A dopant injection method, silicon carbide power device and preparation method thereof

Abstract

The present invention relates to a dopant injection method, a silicon carbide power device and a method for preparing the same. The present invention deposits amorphous SiC at room temperature and injects dopant, and then utilizes high-temperature thermal diffusion to infiltrate the SiC substrate. This process does not need to rely on high-temperature ion injection technology and expensive equipment, has a low degree of damage, and improves ohmic contact characteristics. The MPS diode and other power devices also use the above-mentioned ion injection method in the preparation process, which does not need to rely on high-temperature ion injection technology and expensive equipment, does not damage the SiC substrate, and improves the reverse bias leakage current and Schottky barrier lowering effect of the device. At the same time, the ohmic contact characteristics of the anode metal and the grid layer are improved, and the device can be effectively protected in the case of large current surges.

Description

Technical Field

[0001] The present invention relates to the field of preparation of silicon carbide power devices, and in particular to a method for injecting dopants into a silicon carbide power device, a silicon carbide power device and a preparation method thereof. Background Art

[0002] Silicon carbide semiconductor material is a high-voltage and high-current power device because of its special properties and is therefore widely used. Figure 1 The figure shows a common silicon carbide power device, in which a P-type junction is formed on an N-type epitaxial layer. Figure 2 As shown, currently, ion implantation is generally used to form a P-type junction on the N-type epitaxial layer, and the temperature during ion implantation needs to be more than 500°C. In other words, the ion implantation of silicon carbide power devices is currently carried out at high temperatures, because the N-type epitaxial layer is SiC crystal. At high temperatures, the huge energy generated by ion implantation can easily break the structure of the SiC crystal, thereby affecting the semiconductor properties of the SiC crystal, and further affecting the performance of silicon carbide power devices. Summary of the invention

[0003] In view of the problems existing in the prior art, the object of the present invention is to provide a method for doping a silicon carbide power device and a preparation method of the silicon carbide power device, which can improve the performance of the silicon carbide device.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for doping a silicon carbide power device, comprising:

[0006] Step 1, growing a barrier layer on a SiC substrate, and then etching the barrier layer and the SiC substrate to form a groove;

[0007] Step 2, depositing amorphous SiC in the trench and on the barrier layer, and then injecting dopants at room temperature; or depositing amorphous Si containing dopants in the trench and on the barrier layer;

[0008] Step 3, after defining the area where the dopant is to be implanted, etching or polishing the amorphous SiC to the barrier layer; then removing the barrier layer;

[0009] Step 4: depositing a covering layer on the SiC substrate and the amorphous SiC layer, and then performing heat treatment to form a polycrystalline SiC layer, a P-type junction or an N-type junction, wherein the polycrystalline SiC layer is transformed from the amorphous SiC layer at high temperature; after the heat treatment is completed, removing the covering layer.

[0010] The SiC substrate is either an N-type SiC substrate or a P-type SiC substrate; the dopant is either a P-type dopant or an N-type dopant.

[0011] The material of the cover layer is photoresist, aluminum nitride or boron nitride.

[0012] A method for preparing a silicon carbide power device, wherein the silicon carbide power device prepared by the method is an MPS diode device, and the preparation method is as follows:

[0013] Step 1, growing a SiC epitaxial layer 101 on the surface of a SiC substrate 100;

[0014] Step 2: using the above-mentioned dopant implantation method to form a polycrystalline SiC layer, a P-type junction or an N-type junction in the SiC epitaxial layer 101;

[0015] Step 3, growing an insulating film on the SiC epitaxial layer and the polycrystalline SiC layer; patterning the top insulating film, removing the insulating film in the active area; and then covering the active area and a portion of the adjacent peripheral area with an anode metal; the anode metal has Schottky contact characteristics with the SiC epitaxial layer and ohmic contact characteristics with the polycrystalline SiC layer;

[0016] Step 4: Cover the lower end of the SiC substrate with cathode metal to form ohmic contact characteristics.

