Silicon carbide device manufacturing method

Abstract

The invention discloses a silicon carbide device manufacturing method, which is used for executing the following pretreatment steps on an area needing ohmic contact manufacturing, and comprises the following steps: pretreatment: cleaning the area needing ohmic contact manufacturing on a silicon carbide surface, and exposing the clean silicon carbide surface; depositing a metal film on the surface of the silicon carbide; silicide annealing is carried out under the atmosphere of inert gas or vacuum, a carbon-containing silicide layer is obtained, and the carbon-containing silicide layer is rich in free carbon; cleaning and removing the residual metal film; after-treatment annealing is carried out under the supercritical carbon dioxide atmosphere, a low-carbon silicide layer is obtained, and the low-carbon silicide layer contains trace free carbon; and post-processing: cleaning to remove surface impurities, and exposing the clean surface of the low-carbon silicide layer, so as to grow contact metal on the surface and complete a subsequent device manufacturing process. The semiconductor device has the advantage that the reliability of the semiconductor device can be improved.

Description

Technical Field

[0001] The present application relates to the semiconductor field, and in particular to a method for manufacturing a silicon carbide device. Background Art

[0002] As a new type of compound semiconductor material, silicon carbide (SiC) has the characteristics of large bandgap (three times that of Si), high thermal conductivity (three times that of Si), high saturated electron drift velocity (twice that of Si) and high breakdown field strength (eight times that of Si) compared with traditional silicon (Si) materials. Especially in the power device market, SiC devices have very broad application prospects.

[0003] However, in the manufacturing process of SiC power devices, the manufacturing process of electrodes has always been the focus and difficulty. Sufficiently strong contact needs to be ensured between the lead or the back metal film and the silicon carbide substrate to form a reliable ohmic contact. However, in the actual manufacturing process, the annealing process will form carbon-containing silicides, in which the carbon can be in the form of free elements (including various allotropes of carbon such as graphite, graphene, etc.) or multi-component compounds such as metal carbon silicides. These can be collectively referred to as free carbon. The presence of free carbon will affect the firmness of the ohmic contact between the lead or the back metal film and the silicon carbide substrate (more specifically, the carbon-containing silicide), which may cause the lead or the back metal film to fall off, reducing the reliability of the semiconductor device. Summary of the invention

[0004] In order to solve the above problems in the prior art, the present invention provides a method for manufacturing a silicon carbide device.

[0005] In a first aspect, the present invention provides a method for manufacturing a silicon carbide device, wherein the following pretreatment steps are performed on a region where an ohmic contact is to be manufactured, including:

[0006] Pre-treatment, cleaning the area on the silicon carbide surface where ohmic contact needs to be made to expose the clean silicon carbide surface;

[0007] Depositing a metal film on the surface of the silicon carbide;

[0008] Performing silicide annealing in an inert gas atmosphere or in a vacuum to obtain a carbon-containing silicide layer, wherein the carbon-containing silicide layer is rich in free carbon;

[0009] Cleaning to remove residual metal film;

[0010] Post-treatment annealing is performed in a supercritical carbon dioxide atmosphere to obtain a low-carbon silicide layer, wherein the low-carbon silicide layer contains a trace amount of free carbon;

[0011] Post-processing includes cleaning to remove surface impurities and expose the clean surface of the low-carbon silicide layer so as to grow contact metal on the surface and complete subsequent device manufacturing processes.

[0012] In a possible implementation of the first aspect above, the pretreatment is used to remove contamination and oxides and other substances on the surface of silicon carbide, and the treatment method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

[0013] In a possible implementation of the first aspect, the manufacturing method further includes: the inert gas includes nitrogen, argon, helium, neon and a combination thereof.

[0014] In a possible implementation of the first aspect above, the manufacturing method above also includes: the supercritical carbon dioxide atmosphere is an atmosphere with a temperature greater than 31.265°C and a pressure greater than 72.9 atmospheres, and the post-processing annealing includes conventional heating annealing, rapid thermal annealing, laser annealing and a combination thereof.

