Silicon carbide semiconductor device and method for manufacturing silicon carbide semiconductor device

Abstract

The present disclosure pertains to a silicon carbide semiconductor device comprising: a silicon carbide substrate; a metal silicide layer provided on the silicon carbide substrate; and an electrode layer provided on the metal silicide layer, wherein the metal silicide layer contains carbon clusters, and the density of the carbon clusters of the metal silicide layer on the silicon carbide substrate side is higher than the density of the carbon clusters of the metal silicide layer on the electrode layer side. Consequently, provided is a silicon carbide semiconductor device imparted with excellent ohmic contact properties by suppressing the deterioration of ohmic contact properties due to the carbon clusters present in the metal silicide layer.

Description

Silicon carbide semiconductor device and method for manufacturing silicon carbide semiconductor device

[0001] The present disclosure relates to a silicon carbide semiconductor device and a method for manufacturing a silicon carbide semiconductor device.

[0002] Silicon carbide (SiC) has a wider bandgap than silicon, making it a very promising material for power devices, etc. Schottky barrier diodes (SBDs), metal oxide semiconductor field effect transistors (MOSFETs), and the like that use SiC have been realized.

[0003] In a vertical power device using SiC, a device structure such as a diode or MOSFET is typically first formed on the front surface side of a SiC semiconductor substrate. To form the device structure, for example, an epitaxial growth layer with a desired impurity concentration is grown on the substrate, and impurity ions are implanted into the epitaxial growth layer and activation annealing of the implanted ions is performed. Then, by repeating the ion implantation and activation annealing, a p-type region or an n-type region that functions as the device structure is formed. A metal or the like is stacked on the formed p-type region and n-type region as an electrode. A metal or the like is also stacked on the back surface side of the SiC semiconductor substrate as an electrode.

[0004] SiC has a high barrier to metals, making it difficult to form a practically effective ohmic contact with most metals simply by direct contact. Therefore, various methods have been explored and proposed to form a low-resistance ohmic contact by lowering the barrier between SiC and metals.

[0005] For example, a method of forming a silicide layer as an ohmic contact between a SiC semiconductor substrate and a metal layer is known (see, for example, Patent Documents 1 and 2). The silicide layer can be formed, for example, by forming a metal layer on the surface of the SiC semiconductor substrate and annealing the metal layer at high temperature to cause a metal-silicide reaction (hereinafter sometimes simply referred to as a "silicide reaction") between the SiC and the metal layer. By reacting (thermal reacting) SiC with the metal to form a metal silicide layer, ohmic contact is formed between the SiC and the metal silicide layer, and ohmic contact is formed between the metal silicide layer and the metal layer, resulting in ohmic contact between the SiC and the metal layer.

[0006] JP 2016-149412 A JP 2019-207949 A

[0007] For example, when Ni is used as the metal layer, a silicide reaction between SiC and Ni results in a NiSi (nickel silicide) layer, but the C (carbon) in the SiC does not react and remains in the NiSi layer, forming carbon clusters. The C derived from SiC cannot be eliminated, and the C aggregates in the NiSi layer and exists as carbon clusters. These carbon clusters have a higher resistance than NiSi, causing a problem of deterioration of ohmic contact properties. There has been a demand for a silicon carbide semiconductor device and a method for manufacturing a silicon carbide semiconductor device that suppresses the deterioration of ohmic contact properties due to carbon clusters.

[0008] The present disclosure has been made to solve the above problems, and has an object to provide a silicon carbide semiconductor device and a method for manufacturing a silicon carbide semiconductor device that are capable of suppressing degradation of ohmic contact properties due to carbon clusters present in a metal silicide layer.

[0009] The present disclosure has been made to achieve the above-mentioned object, and provides a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, wherein the metal silicide layer contains carbon clusters, and the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of the carbon clusters on the electrode layer side of the metal silicide layer.

[0010] Such a silicon carbide semiconductor device suppresses deterioration of ohmic contact due to carbon clusters present in the metal silicide layer, and provides excellent ohmic contact.

