Semiconductor device, semiconductor pressure sensor, pressure sensor device, and exhaust gas recirculation system

Abstract

This semiconductor device comprises: a semiconductor substrate (20) that has a semiconductor element part (10); a wiring part (12) that has a metal wiring layer which is provided in a portion on one side of the semiconductor element part (10); and a protective layer (11) that is formed of a silicon compound and is provided in the semiconductor element part (10) and the wiring part (12). A single portion or a plurality of portions in the wiring part (12) are exposed through an electrode opening (4) that penetrates the protective layer (11). An exposed wiring part (12a), which is a portion of the wiring part (12) exposed in the electrode opening (4), and a portion of the protective layer (11) adjacent to the exposed wiring part (12a) are covered with a metal sputtering film (13), the metal sputtering film (13) is covered with a first plating layer (14) that is formed of nickel, the first plating layer (14) is covered with a second plating layer (15) that is formed of a noble metal material, and the second plating layer (15) is covered with a third plating layer (16) that is formed of a noble metal material which is different from the second plating layer (15).

Description

Semiconductor device, semiconductor pressure sensor, pressure sensor apparatus, and exhaust gas recirculation system

[0001] The present disclosure relates to a semiconductor sensor, or a semiconductor device such as an integrated circuit, a semiconductor pressure sensor, a pressure sensor apparatus, and an exhaust gas recirculation system.

[0002] Various technological innovations have been advanced for semiconductor devices in response to demands for higher performance and smaller size. In the field of semiconductor devices, there also exist areas where new technologies such as high heat resistance and high corrosion resistance are required. In the field of semiconductor device packaging, conductive connection technologies focusing on the structure of electrode portions of semiconductor sensors using semiconductor materials for substrates or integrated circuits (ICs: Integrated Circuits) and the materials of the electrode portions have attracted attention.

[0003] A semiconductor sensor or IC using a semiconductor substrate generally has a wiring portion including a metal wiring layer. As the material of the metal wiring layer, for example, aluminum, aluminum-silicon, aluminum-copper, or aluminum-silicon-copper is used. The metal wiring layer is electrically connected to the outside via an electrode opening by a bonding wire or the like. Therefore, the metal wiring layer has a structure in which a part thereof is exposed to the outside. In order for the semiconductor device to stably continue normal operation, the corrosion resistance of the exposed portion of the metal wiring layer is important.

[0004] If the environment in which the semiconductor device is normally used is in the atmosphere at normal temperature, problems such as connection failures do not occur in the semiconductor device even with the connection technology as described above. Therefore, the semiconductor device can maintain high reliability. However, when a semiconductor device is exposed to an environment where high temperature, high humidity, corrosive gas and the like are combined in a complex manner, the metal wiring layer using aluminum is preferentially deteriorated or corroded from the portion exposed to the outside. Therefore, the semiconductor device may lead to a serious failure such as a significant deterioration of functions or disconnection due to corrosion of the wiring portion.

[0005] Pressure sensor devices used for measuring pressure in automobiles are equipped with semiconductor pressure sensors containing semiconductor devices. Pressure sensor devices are mounted in various locations, such as on the intake or exhaust side. In particular, on the exhaust side, the semiconductor device is affected by exhaust gases containing corrosive substances. Therefore, the environmental resistance required of the semiconductor device differs depending on the mounting location. It is also necessary to consider the possibility that substances contained in materials used around the mounting location may adversely affect the semiconductor device. For this reason, the conductive connection parts of semiconductor devices used in automotive pressure sensor devices require even higher reliability, taking into account the mounting environment.

[0006] In conventional semiconductor devices, a certain level of protection for conductive connections was expected by covering the surface of the chip, including the wiring, with a protective gel. However, in harsh environments where corrosive gases are present, corrosive substances can penetrate the wiring due to the deterioration of the gel or the occurrence of cracks, causing corrosion and other problems in the metal wiring layer. Therefore, in harsh mounting environments, it has been difficult for conventional semiconductor devices using aluminum for the electrodes to maintain high reliability.

[0007] For semiconductor devices to continuously exhibit high performance, their electrode structures must be highly corrosion-resistant. To improve corrosion resistance without significantly altering the existing electrode structure or manufacturing process of semiconductor devices, one possible solution is to add a highly protective material to the aluminum-based metal wiring layer. One known method for adding protective materials is to form a highly environmentally resistant metal film on the metal wiring layer through metal plating.

[0008] In a semiconductor sensor, which is a semiconductor device for detecting the physical quantity or chemical components of a corrosive medium, a configuration has been disclosed in which the aluminum pad portion is protected with a precious metal (see, for example, Patent Document 1). In the semiconductor sensor disclosed in Patent Document 1, nickel and gold are sequentially formed on the pad portion as protective materials by electroless plating. By adding gold, which has high corrosion resistance, as a protective film, the probability of contact between the corrosive medium and the aluminum material of the pad portion can be reduced, thereby improving the corrosion resistance of the pad portion.

[0009] Furthermore, a configuration is disclosed in which the electrode portion of a semiconductor pressure sensor, a semiconductor device for measuring the pressure of gases containing corrosive components such as exhaust gas, is coated with a diffusion prevention layer and gold (see, for example, Patent Document 2). In the semiconductor pressure sensor disclosed in Patent Document 2, a layer made of titanium tungsten and a layer made of gold are provided on the aluminum electrode as protective materials. By providing the titanium tungsten layer, the diffusion of the gold coating on the outermost surface to the aluminum electrode is prevented. In addition, by coating the outermost surface of the electrode portion with highly corrosion-resistant gold, corrosion of the electrode portion caused by corrosive substances is prevented.

[0010] International Publication No. 2004 / 059722, International Publication No. 2007 / 052335

[0011] As mentioned above, preventing contact between metal wiring layers using aluminum and corrosive substances is an important challenge in improving the reliability of semiconductor devices. In the semiconductor device structures disclosed in Patent Documents 1 and 2, a layer of gold with excellent corrosion resistance is formed on top of the aluminum electrodes, which prevents a certain amount of corrosive substances from penetrating to the layers below the gold layer.

[0012] Furthermore, semiconductor devices installed in automobiles are used in a variety of environments, making it difficult to fully understand the components of corrosive substances present in those environments. Therefore, simply employing materials or structures resistant to specific corrosive substances may not be sufficient to improve the reliability of semiconductor devices. The challenge lies in developing technologies to improve the corrosion resistance of electrode sections by selecting materials or optimizing structures resistant to a wide range of substances.

[0013] In semiconductor sensors like the one disclosed in Patent Document 1, where an aluminum pad portion (hereinafter referred to as the aluminum electrode) is protected by a corrosion-resistant precious metal, the aluminum electrode is electrically connected to the outside by wire bonding using gold wire. The precious metal on the aluminum electrode is formed by electroless plating. To stabilize the deposition of gold, a nickel plating layer is formed between the gold and the aluminum electrode. A gold plating layer is then formed on top of the nickel plating layer. The aim of forming a composite layer of nickel and gold plating layers is to prevent corrosion of the aluminum electrode against corrosive media and extend the lifespan of the semiconductor device.

[0014] However, the disclosed configuration does not include measures to maintain high reliability in the bonding of the connection between the gold plating layer and the gold wire. It is known that nickel from the nickel plating layer diffuses into the gold plating layer during or after bonding of the gold wire. This diffusion into the upper layer of the underplating material deteriorates the bonding quality of the wire bonding, leading to bonding defects such as wire delamination. Since bonding defects can lead to serious failures in semiconductor devices, the reliability of the semiconductor device is reduced.

[0015] Furthermore, even when the aluminum electrode is protected by a diffusion-blocking layer and a corrosion-resistant gold coating, as in the semiconductor pressure sensor disclosed in Patent Document 2, the aluminum electrode is electrically connected to the outside by wire bonding using gold wire. The diffusion-blocking layer, which is titanium tungsten, is formed by a sputtering method or the like. The outermost gold coating is formed by gold plating. The aim is to extend the lifespan of the semiconductor device by forming a composite layer of the titanium tungsten layer and the gold plating layer, thereby preventing the diffusion of gold into the aluminum electrode and corrosion of the aluminum electrode by corrosive components.

[0016] However, no measures have been taken to maintain high reliability at the interface between the titanium-tungsten layer and the gold plating layer. Titanium, tungsten, or titanium-tungsten are known to have high corrosion resistance because a strong oxide film is formed on their surface upon contact with oxygen. On the other hand, in the formation of gold plating, the passivation properties of the substrate material hinder plating deposition, making it necessary to remove the oxide film from the surface of the substrate material. In gold plating deposition, even partial passivation of the substrate material severely impairs the adhesion of the plating film, leading to problems such as abnormal gold plating deposition or adhesion failures such as peeling of the gold plating layer. Due to poor adhesion, the gold coating formed on the aluminum electrode no longer performs its inherently excellent corrosion-resistant protective function, resulting in a decrease in the reliability of the semiconductor pressure sensor.

[0017] Therefore, this disclosure aims to provide a semiconductor device that is highly reliable even when used in environments affected by corrosive substances.

[0018] The semiconductor device of this disclosure comprises a semiconductor substrate having a semiconductor element portion formed on one of its main surfaces, a wiring portion having a metal wiring layer provided on one side of the semiconductor element portion opposite to the semiconductor substrate side, and a protective layer made of a silicon compound provided on the side of the semiconductor element portion and the wiring portion opposite to the semiconductor substrate side, wherein one or more portions of the wiring portion opposite to the semiconductor substrate side are exposed through electrode openings penetrating the protective layer, the exposed wiring portion which is the portion of the wiring portion exposed at the electrode openings, and the portion of the protective layer adjacent to the exposed wiring portion are covered with a metal sputtered film, the side of the metal sputtered film opposite to the semiconductor substrate side is covered with a first plating layer made of nickel, the side of the first plating layer opposite to the semiconductor substrate side is covered with a second plating layer made of a noble metal material, and the side of the second plating layer opposite to the semiconductor substrate side is covered with a third plating layer made of a different noble metal material than the second plating layer.

