A composite anode structure diamond schottky diode and a preparation method thereof

Abstract

This invention discloses a composite anode structure diamond Schottky diode and its fabrication method. The Schottky diode includes an ohmic electrode, a 100-oriented p-type heavily doped single-crystal diamond substrate, an unintentionally doped diamond layer, a phosphorus-doped diamond layer, a high-conductivity layer, and a Schottky electrode. The unintentionally doped diamond layer is etched into a ramp structure, the phosphorus-doped diamond layer is disposed in the etched area, and the high-conductivity layer is disposed on the surface of the phosphorus-doped diamond layer, achieving an alternating arrangement of the high-conductivity layer and the unintentionally doped diamond layer. This introduces alternating low-barrier Schottky junctions and high-barrier pn junctions at the anode. Due to the different barrier heights of the pn junction and the Schottky junction, during forward conduction, the low-barrier Schottky junction dominates, resulting in low on-resistance; during reverse turn-off, the high-barrier pn junction dominates, resulting in high reverse breakdown voltage. This fabrication method introduces two self-alignments: the etching of the unmasked area is isolated from the growth of the phosphorus-doped diamond layer and the self-masking etching of the Schottky electrode, reducing process complexity.

Description

Technical Field

[0001] This invention relates to a composite anode structure diamond Schottky diode and its fabrication method, belonging to the field of power device technology. Background Technology

[0002] Schottky diodes play a crucial role in many fields, attracting extensive research due to their fast recovery characteristics, low forward voltage drop, and simple structure. Diamond, with its ultra-wide bandgap (5.5 eV), high thermal conductivity, high intrinsic mobility, high breakdown electric field, high saturation velocity, and low dielectric constant, is an ideal choice for fabricating Schottky diodes. However, due to the difficulty of n-type doping in diamond, current diamond Schottky diodes are primarily based on p-type diamond.

[0003] Traditional vertical p-type diamond Schottky diodes face a trade-off between high on-resistance and low reverse voltage. To improve the breakdown voltage, a combination of low work function metals with field-plate structures and edge-junction termination techniques is often used. While this effectively increases the breakdown voltage, it does not improve the forward on-resistance. To reduce the forward on-resistance, a high work function metal is required. However, a high work function metal implies a low Schottky barrier height, resulting in higher leakage current and lower breakdown voltage. Therefore, a dual-barrier composite anode structure can be considered to balance forward on-resistance and reverse voltage.

[0004] Current dual-barrier composite anode structures primarily rely on changing the surface termination type to achieve variations in the barrier height when the metal and diamond surfaces are in contact. However, diamond surface terminations exhibit a strong Fermi pinning effect, limiting the variation in barrier height and resulting in poor performance balancing for the device. Considering that the barrier height of a pn junction is much greater than that of a Schottky junction, and that the breakdown voltage of a pn junction is higher than that of a Schottky junction, the pn junction barrier and the Schottky junction barrier can be combined to realize a composite anode structure Schottky diode. For diamond, the n-type phosphorus doping concentration is relatively low; therefore, it is necessary to increase the phosphorus doping concentration to ensure that the pn junction barrier provides reverse shielding against the Schottky junction barrier. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a composite anode structure diamond Schottky diode and its fabrication method. This invention proposes a composite anode structure diamond Schottky diode composed of alternating high pn junction barriers and low Schottky junction barriers. Due to the different barrier heights of the pn junction and the Schottky junction, during forward conduction, current preferentially conducts in the low-barrier Schottky junction, resulting in lower turn-on voltage and on-resistance. Conversely, during reverse bias, the wide depletion region of the high-barrier pn junction shields the depletion region of the Schottky junction barrier, leading to a higher breakdown voltage.

[0006] The first objective of this invention is to provide a method for fabricating a diamond Schottky diode with a composite anode structure, comprising the following steps:

[0007] Step 1: Grow an unintentionally doped diamond layer on a 100-position p-type heavily doped single-crystal diamond substrate;

[0008] Step 2: Treat the surface of the unintentionally doped diamond layer to form an oxygen terminal, thus creating an anode metal mask array;

[0009] Step 3: Etch the unmasked area into a ramp platform and grow a phosphorus-doped diamond layer;

[0010] Step 4: Remove the anode metal mask array and deposit an ohmic electrode under a 100-oriented p-type heavily doped single-crystal diamond substrate.

