A high reliability glass bead composite diode and preparation method thereof

Abstract

The present invention relates to a high-reliability glass bead composite diode and a preparation method thereof, and belongs to the field of semiconductor technology. The present invention provides a high-reliability glass bead composite diode, including a crystal grain, a welding piece is provided on each side of the crystal grain, a lead is provided on the side of the welding piece away from the crystal grain, a molybdenum grain is also provided between the crystal grain and the welding piece, the crystal grain includes a metal cathode, an N+ substrate, an N region, a P region, a P+ region, an insulating dielectric layer, a Schottky region and a metal anode, and uses boron expansion pre-deposition, boron diffusion, platinum diffusion, sand blowing, photolithography, ion implantation, metal alloying, welding, sintering and other processes; the high-reliability glass bead composite diode provided by the present invention adopts superposition composite technology, and the fast recovery diode contains a Schottky diode, which has ultra-fast and ultra-soft recovery characteristics while also having low forward conduction loss and high reverse breakdown voltage. At the same time, the structure provided by the present invention also effectively solves the problem that the Schottky diode cannot be welded at high temperature.

Description

Technical Field

[0001] The invention relates to a high-reliability glass bead composite diode and a preparation method thereof, belonging to the technical field of semiconductors. Background Art

[0002] Fast recovery diode is a semiconductor diode with good switching characteristics and short reverse recovery time. It is mainly used in electronic circuits such as switching power supplies, PWM pulse width modulators, and frequency converters as high-frequency rectifier diodes, freewheeling diodes, or damping diodes. The internal structure of a fast recovery diode is different from that of an ordinary PN junction diode. Because the base region is very thin and the reverse recovery charge is very small, the reverse recovery time of a fast recovery diode is short, the forward voltage drop is low, and the reverse breakdown voltage is high.

[0003] The Schottky diode is made based on the principle of metal-semiconductor junction formed by the contact between metal and semiconductor. The Schottky barrier is formed at the contact surface of the two, and the metal-semiconductor device has rectification characteristics. Therefore, the Schottky diode is also called metal-semiconductor (contact) diode or surface barrier diode. It is a hot carrier diode. The Schottky diode does not have the diffusion region in the PN junction, so there is no carrier recombination phenomenon in the PN junction, which can achieve faster switching speed and reverse recovery time, which can greatly reduce reverse leakage current and energy consumption during reverse switching.

[0004] However, compared with Schottky diodes, fast recovery diodes have longer reverse recovery time. There are a large number of high-concentration impurities in fast recovery diodes, which leads to the formation of a wider depletion region in the PN junction, prolonging the reverse recovery time. In addition, when the fast recovery diode is forward-conducted, there will be a large forward voltage drop, which will cause a certain power loss. Compared with fast recovery diodes, Schottky diodes also have some disadvantages. The performance of Schottky diodes at high frequencies is relatively poor. This is because it has a certain carrier storage effect when forward-conducted, and the junction capacitance of Schottky diodes is large, which limits its working performance at high frequencies. In addition, since the forward conduction characteristics of Schottky diodes are faster, but the reverse conduction characteristics are poor, the performance of Schottky diodes is not as good as that of fast recovery diodes in situations where strong rectification is required.

[0005] CN104716038B discloses a composite fast recovery diode and a preparation method thereof. The diode comprises a metal cathode layer, an N+ substrate layer, an N-type epitaxial layer, a field oxide layer and a metal anode layer connected in sequence. The field oxide layer has an active region window. The N-type epitaxial layer is located at the active region window and is provided with three or more P-type regions and Schottky regions connected to each P-type region. The N-type epitaxial layer also has a charge accumulation region at the bottom of each P-type region. The preparation steps include: (1) oxidizing and photolithography the active region; (2) N-type impurity ion implantation; (3) N push junction; (4) P region implantation window formation; (5) P-type impurity ion implantation; (6) push junction; (7) Schottky region formation; (8) metal film deposition; (9) back side thinning; and (10) back side metallization. However, the switching time of the composite diode prepared by the above method varies greatly under the influence of temperature, and in the high-temperature welding step of the later packaging, additional metal atoms will diffuse, changing the original barrier height, affecting the Schottky barrier characteristics of the device, and then affecting the key parameters of the device such as the on-state voltage and leakage current. In addition, in the welding step, the temperature rises rapidly and then cools, which will cause stress caused by the difference in thermal expansion coefficients between the materials. This stress may cause micro cracks or fractures inside the chip, affecting the mechanical strength and reliability of the device. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a high-reliability glass bead composite diode. The diode adopts chip stacking composite technology. In the chip assembly, the fast recovery chip includes a Schottky chip, which has ultra-fast and ultra-soft recovery characteristics while also having low forward conduction loss and high reverse breakdown voltage. The structure provided by the present invention effectively solves the problem that the Schottky chip cannot be welded at high temperature, and can also effectively improve the high-temperature working characteristics of the chip.

[0007] The invention provides a high-reliability glass bead composite diode, comprising a crystal grain, wherein a welding piece is respectively arranged on both sides of the crystal grain, a lead is arranged on the side of the welding piece away from the crystal grain, a molybdenum grain is further arranged between the crystal grain and the welding piece, and the crystal grain, the molybdenum grain and the welding piece are wrapped in a glass bead; the crystal grain comprises a metal cathode, an N+ substrate, an N region, a P region, a P+ region, an insulating dielectric layer, a Schottky region and a metal anode, wherein the metal cathode is located on the back of the N+ substrate, the N region is located on the front of the N+ substrate, the P region is located on the side of the N region away from the N+ substrate, the P region contains a plurality of P+ regions, the insulating dielectric layer is located on the side of the P region away from the N region, is in a circular ring shape, and has a width smaller than the P region, the metal anode is located on the side of the insulating dielectric layer away from the P region, covers the insulating dielectric layer, and the Schottky region is located in the circular ring formed by the insulating dielectric layer and is connected to the P+ region.

