A silicon carbide junction barrier schottky diode and method of manufacture thereof

Abstract

The application relates to a silicon carbide junction barrier Schottky diode and a manufacturing method thereof, and belongs to the technical field of semiconductor devices. The Schottky diode comprises a plurality of cells which are sequentially adjacent, and the cells sequentially comprise an ohmic contact cathode metal layer, a substrate layer, an epitaxial layer, a Schottky metal layer and an anode metal layer from bottom to top. A plurality of ion implantation zones are arranged in the upper part of the epitaxial layer, the ion implantation zones comprise a first ion implantation zone, a second ion implantation zone and a third ion implantation zone, the first ion implantation zone extends downwards from the upper surface of the epitaxial layer, the second ion implantation zone extends downwards from the upper surface of the first ion implantation zone, and the third ion implantation zone extends downwards from the upper surface of the second ion implantation zone. The application realizes lower on-resistance and forward voltage drop while ensuring the voltage resistance of the device, and effectively improves the overall performance of the device.

Description

Technical Field

[0001] This invention relates to a silicon carbide junction barrier Schottky diode and its manufacturing method, belonging to the field of semiconductor device technology. Background Technology

[0002] Silicon carbide is a wide bandgap semiconductor. Due to its high thermal conductivity, high electron saturation velocity and high critical breakdown electric field, and the fact that devices made from it can withstand harsh environments such as high temperature and high pressure, it overcomes the limitations of traditional silicon-based devices and shows broad application potential in the field of power devices.

[0003] Silicon carbide Schottky diodes (SBDs), as the earliest commercially available silicon carbide power devices, have significant advantages such as fast switching speed and low dynamic losses. However, the inherent defect of excessive reverse leakage current has long been a key bottleneck restricting their performance improvement and application expansion. To overcome the challenge of excessive reverse leakage current in SBDs, silicon carbide junction barrier Schottky diodes (JBSs) selectively introduce P-type doped regions in the drift layer. While maintaining the low on-state voltage drop advantage of SBDs, the depletion layer formed by the P-region and N-type drift region effectively shields the reverse electric field, thereby significantly reducing the reverse leakage current and improving the reverse breakdown voltage of the device.

[0004] However, while introducing the P-region can significantly improve the device's breakdown voltage, the presence of the depletion region in the PN junction formed between the P-region and the N-type drift region hinders the forward current conduction of the junction barrier Schottky diode, a phenomenon known as the Junction Field-Effect Transistor (JFET) effect. This leads to increased forward resistance and forward voltage drop, resulting in increased conduction losses. Existing technologies often mitigate the JFET effect by increasing the P-region spacing, but this increases reverse leakage current, making a balance difficult to achieve.

[0005] Therefore, there is a need for a diode and its manufacturing method that can mitigate the JFET effect to reduce the forward conduction voltage without sacrificing the reverse breakdown voltage performance of the device. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a silicon carbide junction barrier Schottky diode and its manufacturing method.

[0007] Terminology Explanation: Schottky contacts are designed to describe metal-semiconductor junctions with rectifying properties.

[0008] An ohmic contact is designed to describe the direct mechanical contact and ohmic connection between two components or parts of a semiconductor device.

[0009] The technical solution of the present invention is as follows: This invention provides a silicon carbide junction barrier Schottky diode, comprising a plurality of sequentially adjacent cells. The cells, from bottom to top, include an ohmic contact cathode metal layer, a substrate layer, an epitaxial layer, a Schottky metal layer, and an anode metal layer. Two ion implantation regions are disposed in the upper part of the epitaxial layer, including a first ion implantation region, a second ion implantation region, and a third ion implantation region. The first ion implantation region extends downward from the upper surface of the epitaxial layer, the second ion implantation region extends downward from the upper surface of the first ion implantation region, and the third ion implantation region extends downward from the upper surface of the second ion implantation region.

[0010] According to a preferred embodiment of the present invention, the longitudinal depth of the second ion implantation region is less than that of the first ion implantation region, and the lateral width of the second ion implantation region is equal to that of the first ion implantation region.

