Wire for Package Bonding and Method of manufacturing the same

Abstract

A bonding wire using a copper wire and a method for manufacturing the same are disclosed. A native oxide film formed on a copper wire is modified into a copper sulfide layer through sulfidation treatment. An alumina layer is formed on the modified copper sulfide layer. The conductivity of the bonding wire is increased by the formation of the copper sulfide layer, and insulation between the bonding wires is ensured through the introduction of the alumina layer.

Description

Technology Field

[0001] The present invention relates to a bonding wire used in a semiconductor packaging process and a method for manufacturing the same, and more specifically, to a bonding wire coated with copper sulfide and a method for manufacturing the same. Background Technology

[0002] The packaging process, which is part of the semiconductor manufacturing process, is the process of packaging semiconductor chips to protect them from the external environment and electrically connect them to external circuits. The packaging process consists of a dicing process that individually cuts multiple chips implemented on a wafer, a die attach process that attaches the chips to a lead frame, a bonding process that connects the chips to the lead frame, and a molding process that encapsulates them using a resin-based molding compound.

[0003] In particular, the bonding process is a process that electrically connects the lead frame and the chip pads, and it is a critical factor in determining the performance of the final semiconductor package. The bonding process can be classified into wire bonding, which uses wires, and flip-chip bonding, which forms bumps on the pads.

[0004] In the bonding process described above, wire bonding is a very traditional bonding technique that connects pads and lead frame terminals using wires. While Au is the most commonly used wire, Cu is also being used recently to reduce costs and diversify materials.

[0005] Copper oxide films are formed on bonding wires that use Cu. Specifically, CuO or Cu2O oxide films are formed, and these formed copper oxide films act as a factor that impairs the quality of the bonding process. For instance, if a copper oxide film is distributed on the surface of a molten bonding ball, it causes poor bonding between the pad and the ball, and further oxidation continues even after molding, compromising the long-term stability of the package.

[0006] Therefore, the copper oxide film on the bonding wire must be removed. Various treatment techniques are introduced to remove the copper oxide film. For example, cleaning with an acidic solution and coating using Pd plating are used. The above process involves first removing the copper oxide film, activating the removed surface, and then coating it with another metal such as Pd using plating. This has the disadvantage of increasing process complexity and high production costs.

[0007] In particular, when Pd is coated on copper, electrical insulation is insufficient, and the risk of short circuits between wires in high-density packages increases. Therefore, there is a need to develop a copper-based bonding wire that utilizes copper as a bonding wire, provides insulation to prevent short circuits between wires, and ensures excellent chemical resistance. The problem to be solved

[0008] The first technical problem to be achieved by the present invention is to provide a bonding wire having a copper sulfide layer coated on the surface of a copper wire.

[0009] In addition, the second technical objective of the present invention is to provide a method for manufacturing a bonding wire to achieve the first technical objective. means of solving the problem

[0010] The present invention, for achieving the first technical objective described above, provides a bonding wire comprising: a copper wire containing Cu; a copper sulfide layer coated on the copper wire; and an alumina layer formed on the copper sulfide layer, wherein the alumina layer has an amorphous phase.

[0011] The present invention, for achieving the second technical objective described above, provides a method for manufacturing a bonding wire comprising the steps of: modifying a natural oxide film formed on a copper wire into a copper sulfide layer through sulfidation treatment; forming an alumina layer on the copper sulfide layer through magnetron sputtering; and performing a heat treatment on the alumina layer. Effects of the invention

[0012] According to the present invention described above, a Cu-based bonding wire is manufactured. The natural oxide film formed on the Cu wire is modified into a copper sulfide layer, thereby improving the conductivity of the wire. Additionally, an alumina layer is formed on the copper sulfide layer. Due to the formed alumina layer, electrical short circuits between closely spaced bonding wires can be prevented. In particular, the alumina layer and the copper sulfide layer prevent the reoxidation of the copper wire, and the stability of ball bonding is also improved. The problem of natural oxidation that may occur when applying Cu to the bonding wire as a replacement for expensive Au is resolved, and the stability of the bonding wire is significantly increased due to the presence of a double protective film.