[0011] Step 5: Perform high-temperature annealing on the sample to form a highly conductive layer on the surface of the phosphorus-doped diamond layer;

[0012] Step 6: Form a Schottky electrode over an alternating layer of highly conductive material and an unintentionally doped diamond layer, and perform self-aligned etching isolation to obtain a Schottky diode.

[0013] In one embodiment of the present invention, the doping element of the 100-axis p-type heavily doped single-crystal diamond substrate is boron, and the doping concentration is greater than 10. 19 cm -3 The thickness is 50-1000μm.

[0014] In one embodiment of the present invention, the unintentionally doped diamond layer is epitaxially grown using MPCVD technology, wherein the growth pressure is 90-120 Torr, the methane flow rate is 5-40 sccm, the hydrogen flow rate is 400-500 sccm, the temperature is 800-950℃, and the thickness is 500-2000 nm.

[0015] In one embodiment of the present invention, in step two, the hydrogen-terminated surface of the unintentionally doped diamond layer is transformed into an oxygen-terminated surface by ultraviolet ozone treatment or oxygen plasma treatment; the anode metal mask is made of high-melting-point Ti or W metal and does not chemically react with methane plasma; the width of the anode metal mask array is 1-3 μm and the spacing is 2-6 μm.

[0016] In one embodiment of the present invention, in step three, the unmasked area is subjected to plasma etching to form a slope, the etching depth is 100-1500nm, and the etching depth is less than the thickness of the unintentionally doped diamond layer, and the slope angle is 30-60°.

[0017] In one embodiment of the present invention, the phosphorus-doped diamond layer is epitaxially grown using MPCVD technology, wherein the growth pressure is 90–120 Torr, the methane flow rate is 1–20 sccm, the phosphine flow rate is 40–100 sccm, the hydrogen flow rate is 400–450 sccm, the temperature is 1050–1150 °C, and the doping concentration is greater than 10%. 18 cm -3 The thickness is 20-80nm.

[0018] In one embodiment of the present invention, in step four, the anode mask metal array is removed by high-temperature etching with a sulfuric acid / nitric acid mixed solution; the ohmic electrode is deposited under a 100-oriented p-type heavily doped single-crystal diamond substrate to form a vertical structure diode, and the material of the ohmic electrode is one of Ti, Pt, and Ni, with a thickness of 100-200 nm.

[0019] In one embodiment of the present invention, in step five, the highly conductive layer is formed only on the surface of the phosphorus-doped diamond layer by high-temperature annealing, and the highly conductive layer will not be formed on the surface of the unintentionally doped diamond layer; the annealing temperature is greater than 900°C and the annealing time is greater than 2 min.

[0020] In one embodiment of the present invention, in step six, the Schottky electrode is a high work function metal of Ni, Au, and Pt, covered with an alternating array of highly conductive layers and an unintentionally doped diamond layer surface, and the device is isolated by ICP etching using the Schottky electrode as a self-aligned mask.

[0021] The second objective of this invention is to provide a composite anode structure diamond Schottky diode prepared by the above-described method, wherein the Schottky diode comprises, from bottom to top: an ohmic electrode, a 100-oriented p-type heavily doped single-crystal diamond substrate, an unintentionally doped diamond layer, a phosphorus-doped diamond layer, a high conductivity layer, and a Schottky electrode; wherein the unintentionally doped diamond layer is etched into a ramp structure, the phosphorus-doped diamond layer is disposed in the etched region, the high conductivity layer is disposed on the surface of the phosphorus-doped diamond layer, and the Schottky electrode covers an alternating array of high conductivity layers and the surface of the unintentionally doped diamond layer.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) The diode of the present invention is composed of an anode formed by an alternating array of low-barrier Schottky junctions and a high-barrier pn junction. Since the barrier heights of the pn junction and the Schottky junction are different, the low-barrier Schottky junction dominates the forward conduction and the conduction resistance is low; the high-barrier pn junction dominates the reverse turn-off and the reverse breakdown voltage is high.

[0024] (2) The present invention utilizes an anode metal mask for self-aligned etching and growth of phosphorus-doped diamond layers, which can reduce the complexity of the process. At the same time, the slope structure design can effectively increase the phosphorus doping concentration and effectively increase the barrier height of the pn junction.

