Manufacturing method of laminated substrate, manufacturing method of semiconductor module, and laminated substrate, semiconductor module

Abstract

A method for manufacturing a laminated substrate, a method for manufacturing a semiconductor module, a laminated substrate, and a semiconductor module, which can easily and stably improve dielectric strength voltage, are provided. [Solution] A method for manufacturing a laminated substrate 1 having an insulating substrate 2 made of ceramic and electrodes 3, 4 formed on a front surface 2a and a back surface 2b of the insulating substrate 2, on which a semiconductor element can be mounted on the front surface of the electrode, in which the front surface of the insulating substrate around the outer periphery of the electrode, away from the electrode, is laser processed to modify the surface to make it conductive, thereby obtaining a surface modified portion 5. This makes it possible to stably manufacture a high-voltage laminated substrate using a simple method.

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a laminated substrate, a method for manufacturing a semiconductor module, a laminated substrate, and a semiconductor module. [Background technology]

[0002] A laminated substrate for a semiconductor module is configured to include, for example, a ceramic substrate made of aluminum nitride (AlN) or the like and electrodes provided on the surface of the ceramic substrate (see Patent Documents 1 to 3). Then, a semiconductor element is mounted on the surface of the electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-76197 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-76190 [Patent Document 3] Japanese Patent Application Laid-Open No. 2005-116602 Summary of the Invention [Problem to be solved by the invention]

[0004] However, an electric field concentrates at the edge of the electrode, making it prone to dielectric breakdown. For example, in Patent Documents 1 and 2, a solid insulator is placed between the edge of the electrode and the surface of the ceramic substrate. This is said to improve the dielectric strength.

[0005] However, there are many defects called pits near the edges of the electrodes, which means that the defects cannot be properly filled with solid insulators, making it impossible to ensure sufficient dielectric strength.

[0006] In addition, in Patent Document 3, a bonding layer is provided between the ceramic substrate and the electrode. In Patent Document 3, the bonding layer protrudes outward from the end of the electrode. The surface of the protruding bonding layer is then covered with a coating material.

[0007] However, the protruding surface of the bonding layer has defects due to the etching process used to form the electrodes, and therefore the defects in the bonding layer cannot be adequately filled with the coating material, making it impossible to ensure sufficient dielectric strength.

[0008] Furthermore, the solid insulators and coating materials described in each patent document may peel off, and therefore semiconductor modules manufactured using the laminated substrates described in each patent document cannot achieve sufficient reliability.

[0009] The present disclosure has been made in consideration of these points, and one of its objectives is to provide a method for manufacturing a laminated substrate and a laminated substrate that can easily and stably improve the dielectric strength voltage, as well as a method for manufacturing a semiconductor module and a semiconductor module that are highly reliable. [Means for solving the problem]

[0010] A method for manufacturing a laminated substrate according to one aspect of the present disclosure includes an insulating substrate made of aluminum nitride and an electrode formed on a front surface of the insulating substrate, and a method for manufacturing a laminated substrate capable of mounting a semiconductor element on the front surface of the electrode, the method comprising the steps of: laser processing a front surface of the insulating substrate around an outer periphery of the electrode, the front surface being away from the electrode, to modify the surface to be conductive; and at this time, using a laser output weaker than that used for cutting the insulating substrate; The main component is Al, and in addition to the main component is AlON the electrode The volume resistivity is higher than that of the insulating substrate Lower than the volume resistivity of Has volume resistivity Guidance The present invention is characterized by forming an electrically conductive surface modified portion.

[0011] A laminated substrate according to one aspect of the present disclosure includes an insulating substrate made of aluminum nitride and an electrode formed on a front surface of the insulating substrate, and a semiconductor element can be mounted on the front surface of the electrode. The laminated substrate has: The main component is Al, and in addition to the main component is AlON the electrode The volume resistivity is higher than that of the insulating substrate Lower than the volume resistivity of Has volume resistivity Guidance The insulating substrate further comprises an electrically conductive surface modified portion, the surface modified portion being provided on the front surface of the insulating substrate away from the electrode. [Effects of the Invention]

[0012] According to the method for manufacturing a laminated substrate of the present disclosure, a high-voltage-resistant laminated substrate can be stably manufactured using a simple technique, thereby enabling the manufacture of a highly reliable semiconductor module.

