Front illumination type photodiode, preparation method and X-ray detector

Abstract

The invention discloses a front illumination type photodiode, a preparation method and an X-ray detector, and belongs to the field of semiconductor photoelectric sensors applied to nuclear technology. The front lighting type photodiode comprises an epitaxial layer and a light emitting layer, wherein the epitaxial layer comprises a light sensing area; the first doped region is located on the epitaxial layer, and the first doped region and the photosensitive region are transversely arranged at an interval; the second doped region is located in the photosensitive region, the doping type of the second doped region is opposite to that of the epitaxial layer, and the second doped region is a highly doped region; the second doped region comprises a photosensitive patterning region, the minimum transverse distance between any position in the photosensitive region and the second doped region is within a target distance range, the lower limit value of the target distance range is larger than 0, and the upper limit value of the target distance range is smaller than the transverse diffusion length of photo-generated minority carriers in the photosensitive region. The quantum efficiency of the photodiode can be improved, and the total capacitance is reduced.

Description

Technical Field

[0001] The present application belongs to the field of semiconductor photoelectric sensors for nuclear technology applications, and in particular, relates to a front-illuminated photodiode and a preparation method, and an X-ray detector. Background Art

[0002] In front-illuminated photodiodes, the photosensitive area of ​​the epitaxial layer has a P-type high-doping area. However, the minority carrier lifetime in the P-type high-doping area is extremely short, and it can be considered that all the photogenerated minority carriers in the P-type high-doping area cannot be collected, so the P-type high-doping area is usually called the "dead zone". The photosensitive area of ​​the front-illuminated photodiode in the related art is a P-type high-doping area. A large number of photogenerated carriers are generated in the P-type high-doping area and cannot be collected, which has a great impact on the quantum efficiency. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a front-illuminated photodiode and a preparation method thereof, and an X-ray detector, which can improve the quantum efficiency of the front-illuminated photodiode and reduce the total capacitance.

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

[0005] epitaxial layers, including a photosensitive region;

[0006] A first doped region, located in the epitaxial layer;

[0007] A second doped region is located in the photosensitive region, the second doped region and the first doped region have a doping type opposite to that of the first doped region, and the second doped region is a high 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, and 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 photogenerated minority carriers in the photosensitive region.

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

[0009] According to one embodiment of the present application, the photosensitive patterned area includes a plurality of first highly doped sub-areas, and the plurality of first highly doped sub-areas are laterally spaced apart.

[0010] According to one embodiment of the present application, 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.

[0011] According to an embodiment of the present application, the first highly doped sub-region is a strip-shaped region.

[0012] According to an embodiment of the present application, the photosensitive patterned area further includes at least one second highly doped sub-area, and the second highly doped sub-area is connected to the first highly doped sub-area.

[0013] According to an embodiment of the present 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 the present application, the target distance range includes 2-100 μm.

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

[0016] According to one embodiment of the present 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, the present application provides an X-ray detector comprising the front-illuminated photodiode described in the first aspect.

[0018] In a third aspect, the present application provides a method for preparing a front-illuminated photodiode, comprising:

[0019] providing an epitaxial layer, the epitaxial layer comprising a photosensitive region;

[0020] forming a first doped region in the epitaxial layer;

[0021] A second doped region is formed in the photosensitive region, wherein the doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a high doped region; the second doped region includes a photosensitive patterned region, and the minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range, and 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 photogenerated minority carriers in the photosensitive region.

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

[0023] By patterning the second doped region (highly doped region) in the photosensitive region, the second doped region includes a photosensitive patterned region, thereby reducing the proportion of the second doped region in the photosensitive region, and 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 the photogenerated minority carriers in the photosensitive region, so that the photogenerated minority carriers at each position in the photosensitive region can diffuse laterally to the depletion region and be collected, thereby reducing the proportion of the "dead zone", improving quantum efficiency, reducing the area of ​​the PN junction, and reducing the total capacitance.

