Copper-based wire material and semiconductor device

Abstract

The present invention provides: a copper-based wire material that, even when the size of a member such as a semiconductor device in which the copper-based wire material is used is reduced, is unlikely to cause damage to a bonding counterpart material such as a semiconductor chip during bonding to the bonding counterpart material, and that enables an improvement in bonding properties to bonding counterpart materials; and a semiconductor device that uses the same.　This copper-based wire material comprises not less than 99.96 mass% copper (Cu), wherein in a crystal orientation analysis via electron backscatter diffraction (EBSD) performed in a first measurement region which is in a cross-section perpendicular to the extension direction, the average KAM value of all measurement points included in the first measurement region is not more than 0.70°.

Description

Copper-based wire and semiconductor devices

[0001] The present invention relates to a copper-based wire and a semiconductor device.

[0002] Copper-based wires, taking advantage of their high electrical conductivity, are used in a variety of components, including electric wires and cables, wiring for electronic components, bonding wire for semiconductor devices, and electromagnetic wave shielding materials.

[0003] Among the components in which copper-based wire is used, a semiconductor device comprises at least a semiconductor chip and a bonding wire joined to the semiconductor chip. The bonding wire is used, for example, to electrically connect an electrode provided on the top of the semiconductor chip to an inner lead which is a substrate electrode, and is made of copper-based wire made of copper or a copper alloy.

[0004] As an example of such a copper-based wire material, Patent Document 1 describes a gold-coated bonding wire having a core material containing copper or silver as a main component and a coating layer formed on the surface of the core material and containing gold as a main component, wherein the coating layer has a film thickness of 5 nm to 200 nm and a compressive stress of 290 MPa to 590 MPa when deformed 60% relative to the wire diameter. This makes it possible to provide a bonding wire that can continuously and satisfactorily bond thin, multi-layered chip electrodes such as semiconductor memories, has a wide range of bonding energy conditions that do not damage the chip electrodes, has low resistivity, and is inexpensive.

[0005] International Publication No. 2021 / 205674

[0006] In recent years, with the miniaturization of components in which copper-based wires are used, there are an increasing number of cases in which copper-based wires are required to be easily deformed and to have good bondability to other components.

[0007] For example, bonding wires are bonded to semiconductor chips by ultrasonic bonding. However, if the bonding wire has low deformability and is difficult to deform, the load applied when the bonding wire is pressed against the semiconductor chip can damage the semiconductor chip. Furthermore, in recent years, next-generation power semiconductor chips made of SiC, GaN, etc. have been developed as semiconductor chips that contribute to higher power output and current. However, these semiconductor chips are fragile and have become thinner as they are miniaturized, making them more susceptible to damage. Therefore, there has been a demand for a bonding wire that is less likely to damage the semiconductor chip when bonded to the semiconductor chip and that can improve bonding to the semiconductor chip.

[0008] In this regard, the gold-coated bonding wire described in Patent Document 1 has not been sufficiently considered in terms of controlling crystal orientation, etc., and there is room for improvement, particularly in terms of making the semiconductor chip less likely to be damaged when ultrasonically bonding a copper-based wire to a semiconductor chip, and in improving the bondability to the semiconductor chip.

[0009] Furthermore, in various applications other than bonding wire for semiconductor devices, as components in which copper-based wire is used become smaller, there has been a demand for copper-based wire that is less likely to damage the mating material due to its tendency to deform during bonding, and that can enhance bondability to the mating material.

[0010] Therefore, the present invention has been made in consideration of the above problems, and aims to provide a copper-based wire that is less likely to damage a joining partner material such as a semiconductor chip when joined to the joining partner material, even when a component such as a semiconductor device in which the copper-based wire is used is miniaturized, and that can improve the joinability to the joining partner material, and a semiconductor device using the same.

[0011] As a result of extensive research, the inventors have focused on controlling the crystalline structure of a copper-based wire, more specifically, on controlling the KAM value, which represents the crystal orientation difference between measurement points included in a first measurement region on a cross section perpendicular to the extension direction of the copper-based wire, and have found that by reducing the average KAM value of all measurement points included in this first measurement region, the copper-based wire becomes moderately easy to deform and is easily bonded to a bonding partner such as a semiconductor chip through deformation. As a result, even when a component using the copper-based wire is miniaturized, it is possible to obtain a copper-based wire that is less likely to damage a bonding partner when bonded to the bonding partner and that can improve bonding to the bonding partner. In particular, even when the semiconductor chip becomes thinner due to the miniaturization of semiconductor devices, it is possible to obtain a copper-based wire that is less likely to damage a semiconductor chip when bonded to the semiconductor chip and that can improve bonding to the semiconductor chip, and have completed the present invention.

[0012] To achieve the above object, the present invention provides the following key features. (1) A copper-based wire containing 99.96% by mass or more of copper (Cu), wherein, when viewed in a cross section perpendicular to the drawing direction of the copper-based wire, in a crystal orientation analysis performed in a first measurement region in the cross section by electron backscatter diffraction (EBSD), the average KAM value of all measurement points included in the first measurement region is 0.70° or less. (2) The copper-based wire according to (1) above, wherein the ratio of the number of measurement points having the KAM value of 0.60° or less to the total number of all measurement points included in the first measurement region is 30% or more. (3) The copper-based wire according to (1) or (2) above, wherein the ratio of the number of measurement points having the KAM value of 1.00° or more to the total number of all measurement points included in the first measurement region is 8.0% or less. (4) The copper-based wire rod according to any one of (1) to (3) above, wherein, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a second measurement region in a surface layer portion of the cross section, the average KAM value of all measurement points included in the second measurement region is 0.60° or less. (5) The copper-based wire rod according to any one of (1) to (4) above, wherein the copper-based wire rod is made of oxygen-free copper. (6) A semiconductor device having the copper-based wire according to any one of (1) to (5) above, a semiconductor chip, and a joint formed by joining an end of the copper-based wire to a surface of the semiconductor chip, wherein, in a cross section of the joint cut perpendicular to the extension direction of the copper-based wire, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a third measurement area in a portion of the copper-based wire constituting the joint, the average KAM value of all measurement points included in the third measurement area is in the range of 0.9° to 3.7°. (7) The semiconductor device according to (6) above, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in the third measurement area, in a cross section of the joint, the ratio of the number of measurement points having a KAM value in the range of 2.0° to 5.0° to the total number of measurement points included in the third measurement area is in the range of 41% to 82%.