[0013] Furthermore, the laminated substrate of the present disclosure can stably achieve high breakdown voltage, thereby providing a highly reliable semiconductor module. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1 is a perspective view of a laminated substrate according to a first embodiment. [Figure 1B] FIG. 1 is a plan view of a multilayer substrate according to a first embodiment. [Figure 1C] FIG. 2 is a cross-sectional end view of the laminated substrate according to the first embodiment. [Figure 2A] FIG. 10 is a partially cut end view showing a triple point of a laminated substrate in a comparative example. [Figure 2B] 3 is a partially cutaway end view showing a triple point of the laminated substrate in the first embodiment. FIG. [Figure 3A] FIG. 10 is a perspective view of a laminated substrate according to a second embodiment. [Figure 3B] FIG. 10 is a plan view of a multilayer substrate according to a second embodiment. [Figure 3C] FIG. 10 is a cross-sectional end view of a laminated substrate according to a second embodiment. [Figure 4A]3A to 3C are perspective views illustrating a manufacturing process of the multilayer substrate according to the first embodiment. [Figure 4B] 4B is a perspective view showing a manufacturing process of the laminated substrate next to that of FIG. 4A. FIG. [Figure 4C] FIG. 4C is a perspective view showing a manufacturing process of the laminated substrate next to that of FIG. 4B. [Figure 4D] FIG. 4D is a perspective view showing a manufacturing process of the laminated substrate next to that of FIG. 4C. [Figure 5] 4A to 4D, and are perspective views showing the manufacturing process of the laminated substrate according to the first embodiment. [Figure 6A] 10A to 10C are perspective views illustrating a manufacturing process of the multilayer substrate according to the second embodiment. [Figure 6B] 6B is a perspective view showing a manufacturing process of the laminated substrate next to that of FIG. 6A. FIG. [Figure 6C] FIG. 6C is a perspective view showing a manufacturing process of the laminated substrate next to that of FIG. 6B. [Figure 7] FIG. 10 is a partially cutaway end view showing a laminated substrate according to another embodiment. [Figure 8] 1 is a perspective view of a semiconductor module according to an embodiment of the present invention; [Figure 9] FIG. 1 is a plan view of a semiconductor module according to an embodiment of the present invention. [Figure 10] 10 is a cross-sectional end view taken along line CC shown in FIG. 9. FIG. [Figure 11] 10 is a cross-sectional end view taken along line DD shown in FIG. 9. FIG. [Figure 12A] 10A and 10B are enlarged partial plan views of a laminated substrate illustrating an example of laser processing. [Figure 12B] 10A and 10B are enlarged partial plan views of a laminated substrate illustrating an example of laser processing. [Figure 12C] 10A and 10B are enlarged partial plan views of a laminated substrate illustrating an example of laser processing. DETAILED DESCRIPTION OF THE INVENTION

[0015] The laminated substrate of the first embodiment will be described below. FIG. 1A is a perspective view of the laminated substrate of the first embodiment. FIG. 1B is a plan view of the laminated substrate of the first embodiment. FIG. 1C is a cross-sectional end view of the laminated substrate of the first embodiment. The cross-sectional end view of FIG. 1C is the cross-sectional end face of FIG. 1B cut along line AA. Note that, using FIGS. 1A to 1C, components of the laminated substrate will be described, and a method for manufacturing the laminated substrate, particularly laser processing of an insulating substrate, will also be described.

[0016] As shown in FIGS. 1A to 1C, the laminated substrate 1 includes an insulating substrate 2 made of ceramic and electrodes 3 and 4 formed on a front surface 2a and a back surface 2b of the insulating substrate 2. The areas of the electrodes 3 and 4 are smaller than the front surface 2a and the back surface 2b of the insulating substrate 2. The front surface 2a and the back surface 2b of the insulating substrate 2 have surfaces exposed around the outside of the electrodes 3 and 4. Here, the electrode 3 formed on the front surface 2a of the insulating substrate 2 is a circuit board on which a semiconductor element is mounted in a semiconductor module. The electrode 4 formed on the back surface 2b of the insulating substrate 2 is a metal plate on the base plate side of the semiconductor module. Therefore, the "front surface 2a of the insulating substrate 2" refers to the surface on which the electrode 3 is formed as a circuit board on which a semiconductor element is mounted, and the "back surface 2b of the insulating substrate 2" refers to the surface on which the electrode 4 is formed as a metal plate on the base plate side. The front surface of electrode 3 formed on front surface 2a of insulating substrate 2 is the mounting surface for a semiconductor element, and the back surface of electrode 3 is the bonding surface with insulating substrate 2. The front surface of electrode 4 formed on back surface 2b of insulating substrate 2 is the surface facing the base plate, and the back surface of electrode 4 is the bonding surface with insulating substrate 2. Electrodes 3 and 4 may be made of highly conductive materials such as copper (Cu), aluminum (Al), or an alloy containing at least one of these. Electrodes 3 and 4 may have a plated film of nickel (Ni), gold (Au), or the like formed on their surfaces.

[0017] In this embodiment, the front surface 2a of the insulating substrate 2 around the outer periphery of the electrode 3 is laser-processed. As a result, the metal elements constituting the ceramic are precipitated as metals or alloys on the front surface 2a of the ceramic insulating substrate 2, thereby modifying the surface to be conductive. In this embodiment, the insulating substrate 2 can be made of oxide ceramics, nitride ceramics, carbide ceramics, or boride ceramics. For example, the insulating substrate 2 may be made of a ceramic mainly composed of AlN. In the case of a ceramic mainly composed of AlN, nitrogen (N) is desorbed from the front surface 2a of the insulating substrate 2, and metal Al is precipitated, modifying the surface to be conductive. The term "main component" in the insulating substrate 2 refers to a component that accounts for more than 50% by volume of the components constituting the insulating substrate 2. In FIGS. 1A to 1C, the laser-processed region is shown as a surface-modified region 5. In this embodiment, the surface-modified region 5 is formed in a rectangular ring shape. Furthermore, the term "surface-modified portion" refers to a conductive region or semiconductive region whose main component is a metal or alloy composed of metal elements that constitute ceramics. The term "main component" in the surface-modified portion 5 refers to a volume ratio of more than 50% of the components that constitute the surface-modified portion 5. The boundary between the surface-modified portion 5 and the insulating substrate 2 does not need to be clear, and the proportion of metal elements may gradually increase from the insulating substrate 2 toward the surface-modified portion 5. In this manner, in this embodiment, the front surface 2a of the insulating substrate 2 is a mixture of insulating regions and conductive or semiconductive regions.

