Front-illuminated photodiode and method of fabrication, x-ray detector

Abstract

The application discloses a front-illuminated photodiode and a preparation method and an X-ray detector, and belongs to the field of semiconductor photoelectric sensors in nuclear technology application. The front-illuminated photodiode comprises an epitaxial layer comprising a light-sensing area; a first doped area is located on the epitaxial layer and is arranged laterally apart from the light-sensing area; a second doped area is located on the light-sensing area, the second doped area is opposite to the doping type of the epitaxial layer, and the second doped area is a high-doped area; the second doped area comprises a light-sensing patterned area, the minimum lateral distance between any position in the light-sensing area and the second doped area is within a target distance range, the lower limit value of the target distance range is greater than 0, and the upper limit value of the target distance range is less than the lateral diffusion length of a photo-generated minority carrier in the light-sensing area. The application can improve the quantum efficiency of the photodiode and reduce the total capacitance.

Description

Technical Field

[0001] This application belongs to the field of semiconductor optoelectronic sensors for nuclear technology applications, and particularly relates to a front-illuminated photodiode and its preparation method, and an X-ray detector. Background Technology

[0002] In front-illuminated photodiodes, the photosensitive region of the epitaxial layer is a heavily p-type doped region. However, the minority carrier lifetime in the heavily p-type doped region is extremely short; it can be approximated that all photogenerated minority carriers in the heavily p-type doped region cannot be collected. Therefore, the heavily p-type doped region is often referred to as a "dead zone." Since the photosensitive region of front-illuminated photodiodes in related technologies is also a heavily p-type doped region, a large number of photogenerated carriers are generated within this region and cannot be collected, significantly impacting quantum efficiency. Summary of the Invention

[0003] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a front-illuminated photodiode and its fabrication method, as well as an X-ray detector, which can improve the quantum efficiency of the front-illuminated photodiode and reduce its total capacitance.

[0004] In a first aspect, this application provides a front-illuminated photodiode, comprising:

[0005] Epitaxial layer, including the photosensitive area;

[0006] The first doped region is located in the epitaxial layer;

[0007] The second doped region is located in the photosensitive region. The doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a highly doped region. The second doped region includes a photosensitive patterned region. The minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range. The lower limit of the target distance range is greater than 0, and the upper limit of the target distance range is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region.

[0008] According to the front-illuminated photodiode of this application, by patterning the second doped region (highly doped region) in the photosensitive region, the second doped region includes the photosensitive patterned region, reducing the proportion of the second doped region in the photosensitive region. Furthermore, the minimum lateral distance between each position in the photosensitive region and the second doped region is greater than 0 and less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region. This allows photogenerated minority carriers at each position in the photosensitive region to diffuse laterally to the depletion region and be collected, thereby reducing the proportion of "dead zone", improving quantum efficiency, reducing the area of ​​the PN junction, and reducing the total capacitance.

[0009] According to one embodiment of this application, the photosensitive patterned region includes a plurality of first highly doped sub-regions, which are laterally spaced apart.

[0010] According to one embodiment of this application, the first highly doped sub-region is a dotted region, and the plurality of first highly doped sub-regions are arranged in an array.

[0011] According to one embodiment of this application, the first highly doped subregion is a strip-shaped region.

[0012] According to one embodiment of this application, the photosensitive patterned region further includes at least one second highly doped sub-region, the second highly doped sub-region being connected to the first highly doped sub-region.

[0013] According to one embodiment of this application, the second highly doped sub-region is a strip-shaped region, and the first highly doped sub-region is connected to each of the second highly doped sub-regions.

[0014] According to one embodiment of this application, the target distance range includes 2-100 μm.

[0015] According to one embodiment of this application, the epitaxial layer is an N-type lightly doped epitaxial layer, the first doped region is an N-type cathode heavily doped region, the second doped region is a P-type anode heavily doped region, and the first doped region and the photosensitive region are laterally spaced apart.

[0016] According to one embodiment of this application, the epitaxial layer is a P-type low-doped epitaxial layer, the first doped region is an N-type floating low-doped region, the second doped region is a P-type clamped high-doped region, the first doped region is located in the photosensitive region, and the second doped region is located on the first doped region.

[0017] In a second aspect, this application provides an X-ray detector, including the front-illuminated photodiode described in the first aspect above.

