A trench schottky diode silver surface product front metal preparation method

Abstract

The application discloses a front metal preparation method of a trench Schottky diode silver surface product, takes a silicon substrate on which an epitaxial layer is grown on an N-type substrate, performs trench etching on the surface of the silicon substrate, deposits an oxide layer on the inner wall of the silicon trench, and then deposits polycrystalline silicon and fills the trench, wherein the main front metal adopts a sputtering + evaporation process to effectively solve the poor metal coverage problem caused by a conventional evaporation process; the metal corrosion adopts a wet etching + dry etching process, only one photoetching is needed, and therefore the production cost and time are greatly saved; and the distance difference between TiAl metal and NiAg metal can effectively prevent the failure problem caused by silver migration.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and specifically to a method for preparing the front metal of a trench Schottky diode silver surface product. Background Technology

[0002] Trench Schottky diodes, due to their trench structure, exhibit a lower forward voltage drop compared to planar Schottky diodes. Furthermore, silver-surface Schottky diodes, due to their unique packaging, do not suffer from the forward voltage drop caused by wire bonding, resulting in an even lower forward voltage compared to aluminum-surface diodes. Therefore, the front-side metallization process is particularly important for silver-surface trench Schottky diodes.

[0003] The design challenges of trench Schottky diodes with silver surfaces include poor metal coverage due to trench and via steps, silver migration issues caused by poor hermeticity of the package, and increased production costs and lead time due to multiple photolithography steps resulting from multi-layer metal etching. Therefore, the fabrication of the front-side metal is particularly important for product quality and cost. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing the front metal of a trench Schottky diode silver surface product, which can effectively solve the problem of metal voids caused by surface step differences, reduce the number of photolithography steps, increase production efficiency, and reduce the hidden dangers caused by silver migration.

[0005] To achieve the above objectives, this invention provides a method for fabricating the front-side metal of a trench Schottky diode silver surface product, characterized in that the fabrication method includes the following steps: S1. Take a silicon substrate containing an N-type substrate and grow an epitaxial layer on the substrate, and perform trench etching on the surface of the silicon substrate. S2. A thin oxide layer is deposited on the inner wall of the silicon trench, followed by the deposition of polysilicon to fill the trench. Then, an etching process is used to make the polysilicon layer in the trench and the epitaxial layer on the same plane. S3. The oxide layer of the opening area (the effective die area above the trench) on the surface of the silicon substrate is cleaned by dry etching using photolithography. S4. Deposit a layer of metal and perform heat treatment to form a metal silicide on the surface of the silicon substrate; S5, sputtered metal TiAl (two layers of titanium and aluminum superimposed). S6, evaporated metal Ni Ag (two layers of metal, nickel and silver, stacked). S7. Use wet etching process to etch NiAg, and then use dry etching process to etch TiAl metal.

[0006] Furthermore, the method for trench etching on the surface of the silicon substrate includes dry etching, wherein the trench depth is 2.4 μm to 3.5 μm.

[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 at 3000 Å to 4000 Å; the thickness of the polycrystalline silicon layer is controlled at 6000 Å to 8000 Å.

[0009] Furthermore, in step S4, the metal deposited includes NiPt, with a thickness controlled between 1500 Å and 2000 Å.

[0010] Furthermore, the sputtered metal TiAl is produced by a sputtering process, first depositing a layer of metallic Ti with a thickness of 1000Å~5000Å; then depositing a layer of metallic Al with a thickness of 5000Å~10000Å.

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

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

[0013] The advantages and beneficial effects of this invention are as follows: The front metal of the trench Schottky diode silver surface product of this 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 etching + dry etching process, which only requires one photolithography, greatly saving production costs and time; the distance difference between TiAl metal and NiAg metal can effectively prevent failure problems caused by silver migration (when there is a step difference, the silver migrates outward and falls on the aluminum layer metal, stopping its outward migration and not affecting the product performance; while when there is no step difference, the silver migrates outward and falls on the oxide layer, which easily affects the product performance). Attached Figure Description

[0014] Figure 1 This is a flowchart of the front metal fabrication method for the silver surface of a trench Schottky diode; Figure 2 This is a cross-sectional view of the grooved product morphology of the present invention; Figure 3 This is a cross-sectional view of the metal filling morphology of a conventional grooved product; Figure 4 This is a cross-sectional view of the metal filling morphology of the grooved product of the present invention.

[0015] Marked in the image: 1. Silicon substrate; 2. Oxide layer; 3. Polycrystalline silicon; 4. NiPt barrier; 5. TiAl; 6. NiAg. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0017] Example 1: A method for fabricating 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 with a reverse voltage of 100V and a forward conduction current of 5A as an example. The fabrication method includes the following steps: S1. Take a silicon substrate 1 containing phosphorus-doped N-type substrate with resistivity of 0.0011~0.0015 Ω·cm (including boundary, similar descriptions in this invention also include boundary values) and 100 crystal orientation, and grow an epitaxial layer on the substrate. Perform trench etching on the surface of the silicon substrate. S2. A thin oxide layer 2 is deposited on the inner wall of the silicon trench, followed by the deposition of polycrystalline silicon 3 to fill the trench. Then, an etching process is used to make the polycrystalline silicon layer in the trench and the epitaxial layer on the same plane. In this embodiment, an oxide layer is grown using a hydrogen-oxygen synthesis thermal oxidation process, with the growth temperature controlled at 1050℃±5℃ and the thickness controlled at 3500×(1±4%)Å, generally between 3000Å ​​and 4000Å. A polycrystalline silicon layer is grown using LPCVD (Low Pressure Chemical Vapor Deposition) to fill the trench, with the temperature controlled at 550℃±5℃, generally between 500℃ and 600℃, and the thickness controlled at 7000Å, generally between 6000Å and 8000Å, to ensure that the trench is completely filled. S3. The oxide layer of the opening area on the surface of the silicon substrate 1 is etched clean by dry etching using photolithography. S4. Deposit a layer of metal and perform heat treatment. The heat treatment described in this embodiment includes N2 alloying (using N2, the metal and silicon generate silicide at high temperature). The temperature is controlled at 480℃~500℃ and the time is 50min~70min. The actual temperature is 490℃ and the time is 60min, forming metal silicide 4 on the surface of the silicon substrate. S5, sputtered metal TiAl5; S6, evaporated metal NiAg6; S7. Use wet etching process to etch NiAg, and then use dry etching process to etch TiAl metal.

