Pixel unit and preparation method thereof, optical sensor and optical detector

Abstract

The invention provides a pixel unit and a preparation method thereof, an optical sensor and an optical detector, and relates to the technical field of semiconductors. The pixel unit comprises a substrate; the isolation structure and the photoelectric conversion region are located on the substrate and are in contact with the substrate; the isolation structure surrounds the periphery of the photoelectric conversion region and is used for limiting carriers generated in the photoelectric conversion region in the pixel unit; the electrode contact structure is located in the isolation range of the isolation structure, makes contact with the side, away from the substrate, of the photoelectric conversion area and is used for collecting carriers generated by the photoelectric conversion area and exporting electric signals. The embodiment of the invention is used for providing a technical scheme capable of reducing the situation that incident light penetrates through the boundary of the current pixel unit and escapes to the outside of the pixel or the photosensitive area of the adjacent pixel unit.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a pixel unit and its fabrication method, an optical sensor, and an optical detector. Background Technology

[0002] A single-photon avalanche photodiode (SPAD) is a high-sensitivity photodetector with internal gain. Its core is based on the photoelectric effect of a PN junction and the avalanche multiplication principle, and it is widely used in low-light detection scenarios.

[0003] However, in the pixelated array design of some SPADs, if the isolation capability of the isolation structure is insufficient (such as insufficient depth), the incident light will penetrate the boundary of the current pixel unit and escape to the photosensitive area of ​​the outside of the pixel or the neighboring pixel unit. The neighboring pixel may receive the escaped light, causing optical crosstalk, which will eventually lead to a mismatch between its output electrical signal and the actual light intensity it detects, affecting the detection accuracy. Summary of the Invention

[0004] This application provides a pixel unit and its fabrication method, an optical sensor, and an optical detector, which provide a technical solution that can reduce the penetration of incident light through the boundary of the current pixel unit and allow it to escape to the outside of the pixel or the photosensitive area of ​​a neighboring pixel unit.

[0005] In a first aspect, embodiments of this application provide a pixel unit, the pixel unit comprising: a substrate; An isolation structure and a photoelectric conversion region are located on and in contact with the substrate; the isolation structure surrounds the outer periphery of the photoelectric conversion region and is used to confine the carriers generated by the photoelectric conversion region within the pixel unit; The electrode contact structure is located within the isolation range of the isolation structure and is in contact with the side of the photoelectric conversion region away from the substrate, for collecting the charge carriers generated by the photoelectric conversion region and exporting electrical signals.

[0006] In one optional implementation, the photoelectric conversion region includes: A first conductivity type absorption region is located on the substrate; the first conductivity type absorption region is used to absorb incident light and generate photogenerated carriers; A second conductivity type drift region and a second conductivity type well region; along the lateral direction perpendicular to the substrate, the second conductivity type drift region and the second conductivity type well region are both located on the side of the first conductivity type absorption region away from the substrate and are in contact with the first conductivity type absorption region; along the lateral direction parallel to the substrate, the second conductivity type well region is located on both sides of the second conductivity type drift region, and the first conductivity type absorption region surrounds the second conductivity type well region.

[0007] In one alternative embodiment, the electrode contact structure is embedded within the first conductivity type absorption region and the second conductivity type drift region.

[0008] In one optional embodiment, the electrode contact structure includes a first conductivity type electrode contact area and a second conductivity type electrode contact area. Along the side of the first conductivity type absorption region away from the substrate, the first conductivity type electrode contact region is embedded in the first conductivity type absorption region, and the second conductivity type electrode contact region is embedded in the second conductivity type drift region; Along a transverse direction parallel to the substrate, the first conductivity type electrode contact region is located on the side of the second conductivity type well region away from the second conductivity type drift region.

[0009] In one optional embodiment, the doping concentration of the first conductivity type electrode contact region is greater than the doping concentration of the first conductivity type absorption region. And / or, the doping concentration of the second conductivity type electrode contact region, the second conductivity type drift region, and the second conductivity type electrode contact region decreases sequentially.

[0010] In one alternative embodiment, the isolation structure includes an isolation layer and a metal layer; The insulating layer encloses the metal layer in a transverse direction parallel to the substrate.

[0011] In one alternative implementation, the first conductivity type is N-type or P-type, and the second conductivity type is the opposite of the first conductivity type.

[0012] Secondly, embodiments of this application also provide a method for fabricating a pixel unit, the method comprising: Provide substrate; An isolation structure and a photoelectric conversion region are formed on the substrate in contact with the substrate; wherein the isolation structure surrounds the outer periphery of the photoelectric conversion region and is used to confine the carriers generated by the photoelectric conversion region within the pixel unit; An electrode contact structure is formed on one side of the photoelectric conversion region; the electrode contact structure is located within the isolation range of the isolation structure and is in contact with the side of the photoelectric conversion region away from the substrate, for collecting the charge carriers generated by the photoelectric conversion region and exporting electrical signals.

[0013] In one alternative implementation, it includes: A first conductivity type absorption region precursor structure is formed on the substrate; An isolation structure is formed on the periphery of the first conductivity type absorption region precursor structure on the substrate; The first target region of the first conductivity type absorption region is subjected to a first ion doping treatment to form a second conductivity type drift region; A second ion doping treatment is performed on the second target region of the first conductivity type absorption region to form a second conductivity type well region and a first conductivity type absorption region; wherein, the second target region is located on both sides of the first target region and is in contact with the first target region; The first conductivity type absorption region, the second conductivity type drift region, and the second conductivity type well region constitute the photoelectric conversion region. In one optional embodiment, the dopant ions in both the first ion doping treatment and the second ion doping treatment are of the second conductivity type; The ion doping concentration of the first ion doping treatment is greater than the ion doping concentration of the second ion doping treatment.

[0014] In one alternative embodiment, forming an electrode contact structure on the side of the photoelectric conversion region facing away from the substrate includes: The third target region of the first conductivity type absorption region is subjected to third ion doping treatment to form the first conductivity type electrode contact region; The fourth target region of the second conductivity type drift region is subjected to fourth ion doping treatment to form the second conductivity type electrode contact region; Wherein, the first conductivity type electrode contact region and the second conductivity type electrode contact region constitute the electrode contact structure; the dopant ions in the third ion doping treatment are all of the first conductivity type, and the dopant ions in the fourth ion doping treatment are all of the second conductivity type; The ion doping concentration of the first conductivity type absorption region is less than the ion doping concentration of the first conductivity type electrode contact region.

[0015] In one alternative embodiment, an isolation structure is formed on the periphery of the first conductivity type absorption region precursor structure on the substrate, comprising: An isolation trench is formed on the outer periphery of the first conductivity type absorption region precursor structure on the substrate; An isolation layer and a metal layer are formed sequentially in the isolation groove.

[0016] Thirdly, embodiments of this application provide an optical sensor, including the pixel unit described in the first aspect, or the pixel unit prepared by the method described in the second aspect.

[0017] Fourthly, embodiments of this application provide an optical detector, including pixel units arranged in an array as described in the first aspect.

[0018] With the above technical solution adopted, embodiments of this application provide a pixel unit and its fabrication method, an optical sensor and an optical detector. The pixel unit includes: a substrate; an isolation structure and a photoelectric conversion region located on the substrate; the isolation structure is located on the outer periphery of the photoelectric conversion region and is used to confine the charge carriers generated by the photoelectric conversion region inside the pixel unit; and an electrode contact structure located on the side of the photoelectric conversion region away from the substrate and in contact with the photoelectric conversion region, for collecting the charge carriers generated by the photoelectric conversion region and exporting electrical signals.