[0008] Furthermore, there are at least two P+ regions, and the P+ regions are connected to the insulating dielectric layer and the Schottky region at the same time.

[0009] Furthermore, the crystal grain is a truncated cone, and the side surface is an inward arc.

[0010] Furthermore, the P+ region has a depth of 0.8-1 μm, a width of 20-45 μm, and a doping concentration of 1e16-1e19 cm -3 The P region has a depth of 40-60 μm and a doping concentration of 2e13-2e15 cm -3 ; The depth of the N region is 50-70μm, and the depth of the N+ region is 100-120μm.

[0011] According to the above-mentioned method for preparing a high-reliability glass bead composite diode, the following steps are included:

[0012] S1. Boron sheet treatment: push the boron sheet into the furnace tube, dry it in nitrogen atmosphere, and then heat it up to oxidize the boron sheet in anhydrous oxygen atmosphere;

[0013] S2. The wafer is cleaned in SC1 solution, and then in SC2 solution, and then cleaned and dehydrated with pure water. After dehydration, it is sent to the oven for baking; impurities on the surface of the original wafer are cleaned to ensure that the subsequent process will not be contaminated by impurities;

[0014] S3. The wafer is sent to a diffusion furnace for boron diffusion pre-deposition, washed with hydrofluoric acid and pure water respectively, dehydrated and baked, and then subjected to high-temperature oxidation, washed with hydrofluoric acid, BOE, and pure water respectively, dehydrated and baked, and then the wafer is arranged on a quartz boat and sent to a diffusion furnace for boron diffusion, washed with hydrofluoric acid and pure water respectively, and baked; high-temperature oxidation deposits a layer of B on the EPI layer of the wafer 2 O 3 And make boron diffuse to a certain depth and concentration to meet the design requirements; boron diffusion is to form a p-region with a certain concentration that meets the requirements;

[0015] S4. Sandblast the boron surface of the wafer, clean it with pure water and bake it, send the wafer into the platinum expansion furnace for platinum diffusion, soak the wafer in acid after diffusion, clean it with pure water and bake it, sandblast both sides of the wafer, clean it with pure water, SC1, SC2 and pure water respectively and bake it; the sandblasting step can remove the residual source covering layer on the surface; the solid solubility of platinum atoms in solids varies greatly due to the influence of temperature, so a rapid cooling method should be adopted when cooling down the platinum expansion, otherwise the platinum atoms will precipitate on the surface or accumulate in the interior, and will not play the role of recombination center. Incorporating heavy metal atoms into the PN junction to increase the recombination center can reduce the carrier lifetime, achieve a rapid recovery effect and thus reduce TRR;

[0016] S5. Send the wafer into the thermal oxidation furnace, perform the first photolithography and etching after the initial oxide layer is formed, perform RCA cleaning after the photoresist is removed, send the wafer into the thermal oxidation furnace again, perform ion implantation after the oxide layer grows, inject the diffusion source into the wafer, perform RCA cleaning, place the wafer into the diffusion furnace for diffusion, and then perform the second photolithography and etching, perform RCA cleaning after the photoresist is removed; the initial oxide layer is formed on the wafer surface by combining high temperature and oxygen to form a subsequent silicon dioxide interface, and the oxide layer is formed on the wafer surface to facilitate subsequent photoresist coating. The initial oxide layer can be used as a hard mask during ion implantation and can also be used as a protective layer for subsequent PN junctions; the oxide layer grows to form silicon dioxide on the wafer surface by using oxygen and temperature, which can prevent channel effects and also serve as a sacrificial layer for subsequent steps; after ion implantation, it diffuses to form a P+ region;

[0017] S6. Pre-depositing titanium on the wafer, then plating a barrier metal on the wafer surface, and then sending the wafer into a metal alloying furnace for metal alloying. After metal alloying, removing excess barrier metal with an etching solution, and then plating a welding metal on the wafer surface; the barrier metal is plated on the wafer surface to form a Schottky region, and the metal alloying ensures that the high temperature during subsequent device welding will not damage the device;

[0018] S7. Perform the third photolithography and metal etching, remove the photoresist, grind the back of the wafer, and then clean and dry it; grind the back of the wafer to thin the wafer and reduce the VF value, which is beneficial for subsequent packaging;

[0019] S8. Deposit a layer of aluminum film on the surface of the wafer to form a metal cathode and a metal anode, separate the crystal grains from the glass sheet after sand blowing, rinse and dry the crystal grains, corrode with mixed acid, and then dehydrate and dry; deposit a uniform layer of aluminum film on the surface of the wafer for electrode contact; sand blowing can cut the wafer with regularly arranged iron sheets on the surface to obtain crystal grains with reasonable table shape; use chemical reagents to clean the surface of the aluminum layer and the PN junction of the crystal grains, which can improve the welding quality of the crystal grains and molybdenum grains in the later stage and form a crystal table that meets the size requirements and surface quality;

[0020] S9. Welding is performed in a vacuum welding furnace in the order of leads, solder tabs, molybdenum grains, grains, molybdenum grains, solder tabs, and leads. The grains after welding are washed with mixed acid and water, and glass powder is applied to form a spherical glass frit attachment layer on the molybdenum column portion of the die of the welded member to obtain a diode blank;

[0021] S10. Sintering the diode blank to obtain a diode component, tinning the diode component, cleaning and drying it, and packaging it to obtain the desired product; sintering is to seal the diode blank into a diode component whose electrical parameters and appearance meet the internal passivation requirements; tinning the sintered diode component can protect the lead from oxidation.

