Manufacturing method for SiC ohmic contact at front side of Ni

Abstract

The present description relates to a method of manufacturing a silicon carbide wafer, the method comprising: forming a semiconductor substrate comprising SiC at a surface or at least a specific portion of the surface thereof; cleaning a surface region of the substrate by a hydrogen plasma atmosphere; applying a nickel metal contact material on the cleaned surface area to form a SiC / Ni metal stack on the surface of the SiC substrate or at least part of the SiC substrate; and annealing the SiC / Ni metal stack to form an ohmic contact at an interface between SiC and nickel metal.

Description

Technical Field

[0001] This disclosure generally relates to methods for manufacturing silicon carbide (SiC) wafers, and particularly those methods that include contacting the surface of a silicon carbide semiconductor substrate with a nickel metal contact layer to generate a Ni front-side ohmic contact. Background Technology

[0002] Silicon carbide (SiC) based semiconductor devices and similar semiconductor components are widely used in many microelectronic devices. Microelectronic devices using SiC semiconductor materials are used in power applications, high-temperature applications, high-frequency applications, and so on. Many types of SiC-based devices include integrated circuits, which are formed on semiconductor wafers by depositing various types of thin films of materials.

[0003] Semiconductor devices are coupled to external circuitry via front and back contacts. Forming front contacts with low resistance is one of the challenges of integrated circuits, especially as package sizes are scaled down. To achieve ohmic contacts, silicide reactions are known to be used, which is done by depositing a contact metal, such as a sputtered or deposited NiAl material layer, on the SiC surface of a substrate, followed by thermal annealing. The wafer is typically heated to a sufficiently high temperature to create a thin, molten surface layer. In this molten state, a silicide reaction occurs at the interface between the SiC and the deposited metal. The Al composition used in current processes is considered the reason for good diode p-contacts with acceptable low resistance, but it often leads to reliability issues because after the annealing step, Al, O, and C are found in a mixed layer on top of the NiSi contact layer.

[0004] Therefore, the purpose of this application is to overcome at least some of the aforementioned problems. More specifically, one objective is to improve reliability while providing good ohmic contact on the front or back side of the SiC wafer, especially the front side. Summary of the Invention

[0005] According to an embodiment, a method of manufacturing a SiC wafer may include: forming or providing a semiconductor substrate comprising SiC on or at least a specific portion of its surface; cleaning a surface region of the substrate with a hydrogen plasma atmosphere; and applying a nickel metal contact material to the cleaned surface region to form a SiC / Ni metal stack on or at least in a portion of the surface of the SiC substrate.

[0006] Forming or providing a semiconductor substrate can include forming an integrated circuit on or within a surface region of the semiconductor substrate by depositing thin films of various materials and processing those thin films into an integrated circuit structure, such as by a chemical etching process. In most processes, contaminants in the form of particles or layers on or within the surface of the SiC substrate are generated by chemical or physical processes. By cleaning the surface region of the SiC substrate before forming the metal contact layer, at least partially removing those contaminants from the surface region that will be in contact with the metal contact material. Typically, any chemical or physical process can be used, such as wet chemical etching and / or plasma treatment. According to an embodiment, those contaminants can be removed from the surface by using at least hydrogen plasma treatment.

[0007] Applying a metal contact material means that the metal contact can be formed directly on the clean SiC surface region in which the ohmic contact will be formed, or it can be formed directly on top of the SiC surface to be metallized into an ohmic contact. Discontinuous layers or discontinuous surface particles between the SiC surface region and the Ni metal contact material should be removed before application, or should be present in only a small amount.

[0008] The method may also include annealing the SiC / Ni metal stack to form an ohmic contact at the interface between SiC and nickel metal. In this respect, annealing means heating the metal contact material layer or film to a temperature sufficient to produce a Ni / SiC contact with ohmic behavior and maintaining this temperature for a period of time.

[0009] Those skilled in the art will recognize the additional features and advantages after reading the following detailed description and viewing the accompanying drawings. Attached Figure Description

[0010] The elements in the accompanying drawings are not necessarily proportional to each other; rather, the emphasis is on illustrating the principles of the invention. Similar reference numerals denote corresponding similar parts. Features of the various examples shown can be combined unless they are mutually exclusive. Examples are depicted in the accompanying drawings and described in detail below.

