Semiconductor device

Abstract

The present invention achieves a solder-bonding electrode to which solder can suitably bond and reduces the amount of Au used. Provided is a semiconductor device comprising a semiconductor substrate and a solder-bonding electrode that is provided to the surface of the semiconductor substrate. The solder-bonding electrode has a base metal film and an oxidation-preventing metal film which covers the surface of the base metal film. The oxidation-preventing metal film is constituted by an alloy of Au and an alloying metal which is constituted by a metal other than Au. Thus, it is possible to achieve a solder-bonding electrode to which solder can suitably bond, while reducing the amount of Au used.

Description

Semiconductor device

[0001] (Cross-reference to Related Application) This application is a related application of Japanese Patent Application No. 2025-050251 filed on March 25, 2025, claims priority based on this Japanese Patent Application, and incorporates all contents described in this Japanese Patent Application herein as part of the present specification.

[0002] The technology disclosed in the present specification relates to a semiconductor device.

[0003] Japanese Patent Laid-Open No. 2002-231883 discloses a semiconductor device connected to a conductive layer via solder. When a semiconductor device is connected to a conductive layer by solder, a high current can be passed through the semiconductor device, and the heat dissipation of the semiconductor device can be improved.

[0004] A solder joint electrode of a semiconductor device includes a base metal film forming a base, and an oxidation-resistant metal film covering the surface of the base metal film. Pure gold (that is, Au) is used for the oxidation-resistant metal film. Since Au is highly scarce, there is a need to reduce the amount of Au used. However, when the thickness of the oxidation-resistant metal film is reduced to reduce the amount of Au used, the constituent metal of the underlying base metal film easily diffuses to the surface of the oxidation-resistant metal film. When the constituent metal of the base metal film diffuses to the surface of the oxidation-resistant metal film, an oxide film is formed on the surface of the oxidation-resistant metal film, which degrades the solder wettability of the solder joint electrode. The present specification proposes a technology that can realize a solder joint electrode to which solder can be suitably bonded and reduce the amount of Au used.

[0005] The semiconductor device disclosed in the present specification includes a semiconductor substrate and a solder joint electrode provided on the surface of the semiconductor substrate. The solder joint electrode includes a base metal film and an oxidation-resistant metal film covering the surface of the base metal film. The oxidation-resistant metal film is made of an alloy of Au and an alloying metal other than Au.

[0006] In this semiconductor device, the antioxidant metal film is composed of an alloy of Au and other metals. This configuration allows for a thicker antioxidant metal film while reducing the amount of Au used. Therefore, it is possible to prevent the constituent metals of the underlying metal film from diffusing to the surface of the antioxidant metal film, thereby suppressing the formation of an oxide film on the surface of the antioxidant metal film. Consequently, solder can be suitably bonded to the solder joint electrode. As described above, this semiconductor device makes it possible to realize a solder joint electrode that can be suitably bonded with solder, while also reducing the amount of Au used.

[0007] Cross-sectional view of the semiconductor device of Example 1. Diagram showing the distribution of mole fraction x in the antioxidant metal film of Example 1 (before soldering). Diagram showing the distribution of mole fraction x in the antioxidant metal film of Example 1 (after soldering). Diagram showing the distribution of mole fraction x in the antioxidant metal film of Example 2 (before soldering). Diagram showing the distribution of mole fraction x in the antioxidant metal film of Example 3 (before soldering).

