Copper wirebonds

Abstract

A copper bonding wire is provided that exhibits good bonding properties even with reduced friction during bonding. This copper bonding wire is characterized in that the sum of the proportions of Cu, Cu₂O, CuO, and Cu(OH)₂ on the wire surface, as determined by X-ray photoelectron spectroscopy (XPS), is set to 100%, and the ratio of Cu[II] / Cu[I] to the proportion of Cu₂O equivalent to Cu₁ (Cu[I]) and the total proportion of CuO and Cu(OH)₂ equivalent to Cu₂ (Cu[II]), i.e., Cu[II] / Cu[I], is in the range of 0.8 to 12.

Description

Technical Field

[0001] This invention relates to copper bonding wires. Background Technology

[0002] In semiconductor devices, bonding wires connect electrodes formed on a semiconductor chip to electrodes on a lead frame or substrate. Previously, gold (Au) was the mainstream material for bonding wires, but research and development on replacing it with copper (Cu), mainly for LSI applications, has made progress (e.g., patent documents 1-3). Furthermore, in power semiconductor applications, considering the high thermal conductivity or fusing current, there is a desire to replace Cu with high efficiency and reliability.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 61-48543

[0006] Patent Document 2: Japanese Patent Publication No. 2018-503743

[0007] Patent Document 3: International Publication No. 2017 / 221770 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] As a problem in mass production of installation processes using copper bonding wires (hereinafter also simply referred to as "copper wires"), one reason for the slow expansion of applications is the requirement for special bonding conditions due to poor bonding properties.

[0010] In wedge bonding of copper wires to electrodes on a substrate, there is a tendency for relatively low bond strength. Therefore, as a method to improve the bonding strength of copper wires, friction is often used, which involves moving a wedge or sample stage horizontally several times at a low frequency during bonding. While ultrasonic vibration (60–120 kHz) is typically used in bonding wires, it is insufficient for bonding existing copper wires using only ultrasonic vibration; therefore, friction is used in addition to ultrasonic vibration. Regarding the direction of friction movement, it is usually parallel to the wire direction, but sometimes an arc shape (a combination of the parallel direction and the direction perpendicular to the parallel direction) is used.

[0011] This frictional process leads to problems such as longer bonding times, reduced productivity, and disruption of the wire arc shape. Friction is a unique bonding condition not previously used in gold wire. Even with copper wire, reducing the number of friction cycles or the amount of frictional movement can improve productivity and facilitate the expansion of copper wire applications.

[0012] The objective of this invention is to provide a copper bonding wire that exhibits good bonding properties even with reduced friction during bonding.

[0013] Technical means for solving technical problems

[0014] The inventors of this invention conducted in-depth research on the above-mentioned technical problems and finally discovered that the above-mentioned technical problems could be solved by using a copper bonding wire with the following structure, thus completing this invention.

[0015] That is, the present invention includes the following contents.

[0016] [1] A copper bonding wire, characterized in that the sum of the proportions of Cu, Cu2O, CuO, and Cu(OH)2 on the wire surface as determined by X-ray photoelectron spectroscopy (XPS) is set to 100%, and the ratio of the total proportion of CuO and Cu(OH)2 with Cu2 valence (Cu[II]) to the proportion of Cu2O with Cu1 valence (Cu[I]), i.e., Cu[II] / Cu[I], is in the range of 0.8 to 12.

[0017] [2] The copper bonding wire as described in [1] is characterized in that the ratio of Cu(OH)2 to CuO, i.e., [Cu(OH)2] / [CuO], as determined by X-ray photoelectron spectroscopy (XPS), is in the range of 1 to 5.5.

[0018] [3] The copper bonding wire as described in [1] or [2] is characterized in that the ratio of CuO to Cu2O, i.e., [CuO] / [Cu2O], as determined by X-ray photoelectron spectroscopy (XPS), is in the range of 0.3 to 6.

[0019] [4] The copper bonding wire as described in any of [1] to [3], wherein the sum of Cu[I] and Cu[II] is 50% or more.

[0020] [5] The copper bonding wire as described in any of [1] to [4] includes one or more selected from the group consisting of Pd, Pt, Ag and Rh, the total concentration of which is in the range of 100 to 6000 ppm by mass.

[0021] [6] The copper bonding wire as described in any of [1] to [5] has a diameter of 15 μm or more and 100 μm or less.

[0022] [7] Copper bonding wires as described in any of [1] to [6], for use in semiconductor devices.

[0023] Invention Effects

[0024] According to the present invention, a copper bonding wire can be provided that exhibits good bonding properties even with reduced friction during bonding. Detailed Implementation

[0025] The preferred embodiments of the present invention will now be described in detail.

[0026] [Copper bonding wire]

[0027] The copper bonding wire of the present invention is characterized in that the sum of the proportions of Cu, Cu2O, CuO, and Cu(OH)2 on the wire surface as determined by X-ray photoelectron spectroscopy (XPS) is set to 100%, and the ratio of the total proportion of CuO and Cu(OH)2 with Cu2 valence (Cu[II]) to the proportion of Cu2O with Cu1 valence (Cu[I]), i.e., Cu[II] / Cu[I], is in the range of 0.8 to 12.

[0028] By measuring the surface of a copper wire using X-ray photoelectron spectroscopy (XPS), the chemical bonding state of copper (Cu) elements present near the surface of the copper wire (typically at a depth of a few nm) can be analyzed. Furthermore, the inventors of this invention have discovered a correlation between the chemical bonding state (charge state) of Cu elements on the surface of the copper wire and the properties of the copper wire, ultimately achieving a copper wire that exhibits desired properties by controlling the relevant chemical bonding state of Cu elements.

[0029] In relation to the properties of copper wire, particularly its bonding properties under low friction, the inventors of this invention have discovered that the proportion of Cu material in chemically bonded states (Cu, Cu₂O, CuO, Cu(OH)₂) as determined by X-ray photoelectron spectroscopy (XPS) is important. Furthermore, the term "Cu material in chemically bonded states" refers to Cu element in its metallic state (Cu₀ valence).