[0011] Figure 1 The process steps of a method for forming a SiC wafer according to the general concepts described herein are shown.

[0012] Figure 2 The fabrication of a SiC wafer according to a first embodiment is shown.

[0013] Figure 3 The fabrication of a SiC wafer according to another embodiment is shown, particularly the optional post-processing steps.

[0014] Figure 4 The fabrication of a SiC wafer according to a second embodiment is shown. Detailed Implementation

[0015] In the detailed description below, the semiconductor devices are based on silicon carbide (SiC), a material with potential for high-temperature, high-frequency, and radiation-resistant applications. SiC is a wide-bandgap semiconductor material suitable for semiconductor devices with specific dielectric gate structures, including, for example, diodes, metal-oxide-semiconductor field-effect transistors (MOSFETs), junction field-effect transistors (JFETs), or insulated-gate bipolar transistors (IGBTs). Any other semiconductor devices with dielectric gate structures are included in the general concept of this disclosure, even if they are not explicitly mentioned herein. Many SiC-based device types have current flowing through the substrate material to the front or back of the metallization (e.g., the source or drain of a MOSFET device or one of the electrodes of a diode). Appropriate metallization with good adhesion to SiC allows for good electrical contact, especially ohmic contact, during the annealing process following contact metal deposition.

[0016] Semiconductor devices can be manufactured from semiconductor substrates, where the shape and size of the substrates can vary, and include commonly used circular wafers of different sizes, such as those with diameters between 50 and 450 mm. Any other semiconductor substrate shape and size can be used instead of the typically used circular wafer.

[0017] As described herein, the semiconductor substrate can typically be any semiconductor substrate on which the SiC body is included on its surface, for example, in the form of a SiC-based substrate or as an epitaxial layer on a substrate of any material suitable for use as a semiconductor material in microelectronic devices. Typically, a SiC wafer having those device structures can be a wafer having sidewall and bottom contacts with p-type and n-type SiC, to which front-side contact silicides with one or both of the p-type and n-type SiC will be formed.

[0018] According to a first embodiment of the method for forming a SiC wafer, a semiconductor substrate comprising silicon carbide on its surface can be started from the SiC wafer. How the SiC wafer is obtained is not important to the method described herein, and any common fabrication method can be used for this preparatory step. The thin SiC wafer to be processed according to the method described herein is then treated with a pre-cleaning process that includes at least a hydrogen plasma treatment. The hydrogen plasma can be pure H2 plasma or a mixture of H2 with other gases such as a carrier gas. Ex-situ or in-situ H2 plasma pre-cleaning may be sufficient in most cases to remove particles and contaminants present on the SiC substrate surface before the application of a metal contact material. In-situ hydrogen plasma can also be used for batch production without breaking the vacuum before metal contact deposition. For example, time coupling is not required when working in-situ.

[0019] In some embodiments, the SiC surface can be cleaned solely by hydrogen plasma or in combination with HF pre-cleaning. For example, if resist patterning is used to pattern the front or back surface of a SiC wafer, HF pre-cleaning can be used in addition to hydrogen plasma, as described in more detail later. Patterning the surface with photoresist can be suitably used to create a topology with a negative slope, such that when metal is deposited on the wafer, there is a break between the top and bottom metals, for example, in the contact areas. For example, in some examples, the resist can be removed and the top metal stripped, leaving only the bottom metal in the contact areas. In a subsequent annealing step, a high-temperature treatment is used to form silicide with the remaining metal.

[0020] According to embodiments, such as in the first embodiment described above, a nickel metal contact material can be applied to a clean surface area to form a SiC / Ni metal stack on or at least partially on the surface of the SiC substrate to be contacted. The metal is deposited on those portions of the SiC substrate, where metallization is to be performed to form ohmic contacts. Therefore, the deposited metal then reacts with SiC to form a silicide, serving as an intermediate layer for the ohmic contacts at the surface of the SiC substrate. The silicide intermediate layer, subsequently produced by an annealing reaction, improves the contact resistance (Rt) in the fabricated SiC / Ni / Ni stack. on ).