[0013] In addition, the manufacturing cost of semiconductor packages can be drastically reduced through the application of copper-based bonding wires. Brief explanation of the drawing

[0014] FIG. 1 is a cross-sectional view illustrating a bonding wire according to a preferred embodiment of the present invention. FIG. 2 is a flowchart for explaining a method for manufacturing the bonding wire of FIG. 1 according to a preferred embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a magnetron sputtering apparatus for explaining the formation of the alumina layer of FIG. 1 according to a preferred embodiment of the present invention. FIG. 4 is a schematic cross-sectional view illustrating the deposition process of an alumina layer within the deposition section of FIG. 3 according to a preferred embodiment of the present invention. FIG. 5 is a schematic diagram illustrating the effects of forming the alumina layer of FIG. 4 and heat treatment according to a preferred embodiment of the present invention. Specific details for implementing the invention

[0015] The present invention is susceptible to various modifications and may take various forms; therefore, specific embodiments are illustrated in the drawings and described in detail in the text. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. Similar reference numerals have been used for similar components in the description of each drawing.

[0016] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0017] Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the attached drawings.

[0019] Examples

[0020] FIG. 1 is a cross-sectional view illustrating a bonding wire according to a preferred embodiment of the present invention.

[0021] Referring to FIG. 1, the bonding wire comprises a copper wire (100), a copper sulfide layer (200) formed on the copper wire (100), and an alumina layer (300) formed on the copper sulfide layer (200).

[0022] The copper sulfide layer (200) has a composition of CuS or Cu2S and is a substituted and modified version of the natural oxide film, CuO or Cu2O, formed on the copper wire (100). Copper sulfide has a very high conductivity compared to natural oxide films such as CuO. Therefore, the conductivity of the bonding wire can be greatly improved through the copper sulfide layer (200) formed by modifying the natural oxide film.

[0023] The copper sulfide layer (200) is formed through the modification of a natural oxide film and is formed with a thickness of 2 nm to 3 nm. The formed copper sulfide layer (200) is formed conformally on the copper wire (200).

[0024] An alumina layer (300) is formed on a conformally formed copper sulfide layer (200). The alumina layer (300) is formed with an average thickness of 4 nm to 7 nm. The alumina layer (300) is of an amorphous matrix type, and if the average thickness is less than 4 nm, it is difficult to secure insulation, and if the average thickness exceeds 7 nm, cracks may occur in the alumina layer (300) during the handling process of the bonding wire because a certain flexibility cannot be secured.

[0025] FIG. 2 is a flowchart for explaining a method for manufacturing the bonding wire of FIG. 1 according to a preferred embodiment of the present invention.

[0026] First, pretreatment is performed on the copper wire (S100). A natural oxide film of CuO or Cu2O is formed on the copper wire. Pretreatment is a process for removing foreign substances from the surface of the natural oxide film and for removing contaminants, such as organic matter, generated during handling. To this end, the copper wire is pretreated by immersion in an alkaline solution or by ultrasonic cleaning. However, the above pretreatment process is not an essential process and may be applied selectively depending on the usage environment.

[0027] Next, a sulfidation treatment is performed on the pretreated copper wire (S200). Through the sulfidation treatment, the native oxide film is modified into a copper sulfide layer. Two reactions are considered for the modification of the native oxide film into a copper sulfide layer.

[0028] The first is reforming through the supply of H2S gas. The above reforming process is represented by the following reaction equation 1.

[0029] [Reaction Equation 1]

[0030] CuO + H2S → CuS + H2O

[0031] Cu2O + H2S → Cu2S + H2O

[0032] Through the above reaction, the natural oxide film is easily replaced and modified into a copper sulfide layer.

[0033] The second method utilizes a reaction through immersion in a sulfide solution. The sulfide solution may be ammonium sulfide ((NH4)2S), sodium sulfide (Na2S), or calcium sulfide (CaS). Preferably, the sulfide solution may contain ammonium sulfide ((NH4)2S). When the copper wire with the naturally formed oxide film is impregnated with the solution containing ammonium sulfide, a copper sulfide layer may be formed through a reaction at room temperature and atmospheric pressure as described below.

