法国专利FR3037442A1 SPAD PHOTODIODE COVERED BY A NETWORK

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专利摘要:
A SPAD photodiode (100) having a layer of semiconductor material (110) comprising an N-doped area (111) and a P-doped area (112) separated by an avalanche region (113). The layer of semiconductor material (110) is interposed between a periodic structure (120), and a low index layer (130) having a refractive index lower than that of the layer of semiconductor material and that of the structure periodic. The photodiode thus offers a low temporal dispersion and a high quantum efficiency, without requiring a high charge acceleration voltage.
公开号:FR3037442A1
申请号:FR1555326
申请日:2015-06-11
公开日:2016-12-16
发明作者:Laurent Frey；Norbert Moussy
申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
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专利说明:

[0001] 1 SPAD PHOTODIODE COVERED BY A NETWORK. TECHNICAL FIELD The present invention relates to the field of photodiodes, in particular photodiodes of the SPAD type. STATE OF THE PRIOR ART A photodiode is a light-sensitive component, comprising a semiconductor material layer having an N-doped zone (having an excess of electrons) and a P-doped zone (having an electron defect). The N-doped zone and the P-doped zone are separated by a PN junction, at the level of which a depletion zone is formed, also called space charge zone. Each N or P doped zone is connected to an electrical connector in order to polarize the diode. A photon absorbed by the semiconductor material layer generates an electron-hole pair, i.e., a positive electric charge and a negative electric charge. In a so-called SPAD photodiode, for the English "single-photon avalanche diode", an inverse bias is applied between the N-doped zone and the P-doped zone. The polarization voltage is preferably greater (or equal), in absolute value. , at the breakdown voltage of the photodiode (minimum electrical reverse voltage which makes it conductive in the blocking direction). This polarization creates a strong electric field at the PN junction, which accelerates the photo-generated electric charges. These charges have enough energy to excite other electric charges by impact (ionization by impact). This chain reaction is called an avalanche effect, and takes place in an avalanche zone 3037442 2 between the N-doped zone and the P-doped zone. Thus, the absorption of a photon generates a brief and intense electrical signal. , called useful electrical signal. A SPAD photodiode thus makes it possible to detect with very great precision very low intensity light signals and to date the arrival of each photon. A SPAD type photodiode is also called an avalanche photodiode in Geiger mode. If the photon is absorbed into the avalanche zone, the electron-hole pair immediately triggers the avalanche effect. If the photon is absorbed out of the avalanche zone, the minority charge of the electron-hole pair can diffuse into the semiconductor material layer and then reach the avalanche zone where it triggers the avalanche effect. The temporal resolution of the useful electrical signal is thus limited by the uncertainty of the precise location where the photon is absorbed and where the electron-hole pair is formed. In other words, the transit time from the generated carrier to the avalanche zone is not precisely known, which limits the temporal resolution of the photon detection. This temporal dispersion is also called jitter of the photodiode, or "jitter" in English. One could consider reducing the thickness of the photodiode to a thickness close to that of the avalanche zone. However, the avalanche zone 20 generally has a very small thickness, typically of the order of 0.3 μm. This solution does not allow to absorb enough photons to provide the photodiode a satisfactory sensitivity. Indeed, it takes a certain thickness of material to absorb the light, this thickness depending on the wavelength considered and increasing towards the infrared, especially for silicon. For example, a thickness greater than 1 μm of silicon is required to effectively absorb the near infra-red in silicon. A solution known to offer both a good temporal resolution and a high sensitivity therefore consists in increasing the thickness of semiconductor material in order to effectively absorb the incident photons, and accelerate the carriers migrating towards the avalanche zone in order to decrease the "jitter". To accelerate the carriers to the avalanche zone, an electric field is created throughout the thickness of the layer of semiconductor material. This is accomplished by lowering the average doping level of the semiconductor material, and increasing (in absolute value) the bias voltage across the diode. A disadvantage of this solution is that it requires the use of very high polarization voltages. An object of the present invention is to provide a SPAD type photodiode having a high sensitivity, and which does not exhibit at least one of the disadvantages of the prior art. In particular, an object of the present invention is to provide a SPAD type photodiode having both a high sensitivity in the long wavelengths (greater than 600 nm, and even 800 nm) and low jitter.
