Gold-coated silver bonding wire and method for manufacturing the same, and semiconductor device and method for manufacturing the same

Abstract

The present invention provides a gold-coated silver bonding wire capable of suppressing short circuits caused by ion migration between ball compression parts. The gold-coated silver bonding wire 1 includes a core material 2 containing silver as a main component, and a coating layer 3 provided on the surface of the core material 2 and containing gold as a main component. The gold-coated silver bonding wire 1 contains gold in a range of 2 mass % to 7 mass % relative to the total amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium and tellurium in a range of 1 mass ppm to 80 mass ppm.

Description

Technical Field

[0001] The present invention relates to a gold-coated silver bonding wire and a method for producing the same, and a semiconductor device using the wire and a method for producing the same. Background Art

[0002] The electrodes of the semiconductor chip are connected to the external electrodes of the circuit substrate such as the lead frame or the circuit board by, for example, wire bonding. In wire bonding, generally, one end of the bonding wire is bonded to the electrode of the semiconductor chip by, for example, a method called ball bonding (first bonding), and the other end of the bonding wire is bonded to the external electrode of the circuit substrate by a method called wedge bonding (second bonding). In ball bonding, one end of the bonding wire is melted by discharge or the like, and solidified into a spherical shape by surface tension or the like to form a ball. The solidified ball is called a free air ball (FAB), and is connected to the electrode of the semiconductor chip by ultrasonic and thermal compression bonding methods.

[0003] For the bonding wire, metal wires such as gold wire, silver wire, copper wire, aluminum wire, and covered wires covered with other metals can be used. The semiconductor device is formed by resin-sealing a semiconductor chip and a circuit substrate connected by wire bonding, and for example, a semiconductor storage device with a built-in memory chip is known. In such a semiconductor device, for example, in order to seek high performance and high functionality such as miniaturization of the device and high storage capacity, the formation density of the elements or the wiring density has been advanced, and with this, the formation pitch of the electrodes of the semiconductor chip can be narrowed. If the spacing between the electrodes is narrowed, ion migration occurs between adjacent ball compression parts in the ball compression part obtained by ball bonding one end of the bonding wire, and it becomes easy to cause a short circuit between the electrodes (ion migration).

[0004] Ion migration is the main reason for damaging the reliability or soundness of integrated circuits. As a form of ion migration, there is a state in which the metal between the parallel electrodes on the surface of the substrate is generally called dendrites, or a state in which metal ions dissolved from the anode are precipitated at the boundary between the glass fiber and the epoxy resin in the inner layer of the substrate called CAF (Conductive Anodic Filament). The form of ion migration that is worried about in semiconductor devices is dendrites. In semiconductor devices, gaps are sometimes generated at the boundary between the semiconductor chip or substrate and the epoxy resin. The moisture that penetrates from the epoxy resin and the electric field applied between the electrodes on the insulated chip act to cause ionization of the metal at the anode. The metal ions move between the ball compression parts and are reduced and precipitated at the cathode. Since this phenomenon occurs continuously during the application of the electric field, the metal precipitated in the form of dendrites soon reaches the anode, causing insulation degradation or short circuit.

[0005] It is known that the susceptibility of ion migration varies depending on the type of conductor metal, the strength of the electric field applied between the electrodes, etc. Regarding conductor metals, ion migration is generally easy to occur in the order of silver (Ag) → copper (Cu) → lead (Pb) → tin (Sn) → zinc (Zn) → gold (Au). For example, ion migration is difficult to occur between the compression parts of the ball using gold bonding wire, and on the other hand, it is easy to occur between the compression parts of the ball using silver bonding wire. Silver bonding wire is cheaper than gold bonding wire, but on the other hand, it has the same durability and conductivity. In addition, since it has high deformation ability and easy to absorb stress compared with copper bonding wire, it has excellent fracture resistance such as cracks caused by thermal stress. However, on the other hand, silver bonding wire becomes easy to cause ion migration based on the narrowing of the spacing between the electrodes as described above. In addition, the electric field strength is determined by the voltage applied between the electrodes and the distance between the electrodes, and ion migration becomes easy to cause as the electric field strength increases. In recent years, the reduction of power consumption of semiconductor devices has been promoted, and there is a tendency for the applied voltage to become lower. On the other hand, since the electric field strength is expected to become higher and higher as the pitch is narrowed, there is a strong demand for its suppression. However, in order to suppress the ion migration of silver, a method of alloying with gold or palladium is known, but the silver alloy wire has a problem of increased resistance due to alloying palladium or gold with pure silver.

[0006] Therefore, regarding the silver bonding wire, it is also proposed to form a covering layer of gold or a gold alloy on the surface of the silver core material. However, although the gold in the covering layer functions as a material for suppressing the ionization of silver due to the application of an electric field or moisture, it is not possible to effectively suppress ion migration when only the covering layer is formed. That is, when one end of the gold-coated silver bonding wire is melted to form a ball, the gold in the covering layer enters the molten silver core material and solidifies in this state, increasing the amount of silver exposed on the surface of the FAB. When such a FAB is bonded to an electrode, since a large amount of silver existing on the surface of the ball compression portion causes ion migration, it is not possible to effectively suppress insulation degradation or short circuit between the ball compression portions.

[0007] Regarding conventional covered silver bonding wires, for example, International Publication No. 2013 / 129253 (Patent Document 1) discloses a bonding wire having a lead coating layer containing one or more of Pd, Au, Zn, Pt, Ni, Sn or their alloys or oxides or nitrides of these metals on the surface of the Ag or Ag alloy wire. Patent Document 1 discloses preventing migration of Ag ions dissolved when Ag or Ag alloy wires having a coating layer are used in connections within a power semiconductor device. However, since Patent Document 1 is based on the premise of wedge bonding of the metal wire, it does not consider the ingress of constituent elements of the coating layer into the Ag wire during FAB formation, and further does not disclose a structure for suppressing the ingress of constituent elements into the Ag wire.

[0008] In addition, Japanese Patent Publication No. 2001-196411 (Patent Document 2) discloses a bonding wire having an Ag wire and an Au film covering the Ag wire, wherein the Au film contains at least one element selected from the group consisting of Na, Se, Ca, Si, Ni, Be, K, C, Al, Ti, Rb, Cs, Mg, Sr, Ba, La, Y, and Ce. Patent Document 2 discloses that since the shape of the FAB in the Au-covered Ag wire is not axisymmetric, the Au film is made to contain the above-mentioned elements to suppress arc discharge from concentrating on one point, and an arc is generated from the entire surface to stabilize the shape of the FAB. However, Patent Document 2 does not consider the entry of Au into the Ag wire when the FAB is formed, and further does not disclose a structure for suppressing the entry of Au into the Ag wire. Therefore, Patent Document 2 does not suggest that ion migration occurs when using a gold-covered silver bonding wire, and further does not disclose a structure of a gold-covered silver bonding wire for suppressing ion migration.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: International Publication No. 2013 / 129253

[0012] Patent Document 2: Japanese Patent Application Publication No. 2001-196411 Summary of the invention

[0013] Problems to be solved by the invention

[0014] The problem to be solved by the present invention is to provide a gold-coated silver bonding wire capable of suppressing short circuits caused by ion migration between ball compression parts and a method for manufacturing the same. Another problem is to provide a semiconductor device capable of improving insulation reliability between ball compression parts and a method for manufacturing the same by using such a gold-coated silver bonding wire even when the pitch between electrodes is narrowed.

[0015] Means for solving problems

[0016] The first gold-coated silver bonding wire of the present invention comprises a core material containing silver as a main component and a coating layer provided on the surface of the core material and containing gold as a main component. The first gold-coated silver bonding wire of the present invention contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium and tellurium in a range of 1 mass ppm to 80 mass ppm.

