Manufacturing process of a light sensor

Abstract

Method for manufacturing a light sensor The present description relates to a manufacturing method comprising, for each photodetector (PD) of a matrix of photodetectors of a light sensor (1), a use of a mask obtained by directed self-assembly of a block copolymer to form, by a first etching step, at least a first structuring (122) on the side of a first face (106) of the photodetector intended to receive light. Figure for abstract: Fig. 1D

Description

Title of the invention: Method for manufacturing a light sensor Technical field

[0001] The present description relates generally to electronic devices, and more particularly to light sensors, for example time-of-flight sensors. Prior art

[0002] Light sensors are known comprising a matrix of pixels, in which each pixel comprises at least one photodetector arranged in a semiconductor layer, typically a silicon layer. In other words, these known light sensors comprise a matrix of photodetectors each arranged in a silicon layer of the sensor.

[0003] Among these known light sensors, a distinction is made between front-facing sensors and rear-facing sensors. In a front-facing sensor, the silicon layer comprising the photodetectors is intended to receive light from its front face side, i.e. from the side of its face which is coated with a back-end-of-line interconnection structure or BEOL interconnection structure. Conversely, in a rear-facing sensor, the silicon layer comprising the photodetectors is intended to receive light from its rear face side, i.e. from the side of its face which is opposite its front face.

[0004] In known light sensors having silicon photodetectors, the quantum efficiency of each pixel of the sensor decreases with wavelength, following the decrease in absorption of silicon with wavelength. Indeed, the absorption of silicon is strong in the visible part of the light spectrum, but is weak in the near infrared, i.e. for wavelengths for example ranging from 780 nm to 1100 pm.

[0005] To improve the quantum absorption of the pixels of these known light sensors intended to operate at wavelengths in the near infrared, for example when the sensor is a direct or indirect time-of-flight sensor, surface structurings are provided for each photodetector, on the side of the rear face of the silicon layer for a rear-facing sensor and on the side of the front face for a front-facing sensor. An example of such a surface structuring is described in patent application US 2019 / 0019832 AL

[0006] These known surface structures have, in a plane parallel to the rear face of the silicon layer, minimum dimensions, or critical dimensions, of the order of several hundred nanometers, for example greater than or equal to 200 nm. However, the increase in the quantum efficiency of a pixel comprising a photodetector associated with such surface structures compared to the quantum efficiency of a pixel comprising a similar photodetector but not associated with surface structures decreases with the reduction of the pixel pitch, that is to say with the reduction of the pitch of the photodetectors, or, in other words, with the reduction of the dimensions of the photodetectors. Summary of the invention

[0007] There is a need to overcome all or part of the disadvantages of known light sensors.

[0008] For example, there is a need to overcome all or part of the drawbacks of known light sensors in which the photodetectors are arranged in a silicon layer and are associated with surface structures, for example when these sensors are intended to operate in the near infrared and / or are illuminated from the rear face.

[0009] One embodiment overcomes all or part of the drawbacks of known light sensors.

[0010] For example, one embodiment overcomes all or part of the drawbacks of known light sensors in which the photodetectors are arranged in a silicon layer and are associated with surface structures, for example when these sensors are intended to operate in the near infrared and / or are illuminated from the rear face.

[0011] One embodiment provides a manufacturing method comprising, for each photodetector of a matrix of photodetectors of a light sensor, use of a mask obtained by directed self-assembly of a block copolymer to form, by a first etching step, at least a first structuring on the side of a first face of the photodetector intended to receive light.

[0012] According to one embodiment, the characteristic length of the block copolymer is less than 100 nm, preferably 50 nm.

[0013] According to one embodiment, the directed self-assembly of the block copolymer is implemented by chemo-epitaxy.

[0014] According to one embodiment, the directed self-assembly of the block copolymer is implemented by graphoepitaxy.

[0015] According to one embodiment, the first etching step comprises a transfer of the mask obtained by directed self-assembly of the block copolymer into a hard mask to form through openings therein, then an etching from said openings.

[0016] According to one embodiment, the directed self-assembly of the block copolymer comprises, for each photodetector, an etching of at least one guide cavity, and a deposition of the block copolymer in said at least one guide cavity.

[0017] According to one embodiment, the photodetectors are arranged in a silicon layer and the first structures are formed in an insulating layer resting on the silicon layer.

[0018] According to one embodiment, the photodetectors are arranged in a silicon layer and the first structures are formed in the silicon layer.

[0019] According to one embodiment, the photodetectors are arranged in a layer of silicon and, for each photodetector, said at least one guide cavity is etched directly in the silicon.

[0020] According to one embodiment, for at least one of the photodetectors, several first structurings are formed during the first etching step, the pitch of the first structurings preferably being less than 100 nm.

[0021] According to one embodiment, for at least one photodetector, the method further comprises a formation, by a second etching step, of at least one second structuring on the side of the first face, said at least one second structuring having, in a plane parallel to said first face, a smaller dimension greater than a smaller dimension of the first structurings.

[0022] According to one embodiment, the second etching step is implemented after the first etching step.

[0023] According to one embodiment, the self-assembly of the block copolymer is configured so that, for several of said photodetectors, the first structurings form a random fingerprint-type pattern.

[0024] According to one embodiment, the pitch of the photodetectors is less than or equal to 1.5 pm, for example less than 1 pm.

