Silicon carbide diode device and preparation method thereof

Abstract

The present invention provides a silicon carbide diode device, whose cell structure comprises: an anode metal, a p-type epitaxial layer, an n-type drift layer, an n+ substrate and a cathode metal are arranged from top to bottom, a contact groove is provided on the top of the p-type epitaxial layer, a protrusion is provided on the bottom of the anode metal, and the contact groove and the protrusion match each other. The present invention also provides a method for preparing a silicon carbide diode device, which solves the problem that in a junction barrier Schottky diode, due to the existence of a pn junction region, the effective conduction area of ​​the device is small in the conduction state, resulting in a high conduction resistance.

Description

Technical Field

[0001] The invention relates to a silicon carbide diode device and a preparation method thereof. Background Art

[0002] Silicon carbide is an emerging third-generation semiconductor material with good physical and electrical properties. It is widely used in the preparation of high-voltage, high-power and high-temperature radiation-resistant electronic devices. Silicon carbide Schottky diodes are the earliest commercialized silicon carbide semiconductor devices. Common commercialized Schottky diodes are Schottky barrier diodes and junction barrier Schottky diodes.

[0003] The traditional junction barrier Schottky diode uses the space charge region of the reverse biased PN junction to bear the reverse bias for the SBD structure, so that the Schottky barrier height can be appropriately reduced to reduce the forward voltage drop while ensuring the blocking voltage, and at the same time reduce the reverse bias leakage of the diode. However, since the ion-implanted junction area in the junction barrier Schottky diode cannot conduct electricity, the effective conduction area of ​​the device is reduced. This shortcoming limits the further improvement of the conduction current density of the JBS device. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a silicon carbide diode device and a preparation method thereof, so as to solve the problem that in a junction barrier Schottky diode, due to the presence of a pn junction region, the effective conduction area of ​​the device is small in the on state, resulting in a high on-resistance.

[0005] One of the present inventions is implemented as follows: a silicon carbide diode device, whose cellular structure includes: an anode metal, a p-type epitaxial layer, an n-type drift layer, an n+ substrate and a cathode metal are arranged from top to bottom, a contact groove is provided on the top of the p-type epitaxial layer, a protrusion is provided on the bottom of the anode metal, and the contact groove and the protrusion match each other.

[0006] Furthermore, the doping concentration range of the n-type drift layer is 2×10 14 cm -3 Up to 1×10 16 cm -3 , the thickness of the n-type drift layer is 5um to 200um.

[0007] Furthermore, the doping concentration of the p-type epitaxial layer is greater than or equal to 1×10 19 cm -3 .

[0008] Furthermore, the thickness of the p-type epitaxial layer is 0.2 um to 1 um, the width of the contact groove is 4 um to 16 um, and the distance from the bottom of the contact groove to the top of the n-type drift layer is less than or equal to 5 nm.

[0009] Furthermore, the anode metal is Ni or Ti, and the cathode metal is Ni.

[0010] Furthermore, the width of the anode metal is 14um to 46um.

[0011] The second aspect of the present invention is achieved as follows: a method for preparing a silicon carbide diode device, specifically comprising the following steps:

[0012] Growing an n-type drift layer by epitaxial growth on an n+ substrate;

[0013] growing a p-type epitaxial layer on the n-type drift layer by epitaxial growth;

[0014] forming a contact groove on the p-type epitaxial layer by etching;

[0015] Depositing metal by electron beam evaporation or magnetron sputtering and performing contact annealing to form cathode metal;

[0016] The metal is deposited by electron beam evaporation or magnetron sputtering, and the anode metal is formed by photolithography.

[0017] Furthermore, the step of forming a contact groove on the p-type epitaxial layer by etching is further specifically as follows:

[0018] On the surface of the p-type epitaxial layer, a metal Ni with a thickness of 0.3 μm is evaporated by electron beam evaporation to serve as an etching mask layer material, and the mask layer material is photolithographically opened, and the metal Ni mask layer on the contact groove required to be opened is removed by RIE etching;

[0019] Prepare a companion wafer with the same thickness as the p-type epitaxial layer, and use ICP dry etching to vertically etch the companion wafer and the p-type epitaxial layer until the etching reaches 50 nm from the top of the p-type epitaxial layer;

[0020] Use a mixture of concentrated sulfuric acid and hydrogen peroxide to remove the metal on the surface under heating conditions;

[0021] The companion wafer was observed by SEM to determine the thickness of the remaining p-type epitaxial layer, and the time required to oxidize the remaining 5nm thick p-type epitaxial layer was calculated in combination with the Deal–Grove model.

