Image sensor

Abstract

Image Sensor This description relates to an image sensor (100) comprising a plurality of pixels (PIX) formed in and on a semiconductor substrate (101) and each comprising at least one photodetector (PD) comprising a resonant cavity (103) having, between first (105) and second (107) mirror layers, a photoconversion layer (109) and at least one diffractive structure (111). Figure for the abstract: Fig. 1

Description

Title of the invention: Image sensor technical field

[0001] This description relates generally to electronic devices, more particularly to image sensors comprising resonant cavity photodetectors. Previous technique

[0002] Image sensors incorporating resonant-cavity-enhanced (RCE) photodetectors have been proposed. Examples of such sensors, which provide very good spectral selectivity, are detailed, for instance, in the MDPI review by Jinzhao Li et al. entitled "Metasurface Photodetectors." This review describes image sensors comprising resonant optical cavity photodetectors of varying thicknesses. The thickness of each cavity is controlled, in this case, by grayscale lithography. However, the resulting image sensor has a limited number of spectral channels due to the thickness resolution achievable by grayscale lithography. Furthermore, the aforementioned review indicates that other types of resonant optical cavity photodetectors have been proposed to achieve multispectral functionality.However, all the proposals described result in technologically complex solutions to implement, as they include structures suspended above air cavities. Summary of the invention.

[0003] One objective of an embodiment is to overcome all or part of the drawbacks of known image sensors and their manufacturing processes. In particular, one embodiment aims to overcome all or part of the drawbacks of existing image sensors comprising resonant cavity photodetectors and manufacturing processes for such sensors.

[0004] For this purpose, an embodiment provides an image sensor comprising a plurality of pixels formed in and on a semiconductor substrate and each comprising at least one photodetector comprising a resonant cavity having, between first and second mirror layers, a photoconversion layer and at least one diffractive structure.

[0005] According to one embodiment, each diffractive structure comprises a plurality of first regions in a first material having a first refractive index separated from each other by at least one second region in a second material having a second refractive index lower than the first refractive index.

[0006] According to one embodiment, the first and second materials have the same chemical composition and different structures.

[0007] According to one embodiment, the diffractive structures of the resonant cavities of the photodetectors have the same filling factor.

[0008] According to one embodiment, at least one diffractive structure of the resonant cavity of one of the photodetectors has a different filling factor than at least one diffractive structure of the resonant cavity of another photodetector.

[0009] According to one embodiment, the first regions of at least one diffractive structure of the resonant cavity of one of the photodetectors form a network having a different pitch from that of a network formed by the first regions of at least one diffractive structure of the resonant cavity of another photodetector.

[0010] According to one embodiment, the first regions of at least one diffractive structure of the resonant cavity of one of the photodetectors have different lateral dimensions from those of the first regions of at least one diffractive structure of the resonant cavity of another photodetector.

[0011] According to one embodiment, within the same diffractive structure, one of the first regions has different lateral dimensions from those of another first region.

[0012] According to one embodiment, each first region is a plot.

[0013] According to one embodiment, each first region is a band extending laterally between two opposite sides of the diffractive structure.

[0014] According to one embodiment, the first regions form a grid and the second regions form plots located in squares of the grid.

[0015] According to one embodiment, at least one of the resonant cavities has a different thickness from that of another resonant cavity.

[0016] According to one embodiment, the resonant cavity is made up of a stack comprising, in order from an upper face of the semiconductor substrate, the first mirror layer, the photoconversion layer, the diffractive structure and the second mirror layer.

[0017] According to one embodiment, each resonant cavity further comprises at least one first insulating layer interposed between at least one diffractive structure and the second mirror layer.

[0018] According to one embodiment, each resonant cavity further comprises at least one second insulating layer interposed between the photoconversion layer and at least one diffractive structure.

[0019] According to one embodiment, at least one photodetector is an infrared photodetector, preferably a near-infrared photodetector.

[0020] According to one embodiment, each pixel further comprises, superimposed on said at least one photodetector, a visible photodetector. Brief description of the drawings

[0021] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0022] [Fig.1] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0023] [Fig.2] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0024] [Fig.3] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0025] [Fig.4] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0026] [Fig.5] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0027] [Fig.6] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0028] [Fig.7] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0029] [Fig.8] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment;

[0030] [Fig. 9] is a schematic and partial side and cross-sectional view of an example of an image sensor according to one embodiment; and

[0031] Fig.1OA, Fig.1OB, Fig.1OC, Fig.1OD and Fig.1OE illustrate, by schematic and partial side and section views, structures obtained at the end of successive stages of a manufacturing process of an example of an image sensor according to an embodiment. Description of the implementation methods

[0032] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0033] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the circuits The control circuits for the pixels of the image sensors have not been detailed, as their implementation is within the capabilities of a person skilled in the art based on the information provided in this description. Furthermore, the applications of image sensors incorporating resonant cavity photodetectors have not been detailed, as the described embodiments are compatible with all or most applications of such image sensors, possibly requiring adaptations that a person skilled in the art can make after reading this description.As an example, the image sensors of this description can be implemented in 3D imaging applications, biomonitoring applications — for example, applications aimed at performing optical measurements of blood glucose — and applications using an Ambient Light Sensor (ALS) — for example, white balance adjustment applications (WB).

[0034] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0035] 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", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0036] Unless otherwise specified, the expressions "approximately", "about", "substantially", and "in the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0037] In the following description, the terms "insulating" and "conducting" mean, unless otherwise specified, electrically insulating and electrically conductive respectively.

[0038] Unless otherwise specified, the expression "in contact with" means "in mechanical contact with".

