Avalanche photodiode

Abstract

The utility model relates to an avalanche photodiode. An object of the utility model is to provide an improved avalanche photodiode. An avalanche photodiode includes: a main PN junction adapted to be reverse biased; and a plurality of semiconductor regions, the plurality of semiconductor regions including at least: a first region, which is an epitaxial semiconductor region of a first conductivity type; a second region, the second region being a semiconductor region of a second conductivity type, the second region being arranged to at least partially surround the first region and including a surface in contact with a surface of the first region; and a third region. Thus, an improved avalanche photodiode is provided.

Description

Technical Field

[0001] The present disclosure relates generally to avalanche photodiodes, and more particularly to single photon avalanche diodes, also known as SPAD (“Single Photon Avalanche Diode”) photodiodes, and methods of making the same. Background Art

[0002] A photodiode is a semiconductor component that has the ability to capture radiation in the optical domain and convert it into an electrical signal.

[0003] A SPAD photodiode is a photodiode comprising a PN junction adapted to be reverse biased at a voltage higher than the breakdown voltage or avalanche voltage of the junction. At this bias voltage, the electric field around the PN junction is sufficient to cause photogenerated carriers to reach the space charge region or depletion region of the junction to trigger an avalanche phenomenon, which is reflected by an increase in current in the photodiode. In a SPAD photodiode, a single photogenerated carrier can trigger an avalanche in the depletion region by the impact ionization effect.

[0004] SPAD photodiodes enable the detection of radiation with very low light intensities and are particularly useful for the detection of single photons and the counting of photons.

[0005] An electronic device may include a plurality of photodiodes or a plurality of pixels, each pixel including at least one photodiode. For example, an image sensor is an electronic device that may include a plurality of photodiodes that enable the image sensor to obtain an image of a scene at a given time. An image is typically formed by an array of pixels, each pixel including at least one photodiode.

[0006] The increasing miniaturization of the electronics, in particular of image sensors, leads to a miniaturization of pixels and / or photodiodes.

[0007] In order to miniaturize the SPAD photodiode, one solution is to reduce at least one of its dimensions, such as its width, in the plane of the electronic circuit in which it is integrated. However, reducing the width of the photodiode has the disadvantage of reducing the photon collection volume and thus, in particular, the photon detection probability ("PDP").

[0008] In order to compensate for this reduction in volume, one solution is to increase the height of the photodiode, i.e. the dimension in the direction perpendicular to the plane of the electronic circuit. However, increasing the height of the photodiode may have the disadvantage of reducing the probability that the photogenerated carriers reach the multiplication zone (i.e. the zone where the electric field is strong enough for the impact ionization effect and therefore avalanche to occur), or increasing the time in which the carriers can reach this multiplication zone (especially when the photogenerated carriers are at a greater distance from this multiplication zone of the photodiode). In fact, beyond a given distance from the PN junction, the electric field generated due to the reverse bias of the PN junction cancels out or strongly reduces, and it is less able or even no longer possible to drive the photogenerated carriers towards the multiplication zone. Beyond a given distance from the PN junction, only random diffusion in the photodiode has the possibility of driving the photogenerated carriers to the multiplication zone, and the probability that the photogenerated carriers will never reach the multiplication zone or will reach the multiplication zone with a significant delay is not negligible.

[0009] As a corollary, this may increase the timing jitter, which corresponds to the statistical fluctuations of the detection delay. Utility Model Content

[0010] There is a need for an avalanche photodiode that overcomes all or some of the disadvantages of known avalanche photodiodes, such as avalanche photodiodes of the SPAD type.

[0011] In particular, there is a need for a SPAD photodiode that can be reduced in size without reducing the photon detection probability (PDP) and / or increasing the timing jitter.

[0012] It would be advantageous to have such a photodiode without complicating the method of manufacturing the photodiode and increasing its manufacturing costs.

[0013] An embodiment provides an avalanche photodiode, comprising:

[0014] a main PN junction adapted to be reverse biased; and

[0015] A plurality of semiconductor regions, the plurality of semiconductor regions comprising at least:

[0016] a first epitaxial semiconductor region of a first conductivity type; and

[0017] A second semiconductor region of a second conductivity type is arranged to at least partially surround the first region and includes a surface in contact with a surface of the first region.

[0018] An embodiment provides a method of manufacturing an avalanche photodiode, the avalanche photodiode including a main PN junction adapted to be reverse biased, the method including forming a plurality of semiconductor regions, the plurality of semiconductor regions including at least:

[0019] a first epitaxial semiconductor region of a first conductivity type; and

[0020] A second semiconductor region of a second conductivity type is arranged to at least partially surround the first region and includes a surface in contact with a surface of the first region.

[0021] According to one aspect of the present disclosure, an avalanche photodiode is provided, comprising: a main PN junction suitable for being reverse biased; and a plurality of semiconductor regions, the plurality of semiconductor regions comprising at least: a first region, the first region being an epitaxial semiconductor region of a first conductivity type; a second region, the second region being a semiconductor region of a second conductivity type, the second region being arranged to at least partially surround the first region and including a surface in contact with a surface of the first region; and a third region.

[0022] According to an embodiment, a main PN junction is formed by a fourth region and a fifth region of the plurality of semiconductor regions;

[0023] a fourth region being heavily doped with the first conductivity type, for example more heavily doped than the first region, and formed from the first surface of the photodiode; and

[0024] The fifth region is heavily doped with the second conductivity type, for example, more heavily doped than the second region, and is formed below and in contact with the fourth region;

[0025] The fourth region and the fifth region are located, for example, at the center of the photodiode in a plane parallel to the first surface.

[0026] According to an embodiment, a sixth region of the plurality of semiconductor regions is formed laterally around and at a distance from the fourth region from the first surface of the photodiode, the sixth region being heavily doped with the second conductivity type, eg more heavily doped than the second region.

