Semiconductor junctions and semiconductor devices

Abstract

To provide a semiconductor junction and a semiconductor device that suppress ion migration, and are superior in corrosion resistance at the junction, high in junction strength, and highly reliable.SOLUTION: There are provided: semiconductor junctions A, B, C, and D which are formed of at least two semiconductor constituent members and silver-containing junction material layers 20, 21a, 21b, 22, 23, and 24 joining the semiconductor constituent members together, a corrosion inhibitor coating layer 19 being provided in contact with the silver-containing junction material layers; and a semiconductor device including them.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a semiconductor junction and a semiconductor device. In particular, the present invention relates to a junction and a semiconductor device that suppress electromigration in a junction formed by a silver-containing bonding material layer, have excellent corrosion resistance, high bonding strength, and high reliability.

Background Art

[0002] Power semiconductor modules are widely applied in fields where efficient power conversion is required. For example, the application area is expanding in the field of power electronics such as industrial equipment, electric vehicles, and household appliances. These power semiconductor modules incorporate switching elements and diodes, and Si (silicon) semiconductors or SiC (silicon carbide) semiconductors are used for the elements.

[0003] As members containing metals such as copper (Cu) in power semiconductor modules, for example, conductive connection members such as lead frames and conductive bonding members such as brazing materials and solder materials have been used. Copper and copper alloys react with oxygen, water, etc. in the air, and oxidation and corrosion tend to progress. Therefore, a method of forming a rust preventive film on the surface of copper and copper alloy members has been used. As a rust preventive agent for copper and copper alloys, benzotriazole or its derivative is used and is commercially available.

[0004] A copper-based lead frame with ensured resin adhesion is known by setting the N1s / Cu2p spectral peak intensity ratio of the surface of a film formed by benzotriazole or its derivative on the copper or copper alloy surface within a specific range (for example, refer to Patent Document 1).

[0005] Also, a technique of decomposing a rust preventive agent before the wire bonding and resin sealing processes by applying a non-benzotriazole-based fatty acid ester-based or amine-based rust preventive agent that completely decomposes by heating around 250°C and does not generate a residue to a base metal lead frame is known (for example, refer to Patent Document 2).

[0006] Furthermore, a sealing resin composition that exhibits high adhesion even to lead frames on which a rust-preventive coating has been formed using a benzotriazole-based rust inhibitor is also known (see, for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 9-116066 [Patent Document 2] Japanese Patent Publication No. 2003-197827 [Patent Document 3] Japanese Patent Publication No. 2010-65160 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In multilayer substrates (laminated structures of conductive and insulating substrates) that constitute semiconductor devices, problems arise where the adhesion between these components and the sealing material decreases or the strength decreases near the brazing material used to bond the conductive plate to the insulating substrate, or the bonding material used to bond the semiconductor element to the conductive plate.

[0009] Generally, conductive plates made of copper or copper alloy that constitute a laminated substrate are coated with a benzotriazole-based rust inhibitor during manufacturing, similar to the copper lead frames disclosed in Patent Documents 1 to 3. However, analysis has revealed that these rust inhibitors hardly remain on semiconductor devices after assembly and manufacturing. In recent years, corrosion of metal components has become a problem due to the operating environment of semiconductor modules, the increasing temperatures of semiconductor elements, and the narrowing of the pitch of metal components such as Cu. [Means for solving the problem]

[0010] In view of the above analysis results, the inventors realized that under corrosive environments such as an H2S gas atmosphere, sulfur ions easily reach the metal surface of the components constituting the semiconductor device, and that the cause of corrosion lies in the generation and growth of sulfides. In particular, they realized that silver-containing brazing materials and conductive bonding members containing silver particles are the starting points for migration, and solved the problem by covering the joints made of these members, thus completing the present invention.

[0011] According to one embodiment, the present invention relates to a semiconductor junction, which is formed by at least two semiconductor components and a silver-containing bonding material layer that bonds the semiconductor components, and a rust-preventive coating layer is provided in contact with the silver-containing bonding material layer.

[0012] In the semiconductor junction, the rust inhibitor is preferably benzotriazole or a derivative thereof, or a carboxylate or nitrite of an amine.

[0013] In the semiconductor junction, it is preferable that the silver-containing bonding material layer includes a brazing material, a sintered material, or a soldering material.

[0014] In the semiconductor junction, the rust-preventive coating layer is preferably 1 nm to 10 nm thick.

[0015] In the semiconductor junction, it is preferable that at least one of the semiconductor components is a component containing copper or a copper alloy, and that the rust-preventive coating layer coats the copper or copper alloy.

[0016] In the semiconductor junction, it is preferable that the at least two semiconductor components are selected from an insulating substrate and a conductive plate, a conductive plate and a semiconductor element, a conductive plate and a heat sink, or a semiconductor element and a conductive connecting member.

[0017] According to another embodiment of the present invention, there is provided a semiconductor device including a semiconductor element mounted on a laminated substrate including an insulating substrate and a conductive plate, and a sealing material for sealing the semiconductor element, and relates to a semiconductor device including the semiconductor joint portion according to any one of the above items.

[0018] In the semiconductor device, it is preferable that the sealing material contains a silicone gel.

[0019] According to another embodiment of the present invention, there is provided a method of manufacturing a semiconductor device, including the following steps a) A step of joining a semiconductor element to a laminated substrate including an insulating substrate and a conductive plate joined to the insulating substrate with a first bonding material using a second bonding material b) A step of sealing a sealed member including the semiconductor element and the laminated substrate with a sealing material including, at least one of the first bonding material or the second bonding material is a silver-containing bonding material, and after the step a) and before the step b), the following step c) A step of forming a rust preventive coating layer in contact with the layer of the silver-containing bonding material relates to a method of manufacturing a semiconductor device.

[0020] In the method of manufacturing the semiconductor device, it is preferable that the first bonding material is a silver-containing bonding material, and the step c) includes a step of forming a rust preventive coating layer in contact with the layer of the silver-containing bonding material at the joint between the insulating substrate and the conductive plate.

[0021] In the method of manufacturing the semiconductor device, it is preferable that the second bonding material is a silver-containing bonding material, and the step c) includes a step of forming a rust preventive coating layer in contact with the layer of the silver-containing bonding material at the joint between the laminated substrate and the semiconductor element.