[0018] In this embodiment, the type of laser is not limited, but for example, a carbon dioxide laser, a YAG laser, a fiber laser, or an excimer laser can be used.

[0019] In this embodiment, a conductive surface modified portion 5 is also formed by laser processing around the outer periphery of the electrode 4 formed on the back surface 2b of the insulating substrate 2. Here, "around the outer periphery of the electrode" means the periphery outside the ends 3a, 4a of the electrodes 3, 4. In this embodiment, the surface modified portion 5 is formed all around the outer periphery of the ends 3a, 4a of the electrodes 3, 4 so as to surround the outside of the ends 3a, 4a of the electrodes 3, 4 with a predetermined width. However, the surface modified portion 5 may also be formed on part of the periphery.

[0020] 1C, in the first embodiment, the surface modified portions 5 formed on the front surface 2a and the back surface 2b extend from the outer periphery of the electrodes 3 and 4 to the back surfaces of the electrodes 3 and 4, respectively. This allows the surface modified portions 5 and the electrodes 3 and 4 to be electrically connected.

[0021] FIG. 2A is a partially cutaway end view showing the triple point of a laminated substrate in a comparative example. FIG. 2B is a partially cutaway end view showing the triple point of a laminated substrate in the first embodiment. The laminated substrate 101 shown in FIG. 2A includes electrodes 103 and 104 on a front surface 102a and a back surface 102b of an insulating substrate 102, which is primarily made of AlN. However, in FIG. 2A, the front surface 102a and the back surface 102b of the insulating substrate 102 around the outer periphery of each electrode 103 and 104 are not laser-processed. Therefore, the front surface 102a and the back surface 102b of the insulating substrate 102 do not have a conductive surface-modified portion. Furthermore, the front surface of the laminated substrate 101, on which a semiconductor element is mounted, can be covered with a sealing resin (not shown). For example, the sealing resin can seal the front surface 102a of the insulating substrate 102 and the electrode 103. The sealing resin can be an epoxy resin or a silicone gel. The sealing resin may also contain inorganic fillers such as silicon oxide (SiO2) and aluminum oxide (Al2O3).

[0022] The circled area in Figure 2A is a triple junction where three phases overlap. The three phases are ceramic, metal, and resin or gas. In Figure 2A, the three phases are the insulating substrate 102, electrodes 103 and 104, and a sealing resin or atmosphere (not shown). An electric field concentrates at the triple junction. In addition, numerous depression-like defects called pits exist at the ends of the electrodes 103 and 104. For this reason, dielectric breakdown is likely to occur at the triple junction. As a countermeasure against dielectric breakdown, Patent Documents 1 and 2 propose solidifying the area around the triple junction with a solid insulator. However, the solid insulator cannot adequately fill the defects at the triple junction. Furthermore, the solid insulator may peel off. Therefore, sufficient dielectric strength cannot be achieved. Furthermore, the additional steps for providing the solid insulator and the increased construction materials lead to increased costs.

[0023] In contrast, in FIG. 2B , the front surface 2a and back surface 2b of the insulating substrate 2 around the outer periphery of the electrodes 3 and 4 are laser-processed to modify the surface to be conductive. In FIG. 2B , the surface-modified portion 5 is formed to straddle the area between the back surfaces of the electrodes 3 and 4 and the area outside the ends of the electrodes 3 and 4. This allows the circled triple junction to be shifted outward away from the ends 3a and 4a of the electrodes 3 and 4, where defects such as pits exist. The circled area in FIG. 2B is the triple junction where three phases overlap. In this case, the three phases are the insulating substrate 2, the surface-modified portion 5, and the encapsulating resin or air (not shown). In this way, the triple junction where the electric field concentrates can be separated from the defect portion that is the starting point of dielectric breakdown, thereby stably improving the dielectric strength. In the laminated substrate manufacturing method of this embodiment, a high-voltage laminated substrate 1 can be reliably manufactured by simply laser processing the front surface 2a and back surface 2b of the insulating substrate 2 without changing the encapsulation structure. Furthermore, costs can be reduced by using the same laser for surface modification as that used for cutting the insulating substrate 2. The laser processing for surface modification is performed with a weaker output than that used for laser processing for cutting the insulating substrate 2, for example, to the extent that the front surface 2a and back surface 2b of the insulating substrate 2 are surface modified to be conductive. Furthermore, the laminated substrate of this embodiment can stably achieve high voltage resistance.

