Convex photodiode imaging array

Abstract

Title: Convex Photodiode Imaging Array The invention relates to an array (1) of at least two photodiodes (100a, 100b) in which each photodiode comprises an absorption region (20) and a capture region (70), the capture region (70) comprising an electrically conductive pad (50), the absorption region (20) being in contact with the capture region (70), the absorption region (20) being configured to absorb radiation incident on the photodiode and to allow scattering of charge carriers, in which each absorption region (20) is separated from the other absorption regions (20), and in which the absorption region (20) of each photodiode (100a, 100b) has a convex shape towards the incident radiation. Figure for the abstract: Fig. 2

Description

Title of the invention: Convex photodiode imaging network Technical field

[0001] The present invention relates to the production of an array of photodiodes arranged on a semiconductor substrate. It finds, for example, a particularly advantageous application in the field of imaging, in particular infrared imaging with a small pixel pitch and at a high operating temperature. STATE OF THE ART

[0002] Conventional photodiode arrays have a so-called planar architecture, in which the photodiodes of the array are arranged in a periodic manner on a flat surface. This planar architecture has the advantage of relatively simple manufacturing. On the other hand, it has limitations in terms of performance due to the diffusion of photo-generated charge carriers in the radiation absorption region within each photodiode towards neighboring photodiodes. This contamination of charge carriers, known as crosstalk, causes the deterioration of the performance of a high-density photodiode array by reducing the modulation transfer function (MTF).

[0003] In order to reduce crosstalk, it is possible to reduce the thickness of the absorption layer. However, this solution tends to reduce the quantum efficiency of the network.

[0004] Another solution consists of manufacturing a pn junction photodiode array vertical to the substrate. The contact between the photodiodes and a readout integrated circuit (ROIC) is established by etching an opening between the photodiodes through the multi-layers reaching the electrical pads. The production of such a high-density photodiode array on thick multi-layers appears difficult and likely to cause a loss of quantum efficiency of the array, due to the large volume occupied by the etched openings between the photodiodes.

[0005] Another pre-existing solution is to fabricate mesa-shaped photodiodes, by etching sufficiently deep trenches between the photodiodes to physically separate them. This solution makes it possible to confine the charge carriers in each pixel, and to overcome the crosstalk problem. On the other hand, the presence of the trenches can greatly reduce the quantum efficiency and increase the leakage currents. In addition, the MTF can also be reduced by scattering the incident radiation on the sides of the trenches towards the neighboring photodiodes.

[0006] In order to concentrate the incident radiation at the center of each pixel of the array, a current strategy is to deposit a microlens array on the photodiode array. Each microlens allows the concentration of the incident radiation at the center of each pixel in a focal point coinciding with a region of multiple photodetectors. This solution is difficult to implement because it requires manufacturing steps on the backside of the array to form 3D microstructures. In addition, the MTF can be limited by the diffraction of the incident radiation at the interface between two microlenses, as well as by the lateral diffusion of charge carriers in the case of a planar photodiode array.

[0007] The present invention aims to solve at least in part the problems mentioned above by proposing an array architecture in which the photodiodes are spaced from each other, and in which the geometric shape of the active region of each photodiode allows better concentration of the radiation at the center of the pixel. SUMMARY

[0008] To achieve the above-mentioned objective, according to one embodiment, an array of at least two photodiodes is provided in which each photodiode comprises an absorption region and a capture region, the capture region comprising an electrically conductive pad, the absorption region being in contact with the capture region, the absorption region being configured to absorb radiation incident on the photodiode and to allow diffusion of charge carriers, and in which each absorption region is separated from the other absorption regions, characterized in that the absorption region of each photodiode has a convex shape towards the incident radiation.

[0009] Each photodiode of the array further comprises, according to a non-limiting aspect, a covering region based on a first semiconductor, the covering region covering an upper face of the absorption region facing the incident radiation.

[0010] One of the advantages of this architecture is the physical separation of the absorption regions. This has the effect of electrically isolating the photodiode and reducing crosstalk in the network.