[0018] Thirdly, this application provides a method for fabricating a front-illuminated photodiode, comprising:

[0019] An epitaxial layer is provided, the epitaxial layer including a photosensitive region;

[0020] A first doped region is formed in the epitaxial layer;

[0021] A second doped region is formed in the photosensitive region. The doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a highly doped region. The second doped region includes a photosensitive patterned region. The minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range. The lower limit of the target distance range is greater than 0, and the upper limit of the target distance range is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region.

[0022] The above-described one or more technical solutions in the embodiments of this application have at least one of the following technical effects:

[0023] By patterning the second doped region (highly doped region) in the photosensitive region, making the second doped region include the photosensitive patterned region, the proportion of the second doped region in the photosensitive region is reduced. Furthermore, the minimum lateral distance between each position in the photosensitive region and the second doped region is greater than 0 and less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region. This allows photogenerated minority carriers at each position in the photosensitive region to diffuse laterally to the depletion region and be collected, thereby reducing the proportion of "dead zone", improving quantum efficiency, reducing the area of ​​the PN junction, and lowering the total capacitance.

[0024] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0025] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0026] Figure 1 This is one of the cross-sectional views of the front-illuminated photodiode provided in the embodiments of this application;

[0027] Figure 2 This is a second cross-sectional view of the front-illuminated photodiode provided in the embodiments of this application;

[0028] Figure 3 This is one of the structural schematic diagrams of the front-illuminated photodiode provided in the embodiments of this application;

[0029] Figure 4 This is a second schematic diagram of the structure of the front-illuminated photodiode provided in the embodiments of this application;

[0030] Figure 5 This is the third schematic diagram of the structure of the front-illuminated photodiode provided in the embodiments of this application;

[0031] Figure 6 This is a simulation curve of the front-illuminated photodiode provided in the embodiments of this application;

[0032] Figure 7 This is a schematic flowchart of the fabrication method of the front-illuminated photodiode provided in the embodiments of this application. Detailed Implementation

[0033] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0034] The front-illuminated photodiode and its fabrication method, as well as the X-ray detector, provided in the embodiments of this application are described below with reference to the accompanying drawings.

[0035] Figure 1 and Figure 2 This is a schematic diagram of the structure of a front-illuminated photodiode provided in an embodiment of this application. The front-illuminated photodiode is a CMOS-based front-illuminated photodiode. This front-illuminated photodiode can be applied in an X-ray detector, which is a front-illuminated detector.

[0036] like Figure 1 and Figure 2 As shown, the front-illuminated photodiode provided in this embodiment includes an epitaxial layer 1, and the epitaxial layer 1 includes a photosensitive region 11. One side of the epitaxial layer 1 is the photosensitive side, which refers to the side where light is incident on the epitaxial layer 1. The photosensitive region 11 is located on the photosensitive side of the epitaxial layer 1. In the front-illuminated photodiode, the photosensitive side of the epitaxial layer 1 is located on the front side of the epitaxial layer 1, that is, the photosensitive region 11 is located on the front side of the epitaxial layer 1.

[0037] Epitaxial layer 1 can be a semiconductor layer including silicon, or it can be a semiconductor layer including other elements. The doping type of epitaxial layer 1 can be N-type or P-type. For example, epitaxial layer 1 can be doped with trace amounts of pentavalent elements, such as phosphorus or arsenic, to form an N-type epitaxial layer. Alternatively, epitaxial layer 1 can be doped with trace amounts of trivalent elements, such as boron, to form a P-type epitaxial layer.

[0038] The front-illuminated photodiode also includes a first doped region 2, which is located on the epitaxial layer 1. The first doped region 2 is located on the front side of the epitaxial layer 1, that is, the first doped region 2 and the photosensitive region 11 are located on the same side of the epitaxial layer 1. The first doped region 2 can be a highly doped region or a lightly doped region.

[0039] The first doped region 2 has a first doping type, and the doping type of the first doped region 2 can be the same as or opposite to that of the epitaxial layer 1.

[0040] The front-illuminated photodiode also includes a second doped region 3, which is located on the front side of the epitaxial layer 1 and in the photosensitive region 11. The second doped region 3 has a second doping type, which is opposite to the first doping type. The doping type of the second doped region 3 can be the same as or opposite to that of the epitaxial layer 1. The second doped region 3 is a highly doped region.