[0024] The surface-modified region 5 shown in FIG. 2B is, for example, a conductive region primarily composed of Al. It may be formed of a single layer of Al, or it may contain metal elements other than Al or insulating elements. The definition of "main component" is as described above. For example, the surface-modified region 5 may be 60% by volume Al-40% by volume AlON. The surface-modified region 5 may be semiconductive, containing insulating elements in addition to metal elements such as Al. The semiconductive surface-modified region 5 has a volume resistivity intermediate between that of the electrodes 3 and 4 and the insulating substrate 2. If the surface-modified region 5 is semiconductive, the potential can be lowered, mitigating electric field concentration at the triple point. Therefore, a high-voltage laminated substrate 1 can be obtained more reliably. To obtain a semiconductive surface-modified region 5, the laser processing conditions are adjusted so that insulating elements remain in the surface-modified region 5 and the volume resistivity is higher than that of the electrodes.

[0025] Next, a laminated substrate according to a second embodiment will be described. Fig. 3A is a perspective view of the laminated substrate according to the second embodiment. Fig. 3B is a plan view of the laminated substrate according to the second embodiment. Fig. 3C is a cross-sectional end view of the laminated substrate according to the second embodiment. The cross-sectional end view of Fig. 3C is a cross section taken along line BB in Fig. 3B. Note that Figs. 3A to 3C will be used to explain the components of the laminated substrate, as well as a method for manufacturing the laminated substrate, particularly laser processing of an insulating substrate.

[0026] As shown in FIGS. 3A to 3C, laminated substrate 11 is configured to include insulating substrate 12 made of ceramics, and electrodes 13 and 14 formed on front surface 12a and back surface 12b of insulating substrate 12. Here, electrode 13 formed on front surface 12a of insulating substrate 12 is a circuit board on the side where a semiconductor element is installed in the semiconductor module. Electrode 14 formed on back surface 12b of insulating substrate 12 is a metal plate on the base plate side in the semiconductor module. The definitions of "front surface" and "back surface" are the same as those in the first embodiment described above.

[0027] As shown in FIGS. 3A to 3C, the front surface 12a of the insulating substrate 12 around the outside of the electrodes 13 and 14 is laser-processed to modify the surface to be conductive. At this time, the front surface 12a and back surface 12b of the insulating substrate 12 away from the electrodes 13 and 14 are laser-processed. In FIGS. 3A to 3C, the laser-processed region is shown as a surface-modified region 15. In this embodiment, the surface-modified region 15 is formed in a rectangular ring shape. Like the surface-modified region 5 shown in the first embodiment, the surface-modified region 15 is a conductive region or semiconductive region whose main component is a metal or alloy made from the metal elements that make up ceramics. The material of the surface-modified region 15 is the same as that of the surface-modified region 5.

[0028] However, in the second embodiment shown in FIGS. 3A to 3C , unlike the first embodiment, the surface-modified portion 15 is not in contact with the electrodes 13 and 14 and is not electrically connected. This causes the conductive surface-modified portion 15 to have a floating potential. Therefore, the electric field at the triple points located at the ends 13a and 14a of the electrodes 13 and 14 can be alleviated, thereby improving the dielectric strength. In the method for manufacturing a laminated substrate according to this embodiment, a high-voltage laminated substrate 11 can be stably manufactured by a simple technique of performing laser processing on the front surface 12a and the back surface 12b of the insulating substrate 12. Furthermore, costs can be reduced by using the same laser used for cutting the insulating substrate 12 as the laser used for surface modification. The laser processing for surface modification is performed with a lower output than the laser processing used for cutting the insulating substrate 12, so that the front surface 12a and the back surface 12b of the insulating substrate 12 are surface-modified to be conductive. Furthermore, the laminated substrate according to this embodiment can stably achieve a high dielectric strength.

[0029] It is also possible to combine the surface modified portion 5 shown in Figures 1A and 1B with the surface modified portion 15 shown in Figures 3A and 3B. In this case, as will be described later, the surface modified portion 5 and the surface modified portion 15 can also be formed partially. In particular, by providing two or more surface modified portions in areas where the dielectric strength is weak, the dielectric strength can be improved more stably.

[0030] 1A and 1B and the surface modified portion 15 shown in Fig. 3A and 3B have different widths, but this is for ease of understanding in the drawings, and the widths may be the same or different. Note that the width is the width of laser irradiation, and the surface may be modified to a predetermined width by a single laser irradiation, or may be adjusted to a predetermined width by performing multiple laser irradiations.

[0031] Next, a method for manufacturing the laminated substrate according to the first embodiment will be described in order of steps. FIGS. 4A to 4D are perspective views showing the manufacturing steps for the laminated substrate according to the first embodiment. In FIG. 4A, a nozzle 17 of a laser irradiation device is positioned above the front surface 2a of an insulating substrate 2 made of ceramic, and a laser beam L is irradiated onto the front surface 2a of the insulating substrate 2. As shown in FIG. 4B, a rectangular ring-shaped surface modified portion 5 is formed on the front surface 2a of the insulating substrate 2 by laser processing. For example, N is desorbed and Al is precipitated on the front surface 2a of the insulating substrate 2 irradiated with the laser beam L. Therefore, the surface modified portion 5 is electrically conductive.

[0032] In FIG. 4C, a metal plate 18, which is an electrode material, is bonded to the front surface 2a of the insulating substrate 2. The bonding can be performed by an active metal method using a silver (Ag)-copper (Cu) brazing filler metal containing an active metal such as titanium (Ti), zirconium (Zr), or hafnium (Hf). Alternatively, the bonding can be performed by an oxidation direct bonding method, in which the front surface 2a of the insulating substrate 2 is oxidized in advance and the copper plate is directly bonded using a eutectic reaction between the metal plate 18 and oxygen. Alternatively, for example, when bonding an insulating substrate 2 primarily composed of AlN to a metal plate 18 primarily composed of Al, the bonding can be performed by an aluminum direct bonding method.