[0039] The term "visible light" refers to electromagnetic radiation with a wavelength between 400 nm and 800 nm. The term "infrared radiation" refers to electromagnetic radiation with a wavelength between 800 nm and 1 mm. In the infrared range, near-infrared (Short-Wave Infrared - SWIR) radiation has a wavelength between 800 nm and 1.7 µm.

[0040] The term "transmittance of a layer" refers to the ratio of the intensity of radiation exiting the layer to the intensity of radiation entering the layer. In the following description, a layer is said to be opaque to radiation when its transmittance for that radiation is strictly less than 40%, preferably less than or equal to 25%, and more preferably less than or equal to 10%. Conversely, a layer is said to be transparent to radiation when its transmittance for that radiation is greater than or equal to 40%, preferably greater than or equal to 75%, and more preferably greater than or equal to 90%. The preceding definitions of the terms opaque and transparent are not limited to the case of a single layer, but apply more generally to any element that may be exposed to radiation, for example, a substrate, a region, a stack of several layers, etc.

[0041] The expression "radiation of interest" refers to radiation having a wavelength corresponding substantially to a peak of maximum absorption of a photosensitive element, for example a photodetector of an image sensor pixel.

[0042] The expression "photoconversion layer" of an optoelectronic component, in particular of a photodetector, designates a layer in which the majority of the electromagnetic radiation received by the optoelectronic component is absorbed and in which this radiation is converted into electrical charges.

[0043] The refractive index of a material corresponds to the refractive index of the material for the wavelength range of the radiation captured by the image sensor. Unless otherwise specified, the refractive index is considered to be substantially constant over the wavelength range of the useful radiation, for example, equal to the average of the refractive index over the wavelength range of the radiation of interest captured by the image sensor.

[0044] The [Fig. 1] is a schematic and partial side and cross-sectional view of an example of an image sensor 100 according to one embodiment.

[0045] In the illustrated example, the image sensor 100 is intended to be illuminated or lit, from its upper face, by electromagnetic radiation comprising at least one radiation among visible light and infrared radiation, for example near-infrared radiation.

[0046] In the example shown, the image sensor 100 comprises a plurality of pixels PIX formed in and on a semiconductor substrate 101, for example a wafer or a piece of wafer made of a semiconductor material, for example silicon. The pixels PIX are, for example, arranged in a matrix according to rows and columns. Each pixel PIX has, for example, a square shape when viewed from above. This example is not limiting, however, as each pixel PIX can more generally have any shape when viewed from above, for example a polygonal shape. other than square — for example rectangular, triangular, hexagonal, etc. — or a rounded shape — for example oval, circular, etc. Although not detailed in [Fig. 1], control and readout circuits for the PIX pixels of the image sensor 100 are, for example, formed in and on the semiconductor substrate 101. Furthermore, although only three PIX pixels were shown in [Fig. 1], the image sensor 100 can of course have a much larger number of PIX pixels, for example several thousand or several million PIX pixels.

[0047] According to one embodiment, each pixel PIX of the image sensor 100 comprises a photodetector PD including a resonant cavity 103 having, between first and second mirror layers 105 and 107, a photoconversion layer 109 and at least one diffractive structure 111. For the sake of simplification, the following description details a case in which each pixel PIX of the image sensor 100 comprises a single photodetector PD. This example is not, however, limiting, and each pixel PIX of the image sensor 100 may, alternatively, comprise any number, greater than or equal to two, of photodetectors PD. The alternative embodiment in which each pixel PIX of the image sensor 100 comprises at least two photodetectors PD is readily understood by those skilled in the art from this description.

[0048] By way of example, the resonant cavities 103 of the image sensor 100 are Fabry-Perot type cavities.

[0049] In the illustrated example, the first mirror layer 105, or first optically reflective layer, covers the upper surface of the semiconductor substrate 101. In this example, the first mirror layer 105 is more precisely located on and in contact with the upper surface of the semiconductor substrate 101. The first mirror layer 105 may, for example, have a single-layer structure. In this case, the first mirror layer 105 is, for example, a metallic layer, that is, a layer of a metal or a metal alloy, or a layer of a heavily doped semiconductor material, for example, doped silicon. Alternatively, the first mirror layer 105 may have a multi-layer structure. In this case, the first mirror layer 105 is, for example, a Bragg mirror consisting of a stack of layers with alternating refractive indices.

[0050] In the example shown, the photoconversion layer 109, also called the photosensitive layer or active layer, covers the upper surface of the first mirror layer 105. In this example, the photoconversion layer 109 is located on and in contact with the upper surface of the first mirror layer 105. The photoconversion layer 109 is, for example, an optically absorbing layer designed to absorb, or capture, the radiation illuminating the image sensor 100 and to convert photons of this radiation into electron-hole pairs. The photoconversion layer 109 is, for example, an inorganic semiconductor layer, such as silicon, in a case where the image sensor 100 is a visible or near-infrared sensor. This example is not exhaustive, however, and the photoconversion layer 109 can, alternatively, be made of at least one semiconductor material from the IV family, such as germanium, silicon-germanium, germanium-tin, etc. Furthermore, the photoconversion layer 109 can incorporate a superlattice, quantum dots (for example, based on lead sulfide or indium arsenide), III-V semiconductor materials (such as InGaAs and its derivatives), II-VI semiconductor materials (such as HgCdTe), etc. It can also be layers of organic materials such as PEDOT:PSS or a material from the perovskite family. As an example, the photoconversion layer 109 has a thickness that is generally between X / 6 and X / 4, where / .is the wavelength of the incident radiation. In the case of near-infrared, this corresponds to a thickness between 200 and 400 nm, for example, approximately 250 nm.

[0051] In the illustrated example, the diffractive structure 111 covers the upper face of the photoconversion layer 109. In this example, the diffractive structure 111 is more precisely located on and in contact with the upper face of the photoconversion layer 109.

