A low forward voltage drop diode and a method for manufacturing the same

Abstract

The present application belongs to the technical field of semiconductor discrete device manufacturing, and particularly relates to a low forward voltage drop diode and a preparation method thereof. A titanium-niobium-silicon composite sol concentrated precursor and anhydrous ethanol are prepared into an interface coating liquid, molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol and anhydrous ethanol are prepared into a conductive buffer slurry, and a silicon epitaxial wafer is cleaned, treated with hydrofluoric acid, coated, baked, annealed, deposited with metal, prepared with a conductive buffer layer, solidified with silver paste, deposited with a back aluminum-silicon alloy layer, edge passivated and packaged to obtain the low forward voltage drop diode. The present application can reduce the interface barrier and electrode series resistance, and improve the conduction uniformity and device stability.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor discrete device manufacturing technology, specifically relating to a low forward voltage drop diode and its fabrication method. Background Technology

[0002] With the rapid development of portable electronic devices, low-voltage power management, battery protection, rectification and conversion, and power control circuits, the performance requirements for diodes in terms of miniaturization, high efficiency, and low heat generation are constantly increasing. For diodes, forward voltage drop is a crucial parameter affecting conduction loss and device temperature rise. A high forward voltage drop causes electrical energy to be converted into heat during conduction, reducing system efficiency, increasing the difficulty of heat dissipation design, and affecting package reliability and long-term operational stability. Although traditional silicon-based diodes have mature fabrication processes, low costs, and good stability, forward conduction losses remain significant in low-voltage, high-current, or high-frequency applications, making it difficult to meet the high-efficiency conduction requirements of precision power supplies, mobile terminals, sensor power supplies, and low-energy-consumption modules. Therefore, developing a diode fabrication method that achieves lower forward voltage drop, lower series resistance, and maintains reverse stability based on existing silicon-based processes has significant engineering application value.

[0003] Existing low forward voltage drop diodes typically achieve performance improvements through optimizing the semiconductor substrate, adjusting metal contacts, reducing the barrier height, improving the back ohmic contact, or using special wide bandgap materials. Among these, the interface state between the metal and the silicon epitaxial wafer has a critical impact on the diode's conduction performance. Problems such as numerous dangling bonds, residual contamination, uneven local oxide layers, or discontinuous metal deposition at the interface can easily lead to uneven barrier distribution, localized current congestion, and increased forward voltage drop. Simply reducing the barrier height may increase reverse leakage current and decrease temperature stability. Meanwhile, the lateral conductivity of the front electrode region, the quality of the back ohmic contact, and the passivation state of the chip edges also collectively affect the diode's actual conduction loss and reliability. Existing solutions employ complex epitaxy, ion implantation, vacuum multilayer deposition, or expensive nanomaterial transfer processes. While these can improve device performance, they are costly and involve complex process control, hindering the large-scale production of ordinary low-voltage rectifier devices.

[0004] Therefore, existing technologies still require a low forward voltage drop diode fabrication method that is simple in composition, readily available in raw materials, and highly compatible with various processes. This method should be able to reduce interface defects and barrier inhomogeneities at the metal-silicon epitaxial wafer contact point through a synergistic design of interface modulation, conductive buffering, and edge passivation, while simultaneously reducing the series resistance of the front conductive path and improving leakage current stability in the chip edge region, all based on conventional silicon epitaxial wafers. Titanium-niobium-silicon composite sol-gel concentrate precursors can be used to form ultrathin barrier modulation layers, which is beneficial for improving the contact uniformity between the silicon surface and the Schottky metal layer; molybdenum-tungsten-nitrogen-carbon conductive buffer powders can be used to form conductive buffer layers, which is beneficial for improving the conductivity continuity and current spread capability of the front electrode region. By combining the above-mentioned interface coating, metal deposition, conductive buffering, back contact, edge passivation, and encapsulation steps, the forward conduction performance and operational stability of the diode can be improved without significantly increasing process complexity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for fabricating a low forward voltage drop diode, comprising the following steps: S1. Mix the titanium-niobium-silicon composite sol-gel concentrate precursor with anhydrous ethanol and disperse it ultrasonically to obtain an interface coating liquid; mix molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol and anhydrous ethanol, grind them to obtain a conductive buffer slurry. S2. By weight, the n-type silicon epitaxial wafer is cleaned, rinsed with deionized water, treated with hydrofluoric acid, rinsed again with deionized water, and dried with nitrogen to obtain a pretreated n-type silicon epitaxial wafer; an interface coating solution is applied to the front side of the pretreated n-type silicon epitaxial wafer, baked, and annealed in a nitrogen atmosphere to obtain an n-type silicon epitaxial wafer with an ultrathin barrier control layer; a titanium layer and a nickel layer are sequentially deposited on the ultrathin barrier control layer to obtain a Schottky metal layer; a conductive buffer paste is coated on the Schottky metal layer. The material is dried and heat-treated in a nitrogen atmosphere to obtain a conductive buffer layer. 0.8-3.0 parts of silver conductive paste are coated onto the conductive buffer layer and cured. An aluminum-silicon alloy layer is deposited on the back side of the n-type silicon epitaxial wafer using an aluminum-silicon alloy target and annealed. 0.4-2.0 parts of polyimide passivating adhesive are coated onto the edge of the n-type silicon epitaxial wafer and cured to obtain an n-type silicon epitaxial wafer with an edge passivation layer. The n-type silicon epitaxial wafer with the edge passivation layer is connected to copper leads and encapsulated with epoxy encapsulant.