[0017] The second gold-coated silver bonding wire of the present invention comprises a core material containing silver as a main component and a coating layer provided on the surface of the core material and containing gold as a main component. The second gold-coated silver bonding wire of the present invention contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium and tellurium, and when a free air ball is formed at one end of the gold-coated silver bonding wire, the free air ball has a gold-enriched region at a position corresponding to a position 60% or more from the midpoint of the line connecting the neck of the ball in a cross-sectional view of the bonding wire and the free air ball, on a vertical line extending from the midpoint of a line connecting the lead wire and the neck of the ball to a position corresponding to the lowest point of the ball.

[0018] The method for producing a gold-coated silver bonding wire of the present invention is a method for producing a gold-coated silver bonding wire having a core material containing silver as a main component and a coating layer provided on the surface of the core material and containing gold as a main component, wherein the gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium and tellurium in a range of 1 mass ppm to 80 mass ppm.

[0019] The semiconductor device of the present invention is a semiconductor device comprising one or more semiconductor chips having at least one electrode and a lead frame or a substrate, and connecting at least one selected from the group consisting of an electrode of a semiconductor chip and a lead frame, an electrode of a semiconductor chip and an electrode of a substrate, and electrodes of a plurality of semiconductor chips with a gold-coated silver bonding wire, wherein the gold-coated silver bonding wire comprises a core material containing silver as a main component and a coating layer provided on the surface of the core material and containing gold as a main component, and the gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the total amount of the lead, and contains at least one chalcogen element selected from sulfur, selenium and tellurium in a range of 1 mass ppm to 80 mass ppm.

[0020] The method for manufacturing a semiconductor device of the present invention is a method for manufacturing a semiconductor device comprising one or more semiconductor chips having at least one electrode and a lead frame or a substrate, and connecting at least one selected from between the electrode of the semiconductor chip and the lead frame, between the electrode of the semiconductor chip and the electrode of the substrate, and between the electrodes of the plurality of semiconductor chips with a gold-coated silver bonding wire, wherein the gold-coated silver bonding wire comprises a core material containing silver as a main component and a coating layer provided on the surface of the core material and containing gold as a main component, and the gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the total amount of the lead, and contains at least one chalcogen element selected from sulfur, selenium and tellurium in a range of 1 mass ppm to 80 mass ppm.

[0021] Effects of the Invention

[0022] According to the gold-coated silver bonding wire and the manufacturing method thereof of the present invention, when the chalcogen element (at least one of sulfur, selenium and tellurium) contained in the coating layer forms a free air ball (FAB) at one end of the bonding wire, it promotes the formation of a gold-enriched region on the surface of the FAB. The gold-enriched region on the surface of the FAB suppresses ion migration. Therefore, it is possible to suppress short circuits between electrodes when ball bonding is performed between one end of the gold-coated silver bonding wire of the present invention and an electrode, and it is possible to expect ball bonding in the atmosphere.

[0023] According to the semiconductor device and the manufacturing method thereof of the present invention, the gold-enriched region formed on the surface of the FAB can suppress the occurrence of ion migration. Therefore, since insulation degradation or short circuit can be suppressed even when the spacing between electrodes is narrowed, the manufacturability and reliability of the semiconductor device can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a longitudinal cross-sectional view showing a gold-coated silver bonding wire according to an embodiment.

[0025] Figure 2 It is a transverse cross-sectional view showing a gold-coated silver bonding wire according to an embodiment.

[0026] Figure 3 This is a cross-sectional view showing a state where FAB is formed at one end of a gold-coated silver bonding wire according to the embodiment.

[0027] Figure 4 This is an EPMA image showing a gold-rich region formed on the FAB surface at one end of a conventional gold-coated silver bonding wire.

[0028] Figure 5 This is an EPMA image showing a gold-rich region on the FAB surface formed at one end of the gold-coated silver bonding wire according to the embodiment.

[0029] Figure 6 This is a cross-sectional view showing an example of the analysis position of a gold-enriched region on the FAB surface formed at one end of the gold-coated silver bonding wire according to the embodiment.

[0030] Figure 7 This is a cross-sectional view showing another example of the analysis position of the gold-enriched region on the FAB surface formed at one end of the gold-coated silver bonding wire according to the embodiment.

[0031] Figure 8 This is a cross-sectional view showing a stage before the semiconductor device according to the embodiment is sealed with resin.

[0032] Fig. 9 It is a cross-sectional view showing a stage after the semiconductor device according to the embodiment is sealed with resin.

[0033] Fig.10This is a cross-sectional view showing a ball compression portion bonded to an electrode of a semiconductor chip in a semiconductor device according to an embodiment.

[0034] Fig.11 Yes Fig.10 The cross-sectional view of the ball compression portion shown in FIG. DETAILED DESCRIPTION

[0035] Hereinafter, the gold-coated silver bonding wire and its manufacturing method and the semiconductor device and its manufacturing method according to the embodiments of the present invention are described with reference to the accompanying drawings. In each embodiment, the same symbols are sometimes marked on substantially the same components, and part of the description is omitted. The accompanying drawings are schematic diagrams, and the relationship between thickness and plane size, the ratio of thickness of each part, the ratio of longitudinal size to lateral size, etc. are sometimes different from those of actual devices.

[0036] (Gold-coated silver bonding wire and method for manufacturing the same)

[0037] like Figure 1 and Figure 2 As shown in , the gold-coated silver bonding wire 1 of the embodiment includes a core material (also referred to as a silver core material) 2 having silver (Ag) as a main component and a coating layer 3 provided on the surface of the core material 2 and containing gold (Au) as a main component and at least one chalcogen element selected from sulfur (S), selenium (Se) and tellurium (Te). In the gold-coated silver bonding wire 1 of the embodiment, gold is contained in a range of 2 mass % to 7 mass %, and the chalcogen element is contained in a range of 1 mass ppm to 80 mass ppm relative to the total amount of the core material 2 and the coating layer 3 (the total amount of the lead 1).

[0038] The core material (silver core material) 2 having silver as the main component is a member that mainly constitutes the bonding wire 1 of the embodiment, and mainly assumes the function of the bonding wire 1. Such a core material 2 can be composed of pure silver, or can be composed of a silver alloy obtained by adding additive elements to silver. However, in order to prevent the function as a silver bonding wire from being impaired, the core material 2 is set to contain silver as the main component. Here, the so-called containing silver as the main component means that the core material 2 contains more than 50% by mass of silver. In the case where the core material 2 is composed of a silver alloy, it is preferably used a silver alloy containing at least one element selected from phosphorus (P), gold (Au), palladium (Pd), platinum (Pt), nickel (Ni), copper (Cu), iron (Fe), calcium (Ca), rhodium (Rh), germanium (Ge), gallium (Ga) and indium (In), but it is not limited to this.

[0039] The additive elements in the silver alloy constituting the core material 2 show effects in improving the bonding property with the electrode and the mechanical strength. However, if the content of the additive elements is too high, the resistance of the core material 2 may increase, and the function as a silver bonding wire may decrease. Therefore, it is preferable to set the content of the additive elements so that the specific resistance of the gold-coated silver bonding wire 1 is within the range of 2.3 μΩ·cm or less. Specifically, the silver content in the silver alloy is preferably 98% by mass or more. In the case where the core material 2 is composed of either pure silver or a silver alloy, unavoidable impurities may be contained, but it is preferable that the impurity content is within the range of 2.3 μΩ·cm or less for the specific resistance of the gold-coated silver bonding wire 1.