[0011] In this case, the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer can be set to be at least twice as high as the density of the carbon clusters on the electrode layer side of the metal silicide layer.

[0012] Such a metal silicide layer provides stable and good ohmic characteristics.

[0013] In this case, when the metal silicide layer is viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer can be longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer.

[0014] Such a metal silicide layer provides stable and good ohmic characteristics.

[0015] In this case, the maximum length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer can be three times or more longer than the maximum length of the carbon clusters on the electrode layer side of the metal silicide layer.

[0016] Such a metal silicide layer provides stable and good ohmic characteristics.

[0017] At this time, 80% or more of the carbon clusters on the silicon carbide substrate side of the metal silicide layer may be not in contact with the silicon carbide substrate.

[0018] Such a metal silicide layer provides stable and good ohmic characteristics.

[0019] In this case, the metal silicide layer may be richer in metal on the electrode layer side than on the silicon carbide substrate side.

[0020] This results in more stable and better ohmic characteristics.

[0021] In this case, the metal in the metal silicide layer may be one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr.

[0022] This results in more stable and better ohmic characteristics.

[0023] In this case, the electrode layer can be Ti / TiN / Al or Ti / Ni / Au.

[0024] Such electrodes can be suitably used in the silicon carbide semiconductor device according to the present disclosure.

[0025] The present disclosure also provides a method for manufacturing a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, the method comprising the steps of forming a metal layer on the silicon carbide substrate, heat-treating the metal layer to form a metal silicide layer, and forming an electrode layer on the metal silicide layer, wherein in the step of forming the metal silicide layer, the heat treatment is performed such that the density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of carbon clusters on the electrode layer side of the metal silicide layer.

[0026] According to such a method for manufacturing a silicon carbide semiconductor device, it is possible to suppress deterioration of ohmic contact due to carbon clusters present in the metal silicide layer, and to manufacture a silicon carbide semiconductor device with excellent ohmic contact.

[0027] In this case, in the step of forming the metal silicide layer, when the metal silicide layer is viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer can be longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer.

[0028] Such a metal silicide layer can be manufactured to have stable and good ohmic characteristics.

[0029] At this time, in the step of forming the metal silicide layer, the heat treatment can be performed so that the metal silicide layer becomes metal-rich on the electrode layer side rather than on the silicon carbide substrate side.

[0030] This makes it possible to manufacture a device with more stable and favorable ohmic characteristics.

[0031] At this time, the heat treatment in the step of forming the metal silicide layer can be performed under heat treatment conditions that allow a portion of the metal layer to remain after the heat treatment.

[0032] By carrying out such heat treatment, it is possible to more reliably and stably manufacture a metal silicide layer in which the density of carbon clusters on the silicon carbide substrate side is higher than the density of carbon clusters on the electrode layer side of the metal silicide layer.

[0033] In this case, the metal in the metal layer can be one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr.

[0034] This makes it possible to manufacture a device with more stable and favorable ohmic characteristics.

[0035] In this case, the electrode layer can be Ti / TiN / Al or Ti / Ni / Au.

[0036] In the method for manufacturing a silicon carbide semiconductor device according to the present disclosure, such an electrode can be suitably used.

[0037] As described above, the silicon carbide semiconductor device of the present disclosure can suppress deterioration of ohmic contact due to carbon clusters present in the metal silicide layer, thereby achieving excellent ohmic contact. The method for manufacturing a silicon carbide semiconductor device of the present disclosure can suppress deterioration of ohmic contact due to carbon clusters present in the metal silicide layer, thereby enabling the manufacture of a silicon carbide semiconductor device with excellent ohmic contact.

[0038] 1 shows an example of a metal silicide layer in a silicon carbide semiconductor device according to the present disclosure; 2 shows another example of a metal silicide layer in a silicon carbide semiconductor device according to the present disclosure; 3 shows yet another example of a metal silicide layer in a silicon carbide semiconductor device according to the present disclosure; 4 shows an example of a silicon carbide semiconductor device according to the present disclosure.

[0039] The present disclosure will be described in detail below, but the present disclosure is not limited thereto.