[0033] In FIG. 4D, the metal plate 18 is etched to form the electrode 3 in a predetermined shape. As a result, the electrode 3 is smaller than the front surface 2a of the insulating substrate 2. At this time, the electrode 3 is formed so that a portion of the surface modified portion 5 is exposed around the outer periphery of the electrode 3. Note that, as described in FIG. 1C, a portion of the surface modified portion 5 extends to the back surface of the electrode 3.

[0034] 4A to 4D show the process of forming an electrode 3 and a surface modified portion 5 on the front surface 2a of the insulating substrate 2, but the same process can also be used to form an electrode 4 and a surface modified portion 5 on the back surface 2b of the insulating substrate 2.

[0035] FIG. 5 is a perspective view illustrating the manufacturing process of the laminated substrate according to the first embodiment, replacing FIGS. 4A to 4D. In FIG. 5, first, an electrode 3 having a predetermined shape is formed on the front surface 2a of the insulating substrate 2. As shown in FIG. 5, the electrode 3 is smaller than the front surface 2a of the insulating substrate 2. Then, as shown in FIG. 5, a laser beam L is irradiated from a laser irradiation device onto the front surface 2a of the insulating substrate 2 along the edge 3a of the electrode 3. At this time, the nozzle 17 of the laser irradiation device is positioned obliquely, and the laser beam L is irradiated obliquely onto the front surface 2a of the insulating substrate 2. The same process is performed on the back surface 2b of the insulating substrate 2. This allows the surface modification to extend somewhat to the insulating substrate 2 located behind the electrodes 3 and 4. In this way, a surface-modified portion can be formed that extends from the back surface of the electrodes 3 and 4 to the outside of the edges of the electrodes 3 and 4. However, using the manufacturing process shown in FIGS. 4A to 4D allows the surface modification to be extended to the back surfaces of the electrodes 3 and 4 more simply and reliably.

[0036] Next, a method for manufacturing a laminated substrate according to the second embodiment will be described in order of steps. FIGS. 6A to 6C are perspective views illustrating the manufacturing process of a laminated substrate according to the second embodiment. As shown in FIG. 6A, first, an electrode 13 having a predetermined shape is formed on the front surface 12a of the insulating substrate 12. As shown in FIG. 6A, the electrode 13 is smaller than the front surface 12a of the insulating substrate 12. The electrode 13 is formed according to the steps shown in FIGS. 4C and 4D. Next, as shown in FIG. 6B, a nozzle 17 of a laser irradiation device is positioned above the front surface 12a of the insulating substrate 12, away from the electrode 13, and the front surface 2a of the insulating substrate 12 is irradiated with laser light L. As shown in FIG. 6C, a rectangular ring-shaped surface-modified portion 15 is formed on the front surface 2a of the insulating substrate 2 by laser processing. For example, N is desorbed and Al is precipitated on the front surface 12a of the insulating substrate 12 irradiated with laser light L. Therefore, the surface-modified portion 15 is conductive. As shown in FIG. 6C, the surface modified portion 15 is not in contact with the electrode 13 and is not electrically connected thereto.

[0037] 6A to 6C show a process for forming the electrode 13 and the surface modified portion 15 on the front surface 12a of the insulating substrate 12, but a similar process can also be used to form the electrode 14 and the surface modified portion 15 on the back surface 12b of the insulating substrate 12.

[0038] FIG. 7 is a partially cutaway end view showing a laminated substrate according to another embodiment. In FIG. 7, a metallic bonding layer 26 is provided between an insulating substrate 22 and an electrode 23. That is, the electrode 23 is bonded to the front surface 22a of the insulating substrate 22 via the bonding layer 26. The bonding layer 26 is, for example, a brazing material containing Ag, Cu, and Ti. When a metal plate is etched to form an electrode 23 of a predetermined shape, the bonding layer 26 is left so as to extend slightly beyond the end 23a of the electrode 23, as shown in FIG. 7. Note that, as shown in FIG. 7, the etched surface is inclined from the electrode 23 to the bonding layer 26. The bonding layer 26 extending beyond the end 23a of the electrode 23 is prone to forming fine grooves and holes due to the etching process. Therefore, the sealing resin does not properly fill the fine grooves and holes, resulting in voids. These voids are defects that are likely to be the starting point of dielectric breakdown. 7, the front surface 22a of the insulating substrate 22 around the outer periphery of the bonding layer 26 is laser processed to modify the surface to make it conductive. The surface modified portion 25 shown in FIG. 7 extends to the back surface of the bonding layer 26 and is electrically connected to the electrode 23 via the bonding layer 26. The laser processing can be performed in accordance with the manufacturing process shown in FIG. 4 or FIG. 5.

[0039] This allows the triple point where the three phases overlap and the electric field concentrates to be shifted outward from the defect portion that is the starting point of dielectric breakdown. Therefore, a high-voltage laminated substrate can be stably manufactured using a simple method. It is also possible to perform laser processing on the front surface 22a of the insulating substrate 22, which is located outward from the electrode 23 and the bonding layer 26, as shown in FIG. 6.