[0015] In a possible implementation of the first aspect above, the above manufacturing method also includes: depositing a metal film in the area on the surface of the silicon carbide where the ohmic contact needs to be made, and the material of the metal film includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, vanadium V, chromium Cr, cobalt Co, and platinum Pt.

[0016] In a possible implementation of the first aspect above, the above manufacturing method also includes: depositing a metal film in the area on the silicon carbide surface where the ohmic contact needs to be made, the deposition method includes physical or chemical vapor deposition methods such as evaporation, sputtering or chemical reaction, and the deposition thickness is 1 nanometer to 1 micrometer.

[0017] In a possible implementation of the first aspect above, the above manufacturing method also includes: the post-processing is used to remove contamination and oxides on the surface of metal silicide and silicon carbide, and the processing method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

[0018] In a possible implementation of the first aspect, the manufacturing method further includes: the post-treatment annealing step in a supercritical carbon dioxide atmosphere can be repeatedly performed multiple times.

[0019] In a second aspect, the present invention further provides a method for manufacturing a silicon carbide device, wherein the following pretreatment steps are performed on the area where the ohmic contact needs to be manufactured, including:

[0020] Pre-treatment, cleaning the area on the silicon carbide surface where ohmic contact needs to be made to expose the clean silicon carbide surface;

[0021] Depositing a metal film on the surface of the silicon carbide;

[0022] Annealing is performed in a supercritical carbon dioxide atmosphere to directly obtain a low-carbon silicide layer, wherein the low-carbon silicide layer contains a trace amount of free carbon;

[0023] Post-processing removes the residual metal film to expose the clean surface of the low-carbon silicide layer, so as to grow contact metal on the surface and complete subsequent device manufacturing processes.

[0024] In a possible implementation of the second aspect above, the pre-treatment is used to remove contamination and oxides on the surface of silicon carbide, and the treatment method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

[0025] In a possible implementation of the second aspect above, the manufacturing method above also includes: the supercritical carbon dioxide atmosphere is an atmosphere with a temperature greater than 31.265°C and a pressure greater than 72.9 atmospheres, and the annealing treatment includes conventional heating annealing, rapid thermal annealing, laser annealing and a combination thereof.

[0026] In a possible implementation of the second aspect above, the manufacturing method above also includes: depositing a metal film in the area on the surface of the silicon carbide where the ohmic contact needs to be made, wherein the material of the metal film includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, vanadium V, chromium Cr, cobalt Co, and platinum Pt.

[0027] In a possible implementation of the second aspect above, the manufacturing method above also includes: depositing a metal film in the area on the silicon carbide surface where the ohmic contact needs to be made, the deposition method including physical or chemical vapor deposition methods such as evaporation, sputtering or chemical reaction, and the deposition thickness is 1 nanometer to 1 micrometer.

[0028] In a possible implementation of the second aspect above, the manufacturing method above also includes: the post-processing is used to remove contamination and oxides on the surface of metal silicide and silicon carbide, and the processing method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

[0029] In a possible implementation of the second aspect, the manufacturing method further includes: the annealing step in a supercritical carbon dioxide atmosphere can be repeatedly performed multiple times.

[0030] Compared with the prior art, the present invention utilizes the good fluidity of supercritical carbon dioxide fluid to actively penetrate into the molecular gap of silicide and fully contact with free carbon, so that carbon dioxide can react with free carbon to generate carbon monoxide, and carbon monoxide can be separated from silicide in liquid or gaseous form, thereby removing free carbon from silicide. The bonding degree between silicide and metal film after free carbon is removed is greatly improved, thereby improving the reliability of semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A comparison of the breakdown voltages of two materials, silicon (Sillcon) and silicon carbide (SiC) is shown;

[0032] Figure 2a A schematic diagram of the structure of a planar silicon carbide VDMOS produced by a conventional process is shown;

[0033] Figure 2b A schematic diagram of the structure of a planar silicon carbide IGBT produced by conventional technology is shown;

[0034] Figure 2c A schematic diagram of the structure of a trench-type silicon carbide VDMOS produced by a conventional process is shown;

[0035] Figure 2d A schematic diagram of the structure of a trench silicon carbide IGBT produced by a conventional process is shown;

