Power diode and method for preparing the same

Abstract

The present application discloses a power diode and a method for preparing the same. The power diode includes a plurality of first epitaxial structures, wherein the first epitaxial structure includes a second epitaxial layer and a first conductive layer, wherein the second epitaxial layer is located on the inner surface of the first epitaxial trench, and the first conductive layer is located in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact; and at least one second epitaxial structure, wherein the second epitaxial structure includes a third epitaxial layer and a second conductive layer, wherein the third epitaxial layer is located on the inner surface of the second epitaxial trench, and the second conductive layer is located in the second epitaxial trench, wherein the third epitaxial layer has a second doping type, wherein the first conductive layer and the second conductive layer have different conductive materials, the third epitaxial layer has a second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact. This is to solve the problem that the performance advantage of power devices in the related art is not obvious.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a power diode and a method for preparing the same. Background Art

[0002] Commonly used diodes include ordinary rectifier diodes, Schottky diodes, PIN diodes, and hybrid PIN / Schottky diodes (MPS). They have their own characteristics compared to each other: Schottky rectifiers have lower on-state voltage drop, larger leakage current, and almost zero reverse recovery time; PIN fast recovery rectifiers have faster reverse recovery time, but their on-state voltage drop is very high; MPS can reduce device resistance and will not increase device leakage current.

[0003] At present, with the development of microelectronic devices towards low power consumption, high voltage resistance and high reliability, the requirements for semiconductor materials are gradually increasing. Microelectronic devices are increasingly used in special environments such as high temperature, high radiation, high frequency and high power. In order to meet the application of microelectronic devices in the fields of high temperature resistance and radiation resistance, new semiconductor materials need to be developed to maximize the performance of microelectronic devices. Traditional silicon devices and gallium arsenide devices limit the improvement of device and system performance. The third-generation semiconductor materials represented by silicon carbide (SiC) and gallium nitride (GaN) have become ideal semiconductor materials for making high temperature resistant, high power and radiation resistant electronic devices due to the advantages of the wide bandgap and high critical breakdown electric field of the materials themselves. The SiC-based devices currently under study include high temperature and power SiC devices, microwave and high frequency SiC devices, SiC optoelectronic devices, radiation resistant devices, etc. The critical breakdown field strength of SiC materials is 10 times that of Si materials, the bandgap and thermal conductivity of SiC are both 3 times that of Si materials, and the concentration of intrinsic carriers is only one-tenth of that of silicon materials. These excellent physical properties make semiconductor power devices made of SiC materials have great advantages in high frequency, high temperature, high power and high radiation environments. SiC can form different crystal structures under different environments. The three commonly used crystal structures are 3C-SiC, 4H-SiC and 6H-SiC. 4H-SiC material has become the mainstream material for manufacturing semiconductor devices due to its higher bandgap width and hole mobility and lower intrinsic carrier concentration.

[0004] At present, the SIC diode device structure has not been optimized based on the material characteristics of SIC, resulting in no obvious performance advantage over Si devices in some parameters and low reliability. In terms of process flow, the SIC diode has adopted the traditional process of Si diodes. Affected by the material characteristics of SIC, the process flow is complicated and requires the use of special equipment (for Al ion implantation, special implantation equipment is required), resulting in high production costs. Summary of the invention

[0005] The present application provides a power diode and a method for preparing the same, so as to solve the problem that the performance advantage of power devices in the related art is not obvious.

[0006] According to one aspect of the present application, a power diode is provided, comprising a substrate and a first epitaxial layer located on the substrate, the first epitaxial layer having a first doping type, the first epitaxial layer having a plurality of first epitaxial trenches and at least one second epitaxial trench on a side away from the substrate, the second epitaxial trench being located between any adjacent first epitaxial trenches, the power diode further comprising: a plurality of first epitaxial structures, the first epitaxial structure being located in the first epitaxial trench, the first epitaxial structure comprising a second epitaxial layer and a first conductive layer, the second epitaxial layer being located on an inner surface of the first epitaxial trench, the first conductive layer being located on an inner surface of the first epitaxial trench in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact; at least one second epitaxial structure, the second epitaxial structure is located in the second epitaxial trench, the second epitaxial structure includes a third epitaxial layer and a second conductive layer, the third epitaxial layer is located on the inner surface of the second epitaxial trench, and the second conductive layer is located in the second epitaxial trench, wherein the first conductive layer and the second conductive layer have different conductive materials, the third epitaxial layer has the second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact.

[0007] Optionally, a width of the second epitaxial trench in a first direction is greater than a width of the first epitaxial trench, wherein the first direction is parallel to a surface of the substrate in contact with the first epitaxial layer.

[0008] Optionally, a depth of the second epitaxial trench in a second direction is less than a depth of the first epitaxial trench, wherein the second direction is perpendicular to a surface of the substrate in contact with the first epitaxial layer.

[0009] Optionally, the second doping type is P type, the work function of the first conductive layer is smaller than the work function of the second epitaxial layer, and the work function of the second conductive layer is larger than the work function of the third epitaxial layer; the second doping type is N type, the work function of the first conductive layer is larger than the work function of the second epitaxial layer, and the work function of the second conductive layer is smaller than the work function of the third epitaxial layer.

[0010] Optionally, the power diode further includes: a third conductive layer, the third conductive layer is located on a side of the first epitaxial layer away from the substrate, and the third conductive layer and the first conductive layer have the same conductive material.