[0022] Furthermore, in step S3, nitrogen is passed throughout the boron diffusion pre-deposition process, the temperature is raised from 300°C, oxygen is introduced when the temperature reaches 600°C, the temperature is raised to 1150°C and kept constant for 4-6 hours, and then the oxygen is turned off when the temperature is lowered to 600°C, and the temperature is lowered to 350°C before being taken out of the furnace; the thickness of the oxide film of the high-temperature oxidation is required to be ≥80nm.

[0023] Furthermore, in step S4, the platinum source is diffused, the platinum source is placed on a stirrer for stirring, the wafer is placed on a source coating machine for source coating, preheated for 14-16 minutes at the furnace mouth, and then pushed into the constant temperature zone, nitrogen is passed throughout the process, and the wafer is taken out of the furnace and transferred to the support for natural cooling.

[0024] Furthermore, the pre-deposition in step S6 is two layers, the first layer is titanium silicide, and the second layer is titanium nitride. The titanium silicide layer is 10-40 angstroms, and the titanium nitride layer is 10-30 angstroms; the barrier metals are Ti, Ni and Ag, respectively, the titanium layer is 0.07-0.1μm, the Ni layer is 0.25-0.75μm, and the metal Ag layer is greater than 30um after metal alloying. The titanium silicide, titanium nitride and the alloyed Ag layer jointly protect the internal structure of the chip so that it will not be damaged during sintering.

[0025] Furthermore, the welding temperature in step S9 is 700-720°C, and the sintering temperature in step S10 is 610-760°C.

[0026] Furthermore, in step S8, the thickness of the aluminum film is 10.5±0.7 μm for the metal anode and 9.5±0.7 μm for the metal cathode.

[0027] The beneficial effects of the present invention are:

[0028] 1. The present invention adopts superposition composite technology, and the fast recovery diode in the assembly includes a Schottky diode, which has ultra-fast and ultra-soft recovery characteristics while also having low forward conduction loss and high reverse breakdown voltage. The switching time TRR is less than 15ns, and VB is greater than 1200v, which can reduce the heat loss of the device, save energy, and effectively improve the high-temperature working characteristics of the device Tg to 175°C; the titanium silicide and titanium nitride formed by the pre-deposition of titanium and the Ag layer after metal alloying protect the internal structure of the diode, solving the problem that the Schottky diode cannot be welded at high temperature.

[0029] 2. The glass bead firing passivation technology is adopted. The crystal grains, molybdenum grains and copper wires are encapsulated in the glass to form a whole, which improves the airtightness of the diode, effectively isolates the erosion of external gases, improves the anti-interference ability of components, improves the pressure resistance of glass bead diodes, and improves the reliability and service life of components. The molybdenum grain buffer stress technology effectively prevents the electronic component assembly in the glass ball from being affected by thermal stress when the external environment changes from hot to cold, thereby improving reliability and output yield.

[0030] 3. The outer grain round and inner grain round molding technology has a more reasonable structure, which can effectively avoid the tip discharge phenomenon of the diode under high voltage and improve the stability and reliability of the chip.

[0031] 4. In actual production, it is found that the fast recovery diodes made of epitaxial silicon wafers show obvious negative temperature characteristics within the normal working current range, and the switching time increases rapidly with the increase of temperature; for the fast recovery diodes made of chip stacking and composite, the switching time does not increase much with the increase of temperature; clever selection of the doping concentration of the single crystal silicon substrate can produce a fast recovery diode with a small correlation between the forward voltage drop VF and temperature under the maximum forward current.

[0032] 5. In terms of overall diode layout, avoid excessive density, make the spacing between components more reasonable, and reduce the mutual influence between electronic components. After rigorous testing and evaluation, the reliability and stability of diodes in various extreme working environments are ensured to maximize the reliability requirements of electronic products in complex environments. The resulting products are mainly used in lighting, power supply, screen display and other devices with large temperature differences and high voltages. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the vertical cross-section structure of a high-reliability glass bead composite diode grain;

[0034] Figure 2 This is a schematic diagram of the structure of a high-reliability glass bead composite diode;

[0035] In the figure, 1-metal cathode, 2-N+ substrate, 3-N region, 4-P region, 5-P+ region, 6-insulating dielectric layer, 7-Schottky region, 8-metal anode, 9-glass, 10-soldering piece, 11-molybdenum grain, 12-lead, 13-grain. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0037] In the description of the embodiments of the present invention, it should be understood that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the application are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] The present application provides a high reliability glass bead composite diode, as shown in the attached Figure 2 As shown, it includes a crystal grain 13, a welding piece 10 is provided on each side of the crystal grain 13, a lead 12 is provided on the side of the welding piece 10 away from the crystal grain 13, a molybdenum grain 11 is also provided between the crystal grain 13 and the welding piece 10, and the crystal grain 13, the molybdenum grain 11, the welding piece 10 and one end of the lead 12 are wrapped in glass 9; as shown in the attached Figure 1 As shown, the grain 13 includes a metal cathode 1, an N+ substrate 2, an N region 3, a P region 4, a P+ region 5, an insulating dielectric layer 6, a Schottky region 7 and a metal anode 8. The metal cathode 1 is located on the back side of the N+ substrate 2, the N region 3 is located on the front side of the N+ substrate 2, the P region 4 is located on the side of the N region 3 away from the N+ substrate 2, the P region 4 contains a plurality of P+ regions 5, the insulating dielectric layer 6 is located on the side of the P region 4 away from the N region 3, is in a circular ring shape, and has a width smaller than the P region 4, the metal anode 8 is located on the side of the insulating dielectric layer 6 away from the P region 4, covers the insulating dielectric layer 6, and the Schottky region 7 is located in the circular ring formed by the insulating dielectric layer 6 and is connected to the P+ region 5.

