Silicon carbide ohmic contact preparation method and silicon carbide device preparation method

Abstract

The invention relates to the technical field of semiconductors, and discloses a silicon carbide ohmic contact preparation method and a silicon carbide device preparation method.The silicon carbide ohmic contact preparation method comprises the steps that a silicon carbide substrate is provided, the silicon carbide substrate is provided with a first surface and a second surface which are oppositely arranged, and the first surface is provided with a doped region; performing conductive impurity doping on the doped region to form a doped layer; performing texturing on the surface of one side, deviating from the silicon carbide substrate, of the doping layer to form a textured layer; a carbon layer is formed on the side, away from the surface, of the suede layer, the first surface is covered with the carbon layer, and annealing treatment is carried out; the carbon layer is removed; forming a metal layer on the surface of one side, deviating from the silicon carbide substrate, of the suede layer by adopting a vacuum growth process; wherein the vacuum degree of the vacuum growth process is greater than or equal to 10E-10torr. Conductive impurities in the doped layer can reduce contact resistance. The first surface is textured, so that ohmic contact resistance can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for preparing a silicon carbide ohmic contact and a method for preparing a silicon carbide device. Background Art

[0002] Silicon carbide material is a wide bandgap semiconductor with excellent performance. Silicon carbide not only has wide bandgap, high breakdown voltage, high saturation electron velocity, and high thermal conductivity, but also has excellent physical and chemical stability, strong radiation resistance and mechanical strength. Therefore, it has been widely used in the field of high temperature, high frequency, and high power electronic devices.

[0003] When the metal-semiconductor contact has a linear current-voltage relationship, or its contact resistance is negligible relative to the semiconductor body, it is called an ohmic contact. The quality of the ohmic contact directly affects the efficiency, gain, and switching speed of the silicon carbide device. Therefore, preparing a good silicon carbide ohmic contact is the basis for improving the performance and reliability of silicon carbide devices.

[0004] However, due to the large semiconductor band gap of silicon carbide, there are very few metals with a low enough work function to obtain a low barrier, and the influence of the surface state of silicon carbide, making a good silicon carbide ohmic contact is much more difficult than other semiconductors. Summary of the invention

[0005] In view of this, the present invention provides a method for preparing a silicon carbide ohmic contact and a method for preparing a silicon carbide device, so as to solve the existing problem that the semiconductor band gap width of silicon carbide is large, there are very few metals with a sufficiently low work function to obtain a low barrier, and the influence of the silicon carbide surface state makes it much more difficult to prepare a good silicon carbide ohmic contact than other semiconductors.

[0006] In a first aspect, the present invention provides a method for preparing a silicon carbide ohmic contact, comprising:

[0007] Providing a silicon carbide substrate, the silicon carbide substrate having a first surface and a second surface arranged opposite to each other, the first surface having a doped region;

[0008] doping the doped region with conductive impurities to form a doped layer;

[0009] Performing texturing on a surface of a side of the doped layer facing away from the silicon carbide substrate to form a texturing layer;

[0010] forming a carbon layer on a surface of the suede layer that is away from the silicon carbide substrate, the carbon layer covering the first surface, and performing an annealing treatment;

[0011] removing the carbon layer;

[0012] Forming a metal layer on a surface of the suede layer that is away from the silicon carbide substrate by using a vacuum growth process;

[0013] Wherein, the vacuum degree of the vacuum growth process is greater than or equal to 10E-10 torr.

[0014] Beneficial effects: The conductive impurities in the doping layer can reduce its resistance and increase the current density of the doping layer, thereby reducing the barrier's hindering effect on carriers, so as to reduce the ohmic contact resistance between the metal layer and the doping layer. By velveting the first surface to increase the surface area of ​​the first surface, the contact area between the metal layer and the first surface is increased, which is beneficial to reduce the ohmic contact between the silicon carbide substrate and the metal layer. In addition, since the vacuum growth process is carried out in a vacuum, it effectively avoids contamination by other impurities, which is beneficial to improve the quality and purity of the metal layer, thereby reducing the ohmic contact resistance. In the process of preparing the metal layer, the vacuum growth process can control the movement trajectory of metal atoms so that the metal atoms are tightly combined with the velvet layer, so that the metal atoms are in better contact with the velvet layer, further reducing the ohmic contact resistance. Annealing is used to activate the conductive impurities in the doping layer, and the carbon layer is used to reduce the escape of silicon in the silicon carbide substrate during annealing.

[0015] In an optional embodiment, the doping concentration of the doping layer close to the first surface is greater than the doping concentration close to the second surface.