[0024] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 1 is one of the cross-sectional views of a front-illuminated photodiode provided in an embodiment of the present application;

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

[0028] Figure 3 It is one of the structural schematic diagrams of the front-illuminated photodiode provided in the embodiment of the present application;

[0029] Figure 4 This is the second structural schematic diagram of the front-illuminated photodiode provided in the embodiment of the present application;

[0030] Figure 5 This is the third structural schematic diagram of the front-illuminated photodiode provided in the embodiment of the present application;

[0031] Figure 6 is a simulation curve diagram of a front-illuminated photodiode provided in an embodiment of the present application;

[0032] Figure 7 It is a schematic flow chart of the method for preparing a front-illuminated photodiode provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application.

[0034] The following describes the front-illuminated photodiode and its preparation method, and the X-ray detector provided in the embodiments of the present application with reference to the accompanying drawings.

[0035] Figure 1 and Figure 2 A schematic diagram of the structure of a front-illuminated photodiode provided in an embodiment of the present application. The front-illuminated photodiode is a front-illuminated photodiode based on a CMOS process. The front-illuminated photodiode can be applied to 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 the embodiment of the present application 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, and the photosensitive side 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] The epitaxial layer 1 may be a semiconductor layer including silicon or a semiconductor layer including other elements. The doping type of the epitaxial layer 1 may be N-type or P-type. For example, the epitaxial layer 1 may be doped with a trace amount of pentavalent elements, such as phosphorus, arsenic, etc., to form an N-type epitaxial layer. Alternatively, the epitaxial layer 1 may be doped with a trace amount of trivalent elements, such as boron, etc., to form a P-type epitaxial layer.

[0038] The front-illuminated photodiode further includes a first doped region 2, which is located in 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 high-doped region or a low-doped region.

[0039] The first doping region 2 has a first doping type, and the doping types of the first doping region 2 and the epitaxial layer 1 may be the same or opposite.

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

[0041] The second doping region 3 includes a photosensitive patterned region, which means that there is a gap in the second doping region 3, that is, the lateral cross section of the second doping region 3 has a hollow portion, rather than a solid cross section. The area in the photosensitive region 11 where the second doping region 3 is not provided is a light absorption region. The provision of the photosensitive patterned region in the second doping region 3 can reduce the proportion of the second doping region 3 in the photosensitive region 11, reduce the area of ​​the PN junction, and increase the proportion of the light absorption region in the photosensitive region 11.

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

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

[0044] Among them, the working principle of the front-illuminated photodiode is: when a certain wavelength of light (visible light signal) is incident on the epitaxial layer (such as silicon), and the photon energy is greater than the band gap Eg of silicon (for silicon, that is, the wavelength is less than 1100nm), the electrons in the valence band will absorb the photon energy and transition to the conduction band to form an electron-hole pair. When the electron-hole pair is generated in the depletion region of the PN junction, the electron and the hole will be separated under the action of the built-in electric field. If the circuit outside the PN junction forms a loop, a photocurrent will be formed. When the electron-hole pair is generated outside the depletion region of the 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 then be collected to form a photocurrent.

[0045] However, in semiconductors, doping will form defect centers, allowing non-equilibrium carriers to recombine with the help of impurity centers, that is, SRH (Shockley-Read-Hall) recombination. The higher the doping concentration, the greater the probability of SRH recombination, and the corresponding minority carrier lifetime (the average time from the generation to the recombination of minority carriers) is shorter. The minority carrier lifetime determines the length of time it can diffuse before recombination. In a photodiode, the photogenerated minority carriers generated outside the depletion region need to diffuse into the depletion region to generate effective photocurrent. When the minority carrier lifetime is short, the photogenerated minority carriers will recombine before diffusing to the depletion region, so they cannot be collected, resulting in reduced quantum efficiency.