[0039] The method for preparing the high reliability glass bead composite diode comprises the following steps:

[0040] S1. Boron flake treatment:

[0041] a. After unpacking the boron sheet, push it into the furnace tube, introduce dry nitrogen, and dry the boron sheet at 300-450℃ for at least 1 hour;

[0042] b. At 1000°C, 100% dry O 2 Boron oxide tablets, time is 30 minutes;

[0043] c. Dry the newly oxidized boron sheet at 1150°C, 100% N 2 Stable for 1 hour.

[0044] S2. Wafer cleaning:

[0045] a. Add 7000±100ml of pure water to the cleaning tank and set the temperature to 75±5℃. After the water temperature reaches 75℃, take out 2000±100ml of deionized water, add 1000±50ml of ammonia water and 1000±50ml of hydrogen peroxide to make SC1 solution. Then immediately place the wafer in the SC1 solution and time it for 10±0.5min. During the cleaning process, the solution temperature is 75±5℃.

[0046] b. Put the wafer cleaned with SC1 into the QDR cleaning tank, cover it and clean it for 5 cycles. After each cleaning cycle, add 200±50ml of ammonia and 200±50ml of hydrogen peroxide to the SC1 solution.

[0047] c. Add 7000±100ml of deionized water to the new cleaning tank and set the temperature to 75℃. When the water temperature reaches 75℃, take out 2000±100ml of pure water, add 1000±50ml of ammonia water and 1000±50ml of hydrogen peroxide to make SC2 solution. Then immediately place the wafer in the SC2 solution and time it for 10±0.5min. During the cleaning process, the solution temperature is 75℃.

[0048] d. Put the wafer after SC2 cleaning into QDR cleaning tank and clean it for 5 cycles. After each cleaning cycle, add 200±50ml hydrochloric acid and 200±50ml hydrogen peroxide to the SC2 tank.

[0049] e. Place the wafer in a three-stage pure water overflow tank for step-by-step cleaning. The cleaning time for each stage of the first and second stages is ≥3min. The resistance value of the third stage to pure water is ≥12MΩ·cm. Then, place the wafer in IPA for dehydration for ≥1min. The IPA resistance value is ≥15MΩ·cm.

[0050] f. The dehydrated wafer is sent into the oven at 100±10℃ and baked for 30 minutes.

[0051] S3. Boron diffusion pre-deposition, high temperature oxidation and boron diffusion:

[0052] a. Fill the whole quartz boat with baffles to establish good boundary conditions, so that the boron glass follows Fick's law when diffusing from the source sheet. Preheat the diffusion furnace, send the quartz boat into the diffusion furnace at 300℃, and pass nitrogen throughout the process. When the temperature rises to 600℃, pass oxygen with a nitrogen flow rate of 4LPM and an oxygen flow rate of 0.2LPM. Raise the temperature to 1150℃ and keep the temperature constant for 5h, then turn off the oxygen when the temperature drops to 600℃, and start to take it out of the furnace when the temperature drops to 350℃;

[0053] b. First add 7000mL of deionized water, then add 700mL of hydrofluoric acid and stir evenly, place the pre-deposited wafer in the above hydrofluoric acid for 20 minutes, then place the wafer in a 3-stage pure water overflow tank for step-by-step cleaning, the first and second stage cleaning time is ≥3min, the third stage to pure water resistance value is ≥12MΩ·cm, then place the wafer in IPA for dehydration for ≥1min, IPA resistance value is ≥15MΩ·cm;

[0054] c. The dehydrated wafer is sent to the oven at 100±10℃ for 30min;

[0055] d. Test the surface resistance of the chip, use four probes to test the surface resistance of five points (up, middle, bottom, left, and right) to check whether it meets the requirements;

[0056] e. Send the wafer into the oxidation furnace, the oxidation temperature is 1000±5℃, the oxidation time is constant temperature for 30 minutes, the oxide film thickness is required to be ≥80nm, the oxidation furnace gas setting is: N 2Flow rate is 2LPM, O 2 The flow rate is 4 LPM;

[0057] f. First add 7000mL of deionized water, then add 700mL of hydrofluoric acid and stir evenly, place the pre-deposited wafer in the above-mentioned ratio of hydrofluoric acid for 20min, then soak the wafer in BOE acid for 5min, then soak the wafer in the above-mentioned ratio of hydrofluoric acid for 2min, then place the wafer in a 3-stage pure water overflow tank for step-by-step cleaning, the first and second stage cleaning time ≥3min, the third stage to pure water resistance ≥12MΩ·cm, then place the wafer in IPA for dehydration ≥1min, IPA resistance ≥15MΩ·cm;

[0058] g. The dehydrated wafer is sent to the oven at 100±10℃ for 30min;

[0059] h. Arrange the wafers P-side to P-side on the quartz boat, with the notches flush, and the number of wafers per furnace is ≤150pcs. Preheat the diffusion furnace, and send the quartz boat into the diffusion furnace at 600℃. Pass nitrogen and oxygen throughout the process, with a nitrogen flow rate of 4LPM and an oxygen flow rate of 0.2LPM. Raise the temperature to 1200℃ and keep it constant for 27h, then cool it down to 600℃ and start to take it out of the furnace;

[0060] i. First add 7000mL of deionized water, then add 700mL of hydrofluoric acid and stir evenly, place the diffused wafer in the hydrofluoric acid for 20min, and then place the wafer in a 2-stage deionized water overflow tank for step-by-step cleaning, with each stage cleaning time of 3min;

[0061] j. The dehydrated wafer is sent into the oven at 100±10℃ and baked for 20 minutes.