[0011] A second advantage is the convex shape of the absorption region, which allows to optimize the concentration of the radiation at the center of each photodiode, which improves the quantum efficiency, reduces the volume of the dark current, increases the operating temperature as well as the MTF of the network. BRIEF DESCRIPTION OF THE FIGURES

[0012] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0013] [Fig-1] [Fig.l] represents a top view of an imaging network comprising several photodiodes.

[0014] [Fig.2] [Fig.2] represents a sectional view of a network comprising at least two photodiodes.

[0015] [Fig.3A] Figures 3A and 3B represent two embodiments of the photodiode array according to the invention. [Fig.3A] represents a first embodiment, in which the absorption region and the overlap region on the one hand and the collection region on the other hand have distinct doping types.

[0016] [Fig.3B] [Fig.3B] represents a second embodiment of the network according to the invention, in which the absorption region and the collection region on the one hand and the overlap region on the other hand have distinct types of doping.

[0017] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the dimensions are not representative of reality. DETAILED DESCRIPTION

[0018] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:

[0019] According to an advantageous embodiment, each photodiode 100a, 100b, of the network 1 comprises an absorption region 20 and a capture region 70. The capture region 70 comprises an electrically conductive pad 50, and the absorption region 20 is in contact with the capture region 70. The absorption region 20 is configured to absorb radiation incident on the photodiode and to allow diffusion of charge carriers. Each absorption region 20 is separated from the other absorption regions 20. The absorption region 20 of each photodiode 100a, 100b, has a convex shape towards the incident radiation. This makes it possible to increase the distance traveled by the radiation inside the absorption region 20, and consequently, to improve the absorption of the radiation and the quantum efficiency of the network.

[0020] According to an advantageous embodiment, each photodiode 100a, 100b further comprises a covering region 10 based on a first semiconductor. The covering region 10 covers an upper face 20a of the absorption region 20 facing the incident radiation.

[0021] Advantageously, the overlap region 10 has a first band gap energy Ei0 greater than 0.41 eV. This promotes the transparency of the overlap layer 10 at wavelengths greater than 3 pm.

[0022] According to a preferred example, the upper face 10a of the overlap region 10 facing the incident radiation has a convex surface towards the incident radiation.

[0023] Preferably, the absorption region 20 of each photodiode 100a, 100b has a curvilinear convex shape, preferably a circular arc shape, preferably a half-sphere. According to another example, the absorption region 20 of each photodiode 100a, 100b has a conical or truncated cone shape. According to another example, the absorption region 20 of each photodiode 100a, 100b has a truncated pyramid shape.

[0024] Advantageously, the absorption region 20 has a second band gap energy E2o, with EiO>E2o. The high value of the band gap energy Ei0 allows the reduction of the influence of the defects present on the upper face 20a of the photodiode.

[0025] Preferably, the capture region 70 further comprises a collection region 30 located between the absorption region 20 and the electrically conductive pad 50. The collection region 30 is based on a third semiconductor. The collection region 30 is in contact with the absorption region 20 and with the electrically conductive pad 50.

[0026] Preferably, each photodiode 100a, 100b comprises a passivation layer 40 in contact with a lower face 20b of the absorption region 20 opposite an upper face 20a of the absorption region 20 facing the incident radiation. The passivation layer 40 has openings 45a, 45b, each opening 45a, 45b facing the absorption region 20 of a separate photodiode 100a, 100b. The capture region 70 of said photodiode 100a, 100b extends into said opening 45a, 45b.

[0027] According to one example, the absorption region 20 contains a gap opening zone 60 extending from a lower face 20b of the absorption region 20 opposite an upper face 20a of the absorption region 20 facing the incident radiation. The gap opening zone 60 has a variation in its band gap energy in a direction, called the normal direction, substantially perpendicular to the lower face 20b of the absorption region 20.

[0028] According to one example, the absorption region 20 has a maximum height h20 along the normal direction and the gap opening zone 60 has a maximum height h60 along the normal direction, with h6o <O,5*h2O, de préférence h6o<O,3*h2O, de préférence h6o<O. l*h20.