[0041] The second doped region 3 includes a photosensitive patterned region, which means that the second doped region 3 has gaps, that is, the transverse cross-section of the second doped region 3 has hollowed-out portions, rather than a solid cross-section. The area in the photosensitive region 11 without the second doped region 3 is the light absorption region. The inclusion of the photosensitive patterned region in the second doped region 3 can reduce the proportion of the second doped region 3 in the photosensitive region 11 and reduce the area of ​​the PN junction, while increasing the proportion of the light absorption region in the photosensitive region 11.

[0042] The minimum lateral distance between any location in the photosensitive region 11 and the second doped region 3 (i.e., the closest distance from any location in the photosensitive region 11 to the second doped region 3) is within the target distance range, with the lower limit of the target distance range greater than 0 and the upper limit of the target distance range less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region 11. While reducing the proportion of the second doped region 3 in the photosensitive region 11, the gaps in the second doped region 3 cannot be too large, and it is necessary to ensure that the minimum lateral distance between each location in the photosensitive region 11 and the second doped region 3 is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region 11, so that photogenerated minority carriers generated outside the depletion region can diffuse into the depletion region before recombination, generating an effective photocurrent.

[0043] It should be noted that, in this embodiment, when the front-illuminated photodiode is applied to an X-ray detector, the front-illuminated photodiode is used to convert the visible light signal (the visible light signal converted from the X-ray signal by the scintillator) into an electrical signal, and the electrical signal is processed by the ADC (analog-to-digital converter) and then output to the digital and control circuit.

[0044] The working principle of a front-illuminated photodiode is as follows: When light of a certain wavelength (visible light signal) is incident on an epitaxial layer (such as silicon), and the photon energy is greater than the band gap Eg of silicon (for silicon, this means the wavelength is less than 1100 nm), electrons in the valence band absorb the photon energy and jump to the conduction band, forming an electron-hole pair. When an electron-hole pair is generated within the depletion region of a PN junction, the electron and hole will separate under the influence of the built-in electric field. If the external circuit of the PN junction forms a loop, a photocurrent will be generated. When an electron-hole pair is generated outside the depletion region of a PN junction, if the minority carrier lifetime in the corresponding region is long enough, the minority carriers in the electron-hole pair can diffuse into the depletion region and be collected to form a photocurrent.

[0045] However, in semiconductors, doping creates defect centers, allowing non-equilibrium carriers to recombine via these impurity centers—a phenomenon known as Shockley-Read-Hall (SRH) recombination. Higher doping concentrations increase the probability of SRH recombination, resulting in a shorter minority carrier lifetime (the average time from generation to recombination). The minority carrier lifetime determines the length of diffusion before recombination. In photodiodes, photogenerated minority carriers generated outside the depletion region need to diffuse into it to produce an effective photocurrent. With a short minority carrier lifetime, these carriers recombine before reaching the depletion region, making them uncollectible and reducing quantum efficiency.

[0046] In a front-illuminated photodiode, the doping concentration of the highly doped P-type region is 10. 17 cm -3 Up to 10 20 cm -3 In p-type photodiodes, the minority carrier lifetime is extremely short, meaning that almost all photogenerated minority carriers within the heavily doped p-type region cannot be collected. Therefore, the heavily doped p-type region is often referred to as the "dead zone." When light incident into the epitaxial layer, the light intensity decays exponentially with the depth of incidence; that is, the closer to the surface, the greater the number of photogenerated carriers; the shorter the wavelength, the faster the decay rate. For front-illuminated photodiodes, a large number of photogenerated carriers are generated within the heavily doped p-type region and cannot be collected, resulting in a significant loss of quantum efficiency, which increases with decreasing wavelength.

[0047] In front-illuminated photodiodes, the entire photosensitive area is a highly p-type doped region, which significantly affects quantum efficiency. The visible light incident on the photodiode is mainly at a wavelength of 540 nm. At this wavelength, the theoretical quantum efficiency of a back-illuminated photodiode is 100%, while that of a front-illuminated photodiode is only 84% (when the junction depth is 1 μm).