[0025] According to one embodiment: the photodetectors are arranged in a silicon layer; said at least one guide cavity is etched directly in the silicon; and for at least one photodetector, a width or a diameter of said at least one guide cavity is substantially equal to 1.5 times the characteristic length of the block copolymer. Brief description of the drawings

[0026] 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:

[0027] [Fig.1A] illustrates, by a sectional view, an embodiment of a step of a method of manufacturing a light sensor;

[0028] [Fig.lB] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.lA];

[0029] [Fig.lC] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.lB];

[0030] [Fig.lD] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.lC];

[0031] [Fig.2A] illustrates, by a sectional view, an alternative embodiment of the step of [Fig.1A];

[0032] [Fig.2B] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.2A];

[0033] [Fig.2C] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.2B];

[0034] [Fig.2D] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.2C];

[0035] [Fig.3A] illustrates, by a sectional view, an embodiment of a step implemented after steps similar to the steps of Figures 1A to 1D;

[0036] [Fig.3B] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.3A];

[0037] [Fig.3C] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.3B];

[0038] [Fig.4A] illustrates, by a sectional view, another embodiment of a step implemented after steps similar to the steps of Figures 1A to 1D;

[0039] [Fig.4B] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.4A];

[0040] [Fig.5A] illustrates, by a sectional view, yet another embodiment of a step implemented after steps similar to the steps of Figures 1A to 1D;

[0041] [Fig.5B] illustrates, by a sectional view, an embodiment of a step implemented after the step of [Fig.5A];

[0042] [Fig.6] illustrates by curves the evolution of the quantum efficiency gain of photodetectors associated with surface structures compared to a photodetector not associated with surface structures, for different implementations of the surface structures; and

[0043] [Fig.7] represents a schematic top view of a matrix of photodetectors according to an exemplary implementation. Description of the embodiments

[0044] 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.

[0045] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, known light sensors with backside illumination, intended to operate in the near infrared and comprising silicon photodetectors have not been described in detail, in particular with regard to the implementation of their pixels, the pixel control circuit, the pixel reading circuit and the circuit for processing the data read from the pixels. However, the embodiments, the modes of implementation and their variants described below are compatible with these known light sensors, and, in particular with the usual implementations of their pixels, their pixel reading circuits, their pixel control circuits and their pixel data processing circuits.Furthermore, although the present description is made in relation to examples where the sensors are intended to operate in the near infrared and to be illuminated from the back side, the advantages of the described embodiments apply to front-illuminated sensors and / or to sensors intended to operate in the visible.

[0046] 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.

[0047] 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.

[0048] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0049] In the remainder of the description, unless otherwise indicated, the expression "an element rests on a first layer" means that this element rests on the first layer indirectly, for example with the interposition of an intermediate layer between the first layer and the element, or means, preferably, that this element rests directly on the first layer, that is to say on and in contact with the first layer.

[0050] In the following description, the critical dimension of a surface structuring corresponds, for example, to the smallest dimension of this structuring measured in a plane parallel to the back face of the silicon layer including the photodetectors.

[0051] In the remainder of the description, a reference pixel is a pixel comprising a silicon photodetector with backside illumination, intended to operate in the near infrared, and not associated with surface structures.

[0052] The inventors have found that, compared to a reference pixel, the increase in the quantum efficiency of a similar pixel but in which the photodetector is associated with surface structures formed on the side of its rear face increases with the reduction in the pitch of the structures and / or with the reduction in the critical dimension of the structures, in particular when the structures have critical dimensions for example less than 100 nm and a repetition pitch for example less than 100 nm.

[0053] For structures having a given critical dimension, for example less than 100 nm, and a given repetition pitch, for example less than 100 nm, the more the pitch of the photodetectors decreases, the more the maximum number of structures with which a photodetector can be associated decreases. In other words, for structures having a given critical dimension and a given repetition pitch, in each photodetector, the more the surface of the photodetector intended to receive light decreases, the more the maximum number of structures with which the photodetector can be associated decreases.

[0054] The usual surface structures have critical dimensions of the order of several hundred nanometers, for example critical dimensions greater than or equal to 200 nm, and a repetition pitch also of the order of several hundred nanometers, for example a pitch greater than or equal to 200 nm. Thus, for a photodetector pitch less than or equal to 1.5 pm, or even less than or equal to 1 pm, it becomes impossible to associate a large number of surface structures with the photodetector, for example a number of surface structures greater than or equal to 5, preferably greater than or equal to 10.

[0055] It will be noted that for pixels of relatively large dimensions, for example pixels having sides of length greater than 1.5 pm in top view, structurings of larger dimensions, for example critical dimensions greater than 500 nm, can make it possible to achieve absorption optimums with a relatively small number of structurings, for example less than 5. However, the pitch and critical dimensions of these structurings which are suitable for pixels of relatively large dimensions cannot be implemented for pixels of relatively small dimensions, for example pixels having sides of length less than 1.5 pm, for example less than 1 pm.

[0056] It is proposed here to overcome all or part of the disadvantages of light sensors. usual methods described above by associating, with each photodetector, at least one surface structuring, for example several surface structurings, preferably at least ten surface structurings, obtained by means of a mask itself obtained by directed self-assembly ("Direct Self-Assembly" - DSA) of block copolymer. Such a mask can be obtained by implementing the directed self-assembly of block copolymers by chemo-epitaxy or by graphoepitaxy.

[0057] This makes it possible to take advantage of the fact that a mask obtained by directed self-assembly of block copolymers makes it possible to obtain masking structures having small dimensions in a plane parallel to a face of a layer on which these structures rest, for example smaller dimensions than the critical dimensions of known surface structures. For example, when the period, or characteristic length, LO of the block copolymer is less than or equal to 100 nm, for example less than or equal to 50 nm, the masking structures obtained each have, in a plane parallel to the silicon layer of the photodetectors, a smaller dimension, or critical dimension, less than or equal to 100 nm, or even less than or equal to 50 nm.The use of such masking structures makes it possible to form, by etching, surface structures having critical dimensions similar to or equal to those of the masking structures, for example surface structures having critical dimensions less than or equal to 100 nm, or even less than or equal to 50 nm.