[0062] S4. Boron surface sand blowing and platinum diffusion:

[0063] a. Use C-type sandblasting machine, select 12 nozzles to spray once, the brown corundum powder in the sandblasting machine is 400 mesh, and the gas pressure on the P surface is 0.5±0.1Kg / cm 2 ;

[0064] b. After sandblasting, the wafer is cleaned with pure water for 5 minutes, twice, and then the wafer is put into the oven at 100±10℃ for 20 minutes;

[0065] c. The platinum source is PT920. Place the platinum source on a stirrer and stir. Place the wafer on a source coating machine and coat it with the source. After loading it into the quartz boat, preheat it at the furnace for 15 minutes. Then, complete the process of pushing it into the constant temperature zone within 10 seconds. Keep the temperature at 840℃ for 45-60 minutes. 2 Flow rate 4±0.2LMIN, the process of pulling to the furnace mouth is completed within 10 seconds after leaving the furnace, and then transferred to the support for natural cooling;

[0066] d. Add 5400mL of nitric acid, then 180mL of hydrofluoric acid and 180mL of glacial acetic acid to a plastic container according to the ratio, soak the platinum-expanded wafer in it for 3min, then take it out and rinse it with water for 3min, then ultrasonicate it for 5min, and place the wafer after ultrasonication in an overflow tank and rinse it with water for 5min;

[0067] e. The dehydrated wafer is sent to the oven at 100±10℃ for 20min;

[0068] f. Use C-type sand blasting machine, select 12 nozzles to spray once, the brown corundum powder in the sand blasting machine is 400 mesh, and the gas pressure on the P surface is 0.3-0.4Kg / cm 2 , N-side gas pressure 0.75±0.2Kg / cm 2 ;

[0069] g. After sandblasting, the wafer is cleaned with pure water for 5 minutes, twice, and then cleaned with SC1, SC2, and three-stage overflow water in sequence. The steps are the same as the wafer cleaning of S2. Dry directly after flushing. The oven temperature is 150±10℃ and bake for 30 minutes. Avoid moisture after baking.

[0070] S5. Photolithography and ion implantation:

[0071] a. Arrange the wafers into the quartz boat and set the direction. Send the arranged quartz boat into the thermal oxidation furnace and use high temperature wet oxygen to oxidize SiO 2 The oxidation is formed on the surface of the wafer, and the wafer after oxidation is taken out of the furnace;

[0072] b. Send the thermally oxidized wafer into the HMDS oven for baking to ensure that there is no residual moisture, and cover the wafer surface with a layer of HMDS, a promoter adhesive, and evenly apply the positive photoresist 111XFS produced by Anzhi Company on the wafer surface with a spin coater, bake the wafer coated with photoresist at 90°C, transfer the pattern of the baked wafer with an alignment exposure machine, and use a developer to reveal the required pattern of the exposed wafer, and send the developed wafer into a 130°C oven for baking to solidify the photoresist. After the first yellow light, use BOE acid to remove the oxide layer without photoresist protection, and then go to SPM to remove the photoresist to form the first RING pattern, and then send the wafer to the chemical etching station, and use BOE acid to remove the exposed oxide layer, and then send the wafer with the oxide layer etched to the photoresist removal station, and use sulfuric acid to remove the photoresist;

[0073] c. RCA cleaning: Use SC1 to remove particles and organic matter on the surface of the wafer, then quickly rinse the residue on the surface of the wafer with high-purity water, then use SC2 to remove metal ions remaining on the surface of the wafer, then quickly rinse the residue on the surface of the wafer with high-purity water, then use hydrofluoric acid to etch the oxide layer on the surface of the wafer, then quickly rinse the residue on the surface of the wafer with high-purity water, and finally use a spin dryer to remove the moisture on the surface of the wafer;

[0074] d. Arrange the wafers into the quartz boat and set the direction. Send the arranged quartz boat into the thermal oxidation furnace and use high temperature dry oxygen to oxidize SiO 2 The wafer is formed on the surface of the wafer, and the oxidized wafer is taken out of the furnace. Then, the diffusion source trivalent electron boron ions are implanted into the wafer using an ion implanter. Then, the wafer is cleaned by RCA as described above. The cleaned wafer is placed in a quartz boat and the direction is determined. The arranged oxidized quartz boat is sent to a high-temperature diffusion furnace. The boron diffusion source is formed into a P+ region using high temperature, and the wafer that has been diffused at high temperature is taken out of the furnace.

[0075] e. Perform a second photolithography and etching, the specific steps are the same as the first photolithography and etching, remove the photoresist after etching, and then perform RCA cleaning, the specific steps are the same as above.

[0076] S6. Metal deposition:

[0077] a. Pre-deposit the first layer of titanium on the surface of the wafer by chemical vapor deposition at a deposition temperature of 400°C to generate a layer of titanium silicide, then introduce nitrogen, and pre-deposit the second layer of titanium in a nitrogen atmosphere at a deposition temperature of 400°C to generate a layer of titanium nitride, and then use a vacuum evaporator to plate barrier metal titanium, nickel and silver on the surface of the wafer in order, and then perform metal alloying, arrange the wafer into a quartz boat, and define the direction, and send the arranged metal alloyed quartz boat into a metal alloying furnace, and after completion, take the wafer out of the furnace after metal alloying, and the resulting silver layer is 40um, and BOE acid is used for etching to remove excess barrier metal;

[0078] b. Use an evaporator to plate welding metal aluminum onto the surface of the chip.

