A terminal structure of a silicon carbide MOSFET power device

Abstract

The present invention belongs to the technical field of silicon carbide MOSFET power devices, and specifically relates to a terminal structure of a silicon carbide MOSFET power device. The surface of the N-type silicon carbide epitaxial layer located in the field limiting ring region is an inclined surface structure, and the inclination angle of the inclined surface structure with respect to the horizontal plane is 2° to 6°. A plurality of field limiting rings are formed on the surface of the inclined surface structure by ion implantation. The terminal structure of the present invention can enable the depletion regions in the cell region, the junction termination extension region, and the field limiting ring region to better extend to the field limiting ring at the back end, extend the depletion region in the field limiting ring region, make the electric field distribution in the cell region, the junction termination extension region, and the field limiting ring region more uniform, relieve the phenomenon of electric field concentration, improve the breakdown voltage of the silicon carbide MOSFET power device, and reduce the amplitude of the breakdown voltage reduction caused by the increase in the interface fixed charge density, further improving the reliability of the device.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon carbide MOSFET power devices, and particularly relates to a terminal structure of a silicon carbide MOSFET power device. Background Art

[0002] Silicon carbide is a new generation of wide-bandgap semiconductor material. Silicon carbide MOSFET power devices do not have the minority carrier storage effect, have a fast device switching speed and small switching losses, and are widely used in the field of power electronics.

[0003] Traditional silicon carbide MOSFET power devices include an N-type silicon carbide substrate. A drain metal is formed on the bottom surface of the N-type silicon carbide substrate. An N-type silicon carbide epitaxial layer is grown on the surface of the N-type silicon carbide substrate. A P-type well region is formed on the surface of the N-type silicon carbide epitaxial layer. An N+ region and a first P+ region are formed inside the P-type well region. The N+ region and the first P+ region are adjacent. The above structure constitutes the PN junction of the active region, which belongs to the cell region of the silicon carbide MOSFET power device. Since there is often curvature at the edge of the PN junction in the active region, the electric field is concentrated in the region with a higher curvature, resulting in the breakdown voltage of the silicon carbide MOSFET power device being lower than the expected value.

[0004] In order to alleviate the electric field concentration effect at the junction edge and avoid premature breakdown, when designing a silicon carbide MOSFET power device, a terminal protection structure needs to be designed. This type of technology is usually referred to as the junction termination technology. The main terminal structures of traditional silicon carbide MOSFET power devices are field plates, junction termination extensions, and field limit rings, and these three structures are often combined and used in silicon carbide MOSFET power devices. Specifically, the terminal structure of a traditional silicon carbide MOSFET power device includes: a junction termination extension is formed on the surface of the N-type silicon carbide epitaxial layer. A second P+ region is also formed on the junction termination extension. The junction termination extension is located outside the P-type well region. A plurality of field limit rings are formed on the surface of the N-type silicon carbide epitaxial layer. The field limit rings are located outside the junction termination extension. The region where the junction termination extension is located is the junction termination extension region of the terminal structure, and the region where the field limit rings are located is the field limit ring region of the terminal structure. A gate oxide layer is formed on the surface of the N-type silicon carbide epitaxial layer at the junction of the cell region and the junction termination extension region. One side of the gate oxide layer is in contact with the P-type well region, and the other side is in contact with the junction termination extension. A polysilicon gate is deposited on the gate oxide layer. A silicon dioxide oxide layer is grown on the surface of the polysilicon gate, the surface of the N-type silicon carbide epitaxial layer containing the junction termination extension, and the surface of the N-type silicon carbide epitaxial layer containing the field limit rings. A source metal is deposited on the silicon dioxide oxide layer. A part of the source metal is located in the cell region, and the other part is located in the junction termination extension region. The part of the source metal located in the cell region is in contact with the N+ region and the first P+ region, and the part of the source metal located in the junction termination extension region is in contact with the second P+ region. The part of the source metal located in the junction termination extension region acts as a field plate.

[0005] In the above terminal structure, when the interface fixed charge density between the N-type silicon carbide epitaxial layer and the silicon dioxide oxide layer above it increases, the depletion region in the field limiting ring region is significantly shortened, resulting in a substantial reduction in the breakdown voltage of the device. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a terminal structure for a silicon carbide MOSFET power device. Compared with the traditional terminal structure of a silicon carbide MOSFET power device, the N-type silicon carbide epitaxial layer in the field limiting ring region is a bevel structure, the inclination angle of the bevel structure with respect to the horizontal plane is 2° to 6°, and a plurality of field limiting rings are formed on the bevel structure by ion implantation.

[0007] The present invention is specifically implemented through the following solutions.

[0008] A terminal structure for a silicon carbide MOSFET power device, the terminal structure includes a junction termination extension region and a field limiting ring region. The junction termination extension region is located outside the cell region of the silicon carbide MOSFET power device, and the field limiting ring region is located outside the junction termination extension region. A part of the N-type silicon carbide epitaxial layer is contained in the field limiting ring region. The surface of the N-type silicon carbide epitaxial layer in the field limiting ring region is a bevel structure, the inclination angle of the bevel structure with respect to the horizontal plane is 2° to 6°, and a plurality of field limiting rings are formed on the surface of the bevel structure by ion implantation.