[0019] It should be understood that the isolation structure in this embodiment is located on the outer periphery of the photoelectric conversion area, forming a lateral boundary blockage. This physically blocks the path of incident light through the pixel boundary, reduces the escape of light to the outside or neighboring pixels, ensures that each pixel unit only receives the light signal of its own detection area, improves the matching degree between the output electrical signal and the real light intensity, and improves the resolution and signal-to-noise ratio of imaging / detection.

[0020] Furthermore, the isolation structure also defines the transmission range of charge carriers, confining the charge carriers generated in the photoelectric conversion area within the pixel, avoiding electrical signal interference caused by the diffusion of charge carriers across pixels, and further ensuring the independence of the signal of a single pixel.

[0021] In other words, the isolation result is an isolation structure that extends to the substrate, thus forming full-boundary isolation, completely eliminating the escape gap of photogenerated carriers, and making the crosstalk suppression effect more significant.

[0022] Furthermore, in this embodiment, after charge carriers (electrons / holes) are generated in the photoelectric conversion region, they do not need to be laterally transported over long distances to the electrodes outside the isolation layer. Instead, they can drift directly to the electrode contact structure on the side away from the substrate, reducing recombination losses during transport and improving collection efficiency. The electrode contact structure directly contacts the photoelectric conversion region, avoiding the additional resistance introduced by the intermediate layer. Charge carriers can quickly transfer from the semiconductor region (photoelectric conversion region and electrode contact structure) to the metal electrode, accelerating the electrical signal response speed, which is particularly suitable for high-speed detection scenarios. It should be understood that with the improved charge carrier collection efficiency, even a small number of photogenerated charge carriers generated by weak light signals can be effectively captured, reducing signal attenuation and lowering the lower limit of detector sensitivity, making it more suitable for weak light detection requirements (such as weak light gain scenarios for APDs).

[0023] Finally, in the embodiments of this application, the isolation structure simultaneously serves multiple functions, defining the boundaries of the photoelectric conversion area and separating pixels. It eliminates the need to design separate deep trench isolations for the anode and cathode of the pixel unit, reducing complex process steps such as etching, filling, and planarization. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0025] Figure 1 This is a schematic diagram of the structure of a pixel unit provided in an embodiment of the present invention; Figure 2 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 1 ; Figure 3 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 2 ; Figure 4 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 3 ; Figure 5 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 4 ; Figure 6 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 5 ; Figure 7 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 6 ; Figure 8 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 7 ; Figure 9 A schematic diagram of the steps in a pixel unit fabrication method provided by an embodiment of the present invention. Figure 8 . Attached image description: 10-Substrate; 20-Photoelectric conversion region; 201-Precursor structure of absorption region of first conductivity type; 202-Drift region of second conductivity type; 203-Well region of second conductivity type; 204-Absorption region of first conductivity type; 30-Isolation structure; 301-Isolation trench; 302-Isolation layer; 303-Metal layer; 40-Electrode contact structure; 401-Electrode contact region of first conductivity type; 402-Electrode contact region of second conductivity type. Detailed Implementation

[0027] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. It is understood that the terms “first,” “second,” etc., as used herein may be used to describe various information or data, but these elements are not limited by these terms. These terms are only used to distinguish first information from another type of information. For example, without departing from the scope of this application, first action information may be referred to as second action information, and similarly, second action information may be referred to as first action information. Both first action information and second action information are action information, but they are not the same action information.

[0029] In this document, it should be understood that the terminology used is for convenience of understanding only and does not imply any limitation on its meaning. Furthermore, any number of elements in the accompanying drawings is for illustrative purposes only and not for limitation, and any naming is for distinction only and has no limiting meaning.

[0030] A single-photon avalanche photodiode (SPAD) is a high-sensitivity photodetector with internal gain. Its core is based on the photoelectric effect of a PN junction and the avalanche multiplication principle, and it is widely used in low-light detection scenarios.

[0031] However, in the pixelated array design of some SPADs, if the isolation capability of the isolation structure is insufficient (such as insufficient depth), the incident light will penetrate the boundary of the current pixel unit and escape to the photosensitive area of ​​the outside of the pixel or the neighboring pixel unit. The neighboring pixel may receive the escaped light, causing optical crosstalk, which will eventually lead to a mismatch between its output electrical signal and the actual light intensity it detects, affecting the detection accuracy.

[0032] The technical solutions shown in this application will now be described in detail through specific embodiments. It should be noted that the following embodiments may exist independently or in combination with each other; for identical or similar content, the description will not be repeated in different embodiments.

[0033] Reference Figure 1 This application provides a pixel unit, which includes: Substrate 10; An isolation structure 30 and a photoelectric conversion region 20 are located on and in contact with the substrate 10; the isolation structure 30 surrounds the outer periphery of the photoelectric conversion region 20 and is used to confine the carriers generated by the photoelectric conversion region 20 within the pixel unit. And an electrode contact structure 40, which is located within the isolation range of the isolation structure 30 and is in contact with the side of the photoelectric conversion region 20 away from the substrate, for collecting the charge carriers generated by the photoelectric conversion region 20 and exporting electrical signals.

[0034] In this embodiment, the substrate 10 serves as the physical support for the pixel unit, providing a stable underlying surface for the isolation structure 30 and photoelectric conversion region 20 above, ensuring structural integrity; it can also serve as an auxiliary channel for carrier transport (if the substrate 10 is a conductive semiconductor), working with the photoelectric conversion region 20 to achieve directional migration of carriers; and it adapts to the compatibility of semiconductor processes (such as matching with subsequent photolithography and doping processes).

[0035] In one example, the substrate 10 includes a semiconductor substrate 10 layer (such as a silicon substrate 10 layer) and a silicon dioxide insulating layer formed on the upper surface of the silicon substrate 10; wherein the silicon dioxide insulating layer is a thin structure (typical thickness range: 10-100nm) used to achieve electrical isolation between the silicon substrate 10 and the upper photoelectric conversion region 20 and the isolation structure 30, while providing a flat growth / deposition substrate 10 for subsequent semiconductor layers (such as the N-type epitaxial layer and P-type doped region of the photoelectric conversion region 20).

[0036] It should be understood that the silicon substrate 10 layer, as the core support layer of the substrate 10, provides physical support and semiconductor process compatibility (Si material is the mainstream substrate 10 for semiconductor devices, possessing advantages such as high carrier mobility, strong lattice stability, and mature processes); if the silicon substrate 10 layer is doped (such as N-type or P-type), it can also assist in carrier transport or participate in the electric field modulation of the photoelectric conversion region 20 (such as enhancing the built-in electric field of the PN junction). The silicon dioxide insulating layer is used to block unnecessary electrical connections between the silicon substrate 10 layer and the photoelectric conversion region 20 and the isolation structure 30 above, avoiding signal loss caused by carrier diffusion to the substrate 10 (such as photogenerated carriers being recombinated by the substrate 10). At the same time, after the silicon dioxide insulating layer is prepared by thermal oxidation or deposition process, it has a high surface flatness and can be used as a transition substrate 10 for subsequent semiconductor layers (such as epitaxial layers and doped regions), improving the growth quality of the upper structure (reducing lattice defects).