[0079] S7. Photolithography and backside grinding

[0080] a. Perform the third photolithography, the specific steps are the same as the first photolithography, and then perform metal etching, use silver etching solution silver chloride and nitric acid to remove the silver exposed on the wafer surface, and then use high-purity water to quickly rinse the residue on the wafer surface, and then use nickel etching solution ammonium sulfate and nitric acid to remove the nickel exposed on the wafer surface, and then use high-purity water to quickly rinse the residue on the wafer surface, and then use BOE acid to remove the titanium exposed on the wafer surface, and then use high-purity water to quickly rinse the residue on the wafer surface, and use a spin dryer to remove the moisture on the wafer surface, and finally use NMP to remove the photoresist;

[0081] b. Use a grinder to grind the back of the wafer to thin the wafer;

[0082] d. Place the ground wafer in an ultrasonic oscillation tank for 10 minutes, then change the water, ultrasonicate for another 5 minutes, and dry for later use.

[0083] S8. Aluminum evaporation, sand blasting, grain removal and grain corrosion:

[0084] a. Deposit a uniform aluminum film on the surface of the wafer by electron beam evaporation, place the wafer in a clean rack, and place it in N 2 Bake in oven for 30 minutes, oven set temperature 125℃±5℃, N 2 The flow rate is 5±0.5L / min. After baking, the wafer is loaded into the planetary disk and placed in the aluminum steamer. The speed of the planetary disk is set to 40r / min. Wait for the vacuum to reach 3×10 -6 torr, heating the wafer to 125℃ for 5min, melting aluminum and evaporating it, the thickness of the aluminum layer is 10.5μm on the P side and 9.5μm on the N+ substrate side;

[0085] b. Turn on the vacuum pump, tighten the vacuum pipe connected to the iron sheet suction mold, cut off the airflow, evenly spread the iron sheet on the suction mold, gently shake the suction mold to make the iron sheet fall into the mold hole, pull out the tape and tighten it, stick the tape with the adhesive side down on the front of the suction mold, press the back of the tape with a blade to make the adhesive surface and the iron sheet stick tightly, then tear the tape off the mold surface, stick the iron sheet on the tape, check the arrangement of the iron sheets, and fill in the gaps with tweezers if there are any;

[0086] Then turn on the electric furnace, put the glass sheet and the aluminum plate into the electric furnace, preheat the glass sheet to 160℃, preheat the aluminum plate to 180℃, and heat the wax to 320℃ and melt it in the wax melting tank. After the wax is completely melted, immerse the wafer completely in the wax, take it out and place it on the glass sheet with the phosphorus side facing up, then move the glass sheet out of the heat source, wait for the wax to solidify, stick the tape with iron sheet on the glass sheet, ensure that there is no offset between the iron sheet and the wafer, put the glass sheet on the heated aluminum plate, press the glass sheet repeatedly with a Teflon stick until there are no bubbles, take it off the electric furnace, let it cool, remove the tape and remove the excess wax on the edge, put it into the automatic sandblasting machine, set the speed to 55, the corundum to 280#, the swing to 110, and the air pressure to 3.8Kg for sandblasting; the corundum cuts the wafer with regularly arranged iron sheets on the surface under the action of air flow, so as to obtain grains with reasonable table shape;

[0087] c. In a 2000ml plastic measuring cup, press NaOH:H 2O=40±1g:2000±100ml is prepared with aluminum shrinking etching liquid, and it is prepared twice and poured into a special bucket. After 30 minutes after preparation, wait for the etching liquid to cool to room temperature for use, immerse the glass piece with the chip in the stainless steel cylinder filled with aluminum shrinking etching liquid for aluminum shrinking, the time is 10min, and the aluminum plating layer on the edge of the silicon wafer surface is etched to reduce the grain and separate the grain from the glass piece, take out the glass piece with silicon wafer and rinse it with water for ≥30 minutes, and the water in the stainless steel cylinder needs to be replaced 5-6 times within 30 minutes, pour acetone into the stainless steel cylinder to immerse the glass piece, and check the grain shedding condition after the glass piece is soaked for 30 minutes, until the grain is completely separated from the glass piece, remove the glass piece, ultrasonicate for 5 minutes, pour 2000ML acetone into the stainless steel cylinder for ultrasonicate for 5 minutes, use a magnet to suck out the iron piece, and then pour 500ml new acetone into the stainless steel cylinder to shake the stainless steel cylinder to rinse the grain for 40 seconds, and the grain is placed in an oven for 15 minutes, N 2 The flow rate is 2.5L / min, the drying temperature is 90±5℃, and the grains after drying are sorted to pick out unqualified grains;

[0088] d. After weighing the grains, pour them into a PP mesh can and place them in an etching tank. The etching tank contains a mixed acid with a volume ratio of HF:HNO 3 :H 3 PO 4 =4:15:5, grain etching time 240 seconds, temperature 4°C. After the etching is completed, the PP mesh tank is taken out for three times of pure water washing, each time for 5 minutes, and three times of IPA dehydration, each time for 5 minutes. After the grains are dehydrated, the mouth of the PP mesh tank is covered with clean filter paper and placed in N 2 In the oven, use a clean brush to flatten the grains and bake them. The baking time is 45 minutes, the baking temperature is 50±5℃, N 2 The flow rate is 5LPM.