[0058] Furthermore, this also makes it possible to take advantage of the fact that a mask obtained by directed self-assembly of block copolymers makes it possible to obtain repeated masking structures with a pitch smaller than the repetition pitch of known surface structures. For example, when the period, or characteristic length, L0 of the block copolymer is less than or equal to 100 nm, for example less than or equal to 50 nm, the masking structures obtained each have, in a plane parallel to the silicon layer of the photodetectors, a repetition pitch, less than or equal to 100 nm, or even less than or equal to 50 nm. The use of such masking structures makes it possible to form, by etching, surface structures having a repetition pitch similar or identical to the repetition pitch of the masking structures, for example surface structures having a repetition pitch less than or equal to 100 nm, or even less than or equal to 50 nm.

[0059] By way of example, the use of a mask obtained by directed self-assembly of block copolymers makes it possible to form, by etching, surface structures having critical dimensions of less than 100 nm and a repetition pitch of 100 nm, for example when the characteristic length of the block copolymer used is less than 100 nm.

[0060] Thus, the use of a mask obtained by directed self-assembly of block copolymers can make it possible to associate, with each photodetector of a light sensor, a large number of surface structuring, for example at least 5 surface structuring, preferably at least 10 surface structuring, even when the pitch of the photodetectors becomes less than 1.5 pm, for example less than 1 pm.

[0061] To produce surface structures of small dimensions, i.e. surface structures having, for example, critical dimensions less than 100 nm and having, for example, a repetition pitch less than or equal to 100 nm, one could have thought of using an immersion lithography step to form a mask allowing the formation of the structures by etching. However, immersion photolithography is complex to implement and cannot always be implemented on the side of the rear face of a light sensor due to the topography of the rear face of the sensor.

[0062] Furthermore, it is also proposed here, in addition to the surface structures of small critical dimensions formed by means of a mask obtained by direct self-assembly of block copolymer, to optionally form surface structures of larger critical dimensions. This makes it possible to associate, for at least some photodetectors of the sensor, for example for each photodetector of the sensor, structures of small critical dimensions with structures of large critical dimensions.

[0063] By way of example, these large-sized structures are formed during an etching step, for example an etching step carried out after the etching step making it possible to form the small-sized structures.

[0064] By way of example, structures of small critical dimensions are surface structures obtained by means of a mask obtained from a directed self-assembly of block copolymer, that is to say structures whose critical dimensions are, for example, less than or equal to 100 nm, or even 50 nm, and whose repetition pitch is, for example, less than or equal to 100 nm, or even 50 nm.

[0065] By way of example, structures of large critical dimensions are surface structures obtained by means of a mask obtained from conventional photolithography, i.e. structures whose critical dimensions are, for example, greater than or equal to 200 nm and whose repetition pitch is, for example, greater than or equal to 200 nm.

[0066] For example, for a given photodetector, structures of small critical dimensions can be superimposed on structures of large critical dimensions.

[0067] According to another example, for a given photodetector, structures of small critical dimensions can be arranged around structures of large critical dimensions.

[0068] Exemplary embodiments and alternative embodiments of a sensor of light comprising photodetectors associated with surface structures obtained from a mask itself obtained by directed self-assembly of copolymers will now be described, it being understood that the present description is not limited to these particular examples of process.

[0069] Figures 1A to 1D illustrate an exemplary embodiment of a method for manufacturing a light sensor 1, each figure being a sectional view illustrating a step of the method.

[0070] In this embodiment, the self-assembly of the block copolymer is implemented by graphoepitaxy.

[0071] [Fig.lA] illustrates, by a sectional view, a step of this method. [Fig.lA] illustrates only a part of the light sensor 1.

[0072] The sensor 1 comprises a silicon layer 100. The sensor 1 comprises pixels having photodetectors PD, for example photodiodes or pinched diodes, arranged in the silicon layer 100.

[0073] In [Fig.lA], and in Figures 1B to 1D, only one PD photodetector is shown, although what will be described for the PD photodetector of [Fig.lA] can be applied to any of the PD photodetectors of the sensor 1. For example, each step described for the PD photodetector shown in Figures 1A to 1D is implemented simultaneously for each PD photodetector of the sensor 1.

[0074] Furthermore, although not illustrated in [Fig.1A], the PD photodetectors of the sensor 1 form a matrix of PD photodetectors, in which the photodetectors are organized in rows and columns. For example, the pitch of the PD photodetectors is less than or equal to 1.5 μm, for example less than or equal to 1 μm.

[0075] For example, the photodetectors PD of the sensor 1 are isolated from each other and by vertical isolation structures 102, for example deep trench insulation (DTI) or capacitive deep trench insulation (CDTI).

[0076] By way of example, each photodetector PD corresponds to a portion of the layer 100. By way of example, each photodetector PD extends from a front face 104 of the layer 100 to a rear face 106 of the layer 100.

[0077] The sensor 1 further comprises an interconnection structure 108 of the BEOL type. The interconnection structure 108 rests on the front face 104 of the layer 100. Although this is not detailed in [Fig.lA], the interconnection structure 108 comprises, for example, metallization levels embedded in insulating layers which isolate the metallization levels from each other. The metallization levels, in practice portions of conductive layers, are connected to each other by conductive vias passing through insulating layers of the structure 108. By way of example, the interconnection structure 108 electrically couples together electronic components (not shown in [Fig.lA]) formed on and / or in the layer 100 on the side of its front face 104, for example metal-oxide-semiconductor (MOS - "Metal Oxide Semiconductor") transistors, and / or electrical contacts (not shown in [Fig.lA]) formed on the face of the interconnection structure 108 opposite the front face 104 of the layer 100 and making it possible to connect the sensor 1 to its environment.

