A silicon carbide semiconductor device and a manufacturing method thereof

Abstract

A silicon carbide semiconductor device and a manufacturing method thereof. The manufacturing method of the silicon carbide semiconductor device includes the following steps: providing a semiconductor element structure on a silicon carbide substrate, the semiconductor element structure being formed on a front surface of the silicon carbide substrate; forming a multilayer structure on a back surface of the silicon carbide substrate, the multilayer structure including a plurality of ohmic contact layers and a plurality of capture material layers. By dispersing the capture material into multiple layers and by adjusting the thickness combination of the ohmic contact layer and the capture material layer, even if the capture material layer is relatively thin (a thickness sufficient to be spheroidized), there is still a sufficient content to capture carbon and reduce the accumulation of carbon.

Description

Technical Field

[0001] The present invention relates to a semiconductor device, and particularly to a silicon carbide semiconductor device and a manufacturing method thereof. Background Art

[0002] In terms of characteristics, semiconductor power components generally require a high breakdown voltage, and have as small a conduction resistance as possible, low reverse leakage current, and a relatively fast switching speed to reduce conduction loss and switching loss during operation. Since silicon carbide (SiC) has characteristics such as a wide bandgap (Bandgap Eg = 3.26 eV), a high critical breakdown electric field strength (2.2 MV / cm), and a high thermal conductivity (4.9 W / cm-K), it is considered an excellent material for power switching components. Under the same breakdown voltage condition, the thickness of the voltage-resistant layer (low-doped drift layer) of a power component made of silicon carbide is only one-tenth of that of a silicon (Si) power component, and the theoretical conduction resistance can reach one-hundredth of that of silicon.

[0003] However, after a power component made of silicon carbide undergoes processing steps such as grinding, annealing, and deposition, the excess carbon atoms react with nickel to form nickel silicide and are prone to aggregation and accumulation at grain boundaries, resulting in peeling and cracking between the multi-layer structures of the semiconductor device, causing a significant increase in the resistance value and affecting the reliability of the semiconductor device at the same time. Summary of the Invention

[0004] The main object of the present invention is to solve the problems that peeling and cracking occur between the multi-layer structures of a conventional silicon carbide semiconductor device due to the accumulation of carbon materials during the manufacturing process, resulting in an increase in the resistance value between the devices.

[0005] To achieve the above object, the present invention provides a manufacturing method for a silicon carbide semiconductor device, including the following steps: providing a semiconductor element structure on a silicon carbide substrate, the semiconductor element structure being formed on a front surface of the silicon carbide substrate; forming a multi-layer structure on a back surface of the silicon carbide substrate, the multi-layer structure including a first ohmic contact layer formed on the back surface, a first capture material layer formed on the first ohmic contact layer, a second ohmic contact layer formed on the first capture material layer, a second capture material layer formed on the second ohmic contact layer, and a third ohmic contact layer formed on the second capture material layer.

[0006] In an embodiment of the present invention, after forming the multi-layer structure, a laser annealing step is performed on the multi-layer structure.

[0007] In an embodiment of the present invention, after the laser annealing step, a metal layer is formed on a side of the multi-layer structure away from the silicon carbide substrate.

[0008] In an embodiment of the present invention, the material of the ohmic contact layer is nickel, a nickel-silicon bilayer, nickel silicide, or a combination of the foregoing.

[0009] In an embodiment of the present invention, the material of the capture material layer is titanium, molybdenum, tungsten, tantalum, or a combination of the foregoing.

[0010] In an embodiment of the present invention, the total thickness of the multi-layer structure is between 105 nm and 405 nm.

[0011] In an embodiment of the present invention, the thickness of the ohmic contact layer is between 25 nm and 120 nm, and the thickness of the capture material layer is between 15 nm and 45 nm.

[0012] In an embodiment of the present invention, the thickness of the ohmic contact layer is greater than the thickness of the capture material layer.

[0013] To achieve the above object, the present invention further provides a silicon carbide semiconductor device manufactured by the above method.