[0022] In the method of manufacturing the semiconductor device, the step a) preferably includes a step of joining a heat sink to the laminated substrate using a third bonding material, and the step c) preferably includes a step of forming a rust preventive coating layer in contact with the layer of the silver-containing bonding material at the joint between the laminated substrate and the heat sink.

[0023] In the method for manufacturing the semiconductor device, step a) includes a step of joining a conductive connection member to the semiconductor element using a fourth bonding material, the fourth bonding material is a silver-containing bonding material, and step c) preferably includes a step of forming a rust preventive coating layer in contact with the layer of the silver-containing bonding material at the joint between the semiconductor element and the conductive connection member.

[0024] In the method for manufacturing the semiconductor device, it is preferable to include a wire bonding step after step a) and before step b), and to perform step c) after the wire bonding step and before step b).

Advantages of the Invention

[0025] According to the present invention, it is possible to provide a semiconductor joint having excellent corrosion resistance, high joint strength, and high reliability, which can suppress ion migration, and a semiconductor device including the same.

Brief Description of the Drawings

[0026] [Figure 1] FIG. 1 is a conceptual cross-sectional view showing a cross-sectional structure of a semiconductor device according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of part A in FIG. 1, and is a conceptual cross-sectional view showing a cross-sectional structure of a semiconductor joint according to an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0027] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. Also, in the drawings, there are parts where members constituting the device are described with enlargement or reduction for the purpose of explanation, and the dimensions of each member and the relative dimensions of a plurality of members do not limit the present invention.

[0028] <00The present invention relates to a semiconductor junction according to a first embodiment. Furthermore, according to a second embodiment, it relates to a semiconductor device equipped with said semiconductor junction. First, the overall configuration of the semiconductor device will be described with reference to Figure 1.

[0029] Figure 1 is a conceptual cross-sectional view of a power semiconductor module, which is an example of a semiconductor device according to a second embodiment of the present invention, and Figure 2 is an enlarged cross-sectional view of portion A in Figure 1. Referring to Figures 1 and 2, the power semiconductor module has a laminated substrate 12 laminated on a heat sink 13 via a third bonding material layer 23, and semiconductor elements 11 laminated on the laminated substrate 12 via a second bonding material layer 22. A lead frame 17, which is an example of a conductive connecting member, is bonded to the semiconductor element 11 by a fourth bonding material layer 24, and the lead frame 17 is connected to external terminals (not shown) or wiring terminals on the laminated substrate. The external terminal 15 may be connected to the semiconductor element 11 by a conductive connecting member such as an aluminum wire (not shown). A case 16 containing the external terminal 15 is bonded to the heat sink 13, and the inside of the case 16 is filled with a sealing material 18. The rust-preventive coating layer 19 is formed in such a manner that it covers the surface in which the members constituting the joints A, B, C, and D come into contact with the sealing material 18.

[0030] The semiconductor element 11 is a power chip such as an IGBT (Insulated Gate Bipolar Transistor) or a diode chip, and may be a Si device, or a wide-bandgap semiconductor device such as a SiC device, GaN device, diamond device, or ZnO device. These devices may also be used in combination. For example, a hybrid module using a Si-IGBT and a SiC-SBD can be used. The number of semiconductor elements mounted may be one or multiple. The semiconductor element 11 includes a back electrode and a front electrode (neither shown) that are bonded to the laminated substrate 12.

[0031] The laminated substrate 12 can be composed of an insulating substrate 122, a first conductive plate 121 bonded to one main surface of the insulating substrate 122 by a first bonding material layer 20, and second conductive plates 123a and 123b bonded to the other main surface of the insulating substrate 122 by first bonding material layers 21a and 21b. The first bonding material layers 20, 21a and 21b are all bonding material layers provided in contact with the insulating substrate 122, and in this specification, they are collectively referred to as the first bonding material layer. As the insulating substrate 122, a material with excellent electrical insulation and thermal conductivity can be used. Examples of materials for the insulating substrate 122 include Al2O3, AlN, and SiN. In particular for high-voltage applications, a material that balances electrical insulation and thermal conductivity is preferred, and AlN and SiN can be used, but the material is not limited to these. As the first conductive plate 121 and the second conductive plates 123a and 123b, metallic materials such as Cu and Al, which have excellent processability, can be used. Furthermore, the conductive plate may be Cu or Al that has been treated with Ni plating or other processes for purposes such as rust prevention, or it may have a rust-preventive coating applied during the manufacturing process of the laminated substrate. Conductive plates with a thickness of approximately 0.15 to 0.8 mm are commonly used. Methods for arranging the first conductive plate 121 and the second conductive plates 123a and 123b on the insulating substrate 122 include direct copper bonding or active metal brazing. In the case of laminated substrates manufactured by direct bonding, the first bonding material layers 20, 21a and 21b may not be present.

[0032] In the illustrated embodiment, two second conductive plates 123a and 123b are joined discontinuously on an insulating substrate 122 by first bonding material layers 21a and 123b. Specifically, the two second conductive plates 123a and 123b are arranged separately so as to expose the insulating substrate 122. The distance (pitch) between the two second conductive plates 123a and 123b may be, for example, about 0.5 to 1.5 mm, but is not limited to a specific distance depending on the specifications of the semiconductor device. Generally, the narrower the pitch, the greater the risk of short circuits due to corrosion. However, corrosion prevention effects can be achieved even in semiconductor devices with relatively wide pitches. In other embodiments, there may be cases where only one second conductive plate is joined on the insulating substrate, or where three or more second conductive plates are joined.

[0033] In the illustrated embodiment, a lead frame 17, acting as a conductive connecting member, is bonded to the front electrode of the semiconductor element 11. The lead frame 17 may be made of a metal such as copper or a copper-containing alloy. A Ni or Ni alloy layer, or a Cr or Cr alloy layer, may be formed on the surface of the lead frame 17 by a plating method or the like, and it may also have a rust-preventive coating applied during the manufacturing process. In this case, the thickness of the Ni or Ni alloy layer, or the Cr or Cr alloy layer, can be about 20 μm or less. The lead frame 17 can be bonded to the front electrode of the semiconductor element 11 by a fourth bonding material layer 24 made of sintered material or solder material. Depending on the specifications of the semiconductor device, the lead frame 17 may not be present, and other conductive connecting members such as metal wires or metal pins (implant pins) may function similarly.