[0013] According to the present invention, it is possible to provide a copper-based wire that is less likely to damage a joining partner material such as a semiconductor chip when joined to the joining partner material, even when a component such as a semiconductor device in which the copper-based wire is used is miniaturized, and that can improve the joinability to the joining partner material, and a semiconductor device using the same.

[0014] In particular, it is possible to provide a copper-based wire material that is less likely to damage a semiconductor chip when bonded to it and that can improve bonding to the semiconductor chip, even when the semiconductor chip becomes thinner as the semiconductor device becomes smaller, and a semiconductor device using the same.

[0015] 1 is a perspective view schematically showing the configuration of a semiconductor device including the copper-based wire material of the present invention. 2 is a cross-sectional view schematically showing a cross section of a joint of a semiconductor device including the copper-based wire material of the present invention, cut perpendicular to the extension direction of the copper-based wire material.

[0016] Hereinafter, preferred embodiments of the copper-based wire rod of the present invention will be described in detail. In the component composition of the copper-based wire rod of the present invention, "mass %" may be simply expressed as "%".

[0017] The copper-based wire contains 99.96% by mass or more of copper (Cu), and when viewed in a cross section perpendicular to the extension direction of the copper-based wire, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a first measurement region in the cross section, the average KAM value of all measurement points included in the first measurement region is 0.70° or less.

[0018] In the copper-based wire of the present invention, in particular, by setting the average KAM value of all measurement points included in the first measurement region to 0.70° or less, the copper-based wire becomes moderately easy to deform and is easily joined to a joining partner material such as a semiconductor chip due to deformation during joining. As a result, the load and ultrasonic energy required for joining to a joining partner material such as a semiconductor chip are reduced, so that even if, for example, the joining partner material, a semiconductor chip, becomes thinner as components such as semiconductor devices in which the copper-based wire is used, it is possible to obtain a copper-based wire that is less likely to damage the joining partner material when joining to the joining partner material and that can improve joinability to the joining partner material.

[0019] Generally, materials undergo elastic and plastic deformation. Elastic deformation is when a material returns to its original shape after the applied force is released, while plastic deformation is when the material does not return to its original shape after the force is released. Regarding plastic deformation, when dislocations are present in the metal structure of copper-based wire, slip deformation occurs, in which specific planes of the material are displaced. Furthermore, when a material deforms, numerous lattice defects are introduced, and the interaction of these lattice defects causes the copper-based wire to work harden. When a work-hardened material is heat-treated, the atoms in the copper-based wire actively move and rearrange, reducing the stored strain (recovery) or using the stored strain energy to generate new, fine, strain-free crystals (recrystallization).

[0020] When ultrasonic bonding is performed on copper-based wire, plastic deformation occurs in the copper-based wire. In particular, at the beginning of ultrasonic bonding, slip deformation occurs on the material surface, which causes shear deformation. This causes atoms of the base material that are not covered by an oxide film to be exposed on the surface of the copper-based wire, creating a new surface. This new surface comes into contact with the bonding substrate, and the atoms bond together, bonding the two together. In this case, by reducing the average KAM value in the cross section, slip deformation is more likely to occur on the material surface at the beginning of ultrasonic bonding, making it easier to bond the copper-based wire to a bonding partner such as a semiconductor chip.

[0021] Generally, the crystal orientation often changes around lattice defects, shear bands, and dislocation accumulation. Therefore, the smaller the KAM (Kernel Average Misorientation) value, which represents the difference in crystal orientation between measurement points, the fewer lattice defects tend to be contained in the metal structure. In the present invention, a method different from the conventional method is used to control the KAM value within a certain range in 0.01° increments, thereby reducing the KAM value over the entire measurement area of ​​the copper-based wire, thereby making it possible to make it difficult for a joining partner material such as a semiconductor chip to be damaged and to improve the joinability to the joining partner material.

[0022] [1] Physical Properties of Copper-Based Wire When viewed in a cross section perpendicular to the extension direction of the copper-based wire, the copper-based wire according to the present invention has a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a first measurement region in the cross section, where the average KAM value of all measurement points included in the first measurement region is 0.70° or less. Here, if the average KAM value of all measurement points included in the first measurement region exceeds 0.70°, recrystallization and recovery have not progressed in the metal structure of the copper-based wire, resulting in a high density of lattice defects, resulting in low deformability of the copper-based wire and even greater difficulty in deformation under small loads. In this case, the shear deformation required at the initial stage of bonding is difficult to occur, making bonding to a bonding partner such as a semiconductor chip difficult. On the other hand, when attempting to bond the copper-based wire to a bonding partner by applying a large load to the copper-based wire, the bonding partner is more likely to be damaged. Therefore, the average KAM value of all measurement points included in the first measurement region is preferably 0.65° or less, more preferably 0.60° or less. Here, the first measurement region can be configured, for example, by the entire range of the cross section.

[0023] Furthermore, in the copper-based wire according to the present invention, the ratio of the number of measurement points having a KAM value of 0.60° or less to the total number of all measurement points included in the first measurement region described above is preferably 30% or more. This makes it easier for the copper-based wire to deform uniformly when ultrasonically bonding the copper-based wire, making it easier for new surfaces to appear, especially at the beginning of ultrasonic bonding, and making it easier to bond the copper-based wire to a bonding partner such as a semiconductor chip. Therefore, the ratio of the number of measurement points having a KAM value of 0.60° or less to the total number of all measurement points included in the first measurement region is more preferably 35% or more.

[0024] Furthermore, in the copper-based wire according to the present invention, it is preferable that the ratio of the number of measurement points having a KAM value of 1.00° or more to the total number of all measurement points included in the first measurement region described above is 8.0% or less. This also makes it easier for the copper-based wire to deform uniformly when ultrasonically bonding the copper-based wire. Therefore, the ratio of the number of measurement points having a KAM value of 1.00° or more to the total number of all measurement points included in the first measurement region is more preferably 5.0% or less.