[0040] The gold-coated silver bonding wire 1 of the embodiment has a coating layer 3 provided on the surface of the core material 2 having silver as a main component. The coating layer 3 contains gold as a main component. Here, the so-called containing gold as a main component means that the coating layer 3 contains 50 mass % or more of gold. The coating layer 3 further contains at least one chalcogen element selected from sulfur, selenium and tellurium. It should be noted that the coating layer 3 may also contain elements other than gold and chalcogen elements.

[0041] As described in detail later, the chalcogenide in the cover layer 3 promotes the formation of a gold-enriched region in the surface region of the FAB when the FAB is formed on the gold-coated silver bonding wire 1. The so-called gold-enriched region refers to a region where the gold concentration is higher than that in the ball when the FAB is formed. By forming the gold-enriched region in the surface region of the FAB, when the FAB formed on the gold-coated silver bonding wire 1 is used for ball bonding, ion migration between the ball compression parts can be suppressed. That is, since the cover layer 3 with gold as the main component contains the chalcogenide, gold is suppressed from entering the inside of the molten ball, so that the gold-enriched region can be formed in the surface region of the FAB. Therefore, since the silver concentration on the surface of the FAB can be suppressed to be low, the occurrence of ion migration between the ball compression parts can be suppressed.

[0042] The mechanism of forming the gold-rich region on the surface of the FAB claimed in the present invention has not been fully elucidated, but it is presumed that in the process of forming the FAB, the chalcogen in the cover layer 3 acts on the surface tension of the molten cover layer 3, contributing to the formation of the gold-rich region. In the case of the conventional gold-coated silver bonding wire, since the surface tension of the molten silver is lower than that of the molten gold, the flow (Marangoni convection) generated by the difference in surface tension is generated from the side with smaller surface tension to the side with larger surface tension, that is, from the molten silver (molten ball) to the molten gold (molten covered gold), so the molten gold moves into the ball. On the other hand, in the case where the chalcogen exists in the cover layer 3, the surface tension of the molten cover layer 3 becomes lower than that of the molten silver, and the direction of the Marangoni convection is reversed to the direction from the molten gold to the molten silver, so the molten gold does not enter the inside of the FAB.

[0043] The timing of the effect of the chalcogen element in the coating layer 3 and the process of forming the gold-rich region are described along the formation process of the FAB. The FAB is formed by pulling out a predetermined length of the wire after the second bonding of the gold-coated silver bonding wire 1 to the lead or bump, generating arc discharge between the tip of the cut bonding wire 1 and the discharge torch, and melting the tip of the lead. Since the bonding wire 1 is crushed and deformed by the capillary during the second bonding, the coating layer 3 does not exist in the area where the bonding wire 1 contacts the capillary, and the core material 2 is exposed. In the initial stage of the formation of the molten ball, only the ball where the tip of the lead exposed by the core material 2 is melted exists in the area without the coating layer 3, so the gold-rich region is not formed. If the lead part that has not been deformed is melted, the chalcogen element in the coating layer 3 acts on the surface tension during melting, and the molten gold does not enter the inside of the FAB but exists in the surface area of ​​the FAB. Soon, the small ball gradually grows into a large ball, and gold is continuously supplied from the bonding wire 1. The molten gold is alloyed with the core material 2 melted by the heat of the arc discharge.

[0044] In the gold-coated silver bonding wire 1 having the coating layer 3, the gold content is in the range of 2 mass % to 7 mass % relative to the entire amount of the lead 1. If the gold content is less than 2 mass % relative to the entire amount of the lead 1, it is impossible to suppress the ion migration between the ball compression parts using the FAB formed on the gold-coated silver bonding wire 1 mainly composed of the silver core material 2. If the gold content exceeds 7 mass % relative to the entire amount of the lead 1, the ball shape during melting and the formability of the FAB shape are reduced, and the manufacturing cost of the gold-coated silver bonding wire 1 is increased. Although it varies depending on the diameter of the lead 1 or the thickness of the coating layer 3, the gold content is more preferably 3.5 mass % or more, and more preferably 5.5 mass % or less relative to the entire amount of the lead 1.

[0045] The chalcogen element mainly present in the covering layer 3 is preferably contained in the range of 1 mass ppm to 80 mass ppm relative to the total amount of the above-mentioned gold-coated silver bonding wire 1. If the content of the chalcogen element is less than 1 mass ppm relative to the total amount of the lead 1, the gold enrichment effect during the formation of the FAB and the formation of the gold-enriched region caused by it cannot be fully obtained. If the content of the chalcogen element exceeds 80 mass ppm relative to the total amount of the lead 1, it becomes easy to generate cracks or cracks in the covering layer 3, the formation effect of the covering layer 3 is reduced, and the processability such as wire drawing is reduced, and it becomes difficult to obtain the gold-coated silver bonding wire 1 of the desired wire diameter. It should be noted that the chalcogen element can also be used in combination of two or more. In this case, it is adjusted so that the total amount of the chalcogen element is within the above-mentioned content range.

[0046] The method for calculating the gold content and the chalcogenide content in the total amount of the gold-coated silver bonding wire 1 is described. First, in order to calculate the gold content, the bonding wire 1 is placed in dilute nitric acid, the core material 2 is dissolved, and the solution is collected. Hydrochloric acid is added to the solution, and a fixed volume solution is prepared with ultrapure water. The coating layer 3 is dissolved with dilute aqua regia, and a fixed volume solution is prepared with ultrapure water. The gold content is determined by quantitatively analyzing the gold in these fixed volume solutions using ICP emission spectrometry (ICP-AES: Inductively Coupled Plasma Atomic Emission Spectroscopy).

[0047] Next, the content of chalcogen elements is calculated. Regarding the content of selenium and tellurium in the covering layer 3, the bonding wire 1 is placed in dilute nitric acid, and the covering layer 3 is extracted after the core material 2 is melted. Furthermore, after the covering layer 3 is heated and decomposed with dilute aqua regia, it is measured using a solution fixed to volume with ultrapure water. The quantitative analysis of selenium and tellurium in the fixed volume solution is measured using ICP mass spectrometry (ICP-MS: Inductively Coupled Plasma Mass Spectrometry). On the other hand, regarding the content of selenium and tellurium in the core material 2, the bonding wire 1 is placed in dilute nitric acid, and a solution in which the core material 2 is melted is used and measured by ICP-MS. Thereafter, the gold content and the selenium and tellurium content in the bonding wire 1 as a whole are calculated from the gold content and the selenium and tellurium content in the covering layer 3 and the core material 2. In addition, in addition to the above, there is also a method of installing a hydride generator on the ICP-AES and generating hydrides of selenium and tellurium for analysis.

[0048] The sulfur (S) content of the core material 2 and the cover layer 3 is measured using a combustion infrared absorption method with respect to the bonding wire 1. The weight of the bonding wire 1 per measurement is preferably set to 0.5 g or more. If the sample is difficult to dissolve, a combustion aid may be used as needed.

[0049] The above-mentioned gold-coated silver bonding wire 1 preferably has a wire diameter of 13 μm to 50 μm ( Figure 1 The diameter D shown in FIG. 1 is shown in FIG. 2 ). If the wire diameter of the lead 1 is less than 13 μm, when the bonding wire 1 is used for wire bonding during the manufacture of the semiconductor device, the strength or conductivity may be reduced, and the reliability of the wire bonding may be reduced. If the wire diameter of the lead 1 exceeds 50 μm, the bonding property with respect to the electrode may be reduced. For example, the opening area of ​​the electrode of the semiconductor device with a narrow pitch becomes smaller, and the opening area of ​​the electrode becomes less than 80 μm. Therefore, when the FAB is formed in such a way that the FAB of the gold-coated silver bonding wire 1 is placed in the opening area of ​​the electrode, the risk of forming an asymmetric ball (eccentric ball) increases, so the bonding property with respect to the electrode may be reduced.