[0009] Compared with the traditional terminal structure of a silicon carbide MOSFET power device, the present invention sets the N-type silicon carbide epitaxial layer in the field limiting ring region as a bevel structure, which can better expand the depletion regions of the cell region, the junction termination extension region, and the field limiting ring region to the field limiting rings at the back end, extend the depletion region of the field limiting ring region, make the electric field distribution in the cell region, the junction termination extension region, and the field limiting ring region more uniform, reduce the curvature of the depletion regions of the cell region, the junction termination extension region, and the field limiting ring region, and relieve the phenomenon of electric field concentration.

[0010] In a preferred embodiment of the present invention, before the bevel structure is formed, the thickness of the N-type silicon carbide epitaxial layer in both the junction termination extension region and the field limiting ring region is 10 μm, and the doping concentration is 1×10 16 cm −3 .

[0011] In a preferred embodiment of the present invention, the inclined plane structure is obtained by a dry etching process or a V-shaped cutting process. In the inclined plane structure, the etching depth at the end far from the junction termination extension region is 3.5 μm to 10 μm. It should be noted that the etching depth here corresponds to different inclination angles. The larger the inclination angle, the greater the etching depth at the end of the inclined plane structure far from the junction termination extension region. For example, when the inclination angle is 2°, the etching depth at the end of the inclined plane structure far from the junction termination extension region is 3.5 μm; when the inclination angle is 4°, the etching depth at the end of the inclined plane structure far from the junction termination extension region is 7 μm; when the inclination angle is 6°, the etching depth at the end of the inclined plane structure far from the junction termination extension region is 10 μm.

[0012] In a preferred embodiment of the present invention, the number of field limiting rings is 15 to 25, the ring width of each field limiting ring is 2 μm to 3 μm, and the ring spacing between two adjacent field limiting rings is 0.5 μm to 2.5 μm. Preferably, the number of field limiting rings is 20, the ring width of each field limiting ring is 2.5 μm, and the ring spacing between two adjacent field limiting rings is 1 μm.

[0013] In a preferred embodiment of the present invention, a part of the N-type silicon carbide epitaxial layer is included in the junction termination extension region, and a junction termination extension is formed on the surface of the N-type silicon carbide epitaxial layer in the junction termination extension region. The junction termination extension and several field limiting rings are formed simultaneously by 2 to 3 ion implantations. Each time of ion implantation, ion implantation is carried out on the junction termination extension and several field limiting rings simultaneously. The implanted element is aluminum, the implantation energy each time is 100 keV to 800 keV, and the implantation dose each time is 2×10 13 cm −2 。

[0014] In a preferred embodiment of the present invention, the length of the junction termination extension is 10 μm to 30 μm, preferably 20 μm.

[0015] In a preferred embodiment of the present invention, a second P+ region is formed on the surface of the junction termination extension. The second P+ region and the first P+ region located in the cell region are formed simultaneously by 3 to 4 ion implantations. Each time of ion implantation, ion implantation is carried out on the second P+ region and the first P+ region simultaneously. The implanted element is aluminum, the implantation energy each time is 100 keV to 200 keV, and the implantation dose each time is 1×10 14 cm −2 ~3×10 14 cm −2 。

[0016] In a preferred embodiment of the present invention, a gate oxide layer is formed on the surface of the N-type silicon carbide epitaxial layer at the junction of the cell region and the junction termination extension region. One side of the gate oxide layer is in contact with the P-type well region in the cell region, and the other side is in contact with the junction termination extension. A polysilicon gate is deposited on the gate oxide layer.

[0017] In a preferred embodiment of the present invention, a silicon dioxide oxide layer is grown on the surface of the polysilicon gate, the surface of the N-type silicon carbide epitaxial layer containing a junction termination extension, and the surface of the N-type silicon carbide epitaxial layer containing a field limiting ring. A source metal is deposited on the silicon dioxide oxide layer. A part of the source metal is in contact with the N+ region and the first P+ region in the cell region, and another part is located in the junction termination extension region and is in contact with the second P+ region. The part of the source metal located in the junction termination extension region acts as a field plate.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a terminal structure of a silicon carbide MOSFET power device. In this terminal structure, the N-type silicon carbide epitaxial layer in the field limiting ring region is a bevel structure, and the inclination angle of the bevel structure with respect to the horizontal plane is 2° to 6°. A plurality of field limiting rings are formed on the bevel structure. The bevel structure can enable the depletion regions in the cell region, the junction termination extension region, and the field limiting ring region to better extend to the field limiting ring at the back end, extend the depletion region in the field limiting ring region, make the electric field distribution in the cell region, the junction termination extension region, and the field limiting ring region more uniform, reduce the curvature of the depletion regions in the cell region, the junction termination extension region, and the field limiting ring region, alleviate the phenomenon of electric field concentration, improve the breakdown voltage of the silicon carbide MOSFET power device, reduce the amplitude of the breakdown voltage reduction caused by the increase in the interface fixed charge density, and further improve the reliability of the device. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of a silicon carbide MOSFET power device with a conventional terminal structure.