[0019] The semiconductor device of this disclosure comprises a semiconductor substrate, a wiring section, and a protective layer. One or more portions of the wiring section are exposed through electrode openings that penetrate the protective layer. The exposed wiring section, which is the portion of the wiring section exposed at the electrode openings, and the portion of the protective layer adjacent to the exposed wiring section are covered with a metal sputtered film. The metal sputtered film is covered with a first plating layer made of nickel. The first plating layer is covered with a second plating layer made of a noble metal material. The second plating layer is covered with a third plating layer made of a different noble metal material. As a result, the wiring section is not exposed to the outside, and highly corrosion-resistant dissimilar materials are laminated on the wiring section, which can suppress the penetration of corrosive components into the metal wiring layer made of the corrosive material. Furthermore, since adhesion is ensured between the laminated highly corrosion-resistant dissimilar materials, the occurrence of adhesion defects such as peeling is suppressed, which can suppress the penetration of corrosive components into the metal wiring layer made of the corrosive material. Furthermore, by providing a second plating layer made of a precious metal material between the first plating layer made of nickel and the third plating layer made of a precious metal material, the diffusion of the material from the outermost surface of the first plating layer to the third plating layer can be suppressed. This suppresses the penetration of corrosive components into the metal wiring layer made of the corrosive material, and also suppresses the diffusion of the material from the outermost surface of the first plating layer to the third plating layer. As a result, a highly reliable semiconductor device can be obtained even when used continuously in an environment affected by corrosive substances.

[0020] This is a schematic plan view of a semiconductor pressure sensor according to Embodiment 1. This is a schematic cross-sectional view of a semiconductor pressure sensor cut at the A-A cross-sectional position in Figure 1. This is a schematic cross-sectional view of the main part of a semiconductor pressure sensor cut at the B-B cross-sectional position in Figure 1. This is a diagram showing the configuration of a pressure sensor device according to Embodiment 1. This is a diagram showing the configuration of an exhaust gas recirculation system according to Embodiment 1. This is a diagram showing the manufacturing process of a semiconductor pressure sensor according to Embodiment 1. This is a schematic plan view of a semiconductor pressure sensor according to Embodiment 2. This is a schematic cross-sectional view of the main part of a semiconductor pressure sensor cut at the C-C cross-sectional position in Figure 7. This is a schematic cross-sectional view of the main part of another semiconductor pressure sensor according to Embodiment 2. This is a schematic plan view of the main part of another semiconductor pressure sensor according to Embodiment 2. This is a schematic cross-sectional view of the main part of a semiconductor pressure sensor according to Embodiment 3. This is a schematic plan view of the main part of a semiconductor pressure sensor according to Embodiment 3.

[0021] Hereinafter, a semiconductor device, a semiconductor pressure sensor, a pressure sensor device, and an exhaust gas recirculation system according to embodiments of the present disclosure will be described with reference to the figures. In each figure, the same or equivalent components and parts will be denoted by the same reference numerals. The configuration of the present disclosure can be applied to semiconductor devices having electrode openings in which a part of the metal wiring layer is exposed from the protective layer, and to various sensors or devices. By applying the configuration of the present disclosure, it is possible to provide semiconductor devices and various sensors or devices with excellent environmental resistance. In the embodiments, an example of applying the configuration of the present disclosure to a semiconductor pressure sensor will be described with reference to the figures as an example of application of a semiconductor device. However, the application of the semiconductor device is not limited to semiconductor pressure sensors; it may also be other sensors such as temperature sensors, or integrated circuits such as signal processing circuits.

[0022] Embodiment 1. Figure 1 is a schematic plan view of the semiconductor pressure sensor 1 according to Embodiment 1, showing the protective layer 11 and omitting the wiring portion 12. Figure 2 is a schematic cross-sectional view of the semiconductor pressure sensor 1 cut at the A-A cross-sectional position in Figure 1. Figure 3 is a schematic cross-sectional view of the main part of the semiconductor pressure sensor 1 cut at the B-B cross-sectional position in Figure 1, showing the electrode opening 4. Figure 4 is a diagram showing the configuration of the pressure sensor device 100 according to Embodiment 1. Figure 5 is a diagram showing the configuration of the exhaust gas recirculation system 200 according to Embodiment 1. Figure 6 is a diagram showing the manufacturing process of the semiconductor pressure sensor 1 according to Embodiment 1. The semiconductor pressure sensor 1 shown in this embodiment is manufactured by a semiconductor process and is a sensor that measures the pressure of corrosive gases or gases containing corrosive components.

[0023] <Structure of Semiconductor Pressure Sensor 1> The structure of the semiconductor pressure sensor 1, which is a semiconductor device of this disclosure, will now be described. As shown in Figure 3, the semiconductor pressure sensor 1 comprises a semiconductor substrate 20 having a semiconductor element portion 10 formed on one of its surfaces, the main surface 9a; a wiring portion 12 having a metal wiring layer provided on one side of the semiconductor element portion 10 opposite to the semiconductor substrate 20; and a protective layer 11 made of a silicon compound, provided on the side of the semiconductor element portion 10 and the wiring portion 12 opposite to the semiconductor substrate 20. The semiconductor substrate 20 is, for example, a single-crystal silicon substrate. In this embodiment, as shown in Figure 2, the semiconductor substrate 20 is composed of a first silicon substrate 7 and a second silicon substrate 9. The semiconductor element portion 10 has a piezoresistive element 3, a diffusion wiring layer (not shown), a diaphragm 2, and an insulating layer (not shown). For the insulating layer formed on the outermost surface of the semiconductor element portion 10, a silicon oxide film (SiO2) or the like is used. The insulating layer may contain phosphorus, or phosphorus and boron. The protective layer 11 is a protective film that covers the semiconductor element portion 10. The protective layer 11, which is formed on the outermost surface as an insulating layer, is highly likely to be exposed to the external environment. Therefore, by using a silicon nitride film (SiN) or a silicon oxynitride film (SiON), which has excellent environmental resistance, as the protective layer 11, a semiconductor pressure sensor 1 with excellent environmental resistance can be obtained. The metal wiring layer is formed of, for example, aluminum.

[0024] The semiconductor pressure sensor 1 includes one or more pressure sensing units connected to the wiring section 12. In this embodiment, as shown in Figure 2, the pressure sensing unit is a piezoresistive element 3 formed on one side of the semiconductor element section 10 that is opposite to the semiconductor substrate 20 side. The semiconductor pressure sensor 1 further includes a diaphragm 2, which is a thin portion of the semiconductor substrate 20. The diaphragm 2 is the area indicated by the dashed line in Figures 1 and 2. In this embodiment, as shown in Figure 1, the diaphragm 2 is formed in a rectangular shape when viewed perpendicular to the main surface 9a. The shape of the diaphragm 2 is not limited to this. The shape of the diaphragm 2 may be, for example, circular when viewed perpendicular to the main surface 9a. In Figure 1, the portion of the wiring section 12 between the wiring section 12 and the piezoresistive element 3 is omitted.

[0025] In this embodiment, the piezoresistive elements 3, which are semiconductor elements, are formed adjacent to the diaphragm 2. Four piezoresistive elements 3a, 3b, 3c, and 3d are provided as the piezoresistive elements 3. Each of the piezoresistive elements 3a, 3b, 3c, and 3d is formed adjacent to each side of the diaphragm 2. The number and formation positions of the piezoresistive elements 3 are not limited to these. The formation positions of the piezoresistive elements 3 may be other positions, for example, where a larger strain can be obtained by the deformation of the diaphragm 2.

[0026] When pressure is applied to the diaphragm 2, the diaphragm 2 deforms, causing strain at the location where the piezoresistive element 3 is positioned. Depending on the degree of strain, the resistance value of the piezoresistive element 3 changes due to the piezoresistive effect of the piezoresistive element. This change in resistance value is converted into an electrical signal and taken out externally as a sensor output. By combining the semiconductor pressure sensor 1 with the signal processing circuit 50 described later, the signal processing circuit 50 can perform signal processing such as amplification, compensation, and calibration of the sensor output.

[0027] As shown in Figure 3, one or more portions of the wiring section 12 on the side opposite to the semiconductor substrate 20 are exposed through electrode openings 4 that penetrate the protective layer 11. The electrode openings 4 are provided to electrically connect the piezoresistive element 3 to the outside via the wiring section 12. In this embodiment, as shown in Figure 1, four rectangular electrode openings 4 are arranged in a row. The number, position, and shape of the electrode openings 4 are not limited to this. For example, the number of electrode openings 4 required for connection to the outside may be changed to provide electrodes for pre-checking the electrical characteristics of the semiconductor pressure sensor 1. The number, position, and shape of the electrode openings 4 can be freely determined according to the design of the optimal electrode position, taking into account the productivity of manufacturing processes such as wire bonding.

[0028] <Electrode Aperture 4> The configuration of the electrode aperture 4, which is the main part of this disclosure, will be explained with reference to Figure 3. The exposed wiring portion 12a, which is the portion of the wiring portion 12 exposed in the electrode aperture 4, and the portion of the protective layer 11 adjacent to the exposed wiring portion 12a are covered with a metal sputtered film 13. The side of the metal sputtered film 13 opposite to the semiconductor substrate 20 is covered with a first plating layer 14 made of nickel. The side of the first plating layer 14 opposite to the semiconductor substrate 20 is covered with a second plating layer 15 made of a noble metal material. The side of the second plating layer 15 opposite to the semiconductor substrate 20 is covered with a third plating layer 16 made of a different noble metal material than the second plating layer 15. The third plating layer 16 and the outside are connected by a bonding wire 5.