[0011] According to a preferred embodiment of the present invention, the lateral width of the third ion implantation region is smaller than the lateral width of the second ion implantation region, and the longitudinal depth of the third ion implantation region is greater than the longitudinal depth of the second ion implantation region and less than the longitudinal depth of the first ion implantation region.

[0012] According to a preferred embodiment of the present invention, the substrate layer, the epitaxial layer, and the second ion implantation region are all n-type doped, and the first ion implantation region and the third ion implantation region are both p-type doped.

[0013] According to a preferred embodiment of the present invention, the doping concentration of the first ion implantation region is less than that of the second ion implantation region, and the doping concentration of the second ion implantation region is less than that of the third ion implantation region.

[0014] According to a preferred embodiment of the present invention, the longitudinal depth of the first ion implantation region is 0.3-1 μm, the implanted ion is aluminum ion, and the doping concentration is 1×10⁻⁶. 17 cm -3 Up to 5×10 17 cm -3 .

[0015] According to a preferred embodiment of the present invention, the implanted ions in the second ion implantation region are nitrogen ions, with a vertical depth of 0.1-0.5 μm and a doping concentration of 2 × 10⁻⁶. 17 cm -3 Up to 8×10 17 cm -3 .

[0016] According to a preferred embodiment of the present invention, the implanted ions in the third ion implantation region are aluminum ions, and the doping concentration is greater than 1×10⁻⁶. 18 cm -3 .

[0017] According to a preferred embodiment of the present invention, the substrate layer is made of 4H-SiC, has a thickness of 300-350 μm, is doped with nitrogen or phosphorus, and has a resistivity of 0.014-0.028 Ω·cm.

[0018] According to a preferred embodiment of the present invention, the epitaxial layer is lightly doped n-type with a doping concentration of 1×10⁻⁶. 15 cm -3 Up to 8×10 16 cm -3 .

[0019] According to a preferred embodiment of the present invention, the material of the Schottky metal layer is one or more of Ta, Co, Mo, Ti, Ni, Cr, Pt, Pd, Zr or W.

[0020] According to a preferred embodiment of the present invention, the anode metal layer is made of aluminum or an aluminum-copper alloy, and the ohmic contact cathode metal layer is a stacked structure formed by a Ti layer, a Ni layer, and an Ag layer.

[0021] The manufacturing method of the aforementioned silicon carbide junction barrier Schottky diode includes the following steps: (1) Prepare a substrate layer and form an epitaxial layer on the substrate layer by in-situ growth; (2) A first hard mask layer is fabricated on the epitaxial layer, and the first hard mask layer is etched using a mask to expose the window for ion implantation in the first ion implantation region, and ion implantation is performed to fabricate the first ion implantation region. (3) The first hard mask layer is retained, and the second ion implantation region is formed by compensating doping on the upper part of the first ion implantation region through ion implantation process; (4) On the basis of the first hard mask layer, a sidewall is formed by the sidewall process, and the first hard mask layer and the sidewall together constitute the second hard mask layer. The lateral width of the second hard mask layer is greater than the lateral width of the first hard mask layer. (5) Under the obstruction of the second hard mask layer, the third ion implantation region is formed by ion implantation process; (6) Remove the second hard mask layer and anneal in an inert gas atmosphere to activate the implanted ions; (7) A Schottky metal layer is formed on the upper surface of the epitaxial layer by sputtering deposition and then annealed; (8) Anode metal layer and ohmic contact cathode metal layer are formed on the surface of Schottky metal layer and substrate layer respectively by depositing metal, and then the ohmic contact cathode metal layer is annealed to form ohmic contact, thus completing the device fabrication.

[0022] Technical features and beneficial effects of the present invention: 1. The device of the present invention, by setting a second ion implantation region, and both the second ion implantation region and the epitaxial layer are n-type doped, can effectively reduce the JFET effect of the upper part of the first ion implantation region on the conductive channel, reduce the width of the depletion region in the upper part of the first ion implantation region, increase the width of the current conduction path, reduce the on-resistance, and achieve a low forward conduction voltage drop.

[0023] 2. In the device of the present invention, the ion implantation doping concentration of the second ion implantation region is higher than that of the epitaxial layer, the number of charge carriers increases, the on-resistance decreases, and a low forward conduction voltage drop can be achieved.