[0029] According to one example, the gap opening zone 60 has a minimum height h60 in the normal direction, with preferably h60>100 nm.

[0030] According to one embodiment, the overlap region 10 and the absorption region 20 are doped, the overlap region 10 has the same type of doping as that of the absorption region 20, and in addition, the collection region 30 has a type of doping opposite to that of the absorption region 20.

[0031] According to one embodiment, the overlap region 10 and the absorption region 20 are doped, the overlap region 10 has a doping type opposite to that of the absorption region 20, and in addition, the collection region 30 and the absorption region 20 have the same doping type.

[0032] According to one example, the overlapping regions 10 of at least two of the photodiodes 100a, 100b form a continuous layer.

[0033] According to a preferred example, the absorption region 20 has a doping level of less than 1016 cm 3, preferably less than 2*1015 cm 3, preferably less than 2*1014 cm 3. This allows the photodiode to operate as a depleted PIN photodiode at high operating temperature.

[0034] According to another preferred example, the overlap region 10 has a doping level greater than 1016 cm 3, preferably greater than 1017 cm 3. This gives rise to an effective gap opening by Moss-Burstein effect for N-type doping in the overlap region 10.

[0035] Preferably, the collection region 30 has a doping level greater than 1016 cm 3.

[0036] According to a preferred example, the absorption region 20 has a second band gap energy E20 of between 0.23 and 0.3 eV.

[0037] According to one example, the absorption region 20 is based on a second semiconductor, the first semiconductor, the second semiconductor and the third semiconductor are the same, and are for example based on CdHgTe. The energy of the band gap is thus controlled by varying the percentage of cadmium (Cd) in the composition of CdHgTe.

[0038] According to a preferred example, the absorption region 20 has N-type doping.

[0039] According to one example, the absorption region 20 is based on CdHgTe. According to one example, the covering region 10 is based on CdHgTe. According to one example, the collection region 30 is based on CdHgTe. The absorption region 20, the covering region 10 and the collection region 30 may all three be based on the material, without this material being in the same composition in the three regions. The percentages of each of the elements constituting the material may vary from one region to another. For example, when the absorption region 20, the covering region 10 and the collection region 30 are all three based on CdHgTe, the proportion of cadmium may vary from region to region.

[0040] It is specified that, in the context of the present invention, the terms "on", "overcomes", "covers", "underlying", "facing" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition, transfer, bonding, assembly or application of a first layer on a second layer does not necessarily mean that the two layers are in direct contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it or by being separated from it by at least one other layer or at least one other element.

[0041] A layer may also be composed of several sub-layers of the same material or of different materials.

[0042] A substrate, a layer, a device, “based” on a material M, is understood to mean a substrate, a layer, a device comprising this material M only or this material M and possibly other materials, for example alloying elements, impurities or doping elements. Thus a material based on a III-V material may comprise a III-V material with added dopants.

[0043] A reference frame, preferably orthonormal, comprising the axes X, Y, Z is represented in [Fig.2]. This reference frame is applicable by extension to the other figures.

[0044] In the present patent application, we will preferably speak of thickness for a layer and of height for a structure or a device. The height is taken perpendicular to the horizontal plane XY. The thickness is taken in a direction normal to the main extension plane of the layer. Thus, a layer typically has a thickness along Z, when it extends mainly along the horizontal plane XY, and a projecting element, for example an isolation trench, has a height along Z. The relative terms “on”, “under”, “underlying” preferably refer to positions taken along the Z direction.

[0045] The terms “substantially”, “approximately”, “of the order of” mean “to within 10%, preferably to within 5%”.

[0046] The invention relates to an array 1 of photodiodes 100a, 100b being for example arranged on a semiconductor substrate, as illustrated in top view in [Fig.l]. The array 1 comprises at least two photodiodes 100a and 100b. The array 1 can also be described as an array of pixels. Each of the photodiodes 100a, 100b is advantageously part of a pixel. A pixel can comprise a single photodiode 100a, 100b or a plurality of photodiodes 100a, 100b.

