Photoelectric detector and forming method thereof

Abstract

The invention discloses a photoelectric detector and a forming method thereof. The first well region is located in the substrate, and the substrate exposes the top surface of the first well region; the second well region is located in the substrate at the side part of the first well region, the top surface of the second well region is exposed out of the substrate, and the doping type of the second well region is different from that of the first well region; the drift region is located in the substrate between the first well region and the second well region, the top surface of the drift region is exposed out of the substrate, the side wall of one side of the drift region is in contact with or spaced from the side wall of the first well region, the side wall of the other side of the drift region is in contact with the side wall of the second well region, and the doping type of the drift region is the same as that of the second well region; the cathode contact region is located in the first well region, and the first well region is exposed out of the top surface of the cathode contact region; the anode contact region is located in the second well region, and the second well region is exposed out of the top surface of the anode contact region; and the gate structure is located at the top of the substrate at the junction of the first well region and the drift region. The photon detection efficiency of the photoelectric detector can be improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of semiconductor manufacturing, and in particular to a photodetector and a method for forming the same. Background Art

[0002] Silicon-based avalanche photodiode (APD) is widely used in photon detection fields such as lidar and 3D imaging due to its small size, low operating voltage, no influence of magnetic fields, low noise, good stability and the ability to operate at room temperature.

[0003] Photon detection efficiency (PDE) and dark count rate (DCR) are the two most critical performance parameters of APD devices. PDE is used to characterize the detection efficiency of APD devices for photons, which is related to the wavelength of photons and the quantum efficiency of the device. DCR is used to characterize the noise inside the APD device. A large DCR will seriously affect the detection distance and detection accuracy of the detector.

[0004] Currently, the performance of photodetectors still needs to be improved. Summary of the invention

[0005] The problem solved by the embodiments of the present invention is to provide a photodetector and a method for forming the same, which is beneficial to further improve the performance of the photodetector.

[0006] To solve the above problems, an embodiment of the present invention provides a photodetector, comprising: a substrate; a first well region, located in the substrate, the substrate exposing the top surface of the first well region; a second well region, located in the substrate at the side of the first well region, the substrate exposing the top surface of the second well region, and the doping type of the second well region is different from the doping type of the first well region; a drift region, located in the substrate between the first well region and the second well region, the substrate exposing the top surface of the drift region, and the sidewall on one side of the drift region is in contact with or spaced from the sidewall of the first well region, and the sidewall on the other side of the drift region is in contact with the sidewall of the second well region, and the doping type of the drift region is the same as the doping type of the second well region; a cathode contact region, located in the first well region, and the first well region exposing the top surface of the cathode contact region; an anode contact region, located in the second well region, and the second well region exposing the top surface of the anode contact region; a gate structure, located at the top of the substrate at the junction of the first well region and the drift region.

[0007] Optionally, the photodetector also includes: a first doped region, located at the bottom of the drift region, the top surface of the first doped region is in contact with the bottom surface of the drift region, the side wall of the first doped region is in contact with the side wall of the second well region, and the doping type of the first doped region is opposite to the doping type of the drift region.

[0008] Optionally, along a normal direction of the substrate surface, a thickness of the first doping region is 450 nanometers to 500 nanometers.

[0009] Optionally, with a direction perpendicular to an extension direction of the gate structure and parallel to the substrate surface as a lateral direction, a ratio of a lateral dimension of the first doping region to a lateral dimension of the drift region is greater than or equal to 60%.

[0010] Optionally, the photodetector further includes: a field oxide layer, located between the gate structure and the substrate, and on the top of the drift region.

[0011] Optionally, the material of the field oxide layer includes silicon oxide.

[0012] Optionally, along the normal direction of the substrate surface, the thickness of the field oxide layer is 12 nanometers to 14 nanometers.

[0013] Optionally, the photodetector further includes: a silicide blocking layer located on the top of the first well region, the top of the second well region, the top of the drift region, and the sidewall and a portion of the top of the gate structure.

[0014] Optionally, the material of the silicide blocking layer includes one or both of silicon oxide and silicon nitride.

[0015] Optionally, the photodetector also includes: a first interconnection line, located at the top of the cathode contact area and the top of the gate structure, the cathode contact area and the gate structure share the first interconnection line, the first interconnection line is electrically connected to the cathode contact area and to the gate structure, and the first interconnection line is connected to a negative potential; a second interconnection line, located at the top of the anode contact area, the second interconnection line is electrically connected to the anode contact area, and the second interconnection line is connected to a positive potential.

[0016] Optionally, along a normal direction of the substrate surface, a thickness of the second well region is 1750 nanometers to 1900 nanometers.

[0017] Correspondingly, an embodiment of the present invention also provides a method for forming a photodetector, comprising: providing a substrate, a first well region being formed in the substrate, the substrate exposing the top surface of the first well region, a second well region being also formed in the substrate, the substrate exposing the top surface of the second well region, and the doping type of the second well region is different from the doping type of the first well region, a drift region is formed in the substrate between the first well region and the second well region, the substrate exposing the top surface of the drift region, and the sidewall on one side of the drift region is in contact with or spaced from the sidewall of the first well region, the sidewall on the other side of the drift region is in contact with the sidewall of the second well region, and the doping type of the drift region is the same as the doping type of the second well region; forming a cathode contact region in the first well region, and the first well region exposing the top surface of the cathode contact region; forming an anode contact region in the second well region, and the second well region exposing the top surface of the anode contact region; after forming the cathode contact region and the anode contact region, forming a gate structure at the top of the substrate at the junction of the first well region and the drift region.

[0018] Optionally, the method for forming the photodetector also includes: forming a first doped region in the substrate located at the bottom of the drift region, the top surface of the first doped region is in contact with the bottom surface of the drift region, the side wall of the first doped region is in contact with the side wall of the second well region, and the doping type of the first doped region is opposite to the doping type of the drift region.

[0019] Optionally, the process of forming the first doping region at the bottom of the drift region includes an ion implantation process.

[0020] Optionally, after forming the cathode contact region and the anode contact region and before forming the gate structure, it also includes: forming a field oxide layer on the top of the substrate at the junction of the first well region and the drift region, and on the top of the drift region; in the step of forming the gate structure, the gate structure covers the top surface of the field oxide layer at the junction of the first well region and the drift region.

