Semiconductor device and method for manufacturing the same

Abstract

To provide a semiconductor device improved in bonding reliability, and a method of manufacturing the semiconductor device.SOLUTION: A semiconductor device which has a semiconductor element with a Ni-V electrode and a conductor bonded through a Sn-based lead-free solder has a Sn-V compound layer and a (Ni, Cu) 3Sn4 compound layer, adjoining the Sn-V compound, formed respectively in adjacency to a boundary surface between the semiconductor element and the Sn-based lead-free solder. A method of manufacturing the semiconductor device according to the present invention comprises: letting the Ni-V electrode react on the Sn-based lead-free solder to form a Sn-V layer and the (Ni, Cu) 3Sn4 compound layer; and after forming the Sn-V layer, leaving a layer of the Ni-V electrode which does not react on the Sn-based lead-free solder yet.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device. [Background technology]

[0002] The use of lead in electronic control devices installed in automobiles is restricted by the RoHS Directive (Restriction of Hazardous Substances Directive) and the ELV Directive (End-of Life Vehicles Directive). Accordingly, the solder used for joining related to the devices is being shifted to lead-free, and for example, lead-free solder mainly made of the composition Sn-3Ag-0.5Cu, which uses Sn (tin), Ag (silver), and Cu (copper), is being used.

[0003] The electrodes of semiconductor elements in electronic control devices use Ni (nickel) electrodes that are used to bond with solder, and are often formed by sputtering. In recent years, magnetron sputtering, which can form films quickly and efficiently, is becoming the mainstream method. When forming Ni electrodes by magnetron sputtering, pure Ni is highly magnetic and difficult to control, so Ni-V, which has V (vanadium) added, is used to create the electrode film. As a result, there is a demand for inverters to bond Ni-V electrodes with highly reliable lead-free solder.

[0004] As background art to the present invention, the following Patent Document 1 describes a technology in which a Cu film is formed on a Ni-V electrode and joined with a Sn-based lead-free solder, and in the process, the Cu reacts completely with the Sn to precipitate a (Cu,Ni)6Sn5 compound on the Ni-V electrode, thereby suppressing the reaction between the Ni-V electrode and the Sn-based lead-free solder and reducing changes in the joint interface over time due to temperature changes in the usage environment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4656275 Summary of the Invention [Problem to be solved by the invention]

[0006] In the method described in Patent Document 1, since a Sn-V compound layer is not formed, the strength of the bonded interface is reduced, which may impair the reliability of the semiconductor device, and when a large shear stress occurs in such a bond, creep voids may be generated near the bonded interface, which may further impair the reliability of the device. In view of this, the present invention aims to provide a semiconductor device and a method for manufacturing the semiconductor device with improved bond reliability. [Means for solving the problem]

[0007] The semiconductor device of the present invention is a semiconductor device in which a semiconductor element having a Ni-V electrode and a conductor are joined via Sn-based lead-free solder, and a Sn-V compound layer and a (Ni,Cu)3Sn4 compound layer or a Ni3Sn4 compound layer are formed adjacent to the interface between the semiconductor element and the Sn-based lead-free solder. In addition, the manufacturing method of a semiconductor device of the present invention is a manufacturing method of a semiconductor device in which a semiconductor element having a Ni-V electrode and a conductor are joined with Sn-based lead-free solder, and by reacting the Sn-based lead-free solder with the Ni-V electrode, a Sn-V layer and a (Ni,Cu)3Sn4 compound layer or a Ni3Sn4 compound layer are formed adjacent to the interface between the semiconductor element and the Sn-based lead-free solder, and after the Sn-V layer is formed, an unreacted layer that has not reacted with the Sn-based lead-free solder remains in the Ni-V electrode. Effect of the Invention