[0047] When using the network 1, the latter is exposed to incident radiation 15. This incident radiation preferably has a non-zero component in the Z direction.

[0048] According to one embodiment, each photodiode 100a, 100b comprises the elements illustrated in [Fig.2], which will be detailed in the following.

[0049] Each photodiode 100a, 100b comprises an absorption region 20 based on a semiconductor material. This absorption region 20 allows the absorption of the incident radiation 15 at the photodiode 100a, 100b and the generation of electron-hole pairs. The charge carriers are then diffused through the absorption region 20 towards a capture zone 70.

[0050] The absorption regions 20 of distinct photodiodes 100a, 100b are physically separated or spaced apart from each other. In other words, there is no contact between the absorption regions 20 of the network 1. This makes it possible to guarantee confinement of the photo-generated charge carriers in each of the absorption regions 20, and, consequently, to guarantee a good level of the MTF.

[0051] In order to improve the sensitivity of the photodiode 100a, 100b to the incident radiation, the geometric shape of the absorption region 20 is optimized in order to concentrate the incident radiation at the center of the photodiode 100a, 100b.

[0052] According to the invention, the absorption region 20 of each photodiode 100a, 100b has a convex shape towards the incident radiation 15. The convex geometric shape of the absorption region 20 can adopt one of the following configurations: a shape whose upper face facing the incident radiation 15 is curvilinear convex, preferably in the shape of an arc of a circle, preferably a half-sphere, a truncated cone, a truncated pyramid, or any three-dimensional geometric shape E, such that any segment having its ends in E is entirely included in E, and whose upper face facing the incident radiation allows the concentration of the radiation at the center of the lower face of E, opposite the upper face of E. The convex shape is advantageously configured to deflect the direction of propagation of the radiation propagating in the photodiode from the direction of the incident radiation.The convexity of the absorption region 20 is given by the shape of its upper face 20a. The absorption region 20 also has a lower face 20b opposite the upper face 20a.

[0053] The convex shape of the region 20 allows the refraction of the incident radiation towards the center of the photodiode 100a, 100b, which makes it possible to increase the distance traveled by the radiation inside the absorption region 20, and consequently, to improve the absorption of the radiation and the quantum efficiency of the grating 1. It is important to note that the refraction of the radiation is greater when the radiation is incident on the sides of the upper face 20a of the absorption region 20, occupying a main part of the surface of the photodiode.

[0054] The absorption region 20 is manufactured from a semiconductor material, preferably one of the following materials: an ILVI semiconductor such as CdHgTe (or HgCdTe), an IILV semiconductor, for example a bulk material such as InAsSb, or a material with an effective energy band structure, which can be obtained, for example, in the case of type II superlattices.

[0055] The absorption region 20 is advantageously doped, preferably with N-type doping. It also has a band gap energy E20. Said energy is adapted to promote the detection of radiation in a given spectral band, preferably in the mid-infrared. The value of E20 is preferably between 0.23 eV and 0.3 eV at a given operating temperature.

[0056] The doping level of the absorption region 20 is advantageously less than 10 16 cm 3, preferably less than 2*1015 cm 3, preferably less than 2*1014 cm 3. The low doping of the absorption region 20 allows the photodiode to operate as a depleted PIN photodiode at high operating temperature. The reduction or even elimination of free carriers within the absorption region 20 makes it possible to reduce or even eliminate the Auger generation of the dark current and to obtain a very high operating temperature. In this case, the electrical separation of the absorption regions 20 of the different photodiodes eliminates the modulation of the field as a function of the detected current when the photodiodes are hybridized with a CMOS circuit operating in direct injection.Thus, the operation of a network 1 of photodiodes whose absorption regions 20 are depleted according to this embodiment is more stable than that expected for a matrix produced according to the state of the art.

