CN109755116B - A method of making unidirectional TVS chip by printing process - Google Patents

Abstract

The invention relates to a method for manufacturing a unidirectional TVS chip by adopting a printing process, which comprises the steps of silicon chip pretreatment, secondary diffusion texturing, glass passivation printing and drawing, metallization and test sorting, wherein the step of boron diffusion adopts negative pressure diffusion, wet texturing or laser texturing is adopted, and a printing mode is adopted in the glass passivation process to coat a protective layer and glass pulp, so that the glass passivation process is simplified, and the preparation speed is increased. Compared with the traditional method, the printing process has the advantages that the production process for manufacturing the unidirectional TVS chip is large-scale, automatic, informationized and less humanized; the unidirectional TVS chip product has low production cost, high quality, high consistency and good market compatibility; the printing process has high efficiency and high precision, replaces the processes of coating, film coating, electrophoresis and the like in the existing process flow, improves the product consistency and reduces the environmental protection and safety risks while realizing the automatic and less-human production.

Description

A method of making unidirectional TVS chip by printing process

technical field

The invention belongs to the technical field of unidirectional TVS chips, and in particular relates to a method for making unidirectional TVS chips by using a printing process.

Background technique

Transient (transient) voltage suppression diodes, that is, TVS (Transient Voltage Suppressor) diodes are widely used in various electronic circuit systems, and are used in conjunction with resistors, capacitors and other components to protect against transient high voltages. One-way transient voltage suppressor (one-way TVS) Under normal working conditions, the TVS presents a high impedance state to the protected line. When the instantaneous voltage exceeds its breakdown voltage, the TVS provides a low impedance path to instantaneous current. The instantaneous current flowing to the protected component is diverted to the TVS diode, and the voltage across the protected component is limited to the clamped voltage across the TVS. When this overvoltage condition disappears, the TVS diode will return to high impedance. state. TVS is widely used in various protection electronic circuits, with broad market prospects and large development space.

At present, three processes are mainly used in the industry to produce unidirectional TVS chips: knife scraping process, electrophoresis process, and photoresist glass process. Among these three processes, the one-way TVS process of knife scraping method is simple and low in cost. There is no oxide film protection on the edge of the mesa and passivation glass, the solder is easy to flow on the glass, the reliability will be reduced, and it is easy to fail during application; the sharp corners of the electrophoresis process grooves are protected by passivation glass, and the reliability is relatively high, but in production Due to the large number of platinum production processes and the need to use a large amount of acetone for production, there are potential safety hazards and relatively high costs; the photoresist glass method adopts three layers of passivation protection (SIPOS, glass, silicon dioxide), and the reverse voltage is higher using silicon The sheet resistivity range is wider and the reliability is high, but 3 times of photolithography are required in the production, and the production cost is high.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides a method for manufacturing a unidirectional TVS chip by using a printing process, which further improves the production capacity on the basis of improving the quality of the existing products.

The technical scheme adopted in the present invention is: a method for making a unidirectional TVS chip by a printing process, and the preparation steps include:

S1 secondary diffusion texturing;

S2 glass passivation printing drawing;

S3 metallization.

Wherein, the S1 step secondary diffusion texturing includes the steps:

S1-1 pre-diffusion treatment;

S1-2 phosphorus diffusion;

S1-3 Boron diffusion;

S1-4 texturing;

Preferably, the boron diffusion is negative pressure diffusion;

Preferably, the phosphorus diffusion in step S1-2 is to carry out phosphorus diffusion by depositing a phosphorus source on the surface of the silicon wafer by carrying phosphorus oxychloride with nitrogen gas;

Preferably, in the boron diffusion in step S1-3, the boron diffusion source is coated on the surface of the silicon wafer to be expanded by printing, and the multiple coated silicon wafers are stacked in such a way that the boron-coated surfaces are opposite to each other, Diffusion takes place, which is isothermal diffusion.

Preferably, in the above technical solution, between the step S1-2 and the step S1-3, a single-side sanding step is further included, and the single-side sanding step is to perform single-side sanding on any side of the silicon wafer after the phosphorus is diffused. sand;

Preferably, the surface to be expanded is a single-sided sanded surface.

