Photodiode structure and preparation method

Abstract

The present invention provides a photodiode structure and a preparation method, belonging to the field of semiconductor technology. The photodiode structure includes: a substrate, a cutoff ring, a guard ring, an anti-inversion terminal and a neutralization layer are arranged on the substrate, the cutoff ring, the guard ring, the anti-inversion terminal and the neutralization layer are all obtained by doping on the substrate, the front of the substrate is sequentially provided with an oxide layer, a hole, a front metal layer and an insulating layer, the back of the substrate is injected with ions, and the back of the substrate is provided with a metal layer; wherein: the cutoff ring is close to the outermost edge of the substrate; the anti-inversion terminal includes an area from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; the neutralization layer is located between the guard ring and the cutoff ring, and the neutralization layer penetrates through the surface of the anti-inversion terminal into the body of the anti-inversion terminal. The area with high ion concentration can be transferred from the surface to the body, which reduces the surface electric field, reduces the surface leakage current, and improves the lateral withstand voltage of the device.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a photodiode structure and a photodiode preparation method. Background Art

[0002] An important parameter of a photodiode is the dark (leakage) current, which is required to be small, in the order of nA. If the dark current is large, the detection noise will be large and the yield will be reduced. For example, APD (Avalanche Photodiode), abbreviated as APD photodiode, has an avalanche multiplication function compared to ordinary photodiodes. The electron-hole pairs generated by light are avalanche multiplied by 10 to 100 times, which significantly improves the detection sensitivity of APD photodiodes.

[0003] The dark current parameter of the photodiode is unqualified. The main reasons are as follows: 1. Dark current in the photosensitive area: injection damage repair and anti-reflection layer interface. 2. Dark current at the lateral terminal of the device: the field oxide layer fixes cations and mobile Na+ ions, causing the lightly doped P-type substrate to invert to N, causing leakage. Figure 1 and Figure 2 It can be seen from the comparison.

[0004] In order to reduce the dark current of the lateral terminal of the second type of device, the existing technology mainly reduces the introduction of Na+ ions, and the main means are to purchase expensive cleaning and diffusion equipment, and strengthen the supporting clean facilities and management of the workshop. However, due to factors such as workshop employees and natural consumption of NaCl salt, Na+ cannot be eradicated, and the effect is discounted. In addition, because silicon dioxide has the physical properties of absorbing boron and expelling phosphorus, the surface P-type ion concentration is further reduced, making it easier to invert to N.

[0005] Therefore, the existing photodiode structure has the problem of being unable to effectively reduce the lateral terminal dark current. Summary of the invention

[0006] The purpose of the embodiments of the present invention is to provide a photodiode structure and a method for preparing a photodiode, wherein the photodiode structure can effectively achieve low leakage current and high lateral withstand voltage of the diode.

[0007] In order to achieve the above-mentioned object, the first aspect of the present application provides a photodiode structure, including a substrate, on which a cutoff ring, a guard ring, an anti-inversion terminal, a photosensitive region and a neutralization layer are arranged, and the cutoff ring, the guard ring, the anti-inversion terminal and the neutralization layer are all obtained by doping on the substrate, and the front side of the substrate is sequentially provided with an oxide layer, a hole, a front metal layer and an insulating layer, and the back side of the substrate is injected with ions, and the back side of the substrate is provided with a metal layer; wherein:

[0008] The cut-off ring is close to the outermost edge of the substrate;

[0009] The anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration;

[0010] The neutralization layer is located between the protection ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-reflection type terminal and goes deep into the body of the anti-reflection type terminal.

[0011] In the embodiment of the present application, there are multiple guard rings, and the neutralization layer is located between the guard ring closest to the cut-off ring and the cut-off ring.

[0012] In an embodiment of the present application, there are multiple neutralization layers, and the multiple neutralization layers are arranged at intervals between the protection ring and the cut-off ring.

[0013] In the embodiment of the present application, there are multiple guard rings and multiple neutralization layers, one of which is located between the guard ring closest to the cut-off ring and the cut-off ring, and the other neutralization layers are respectively located between two guard rings.