[0030] In this invention, it refers to the proportion of Cu substances in the chemically bonded states of Cu, Cu2O, CuO, and Cu(OH)2 as determined by X-ray photoelectron spectroscopy (XPS), and is simply referred to as "the proportion of Cu, Cu2O, CuO, and Cu(OH)2 determined by X-ray photoelectron spectroscopy (XPS)".

[0031] When the sum of the proportions of Cu, Cu₂O, CuO, and Cu(OH)₂ determined by X-ray photoelectron spectroscopy (XPS) is set to 100%, the ratio of the total proportion of CuO and Cu(OH)₂ with a Cu₂ valence (Cu[II]) to the proportion of Cu₂O with a Cu₁ valence (Cu[I]), i.e., Cu[II] / Cu[I], is in the range of 0.8 to 12. Therefore, a copper wire can be made that exhibits good bonding properties even with reduced friction during bonding.

[0032] Here, the proportion of Cu2O with Cu1 valence equivalent (Cu[I]), as mentioned above, refers to the proportion of Cu substances in the Cu2O chemical bonding state when the total amount of Cu substances in the chemical bonding states of Cu, Cu2O, CuO, and Cu(OH)2 as determined by X-ray photoelectron spectroscopy (XPS) is set to 100%.

[0033] Similarly, the so-called proportion of CuO and Cu(OH)2 with equivalent Cu2 valence (Cu[II]), as mentioned above, refers to the total proportion of Cu substances in the chemical bonded states of CuO and Cu(OH)2 when the total amount of Cu substances in the chemical bonded states of Cu, Cu2O, CuO and Cu(OH)2 as determined by X-ray photoelectron spectroscopy (XPS) is set to 100%.

[0034] XPS analysis of the surface of copper bonding wires allows for the precise identification and calculation of Cu1 and Cu2 valences present on the surface. By controlling the ratio of Cu1 to Cu2 valences obtained in the XPS measurement, copper wires exhibiting good bonding properties even with reduced friction during bonding can be achieved. Furthermore, existing analytical methods for analyzing the surface of copper wires with diameters of approximately 10–100 μm have conventionally employed AES (Auger spectrophotometry), SEM (secondary electron microscopy), and TEM (transmission electron microscopy). However, these methods struggle to determine the chemical bonding state of Cu on the copper wire surface and accurately resolve Cu substances in specific chemical bonding states. The inventors of this invention conducted AES and TEM analyses of the surfaces of several copper wires, but confirmed that the surface characteristics of the copper wire determined by these methods are not necessarily correlated with the bonding properties of the copper wire, particularly the bonding properties under low friction, which is the subject of this invention. On the other hand, it was also found that by controlling the ratio of Cu1 valence to Cu2 valence obtained by XPS measurement, copper wire can achieve good bonding even with reduced friction during bonding, thus enabling stable mass production.

[0035] The condition associated with this ratio Cu[II] / Cu[I] will be referred to as "Condition 1".

[0036] From the viewpoint of achieving copper wires with superior bonding properties under low friction, it is preferable to increase the proportion of Cu2 valence relative to Cu1 valence present near the surface of the copper wire. The lower limit of the ratio Cu[II] / Cu[I] is preferably 0.9 or more, more preferably 1 or more, and even more preferably 1.2 or more, 1.4 or more, 1.5 or more, 1.6 or more, 1.8 or more, 2 or more, 2.2 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.8 or more, or 3 or more. Regarding this effect, it can be inferred that it influences: the protective function of the copper wire surface is improved by utilizing the Cu2 valence (equivalent to Cu material), and the development of oxidation can be suppressed by controlling the Cu1 valence.

[0037] From the viewpoint of achieving better copper wire bonding with low friction, the upper limit of the ratio Cu[II] / Cu[I] is preferably 11.5 or less, more preferably 10 or less, and even more preferably 9.5 or less, 9 or less, 8.5 or less, 8 or less, 7.5 or less, or 7 or less.

[0038] In copper wires with a surface having a Cu[II] / Cu[I] ratio within the aforementioned range as determined by X-ray photoelectron spectroscopy (XPS), the gap and unevenness of the bonding interface can be reduced by ordinary ultrasonic vibration, thereby improving the adhesion. Since Cu diffusion through this bonding interface to the bonding object is promoted, it is believed that good adhesion can be achieved even by reducing the number of frictions or the amount of movement. The inventors of this invention have confirmed that by simply adjusting the ratio of Cu[I] and Cu[II] near the surface of the copper wire separately, the adhesion will deviate, and it will be difficult to achieve the desired characteristics. The key point is to control the Cu[II] / Cu[I] ratio.

[0039] From the viewpoint of further enjoying the effects brought about by controlling the ratio Cu[II] / Cu[I], the lower limit of the sum of Cu[I] and Cu[II] is preferably 50% or more, and more preferably 60% or more. The upper limit of this ratio is preferably 95% or less or 90% or less, from the viewpoint of facilitating lead manufacturing.

[0040] Regarding the bonding properties of copper wires, the in-plane distribution of Cu[I] and Cu[II] on the surface of the copper wire, the distribution morphology of Cu material in various states of Cu[I] and Cu[II] (granular distribution, linear distribution, planar distribution, etc.), and the surface morphology of the copper wire have relatively little influence; the ratio Cu[II] / Cu[I] has a greater impact. In this respect, XPS analysis, with an analysis depth of approximately a few nm, did not reveal a correlation between the distribution of Cu[I] and Cu[II] at this depth and the bonding properties.

[0041] The inventors of this invention have also discovered that by controlling the chemical bonding state of Cu material present near the surface of the copper wire, it is possible to achieve a copper wire that exhibits good bonding properties even with reduced friction during bonding, and also has excellent stability in the arc shape.

[0042] When copper wire is deformed to form arcs, bending or buckling of the leads can occur, leading to poor contact between adjacent leads. For example, gold leads are prone to deformation (bending), so trapezoidal or M-shaped arcs are used when forming long-span arcs. However, when forming trapezoidal or M-shaped arcs with copper wire, bending or kinking can sometimes occur. Furthermore, when forming short-span arcs with large height differences between the semiconductor device and the substrate, copper wire tends to experience arc tilting and poor bonding more frequently. Thus, the unstable arc shape of copper wires is a cause for concern, leading to difficulties in manufacturing management during assembly and reduced yield.