[0089] S9. Welding, pickling, and glass powder application:

[0090] a. Load the raw materials into the graphite boat in the order of lead wire, welding sheet, molybdenum grain, crystal grain, molybdenum grain, welding sheet and lead wire. Use copper nail head lead wire. Put the loaded graphite boat into the vacuum welding furnace for welding. After stabilizing at 710℃ for 10 minutes, stop heating, cool the water jacket to below 100℃ and take it out of the furnace;

[0091] b. Perform acid corrosion on the PN junction surface of the grains in the finished welding product, put it into the pickling machine, pickle it for 166 seconds with mixed acid 1, nitric acid: sulfuric acid: hydrofluoric acid: phosphoric acid = 1:0.48:1:2.3, the temperature is 10°C, and then rinse with deionized water at 35°C for 60 seconds, and pickle it for 60 seconds with mixed acid 2, phosphoric acid: hydrogen peroxide: deionized water = 1:1:2, the temperature is 62°C, and then rinse with deionized water at 35°C for 60 seconds, and then use N 2Blow dry with an air gun, repeat the above pickling steps, then use deionized water ultrasonic cleaning, high pressure flushing and store in a nitrogen box for use. The nitrogen box flow rate is 0.6±0.1m 3 / H;

[0092] c. Fix the welded parts on the top of the conversion rack, arrange the graphite strips for sintering under the conversion rack, take the welded parts with a comb, take out a row of welded parts each time, align the lead position and drop them into the holes of the graphite strips, place the lead on one side of the graphite strip with the welded parts flat on the stainless steel table, ensure that the molybdenum grains and the crystal grains do not touch the stainless steel table, then press the straightening strip parallel to the direction of the graphite strip horizontally on the lead on the stainless steel table, and gently rub it 1 to 3 times. If it is found that there is still unstraightened material on the same side of the graphite strip, pull it out with tweezers, turn it over, insert the graphite strip and repeat the previous steps. After the straightening is completed, put the straightened materials into the material rack one by one, and place an empty graphite strip when the glass spotting machine converts the working materials. When it reaches the suction nozzle of the glass spotting machine, adjust the height nut of the suction nozzle of the glass spotting machine, and rotate it accordingly based on the scale line of the nut, then put the material in for glass spotting. When the top of the glass spotting suction rod is at the bottom point, the distance from the edge of the wafer is greater than 1mm. Put the material rack in the specified position of the automatic glass spotting machine, and install the glass slurry tank in place. Before glass spotting, adjust the surface wetness of the molybdenum grains. With the grain as the center, bend the lead into a U shape, and then rub the molybdenum grains and the grain part on the back of the hand. When the eyes and the back of the hand are in a line, ensure that residual water marks can be observed on the surface of the hand skin, and then put the glass powder on the glass spotting machine and send it out after baking. The size before glass spotting baking is 4.1~4.3mm, and the size after baking at 600℃ is 3.8~4.1mm;

[0093] S10. Sintering, tinning, packaging:

[0094] a. The furnace temperature is set at 750℃, 745℃, 745℃, 695℃, 620℃, each temperature is controlled at ±10℃, cooling water temperature is <50℃, water flow rate is 400L / H, each water flow rate is controlled at ±50L / H, nitrogen pressure is 2~3Kg / cm 2 , nitrogen flow setting 120CFH, 40CFH, 240CFH, 140CFH, 40CFH, 100CFH, each section N 2 The flow rate is controlled at ±10CFH, the chain speed is 12.5cm / min, and the stainless steel basket with the glass-pointed diode graphite strips is placed into the sintering furnace. During sintering, it is continuously fed into the furnace, and the temperature is balanced by special graphite strips before and after.

[0095] b. Transfer the sintered materials to the pickling board one by one in order, and soak the pickling board in mixed acid 2 for 10 seconds, then rinse with pure water for 20 seconds, and then dehydrate with IPA for 20 seconds and blow dry. Put the tinning tray on the tinning tray rack, put the materials into the tinning tray, shake it gently a few times to make all the materials enter the tinning tray, remove the tinning tray rack, push the tinning tray into the hanging place of the tinning machine, and complete the flux dipping, wetting and retention, tinning, and single-sided tinning. Adjust the height so that the minimum distance from the tin liquid surface to the material nail head is 0.5mm, with no copper leakage as the standard. After hanging back in place, take out the tinning tray, put the tinning tray down on the tinning tray rack, with the tinned nail head lead facing up, and then cool the material and the tinning tray rack naturally together, and tinn the other end according to the above steps. After hanging back in place, take down the tinning tray and put it on the feed trough, with the tinning plate facing up, so that the material falls evenly into the cleaning net basket, spray with pure water for 10 minutes, then soak in 30℃ pure water for 10 minutes, then soak in 85-95℃ pure water for 20 minutes, drain for 2 minutes, dehydrate with anhydrous ethanol, and dry at 80±5℃ for 30min. The obtained product is tested, arranged, printed, tested and packaged with a consistent machine until it is finished.

Claims

1. A high reliability glass bead composite diode, characterized in that: The invention comprises a crystal grain (13), wherein a welding piece (10) is provided on each side of the crystal grain (13), a lead (12) is provided on the side of the welding piece (10) away from the crystal grain (13), a molybdenum grain (11) is provided between the crystal grain (13) and the welding piece (10), and the crystal grain (13), the molybdenum grain (11) and the welding piece (10) are wrapped in glass (9); the crystal grain (13) comprises a metal cathode (1), an N+ substrate (2), an N region (3), a P region (4), a P+ region (5), an insulating dielectric layer (6), a Schottky region (7) and a metal anode (8), wherein the metal cathode (1) is located on the back side of the N+ substrate (2), and the N region ( 3) is located on the front side of the N+ substrate (2), the P region (4) is located on the side of the N region (3) away from the N+ substrate (2), the P region (4) contains a plurality of P+ regions (5), the insulating dielectric layer (6) is located on the side of the P region (4) away from the N region (3), is in a circular ring shape, and has a width smaller than the P region (4), the metal anode (8) is located on the side of the insulating dielectric layer (6) away from the P region (4), covers the insulating dielectric layer (6), the Schottky region (7) is located in the circular ring formed by the insulating dielectric layer, and is connected to the P+ region (5); there are at least two P+ regions (5), and the P+ region (5) contacts the insulating dielectric layer (6) and the Schottky region (7) at the same time.

