Passivating coatings on copper metal surfaces for copper wire bonding applications

Abstract

The present invention provides improved techniques for bonding devices with copper-to-copper or other types of bonding. The substrate is cleaned to remove surface oxides and contaminants, and then rinsed. The rinsed substrate is supplied to a coating unit, where a protective coating is applied to the substrate. The protective coating may be applied by immersing the substrate in a bath or by chemical vapor deposition. In one aspect, the protective coating may be copper selective such that the protective coating is applied only to the copper feature of the substrate. The protective coating minimizes the formation of oxides and other bond weakening forces that may be formed in a bonding process (e.g., a copper bond pad that bonds a copper wire to a substrate). In one aspect, an annealing process is used to cure the protective coating, removing small defects and other anomalies in the protective coating prior to the bonding process.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Application No. 63 / 345,868, filed on May 25, 2022, entitled “PASSIVATION COATING ON COPPER METAL SURFACE FOR COPPER WIRE BONDING APPLICATION,” the disclosure of which is hereby incorporated by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to bimetallic devices and, more particularly, to techniques for reducing the formation of bond weakening forces in copper wire bonding applications. Background Art

[0004] Copper (Cu) is the fifth most abundant material in the earth's crust and is one of the most commonly used metals in a wide range of industrial applications. For example, copper is often used in wires, metal sheets, heat exchanger parts, electrical and electronic applications, marine industries, and many other industrial applications. Copper has rapidly replaced gold (Au) as the preferred wire bonding material in microelectronic packaging due to its higher electrical conductivity, lower cost, and better mechanical strength (which leads to reduced pad size and pad spacing). However, corrosion-related failures need to be minimized to ensure package reliability. For example, aluminum (Al) bonding pads are particularly susceptible to corrosion and have a unique "mud-crack" appearance. Especially under harsh conditions such as automotive environments, this corrosion can cause critical failures of Cu wire bonding components. The emerging trend of wearable electronic devices also imposes new and more stringent packaging reliability requirements to ensure protection from sweat / mud / rain corrosion under all-terrain non-stop use conditions.

[0005] When bonding two different metals (e.g., Al bonding pad connected to Cu wire, etc.), the corrosion problem is exacerbated because the galvanic contact provides a thermodynamic driving force for accelerated Al corrosion, which can lead to weak bonding and cause the Cu wire to separate from the Al bonding pad or other failures. For example, referring to FIG. 1 , a block diagram is shown, which shows various aspects of a bonding process according to the prior art. As shown in FIG. 1 , a Cu wire 102 can be bonded to an Al substrate 104 (e.g., a board, a bonding pad, etc.). In order to promote the bonding of the Cu wire 102 to the Al substrate 104, heat can be introduced. For example, a common bonding process may involve a temperature of 195° C. to 205° C. (e.g., about 200° C.). At such a temperature, the Cu wire 102 and the Al substrate 104 will be directly connected and some intermetallic compounds will be formed between them. If it is desired to eliminate this bimetallic contact, the Al substrate can be replaced with Cu or a Cu-containing alloy. In this case, at a wire bonding temperature of about 200° C., Cu will undergo rapid oxidation, resulting in non-stickiness at the bonding site 106 on the pad. When such oxidation occurs during the bonding process, the Cu-to-Cu bond between the Cu wire 102 and the Cu substrate 104 is weakened, thereby increasing the likelihood of a bond failure (i.e., causing the Cu wire 102 to separate from the Cu substrate 104), or even no connection at all. More details on Cu-to-Cu bond failure according to the process shown in FIG. 1 are described in detail below.

[0006] The above-mentioned Cu oxidation problem and Al bond pad corrosion problem are two unresolved technical challenges that pose reliability issues for next-generation packaging applications involving semiconductor devices. For example, next-generation automotive chips require very low defect rates, approaching zero parts per billion (ppb). Due to the above-mentioned Cu-Al bimetallic corrosion and Cu oxidation problems that occur during the bonding process, it is not possible to achieve such low defect rates when utilizing Cu to Al and unassisted Cu to Cu direct bonding. In addition, current packages with Cu wire bonds to Al bond pads can exhibit low ppm defects (e.g., multiple lift ball defects) that are still 1000% higher than acceptable limits. Moreover, defects in Cu to Al bonding often occur due to difficult to track causes, which makes attempts to mitigate such defects challenging. Summary of the invention

[0007] The present invention provides techniques for minimizing defects (e.g., corrosion, oxidation, etc.) in wire bonding applications involving Cu wires. Non-limiting examples of Cu wire bonding applications to which the disclosed techniques can be applied include Cu-Al wire bonding applications, Cu-Cu wire bonding applications, and Cu lead frame applications. The disclosed bonding techniques enable Cu to Al bonding and Cu to Cu bonding in electrical devices while mitigating the problems associated with the above-mentioned corrosion and oxidation. According to aspects of the present disclosure, substrates (e.g., Cu and Cu alloys) and Cu to Al bonded components can be cleaned (e.g., using mild acidic solutions or dry etching techniques) to remove surface oxides and contaminants.

[0008] Once cleaned, the substrate can be rinsed (e.g., using water) and then provided to a coating unit where a protective coating is applied to the substrate. The protective coating can be applied by immersing the substrate in a bath or by chemical vapor deposition. On the one hand, the protective coating can be copper selective so that the protective coating is attached only or primarily to copper features of the substrate, such as copper bonding pads. The protective or passivating coating can minimize the appearance of corrosion defects generated during Cu wire bonding (e.g., corrosion defects that may occur during bonding processes involving Cu to Al bonded devices). On the other hand, the protective coating can minimize the formation of oxides and other bond weakening forces that can be formed during storage, especially during bonding processes (e.g., as a non-limiting example, Cu wires are bonded to Cu bonding pads of substrates). Eliminating or minimizing the extreme oxidation that occurs during Cu wire bonding significantly improves the bonding quality between two Cu features (e.g., Cu wires and bonding pads, lead frames, etc.), and can improve the reliability of the resulting bonded devices. For example, an obstacle to achieving Cu-Cu bonding is the environmental and thermally driven oxidation of Cu, which produces oxides greater than 100nm thick. This oxide layer prevents the connection of two Cu interfaces. By depositing a removable ultra-thin passivation film to protect the Cu surface from oxidation, the substrate can be kept clean and oxide-free for subsequent bonding to the next copper feature. On the one hand, an annealing process can be used to cure the protective coating, removing small defects and other anomalies in the protective coating before the bonding process. It is also worth noting that the passivation coating can also be used to protect other types of devices (such as Cu lead frames) from oxidation, facilitating the bonding of Cu wires without the need for expensive Ag coatings.