[0025] (3) The phosphorus-doped diamond layer of the present invention has similar insulating properties to intrinsic diamond, and the resulting pn junction has a high withstand voltage, which reduces the breakdown voltage variation caused by the reduction in thickness of the unintentionally doped diamond layer after etching, and maintains a high breakdown voltage.

[0026] (4) The present invention utilizes high-temperature annealing to form a highly conductive layer on the surface of phosphorus-doped diamond layer, which is beneficial to forming good pn junction metal contact and reducing on-resistance.

[0027] (5) The present invention utilizes Schottky electrode self-alignment for device isolation etching, which can reduce process costs and reduce the interface states of the metal / unintentionally doped diamond layer during the etching process, further reducing the on-resistance; after etching, it is also beneficial to optimize the electric field distribution of the device and improve the breakdown voltage. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic cross-sectional view of the composite anode structure diamond Schottky diode of the present invention.

[0030] Figure 2 This is a comparison diagram of the forward conduction characteristics of the improved SBD in Embodiment 3 of the present invention and the conventional SBD in the comparative example.

[0031] Figure 3 This is a comparison diagram of the reverse withstand voltage characteristics of the improved SBD in Embodiment 3 of the present invention and the conventional SBD in the comparative example.

[0032] In the figure: 1. 100-oriented p-type heavily doped single-crystal diamond substrate; 2. Unintentionally doped diamond layer; 3. Phosphorus-doped diamond layer; 4. Ohmic electrode; 5. High conductivity layer; 6. Schottky electrode. Detailed Implementation

[0033] The technical solution of the present invention will now be clearly and completely described 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.

[0034] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0036] Example 1

[0037] like Figure 1 As shown, this embodiment provides a method for fabricating a composite anode structure diamond Schottky diode, including the following steps:

[0038] Step 1: Grow an unintentionally doped diamond layer 2 on a 100-oriented p-type heavily doped single-crystal diamond substrate 1;

[0039] Step 2: Treat the surface of the unintentionally doped diamond layer 2 to form an oxygen terminal, thereby forming an anode metal mask array;

[0040] Step 3: Etch the unmasked area into a sloping platform and grow a phosphorus-doped diamond layer 3;

[0041] Step 4: Remove the anode metal mask array and deposit an ohmic electrode 4 under the 100-oriented p-type heavily doped single crystal diamond substrate 1.

[0042] Step 5: Perform high-temperature annealing on the sample to form a highly conductive layer 5 on the surface of the phosphorus-doped diamond layer 3;

[0043] Step 6: A Schottky electrode 6 is formed on top of the alternating highly conductive layer 5 and the unintentionally doped diamond layer 2, and self-aligned etching is performed to isolate it, thus obtaining a Schottky diode.

[0044] Optionally, the shape of the p-type heavily doped single-crystal diamond substrate 1 is not limited, the doping element is boron, and the doping concentration is greater than 10. 19 cm -3 The thickness is 50-1000μm.

[0045] Optionally, the unintentionally doped diamond layer 2 is epitaxially grown using MPCVD technology, wherein the growth pressure is 90–120 Torr, the methane flow rate is 5–40 sccm, the hydrogen flow rate is 400–500 sccm, the temperature is 800–950℃, and the thickness is 500–2000 nm.

[0046] Optionally, in step two, the hydrogen-terminated surface of the unintentionally doped diamond layer 2 is transformed into an oxygen-terminated surface through ultraviolet ozone treatment or oxygen plasma treatment.

[0047] Optionally, in step two, the anode metal mask is made of a high-melting-point metal that is chemically stable in a methane plasma atmosphere, such as Ti or W, to avoid affecting the subsequent etching and growth process of the phosphorus-doped diamond layer 3; the width of the anode metal mask array is 1-3 μm and the spacing is 2-6 μm to achieve a good high-low barrier composite structure.

[0048] Optionally, in step three, the unmasked area is subjected to plasma etching to form a slope with an etching depth of 100-1500 nm, and the etching depth is less than the thickness of the unintentionally doped diamond layer 2. The slope angle is 30-60° to achieve the growth of a high-concentration phosphorus-doped diamond layer 3.