[0002] SUMMARY OF THE INVENTION This object is achieved with a SPAD type photodiode having a layer of semiconductor material comprising an N-doped zone and a P-doped zone, separated by an avalanche zone.
[0003] According to the invention, the photodiode further comprises: a first so-called low index layer; and a periodic structure having a plurality of elementary patterns; the first low index layer having a refractive index lower than that of the semiconductor material layer and that of the periodic structure, and the layer of semiconductor material being interposed between the first low index layer and the periodic structure .
[0004] Preferably, the periodic structure comprises a plurality of regularly spaced studs, the spaces between the studs being at least partially filled with a material called low index material, having a refractive index lower than that of the layer of semiconductor material and that of the periodic structure. Advantageously, the periodic structure has N or P doping, and only one of the elementary patterns is connected to an electrical contact element, to polarize the photodiode. The layer of semiconductor material may be silicon, and the first layer may be silicon dioxide. Preferably, a difference between the refractive index of the semiconductor material layer and the refractive index of the first low index layer is greater than or equal to 0.5. The periodic structure advantageously has a pitch of between 100 nm and 1000 nm. The thickness of the layer of semiconductor material is advantageously between 0.5 μm and 3 μm. The height of the elementary patterns is preferably less than 1 μm. A ratio of the width of a pad, divided by the pitch of the periodic structure, may be between 0.25 and 0.80. The periodic structure preferably forms a network in two dimensions, the pitch of this network being identical in each of said two dimensions. The periodic structure may be formed in the same block of semiconductor material as the layer of semiconductor material. Alternatively, the periodic structure may be formed in a polycrystalline silicon layer deposited on the layer of semiconductor material. The invention also relates to a matrix of at least two photodiodes in which: the periodic structure comprises a plurality of regularly spaced studs, the spaces between the studs being at least partially filled with a material called low index material, having a refractive index less than that of the layer of semiconductor material and that of the periodic structure; and the adjacent periodic structures are separated by trenches filled by said low index material. The invention also relates to a method for manufacturing a photodiode according to the invention, comprising a step of structuring an upper region of a semiconductor material block, to form an assembly constituted by the periodic structure mounted on the layer of semiconductor material. The invention also relates to a method of manufacturing a matrix of photodiodes according to the invention, comprising the following steps: structuring an upper region of a semiconductor material block, to form an assembly consisting of a plurality periodic structures mounted on a layer of semiconductor material; etching trenches between two adjacent periodic structures, the trench etching and structuring steps being performed by a single etching step; and deposition of the low index material, filling the trenches and the spaces between studs forming the periodic structures, said low-index material having a refractive index lower than that of the block made of semiconductor material.
[0005] BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood on reading the description of exemplary embodiments given purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIG. schematic a first embodiment of a photodiode according to the invention; FIG. 2 schematically illustrates a second embodiment of a photodiode according to the invention; FIG. 3 illustrates a distribution of the absorption of light in the photodiode illustrated in FIG. 2; FIG. 4 illustrates the quantum efficiency in a photodiode according to the invention; FIG. 5 illustrates a method of manufacturing an exemplary photodiode according to the second embodiment of the invention; FIG. 6 illustrates a third embodiment of a photodiode according to the invention; FIG. 7 illustrates a fourth embodiment of a photodiode according to the invention; FIG. 8 illustrates a fifth embodiment of a photodiode 20 according to the invention; and FIG. 9 illustrates a distribution of the absorption of light in the photodiode illustrated in FIG. 8. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS The invention will firstly be illustrated by means of FIG. schematically a first embodiment of a photodiode 100 according to the invention.