[0009] Use of the techniques disclosed herein can facilitate reliable manufacturing of next generation packaging technologies for automotive applications that require more robust, corrosion resistant, and highly conductive connections (e.g., to meet required AEC Grade 1, Grade 0 safety standards). Thus, the techniques disclosed herein can improve the reliability of Cu-Al wire bonded devices (e.g., by mitigating or minimizing the formation of corrosion at the Cu-Al bonding sites) and contribute to the highest bond reliability for direct Cu-Cu wire bonding applications (e.g., by mitigating or minimizing corrosion at the Cu-Cu bonding sites).

[0010] The above content has been summarized quite extensively the features and technical advantages of the present invention so that the subsequent detailed description of the present invention can be better understood. The additional features and advantages of the present invention that form the subject of the claims of the present invention will be described below. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments can be easily used as the basis for modifying or designing other structures for performing the same purpose of the present invention. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present invention as set forth in the appended claims. From the following description considered in conjunction with the accompanying drawings, the novel features and other objects and advantages that are considered to be the characteristics of the present invention with respect to its organization and method of operation will be better understood. However, it should be clearly understood that each of the figures is provided for the purpose of illustration and description only and is not intended to be a limitation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] For a more complete understanding of the present invention, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

[0012] FIG1 shows a block diagram illustrating aspects of a bonding process according to the prior art;

[0013] FIG. 2A to FIG. 2D shows a block diagram illustrating a technique for preventing non-stick on pads of Cu wire bonds according to aspects of the present disclosure;

[0014] Figure 3 shows a block diagram illustrating an exemplary system for producing a device with metal bonding according to aspects of the present disclosure;

[0015] Figure 4 shows an image of a Cu surface having a protective coating applied according to the present disclosure;

[0016] Figure 5 shows a graph illustrating oxide suppression according to aspects of the present disclosure;

[0017] Figure 6 A diagram illustrating the bonding reliability between a Cu wire and an Al substrate is shown;

[0018] Figure 7A diagram illustrating the bonding reliability between a Cu wire and a Cu substrate is shown;

[0019] FIG. 8A to FIG. 8C shows block diagrams and images illustrating exemplary aspects of bonding Cu wires to a lead frame in accordance with aspects of the present disclosure; and

[0020] Fig. 9 A flow chart is shown of an exemplary method of performing bonding of a Cu device according to aspects of the present disclosure.

[0021] It should be understood that the drawings are not necessarily drawn to scale and that the disclosed embodiments are sometimes illustrated in diagrammatic and partial views. In some cases, details that are not necessary for understanding the disclosed methods and apparatus or that make other details difficult to notice may have been omitted. Of course, it should be understood that the present disclosure is not limited to the particular embodiments shown herein. DETAILED DESCRIPTION

[0022] Reference FIG. 2A to FIG. 2D , a block diagram illustrating a technique for bonding Cu wires according to various aspects of the present disclosure is shown. FIG. 2A to FIG. 2C , a Cu wire 102 and a Cu substrate 104 are shown. The Cu wire 102 may be one of various bonding wires containing Cu metal. For example, the Cu wire 102 may include a Cu wire, a wire formed of a Cu alloy, and a metal-coated Cu wire (e.g., palladium-coated Cu (PCC)). The Cu substrate 104 represents a substrate having a Cu feature, which corresponds to a metal structure to which the Cu wire can be bonded according to the present disclosure. The Cu feature may include, for example, a metal bonding pad to which the Cu wire can be bonded. It is worth noting that, as a non-limiting example, the Cu feature may include a Cu feature (e.g., a Cu bonding pad) and a feature formed of a Cu alloy (e.g., a Cu alloy bonding pad). Compared to FIG. 1 , on the one hand, FIG. 2A to FIG. 2C The Cu substrate 104 in FIG. 1 has been coated with a protective coating 202 according to the concepts disclosed herein. The protective coating 202 can protect the Cu substrate 104 before starting the bonding process. Figure 2B As shown, during the bonding process, the Cu wire 102 can be pressed into and through the coating 202, thereby contacting the Cu substrate 104. During the bonding process, the presence of the protective coating 202 minimizes the development of oxidation between the Cu wire 102 and the Cu substrate 104, thereby improving the strength of the bond formed between the Cu wire 102 and the Cu substrate 104.

[0023] exist Figure 2D middle, FIG. 2A to FIG. 2CThe substrate 104 is replaced by the substrate 204, which may be a substrate including an Al bonding pad. As described above, when the Cu wire 102 is bonded to the Al substrate 204 (e.g., Al bonding pad) according to the prior art, the resulting Cu-Al bimetallic contact may cause galvanic corrosion, resulting in corrosion defect failure. In order to mitigate such corrosion defects and failures, as Figure 2D As shown, a Cu wire may be bonded to an Al bonding pad, and the Cu wire may be coated with a protective coating 202 according to the concepts disclosed herein. The protective coating 202 may be used to passivate the Cu bonding wire 102, terminating the source of Cu-Al bimetallic contact, which may eliminate failures caused by corrosion defects.

[0024] It should be understood that the advantages provided by various aspects of the present disclosure are not based solely on FIG. 2A to FIG. 2D In contrast, the present disclosure provides innovative techniques for applying the protective coating 202 to metal devices and eliminating defects present in the protective coating 202. Therefore, it should be understood that the disclosed Cu wire bonding techniques, whether involving Cu to Cu bonded devices (e.g., Cu, Cu alloys, coated Cu, or combinations thereof), or Cu to Al bonded devices, in addition to enhancing the ability to mitigate corrosion and oxidation during the bonding process, also improve the manner in which the protective coating 202 is applied to metal devices, as described in more detail below.