[0046] In the front-illuminated photodiode, the doping concentration of the P-type high-doped region is 10 17 cm -3 Up to 10 20 cm -3 , the minority carrier lifetime is extremely short, and it can be roughly considered that all the photogenerated minority carriers in the P-type high-doped region cannot be collected. Therefore, the P-type high-doped region is also often called the "dead zone". When light is incident on the inside of the epitaxial layer, the light intensity decays exponentially with the depth of incidence, that is, the closer to the surface, the more photogenerated carriers there are; the shorter the wavelength, the faster the decay rate. For front-illuminated photodiodes, a large number of photogenerated carriers are generated in the P-type high-doped region and cannot be collected, so the quantum efficiency will be lost a lot, and the loss amount increases with the shortening of the wavelength.

[0047] In the front-illuminated photodiode in the related art, the entire photosensitive area is a P-type high-doped area, which has a great impact on the quantum efficiency. The wavelength of visible light incident on the photodiode is mainly 540nm. At this wavelength, the theoretical quantum efficiency of the back-illuminated photodiode is 100%, while the quantum efficiency of the front-illuminated photodiode is only 84% (when the junction depth is 1μm).

[0048] In order to improve quantum efficiency, the related technology proposes to change the P-type high-doping area into a P-type low-doping area, so that the minority carrier lifetime in this area is increased, thereby increasing the number of minority carriers that can be collected. At the same time, a P-type high-doping area is set in the P-type low-doping area to connect the metal through hole (the entire photosensitive area is a P-type low-doping area, and only the area in contact with the metal is a P-type high-doping area) to ensure low-resistance contact.

[0049] However, due to the limitations of the ion implantation and diffusion mechanism of the doping elements in the process, the P-type low-doped area cannot be uniformly doped, and there is still a high-doped area on the surface. This area is still a "dead zone", so the quantum efficiency improvement is limited. In addition, the total area of ​​the P-type doped area has not changed, the PN junction area has not changed, and there is no obvious difference in junction capacitance. Moreover, during the production process, different ion implantation doses are used for the P-type high-doped area and the P-type low-doped area, so different masks are required for photolithography and ion implantation, which increases the total number of masks, thereby increasing the complexity of the process and increasing production costs.

[0050] In this embodiment, the second doping region 3 (high doping region) in the photosensitive region 11 is patterned so that there is a gap in the second doping region 3, reducing the proportion of the second doping region 3 in the photosensitive region 11, and the minimum lateral distance between each position in the photosensitive region 11 and the second doping region 3 is greater than 0, and less than the lateral diffusion length of the photogenerated minority carriers in the photosensitive region 11, so that the photogenerated minority carriers at each position in the gap region in the second doping region 3 can be laterally diffused to the depletion region and collected, that is, the gap region in the second doping region 3 is no longer a "dead zone", increasing the proportion of the light absorption region in the photosensitive region 11, thereby improving the quantum efficiency. In addition, the area of ​​the second doping region 3 is reduced, the area of ​​the PN junction is reduced, and the total capacitance is also reduced. Moreover, the photosensitive region 11 in this embodiment does not need to be set with a low doping region, that is, there is no need to add an additional mask, which avoids increasing the process complexity and the production cost.

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

[0052] The first doping region 2 is arranged in a lateral spacing from the photosensitive region 11, and the lateral direction refers to a direction parallel to the front surface of the epitaxial layer 1. The region in the photosensitive region 11 where the second doping region 3 is not arranged is the epitaxial layer 1, that is, the gap region in the second doping region 3 is the epitaxial layer 1, that is, the gap region in the second doping region 3 is the light absorption region.

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

[0054] In this embodiment, the second doping region 3 in the photosensitive region 11 is patterned to reduce the proportion of the "dead zone" and increase the proportion of the light absorption region in the photosensitive region 11, thereby improving the quantum efficiency of the photodiode. In addition, the area of ​​the second doping region 3 is reduced, the area of ​​the PN junction formed between the second doping region 3 and the epitaxial layer 1 is reduced, and the total capacitance is also reduced, thereby reducing the readout electronic noise of the ADC and improving the signal-to-noise ratio.