[0049] Optionally, the phosphorus-doped diamond layer 3 is epitaxially grown using MPCVD technology, wherein the growth pressure is 90–120 Torr, the methane flow rate is 1–20 sccm, the phosphine flow rate is 40–100 sccm, the hydrogen flow rate is 400–450 sccm, the temperature is 1050–1150 °C, and the doping concentration is greater than 10%. 18 cm -3 The thickness is 20-80nm.

[0050] Optionally, in step four, the anode mask metal array is removed by high-temperature corrosion using a sulfuric acid / nitric acid mixed solution.

[0051] Optionally, in step four, the ohmic electrode 4 is deposited under a 100-oriented p-type heavily doped single-crystal diamond substrate 1 to form a vertical structure diode. The material of the ohmic electrode 4 is one of Ti, Pt, and Ni, and the thickness is 100-200 nm.

[0052] Optionally, in step five, the sample undergoes high-temperature annealing. This not only forms a good ohmic contact but also creates a highly conductive layer 5 on the surface of the phosphorus-doped diamond layer 3 array, thus acting as a metal electrode. However, this highly conductive layer 5 does not form on the surface of the unintentionally doped diamond layer 2 array, maintaining the intrinsic insulating properties of diamond. The annealing temperature is greater than 900°C, and the annealing time is greater than 2 minutes. Therefore, the highly conductive layer 5 is only formed on the surface of the phosphorus-doped diamond layer 3 by high-temperature annealing, and does not form on the surface of the unintentionally doped diamond layer 2.

[0053] Optionally, in step six, the Schottky electrode 6 is a high work function metal such as Ni, Au, or Pt to achieve a lower Schottky barrier; the Schottky electrode 6 covers the surface of an array of alternating high conductivity layers 5 and an unintentionally doped diamond layer 2, and the device is isolated by ICP etching using the Schottky electrode 6 as a self-aligned mask.

[0054] Example 2

[0055] This embodiment provides a composite anode structure diamond Schottky diode prepared by the preparation method described in Embodiment 1. The Schottky diode comprises, from bottom to top: an ohmic electrode 4, a 100-oriented p-type heavily doped single-crystal diamond substrate 1, an unintentionally doped diamond layer 2, a phosphorus-doped diamond layer 3, a high conductivity layer 5, and a Schottky electrode 6. The unintentionally doped diamond layer 2 is etched into a slope structure, the phosphorus-doped diamond layer 3 is disposed in the etched area, the high conductivity layer 5 is disposed on the surface of the phosphorus-doped diamond layer 3, and the Schottky electrode 6 covers the surface of the alternating array of high conductivity layers 5 and the unintentionally doped diamond layer 2.

[0056] Example 3

[0057] This embodiment provides a method for fabricating a composite anode structure diamond Schottky diode, including:

[0058] (1) The doping concentration of the high-temperature and high-pressure synthesized material is 3×10⁻⁶. 19 cm -3、 A 100 μm thick, 100-oriented, p-type boron-doped single-crystal diamond substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 min each, and then purged with nitrogen for 20 s. The substrate was then placed in an MPCVD instrument to grow a 500 nm unintentionally doped diamond layer on the front side. The growth pressure was 90 Torr, the methane flow rate was 5 sccm, the hydrogen flow rate was 480 sccm, and the temperature was 800 °C.

[0059] (2) The surface hydrogen terminals of the unintentionally doped diamond layer were transformed into oxygen terminals by ultraviolet ozone irradiation. 30 rectangular patterns with a length of 100 μm, a width of 1 μm and a spacing of 2 μm were obtained by photolithography. 100 nm of metal W was deposited by magnetron sputtering. After stripping, an anode metal mask array was obtained.

[0060] (3) The unmasked area was etched 200 nm using an ICP device to form a slope structure with a gradient of 60°. Then, a 20 nm thick layer with a doping concentration of 2 × 10⁻⁶ was grown in the unmasked area using an MPCVD device. 18 cm -3 The growth of the phosphorus-doped diamond layer was carried out at a pressure of 100 Torr, a methane flow rate of 1 sccm, a phosphine flow rate of 40 sccm, a hydrogen flow rate of 450 sccm, and a temperature of 1150℃.