[0021] In some embodiments, the nickel metal contact material may be pure nickel metal or a nickel-based alloy. The alloy metal may be titanium or aluminum. Alternatively, nickel silicide may be suitably used as the contact material.

[0022] In some embodiments, the applied metal contact material (e.g., nickel metal contact material) and the SiC substrate are heated to form silicide, particularly a NiSi layer, at the intermediate layer of the SiC / Ni metal stack. In this annealing step, any high-temperature treatment can be used, employing a temperature and time suitable for the silicide reaction between the SiC substrate surface and the deposited nickel metal contact. Suitable annealing processes are known in the art. Higher annealing temperatures may be required if the Ni-SiC interface quality is poor. Therefore, hydrogen plasma pre-cleaning enables the formation of silicide contacts using lower annealing temperatures.

[0023] The substrate can be a SiC substrate, including a front surface on which or therein forming a semiconductor element and a rear surface facing the front surface. For example, a SiC substrate can be used to fabricate a semiconductor device in which the SiC substrate serves as the body region, wherein a drift region of a first conductivity type, a body region of a second conductivity type, and a source region of the first conductivity type are provided. Furthermore, the body region can be provided with a gate structure, which includes a gate electrode and a gate dielectric isolating the gate electrode from the SiC body, wherein the gate structure can be disposed adjacent to the source region, the body region, and the drift region.

[0024] The drift region of the first conductivity type can be fabricated by doping a corresponding region of the SiC bulk. Similarly, the source region can be fabricated by doping a corresponding region of the SiC bulk. Depending on the type of semiconductor device, for example, the first conductivity type can mean doping with negative charge carriers, and the second conductivity type can mean doping with positive charge carriers (holes), or vice versa. For each embodiment, the general conductivity of the first or second type should be the same; however, different charge carrier concentrations, also referred to as n+ or n- or p+ or p- doped substrates or active regions, can be used within a single conductivity type.

[0025] The SiC body may include well regions with a high doping level to increase charge transfer through the conductive channel. Furthermore, the SiC body may include a SiC epitaxial layer with the same conductivity type as the drift region of the SiC body. Additionally, a drain electrode may be provided adjacent to the drift region of the SiC body and / or the SiC epitaxial layer. Typically, the dielectric structures described herein can be used in n-channel or p-channel transistors.

[0026] This disclosure includes planar or trench semiconductor devices comprising, for example, a common gate structure based on SiO2 as the gate dielectric, and a source metal electrically contacting the source region, wherein an interlayer dielectric isolates the gate electrode from the source metal. For example, the source electrode may be made of or include a nickel metal contact, as described in detail herein. Of course, any other electrode may be fabricated according to the methods described herein.

[0027] Typically, planar semiconductor devices may include a gate structure that can extend between a source region and a drain region. The gate structure may be disposed on a portion of the source region and a portion of the drain region. In some examples, as described herein, a first source region and a second source region may be provided within a pnp junction. The gate structure may then be disposed on the SiC body and may be disposed on a portion of the first source region and a portion of the second source region.

[0028] In trench semiconductor devices, the gate structure includes trench sidewalls and a trench bottom region, on which nickel-based metal contacts according to the present description are formed. Due to the specific form of the trench-based gate structure, the SiC substrate regions at the sidewalls and bottom of each trench can have different crystal planes on the surface of the SiC substrate. Different crystal planes can be siliconized differently and can respond differently to pre-cleaning. Using hydrogen plasma-based pre-cleaning can be advantageous in simultaneously cleaning different exposed planes in the trench-shaped gate structure. The reason may be that hydrogen plasma without bias is isotropic. Therefore, it will work on the trench sidewalls because it has no directionality. Thus, unlike wet chemical cleaning methods such as HF cleaning, or directional sputtering cleaning methods such as using gases such as inert gases, hydrogen plasma pre-cleaning of the SiC substrate can produce a cleaner surface at both the trench sidewalls and the trench bottom region.

