Front metal preparation method of groove Schottky diode silver surface product

Abstract

The invention discloses a front metal preparation method of a groove Schottky diode silver surface product, which comprises the following steps of: taking a silicon substrate with an epitaxial layer grown on an N-type substrate, carrying out groove etching on the surface of the silicon substrate, depositing an oxide layer on the inner wall of a silicon groove, then depositing polycrystalline silicon and filling the groove with the polycrystalline silicon; the sputtering and evaporation process is mainly adopted for front metal, so that the problem of poor metal coverage caused by a conventional evaporation process is effectively solved; a wet etching and dry etching process is adopted for metal corrosion, and only one-time photoetching is needed, so that the production cost and time are greatly saved; and the distance difference between the TiAl metal and the NiAg metal can effectively prevent the failure problem caused by silver migration.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for preparing a front metal of a silver-faced trench Schottky diode product. Background Art

[0002] Trench Schottky diodes, due to their trench structure, exhibit lower forward voltage drop compared to planar Schottky diodes. Silver-faced Schottky diodes, due to their unique packaging, eliminate the forward voltage drop associated with wire bonding compared to aluminum-faced versions, resulting in even lower forward voltage. Therefore, the front-side metallization process for silver-faced trench Schottky diodes is particularly important.

[0003] The design challenges of silver-faced trench Schottky diodes include poor metal coverage due to trench and hole steps, silver migration caused by poor package airtightness, and multiple photolithography cycles due to multi-layer metal corrosion, which increases production costs and lead times. Therefore, the preparation of the front-side metal is particularly important for product quality and cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a front metal preparation method for silver-faced products of trench Schottky diodes, which can effectively solve the problem of metal voids caused by surface step differences, while reducing the number of photolithography times, increasing production efficiency, and also reducing the hidden dangers caused by silver migration.

[0005] To achieve the above-mentioned object, the present invention provides a method for preparing a front metal of a silver-faced trench Schottky diode product, characterized in that the preparation method comprises the following steps: S1, taking a silicon substrate including an N-type substrate and an epitaxial layer grown on the substrate, and performing trench etching on the surface of the silicon substrate; S2. Deposit a thin oxide layer on the inner wall of the silicon trench, then deposit polysilicon to fill the inside of the trench, and then use an etching process to make the polysilicon layer in the trench and the epitaxial layer in the same plane; S3. Using a photolithography process and dry etching, the oxide layer in the opening area on the surface of the silicon substrate (the effective tube core area above the trench is the opening area) is etched cleanly; S4, depositing a layer of metal and performing heat treatment to form metal silicide on the surface of the silicon substrate; S5, sputtered metal Ti Al (two layers of metal, titanium and aluminum, superimposed); S6, evaporation of metal Ni Ag (nickel and silver two layers of metal superposition); S7. Etch NiAg using a wet etching process, and then etch TiAl metal using a dry etching process.

[0006] Furthermore, it is characterized in that the method of etching grooves on the surface of the silicon substrate includes dry etching, and the groove depth is 2.4μm~3.5μm.

[0007] Furthermore, the epitaxial layer has a thickness of (7-8.5)×(1±5%) μm and a resistivity of (0.8-1.3)×(1±3%) Ω·cm.

[0008] Furthermore, the thickness of the oxide layer is controlled to be between 3000Å ​​and 4000Å; and the thickness of the polysilicon layer is controlled to be between 6000Å and 8000Å.

[0009] Furthermore, the metal deposited in step S4 includes NiPt, and the thickness is controlled to be 1500Å~2000Å.

[0010] Furthermore, the sputtered metal TiAl adopts a sputtering process to first deposit a layer of metal Ti with a thickness of 1000Å~5000Å; and then deposit a layer of metal Al with a thickness of 5000Å~10000Å.

[0011] Furthermore, the evaporation of metal NiAg includes using an evaporation process to first deposit a layer of metal Ni with a thickness of 1000Å~3000Å; and then deposit a layer of metal Ag with a thickness of 30000Å~35000Å.

[0012] Furthermore, through the photolithography process, the photoresist is used as a mask layer to etch NiAg using a wet etching process, and then the TiAl metal is etched using a dry etching process.

[0013] The advantages and beneficial effects of the present invention are as follows: the front metal of the silver-faced trench Schottky diode product of the present invention adopts a sputtering + evaporation process to effectively solve the problem of poor metal coverage caused by conventional evaporation processes (such as metal voids, where the step height at the opening is relatively high, and if only the evaporation process is used, voids are easily caused at the opening); the metal corrosion adopts a wet corrosion + dry etching process, and only one photolithography is required, which greatly saves production costs and time; the distance difference between the TiAl metal and the NiAg metal can effectively prevent failure problems caused by silver migration (when there is a step difference, silver migrates outward and lands on the aluminum layer metal, stopping outward migration and not affecting product performance; when there is no step difference, silver migrates outward and lands on the oxide layer, which is likely to affect product performance). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a flow chart of the front metal preparation method for the silver side product of the trench Schottky diode; Figure 2 This is a cross-sectional view of the groove product of the present invention; Figure 3 This is a cross-sectional view of the metal filling morphology of a conventional trench product; Figure 4 This is a cross-sectional view of the metal filling morphology of the groove product of the present invention.