[0017] A silicon carbide power device, which is a MPS diode, wherein the MPS diode has an active region and a peripheral region;

[0018] The MPS diode comprises a SiC substrate and a SiC epitaxial layer arranged on the SiC substrate, a plurality of grooves are formed on the upper end of the SiC epitaxial layer, a polycrystalline SiC layer is arranged in the groove, a plurality of P-type junctions corresponding to the polycrystalline SiC layer are also formed on the SiC epitaxial layer, and the P-type junctions are formed by the penetration of P-type dopants in the polycrystalline SiC layer into the SiC epitaxial layer; the P-type junctions located in the active area are P-type grids, and the P-type junctions located in the peripheral area are P-type guard junctions;

[0019] An insulating film is provided on the SiC epitaxial layer and the polycrystalline SiC layer, and the insulating film is located in the peripheral area; an anode metal is provided on the active area and a part of the adjacent peripheral area, and the anode metal has Schottky contact characteristics with the SiC epitaxial layer and ohmic contact characteristics with the polycrystalline SiC layer.

[0020] The SiC substrate is an N-type SiC substrate or a P-type SiC substrate, and the SiC epitaxial layer is an N-type SiC epitaxial layer or a P-type SiC epitaxial layer.

[0021] After adopting the above scheme, the present invention first deposits amorphous SiC at room temperature and injects dopants, and then utilizes high-temperature thermal diffusion to infiltrate the SiC substrate. This process does not need to rely on high-temperature ion injection technology and expensive equipment, and the degree of damage is small, while improving the ohmic contact characteristics. The power devices such as MPS diodes also use the above ion implantation method in the preparation process, which does not need to rely on high-temperature ion injection technology and expensive equipment, does not damage the SiC substrate, and improves the reverse bias leakage current of the device and the Schottky barrier reduction effect. At the same time, the ohmic contact characteristics of the anode metal and the grid layer are improved, which can effectively protect the device in the case of large current surges. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of the existing silicon carbide JBS diode;

[0023] Figure 2 The present invention is a flow chart of the existing dopant injection method;

[0024] Figure 3A and Figure 3B is a flow chart of the dopant injection method of the present invention;

[0025] Figure 4-Figure 12 This is a diagram of the preparation process of the MPS diode of the present invention. DETAILED DESCRIPTION

[0026] Such as 3A and Figure 3B As shown, this embodiment discloses a method for doping a silicon carbide power device, which is specifically as follows:

[0027] Step 1: growing a barrier layer on a SiC substrate, and then etching the barrier layer and the SiC substrate to form a groove.

[0028] The SiC substrate may be either an N-type SiC substrate or a P-type SiC substrate. In this embodiment, an N-type SiC substrate is used. The barrier layer is grown on the SiC substrate by CVD chemical vapor deposition, sputtering, epitaxy, etc. The barrier layer is a silicon oxide film with a thickness of about 0.1-2 μm.

[0029] Step 2: deposit amorphous SiC in the trench and on the barrier layer, and then inject dopants at room temperature; or deposit amorphous SiC containing dopants in the trench and on the barrier layer.

[0030] In this embodiment, the dopant is a P-type dopant, which may be aluminum, boron, etc. If the dopant is an N-type dopant, nitrogen, phosphorus, arsenic, etc. may be used.

[0031] Step 3: After defining the area where the dopant is to be implanted, the amorphous SiC is etched or polished to the barrier layer; and then the barrier layer is removed.

[0032] Step 4: deposit a capping layer on the SiC substrate and the amorphous SiC layer, and then perform heat treatment: at a temperature above 1500°C, allow the dopant to penetrate into the SiC substrate to form a P-type junction or an N-type junction. At the same time, the amorphous SiC layer is transformed into a polycrystalline SiC layer at high temperature. After the heat treatment is completed, remove the capping layer.

[0033] The material of the cover layer may be photoresist, aluminum nitride AlN, or boron nitride BN.

[0034] The method of injecting dopants into the SiC substrate in the above manner does not require the dopants to be injected at high temperatures, nor does it require expensive equipment. In addition, ion implantation at room temperature does not damage the lattice of the SiC substrate, preventing the degradation of device electrical properties such as leakage current and Schottky barrier lowering effect. In addition, the polycrystalline SiC layer produced during the doping process can improve the ohmic contact characteristics and further improve the performance of silicon carbide power devices.