[0021] Optionally, after forming the gate structure, the method for forming the photodetector also includes: forming a silicide blocking layer on the top of the first well region, the top of the second well region, the top of the drift region, and the sidewalls and part of the top of the gate structure, the silicide blocking layer exposing the top surfaces of the cathode contact region and the anode contact region; forming a first interconnect line on the top surface of the cathode contact region exposed by the silicide blocking layer and on the top of the gate structure, the cathode contact region and the gate structure share the first interconnect line, the first interconnect line is electrically connected to the cathode contact region and to the gate structure, and the first interconnect line is connected to a negative potential; forming a second interconnect line on the top surface of the anode contact region, the second interconnect line is electrically connected to the anode contact region, and the second interconnect line is connected to a positive potential.

[0022] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0023] An embodiment of the present invention provides a method for forming a photodetector, wherein a drift region is formed in a substrate between a first well region and a second well region, the substrate exposes the top surface of the drift region, and the sidewall on one side of the drift region is in contact with or spaced from the sidewall of the first well region, and the sidewall on the other side of the drift region is in contact with the sidewall of the second well region, the doping type of the drift region is the same as the doping type of the second well region, a cathode contact region is formed in the first well region, and the first well region exposes the top surface of the cathode contact region, an anode contact region is formed in the second well region, and the second well region exposes the top surface of the anode contact region, and after the cathode contact region and the anode contact region are formed, a gate structure is formed on the top of the substrate at the junction of the first well region and the drift region. On the one hand, a depletion region is formed by utilizing the first well region and the drift region, and the drift region will be fully depleted under the action of a reverse voltage, thereby forming an avalanche region in the photodetector. Photogenerated carriers will be multiplied under the action of a strong electric field in the avalanche region, so that the photodetector can also work normally and play the function of a photodetector. On the other hand, compared with the existing photodetector in which the cathode contact layer and the anode contact layer are isolated by an isolation layer, compared with the existing photodetector in which an isolation layer is formed, the photodetector in the embodiment of the present invention does not form an isolation layer, which can avoid the dark count rate (DCR) of the photodetector being affected by surface defects of the isolation layer. Since the probability of the dark count rate of the photodetector being affected is reduced, the photon detection efficiency (PDE) of the photodetector can be improved, thereby improving the performance of the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure corresponding to a photoelectric detector;

[0025] Figure 2 is a schematic structural diagram of an embodiment of a photoelectric detector of the present invention;

[0026] Figures 3 to 9 It is a schematic structural diagram corresponding to each step in an embodiment of a method for forming a photodetector of the present invention. DETAILED DESCRIPTION

[0027] At present, the performance of photoelectric detectors still needs to be improved. Now we analyze the reasons why the performance of a photoelectric detector needs to be improved by combining it with a photoelectric detector.

[0028] Figure 1 It is a schematic diagram of the structure corresponding to a photoelectric detector.

[0029] The photodetector includes: a substrate 18; a first well region 14, located in the substrate 18; a second well region 12, located in the substrate 18 adjacent to the first well region 14, and the doping type of the second well region 12 is different from the doping type of the first well region 14; a shallow trench isolation structure 13, located in the substrate 18 on the side of the first well region 14, and in the substrate 18 on the side of the second well region 12; a third well region 15, located in the substrate 18 at the bottom of the first well region 14, the bottom of the second well region 12, and the bottom of the shallow trench isolation structure 13, and the doping type of the third well region 15 is the same as the doping type of the first well region 14; a silicide barrier layer 16, located on the top of the shallow trench isolation structure 13.

[0030] As an example, the type of doped ions in the first well region 14 is N-type ions; the type of doped ions in the second well region 12 is P-type ions; and the type of doped ions in the third well region 15 is N-type ions.

[0031] Research has found that the shallow trench isolation structure 13 provided in the photodetector can prevent the cathode electrically connected to the first well region 14 and the anode electrically connected to the second well region 12 from electrical breakdown on the surface. However, during the formation process of the shallow trench isolation structure 13, the bombardment of high-energy particles will cause the lattice at the surface of the trench isolation structure 13 to be destroyed, thereby forming defect energy levels. In the absence of light, the defect energy levels can assist the valence band electrons to transition to the conduction band to form free carriers. The free carriers cause the dark count rate of the photodetector to increase. In addition, due to the curvature of the trench isolation structure 13, the electric field lines are more concentrated and the local field strength is stronger. The larger field strength can also assist electron transitions, causing the dark count rate to increase, thereby reducing the performance of the photodetector.

[0032] In order to solve the technical problem, an embodiment of the present invention provides a method for forming a photodetector, including: providing a substrate, a first well region is formed in the substrate, the substrate exposes the top surface of the first well region, a second well region is also formed in the substrate, the substrate exposes the top surface of the second well region, and the doping type of the second well region is different from the doping type of the first well region, a drift region is formed in the substrate between the first well region and the second well region, the substrate exposes the top surface of the drift region, and the sidewall on one side of the drift region is in contact with or spaced from the sidewall of the first well region, the sidewall on the other side of the drift region is in contact with the sidewall of the second well region, and the doping type of the drift region is the same as the doping type of the second well region; forming a cathode contact region in the first well region, and the first well region exposes the top surface of the cathode contact region; forming an anode contact region in the second well region, and the second well region exposes the top surface of the anode contact region; after forming the cathode contact region and the anode contact region, forming a gate structure at the top of the substrate at the junction of the first well region and the drift region.

[0033] The embodiment of the present invention provides a method for forming a photodetector. On the one hand, a depletion region is formed by using a first well region and a drift region. Under the action of a reverse voltage, the drift region will be fully depleted, thereby forming an avalanche region in the photodetector. Photogenerated carriers will be multiplied under the action of a strong electric field in the avalanche region, so that the photodetector can also work normally and play the function of a photodetector. On the other hand, compared with the existing photodetector in which a cathode contact layer and an anode contact layer are isolated by an isolation layer, compared with the existing photodetector formed with an isolation layer, the photodetector of the embodiment of the present invention does not form an isolation layer, which can avoid the dark count rate (DCR) of the photodetector being affected by surface defects of the isolation layer. Since the probability of the dark count rate of the photodetector being affected is reduced, the photon detection efficiency (PDE) of the photodetector can be improved, thereby improving the performance of the photodetector.