[0050] In the gold-coated silver bonding wire 1 having the above-mentioned wire diameter, the thickness of the coating layer 3 is preferably 20 nm to 500 nm depending on the wire diameter. The thickness of the coating layer 3 represents the thickness of the region containing gold as the main component in the depth direction from the surface of the lead 1 relative to the vertical direction toward the core material 2. If the thickness of the coating layer 3 is less than 20 nm, it may not be possible to fully suppress the ion migration between the ball compression parts of the FAB formed on the gold-coated silver bonding wire 1 by the coating layer 3 containing gold as the main component. If the thickness of the coating layer 3 exceeds 500 nm, the formability of the coating layer 3 may be reduced. It should be noted that the thickness of the coating layer 3 is preferably set according to the wire diameter of the gold-coated silver bonding wire 1.

[0051] Since the effect of suppressing ion migration becomes greater as the gold content in the covering layer 3 increases, it is sufficient as long as at least 50% by mass of gold is contained in the covering layer 3. Furthermore, the gold content is preferably 80% by mass or more, and more preferably 99% by mass or more. The gold content of the covering layer 3 can be measured by quantitative analysis of the outermost surface of the lead wire using Auger electron spectroscopy (AES) from the surface of the bonding wire 1. It should be noted that the gold content here is a value relative to the total amount of the detected metal elements, and does not include carbon or oxygen present on the surface due to adsorption or the like.

[0052] The thickness of the covering layer 3 is measured as follows. That is, in the gold-coated silver bonding wire 1, element concentration analysis is performed from its surface in the depth direction by AES, and the portion located at 50% when the maximum value of the gold content present near the surface is set to 100% is taken as the boundary, and the area from the boundary to the surface is obtained as the thickness of the covering layer 3. The thickness from the surface to the depth direction of the gold-coated silver bonding wire 1 can be measured by AES analysis. For example, as a means of analyzing the concentration of each element of the covering layer 3 from the lead surface toward the silver core material 2, concentration measurement using AES analysis is effective. Here, as an example, an Auger electron spectrometer manufactured by JEOL (trade name: JAMP-9500F) is used and set to an acceleration voltage of 10 kV for the primary electron beam, an irradiation current of 50 nA, and a beam diameter of approximately 4 μmφ. By sputtering SiO with an Ar ion sputtering speed of 100 μm, the concentration of the silver core material 2 is 0.1 μm / s. 2 The conversion value was about 3.0 nm / min.

[0053] Next, when wire bonding is performed using the gold-coated silver bonding wire 1 of the embodiment, as shown in FIG. Figure 3As shown in , FAB4 is formed at one end of the gold-coated silver bonding wire 1. As the formation conditions of FAB4, for example, when the wire diameter of the gold-coated silver bonding wire 1 is 13μm to 50μm, the arc discharge conditions are set so that the discharge current value becomes 30mA to 120mA and the FAB4 diameter becomes 1.5 times to 2.0 times the lead wire diameter. The bonder device can use a commercially available product such as a bonder device made by Kulicke & Soffa (fully automatic bonder: IConn PLUS). When using this bonder device, as the settings of the device, it is preferred to apply a discharge time of 50μs to 1000μs, an EFO-Gap of 20mil to 40mil (about 635μm to 1143μm), and a tail length of 6mil to 12mil (about 152μm to 305μm). In addition, when a joint device other than the joint device is used, the same conditions as those of the joint device, for example, the condition that the diameter of the FAB 4 is the same size as that of the joint device, may be used.

[0054] At this time, when the gold-coated silver bonding wire 1 of the embodiment is used, the chalcogenide contained in the coating layer 3 forms a gold-enriched region 5 in the surface area of ​​the FAB4, for example, within a range of 10 μm or less from the surface relative to the depth direction (or less than 10% relative to the diameter of the FAB4), although it also varies depending on the diameter of the formed FAB4. Since the gold-enriched region 5 is maintained even after the FAB4 is bonded to the electrode, it has an effect on suppressing ion migration. The gold-enriched region 5 has a concentration gradient from the surface to the inside of the FAB4 within the above range. However, the concentration gradient of the gold-enriched region 5 is not very important, and the gold concentration on the surface of the FAB4 is more important to suppress ion migration.

[0055] That is, when a gold layer containing no chalcogen element is formed on the surface of the silver core material as in the conventional gold-coated silver bonding wire, when one end of the lead wire having the gold layer is melted to form a ball, although the gold in the gold layer enters the inside of the molten ball mainly composed of the silver core material and a gold-rich region is partially formed on the neck side of the molten ball, no gold-rich region is formed on most of the ball surface. The composition of the FAB surface formed by solidifying the molten ball remains the same. Therefore, Figure 4 As shown in , even if a gold layer is formed on the surface of the silver core material, a gold-rich region cannot be formed at a position effective for suppressing ion migration.

[0056] On the other hand, if the cover layer 3 contains a predetermined amount of chalcogen, the entry of gold into the molten ball is suppressed, and the gold that is not absorbed into the molten ball exists near the surface to form a gold-rich region. The molten ball having the gold-rich region near the surface is solidified to form FAB4, thereby Figure 5As shown in , a gold-enriched region 5 is formed on the surface area of ​​FAB4. The gold-enriched region 5 shows the effect of suppressing the occurrence of ion migration between the compressed parts of the ball as described above. It should be noted that the gold-enriched region 5 of FAB4 is preferably formed on the surface that is 60% or more away from the gold-coated silver bonding wire 1 and the neck 6 of FAB4 in terms of suppressing the occurrence of ion migration. The gold-enriched region 5 may not be formed on the entire surface of FAB4, but as long as the gold-enriched region 5 is formed on the surface that is 60% or more away from the neck 6, the ion migration suppression effect can be obtained. It should be noted that the surface of FAB4 that is 60% or more away from the neck 6 specified here refers to the part (the surface of the ball 4) that is 60% or more away from the midpoint of the line connecting the lead 1 and the neck 6 of the ball 4 on the vertical line extending from the midpoint of the line connecting the lead 1 and the neck 6 of the ball 4 to the position corresponding to the lowest point of the ball 4 in the cross-sectional view of the bonding wire 1 and the FAB (ball) 4. The specific method for specifying the formation range of the gold-enriched region 5 and the measurement method will be described in detail later.

[0057] like Figure 4 and Figure 5 The formation of the gold-enriched region 5 as shown in FIG. 1 can be observed from the cross section of the ball by surface analysis using an electron probe microanalyzer (EPMA) (for example, an accelerating voltage of 15 kV and an irradiation current of 290 nA).

[0058] In terms of obtaining the above-mentioned inhibitory effect of ion migration well, the gold concentration of the gold-enriched region 5 is preferably 8% by mass or more relative to the total amount of silver and gold, and more preferably 10% by mass or more. In other words, by setting the gold concentration on the surface of FAB4 to 8% by mass or more relative to the total amount of silver and gold, the ion migration between the ball compression parts formed using FAB4 can be suppressed. Since if the gold concentration on the surface of FAB4 is lower than 8% by mass and the gold concentration on the surface of FAB4 is low, the silver concentration on the surface becomes relatively high, so the above-mentioned ion migration cannot be effectively suppressed. That is, the surface of such FAB4 does not show the effect of the gold-enriched region 5.