[0037] In this embodiment, the isolation structure 30 is used to divide the lateral range of a single pixel unit, completely separating the pixel from adjacent pixels to avoid spatial signal interference. It is used to block the path of incident light through the pixel boundary, thereby preventing unabsorbed light (such as oblique light or short-wavelength light) from escaping to the outside or neighboring pixels, ensuring that each pixel only receives the light signal of its own detection area. It is also used to limit the transmission range of charge carriers through insulation properties, confining the electrons / holes generated by the photoelectric conversion region 20 inside the pixel, and avoiding electrical signal superposition distortion caused by the diffusion of charge carriers across pixels.

[0038] Based on this, the isolation structure 30 in the embodiments of this application extends through the pixel unit to the substrate 10.

[0039] In this embodiment, the photoelectric conversion region 20 has the following functions: light absorption, by absorbing incident photons through a semiconductor material (such as Si), exciting valence band electrons to transition to the conduction band, generating photogenerated carriers (electron-hole pairs); carrier separation, by using the built-in electric field of the PN junction to separate photogenerated electrons and holes, with electrons drifting to the N-type region and holes drifting to the P-type region, in preparation for subsequent collection.

[0040] Furthermore, in this embodiment, the outer periphery of the photoelectric conversion region 20 is defined by the isolation structure 30, ensuring that charge carriers can only migrate directionally toward the upper surface electrode away from the substrate 10, thus avoiding lateral diffusion loss.

[0041] In this embodiment, the electrode contact structure 40 is used to export electrical signals and mainly has the following functions: carrier collection: through direct contact with the photoelectric conversion region 20, it quickly captures the separated carriers (holes through the P+ contact region and electrons through the N+ contact region); signal export: it converts the collected carriers into detectable electrical signals (such as current and voltage) and transmits them to the peripheral readout circuit (such as an amplifier or analog-to-digital converter) of the pixel unit.

[0042] It should be understood that the electrode contact structure 40 is located on the upper surface of the photoelectric conversion region 20, which shortens the carrier transport path (eliminating the need for long-distance lateral migration to the outside of the isolation structure 30) and reduces carrier recombination losses; and direct contact can avoid the additional resistance caused by the intermediate layer, thereby improving signal response speed and collection efficiency.

[0043] The following describes the working principle of the pixel unit in the embodiments of this application: Light incidence: After being focused by the optical lens (or sensor module), the incident light penetrates the substrate 10 and enters the photoelectric conversion region 20; Carrier generation and separation: The semiconductor material of the photoelectric conversion region 20 absorbs incident light and generates electron-hole pairs. Under the action of the built-in electric field of the PN junction, electrons separate into the N-type region and holes separate into the P-type region. Carrier collection: The separated carriers migrate upward along the direction perpendicular to the substrate 10 and are quickly captured by the electrode contact structure 40 on the upper surface (electrons enter the N-type contact electrode, and holes enter the P-type contact electrode). Signal output: The electrodes convert charge carriers into electrical signals, which are then transmitted to the peripheral circuit, completing the full conversion from optical signals to electrical signals; Boundary isolation: Throughout the process, the isolation structure 30 blocks the lateral escape of light and charge carriers, ensuring that the signal of each pixel is independent and free from interference.

[0044] Based on the above description, the isolation structure 30 in this embodiment is located on both sides of the photoelectric conversion area 20, forming a lateral boundary blockage. It physically blocks the path of incident light through the pixel boundary, preventing light from escaping to the outside or neighboring pixels, ensuring that each pixel unit only receives the light signal of its own detection area, improving the matching degree between the output electrical signal and the real light intensity, and improving the resolution and signal-to-noise ratio of imaging / detection.

[0045] Furthermore, the isolation structure 30 also defines the transmission range of the charge carriers, confining the charge carriers generated by the photoelectric conversion region 20 within the pixel, avoiding electrical signal interference caused by the diffusion of charge carriers across pixels, and further ensuring the independence of the signal of a single pixel.

[0046] In other words, the isolation structure 30 extends to the substrate 10, thus forming full-boundary isolation, completely eliminating the escape gap of light carriers, and achieving a more significant crosstalk suppression effect.

[0047] Furthermore, in this embodiment, after charge carriers (electrons / holes) are generated in the photoelectric conversion region 20, they do not need to be transported laterally over a long distance to the electrodes outside the isolation layer. Instead, they can drift directly to the electrode contact structure 40 on the side opposite to the substrate 10, reducing recombination losses during transport and improving collection efficiency. The electrode contact structure 40 is in direct contact with the photoelectric conversion region 20, avoiding the additional resistance caused by the intermediate layer. Charge carriers can quickly transfer from the semiconductor region (photoelectric conversion region 20 and electrode contact structure 40) to the metal electrode, accelerating the electrical signal response speed, which is particularly suitable for high-speed detection scenarios. It should be understood that after the increase in charge carrier collection efficiency, even a small number of photogenerated charge carriers generated by weak light signals can be effectively captured, reducing signal attenuation and lowering the lower limit of detector sensitivity, making it more suitable for weak light detection requirements (such as weak light gain scenarios for APDs).

[0048] Finally, in this embodiment, the isolation structure 30 simultaneously serves multiple functions, defining the boundary of the photoelectric conversion region 20 and separating pixels. It eliminates the need to design separate deep trench isolations for the anode and cathode of the pixel units, reducing complex process steps such as etching, filling, and planarization.

[0049] In one possible viewing configuration, the photoelectric conversion region 20 includes: A first conductivity type absorption region 204 is located on the substrate 10; the first conductivity type absorption region 204 is used to absorb incident light and generate photogenerated carriers; The second conductivity type drift region 202 and the second conductivity type well region 203 are located on the side of the first conductivity type absorption region 204 away from the substrate 10 and are in contact with the first conductivity type absorption region 204. The second conductivity type well region 203 is located on both sides of the second conductivity type drift region 202 in the transverse direction perpendicular to the substrate 10, and the first conductivity type absorption region 204 surrounds the second conductivity type well region 203.

[0050] The electrode contact structure 40 is embedded within the first conductivity type absorption region 204 and the second conductivity type drift region 202.

[0051] In this embodiment, the first conductivity type absorption region 204 is the main region above the substrate 10, extending longitudinally through the lower to middle part of the photoelectric conversion region 20, and laterally defined by the isolation structure 30, enclosing the second conductivity type well region 203. The second conductivity type drift region 202 is located longitudinally on the upper surface of the first conductivity type absorption region 204 (facing away from the substrate 10); laterally, it is located between the second conductivity type well regions 203, forming a central strip shape, and directly contacting the absorption region. The second conductivity type well regions 203 are in the same layer as the drift regions longitudinally (on the upper surface of the absorption region); laterally, they are symmetrically distributed on both sides of the drift regions and surrounded by the first conductivity type absorption region 204. The electrode contact structure 40 is embedded in the first conductivity type absorption region 204 (corresponding to the N-type electrode) and the second conductivity type drift region 202 (corresponding to the P-type electrode), forming an ohmic contact with the semiconductor.

[0052] More specifically, along the longitudinal direction of the substrate 10, the first conductivity type absorption region 204 serves as the main light absorption layer, located above the substrate 10, and has a relatively large thickness (to ensure light absorption efficiency), responsible for generating a large number of photogenerated carriers. The second conductivity type drift / second conductivity type well region 203 is located on the upper surface of the absorption region, forming a longitudinal PN junction, with a built-in electric field direction from the P-type region to the N-type region, providing power for carrier separation.