[0006] In this invention, the formation process of the low forward voltage drop diode includes silicon surface pretreatment, formation of an ultrathin barrier control layer, formation of a Schottky metal layer, formation of a conductive buffer layer, formation of a back contact, edge passivation, and encapsulation. After cleaning, rinsing with deionized water, hydrofluoric acid treatment, rinsing with deionized water again, and nitrogen drying, surface organic contaminants, soluble residues, and the natural oxide layer are removed from the n-type silicon epitaxial wafer. After an interface coating solution is applied to the front side of the pretreated n-type silicon epitaxial wafer, the titanium-niobium-silicon composite sol-gel concentrate precursor undergoes further dehydration and polycondensation during baking and nitrogen atmosphere annealing, forming an ultrathin barrier control layer on the surface of the n-type silicon epitaxial wafer, thus changing the interfacial contact state between the silicon surface and the subsequent metal layers. Subsequently, a titanium layer and a nickel layer are sequentially deposited on the ultrathin barrier control layer. The titanium layer contacts the ultrathin barrier control layer and forms an adhesion transition structure, and the nickel layer and titanium layer together constitute the Schottky metal layer. A conductive buffer paste is coated onto a Schottky metal layer, followed by drying and heat treatment in a nitrogen atmosphere. Terpineol evaporates, ethyl cellulose decomposes upon heating, and molybdenum-tungsten-nitrogen-carbon conductive buffer powder remains on the surface of the Schottky metal layer, forming a conductive buffer layer. After curing, a silver conductive paste forms a front-side conductive connection structure. An aluminum-silicon alloy target is deposited on the back side of an n-type silicon epitaxial wafer and annealed to form a back-side contact layer. After curing, polyimide passivating adhesive covers the edge area of ​​the n-type silicon epitaxial wafer. Copper leads and epoxy encapsulation adhesive form the external electrical connection structure and encapsulation protection structure, respectively, resulting in a low forward voltage drop diode.

[0007] According to a preferred embodiment of the present invention, in step S1, the amounts of the titanium-niobium-silicon composite sol-gel concentrate precursor and anhydrous ethanol, by weight, are 0.04-0.20 parts and 8.0-20.0 parts, respectively; the amounts of the molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol, and anhydrous ethanol are 0.15-0.80 parts, 0.05-0.30 parts, 0.8-3.0 parts, and 1.0-5.0 parts, respectively; and the ultrasonic dispersion time is 20-40 min.

[0008] According to a preferred embodiment of the present invention, in step S2, the thickness of the ultrathin barrier control layer is 1-5 nm; the thickness of the titanium layer is 5-20 nm; and the thickness of the nickel layer is 20-80 nm; the baking step includes processing at 80-120°C; and the heat treatment step includes processing at 250-350°C.

[0009] According to a preferred embodiment of the present invention, the preparation method of the titanium-niobium-silicon composite sol-gel concentrate precursor includes: A1. By weight, mix 10.0-18.0 parts tetrabutyl titanate, 3.0-8.0 parts tetraethyl orthosilicate, and 60.0-90.0 parts anhydrous ethanol, add 1.0-3.0 parts acetylacetone, and continue mixing to obtain a titanium silicon alkoxide premix; dissolve 1.0-4.0 parts niobium ammonium oxalate hydrate in 10.0-25.0 parts deionized water to obtain a niobium oxalate solution; add the niobium oxalate solution to the titanium silicon alkoxide premix, adjust the pH with ammonia, and continue stirring to obtain a titanium niobium silicon composite sol; A2. Concentrate the titanium-niobium-silicon composite sol under reduced pressure.

[0010] In this invention, the formation process of the titanium-niobium-silicon composite sol-gel concentrate precursor includes alkoxide coordination, hydrolysis-condensation, and vacuum concentration. Tetrabutyl titanate and tetraethyl orthosilicate are mixed in anhydrous ethanol to form a homogeneous alkoxide system. Upon addition of acetylacetone, coordination occurs with the titanium centers in tetrabutyl titanate, occupying some coordination sites, reducing the hydrolysis rate of tetrabutyl titanate upon contact with water, and minimizing the rapid precipitation of local titanium oxide species, resulting in a titanium-silicon alkoxide premix. Niobium ammonium oxalate hydrate dissolves in deionized water to form a niobium oxalate solution, in which niobium exists in the oxalate-coordinated form and enters the titanium-silicon alkoxide premix with the aqueous phase. After water enters the system, tetrabutyl titanate and tetraethyl orthosilicate gradually hydrolyze, forming titanium-containing hydroxyl structures and silicon-containing hydroxyl structures, respectively. The niobium-containing species in the niobium ammonium oxalate hydrate simultaneously enter the hydrolysis-condensation system. After adjusting the pH of the system with ammonia, dehydration condensation occurs between titanium-containing hydroxyl structures, silicon-containing hydroxyl structures, and niobium-containing species, connecting them via oxygen bridges to form a titanium-niobium-silicon composite sol. After vacuum concentration, some anhydrous ethanol and water are removed from the titanium-niobium-silicon composite sol, increasing the inorganic component content and yielding a concentrated precursor. This precursor, remaining in a sol concentrate state, is redispersed in anhydrous ethanol to form an interface coating solution. During subsequent baking and nitrogen atmosphere annealing, condensation continues, forming an ultrathin barrier control layer.

[0011] According to a preferred embodiment of the present invention, in step A1, the pH is adjusted to 4.0-5.0 using ammonia.