[0034] The heat sink 13 is bonded to the first conductive plate 121 by a third bonding material layer 23. The heat sink 13 is made of a metal with excellent thermal conductivity, such as copper or aluminum. Furthermore, the heat sink 13 can be coated with Ni or a Ni alloy to prevent corrosion. The heat sink 13 conducts heat generated by the semiconductor element 11 and transmitted through the laminated substrate 12 to the cooling device. The heat sink 13 itself may also function as the cooling device.

[0035] Case 16 houses the encapsulant and constitutes the outer surface of the semiconductor device. Case 16 may be made of a thermoplastic resin such as polyphenylene sulfide (PPS) or polybutylene terephthalate (PBT). Some semiconductor devices do not have a case; in such cases, a encapsulant made of a cured thermosetting resin constitutes the outer surface of the semiconductor device.

[0036] The case 16 is filled with a sealing material 18. The sealing material 18 insulates and seals the components, including the semiconductor element 11, the lead frame 17, the second bonding material layer 22, the third bonding material layer 23, the fourth bonding material layer 24, the rust inhibitor coating layer 19, the first bonding material layers 20, 21a, and 21b, and the external terminals 15. The sealing material 18 seals these components in such a manner that it does not come into contact with the bonding material layers to which the rust inhibitor coating layer 19 is applied or with other semiconductor components.

[0037] In one embodiment, the encapsulant 18 is preferably a silicone gel. Silicone gels are preferred because they have a stress-relaxing effect against vibration and thermal stress, and they have high insulating properties. However, compared to encapsulants made of thermosetting resins, they have a tendency to permeate sulfur-containing gases such as H2S, which can cause corrosion of silver-containing bonding materials. Therefore, corrosion problems are significant in semiconductor devices where the encapsulant 18 is made of silicone gel. The semiconductor bonding portion equipped with a rust-preventive coating layer in the present invention is particularly advantageous in semiconductor devices where the encapsulant 18 is made of silicone gel. Silicone gel is an organosilicon polymer whose main chain is composed of siloxane bonds. A silicone polymer with an elastic modulus of 100 MPa or less and an indentation (1 / 10 mm) of 0.1 to 500 can be preferably used. The encapsulant 18 made of silicone gel can be obtained by heating and curing an organic polysiloxane as the main component, with the addition of a crosslinking agent, catalyst, etc.

[0038] In another embodiment, the encapsulant 18 may be composed of a highly heat-resistant thermosetting resin composition. The thermosetting resin composition comprises a thermosetting resin main component, a curing agent, and an inorganic filler, and may optionally include a curing accelerator and additives.

[0039] The thermosetting resin main component is not particularly limited, and examples include epoxy resins, phenolic resins, maleimide resins, etc., that have heat resistance and high insulation properties. Among these, epoxy resins having at least two epoxy groups in one molecule are particularly preferred because they have high dimensional stability, water resistance, chemical resistance, and electrical insulation properties. Specifically, it is preferable to use aliphatic epoxy resins such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD ​​type epoxy resin, monofunctional epoxy resin, difunctional epoxy resin, alicyclic epoxy resins such as trifunctional or polyfunctional epoxy resin, or mixtures of these in any mixing ratio.

[0040] The inorganic filler may be a metal oxide or metal nitride with high thermal conductivity and a low coefficient of linear expansion. Examples include, but are not limited to, fused silica, silica (silicon oxide), alumina, aluminum hydroxide, titania, zirconia, aluminum nitride, talc, clay, mica, and glass fibers. It is preferable to use an inorganic filler with an average particle size of about 0.2 to 20 μm. The amount of inorganic filler added to the encapsulant 18 is preferably 100 to 600 parts by mass, and more preferably 200 to 400 parts by mass, when the mass of the matrix resin is 100 parts by mass. If the amount of inorganic filler is less than 100 parts by mass, the coefficient of thermal expansion of the encapsulant 18 may increase, making it prone to delamination and cracking. If the amount is greater than 600 parts by mass, the viscosity of the composition may increase, resulting in poor extrusion moldability.

[0041] The curing agent is not particularly limited as long as it can react with the thermosetting resin main component, preferably the epoxy resin main component, and cure, but it is preferable to use an acid anhydride-based curing agent. The amount of curing agent is preferably 50 parts by mass or more and 170 parts by mass or less, and more preferably 80 parts by mass or more and 150 parts by mass or less, per 100 parts by mass of the epoxy resin main component. If the amount of curing agent is less than 50 parts by mass, the glass transition temperature may decrease due to insufficient crosslinking, and if it is more than 170 parts by mass, it may be accompanied by a decrease in moisture resistance, high heat distortion temperature, and heat stability.

[0042] The thermosetting resin composition constituting the sealing material 18 may further contain a curing accelerator as an optional component. The amount of curing accelerator added is preferably 0.01 parts by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the main thermosetting resin component.

[0043] Whether the encapsulant 18 is a silicone gel or a thermosetting resin, the encapsulant 18 may contain optional additives as long as they do not impair its properties. Examples of additives include flame retardants, pigments for coloring the resin, plasticizers or silicone elastomers to improve crack resistance, etc., which can be added as appropriate depending on the type of encapsulant, but the types of additives are not limited to these. These optional components and their amounts can be appropriately determined by a person skilled in the art according to the specifications required for the semiconductor device and / or encapsulant.

[0044] Next, a semiconductor junction according to the first embodiment of the present invention will be described. The semiconductor junction is formed by at least two semiconductor components and a silver-containing bonding material layer that bonds the semiconductor components, and a rust-preventive coating layer is provided in contact with the silver-containing bonding material. In the following description, the term "semiconductor junction" may be omitted and simply referred to as "junction."

[0045] A semiconductor component is any component that constitutes a semiconductor device and can be joined by a silver-containing bonding material layer. Typically, the semiconductor component may be the component described in Figure 1, and conductive connecting members such as metal wires and metal pins (not shown). In one embodiment, at least one of the two semiconductor components may be a component containing copper or a copper alloy. Components containing copper or a copper alloy include, but are not limited to, the first conductive plate 121, the second conductive plates 123a and b, the heat sink 13, the lead frame 17, conductive connecting members such as metal pins, and connecting terminals, which are part of the laminated substrate 12. The copper or copper alloy portion of the component containing copper or a copper alloy can come into contact with the silver-containing bonding material layer to form a joint. The semiconductor components constituting the joint are at least two components joined by the silver-containing bonding material layer, but there may be three or more components.