[0043] In a preferred embodiment of the present invention, the ratio of Cu(OH)2 to CuO, i.e., [Cu(OH)2] / [CuO], as determined by X-ray photoelectron spectroscopy (XPS), is in the range of 1 to 5.5.

[0044] Here, the proportion of CuO determined by X-ray photoelectron spectroscopy (XPS) [CuO], as mentioned above, refers to the proportion of Cu substances in the chemically bonded state of CuO when the total amount of Cu substances in the chemically bonded states of Cu, Cu2O, CuO, and Cu(OH)2 determined by X-ray photoelectron spectroscopy (XPS) is set to 100%.

[0045] Similarly, the proportion of Cu(OH)2 determined by X-ray photoelectron spectroscopy (XPS) [Cu(OH)2] refers to the proportion of Cu substances in the chemically bonded state of Cu(OH)2 when the total amount of Cu substances in the chemically bonded states of Cu, Cu2O, CuO, and Cu(OH)2 determined by X-ray photoelectron spectroscopy (XPS) is set to 100%.

[0046] The condition associated with this ratio [Cu(OH)2] / [CuO] will be referred to as "Condition 2".

[0047] By keeping the ratio [Cu(OH)2] / [CuO] in the range of 1 to 5.5, defects such as tilting, bending, and sagging during the formation of the arc can be suppressed. Even when forming long-span arcs or short-span arcs with large height differences, copper wires with excellent arc shape stability can be achieved.

[0048] From the viewpoint of achieving superior copper wire through the stability of the arc shape, the lower limit of the ratio [Cu(OH)2] / [CuO] is preferably 1.1 or higher, and more preferably 1.2 or higher, 1.3 or higher, 1.4 or higher, 1.5 or higher, or higher than 1.5.

[0049] When using copper wire, it was confirmed that the slippage between the lead surface and the cutting tool affects the stability of the wire arc shape. During arc formation, tension and deformation are applied to the lead wire, causing wear on the inner wall or tip of the cutting tool. Aluminum (Al) oxides are generally used as the material for the cutting tool, with common alumina containing aluminum oxide (Al₂O₃) or zirconium (Zr) being frequently used. The inventors of this invention discovered that Cu substances in a chemically bonded state with a Cu²⁺ valence near the surface of the copper wire affect the slippage with the Al oxide, with the ratio of Cu(OH)₂ to CuO having a significant impact. Increasing the proportion of Cu(OH)₂ reduces friction with the Al oxide, suggesting that reducing the proportion of CuO can decrease grinding and snagging.

[0050] From the viewpoint of achieving superior copper wire through the stability of the arc shape, the upper limit of the ratio [Cu(OH)2] / [CuO] is preferably 5.4 or less, and more preferably 5.3 or less, 5.2 or less, 5.1 or less, or 5 or less.

[0051] By forming a surface with a [Cu(OH)2] / [CuO] ratio within the aforementioned preferred range, copper wires exhibiting excellent arc shape stability can be achieved even when forming long-span arcs or short-span arcs with large height differences. For example, in the case of forming long-span trapezoidal arcs, even with a lead length of 4 mm or more, the arc shape formed by the horizontal and inclined portions of the lead can be stabilized. Furthermore, for example, in the case of forming short-span arcs with large height differences, even when the lead length is 0.5 mm or less, and the height difference between the two joints (i.e., the first joint with the electrode on the semiconductor chip and the second joint with the electrode on the lead frame or circuit board) is 0.1 mm or more, tilting and sagging can be suppressed, thereby stabilizing the arc shape.

[0052] The inventors of this invention have also discovered that by controlling the chemical bonding state of Cu material present near the surface of the copper wire, it is possible to achieve a copper wire that exhibits good bonding properties even with reduced friction during bonding, and provides good cutting tool life.

[0053] Concerns exist regarding copper wire, including the potential for early-stage damage such as clogging of the cleaver and the formation of deposits. During the bonding process, connecting multiple leads can lead to clogging of the cleaver's orifice, contamination of the inner wall and tip, and poor bonding. This may necessitate more frequent cleaver replacements to prevent such defects. Regarding cleaver replacement, issues include production interruptions due to equipment shutdowns and the need for additional operators. Furthermore, future demands for high-density installations require thinner copper wire diameters. However, using thinner wires reduces the gap between the cleaver and the lead (narrowing the lead's through-hole), raising concerns about a shortened cleaver lifespan.

[0054] In a preferred embodiment of the present invention, the ratio of CuO to Cu2O, i.e., [CuO] / [Cu2O], as determined by X-ray photoelectron spectroscopy (XPS), is in the range of 0.3 to 6.

[0055] Here, the proportion of Cu2O determined by X-ray photoelectron spectroscopy (XPS) [Cu2O], as mentioned above, refers to the proportion of Cu substances in the chemically bonded state of Cu2O when the total amount of Cu substances in the chemically bonded states of Cu, Cu2O, CuO, and Cu(OH)2 determined by X-ray photoelectron spectroscopy (XPS) is set to 100%.

[0056] The proportion of CuO determined by X-ray photoelectron spectroscopy (XPS) is as described above in relation to condition 2.

[0057] The condition related to this ratio [CuO] / [Cu2O] will be referred to as "Condition 3".

[0058] By maintaining a [CuO] / [Cu2O] ratio in the range of 0.3 to 6, the service life until the cutting tool is replaced can be increased in the mass production process of the joint (referred to as "cutting tool life").

[0059] From the viewpoint of further improving the lifespan of the chopping blade, the lower limit of the ratio [CuO] / [Cu2O] is preferably 0.4 or higher, and more preferably 0.5 or higher, 0.6 or higher, 0.7 or higher, 0.8 or higher, 0.9 or higher, or 1 or higher.