[0048] To improve quantum efficiency, related technologies have proposed replacing the highly doped P-type region with a low-doped P-type region, thereby increasing the minority carrier lifetime in this region and thus increasing the number of minority carriers that can be collected. Simultaneously, a highly doped P-type region is set within the low-doped P-type region to connect the metal vias (the entire photosensitive area is a low-doped P-type region, with only the area in contact with the metal being a highly doped P-type region), ensuring low-resistance contact.

[0049] However, due to limitations imposed by the ion implantation and diffusion mechanisms of doping elements in the process, uniform doping of the P-type low-doped region cannot be achieved, and highly doped areas still exist on the surface. These areas remain "dead zones," thus limiting the improvement in quantum efficiency. Furthermore, the total area of ​​the P-type doped region remains unchanged, the PN junction area remains unchanged, and the junction capacitance shows no significant difference. Moreover, different ion implantation doses are used for the highly doped and low-doped P-type regions during production, requiring different photomasks for lithography and ion implantation. This increases the total number of photomasks, thereby increasing process complexity and production costs.

[0050] In this embodiment, the second doped region 3 (highly doped region) in the photosensitive region 11 is patterned to create gaps within it, reducing its proportion within the photosensitive region 11. Furthermore, the minimum lateral distance between each position in the photosensitive region 11 and the second doped region 3 is greater than 0 and less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region 11. This allows photogenerated minority carriers at each position within the gaps in the second doped region 3 to diffuse laterally to the depletion region for collection, meaning the gaps in the second doped region 3 are no longer "dead zones." This increases the proportion of the light absorption region in the photosensitive region 11, thereby improving quantum efficiency. Additionally, the reduced area of ​​the second doped region 3 leads to a smaller PN junction area and a lower total capacitance. Moreover, in this embodiment, the photosensitive region 11 does not require a low-doped region, eliminating the need for an additional photomask, thus avoiding increased process complexity and production costs.

[0051] In some embodiments, the front-illuminated photodiode can be a PN-type photodiode. For example... Figure 1 As shown, epitaxial layer 1 is a first-doped epitaxial layer, meaning the doping type of epitaxial layer 1 is the same as that of the first doped region 2, and opposite to that of the second doped region 3. The first doped region 2 is a highly doped region, with a doping concentration greater than that of epitaxial layer 1. For example, epitaxial layer 1 may be an N-type low-doped epitaxial layer, the first doped region 2 a highly doped N-type region, and the second doped region 3 a highly doped P-type region.

[0052] The first doped region 2 and the photosensitive region 11 are arranged laterally at intervals, where "lateral" refers to the direction parallel to the front side of the epitaxial layer 1. The area in the photosensitive region 11 where the second doped region 3 is not located is the epitaxial layer 1, that is, the gap region in the second doped region 3 is the epitaxial layer 1, and the gap region in the second doped region 3 is the light absorption region.

[0053] The first doped region 2 and the second doped region 3 are the electrode regions of the photodiode. The first doped region 2 is the cathode region, and the second doped region 3 is the anode region.

[0054] In this embodiment, the second doped region 3 in the photosensitive region 11 is patterned to reduce the proportion of "dead zones" and increase the proportion of light absorption regions in the photosensitive region 11, thereby improving the quantum efficiency of the photodiode. Furthermore, the reduced area of ​​the second doped region 3 and the reduced area of ​​the PN junction formed between the second doped region 3 and the epitaxial layer 1 result in a decrease in the total capacitance, thereby reducing the readout electronics noise of the ADC and improving the signal-to-noise ratio.

[0055] In some embodiments, the front-illuminated photodiode can be a clamped active photodiode. For example... Figure 2 As shown, epitaxial layer 1 is a second-doped epitaxial layer, meaning the doping type of epitaxial layer 1 is the same as the doping type of the second doped region 3, and opposite to the doping type of the first doped region 2. The first doped region 2 is a low-doped region. For example, epitaxial layer 1 is a P-type low-doped epitaxial layer, the first doped region 2 is an N-type low-doped region, and the second doped region 3 is a P-type high-doped region. In some embodiments, the first doped region 2 is an N-type floating region, and the second doped region 3 is a P-type clamping region.