[0025] Reference Figure 3 , a block diagram illustrating an exemplary system for producing a device with metal bonding according to various aspects of the present disclosure is shown. It should be noted that the following reference is made to Cu wire bonding applications involving substrates. Figure 3 However, it should be understood that reference Figure 3 The concepts illustrated and described may be implemented for metal devices involving other forms of Cu wire bonding applications. For example, reference Figure 3 The process described for application to substrates may also be applied to Cu wire bonded semiconductor devices (e.g., in applications involving application of a protective or passivation coating to Cu wires bonded to substrates having Al bond pads, such as Figure 2D as shown), or other types of metal devices (eg, lead frames, etc.).

[0026] like Figure 3 As shown, the system may include a cleaning unit 310, a rinsing unit 320, a coating unit 330, and a bonding unit 340. The cleaning unit 310 may be configured to clean a substrate, for example FIG. 2A to FIG. 2CThe substrate 104. The cleaning unit 310 may include a wet etching unit 312, a dry etching unit 314, or both. The wet etching unit 312 may include a container, such as a plastic or glass container, which may be filled with a cleaning solution, and the substrate may be placed in the cleaning solution. When immersed in a cleaning solution bath, any contaminants and oxides present on the substrate surface may be removed by the cleaning solution. For example, the cleaning solution may be an acid, and the substrate may be placed in an acid bath for a period of time to clean the substrate surface. In one aspect, the time period for which the substrate is placed in the cleaning solution bath may be about 1 minute. In other or alternative aspects, the time period may be longer or shorter than 1 minute (e.g., 30 seconds (s), 40s, 45s, 50s, 55s, 30s to 55s, 55s to 65s, 65s to 85s, 70s, 80s, 90s, etc.). In one aspect, the acid used as the cleaning solution may be 3.5% sulfuric acid. In additional or alternative aspects, the wet etching unit 312 can use other preparations of sulfuric acid or other types of acids (e.g., acetic acid, hydrochloric acid, citric acid, other mild acids, etc.), or cleaning solutions. The dry etching unit 314 may include an etching device that is configured to clean the surface of the metal device without using a cleaning solution (such as used by the wet etching unit 312). For example, the dry etching unit 314 may include a plasma etcher using Ar, H2, N2, O2, or a mixture thereof. The plasma etcher can treat the surface of the substrate (or other metal device, or Cu wire-bonded semiconductor device) with plasma to remove surface contaminants and oxides of the substrate. It should be noted that the plasma etching described herein is for illustrative purposes, not for limitation, and if desired, the dry etching unit 314 can use other techniques (e.g., laser etching, etc.).

[0027] Once cleaned, the substrate may be provided to a rinse unit 320. The rinse unit 320 may be configured to rinse the cleaning solution off the substrate. Deionized water or other rinse agents may be used for rinsing. After rinsing is complete, the substrate may be provided to a coating unit 330 where a protective coating is applied to the substrate. Figure 3 As shown, the protective coating may be applied by coating unit 330 in a variety of ways, including by a bath (e.g. Figure 3 332), or by chemical vapor deposition (CVD) (eg Figure 3CVD coating unit 334 is shown. Bath coating unit 332 can include a container (e.g., a glass or plastic container) and can apply the protective coating by immersing the (cleaned and rinsed) substrate in a bath of non-aqueous liquid. The non-aqueous liquid bath can include a solvent and one or more inhibitor compounds (i.e., materials that provide the protective coating). The solvent can include ethanol, isopropanol, acetone, hexane, other solvents, or mixtures thereof (e.g., water and ethanol; water and isopropanol; acetone and hexane; water, acetone, and hexane; etc.). The one or more inhibitor compounds can be 5-mercapto-1-phenyl-tetrazole, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, sulfathiazole, 5-amino-1,3,4-thiadiazole-2-thiol, 1-phenyl-1H-tetrazole-5-thiol, 2-(2-dihydroxy-5-methyl)-phenyl-benzotriazole, 5-methyl-benzotriazole, amino-tert-butylpyrazole, tetrazole, dodecanethiol, azoimidotoluene (azimino toluene), 1,2,4-triazole, cyclopropanediol, 4-(2-aminothiazol-4-yl)-phenol, 5-methyl-2-phenyl-2,4-dihydropyrazol-3-one, phenyl isothiocyanate, 4-methyl-5-imidazolecarboxaldehyde, 5-(3-aminophenyl)-tetrazole, 2-amino-4-(4-chlorophenyl)-thiazole, 1-H-benzotriazole, 2-mercapto-benzoxazole, 5-methyl-benzotriazole, 5-methyl-benzimidazole, 2-mercaptobenzimidazole, pyrazole, toluene-triazole (toly-t In one aspect, the inhibitor compound may be Cu selective, such that when the substrate is immersed in the non-aqueous liquid bath provided by the bath coating unit 332, the inhibitor compound forms a protective coating on the Cu components (e.g., Cu bonding pads, circuits, wires, etc.) of the immersed substrate, but does not form a protective coating on other parts of the substrate (e.g., silicon wafers, ceramic substrates, substrates formed of organic materials, etc.). In alternative aspects, the bath used to apply the coating can use water alone (i.e., a water bath) or in combination with other solvents (e.g., water and ethanol; water and isopropanol; water and acetone; water and hexane; water, acetone, and hexane; etc.). In one aspect, the bath can be heated. For example, the bath can be heated to a temperature of 15° C. to 105° C.In some aspects, the bath can be heated to a temperature of 20° C. to 100° C., 25° C. to 100° C., 25° C. to 95° C., 30° C. to 90° C., 35° C. to 85° C., 35° C. to 90° C., 40° C. to 100° C., 40° C. to 90° C., or other temperatures in the range of 20° C. to 100° C. In some aspects, the bath can be heated to a temperature of about 70° C. In some aspects, the bath can be heated to a temperature of 50° C. to 90° C., 55° C. to 85° C., 60° C. to 80° C., 65° C. to 75° C., 68° C. to 72° C., 70° C. to 90° C., or 60° C. to 90° C. In some aspects, the bath can be mechanically stirred or agitated, such as by ultrasonic vibration (as a non-limiting example).