[0016] Beneficial effects: The portion of the doping layer with relatively low doping concentration can slow down the carrier transmission efficiency to reduce interface defects, thereby reducing the recombination loss at the interface with the metal layer. In addition, the portion of the doping layer with relatively high doping concentration can reduce the ohmic contact resistance between the metal layer and the metal layer to reduce resistance loss.

[0017] In an optional embodiment, the doping region near the first surface is doped with conductive impurities by ion implantation, wherein the conductive impurities are pentavalent elements or trivalent elements, and the concentration of the conductive impurities implanted is 3E14-5E15cm -2 The electric energy of the conductive impurities injected is 5 to 30 KeV.

[0018] Beneficial effects: Conductive impurities can be injected into the portion of the doped region close to the first surface through the ion implantation process to increase the carrier concentration of the portion of the doped region close to the first surface. In addition, the ion implantation process can accurately control the doping concentration by adjusting the energy and number of ions. The ion implantation process can also achieve uniform doping over a large area and improve the preparation efficiency. In addition, the ion implantation process can reduce the entry of harmful substances into silicon carbide and ensure the purity of the doping.

[0019] In an optional embodiment, the doping region near the second surface is doped with conductive impurities by an ion implantation process, wherein the conductive impurities are pentavalent elements or trivalent elements, and the concentration of the conductive impurities implanted is 3E11-5E13cm -2 The electric energy of the conductive impurities injected is 50 to 300 KeV.

[0020] Beneficial effect: By injecting conductive impurities into the part of the doped region close to the second surface through an ion implantation process, the part with relatively low doping concentration in the doped layer can slow down the transmission efficiency of carriers to reduce interface defects, thereby reducing the recombination loss at the interface with the metal layer.

[0021] In an optional implementation, a dry etching process is used to texture the surface of the doping layer on a side facing away from the silicon carbide substrate.

[0022] Beneficial effects: The dry etching process can significantly improve the efficiency of the velvet production. The dry etching process can accurately control the depth and uniformity of the etching, and the dry etching process reduces the use of chemicals, thereby reducing the use and processing costs of chemicals. In addition, the dry etching process has good stability and can ensure the stability of the prepared velvet structure.

[0023] In an optional embodiment, the material of the metal layer includes one or more of nickel, vanadium, and titanium.

[0024] Beneficial effects: Nickel, vanadium, and titanium all have good electrical conductivity, ensuring smooth transmission of current between the metal layer and the silicon carbide substrate, reducing energy loss. Nickel, vanadium, and titanium all have good chemical stability and are not easily oxidized or corroded, ensuring the reliability of ohmic contact. In addition, the work function of nickel, vanadium, and titanium is similar to that of silicon carbide, so that a lower barrier height can be formed at the contact interface between silicon carbide and the metal layer, thereby effectively reducing the ohmic contact resistance.

[0025] In an optional implementation, the carbon layer is formed on a surface of the suede layer that is away from the silicon carbide substrate by using a DC magnetron sputtering method.

[0026] Beneficial effects: DC magnetron sputtering has a high deposition rate and can increase the rate of carbon layer formation. In addition, DC sputtering can form a high-purity carbon layer with good uniformity, thereby improving the quality of the carbon layer and improving the anti-silicon escape effect of the carbon layer.

[0027] In an optional embodiment, the carbon layer has a thickness of 10 nm-200 nm.

[0028] In an optional embodiment, the thickness of the metal layer is 10 nm-200 nm.

[0029] The present invention also provides a method for preparing a silicon carbide device, including the above-mentioned method for preparing the silicon carbide ohmic contact.

[0030] The silicon carbide ohmic contact preparation method is used to prepare silicon carbide devices, which can form good ohmic contacts to reduce the power consumption of silicon carbide devices, and can improve the current transmission capacity at the interface between silicon carbide and metal to improve the carrying capacity of silicon carbide devices, which helps to achieve higher power density. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 Schematic diagram of the structure of a silicon carbide substrate in the preparation of a silicon carbide ohmic contact in an embodiment of the present invention;

[0033] Figure 2 It is a schematic structural diagram of a silicon carbide substrate and a doping layer in the preparation of a silicon carbide ohmic contact in an embodiment of the present invention;

[0034] Figure 3 It is a schematic structural diagram of a silicon carbide substrate, a doping layer, and a suede layer in the preparation of a silicon carbide ohmic contact in an embodiment of the present invention;

[0035] Figure 4 It is a schematic structural diagram of a silicon carbide substrate, a doping layer, a suede layer, and a carbon layer in the preparation of a silicon carbide ohmic contact in an embodiment of the present invention;