[0059] As described above, in the cross-sectional view of the bonding wire 1 and the FAB (ball) 4, the gold-enriched region 5 is formed on the surface of the ball 4 at a position corresponding to 60% or more from the midpoint of the line connecting the lead 1 and the neck 6 of the ball 4 to the vertical line extending from the midpoint of the line connecting the lead 1 and the neck 6 of the ball 4 to the position corresponding to the lowest point of the ball 4. For the formation range of the gold-enriched region 5 formed on the surface of the FAB 4, refer to Figure 6 and Figure 7 It should be noted that, Figure 6 and Figure 7This is a cross-sectional view, but no hatching is added to clearly show the formation range and analysis position of the gold-enriched region 5. Figure 6 Indicates the case where point A and point B described below are horizontal. First, in the cross-sectional view of the lead 1 and the ball (FAB) 4, a line (line AB) perpendicular to the length direction (axial direction) of the lead is drawn through point A and point B indicating the neck (boundary) of the lead 1 and the ball 4, and the midpoint of the point A and point B is set as point N. Next, a line (line C) perpendicular to the length direction of the lead 1 is drawn through the front end (point C / lowest point) of the ball 4. Lines (line FG, line HI) perpendicular to line AB and line C are arbitrarily drawn on the left and right of the ball 4. Next, the intersection point of line AB and line FG is set as point A', the intersection point of line C and line FG is set as point C', the intersection point of line HI and line AB is set as point B', and the intersection point of line HI and line C is set as point C". Next, any point on line A'C' passing through points A' and C' is set as point D'. Similarly, any point on line B'C" is set as point E'. In addition, points D' and E' are projected onto the circumference of sphere 4 as points D and E. Furthermore, on line A'C', a point that is 50% of the distance from point A' is set as point D. 1 ', set the 60% point to point D 2 ', set the 70% point to point D 3 ', the point where each point is projected onto the circumference of the sphere 4 is set as point D 1 , point D 2 , point D 3 Similarly, on line B'C", the point that is 50% of the distance from point B' is set as point E. 1 ', set the 60% point to point E 2 ', set the 70% point to point E 3 ', the point where each point is projected onto the circumference of the ball 4 is set as point E 1 , point E 2 , point E 3 .

[0060] here, Figure 6 The case where point A and point B of the neck 6 are horizontal is shown, but the case where point A and point B are not horizontal is shown in FIG. Figure 7 In that case, draw a line (line AB) through points A and B that represent the boundary between lead 1 and ball 4, and set the midpoint of line AB to point N. Next, draw a line (line C) perpendicular to the length direction of lead 1 through the front end of ball 4 (point C / lowest point). Draw line A'B' parallel to line C through point N, the midpoint of line AB, and extending to the left and right sides of ball 4. Using line C and line A'B' as a reference, Figure 6In the same way, draw lines FG and HI, and set the intersection point of line A'B' and line FG (point A'), the intersection point of line C and line FG (point C'), the intersection point of line HI and line A'B' (point B'), and the intersection point of line HI and line C (point C"), respectively. And, set any point on line A'C' passing through points A' and C' as point D', and set any point on line B'C" as point E'. Set points D and E as points that project points D' and E' onto the circumference of sphere 4. Furthermore, on line A'C', set a point that is 50% of the distance from point A' as point D. 1 ', set the 60% point to point D 2 ', set the 70% point to point D 3 ', the point where each point is projected onto the circumference of the sphere 4 is set as point D 1 , point D 2 , point D 3 Similarly, on line B'C", the point that is 50% of the distance from point B' is set as point E. 1 ', set the 60% point to point E 2 ', set the 70% point to point E 3 ', the point where each point is projected onto the circumference of the ball 4 is set as point E 1 , point E 2 , point E 3 .

[0061] As a method for confirming the formation range of the gold-enriched region 5 formed on the surface of the FAB 4, there is a method of using the above-mentioned Figure 6 and Figure 7 The method of linear analysis of point D and point E of FAB4 shown in the figure. When the gold concentration reaches 8 mass % or more by measuring each point by linear analysis, it can be said that a gold-enriched region 5 is formed up to that point. The gold-enriched region 5 is formed gradually from the lead 1 side toward the front end side of the ball 4, so the existence of gold-enriched regions at points D and E means that gold-enriched regions 5 are also formed on the circumference of the lead 4 side (curves AD and BE shown in the figure) compared to these points. If point D and point E are equivalent to point D which is 60% of the distance from point A' and point B' 2 ' and point E 2 ' point (point D 2 and point E 2 ), then the ion migration can be effectively prevented. That is, point D 2 With point E 2 During ball bonding, the portion located near the end of the bonding interface between the ball compression portion and the chip electrode corresponds to the portion closest to the adjacent ball compression portion to be ball bonded. 2 and point E 2The formation of the gold-enriched region 5 is the most effective in preventing ion migration. However, when the ball compression portion is sparsely formed, due to contact with the capillary, damage during plastic deformation, friction with ultrasonic waves applied when bonding with the electrode on the chip, etc., it is possible that the region without gold enrichment is partially exposed in the curve AD and the curve BE. However, since the gold-enriched region 5 is formed at point D 2 and point E 2 Since the effect of suppressing ion migration is important, even when the gold-enriched region 5 is not locally formed in the curve AD and the curve BE, there is no adverse effect on the effect of suppressing ion migration.

[0062] A method for measuring the gold concentration of the gold-enriched region 5 on the surface of the FAB4 formed at one end of the gold-coated silver bonding wire 1 of the embodiment is specifically described. First, the FAB4 formed on the lead 1 (including the lead portion connected to the ball) is placed in a cylindrical mold (mold) in a direction in which the cross section of the ball 4 parallel to the length direction of the lead 1 can be grinded, and an embedded resin is poured, and a curing agent is added to solidify it. Thereafter, the solidified cylindrical resin is roughly ground using a grinder in a manner that the vicinity of the center of the ball 4 is exposed as much as possible. Once ground to approximately the center cross section of the ball 4, fine-tuning is performed using an ion milling device in a manner that includes the final fine grinding and the surface of the center of the ball is just exposed and becomes the position of the analysis surface. If the width of the cross section of the lead 1 becomes the length of the diameter of the lead 1, the cross section becomes the standard for the surface containing the center of the ball 4.

[0063] In order to quantitatively determine the presence or absence of the formation of the gold-enriched region 5, the gold-enriched region 5 can be confirmed by performing linear analysis using energy dispersive X-ray spectrometry (EDX: Energy Dispersive X-ray Spectrometry) attached to a field emission scanning electron microscope (FE-SEM: Field Emission-Scanning Electron Microscope) from the outside of the ball 4 (embedded resin side) toward the inner center of the ball 4 in the analysis surface (polished cross section) of the above-mentioned FAB 4. As for the linear analysis conditions, FE-SEM SU8220 manufactured by Hitachi High-Technologies Corporation and X Flash (R) 5060FQ manufactured by Bruker Corporation were used, and the acceleration voltage was set to 6 keV, the measurement length was 2 μm, the measurement interval was 0.03 μm, and the measurement time was 60 seconds. Using the concentration curve of the linear analysis, if there is a portion where the gold concentration is 8% by mass or more relative to the total amount of silver and gold between the interface between FAB4 and the embedding resin and the position of 100 nm inside FAB4, it can be determined that a gold-enriched region 5 is formed. Here, the interface between FAB4 and the embedding resin can be easily determined by the contrast difference of the FE-SEM image of the cross section of the ball, and by comparing the image with the graph of the linear analysis, it can be confirmed whether a gold-enriched region is formed at the necessary position.

[0064] Next, the method for manufacturing the gold-coated silver bonding wire of the embodiment will be described. It should be noted that the method for manufacturing the gold-coated silver bonding wire of the embodiment is not particularly limited to the manufacturing method described below. The gold-coated silver bonding wire 1 of the embodiment is obtained by, for example, forming a gold layer containing gold as a main component and at least one chalcogen element selected from sulfur, selenium and tellurium on the surface of a silver wire material containing silver as a main component, which serves as the core material 2, and performing a wire drawing process to a wire diameter required for the gold-coated silver bonding wire 1, and performing a heat treatment as needed. The wire drawing process for obtaining the gold-coated silver bonding wire 1 can be performed on the lead wire material or on the silver wire material.

