Dome lens and guard ring for single photon avalanche diode photodetectors and related methods

Abstract

The present disclosure relates to a dome lens and guard ring for single photon avalanche diode photodetectors and related methods. A structure includes at least one single photon avalanche diode (SPAD), at least one dome lens positioned over each SPAD, and a metal guard ring surrounding each SPAD. A front-side illuminated SPAD photodetector and a method of forming the structure are also provided. The dome lens, together with the metal guard ring, improves SPAD efficiency in terms of photo-detection probability (PDP) and light absorption with minimal area increase.

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to photodetector structures. More specifically, various embodiments of this disclosure provide structures and related methods for dome-shaped lenses and protective rings for single-photon avalanche diode (SPAD) photodetectors. Background Technology

[0002] Photodetectors convert light power into voltage or current. Photodetectors can be formed as avalanche photodiodes (APDs). Due to their internal gain, avalanche photodiodes are much more sensitive to incident light compared to other types of photodetectors, such as PIN photodiodes. Furthermore, APDs typically offer a significantly increased receiver signal-to-noise ratio (SNR). A single-photon avalanche diode photodetector (SPAD) is a type of APD that is electrically biased significantly above its reverse bias breakdown voltage, which increases the sensitivity to light to the single-photon level. In microelectronic circuits, the sensitivity of a SPAD, i.e., the probability of photodetection (PDP), can be limited by the ability to efficiently direct light (photons) to the effective area of ​​the SPAD using, for example, a single planar microlens arrangement. Summary of the Invention

[0003] All the aspects, examples, and features mentioned below can be combined in any technically possible way.

[0004] One aspect of this disclosure provides a structure comprising: at least one single-photon avalanche diode (SPAD) located in a substrate; at least one dome-shaped lens located above each SPAD; and a metal protective ring surrounding each SPAD.

[0005] One aspect of this disclosure provides a front-illuminated single-photon avalanche diode (FSI SPAD) photodetector, comprising: at least one FSI SPAD located in a substrate; at least one dome-shaped lens located above each FSI SPAD; and a metal protective ring surrounding each FSI SPAD.

[0006] One aspect of this disclosure provides a method comprising: forming at least one single-photon avalanche diode (SPAD) in a substrate; forming a metal protective ring around each SPAD; and forming at least one dome-shaped lens over each SPAD.

[0007] Two or more aspects described herein, including those described in the summary section, can be combined to form implementations not specifically described herein. Details of one or more implementations are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the specification, drawings, and claims. Attached Figure Description

[0008] Embodiments of this disclosure will be described in detail with reference to the following accompanying drawings, wherein like reference numerals denote like elements, and wherein:

[0009] Figure 1 A cross-sectional view of a structure including a single-photon avalanche diode (SPAD) with a dome-shaped lens and a metal guard ring according to an embodiment of the present disclosure is shown.

[0010] Figure 2 A cross-sectional view of a SPAD structure including a dome-shaped lens and a metal protective ring according to other embodiments of the present disclosure is shown;

[0011] Figure 3A -B illustrates various embodiments of the present disclosure. Figure 1 A schematic top view of the structure, intercepted by the illustrative view line AA;

[0012] Figure 4 A partial top view of the arrangement of dome-shaped lenses according to an embodiment of the present disclosure is shown;

[0013] Figure 5 A partial top view of the arrangement of dome-shaped lenses according to other embodiments of the present disclosure is shown;

[0014] Figure 6 A partial top view of the arrangement of dome-shaped lenses according to another embodiment of the present disclosure is shown;

[0015] Figure 7 A cross-sectional view of a metal protective ring according to an embodiment of the present disclosure is shown;

[0016] Figure 8 A cross-sectional view of a metal protective ring according to other embodiments of the present disclosure is shown;

[0017] Figure 9 Other embodiments according to this disclosure are shown along Figure 1 A schematic top view of the structure, intercepted by the illustrative view line AA;

[0018] Figure 10 Further embodiments according to this disclosure are shown along Figure 1 A schematic top view of the structure, intercepted by the illustrative view line AA;

[0019] Figure 11 The following is illustrated according to an embodiment of the present disclosure. Figure 1 A schematic top view of the structure, intercepted by the illustrative view line BB;

[0020] Figure 12A cross-sectional view of a SPAD structure including a dome-shaped lens and a metal protective ring according to another embodiment of the present disclosure is shown.

