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EP-4361301-B1 - BONDING WIRE FOR SEMICONDUCTOR DEVICES

EP4361301B1EP 4361301 B1EP4361301 B1EP 4361301B1EP-4361301-B1

Inventors

  • ODA, DAIZO
  • ETO, Motoki
  • YAMADA, TAKASHI
  • HAIBARA, TERUO
  • OISHI, RYO

Dates

Publication Date
20260506
Application Date
20220323

Claims (11)

  1. A bonding wire (1) for semiconductor devices, the bonding wire comprising: a core material of Cu or Cu alloy; and a coating layer containing conductive metal formed on a surface of the core material, wherein the coating layer has a region containing Pd as a main component on a core material side, and has a region containing Ni and Pd in a range from a wire surface to a depth of 0.5d when a thickness of the coating layer is defined as d (nm) in a thickness direction of the coating layer, a thickness d of the coating layer is 10 nm or more and 130 nm or less, a ratio C Ni /C Pd of a mass% concentration C Ni of Ni to a mass% concentration C Pd of Pd relative to the entire wire is 0.02 or more and 0.7 or less, and it is characterised in that the conductive metal contained in the coating layer is other than Cu and that a position indicating a maximum concentration of Ni is present in a range from the wire surface to a depth of 0.5d in a concentration profile in a depth direction of the wire, and the maximum concentration of Ni is 10 atomic% or more.
  2. The bonding wire according to claim 1, wherein the coating layer contains Au on a wire surface side in the thickness direction of the coating layer.
  3. The bonding wire according to claim 1 or 2, wherein a ratio C Pd /C M of the mass% concentration C Pd of Pd to a total mass% concentration C M of Pd, Ni, and Au relative to the entire wire is 0.5 or more.
  4. The bonding wire according to any one of claims 1 to 3, wherein a maximum concentration of Pd is 80 atomic% or more in the concentration profile in the depth direction of the wire.
  5. The bonding wire according to any one of claims 1 to 4, wherein the concentration profile in the depth direction of the wire is obtained by performing the measurement using Auger electron spectroscopy, AES, a defined condition while digging down the wire from its surface in the depth direction by Ar sputtering, wherein the defined condition requires that a center of width of a measuring surface (2) is aligned with a center of width of the wire, the width of the measuring surface is 5% or more and 15% or less of a diameter of the wire, and a length of the measuring surface is five times the width of the measuring surface.
  6. The bonding wire according to any one of claims 1 to 5, wherein when forming a free air ball (10), FAB, by using the wire and then measuring crystal orientations in a cross-section of the FAB perpendicular to a compression-bonding direction, a proportion of a crystal orientation <100> angled at 15° or less to the compression-bonding direction is 30% or more.
  7. The bonding wire according to claim 6, wherein the proportion of the crystal orientation <100> angled at 15° or less to the compression-bonding direction is 50% or more.
  8. The bonding wire according to any one of claims 1 to 7, wherein the bonding wire contains at least one first additive element selected from the group consisting of B, P and Mg and a total concentration of the first additive element is 1 ppm by mass or more and 100 ppm by mass or less relative to the entire wire.
  9. The bonding wire according to any one of claims 1 to 8, wherein the bonding wire contains at least one second additive element selected from the group consisting of Se, Te, As and Sb and a total concentration of the second additive element is 1 ppm by mass or more and 100 ppm by mass or less relative to the entire wire.
  10. The bonding wire according to any one of claims 1 to 9, wherein the bonding wire contains at least one third additive element selected from the group consisting of Ga, Ge and In and a total concentration of the third additive element is 0.011% by mass or more and 1.5% by mass or less relative to the entire wire.
  11. A semiconductor device comprising the bonding wire according to any one of claims 1 to 10.