[0046] The silver-containing bonding layer may be a layer made of any bonding material containing silver. Examples of silver-containing bonding materials include brazing materials, sintered materials, and solder materials. The silver content in the silver-containing bonding material is not particularly limited. For example, the bonding material may contain silver to an extent that is susceptible to corrosion by water vapor (H2O) or compounds containing sulfur (S) atoms, particularly H2S gas. Examples of brazing materials include silver brazing material. Silver brazing material can be an alloy containing about 40 to 90% by mass of silver and about 15 to 40% of copper, and optionally containing one or two metals selected from titanium (Ti), zinc (Zn), nickel (Ni), tin (Sn), and lithium (Li), with a liquidus temperature of about 620°C to 800°C. In particular, brazing material made of Ag-Cu-Ti alloy (Ti content of about 1 to 5% by mass) is preferred. Examples of sintered materials include sintered materials containing silver nanoparticles and / or silver microparticles, and optionally containing particles of gold, copper, nickel, carbon, etc., which are sintered and integrated together. These sintered materials are formed by heating and sintering a conductive paste or sheet containing metal particles and a resin binder to form a bonding layer (bonding material layer). The bonding layer may contain 50% by mass or more of silver, preferably 80% by mass or more. Examples of solder materials include, but are not limited to, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Sb-Ag-Cu, and Sn-Ag solder materials. Preferably, it may contain 1% by mass or more of Ag, and about 20% by mass or less. Bonding materials that may contain silver only as an unavoidable impurity may not be considered silver-containing bonding materials.

[0047] The rust inhibitor coating layer is a coating layer derived from a rust inhibitor, and may be a coating layer formed by the partial chemical bonding of the rust inhibitor with a silver-containing bonding material or a metal surface such as copper. The rust inhibitor may be a commercially available rust inhibitor for metals such as copper and silver. Examples include, but are not limited to, benzotriazole (BTA) or its derivatives, and amine carboxylates or nitrites. Specifically, dicyclohexylammonium nitride (DICHAN), monoethanolamine benzoate (MEA·BA), cyclohexylamine benzoate (CHA·BA), dicyclohexylammonium cyclohexane carboxylate (DICHA·CHC), cyclohexylamine cyclohexane carboxylate (CHA·CHC), dicyclohexylammonium benzoate (DICHA·BA), diisopropylammonium benzoate (DIPA·BA), dicyclohexylammonium acrylate (DICHA·AA), cyclohexylamine acrylate (CHA·AA), and dicyclohexylammonium salicylate (DICHA·SA) can be used, but are not limited to these. Any commercially available and known rust inhibitor with rust-preventive properties can be used.

[0048] Figure 2 is a conceptual diagram of a semiconductor junction according to this embodiment, comprising a second conductive plate 123a, b, a first bonding material layer 21a, b, an insulating substrate 122, and a rust inhibitor coating layer 19. In the embodiment shown in Figure 2, the first bonding material layer 21a is a silver-containing bonding material layer, and it is in contact with the second conductive plate 123a and the insulating substrate 122, bonding them together. A rust inhibitor coating layer 19 is provided on the surface of the first bonding material layer 21a that is not in contact with either the second conductive plate 123a or the insulating substrate 122. Such a surface can also be described as the exposed surface after bonding by the first bonding material layer 21a but before sealing in the semiconductor device manufacturing process. When the first bonding material layer 21a is a silver-containing bonding material layer, the silver-containing bonding material may typically be silver solder.

[0049] The rust inhibitor coating layer 19 is preferably provided in such a manner that it covers the entire exposed surface of the first bonding material layer 21a, and the exposed surface does not come into contact with the sealing material 18. This is to prevent contact between the first bonding material layer 21a and sulfur-containing gases or water that can permeate the sealing material 18. The thickness of the rust inhibitor coating layer 19 can be 1 nm to 10 nm, and is preferably 1 nm to 5 nm. If it exceeds 10 nm, the adhesion with the sealing material will deteriorate, and there may be concerns about a decrease in insulation performance due to the generation of air bubbles. If it is less than 1 nm, sufficient rust prevention effect may not be expected. The thickness of the rust inhibitor coating layer 19 may be substantially uniform as long as it is within the range of 1 nm to 10 nm, and may vary depending on the location. For example, a relatively thick rust inhibitor coating layer 19 can be formed between adjacent conductive plates where dielectric breakdown is a concern. If one of the semiconductor components to be joined, which is in contact with the first bonding material layer 21a, is a component containing copper or a copper alloy, it is preferable that the rust inhibitor coating layer 19 be provided in such a manner that it covers the entire copper or copper alloy portion of the semiconductor component. This is because components containing copper or copper alloys can also react with gases such as oxygen in the air or with water, and oxidation and corrosion can easily progress. Specific examples of components containing copper or copper alloys that are in contact with the first bonding material layer 21a include, for example, the second conductive plates 123a and 123b. The same applies to the first bonding material layer 21b in Figure 2 as to the first bonding material layer 21a; if one of the semiconductor components to be joined, which is in contact with the first bonding material layer 21b, is a component containing copper or a copper alloy, it is preferable that the rust inhibitor coating layer 19 be provided in such a manner that it covers the exposed surface of the first bonding material layer 21b and the entire copper or copper alloy portion of the semiconductor component.