[0014] In an embodiment of the present application, the ions in the neutralization layer are P-ions, an N-type structure is provided between the guard ring and the cut-off ring, and the neutralization layer is located on the N-type structure.

[0015] In the embodiment of the present application, the concentration of the anti-reflection terminal at a distance of 0 to 1 um from the substrate surface is lower than the concentration at a distance of 2 to 3 um from the substrate surface.

[0016] A second aspect of the present application provides a photodiode preparation method for preparing the above-mentioned photodiode structure, the photodiode preparation method comprising:

[0017] A cut-off ring, a guard ring and a photosensitive area are sequentially constructed on the substrate, wherein the cut-off ring is close to the outermost edge of the substrate;

[0018] constructing an anti-inversion terminal on the substrate, wherein the anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and a surface doping concentration of the anti-inversion terminal is higher than a body doping concentration;

[0019] Constructing a neutralization layer on the substrate, wherein the neutralization layer is located between the guard ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-reflection terminal and penetrates into the body of the anti-reflection terminal;

[0020] sequentially constructing a hole, a front metal layer and an insulating layer on the front side of the substrate;

[0021] Ions are implanted into the back side of the substrate to construct a back side metal layer.

[0022] In an embodiment of the present application, there are multiple guard rings, and a neutralization layer is constructed on the substrate, including:

[0023] A neutralizing layer is formed on the substrate in a region between a guard ring closest to the stop ring and the stop ring.

[0024] In an embodiment of the present application, a neutralization layer is constructed on the substrate, including:

[0025] A plurality of neutralization layers are formed at intervals in the region between the guard ring and the stop ring on the substrate.

[0026] In an embodiment of the present application, there are multiple guard rings, and a neutralization layer is constructed on the substrate, including:

[0027] Constructing a neutralization layer in a region between a guard ring closest to the cut-off ring and the cut-off ring on the substrate;

[0028] A neutralization layer is respectively constructed in the region between any two guard rings on the substrate.

[0029] In an embodiment of the present application, the ions in the neutralization layer are P-ions, and the neutralization layer is constructed on the substrate, including:

[0030] An N-type structure is constructed in the area between the guard ring and the cut-off ring on the substrate;

[0031] Performing photolithography on the N-type structure and injecting a second dopant into the substrate to form a second terminal doping region, wherein the second dopant is a P- ion;

[0032] The photoresist of the substrate where the second terminal doping region is formed is removed to expose the second terminal doping region to obtain a neutralization layer.

[0033] Through the above technical scheme, by arranging a cut-off ring, a guard ring, an anti-inversion terminal, a photosensitive area and a neutralization layer on the substrate, the front side of the substrate is sequentially provided with an oxide layer, a hole, a front metal layer and an insulating layer, ions are injected into the back side of the substrate, and a metal layer is arranged on the back side of the substrate; wherein: the cut-off ring is close to the outermost edge of the substrate; the anti-inversion terminal includes an area from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; the neutralization layer is located between the guard ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-inversion terminal into the body of the anti-inversion terminal. The anti-inversion structure is formed by diffuse doping, and its surface concentration is relatively high. On the basis of the anti-inversion structure, a neutralization layer is added, and the part with a higher surface concentration of the anti-inversion structure is neutralized by the newly added neutralization layer to form a neutralization layer with a low doping concentration, so that the area with high ion concentration can be transferred from the surface to the body, reducing the surface electric field, reducing the surface leakage current, and also improving the lateral withstand voltage of the device. The sensitivity of the device to Na+ ions is also reduced, and the workshop equipment and management costs are reduced.

[0034] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0036] Figure 1 The schematic diagram of the original APD photodiode structure is shown schematically;

[0037] Figure 2 The schematic diagram of the oxide layer inducing N-inversion is shown;

[0038] Figure 3 A schematic diagram of the structure of an APD photodiode with a novel junction terminal structure according to an embodiment of the present application is shown;

[0039] Figure 4 A schematic diagram of a process flow diagram of a novel APD structure according to an embodiment of the present application is shown;

[0040] Figure 5 A schematic diagram of a terminal structure 2-section according to an embodiment of the present application is shown schematically;

[0041] Figure 6 A schematic diagram showing a two-stage diagram of adding an N-type structure to the terminal structure according to an embodiment of the present application;

