Vertical structure diamond field effect schottky diode and method of making same

Abstract

The application provides a vertical structure diamond field effect Schottky diode and a preparation method thereof, and belongs to the technical field of semiconductor devices, and comprises the following steps: epitaxially growing a high-doped concentration p-type diamond epitaxial layer on a diamond substrate; growing a lightly-doped p-type diamond epitaxial layer on the front surface of the high-doped concentration p-type diamond epitaxial layer, and removing the diamond substrate on the back of the high-doped concentration p-type diamond epitaxial layer; etching a cylindrical cathode region and a field effect control region on the lightly-doped p-type diamond epitaxial layer, wherein the cathode region is at the top of the cylinder; forming N-type doping on the lightly-doped p-type diamond epitaxial layer; depositing an anode metal on the back of the high-doped concentration p-type diamond epitaxial layer; forming aluminum oxide on the photoetched cathode region, depositing a cathode metal, and manufacturing a cathode electrode on the cathode metal. The Schottky diode prepared by the application reduces the forward conduction resistance, improves the reverse breakdown voltage, and thus improves the power quality factor of the device.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device fabrication technology, specifically relating to a vertical structure diamond field-effect Schottky diode and its fabrication method. Background Technology

[0002] The power electronics and microwave radio frequency fields are increasingly trending towards miniaturization, high power, and low loss, which places higher demands on power semiconductor devices. Diamond has a large bandgap, high breakdown electric field, and high thermal conductivity. Furthermore, diamond semiconductor materials also possess high electron and hole mobility. Due to its superior properties, diamond is considered a fourth-generation semiconductor material. Its figure of merit in power electronic devices is significantly superior to SiC and GaN materials, making it an ideal material for fabricating high-power, high-frequency, high-temperature, and low-power-loss semiconductor devices. Schottky diodes, with their unidirectional conductivity, play a crucial role in power systems and radio frequency applications.

[0003] Currently, the most commonly used Schottky diodes are silicon and silicon carbide diodes. Due to the difficulty in processing diamond materials, they are still in the experimental stage and cannot be fabricated on diamond substrates. Summary of the Invention

[0004] This invention provides a vertical structure diamond field-effect Schottky diode and its fabrication method, aiming to utilize diamond to fabricate diamond Schottky diodes with higher breakdown voltage and thermal conductivity, which can effectively reduce heat dissipation costs and facilitate miniaturization.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a method for fabricating a vertical structure diamond field-effect Schottky diode, the method comprising:

[0006] Step 1: Epitaxially grow a highly doped p-type diamond epitaxial layer on a diamond substrate;

[0007] Step 2: Grow one or more lightly doped p-type diamond epitaxial layers on the front side of the highly doped p-type diamond epitaxial layer, and remove the diamond substrate on the back side of the highly doped p-type diamond epitaxial layer.

[0008] Step 3: Deposit a medium as a mask sacrificial layer on the lightly doped p-type diamond epitaxial layer, etch out a window, and use dry etching technology to etch out a cylindrical cathode region and a field effect control region, wherein the cathode region is at the top of the cylinder and the sidewall of the cylinder is the field effect control region.

[0009] Step 4: In the N-type implantation region on the lightly doped p-type diamond epitaxial layer, one or more impurities of nitrogen, phosphorus, and sulfur are implanted using ion implantation technology to form N-type doping; then the mask sacrificial layer at the top of the cylinder is removed, and high-temperature annealing is used to activate the impurities.

[0010] Step 5: Anode metal is deposited on the back side of the highly doped p-type diamond epitaxial layer, and annealed to form an ohmic contact for fabricating the anode electrode;

[0011] Step 6: Deposit the field-effect region dielectric layer in the field-effect control region using atomic layer deposition (ALD) technology;

[0012] Step 7: Photolithography exposes the cathode region to form a cathode window;

[0013] Step 8: Photolithography is performed on the cathode region again, and aluminum oxide is formed in the cathode region. A metal that forms a Schottky contact with diamond is selected and the cathode metal is deposited.

[0014] Step nine: Deposit a passivation dielectric layer on the cathode metal;

[0015] Step 10: Photolithographically pattern the electrode on the passivation dielectric layer and etch it to form the cathode electrode.

[0016] In conjunction with the first aspect, in one feasible manner, in step one, the thickness of the highly doped p-type diamond epitaxial layer is between 1 nm and 1 mm.

[0017] In conjunction with the first aspect, in one feasible manner, in step two, the thickness of the lightly doped p-type diamond epitaxial layer is between 1 nm and 1 mm.