[0029] The details and characteristics of each layer provided in the electrode opening 4 will be explained in order. First, the metal sputtered film 13 will be described. The metal sputtered film 13 can be easily and accurately formed by a film deposition process such as the sputtering method of semiconductor processes. The metal sputtered film 13 is formed in the desired position by patterning the necessary areas using photolithography. The portion of the protective layer 11 adjacent to the exposed wiring portion 12a covered by the metal sputtered film 13 is the side wall of the electrode opening 4 and the surface portion of the protective layer 11. At these locations, the metal sputtered film 13 is in contact with the silicon nitride film, which is the protective layer 11.

[0030] In this embodiment, the metal sputtered film 13 is formed from the same material as the wiring portion 12. This configuration ensures high adhesion at the interface between the wiring portion 12 and the metal sputtered film 13. In this embodiment, the metal sputtered film 13 is aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper. This configuration ensures good adhesion between the metal sputtered film 13, such as aluminum silicon, and the silicon nitride film, which is the protective layer 11 and insulating film. Because of the good adhesion between the metal sputtered film 13 and the protective layer 11, defects such as peeling of the metal sputtered film 13 can be suppressed. Since defects such as peeling of the metal sputtered film 13 are suppressed, the semiconductor pressure sensor 1 can maintain high reliability. The ratio of silicon, copper, or silicon copper added to the aluminum film in the wiring portion 12 can be arbitrarily designed according to the function and purpose required of the wiring portion 12.

[0031] When the angle of the side wall of the electrode opening 4 is formed perpendicular to the surface of the wiring portion 12, a right-angle corner is formed between the surface of the wiring portion 12 and the side wall. During the deposition of the metal sputtered film 13, corners are areas where the film tends to adhere poorly. Therefore, there is a possibility that voids will occur in the corners in the early stages of deposition. In this embodiment, when viewed perpendicular to the main surface 9a of the semiconductor substrate, the side wall of the protective layer 11 at the electrode opening 4 is inclined so that the opening area narrows toward the wiring portion 12. By making the side wall of the protective layer 11 tapered in this way, the angle between the surface of the wiring portion 12 and the side wall of the protective layer 11 can be made larger than a right angle, thereby suppressing the occurrence of voids in the portion between the surface of the wiring portion 12 and the side wall of the protective layer 11 in the early stages of deposition. Since the occurrence of voids is suppressed, defects such as peeling of the metal sputtered film 13 can be suppressed. Since defects such as peeling of the metal sputtered film 13 are suppressed, the semiconductor pressure sensor 1 can maintain high reliability.

[0032] Next, the first plating layer 14 will be described. In this embodiment, the first plating layer 14 is nickel. The plating layer is preferably formed by electroless plating. By forming the plating layer by electroless plating, a uniform thickness can be ensured for complex shapes. Furthermore, electroless plating can selectively form a plating layer on the underlying metal material. Therefore, the photolithography patterning process of semiconductor processes becomes unnecessary. Because the patterning process is unnecessary, the corrosion resistance of the electrode opening 4 can be improved without complicating the process. Including the side walls of the metal sputtered film 13, the first plating layer 14 covers the metal sputtered film 13. Since the plating layer made of nickel is a material with excellent corrosion resistance, the corrosion resistance of the underlying metal sputtered film 13 and the wiring portion 12 can be improved.

[0033] Furthermore, the nickel plating layer ensures high reliability in terms of adhesion between the metal sputtered film 13 and the aluminum film. In electroless nickel plating on aluminum films, pre-treatment techniques for plating, such as zincate treatment, which suppresses the formation of oxide films by zinc substitution on the aluminum surface, have been established. In addition, by performing double zincate treatment, it becomes possible to form a dense zinc film, thereby further improving the adhesion between the aluminum film of the metal sputtered film 13 and the first plating layer 14 made of nickel. As the adhesion between the aluminum film of the metal sputtered film 13 and the first plating layer 14 made of nickel is further improved, the occurrence of adhesion defects such as peeling of the first plating layer 14 can be suppressed. As the occurrence of adhesion defects of the first plating layer 14 is suppressed, the semiconductor pressure sensor 1 can maintain high reliability.

[0034] The first plating layer 14 may be a plating layer made of nickel containing phosphorus. By including phosphorus in the first plating layer 14 made of nickel, the corrosion resistance and acid resistance of the first plating layer 14 can be improved. By increasing the phosphorus content of the first plating layer 14 made of nickel, the corrosion resistance and acid resistance of the first plating layer 14 can be further improved. In this way, by making the first plating layer 14 a plating layer made of nickel containing phosphorus, the corrosion resistance and acid resistance of the first plating layer 14 are improved, and thus the corrosion resistance and acid resistance of the underlying metal sputter film 13 and wiring portion 12 can be further improved.

[0035] As in this embodiment, by providing the metal sputtered film 13, the adhesion of the first plating layer 14 becomes very good. The reason for this is explained below. If the metal sputtered film 13 is not provided, the first plating layer 14 will be formed on both the exposed wiring portion 12a of the wiring portion 12 and the protective layer 11 made of silicon nitride film. The adhesion between the wiring portion 12 made of aluminum and the first plating layer 14 made of nickel can be ensured by pre-treatment before plating. On the other hand, the adhesion between the protective layer 11, which is an insulating film, and the first plating layer 14 made of nickel is not good. Therefore, if components of the external environment penetrate into the underlying wiring portion 12 from the interface between the protective layer 11 and the first plating layer 14, it may chemically alter the wiring portion 12.

[0036] Compared to a state where the wiring portion 12 is exposed to the external environment without the first plating layer 14, the influence of the components of the external environment on the wiring portion 12 when the first plating layer 14 is provided is minimal. However, if the semiconductor pressure sensor 1 is used in an environment where it is continuously exposed to corrosive substances for a long time, the corrosive components that penetrate the wiring portion 12 through the interface between the protective layer 11 and the first plating layer 14 may reach a level that cannot be ignored.

[0037] If corrosive components reach the aluminum wiring section 12, problems such as corrosion of the wiring section 12 will occur, reducing the reliability of the semiconductor pressure sensor 1. As a method to suppress the effects of corrosive component penetration through the interface, it is conceivable to form a protective gel or an organic protective film such as parylene to cover the interface between the protective layer 11 and the first plating layer 14. However, since gels and organic protective films cannot completely prevent the penetration of corrosive components, they are not sufficient methods to counteract the penetration of corrosive components through the interface.

[0038] In this embodiment, the metal sputtered film 13 is in contact with the wiring portion 12 and a part of the protective layer 11 on the side of the semiconductor substrate 20 at the electrode opening 4, and in contact with the first plating layer 14 on the side opposite to the semiconductor substrate 20. High adhesion is maintained between the metal sputtered film 13 and the wiring portion 12, and between the metal sputtered film 13 and the first plating layer 14, as described above. The adhesion between the metal sputtered film 13 and the protective layer 11 will now be described. The protective layer 11, made of a silicon nitride film, can be easily and accurately formed by the film deposition process of a semiconductor process, similar to the metal sputtered film 13. In particular, silicon nitride films produced by the plasma chemical vapor deposition (CVD) method have high environmental resistance because they are dense. For example, if the protective layer 11 is a silicon nitride film produced by plasma CVD and the metal sputtered film 13 is an aluminum silicon film produced by sputtering, it is common for the structure of a semiconductor sensor or signal processing circuit 50 to be formed so that the silicon nitride film and the aluminum silicon film are in contact. The interface between the silicon nitride film and the aluminum silicon film ensures good adhesion, allowing the semiconductor device to maintain high reliability.

[0039] The relationship between the metal sputtered film 13 and the protective layer 11 in this embodiment is similar, and therefore, it has better adhesion compared to metal films produced by vapor deposition or plating. As a result, the metal sputtered film 13, which has good adhesion, is in contact with the protective layer 11 for the majority of the surface, and the first plating layer 14 made of nickel has almost no contact with the protective layer 11. By providing the metal sputtered film 13, the influence of the interface between the protective layer 11 and the first plating layer 14, which does not have good adhesion, can be suppressed. Because the influence of the interface between the protective layer 11 and the first plating layer 14 is suppressed, the semiconductor pressure sensor 1 can be used with high reliability even in environments where it is continuously exposed to corrosive substances for a long time.

[0040] Next, the second plating layer 15 and the third plating layer 16 will be described. The second plating layer 15 is made of a precious metal material. The third plating layer 16 is made of a different precious metal material than the second plating layer 15. Among the precious metal materials, it is preferable to select a material with a low ionization tendency from the viewpoint of corrosion resistance. The ionization tendency indicates the tendency of each material to be less susceptible to corrosion. In terms of ionization tendency, gold, platinum, palladium, and silver are arranged in that order, and it is known that the ionization tendency decreases in this order, and that gold is the most corrosion-resistant material. In this embodiment, the second plating layer 15 is a plating layer made of palladium or platinum. In this embodiment, the third plating layer 16 is a plating layer made of gold. The outermost surface of the electrode opening 4 is provided with a third plating layer 16 made of gold, which has the best corrosion resistance. Including the side walls of the first plating layer 14, the second plating layer 15 covers the first plating layer 14. The third plating layer 16 covers the second plating layer 15, including the side walls of the second plating layer 15.