[0006] The photodiode 100 is adapted to detect electromagnetic radiation at wavelengths in the red and the near infrared, in particular between 600 nm and 1000 nm. In the following, we take the example of a photodiode adapted to detect electromagnetic radiation at 5850 nm. The photodiode 100 has a semiconductor material layer 110 having an N-doped zone 111 and a P-doped zone 112. The N-doped zone 111 and the P-doped zone 112 are superimposed and separated by a PN junction 114. Avalanche 113 (shown between two dashed lines) extends into and around the PN junction. As a variant, the zone 111 is doped with P, and the zone 112 is doped N. The photodiode 100 is of SPAD type, adapted to be reverse biased by a bias voltage greater than the breakdown voltage, for example between 1 and 3 times the breakdown voltage. In particular, the N-doped zone 111 is connected to a first electrical connector (not shown) adapted to be worn at a first electrical potential, and the P-doped zone is connected to a second electrical connector (not shown) adapted to be worn. to a second electrical potential, the first and second electrical potentials together defining a higher voltage (in absolute value) than the breakdown voltage. The semiconductor material forms an absorbent medium, consisting of silicon for example, the photodiode being adapted to detect electromagnetic radiation 140 at a wavelength of 850 nm. A periodic structure 120 is disposed directly on the layer of semiconductor material 110. This periodic structure 120 can be etched in a block of semiconductor material, so as to directly form the assembly constituted by the layer 110 and the structure As a variant, the periodic structure 120 is made of a non-metallic material, different from that of the layer 110. This material is essentially transparent at the wavelength that the photodiode 100 is adapted to detect. Throughout the text "essentially transparent" means for example "having an extinction coefficient of less than a few 10-2 at the working wavelength, for example 5.10-2". The periodic structure 120 has a plurality of elementary patterns, i.e. a plurality of studs 121 regularly spaced from each other. A stud here designates a solid volume of any shape, for example a cylinder, or a cube, or a cylindrical ring, or a cube pierced with a through hole (the several studs then drawing a grid). The shape of the stud can give the periodic structure a periodicity in one or two dimensions of space. In the first case, we also talk about bar, or line. The periodic structure 120 preferably has a two-dimensional periodicity (each associated with an axis parallel to the upper surface of the photodiode). The period may be different for each of the two dimensions. We then have a quantum efficiency that depends on the polarization of the light, which can make it possible to detect a particular polarization. The periodic structure 15 advantageously has at least five elementary patterns according to each dimension of the space where it has a periodicity (ie at least 5 × 5 elementary patterns in the case of a periodicity in two dimensions). The periodic structure 120 may be covered with a thin passivation layer (thermal oxide for example), which follows the shape of the elementary patterns without completely filling the spaces, or gaps 122 between them. The optical index of this passivation layer may be arbitrary. The periodic structure 120 forms a sub-wavelength resonant grating, the pitch being less than the wavelength in the material of the incident medium, of the electromagnetic radiation that the photodiode 100 is adapted to detect. The incident medium is that which covers the periodic structure, here of the air. The pitch is here less than 850 nm. Here, this material is air (the incident medium is the medium). This step is in particular less than 850 nm.
[0007] It will be recalled that the wavelength in a material is the wavelength in the vacuum divided by the optical index of this material. The layer of semiconductor material 110 is deposited directly on a first so-called low index layer 130, having a refractive index of less than that of the layer 110 and that of the periodic structure 120. Throughout the text, cues are considered. of refraction at a wavelength that the photodiode is adapted to detect, in particular at 850 nm. The first low index layer 130 forms a lower sheath of a waveguide. The upper sheath of the waveguide is formed here by the air surrounding the photodiode, and here filling the spaces 122 between the pads (or what remains after application of the thin passivation layer defined above). The combination of this waveguide and the periodic structure 120 generates guided modes in the layer of semiconductor material 110. It is surprisingly found that for certain values of the geometric parameters of the photodiode (dimensions of the pads of the periodic structure 120, thicknesses of the periodic structure 120 and of the semiconductor material layer 110), the electromagnetic field is locally reinforced in regions located inside the layer of semiconductor material 110, and that this field is almost null in the periodic structure. In particular, the electromagnetic field is concentrated in at least one sub-layer of the layer of semiconductor material 110. The skilled person would have expected a more homogeneous distribution of the electromagnetic field in a multimode waveguide of great thickness (here about 5 to 10 times the wavelength in the layer of semiconductor material 110, see below).