[0022] The p-type epitaxial layer is oxidized according to the calculated required time to form an oxide layer, and the oxide layer is removed using a BOE solution to finally form the contact groove.

[0023] Furthermore, the cathode metal is deposited by electron beam evaporation or magnetron sputtering and contact annealing is further specifically as follows: on one side of the n+ substrate, metal Ni is deposited by electron beam evaporation or magnetron sputtering, and contact annealing is performed under the protection of nitrogen, the annealing time is 2 minutes, and the annealing temperature is 975°C.

[0024] Furthermore, the metal is deposited by electron beam evaporation or magnetron sputtering, and the anode metal is formed by photolithography as follows: 200nm metal Ni or Ti is deposited by electron beam evaporation or magnetron sputtering, and contact annealing is performed under nitrogen protection, the annealing time is 2min, and the annealing temperature is 500°C.

[0025] The advantages of the present invention are: a silicon carbide diode device and a preparation method thereof can be applied to a wide voltage range and have good conduction characteristics and reverse recovery characteristics. The preparation process of the structure is compatible with conventional silicon carbide diode devices, because under the condition of the same device area, it has a larger current conduction area;

[0026] In addition, based on the conventional SBD device, the present invention introduces a highly doped p-type anode region, so that when the device is forward-conducted, carriers can pass through the p-type region by tunneling effect; in the reverse blocking state, the epitaxial pn junction is subjected to reverse bias. Compared with SBD and JBS devices that use Schottky junctions to withstand reverse bias, this diode uses pn junctions to withstand reverse bias voltage, which can reduce leakage current in the blocking state. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0028] Figure 1 Schematic diagram of the cell structure of a silicon carbide diode device according to an embodiment of the present invention.

[0029] Figure 2 The figure is a flowchart of the steps of an embodiment of the present invention.

[0030] Figure 3 A schematic diagram of forming a contact groove in a method for manufacturing a silicon carbide diode device provided in an embodiment of the present invention Figure 1 .

[0031] Figure 4 A schematic diagram of forming a contact groove in a method for manufacturing a silicon carbide diode device provided in an embodiment of the present invention Figure 2 .

[0032] Figure 5 A schematic diagram of forming a contact groove in a method for manufacturing a silicon carbide diode device provided in an embodiment of the present invention Figure 3 .

[0033] Figure 6 A schematic diagram of forming a contact groove in a method for manufacturing a silicon carbide diode device provided in an embodiment of the present invention Figure 4 .

[0034] Figure 7 A flow chart of the steps of forming a contact groove in a method for manufacturing a silicon carbide diode device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0035] See also Figure 1 As shown, the silicon carbide diode device of the present invention is formed by connecting a plurality of cellular structures in parallel, and the cellular structure includes: an anode metal 4, a p-type epitaxial layer 3, an n-type drift layer 2, an n+ substrate 1 and a cathode metal 5 are arranged from top to bottom, a contact groove is provided on the top of the p-type epitaxial layer 3, a protrusion is provided on the bottom of the anode metal 4, the contact groove and the protrusion match each other, and the doping concentration range of the n-type drift layer 2 is 2×10 14 cm -3 Up to 1×10 16 cm -3 The thickness of the n-type drift layer 2 is 5 um to 200 um, and the doping concentration of the p-type epitaxial layer 3 is greater than or equal to 1×10 19 cm -3 , the thickness of the p-type epitaxial layer 3 is 0.2um to 1um, the width of the contact groove is 4um to 16um, the distance from the bottom of the contact groove to the top of the n-type drift layer 2 is less than or equal to 5nm, the anode metal 4 is Ni or Ti, the cathode metal 5 is Ni, and the width of the anode metal 4 is 14um to 46um; by changing the thickness of the p-type epitaxial layer 3, the doping concentration and the width and depth of the central contact groove, it is possible to make a preference between on-resistance and blocking leakage.

[0036] The anode metal 4 is Ni / Ti, the purpose is to form an anode contact, fill the contact groove and form a field plate structure, the length of the field plate is 5um to 15um, the purpose is to reduce the electric field concentration at the edge of the device cell. The cathode metal 5 is Ni, the purpose is to form a cathode ohmic contact.

[0037] like Figure 2 As shown, the method for preparing the silicon carbide diode device of the present invention specifically comprises the following steps:

[0038] An n-type drift layer 2 is grown on an n+ substrate 1 by epitaxial growth;

[0039] Growing a p-type epitaxial layer 3 on the n-type drift layer 2 by epitaxial growth;

[0040] forming a contact groove on the p-type epitaxial layer 3 by etching;

[0041] Depositing metal by electron beam evaporation or magnetron sputtering and performing contact annealing to form cathode metal 5;

[0042] The metal is deposited by electron beam evaporation or magnetron sputtering, and the anode metal 4 is formed by photolithography.