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

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

[0057] In this embodiment, the second doping region 3 in the photosensitive region 11 is patterned to reduce the proportion of the "dead zone" and increase the proportion of the light absorption region in the photosensitive region 11, thereby improving the quantum efficiency of the photodiode. In addition, the area of ​​the second doping region 3 is reduced, the area of ​​the PN junction formed between the second doping region 3 and the epitaxial layer 1 is reduced, and the total capacitance is also reduced. However, the readout electronic noise of the clamped active photodiode is mainly affected by the parasitic capacitance at FD 6. In this embodiment, the parasitic capacitance at FD 6 is not changed, so the readout electronic noise is not affected.

[0058] In some embodiments, the target distance range includes 2-100 μm, that is, the minimum lateral distance between any position in the photosensitive region 11 and the second doping region 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 at 2-100 μm, which can avoid the gap in the second doping 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 a fast response speed of the front-illuminated diode.

[0060] In some embodiments, the second doping region 3 and the boundary of the photosensitive region 11 are spaced apart, that is, the second doping region 3 is not disposed at the edge of the photosensitive region 11. The spacing between the second doping region 3 and the boundary of the photosensitive region 11 is within the target distance range, so that the photogenerated minority carriers at the edge of the photosensitive region 11 can be laterally diffused to the depletion region and collected, further reducing the proportion of the "dead zone" and thus further improving the 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, and the plurality of first highly doped sub-regions 31 are laterally spaced apart so that there are gaps in the second doping region 3 (i.e., gaps between the plurality of first highly doped sub-regions 31), thereby reducing the proportion of the second doping region 3 in the photosensitive region 11.

[0062] The first highly doped sub-region 31 may be circular, rectangular, elliptical or irregular in shape, etc., which is not specifically limited here. The number of the first highly doped sub-regions 31 may be set according to actual needs, which is not specifically limited here. The sizes of different first highly doped sub-regions 31 may be the same or different. The shapes of different first highly doped sub-regions 31 may 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 a plurality of first highly doped sub-regions 31 are distributed in an array. The shapes and sizes (such as diameter or area, etc.) of the plurality of first highly doped sub-regions 31 may be the same, and the plurality of first highly doped sub-regions 31 are evenly distributed in an array in the photosensitive region 11. For example, the plurality of first highly doped sub-regions 31 constitute a plurality of rows of first highly doped sub-regions, and the first highly doped sub-regions in two adjacent rows 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 region, and multiple first highly doped sub-regions 31 can be arranged in parallel and at intervals. The shapes and sizes (such as length, width or area, etc.) 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 at intervals 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 evenly distributed.

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

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

[0067] The photosensitive patterned area may include a second highly doped sub-area 32, and the second highly doped sub-area 32 may be connected to part of the first highly doped sub-area 31, or may be connected to all of the first highly doped sub-areas 31. The second highly doped sub-area 32 may be in a straight line, an arc line, or a folded line shape, etc., which is not specifically limited here. The connection position between the second highly doped sub-area 32 and the first highly doped sub-area 32 is not specifically limited.

[0068] The photosensitive patterned area may include a plurality of second highly doped sub-areas 32, and each second highly doped sub-area 32 may be connected to a portion of the first highly doped sub-areas 31, or may be connected to all of the first highly doped sub-areas 31. The number of first highly doped sub-areas 31 connected to different second highly doped sub-areas 32 may be the same or different. The shapes of different second highly doped sub-areas 32 may be the same or different.

[0069] In this embodiment, the second highly doped sub-regions 32 are provided to connect the first highly doped sub-regions 31 distributed at intervals, so as to facilitate the connection of the second doped region 3 with 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 region, and the first highly doped sub-region 31 and the second highly doped sub-region 32 can be perpendicular and connected. Wherein, both the first highly doped sub-region 31 and the second highly doped sub-region 32 can be strip regions, a plurality of first highly doped sub-regions 31 can be distributed in parallel and at intervals, and 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 plurality of 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 sub-region 32, as Figure 3As shown, each first highly doped sub-region 31 may extend along the first direction, a plurality of first highly doped sub-regions 31 may be sequentially spaced and distributed along the second direction (the plurality of first highly doped sub-regions 31 may be uniformly distributed), and the second highly doped sub-region 32 extends along the second direction and is respectively 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 may be connected to one end of the plurality of first highly doped sub-regions 31 to form a rake-shaped region.