[0021] Figure 2 It is a schematic structural diagram of a silicon carbide MOSFET power device with the terminal structure of the present invention.

[0022] Figure 3 It is a comparative curve graph of the breakdown voltages of silicon carbide MOSFET power devices with different inclination angles.

[0023] Figure 4 It is a curve graph of the breakdown voltages of a silicon carbide MOSFET power device with an inclination angle of 6° and a conventional silicon carbide MOSFET power device varying with the interface fixed charge density.

[0024] Description of the Reference Numerals:

[0025] 1. Drain metal, 2. N-type silicon carbide substrate, 3. N-type silicon carbide epitaxial layer, 4. Silicon dioxide oxide layer, 5. Source metal, 6. Polysilicon gate, 7. N+ region, 8. First P+ region, 9. P-type well region, 10. Junction termination extension, 11. Field limiting ring, 12. Second P+ region, C1. Cell region, C2. Junction termination extension region, C3. Field limiting ring region. Detailed implementation manners

[0026] In order to enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings. However, the specific embodiments cited do not limit the present invention.

[0027] The traditional terminal structure of a silicon carbide MOSFET power device, such as Figure 1 shown, includes a junction termination extension region C2 and a field limiting ring region C3. The junction termination extension region C2 is located outside the cell region C1 of the silicon carbide MOSFET power device. The field limiting ring region C3 is located outside the junction termination extension region C2. The source metal 5 located in a part of the junction termination extension region C2 acts as a field plate. Among them, a part of the N-type silicon carbide epitaxial layer 3 is included in the field limiting ring region C3, and the N-type silicon carbide epitaxial layer 3 located in the field limiting ring region C3 is a planar structure.

[0028] The present invention provides a terminal structure of a silicon carbide MOSFET power device, such as Figure 2 shown. The terminal structure includes a junction termination extension region C2 and a field limiting ring region C3. The junction termination extension region C2 is located outside the cell region C1 of the silicon carbide MOSFET power device. The field limiting ring region C3 is located outside the junction termination extension region C2. A part of the N-type silicon carbide epitaxial layer 3 is included in the field limiting ring region C3. The surface of the N-type silicon carbide epitaxial layer 3 located in the field limiting ring region C3 is an inclined plane structure, and the inclination angle of the inclined plane structure with respect to the horizontal plane is 2° - 6°. A plurality of field limiting rings 11 are formed on the surface of the inclined plane structure by ion implantation.

[0029] Compared with Figure 1 the traditional terminal structure in, the present invention improves the field limiting ring region C3. The N-type silicon carbide epitaxial layer 3 in the field limiting ring region C3 is an inclined plane structure, which can enable the depletion regions of the cell region C1, the junction termination extension region C2, and the field limiting ring region C3 to better extend to the field limiting rings 11 at the back end, making the electric field intensity distribution more uniform and alleviating the phenomenon of electric field concentration.

[0030] The inclined plane structure of the present invention is obtained by a dry etching process or a V-shaped cutting process. In the inclined plane structure, the etching depth at one end away from the junction termination extension region C2 is 3.5 μm to 10 μm. The number of field limit rings 11 is 15 to 25, the ring width of each field limit ring 11 is 2 μm to 3 μm, and the ring spacing between two adjacent field limit rings 11 is 0.5 μm to 2.5 μm.

[0031] The junction termination extension region C2 of the present invention is arranged as follows: A junction termination extension 10 is formed on the surface of the N-type silicon carbide epitaxial layer 3 in the junction termination extension region C2. The junction termination extension 10 and several field limit rings 11 are formed simultaneously by 2 to 3 ion implantations. Each time of ion implantation, the junction termination extension 10 and several field limit rings 11 are ion implanted simultaneously. The implanted element is aluminum, the implantation energy each time is 100 keV to 800 keV, and the implantation dose each time is 2×10 13 cm −2 . The length of the junction termination extension 10 is 10 μm to 30 μm. A second P+ region 12 is formed on the surface of the junction termination extension 10. The second P+ region 12 and the first P+ region 8 located in the cell region C1 are formed simultaneously by 3 to 4 ion implantations. Each time of ion implantation, the second P+ region 12 and the first P+ region 8 are ion implanted simultaneously. The implanted element is aluminum, the implantation energy each time is 100 keV to 200 keV, and the implantation dose each time is 1×10 14 cm −2 ~3×10 14 cm −2 .