[0008] The semiconductor device 10 of Embodiment 1 shown in Figure 1 is a so-called power semiconductor device. The semiconductor device 10 may be a diode, a switching device such as a MOSFET (metal-oxide-semiconductor field effect transistor) or an IGBT (insulated gate bipolar transistor), or a device that combines a diode and a switching device. The semiconductor device 10 has a semiconductor substrate 12, an upper electrode 14, and a lower electrode 16. In this embodiment, the semiconductor substrate 12 is made of silicon (Si). However, the material constituting the semiconductor substrate 12 is not particularly limited, and for example, the semiconductor substrate 12 may be silicon carbide (SiC), gallium nitride (GaN), gallium oxide (GaO), aluminum nitride (AlN), boron nitride (BN), germanium oxide (GeO) ２), or it may be made of diamond or the like. The upper electrode 14 is in contact with the upper surface 12a of the semiconductor substrate 12. The upper electrode 14 covers the central part of the upper surface 12a. The lower electrode 16 is in contact with the lower surface 12b of the semiconductor substrate 12. The lower electrode 16 covers the entire area of ​​the lower surface 12b. The upper electrode 14 is often formed by a wet process and is difficult to alloy with other metals, whereas the lower electrode 16 is formed by a dry process and can be easily formed with the desired alloy. Here, a wet process is a surface treatment method that uses a solution and includes, but is not limited to, plating, coating, etc. A dry process is a surface treatment method that does not use a solution and includes, but is not limited to, physical vapor deposition (PVD) and chemical vapor deposition (CVD). For example, PVD includes sputtering, vacuum deposition, and ion plating. Therefore, in this embodiment, the technology disclosed herein is applied only to the lower electrode 16. In other words, the semiconductor device manufacturing method of this embodiment includes a step of forming the lower electrode 16 by a dry process. When the semiconductor device is a diode, the upper electrode 14 functions as the anode electrode and the lower electrode 16 functions as the cathode electrode. When the semiconductor device is a switching element, the upper electrode 14 functions as the source electrode or emitter electrode and the lower electrode 16 functions as the drain electrode or collector electrode. The lower electrode 16 is an electrode to which solder is bonded to the surface. The area of ​​the lower electrode 16 is larger than the area of ​​the upper electrode 14. With this configuration, it is possible to ensure electrical contact on the lower electrode 16 side while improving heat dissipation. In addition, since the lower electrode 16 is formed by performing a dry process (e.g., sputtering) on ​​the entire lower surface 12b, process costs can be reduced.

[0009] As shown in Figure 1, the lower electrode 16 has a contact film 16a, a barrier metal film 16b, an underlay metal film 16c, and an anti-oxidation metal film 16d.

[0010] The contact film 16a covers the lower surface 12b of the semiconductor substrate 12. In this embodiment, the contact film 16a is made of aluminum silicide.

[0011] The barrier metal film 16b covers the lower surface of the contact film 16a. In this embodiment, the barrier metal film 16b is made of titanium (Ti).

[0012] The base metal film 16c covers the lower surface of the barrier metal film 16b. The base metal film 16c is composed of a metal with a lower self-diffusion coefficient than the antioxidant metal film 16d. In this embodiment, the base metal film 16c is composed of nickel (Ni).

[0013] The antioxidant metal film 16d covers the underside of the underlying metal film 16c. The underside of the antioxidant metal film 16d is exposed. The antioxidant metal film 16d is composed of an alloy of gold (Au) and an alloying metal (i.e., an Au alloy). The alloying metal is composed of a metal other than Au. The alloying metal may be a single metal or may contain multiple metals. A metal with a lower self-diffusion coefficient than Au can be used as the alloying metal. Also, a metal with a relatively small ionization tendency can be used as the alloying metal. For example, one or more metals selected from silver (Ag), platinum (Pt), palladium (Pd), copper (Cu), rhodium (Rh), nickel (Ni), cobalt (Co), and tin (Sn) can be used as the alloying metal. When the element symbol of the alloying metal is A, the Au alloy constituting the antioxidant metal film 16d is Au ｘ A １－ｘ It is represented by the chemical formula shown. The mole fraction x is between 0.001 and 0.999. The antioxidant metal film 16d has higher solder wettability than the underlying metal film 16c. Furthermore, the antioxidant metal film 16d is less susceptible to oxidation than the underlying metal film 16c.

[0014] Figure 2 shows the distribution of the mole fraction x of Au and the mole fraction 1-x of alloying metal A in the thickness direction within the antioxidant metal film 16d. As shown in Figure 2, in Example 1, the mole fractions x and 1-x are uniformly distributed in the thickness direction.