[0027] According to an embodiment, a third region among the multiple semiconductor regions is formed between the first surface and the first region of the photodiode, the third region is an epitaxial region of the first conductivity type, and the fourth region, the fifth region and the sixth region are formed in the third region by doping (for example, by ion implantation).

[0028] According to a specific embodiment, the first region and the third region are epitaxially grown and doped under similar conditions, for example corresponding to regions of the same epitaxial layer.

[0029] According to an embodiment, a guard ring region of the plurality of semiconductor regions is formed around the fourth region, the guard ring region having the first conductivity type and being more lightly doped than the fourth region.

[0030] According to an embodiment, the semiconductor region is formed in a well defined by a deep trench insulation extending in a direction perpendicular to the first surface of the photodiode.

[0031] According to an embodiment, the second region includes a lateral portion between the first region and the deep trench isolation.

[0032] According to an embodiment, the second region includes a buried portion between the first region and a second surface of the photodiode opposite to the first surface.

[0033] According to an embodiment, the first region is doped in a substantially constant manner in a direction perpendicular to the first surface of the photodiode.

[0034] According to an embodiment, the first region is doped gradually in a direction perpendicular to the first surface, for example in a decreasing manner between the first surface and a second surface of the photodiode opposite to the first surface.

[0035] According to an embodiment, the first region includes a first portion and a second portion, the second portion being narrower than the first portion in a plane parallel to the first surface and being located between the first portion and the main PN junction.

[0036] According to an embodiment, the first region surrounds the main PN junction, for example includes a first portion located below the main PN junction and a second portion extending all the way to the first surface of the photodiode.

[0037] According to an embodiment, the first region is inside the second region.

[0038] According to an embodiment, in a plane parallel to the first surface of the photodiode, each dimension of the photodiode is smaller than 6 μm and / or the height of the photodiode is in the range from 3 μm to 15 μm, for example in the range from 6 μm to 10 μm.

[0039] According to an embodiment, forming a plurality of semiconductor regions includes:

[0040] forming an epitaxial layer of a first conductivity type by epitaxial growth, the epitaxial layer of the first conductivity type being intended to form a first semiconductor region; and then

[0041] forming at least a first portion of the second region by partial doping of the epitaxial layer, for example by ion implantation; and

[0042] The fourth region and the fifth region are formed by partially doping the epitaxial layer from the first surface of the photodiode, for example by ion implantation.

[0043] According to an embodiment, the lateral portion of the second region is formed by partial doping of the epitaxial layer, eg by ion implantation, by partial change of the conductivity of the epitaxial layer, by diffusion from the deep trench isolation, or by charge inversion material in the deep trench isolation.

[0044] According to an embodiment, the buried part of the second region is formed from the second surface of the photodiode by epitaxial growth or by partial doping of an epitaxial layer, for example by ion implantation. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The above features and advantages as well as other features and advantages will be described in detail in the remainder of this disclosure with respect to specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0046] Figure 1 is a partial simplified cross-sectional view showing an example of a photodiode;

[0047] Figure 2 is a partial simplified cross-sectional view showing a photodiode according to an embodiment;

[0048] Figure 3 In a very simplified way, the Figure 2 The doping distribution in any cell of the photodiode is similar to that of the photodiode;

[0049] Figure 4 is a partial simplified cross-sectional view showing another example of a photodiode;

[0050] Figure 5 is a partial simplified cross-sectional view showing a photodiode according to another embodiment; and

[0051] Fig. 6A , Figure 6B , Figure 6C , Fig.6D , Fig. 6E , Fig. 6F and Figure 6G : are cross-sectional views showing steps of a method of manufacturing a photodiode according to an embodiment. DETAILED DESCRIPTION

[0052] This application claims the benefit of priority to French Patent Application No. 2214005, filed on December 20, 2022, entitled “Photodiode à avalanche”, which is incorporated herein by reference to the fullest extent permitted by law.

[0053] Like features are denoted by like reference numerals in the various figures. In particular, common structural and / or functional features among the various embodiments may have the same reference numerals and may employ the same structures, dimensions, and material properties.

[0054] For the sake of clarity, only the steps and elements useful for understanding the described embodiments are illustrated and described in detail. In particular, the SPAD photodiode typically includes a secondary circuit, in particular a circuit for biasing the PN junction to a voltage above its avalanche threshold, a readout circuit suitable for detecting the start of the avalanche of the photodiode, and a quenching circuit having the function of interrupting the avalanche of the photodiode once it starts. These secondary circuits are not shown in the drawings and will not be described in detail, and the described embodiments are compatible with the secondary circuits of the SPAD photodiodes equipped with known.

[0055] Unless otherwise indicated, when referring to two elements being connected together, this means a direct connection without any intermediate elements except conductors, and when referring to two elements being coupled together, this means the two elements may be connected or they may be coupled via one or more other elements.

[0056] In the following description, when referring to terms defining absolute positions, such as terms "front", "back", "top", "bottom", "left", "right", etc., or terms defining relative positions, such as terms "above", "below", "upper", "lower", etc., or terms defining directions, such as terms "horizontal", "vertical", etc., unless otherwise specified, it refers to the orientation of the drawing or to the photodiode in the normal use position.

[0057] In the following description, the height or depth corresponds to a dimension intercepted in a Z direction, which may correspond to a vertical direction, and the width corresponds to a dimension intercepted in an X direction, which may correspond to a horizontal direction.

[0058] Unless otherwise indicated, the expressions "about", "approximately", "substantially" and "approximately" mean plus or minus 10%, preferably plus or minus 5%.

[0059] In the following description, when a region is mentioned, it refers to a semiconductor region.

[0060] In the following description, when an epitaxial layer or region is mentioned, it means a layer or region formed by epitaxial growth.

[0061] In the examples given below, it is considered that the first conductivity type is N-type and the second conductivity type is P-type, but these examples can also be applied if the conductivity types are opposite, that is, the first conductivity type is P-type and the second conductivity type is N-type, accompanied by, for example, appropriate anode and cathode voltage reversal.