[0040] In this embodiment, as shown in Fig. 7, electrode 23 may be bonded to insulating substrate 22 via bonding layer 26, or may be bonded directly. Laser processing can also be performed on the back surface of insulating substrate 22 in accordance with Fig. 7. As described above, a semiconductor module can be manufactured using the manufactured high-voltage laminated substrate.

[0041] FIG. 8 is a perspective view of the semiconductor module of this embodiment. FIG. 9 is a plan view of the semiconductor module of this embodiment. FIG. 10 is a cross-sectional end view taken along line CC shown in FIG. 9. FIG. 11 is a cross-sectional end view taken along line DD shown in FIG. 9. Note that FIGS. 9 to 11 are plan views and cross-sectional end views in a state where the lid 41 and sealing resin shown in FIG. 8 have been removed. In addition, the shaded portion in FIG. 9 indicates a circuit board. The dimensional ratios of the respective views in FIGS. 8 to 11 are not necessarily the same in order to make the drawings easier to understand.

[0042] Here, the laminated substrate shown in Figures 1 to 7 is illustrated schematically to make the features of this embodiment easier to understand. An example of the structure of a laminated substrate applied to a semiconductor module is shown in Figures 9 to 11. However, to avoid cluttering the drawings, Figures 9 to 11 do not show a surface modified by laser processing. The surface modified portion will be described in detail using Figure 12. Furthermore, Figures 9 to 11 do not show electronic components other than semiconductor elements, wiring members such as wires and lead frames, sealing resins, etc.

[0043] The semiconductor module 30 is a package of multiple semiconductor elements 38, and is configured by accommodating a laminated substrate 31 on which the semiconductor elements 38 are mounted in an accommodating section 37 defined by a base plate 43 and a case 36.

[0044] 10 and 11 includes an insulating substrate 32 made of ceramic, a circuit board 33 formed on the front surface of the insulating substrate 32, and a metal plate 34 formed on the back surface of the insulating substrate 32. The circuit board 33 and the metal plate 34 correspond to "electrodes" in this embodiment. A main current applied from the connection terminal 42 is input to the semiconductor element 38 via the circuit board 33. Therefore, the circuit board 33 is at a high potential. Therefore, a high voltage is applied between the circuit boards 33 and between the circuit board 33 and the metal plate 34.

[0045] A method for manufacturing a semiconductor module according to this embodiment will now be described. Specifically, as shown in Figures 10 and 11, a plurality of semiconductor elements 38 are bonded to a circuit board 33 via a solder layer 39. A metal plate 34 formed on the rear surface of an insulating substrate 32 is bonded to a base plate 43, which may be a copper plate, via a solder layer 40. This allows heat from the semiconductor elements 38 to be conducted to the base plate 43 via the laminated substrate 31. In addition to the semiconductor elements 38, various electronic components and wiring materials are also arranged on the circuit board 33 of the laminated substrate 31.

[0046] Although not shown, the laminated substrate 31 and the semiconductor element 38 housed in the housing portion 37 may be covered with a sealing resin. The sealing resin may be a single layer or multiple layers. When multiple layers are used, the materials may be the same or different. Then, a lid 41 shown in FIG. 8 is bonded onto the sealing resin. In this embodiment, as shown in FIGS. 8 and 9, the tip of the connection terminal 42 extends from the case 36. Furthermore, a through hole 44 is formed in the base plate 43. A screw such as a bolt can be passed through the through hole 44 to fix the device to an external heat dissipation fin, a water-cooling jacket, or the like.

[0047] The semiconductor element 38 is formed of silicon (Si), silicon carbide (SiC), or the like. For example, the semiconductor element 38 includes a switching element such as an IGBT (Insulated Gate Bipolar Transistor) or a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The semiconductor element 38 includes, for example, a drain electrode (or collector electrode) as a main electrode on the back surface and a gate electrode and a source electrode (or emitter electrode) as main electrodes on the front surface. The "front surface" refers to the surface on which the tip of the connection terminal 42 extends from the case 36. The "back surface" refers to the surface opposite the "front surface" and on which the base plate 43 is provided. The semiconductor element 38 also includes a diode such as an SBD (Schottky Barrier Diode) or an FWD (Free Wheeling Diode) as necessary. The semiconductor element 38 includes a cathode electrode as a main electrode on the back surface and an anode electrode as a main electrode on the front surface.

[0048] 12A to 12C are partially enlarged plan views of a laminated substrate showing an example of laser processing. FIGS. 12A to 12C show a set of circuit boards 33 provided on the laminated substrate 31 shown in FIG. 9, with the semiconductor elements 38 on the circuit boards 33 omitted. In FIG. 12A, the front surface 32a of the insulating substrate 32 is laser processed along the entire periphery of each circuit board 33. This allows a surface modified portion 45 to be formed on the front surface 32a of the insulating substrate 32, surrounding the entire periphery of each circuit board 33. The surface modified portion may be formed using any of the methods shown in FIGS. 4 to 7.