Description

TECHNICAL FIELD The present invention relates to a bonding wire for semiconductor devices. Furthermore, the present invention relates to a semiconductor device including the bonding wire. BACKGROUND ART In semiconductor devices, electrodes formed on a semiconductor chip are connected with a lead frame or electrodes on a substrate using a bonding wire. A bonding method for bonding wires is typically a thermocompression bonding method using ultrasonic waves, and a general-purpose bonding device, a capillary jig used for bonding by inserting a bonding wire therethrough, and the like are used. A bonding process is carried out by performing 1st bonding of a wire part onto an electrode on the semiconductor chip; forming a loop; and finally performing 2nd bonding of a wire part onto the lead frame or an external electrode on the substrate. In the 1st bonding, a tip end of wire is heated and melted by arc heat input to form a free air ball (FAB: Free Air Ball; hereinafter also simply referred to as "ball" or "FAB") through surface tension, and then this ball part is compression-bonded (hereinafter referred to as "ball-bonded") onto the electrode on the semiconductor chip. In the 2nd bonding, the wire part is compression-bonded (hereinafter referred to as "wedge-bonded") onto the external electrode by applying ultrasonic waves and load to the wire part without forming the ball. Gold (Au) has been the common material of the bonding wire, but has been being replaced with copper (Cu) mainly for LSI use (e.g., Patent Literatures 1 to 3). Meanwhile, for on-vehicle device use on the background of recent proliferation of electric vehicles and hybrid vehicles, and further for power device (power semiconductor device) use in large power equipment such as air conditioners and photovoltaic power generation systems, there has been a growing demand for replacement with Cu that has high efficiency and reliability due to its high thermal conductivity and fusing current characteristic. Cu has the drawback of being more susceptible to oxidation than Au. As a method of preventing the surface oxidation of the Cu bonding wire, there has been proposed a structure in which a surface of a Cu core material is coated with a metal such as Pd and Ni (Patent Literature 4). There has been also proposed a Pd-coated Cu bonding wire which has an improved bond reliability of the 1st bonded part by coating a surface of a Cu core material with Pd and adding Pd and Pt into the Cu core material (Patent Literature 5). RELATED ART REFERENCE Patent Literature Patent Literature 1: JP-A-S61-48543Patent Literature 2: JP-T-2018-503743Patent Literature 3: WO 2017/221770Patent Literature 4: JP-A-2005-167020Patent Literature 5: WO 2017/013796Patent Literature 6: US 2016/315063 A1 SUMMARY OF INVENTION The invention is defined in independent claim 1. Further preferred embodiments are defined in the dependent claims. Only embodiments of the description comprising all the technical features of the claims fall under the scope of protection of the claims while the remaining ones correspond to illustrative examples which are useful for the understanding of the relevant technical context. PROBLEM TO BE SOLVED BY THE INVENTION The on-vehicle devices and the power devices tend to be exposed to higher temperature as compared with general electronic devices during operation, and the bonding wire used therefor is required to exhibit a favorable bond reliability in a rigorous high-temperature environment. The present inventors have conducted the evaluation based on characteristics required for the on-vehicle devices and the like and found that, in a conventional Cu bonding wire having a Pd-coating layer, the Pd-coating layer may sometimes be partially exfoliated during the bonding process of the wire, thereby causing exposure of the Cu core material, and as a result, a contact area between the Pd-coating part and the Cu-exposed part is exposed to an environment containing oxygen, water vapor, and sulfur compound-based outgas generated from a sealing resin under the high-temperature environment, resulting in local corrosion of Cu, that is, galvanic corrosion, which makes it difficult to sufficiently achieve the bond reliability of the 2nd bonded part. On the other hand, the bare Cu bonding wire without the Pd-coating layer does not cause a galvanic corrosion, but provides a poor FAB shape and consequently an inferior compression-bonding shape of the 1st bonded part and thus cannot be sufficiently applied for a narrow-pitch bonding required for high-density mounting. An object of the present invention is to provide a novel Cu bonding wire that achieves a favorable FAB shape and reduces a galvanic corrosion in a high-temperature environment to achieve a favorable bond reliability of the 2nd bonded part. MEANS FOR SOLVING PROBLEM As a result of earnest investigation as to the problem described above, the present inventors have found that the problem described above can be solved