[0032] The terminal structure of the silicon carbide MOSFET power device provided by the present invention further includes a field plate structure, specifically, the part of the source metal 5 located in the junction termination extension region C2 serves as the field plate. A gate oxide layer is formed on the surface of the N-type silicon carbide epitaxial layer 3 at the junction of the cell region C1 and the junction termination extension region C2. One side of the gate oxide layer is in contact with the P-type well region 9 in the cell region C1, and the other side is in contact with the junction termination extension 10. A polysilicon gate 6 is deposited on the gate oxide layer. A silicon dioxide oxide layer 4 is grown on the surface of the polysilicon gate 6, on the surface of the N-type silicon carbide epitaxial layer 3 containing the junction termination extension 10, and on the surface of the N-type silicon carbide epitaxial layer 3 containing the field limit rings 11. A source metal 5 is deposited on the silicon dioxide oxide layer 4. A part of the source metal 5 is in contact with the N+ region 7 and the first P+ region 8 in the cell region C1, and the other part is located in the junction termination extension region C2 and is in contact with the second P+ region 12.

[0033] The content of the present invention will be specifically described below through the following examples and comparative examples. In the following examples and comparative examples, the N-type silicon carbide substrate is specifically a 4H-silicon carbide substrate, and the N-type silicon carbide epitaxial layer is specifically a 4H-silicon carbide epitaxial layer.

[0034] Example 1

[0035] Example 1 provides a terminal structure of a silicon carbide MOSFET power device. The terminal structure includes a junction termination extension region C2 and a field limiting ring region C3. A part of the N-type silicon carbide epitaxial layer 3 is contained in the field limiting ring region C3. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 . The surface of the N-type silicon carbide epitaxial layer 3 located in the field limiting ring region C3 is an inclined plane structure. The inclination angle of the inclined plane structure with the horizontal plane is 2°. The inclined plane structure is obtained by a dry etching process, and the etching depth at the end far from the junction termination extension region C2 is 3.5 μm. 20 field limiting rings 11 are formed on the surface of the inclined plane structure by ion implantation. The ring width of each field limiting ring 11 is 2.5 μm, and the ring spacing between two adjacent field limiting rings 11 is 1 μm.

[0036] The terminal structure of Example 1 is used in a silicon carbide MOSFET power device. The overall structure is as shown in Figure 2 and the manufacturing method includes the following steps:

[0037] (1) Provide a substrate containing a drain metal 1, an N-type silicon carbide substrate 2, and an N-type silicon carbide epitaxial layer 3. Clean the N-type silicon carbide epitaxial layer 3 and mark the etching position. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 .

[0038] (2) Inject aluminum ions on the surface of the N-type silicon carbide epitaxial layer 3. The number of injection times is 3 times. The injection energies are 100 KeV, 500 KeV, and 800 KeV respectively each time, and the injection doses are 5×10 11 cm −2 , 1×10 12 cm −2 and 2×10 13 cm −2 respectively each time to form a P-type well region 9.

[0039] (3) Perform nitrogen ion implantation. The number of injection times is 3 times. The injection energies are 60 KeV, 100 KeV, and 120 KeV respectively each time, and the injection doses are 1.5×10 15 cm −2 , 2×10 15 cm −2 and 1.5×10 15 cm −2 respectively each time to form an N+ region 7 inside the P-type well region 9.

[0040] (4) Etch the N-type silicon carbide epitaxial layer 3 in the field limiting ring region C3 to form an inclined surface structure with an etching angle of 2°, and the etching depth at one end far from the junction termination extension region C2 is 3.5 μm.

[0041] (5) Perform aluminum ion implantation on the surface of the N-type silicon carbide epitaxial layer 3 in the junction termination extension region C2 and the surface of the inclined surface structure simultaneously. The number of implantations is 3 times, and the implantation energies are 100 keV, 400 keV, and 800 keV respectively for each implantation. The implantation dose for each time is 2×10 13 cm −2 -², simultaneously forming junction terminations 10 and 20 field limiting rings 11. The ring width of each field limiting ring 11 is 2.5 μm, the ring spacing between two adjacent field limiting rings 11 is 1 μm, and the length of the junction termination 10 is 20 μm.

[0042] (6) Perform aluminum ion implantation on the inner side of the N+ region 7 and the surface of the junction termination 10 simultaneously. The number of implantations is 3 times, and the implantation energies are 100 keV, 150 keV, and 200 keV respectively. The implantation doses for each time are 1×10 14 cm −2 -², 3×10 14 cm −2 -², and 3×10 14 cm −2 -², forming a first P+ region 8 and a second P+ region 12.

[0043] (7) Anneal the structure prepared in step (6) at a high temperature to activate the implanted ions. The temperature is 1650 °C, and the annealing time is 10 min.

[0044] (8) Dry-oxidize the structure prepared in step (7) at 1200 °C for 2 hours, and then wet-oxidize it at 900 °C for 1 hour to form a gate oxide layer on the surface of the N-type silicon carbide epitaxial layer 3 at the junction of the cell region C1 and the junction termination extension region C2.

[0045] (9) Use low-pressure chemical vapor deposition process to deposit a polysilicon gate 6 with a thickness of 450 nm on the gate oxide layer formed in step (8). The temperature is 600 °C, and the growth time is 2 hours.

[0046] (10) Use plasma-enhanced chemical vapor deposition process to deposit a silicon dioxide oxide layer 4 with a thickness of 1.2 μm on the structure prepared in step (9). The temperature is 400 °C, the RF power is 1000 W, and the growth time is 12 min.

