Semiconductor device and method for its manufacture

Abstract

Semiconductor device (100) comprising: - a semiconductor element (14); - a linear wire segment (17) connected to an upper surface of the semiconductor element (14); - a coating material (21) in contact with the semiconductor element (14) and the wire segment (17) in an upper region of the semiconductor element (14); and - a sealing agent (20) protecting the semiconductor element (14), the wire segment (17), and the coating material (21), wherein the coating material (21) contains: - substances with covalent bonds in the form Si-OM between oxygen O and silicon Si and a metal M, respectively, - a silicon oxide, and - siloxane.

Description

Field of invention The present invention relates to a semiconductor device and a method for its manufacture. Description of the state of the art Structures have been proposed that, for example, coat semiconductor elements with a coating material such as polyimide and protect the semiconductor elements to increase the reliability of the semiconductor device (e.g., Japanese patent application JP 2006-351 737 A). Furthermore, resins have been proposed that each comprise at least one side group including a -Si(OR)3 group to support adhesion (e.g., Japanese patent application JP 2010-521 552 A). Typically, when a coating material reacts with energy such as heat, light, or plasma, not only is an intended reactant produced, but also a byproduct that differs from the reactant. This is because the composition of the reacted coating material differs from that of the unreacted coating material. Even if a composition is determined before the reaction, the desired adhesion and reliability may not be achieved in some cases, depending on the proportion of the byproduct in the whole after the reaction. Consequently, there is little scope for improvements regarding the adhesion and reliability of coating materials. Traditionally, applying a coating to semiconductor elements that generate a large amount of heat in a semiconductor device promotes adhesion between the semiconductor elements and a sealant, thus increasing the reliability of the semiconductor device. Although wire segments with diameters ranging from a few tens to a few hundred micrometers are very thin, the heat transferred to the linear wire segments that are to be connected to the semiconductor elements is relatively equal to the heat transferred to the semiconductor elements themselves. Consequently, the wire segments tend to exhibit a cracking problem. Publication JP 2006-351 737 A discloses a semiconductor power module with a balanced resin sealing structure that not only prevents deformation of the power module but also improves the thermal fatigue resistance and moisture resistance of the solder. In this known semiconductor power module, the entire or a portion of the module mounting surface and the wires are first coated and covered with a soft and thin polyimide or polyamide-imide system resin. After this resin has cured, each semiconductor chip 1 is sealed with an epoxy resin 10 whose physical properties correspond to the coefficient of linear expansion of the solder (12 × 10⁶ / °C to 30 × 10⁶ / °C) at a low elastic modulus of 3 GPa to 20 GPa. Publication US 2008 / 0223255A1 teaches film-forming materials comprising resins and / or crosslinkers with a -Si(OR)3 group. Film-forming resins can include epoxy, acrylic, polyurethane, polycarbonate, polysiloxane, polyvinyl, polyether aminoplast, and polyester resins. One method for producing a film-forming resin involves reacting various polymers to incorporate a side group containing a -Si(OR)3 group. Film-forming resins can be used in methods for producing coating compositions. Coating compositions can be used to coat a substrate, such as a metal substrate. Electrodeposition-applied coatings containing the film-forming resins can be cured to form crosslinked films on substrates. Summary The present invention was implemented in consideration of the problem, and it is an objective to provide a technology to enable an increase in the reliability of a semiconductor device. The problem underlying the invention is solved according to the invention in a semiconductor device by the features of claim 1 and in a method for manufacturing the semiconductor device by the features of claim 8. Advantageous embodiments are the subject of the respective dependent claims. The semiconductor device according to the present invention comprises: a semiconductor element; a linear wire segment connected to an upper surface of the semiconductor element; a coating material in contact with the semiconductor element and the wire segment in an upper region of the semiconductor element; and a sealing agent protecting the semiconductor element, the wire segment, and the coating material. The coating material contains substances with covalent bonds in the form -Si-OM between oxygen and silicon (Si) and metal (M), a silicon oxide, and siloxane. This structure can increase the reliability of the semiconductor device. These and other tasks, features, aspects and advantages of the present invention will become clearer with reference to the following detailed description of the present invention in conjunction with the accompanying figures. Brief description of the characters Fig. 1 is a cross-sectional view illustrating a structure of a semiconductor device according to a preferred embodiment 1; and Fig. 2 is a cross-sectional view illustrating a structure of a semiconductor device according to a modification. Description of preferred embodiments The following describes embodiments with reference to the accompanying figures. The features described below in the embodiments are purely examples, and not all features are necessarily required. In the following description, identical components in a multitude of embodiments are identified by means of identical or similar reference numerals, and the differing components are mainly described. In the following description, a specific position and direction such as "top," "bottom," "left," "right," or "back" need not necessarily correspond to an actual position and direction. [Preferred embodiment 1] Fig. 1 is a cross-sectional view illustrating the structure of a semiconductor device 