Semiconductor device

Abstract

Provided is a semiconductor device that achieves improved reliability when a semiconductor element is operated at a high temperature.　Provided is a semiconductor device (1), in which the maximum value of the operating temperature of a semiconductor element (50) is 150°C or higher. The semiconductor device comprises: a conductor pattern (20); a semiconductor element (50) that is disposed on the conductor pattern (20) via a bonding member (40); and a sealing member (30) that contacts the conductor pattern (20), the bonding member (40), and the semiconductor element (50) and thereby seals these components, and that has added thereto an ion scavenger (32) for capturing ions of a metal (metal ions (42)), the metal being contained in the bonding member (40).

Description

Semiconductor Devices

[0001] The present invention relates to a semiconductor device.

[0002] In reliability tests for semiconductor devices, it is required that the device does not fail under specified conditions. For example, Patent Document 1 describes a semiconductor package that improves reliability after long-term storage by keeping the chlorine and sulfur contents in the sealing material below a predetermined value.

[0003] Japanese Patent Application Laid-Open No. 2021-019031

[0004] The semiconductor package of Patent Document 1 is described as having a reduced defect rate when tested in a high-temperature environment without being operated. However, when the semiconductor package is operated, the influence of current and voltage inside the semiconductor device causes failures in a different manner than when the semiconductor device is not operated, and different measures are required compared to when the semiconductor device is not operated. The inventors have confirmed that when the temperature at which the semiconductor element is operated is increased, metal contained in the bonding material, such as solder, migrates into the sealing material, causing failures. The present invention has been made to solve this problem, and an object of the present invention is to provide a semiconductor device that improves the reliability of the semiconductor element when it is operated at high temperatures.

[0005] In order to solve this problem, the semiconductor device of the present invention is a semiconductor device in which the maximum operating temperature of a semiconductor element is 150°C or higher, and includes a conductor pattern, the semiconductor element disposed on the conductor pattern via a bonding member, and a sealing member that contacts the conductor pattern, the bonding member, and the semiconductor element to seal them, and to which an ion trapping agent that captures metal ions contained in the bonding member has been added.

[0006] According to the present invention, it is possible to provide a semiconductor device that improves the reliability when the semiconductor element is operated at high temperatures.

[0007] FIG. 1 is a cross-sectional view illustrating an enlarged outline of a portion of a semiconductor device according to an embodiment; FIG. 2 is a cross-sectional view illustrating an outline of a state in which metal contained in a bonding member is ionized and metal ions move into a sealing member in a semiconductor device according to an embodiment; FIG. 3 is a cross-sectional view illustrating an outline of a state in which metal ions have further moved in a semiconductor device according to an embodiment; FIG. 4 is a cross-sectional view illustrating an outline of a state in which metal ions are captured by an ion capturing agent in a semiconductor device according to an embodiment; and FIG. 5 is a cross-sectional view illustrating an outline of a state in which a short circuit occurs due to metal ions in a conventional semiconductor device.

[0008] The present invention will be described with reference to the drawings. Note that the present invention is not limited to the following embodiments and examples. The drawings show components necessary for the explanation, and the size and shape of each component may be exaggerated.

[0009] [Semiconductor Device] A semiconductor device 1 according to an embodiment will be described with reference to FIG. 1 . The semiconductor device 1 is a device in which a semiconductor element is encapsulated together with a substrate or the like, and includes various forms, such as a unit in which one or more semiconductor elements are arranged on a single substrate, or a module in which multiple units are integrated into one. However, the various forms of semiconductor device 1 share a common configuration in the vicinity of the semiconductor element. As illustrated in FIG. 1 , the semiconductor device 1 is a semiconductor device in which the maximum operating temperature of the semiconductor element 50 is 150° C. or higher, and includes a conductor pattern 20, a semiconductor element 50 disposed on the conductor pattern 20 via a bonding member 40, and a sealing member 30 in contact with and encapsulating the conductor pattern 20, the bonding member 40, and the semiconductor element 50, and to which an ion trapping agent 32 is added that captures metal ions contained in the bonding member 40. Each component of the semiconductor device 1 will now be described.

[0010] (Conductor Pattern) The conductor pattern 20 is a conductive member to which electrodes of the semiconductor element 50 are bonded. Here, the conductor pattern 20 is part of the wiring that connects the semiconductor element 50 to the outside of the semiconductor device 1. The conductor pattern 20 can be formed to a predetermined shape and thickness, and has an area to which the electrodes of the semiconductor element 50 are bonded. The conductor pattern 20 is formed on the insulating substrate 10. The insulating substrate 10 is an insulating plate-shaped member. The material of the conductor pattern 20 can be a metal such as gold, silver, copper, or an alloy thereof, and is copper in this example. The material of the insulating substrate 10 is, for example, a ceramic such as silicon nitride or a highly thermally conductive resin.