[0021] Figure 13 A cross-sectional view of the initial process for forming a SPAD according to an embodiment of the present disclosure is shown;

[0022] Figure 14 A cross-sectional view of a metal protective ring formed according to an embodiment of the present disclosure is shown;

[0023] Figure 15 and 16 A cross-sectional view of a mask for forming a dome-shaped lens, according to an embodiment of the present disclosure, is shown; and

[0024] Figure 17 A cross-sectional view of a dome-shaped lens according to an embodiment of the present disclosure is shown.

[0025] Note that the accompanying drawings of this disclosure are not necessarily drawn to scale. The drawings are intended to depict only typical aspects of this disclosure and should not be considered as limiting the scope of this disclosure. In the drawings, the same numbers denote the same elements between the figures. Detailed Implementation

[0026] In the following description, reference is made to the accompanying drawings, which form a part thereof, and specific exemplary embodiments in which the present teachings may be practiced are illustrated by way of illustration. These embodiments have been described in sufficient detail to enable those skilled in the art to practice the present teachings, and it should be understood that other embodiments may be used and modifications may be made without departing from the scope of the present teachings. Therefore, the following description is merely illustrative.

[0027] It will be understood that when an element, such as a layer, region, or substrate, is described as being "on" or "above" another element, it can be directly on the other element, or there may be intermediate elements. In contrast, when an element is described as being "directly on" or "directly above" another element, there are no intermediate elements. It should also be understood that when an element is described as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. In contrast, when an element is described as being "directly connected" or "directly coupled" to another element, there are no intermediate elements.

[0028] References to "one embodiment" or "an embodiment" and other variations thereof in the specification mean that a particular feature, structure, characteristic, etc., described in connection with that embodiment is included in at least one embodiment of the present disclosure. Therefore, the phrase "in one embodiment" or "in one embodiment," and any other variations appearing throughout the specification, do not necessarily refer to the same embodiment. It should be understood that the use of " / ", "and / or", and "at least one" in cases such as "A / B", "A and / or B", and "at least one of A and B" is intended to include selecting only the first listed option (A), or only the second listed option (B), or both options (A and B). As other examples, in the cases of “A, B, and / or C” and “at least one of A, B, and C”, these phrases are intended to encompass selecting only the first listed option (A), or only the second listed option (B), or only the third listed option (C), or only the first and second listed options (A and B), or only the first and third listed options (A and C), or only the second and third listed options (B and C), or all three options (A, B, and C). As will be apparent to those skilled in the art, this can be extended to many of the listed items.

[0029] Embodiments of this disclosure include a structure comprising at least one single-photon avalanche diode (SPAD), at least one dome-shaped lens positioned above each SPAD, and a metal protective ring surrounding each SPAD. A front-illuminated SPAD photodetector and a method of forming the structure are also provided. The dome-shaped lens, together with the metal protective ring, increases SPAD efficiency in terms of probability of photodetection (PDP) and light absorption with minimal area size.

[0030] Figure 1 A cross-sectional view of structure 100 according to an embodiment of the present disclosure is shown. Structure 100 according to the present disclosure operates using a diode, specifically those diodes capable of functioning as photodiodes or photodetectors. That is, a diode that converts light into electrical energy. Typically, a diode is a two-terminal element whose behavior differs from that of the conductive or insulating material between two electrical contacts. Specifically, a diode provides high conductivity from one contact to the other in one direction (i.e., the "forward" direction), but provides little or no conductivity in the opposite direction (i.e., the "reverse" direction). In the case of a PN junction, the orientation of the diode in the forward and reverse directions can depend on the type and magnitude of the voltage applied to the material components of one or both terminals, which affects the size of the barrier. In the case of a junction between two semiconductor materials, the barrier will form along the interface between the two semiconductor materials.