[0011] Optionally, the power diode further includes: a fourth conductive layer, and the third conductive layer is at least located on a side of the third conductive layer facing away from the substrate.

[0012] Optionally, the doping concentration of the second epitaxial layer and the third epitaxial layer is 1×10 15 cm -3 ~1×10 18 cm -3 , the second doping type is P type, the doping concentration of the second epitaxial layer is greater than the doping concentration of the third epitaxial layer, and the second doping type is N type, the doping concentration of the second epitaxial layer is less than the doping concentration of the third epitaxial layer.

[0013] According to another aspect of the present application, a method for preparing a power diode is provided, which is used to prepare any one of the power diodes described above, and the preparation method includes: providing a substrate; forming a first epitaxial layer on the substrate, and forming a plurality of first epitaxial trenches and at least one second epitaxial trench in the first epitaxial layer, wherein the second epitaxial trench is located between any adjacent first epitaxial trenches; forming a first epitaxial structure in the first epitaxial trench, wherein the first epitaxial structure includes a second epitaxial layer and a first conductive layer, wherein the second epitaxial layer is located on the inner surface of the first epitaxial trench, and the first conductive layer is located in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact; forming a second epitaxial structure in the second epitaxial trench, wherein the second epitaxial structure includes a third epitaxial layer and a second conductive layer, wherein the third epitaxial layer is located on the inner surface of the second epitaxial trench, and the second conductive layer is located in the second epitaxial trench, wherein the first conductive layer and the second conductive layer have different conductive materials, the third epitaxial layer has the second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact.

[0014] Optionally, the steps of forming the first epitaxial trench and the second epitaxial trench include: using an etching process to form a plurality of the first epitaxial trenches and at least one second epitaxial trench in the first epitaxial layer; using an epitaxial growth process to fill the first epitaxial trench and the second epitaxial trench with a second epitaxial material and a third epitaxial material, respectively, the second epitaxial material and the third epitaxial material both having the second doping type; using an etching process to form a first trench and a second trench in the second epitaxial material and the third epitaxial material, respectively, the remaining second epitaxial material being the second epitaxial layer, and the remaining third epitaxial material being the third epitaxial layer; using a deposition process to fill the second trench with a second conductive material, using an annealing process to anneal the second conductive material, and the annealed second conductive material forming the second conductive layer; using a deposition process to fill the first trench with a first conductive material to form the first conductive layer.

[0015] Optionally, the temperature of the annealing process is greater than 900°C.

[0016] Through the technical solution of the present application, a power diode is provided, which has a plurality of first epitaxial trenches and at least one second epitaxial trench, a first epitaxial structure is formed in the first epitaxial trench, a second epitaxial structure is formed in the second epitaxial trench, and a second epitaxial layer in the first epitaxial structure forms a Schottky contact with the first conductive layer, and an ohmic contact is formed with the third epitaxial layer in the second epitaxial structure. That is, in the power diode, the surge capability of the device is improved by forming alternating ohmic contacts and Schottky contacts in the trenches, wherein the ohmic contact can increase the discharge area and improve the surge capability of the device, and the Schottky contact can ensure the withstand voltage capability of the device and reduce the forward voltage drop of the power diode. The alternating combination of the ohmic contact and the Schottky contact improves the surge capability of the power diode and reduces the forward voltage drop on the basis of ensuring the withstand voltage performance, thereby improving the performance advantage of the power diode device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0018] Figure 1 is a schematic diagram of a cross-sectional structure of a power diode according to an embodiment of the present application;

[0019] Figure 2 is a schematic cross-sectional structure diagram of another power diode according to an embodiment of the present application;

[0020] Figure 3 is a flow chart of a method for preparing a power diode according to an embodiment of the present application;

[0021] Figure 4 It is a schematic cross-sectional structure diagram of a substrate and a first epitaxial layer provided in a method for preparing a power diode provided in an embodiment of the present application;

[0022] Figure 5 is Figure 4 A schematic cross-sectional structure diagram of a first epitaxial trench and a second epitaxial trench formed in a first epitaxial layer is shown;

[0023] Figure 6 is Figure 5 A schematic cross-sectional structure diagram showing a second epitaxial material and a third epitaxial material formed in the first epitaxial trench and the second epitaxial trench respectively;

[0024] Figure 7 is Figure 6 A schematic cross-sectional structure diagram showing a first trench and a second trench formed in the second epitaxial material and the third epitaxial material respectively;

[0025] Figure 8 is Figure 7 A schematic cross-sectional structure diagram of a first conductive layer formed in a first trench shown;

[0026] Fig. 9 is Figure 8 A schematic cross-sectional structure diagram of a second conductive layer formed in a second trench shown;

[0027] Fig.10 is Fig. 9 A schematic cross-sectional structure diagram of a third conductive layer formed on the structure shown;

[0028] Fig.11 is Fig.10 A schematic cross-sectional structure diagram of a fourth conductive layer formed on the third conductive layer shown;

[0029] Fig.12 is Fig.11 The cross-sectional structure diagram of the fifth conductive layer formed on the side of the substrate facing away from the first epitaxial layer is shown.

