Laser wire bonding configuration for semiconductor devices

Abstract

Provide a laser wire bonding configuration for a semiconductor device. 【Solution means】The laser wire bonding configuration for a semiconductor device according to the present invention includes a substrate 30 and a wire 40. The surface of the substrate 30 has a molten pool 31 formed by a blue laser with a wavelength range between 400 nm and 500 nm at the bonding position that has been cleaned. The molten pool 31 presents an arc-shaped recess, and the maximum diameter of the arc-shaped recess is in the range between 330 μm and 360 μm, and the maximum depth is in the range between 67 μm and 77 μm. The wire 40 is fused with the substrate 30 by wire bonding, and in the joined state, forms a sphere higher than the substrate 30, and the bonding end 41 is completely covered in the molten pool 31.

Description

Technical Field

[0001] The present invention relates to a laser wire bonding configuration for semiconductor devices, and more particularly, to a new process of wire bonding that can reduce impurities at the bonding interface, make the metal more easily meltable, lower the electrical resistance value after bonding, and increase the conductivity.

Background Art

[0002] Wire bonding is a process technology in the semiconductor industry that connects a chip and a lead frame with a metal wire.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Conventional wire bonding technologies mainly include thermocompression bonding, ultrasonic welding, and ultrasonic thermocompression bonding. The main metal wires used are gold wires, silver wires, copper wires, aluminum wires, etc. However, all of these wire bondings bond the wire to a flat substrate and form a physical bond between the substrate and the wire by applying pressure, thermal energy, or ultrasonic vibration. Therefore, stress and strain are likely to change, and an intermetallic compound (IMC) is generated at the interface. This IMC not only increases the resistance value but also affects the long-term reliability. Even if physically forced to bond using a machine, it is not easy to reduce the contact area, the radius size of the wire cannot be reduced, and in a 3D package that requires high density, it has become a bottleneck in the process.

[0004] When IMC is generated, it affects the strength of the solder balls on the substrate, and in the long run, wire bonding becomes the main cause of device failure. Comparing the lengths of copper wires and gold wires bonded to an aluminum substrate, the use of copper wires is superior because the rate of IMC growth on an aluminum substrate with gold is shorter than that on an aluminum substrate with copper. Therefore, how to stop the growth of IMC has become the most important step in obtaining a highly reliable bond. To reduce the generation of IMC, in the wire bonding process (especially for ICs), plasma cleaning is used first, and argon ion plasma cleaning can enhance the bonding strength when bonding gold and copper wires to the substrate. However, the IMC problem cannot be completely solved.

[0005] In addition, compared with gold wires, copper wires have the advantages of low cost and suitable electrical conductivity, thermal conductivity, and mechanical strength. Therefore, by further designing the wire diameter of copper bonding wires to be thinner and enabling suitable heat dissipation efficiency, currently, copper wires are gradually replacing conventional gold wires and are also applied to the wire bonding process of semiconductor chips.

[0006] Referring to FIGS. 1A and 1B, a conventional copper wire bonding process includes the following steps. First, a chip 11 and a substrate 12 are provided. The chip 11 has a plurality of connection pads 111 (e.g., aluminum pads), and the substrate 12 has a plurality of solder pads 121 (e.g., copper pads). The chip 11 is placed on the substrate 12. Next, by electronically igniting a copper wire 14 with a welding needle 13, a solder ball is formed, a ball bond end 141 (i.e., the first end) is formed, and the ball bond end 141 is thermocompression bonded to the connection pad 111 of the chip 11 by the welding needle 13. Then, by moving the welding needle 13, the copper wire 14 is guided to correspond above the solder pad 121 of the substrate 12. Finally, the copper wire 14 is thermocompression bonded by the welding needle 13 to be torn off from the solder pad 121 to form a terminal 142 (i.e., the second end). However, an intermetallic compound (IMC) 15 is formed between the front and rear ends of the copper wire 14 and the solder ball. As described above, the IMC not only increases the resistance value but also affects the long-term reliability. Even if physically forced to bond using a machine, it is difficult to reduce the contact area, the radius size of the wire cannot be reduced, and in a 3D package with high density requirements, it has become a bottleneck in the process.

[0007] Therefore, the inventor believes that the above-mentioned drawbacks can be improved and, as a result of intensive studies, has arrived at the proposal of the present invention that reasonably and effectively improves the problems.