[0053] After carrier separation, electrons (N-type carriers) migrate into the first conductivity type absorption region 204, and holes (P-type carriers) migrate into the second conductivity type drift region 202 / second conductivity type well region 203. Ultimately, they all converge on the upper surface electrode contact structure 40. The transmission path is longitudinal, the shortest, and has no lateral detours.

[0054] Along the lateral direction of substrate 10, the second conductivity type drift region 202 is centrally located, serving as a channel for carrier separation. Laterally facing the incident light focusing area, it ensures that photogenerated carriers preferentially separate near the drift region, shortening the hole transport distance. The second conductivity type well region 203 is symmetrically distributed on both sides of the first conductivity type drift region. On one hand, it expands the lateral contact range of the PN junction, increasing the carrier separation area; on the other hand, it acts as a carrier guiding wall, preventing holes from diffusing laterally. Holes are intercepted by the second conductivity type well region 203 and guided to the upper surface electrode. Furthermore, the first conductivity type absorption region 204 surrounds the well region, forming a structure where the first conductivity type absorption region 204 encloses the second conductivity type well region 203. This blocks holes from escaping towards the isolation structure 30 laterally, while ensuring that electrons generated in the absorption region are confined within the main body, preventing cross-pixel diffusion. Moreover, the second well region reduces the electric field strength of the PN junction at the edge, thereby reducing the probability of edge breakdown and allowing the pixel unit to better detect photogenerated carrier signals.

[0055] The electrode contact structure 40 is embedded in the second conductivity type drift region 202, so that the second electrode of the pixel unit and the second conductivity type drift region 202 form an ohmic contact through the high concentration of the second conductivity type electrode contact region 402, directly collecting holes in the drift region without intermediate layer loss. The electrode contact structure 40 also embeds a first conductivity type absorption region 204, so that the first electrode of the pixel unit and the first conductivity type absorption region 204 form an ohmic contact through a high concentration of the first conductivity type electrode contact region 401, and collect electrons in the absorption region.

[0056] Based on the above structure, when the first conductivity type is N-type and the second conductivity type is P-type, the photoelectric conversion principle of the pixel unit of this application is as follows: the incident light penetrates the unblocked area of ​​the upper surface electrode and enters the first conductivity type absorption region 204. The first conductivity type semiconductor (such as Si) absorbs the incident light photons, and the valence band electrons are excited to the conduction band, generating a large number of photogenerated carriers.

[0057] The built-in electric field of the PN junction formed by the absorption region (N-type) and the drift / well region (P-type) forces the separation of electron-hole pairs.

[0058] Electrons (negatively charged) migrate into the N-type absorption region under the influence of the electric field, and eventually converge in the N-type electrode contact region embedded in the absorption region.

[0059] Holes (positively charged) migrate toward the P-type drift region / well region. Some holes are directly collected by the P-type electrode contact region in the drift region, while others diffuse toward the well regions on both sides and are guided to the P-type electrode contact region by the well regions.

[0060] Carrier collection and signal extraction: the N-type electrode contact area collects electrons and the P-type electrode collects holes, forming a reverse current. This current is then extracted to the peripheral readout circuit through the metal electrode electrically connected to the electrode contact structure 40, completing the conversion from optical signal to electrical signal.

[0061] Based on the above description, the first conductivity type absorption region 204 in this embodiment serves as the main body of the photoelectric conversion region 20. It has a large thickness and a wide lateral range, which can fully absorb incident light (especially for medium and long wavelength light, sufficient thickness is required to ensure absorption), reduce light penetration loss, and increase the total amount of photogenerated carriers.

[0062] Furthermore, the pixel unit PN junction in this embodiment has a wide lateral range (drift region and two side well regions). After photogenerated carriers are generated at any position in the absorption region, they can quickly reach the vicinity of the PN junction and be separated, reducing the recombination loss of unseparated carriers.

[0063] Furthermore, the pixel unit in this embodiment adopts a structure of isolation structure 30 and absorption region surrounding the well region, which blocks carrier diffusion across pixels from both the outside (isolation structure 30) and the inside (absorption region) to prevent light from escaping.

[0064] Optionally, the electrode contact structure 40 includes a first conductivity type electrode contact area 401 and a second conductivity type electrode contact area 402.

[0065] Along the side of the first conductivity type absorption region 204 away from the substrate 10, the first conductivity type electrode contact region 401 is embedded in the first conductivity type absorption region 204, and the second conductivity type electrode contact region 402 is embedded in the second conductivity type drift region 202.

[0066] Along a transverse direction parallel to the substrate 10, the first conductivity type electrode contact region 401 is located on the side of the second conductivity type well region 203 away from the second conductivity type drift region 202.

[0067] In this embodiment, the first conductivity type electrode contact area 401 is located longitudinally on the upper surface of the first conductivity type absorption area 204 away from the substrate 10 and embedded inside the absorption area; it is symmetrically distributed laterally on the outer side of the second conductivity type well area 203 away from the second conductivity type drift area 202.

[0068] The second conductivity type electrode contact area 402 is located vertically on the upper surface of the second conductivity type drift area 202 away from the substrate 10 and embedded inside the second conductivity type drift area 202; it is located laterally in the middle region of the second conductivity type drift area 202 (directly opposite the incident light focusing area).

[0069] Based on this, after the carriers generated in the photoelectric conversion region 20 are separated, they do not need to cross layers vertically or detour laterally. They only need to migrate upwards in a direction perpendicular to the substrate 10 to reach the first and second electrodes. The transmission path is the shortest (only the vertical thickness of the corresponding conductive region), minimizing the recombination loss of carriers during transmission (the carrier recombination probability is positively correlated with the transmission distance).

[0070] The first conductivity type electrode contact area 401 is used to connect to the first electrode of the pixel structure, and the second conductivity type electrode contact area 402 is used to connect to the second electrode of the pixel structure. For example, the first electrode can be a cathode or an anode, and the second electrode can correspondingly be a cathode or an anode.

[0071] For example, the first conductivity type is N-type, and the second conductivity type is P-type. The complete process of carrier generation and signal derivation is as follows: Incident light generates electron-hole pairs in the N-type absorption region. The built-in electric field of the PN junction separates electrons into the N-type absorption region and holes into the P-type drift / well region. Under the influence of the electric field, electrons migrate into the interior of the N-type absorption region. Since the N-type electrode contact region is located on the outer upper surface of the absorption region, electrons migrate laterally over a short distance in the longitudinal direction to the symmetrical N-type electrode contact region. Holes converge toward the P-type drift region under the influence of the electric field. Some are directly collected by the central P-type electrode contact region, while others diffuse toward the P-wells on both sides and are guided back to the central drift region by the electric field of the P-wells, eventually merging into the P-type electrode contact region (without escaping to the outside). Carrier collection and signal extraction: electrons are collected in the N-type electrode contact area and holes are collected in the P-type electrode contact area, forming a reverse photocurrent, which is quickly extracted to the peripheral readout circuit through the first electrode and the second electrode layer.

[0072] Based on the above description, the vertical single-sided embedding design of the electrode contact structure 40 results in a carrier transmission distance that is only the vertical thickness of the photoelectric conversion region 20, which is much shorter than the long lateral transmission distance of traditional electrodes outside the isolation zone, thus reducing recombination losses.