[0042] Figure 7The diagram schematically shows a terminal NP swap according to an embodiment of the present application. DETAILED DESCRIPTION

[0043] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0044] It should be noted that, in order to facilitate the description of the scheme, this embodiment is mainly described with APD avalanche photodiodes. Compared with ordinary photodiodes, APD photodiodes have added an avalanche multiplication function. The electron-hole pairs generated by light are avalanche multiplied by 10 to 100 times, which significantly improves the detection sensitivity of APD photodiodes. Because the avalanche effect of electrons is better than that of holes, APD devices are all electron avalanche type. In terms of substrate selection, ordinary photodiodes can use P-type semiconductor wafer substrates or N-type; while APD devices must use P-type substrates. The P-type substrate serves as a photosensitive absorption layer, and the electron-hole pairs generated by light. The electrons are negatively charged and flow to the positive electrode with a positive voltage, and are amplified by a PN junction avalanche; the holes are positively charged and flow directly to the negative electrode. APD photodiodes use lightly doped P-type substrates with a capacitance of more than 1000 ohms / cm.

[0045] Please see Figure 3 , Figure 3 The schematic diagram of the APD photodiode structure of the novel junction terminal structure according to the embodiment of the present application is schematically shown. This embodiment provides a photodiode structure, including a substrate, on which a cutoff ring, a guard ring, an anti-inversion terminal, a photosensitive area and a neutralization layer are arranged, and the cutoff ring, the guard ring, the anti-inversion terminal and the neutralization layer are all obtained by doping on the substrate, the front side of the substrate is sequentially provided with an oxide layer, a hole, a front metal layer and an insulating layer, the back side of the substrate is injected with ions, and the back side of the substrate is provided with a metal layer; wherein: the cutoff ring is close to the outermost edge of the substrate; the anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; the neutralization layer is located between the guard ring and the cutoff ring, and the neutralization layer penetrates through the surface of the anti-inversion terminal into the body of the anti-inversion terminal.

[0046] In this embodiment, the substrate is a doped substrate, which may be doped P- or N-, and the corresponding substrate may be a substrate P- or N-. In order to facilitate the description of the scheme, this embodiment mainly describes the scheme with substrate P-. The cut-off ring, guard ring, anti-inversion terminal and neutralization layer are all obtained by doping on the substrate. The cut-off ring is near the edge of the substrate. The guard ring may be one or more. The guard ring and the cut-off ring are obtained by injecting dopants into the corresponding positions, and the dopants in the guard ring and the cut-off ring are different. For example, the cut-off ring is injected with P+, and the guard ring is injected with N. The area where the anti-inversion terminal is located is the area from the guard ring to the outermost edge of the substrate. The whole is a ring, which can be obtained by injecting P in this area. The anti-inversion terminal formed is a P anti-inversion terminal. The anti-inversion terminal includes a surface part and a body part in sequence from the substrate surface to the inside of the substrate, wherein the doping concentration of the surface part is lower than that of the body part. The neutralization layer is between the guard ring and the cut-off ring. The neutralization layer is an annular region. The N-neutralization layer can be obtained by doping N in the region. The depth of the neutralization layer extends from the surface of the anti-reflection terminal to the body of the anti-reflection terminal. The specific depth can be determined according to actual conditions. A photosensitive area is also provided on the substrate. The front side of the substrate refers to the side with the cut-off ring, the guard ring, the anti-reflection terminal and the neutralization layer, and the other side is the bottom side of the substrate.

[0047] It should be noted that the oxide layer, holes, front metal layer and insulating layer on the front side of the substrate can be realized by using existing technologies, which will not be described in detail here. Ion implantation on the back side of the substrate and the metal layer on the back side of the substrate can be realized by using existing technologies, which will not be described in detail here.