[0031] An avalanche junction, also known as an avalanche diode or avalanche photodiode, is a special type of diode structure used for bidirectional control of current flow through an integrated circuit (IC) structure. An avalanche photodiode (APD) can function as a photodetector. The avalanche junction differs from a PN diode in that it has a much wider depletion region—a region of lighter-doped semiconductor material between the diode's oppositely doped terminals. Applying a voltage across the depletion region can accelerate minority charge carriers in the insulating material to the point of ionization within the crystal lattice. This accelerated minority charge carriers then generate more charge carriers and further ionization. This effect is known as "avalanche breakdown."

[0032] continue Figure 1 Structure 100 may include at least one single-photon avalanche diode (SPAD) 102 (see dashed box) located in substrate 104. As described, SPAD 102 is an avalanche photodiode (APD) that is electrically biased significantly above its reverse bias breakdown voltage, which improves sensitivity to light and allows the photodiode to operate with lower damage or noise than other APDs. SPADs can detect even single photons with high sensitivity.

[0033] Substrate 104 comprises, for example, one or more semiconductor materials. Substrate 104 may be formed at least partially of any currently known or later developed semiconductor material, which may include, but is not limited to: silicon, germanium, silicon-germanium, and materials substantially composed of Al. X1 Ga X2 In X3 As Y1 P Y2 N Y3 Sb Y4 The material is composed of one or more III-V compound semiconductors of the defined components, wherein X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions that are all greater than or equal to zero, and X1 + X2 + X3 + Y1 + Y2 + Y3 + Y4 = 1 (1 is the total relative molar amount). The substrate 104 may take the form of a bulk substrate, a semiconductor-on-insulator (SOI) substrate, and / or various other types of substrates. In the case of an SOI substrate, the semiconductor top layer 106 of the SOI substrate may be located on a buried insulating layer 108 (shown in dashed lines) composed of any currently known or later developed insulating material (e.g., any one or more of the various oxides, nitrides, and / or other insulating materials discussed herein).

[0034] Some portions of substrate 104 may include dopants that provide doping wells therein. In semiconductor fabrication, a "well" refers to a portion of the substrate containing a specific type and concentration of impurities (dopants) to control its conductivity. As an example, the semiconductor layer 106 of substrate 104 may have a low amount of P-type doping. When referring to dopants, P-type dopants are elements introduced into semiconductor materials to generate free holes by "accepting" electrons from semiconductor atoms and thus "releasing" holes. The acceptor atom must have one less valence electron than the matrix semiconductor. P-type dopants can include, but are not limited to, boron (B), indium (In), and gallium (Ga). Boron (B) is the most common acceptor in integrated circuit technology. In contrast, N-type dopants are introduced into semiconductor materials to generate free electrons (by "donating" electrons to the semiconductor). N-type dopants can include, but are not limited to, phosphorus (P), arsenic (Ar), antimony (Sb), bismuth (Bi), and lithium (L). Phosphorus and arsenic are the most common examples of n-type doping in integrated circuit technology. As is well known in the art, doping type can be represented as "p" or "n" followed by a "plus" or "minus" sign, where a minus sign indicates a concentration lower than the baseline concentration, and a plus sign (or two plus signs) indicates a concentration higher than the baseline concentration.

[0035] SPAD 120 may include a plurality of wells, including an n-well 110, a p-well 112 above the n-well 110, a p+ well 114 within the p-well 112, and a p++ well 116 within the p+ well 114. The p++ well 116 provides the anode region 130 of SPAD 102. SPAD 102 may also include an n-well 118 coupling the n-well 110 to the n+ well 120. The n+ well 120 provides the cathode region 132 of SPAD 102. Each well within substrate 104 may be formed by any doping technique now known or developed thereafter, such as by ion implantation or in-situ doping. Wells 112, 114, 116, and 120 may share an upper surface with the upper surface of substrate 104. n-wells 110 and 118 may have a doping type opposite to that of substrate 104; for example, if substrate 104 is p-type doped, they may be lightly N-type doped (referred to as "n-doped"). n+ well 120 has a higher n-type doping concentration than n-wells 110 and 118. p+ well 114 has a higher p-type doping concentration than substrate 104, and p++ well 116 has a higher p-type doping concentration than p+ well 114 and substrate 104. Therefore, wells 110, 112, 114, 116, 118, and 120 can be distinguished from substrate 104 at least in part based on doping concentration, dopant type, and / or material, etc.