[0041] By forming a third plating layer 16 made of gold, which has the best corrosion resistance, on the outermost surface, the environmental resistance of the semiconductor pressure sensor 1 can be improved. Furthermore, by using palladium or platinum, which are cheaper than gold, for the material of the second plating layer 15, the thickness of the third plating layer 16 made of gold can be reduced, thus reducing the cost of the semiconductor pressure sensor 1. In addition, by providing two plating layers, the second plating layer 15 and the third plating layer 16, on the side of the first plating layer 14 made of nickel that is opposite to the semiconductor substrate 20, the corrosion resistance of the semiconductor pressure sensor 1 can be significantly improved. The reasons for this are explained below. If the second plating layer 15 is not provided, the third plating layer 16 made of gold will be formed on the side of the first plating layer 14 made of nickel that is opposite to the semiconductor substrate 20. This configuration presents two problems.

[0042] The first problem is that nickel from the first plating layer 14 diffuses into the gold of the third plating layer 16. For example, the third plating layer 16 is electrically connected to the outside by wire bonding using gold wire. During or after wire bonding, the heat from the semiconductor mounting process causes nickel from the first plating layer 14 to diffuse into the gold, altering the surface of the gold in the third plating layer 16 or contaminating the gold. As a result, the connection strength between the third plating layer 16 and the gold wire decreases. This deterioration in the quality of the wire bonding leads to bonding defects such as wire delamination, which reduces the reliability of the semiconductor pressure sensor 1.

[0043] Although increasing the gold thickness of the third plating layer 16 can suppress the diffusion of nickel to the gold surface, there is a problem that increasing the thickness of the gold film raises the cost of the semiconductor pressure sensor 1. In the present embodiment, the second plating layer 15 made of palladium or platinum is formed as an intermediate layer between the first plating layer 14 and the third plating layer 16. Since palladium and platinum tend to be less prone to oxidation similarly to gold, providing the second plating layer 15 made of palladium or platinum as the intermediate layer can suppress the diffusion of nickel from the first plating layer 14 to the gold surface of the third plating layer 16. Since the diffusion of nickel to the gold surface is suppressed, the decrease in the connection strength of wire bonding is inhibited, so that high connection reliability can be obtained at the conductive connection portion with the outside formed in the electrode opening 4 of the semiconductor pressure sensor 1. Hereinafter, in semiconductor devices and various sensors or apparatuses, the portion connected to the outside is referred to as a conductive connection portion.

[0044] The second problem is that defects in the plating film such as pinholes or pits are formed in the first plating layer 14 and the third plating layer 16. As a defect of the gold plating film that is the third plating layer 16, through-holes of a level reaching the nickel plating film that is the underlying first plating layer 14 are formed. Further, as a defect of the nickel plating film, through-holes of a level reaching the underlying metal sputtered film 13 made of aluminum are formed. When these through-holes communicate with each other, the defects of the plating film become intrusion paths for corrosive components, and corrosive substances in the external environment intrude into the interior. The intrusion of corrosive substances in the external environment into the interior may corrode the underlying material.

[0045] While increasing the thickness of the gold in the third plating layer 16 can suppress the effects of defects in the plating film, such as through holes, it is difficult to completely suppress defects. Furthermore, increasing the thickness of the gold film increases the cost of the semiconductor pressure sensor 1. In the configuration of this disclosure, the second plating layer 15 is formed as an intermediate layer between the first plating layer 14 and the third plating layer 16. Even if defects in the plating film, such as through holes, are formed in each of the first plating layer 14, the second plating layer 15, and the third plating layer 16, the probability of the through holes connecting can be reduced because the plating films are stacked.

[0046] Furthermore, by laminating the plating films, the intrusion paths of corrosive components and other substances that penetrate through the through holes become more complex, resulting in a longer time required for them to reach the bottom layer. By providing a second plating layer 15 as an intermediate layer, the intrusion paths of corrosive components into the aluminum metal sputtered film 13 become more complex, thereby suppressing corrosion of the metal sputtered film 13 and the wiring portion 12. Since corrosion of the metal sputtered film 13 and the wiring portion 12 is suppressed, the corrosion resistance of the electrode opening 4 is improved, and high reliability can be obtained at the conductive connection portion with the outside formed in the electrode opening 4 of the semiconductor pressure sensor 1.

[0047] In addition to addressing the two issues mentioned above, providing a second plating layer 15 made of palladium or platinum as an intermediate layer is also effective in reducing costs. By providing the second plating layer 15, the two issues mentioned above can be solved without increasing the thickness of the third plating layer 16 made of gold, thus allowing the thickness of the third plating layer 16 made of gold to be reduced. As the thickness of the third plating layer 16 is reduced, the semiconductor pressure sensor 1 can be made less expensive.

[0048] Further effects will be described. Each of the first plating layer 14, the second plating layer 15, and the third plating layer 16 is made of a different material with high corrosion resistance, and each layer is resistant to different corrosive substances. In particular, for semiconductor devices such as the semiconductor pressure sensor 1 mounted on automobiles, it is difficult to fully grasp the components of corrosive substances contained in the mounting environment, and it is required to optimize the selection of materials resistant to various substances or the structure. To address these issues, in the configuration of the present disclosure, since each plating layer is resistant to different corrosive substances, it is possible to provide a structure that can cope with failure modes of the semiconductor device against intrusion of various corrosive substances. When a corrosive component that is not resistant to one plating layer intrudes, even if one plating layer loses its protective function, the provision of the other two plating layers can suppress corrosion of the wiring portion 12 made of aluminum as the lowermost layer. Since corrosion of the wiring portion 12 is suppressed, failure of semiconductor devices such as the semiconductor pressure sensor 1 can be suppressed. Since failure of the semiconductor device is suppressed, the service life of the semiconductor device can be significantly prolonged.

[0049] The effects of the basic configuration of the electrode opening 4, which is the main part of this disclosure, are summarized below. Since the electrode opening 4 is covered with a metal sputtered film 13, a first plating layer 14, a second plating layer 15, and a third plating layer 16, the wiring portion 12 is not exposed to the outside, and since highly corrosion-resistant dissimilar materials are laminated on the wiring portion 12, the penetration of corrosive components into the metal wiring layer made of the corrosive material can be suppressed. In addition, since adhesion is ensured between the laminated highly corrosion-resistant dissimilar materials, the occurrence of adhesion defects such as peeling is suppressed, and the penetration of corrosive components into the metal wiring layer made of the corrosive material can be suppressed. Furthermore, since a second plating layer 15 made of a noble metal material is provided between the first plating layer 14 made of nickel and the third plating layer 16 made of a noble metal material, the diffusion of the material from the outermost surface of the first plating layer 14 to the third plating layer 16 can be suppressed. Since the penetration of corrosive components into the metal wiring layer made of the corrosive material is suppressed, and the diffusion of the material from the outermost surface of the first plating layer 14 to the third plating layer 16 is also suppressed, a semiconductor device such as a semiconductor sensor or signal processing circuit 50 with high precision and high reliability can be obtained even when used continuously in an environment affected by corrosive substances.

[0050] In this embodiment, the semiconductor pressure sensor 1, as shown in Figure 1, comprises an electrode opening 4 with the above-described configuration and a piezoresistive element 3, which is a pressure detection unit connected to the wiring section 12. With this configuration, the intrusion of corrosive components into the metal wiring layer made of the corrosive material is suppressed, and the diffusion of the material of the first plating layer 14 to the third plating layer 16 on the outermost surface is suppressed. As a result, a semiconductor pressure sensor 1 with high reliability can be obtained even when used continuously in an environment affected by corrosive substances.

[0051] In this embodiment, a piezoresistive element 3 is provided as the pressure sensing unit, but the semiconductor pressure sensor 1 is not limited to a piezoresistive semiconductor pressure sensor 1. It may also be a capacitive semiconductor pressure sensor in which an electrode is provided as the pressure sensing unit, and the deformation of the diaphragm due to pressure changes is detected as the displacement of the electrode formed on the diaphragm. When the pressure sensing unit is a piezoresistive element 3, the semiconductor pressure sensor 1 can be made smaller, more sensitive, and more accurate.

[0052] <Pressure Sensor Device 100> A typical example of a sensor device equipped with a semiconductor pressure sensor 1 is a pressure sensor device 100 that is installed in environments containing corrosive substances. The pressure sensor device 100 will be explained using Figure 4. The pressure sensor device 100 comprises the semiconductor pressure sensor 1 with the above configuration and a signal processing circuit 50 connected to the piezoresistive element 3 via a wiring section 12, which processes the output of the piezoresistive element 3. In Figure 4, the portion of the wiring section 12 between the wiring section 12 and the piezoresistive element 3 is omitted. The electrode opening 4 and the signal processing circuit 50 are connected by a bonding wire 5.

[0053] A Wheatstone bridge 51 is formed by four piezoresistive elements 3a, 3b, 3c, and 3d. A sensor output (output potential difference) proportional to the pressure applied to the diaphragm 2 can be obtained from the Wheatstone bridge 51. The signal processing circuit 50 performs signal processing such as amplification, compensation, and calibration of the sensor output. By equipping the pressure sensor device 100 with the semiconductor pressure sensor 1 with the above configuration, a highly reliable pressure sensor device 100 can be obtained even when used continuously in environments affected by corrosive substances.

[0054] Furthermore, it is preferable to use the configuration of the electrode opening 4 described above for the conductive connection portion of the signal processing circuit 50. By configuring it in this way, the corrosion resistance of the conductive connection portion of the signal processing circuit 50 can be improved. In addition, it is desirable to provide an organic protective film such as parylene, a protective gel such as fluororesin, or both an organic protective film and a gel on the surface of the semiconductor pressure sensor 1 and the signal processing circuit 50. By configuring it in this way, the surfaces of the semiconductor pressure sensor 1 and the signal processing circuit 50 are protected, improving the environmental resistance of the semiconductor pressure sensor 1 and the signal processing circuit 50, and thus the pressure sensor device 100 can achieve high reliability.

