Semiconductor device, power conversion device, and method for manufacturing the semiconductor device

Abstract

The purpose of the present invention is to provide a technique capable of improving long-term reliability of a semiconductor element by suppressing the occurrence of cracks in an electrode provided on an upper surface of a semiconductor substrate. A semiconductor element (100) of the front-back conduction-type, said semiconductor element comprising: a semiconductor substrate (1); an electrode (3) provided on the upper surface of the semiconductor substrate (1); a protective film (4) which covers the end of the electrode (3); a bonding electrode (6) provided on the upper side of the electrode (3) and on the inner end side of the protective film (4); a metal adhesive film (5) which is provided between the bonding electrode (6) and the electrode (3) and protective film (4), and covers the end of the interface between the electrode (3) and the protective film (4); and a back electrode (8) provided on the lower surface of the semiconductor substrate (1).

Description

Semiconductor element, semiconductor device, power conversion device, and method for manufacturing semiconductor element

[0001] The present disclosure relates to a semiconductor element, a semiconductor device, a power conversion device, and a method for manufacturing a semiconductor element.

[0002] A front-back conductive semiconductor element can control the current flowing between a front electrode on the front side and a back electrode on the back side. Therefore, such semiconductor elements can be used as switching elements through which large currents flow. Soldering is used to improve the electrical conductivity and heat dissipation performance of semiconductor modules (equivalent to semiconductor devices) that incorporate front-back conductive semiconductor elements. Because a nickel film of several micrometers is required for soldering, plating is used.

[0003] For example, Patent Document 1 discloses a zincate plating method as a method for selectively forming a plating film only on the surface of an aluminum alloy electrode in a front-back conduction type semiconductor element. The electrode film is structured such that nickel and gold are plated on an aluminum electrode in this order. In such a conventional manufacturing method, a nickel plating film is formed isotropically on the aluminum alloy.

[0004] Japanese Patent Application Laid-Open No. 2005-51084

[0005] When conventional semiconductor elements with front-to-back conduction are soldered to external electrodes, gaps form between the bonding electrode (the surface electrode) and the protective film, and solder penetrates into the gaps. Because stress concentrates at the interface between the bonding electrode and the protective film through which the solder has penetrated, thermal fatigue is applied to the semiconductor device during heat cycle testing, etc., resulting in high stress depending on the difference in thermal expansion coefficients between the bonding electrode and the solder. When high stress occurs, cracks form in the electrodes provided on the top surface of the semiconductor substrate below the ends of the bonding electrode. This poses a problem of reduced durability of the semiconductor element.

[0006] Therefore, an object of the present disclosure is to provide a technique that can suppress the occurrence of cracks in electrodes provided on the upper surface of a semiconductor substrate and improve the long-term reliability of semiconductor elements.

[0007] The semiconductor element according to the present disclosure is a front-back conductive semiconductor element comprising a semiconductor substrate, an electrode provided on the upper surface of the semiconductor substrate, a protective film covering the end of the electrode, a bonding electrode provided on the upper side of the electrode and on the inner end side of the protective film, a metal adhesive film provided between the electrode, the protective film, and the bonding electrode, covering the end of the interface between the electrode and the protective film, and a back electrode provided on the lower surface of the semiconductor substrate.

[0008] According to the present disclosure, the metal adhesive film covers the edge of the interface between the electrode and the protective film, thereby preventing the solder from penetrating into the interface between the electrode and the protective film during soldering. This disperses thermal stress caused by heat cycle tests and the like, preventing cracks from occurring in the electrode, thereby improving the long-term reliability of the semiconductor element.

[0009] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0010] 1 is a cross-sectional view of a semiconductor device according to a first embodiment. FIG. 2 is a cross-sectional view of a semiconductor element according to the first embodiment. FIG. 3 is a flowchart showing a manufacturing process of a semiconductor element according to the first embodiment. FIG. 4 is a cross-sectional view showing a protective film forming step in the manufacturing process of a semiconductor element according to the first embodiment. FIG. 5 is a cross-sectional view showing a resist forming step in the manufacturing process of a semiconductor element according to the first embodiment. FIG. 6 is a cross-sectional view showing a metal adhesive film removing step in the manufacturing process of a semiconductor element according to the first embodiment. FIG. 7 is a cross-sectional view showing a back electrode forming step in the manufacturing process of a semiconductor element according to the first embodiment. FIG. 8 is a cross-sectional view of a semiconductor device according to a second embodiment. FIG. 9 is a cross-sectional view of a semiconductor element according to the second embodiment. FIG. 10 is a flowchart showing a manufacturing method of a semiconductor element according to the second embodiment. FIG. 11 is a cross-sectional view showing a bonding electrode forming step in the manufacturing process of a semiconductor element according to the second embodiment. FIG. 12 is a cross-sectional view of a semiconductor device according to a third embodiment. FIG. 13 is a cross-sectional view of a semiconductor element according to the third embodiment. FIG. 14 is a flowchart showing a manufacturing process of a semiconductor element according to the third embodiment. FIG. 15 is a cross-sectional view showing a second metal adhesive film removing step in the manufacturing process of a semiconductor element according to the third embodiment. FIG. 16 is a cross-sectional view showing a resist forming step in the manufacturing process of a semiconductor element according to the third embodiment.

[0011] First Embodiment A first embodiment will be described below with reference to the drawings. Fig. 1 is a cross-sectional view of a semiconductor device according to the first embodiment, specifically a cross-sectional view of the periphery of an end portion of the semiconductor device according to the first embodiment. Note that the cross-sectional views from Fig. 2 onwards also show portions corresponding to Fig. 1.

[0012] As shown in FIG. 1, the semiconductor device includes a base plate 10 , a sintered material 9 , a semiconductor element 100 , solder 11 , external electrodes 12 , and a sealing material 13 .