[0024] 3. In the device of the present invention, since the second ion implantation region is located above the first ion implantation region, and the lower part of the first ion implantation region still plays a role in electric field shielding, the reverse withstand voltage capability is basically unaffected.

[0025] 4. The manufacturing method of the device of the present invention uses the same mask to form the first ion implantation region and the second ion implantation region. Then, sidewalls are formed on both sides of the mask and ion implantation is performed to form a third ion implantation region with a narrower lateral width. This process is stable and controllable, which makes the ion implantation region have good symmetry and helps to ensure device performance. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view of the cell of the silicon carbide junction barrier Schottky diode of the present invention; Figure 2 This is a schematic cross-sectional view of the cell of the device after the epitaxial layer is formed in the manufacturing method of the present invention; Figure 3 This is a cross-sectional schematic diagram of the cell of the device after the formation of the first ion implantation region in the manufacturing method of the present invention; Figure 4 This is a cross-sectional schematic diagram of the cell of the device after the second ion implantation region is formed in the manufacturing method of the present invention; Figure 5 This is a cross-sectional schematic diagram of the cell of the device after the formation of the third ion implantation region in the manufacturing method of the present invention; Figure 6 This is a cross-sectional schematic diagram of the cell of the device after the Schottky metal layer is formed in the manufacturing method of the present invention; Figure 7 This is a schematic cross-sectional view of a cell in a traditional junction barrier Schottky diode. Figure 8 This is a comparison diagram of the forward characteristics of the silicon carbide junction barrier Schottky diode of the present invention and that of the conventional structure; Figure 9 This is a comparison diagram of the reverse characteristics of the silicon carbide junction barrier Schottky diode of the present invention and the conventional structure; Wherein: 1. Substrate layer; 2. Epitaxial layer; 3. First ion implantation region; 4. Second ion implantation region; 5. Third ion implantation region; 6. Schottky metal layer; 7. Anode metal layer; 8. Ohmic contact cathode metal layer. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments and accompanying drawings, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and should not be construed as limiting this invention.

[0029] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all techniques existing in the art can be used.

[0030] Example 1 like Figure 1 As shown, a silicon carbide junction barrier Schottky diode includes a plurality of sequentially adjacent cells, which, from bottom to top, include an ohmic contact cathode metal layer 8, a substrate layer 1, an epitaxial layer 2, a Schottky metal layer 6, and an anode metal layer 7. Two ion implantation regions are provided in the upper part of the epitaxial layer 2. The ion implantation regions include a first ion implantation region 3, a second ion implantation region 4, and a third ion implantation region 5. The first ion implantation region 3 extends inward from the upper surface of the epitaxial layer 2. The second ion implantation region 4 extends inward from the upper surface of the first ion implantation region 3. The longitudinal depth of the second ion implantation region 4 is less than that of the first ion implantation region 3. The third ion implantation region 5 extends inward from the upper surface of one side of the second ion implantation region 4. The longitudinal depth of the third ion implantation region 5 is greater than that of the second ion implantation region 4 and less than that of the first ion implantation region 3. Substrate 1, epitaxial layer 2, and second ion implantation region 4 are all n-type doped, while first ion implantation region 3 and third ion implantation region 5 are both p-type doped.

[0031] The doping concentration of the first ion implantation region 3 is less than that of the second ion implantation region 4, and the doping concentration of the second ion implantation region 4 is less than that of the third ion implantation region 5.

[0032] The vertical depth of the first ion implantation region 3 is 1 μm, the implanted ions are aluminum ions, and the doping concentration is 4 × 10⁻⁶. 17 cm -3 .

[0033] The implanted ions in the second ion implantation region 4 are nitrogen ions, with a vertical depth of 0.4 μm and a doping concentration of 7 × 10⁻⁶. 17 cm -3 .

[0034] The implanted ions in the third ion implantation region 5 are aluminum ions, with a doping concentration of 5 × 10⁻⁶. 18 cm -3 .

[0035] The substrate 1 is made of 4H-SiC with a thickness of 350 nm, the doping source is nitrogen, and the resistivity is 0.028 Ω•cm.