[0060] It is believed that the interaction between CuO and Cu2O oxides affects the cutting and damage to the surface of the cleaver and the lead wire, as well as the clogging of the lead wire through-hole, thus impacting the cleaver's lifespan. It is also believed that CuO forms a dense film, which helps reduce wear caused by friction with the cleaver's material, i.e., Al-based oxides. On the other hand, Cu2O forms relatively quickly and contains lattice defects and voids, making it more prone to cutting.

[0061] The inventors of this invention have discovered that it is difficult to improve the blockage and grinding of the lead wire through-hole by simply adjusting the ratio of CuO and Cu2O near the surface of the copper wire separately. By controlling both together, and controlling the ratio [CuO] / [Cu2O], the life of the cutting tool can be greatly improved.

[0062] From the viewpoint of achieving excellent blade life and good low-temperature bonding, the upper limit of the ratio [CuO] / [Cu2O] is preferably 5.5 or less, and more preferably 5 or less, 4.5 or less, 4 or less, 3.8 or less, 3.6 or less, 3.5 or less, 3.4 or less, 3.2 or less, 3 or less, or 2.8 or less.

[0063] In the copper wire of the present invention, when the total amount of Cu material in the chemically bonded states of Cu, Cu2O, CuO, and Cu(OH)2 as determined by X-ray photoelectron spectroscopy (XPS) on the surface of the lead wire is set to 100%, the proportion of Cu material in the chemically bonded state of Cu is preferably 5% or more, more preferably 10% or more. The upper limit of this proportion is preferably 50% or less, more preferably 40% or less.

[0064] The copper wire of the present invention is made of copper or a copper alloy. The copper content in the lead is not particularly limited to a range that does not impair the effects of the present invention. For example, the copper content in the lead can be 95% by mass or more, preferably 96% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass or more, 99.2% by mass or more, 99.4% by mass or more, or 99.5% by mass or more.

[0065] The copper wire of the present invention may also contain dopants. It may contain any dopants that improve the properties of the copper wire, but preferably one or more selected from the group consisting of Pd, Pt, Ag, and Rh. By containing this specific dopant and satisfying condition 1 above, its shelf life in the atmosphere can be improved.

[0066] Preferably, the copper wire of the present invention, when the lead wire as a whole is set to 100% by mass, contains one or more selected from the group consisting of Pd, Pt, Ag, and Rh, with a total concentration in the range of 100 to 6000 ppm by mass. Therefore, in a preferred embodiment, the copper bonding wire of the present invention is characterized by containing one or more selected from the group consisting of Pd, Pt, Ag, and Rh, with a total concentration in the range of 100 to 6000 ppm by mass.

[0067] The lower limit of the total content of the aforementioned dopants in the copper wire is preferably 150 ppm by mass or more, and more preferably 200 ppm by mass, 250 ppm by mass or more, or 300 ppm by mass or more. Furthermore, from the viewpoint of suppressing the increase in lead wire stiffness and improving storage life in the atmosphere, the upper limit of this total content is preferably 5500 ppm by mass or less, and more preferably 5000 ppm by mass or less, 4500 ppm by mass or less, 4000 ppm by mass or less, 3500 ppm by mass or less, or 3000 ppm by mass or less.

[0068] After copper wire is wound onto a spool and formed into a package, the package is sealed in a protective bag to prevent the spread of oxygen or moisture before shipment. Furthermore, in the manufacture of semiconductor devices, the protective bag is opened before being supplied for connection between electrodes. The service life of the leads after opening is typically set at approximately 2 to 6 days. By satisfying condition 1 and containing one or more of the elements selected from the group consisting of Pd, Pt, Ag, and Rh in the aforementioned preferred amounts, the storage life in the atmosphere after opening the protective bag can be improved. For example, a copper wire can be provided that, even after being kept in the atmosphere for 7 days after opening the protective bag, exhibits good bonding properties under low-friction conditions and good stability of the wire arc shape. Regarding this effect, it is believed that the reason is that by satisfying the ratio Cu[II] / Cu[I] of condition 1, and containing one or more selected from the group consisting of Pd, Pt, Ag and Rh in the above-mentioned preferred content, even while the lead is stored in the atmosphere, the noble metal elements Pd, Pt, Ag and Rh promote the formation of divalent Cu by inhibiting the growth of monovalent Cu, i.e. Cu2O, thereby improving the effect of maintaining the ratio Cu[II] / Cu[I] within the appropriate range of the present invention.

[0069] In the copper bonding wire of the present invention, the remaining portion other than the dopant is composed of copper and unavoidable impurities.

[0070] The diameter of the copper bonding wire of the present invention is not particularly limited, and can be appropriately determined according to the specific purpose. Preferably, it can be 15 μm or more, 18 μm or more, or 20 μm or more. The upper limit of the diameter is not particularly limited, for example, it can be 200 μm or less, 150 μm or less, or 100 μm or less. In one embodiment, the diameter of the copper bonding wire of the present invention is 15 μm or more and 100 μm or less.

[0071] The copper bonding wire of the present invention can be used in the manufacture of semiconductor devices to connect electrodes on a semiconductor chip to electrodes on a lead frame or circuit board. The first connection (1st connection) to the electrode on the semiconductor chip can be either a ball joint or a wedge joint. In a ball joint, the lead tip is heated and melted by an electric arc, and a ball (FAB: Free Air Ball) is formed by surface tension. This ball is then pressed onto the electrode of the heated semiconductor element. In a wedge joint, no ball is formed; instead, heat, ultrasonic waves, or pressure are applied to press the lead onto the electrode. The second connection (2nd connection) to the electrode on the lead frame or circuit board can be a wedge joint. According to the copper bonding wire of the present invention, which satisfies condition 1 above, good bonding performance can be achieved even with reduced friction during bonding. Furthermore, by satisfying condition 2 above, excellent arc shape stability can be achieved even in the case of forming long-span arcs or short-span arcs with large height differences. By satisfying condition 3 above, the cleaver life can be improved. Thus, the present invention significantly contributes to the expansion of copper wire applications.