[0062] For example, the P-type region is doped with boron atoms (B), and / or the N-type region is doped with arsenic atoms (As).

[0063] Figure 1 is a partially simplified cross-sectional view showing an example of a SPAD type photodiode 100 .

[0064] The photodiode 100 includes a first P-type epitaxial semiconductor region 111 and a second P-type semiconductor region 112 that is more heavily doped than the first region 111. The second region 112 surrounds the first region 111.

[0065] For example, the first region 111 forms a collecting volume within which charge carriers are generated with a high probability when photons are absorbed (photogeneration).

[0066] The photodiode 100 further comprises a third P-type epitaxial semiconductor region 113 flush with the upper surface 100A of the photodiode 100, which is also more lightly doped than the second region 112. For example, the third region 113 is epitaxially grown and doped under similar conditions as the first region 111.

[0067] The first region 111 may include a first portion 111A and a second portion 111B that is narrower than the first portion 111A and couples the first portion 111A to the third region 113 .

[0068] The photodiode 100 also includes a fourth heavily doped N-type semiconductor region 114 flush with the upper surface 100A of the photodiode 100 and a fifth heavily doped P-type semiconductor region 115 that is more heavily doped than the second region 112 , and the fifth heavily doped P-type semiconductor region 115 is below and in contact with the fourth region 114 .

[0069] For example, the fourth region 114 has a cylindrical shape. In other words, the fourth region 114 may have a circular or elliptical shape in a top view. Similarly, the fifth region 115 may have a cylindrical shape. As a variant, the fourth region and / or the fifth region may have other shapes, for example, a quadrilateral or a quadrilateral with rounded corners in a top view, or a substantially hemispherical shape, or may include a portion of a substantially hemispherical shape, as described below. Figure 4 as shown in .

[0070] The coupling between the fourth and fifth regions provides a top PN junction 130 or main PN junction. For SPAD photodiode operation, the PN junction can be reverse biased beyond the breakdown voltage to form an electric field around the PN junction sufficient to allow photogenerated carriers to reach the space charge region or depletion region of the PN junction to trigger avalanche phenomena.

[0071] The area surrounded by the dotted line substantially corresponds to the multiplication region 131, ie, a region where the electric field is strong enough so that the probability of the avalanche phenomenon occurring is high.

[0072] In the example shown, the guard ring region 117 surrounds the fourth region 114. The guard ring region is an N-type semiconductor region that is more lightly doped than the fourth region 114. For example, the guard ring region 117 has the shape of a circular or elliptical ring, a square frame, or a square frame with rounded corners.

[0073] The photodiode 100 further includes a sixth heavily doped P-type semiconductor region 116, which is more heavily doped than the second region 112, is flush with the upper surface 100A of the photodiode, and is located around the guard ring region 117 and laterally at a distance from the guard ring region 117. For example, in a top view, the sixth region 116 has a shape of a circular or elliptical ring, a square frame, or a square frame with rounded corners.

[0074] The fourth region 114 , the fifth region 115 , the sixth region 116 , and the guard ring region 117 are typically formed by, for example, ion implantation at least partially in the third region 113 .

[0075] The semiconductor region 111 , the semiconductor region 112 , the semiconductor region 113 , the semiconductor region 114 , the semiconductor region 115 , the semiconductor region 116 , and the semiconductor region 117 are made of silicon, for example.

[0076] These semiconductor regions are located in a well 110 defined by a deep trench isolation 120 (DTI). For example, the trench 120 surrounds the well 110. For example, in a top view, the trench 120 has the shape of a circular or elliptical ring, a square frame, or a square frame with rounded corners. As a variant, the trench 120 has any closed shape.

[0077] The photodiode 100 further includes a cathode 121 and an anode 122 .

[0078] The cathode 121 is located in front of the fourth region 114. The cathode 121 is, for example, located on the top of the fourth region 114 and in contact with the fourth region 114, or in contact with a contact region located inside or on the top of the fourth region 114. For example, the cathode 121 substantially has a parallelepiped or cylindrical shape.

[0079] The anode 122 is located in front of the sixth region 116. The anode 122 is, for example, located on top of the sixth region 116 and in contact with the sixth region 116, or in contact with a contact region located inside or on top of the sixth region 116. Preferably, the anode 122 has a shape similar to that of the sixth region 116 in a top view.

[0080] For example, for the photodiode shown, in operation, the anode is connected to ground and a bias voltage is applied to the cathode.

[0081] For example, in a top view, the photodiode 100 is included in a square having a side length of, for example, less than about 6 μm. For example, the height of the photodiode 100 is in the range of about 3 μm to 15 μm, for example equal to about 6 μm or about 10 μm.

[0082] For the miniaturization of SPAD photodiodes, for example in order to reduce the width of the photodiode and compensate for this reduction by increasing the height of the photodiode, a solution is sought such that the increase in the height of the photodiode is not reflected as a degradation of the timing jitter and / or a reduction in the photon detection probability (PDP).

[0083] In the example of the photodiode 100, the first epitaxial region 111 included in the second region 112 and doped more lightly with the same conductivity type as the second region 112 generates a depletion region 132, as schematically shown by the curve in the stripe-dot line. The depletion region defines a volume in which the transport of carriers is relatively fast. Having as large a depletion volume as possible enables improved timing jitter compared to a photodiode with a lower depletion volume.

[0084] However, it can be observed that the depletion region 132 extends all the way to the center of the epitaxial region 111, but it does not reach the bottom of the epitaxial region 111, i.e., the bottom of the photogenerated carrier collection volume. Therefore, the photogenerated carriers at the bottom of the volume may not reach the multiplication region 131, or have a random and significant displacement time. Not to mention that the depletion region 132 of the photodiode 100 may not be sufficient to maintain acceptable timing jitter when the height of the photodiode increases. In fact, by increasing the height of the photodiode, the depletion region remains constant, and critical regions that are non-depleted and far away from the multiplication region are added at the bottom of the epitaxial region. If carriers are photogenerated in these critical regions, then as the height increases, these carriers may take longer to trigger the avalanche, resulting in a degradation of the timing jitter.