[0036] Figure 3a The production process of traditional craft is shown;

[0037] Figure 3b A diagram showing a wafer where a metal film has fallen off due to unstable bonding between the metal film and silicide;

[0038] Figure 4a A production process according to the manufacturing method proposed in this application is shown;

[0039] Figure 4b Another production process according to the manufacturing method proposed in this application is shown;

[0040] Figure 5a A schematic structural diagram of a planar silicon carbide VDMOS produced according to the manufacturing method proposed in this application is shown;

[0041] Figure 5b A schematic diagram of the structure of a planar silicon carbide IGBT produced according to the manufacturing method proposed in this application is shown;

[0042] Figure 5c A schematic structural diagram of a trench silicon carbide VDMOS produced according to the manufacturing method proposed in this application is shown;

[0043] Figure 5d A schematic structural diagram of a trench silicon carbide IGBT produced according to the manufacturing method proposed in this application is shown. DETAILED DESCRIPTION

[0044] Illustrative embodiments of the present application include, but are not limited to, methods of fabricating silicon carbide devices.

[0045] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0046] The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms of "a", "said" and "the" used in this application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used in this article refers to and includes any or all possible combinations of one or more associated listed items. "Include" or "include" and similar words mean that the elements or objects appearing in front of "include" or "include" cover the elements or objects listed after "include" or "include" and their equivalents, and do not exclude other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, and can include electrical connections, whether direct or indirect.

[0047] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0048] The embodiments of the present application will be described in further detail below in conjunction with the accompanying drawings.

[0049] As described in the background art, silicon carbide (SiC), as a new type of material, has many advantages over silicon (Sillcon) material.

[0050] First, the electron breakdown field strength of silicon carbide is eight times that of silicon. Figure 1 A comparison chart of the breakdown voltages of two materials, silicon (Sillcon) and silicon carbide (SiC), used to manufacture semiconductor devices is shown. A higher electron breakdown field strength brings a higher breakdown voltage to the semiconductor device. As can be seen from the figure, the breakdown voltage of semiconductor devices made of silicon carbide materials is much higher than the breakdown voltage of semiconductor devices made of silicon materials. Therefore, under the condition of increasing the doping density, the width of the drift region of the silicon carbide power device can be reduced, thereby reducing the size of the semiconductor device. According to Figure 1 As shown, it can be further seen that the performance of silicon carbide VDMOS devices and silicon carbide IGBT devices is more ideal. According to some data comparisons in the industry, silicon carbide power devices, especially silicon carbide VDMOS devices and silicon carbide IGBT devices, are the next generation of devices that will replace the previous generation of silicon VDMOS devices and silicon IGBT devices. They are key devices for achieving energy conservation and emission reduction goals such as carbon peak and carbon neutrality.

[0051] Let's continue to compare the two materials of silicon (Sillcon) and silicon carbide (SiC). Silicon carbide is a complex of atoms rather than a single crystal. The physical properties of silicon carbide depend on the arrangement structure of carbon atoms and silicon atoms in the crystal. The main difference in performance lies in the relative number of carbon atoms and silicon atoms and the different structures of atomic arrangement. The most common and typical is the hexagonal structure, among which 4H-SiC, 6H-SiC and 3C-SiC are common. Table 1 shows a comparison of various properties between silicon Si, silicon carbide 4H-SiC, silicon carbide 6H-SiC and silicon carbide 3C-SiC. As can be seen from Table 1, the above three structures of silicon carbide have innate overwhelming advantages in high pressure, high temperature, high frequency, high current and other occasions, and are typical representatives of the third generation of semiconductors.

[0052] Table 1

[0053]

[0054]

[0055] Figure 2a -d shows the cross-sectional structure of some semiconductor devices produced by conventional processes. A common problem of these semiconductor devices is that the lead metal or back metal of the device is not tightly bonded to the silicon carbide substrate, which can easily cause the lead metal or back metal to fall off, resulting in damage to the device.