[0073] In this embodiment, the electrode can be connected to the corresponding electrode contact area, and an ohmic contact can be formed through the highly doped electrode contact area (N+ / P+). This results in low contact resistance, fast carrier transfer speed, and a response time down to the nanosecond level (suitable for high-speed detection scenarios).

[0074] In one alternative embodiment, the doping concentration of the first conductivity type electrode contact region 401 is greater than the doping concentration of the first conductivity type absorption region 204. And / or, the doping concentrations of the second conductivity type electrode contact region 402, the second conductivity type drift region 202, and the second conductivity type electrode contact region 402 decrease sequentially.

[0075] In this embodiment, the first conductivity type electrode contact area 401 is embedded in the first conductivity type absorption area 204 to form an ohmic contact with the metal electrode; the second conductivity type electrode contact area 402 is embedded in the second conductivity type drift area 202 to form an ohmic contact with the metal electrode.

[0076] It should be understood that the first conductivity type electrode contact region 401 (such as N+) is a bridge between the metal electrode and the semiconductor absorption region. A high doping concentration can solve the problem of excessive metal-semiconductor contact resistance and accelerate the convergence of charge carriers to the electrode.

[0077] Specifically, when a metal and a semiconductor come into contact, a Schottky barrier is formed (which hinders charge carriers from crossing the metal-semiconductor interface): if the doping concentration of the first conductivity type electrode contact region 401 is low, the barrier height is high, making it difficult for charge carriers to pass through, resulting in extremely high contact resistance, leading to signal attenuation and slower response; while the effect of a high doping concentration in the first conductivity type electrode contact region 401 is: By narrowing the barrier width and high doping, the carrier concentration on the surface of the first conductivity type electrode contact region 401 is extremely high. The Schottky barrier width is compressed to the tunneling limit, and the carriers can quickly cross the interface through the tunneling effect, resulting in a decrease in contact resistance. Forming an ohmic contact: satisfying the condition of matching the work function of the metal with the Fermi level of the semiconductor, transforming from a Schottky contact to an ohmic contact, ensuring that the electrode efficiently collects charge carriers; The first conductivity type electrode contact area 401 and the first conductivity type absorption area 204 form a carrier concentration gradient from high concentration to low concentration, which guides the carriers (such as electrons) in the absorption area to converge rapidly to the electrode, reducing recombination loss during the transmission process.

[0078] Based on the above description, the doping concentration of the first conductivity type electrode contact region 401 is greater than that of the first conductivity type absorption region 204, which accelerates carrier migration and reduces the response time from μs to ns, making it suitable for high-speed photodetection scenarios; the ohmic contact has no dead zone voltage, avoiding the problem of signal failure under low light intensity and improving weak light detection sensitivity.

[0079] In this embodiment, the second conductivity type contact region is used to reduce the resistance of the ohmic contact, collect holes, and guide the holes in the drift region to converge towards the metal electrode through the concentration gradient.

[0080] The second conductivity type drift region 202 is used for carrier separation. Lower doping increases the width of the depletion layer of the drift region (the depletion layer of the PN junction is mainly distributed on the low-doped side), expanding the separation range of photogenerated carriers (more photogenerated holes can be captured by the electric field); at the same time, the low doping carrier concentration is low and the electric field intensity is uniformly distributed, avoiding the transport disorder of carriers caused by electric field distortion. The second conductivity type well region 203 is used for lateral interception and electric field guidance. It intercepts holes that diffuse outward and guides them to migrate towards the central second conductivity type drift region 202 / second conductivity type electrode contact region 402. At the same time, it enhances the electric field strength of the PN junction between the second conductivity type well region 203 and the first conductivity type absorption region 204, thereby improving the lateral carrier separation efficiency.

[0081] Based on the above description, the low doping of the second conductivity type drift region 202 causes the PN junction depletion layer to be mainly concentrated at the contact surface between the second conductivity type drift region 202 and the first conductivity type absorption region 204. The electric field is uniform and has a wide coverage, resulting in high separation efficiency of photogenerated carriers. This avoids breakdown caused by excessively strong local electric fields or incomplete separation caused by excessively weak local electric fields.

[0082] The PN junction formed by the second conductivity type well region 203 and the first conductivity type absorption region 204 can effectively intercept holes that diffuse laterally, preventing them from escaping to the N-type electrode or the isolation structure 30, and further blocking electrical crosstalk.

[0083] Optionally, the first conductivity type is N-type or P-type, and the second conductivity type is the opposite of the first conductivity type.

[0084] In one example, when the first conductivity type is N-type, the second conductivity type is P-type. Based on the characteristics of N-type, such as high carrier (electron) mobility, fast response speed, and the ease of achieving long carrier lifetime and high light absorption efficiency with low doping in the absorption region, this pixel unit can be applied to conventional imaging sensors and low-light detectors (APDs).

[0085] Based on this, the N-type electrode (the first electrode mentioned above) connected to the first conductivity type electrode contact area 401 collects electrons (usually the cathode), and the P-type electrode (the second electrode mentioned above) connected to the second conductivity type electrode contact area 402 collects holes (usually the anode).

[0086] In this example, the pixel unit can be specifically applied to: Conventional imaging sensors (such as mobile phone cameras and security cameras): Because the mobility of N-type carriers (electrons) is about three times that of holes, they can be quickly collected by electrodes, resulting in a shorter response time. Therefore, they have high response speed and high quantum efficiency. Low-light detectors (such as APD and SPAD arrays): Low doping of the N-type absorption region can easily achieve a long carrier lifetime, reduce carrier recombination loss under low light, and improve detection sensitivity; High-speed optical detection (such as lidar and fiber optic communication): The electronic transmission speed is fast and can adapt to the detection requirements of nanosecond-level optical pulse signals.

[0087] In another example, when the first conductivity type is P-type, the second conductivity type is N-type. P-type semiconductors have a superior absorption coefficient for some long-wavelength light and strong radiation resistance, making them suitable for harsh environments (such as aerospace exploration). In this case, the pixel unit can be applied to special spectral detection (such as infrared) and radiation-resistant devices.

[0088] Based on this, the P-type electrode (the first electrode mentioned above) connected to the first conductivity type electrode contact area 401 collects electrons (usually the cathode), and the N-type electrode (the second electrode mentioned above) connected to the second conductivity type electrode contact area 402 collects holes (usually the anode).

[0089] In this example, the pixel unit can be specifically applied to: Long-wavelength light detection (such as near-infrared and mid-infrared sensors): P-type semiconductors absorb long-wavelength light more shallowly, resulting in shorter carrier transport paths and reduced recombination losses.

[0090] Radiation resistant environments (such as aerospace and nuclear industry detection): P-type semiconductors have strong resistance to total dose radiation, are less prone to lattice defects caused by radiation, and have higher device stability.

[0091] P-type substrate 10 process scenario: If a P-type silicon substrate 10 is used (lower cost and more mature process), selecting a P-type absorption region can avoid the problem of increased leakage current caused by the opposite conductivity type of the substrate 10 and the absorption region.

[0092] Based on the above description, the pixel unit provided in this application embodiment can be compatible with the performance requirements of different application scenarios (response speed, spectral adaptation, stability); and can be adapted to different semiconductor process routes (substrate type, doping process).