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

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

[0074] Use Figure 5 The front-illuminated photodiode (PN type photodiode) shown in the figure is simulated, that is, the second doped region 3 in the front-illuminated photodiode is a grid-shaped region. The wavelength of visible light is 540nm, the junction depth is 1.1μm, the resistance of the epitaxial layer 1 is 500ohm, the line width of the grid (that is, the width of the first high-doped sub-region 31 and the width of the second high-doped sub-region 32) is 2μm, and the side length of the grid (that is, the spacing between two adjacent first high-doped sub-regions 31 and the spacing between two adjacent second high-doped sub-regions 32) increases from 10μm to 60μm, and the internal quantum efficiency and junction capacitance are simulated. Figure 6 It can be seen that the theoretical quantum efficiency of the PN-type photodiode in the related art (the photosensitive area is a P-type high-doped area, and the resistance of the epitaxial layer is 500ohm and 1500ohm respectively) is only 83.6%, while the theoretical quantum efficiency in this embodiment can reach more than 95%, which is close to the theoretical value (100%) of the back-illuminated photodiode. At the same time, without changing the resistance of the epitaxial layer (i.e., the doping concentration), the unit area junction capacitance of this embodiment is greatly reduced. According to the simulation results, the quantum efficiency of this embodiment is above 98%, and the total capacitance is reduced by more than 50%.

[0075] In summary, according to the front-illuminated photodiode provided by the embodiment of the present application, the second doped region 3 in the photosensitive region 11 is patterned so that the second doped region 3 includes a photosensitive patterned region, the proportion of the second doped region 3 in the photosensitive region 11 is reduced, and 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 the photogenerated minority carriers in the photosensitive region 11, so that the photogenerated minority carriers at each position in the photosensitive region 11 can be laterally diffused to the depletion region and collected, thereby reducing the proportion of the "dead zone" and improving the quantum efficiency, which can reach a level equivalent to that of the back-illuminated photodiode, and reducing the area of ​​the PN junction, reducing the total capacitance, thereby reducing the ADC electronic noise, and further improving the signal-to-noise ratio. In addition, while improving performance, no additional production cost is added.

[0076] Accordingly, an embodiment of the present application also provides an X-ray detector.

[0077] The X-ray detector provided in the embodiment of the present application includes a front-illuminated photodiode, which is the front-illuminated photodiode 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. Scintillators are used to convert X-ray signals into visible light signals, and then the visible light signals are converted into electrical signals through front-illuminated photodiodes, which are then processed by ADC and output to ASIC circuits.

[0079] According to the X-ray detector provided in the embodiment of the present 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 ADC electronic noise and further improving the signal-to-noise ratio.

[0080] Correspondingly, an embodiment of the present application also provides a method for preparing a front-illuminated photodiode, which can prepare the front-illuminated photodiode in the above embodiment.

[0081] like Figure 7 As shown, the method for preparing a front-illuminated photodiode provided in an embodiment of the present application includes steps 110 to 130.

[0082] Step 110: providing an epitaxial layer, wherein the epitaxial layer includes a photosensitive region.

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

[0084] Step 120 : forming a 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, forming a second doped region in the photosensitive region, wherein the second doped region has a doping type opposite to that of the first doped region; the second doped region includes a photosensitive patterned region, and the minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range, and 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 photogenerated minority carriers in the photosensitive region.

[0087] Combination Figure 1 As shown, a second doping 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 , and the plurality of first highly doped sub-regions 31 are laterally spaced apart.

