Semiconductor device and method for manufacturing semiconductor device

Abstract

A semiconductor device according to an embodiment comprises: an insulating substrate having a circuit pattern; a semiconductor chip fixed onto the insulating substrate and electrically connected to the circuit pattern; and a power supply terminal containing a metal that is of the same type as the circuit pattern, the power supply terminal being electrically connected to the circuit pattern. The power supply terminal includes: a flat plate-form joint portion joined to the circuit pattern; a penetration portion penetrating the joint portion in the thickness direction of the joint portion; and an extension portion that is bent from one end portion of the joint portion and extends upward, the extension portion being configured to be capable of connecting the circuit pattern and an external device. The joint portion and the circuit pattern are joined by a bonding material containing metal particles of the same type as the power supply terminal and the circuit pattern.

Description

Semiconductor device and method for manufacturing the same

[0001] FIELD Embodiments of the present invention relate to a semiconductor device and a method for manufacturing the semiconductor device.

[0002] During the manufacture of semiconductor devices, a process may be performed in which external terminals, such as power terminals and signal terminals, are joined to a circuit pattern on an insulating substrate on which a semiconductor chip is mounted. The external terminals and the circuit pattern are ultrasonically joined, for example, while applying a load. This breaks the natural oxidation coating formed on the surfaces of the circuit pattern and the external terminals, allowing them to be electrically joined.

[0003] JP 2005-259880 A International Publication No. 2020 / 245880

[0004] However, when the external terminals and the circuit pattern are joined by ultrasonic bonding, the pressure applied thereto, the ultrasonic vibrations, and the like can damage the insulating substrate.

[0005] An object of one embodiment is to provide a semiconductor device and a method for manufacturing the semiconductor device that can bond external terminals to a circuit pattern on an insulating substrate while suppressing damage.

[0006] The semiconductor device of the embodiment comprises an insulating substrate having a circuit pattern, a semiconductor chip fixed on the insulating substrate and electrically connected to the circuit pattern, and a power supply terminal containing the same type of metal as the circuit pattern and electrically connected to the circuit pattern, the power supply terminal having a flat joint portion joined to the circuit pattern, a through portion penetrating the joint portion in the thickness direction of the joint portion, and an extension portion bending and extending upward from one end of the joint portion and configured to be able to connect the circuit pattern to an external device, the joint portion and the circuit pattern being joined by a bonding material containing particles of the same type of metal as the power supply terminal and the circuit pattern.

[0007] FIG. 1 is a schematic diagram showing an example of the configuration of a semiconductor device according to an embodiment. FIG. 2 is an enlarged view of a joint provided in a power supply terminal according to an embodiment. FIG. 3 is an enlarged perspective view of a joint provided in a signal terminal according to an embodiment. FIG. 4 is a cross-sectional view showing an example of a procedure for a method for manufacturing a semiconductor device according to an embodiment. FIG. 5 is a cross-sectional view showing an example of a procedure for a method for manufacturing a semiconductor device according to an embodiment. FIG. 6 is a cross-sectional view showing an example of a procedure for a method for manufacturing a semiconductor device according to an embodiment. FIG. 7 is a cross-sectional view showing an example of a procedure for a method for manufacturing a semiconductor device according to an embodiment. FIG. 8 is a cross-sectional view showing a state in which a power supply terminal according to an embodiment and a comparative example is connected to a circuit pattern. FIG. 9 is an enlarged view of a joint provided in a power supply terminal according to a first modification of the embodiment. FIG. 10 is a plan view of the underside of a joint provided in a power supply terminal according to a second modification of the embodiment.

[0008] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following embodiments. Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art or that are substantially the same.

[0009] 1 is a cross-sectional view showing an example of the configuration of a semiconductor device 1 according to an embodiment. As shown in FIG. 1, the semiconductor device 1 according to the embodiment includes a base plate 10, a circuit board 20, a semiconductor chip 30, a package 40, a power terminal 51, and a signal terminal 52.

[0010] The base plate 10 is a flat plate-like member made of, for example, AlSiC, etc. The base plate 10 functions as a support member that supports the entire semiconductor device 1, and also functions as a heat sink that dissipates heat generated during operation of the semiconductor chip 30.

[0011] A circuit board 20 is provided on the base plate 10. The circuit board 20 includes a flat insulating substrate 21 and circuit patterns 22a and 22b provided on both sides of the insulating substrate 21.

[0012] The insulating substrate 21 is a flat plate made of ceramic, such as SiN or AlN. The circuit patterns 22a and 22b are made of Cu, for example. The circuit pattern 22a is provided on the lower surface of the insulating substrate 21 so as to face the base plate 10 and is connected to the base plate 10 by solder 12. The circuit pattern 22b is provided on the upper surface of the insulating substrate 21.

[0013] The underside of the semiconductor chip 30 is fixed to the circuit pattern 22b of the circuit board 20. The semiconductor chip 30 and the circuit pattern 22b are fixed together with a sintered material 32 such as Cu or Ag. The sintered material 32 such as Cu or Ag can be obtained by sintering a Cu paste or an Ag paste.

[0014] The semiconductor chip 30 is, for example, a metal-oxide-semiconductor field-effect transistor (MOSFET) or the like, and is made of SiC. When the semiconductor chip 30 is a MOSFET, it is provided with a gate pad which is a gate electrode, a P electrode which is a drain electrode, and an N electrode which is a source electrode. In other words, the gate electrode and the N electrode which is a source electrode are provided on the top surface of the semiconductor chip 30, and the P electrode which is a drain electrode is provided on the bottom surface of the semiconductor chip 30 bonded to the circuit pattern 22b.

[0015] The SiC semiconductor chip has high resistance to high temperatures and can operate reliably at high temperatures. The sintered material 32 obtained by sintering the Cu paste or Ag paste described above is a material that is less susceptible to deterioration even in the high-temperature operating environment of the SiC semiconductor chip 30.