[0025] Furthermore, in the copper-based wire according to the present invention, when viewed in a cross section perpendicular to the extension direction of the copper-based wire, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a second measurement region in the surface layer portion of the cross section, the average KAM value of all measurement points included in the second measurement region is preferably 0.60° or less. By reducing the average KAM value in the surface layer portion, the deformability of the surface layer portion of the copper-based wire is further enhanced at the initial stage of ultrasonic bonding. This makes it easier for the oxide film formed on the surface of the copper-based wire to be destroyed, making it easier to expose a new surface, making it easier to bond the copper-based wire to a bonding partner such as a semiconductor chip, even when the load applied to the copper-based wire during ultrasonic bonding is small. Therefore, the average KAM value of all measurement points included in the second measurement region is preferably 0.58° or less, more preferably 0.55° or less.

[0026] In this specification, the "surface layer portion" of the copper-based wire material is a portion of the copper-based wire material having a surface that can be bonded to a mating bonding material, and is a portion that is located on the outer periphery side of a position 30% from the periphery with respect to the length of a line segment connecting the periphery and the center of the cross section when the copper-based wire material is viewed in cross section. In this case, the surface layer portion is an annular portion.

[0027] The "KAM value" in this specification can be obtained from crystal orientation analysis data obtained by continuously measuring crystal orientation data using an EBSD detector (TSL, OIM5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL Ltd., JSM-7001FA), and calculating (processing) the measured crystal orientation data using analysis software (TSL Solutions, OIM Analysis). "EBSD" stands for Electron Backscatter Diffraction, and is a crystal orientation analysis technique that utilizes reflected electron Kikuchi diffraction that occurs when a copper-based wire, which is a measurement sample, is irradiated with an electron beam in a scanning electron microscope (SEM). The measurement object is a surface of a copper-based wire (or a copper-based wire bonded to a semiconductor chip, which is a bonding partner) whose cross section perpendicular to the extension direction is polished to a mirror finish, and then subjected to colloidal silica polishing and buffing to remove as much surface distortion as possible. When the first measurement region is used as the measurement region, the measurement region can be, for example, the entire cross section of the copper-based wire. When the second measurement region is used as the measurement region, the measurement region can be, for example, the surface portion of the copper-based wire when viewed in cross section. When the third measurement region described below is used as the measurement region, the measurement region can be, for example, the entire cross section of the bond between the copper-based wire and the bonding partner. In particular, in the case of a semiconductor device described below, the measurement region can be, for example, the entire cross section of the bond between the copper-based wire and the bonding partner semiconductor chip. Measurement can be performed, for example, with a step size of 1 μm. That is, measurement points in the measurement region are provided, for example, every 1 μm. Among these measurement points, measurement points with a reliability index (CI) of 0.1 or more are extracted as measurement points, and the Map-Kernel Average Misorientation analysis software is selected to calculate the KAM value at each measurement point.

[0028] Here, the CI value is a value used as an index for indexing a crystal orientation analysis pattern obtained by the EBSD method and for evaluating whether the calculated crystal orientation is correct. In other words, the CI value is a value reflecting the reliability of the crystal orientation measured by the EBSD method in a cross section perpendicular to the drawing direction of the above-mentioned copper-based wire rod. This CI value can be calculated from the Map-Confidence Index of the analysis software (manufactured by TSL, OIM Analysis) by analyzing the crystal orientation data obtained in the cross section by the EBSD detector as described above.

[0029] [2] Copper-based wire material The copper-based wire contains 99.96% by mass or more of copper (Cu). The copper-based wire may be a copper alloy containing small amounts of elements such as silver (Ag), chromium (Cr), and tin (Sn). However, it is preferable for the copper-based wire to have high conductivity in order to facilitate deformation of the copper-based wire, ensure electrical continuity between the bonding material (e.g., a semiconductor chip) and the substrate electrode, and respond to the recent trend toward higher power and larger current. Therefore, the copper-based wire is preferably made of pure copper containing 99.96% by mass or more of copper (Cu) and inevitable impurities. Among these, it is more preferable for the copper-based wire to be made of oxygen-free copper, i.e., pure copper containing 99.96% by mass or more of Cu and 10 ppm or less of oxygen and inevitable impurities.

[0030] The remainder other than the above elements are inevitable impurities. The inevitable impurities refer to impurities at a level that is inevitably mixed in during the manufacturing process. Depending on the content of the inevitable impurities, they may be a factor that reduces the electrical conductivity of the copper-based wire rod, so it is preferable that the content of the inevitable impurities is small.

[0031] Examples of unavoidable impurities include elements such as aluminum (Al), silver (Ag), beryllium (Be), cadmium (Cd), chromium (Cr), iron (Fe), magnesium (Mg), nickel (Ni), phosphorus (P), lead (Pb), silicon (Si), tin (Sn), titanium (Ti), etc. The upper limit of the content of unavoidable impurities is preferably low from the viewpoint of electrical conductivity, and more specifically, the total content of the above elements is preferably 50 ppm or less.

[0032] [3] Shape and Use of Copper-Based Wire The shape of the copper-based wire can be selected appropriately depending on the current flow rate of the mating member, such as a semiconductor device, the routing space, etc., but among these, it is preferable to use copper-based wire having a round wire, ribbon wire, or rectangular wire shape. Here, a round wire has a circular cross section perpendicular to the extension direction of the conductor of the copper-based wire. A ribbon wire has a cross section perpendicular to the extension direction of the conductor of the copper-based wire, which is surrounded by two straight lines and two curved lines connecting the ends of the two straight lines, i.e., a track shape. A rectangular wire has a cross section surrounded by four straight lines.

[0033] When the copper-based wire is a round wire, it is preferable that the diameter of the copper-based wire (round wire) is in the range of 100 μm to 500 μm, in terms of allowing a relatively high current to flow through the copper-based wire.Furthermore, it is preferable that the diameter of the copper-based wire (round wire) is 500 μm or less, in terms of being able to meet the demand for miniaturization of semiconductor devices and the like in which the copper-based wire is used.