[0040] As described above, there has been a demand for a silicon carbide semiconductor device and a method for manufacturing a silicon carbide semiconductor device that can suppress deterioration of ohmic contact properties due to carbon clusters present in a metal silicide layer.

[0041] As a result of extensive research into the above-mentioned problems, the present inventors have found that a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, wherein the metal silicide layer contains carbon clusters and the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of the carbon clusters on the electrode layer side of the metal silicide layer, can suppress deterioration of ohmic contact properties due to carbon clusters present in the metal silicide layer, and achieve excellent ohmic contact properties, thereby completing the present disclosure.

[0042] The present inventors have also discovered that a method for manufacturing a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, the method comprising the steps of forming a metal layer on the silicon carbide substrate, heat-treating the metal layer to form a metal silicide layer, and forming an electrode layer on the metal silicide layer, wherein in the step of forming the metal silicide layer, the heat treatment is performed such that the density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of carbon clusters on the electrode layer side of the metal silicide layer, makes it possible to suppress deterioration of ohmic contact properties due to carbon clusters present in the metal silicide layer and to manufacture a silicon carbide semiconductor device with excellent ohmic contact properties, and have completed the present disclosure.

[0043] Hereinafter, the description will be made with reference to the drawings. In this specification, the silicon carbide substrate side of the metal silicide layer refers to the region on the silicon carbide substrate side across the center of the metal silicide layer in the thickness direction (the position where the thickness is half), and the electrode layer side of the metal silicide layer refers to the region on the electrode layer side across the center of the metal silicide layer in the thickness direction (the position where the thickness is half).

[0044] [Silicon Carbide Semiconductor Device] First, a silicon carbide semiconductor device according to the present disclosure will be described. FIG. 4 is a diagram showing an example of a silicon carbide semiconductor device according to the present disclosure. As shown in FIG. 4 , silicon carbide semiconductor device 10 according to the present disclosure includes silicon carbide substrate 1, metal silicide layer 2 on silicon carbide substrate 1, and electrode layer 3 on metal silicide layer 2. Silicon carbide semiconductor device 10 according to the present disclosure may also include a device structure 4 such as a diode or MOSFET. More specifically, device structure 4 may be provided on first main surface 1A of silicon carbide substrate 1, and metal silicide layer 2 and electrode layer 3 thereon may be provided on second main surface 1B opposite to the first main surface. For convenience of explanation, metal silicide layer 2 and electrode layer 3 are shown above silicon carbide substrate 1, and device structure 4 is shown below silicon carbide substrate 1, but the hierarchical relationship shown in FIG. 4 is not necessarily the same in actual implementation.

[0045] 4, the metal silicide layer and the electrode layer 3 thereon may be provided on the same side as the first main surface 1A on which the device structure is provided. For example, the present invention can be applied as an ohmic contact layer for the source portion of a MOSFET. It can also be applied when forming an ohmic contact on the peripheral guard ring of an SBD or a PN diode.

[0046] The metal silicide layer 2 contains carbon clusters 5, and the density of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 is higher than the density of the carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2. By providing such a metal silicide layer 2, the ohmic contact characteristics between the silicon carbide substrate 1 and the electrode layer 3 are improved.

[0047] (Silicon Carbide Substrate) The silicon carbide substrate in the silicon carbide semiconductor device according to the present disclosure is not particularly limited. A single crystal substrate cut from a single crystal ingot grown by sublimation or the like may be used, or an epitaxial substrate having a SiC layer epitaxially grown on a single crystal substrate may also be used. The crystal structure of the silicon carbide substrate is not particularly limited, and may be 4H—SiC, 6H—SiC, 3C—SiC, or the like, and the device structure and the plane orientation on which the metal silicide layer is formed are also not particularly limited. In addition, the conductivity type of the silicon carbide substrate is not particularly limited, and may be either p-type or n-type.