[0013] The semiconductor element 100 is a front-back conduction type metal oxide semiconductor field effect transistor (MOSFET) and is disposed between a base plate 10 and an external electrode 12. A back electrode 8 of the semiconductor element 100 is bonded to the upper surface of the base plate 10 via a sintered material 9. A bonding electrode 6 of the semiconductor element 100 is bonded to the external electrode 12 via solder 11. The solder 11 is a bonding material containing one or more of the metals tin, silver, and copper. A sealing material 13 covers the sides of the semiconductor element 100. However, the semiconductor element 100 may also be a front-back conduction type insulated gate bipolar transistor (IGBT) or diode.

[0014] Next, a description will be given of the semiconductor element 100. Fig. 2 is a cross-sectional view of the semiconductor element 100 according to the first embodiment.

[0015] As shown in FIG. 2 , the semiconductor element 100 includes a semiconductor substrate 1, a gate structure 2, an electrode 3, a protective film 4, a bonding electrode 6, a metal adhesive film 5, an oxide film 7, a back electrode 8, and an anti-oxidation film 92.

[0016] The semiconductor substrate 1 is primarily made of silicon carbide (SiC). However, the semiconductor substrate 1 is not limited to this and may be primarily made of silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), or the like. The size of the semiconductor substrate 1 is, for example, approximately 10 mm x 10 mm.

[0017] The gate structure 2 is patterned and provided on the upper surface of the semiconductor substrate 1. The gate structure 2 is composed of a gate oxide film made of an insulating material such as silicon oxide, and a gate electrode made of a conductive material such as polysilicon.

[0018] The electrode 3 is provided on the upper surface of the semiconductor substrate 1 where the gate structure 2 is exposed. The electrode 3 is formed in a flat plate shape, and the upper surface of the electrode 3 is flat. The electrode 3 is formed by depositing a film of aluminum or an aluminum alloy made of aluminum and copper or silicon, while appropriately using a barrier metal made of titanium or a titanium compound such as titanium nitride.

[0019] The protective film 4 is provided on the edge of the semiconductor substrate 1 and covers the edge of the electrode 3. The protective film 4 is made of polyimide. The inner end surface of the protective film 4 (the end surface on the right side in FIG. 2 ) is formed in a tapered shape in cross section.

[0020] The bonding electrode 6 is provided on the upper side of the electrode 3 and on the inner end side of the protective film 4. Specifically, the bonding electrode 6 is formed in a plate shape and extends from the electrode 3 through the inner end surface of the protective film 4 to the flat portion. The bonding electrode 6 is made of one or more metals selected from nickel, silver, and copper. In this embodiment, the bonding electrode 6 is a nickel-plated film formed by electrolytic plating, and has a thickness of 5.0 μm.

[0021] The metal adhesive film 5 is provided along the lower surface of the bonding electrode 6. Specifically, the metal adhesive film 5 is provided over the entire lower surface of the bonding electrode 6. The metal adhesive film 5 is provided between the electrode 3 and the protective film 4 and the bonding electrode 6, and covers the edge of the interface between the electrode 3 and the protective film 4. The metal adhesive film 5 is composed of a single layer or a multilayer film containing one or more metals selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum. In this embodiment, the metal adhesive film 5 is a copper film formed by sputtering, and has a thickness of 0.1 μm.

[0022] The oxide film 7 is provided on the end surface of the bonding electrode 6. Specifically, the oxide film 7 may be provided on the entire end surface of the bonding electrode 6, or may be provided on a part of the end surface, such as the periphery of the end surface of the bonding electrode 6. The oxide film 7 is made of one or more metals selected from nickel, silver, and copper. In this embodiment, the oxide film 7 is a nickel oxide film formed by subjecting the bonding electrode 6 to an oxidation treatment.

[0023] The back electrode 8 is provided over the entire lower surface of the semiconductor substrate 1. The back electrode 8 is composed of multiple metal layers. However, since the back electrode 8 is used for bonding, it is desirable that nickel or gold, which has excellent bonding properties, be disposed on the outermost surface. The anti-oxidation film 92 is provided along the upper surface of the bonding electrode 6. Specifically, the anti-oxidation film 92 is provided over the entire upper surface of the bonding electrode 6.

[0024] 2 , the length w from the triple point 20 where the electrode 3, the protective film 4, and the metal adhesive film 5 meet to the end of the metal adhesive film 5 along the protective film 4 is 2.0 μm or more longer than the length t in the thickness direction of the bonding electrode 6 (w≧t+2 μm). In addition, the end of the metal adhesive film 5 is located on the flat portion of the protective film 4. In other words, the end of the metal adhesive film 5 rides up onto the protective film 4.

[0025] The length w from the triple point 20 to the end of the metal adhesive film 5 along the protective film 4 and the length t in the thickness direction of the bonding electrode 6 can be calculated by observing a cross section obtained by irradiating a gallium ion beam using a focused ion beam device (FIB device) at 5000x magnification using a scanning electron microscope (SEM).

[0026] <Method of Manufacturing Semiconductor Element> Next, a method of manufacturing the semiconductor element 100 will be described with reference to FIGS. 3 to 7. FIG. 3 is a flowchart showing the manufacturing steps of the semiconductor element 100 according to the first embodiment. FIG. 4 is a cross-sectional view showing a protective film forming step in the method of manufacturing the semiconductor element 100 according to the first embodiment. FIG. 5 is a cross-sectional view showing a resist forming step. FIG. 6 is a cross-sectional view showing a metal adhesive film removing step. FIG. 7 is a cross-sectional view showing a back electrode forming step.

[0027] As shown in FIG. 3, the manufacturing process of the semiconductor element 100 includes an electrode forming process (step S1), a protective film forming process (step S2), a metal adhesive film forming process (step S3), a resist forming process (step S4), a bonding electrode forming process (step S5), a metal adhesive film removing process (step S6), a heat treatment process (step S7), and a back electrode forming process (step S8).