[0072] <XPS-based methods for measuring and evaluating copper bonding wires>

[0073] The following section describes the methods for measuring and evaluating copper bonding wires based on X-ray photoelectron spectroscopy (XPS).

[0074] -Preparation of the test sample-

[0075] The test specimen can be prepared by winding copper wire around a test stage. Specifically, a glass plate is prepared as the test stage, and copper wire is heavily wound around this glass plate to prepare the test specimen. In this case, (i) the glass plate serving as the test stage becomes invisible due to the dense winding of the copper wire, and (ii) the surface of the resulting test specimen is flattened by winding the copper wire around the glass plate. Here, "flattened" refers to a surface that is not extremely uneven, being so flat as to be approximately parallel to the main surface of the test stage.

[0076] Here, no special pretreatment is required when providing the copper wire for measurement; the measurement can be performed on copper wire in the same state as when it is provided for connection between electrodes during the manufacture of the semiconductor device. As mentioned earlier, after its manufacture, the copper wire is sealed in a protective bag that blocks oxygen or moisture and shipped from the factory. Then, during the manufacture of the semiconductor device, the protective bag is opened before it is provided for connection between electrodes. The opening of the protective bag is carried out in a cleanroom where the semiconductor device is manufactured, and the storage period after opening is usually set at about 2 to 6 days. Therefore, after the protective bag is opened, it can be provided for measurement at least 3 days after being placed in a cleanroom or an environment based on this. Preferably, the measurement sample is prepared immediately after opening the protective bag (e.g., within 3 hours, 2 hours, 1 hour, or 30 minutes), and the XPS measurement is performed rapidly in the vacuum atmosphere of the XPS measurement apparatus.

[0077] - XPS-based measurement and evaluation -

[0078] XPS measurements were performed on the obtained test samples to obtain the spectra of Cu2p3 / 2, CuLMM, and O1s. Here, Cu2p3 / 2 is the spectrum of electrons (photoelectrons) originating from the 2p3 / 2 orbital of Cu, and CuLMM is the spectrum of Auger electrons originating from the LMM transition of Cu. In addition, O1s is the spectrum of electrons originating from the 1s orbital of oxygen (O).

[0079] XPS measurements can be performed under the conditions described in the section on [Measurement and Evaluation of Copper Bonds Based on XPS] described later. Furthermore, the XPS measurement area (detection target area) is preferably a region with a diameter of at least 100 μm, and the number of measurements is at least two. Taking conditions 1 to 3 above as examples, the proportion of Cu material in each of the aforementioned chemical bonding states is a proportion obtained based on the results of measurements performed on measurement areas exceeding this value.

[0080] Next, the detected spectrum is analyzed. The spectrum is analyzed using the analysis software attached to the XPS device, and the waveforms are separated according to the chemical bonding state category of Cu. The proportion of the chemical bonding state categories of Cu can be calculated in the following order (1) to (3).

[0081] (1) Using the Cu2p3 / 2 spectrum, separate the waveform of the sum of Cu[0]+Cu[I] from the waveform of Cu[II] and obtain their respective ratios.

[0082] (2) Using the CuLMM spectrum, separate the waveforms of Cu[0] and Cu[I] and obtain their respective ratios.

[0083] (3) Using the Ols spectrum, the waveforms of CuO and Cu(OH)2 are separated to obtain their respective proportions. The proportion of O2 component (derived from Cu2O) in the Ols spectrum is adjusted to achieve 1 / 2 of the proportion of Cu[I].

[0084] <Method for manufacturing copper bonding wire>

[0085] An example of a method for manufacturing the copper bonding wire of the present invention will be described.

[0086] Raw copper with a purity of 3N to 6N (99.9 to 99.9999% by mass) is processed into large diameter through continuous casting, and then refined into fine wires with the final wire diameter through wire drawing.

[0087] Furthermore, when adding dopants, a copper alloy containing the necessary concentration of dopants can be used as the raw material. When adding dopants, high-purity dopant components can be added directly, or a master alloy containing about 1% dopant components can be used. Alternatively, during the lead manufacturing process, the dopant components can be attached to the lead surface to make it contain dopants. In this case, it can be incorporated into one step of the lead manufacturing process or into multiple steps. As an attachment method, it can be applied from (1) an aqueous solution. dry Choose from heat treatment, (2) plating (wet) and (3) vapor deposition (dry).

[0088] Wire drawing can be performed using a continuous wire drawing device capable of setting multiple diamond-coated dies. It can also be performed during the wire drawing process, if needed. Furthermore, heat treatment is performed after wire drawing.

[0089] - Control of the ratio Cu[II] / Cu[I] -

[0090] From the viewpoint of achieving a copper bonding wire with a Cu[II] / Cu[I] ratio within a specified range as determined by X-ray photoelectron spectroscopy (XPS), preferred heat treatment conditions and surface properties before heat treatment will be described.

[0091] In the heat treatment process of copper wire, it is preferable to use a method that continuously heats the copper wire while sweeping it in a heating furnace, thereby increasing both the heating and cooling rates of the lead wire. That is, from the viewpoint of controlling the ratio of Cu valences on the surface of the copper wire, Cu[II] / Cu[I], within a specified range, it is preferable to rapidly heat and quench the copper wire in the heat treatment process.