[0036] Figure 5 It is a schematic structural diagram of a silicon carbide substrate, a doping layer, a suede layer, and a metal layer in the preparation of a silicon carbide ohmic contact in an embodiment of the present invention;

[0037] Description of reference numerals:

[0038] 101, silicon carbide substrate; 1011, first surface; 1012, second surface; 1013, doped region; 102, suede layer; 103, carbon layer; 104, metal layer. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only some structures related to the present invention are shown in the accompanying drawings, rather than all structures. In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. In addition, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0040] When the metal-semiconductor contact has a linear current-voltage relationship, or its contact resistance is negligible relative to the semiconductor body, it is called an ohmic contact. The quality of the ohmic contact directly affects the efficiency, gain, and switching speed of silicon carbide devices. Therefore, preparing a good silicon carbide ohmic contact is the basis for improving the performance and reliability of silicon carbide devices. Due to the large semiconductor bandgap of silicon carbide, and the very few metals with a low enough work function to obtain a low barrier, coupled with the influence of the surface state of silicon carbide, it is much more difficult to prepare a good silicon carbide ohmic contact than other semiconductors.

[0041] Therefore, the embodiment of the present invention provides a method for preparing an ohmic contact of silicon carbide, wherein the conductive impurities in the doping layer can reduce its resistance and increase the current density of the doping layer to reduce the ohmic contact resistance between the metal layer 104 and the doping layer. The first surface 1011 is textured to increase the contact area between the metal layer 104 and the first surface 1011, thereby facilitating the reduction of the ohmic contact between the silicon carbide substrate 101 and the metal layer 104. The metal layer 104 is formed by a vacuum growth process, thereby avoiding contamination by other impurities, improving the quality and purity of the metal layer 104, and thus reducing the ohmic contact resistance.

[0042] An embodiment of the present invention provides a method for preparing a silicon carbide ohmic contact, such as Figures 1 to 5 As shown, the following steps are included:

[0043] S101, such as Figure 1As shown, a silicon carbide substrate 101 is provided. The silicon carbide substrate 101 has a first surface 1011 and a second surface 1012 that are opposite to each other. The first surface 1011 is provided with a doping region 1013 .

[0044] Specifically, the material of the silicon carbide substrate 101 may be silicon carbide or an isomer of silicon carbide or N-type doped silicon carbide or P-type doped silicon carbide, and the doped region 1013 is a region where an ohmic contact needs to be formed, or the doped region 1013 includes an ohmic contact region.

[0045] S102 , cleaning the silicon carbide substrate 101 .

[0046] Specifically, the silicon carbide substrate 101 is cleaned with sulfuric acid and hydrogen peroxide solution and then dried to improve the cleanliness of the surface of the silicon carbide substrate 101 and to improve the adhesion of other structures on the surface of the silicon carbide substrate 101 .

[0047] S103, such as Figure 2 As shown, the doping region 1013 is doped with conductive impurities to form a doping layer.

[0048] Specifically, first, the doping region 1013 near the second surface 1012 is doped with conductive impurities by an ion implantation process, wherein the concentration of the conductive impurities implanted is 3E11-5E13cm -2 The electric energy of the conductive impurity injection is 50-300 KeV. Then, the conductive impurity is injected into the doped region 1013 near the first surface 1011 by ion implantation, wherein the concentration of the conductive impurity injection is 3E14-5E15 cm -2, the electric energy of the conductive impurity injection is 5 to 30 KeV. The doping concentration of the doping layer close to the first surface 1011 is greater than the doping concentration close to the second surface 1012. The relatively low doping concentration portion of the doping layer can slow down the carrier transmission efficiency to reduce interface defects, thereby reducing the recombination loss at the interface with the metal layer 104. In addition, the relatively high doping concentration portion of the doping layer can reduce the ohmic contact resistance between the metal layer 104 and the metal layer 104 to reduce resistance loss. The ion implantation process can accurately control the doping concentration by adjusting the energy and number of ions. The ion implantation process can also achieve uniform doping over a large area and improve the preparation efficiency. In addition, the ion implantation process can reduce the entry of harmful substances into silicon carbide and ensure the purity of the doping. By setting the surface injection electric energy to 5 to 30 KeV, it can be ensured that the injected conductive impurities are concentrated on the silicon carbide surface, which is beneficial to reducing ohmic contact. The conductive impurities are pentavalent elements or trivalent elements, the pentavalent elements are one or more of phosphorus, arsenic, antimony, and bismuth, and the trivalent elements are one or more of boron, aluminum, and gallium. The conductivity type of the conductive impurities can be set as needed. Preferably, the conductivity type of the conductive impurities is the same as the conductivity type of the adjacent material to ensure the smooth flow of carriers.