[0057] In order to extract the charge carriers to a multiplexing circuit often produced in CMOS (or “complementary metal oxide semiconductor” in English) technology in silicon, each photodiode 100a, 100b further comprises a capture region 70 in contact with the absorption region 20, as illustrated in [Fig.2]. The capture region 70 comprises an electrically conductive pad 50 typically connected to an input node of the CMOS circuit.

[0058] The capture region 70 may further comprise a collection region 30 located between the absorption region 20 and the electrically conductive pad 50. The collection region 30 is based on a semiconductor material, preferably the same material as that constituting the absorption region 20, such as CdHgTe for example. In the case where the collection region 30 and the absorption region 20 are based on the same semiconductor material, it is possible that the composition of this semiconductor material is distinct from one region 30 to the other 20. For example, the cadmium present in the CdHgTe constituting the collection region 30 may be found in a different percentage than in the absorption region 20. The collection region 30 is in contact with the absorption region 20 and with the electrically conductive pad 50, and preferably ensures the transfer of charge carriers from the absorption region 20 to the pad 50.

[0059] The collection region 30 advantageously has a doping level greater than 1016 cm3. This makes it possible to obtain good ohmic contact with the pad 50 and to limit the extension of the space charge zone in the region 30. The collection region 30 may have a doping type opposite to that of the absorption region 20, according to a first embodiment, or the same type of doping as that of the absorption region 20, according to a second embodiment. These two particular embodiments will be described in detail further on.

[0060] Each photodiode 100a, 100b preferably comprises a passivation layer 40 which provides its electrical, mechanical and chemical protection. The passivation layer 40 is preferably based on a material from the same group of semiconductors as the materials forming the covering region 10, the absorption region 20 and the collection region 30. When the covering region 10, the absorption region 20 and the collection region 30 are based on an ILVI material, for example CdHgTe, the passivation layer 40 is made on the basis of another ILVI semiconductor material such as ZnS. The passivation layer 40 is in contact with a portion of the lower face 20b of each photodiode 100a, 100b. It has openings 45a, 45b, each opening 45a, 45b facing the absorption region 20 of a separate photodiode 100a, 100b.The capture region 70 extends into the openings 45a, 45b of the passivation layer 40 to provide electrical contact with the absorption region 20.

[0061] Each photodiode 100a, 100b, preferably further comprises a covering region 10 based on a semiconductor material, preferably the same material as that constituting the absorption region 20 such as CdHgTe for example. In the case where the covering region 10 and the absorption region 20 are based on the same semiconductor material, it is possible for the composition of this semiconductor material to be distinct from one region 10 to the other 20. For example, the cadmium present in the CdHgTe constituting the covering region 10 may be in a different percentage than in the absorption region 20. The covering region 10 covers the upper face 20a of the absorption region 20 facing the incident radiation, preferably in its entirety.The overlap region 10 may cover the entire surface of the array 1 in a continuous manner, so that it is contiguous between the photodiodes 100a and 100b, or it may cover each separate photodiode 100a, 100b in a non-contiguous manner. The overlap region 10 has a preferably constant or conformal thickness. This thickness is typically between 0.1*h20 and 0.25*h20. Advantageously, the overlap region 10 separates the photodiodes 100a, 100b from each other in the XY plane. Thus, the overlap region 10 makes it possible to prevent the diffusion between the photodiodes 100a and 100b of the array 1, of the minority carriers generated in the . absorption region 20. This is in favor of an increase in the MTF of each photodiode 100a, 100b.

[0062] The upper face 10a of the overlap region 10 facing the incident radiation 15 preferably has a convex shape towards the incident radiation. Said upper face 10a of the overlap region 10 may adopt a curvilinear convex shape, preferably in the shape of an arc of a circle, preferably a surface shape of a half-sphere, a surface shape of a truncated cone, or even a surface shape of a truncated pyramid. Whatever the geometric shape of the upper face 10a of the overlap region 10, it may cover the photodiodes 100a, 100b, of the network 1 either in a continuous manner contiguous between the photodiodes 100a and 100b, or in a non-contiguous manner between the different photodiodes. Furthermore, it is advantageously provided that the upper face 10a of the overlap region 10 and the upper face 20a of the absorption region 20 have geometries of the same type.For example, according to an advantageous embodiment, the upper face 10a of the overlap region 10 and the upper face 20a of the absorption region 20 both have the shape of an arc of a circle, preferably concentric.