[0047] (11) Etch the silicon dioxide oxide layer 4 above the N+ region 7, the first P+ region 8, and the second P+ region 12 respectively. Deposit the source metal 5 on the silicon dioxide oxide layer 4. A part of the source metal 5 is in contact with the N+ region 7 and the first P+ region 8, and the other part is located in the junction termination extension region C2 and is in contact with the second P+ region 12. Make the source metal 5 have an ohmic contact with the drain metal 1. Both the source metal 5 and the drain metal 1 are nickel. After metallization, a silicon carbide MOSFET power device with the terminal structure of Embodiment 1 is obtained.

[0048] Embodiment 2

[0049] Embodiment 2 provides a terminal structure of a silicon carbide MOSFET power device. The terminal structure includes a junction termination extension region C2 and a field limiting ring region C3. A part of the N-type silicon carbide epitaxial layer 3 is contained in the field limiting ring region C3. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 . The surface of the N-type silicon carbide epitaxial layer 3 located in the field limiting ring region C3 is an inclined plane structure. The inclination angle of the inclined plane structure with respect to the horizontal plane is 4°. The inclined plane structure is obtained by a dry etching process, and the etching depth at the end far from the junction termination extension region C2 is 7 μm. 20 field limiting rings 11 are formed on the surface of the inclined plane structure by ion implantation. The ring width of each field limiting ring 11 is 2.5 μm, and the ring spacing between two adjacent field limiting rings 11 is 1 μm.

[0050] Apply the terminal structure of Embodiment 2 to a silicon carbide MOSFET power device. The preparation method of the overall structure includes the following steps:

[0051] (1) Provide a substrate containing a drain metal 1, an N-type silicon carbide substrate 2, and an N-type silicon carbide epitaxial layer 3. Clean the N-type silicon carbide epitaxial layer 3 and mark the etching position. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 .

[0052] (2) Inject aluminum ions on the surface of the N-type silicon carbide epitaxial layer 3. The number of injection times is 3 times. The injection energies are 100 KeV, 500 KeV, and 800 KeV respectively each time, and the injection doses are 5×10 11 cm −2 , 1×10 12 cm −2 and 2×10 13 cm −2 respectively to form a P-type well region 9.

[0053] (3) Perform nitrogen ion implantation. The number of injection times is 3 times. The injection energies are 60 KeV, 100 KeV, and 120 KeV respectively each time, and the injection doses are 1.5×1015 cm −2 , 2×10 15 cm −2 and 1.5×10 15 cm −2 , an N+ region 7 is formed inside the P-type well region 9.

[0054] (4) The N-type silicon carbide epitaxial layer 3 in the field limiting ring region C3 is etched to form a slope structure. The etching angle is 4°, and the etching depth at the end away from the junction terminal extension region C2 is 7 μm.

[0055] (5) Aluminum ion implantation was performed simultaneously on the surface of the N-type silicon carbide epitaxial layer 3 and the surface of the bevel structure in the junction terminal extension region C2. The number of implantations was 3 times, and the energy of each implantation was 100 KeV, 400 KeV, and 800 KeV, respectively. The dose of each implantation was 2×10 13 cm −2 , and a junction terminal extension 10 and 20 field limiting rings 11 are formed at the same time. The width of each field limiting ring 11 is 2.5 μm, the ring spacing between two adjacent field limiting rings 11 is 1 μm, and the length of the junction terminal extension 10 is 20 μm.

[0056] (6) Aluminum ion implantation is performed simultaneously on the inner side of the N+ region 7 and the surface of the junction terminal extension 10. The number of implantations is 3, and the implantation energies are 100 KeV, 150 KeV, and 200 KeV, respectively. The dose of each implantation is 1×10 14 cm −2 , 3×10 14 cm −2 and 3×10 14 cm −2 , forming a first P+ region 8 and a second P+ region 12.

[0057] (7) The structure prepared in step (6) is subjected to high temperature annealing to activate the implanted ions; the temperature is 1650° C. and the annealing time is 10 min.

[0058] (8) The structure prepared in step (7) is subjected to dry oxygen oxidation at 1200° C. for 2 hours and then to wet oxygen oxidation at 900° C. for 1 hour to form a gate oxide layer on the surface of the N-type silicon carbide epitaxial layer 3 at the junction of the cell region C1 and the junction terminal extension region C2.

[0059] (9) Using a low pressure chemical vapor deposition process, a polysilicon gate 6 with a thickness of 450 nm is deposited on the gate oxide layer formed in step (8) at a temperature of 600° C. and a growth time of 2 hours.

[0060] (10) Using the plasma enhanced chemical vapor deposition process, deposit a 1.2 μm thick silicon dioxide oxide layer 4 on the structure prepared in step (9) at a temperature of 400 °C, with a radio frequency power of 1000 W and a growth time of 12 min.