[0036] Epitaxial layer 2 is lightly doped n-type with a doping concentration of 8 × 10⁻⁶. 15 cm -3 The thickness is 10 micrometers.

[0037] The material of Schottky metal layer 6 is Ti.

[0038] The anode metal layer 7 is made of aluminum, and the ohmic contact cathode metal layer 8 is a stacked structure formed by Ti layer, Ni layer and Ag layer.

[0039] The manufacturing method of the aforementioned silicon carbide junction barrier Schottky diode device, such as... Figures 2-6 As shown, the steps are as follows: (1) Prepare a substrate layer 1, and form an epitaxial layer 2 on the substrate layer 1 by in-situ growth.

[0040] (2) A first hard mask layer is fabricated on the upper side of the epitaxial layer 2. The first hard mask layer is etched using a mask to expose the window for ion implantation in the first ion implantation region 3. Ion implantation is performed to fabricate the first ion implantation region 3.

[0041] (3) The first hard mask layer is retained, and the second ion implantation region 4 is formed by compensation doping on the upper part of the first ion implantation region 3 through ion implantation process.

[0042] (4) On the basis of the first hard mask layer, a sidewall is formed by the sidewall process, and the first hard mask layer and the sidewall together constitute the second hard mask layer. The lateral width of the second hard mask layer is greater than the lateral width of the first hard mask layer.

[0043] (5) Under the obstruction of the second hard mask layer, a third ion implantation region 5 is formed by ion implantation process, such that the third ion implantation region 5 penetrates part of the second ion implantation region 4 in the longitudinal direction, and the longitudinal depth of the third ion implantation region 5 is greater than that of the second ion implantation region 4 and less than that of the first ion implantation region 3.

[0044] (6) Remove the second hard mask layer and anneal in an inert gas atmosphere to activate the implanted ions.

[0045] (7) A Schottky metal layer 6 is formed on the upper surface of the epitaxial layer 2 by sputtering deposition and then annealed to form a Schottky contact.

[0046] (8) Anode metal layer 7 and ohmic contact cathode metal layer 8 are formed on the surfaces of Schottky metal layer 6 and substrate layer 1 respectively by depositing metal. Then, the ohmic contact cathode metal layer 8 is annealed to form an ohmic contact, thus completing the device fabrication.

[0047] Example 2 A silicon carbide junction barrier Schottky diode, as described in Example 1, differs in that: The second ion implantation region 4 has a vertical depth of 0.3 μm and a doping concentration of 6 × 10⁻⁶. 17 cm -3 .

[0048] The substrate 1 has a thickness of 300 μm, is doped with phosphorus, and has a resistivity of 0.015 Ω·cm.

[0049] The doping concentration of epitaxial layer 2 is 1×10 16 cm -3 The thickness is 5 micrometers.

[0050] The material of Schottky metal layer 6 is Ni; The anode metal layer 7 is made of an aluminum-copper alloy.

[0051] Other conditions and steps are the same as in Example 1.

[0052] Example 3 A silicon carbide junction barrier Schottky diode, as described in Example 1, differs in that: The longitudinal depth of the second ion implantation region 4 is 0.2 μm.

[0053] Doping concentration is 4×10 17 cm -3 .

[0054] The doping concentration of epitaxial layer 2 is 3×10 16 cm -3 The thickness is 30 micrometers.

[0055] Other conditions and steps are the same as in Example 1.

[0056] Comparative Example 1 A traditional junction barrier Schottky diode, such as Figure 7 As shown, the difference from Example 1 is that the ion implantation region only includes the first ion implantation region 3, while the other structures and conditions are the same as in Example 1.

[0057] Test case The silicon carbide junction barrier Schottky diode of Example 1 and the conventional junction barrier Schottky diode (JBS) of Comparative Example 1 were compared using computer-aided design (TCAD) simulation technology. The results show the forward and reverse characteristics of the two diodes. Figure 8 Figure 9 As shown. In Figure 8 In the forward characteristics shown, the silicon carbide junction barrier Schottky diode of Example 1 exhibits a lower forward voltage in the same active region at a current density of 200 A / cm². 2 Under these conditions, the forward voltage drop is 1.428V, and it turns on relatively early. Figure 9 In the reverse characteristics shown, the reverse breakdown voltage and reverse leakage current of the silicon carbide junction barrier Schottky diode of Example 1 are basically unaffected.

