Patent Publication Number: US-2023140664-A1

Title: Semiconductor device and method for manufacturing the same

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a semiconductor device and a method for manufacturing the same. 
     DESCRIPTION OF THE BACKGROUND ART 
     Structures that coat, for example, semiconductor elements with a coating material such as polyimide and protect the semiconductor elements for enhancing the reliability of semiconductor devices have been proposed (e.g., Japanese Patent Application Laid-Open No. 2006-351737). Furthermore, resins each with at least one pendent group comprising a -Si (OR) 3  group for promoting adhesion have been proposed (e.g., Japanese Unexamined Patent Application Publication No. 2010-521552). 
     Typically, when a coating material reacts with energy such as heat, light, or plasma, not only an intended reactant but also a byproduct different from the reactant are produced. This is because a composition of the reacted coating material differs from a composition of the unreacted coating material. Consequently, even if a composition is designated before the reaction, intended adhesion and reliability cannot be obtained in some cases, depending on a proportion of the byproduct to the whole after the reaction. Thus, there is room for improvement in improving the adhesion and reliability of coating materials. 
     Conventionally, applying a coating to semiconductor elements that generate a large amount of heat in a semiconductor device promotes the adhesion between the semiconductor elements and a sealant to enhance the reliability of the semiconductor device. Even though pieces of wire with diameters ranging from several tens to several hundred µm are very thin, the heat given to the pieces of linear wires to be connected to semiconductor elements is as relatively high as the heat given to the semiconductor elements. Thus, the pieces of wire tend to have a problem of a rupture. 
     SUMMARY 
     The present disclosure has been made in view of the problem, and has an object of providing a technology for enabling enhancement of the reliability of a semiconductor device. 
     The semiconductor device according to the present disclosure includes: a semiconductor element; a piece of linear wire connected to an upper surface of the semiconductor element; a coating material in contact with the semiconductor element, and the piece of wire in an upper region on the semiconductor element; and a sealant protecting the semiconductor element, the piece of wire, and the coating material. The coating material contains substances with covalent bonds between oxygen and each of silicon and a metal, a silicon oxide, and siloxane. 
     This structure can enhance the reliability of the semiconductor device. 
     These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view illustrating a structure of a semiconductor device according to Preferred Embodiment 1; and 
         FIG.  2    is a cross-sectional view illustrating a structure of a semiconductor device according to a modification. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments will be hereinafter described with reference to the attached drawings. The features to be described in embodiments below are mere exemplification, and all of the features are not necessarily essential. In the description below, identical constituent elements in a plurality of embodiments will be denoted by the same or similar reference numerals, and the different constituent elements will be mainly described. In the following description, a particular position and a particular direction such as “up”, “down”, “left”, “right”, “front”, or “back” need not always coincide with an actual position and an actual direction. 
     Preferred Embodiment 1 
       FIG.  1    is a cross-sectional view illustrating a structure of a semiconductor device  100  according to Preferred Embodiment 1. The semiconductor device  100  in  FIG.  1    includes a base plate  11 , bonding components  12  and  13 , semiconductor elements  14 , pieces of wire  17 , a casing  18 , a sealant  20 , a coating material  21 , and insulating substrates  30 . 
     Each of the insulating substrates  30  includes an insulating layer  32 , a conductor  31  disposed on the insulating layer  32 , and a conductive circuit  33  disposed on the insulating layer  32  on the opposite side of the conductor  31 . 
     The insulating layer  32  may be, but not exclusively, made of an inorganic ceramic material such as alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), or boron nitride (BN). The insulating layer  32  may be made of a resin in which at least one impalpable particle or filler is dispersed. The at least one impalpable particle or filler may be made of, for example, an inorganic ceramic material such as alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), boron nitride (BN), diamond (C), silicon carbide (SiC), or boron oxide (B 2 O 3 ), or a resin such as a silicone resin or an acrylic resin. The resin in which at least one impalpable particle or filler is dispersed may be, but not exclusively, any resin with electrical insulating properties, for example, an epoxy resin, a polyimide resin, a silicone resin, or an acrylic resin. 
     The conductor  31  and the conductive circuit  33  may be, but not exclusively, made of a metal such as copper or aluminum. The conductor  31  and the conductive circuit  33  may be made of the same material or different materials. The number of the conductive circuits  33  may be one or two or more, and is determined, for example, according to the rated capacity and the wiring specification of the semiconductor device  100 . 