[0008] According to the present invention, it is possible to provide a semiconductor device and a method for manufacturing the semiconductor device with improved bonding reliability. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic diagram of the liberation of an intermetallic compound at the interface between a semiconductor element and a Sn-based lead-free solder. [Diagram 2] FIG. 2 is a schematic diagram of creep voids at the reaction interface between a semiconductor element and Sn-based lead-free solder. [Diagram 3] FIG. 2 is a schematic diagram of a mechanism for forming a precipitation-type intermetallic compound layer in the prior art. [Figure 4] This is a schematic diagram of the mechanism of intermetallic compound formation due to the reaction between a Ni electrode and a Sn-based lead-free solder. [Diagram 5] 1 is a schematic diagram of the reaction progress between a Ni-V electrode and a Sn-based lead-free solder. [Figure 6] FIG. 1 is a graph showing the relationship between the (Ni,Cu)--Sn compound at the reaction interface and the creep void ratio. [Figure 7] FIG. 13 is a graph showing the relationship between the holding time at 150° C. and the thickness loss of the Ni-V electrode. [Figure 8] 1 is a schematic diagram of a semiconductor device according to an embodiment of the present invention; [Figure 9] This is a modified example of FIG. [Figure 10] 1 is a table showing examples according to different conditions according to an embodiment of the present invention. [Figure 11] 1 is a table of comparative examples according to different conditions, according to an embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following description and drawings are examples for explaining the present invention, and appropriate omissions and simplifications have been made for clarity of explanation. The present invention can be implemented in various other forms. Unless otherwise specified, each component may be singular or plural.

[0011] In order to facilitate understanding of the invention, the position, size, shape, range, etc. of each component shown in the drawings may not represent the actual position, size, shape, range, etc. Therefore, the present invention is not necessarily limited to the position, size, shape, range, etc. disclosed in the drawings.

[0012] (Comparison with the prior art, one embodiment of the present invention) Fig. 1 is a schematic diagram of the liberation of intermetallic compounds at the reaction site between a semiconductor element having a Ni electrode and Sn-3Ag-0.5Cu solder (Sn-based lead-free solder), and Fig. 2 is a schematic diagram of creep voids at the joint between a semiconductor element and Sn-based lead-free solder.

[0013] In order for the semiconductor element 1 and the Sn-3Ag-0.5Cu solder 5 to react well, it is necessary to react the solder 5 with the Ni-based electrode sputtered onto the semiconductor element 1. However, if the reaction between the solder 5 and the Ni-based electrode proceeds too far when the semiconductor element 1 and the Sn-3Ag-0.5Cu solder 5 react, the (Ni,Cu)3Sn4 compound 4 generated by the reaction between the Ni-based electrode formed on the semiconductor element 1 and the solder 5 will peel off from the interface of the reaction area (the layer between the Al-based electrode 2 and the Ti-based electrode 3), as shown in Fig. 1.

[0014] With this type of interface structure, when the semiconductor device is used in an operating environment of 150°C when Ni-V electrode chips are used, there is a high risk of the interface peeling off, making it difficult to maintain the bonded state of the device and compromising reliability.

[0015] 2, when bonding is performed using Ni-V electrode 7, the reaction with Sn-based lead-free solder 9 is faster than when bonding is performed using Ni-based electrode 6, so there is a concern that the risk of bond peeling will increase. Furthermore, in an operating environment of 150°C, when a large shear stress is applied to the bonding part of semiconductor element 1 with Ni-based electrode 6, creep voids 21 will occur near compound 4 at the bonding interface, and the generation of voids 21 will be more likely to progress in an operating environment of 150°C or higher, which may impair the reliability of the device.

[0016] In addition, the voids 21 formed near the interface between the solder 5 and the intermetallic compound 4 tend to be generated easily when the thickness of the intermetallic compound 4 is thin due to the large shear stress applied thereto. In other words, it is found that the generation of such voids 21 and the peeling of the device are determined depending on the shape of the intermetallic compound 4.

[0017] FIG. 3 is a schematic diagram of the mechanism of formation of a precipitation-type intermetallic compound layer in the prior art.

[0018] Conventionally, a Cu film 8 is formed adjacent to a Ni-V electrode 7 (FIG. 3(a)). When the Cu film 8 reacts with a Sn-based lead-free solder 9, a Cu6Sn5-based compound 10 is formed (FIG. 3(b)). The compound 10 precipitates on the Ni-V electrode 7, forming a layer of an intermetallic compound 10 at the interface of the reaction area (FIG. 3(c)). The metallic compound layer 10 in FIG. 3 has a lower bonding strength than the metallic compound layer 11 in FIG. 4 described below, which may impair reliability.