[0034] [Reaction Equation 2]

[0035] CuO + (NH4)2S → CuS + 2(NH3) + H2O

[0036] Cu2O + (NH4)2S → Cu2S + 2(NH3) + H2O

[0037] The above sulfide solution preferably uses water as a solvent and has a concentration of 1 wt% to 5 wt%. If the concentration is less than 1 wt%, excessive time is required for the uniform formation of the copper sulfide layer, or a uniform film is not formed, and islands are formed in the copper sulfide layer. Furthermore, if the concentration exceeds 5 wt%, an irregular shape appears on the surface due to the excessive growth of the copper sulfide layer.

[0038] It is preferable that the copper wire be immersed for 5 to 30 seconds, and the natural oxide film is modified into a copper sulfide layer through a rapid reaction. In particular, those skilled in the art should be aware that if the temperature is increased or the reaction time is increased during the reaction through immersion, an irregular shape may be formed on the copper wire.

[0039] Through the above process, the natural oxide film is modified into a copper sulfide layer, and the copper sulfide layer is conformally formed on the copper wire.

[0040] Next, an alumina layer is formed on the copper sulfide layer (S300). It is preferable that the alumina layer be formed through a magnetron sputtering process. Through this, an alumina layer can be formed on a wire having a circular cross-section.

[0041] A bonding wire in which a copper sulfide layer and an alumina layer are continuously formed is manufactured through the process described above.

[0042] When the alumina layer is formed, it is preferable to perform a heat treatment (S400). Through the heat treatment, interfacial defects between the copper sulfide layer and the alumina layer are healed, and the bonding strength between the two heterogeneous film materials is increased. It is preferable to perform the heat treatment at a temperature of 400°C to 500°C in an inert atmosphere of argon or nitrogen gas. In addition, it is preferable that the heat treatment time be 30 minutes to 2 hours. If the heat treatment temperature is below 400°C, the healing of interfacial defects is not smooth, and the alumina layer may peel off from the copper sulfide layer due to weak interfacial characteristics. In addition, if the heat treatment temperature exceeds 500°C, a phase transition to amorphous alumina occurs, and a phase transition to gamma alumina proceeds. It is generally known that the phase transition of gamma alumina occurs at temperatures above 400°C, but considering the heat treatment time of the present invention, some parts of the amorphous matrix will have a quasi-crystalline phase of gamma alumina, but the phase transition of gamma alumina is not completed overall. Therefore, the formed amorphous network is maintained, and ductility can be ensured in the bonding wire.

[0043] In particular, through the above heat treatment, the alumina layer has a smooth surface and a uniform thickness.

[0044] FIG. 3 is a schematic diagram illustrating a magnetron sputtering apparatus for explaining the formation of the alumina layer of FIG. 1 according to a preferred embodiment of the present invention.

[0045] Referring to FIG. 3, the sputtering device has a winding section (10), a winding section (30), and a deposition section (20).

[0046] An unwinder (11), a winding roll (12), and a dancer (13) are arranged in the unwinding section (10).

[0047] An unwinder (11) is provided to unwind a wire coated with a copper sulfide layer and is driven by a motor. Additionally, an unwinding roll (12) changes the position of the wire and is provided to maintain a distance from each other when multiple wires are fed into the deposition unit (20). A dancer (13) senses the tension of the unwinding wire and controls the drive of the motor connected to the unwinder (11) to maintain a constant tension.

[0048] The winding section (30) is positioned opposite the unwinding section (10) with the deposition section (20) as the center and is connected to the deposition section (20).

[0049] The above winding unit (30) has a winder (31) and a winding roll (32). A bonding wire coated with an alumina layer in the deposition unit (20) is wound through the winder (31). Additionally, the winding roll (32) may be provided in multiple numbers, and a spacing space is secured between multiple wires wound on the winder (31).

[0050] A wire coated with a copper sulfide layer is supplied to the deposition unit (20) through the unwinder (11). Since the copper sulfide layer has a very thin thickness of 2 nm to 3 nm, flexibility is ensured, and due to the secured flexibility, it is easily unwound or wound onto the unwinder (11) and the winder (31).