100 according to a preferred embodiment 1. The semiconductor device 100 in Fig. 1 comprises a base plate 11, connecting components 12 and 13, semiconductor elements 14, wire segments 17, a housing 18, a sealing agent 20, a coating material 21, and insulating substrates 30. Each of the insulating substrates 30 comprises an insulating layer 32, a conductor 31 which is arranged on the insulating layer 32, and a circuit 33 which is arranged from the insulating layer 32 on the opposite side of the conductor 31. The insulating layer 32 can, but not exclusively, be formed from an inorganic ceramic material such as aluminum oxide (Al₂O₃), aluminum nitride (AlN), silicon nitride (Si₃N₄), silicon dioxide (SiO₂), or boron nitride (BN). The insulating layer 32 can also be formed from a resin in which at least one imperceptible particle or filler material is dispersed. This at least one imperceptible particle or filler material can, for example, be an inorganic ceramic material such as aluminum oxide (Al₂O₃), aluminum nitride (AlN), silicon nitride (Si₃N₄), silicon dioxide (SiO₂), boron nitride (BN), diamond (C), silicon carbide (SiC), or boron oxide (B₂O₃), or a resin such as a silicone resin or an acrylic resin.The resin in which at least one imperceptible particle or filler material is distributed can be, but not exclusively, a resin with an electrical insulating property, for example an epoxy resin, a polyimide resin, a silicone resin, or an acrylic resin. The conductor 31 and the circuit 33 may, but are not limited to, being made of a metal such as copper or aluminum. The conductor 31 and the circuit 33 may be made of the same materials or of different materials. The number of circuits 33 may be one or two and is determined, for example, in accordance with the nominal capacitance and wiring specification of the semiconductor device 100. The base plate 11 is connected to the conductors 31 of the insulating substrates 30 by the connecting components 12. The base plate 11 can, but is not limited to, be made of a metal such as copper, aluminum, or a copper-molybdenum alloy (CuMo), or a composite material such as a silicon carbide-aluminum composite (AlSiC) or a silicon carbide-magnesium composite (MgSiC). The base plate 11 can also be made of an organic material such as an epoxy resin, a polyimide resin, an acrylic resin, or polyphenylene sulfide (PPS) resin. The connecting components 12 can, but are not limited to, any components and, for example, be made of solder. Each of the semiconductor elements 14 is connected to the circuit 33 of the insulating substrate 30 by the connection component 13. Specifically, the connection component 13 is connected to the lower surface of the semiconductor element 14, and the circuit 33, the insulating layer 32, and the conductor 31 are connected to the lower surface of the semiconductor element 14 by the connection component 13 in that order. Examples of the semiconductor elements 14 include an insulated-gate bipolar transistor (IGBT), a metal-oxide-semiconductor field-effect transistor (MOSFET), a PN junction diode (PND), a Schottky diode (SBD), and a freewheeling diode (FWD). The semiconductor element 14 may, but is not limited to, being made of ordinary silicon (Si) or a wide-bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond. A wide-bandgap semiconductor element 14 enables stable operation at high temperatures and high voltages and faster switching in the semiconductor device 100. The interconnects 13 may, but are not limited to, any interconnect components. The interconnects 12 and 13 may be made of the same material or of different materials. The number of each insulating substrate 30 and semiconductor element 14 can be one, two, or more, and is determined, for example, in accordance with the nominal capacitance and wiring specification of the semiconductor device 100. The number of interconnect components 12 and the number of interconnect components 13 are each determined by the number of insulating substrates 30 and the number of semiconductor elements 14, respectively. The housing 18 surrounds the semiconductor elements 14 and the wire segments 17, and exposes surfaces of the base plate 11 that face the semiconductor elements 14. The housing 18 can, but is not limited to, be made of any material with electrical insulating properties, for example, an epoxy resin, a polyimide resin, an acrylic resin, or polyphenylene sulfide (PPS) resin. Terminals 19 are embedded in the housing 18, with one end of each terminal 19 exposed. The terminals 19 can be made of the same or a different material as the circuit 33. One end of the linear wire segment 17 is connected to the upper surface of the semiconductor element 14. The other end of the wire segment 17 is connected, for example, to the circuit 33 of the insulating substrate 30, or to the terminal 19. The wire segments 17 are made of a conductive material such as copper or aluminum. The diameter of the wire segment 17 ranges, for example, from a few tens to a few hundred micrometers. The sealant 20 protects the semiconductor elements 14, the wire segments 17, and the coating material 21. The sealant 20 can be composed of an insulating resin such as an epoxy resin, a silicone resin, polyurethane, a polyimide resin, a polyamide resin, or an acrylic resin. The epoxy resin is an epoxy material, and the silicone resin is a silicone gel. The sealant 20 can also be composed of an insulating resin in which particles or fillers are dispersed to improve strength and thermal conductivity. These particles or fillers can be, for example, an inorganic ceramic material such as aluminum oxide (Al₂O₃), aluminum nitride (AlN), silicon nitride (Si₃N₄), silicon dioxide (SiO₂), boron nitride (BN), diamond (C), silicon carbide (SiC), or boron oxide (B₂O₃). The coating material 21 is in contact with the semiconductor elements 14 and the wire pieces 17 in upper regions 14a on the semiconductor elements 14. The coating material 21 is further in contact with the connecting components 13 and the electrical circuits 33 according to embodiment 1. The coating material 21 consists of a silane adhesion promoter with a -Si(OR)x group prior to the reaction. R denotes a hydrocarbon group, and x denotes a number from 1 to 3. The number of