the deposition of a first layer of a first resin, the first resin being non-photosensitive, the first layer of the first resin covering the electrically conductive pad (13) and filling the gap (17) and crosslinking the first layer of the first resin, the chemical plasma etching of the first layer of the first resin to delimit a first block (20) of the first resin in the gap (17),and the deposition of a first protective layer (22) on the first block (20). Figure for the abstract: Fig. 13,

Description

Title of the invention: Method for treating contact recovery pads Technical field

[0001] The present description relates generally to the field of electronic circuits, in particular image sensors, comprising contact recovery pads, and more particularly relates to a method of manufacturing an image sensor. Prior art

[0002] An image sensor generally comprises a plurality of photodetectors, for example photodiodes, integrated in and on a semiconductor substrate. The photodetectors may be topped with a layer of microlenses. This layer of microlenses makes it possible to focus the incident radiation onto the photodetectors. An image sensor may further comprise contact pads which extend over one face of the substrate and through the semiconductor substrate, in particular when the image sensor is intended to be illuminated by this face. Such contact pads lead to the presence of significant reliefs which may in particular disrupt the manufacturing steps which follow the formation of the contact pads, and in particular the formation of the microlens layer.

[0003] It would be desirable to improve at least in part certain aspects of the known methods of manufacturing an image sensor comprising a microlens layer. Summary of the invention

[0004] One embodiment overcomes all or part of the drawbacks of known image sensors.

[0005] One embodiment provides a method of manufacturing an electronic circuit comprising the following steps in order: a) forming an opening in a semiconductor substrate comprising a first face and a second face opposite the first face, the opening extending from the first face to the second face, and forming at least one electrically conductive pad comprising a first portion extending over the first face and a second portion covering the sides of the opening and delimiting a gap in the opening; b) depositing a first layer of a first resin, the first resin being non-photosensitive, the first layer of the first resin covering the electrically conductive pad and filling the gap and crosslinking the first layer of the first resin; c) chemical plasma etching of the first layer in the first resin for delimiting a first block of the first resin in the gap; and d) depositing a first protective layer on the first block (20).

[0006] According to one embodiment, the first face comprises a depression in which the first portion is located, a groove being present between the first portion and the side of the depression, the first layer of the first resin filling the groove in step b), and a second block of the first resin being further delimited in the groove in step c).

[0007] According to one embodiment, the method further comprises, after step d), the following steps in order: e) forming a plurality of microlenses in a second layer of the first resin and covering the first protective layer, the plurality of microlenses not covering said at least one electrically conductive pad; and f) depositing a second protective layer on the plurality of microlenses and on the first protective layer around the plurality of microlenses.

[0008] According to one embodiment, the formation of the plurality of microlenses comprises the following steps in order: g) depositing the second layer of the first resin covering the first protective layer; h) forming a mask of a second resin, on and in contact with the second layer of the first resin; (i) formation of microlens-like structures in the mask; and j) transferring said structurings in the second layer to the first resin by physical etching to form the plurality of microlenses in the second layer.

[0009] According to one embodiment, after step j), the mask is removed using a solvent.

[0010] According to one embodiment, the method further comprises, after step f), the following step: k) removing the first protective layer and the second protective layer from at least a portion of the first portion while retaining the first protective layer and the second protective layer on the first block.

[0011] According to one embodiment, the method comprises, in step k), removing the first protective layer and the second protective layer on at least a part of the first portion while retaining the first protective layer and the second protective layer on the second block.

[0012] According to one embodiment, the method comprises, before step a), the formation of a plurality of photodetectors in the semiconductor substrate.

[0013] According to one embodiment, the plasma comprises dioxygen.

[0014] According to one embodiment, the first protective layer is made of an oxide, for example example in silicon oxynitride (SiON).

[0015] According to one embodiment, step b) successively comprises the deposition of a first sub-layer of the first resin having a first viscosity, the crosslinking of the resin of the first sub-layer, the deposition of a second sub-layer of the first resin having a second viscosity on the first sub-layer, and the crosslinking of the first resin of the second sub-layer.

[0016] According to one embodiment, the first viscosity is lower than the second viscosity, the first viscosity being between 1 mPa.s and 30 mPa.s, and the second viscosity being between 30 mPa.s and 150 mPa.s.