[0043] The step of forming the contact groove on the p-type epitaxial layer 3 by etching is further specifically as follows:

[0044] On the surface of the p-type epitaxial layer, a metal Ni with a thickness of 0.3 μm is evaporated by electron beam evaporation to serve as an etching mask layer material, and the mask layer material is photolithographically opened, and the metal Ni mask layer on the contact groove required to be opened is removed by RIE etching;

[0045] Prepare a companion wafer with the same thickness as the p-type epitaxial layer, and use ICP dry etching to vertically etch the companion wafer and the p-type epitaxial layer until the etching reaches 50 nm from the top of the p-type epitaxial layer;

[0046] Use a mixture of concentrated sulfuric acid and hydrogen peroxide to remove the metal on the surface under heating conditions;

[0047] The companion wafer was observed by SEM to determine the thickness of the remaining p-type epitaxial layer, and the time required to oxidize the remaining 5nm thick p-type epitaxial layer was calculated in combination with the Deal–Grove model.

[0048] The p-type epitaxial layer is oxidized according to the calculated required time to form an oxide layer, and the oxide layer is removed using a BOE solution to finally form the contact groove.

[0049] The cathode metal 5 is deposited by electron beam evaporation or magnetron sputtering and contact annealing is further specified as follows: on one side of the n+ substrate 1, metal Ni is deposited by electron beam evaporation or magnetron sputtering, and contact annealing is performed under the protection of nitrogen. The annealing time is 2 minutes and the annealing temperature is 975°C. The thickness of the deposited metal can be controlled according to user needs.

[0050] The method of depositing metal by electron beam evaporation or magnetron sputtering and forming anode metal 4 by photolithography is further specified as follows: 200nm metal Ni or Ti is deposited by electron beam evaporation or magnetron sputtering, and contact annealing is performed under nitrogen protection. The annealing time is 2min and the annealing temperature is 500°C. The thickness of the deposited metal can be controlled according to user needs.

[0051] Embodiment 1 of the present invention

[0052] The method for preparing a silicon carbide diode device of the present invention comprises:

[0053] S1, epitaxially growing an n-type drift layer 2 on an n+ substrate 1;

[0054] S2, growing a highly doped p-type epitaxial layer 3 on the n-type drift layer 2 by epitaxial growth;

[0055] S3, forming a contact groove on the p-type epitaxial layer 3 by etching;

[0056] S4, on the back side of the device, deposit cathode metal 5 by electron beam evaporation or magnetron sputtering, and perform contact annealing;

[0057] S5. On the front side of the device, deposit anode metal 4 by electron beam evaporation or magnetron sputtering, and form a field plate pattern by photolithography.

[0058] In step S3, a contact groove needs to be formed by etching, and the bottom of the contact groove is less than 5 nm away from the top of the n-type drift layer 2. The present invention provides a feasible method under existing process conditions.

[0059] like Figures 3 to 7 As shown, first, a metal Ni with a thickness of 0.3um is evaporated on the surface of the wafer by electron beam evaporation as an etching mask layer material, and the mask layer material is photolithographically opened, and the metal Ni mask layer above the contact groove is removed by RIE etching. Then, a SiC companion wafer with the same epitaxial structure is prepared, and the main wafer (the main wafer is the p-type epitaxial layer made by the present invention) and the companion wafer (that is, SiC with the same structure and thickness as the p-type epitaxial layer, used for process verification) are vertically etched by ICP dry etching, and the etching is stopped after being about 50nm away from the top of the p-type epitaxial layer 3. Then, a concentrated sulfuric acid and hydrogen peroxide mixture is used to remove the metal on the surface under heating conditions. Then, the etched companion wafer is observed by SEM to determine the thickness of the remaining p-type epitaxial layer 3, and the time required to oxidize the remaining 5nm p-type epitaxial layer 3 is calculated in combination with the Deal-Grove model. Finally, the main chip is oxidized according to the calculation conditions to form a SiO2 oxide layer 6, and the SiO2 oxide layer 6 is removed using a BOE solution, thereby finally forming the contact groove.

[0060] The step S4 uses metal Ni as the cathode ohmic contact material, and the process includes: flipping the wafer, depositing 200nm of metal Ni on the back side of (1) n+ substrate 1 by electron beam evaporation, and performing contact annealing for 2 minutes under the protection of N2 gas, with the annealing temperature at 975°C.