[0028] The CVD coating unit 334 may include a CVD chamber in which the substrate may be placed during the application of the protective coating. To apply the protective coating, the CVD chamber may be heated after the substrate is placed in the CVD chamber, and a gas of one or more inhibitor compounds may be introduced into the CVD chamber. Alternatively, during the heating process, a certain amount of one or more inhibitor compounds may be placed in the CVD chamber with the substrate, and when the heating occurs, the one or more inhibitor compounds may be vaporized, thereby releasing vaporized molecules of the one or more inhibitor compounds in the CVD chamber. In one aspect, the heating of the CVD chamber may be performed at a temperature of 80° C. to 200° C. In one aspect, the heating of the CVD chamber may be performed at a temperature of approximately 90° C. to 110° C. The vaporized inhibitor compound may be deposited on the surface of the substrate, thereby forming a protective coating or passivation layer on the substrate. In an embodiment utilizing the CVD coating unit 334, the inhibitor compound may be the same inhibitor compound described above with reference to the bath coating unit 332. Furthermore, the inhibitor compound may be Cu selective, thereby ensuring that the protective coating obtained by the CVD coating unit 334 is provided on Cu components (e.g., Cu bonding pads, circuits, wires, lead frames, etc.) and not on other portions of the substrate (e.g., silicon wafers, etc.).

[0029] In one aspect, the temperature used to heat the CVD chamber can be configured to control the properties of the applied protective coating, the properties or characteristics of the coated metal device (e.g., Cu wire, substrate with Cu bonding pad, lead frame, etc.). For example, certain temperatures can promote the formation of an ultra-thin protective coating, while other temperatures can promote the formation of a thicker protective coating. As another example, a metal device placed in a CVD chamber can be heated during the heating of the CVD chamber, which can change the properties or characteristics of the surface of the metal device (e.g., heating at certain temperatures can promote or cause oxidation of the Cu metal device (e.g., Cu wire or bonding pad)). Therefore, the heating of the CVD chamber can be controlled to reduce undesirable changes in the properties or characteristics of the metal device and promote the formation of a protective coating of the desired thickness.

[0030] In one aspect, the coated substrate can be rinsed after being immersed in the bath coating unit 332 or deposited by the CVD coating unit 334. Rinsing the coated substrate can remove excess inhibitor compounds from the substrate surface. In one aspect, rinsing can be performed using the same or similar solvents as described above with reference to the bath coating unit 332.

[0031] As a result of the operation of the coating unit 330 (eg, the bath coating unit 332 or the CVD coating unit 332), a protective coating may be deposited on the substrate to produce a coated substrate 302 (eg, FIG. 2A to FIG. 2C The substrate 104 and the protective coating 202, or Figure 2D 102 and protective coating 202). The thickness of the protective coating can be between 1 nanometer (nm) and 200 nm. In one aspect, the protective coating can have a thickness between 1 nm and 20 nm, 10 nm and 50 nm, 25 nm and 75 nm, 50 nm and 100 nm, 75 nm and 125 nm, 100 nm and 150 nm, 125 nm and 175 nm, 150 nm and 200 nm, or a combination thereof. It should be noted that the various example thickness ranges described above are for illustrative purposes only and are not intended to be limiting. As described above, Figure 3 The system provides the capability to control the thickness of the protective coating, allowing for thicker protective coatings or thinner protective coatings to be produced, depending on the specific Cu bonding application involved and whether a particular Cu bonding application would benefit from a specific thickness of protective coating.

[0032] As described above, when a Cu selective inhibitor compound is used, a protective coating can be provided on the Cu features of the substrate (e.g., bonding pads, circuits, wires, lead frames, etc.), while the non-Cu portions of the substrate (e.g., silicon) can be unaffected by the protective coating. It is advantageous to apply one or more inhibitor compounds and form a protective coating using the above-mentioned techniques (e.g., bath or CVD) compared to other possible application techniques. For example, the protective coating can be brushed or rolled, but the brushing technique causes the protective coating to be deposited on the entire surface of the substrate, not just on the Cu parts or structures. In addition, the brushing or rolling application method also tends to result in uneven coatings (e.g., in thickness). In contrast, the bath method and CVD method disclosed herein can provide conformal coatings around a variety of complex geometries with thickness variations of only 5% to 10%. Another advantage provided by the bath method described above with reference to the bath unit 332 is the use of non-aqueous solvents, which eliminates the possibility of residual moisture being retained in the final product after packaging. However, as described above, in some implementations, aqueous bath solutions can also be used to apply one or more inhibitor compounds.

[0033] After the coated Cu substrate 302 is produced, it can be provided to a bonding unit 340. The bonding unit 340 can be configured to perform bonding of two or more Cu devices, such as bonding a Cu wire to a Cu bonding pad on the coated substrate 302. FIG. 2A to FIG. 2C As stated above, according to Figure 3 The above-mentioned features of the system and the protective coating applied to achieve Cu-to-Cu direct bonding can minimize or mitigate bimetallic corrosion and intermetallic compound formation at the bonding site, thereby producing a better bond (e.g., better conductivity and bond strength) between two Cu devices (e.g., Cu, Cu alloy, or coated Cu devices). As described in more detail below, according to reference Figure 3 The bonding process based on the concept described in the system has achieved greater success in Cu-to-Cu bonding, enabling the realization of next-generation chips and devices that meet ppb failure requirements. Similarly, this bonding process has also achieved greater success in Cu-to-Al bonding.

[0034] In some aspects, the system 300 can include an annealing unit 350. The annealing unit 350 can be configured to anneal the coated substrate 302. For example, the annealing unit 350 can heat the coated substrate 302 to a desired temperature (e.g., a temperature between 100° C. and 260° C.). The annealing can be performed in a desired environment, such as air (e.g., convection or static), vacuum (e.g., 1 x 10 -9Torr to 1 Torr), or under an inert gas (e.g., nitrogen, argon, forming gas - 95 / 5 nitrogen-hydrogen mixture), as non-limiting examples. Annealing the coated substrate 302 can remove micro defects or other defects in the applied coating, thereby improving protection against oxidation and degradation of the bonds formed during bonding at the bonding unit 340.