[0017] An embodiment also provides an electronic circuit comprising: - a semiconductor substrate comprising a first face, a second face opposite the first face, and an opening extending from the first face to the second face; - an electrically conductive pad comprising a first portion extending over the first face and a second portion covering the sides of the opening and delimiting a gap in the opening; - a first block of a first resin in the gap, the first resin being non-photosensitive, the first block of the first resin being crosslinked; and - a first protective layer covering the first block.

[0018] According to one embodiment, the electronic circuit further comprises: - a plurality of photodetectors in and on the semiconductor substrate; - a plurality of microlenses made of the first resin and covering the first protective layer, the plurality of microlenses not covering said at least one electrically conductive pad; and - a second protective layer on the plurality of microlenses and on the first protective layer around the plurality of microlenses.

[0019] According to one embodiment, the first face comprises a depression in which the first portion is located, a groove being present between the first portion and the side of the depression, the electronic circuit comprising a second block of the first resin in the groove, the first protective layer covering the second block. Brief description of the drawings

[0020] 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:

[0021] [Fig.l], [Fig.2], [Fig.3], [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8], [Fig.9], [Fig.10], [Fig.11], [Fig.12], and [Fig.13] are sectional views illustrating a device obtained at the end of successive steps of an embodiment of a method for manufacturing an image sensor; and

[0022] [Fig. 14] is an image obtained by scanning electron microscopy illustrating another embodiment 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 embodiments described have been shown and are detailed. In particular, the production 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. Generally, this embodiment of the manufacturing method can be implemented for any type of electronic circuit comprising contact pads, the steps relating to elements specific to an image sensor then not being implemented.

[0029] Figures 1 to 13 illustrate, schematically and partially, devices or 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. For example, the photodetectors 12 are photodiodes, for example, adapted to capture infrared, visible and / or ultraviolet radiation. For example, the photodetectors 12 are photodetectors produced in CMOS technology (from the English "Complementary Metal Oxide Semiconductor" - complementary metal oxide semiconductor).

[0031] The substrate 10 comprises an upper face 10s and a lower face 10i, opposite the upper face 10s. The substrate 10 may be covered, on the side of the upper face 10s, by one or more than one element, not shown in the figures, for example a protective dielectric layer, colored filters covering the photodetectors 12, an opaque screen covering areas of the substrate 10 not comprising photodetectors 12, etc. The substrate 10 is covered, on the side of the lower face 10i, by an interconnection structure 14, 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.

[0032] In this example, the substrate 10 is intended to be illuminated by its upper face 10s. The starting structure further comprises one or more contact recovery pads 13, a single contact recovery pad 13 being shown in [Fig.l]. According to one embodiment, the contact recovery pad 13 is electrically insulated from the substrate 10 by at least one insulating layer, not shown. The pads 13 are arranged out of line with the photodetectors 12 so as not to mask the photodetectors 12. By way of example, in top view, the photodetectors 12 are located in a central region of the substrate 10, and the pads 13 are located opposite a peripheral region of the substrate 10.

[0033] Each contact recovery pad 13 comprises a contact area 13c which extends into a depression 15 provided in the upper face 10s of the substrate 10. The contact area 13c of each pad 13 is intended to be connected to an external device, for example by means of an electrically conductive wire, for example a metal wire. The contact area 13c comprises an upper face 13s. The substrate 10 comprises, for each contact recovery pad 13, a through opening 16 which extends from the upper face 10s to the lower face 10i. The opening 16 opens into the depression 15. According to one embodiment, the opening 16 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 16 is square or rectangular, in particular inscribed in a rectangle whose short side varies from 2 pm to 10 pm and whose long side varies from 5 pm to 100 pm.The contact recovery pad 13 comprises a junction portion 13j which extends into the through opening 16. By way of example, the junction portion . 13j of the contact recovery pad 13 is connected to one or more metallization levels of the interconnection structure 14 arranged on the side of the lower face 10i of the substrate 10. For example, the contact recovery pads 13 are made of a metallic material, for example aluminum. The junction portion 13j covers the sides of the opening 16. However, the opening 16 is not completely filled by the junction portion 13j so that a gap 17 filled with air, and opening onto the outside, remains in the opening 16. For example, the junction portion 13j has a thickness, measured relative to the sides of the opening 16, which is between 200 nm and 2 pm, and is for example equal to approximately 2 pm. For example, the depth of the gap 17 is between 3 μm and 10 μm, and is for example equal to approximately 6 μm. For example, the thickness of the contact zone 13c is equal to the thickness of the junction portion 13j.For example, the depth of the depression 15 is substantially equal to the thickness of the contact zone 13c and is between 200 nm and 2 pm.