[0011] (Semiconductor Element) The semiconductor element 50 is a semiconductor chip on which transistors, diodes, etc. are formed. The semiconductor element 50 includes an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), a diode, etc. The semiconductor element 50 may be a single element such as an IGBT, or may include multiple IGBTs, for example, an IGBT and a diode. The semiconductor in the semiconductor element 50, i.e., the semiconductor that is the material of the wafer or the like on which the semiconductor element 50 is formed, may be silicon (Si) or silicon carbide (SiC). Here, the semiconductor in the semiconductor element 50 is Si and includes an IGBT. The semiconductor in the semiconductor element 50 may be SiC and may include a MOSFET.

[0012] The semiconductor element 50 is disposed on the conductor pattern 20 via a bonding member 40. The semiconductor element 50 has electrodes on the surface facing the conductor pattern 20 and the opposite surface. Note that, for convenience of illustration, the surface facing the conductor pattern 20 may be referred to as the lower surface and the opposite surface as the upper surface. The electrode 51 on the lower surface is bonded to the conductor pattern 20 via the bonding member 40. Here, there is only one electrode 51 on the lower surface, and it is covered by the bonding member 40. A bonding wire or the like is connected to the electrode 52 on the upper surface. The electrode 52 on the upper surface is in contact with the sealing member 30. That is, the semiconductor element 50 has a region where the material of the electrode 52 is the uppermost surface, and the sealing member 30 is in contact with the electrode 52 in that region. Here, the electrode 52 on the upper surface is provided near the periphery of the semiconductor element 50. The semiconductor element 50 may have an electrode on its upper surface in addition to the electrode 52. Note that bonding wires, lead frames, and the like are not shown.

[0013] In the semiconductor device 1, minimum and maximum operating temperatures of the semiconductor element 50 are specified. The operating temperature refers to the temperature range within which the semiconductor element 50 maintains its expected functionality and operates normally. While semiconductor elements 50 are generally sensitive to heat, the maximum operating temperature of the semiconductor element 50 is 150°C or higher, for example, 150°C or 175°C. If the maximum operating temperature is 150°C, the semiconductor element 50 can operate normally at temperatures lower than 150°C. The maximum operating temperature may be between 150°C and 175°C, or may be 175°C or higher. The operating temperature refers to the temperature of the semiconductor element 50 itself, for example, the temperature of the pn junction surface. The semiconductor device 1 is used so that the operating temperature of the semiconductor element 50 is within the specified range. The operating temperature of the semiconductor element 50 during operation can be calculated using power loss and thermal resistance. The maximum operating temperature can be increased by using materials that can withstand higher temperatures.

[0014] (Bonding Member) The bonding member 40 is a member that bonds and electrically connects the semiconductor element 50 and the conductor pattern 20. The bonding member 40 can be a solder or conductive paste containing a metal such as gold, silver, or copper, and in this example, is a solder containing tin (Sn). When the bonding member 40 is solder, a solder whose solidus temperature is higher than the maximum operating temperature of the semiconductor element 50 is used. The bonding member 40 is bonded to the conductor pattern 20 on the side thereof, and is bonded to an electrode 51 on the underside of the semiconductor element 50 on the opposite side thereof. The bonding member 40 is in contact with the sealing member 30 between the conductor pattern 20 and the semiconductor element 50.

[0015] (Sealing Member) The sealing member 30 is a member that seals the semiconductor element 50 and the like. The sealing member 30 comes into contact with the conductor patterns 20, the bonding members 40, and the semiconductor element 50 to seal them. The sealing member 30 also comes into contact with the electrodes 52 of the semiconductor element 50. The sealing member 30 can also seal other members such as bonding wires. Here, the sealing member 30 is a potting resin. The potting resin can come into contact with the conductor patterns 20, the bonding members 40, and the semiconductor element 50 to seal them. The sealing member 30 may also be a molding resin. In the case of a molding resin, the sealing member 30 also comes into contact with the conductor patterns 20, the bonding members 40, and the semiconductor element 50 to seal them.

[0016] Potting resin and molding resin are formed using different methods, and differ in the types and ratios of components contained therein. Here, a semiconductor element 50 or the like sealed with potting resin or molding resin will be described as a sealed body. Note that the semiconductor device 1 may have multiple sealed bodies. Potting resin is formed by the potting method, and molding resin is formed by the molding method. In the potting method, a case member that will become part of the sealed body after hardening serves as a frame, and unhardened resin is injected and hardened. On the other hand, in the molding method, the resin is molded in a mold and then removed from the mold after molding. Therefore, the appearance of potting resin and molding resin differs in terms of whether or not the sealed body has a case member. Note that in the case of molding resin, the outer surface of the sealed body is formed by the sealing member 30.