[0019] Figure 4 is a schematic diagram of the mechanism of intermetallic compound formation caused by the reaction between Ni-V electrodes and Sn-based lead-free solder. Note that Figure 4 explains the mechanism of intermetallic compound formation caused by the reaction between Ni-V electrodes and Sn-based lead-free solder that does not contain Cu.

[0020] As shown in Fig. 4, a reaction layer of Ni3Sn4-based compound 11 (Fig. 4(b)) and a layer of Sn-V compound 12 (Fig. 4(c)) are formed by the reaction between Ni-V electrode 7 and Sn-based lead-free solder 9. Fig. 4 differs from Fig. 3 in that an intermetallic compound layer is formed while forming Ni3Sn4-based compound 11 and Sn-V compound layer 12. This formation method is adopted in the present invention.

[0021] FIG. 5 is a schematic diagram of the reaction progress between a Ni-V electrode and a Sn-based lead-free solder.

[0022] As shown in the reaction progression of (a) to (d) in FIG. 5, a semiconductor element 1 having a Ni-V electrode 7 and an Sn-based lead-free solder 9 are reacted with each other with electrodes 2 and 3 in between to form an Sn-V compound layer 12 at the interface of the reaction portion, and a layer of a (Ni,Cu)3Sn4 compound 13 is formed adjacent to the Sn-V compound 12, thereby obtaining good bonding strength of the device. This ensures the reliability of the device in a usage environment of 150°C. If the Sn-based lead-free solder is an Sn-based lead-free solder that does not contain Cu, the layer of the (Ni,Cu)3Sn4 compound 13 will be a layer of a Ni3Sn4-based compound.

[0023] However, as shown in FIG. 5(e), if the reaction between the semiconductor element 1 and the Sn-based lead-free solder 9 proceeds too far, the layer of the (Ni,Cu)3Sn4 compound 13 peels off from the Sn-V compound 12 at the interface of the reaction portion, and in an operating environment of 150°C, peeling may occur at the interface between the Sn-V compound 12 and the Sn-based lead-free solder 9, or cracks due to thermal shock may progress straight along the interface. In this state, the life of the device is shortened and the reliability of the device is impaired. Therefore, the present invention is characterized by maintaining the stage of FIG. 5(d).

[0024] In other words, by leaving the Ni-V layer 7 unreacted with the Sn-based lead-free solder 9 as shown in (c) of Figure 5, it becomes easier to maintain the bond with the adjacent Ti layer 3, and a device with higher bond reliability can be obtained in an operating environment of 150°C.

[0025] In addition, the layer of the (Ni,Cu)3Sn4 compound 13 can be more reliable by being adjacent to the entire area of ​​the layer of the Sn-V compound 12 than by being adjacent to only a part of it.

[0026] FIG. 6 is a diagram showing the relationship between the (Ni,Cu)--Sn compound at the reaction interface and the creep void ratio.

[0027] The voids 21 that occur near the reaction interface depend on the thickness of the layer of the (Ni,Cu)3Sn4 compound 13 that is formed at the reaction interface. Figure 6 shows the results of a creep test performed at 150°C on a sample that was joined to a Ni-plated Cu plate using Sn-3Ag-0.5Cu solder 5 with an area of ​​5 mm x 5 mm x 1 mm and a 600 g weight attached.

[0028] As shown in the test results in Figure 6, when the average thickness of the Ni3Sn4 compound layer formed at the joint interface was thinner than 2 μm, many voids 21 were generated, but when the average thickness was 2 μm or more, the voids 21 were suppressed. From this, it was found that by making the thickness of the (Ni,Cu)3Sn4 compound 13 layer 2 μm or more, the reliability of the device can be ensured in an operating environment of 150 degrees.

[0029] FIG. 7 is a graph showing the relationship between the retention time of the joint in a 150° C. environment and the thickness loss of the Ni-V electrode.