[0012] According to a preferred embodiment of the present invention, in step A2, the temperature for vacuum concentration is 50-65°C.

[0013] According to a preferred embodiment of the present invention, the preparation method of the molybdenum-tungsten-nitrogen-carbon conductive buffer powder includes: B1. By weight, add 6.0-12.0 parts of ammonium molybdate tetrahydrate, 3.0-8.0 parts of ammonium metatungstate and 12.0-25.0 parts of dicyandiamide to 40.0-80.0 parts of deionized water and stir at 50-70℃ to obtain a molybdenum-tungsten-nitrogen-carbon precursor solution. B2. Concentrate the molybdenum-tungsten-nitrogen-carbon precursor solution at 70-85℃ to obtain a gel; dry and pulverize the gel, heat it to 780-820℃ under a nitrogen atmosphere, keep it at that temperature, cool it to room temperature, ball mill it, and sieve it.

[0014] In this invention, the formation process of the molybdenum-tungsten-nitrogen-carbon conductive buffer powder includes aqueous dissolution, concentration into a gel, drying, and thermal conversion under a nitrogen atmosphere. Ammonium molybdate tetrahydrate dissolves in deionized water to form molybdenum-containing oxygen species, and ammonium metatungstate dissolves in deionized water to form tungsten-containing oxygen species. Dicyandiamide, after dissolution, is in the same aqueous phase system as the molybdenum-containing oxygen species and the tungsten-containing oxygen species. After stirring, ammonium molybdate tetrahydrate, ammonium metatungstate, and dicyandiamide form a molybdenum-tungsten-nitrogen-carbon precursor solution in the aqueous phase. During the heating and concentration process, the molybdenum-tungsten-nitrogen-carbon precursor solution gradually loses water, the distribution distance between the molybdenum-containing oxygen species, the tungsten-containing oxygen species, and dicyandiamide decreases, the system viscosity increases, and it transforms into a gel. After drying, the gel forms a solid precursor containing molybdenum, tungsten, nitrogen, and carbon components. After being pulverized, the solid precursor is heated and held at a temperature under a nitrogen atmosphere. Dicyandiamide decomposes and condenses upon heating, forming a nitrogen-carbon structure and carbonaceous reducing components. Molybdenum-containing oxygen species and tungsten-containing oxygen species undergo reduction, carbonization, and nitrogen-carbon coating in the nitrogen-carbon environment, forming a composite conductive phase containing molybdenum, tungsten, nitrogen, and carbon. After cooling, the mixture is ball-milled and sieved to break up agglomerated particles and remove coarse particles, yielding a molybdenum-tungsten-nitrogen-carbon conductive buffer powder.

[0015] According to a preferred embodiment of the present invention, in step B1, the stirring time at 50-70°C is 1-2 hours.

[0016] According to a preferred embodiment of the present invention, in step B2, the drying temperature is 100-120°C and the drying time is 8-12 hours; the temperature is raised to 780-820°C and held for 1-3 hours.

[0017] The present invention also provides a low forward voltage drop diode prepared according to the method for preparing a low forward voltage drop diode.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, a titanium-niobium-silicon composite sol-gel concentrate precursor is mixed with anhydrous ethanol to prepare an interface coating solution, which is then coated onto the front side of a pretreated n-type silicon epitaxial wafer. After baking and annealing in a nitrogen atmosphere, an ultrathin barrier control layer is formed. The ultrathin barrier control layer is located between the n-type silicon epitaxial wafer and the titanium and nickel layers, so that a continuous interface is formed on the front side of the n-type silicon epitaxial wafer before the deposition of the titanium and nickel layers. This reduces the interface non-uniformity caused by the direct deposition of the titanium and nickel layers after cleaning, deionized water rinsing, hydrofluoric acid treatment, deionized water rinsing, and nitrogen drying on the surface of the n-type silicon epitaxial wafer, and reduces the interface impedance between the Schottky metal layer and the n-type silicon epitaxial wafer, thereby reducing the forward conduction voltage drop of the low forward voltage drop diode.

[0019] (2) In this invention, a conductive buffer slurry is prepared by mixing molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol, and anhydrous ethanol. The conductive buffer slurry is then coated onto a Schottky metal layer and dried and heat-treated in a nitrogen atmosphere to form a conductive buffer layer. The molybdenum-tungsten-nitrogen-carbon conductive buffer powder is distributed in the conductive buffer layer. Ethyl cellulose and terpineol adjust the coating film state of the conductive buffer slurry, so that the conductive buffer layer forms a continuous conductive path after covering the surface of the Schottky metal layer. This reduces local current concentration on the surface of the Schottky metal layer, reduces the series resistance during the forward current transmission process, and reduces the heat generation of the low forward voltage drop diode during conduction.