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] Figure 2 It is a schematic structural diagram of an embodiment of a photoelectric detector of the present invention.

[0036] The photodetector comprises: a substrate 200; a first well region 203, located in the substrate 200, the substrate 200 exposing the top surface of the first well region 203; a second well region 201, located in the substrate 200 at the side of the first well region 203, the substrate 200 exposing the top surface of the second well region 201, the doping type of the second well region 201 is different from the doping type of the first well region 203; a drift region 202, located in the substrate 200 between the first well region 203 and the second well region 201, the substrate 200 exposing the top surface of the drift region 202, and the side wall of one side of the drift region 202 is aligned with the side wall of the drift region 202. The side walls of the first well region 203 are in contact or spaced apart, the side wall on the other side of the drift region 202 is in contact with the side wall of the second well region 201, and the doping type of the drift region 202 is the same as the doping type of the second well region 201; the cathode contact region 280 is located in the first well region 203, and the first well region 203 exposes the top surface of the cathode contact region 280; the anode contact region 206 is located in the second well region 201, and the second well region 201 exposes the top surface of the anode contact region 206; the gate structure 212 is located on the top of the substrate 200 at the junction of the first well region 203 and the drift region 202.

[0037] Specifically, on the one hand, a depletion region (not shown) is formed by utilizing the first well region 203 and the drift region 202, and the drift region 202 is fully depleted under the action of a reverse voltage, thereby forming an avalanche region in the photodetector, and photogenerated carriers are multiplied under the action of a strong electric field in the avalanche region, so that the photodetector can also work normally and function as a photodetector. On the other hand, compared with the existing photodetector in which the cathode contact layer and the anode contact layer are isolated by an isolation layer, compared with the existing photodetector in which an isolation layer is formed, no isolation layer is formed in the photodetector of the embodiment of the present invention, which can avoid the dark count rate (DCR) of the photodetector being affected by surface defects of the isolation layer. Since the probability of the dark count rate of the photodetector being affected is reduced, the photon detection efficiency (PDE) of the photodetector can be improved, thereby improving the performance of the photodetector.

[0038] The substrate 200 is used to provide a process platform for forming a photodetector. Specifically, the formed photodetector is LDMOS.

[0039] In this embodiment, taking the formed LDMOS as a planar transistor as an example, the base 200 is correspondingly a planar substrate.

[0040] In this embodiment, the substrate 200 is a silicon substrate. In other embodiments, the substrate may also be a substrate of other materials such as a germanium substrate, a silicon germanium substrate, a silicon carbide substrate, a gallium arsenide substrate, or an indium gallium substrate, and the substrate may also be a silicon on insulator substrate or a germanium on insulator substrate or other types of substrates.

[0041] In this embodiment, the first well region 203, the second well region 201 and the drift region 202 are arranged in the substrate 200, and the side wall of the drift region 202 on one side is in contact with or separated from the side wall of the first well region 203, the first well region 203 serves as a lateral diffusion region to form a channel with a concentration gradient, and the drift region 202 is used to withstand a larger partial pressure.

[0042] In this embodiment, the doping type of the second well region 201 is different from the doping type of the first well region 203, and the doping type of the drift region 202 is the same as the doping type of the second well region 201, which means that the doping type of the first well region 203 is different from the doping type of the drift region 202.

[0043] Specifically, the doping type of the first well region 203 is different from the doping type of the drift region 202, and the side wall of the drift region 202 on one side is in contact with or spaced from the side wall of the first well region 203, so that a PN junction is formed between the first well region 203 and the drift region 202, and a multiplication region is formed in the photodetector using the PN junction, that is, when the photodetector is under a higher reverse voltage, the free electrons and holes generated by the absorbed photons can be accelerated, thereby being able to obtain more energy, and colliding with the lattice in the substrate 200 to generate new electron-hole pairs, thereby causing a sharp increase in the photocurrent of the photodetector, resulting in current gain, and thus being able to improve the sensitivity and signal-to-noise ratio of the photodetector.

[0044] As an example, the doping ions in the first well region 203 are P-type ions, the doping ions in the drift region 202 are N-type ions, and the doping ions in the second well region 201 are N-type ions.

[0045] In other embodiments, the doping ions in the first well region may be N-type ions, the doping ions in the drift region may be P-type ions, and the doping ions in the second well region may be P-type ions.

[0046] In this embodiment, in the process of forming the first well region 203, the second well region 201 and the drift region 202, the first well region 203, the second well region 201 and the drift region 202 are respectively formed in different regions of the substrate 200 by selectively doping the substrate 200.

[0047] It should be noted that a relatively large surface electric field will be generated between the anode contact region 206 and the drift region 202. On the one hand, the second well region 201 plays a role of a slow change in concentration gradient between the anode contact region 206 and the drift region 202, thereby reducing the surface electric field between the anode contact region 206 and the drift region 202. On the other hand, the doped ions in the second well region 201 are more concentrated at the bottom, which will make the electric field strength at the bottom of the second well region 201 higher than the electric field strength on the surface, thereby being able to lead the surface electric field of the photodetector into the body, thereby reducing the surface electric field of the photodetector, thereby reducing the dark count rate (DCR) of the photodetector. The reduction in the dark count rate of the photodetector can improve the detection distance and detection accuracy of the photodetector. At the same time, the second well region 201 can also generate a depletion region between the first doped region formed subsequently, thereby increasing the volume of the avalanche region of the photodetector, thereby improving the photon detection efficiency of the photodetector.

[0048] It should also be noted that the thickness of the second well region 201 should not be too large or too small along the normal direction of the surface of the substrate 200. A negative voltage is applied to the first well region 103 through the cathode contact region, and a positive voltage is applied to the second well region 101 through the subsequently formed anode contact region. The voltage difference between the two can further increase the area of ​​the depletion region. If the thickness of the second well region 201 is too large, the process difficulty of injecting the second well region 201 into the substrate 200 is increased. At the same time, the concentration of the doped ions in the second well region gradually decreases when diffusing from bottom to top, so that the effect of further increasing the area of ​​the depletion region through the voltage difference is not significant; if the thickness of the second well region 201 is too small, it is easy to cause the second well region 201 to fail to fully cover the sidewall of the first doped region, reducing the volume of the depletion region generated between the second well region 201 and the first doped region, making the avalanche region of the photodetector smaller, thereby affecting the photon detection efficiency (PDE) of the photodetector. To this end, in this embodiment, along the normal direction of the surface of the substrate 200 , the thickness of the second well region 201 is 1750 nanometers to 1900 nanometers.