[0050] In the embodiments shown in Figures 1 and 2, the joint formed by the second conductive plate 123a, the first bonding material layer 21a, and the insulating substrate 122 is in close proximity to the joint formed by the second conductive plate 123b, the first bonding material layer 21b, and the insulating substrate 122. The rust-preventive coating layer 19 is provided continuously in such a manner that it covers the exposed surfaces of the first bonding material layers 21a and 21b, and also covers the surfaces of the two second conductive plates 123a and 123b. Alternatively, the rust-preventive coating layer 19 may be provided continuously in such a manner that it covers at least a portion of the opposing sides of the second conductive plates 123a and 123b, and the surface of the insulating substrate 122 between the second conductive plate 123a and the second conductive plate 123b, as long as it covers the exposed surfaces of the first bonding material layers 21a and 21b. The side surfaces of the second conductive plates 123a and 123b refer to the surfaces perpendicular to the thickness direction of the conductive plates. In semiconductor devices, when two or more joints are located in close proximity, it is preferable to provide a continuous, continuous rust-preventive coating layer 19 that covers the entire adjacent portion. Here, proximity refers, for example, to a case where the distance between the second conductive plate 123a and the second conductive plate 123b is approximately 1.0 mm or less. When the distance between the second conductive plate 123a and the second conductive plate 123b is close, migration due to corrosion is likely to occur, so it is preferable to protect the area with a continuous rust-preventive coating layer 19. By continuously covering the opposing side surfaces of the two second conductive plates 123a and 123b with the rust-preventive coating layer 19, corrosion near the adjacent joints can be suppressed.

[0051] When sulfur-containing gases or water reach the bonding material layer, needle-shaped compounds mainly composed of sulfides such as silver sulfide (AgS) and copper sulfide (CuS) may be formed. For example, in Figure 2, if sulfides are formed at the right end of the first bonding material layer 21b, the sulfidation of the first bonding material layer 21b leads to a decrease in bonding strength, an increase in electrical resistance, and a decrease in dielectric breakdown voltage. Furthermore, if these sulfides grow further to the right along the insulating substrate 122, the dielectric breakdown voltage will decrease even further. Finally, the grown sulfides may reach the left end of the first bonding material layer 21a. Since sulfides are conductive, a short circuit may occur between the first bonding material layers 21a and 21b, resulting in dielectric breakdown. To prevent such performance degradation due to corrosion, it is preferable to provide a continuous rust-preventive coating layer 19 in the manner shown in Figure 2. Furthermore, even when the sides of the two second conductive plates 123a and 123b face each other and are not in close proximity, the rust-preventive coating layer 19 may cover the exposed surface of the first bonding material layer (21a or 21b). In this case, the rust-preventive coating layer may be continuously provided in such a manner that it covers at least a portion of the sides of the second conductive plates 123a and 123b and the surface of the insulating substrate 122. The first conductive substrate 121 is bonded to the other main surface (back surface) of the insulating substrate 122 via the first bonding material layer 20. Therefore, the rust-preventive coating layer 19 may be provided so as to cover the first bonding material layer 20.

[0052] Referring to Figure 1, other examples of semiconductor junctions include junction B between the second conductive plate 123a, the second bonding material layer 22, and the semiconductor element 11; junction C between the first conductive plate 121, the third bonding material layer 23, and the heat sink 13; and junction D between the semiconductor element 11, the fourth bonding material layer 24, and the lead frame 17.

[0053] In the semiconductor junction B, the back electrode of the semiconductor element 11 and the front surface of the second conductive plate 123a (the surface facing the surface joined to the insulating substrate 122) are in contact with the second bonding material layer 22. The rust inhibitor coating layer 19 is provided in such a manner that it covers the entire exposed surface of the second bonding material layer 22 and the entire surface of the second conductive plate 123a, including the side surface. However, the manner in which the rust inhibitor is applied is not limited to the illustrated manner. As long as the rust inhibitor coating layer 19 covers the entire exposed surface of the second bonding material layer 22, it may also be continuously formed on a part of the surface of the second conductive plate 123a, including the side surface that is in contact with the second bonding material layer 22. Alternatively, the rust inhibitor coating layer 19 may be formed on a part of the upper surface of the second conductive plate 123a. However, the rust inhibitor coating layer 19 covering the entire surface of the second conductive plate 123a, including the side surface, can improve corrosion resistance and is particularly preferable from the standpoint of manufacturing efficiency.

[0054] Similarly, in the semiconductor junction C, the first conductive plate 121 and the heat sink 13 are in contact with the third bonding material layer 23. The rust-preventive coating layer 19 is provided in such a manner that it covers the entire exposed surface of the third bonding material layer 23 and the entire surface of the heat sink 13. The rust-preventive coating layer 19 may be provided continuously in such a manner that it covers the entire exposed surface of the third bonding material layer 23, or a portion thereof, of the exposed surface of the heat sink 13. Alternatively, the rust-preventive coating layer 19 may be provided continuously in such a manner that it covers the entire exposed surface of the third bonding material layer 23, or a portion thereof, of the exposed portion of the first conductive plate 121 and the entire exposed surface of the heat sink 13. The rust-preventive coating layer 19, provided to cover the exposed surface of the third bonding material layer 23, may be provided continuously to the exposed surface of the first bonding material layer 20, or to the exposed surfaces of the first bonding material layers 21a and 21b, or even further to the exposed surface of the second bonding material layer 22. Alternatively, the rust-preventive coating layer 19 may be provided in such a manner that it covers the entire or a part of the exposed surface of the insulating substrate 122, including the side surface. If the second bonding material layer 22 and the third bonding material layer 23 are silver-containing bonding material layers, the silver-containing bonding material may typically be a silver sintered material or a silver-containing solder material.

[0055] At the semiconductor junction D, the front electrode of the semiconductor element 11 and one end of the lead frame 17 are in contact with the fourth bonding material layer 24. The rust-preventive coating layer 19 is provided in such a manner that it covers the entire exposed surface of the fourth bonding material layer 24 and the entire surface of the lead frame 17. Although not shown in the figures, the rust-preventive coating layer 19 may also be provided in such a manner that it covers a portion of the lead frame 17, as long as it covers the entire exposed surface of the fourth bonding material layer 24. Furthermore, the rust-preventive coating layer 19 may be provided continuously up to the periphery of the semiconductor element 11, in such a manner that it covers a portion or all of the front surface of the semiconductor element 11, as long as it covers the entire exposed surface of the fourth bonding material layer 24. If the fourth bonding material layer 24 is a silver-containing bonding material layer, the silver-containing bonding material may typically be a silver sintered material or a silver-containing solder material.