[0014] To achieve the above object, the present invention further provides a method for manufacturing a silicon carbide semiconductor device, including the following steps: providing a semiconductor element structure on a silicon carbide substrate, the semiconductor element structure being formed on a front surface of the silicon carbide substrate; forming a first multi-layer structure on a back surface of the silicon carbide substrate, the first multi-layer structure including a plurality of ohmic contact layers and at least one capture material layer disposed between the ohmic contact layers; performing a first laser annealing step on the first multi-layer structure to form a first ohmic contact attached to the silicon carbide substrate; forming a second multi-layer structure on the first ohmic contact, the second multi-layer structure including at least one of the capture material layers and at least one of the ohmic contact layers disposed on the capture material layer; and performing a second laser annealing step on the second multi-layer structure to jointly form a second ohmic contact attached to the silicon carbide substrate with the first ohmic contact.

[0015] In an embodiment of the present invention, the total thickness of the first multi-layer structure is between 65 nm and 285 nm.

[0016] In an embodiment of the present invention, the total thickness of the second multi-layer structure is between 40 nm and 165 nm.

[0017] In an embodiment of the present invention, the thickness of the ohmic contact layer is between 25 nm and 120 nm, and the thickness of the capture material layer is between 15 nm and 45 nm. Description of the Drawings

[0018] Figures 1A to 1D Schematic diagram of the manufacturing process of the first embodiment of the present invention.

[0019] Figure 2 Schematic diagram of the spheroidization of the capture material in an embodiment of the present invention.

[0020] Figures 3A to 3E Schematic diagram of the manufacturing process of the second embodiment of the present invention. Detailed implementation manners

[0021] The present invention provides a method for manufacturing a silicon carbide semiconductor device. Refer to Figures 1A to 1D As shown, it is a schematic diagram of the manufacturing process of the first embodiment of the present invention. As Figure 1A shown, first provide a silicon carbide substrate 10 and a semiconductor element structure 20. The silicon carbide substrate 10 includes a front surface 11 and a back surface 12 opposite to the front surface, and the semiconductor element structure 20 is disposed on the front surface 11 of the silicon carbide substrate 10. In the present invention, the semiconductor element structure 20 is a structure of a vertical semiconductor power element, whereby a power transistor element is formed on the silicon carbide substrate 10, such as a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), a Junction Field Effect Transistor (JFET), or an Insulated Gate Bipolar Transistor (IGBT). After disposing the semiconductor element structure 20, optionally, a back grinding step is performed on the back surface 12 of the silicon carbide substrate 10 to thin the silicon carbide substrate 10 after grinding to a thickness between 50 μm and 150 μm; in addition, after the back grinding step, a dry etching may optionally be performed on the back surface 12 of the silicon carbide substrate 10 to release stress.

[0022] As Figure 1BAs shown, a plurality of ohmic contact layers and a plurality of gettering material layers are alternately deposited on the back surface 12 of the silicon carbide substrate 10 to form a multi-layer structure 30. The multi-layer structure 30 includes a first ohmic contact layer 31A formed on the back surface 12, a first gettering material layer 32A formed on the first ohmic contact layer 31A, a second ohmic contact layer 31B formed on the first gettering material layer 32A, a second gettering material layer 32B formed on the second ohmic contact layer 31B, and a third ohmic contact layer 31C formed on the second gettering material layer 32B. In this embodiment, the first ohmic contact layer 31A, the first gettering material layer 32A, the second ohmic contact layer 31B, the second gettering material layer 32B, and the third ohmic contact layer 31C are deposited in sequence.

[0023] The ohmic contact layers 31A, 31B, 31C and the gettering material layers 32A, 32B can be formed by techniques such as evaporation, sputtering, chemical vapor deposition or spin coating. The ohmic contact layers 31A, 31B, 31C are metals or metal compounds for forming ohmic contacts. The ohmic contact layers 31A, 31B, 31C can be made of nickel, a nickel / silicon bilayer or nickel silicide. The gettering material layers 32A, 32B include at least one gettering material for getting carbon diffused from the silicon carbide substrate 10 in subsequent processes. The gettering material layers 32A, 32B can be made of titanium, molybdenum, tungsten, tantalum or a combination thereof. In this embodiment, the gettering material layers 32A, 32B are composed of only a single type of the gettering material.