[0051] In one embodiment, the wire is moved in a straight line from the unwinding section (10) to the winding section (30), and an alumina layer is coated through deposition within the deposition section (20). The deposition is performed through a magnetron sputtering process. At least three sputter guns (21, 22, 23) are prepared for magnetron sputtering. It is preferable that each sputter gun (21, 22, 23) be spaced apart from each other at equal intervals in the direction in which the wire travels. Additionally, it is preferable that the three sputter guns (21, 22, 23) be arranged so as to be rotated 120° each around the direction in which the wire travels. As the wire coated with a copper sulfide layer moves within the deposition chamber (24), an alumina layer is deposited through magnetron sputtering.

[0052] If the sputter guns are arranged in n numbers of three or more, it is preferable that the sputter guns (21, 22, 23) be arranged so as to rotate each with an angle of 360° / n around the direction of travel of the wire.

[0053] FIG. 4 is a schematic cross-sectional view illustrating the deposition process of an alumina layer within the deposition section of FIG. 3 according to a preferred embodiment of the present invention.

[0054] Referring to FIG. 4, three sputter guns (21, 22, 23) are arranged with a rotational spacing of 120° between them. It is assumed that the wire placed at the center is discharged in the direction of the ground. An alumina target having the composition of Al2O3 is prepared in each sputter gun (21, 22, 23). Due to the characteristics of magnetron sputtering, the deposition material discharged from the sputter gun has directionality and is supplied onto the wire.

[0055] The deposition area is defined as the region where the deposition material supplied from each sputter gun (21, 22, 23) is distributed at high density.

[0056] Since the sputter guns (21, 22, 23) are spaced apart from each other at equal intervals in the direction of travel of the wire, the wire experiences deposition areas in the order of the first sputter gun (21), the second sputter gun (22), and the third sputter gun (23) as it moves. Accordingly, three sputtering depositions are sequentially performed on the wire.

[0057] Through the above sputtering method, an alumina layer (300) can be formed on the copper sulfide layer (200) with a predetermined thickness.

[0058] FIG. 5 is a schematic diagram illustrating the effects of forming the alumina layer of FIG. 4 and heat treatment according to a preferred embodiment of the present invention.

[0059] Referring to FIG. 5, the wire sequentially passes through the deposition regions of three sputter guns as described in FIG. 4. A first alumina layer (310) is formed through the first deposition region, and a second alumina layer (320) is formed while passing through the second deposition region. Finally, a third alumina layer (330) is formed while passing through the third deposition region.

[0060] In addition, due to the specificity of the arrangement structure of the sputter guns, regions where the deposition areas intersect each other appear. Accordingly, in the intersecting regions, a second alumina layer (320) is formed on the first alumina layer (310), a third alumina layer (330) is formed on the second alumina layer (320), and a third alumina layer (330) is formed on the first alumina layer (310). That is, in the intersecting regions, a stacked structure of two alumina layers appears, and these are formed at different times. Due to the presence of an atmosphere gas within the deposition section and the time interval in the deposition process, an interface appears between the two alumina layers, which has a weaker bonding force compared to an alumina layer formed by a single sputter gun. Furthermore, even if three sputter guns are used, a disadvantage is that the overall thickness of the formed alumina layer is not uniform.

[0061] When heat treatment is performed after the sputtering process for forming an alumina layer, movement of alumina on the surface occurs. This is related to Gibbs free energy. This is a spontaneous phenomenon in which a material system attempts to enter a thermodynamically stable state. That is, in order to reduce the total free energy of a system forming a film, atoms or materials on the surface are rearranged or moved through the supply of energy. In particular, atoms in protruding areas with a low number of bonds possess high energy and therefore move to a stable position. Through this, the alumina layer (300) formed by heat treatment is flattened.

[0062] In addition, the alumina layers in the intersecting regions, which have interfaces according to stacking and have loose bonding forces, have high mutual bonding forces, form a single amorphous network structure, and are formed as a single alumina layer.