[0035] In one aspect, substrates and other metal devices (e.g., wires, lead frames, etc.) processed using the system 300 can be maintained in a "wet" state prior to application of a protective coating at the coating unit 330. To maintain the substrate in a "wet" state prior to coating, the substrate 104 can be placed in a container of water after cleaning by the cleaning unit 310 and then transported to the rinsing unit 320 in the container of water. After rinsing, the substrate can be placed in the same or a new (clean) container of water for transport to the coating unit 330. As described above, at the coating unit 330, the cleaned and rinsed substrate can be removed and provided to the coating unit 310 for coating (e.g., via a bath coating unit 332 or a CVD coating unit 334). In additional or alternative aspects, the substrate can be misted with water rather than placed in a water bath during transport between the cleaning unit 310, the rinsing unit 320, and the coating unit 330. Keeping the substrate in a "wet" state after cleaning and before applying the protective coating can minimize the formation of surface oxides or other contaminants on the substrate, which will improve the adhesion of the protective coating to or deposition of the protective coating onto the Cu components of the substrate.

[0036] Using the above reference Figure 3 The process described in system 300 enables the formation of Cu-to-Cu bonds in a reliable manner because the inhibitor compound used to provide the protective coating eliminates oxidation of the bonding site (or corrosion of the bonding site in the case of Cu-to-Al bonding). In addition, because the inhibitor compound can be Cu selective, the substrate is not coated with excess material, thereby minimizing the impact of the protective coating on the substrate or other components and features. The disclosed technology also provides a low-cost and rapid coating process that is compatible with Cu CMP processing for wafer manufacturing. For example, the disclosed coating process can be performed at a cost of less than $15 per wafer. The disclosed coating process also minimizes or eliminates wafer warpage that can be caused by other coating techniques. In addition, the coating process improves packaging reliability and enables more reliable use of Cu-to-Cu bonded devices, which is a more ideal form of bonded device compared to Cu-to-Al bonded devices.

[0037] Reference Figure 4 , shows an image of a Cu surface having a protective coating applied according to the present disclosure. Figure 4The passivated Cu surface shows a visible grain structure as can be seen in the (Scanning Electron Microscope (SEM)) images, which indicates that the protective coating is conformal on the Cu surface. Figure 4 It is demonstrated that the coating techniques disclosed herein provide uniform application of a protective coating (eg, one or more inhibitor compounds) on a Cu surface.

[0038] Reference Figure 5 , shows a graph illustrating oxide suppression according to various aspects of the present disclosure. Figure 5 In the graph of FIG. 5 , trend line 510 and trend line 520 are shown. Trend line 510 represents oxidation of untreated Cu, while trend line 520 represents oxidation of Cu treated with a protective coating according to the concepts disclosed herein. The thickness of the protective coating associated with the Cu represented by trend line 510 is about 11 nm. Figure 5 In the example of FIG. 5 , the data used to calculate trend line 510 is obtained by annealing unprotected Cu corresponding to trend line 510 and protected Cu corresponding to trend line 520 at 200° C., which simulates a common temperature for bonding processes for bonding Cu wires and devices. Figure 5 As can be observed in FIG. 5 , the protective coating inhibits oxidation by 77% compared to oxidation of the unprotected Cu represented by trend line 510 .

[0039] Reference Figure 6 and Figure 7 , a graph showing the reliability of the bonding between wires and devices is shown. Figure 6 In FIG. 1 , a diagram illustrating a wire lift-off test caused by corrosion of a Cu wire bonded to an Al bond pad is shown. Figure 7 , a diagram illustrating a wire peel test for a Cu wire bonded to a Cu bonding pad is shown. Figure 6 As shown, at 610, within approximately 1 hour, 100% of the Cu wires were debonded from their Al bonding pads, while no Cu wires were debonded from the same type of Cu-to-Al bonded device protected by a passivation coating applied according to the concepts disclosed herein, as shown at 620. Figure 7 In the 2017 study, Cu-to-Cu wire bonds made with a passivation coating on the Cu bond pads remained intact after 38 days. These corrosion screening results were obtained by subjecting the bonded devices to an acid chloride solution (e.g., about 100 ppm Cl at a pH of 5). - ) and observing the bonds under a microscope. Images taken periodically with the microscope are used to count the number of wire bonds that have peeled or broken. Figure 6 As shown in Figure 2, Cu passivation coating on Al wire bonding devices can greatly suppress corrosion-induced Cu wire peeling defects. Figure 6 and Figure 7As can be seen from the results, by referring to Figure 3 The passivated Cu bond pad of the present invention replaces the Al bond pad, compared with the bond not formed according to the concepts disclosed herein ( Figure 6 710), significantly improving the service life of Cu to Cu wire bonding ( Figure 7 ). Figure 6 and Figure 7 The results shown in show that replacing Al with Cu and the techniques enabling direct Cu-to-Cu bonding disclosed herein significantly improve the reliability of Cu-bonded devices, which may enable next-generation automotive chips and other bonded device applications with high reliability standards and low failure rates.

[0040] Reference Fig. 8A , a block diagram illustrating another exemplary Cu wire bonding application according to the present disclosure is shown. Figures 2A to 7 As described and illustrated, various aspects of the present disclosure can facilitate various Cu wire bonding applications, such as bonding Cu wires to metal features of a substrate or chip (e.g., Cu bond pads, Al bond pads, etc.) in a manner that prevents oxidation, corrosion, or other forces that can weaken the bond. Fig. 8A Another application (i.e., lead frame) is shown to which the protective coating technology for bonding Cu wires to metal features can be applied. For example, the wires bonded to the bonding pads can transmit the signals of the integrated circuit on the die to the outside world, while the lead frame is used to receive the other end of the Cu wire bonded to the bonding pads of the die.