[0015] As described above, in the semiconductor device 10 of Example 1, the antioxidant metal film 16d is made of an Au alloy. Even though the antioxidant metal film 16d is made of an Au alloy, high solder wettability can be obtained in the antioxidant metal film 16d, just as in the case where the antioxidant metal film is made of pure Au (i.e., pure gold). In particular, since a metal with a low ionization tendency is used as the alloying metal, high solder wettability can be obtained in the antioxidant metal film 16d.

[0016] Furthermore, when the antioxidant metal film 16d is composed of an Au alloy, the amount of Au used can be reduced without decreasing the thickness of the antioxidant metal film 16d, compared to when the antioxidant metal film is composed of pure Au. Since the amount of Au used can be reduced, the manufacturing cost of the semiconductor device 10 can be reduced. In addition, since the thickness of the antioxidant metal film 16d can be maintained, the diffusion of Ni constituting the underlying metal film 16c to the lower surface of the antioxidant metal film 16d can be suppressed. In particular, since a metal with a low self-diffusion coefficient is used as the alloying element for the antioxidant metal film 16d, the diffusion of Ni constituting the underlying metal film 16c into the antioxidant metal film 16d can be effectively suppressed. As a result, the formation of an oxide film (i.e., a Ni oxide film) on the lower surface of the antioxidant metal film 16d can be suppressed. Consequently, the decrease in solder wettability due to the formation of an oxide film can be suppressed.

[0017] Figure 3 shows the distribution of mole fraction x in the thickness direction after the solder layer 18 is joined to the lower surface of the antioxidant metal film 16d. During solder joining, thermal diffusion of metal occurs between the solder layer 18 and the antioxidant metal film 16d. As a result, near the interface 19 between the solder layer 18 and the antioxidant metal film 16d (i.e., the portion adjacent to the solder layer 18), the mole fraction x of Au in the antioxidant metal film 16d decreases, and the mole fraction 1-x of the alloying metal increases. Consequently, the mole fraction x is distributed such that it decreases from the center C1 toward the interface 19 in the thickness direction of the antioxidant metal film 16d. When thermal diffusion occurs, an alloy layer is formed at the interface 19 by the solder layer 18 and the antioxidant metal film 16d, so the bonding strength between the solder layer 18 and the antioxidant metal film 16d increases. Therefore, if a distribution of mole fraction x is lower in the portion adjacent to the solder layer 18 than in the center C1, high bonding strength can be obtained at the interface 19.

[0018] Furthermore, during soldering, thermal diffusion of metal occurs between the antioxidant metal film 16d and the base metal film 16c. As a result, as shown in Figure 3, near the interface 17 between the antioxidant metal film 16d and the base metal film 16c (i.e., the portion adjacent to the base metal film 16c), the mole fraction x of Au in the antioxidant metal film 16d decreases, and the mole fraction 1-x of the alloying metal increases. Consequently, the mole fraction x is distributed to decrease from the center C1 of the antioxidant metal film 16d towards the interface 17. When thermal diffusion occurs, an alloy layer is formed at the interface 17 by the antioxidant metal film 16d and the base metal film 16c, thus increasing the bonding strength between the antioxidant metal film 16d and the base metal film 16c. Therefore, if the mole fraction x is lower in the portion adjacent to the base metal film 16c than in the center C1, high bonding strength can be obtained at the interface 17.

[0019] In the semiconductor device of Example 2 shown in Figure 4, the distribution of the mole fraction x of Au within the antioxidant metal film 16d is different from that of Example 1 (i.e., Figure 2). The other configurations of the semiconductor device of Example 2 are the same as those of Example 1.

[0020] As shown in Figure 4, in Example 2, in the state before soldering, the mole fraction x gradually increases from the lower surface of the antioxidant metal film 16d toward the base metal film 16c. Therefore, the mole fraction x of Au in the antioxidant metal film 16d is higher in the portion adjacent to the base metal film 16c than in the central part C1. Since the mole fraction x of Au is high at the interface 17, oxidation of the base metal film 16c at the interface 17 can be effectively suppressed. Also, because the mole fraction x of Au is high at the interface 17, Au easily diffuses from the antioxidant metal film 16d to the base metal film 16c during soldering. Therefore, the antioxidant metal film 16d and the base metal film 16c easily form an alloy layer during soldering. Therefore, the bonding strength between the antioxidant metal film 16d and the base metal film 16c can be increased.