[0092] Specifically, when the highest temperature inside the furnace is set as T (°C) and the travel time from the furnace inlet to the highest temperature range inside the furnace is set as H (seconds), the hypothetical (apparent) heating rate is expressed as T / H (°C / second). Regarding the cooling rate, when the travel time from the highest temperature range inside the furnace to the furnace outlet is set as C (seconds), the hypothetical (apparent) cooling rate is expressed as T / C (°C / second). The hypothetical heating rate T / H is preferably 400°C / second or higher, more preferably 500°C / second or higher, or 600°C / second or higher. The upper limit of T / H is not particularly limited; for example, it can be set to 2000°C / second or lower, or 1500°C / second or lower. The hypothetical cooling rate T / C is preferably 500°C / second or higher, more preferably 600°C / second or higher, or 700°C / second or higher. The upper limit of T / C is not particularly limited; for example, it can be set to 3000°C / second or less, 2500°C / second or less, or 2000°C / second or less. As a method to achieve the hypothetical heating rate and hypothetical cooling rate, it is preferable to optimize the flow rate of the atmosphere gas, the position of the atmosphere gas inlet, or the length, diameter, and shape of the atmosphere gas flow pipe in the furnace, and to optimize the shape, length, position, and set temperature of the heater section. For example, in order to increase the hypothetical heating rate, a heater section can be installed near the furnace inlet to increase its set temperature, or in order to increase the hypothetical cooling rate, the flow rate of the atmosphere gas on the cooling side can be increased. By setting the heating rate and cooling rate in the heat treatment process to the above-mentioned preferred ranges, and controlling the maximum temperature T in the furnace to be in the range of 400 to 900°C, the stability of oxides, hydroxides, etc. on the surface of the copper wire can be changed, thereby advantageously adjusting the ratio Cu[II] / Cu[I] to the range of 0.8 to 12. Preferably, by setting the hypothetical heating rate T / H to 600°C / second or higher and the hypothetical cooling rate T / C to 700°C / second or higher, it helps to adjust the ratio Cu[II] / Cu[I] to a preferred range of 2 to 10.

[0093] Furthermore, from the viewpoint of controlling the Cu[II] / Cu[I] ratio within a specified range, it is preferable to reduce the amount of organic matter adhering to and remaining on the surface of the copper wire during the wire drawing process. In the copper wire drawing process, water- and oil-based lubricants are typically used to reduce friction between the copper wire and the die surface. The oil-based lubricants used utilize substances that are easily volatile during heat treatment, such as low-molecular-weight, low-melting-point lubricants, thereby promoting the formation of Cu2 valence and adjusting the proportion of Cu1 valence. It is inferred that this affects: the protective function of the copper wire surface is improved by increasing the Cu2 valence (equivalent to Cu substances), and the development of oxidation can be suppressed by controlling the Cu1 valence.

[0094] - Control of the ratio [Cu(OH)2] / [CuO] -

[0095] When controlling the ratio [Cu(OH)2] / [CuO], in addition to the aforementioned rapid heating and quenching heat treatment conditions, it is preferable to water cool the lead wire near the outlet of the heating furnace.

[0096] It is believed that water cooling, compared to atmospheric cooling, accelerates the cooling rate and inhibits CuO formation, or that passing the copper wire through water at high temperatures promotes Cu(OH)2 formation, thereby advantageously adjusting the [Cu(OH)2] / [CuO] ratio to a specified range. By optimizing the cooling time, water temperature, and distance from the furnace outlet to the cooling water during water cooling, the [Cu(OH)2] / [CuO] ratio can be adjusted to the aforementioned preferred range. The water used in water cooling may contain a small amount of surfactant. Surfactants can also improve the looseness of the copper wire during use.

[0097] - Control of the [CuO] / [Cu2O] ratio -

[0098] When controlling the ratio [CuO] / [Cu2O], in addition to the aforementioned rapid heating and quenching heat treatment conditions, it is preferable to optimize the oxygen partial pressure and water vapor content in the gas atmosphere used in the heat treatment process.

[0099] The higher the oxygen partial pressure and the amount of water vapor, the more it promotes the formation of CuO, and the ratio [CuO] / [Cu2O] tends to increase.

[0100] [Semiconductor Devices]

[0101] By using the copper bonding wires for semiconductor devices of the present invention, electrodes on a semiconductor chip are connected to electrodes on a lead frame or circuit board, thereby enabling the manufacture of semiconductor devices.

[0102] In one embodiment, the semiconductor device of the present invention is characterized by including a circuit substrate, a semiconductor chip, and copper bonding wires for conducting the circuit substrate and the semiconductor chip, wherein the copper bonding wires are the copper bonding wires of the present invention.

[0103] In the semiconductor device of the present invention, the circuit board and the semiconductor chip are not particularly limited, and known circuit boards and semiconductor chips that can be used to construct the semiconductor device can be used. Alternatively, a lead frame can be used instead of the circuit board. For example, as described in Japanese Patent Application Publication No. 2002-246542, the semiconductor device can be structured to include a lead frame and a semiconductor chip mounted on the lead frame.

[0104] Semiconductor devices include various semiconductor devices used in electrical products (e.g., computers, mobile phones, digital cameras, televisions, air conditioners, solar power systems, etc.) and vehicles (e.g., motorcycles, automobiles, trams, ships, and aircraft, etc.).

[0105] [Example]

[0106] The present invention will now be described in detail with reference to embodiments shown. However, the present invention is not limited to the embodiments shown below.

[0107] (Sample)

[0108] First, the method for preparing the sample will be explained. The Cu used as the raw material for the lead wire is a material with a purity of 99.9% by mass or higher (3N) to 99.999% by mass or higher (5N), with the remainder consisting of unavoidable impurities. This copper of the specified purity is manufactured by continuous casting to a wire diameter of a few millimeters. Furthermore, when adding dopants Pd, Pt, or Ag, substances with a purity of 99% by mass or higher for Pd, Pt, or Ag, with the remainder consisting of unavoidable impurities, or a master alloy incorporating the dopants at a high concentration in Cu, are used. Then, the dopant content is added to the copper of the specified purity as per the target value, and the wire is manufactured by continuous casting to a wire diameter of a few millimeters. The resulting wire is then drawn to produce a lead wire with a diameter of 0.3 to 1.4 mm. During drawing, a commercially available lubricant is used, and the drawing speed is set to 30 to 200 m / min. In addition, multiple dies with a reduction rate ranging from 10% to 26% (more than half of which have a reduction rate of 10% to 21%) are used for wire drawing to achieve the final wire diameter. Depending on the requirements, 0 to 2 heat treatments at 200% to 600% for 5 to 15 seconds are performed during the wire drawing process. Here, the final wire diameter is set to 20 μm.