[0049] In Figures 12B and 12C, surface-modified portions 45a, 45b are formed on a portion of the periphery of each circuit board 33. In this way, it is not necessary to form a surface-modified portion around the entire periphery of the circuit board 33. For example, as shown in Figure 12B, surface-modified portions 45b can be formed only on the corners of each circuit board 33. Also, as shown in Figure 12C, surface-modified portions 45b can be formed only on the inner side where the circuit boards 33 face each other. However, the positions of the surface-modified portions shown in Figures 12B and 12C are merely examples. If the areas around the circuit board 33 where the dielectric strength is weak are known, the dielectric strength can be improved by selectively modifying the surface of the front surface 32a of the insulating substrate 32 in those weak areas to make them conductive.

[0050] It is also preferable to perform laser processing on the back surface of the insulating substrate 32, and to modify the surface of the outer periphery of the metal plate 34 to make it conductive. At this time, the surface of the entire periphery of the metal plate 34 may be modified, or the surface may be modified partially.

[0051] The present embodiment is not limited to the above-described embodiments and modifications, and may be variously changed, substituted, or modified within the scope of the spirit of the technical idea. Furthermore, if the technical idea can be realized in a different way due to technological advances or derived other technologies, it may be implemented using that method. Therefore, the claims cover all embodiments that may fall within the scope of the technical idea.

[0052] The features of the above embodiment are summarized below. The method for manufacturing a laminated substrate described in the above embodiment is a method for manufacturing a laminated substrate having an insulating substrate made of ceramic and an electrode formed on the front surface of the insulating substrate, on which a semiconductor element can be mounted, characterized in that the front surface of the insulating substrate around the outer periphery of the electrode is laser processed to make the surface conductive. With this configuration, a high-voltage laminated substrate can be stably manufactured using the simple technique of laser processing without changing the sealing structure, etc. Furthermore, by using the same laser used to cut the insulating substrate as the laser used for surface modification, costs can be reduced.

[0053] In the method for manufacturing a laminated substrate described in the above embodiment, the insulating substrate is preferably made of ceramics containing aluminum nitride as a main component, which makes it possible to more suitably manufacture a laminated substrate with high withstand voltage in a stable manner.

[0054] In the manufacturing method of the laminated substrate described in the above embodiment, laser processing can be performed so that the surface modification extends to the back surface of the electrode. The surface modification portion formed on the front surface of the insulating substrate is formed from the back surface of the electrode, extending outward from the edge of the electrode. This allows the triple point to be shifted outward from the edge of the electrode, where defects such as pits are likely to exist. As a result, the dielectric strength can be stably improved.

[0055] In the method for manufacturing a laminated substrate described in the above embodiment, the front surface of the insulating substrate away from the electrodes can be laser processed. This allows a floating potential to be provided outside the electrodes, thereby mitigating electric field concentration at the triple junction. As a result, the dielectric strength can be stably improved.

[0056] In the method for manufacturing a laminated substrate described in the above embodiment, laser processing can be performed on the front surface of the insulating substrate before forming the electrode. This allows the surface modified portion to be formed first by laser processing, and then the electrode to be formed so as to overlap a part of the surface modified portion. Therefore, the surface modified portion can be easily formed so as to straddle the back surface of the electrode and the outer side of the end of the electrode.

[0057] In the method for manufacturing a laminated substrate described in the above embodiment, laser processing can be performed after the electrodes are formed on the front surface of the insulating substrate. This allows the front surface of the insulating substrate exposed outside the electrodes to be easily laser processed. In particular, the front surface of the insulating substrate located away from the electrodes can be easily and reliably laser processed.

[0058] In the method for manufacturing a laminated substrate described in the above embodiment, the entire periphery of the electrode can be laser processed. This embodiment also includes a form in which the front surface of the insulating substrate is partially laser processed along the periphery of the electrode, but by laser processing the entire periphery, the dielectric strength voltage can be more stably improved.

[0059] In the method for manufacturing a laminated substrate described in the above embodiment, a metal bonding layer is provided between the insulating substrate and the electrode, extending outward beyond the electrode. The method is characterized in that the front surface of the insulating substrate around the outer periphery of the bonding layer is laser processed. This allows the triple point to be shifted outward from the edge of the electrode or the bonding layer, where defects are likely to occur. Alternatively, a conductive surface modification portion can be formed at a position further outward than the edge of the electrode or the bonding layer, where defects are likely to occur. As a result, the dielectric strength can be stably improved using a simple method.

[0060] In the method for manufacturing a laminated substrate described in the above embodiment, the insulating substrate has the electrodes on both the front and back surfaces, and the front and back surfaces of the insulating substrate are laser processed. By laser processing not only the front surface but also the back surface of the insulating substrate in this way, it is possible to more stably improve the dielectric strength voltage.

[0061] In this embodiment, at least the front surface of the insulating substrate on which the semiconductor element is mounted is laser processed. That is, in a configuration in which an electrode is not formed on the rear surface of the insulating substrate or in which the electrode is formed with a size approximately the same as that of the rear surface of the insulating substrate, the rear surface of the insulating substrate does not need to be laser processed. In a configuration in which the electrode is formed with an area smaller than that of the rear surface of the insulating substrate and a part of the rear surface of the insulating substrate is exposed, it is preferable to laser process the rear surface of the insulating substrate in the same way as the front surface of the insulating substrate.