[0018] In conjunction with the first aspect, in one feasible manner, in step four, the mask sacrificial layer is wet-removed, and impurity activation is achieved by high-temperature vacuum annealing at 1380–1450°C.

[0019] In conjunction with the first aspect, in one feasible manner, in step five, the anode metal is one or more of Ti, Pt, Au, and Ir.

[0020] In conjunction with the first aspect, in one feasible manner, in step six, the field-effect region dielectric layer includes any one of alumina, HfO2, SiNx, SiO2, TiO2, MoO3, and AlN; with a thickness of 5 nm to 1 μm.

[0021] In conjunction with the first aspect, in one feasible manner, the preparation of alumina in step eight involves electron beam evaporation of a thin layer of aluminum, followed by auto-oxidation to form alumina; or, atomic layer deposition of a thin layer of alumina.

[0022] In conjunction with the first aspect, in one feasible manner, in step eight, the cathode metal is formed into a Schottky contact using one or more combinations of Al, Ni, Ti, and Au.

[0023] In conjunction with the first aspect, in one feasible manner, in step nine, the passivation dielectric layer material is one or more combinations of aluminum oxide, HfO2, SiN, SiO2, TiO2, and AlN; and the thickness is between 5 nm and 20 μm.

[0024] Secondly, embodiments of the present invention also provide a vertical structure diamond field-effect Schottky diode, which is prepared using the method described above.

[0025] The method for fabricating a vertical-structure diamond field-effect Schottky diode provided by this invention has the following advantages compared with existing technologies: Currently, only boron doping in diamond achieves a high activation rate, enabling p-type carriers; while a suitable doping source with a high activation rate for N-type doping in diamond has not yet been found. Therefore, this invention epitaxially grows a highly doped p-type diamond epitaxial layer on a diamond substrate, epitaxially grows a lightly doped p-type diamond epitaxial layer on the front side of the highly doped p-type diamond epitaxial layer, fabricates a cathode electrode on it, and fabricates an anode electrode on the back side of the highly doped p-type diamond epitaxial layer. When grounded and a negative voltage is applied to the cathode, the cathode Schottky contact becomes conductive, and the negative voltage induces hole carriers in the field-effect region, increasing the carrier concentration in the active region and reducing the on-resistance. When a positive voltage is applied to the cathode, the cathode Schottky contact becomes cut off, and the positive voltage forms a space charge region in the columnar region, reducing the carrier concentration and making the reverse electric field distribution more uniform, thus improving the flagship breakdown voltage. Furthermore, inserting a thin layer of alumina between the cathode metal and diamond can improve the device's breakdown voltage. The addition of N-type doping in the field-effect region optimizes the reverse electric field distribution, further improving the device's reverse breakdown voltage.

[0026] Therefore, the present invention provides a vertical structure diamond field-effect Schottky diode and its fabrication method, which significantly improves the breakdown voltage of the diamond Schottky diode, reduces the forward conduction resistance of the device, and thus improves the power quality factor of the device. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the intermediate product prepared in step one of the embodiments of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the intermediate product prepared in step two of this invention.

[0029] Figure 3 This is a schematic diagram of the structure of the intermediate product prepared in step three of this embodiment of the invention;

[0030] Figure 4 This is a schematic diagram of the structure of the intermediate product prepared in step four of this embodiment of the invention;

[0031] Figure 5 This is a schematic diagram of the structure of the intermediate product prepared in step six of this embodiment of the invention;

[0032] Figure 6 This is a schematic diagram of the structure of the intermediate product prepared in step eight of this embodiment of the invention;

[0033] Figure 7 This is a schematic diagram of the structure of the intermediate product prepared in step nine of this embodiment of the invention;

[0034] Figure 8 for Figure 7 A top view diagram of the intermediate product prepared in step nine;

[0035] Explanation of reference numerals in the attached figures:

[0036] 1. Diamond substrate; 2. Highly doped p-type diamond epitaxial layer; 3. Lightly doped p-type diamond epitaxial layer; 4. Mask sacrificial layer; 5. N-type implantation region; 6. Anode metal; 7. Field effect region dielectric layer; 8. Alumina; 9. Cathode metal; 10. Passivation dielectric layer. Detailed Implementation

[0037] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0038] Please refer to the following: Figures 1 to 8 The fabrication method of the vertical structure diamond field-effect Schottky diode provided by the present invention will now be described. The fabrication method of the vertical structure diamond field-effect Schottky diode includes the following steps:

[0039] Step 1: A 5μm thick, highly doped p-type diamond epitaxial layer 2 is epitaxially grown on diamond substrate 1 to reduce the anodic ohmic contact resistance. See [link to relevant documentation]. Figure 1 ;

[0040] Step 2: A 20 μm thick lightly doped p-type diamond epitaxial layer 3 is grown on the front side of the highly doped p-type diamond epitaxial layer 2, and the diamond substrate 1 on the back side of the highly doped p-type diamond epitaxial layer 2 is removed by dry etching. See [link to previous steps]. Figure 2The reason for choosing epitaxial layer fabrication is that epitaxial layers have higher quality, which can improve the breakdown voltage and stability of the device. Removing the back diamond substrate 1 can make the device thinner, which is beneficial for heat dissipation.