carbons in the hydrocarbon group ranges from 1 to 10. A functional group to be bonded with Si can be, for example, an epoxy group, an amino group, a vinyl group, a styryl group, a methacrylic group, an acrylic group, a mercapto group, an isocyanate, an isocyanate, or an acid anhydride. When energy such as heat or light is applied to the silane adhesion promoter of the coating material 21, a reaction occurs in which the silane adhesion promoter is converted into substances with Si-OM covalent bonds (M denotes a metal), a silicon oxide, and siloxane. Consequently, the coating material 21 of the semiconductor device contains 100 substances with covalent bonds between oxygen and silicon, as well as between the metal, the silicon oxide, and siloxane. Among these, the substances with covalent bonds influence the adhesion between the coating material 21 and the components in contact with the coating material 21. In addition, the silicon oxide and the siloxane influence the wettability on the substrate. The number of substances with covalent bonds in the coating material 21 should be greater than or equal to 0.1% of the number of silicon atoms in the coating material 21. If the number of substances with covalent bonds contributing to adhesion is greater than or equal to 0.1% of the number of silicon atoms, the substances with covalent bonds can achieve stronger adhesion than those in a structure using the coating material 21 in a different number range and in a structure without the coating material 21. The number of silicon atoms in the coating material 21 can be measured, for example, using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The coating material 21 is a relatively thin layer, and it should have a thickness in the range of 10 nm to 100 µm. If the coating material 21 is thinner than 10 nm, a thinner section of the coating material 21, or a section without the coating material 21, will remain on the semiconductor device 100. Consequently, the reliability of the semiconductor device 100 may decrease from this section onward. If the coating material 21 is thicker than 100 µm, the reaction of the coating material 21, triggered by the supplied energy, will not proceed sufficiently, and it is possible that the coating material 21 will not be able to exhibit adequate strength. Therefore, the coating material 21 preferably has a thickness of more than or equal to 10 nm but not more than 100 µm, and more preferably has a thickness of more than or equal to 10 nm but not more than 1 µm. The coating material 21 plays a role in supporting adhesion, for example, between the semiconductor elements 14 and the sealant 20. The coating material 21, with an adhesive force greater than the stress resulting from the heat generated when the semiconductor elements 14 operate, can prevent deterioration of the semiconductor device 100. In embodiment 1, the coating material 21 is applied to the upper surfaces of the semiconductor elements 14, and these upper surfaces are connected to the wire segments 17. Typically, the wire segment 17 is thin, with a diameter ranging from a few tens to a few hundred micrometers. In addition, the stress caused by the expansion of the materials of the semiconductor elements 14 and the wire segments 17, which generate heat, leads to slight deterioration of the wire segment material.Since the coating material 21 is in contact not only with the semiconductor elements 14, but also with the wire pieces 17 in embodiment 1, the reliability of the semiconductor device 100 can be increased. The coating material 21 does not need to be applied to all of the wire pieces 17. As long as the coating material 21 is in contact with a section of the wire pieces 17 that is exposed to the heat generated when the semiconductor elements 14 operate, for example, a section of the wire pieces 17 in the upper regions 14a on the semiconductor elements 14, an improvement in the reliability of the semiconductor device 100 is expected. The coating material 21 may also contain carbon atoms, and the percentage of the number of atoms occupied by carbon atoms in the coating material 21 may be 50% or less. Since the structure is obtained as a result of the reaction of the coating material 21, which is at least advanced to some extent, the coating material 21 may produce at least some advantages. The metal for the covalent bonds can be a metal contained in the coating material 21 before the coating material 21 reacts, or at least a metal contained in the wire segments 17, the connecting components 13, and the circuits 33. If, for example, the metal for the covalent bonds is the metal contained in the wire segments 17, the metal is able to covalently bond the wire segments 17 themselves. Consequently, the adhesion of the coating material 21 can be further enhanced. In a typical formation of the coating material 21, a reaction of a silane adhesion promoter proceeds by diluting the silane adhesion promoter using water or alcohol as a solvent to convert the -Si(OR)x group to a -Si(OH)x group. Without the addition of a solvent containing water or alcohol to the chemical solution of the coating material 21, the reaction proceeds via the moisture of the chemical solution itself, via the medium of water in the air, or by the addition of high energy such as heat or light. Consequently, the addition of the solvent is not necessary. Therefore, the coating material 21 can be formed by applying the chemical solution of the coating material 21 to the semiconductor elements 14 and the wire segments 17 without adding the solvent containing water or alcohol to the chemical solution.Since the manufacturing process can reduce the time required to prepare a solution or the time required for the reaction, an increase in the efficiency of the manufacturing process of the semiconductor device 100 can be expected. [Modification] Fig. 2 is a cross-sectional view illustrating the structure of the semiconductor device 100 according to this modification. As shown in Fig. 2, the housing 18 can be designed with the exposed conductor 31 in the absence of the base plate 11. Since the conductor 31 serves as the base plate 11 in this structure, the cost of the device can be reduced. The embodiments can be modified and omitted as appropriate.