[0056] The first doped region 2 is located in the photosensitive region 11, and the second doped region 3 is located on top of the first doped region 2, i.e., the second doped region 3 and the first doped region 2 are arranged vertically. The area in the photosensitive region 11 where the second doped region 3 is not located is the first doped region 2, i.e., the gap region in the second doped region 3 is the first doped region 2, i.e., the gap region in the second doped region 3 is the light absorption region. The gap region in the second doped region 3 is determined by the doping concentration of the first doped region 2 and the reset voltage, and it is necessary to ensure that the first doped region 2 between the second doped regions 3 is completely depleted after reset.

[0057] In this embodiment, the second doped region 3 in the photosensitive region 11 is patterned to reduce the proportion of "dead zone" and increase the proportion of light absorption region in the photosensitive region 11, thereby improving the quantum efficiency of the photodiode. Furthermore, the area of ​​the second doped region 3 is reduced, and the area of ​​the PN junction formed between the second doped region 3 and the epitaxial layer 1 is also reduced, resulting in a lower total capacitance. However, the readout electronics noise of the clamped active photodiode is mainly affected by the size of the parasitic capacitance at FD6. This embodiment does not change the parasitic capacitance at FD6, therefore it has no effect on the readout electronics noise.

[0058] In some embodiments, the target distance range includes 2-100 μm, that is, the minimum lateral distance between any position in the photosensitive area 11 and the second doped area 3 is greater than or equal to 2 μm and less than or equal to 100 μm.

[0059] In this embodiment, the target distance range is set to 2-100μm, which can avoid the gap in the second doped region 3 being too small to meet the actual application requirements, and at the same time avoid the problem of too large a gap leading to too low minority carrier diffusion efficiency and too long time. That is, this embodiment still retains the advantage of the fast response speed of the front-illuminated diode.

[0060] In some embodiments, the boundary between the second doped region 3 and the photosensitive region 11 is spaced apart, meaning the second doped region 3 is not located at the edge of the photosensitive region 11. The distance between the boundary between the second doped region 3 and the photosensitive region 11 is within the target distance range, so that photogenerated minority carriers at the edge of the photosensitive region 11 can diffuse laterally to the depletion region and be collected, further reducing the proportion of "dead zone" and thus further improving quantum efficiency.

[0061] In some embodiments, when the front-illuminated photodiode is a PN-type photodiode, the photosensitive patterned area includes a plurality of first highly doped sub-regions 31, which are laterally spaced to create gaps in the second doped area 3 (i.e., gaps between the plurality of first highly doped sub-regions 31), thereby reducing the proportion of the second doped area 3 in the photosensitive area 11.

[0062] The first highly doped sub-region 31 can be circular, rectangular, elliptical, or irregular in shape, etc., without specific limitations. The number of first highly doped sub-regions 31 can be set according to actual needs, without specific limitations. The sizes of different first highly doped sub-regions 31 can be the same or different. The shapes of different first highly doped sub-regions 31 can be the same or different.

[0063] In some embodiments, when the front-illuminated photodiode is a PN-type photodiode, such as Figure 3 As shown, the first highly doped sub-region 31 is a dot-shaped region, and multiple first highly doped sub-regions 31 are arranged in an array. The shape and size (such as diameter or area) of the multiple first highly doped sub-regions 31 can be the same, and the multiple first highly doped sub-regions 31 are uniformly distributed in an array in the photosensitive region 11. For example, the multiple first highly doped sub-regions 31 form multiple rows of first highly doped sub-regions, and adjacent rows of first highly doped sub-regions are staggered.

[0064] In some embodiments, when the front-illuminated photodiode is a PN-type photodiode, the first highly doped sub-region 31 is a strip-shaped region, and multiple first highly doped sub-regions 31 can be arranged in parallel and spaced apart. The shape and size (e.g., length, width, or area) of the multiple first highly doped sub-regions 31 can be the same, and the multiple first highly doped sub-regions 31 are distributed in parallel and spaced apart in the photosensitive region 11. The spacing between two adjacent first highly doped sub-regions 31 can be the same, that is, the multiple first highly doped sub-regions 31 can be uniformly distributed.

[0065] For example, the lateral direction can include a first direction and a second direction that are perpendicular to each other. The photosensitive area 11 can be rectangular, the first direction can be the length direction of the photosensitive area 11, and the second direction can be the width direction of the photosensitive area 11. Each first highly doped sub-region 31 can extend along the first direction, and multiple first highly doped sub-regions 31 can be distributed sequentially at intervals along the second direction.