[0041] Step 3: Deposit a dielectric material as a mask sacrificial layer 4 on the lightly doped p-type diamond epitaxial layer 3 (see...). Figure 3 The window is etched out, and the cylindrical cathode region and field effect control region are etched out using dry etching technology. The cathode region is located at the top of the cylinder, and the side wall of the cylinder is the field effect control region.

[0042] Step four, N-type implantation region 5 on the lightly doped p-type diamond epitaxial layer 3 (see...) Figure 4 The device employs ion implantation technology to implant one or more impurities, such as nitrogen, phosphorus, and sulfur, to form an N-type doped layer. Then, the mask sacrificial layer 4 at the top of the cylinder is removed, and high-temperature annealing is used to activate the impurities. Since the electric field at the bottom of the field-effect control region is relatively large and concentrated when a reverse voltage is applied, the dielectric is subjected to a very high electric field. Adding an N-type doped region can optimize the electric field distribution, reduce the dielectric electric field, and thus improve the device breakdown voltage.

[0043] Step 5: Deposit Ti or Au as anode metal 6 on the back side of the highly doped p-type diamond epitaxial layer 2, and anneal it to form an ohmic contact for fabricating the anode electrode;

[0044] Step 6: Deposit a 100 nm thick layer of alumina 8 in the field-effect control region using atomic layer deposition (ALD) as the dielectric layer 7 of the field-effect region (see [link to ADP)). Figure 5 Atomic layer deposition (ALD) is used because it offers excellent shape preservation.

[0045] Step 7: Photolithography of the cathode region, followed by dry etching or wet etching to create the cathode window;

[0046] Step 8: Photolithography is performed on the cathode region again, and a 0.5 nm thick aluminum layer is evaporated by electron beam, which then self-oxidizes to form aluminum oxide 8 (see...). Figure 6 Ni / Au is deposited as cathode metal 9, which can form a Schottky contact with diamond and peel off to form cathode electrode and field effect region electrode; adding a layer of self-oxidizing aluminum oxide 8 between cathode metal 9 and diamond helps to reduce reverse leakage and increase breakdown voltage, but the disadvantage is that it may increase forward conduction resistance.

[0047] Step nine, deposit a passivation dielectric layer 10 on the cathode metal 9 using chemical vapor deposition (CVD) (see Figure 7 );

[0048] Step 10: Photolithographically pattern the electrode pattern on the passivation dielectric layer 10, and use dry etching or wet etching techniques to etch the cathode electrode. The electrode is then thickened to facilitate subsequent bonding and wire lead-out.

[0049] The working principle of this invention is as follows: Currently, only boron doping in diamond has a high activation rate, achieving p-type carriers; a suitable doping source with a high activation rate for N-type doping in diamond has not yet been found. In this invention, the anode is grounded. When a negative voltage is applied to the cathode, the cathode Schottky contact conducts, and the negative voltage induces hole carriers in the field-effect region, increasing the carrier concentration in the active region and reducing the on-resistance. When a positive voltage is applied to the cathode, the cathode Schottky contact is cut off, and the positive voltage forms a space charge region in the columnar region, reducing the carrier concentration and making the reverse electric field distribution more uniform, thus improving the flagship breakdown voltage. Furthermore, inserting a thin layer of alumina 8 between the cathode metal 9 and the diamond can improve the device's breakdown voltage; the addition of N-type doping in the field-effect region optimizes the reverse electric field distribution, further improving the device's reverse breakdown voltage. Therefore, the Schottky diode prepared by this invention reduces the forward on-resistance and improves the reverse breakdown voltage, thereby improving the device's power quality factor.

[0050] This invention uses a diamond substrate 1 and employs techniques such as chemical vapor deposition, dry etching, metal evaporation, dielectric deposition, ohmic contact, and Schottky contact to realize a vertical structure diamond field-effect Schottky diode. By designing different epitaxial layer thicknesses, different breakdown voltages can be achieved. Through the repetition of a large number of unit cells, the device can carry greater power.