[0085] The present inventors provide a photodiode and a method for manufacturing such a photodiode, which enable the aforementioned improvement needs to be addressed and all or part of the disadvantages of the aforementioned photodiodes to be overcome. In particular, the present inventors provide a photodiode and a method for manufacturing such a photodiode, which enable the height of the photodiode to be increased without increasing the time jitter and without reducing the photon detection probability (PDP) or even increasing the photon detection probability.

[0086] Embodiments of the photodiode will be described below. Based on the guidance of this specification, those skilled in the art will come to think of the described but non-limiting embodiments and various modifications.

[0087] Figure 2 is a partially simplified cross-sectional view showing an avalanche photodiode 200 according to an embodiment.

[0088] According to a preferred embodiment, the photodiode 200 is a SPAD type photodiode.

[0089] The photodiode 200 has an upper surface 200A (first surface) and a lower surface 200B (second surface), the lower surface 200B being opposite to the upper surface and preferably being substantially parallel to the upper surface.

[0090] The photodiode 200 includes a first epitaxial semiconductor region 211 of a first conductivity type (in the example, N type) and a second semiconductor region 212 of a second conductivity type (in the example, P type). The second region 212 at least partially surrounds the first region 211 and includes a surface in contact with a surface of the first region 211. For example, the first region 211 is included in the second region 212.

[0091] Therefore, the photodiode 200 may differ from the photodiode 100 mainly in that the first epitaxial region 211 is of N-type instead of P-type.

[0092] The photodiode 200 includes an upper semiconductor region 213 (third region) flush with the level of the upper surface 200A of the photodiode 200. The third region 213 is an N-type epitaxial region.

[0093] For example, the first region and the third region are epitaxially grown and doped under similar conditions, for example, they correspond to regions of the same layer formed by epitaxial growth. For example, the third region 213 may correspond to an upper portion (or third portion) of a layer formed by epitaxial growth.

[0094] The photodiode 200 also includes: a fourth heavily doped N-type semiconductor region 214, preferably more heavily doped than the first region 211 and flush with the upper surface 200A of the photodiode 200; and a fifth heavily doped P-type semiconductor region 215, preferably more heavily doped than the second region 212, below the fourth region 214 and in contact with the fourth region 214.

[0095] For example, the fourth region 214 has a cylindrical shape. In other words, the fourth region 114 may have a circular or elliptical shape in a top view. Similarly, the fifth region 215 may have a cylindrical shape. As a variation, the fourth region and / or the fifth region may have other shapes, for example, a quadrilateral or a quadrilateral with rounded corners in a top view, or a substantially hemispherical shape, or may include a portion of a substantially hemispherical shape, as described below, for example. Figure 5 as shown in .

[0096] The coupling between the fourth and fifth regions provides a top PN junction 230 or main PN junction. For SPAD photodiode operation, the PN junction can be reverse biased beyond the breakdown voltage to form an electric field around the PN junction sufficient to allow photogenerated carriers to reach the multiplication region to trigger avalanche phenomena.

[0097] The area surrounded by the dotted line substantially corresponds to the multiplication region 231, ie, a region where the electric field is strong enough so that the probability of the avalanche phenomenon occurring is high.

[0098] like Figure 2 As shown in , the guard ring region 217 can surround the fourth region 214. The guard ring region 217 is an N-type semiconductor region that is more lightly doped than the fourth region 214. The guard ring region 217 particularly enables to avoid premature start-up of the photodiode at the periphery of the main PN junction, and can reduce the probability that minority carriers originate from the periphery of the junction. For example, the guard ring region 217 has the shape of a circular or elliptical ring, a square frame, or a square frame with rounded corners.

[0099] The photodiode 200 further includes a sixth heavily doped P-type semiconductor region 216, which is preferably more heavily doped than the second region 212, flush with the upper surface 200A of the photodiode 200, and laterally located around the guard ring region 217 and at a distance from the guard ring region 217. The sixth region may be a contact region. For example, in a top view, the sixth region 216 has a shape of a circular or elliptical ring, a shape of a square frame or a shape of a square frame with rounded corners, or more generally a quadrilateral or a quadrilateral with rounded corners.

[0100] The fourth region 214 , the fifth region 215 , the sixth region 216 , and the guard ring region 217 are preferably formed by, for example, ion implantation at least partially in the third region 213 .

[0101] The semiconductor region 211 , the semiconductor region 212 , the semiconductor region 213 , the semiconductor region 214 , the semiconductor region 215 , the semiconductor region 216 , and the semiconductor region 217 are made of silicon, for example.

[0102] These semiconductor regions are located in a well 210 defined by a deep trench isolation 220 (DTI). For example, the trench 220 surrounds the well 210. For example, in a top view, the trench 220 has the shape of a circular or elliptical ring, a square frame or a square frame with rounded corners, or more generally a quadrilateral or a quadrilateral with rounded corners. As a variant, the trench 220 has any closed shape.

[0103] For example, the trench may be filled with a conductive or semiconductor element, such as metal or polysilicon, isolated from the rest of the photodiode by a spacer layer. The trench 220 may thus form a capacitive deep trench isolation (CDTI).

[0104] The surfaces where the first region 211 and the second region 212 are in contact form PN junctions complementary to the main PN junction 230. These complementary junctions enable the formation of a depletion region 232 (schematically shown by a dotted curve) and enable the generation of electric field lines deep in the photodiode, with the inevitable result that the transport of photogenerated carriers in the most critical region of the photodiode (e.g. at the bottom of the photodiode) towards the multiplication region is accelerated. In fact, the transport of photogenerated carriers in the depletion region is faster than in the non-depletion region.