[0028] (Electrode Forming Step: First Step) In the electrode forming step (step S1), an aluminum alloy having low electrical resistance is patterned by sputtering, which is an easy process to control, to form an electrode 3 having high adhesion to the semiconductor substrate 1 on the upper surface of the semiconductor substrate 1 where the gate structure 2 is exposed. Depending on the application, titanium or a titanium compound such as titanium nitride may be formed as a barrier metal between the semiconductor substrate 1 and the aluminum alloy, and between the gate structure 2 and the aluminum alloy.

[0029] The length of the electrode 3 in the thickness direction is preferably, for example, 0.5 μm or more and 5.0 μm or less. When the semiconductor substrate 1 is made of silicon carbide (SiC), in addition to aluminum, for example, about 1 mass % of silicon, about 1 mass % of silicon, or about 0.5 mass % of copper may be added to the electrode 3 in order to further improve adhesion to the semiconductor substrate 1, and the concentration thereof is preferably constant throughout the electrode 3.

[0030] (Protective Film Formation: Second Step) In the protective film formation step (step S2), polyimide is generally used. Polyimide is uniformly applied to the upper surfaces of the semiconductor substrate 1 and the electrode 3, and then exposed to light, developed, and subjected to heat treatment to pattern the protective film 4. As shown in FIG. 4, the inner end surface of the protective film 4 often becomes tapered due to the heat treatment after development, but the shape of the protective film 4 is not limited, and it may also be reverse tapered.

[0031] (Metal Adhesive Film Formation: Third Step) In the metal adhesive film formation step (step S3), first, a plasma treatment is performed to remove the oxide film formed on the electrode 3. Preferably, oxygen gas is used. At this time, the surface of the protective film 4 becomes rough, and the arithmetic mean roughness of the surface becomes about 50 nm. The cumulative mean roughness of the surface of the protective film 4 can be measured by AFM (Atomic Force Microscopy). Here, the surface of the protective film 4 refers to the top surface and side surface of the protective film 4.

[0032] Thereafter, a copper film with low electrical resistance is formed on the upper surface of the semiconductor substrate 1 by sputtering. By using the sputtering method, metal particles penetrate into the gaps in the roughened portions of the surface of the protective film 4, creating an anchor effect. This allows the formation of a metal adhesive film 5 that has stronger adhesion to the protective film 4 than a metal film formed by electroless plating. However, the metal adhesive film 5 may have a multilayer structure in order to reduce contact resistance with the electrode 3 and improve electrical conductivity.

[0033] (Resist Formation) In the resist formation step (step S4), a resist 91 is formed on the upper surface of the end portion of the metal adhesive film 5. Next, as shown in FIG.

[0034] 6, in the bonding electrode formation step (step S5), a nickel film that will become the bonding electrode 6 is formed by electrolytic plating on the upper surface of the metal adhesive film 5 that is exposed by patterning the resist 91. Furthermore, to improve the bondability with the solder 11 (see FIG. 1), an oxidation prevention film 92 made of a gold plating film is formed on the upper surface of the nickel film. However, the oxidation prevention film 92 may be other plating film or a discoloration prevention agent in addition to the gold plating film.

[0035] (Metal Adhesive Film Removal: Fifth Step) As shown in Fig. 6, in the metal adhesive film removal step (step S6), first, the resist 91 (see Fig. 5) is removed. A tetramethylammonium hydroxide (TMAH) aqueous solution can be used to remove the resist 91. Thereafter, the metal adhesive film 5 located below the resist 91 is removed using a remover that selectively dissolves the metal adhesive film 5 without damaging the outermost surface of the bonding electrode 6.

[0036] 6, a heat treatment process (step S7) is performed to selectively form an oxide film 7 on the end faces of the metal adhesive film 5 that are not covered with the anti-oxidation film 92. The heat treatment temperature is 80° C. or higher, preferably 90° C., and the treatment is performed for 10 minutes. This process may be performed after the formation of the back electrode 8 (see FIG. 2).

[0037] (Back electrode formation) As shown in FIG. 7 , in the back electrode formation process (step S8), in order to form a back electrode 8 composed of a plurality of metal layers on the underside of the semiconductor substrate 1 opposite to the upper surface on which the electrode 3 is formed, for example, nickel is patterned by sputtering, which is an easy process to control, and then gold is patterned by sputtering, which is an easy process to control.

[0038] Through the steps described above, it is possible to obtain the semiconductor element 100 having the metal adhesive film 5 provided at the edge of the interface between the electrode 3 and the protective film 4. Depending on the application, a barrier metal such as a titanium alloy or a nickel alloy may be formed between the semiconductor substrate 1 and the nickel.

[0039] The semiconductor element 100 obtained by the above process is bonded to a base plate 10 via a sintered material 9 using Ag particles, as shown in FIG. 1 . It is further bonded to external electrodes 12 via solder 11. During this process, the anti-oxidation film 92 dissolves into the molten solder 11, disappearing due to so-called solder erosion. The bonding methods are not limited to these, and it is also possible to use solder 11 for bonding to the base plate 10, Ag particles or Cu particles for bonding to the external electrodes 12, or to perform wire bonding as appropriate. The semiconductor element 100 is then sealed with a sealing material 13. This completes the process of obtaining a semiconductor device having the semiconductor element 100.

[0040] <Effects> Next, the effects of this embodiment will be described in comparison with the related art. Fig. 18 is a cross-sectional view of a semiconductor device according to the related art.

[0041] 18 , in the related art, a bonding electrode 6 made of a nickel alloy is formed on the upper surface of an electrode 3 by electroless plating. The bonding electrode 6 formed by the electroless method has weak adhesion to the protective film 4, so a gap occurs at the interface between the bonding electrode 6 and the protective film 4 when soldering to the external electrode 12. Furthermore, due to the nature of electroless plating, plating grows from the upper surface of the electrode 3, so the bonding electrode 6 cannot go beyond the tapered surface that is the inner end face of the protective film 4 and onto the flat surface of the protective film 4.