[0030] The graph in Figure 7 shows the thickness at which the Ni-V electrode disappears when a 150°C high temperature retention test is carried out for up to 1000 hours for a sample that uses Sn-3Ag-0.5Cu solder on Ni-plated Cu leads of a semiconductor element with Ni-V electrodes. The horizontal axis of the graph is the 0.5th power of time, and the standard of 1000 hours corresponds to the 10-year warranty period for an automobile.

[0031] Test results showed that 300 nm of the Ni-V electrode was lost after 1000 hours in a 150°C operating environment. In other words, to obtain higher reliability, it is considered desirable to have a structure that leaves at least 300 nm of unreacted Ni-V electrode at the time of reaction. In order to leave 300 nm of unreacted Ni-V electrode, it is desirable to use a semiconductor element with a Ni-V electrode that is 700 nm or thicker before reaction.

[0032] Fig. 8 is a schematic diagram of a semiconductor device according to one embodiment of the present invention, and Fig. 9 is a modified example of Fig. 8. The table in Fig. 10 is a table of examples according to different conditions according to one embodiment of the present invention, and the table in Fig. 11 is a table of comparative examples according to different conditions according to one embodiment of the present invention.

[0033] Example 1-4 in the table of Fig. 10 to which the present invention is applied will be described with reference to Fig. 8. Examples 1-4 in the table of Fig. 10 are applied to the present invention under the conditions that the composition of the Sn-based lead-free solder 9 is changed, there is no liberation from the interface of the (Ni,Cu)3Sn4 compound 13 layer, there is a Sn-V compound layer, and there is no unreacted Ni-V layer. When the Sn-based lead-free solder 9 does not contain Cu, the (Ni,Cu)3Sn4 compound becomes a Ni3Sn4-based compound.

[0034] Sn-based lead-free solder 9 is supplied to the solder mounting positions of collector-side lead frames 31, 32 made of Cu with roughened Ni plating (enlarged view A). A semiconductor element 1 having Ni-V electrodes 7 with a thickness of 800 nm on both sides is mounted thereon, and the semiconductor element 1 and the lead frames 31, 32 are joined. Furthermore, Sn-based lead-free solder 9 is supplied onto the electrodes on the upper surfaces of the joined semiconductor element 1.

[0035] In this way, the unreacted Ni-V layer 7 remains with an average thickness of 300 nm or more at the junction of the semiconductor element 1, and a layer of the (Ni,Cu)3Sn4 compound 13 with an average thickness of 2 μm or more is formed adjacent to the Sn-V layer 12 formed by the reaction. Thereafter, resin sealing 33 is performed by transfer molding to produce a semiconductor device.

[0036] The semiconductor device thus fabricated was subjected to a 150°C high temperature retention test for 1000 hours, a power cycle test for 50,000 cycles under the conditions of Tjmax 150°C, and ΔTj 100°C (Fig. 10). In this case, if the reduction in the bonding area of ​​the device after the test was within 10%, it was judged as ○, and if the bonding area of ​​the device deteriorated by more than 10%, it was judged as ×. This deterioration of the bonding was confirmed by observing ultrasonic images and cross sections.

[0037] As a result, in all of Examples 1 to 4, no deterioration such as peeling or the generation of creep voids or the like was confirmed in the reaction portion after the reliability test, and it was confirmed that the bonding reliability was sufficient.

[0038] Next, Examples 5-8 in the table of Fig. 10 to which the present invention is applied will be described with reference to Fig. 9. As with Examples 1-4, Examples 5-8 in the table of Fig. 10 are applied to the present invention under the conditions that the composition of the Sn-based lead-free solder 9 is changed, there is no liberation from the interface of the (Ni,Cu)3Sn4 compound 13 layer, there is a Sn-V compound layer, and there is no unreacted Ni-V layer. When the Sn-based lead-free solder 9 does not contain Cu, the (Ni,Cu)3Sn4 compound becomes a Ni3Sn4-based compound.