[0036] As described, SPAD 102 may include an anode region 130 and a cathode region 132. A distance separates the anode region 130 from the cathode region 132 and ensures that an avalanche junction will form within the depletion region defined by the n-well 110. As described herein, the anode region 130 may be a region of semiconductor material within the n-well 110 having the opposite polarity to the n-well 110; for example, it may be a more heavily doped p-type region (“p++ doped”) to form a strong PN junction between the anode region 130 and the n-well 110 below it. The cathode region 132 may have the same doping type as the n-well 110, but with a higher doping concentration. For example, if the n-well 110 has “n-” doping, the cathode region 132 may have “n+” doping. Light L incident on the anode region 130 can create a current path within the structure 100.

[0037] The SPAD 102 in structure 100 operates on the same principle as other diode junctions in an integrated circuit. That is, the anode region 130 and the cathode region 132 provide two oppositely doped regions that allow current to flow easily from the anode region 130 to the cathode region 132, but prevent current from flowing in the opposite direction. The SPAD is specifically configured to operate at higher voltages than other types of diodes. In a conventional diode, voltage and structural breakdown occurs when the voltage applied to it exceeds the diode's inherent peak voltage. However, by forming an avalanche junction in the SPAD, the SPAD can continue to operate above its breakdown voltage. The n-well 110 serves as a wider depletion region between the anode region 130 and the cathode region 132, allowing these portions of structure 100 to exhibit "avalanche breakdown" above its breakdown voltage. Photons incident on the anode region 130 will thus be given sufficient energy to induce a current from the anode region 130 to the cathode region 132, enabling these regions to detect the incident light.

[0038] Although a specific arrangement of the doped traps is shown, SPAD 102 can include any SPAD photodetector now known or developed later. For example, in other embodiments, cathode region 132 may be located at the center of anode region 130. In a particular embodiment, SPAD 102 may constitute a front-side-illuminated SPAD (FSI SPAD) photodetector. “Front-side-illuminated” indicates that the light L (e.g., visible light) sensed by the FSI SPAD enters through the top layer of the structure (e.g., chip). Light L in Figure 1The structure 100 is indicated by a dashed arrow and enters from the top of the page. Although light L is shown as traveling through and illuminating the upper (i.e., “front”) side of structure 100, in some cases, light (not shown) traveling from the bottom (i.e., “back”) side of structure 100 can also generate a current. At least the anode region 130, n-well 110, and cathode region 132 collectively define a SPAD 102 within structure 100. Hereinafter, SPAD 102 will uniformly refer to a SPAD or more specifically to an FSI SPAD photodetector. Structure 100 may include any number of SPADs 102, for example, arranged side-by-side or in an array, to detect light L.

[0039] Structure 100 may further include at least one dome-shaped lens 140 located above each SPAD 102. Each dome-shaped lens 140, together with the metal protective ring 150 described herein, is used to guide light L in a more concentrated manner toward the anode region 130 to improve light absorption. Figure 1 In the illustrated embodiment, multiple dome-shaped lenses 140 are used above each SPAD 102. Figure 2 In another example shown in the cross-sectional view, a single dome-shaped lens 140 can be used. Any number of dome-shaped lenses 140 can be used.

[0040] The dome-shaped lens 140 can be located at any back-end process (BEOL) interconnect layer 142 above the SPAD 102. The dome-shaped lens 140 may comprise, for example, oxide or nitride. Figure 1 In the middle, the dome-shaped lens 140 is located above the last BEOL interconnect layer 144, and in Figure 2 In this embodiment, a dome-shaped lens 140 is situated above SPAD 102, specifically above the third metal / via layer 146 of the anode region 130. Although shown as situated within both the metal and via layers, the dome-shaped lens 140 may be situated within one or the other layer. As used herein, "dome-shaped" indicates that the lens 140 has a rounded upper surface. The radius of the rounded upper surface may vary depending on, for example, the patterning parameters used to form the lens 140, such as etching parameters; the number of lenses 140; and the size of the space used by the lens 140.