[0024] As Figure 1CAs shown, after depositing the multi-layer structure 30, a laser annealing step is performed on the multi-layer structure 30 to form an ohmic contact 40. When the multi-layer structure 30 is subjected to the laser annealing, the components of the multi-layer structure 30 will diffuse downward, while the components of the silicon carbide substrate 10 will diffuse upward. The silicon carbide substrate 10 will react with the metals in the ohmic contact layers 31A, 31B, and 31C to form metal silicides (such as nickel silicide), and carbon will be precipitated. The precipitated carbon will be captured by the capture material in the capture material layer 32 to form a carbon compound (such as titanium carbide), thereby preventing the precipitated carbon from remaining at the interface between the silicon carbide substrate 10 and the ohmic contact 40 and / or on the upper surface of the ohmic contact 40, or forming defects such as carbon clusters or carbon interstitials. The aforementioned defects will cause problems such as interface peeling and cracking, and increase the resistance value. In different embodiments, the light source of the laser annealing step can be selected from ultraviolet light or green laser light. The temperature of the laser annealing step is between 800°C and 1500°C, and the time of the laser annealing step is between 10 ns and 150 ns.

[0025] As Figure 1D shown, after the laser annealing, a metal layer 50 is disposed on the other side of the ohmic contact 40 away from the silicon carbide substrate 10. In other embodiments, before disposing the metal layer 50, a nickel silicide layer can be deposited first, and then the metal layer 50 can be deposited.

[0026] In the present invention, the multi-layer structure 30 includes at least three layers of ohmic contact thick layers and at least two layers of capture material thin layers sandwiched between the ohmic contact thick layers. In terms of thickness design, the multi-layer structure 30 needs to select an appropriate total thickness. If the thickness of the multi-layer structure 30 is too thick, too much of the silicon carbide substrate 10 will be consumed; if the thickness of the multi-layer structure 30 is too thin, an effective ohmic contact 40 cannot be formed. Only when the multi-layer structure 30 has an appropriate total thickness can a low contact resistance be obtained. According to an embodiment of the present invention, the total thickness of the multi-layer structure 30 is between 105 nm and 450 nm, preferably between 150 nm and 200 nm. After the laser annealing, the thickness of the ohmic contact 40 is between 200 nm and 600 nm, and the thickness of the ohmic contact 40 is greater than the thickness of the multi-layer structure 30 before the laser annealing.

[0027] The prior art uses a single-layer capture material layer. If the single-layer capture material layer is too thin, the capture material will be insufficient to react with the carbon dissipated from the silicon carbide substrate. However, if the single-layer capture material layer is too thick, the capture material will not be able to form balling at the high temperature of laser annealing, thus unable to react with the carbon of the silicon carbide substrate, and it will also affect the diffusion of silicon in the silicon carbide substrate. Moreover, the oversaturated capture material will react with the silicon of the silicon carbide substrate to form titanium silicide, which will have an adverse effect on the device.

[0028] Refer to Figure 2 , which is a schematic diagram of the balling of the capture material in an embodiment of the present invention. To solve the problems faced by the aforementioned prior art, the present invention proposes that in the multi-layer structure 30 for ohmic contact, at least two layers of the capture material layers 32A and 32B are provided, and the capture material layers 32A and 32B will form balling 321A and 321B during high-temperature annealing. By dispersing the capture material into multiple layers and expanding the capture material to a three-dimensional structure, the capture effect can be exerted in the vertical direction (as shown by the arrows in Figure 2 ); and by adjusting the thickness combination of the ohmic contact layers 31A, 31B, 31C and the capture material layers 32A, 32B, even if the capture material layers 32A, 32B are relatively thin (thickness sufficient for balling), there is still sufficient content to capture carbon and does not affect the diffusion of silicon in the silicon carbide substrate, so as to achieve the best capture ability.

[0029] In this embodiment, the thicknesses T 1A 、T 1B 、T 1C of the ohmic contact layers 31A, 31B, 31C are respectively greater than the thicknesses T 2A 、T 2B of the capture material layers 32A, 32B. In other words, the thickness T 1A 、T 1B 、T 1C of any one of the ohmic contact layers 31A, 31B, 31C is greater than the thickness T 2A 、T 2B of any one of the capture material layers 32A, 32B. The thicknesses T 1A 、T 1B 、T 1C of the ohmic contact layers 31A, 31B, 31C are respectively between 25 nm and 120 nm. The thicknesses T 1A 、T 1B 、T 1C of the ohmic contact layers 31A, 31B, 31C can be the same or different. The thicknesses T 2A 、T 2Bare respectively between 15 nm and 45 nm, and the thicknesses T 2A and T 2B of the capture material layers 32A and 32B may be the same or different. According to an embodiment of the present invention, the thicknesses T 1A and T 1B and T 1C of the ohmic contact layers 31A, 31B, and 31C are respectively between 40 nm and 60 nm, and the thicknesses T 2A and T 2B of the capture material layers 32A and 32B are respectively between 20 nm and 30 nm; according to another embodiment of the present invention, the thicknesses T 1A and T 1B and T 1C of the ohmic contact layers 31A, 31B, and 31C are each 50 nm, and the thicknesses T 2A and T 2B of the capture material layers 32A and 32B are each 25 nm.