[0034] By way of example, the contact pads 13 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 13 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] According to one embodiment, the upper face 10s is flat outside the depressions 15 and the through openings 16. A groove 18 filled with air may be present in the depression 15 between the side of the depression 15 and the contact recovery pad 13.

[0036] Figures 2 to 4 illustrate devices obtained at the end of planarization steps of the structure of [Fig.l] to obtain a substantially flat face on the side of the upper face 10s of the substrate 10.

[0037] [Fig.2] illustrates a device obtained at the end of a step of forming a layer of resin 19 on the side of the upper face 10s of the substrate 10.

[0038] The layer 19 is, for example, deposited full plate over the entire surface of the upper face 10s of the substrate 10, for example by deposition with a spinner. The layer 19 thus covers the contact pads 13, and the photodetectors 12. The resin layer 19 fills in particular, for each contact pad 13, the gap 17 and the groove 18 when the latter is present. The layer 19 has, for example, outside the zones where it covers the contact pads 13, a thickness of between 1 μm and 6 μm, for example of the order of 4 μm. According to one embodiment, the layer 19 has a substantially flat upper face 19s.

[0039] The resin of layer 19 is, for example, a crosslinked resin which cannot be dissolved in the usual liquid solvents for developing and / or etching the resins. The resin of layer 19 is, for example, a non-photosensitive resin. For example, the resin of layer 19 is chosen so that it can be crosslinked, for example by UV rays or from a certain temperature, for example, of the order of 200°C. For example, the resin of layer 19 is chosen so that it can be etched by reactive ion bombardment, also called RIE (reactive-ion etching), using a plasma, for example oxygen-based. For example, the resin of layer 19 comprises a polymer, for example of the acrylic type or of the polyhydroxystyrene type.

[0040] Advantageously, the viscosity of the resin making up the layer 19 is chosen so as to obtain complete filling, for each contact recovery pad 13, of the gap 17, and of the groove 18 when it is present, and to obtain a substantially flat upper face 19s. According to one embodiment, the layer 19 is produced by a single deposition operation. According to one embodiment, the formation of the layer 19 comprises the deposition of a first sub-layer 19a of the resin of the layer 19 having a first viscosity, the crosslinking of the resin of the first sub-layer 19a, the deposition of a second sub-layer 19b of the resin of the layer 19 having a second viscosity, and the crosslinking of the resin of the second sub-layer 19b. The first sub-layer allows the filling of the gaps 17. The first viscosity may be lower than the second viscosity. According to one embodiment, the first viscosity is between 1 mPa.s and 30 mPa.s, and is for example equal to 25 mPa.s. According to one embodiment, the second viscosity is between 30 mPa.s and 150 mPa.s, and is for example equal to 50 mPa.s. The first viscosity is, advantageously, adapted to facilitate the filling of the interstices 17. The second viscosity is, advantageously, adapted to facilitate obtaining the substantially flat upper face 19s.

[0041] [Fig. 3] illustrates a device obtained at the end of a step of etching the resin layer 19 until the upper face 10s of the substrate 10 and the upper face of the contact recovery pad 13 are exposed. The etching step delimits a block 20 of the material making up the layer 19 in the gap 17 delimited by each contact recovery pad 13. When the groove 19 is present, the etching step delimits a block 21 of the material making up the layer 19 in the groove 18.

[0042] According to one embodiment, the etching carried out during this step is an etching by remote plasma, and therefore isotropic (process sometimes referred to by the English terms "dry-stripping" or "dry-ashing"). The chemical etching plasma used preferably comprises dioxygen. For example, the chemical etching plasma comprises dioxygen, dinitrogen and dihydrogen. For example, the temperature of the material etched during this step is between 80°C and 200°C, for example of the order of 170°C. This embodiment has the advantage of being selective on the upper face material 10s.