2. According to claim 1, a high reliability glass bead composite diode is characterized in that: The crystal grain (13) is a truncated cone, and the side surface is an inward arc.

3. The high reliability glass bead composite diode according to claim 1, characterized in that: The P+ region (5) has a depth of 0.8-1 μm, a width of 20-45 μm, and a doping concentration of 1e16-1e19 cm -3 The P region (4) has a depth of 40-60 μm and a doping concentration of 2e13-2e15 cm -3 The N region (3) has a depth of 50-70 μm, and the N+ substrate (2) has a depth of 100-120 μm.

4. The method for preparing a high-reliability glass bead composite diode according to claim 1, characterized in that: The following steps are involved: S1. Boron sheet treatment: push the boron sheet into the furnace tube, dry it in nitrogen atmosphere, and then heat it up to oxidize the boron sheet in anhydrous oxygen atmosphere; S2. The wafer is placed in SC1 solution for cleaning, and then the wafer is placed in SC2 solution for cleaning, and then washed and dehydrated with pure water, and then sent to the oven for baking after dehydration; S3. The wafer is sent to a diffusion furnace for boron diffusion pre-deposition, washed with hydrofluoric acid and pure water, dehydrated and baked, and then subjected to high-temperature oxidation, washed with hydrofluoric acid, BOE, and pure water, dehydrated and baked, and then the wafer is sent to a diffusion furnace for boron diffusion, washed with hydrofluoric acid and pure water, and baked; S4. The wafer is sandblasted on the boron side, washed with pure water and then baked. The wafer is sent to a platinum expansion furnace for platinum diffusion. After the diffusion is completed, the wafer is acid-soaked, washed with pure water and then baked. After sandblasting on both sides of the wafer, it is washed with pure water, SC1, SC2, and pure water respectively and then baked; S5. The wafer is sent to a thermal oxidation furnace, and after the initial oxide layer is formed, the first photolithography and etching are performed, and after the photoresist is removed, RCA cleaning is performed, and the wafer is sent to the thermal oxidation furnace again, and after the oxide layer grows, ion implantation is performed, and the diffusion source is driven into the wafer, and then RCA cleaning is performed, and the wafer is placed in a diffusion furnace for diffusion, and then the second photolithography and etching are performed, and after the photoresist is removed, RCA cleaning is performed; S6. Pre-depositing titanium on the wafer, then plating the barrier metal on the wafer surface, and then sending the wafer into a metal alloying furnace for metal alloying. After the metal alloying, the excess barrier metal is removed with an etching solution, and then the welding metal is plated on the wafer surface; S7. Perform the third photolithography and etching, remove the photoresist, grind the back of the wafer, and then clean and dry it; S8. Depositing an aluminum film on the surface of the wafer to form a metal cathode and a metal anode, separating the crystal grains from the glass sheet after sand blowing, washing and drying the crystal grains, corroding them with a mixed acid, and then dehydrating and drying; S9. Welding is performed in a welding furnace in the order of lead, solder sheet, molybdenum grain, grain, molybdenum grain, solder sheet, and lead, wherein the lead is a nail head lead, and the grain after welding is washed with mixed acid and water, and glass powder is applied to form a spherical glass material attachment layer on the molybdenum column portion of the core of the welded part to obtain a diode blank; S10. Sintering the diode blank to obtain a diode component, tinning the diode component, cleaning and drying it, and packaging it to obtain the desired product.

5. The method for preparing a high reliability glass bead composite diode according to claim 4, characterized in that: In step S3, nitrogen is passed throughout the boron diffusion pre-deposition process, the temperature is raised from 300°C, oxygen is introduced when the temperature reaches 600°C, the temperature is raised to 1150°C and kept constant for 4-6 hours, then the oxygen is turned off when the temperature drops to 600°C, and the temperature is dropped to 350°C before being taken out of the furnace; the thickness of the oxide film of the high-temperature oxidation is required to be ≥80nm.

6. The method for preparing a high reliability glass bead composite diode according to claim 4, characterized in that: In step S4, the platinum source is diffused, the platinum source is placed on a stirrer for stirring, the wafer is placed on a source coating machine for source coating, preheated for 14-16 minutes at the furnace mouth, and then pushed into the constant temperature zone, nitrogen is passed throughout the process, and the wafer is taken out of the furnace and transferred to the support for natural cooling.

7. The method for preparing a high reliability glass bead composite diode according to claim 4, characterized in that: The pre-deposition in step S6 is two layers, the first layer is titanium silicide, the second layer is titanium nitride, the titanium silicide layer is 10-40 angstroms, and the titanium nitride layer is 10-30 angstroms; the barrier metals are Ti, Ni and Ag, respectively, the titanium layer is 0.07-0.1μm, the Ni layer is 0.25-0.75μm, and the metal Ag layer is greater than 30um after metal alloying.

8. The method for preparing a high-reliability glass bead composite diode according to claim 4, characterized in that: The welding temperature in step S9 is 700-720° C., and the sintering temperature in step S10 is 610-760° C.

9. The method for preparing a high-reliability glass bead composite diode according to claim 4, characterized in that: In the step S8, the thickness of the aluminum film is 10.5±0.7 μm for the metal anode and 9.5±0.7 μm for the metal cathode.

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