[0029] HF etching is typically a wet chemical cleaning method. When using wet chemical processes such as HF etching to clean narrow and / or deep trench structures, chemicals must penetrate the trench structure. If chemicals do penetrate the trench, it can be difficult to remove them from high aspect ratio trenches, and there is a risk of leaving undesirable residues in the trench. Furthermore, gases may be generated during wet etching, and bubbles may become trapped in the trench. Therefore, using wet chemical etching alone may not easily achieve reliable results. Thus, at least one hydrogen plasma cleaning step can be applied before applying nickel metal contacts to the surface of the SiC substrate to be contacted. Wet chemical cleaning methods can be more preferably used in planar semiconductor devices or on the back surface of SiC substrates, which is typically less structured than the front side. Sometimes, the back side also includes structured surface regions, making hydrogen plasma cleaning, as described herein, advantageously applicable to these types of SiC substrates as well.

[0030] Gas sputtering, such as Ar or other rare or inert gases, can be used in conjunction with hydrogen plasma cleaning, or as an additional cleaning step, for example, prior to hydrogen plasma cleaning as described herein. In trench structures, sputtering cleaning techniques present challenges in reaching any area of ​​the trench due to the directionality of the sputtering method. Sputtering can also imply a risk of crystal damage, and additionally, a risk of knocking any surface contaminants into the lattice. The bias voltage used to accelerate atoms to the sputtered SiC surface can clean some portions of the trench better than others. Therefore, hydrogen plasma cleaning, as described herein, overcomes the problems of conventional cleaning methods.

[0031] In some embodiments of the manufacturing method described herein, the front surface is cleaned, and contacts are formed in the surface regions where SiC is directly present on the substrate surface. As previously mentioned, at least the source or drain regions of the SiC substrate are cleaned using hydrogen plasma cleaning, where a metallic contact material is applied. Gate regions typically provided with gate dielectrics (e.g., SiO2-based layers or structures) can also be cleaned. When depositing nickel metal as the contact material, it can be applied to any region, for example, by sputtering nickel metal material in the form of a thin layer. However, during the annealing step, silicide reaction occurs only in those regions where SiC is directly present on the surface, meaning, for example, the source and drain regions of the SiC body. Typically, in those regions covered by dielectric layers, particularly oxide layers, silicide reaction does not occur, or only insufficient amounts of silicide are formed on those oxide surfaces by the annealing process.

[0032] According to some embodiments, the fabrication of ohmic contacts is performed at a SiC surface region, for example, on the front side of a SiC substrate, where the SiC surface region comprises an n- or p-doped SiC substrate. For example, such an n-doped or p-doped SiC substrate can be a source or drain region on the front side of a planar or trench-based semiconductor device. Therefore, source and drain metallization with good ohmic front-side contact silicides can be achieved using a simple method with only a few steps. The method described herein has reduced system complexity compared to the commonly used NiAl processing for ohmic contact formation. Furthermore, the complexity of Al interactions can be avoided, as Al is typically absent in the system when using conventional pure Ni process techniques. The contact physics is easier to understand and predict because it is a less complex ohmic contact system based solely on the formation of a NiSi intermediate layer. In some examples, better R... on Improved Ron values ​​for front-side contacts. The contact resistance in the n-doped contact region is comparable to or even better than that of NiSi contacts using a NiAl processing technique. In some examples, the Ron value can be improved by approximately 10%. In the p-doped contact region, an improvement of approximately 20% can be achieved. Therefore, if the method described herein is used, Al is not required to form NiSi to achieve good p-type or n-type contacts. Although the effect on front-side contacts has been investigated, this method can also be readily adapted and applied to back-side contacts. Similar results in contact resistance are expected. Furthermore, the simpler system and lower complexity of this method also appear to favor back-side contacts.