[0035] like Figure 4-Figure 12 As shown, based on the above-mentioned dopant injection method, this embodiment also discloses a method for preparing a silicon carbide power device. The silicon carbide power device prepared by the method is an MPS diode device. The preparation method is specifically as follows:

[0036] Step 1: growing a SiC epitaxial layer 101 on the surface of the SiC substrate 100 .

[0037] Step 2: Use the above-mentioned dopant injection method to form a polycrystalline SiC layer, a P-type junction or an N-type junction in the SiC epitaxial layer 101. The details are as follows:

[0038] Step 2.1, growing an etching barrier layer 301 on the SiC epitaxial layer 101 ; after defining the position of the groove, etching the barrier layer 301 and the N-type epitaxial layer 101 thereunder by a photolithography process to form a groove 110 .

[0039] Step 2.2, depositing amorphous SiC302 or amorphous SiC containing dopants.

[0040] Step 2.3, after defining the area where the dopant is to be implanted, the amorphous SiC is etched or polished to the barrier layer; and then the barrier layer is removed.

[0041] Step 2.4, depositing a capping layer 303 on the SiC substrate and the amorphous SiC layer, and then performing a heat treatment: at a temperature above 1500°C, the dopant is allowed to penetrate into the SiC substrate to form a P-type junction or an N-type junction, and at the same time, the amorphous SiC layer is transformed into a polycrystalline SiC layer at high temperature; after the heat treatment is completed, the capping layer 303 is removed. The P-type junction or N-type junction is located in the active area of ​​the MPS diode to form a P-type or N-type grid, and is located in the peripheral area of ​​the MPS diode to form a P-type or N-type protection trench.

[0042] Step 3, growing an insulating film on the SiC epitaxial layer and the polycrystalline SiC layer; patterning the top insulating film, and removing the insulating film in the active area; and then covering the active area and a portion of the adjacent peripheral area with an anode metal; the anode metal has Schottky contact characteristics with the SiC epitaxial layer and ohmic contact characteristics with the polycrystalline SiC layer.

[0043] The anode metal (106) may be composed of multiple layers of metals such as Ni, Au, Pt, Ti, Al, Nb, Ta, or a combination thereof.

[0044] Step 4: Cover the lower end of the SiC substrate with cathode metal to form ohmic contact characteristics.

[0045] The silicon carbide power device prepared by the above preparation method is an MPS diode, and its structure is as follows: Fig.12 As shown. An N-type epitaxial layer 101 is grown on an N+ type substrate 100, and a plurality of grooves 110 are etched on a portion of the surface of the N-type epitaxial layer 101. The interior of the grooves 110 is filled with P-type amorphous SiC or polycrystalline SiC104. The P-type grid 102 and the P protection groove 103 are formed by polycrystalline SiC104 diffusing from the lower wall and side wall of the N-type epitaxial layer 101 contacted by the grooves 110 to the N-type epitaxial layer 101. The P-type polycrystalline SiC104 is formed from amorphous P-type SiC during the heat treatment process.

[0046] The P-type grid 102 is in the active region 120 of the SiCMPS diode, and the P-type protection trench 103 is located at the periphery 121 of the SiCMPS diode. The P-type grid 102 can improve the reverse bias voltage leakage current of the device and improve the electric field effect of the anode metal and the N-type SiC interface 108. The P-type protection trench 103 acts on the edge to generate floating protection, which is used to improve the reverse bias field voltage of the MPS device. The N-type epitaxial layer 101 and the polycrystalline SiC 104 grow an insulating film 105; for example, the silicon oxide in the active region is removed by patterning the top insulating silicon oxide film. The anode metal 106 covers the active region 120 and the adjacent peripheral region 121. The anode metal 106 can be composed of multiple metal layers, composed of Ni, Au, Pt, Ti, Al, Nb, Ta, etc. or a combination thereof. The anode metal 106 has Schottky contact characteristics with the N-type epitaxial layer and ohmic contact characteristics with the polycrystalline SiC 104. A cathode metal 107 is prepared under the N-type substrate 100 to form an ohmic contact characteristic.