[0061] (4) The anode metal mask array was removed by heating a mixed acid solution of sulfuric acid and nitric acid = 1:1 at 300°C for 2 hours to form a structure in which the surface of phosphorus-doped diamond layer and unintentionally doped diamond layer are alternately arranged. Then, a 200nm thick layer of metallic titanium was deposited on the back side of the substrate as an ohmic electrode.

[0062] (5) Place the sample in a rapid annealing device and anneal at 1000℃ for 5 min to form a highly conductive layer on the surface of the phosphorus-doped diamond layer array and to form a good ohmic contact between the ohmic electrode and the p-type heavily doped single crystal diamond substrate.

[0063] (6) A Schottky electrode pattern with a length of 100 μm and a width of 110 μm is formed by photolithography on the surface of the high conductivity layer and the unintentionally doped diamond layer. A 100 nm metal Pt is deposited by magnetron sputtering. After being stripped, it is placed in an ICP etching device to etch 500 nm, and finally a Schottky diode is obtained.

[0064] Example 4

[0065] This embodiment provides a method for fabricating a composite anode structure diamond Schottky diode, including:

[0066] (1) The doping concentration of the high-temperature and high-pressure synthesized material is 1×10⁻� 20 cm -3 A 500 μm thick, 100-oriented p-type boron-doped single-crystal diamond substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 min each, and then purged with nitrogen for 20 s. The substrate was then placed in an MPCVD instrument to grow a 1000 nm unintentionally doped diamond layer on the front side. The growth pressure was 100 Torr, the methane flow rate was 15 sccm, the hydrogen flow rate was 480 sccm, and the temperature was 850 °C.

[0067] (2) The surface hydrogen terminals of the unintentionally doped diamond layer were transformed into oxygen terminals by ultraviolet ozone irradiation. 30 rectangular patterns with a length of 150 μm, a width of 2 μm and a spacing of 3 μm were obtained by photolithography. 100 nm of metal W was deposited by magnetron sputtering. After stripping, an anode metal mask array was obtained.

[0068] (3) The unmasked area was etched to 600 nm using an ICP device to form a slope structure with a gradient of 45°. Then, a 50 nm thick layer with a doping concentration of 5 × 10⁻⁶ was grown in the unmasked area using an MPCVD device. 18 cm -3 The phosphorus-doped diamond layer was grown at a pressure of 110 Torr, a methane flow rate of 1 sccm, a phosphine flow rate of 60 sccm, a hydrogen flow rate of 450 sccm, and a temperature of 1100℃.

[0069] (4) The anode metal mask array was removed by heating a mixed acid solution of sulfuric acid and nitric acid = 1:1 at 300°C for 2 hours to form a structure in which the surface of phosphorus-doped diamond layer and unintentionally doped diamond layer are alternately arranged. Then, a 200nm thick layer of metallic titanium was deposited on the back side of the substrate as an ohmic electrode.

[0070] (5) Place the sample in a rapid annealing device and anneal at 1100℃ for 3 min to form a highly conductive layer on the surface of the phosphorus-doped diamond layer array and to form a good ohmic contact between the ohmic electrode and the p-type heavily doped single crystal diamond substrate.

[0071] (6) A Schottky electrode pattern with a length of 160 μm and a width of 160 μm is formed by photolithography on the surface of the high conductivity layer and the unintentionally doped diamond layer. 200 nm of metallic Ni is deposited by magnetron sputtering. After being stripped, it is placed in an ICP etching device to etch 1000 nm to finally obtain a Schottky diode.

[0072] Example 5

[0073] This embodiment provides a method for fabricating a composite anode structure diamond Schottky diode, including:

[0074] (1) The doping concentration of the high-temperature and high-pressure synthesized material is 1×10⁻� 20 cm -3 A 1000 μm thick, 100-oriented, p-type boron-doped single-crystal diamond substrate was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 min each, and then purged with nitrogen for 20 s. The substrate was then placed in an MPCVD instrument to grow a 1900 nm unintentionally doped diamond layer on the front side. The growth pressure was 120 Torr, the methane flow rate was 20 sccm, the hydrogen flow rate was 480 sccm, and the temperature was 950 °C.

[0075] (2) The hydrogen terminals on the surface of the unintentionally doped diamond layer were transformed into oxygen terminals by ultraviolet ozone irradiation. 30 rectangular patterns with a length of 180 μm, a width of 2 μm and a spacing of 4 μm were obtained by photolithography. 200 nm of metallic Ti was deposited by magnetron sputtering. After stripping, an anode metal mask array was obtained.