[0043] According to one embodiment, the etching carried out during this step is etching by ion bombardment, reactive dry etching or spray etching ("dry etching" in English). Such etching results in material removal by bombardment, for example, using a dioxygen-based plasma.

[0044] The aforementioned etching is stopped when the upper face 10s of the substrate 10 or the upper face 13s of the contact recovery pad 13 is revealed.

[0045] [Fig.4] illustrates a device obtained at the end of a step of depositing a protective layer 22 made of an electrically insulating material on the surface of the device illustrated in [Fig.3],

[0046] The layer 22 extends for example continuously over the entire upper surface of the device of [Fig. 4]. Thus, the layer 22 covers in particular the upper face 13s of the pads 13, the blocks 20 and the blocks 21, and the upper face 10s of the substrate 10. The layer 22 is, for example, made of an oxide, for example silicon oxynitride (SiON) or silicon oxide (SiO2) deposited at low temperature, for example 150°C.

[0047] By way of example, the protective layer 22 is deposited, by a conformal deposition method on the upper face of the device illustrated in [Fig. 3], for example by chemical vapor deposition, for example plasma-enhanced chemical vapor deposition (PECVD). The layer 22 has, for example, a thickness of between 30 nm and 200 nm, for example of the order of 50 nm. By way of example, the temperature during the formation of the protective layer 22 is between 150°C and 250°C, for example of the order of 150°C.

[0048] Figures 5 to 7 illustrate devices obtained at the end of steps of forming optical filters and a layer of microlenses on the side of the upper face 10s of the substrate 10, opposite the photodetectors 12.

[0049] [Fig. 5] illustrates a device obtained at the end of a step of forming optical filters 23 on the protective layer 22 and a step of forming a resin layer 24 on the optical filters 23 and on the protective layer 22 around the optical filters 23.

[0050] The optical filters 23 are formed on the protective layer 22 directly above the photodetectors 12. The optical filters may comprise color filters and / or interference filters. Advantageously, the protective layer 22 protects the blocks 20 and 21 during the formation of the optical filters 23 or during the recycling (rework) of the latter.

[0051] The resin layer 24 is, for example, deposited full plate over the entire surface of the protective layer 22. The layer 24 has, for example, a thickness of between 1 pm and 5 pm, for example around 4 pm.

[0052] According to one embodiment, the resin of layer 24 is the same as the resin of layer 19. The resin of layer 24 is, for example, a crosslinked resin which cannot be dissolved in the usual liquid solvents for developing and / or etching resins. The resin of layer 24 is, for example, a non-photosensitive resin. For example, the resin of layer 24 is chosen so that it can be crosslinked, for example by UVs or from a certain temperature, for example, of the order of 200°C. For example, the resin of layer 24 is chosen so that it can be etched by RIE etching, in particular using an oxygen-based plasma. For example, the resin of layer 24 comprises a polymer, for example of the acrylic type.

[0053] [Fig. 6] illustrates a device obtained at the end of a step of forming an etching mask 25 on the upper face of the resin layer 24. The mask 25 comprises structures in the form of microlenses, intended to be transferred into the resin layer 24 during a subsequent etching step, so as to form microlenses in the layer 24.

[0054] By way of example, the mask 25 is formed from a layer of photosensitive resin. The resin of the mask 25 is for example first deposited full plate, on and in contact with the upper face of the layer 24. At this stage, the resin of the mask 25 has for example a substantially uniform thickness over the entire surface of the structure. The deposition of the resin of the mask 25 can be done by a spin coating technique or by any other suitable deposition technique. The resin layer of the mask 25 is then structured, for example by photolithography, so as to form, opposite the photodetectors 12, separate resin pads 26. In this example, an individual resin pad 26 is provided opposite each photodetector 12 of the sensor. A finishing annealing is then carried out, during which the resin pads 26 deform to take the form of microlenses. After finishing, the resin pads 26 are, for example, separated.The embodiments described are however not limited to this particular case. The pads 26 have for example a thickness less than the thickness of the layer 24.

[0055] [Fig.7] illustrates a device obtained at the end of a physical etching step of the layer 24 and the mask 25, leading to the transfer of the pattern of the mask 25 into an upper part of the layer 24. The etching is for example stopped when all the resin of the mask 25 has been consumed.