[0033] As described above, substrate surface cleaning is one of the key steps in the methods described herein, as contaminants on the substrate surface (e.g., oxide or carbon particles) can, for example, hinder silicide formation in those areas. Therefore, a pre-cleaning step using hydrogen plasma is employed to clean or condition the substrate surface. HF pre-cleaning can be used alone or in combination. In some embodiments, substrate surface cleaning is performed using a hydrogen plasma treatment with a pure hydrogen atmosphere or an atmosphere comprising hydrogen mixed with other gases. This other gas can be a carrier gas or an inert gas, such as a rare gas, such as Ar, Xe, Kr. Hydrogen plasma can be used isotropically or as an anisotropic cleaning using a bias voltage. Isotropic plasma may be suitable for cleaning trench-based structures typically located on the front side of semiconductor devices. Because isotropic hydrogen plasma is non-directional, trench-like sidewall contacts can be reliably cleaned even if the trenches are narrow and deep. Typically, hydrogen plasma can remove oxides, silicon, and / or carbon, or any substance that reacts with hydrogen ions and hydrogen radicals. If it does not react directly, it can be sputtered using a bias voltage and / or a sputtering / carrier gas. Furthermore, hydrogen plasma pre-cleaning reduces defects on the SiC substrate surface, such as those on the contact sidewalls. Therefore, through specific pre-cleaning treatments, reliable and uniform deposition of nickel metal contact materials, as well as uniform annealing and silicide formation reactions, can be achieved. Hydrogen plasma also improves metal wetting and reduces dewetting of the interlayer dielectric and the metal on SiC. Therefore, by reducing the defect density on the SiC substrate surface, a more uniform thickness of the silicide interlayer can be achieved after the annealing process. More specifically, by altering the properties at the interface during hydrogen plasma pre-cleaning, the thin melting caused by the use of thin metal films and the dewetting effect caused by the surface properties at the interface can be improved. It has been noted that this behavior is more pronounced for certain metals, particularly nickel. For example, NiAl exhibits better wetting ability compared to pure nickel metal. Therefore, the methods described herein can be used to prepare pure nickel contacts. Alternatively, nickel alloys with good wetting properties can be used. An example of such alloys is a nickel-titanium alloy.

[0034] After the surface has been cleaned and is free of contaminants and / or defects, it is not necessary to use an interlayer dielectric (e.g., AlO). xThe protection of the SiC substrate is thus achieved. Therefore, in some embodiments of the methods described herein, after pre-cleaning with hydrogen plasma, nickel metal or a nickel-based alloy is applied to the cleaned SiC surface by a deposition method, such as sputtering and / or vapor deposition. Sputtering or evaporation processes can produce a thin film layer on the substrate. The metal contact material can be applied at a thickness of approximately 10 to 200 nm, particularly approximately 30 to 100 nm, and more typically approximately 50 nm. Because a very thin nickel metal contact material layer may be suitable for application and annealing, only a small amount of contaminants, such as carbon particles, may be present on the metal contact surface after annealing. A very thin nickel layer or nickel-based metal contact layer can produce less carbon contaminants or even no carbon contaminants. Furthermore, a thinner metal means less SiC consumption during the silicide reaction. Controlling the depth of silicide application may be suitable, for example, for contact at the implantation peak. Therefore, it is preferable to apply the thinnest possible layer of nickel metal on the SiC substrate.

[0035] After applying the nickel contact material, the method includes a step of heating at least the SiC / Ni metal, which is formed at least at those portions of the SiC substrate surface where ohmic contacts will be created. Annealing can include rapid thermal processing (RTP), high-temperature furnace processes, or laser thermal annealing, with an annealing temperature suitable for melting a thin nickel metal layer at least on the surface of the SiC substrate, thus enabling the formation of silicide (NiSi) at the interface between the SiC substrate and the nickel metal contact layer. When applying rapid thermal processing (RTP), a suitable temperature can be 450°C or higher, more preferably above 550°C. A suitable annealing temperature range is between 500°C and 1000°C. Lower RTP temperatures can be achieved because the thickness of the applied nickel metal contact layer can be less than that in commonly used methods, such as those using NiAl alloys. Lower temperatures can lead to improved silicide formation. When using lower temperatures, time may be a factor. Therefore, using a longer RTP process time rather than increasing the annealing temperature may be preferred.