[0030] The above drawings include the following reference numerals:

[0031] 10. Substrate; 20. First epitaxial layer; 30. First epitaxial trench; 31. First epitaxial structure; 311. Second epitaxial layer; 3111. Second epitaxial material; 312. First conductive layer; 3121. First trench; 40. Second epitaxial trench; 41. Second epitaxial structure; 411. Third epitaxial layer; 4111. Third epitaxial material; 412. Second conductive layer; 4121. Second trench; 50. Third conductive layer; 60. Fourth conductive layer; 70. Fifth conductive layer. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0033] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] As described in the background technology, in the prior art, the current SIC power diode device structure has not been optimized for the material properties of SIC, resulting in no obvious performance advantage in some parameters compared to Si devices, and low reliability. In terms of process flow, the SIC diode uses the traditional process of Si diodes. Affected by the material properties of SIC, the process flow is complicated, special equipment is required (for Al ion implantation, special implantation equipment is required), and the production cost is high. In order to solve the above technical problems, the present application provides a power diode and a preparation method thereof.

[0036] According to one aspect of the present application, a power diode is provided, such as Figure 1 and Figure 2As shown, the power diode includes a substrate 10 and a first epitaxial layer 20 located on the substrate 10, the first epitaxial layer 20 has a first doping type, the first epitaxial layer 20 has a plurality of first epitaxial trenches 30 and at least one second epitaxial trench 40 on a side away from the substrate 10, the second epitaxial trench 40 is located between any adjacent first epitaxial trenches 30, the power diode also includes: a plurality of first epitaxial structures 31, the first epitaxial structure 31 is located in the first epitaxial trench 30, the first epitaxial structure 31 includes a second epitaxial layer 311 and a first conductive layer 312, the second epitaxial layer 311 is located on the inner surface of the first epitaxial trench 30, the first conductive layer 312 is located in the first epitaxial trench 30, wherein the second epitaxial layer 311 has a second doping type, and the second epitaxial layer 311 and the first conductive layer 312 form a Schottky contact; at least one second epitaxial structure 41, the second epitaxial structure 41 is located in the second epitaxial trench 40, the second epitaxial structure 41 includes a third epitaxial layer 411 and a second conductive layer 412, the third epitaxial layer 411 is located on the inner surface of the second epitaxial trench 40, and the second conductive layer 412 is located in the second epitaxial trench 40, wherein the first conductive layer 312 and the second conductive layer 412 have different conductive materials, the third epitaxial layer 411 has a second doping type, and the third epitaxial layer 411 and the second conductive layer 412 form an ohmic contact. The power diode has a plurality of first epitaxial trenches 30 and at least one second epitaxial trench 40, a first epitaxial structure 31 is formed in the first epitaxial trench 30, a second epitaxial structure 41 is formed in the second epitaxial trench 40, and a second epitaxial layer 311 and a first conductive layer 312 in the first epitaxial structure 31 form a Schottky contact, and a third epitaxial layer 411 and a second conductive layer 412 in the second epitaxial structure 41 form an ohmic contact, that is, in the power diode, the device surge capability is improved by forming alternating ohmic contacts and Schottky contacts in the trenches, wherein the ohmic contact can increase the discharge area and improve the device surge capability, and the Schottky contact can ensure the device withstand voltage capability and reduce the forward voltage drop of the power diode, and the alternating combination of the ohmic contact and the Schottky contact improves the device surge capability and reduces the forward voltage drop on the basis of ensuring the withstand voltage performance, thereby improving the performance advantage of the power diode device.

[0037] Specifically, when the conductive material is specifically a metal material in contact with a semiconductor material, the energy band in the semiconductor material is bent at the contact interface, forming a Schottky barrier. The existence of the Schottky barrier causes electrons to move only from the semiconductor material to the metal material, and the electrons cannot move in the opposite direction. The current and voltage are in a nonlinear relationship. This asymmetry causes the Schottky contact to have not only rectification characteristics, but also low forward voltage and low reverse leakage current characteristics. The metal material and the semiconductor material can also form an ohmic contact when in contact, and a low barrier height is formed at the contact interface between the metal material and the semiconductor material. Electrons are easily transmitted between the metal material and the semiconductor material. Therefore, the ohmic contact makes the contact interface have a low contact resistance, and the current and voltage are in a linear relationship, which improves the device surge capability. Among them, in the present application, Schottky contact and ohmic contact are integrated in the power diode, which can ensure that the power diode has a withstand voltage performance, and can improve the device surge capability and reduce the forward voltage drop.

[0038] In some optional embodiments, such as Figure 1 and Figure 2 As shown, the width of the second epitaxial trench 40 is greater than the width of the first epitaxial trench 30 in the first direction A, wherein the first direction A is parallel to the surface of the substrate 10 contacting the first epitaxial layer 20 .

[0039] Specifically, the resistance of the Schottky contact is determined by factors such as the height of the Schottky barrier and the contact area. Among them, the larger the contact area of ​​the Schottky contact, the longer the path of the current through the Schottky contact, which increases the resistance of the Schottky contact. The contact area is also an important factor affecting the resistance of the ohmic contact. The ohmic contact makes the metal material and the semiconductor material act as a common conductor. The larger the contact area, the smaller the resistance of the ohmic contact. In the present application, the width of the first epitaxial groove in the first direction is less than the width of the second epitaxial groove. It can be regarded as that in the second direction, that is, the conduction direction of the power diode current, the area of ​​the Schottky contact formed by the third epitaxial layer and the second conductive layer is less than the area of ​​the ohmic contact formed by the second epitaxial layer and the first conductive layer, so that the first epitaxial groove forming the Schottky contact has a smaller contact area, and the second epitaxial groove forming the ohmic contact has a larger contact area, thereby reducing the on-resistance of the power diode, reducing the forward voltage drop of the power diode, and improving the surge capacity of the power diode.