[0065] When silver is used as the core material 2, a silver core material or a silver alloy core material is obtained by dissolving silver of a specified purity. When a silver alloy is used, silver of a specified purity is dissolved together with an additive element. A heating furnace such as an arc heating furnace, a high-frequency heating furnace, a resistance heating furnace, or a continuous casting furnace is used for the dissolution. In order to prevent the mixing of oxygen or hydrogen from the atmosphere, the upper part of the silver molten metal in the heating furnace is preferably kept in a vacuum or an inert gas atmosphere such as argon or nitrogen. The dissolved core material is cast and solidified in a heating furnace in a manner to obtain a specified wire diameter, or the molten core material is cast into a mold to produce an ingot, and the ingot is rolled and then drawn to a specified wire diameter to obtain a silver wire (including a pure silver wire and a silver alloy wire).

[0066] As a method for forming a gold layer on the surface of the silver wire, for example, a plating method (wet method) or a vapor deposition method (dry method) is used. The plating method may be any of an electrolytic plating method and an electroless plating method. Electrolytic plating such as strike plating or thin plating has a fast plating speed, and if it is suitable for gold plating, it is preferred because the adhesion of the gold layer to the silver wire is good. In order to make the gold layer contain chalcogen elements by the plating method, for example, in the above-mentioned electrolytic plating, a plating solution is used in which a plating additive containing at least one selected from sulfur, selenium and tellurium is contained in the gold plating solution. At this time, by adjusting the type or amount of the plating additive, the chalcogen content in the covering layer 3 can be adjusted, and the chalcogen content in the lead 1 can be adjusted.

[0067] As the evaporation method, physical evaporation (PVD) such as sputtering, ion plating, and vacuum evaporation, and chemical evaporation (CVD) such as thermal CVD, plasma CVD, and metal organic vapor deposition (MOCVD) can be used. According to these methods, there is no need to wash the gold coating after it is formed, and there is no worry about surface contamination during washing. As a method for making the gold layer contain chalcogen elements by evaporation, there is a method of using a gold target containing chalcogen elements and forming a gold layer by magnetron sputtering. In the case of applying methods other than these, it is sufficient to use a raw material obtained by making the gold material contain chalcogen elements.

[0068] In this way, the silver wire covered with the gold layer containing the chalcogen element is drawn to the final wire diameter, and heat-treated as needed, thereby manufacturing the gold-coated silver bonding wire 1 in which the coating layer 3 is provided on the surface of the silver core material 2. The drawing process can be performed at the stage of the silver wire, or the silver wire can be drawn to a certain wire diameter and then drawn to the final wire diameter after the gold layer is formed. The drawing process and heat treatment can also be performed in stages.

[0069] The processing rate of the wire drawing process is determined according to the final wire diameter or purpose of the gold-coated silver bonding wire 1 to be manufactured. The processing rate of the wire drawing process is generally preferably 90% or more, which is the processing rate of processing the silver wire to the final wire diameter. The processing rate can be calculated as the reduction rate of the cross-sectional area of ​​the lead. The wire drawing process is preferably performed using multiple diamond wire drawing dies in a manner that the wire diameter is reduced in stages. In this case, the cross-sectional reduction rate (processing rate) of each diamond wire drawing die is preferably 5% to 15%.

[0070] It is preferred that the final heat treatment be performed after the silver wire covered with the gold layer is drawn to the final wire diameter. The final heat treatment is performed in consideration of the stress relief heat treatment for removing the strain of the metal structure remaining inside the lead 1 or the required lead characteristics in terms of the final wire diameter. The temperature and time of the stress relief heat treatment are preferably determined in consideration of the required lead characteristics. In addition, a heat treatment corresponding to the purpose can also be performed at any stage of the lead manufacturing. As such a heat treatment, there are stress relief heat treatment during the drawing process of the lead, diffusion heat treatment for improving the bonding strength after the gold layer is formed, and the like. By performing the diffusion heat treatment, the bonding strength between the core material 2 and the covering layer 3 can be improved. Regarding the heat treatment, a mobile heat treatment in which the lead is passed through a heating atmosphere heated to a specified temperature for heat treatment is preferred because the heat treatment conditions are easy to adjust. In the case of a mobile heat treatment, the heat treatment time can be calculated by the passing speed of the lead and the passing distance of the lead in the heating container. As a heating container, an electric furnace or the like is used.

[0071] (Semiconductor device and method of manufacturing the same)

[0072] Next, refer to Figure 8 to Figure 11 A semiconductor device using the gold-coated silver bonding wire 1 of the embodiment will be described. Figure 8 is a cross-sectional view showing a stage before resin sealing of a semiconductor device according to an embodiment, Fig. 9 is a cross-sectional view showing a stage after resin sealing of the semiconductor device according to the embodiment. Fig.10 is a cross-sectional view showing a ball compression portion bonded to an electrode of a semiconductor chip in a semiconductor device according to an embodiment. Fig.11 Yes Fig.10 The cross-sectional view of the ball compression portion shown in FIG.

[0073] The semiconductor device 10 of the embodiment (the semiconductor device 10X before resin sealing) is as follows: Figure 8 and Fig. 9As shown in , it comprises a circuit substrate 12 having an external electrode 11, a plurality of semiconductor chips 14 (14A, 14B, 14C) arranged on the circuit substrate 12 and each having at least one electrode (chip electrode) 13, and bonding wires 15 (gold-coated silver bonding wires 1) connecting the external electrode 11 of the circuit substrate 12 and the electrode 13 of the semiconductor chip 14 and between the electrodes 13 of the plurality of semiconductor chips 14. For the circuit substrate 12, for example, a printed circuit wiring board or a ceramic circuit substrate having a wiring network provided on the surface or inside of an insulating base material such as a resin material or a ceramic material is used.

[0074] It should be noted that Figure 8 and Fig. 9 The semiconductor device 10 is shown in which a plurality of semiconductor chips 14 are mounted on a circuit substrate 12, but the configuration of the semiconductor device 10 is not limited thereto. For example, the semiconductor chip may be mounted on a lead frame, in which case the electrodes of the semiconductor chip are connected to the external leads functioning as the external electrodes of the lead frame via bonding wires 15. The number of circuit substrates or lead frames mounted with respect to the semiconductor chip may be either one or more. The bonding wire 15 is applied to at least one of the external electrode 11 of the circuit substrate 12 and the electrode 13 of the semiconductor chip 14, the electrode between the lead frame and the semiconductor chip, and the electrode 13 of the plurality of semiconductor chips 14.

[0075] Figure 8 and Fig. 9 Among the plurality of semiconductor chips 14 of the semiconductor device 10 shown in FIG, semiconductor chips 14A and 14C are mounted on the chip mounting region of the circuit substrate 12 via a die solder material 16. The semiconductor chip 14B is mounted on the semiconductor chip 14A via the die solder material 16. One electrode 13 of the semiconductor chip 14A is connected to the external electrode 11 of the circuit substrate 12 via a bonding wire 15, another electrode 13 is connected to the electrode 13 of the semiconductor chip 14B via the bonding wire 15, and another electrode 13 is connected to the electrode 13 of the semiconductor chip 14C via the bonding wire 15. Another electrode 13 of the semiconductor chip 14B is connected to the external electrode 11 of the circuit substrate 12 via the bonding wire 15. Another electrode 13 of the semiconductor chip 14C is connected to the external electrode 11 of the circuit substrate 12 via the bonding wire 15.