[0008] Regions in which the electromagnetic field is more intense are used to make a SPAD photodiode of the same sensitivity and greater temporal resolution, compared to a SPAD photodiode according to the prior art.
[0009] For this purpose, the regions where the electromagnetic field is reinforced in or near the avalanche zone of the SPAD photodiode are positioned. Thus, photon absorption is enhanced in or near the avalanche zone. It is then possible to reduce the thickness of a region of the semiconductor material located outside the avalanche zone, and whose role is simply to absorb photons which will then diffuse to the avalanche zone. In the prior art, a SPAD photodiode detecting radiation at 850 nm and absorbing 90% of the incident photons, consists of a 40 μm thick silicon layer. Thanks to the invention, this thickness is reduced to a few microns only, in any case less than 10 .mu.m. Thanks to this reduced thickness, the transit time of the carriers to the avalanche zone is reduced. It is thus possible, at equal sensitivity, both to reduce the polarization voltage and to improve the temporal resolution of the SPAD photodiode (i.e. to reduce the jitter). For example, this polarization voltage (20V instead of 40V) is reduced by a factor of two. A photodiode with low time dispersion and high quantum efficiency is obtained. A SPAD photodiode is used for example to measure a flight time, that is to say a time elapsed between the emission of a laser signal, and the detection of a backscattered signal on an object to be detected. Time of flight measurements are commonly used in telemetry, presence detection, 3D motion recognition, and so on. The invention makes it possible to increase the accuracy of this measurement of flight time. The invention also avoids having to lower the average doping level in the layer of semiconductor material, which is particularly advantageous in CMOS technology. The reduced thickness of the layer of semiconductor material also reduces the dark current. This advantage is found in any type of photodiode, the regions where the electromagnetic field is reinforced being positioned in or near the PN junction.
[0010] FIG. 2 schematically illustrates a second embodiment of a photodiode 200 according to the invention. The photodiode 200 differs from the photodiode illustrated in FIG. 1 only in that the spaces 222 between the pads are filled with a low index material (solid material). The low index material has a refractive index lower than that of the layer of semiconductor material 210 and that of the periodic structure 220. Preferably, this low index material is identical to the material of the first low index layer. Preferably, the spaces 222 are fully filled with the low index material. The low index material forms a second low index layer 250. It can constitute a passivation layer between the pads, in direct contact with the periodic structure 210. The second low index layer 250 is essentially transparent to the wavelength that the photodiode 200 is adapted to detect.
[0011] In the example illustrated in FIG. 2, the second low index layer 250, made of said low index material, covers the periodic structure 210, is inserted between the pads 210 and protrudes above them. According to a variant not shown, said second low index layer 250 is flush with the top of the pads. A third layer can then cover the assembly thus formed, on the side of the pads. This third layer is then essentially transparent to the wavelength that the photodiode 200 is adapted to detect. This third layer may consist of a material having a refractive index lower than that of the layer of semiconductor material 210 and that of the periodic structure 220. The third layer and the second low index layer may be made of different materials. Figure 3 illustrates a distribution of absorption in the photodiode 200. It is observed that the absorption exhibits large intensity variations, and is concentrated mainly in regions outside the periodic structure 220, at the same time. inside the layer 210 in semiconductor material (the representation in black and white loses part of the information). A white rectangle represents an underlayer 270 of the semiconductor material layer 210, receiving the regions where the absorption is concentrated. For