[0051] In step one, diamond P-type doping generally employs (but is not limited to) bulk boron doping, with a high doping concentration of 1×10⁻⁶. 18 cm -3 Up to 1×10 22 cm -3 The thickness of the highly doped p-type diamond epitaxial layer 2 can be adjusted from 1 μm to 1 mm according to actual needs.

[0052] In step two, diamond P-type doping generally employs (but is not limited to) bulk boron doping, with a light doping concentration of 1×10⁻⁶. 14 cm -3 Up to 1×10 17 cm -3 The thickness of the lightly doped p-type diamond epitaxial layer 3 can be adjusted between 1nm and 1mm according to actual needs.

[0053] In step three, the mask sacrificial layer 4 can be a different medium, such as aluminum oxide 8, silicon dioxide, silicon nitride, etc.; or it can be a metal, such as nickel, titanium, gold, etc., and the etched window is prepared by a stripping process.

[0054] In step three, the cathode pattern is a cylindrical or rectangular column pattern. After etching, it forms a column. The diameter of the cylinder or the height of the rectangular column will affect the breakdown voltage and conduction current of the device.

[0055] In step four, N-type doping can also be achieved through chemical vapor phase epitaxy. Since the dielectric acts as a mask, diamond can be selectively grown, epitaxially only on the diamond surface, while no epitaxial layer is formed on the dielectric surface.

[0056] In step four, the mask sacrificial layer 4 is removed by wet process, and impurities are activated by high-temperature vacuum annealing at 1380-1450℃.

[0057] In step five, the back anode metal 6-ohm contact is prepared by using one or more of Ti, Pt, Au, Ir, etc., after high-temperature alloy annealing.

[0058] In step six, the field-effect region dielectric layer 7 includes any one of alumina, HfO2, SiNx, SiO2, TiO2, MoO3, and AlN; the thickness is 5nm to 1μm.

[0059] In step eight, the aluminum oxide 8 is prepared by electron beam evaporation of a thin layer of aluminum, which is then self-oxidized to form aluminum oxide 8; or by atomic layer deposition of a thin layer of aluminum oxide 8.

[0060] In step eight, the cathode metal 9 is formed using one or more of Al, Ni, Ti, and Au to form a Schottky contact.

[0061] In step nine, the preparation of the passivation dielectric layer 10 includes, but is not limited to, using CVD technology, and can also employ ALD technology or other thin film deposition techniques. The material is one or more combinations of alumina 8, HfO2, SiN, SiO2, TiO2, and AlN; the thickness is between 5 nm and 20 μm.

[0062] This invention uses a cylindrical unit cell as an example to explain in detail the fabrication process of a Schottky diode.

[0063] Example 1:

[0064] Step 1: Epitaxial growth of 5 μm of high-quality boron doped with a concentration of 10 on a high-quality diamond substrate 1. 21 cm -3 2. High-doped p-type diamond epitaxial layer.

[0065] Step 2: A 20 μm thick lightly doped p-type diamond epitaxial layer 3 is grown on the highly doped p-type diamond epitaxial layer 2. The dopant is boron, and the doping concentration is 10. 15 cm -3 Dry etching is used to remove the back substrate layer.

[0066] Step 3: On the lightly doped p-type diamond epitaxial layer 3, a 200nm silicon dioxide dielectric is deposited by PECVD as a mask sacrificial layer 4. A window is etched out by photolithography, and the silicon dioxide in the window is etched away by dry etching. The 5μm lightly doped p-type diamond epitaxial layer 3 is removed by dry etching, and a cylindrical cathode region and a field-effect control region are etched out. The cathode region is at the top of the column, and the sidewall of the column is the field-effect control region.

[0067] Step four: Implant a layer of nitrogen impurity using ion implantation technology to form N-type doping, with an impurity concentration of approximately 10. 14 Up to 10 20 cm -3 The mask sacrificial layer 4 was removed by wet etching, and impurities were activated by high-temperature vacuum annealing at 1400℃.

[0068] Step 5: Deposit Ti / Au as anode metal 6 in the highly doped P-type region on the back of the diamond, and anneal it in hydrogen at 600℃ to form an ohmic contact for fabricating the anode electrode.

[0069] Step six: Atomic layer deposition (ALD) is used to deposit 100 nm alumina 8 as the medium for the field-effect region.

[0070] Step 7: Photolithography of the cathode area, dry etching to create the cathode window.

[0071] Step 8: Photolithography is used to create the cathode region and field effect region windows. An electron beam evaporates a 0.5 nm thick aluminum layer, which self-oxidizes to form aluminum oxide 8. Ni / Au is deposited as the cathode metal 9, which can form a Schottky contact with diamond. The cathode electrode and field effect region electrode are then peeled off.