[0040] In addition, the width of the second epitaxial structure is greater than that of the first epitaxial structure, which can be regarded as integrating the MPS structure into the power diode, which can effectively increase the breakdown voltage of the power diode and reduce the forward voltage drop of the power diode.

[0041] In other optional embodiments, such as Figure 1 and Figure 2As shown, the depth of the second epitaxial trench 40 in the second direction B is less than the depth of the first epitaxial trench 30 , wherein the second direction B is perpendicular to the surface of the substrate 10 contacting the first epitaxial layer 20 .

[0042] Specifically, in the above structure, when the power diode works in reverse, the second epitaxial trench forming the ohmic contact has the hidden danger of generating a large leakage current. In order to eliminate the above hidden danger, a structure in which the depth of the second epitaxial trench is less than the depth of the first epitaxial trench is adopted. This is because the first epitaxial trench located on both sides of the ohmic contact forms a Schottky contact, and when the power diode works in reverse, a depletion layer can be formed at the bottom of the first epitaxial trench, and the depth of the first epitaxial trench is greater than that of the second epitaxial trench, so that the depletion layer formed by the first epitaxial trench can protect the second epitaxial trench, thereby preventing the second epitaxial trench from generating a large leakage current, thereby increasing the breakdown voltage of the device.

[0043] In some optional embodiments, the second doping type is P type, the work function of the first conductive layer is smaller than the work function of the second epitaxial layer, and the work function of the second conductive layer is greater than the work function of the third epitaxial layer; the second doping type is N type, the work function of the first conductive layer is greater than the work function of the second epitaxial layer, and the work function of the second conductive layer is smaller than the work function of the third epitaxial layer.

[0044] Specifically, whether the metal material contacts the semiconductor material to form an ohmic contact or a Schottky contact depends mainly on the difference in their work functions and the type of semiconductor (P-type and N-type). When the work functions of the metal material and the semiconductor material are close, it is easier for electrons to flow from the metal material to the semiconductor material or from the semiconductor material to the metal material, and it is easier to form an ohmic contact. For N-type semiconductor materials, it is easier to form an ohmic contact when they contact metals with lower work functions (such as aluminum, germanium, etc.), while for P-type semiconductor materials, it is easier to form an ohmic contact when they contact metals with higher work functions (such as gold, platinum, etc.). When the work functions of the metal material and the semiconductor material differ greatly, it is more conducive to the formation of a Schottky barrier and easier to form a Schottky contact. For N-type semiconductor materials, it is easier to form a Schottky contact when they contact metals with higher work functions (such as nickel, gold, etc.), while for P-type semiconductor materials, it is easier to form a Schottky contact when they contact metals with lower work functions (such as titanium, aluminum, etc.).

[0045] Exemplarily, the second doping type is P type, the material of the first conductive layer is metallic nickel, the work function of metallic nickel is 4.6eV, the material of the second conductive layer is metallic titanium, the work function of metallic titanium is 4.33eV, wherein the metallic nickel material forms a Schottky contact with the second epitaxial layer, and the metallic titanium also forms a Schottky contact with the third epitaxial layer, thereby reducing the on-resistance and forward voltage drop of the power diode structure, and the metallic aluminum has good electrical conductivity, thereby improving the current transmission efficiency of the diode structure.

[0046] In some optional embodiments, such as Figure 1 and Figure 2 As shown, the power diode further includes: a third conductive layer 50 , which is located on a side of the first epitaxial layer 20 away from the substrate 10 , and the third conductive layer 50 and the first conductive layer 312 have the same conductive material.

[0047] Specifically, the third conductive layer 50 and the first epitaxial layer 20 form a metal material and semiconductor material contact, having a rectifying structure similar to a PN junction, which can reduce leakage current and increase the voltage of the diode when the power diode works in reverse, and can serve as a channel for conducting current and reduce the resistance of the device when the power diode works in the forward direction.

[0048] For example, Figure 1 As shown, the third conductive layer 50 is located at the first epitaxial structure 31 and the second epitaxial structure 41 at the side away from the substrate 10. In this structure, the third conductive layer 50 can be completed in the same process as the first conductive layer 312, simplifying the preparation process. In another exemplary structure, as shown in FIG. Figure 2 As shown, the third conductive layer 50 is only located on the side of the first epitaxial layer 20 away from the substrate 10, and the first conductive layer 312 in the first epitaxial structure 31 and the second conductive layer 412 in the second epitaxial structure 41 are directly in contact with the source electrode. The source electrode has a high current conduction capability, which can improve the conductivity of the current in the Schottky contact and the ohmic contact, thereby improving the conduction capability of the power diode.

[0049] In some optional embodiments, such as Figure 1 and Figure 2 As shown, the power diode further includes: a fourth conductive layer 60 , and the fourth conductive layer 60 is at least located on a side of the third conductive layer 50 facing away from the substrate 10 .

[0050] Specifically, the fourth conductive layer 60 is a thickened metal, and generally adopts a metal material with good conductivity, such as aluminum, gold, etc. On the one hand, it improves the current transmission efficiency of the power diode, and on the other hand, it supports the power diode structure and facilitates packaging.

[0051] In other optional embodiments, the fourth conductive layer includes multiple conductive material layers, each conductive material layer has a different work function. Specifically, a work function gradient can be formed, which can reduce the potential barrier of electrons in the fourth conductive layer and improve the conductivity of the fourth conductive layer.