[0042] As a result, when soldered to the external electrode 12, the solder 11 penetrates the interface between the bonding electrode 6 and the protective film 4tp. Because the interface where the solder 11 penetrates is a structure where stress is concentrated, thermal fatigue is applied to the semiconductor device during a heat cycle test or the like, and high stress is generated according to the difference in thermal expansion coefficients between the bonding electrode 6 and the solder 11. Furthermore, many nickel alloys formed by electroless plating use hypophosphorous acid as a reducing agent, and the plating film contains phosphorus. Therefore, when heat is applied during a heat cycle test or the like, the alloy becomes brittle and prone to cracks 21. As a result, in the related art, cracks 21 occur in the electrode 3 below the interface between the bonding electrode 6 and the protective film 4. This reduces the durability of the semiconductor element 101. There is also concern about poor connection between the semiconductor substrate 1 and the external electrode 12.

[0043] On the other hand, the semiconductor element 100 according to the first embodiment is a front-back conductive semiconductor element, and includes a semiconductor substrate 1, an electrode 3 provided on the upper surface of the semiconductor substrate 1, a protective film 4 covering the end of the electrode 3, a bonding electrode 6 provided on the upper side of the electrode 3 and on the inner end side of the protective film 4, a metal adhesive film 5 provided between the electrode 3, the protective film 4, and the bonding electrode 6, covering the end of the interface between the electrode 3 and the protective film 4, and a back electrode 8 provided on the lower surface of the semiconductor substrate 1.

[0044] The manufacturing method of the semiconductor element 100 includes a first step of forming an electrode 3 on the upper surface of the semiconductor substrate 1, a second step of forming a protective film 4 so as to cover the end of the electrode 3, a third step of forming a metal adhesive film 5 so as to cover the electrode 3 and the protective film 4, a fourth step of forming a bonding electrode 6 on the upper surface of the metal adhesive film 5, and a fifth step of removing a portion of the metal adhesive film 5 located on the protective film 4. In the fifth step, the metal adhesive film 5 is patterned so as to cover the end of the interface between the electrode 3 and the protective film 4.

[0045] Therefore, since the metal adhesive film 5 covers the edge of the interface between the electrode 3 and the protective film 4, it is possible to prevent the solder 11 from penetrating into the interface between the electrode 3 and the protective film 4 during soldering. This disperses thermal stress caused by a heat cycle test or the like, and prevents cracks 21 from occurring in the electrode 3, improving the long-term reliability of the semiconductor element 100. Furthermore, the yield of the semiconductor element 100 is also improved.

[0046] The bonding electrodes 6 can be connected to the external electrodes 12 by a bonding material containing at least one metal selected from the group consisting of tin, silver, and copper. Therefore, poor connection between the semiconductor substrate 1 and the external electrodes 12 can also be suppressed.

[0047] The electrode 3 is made of aluminum or an aluminum alloy, the protective film 4 is made of polyimide, the metal adhesive film 5 is a single-layer film or a multi-layer film containing one or more metals selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum, and the bonding electrode 6 is made of one or more metals selected from the group consisting of nickel, silver, and copper. The metal adhesive film 5 is formed by sputtering, and the bonding electrode 6 is formed by electrolytic plating.

[0048] Therefore, by using electrolytic plating, the plating film does not contain phosphorus, and therefore embrittlement of the bonding electrode 6 due to heat can be suppressed.

[0049] Furthermore, the length from the triple point 20 where the electrode 3, protective film 4, and metal adhesive film 5 contact to the end of the metal adhesive film 5 along the protective film 4 is at least 2.0 μm longer than the length of the bonding electrode 6 in the thickness direction. Therefore, the end of the metal adhesive film 5 rides on the inner end surface of the protective film 4, so that the protective film 4 buffers stress and prevents stress from concentrating at the triple point 20. This distributes thermal stress and prevents cracks 21 from occurring in the electrode 3.

[0050] In the third step, a plasma treatment is performed to roughen the top and side surfaces of the protective film 4, and then the metal adhesive film 5 is formed by sputtering. The arithmetic mean roughness of the protective film 4 is 10 nm or more and 200 nm or less.

[0051] Therefore, the adhesive strength between the protective film 4 and the metal adhesive film 5 increases, and the penetration of the solder 11 into the interface between the electrode 3 and the protective film 4 during soldering can be further suppressed.

[0052] An oxide film 7 made of one or more metals selected from nickel, silver, and copper is provided on the end surface of the bonding electrode 6. The manufacturing method for the semiconductor element 100 further includes a step of forming a resist 91 between the third and fourth steps, and a step of removing the resist 91 before removing a portion of the metal adhesive film 5 in a fifth step. The manufacturing method further includes a step of forming an oxide film 7 made of one or more metals selected from nickel, silver, and copper on the end surface of the bonding electrode 6 by heat treatment after the fifth step.

[0053] Therefore, the solder 11 is repelled by the oxide film 7 which has poor wettability with the solder 11, and the solder 11 is further prevented from penetrating into the interface between the electrode 3 and the protective film 4.

[0054] Second Embodiment Next, a semiconductor element 100A according to a second embodiment will be described. Fig. 8 is a cross-sectional view of a semiconductor device according to the second embodiment. Fig. 9 is a cross-sectional view of a semiconductor element 100A according to the second embodiment. Note that in the second embodiment, the same components as those described in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0055] As shown in FIGS. 8 and 9, the second embodiment differs from the first embodiment in the shapes of the bonding electrode 6 and the metal adhesive film 5. In the second embodiment, as shown in FIG.

[0056] The bonding electrode 6 is provided on the upper side of the electrode 3 and on the inner end side of the protective film 4. Specifically, the bonding electrode 6 is formed in a plate shape and extends from the electrode 3 along the inner end surface of the protective film 4.

[0057] The metal adhesive film 5 is provided along the lower surface of the bonding electrode 6. Specifically, the metal adhesive film 5 is provided over the entire lower surface of the bonding electrode 6. The metal adhesive film 5 is provided between the electrode 3 and the protective film 4 and the bonding electrode 6, and covers the edge of the interface between the electrode 3 and the protective film 4.