[0034] Furthermore, when the copper-based wire is formed of a copper-based wire having a ribbon wire or a rectangular wire shape, it is preferable that the thickness of the copper-based wire (ribbon wire, rectangular wire) is 100 μm or more, from the viewpoint of being able to pass a relatively high current through the copper-based wire. Furthermore, it is preferable that the thickness of the copper-based wire (ribbon wire, rectangular wire) is 500 μm or less, from the viewpoint of being able to meet the demand for miniaturization of semiconductor devices and the like in which the copper-based wire is used. On the other hand, the width of the copper-based wire (ribbon wire, rectangular wire) is not particularly limited, but is preferably in the same range as the thickness of the copper-based wire (ribbon wire, rectangular wire), i.e., in the range of 100 μm or more and 500 μm or less, from the viewpoint of being able to pass a higher current, for example.

[0035] The "thickness" and "width" of a copper-based wire rod are defined as the size along the direction in which the longest side appears when viewed in a cross section perpendicular to the drawing direction, and the size along the direction perpendicular to this "width" is defined as the "thickness." In addition, in the case of a round wire whose cross section of the copper-based wire rod is circular, the wire diameter of the round wire can be defined as the "thickness" and "width," and these can be considered to be equal.

[0036] The copper-based wire of the present invention is not particularly limited in its application, but is preferably used for conductive components that require ease of deformation and bondability with a bonding partner, and is more preferably used as a bonding wire. More specifically, the copper-based wire 1 of the present invention is preferably used as a bonding wire 4 that electrically connects an electrode 2a provided on a semiconductor chip 2 arranged on a die pad 3 to an inner lead 5, which is a substrate electrode, as shown in the semiconductor device 10 of FIG. 1. This allows the bonding wire 4 to be bonded to the semiconductor chip 2 and the inner lead 5 even with a small load during ultrasonic bonding, making it less likely to damage the semiconductor chip 2 and other components of the semiconductor device 10.

[0037] [4] Regarding the Semiconductor Device As shown in FIG. 1 , the semiconductor device 10 of the present invention includes the copper-based wire 1, the semiconductor chip 2, and a joint 6 formed by bonding an end of the copper-based wire 1 to the surface of the semiconductor chip 2. When viewed in a cross section of the joint 6 cut perpendicular to the extension direction of the copper-based wire 1, the semiconductor device 10 has a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a third measurement region in the copper-based wire 1 constituting the joint 6. The average KAM value of all measurement points included in the third measurement region is in the range of 0.9° to 3.7°. When the copper-based wire 1 bonded to the semiconductor chip 2 is bonded to the semiconductor chip 2, deformation is promoted by ultrasonic vibration, resulting in a greater number of lattice defects. Therefore, the average KAM value of all measurement points included in the third measurement region is in the range of 0.9° to 3.7°, which allows for stronger bonding with the semiconductor device 10. Here, if the average KAM value of all measurement points included in the third measurement region is less than 0.9°, it is considered that the deformation at the joint 6 is insufficient, and the bonding strength between the copper-based wire 1 and the semiconductor chip 2 may not be sufficiently enhanced. Furthermore, if the average KAM value of all measurement points included in the third measurement region exceeds 3.7°, excessive deformation at the joint 6 reduces the cross-sectional area of ​​the joint 6, which may reduce the durability to tension and bending when both ends of the copper-based wire 1 are bonded to the semiconductor chip 2 or the inner lead 5 to form a loop. Furthermore, when forming a loop by ultrasonic bonding, the copper-based wire becomes difficult to deform, which may cause the semiconductor chip to crack. Therefore, it is more preferable that the average KAM value of all measurement points included in the third measurement region be in the range of 1.2° to 3.7°.

[0038] In this specification, the portion of the copper-based wire 1 constituting the joint 6 refers to the portion of the joint 6 between the copper-based wire 1 and the semiconductor chip 2 that is made of the copper-based wire 1 .

[0039] Furthermore, in the semiconductor device 10, when viewed in a cross section of the bond 6, it is preferable that the ratio of the number of measurement points having a KAM value in the range of 2.0° to 5.0° to the total number of measurement points included in the third measurement region in a crystal orientation analysis by electron backscatter diffraction (EBSD) method is in the range of 41% to 82%. By including a moderate number of measurement points with high KAM values ​​in this way, moderate deformation occurs in the bond 6 at the beginning of ultrasonic bonding, making bonding easier, and by suppressing a reduction in cross-sectional area due to excessive deformation, durability to tension and bending can be improved.

[0040] In the semiconductor device 10, when viewed in cross section at the joint 6, the ratio (C / A) of the joint height (C) to the thickness (A) of the copper-based wire 1 is preferably in the range of 0.78 to 0.90. By setting this ratio (C / A) to 0.90 or less, the deformability of the copper-based wire 1 can be further improved. On the other hand, if this ratio (C / A) is less than 0.78, the cross-sectional area of ​​the copper-based wire 1 is reduced, and there is a risk that the copper-based wire 1 will not be able to withstand tension after being joined. Therefore, this ratio (C / A) is more preferably in the range of 0.78 to 0.83.

[0041] Here, the measured value of the bond height (C) can be obtained by observing cross sections of the bond 6 where the copper-based wire 1 and the semiconductor chip 2 are bonded in the semiconductor device 10, cut vertically at three different positions in the extension direction of the copper-based wire 1 as shown in Figure 2, measuring the maximum height of the copper-based wire 1 from the surface of the semiconductor chip 2 (height h in Figure 2), and calculating the average value of the measurement results at the three cross sections.

[0042] In the semiconductor device 10, when viewed in cross section at the joint 6, the ratio (D / B) of the joint width (D) to the width (B) of the copper-based wire 1 is preferably in the range of 1.00 to 1.32. By making this ratio (D / B) 1.00 or more, the joint area between the copper-based wire 1 and the semiconductor chip 2 is increased, thereby reducing the pressure applied to the joint surface 6a, making the semiconductor chip 2 even less likely to be damaged. On the other hand, if this ratio (D / B) exceeds 1.32, the cross-sectional area of ​​the copper-based wire 1 is reduced, which may cause the copper-based wire 1 to be unable to withstand tension after joining. Therefore, it is more preferable that this ratio (D / B) be in the range of 1.10 to 1.32.

[0043] Here, the bonding width (D) can be obtained by observing cross sections of the bonding portion 6 of the semiconductor device 10 where the copper-based wire 1 and the semiconductor chip 2 are bonded, cut perpendicularly at three different positions in the extension direction of the copper-based wire 1 as shown in Figure 2, measuring the length of the bonding surface 6a where the copper-based wire 1 and the semiconductor chip 2 are in contact (width w in Figure 2), and calculating the average value of the measurement results for the three cross sections.