[0048] For example, a 4H—SiC substrate can be used. The plane orientation of the first main surface (front surface) of the 4H—SiC substrate can be expressed as (0001), and the plane orientation of the second main surface (rear surface) can be expressed as (000-1). In view of the advantages of epitaxial growth when fabricating a device structure, etc., it is preferable to use a substrate that is off-axis by several degrees (for example, greater than 0° to 10° or less, preferably 1° to 8°, more preferably 2° to 6°) in the [00-20] direction. Note that the device structure and the surfaces on which the metal silicide layer / electrode layer are provided (first main surface (front surface) and second main surface (rear surface)) are not particularly limited.

[0049] (Metal Silicide Layer) The metal silicide layer 2 contains carbon clusters 5. The density of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 is higher than the density of the carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2. In other words, when the metal silicide layer 2 is divided into the electrode layer side and the silicon carbide substrate side with the middle of the thickness direction as the boundary, the carbon cluster density is higher in the region on the silicon carbide substrate side.

[0050] The density of carbon clusters in a metal silicide layer is defined as the mass of carbon clusters per unit volume of the metal silicide layer, but since the present disclosure focuses on the distribution of carbon clusters in the metal silicide layer, it can be replaced with an evaluation based on a cross-sectional observation image, etc. Of course, it is also possible to determine the actual carbon cluster content by performing elemental analysis in the depth direction and compare the magnitude of the density.

[0051] 1-3 shows a cross-sectional SEM photograph of the silicon carbide substrate, metal silicide layer, and electrode layer of a silicon carbide semiconductor device according to the present disclosure. In the example shown in FIG. 1-3, a NiSi metal silicide layer and a Ti / TiN / Al electrode layer are formed on a SiC substrate.

[0052] In FIG. 1-3, the black portions of the metal silicide layer (NiSi layer) are carbon clusters. As shown in FIG. 1-3, the density of carbon clusters 5 in the metal silicide layer 2 is higher on the silicon carbide substrate 1 side than on the electrode layer 3 side. A silicon carbide semiconductor device including a metal silicide layer having such a carbon cluster density distribution exhibits good ohmic characteristics (reduction in ohmic characteristics is suppressed). On the other hand, if the density of carbon clusters 5 in the metal silicide layer 2 is higher on the electrode layer 3 side than on the silicon carbide substrate 1 side or is uniform in the thickness direction of the metal silicide layer 2, the ohmic characteristics will deteriorate.

[0053] As will be described later, the carbon clusters 5 in the metal silicide layer 2 are formed by clustering of C in SiC due to a silicide reaction between Si in SiC and metal. When carbon clusters formed by such a reaction have a higher density of carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 than on the electrode layer 3 side, the carbon clusters 5 are not formed in a complete layer. In other words, when a cross-section of any portion is taken, carbon clusters are not formed without gaps in the lateral direction, and metal silicide is present between the carbon clusters in the lateral direction in the cross-section. For example, if the carbon clusters are present in a complete layer, there is a concern that they may peel off from that portion. Furthermore, if the carbon clusters are present in a complete layer, the resistance of the carbon cluster layer is higher than that of the metal silicide, resulting in increased conduction loss. Such a carbon cluster layer can occur, for example, when an excessive silicide reaction causes carbon to precipitate on the surface of the metal silicide layer 2 facing the electrode layer 3, resulting in the formation of a complete layer of carbon clusters.

[0054] In the metal silicide layer 2 according to the present disclosure, the carbon cluster density is low on the electrode layer 3 side, which increases the adhesion between the metal silicide layer 2 and the electrode layer 3 and prevents peeling of the electrode layer 3. Furthermore, since the current in the device flows vertically, the presence of the metal silicide portion with low resistance prevents the resistance from increasing.

[0055] In this case, it is preferable that the density of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 is at least two times higher than the density of the carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2. Such a silicon carbide semiconductor device will have stable and better ohmic characteristics. There is no particular upper limit to the density, but it may be, for example, 30 times or less, preferably 20 times or less.