[0076] The semiconductor chip 14 has an integrated circuit (IC) including a silicon (Si) semiconductor or a compound semiconductor. The chip electrode 13 includes, for example, an aluminum electrode having an aluminum (Al) layer, an aluminum alloy layer such as AlSiCu, or AlCu at least on the outermost surface. The aluminum electrode is formed, for example, by covering the surface of the silicon (Si) substrate with an electrode material such as Al or an Al alloy in a manner electrically connected to the internal wiring. The semiconductor chip 14 communicates data with an external device via the external electrode 11 and the bonding wire 15, or is supplied with power by an external device.

[0077] The external electrode 11 of the circuit substrate 12 is electrically connected to the electrode 13 of the semiconductor chip 14 mounted on the circuit substrate 12 via the bonding wire 15. In the semiconductor device 10 of the embodiment, the bonding wire 15 includes the gold-coated silver bonding wire 1 of the above-mentioned embodiment. In the bonding wire 15, one end thereof is ball-bonded (first bonding) to the chip electrode 13, and the other end is wedge-bonded (second bonding) to the external electrode 11 (positive bonding). It should be noted that the formation order of the ball bonding (first bonding) and the wedge bonding (second bonding) can also be reversed. That is, one end of the bonding wire 15 can also be ball-bonded (first bonding) to the external electrode 11, and the other end can be wedge-bonded (second bonding) to the chip electrode 13 (reverse bonding). The same is true for connecting the electrodes 13 of multiple semiconductor chips 14 through the bonding wire 15. It should be noted that the electrodes 13 of the semiconductor chip 14 electrically bonded by the bonding wire 15 also include bumps (not shown) pre-bonded to the electrodes located on the semiconductor chip 14.

[0078] For example, when one end of the bonding wire 15 is ball-bonded to the chip electrode 13, the one end of the bonding wire 15 is melted by discharge or the like and solidified into a ball shape by surface tension or the like, thereby forming a ball-shaped bonding wire. Figure 3 As described above, in the process of forming FAB4, the gold-rich region 5 is formed on the surface of FAB4 through the cover layer 3 on the surface of the lead 1. By bonding such FAB4 to the chip electrode 13 using ultrasonic and thermal compression bonding, a gold-rich region 5 is formed on the chip electrode 13. Fig.10 or Fig.11 Then, a sealing resin layer 18 is formed on the circuit substrate 12 in such a manner that the plurality of semiconductor chips 14 and the bonding wires 15 are sealed with resin, thereby manufacturing the semiconductor device 10. Specifically, the semiconductor device includes a logic IC, an analog IC, a discrete semiconductor, a memory, an optical semiconductor, and the like.

[0079] Since the surface area of ​​FAB4 is formed Figure 3Since the gold-enriched region 5 shown in the figure is formed on the surface of the ball compression portion 17 in the same manner as FAB4, a gold-enriched region 5 is also formed on the surface of the ball compression portion 17. Here, when FAB4 is joined to a chip electrode 13 such as an aluminum electrode, a joint is formed in which the constituent elements of the chip electrode 13 such as aluminum and the constituent elements of FAB4 having the gold-enriched region 5 are mixed or alloyed. The gold-enriched region 5 of the ball compression portion 17 exists on the surface exposed from the chip electrode 13 in the portion that does not participate in the formation of the joint. The gold-enriched region 5 of the ball compression portion 17 is formed at least on the surface of the ball compression portion 17 in the same manner as FAB4, and further, for example, from the surface of the ball compression portion 17 to a range of less than 10 μm relative to the depth direction (or less than 10% relative to the diameter of the FAB), and has a gold concentration of more than 8 mass % relative to the total amount of silver and gold. Thus, the occurrence of ion migration between the ball compression portions 17 can be suppressed.

[0080] As described above, ion migration is a phenomenon in which the metal is ionized by the application of an electric field and moisture, and the metal ions migrate between the ball compression parts and then precipitate, causing insulation degradation or short circuits. Silver is a metal that easily causes ion migration. In view of this, since there is a gold-enriched area (gold-enriched area) 5 on the surface of the ball compression part 17 where ion migration is difficult to occur, the silver concentration on the surface is relatively reduced, so that ion migration between the ball compression parts 17 formed by using the gold-coated silver bonding wire 1 can be suppressed. Therefore, a decrease in the reliability or soundness of the semiconductor device 10 caused by poor insulation or short circuits between the ball compression parts 17 can be suppressed, and a semiconductor device 10 with excellent insulation reliability, etc. can be provided. Furthermore, as Fig.10 As shown in , even when the chip electrodes 13 are formed at a narrow pitch P of 100 μm or less, insulation failure and short circuit between the ball compression portions 17 can be effectively suppressed.

[0081] It should be noted that the gold-enriched region 5 of the ball compression portion 17 has basically the same structure as the gold-enriched region 5 of FAB4, and the specific structure is as described above. In addition, the identification or measurement of the gold-enriched region 5 of the ball compression portion 17 is preferably carried out in the same manner as the gold-enriched region 5 of FAB4 described above, and each has the same conditions.

[0082] Example

[0083] Next, examples of the present invention will be described. The present invention is not limited to the following examples. Examples 1 to 44 are examples, and Examples 45 to 60 are comparative examples.

[0084] (Examples 1 to 44)

[0085] As the core material, a silver core material with a purity of 99% produced by continuous casting was prepared and processed to an intermediate wire diameter of 0.05 mm to 1.0 mm by continuous wire drawing. Furthermore, a gold coating layer was formed on the silver wire material of the intermediate wire diameter as follows. In a gold electrolytic plating bath to which appropriate amounts of sulfur, selenium, and tellurium additives were added, the silver wire material was continuously fed and immersed in the gold electroplating bath at a current density of 0.20 A / dm 2 ~1.0A / dm 2 A current was passed to form a gold coating layer containing a chalcogenide element. The wires were then drawn to a final wire diameter of 20 μm and subjected to final heat treatment to produce gold-coated silver bonding wires of Examples 1 to 36. These gold-coated silver bonding wires were subjected to the characteristic evaluation described below.

[0086] (Comparative Examples 45 to 50)

[0087] Gold-coated silver bonding wires were produced in the same manner as in Example 1 except that no additive of a chalcogen element was added to the Au plating bath. These gold-coated silver bonding wires were subjected to the characteristic evaluation described below.

[0088] (Comparative Examples 51 to 60)

[0089] Gold-coated silver bonding wires were produced in the same manner as in Example except that an Au plating bath adjusted so that the chalcogen content in the coating layer would be the value shown in Table 1 was used. These gold-coated silver bonding wires were subjected to the characteristic evaluation described below.

[0090] (Content Determination)

[0091] The gold content and the chalcogenide content in the gold-coated silver bonding wire were measured by the above-mentioned method. The results are shown in Table 1.

[0092] (Lead appearance inspection)

[0093] The appearance of the gold-coated silver bonding wires of the intermediate wire diameter and the final wire diameter was checked using a laser microscope (trade name: VK-X200) manufactured by KEYENCE CORPORATION to confirm the presence or absence of cracks (crazing) in the gold film based on high magnification. The case where cracks were generated in the gold film due to the tensile stress generated mainly during the wire drawing process and the silver core material was exposed in even one of the 10 leads was set as "B" (unqualified), and the case where no silver core material was exposed in any of the 10 leads was set as "A" (qualified). The results are shown in Table 1.