Claims

Semiconductor device (100) comprising: - a semiconductor element (14); - a linear wire segment (17) connected to an upper surface of the semiconductor element (14); - a coating material (21) in contact with the semiconductor element (14) and the wire segment (17) in an upper region of the semiconductor element (14); and - a sealing agent (20) protecting the semiconductor element (14), the wire segment (17), and the coating material (21), wherein the coating material (21) contains: - substances with covalent bonds in the form Si-OM between oxygen O and silicon Si and a metal M, respectively, - a silicon oxide, and - siloxane. Semiconductor device (100) according to claim 1, wherein the number of substances in the coating material (21) is greater than or equal to 0.1% of the number of silicon atoms in the coating material (21). Semiconductor device (100) according to claim 1 or 2, further comprising: - a connecting component (13) which is connected to a lower surface of the semiconductor element (14); and - an electrical circuit (33) which is connected to the semiconductor element (14) through the connecting component (13), wherein the coating material (21) is further in contact with the connecting component (13) and the electrical circuit (33). Semiconductor device (100) according to claim 1 or 2, further comprising: - a circuit (33), an insulating layer (32), and a conductor (31), which are connected in this order to a lower surface of the semiconductor element (14) by a connecting component (13); and - a housing (18) which exposes the conductor (31) and surrounds the semiconductor element (14) and the wire piece (17). Semiconductor device (100) according to any one of claims 1 to 4, wherein the coating material (21) has a thickness that is more than or equal to 10 nm but not more than 100 µm. Semiconductor device (100) according to any one of claims 1 to 5, wherein:- the coating material (21) furthermore contains carbon atoms, and- a percentage of the number of atoms occupied by the carbon atoms in the coating material (21) is 50% or less. Semiconductor device (100) according to any one of claims 1 to 6, wherein the sealing agent (20) comprises an epoxy material or a silicone gel. Method for producing the semiconductor device (100) according to one of claims 1 to 7,- comprising forming a coating material (21) by applying a chemical solution of the coating material (21) to the semiconductor element (14) and the wire piece (17),- without adding a solvent to the chemical solution which contains water or alcohol.

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