[0052] In general, the diffractive structure 111 comprises a plurality of first regions 113 made of a first material having a first refractive index n1, the first regions 113 being disjoint and laterally separated from each other by at least one second region 115 made of a second material having a second refractive index n2, different from the first refractive index n1. The first regions 113 have at least one lateral dimension strictly smaller than a wavelength of radiation of interest intended to illuminate the image sensor 100. By way of example, the first and second materials have different chemical compositions.Alternatively, the first and second materials may have identical chemical compositions and differ in their structure, one of the materials corresponding, for example, to an amorphous phase of a phase-change material, for example a chalcogenide material such as GST, Sb2S3, Sb2Se3, etc., the other material then corresponding to the crystalline phase of this material.

[0053] The first and second materials are, for example, chosen so that they exhibit the greatest possible refractive index contrast, or, in other words, so that the difference between the first and second refractive indices ni and n2 is as great as possible. The first refractive index ni is, for example, strictly greater than the second refractive index n2. Furthermore, the first and second materials exhibit, for example, at the wavelength of the radiation of interest, an extinction coefficient of approximately zero. For example, each first region 113 is made of silicon and each second region 115 is made of silicon oxide. In the case of detection in the visible spectrum, each first region 113 can, alternatively, be made of a metal oxide such as HfO2, Nb2O5, or TiO2. It can also be, for example, GaP or any other material with a high refractive index and a low extinction coefficient for the spectral band of interest. This example is not limiting, however, and each second region 115 can, alternatively, consist of an air-filled cavity or a cavity with a partial vacuum.

[0054] In the example shown, the first regions 113 have the same height, or thickness, that is to say the same dimension along a direction orthogonal to the first and second mirror layers 105 and 107. In this example, the second regions 115 also have the same height, or thickness, for example a height substantially equal to that of the first regions 113.

[0055] Each first region 113 is, for example, a plot. In this case, the diffractive structure 111 comprises, for example, a single second region 115 covering the lateral walls, or flanks, of the first regions 113. By way of example, the second region 115 fills, that is, completely fills, all the free spaces extending laterally between the first regions 113. In this example, the second region 115 is located on and in contact with all the lateral walls of the first regions 113. Each plot has, for example, a rectangular or square cross-section in top view. This example is not, however, limiting; each plot may more generally have, in top view, a cross-section of any shape, for example, a polygonal cross-section other than square or rectangular—for example, triangular, hexagonal, etc.—or a rounded cross-section—for example, oval, circular, etc.In the case where each first region 113 is a plot of rectangular, square or circular cross-section, the width, side or diameter, respectively, of the plot is for example strictly less than the wavelength of the radiation of interest, for example at least two to ten times less than the wavelength of the radiation of interest.

[0056] By way of alternative, each first region 113 may have the form of a band extending laterally along a direction parallel to the upper face of the photoconversion layer 109, for example, a direction substantially orthogonal to the cross-sectional plane of [Fig. 1], between two opposite sides of the diffractive structure 111. Each band has, for example, a rectangular shape in top view. In this alternative, the diffractive structure comprises, for example, several second regions 115, each second region 115 being then interposed laterally between two neighboring first regions 113. By way of example, each second region 115 fills, that is, completely fills, all the free spaces extending laterally between two adjacent first regions 113. In this example, each second region 115 is located on and in contact with the lateral walls of the opposite adjacent first regions 113. In the case where each first region 113 is a rectangular band, the width of each band is, for example, strictly less than the wavelength of the radiation of interest.

[0057] As an alternative, the first regions 113 can form a grid, each second region 115 then being in the form of a plot located in one of the cells of the grid. As an alternative, the first and second regions 113 and 115 can have a "free-form" shape, that is to say that the regions 113 and 115 in this case have no defined and repeatable shape and / or dimension and / or symmetry from one pixel PIX to another.

[0058] Each first region 113 corresponds, for example, to a unit element of the diffractive structure 111. The diffractive structure 111 is, for example, a meta-surface. Each first region 113 corresponds, for example, to a meta-atom of the meta-surface.

[0059] By way of example, the diffractive structure can be made so as to form a resonant waveguide grating (RWG), or guided mode resonant filter.

[0060] The diffractive structure 111 can exhibit a resonance frequency that depends on several parameters, including: the lateral dimensions of the first regions 113, the refractive indices ni and n2 of the first and second regions 113 and 115, and the spatial distribution of the first and second regions 113 and 115. By modifying these parameters, it is therefore possible to control the resonance frequency of the diffractive structure 111, for example, so that the resonance frequency corresponds to a wavelength that one wishes to capture using the PD photodetectors. Compared to the use of colored filters or the use of cavities analogous to the cavities 103 but lacking the diffractive structure 111, the use of the diffractive structure 111 provides better wavelength selectivity.

[0061] In the illustrated example, the second mirror layer 107, or second optically reflective layer, covers the upper face of the diffractive structure 111. In this example, the second mirror layer 107 is more precisely located on and in contact with the upper face of the diffractive structure 111. The second mirror layer 107 is, for example, analogous or identical to the first mirror layer 105.

[0062] Each PD photodetector thus comprises a vertical stack including, in order from the top face of the substrate 101, the first mirror layer 105, the photoconversion layer 109, the diffractive structure 111 and the second layer mirror 107. In the example illustrated in [Fig.1], the stack is more precisely made up, in order from the top face of the substrate 101, of the first mirror layer 105, the photoconversion layer 109, the diffractive structure 111 and the second mirror layer 107.