[0016] The semiconductor chip 30 on the top surface thereof is electrically connected to the circuit pattern 22b around the semiconductor chip 30 by wires 35 made of Al or the like. The wires 35 connecting the semiconductor chip 30 to the circuit pattern 22b include a gate wire connecting the gate electrode of the semiconductor chip 30 to the circuit pattern 22b, and a wire connecting the N electrode, which is the source electrode of the semiconductor chip 30, to the circuit pattern 22b.

[0017] The package 40 includes a rectangular case 41 that encloses the circuit board 20, semiconductor chip 30, etc. on the base plate 10, and a lid 42 that closes the rectangular case 41. The case 41 and lid 42 may be made of, for example, thermoplastic polyphenylene sulfide (PPS) resin. The case 41 is fixed to the base plate 10 with a joining material 44 such as silicone resin. The lid 42 is similarly fixed to the upper end of the case 41 with a joining material 44 such as silicone resin.

[0018] The power supply terminals 51 and the signal terminals 52 are long Cu members, one end of which is connected to the circuit pattern 22b of the circuit board 20 by a Cu sintered material 60, and the other end of which is bent so as to fit along the top surface of the lid 42 of the package 40. These power supply terminals 51 and signal terminals 52 are preferably made of oxygen-free copper C1020 or the like.

[0019] The power supply terminal 51 and the signal terminal 52 function as external terminals that connect the semiconductor chip 30 to devices external to the semiconductor device 1 via the circuit board 20. The power supply terminals 51 include, for example, a P terminal that is electrically connected to a P electrode of the semiconductor chip 30, an N terminal that is electrically connected to an N electrode of the semiconductor chip 30, and an AC terminal (not shown) that is an output terminal.

[0020] The Cu sintered material 60 as the joining material is obtained by, for example, sintering a pressureless Cu paste. That is, as will be described later, by interposing the pressureless Cu paste between an external terminal such as the power terminal 51 and the circuit pattern 22b and heating and sintering the paste, the external terminal and the circuit pattern 22b can be joined together.

[0021] Here, the power supply terminals 51, the signal terminals 52, and the circuit pattern 22b are all primarily made of, for example, Cu. By using a pressureless Cu paste containing the same type of metal that has a high affinity with the metal that makes up the power supply terminals 51, the signal terminals 52, and the circuit pattern 22b, the power supply terminals 51, the signal terminals 52, and the circuit pattern 22b can be firmly bonded to each other. Furthermore, by using a pressureless Cu paste instead of, for example, an Ag paste containing expensive Ag, it is possible to reduce the manufacturing cost of the semiconductor device 1.

[0022] The pressureless Cu paste is a paste-like material formed by, for example, nano-sized Cu particles dispersed in an organic solvent. The organic solvent includes, for example, an organic protective agent and a sintering accelerator. The organic solvent is, for example, a carboxylic acid compound. The organic protective agent protects the Cu particles in the pressureless Cu paste, disperses the nano-sized Cu particles to homogenize them, and inhibits bonding at room temperature using the pressureless Cu paste. The sintering accelerator promotes sintering of the pressureless Cu paste when the pressureless Cu paste is heated.

[0023] Furthermore, the pressureless Cu paste can be sintered by heating at a predetermined temperature without applying a load and used for joining to other components. The pressureless Cu paste uses an organic protective agent that decomposes at a relatively low temperature, for example, which is different from the pressureless Cu paste that is sintered while applying a load, making joining without pressure possible.

[0024] By forming the Cu sintered material 60 from such a pressureless Cu paste, Cu particles contained in the pressureless Cu paste or traces thereof may be observable in the Cu sintered material 60. Furthermore, the Cu sintered material 60 may contain voids generated by the organic solvent vaporized during sintering.

[0025] The circuit board 20 and semiconductor chip 30 in the package 40, including the connection portions between the power terminals 51 and signal terminals 52 and the circuit board 20, are sealed with a potting material 33 such as silicone gel.

[0026] Next, a more detailed configuration example of the connection portion between the power terminal 51 and the signal terminal 52 and the circuit board 20 will be described with reference to FIGS. 2 and 3. FIG.

[0027] 2A and 2B are enlarged views of a joint 512 included in the power terminal 51 according to the embodiment. More specifically, Fig. 2A is a perspective view of the joint 512, Fig. 2B is a plan view of the lower surface of the joint 512, and Fig. 2C is a cross-sectional view of the joint 512 as viewed from the side.

[0028] 2 , the power supply terminal 51 includes an extension portion 511 and a joint portion 512. The joint portion 512 is a flat portion that is joined to the circuit pattern 22 b. The extension portion 511 bends and extends upward from one end of the joint portion 512, and is configured to be able to electrically connect the circuit pattern 22 b to an external device of the semiconductor device 1.

[0029] The joint portion 512 is provided with a through-hole 513 that penetrates the joint portion 512 in the thickness direction. In the example of Fig. 2, the through-hole 513 has a circular shape. In this case, the shape of the through-hole 513 may be a perfect circle, at least in design. However, from the standpoint of processing accuracy, etc., this does not mean that the finished shape of the through-hole 513 will also be a perfect circle.

[0030] Furthermore, in order to maintain sufficient strength of the entire joint 512, it is preferable that a width of at least a predetermined distance be left from the outer edge of the through-hole 513 to each end of the joint 512. As an example, if the thickness of the joint 512 is 1 mm or more and 1.5 mm or less, it is considered that sufficient strength can be ensured if a width of 1 mm or more is maintained from the outer edge of the through-hole 513 to each end of the joint 512.