[0066] In some embodiments, when the front-illuminated photodiode is a PN-type photodiode or a clamped active photodiode, such as Figure 4 and Figure 5 As shown, the photosensitive patterned region also includes at least one second highly doped sub-region 32, which is connected to the first highly doped sub-region 31.

[0067] The photosensitive patterned region may include a second heavily doped sub-region 32, which may be connected to a portion of the first heavily doped sub-region 31 or to all of the first heavily doped sub-regions 31. The second heavily doped sub-region 32 may be linear, arc-shaped, or polygonal, etc., and is not specifically limited here. The connection position between the second heavily doped sub-region 32 and the first heavily doped sub-region 32 is not specifically limited.

[0068] The photosensitive patterned region may include multiple second highly doped sub-regions 32. Each second highly doped sub-region 32 may be connected to a portion of the first highly doped sub-regions 31, or it may be connected to all of the first highly doped sub-regions 31. The number of first highly doped sub-regions 31 connected to different second highly doped sub-regions 32 may be the same or different. The shapes of different second highly doped sub-regions 32 may be the same or different.

[0069] In this embodiment, a second highly doped sub-region 32 is provided to connect the spaced-apart first highly doped sub-regions 31, which facilitates the connection of the second doped region 3 to the metal electrode.

[0070] In some embodiments, when the front-illuminated photodiode is a PN-type photodiode or a clamped active photodiode, the second highly doped sub-region 32 is a strip-shaped region, and the first highly doped sub-region 31 and the second highly doped sub-region 32 can be perpendicular to each other and connected. Both the first highly doped sub-region 31 and the second highly doped sub-region 32 can be strip-shaped regions, and multiple first highly doped sub-regions 31 can be distributed in parallel and at intervals. The extension direction of the second highly doped sub-region 32 is perpendicular to the extension direction of the first highly doped sub-region 31, and the extension direction of the second highly doped sub-region 32 is the same as the distribution direction of the multiple first highly doped sub-regions 31, so that the second highly doped sub-region 32 is connected to each first highly doped sub-region 31.

[0071] In the case where the photosensitive patterned region includes a second highly doped subregion 32, such as Figure 3As shown, each first highly doped sub-region 31 can extend along a first direction, and multiple first highly doped sub-regions 31 can be distributed sequentially at intervals along a second direction (the multiple first highly doped sub-regions 31 can be evenly distributed). A second highly doped sub-region 32 extends along the second direction and is connected to each first highly doped sub-region 31. The connection position between the second highly doped sub-region 32 and the first highly doped sub-region 31 is not specifically limited; for example, the second highly doped sub-region 32 can be connected to one end of multiple first highly doped sub-regions 31 to form a rake-shaped region.

[0072] In the case where the photosensitive patterned region includes multiple second highly doped sub-regions 32, such as Figure 4 As shown, each first highly doped sub-region 31 can extend along a first direction, and multiple first highly doped sub-regions 31 can be sequentially spaced along a second direction (the multiple first highly doped sub-regions 31 can be uniformly distributed). Each second highly doped sub-region 32 extends along a second direction, and multiple second highly doped sub-regions 32 can be sequentially spaced along the first direction (the multiple second highly doped sub-regions 32 can be uniformly distributed). Each second highly doped sub-region 32 is connected to each first highly doped sub-region 31 to form a grid-like region. The spacing between two adjacent first highly doped sub-regions 31 can be the same as the spacing between two adjacent second highly doped sub-regions 32.

[0073] The following is a simulation description of the front-illuminated photodiode provided in the embodiments of this application.

[0074] Adopting such Figure 5 The simulation of a front-illuminated photodiode (PN-type photodiode) is shown, where the second doped region 3 is a grid-like region. The visible light wavelength is 540 nm, the junction depth is 1.1 μm, the resistance of epitaxial layer 1 is 500 ohms, the linewidth of the grid (i.e., the width of both the first highly doped sub-region 31 and the second highly doped sub-region 32) is 2 μm, and the side length of the grid (i.e., the spacing between two adjacent first highly doped sub-regions 31 and the spacing between two adjacent second highly doped sub-regions 32) increases from 10 μm to 60 μm. The internal quantum efficiency and junction capacitance are simulated. Figure 6 It can be seen that the theoretical quantum efficiency of PN-type photodiodes in related technologies (where the photosensitive region is a highly doped P-type region, and the epitaxial layer resistance is 500 ohms and 1500 ohms respectively) is only 83.6%, while the theoretical quantum efficiency in this embodiment can reach over 95%, close to the theoretical value (100%) of back-illuminated photodiodes. Simultaneously, without changing the epitaxial layer resistance (i.e., doping concentration), the junction capacitance per unit area is significantly reduced in this embodiment. Simulation results predict that the quantum efficiency of this embodiment is above 98%, and the total capacitance is reduced by more than 50%.