[0041] Figure 3A -B illustrates various embodiments along Figure 1 The illustrative view line AA is a schematic top view of structure 100. Structure 100 includes a dome-shaped lens 140, a SPAD 102, and a metal protective ring 150. As shown, in a particular embodiment, structure 100 may include a first SPAD 102A adjacent to a second SPAD 102B. In a particular embodiment, as... Figure 3AAs shown, when using more than one lens 140, they can, for example, be arranged as an array of aligned columns and rows. These columns and rows are shown vertically and horizontally on the page, but it should be understood that they are located in a plane in the final product. Any number of columns and rows can be used. In other embodiments, such as Figure 3B As shown, when using a single lens 140, it can be centered above SPAD 102 and / or within the metal protective ring 150.

[0042] Such as the dome-shaped lens 140 on the SPAD 102 Figure 4 and Figure 5 As shown in the partial top view, lens 140 can alternatively be arranged in staggered columns and rows. Figure 4 ), or arranged into shapes or patterns, such as, but not limited to, circles, concentric circles (as shown in the figure), ovals, crosses, etc. Figure 5 Lenses 140 can be spaced apart from each other, as shown in Figure 3-5, or they can be adjacent to each other, as shown in Figure 3-5. Figure 6 A partial top view is shown. It will be appreciated that the lens 140 can be arranged in a variety of alternative ways to focus light L onto the SPAD 102, specifically onto its anode region 130, depending on, but not limited to, the size of the SPAD 102, the configuration and / or location of the anode region 130 therein, and the area space within the metal protective ring 150.

[0043] like Figure 1 As shown in Figure -3, structure 100 may further include a metal protective ring 150 surrounding each SPAD 102. In some embodiments, as per [reference to...] Figure 3A As described in -B, at least one SPAD 102 may include a first SPAD 102A adjacent to the second SPAD 102B, wherein each of the first and second SPADs 102A, 102B includes at least one dome-shaped lens 140 located thereon. That is, Figure 3A -B shows that structure 100 includes a first SPAD 102A adjacent to the second SPAD 102B, and each SPAD 102A, 102B includes a dome-shaped lens 140 located thereon. Although SPADs 102A, 102B are shown to have the same arrangement of dome-shaped lenses 140, they may be arranged in different ways for each SPAD 102. Figure 3A It shows that multiple lenses 140 can be used, while Figure 3B It shows that a single dome-shaped lens 140 can be used, with Figure 2 Same as in China.

[0044] like Figure 3A As shown in -B, a metal protective ring 150 surrounds each SPAD 102A, 102B. (See diagram below.) Figure 1-2 As shown, the metal guard ring 150 includes a plurality of vertically stacked wirings 152 and vias 154 located in any number of BEOL interconnect layers 142. The metal guard ring 150 can take various forms. Figure 7 and Figure 8 Cross-sectional views of two different arrangements of the metal protective ring 150 are shown. Figure 1 , 2 In 7, the metal protective ring 150 includes a single wall of vertically stacked metal wiring 152 and vias 154. In this arrangement, for example, the maximum width of its metal wiring 152 can be about 0.2 micrometers. Figure 8 Another option is shown, in which the metal guard ring 150 includes rows 156 of a pair of vertically stacked and staggered wirings 152 and vias 154 forming, for example, an inverted V-shaped cross section. In this arrangement, for example, the maximum width W2 of the furthest separated metal wirings 152 can be between about 2 and 8 micrometers. Other arrangements of the metal guard ring 150 may also be used.