[0063] The first and second mirror layers 105 and 107 are intended to confine, in the resonant cavity 103, the incident radiation illuminating the image sensor 100. When this radiation reaches the upper face of the image sensor 100, it passes through the second mirror layer 107, the diffractive structure 111 and the photoconversion layer 109. In passing through the photoconversion layer 109, some photons of the radiation are absorbed and converted into electron-hole pairs. The residual photons, that is to say the photons not having been absorbed by the photoconversion layer 109, reach the top face of the first mirror layer 105 and are then reflected or sent back, upwards, towards the second mirror layer 107. Some photons are again absorbed and converted into electron-hole pairs by the photoconversion layer 109, while the other photons pass through the photoconversion layer 109 and the diffractive structure 111.These photons reach the lower face of the second mirror layer 107 which reflects or sends them back down towards the first mirror layer 105.

[0064] Photons with a wavelength compatible with, or selected by, the resonant cavity 103 can thus make several round trips inside the resonant cavity 103 before being absorbed by the photoconversion layer 109, thereby improving the absorption efficiency for this wavelength. The photoconversion layer 109 predominantly absorbs photons of radiation with a wavelength corresponding approximately to the resonant frequency of the resonant cavity associated with the diffractive structure 111. This allows the PD photodetectors of the PIX pixels of the image sensor 100 of [Fig. 1] to exhibit a higher efficiency or photoconversion rate than similar PD photodetectors lacking the optically resonant cavities 103, or to provide, for the same photoconversion rate, a thinner photoconversion layer 109.

[0065] Figure 1 illustrates an embodiment in which the first regions 113 of the diffractive structures 111 of all the PD photodetectors of the image sensor 100 have substantially identical lateral dimensions. Furthermore, in this embodiment, the first regions 113 form an array with a substantially constant pitch. In the case where each first region 113 is a dot, the grating pitch corresponds, for example, to a center-to-center distance between two adjacent dots. In the case where each first region 113 is a strip, the grating pitch corresponds, for example, to a distance between two centerlines of two neighboring bands. More precisely, in this case, the first regions 113 within the diffractive structure 111 of a single pixel PIX have identical lateral dimensions and a substantially constant pitch. Furthermore, in the embodiment of [Fig. 1], the first regions 113 of the diffractive structure 111 of each photodetector PD have lateral dimensions and a pitch substantially identical to the lateral dimensions and pitch of the first regions 113 of the diffractive structures 111 of the other photodetectors PD of the image sensor 100.

[0066] The diffractive structures 111 can enable the image sensor 100 to exhibit better angular tolerance than an image sensor lacking the diffractive structures 111.

[0067] Although not shown in [Fig. 1] to avoid cluttering the drawing, a peripheral insulating trench can be formed around the resonant cavity 103 of each photodetector PD of the image sensor 100. In this case, the trench extends, for example, vertically from the top face of the resonant cavity 103 over all or part of the height of the resonant cavity 103 of the photodetector PD. By way of example, the insulating trench may comprise a central region made of a conductive material, for example, a metal, a metal alloy, or a doped semiconductor material, surrounded by an insulating peripheral region, for example, made of an oxide. Alternatively, the central region may be made of a material having a low refractive index, for example, strictly lower than that of the photoconversion layer 109.

[0068] Fig. 2 is a schematic and partial side and cross-sectional view of an example of an image sensor 200 according to one embodiment.

[0069] The image sensor 200 of [Fig.2] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0070] The image sensor 200 of [Fig. 2] differs from the image sensor 100 of [Fig. 1] in that the diffractive structures 111 of the PD photodetectors of the PIX pixels of the image sensor 200 of [Fig. 2] have different fill factors. The fill factor of each diffractive structure 111 corresponds to the ratio between, on the one hand, the cumulative surface area, viewed from above, of the first regions 113, and, on the other hand, the surface area of ​​the second region 115 or the cumulative surface area of ​​the second regions 115, viewed from above, of the diffractive structure 111.

[0071] In the illustrated example, the first regions 113 of the diffractive structures 111 form a grating with a substantially constant pitch over the entire image sensor 200. In this example, the first regions 113 of the diffractive structure 111 of one of the PD photodetectors (for example, the diffractive structure 111 of the PD photodetector of the central pixel PIX, in the orientation of [Fig. 2]) exhibit lateral dimensions different from those of the first regions 113 of the diffractive structure 111 of one of the other PD photodetectors of the image sensor 200 (for example the diffractive structure 111 of the PD photodetector of the left PIX pixel, in the orientation of [Fig.2]).

[0072] The range of wavelengths absorbed by each resonant cavity 103 depends, in addition to the thickness of the cavity 103, on the fill factor of the diffractive structure 111. In a case where the diffractive structure is periodic and symmetrical, the higher the fill factor of the diffractive structure 111, the longer the wavelength of the radiation predominantly absorbed by the corresponding pixel PIX, at a constant grating spacing. However, in practice, the diffractive structure 111 may not be periodic and / or symmetrical, for example, because the optimization of this structure takes into account parameters other than the wavelength of interest, such as the angular tolerance to the angle of incidence, the crosstalk between pixels, the position of the pixel relative to the matrix, etc.Each resonant cavity 103 has an effective optical index that depends on the material of the first regions 113, this material being, for example, identical for all the cavities 103 of the image sensor 200, the fill factor, the pitch of the diffractive structure 111 and, to a second order, the geometry of the regions 113 and 115 of the diffractive structure 111 of the resonant cavity 103 under consideration. As a first approximation, providing resonant cavities 103 whose diffractive structures 111 have different fill factors makes it possible to obtain different optical indices inside these cavities, and therefore to absorb the incident radiation in different wavelength ranges.

[0073] Furthermore, the fact of providing, as in the example illustrated in [Fig.2], groups of adjacent resonant cavities 103 of the same thickness but whose diffractive structures have, within the same group, different filling factors allows the image sensor 200 to benefit from a spatial resolution higher than that which would be presented for example by the image sensor 200 without the diffractive structures 111.