[0072] Step 9: Deposit 200 nm silicon nitride as a passivation dielectric layer 10 using low-pressure chemical vapor deposition.

[0073] Step 10: Photolithographically create the electrode pattern, then use dry or wet etching techniques to etch the electrode and thicken it to facilitate subsequent bonding and wire lead-out.

[0074] Example 2:

[0075] In step one, the thickness of the highly doped p-type diamond epitaxial layer 2 is 50 μm; the high doping concentration is 1 × 10⁻⁶. 18 cm -3 ;

[0076] In step two, the light doping concentration is 1×10⁻⁶. 14 cm -3 The thickness of the lightly doped p-type diamond epitaxial layer 3 is 50 μm;

[0077] In step four, the N-type doping impurity concentration is approximately 10. 14The mask sacrificial layer 4 was removed by wet etching, and impurities were activated by high-temperature vacuum annealing at 1450℃.

[0078] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0079] Based on the same inventive concept, this application also provides a vertical structure diamond field-effect Schottky diode, which is prepared using the method described above.

[0080] The vertical structure diamond field-effect Schottky diode prepared by this invention significantly improves the breakdown voltage of the diamond Schottky diode and reduces the forward conduction resistance of the device, thereby improving the power quality factor of the device.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a vertical structure diamond field effect Schottky diode, characterized in that, The method comprises: Step one, epitaxially growing a high-doped p-type diamond epitaxial layer (2) on a diamond substrate (1); Step two, growing one or more lightly-doped p-type diamond epitaxial layers (3) on the front side of the high-doped p-type diamond epitaxial layer (2), and removing the diamond substrate (1) on the back side of the high-doped p-type diamond epitaxial layer (2); Step three, depositing a dielectric as a mask sacrificial layer (4) on the lightly-doped p-type diamond epitaxial layer (3), etching a window, and using a dry etching technique to etch a cylindrical cathode region and a field effect control region, wherein the cathode region is at the top of the cylinder and the sidewall of the cylinder is the field effect control region; Step four, using ion implantation technology to implant one or more impurities of nitrogen, phosphorus, and sulfur in an N-type injection region (5) on the lightly-doped p-type diamond epitaxial layer (3) to form N-type doping, then removing the mask sacrificial layer (4) at the top of the cylinder and performing high-temperature annealing to activate the impurities; Step five, depositing an anode metal (6) on the back side of the high-doped p-type diamond epitaxial layer (2) to form an ohmic contact after annealing, which is used to prepare an anode electrode; Step six, depositing a field effect region dielectric layer (7) on the field effect control region using atomic layer deposition technology; Step seven, exposing the cathode region by photolithography to form a cathode window; Step eight, photolithographing the cathode region again and forming aluminum oxide (8) in the cathode region, depositing a cathode metal (9) by selecting a metal that forms a Schottky contact with diamond; Step nine, depositing a passivation dielectric layer (10) on the cathode metal (9); Step ten, photolithographing an electrode pattern on the passivation dielectric layer (10) and etching to form a cathode electrode.

2. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step one, the thickness of the high-doped p-type diamond epitaxial layer (2) is between 1 nm and 1 mm. ​ 3. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step two, the thickness of the lightly-doped p-type diamond epitaxial layer (3) is between 1 nm and 1 mm. ​ 4. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step four, the mask sacrificial layer (4) is removed by wet etching and impurity activation is achieved by high-temperature vacuum annealing at 1380-1450°C. ​ 5. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step five, the anode metal (6) is one or more of Ti, Pt, Au, and Ir. ​ 6. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step six, the field effect region dielectric layer (7) includes any one of aluminum oxide (8), HfO2, SiNx, SiO2, TiO2, MoO3, and AlN, and the thickness is between 5 nm and 1 μm. ​ 7. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step eight, the aluminum oxide (8) is prepared by electron beam evaporation of a thin layer of aluminum and self-oxidation to form aluminum oxide (8), or by atomic layer deposition of a thin layer of aluminum oxide (8). ​ 8. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step eight, the cathode metal (9) forms a Schottky contact using one or more combinations of Al, Ni, Ti, and Au. ​ 9. The method of claim 1, wherein the vertical structure diamond field effect Schottky diode is prepared by the steps of: In step nine, the passivation dielectric layer (10) is one or more combinations of aluminum oxide (8), HfO2, SiN, SiO2, TiO2, and AlN, and the thickness is between 5 nm and 20 μm. ​ 10. A vertical structure diamond field effect Schottky diode, characterized by, The method is prepared according to any one of claims 1-9.

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