Preferably, in the above technical solutions, the texturing process in steps S1-4 is wet texturing or laser texturing;

Preferably, the wet texturing includes first-level cleaning liquid cleaning; first-level pure water cleaning; second-level cleaning liquid cleaning; second-level pure water cleaning; third-level cleaning liquid cleaning; third-level pure water cleaning ;

Preferably, the laser texturing includes laser texturing; cleaning after texturing: after the silicon wafer is textured, it is immersed in an HF solution for cleaning, and after the HF solution cleaning, overflow cleaning and drying are performed.

Wherein, the S2 step glass passivation printing drawing includes the steps:

S2-1, printing protective glue: protect the silicon wafer without corrosion during subsequent trench etching; S2-2, trench etching and grooving: groove the silicon wafer; S2-3, LPCVD precipitation SiO ₂ : pass LPCVD technology precipitates SiO ₂ to make the electrical parameters more stable; S2-4, glass firing: the glass powder in the passivation layer is solidified at high temperature, and finally the passivation effect is achieved;

Preferably, the printing protective glue in the step S2-1 adopts the screen printing technology.

Preferably in the above technical solutions, the printing protective adhesive is a double-sided printing protective adhesive;

Preferably, the protective glue is acid-resistant wax.

Preferably, in the above technical solution, the groove etching and grooving in step S2-2 includes laser grooving; acid etching; acid cleaning.

Wherein, described S3 step metallization comprises steps:

S3-1 Nickel plating once: Nickel plating on the surface of the silicon wafer once;

S3-2 Nickel sintering: the nickel atoms are diffused into the silicon wafer, and the nickel layer and the silicon layer are combined with each other;

S3-3 Secondary nickel plating: secondary nickel plating on the surface of the silicon wafer;

S3-4 is gold-plated; gold-plated on the surface of the silicon wafer.

Wherein, after the step S3, there is also a test and sorting step, which specifically includes: dot testing; laser scribing; automatic sorting;

Preferably, the dotting test is specifically a multi-dot dotting test of the needle row.

Wherein, the diameter of the silicon wafer is 5 inches, and the silicon wafer is sliced by diamond wire.

The advantages and positive effects that the present invention has are:

1 Since the unidirectional TVS chip requires a high concentration of phosphorus diffusion sources, the printing process cannot meet the required concentration, so the phosphorus source is not applied by the screen printing process, and the boron diffusion source is printed on the boron surface of the silicon wafer to be coated by the screen printing process. , which simplifies the coating process of the silicon wafer liquid source and shortens the processing cycle; after the liquid source is coated, the negative pressure diffusion process is used to reduce the return of the silicon wafer edge to the source, and the diffusion process steps are simplified and the diffusion efficiency is improved. The PN junctions are made uniform and the processing cost of the silicon wafer is reduced. Wet texturing or laser texturing is used to replace the traditional dry sanding, so that the surface of the silicon wafer is made of wormhole-like texture, which increases the surface area of the silicon wafer. The roughness is beneficial to the coating of the protective layer in the subsequent glass passivation process of the silicon wafer, so that the adhesion of the protective layer is increased in the glass passivation process;

2. Compared with the traditional method, the glass passivation process reduces the steps of oxidation, photolithography, development, and back glue, and reduces the use of corresponding solvent reagents. This scheme replaces organic and cyanide and other dangerous chemicals (such as acetone, potassium gold cyanide, etc.) ), making the process safer and more environmentally friendly.

Detailed ways

There are three production processes for one-way TVS: knife scraping method, electrophoresis method, and photoresist method. The technical difficulty and product quality increase in turn, but the overall technical difficulty is still low, the investment is low, and the volume is fast. With the increase in market demand, A large number of workshop-style manufacturers have entered, so that the supply of products exceeds the demand, which requires a high-yield and high-efficiency unidirectional TVS chip preparation process. This solution involves a method for manufacturing unidirectional TVS chips using a printing process, including silicon wafer pretreatment. , secondary diffusion texturing, glass passivation printing and drawing, metallization and testing and sorting several steps, specifically cleaning after DW slicing, annealing, cleaning after annealing, silicon wafer sorting, pre-diffusion treatment, phosphorus diffusion, single-sided printing Sand, Boron Diffusion, Texturing, Printing Resin, Trench Etching, LPCVD Deposition SIPOS, Printing Glass Paste, Glass Firing, LPCVD Deposition SiO ₂ , Printing Resin, Removing SiO ₂ and SIPOS, Metallization, Testing, Diamond Scribing , sorting, packaging and storage. Among them, the raw material of the silicon wafer is the silicon wafer obtained by 5-inch diamond wire slicing. Compared with the original process, the diameter of the silicon wafer is changed from 4 inches to 5 inches. The cost of the support chip is low, and the silicon wafer is changed from the original grinding wafer to DW slicing, which saves the grinding and cleaning processes after the silicon wafer is cut, simplifies the process steps, improves the yield of silicon wafers, and reduces the cost of silicon wafers.