[0049] In an alternative embodiment, an etching process and a vapor deposition process may also be used to form a doping layer. Specifically, a mask dielectric layer is deposited in the doping region 1013, the mask dielectric layer outside the doping region 1013 is removed by photolithography to expose the doping region 1013, the doping region 1013 is selectively etched to form a groove, and silicon carbide doped with conductive impurities is epitaxially grown in the groove by a vapor deposition process to form a doping layer, and then the mask dielectric layer is removed.

[0050] S104, such as Figure 3 As shown, a surface of the doped layer facing away from the silicon carbide substrate 101 is textured to form a texture layer 102 .

[0051] Specifically, a dry etching process is used to texture the surface of the doped layer on the side away from the silicon carbide substrate 101. The dry etching process can significantly improve the efficiency of texture, and the dry etching process can accurately control the depth and uniformity of etching, and the dry etching reduces the use of chemicals, thereby reducing the use and processing costs of chemicals. In addition, the dry etching process has good stability, which can ensure the stability of the prepared texture structure.

[0052] S105, such as Figure 4 As shown, a carbon layer 103 is formed on the surface of the suede layer 102 which is away from the silicon carbide substrate 101, the carbon layer covers the first surface, and an annealing treatment is performed.

[0053] Specifically, a carbon layer 103 is formed on the surface of the velvet layer 102 away from the silicon carbide substrate by a DC magnetron sputtering method. The thickness of the carbon layer is 10-200nm. The specific thickness and actual needs can be selected. It should be noted that the deposition power of the above-mentioned DC magnetron sputtering method is 100W, the deposition rate is 2.4nm / s, and the chamber vacuum is less than 6e-6mTorr. The DC magnetron sputtering method has a high deposition rate, which can increase the formation rate of the carbon layer 103. In addition, DC sputtering can form a high-purity carbon layer, and the formed carbon layer has good uniformity. It should be noted that the carbon layer covers the velvet layer and covers the area of ​​the first surface outside the velvet layer. After the carbon layer is formed, annealing treatment is performed. The annealing treatment is used to activate the conductive impurities in the doping layer. The carbon layer is to reduce the silicon escape of the silicon carbide substrate 101 during annealing. In an alternative embodiment, the carbon layer 103 can be formed by a vapor deposition process.

[0054] S106, using a dry etching process to remove the carbon layer, and then using a vacuum growth process to form a metal layer 104 on a surface of the suede layer 102 that is away from the silicon carbide substrate; wherein the vacuum degree of the vacuum growth process is greater than or equal to 10E-10 torr.

[0055] Specifically, the carbon layer is etched and removed by a dry etching process, and then the metal layer 104 is formed by an ultra-vacuum metal growth process. In an ultra-vacuum environment, metal atoms are deposited on the velvet layer 102 by evaporation, sputtering or ion plating. Due to the extremely high vacuum degree, there is almost no interference from gas molecules or impurities, so the metal atoms can be directly and orderly deposited on the velvet layer 102 to form a uniform and dense metal layer 104, wherein the vacuum value is greater than 10E-10torr, and the thickness of the metal layer 104 is 10-200nm. The ultra-vacuum metal growth process includes one of molecular beam epitaxy, electron beam evaporation, magnetron sputtering, and vacuum metallization coating. Since the vacuum growth process is carried out in a vacuum, the contamination of other impurities is effectively avoided, which is conducive to improving the quality and purity of the metal layer 104, thereby reducing the ohmic contact resistance. In the process of preparing the metal layer 104, the vacuum growth process can control the movement trajectory of the metal atoms so that the metal atoms are tightly combined with the velvet layer 102, so that the metal atoms are in better contact with the velvet layer 102, thereby further reducing the ohmic contact resistance. The material of the metal layer 104 includes one or more of nickel, vanadium, and titanium. Preferably, in this embodiment, the metal layer 104 uses nickel, which has good electrical conductivity, ensuring the smooth transmission of current between the metal layer 104 and the silicon carbide substrate 101, and reducing energy loss. And nickel has good chemical stability, is not easy to oxidize or corrode, and ensures the reliability of ohmic contact. In addition, the work function of nickel is similar to that of silicon carbide, so that a lower barrier height can be formed at the contact interface between the silicon carbide substrate and the metal layer, thereby effectively reducing the ohmic contact resistance.