[0058] The length w from the triple point 20 where the electrode 3, the protective film 4, and the metal adhesive film 5 meet to the end of the metal adhesive film 5 along the protective film 4 is longer by 2.0 μm or more than the length t of the bonding electrode 6 in the thickness direction (w≧t+2 μm). The end face of the metal adhesive film 5 is located at the same height as the upper surface of the protective film 4. The oxide film 7 is provided on the end face of the bonding electrode 6. Specifically, the oxide film 7 may be provided on the entire end face of the bonding electrode 6, or may be provided on a portion of the end face of the bonding electrode 6, such as the periphery.

[0059] Next, a method for manufacturing the semiconductor element 100A will be described with reference to Figures 10 and 11. Figure 10 is a flowchart showing a method for manufacturing the semiconductor element 100A according to the second embodiment. Figure 11 is a cross-sectional view showing a bonding electrode forming step in the method for manufacturing the semiconductor element 100A according to the second embodiment.

[0060] 10, in the second embodiment, the resist formation step (step S4) is omitted compared to the first embodiment, and the metal adhesive film removal step (step S6) is performed by CMP (Chemical Mechanical Polishing). In the present embodiment, the steps up to the metal adhesive film formation step (step S2) are the same as those in the first embodiment, and therefore a description thereof will be omitted.

[0061] 11 , in the bonding electrode formation step (step S5), a nickel film that will become the bonding electrode 6 is formed on the upper surface of the metal adhesive film 5 by electrolytic plating. Furthermore, an oxidation-resistant film 92 is formed on the upper surface of the nickel film to improve bonding with the solder 11. The oxidation-resistant film 92 is made of a gold plating film or an antioxidant.

[0062] (Metal Adhesive Film Removal: Fifth Step) CMP is used to remove the metal adhesive film 5. CMP refers to a process that flattens irregularities by improving the mechanical polishing performance through the surface chemical action of the slurry. When CMP is performed on the nickel plating layer, thermal energy is generated, which accelerates chemical reactions at the steps. Therefore, the metal adhesive film 5, bonding electrode 6, and antioxidant film 92 located above the top surface of the protective film 4 can be removed all at once.

[0063] By CMP, it is possible to form a structure in which only the metal adhesive film 5, the bonding electrode 6, and the oxidation-preventing film 92 located below the upper surface of the protective film 4 are retained, and the end surface of the bonding electrode 6 is not covered with the oxidation-preventing film 92. Finally, by performing heat treatment, it is possible to selectively form an oxide film 7 on the end surface of the metal adhesive film 5 that is not covered with the oxidation-preventing film 92, as shown in FIG.

[0064] The steps after the next heat treatment step (step S7) are the same as those in the first embodiment, and therefore the description thereof will be omitted.

[0065] The semiconductor element 100A obtained by the above steps is bonded to a base plate 10 via a sintered material 9 using Ag particles, as shown in FIG. 8 . It is further bonded to external electrodes 12 via solder 11. During this process, the anti-oxidation film 92 dissolves into the molten solder 11, disappearing due to so-called solder erosion. The bonding methods are not limited to these, and it is also possible to use solder 11 for bonding to the base plate 10, Ag particles or Cu particles for bonding to the external electrodes 12, or to perform wire bonding as appropriate. The semiconductor element 100A is then sealed with a sealing material 13. This completes the process of obtaining a semiconductor device having the semiconductor element 100A.

[0066] As described above, in the second embodiment, similarly to the first embodiment, thermal stress caused by a heat cycle test or the like is dispersed, and the occurrence of cracks 21 in the electrodes 3 can be suppressed, thereby improving the long-term reliability of the semiconductor element 100A. In addition, the yield of the semiconductor element 100A is also improved.

[0067] Furthermore, the manufacturing method of the semiconductor element 100A further includes, in the fifth step, a step of simultaneously removing the metal adhesive film 5 and the bonding electrode 6 located above the upper surface of the protective film 4 by using a CMP method. Therefore, the steps of forming the resist 91 and removing the resist 91 are not necessary, and the number of steps is reduced compared to the first embodiment, thereby simplifying the manufacturing method.

[0068] Third Embodiment Next, a semiconductor element 100B according to a third embodiment will be described. Fig. 12 is a cross-sectional view of a semiconductor device according to the third embodiment. Fig. 13 is a cross-sectional view of a semiconductor element 100B according to the third embodiment. Note that in the third embodiment, the same components as those described in the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted.

[0069] As shown in FIGS. 12 and 13, the third embodiment differs from the first embodiment in the shape of the metal adhesive film 5. In the third embodiment, as shown in FIG.

[0070] The metal adhesive film 5 is a multilayer film consisting of a first metal adhesive film 5a and a second metal adhesive film 5b provided on the upper surface of the first metal adhesive film 5a. The end of the first metal adhesive film 5a extends outward beyond the second metal adhesive film 5b and the bonding electrode 6. The first metal adhesive film 5a is a barrier metal made of a metal film containing, for example, titanium, thallium, or tungsten. The second metal adhesive film 5b is a metal film containing copper to improve electrical conductivity.

[0071] In the third embodiment, the length w from the triple point 20 where the electrode 3, the protective film 4, and the first metal adhesive film 5a meet to the end of the first metal adhesive film 5a along the protective film 4 is 2.0 μm or more longer than the length t in the thickness direction of the bonding electrode 6 (w≧t+2 μm). In addition, the end of the first metal adhesive film 5a is located on the flat portion of the protective film 4. That is, the end of the first metal adhesive film 5a rides up onto the protective film 4.

[0072] Next, a method for manufacturing the semiconductor device 100B will be described with reference to Figures 14 to 16. Figure 14 is a flowchart showing the manufacturing process of the semiconductor device 100B according to the third embodiment. Figure 15 is a cross-sectional view showing a second metal adhesive film removal step in the manufacturing process of the semiconductor device 100B according to the third embodiment. Figure 16 is a cross-sectional view showing a resist formation step in the manufacturing process of the semiconductor device 100B according to the third embodiment.