example, the underlayer 270 absorbs 75% of an incident light flux, and has a thickness close to 1 μm. The sublayer 270 is named a region of high sensitivity. The avalanche zone 213 is positioned in this sublayer 270. In the following, preferred dimensions and indices of the photodiode according to the invention are described, the wavelength to be detected being chosen equal to 850 nm. The difference in index between the semiconductor material layer 210 and the first low index layer 230 is greater than 0.5, preferably greater than 1. In the same way, the index difference between the periodic structure 220 and The first low index layer 230 is greater than 0.5, preferably greater than 1. When the photodiode comprises a second low index layer, the same index differences are verified between this second layer and the semi-material layer. conductive, respectively the periodic structure.
[0012] For example, the layer of semiconductor material and the periodic structure are of silicon (n = 3.65 at 850 nm), and the first low index layer (and possibly the second low index layer) is made of silicon dioxide. silicon (n = 1.45 at 850 nm). The first low index layer 230 advantageously has a thickness greater than 50 nm, preferably greater than 500 nm. The thickness of the layer of semiconductor material 210 is denoted h2. The greater this thickness, the greater the spectral density of the modes in the layer of semiconductor material is important. A high spectral density of modes offers a large angular acceptance of the photodiode. Preferably, h 2 3037442 13 is greater than 0.7 μm when the periodic structure 220 has a periodicity in two dimensions. This gives a quantum efficiency, averaged over a cone of angles of incidence of a few tens of degrees, greater by a factor of 5 to 10 compared to the prior art, over a spectral width of several hundreds of nanometers. This condition corresponds to h2 greater than 1.0 μm when the periodic structure 220 has a periodicity in one dimension. In any case, the thickness h2 is greater than 0.5 μm, in order to benefit from sufficient absorption.
[0013] The thickness h 2 is preferably less than 3 μm. The h1 peak-valley height of the pads of the periodic structure is less than or equal to 1 μm, typically between 0.1 μm and 1.0 μm. The pads are for example cubes side a. Alternatively, it may be cylindrical pads of diameter a. In a variant, the periodic structure is formed by bars of width a, for example parallelepipeds with a rectangular base. The ratio -a between the width has pads, and the pitch P of the periodic structure P is between 0.25 and 0.80 (the width a and the pitch P being measured along the same axis). This ratio is checked according to one or two axes, depending on whether the periodic structure 220 has a periodicity in one or two dimensions.
[0014] An operation of the photodiode independent of the polarization of the incident light radiation is provided by a periodic structure 220, having a periodicity in two dimensions, and with the same dimensions of the pads considered in each of these two dimensions. The pitch P of the periodic structure 220 is advantageously greater than A. AT. Ratio -, and less than the ratio -, with: ne ff ng in f - At the wavelength that the photodiode is intended to detect, the actual index of the waveguide formed in the photodiode, equal in first approximation to the refractive index of the layer 210 of semiconductor material, and% trip the refractive index of the first low index layer 230.
[0015] In other words, the photodiode being intended to detect radiation at a wavelength of interest, the periodic structure has a pitch P: greater than the ratio of the wavelength of interest divided by the refractive index of the layer of semiconductor material; and less than the ratio of the wavelength of interest divided by the refractive index of the first low index layer. In practice, the pitch P is generally between 100 nm and 1000 nm, more preferably between 200 nm and 700 nm. Taking the example of a first low silicon dioxide (SiO 2) subscript and a layer of silicon semiconductor material (Si), the pitch P is between 230 nm and 580 nm. One method for determining optimal dimensions of the photodiode according to the invention may be to: set a pitch P, within the limits specified above; set a height h1, called the depth of the network; then adjust the width to plots and the thickness h = h1 + h2 by optimization of a quantum efficiency computed by numerical simulation.
[0016] FIG. 4 represents the quantum efficiency at 850 nm in a photodiode according to the invention, as a function of the width a of the pads (abscissa axis) and of the thickness h = h1 + h2 of the periodic structure and the layer of semiconductor material, both of silicon. P = 500 nm and h1 = 300 nm.