[0045] The metal protective ring 150 can have various lateral arrangements around the SPAD 102. Figure 3A In SPAD 102A-B, the metal protective ring 150A surrounding the first SPAD 102A and the metal protective ring 150B surrounding the adjacent second SPAD 102B share their wall portion 160. That is, the metal protective rings 150A and 150B share the wall portion 160. Figure 9 The diagram illustrates an edge including a dome-shaped lens 140, SPAD 102A-B, and a metal protective ring 150A-B according to other embodiments. Figure 1 The illustrative view line AA in the diagram shows a schematic top view of structure 100. Figure 9 In this configuration, structure 100 includes a first SPAD 102A adjacent to the second SPAD 102B. However, in this case, a metal protective ring 150A surrounding the first SPAD 102A is adjacent to a metal protective ring 150B surrounding the second SPAD 102B, for example, along its adjacent portions 162, 164. Figure 10 The image shows an edge including a dome-shaped lens 140, a SPAD 102, and metal protective rings 150A-B according to another embodiment. Figure 1 The illustrative view line AA in the diagram shows a schematic top view of structure 100. Figure 10 In this configuration, structure 100 includes a first SPAD 102A adjacent to the second SPAD 102B. Here, a metal guard ring 150A surrounding the first SPAD 102A is spaced apart from the metal guard ring 150B surrounding the second SPAD 102B by a dielectric 166 (i.e., the dielectric of the BEOL interconnect layer 142). Other arrangements of adjacent or interconnected metal guard rings 150 are also possible.

[0046] Figure 11 It is shown that, according to other embodiments, along Figure 1 The illustrative view line BB in the figure shows a schematic top view of structure 100, in which the dome-shaped lens 140 is not shown, but its SPAD 102 and metal protective ring 150 are shown. Figure 1 , 2 As shown in Figure 11, a metal protective ring 150 is located within a plurality of interconnect layers 142 extending above SPAD 102. Structure 100 may also include an electrical connection 170 to SPAD 102. Figure 11 As shown, electrical connection 170 extends through an opening 172 in a metal guard ring 150 into SPAD 102 in at least one of a plurality of interconnect layers 142 adjacent to SPAD 102 (e.g., first and second metal layers M1 and M2). Electrical connection 170 may include any number of wirings and / or vias extending through the opening 172. In the example shown, electrical connection 170 is located in the first and second metal layers M1 and M2; however, it may be located in only the first metal layer M1.

[0047] exist Figure 1 and Figure 2 In this embodiment, a metal guard ring 150 is shown as electrically connected to the cathode region 132. In this case, electrical communication with the cathode region 132 can be made through the metal guard ring 150, i.e., through one or more of its metal and / or via layers. In other embodiments, such as... Figure 12 As shown in the cross-sectional view, the metal guard ring 150 may not be connected to the cathode region 132. In this case, one or more additional electrical connections 180, similar to electrical connection 170, may be formed to the cathode region 132. The electrical connections 180 can be formed through the opening 172 ( Figure 11 ) Leave the metal protective ring 150.

[0048] Figure 13-17 A cross-sectional view of a method according to an embodiment of the present disclosure is shown. The method can form structure 100. Figure 13 At least one SPAD 102 is shown formed in a substrate 104. As described herein, the SPAD 102 can be formed using any doping technique now known or developed thereafter, such as, but not limited to, ion implantation and in-situ doping. Any various trench isolation 182 configurations, i.e., dielectric-filled trenches, can be formed in the substrate 104 to isolate portions of the SPAD 102.

[0049] Figure 14A cross-sectional view is shown of a metal guard ring 150 formed around each SPAD 102. The metal guard ring 150 can be formed using any BEOL interconnect technology now known or developed later. More specifically, the metal guard ring 150 can be formed within a plurality of BEOL interconnect layers 142 extending above the SPAD 102, and as... Figure 12 As shown, the electrical interconnect 170 extends through an opening 172 in a metal guard ring 150 into the SPAD 102 in at least one of a plurality of interconnect layers adjacent to the SPAD 102 (e.g., M1 and / or M2). The metal wiring and vias of the metal guard ring 150 can be formed, for example, by depositing a dielectric layer (e.g., any interlayer dielectric (ILD) material, such as oxides and / or nitrides), patterning a mask (not shown), etching the dielectric layer using the mask to form openings therein, depositing conductors, planarizing to remove excess conductors, and repeating the process until a metal guard ring 150 of the desired height is produced. The conductors used can include any suitable conductor material for metal wiring and / or vias at a given BEOL interconnect layer 142, such as, but not limited to, copper, aluminum, tungsten, etc., within a refractory metal liner. The metal wiring and vias can be formed together, i.e., using a dual damascene process, or they can be formed separately, i.e., using a single damascene process. The metal guard ring 150 may be formed in the desired number of BEOL interconnect layers 142, but typically extends through most (if not all) of the BEOL interconnect layers 142 to ensure that light L is concentrated toward the SPAD 102, as described herein.