[0049] In this embodiment, the photodetector also includes: a first doped region 205, located at the bottom of the drift region 202, the top surface of the first doped region 205 is in contact with the bottom surface of the drift region 202, the side wall of the first doped region 205 is in contact with the side wall of the second well region 201, and the doping type of the first doped region 205 is opposite to the doping type of the drift region 202.

[0050] Specifically, the doping type of the first doping region 205 is opposite to the doping type of the drift region 202, so that a depletion region is generated between the first doping region 205 and the drift region 202, and a drift region 202 is generated between the first doping region 205 and the second well region 201, thereby increasing the volume of the avalanche region of the photodetector, thereby improving the photon detection efficiency of the photodetector.

[0051] In this embodiment, the doping type of the first doping region 205 is opposite to the doping type of the drift region 202 . As an example, the doping ions in the first doping region 205 are P-type ions.

[0052] It should be noted that, along the normal direction of the surface of the substrate 200, the thickness of the first doping region 205 should not be too large or too small. If the thickness of the first doping region 205 is too large, when the thickness of the drift region 202 meets the process requirements, it is easy to cause the depth of the first doping region 205 in the substrate 200 to be too large, and accordingly, it increases the process difficulty of forming the first doping region 205 in the substrate 200 through the ion implantation process; if the thickness of the first doping region 205 is too small, it is easy to cause the depletion region formed between the first doping region 205 and the second well region 201 to be too small, so that the avalanche region of the photodetector becomes smaller, thereby affecting the photon detection efficiency (PDE) of the photodetector. For this reason, in this embodiment, along the normal direction of the surface of the substrate 200, the thickness of the first doping region 205 is 450 nanometers to 500 nanometers.

[0053] It should also be noted that, with the direction perpendicular to the extension direction of the gate structure 212 and parallel to the surface of the substrate 200 as the lateral direction, the ratio of the lateral dimension of the first doping region 205 to the lateral dimension of the drift region 202 should not be too small. If the ratio of the lateral dimension of the first doping region 205 to the lateral dimension of the drift region 202 is too small, it is easy to cause the volume of the depletion region formed between the first doping region 205 and the drift region 202 to become smaller, so that the volume of the avalanche region of the photodetector is also reduced, thereby affecting the photon detection efficiency (PDE) of the photodetector. For this reason, in this embodiment, with the direction perpendicular to the extension direction of the gate structure 212 and parallel to the surface of the substrate 200 as the lateral direction, the ratio of the lateral dimension of the first doping region 205 to the lateral dimension of the drift region 202 is greater than or equal to 60%.

[0054] It should be noted that by setting a cathode contact area 280 and electrically connecting the cathode contact area 280 to the first interconnection line 230, a negative voltage signal can be provided to the photodetector through the first interconnection line 230, and by setting an anode contact area 206 and electrically connecting the anode contact area 206 to the second interconnection line 240, a positive voltage signal can be provided to the photodetector through the second interconnection line 240.

[0055] In this embodiment, the ions doped in the cathode contact region 280 are P-type ions, and the ions doped in the anode contact region 206 are N-type ions.

[0056] In this embodiment, the photodetector further includes a field oxide layer 208 located between the gate structure 212 and the substrate 200 and on the top of the drift region 202 .

[0057] Specifically, by setting the field oxide layer 208, the surface electric field of the drift region 202 can be weakened, thereby improving the photon detection efficiency of the photodetector. At the same time, by setting the field oxide layer 208, the breakdown voltage of the photodetector can be further improved, thereby achieving the effect of improving the breakdown voltage of the photodetector.

[0058] In this embodiment, the material of the field oxide layer 208 includes SiO 2 .

[0059] Specifically, SiO 2 It is a commonly used material for the field oxide layer 208, which has the advantages of low process cost and suitability for mass production. 2 The material can also weaken the surface electric field of the drift region 202 and improve the photon detection efficiency of the photodetector.

[0060] It should be noted that the thickness of the field oxide layer 208 along the normal direction of the surface of the substrate 200 should not be too large or too small. If the thickness of the field oxide layer 208 is too large, it is easy to cause the field oxide layer 208 to have an insignificant effect in reducing the electric field strength under the gate structure formed subsequently, increasing the probability of the photodetector breaking down, thereby affecting the performance of the semiconductor structure; if the thickness of the field oxide layer 208 is too small, the field oxide layer 208 is affected in weakening the surface electric field of the drift region 202, reducing the photon detection efficiency of the photodetector. At the same time, if the thickness of the field oxide layer 208 is too small, it also reduces the breakdown voltage of the photodetector, thereby reducing the effect of the breakdown voltage of the photodetector. For this reason, in the present embodiment, along the normal direction of the surface of the substrate 200, the thickness of the field oxide layer 208 is 12 nanometers to 14 nanometers.

[0061] The gate structure 212 is used to control the opening and closing of the photodetector channel.

[0062] In this embodiment, the material of the gate structure 212 is polysilicon.

[0063] As can be seen from the foregoing, a field oxide layer 208 is provided on the top of the substrate 200 at the junction of the first well region 203 and the drift region 202, and on the top of the drift region 202. Therefore, the gate structure 212 also covers the top surface of the field oxide layer 208 at the junction of the first well region 203 and the drift region 202.

[0064] In this embodiment, the photodetector further includes: a silicide blocking layer 220 located on the top of the first well region 203 , the top of the second well region 201 , the top of the drift region 202 , and the sidewall and a portion of the top of the gate structure 212 .

[0065] The silicide blocking layer 220 is provided to prevent the growth of the silicide layer, thereby ensuring the normal operation of the photodetector.