[0031] 2B, the through portion 513 is provided on the lower surface of the joint portion 512, i.e., in the central portion of the joint surface of the joint portion 512 with the circuit pattern 22b. That is, the center point of the through portion 513 as viewed from above substantially coincides with the center point of the joint surface of the joint portion 512. Here, "substantially coincident" may include a case where the center point of the through portion 513 and the center point of the joint portion 512 completely coincide with each other, as well as a case where there is a positional error that occurs when the through portion 513 is formed.

[0032] Such a through portion 513 can be formed by, for example, wire electric discharge machining. In wire electric discharge machining, an electric current is passed through a brass wire, for example, to generate an electric discharge between the wire and the joint 512, which is the workpiece. The joint 512 of the workpiece is partially melted and cut by the heat of the electric discharge.

[0033] However, the through portion 513 may be formed by other methods such as electron beam irradiation or laser irradiation.

[0034] The Cu sintered material 60 is interposed between the lower surface of the bonding portion 512 and the upper surface of the circuit pattern 22b to bond them together.

[0035] The Cu sintered material 60 is also filled in the through-hole 513 of the joint 512. At this time, it is preferable that the Cu sintered material 60 reaches the height position of the upper end of the through-hole 513, and the upper end of the Cu sintered material 60 may be in a state of protruding somewhat from the upper surface of the joint 512. By filling the through-hole 513 with the Cu sintered material 60 in this way, an anchor effect is obtained by the Cu sintered material 60, and the shear strength of the joint between the power terminal 51 and the Cu sintered material 60 is increased, resulting in a highly reliable joint.

[0036] In addition, the allowable thickness of the Cu sintered material 60 in the through-hole 513 is preferably such that it does not hinder the escape of the organic solvent in the pressureless Cu paste when the pressureless Cu paste is sintered. As an example, the height from the bonding interface between the circuit pattern 22b and the Cu sintered material 60 to the upper end of the Cu sintered material 60 protruding in the through-hole 513 may be less than 1.5 times the thickness of the bonding portion 512 itself. In other words, the protruding height of the Cu sintered material 60 from the through-hole 513 may be less than half the thickness of the bonding portion 512.

[0037] However, in order to improve the shear strength by the Cu sintered material 60 and to ensure the removal of the organic solvent during sintering, it is more preferable that the upper surface of the Cu sintered material 60 in the through-hole 513 is at a height position that is substantially equal to the upper surface of the joint 512. The term "substantially equal height position" refers to a case where the heights of the upper surfaces of the Cu sintered material 60 and the joint 512 are completely equal, and may also include an error in the amount of filling when filling the Cu sintered material 60.

[0038] Furthermore, the Cu sintered material 60 has a tapered shape and covers the side surface of the joint 512. That is, the Cu sintered material 60 has a tapered shape on the side surface of the joint 512 that widens from the upper surface of the joint 512 toward the circuit pattern 22b of the circuit board 20. However, the tapered portion of the Cu sintered material 60 may bend between the upper surface of the joint 512 and the circuit pattern 22b. That is, the inclined surface of the Cu sintered material 60 in the tapered portion may be curved.

[0039] FIG. 3 is an enlarged perspective view of a joint portion 522 of the signal terminal 52 according to the embodiment.

[0040] 3 , the signal terminal 52 includes an extension 521 and a joint 522. The joint 522 is a flat portion that is joined to the circuit pattern 22 b. The extension 521 bends and extends upward from one end of the joint 522, and is configured to be able to electrically connect the circuit pattern 22 b to an external device of the semiconductor device 1.

[0041] Furthermore, the joint portion 522 of the signal terminal 52 may be formed smaller than, for example, the joint portion 512 of the power supply terminal 51. That is, the joint surface of the joint portion 522 of the signal terminal 52 with the circuit pattern 22b may have a smaller area than the joint surface of the joint portion 512 of the power supply terminal 51. This is because the amount of current flowing through the signal terminal 52 tends to be smaller than the amount of current flowing through the power supply terminal 51.

[0042] The joint portion 522 of the signal terminal 52 does not have a through portion formed therein, unlike the joint portion 512 of the power terminal 51 .

[0043] The Cu sintered material 60 is interposed between the lower surface of the bonding portion 522 and the upper surface of the circuit pattern 22b to bond them together.

[0044] The Cu sintered material 60 has a tapered shape and covers the side surface of the joint 522. That is, the Cu sintered material 60 has a tapered shape on the side surface of the joint 522 that widens from the upper surface of the joint 522 toward the circuit pattern 22b of the circuit board 20. However, the tapered portion of the Cu sintered material 60 may bend between the upper surface of the joint 522 and the circuit pattern 22b. That is, even at the joint 522 of the signal terminal 52, the inclined surface of the Cu sintered material 60 in the tapered portion may be curved.

[0045] 2 and 3, the extension 511 and the joint 512 of the power terminal 51, and the extension 521 and the joint 522 of the signal terminal 52 have portions bent at approximately right angles between them. However, these bent portions may have obtuse angles, and the extension 511 and the joint 512, and the extension 521 and the joint 522 may be connected by a gently curved surface.

[0046] In this way, the shape of the bent portion can vary depending on the bending method used when bending a long metal material to form the power terminal 51 and the signal terminal 52, which respectively have the joints 512 and 522.

[0047] (Method for Manufacturing Semiconductor Device) Next, an example of a method for manufacturing the semiconductor device 1 according to the embodiment will be described with reference to Figures 4 to 7. Figures 4 to 7 are cross-sectional views showing an example of the procedure of the method for manufacturing the semiconductor device 1 according to the embodiment.

[0048] As shown in Figure 4(a), a semiconductor chip 30 is placed on the circuit pattern 22b of the circuit board 20 via Cu paste, Ag paste, or the like, and the Cu paste or Ag paste is heated to sinter it, thereby forming a sintered material 32 that fixes the circuit pattern 22b and the semiconductor chip 30 together.

[0049] When sintering the Cu paste or Ag paste, the paste may be heated and a load may be applied to the semiconductor chip 30 so that the semiconductor chip 30 is fixed more firmly onto the circuit board 20 .