[0062] The method for manufacturing a semiconductor module described in the above embodiment is characterized in that the semiconductor element is mounted on the laminated substrate manufactured by the method for manufacturing a laminated substrate described above. According to this embodiment, a laminated substrate with high voltage resistance and excellent stability can be used in manufacturing a semiconductor module, and a semiconductor module with excellent reliability can be manufactured.

[0063] The laminated substrate described in the above embodiment is a laminated substrate having an insulating substrate made of ceramics and an electrode formed on the front surface of the insulating substrate, on which a semiconductor element can be mounted, and is characterized in that a surface modification portion is provided on the front surface of the insulating substrate around the outer periphery of the electrode, the surface of the insulating substrate containing a metal or alloy composed mainly of metal elements that constitute the ceramic. The laminated substrate of this embodiment can stably achieve high voltage resistance.

[0064] In the laminated substrate described in the above embodiment, it is preferable that the insulating substrate is a ceramic material mainly composed of aluminum nitride, and the surface modified portion is a metal material mainly composed of aluminum. With this configuration, a surface modified portion with excellent conductivity can be formed on the front surface of the insulating substrate.

[0065] The laminated substrate described in the above embodiment can have the surface modified portion extending to the back surface of the electrode. This electrically connects the surface modified portion to the electrode, and the triple point shifts outward from the edge of the electrode where defects such as pits are likely to exist. As a result, the dielectric strength can be stably improved.

[0066] The laminated substrate described in the above embodiment can have the surface modification portion on the front surface of the insulating substrate, away from the electrodes. This provides a floating potential outside the electrodes, mitigating electric field concentration at the triple junction. As a result, the dielectric strength can be stably improved.

[0067] The laminated substrate according to the above embodiment may have the surface modified portion over the entire periphery of the electrode, thereby enabling a more stable improvement in the dielectric strength voltage.

[0068] The laminated substrate described in the above embodiment has a metallic bonding layer between the insulating substrate and the electrode that extends beyond the electrode. The surface modification portion can be provided on the front surface of the insulating substrate around the outer periphery of the bonding layer. This shifts the triple point outward from the edge of the electrode or the bonding layer, where defects are likely to occur. Alternatively, the surface modification portion is formed at a position farther outward than the edge of the electrode or the bonding layer, where defects are likely to occur. As a result, the dielectric strength can be stably improved.

[0069] The laminated substrate described in the above embodiment may have the electrodes on both the front and back surfaces of the insulating substrate, and the surface modified portion may be provided on both the front and back surfaces of the insulating substrate. In this way, by forming the surface modified portion not only on the front surface but also on the back surface of the insulating substrate, the dielectric strength can be improved more stably.

[0070] The semiconductor module according to the above embodiment is characterized in that the semiconductor element is mounted on the laminated substrate according to the above embodiment. According to the present embodiment, the laminated substrate having high withstand voltage and excellent stability is used for the semiconductor module, and a highly reliable semiconductor module can be provided. [Explanation of symbols]

[0071] 1, 11, 31: Laminated substrate 2, 12, 22, 32: Insulating substrate 3, 4, 13, 14, 23: Electrode 5, 15, 25, 45, 45a, 45b: Surface modified part 17: Nozzle 18:Metal plate 26: Bonding layer 30: Semiconductor module 33: Circuit board 34: Metal plate 36: Case 37: Storage section 38: Semiconductor element 39, 40: Solder layer 40: Solder layer 41: Lid 42: Connection terminal 43: Base plate 44:Through hole L: Laser

Claims

1. A method for manufacturing a laminated substrate having an insulating substrate made of aluminum nitride and an electrode formed on a front surface of the insulating substrate, wherein a semiconductor element can be mounted on the front surface of the electrode, the method comprising: A front surface of the insulating substrate, which is located around the outer periphery of the electrode and away from the electrode, is laser processed to be surface-modified to be conductive; At this time, the output is weakened compared to the laser processing used when cutting the insulating substrate, and a conductive surface modified portion is formed that contains Al as a main component and AlON in addition to the main component, and has a volume resistivity higher than that of the electrode and lower than that of the insulating substrate.

2. 2. The method for manufacturing a laminated substrate according to claim 1, wherein the laser processing is performed over the entire periphery of the electrode.

3. 3. A method for manufacturing a semiconductor module, comprising the steps of: mounting the semiconductor element on the laminated substrate manufactured by the method for manufacturing a laminated substrate according to claim 1.

4. A laminated substrate having an insulating substrate made of aluminum nitride and an electrode formed on a front surface of the insulating substrate, wherein a semiconductor element can be mounted on the front surface of the electrode, A laminated substrate characterized in that the front surface of the insulating substrate around the outside of the electrode is provided with a conductive surface modified portion containing Al as a main component and AlON as an additional component, and having a volume resistivity higher than the volume resistivity of the electrode and lower than the volume resistivity of the insulating substrate, the surface modified portion being provided on the front surface of the insulating substrate away from the electrode.

5. The laminated substrate according to claim 4 , wherein the surface modified portion is provided over the entire periphery of the electrode.

6. 6. A semiconductor module comprising the laminated substrate according to claim 4 or 5, and the semiconductor element mounted on the laminated substrate.

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