[0030] In this embodiment, the distance between the capture material layer 32A and the lower surface 302 of the multi-layer structure 30 is equal to the distance between the capture material layer 32B and the upper surface 301 of the multi-layer structure 30. In other words, the thicknesses T 1A and T 1C of the ohmic contact layers 31A and 31C are the same. According to an embodiment of the present invention, the distance between the capture material layer 32A and the lower surface 302 of the multi-layer structure 30 may be greater than the distance between the capture material layer 32B and the upper surface 301 of the multi-layer structure 30, so that the ohmic contact layer 31A has sufficient content to react with the underlying silicon carbide substrate 10 to avoid poor adhesion. For example, the thicknesses T 1A and T 1B and T 1C of the ohmic contact layers 31A, 31B, and 31C are 25 nm, 50 nm, and 75 nm respectively, and the thicknesses T 2A and T 2B of the capture material layers 32A and 32B are each 25 nm.

[0031] According to other embodiments of the present invention, the ohmic contact layer and the capture material layer may also be combined in other numbers, such as four layers of the ohmic contact layer and three layers of the capture material layer; or five layers of the ohmic contact layer and four layers of the capture material layer. In the foregoing combinations, the thickness of the capture material layer may be less than 15 nm. In this way, at the high temperature of laser annealing, the capture material of the capture material layer can form more spheres.

[0032] According to the multi-layer structure 30 of the present invention, the carbon dissipated from the silicon carbide substrate 10 is effectively reduced from accumulating between the multi-layer structures 30, solving problems such as easy peeling and cracking of the conventional ohmic contact, and further avoiding the increase in the resistance value.

[0033] Refer to Figures 3A to 3E As shown, it is a schematic manufacturing process diagram of the second embodiment of the present invention. The difference between this embodiment and Figures 1A to 1D the embodiment is that the multi-layer structure 30 undergoes at least two laser annealing steps.

[0034] First, as Figure 3A and Figure 3B shown, a first ohmic contact layer 31A, a first capture material layer 32A, and a second ohmic contact layer 31B are sequentially deposited on the back surface 12 of the silicon carbide substrate 10, and a first multi-layer structure 30A is formed on the back surface 12 of the silicon carbide substrate 10. A first laser annealing step is performed on the first multi-layer structure 30A to form a first ohmic contact 40A. Among them, the thickness of the first multi-layer structure 30A is between 65 nm and 285 nm.

[0035] After that, as Figure 3C and Figure 3D shown, a second capture material layer 32B and a third ohmic contact layer 31C are sequentially deposited on the first ohmic contact 40A, and a second multi-layer structure 30B is formed on the ohmic contact 40A. After depositing the second multi-layer structure 30B, a second laser annealing step is performed on the second multi-layer structure 30B to make the first ohmic contact 40A and the second multi-layer structure 30B jointly form a second ohmic contact 40B. Among them, the thickness of the second multi-layer structure 30B is between 40 nm and 165 nm. In this embodiment, the thickness and quantity selection of the first ohmic contact layer 31A, the first capture material layer 32A, the second ohmic contact layer 31B, the second capture material layer 32B, and the third ohmic contact layer 31C can be as in the above embodiment.

[0036] As Figure 3E shown, after laser annealing, the metal layer 50 is disposed on the other side of the second ohmic contact 40B away from the silicon carbide substrate 10. In other embodiments, before disposing the metal layer 50, a nickel silicide layer can be deposited first, and then the metal layer 50 is deposited.

[0037] Thus, through the two laser annealing steps of the second ohmic contact 40B, the crystallization effect of the second ohmic contact 40B is better and it can more effectively capture carbon, thus greatly improving its adhesion ability.