[0056] Figure 2aThe schematic diagram of the structure of a planar silicon carbide VDMOS produced by conventional technology is shown. It includes: an N-type silicon carbide substrate, a drain terminal 50 is made on the back side of the substrate (i.e., the bottom side in the figure), and a gate 30 and a source terminal 40 are made on the front side of the substrate (i.e., the top side in the figure). Lead metal or back metal needs to be made on the drain terminal 50, the gate 30 and the source terminal 40 to achieve electrical connection with the device pins. A gate oxide layer 20 is also included below the gate 30. The source terminal 40 is an N-type doped region in the P-type body region 10 (or called a P well). Among them, in the conventional process, the source terminal 40 and the drain terminal 50 are usually provided with ohmic contact to the lead metal or the back metal by making a metal silicide layer on the N-type silicon carbide substrate.

[0057] Figure 2b The schematic diagram of the structure of a planar silicon carbide IGBT produced by conventional technology is shown. It includes: an N-type silicon carbide substrate, a P-type region is made on the back side (i.e., the bottom side in the figure) of the N-type silicon carbide substrate, a drain terminal 50 is made on the P-type region, and a gate 30 and a source terminal 40 are made on the front side (i.e., the top side in the figure). Lead metal or back metal needs to be made on the drain terminal 50, the gate 30 and the source terminal 40 to achieve electrical connection with the device pins. A gate oxide layer 20 is also included below the gate 30. The source terminal 40 is an N-type doped region in the P-type body region 10 (or called a P well). Among them, in the conventional process, the source terminal 40 and the drain terminal 50 are usually provided with ohmic contact to the lead metal or back metal by making a metal silicide layer on the N-type silicon carbide substrate.

[0058] Figure 2c The schematic diagram of the structure of a trench silicon carbide VDMOS produced by conventional technology is shown. It includes: an N-type silicon carbide substrate, a drain terminal 50 is made on the back side of the substrate (i.e., the bottom side in the figure), and a gate 30 and a source terminal 40 are made on the front side of the substrate (i.e., the top side in the figure). Lead metal or back metal needs to be made on the drain terminal 50, the gate 30 and the source terminal 40 to achieve electrical connection with the device pins. The source terminal 40 is an N-type doped area in the P-type body region 10 (or called P well). Among them, in the conventional process, the source terminal 40 and the drain terminal 50 are usually provided with ohmic contact to the lead metal or back metal by making a metal silicide layer on the N-type silicon carbide substrate.

[0059] Figure 2dThe schematic diagram of the structure of a trench silicon carbide IGBT produced by conventional technology is shown. An N-type silicon carbide substrate is provided with a P-type region on the back side (i.e., the bottom side in the figure), a drain terminal 50 is provided on the P-type region, and a gate 30 and a source terminal 40 are provided on the front side (i.e., the top side in the figure). Lead metal or back metal needs to be provided on the drain terminal 50, the gate 30 and the source terminal 40 to achieve electrical connection with the device pins. The source terminal 40 is an N-type doped region in the P-type body region 10 (or P-well). Among them, in conventional technology, the source terminal 40 and the drain terminal 50 are usually provided with ohmic contact to the lead metal or back metal by making a metal silicide layer on the N-type silicon carbide substrate.

[0060] Figure 3a The production process of the traditional technology is shown. Figure 2a The source terminal 40 and the drain terminal 50 in the device shown in -d are usually connected by Figure 3a The process shown is used to manufacture.

[0061] First, a silicon carbide 301 substrate is prepared and necessary pretreatment is performed on the silicon carbide 301, such as RCA cleaning (a wet chemical cleaning method), water cleaning, ozone cleaning, etc., to ensure that the surface of the silicon carbide 301 is clean.

[0062] Then, a metal film 302 is deposited in the region where the source or drain terminal is to be made. It should be known to those skilled in the art that before the metal film 302 is deposited, the region where the source or drain terminal is to be made has been doped with impurities on the substrate, for example, Figure 2a As shown in the source end 40 part in -d, the area where the source end needs to be made is the area that has been N-type doped. In this step, the metal film 302 will be deposited on the area that has been N-type doped. Specifically, the metal used to deposit the metal film 302 includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, cobalt Co, platinum Pt. The deposition method includes a variety of physical vapor deposition methods such as evaporation and sputtering or chemical vapor deposition methods.