[0020] (3) In this invention, a silver conductive paste is coated onto a conductive buffer layer and cured. An aluminum-silicon alloy layer is deposited on the back side of an n-type silicon epitaxial wafer using an aluminum-silicon alloy target and annealed. Polyimide passivating adhesive is coated onto the edge of the n-type silicon epitaxial wafer and cured to form an n-type silicon epitaxial wafer with an edge passivation layer. The n-type silicon epitaxial wafer with the edge passivation layer is then connected to copper leads and encapsulated with epoxy encapsulant. The silver conductive paste, aluminum-silicon alloy layer, polyimide passivating adhesive, copper leads, and epoxy encapsulant correspond to front current lead-out, back contact, edge protection, external connection, and encapsulation protection, respectively, which reduces the contact loss, edge leakage, and encapsulation failure risk of the low forward voltage drop diode, and improves the device's conduction stability and long-term use stability. Detailed Implementation

[0021] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0022] Example 1

[0023] This embodiment provides a method for fabricating a low forward voltage drop diode, the steps of which include: S1. Mix 0.12g of titanium-niobium-silicon composite sol-concentrated precursor (dry basis) and 14.0g of anhydrous ethanol, and ultrasonically disperse at 200W ultrasonic power for 30min to obtain an interface coating solution; mix 0.475g of molybdenum-tungsten-nitrogen-carbon conductive buffer powder, 0.175g of ethyl cellulose, 1.9g of terpineol and 3.0g of anhydrous ethanol, and grind for 30min until the slurry is uniform to obtain a conductive buffer slurry; S2. Take one n-type silicon epitaxial wafer, the diameter of which is 100mm and the crystal orientation is... <100> A substrate with a thickness of 525 μm, an epitaxial layer thickness of 5 μm, and an epitaxial layer resistivity of 1.5 Ω·cm was used. The n-type silicon epitaxial wafer was ultrasonically cleaned in anhydrous ethanol for 5 min, then rinsed three times with deionized water for 30 s each time. It was then treated with 1% hydrofluoric acid for 60 s, rinsed three times with deionized water for 30 s each time, and dried with nitrogen for 60 s to obtain a pretreated n-type silicon epitaxial wafer. An interface coating solution was spin-coated onto the front side of the pretreated n-type silicon epitaxial wafer at a speed of 3000 r / min for 30 s. It was then baked at 100℃ for 10 min and annealed at 320℃ in a nitrogen atmosphere for 10 min to obtain an n-type silicon epitaxial wafer with a 3 nm thick ultrathin barrier control layer. A 12.5 nm thick titanium layer and a 50 nm thick nickel layer were sequentially deposited on the ultrathin barrier control layer using magnetron sputtering. A Schottky metal layer was obtained; conductive buffer paste was screen-printed onto the Schottky metal layer, dried, and heat-treated at 300℃ for 10 min in a nitrogen atmosphere to obtain a conductive buffer layer; 1.9 g of silver conductive paste was coated onto the conductive buffer layer and cured at 200℃ for 30 min; an aluminum-silicon alloy layer with a thickness of 500 nm was deposited on the back side of the n-type silicon epitaxial wafer using an aluminum-silicon alloy target by magnetron sputtering and annealed at 400℃ for 10 min in a nitrogen atmosphere; 1.2 g of polyimide passivation adhesive was coated on the edge of the n-type silicon epitaxial wafer and cured at 250℃ for 30 min to obtain an n-type silicon epitaxial wafer with an edge passivation layer; the n-type silicon epitaxial wafer with the edge passivation layer was diced into 1 mm × 1 mm chips, the chips were connected to copper leads, encapsulated with epoxy encapsulant, and cured at 150℃ for 1 h to obtain a low forward voltage drop diode.

[0024] Preparation steps of titanium-niobium-silicon composite sol-gel concentrated precursor: A1. Add 14.0 g tetrabutyl titanate, 5.5 g tetraethyl orthosilicate, and 75.0 g anhydrous ethanol to a reaction vessel. Stir at 300 r / min for 15 min at 25 °C to disperse the tetrabutyl titanate and tetraethyl orthosilicate in the anhydrous ethanol. Then add 2.0 g acetylacetone and continue mixing at 300 r / min for 45 min at 25 °C to obtain a titanium silicon alkoxide premix. Add 2.5 g niobium ammonium oxalate hydrate to 17.5 g deionized water and stir at 300 r / min for 20 min at 25 °C until the niobium ammonium oxalate hydrate dissolves to obtain a niobium oxalate solution. Add the niobium oxalate solution dropwise to the titanium silicon alkoxide premix. After the addition is complete, adjust the pH to 4.5 with ammonia water. Continue stirring at 300 r / min for 3 h at 25 °C to obtain a titanium niobium silicon composite sol. A2. The titanium-niobium-silicon composite sol was concentrated under reduced pressure at 57.5℃ to a free-flowing viscous liquid state. A small amount of the concentrate was dried at 105℃ to constant weight, and the dry basis content was calculated to obtain the titanium-niobium-silicon composite sol concentrated precursor.

[0025] Preparation steps of molybdenum-tungsten-nitrogen-carbon conductive buffer powder: B1. Add 9.0g of ammonium molybdate tetrahydrate, 5.5g of ammonium metatungstate and 18.5g of dicyandiamide to 60.0g of deionized water, and stir at 300r / min for 1.5h at 60℃ to disperse and dissolve the ammonium molybdate tetrahydrate, ammonium metatungstate and dicyandiamide in the deionized water to obtain a molybdenum-tungsten-nitrogen-carbon precursor solution. B2. The molybdenum-tungsten-nitrogen-carbon precursor solution was concentrated at 77.5℃ to obtain a gel. The gel was dried at 110℃ for 10h, then pulverized until there were no obvious lumps. The temperature was raised to 800℃ and held for 2h under a nitrogen atmosphere. After cooling to room temperature, it was ball-milled for 30min and passed through a 300-mesh sieve to obtain molybdenum-tungsten-nitrogen-carbon conductive buffer powder.