[0078] At the step of [Fig. 1 A], a layer 110 has been deposited on the layer 100, on the side of its rear face 106. The layer 110 can be deposited directly on the layer 100, or on one or more layers resting on the face 106 of the layer 100. For example, the layer 110 is a resin layer.

[0079] In the example of [Fig. 1A], the layer 110 is deposited on a layer 112 of hard mask, for example made of silicon oxide, the layer 112 resting on the rear face 106 of the layer 100. In other words, in the example of [Fig. 1A], the layer 112 is deposited on the layer 100 on the side of its rear face 106, then the layer 110 is deposited on and in contact with the layer 112.

[0080] Still in the step of [Fig. 1 A], for each PD photodetector, at least one guide cavity 114 is etched in the layer 100. More particularly, for each PD photodetector, at least one guide cavity 114 is etched opposite the PD photodetector. Each guide cavity 114 passes through the layer 100 in a direction orthogonal to the face 106 of the layer 100.

[0081] By way of example, each cavity 114 has, in a plane parallel to the face 106, a smallest dimension, or critical dimension, equal to N*L0, with N a positive integer and L0 the characteristic length of the block copolymer which will be used during the directed self-assembly.

[0082] As illustrated in [Fig. 1 A], in cases where layer 110 rests on and in contact with an underlying hard mask layer 112, cavities 114 open onto this layer 112.

[0083] As is customary in methods of self-assembly of block copolymers by graphoepitaxy, the dimensions of the guide cavities 114 are adapted according to the block copolymer used. The choice of the dimensions of the guide cavities 114 according to a block copolymer is within the reach of the person skilled in the art.

[0084] [Fig.lB] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.lB] represents the structure described in relation to [Fig.lA] at a next step of the method.

[0085] In the step of [Fig. 1B], a block copolymer was deposited in each cavity 114. In addition, an annealing step was implemented. The annealing step allows the block copolymer to organize itself, in each cavity, according to an alternation of phases 116 comprising first blocks of the block copolymer and phases 118 comprising second blocks of the block copolymer.

[0086] More particularly, the aim being to use the block copolymer to produce an etching mask allowing the formation by etching of surface structures on the side of the face 106 of the layer 100, the conditions (temperature, solvent) of the annealing, the mass ratio of the monomers of the first blocks of the block copolymer and of the monomers of the second blocks of the block copolymer and the dimensions of the cavities 114 are determined so that each phase 116 and each phase 118 extend over the entire height, or thickness, of the copolymer material arranged in the cavities 114, and opens onto the layer underlying the layer 110, namely here onto the layer 112.

[0087] [Fig.lC] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.lC] represents the structure described in relation to [Fig.lB] at a next step of the method.

[0088] In the step of [Fig. 1C], the 118 or 116 phases of the block copolymer have been removed. In this example, it is the 116 phases that are removed. The 116 phases are, for example, removed by a chemical treatment.

[0089] As a result, in the cavities 114, the phases 118 left in place form masking structures, or, in other words, a mask 120 obtained by directed self-assembly of the block copolymer.

[0090] Furthermore, at the step of [Fig. IC], in this example where layer 110 rests on layer 112, the portions of layer 112 exposed following the removal of phases 116 of the block copolymer have been removed by etching. In other words, mask 120 has been transferred into layer 112 to form through openings therein.

[0091] [Fig.lD] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.lD] represents the structure described in relation to [Fig.lC] at a next step of the method.

[0092] At the step of [Fig.1D], surface structures 122 have been formed by etching in the layer 100, on the side of the rear face 106 of this layer 100.

[0093] More particularly, in this example where layer 110 rests on layer 112, the etching of layer 100 is carried out from the openings formed in the previous step in hard mask 112, after having previously removed mask 120 and layer 110.

[0094] As an example, depending on the conditions of implementation of the directed self-assembly of the block copolymer, the structures 122 may correspond: - to cylindrical holes in the layer 100, these holes each being arranged opposite a corresponding recess of the mask 120, where a phase 116 has been removed in this example, - to cylindrical pillars in the layer 100, these pillars each being arranged opposite a corresponding portion of the mask 120, where a phase 118 has been left in place in this example, - to trenches parallel to each other or forming a random pattern of the fingerprint type, these trenches each being arranged opposite a corresponding recess of the mask 120, where a phase 116 has been removed in this example, or - to slats parallel to each other or forming a random pattern of the fingerprint type, each slat being arranged opposite a corresponding portion of the mask 120, where a phase 118 has been left in place in this example.

[0095] Furthermore, in this example, at the step of [Fig.1D], the layer 112 has been removed after the formation of the structures 122.

[0096] In this example, at the step of [Fig. 1D], the portion of the layer 100 corresponding to the photodetector PD comprises, on the side of its rear face 106, at least one zone 124 provided with structures 122, and at least one zone 126 devoid of structure 122. In other words, the photodetector is associated with at least one zone 124 provided with structures 122 and at least one zone 126 devoid of structure 122, the zones 124 and 126 being formed opposite the photodetector PD, on the side of the rear face 106 of the layer 100.

[0097] In another example, the structures 122 are formed over all or almost all of the surface of the photodetector PD on the side of the rear face 106 of the layer 100, for example over at least 80% of this surface of the photodetector PD. In other words, in another example, only a zone 124 provided with structures 122 is formed opposite the photodetector PD, on the side of the rear face 106 of the layer 100, and this zone 122 extends over all or almost all of the surface of the photodetector on the side of the rear face 106 of the layer 100.

[0098] In a following step not illustrated, the recesses (trenches or cylindrical holes) formed in the layer 100 during etching to form the structures 122 may each be filled with a material of optical index different from that of the layer 100 in which the structures 122 are formed. For example, the recesses may be filled with silicon oxide, aluminum oxide or hafnium oxide. For example, this material is deposited so as to completely fill each recess, and the deposition of the material is, for example, followed by a chemical mechanical polishing (CMP) step.