[0048] In the above implementation process, a cut-off ring, a guard ring, an anti-inversion terminal, a photosensitive area and a neutralization layer are arranged on the substrate, an oxide layer, a hole, a front metal layer and an insulating layer are arranged in sequence on the front side of the substrate, ions are injected into the back side of the substrate, and a metal layer is arranged on the back side of the substrate; wherein: the cut-off ring is close to the outermost edge of the substrate; the anti-inversion terminal includes an area from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; the neutralization layer is located between the guard ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-inversion terminal into the body of the anti-inversion terminal. The anti-inversion structure is formed by diffusion doping, and its surface concentration is relatively high. On the basis of the anti-inversion structure, a neutralization layer is added, and the part with a higher surface concentration of the anti-inversion structure is neutralized by the newly added neutralization layer to form a neutralization layer with a low doping concentration, so that the area with high ion concentration can be transferred from the surface to the body, reducing the surface electric field, reducing the surface leakage current, and also improving the lateral withstand voltage of the device. The sensitivity of the device to Na+ ions is also reduced, and the workshop equipment and management costs are reduced.

[0049] In some embodiments, there are multiple guard rings, and the neutralization layer is located between the guard ring closest to the stop ring and the stop ring.

[0050] In this embodiment, when there are multiple guard rings, the neutralization layer is located in the region between the outermost guard ring and the stop ring.

[0051] In some embodiments, there are a plurality of neutralization layers, and the plurality of neutralization layers are disposed at intervals between the guard ring and the cut-off ring.

[0052] In this embodiment, the neutralization layer may include a plurality of annular parts, which are arranged at intervals.

[0053] By setting multiple neutralization layers, the terminal structure is made multi-segmented, so that more parts are transferred from the surface to the body in the area with high ion concentration, further reducing the surface electric field, reducing the surface leakage current, and improving the lateral withstand voltage of the device.

[0054] In some embodiments, there are multiple guard rings and multiple neutralization layers, one of which is located between the guard ring closest to the cut-off ring and the cut-off ring, and the other neutralization layers are respectively located between two guard rings.

[0055] In this embodiment, one neutralization layer is located between the guard ring closest to the cut-off ring and the cut-off ring, and other neutralization layers are located between two guard rings, respectively, so that a plurality of diode structures can be formed.

[0056] By forming a plurality of diode structures, the voltage division capability of the device can be improved, and the lateral withstand voltage of the device can be further improved.

[0057] In some embodiments, the ions in the neutralization layer are P-ions, an N-type structure is disposed between the guard ring and the cut-off ring, and the neutralization layer is located on the N-type structure.

[0058] In this embodiment, when the anti-inversion terminal is a P anti-inversion terminal, the neutralization layer is doped with N to obtain an N-neutralization layer. Correspondingly, when the ions in the neutralization layer are P-ions, an N-type structure is arranged on the P anti-inversion terminal, and then a P-neutralization layer is arranged on the N-type structure, that is, the neutralization layer is doped with P-ions.

[0059] It should be noted that an N-type structure may be provided between the guard ring and the cut-off ring, and the neutralization layer may be located on the N-type structure and be regarded as a neutralization layer as a whole. Therefore, the neutralization layer of the structure may also be located between the guard ring closest to the cut-off ring and the cut-off ring, may be arranged at intervals between the guard ring and the cut-off ring, or one of the neutralization layers may be located between the guard ring closest to the cut-off ring and the cut-off ring, and the other neutralization layers may be located between the two guard rings, which is not limited in this embodiment.

[0060] By arranging an N-type structure between the guard ring and the cut-off ring, and the neutralization layer being located on the N-type structure, an NP-swapped terminal structure can be realized.

[0061] In some embodiments, the concentration of the anti-reflection terminal at a distance of 0 to 1 um from the substrate surface is lower than the concentration at a distance of 2 to 3 um from the substrate surface.

[0062] In this embodiment, through software simulation calculation, it is obtained that the concentration of the anti-inversion terminal at 0-1 um from the substrate surface is lower than the concentration at 2-3 um from the substrate surface, with a lower surface doping concentration and a higher body doping concentration, so that the device has a higher breakdown voltage and a lower leakage current.