[0061] (11) Etch the silicon dioxide oxide layer 4 above the N+ region 7, the first P+ region 8, and the second P+ region 12 respectively. Deposit the source metal 5 on the silicon dioxide oxide layer 4. A part of the source metal 5 contacts the N+ region 7 and the first P+ region 8 in the cell region C1, and another part is located in the junction termination extension region C2 and contacts the second P+ region 12. Make the source metal 5 in ohmic contact with the drain metal 1. Both the source metal 5 and the drain metal 1 are nickel. After metallization, a silicon carbide MOSFET power device with the terminal structure of Example 2 is obtained.

[0062] Example 3

[0063] Example 3 provides a terminal structure of a silicon carbide MOSFET power device. The terminal structure includes a junction termination extension region C2 and a field limiting ring region C3. A part of the N-type silicon carbide epitaxial layer 3 is contained in the field limiting ring region C3. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 . The surface of the N-type silicon carbide epitaxial layer 3 in the field limiting ring region C3 is an inclined plane structure. The inclination angle of the inclined plane structure with the horizontal plane is 6°. The inclined plane structure is obtained by a dry etching process, and the etching depth at the end far from the junction termination extension region C2 is 10 μm. Twenty field limiting rings 11 are formed on the surface of the inclined plane structure by ion implantation. The ring width of each field limiting ring 11 is 2.5 μm, and the ring spacing between two adjacent field limiting rings 11 is 1 μm.

[0064] Apply the terminal structure of Example 3 to a silicon carbide MOSFET power device. The preparation method of the overall structure includes the following steps:

[0065] (1) Provide a substrate containing a drain metal 1, an N-type silicon carbide substrate 2, and an N-type silicon carbide epitaxial layer 3. Clean the N-type silicon carbide epitaxial layer 3 and mark the etching position. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 .

[0066] (2) Inject aluminum ions on the surface of the N-type silicon carbide epitaxial layer 3. The number of injection times is 3 times. The injection energies are 100 KeV, 500 KeV, and 800 KeV respectively each time, and the injection doses are 5×10 11 cm −2 , 1×10 12 cm −2 and 2×10 13 cm−2 , a P-type well region 9 is formed.

[0067] (3) Perform nitrogen ion implantation 3 times, with the energies of each implantation being 60 KeV, 100 KeV, and 120 KeV respectively, and the doses of implantation being 1.5×10 15 cm −2 , 2×10 15 cm −2 and 1.5×10 15 cm −2 respectively, to form an N+ region 7 inside the P-type well region 9.

[0068] (4) Etch the N-type silicon carbide epitaxial layer 3 in the field limiting ring region C3 to form an inclined surface structure, with an etching angle of 6° and an etching depth of 10 μm at one end away from the junction termination extension region C2.

[0069] (5) Perform aluminum ion implantation on the surface of the N-type silicon carbide epitaxial layer 3 in the junction termination extension region C2 and the surface of the inclined surface structure simultaneously 3 times, with the energies of each implantation being 100 KeV, 400 KeV, and 800 keV respectively, and the dose of each implantation being 2×10 13 cm −2 respectively, to form a junction termination extension 10 and 20 field limiting rings 11 simultaneously. The ring width of each field limiting ring is 2.5 μm, the ring spacing between two adjacent field limiting rings is 1 μm, and the length of the junction termination extension 10 is 20 μm.

[0070] (6) Perform aluminum ion implantation on the inside of the N+ region 7 and the surface of the junction termination extension 10 simultaneously 3 times, with the energies of implantation being 100 KeV, 150 KeV, and 200 KeV respectively, and the doses of implantation being 1×10 14 cm −2 , 3×10 14 cm −2 and 3×10 14 cm −2 respectively, to form a first P+ region 8 and a second P+ region 12.

[0071] (7) Anneal the structure prepared in step (6) at a high temperature of 1650 °C for 10 min to activate the implanted ions.

[0072] (8) Dry-oxidize the structure prepared in step (7) at 1200 °C for 2 hours, and then wet-oxidize it at 900 °C for 1 hour to form a gate oxide layer on the surface of the N-type silicon carbide epitaxial layer 3 at the junction of the cell region C1 and the junction termination extension region C2.

[0073] (9) Using a low-pressure chemical vapor deposition process, a polysilicon gate 6 with a thickness of 450 nm is deposited on the gate oxide layer formed in step (8) at a temperature of 600 °C for a growth time of 2 hours.

[0074] (10) Using a plasma-enhanced chemical vapor deposition process, a silicon dioxide oxide layer 4 with a thickness of 1.2 μm is deposited on the structure prepared in step (9) at a temperature of 400 °C, a radio frequency power of 1000 W, and a growth time of 12 min.

[0075] (11) Etch the silicon dioxide oxide layer 4 above the N+ region 7, the first P+ region 8, and the second P+ region 12 respectively. Deposit source metal 5 on the silicon dioxide oxide layer 4. A part of the source metal 5 is in contact with the N+ region 7 and the first P+ region 8 in the cell region C1, and the other part is located in the junction termination extension region C2 and is in contact with the second P+ region 12. Make the source metal 5 in ohmic contact with the drain metal 1. Both the source metal 5 and the drain metal 1 are nickel. After metallization, a silicon carbide MOSFET power device with the terminal structure of Example 3 is obtained.