[0056] The difference in density of the carbon clusters 5 in the metal silicide layer 2 can also be expressed by the difference in length of the carbon clusters 5 observed when the metal silicide layer 2 is viewed in cross section. For example, as shown in FIG. 1-3 , when the metal silicide layer 2 is viewed in cross section, the average length of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 can be made longer than the average length of the carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2. This can be achieved by averaging the lengths of the carbon clusters observed in cross section for each region (silicon carbide substrate 1 side / electrode layer 3 side).

[0057] In this case, the maximum length of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 is preferably at least three times longer than the maximum length of the carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2. It is more preferably at least five times longer, and even more preferably at least ten times longer. This can be achieved by extracting and comparing the maximum lengths of carbon clusters observed in cross section for each region (silicon carbide substrate 1 side / electrode layer 3 side). The upper limit of the ratio is not particularly limited, but may be, for example, 20 times or less, preferably 15 times or less.

[0058] It is also preferable that 80% or more of the carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 are not in contact with the silicon carbide substrate 1. Such a silicon carbide semiconductor device will have stable and better ohmic characteristics. There is no particular upper limit, and for example, 100% of the carbon clusters 5 may not be in contact with the silicon carbide substrate 1.

[0059] Furthermore, it is preferable that the metal silicide layer 2 is richer in metal on the electrode layer 3 side than on the silicon carbide substrate 1 side, so that the ohmic characteristics are more stable and excellent (deterioration of the ohmic characteristics is suppressed).

[0060] The thickness of the metal silicide layer 2 is not particularly limited and can be determined in accordance with the design of the silicon carbide semiconductor device as long as it can exhibit ohmic contact characteristics. For example, it can be 1.00 μm or less, and preferably 0.05 μm (500 Å) to 0.40 μm (4000 Å).

[0061] The metal in the metal silicide layer 2 is not particularly limited as long as it can form a metal silicide by reacting with SiC. For example, it can be one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr. Of these, it is preferable to use Ni, because Ni is a material that is more stable and has good ohmic characteristics when silicided.

[0062] (Electrode Layer) The material used for the electrode layer 3 is not particularly limited. It may be a single layer or a multi-layer laminate (3A, 3B, 3C). For example, Ti / TiN / Al or Ti / Ni / Au is preferable. Furthermore, Pd / Ti / Ni / Au can also be used. Note that the above laminate is written in the order of proximity to the semiconductor surface, and when written as Ti / TiN / Al, it means that Ti, TiN, and Al are laminated on the metal silicide in this order.

[0063] As described above, the silicon carbide semiconductor device according to the present disclosure suppresses deterioration of ohmic contact due to carbon clusters present in the metal silicide layer, thereby providing excellent ohmic contact.

[0064] The silicon carbide semiconductor device according to the present disclosure, which includes the metal silicide layer 2 in which the density of carbon clusters 5 on the silicon carbide substrate 1 side of the metal silicide layer 2 is higher than the density of carbon clusters 5 on the electrode layer 3 side of the metal silicide layer 2 as described above, can be manufactured by the method described below.

[0065] [Method for manufacturing a silicon carbide semiconductor device] Next, a method for manufacturing a silicon carbide semiconductor device according to the present disclosure will be described. The method for manufacturing a silicon carbide semiconductor device according to the present disclosure is a method for manufacturing a silicon carbide semiconductor device 10 including a silicon carbide substrate 1, a metal silicide layer 2 on the silicon carbide substrate 1, and an electrode layer 3 on the metal silicide layer 2. The method includes the steps of forming a metal layer on the silicon carbide substrate 1, heat-treating the metal layer to form the metal silicide layer 2, and forming the electrode layer 3 on the metal silicide layer 2. In the step of forming the metal silicide layer 2, the heat treatment is performed so that the density of carbon clusters on the silicon carbide substrate 1 side of the metal silicide layer 2 is higher than the density of carbon clusters on the electrode layer 3 side of the metal silicide layer 2.

[0066] (Step of forming metal layer) In the step of forming the metal layer, a metal capable of forming a metal silicide by reaction with the silicon carbide substrate is formed. The type of metal is not particularly limited, but may be, for example, one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr. Of these, it is preferable to use Ni. The method of forming the metal layer is not particularly limited, and can be a well-known film formation method such as sputtering or EB deposition.