     The base plate  11  is bonded to the conductors  31  of the insulating substrates  30  through the bonding components  12 . The base plate  11  may be, but not exclusively, 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  may be made of an organic material such as an epoxy resin, a polyimide resin, an acrylic resin, or polyphenylene sulfide (PPS) resin. The bonding components  12  may be, but not exclusively, any bonding components, and made of, for example, solder. 
     Each of the semiconductor elements  14  is bonded to the conductive circuit  33  of the insulating substrate  30  through the bonding component  13 . Specifically, the bonding component  13  is connected to the lower surface of the semiconductor element  14 , and the conductive circuit  33 , the insulating layer  32 , and the conductor  31  are connected to the lower surface of the semiconductor element  14  through the bonding component  13  in this order. 
     Examples of the semiconductor elements  14  may include an insulated-gate bipolar transistor (IGBT), a metal oxide semiconductor field effect transistor (MOSFET), a PN junction diode (PND), a Schottky barrier diode (SBD), and a freewheeling diode (FWD). The semiconductor element  14  may be, but not exclusively, made of normal silicon (Si), or a wide bandgap semiconductor such as silicon carbide (SiC), gallium nitride (GaN), or diamond. The semiconductor element  14  made of a wide bandgap semiconductor enables stable operations at high temperatures and high voltages and faster switching in the semiconductor device  100 . The bonding components  13  may be, but not exclusively, any bonding components. The bonding components  12  and  13  may be made of the same material or different materials. 
     The number of each of the insulating substrates  30  and the semiconductor elements  14  may be one or two or more, and is determined, for example, according to the rated capacity and the wiring specification of the semiconductor device  100 . The number of the bonding components  12  and the number of the bonding components  13  are determined by the number of the insulating substrates  30  and the number of the semiconductor elements  14 , respectively. 
     The casing  18  surrounds the semiconductor elements  14  and the pieces of wire  17 , and exposes surfaces of the base plate  11  which are opposite to the semiconductor elements  14 . The casing  18  may be, but not exclusively, 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 casing  18  with one end of each of the terminals  19  being exposed. The terminals  19  may be made of a material identical to or different from that of the conductive circuit  33 . 
     One end of the piece of linear wire  17  is connected to the upper surface of the semiconductor element  14 . The other end of the piece of wire  17  is connected to, for example, the conductive circuit  33  of the insulating substrate  30 , or the terminal  19 . The pieces of wire  17  are made of a conductive material such as copper or aluminum. The diameter of the piece of wire  17  ranges, for example, from several tens to several hundred µm. 
     The sealant  20  protects the semiconductor elements  14 , the pieces of wire  17 , and the coating material  21 . The sealant  20  may be made 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 silicone gel. The sealant  20  may be made of an insulating resin in which particles or fillers for improving the strength and the thermal conductivity are dispersed. The particles or fillers may be made of, for example, an inorganic ceramic material such as alumina (Al 2 O 3 ), aluminum nitride (AIN), silicon nitride (Si 3 N 4 ), silicon dioxide (SiO 2 ), boron nitride (BN), diamond (C), silicon carbide (SiC), or boron oxide (B 2 O 3 ). 
     The coating material  21  is in contact with the semiconductor elements  14 , and the pieces of wire  17  in upper regions  14   a  on the semiconductor elements  14 . The coating material  21  is further in contact with the bonding components  13  and the conductive circuits  33  according to Embodiment 1. 
     The coating material  21  is made of a silane coupling agent with a -Si (OR) x  group before reaction. R should denote a hydrocarbon group, and x should denote any one of 1 to 3. The number of carbons in the hydrocarbon group should range from 1 to 10. A functional group to be connected to Si may be, for example, an epoxy group, an amino group, a vinyl group, a styryl group, a methacryl group, an acrylic group, a mercapto group, isocyanate, isocyanurate, or an acid anhydride. 
     When energy such as heat or light is given to the silane coupling agent of the coating material  21 , a reaction occurs in which the silane coupling agent is converted into substances with —Si—O—M covalent bonds (M denotes a metal), a silicon oxide, and siloxane. Thus, the resulting coating material  21  of the semiconductor device  100  contains substances with covalent bonds between oxygen and each of silicon and the metal, the silicon oxide, and siloxane. Among these, the substances with covalent bonds influence the adhesion between the coating material  21  and the constituent elements that are in contact with the coating material  21 . Moreover, the silicon oxide and siloxane influence the wettability on the adherend. 