[0017] The sealing member 30 can be a resin composition for semiconductor sealing, such as an epoxy resin composition. The sealing member 30 has a glass transition temperature equal to or higher than the maximum operating temperature of the semiconductor element 50. For example, if the maximum operating temperature is 150°C, the glass transition temperature of the sealing member 30 is desirably 150°C or higher, and if the maximum operating temperature is 175°C, the glass transition temperature of the sealing member 30 is desirably 175°C or higher. An ion trapping agent 32 is added to the sealing member 30.

[0018] (Ion trapping agent) The ion trapping agent 32 is a substance added to the sealing member 30 and traps metal ions 42, which are ions of the metal contained in the bonding member 40. Generally, three types of ion trapping agents are known: a cation trapping type that traps cations, an anion trapping type that traps anions, and a dual ion trapping type that traps both cations and anions. As an example, the metal ions contained in the bonding member 40 are tin ions, which are cations. The ion trapping agent 32 can trap the metal ions 42 by being either a cation trapping type or a dual ion trapping type. The ion trapping agent 32 may contain two types: a cation trapping type and a dual ion trapping type.

[0019] The ion trapping agent 32 may be a commercially available ion trapping agent. Examples of commercially available ion trapping agents include IXEPLAS (registered trademark) from Toagosei Co., Ltd., and the ADK STAB (registered trademark) CDA series and ZS series from ADEKA Corporation. The amount of the ion trapping agent 32, expressed as a mass ratio relative to the sealing member 30, may be 10 ppm or more and 10% or less, and preferably 100 ppm or more and 1% or less. The lower limit of this ratio can be adjusted depending on the amount of metal ions 42 in the sealing member 30. On the other hand, by reducing the upper limit of this ratio, the effect on the properties of the sealing member 30 as a resin composition for semiconductor encapsulation can be suppressed.

[0020] The semiconductor device 1 having the above-described configuration includes a sealing member to which an ion trapping agent that traps metal ions contained in the bonding member is added. This makes it possible to suppress the migration of metal into the sealing member, which can cause failures, even when the semiconductor element is operated at high temperatures, thereby improving reliability.

[0021] Conventionally, reliability tests for semiconductor devices have been conducted by operating the semiconductor element under conditions that maximize its operating temperature and maintaining this condition for a long period of time, such as 1,000 hours. Such tests were also conducted on a conventional semiconductor device 100 having a semiconductor element 50, as shown in FIG. 3 . However, when the maximum operating temperature was set to 175°C, a higher value than conventional tests, a previously unseen short-circuit failure occurred. In the conventional semiconductor device 100, the conductor pattern 20 is made of copper, the bonding member 40 is made of solder containing tin, and the sealing member 300 is in contact with the electrodes 52 of the semiconductor element 50. The semiconductor element 50 is made of silicon and includes an IGBT. However, the sealing member 300 does not contain an ion capture agent 32.

[0022] When the cause of this short-circuit failure was investigated, it was confirmed that metal ions 42 were present in the sealing member 300 from the edge of the top surface of the semiconductor element 50 to the conductive pattern 20, as illustrated in FIG. 3 . The metal ions 42 were tin ions, ions of a metal contained in the bonding member 40. An electrode 52 was located on the periphery of the top surface of the semiconductor element 50, and the sealing member 300 was in contact with the electrode 52 of the semiconductor element 50. Therefore, it is believed that tin ions distributed in the sealing member 300 formed a current path P1, causing the short-circuit failure. Therefore, when an ion trapping agent 32 that traps tin ions was added to the sealing member of the semiconductor device 1, no short-circuit failure occurred. This result will be explained with reference to FIGS. 2A to 2C . In this semiconductor device 1, the conductive pattern 20 is made of copper, the bonding member 40 is a solder containing tin, and the sealing member 30 is in contact with the electrode 52 of the semiconductor element 50. The semiconductor element 50 uses silicon as a semiconductor and includes an IGBT. The maximum operating temperature of the semiconductor element 50 is set to 175° C., and the sealing member 30 is doped with an ion trapping agent 32 that traps tin ions.

[0023] As illustrated in FIG. 2A , when a reliability test operating at high temperatures is initiated, metal contained in the bonding member 40 near the conductive pattern 20 ionizes, causing metal ions 42 to migrate into the sealing member 30. In this case, the metal ions 42 are tin ions. This is thought to be due in part to the fact that residues of etching solutions, cleaning agents, and the like used in the formation process of the conductive pattern 20 may adhere to the surface of the conductive pattern 20, and the components of such residues promote the ionization of the metal contained in the bonding member 40, which has a higher ionization tendency than the metal of the conductive pattern 20. The generation of tin ions is explained by the fact that tin has a higher ionization tendency than copper. As the reliability test continues, the migration of the metal ions 42 continues, as illustrated in FIG. 2B , and the metal ions 42 in the sealing member 30 move in the direction of the electric field. The electric field is generated by the application of current and voltage under the test conditions.