[0066] As an example, the material of the silicide blocking layer 220 is silicon oxide. In other embodiments, the material of the silicide blocking layer may also be silicon nitride, or the silicide blocking layer may also be a stacked structure consisting of a silicon oxide layer and a silicon nitride layer.

[0067] In this embodiment, the photodetector also includes: a first interconnection line 230, located on the top of the cathode contact layer and the top of the gate structure 212, the cathode contact layer and the gate structure 212 share the first interconnection line 230, and the first interconnection line 230 is electrically connected to the cathode contact layer and the gate structure 212, and the first interconnection line 230 is connected to a negative potential; a second interconnection line 240, located on the top of the anode contact layer, and the second interconnection line 240 is electrically connected to the anode contact layer, and the second interconnection line 240 is connected to a positive potential.

[0068] Specifically, by forming the first interconnection line 230 and the second interconnection line 240 , a voltage signal can be provided to the photodetector.

[0069] It should be noted that the PN junction electric field below the gate structure 212 is relatively strong and is very prone to breakdown. The cathode contact area 280 and the gate structure 212 share the first interconnect line 230, and the first interconnect line 230 is electrically connected to the cathode contact area 280 and the gate structure 212, so that a part of the electric field lines terminate at the gate structure 212, thereby reducing the electric field strength below the PN junction and increasing the breakdown voltage of the device, thereby further reducing the surface electric field below the gate structure 212, thereby reducing the dark count rate (DCR) of the photodetector. The dark count rate of the photodetector is reduced, which can improve the detection distance and detection accuracy of the photodetector.

[0070] In this embodiment, the materials of the first interconnection line 230 and the second interconnection line 240 include one or both of copper and aluminum.

[0071] Accordingly, an embodiment of the present invention also provides a method for forming a photodetector. Figures 3 to 9 , shows a schematic structural diagram corresponding to each step in an embodiment of a method for forming a photodetector of the present invention.

[0072] refer to Figure 3 , providing a substrate 100, wherein a first well region 103 is formed in the substrate 100, and the substrate 100 exposes the top surface of the first well region 103; a second well region 101 is also formed in the substrate 100, and the substrate 100 exposes the top surface of the second well region 101, and the doping type of the second well region 101 is different from the doping type of the first well region 103; a drift region 102 is formed in the substrate 100 between the first well region 103 and the second well region 101, and the substrate 100 exposes the top surface of the drift region 102, and the sidewall on one side of the drift region 102 is in contact with or spaced from the sidewall of the first well region 103, and the sidewall on the other side of the drift region 102 is in contact with the sidewall of the second well region 101, and the doping type of the drift region 102 is the same as the doping type of the second well region 101.

[0073] The substrate 100 is used to provide a process platform for the subsequent formation of a photodetector. Specifically, the formed photodetector is LDMOS.

[0074] Specifically, on the one hand, a depletion region (not shown) is formed by utilizing the first well region 103 and the drift region 102, and the drift region 102 is fully depleted under the action of a reverse voltage, thereby forming an avalanche region in the photodetector. Photogenerated carriers are multiplied under the action of a strong electric field in the avalanche region, so that the photodetector can also work normally and function as a photodetector. On the other hand, compared with the solution of isolating the cathode contact layer and the anode contact layer by an isolation layer in the existing photodetector, an isolation layer is not formed in the photodetector of the embodiment of the present invention, which can avoid the dark count rate (DCR) of the photodetector being affected by surface defects of the isolation layer. Since the probability of the dark count rate of the photodetector being affected is reduced, the photon detection efficiency (PDE) of the photodetector can be improved, thereby improving the performance of the photodetector.

[0075] In this embodiment, taking the formed LDMOS as a planar transistor as an example, the base 100 is correspondingly a planar substrate.

[0076] In this embodiment, the substrate 100 is a silicon substrate. In other embodiments, the substrate may also be a substrate of other materials such as a germanium substrate, a silicon germanium substrate, a silicon carbide substrate, a gallium arsenide substrate, or an indium gallium substrate, and the substrate may also be a silicon on insulator substrate or a germanium on insulator substrate or other types of substrates.

[0077] The first well region 103, the second well region 101 and the drift region 102 are formed in the substrate 100, and the side wall of the drift region 102 is in contact with or spaced apart from the side wall of the first well region 103. The first well region 103 serves as a lateral diffusion region to form a channel with a concentration gradient, and the drift region 102 is used to withstand a larger partial pressure.

[0078] In this embodiment, the doping type of the second well region 101 is different from the doping type of the first well region 103 , and the doping type of the drift region 102 is the same as the doping type of the second well region 101 , which means that the doping type of the first well region 103 is different from the doping type of the drift region 102 .

[0079] Specifically, the doping type of the first well region 103 is different from the doping type of the drift region 102, and the side wall of the drift region 102 on one side is in contact with or spaced from the side wall of the first well region 103, so that a PN junction is formed between the first well region 103 and the drift region 102, and a multiplication region is formed in the photodetector using the PN junction, that is, when the photodetector is under a higher reverse voltage, the free electrons and holes generated by the absorbed photons can be accelerated, thereby being able to obtain more energy, and colliding with the lattice in the substrate 100 to generate new electron-hole pairs, thereby causing a sharp increase in the photocurrent of the photodetector, resulting in current gain, thereby being able to improve the sensitivity and signal-to-noise ratio of the photodetector.

[0080] As an example, the doping ions in the first well region 103 are P-type ions, the doping ions in the drift region 102 are N-type ions, and the doping ions in the second well region 101 are N-type ions.

[0081] In other embodiments, the doping ions in the first well region may be N-type ions, the doping ions in the drift region may be P-type ions, and the doping ions in the second well region may be P-type ions.

[0082] In this embodiment, by selectively performing a doping process on the substrate 100 , the first well region 103 , the second well region 101 and the drift region 102 are respectively formed in different regions of the substrate 100 .

[0083] As an example, the process of performing doping treatment on the substrate 100 includes an ion implantation process.