[0105] Therefore, these complementary junctions will be able to generate holes, which will also be able to participate in the avalanche phenomenon, as a supplement to the contribution of the electrons of the main PN junction. In fact, the holes are collected via the anode 222 (described below), and the anode is directly coupled to the P-type region adjacent to these complementary junctions through the P-type doping continuity.

[0106] and Figure 1 Compared to the photodiode 100 of FIG. 200 , this makes it possible to extend the depletion region toward the bottom of the photodiode, thereby accelerating the transport of photogenerated carriers in the most critical region of the photodiode (e.g., at the bottom of the photodiode). In fact, in the photodiode 200, the photogenerated carriers are already present in the depletion region 232, or at least in its immediate neighborhood, and they are Figure 1Compared to the case of photodiode 100 in which the depletion region is farther from the bottom of the photodiode, there is a higher probability of joining the multiplication region within a shorter delay. As a corollary, the depletion region 232 of photodiode 200 can enable reduction of timing jitter even when the height of the photodiode increases.

[0107] For example, the photodiode 200 forms a fully depleted SPAD photodiode.

[0108] For example, the first region 211 forms a collection volume within which there is a high probability of generating carriers upon absorption of photons. For example, photogenerated carriers in the first region 211 may be driven towards the multiplication region 231, and this is more efficient as the electric field lines are optimized.

[0109] Advantageously, the doping of the first epitaxial region 211 can be adjusted to optimize the field lines. As described below, the first epitaxial region 211 can have a substantially constant doping in the Z direction, or a gradual doping in the Z direction, such as a doping that decreases between the upper surface 200A of the photodiode and the lower surface 200B of the photodiode.

[0110] like Figure 2 As shown in FIG. 1 , the first region 211 may include a first portion 211A and a second portion 211B that is narrower than the first portion 211A and couples the first portion 211A to the third region 213 . This shape may correspond to a funnel shape that facilitates conduction of photogenerated carriers toward the multiplication region 231 .

[0111] In addition, the second region 212 may include:

[0112] A first portion 212A laterally disposed between the second portion 211B of the first region 211 and the deep trench isolation 220 ;

[0113] a second portion 212B (lateral portion) laterally located between the first portion 211A of the first region 211 and the deep trench isolation 220 ; and

[0114] The third portion 212C (buried portion) is located below the first region 211 and between the first region 211 and the lower surface 200B of the photodiode 200 .

[0115] The second region 212 may extend vertically toward the upper surface 200A of the photodiode 200 to also be laterally located between the third region 213 and the deep trench isolation 220 .

[0116] The presence of the third portion 212C of the second N-type region 212 below the first N-type region 211 enables the formation of a passivation area of ​​the photodiode 200, for example, making it less susceptible to dark current, and the same is true for the presence of the second portion 212B of the second P-type region 212 between the first N-type region 211 and the deep trench isolation 220. For example, this enables a dark count rate (“DCR”) to be reduced.

[0117] Preferably, the width and / or height of the first epitaxial region 211 is optimized so that the volume of the first region is as large as possible and thus can collect as many photons as possible, for example to increase the photon detection probability PDP, while maintaining a distance from the lower surface 200B of the photodiode 200 on the one hand and from the deep trench isolation 220 on the other hand sufficient to limit the dark count rate DCR. For example, the second portion 212B of the second region 212 has a width of approximately a few hundred nanometers, the third portion 212C of the second region 212 has a height of approximately from a few hundred nanometers to one micrometer, and the dimensions of the first epitaxial region 211 are derived from the dimensions of the second and third portions of the second region 212 and the dimensions of the diode. As a non-limiting example, the first epitaxial region 211 may have a width of approximately 5 μm and a height of approximately 7 μm.

[0118] The photodiode 200 further includes a cathode 221 and an anode 222 .

[0119] The cathode 221 is located in front of the fourth region 214. The cathode 221 is, for example, located on the top of the fourth region 214 and in contact with the fourth region 214, or in contact with a contact region located inside or on the top of the fourth region 214. For example, the cathode 221 substantially has a parallelepiped or cylindrical shape.

[0120] The anode 222 is located in front of the sixth region 216. The anode 222 is, for example, located on top of the sixth region 216 and in contact with the sixth region 216, or in contact with a contact region located inside or on top of the sixth region 216. Preferably, the anode 222 has a shape similar to that of the sixth region 216 in a top view.

[0121] For example, for the photodiode shown, whose first conductivity type is N-type and whose second conductivity type is P-type, in operation, the anode is connected to ground and a bias voltage is applied to the cathode.

[0122] As a variant, if the first conductivity type is P type and the second conductivity type is N type and the anode and cathode are reversed, then in operation the cathode is connected to ground and a bias voltage is applied to the anode.

[0123] For example, in a top view, the photodiode 200 is included in a square with a side length less than 6 μm. For example, the height of the photodiode 200 is in the range of about 3 μm to 15 μm, for example equal to about 6 μm or equal to about 10 μm.

[0124] Figure 3 In a very simplified way, the Figure 2 The doping distribution of the first epitaxial region and the second semiconductor region of the photodiode 200 in any unit cell is similar. The doping distribution is based on a substantially laterally centered vertical line ( Figure 2 The dashed line in the figure indicates the Z direction.

[0125] The first N-type epitaxial region 211 may have a substantially constant N doping, particularly in the Z direction. Figure 3 It is shown by the dashed curve 301.

[0126] As a variation, the doping of the first epitaxial region 211 may be gradual in the Z direction, for example, decreasing between the upper surface 200A of the photodiode and the lower surface 200B of the photodiode, for example, from 10 15 cm -3 to 5.10 14 cm -3 This is Figure 3 302 is shown in FIG.

[0127] Curve 303 shows a gradual P doping of the second region 212 (more precisely, the third portion 212C of the second region located below the first region 211), which increases between the first region 211 and the lower surface 200B of the photodiode 200, for example, from 2.10 12 cm -3 Until 9.10 18 cm -3 .