1. Silicon wafer pretreatment

The silicon wafer obtained by diamond wire slicing is pretreated, the impurities on the surface of the silicon wafer are cleaned, and the surface damage part is removed, which specifically includes the following steps:

A Slice cleaning: The silicon wafer is subjected to alkali treatment and nitric acid treatment to clean the metal impurities on the surface of the silicon wafer. The sodium hydroxide solution can be used for the alkali treatment. The purpose of cleaning the silicon wafer is to prevent contamination after annealing.

B Annealing: An automatic wafer loading system is used for annealing, which liberates manpower. The annealing process aims to eliminate the influence of oxygen donors on resistivity.

C Cleaning after annealing: use hydrofluoric acid etching to remove the oxide layer formed on the surface after annealing.

Second, the second diffusion texturing

Phosphorus diffusion is to carry out phosphorus diffusion by depositing phosphorus source on the surface of silicon wafer by carrying phosphorus oxychloride with nitrogen. The single-sided sanding process is to perform single-sided sanding on any side after phosphorus diffusion. The boron diffusion source is printed on the surface of the silicon wafer. The method is coated on the surface of the silicon wafer to be expanded, and multiple coated silicon wafers are placed in a forward stacking manner to perform a high-temperature negative pressure diffusion process. The fabricated PN junction is uniform, which reduces the back-to-source situation, improves the diffusion efficiency, improves the conductivity of the silicon wafer, and textures the surface of the silicon wafer to provide the basis for the glass passivation module, which specifically includes the following steps:

D silicon wafer sorting: The cleaned silicon wafers are screened by a sorting integrated machine, marked and blue-inserted according to the parameters of detecting appearance and resistivity, and qualified silicon wafers are sorted.

E Pre-diffusion treatment: Place the silicon wafer in the etching solution at 0-15℃ for 9-50s to thin both sides of the silicon wafer, change the thickness of the silicon wafer to 10-20μm, and clean the etching solution after the etching. The thinned silicon wafer is placed in alkaline solution for treatment. After completion, the silicon wafer is placed in pure water for overflow cleaning to remove the alkaline solution on the surface of the silicon wafer, and then placed in acid solution for acid treatment, which is also washed with overflow water. Remove the acid solution on the surface of the silicon wafer, and spin dry to remove the water and other impurities on the surface of the silicon wafer.

Wherein, the etching solution is a mixture of nitric acid: hydrofluoric acid: glacial acetic acid: pure water in a ratio of 12:6:6:1, and the etching solution can well etch and thin the silicon wafer.

F Phosphorus Diffusion: Since the unidirectional TVS chip requires a high concentration of phosphorus diffusion sources, the printing process cannot reach the required concentration, so the screen printing process is not used to coat the phosphorus source. When the furnace temperature of the phosphorus diffusion furnace reaches 1000 ℃ The phosphorus-diffused silicon wafer is pushed to the constant temperature zone, and when the temperature rises to 1200 °C, the phosphorus source is deposited on the surface of the silicon wafer by means of nitrogen carrying phosphorus oxychloride, and phosphorus is diffused for 2 hours before being released;

G single-side sanding: use a chain sander under the pressure of 0.12-0.14mpa to perform single-side sanding on any side after phosphorus diffusion, and the sand-removing amount is 15-20 μm, and cleaning after sanding;

H printing boron diffusion source: use the screen printing process to print the boron diffusion source on the sanded surface of the silicon wafer after sand cleaning. After each printing, the silicon wafer needs to be placed in an oven to dry the diffusion source. The time is 1-30min, and the drying temperature is 150-180°C. After the baking is completed, spray Al ₂ O ₃ powder or silicon powder on both sides of the silicon wafer, and stack the silicon wafers on a boat. The surface is opposite to the boron source surface, and the phosphorus source surface and the phosphorus source surface are opposite to each other for lamination. After lamination, they are placed in a silicon carbide boat, and baffles are placed at the front and rear of the carbon boat to compress the silicon wafers.