[0063] Then, rapid thermal annealing (RTP) or laser annealing (Laser Annealing) is performed in an atmosphere of an inert gas such as argon or nitrogen, so as to form a layer of carbon-containing silicide 303 between the silicon carbide 301 and the metal film 302. The carbon-containing silicide is a metal silicide with a conductivity between that of metal and silicon.

[0064] Usually, in the subsequent steps, the lead metal or the back metal 304 is made on the carbon-containing silicide 303, and an ohmic contact is achieved between the carbon-containing silicide 303 and the lead metal or the back metal 304, so that the pins of the device can be led out. However, since the carbon atoms in the silicon carbide 301 are released during the annealing process, they may form elemental carbon, or react with the newly generated silicide to form carbon silicide, that is, the carbon-containing silicide 303 contains impurities in addition to the desired metal silicide, such as elemental carbon, carbon silicide and other multi-component compounds. These impurities will affect the bonding between the carbon-containing silicide 303 and the lead metal or the back metal 304. When the impurity content is high, the lead metal or the back metal 304 will fall off from the carbon-containing silicide 303, thereby affecting the quality of the device.

[0065] Figure 3b The figure shows a wafer where the metal film has fallen off due to the unstable bonding force between the metal film (i.e., the lead metal or the back metal 304) and the silicide (i.e., the carbon-containing silicide 303). The problem of metal film falling off seriously affects the reliability of the device. In severe cases, it will cause the device to have problems such as open circuit and short circuit in actual application. In the wafer shown in the figure, although only the metal film in a part of the area has fallen off, the entire wafer will be deemed to have too low reliability and become waste, and can no longer be used to manufacture semiconductor devices. It can be seen that the problem of metal film falling off has a great impact on economic benefits.

[0066] Figure 4a A production process of a method for manufacturing a silicon carbide device according to the present application is shown. The manufacturing method is applicable to areas where ohmic contacts need to be manufactured. The manufacturing method pre-treats the areas where ohmic contacts need to be manufactured, thereby reducing the content of free carbon (including single carbon, carbon silicide and other multinary compounds) in carbon-containing silicides, thereby improving the bonding strength between silicides and lead metals or back metals, and reducing the risk of metal film falling off.

[0067] First, the silicon carbide wafer can be manufactured according to the commonly used silicon carbide device manufacturing process. In the silicon carbide device manufacturing scenario, the typical application is to manufacture the drain and source terminals. When the conventional process is carried out to the step of preparing to manufacture the source and drain terminals, the exposed source or drain area (such as Figure 2a The silicon carbide 301 substrate is cleaned in the region shown as the source end 40 and the drain end 50, that is, necessary pre-treatment is performed on the silicon carbide 301 substrate to remove contamination and oxides on the silicon carbide surface, for example, various cleaning methods are used to clean the silicon carbide 301 surface in the exposed source end or drain end region to ensure that the surface of the silicon carbide 301 is kept clean. The cleaning method may include chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering, or any combination thereof.

[0068] Then, a metal film 302 is deposited on the cleaned surface of the silicon carbide 301. The metal used to deposit the metal film 302 includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, vanadium V, chromium Cr, cobalt Co, platinum Pt. The deposition method includes evaporation or sputtering, and the deposition thickness is 5 nanometers to 1 micrometer.

[0069] Then, silicide annealing is performed in an inert gas atmosphere to form a layer of carbon-containing silicide 303 between silicon carbide 301 and metal film 302. Conventional thermal annealing, rapid thermal annealing (RTP) or laser annealing, or a combination of the above annealing methods can be used for silicide annealing. The temperature range of conventional thermal annealing is 31 degrees Celsius to 1400 degrees Celsius, the temperature range of RTP annealing is 100 degrees Celsius to 1400 degrees Celsius, and the temperature range of laser annealing is room temperature to 1400 degrees Celsius. The form of free carbon in carbon-containing silicide 303 can be a free element (including various allotropes of carbon such as graphite, graphene, etc.) or a multi-component compound such as metal carbon silicide. As mentioned above, carbon-containing silicide 303 is a metal silicide, which has good electrical conductivity, so it will be used to make ohmic contacts in subsequent steps. However, if the free carbon content is too high, it will affect the firmness of the ohmic contact. Therefore, it is considered to remove part of the free carbon in the carbon-containing silicide 303.