[0056] Next, a semiconductor device according to a second embodiment of the present invention will be described. The semiconductor device includes a semiconductor element mounted on a laminated substrate and a sealing material that seals the semiconductor element, and comprises the semiconductor junction described in the first embodiment. The specific structure of the semiconductor device may be the structure illustrated in Figure 1. Instead of the structure illustrated in Figure 1, a caseless structure may be used, and the heat sink may not be bonded to the laminated substrate. In the caseless structure, the back surface of the first conductive plate 121 is generally in contact with the sealing material, so from the viewpoint of adhesion with the sealing material, it may be preferable not to provide a rust inhibitor coating layer on the back surface of the first conductive plate 121. Alternatively, a lead frame may not be provided, and the printed circuit board may be connected to the front electrode of the semiconductor element by metal pins. As the printed circuit board, a polyimide film substrate or an epoxy film substrate with a conductive layer of Cu, Al, etc. can be used. As the metal pins, copper pins made of copper can be used. Both the conductive layer of the printed circuit board and the metal pins may be made of Cu or Al and treated with Ni plating or the like for rust prevention purposes. This printed circuit board and metal pins can electrically connect semiconductor elements to each other, or between semiconductor elements and a multilayer substrate. The metal pins and the multilayer substrate or semiconductor elements can be joined using sintered material or solder. Furthermore, by extending the metal pins from the multilayer substrate to the outside of the sealing material, the metal pins can be used as external connection terminals.

[0057] The semiconductor device according to the second embodiment comprises at least one semiconductor junction described in the first embodiment. The semiconductor device illustrated in Figure 1 comprises semiconductor junctions A, B, C, and D, but the semiconductor device according to the second embodiment comprises one or more of these. If the first bonding material layers 20, 21a, b, the second bonding material layer 22, the third bonding material layer 23, or the fourth bonding material layer 24 are not silver-containing bonding material layers, then the junction comprising such bonding material layers does not correspond to the semiconductor junction according to the first embodiment. Depending on the specifications of the semiconductor device, it may be preferable to form the bonding material layers using a bonding material that does not contain silver, and the first bonding material layers 20, 21a, and b may not exist. A rust-preventive coating layer can be optionally provided to a junction in which a bonding material layer is formed using a bonding material that does not contain silver, for example, a junction consisting of a bonding material layer containing copper, thereby preventing corrosion.

[0058] In the semiconductor device according to the second embodiment, when at least two silver-containing bonding material layers are located in close proximity, as shown in joint A in Figure 2, it is preferable to also form a rust-preventive coating layer on the insulating member between the two silver-containing bonding material layers, so that the rust-preventive coating layer is located between the two silver-containing bonding material layers. This is to prevent dielectric breakdown due to a decrease in dielectric breakdown voltage.

[0059] In the semiconductor device according to the second embodiment, a primer layer such as polyimide or polyamideimide may be optionally provided between the member to be sealed and the sealing material 18. In this case, it is preferable to provide the primer layer in a location where the rust inhibitor coating layer is not formed. This is because providing the primer layer above or below the rust inhibitor coating layer may reduce the adhesion between the primer layer or the rust inhibitor coating layer and the sealing material layer, potentially reducing corrosion resistance or insulation properties.

[0060] Next, the semiconductor device according to the second embodiment will be described from the viewpoint of the manufacturing method. The manufacturing method of the semiconductor device according to the second embodiment is as follows: a) A step of bonding a semiconductor element to a laminated substrate which includes an insulating substrate and a conductive plate bonded to the insulating substrate with a first bonding material, using a second bonding material. b) A step of sealing the sealed member, including the semiconductor element and the conductive connecting member, with a sealing material. Includes, At least one of the first or second bonding material is a silver-containing bonding material, After step a) and before step b), c) A step of forming a rust-preventive coating layer in contact with the silver-containing bonding material. Includes.

[0061] In step a), semiconductor elements are bonded to the laminated substrate 12 using a second bonding material. The laminated substrate 12 is bonded to one main surface of the insulating substrate 122. 1 The conductive plate 121 is on the other main surface 2nd A conductive plate 123a, b can be prepared by joining them with a first bonding material. The first bonding material may typically be a brazing material, and may be the silver brazing material described in the second embodiment as the composition of the first bonding material layers 20, 21a, and b, or it may be any other brazing material. The second bonding material may typically be a sintered material or solder material, and may be the silver sintered material or silver-containing solder material described in the first embodiment as the composition of the second bonding material layer 22.

[0062] In the manufacture of a semiconductor device equipped with a heat sink 13, a third bonding material is used to connect the heat sink and the semiconductor device. 1The step of joining the conductive plate 121 can be carried out in step a). The third joining material is typically a sintered material or a solder material, and may be the silver sintered material or silver-containing solder material described as the composition of the third joining material layer 23 in the first embodiment. In the case of the silver sintered material or silver-containing solder material described as the composition of the third joining material layer 23, it is preferable to form the rust inhibitor coating layer 19 in step c). Furthermore, when joining a lead frame or metal pins to the front electrode of the semiconductor element 11 as a conductive connecting member, it is preferable to carry out this in step a). In this case, the joining material for joining the lead frame or metal pins may be the silver sintered material or silver-containing solder material described as the composition of the fourth joining material layer 24 in the first embodiment. In the case of the silver sintered material or silver-containing solder material described as the composition of the fourth joining material layer 24, it is preferable to form the rust inhibitor coating layer 19 in step c).

[0063] The bonding temperature in step a) may be higher than approximately 200°C and up to about 350°C, depending on the type of bonding material.

[0064] As an optional step, in semiconductor devices equipped with a case, a step of bonding the case 16 to the heat sink 13 can be performed after the completion of step a) and before step b). Bonding can be performed using an adhesive such as a thermosetting resin.

[0065] As an optional step, a wire bonding step may be performed between step a) and step b). Wire bonding typically involves using a conductive connecting member, such as an aluminum wire, to bond the semiconductor element 11 to the other. 2nd The conductive plate 123b connects the semiconductor element 11 to the external terminal, the conductive plate to the external terminal, and / or connects multiple conductive plates.