[0073] 14, in the manufacturing process of embodiment 3, instead of the metal adhesive film removal step (step S6), a second metal adhesive film removal step (step S6A), a resist formation step (step S6B), and a first metal adhesive film removal step (step S6C) are provided. In this embodiment, the steps up to the bonding electrode formation step (step S5) are the same as in embodiment 1, and therefore a description thereof will be omitted.

[0074] 15, in the second metal adhesive film removal step (step S6A), the resist 91 (see FIG. 5) is first removed. A tetramethylammonium hydroxide (TMAH) aqueous solution can be used to remove the resist 91. Thereafter, the second metal adhesive film 5b located below the resist 91 is removed using a remover that selectively dissolves the second metal adhesive film 5b.

[0075] (Resist formation: fifth step) As shown in Figure 16, in the resist formation step (step S6B), a resist 93 is patterned and formed on the upper surface of the second metal adhesive film 5b, the upper surface of the bonding electrode 6, and the upper surface of a portion of the first metal adhesive film 5a.

[0076] (First Metal Adhesive Film Removal: Fifth Step) In the first metal adhesive film removal step (step S6C), a remover that selectively dissolves the first metal adhesive film 5a is used to remove the first metal adhesive film 5a located in areas where the resist 93 is not formed. Thereafter, the resist 93 is removed. A tetramethylammonium hydroxide (TMAH) aqueous solution can be used to remove the resist 93.

[0077] The steps after the next heat treatment step (step S7) are the same as those in the first embodiment, and therefore the description thereof will be omitted.

[0078] The semiconductor element 100B obtained by the above steps is bonded to a base plate 10 via a sintered material 9 using Ag particles, as shown in FIG. 12 . It is further bonded to external electrodes 12 via solder 11. During this process, the anti-oxidation film 92 dissolves into the molten solder 11, disappearing due to so-called solder erosion. The bonding methods are not limited to these, and it is also possible to use solder 11 for bonding to the base plate 10, Ag particles or Cu particles for bonding to the external electrodes 12, or to perform wire bonding as appropriate. The semiconductor element 100B is then sealed with a sealing material 13. This completes the process of obtaining a semiconductor device having the semiconductor element 100B.

[0079] <Effects> As described above, in the third embodiment, similar to the first embodiment, thermal stress caused by heat cycle testing and the like is dispersed, and the occurrence of cracks 21 in the electrodes 3 can be suppressed, thereby improving the long-term reliability of the semiconductor element 100B. The yield of the semiconductor element 100B is also improved. Furthermore, in the manufacturing method of the semiconductor element 100B, the end of the first metal adhesive film 5a is provided outside the second metal adhesive film 5b and the bonding electrodes 6, so that the components of the second metal adhesive film 5b can be prevented from diffusing into the protective film 4. Therefore, the reliability of the product can be improved.

[0080] Fourth Embodiment In this embodiment, the semiconductor device according to the above-described first to third embodiments is applied to a power conversion device. Although the application of the semiconductor device according to the first to third embodiments is not limited to a specific power conversion device, the following will describe a case where the semiconductor device according to the first to third embodiments is applied to a three-phase inverter as the fourth embodiment.

[0081] FIG. 17 is a block diagram showing the configuration of a power conversion system to which the power conversion device according to the fourth embodiment is applied.

[0082] The power conversion system shown in Fig. 17 is composed of a power supply 150, a power conversion device 200, and a load 300. The power supply 150 is a DC power supply and supplies DC power to the power conversion device 200. The power supply 150 can be composed of various components, such as a DC system, a solar cell, or a storage battery, or it may be composed of a rectifier circuit connected to an AC system or an AC / DC converter. The power supply 150 may also be composed of a DC / DC converter that converts DC power output from a DC system into a predetermined power.

[0083] The power conversion device 200 is a three-phase inverter connected between the power supply 150 and the load 300, and converts DC power supplied from the power supply 150 into AC power and supplies the AC power to the load 300. As shown in Fig. 17 , the power conversion device 200 includes a main conversion circuit 201 that converts DC power into AC power and outputs it, a drive circuit 202 that outputs drive signals that drive each switching element of the main conversion circuit 201, and a control circuit 203 that outputs control signals to the drive circuit 202.

[0084] The load 300 is a three-phase electric motor driven by AC power supplied from the power conversion device 200. The load 300 is not limited to a specific application, but is an electric motor mounted on various electrical devices, and is used as an electric motor for, for example, a hybrid vehicle, an electric vehicle, a railroad car, an elevator, or an air conditioning device.

[0085] The power conversion device 200 will be described in detail below. The main conversion circuit 201 includes switching elements (not shown) and freewheeling diodes (not shown). The switching elements convert DC power supplied from the power supply 150 into AC power, which is supplied to the load 300. While the main conversion circuit 201 can have a variety of specific circuit configurations, the main conversion circuit 201 according to this embodiment is a two-level, three-phase full-bridge circuit that can be configured with six switching elements and six freewheeling diodes connected in anti-parallel to each switching element. At least one of the switching elements and freewheeling diodes of the main conversion circuit 201 is configured with a semiconductor device according to any one of the first to third embodiments. Two of the six switching elements are connected in series to form upper and lower arms, which constitute each phase (U phase, V phase, and W phase) of the full-bridge circuit. The output terminals of each upper and lower arm, i.e., the three output terminals of the main conversion circuit 201, are connected to the load 300.

[0086] The drive circuit 202 generates drive signals for driving the switching elements of the main conversion circuit 201 and supplies them to the control electrodes of the switching elements of the main conversion circuit 201. Specifically, in accordance with control signals from a control circuit 203 (described later), the drive circuit 202 outputs to the control electrodes of each switching element a drive signal that turns the switching element on and a drive signal that turns the switching element off. When maintaining a switching element in the on state, the drive signal is a voltage signal (on signal) that is equal to or higher than the threshold voltage of the switching element, and when maintaining a switching element in the off state, the drive signal is a voltage signal (off signal) that is equal to or lower than the threshold voltage of the switching element.