[0074] By way of example, the image sensor 200 is a multispectral sensor.

[0075] Fig. 3 is a schematic and partial side and cross-sectional view of an example of an image sensor 300 according to one embodiment.

[0076] The image sensor 300 of [Fig.3] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0077] The image sensor 300 of [Fig.3] differs from the image sensor 100 of [Fig.1] in that the diffractive structures 111 of the PD photodetectors of the PIX pixels of the image sensor 300 of [Fig.3] have different filling factors. In the illustrated example, the first regions 113 of the diffractive structures 111 have different lateral dimensions from one PD photodetector to another and a substantially constant spacing. In this example, the first regions 113 of the diffractive structure 111 of one of the PD photodetectors (for example, the diffractive structure 111 of the PD photodetector of the central PIX pixel, in the orientation of [Fig. 3]) have different lateral dimensions than the first regions 113 of the diffractive structure 111 of one of the other PD photodetectors of the image sensor 300 (for example, the diffractive structure 111 of the PD photodetector of the leftmost PIX pixel, in the orientation of [Fig. 3]).

[0078] Figure 2 illustrates a case in which different filling factors of the diffractive structures 111 are obtained by modifying the lateral dimensions of the first regions 113 without modifying the spacing of the grating formed by the first regions 113. Furthermore, Figure 3 illustrates a case in which different filling factors of the diffractive structures 111 are obtained by modifying the lateral dimensions of the first regions 113 and by modifying the spacing of the grating formed by the first regions 113. These examples are not, however, limiting, and a person skilled in the art is able, as an alternative, to provide other means of obtaining different filling factors of the diffractive structures 111, for example by modifying the spacing of the grating formed by the first regions 113 without modifying the lateral dimensions of the first regions 113.Other methods for modifying the resonance wavelength have also been described above.

[0079] Fig. 4 is a schematic and partial side and cross-sectional view of an example of a 400 image sensor according to one embodiment.

[0080] The image sensor 400 of [Fig.4] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0081] The image sensor 400 of [Fig. 4] differs from the image sensor 100 of [Fig. 1] in that the first regions 113 of the diffractive structures 111 of the PD photodetectors of the PIX pixels of the image sensor 400 of [Fig. 4] have different lateral dimensions within the same diffractive structure 111. In the example shown, the first regions 113 that are part of the same diffractive structure 111 of the same PIX pixel form a grating with a substantially constant pitch. Furthermore, in this example, the first regions 113 of the diffractive structures 111 of the PD photodetectors of all the PIX pixels of the image sensor 400 form a grating with a substantially constant pitch.This example is not exhaustive, however, and a person skilled in the art may, as a variant or supplement, provide that the first regions 113 of the diffractive structure 111 of the PD photodetector of at least one of the PIX pixels of the image sensor 400 form a network presenting . a step different from that formed by the first regions 113 of the diffractive structure 111 of the PD photodetector of one of the other PIX pixels of the image sensor 400.

[0082] Fig. 5 is a schematic and partial side and cross-sectional view of an example of an image sensor 500 according to one embodiment.

[0083] The image sensor 500 of [Fig. 5] includes elements in common with the image sensor 100 of [Fig. 1]. These common elements will not be detailed again below.

[0084] The image sensor 500 of [Fig. 5] differs from the image sensor 100 of [Fig. 1] in that each resonant cavity 103 of the image sensor 500 of [Fig. 5] further comprises an insulating layer 501 interposed between the photoconversion layer 109 and the diffractive structure 111. In the example shown, the insulating layer 501 is located on and in contact, by its lower face, with the upper face of the photoconversion layer 109. Furthermore, in this example, the insulating layer 501 is located below and in contact, by its upper face, with the lower face of the diffractive structure 111. In the illustrated example, the insulating layer 501 has a substantially constant thickness. The insulating layer 501 is a transparent layer to the radiation of interest of the image sensor 500. As an example, the insulating layer 501 is made of an oxide, for example silicon oxide.The 501 insulating layer can have a single-layer or multi-layer structure, for example a structure comprising several layers, for example two layers, of transparent materials of different optical indices and exhibiting a strong contrast of optical indices, i.e. a large difference in optical indices.

[0085] By way of example, the insulating layer 501 serves as a waveguide, for instance, in the case where the diffractive structure 111 forms a guided-mode resonant filter. In this case, one or more layers having optical indices and thicknesses optically coupled to the diffractive structure 111 in order to guide the light and induce resonances can more generally be provided. Furthermore, the presence of the insulating layer 501 increases the optical path length of the light in the cavity, which constitutes another means of tailoring the resonant wavelength of the filter.

[0086] Fig. 6 is a schematic and partial side and cross-sectional view of an example of a 600 image sensor according to one embodiment.

[0087] The image sensor 600 of [Fig.6] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0088] The image sensor 600 of [Fig. 6] differs from the image sensor 100 of [Fig. 1] in that each resonant cavity 103 of the image sensor of [Fig. 6] further comprises an insulating layer 601 interposed between the diffractive structure 111 and the second mirror layer 107. In the example shown, the insulating layer 601 is located on and in contact, via its lower face, with the upper face of the diffractive structure 111. Furthermore, in this example, the insulating layer 601 is located below and in contact, via its upper face, with the lower face of the second mirror layer 107. In the illustrated example, the insulating layer 601 has a substantially constant thickness. The insulating layer 601 is transparent to the radiation of interest from the image sensor 600. As an example, the insulating layer 601 is made of an oxide, for example, silicon dioxide. The insulating layer 601 may have a single-layer or multi-layer structure, for example, a structure comprising several layers, for example, two layers, made of transparent materials with different refractive indices and exhibiting a high contrast in refractive indices.