[0109] After processing, the leads are continuously heated while being swept through a heat treatment furnace. The maximum temperature inside the furnace is 400–850°C, and heat treatment is performed while 5 vol% H₂–N₂ gas flows through the furnace. When the maximum temperature inside the furnace is defined as T (°C), the time taken from the furnace inlet to the maximum temperature range is defined as H (seconds), and the time taken from the maximum temperature range to the furnace outlet is defined as C (seconds), the hypothetical (apparent) heating rate is expressed as T / H (°C / second), and the hypothetical cooling rate is expressed as T / C (°C / second). In this embodiment, the hypothetical heating rate T / H is set to a range of 400–1500°C / second, and the hypothetical cooling rate T / C is set to a range of 500–2000°C / second. In a comparative example, T / H is set to less than 400°C / second, and T / C is set to less than 500°C / second, which is an example of typical manufacturing conditions for copper bonding wires.

[0110] (Experimental and evaluation methods)

[0111] The following section explains the testing and evaluation methods.

[0112] [XPS-based measurement and evaluation of copper bonding wires]

[0113] 1. Preparation of the test sample

[0114] Using commercially available protective bags, the copper bonding wires manufactured in the examples and comparative examples were sealed in the bags under a nitrogen atmosphere and opened within one week thereafter. Within two days of opening, the test samples described below were prepared and placed in the vacuum chamber of the XPS apparatus. The test samples were prepared by winding them onto a 10 mm wide glass plate. In preparing the test samples, (i) the copper wires were wound so densely that the glass plate became invisible, and (ii) the surface of the resulting test sample was flattened.

[0115] 2. XPS-based measurement and evaluation

[0116] For the test sample obtained in section 1 above, XPS measurements were performed under the following conditions to detect the spectra of Cu2p3 / 2, CuLMM, and Ols.

[0117] • Measuring apparatus: Quantera II manufactured by PHI Corporation

[0118] • Achieved vacuum level: approximately 1×10 －8 Torr

[0119] • X-ray source: Monochromatic Al (1486.6 eV)

[0120] • X-ray beam diameter: 100μmΦ (25W, 15kV)

[0121] • Detection area: ≥10000μm 2

[0122] • Photoelectron fly-off angle: 45 degrees

[0123] The detected spectrum was analyzed using analysis software attached to the XPS device, and separated according to the chemical bonding state category of Cu. The proportion of Cu chemical bonding state categories was calculated according to the following steps (1) to (3).

[0124] (1) Using the Cu2p3 / 2 spectrum, separate the waveform of the sum of Cu[0]+Cu[I] from the waveform of Cu[II] and obtain their respective ratios.

[0125] (2) Using the CuLMM spectrum, separate the waveforms of Cu[0] and Cu[I] and obtain their respective ratios.

[0126] (3) Using the Ols spectrum, separate the waveforms of CuO and Cu(OH)2 to obtain their respective proportions. Adjust the proportion of the O2 component (derived from Cu2O) in the Ols spectrum to make it reach 1 / 2 of the proportion of Cu[I].

[0127] [Performance testing and evaluation of copper bonding wires]

[0128] For each lead in the embodiments and comparative examples, bonding was performed using a commercially available wire bonding machine (IConn manufactured by K&S). For the lead frame, a Cu alloy lead frame plated with Ag was used, and for the semiconductor device, a Si chip was used. For the electrodes, electrodes obtained by plating Ag onto the aforementioned lead frame were used. Furthermore, ball bonding was performed on the semiconductor device, and wedge bonding was performed on the lead frame. In addition, ball formation was performed under a flow rate of N2 + 5% H2 gas of 0.4 L / min or more and less than 0.6 L / min.

[0129] <Friction Evaluation>

[0130] In the friction evaluation, the number of friction cycles required for wedge bonding, which typically requires more than two cycles, was reduced to one or zero cycles (no friction) before bonding the leads. The bonding temperature was set to a low temperature of 150°C, and the bonding load conditions were 50–80 gf. Under ultrasonic vibration conditions, the USG current setting was adjusted within the range of 15–40. Regarding friction conditions, the scrub amplitude was set within the range of 2.5–3.5 μm, and the scrub frequency was adjusted within the range of 170–250 kHz. The scrub mode was selected as in-line, and the friction movement direction was parallel to the lead direction. 200 leads were connected, and the number of poorly connected leads that peeled off during bonding or caused the wire bonding machine to stop was counted. For each lead, the average number of poorly connected leads was calculated twice, and the evaluation was performed according to the following criteria. The evaluation results are shown in the "Joint Quality" column of Table 1.

[0131] Evaluation Criteria:

[0132] ◎:0

[0133] ○: 1~3

[0134] △: 4~6

[0135] ×: 7 or more

[0136] <Linear Arc Shape Stability>

[0137] The stability of the arc shape (reproducibility of the arc profile) is tested and evaluated for the formation of long-span trapezoidal arcs and short-span arcs with large height differences, as follows.

[0138] (1) Stability of the arc shape when a long-span trapezoidal arc is formed

[0139] 144 trapezoidal arcs were connected under conditions more stringent than usual arc formation requirements, with a lead wire length of 5 mm and an arc height of 0.4 mm. The arc portions were observed using an optical microscope; any bending exceeding 0.2 mm was considered defective. Evaluation was conducted according to the following criteria: the bending amount was determined by the distance between the point of maximum bending and the straight line connecting the two points of connection. The evaluation results are shown in the "Arch Shape Stability" column of Table 1, specifically in the "Long Trapezoidal" column.

[0140] Evaluation Criteria:

[0141] ◎: No undesirable locations

[0142] ○: The defective location is 1-3.

[0143] △: The defective location is 4-7.

[0144] ×: The defective location has a score of 8 or higher.

[0145] (2) Stability of arc shape when forming short-span arcs with large height differences

[0146] 200 wire arcs with large height differences were connected using a lead wire length of 0.6 mm and a height difference of 0.5 mm from the wedge joint to the ball joint. The arc sections were observed using an optical microscope; any bending amount exceeding 0.05 mm was considered defective. Evaluation was conducted according to the following criteria. The evaluation results are shown in the "Wire Arc Shape Stability" and "Short and Large Height Difference" columns of Table 1.