[0070] Furthermore, the inert gas may include one of nitrogen, argon, helium, and neon, or a combination of two or more thereof.

[0071] Before formally removing the free carbon, if some metal film 302 remains after silicide annealing, the remaining metal film 302 can be removed first to expose the complete carbon-containing silicide 303. For example, a corresponding solvent can be used to dissolve the transition metal constituting the metal film 302.

[0072] Then, post-treatment annealing is performed in a supercritical carbon dioxide (SCFCO2) atmosphere, that is, annealing is performed again. After the secondary annealing performed in a supercritical carbon dioxide (SCFCO2) atmosphere, the impurities in the carbon-containing silicide 303 can be removed, thereby obtaining a carbon-less silicide 305, which may still contain a trace of free carbon, but will not affect the firmness of the bond between the silicide and the metal film. Supercritical fluid has the dual characteristics of liquid and gas, and has a density close to that of liquid, and a viscosity coefficient close to that of gas and a higher diffusion coefficient, so supercritical fluid has a strong solubility and good flow and transfer performance. The density of a supercritical fluid near the critical temperature and critical pressure is only a function of temperature and pressure, so at a suitable temperature and pressure, it can provide enough density to ensure sufficiently strong solubility. Table 2 gives the supercritical data of some common substances.

[0073] Table 2

[0074] molecular Critical temperature Critical pressure Critical density molecular Critical temperature Critical pressure Critical density H2 -239.9 12.8 0.032 CF3Cl 28.8 38.7 0.579 N2 -147.0 33.5 0.314 NH3 132.3 111.3 0.235 XE 16.6 57.7 1.110 CH3OH 240.0 78.5 0.272 CO2 31.265 72.9 0.468 CH3CN 274.7 47.7 0.237 C2H6 32.3 48.2 0.203 H2O 374.2 218.3 0.315 CF3H 25.9 47.8 0.526 (unit:) ℃ atm <![CDATA[g / cm 3 ]]>

[0075] Obviously, according to the data of critical temperature and critical pressure of the substances listed in Table 2, the temperature and pressure conditions of substances such as Xe, CO2, C2H6, CF3H, CF3Cl are relatively easy to obtain in practice. Combined with the critical density data, the most widely used in industrial practice is carbon dioxide (CO2), which has a critical temperature of 31.265°C, a critical pressure of 72.9atm, and a critical density of 0.468. Supercritical fluid carbon dioxide is abbreviated as SCFCO2. The industry has developed supercritical fluid extraction, separation, cleaning and other technologies using SCFCO2 as the main active ingredient, making full use of its lack of surface tension and low viscosity coefficient. The present application also uses its low viscosity and good flow properties to remove impurities in carbon-containing silicide 303.

[0076] First, put the silicon carbide 301 with carbon-containing silicide 303 on the surface into the reaction chamber, and then inject SCFCO2 into the reaction chamber. Under the catalysis of critical temperature and critical pressure, SCFCO2 can achieve molecular-level contact with the carbon-containing silicide 303, so that the free carbon in the carbon-containing silicide 303 can react with carbon dioxide to produce carbon monoxide. Carbon monoxide can escape from the reaction chamber as a reaction product, that is, the purpose of removing or partially removing free carbon impurities is achieved. Another advantage of using carbon dioxide as a reactant in this embodiment is that carbon dioxide is inert to silicide and metal, and it will not react chemically with silicide and metal, that is, it will not cause consumption of silicide and metal. That is to say, in other embodiments, other substances that can react with free carbon but not with silicide and metal can also be selected as reactants to remove impurities.

[0077] After the reaction of SCFCO2 and the carbon-containing silicide 303, the carbon-containing silicide 303 removes impurities and becomes low-carbon silicide 305. After the lead metal or back metal 304 (i.e., contact metal) is further made on the low-carbon silicide 305, the bonding degree between the two is greatly improved, solving the defect of the aforementioned metal film being easy to fall off.