[0094] (Determination of gold-enriched areas)

[0095] Next, the gold-coated silver bonding wire was formed in the atmosphere using a commercially available wire bonding apparatus (manufactured by Kulicke & Soffa, IConn PLUS) and the EFO conditions were set so that the diameter of the FAB would be 36 μm. The FAB was then spectrally imaged by FE-SEM / EDX at points D (point D 1 , point D 2 , point D 3 ), point E(point E 1 , point E 2 , point E 3 ) position. The results of the linear analysis of each point are that if the gold concentration is less than 8% by mass relative to the total of gold and silver, it is set as "B" (no gold enrichment area), and if it is more than 8% by mass, it is set as "A" (gold enrichment area). It should be noted that the results are the same as the point (point D) due to the distance from the neck formation range. 1 , point E 1 )、(Point D 2 , point E 2 )、(Point D 3 , point E 3 ) is necessary to solve the problem of ion migration, so only when the conditions are met at each point at the same time is it determined as "A" (gold-enriched area). For example, at point D 2 , point E 2 When the judgment is A, the judgment of 60% of the analysis position of the gold-enriched area is set as "A", and at point D 2 , point E 2 When at least any one of the determinations was B, the determination of 60% of the analysis positions in the gold-enriched region was set to "B".

[0096] (Ion migration evaluation)

[0097] For the gold-coated silver bonding wire produced, a commercially available wire bonding device (manufactured by Kulicke & Soffa, IConn PLUS) was used to set the EFO conditions so that the diameter of the FAB became 36 μm, and the FAB was formed in the atmosphere. After that, the aluminum alloy pad on the evaluation Si chip heated to 150°C was bonded for the first time by a ball bonding method using ultrasonic and thermal compression bonding, under bonding conditions where the average diameter of the press-bonded ball became 45 μm, and the lead terminal of the BGA substrate on which the Au plating layer was applied on Ni using electrolytic plating was bonded by an intermittent bonding method using ultrasonic and thermal compression bonding under prescribed bonding conditions, and a total of 32 leads were connected to each chip. The connected leads consisted of a total of 16 circuits with two leads formed by connecting the chip electrodes to the lead terminals and a pair of chip electrodes. For these circuits, by installing them on a special fixture that can apply bias, a voltage is applied to the ball compression part of the circuit that is finally connected from the lead terminal on the BGA substrate through the terminal of the fixture by a voltage source such as a multimeter. The ball compression part becomes consistent with either the anode or the cathode. That is, eight pairs of anodes and cathodes are formed for each chip. The anode and the cathode are insulated in the chip, and the distance between the ball compression parts that become the anode and the cathode is 125μm, although it varies slightly depending on the position accuracy of the joint or the diameter of the crimped ball.

[0098] Before the evaluation of ion migration, the BGA substrate in the state of wiring was baked in a high temperature furnace at 175°C for 3 hours. Next, the BGA substrate that has been baked was mounted on a special fixture, and pure water was dripped on the chip electrode. Afterwards, a constant voltage source (Hewlett-Packard Company, E3632A) was used to apply a constant voltage of 2V to eight pairs of anodes and cathodes in such a way that the electric field strength between the electrodes became 16kV. The constant voltage application time was set to 60 seconds. The presence or absence of ion migration was visually determined using a stereo microscope after the application time. When metal (dendrites) precipitated in a dendritic form was confirmed between the anode and cathode, it was determined that ion migration occurred. The situation where ion migration occurred in one or more of the eight pairs was judged as "B" (unqualified), and the situation where it was not generated at all was judged as "A" (qualified). The judgment results are shown in Table 1.

[0099]

Table 1

[0100]

[0101] *1: Ion migration (IM) evaluation

[0102] As shown in Table 1, according to the gold-coated silver bonding wires of Examples 1 to 36, it is possible to form a FAB having a gold-enriched region in an appropriate region on the surface. Furthermore, when such a FAB ball is bonded to an electrode of a semiconductor chip to manufacture a semiconductor device, poor insulation or short circuit between the compression parts of the ball can be suppressed. Therefore, a sound wire bonding structure and a semiconductor device with excellent insulation reliability can be provided at a low cost. In contrast, as shown in the results of Comparative Examples 45 to 50 in Table 1, it can be seen that if a chalcogen element is not added to the covering layer, a gold-enriched region is not formed. In addition, as shown in the results of Comparative Examples 52, 54, 57, and 60 in Table 1, if the content of the chalcogen element in the covering layer is too much (an amount exceeding 80 ppm relative to the total amount of the lead), cracks or fissures will occur in the gold covering layer. Furthermore, as shown in the results of Comparative Examples 51, 53, 55, 56, 58, and 59 in Table 1, if the content of the chalcogen element in the coating layer is too low (less than 1 ppm relative to the entire lead), a gold-rich region is formed on a portion of the surface of the FAB, but the gold-rich region required to suppress ion migration cannot be formed. Therefore, in the gold-coated silver bonding wire of the comparative example, insulation failure or short circuit between the ball compression parts using the FAB formed at one end cannot be suppressed.

[0103] Explanation of symbols

[0104] 1 gold-coated silver bonding wire, 2 core material (silver core material), 3 covering layer, 4 FAB (ball), 5 gold-enriched area, 6 neck, 10 semiconductor device, 11 external electrode, 12 circuit substrate, 13 chip electrode, 14 semiconductor chip, 15 bonding wire, 16 tube core welding material, 17 ball compression part, 18 sealing resin layer.

Claims

1. A gold-coated silver bonding wire having: A core material comprising silver as a main component; and a covering layer provided on the surface of the core material and containing gold as a main component, in, The gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium, and tellurium in a range of 1 mass ppm to 80 mass ppm.

2. A gold-coated silver bonding wire having: A core material comprising silver as a main component; and a covering layer provided on the surface of the core material and containing gold as a main component, in, The gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium and tellurium, When a free air ball is formed at one end of the gold-coated silver bonding wire, the free air ball has a gold-enriched region at a position corresponding to 60% or more of the position from the midpoint of the line connecting the neck in a cross-sectional view of the bonding wire and the free air ball, on a vertical line extending from the midpoint of a line connecting the lead wire and the neck of the ball to a position corresponding to the lowest point of the ball, The gold-coated silver bonding wire contains the chalcogen element in a range of 1 mass ppm to 80 mass ppm based on the entire amount of the bonding wire.

3. The gold-coated silver bonding wire according to claim 2, wherein: The gold concentration in the gold-enriched region is 8 mass % or more relative to the total amount of the silver and the gold.

4. A method for manufacturing a gold-coated silver bonding wire, the gold-coated silver bonding wire having: A core material comprising silver as a main component; and a covering layer provided on the surface of the core material and containing gold as a main component, in, The gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium, and tellurium in a range of 1 mass ppm to 80 mass ppm.

5. A semiconductor device comprising: One or more semiconductor chips having at least one electrode; and Lead frame or substrate, Furthermore, at least one selected from the group consisting of the electrode of the semiconductor chip and the lead frame, the electrode of the semiconductor chip and the electrode of the substrate, and the electrodes of the plurality of semiconductor chips is connected with a gold-coated silver bonding wire, wherein: The gold-capped silver bonding wire has: A core material comprising silver as a main component; and a covering layer provided on the surface of the core material and containing gold as a main component, The gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium, and tellurium in a range of 1 mass ppm to 80 mass ppm.

6. A method for manufacturing a semiconductor device, the semiconductor device comprising: One or more semiconductor chips having at least one electrode; and Lead frame or substrate, Furthermore, at least one selected from the group consisting of the electrode of the semiconductor chip and the lead frame, the electrode of the semiconductor chip and the electrode of the substrate, and the electrodes of the plurality of semiconductor chips is connected with a gold-coated silver bonding wire, wherein: The gold-capped silver bonding wire has: A core material comprising silver as a main component; and a covering layer provided on the surface of the core material and containing gold as a main component, The gold-coated silver bonding wire contains gold in a range of 2 mass % to 7 mass % relative to the entire amount of the lead wire, and contains at least one chalcogen element selected from sulfur, selenium, and tellurium in a range of 1 mass ppm to 80 mass ppm.

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