[0076] (3) The unmasked area was etched to 1200 nm using an ICP device to form a slope structure with a gradient of 30°. Then, an 80 nm thick layer with a doping concentration of 5 × 10⁻⁶ was grown in the unmasked area using an MPCVD device. 18 cm -3 The phosphorus-doped diamond layer was grown at a pressure of 110 Torr, a methane flow rate of 1 sccm, a phosphine flow rate of 60 sccm, a hydrogen flow rate of 450 sccm, and a temperature of 1100℃.

[0077] (4) The anode metal mask array was removed by heating a mixed acid solution of sulfuric acid and nitric acid = 1:1 at 300°C for 2 hours to form a structure in which the surface of phosphorus-doped diamond layer and unintentionally doped diamond layer are alternately arranged. Then, a 200nm thick layer of metallic titanium was deposited on the back side of the substrate as an ohmic electrode.

[0078] (5) Place the sample in a rapid annealing apparatus and anneal at 950°C for 10 min to form a highly conductive layer on the surface of the phosphorus-doped diamond layer array and to form a good ohmic contact between the ohmic electrode and the p-type heavily doped single crystal diamond substrate.

[0079] (6) A Schottky electrode pattern with a length of 200 μm and a width of 200 μm is formed by photolithography on the surface of the high conductivity layer and the unintentionally doped diamond layer. A 200 nm layer of metal Au is deposited by magnetron sputtering. After being stripped, the layer is placed in an ICP etching device and etched for 1500 nm to finally obtain a Schottky diode.

[0080] Comparative Example

[0081] The difference between this comparative example and Example 3 is that this comparative example is a conventional vertical structure diamond Schottky diode, which, from bottom to top, includes an ohmic electrode, a 100-oriented p-type heavily doped single-crystal diamond substrate, an unintentionally doped diamond layer, and a Schottky electrode. Its fabrication method involves first growing an unintentionally doped diamond layer on the surface of the p-type heavily doped single-crystal diamond substrate, treating the surface to oxygen termination, and then fabricating the ohmic electrode on the back side of the p-type heavily doped single-crystal diamond substrate and the Schottky electrode on the front side. It is a single-barrier device, without unintentionally doped diamond layer etching, phosphorus-doped diamond layer growth, or a high-conductivity layer.

[0082] Comparison of diode performance with Example 3 Figure 2 and Figure 3As shown, it can be seen that the improved SBD (Schottky barrier diode) in Example 3 has a higher reverse withstand voltage than the conventional SBD in the comparative example, despite a certain loss in conduction performance.

[0083] Testing process: The sample was placed on the sample stage of the Agilent B1505A testing equipment, and a voltage was introduced to the sample surface using a probe to collect the current signal of the device. The result showed that the on-resistance of the composite anode structure diamond Schottky diode prepared in this invention was 4.5 mΩ·cm. 2 The breakdown voltage is 300V; the on-resistance of a traditional vertical-structure diamond Schottky diode is 1.2mΩ·cm. 2 The breakdown voltage is 190V. The results show that the composite anode structure diamond Schottky diode of this invention has a comparable on-resistance to conventional Schottky diodes, but with a higher reverse breakdown voltage.

[0084] In summary, this invention provides a composite anode structure diamond Schottky diode and its fabrication method. The Schottky diode includes an ohmic electrode, a p-type heavily doped single-crystal diamond substrate, an unintentionally doped diamond layer, a phosphorus-doped diamond layer, a high-conductivity layer, and a Schottky electrode. The unintentionally doped diamond layer is etched into a ramp structure, the phosphorus-doped diamond layer is disposed in the etched area, and the high-conductivity layer is disposed on the surface of the phosphorus-doped diamond layer. This achieves an alternating arrangement of the high-conductivity layer and the unintentionally doped diamond layer on the surface, thereby introducing alternating low-barrier Schottky junctions and high-barrier pn junctions in the anode, achieving a trade-off between forward conduction resistance and reverse breakdown voltage. This fabrication method introduces two self-alignments: etching of the unmasked area and growth of the phosphorus-doped diamond layer, and self-masking etching isolation of the Schottky electrode, reducing process complexity.