Claims

1. A silicon carbide junction barrier Schottky diode, characterized in that, The Schottky diode comprises a plurality of sequentially adjacent cells, which, from bottom to top, include an ohmic contact cathode metal layer, a substrate layer, an epitaxial layer, a Schottky metal layer, and an anode metal layer. Two ion implantation regions are provided in the upper part of the epitaxial layer. The ion implantation regions include a first ion implantation region, a second ion implantation region, and a third ion implantation region. The first ion implantation region extends downward from the upper surface of the epitaxial layer, the second ion implantation region extends downward from the upper surface of the first ion implantation region, and the third ion implantation region extends downward from the upper surface of the second ion implantation region.

2. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, Includes one or more of the following conditions: The longitudinal depth of the second ion implantation region is less than that of the first ion implantation region, and the lateral width of the second ion implantation region is equal to that of the first ion implantation region. The lateral width of the third ion implantation region is smaller than that of the second ion implantation region, and the longitudinal depth of the third ion implantation region is greater than that of the second ion implantation region and less than that of the first ion implantation region. The substrate layer, epitaxial layer, and second ion implantation region are all n-type doped, and the first ion implantation region and the third ion implantation region are both p-type doped. The doping concentration of the first ion implantation region is less than that of the second ion implantation region, and the doping concentration of the second ion implantation region is less than that of the third ion implantation region.

3. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The vertical depth of the first ion implantation region is 0.3-1 μm, the implanted ions are aluminum ions, and the doping concentration is 1×10⁻⁶. 17 cm -3 Up to 5×10 17 cm -3 .

4. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The implanted ions in the second ion implantation region are nitrogen ions, with a vertical depth of 0.1-0.5 μm and a doping concentration of 2 × 10⁻⁶. 17 cm -3 Up to 8×10 17 cm -3 .

5. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The implanted ions in the third ion implantation region are aluminum ions, with a doping concentration greater than 1×10⁻⁶. 18 cm -3 .

6. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The substrate is made of 4H-SiC with a thickness of 300-350 μm, and the doping source is nitrogen or phosphorus, with a resistivity of 0.014-0.028 Ω•cm.

7. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The epitaxial layer is lightly doped n-type with a doping concentration of 1×10⁻⁶. 15 cm -3 Up to 8×10 16 cm -3 .

8. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The material of the Schottky metal layer is one or more of tantalum, cobalt, molybdenum, titanium, nickel, chromium, platinum, palladium, zirconium, or tungsten.

9. The silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The anode metal layer is made of aluminum or an aluminum-copper alloy, and the ohmic contact cathode metal layer is a stacked structure formed by titanium, nickel and silver layers.

10. The method for manufacturing the silicon carbide junction barrier Schottky diode according to claim 1, characterized in that, The steps include the following: (1) Prepare a substrate layer and form an epitaxial layer on the substrate layer by in-situ growth; (2) A first hard mask layer is fabricated on the epitaxial layer, and the first hard mask layer is etched using a mask to expose the window for ion implantation in the first ion implantation region, and ion implantation is performed to fabricate the first ion implantation region. (3) The first hard mask layer is retained, and the second ion implantation region is formed by compensating doping on the upper part of the first ion implantation region through ion implantation process; (4) On the basis of the first hard mask layer, a sidewall is formed by the sidewall process, and the first hard mask layer and the sidewall together constitute the second hard mask layer. The lateral width of the second hard mask layer is greater than the lateral width of the first hard mask layer. (5) Under the obstruction of the second hard mask layer, the third ion implantation region is formed by ion implantation process; (6) Remove the second hard mask layer and anneal in an inert gas atmosphere to activate the implanted ions; (7) A Schottky metal layer is formed on the upper surface of the epitaxial layer by sputtering deposition and then annealed; (8) Anode metal layer and ohmic contact cathode metal layer are formed on the surface of Schottky metal layer and substrate layer respectively by depositing metal, and then the ohmic contact cathode metal layer is annealed to form ohmic contact, thus completing the device fabrication.

Images