[0063] The overlap region 10 has a band gap energy Ei0 with Ei0>E 20- Preferably, said band gap energy Ei0 of the overlap layer 10 is greater than 0.41 eV. This promotes the transparency of the overlap layer 10 at wavelengths greater than 3 pm. The high value of the band gap energy Ei0 further allows the reduction of the influence of defects present on the upper face 10a of the photodiode which can induce an excess of dark current and noise. It also allows the absorption of the incident radiation 15 in the overlap region 10 to be reduced.

[0064] The overlap region 10 may have the same type of doping as that of the absorption region 20, according to a first embodiment, or a type of doping opposite to that of the absorption region 20 according to a second embodiment. Preferably, the overlap region 10 has a doping level greater than 10 16 cm3, preferably greater than 1017 cm3.

[0065] The high doping level of the overlap region 10 gives rise to an effective gap opening by Moss-Burstein effect in the case where the overlap region 10 and the absorption region 20 have N-type doping. This gap opening induces a curvature of the valence band in the overlap region 10. This has the effect of limiting the interaction between the minority charge carriers and the defects present on the upper face 10a of the photodiode, in favor of a reduction in dark current and an increase in the quantum efficiency of each photodiode.

[0066] Within a photodiode 100a, 100b, the overlap region 10 and the region of collection 30 preferably both admit a rotational symmetry around the same axis (parallel to the Z axis in the figures). Associated with the reduction in the number of free carriers within the absorption region 20, the symmetrical configuration of the overlap region 10 around the collection region 30 allows a very significant or even complete depletion of the absorption region 20, with very little or even no non-depleted pocket. This makes it possible to limit the dark current.

[0067] According to an alternative embodiment of the invention, the absorption region 20 contains a gap opening zone 60 which extends from the lower face 20b of the absorption region 20, as illustrated in [Fig. 2]. The gap opening zone 60 has a variation in its band gap energy in a direction, called the normal direction, substantially perpendicular to the lower face 20b of the absorption region 20. The normal direction corresponds to the Z direction in the figures. The gap opening zone 60 preferably extends all around the collection region 30 in projection in the XY plane.

[0068] The absorption region 20 has a maximum height h2o typically measured along the normal direction. In the case where the absorption region 20 has the shape of a spherical cap, the maximum height h2o typically corresponds to the height of the spherical cap. In the case where the absorption region 20 has a truncated cone or pyramidal shape, the maximum height h20 typically corresponds to the height measured between its small base and its large base. The gap opening zone 60 has a maximum height h60 along the normal direction. Advantageously, h60 <0.5*h20, preferably h60 <0.3*h20, preferably h60 <0.1*h20. The height h60 of the gap opening zone 60 is preferably greater than or equal to 100 nm.

[0069] According to an alternative embodiment of the invention, the upper face 10a of the overlap region 10 is covered with a layer transparent to the radiation incident on the photodiodes 100a, 100b of the network 1. The purpose of this layer is to improve the transmission of the incident radiation towards the absorption region 20, thanks to its refractive index carefully chosen according to the application.

[0070] According to an alternative embodiment of the invention, an electrically conductive region arranged outside the array 1 of photodiodes makes it possible to establish an ohmic contact with the overlap region 10.

[0071] By varying the type of doping of the absorption 20, covering 10 and collection 30 regions, two main embodiments of the invention are possibly conceivable.

[0072] According to the first of these two embodiments, as illustrated in [Fig.3A], the overlap region 10 has the same type of doping as that of the absorption region 20, preferably of type N. Furthermore, the collection region 30 has a type of doping opposite to that of the absorption region 20, preferably of type P, thus forming a pn junction with the absorption region 20 in each photodiode 100a, 100b of the array 1. The pn junction thus formed induces the separation of the photo-generated charges in the absorption region 20 and their extraction towards the pad 50. In the case of N-type doping in the overlap region 10 and the absorption region 20, an effective gap opening is possible. This effective gap opening and the separation of the absorption regions of each photodiode 100a, 100b, imply that the charge carriers separated by each pn junction of an individual photodiode are therefore those generated in the absorption region 20 of the same photodiode. Consequently, the MTF of an array 1 produced according to this first mode is improved.