[0052] In some optional embodiments, the doping concentrations of the second epitaxial layer and the third epitaxial layer are both 1×10 15 cm -3 ~1×10 18cm -3 , the second doping type is P type, the doping concentration of the second epitaxial layer is greater than the doping concentration of the third epitaxial layer, the second doping type is N type, and the doping concentration of the second epitaxial layer is less than the doping concentration of the third epitaxial layer.

[0053] Specifically, doping semiconductor materials with different concentrations can change the concentration of carriers in the semiconductor material. In the structure forming an ohmic contact, the semiconductor material is an N-type semiconductor. Increasing the doping concentration of the N-type semiconductor can increase the concentration of electrons in the semiconductor material, promote the flow of electrons from the N-type semiconductor to the metal, thereby reducing the contact resistance of the ohmic contact, which is conducive to the formation of the ohmic contact; the semiconductor material is a P-type semiconductor, reducing the doping concentration of the P-type semiconductor, reducing the concentration of electrons in the semiconductor material, can promote the flow of electrons from the metal material to the P-type semiconductor, thereby reducing the contact resistance of the ohmic contact, which is conducive to the formation of the ohmic contact. In the structure forming a Schottky contact, because the Schottky contact has a unidirectional conduction characteristic, the semiconductor material is an N-type semiconductor, and the doping concentration of the N-type semiconductor needs to be reduced so that electrons can flow from the metal material to the N-type semiconductor; the semiconductor material is a P-type semiconductor, and the doping concentration of the P-type semiconductor needs to be increased to reduce the concentration of electrons in the semiconductor material, thereby promoting the flow of electrons from the metal material to the N-type semiconductor. Therefore, when the second doping type is P type, the doping concentration of the second epitaxial layer is greater than the doping concentration of the third epitaxial layer; when the second doping type is N type, the doping concentration of the second epitaxial layer is less than the doping concentration of the third epitaxial layer, which is beneficial for the second epitaxial structure to form an ohmic contact and the first epitaxial structure to form a Schottky contact, thereby improving the surge capability of the power diode and reducing the forward voltage drop, thereby improving the performance advantages of the power diode device.

[0054] In another exemplary embodiment, the second doping type is P-type. In order to make the first epitaxial structure form a Schottky contact better and the second epitaxial structure form an ohmic contact, the doping concentration of the third epitaxial material is greater than the doping concentration of the second epitaxial material. Specifically, the doping concentration of the third epitaxial layer is 1×10 17 cm -3 , the doping concentration of the second epitaxial layer is 1×10 16 cm -3 .

[0055] like Figure 1 and Figure 2 As shown, the power diode further includes a fifth conductive layer 70, which is located on the side of the substrate 10 away from the first epitaxial layer 20 and in contact with the substrate 10, wherein the fifth conductive layer 70 and the substrate 10 can form an ohmic contact to reduce the on-resistance and on-voltage drop of the power diode.

[0056] Specifically, the materials of the first conductive layer, the second conductive layer, the third conductive layer, the fourth conductive layer and the fifth conductive layer include, but are not limited to, alloy materials composed of any one or more of silver, copper, aluminum, gold, titanium, nickel, platinum and palladium metals. Those skilled in the art can make reasonable selections according to actual needs, and no specific limitation is made without application. Among them, the first conductive layer, the second conductive layer, the third conductive layer, the fourth conductive layer and the fifth conductive layer can all include multiple layers of different conductive materials in the second direction.

[0057] According to another aspect of the present application, a method for preparing a power diode is provided, such as Figure 3 As shown, the preparation method is used to prepare any of the above-mentioned power diodes, and the preparation method comprises the following steps:

[0058] Step S101: providing a substrate;

[0059] Step S102: forming a first epitaxial layer on a substrate, and forming a plurality of first epitaxial trenches and at least one second epitaxial trench in the first epitaxial layer, wherein the second epitaxial trench is located between any adjacent first epitaxial trenches;

[0060] Step S103: forming a first epitaxial structure in the first epitaxial trench, the first epitaxial structure comprising a second epitaxial layer and a first conductive layer, the second epitaxial layer being located on an inner surface of the first epitaxial trench, the first conductive layer being located in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact;

[0061] Step S104: forming a second epitaxial structure in the second epitaxial trench, the second epitaxial structure comprising a third epitaxial layer and a second conductive layer, the third epitaxial layer being located on an inner surface of the second epitaxial trench, the second conductive layer being located in the second epitaxial trench, wherein the third epitaxial layer has a second doping type, wherein the first conductive layer and the second conductive layer have different conductive materials, the second epitaxial layer and the third epitaxial layer have a second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact.

[0062] In the above preparation method, the power diode has a plurality of first epitaxial trenches and at least one second epitaxial trench, a first epitaxial structure is formed in the first epitaxial trench, a second epitaxial structure is formed in the second epitaxial trench, the first epitaxial structure and the second epitaxial structure are formed by a trench and secondary epitaxial scheme, and the second epitaxial layer and the first conductive layer in the first epitaxial structure form a Schottky contact, and the third epitaxial layer and the second conductive layer in the second epitaxial structure form an ohmic contact, that is, in the power diode, the device surge capacity is improved by forming alternating ohmic contacts and Schottky contacts in the trench, wherein the ohmic contact can increase the discharge area and improve the device surge capacity, the Schottky contact can ensure the device withstand voltage and reduce the forward voltage drop of the power diode, and the alternating combination of the ohmic contact and the Schottky contact improves the surge capacity of the power diode and reduces the forward voltage drop on the basis of ensuring the withstand voltage performance, thereby improving the performance advantage of the power diode device. In addition, in the above trench and secondary epitaxial scheme, ion implantation is not required, the process is simplified, and the production cost is reduced.