     The number of the substances with covalent bonds in the coating material  21  should be higher than or equal to 0.1% of the number of silicon atoms in the coating material  21 . When the number of the substances with covalent bonds that contribute to the adhesion is higher than or equal to 0.1% of the number of silicon atoms, the substances with covalent bonds can achieve adhesion higher than those of a structure using the coating material  21  in another numerical range and a structure without the coating material  21 . Here, the number of silicon atoms in the coating material  21  can be measured using, for example, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). 
     The coating material  21  is a relatively thin film, and should have a thickness ranging from 10 nm to 100 µm. If the coating material  21  is thinner than 10 nm, a thinner portion of the coating material  21  or a portion without the coating material  21  will remain in the semiconductor device  100 . Thus, the reliability of the semiconductor device  100  may decrease from the portion. If the coating material  21  is thicker than 100 µm, the reaction of the coating material  21  triggered by the given energy does not sufficiently proceed, and the coating material  21  may not be able to possess adequate strength. Thus, the coating material  21  preferably has a thickness more than or equal to 10 nm but not more than 100 µm, and more preferably has a thickness more than or equal to 10 nm but not more than 1 µm. 
     The coating material  21  serves a role in promoting the adhesion, for example, between the semiconductor elements  14  and the sealant  20 . The coating material  21  with adhesion strength greater than the stress arising 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 the upper surfaces of the semiconductor elements  14  are connected to the pieces of wire  17 . Typically, the piece of wire  17  with a diameter ranging from several tens to several hundred µm is thin. In addition to this, the stress caused by expansion of the materials of the semiconductor elements  14  and the pieces of wire  17  which generate heat causes the material of the pieces of wire  17  to easily deteriorate. In contrast, since the coating material  21  is in contact with not only the semiconductor elements  14  but also the pieces of wire  17  in Embodiment 1, the reliability of the semiconductor device  100  can be enhanced. 
     The coating material  21  need not be applied to the entirety of the pieces of wire  17 . As long as the coating material  21  is in contact with a portion of the pieces of wire  17  subjected to the heat generated when the semiconductor elements  14  operate, for example, a portion of the pieces of wire  17  in the upper regions  14   a  on the semiconductor elements  14 , the improvement in reliability of the semiconductor device  100  is expected. 
     The coating material  21  may further contain carbon atoms, and a percentage of the number of atoms by which the carbon atoms occupies in the coating material  21  may be 50% or less. Since this structure is obtained as a result of the reaction of the coating material  21  which has proceeded at least to some extent, the coating material  21  can produce at least some advantages. 
     The metal for covalent bonds may be a metal included in the coating material  21  before the reaction of the coating material  21 , or at least one of a metal contained in the pieces of wire  17 , a metal contained in the bonding components  13 , and a metal contained in the conductive circuits  33 . For example, when the metal for covalent bonds is the metal contained in the pieces of wire  17 , the metal is capable of covalently bonding to the pieces of wire  17  itself. Thus, the adhesion of the coating material  21  can be further promoted. 
     In typical formation of the coating material  21 , a reaction of a silane coupling agent proceeds by diluting the silane coupling agent using water or alcohol as a solvent to convert the -Si (OR)x group into a -Si (OH) x  group. However, without adding a solvent containing water or alcohol to the chemical solution of the coating material  21 , the reaction proceeds with moisture of the chemical solution itself, via the medium of water in the air, or by addition of high energy such as heat or light. Thus, adding the solvent is unnecessary. In view of this, the coating material  21  may be formed by applying the chemical solution of the coating material  21  to the semiconductor elements  14  and the pieces of wire  17 , without adding the solvent containing water or alcohol to the chemical solution. Since such a manufacturing method can shorten the time for preparing a solution or the time required for the reaction, increase in the efficiency of manufacturing processes of the semiconductor device  100  can be expected. 
     Modification 
       FIG.  2    is a cross-sectional view illustrating a structure of the semiconductor device  100  according to this modification. As illustrated in  FIG.  2   , the casing  18  may be formed with the conductor  31  being exposed, 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 appropriately modified or omitted. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.