[0073] According to the second of these two embodiments, as illustrated in [Fig.3B], the overlap region 10 has a doping type opposite to that of the absorption region 20, preferably of the P type, thus forming a pn junction with the absorption region 20 in each diode of the network 1. The pn junction thus makes it possible to collect individually the holes generated in the absorption region 20. The absorption regions of each photodiode 100a, 100b being non-contiguous, the charge carriers separated by each pn junction of an individual photodiode are therefore those generated in the absorption region 20 of the same photodiode. As a result, the MTF of a network 1 produced according to this second mode is improved. Furthermore, the collection region 30 has the same type of doping as that of the absorption region 20, preferably N-type. This promotes good ohmic contact with the pad 50.

[0074] Example of a manufacturing method for obtaining a network according to the invention

[0075] The network 1 according to the invention, comprising all the elements detailed above, can be produced according to a method comprising the following successive steps: 1. An epitaxial layer, preferably based on a CdHgTe material, is first fabricated on a substrate, preferably based on a CdZnTe material, by liquid phase growth or by molecular beam. 2. A doping species is implanted locally at a plurality of zones of the epitaxial layer. These zones will form the collection regions 30 of each photodiode 100a, 100b of the network 1, or even of several networks 1. The doping species is preferably an acceptor type dopant, preferably taken from the element As and the element Sb. 3. A passivation layer 40 is then deposited on the epitaxial layer. 4. The whole is then annealed, preferably under Hg pressure, in order to activate the localized dopant, thus forming the collection regions 30. Annealing also makes it possible to fill potential gaps with Hg ions and to obtain N-type doping in the epitaxial layer in order to form the absorption regions 20. This annealing will also make it possible to form the areas gap opening 60 by interdiffusion with the passivation layer 40 which, preferably, is made from the same semiconductor material as that of the absorption regions 20. 5. The openings 45a, 45b in the passivation layer 40 are then etched locally, each opening 45a, 45b facing a distinct collection region 30. 6. The pads 50 based on an electrically conductive material are then deposited locally at the level of each photodiode 100a, 100b of each network 1, in the openings 45a, 45b of the passivation layer 40 and preferably also in contact with the lower face 40b of the passivation layer 40. 7. An etching in the substrate is carried out at the periphery of each network 1 of detection in order to form an opening associated with each detection network 1. A continuous metal layer is then formed locally on the pads 50 of each photodiode network as well as in the opening associated with the network considered, thus forming through a collective contact to all the photodiodes 100a, 100b of each network 1. 8. The networks 1 manufactured on the same wafer are then cut, to obtain a set of preferably identical networks 1. The following steps are therefore carried out independently on each network, referring to the network 1 of the present invention. 9. Network 1 is then hybridized on a reading circuit, produced using Si-CMOS technology. 10. The substrate on which the epitaxial layer has been grown is then removed by polishing, or by chemical etching, or a combination of both. 11. The absorption regions 20 of the grating 1 are then structured in a convex shape. The structuring is preferably carried out by transferring a grayscale (or “gray-tone” or “gray-scale”) lithography which forms a complex structure in a resist layer. The convex structure is then transferred into the absorption region 20 by dry etching, preferably ion etching. 12. The electrical properties of a surface portion of the absorption region 20 are then modified by a high doping level to form the overlap region 10. This doping is preferably of type N, which induces an effective gap opening by the Moss-Burstein effect. The modification of the doping and the band gap of the overlap region 10 can be obtained by ion implantation of an element acting as a donor in the semiconductor, such as element B.

[0076] This method can be implemented to manufacture a single network or several distinct networks on the substrate. These steps can in fact be carried out simultaneously to form several photodiodes but also several networks.