[0063] This embodiment also provides a photodiode preparation method for preparing the above-mentioned photodiode structure, and the photodiode preparation method comprises the following steps:

[0064] Step 210: constructing a cutoff ring, a guard ring and a photosensitive area on the substrate in sequence, wherein the cutoff ring is close to the outermost edge of the substrate;

[0065] In this embodiment, taking the construction of a stop ring P+ and a guard ring N on a substrate P- as an example, the process includes: Substrate casting: placing the substrate to be processed on the processing equipment to prepare for the subsequent process steps. RCA cleaning: using the RCA cleaning method to clean the substrate surface to remove organic and inorganic impurities on the surface to ensure the smooth progress of the subsequent process steps. Sacrificial oxidation: forming an oxide layer on the substrate surface to serve as the bottom layer of the photolithography pattern. Photolithography: performing photolithography on the oxide layer, using photoresist to cover the entire substrate surface, and then forming the desired pattern through the steps of exposure and development. Etching: transferring the photolithography pattern to the oxide layer using an etching process to form the desired structure. Degumming: removing the photoresist to expose the oxide layer below. Stop ring P+ (first time) photolithography: performing the first photolithography on the oxide layer to define the shape and position of the stop ring P+. Stop ring P+ injection: injecting P+ dopants into the substrate by ion implantation or other methods to form a P+ doped region. Degumming: removing the photoresist to expose the P+ doped region, that is, obtaining the stop ring P+. Then, photolithography is performed on the oxide layer, and the entire surface is covered with photoresist, and then the required guard ring pattern is formed through the steps of exposure and development. Etching: The photolithography pattern is transferred to the oxide layer using an etching process to form the structure of the guard ring. Stripping: Remove the photoresist to expose the oxide layer underneath. Guard ring N photolithography: Photolithography is performed on the oxide layer to define the shape and position of the guard ring P+. Guard ring N injection: N dopants are injected into the substrate by ion implantation and other methods to form an N-doped area. Stripping: Remove the photoresist to expose the N-doped area to obtain the guard ring N. Photolithography is performed on the substrate to define the shape and position of the photosensitive area, and then the photosensitive area is etched with a hydrofluoric acid solution, and then the photosensitive area is cleaned using the RCA cleaning method to remove possible residual impurities, followed by oxidation treatment to form an oxide layer or as a sacrificial layer for subsequent process steps to form a photosensitive area. Photolithography is performed on the substrate to define the shape and position of the photosensitive area P. Then, high-energy P-type dopants are injected into the substrate through ion implantation and other methods to form a P-type doped area. The photoresist is then removed to expose the doped area below. Then, rapid thermal annealing is performed to activate the doped material and repair lattice defects. Then, N+ type dopants are injected into the substrate through ion implantation and other methods to form an N+ type doped area. Then, the doped area is annealed with a laser. Then, BOE etching and RCA cleaning are performed to clean and remove residual impurities. Then, oxidation treatment is performed under low temperature conditions. Then, low-pressure chemical vapor deposition is performed to deposit thin film materials to form the photosensitive area P.

[0066] Step 220: constructing an anti-inversion terminal on the substrate, wherein the anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and a surface doping concentration of the anti-inversion terminal is higher than a body doping concentration;

[0067] In this embodiment, photolithography may be performed on the oxide layer to define the shape and position of the anti-inversion terminal, and then high-energy P-type dopants may be implanted into the substrate by ion implantation or the like to form a terminal P-doped region. Or, ordinary implantation may be performed, and then diffusion oxidation is performed to form a terminal P-doped region. Then, a stripping step is performed to remove the photoresist to expose the doped region below to obtain an anti-inversion terminal.

[0068] Step 230: constructing a neutralization layer on the substrate, wherein the neutralization layer is located between the guard ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-reflection terminal and penetrates into the body of the anti-reflection terminal;

[0069] In this embodiment, photolithography is performed on the oxide layer to define the shape and position of the terminal N. Then, N-type dopants are implanted into the substrate by ion implantation or other methods to form a terminal N doped region, and then the photoresist is removed to expose the doped region below, followed by BOE etching, that is, etching the surface with a hydrofluoric acid solution, followed by an RCA cleaning step, using an RCA cleaning method to clean the surface to remove possible residual impurities, followed by diffusion oxidation advancement, that is, oxidation treatment is performed to advance the formation of the oxide layer, and finally a neutralization layer is formed.