[0147] Evaluation Criteria:

[0148] ◎: No undesirable locations

[0149] ○: The defective location is 1-3.

[0150] △: The defective location is 4-7.

[0151] ×: The defective location has a score of 8 or higher.

[0152] [Lifespan of the cleaver]

[0153] To conduct accelerated bonding tests to assess contamination and clogging of the wire bonders, 50,000 trapezoidal wires with a lead length of 1.5 mm were bonded using wire bonders with apertures as small as 25 μm, a bonding temperature of 150°C, and two friction cycles. The wire bonders were then removed from the wire bonding machine and examined using an optical microscope. Defects were recorded by counting the number of wire bonders with contamination, deposits, or cutting debris larger than 3 μm at the tip and internal parts. Evaluation was conducted according to the following criteria. The evaluation results are shown in the "Wire Bonder Life" and "50,000 Bonds" columns of Table 1.

[0154] Evaluation Criteria:

[0155] ◎: Number of defects: 0

[0156] ○: Number of defects: 1

[0157] △: Number of defects 2

[0158] ×: Number of defects 3 or more

[0159] An evaluation was also conducted for the case of connecting 200,000 trapezoidal arc wires under the same conditions as described above, based on the following criteria. The evaluation results are shown in the "Cut-off Life" and "200,000 Connections" columns of Table 1.

[0160] Evaluation Criteria:

[0161] ◎: Number of defects: 0

[0162] ○: Number of defects 1-2

[0163] △: Number of defects 3-4

[0164] ×: Number of defects 5 or more

[0165] Table 1 shows the evaluation results of the embodiments and comparative examples.

[0166] [Table 1]

[0167]

[0168] It has been confirmed that in Examples No. 1 to 16, the ratio of Cu[II] / Cu[I] measured by XPS is within the range of the present invention, and good bonding properties are exhibited even when friction is reduced by 1 or 0 times during bonding. Furthermore, the sum of Cu[I] and Cu[II] measured by XPS is 50% or more in any of the examples.

[0169] Furthermore, it was confirmed that the ratio [Cu(OH)2] / [CuO] measured by XPS in Examples No.1-5, 7-11, 13, 15 and 16 was within a preferred range, and the shape stability of the arc was excellent even when forming long-span arcs or short-span arcs with large height differences.

[0170] It has been confirmed that the ratio of [CuO] / [Cu2O] measured by XPS in Examples No.1, 2, 4 to 16 is within the preferred range, resulting in excellent cleaver life.

[0171] On the other hand, in Comparative Examples No. 1 to 4, the ratio Cu[II] / Cu[I] measured by XPS was outside the scope of the present invention. If the number of frictions during the joint was 1 or 0 and friction was reduced, poor connection occurred. In addition, the stability of the arc shape and the life of the cutting tool were also poor.

Claims

1. A copper bonding wire, characterized in that, The sum of the proportions of Cu, Cu2O, CuO, and Cu(OH)2 measured by X-ray photoelectron spectroscopy (XPS) at an analytical depth of a few nm on the surface of the line is set as 100%. The ratio of Cu[II] to Cu[I], which is the ratio of CuO and Cu(OH)2 with a Cu2 valence equivalent, is in the range of 0.8 to 12.

2. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] / Cu[I] is 1 or more.

3. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is 1.2 or higher.

4. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is 1.5 or higher.

5. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is 2 or more.

6. The copper bonding wire according to claim 1, characterized in that, The Cu[II] / Cu[I] ratio is 2.5 or higher.

7. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is 3 or more.

8. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is less than 10.

9. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu[II] to Cu[I] is 8 or less.

10. The copper bonding wire according to claim 1, characterized in that, The ratio of Cu(OH)2 to CuO, i.e., [Cu(OH)2] / [CuO], as determined by X-ray photoelectron spectroscopy (XPS), is in the range of 1 to 5.

5.

11. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 1.1 or higher.

12. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 1.2 or higher.

13. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 1.4 or higher.

14. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 1.5 or higher.

15. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 5.4 or less.

16. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 5.2 or less.

17. The copper bonding wire according to claim 10, characterized in that, The ratio of [Cu(OH)2] / [CuO] is 5 or less.

18. The copper bonding wire according to claim 1, characterized in that, The ratio of CuO to Cu2O, i.e., [CuO] / [Cu2O], determined by X-ray photoelectron spectroscopy (XPS), is in the range of 0.3 to 6.

19. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] to [Cu2O] is 0.4 or higher.

20. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] to [Cu2O] is 0.6 or higher.

21. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] to [Cu2O] is 0.8 or higher.

22. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] / [Cu2O] is 1 or higher.

23. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] / [Cu2O] is 5 or less.

24. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] / [Cu2O] is 4 or less.

25. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] to [Cu2O] is 3.5 or less.

26. The copper bonding wire according to claim 18, characterized in that, The ratio of [CuO] / [Cu2O] is 3 or less.

27. The copper bonding wire according to claim 1, characterized in that, The sum of Cu[I] and Cu[II] is more than 50%.

28. The copper bonding wire according to claim 1, characterized in that, It includes one or more selected from the group consisting of Pd, Pt, Ag and Rh, with a total concentration ranging from 100 to 6000 ppm by mass.

29. The copper bonding wire according to claim 28, characterized in that, The total concentration of Pd, Pt, Ag and Rh is above 200 ppm by mass.

30. The copper bonding wire according to claim 28, characterized in that, The total concentration of Pd, Pt, Ag and Rh is above 300 ppm by mass.

31. The copper bonding wire according to claim 28, characterized in that, The total concentration of Pd, Pt, Ag and Rh is below 5000 ppm by mass.

32. The copper bonding wire according to claim 28, characterized in that, The total concentration of Pd, Pt, Ag and Rh is below 4000 ppm by mass.

33. The copper bonding wire according to claim 28, characterized in that, The total concentration of Pd, Pt, Ag and Rh is below 3000 ppm by mass.

34. The copper bonding wire according to claim 1, The diameter of the copper bonding wire is between 15μm and 100μm.

35. The copper bonding wire according to any one of claims 1 to 34, Used in semiconductor devices.

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