[0017] Thus, couples of width a and of thickness h = h1 + h2, corresponding to greater quantum efficiencies, are identified. A pair, located in FIG. 4, is preferably chosen in a large zone associated with large quantum efficiencies. This provides a good tolerance on the dimensions 5 of the photodiode. Thus, for example, h = 1550 nm and a = 350 nm are chosen. h = 1550 corresponds to about 5 to 10 times the wavelength in the material of the semiconductor material layer 110: 1550 nm 7 wavelength in the vacuum that the photodiode is adapted to detect: 850 nm - index FIG. 5 shows a method for producing an example of a photodiode as schematically illustrated in FIG. 2. Preferably, several photodiodes are produced simultaneously according to this method, thus forming a matrix of photodiodes according to the invention.
[0018] We start from a so-called silicon on insulator substrate (or SOI), formed by a thin layer of silicon on a silicon dioxide layer. Silicon dioxide forms the first low-index layer 530. The thin silicon layer can be thickened, then N- or P-doped. The layer 515 is obtained. For example, the layer 515 is thickened and has, for example, a doping of the same type that the doping of a doped zone which covers it in fine in the photodiode (here a doping P). As a variant, the layer 515 remains thin and has a doping of the opposite type to the doping of a doped zone which covers it in fine in the photodiode, in order to avoid the rise towards the surface of carriers generated by the defects of the interface between a first low index layer 530 and a silicon layer 515. In a first step 501, a layer 516 of weakly doped silicon P is epitaxially deposited on the layer 515. The layer 516 (and optionally the layer 515 ) forms a block of semiconductor material.
[0019] In step 502, in the same etching step, the periodic structure 520 according to the invention and insulation trenches 570 are produced. The isolation trenches thus have a depth equal to the peak-valley height. studs 521 of the periodic structure.
[0020] The isolation trenches 570 are intended to separate photodiodes close to the same matrix of photodiodes, and are named STI (for English "Shallow Trench Isolation"). The etching of the periodic structure separates, in the silicon layer 516, a periodic structure 520 according to the invention and a layer which will form the layer 10 of semiconductor material according to the invention, after definition of the doped zones. The step of etching isolation trenches is commonly used to manufacture a matrix of photodiodes according to the invention, so that the implementation of the invention simply requires modifying a mask used for etching.
[0021] Preferably, the etched surfaces are passivated by a thin layer of thermal oxide. In step 503, the isolation trenches 570 and the spaces 522 between the pads 521 of the periodic structure 520 are filled with a plasma-deposited oxide, for example silicon dioxide. This oxide forms the low index material according to the invention, located between the studs of the periodic structure (second low index 550). The high sensitivity region 570, as described with reference to FIG. 3, is surrounded by dashed lines. In a step 504, a PN junction is made under the periodic structure 520, and in the high sensitivity region 570. This PN junction is formed by ion implantation, forming in the layer 516 and under the periodic structure, an N doped zone. , 511, and a P-doped area, 512. Alternatively, the layer 515 is thickened and strongly P-doped, and the layer 516 is N-doped, forming a PN junction.
[0022] The N-doped zone and the P-doped zone are separated by the PN junction, at the level of which will be (after application of a suitable bias voltage) an avalanche zone 513. The PN junction is preferably sufficiently remote. of the periodic structure so that the avalanche zone 513 does not impinge on the periodic structure 520. For example, the PN junction is located at more than 200 nm under the periodic structure. For this, the N-doped zone 511 is produced by implantation, for example, of phosphorus between 100 and 200 keV. The periodic structure 520 may remain undoped. In a variant, the periodic structure is N-doped, like the upper doped zone 511. The P-doped zone 512 is connected to the surface of the photodiode by P-doped regions 582 formed by several successive implantations. The N-doped zone 511 is connected to the surface of the photodiode by a single N-doped region 581, located in a single stud of the periodic structure. Region 581 is formed by low energy ion implantation, and is preferably at the edge of the photodiode. The N-doped zone 511 is connected to a potential VHv via the region 581 and a first electrical connector (not shown). The P-doped zone 512 is connected to a VLv potential via the regions 582 and a second electrical connector (not shown). The VHv potential is much higher than the VLv potential. The electrical potentials VLv and VHv together define a bias voltage of the photodiode greater than its breakdown voltage, to form a SPAD type photodiode. In particular, the P-doped zone 512 can be connected to ground, and the N-doped zone 511 can be connected to a voltage source via an extinction resistor R (commonly referred to as a resistor). quench) used to stop the avalanche phenomenon (R = 100 kb for example). The fact that the N-doped zone is not connected to the VHv potential by each of the blocks of the periodic structure also contributes to stopping the avalanche phenomenon.