[0050] Wires 35 are also formed to connect the gate electrode and source electrode (not shown) of the semiconductor chip 30 to the circuit pattern 22b of the circuit board on the upper surface of the semiconductor chip 30. The gate electrode and source electrode of the semiconductor chip 30 and the circuit pattern 22b of the circuit board can be connected to the wires 35 by ultrasonic bonding using ultrasonic waves, for example.

[0051] 4B, the circuit board 20 on which the semiconductor chip 30 is mounted is fixed onto the base plate 10. More specifically, the circuit pattern 22a on the back surface of the circuit board 20 and the base plate 10 are joined using solder 12, for example.

[0052] As shown in FIG. 4C, a rectangular case 41 that will become part of the package 40 is fixed onto the base plate 10 with joining material 44 so as to surround the circuit board 20 and the semiconductor chip 30 .

[0053] As shown in FIG. 5A, a pressureless Cu paste 60p is applied by a dispenser or the like to the circuit pattern 22b of the circuit board 20 at the portion where the power terminal 51 and the signal terminal 52 are to be connected.

[0054] As shown in FIG. 5B, the power terminals 51 and the signal terminals 52 are disposed on the circuit pattern 22b of the circuit board 20 via pressureless Cu paste 60p.

[0055] 6(a), the pressureless Cu paste 60p interposed between the power terminal 51, the signal terminal 52, and the circuit pattern 22b of the circuit board 20 is sequentially heated and sintered. At this time, it is preferable to use a local heating device 100 capable of locally heating the pressureless Cu paste 60p.

[0056] The local heating device 100 includes a local heating unit 11 and an inert gas supply unit 12 .

[0057] The local heating unit 11 includes a power supply line 111 and a heater 112 connected to the power supply line 111. Power is supplied from the power supply line 111 to the heater 112, causing the heater 112 to generate heat. The heater 112 may be, for example, a halogen heater.

[0058] The inert gas supply unit 12 includes an inert gas supply line 121 and an inert gas supply pipe 122 connected to the inert gas supply line 121. An inert gas supply source (not shown) is connected to the other end of the inert gas supply line 121. The inert gas supply unit 12 can spray an inert gas such as nitrogen or a rare gas onto the portion heated by the local heating unit 11 via the inert gas supply line 121 and the inert gas supply pipe 122.

[0059] When sintering the pressureless Cu paste 60p, if the entire semiconductor device 1 during manufacture is heated, defects may occur, for example, due to melting of the solder 12 connecting the base plate 10 and the circuit board 20. However, by using the local heating device 100 to locally heat the pressureless Cu paste 60p interposed between the power supply terminals 51 and signal terminals 52 and the circuit pattern 22b of the circuit board 20, it is possible to prevent other components from being heated as well.

[0060] In addition, by using the local heating device 100 to heat the joint containing the unpressurized Cu paste 60p while spraying inert gas, it is possible to prevent the surfaces of the joints, such as the joints 512 and 522 of the power terminal 51 and the signal terminal 52, and the circuit pattern 22b of the circuit board 20, from being oxidized.

[0061] Laser irradiation or the like can also be considered as a method for locally heating the pressureless Cu paste 60p. However, laser irradiation is not preferable because it generates sputtering, which may cause debris from the irradiated components, such as the joints 512 and 522 or the circuit pattern 22b, to fly around.

[0062] 6(b) is an enlarged cross-sectional view of the joint portion of the power terminal 51, showing heating by the local heating device 100. As shown in FIG. 6(b), when heating is performed by the local heating device 100, a very small heating head 112a provided at the tip of the heater 112 is brought close to but not in contact with the joint portion 512 of the power terminal 51, the circuit pattern 22b of the circuit board 20, the pressureless Cu paste 60p, etc., and heating is performed while spraying inert gas from the inert gas supply pipe 122.

[0063] As a result, the pressureless Cu paste 60p is heated, and the organic solvent in the pressureless Cu paste 60p evaporates and escapes from the pressureless Cu paste 60p. As the organic solvent evaporates, the density of the Cu particles in the pressureless Cu paste 60p increases, causing the Cu particles to bond together. This also causes the shape of the pressureless Cu paste 60p, which was previously in a paste form, to change.

[0064] Specifically, the non-pressurized Cu paste 60p interposed between the joint 512 of the power terminal 51 and the circuit pattern 22b of the circuit board 20 spreads to the surrounding area, covering the side surface of the joint 512 and forming a trailing Cu sintered material 60 that extends toward the circuit pattern 22b. Note that such a trailing shape cannot be obtained in the case of pressurized Cu paste, which is sintered while applying a load.

[0065] Furthermore, the pressureless Cu paste 60p rises from the lower surface side of the joint portion 512 of the power terminal 51 into the through portion 513, thereby obtaining the Cu sintered material 60 filled into the through portion 513. At this time, it is preferable to adjust the amount of the initial pressureless Cu paste 60p to be applied so that the upper surface of the Cu sintered material 60 filled into the through portion 513 does not protrude more than half the thickness of the joint portion 512, and more preferably is at a height position approximately equal to that of the upper surface of the joint portion 512.

[0066] Although not shown, when heating the joint 522 of the signal terminal 52 using the local heating device 100, the heating head 112a at the tip of the heater 112 is brought close to but not in contact with the joint 522 of the signal terminal 52, the circuit pattern 22b of the circuit board 20, and the unpressurized Cu paste 60p, etc., and heating is performed while spraying inert gas from the inert gas supply pipe 122.

[0067] As a result, the organic solvent evaporates and escapes from the pressureless Cu paste 60p, and the Cu particles in the pressureless Cu paste 60p bond to each other, and the shape of the pressureless Cu paste 60p, which was in a paste state, changes.