[0066] Step b) is a sealing step using the sealing material 18. When sealing is performed with a sealing material containing a thermoplastic resin such as silicone gel, it is preferable to inject the silicone gel into the case 16 and heat it at 100 to 150°C for 0.5 to 2 hours. On the other hand, when sealing is performed with a sealing material containing a thermosetting resin such as epoxy resin, the thermosetting resin composition constituting the sealing material is injected into the case 16 and heated to cure. The heat curing step can be, for example, a two-stage curing step. When epoxy resin is used as the main thermosetting resin, it can also be carried out in three stages by heating at 80 to 120°C for 1 to 2 hours, at 120 to 160°C for 1 to 2 hours, and at 170 to 190°C for 1 to 2 hours. However, it is not limited to specific temperatures and times, and there may be cases where two-stage or three-stage curing is not necessary. In the manufacture of semiconductor devices without a case, the sealed member assembled in step b) and with the rust-preventive coating layer formed thereon can be placed in a suitable mold, and the sealing material can be filled into the mold and heated to cure. Examples of such sealing methods include vacuum casting, transfer molding, and liquid transfer molding, but are not limited to the specified method. In step b), the rust inhibitor coating layer 19 is heated to less than 200°C while covered with the sealing material, but the rust inhibitor coating layer 19 itself does not disappear.

[0067] c) The step of forming the rust inhibitor coating layer 19 is carried out by applying the rust inhibitor to the exposed surface of the bonding material layer made of silver-containing bonding material. Step c) is carried out after step a) and before step b). When the case bonding step is performed, step c) may be carried out before or after the bonding step. It is preferable that there are no steps between steps b) and c) that reach temperatures exceeding 200°C. In step a), when forming the second bonding material layer, the third bonding material layer, or the fourth bonding material layer, there may be steps that reach temperatures exceeding 200°C. For this reason, by performing step c) after step a), the rust inhibitor coating layer is not exposed to temperatures exceeding 200°C, and a decrease in rust prevention function due to decomposition or modification of the rust inhibitor coating layer can be suppressed. Also, when wire bonding is performed as an optional step, it is preferable to carry out step c) after wire bonding. This is to prevent the rust inhibitor coating layer from being affected by the heat from wire bonding.

[0068] The rust inhibitor coating layer can be formed by spraying a solution containing the rust inhibitor, immersion in a solution containing the rust inhibitor, or application using a dispenser. In any of these methods, a solution is prepared by diluting the rust inhibitor with a solvent such as isopropyl alcohol or methanol. The concentration of the solution is preferably adjusted according to the desired film thickness. To achieve the preferred film thickness of 1 to 10 nm mentioned above, the concentration of the rust inhibitor can be approximately 1 to 10% by mass. Conditions such as concentration and application amount for forming the desired film thickness can be determined by preliminary experiments. For example, by forming a rust inhibitor coating layer on a copper plate or ceramic plate under different film formation conditions and measuring the film thickness with an atomic force microscope (AFM), the relationship between film formation conditions and film thickness can be obtained, and the film formation conditions can be determined. The spraying method and immersion method are preferably carried out for approximately 30 seconds or more at a temperature of approximately 50 to 70°C. Furthermore, in the case of spraying and immersion methods, areas where it is undesirable to apply the rust inhibitor and their surroundings can be masked, but the process can also be carried out without masking. Masking can be performed by applying a film or forming a resist layer. In the coating method, a dispenser is used to apply a diluted solution of the rust inhibitor to the designated area. After spraying, immersion, or coating, it is preferable to dry the area at approximately 70-90°C for approximately 5-20 minutes. The thickness of the formed rust inhibitor coating layer can be evaluated using AFM (Automated Microscope) based on the difference in height between the area where the rust inhibitor coating layer is formed and the untreated area, before encapsulation. The thickness of the rust inhibitor coating layer can also be estimated by surface analysis using X-ray photoelectron spectroscopy (ESCA) based on the depth at which the elements constituting the rust inhibitor exist. In semiconductor devices after encapsulation, the thickness of the rust inhibitor coating layer can be evaluated by performing cross-sectional measurements using a scanning electron microscope (SEM) at locations including the cross-section of the rust inhibitor coating layer thickness.

[0069] By manufacturing a semiconductor device equipped with a semiconductor element junction according to this embodiment using the above manufacturing method, it is possible to produce a highly reliable semiconductor device with excellent corrosion resistance and junction strength without causing a decrease in rust prevention performance due to vaporization of the rust-preventive coating layer. [Examples]

[0070] The present invention will be described in more detail below with reference to examples of the present invention. However, the present invention is not limited to the scope of the following examples.

[0071] (1) Manufacturing of power semiconductor test modules A power semiconductor test module, as shown in Figure 1, was manufactured. The test module was a MOSFET module equipped only with semiconductor junction A. The laminated substrate 12 consisted of conductive plates 121, 123a, and 123b made of copper foil, bonded to a ceramic insulating substrate 122 by first bonding material layers 21a and 21b made of silver solder (80% Ag, 20% Cu) with a thickness of approximately 15 μm. The rust inhibitor coating layer formation process was performed after the wire bonding process and before the sealing process by applying a rust inhibitor solution with a dispenser. The temperature during the rust inhibitor coating layer formation process was 60°C, and after application, it was dried at 80°C for 10 minutes. Silicone gel was used as the sealing material and heated at 150°C for 1 hour. The lid of the outer case, not shown in Figure 1, was of the snap-fit ​​type, meaning it was designed to allow outside air to enter. No primer was used because applying a primer to the surface of the sealed component may reduce corrosion resistance. In Example 4, the joint between a second conductive plate 123a made of copper foil and the back electrode of a semiconductor element 11 was evaluated by a second bonding material layer 22 made of Ag sintered body with a thickness of 100 μm. A sheet material of Ag nanoparticles was used as the Ag sintered body. After placing the sheet material at the location corresponding to the semiconductor element on the conductive plate, the semiconductor element was placed on the sheet material and sintered by heating at 250°C for 5 minutes under a pressure of 10 MPa to form the joint.

[0072] The thickness of the rust inhibitor coating layer was evaluated by applying the rust inhibitor solution to a flat surface (copper foil or ceramic surface) using a dispenser and measuring the thickness by the difference in height between the coated and uncoated areas using an AFM. The thickness of the rust inhibitor coating layer was adjusted by changing the concentration of the rust inhibitor solution.