[0063] Through the process described above, an alumina layer (300) having a uniform thickness is formed on the copper sulfide layer (200).

[0064] In the present invention described above, a Cu-based bonding wire is manufactured. The natural oxide film formed on the Cu wire is modified into a copper sulfide layer, thereby improving the conductivity of the wire. Additionally, an alumina layer is formed on the copper sulfide layer. Due to the formed alumina layer, electrical short circuits between closely spaced bonding wires can be prevented. In particular, the alumina layer and the copper sulfide layer prevent the reoxidation of the copper wire, and the stability of ball bonding is also improved. The problem of natural oxidation that may occur when applying Cu to bonding wires as a replacement for expensive Au is resolved, and the stability of the bonding wire is significantly increased due to the presence of a double protective film.

[0065] In addition, the manufacturing cost of semiconductor packages can be drastically reduced through the application of copper-based bonding wires. Explanation of the symbols

[0066] 100: Copper wire 200: Copper sulfide layer 300: Alumina layer

Claims

Claim 1 A bonding wire comprising: a copper wire containing Cu; a copper sulfide layer coated on the copper wire; and an alumina layer formed on the copper sulfide layer, wherein the alumina layer has an amorphous phase and the copper sulfide layer is characterized by a modified natural oxide film of CuO or Cu2O. Claim 2 A bonding wire according to claim 1, characterized in that the copper sulfide layer has a thickness of 2 nm to 3 nm and has CuS or Cu2S. Claim 3 A bonding wire according to claim 1, characterized in that the alumina layer has a thickness of 4 nm to 7 nm. Claim 4 delete Claim 5 A bonding wire according to claim 1, wherein the alumina layer is formed on the copper sulfide layer through magnetron sputtering and is composed of a first alumina layer, a second alumina layer, and a third alumina layer formed at different times, and wherein the first to third alumina layers are formed with their centers spaced apart from each other by 120°. Claim 6 A bonding wire according to claim 5, characterized in that the first to third alumina layers overlap each other in the boundary region of the two alumina layers. Claim 7 A bonding wire according to claim 6, characterized in that the first to third alumina layers are formed into a single film having a uniform thickness through heat treatment. Claim 8 A method for manufacturing a bonding wire comprising: a step of modifying a natural oxide film formed on a copper wire into a copper sulfide layer through sulfidation treatment; a step of forming an alumina layer on the copper sulfide layer through magnetron sputtering; and a step of performing a heat treatment on the alumina layer, wherein the step of modifying the natural oxide film into a copper sulfide layer is performed by supplying H2S gas or by immersing the copper wire formed on the natural oxide film in a sulfide solution. Claim 9 delete Claim 10 A method for manufacturing a bonding wire according to claim 8, wherein the sulfide solution comprises ammonium sulfide, and the ammonium sulfide has a concentration of 1 wt% to 5 wt%. Claim 11 A method for manufacturing a bonding wire according to claim 8, wherein the step of forming an alumina layer through magnetron sputtering comprises: a step of forming a first alumina layer through a first sputter gun; a step of forming a second alumina layer through a second sputter gun positioned at an angle of 120° from the first sputter gun; and a step of forming a third alumina layer through a third sputter gun positioned at an angle of 120° from the second sputter gun, wherein the first sputter gun to the third sputter gun are positioned spaced apart at equal intervals in the direction of travel of the copper wire. Claim 12 A method for manufacturing a bonding wire according to claim 11, characterized in that three overlapping regions are formed in the boundary region of the first alumina layer to the third alumina layer, wherein a second alumina layer formed on the first alumina layer, a third alumina layer formed on the second alumina layer, and a third alumina layer formed on the first alumina layer. Claim 13 A method for manufacturing a bonding wire according to claim 11, characterized in that the heat treatment is carried out at a temperature of 400℃ to 500℃. Claim 14 A method for manufacturing a bonding wire according to claim 13, characterized in that the alumina layer heat-treated through the above heat treatment is formed as a single layer. Claim 15 A method for manufacturing a bonding wire according to claim 14, wherein the heat-treated alumina layer has a quasicrystalline phase of gamma alumina.

Images