[0018] Preferably, the method for trench etching on the silicon substrate surface includes dry etching, wherein the trench depth is 2.4 μm to 3.5 μm. This embodiment uses dry etching, and the trench 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 oxide layer thickness is controlled at 3000 Å to 4000 Å; the polycrystalline silicon layer thickness is controlled at 6000 Å to 8000 Å. In this embodiment, the oxide layer thickness is controlled at 3500 × (1 ± 2%) Å; the polycrystalline silicon layer thickness is controlled at 7000 × (1 ± 3%) Å.

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

[0022] Preferably, the sputtered 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; in this embodiment, a sputtering process is used, and the thickness of metal Ti is 3000×(1±5%)Å; the thickness of metal Al is 8000×(1±5%)Å.

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

[0024] Preferably, NiAg is etched using a wet etching process with photoresist as a masking layer, and then TiAl metal is etched using a dry etching process.

[0025] To verify the effectiveness of the process of this invention, 10 stress tests were conducted on the sample wafers, which met the product requirements (greater than 200N); after die packaging, die pushing and pulling tests were performed, which also met the product requirements. Specific data are shown in Tables 1 and 2.

[0026] Table 1. Pressure test data of the disc at 10 points in this invention. Table 2. Test data of the finished tube of the present invention for crystal pushing and pulling force. from Figure 3 and Figure 4 The cross-sectional view of the metal filling morphology of conventional grooved products and the grooved products of the present invention shows that the metal morphology above the groove of the product of the present invention is superior, with virtually no metal gaps or voids.

[0027] Example 2: The difference from Example 1 is that in step S1 of this example, the trench depth is 2.4μm±0.1μm, 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 at 3000×(1±2%)Å; the polycrystalline silicon layer growth thickness is controlled at 6000×(1±3%)Å within the temperature thickness range.

[0029] In step S4, the heat treatment temperature is 480℃ and the time is 50min, and the NiPt thickness is 1500×(1±2%)Å; In step S5, this embodiment uses a sputtering process, with a Ti metal thickness of 1000 × (1 ± 5%) Å and an Al metal thickness of 5000 × (1 ± 5%) Å. In step S6, the thickness of the Ni metal in this embodiment is 1000 × (1 ± 3%) Å; the thickness of the Ag metal is 30000 × (1 ± 5%) Å. Example 3: The difference from Example 1 is that in step S1 of this example, the trench depth is 3.5μm±0.1μm, 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 at 4000×(1±2%)Å; the polycrystalline silicon layer growth thickness is controlled at 8000×(1±3%)Å within the temperature thickness range.

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

[0032] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, such as combinations of different process parameters. Within the permissible range, these improvements and modifications should also be considered within 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 includes the following steps: S1. Take a silicon substrate (1) containing an N-type substrate and grow an epitaxial layer on the substrate, and perform trench etching on the surface of the silicon substrate. S2. An oxide layer (2) is deposited on the inner wall of the silicon trench, followed by the deposition of polycrystalline silicon (3) to fill the trench. Then, an etching process is used to make the polycrystalline silicon layer in the trench and the epitaxial layer on the same plane. The growth temperature of the oxide layer is controlled at 1050℃±5℃ and the thickness is controlled at 3000Å~4000Å. The growth temperature of the polycrystalline silicon is controlled at 500℃~600℃ and the thickness is controlled at 6000Å~8000Å. S3. Etch clean the oxide layer in the opening area on the surface of the silicon substrate (1); S4. Deposit a layer of metal and perform heat treatment, the heat treatment including passing N2, temperature controlled at 480℃~500℃, time of 50min~70min, to form metal silicide on the surface of the silicon substrate (4). S5, Sputtering metal TiAl (5), wherein the sputtering metal TiAl includes a sputtering process, 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; S6. Evaporating metal NiAg (6), wherein the evaporation of metal NiAg includes the following steps: first, depositing a layer of metal Ni with a thickness of 1000Å~3000Å ​​using an evaporation process; then depositing a layer of metal Ag with a thickness of 30000Å~35000Å. S7. NiAg is etched using a wet etching process, and TiAl metal is etched using a dry etching process, completing the photolithography in one step.

2. The method for preparing the front metal of a trench Schottky diode silver surface product 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 the front metal of a trench Schottky diode silver surface product according to claim 1, characterized in that, Methods for trench etching on the surface of a silicon substrate include dry etching, wherein the trench depth is 2.4 μm to 3.5 μm.

4. The method for preparing the front metal of a trench Schottky diode silver surface product according to claim 1, characterized in that, In step S4, the deposited metal includes NiPt, and the thickness is controlled between 1500 Å and 2000 Å.

5. The method for preparing the front metal of a trench Schottky diode silver surface product according to claim 1, characterized in that, The NiAg is etched using a wet etching process with photoresist as a masking layer, and then TiAl metal is etched using a dry etching process.

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