[0073] The corrosion resistance was evaluated by conducting a corrosive gas exposure test on the test module. Hydrogen sulfide (H2S) at a concentration of 10 ppm was used as the corrosive gas, and the test module was exposed to it for 1000 hours at 40°C and 80% RH. After exposure, 2nd The corrosion products between conductive plates 123a and 123b (hereinafter also referred to as Cu-Cu) were observed under a 300x optical microscope, and the length of the corrosion products was measured. The Cu-Cu distance was manufactured aiming for 0.8 mm. However, in Example 4, the corrosion products on the side surface of the second bonding material layer 22 (hereinafter also referred to as Ag sintered body), which is made of silver-containing bonding material, were examined for the presence or absence of sulfides by cross-sectional compositional analysis, observed under a 300x optical microscope, and the length (size) of the corrosion products was similarly measured. The length (size) of the corrosion products was defined as the maximum length of the corrosion product in the microscopic observation image. The corrosion products are sulfides that can be identified by cross-sectional compositional analysis, etc., and can be distinguished by their characteristic of growing in a dendritic or whisker-like manner from the edges of the conductive plate (Cu) and bonding material layer. The evaluation criteria were as follows: a length of corrosion product exceeding 100 μm was classified as "D," 50-100 μm as "C," greater than 0 but less than 50 μm as "B," and no corrosion was observed as "A." Even in cases where the evaluation was "C," it was confirmed that no dielectric breakdown due to migration occurred, and the module functioned without problems.

[0074] The results are shown in Table 1. Note that the rust inhibitors are listed by abbreviations, but their official names are as described above. [Table 1]

[0075] Next, we evaluated the corrosion resistance effect by changing the type of rust inhibitor. The results are shown in Table 2. [Table 2]

[0076] Tables 1 and 2 show that, regardless of which rust inhibitor was used in each example, the formation of a rust inhibitor coating layer suppressed the growth of corrosion products compared to cases where no rust inhibitor coating layer was formed, resulting in the formation of a highly reliable joint.

[0077] [Example: Detection of rust inhibitor coating layer by X-ray photoelectron spectroscopy (ESCA)] Reference Example 1 consisted of a copper surface coated with BTA as a rust inhibitor, forming a 2 nm thick rust inhibitor coating layer. Reference Example 2 consisted of a copper plate sample without a rust inhibitor coating layer. Surface analysis of each sample was performed using ESCA to obtain semi-quantitative values ​​of the surface composition ratio. The results are shown in Table 3. The units of the values ​​in the table are atomic percent (at%). For each sample, the results of the surface composition ratio at two different locations are shown in the table. When the composition ratio was measured from the outermost surface to a depth of 10 nm, in Reference Example 1, nitrogen (N) components were detected up to a depth of approximately 2 nm from the outermost surface, confirming that the ratio of nitrogen (N) components did not decrease. From this, the thickness of the rust inhibitor coating layer could be estimated to be about 1-2 nm. From this reference example, it was confirmed that the thickness of the rust inhibitor coating layer before sealing can also be analyzed and evaluated by ESCA.

[0078] [Table 3] [Explanation of symbols]

[0079] 11 Semiconductor element, 12 Multilayer substrate, 121 First conductive plate, 122 Insulating substrate, 123a, b Second conductive plate, 13 Heat sink, 15 External terminals, 16 Case, 17 Lead frame, 18 Sealing material, 19 Anti-corrosion coating layer 20, 21a, b 1st bonding material layer, 22 2nd bonding material layer, 23 3rd bonding material layer 24 4th bonding material layer A, B, C, D Semiconductor junction

Claims

1. A semiconductor device comprising a semiconductor element mounted on a laminated substrate having an insulating substrate and a conductive plate, and a silicone gel encapsulant for sealing the semiconductor element, wherein the semiconductor device comprises a semiconductor junction formed by at least two semiconductor components and a silver-containing bonding material layer for joining the semiconductor components, and a rust-preventive coating layer is provided in contact with the silver-containing bonding material layer.

2. The semiconductor device according to claim 1, wherein the rust inhibitor is benzotriazole or a derivative thereof, or a carboxylate or nitrite of an amine.

3. The semiconductor device according to claim 1 or 2, wherein the silver-containing bonding layer includes a brazing material, a sintered material, or a soldering material.

4. The semiconductor device according to any one of claims 1 to 3, wherein the rust-preventive coating layer has a thickness of 1 nm to 10 nm.

5. The semiconductor device according to any one of claims 1 to 4, wherein at least one of the semiconductor components is a component containing copper or a copper alloy, and the rust-preventive coating layer coats the copper or copper alloy.

6. The semiconductor device according to any one of claims 1 to 5, wherein the at least two semiconductor components are selected from an insulating substrate and a conductive plate, a conductive plate and a semiconductor element, a conductive plate and a heat sink, or a semiconductor element and a conductive connecting member.

7. a) A step of bonding a semiconductor element to a laminated substrate which includes an insulating substrate and a conductive plate bonded to the insulating substrate with a first bonding material, using a second bonding material, b) A step of sealing the member to be sealed, including the semiconductor element and the laminated substrate, with a silicone gel encapsulant. A method for manufacturing a semiconductor device, including At least one of the first or second bonding material is a silver-containing bonding material, After step a) and before step b), c) A step of forming a rust-preventive coating layer in contact with the silver-containing bonding material layer. A method for manufacturing a semiconductor device according to any one of claims 1 to 6, including the method described in any one of claims 1 to 6.

8. The first bonding material is a silver-containing bonding material, The method according to claim 7, wherein step c) includes the step of forming a rust inhibitor coating layer in contact with the layer of silver-containing bonding material at the joint between the insulating substrate and the conductive plate.

9. The second bonding material is a silver-containing bonding material, The method according to claim 7 or 8, wherein step c) includes the step of forming a rust inhibitor coating layer in contact with the layer of silver-containing bonding material at the junction between the laminated substrate and the semiconductor element.

10. Step a) includes a step of bonding a heat sink to the laminated substrate using a third bonding material, The method according to any one of claims 7 to 9, wherein step c) includes the step of forming a rust inhibitor coating layer in contact with the layer of silver-containing bonding material at the joint between the laminated substrate and the heat sink.

11. Step a) includes a step of joining a conductive connecting member to the semiconductor element using a fourth bonding material, The fourth bonding material is a silver-containing bonding material, The method according to any one of claims 7 to 10, wherein step c) includes the step of forming a rust inhibitor coating layer in contact with the layer of silver-containing bonding material at the joint between the semiconductor element and the conductive connecting member.

12. The method according to any one of claims 7 to 11, wherein a wire bonding step is performed after step a) and before step b), and step c) is performed after the wire bonding step and before step b).

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