I Diffusion: The silicon wafers mounted in the carbonization boat are diffused under negative pressure in the diffusion furnace, generally 10-101Kpa. The temperature of the diffusion furnace is increased from 650 °C to 1300 °C for constant temperature diffusion, and the constant temperature time is 5-10h, so that the silicon wafers A uniform PN junction is formed on the surface.

J Diffusion post-processing:

If wet texturing is used for texturing, the post-diffusion treatment is:

The diffused silicon wafers are placed in hydrofluoric acid for post-diffusion treatment. After the silicon wafers are separated, they are rinsed and the surface is cleaned with a mixture of high-temperature water vapor and hydrofluoric acid to remove phosphorus and borosilicate glass on the surface of the diffused silicon wafers.

If laser texturing is used for texturing, the post-diffusion treatment is:

Place the diffused silicon wafer in glass etching solution for post-diffusion treatment, soaking time is 0.5-4h; ultrasonic cleaning 5-30min; one overflow cleaning 5-30min; nitric acid cleaning 5-30min; -30min; spin drying machine.

The glass etching solution is ammonium hydrofluoride, oxalic acid, ammonium sulfate, glycerin, barium sulfate and hot pure water in a volume ratio of 6-10:8-15:20-30:4-15:10-22:110-120 The resulting solution is mixed in proportions.

K fleece:

Wet texturing: configure first-level cleaning solution, second-level cleaning solution and third-level cleaning solution respectively, place the treated silicon wafer in first-level cleaning solution at 50-70℃ for 3-10min, rinse with water for 10-20min, Then move it to the secondary cleaning solution at 70-90°C for 20-30 minutes, rinse with water for 10-20 minutes, then move to the third cleaning solution for 3-10 minutes, rinse with water for 10-20 minutes, and rinse the silicon The surface roughness of the sheet was tested.

The first-level cleaning solution is a solution formed by mixing hydrogen peroxide, pure water and potassium hydroxide solution with a mass fraction of 30% in a volume ratio of 6 to 10: 110 to 120: 1 to 8;

The secondary cleaning solution is a solution formed by mixing a potassium hydroxide solution with a mass fraction of 10-30%, a texturing additive and pure water in a volume ratio of 0.35-0.42:0.04-0.09:5-10;

The tertiary cleaning solution is a solution formed by mixing hydrofluoric acid, hydrochloric acid and pure water in a volume ratio of 10-15:30-40:60-80.

Laser texturing: use a laser to scan the surface of the silicon wafer, the diameter of the spot formed by the laser beam is controlled at 10-80μm, and the laser beam is scanned multiple times in the longitudinal direction in turn, forming one scanning track on the surface of the silicon wafer. Laser scanning is performed on both sides of the silicon wafer; acid solution is used for immersion cleaning, and after acid solution cleaning, two-stage overflow cleaning and drying are performed. The acid solution used here is hydrofluoric acid solution cleaning; two-stage overflow cleaning; and drying.

During laser scanning, the laser used is an infrared laser or other lasers. The laser frequency of the infrared laser is 0.1MHz-1MHz, the power is 10-50W, and the scanning speed of the laser is 3-40m/s, which makes the surface of the silicon wafer rough. The thickness is increased from 0.3m to 0.5-1.5μm; and the laser scanning is not limited by the environment.

Compared with the traditional process, this scheme adopts the screen printing process to print the boron diffusion source on the boron-coated surface of the silicon wafer, which simplifies the coating process of the liquid source of the silicon wafer and reduces the processing cycle; The pressure diffusion process reduces the back-to-source situation at the edge of the silicon wafer, and the diffusion process steps are simplified and the diffusion efficiency is improved; it can make the fabricated PN junction uniform, and reduce the processing cost of the silicon wafer; use wet texturing or laser texturing instead of traditional The dry sanding method makes the surface of the silicon wafer get a wormhole-like suede, which improves the adhesion between the subsequent printing wax and the surface of the silicon wafer.