[0050] Figure 1 , 2 Figures 12 and 15-17 show cross-sectional views of at least one dome-shaped lens 140 formed over each SPAD 102. The dome-shaped lens 140 can be formed at any given BEOL interconnect layer 142. Figure 15 As shown, forming the dome-shaped lens 140 may include forming a dielectric layer 190 on each SPAD 102 and performing a grayscale lithography process on the dielectric layer 190. The dielectric layer 190 may include, for example, an oxide or a nitride. The grayscale lithography process includes generating a 2.5-dimensional (2.5D) surface profile using grayscale values ​​through a single exposure. Figure 15 As shown, the process includes using optical grayscale masks 192 with different grayscale pixel intensities and different spacings to modulate the laser intensity pixel-by-pixel on top of a photoresist 194 on a dielectric layer 190. Figure 16 As shown, the process includes stripping the exposed photoresist 194 by developing the photoresist 194. For example... Figure 17As shown, the remaining three-dimensional contour on the surface of the photoresist 194 can then be transferred to the dielectric layer 190 to produce a dome lens 140, for example, by etching the dielectric layer 190 using a suitable dry etching chemical action such as, but not limited to, reactive ion etching to form the dome lens 140. The upper surface can then be rounded using wet etching to complete the dome lens 140, as shown. Figure 1-2 As shown in Figure 12. (Note that the shadow of the dome lens 140 differs from that of the ILD of the BEOL interconnect layer 142, which is positioned for comparison in the illustration; it can be appreciated that the materials can be the same, such as oxides or nitrides). It will be appreciated that, in the case where the metal guard ring 150 extends in the same layer as the dome lens 140, as... Figure 2 As shown, one or more additional layers of a metal guard ring 150 can then be formed in the dielectric layer 190 and possibly above the additional BEOL interconnect layer 142, with the dome-shaped lens 140 resting horizontally.

[0051] The embodiments disclosed herein offer various technical and commercial advantages, examples of which are discussed herein. The dome-shaped lens, together with a metal protective ring, increases SPAD efficiency in terms of probability of light detection (PDP) and light absorption with a minimal area size. More specifically, the dome-shaped lens and metal protective ring confine more light, resulting in higher intensity and more dispersed light reaching the SPAD.

[0052] The structures and methods described above are used for the manufacture of integrated circuit chips. The resulting integrated circuit chips can be distributed by the manufacturer in the form of raw wafers (i.e., as a single wafer with multiple unpackaged chips), as bare dies, or in packages. In the latter case, the chips are mounted in single-chip packages (e.g., plastic carriers with leads attached to a motherboard or other higher-level carriers) or multi-chip packages (e.g., ceramic carriers with surface interconnects and / or buried interconnects). In any case, the chips are then integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of (a) an intermediate product (e.g., a motherboard) or (b) a final product. The final product can be any product that includes integrated circuit chips, ranging from toys and other low-end applications to advanced computer products with displays, keyboards or other input devices, and central processing units.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that, when used in this specification, the terms “comprising” and / or “including” specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof. “Optional” or “optionally” indicates that an event or condition subsequently described may or may not occur, and the description includes cases where the event occurs and cases where the event does not occur.

[0054] The approximate language used throughout the specification and claims can be used to modify any quantitative expression that allows for variation without causing a change in its associated essential function. Therefore, values ​​modified by one or more terms such as “about,” “approximate,” and “substantially” are not limited to the specified exact values. In at least some cases, approximate language may correspond to the precision of the instrument used to measure the value. In this document and throughout the specification and claims, range limitations can be combined and / or interchanged, such ranges being identified and including all subranges contained therein, unless the context or language indicates otherwise. The term “approximate” applied to a specific value within a range applies to both values ​​and, unless otherwise dependent on the precision of the instrument used to measure the value, may indicate + / - 10% of said value.