[0056] Thus, in the device illustrated in [Fig.7], the layer 24 comprises microlenses 28 facing the photodetectors 12. For example, the microlenses 28 have a height of between 0.5 pm and 3 pm. At this stage, the connection pads 13 remain covered by the resin of the layer 24.

[0057] The blocks 20 and 21 being made of a crosslinked non-photosensitive resin, which can be the same resin as that used for the microlenses 28, there is advantageously no degradation of the resin of the blocks 20 and 21 during the formation of the optical filters 23 and the microlenses 28.

[0058] Figures 8 to 13 illustrate devices obtained at the end of steps of removing the resin from the resin layer 24 opposite the pads 13, to allow electrical contact to be reestablished on the pads 13.

[0059] [Fig.8] illustrates a device obtained at the end of a step of forming a masking layer 30 of resin on the upper face of the layer 24.

[0060] By way of example, the layer 30 is first deposited full plate on the upper face of the layer 24, for example in contact with the upper face of the layer 24. The layer 30 is then removed, for example by photolithography, opposite the pads 13, so as to expose the portion of the resin layer 24 coating the pads 13. The resin of the layer 30 is, for example, a photosensitive resin. By way of example, the layer 30 has a thickness greater than the maximum thickness of the layer 24. By way of example, the layer 30 has a thickness of between 4 μm and 10 μm, for example of the order of 6 μm.

[0061] [Fig.9] illustrates a device obtained at the end of a step of etching layer 24 through layer 30. During this step, layer 30 is used as an etching mask.

[0062] More particularly, during this step, the part of the layer 24 not covered by the layer 30 is removed so as to reveal the protective layer 22. The protective layer 22 can act as an etching stop layer.

[0063] According to one embodiment, the etching implemented during this step is a remote 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 24 through the mask formed by the resin layer 30. This technique has the advantage of being less aggressive than a physical etching, and does not generate fibers or filaments based on etching products and carbon on the sides of the layer 24.

[0064] The etching plasma used preferably comprises dioxygen. For example, the chemical etching plasma comprises dioxygen, dinitrogen and dihydrogen. For example, the temperature of the etched material during this step is between 80°C and 200°C, for example of the order of 170°C.

[0065] According to one embodiment, the etching implemented during this step is an etching by ion bombardment, reactive dry etching or spray etching ("dry etching" in English). Such etching results in a removal of material by bombardment, for example, using a dioxygen-based plasma. 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 28. During the aforementioned step, the layers 30 and 24 are consumed simultaneously.

[0066] The aforementioned etching is stopped when the protective layer 22 is revealed. At this stage, a part of the layer 30 remains on the surface of the layer 24 opposite the microlenses 28.

[0067] [Fig. 10] illustrates a device obtained at the end of a step of removing the remaining part of the layer 30 so as to release the upper face of the microlenses 28. 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 30 relative to the material of the layer 24.

[0068] [Fig. 11] illustrates a device obtained at the end of a step of depositing a protective layer 32 made of an electrically insulating material on the surface of the device illustrated in [Fig. 10],

[0069] The layer 32 extends for example continuously over the entire upper surface of the device of [Fig. 10]. Thus, the layer 32 covers in particular the microlenses 28 of the layer 24 and on the protective layer 22 in particular on the pads 13. By way of example, the layer 32 is made of a material which makes it possible to protect the layer 24 from humidity. The layer 32 is, for example, made of an oxide, for example silicon oxynitride (SiON) or an oxide deposited at low temperature, for example 150°C. According to one embodiment, the layer 32 is of the same material as the layer 22.

[0070] For example, the protective layer 32 is deposited, by a conformal deposition method on the upper face of the device illustrated in [Fig. 10], for example by chemical vapor deposition, for example plasma-enhanced chemical vapor deposition (PECVD). The layer 32 has, for example, a thickness of between 50 nm and 500 nm, for example of the order of 150 nm. Advantageously, the method for forming the layer 32 is the same as that used for forming the layer 22.

[0071] Figures 12 to 13 illustrate devices obtained at the end of steps of localized removal of the protective layers 22 and 32 opposite each of the contact resumption pads 13, to allow the resumption of electrical contact on the pads 13.