[0068] At the joint 522 of the signal terminal 52 that does not have a through portion, the pressure-free Cu paste 60p interposed between the joint 522 and the circuit pattern 22b spreads around, covering the side of the joint 522 and forming a trailing Cu sintered material 60 that extends toward the circuit pattern 22b.

[0069] In this way, by using the Cu sintered material 60 obtained by sintering the pressureless Cu paste 60p, it is possible to connect the power supply terminal 51 and the signal terminal 52 to the circuit pattern 22b of the circuit board 20, for example, without applying a load.

[0070] 7A, potting material 33 is poured into the space surrounded by base plate 10 and case 41, and the semiconductor device 1 in the middle of manufacture is heated and cured in an oven. This hardens potting material 33, maintaining the insulation properties inside case 41.

[0071] 7(b), the lid 42 is placed and fixed to the upper end of the case 41 with the joining material 44 interposed therebetween. Thereafter, the upper ends of the extensions 511, 521 of the power terminal 51 and the signal terminal 52 protruding from the upper surface of the lid 42 are bent.

[0072] In this manner, the semiconductor device 1 of the embodiment is manufactured.

[0073] Comparative Example Next, an example in which a power supply terminal 51x of a comparative example or the power supply terminal 51 of the embodiment is connected to a circuit pattern 22b will be described with reference to FIG.

[0074] 8A and 8B are cross-sectional views showing how the power terminals 51 and 51x according to the embodiment and the comparative example are connected to the circuit pattern 22b. More specifically, Fig. 8A shows how the power terminal 51x according to the comparative example is connected to the circuit pattern 22b, and Fig. 8B shows how the power terminal 51 according to the embodiment is connected to the circuit pattern 22b.

[0075] As shown in FIG. 8A, the power terminal 51x of the comparative example includes a bonding portion 512x that is bonded to the circuit pattern 22b. However, the bonding portion 512x does not have a through-hole. A pressureless Cu paste 60x is interposed between the bonding portion 512x and the circuit pattern 22b and locally heated. This vaporizes the organic solvent in the pressureless Cu paste 60x and allows it to escape from the pressureless Cu paste 60x.

[0076] At this time, the organic solvent mainly escapes from the side surfaces of the pressureless Cu paste 60x exposed in the gap between the bonding portion 512x and the circuit pattern 22b. As a result, the density of Cu particles increases in the central portion of the pressureless Cu paste 60x, and sintering proceeds relatively quickly.

[0077] In contrast, near the edge of the side of the pressureless Cu paste 60x, sintering is difficult to proceed due to the organic solvent leaking from the center of the pressureless Cu paste 60x, and bubbles 61x are likely to occur due to the evaporated organic solvent.

[0078] Although such bubbles 61x are generated in the center of the pressureless Cu paste 60x, bubbles 61x are more likely to be generated near the edges of the pressureless Cu paste 60x than near the center. These bubbles 61x remain as voids in the Cu sintered material formed by heating.

[0079] Therefore, in the Cu sintered material of the comparative example, the density of Cu particles in the center is higher than that near the edges, and the porosity near the edges is higher than that of the central portion, resulting in a density difference where the center is dense and the edges are sparse. Such a density difference deteriorates the electrical characteristics and bonding strength at the bonding portion between the power terminal 51x and the circuit pattern 22b.

[0080] 8B, in the power supply terminal 51 of the embodiment, as described above, the through-hole 513 is provided in the joint 512. In this case, the organic solvent vaporized by local heating of the joint portion escapes not only from the side surface of the pressure-free Cu paste 60p exposed from the gap between the joint 512 and the circuit pattern 22b, but also from the upper end of the pressure-free Cu paste 60p filled in the through-hole 513.

[0081] As described above, the through-hole 513 is provided in the center of the bonding surface of the bonding portion 512 with the circuit pattern 22b, and is located directly above the center of the pressure-free Cu paste 60p. This reduces the amount of organic solvent that escapes from the vicinity of the edge of the side surface of the pressure-free Cu paste 60p. This also reduces the variation in the amount of evaporated organic solvent that escapes between the center of the pressure-free Cu paste 60p and the vicinity of the edge of the side surface of the pressure-free Cu paste 60p, thereby stabilizing the progress of sintering and the likelihood of bubbles 61 being generated by evaporated organic solvent.

[0082] This reduces the variation in Cu particle density and porosity between the center and the edges of the Cu sintered material 60 formed by heating, resulting in a Cu sintered material 60 with a small density difference. This also reduces the overall porosity of the Cu sintered material 60. This improves the electrical characteristics of the joint between the power terminal 51 and the circuit pattern 22b. Here, the porosity is, for example, the ratio of the area occupied by voids to the area occupied by the Cu sintered material 60 in a cross section taken perpendicular to the thickness direction of the joint 512.

[0083] As described above, the joint 522 of the signal terminal 52 of the embodiment is configured to have a smaller area of ​​the joint surface with the circuit pattern 22p than, for example, the joint 512 of the power terminal 51. Therefore, even if the joint 522 of the signal terminal 52 does not have a through portion, variations in the density and porosity of the Cu particles between the center and the vicinity of the edge during sintering by heating are suppressed, and a Cu sintered material 60 with a small density difference can be obtained.

[0084] (Overview) A semiconductor device includes, for example, a semiconductor chip mounted on a circuit board having a circuit pattern. External terminals such as power terminals and signal terminals may be connected to the circuit pattern on the circuit board. The circuit pattern and the external terminals are connected, for example, by ultrasonic bonding while applying a load. The tip of a bonding tool used for ultrasonic bonding has, for example, multiple protrusions. These protrusions bite into the external terminals and apply ultrasonic vibrations, firmly bonding the external terminals to the circuit pattern.

[0085] However, with this method, there is a risk of damaging the circuit board due to the application of a load and ultrasonic vibrations. Furthermore, when the protrusion at the tip of the bonding tool is driven into the external terminal, debris from the external terminal is generated and scattered, which may cause a short circuit between the circuit pattern and surrounding wiring.