[0044] In the semiconductor device 10, the electrodes 2a and inner leads 5 of the semiconductor chip 2 to which the copper-based wire 1 is bonded can be made of a highly conductive material, such as copper, a copper alloy, aluminum, an aluminum alloy, etc. The copper-based wire 1 can be easily bonded to the electrodes 2a and inner leads 5 made of these materials by ultrasonic bonding.

[0045] The shape of the surface 1a of the copper-based wire 1 in the semiconductor device 10 varies depending on the shape of the jig that applies a load to the copper-based wire 1 during ultrasonic bonding, and is not limited to the shape shown in Figure 2.

[0046] [5] An Example of a Method for Producing a Copper-Based Wire Rod Next, a method for producing a copper-based wire rod according to an embodiment will be described.

[0047] In the method for producing a copper-based wire rod according to the embodiment, a casting step is first performed in which a copper-based material such as electrolytic copper is melted in a reducing atmosphere to obtain a cylindrical ingot called a billet.

[0048] After the casting process, the billet is subjected to the extrusion or rolling process. In the extrusion process, the billet is processed into a round bar by hot extrusion. In the rolling process, the billet is processed into a round bar by repeatedly rolling it from the top or bottom or the left or right.

[0049] After the extrusion or rolling process, a wiredrawing process is carried out in which the round bar obtained in the above process is drawn to a predetermined wire diameter. The wiredrawing process preferably includes a peeling process to remove surface defects that have occurred up to that point.

[0050] Thereafter, a heat treatment step is performed. Here, the heat treatment step performed on the copper-based wire material includes a first heat treatment step and a second heat treatment step.

[0051] In the first heat treatment step, the copper-based wire is heat-treated at a heat treatment temperature in the range of 500°C to 700°C. By performing the first heat treatment step, the copper-based wire after the wire drawing step can be recrystallized, thereby reducing the average KAM value measured in the first measurement region and the second measurement region of the cross section. Here, if the heat treatment temperature in the first heat treatment step is less than 500°C, the crystalline phase generated by recrystallization becomes fine, making it difficult to remove strain, which may adversely affect the distribution of strain introduced by the first wire-drawing step, the drawing step, and the second wire-drawing step described below. Furthermore, if the heat treatment temperature in the first heat treatment step is more than 700°C, while strain is sufficiently removed, the crystalline phase may become coarse, resulting in the risk of wire breakage.

[0052] The heat treatment time in the first heat treatment step is not particularly limited and may be, for example, 1 second or more. Therefore, the heat treatment in the first heat treatment step is preferably annealing while running, in which the wire is passed through a heating furnace, from the viewpoint of avoiding adhesion between the wires. Furthermore, the heat treatment time in the first heat treatment step is preferably short in consideration of manufacturing costs, and may be, for example, 30 seconds or less.

[0053] After the first heat treatment step, a first wire-passing step is performed to apply a bend to the copper-based wire. Applying a bend using a pulley, capstan, or the like in the first wire-passing step can adjust the strain introduced, particularly in the surface layer portion of the copper-based wire. The conditions for the first wire-passing step are that the bending strain (=φ / (φ+2R)φ: wire diameter, R: bending radius) applied using a pulley, capstan, or the like is 1.00% or less, and the number of times the bending strain is applied is 6 or less. If a bending strain higher than 1.00% is applied or if the bending strain is applied 7 or more times, the strain distribution after the first wire-passing step is biased toward the surface layer portion of the copper-based wire, which affects the strain distribution applied in the drawing step described below, and the KAM value of the surface layer portion of the copper-based wire is likely to increase. For example, when the wire diameter in the first wiring step is 0.5 mm or less, the strain introduced into the outer periphery can be reduced to 1.00% or less by setting the pulley diameter to 50 mm or more. In this case, the influence of the strain introduced into the surface layer of the copper-based wire can be reduced, and therefore the increase in the KAM value of the surface layer of the copper-based wire can be suppressed.

[0054] The copper-based wire rod after the first wire-drawing step is subjected to a drawing step. In the drawing step, the copper-based wire rod can be formed by wire drawing or rolling. For example, when forming a round wire as the copper-based wire rod, wire drawing can be performed using, for example, a round hole die. When forming a ribbon wire as the copper-based wire rod, wire drawing can be performed using, for example, a cassette roller die. When forming a rectangular wire as the copper-based wire rod, wire drawing can be performed using, for example, a cassette roller die or a rectangular die.

[0055] The total processing rate of the wire drawing or rolling in the drawing step is in the range of 10% to 60%. If the total processing rate in the drawing step is less than 10%, the driving force for recrystallization will be insufficient during the second heat treatment step described below, making it difficult to obtain a metal structure with a low KAM value in the surface layer portion after the second heat treatment step. On the other hand, if the total processing rate exceeds 60%, strain tends to be introduced throughout the copper-based wire rod, increasing the KAM value of the copper-based wire rod. In particular, the total processing rate in the drawing step is preferably in the range of 15% to 50%.

[0056] Furthermore, when wire drawing is performed using a die such as a round hole die or a rectangular die in the drawing process, the die angle of the die is preferably 10° or more, more preferably 15° or more. This allows for strong strain to be applied to the central portion of the copper-based wire, making it easier to further reduce the KAM value of the surface layer portion of the copper-based wire. The upper limit of the die angle is not particularly limited, but may be 20° or less, for example, from the viewpoint of improving the workability of wire drawing.

[0057] In addition, when wire drawing is performed using a die in the drawing process, it is preferable to set the processing rate per pass to 20% or less. This allows a strong strain to be applied to the central part of the copper-based wire, making it easier to further reduce the KAM value in the surface layer part of the copper-based wire. Therefore, it is more preferable to set the processing rate per pass in the drawing process to 15% or less.

[0058] In this specification, the "processing rate" is expressed as a value (%) obtained by subtracting the cross-sectional area after wiredrawing (after rolling) from the cross-sectional area before wiredrawing (before rolling), dividing the result by the cross-sectional area before wiredrawing (before rolling), and multiplying the result by 100. Here, the processing rate per pass is the processing rate per one wiredrawing (rolling), and the total processing rate is the processing rate before and after the drawing step.