[0078] Furthermore, before making the lead metal or the back metal 304, the surface of the low-carbon silicide 305 and the silicon carbide 301 may be cleaned again (post-processed) to remove stains and oxides on the surface. The cleaning method may include chemical corrosion, chemical cleaning, dry etching, ion milling, reverse sputtering, or any combination thereof.

[0079] In an improved embodiment, SCFCO2 can be injected into the reaction chamber in small amounts and multiple times, that is, multiple post-processing annealing can be performed repeatedly, and the content of free carbon in the carbon-containing silicide 303 is checked after each annealing to determine whether the next post-processing annealing is needed. In this way, the content of free carbon in the carbon-containing silicide 303 can be accurately controlled.

[0080] Figure 4b Another production process according to the manufacturing method proposed in this application is shown. Figure 4b and Figure 4a The production process shown is similar, the difference is that the two annealing processes are combined into one annealing process, which can reduce the process steps and speed up the manufacturing process.

[0081] Since carbon dioxide is inert to silicide and metal, after the metal film 302 is deposited on the silicon carbide 301, RTP annealing or laser annealing can be performed directly in a SCFCO2 atmosphere. RTP annealing or laser annealing catalyzes the reaction between the metal film 302 and the silicon carbide 301 to generate metal silicide, while at the same time, SCFCO2 penetrates into the molecular gap of the metal silicide, reacts with free carbon, removes undesirable impurities, and directly obtains the carbon-poor silicide 305. In such a reaction environment, two results may occur. One is that the metal film 302 does not react completely, and residual metal remains on the carbon-poor silicide 305. The other is that the metal film 302 reacts completely, and only the carbon-poor silicide 305 exists on the silicon carbide 301. In the former case, the metal film 302 needs to be removed. Then, the subsequent device manufacturing steps are continued on the substrate where only the low-carbon silicide 305 exists on the silicon carbide 301. For example, the lead metal or the back metal 304 can be made on the low-carbon silicide 305, and the bonding degree between the silicide and the metal film is greatly improved, solving the defect that the metal film is easy to fall off.

[0082] Figure 5a-d corresponds to Figure 2a -d, the metal silicide layer 60 in the VDMOS device and the IGBT device manufactured according to the above method is shown in the source terminal 40 and the drain terminal 50, which contains less free carbon and will not affect the bonding degree between the metal film and the silicide.

[0083] Figure 5a A schematic structural diagram of a planar silicon carbide VDMOS produced according to the manufacturing method proposed in this application is shown.

[0084] Figure 5b A schematic structural diagram of a planar silicon carbide IGBT produced according to the manufacturing method proposed in this application is shown.

[0085] Figure 5c A schematic structural diagram of a trench silicon carbide VDMOS produced according to the manufacturing method proposed in this application is shown.

[0086] Figure 5d A schematic structural diagram of a trench silicon carbide IGBT produced according to the manufacturing method proposed in this application is shown.

[0087] In summary, the present application utilizes the good fluidity of supercritical carbon dioxide fluid to actively penetrate into the molecular gaps of silicide and fully contact with free carbon, so that carbon dioxide can react with free carbon to generate carbon monoxide, and carbon monoxide can be separated from silicide in liquid or gaseous form, thereby removing free carbon from silicide. The bonding degree between silicide and metal film after free carbon is removed is greatly improved, thereby improving the reliability of semiconductor devices.

[0088] It should be noted that in the examples and description of this patent, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article 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, article or device. In the absence of further restrictions, the elements defined by the sentence "including one" do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0089] Although the present application has been illustrated and described with reference to certain preferred embodiments thereof, it will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present application.