[0063] The following will describe in more detail the exemplary embodiments of the method for preparing a power diode provided by the present application in conjunction with the accompanying drawings. However, these exemplary embodiments can be implemented in a variety of different forms and should be interpreted as being limited to the embodiments described herein. It should be understood that these embodiments are provided to make the disclosure of the present application thorough and complete, and to fully convey the concepts of these exemplary embodiments to those of ordinary skill in the art.

[0064] First, if Figure 4 As shown, step S101 is performed: providing a substrate 10 .

[0065] Specifically, the material of the substrate 10 includes silicon carbide, silicon, silicon nitride, gallium nitride, gallium oxide, aluminum oxide, and aluminum nitride, among which the substrate 10 can specifically be made of silicon carbide to enhance the performance advantages of silicon carbide devices in some parameters. For the specific material of the substrate 10, those skilled in the art can reasonably select it according to actual needs, and no specific limitation is made without application.

[0066] Then, after providing the substrate, as Figures 4 to 5 As shown, proceed to step S102: Figure 4 As shown, a first epitaxial layer 20 is formed on a substrate 10; then, as shown Figure 5 As shown, a plurality of first epitaxial trenches 30 and at least one second epitaxial trench 40 are formed in the first epitaxial layer 20 , wherein the second epitaxial trench 40 is located between any adjacent first epitaxial trenches 30 .

[0067] Specifically, the process of forming the first epitaxial layer 20 includes but is not limited to a deposition process and an epitaxial growth process. In the epitaxial growth process, the doping concentration of impurities is relatively easy to control, and the activation rate is relatively fixed, and the target doping distribution is easy to achieve. It is not only suitable for silicon-based power devices, but also can avoid the difficulty of injection doping of silicon carbide power devices and improve the efficiency of its terminal structure. The deposition process is relatively mature, simple to operate, and has a low cost. Among them, the deposition process includes but is not limited to physical vapor deposition (PVD), chemical vapor deposition (CVD) and atomic layer deposition (ALD). Among them, physical vapor deposition (PVD) includes but is not limited to magnetron sputtering process, reactive sputtering process, DC sputtering process, AC sputtering process, vacuum coating process, arc evaporation process, chemical vapor deposition (CVD) includes but is not limited to plasma enhanced chemical vapor deposition (PECVD), metal organic chemical vapor deposition (MOCVD), laser induced chemical vapor deposition (LCVD), and those skilled in the art can make reasonable selections according to actual needs, and no specific limitation is made without application.

[0068] Specifically, after forming the first epitaxial layer 20, an etching process is used to form a plurality of first epitaxial grooves 30 and at least one second epitaxial groove 40. The etching process includes but is not limited to dry etching (Dry Etching), wet etching (Wet Etching), deep etching (Deep Etching), ion beam etching (IBE) and electrolytic etching, wherein dry etching includes physical etching, chemical vapor etching and plasma etching, and deep etching includes deep reactive ion etching and laser etching. Those skilled in the art can make reasonable selections according to actual needs, and this application does not make specific limitations.

[0069] After forming the first epitaxial trench and the second epitaxial trench, as Figures 6 to 9 As shown, step S103 and step S104 are performed: a first epitaxial structure 31 and a second epitaxial structure 41 are formed.

[0070] Specifically, a first epitaxial structure is formed in the first epitaxial trench, and a second epitaxial structure is formed in the second epitaxial trench. The steps of forming the first epitaxial structure and the second epitaxial structure include: first, as Figure 6 As shown, the second epitaxial material 3111 and the third epitaxial material 4111 are filled in the first epitaxial trench 30 and the second epitaxial trench 40 respectively by an epitaxial growth process, and the second epitaxial material 3111 and the third epitaxial material 4111 both have the second doping type; then, as shown in FIG. Figure 7 As shown, the first trench 3121 and the second trench 4121 are formed in the second epitaxial material and the third epitaxial material respectively by etching process, the remaining second epitaxial material is the second epitaxial layer 311, and the remaining third epitaxial material is the third epitaxial layer 411; then, as shown in Figure 8As shown, a second conductive material is filled in the second trench by a deposition process, and the second conductive material is annealed by an annealing process, and the annealed second conductive material forms a second conductive layer 412; finally, as shown Fig. 9 As shown, a first conductive material is filled in the first trench by a deposition process to form a first conductive layer 312 .

[0071] Specifically, the material of the first epitaxial layer, the second epitaxial material and the third epitaxial material can include silicon carbide, silicon, quartz, silicon nitride, gallium nitride, gallium oxide, aluminum oxide and aluminum nitride, etc. Personnel in the art can make reasonable selections according to actual needs, and no specific limitation is made without application. Exemplarily, the material of the first epitaxial layer, the second epitaxial material and the third epitaxial material are silicon carbide materials, which can improve the problem that the product performance advantage of SiC diode devices in some parameters is not obvious.