[0038] In summary, in the multi-layer structure for forming an ohmic contact of the present invention, at least two thin layers of a capture material are incorporated. By designing the capture material as a multi-thin layer structure, the capture material layer can effectively spheroidize on different planes and can also provide a sufficient content. Thus, without affecting the diffusion of silicon in the silicon carbide substrate, carbon can be sufficiently captured, thereby preventing the precipitated carbon from remaining at the interface between the silicon carbide substrate and the ohmic contact layer and / or on the upper surface of the ohmic contact layer, or forming defects such as carbon clusters or interstitial carbon, thereby increasing the adhesion of the interface. Moreover, due to the reduction of defects, an increase in the resistance value is avoided, thereby improving the performance of the silicon carbide semiconductor device.

Claims

1. A method for manufacturing a silicon carbide semiconductor device, characterized in that Comprising the following steps: Providing a semiconductor element structure on a silicon carbide substrate, the semiconductor element structure being formed on a front surface of the silicon carbide substrate; and forming a multilayer structure on a back surface of the silicon carbide substrate, the multilayer structure including a first ohmic contact layer formed on the back surface, a first capture material layer formed on the first ohmic contact layer, a second ohmic contact layer formed on the first capture material layer, a second capture material layer formed on the second ohmic contact layer, and a third ohmic contact layer formed on the second capture material layer, the materials of the first ohmic contact layer, the second ohmic contact layer, and the third ohmic contact layer being nickel, a nickel-silicon bilayer, nickel silicide, or a combination thereof, the materials of the first capture material layer and the second capture material layer being titanium, molybdenum, tungsten, tantalum, or a combination thereof, the total thickness of the multilayer structure being between 105 nm and 405 nm, and the thickness of any one of the first ohmic contact layer, the second ohmic contact layer, and the third ohmic contact layer being greater than the thickness of any one of the first capture material layer and the second capture material layer.

2. The manufacturing method of the silicon carbide semiconductor device according to claim 1, characterized in that After forming the multilayer structure, performing a laser annealing step on the multilayer structure.

3. The manufacturing method of the silicon carbide semiconductor device according to claim 2, characterized in that After the laser annealing step, forming a metal layer on a side of the multilayer structure away from the silicon carbide substrate.

4. The manufacturing method of the silicon carbide semiconductor device according to claim 1, characterized in that The thicknesses of the first ohmic contact layer, the second ohmic contact layer, and the third ohmic contact layer are between 25 nm and 120 nm, and the thicknesses of the first capture material layer and the second capture material layer are between 15 nm and 45 nm.

5. A silicon carbide semiconductor device, characterized in that Manufactured by the manufacturing method according to any one of claims 1 to 4.

6. A method for manufacturing a silicon carbide semiconductor device, characterized in that Comprising the following steps: Providing a semiconductor element structure on a silicon carbide substrate, the semiconductor element structure being formed on a front surface of the silicon carbide substrate; forming a first multilayer structure on a back surface of the silicon carbide substrate, the first multilayer structure including a plurality of ohmic contact layers and at least one capture material layer disposed between the plurality of ohmic contact layers, including sequentially depositing a first ohmic contact layer, a first capture material layer, and a second ohmic contact layer on the back surface of the silicon carbide substrate to form a first multilayer structure on the back surface of the silicon carbide substrate; Performing a first laser annealing step on the first multilayer structure to form a first ohmic contact attached to the silicon carbide substrate; forming a second multilayer structure on the first ohmic contact, the second multilayer structure including at least one of the capture material layers and at least one of the ohmic contact layers disposed on the capture material layer, including sequentially depositing a second capture material layer and a third ohmic contact layer on the first ohmic contact to form a second multilayer structure on the first ohmic contact; And performing a second laser annealing step on the second multilayer structure to cause the second multilayer structure and the first ohmic contact to jointly form a second ohmic contact attached to the silicon carbide substrate, the thickness of any one of the first ohmic contact layer, the second ohmic contact layer, and the third ohmic contact layer being greater than the thickness of any one of the first capture material layer and the second capture material layer.

7. The manufacturing method of the silicon carbide semiconductor device according to claim 6, characterized in that The total thickness of the first multilayer structure is between 65 nm and 285 nm.

8. The manufacturing method of the silicon carbide semiconductor device according to claim 6, characterized in that The total thickness of the second multi-layer structure is between 40 nm and 165 nm.

9. The manufacturing method of the silicon carbide semiconductor device according to claim 6, wherein The thickness of the ohmic contact layer is between 25 nm and 120 nm, and the thickness of the capture material layer is between 15 nm and 45 nm.

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