[0039] A sheet of Sn-based lead-free solder 44 is placed on heat dissipation base 45, a ceramic substrate 43 is laminated on top of that, a sheet of Sn-based lead-free solder 9 is placed on substrate 43, and a semiconductor element 1 is placed thereon and heated to perform bonding. After bonding, aluminum wire 42 and terminal 41 are bonded, and then case 47 is attached and sealed with gel 46 to produce a semiconductor device.

[0040] The semiconductor device thus fabricated was subjected to a 150°C high temperature retention test for 1000 hours, a power cycle test for 50,000 cycles under the conditions of Tjmax 150°C, and ΔTj 100°C. In this test, if the reduction in the bonding area of ​​the device after the test was within 10%, it was judged as ○, and if the bonding area of ​​the device deteriorated by more than 10%, it was judged as × (Figure 10). The deterioration of the bonding was confirmed by observing ultrasonic images and cross sections.

[0041] As a result, in all of Examples 5 to 8, no deterioration such as peeling was observed in the reaction section after the reliability test. Although slight creep voids were observed, it was confirmed that the bonding reliability of the device was sufficient.

[0042] Next, in Comparative Example 1-2 in the table of FIG. 11, the composition of the Sn-based lead-free solder 9 was unified to Sn-3Ag-0.5Cu, and semiconductor devices were fabricated and reliability tests were performed under the conditions of separation from the interface of the (Ni,Cu)3Sn4 compound 13 layer, the presence of a Sn-V compound layer, and the absence of an unreacted Ni-V layer, and the reverse conditions. Comparative Example 1 in FIG. 11 peeled off at the joint of the device in both the high temperature retention test and the power cycle test, resulting in an ×. Comparative Example 2 in FIG. 11 was ○ in the high temperature retention test, but peeled off at the interface of the reaction part in the power cycle test, resulting in an ×. This shows that in the embodiment of FIG. 8, reliability is impaired unless both the Sn-V compound 12 and the unreacted Ni-V layer 7 remain.

[0043] In Comparative Example 3-4 in the table of FIG. 11, a semiconductor device was fabricated in the same manner as in Examples 5-8 in FIG. 10, and a reliability test was performed. In Comparative Example 3 in FIG. 11, peeling occurred at the joint of the device in both the high temperature retention test and the power cycle test, resulting in an X. In Comparative Example 4 in FIG. 11, peeling occurred at the reaction interface in the power cycle test, resulting in an X. This shows that in the embodiment of FIG. 9, reliability is impaired unless both the Sn-V compound 12 and the unreacted Ni-V layer 7 remain.

[0044] As described above, the experimental results shown in Figures 10 and 11 indicate that when a semiconductor element and a conductor are joined with Sn-based lead-free solder, both the Sn-V compound 12 and the unreacted Ni-V layer 7 remain, and therefore the reliability of the device can be ensured both in maintaining the joint in a high-temperature operating environment of 150°C and during power cycles.

[0045] In the present invention, an example has been described in which a layer of a (Ni,Cu)3Sn4 compound 13 is formed by using a Sn-based lead-free solder containing Cu. However, if a Sn-based lead-free solder not containing Cu is used, a layer of a Ni3Sn4 compound is formed, and the same effect can be achieved.

[0046] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0047] (1) A semiconductor device in which a semiconductor element 1 having a Ni-V electrode 7 and conductors 31, 32 are bonded via an Sn-based lead-free solder 9, and a Sn-V compound layer 13 and a (Ni,Cu)3Sn4 compound layer 4 or a Ni3Sn4 compound layer are formed adjacent to the interface between the semiconductor element 1 and the Sn-based lead-free solder 9. In this way, a semiconductor device with improved bonding reliability can be provided.

[0048] (2) In the semiconductor device, the Sn-V compound layer 13 is a layer formed by a reaction between a part of the Ni-V electrode 7 and the Sn-based lead-free solder 9. This improves the bonding reliability of the device.

[0049] (3) In the semiconductor device, the (Ni,Cu)3Sn4 compound layer 4 or the Ni3Sn4 compound layer is disposed adjacent to the interface over the entire area of ​​the Sn-V compound layer 13. This can improve the bonding strength of the device.