[0059] The copper-based wire rod after the drawing process is subjected to a second wire-running process in which a bending force is applied. Applying a bending force using a pulley, capstan, or the like in the second wire-running process can adjust the strain introduced, particularly in the surface layer portion of the copper-based wire rod. The conditions for the second wire-running process are that the bending strain applied using a pulley, capstan, or the like is 1.00% or less, and the number of times the bending strain is applied is 6 or less. Here, if a bending strain higher than 1.00% is applied or if the bending strain is applied 7 or more times, the amount of strain applied by unbending and unwinding increases, which affects the distribution of the strain applied in the drawing process, and therefore the KAM value of the surface layer portion of the copper-based wire rod is likely to increase. In particular, in the copper-based wire rod manufacturing method of this embodiment, the total processing rate in the drawing process is low, and the strain applied to the copper-based wire rod is relatively small, so the impact of the second wire-running process is significant. On the other hand, by setting the bending strain applied in the second wiring process to 1.00% or less and setting the number of times the bending strain is applied to 6 or less, the strain distribution obtained in the above-mentioned drawing process is maintained, and the KAM value of the surface layer portion of the copper-based wire can be maintained at a low level.

[0060] After the second wiring step, the second heat treatment step is performed. In the second heat treatment step, recrystallization is required to obtain a predetermined low KAM value, so the heat treatment needs to be performed for a relatively long time. Therefore, it is preferable to use a batch type heat treatment (batch annealing) in which the copper-based wire rod wound on a spool or the like is placed in a heating furnace and heat-treated.

[0061] When the second heat treatment step is performed by batch heat treatment, the heat treatment temperature is preferably in the range of 350° C. or higher and lower than 500° C. Here, by setting the heat treatment temperature in the second heat treatment step to 350° C. or higher, recrystallization and recovery occur in the metal structure of the copper-based wire, so that a copper-based wire having a desired low KAM value can be obtained. On the other hand, the upper limit of the heat treatment temperature in the second heat treatment step is not particularly limited, but is preferably lower than 500° C. from the viewpoint of not affecting the unwinding of the wire due to adhesion of the copper-based wire wound on a spool or the like.

[0062] When the second heat treatment step is performed by a batch-type heat treatment, the heat treatment time is preferably long from the viewpoint of causing sufficient recrystallization and recovery in the metal structure of the copper-based wire rod, and more specifically, is preferably one hour or more.

[0063] The second heat treatment step can also be performed by running heat treatment, in which the wire is passed through a heating furnace. When running heat treatment is performed, the heat treatment time is shortened, so the heat treatment needs to be performed at a higher temperature than in the case of batch heat treatment. In this case, the problem of adhesion of the copper-based wire in the heating furnace does not occur, so the heat treatment temperature in the second heat treatment step can be 500°C or higher.

[0064] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept of the present invention and the scope of the claims, and can be modified in various ways within the scope of the present invention.

[0065] Next, in order to further clarify the effects of the present invention, examples of the present invention and comparative examples will be described, but the present invention is not limited to these examples of the present invention.

[0066] (Invention Examples 1 to 24 and Comparative Examples 1 to 5) Copper-based materials composed of the ingredients shown in Table 1 were subjected to a casting process, an extrusion process, and a wiredrawing process. In the wiredrawing process, a round-hole die was used to draw the 8 mm diameter round bar obtained by the extrusion process, and a peeling process was performed to remove surface defects that had occurred up to that point, thereby forming a copper-based wire rod with a smaller wire diameter. Subsequently, a first heat treatment process was performed in which the copper-based wire rod was heat-treated for 5 seconds under conditions in the range of 600°C to 700°C, and then a first wire-drawing process was performed under the conditions shown in Table 2. Next, a drawing process was performed using a round-hole die under the conditions shown in Table 2 to finish the copper-based wire into an even thinner round wire with a wire diameter of 500 μm (both thickness and width: 500 μm), and then a second wire-drawing process was performed under the conditions shown in Table 2. Thereafter, a second heat treatment step was performed by batch heat treatment at a heat treatment temperature of 400° C. for 1 hour to obtain a copper-based wire rod. On the other hand, for Comparative Examples 1 to 5, the conditions of the magnitude of the bending strain applied in the first wire-passing step and the second wire-passing step and the number of times the bending strain was applied were changed to obtain a copper-based wire rod.

[0067] One end of the obtained copper-based wire was ultrasonically bonded to a semiconductor chip, which was the mating material, and the other end was connected to a copper plate that served as a substrate electrode (inner lead), thereby obtaining a test specimen of a semiconductor device, which is a component that uses the copper-based wire.

[0068] (Invention Examples 25 to 27) A copper-based material composed of the ingredients shown in Table 4 was subjected to a casting process, an extrusion process, and a wiredrawing process. In the wiredrawing process, a round-hole die was used to draw an 8 mm diameter round bar obtained by the extrusion process, and a peeling process was performed to remove surface defects that had occurred up to that point, thereby forming a copper-based wire rod with a smaller wire diameter. Subsequently, a first heat treatment process was performed in which the copper-based wire rod was heat-treated for 5 seconds under conditions in which the temperature was in the range of 600°C to 700°C, and then a first wire-drawing process was performed under the conditions shown in Table 5. Next, a drawing process was performed using a rectangular die or a cassette roller die (CRD) that draws wire through a gap between two rolls to produce a ribbon wire or rectangular wire having the thickness and width shown in Table 5, and then a second wire-drawing process was performed under the conditions shown in Table 5. Thereafter, a second heat treatment step was carried out by batch heat treatment at a heat treatment temperature of 400° C. for 1 hour to obtain a copper-based wire material.

[0069] One end of the obtained copper-based wire was ultrasonically bonded to a semiconductor chip, which was the mating material, and the other end was connected to a copper plate that served as a substrate electrode (inner lead), thereby obtaining a test specimen of a semiconductor device, which is a component that uses the copper-based wire.

[0070] The ultrasonic bonding conditions were such that the bonding load, which is the load applied to the copper-based wire during bonding, was 2000 gf, and the other conditions were the same for all examples and comparative examples.

[0071] [Various Measurement and Evaluation Methods] The copper-based wire rods according to the above-described invention examples and comparative examples were used to carry out the following characteristic evaluations. The evaluation conditions for each characteristic were as follows.