[0077] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

Claims

Claims

1. Array (1) of at least two photodiodes (100a, 100b) in which each photodiode comprises an absorption region (20) and a capture region (70), the capture region (70) comprising an electrically conductive pad (50), the absorption region (20) being in contact with the capture region (70), the absorption region (20) being configured to absorb radiation incident on the photodiode and to allow diffusion of charge carriers, and in which each absorption region (20) is separated from the other absorption regions (20), characterized in that the absorption region (20) of each photodiode (100a, 100b) has a convex shape towards the incident radiation.

2. Network (1) according to the preceding claim in which each photodiode (100a, 100b) further comprises a covering region (10) based on a first semiconductor, the covering region (10) covering an upper face (20a) of the absorption region (20) facing the incident radiation, the covering region (10) having a first bandgap energy Ei0.

3. Network (1) according to the preceding claim in which the first band gap energy Ei0 is greater than 0.41 eV.

4. Network (1) according to any one of the two preceding claims in which the absorption region (20) has a second band gap energy E20, with Eio>E2O.

5. Network (1) according to any one of the three preceding claims in which the upper face (10a) of the overlap region (10) facing the incident radiation, has a surface convex towards the incident radiation.

6. An array (1) according to any preceding claim wherein the absorption region (20) of each photodiode (100a, 100b) has a curvilinear convex shape.

7. Network (1) according to the preceding claim in which the absorption region (20) of each photodiode (100a, 100b) has the shape of an arc of a circle, preferably a half-sphere.

8. Network (1) according to any one of the preceding claims, in which the capture region (70) further comprises a collection region (30) located between the absorption region (20) and the electrically conductive pad (50), the collection region (30) being based on a third semiconductor, the collection region (30) being in contact with the absorption region (20) and with the electrically conductive pad (50).

9. Network (1) according to any one of the preceding claims, comprising a passivation layer (40) in contact with a lower face (20b) of the absorption region (20) opposite an upper face (20a) of the absorption region (20) facing the incident radiation, the passivation layer (40) having openings (45a, 45b), each opening (45a, 45b) facing the absorption region (20) of a separate photodiode (100a, 100b), the capture region (70) of said photodiode (100a, 100b) extending into said opening (45a, 45b).

10. Network (1) according to any one of the preceding claims, in which the absorption region (20) contains a gap opening zone (60) extending from a lower face (20b) of the absorption region (20) opposite an upper face (20a) of the absorption region (20) facing the incident radiation, the gap opening zone (60) having a variation in its forbidden band energy in a direction, called the normal direction, substantially perpendicular to the lower face (20b) of the absorption region (20).

11. A grating (1) according to any preceding claim in combination with claim 2, wherein the overlap region (10) and the absorption region (20) are doped, the overlap region (10) having the same type of doping as that of the absorption region (20).

12. Network (1) according to the preceding claim in combination with claim 8, wherein the collection region (30) has a doping type opposite to that of the absorption region (20).

13. A grating (1) according to any one of claims 1 to 10 in combination with claim 2, wherein the overlap region (10) and the absorption region (20) are doped, the overlap region (10) having a doping type opposite to that of the absorption region (20).

14. Network (1) according to the preceding claim in combination with claim 8, wherein the collection region (30) and the absorption region (20) have the same type of doping.

15. A network (1) according to any preceding claim in combination with claim 2 wherein the re- covering (10) of at least two of the photodiodes (100a, 100b) form a continuous layer.

16. Network (1) according to any one of the preceding claims in which the absorption region (20) has a doping level of less than 1016 cm 3, preferably less than 2*1015 cm 3, preferably less than 2*1014 cm 3.

17. Network (1) according to any one of the preceding claims in combination with claim 2 in which the overlap region (10) has a doping level greater than 1016 cm 3, preferably greater than 1017 cm 3.

18. A network (1) according to any preceding claim in combination with claim 8 wherein the collection region (30) has a doping level greater than 1016 cm 3.

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