[0036] Alternatively, other annealing methods besides RTP can be used. Typical annealing methods may include, for example, furnace or smelting heating or laser thermal annealing. RTP and / or other annealing methods may be combined or applied in one or more separate steps. In some examples, two RTP steps may be applied, optionally with metal etching between the two steps. As explained later, metal etching or plasma etching may be applied to remove oxides or carbon contaminants from the surface of the obtained NiSi layer. For example, etching may also be used to remove excess unreacted metals and / or alloys present on the dielectric layer. This allows for the structuring of the silicide metal without requiring methods such as stripping photoresist. In some embodiments, a second RTP step may be used to change the phase of the silicide metal. Some phases produce better contact than others, and the second RTP step may be appropriately used to achieve the desired phase. Intermediate etching of the obtained contaminant particles or layers can improve the reliability of the semiconductor device and / or the contact resistance of the obtained nickel contacts.

[0037] Some embodiments of the methods described herein may include a step of removing contaminants and / or unreacted Ni metal from the SiC / Ni metal stack after annealing. Following the first RTP, metal etching techniques or oxygen plasma treatment may be used as a post-treatment. Some embodiments may also include oxygen plasma treatment of the nickel metal contact material. This oxygen plasma treatment may be one or more O2 flash treatments, as used in common NiAl-based contact processes, and may also be used herein, if desired.

[0038] After removing contaminants and / or unreacted Ni metal in the post-treatment described above, the method may further include an additional thermal annealing treatment. This could be a second RTP or any other heat treatment, with rapid heat treatment techniques being preferred.

[0039] This paper also describes a SiC wafer comprising a silicon carbide (SiC) semiconductor substrate and a Ni metal contact layer on its main surface, the wafer being fabricated by any of the methods described above, wherein the ohmic contact is provided by a nickel silicide layer formed by an annealing step. Such a SiC wafer, as described herein, with front-side and / or back-side ohmic contacts, can serve as the basis for semiconductor devices with different functions. Pure nickel contacts on SiC with a thin silicide layer (NiSi) may be useful for scaling down device structures while maintaining or improving contact reliability and / or contact resistance, for example, compared to contacts using NiAl-based contact processes. Fewer steps, easier fabrication, reduced contaminants, and so on are likely the main advantages of the methods and semiconductor devices described herein.

[0040] The following sections will explain two typical variations of this method in detail with reference to the accompanying drawings.

[0041] exist Figure 1 and 2 In the first example of the method for forming a semiconductor device shown, the semiconductor substrate composed of SiC, or at least including SiC in the areas to be contacted, can be formed by any common method. The steps for forming the semiconductor SiC substrate are as follows: Figure 1 As shown in step A. The SiC substrate 10 can be fabricated by providing different doped device structures in or on the surface of the SiC wafer. Therefore, a planar MOSFET can be fabricated in the following steps. The front surface of the SiC substrate thus prepared can optionally be pre-cleaned by a wet chemical cleaning step, such as using HF etching, to reduce most contaminants, such as oxide particles or carbon clusters on top of the SiC substrate 10 in region 12. In the optional pre-cleaning step ( Figure 1 (Not shown in the image) Subsequently, or simultaneously, a SiC substrate comprising SiC at least on or at least a portion of the surface has been provided for the method described herein. Thereafter, cleaning (step C) can be performed using a hydrogen (H2) plasma atmosphere. This cleaning step allows for further reduction of the amount of remaining carbon clusters or oxide particles or other contaminants in region 12 above the substrate surface to be contacted. Furthermore, hydrogen plasma cleaning can reduce defects in the surface region of the SiC substrate to be contacted. This is considered to be due to chemical interactions or reactions with Si and / or C atoms at the SiC surface. One assumption is that dangling bonds will be saturated by the hydrogen plasma. Generally, it is also possible to clean those portions of the SiC substrate surface where other device structures (e.g., interlayer dielectric layers) have already been disposed, but a significant reduction in the layer thickness of these device structures already included in the front side of the SiC substrate may not be observed.