3. Glass passivation printing

In the original process, the oxide layer plays the role of shielding. For the electrophoresis process, the electrode surface with the oxide layer cannot be electrophoresed with glass, and the grooves in the area without the oxide layer can be electrophoresed with glass. After firing, it can passivate and protect the diffusion junction. In this scheme, the glass is printed instead of the electrophoresis process after etching, and the glass is directly printed in the groove, and the electrode surface does not need an oxide layer. Therefore, compared with the traditional process, the steps of oxidation, photolithography, and development of the adhesive are omitted. , thereby reducing the use of the corresponding solvent reagents, this scheme replaces organic and cyanide and other dangerous chemicals (such as: acetone, potassium aurocyanide), making the process safer and more environmentally friendly; The groove production method greatly shortens the groove production time and improves the production efficiency of one-way TVS. Specifically include the following steps:

L Printing protective glue: The printing protective glue includes several steps of loading, marking surface identification, flipping the silicon wafer, printing the protective glue on both sides of the silicon wafer and baking. Prepare for trench corrosion, make patterns, protect areas that are not corroded, and avoid corrosion of areas that should not be corroded during trench corrosion.

The protective glue is an acid-resistant wax, and the main components of the acid-resistant wax include: 2-butoxyethanol, talc, no asbestos fibers, and 2-(2-ethoxyethoxy) ethyl acetate.

The specific steps are:

Loading, the purpose of loading is to transfer the product from the basket to the printing place, and at the same time perform appearance inspection, preferably using a robot for loading. There is a visual inspection station at the top of the wafer to remove defective and damaged silicon wafers. After the visual inspection, the single channel is changed to a double channel. A turnover buffer station is added at the upper wafer to ensure continuous material during the turnover of the wafer basket. Preferably, the buffer station has a buffer capacity of 50-100 wafers.

Marking surface identification, using an image system to identify the marking surface of the silicon wafer.

Flip the silicon wafer to realize the sorting and flipping function of the silicon wafer, turn it 180 degrees, and place the marking side up.

The silicon wafer is printed with protective adhesive on both sides to prepare for the subsequent groove corrosion, so as to avoid the corrosion of the place that should not be corroded when the groove is corroded. There is a positioning device in front of the printing machine to ensure that the silicon wafer corresponds to the template. Specifically, it includes: printing protective glue on the back, drying, turning over, printing protective glue on the front, and drying. Among them, the steps of printing protective glue on the front and back are: 1. The suction device puts two silicon wafers on the slide table, aligns the photos, and adjusts the position of the silicon wafers; 2. The ink return knife returns the material to the initial printing position , the scraper presses down and pushes the paste forward, reaches the end of printing, and the scraper lifts; 3. Transfer the printed product to the outgoing place; 4. The product is placed on the conveyor belt by the suction device. During the whole printing process, it is required to continuously replenish the material during the printing process; the automatic feeding device is added during the conveying process before printing the protective glue, which forms an interlock with the front-end discharge, and the front-end stops discharging when the material is full.

The drying step is to pass the product through the high temperature chain test furnace to achieve the purpose of baking the printing paste. According to the process requirements, the material of the printing paste and the furnace temperature of the chain test furnace, the silicon wafer is baked in the chain test furnace. The time is also different. The standard is that the product just reaches the drying effect when the product is out of the chain test furnace. The conveyor belt in the chain test furnace is made of high temperature resistant material.

Turn over, that is, turn the dried silicon wafer 180 degrees. The appearance inspection station can be set up at the turning operation place to inspect the defects such as the chipping of silicon wafers, and reject the defective products. A turnover buffer station can also be added at the turning operation to ensure continuous material during the turnover of the silicon wafer basket. Preferably, the buffer station has a buffer capacity of (50-100) silicon wafers. Corresponds to the turnover buffer station at the top sheet.

Basketing, the double-sided printed protective adhesive and dried silicon wafers are loaded into baskets, which is convenient for subsequent turnover. Each basket is packed in a certain quantity, usually 100 pieces/basket.

Baking, baking the silicon wafer basket with the silicon wafers installed in the oven, the purpose is to further dry the printed protective glue.

M laser grooving: According to the pattern formed by the photoresist, laser is used to groov the channel pattern, the purpose is to eliminate the edge burrs caused by the printing glue, and at the same time, it can speed up the subsequent groove corrosion rate; specifically, the laser is used on the surface of the silicon wafer. Scan, burn the exposed position of the unprinted protective glue on the silicon wafer to achieve the purpose of grooving.

N groove corrosion: groove shape and depth required by etching, degumming and cleaning operations; wherein the corrosion is made of mixed acid etching, mixed acid is nitric acid: hydrofluoric acid: acetic acid is a 6:4:1 mixture, including acid etching and acid cleaning, after obtaining the groove shape, rinse the mixed acid carried on the surface of the silicon wafer after the trench etching; then remove the photoresist through the process of (5% to 10% KOH solution alkali cleaning, and then remove the photoresist from the surface of the silicon wafer through the cleaning step. The acid-base cleaning agent and impurities and impurities are removed.