[0086] In order to solve the above problems, the inventors have investigated methods for connecting external terminals and circuit patterns without applying pressure, and have come up with the idea of ​​using a pressure-free Cu paste. By heating and sintering the pressure-free Cu paste, a strong bond can be obtained even without applying pressure, and the external terminals and circuit patterns can be connected with high reliability.

[0087] However, when pressureless Cu paste is used, the heat generated during sintering can heat other components as well, potentially melting, for example, the solder that secures the circuit board and base plate. Furthermore, it was discovered that, while sintering of pressureless Cu paste proceeds relatively quickly in the center, sintering does not proceed near the edges, and the porosity increases, resulting in a sparse structure. The inventors conducted further research and have now come to a solution to the above problem.

[0088] According to the embodiment of the semiconductor device 1, the semiconductor device 1 includes a power supply terminal 51 that contains the same type of metal as the circuit pattern 22b of the circuit board 20 and is electrically connected to the circuit pattern 22b, and the joint portion 512 of the power supply terminal 51 and the circuit pattern 22b are joined by a Cu sintered material 60 that contains particles of the same type of metal as the power supply terminal 51 and the circuit pattern 22b.

[0089] In this way, by using the Cu sintered material 60 to connect the circuit pattern 22b and the power terminal 51, the power terminal 51 can be joined to the circuit pattern 22b while suppressing damage to the circuit pattern 22b, the power terminal 51, etc. In addition, it is possible to suppress the scattering of debris from the power terminal 51, which could cause a short circuit in the surrounding wiring, etc. Therefore, a highly reliable semiconductor device 1 can be obtained. Furthermore, by using the Cu sintered material 60 containing the same type of metal as the circuit pattern 22b and the power terminal 51, the circuit pattern 22b and the power terminal 51 can be firmly joined.

[0090] According to the semiconductor device 1 of the embodiment, the power supply terminal 51 has a flat joint portion 512 joined to the circuit pattern 22b, and a through portion 513 penetrating the joint portion 512 in the thickness direction of the joint portion 512.

[0091] In this way, the joint 512 has the through portion 513, which reduces the difference in density between the center portion and the vicinity of the end portion of the Cu sintered material 60 and also reduces the porosity of the entire Cu sintered material 60. This improves the electrical characteristics and bonding strength of the bonding portion between the joint 512 and the circuit pattern 22b, and enables the power supply terminal 51 and the circuit pattern 22b to be connected with high reliability.

[0092] According to the semiconductor device 1 of the embodiment, the Cu sintered material 60 is interposed between the bonding portion 512 and the circuit pattern 22b, and is also filled in the through portion 513. This increases the bonding strength between the bonding portion 512 and the circuit pattern 22b against stress that would cause the bonding portion 512 and the circuit pattern 22b to shift laterally, i.e., shear stress.

[0093] According to the semiconductor device 1 of the embodiment, the Cu sintered material 60 has a trailing shape and covers the side surface of the joint 512. As described above, by using a non-pressurized Cu paste instead of a pressurized Cu paste, it is possible to form the Cu sintered material 60 having such a shape during sintering. The trailing shape of the Cu sintered material 60 can further increase the bonding strength between the joint 512 and the circuit pattern 22b.

[0094] According to the semiconductor device 1 of the embodiment, the through portion 513 has a circular shape when viewed from the top surface of the joint portion 512, and the center point of the through portion 513 viewed from the top surface of the joint portion 512 substantially coincides with the center point of the joint surface of the joint portion 512 with the circuit pattern 22b. By providing the through portion 513 at such a position, the difference in density between the central portion and the end portions of the Cu sintered material 60 can be further reduced.

[0095] The semiconductor device 1 of the embodiment further includes a signal terminal 52 that contains the same type of metal as the circuit pattern 22b and is electrically connected to the circuit pattern 22b, and the Cu sintered material 60 is also interposed between the circuit pattern 22b and a joint 522 of the signal terminal 52. In this way, by applying the Cu sintered material 60 also to the joint between the signal terminal 52 and the circuit pattern 22b, the signal terminal 52 can be joined to the circuit pattern 22b while suppressing damage.

[0096] According to the semiconductor device 1 of the embodiment, the joints 522 of the signal terminals 52 are smaller than the joints 512 of the power supply terminals 51, and the through-holes 513 are selectively formed in the joints 512 of the power supply terminals 51. In this way, the joints 522 of the signal terminals 52 are often formed smaller than the joints 512 of the power supply terminals 51. In this case, even if a through-hole is not provided in the joints 522 of the signal terminals 52, it is possible to suppress the variation in density difference between the center portion and the end portions of the Cu sintered material 60.

[0097] According to the manufacturing method of the semiconductor device 1 of the embodiment, when connecting the power terminal 51 and the circuit pattern 22b, the pressureless Cu paste 60p is locally heated and sintered without applying a load to the power terminal 51 and the circuit pattern 22b. This makes it possible to bond the power terminal 51 to the circuit pattern 22b while suppressing damage caused by, for example, the application of a load and ultrasonic bonding. Furthermore, because the pressureless Cu paste 60p is locally heated, it is possible to suppress damage caused by heating of other components.

[0098] According to the manufacturing method of the semiconductor device 1 of the embodiment, when sintering the pressureless Cu paste 60p, an inert gas is sprayed onto the pressureless Cu paste 60p, and the heating head 112a of the heater 112 is brought close to the joint portion 512 of the power terminal 51 without contacting the joint portion 512, thereby locally heating the pressureless Cu paste 60p.

[0099] In this way, by sintering the pressureless Cu paste 60p by localized heating, it is possible to prevent other components from being heated. Furthermore, by spraying an inert gas onto the pressureless Cu paste 60p when heating it, it is possible to prevent oxidation of the bonding portion 512 and the circuit pattern 22b.