[0015] Markings in the figure: 1. Silicon substrate; 2. Oxide layer; 3. Polysilicon; 4. NiPt barrier; 5. TiAl; 6. NiAg. DETAILED DESCRIPTION

[0016] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0017] Example 1: A method for preparing the front metal of a trench Schottky diode silver surface product, such as Figure 1 and Figure 2 As shown, this embodiment takes the design of a trench Schottky diode product with a reverse voltage of 100V and a forward conduction current of 5A as an example. The preparation method includes the following steps: S1. A silicon substrate 1 having an N-type substrate doped with phosphorus, a resistivity of 0.0011 to 0.0015 Ω·cm (including the limit, similar expressions in the present invention include the limit value), and a crystal orientation of 100, on which an epitaxial layer is grown, is prepared, and a trench is etched on the surface of the silicon substrate. S2. Depositing a thin oxide layer 2 on the inner wall of the silicon trench, followed by depositing polysilicon 3 to fill the interior of the trench, and then using an etching process to align the polysilicon layer in the trench with the epitaxial layer. In this embodiment, a hydrogen-oxygen synthesis thermal oxidation process is used to grow an oxide layer, with the growth temperature controlled at 1050°C ± 5°C and the thickness controlled to 3500× (1 ± 4%) Å, generally 3000Å ​​to 4000Å (angstroms). LPCVD (Low Pressure Chemical Vapor Deposition) is used to grow a polysilicon layer to fill the interior of the trench, with the temperature controlled at 550°C ± 5°C, generally 500°C to 600°C, and the thickness controlled to 7000Å, generally 6000Å to 8000Å, to ensure that the trench is fully filled. S3, using a photolithography process to dry-etch the oxide layer in the opening area on the surface of the silicon substrate 1; S4, depositing a layer of metal and performing heat treatment. The heat treatment in this embodiment includes performing N2 alloying (N2 is passed through, and metal and silicon form silicide at high temperature), the temperature is controlled at 480°C to 500°C, the time is 50min to 70min, and the actual temperature is 490°C, the time is 60min, to form metal silicide 4 on the surface of the silicon substrate; S5, sputtered metal TiAl5; S6, evaporated metal NiAg6; S7. Etch NiAg using a wet etching process, and then etch TiAl metal using a dry etching process.

[0018] Preferably, the method of etching the grooves on the surface of the silicon substrate includes dry etching, and the groove depth is 2.4 μm to 3.5 μm. In this embodiment, dry etching is used, and the groove depth is 3.0 μm ± 0.1 μm.

[0019] Preferably, the epitaxial layer has a thickness of (7-8.5)×(1±5%)μm and a resistivity of (0.8-1.3)×(1±3%)Ω·cm. In this embodiment, the epitaxial layer has a thickness of 7.5×(1±5%)μm and a resistivity of 1.0×(1±3%)Ω·cm.

[0020] Preferably, the thickness of the oxide layer is controlled to be 3000Å~4000Å; the thickness of the polysilicon layer is controlled to be 6000Å~8000Å. In this embodiment, the thickness of the oxide layer is controlled to be 3500×(1±2%)Å; the thickness of the polysilicon layer is controlled to be 7000×(1±3%)Å.

[0021] Preferably, the metal deposited in step S4 includes NiPt (nickel platinum alloy), and the thickness is controlled to be 1500Å~2000Å, and in this embodiment is 1800×(1±2%)Å.

[0022] Preferably, the sputtering of metal TiAl includes first depositing a layer of metal Ti with a thickness of 1000Å~5000Å; then depositing a layer of metal Al with a thickness of 5000Å~10000Å; this embodiment adopts the sputtering process, and the thickness of metal Ti is 3000×(1±5%)Å; the thickness of metal Al is 8000×(1±5%)Å.

[0023] Preferably, the evaporated metal NiAg includes using an evaporation process to first deposit a layer of metal Ni with a thickness of 1000Å~3000Å; then deposit a layer of metal Ag with a thickness of 30000Å~35000Å; in this embodiment, the thickness of the metal Ni is 2000×(1±3%)Å; the thickness of the metal Ag is 32000×(1±5%)Å.

[0024] Preferably, through a photolithography process, the photoresist is used as a mask layer to etch NiAg using a wet etching process, and then the TiAl metal is etched using a dry etching process.