[0072] [1] Component Analysis Three samples were measured using an optical emission spectrometer (manufactured by Shimadzu Corporation) to determine the total amount of unavoidable impurities for all samples in Inventive Examples 1 to 27 and Comparative Examples 1 to 5. For the Inventive Examples and Comparative Examples in Tables 1 and 4, where the "raw material" is listed as "oxygen-free copper," the oxygen content of small pieces cut from the billets was measured three times using an oxygen / nitrogen analyzer (manufactured by Horiba, Ltd.). All samples were confirmed to be oxygen-free copper with an average oxygen content of 10 ppm or less. For the Inventive Examples in Table 1, where the "raw material" is listed as "tough pitch copper," the oxygen content of small pieces cut from the billets was measured three times using an oxygen / nitrogen analyzer (manufactured by Horiba, Ltd.). All samples were confirmed to be tough pitch copper with an average oxygen content of 200 ppm or more and 400 ppm or less.

[0073] [2] Measurement of KAM values ​​at measurement points included in the first measurement region, the second measurement region, and the third measurement region The KAM values ​​at measurement points included in the first measurement region, the second measurement region, and the third measurement region were obtained from crystal orientation analysis data calculated (processed) using analysis software (TSL Solutions, OIM Analysis) after continuously measuring crystal orientation data using an EBSD detector (TSL OIM 5.0 HIKARI) attached to a high-resolution scanning analytical electron microscope (JEOL JSM-7001FA). The measurement object was a copper-based wire not bonded to a semiconductor chip or a copper-based wire bonded to a semiconductor chip, whose cross section perpendicular to the extension direction was polished to a mirror finish and further subjected to colloidal silica polishing and buffing to remove surface distortion as much as possible. When the first measurement area was used as the measurement area, the measurement area was the entire cross section of the copper-based wire not bonded to a semiconductor chip. When the second measurement area was used as the measurement area, the measurement area was the surface portion of the cross section of the copper-based wire not bonded to a semiconductor chip, i.e., the annular portion located 30% from the periphery of the line segment connecting the periphery (surface) of the cross section of the copper-based wire to the center of the cross section. When the third measurement area was used as the measurement area, the measurement area was the entire cross section of the bonded portion between the copper-based wire and the semiconductor chip in a semiconductor device specimen to which the copper-based wire was bonded. Measurements were performed with a step size of 1 μm. Among the measurement points in the measurement area, measurement points with a reliability index (CI) of 0.1 or more were extracted as measurement points, and the Map-Kernel Average Misorientation analysis software was selected to calculate the KAM value at each measurement point.

[0074] Here, the reliability index (CI) was calculated from the Map-Confidence Index of analysis software (manufactured by TSL, OIM Analysis) by analyzing crystal orientation data obtained in a cross section by an EBSD detector.

[0075] The following numerical values ​​(a) to (f) were calculated from the KAM value data obtained in each measurement region. The results are shown in Tables 3 and 6. (a) The average KAM values ​​of all measurement points included in the first measurement region. (b) The ratio of the number of measurement points with a KAM value of 0.60° or less to the total number of all measurement points included in the first measurement region. (c) The ratio of the number of measurement points with a KAM value of 1.00° or more to the total number of all measurement points included in the first measurement region. (d) The average KAM values ​​of all measurement points included in the second measurement region. (e) The average KAM values ​​of all measurement points included in the third measurement region. (f) The ratio of the number of measurement points with a KAM value in the range of 2.0° to 5.0° to the total number of all measurement points included in the third measurement region.

[0076] [2] Evaluation of Bondability When ultrasonic bonding was performed on 20 copper-based wires and 20 semiconductor chips, the copper-based wires and semiconductor chips used in the examples and comparative examples, the number of copper-based wires and semiconductor chips that could be bonded without breaking the semiconductor chips was counted, and the percentage of the number of semiconductor chips that could be bonded without breaking the semiconductor chips out of 20 was calculated (bonding probability). A bonding probability of 100% was evaluated as "A," a bonding probability of 90% or more but less than 100% was evaluated as "B," a bonding probability of 70% or more but less than 90% was evaluated as "C," and a bonding probability of less than 70% was evaluated as "D." In this example, "A," "B," and "C" were evaluated as pass levels. The results are shown in Tables 3 and 6.

[0077] [3] Calculation of the ratio of the bond height to the thickness of the copper-based wire. For the portion of the obtained semiconductor device specimen where the copper-based wire and the semiconductor chip are bonded, cross sections of the bond were cut perpendicularly at three different positions in the extension direction of the copper-based wire, and the maximum height of the copper-based wire from the surface of the semiconductor chip (height h in FIG. 2) was measured as the bond height. The average value of the measurement results at the three cross sections was used as the measured bond height (C). In addition, the ratio (C / A) of the obtained measured bond height (C) to the thickness (A) of the copper-based wire before bonding was calculated. The results are shown in Tables 3 and 6.

[0078] Regarding the calculated value of the ratio of the bond height to the thickness of the copper-based wire (C / A), if it was 0.78 or more and 0.83 or less, the copper-based wire was evaluated as being particularly excellent in terms of high deformability, with a rating of "◎". Furthermore, if the calculated value of the ratio of the bond height to the thickness of the copper-based wire (C / A) was greater than 0.83 and less than 0.90, the copper-based wire was evaluated as being good in terms of high deformability, with a rating of "○". On the other hand, if the calculated value of the ratio of the bond height to the thickness of the copper-based wire (C / A) exceeded 0.90, the copper-based wire was evaluated as being poor in terms of low deformability, with a rating of "×". Furthermore, if the calculated value of the ratio of the bond height to the thickness of the copper-based wire (C / A) was less than 0.78, the cross-sectional area of ​​the copper-based wire was reduced, and the copper-based wire may not be able to withstand tension after ultrasonic bonding, with a rating of "×". In this example, "◎" and "○" were evaluated as pass levels. The results are shown in Tables 3 and 6.

[0079] [4] Calculation of the ratio of the bond width to the width of the copper-based wire. For the bonded portion of the obtained semiconductor device specimen, the copper-based wire and the semiconductor chip were cut perpendicularly at three different positions along the extension direction of the copper-based wire. The cross sections of the bonded portion were observed. The length of the bonded surface where the copper-based wire and the semiconductor chip contacted (width w in FIG. 2) was measured as the bond width. The average of the measurement results for the three cross sections was used as the measured bond width (D). The ratio (D / B) of the measured bond width (D) to the width (B) of the copper-based wire before bonding was calculated. The results are shown in Tables 3 and 6.

