Schottky diode and preparation method thereof

Abstract

The invention discloses a Schottky diode and a preparation method thereof, the Schottky diode comprises a heavily doped N-type substrate layer and a lightly doped N-type epitaxial layer formed on the upper surface of the heavily doped N-type substrate layer, the upper part of the lightly doped N-type epitaxial layer is provided with a groove structure, the groove structure is filled with doped polycrystalline silicon, the doped polycrystalline silicon is polycrystalline silicon doped with P-type impurities, and the doped polycrystalline silicon is doped with P-type impurities. Doped polycrystalline silicon is used as a solid phase diffusion source, and solid phase diffusion is carried out on the doped polycrystalline silicon to diffuse P-type impurities to the lightly doped N-type epitaxial layer, so that P-type regions are formed on the side wall and the bottom of the groove structure. According to the Schottky diode and the preparation method thereof, the P-type region is formed on the side wall and the bottom of the groove structure, the P-type region and the lightly doped N-type epitaxial layer form the depletion region, a good three-dimensional heat dissipation channel is formed, the heat dissipation burden is reduced, the P-type region is formed through solid-phase diffusion, and compared with ion implantation, the junction depth is easier to control.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a Schottky diode and its fabrication method. Background Technology

[0002] Schottky diodes are low-power, high-current, and ultra-high-speed semiconductor devices, characterized by extremely short reverse recovery times (as low as a few nanoseconds) and forward voltage drops of only about 0.4V, with rectified currents reaching thousands of amperes. Existing trench MOS barrier Schottky (TMBS) diodes, such as the semiconductor device provided in Chinese patent CN107170837A (a semiconductor device and manufacturing method), include an N-type drift region with a P-type buried layer, a trench structure, and a gate oxide layer. The trench structure is filled with polysilicon to form a trench-shaped polysilicon electrode. The trench structure is located at the end of the N-type drift region, and the trench structure is isolated from the N-type drift region by the gate oxide layer. The P-type buried layer is located between any two adjacent trenches, so that when the device is in reverse blocking state, the breakdown point can be transferred from the bottom of the trench to the P-type buried layer, effectively preventing hot carriers generated during trench bottom breakdown from entering the gate oxide layer. However, under non-repetitive surge or energy-carrying stress, existing trench Schottky barrier diodes have insufficient three-dimensional thermal conductivity channels within the chip, resulting in delayed lateral heat diffusion and increased system heat dissipation burden. Moreover, the P-type region of most existing trench Schottky barrier diodes is implanted using ion implantation, making it difficult to control the junction depth. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a Schottky diode and its fabrication method, so as to solve the problems of insufficient three-dimensional heat conduction channels, high system heat dissipation burden, and difficulty in controlling junction depth of existing trench Schottky barrier diodes.

[0004] In a first aspect, the present invention provides a Schottky diode, comprising a heavily doped N-type substrate layer and a lightly doped N-type epitaxial layer formed on the upper surface of the heavily doped N-type substrate layer. The upper part of the lightly doped N-type epitaxial layer is provided with a trench structure, and the trench structure is filled with doped polysilicon, wherein the doped polysilicon is doped with P-type impurities. The doped polysilicon serves as a solid-state diffusion source, and P-type impurities are diffused into the lightly doped N-type epitaxial layer by solid-state diffusion, thereby forming P-type regions on the sidewalls and bottom of the trench structure.

[0005] Secondly, the present invention also provides a method for fabricating a Schottky diode, which is used to fabricate the aforementioned Schottky diode. The method for fabricating the Schottky diode includes the following steps: depositing a lightly doped N-type epitaxial layer on the upper side of a heavily doped N-type substrate; depositing an oxide layer on the lightly doped N-type epitaxial layer to form a semiconductor; performing a first photolithography on the semiconductor from top to bottom, first etching the oxide layer, then etching the lightly doped N-type epitaxial layer, followed by a first trench etching to form a trench structure; filling the trench structure with undoped polysilicon, and after the first deposition of the undoped polysilicon, using dry etching to form the trench structure. The undoped polysilicon at the bottom of the trench structure is then deposited a second time, and a doping gas is introduced to perform in-situ heavy doping, making the polysilicon within the trench structure doped polysilicon. The doping gas is used to dop the undoped polysilicon with P-type impurities. An oxide layer is deposited at the top of the trench structure, and the semiconductor is subjected to a single thermal diffusion to diffuse P-type impurities into the lightly doped N-type epitaxial layer, forming P-type regions on the sidewalls and bottom of the trench structure. After BPSG oxide layer deposition, contact hole etching is performed, and barrier metal is sputtered to form metal electrodes, thus obtaining a Schottky diode.