[0041] As an illustrative example, Fig. 8A An integrated circuit chip 800 is shown, which has a bonding pad 802, a bonding pad 804, and a bonding pad 806 (eg, a Cu bonding pad or an Al bonding pad), as described above with reference to FIG. Figures 2A to 3 According to the present disclosure, Cu wires 810, 812, and 814 are bonded to bonding pads 802, 804, and 806. Lead frame components 820, 822, and 824 have lead frame bonding pads 830, 832, and 834. Prior to the present disclosure, when lead frame components 820, 822, and 824 include Cu bonding pads 830, 832, and 834, the Cu bonding pads of the lead frame components need to be plated with silver (Ag) to prevent oxidation of the Cu lead frame components or the bonding pads ( Fig. 8A), which increases the cost and complexity of manufacturing. However, using the embodiments of the present disclosure, the Cu lead frame bonding pads 830, Cu lead frame bonding pads 832, and Cu lead frame bonding pads 834 can be made using the above-mentioned reference Figures 2A to 3 Protective coating treatment is performed to prevent oxidation of Cu lead frame components or bonding pads, such as Figure 8B As shown. As described above, due to the use of a Cu selective passivation coating or protective coating, the protective coating applied using the technology disclosed herein can be applied to the Cu portion of the lead frame (e.g., Cu lead frame component 820, Cu lead frame component 822, Cu lead frame component 824 and Cu lead frame bonding pads 830, Cu lead frame bonding pads 832, Cu lead frame bonding pads 834) without being applied to other portions of the lead frame. In addition, the protective coating can prevent oxidation from occurring during the bonding process of the Cu wires 810, Cu wires 812, Cu wires 814 to the Cu lead frame bonding pads 830, Cu lead frame bonding pads 832, Cu lead frame bonding pads 834, thereby achieving a better connection between the integrated circuit and the lead frame, thereby improving reliability (e.g., by minimizing Cu wire peeling due to oxidation, corrosion, etc.).

[0042] Reference Fig. 9 , a flowchart of an exemplary method for bonding a Cu device according to aspects of the present disclosure is shown as method 900. In one aspect, method 900 can be performed using a system (e.g., Figure 3 At step 910, the method 900 includes cleaning the substrate to remove surface oxides, contaminants, or both. Figure 3 As described above, the substrate (or Cu wire, lead frame, Cu wire-bonded semiconductor device, or other metal structure) can be immersed in a cleaning unit (e.g., Figure 3 The cleaning can be performed by immersing the substrate in a cleaning solution in a container of a wet etching unit 312 of the present invention. The cleaning solution can include an acid, such as an acidic solution formed using sulfuric acid, acetic acid, HCl, citric acid, or other mild acidic solutions. As described above, the cleaning can be performed by immersing the substrate in the cleaning solution for a period of time (e.g., about 1 minute). Alternatively, the cleaning can be performed without a cleaning solution, such as by Figure 3 For example, the substrate (or Cu wire, lead frame, Cu wire bonded semiconductor device, or other metal structure) can be processed by a plasma etcher or other form of "dry" etching to remove surface oxides, contaminants, etc. At step 920, method 900 includes rinsing the substrate after cleaning. In one aspect, a rinsing unit (e.g., Figure 3The substrate may be rinsed by a rinsing unit 320), and the rinsing of the substrate may utilize water to remove any cleaning solution or dry etching removed particles still present on the substrate after cleaning.

[0043] At step 930, method 900 includes placing the substrate in a coating unit after rinsing. Figure 3 The coating unit (e.g., Figure 3 The coating unit 330 can be configured to apply a protective coating to at least a portion of the substrate. For example, the protective coating can be Cu selective, so that the portion of the substrate covered by the protective coating corresponds to at least one or more copper features of the substrate, such as a bonding pad or other copper feature. The protective coating applied to the substrate at step 930 may include one or more inhibitor compounds, such as 5-mercapto-1-phenyl-tetrazole, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, sulfathiazole, 5-amino-1,3,4-thiadiazole 2-thiol, 1-phenyl-1H-tetrazole-5-thiol, 2-(2-dihydroxy-5-methyl)-phenyl-benzotriazole, 5-methyl-benzotriazole, amino-tert-butylpyrazole, tetrazole, dodecanethiol, azoimidotoluene (azimino toluene), 1,2,4-triazole, cyclopropanediol, 4-(2-aminothiazol-4-yl)-phenol, 5-methyl-2-phenyl-2,4-dihydropyrazol-3-one, phenyl isothiocyanate, 4-methyl-5-imidazolecarboxaldehyde, 5-(3-aminophenyl)-tetrazole, 2-amino-4-(4-chlorophenyl)-thiazole, 1-H-benzotriazole, 2-mercapto-benzoxazole, 5-methyl-benzotriazole, 5-methyl-benzimidazole, 2-mercaptobenzimidazole, pyrazole, toluene-triazole (toluene), ly-triazole), 4-methyl-5-hydroxymethylimidazole, diniconazole, 4-(4-aminophenylvinyl)-N,N-dimethylaniline, 8-methyl-benzotriazole, 3,5-diamino-1,2,4-triazole, phenylurea, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, 5-mercapto-1-phenyl-tetrazolyl, phenylmethylbenzotriazole, benzoxazole, other azole-based compounds and non-azole-based compounds, or combinations thereof. As described above with reference to Figure 3 As described above, the protective coating can be copper selective, such that the coating adheres to one or more copper features of the substrate, and any portion of the protective coating that is not attached to the copper features can be removed. For example, in one aspect, the substrate can be rinsed a second time after applying the protective coating to remove excess coating material (e.g., as described above with reference to Figure 3 As mentioned above Figure 3 The coating unit may be a bath coating unit (e.g., Figure 3 A bath coating unit 332), or a CVD coating unit (e.g., Figure 3 CVD coating unit 334). In some aspects, as described above with reference to Figure 3 As described above, between step 910 , step 920 , and step 930 , the substrate may be kept in a wet state.