[0128] The inventors can show through simulation that the photodiode according to the embodiment, for example Figure 2 The inventors have also shown that a photodiode having no P-type region portion below the N-type epitaxial region further enables the number of carriers that trigger an avalanche to be increased in a very short time and reduces the time jitter. However, as described below, it may have the disadvantage of increasing the dark count rate DCR.

[0129] Figure 4 4 is a partially simplified cross-sectional view showing another example of a photodiode 400. Only half of the photodiode in the X direction is shown. The photodiode 400 can be distinguished from the photodiode 100 mainly in the shape of the first epitaxial region 411 and the second region 412, both of which have the same conductivity type, which is P-type in this example. In addition, the photodiode 400 does not include a guard ring region. The second region 412 can be progressively doped, where the doping decreases from the lower surface 400B to the first region 411.

[0130] The second region 412 surrounds the first region 411 , and includes a surface in contact with a surface of the first region 411 .

[0131] The photodiode 400 further includes a fourth heavily doped N-type semiconductor region 414 flush with the upper surface 400A of the photodiode 400, and a fifth heavily doped P-type semiconductor region 415 in contact with and surrounding the fourth region 414, and the coupling between the fourth region 414 and the fifth region 415 provides a top PN junction 430 or a main PN junction. The photodiode 400 further includes a sixth heavily doped P-type semiconductor region 416 flush with the upper surface 400A of the photodiode 400, which also corresponds to the upper surface of the second region 412 and is located around the first region 411.

[0132] The first region 411 includes a first portion 411A located below the fifth region 415 and a second portion 411B located laterally between the fifth region 415 and the second region 412 and extending all the way to the upper surface 400A of the photodiode 400 .

[0133] The semiconductor region is located in a well 410 defined by a deep trench isolation 420 .

[0134] Figure 5 FIG. 5 is a partial simplified cross-sectional view showing a photodiode 500 according to another embodiment. Only half of the photodiode in the X direction is shown. The photodiode 500 can be connected to Figure 4 The main difference between the photodiode 400 and the first epitaxial region 511 is that the first epitaxial region 511 is of N-type instead of P-type.

[0135] The surface where the first region 511 and the second region 512 are in contact forms a PN junction complementary to the main PN junction 530, which is formed by coupling between the fourth region 514 and the fifth region 515 of the photodiode 500. These complementary PN junctions enable the formation of a depletion region 532 schematically shown by a dotted line curve, which is larger than Figure 4The depletion region 432 of the photodiode 400 extends more toward the bottom of the photodiode 500. For example, as shown, the first region 511 surrounds the main PN junction 530.

[0136] The semiconductor region is located in a well 510 defined by a deep trench isolation 520 .

[0137] The first region 511 includes a first portion 511A located below the fifth region 515 and a second portion 511B located laterally between the fifth region 515 and the second region 512 and extending all the way to the upper surface 500A of the photodiode 500 .

[0138] The second region 512 includes a lateral portion 512B between the first region 511 and the deep trench isolation 520 , and a buried portion 512C between the first region 511 and the lower surface 500B of the photodiode 500 .

[0139] The inventors can show through simulation that the photodiode with complementary PN junction according to the embodiment, for example Figure 5 The photodiode 500 type photodiode, with Figure 4 Compared with the photodiode 400 type without a complementary PN junction, the electric field lines can be generated in a deeper region of the photodiode.

[0140] The inventors can also show through simulation that the photodiode according to the embodiment, for example Figure 5 The photodiode 500 type of photodiode enables the height of the photodiode to be increased without increasing the avalanche start time. On the contrary, the inventors have observed that for Figure 4 The fact of increasing the height of the photodiode 400 type photodiode significantly increases the avalanche start time.

[0141] Thus, a photodiode according to an embodiment enables increasing the height of the photodiode and thus having a larger collection volume for equal width, for example to increase the photon detection probability (PDP) without increasing the temporal jitter.

[0142] Fig. 6A , Figure 6B , Figure 6C , Fig.6D , Fig. 6E , Fig. 6F and Figure 6G : are cross-sectional views showing steps of a method of manufacturing a photodiode according to an embodiment.

[0143] Fig. 6AThe structure obtained at the end of an epitaxial growth step of an epitaxial layer 601 of a first conductivity type, in the method example shown, of N-type, formed on a substrate 608, for example a silicon substrate (Si). The epitaxial growth can be carried out at a constant doping concentration or with a progressive doping concentration in the Z direction, for example with a doping concentration decreasing between the upper surface 600A of the photodiode and the substrate 608. The epitaxial layer 601 enables the formation of a future first N-type region.

[0144] Figure 6B The structure obtained at the end of the step of doping by ion implantation to form a first portion 602A (first portion of the second region) of the second conductivity type (P type in the method example shown) in the epitaxial layer 601 is shown.

[0145] The first portion 602A is formed, for example, at a distance d1 to a distance d2 from the upper surface 600A of the photodiode by configuring the parameters of the ion implantation to allow such implantation between d1 and d2.

[0146] The first P-type portion 602A defines a first portion 601A (a first portion of the first region) of the N-type epitaxial layer below the first P-type portion 602A and a third portion 601C of the N-type epitaxial layer above the first portion 602A.

[0147] Ion implantation in the epitaxial layer 601 can be performed through a mask 604 (e.g., a mask obtained by photolithography) to form the first portion 602A. For example, the mask 604 is adapted so that the first portion 602A is annular, i.e., while keeping the second portion 601B of the N-type epitaxial layer 601 (the second portion of the first region) at the center of the first P-type portion 602A.

[0148] The second N-type portion 601B enables the first region to be funnel-shaped, which facilitates the conduction of photogenerated carriers from the first portion 601A of the first region to the top PN junction 630 described below.