[0021] Furthermore, in Example 2, in the state before soldering, the mole fraction x of Au is lower in the surface layer near the bottom of the antioxidant metal film 16d than in the central C1. Therefore, the mole fraction 1-x of the alloying metal in the antioxidant metal film 16d is higher in the surface layer near the bottom of the antioxidant metal film 16d than in the central C1. As a result, the alloying metal in the antioxidant metal film 16d and the solder in the solder layer easily form an alloy during soldering. Therefore, the bonding strength between the antioxidant metal film 16d and the solder layer can be increased.

[0022] In the semiconductor device of Example 3 shown in Figure 5, the distribution of the mole fraction x of Au within the antioxidant metal film 16d is different from that of Example 1 (i.e., Figure 2). The other configurations of the semiconductor device of Example 3 are the same as those of Example 1.

[0023] As shown in Figure 5, in Example 3, in the state before soldering, the mole fraction x gradually decreases from the lower surface of the antioxidant metal film 16d toward the base metal film 16c. Therefore, the mole fraction x of Au in the antioxidant metal film 16d is lower in the portion adjacent to the base metal film 16c than in the central C1. Consequently, the mole fraction 1-x of the alloying metal in the antioxidant metal film 16d is higher in the portion adjacent to the base metal film 16c than in the central C1. As described above, the self-diffusion coefficient of the alloying metal is lower than the self-diffusion coefficient of Au. Since the alloying metal is present at a high mole fraction in the portion adjacent to the base metal film 16c, the diffusion of the metal constituting the base metal film 16c (i.e., Ni) into the antioxidant metal film 16d can be more effectively suppressed. Therefore, according to the configuration of Example 3, the formation of an oxide film on the lower surface of the antioxidant metal film 16d can be more effectively suppressed, and the decrease in solder wettability can be more effectively suppressed.

[0024] Furthermore, in Example 3, before soldering, the mole fraction x of Au is higher in the surface layer near the bottom of the antioxidant metal film 16d than in the central C1. Therefore, during soldering, the Au of the antioxidant metal film 16d and the solder of the solder layer easily form an alloy layer. As a result, the bonding strength between the antioxidant metal film 16d and the solder layer can be increased.

[0025] In Figures 2-5, the mole fraction x of Au is higher than the mole fraction 1-x of the alloying metal. However, in other embodiments, the mole fraction 1-x may be higher than the mole fraction x in part or all of the thickness direction of the antioxidant metal film.

[0026] The following lists the configurations of the technologies disclosed herein. (Configuration 1) A semiconductor device comprising: a semiconductor substrate; and a solder joint electrode provided on the surface of the semiconductor substrate, wherein the solder joint electrode comprises: a base metal film; and an antioxidant metal film covering the surface of the base metal film, and the antioxidant metal film is composed of an alloy of Au and an alloy of metals other than Au. (Configuration 2) The semiconductor device according to Configuration 1, wherein a first electrode is provided on a first surface of the semiconductor substrate; a second electrode is provided on a second surface of the semiconductor substrate; the area of ​​the second electrode is the same as or larger than the area of ​​the first electrode; and the solder joint electrode is the second electrode. (Configuration 3) The semiconductor device according to Configuration 1 or 2, wherein the mole fraction of Au in the antioxidant metal film changes in the thickness direction of the antioxidant metal film. (Configuration 4) The semiconductor device according to Configuration 3, wherein the alloying metal contains a metal with a lower diffusion coefficient than Au, and the mole fraction of Au in the antioxidant metal film is lower in the portion adjacent to the underlying metal film than in the center in the thickness direction of the antioxidant metal film. (Configuration 5) The semiconductor device according to Configuration 3 or 4, wherein the surface of the antioxidant metal film located on the opposite side from the underlying metal film is covered with a solder layer, and the mole fraction of Au in the antioxidant metal film is lower in the portion adjacent to the solder layer than in the center in the thickness direction of the antioxidant metal film. (Configuration 6) The semiconductor device according to Configuration 3 or 5, wherein the mole fraction of Au in the antioxidant metal film is higher in the portion adjacent to the underlying metal film than in the center in the thickness direction of the antioxidant metal film. (Configuration 7) The semiconductor device according to any one of Configurations 3, 4, or 6, wherein the mole fraction of Au in the antioxidant metal film is higher in the surface layer of the antioxidant metal film than in the center in the thickness direction of the antioxidant metal film. (Configuration 8) The semiconductor device according to Configuration 1, wherein the mole fraction of Au in the antioxidant metal film is constant in the thickness direction of the antioxidant metal film. (Configuration 9) The semiconductor device according to any one of Configurations 1 to 7, wherein the alloying metal includes at least one of Ag, Pt, Pd, Cu, Rh, Ni, Co, and Sn.(Configuration 10) A method for manufacturing a semiconductor device as described in Configuration 2, comprising the step of forming the second electrode by a dry process.