[0055] <Exhaust Gas Recirculation System 200> Examples of environments in which the pressure sensor device 100 is installed include exhaust gas recirculation devices (EGR) and exhaust gas emission control devices. These devices are installed in gasoline engine vehicles or diesel engine vehicles and contribute to the reduction of harmful substances contained in exhaust gas. In this embodiment, as shown in Figure 5, the exhaust gas recirculation system 200 comprises the pressure sensor device 100 with the above-described configuration and an exhaust gas recirculation device 101 connected to the pressure sensor device 100, which controls the engine based on the exhaust gas pressure detected by the pressure sensor device 100.

[0056] The pressure sensor device 100 installed in the exhaust gas recirculation system 200 will be affected by multiple hazardous substances. Examples of hazardous substances include carbon monoxide, hydrocarbons, nitrogen oxides, sulfur oxides, or particulate matter. In addition, corrosive components generated from various components such as resin parts, exhaust pipes, or hoses may affect the pressure sensor device 100. Examples of corrosive components include acidic components such as nitric acid, sulfuric acid, or hydrochloric acid, or halogen components such as chlorine, fluorine, bromine, or iodine. Corrosive components, in the form of gases or ions, adversely affect the materials of the conductive connection parts of semiconductor devices. Furthermore, the effects of temperature or humidity may influence the progression or acceleration of corrosion. It is known that corrosive components can corrode the aluminum wiring section 12 in the conductive connection part, or the alloy layer such as an aluminum-gold alloy between the electrode and the gold wire. Corrosion of the conductive connection part can lead to fatal failures in semiconductor devices, making it impossible to maintain high reliability.

[0057] If the signal processing circuit 50 connected to the semiconductor pressure sensor 1 of the pressure sensor device 100 uses a conductive connection part with improved corrosion resistance, similar in configuration to the semiconductor pressure sensor 1, corrosion of the conductive connection part will be suppressed even if the pressure sensor device 100 is used continuously in a harsh environment where gases containing corrosive substances are present, thereby obtaining a pressure sensor device 100 with high environmental resistance and high reliability. Furthermore, since the exhaust gas recirculation system 200 is equipped with the pressure sensor device 100 of this disclosure, the pressure sensor device 100 can accurately measure the pressure of exhaust gases such as nitrogen oxides or gases containing halogens such as chlorine while maintaining high reliability, thereby obtaining an exhaust gas recirculation system 200 with high reliability.

[0058] <Manufacturing Method for Semiconductor Pressure Sensor 1> An outline of the manufacturing method for semiconductor pressure sensor 1 will be explained using Figures 2, 3, and 6. Multiple semiconductor pressure sensors 1 are manufactured simultaneously on a single wafer, which is a single-crystal silicon substrate, using a semiconductor process. Here, the manufacturing method for one semiconductor pressure sensor 1 will be described. The semiconductor pressure sensor 1 is a square with sides of about 1 to 1.6 mm in a plan view. The diaphragm 2 is a square with sides of about 400 μm. The manufacturing method for semiconductor pressure sensor 1 shown in Embodiment 1 includes, as shown in Figure 6, an SOI structure formation step (S11), a diaphragm formation step (S12), a resistor formation step (S13), a wiring formation step (S14), a protective film formation step (S15), an electrode opening formation step (S16), a metal sputtered film formation step (S17), a plating layer formation step (S18), and a dicing step (S19).

[0059] Each step will be explained in order. The SOI structure formation step is the process of forming the structure of the SOI (Silicon on Insulator) wafer and the cavity 6 shown in Figure 2. First, recesses 6a are formed on the main surface 7a of the first silicon substrate 7 by etching. In order to accurately form the shape of the cavity 6, that is, the shape of the diaphragm 2, it is preferable to use inductively coupled reactive ion etching (ICP-RIE) using the Bosch process. However, the etching method is not limited to this, and recesses 6a may also be formed by wet anisotropic etching using an etching solution such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH).

[0060] Next, an embedded oxide film 8 is formed on the main surface 7a of the first silicon substrate 7 by thermal oxidation. The embedded oxide film 8 is also formed on the surface of the recess 6a. In this embodiment, an example is shown in which the embedded oxide film 8 is formed on the main surface 7a of the first silicon substrate 7, but it is not limited to this. The embedded oxide film 8 may also be formed on the main surface 9b of the second silicon substrate 9. Next, substrate bonding is performed to join the main surface 7a of the first silicon substrate 7 and the main surface 9b of the second silicon substrate 9. Substrate bonding is performed in a vacuum with the embedded oxide film 8 in between. A cavity 6 is formed by the substrate bonding. It is preferable to perform the substrate bonding in an oxidizing atmosphere at a high temperature of about 1100°C.

[0061] The diaphragm formation process is a process of forming a diaphragm 2 by adjusting the thickness of the second silicon substrate 9. The area covering a part of the recess 6a of the second silicon substrate 9 becomes the diaphragm 2. Therefore, after joining the first silicon substrate 7 and the second silicon substrate 9, the thickness of the second silicon substrate 9 is adjusted according to the range of pressure to be measured. Specifically, the thickness of the second silicon substrate 9 is adjusted to a predetermined thickness, for example, about 10 to 30 μm, by grinding and polishing the entire main surface 9a of the second silicon substrate 9. The diaphragm formation process is necessary because it is difficult to handle a thin second silicon substrate 9 during joining. Through this process, a diaphragm 2 having a predetermined thickness is formed.

[0062] The resistor formation process is a process of forming the piezoresistive elements 3 on the main surface 9a of the second silicon substrate 9. The piezoresistive elements 3 are each formed on the outer periphery of the diaphragm 2. In this embodiment, the piezoresistive elements 3a, 3b, 3c, and 3d are formed on each side of the outer periphery of the rectangular cavity 6 when viewed in a direction perpendicular to the main surface 9a of the second silicon substrate 9. The piezoresistive elements 3 are formed by ion implantation of impurities such as boron at the above-mentioned positions on the main surface 9a of the second silicon substrate 9, followed by heat treatment and other processes.

[0063] The wiring formation process is a process of forming a wiring section 12 having a diffusion wiring layer, an insulating layer, and a metal wiring layer on the main surface 9a of the second silicon substrate 9. The diffusion wiring layer is formed by ion implantation and subsequent heat treatment. The insulating layer is formed by depositing a silicon oxide film (SiO2) or the like by CVD. The insulating layer may contain phosphorus, or phosphorus and boron. The insulating layer may also use a tetraethyl orosilicate (TEOS) oxide film with excellent insulating properties produced by CVD. The wiring section 12 having a metal wiring layer, as shown in Figure 3, is formed by depositing aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper by sputtering or electron beam deposition.

[0064] The protective film formation process involves forming a protective layer 11 made of a silicon compound on the main surface 9a of the second silicon substrate 9. The protective layer 11 is formed by depositing a silicon nitride film or the like using a plasma CVD method.

[0065] The electrode opening formation process involves forming an electrode opening 4 by penetrating a protective layer 11 made of a silicon compound and exposing a portion of the wiring section 12 having a metal wiring layer. The silicon compound, such as a silicon nitride film, is preferably etched using dry etching with a fluorine compound gas, which enables high etching speed and high uniformity. Alternatively, the silicon compound may be etched by wet etching. As described above, the side walls of the electrode opening 4 are preferably configured in a tapered shape.

[0066] In the metal sputtering film formation process, first, aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper is deposited on the exposed wiring portion 12a and the protective layer 11 by sputtering, using the same material and method as the wiring portion 12 having a metal wiring layer. Next, the metal sputtering film 13 is patterned by photolithography so that it covers only the necessary areas such as the electrode opening 4. When the side wall of the electrode opening 4 is tapered, the generation of voids is suppressed, so a uniform and dense metal sputtering film 13 is formed. Tapering the side wall of the electrode opening 4 leads to maximizing the effect of the metal sputtering film 13, and therefore the reliability of the semiconductor pressure sensor 1 can be further improved by tapering the side wall of the electrode opening 4.

[0067] The plating layer formation process involves forming a first plating layer 14 made of nickel, a second plating layer 15 made of a precious metal material, and a third plating layer 16 made of a precious metal material different from the second plating layer 15, on necessary locations such as the electrode opening 4 by electroless plating. Electroless plating allows for the selective formation of plating layers on the underlying metal material. Therefore, since it does not use the photolithography patterning process of semiconductor processes, it has the advantage of covering the electrode opening 4 without complicating the process. Furthermore, because electroless plating uses a chemical reduction reaction, it can form a uniform plating film on stepped shapes such as the electrode opening 4. Thus, since the formation of the plating layer by electroless plating does not create a weak area at the step of the electrode opening 4, a highly reliable conductive connection can be obtained by electroless plating.

[0068] The first plating layer 14 is formed by immersing the semiconductor pressure sensor 1 in a plating solution composed of nickel salts, reducing agents such as hypophosphate, and stabilizers. As mentioned above, it is desirable for the nickel plating film to contain phosphorus. The chemical resistance, corrosion resistance, or hardness of the plating film can be changed by varying the phosphorus content. It is known that high-phosphorus nickel plating films, which have a high phosphorus content, have improved acid resistance and corrosion resistance compared to low-phosphorus or medium-phosphorus nickel plating films. Medium-phosphorus nickel plating films have characteristics such as high adhesion to the material and high corrosion resistance, so the phosphorus content is optimized according to the physical properties required for the plating film. Designing the thickness of the nickel plating film to be approximately 1 to 10 μm is expected to be effective in improving environmental resistance.