[0006] The beneficial technical effects of this invention are as follows: The Schottky diode of this invention forms a P-type region on the sidewalls and bottom of the trench structure by filling the trench structure with polycrystalline silicon doped with P-type impurities and performing solid-phase diffusion. This P-type region is located between the trench structure and the lightly doped N-type epitaxial layer, forming a depletion region with the lightly doped N-type epitaxial layer, thereby increasing additional heat conduction channels and forming a good three-dimensional heat dissipation channel. Furthermore, the direct contact between the polycrystalline silicon and the monocrystalline silicon improves heat dissipation, sharing current and heat during surges, improving heat dissipation efficiency, reducing the heat dissipation burden, and providing electrical isolation through the P-type region, thus enhancing the surge capability of the device. Moreover, forming the P-type region through solid-phase diffusion makes it easier to control the junction depth compared to ion implantation, facilitating improved production efficiency and quality. The fabrication method of the Schottky diode of this invention also possesses the above-mentioned functions. Attached Figure Description

[0007] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0008] Figure 1 This is a schematic diagram of the structure of a Schottky diode provided in an embodiment of the present invention. Detailed Implementation

[0009] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0010] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a Schottky diode provided in an embodiment of the present invention. The Schottky diode includes a heavily doped N-type substrate layer 1 and a lightly doped N-type epitaxial layer 2 formed on the upper surface of the heavily doped N-type substrate layer 1. A trench structure is provided on the upper part of the lightly doped N-type epitaxial layer 2. The trench structure is filled with doped polysilicon 10, which is doped with P-type impurities. The doped polysilicon 10 serves as a solid-state diffusion source. By performing solid-state diffusion on the doped polysilicon 10, P-type impurities are diffused into the lightly doped N-type epitaxial layer 2, thereby forming P-type regions 3 on the sidewalls and bottom of the trench structure. The P-type regions 3 are located between the trench structure and the lightly doped N-type epitaxial layer 2.

[0011] In this process, P-type impurities are diffused into the lightly doped N-type epitaxial layer 2 to form P-type regions 3 on the sidewalls and bottom of the trench structure, with the P-type regions 3 filled with monocrystalline silicon corresponding to the P-type material. The Schottky diode is formed by filling the trench structure with polycrystalline silicon doped with P-type impurities and performing solid-phase diffusion to form P-type regions 3 on the sidewalls and bottom of the trench structure. These P-type regions 3 are located between the trench structure and the lightly doped N-type epitaxial layer 2, forming a depletion region with the lightly doped N-type epitaxial layer 2. This increases the number of additional heat conduction channels, creating a good three-dimensional heat dissipation channel. Furthermore, the direct contact between the polycrystalline silicon and monocrystalline silicon improves heat dissipation, sharing current and heat during surges, increasing heat dissipation efficiency, reducing the heat dissipation burden, and providing electrical isolation through the P-type regions 3, thus enhancing the device's surge capability. Moreover, forming the P-type regions 3 through solid-phase diffusion makes it easier to control the junction depth compared to ion implantation, facilitating improved production efficiency and quality.

[0012] Preferably, the Schottky diode further includes a metal electrode 11, which is disposed above the lightly doped N-type epitaxial region 2. The metal electrode 11 contacts the lightly doped N-type epitaxial layer 2 to form a Schottky barrier contact region. An isolation layer is provided between the metal electrode 11 and the P-type region 3. The P-type region 3 and the lightly doped N-type epitaxial layer 2 form a depletion region, thereby adding two shielding layers outside the metal-silicon Schottky barrier. This shielding layer pulls down the equipotential surface, weakening the sharp electric field at the metal-silicon contact, thereby mitigating the barrier reduction caused by image force. The region of the P-type region 3 near the bottom of the trench structure can alleviate the surface barrier reduction effect and reduce leakage current. The top of the P-type region 3 is isolated from the metal electrode 11 by the isolation layer to avoid introducing additional leakage current. The isolation layer can be the trench dielectric.

[0013] When a surge occurs, the P-type region 3 is forward biased, forming a parallel PN junction and inducing minority carrier injection within the lightly doped N-type epitaxial layer 2. This pulls down current and heat, spreading the current and heat laterally and improving surge capability. When reverse biased, the P-type region 3 forms electrical isolation. The PN junction formed by the P-type region 3 and the lightly doped N-type epitaxial layer 2 is reverse biased. The electric field formed in the region of the P-type region 3 at the bottom of the trench structure is stronger than the electric field formed in the region of the P-type region 3 at the sidewall of the trench structure, thus providing an electric field shielding effect and mitigating the reduction of the surface barrier.