[0093] In one optional embodiment, the isolation structure 30 includes an isolation layer 302 and a metal layer 303; Along a transverse direction parallel to the substrate 10, the isolation layer 302 encloses the metal layer 303.

[0094] In the embodiments of this application, the isolation layer 302 may be made of an insulating material, such as silicon dioxide, silicon nitride, or a composite layer of silicon dioxide and silicon nitride.

[0095] Specifically, the isolation layer 302 completely wraps around the metal layer 303 laterally, with its inner side in contact with the photoelectric conversion region 20 (absorption region / well region) and its outer side forming the boundary of the pixel unit; it extends vertically through the entire vertical height of the pixel unit (from the substrate 10 to the upper surface of the photoelectric conversion region 20, and is flush with the electrode contact structure 40).

[0096] The metal layer 303 can be made of a highly conductive metal, such as W, TiN, AlCu alloy, or a multilayer metal stack.

[0097] Specifically, the metal layer 303 is completely covered by the isolation layer 302 in the horizontal direction, and is at the same height as the isolation layer 302 in the vertical direction.

[0098] It should be understood that the isolation layer 302 is made of an insulating material, which has a low absorption coefficient for visible / near-infrared light, thus forming a physical barrier to block unabsorbed light from the photoelectric conversion region 20 from penetrating the pixel boundary and escaping to neighboring pixels, thereby structurally eliminating optical crosstalk. Furthermore, the insulating properties of the isolation layer 302 can block electrical connections between adjacent pixels, preventing charge carriers from diffusing across pixels through the isolation region, while also preventing the electrodes of this pixel from forming leakage paths with the electrodes of adjacent pixels, ensuring that the electrical signals of each pixel are independent. Finally, the insulating layer completely encapsulates the metal layer 303, preventing direct contact between the metal layer 303 and the photoelectric conversion region 20 and the electrode contact structure 40, while also preventing metal atoms from diffusing into the semiconductor region to form lattice defects that would affect carrier lifetime.

[0099] In this embodiment, the metal layer 303 can form an equipotential shielding layer by grounding or applying a fixed potential. On the one hand, it can shield the electric field interference of adjacent pixel electrodes (avoiding electric crosstalk caused by electric field coupling); on the other hand, it can adjust the electric field distribution of the photoelectric conversion region 20. For example, in the APD, the metal layer 303 can be subjected to a reverse bias to assist in the expansion of the depletion layer and improve the carrier separation efficiency.

[0100] Secondly, embodiments of this application also provide a method for fabricating a pixel unit, the method comprising: First, refer to Figure 2 Substrate 10 is provided; As described in the first aspect, the substrate 10 is selected as a stacked structure formed by a silicon substrate 10 and a silicon dioxide layer.

[0101] The preparation method includes preparing a silicon dioxide layer on a single-crystal silicon wafer using a thermal oxidation process.

[0102] Second, refer to Figures 3 to 7 An isolation structure and a photoelectric conversion region in contact with the substrate 10 are formed on the substrate 10; wherein the second isolation structure is located on the outer periphery of the photoelectric conversion region and is used to confine the charge carriers generated by the photoelectric conversion region inside the pixel unit.

[0103] In this step, the boundary pattern between the isolation structure and the photoelectric conversion region is first defined using photolithography. Then, the isolation structure is fabricated through trench etching, insulating layer filling, and metal layer 303 filling. Finally, the photoelectric conversion region is formed using ion implantation.

[0104] Third, refer to Figure 8 and Figure 9An electrode contact structure (401 and 402) is formed on the side of the photoelectric conversion region (202, 203 and 204) opposite to the substrate 10; the electrode contact structure is in contact with the photoelectric conversion region and is used to collect the charge carriers generated by the photoelectric conversion region and output the electrical signal.

[0105] In this step, the pattern of the electrode contact structure is first defined using photolithography, and then the electrode contact structure is formed using ion implantation.

[0106] It is worth noting that after the electrode contact structure is formed, metal electrodes (first electrode and second electrode) are formed on the electrode structure.

[0107] Based on the above description, the pixel structure fabrication method provided in this application is fully compatible with CMOS mass production processes. All steps, including photolithography, etching, ion implantation, CMP, and PECVD, are mature processes in semiconductor factories and do not require special equipment. Moreover, it is only necessary to adjust the photolithography mask pattern, ion implantation impurity type, and dosage to adapt to designs where the first conductivity type is N-type or P-type and the second conductivity type is P-type or N-type, thus being compatible with different detection scenarios.

[0108] In one optional embodiment, forming an isolation structure and a photoelectric conversion region in contact with the substrate 10 on the substrate 10 includes the following steps: First step, refer to Figure 3 A first conductivity type absorption region 204 precursor structure 201 is formed on the substrate 10.

[0109] In this embodiment, a first conductivity type absorption region 204 precursor structure 201 can be formed on the substrate 10 by depositing a semiconductor material layer and ion implantation.

[0110] The second step, refer to Figure 4 and Figure 5 On the substrate 10, an isolation structure (302 and 303) is formed around the first conductivity type absorption region precursor structure 201.

[0111] In the embodiments of this application, the second isolation structure can be obtained through photolithography definition, trench etching, filling of isolation layer 302, filling of metal layer 303, and CMP planarization. It should be understood that the above process can adopt existing process methods, which will not be described in detail here.

[0112] Third step, refer to Figure 6 The first target region of the first conductivity type absorption region 204 is subjected to a first ion doping treatment to form a second conductivity type drift region 202.

[0113] Optionally, the first target region is the central position of the precursor structure 201 of the first conductivity type absorption region 204. By doping with ions of the second conductivity type, this region is transformed from the first conductivity type to the second conductivity type, forming a drift region, which constitutes a PN junction with the surrounding first conductivity type regions.

[0114] The specific process flow may include: defining a first target region using photolithography, performing a first ion doping treatment on the first target region, followed by resist removal and cleaning. Specifically, oxygen plasma ashing can be used to remove the photoresist, and then 10% HF solution can be used to clean residual impurities. Finally, annealing is performed. Specifically, annealing is used to activate doped ions, repair implantation damage, and allow doped ions to diffuse slightly, forming a regular second conductivity type drift region 202.

[0115] It should be understood that the above process can be carried out using existing process methods, which will not be described in detail here.

[0116] Step 4, refer to Figure 7 A second ion doping treatment is performed on the second target region of the first conductivity type absorption region 204 to form a second conductivity type well region 203 and a first conductivity type absorption region 204; wherein the second target region is located on both sides of the first target region and is in contact with the first target region.

[0117] The first conductivity type absorption region 204, the second conductivity type drift region 202, and the second conductivity type well region 203 constitute the first conductivity type absorption region 204.

[0118] In this embodiment, the second target region is located on both sides of the first target region, and a second conductivity type well region 203 is formed by doping with second conductivity type ions; while the precursor structure region not covered by the first and second target regions is the final first conductivity type absorption region 204.

[0119] The fabrication process of the second conductivity type well region 203 is the same as that of the second conductivity type drift region 202 in the third step, and will not be described again here.

[0120] Based on the above description, in the embodiments of this application, a continuous first conductivity type absorption region 204 precursor structure 201 is first formed, and then first and second isolation structures are formed on both sides, avoiding the gap problem between the absorption region and the isolation structure caused by the traditional method of first isolating and then doping, thus improving the optical crosstalk suppression effect.