[0026] Example 2

[0027] This embodiment provides a method for fabricating a low forward voltage drop diode, the steps of which include: S1. Mix 0.04g of titanium-niobium-silicon composite sol-concentrated precursor (dry basis) and 8.0g of anhydrous ethanol, and ultrasonically disperse at 200W ultrasonic power for 20min to obtain an interface coating solution; mix 0.15g of molybdenum-tungsten-nitrogen-carbon conductive buffer powder, 0.05g of ethyl cellulose, 0.8g of terpineol and 1.0g of anhydrous ethanol, and grind for 30min until the slurry is uniform to obtain a conductive buffer slurry; S2. Take one n-type silicon epitaxial wafer, the diameter of which is 100mm and the crystal orientation is... <100> A substrate with a thickness of 525 μm, an epitaxial layer thickness of 5 μm, and an epitaxial layer resistivity of 1.5 Ω·cm was used. The n-type silicon epitaxial wafer was ultrasonically cleaned in anhydrous ethanol for 5 min, then rinsed three times with deionized water for 30 s each time. It was then treated with 1% hydrofluoric acid for 60 s, rinsed three times with deionized water for 30 s each time, and dried with nitrogen for 60 s to obtain a pretreated n-type silicon epitaxial wafer. An interface coating solution was spin-coated onto the front side of the pretreated n-type silicon epitaxial wafer at a spin speed of 3000 r / min for 30 s. It was then baked at 80 °C for 10 min and annealed at 280 °C for 10 min in a nitrogen atmosphere to obtain an n-type silicon epitaxial wafer with a 1 nm thick ultrathin barrier control layer. A 5 nm thick titanium layer and a 20 nm thick nickel layer were sequentially deposited on the ultrathin barrier control layer using magnetron sputtering. A Schottky metal layer is formed; conductive buffer paste is screen-printed onto the Schottky metal layer, dried, and heat-treated at 250°C for 10 min in a nitrogen atmosphere to obtain a conductive buffer layer; 0.8 g of silver conductive paste is coated onto the conductive buffer layer and cured at 200°C for 30 min; an aluminum-silicon alloy layer with a thickness of 500 nm is deposited on the back side of the n-type silicon epitaxial wafer using an aluminum-silicon alloy target by magnetron sputtering and annealed at 400°C for 10 min in a nitrogen atmosphere; 0.4 g of polyimide passivation adhesive is coated onto the edge of the n-type silicon epitaxial wafer and cured at 250°C for 30 min to obtain an n-type silicon epitaxial wafer with an edge passivation layer; the n-type silicon epitaxial wafer with the edge passivation layer is diced into 1 mm × 1 mm chips, the chips are connected to copper leads, encapsulated with epoxy encapsulant, and cured at 150°C for 1 h to obtain a low forward voltage drop diode.

[0028] Preparation steps of titanium-niobium-silicon composite sol-gel concentrated precursor: A1. Add 10.0g tetrabutyl titanate, 3.0g tetraethyl orthosilicate, and 60.0g anhydrous ethanol to a reaction vessel. Stir at 300r / min for 15min at 25℃ to disperse tetrabutyl titanate and tetraethyl orthosilicate in anhydrous ethanol. Then add 1.0g acetylacetone and continue mixing at 300r / min for 30min at 25℃ to obtain a titanium silicon alkoxide premix. Add 1.0g niobium ammonium oxalate hydrate to 10.0g deionized water and stir at 300r / min for 20min at 25℃ until the niobium ammonium oxalate hydrate dissolves to obtain a niobium oxalate solution. Add the niobium oxalate solution dropwise to the titanium silicon alkoxide premix. After the addition is complete, adjust the pH to 4.0 with ammonia water and continue stirring at 300r / min for 2h at 25℃ to obtain a titanium niobium silicon composite sol. A2. The titanium-niobium-silicon composite sol was concentrated under reduced pressure at 50°C to a fluid, viscous liquid state. A small amount of the concentrate was dried at 105°C to constant weight, and the dry basis content was calculated to obtain the titanium-niobium-silicon composite sol concentrated precursor.

[0029] Preparation steps of molybdenum-tungsten-nitrogen-carbon conductive buffer powder: B1. Add 6.0g of ammonium molybdate tetrahydrate, 3.0g of ammonium metatungstate and 12.0g of dicyandiamide to 40.0g of deionized water, and stir at 300r / min for 1h at 50℃ to disperse and dissolve the ammonium molybdate tetrahydrate, ammonium metatungstate and dicyandiamide in the deionized water to obtain a molybdenum-tungsten-nitrogen-carbon precursor solution. B2. The molybdenum-tungsten-nitrogen-carbon precursor solution was concentrated at 70°C to obtain a gel. The gel was dried at 100°C for 8 hours, then pulverized until no obvious lumps were found. The temperature was raised to 780°C and held for 1 hour under a nitrogen atmosphere. The mixture was then cooled to room temperature, ball-milled for 30 minutes, and passed through a 300-mesh sieve to obtain molybdenum-tungsten-nitrogen-carbon conductive buffer powder.