[0044] At step 940, method 900 includes annealing the substrate after applying the protective coating. As described above, annealing can reduce or remove minor defects in the protective coating after it is applied. As shown by arrow 932, in some aspects, step 940 can be omitted. In one aspect, the substrate is held in a storage facility for a period of time before bonding. By using the protective coating, one or more copper features of the substrate can be prevented from generating oxides or other negative artifacts that would reduce the quality of subsequent bonding processes, thereby improving the quality of any subsequently formed bonds. At step 950, method 900 includes bonding the first end of the copper wire to the substrate. As described above with reference to Fig. 8A As described above, the first end of the copper wire can be bonded to a metal structure or feature of the integrated circuit (e.g. Fig. 8A The copper wire is bonded to a bonding pad (e.g., a Cu bonding pad or an Al bonding pad) of the integrated circuit 800. Subsequently, the second end of the copper wire can be bonded to a metal structure of another substrate or device (e.g., a bonding pad of a lead frame). It is noteworthy that one or more steps of method 900 can be performed multiple times, such as a bonding step during which the copper wire can be bonded to multiple metal structures or features of the first device and / or the second device (e.g., a bonding pad of an integrated circuit or chip, and a bonding pad of a lead frame). It is further noted that although primarily described with respect to bonding of Cu wires to integrated circuits, chips, lead frames, and other semiconductor devices, the techniques disclosed herein can be readily applied to any use case involving Cu wire bonding and desiring to mitigate oxidation during the Cu wire bonding process.

[0045] As above Figure 6 and Figure 7As described, the bonding performed in step 950 can be structurally improved compared to other bonding processes, particularly for Cu-to-Cu bonding. For example, the bond formed in step 950 can exhibit increased strength (i.e., less likely to break, or the bonded wires less likely to peel from their respective bonding pads). This structural resilience can increase the useful life of the device and reduce failure rates, thereby enabling the advantages of Cu-to-Cu bonding to be used in certain environments (e.g., automotive applications) where the bonded devices are subject to harsh environments or corrosive forces. In addition to improving the reliability and safety of the device, the use of method 900 and system 300 also eliminates common corrosion problems caused by intermetallic compounds and galvanic contacts associated with common Cu-Al connections and Cu-Sn connections. Moreover, method 900 can be applied to wire bonding applications involving Cu wire-bonded semiconductor devices, such as applying a passivation coating or protective coating to a Cu wire that has been bonded to an Al bonding pad, such as Figure 2D As shown above, method 900 and system 300 provide a chemically driven method for selectively protecting Cu features from oxidation through a wide selection of processes. This capability enables low temperature vapor phase application of protective coatings for dry processes (e.g., for IC chip designs having features that would be damaged by liquid immersion). In addition, unlike volatile corrosion inhibitors, the inhibitor compounds used to apply the protective coating according to the concepts disclosed herein remain intact and bonded to the Cu surface even under ambient conditions, making them ideal for situations where the substrate may need to be stored prior to the bonding process. In addition, the techniques disclosed herein can also selectively control the coating thickness, such as by changing process conditions (e.g., exposure time, temperature, concentration of the inhibitor compound, etc.).

[0046] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the spirit and scope of the present invention as defined by the appended claims. In addition, the scope of the present application is not intended to be limited to the specific embodiments of the process, machine, manufacture, material composition, component, method and step described in the specification. Those skilled in the art should be easily understood from the disclosure of the present invention, and according to the present invention, the process, machine, manufacture, material composition, component, method or step currently existing or to be developed later can be utilized, which performs substantially the same function as the corresponding embodiment described herein or realizes substantially the same result. Therefore, the appended claims are intended to include such processes, machines, manufactures, material compositions, components, methods or steps within their scope.

[0047] Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification.

Claims

1. A method comprising: immersing the substrate in a cleaning solution to remove surface oxides, contaminants, or both; rinsing the substrate to remove excess cleaning solution; placing the substrate in a coating unit after the rinsing, wherein the coating unit is configured to apply a protective coating to at least a portion of the substrate; annealing the substrate after applying the protective coating; and A first end of a copper wire is bonded to the substrate.

2. The method according to claim 1, wherein: The cleaning solution includes an acid.

3. The method according to claim 1, wherein: The coating unit includes a bath coating unit, wherein the protective coating is applied by immersing the substrate in a solution including a solvent and one or more inhibitor compounds, and wherein the protective coating is formed from the one or more inhibitor compounds. The method of claim 3 , further comprising rinsing the substrate prior to the annealing and prior to the bonding.

5. The method according to claim 1, wherein: The coating unit includes a chemical vapor deposition (CVD) coating unit having a CVD chamber, wherein the protective coating is applied by placing the substrate in the CVD chamber and heating one or more inhibitor compounds, wherein the heating is configured to vaporize the one or more inhibitor compounds, and wherein the protective coating is formed by deposition of the vaporized one or more inhibitor compounds on the surface of the substrate.

6. The method according to claim 1, wherein: The protective coating includes one or more inhibitor compounds, and wherein the one or more inhibitor compounds include 5-mercapto-1-phenyl-tetrazole, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, sulfathiazole, 5-amino-1,3,4-thiadiazole 2-thiol, 1-phenyl-1H-tetrazole-5-thiol, 2-(2-dihydroxy-5-methyl)-phenyl-benzotriazole, 5-methyl-benzotriazole, amino-tert-butylpyrazole, tetrazole, dodecanethiol, azoimidotoluene, 1,2,4-triazole, cyclopropanediol, 4-(2-aminothiazol-4-yl)-phenol, 5-methyl-2-phenyl-2,4-dihydropyrazol-3-one, phenyl isothiocyanate, 4-methyl -5-imidazolecarboxaldehyde, 5-(3-aminophenyl)-tetrazole, 2-amino-4-(4-chlorophenyl)-thiazole, 1-H-benzotriazole, 2-mercapto-benzoxazole, 5-methyl-benzotriazole, 5-methyl-benzimidazole, 2-mercaptobenzimidazole, pyrazole, toluene-triazole, 4-methyl-5-hydroxymethylimidazole, diniconazole, 4-(4-aminophenylvinyl)-N,N-dimethylaniline, 8-methyl-benzotriazole, 3,5-diamino-1,2,4-triazole, phenylurea, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, 5-mercapto-1-phenyl-tetrazole, phenylmethylbenzotriazole, benzoxazole, other azole-based and non-azole-based compounds, or combinations thereof.

7. The method according to claim 1, wherein: The protective coating is copper selective.

8. The method according to claim 1, wherein: The substrate is maintained in a wet state between the cleaning, the rinsing, and the applying of the protective coating.

9. The method according to claim 1, wherein: Prior to said bonding, said substrates are held in a storage facility for a period of time.