[0042] The cleaning process (step C) in a hydrogen plasma atmosphere or a hydrogen-containing plasma atmosphere can be performed at adjusted time, temperature and pressure to clean or condition the surface without large SiC substrate surface rearrangement.

[0043] During and after cleaning the substrate surface, it is likely preferable to avoid any oxidizing atmosphere before proceeding to the next process step. Therefore, a method that does not alter the working embodiment will be preferred for avoiding the formation of native oxides (SiOxCy) or carbon clusters or other unwanted contaminants on the cleaned substrate surface. Furthermore, as in commonly used NiAl processes, forming a passivation layer on the cleaned surface is unnecessary. Thus, the fewer steps make this method superior to conventional manufacturing processes.

[0044] Typically, the method described in this first embodiment includes depositing a nickel metal contact material or a nickel-based alloy contact material on or above a clean SiC substrate at least at the portion to be contacted. Figure 1Step E in the above text. In this respect, the above does indeed mean the direct deposition of the contact material 20 on the SiC substrate surface 10 or via an intermediate layer (e.g., a passivation layer, if present). Since pure Ni does react with SiC but not with native oxides or carbon clusters, the nickel metal contact material 20 can typically be deposited directly onto the SiC substrate surface 10 using any sputtering or evaporation method commonly used in this art. The application of the nickel metal contact material 20 to the SiC substrate surface can be performed in an inert or non-oxidizing atmosphere (in-situ or ex-situ process). Where technically possible and suitable, the entire process can be performed without exposing the treated surface to an oxidizing atmosphere, at least before the nickel metal contact material has been applied to the substrate.

[0045] After applying nickel metal contact material 20 to the SiC substrate 10 (step E), the SiC and Ni stack is heated to a temperature of at least 450°C for a sufficient time to allow at least partial melting of the nickel metal component and the formation of silicides, such as NiSi, at the interface between the SiC substrate 10 and the nickel metal contact material 20 (step G). The resulting thin NiSi or silicide contact layer 15 is believed to improve the contact resistance of the fabricated contact in areas where pure nickel or nickel-based alloys are in direct contact with the SiC substrate 10. In areas where an ILD (e.g., oxide) device structure has been previously provided, no silicide reaction occurs, and the pure nickel metal contact material remains on its surface. In areas where no ILD is provided and the SiC substrate is exposed, a silicide reaction occurs, and nickel ohmic contacts are formed.

[0046] like Figure 3 As shown, the silicide reaction (step G) can produce a SiC substrate 10 and nickel silicide 15 (e.g., NiSi). x The stack of unreacted nickel metal 20 and the silicide layer. During annealing, carbon clusters 30 generated by the decomposition of SiC during the silicide reaction can be generated within the silicide layer, at the interface between SiC and NiSi, or on the surface of the nickel metal layer 20. These carbon clusters can be removed in step H by an O2 flash process. In particular, those carbon clusters 30 on the metal surface or within the unreacted metal layer can be removed by this post-processing. Alternatively, or additionally, wet etching (e.g., Piranha etching) can be used in step H to remove the unreacted nickel metal 20 including the carbon clusters 30 in one step, thereby preserving the silicide surface as a contact. Optionally, a second RTP can be performed to improve ohmic contact. Similar temperatures and conditions to those in the first RTP can be applied here.

[0047] After annealing, not only can the unreacted material on the contact side be easily removed, but the unreacted metal on top of the oxide or other layers that do not form any silicide (not shown in the figure) can also be removed by wet chemical etching methods such as Piranha or Karo etching, thereby leaving silicide in the contact area.

[0048] This variant of the method described herein, referred to herein as "no-stripping," is likely preferred because metal structuring is not required during the process due to the selectivity of the silicide reaction. Furthermore, photoresist agents (resins, etc.) are not required in this variant. Therefore, resist coating and removal steps are unnecessary, and this method generates fewer contaminants. A further advantage is improved contact performance, as complete metal coverage of the ILD during the annealing process of the substrate stack prevents dopant diffusion outwards into NiSi.