[0047] The preparation process of the above-mentioned MPS diode is simple, because it does not require ion implantation at high temperature, does not require expensive equipment, and ion implantation at room temperature will not damage the SiC substrate, thereby improving the reverse bias leakage current and Schottky barrier lowering effect of the device. At the same time, the ohmic contact characteristics of the anode metal and the P grid layer are improved, which can effectively protect the device in the case of large current surges. The trench-type P-type grid and P-type protection trench formed by the trench filling polycrystalline SiC injection can more effectively block the influence of leakage current and Schottky field voltage when the reverse bias voltage is applied.

[0048] The key to the present invention is that the present invention first deposits amorphous SiC at room temperature and injects dopants, and then utilizes high-temperature thermal diffusion to infiltrate the SiC substrate. This process does not require high-temperature ion injection technology and expensive equipment, has a small degree of damage, and improves ohmic contact characteristics. The MPS diode and other power devices also use the above ion injection method in the preparation process, which does not require high-temperature ion injection technology and expensive equipment, does not damage the SiC substrate, and improves the reverse bias leakage current of the device and the Schottky barrier lowering effect.

[0049] The above description is merely an embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any minor modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A silicon carbide power device, characterized in that: The silicon carbide power device is an MPS diode, and the MPS diode is provided with an active region and a peripheral region; The preparation method of the MPS diode is as follows: Step 1, growing a SiC epitaxial layer on the surface of a SiC substrate; Step 2: forming a polycrystalline SiC layer, a P-type junction or an N-type junction on the SiC epitaxial layer 101; the details are as follows: Step 2.1, growing an etching barrier layer on the SiC epitaxial layer; after defining the position of the groove, etching the barrier layer and the N-type epitaxial layer thereunder by a photolithography process to form a groove; Step 2.2, depositing amorphous SiC in the trench and on the barrier layer, and then injecting dopants at room temperature; or depositing amorphous SiC containing dopants in the trench and on the barrier layer; Step 2.3, after defining the area where the dopant is to be implanted, etching or polishing the amorphous SiC to the barrier layer; then removing the barrier layer; Step 2.4, depositing a cover layer on the SiC substrate and the amorphous SiC layer, and then performing heat treatment to form a P-type junction or an N-type junction. At the same time, the amorphous SiC layer is transformed into a polycrystalline SiC layer at high temperature; after the heat treatment is completed, the cover layer is removed; the P-type junction or N-type junction is located in the active area of ​​the MPS diode to form a P-type or N-type grid, and is located in the peripheral area of ​​the MPS diode to form a P-type or N-type protection groove; Step 3, growing an insulating film on the SiC epitaxial layer and the polycrystalline SiC layer; Patterning the top insulating film and removing the insulating film in the active area; then covering the active area and a portion of the adjacent peripheral area with an anode metal; the anode metal has a Schottky contact characteristic with the SiC epitaxial layer and an Ohmic contact characteristic with the polycrystalline SiC layer; Step 4: Cover the lower end of the SiC substrate with cathode metal to form ohmic contact characteristics; The MPS diode obtained by the above preparation method includes a SiC substrate and a SiC epitaxial layer arranged on the SiC substrate, a plurality of grooves are formed on the upper end of the SiC epitaxial layer, a polycrystalline SiC layer is arranged in the groove, and a plurality of P-type junctions corresponding to the polycrystalline SiC layer are also formed on the SiC epitaxial layer, and the P-type junctions are formed by the penetration of P-type dopants in the polycrystalline SiC layer into the SiC epitaxial layer; the P-type junctions located in the active area are P-type grids, and the P-type junctions located in the peripheral area are P-type guard junctions; An insulating film is provided on the SiC epitaxial layer and the polycrystalline SiC layer, and the insulating film is located in the peripheral area; an anode metal is provided on the active area and a part of the adjacent peripheral area, and the anode metal has Schottky contact characteristics with the SiC epitaxial layer and ohmic contact characteristics with the polycrystalline SiC layer.

2. The silicon carbide power device according to claim 1, characterized in that: The SiC substrate is an N-type SiC substrate or a P-type SiC substrate, and the SiC epitaxial layer is an N-type SiC epitaxial layer or a P-type SiC epitaxial layer.

3. A silicon carbide power device according to claim 1, characterized in that: The material of the cover layer is photoresist, aluminum nitride or boron nitride.

Images