[0099] The implementation of the method described in relation to figures 1A to 1D comprises the use of the mask 120 obtained by directed self-assembly of the block copolymer to form, during the etching described in relation to the step of [Fig.1D], at least one structuring 122 on the side of the rear face 106 of the photodetector PD.

[0100] In the example of Figures 1A to 1D, the etching to form the structures 122 does not directly use the mask 120 but rather the hard mask 112. However, the mask 120 is used to form through openings in the hard mask 112, therefore to form by etching the structures 122. In another example not illustrated, the hard mask layer 112 is omitted, and the etching to form the structures 122 then directly uses the mask 120.

[0101] In the example of Figures 1A to 1D, at the step of [Fig.lC], the phases 118 are left in place and the phases 116 are removed. The reverse is also possible.

[0102] In the example illustrated by FIGS. 1A to 1D, for each PD photodetector, two guide cavities 114 are etched facing the PD photodetector in the step of [Fig. 1A]. In other examples not illustrated, for each PD photodetector, the number of guide cavities 114 etched facing the PD photodetector may be smaller or larger than two. For example, a single cavity 114 may be etched facing each PD photodetector. For example, this single cavity 114 extends facing almost the entire surface of the PD photodetector on the side of the rear face 106 of the layer 100, for example over more than 80% of the surface of the PD photodetector, so as to increase the number of structurings 122 formed compared to the case where such a single cavity would cover a smaller part of the surface of the PD photodetector.

[0103] In the example of Figures 1A to 1D, for each cavity 114, the directed self-assembly of the block copolymer is such that several structures 122 are formed from the mask 120 corresponding to this cavity. In another example, the directed self-assembly of the block copolymer is such that a single structure 122 is formed from the mask 120 corresponding to a guide cavity.

[0104] Although examples of embodiments of a method in which the directed self-assembly of the block copolymer is carried out by graphoepitaxy have been described in relation to Figures 1A to 1D, the person skilled in the art is able, from the description given above, to adapt these examples to the case where the directed self-assembly of the block copolymer is carried out by chemo-epitaxy.

[0105] For example, the person skilled in the art is able to provide chemical guidance structures for self-assembly by chemo-epitaxy, so as to obtain, on the side of the rear face 106 of the layer 100, opposite at least one PD photodetector or each PD photodetector, zones 124 and 126 or a single zone 124.

[0106] By way of example, figures 6 and 7 of patent application EP 3503165 A1 illustrate an example of a chemo-epitaxy method making it possible to obtain first zones where the block copolymer is organized in alternating phases perpendicular to the rear face 106 of the layer 100 and second zones where the block copolymer is organized in alternating phases parallel to the face 106. In such an example, the first zones each make it possible to form a zone 124 provided with structures 122, and the second zones each make it possible to form a zone 126 devoid of structures 122.

[0107] By way of example, at least one photodetector PD or each photodetector PD is associated with (or opposite) several zones 124 and associated with (or opposite) at least one zone 126. The dimensions of the zones 124 and 126 associated with the photodetector are then, for example, chosen so that each zone 126 corresponds to a structuring of large critical dimensions. In this case, the structurings 122 of small critical dimensions are arranged around each structuring of large critical dimensions. By way of another example, the dimensions of the zones 124 and 126 associated with the photodetector are chosen so that each zone 124 corresponds to a structuring of large critical dimensions. In this case, structurings 122 of small critical dimensions are arranged inside each structuring of large critical dimensions.

[0108] In the embodiment of Figures 1A to 1D, the guide cavities 114 are formed in the layer 110 which rests on the rear face 106 of the layer 100. In an alternative embodiment, the guide cavities 114 are formed, i.e. etched, directly in the layer 100.

[0109] The person skilled in the art will know how to adapt the different examples described in relation to FIGS. 1A to 1D where the cavities are etched in the layer 110, to the case where these cavities are etched directly in the layer 100.

[0110] Figures 2A to 2D illustrate an example of an alternative embodiment of the method described in relation to Figures 1A to 1D, in the case where the guide cavities 114 are etched directly in the layer 100.

[0111] Figures 2A to 2D illustrate only a part of the light sensor 1, and, more particularly, a single PD photodetector of the sensor 1. However, the steps described in relation to Figures 2A to 2D for a single PD photodetector are, preferably, implemented simultaneously in several PD photodetectors of the sensor 1, for example in all the PD photodetectors of the sensor.

[0112] [Fig.2A] illustrates, by a sectional view, a step of this variant embodiment of the method of figures 1A to 1D. Figures 1A and 2A are similar, and only the differences between these two figures are highlighted here.

[0113] In [Fig.2A], instead of depositing a layer 110 and forming guide cavities 114 therein as in [Fig. 1A], one or more guide cavities 114 are etched directly in the layer 100.

[0114] In the example of [Fig.2A], a single cavity 114 is etched for the photodetector PD, but in other examples not illustrated, several cavities 114 are etched for this photodetector.

[0115] As an example, the cavity 114 is etched by forming a mask 200, for example a hard mask, on and in contact with the face 106 of the layer 100, the mask 200 comprising a through opening at each location where a cavity 114 will be engraved.

[0116] In this example, the dimensions of the cavity 114 are chosen so that the mask 120 which will be obtained in the cavity 114 by directed self-assembly of the copolymer only results in the formation of a single structuring 122. For example, the cavity 114 has a width or a diameter equal to 1.5*L0.

[0117] In other examples not illustrated, the dimensions of the cavity 114 are chosen so that the mask 120 obtained in the cavity 114 by directed self-assembly of the copolymer makes it possible to form several structures 122.

[0118] [Fig.2B] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.2B] represents the structure described in relation to [Fig.2A] at a next step of the method.