[0089] The insulating layer 601 is for example analogous to the insulating layer 501.

[0090] Fig. 7 is a schematic and partial side and cross-sectional view of an example of a 700 image sensor according to one embodiment.

[0091] The image sensor 700 of [Fig.7] includes elements in common with the image sensor 600 of [Fig.6]. These common elements will not be detailed again below.

[0092] The image sensor 700 of [Fig.7] differs from the image sensor 600 of [Fig.6] in that the insulating layer 601 of the image sensor 700, interposed between the diffractive structure 111 and the second mirror layer 107, has a variable thickness. In the example shown, the insulating layer 601 of the resonant cavity 103 of the PD photodetector of one of the PIX pixels of the image sensor 700 (for example, the insulating layer 601 of the cavity 103 of the central PIX pixel, in the orientation of [Fig. 7]) has a different thickness than the insulating layer 601 of the resonant cavity 103 of the PD photodetector of one of the other PIX pixels of the image sensor 700 (for example, the insulating layer 601 of the cavity 103 of the leftmost PIX pixel, in the orientation of [Fig. 7]. Thus, unlike the image sensors 100, 200, 300, 400, 500 and 600 previously described in relation to Figures 1 to 6, the image sensor 700 of [Fig. 7] has a different thickness.7] includes at least one resonant cavity 103 having a height, or thickness, different from those of the other cavities 103. .

[0093] The presence of resonant cavities 103 of different thicknesses allows the image sensor 700 to access a wider spectral band than that which would be obtained by means of resonant cavities 103 differing only in the filling factors of their diffractive structures 111. Furthermore, the presence of diffractive structures 111 having different filling factors allows the image sensor 700 to exhibit a spectral resolution higher than that which would be obtained by means of a filter comprising only resonant cavities 103 of different thicknesses. for example due to inherent limitations in the processes of creating cavities of varying thicknesses.

[0094] Thus, combining, in the image sensor 700, resonant cavities 103 of different thicknesses and, inside the cavities, diffractive structures 111 with different filling factors makes it possible to access a wider spectral band or a higher resolution than that of an image sensor having only one or the other of these characteristics.

[0095] Figure 8 is a schematic and partial side and cross-sectional view of an example of image sensor 800 according to one embodiment.

[0096] The image sensor 800 of [Fig.8] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0097] The image sensor 800 of [Fig.8] differs from the image sensor 100 of [Fig.1] in that each resonant cavity 103 of the image sensor 800 of [Fig.8] includes another diffractive structure 801 interposed between the first and second mirror layers 105 and 107. In the example shown, each resonant cavity 103 further includes an insulating layer 803 interposed between the diffractive structures 111 and 801. As an alternative, the layer 803 is omitted. In the illustrated example, the insulating layer 803 is located on and in contact, by its lower face, with the upper face of the diffractive structure 111. Furthermore, in this example, the insulating layer 803 is located below and in contact, by its upper face, with the lower face of the diffractive structure 801. In the example shown, the diffractive structure 801 is located below and in contact, by its upper face, with the lower face of the second mirror layer 107.In the illustrated example, the insulating layer 803 has a substantially constant thickness. The insulating layer 803 is transparent to the radiation of interest from the image sensor 800. As an example, the insulating layer 803 is made of an oxide, for example silicon oxide.

[0098] By way of example, the diffractive structure 801 is analogous or identical to the diffractive structure 111. In the case where the diffractive structures 801 and 111 are identical, apart from manufacturing variations, this allows, for example, an increase in the thickness of the image sensor 800. By way of alternative, the diffractive structure 801 is different from the diffractive structure 111. This then provides, for example, greater freedom in the design and manufacture of the image sensor 800.

[0099] Image sensor 800, for example, because it includes the diffractive structure 801, has a higher spatial resolution than image sensor 100.

[0100] Figure 9 is a schematic and partial side and cross-sectional view of an example of image sensor 900 according to one embodiment.

[0101] The image sensor 900 of [Fig.9] includes elements in common with the image sensor 100 of [Fig.1]. These common elements will not be detailed again below.

[0102] The image sensor 900 of [Fig. 9] differs from the image sensor 100 of [Fig. 1] in that each pixel PIX of the image sensor 900 of [Fig. 9] also includes another photodetector PD' located on and directly above the photodetector PD formed in the resonant cavity 103. The photodetector PD' is, for example, sensitive in a different wavelength range than the sensitivity range of the photodetector PD. The photodetector PD' is, for example, a visible photodetector, that is, designed to capture visible light and convert this light into electron-hole pairs. In the example shown, the second mirror layer 107 is, for example, a layer of an oxide, for example silicon oxide, interposed between the photodetectors PD and PD'. As an example, the second mirror layer 107 is produced during a transfer step, for example by molecular bonding, of the PD' photodetectors visible on the PD photodetectors.

[0103] In the illustrated example, each visible photodetector PD' comprises a photoconversion layer 901, also called the active layer or photosensitive layer, interposed between the second mirror layer 107 and an insulating layer 903. In this example, the photoconversion layer 901 is located on and in contact, by its lower face, with the upper face of the second mirror layer 107 and below and in contact, by its upper face, with the lower face of the insulating layer 903. The insulating layer 903 is transparent to the radiation of interest from the image sensor 900. By way of example, the insulating layer 903 is made of an oxide, for example, silicon dioxide. The insulating layer 903 may have a single-layer or multi-layer structure, for example, a structure comprising a stack of layers made of insulating materials selected from silicon dioxide, silicon nitride, silicon oxynitride, etc.The insulating layer 903, for example, serves to passivate the sensor.