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

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

[0092] In some embodiments, Figure 4 and Figure 5 As shown, the photosensitive patterned region further includes at least one second highly doped sub-region 32 , and the second highly doped sub-region 32 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, Figure 1 As shown, the epitaxial layer 1 is an N-type low-doped epitaxial layer, the first doping region 2 is an N-type cathode high-doping region, the second doping region 3 is a P-type anode high-doping region, and the first doping region 2 is laterally spaced from the photosensitive region 11. During the preparation process, the order of forming the first doping region 2 and the second doping region 3 is not specifically limited.

[0095] In some embodiments, Figure 2As shown, the epitaxial layer is a P-type low-doped epitaxial layer, the first doping region 2 is an N-type floating low-doping region, the second doping region 3 is a P-type clamped high-doping region, the first doping region 2 is located in the photosensitive region 11, and the second doping region 3 is located on the first doping region 2. During the preparation process, the first doping region 2 is formed first, and then the second doping region 3 is formed on the first doping region 2.

[0096] According to the preparation method of the front-illuminated photodiode provided in the embodiment of the present application, the second doping region 3 in the photosensitive region 11 is patterned so that the second doping region 3 includes a photosensitive patterned region, the proportion of the second doping region 3 in the photosensitive region 11 is reduced, and the minimum lateral distance between each position in the photosensitive region 11 and the second doping region 3 is greater than 0, and less than the lateral diffusion length of the photogenerated minority carriers in the photosensitive region 11, so that the photogenerated minority carriers at each position in the photosensitive region 11 can be laterally diffused to the depletion region and collected, thereby reducing the proportion of the "dead zone" and improving the quantum efficiency, which can reach a level equivalent to that of the back-illuminated photodiode, and reducing the area of ​​the PN junction, reducing the total capacitance, thereby reducing the ADC electronic noise, and further improving the signal-to-noise ratio. In addition, there is no need to add an additional mask, thereby avoiding increasing the process complexity and avoiding increasing the production cost.

[0097] The terms "first", "second", etc. 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 the terms used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described herein, and the objects distinguished by "first", "second", etc. are generally of the same type, and the number of objects is not limited. For example, the first object can be one or more.

[0098] In the description of the present application, “plurality” means two or more.

[0099] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

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

Claims

1. A front-illuminated photodiode, characterized in that: include: epitaxial layers, including photosensitive regions; A first doped region, located in the epitaxial layer; A second doped region is located in the photosensitive region, the second doped region and the first doped region have a doping type opposite to that of the first doped region, and the second doped region is a high 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, and 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 photogenerated minority carriers in the photosensitive region.

2. The front-illuminated photodiode according to claim 1, characterized in that: The photosensitive patterned area includes a plurality of first highly doped sub-areas, and the plurality of first highly doped sub-areas are laterally spaced apart.

3. The front-illuminated photodiode according to claim 2, 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.

4. The front-illuminated photodiode according to claim 2, characterized in that: The first highly doped sub-region is a strip-shaped region.

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

6. The front-illuminated photodiode according to claim 5, 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.

7. The front-illuminated photodiode according to claim 1, characterized in that: The target distance range includes 2-100μm.

8. The front-illuminated photodiode according to any one of claims 1 to 7, characterized in that: The epitaxial layer is an N-type low-doped epitaxial layer, the first doped region is an N-type cathode high-doped region, the second doped region is a P-type anode high-doped region, and the first doped region is laterally spaced from the photosensitive region.

9. The front-illuminated photodiode according to claim 1, 5, 6 or 7, characterized in that: 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.

10. An X-ray detector, characterized in that: Comprising a front-illuminated photodiode as described in any one of claims 1-9.

11. A method for preparing a front-illuminated photodiode, characterized in that: include: providing an epitaxial layer, the epitaxial layer comprising a photosensitive region; forming a first doped region in the epitaxial layer; A second doped region is formed in the photosensitive region, wherein the doping type of the second doped region is opposite to that of the first doped region, and the second doped region is a high doped region; the second doped region includes a photosensitive patterned region, and the minimum lateral distance between any position in the photosensitive region and the second doped region is within a target distance range, and 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 photogenerated minority carriers in the photosensitive region.

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