O LPCVD deposition of SIPOS: Promote the growth of a polycrystalline passivation layer at the bottom of the trench by LPCVD technology.

P-printed glass paste: The glass paste passivation layer is printed on the silicon wafer by the screen printing process. The printing process includes two printings, and the silicon wafer needs to be dried after each printing.

The glass slurry is a slurry formed by mixing cellulose, thixotropic agent and glass powder in proportion.

Add 2-4g of cellulose to 100ml of butyl carbitol, heat and stir for 30-60min; then add 0.5-1.5% thixotropic agent, heat and stir for 30-60min; finally add 150-220g of glass powder and stir evenly for 30 minutes ~60min to make glass paste.

Printing the glass paste passivation layer includes the steps of film loading, primary printing, drying, secondary printing, drying, and basket loading, as follows:

The film is loaded by a robot, and there is also a visual inspection station and a turnover buffer station at the loading position.

There is a positioning device in front of the printing table for one-time printing, which is used to position the transferred silicon wafer to ensure that the silicon wafer corresponds to the template. The purpose of the primary and secondary printing is to print the glass paste passivation layer, including:

a Put the two silicon wafers on the slide table by the suction device, take pictures and align them, and adjust the position of the silicon wafers to be 1-3mm below the screen plate, that is, the plate spacing is 1-3mm, and ensure that the silicon wafers are horizontally aligned Appropriate printing position; b The ink returning knife returns the material to the initial printing position, and the scraper presses downward (preferably, the scraper moves down 1-3mm) to contact the upper surface of the screen, push the paste forward, and after reaching the printing end position, The squeegee is lifted; the preferred ranges of printing parameters are as follows: the force given by the printing equipment to the squeegee is (30-120) N, the printing speed is (50-300) mm/S, and the angle between the squeegee and the silicon wafer plane is 40°～ 90°, the material hardness of the scraper itself is between (40 ~ 80) HRC;

c Transfer the printed product to the outgoing place, and the suction device places the product on the conveyor belt.

During the first printing and the second printing, the material needs to be continuously replenished; the automatic feeding device is added during the pre-printing transmission process to form an interlock with the front-end material discharge. When the material is full, the front-end material stops discharging.

The purpose of drying is to dry the printed passivation layer, and the product is dried through a high temperature chain test furnace. According to the process requirements, the material of the printed passivation layer and the furnace temperature of the chain test furnace, the silicon wafer is The baking time in the chain test furnace is also different. The standard is that the drying effect is just achieved when the product is out of the chain test furnace. The conveyor belt in the chain test furnace is made of high temperature resistant material.

Basket loading: transfer the dried silicon wafers into the silicon wafer basket to facilitate subsequent turnover, preferably 100 pieces/basket.

Q Glass firing: The silicon wafer with the printed glass passivation layer is fired in a firing furnace, so that the glass is transformed from a powder state to a glass state, and the organic matter in the glass paste is removed.

R LPCVD deposition of SiO ₂ : SiO ₂ is deposited by LPCVD technology, and an oxide ring is formed on the edge of the glass passivation layer.

S printing wax: The photoresist is printed on the P side by screen printing technology as a corrosion-resistant protective wax. The process is the same as step J.

T remove SiO ₂ and SIPOS: use hydrofluoric acid and mixed acid to remove SiO ₂ and SIPOS, respectively, remove the oxide layer (SiO ₂ ) and SIPOS on the electrode surface and keep the oxide layer (SiO ₂ ) and SIPOS on the passivation glass.

4. Metallization

Nickel-gold plating is carried out on the surface of the silicon wafer, and two nickel-plating and one gold-plating are carried out in total.

U firstly plated nickel on the surface of the silicon wafer by chemical method, nickel-silicon sintered in a chain sintering furnace after nickel plating, sintered and then chemically plated with nickel on the surface of the silicon wafer after primary nickel sintering, and then chemically plated with nickel Method Gold plating (silver plating) is performed on the surface of the silicon wafer after secondary nickel plating.