[0072] Exemplarily, when etching the first epitaxial trench and the second epitaxial trench, the width of the second epitaxial trench in the first direction is greater than the width of the first epitaxial trench, wherein the first direction is parallel to the surface of the substrate in contact with the first epitaxial layer, the depth of the second epitaxial trench is less than the depth of the first epitaxial trench, and the second direction is perpendicular to the surface of the substrate in contact with the first epitaxial layer. When subsequently forming the first epitaxial structure and the second epitaxial structure, a first epitaxial structure with a deeper depth and a narrower width is formed, and a second epitaxial structure with a shallower depth and a wider width is formed, that is, a Schottky contact structure with a deeper depth and a smaller area is formed, which can increase the discharge area of ​​the Schottky contact and enhance the surge capability of the power diode; in addition, an ohmic contact structure with a shallower depth and a larger area is formed, which can ensure the voltage withstand capability of the power diode and reduce the forward voltage drop of the power diode.

[0073] In another exemplary embodiment, the second doping type is P-type. In order to make the first epitaxial structure form a Schottky contact better and the second epitaxial structure form an ohmic contact, the doping concentration of the third epitaxial material is greater than the doping concentration of the second epitaxial material. Specifically, the doping concentration of the third epitaxial layer is 1×10 17 cm -3 , the doping concentration of the second epitaxial layer is 1×10 16 cm -3 .

[0074] In another exemplary embodiment, the second doping type is P type, the material of the first conductive layer is metallic nickel, the work function of metallic nickel is 4.6eV, and the material of the second conductive layer is metallic titanium, the work function of metallic titanium is 4.33eV, wherein the metallic nickel material forms a Schottky contact with the second epitaxial layer, and the metallic titanium also forms a Schottky contact with the third epitaxial layer, thereby reducing the on-resistance and forward voltage drop of the power diode structure, and the metallic aluminum has good conductivity, thereby improving the current transmission efficiency of the diode structure.

[0075] In some optional embodiments, the temperature of the annealing process is greater than 900°C.

[0076] Specifically, annealing the second conductive layer can eliminate the internal stress of the metal material, improve the ductility of the metal material, remove impurities and defects in the metal material, improve the internal uniformity of the metal material, and reduce the movement of electrons in the second conductive layer. In addition, the annealing temperature is greater than 900°C, so that the second conductive layer and the third epitaxial layer can form an ohmic contact. The annealing temperature is specifically 950°C, 1000°C, 1100°C, 1200°C or 1300°C.

[0077] In some optional embodiments, after forming the first epitaxial structure and the second epitaxial structure, the above preparation method further includes: Figures 10 to 12 As shown, a third conductive layer 50, a fourth conductive layer 60 and a fifth conductive layer 70 are formed.

[0078] Specifically, first, Fig.10 As shown, a deposition process is used to form a third conductive layer 50, and the third conductive layer 50 is located on a side of the substrate structure away from the substrate 10; then, as shown Fig.11 As shown, a fourth conductive layer 60 is formed on the side of the third conductive layer 50 away from the substrate 10 by a deposition process; then, as shown in FIG. Fig.12 As shown, a fifth conductive layer 70 is formed on the side of the substrate 10 away from the first epitaxial layer 20 by a deposition process. The third conductive layer 50 and the second conductive layer 412 can be formed in the same step, or in different steps.

[0079] Wherein, the third conductive layer 50 and the fourth conductive layer 60 are used as a positive electrode together, and the fourth conductive layer 60 is used as a negative electrode; the third conductive layer 50 and the fourth conductive layer 60 are used as a negative electrode together, and the fourth conductive layer 60 is used as a positive electrode, which can form an ohmic contact with the substrate to provide current for the power diode and reduce the on-resistance of the device. In addition, the third conductive layer and the fourth conductive layer both include multiple material layers.

[0080] Exemplarily, the second doping type is P type, the third conductive layer material is metal titanium, and the metal titanium forms a Schottky contact with the first epitaxial layer. The power diode reduces leakage current when working in reverse and can increase the diode voltage. When the power diode works in the forward direction, it can serve as a channel for the diode's on-current; the fourth conductive layer material is metal aluminum, metal aluminum 4.1eV, metal aluminum has good conductivity, and improves the current transmission efficiency of the power diode; the fifth conductive layer includes a three-layer structure of metal titanium, metal nickel and metal silver, and the fifth conductive layer forms an ohmic contact with the substrate to reduce the on-resistance and on-voltage drop of the power diode.

[0081] Specifically, the materials of the first conductive layer, the second conductive layer, the third conductive layer, the fourth conductive layer and the fifth conductive layer include but are not limited to alloy materials composed of any one or more of silver, copper, aluminum, gold, titanium, nickel, platinum and palladium metals. Those skilled in the art can make reasonable selections based on actual needs, and no specific limitation is made without application.

[0082] The power diode formed by the method for preparing the power diode of the present application will be described below in conjunction with an embodiment.

[0083] Example 1

[0084] The method for preparing a power diode provided in this embodiment includes the following steps: Figures 4 to 12 As shown:

[0085] Provide an N-type SiC substrate 10, such as Figure 4 As shown;

[0086] An N-type SiC first epitaxial layer 20 is formed on the N-type SiC substrate 10 by using an epitaxial growth process. Figure 4 As shown;

[0087] The first epitaxial trench 30 and the second epitaxial trench 40 are formed on the N-type SiC first epitaxial layer 20 by etching process. Figure 5 As shown;

[0088] The second epitaxial material 3111 is filled in the first epitaxial trench 30, and the third epitaxial material 4111 is filled in the second epitaxial trench 40 by an epitaxial growth process. Figure 6 As shown;

[0089] The first trench 3121 is formed in the second epitaxial material by etching process, and the second trench 4121 is formed in the third epitaxial material. Figure 7 As shown;

[0090] A deposition process is used to fill metal nickel in the second trench, and an annealing process is used to anneal the metal nickel at a temperature of 1000° C. to form a second conductive layer 412. Figure 8 As shown;

[0091] A deposition process is used to fill metal titanium in the first trench to form a first conductive layer 312. Fig. 9 As shown;

[0092] A deposition process is used to continue depositing metal titanium on the substrate structure to form a third conductive layer 50. Fig.10 As shown;

[0093] A deposition process is used to continue to deposit metal aluminum on the third conductive layer 50 to form a fourth conductive layer 60. Fig.11 As shown;

[0094] A deposition process is used to sequentially deposit metal titanium, metal nickel and metal silver on the side of the substrate 10 away from the first epitaxial layer 20 to form a fifth conductive layer 70. Fig.12 shown.