[0087] The control circuit 203 controls the switching elements of the main conversion circuit 201 so that the desired power is supplied to the load 300. Specifically, it calculates the time (on time) that each switching element of the main conversion circuit 201 should be in the on state based on the power to be supplied to the load 300. For example, the main conversion circuit 201 can be controlled by PWM control, which modulates the on time of the switching elements according to the voltage to be output. The control circuit 203 then outputs a control command (control signal) to the drive circuit 202 so that an on signal is output to the switching element that should be in the on state at each point in time, and an off signal is output to the switching element that should be in the off state at each point in time. In accordance with this control signal, the drive circuit 202 outputs an on signal or an off signal as a drive signal to the control electrode of each switching element.

[0088] In the power conversion device according to this embodiment, the semiconductor devices according to the first to third embodiments are applied as switching elements of the main conversion circuit 201, and therefore, it is possible to achieve an improvement in long-term reliability.

[0089] In the present embodiment, an example has been described in which the semiconductor device according to the first to third embodiments is applied to a two-level three-phase inverter, but the application of the semiconductor device according to the first to third embodiments is not limited to this and can be applied to various power conversion devices. In the present embodiment, a two-level power conversion device is described, but a three-level or multi-level power conversion device may also be used, and when power is supplied to a single-phase load, the semiconductor device according to the first to third embodiments may be applied to a single-phase inverter. Furthermore, when power is supplied to a DC load or the like, the semiconductor device according to the first to third embodiments can also be applied to a DC / DC converter or an AC / DC converter.

[0090] Furthermore, the power conversion device to which the semiconductor device according to the first to third embodiments is applied is not limited to the case where the load described above is an electric motor, but can also be used, for example, as a power supply device for an electric discharge machine, a laser processing machine, an induction heating cooker, or a contactless power supply system, and can also be used as a power conditioner for a solar power generation system, a power storage system, etc.

[0091] Although this disclosure has been described in detail, the above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0092] It should be noted that the embodiments can be freely combined, and each embodiment can be modified or omitted as appropriate.

[0093] Various aspects of the present disclosure are summarized below as appendices.

[0094] (Note 1) A front-back conductive semiconductor element comprising: a semiconductor substrate; an electrode provided on an upper surface of the semiconductor substrate; a protective film covering an end of the electrode; a bonding electrode provided on the upper side of the electrode and on an inner end side of the protective film; a metal adhesive film provided between the electrode, the protective film, and the bonding electrode, covering an end of an interface between the electrode and the protective film; and a back electrode provided on the lower surface of the semiconductor substrate.

[0095] (Appendix 2) A semiconductor element according to appendix 1, wherein the electrode is made of aluminum or an aluminum alloy, the protective film is made of polyimide, the metal adhesive film is made of a single layer film or a multilayer film containing one or more metals selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum, and the bonding electrode is made of one or more metals selected from the group consisting of nickel, silver, and copper.

[0096] (Appendix 3) A semiconductor element according to Appendix 1 or Appendix 2, wherein the length from the triple point where the electrode, the protective film, and the metal adhesive film contact to the end of the metal adhesive film along the protective film is 2.0 μm or more longer than the length of the bonding electrode in the thickness direction.

[0097] (Supplementary Note 4) The semiconductor element according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the bonding electrode is connectable to an external electrode by a bonding material containing one or more metals selected from the group consisting of tin, silver, and copper.

[0098] (Supplementary Note 5) The semiconductor element according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the protective film has an arithmetic mean roughness of 10 nm or more and 200 nm or less.

[0099] (Supplementary Note 6) The semiconductor element according to any one of Supplementary Note 1 to Supplementary Note 5, wherein an oxide film made of at least one metal selected from the group consisting of nickel, silver, and copper is provided on an end surface of the bonding electrode.

[0100] (Supplementary Note 7) A semiconductor device comprising: a semiconductor element according to any one of Supplementary Note 1 to Supplementary Note 6; a base plate joined to the back electrode of the semiconductor element; and an external electrode joined to the joining electrode of the semiconductor element via solder.

[0101] (Supplementary Note 8) A power conversion device comprising: a main conversion circuit having a semiconductor device including the semiconductor element according to any one of Supplementary Note 1 to Supplementary Note 6, which converts input power and outputs the converted power; a drive circuit which outputs a control signal for controlling the semiconductor device to the semiconductor device; and a control circuit which outputs a control signal for controlling the drive circuit to the drive circuit.

[0102] (Appendix 9) A manufacturing method for a front-to-back conductive semiconductor element, comprising: a first step of forming an electrode on the top surface of a semiconductor substrate; a second step of forming a protective film so as to cover the end of the electrode; a third step of forming a metal adhesive film so as to cover the electrode and the protective film; a fourth step of forming a bonding electrode on the top surface of the metal adhesive film; and a fifth step of removing a portion of the metal adhesive film located on the protective film, wherein in the fifth step, the metal adhesive film is patterned so as to cover the end of the interface between the electrode and the protective film.

[0103] (Appendix 10) The method for manufacturing a semiconductor element according to appendix 9, wherein the electrode is made of aluminum or an aluminum alloy, the protective film is made of polyimide, the metal adhesive film is made of a single layer film or a multilayer film containing one or more metals selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum, and the bonding electrode is made of one or more metals selected from the group consisting of nickel, silver, and copper.

[0104] (Supplementary Note 11) The method for manufacturing a semiconductor element according to Supplementary Note 9 or Supplementary Note 10, wherein the metal adhesive film is formed by a sputtering method, and the bonding electrode is formed by an electrolytic plating method.

[0105] (Appendix 12) A method for manufacturing a semiconductor element described in any one of Appendices 9 to 11, wherein the length from the triple point where the electrode, the protective film, and the metal adhesive film contact to the end of the metal adhesive film along the protective film is 2.0 μm or more longer than the length of the bonding electrode in the thickness direction.

[0106] (Appendix 13) The method for manufacturing a semiconductor element according to appendix 11, wherein in the third step, a plasma treatment is performed to roughen the top and side surfaces of the protective film, and then the metal adhesive film is formed by the sputtering method.