[0070] Step 240: sequentially constructing a hole, a front metal layer and an insulating layer on the front side of the substrate;

[0071] In the present embodiment, photolithography is performed on the substrate to define the shape and position of the hole, followed by hole BOE etching, and the area after photolithography is etched using a hydrofluoric acid solution (BOE) to form a hole, and then the photoresist is removed to expose the hole structure below, and a metal deposition process is performed on the substrate to form a metal layer. Then, photolithography is performed on the metal layer to define the structure and pattern on the metal layer. Then, the area on the metal layer is etched to form the required metal structure, and then the photoresist is removed to expose the metal structure below. Then, the metal layer is alloyed to improve the performance of the metal layer, and a polyimide (PI) solution is spin-coated on the substrate to form a thin film. Then, photolithography is performed on the PI film to define the structure and pattern on the PI film. Then, the PI film is cured to have the required physical and chemical properties.

[0072] It should be noted that the above steps 230-240 form a PN junction terminal structure, and the PN junction terminal structure can be realized by one high-energy P-type injection, one N-type injection, and one diffusion-pushing junction, or by one ordinary P-type injection, one diffusion-pushing junction, one N-type injection, and a second diffusion-pushing junction, which is not limited in this embodiment.

[0073] Due to the large curvature of the surface electric field and the increase in interface states, the breakdown voltage and leakage current of the surface PN junction are much greater than those of the PN junction. By utilizing this characteristic, the weak link is transferred from the surface to the body through the two injections in steps 230-240, so that the diode can achieve low leakage current and high lateral withstand voltage.

[0074] Step 250: Implant ions into the back side of the substrate and construct a back side metal layer.

[0075] In this embodiment, the back side of the device may be thinned to reduce the thickness of the device, followed by injection of materials or dopants to change the performance of the device. The substrate is then laser treated to improve the material or dopants injected into the back side. The back side of the substrate is metallized, followed by alloying of the back metal layer, and the device is then tested to verify its performance, function, or quality. The tests include electrical testing, structural testing, performance testing, etc. to ensure that the device meets the specification requirements.

[0076] In the above implementation process, a cutoff ring, a guard ring and a photosensitive area are sequentially constructed on the substrate, wherein the cutoff ring is close to the outermost edge of the substrate; an anti-inversion terminal is constructed on the substrate, wherein the anti-inversion terminal includes the area from the guard ring to the outermost edge of the substrate, wherein the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; a neutralization layer is constructed on the substrate, wherein the neutralization layer is located between the guard ring and the cutoff ring, and wherein the neutralization layer penetrates through the surface of the anti-inversion terminal and penetrates into the body of the anti-inversion terminal; holes, a front metal layer and an insulating layer are sequentially constructed on the front side of the substrate, and ions are injected into the back side of the substrate to construct a back metal layer. Since the anti-inversion structure is formed by diffusion doping, its surface concentration is relatively high. On the basis of the anti-inversion structure, a neutralization layer is added, and the part with a higher surface concentration of the anti-inversion structure is neutralized by the newly added neutralization layer to form a neutralization layer with a low doping concentration, thereby transferring the area with a high ion concentration from the surface to the body, reducing the surface electric field, reducing the surface leakage current, and improving the lateral withstand voltage of the device. The sensitivity of the device to Na+ ions is also reduced, and the workshop equipment and management costs are reduced.

[0077] The following is an example of preparing an APD photodiode. Figure 4 , including steps 1-11, the process flow is as follows:

[0078] 1: Substrate casting--RCA cleaning--sacrificial oxidation--(zero layer) photolithography--zero layer etching--stripping--stop ring P+ (first time) photolithography--stop ring P+ injection--stripping (stop ring P+);

[0079] 2: Guard ring N (second time) photolithography -- guard ring N injection -- degumming -- (guard ring);

[0080] 3: Terminal P (3rd time) photolithography -- Terminal P high energy injection -- degumming -- (Terminal P);

[0081] 4: Terminal N (4th time) photolithography--terminal N injection--stripping--BOE etching--RCA cleaning--diffusion oxidation advancement--(terminal N);

[0082] 5: Photosensitive area (5th time) photolithography -- photosensitive area BOE etching -- RCA cleaning -- sacrificial oxidation -- (photosensitive area);