[0104] In the example shown, the photoconversion layer 901 of each visible photodetector PD' is laterally bordered by an isolation trench 905. In this example, the isolation trench 905 covers the sides of the photoconversion layer 901. The isolation trench 905 is, for example, more precisely located on and in contact with all sides of the photoconversion layer 901.

[0105] Although not illustrated in [Fig.9], the image sensor 900 may further comprise coloured filters and microlenses coating the upper face of the insulating layer 903. In this case, the coloured filters of the image sensor 900 are, for example, red, green and blue filters arranged in a matrix, for example a Bayer matrix.

[0106] Fig. 1OA, Fig. 1OB, Fig. 1OC, Fig. 1OD, and Fig. 1OE illustrate, by means of schematic and partial side and cross-sectional views, structures obtained at the end of successive steps in a manufacturing process for an image sensor 1000 according to an embodiment. The image sensor 1000 includes elements in common with the image sensor 100 of Fig. 1. These common elements will not be detailed again below.

[0107] For the sake of simplification, only two PIX pixels, each comprising a single PD photodetector, have been illustrated in Figures 10A to 10E, it being understood that the image sensor 1000 may, as an alternative, comprise a larger number of PIX pixels and that each PIX pixel may comprise several PD photodetectors.

[0108] Fig. 1OA illustrates a structure obtained at the end of a formation step, on a temporary support substrate 1001, or handle, of a stack comprising, in this order from the top face of the temporary support substrate 1001, an insulating layer 1003, the photoconversion layer 109, an insulating layer 1005 and the first mirror layer 105.

[0109] In the example shown, each PD photodetector includes a doped region 1007 that forms a semiconductor junction within the layer 109, thus enabling the extraction of photogenerated charges. The doped region 1007 extends into the photoconversion layer 109 from the top surface of the layer 109 to a depth less than the thickness of the layer 109. By way of example, the conductive region 1007 corresponds to an area of ​​the photoconversion layer 109 with a doping level that is strictly higher, for example, at least ten, one hundred, or one thousand times higher, than that of the rest of the photoconversion layer 109. The doped region 1007, for example, acts as the lower electrode of the PD photodetector and is isolated from the doped regions 1007 of the other PD photodetectors of the image sensor 1000.

[0110] Although not illustrated in [Fig.1OA] so as not to overload the drawing, a portion of the photoconversion layer 109 located on and in contact with the underlying insulating layer 1003 can, for each PD photodetector of the image sensor 1000, be doped so as to form another electrode of the photodetector 1000. Unlike the doped regions 1007, this electrode can be common to several PD photodetectors, or even to all the PD photodetectors, of the image sensor 1000.

[0111] Fig. 10B illustrates a structure obtained after a subsequent step of depositing an insulating layer 1009 on the upper face of the structure of Fig. 1OA, opening the insulating layer 1009 and the mirror layer 105 above the doped regions 1007, forming conductive vias 1011 in the openings and creating contact re-establishment elements 1013 in the insulating layer 1009.

[0112] The insulating layer 1009 covers the mirror layer 105. In the example shown, the insulating layer 1009 is more precisely located on and in contact with the mirror layer 105. By way of example, the insulating layer 1009 is made of an oxide, for example silicon oxide.

[0113] In the illustrated example, the contact elements 1013 extend into the insulating layer 1009 from the upper surface of the layer 1009 to a depth less than the thickness of the layer 1009. Each contact element 1013 is, for example, located directly above a doped region 1007. By way of example, the contact elements 1013 are made of a metal or a metal alloy. The contact elements 1013 are, for example, produced by implementing a Damascus-type process.

[0114] In the example shown, each conductive via 1011 extends from the lower face of one of the contact elements 1013, through the insulating layer 1009, the mirror layer 105, and the insulating layer 1005, to the upper face of the underlying doped region 1007. By way of example, each conductive via 1011 has a central conductive region whose sides are coated with an insulating region, for example, an oxide, such as silicon oxide. This allows, in particular, the central region of the via 1011 to be isolated from the mirror layer 105. In practice, first holes are, for example, formed in the layer 105 and then filled with oxide, and second holes with lateral dimensions smaller than the first holes are then formed in the oxide.

[0115] [Fig. 10C] illustrates a structure obtained at the end of a formation step, on the semiconductor substrate 101, of an interconnect stack 1015 and an insulating layer 1017 in which contact re-establishment elements 1019 are formed. The structure represented in [Fig. 10C] can indifferently be made before, during or after the structure previously described in relation to Figures 10A and 10B.

[0116] By way of example, the semiconductor substrate 101 is of the CMOS type (from the English "Complementary Metal-Oxide-Semiconductor") and includes CMOS transistors for controlling the PIX pixels of the image sensor 1000.

[0117] The interconnect stack 1015, for example, covers the upper surface of the semiconductor substrate 101. In the example shown, the interconnect stack 1015 is more precisely located on and in contact with the upper surface of the semiconductor substrate 101. By way of example, the interconnect stack 1015 comprises conductive layers, for example, metallic layers also called metallization levels, and alternating insulating layers. The interconnect stack 1015 allows, for example, the contact-reconnecting elements 1019 to be connected to the transistors formed in the semiconductor substrate 101.

[0118] In the example shown, the insulating layer 1017 covers the upper face of the interconnection stack 1015. As an alternative, the insulating layer 1017 may be part of the interconnection stack 1015.

[0119] In the illustrated example, the contact elements 1019 each have a height substantially equal to the thickness of the insulating layer 1017. Each contact element 1019 is, for example, intended to be brought into contact with one of the contact elements 1013. By way of example, the contact elements 1019 are made of a metal or a metal alloy. The contact elements 1019 are, for example, produced by implementing a "Damascene" type process.