[0067] (Step of forming a metal silicide layer) In the step of forming a metal silicide layer, the metal layer is heat-treated to react with the silicon carbide substrate. The heat treatment method is not particularly limited as long as it can cause a silicide reaction, and general heat treatment methods such as RTA and laser annealing can be used. In the step of forming a metal silicide layer according to the present disclosure, the heat treatment is performed so that the density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of carbon clusters on the electrode layer side of the metal silicide layer.

[0068] It is also preferable that, when viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer, which allows the production of a metal silicide layer with stable and excellent ohmic characteristics.

[0069] Typical heat treatment conditions include, for example, the treatment temperature, treatment time, and power output of the heating means (e.g., laser). Increasing the treatment temperature, lengthening the treatment time, and increasing the power output of the heating means (e.g., laser) accelerates the silicidation reaction between the metal from the metal layer and the Si in the SiC, and also increases the rate at which carbon clusters derived from the C in the SiC diffuse away from the substrate. Therefore, by adjusting these conditions, the position at which the density of carbon clusters is high can be adjusted. However, the degree of progress of the metal silicidation reaction varies depending on factors such as the thickness of the metal layer. For example, if the metal layer is thin, the entire metal layer will be uniformly silicided even with a shorter and / or lower heat treatment time than if the metal layer is thicker. Furthermore, the tendency varies depending on the type of metal element. Therefore, it is difficult to specify the heat treatment conditions of the present disclosure in numerical ranges.

[0070] Here, an example of processing conditions when a Ni layer of about 1000 Å is formed as a metal layer on a substrate is shown. However, the processing conditions in the present disclosure are not limited to the following conditions. When SiC and Ni are subjected to a silicide reaction by RTA heating at a temperature of 950 to 1050°C, preferably 975 to 1000°C, for 1 to 3 minutes, a NiSi layer of about 1200 to 2500 Å (0.12 to 0.25 μm) in thickness having the above-mentioned carbon cluster density distribution is formed. Usually, a NiSi layer is formed that is about twice the thickness of the Ni layer formed. In this way, the contact resistance of the NiSi layer is reduced to 5×10 －５ Ω cm ２ The lower limit of the contact resistance of the NiSi layer is, for example, 5×10 －６ Ω cm ２ It is more than enough.

[0071] In controlling the density of carbon clusters, it is believed that by reacting with SiC in a metal-rich state (a state in which there is a sufficient supply of metal), a metal silicide with a high metal composition ratio is formed, and the density of the carbon clusters decreases. On the other hand, when the ratio of Si in the metal silicide is high, more C (carbon) is liberated from SiC. In other words, the density of the carbon clusters increases.

[0072] From this perspective, it is preferable to perform the heat treatment in the step of forming the metal silicide layer under heat treatment conditions that allow a portion of the metal layer to remain after the heat treatment. When a portion of the metal layer remains after the heat treatment, the supply of metal components continues in the upper part of the metal silicide layer (the electrode layer side), maintaining a metal-rich state, and therefore the density of carbon clusters becomes lower than that in the lower part of the metal silicide layer. That is, the lower part of the metal silicide layer is in a Si-rich state, so the density of carbon clusters becomes higher more reliably and more stably. Therefore, it is possible to more reliably obtain a metal silicide layer with a higher density of carbon clusters on the silicon carbide substrate side (lower part) than on the electrode layer side (upper part) of the metal silicide layer. The metal layer remaining after the heat treatment can be removed as appropriate.

[0073] Alternatively, for example, the processing temperature, processing time, and output of the heating means (e.g., laser) may be set as initial conditions for heat treatment to form a metal silicide layer, and the density of carbon clusters within the metal silicide layer may be evaluated. The results may then be used to adjust at least one of the processing temperature, processing time, and output of the heating means (e.g., laser) to adjust the position where the carbon cluster density is high. For example, if the density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is lower than the density of carbon clusters on the electrode layer side of the metal silicide layer, or if the density of carbon clusters is uniform throughout the metal silicide layer, adjustments may be made to lower the processing temperature, shorten the processing time, and lower the output of the heating means (e.g., laser). The heat treatment conditions may then be set so that part of the metal layer remains.