[0100] According to the manufacturing method of the semiconductor device 1 of the embodiment, when pressure-free Cu paste 60p is interposed between the joint 512 and the circuit pattern 22b, the amount of pressure-free Cu paste 60p used is adjusted so that the thickness of the through portion 513, which is formed by sintering the pressure-free Cu paste 60p and extends from the joint interface with the circuit pattern 22b to the upper end of the Cu sintered material 60, is equal to or greater than the thickness of the joint 512 and less than 1.5 times the thickness of the joint 512.

[0101] In this way, by filling the through-hole 513 sufficiently with Cu sintering material 60, the bonding strength between the joint 512 and the circuit pattern 22b against shear stress is increased. On the other hand, since there is no need to sinter the excess pressureless Cu paste 60p that significantly exceeds the upper surface of the joint 512, the pressureless Cu paste 60p is more easily sintered and the sintering time can be shortened.

[0102] (Modification 1) Next, a semiconductor device according to Modification 1 of the embodiment will be described with reference to Fig. 9. In the semiconductor device according to Modification 1, the shape of the through portion 513s that the power supply terminal 51s has in the joint portion 512 is different from that of the above-described embodiment.

[0103] 9A and 9B are enlarged views of a joint 512 included in a power terminal 51s according to the first modification of the embodiment. More specifically, Fig. 9A is a perspective view of the joint 512, and Fig. 9B is a plan view of the lower surface side of the joint 512.

[0104] In FIG. 9, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the description thereof may be omitted.

[0105] 9 , the joint 512 of the power terminal 51s of the first modification is provided with a through-hole 513s that is rectangular when viewed from above. In this case, the shape of the through-hole 513s may be square, at least in design. However, this does not mean that the finished shape of the through-hole 513s will also be square, from the standpoint of processing accuracy, etc.

[0106] 9B, the through-hole 513 of the first modification is also provided on the lower surface of the joint 512, that is, in the central portion of the joint surface between the joint 512 and the circuit pattern 22b. That is, the center point of the through-hole 513s as viewed from above substantially coincides with the center point of the joint surface of the joint 512.

[0107] The through portion 513 of the first modification can also be formed by, for example, wire electric discharge machining.

[0108] In the semiconductor device of Modification 1, the through portion 513s has a rectangular shape when viewed from the top surface of the bonding portion 512, and the center point of the through portion 513s when viewed from the top surface of the bonding portion 512 substantially coincides with the center point of the bonding surface of the bonding portion 512 with the circuit pattern 22b. This provides the same effects as the semiconductor device of the above-described embodiment.

[0109] Furthermore, when the width of the through-hole 513s is made equal to the diameter of the circular through-hole 513 in the above-described embodiment, the square through-hole 513s has a larger opening area at the joint 512. This further increases the amount of organic solvent that escapes from the upper end of the central portion of the pressureless Cu paste 60p. This further reduces the density difference between the central portion and the edge portions of the Cu sintered material 60, and also reduces the porosity of the entire Cu sintered material 60.

[0110] 10, a semiconductor device according to a second modification of the embodiment will be described. In the semiconductor device according to the second modification, the through portions 513e, 513u, 513r, and 513c of the power supply terminal provided in the joint portion 512 have shapes that are further different from those in the above-described embodiment.

[0111] Fig. 10 is a plan view of the underside of a joint 512 included in a power terminal according to Modification 2 of the embodiment. In Fig. 10, the same components as those in the above-described embodiment are denoted by the same reference numerals, and the description thereof may be omitted.

[0112] 10( a), the through-hole portion 13e of the second modification has an elliptical shape with its major axis in the longitudinal direction of the joint portion 512. The through-hole portion 513e of the second modification having an elliptical shape is also provided on the lower surface of the joint portion 512, that is, in the central portion of the joint surface of the joint portion 512 with the circuit pattern 22b. In other words, the center point of the through-hole portion 513e when viewed from above substantially coincides with the center point of the joint surface of the joint portion 512.

[0113] 10B, the through-hole 513u of the second modification opens at the other end of the joint 512, which is opposite to the one end of the joint 512 that has a bent portion with the extension 511. The end of the through-hole 513u has a curved surface on the one end side of the joint 512. That is, the through-hole 513u has a U-shape when viewed from above.

[0114] 10(c), the through-hole portion 13r of Modification 2 has a rectangular shape with its long sides aligned in the longitudinal direction of the joint portion 512. The rectangular through-hole portion 513r of Modification 2 is also provided on the lower surface of the joint portion 512, i.e., in the central portion of the joint surface of the joint portion 512 with the circuit pattern 22b. In other words, the center point of the through-hole portion 513r as viewed from above substantially coincides with the center point of the joint surface of the joint portion 512.

[0115] 10(d), the through portion 513c of the second modification opens at the other end opposite to the one end of the joint portion 512 that has a bent portion with the extension portion 511. Furthermore, the end of the through portion 513c is angular on the one end side of the joint portion 512. That is, the through portion 513c viewed from above has a rectangular shape with one short side open.

[0116] According to the semiconductor device of the second modification, the shapes of the through-holes 513e, 513u, 513r, and 513c have a longitudinal direction and a lateral direction when viewed from above the joint 512. This provides the same effects as the semiconductor device of the above-described embodiment.

[0117] Furthermore, when the width in the short direction of the through-holes 513e, 513r is made equal to the width of the circular through-hole 513 of the above-described embodiment and the square through-hole 513s of the above-described modified example 1, the through-holes 513e, 513r of modified example 2 have a larger opening area at the joint 512. This makes it possible to further increase the amount of organic solvent that escapes from the upper end of the central portion of the pressureless Cu paste 60p, further reducing the density difference between the central portion and the vicinity of the end of the Cu sintered material 60, and also reducing the porosity of the entire Cu sintered material 60.