[0149] Figure 6C The structure obtained at the end of several steps of doping by ion implantation to form in the third portion 601C of the epitaxial layer 601:

[0150] A heavily doped N-type region 604 (fourth region) and a heavily doped P-type region 605 (fifth region), wherein the fourth region and the fifth region form a top PN junction 630, the N-type region 604 being flush with the upper surface 600A of the photodiode 600 and on top of the P-type region 605;

[0151] a guard ring region 607 , which is located around the N-type region 604 and is more lightly N-doped than the region 604 ;

[0152] The heavily doped P region 606 (sixth region) is flush with the upper surface 600A, and is laterally formed around the guard ring region 607 and is spaced a certain distance from the guard ring region 607 .

[0153] The N-type region 604 and the P-type region 605 may be formed over the second portion 601B of the epitaxial layer 601 , or even extend partially over the first P-type portion 602A.

[0154] Each ion implantation may be performed through a mask (not shown), for example a mask obtained by photolithography and then removed after the ion implantation.

[0155] Fig.6D The structure obtained at the end of a step of etching from the upper surface 600A of the photodiode along the entire periphery of the epitaxial layer 601 across the width L1 of the lateral edge 601D is shown, the etching continuing for example down to a depth d3 in the silicon substrate 608. This forms a lateral trench 622. As a variant, the etching can be carried out up to the limit between the silicon substrate 608 and the epitaxial layer 601.

[0156] Fig. 6E The structure obtained after the following steps is shown:

[0157] The step of filling the lateral trench 622 with an isolation material such as silicon dioxide (SiO2) to form a deep trench isolation 620; and

[0158] A step of forming a second P-type portion 602B (a second portion of the second region) laterally between the deep trench isolation 620 and the etched epitaxial layer 601 .

[0159] For example, deep trench isolation 620 surrounds previously formed regions.

[0160] For example, the second P-type portion 602B forms a passivation region of the photodiode, for example making it less susceptible to dark current.

[0161] For example, the formation of the second portion 602B may be performed in the following manner depending on the desired passivation type:

[0162] by doping, for example by ion implantation;

[0163] By adding a doping material or a charge-inversion material in the isolation material during filling of the lateral trench 622 .

[0164] Therefore, by using specific materials, the conductivity along the deep trench isolation 620 can be reversed without ion implantation.

[0165] FIG. 6A to FIG. 6E It is shown that the deep trench isolation 620 is formed after the doping step. This is not limiting and as a variant, the deep trench isolation may be formed before the doping step.

[0166] Fig. 6F The structure obtained at the end of the step of etching the substrate 608 is shown.

[0167] 6A to 6F It is shown that the deep trench isolation 620 is formed before the step of etching the substrate 608. This is not restrictive, and as a variation, the deep trench isolation can be formed after this step of etching the substrate. In addition, the deep trench isolation can be formed from the lower surface 600B of the photodiode.

[0168] Figure 6G The structure obtained at the end of the optional step of forming the third P-type portion 602C (third portion of the second region) is shown.

[0169] The third P-type portion 602C may be formed by doping (eg, by ion implantation), for example, from the lower surface 600B of the photodiode.

[0170] As a variation, the third P-type portion 602C may be formed by epitaxial growth, in which case the third P-type portion 602C is formed before the N-type epitaxial layer 601 is formed by epitaxial growth.

[0171] For example, the third P-type portion 602C forms a passivation region of the photodiode, for example, making it less susceptible to dark current.

[0172] Figure 6G The obtained photodiode 600 shown in FIG. is similar to Figure 2 The photodiode 200.

[0173] Based on the above manufacturing method example, those skilled in the art can use this method to manufacture other photodiodes according to the embodiment, such as Figure 5 The photodiode 500.

[0174] An advantage of the described embodiments is therefore that a photodiode can be formed without complicating the manufacturing method for this purpose.

[0175] Another advantage of the described embodiments is that they are suitable for photodiodes of small size, for example with a side length shorter than 6 μm, and / or for photodiodes with a height, for example in the range of 4 μm to 10 μm or even more.

[0176] Another advantage of the described embodiments is that they enable the size of the photodiode, eg the width, to be reduced without thereby reducing the photon detection probability and / or increasing the timing jitter.

[0177] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these various embodiments and variations may be combined, and those skilled in the art will recognize other variations.

[0178] Finally, based on the functional indications given above, the actual implementation of the described embodiments and variants is within the capabilities of a person skilled in the art.

[0179] The avalanche photodiode (200; 500) can be summarized as including a main PN junction (230; 530) suitable for being reverse biased; and a plurality of semiconductor regions, the plurality of semiconductor regions including at least: a first epitaxial semiconductor region (211; 511) of a first conductivity type; and a second semiconductor region (212; 512) of a second conductivity type, the second region being arranged to at least partially surround the first region and including a surface in contact with a surface of the first region.

[0180] A method for manufacturing an avalanche photodiode (600), which can be summarized as including a main PN junction (630) suitable for being reverse biased, the method including forming a plurality of semiconductor regions, the plurality of semiconductor regions including at least: a first epitaxial semiconductor region of a first conductivity type; and a second semiconductor region of a second conductivity type, the second region being arranged to at least partially surround the first region and including a surface in contact with a surface of the first region.

[0181] The main PN junction (230; 530) can be formed by a fourth region (214; 514) and a fifth region (215; 515) among multiple semiconductor regions; the fourth region is more heavily doped with the first conductivity type, for example, more heavily doped than the first region, and is formed from the first surface (200A; 500A) of the photodiode; and the fifth region is heavily doped with the second conductivity type, for example, more heavily doped than the second region, and is formed below the fourth region and in contact with the fourth region; the fourth region and the fifth region are located, for example, at the center of the photodiode in a plane parallel to the first surface.

[0182] A sixth region (216; 516) of the plurality of semiconductor regions may be formed laterally from the first surface (200A; 500A) of the photodiode around the fourth region (214; 514) and at a distance from the fourth region (214; 514), the sixth region being heavily doped with the second conductivity type, for example more heavily doped than the second region.