[0023] The voltage at the terminals of the photodiode 500 is measured by a follower amplifier arrangement. A variant of the photodiode described above can be made by inverting all the N and P dopings.
[0024] The first low index layer can also be formed in a thicker silicon dioxide layer than the insulating oxide of a standard SOI. FIG. 6 illustrates a third embodiment of a photodiode 600 according to the invention.
[0025] The photodiode illustrated in FIG. 6 differs from the embodiment of FIG. 5 only in that it is adapted to measure photons arriving on the photodiode on the initial SOI side, and not on the opposite side thereof. We are talking about BSI illumination, for the English "Bock Side Illumination". We start from an SOI as described with reference to FIG. 6. In this embodiment, the technological steps are made on the front face of an SOI, and then the completed assembly is returned. The silicon of the SOI is thickened to form an N-doped silicon layer 615. A silicon layer 616 is produced by epitaxy above the layer 615. Trenches are dug between the future photodiodes, then filled with silicon dioxide. , this silicon dioxide completely covering the layer 615 and forming the first low index layer 630 according to the invention. In the silicon layer 616, a PN junction is formed between an N-doped zone 611 and a P-doped zone 612, and highly doped regions 681, 682 intended to connect the N-doped zone 611 and the P-doped zone 612 to the VHV potential. Respectively VIA /. The first low index layer 630 can be etched locally to pass electrical connectors. Then, the thus-formed stack is returned, and its upper surface is etched to remove oxide from the SOI and etch the silicon layer 615 to form the periodic structure 620. The periodic structure is then covered with a silicon dioxide layer forming the second low index layer 650. Here, the etched faces of the periodic structure are not passivated by oxide deposition, and the silicon layer 615 is doped N (doping of the opposite type to the of the adjacent doped zone), in order to prevent carriers generated by the interface defects of the periodic structure from diffusing into the avalanche zone. FIG. 7 illustrates a fourth embodiment of a photodiode 700 10 according to the invention. The photodiode illustrated in FIG. 7 differs from the embodiment of FIG. 5 only in that the periodic structure 720 is not formed in the same silicon block as the layer made of semiconductor material, but in a layer of silicon. 'a different material.
[0026] For example, after having epitaxially produced the silicon layer 716 on an SOI, the assembly is covered by a polycrystalline silicon layer, in which the periodic structure according to the invention will be etched, and also serving as a grid for a neighboring transistor 790.
[0027] FIG. 8 illustrates a fifth embodiment of a photodiode 800 according to the invention. The photodiode illustrated in FIG. 8 differs from the embodiment of FIG. 5 only in that it has two superimposed PN junctions, each associated with an avalanche zone 813A, 813B, and sharing a same interleaved doped zone. In particular, a P-doped zone is located between two N-doped zones, forming a PN junction on each side. The two PN junctions are each located in a high sensitivity region 870A, 870B as described with reference to FIG. 3. These high sensitivity regions 870A, 870B are illustrated in FIG. 9, showing the electromagnetic field distribution in FIG. the photodiode. The high sensitivity regions 870A, 870B are superimposed, and separated by an underlayer in which the intensity of the electromagnetic field is very low (average intensity at least 10 times less than in the regions 870A, 870B). Such a photodiode is obtained by means of a method as illustrated in FIG. 5, this time the silicon layer 816 being lightly doped P, on an N-doped silicon layer 815 forming one of the two zones. The photodiode 800 thus forms a bi-spectral detector, each PN junction being dedicated to the detection of a different wavelength. The invention is not limited to the examples described above, and many variants may be implemented without departing from the scope of the present invention.
[0028] For example, the periodic structure may be in the form of a grid, a shape complementary to a square mesh of cubic studs. The invention is particularly advantageous for a semiconductor material layer made of silicon, this material having a low absorption, in particular in the red and the infrared. However, the invention is not limited to this semiconductor material or wavelengths.