[0014] Specifically, the P-type impurity is one of boron, boron difluoride, aluminum, or gallium.

[0015] Specifically, the P-type region 3 is formed by a single isothermal drive into the doped polycrystalline silicon.

[0016] Specifically, the doped polycrystalline silicon 10 is driven in isothermally at a diffusion temperature of 900-1050℃. The diffusion time is 1-60 min.

[0017] Specifically, the bottom ends of the P-shaped region 3 are rounded.

[0018] Preferably, the lateral depth of the P-type region 3 located on both sides of the trench structure is 0.1-0.3µm, and the depth of the P-type region 3 located at the bottom of the trench structure is 0.1-2µm.

[0019] Specifically, the Schottky diode fabrication method provided in this embodiment of the invention is used to fabricate the above-mentioned Schottky diode, and the Schottky diode fabrication method includes the following steps: A lightly doped N-type epitaxial layer is deposited on the top side of a heavily doped N-type substrate; A semiconductor is formed by depositing an oxide layer on a lightly doped N-type epitaxial layer. The semiconductor is subjected to the first photolithography from top to bottom, first etching the oxide layer, then etching the lightly doped N-type epitaxial layer, and then performing the first trench etching to form a trench structure. Undoped polysilicon is used to fill the trench structure. After the first deposition of the undoped polysilicon, the bottom of the trench structure is etched by dry etching. Then, the undoped polysilicon is deposited a second time and a doping gas is introduced to perform in-situ heavy doping, so that the polysilicon in the trench structure is doped polysilicon. The doping gas is used to dop the undoped polysilicon with P-type impurities. An oxide layer is deposited at the top of the trench structure, and the semiconductor is subjected to a single thermal diffusion to diffuse P-type impurities into the lightly doped N-type epitaxial layer, forming P-type regions on the sidewalls and bottom of the trench structure. After depositing a BPSG oxide layer (BSPG oxide layer: boron phosphosilicate glass oxide layer) on the oxide layer, the contact holes are etched, and a barrier metal is sputtered to form a metal electrode, thus obtaining a Schottky diode.

[0020] In this process, a Schottky barrier contact region is formed between the metal electrode and the lightly doped N-type epitaxial layer. Undoped polysilicon is used to fill the trench structure. After a first deposition of the undoped polysilicon, the bottom of the trench structure is dry-etched to form a bottom layer of undoped polysilicon within the trench structure. This reduces overall stress and the risk of wafer warpage. The undoped polysilicon avoids lattice distortion caused by high doping concentrations and provides a buffer layer for subsequent heavy doping. Etching removes the bottom undoped polysilicon to form a locally heavily doped region, allowing precise control of the bottom doping concentration of the trench structure and preventing leakage problems caused by high doping on the sidewalls. A second deposition is performed on the etched undoped polysilicon, and dopant gas is introduced for in-situ heavy doping, making the polysilicon within the trench structure doped polysilicon, forming a highly conductive bottom channel. The heavily doped layer reduces contact resistance and improves carrier migration efficiency, while the lightly doped layer maintains a low junction capacitance. This staged deposition disperses stress through doping gradients, avoiding wafer deformation caused by a single high-doping deposition. The method for fabricating the Schottky diode involves filling a trench structure with polycrystalline silicon doped with P-type impurities and performing a single thermal diffusion process to form a P-type region on the sidewalls and bottom of the trench structure. This P-type region is positioned between the trench structure and the lightly doped N-type epitaxial layer, forming a depletion region with the lightly doped N-type epitaxial layer. This increases the number of additional heat conduction channels, creating a good three-dimensional heat dissipation channel. Furthermore, the direct contact between the polycrystalline silicon and the monocrystalline silicon enhances heat dissipation, sharing current and heat during surges, improving heat dissipation efficiency, reducing the heat dissipation burden, and providing electrical isolation through the P-type region, thus improving the device's surge capability. Moreover, forming the P-type region through a single thermal diffusion method allows for easier control of the junction depth compared to ion implantation, facilitating improved production efficiency and quality.

[0021] Specifically, in some embodiments, the thickness of the undoped polysilicon is 500-2000 Å.

[0022] Preferably, the doped polysilicon within the trench structure is in two layers, with the upper layer being a lightly doped layer and having a doping concentration of not less than 1E17-1E18 cm⁻¹. -3 The lower layer of doped polysilicon is a heavily doped layer with a doping concentration of 1E19-1E20 cm⁻¹. -3 The layered structure, combined with the Schottky barrier properties (metal-semiconductor junction), can further reduce charge storage effects and improve reverse recovery speed. Moreover, the heavily doped bottom layer enhances conduction capability, while the lightly doped layer suppresses reverse leakage current and optimizes high-frequency switching performance.