[0072] [Fig. 12] illustrates a device obtained at the end of a step of depositing a layer of resin 33 on the upper face of the device of [Fig. 1 1], and of forming, in the layer of resin 33, through openings 34 exposing, for each recovery pad contact 13, a part of the protective layer 32 covering the contact area 13c of the contact recovery pad 13 (for example, the part of the contact area 13c to the left of the junction portion 13j in [Fig. 12]). The openings 34 are for example formed by photolithography.

[0073] [Fig. 13] illustrates a device obtained at the end of a step of etching the protective layer 32 and the protective layer 22 in the openings 34 of the resin layer 33 which is used as an etching mask followed by a step of removing the resin layer 33. An opening 35 is then formed in the protective layer 32 and the protective layer 22, in the extension of each opening 34, which exposes a part of the contact zone 13c of the contact recovery pad 13. According to one embodiment, the removal of the resin layer 33 can be carried out by the same etching method as that described previously in relation to [Fig. 9] for the etching of the layer 24. The protective layer 32 makes it possible to protect the microlenses 28 and the resin blocks 20 and 21 during the etching of the resin layer 33.

[0074] The resin block 20 is kept in the gap 17 and the resin block 21 is kept in the groove 18. This advantageously makes it possible to obtain a relatively flat upper surface, or in any case, one having reliefs of reduced amplitude, above the junction portion 13j of each contact recovery pad 13 and above the groove 18 surrounding each contact recovery pad 13.

[0075] [Fig. 14] is an image obtained by scanning electron microscopy of the electronic circuit of [Fig. 13], the gap 17 being substantially completely filled by the resin block 20, not directly visible in [Fig. 14], covered by the protective layer 32, and the groove 18 being substantially completely filled by the resin block 21, not directly visible in [Fig. 14].

[0076] In the embodiments described previously in relation to FIGS. 1 to 14, the contact zone 13c of each contact recovery pad 13 is housed in a depression 15 formed in the upper face 10s of the substrate 10 so that the upper face of the contact zone 13c is substantially coplanar with the upper face 10s of the substrate 10. As a variant, the contact zone 13c of each contact recovery pad 13 may rest on the upper face 10s of the substrate 10 which is substantially planar so that the contact zone 13c rises in relief relative to the upper face 10s of the substrate 10.

[0077] An advantage of the embodiments described above is that, after the formation of the blocks 20 and 21 and the protective layer 22, the upper face of the device obtained is substantially flat, or in any case, has reliefs of reduced amplitudes. The implementation of the subsequent steps of the method of manufacturing the image sensor is, advantageously, simpler. In particular, the formation of the layer 24 with a substantially constant thickness is simpler, which makes it possible to avoid a striation phenomenon (i.e. a long-distance periodic disturbance in the spreading of the resin during its centrifugal deposition process) of the resin(s) present above the matrix of photodetectors, at least in the zone in which the microlenses 28 are formed.

[0078] An advantage is that the resin used to form the resin blocks 20 and 21 can be the same as the resin used to form the microlens layer 28. The manufacturing, handling, crosslinking, and etching processes for this resin are then advantageously well controlled.

[0079] In the embodiments described above, the protective layer 22 is shown in direct mechanical contact with the contact recovery pad 13. As a variant, the contact recovery pad 13 may be covered with a dielectric layer, for example a layer of silicon oxide, deposited before the deposition of the resin layer 19. In this case, during the formation of the protective layer 22 on the contact recovery pad 13, the protective layer 22 may come into direct mechanical contact with the dielectric layer on the contact zone 13c, the block 20 being interposed between the dielectric layer and the part of the protective layer 22 which covers the block 20.

[0080] 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 particular, the described embodiments are not limited to the examples of dimensions and materials mentioned above.