[0107] (Supplementary Note 14) The method for manufacturing a semiconductor element according to any one of Supplementary Note 9 to Supplementary Note 13, wherein the bonding electrode is connectable to an external electrode by a bonding material containing one or more metals selected from the group consisting of tin, silver, and copper.

[0108] (Appendix 15) A method for manufacturing a semiconductor element described in any one of Appendices 9 to 14, further comprising: a step of forming a resist between the third step and the fourth step; and a step of removing the resist before removing a portion of the metal adhesive film in the fifth step.

[0109] (Appendix 16) The method for manufacturing a semiconductor element according to any one of Appendices 9 to 14, further comprising the step of simultaneously removing the metal adhesive film and the bonding electrode located above the upper surface of the protective film using a CMP method in the fifth step.

[0110] (Appendix 17) The method for manufacturing a semiconductor element according to any one of Appendices 9 to 16, further comprising a step of forming an oxide film made of one or more metals selected from nickel, silver, and copper on the end surface of the bonding electrode by heat treatment after the fifth step.

[0111] REFERENCE SIGNS LIST 1 semiconductor substrate, 3 electrode, 4 protective film, 5 metal adhesive film, 6 bonding electrode, 7 oxide film, 8 back electrode, 10 base plate, 11 solder, 12 external electrode, 100, 100A, 100B semiconductor element, 200 power conversion device, 201 main conversion circuit, 202 drive circuit, 203 control circuit.

Claims

1. A front-to-back conduction type semiconductor device, a semiconductor substrate; a gate structure provided on an upper surface of the semiconductor substrate; an electrode provided on an upper surface of the semiconductor substrate and the gate structure; a protective film covering the end of the electrode; a bonding electrode provided on a flat portion of the upper surface from above the electrode through an inner end surface of the protective film; a metal adhesive film provided between the electrode and the protective film and the bonding electrode, the metal adhesive film covering an edge of the interface between the electrode and the protective film; a back electrode provided on the lower surface of the semiconductor substrate; A semiconductor device comprising:

2. the electrodes are made of aluminum or an aluminum alloy; the protective film is made of polyimide, the metal adhesive film is a single layer or multilayer film containing at least one metal selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum; 2. The semiconductor device according to claim 1, wherein said bonding electrode is made of at least one metal selected from the group consisting of nickel, silver, and copper.

3. 3. The semiconductor device according to claim 1, wherein the length from the triple point where the electrode, the protective film, and the metal adhesive film contact to the end of the metal adhesive film along the protective film is 2.0 μm or more longer than the thickness direction length of the bonding electrode.

4. 3. The semiconductor device according to claim 1, wherein the bonding electrodes are connectable to external electrodes by a bonding material containing at least one metal selected from the group consisting of tin, silver, and copper.

5. 3. The semiconductor device according to claim 1, wherein the protective film has an arithmetic mean roughness of 10 nm or more and 200 nm or less.

6. 3. The semiconductor device according to claim 1, wherein an oxide film made of at least one metal selected from the group consisting of nickel, silver, and copper is provided on an end surface of said bonding electrode.

7. A base plate joined to the back electrode; an external electrode joined to the joining electrode via solder; The semiconductor device according to claim 1 or 2, comprising:

8. a main conversion circuit including the semiconductor device according to claim 1 or 2, which converts input power and outputs the converted power; a drive circuit that outputs a control signal to the semiconductor device; a control circuit that outputs a control signal to the drive circuit to control the drive circuit; A power conversion device comprising:

9. A method for manufacturing a front-back conduction type semiconductor device, comprising: a first step of forming an electrode on an upper surface of a semiconductor substrate on which a gate structure is formed; a second step of forming a protective film so as to cover the end of the electrode; a third step of forming a metal adhesive film so as to cover the electrode and the protective film; a fourth step of forming a bonding electrode on the upper surface of the metal adhesive film; a fifth step of removing a portion of the metal adhesive film located on the protective film, In the fifth step, the metal adhesive film is patterned to cover an edge of the interface between the electrode and the protective film.

10. the electrodes are made of aluminum or an aluminum alloy; the protective film is made of polyimide, the metal adhesive film is a single layer or multilayer film containing at least one metal selected from the group consisting of gold, silver, copper, palladium, chromium, titanium, nickel, cobalt, and aluminum; The bonding electrode is made of one or more metals selected from the group consisting of nickel, silver, and copper. The method for manufacturing a semiconductor device according to claim 9 .

11. The metal adhesive film is formed by a sputtering method, 11. The method for manufacturing a semiconductor device according to claim 9, wherein the bonding electrodes are formed by electrolytic plating.

12. 11. The method for manufacturing a semiconductor device according to claim 9 or 10, wherein the length from the triple point where the electrode, the protective film, and the metal adhesive film contact to the end of the metal adhesive film along the protective film is 2.0 μm or more longer than the thickness direction length of the bonding electrode.

13. 12. The method for manufacturing a semiconductor device according to claim 11, wherein in the third step, a plasma treatment is performed to roughen the top and side surfaces of the protective film, and then the metal adhesive film is formed by the sputtering method.

14. 11. The method for manufacturing a semiconductor device according to claim 9, wherein the bonding electrodes are connectable to external electrodes by a bonding material containing at least one metal selected from the group consisting of tin, silver, and copper.

15. a step of forming a resist between the third step and the fourth step; 11. The method for manufacturing a semiconductor device according to claim 9, further comprising the step of removing the resist before removing the part of the metal adhesive film in the fifth step.

16. 11. The method for manufacturing a semiconductor device according to claim 9, further comprising the step of simultaneously removing the metal adhesive film and the bonding electrode located above an upper surface of the protective film by using a CMP method in the fifth step.

17. 11. The method for manufacturing a semiconductor device according to claim 9, further comprising the step of forming an oxide film made of one or more metals selected from nickel, silver, and copper on an end surface of the bonding electrode by heat treatment after the fifth step.