[0119] In the step of [Fig.2B], the block copolymer was deposited in each cavity 114. In addition, an annealing step was implemented so that the block copolymer is organized according to an alternation of phases 116 and phases 118. In this example where the cavity 114 has a width or a diameter equal to l.5*L0, a single phase 116 is formed, in a central region of the cavity 114.

[0120] [Fig.2C] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.2C] represents the structure described in relation to [Fig.2B] at a next step of the method.

[0121] At the step of [Fig.2C], the 118 or 116 phases of the block copolymer have been removed. In this example, the 116 phase is removed. The 116 phase is, for example, removed by a chemical treatment. The 118 phases left in place form masking structures, or, in other words, a mask 120 obtained by directed self-assembly of the block copolymer.

[0122] Furthermore, in the step of [Fig.2C], a portion of the layer 100 exposed at the bottom of the cavity 114 following the removal of the phase 116 of the copolymer has been removed by etching. This results in the formation of a structuring 122 corresponding here to a hole or a trench.

[0123] In another example not illustrated, the phase 118 of the copolymer is removed while the phase 116 is left in place, and the structuring 122 obtained during etching then corresponds to a pillar or a lamella.

[0124] [Fig.2D] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.2D] represents the structure described in relation to [Fig.2C] at a next step of the method.

[0125] At the step of [Fig.2D], masks 120 and 200 have been removed.

[0126] In a following step not illustrated, the cavity 114 and the portion(s) of the layer 100 etched in the step of [Fig.2C], i.e. the structuring 122 in the example of figures 2A to 2D, can be filled with a material of optical index different from that of silicon, for example during a material deposition step which can be followed by a CMP step.

[0127] An advantage of etching the guide cavities 114 directly in the silicon of the layer 100 is that each cavity 114 can then correspond to a structuring of larger critical dimension than those of the structurings 122, for example to a structuring of large critical dimension. In this case, structurings 122 of small dimensions are then stacked with structurings of larger dimensions.

[0128] More generally, structures of larger critical dimensions than those of the structures 122, for example structures of large critical dimensions, can be associated with structures 122.

[0129] Other examples of methods for associating structurations 122 with structurations of larger critical dimensions than those of structurations 122, for example structurations of large critical dimensions, will now be described. In these examples, the structurations of larger critical dimensions than those of structuration 122 are formed during an etching step, for example an additional etching step implemented after the etching to form the structurations 122.

[0130] Figures 3A to 3C illustrate a first example of a method comprising an additional etching step to form structures of larger critical dimensions than those of structures 122.

[0131] Figures 3A to 3C illustrate only a part of the light sensor 1, and, more particularly, a single PD photodetector of the sensor 1. However, the steps described in relation to Figures 3A to 3C for a single PD photodetector are, preferably, implemented simultaneously in several PD photodetectors of the sensor 1, for example in all the PD photodetectors of the sensor.

[0132] In this first example, as illustrated in [Fig.3A], structures 122 have been formed on the side of the rear face 106 of the layer 100 over almost the entire surface of the photodetector PD arranged on the side of the face 106 of the layer 100, for example an excess of 80% of this surface. Thus, in [Fig.1A], all the structures 122 belong to a single zone 124, and no zone 126 is associated with the photodetector PD.

[0133] In this example, the structures 122 were obtained by means of directed self-assembly implemented by chemo-epitaxy or by graphoepitaxy.

[0134] Furthermore, in the step of [Fig.3A], a mask 300 is formed on the side of the rear face 106. The mask 300 comprises portions covering structures 122, and openings 302 opening onto structures 122. Each opening 302 is arranged at a location where it is desired to form a corresponding structure. of greater critical dimension than those of the 122 structures.

[0135] In the example of [Fig.3A], the mask 300 comprises several openings 302 for the illustrated PD photodetector. In another example not illustrated, the mask 300 may comprise only a single opening 302 for the PD photodetector.

[0136] [Fig.3B] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.3B] represents the structure described in relation to [Fig.3A] at a next step of the method.

[0137] At the step of [Fig.3B], structures 304 of larger critical dimensions than those of the structures 122 have been formed in the layer 100, by etching on the side of the rear face 106 of this layer 100. The structures 304 are each formed from a corresponding opening 302.

[0138] [Fig.3C] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.3C] represents the structure described in relation to [Fig.3B] at a next step of the method.

[0139] At the step of [Fig.3C], the mask 300 has been removed, and, at a following step not illustrated, the structures 122 and 304 can be filled with a material of optical index different from that of silicon.

[0140] The photodetector PD thus obtained is therefore associated with structures 122 of small critical dimensions and with structures 304 of larger critical dimensions, for example with structures 304 of large critical dimensions. In addition, certain structures 122 are stacked with a corresponding structure 304, and other structures 122 are not stacked with a structure 304 and are arranged around the structures 304.

[0141] Figures 4A and 4B illustrate a second example of a method comprising an additional etching step to form structures of larger critical dimensions than the structures 122.

[0142] Figures 4A and 4B illustrate only a part of the light sensor 1, and, more particularly, a single PD photodetector of the sensor 1. However, the steps described in relation to Figures 4A and 4B for a single PD photodetector are, preferably, implemented simultaneously in several PD photodetectors of the sensor 1, for example in all the PD photodetectors of the sensor.

[0143] In this second example, as illustrated in [Fig.4A], structures 122 have been formed on the side of the rear face 106 of the layer 100. However, unlike in [Fig.3A], on the side of the face 106, there are zones 126 devoid of structures 122, and one or more zones 124 provided with structures 122.

[0144] In this example, the structures 122 were obtained by means of directed self-assembly implemented by chemo-epitaxy or by graphoepitaxy.