[0080] Regarding the calculated value of the ratio of the bonding width to the width of the copper-based wire (D / B), when it was 1.10 or more and 1.32 or less, the copper-based wire had high deformability and the pressure applied to the bonding surface with the semiconductor chip was small, making the semiconductor less likely to break. This was evaluated as "◎". Furthermore, when the calculated value of the ratio of the bonding width to the width of the copper-based wire (D / B) was 1.00 or more and less than 1.10, the copper-based wire had high deformability and was good in that the semiconductor was less likely to break. This was evaluated as "◯". On the other hand, when the calculated value of the ratio of the bonding width to the width of the copper-based wire (D / B) was less than 1.00, the copper-based wire had low deformability or the semiconductor was easily broken. This was evaluated as "×". In addition, when the calculated value of the ratio of the bonding width to the width of the copper-based wire (D / B) exceeded 1.32, the cross-sectional area of ​​the copper-based wire was reduced, and the copper-based wire was evaluated as being defective because it may not be able to withstand the tension after ultrasonic bonding. In this example, "◎" and "◯" were evaluated as pass levels. The results are shown in Tables 3 and 6.

[0081] [5] Overall Evaluation When all three of the evaluation results relating to the probability of bonding between the copper-based wire and the semiconductor chip, the ratio of the bonding height to the thickness of the copper-based wire (C / A), and the ratio of the bonding width to the width of the copper-based wire (D / B) were evaluated as "A" or "◎", it was determined that all three of these characteristics were particularly excellent, and the overall evaluation was evaluated as "A". Furthermore, when at least one of the evaluation results relating to the probability of bonding between the copper-based wire and the semiconductor chip, the ratio of the bonding height to the thickness of the copper-based wire (C / A), and the ratio of the bonding width to the width of the copper-based wire (D / B) was evaluated as "B" or "◯", and all three evaluation results were evaluated as "A", "B", "◎", or "◯", it was determined that all three of these characteristics were excellent, and the overall evaluation was evaluated as "B". In addition, among the three evaluation results regarding the probability of bonding between the copper-based wire and the semiconductor chip, the ratio of the bonding height to the thickness of the copper-based wire (C / A), and the ratio of the bonding width to the width of the copper-based wire (D / B), if the probability of bonding between the copper-based wire and the semiconductor chip was evaluated as "C", and if either the ratio of the bonding height to the thickness of the copper-based wire (C / A) or the ratio of the bonding width to the width of the copper-based wire (D / B) was evaluated as "◎" or "◯", it was determined that all three characteristics were good, and the overall evaluation was evaluated as "C". On the other hand, among the three evaluation results regarding the probability of bonding between the copper-based wire and the semiconductor chip, the ratio of the bonding height to the thickness of the copper-based wire (C / A), and the ratio of the bonding width to the width of the copper-based wire (D / B), if at least one of the evaluation results was "D" or "×", it was determined that at least one of these three characteristics was insufficient, and the overall evaluation was evaluated as "D". The results are shown in Tables 3 and 6.

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] As shown in Tables 1 to 6, in Examples 1 to 27 of the present invention, the average KAM value of all measurement points included in the first measurement region was controlled to 0.70° or less. Therefore, when joining the copper-based wire to the semiconductor chip, which is the joining partner material, it was possible to make the semiconductor chip less likely to be damaged, and to improve the joining ability of the copper-based wire to the semiconductor chip.

[0089] On the other hand, in Comparative Examples 1 to 5, the average KAM value of all measurement points included in the first measurement region exceeded 0.70°. Therefore, in Comparative Examples 1 to 5, there were many copper-based wires in which the semiconductor chip was damaged when being joined to the semiconductor chip, which was the joining partner material, and many copper-based wires that were not ultrasonically joined to the semiconductor chip.

[0090] REFERENCE SIGNS LIST 1 Copper-based wire 1a Surface of copper-based wire 10 Semiconductor device 2 Semiconductor chip 2a Electrode of semiconductor chip 3 Die pad 4 Bonding wire 5 Inner lead 6 Bonding portion 6a Bonding surface h Bonding height w Bonding width

Claims

1. A copper-based wire containing 99.96% or more by mass of copper (Cu), wherein, when viewed in a cross section perpendicular to the extension direction of the copper-based wire, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in a first measurement area in the cross section, the average KAM value of all measurement points included in the first measurement area is 0.70° or less.

2. The copper-based wire according to claim 1, wherein the ratio of the number of measurement points having a KAM value of 0.60° or less to the total number of all measurement points included in the first measurement region is 30% or more.

3. The copper-based wire according to claim 1, wherein the ratio of the number of measurement points at which the KAM value is 1.00° or more to the total number of all measurement points included in the first measurement region is 8.0% or less.

4. The copper-based wire rod according to claim 1, wherein, in a crystal orientation analysis by electron backscatter diffraction (EBSD) performed in a second measurement region in a surface layer portion of the cross section, the average KAM value of all measurement points included in the second measurement region is 0.60° or less when viewed in the cross section.

5. The copper-based wire according to claim 1, wherein the copper-based wire is made of oxygen-free copper.

6. A semiconductor device comprising the copper-based wire according to any one of claims 1 to 5, a semiconductor chip, and a joint formed by joining an end of the copper-based wire to the surface of the semiconductor chip, wherein, when viewed in a cross section of the joint cut perpendicular to the extension direction of the copper-based wire, in a crystal orientation analysis by electron backscatter diffraction (EBSD) method carried out in a third measurement region in the copper-based wire portion constituting the joint, the average KAM value of all measurement points included in the third measurement region is in the range of 0.9° to 3.7°.

7. The semiconductor device of claim 6, wherein, in a crystal orientation analysis performed by electron backscatter diffraction (EBSD) in the third measurement region when viewed in a cross section of the junction, the ratio of the number of measurement points having a KAM value in the range of 2.0° or more and 5.0° or less to the total number of all measurement points included in the third measurement region is in the range of 41% or more and 82% or less.

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