[0120] Fig.1OD illustrates a structure obtained after a subsequent step of transferring the structure of Fig.1OB onto the structure of Fig.1OC and removing the temporary support substrate 1001.

[0121] The structure of [Fig. 10B] is, for example, inverted and then brought into contact, by means of faces of the insulating layer 1009 and contact elements 1013 opposite the temporary support substrate 1001 (the lower faces of the insulating layer 1009 and the contact elements 1013, in the orientation of [Fig. 1OD]), with the upper faces of the insulating layer 1017 and the contact elements 1019 of the structure of [Fig. 1OC], respectively. By way of example, the structures are mechanically joined, i.e., mechanically fixed to one another, by bonding the contacting surfaces. The bonding is, for example, a direct type of bonding, such as molecular bonding. In the case where the insulating regions 1009 and 1017 are oxide and the contact re-establishment elements 1013 and 1019 are metallic, the molecular bonding is said to be "hybrid".

[0122] The removal of the temporary support substrate 1001 is, for example, carried out by chemical and mechanical polishing (CMP). In the example shown, the temporary support substrate 1001 is completely removed at the end of this step.

[0123] At the end of this step, the doped regions 1007 are for example connected to the control transistors of the PIX pixels formed in the semiconductor substrate 101.

[0124] Fig.1OE illustrates a structure obtained at the end of a further step of formation of the diffractive structures 111 and then of the second mirror layer 107 on the side of the upper face of the structure of Fig.1OD.

[0125] Diffractive structures 111 are, for example, produced by depositing a first layer of the first material in the first regions 113, followed by a photolithography step and then etching the first layer so as to form through-holes in the first layer. The openings formed in the first layer are then, for example, filled by depositing a second layer of the second material. material of the second region(s) 115. A mechano-chemical polishing operation can be implemented after the deposition of the second layer so that the upper face of each diffractive structure 111 presents a substantially flat surface.

[0126] The mirror layer 107 is then deposited, for example, on the diffractive structure 111.

[0127] 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 become apparent to them. In particular, those skilled in the art are able to make combinations between the embodiments of Figures 1 to 9 and 10E. Furthermore, those skilled in the art are able to adapt the method described in relation to Figures 10A to 10E to produce the image sensors previously described in relation to Figures 2 to 9, based on the indications in this description.

[0128] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional specifications given above. In particular, the described embodiments are not limited to the specific examples of materials and dimensions mentioned in this description.

Claims

Demands

1. Image sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) comprising a plurality of pixels (PIX) formed in and on a semiconductor substrate (101) and each comprising at least one photodetector (PD) comprising a resonant cavity (103) having, between first (105) and second (107) mirror layers, a photoconversion layer (109) and at least one diffractive structure (111).

2. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to claim 1, wherein each diffractive structure (111) comprises a plurality of first regions (113) in a first material having a first refractive index separated from each other by at least one second region (115) in a second material having a second refractive index lower than the first refractive index.

3. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to claim 2, wherein the first and second materials have the same chemical composition and different structures.

4. Sensor (100; 500; 600; 700; 800; 900; 1000) according to claim 2 or 3, wherein the diffractive structures (111) of the resonant cavities (103) of the photodetectors (PD) have the same filling factor.

5. Sensor (200; 300; 400) according to claim 2 or 3, wherein said at least one diffractive structure (111) of the resonant cavity (103) of one of the photodetectors (PD) has a different filling factor than said at least one diffractive structure (111) of the resonant cavity (103) of another photodetector (PD).

6. Sensor (300) according to claim 5, wherein the first regions (113) of said at least one diffractive structure (111) of the resonant cavity (103) of one of the photodetectors (PD) form an array having a different pitch than that of an array formed by the first regions (113) of said at least one diffractive structure (111) of the resonant cavity (103) of another photodetector (PD).

7. Sensor (200; 300) according to claim 5 or 6, wherein the first regions (113) of said sensor have at least one diffractive structure (111) of the resonant cavity (103) of one of the photodetectors (PD) have different lateral dimensions from those of the first regions (113) of said at least one diffractive structure (111) of the resonant cavity (103) of another photodetector (PD).

8. Sensor (400) according to any one of claims 4 to 7, wherein, within the same diffractive structure (111), one of the first regions (113) has lateral dimensions different from those of another first region (113).

9. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 3 to 8, wherein each first region (113) is a plot.

10. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 3 to 8, wherein each first region (113) is a band extending laterally between two opposite sides of the diffractive structure (111).

11. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 3 to 8, wherein the first regions (113) form a grid and the second regions (115) form plots located in squares of the grid.

12. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 1 to 11, wherein at least one of the resonant cavities (103) has a thickness different from that of another resonant cavity (103).

13. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 1 to 12, wherein the resonant cavity (103) is made up of a stack comprising, in order from an upper face of the semiconductor substrate (101), the first mirror layer (105), the photoconversion layer (109), the diffractive structure (111) and the second mirror layer (107).

14. Sensor (600; 700) according to any one of claims 1 to 13, wherein each resonant cavity (103) further comprises at least one first insulating layer (601) interposed between said at least one diffractive structure (111) and the second mirror layer (107).

15. Sensor (500) according to any one of claims 1 to 14, wherein each resonant cavity (103) further comprises at least one second insulating layer (501) interposed between the layer of photoconversion (109) and said at least one diffractive structure (111).

16. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 1 to 15, wherein said at least one photodetector (PD) is an infrared photodetector, preferably a near-infrared photodetector.

17. Sensor (100; 200; 300; 400; 500; 600; 700; 800; 900; 1000) according to any one of claims 1 to 16, wherein each pixel (PIX) further comprises, superimposed on said at least one photodetector (PD), a visible photodetector (PD').

Images