[0121] Furthermore, all steps utilize mature CMOS mass production processes, requiring no special equipment and adaptable to large-scale array production.

[0122] In the embodiments of this application, the doped ions in the first ion doping treatment and the second ion doping treatment are both of the second conductivity type.

[0123] The ion doping concentration of the first ion doping treatment is greater than the ion doping concentration of the second ion doping treatment.

[0124] In this embodiment of the application, as described in the first aspect, the second conductivity type drift region 202 is used for carrier separation. Lower doping increases the width of the depletion layer of the drift region (the depletion layer of the PN junction is mainly distributed on the low-doped side), expanding the separation range of photogenerated carriers (more photogenerated holes can be captured by the electric field); at the same time, the low-doped carrier concentration is low and the electric field intensity distribution is uniform, avoiding the transport disorder of carriers caused by electric field distortion. The second conductivity type well region 203 is used for lateral interception and electric field guidance. It intercepts holes that diffuse outward and guides them to migrate towards the central second conductivity type drift region 202 / second conductivity type electrode contact region 402. At the same time, it enhances the electric field strength of the PN junction between the second conductivity type well region 203 and the first conductivity type absorption region 204, thereby improving the lateral carrier separation efficiency.

[0125] Based on the above description, the low doping of the second conductivity type drift region 202 causes the PN junction depletion layer to be mainly concentrated at the contact surface between the second conductivity type drift region 202 and the first conductivity type absorption region 204. The electric field is uniform and has a wide coverage, resulting in high separation efficiency of photogenerated carriers. This avoids breakdown caused by excessively strong local electric fields or incomplete separation caused by excessively weak local electric fields.

[0126] The PN junction formed by the second conductivity type well region 203 and the first conductivity type absorption region 204 can effectively intercept holes that diffuse laterally, preventing them from escaping to the N-type electrode or isolation structure, and further blocking electrical crosstalk.

[0127] In one optional embodiment, forming an electrode contact structure on the side of the photoelectric conversion region opposite to the substrate 10 includes: First, refer to Figure 8 The third target region of the first conductivity type absorption region 204 is subjected to a third ion doping treatment to form the first conductivity type electrode contact region 401.

[0128] In this embodiment, the third target regions are symmetrically distributed on the surface of the first conductive type absorption region 204 outside the second conductive type well region 203, and there are a total of 2 regions.

[0129] The specific process flow for forming the first conductivity type electrode contact region 401 may include: defining a third target region using photolithography, performing third ion doping treatment on the third target region, and then performing resist removal and cleaning. Existing processes can be used for the specific process, and no special limitations are specified here.

[0130] Then, refer to Figure 9 The fourth target region of the second conductivity type drift region 202 is subjected to fourth ion doping treatment to form the second conductivity type electrode contact region 402. In this embodiment, the fourth target region is distributed in the central region of the second conductivity type drift region 202, and there are two of them.

[0131] The specific process flow for forming the second conductivity type electrode contact region 402 may include: defining the fourth target region using photolithography, performing fourth ion doping treatment on the fourth target region, and then performing resist removal and cleaning. Existing processes can be used for the specific process, and no special limitations are specified here.

[0132] In this embodiment, the position, size and number of the third / fourth target regions can be flexibly adjusted by simply adjusting the window pattern of the photomask to adapt to different pixel designs; and all processes are mature CMOS mass production processes, requiring no special equipment, thus improving yield.

[0133] Wherein, the first conductivity type electrode contact region 401 and the second conductivity type electrode contact region 402 constitute the electrode contact structure; the dopant ions in the third ion doping treatment are all of the first conductivity type, and the dopant ions in the fourth ion doping treatment are all of the second conductivity type. The ion doping concentration of the first conductivity type absorption region 204 is less than the ion doping concentration of the first conductivity type electrode contact region 401.

[0134] It should be understood that the first conductivity type electrode contact region 401 (such as N+) is a bridge between the metal electrode and the semiconductor absorption region. A high doping concentration can solve the problem of excessive metal-semiconductor contact resistance and accelerate the convergence of charge carriers to the electrode.

[0135] Specifically, when a metal and a semiconductor come into contact, a Schottky barrier is formed (which hinders charge carriers from crossing the metal-semiconductor interface): if the doping concentration of the first conductivity type electrode contact region 401 is low, the barrier height is high, making it difficult for charge carriers to pass through, resulting in extremely high contact resistance, leading to signal attenuation and slower response; while the effect of a high doping concentration in the first conductivity type electrode contact region 401 is: By narrowing the barrier width and high doping, the carrier concentration on the surface of the first conductivity type electrode contact region 401 is extremely high. The Schottky barrier width is compressed to the tunneling limit, and the carriers can quickly cross the interface through the tunneling effect, resulting in a decrease in contact resistance. Forming an ohmic contact: satisfying the condition of matching the work function of the metal with the Fermi level of the semiconductor, transforming from a Schottky contact to an ohmic contact, ensuring that the electrode efficiently collects charge carriers; The first conductivity type electrode contact area 401 and the first conductivity type absorption area 204 form a carrier concentration gradient from high concentration to low concentration, which guides the carriers (such as electrons) in the absorption area to converge rapidly to the electrode, reducing recombination loss during the transmission process.

[0136] Based on the above description, the doping concentration of the first conductivity type electrode contact region 401 is greater than that of the first conductivity type absorption region 204, which accelerates carrier migration and reduces the response time from μs to ns, making it suitable for high-speed photodetection scenarios; the ohmic contact has no dead zone voltage, avoiding the problem of signal failure under low light intensity and improving weak light detection sensitivity.

[0137] In one alternative embodiment, an isolation structure is formed on the outer periphery of the first conductivity type absorption region 204 precursor structure 201 on the substrate 10, comprising: First, referring to 4, on the substrate 10, isolation trenches 301 extending through the substrate 10 are formed on both sides of the precursor structure 201 of the first conductivity type absorption region 204.

[0138] In this embodiment, the isolation trench pattern is first determined by photolithography, then the isolation trench is etched to penetrate to the substrate 10, and finally, post-processing of the isolation trench can be performed to remove polymer residue and optimize the trench wall.

[0139] Then, referring to 5, an isolation layer 302 and a metal layer 303 are sequentially formed in the isolation groove 301.

[0140] In this embodiment, plasma-enhanced chemical vapor deposition (PECVD) is first used to sequentially form an isolation layer 302 in the isolation tank 301, and then physical vapor deposition (PVD) and electroplating are used to thicken it. PVD deposits a seed crystal layer to ensure adhesion, and electroplating quickly fills the deep tank, taking into account both density and efficiency.

[0141] It is worth noting that the metal layer 303 needs to fill the remaining space of the isolation trench (within the area covered by the isolation layer 302) to enhance electric field shielding (blocking electric field interference from adjacent pixels) and heat dissipation (exhausting the operating heat of the device). At the same time, it needs to be tightly attached to the isolation layer 302 without any gaps.

[0142] In this embodiment, the isolation trench extends through the substrate 10, rather than just on the surface of the photoelectric conversion region, forming a complete isolation barrier from the bottom substrate 10 to the surface, completely preventing carriers from escaping laterally through the substrate 10; the full-thickness isolation also blocks light leakage from the pixel edge, reducing optical crosstalk and improving imaging resolution.