[0081] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. A method of manufacturing an electronic circuit comprising the following steps in order: a) forming an opening (16) in a semiconductor substrate (10) comprising a first face (10s) and a second face (10i) opposite the first face (10s), the opening (16) extending from the first face (10s) to the second face (10i), and forming at least one electrically conductive pad (13) comprising a first portion (13c) extending over the first face (10s) and a second portion (13j) covering the sides of the opening (16) and delimiting a gap (17) in the opening (16); b) depositing a first layer (19) of a first resin, the first resin being non-photosensitive, the first layer (19) of the first resin covering the electrically conductive pad (13) and filling the gap (17) and crosslinking the first layer (19) of the first resin;c) chemical plasma etching of the first layer (19) of the first resin to delimit a first block (20) of the first resin in the gap (17); and d) depositing a first protective layer (22) on the first block (20).;

2. A method according to claim 1, wherein the first face (10s) comprises a depression (15) in which the first portion (13c) is located, a groove (18) being present between the first portion (13c) and the flank of the depression (15), the first layer (19) of the first resin filling the groove (18) in step b), and a second block (21) of the first resin being further delimited in the groove (18) in step c).

3. The method of claim 1 or 2, further comprising, after step d), the following steps in order: e) forming a plurality of microlenses (28) in a second layer (24) of the first resin and covering the first protective layer (22), the plurality of microlenses (28) not covering said at least one electrically conductive pad (13); and f) depositing a second protective layer (32) on the plurality of microlenses (28) and on the first protective layer (22) around the plurality of microlenses (28).

4. The method of claim 3, wherein forming the plurality of microlenses (28) comprises the following steps in order: g) depositing the second layer (24) of the first resin covering the first protective layer (22); h) forming a mask (25) of a second resin, on and in contact with the second layer (24) of the first resin; i) forming microlens-shaped structures (26) in the mask (25); and j) transferring said structures (26) into the second layer (24) of the first resin by physical etching to form the plurality of microlenses (28) in the second layer (24).

5. A method according to claim 4, wherein, after step j), the mask (25) is removed using a solvent.

6. A method according to any one of claims 3 to 5, further comprising, after step f) the following step: k) removing the first protective layer (22) and the second protective layer (32) on at least a part of the first portion (13c) while retaining the first protective layer (22) and the second protective layer (32) on the first block (20).

7. A method according to claim 6 in its attachment to claim 2, comprising, in step k), removing the first protective layer (22) and the second protective layer (32) on at least a part of the first portion (13c) while retaining the first protective layer (22) and the second protective layer (32) on the second block (21).

8. A method according to any one of claims 1 to 7, comprising, before step a), forming a plurality of photodetectors (12) in the semiconductor substrate (10).

9. A method according to any one of claims 1 to 8, wherein the plasma comprises dioxygen.

10. A method according to any one of claims 1 to 9, wherein the first protective layer (22) is made of an oxide, for example silicon oxynitride (SiON).

11. A method according to any one of claims 1 to 10, wherein step b) successively comprises the deposition of a first sub-layer (19a) of the first resin having a first viscosity, the crosslinking of the resin of the first sub-layer (19a), the deposition of a second sub-layer (19b) of the first resin having a second viscosity on the first sub-layer (19a), and the crosslinking of the first resin of the second sub-layer (19b).

12. The method of claim 11, wherein the first viscosity is lower than the second viscosity, the first viscosity being between 1 mPa.s and 30 mPa.s, and the second viscosity being between 30 mPa.s and 150 mPa.s.

13. Electronic circuit comprising: - a semiconductor substrate (10) comprising a first face (10s), a second face (10i) opposite the first face (10s), and an opening (16) extending from the first face (10s) to the second face (10i); - an electrically conductive pad (13) comprising a first portion (13c) extending over the first face (10s) and a second portion (13j) covering the sides of the opening (16) and delimiting a gap (17) in the opening (16); - a first block (20) made of a first resin in the gap (17), the first resin being non-photosensitive, the first block (20) made of the first resin being crosslinked; and - a first protective layer (22) covering the first block (20).

14. An electronic circuit according to claim 13, further comprising: - a plurality of photodetectors (12) in and on the semiconductor substrate (10); - a plurality of microlenses (28) made of the first resin and covering the first protective layer (22), the plurality of microlenses (28) not covering said at least one electrically conductive pad (13); and - a second protective layer (32) on the plurality of microlenses (28) and on the first protective layer (22) around the plurality of microlenses (28).

15. An electronic circuit according to claim 13 or 14 wherein the first face (10s) comprises a depression (15) in which the first portion (13c) is located, a groove (18) being present between the first portion (13c) and the flank of the depression (15), the electronic circuit comprising a second block (21) of the first resin in the groove (18), the first protective layer (22) covering the second block (21).

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