权利要求:
Claims (15)
[0001]
REVENDICATIONS1. A SPAD-type photodiode (100; 200; 500; 600; 700; 800) having a layer of semiconductor material (110; 210) comprising an N-doped region (111; 511; 611) and a P-doped region (112; 512; 612), separated by an avalanche zone (113; 213; 513; 813A; 813B), characterized in that it further comprises: a first low-index layer (130; 230; 530; 630; 730); and a periodic structure (120; 220; 520; 620; 720) having a plurality of elementary patterns; the first low index layer (130; 230; 530; 630; 730) having a refractive index lower than that of the layer of semiconductor material and that of the periodic structure, and the layer of semiconductor material (110 210) being interposed between the first low index layer and the periodic structure.
[0002]
2. Photodiode (200; 500; 600; 700; 800) according to claim 1, characterized in that the periodic structure comprises a plurality of regularly spaced pads (212; 521), the gaps (122; 222; pads being at least partially filled with a material called low index material, having a refractive index lower than that of the layer of semiconductor material and that of the periodic structure.
[0003]
3. Photodiode (100; 200; 500; 700; 800) according to claim 1 or 2, characterized in that the periodic structure (520; 720) has N or P doping and in that only one of the elementary patterns is connected to an electrical contact element, for biasing the photodiode.
[0004]
4. Photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 3, characterized in that the semiconductor material layer is made of silicon, and the first low index layer is (130, 230, 530, 630, 730) is silicon dioxide.
[0005]
5. Photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 4, characterized in that a difference between the refractive index of the layer of semiconductor material ( 110; 210) and the refractive index of the first low index layer (130; 230; 530; 630; 730) is greater than or equal to 0.5. 10
[0006]
6. Photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 5, characterized in that the periodic structure (120; 220; 520; 620; 720) has a pitch (P ) between 100 nm and 1000 nm.
[0007]
The photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 6, characterized in that the thickness (h2) of the layer of semiconductor material (110; ) is between 0.5 μm and 3 μm.
[0008]
The photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 7, characterized in that the height (h1) of the elementary patterns 20 is less than 1 μm.
[0009]
9. Photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 8, characterized in that a ratio (c),) of the width (a) of a stud, divided by the pitch (P) of the periodic structure (120; 220; 520; 620; 720) is between 0.25 and 0.80.
[0010]
10. Photodiode (100; 200; 500; 600; 700; 800) according to any one of claims 1 to 9, characterized in that the periodic structure (120; 220; 3037442 23 520; 620; 720) forms a network. in two dimensions, the pitch (P) of this network being identical in each of said two dimensions.
[0011]
11. Photodiode (100; 200; 500; 600; 800) according to any one of claims 1 to 10, characterized in that the periodic structure (120; 220; 520; 620) is formed in the same block of material semiconductor than the layer of semiconductor material (110; 210).
[0012]
12. Photodiode (700) according to any one of claims 1 to 10, characterized in that the periodic structure (720) is formed in a polycrystalline silicon layer deposited on the layer of semiconductor material.
[0013]
13. Matrix of at least two photodiodes (200; 500; 800) according to claim 11, characterized in that: the periodic structure comprises a plurality of regularly spaced pads (212; 521), the gaps (122; 222; ) between the pads being at least partially filled with a material called low index material, having a refractive index lower than that of the layer of semiconductor material and that of the periodic structure; and the adjacent periodic structures (220; 520) are separated by trenches (570) filled with said low index material.
[0014]
14. A method of manufacturing a photodiode (100; 200; 500; 600; 800) according to any one of claims 1 to 11, characterized by a step of structuring an upper region of a block made of semi material -conducteur, to form an assembly constituted by the periodic structure (120; 220; 520; 620) mounted on the layer of semiconductor material (110; 210). 3037442 24
[0015]
15. A method of manufacturing a matrix of photodiodes (200; 500; 800) according to claim 13, characterized in that it comprises the following steps: structuring of an upper region of a block (516) of semiconductor material to form an assembly consisting of a plurality of periodic structures (520) mounted on a layer of semiconductor material; etching trenches (570) between two adjacent periodic structures (520), the trench etching and structuring steps being performed by a single etching step (502); and deposition (503) of the low index material, filling the trenches (570) and spaces (522) between studs forming the periodic structures, said low index material having a refractive index lower than that of the semiconductor material block .

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同族专利:

公开号 | 公开日

US9741879B2|2017-08-22|

US20160365464A1|2016-12-15|

FR3037442B1|2018-07-06|

EP3104421A1|2016-12-14|

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2016-07-08| PLFP| Fee payment|Year of fee payment: 2 |

2016-12-16| PLSC| Search report ready|Effective date: 20161216 |

2017-06-30| PLFP| Fee payment|Year of fee payment: 3 |

2018-06-27| PLFP| Fee payment|Year of fee payment: 4 |

2020-06-30| PLFP| Fee payment|Year of fee payment: 6 |

2021-06-30| PLFP| Fee payment|Year of fee payment: 7 |

优先权:

申请号 | 申请日 | 专利标题

FR1555326|2015-06-11|

FR1555326A|FR3037442B1|2015-06-11|2015-06-11|SPAD PHOTODIODE COVERED BY A NETWORK|FR1555326A| FR3037442B1|2015-06-11|2015-06-11|SPAD PHOTODIODE COVERED BY A NETWORK|

EP16173520.4A| EP3104421A1|2015-06-11|2016-06-08|Spad photodiode covered with a grating|

US15/179,101| US9741879B2|2015-06-11|2016-06-10|SPAD photodiode covered with a network|

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