[0183] A third semiconductor region (213) among the multiple semiconductor regions can be formed between the first surface (200A) and the first region (211) of the photodiode, the third region is an epitaxial region of the first conductivity type, and the fourth region, the fifth region and the sixth region (214, 215, 216) are formed in the third region by doping, for example by ion implantation.

[0184] The first region and the third region may be epitaxially grown and doped under similar conditions, for example corresponding to regions of the same epitaxial layer.

[0185] A guard ring region (217) of the plurality of semiconductor regions may be formed around the fourth region (214), the guard ring region having the first conductivity type and being more lightly doped than the fourth region (214).

[0186] The semiconductor region may be formed in a well (210; 510) defined by a deep trench isolation (220; 520) extending in a direction (Z) perpendicular to the first surface (200A; 500A) of the photodiode.

[0187] The second region (212; 512) may include a lateral portion (212B; 512B) located between the first region (211; 511) and the deep trench isolation (220; 520).

[0188] The second region (212; 512) may include a buried portion (212C; 512C) between the first region (211; 511) and a second surface (200B; 500B) of the photodiode opposite to the first surface.

[0189] The first region (211) may be doped in a substantially constant manner in a direction (Z) perpendicular to the first surface (200A) of the photodiode.

[0190] The first region (511) may be doped progressively in a direction (Z) perpendicular to the first surface (500A), for example doped in a decreasing manner between the first surface and a second surface (500B) of the photodiode opposite to the first surface.

[0191] The first region (211) may include a first portion (211A) and a second portion (211B) narrower than the first portion in a plane parallel to the first surface (200A) and located between the first portion (211A) and the main PN junction (230).

[0192] The first region (511) surrounds the main PN junction (530), and may include, for example, a first portion (511A) located below the main PN junction (530) and a second portion (511B) extending to the first surface (500A) of the photodiode (500).

[0193] The first region may be internal to the second region.

[0194] In a plane parallel to the first surface (200A) of the photodiode, each dimension of the photodiode may be less than 6 μm and / or the height of the photodiode is in the range from 3 μm to 15 μm, for example in the range from 6 μm to 10 μm.

[0195] Forming multiple semiconductor regions may include forming an epitaxial layer (601) of a first conductivity type intended to form a first semiconductor region by epitaxial growth; then, forming at least one first portion (602A) of a second region by partially doping the epitaxial layer, for example by ion implantation; and forming a fourth region and a fifth region by partially doping the epitaxial layer from a first surface (600A) of the photodiode, for example by ion implantation.

[0196] The lateral portion (602B) of the second region may be formed by partial doping of the epitaxial layer, for example by ion implantation, by partial change of the conductivity of the epitaxial layer, by diffusion from a deep trench isolation, or by a charge inversion material in the deep trench isolation.

[0197] The buried portion (602C) of the second region may be formed from the second face (600B) of the photodiode by epitaxial growth or by partial doping of the epitaxial layer, for example by ion implantation.

[0198] The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications, and publications to provide yet further embodiments.

[0199] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the appended claims, the terms used should not be interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted as including all possible embodiments and the full range of equivalent forms granted by these claims. Therefore, the claims are not limited by the present disclosure.

Claims

1. An avalanche photodiode, characterized in that: include: A main PN junction adapted to be reverse biased; as well as A plurality of semiconductor regions, the plurality of semiconductor regions comprising at least: a first region, the first region being an epitaxial semiconductor region of a first conductivity type; a second region, the second region being a semiconductor region of a second conductivity type, the second region being arranged to at least partially surround the first region and including a surface in contact with a surface of the first region; and The third area.

2. The photodiode according to claim 1, wherein: A main PN junction is formed by a fourth region and a fifth region of the plurality of semiconductor regions; The fourth region is heavily doped with the first conductivity type and is formed from the first surface of the photodiode; as well as The fifth region is heavily doped with the second conductivity type and is formed below and in contact with the fourth region; The fourth region and the fifth region are located at the center of the photodiode in a plane substantially parallel to the first surface. 3 . The photodiode of claim 2 , wherein a sixth region of the plurality of semiconductor regions is formed laterally around and at a distance from the fourth region from the first surface of the photodiode, the sixth region being heavily doped with the second conductivity type.

4. The photodiode according to claim 3, wherein a third region among the plurality of semiconductor regions is formed between the first surface and the first region of the photodiode, the third region is an epitaxial region of the first conductivity type, and the fourth region, the fifth region and the sixth region are formed by doping. 5 . The photodiode of claim 2 , wherein a guard ring region of the plurality of semiconductor regions is formed around the fourth region, the guard ring region having the first conductivity type and being more lightly doped than the fourth region. 6 . The photodiode of claim 2 , wherein the semiconductor region is formed in a well defined by a deep trench isolation extending in a direction perpendicular to the first surface of the photodiode. 7 . The photodiode of claim 6 , wherein the second region comprises a lateral portion between the first region and the deep trench isolation. 8 . The photodiode of claim 2 , wherein the second region includes a buried portion between the first region and a second surface of the photodiode opposite to the first surface.

9. The photodiode of claim 2, wherein the first region is doped in a substantially constant manner in a direction perpendicular to the first surface of the photodiode.

10. The photodiode of claim 2, wherein the first region is gradually doped in a direction perpendicular to the first surface. 11 . The photodiode of claim 2 , wherein the first region includes a first portion and a second portion, the second portion being narrower than the first portion in a plane parallel to the first surface and being located between the first portion and the main PN junction. 12 . The photodiode of claim 2 , wherein the first region surrounds the main PN junction and comprises a first portion located below the main PN junction and a second portion extending to the first surface of the photodiode.

13. The photodiode of claim 1, wherein the first region is located inside the second region.

14. The photodiode of claim 1, wherein each dimension of the photodiode in a plane parallel to the first surface of the photodiode is less than 6 μm, and / or the height of the photodiode is in the range from 3 μm to 15 μm.

15. The photodiode of claim 2, wherein: The fourth region is more heavily doped with the first conductivity type than the first region.

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