[0030] Example 3

[0031] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for fabricating a low forward voltage drop diode, the steps of which include: S1. Mix 0.20g of titanium-niobium-silicon composite sol-concentrated precursor (dry basis) and 20.0g of anhydrous ethanol, and ultrasonically disperse at 200W ultrasonic power for 40min to obtain an interface coating solution; mix 0.80g of molybdenum-tungsten-nitrogen-carbon conductive buffer powder, 0.30g of ethyl cellulose, 3.0g of terpineol and 5.0g of anhydrous ethanol, and grind for 30min until the slurry is uniform to obtain a conductive buffer slurry; S2. Take one n-type silicon epitaxial wafer, the diameter of which is 100mm and the crystal orientation is... <100> A substrate with a thickness of 525 μm, an epitaxial layer thickness of 5 μm, and an epitaxial layer resistivity of 1.5 Ω·cm was used. The n-type silicon epitaxial wafer was ultrasonically cleaned in anhydrous ethanol for 5 min, then rinsed three times with deionized water for 30 s each time. Following this, it was treated with 1% hydrofluoric acid for 60 s, rinsed three times with deionized water for 30 s each time, and dried with nitrogen for 60 s to obtain a pretreated n-type silicon epitaxial wafer. An interface coating solution was spin-coated onto the front side of the pretreated n-type silicon epitaxial wafer at a speed of 3000 r / min for 30 s. It was then baked at 120 °C for 10 min and annealed at 380 °C for 10 min in a nitrogen atmosphere to obtain an n-type silicon epitaxial wafer with a 5 nm thick ultrathin barrier control layer. A 20 nm thick titanium layer and an 80 nm thick nickel layer were sequentially deposited on the ultrathin barrier control layer using magnetron sputtering. A Schottky metal layer was obtained; conductive buffer paste was screen-printed onto the Schottky metal layer, dried, and heat-treated at 350°C for 10 min in a nitrogen atmosphere to obtain a conductive buffer layer; 3.0 g of silver conductive paste was coated onto the conductive buffer layer and cured at 200°C for 30 min; an aluminum-silicon alloy layer with a thickness of 500 nm was deposited on the back side of the n-type silicon epitaxial wafer using an aluminum-silicon alloy target by magnetron sputtering and annealed at 400°C for 10 min in a nitrogen atmosphere; 2.0 g of polyimide passivation adhesive was coated onto the edge of the n-type silicon epitaxial wafer and cured at 250°C for 30 min to obtain an n-type silicon epitaxial wafer with an edge passivation layer; the n-type silicon epitaxial wafer with the edge passivation layer was diced into 1 mm × 1 mm chips, the chips were connected to copper leads, encapsulated with epoxy encapsulant, and cured at 150°C for 1 h to obtain a low forward voltage drop diode.

[0032] Preparation steps of titanium-niobium-silicon composite sol-gel concentrated precursor: A1. Add 18.0 g tetrabutyl titanate, 8.0 g tetraethyl orthosilicate, and 90.0 g anhydrous ethanol to a reaction vessel. Stir at 300 r / min for 15 min at 25 °C to disperse the tetrabutyl titanate and tetraethyl orthosilicate in the anhydrous ethanol. Then add 3.0 g acetylacetone and continue mixing at 300 r / min for 60 min at 25 °C to obtain a titanium silicon alkoxide premix. Add 4.0 g niobium ammonium oxalate hydrate to 25.0 g deionized water and stir at 300 r / min for 20 min at 25 °C until the niobium ammonium oxalate hydrate dissolves to obtain a niobium oxalate solution. Add the niobium oxalate solution dropwise to the titanium silicon alkoxide premix. After the addition is complete, adjust the pH to 5.0 with ammonia water and continue stirring at 300 r / min for 4 h at 25 °C to obtain a titanium niobium silicon composite sol. A2. The titanium-niobium-silicon composite sol was concentrated under reduced pressure at 65°C to a fluid, viscous liquid state. A small amount of the concentrate was dried at 105°C to constant weight, and the dry basis content was calculated to obtain the titanium-niobium-silicon composite sol concentrated precursor.

[0033] Preparation steps of molybdenum-tungsten-nitrogen-carbon conductive buffer powder: B1. Add 12.0g ammonium molybdate tetrahydrate, 8.0g ammonium metatungstate and 25.0g dicyandiamide to 80.0g deionized water, stir at 300r / min for 2h at 70℃ to disperse and dissolve ammonium molybdate tetrahydrate, ammonium metatungstate and dicyandiamide in deionized water to obtain molybdenum-tungsten-nitrogen-carbon precursor solution; B2. The molybdenum-tungsten-nitrogen-carbon precursor solution was concentrated at 85°C to obtain a gel. The gel was dried at 120°C for 12 hours, then pulverized until no obvious lumps were found. The temperature was raised to 820°C and held for 3 hours under a nitrogen atmosphere. The mixture was then cooled to room temperature, ball-milled for 30 minutes, and passed through a 300-mesh sieve to obtain molybdenum-tungsten-nitrogen-carbon conductive buffer powder.

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is that the titanium-niobium-silicon composite sol-gel concentrate precursor was not prepared and used; otherwise, it was the same as Example 1.

[0035] Comparative Example 2 The difference between this comparative example and Example 1 is that the molybdenum-tungsten-nitrogen-carbon conductive buffer powder was not prepared and used; otherwise, it was the same as Example 1.

[0036] Comparative Example 3 The difference between this comparative example and Example 1 is that the titanium-niobium-silicon composite sol-gel concentrate precursor and the molybdenum-tungsten-nitrogen-carbon conductive buffer powder are not prepared and used; otherwise, they are the same as in Example 1.

[0037] The performance of the low forward voltage drop diodes obtained in Examples 1-3 and Comparative Examples 1-3 were tested in accordance with national and industry standard testing specifications.