[0074] (Step of forming electrode layer) The method for forming the electrode layer is not particularly limited. The electrode layer can be formed by a well-known film formation method such as sputtering or EB deposition. The electrode layer can be Ti / TiN / Al or Ti / Ni / Au. It can also be Pd / Ti / Ni / Au.

[0075] As described above, according to the method for manufacturing a silicon carbide semiconductor device according to the present disclosure, it is possible to suppress deterioration of ohmic contact properties due to carbon clusters present in a metal silicide layer, and to manufacture a silicon carbide semiconductor device with excellent ohmic contact properties.

[0076] The present disclosure will be specifically described below using examples, but the present disclosure is not limited thereto.

[0077] (Example) Using a 4H-SiC substrate with n-type conductivity, a Ni layer was formed on the substrate as a metal layer, and then heat treatment was performed by RTA heating at a temperature of 975°C for 2 minutes to cause a silicide reaction between the SiC and Ni, forming a NiSi layer with a thickness of approximately 1800 to 2000 Å (0.18 to 0.20 μm). The heat treatment temperature and time were set so that a portion of the Ni layer remained on the surface after the heat treatment. Thereafter, a Ti / TiN / Al layer was formed as an electrode layer. When the ohmic characteristics of the NiSi layer obtained in this manner were evaluated, the contact resistance was found to be 1×10 －５ Ω cm ２ The thickness of the NiSi layer was about 100 μm, and good ohmic contact was obtained. The results of cross-sectional SEM observation are shown in Figures 1 to 3. It can be seen that the density of carbon clusters is higher on the SiC substrate side than on the middle of the NiSi layer in the thickness direction, and the length of the linear carbon clusters, which appear black, is also longer on the SiC substrate side.

[0078] As described above, according to the examples of the present disclosure, it is possible to suppress the deterioration of ohmic contact properties due to carbon clusters present in the metal silicide layer, and to achieve excellent ohmic contact properties.

[0079] This specification includes the following aspects. [1]: A silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, wherein the metal silicide layer contains carbon clusters, and the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of the carbon clusters on the electrode layer side of the metal silicide layer. [2]: The silicon carbide semiconductor device of [1] above, wherein the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is at least two times higher than the density of the carbon clusters on the electrode layer side of the metal silicide layer. [3]: The silicon carbide semiconductor device of [1] or [2] above, wherein, when the metal silicide layer is viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer. [4]: The silicon carbide semiconductor device of [1], [2] or [3] above, wherein the maximum length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is at least three times longer than the maximum length of the carbon clusters on the electrode layer side of the metal silicide layer. [5]: The silicon carbide semiconductor device of [1], [2], [3] or [4] above, wherein 80% or more of the carbon clusters on the silicon carbide substrate side of the metal silicide layer are not in contact with the silicon carbide substrate. [6]: The silicon carbide semiconductor device of [1], [2], [3], [4] or [5] above, wherein the metal silicide layer is more metal-rich on the electrode layer side than on the silicon carbide substrate side. [7]: The silicon carbide semiconductor device according to [1], [2], [3], [4], [5] or [6], wherein the metal in the metal silicide layer is one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V and Cr. [8]: The silicon carbide semiconductor device according to [1], [2], [3], [4], [5], [6] or [7], wherein the electrode layer is Ti / TiN / Al or Ti / Ni / Au.[9]: A method for manufacturing a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, comprising the steps of forming a metal layer on the silicon carbide substrate, heat-treating the metal layer to form the metal silicide layer, and forming an electrode layer on the metal silicide layer, wherein in the step of forming the metal silicide layer, the heat treatment is performed such that a density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than a density of carbon clusters on the electrode layer side of the metal silicide layer.

[10] : The method for manufacturing a silicon carbide semiconductor device according to [9], wherein in the step of forming the metal silicide layer, an average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is longer than an average length of the carbon clusters on the electrode layer side of the metal silicide layer when viewed in cross section of the metal silicide layer.