[0085] This document uses specific embodiments to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for fabricating a diamond Schottky diode with a composite anode structure, characterized in that, Includes the following steps: Step 1: Grow an unintentionally doped diamond layer (2) on a 100-oriented p-type heavily doped single-crystal diamond substrate (1); Step 2: The surface of the unintentionally doped diamond layer (2) is treated to form an oxygen terminal to create an anode metal mask array; Step 3: Etch the unmasked area into a ramp platform and grow a phosphorus-doped diamond layer (3); Step 4: Remove the anode metal mask array and deposit an ohmic electrode (4) under the 100-oriented p-type heavily doped single crystal diamond substrate (1); Step 5: Perform high-temperature annealing on the sample to form a highly conductive layer (5) on the surface of the phosphorus-doped diamond layer (3); Step 6: A Schottky electrode (6) is formed over an alternating high conductivity layer (5) and an unintentionally doped diamond layer (2), and self-aligned etching is performed to obtain a Schottky diode.

2. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: The doping element of the 100 crystal orientation p-type heavily doped monocrystalline diamond substrate (1) is boron, the doping concentration is greater than 10 19 cm -3 , and the thickness is 50-1000 μm.

3. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: The unintentionally doped diamond layer (2) is epitaxially grown by MPCVD technology, wherein the growth pressure is 90-120 Torr, the methane flow rate is 5-40 sccm, the hydrogen flow rate is 400-500 sccm, the temperature is 800-950℃, and the thickness is 500-2000 nm.

4. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: In step two, the hydrogen-terminated surface of the unintentionally doped diamond layer (2) is transformed into an oxygen-terminated surface by ultraviolet ozone treatment or oxygen plasma treatment; the anode metal mask is made of high-melting-point Ti or W metal and does not react chemically with methane plasma; the width of the anode metal mask array is 1-3 μm and the spacing is 2-6 μm.

5. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: In step three, the unmasked area is plasma etched to form a slope with an etching depth of 100-1500nm and a depth less than the thickness of the unintentionally doped diamond layer (2). The slope angle is 30-60°.

6. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: The phosphorus-doped diamond layer (3) is epitaxially grown using MPCVD technology, wherein the growth pressure is 90–120 Torr, the methane flow rate is 1–20 sccm, the phosphine flow rate is 40–100 sccm, the hydrogen flow rate is 400–450 sccm, the temperature is 1050–1150 °C, and the doping concentration is greater than 10%. 18 cm -3 The thickness is 20-80nm.

7. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: In step four, the anode metal mask array is removed by high-temperature corrosion using a sulfuric acid / nitric acid mixed solution; the ohmic electrode (4) is deposited under a 100-oriented p-type heavily doped single-crystal diamond substrate (1) to form a vertical structure diode. The material of the ohmic electrode (4) is one of Ti, Pt, or Ni, and the thickness is 100-200 nm.

8. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: In step five, the high conductivity layer (5) is formed only on the surface of the phosphorus-doped diamond layer (3) by high-temperature annealing, and the high conductivity layer (5) will not be formed on the surface of the unintentionally doped diamond layer (2); the annealing temperature is greater than 900°C and the annealing time is greater than 2 min.

9. The method for fabricating a composite anode structure diamond Schottky diode according to claim 1, characterized in that: In step six, the Schottky electrode (6) is a high work function metal of Ni, Au, and Pt, covering an array of alternating high conductivity layers (5) and an unintentionally doped diamond layer (2) surface. The Schottky electrode (6) is used as a self-aligned mask, and device isolation is achieved by ICP etching.

10. The composite anode structure diamond Schottky diode prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The Schottky diode comprises, from bottom to top: an ohmic electrode (4), a 100-oriented p-type heavily doped single-crystal diamond substrate (1), an unintentionally doped diamond layer (2), a phosphorus-doped diamond layer (3), a high conductivity layer (5), and a Schottky electrode (6); wherein the unintentionally doped diamond layer (2) is etched into a ramp structure, the phosphorus-doped diamond layer (3) is disposed in the etched area, the high conductivity layer (5) is disposed on the surface of the phosphorus-doped diamond layer (3), and the Schottky electrode (6) covers the alternating array of high conductivity layers (5) and the surface of the unintentionally doped diamond layer (2).

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