[0095] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0096] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A power diode, characterized in that: The power diode comprises a substrate and a first epitaxial layer on the substrate, wherein the first epitaxial layer has a first doping type, the first epitaxial layer has a plurality of first epitaxial trenches and at least one second epitaxial trench on a side away from the substrate, and the second epitaxial trench is located between any adjacent first epitaxial trenches, and the power diode further comprises: A plurality of first epitaxial structures, wherein the first epitaxial structure is located in the first epitaxial trench, the first epitaxial structure comprises a second epitaxial layer and a first conductive layer, the second epitaxial layer is located on an inner surface of the first epitaxial trench, the first conductive layer is located in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact; At least one second epitaxial structure, the second epitaxial structure is located in the second epitaxial trench, the second epitaxial structure includes a third epitaxial layer and a second conductive layer, the third epitaxial layer is located on the inner surface of the second epitaxial trench, and the second conductive layer is located in the second epitaxial trench, wherein the first conductive layer and the second conductive layer have different conductive materials, the third epitaxial layer has the second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact.

2. The power diode according to claim 1, characterized in that: The width of the second epitaxial trench is greater than the width of the first epitaxial trench in a first direction, wherein the first direction is parallel to a surface of the substrate contacting the first epitaxial layer.

3. The power diode according to claim 1, characterized in that: A depth of the second epitaxial trench in a second direction is less than a depth of the first epitaxial trench, wherein the second direction is perpendicular to a surface of the substrate contacting the first epitaxial layer.

4. The power diode according to any one of claims 1 to 3, characterized in that: The second doping type is P type, the work function of the first conductive layer is smaller than the work function of the second epitaxial layer, and the work function of the second conductive layer is larger than the work function of the third epitaxial layer; the second doping type is N type, the work function of the first conductive layer is larger than the work function of the second epitaxial layer, and the work function of the second conductive layer is smaller than the work function of the third epitaxial layer.

5. The power diode according to claim 1, characterized in that: Also includes: A third conductive layer is located on a side of the first epitaxial layer away from the substrate, and the third conductive layer and the first conductive layer have the same conductive material.

6. The power diode according to claim 5, characterized in that: Also includes: A fourth conductive layer, wherein the fourth conductive layer is at least located on a side of the third conductive layer facing away from the substrate.

7. The power diode according to claim 1, characterized in that: The doping concentrations of the second epitaxial layer and the third epitaxial layer are both 1×10 15 cm -3 ~1×10 18 cm -3 , the second doping type is P type, the doping concentration of the second epitaxial layer is greater than the doping concentration of the third epitaxial layer, and the second doping type is N type, the doping concentration of the second epitaxial layer is less than the doping concentration of the third epitaxial layer.

8. A method for preparing a power diode, characterized in that: Used to prepare the power diode according to any one of claims 1 to 7, the preparation method comprising: providing a substrate; Forming a first epitaxial layer on the substrate, and forming a plurality of first epitaxial trenches and at least one second epitaxial trench in the first epitaxial layer, wherein the second epitaxial trench is located between any adjacent first epitaxial trenches; Forming a first epitaxial structure in the first epitaxial trench, the first epitaxial structure comprising a second epitaxial layer and a first conductive layer, the second epitaxial layer being located on an inner surface of the first epitaxial trench, the first conductive layer being located in the first epitaxial trench, wherein the second epitaxial layer has a second doping type, and the second epitaxial layer and the first conductive layer form a Schottky contact; A second epitaxial structure is formed in the second epitaxial trench, the second epitaxial structure comprising a third epitaxial layer and a second conductive layer, the third epitaxial layer is located on the inner surface of the second epitaxial trench, the second conductive layer is located in the second epitaxial trench, wherein the first conductive layer and the second conductive layer have different conductive materials, the third epitaxial layer has the second doping type, and the third epitaxial layer and the second conductive layer form an ohmic contact.

9. The preparation method according to claim 8, characterized in that: The steps of forming the first epitaxial structure and the second epitaxial structure include: Filling the first epitaxial trench and the second epitaxial trench with a second epitaxial material and a third epitaxial material respectively by an epitaxial growth process, wherein the second epitaxial material and the third epitaxial material both have the second doping type; Using an etching process to form a first trench and a second trench in the second epitaxial material and the third epitaxial material respectively, the remaining second epitaxial material is the second epitaxial layer, and the remaining third epitaxial material is the third epitaxial layer; Filling the second trench with a second conductive material using a deposition process, annealing the second conductive material using an annealing process, and forming the second conductive layer with the annealed second conductive material; A first conductive material is filled in the first trench by a deposition process to form the first conductive layer.

10. The preparation method according to claim 9, characterized in that: The temperature of the annealing process is greater than 900°C.

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