[0061] The step S5 requires the use of anode metal 4Ti / Ni to fill the contact groove, including: on the back of the wafer, spread the glue and harden the film to protect the ohmic contact formed on the back. Then flip the wafer and deposit metal Ti / Ni by electron beam evaporation. After spread glue, photolithography, development and hardening, the metal is etched to form a field plate structure. Then, under the protection of N2 gas, Schottky contact annealing is performed for 2 minutes at an annealing temperature of 500°C.

[0062] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A silicon carbide diode device, characterized in that: The cell structure includes: an anode metal, a p-type epitaxial layer, an n-type drift layer, an n+ substrate and a cathode metal are arranged from top to bottom, a contact groove is provided on the top of the p-type epitaxial layer, a protrusion is provided on the bottom of the anode metal, and the contact groove and the protrusion match each other; the doping concentration range of the n-type drift layer is 2×10 14 cm -3 Up to 1×10 16 cm -3 The thickness of the n-type drift layer is 5um to 200um; the doping concentration of the p-type epitaxial layer is greater than or equal to 1×10 19 cm -3 ; The thickness of the p-type epitaxial layer is 0.2um to 1um, the width of the contact groove is 4um to 16um, and the distance from the bottom of the contact groove to the top of the n-type drift layer is less than or equal to 5nm.

2. A silicon carbide diode device according to claim 1, characterized in that: The anode metal is Ni or Ti, and the cathode metal is Ni.

3. A silicon carbide diode device according to claim 1, characterized in that: The width of the anode metal is 14um to 46um.

4. A method for preparing a silicon carbide diode device, characterized in that: The specific steps include: Growing an n-type drift layer by epitaxial growth on an n+ substrate; growing a p-type epitaxial layer on the n-type drift layer by epitaxial growth; forming a contact groove on the p-type epitaxial layer by etching; Depositing metal by electron beam evaporation or magnetron sputtering and performing contact annealing to form cathode metal; Deposit metal by electron beam evaporation or magnetron sputtering, and form anode metal by photolithography; The doping concentration of the n-type drift layer is in the range of 2×10 14 cm -3 Up to 1×10 16 cm -3 The thickness of the n-type drift layer is 5um to 200um; the doping concentration of the p-type epitaxial layer is greater than or equal to 1×10 19 cm -3 ; The thickness of the p-type epitaxial layer is 0.2um to 1um, the width of the contact groove is 4um to 16um, and the distance from the bottom of the contact groove to the top of the n-type drift layer is less than or equal to 5nm.

5. The method for preparing a silicon carbide diode device according to claim 4, characterized in that: The step of forming a contact groove on the p-type epitaxial layer by etching is further specifically as follows: On the surface of the p-type epitaxial layer, a metal Ni with a thickness of 0.3 μm is evaporated by electron beam evaporation to serve as an etching mask layer material, the mask layer material is photolithographically opened, and the metal Ni mask layer on the contact groove required to be opened is removed by RIE etching; Prepare a companion wafer with the same thickness as the p-type epitaxial layer, and use ICP dry etching to vertically etch the companion wafer and the p-type epitaxial layer until the etching reaches 50 nm from the top of the p-type epitaxial layer; Use a mixture of concentrated sulfuric acid and hydrogen peroxide to remove the metal on the surface under heating conditions; The companion wafer was observed by SEM to determine the thickness of the remaining p-type epitaxial layer, and the time required to oxidize the remaining 5nm thick p-type epitaxial layer was calculated in combination with the Deal–Grove model. The p-type epitaxial layer is oxidized according to the calculated required time to form an oxide layer, and the oxide layer is removed using a BOE solution to finally form the contact groove.

6. The method for preparing a silicon carbide diode device according to claim 4, characterized in that: The cathode metal is deposited by electron beam evaporation or magnetron sputtering and contact annealing is further specifically as follows: metal Ni is deposited on one side of the n+ substrate by electron beam evaporation or magnetron sputtering, and contact annealing is performed under the protection of nitrogen, the annealing time is 2 minutes, and the annealing temperature is 975°C.

7. The method for preparing a silicon carbide diode device according to claim 4, characterized in that: The method of depositing metal by electron beam evaporation or magnetron sputtering and forming anode metal by photolithography is further specifically as follows: 200nm metal Ni or Ti is deposited by electron beam evaporation or magnetron sputtering, and contact annealing is performed under nitrogen protection, the annealing time is 2min, and the annealing temperature is 500°C.

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