[0143] Furthermore, in this embodiment, the isolation layer 302 directly contacts the trench wall to achieve electrical insulation and prevent the metal layer 303 from forming a conductive path with the semiconductor, which would lead to a short circuit. The metal layer 303 serves as the core and utilizes the high conductivity of the metal to achieve electric field shielding (the electric field of adjacent pixels is absorbed by the metal layer 303, without interfering with the carrier separation of this pixel). At the same time, the high thermal conductivity of the metal can quickly dissipate the heat generated when the photoelectric conversion area is working, preventing the device from overheating and causing performance degradation.

[0144] Finally, all processes in the embodiments of this application are mature CMOS mass production processes, requiring no special equipment and achieving high yield; and the trench width, depth, and filling layer thickness can be flexibly adjusted through the mask and process parameters to adapt to different pixel sizes and the thickness of the first conductivity type absorption region 204 precursor structure 201.

[0145] Thirdly, embodiments of this application provide an optical sensor, including the pixel unit described in the first aspect, or the pixel unit prepared by the method described in the second aspect.

[0146] In this embodiment, the optical sensor features low crosstalk, high quantum efficiency, fast response speed, and excellent low-light sensitivity; it is compatible with CMOS mass production, boasting high yield and low cost; it has a stable structure and a wide operating temperature range. It can be applied to mobile phone / security imaging, lidar, fiber optic communication, biomedical low-light imaging, aerospace radiation-resistant detection, and industrial extreme environment sensing.

[0147] Fourthly, embodiments of this application provide an optical detector, including pixel units arranged in an array as described in the first aspect.

[0148] In this embodiment, the optical detector is arrayed, resulting in excellent resolution and signal uniformity; low crosstalk, high quantum efficiency, and fast response; it is also compatible with CMOS mass production, with high yield and controllable cost; the structure is stable and adaptable to wide temperature ranges and harsh environments. It can be applied to high-resolution imaging (mobile phones / security cameras), lidar (autonomous driving / ranging), biomedical low-light imaging (fluorescence / pathological detection), high-speed optical communication receiving arrays, aerospace radiation-resistant detection, and industrial extreme environment sensor scenarios.

[0149] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A pixel unit, characterized in that, The pixel unit includes: Substrate; An isolation structure and a photoelectric conversion region are located on and in contact with the substrate; the isolation structure surrounds the outer periphery of the photoelectric conversion region and is used to confine the carriers generated by the photoelectric conversion region within the pixel unit; The electrode contact structure is located within the isolation range of the isolation structure and is in contact with the side of the photoelectric conversion region away from the substrate, for collecting the charge carriers generated by the photoelectric conversion region and exporting electrical signals.

2. The pixel unit according to claim 1, characterized in that, The photoelectric conversion region includes: A first conductivity type absorption region is located on the substrate; the first conductivity type absorption region is used to absorb incident light and generate photogenerated carriers; A second conductivity type drift region and a second conductivity type well region; along the lateral direction perpendicular to the substrate, the second conductivity type drift region and the second conductivity type well region are both located on the side of the first conductivity type absorption region away from the substrate and are in contact with the first conductivity type absorption region; along the lateral direction parallel to the substrate, the second conductivity type well region is located on both sides of the second conductivity type drift region, and the first conductivity type absorption region surrounds the second conductivity type well region.

3. The pixel structure according to claim 2, characterized in that, The electrode contact structure is embedded within the first conductivity type absorption region and the second conductivity type drift region.

4. The pixel unit according to claim 3, characterized in that, The electrode contact structure includes a first type of conductive electrode contact area and a second type of conductive electrode contact area. Along the side of the first conductivity type absorption region away from the substrate, the first conductivity type electrode contact region is embedded in the first conductivity type absorption region, and the second conductivity type electrode contact region is embedded in the second conductivity type drift region; Along a transverse direction parallel to the substrate, the first conductivity type electrode contact region is located on the side of the second conductivity type well region away from the second conductivity type drift region.

5. The pixel unit according to claim 4, characterized in that, The doping concentration of the first conductivity type electrode contact region is greater than the doping concentration of the first conductivity type absorption region; And / or, the doping concentration of the second conductivity type electrode contact region, the second conductivity type drift region, and the second conductivity type electrode contact region decreases sequentially.

6. The pixel unit according to any one of claims 1-5, characterized in that, The isolation structure includes an isolation layer and a metal layer; The insulating layer encloses the metal layer in a transverse direction parallel to the substrate.

7. The pixel unit according to any one of claims 2-5, characterized in that, The first conductivity type is N-type or P-type, and the second conductivity type is the opposite of the first conductivity type.

8. A method for fabricating a pixel unit, characterized in that, The preparation method includes: Provide substrate; An isolation structure and a photoelectric conversion region are formed on the substrate in contact with the substrate; wherein the isolation structure surrounds the outer periphery of the photoelectric conversion region and is used to confine the carriers generated by the photoelectric conversion region within the pixel unit; An electrode contact structure is formed on one side of the photoelectric conversion region; the electrode contact structure is located within the isolation range of the isolation structure and is in contact with the side of the photoelectric conversion region away from the substrate, for collecting the charge carriers generated by the photoelectric conversion region and exporting electrical signals.

9. The preparation method according to claim 8, characterized in that, Forming an isolation structure and a photoelectric conversion region in contact with the substrate on the substrate includes: A first conductivity type absorption region precursor structure is formed on the substrate; An isolation structure is formed on the periphery of the first conductivity type absorption region precursor structure on the substrate; The first target region of the first conductivity type absorption region is subjected to a first ion doping treatment to form a second conductivity type drift region; A second ion doping treatment is performed on the second target region of the first conductivity type absorption region to form a second conductivity type well region and a first conductivity type absorption region; wherein, the second target region is located on both sides of the first target region and is in contact with the first target region; The first conductivity type absorption region, the second conductivity type drift region, and the second conductivity type well region constitute the photoelectric conversion region.

10. The method according to claim 9, characterized in that, The doped ions in both the first ion doping treatment and the second ion doping treatment are of the second conductivity type; The ion doping concentration of the first ion doping treatment is greater than the ion doping concentration of the second ion doping treatment.

11. The method according to claim 9, characterized in that, The electrode contact structure formed on the side of the photoelectric conversion region opposite to the substrate includes: The third target region of the first conductivity type absorption region is subjected to third ion doping treatment to form the first conductivity type electrode contact region; The fourth target region of the second conductivity type drift region is subjected to fourth ion doping treatment to form the second conductivity type electrode contact region; Wherein, the first conductivity type electrode contact region and the second conductivity type electrode contact region constitute the electrode contact structure; the dopant ions in the third ion doping treatment are all of the first conductivity type, and the dopant ions in the fourth ion doping treatment are all of the second conductivity type; The ion doping concentration in the absorption region of the first conductivity type is lower than the ion doping concentration in the electrode contact region of the first conductivity type.

12. The preparation method according to claim 9, characterized in that, On the substrate, an isolation structure is formed around the periphery of the first conductivity type absorption region precursor structure, comprising: An isolation trench is formed on the outer periphery of the first conductivity type absorption region precursor structure on the substrate; An isolation layer and a metal layer are formed sequentially in the isolation groove.

13. An optical sensor, characterized in that, Includes the pixel unit as described in any one of claims 1-7.

14. An optical detector, characterized in that, Includes pixel units arranged in an array as described in any one of claims 1-7.

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