Soak the silicon wafer with ammonium fluoride etching solution for 10 to 30 minutes to remove the oxide layer on the surface of the silicon wafer, and then carry out ultrasonic overflow cleaning in the water tank after removing the oxide layer; The surface is cleaned, and then the hydrofluoric acid on the surface is washed with pure water; the silicon wafer is soaked in an activation solution to activate the atoms on the surface of the silicon wafer, and then cleaned with water after activation; 10 Carry out nickel plating in the nickel plating solution, shake the flower basket to make the reaction uniform; sinter the silicon wafer at 500-650 ℃, so that the nickel atoms diffuse into the silicon, and the nickel layer and the silicon layer are combined with each other; the silicon wafer is subjected to nitric acid. Cleaning, removing the oxidized part of the surface at high temperature, and then cleaning with pure water; soaking the silicon wafer with an activation solution to activate the atoms on the surface of the silicon wafer, and then cleaning with pure water; performing secondary nickel plating, soaking the silicon wafer at a temperature of 60-100 °C, Nickel plating is carried out in an alkaline nickel plating solution, shake the flower basket to make the reaction uniform, and then clean with pure water; soak the silicon wafer with hydrochloric acid, clean and neutralize the alkaline residue on the surface, and then clean with pure water; soak the silicon wafer at a temperature of 60～ At 100°C, gold plating is carried out in an acidic silver plating solution, and the flower basket is shaken to make the reaction uniform, so as to complete the surface metallization.

5. Test sorting

The yield rate of one-way TVS chips is determined by testing and sorting, and the defective products are eliminated to screen out high-quality chips.

V test: test the electrical defective cores for dot marking, and eliminate the electrical defective products. Among them, the probe needle row or probe needle plate test is used, which can test 50 to 1000 chips at a time, instead of the traditional random test and single-pin dot test. Upload the product to the testing machine, arrange the test pins into pin rows or pin boards, contact the silicon wafer, test the electrical properties, compare with the preset test standards, and mark the bad core particles with ink dots

W diamond knife scribing: use high-speed diamond knife cutting method to split the chip into the required size.

X-split: The silicon wafer is transferred to the split area along the belt, and the automatic split rod rolls one time in the horizontal and vertical directions to separate the chips.

Y sorting: The core particles are transferred along the belt to the sorting area, and the CCD technology is used to automatically identify the leftover materials and defective products for removal, and collect the good products.

Since the unidirectional TVS chip requires a high concentration of phosphorus diffusion sources, the printing process cannot meet the required concentration, so the phosphorus source is not applied by the screen printing process. The coating process of the silicon wafer liquid source is simplified, and the processing cycle is shortened; after the liquid source is coated, a negative pressure diffusion process is used to reduce the return to the source of the silicon wafer edge, and the diffusion process steps are simplified, which improves the diffusion efficiency. The produced PN junction is uniform, which reduces the processing cost of the silicon wafer. The traditional dry sanding is replaced by wet texturing or laser texturing, so that the surface of the silicon wafer is made of wormhole-like texture, which increases the roughness of the silicon wafer surface. It is beneficial to the coating of the protective layer in the subsequent glass passivation process of the silicon wafer, so that the adhesion of the protective layer is increased in the glass passivation process. Reduce the use of corresponding solvent reagents, this scheme replaces organic and cyanide and other dangerous chemicals (such as: acetone, potassium aurocyanide), making the process safer and more environmentally friendly.

As used in the specification and claims, certain terms are used to refer to particular components. Those skilled in the art should understand that different manufacturers may use different nouns to refer to the same component. The present specification and claims do not use the difference in name as a way to distinguish components, but use the difference in function of the components as a criterion for distinguishing. The "comprising" mentioned throughout the specification and claims is an open-ended term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range, and basically achieve the technical effect. Subsequent descriptions in the specification are preferred embodiments for implementing the present application, however, the descriptions are still intended to illustrate the general principles of the present application and are not intended to limit the scope of the present application. The scope of protection of this application should be determined by the appended claims.

It should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a commodity or system comprising a list of elements includes not only those elements, but also includes not explicitly listed other elements, or elements inherent to the commodity or system. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or system that includes the element.

An embodiment of the present invention has been described in detail above, but the content is only a preferred embodiment of the present invention, and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still belong to the scope of the patent of the present invention.