[0145] Further, in the step of [Fig.4A], a mask 400 is formed on the back face side 106. The mask 400 comprises portions each covering a corresponding zone 126, and further comprises at least one opening 402 opening onto structures 122. Each opening 402 opens onto a corresponding zone 124. In the example of [Fig.4A], there are as many openings 402 as there are zones 124.

[0146] [Fig.4B] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.4B] represents the structure described in relation to [Fig.4A] at a next step of the method.

[0147] At the step of [Fig.4B], structures 404 of larger critical dimensions than the structures 122 have been formed in the layer 100, by etching on the side of the rear face 106 of this layer 100. The structures 404 are each formed from a corresponding opening 402

[0148] Furthermore, in the step of [Fig.4B], the mask 400 has been removed, and, in a following step not illustrated, the structures 122 and 404 can be filled with a material of optical index different from that of silicon.

[0149] The PD photodetector thus obtained is associated with structures 122 and at least one structure 404 of larger critical dimension than those of the structures 122, for example at least one structure 404 of large critical dimension.

[0150] Furthermore, in the example of Figures 4A and 4B, each structuring 122 is stacked with a corresponding structuring 404, and no structuring 122 is arranged around the structurings 404. In other words, the structurings 404 are formed only opposite areas 124 provided with structurings 122.

[0151] Figures 5A and 5B illustrate a third example of a method comprising an additional etching step to form large-scale structures.

[0152] Figures 5A and 5B illustrate only a part of the light sensor 1, and, more particularly, a single PD photodetector of the sensor 1. However, the steps described in relation to Figures 5A and 5B for a single PD photodetector are, preferably, implemented simultaneously in several PD photodetectors of the sensor 1, for example in all the PD photodetectors of the sensor.

[0153] In this third example, as illustrated in [Fig.5A], structures 122 have been formed on the side of the rear face 106 of the layer 100. As in [Fig.4A], on the side of the face 106, there are one or more zones 126 devoid of structure 122, and one or more zones 124 provided with structures 122.

[0154] In this example, the structures 122 were obtained by means of directed self-assembly implemented by chemo-epitaxy or by graphoepitaxy.

[0155] Furthermore, in the step of [Fig.5A], a mask 520 is formed on the side of the rear face 106. The mask 520 comprises portions each covering a corresponding zone 124 and therefore the structures 122. The mask 520 further comprises at least one opening 502 opening onto a zone 126 devoid of structure 122. In In this example, the mask 520 includes three openings 502, although in other examples not shown the mask may include one, two, or more than three openings 502.

[0156] [Fig.5B] illustrates, by a sectional view, a next step of the method. More particularly, [Fig.5B] represents the structure described in relation to [Fig.5A] at a next step of the method.

[0157] At the step of [Fig.5B], structures 504 of larger critical dimensions than those of the structures 122 have been formed in the layer 100, by etching on the side of the rear face 106 of this layer 100. The structures 504 are each formed from a corresponding opening 502.

[0158] Furthermore, in the step of [Fig.5B], the mask 520 has been removed, and, in a following step not illustrated, the structures 122 and 504 can be filled with a material of optical index different from that of silicon.

[0159] The PD photodetector thus obtained is associated with structures 122 and with structures 504 of larger critical dimensions than those of the structures 122, for example structures 504 of large critical dimensions.

[0160] Furthermore, no structuring 122 is stacked with a structuring 504, and the structurings 122 are arranged around the structurings 504. In other words, the structurings 504 are formed only opposite areas 126 devoid of structurings 122.

[0161] Although the case where the structures 304, 404 and 504 are formed during an etching subsequent to the etching to form the structures 122 has been described in connection with FIGS. 3A to 3C, 4A and 4B, and 5A and 5B, in other examples not illustrated, this order of etchings may be reversed or the two etchings may be implemented simultaneously. The implementation of these other examples is within the ability of a person skilled in the art.

[0162] Furthermore, the person skilled in the art is able to adapt the preceding examples of manufacturing methods making it possible to associate structures 122 with structures of larger critical dimensions than those of the structures 122, in the case where the directed self-assembly is implemented by graphoepitaxy and the guide cavities 114 are etched directly in the layer 100.

[0163] Examples of embodiments and variants in which the structures are formed in the layer 100, by etching away portions of this layer 100, have been described above in relation to FIGS. 1A to 5B.

[0164] Alternatively, the structures 122 are formed in an insulating layer resting on the rear face 106 of the layer 100 comprising the PD photodetectors. The implementation of such a variant and its adaptation to the various examples described previously is within the reach of those skilled in the art.

[0165] In particular, in such a variant, the etching to form the structures 122 consists of removing portions of the insulating layer in which the structures 122 are formed rather than portions of the layer 100 as described previously. For example, the insulating layer in which the structures 122 are formed has its face facing the face 106 which is arranged less than 1 μm from the face 106, for example less than 500 nm from the face, or even which is in contact with the face 106.

[0166] [Fig.6] illustrates by curves examples of quantum efficiency gain G of pixels each comprising a PD photodetector associated with structurings 122 relative to a reference pixel (without structurings), for different implementations of the structurings and for light received at a wavelength of approximately 940 nm.

[0167] In the example of [Fig.6], the structures are cylindrical pillars arranged in a network according to a pitch P, the network covering all or almost all of the surface of the photodetector PD intended to receive light, for example at least 80 of this surface.

[0168] The step P, in nanometers, corresponds to the abscissa axis, the relative gain G, in percent, corresponding to the ordinate axis.

[0169] Curve 600 illustrates the case of pillars 122 with a height equal to 280 nm and a diameter equal to 40 nm, curve 602 illustrating the case of pillars 122 with a height equal to 240 nm and a diameter equal to 50 nm and curve 604 illustrating the case of pillars 122 with a height equal to 240 nm and a diameter equal to 60 nm.