[0075] In summary, the front-illuminated photodiode provided in this application, by patterning the second doped region 3 in the photosensitive region 11 to include the photosensitive patterned region, reduces the proportion of the second doped region 3 in the photosensitive region 11. Furthermore, the minimum lateral distance between each position in the photosensitive region 11 and the second doped region 3 is greater than 0 and less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region 11. This allows photogenerated minority carriers at each position in the photosensitive region 11 to diffuse laterally to the depletion region for collection, thereby reducing the proportion of "dead zones," improving quantum efficiency to a level comparable to that of back-illuminated photodiodes, and reducing the area of ​​the PN junction, lowering the total capacitance, thereby reducing ADC electronic noise and further improving the signal-to-noise ratio. In addition, performance is improved without increasing production costs.

[0076] Accordingly, this application also provides an X-ray detector.

[0077] The X-ray detector provided in this application includes a front-illuminated photodiode, which is the same as the front-illuminated photodiode described in the above embodiment, and will not be described in detail here.

[0078] Among them, X-ray detectors can be used in security inspection and medical fields. They use scintillators to convert X-ray signals into visible light signals, and then use front-illuminated photodiodes to convert the visible light signals into electrical signals. After being processed by an ADC, the signals are output to an ASIC circuit.

[0079] According to the X-ray detector provided in the embodiments of this application, by reducing the proportion of the second doped region in the photosensitive region, the proportion of the "dead zone" is reduced, the quantum efficiency is improved, and the area of ​​the PN junction is reduced, the total capacitance is reduced, thereby reducing the electronic noise of the ADC and further improving the signal-to-noise ratio.

[0080] Accordingly, this application also provides a method for fabricating a front-illuminated photodiode, which can fabricate the front-illuminated photodiode described in the above embodiments.

[0081] like Figure 7 As shown, the method for fabricating a front-illuminated photodiode provided in this application includes steps 110 to 130.

[0082] Step 110: Provide an epitaxial layer, which includes a photosensitive area.

[0083] Combination Figure 1 As shown, the front side of the epitaxial layer 1 has a photosensitive area 11.

[0084] Step 120: Form the first doped region in the epitaxial layer.

[0085] Combination Figure 1As shown, a first doped region 2 is formed in a specific area of ​​the epitaxial layer 1 by ion implantation.

[0086] Step 130: Form a second doped region in the photosensitive region. The doping type of the second doped region is opposite to that of the first doped region. The second doped region includes a photosensitive patterned region. The minimum lateral distance between any position in the photosensitive region and the second doped region is within the target distance range. The lower limit of the target distance range is greater than 0, and the upper limit of the target distance range is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region.

[0087] Combination Figure 1 As shown, a second doped region 3 is formed in the photosensitive region 11 by ion implantation.

[0088] In some embodiments, the target distance range includes 2-100 μm.

[0089] In some embodiments, the photosensitive patterned region includes a plurality of first highly doped sub-regions 31, which are laterally spaced.

[0090] In some embodiments, such as Figure 3 As shown, the first highly doped sub-region 31 is a dot-shaped region, and multiple first highly doped sub-regions 31 are distributed in an array.

[0091] In some embodiments, such as Figure 4 and Figure 5 As shown, the first highly doped subregion 31 is a strip-shaped region.

[0092] In some embodiments, such as Figure 4 and Figure 5 As shown, the photosensitive patterned region also includes at least one second highly doped sub-region 32, which is connected to the first highly doped sub-region 31.

[0093] In some embodiments, the second highly doped sub-region 32 is a strip-shaped region, and the first highly doped sub-region 31 is connected to the second highly doped sub-region 32.