[0069] Before forming the first plating layer 14, pre-plating treatments such as degreasing, etching, or zincate treatment are required. The oxide film formed on the surface of the metal sputtered film 13 made of aluminum, which is provided in the layer below the first plating layer 14, is removed by the pre-plating treatment. This improves the adhesion between the first plating layer 14 and the metal sputtered film 13. It is preferable to perform a double zincate treatment to remove the zincate after the zincate treatment. By performing a double zincate treatment, a uniform and dense zinc film can be formed, further improving the adhesion between the first plating layer 14 and the metal sputtered film 13. Improved adhesion suppresses defects such as film peeling at the conductive connection portion of the semiconductor pressure sensor 1, thus enabling the semiconductor pressure sensor 1 to maintain high reliability.

[0070] The second plating layer 15 is made of a precious metal material such as palladium or platinum. The electroless palladium plating layer is formed by immersing the semiconductor pressure sensor 1 in a plating solution composed of a palladium complex, a reducing agent such as hypophosphate or formate, and a stabilizer. The palladium plating film may contain phosphorus. The electroless platinum plating layer is formed by immersing the semiconductor pressure sensor 1 in a plating solution composed of a platinum complex, a reducing agent, and a stabilizer. By providing a second plating layer 15 made of a precious metal material with excellent environmental resistance, the diffusion of nickel from the lower first plating layer 14 to the upper third plating layer 16 can be suppressed. Because the diffusion of nickel to the third plating layer 16 is suppressed, the reliability of the connection between the electrode material and the gold wire in the conductive connection part can be improved. Because high wire bonding performance is maintained, the reliability of the semiconductor pressure sensor 1 can be improved.

[0071] The third plating layer 16 is made of a precious metal material such as gold. The electroless gold plating layer is formed by immersing the semiconductor pressure sensor 1 in a plating solution composed of gold salts, a reducing agent, and a stabilizer. Electroless gold plating is broadly classified into cyanide baths and cyanide-free baths that do not use cyanide compounds. Generally, electroless plating using a cyanide bath is commonly used. By forming a thick gold plating layer, it is expected that sufficient environmental resistance can be achieved. On the other hand, since gold is expensive compared to other precious metal materials, forming a thick gold plating layer has a significant impact on costs. By designing the thickness of the gold plating layer to be approximately 0.05 to 1 μm, it is expected that environmental resistance can be effectively improved. The optimal thickness of the gold plating layer is selected considering the balance between the desired environmental resistance performance and cost.

[0072] In a later step, a wire made of gold or aluminum is bonded to the third plating layer 16 by wire bonding. The conductive connection portion formed in this way consists of a wiring portion 12 having a metal wiring layer, a metal sputtered film 13, a first plating layer 14, a second plating layer 15, a third plating layer 16, and a bonding wire 5. In this embodiment, the corrosion resistance of the conductive connection portion is improved by using a gold wire, which has excellent environmental resistance, as the bonding wire 5. In general wire bonding, an intermetallic compound layer of gold and aluminum is formed between the aluminum electrode and the bonding wire. It is known that if this intermetallic compound layer is corroded by halogen gases such as bromine contained in resin parts and corrosion products are formed, the bonding strength between the aluminum electrode and the bonding wire decreases. In the conductive connection portion of this embodiment, since the connection is made between the third plating layer 16 made of gold and a gold wire, an intermetallic compound layer of gold and aluminum is not formed. Therefore, even if the semiconductor pressure sensor 1 is used continuously in an environment where corrosive components such as halogen gases are generated, the decrease in bonding strength due to corrosion of the conductive connection portion can be suppressed.

[0073] Here, we compare the configurations of the two plating layers. Configuration pattern 1 consists of a first plating layer 14 made of nickel and a third plating layer 16 made of gold. Configuration pattern 2, as shown in this embodiment, consists of a first plating layer 14 made of nickel, a second plating layer 15 made of palladium or platinum, and a third plating layer 16 made of gold. In wire bonding, surface roughness and hardness greatly affect the bonding strength. It is known that in configuration pattern 2, the deposited particles of the gold plating film tend to be finer than in configuration pattern 1, resulting in a flatter average surface roughness on the outermost surface of the electrode. Furthermore, configuration pattern 2 is advantageous for bonding because the surface hardness of the gold plating film is higher than in configuration pattern 1.

[0074] By designing the thickness of the second plating layer 15 to be approximately 0.05 to 0.5 μm, the third plating layer 16 can be made to have the surface roughness and hardness necessary for good bonding, so that the semiconductor pressure sensor 1 can obtain a conductive connection part with high bonding strength. Furthermore, in order to improve connection reliability and corrosion resistance in configuration pattern 1, it is necessary to suppress the diffusion of nickel into the gold plating layer and minimize the effects of defects in the plating film such as pinholes. Therefore, it is necessary to make the gold plating layer thicker, which presents a challenge in configuration pattern 1 as it results in high costs. On the other hand, in configuration pattern 2, since the second plating layer 15 is provided, the diffusion of nickel into the gold plating layer can be suppressed. Also, by increasing the number of plating layers, defects in the lower plating film can be filled in by the upper plating film, thus minimizing the effects of defects in the plating film. Therefore, the third plating layer 16 made of gold can be made thinner, so that the semiconductor pressure sensor 1 can be made low cost and have excellent environmental resistance.

[0075] The dicing process is a process of separating the semiconductor pressure sensor 1 into individual pieces. The semiconductor pressure sensor 1 shown in Figure 1 can be obtained up to the plating layer formation process described above. Since multiple semiconductor pressure sensors 1 are manufactured on a wafer, the semiconductor pressure sensor 1 is separated into individual pieces by dicing.

[0076] Furthermore, the applications of the semiconductor pressure sensor 1 disclosed herein are not limited to vehicles equipped with EGR or exhaust gas emission control devices. In vehicles equipped with fuel cells, trace amounts of corrosive components may be generated from the FC stack and other components, potentially creating an environment containing corrosive components. Therefore, corrosion resistance is required for semiconductor pressure sensors. For this reason, the semiconductor pressure sensor 1 disclosed herein, which has excellent corrosion resistance, is also suitable for applications in such environments.

[0077] As described above, the semiconductor device according to Embodiment 1 comprises a semiconductor substrate 20 having a semiconductor element portion 10, a wiring portion 12 having a metal wiring layer provided on one side of the semiconductor element portion 10, and a protective layer 11 made of a silicon compound provided on the semiconductor element portion 10 and the wiring portion 12, wherein one or more portions of the wiring portion 12 are exposed through electrode openings 4 that penetrate the protective layer 11, and the exposed wiring portion 12a is the portion of the wiring portion 12 exposed at the electrode openings 4, and the portion of the protective layer 11 adjacent to the exposed wiring portion 12a However, since the wiring portion 12 is covered with a metal sputtered film 13, the metal sputtered film 13 is covered with a first plating layer 14 made of nickel, the first plating layer 14 is covered with a second plating layer 15 made of a precious metal material, and the second plating layer 15 is covered with a third plating layer 16 made of a different precious metal material than the second plating layer 15, the wiring portion 12 is not exposed to the outside, and highly corrosion-resistant dissimilar materials are laminated on the wiring portion 12, so the penetration of corrosive components into the metal wiring layer made of the corrosive material can be suppressed. In addition, since good adhesion is ensured between the laminated highly corrosion-resistant dissimilar materials, the occurrence of adhesion defects such as peeling is suppressed, so the penetration of corrosive components into the metal wiring layer made of the corrosive material can be suppressed.

[0078] Furthermore, by providing a second plating layer 15 made of a precious metal material between the first plating layer 14 made of nickel and the third plating layer 16 made of a precious metal material, the diffusion of the outermost surface material of the first plating layer 14 to the third plating layer 16 can be suppressed. As the penetration of corrosive components into the metal wiring layer made of the corrosive material is suppressed, and the diffusion of the outermost surface material of the first plating layer 14 to the third plating layer 16 is suppressed, a semiconductor device such as a semiconductor sensor or signal processing circuit 50 with high precision and high reliability can be obtained even when used continuously in an environment affected by corrosive substances.

[0079] When viewed perpendicular to the main surface 9a of the semiconductor substrate 20, if the sidewall of the protective layer 11 at the electrode opening 4 is inclined toward the wiring portion 12 such that the opening area narrows, the angle between the surface of the wiring portion 12 and the sidewall can be made greater than a right angle. This suppresses the generation of voids in the portion between the surface of the wiring portion 12 and the sidewall during the initial stages of film formation. Because the generation of voids is suppressed, defects such as peeling of the metal sputtered film 13 can be suppressed. Because defects such as peeling of the metal sputtered film 13 are suppressed, semiconductor devices such as semiconductor sensors or signal processing circuits 50 can maintain high reliability.

[0080] When the metal sputtered film 13 is formed from the same material as the wiring portion 12, high adhesion can be ensured at the interface between the wiring portion 12 and the metal sputtered film 13. Furthermore, when the metal sputtered film 13 is aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper, good adhesion can be maintained between the metal sputtered film 13, such as aluminum silicon, and the silicon nitride film, which is the protective layer 11 and insulating film. Because of the good adhesion between the metal sputtered film 13 and the protective layer 11, defects such as peeling of the metal sputtered film 13 can be suppressed. Since defects such as peeling of the metal sputtered film 13 are suppressed, semiconductor devices such as semiconductor sensors or signal processing circuits 50 can maintain high reliability.

[0081] If the first plating layer 14 is a plating layer made of nickel containing phosphorus, the corrosion resistance and acid resistance of the first plating layer 14 can be improved. Because the corrosion resistance and acid resistance of the first plating layer 14 are improved, the corrosion resistance and acid resistance of the underlying metal sputter film 13 and wiring portion 12 can be further improved.