[0049] Now for reference Figure 4 Another variation, referred to herein as the "stripping" method, uses photoresist 40 and ILD etching to create a topology with a negative slope on the SiC substrate surface 10. Following ILD etching, the SiC surface is cleaned by at least hydrogen plasma cleaning (step C) and optionally HF etching (step B) to remove the photoresist material from the contact areas of the substrate. When the nickel metal layer 20 is deposited on the wafer, a disconnect exists between the top metal on the photoresist 40 and the bottom metal in the contact areas at the exposed and cleaned SiC substrate 10 regions. In step F, the photoresist 40 is removed, and the top metal is stripped away, leaving only the bottom metal 20 in the contact areas(s). In step G, silicide is formed by reacting the SiC and the remaining metal 20 (e.g., pure nickel metal or a nickel-based alloy) using high-temperature annealing (e.g., 450–1000 °C).

[0050] As shown in the variation of the method described above, using pure nickel (e.g., with a purity greater than 99% or even greater than 99.9%) eliminates the need for post-silicide metal etching because no metal residue remains on the substrate or the sidewalls of the trench. Hydrogen plasma cleaning also improves wetting, and pure nickel does not react with potential contaminants (e.g., particles or substances containing O, C, or P) or reacts at a low rate.

[0051] Although specific examples have been shown and described herein, those skilled in the art will understand that various alternatives and / or equivalent embodiments may be used instead of the specific examples shown and described without departing from the scope of this disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

[0052] It should be noted that the methods and apparatuses, including their preferred embodiments as outlined in this document, can be used alone or in combination with other methods and apparatuses disclosed in this document. Furthermore, the features outlined in the context of the apparatus also apply to the corresponding methods, and vice versa. Moreover, all aspects of the methods and apparatuses outlined in this document can be combined arbitrarily. In particular, the features of the claims can be combined with each other in any manner.

[0053] It should be noted that the description and accompanying drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements, which, although not explicitly described or shown herein, embody the principles of this disclosure and are included within its spirit and scope. Furthermore, all examples and embodiments outlined in this document are primarily and explicitly intended for illustrative purposes only to aid the reader in understanding the principles of the proposed methods and systems. Moreover, all statements and specific examples of the principles, aspects, and embodiments of this disclosure provided herein are intended to cover their equivalents.

Claims

1. A method for manufacturing silicon carbide (SiC) wafers, comprising: A semiconductor substrate comprising SiC formed on or at least a specific portion of its surface; Cleaning the surface area of ​​the substrate using a hydrogen plasma atmosphere; A nickel metal contact material is applied to a clean surface area to form a SiC / Ni metal stack on the surface of the SiC substrate or at least a portion of the SiC substrate. and The SiC / Ni metal stack is annealed to form an ohmic contact at the interface between SiC and nickel metal.

2. The method of claim 1, wherein the substrate is a SiC substrate, including a front surface on which or therein forming a semiconductor element and a rear surface facing the front surface.

3. The method according to any one of claims 1 and 2, wherein the front surface of the substrate is cleaned, and a contact is formed in the surface region where SiC is directly present on the front surface of the substrate.

4. The method according to any one of the preceding claims, wherein the SiC surface region comprises an n- or p-doped SiC substrate.

5. The method according to any one of the preceding claims, wherein cleaning of the substrate surface region is performed by hydrogen plasma treatment using a pure hydrogen atmosphere or an atmosphere comprising hydrogen mixed with a carrier gas or an inert gas.

6. The method according to any one of the preceding claims, wherein the nickel metal is applied by a deposition method selected from sputtering and / or vapor deposition processes.

7. The method according to any one of the preceding claims, wherein the annealing includes rapid heat treatment, high-temperature furnace process or laser thermal annealing.

8. The method of claim 7, wherein the rapid heat treatment is performed at a temperature of 550°C or higher.

9. The method according to any one of the preceding claims further comprises the step of removing contaminants and / or unreacted Ni metal from the SiC / Ni metal stack after annealing.

10. The method of claim 9, further comprising an additional thermal annealing treatment following the removal of contaminants and / or unreacted Ni metal.

11. The method according to any one of the preceding claims further includes oxygen plasma treatment of the nickel metal contact material.

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