[0038] The low forward voltage drop diodes prepared in Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were used as test samples. Ten devices with complete packages, no cracks, no loose leads, and clear polarity markings were randomly selected from each group. Before testing, all devices were placed in an environment of 25°C and 50% relative humidity for 24 hours. The testing equipment included a semiconductor parameter tester, a constant temperature test chamber, a DC constant current power supply, a digital temperature recorder, and contact thermocouples. Before testing, the semiconductor parameter tester underwent open-circuit and short-circuit calibrations. The contact resistance of the test fixtures should be less than 0.01Ω. All electrical parameter tests were performed at 25°C.

[0039] During the forward voltage drop test, connect the positive terminal of the device to the positive terminal of the semiconductor parameter tester and the negative terminal to the negative terminal of the semiconductor parameter tester. Apply a forward current using a pulse or short-time DC method. Control the pulse width or reading time within a range that does not cause significant self-heating. Set the forward current to 100mA. After the current stabilizes, read the voltage across the two terminals. Repeat the test 3 times for each device and take the average value as the forward voltage drop of a single device. Then calculate the average value of 10 devices.

[0040] During series resistance testing, forward voltages corresponding to forward currents of 50mA, 100mA, 150mA, and 200mA are collected in the same test fixture. The linear segment of the current-voltage curve in the range of 100mA to 200mA is selected, and the series resistance is calculated by dividing the voltage change by the current change. Each device is tested three times, and the average value is taken. Then, the average value of 10 devices is calculated.

[0041] During the reverse leakage current test, the device is connected in reverse and a 20V reverse voltage is applied. After the voltage reaches the set value, it is held for 10 seconds. The stable reverse current is then read. If the current reading fluctuates by more than 5%, the stabilization time is extended to 30 seconds before reading. The test is repeated 3 times for a single device, and the average value is taken. Then the average value of 10 devices is calculated.

[0042] During the reverse breakdown voltage test, the device is connected in reverse, and the reverse voltage is gradually increased from 0V using the current limiting protection method. The current limit is set to 1mA. When the reverse current reaches 1mA, the corresponding reverse voltage is recorded as the reverse breakdown voltage. Once the criterion is reached, the voltage increase is immediately stopped and the voltage is reduced to 0V to avoid damage to the device during the breakdown process. Each device is tested once, and the average value of 10 devices is calculated.

[0043] During the conduction temperature rise test, the device is fixed on a test fixture with the same heat dissipation conditions. The ambient temperature is maintained at 25°C. A continuous positive current of 100mA is applied to the device and maintained for 30 minutes. A thermocouple is attached to the highest temperature area on the package surface. The ambient temperature and the package surface temperature are recorded at the same time. The conduction temperature rise is the difference between the package surface temperature and the ambient temperature. Each device is tested once, and the average value of 10 devices is calculated.

[0044] When testing the rate of change of forward voltage drop after high-temperature reverse bias, first record the forward voltage drop before aging according to the above forward voltage drop test method. Then place the device in an 85℃ constant temperature test chamber and apply a 20V reverse bias voltage. After maintaining this for 168h, stop the bias voltage and remove the device. Recover in a 25℃ environment for 2h. Then test the forward voltage drop after aging with a 100mA forward current. Calculate the rate of change by dividing the difference between the forward voltage drop after aging and the forward voltage drop before aging by the forward voltage drop before aging and multiplying by 100%. Calculate one rate of change for each device and finally take the average value of 10 devices.

[0045] The performance test data above are shown in Table 1.

[0046] Table 1: Performance Test Results

[0047] The test results in Table 1 clearly show that the forward voltage drop of Examples 1-3 is 0.278-0.312V, which is significantly lower than that of Comparative Examples 1-3 (0.329-0.392V). Among them, compared with Comparative Example 3 (which did not use the titanium-niobium-silicon composite sol-gel concentrated precursor and molybdenum-tungsten-nitrogen-carbon conductive buffer powder), the forward voltage drop of Example 1 decreased from 0.392V to 0.278V. This indicates that the present invention can solve the problem of high forward voltage drop caused by high metal / silicon interface impedance and large series resistance of the front conductive path in existing low forward voltage drop diodes.

[0048] The series resistance of Examples 1-3 was 0.36-0.43Ω, which was lower than that of Comparative Examples 1-3 (0.47-0.86Ω). In particular, compared with Comparative Example 2 (which did not use molybdenum-tungsten-nitrogen-carbon conductive buffer powder), the series resistance of Example 1 decreased from 0.72Ω to 0.36Ω, and the conduction temperature rise decreased from 26.5℃ to 13.6℃. This indicates that the conductive buffer layer formed by the molybdenum-tungsten-nitrogen-carbon conductive buffer powder can improve the continuity of current transmission on the surface of the Schottky metal layer and reduce local current concentration and conduction heat generation.

[0049] Compared to Comparative Example 1, which did not use the titanium-niobium-silicon composite sol-gel concentration precursor, Example 1 showed that the reverse leakage current decreased from 8.9 μA to 3.8 μA, the reverse breakdown voltage increased from 39.4 V to 47.2 V, and the forward voltage drop change rate after high-temperature reverse bias decreased from 5.8% to 1.8%. This indicates that the ultrathin barrier control layer formed by the titanium-niobium-silicon composite sol-gel concentration precursor can improve the interface state between the n-type silicon epitaxial wafer and the titanium and nickel layers, reducing leakage current and stability degradation caused by interface inhomogeneity.