[0084] It should be noted that a relatively large surface electric field will be generated between the subsequently formed anode contact region and the drift region 102. On the one hand, the second well region 101 plays a role of a gradual change in concentration gradient between the anode contact region and the drift region 102, thereby reducing the surface electric field between the anode contact region and the drift region 102. On the other hand, the doped ions in the second well region 101 are more concentrated at the bottom, which will make the electric field strength at the bottom of the second well region 101 higher than the electric field strength on the surface, thereby being able to lead the surface electric field of the photodetector into the body, thereby reducing the surface electric field of the photodetector, thereby reducing the dark count rate (DCR) of the photodetector. The reduction in the dark count rate of the photodetector can improve the detection distance and detection accuracy of the photodetector. At the same time, the second well region 101 can also generate a depletion region with the subsequently formed first doping region, thereby increasing the volume of the avalanche region of the photodetector, thereby improving the photon detection efficiency of the photodetector.

[0085] It should also be noted that the thickness of the second well region 101 should not be too large or too small along the normal direction of the surface of the substrate 100. A negative voltage is applied to the first well region 103 through the cathode contact region formed subsequently, and a positive voltage is applied to the second well region 101 through the anode contact region formed subsequently. The voltage difference between the two can further increase the area of ​​the depletion region. If the thickness of the second well region 101 is too large, the process difficulty of injecting the second well region 101 into the substrate 100 is increased. At the same time, the concentration of the doped ions in the second well region gradually decreases when diffusing from bottom to top, so that the effect of further increasing the area of ​​the depletion region by the voltage difference is not significant; if the thickness of the second well region 101 is too small, it is easy to cause the second well region 101 to fail to fully cover the sidewalls of the first doped region formed subsequently, reducing the volume of the depletion region generated between the second well region 101 and the first doped region, making the avalanche region of the photodetector smaller, thereby affecting the photon detection efficiency (PDE) of the photodetector. To this end, in this embodiment, along the normal direction of the surface of the substrate 100 , the thickness of the second well region 101 is 1750 nanometers to 1900 nanometers.

[0086] refer to Figure 4 A first doped region 105 is formed in the substrate 100 and is located at the bottom of the drift region 102. The top surface of the first doped region 105 is in contact with the bottom surface of the drift region 102, the side wall of the first doped region 105 is in contact with the side wall of the second well region 101, and the doping type of the first doped region 105 is opposite to the doping type of the drift region 102.

[0087] Specifically, the doping type of the first doping region 105 is opposite to the doping type of the drift region 102, so that a depletion region is generated between the first doping region 105 and the drift region 102, and a drift region 102 is generated between the first doping region 105 and the second well region 101, thereby increasing the volume of the avalanche region of the photodetector, thereby improving the photon detection efficiency of the photodetector.

[0088] In this embodiment, the process of forming the first doping region 105 located at the bottom of the drift region 102 in the substrate 100 includes an ion implantation process.

[0089] It should be noted that the ion implantation process has the characteristics of high ion implantation accuracy and excellent process controllability. By selecting the ion implantation process to form the first doped region 105, the implantation depth of the first doped region 105 in the substrate 100 can meet the process requirements, so that the top surface of the first doped region 105 can contact the bottom surface of the drift region 102, and the side wall of the first doped region 105 can contact the side wall of the second well region 101.

[0090] In this embodiment, the doping type of the first doping region 105 is opposite to the doping type of the drift region 102 . As an example, the doping ions in the first doping region 105 are P-type ions.

[0091] It should be noted that, along the normal direction of the surface of the substrate 100, the thickness of the first doping region 105 should not be too large or too small. If the thickness of the first doping region 105 is too large, when the thickness of the drift region 102 meets the process requirements, it is easy to cause the depth of the first doping region 105 in the substrate 100 to be too large, and accordingly, it increases the process difficulty of forming the first doping region 105 in the substrate 100 through the ion implantation process; if the thickness of the first doping region 105 is too small, it is easy to cause the depletion region formed between the first doping region 105 and the second well region 101 to be too small, so that the avalanche region of the photodetector becomes smaller, thereby affecting the photon detection efficiency (PDE) of the photodetector. For this reason, in this embodiment, along the normal direction of the surface of the substrate 100, the thickness of the first doping region 105 is 450 nanometers to 500 nanometers.

[0092] It should also be noted that, with the direction perpendicular to the extension direction of the gate structure and parallel to the surface of the substrate 100 as the lateral direction, the ratio of the lateral dimension of the first doping region 105 to the lateral dimension of the drift region 102 should not be too small. If the ratio of the lateral dimension of the first doping region 105 to the lateral dimension of the drift region 102 is too small, it is easy to cause the volume of the depletion region formed between the first doping region 105 and the drift region 102 to become smaller, so that the volume of the avalanche region of the photodetector is also reduced, thereby affecting the photon detection efficiency (PDE) of the photodetector. For this reason, in this embodiment, with the direction perpendicular to the extension direction of the gate structure and parallel to the surface of the substrate 100 as the lateral direction, the ratio of the lateral dimension of the first doping region 105 to the lateral dimension of the drift region 102 is greater than or equal to 60%.

[0093] refer to Figure 5 , a cathode contact region 180 is formed in the first well region 103, and the first well region 103 exposes the top surface of the cathode contact region 180; an anode contact region 106 is formed in the second well region 101, and the second well region 101 exposes the top surface of the anode contact region 106.

[0094] It should be noted that, by forming the cathode contact area 180, the cathode contact area 180 can be electrically connected to the first interconnection line formed subsequently, so that a negative voltage signal can be provided to the photodetector through the first interconnection line, and by forming the anode contact area 106, the anode contact area 106 can be electrically connected to the second interconnection line formed subsequently, so that a positive voltage signal can be provided to the photodetector through the second interconnection line.

[0095] In this embodiment, the steps of forming the cathode contact region 180 and the anode contact region 106 include: forming a first graphic layer (not shown) on the top of the substrate 100, the first graphic layer covering the drift region 102 and the second well region 101, and a portion of the top surface of the first well region 103; using the first graphic layer as a mask, doping the exposed first well region 103 to form the cathode contact region 180; after forming the cathode contact region 180, removing the first graphic layer; forming a second graphic layer (not shown) on the top of the substrate 100, the second graphic layer covering the top of the drift region 102 and the first well region 103, the top of the cathode contact region 180, and a portion of the top surface of the second well region 101; using the second graphic layer as a mask, doping the exposed second well region 101 to form the anode contact region 106; removing the second graphic layer.