[0056] It should be noted that the metal layer may only cover the suede layer. Of course, the metal layer may also cover the area of ​​the first surface except the suede layer.

[0057] In this embodiment, the conductive impurities in the doping layer can reduce its resistance and increase the current density of the doping layer, thereby reducing the barrier's blocking effect on carriers, so as to reduce the ohmic contact resistance between the metal layer 104 and the doping layer. By making the first surface 1011 velvet to increase the surface area of ​​the first surface 1011, the contact area between the metal layer 104 and the first surface 1011 is increased, which is conducive to reducing the ohmic contact between the silicon carbide substrate 101 and the metal layer 104. In addition, since the vacuum growth process is carried out in a vacuum, the contamination of other impurities is effectively avoided, which is conducive to improving the quality and purity of the metal layer 104, thereby reducing the ohmic contact resistance. In the process of preparing the metal layer 104, the vacuum growth process can control the movement trajectory of the metal atoms so that the metal atoms are tightly combined with the velvet layer 102, so that the metal atoms are in better contact with the velvet layer 102, thereby further reducing the ohmic contact resistance.

[0058] In a second aspect, the present invention also provides a method for preparing a silicon carbide device, including the above-mentioned method for preparing a silicon carbide ohmic contact. The silicon carbide device is one of a Schottky diode, a field effect transistor or other silicon carbide devices. The silicon carbide ohmic contact preparation method is used to prepare the silicon carbide device, which can form a good ohmic contact to reduce the power consumption of the silicon carbide device, and can improve the current transmission capacity at the interface between silicon carbide and metal, so as to improve the carrying capacity of the silicon carbide device, which helps to achieve a higher power density.

[0059] In the above description, the technical details of the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0060] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for preparing a silicon carbide ohmic contact, characterized in that: include: Providing a silicon carbide substrate (101), wherein the silicon carbide substrate (101) has a first surface (1011) and a second surface (1012) arranged opposite to each other, and the first surface (1011) has a doped region (1013); Doping the doped region (1013) with conductive impurities to form a doped layer; Performing texturing on a surface of a side of the doped layer facing away from the silicon carbide substrate (101) to form a texturing layer (102); forming a carbon layer (103) on a surface of the suede layer (102) facing away from the silicon carbide substrate (101), the carbon layer covering the first surface, and performing an annealing treatment; removing the carbon layer; Using a vacuum growth process to form a metal layer (104) on a surface of the suede layer (102) that is away from the silicon carbide substrate (101); Wherein, the vacuum degree of the vacuum growth process is greater than or equal to 10E-10 torr.

2. The method for preparing a silicon carbide ohmic contact according to claim 1, characterized in that: The doping concentration of the doping layer close to the first surface (1011) is greater than the doping concentration close to the second surface (1012).

3. The method for preparing a silicon carbide ohmic contact according to claim 2, characterized in that: The doping region (1013) near the first surface (1011) is doped with conductive impurities by an ion implantation process, wherein the conductive impurities are pentavalent elements or trivalent elements, and the implantation concentration of the conductive impurities is 3E14-5E15cm -2 The electric energy of the conductive impurities injected is 5 to 30 KeV.

4. The method for preparing silicon carbide ohmic contact according to claim 3, characterized in that: The doping region (1013) near the second surface (1012) is doped with conductive impurities by an ion implantation process, wherein the conductive impurities are pentavalent elements or trivalent elements, and the implantation concentration of the conductive impurities is 3E11-5E13cm -2 The electric energy of the conductive impurities injected is 50 to 300 KeV.

5. The method for preparing silicon carbide ohmic contact according to claim 1, characterized in that: A dry etching process is used to texture the surface of the doped layer on one side facing away from the silicon carbide substrate (101).

6. The method for preparing silicon carbide ohmic contact according to claim 1, characterized in that: The material of the metal layer (104) includes one or more of nickel, vanadium and titanium.

7. The method for preparing a silicon carbide ohmic contact according to claim 1, characterized in that: The carbon layer (103) is formed on a surface of the suede layer (102) that is away from the silicon carbide substrate (101) by using a direct current magnetron sputtering method.

8. The method for preparing a silicon carbide ohmic contact according to claim 1, characterized in that: The thickness of the carbon layer (103) is 10nm-200nm.

9. The method for preparing a silicon carbide ohmic contact according to claim 1, characterized in that: The thickness of the metal layer (104) is 10nm-200nm.

10. A method for preparing a silicon carbide device, characterized in that: A method for preparing a silicon carbide ohmic contact comprising the method described in any one of claims 1 to 8.

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