[0118] According to the semiconductor device of Modification 2, the through-holes 513u and 513c open to the other end side of the joint portion 512. This further increases the opening area of ​​the joint portion 512. This further increases the amount of organic solvent that escapes from the upper end of the central portion of the pressureless Cu paste 60p, further reducing the density difference between the central portion and the vicinity of the end of the Cu sintered material 60, and also reducing the porosity of the entire Cu sintered material 60.

[0119] In the above-described embodiment and modified examples 1 and 2, the semiconductor chip 30 is made of SiC. However, the configurations of the above-described embodiment and modified examples 1 and 2 are applicable even if the semiconductor chip 30 is made of other materials, such as Si, GaAs, or GaN. Furthermore, the semiconductor chip 30 is not limited to the above-described MOSFET, and may be a semiconductor chip of a type different from a MOSFET, such as an insulated gate bipolar transistor (IGBT).

[0120] In the above-described embodiment and modified examples 1 and 2, only one through-hole portion 513, 513s, 513e, 513u, 513r, 513c is provided. However, the joint portion 512 may be provided with a plurality of through-hole portions.

[0121] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

Claims

1. A semiconductor device comprising: an insulating substrate having a circuit pattern; a semiconductor chip fixed on said insulating substrate and electrically connected to said circuit pattern; and a power supply terminal containing the same type of metal as said circuit pattern and electrically connected to said circuit pattern, said power supply terminal having a flat joint portion joined to said circuit pattern, a through portion passing through said joint portion in a thickness direction of said joint portion, and an extension portion bent and extending upward from one end of said joint portion, said extension portion being configured to be able to connect said circuit pattern to an external device, said joint portion and said circuit pattern being joined by a bonding material containing particles of the same type of metal as said power supply terminal and said circuit pattern.

2. The semiconductor device according to claim 1, wherein the bonding material is interposed between the bonding portion and the circuit pattern and fills the through portion.

3. The semiconductor device according to claim 2, wherein the thickness of the bonding material at the through portion from the bonding interface with the circuit pattern to the upper end of the bonding material is equal to or greater than the thickness of the bonding portion, but less than 1.5 times the thickness of the bonding portion.

4. The semiconductor device according to claim 1, wherein the bonding material has a trailing shape and covers a side surface of the bonding portion.

5. The semiconductor device according to claim 1, wherein the bonding material contains voids.

6. The semiconductor device according to claim 1, wherein the bonding material is derived from a pressureless metal paste in which the particles are contained in an organic solvent and which can be sintered without pressure.

7. The semiconductor device according to claim 1, wherein the through portion has a circular or rectangular shape when viewed from above the joint portion.

8. The semiconductor device according to claim 1, wherein the shape of said through portion when viewed from above said joint portion has a long side direction and a short side direction.

9. The semiconductor device according to claim 8, wherein the through portion opens to the other end side of the joint portion.

10. The semiconductor device according to claim 7 or 8, wherein a center point of said through portion when viewed from above said joint portion substantially coincides with a center point of a joint surface of said joint portion with said circuit pattern.

11. The semiconductor device according to claim 1, further comprising a signal terminal containing the same type of metal as the circuit pattern and electrically connected to the circuit pattern, the bonding material also being interposed between a bonding portion of the signal terminal and the circuit pattern.

12. The semiconductor device according to claim 11, wherein the joint of the signal terminal is smaller than the joint of the power supply terminal, and the through portion is selectively formed at the joint of the power supply terminal, out of the joint of the power supply terminal and the joint of the signal terminal.

13. A method for manufacturing a semiconductor device, comprising: fixing a semiconductor chip on an insulating substrate having a circuit pattern and electrically connecting the circuit pattern; electrically connecting a power supply terminal containing the same type of metal as the circuit pattern to the circuit pattern, the power supply terminal having a flat joint portion joined to the circuit pattern, a through portion penetrating the joint portion in the thickness direction of the joint portion, and an extension portion bending and extending upward from one end of the joint portion; when the power supply terminal and the circuit pattern are connected, a pressure-free metal paste containing particles of the same type of metal as the power supply terminal and the circuit pattern and capable of sintering without pressure is interposed between the joint portion of the power supply terminal and the circuit pattern; and locally heating and sintering the pressure-free metal paste without applying a load to the power supply terminal and the circuit pattern.

14. The method for manufacturing a semiconductor device according to claim 13, wherein when the pressure-free metal paste is sintered, an inert gas is sprayed onto the pressure-free metal paste while a heating head of a heater is brought close to the joint portion of the power supply terminal without contacting the joint portion, thereby locally heating the pressure-free metal paste.

15. The method for manufacturing a semiconductor device according to claim 13, wherein when the pressureless metal paste is sintered, the pressureless metal paste is filled into the through portion.

16. A method for manufacturing a semiconductor device as described in claim 15, wherein when the pressureless metal paste is interposed between the joint and the circuit pattern, the amount of the pressureless metal paste used is adjusted so that the thickness of the joining material produced by sintering the pressureless metal paste at the penetration portion from the joint interface with the circuit pattern to the upper end is equal to or greater than the thickness of the joint and less than 1.5 times the thickness of the joint.

17. The method for manufacturing a semiconductor device according to claim 13, wherein the through portion has a circular or rectangular shape when viewed from above the joint portion.

18. The method for manufacturing a semiconductor device according to claim 13, wherein the shape of the through portion when viewed from above the joint portion has a longitudinal direction and a lateral direction.

19. The method for manufacturing a semiconductor device according to claim 18, wherein the through portion opens to the other end side of the joint portion.

20. The method for manufacturing a semiconductor device according to claim 17 or 18, wherein the center point of the through portion when viewed from above the joint portion substantially coincides with the center point of the joint surface between the joint portion and the circuit pattern.

Images