[0055] All the means or steps plus functional elements in the following claims are intended to include any structure, material, action, and equivalent that performs the function in combination with other claimed elements of the specific claim. The present disclosure has been described for purposes of illustration and description, but such description is not intended to be exhaustive or to limit the disclosure to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles and practical application of the disclosure and to enable others skilled in the art to understand the various embodiments of the disclosure with various modifications suitable for the particular intended use.

Claims

1. A structure comprising: At least one single-photon avalanche diode (SPAD) located in a substrate; At least one dome-shaped lens located above each SPAD; as well as A metal protective ring surrounds each SPAD.

2. The structure according to claim 1, wherein, The SPAD is a front-lit SPAD.

3. The structure according to claim 1, wherein, The at least one dome-shaped lens includes a plurality of dome-shaped lenses located on each SPAD.

4. The structure according to claim 1, wherein, The metal protective ring includes multiple vertically stacked wiring and vias.

5. The structure according to claim 1, wherein, The metal protective ring includes a pair of vertically stacked and interlaced rows of wiring and vias.

6. The structure according to claim 1, wherein, The metal protective ring is located within a plurality of interconnect layers extending above the SPAD, and the structure also includes an electrical connection that extends through an opening in the metal protective ring into the SPAD in at least one of the plurality of interconnect layers adjacent to the SPAD.

7. The structure according to claim 1, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD is adjacent to the metal protective ring surrounding the second SPAD.

8. The structure according to claim 1, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD shares a portion of its portion with the metal protective ring surrounding the second SPAD.

9. The structure according to claim 1, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD is spaced apart from the metal protective ring surrounding the second SPAD by a dielectric.

10. A front-illuminated single-photon avalanche diode (FSI) SPAD photodetector, comprising: At least one FSI SPAD located in the substrate; At least one dome-shaped lens located above each FSI SPAD; as well as A metal protective ring surrounds each FSI SPAD.

11. The FSI SPAD photodetector according to claim 10, wherein, The at least one dome-shaped lens includes a plurality of dome-shaped lenses located on each SPAD.

12. The FSI SPAD photodetector according to claim 10, wherein, The metal protective ring includes multiple vertically stacked wiring and vias.

13. The FSI SPAD photodetector according to claim 10, wherein, The metal protective ring includes a pair of vertically stacked and interlaced rows of wiring and vias.

14. The FSI SPAD photodetector according to claim 10, wherein, The metal protective ring is located within a plurality of interconnect layers extending above the SPAD, and the FSI SPAD photodetector also includes an electrical connection that extends through an opening in the metal protective ring into the SPAD in at least one of the plurality of interconnect layers adjacent to the SPAD.

15. The FSI SPAD photodetector according to claim 10, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD is adjacent to the metal protective ring surrounding the second SPAD.

16. The FSI SPAD photodetector according to claim 10, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD shares a portion of its portion with the metal protective ring surrounding the second SPAD.

17. The FSI SPAD photodetector according to claim 10, wherein, The at least one SPAD includes a first SPAD adjacent to the second SPAD, wherein each of the first SPAD and the second SPAD includes the at least one dome-shaped lens located thereon, and wherein the metal protective ring surrounding the first SPAD is spaced apart from the metal protective ring surrounding the second SPAD by a dielectric.

18. A method comprising: At least one single-photon avalanche diode (SPAD) is formed in the substrate; A metal protective ring is formed around each SPAD; as well as At least one dome-shaped lens is formed on each SPAD.

19. The method according to claim 18, wherein, Forming the at least one dome-shaped lens includes: forming a dielectric layer on each SPAD, performing a grayscale photolithography process on the dielectric layer, and etching the dielectric layer to form the at least one dome-shaped lens.

20. The method according to claim 18, wherein, Forming the metal guard ring includes forming the metal guard ring within a plurality of interconnect layers extending above the SPAD, wherein an electrical connection is made in at least one of the plurality of interconnect layers adjacent to the SPAD, extending through an opening in the metal guard ring to the SPAD.

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