[0096] In this embodiment, the material of the first pattern layer and the material of the second pattern layer are both photoresist.

[0097] Specifically, in the process of forming the cathode contact region 180 and the anode contact region 106, the photoresist can play a protective role, that is, it is difficult for the doped ions to pass through the photoresist, thereby reducing the probability of doped ions in the first well region 103, the second well region 101 and the drift region 102 covered by the photoresist. At the same time, the photoresist has the characteristic of being easy to remove, thereby reducing the probability of residual photoresist on the top of the photodetector.

[0098] In this embodiment, the process of performing doping treatment on the exposed first well region 103 and the process of performing doping treatment on the exposed second well region 101 include an ion implantation process.

[0099] In this embodiment, the process of removing the first pattern layer and the second pattern layer includes an ashing process.

[0100] In this embodiment, the ions doped in the cathode contact region 180 are P-type ions, and the ions doped in the anode contact region 106 are N-type ions.

[0101] refer to Figure 6 After forming the cathode contact region 180 and the anode contact region 106 , and before subsequently forming the gate structure, the method further includes: forming a field oxide layer 108 on the top of the substrate 100 at the junction of the first well region 103 and the drift region 102 , and on the top of the drift region 102 .

[0102] Specifically, by forming the field oxide layer 108, the surface electric field of the drift region 102 can be weakened, thereby improving the photon detection efficiency of the photodetector. At the same time, by forming the field oxide layer 108, the breakdown voltage of the photodetector can be further improved, thereby achieving the effect of improving the breakdown voltage of the photodetector.

[0103] In this embodiment, the material of the field oxide layer 108 includes SiO 2 .

[0104] Specifically, SiO 2 It is a commonly used material for the field oxide layer 108, has low process cost and is suitable for mass production. 2 The material can also weaken the surface electric field of the drift region 102 and improve the photon detection efficiency of the photodetector.

[0105] In this embodiment, the process of forming the field oxide layer 108 includes a local oxidation of silicon (LOCOS) process. 2 The silicon oxide is diffused in various directions and reacts with the substrate 100 to form silicon oxide.

[0106] It should be noted that the thickness of the field oxide layer 108 along the normal direction of the surface of the substrate 100 should not be too large or too small. If the thickness of the field oxide layer 108 is too large, it is easy to cause the field oxide layer 108 to have an insignificant effect in reducing the electric field strength under the gate structure formed subsequently, increasing the probability of the photodetector breaking down, thereby affecting the performance of the semiconductor structure; if the thickness of the field oxide layer 108 is too small, the field oxide layer 108 is affected in weakening the surface electric field of the drift region 102, reducing the photon detection efficiency of the photodetector. At the same time, if the thickness of the field oxide layer 108 is too small, it also reduces the breakdown voltage of the photodetector, thereby reducing the effect of the breakdown voltage of the photodetector. For this reason, in the present embodiment, along the normal direction of the surface of the substrate 100, the thickness of the field oxide layer 108 is 12 nanometers to 14 nanometers.

[0107] refer to Figure 7 After forming the cathode contact region 180 and the anode contact region 106 , a gate structure 112 is formed on the top of the substrate 100 at the junction of the first well region 103 and the drift region 102 .

[0108] The gate structure 112 is used to control the opening and closing of the photodetector channel.

[0109] It should be noted that, after forming the cathode contact region 180 and the anode contact region 106 , the gate structure 112 is formed, which can reduce the risk of the gate structure 112 being doped with ions and improve the electrical performance of the gate structure 112 .

[0110] In this embodiment, the material of the gate structure 112 is polysilicon.

[0111] As can be seen from the above, a field oxide layer 108 is formed on the top of the substrate 100 at the junction of the first well region 103 and the drift region 102, and on the top of the drift region 102. Therefore, in the step of forming the gate structure 112, the gate structure 112 also covers the top surface of the field oxide layer 108 at the junction of the first well region 103 and the drift region 102.

[0112] In this embodiment, the step of forming the gate structure 112 includes: forming a gate material layer covering the first well region 103, the drift region 102 and the second well region 101; performing a patterning process on the gate material layer to retain the gate material layer on the top of the substrate 100 at the junction of the first well region 103 and the drift region 102, and using the gate material layer on the top of the substrate 100 at the junction of the first well region 103 and the drift region 102 as the gate structure 112.

[0113] In this embodiment, the gate material layer is patterned by a dry etching process.

[0114] Specifically, the gate material layer is patterned by a dry etching process, which can effectively improve the sidewall morphology quality of the gate structure 112 .

[0115] refer to Figure 8 After forming the gate structure 112, the method for forming the photodetector further includes: forming a silicide block (SAB) layer on the top of the first well region 103, the top of the second well region 101, the top of the drift region 102, and the sidewalls and part of the top of the gate structure 112, wherein the silicide block layer 120 exposes the top surfaces of the cathode contact region 180 and the anode contact region 106.

[0116] By forming the silicide blocking layer 120, the subsequent growth of a silicide layer is prevented, thereby ensuring the normal operation of the photodetector.

[0117] In this embodiment, the silicide blocking layer 120 is formed by a deposition process, a photolithography process, and an etching process.

[0118] As an example, the material of the silicide blocking layer 120 is silicon oxide. In other embodiments, the material of the silicide blocking layer may also be silicon nitride, or the silicide blocking layer may also be a stacked structure consisting of a silicon oxide layer and a silicon nitride layer.

[0119] refer to Fig. 9 A first interconnect line 130 is formed on the top surface of the cathode contact area 180 exposed by the silicide blocking layer 120 and on the top of the gate structure 112, the cathode contact area 180 and the gate structure 112 share the first interconnect line 130, and the first interconnect line 130 is electrically connected to the cathode contact area 180 and the gate structure 112, and the first interconnect line 130 is connected to a negative potential; a second interconnect line 140 is formed on the top surface of the anode contact area 106, and the second interconnect line 140 is electrically connected to the anode contact area 106, and the second interconnect line 140 is connected to a positive potential.

[0120] Specifically, by forming the first interconnection line 130 and the second interconnection line 140 , a voltage signal can be provided to the photodetector.