[0076] Comparative Example 1

[0077] Comparative Example 1 provides a terminal structure of a silicon carbide MOSFET power device. The terminal structure includes a junction termination extension region C2 and a field limiting ring region C3. A part of the N-type silicon carbide epitaxial layer 3 is contained in the field limiting ring region C3. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 . The surface of the N-type silicon carbide epitaxial layer 3 located in the field limiting ring region C3 is a planar structure.

[0078] The terminal structure of Comparative Example 1 is used for a silicon carbide MOSFET power device. The overall structure is as Figure 1 shown. The preparation method includes the following steps:

[0079] (1) Provide a substrate containing a drain metal 1, an N-type silicon carbide substrate 2, and an N-type silicon carbide epitaxial layer 3. Clean the N-type silicon carbide epitaxial layer 3. The thickness of the N-type silicon carbide epitaxial layer 3 is 10 μm, and the doping concentration is 1×10 16 cm −3 .

[0080] (2) Inject aluminum ions on the surface of the N-type silicon carbide epitaxial layer 3. The number of injection times is 3 times. The injection energies are 100 KeV, 500 KeV, and 800 KeV respectively. The injection doses per time are 5×10 11 cm −2 , 1×10 12 cm −2 and 2×10 13 cm −2, a P-type well region 9 is formed.

[0081] (3) Perform nitrogen ion implantation three times, with the energies of each implantation being 60 keV, 100 keV, and 120 keV respectively, and the implantation doses being 1.5×10 15 cm −2 , 2×10 15 cm −2 and 1.5×10 15 cm −2 respectively, to form an N+ region 7 inside the P-type well region 9.

[0082] (4) Simultaneously perform aluminum ion implantation on the surface of the N-type silicon carbide epitaxial layer 3 in the junction termination extension region C2 and the field limiting ring region C3 three times, with the energies of each implantation being 100 keV, 400 keV, and 800 keV respectively, and the implantation dose of each time being 2×10 13 cm −2 respectively, to form a junction termination extension 10 and 20 field limiting rings 11. The ring width of each field limiting ring 11 is 2.5 μm, the ring spacing between two adjacent field limiting rings 11 is 1 μm, and the length of the junction termination extension 10 is 20 μm.

[0083] (5) Simultaneously perform aluminum ion implantation on the surface inside the N+ region 7 and the junction termination extension 10 three times, with the implantation energies being 100 keV, 150 keV, and 200 keV respectively, and the implantation doses being 1×10 14 cm −2 , 3×10 14 cm −2 and 3×10 14 cm −2 respectively, to form a first P+ region 8 and a second P+ region 12.

[0084] (6) Anneal the structure prepared in step (5) at a high temperature of 1650 °C for 10 minutes to activate the implanted ions.

[0085] (7) Dry-oxidize the structure prepared in step (6) at 1200 °C for 2 hours, and then wet-oxidize it at 900 °C for 1 hour to form a gate oxide layer on the surface of the N-type silicon carbide epitaxial layer 3 at the junction of the cell region C1 and the junction termination extension region C2.

[0086] (8) Use a low-pressure chemical vapor deposition process to deposit a polysilicon gate 6 with a thickness of 450 nm on the gate oxide layer formed in step (7) at a temperature of 600 °C for a growth time of 2 hours.

[0087] (9) Using the plasma enhanced chemical vapor deposition process, deposit a silicon dioxide oxide layer 4 with a thickness of 1.2 μm on the structure prepared in step (8), at a temperature of 400 °C, a radio frequency power of 1000 W, and a growth time of 12 min.

[0088] (10) Etch the silicon dioxide oxide layer 4 above the N+ region 7, the first P+ region 8, and the second P+ region 12 respectively. Deposit the source metal 5 on the silicon dioxide oxide layer 4. A part of the source metal 5 is in contact with the N+ region 7 and the first P+ region 8 in the cell region C1, and another part is located in the junction termination extension region C2 and is in contact with the second P+ region 12. Make the source metal 5 have an ohmic contact with the drain metal 1. Both the source metal 5 and the drain metal 1 are nickel. After metallization, a silicon carbide MOSFET power device with the terminal structure of Comparative Example 1 is obtained.

[0089] Perform performance tests on the silicon carbide MOSFET power devices containing the terminal structures of Examples 1 to 3 and Comparative Example 1 respectively. The inclination angle in Example 1 is 2°, the inclination angle in Example 2 is 4°, the inclination angle in Example 3 is 6°, and there is no etching in Comparative Example 1, that is, the inclination angle is 0°.

[0090] Figure 3 It is a comparative graph of the breakdown voltages of silicon carbide MOSFET power devices with different inclination angles, obtained by simulating with semiconductor process and device simulation software. As Figure 3 shown, when the inclination angles are 0°, 2°, 4°, 6° in sequence, and the interface fixed charge density is 1×10 12 cm −2 , the breakdown voltage of the silicon carbide MOSFET power device gradually increases. The silicon carbide MOSFET power device with an inclined plane structure in the field limiting ring region has a significantly improved breakdown voltage compared with the traditional silicon carbide MOSFET power device without an inclined plane structure.