[0027] In this specification, the mole fraction of Au refers to the proportion of moles of Au in the antioxidant metal film. That is, the mole fraction of Au is the value obtained by dividing the number of moles of Au contained in the antioxidant metal film by the number of moles of the antioxidant metal film.

[0028] According to configuration 5, the diffusion of metal from the underlying metal film to the antioxidant metal film can be suppressed, thereby effectively suppressing the formation of an oxide film on the surface of the antioxidant metal film.

[0029] According to configuration 6, high bonding strength can be obtained at the interface between the antioxidant metal film and the solder layer.

[0030] According to configuration 7, oxidation of the underlying metal film can be effectively suppressed at the interface between the antioxidant metal film and the underlying metal film.

[0031] According to configuration 8, high bonding strength can be obtained at the interface between the antioxidant metal film and the solder layer.

[0032] Although embodiments have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. The technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness.

Claims

1. A semiconductor device comprising: a semiconductor substrate; and a solder joint electrode provided on the surface of the semiconductor substrate, wherein the solder joint electrode comprises a base metal film and an antioxidant metal film covering the surface of the base metal film, and the antioxidant metal film is composed of an alloy of Au and an alloying metal other than Au.

2. The semiconductor device according to claim 1, wherein a first electrode is provided on the first surface of the semiconductor substrate, a second electrode is provided on the second surface of the semiconductor substrate, the area of ​​the second electrode is the same as or larger than the area of ​​the first electrode, and the solder joint electrode is the second electrode.

3. The semiconductor device according to claim 1, wherein the mole fraction of Au in the antioxidant metal film changes in the thickness direction of the antioxidant metal film.

4. The semiconductor device according to claim 3, wherein the alloying metal contains a metal with a lower diffusion coefficient than Au, and the mole fraction of Au in the antioxidant metal film is lower in the portion adjacent to the underlying metal film than in the center in the thickness direction of the antioxidant metal film.

5. The semiconductor device according to claim 3 or 4, wherein the surface of the antioxidant metal film located on the opposite side from the underlying metal film is covered with a solder layer, and the mole fraction of Au in the antioxidant metal film is lower in the portion adjacent to the solder layer than in the center in the thickness direction of the antioxidant metal film.

6. The semiconductor device according to claim 3, wherein the mole fraction of Au in the antioxidant metal film is higher in the portion adjacent to the underlying metal film than in the central part in the thickness direction of the antioxidant metal film.

7. The semiconductor device according to claim 3, wherein the mole fraction of Au in the antioxidant metal film is higher in the surface layer of the antioxidant metal film than in the center in the thickness direction of the antioxidant metal film.

8. The semiconductor device according to claim 1, wherein the mole fraction of Au in the antioxidant metal film is constant in the thickness direction of the antioxidant metal film.

9. The semiconductor device according to claim 1, wherein the alloying element comprises at least one of Ag, Pt, Pd, Cu, Rh, Ni, Co, and Sn.

10. A method for manufacturing a semiconductor device according to claim 2, comprising the step of forming the second electrode by a dry process.

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