[0082] If the second plating layer 15 is made of palladium or platinum, the material of the second plating layer 15 can be made of palladium or platinum, which are cheaper than gold, and the thickness of the third plating layer 16 made of gold can be reduced, thereby reducing the cost of semiconductor devices such as semiconductor sensors or signal processing circuits 50. Also, if the third plating layer 16 is made of gold, the third plating layer 16 made of gold, which has the best corrosion resistance, is formed on the outermost surface, thereby improving the environmental resistance of semiconductor devices such as semiconductor sensors or signal processing circuits 50.

[0083] When the semiconductor pressure sensor 1 according to Embodiment 1 comprises a semiconductor device with the above-described configuration and one or more pressure sensing units connected to the wiring section 12, the intrusion of corrosive components into the metal wiring layer made of the corrosive material is suppressed, and the diffusion of the material of the first plating layer 14 to the third plating layer 16 on the outermost surface is suppressed. Therefore, even when used continuously in an environment affected by corrosive substances, a semiconductor pressure sensor 1 with high reliability can be obtained. Furthermore, when the pressure sensing unit is a piezoresistive element 3 formed on one side of the semiconductor element section 10 opposite to the semiconductor substrate 20 side, the semiconductor pressure sensor 1 can be miniaturized, made more sensitive, and made more accurate.

[0084] If the pressure sensor device 100 according to Embodiment 1 comprises a semiconductor pressure sensor 1 with the above-described configuration and a signal processing circuit 50 connected to a piezoresistive element 3 via a wiring section 12 and processing the output of the piezoresistive element 3, then a highly reliable pressure sensor device 100 can be obtained even when used continuously in an environment affected by corrosive substances.

[0085] If the exhaust gas recirculation system 200 according to Embodiment 1 includes a pressure sensor device 100 with the above-described configuration and an exhaust gas recirculation device 101 connected to the pressure sensor device 100, which controls the engine based on the exhaust gas pressure detected by the pressure sensor device 100, then the pressure of exhaust gas such as nitrogen oxides or gases containing halogens such as chlorine can be measured normally while maintaining high reliability, thus providing a highly reliable exhaust gas recirculation system 200.

[0086] Embodiment 2. The semiconductor pressure sensor 1 according to Embodiment 2 will be described. Figure 7 is a schematic plan view of the semiconductor pressure sensor 1 according to Embodiment 2, showing the protective layer 11 and omitting the wiring portion 12. Figure 8 is a schematic cross-sectional view of the main part of the semiconductor pressure sensor cut at the C-C cross-sectional position in Figure 7, showing the electrode opening 4. Figure 9 is a schematic cross-sectional view of the main part of another semiconductor pressure sensor 1 according to Embodiment 2, cut at the same position as in Figure 8. Figure 10 is a schematic plan view of the main part of the semiconductor pressure sensor 1 shown in Figure 9, showing the part inside the additional metal sputtered film 13a viewed perpendicular to the main surface 9a after removing the plating film. The semiconductor pressure sensor 1 according to Embodiment 2 has a different metal sputtered film configuration from Embodiment 1. The configurations shown in Figures 8 and 9 are modified versions of the configuration shown in Figure 3 of Embodiment 1.

[0087] <Modification 1: Enlarged Pattern of Metal Sputtered Film 13> First, Modification 1 will be explained using Figure 8. In the semiconductor pressure sensor 1 shown in Figure 3 of Embodiment 1, the metal sputtered film 13 was formed to cover the exposed wiring portion 12a of the wiring portion 12 having a metal wiring layer, and the portion of the protective layer 11 made of a silicon compound adjacent to the exposed wiring portion 12a. In Modification 1, in addition to the configuration in Figure 3, as shown in Figure 8, the metal sputtered film 13 is formed in a pattern such that the film extends in a direction parallel to the main surface 9a of the second silicon substrate 9 (the horizontal direction in the figure).

[0088] The upper layer of the metal sputtered film 13 has the same configuration as in Embodiment 1, with a first plating layer 14 made of nickel, a second plating layer 15 made of a noble metal material, and a third plating layer 16 made of a noble metal material different from the second plating layer 15, provided in that order. As shown in Figure 7, the metal sputtered film 13, including the upper plating layer, can be extended in a direction parallel to the main surface 9a, within a range where adjacent electrodes do not come into contact with each other.

[0089] By expanding the metal sputtered film 13 in this way, the path for corrosive substances that penetrate from the outside through the interface between the protective layer 11 and the first plating layer 14 to reach the wiring portion 12 can be expanded. Since the path for corrosive substances is expanded and the penetration path is lengthened, the lifespan of the semiconductor pressure sensor 1 against failure due to corrosion of the electrode portion can be extended.

[0090] <Modification 2: Separation Pattern of Metal Sputtered Film 13> Next, Modification 2 will be explained using Figures 9 and 10. As shown in Figure 9, an additional metal sputtered film 13a is provided on one side of the protective layer 11 that is opposite to the semiconductor substrate 20, with a gap between it and the metal sputtered film 13, surrounding the metal sputtered film 13. The side of the additional metal sputtered film 13a opposite to the semiconductor substrate 20 is covered with an additional first plating layer 14a made of nickel. The side of the additional first plating layer 14a opposite to the semiconductor substrate 20 is covered with an additional second plating layer 15a made of a noble metal material. The side of the additional second plating layer 15a opposite to the semiconductor substrate 20 is covered with an additional third plating layer 16a made of a different noble metal material than the additional second plating layer 15a.

[0091] As shown in Figure 10, the additional metal sputtered film 13a is patterned on the protective layer 11 made of a silicon compound, surrounding the outer periphery of the electrode opening 4 and the metal sputtered film 13, as indicated by the dashed line, and is separated from the metal sputtered film 13 covering the electrode opening 4. In the configuration shown in Figure 10, since the electrode opening 4 is formed in a circular shape, the metal sputtered film 13 is formed in a circular shape, and the additional metal sputtered film 13a is formed in a circular ring shape to surround the electrode opening 4. When the electrode opening 4 is formed in a rectangular shape, it is preferable that the metal sputtered film 13 is formed in a rectangular shape, and the additional metal sputtered film 13a is formed in a rectangular ring shape to surround the electrode opening 4.

[0092] The first plating layer 14 and the additional first plating layer 14a are provided independently of each other. The second plating layer 15 and the additional second plating layer 15a are provided independently of each other. The third plating layer 16 and the additional third plating layer 16a are provided continuously and integrally. In order to make the third plating layer 16 and the additional third plating layer 16a a continuous shape, it is desirable to set the distance between the second plating layer 15 and the additional second plating layer 15a to within twice the thickness of the third plating layer 16.

[0093] By forming the metal sputtered film 13 and the additional metal sputtered film 13a separately, it is possible to stop corrosive substances from penetrating from the outside through the interface between the protective layer 11 and the additional first plating layer 14a, and further penetrating through the additional metal sputtered film 13a. Therefore, it is possible to suppress the corrosive substances from reaching the wiring section 12, resulting in a conductive connection section with excellent corrosion resistance. Because it has a conductive connection section with excellent corrosion resistance, the semiconductor pressure sensor 1 can maintain high reliability even when used for a long time in an environment containing corrosive substances.

[0094] <Method for Manufacturing Semiconductor Pressure Sensor 1> A method for manufacturing a semiconductor pressure sensor 1 according to Embodiment 2 of this disclosure will be described. The method for manufacturing a semiconductor pressure sensor 1 is the same as in Embodiment 1 and includes the following steps as shown in Figure 6: SOI structure formation step (S11), diaphragm formation step (S12), resistor formation step (S13), wiring formation step (S14), protective film formation step (S15), electrode opening formation step (S16), metal sputtered film formation step (S17), plating layer formation step (S18), and dicing step (S19). The SOI structure formation step, diaphragm formation step, resistor formation step, wiring formation step, protective film formation step, electrode opening formation step, plating layer formation step, and dicing step are the same as the method for manufacturing a semiconductor pressure sensor 1 shown in Embodiment 1, except for the metal sputtered film formation step, so their description will be omitted.

[0095] In the metal sputtering film formation process, first, aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper is deposited by sputtering or the like using the same material and method as the wiring section 12 having the metal wiring layer. Next, the metal sputtering film is patterned by photolithography so that the metal sputtering film 13 covers only the necessary areas, such as the exposed wiring section 12a of the wiring section 12 having the metal wiring layer and the portion of the protective layer 11 adjacent to the exposed wiring section 12a. In the modified example 2, the metal sputtering film is patterned by photolithography so that an additional metal sputtering film 13a is formed.

[0096] The metal sputtered film 13 and the additional metal sputtered film 13a in this embodiment can be formed simply by changing the reticle to one with a different pattern than the one used in Embodiment 1 and performing photolithography. Therefore, without changing the process, further improvements in environmental resistance can be achieved at the same cost level as Embodiment 1. When it is necessary to significantly extend the lifespan of semiconductor devices in harsh environments containing corrosive substances, the configuration of the semiconductor pressure sensor 1 in this embodiment is extremely effective, and the semiconductor pressure sensor 1 can be used for a long time even in environments exposed to corrosive components.

[0097] As described above, in the semiconductor pressure sensor 1 according to the modified example 2 of Embodiment 2, an additional metal sputtered film 13a is provided on one side of the protective layer 11 opposite to the semiconductor substrate 20, with a gap between it and the metal sputtered film 13 and surrounding it. The side of the additional metal sputtered film 13a opposite to the semiconductor substrate 20 is covered with an additional first plating layer 14a made of nickel. The side of the additional first plating layer 14a opposite to the semiconductor substrate 20 is covered with an additional second plating layer 15a made of a precious metal material. The side of the additional second plating layer 15a opposite to the semiconductor substrate 20 is covered with an additional third plating layer 16a made of a precious metal material different from the additional second plating layer 15a. Therefore, the intrusion of corrosive components and the like into the wiring portion 12, which is made of the metal wiring layer of the semiconductor pressure sensor 1, from the outside can be further suppressed.