10. The method according to claim 1, wherein: The first end of the copper wire is pressed into a portion of the protective coating applied to the substrate prior to the bonding.

11. A system comprising: a cleaning unit configured to clean the one or more metal structures prior to initiating a bonding process involving the one or more metal structures; a rinsing unit configured to rinse the one or more metal structures after the one or more metal structures are cleaned by the cleaning unit; a coating unit configured to apply a protective coating to at least a portion of the one or more metal structures; a bonding unit configured to bond a first end of the copper wire to a first metal structure of the one or more metal structures after applying the protective coating; and At least one wetting device configured to maintain the one or more metal structures in a wet state between the cleaning and the rinsing and between the rinsing and the coating.

12. The system according to claim 11, wherein: The coating unit comprises a bath coating unit comprising a solution comprising a solvent and one or more inhibitor compounds, and wherein the protective coating is applied by immersing the one or more metal structures in the solution.

13. The system according to claim 12, wherein: The protective coating is formed from the one or more inhibitor compounds, and wherein at least one of the one or more inhibitor compounds is copper selective.

14. The system of claim 11, further comprising an annealing unit configured to anneal the one or more metal structures after applying the protective coating and before the bonding.

15. The system according to claim 11, wherein: The cleaning unit includes a wet etching unit, a dry etching unit, or both.

16. The system according to claim 11, wherein: The coating unit includes a chemical vapor deposition (CVD) coating unit having a CVD chamber, wherein the protective coating is applied by placing the one or more metal structures in the CVD chamber and heating one or more inhibitor compounds, wherein the one or more inhibitor compounds are vaporized by the heating, and wherein the protective coating is formed by deposition of the vaporized one or more inhibitor compounds on the surface of the copper wire, on the surface of the one or more metal structures, or on the surfaces of both.

17. The system of claim 11, wherein: The one or more metal structures include a copper bond pad, an aluminum bond pad, a lead frame, a copper wire, or a combination thereof.

18. The system of claim 11, wherein: The protective coating is copper selective.

19. The system of claim 11, wherein: Prior to said bonding, said one or more metal structures are maintained in a storage facility for a period of time.

20. The system of claim 11, wherein: The one or more metal structures include at least one of copper, copper alloy, copper plating, or a combination thereof.

21. The system of claim 11, wherein: The bonding unit is configured to bond the second end of the copper wire to a second metal structure of the one or more metal structures, wherein the first metal structure comprises a bonding pad of an integrated circuit device and the second metal structure comprises a lead frame bonding pad.

22. A method comprising: cleaning one or more metal features to remove surface oxides, contaminants, or both from surfaces of the one or more metal features; rinsing the substrate to remove residual artifacts remaining after the cleaning; bonding a first end of a copper wire to a first metal feature of the one or more metal features to produce a copper wire bonded device; The copper wire bonding device is placed in a coating unit after the bonding, wherein the coating unit is configured to apply a protective coating to at least a portion of the copper wire bonding device.

23. The method of claim 22, further comprising annealing the copper wire bond device after applying the protective coating.

24. The method according to claim 22, wherein: The cleaning includes placing the one or more metal features in a bath solution including an acid.

25. The method according to claim 22, wherein: The coating unit includes a bath coating unit, wherein the protective coating is applied to the copper wire bonding device by immersing the copper wire bonding device in a solution including a solvent and one or more inhibitor compounds, and wherein the protective coating is formed by at least one of the one or more inhibitor compounds.

26. The method of claim 22, wherein: The coating unit includes a chemical vapor deposition (CVD) coating unit having a CVD chamber, wherein the protective coating is applied by placing the one or more metal structures in the CVD chamber and heating one or more inhibitor compounds, wherein the heating is configured to vaporize the one or more inhibitor compounds, and wherein the protective coating is formed by deposition of the vaporized one or more inhibitor compounds on the surface of one or more copper features.

27. The method of claim 22, wherein: The protective coating includes one or more inhibitor compounds, wherein the one or more inhibitor compounds include 5-mercapto-1-phenyl-tetrazole, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, sulfathiazole, 5-amino-1,3,4-thiadiazole 2-thiol, 1-phenyl-1H-tetrazole-5-thiol, 2-(2-dihydroxy-5-methyl)-phenyl-benzotriazole, 5-methyl-benzotriazole, amino-tert-butylpyrazole, tetrazole, dodecanethiol, azoimidotoluene, 1,2,4-triazole, cyclopropanediol, 4-(2-aminothiazol-4-yl)-phenol, 5-methyl-2-phenyl-2,4-dihydropyrazol-3-one, phenyl isothiocyanate, 4-methyl- 5-imidazolecarboxaldehyde, 5-(3-aminophenyl)-tetrazole, 2-amino-4-(4-chlorophenyl)-thiazole, 1-H-benzotriazole, 2-mercapto-benzoxazole, 5-methyl-benzotriazole, 5-methyl-benzimidazole, 2-mercaptobenzimidazole, pyrazole, toluene-triazole, 4-methyl-5-hydroxymethylimidazole, diniconazole, 4-(4-aminophenylvinyl)-N,N-dimethylaniline, 8-methyl-benzotriazole, 3,5-diamino-1,2,4-triazole, phenylurea, 5-(4-methoxyphenyl)-2-amino-1,3,4-thiadiazole, 5-mercapto-1-phenyl-tetrazole, phenylmethylbenzotriazole, benzoxazole, other azole-based and non-azole-based compounds, or combinations thereof.

28. The method of claim 22, wherein: The protective coating is copper selective.

29. The method of claim 22, wherein: The one or more metal features are maintained in a wet state between the cleaning, the rinsing, and placing the copper wire bond device in the coating unit.

30. A system comprising: a cleaning unit configured to clean one or more metal structures; a rinsing unit configured to rinse the one or more metal structures after cleaning; a bonding unit configured to bond a first end of the copper wire to a first metal structure of the one or more metal structures after cleaning and rinsing; a coating unit configured to apply a protective coating to the one or more metal structures before bonding, to apply a protective coating to a first end of the copper wire bonded to the first metal structure after bonding, or both; and At least one wetting device configured to maintain the one or more metal structures in a wet state between cleaning and rinsing and between rinsing and coating.

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