[0121] It should be noted that the PN junction electric field below the gate structure 112 is relatively strong and is very prone to breakdown. The cathode contact area 180 and the gate structure 112 share the first interconnect line 130, and the first interconnect line 130 is electrically connected to the cathode contact area 180 and the gate structure 112, so that a part of the electric field lines terminate at the gate structure 112, thereby reducing the electric field strength below the PN junction and increasing the breakdown voltage of the device, and further reducing the surface electric field below the gate structure 112, thereby reducing the dark count rate (DCR) of the photodetector. The dark count rate of the photodetector is reduced, and the detection distance and detection accuracy of the photodetector can be improved.

[0122] In this embodiment, the materials of the first interconnection line 130 and the second interconnection line 140 include one or both of copper and aluminum.

[0123] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A photoelectric detector, characterized in that: include: substrate; A first well region is located in the substrate, and the substrate exposes a top surface of the first well region; A second well region is located in the substrate at the side of the first well region, the substrate exposes a top surface of the second well region, and the doping type of the second well region is different from the doping type of the first well region; a drift region, located in the substrate between the first well region and the second well region, wherein the substrate exposes a top surface of the drift region, and a sidewall on one side of the drift region is in contact with or spaced from a sidewall of the first well region, and a sidewall on the other side of the drift region is in contact with a sidewall of the second well region, and a doping type of the drift region is the same as a doping type of the second well region; A cathode contact region, located in the first well region, and the first well region exposes a top surface of the cathode contact region; an anode contact region, located in the second well region, and the second well region exposes a top surface of the anode contact region; The gate structure is located on the top of the substrate at the junction of the first well region and the drift region.

2. The photodetector according to claim 1, wherein: The photodetector also includes: a first doped region located at the bottom of the drift region, the top surface of the first doped region contacts the bottom surface of the drift region, the side wall of the first doped region contacts the side wall of the second well region, and the doping type of the first doped region is opposite to the doping type of the drift region.

3. The photodetector according to claim 2, wherein: Along the normal direction of the substrate surface, the thickness of the first doping region is 450 nanometers to 500 nanometers.

4. The photodetector according to claim 2, wherein: Taking the direction perpendicular to the extension direction of the gate structure and parallel to the surface of the substrate as the lateral direction, the ratio of the lateral dimension of the first doping region to the lateral dimension of the drift region is greater than or equal to 60%.

5. The photodetector according to claim 1, wherein: The photodetector further includes a field oxide layer located between the gate structure and the substrate and on the top of the drift region.

6. The photodetector according to claim 5, characterized in that The material of the field oxide layer includes silicon oxide.

7. The photodetector according to claim 5, characterized in that Along the normal direction of the substrate surface, the thickness of the field oxide layer is 12 nanometers to 14 nanometers.

8. The photodetector according to claim 1, wherein: The photodetector further includes: a silicide blocking layer located on a top of the first well region, a top of the second well region, a top of the drift region, and a sidewall and a portion of a top of the gate structure.

9. The photodetector according to claim 8, wherein: The material of the silicide blocking layer includes one or both of silicon oxide and silicon nitride.

10. The photodetector according to claim 1, wherein: The photodetector further includes: a first interconnection line, located on the top of the cathode contact region and the top of the gate structure, the cathode contact region and the gate structure share the first interconnection line, and the first interconnection line is electrically connected to the cathode contact region and the gate structure, and the first interconnection line is connected to a negative potential; The second interconnection line is located on the top of the anode contact area, and the second interconnection line is electrically connected to the anode contact area, and the second interconnection line is connected to a positive potential.

11. The photodetector according to claim 1, wherein: Along the normal direction of the substrate surface, the thickness of the second well region is 1750 nanometers to 1900 nanometers.

12. A method for forming a photodetector, characterized in that: include: A substrate is provided, wherein a first well region is formed in the substrate, the substrate exposes a top surface of the first well region, a second well region is further formed in the substrate, the substrate exposes a top surface of the second well region, and a doping type of the second well region is different from a doping type of the first well region, a drift region is formed in the substrate between the first well region and the second well region, the substrate exposes a top surface of the drift region, a sidewall on one side of the drift region is in contact with or spaced from a sidewall of the first well region, a sidewall on the other side of the drift region is in contact with a sidewall of the second well region, and a doping type of the drift region is the same as a doping type of the second well region; forming a cathode contact region in the first well region, wherein the first well region exposes a top surface of the cathode contact region; forming an anode contact region in the second well region, wherein the second well region exposes a top surface of the anode contact region; After the cathode contact region and the anode contact region are formed, a gate structure is formed on the top of the substrate at the junction of the first well region and the drift region.

13. The method for forming a photodetector according to claim 12, further comprising: A first doped region is formed in the substrate and is located at the bottom of the drift region. The top surface of the first doped region contacts the bottom surface of the drift region, the sidewall of the first doped region contacts the sidewall of the second well region, and the doping type of the first doped region is opposite to the doping type of the drift region.

14. The method for forming a photodetector according to claim 12, wherein: The process of forming the first doping region at the bottom of the drift region in the substrate includes an ion implantation process.

15. The method for forming a photodetector according to claim 12, wherein: After forming the cathode contact region and the anode contact region and before forming the gate structure, the method further includes: forming a field oxide layer on the top of the substrate at the junction of the first well region and the drift region and on the top of the drift region; In the step of forming the gate structure, the gate structure covers a top surface of the field oxide layer at the junction of the first well region and the drift region.

16. The method for forming a photodetector according to claim 12, wherein: After forming the gate structure, the method for forming the photodetector further includes: forming a silicide barrier layer on the top of the first well region, the top of the second well region, the top of the drift region, and the sidewall and part of the top of the gate structure, wherein the silicide barrier layer exposes the top surfaces of the cathode contact region and the anode contact region; forming a first interconnection line on the top surface of the cathode contact region exposed by the silicide barrier layer and on the top of the gate structure, wherein the cathode contact region and the gate structure share the first interconnection line, and the first interconnection line is electrically connected to the cathode contact region and the gate structure, and the first interconnection line is connected to a negative potential; A second interconnection line is formed on the top surface of the anode contact region, and the second interconnection line is electrically connected to the anode contact region, and the second interconnection line is connected to a positive potential.

Images