[0091] Figure 4 It is a graph of the breakdown voltage of the silicon carbide MOSFET power device with an inclination angle of 6° and the traditional silicon carbide MOSFET power device changing with the interface fixed charge density, obtained by simulating with semiconductor process and device simulation software. As Figure 4 shown, by changing the interface fixed charge density of the silicon carbide MOSFET power device respectively, it can be seen that for the silicon carbide MOSFET power device with an inclination angle of 6°, as the interface fixed charge density increases, the degree of decrease in the breakdown voltage is lower.

[0092] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A terminal structure of a silicon carbide MOSFET power device, the terminal structure comprising a junction termination extension region (C2) and a field limiting ring region (C3), the junction termination extension region (C2) being located outside the cell region (C1) of the silicon carbide MOSFET power device, the field limiting ring region (C3) being located outside the junction termination extension region (C2), and a part of the N-type silicon carbide epitaxial layer (3) being contained in the field limiting ring region (C3), characterized in that: The surface of the N-type silicon carbide epitaxial layer (3) located in the field limiting ring region (C3) is an inclined plane structure, the inclination angle of the inclined plane structure with respect to the horizontal plane is 2° to 6°, and a plurality of field limiting rings (11) are formed on the surface of the inclined plane structure by ion implantation; A part of the N-type silicon carbide epitaxial layer (3) is contained in the junction termination extension region (C2), and a junction termination extension (10) is formed on the surface of the N-type silicon carbide epitaxial layer (3) in the junction termination extension region (C2); a second P+ region (12) is formed on the surface of the junction termination extension (10); It further includes a source metal (5), a part of the source metal (5) is in contact with the N+ region (7) and the first P+ region (8) in the cell region (C1), and another part is located in the junction termination extension region (C2) and is in contact with the second P+ region (12); The N-type silicon carbide epitaxial layer (3) located in the junction termination extension region (C2) is a horizontal plane; The junction termination extension (10) and a plurality of field limiting rings (11) are simultaneously formed by 2 to 3 times of ion implantation. During each ion implantation, the junction termination extension (10) and the plurality of field limiting rings (11) are simultaneously implanted with ions. The implanted element is aluminum. The implantation energy for each time is 100 keV to 800 keV, and the implantation dose for each time is 2×10 13 cm -2 .

2. The terminal structure of the silicon carbide MOSFET power device according to claim 1, wherein The inclined plane structure is obtained by a dry etching process or a V-type cutting process, and in the inclined plane structure, the etching depth at the end far from the junction termination extension region (C2) is 3.5 μm to 10 μm.

3. The terminal structure of the silicon carbide MOSFET power device according to claim 1, characterized in that The number of the field limiting rings (11) is 15 to 25, the ring width of each field limiting ring (11) is 2 μm to 3 μm, and the ring spacing between two adjacent field limiting rings (11) is 0.5 μm to 2.5 μm.

4. The terminal structure of the silicon carbide MOSFET power device according to claim 1, characterized in that, The length of the junction termination extension (10) is 10 μm to 30 μm.

5. The terminal structure of the silicon carbide MOSFET power device according to claim 1, wherein The second P+ region (12) and the first P+ region (8) located in the cell region (C1) are formed simultaneously by 3 to 4 ion implantations. During each ion implantation, the second P+ region (12) and the first P+ region (8) are ion implanted simultaneously, and the implanted element is aluminum. The energy of each implantation is 100 keV to 200 keV, and the dose of each implantation is 1×10 14 cm -2 ~3×10 14 cm -2 .

6. The terminal structure of the silicon carbide MOSFET power device according to claim 5, wherein A gate oxide layer is formed on the surface of the N-type silicon carbide epitaxial layer (3) at the junction of the cell region (C1) and the junction termination extension region (C2), one side of the gate oxide layer is in contact with the P-type well region (9) in the cell region (C1), the other side of the gate oxide layer is in contact with the junction termination extension (10), and a polysilicon gate (6) is deposited on the gate oxide layer.

7. The terminal structure of the silicon carbide MOSFET power device according to claim 6, characterized in that, A silicon dioxide oxide layer (4) is grown on the surface of the polysilicon gate (6), the surface of the N-type silicon carbide epitaxial layer (3) containing the junction termination extension (10), and the surface of the N-type silicon carbide epitaxial layer (3) containing the field limiting ring (11), and a source metal (5) is deposited on the silicon dioxide oxide layer (4), a part of the source metal (5) is in contact with the N+ region (7) and the first P+ region (8) in the cell region (C1), and another part is located in the junction termination extension region (C2) and is in contact with the second P+ region (12).

8. The terminal structure of the silicon carbide MOSFET power device according to claim 1, characterized in that, Before the formation of the inclined plane structure, the thickness of the N-type silicon carbide epitaxial layer (3) in the junction termination extension region (C2) and the field limiting ring region (C3) is 10 μm, and the doping concentration is 1×10 16 cm -3 .

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