[0050] The reverse leakage current of Examples 1-3 is 3.8-4.7μA, which is lower than that of Comparative Examples 1-3 (5.4-12.6μA). The reverse breakdown voltage is 45.1-47.2V, which is higher than that of Comparative Examples 1-3 (37.6-43.0V). The forward voltage drop change rate after high-temperature reverse bias is 1.8-2.5%, which is lower than that of Comparative Examples 1-3 (4.2-8.9%). This indicates that the present invention, through the combination of titanium-niobium-silicon composite sol-gel concentrated precursor, molybdenum-tungsten-nitrogen-carbon conductive buffer powder, Schottky metal layer, aluminum-silicon alloy layer and polyimide passivating adhesive, solves the problems of high series resistance, increased reverse leakage current, decreased breakdown voltage, increased conduction temperature rise and insufficient high-temperature reverse bias stability of existing low forward voltage drop diodes when reducing forward voltage drop.

Claims

1. A method for fabricating a low forward voltage drop diode, characterized in that the steps include... include: S1. Mix the titanium-niobium-silicon composite sol-gel concentrate precursor with anhydrous ethanol and disperse by ultrasonication to obtain the interface coating solution; Molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol and anhydrous ethanol were mixed and ground to obtain a conductive buffer slurry. S2. Pre-treat the n-type silicon epitaxial wafer to obtain a pre-treated n-type silicon epitaxial wafer; An interface coating solution is applied to the front side of a pretreated n-type silicon epitaxial wafer, which is then baked and annealed to obtain an n-type silicon epitaxial wafer with an ultrathin barrier control layer. A titanium layer and a nickel layer are sequentially deposited on an ultrathin barrier modulation layer to obtain a Schottky metal layer; a conductive buffer paste is coated on the Schottky metal layer, dried, and heat-treated to obtain a conductive buffer layer; a silver conductive paste is coated on the conductive buffer layer and cured; an aluminum-silicon alloy layer is deposited on the back side of an n-type silicon epitaxial wafer and annealed; a polyimide passivation adhesive is coated on the edge of the n-type silicon epitaxial wafer and cured to obtain an n-type silicon epitaxial wafer with an edge passivation layer. An n-type silicon epitaxial wafer with an edge passivation layer is connected to copper leads and then packaged.

2. The method for fabricating a low forward voltage drop diode according to claim 1, characterized in that, In step S1, the amounts of the titanium-niobium-silicon composite sol-gel concentrate precursor and anhydrous ethanol, by weight, are 0.04-0.20 parts and 8.0-20.0 parts, respectively; the amounts of the molybdenum-tungsten-nitrogen-carbon conductive buffer powder, ethyl cellulose, terpineol, and anhydrous ethanol are 0.15-0.80 parts, 0.05-0.30 parts, 0.8-3.0 parts, and 1.0-5.0 parts, respectively; and the ultrasonic dispersion time is 20-40 minutes.

3. The method for fabricating a low forward voltage drop diode according to claim 1, characterized in that, In step S2, the thickness of the ultrathin barrier control layer is 1-5 nm; the thickness of the titanium layer is 5-20 nm; and the thickness of the nickel layer is 20-80 nm. The baking step includes processing at 80-120°C; the heat treatment step includes processing at 250-350°C.

4. The method for fabricating a low forward voltage drop diode according to claim 1, characterized in that, The preparation method of the titanium-niobium-silicon composite sol-gel concentrated precursor includes: A1. By weight, mix 10.0-18.0 parts tetrabutyl titanate, 3.0-8.0 parts tetraethyl orthosilicate, and 60.0-90.0 parts anhydrous ethanol, add 1.0-3.0 parts acetylacetone, and continue mixing to obtain a titanium silicon alkoxide premix; dissolve 1.0-4.0 parts niobium ammonium oxalate hydrate in 10.0-25.0 parts deionized water to obtain a niobium oxalate solution; add the niobium oxalate solution to the titanium silicon alkoxide premix, adjust the pH with ammonia, and continue stirring to obtain a titanium niobium silicon composite sol; A2. Concentrate the titanium-niobium-silicon composite sol under reduced pressure.

5. The method for fabricating a low forward voltage drop diode according to claim 4, characterized in that, In step A1, the pH is adjusted to 4.0-5.0 using ammonia.

6. The method for fabricating a low forward voltage drop diode according to claim 4, characterized in that, In step A2, the temperature for vacuum concentration is 50-65℃.

7. The method for fabricating a low forward voltage drop diode according to claim 1, characterized in that, The preparation method of the molybdenum-tungsten-nitrogen-carbon conductive buffer powder includes: B1. By weight, add 6.0-12.0 parts of ammonium molybdate tetrahydrate, 3.0-8.0 parts of ammonium metatungstate and 12.0-25.0 parts of dicyandiamide to 40.0-80.0 parts of deionized water and stir at 50-70℃ to obtain a molybdenum-tungsten-nitrogen-carbon precursor solution. B2. Concentrate the molybdenum-tungsten-nitrogen-carbon precursor solution at 70-85℃ to obtain a gel; dry and pulverize the gel, heat it to 780-820℃ under a nitrogen atmosphere, keep it at that temperature, cool it to room temperature, ball mill it, and sieve it.

8. The method for fabricating a low forward voltage drop diode according to claim 7, characterized in that, In step B1, the stirring time is 1-2 hours at 50-70℃.

9. The method for fabricating a low forward voltage drop diode according to claim 7, characterized in that, In step B2, the drying temperature is 100-120℃ and the drying time is 8-12 hours; The temperature is raised to 780-820℃ and held for 1-3 hours.

10. A low forward voltage drop diode, characterized in that, The low forward voltage drop diode The low forward voltage drop diode is prepared according to any one of claims 1-9.

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