Claims

1. A method for manufacturing a silicon carbide device, characterized in that: The following pre-treatment steps are performed on the area where ohmic contact is to be made, including: Pre-treatment, cleaning the area on the silicon carbide surface where ohmic contact needs to be made to expose the clean silicon carbide surface; Depositing a metal film on the surface of the silicon carbide; Performing silicide annealing in an inert gas atmosphere or in a vacuum to obtain a carbon-containing silicide layer, wherein the carbon-containing silicide layer is rich in free carbon; Cleaning to remove residual metal film; Post-treatment annealing is performed in a supercritical carbon dioxide atmosphere to obtain a low-carbon silicide layer, wherein the low-carbon silicide layer contains a trace amount of free carbon; Post-processing includes cleaning to remove surface impurities and expose the clean surface of the low-carbon silicide layer so as to grow contact metal on the surface and complete subsequent device manufacturing processes.

2. The method according to claim 1, characterized in that: The pre-treatment is used to remove contamination and oxides on the surface of silicon carbide, and the treatment method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

3. The method according to claim 1, characterized in that: The inert gas includes nitrogen, argon, helium, neon and combinations thereof.

4. The method according to claim 1, characterized in that: The supercritical carbon dioxide atmosphere is an atmosphere with a temperature greater than 31.265° C. and a pressure greater than 72.9 atmospheres. The post-treatment annealing includes conventional heating annealing, rapid thermal annealing, laser annealing and a combination thereof.

5. The method according to claim 1, characterized in that: In the metal film deposited in the area on the silicon carbide surface where ohmic contact needs to be made, the material of the metal film includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, vanadium V, chromium Cr, cobalt Co, and platinum Pt.

6. The method according to claim 1, characterized in that: In the metal film deposited in the area on the silicon carbide surface where ohmic contact needs to be made, the deposition method includes physical or chemical vapor deposition methods such as evaporation, sputtering or chemical reaction, and the deposition thickness is 1 nanometer to 1 micrometer.

7. The method according to claim 1, characterized in that: The post-processing is used to remove contamination and oxides on the surface of metal silicide and silicon carbide, and the processing method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

8. The method according to claim 1, characterized in that: The post-treatment annealing step in a supercritical carbon dioxide atmosphere may be performed repeatedly for multiple times.

9. A method for manufacturing a silicon carbide device, characterized in that: The following pre-treatment steps are performed on the area where ohmic contact is to be made, including: Pre-treatment, cleaning the area on the silicon carbide surface where ohmic contact needs to be made to expose the clean silicon carbide surface; Depositing a metal film on the surface of the silicon carbide; Annealing is performed in a supercritical carbon dioxide atmosphere to directly obtain a low-carbon silicide layer, wherein the low-carbon silicide layer contains a trace amount of free carbon; Post-processing removes the residual metal film to expose the clean surface of the low-carbon silicide layer, so as to grow contact metal on the surface and complete subsequent device manufacturing processes.

10. The manufacturing method according to claim 9, characterized in that: The pre-treatment is used to remove contamination and oxides on the surface of silicon carbide, and the treatment method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

11. The method according to claim 9, characterized in that: The supercritical carbon dioxide atmosphere is an atmosphere with a temperature greater than 31.265° C. and a pressure greater than 72.9 atmospheres. The annealing treatment includes conventional thermal annealing, rapid thermal annealing, laser annealing and a combination thereof.

12. The method according to claim 9, characterized in that: In the metal film deposited in the area on the silicon carbide surface where ohmic contact needs to be made, the material of the metal film includes at least one of the following transition metals: nickel Ni, titanium Ti, molybdenum Mo, tungsten W, tantalum Ta, niobium Nb, vanadium V, chromium Cr, cobalt Co, and platinum Pt.

13. The manufacturing method according to claim 9, characterized in that: In the metal film deposited in the area on the silicon carbide surface where ohmic contact needs to be made, the deposition method includes physical or chemical vapor deposition methods such as evaporation, sputtering or chemical reaction, and the deposition thickness is 1 nanometer to 1 micrometer.

14. The manufacturing method according to claim 9, characterized in that: The post-processing is used to remove contamination and oxides on the surface of metal silicide and silicon carbide, and the processing method includes one or any combination of chemical corrosion, chemical cleaning, dry etching, ion milling, and reverse sputtering.

15. The manufacturing method according to claim 9, characterized in that: The step of performing annealing in a supercritical carbon dioxide atmosphere may be performed repeatedly for multiple times.

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