[0050] (4) The average thickness of the (Ni,Cu)3Sn4 compound layer 4 or the Ni3Sn4 compound layer of the semiconductor device is 2 μm or more. By doing so, a semiconductor device with improved bonding reliability can be provided.

[0051] (5) The average thickness of the unreacted layer of the Ni-V electrode 7 of the semiconductor device that has not reacted with the Sn-based lead-free solder 9 is 300 nm or more. By doing so, it is possible to provide a semiconductor device with improved joint reliability equivalent to a 10-year warranty for an automobile.

[0052] (6) In the semiconductor device, when a semiconductor element 1 having a Ni-V electrode 7 and conductors 31, 32 are joined with Sn-based lead-free solder 9, a Sn-V layer 12 and a (Ni,Cu)3Sn4 compound layer 4 or a Ni3Sn4 compound layer are formed adjacent to the interface between the semiconductor element 1 and the Sn-based lead-free solder 9 by reacting the Sn-based lead-free solder 9 with the Ni-V electrode 7, and after the Sn-V layer 12 is formed, an unreacted layer that has not reacted with the Sn-based lead-free solder 9 remains in the Ni-V electrode 7. In this way, the semiconductor device of the present invention can be realized.

[0053] The present invention is not limited to the above-described embodiment, and various modifications and other configurations can be combined without departing from the spirit of the present invention. Furthermore, the present invention is not limited to those having all of the configurations described in the above-described embodiment, and includes those in which some of the configurations are omitted. [Explanation of symbols]

[0054] 1. Semiconductor element 2 Al-based electrode 3 Ti-based electrode, Ti layer 4 (Ni,Cu)3Sn4 compound 5 Sn-3Ag-0.5Cu solder 6 Ni-based electrode 7 Ni-V electrode 8. Cu film 9 Sn-based lead-free solder 10 Cu6Sn5-based compounds 11 Ni3Sn4 based compounds 12 Sn-V compound 13 (Ni,Cu)3Sn4 compound 21 Creep Void 31 Emitter lead 32 Collector side lead 33 Resin 41 Terminal 42 Aluminum Wire 43 Ceramic Substrate 44 Sn-based lead-free solder 45 Heat dissipation base 46 Gel 47 cases

Claims

1. A semiconductor device in which a semiconductor element having a Ni-V electrode and a conductor are joined via a Sn-based lead-free solder, A Sn-V compound layer is formed adjacent to the interface between the semiconductor element and the Sn-based lead-free solder, and a (Ni, Cu)3Sn4 compound layer or a Ni3Sn4 compound layer is formed adjacent to the Sn-V compound. Semiconductor device.

2. 2. The semiconductor device according to claim 1, The Sn--V compound layer is a layer formed by a reaction between a part of the Ni--V electrode and the Sn-based lead-free solder. Semiconductor device.

3. 3. The semiconductor device according to claim 1, The (Ni, Cu) 3 Sn 4 compound layer or the Ni 3 Sn 4 compound layer is disposed adjacent to the interface over the entire area of ​​the Sn—V compound layer. Semiconductor device.

4. 3. The semiconductor device according to claim 1, The (Ni, Cu)3Sn4 compound layer or the Ni3Sn4 compound layer has an average thickness of 2 μm or more. Semiconductor device.

5. 3. The semiconductor device according to claim 2, The average thickness of the unreacted layer of the Ni-V electrode that has not reacted with the Sn-based lead-free solder is 300 nm or more. Semiconductor device.

6. A method for manufacturing a semiconductor device in which a semiconductor element having a Ni-V electrode and a conductor are joined with a Sn-based lead-free solder, comprising: By reacting the Sn-based lead-free solder with the Ni-V electrode, a Sn-V layer and a (Ni, Cu)3Sn4 compound layer or a Ni3Sn4 compound layer are formed adjacent to the interface between the semiconductor element and the Sn-based lead-free solder, After the Sn--V layer is formed, an unreacted layer that has not reacted with the Sn-based lead-free solder is left on the Ni--V electrode. A method for manufacturing a semiconductor device.

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