[0098] Embodiment 3. A semiconductor pressure sensor 1 according to Embodiment 3 will be described. Figure 11 is a schematic cross-sectional view showing the main part of the semiconductor pressure sensor 1 according to Embodiment 3, cut at the same position as in Figure 3, and Figure 12 is a schematic plan view showing the main part of the semiconductor pressure sensor 1 shown in Figure 11, showing the metal sputtered film 13b viewed perpendicular to the main surface 9a. The configuration of the metal sputtered film 13b in the semiconductor pressure sensor 1 according to Embodiment 3 differs from that of Embodiment 1. The configuration shown in Figure 11 is a modified example of the configuration shown in Figure 3 of Embodiment 1.

[0099] In the semiconductor pressure sensor 1 shown in Figure 3 of Embodiment 1, the metal sputtered film 13 was formed to extend continuously as a film in a direction parallel to the main surface 9a of the second silicon substrate 9 (the lateral direction in the figure). In this embodiment, as shown in Figure 12, the metal sputtered film 13b has a mesh structure consisting of a plurality of through holes 13b1. The wiring portion 12 and the first plating layer 14 are in contact at the portions of the through holes 13b1.

[0100] This configuration allows the metal sputtered film 13b to have a larger contact area with the first plating layer 14. A known technique involves forming multiple recesses on the surface of the material during pre-plating treatments such as etching to improve the adhesion of the plating film through an anchoring effect. However, there are limitations to forming multiple recesses on the surface by etching, and further improvements in adhesion require other methods. In this embodiment, a mesh structure is formed on the metal sputtered film 13b during the photolithography pattern formation of the metal sputtered film 13b, thereby increasing the contact area between the metal sputtered film 13b and the first plating layer 14. Increasing the contact area improves the adhesion between the metal sputtered film 13b and the first plating layer 14, further improving the adhesive strength between the metal sputtered film 13b and the first plating layer 14. Further improvement in the adhesive strength between the metal sputtered film 13b and the first plating layer 14 allows for a more reliable configuration in the conductive connection portion of the semiconductor pressure sensor 1. The mesh structure can be freely designed as long as it increases the contact area, such as a grid or honeycomb shape.

[0101] A method for manufacturing a semiconductor pressure sensor 1 according to Embodiment 3 of this disclosure will now be described. Similar to Embodiment 1, the method for manufacturing the semiconductor pressure sensor 1 includes the following steps as shown in Figure 6: SOI structure formation step (S11), diaphragm formation step (S12), resistor formation step (S13), wiring formation step (S14), protective film formation step (S15), electrode opening formation step (S16), metal sputtered film formation step (S17), plating layer formation step (S18), and dicing step (S19). The SOI structure formation step, diaphragm formation step, resistor formation step, wiring formation step, protective film formation step, electrode opening formation step, plating layer formation step, and dicing step, excluding the metal sputtered film formation step, are the same as the method for manufacturing a semiconductor pressure sensor 1 shown in Embodiment 1, so their description will be omitted.

[0102] In the metal sputtered film formation process, first, aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper is deposited by sputtering or the like using the same material and method as the wiring section 12 having the metal wiring layer. Next, the metal sputtered film 13b is patterned by photolithography so that it covers only the necessary areas, such as the exposed wiring section 12a of the wiring section 12 having the metal wiring layer and the portion of the protective layer 11 adjacent to the exposed wiring section 12a. Simultaneously with this patterning of the metal sputtered film, multiple through holes 13b1 are also formed. Dry etching such as ion milling is preferred for patterning the metal sputtered film 13b.

[0103] The metal sputtered film 13b and the multiple through-holes 13b1 in this embodiment can be formed simply by changing the reticle to one on which a different pattern is drawn than the pattern used in Embodiment 1 or Embodiment 2, and then performing photolithography. Therefore, without changing the process, it is possible to further improve the adhesion between the metal sputtered film 13b and the first plating layer 14 at a cost equivalent to that of Embodiment 1 or Embodiment 2. Because the adhesion is improved, the loss of protective function of the multiple plating layers provided to enhance environmental resistance due to peeling of the film at the conductive connection part is suppressed, so that the semiconductor pressure sensor 1 can be used stably for a long time. In addition, the high reliability of the semiconductor pressure sensor 1 can be maintained.

[0104] In this embodiment, the configuration of the metal sputtered film 13b, excluding the through-hole 13b1 portion, may be either the configuration shown in Figure 3 of Embodiment 1, or the configuration shown in Figure 8 or Figure 9 of Embodiment 2. The combination of structures for the metal sputtered film 13b may be freely selected according to the desired performance.

[0105] As described above, in the semiconductor pressure sensor 1 according to Embodiment 3, since the metal sputtered film 13b has a mesh structure consisting of a plurality of through holes 13b1, the contact area between the metal sputtered film 13b and the first plating layer 14 can be increased, thereby increasing the adhesion between the metal sputtered film 13b and the first plating layer 14, and further improving the adhesive strength between the metal sputtered film 13b and the first plating layer 14. By further improving the adhesive strength between the metal sputtered film 13b and the first plating layer 14, higher reliability can be obtained in the conductive connection part of the semiconductor pressure sensor 1, and thus the semiconductor pressure sensor 1 can maintain high reliability.

[0106] Furthermore, while this disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but are applicable individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are envisioned within the scope of the art disclosed in this specification. For example, these include modifying, adding or omitting at least one component, or even extracting at least one component and combining it with a component from another embodiment.

[0107] 1 Semiconductor pressure sensor, 2 Diaphragm, 3, 3a, 3b, 3c, 3d Piezoresistive element, 4 Electrode opening, 5 Bonding wire, 6 Cavity, 6a Recess, 7 First silicon substrate, 7a Main surface, 8 Embedded oxide film, 9 Second silicon substrate, 9a Main surface, 9b Main surface, 10 Semiconductor element part, 11 Protective layer, 12 Wiring part, 12a Exposed wiring part, 13 Metal sputtered film, 13a Additional metal sputtered film, 13b Metal sputtered film, 13b1 Through hole, 14 First plating layer, 14a Additional first plating layer, 15 Second plating layer, 15a Additional second plating layer, 16 Third plating layer, 16a Additional third plating layer, 20 Semiconductor substrate, 50 Signal processing circuit, 51 Wheatstone bridge, 100 Pressure sensor device, 101 Exhaust gas recirculation device, 200 exhaust gas recirculation system

Claims

1. A semiconductor device comprising: a semiconductor substrate having a semiconductor element portion formed on one of its main surfaces; a wiring portion having a metal wiring layer provided on one side of the semiconductor element portion opposite to the semiconductor substrate side; and a protective layer made of a silicon compound provided on the side of the semiconductor element portion and the wiring portion opposite to the semiconductor substrate side, wherein one or more portions of the wiring portion opposite to the semiconductor substrate side are exposed through electrode openings penetrating the protective layer; the exposed wiring portion, which is the portion of the wiring portion exposed at the electrode openings, and the portion of the protective layer adjacent to the exposed wiring portion are covered with a metal sputtered film; the side of the metal sputtered film opposite to the semiconductor substrate side is covered with a first plating layer made of nickel; the side of the first plating layer opposite to the semiconductor substrate side is covered with a second plating layer made of a noble metal material; and the side of the second plating layer opposite to the semiconductor substrate side is covered with a third plating layer made of a different noble metal material than the second plating layer.

2. The semiconductor device according to claim 1, wherein an additional metal sputtered film is provided in the protective layer on one side opposite to the semiconductor substrate, with a gap between it and the metal sputtered film, the side of the additional metal sputtered film opposite to the semiconductor substrate is covered with an additional first plating layer made of nickel, the side of the additional first plating layer opposite to the semiconductor substrate is covered with an additional second plating layer made of a noble metal material, and the side of the additional second plating layer opposite to the semiconductor substrate is covered with an additional third plating layer made of a noble metal material different from the additional second plating layer.

3. The semiconductor device according to claim 1 or 2, wherein, when viewed perpendicular to the main surface of the semiconductor substrate, the side wall of the protective layer at the electrode opening is inclined such that the opening area narrows toward the wiring portion.

4. The semiconductor device according to any one of claims 1 to 3, wherein the metal sputtered film has a mesh structure consisting of a plurality of through holes.

5. The semiconductor device according to any one of claims 1 to 4, wherein the metal sputtered film is formed of the same material as the wiring portion.

6. The semiconductor device according to any one of claims 1 to 5, wherein the metal sputtered film is aluminum, aluminum silicon, aluminum copper, or aluminum silicon copper.

7. The semiconductor device according to any one of claims 1 to 6, wherein the first plating layer is a plating layer made of nickel containing phosphorus.

8. The semiconductor device according to any one of claims 1 to 7, wherein the second plating layer is a plating layer made of palladium or platinum.

9. The semiconductor device according to any one of claims 1 to 8, wherein the third plating layer is a gold plating layer.

10. A semiconductor pressure sensor comprising a semiconductor device as described in any one of claims 1 to 9, and one or more pressure sensing units connected to the wiring portion.

11. The semiconductor pressure sensor according to claim 10, wherein the pressure sensing unit is a piezoresistive element formed on one side of the semiconductor element unit that is opposite to the side of the semiconductor substrate.

12. A pressure sensor device comprising a semiconductor pressure sensor as described in claim 11, and a signal processing circuit connected to the piezoresistive element via the wiring section for processing the output of the piezoresistive element.

13. An exhaust gas recirculation system comprising: a pressure sensor device as described in claim 12; and an exhaust gas recirculation device connected to the pressure sensor device, which controls the engine based on the exhaust gas pressure detected by the pressure sensor device.

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