[0083] 6: Photosensitive area P (6th time) photolithography-high energy P injection-stripping-RTP annealing-photosensitive area N+ injection-laser annealing-BOE etching-RCA cleaning-low temperature oxidation-low pressure chemical vapor deposition (LPCVD)--(photosensitive area P);

[0084] 7: Hole (7th time) photolithography -- hole BOE etching -- degumming -- (hole) (drilling a hole in the oxide layer);

[0085] 8: Front metallization -- metal (8th time) photolithography -- metal corrosion -- degumming -- alloy -- (front metallization);

[0086] 9: PI spin coating -- PI (9th time) photolithography -- PI curing -- (PI);

[0087] 10: Back thinning -- back injection (10th layer) -- laser annealing -- (back injection);

[0088] 11: Back Metal (11th layer) - Alloy - Test (Back Metal).

[0089] In some embodiments, there are a plurality of guard rings, and constructing a neutralization layer on the substrate includes: constructing a neutralization layer in a region between a guard ring closest to the cut-off ring on the substrate and the cut-off ring.

[0090] In this embodiment, the construction process is the same as the step 230, except that the photolithography positioning is performed on the oxide layer at the area between the guard ring closest to the cut-off ring and the guard ring. Figure 4 As shown, the neutralization layer in the figure is between the guard ring closest to the cut-off ring and the cut-off ring.

[0091] In some embodiments, constructing a neutralization layer on the substrate comprises:

[0092] A plurality of neutralization layers are formed at intervals in the region between the guard ring and the stop ring on the substrate.

[0093] In this embodiment, the above construction process is the same as the above step 230, and will not be repeated here. Figure 5 As shown, there are two neutralization layers between the guard rings.

[0094] By constructing multiple neutralization layers, the terminal structure is made multi-segmented, so that more parts are transferred from the surface to the body in the area with high ion concentration, further reducing the surface electric field, reducing the surface leakage current, and improving the lateral withstand voltage of the device.

[0095] In some embodiments, the guard ring has a plurality of members, and a neutralization layer is constructed on the substrate, including:

[0096] First, a neutralization layer is constructed on the substrate in a region between a guard ring closest to the cut-off ring and the cut-off ring;

[0097] Then, a neutralization layer is respectively constructed in the region between any two guard rings on the substrate.

[0098] The above construction process is the same as the above step 230, except that when performing photolithography positioning on the oxide layer, one is in the area between the guard ring closest to the cut-off ring and the cut-off ring, and the other is in the area between any two guard rings. Figure 6 As shown, one neutralizing layer is between the guard ring and the cutoff ring, and another neutralizing layer is between the two guard rings.

[0099] One neutralization layer is located between the guard ring closest to the cut-off ring and the cut-off ring, and the other neutralization layers are located between two guard rings, so that multiple diode structures can be formed. By forming multiple diode structures, the voltage division capability of the device can be improved, and the lateral withstand voltage of the device can be further improved.

[0100] In some embodiments, the ions in the neutralization layer are P-ions, and constructing the neutralization layer on the substrate comprises:

[0101] First, an N-type structure is constructed in the region between the guard ring and the cut-off ring on the substrate;

[0102] Then, photolithography is performed on the N-type structure, and a second dopant is implanted into the substrate to form a second terminal doping region, wherein the second dopant is a P- ion;

[0103] Finally, the photoresist of the substrate where the second terminal doping region is formed is removed to expose the second terminal doping region, so as to obtain a neutralization layer.

[0104] In this embodiment, when the anti-inversion terminal is a P anti-inversion terminal, the neutralization layer is doped with N to obtain an N-neutralization layer. Correspondingly, when the ions in the neutralization layer are P-ions, an N-type structure is arranged on the P anti-inversion terminal, and then a P-neutralization layer is arranged on the N-type structure, that is, the neutralization layer is doped with P-ions. Figure 7 As shown, an N-type structure is first constructed on the anti-inversion terminal, and then a P-neutralizing layer is constructed on the N-type structure to form a neutralizing layer.