Claims (13)

1. a method that adopts printing technology to make one-way TVS chip, is characterized in that: preparation step comprises: S1 secondary diffusion texturing; S2 glass passivation printing drawing; S3 metallization; The S1 step of secondary diffusion texturing includes the steps: S1-1 pre-diffusion treatment; S1-2 phosphorus diffusion; S1-3 Boron diffusion; S1-4 texturing; The boron diffusion is negative pressure diffusion; The phosphorus diffusion in the step S1-2 is to carry out phosphorus diffusion by depositing a phosphorus source on the surface of the silicon wafer by carrying phosphorus oxychloride with nitrogen; In the boron diffusion in the step S1-3, the boron diffusion source is coated on the surface of the silicon wafer to be expanded by printing, and multiple coated silicon wafers are stacked in a manner that the boron-coated surfaces are opposite to each other for diffusion. The temperature of the diffusion furnace is raised from 650°C to 1300°C for constant temperature diffusion, and the constant temperature time is 5-10h; The S1-4 step texturing process is wet texturing or laser texturing; The laser texturing includes laser texturing; cleaning after texturing: after the silicon wafer is textured, it is immersed and cleaned in HF solution, and after the HF solution is cleaned, it is washed with overflowing water and dried; The diameter of the spot formed by the laser beam is controlled at 10-80μm, and the laser beam is scanned horizontally for multiple times in the longitudinal direction, forming a scanning track on the surface of the silicon wafer, and laser scanning is performed on both sides of the silicon wafer; In laser scanning, the laser used is an infrared laser, the laser frequency of the infrared laser is 0.1MHz-1MHz, the power is 10-50W, and the scanning speed of the laser is 3-40m/s. 2. a kind of method that adopts printing process to make unidirectional TVS chip according to claim 1, is characterized in that: between described S1-2 step and described S1-3 step, also comprise step one-sided sanding, described The single-side sanding step is to perform single-side sanding on any side of the silicon wafer after phosphorus diffusion. 3. A method of making a unidirectional TVS chip by a printing process according to claim 2, wherein the surface to be expanded is a single-sided sanding surface. 4. a kind of method that adopts printing technique to make unidirectional TVS chip according to claim 2, is characterized in that: The wet texturing comprises first-level cleaning liquid cleaning; first-level pure water cleaning; second-level cleaning liquid cleaning; second-level pure water cleaning; third-level cleaning liquid cleaning; third-level pure water cleaning. 5. a kind of method that adopts printing technology to make unidirectional TVS chip according to claim 1, is characterized in that: described S2 step glass passivation printing drawing comprises the steps: S2-1, printing protective glue: protect the silicon wafer without corrosion during subsequent trench etching; S2-2, trench etching and grooving: groove the silicon wafer; S2-3, LPCVD precipitation SiO ₂ : pass LPCVD technology precipitates SiO ₂ to make electrical parameters more stable; S2-4, glass firing: After high temperature, the glass powder in the passivation layer is solidified, and finally the passivation effect is achieved. 6 . The method for manufacturing a unidirectional TVS chip by a printing process according to claim 5 , wherein the printing protective glue in the step S2-1 adopts a screen printing technology. 7 . 7 . The method according to claim 5 , wherein the printing protective adhesive is a double-sided printing protective adhesive. 8 . 8 . The method of claim 7 , wherein the protective glue is acid-resistant wax. 9 . 9 . The method for manufacturing a unidirectional TVS chip by a printing process according to claim 5 or 6 , wherein the groove etching and grooving in step S2-2 comprises laser grooving; acid etching; and acid cleaning. 10 . 10. A method for making a unidirectional TVS chip by a printing process according to claim 1, wherein the metallization in the S3 step comprises the steps: S3-1 Nickel plating once: Nickel plating on the surface of the silicon wafer once; S3-2 Nickel sintering: the nickel atoms are diffused into the silicon wafer, and the nickel layer and the silicon layer are combined with each other; S3-3 Secondary nickel plating: secondary nickel plating on the surface of the silicon wafer; Gold-plated S3-4; gold-plated on the surface of the silicon wafer. 11. a kind of method that adopts printing process to make unidirectional TVS chip according to claim 1, it is characterized in that: after described S3 step, also comprises test and sorting step, specifically comprises: Dotting test; Laser scribing; Automatic sorting select. 12 . The method for manufacturing a unidirectional TVS chip by a printing process according to claim 11 , wherein the dot-spotting test is specifically a pin-row multi-spot dot-spotting test. 13 . 13 . The method according to claim 1 , wherein the diameter of the silicon wafer is 5 inches, and the silicon wafer is sliced by diamond wire. 14 .