[11] : The method for manufacturing a silicon carbide semiconductor device according to [9] or

[10] above, wherein, in the step of forming the metal silicide layer, the heat treatment is performed so that the metal silicide layer becomes richer in metal on the electrode layer side than on the silicon carbide substrate side.

[12] : The method for manufacturing a silicon carbide semiconductor device according to [9],

[10] or

[11] above, wherein the heat treatment in the step of forming the metal silicide layer is performed under heat treatment conditions such that a portion of the metal layer remains after the heat treatment.

[13] : The method for manufacturing a silicon carbide semiconductor device according to [9],

[10] ,

[11] or

[12] above, wherein the metal in the metal layer is one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V and Cr.

[14] : The method for manufacturing a silicon carbide semiconductor device according to [9],

[10] ,

[11] ,

[12] or

[13] , wherein the electrode layer is Ti / TiN / Al or Ti / Ni / Au.

[0080] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure.

Claims

1. A silicon carbide semiconductor device comprising a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, wherein the metal silicide layer contains carbon clusters, and the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of the carbon clusters on the electrode layer side of the metal silicide layer.

2. The silicon carbide semiconductor device according to claim 1, wherein the density of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is at least twice as high as the density of the carbon clusters on the electrode layer side of the metal silicide layer.

3. The silicon carbide semiconductor device according to claim 1, characterized in that, when the metal silicide layer is viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer.

4. The silicon carbide semiconductor device according to claim 1, wherein the maximum length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is at least three times longer than the maximum length of the carbon clusters on the electrode layer side of the metal silicide layer.

5. The silicon carbide semiconductor device according to claim 1, wherein 80% or more of the carbon clusters on the silicon carbide substrate side of the metal silicide layer are not in contact with the silicon carbide substrate.

6. The silicon carbide semiconductor device according to claim 1, wherein the metal silicide layer is richer in metal on the electrode layer side than on the silicon carbide substrate side.

7. The silicon carbide semiconductor device according to claim 1, wherein the metal in the metal silicide layer is one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr.

8. The silicon carbide semiconductor device according to any one of claims 1 to 7, wherein the electrode layer is Ti / TiN / Al or Ti / Ni / Au.

9. A method for manufacturing a silicon carbide semiconductor device including a silicon carbide substrate, a metal silicide layer on the silicon carbide substrate, and an electrode layer on the metal silicide layer, comprising the steps of: forming a metal layer on the silicon carbide substrate; heat-treating the metal layer to form a metal silicide layer; and forming an electrode layer on the metal silicide layer, wherein in the step of forming the metal silicide layer, the heat treatment is performed so that the density of carbon clusters on the silicon carbide substrate side of the metal silicide layer is higher than the density of carbon clusters on the electrode layer side of the metal silicide layer.

10. A method for manufacturing a silicon carbide semiconductor device as described in claim 9, characterized in that in the step of forming the metal silicide layer, when the metal silicide layer is viewed in cross section, the average length of the carbon clusters on the silicon carbide substrate side of the metal silicide layer is longer than the average length of the carbon clusters on the electrode layer side of the metal silicide layer.

11. The method for manufacturing a silicon carbide semiconductor device according to claim 9, wherein in the step of forming the metal silicide layer, the heat treatment is performed so that the metal silicide layer becomes richer in metal on the electrode layer side than on the silicon carbide substrate side.

12. The method for manufacturing a silicon carbide semiconductor device according to claim 9, wherein the heat treatment in the step of forming the metal silicide layer is carried out under heat treatment conditions such that a portion of the metal layer remains after the heat treatment.

13. The method for manufacturing a silicon carbide semiconductor device according to claim 9, wherein the metal in the metal layer is one or more of Ni, Mo, W, Ta, Ti, Co, Pt, Zr, Hf, V, and Cr.

14. The method for manufacturing a silicon carbide semiconductor device according to any one of claims 9 to 13, wherein the electrode layer is made of Ti / TiN / Al or Ti / Ni / Au.

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