[0170] Curves 600, 602 and 604 show that, for pillars 122 of given dimensions, the gain in quantum efficiency is greater when the repetition pitch P of the pillars 122 decreases.

[0171] [Fig.7] represents a schematic top view of a matrix of PD photodetectors of the sensor 1 according to an exemplary implementation. In the example of [Fig.7], several PD photodetectors, for example all the PD photodetectors of the sensor 1, are each associated with structures 122 forming a random pattern of fingerprint type. Because these patterns are random, they are different from one PD photodetector to another. As a result, the response of the matrix of PD photodetectors, or, more broadly, the response of the sensor 1, is unique. This unique response is, for example, used to identify the sensor 1.

[0172] 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.

[0173] Finally, the practical implementation of the embodiments and variants described is within the reach of the person skilled in the art from the functional indications given below. above.

[0174] In particular, the person skilled in the art is able to choose a block copolymer according to the shape and dimensions targeted for the structures 122. An example of a block copolymer is PS-b-PMMA (polystyrene-block-polymethylmethacrylate), and other examples of block copolymers are, for example, given in paragraph

[0022] of application EP 3 503 165 A1.

[0175] Similarly, to form the structures 122, the person skilled in the art is able to choose a given graphoepitaxy method from among the known graphoepitaxy methods. For example, although this has not been described previously, the person skilled in the art is able to provide for functionalizing the bottom and / or the walls of the guide cavities depending on the chosen copolymer, to obtain the mask which will be used for the formation of the structures 122 by etching. An example of such functionalization is described in patent application EP 3 465 739 A1.

[0176] Furthermore, to form the structures 122, the person skilled in the art is able to choose a given chemo-epitaxy method from among the known chemo-epitaxy methods. For example, although this has not been detailed previously, the person skilled in the art can choose the chemo-epitaxy method from among the LiNe method, the COOL method, the SMART method or even the method described in patent application EP 3 503 165 A1.

[0177] Obtaining structuring of critical dimensions less than 200 nm, for example less than 100 nm, or even 50 nm, with a repetition pitch less than 200 nm, for example less than 100 nm, or even 50 nm, makes it possible to improve the near-infrared quantum absorption of a pixel with backside illumination having a silicon photodetector with sides (in top view) of length less than 1.5 pm, or even 1 pm. However, structures having these critical dimensions and this repetition pitch can also make it possible to improve the near-infrared quantum absorption of a front-illuminated pixel having a silicon photodetector with sides (in top view) of length less than 1.5 pm, or even 1 pm, or to improve the visible quantum absorption of a pixel having a front-illuminated or back-illuminated silicon photodetector.Thus, the present description is not limited to pixels which are intended to operate in the near infrared and / or which have silicon photodetectors having sides of length less than 1.5 pm and / or which are back-illuminated.

Claims

Claims

1. Manufacturing method comprising, for each photodetector (PD) of a matrix of photodetectors of a light sensor (1), use of a mask (120) obtained by directed self-assembly of a block copolymer to form, by a first etching step, at least one first structuring (122) on the side of a first face (106) of the photodetector intended to receive light, said at least one first structuring being formed opposite the photodetector.

2. The method of claim 1, wherein the characteristic length of the block copolymer is less than 100 nm, preferably 50 nm.

3. A method according to claim 1 or 2, wherein the directed self-assembly of the block copolymer is carried out by chemo-epitaxy.

4. A method according to any one of claims 1 or 2, wherein the directed self-assembly of the block copolymer is carried out by graphoepitaxy.

5. Method according to claim 4, in which the first etching step comprises a transfer of the mask (120) obtained by directed self-assembly of the block copolymer into a hard mask (112) to form through openings therein, then an etching from said openings.

6. Method according to claim 4 or 5, in which the directed self-assembly of the block copolymer comprises, for each photodetector (PD), an etching of at least one guide cavity (114), and a deposition of the block copolymer in said at least one guide cavity (114).

7. A method according to any one of claims 1 to 6, wherein the photodetectors (PD) are arranged in a silicon layer (100) and the first structurings (122) are formed in an insulating layer resting on the silicon layer (100).

8. A method according to any one of claims 1 to 6, wherein the photodetectors (PD) are arranged in a silicon layer (100) and the first structurations (122) are formed in the silicon layer (100).

9. Method according to claim 6, wherein the photodetectors (PD) are arranged in a silicon layer (100) and, for each photodetector (PD), said at least one guide cavity (114) is etched directly in the silicon (100).

10. Method according to any one of claims 1 to 9, wherein, for at least one of the photodetectors (PD), several first structurations (122) are formed during the first etching step, the pitch of the first structurations (122) preferably being less than 100 nm.

11. Method according to any one of claims 1 to 10, wherein, for at least one photodetector (PD), the method further comprises forming, by a second etching step, at least one second structuring (304, 404, 504) on the side of the first face (106), said at least one second structuring (304, 404, 504) having, in a plane parallel to said first face (106), a smaller dimension greater than a smaller dimension of the first structurings (122).

12. The method of claim 11, wherein the second etching step is performed after the first etching step.

13. A method according to any one of claims 1 to 11, wherein the self-assembly of the block copolymer is configured so that, for several of said photodetectors (PD), the first structurations (122) form a random fingerprint-like pattern.

14. Method according to any one of claims 1 to 13, in which the pitch of the photodetectors (PD) is less than or equal to 1.5 pm, for example less than 1 pm.

15. The method of claim 6, wherein: the photodetectors (PD) are arranged in a silicon layer (100); said at least one guide cavity (114) is etched directly in the silicon (100); and for at least one photodetector (PD), a width or diameter of said at least one guide cavity (114) is substantially equal to 1.5 times the characteristic length of the block copolymer.

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