[0024] However, as illustrated in FIG. 2C , the ion trapping agent 32 of the sealing member 30 traps the metal ions 42, so no current path is formed. By adding an ion trapping agent that traps tin ions to the sealing member 30, the semiconductor device 1 can suppress the occurrence of short-circuit failures and improve reliability. The maximum operating temperature may exceed 175°C. The semiconductor device 1 can suppress the occurrence of short-circuit failures and improve reliability when the maximum operating temperature of the semiconductor element 50 is 175°C or higher.

[0025] This short-circuit failure tends to occur more easily when the operating temperature is high, the applied current and voltage are large, and the test time is long. Therefore, it is believed that the conventional semiconductor device 100 is more susceptible to short-circuit failures because it includes an IGBT that can apply a large current and voltage and has a higher maximum operating temperature of 175°C than conventional devices. Even in the conventional semiconductor device 100, where the maximum operating temperature is 150°C, similar short-circuit failures are likely to occur due to changes in conditions, such as an increase in the applied current and voltage or a longer test time. The semiconductor device 1 can also address these conditions, and the ion trapping agent added to the sealing member traps metal ions, suppressing the occurrence of short-circuit failures and improving reliability.

[0026] When the semiconductor in the semiconductor element 50 is silicon carbide, it is expected that a reliability test will be performed at a higher temperature and under conditions of a larger applied current and voltage, making it more likely that a short circuit failure will occur. Even when the semiconductor in the semiconductor element 50 is silicon carbide, the ion trapping agent added to the sealing member traps metal ions, suppressing the occurrence of a short circuit failure and improving reliability.

[0027] Regarding the ionization of the metal contained in the joining member 40, when attention is paid to the ionization tendency, it is predicted that a similar phenomenon will occur not only when the metal of the conductor pattern 20 is copper and the metal of the joining member 40 is tin, but also when the ionization tendency of the metal of the joining member 40 is greater than that of the metal of the conductor pattern 20.

[0028] In order to confirm the effects of the present invention, IGBT modules of an example and a comparative example were manufactured and subjected to reliability tests. The example had the structure illustrated in FIG. 1, with a sealing member in contact with the electrodes of the IGBT. The semiconductor element was an IGBT, the bonding member was tin-copper-antimony solder, the conductor pattern material was copper, and the sealing member was a potting resin with an ion trapping agent added. The ion trapping agent was of a dual ion trapping type and was capable of trapping tin ions. The comparative example differed from the example in that no ion trapping agent was added to the sealing member.

[0029] As a reliability test, a collector-emitter DC blocking test was performed under the same conditions for the example and the comparative example. The collector-emitter DC blocking test is a test in which a predetermined voltage is applied to the terminals of the IGBT and the IGBT is continuously operated under conditions where the IGBT reaches its maximum operating temperature. The maximum operating temperature of the IGBT was 175°C. As a result of the test, a short circuit failure occurred in the comparative example after 1000 hours. On the other hand, no failure occurred in the example even after 1000 hours. In other words, the example of the present invention solves the problem of short circuit failure in the blocking test by adding an ion scavenger to the sealing resin, and can improve the reliability of semiconductor devices when operated at high temperatures.

[0030] REFERENCE SIGNS LIST 1 semiconductor device 10 insulating substrate 20 conductive pattern 30 sealing member 32 ion trapping agent 40 bonding member 42 metal ion 50 semiconductor element 51 electrode (lower surface) 52 electrode (upper surface)

Claims

1. A semiconductor device in which the maximum operating temperature of a semiconductor element is 150°C or higher, comprising: a conductor pattern; the semiconductor element disposed on the conductor pattern via a bonding material; and a sealing material that contacts and seals the conductor pattern, the bonding material, and the semiconductor element, and to which an ion capturing agent that captures metal ions contained in the bonding material has been added.

2. The semiconductor device according to claim 1, wherein the sealing member contacts the electrodes of the semiconductor element.

3. The semiconductor device according to claim 1, wherein said metal ions are tin ions.

4. The semiconductor device according to claim 1, wherein the joining material is a solder containing tin.

5. The semiconductor device according to claim 1, wherein the semiconductor element comprises an insulated gate bipolar transistor.

6. The semiconductor device according to claim 1, wherein the semiconductor in said semiconductor element is silicon carbide.

7. The semiconductor device according to claim 1, wherein the maximum operating temperature is 175° C. or higher.

8. The semiconductor device according to claim 1, wherein the ion trapping agent is a cation trapping type that traps cations.

9. The semiconductor device according to claim 1, wherein the ion trapping agent is a dual ion trapping agent that traps both positive and negative ions.

10. A semiconductor device according to any one of claims 1 to 9, wherein the sealing member is a potting resin.

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