[0105] By constructing an N-type structure between the guard ring and the cut-off ring, and the neutralization layer being located on the N-type structure, an NP-swapped terminal structure can be realized.

[0106] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0107] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A photodiode structure, characterized in that: The invention comprises a substrate, on which a cut-off ring, a guard ring, an anti-inversion terminal, a photosensitive region and a neutralization layer are arranged, wherein the cut-off ring, the guard ring, the anti-inversion terminal and the neutralization layer are all obtained by doping on the substrate, an oxide layer, a hole, a front metal layer and an insulating layer are arranged in sequence on the front side of the substrate, ions are injected on the back side of the substrate, and a metal layer is arranged on the back side of the substrate; wherein: The cut-off ring is close to the outermost edge of the substrate; The anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and the surface doping concentration of the anti-inversion terminal is higher than the body doping concentration; The neutralization layer is located between the protection ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-reflection type terminal and goes deep into the body of the anti-reflection type terminal.

2. The photodiode structure according to claim 1, characterized in that: There are a plurality of guard rings, and the neutralization layer is located between the guard ring closest to the cut-off ring and the cut-off ring.

3. The photodiode structure according to claim 1, characterized in that: There are a plurality of neutralization layers, and the plurality of neutralization layers are arranged at intervals between the protection ring and the cut-off ring.

4. The photodiode structure according to claim 1, characterized in that: There are a plurality of guard rings and a plurality of neutralization layers, one of which is located between the guard ring closest to the cut-off ring and the cut-off ring, and the other neutralization layers are respectively located between two guard rings.

5. The photodiode structure according to any one of claims 1 to 4, characterized in that: The ions in the neutralization layer are P-ions, an N-type structure is arranged between the guard ring and the cut-off ring, and the neutralization layer is located on the N-type structure.

6. The photodiode structure according to claim 1, characterized in that: The concentration of the anti-reflection terminal at a distance of 0 to 1 um from the substrate surface is lower than the concentration at a distance of 2 to 3 um from the substrate surface.

7. A method for preparing a photodiode, characterized in that: For preparing the photodiode structure according to claim 1, the photodiode preparation method comprises: A cut-off ring, a guard ring and a photosensitive area are sequentially constructed on the substrate, wherein the cut-off ring is close to the outermost edge of the substrate; constructing an anti-inversion terminal on the substrate, wherein the anti-inversion terminal includes a region from the guard ring to the outermost edge of the substrate, and a surface doping concentration of the anti-inversion terminal is higher than a body doping concentration; Constructing a neutralization layer on the substrate, wherein the neutralization layer is located between the guard ring and the cut-off ring, and the neutralization layer penetrates through the surface of the anti-reflection terminal and penetrates into the body of the anti-reflection terminal; sequentially constructing a hole, a front metal layer and an insulating layer on the front side of the substrate; Ions are implanted into the back side of the substrate to construct a back side metal layer.

8. The method for preparing a photodiode according to claim 7, characterized in that: The protective ring has a plurality of parts, and a neutralization layer is constructed on the substrate, including: A neutralizing layer is formed on the substrate in a region between a guard ring closest to the stop ring and the stop ring.

9. The method for preparing a photodiode according to claim 7, characterized in that: A neutralizing layer is constructed on the substrate, comprising: A plurality of neutralization layers are formed at intervals in the region between the guard ring and the stop ring on the substrate.

10. The method for preparing a photodiode according to claim 7, characterized in that: The protective ring has a plurality of parts, and a neutralization layer is constructed on the substrate, including: Constructing a neutralization layer in a region between a guard ring closest to the cut-off ring and the cut-off ring on the substrate; A neutralization layer is respectively constructed in the region between any two guard rings on the substrate.

11. The method for preparing a photodiode according to claim 7, characterized in that: The ions in the neutralization layer are P-ions, and the neutralization layer is constructed on the substrate, comprising: An N-type structure is constructed in the area between the guard ring and the cut-off ring on the substrate; Performing photolithography on the N-type structure and injecting a second dopant into the substrate to form a second terminal doping region, wherein the second dopant is a P- ion; The photoresist of the substrate where the second terminal doping region is formed is removed to expose the second terminal doping region to obtain a neutralization layer.

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