[0094] In some embodiments, such as Figure 1 As shown, epitaxial layer 1 is an N-type lightly doped epitaxial layer, first doped region 2 is an N-type cathode heavily doped region, and second doped region 3 is a P-type anode heavily doped region. The first doped region 2 and photosensitive region 11 are laterally spaced apart. The order in which the first doped region 2 and the second doped region 3 are formed during the fabrication process is not specifically limited.

[0095] In some embodiments, such as Figure 2As shown, the epitaxial layer is a P-type lightly doped epitaxial layer, the first doped region 2 is an N-type floating lightly doped region, and the second doped region 3 is a P-type clamped heavily doped region. The first doped region 2 is located in the photosensitive region 11, and the second doped region 3 is located on the first doped region 2. In the fabrication process, the first doped region 2 is formed first, and then the second doped region 3 is formed on the first doped region 2.

[0096] According to the fabrication method of the front-illuminated photodiode provided in the embodiments of this application, by patterning the second doped region 3 in the photosensitive region 11, the second doped region 3 includes the photosensitive patterned region, reducing the proportion of the second doped region 3 in the photosensitive region 11. Furthermore, the minimum lateral distance between each position in the photosensitive region 11 and the second doped region 3 is greater than 0 and less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region 11. This allows photogenerated minority carriers at each position in the photosensitive region 11 to diffuse laterally to the depletion region for collection, thereby reducing the proportion of "dead zone" and improving quantum efficiency, achieving a level comparable to that of a back-illuminated photodiode. It also reduces the area of ​​the PN junction, lowers the total capacitance, thereby reducing ADC electronic noise and further improving the signal-to-noise ratio. Moreover, no additional photomask is required, thus avoiding increased process complexity and production costs.

[0097] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and are not limited in number; for example, a first object can be one or more.

[0098] In the description of this application, "multiple" means two or more.

[0099] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0100] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A front-illuminated photodiode, characterized in that, include: An epitaxial layer includes a photosensitive region located on one side of the epitaxial layer; A first doped region is located in the epitaxial layer, and the first doped region and the photosensitive region are located on the same side of the epitaxial layer; The second doped region is located in the photosensitive region. The doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a highly doped region. The second doped region includes a photosensitive patterned region. The minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range. The lower limit of the target distance range is greater than 0, and the upper limit of the target distance range is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region. The region in the photosensitive area where the second doped region is not provided is a light absorption region; The photosensitive patterned area includes a plurality of first highly doped sub-regions, which are arranged laterally at intervals. The first doped region is a cathode region, and the second doped region is an anode region; The epitaxial layer is an N-type lightly doped epitaxial layer, the first doped region is an N-type cathode heavily doped region, the second doped region is a P-type anode heavily doped region, and the first doped region and the photosensitive region are laterally spaced apart; or, the epitaxial layer is a P-type lightly doped epitaxial layer, the first doped region is an N-type floating lightly doped region, the second doped region is a P-type clamped lightly doped region, the first doped region is located in the photosensitive region, and the second doped region is located on the first doped region.

2. The front-illuminated photodiode according to claim 1, characterized in that, The first highly doped sub-region is a dot-shaped region, and the plurality of first highly doped sub-regions are distributed in an array.

3. The front-illuminated photodiode according to claim 1, characterized in that, The first highly doped subregion is a strip-shaped region.

4. The front-illuminated photodiode according to claim 3, characterized in that, The photosensitive patterned region further includes at least one second highly doped sub-region, which is connected to the first highly doped sub-region.

5. The front-illuminated photodiode according to claim 4, characterized in that, The second highly doped sub-region is a strip-shaped region, and the first highly doped sub-region is connected to each of the second highly doped sub-regions.

6. The front-illuminated photodiode according to claim 1, characterized in that, The target distance ranges from 2 to 100 μm.

7. An X-ray detector, characterized in that, Including the front-illuminated photodiode as described in any one of claims 1-6.

8. A method for fabricating a front-illuminated photodiode, characterized in that, For fabricating a front-illuminated photodiode as described in any one of claims 1-6, comprising: An epitaxial layer is provided, the epitaxial layer including a photosensitive region; A first doped region is formed in the epitaxial layer; A second doped region is formed in the photosensitive region. The doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a highly doped region. The second doped region includes a photosensitive patterned region. The minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range. The lower limit of the target distance range is greater than 0, and the upper limit of the target distance range is less than the lateral diffusion length of photogenerated minority carriers in the photosensitive region.

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