[0023] In summary, the Schottky diode of the present invention forms a P-type region on the sidewalls and bottom of the trench structure by filling the trench structure with polycrystalline silicon doped with P-type impurities and performing solid-state diffusion. This P-type region is located between the trench structure and the lightly doped N-type epitaxial layer, forming a depletion region with the lightly doped N-type epitaxial layer. This increases additional heat conduction channels, creating a good three-dimensional heat dissipation channel. Furthermore, the direct contact between the polycrystalline silicon and the monocrystalline silicon improves heat dissipation, sharing current and heat during surges, improving heat dissipation efficiency, reducing the heat dissipation burden, and providing electrical isolation through the P-type region, thus enhancing the device's surge capability. Moreover, forming the P-type region through solid-state diffusion allows for easier control of the junction depth compared to ion implantation, facilitating improved production efficiency and quality. The fabrication method of the Schottky diode of the present invention also possesses the above-mentioned functions.

[0024] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A Schottky diode, characterized by, The Schottky diode comprises a heavily doped N-type substrate layer and a lightly doped N-type epitaxial layer formed on the upper surface of the heavily doped N-type substrate layer, an upper portion of the lightly doped N-type epitaxial layer being provided with a trench structure, and the trench structure being filled with doped polysilicon, the doped polysilicon being P-type impurity-doped polysilicon, the doped polysilicon serving as a solid-phase diffusion source, and P-type impurities are diffused into the lightly doped N-type epitaxial layer by solid-phase diffusion of the doped polysilicon, so as to form a P-type region on the sidewalls and the bottom of the trench structure.

2. The Schottky diode of claim 1, wherein The Schottky diode further comprises a metal electrode provided above the lightly doped N-type epitaxial region, the metal electrode being in contact with the lightly doped N-type epitaxial layer to form a Schottky barrier contact region, and an isolation layer being provided between the metal electrode and the P-type region.

3. The Schottky diode of claim 1, wherein The P-type impurities are one of boron, difluoroboron, aluminum and gallium.

4. The Schottky diode of claim 1, wherein The P-type region is formed by single isothermal drive-in of the doped polysilicon.

5. The Schottky diode of claim 4, wherein, The isothermal drive-in of the doped polysilicon is performed at a diffusion temperature of 900-1050°C.

6. The Schottky diode of claim 1, wherein The two ends of the bottom of the P-type region are rounded.

7. The Schottky diode of claim 1, wherein The lateral depth of the P-type region in the regions located on the two sidewalls of the trench structure is 0.1-0.3 µm, and the junction depth of the P-type region in the region located on the bottom of the trench structure is 0.1-2 µm.

8. A method of manufacturing a Schottky diode, characterized by, A method for preparing the Schottky diode as claimed in any one of claims 1-7, the method comprising the following steps: depositing a lightly doped N-type epitaxial layer on the upper side of the heavily doped N-type substrate layer; depositing an oxide layer on the lightly doped N-type epitaxial layer to form a semiconductor; performing first photolithography on the semiconductor from top to bottom, etching the oxide layer first, then etching the lightly doped N-type epitaxial layer, and then performing first trench etching to form a trench structure; filling the trench structure with undoped polysilicon, dry-etching the undoped polysilicon on the bottom of the trench structure after first deposition of the undoped polysilicon, and then performing second deposition of the undoped polysilicon and introducing a doping gas to perform in-situ re-doping, so that the polysilicon in the trench structure is doped polysilicon, wherein the doping gas is used to dope P-type impurities into the undoped polysilicon; depositing an oxide layer at the upper opening of the trench structure, and performing single thermal diffusion on the semiconductor to diffuse P-type impurities into the lightly doped N-type epitaxial layer, so as to form a P-type region on the sidewalls and the bottom of the trench structure; performing contact hole etching after BPSG oxide layer deposition of the oxide layer, sputtering a barrier metal to form a metal electrode, and obtaining a Schottky diode.

9. The method of claim 8, wherein the metal layer is formed by sputtering. The thickness of the undoped polysilicon is 500-2000 Å.

10. The method of claim 8, wherein the metal layer is formed by a method selected from the group consisting of sputtering, vacuum deposition, and plating. The doped polysilicon in the trench structure is layered in up and down, the doped polysilicon in the upper layer is a lightly doped layer, the doping concentration of the lightly doped layer is not less than 1E17-1E18 cm -3 , the doped polysilicon in the lower layer is a heavily doped layer, the doping concentration of the heavily doped layer is 1E19-1E20 cm -3 .

Images