[0025] To verify the effectiveness of the process, a sample wafer was subjected to a 10-point stress test, which met product requirements (greater than 200N). After die packaging, wafer pushing and tensile testing also met product requirements. Specific data are shown in Tables 1 and 2.

[0026] Table 1 10-point pressure test data of the wafer of the present invention Table 2: Crystal pushing and tensile test data of finished tubes of the present invention from Figure 3 and Figure 4 From the cross-sectional diagram of the metal filling morphology of conventional trench products and the trench products of the present invention, it can be seen that the metal morphology above the trench of the product of the present invention is better, and there are basically no metal gaps or voids.

[0027] Example 2: The difference from Example 1 is that in step S1 of this embodiment, the trench depth is 2.4 μm±0.1 μm, the epitaxial layer thickness is 7.0×(1±5%) μm, and the resistivity is 0.8×(1±3%) Ω·cm.

[0028] In step S2, the oxide layer thickness is controlled to be 3000×(1±2%)Å; the polysilicon layer growth thickness is controlled to be 6000×(1±3%)Å within a temperature thickness range.

[0029] In step S4, the heat treatment temperature is 480°C, the time is 50 min, and the NiPt thickness is 1500×(1±2%)Å; In step S5, the present embodiment adopts sputtering process, the thickness of metal Ti is 1000×(1±5%)Å; the thickness of metal Al is 5000×(1±5%)Å In step S6, the thickness of the metal Ni in this embodiment is 1000×(1±3%)Å; the thickness of the metal Ag is 30000×(1±5%)Å. Example 3: The difference from Example 1 is that in step S1 of this embodiment, the trench depth is 3.5 μm±0.1 μm, the epitaxial layer thickness is 8.5×(1±5%) μm, and the resistivity is 1.3×(1±3%) Ω·cm.

[0030] In step S2, the oxide layer thickness is controlled to be 4000×(1±2%)Å; the polysilicon layer growth thickness is controlled to be 8000×(1±3%)Å within a temperature thickness range.

[0031] In step S4, the heat treatment temperature is 500°C, the time is 70 min, and the NiPt thickness is 2000×(1±2%)Å; In step S5, the present embodiment adopts sputtering process, the thickness of metal Ti is 5000×(1±5%)Å; the thickness of metal Al is 10000×(1±5%)Å In step S6, in this embodiment, the thickness of the metal Ni is 3000×(1±3%)Å; the thickness of the metal Ag is 35000×(1±5%)Å.

[0032] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the technical principles of the present invention, several improvements and modifications can be made, such as the combination of different process parameters. Within the allowable range, these improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing the front metal of a trench Schottky diode silver surface product, characterized in that: The preparation method comprises the following steps: S1, taking a silicon substrate (1) comprising an N-type substrate and an epitaxial layer grown on the substrate, and performing trench etching on the surface of the silicon substrate; S2, depositing an oxide layer (2) on the inner wall of the silicon trench, and then depositing polysilicon (3) to fill the inside of the trench, and then using an etching process to make the polysilicon layer in the trench and the epitaxial layer in the same plane; S3, etching the oxide layer in the opening area on the surface of the silicon substrate (1) cleanly; S4, depositing a layer of metal and performing heat treatment to form a metal silicide (4) on the surface of the silicon substrate; S5, sputtered metal TiAl (5); S6, evaporated metal NiAg (6); S7. Etch NiAg using a wet etching process, and then etch TiAl metal using a dry etching process.

2. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: The epitaxial layer has a thickness of (7-8.5)×(1±5%) μm and a resistivity of (0.8-1.3)×(1±3%) Ω·cm.

3. The method for preparing a front metal of a trench Schottky diode silver surface product according to claim 1, characterized in that: The method for etching a groove on the surface of a silicon substrate includes dry etching, and the groove depth is 2.4 μm to 3.5 μm.

4. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: The thickness of the oxide layer is controlled to be between 3000Å ​​and 4000Å; the thickness of the polysilicon layer is controlled to be between 6000Å and 8000Å.

5. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: The metal deposited in step S4 includes NiPt, and the thickness is controlled to be 1500Å~2000Å.

6. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: The sputtering of metal TiAl includes adopting a sputtering process to first deposit a layer of metal Ti with a thickness of 1000Å to 5000Å; and then depositing a layer of metal Al with a thickness of 5000Å to 10000Å.

7. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: The evaporation of metal NiAg includes adopting an evaporation process to first deposit a layer of metal Ni with a thickness of 1000Å~3000Å; and then depositing a layer of metal Ag with a thickness of 30000Å~35000Å.

8. The method for preparing a front metal of a silver-faced trench Schottky diode according to claim 1, characterized in that: Through the photolithography process, the photoresist is used as a mask layer to etch NiAg using a wet etching process, and then the TiAl metal is etched using a dry etching process.

Images