[0008] The present invention is made by the intensive research of the inventor in view of the above problems, and its purpose is to provide a laser wire bonding configuration for a semiconductor device that can reduce impurities at the bonding interface, more easily melt the metal, reduce the electrical resistance value after bonding, and promote the effect of high conductivity.

[0009] Another object of the present invention is to provide a laser wire bonding configuration for a semiconductor device, which is particularly applicable to copper wire bonding, has the advantages of low cost, suitable conductivity, heat conductivity, and mechanical strength, allows for a further reduction in the wire diameter of the copper wire, and provides suitable heat dissipation efficiency.

Means for Solving the Problem

[0010] To achieve the above object, the present invention provides a laser wire bonding configuration for a semiconductor device. The laser wire bonding configuration for a semiconductor device includes a substrate and a wire. On the bonding position of the substrate with a cleaned surface, a molten pool is formed by a blue laser with a wavelength range between 400 nm and 500 nm. The molten pool presents an arc-shaped recess, the maximum diameter of the arc-shaped recess ranges between 330 μm and 360 μm, and the maximum depth ranges between 67 μm and 77 μm. The wire is fused with the substrate by wire bonding. In the joined state, a sphere higher than the substrate is formed, and the bonding end is completely covered in the molten pool.

Effect of the Invention

[0011] Since the present invention is configured as described above, it has the following effects. In the laser process according to the present invention, before wire bonding, using a laser processing system, cleaning is performed to remove the surface oxide on the position where the wire and the substrate are to be joined, a part of the substrate is heated, and after forming a molten pool at the bonding position, wire bonding is used to join the wire and the substrate. By cleaning the surface of the substrate with a laser, impurities at the bonding interface can be reduced. After heating a part and then forming a molten pool, the metal can be more easily melted. By further shortening the bonding time and increasing the bonding strength, the formation of intermetallic compounds is prevented, the electrical resistance value after bonding is reduced, and the conductivity is increased.

[0012] From the descriptions in the following specification and drawings, at least the following matters will become clear.

Brief Description of the Drawings

[0013]

Fig. 1A

Fig. 1B

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7A

Fig. 7B

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the laser wire bonding configuration for a semiconductor element of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, and members, materials, etc. described below can be variously modified within the scope of the gist of the present invention.

[0015] First, an example of a specific embodiment of the laser wire bonding configuration for a semiconductor element according to the present invention will be described with reference to FIGS. 2 to 5.

[0016] The present invention for solving the above problems mainly includes the following members, which will be described respectively.

[0017] First, there is a laser processing system having a laser light source 20 for generating a laser beam (L). In this embodiment, the type of the laser light source 20 used in the laser processing system includes a conventionally commonly used fiber laser or a general free space laser, but the present invention is not limited thereto.

[0018] Next is the wire 40. In this embodiment, the wire 40 is preferably a copper wire, but the present invention is not limited thereto.

[0019] Before wire bonding, the laser processing system is used to clean the surface of the positions where the wire 40 and the substrate 30 are joined by the laser light source 20. In this embodiment, according to the absorption rates of the materials of the wire 40 and the substrate 30, it is possible to prevent the scattering of the laser light source that matches, and to improve the process speed and the quality of the wiring. For example, the commonly used metals for the wire 40 and the substrate 30 are Au, Cu, Ag, Al, and their compounds, and the wavelength of the laser light source 20 used for cleaning the surface of the substrate 30 may be in the range between 300 nm and 1100 nm.

[0020] Using a laser processing system, a molten pool 31 is formed at the bonding position by the laser beam (L) of the laser light source 20. In this embodiment, the wavelength of the laser light source 20 may be a laser beam in the range between 300 nm and 600 nm, and a wavelength that is adapted to the material of the substrate 30 is selected. Further, although it includes using energy in the range between 200 and 300 W (watts), the present invention is not limited thereto, and a part of the substrate 30 can be heated in the range between about 2 and 3 ms (ms) to form the molten pool 31 at the bonding position. In the selection of the laser of the present invention, the absorbability of silver, gold, copper, and aluminum with respect to an IR laser is not excellent, and generally, it is only about 5%. Therefore, in this embodiment, by making the substrate 30 of copper material, a part of the substrate 30 can be heated by a laser beam in the range between 300 nm and 600 nm to form the molten pool 31, and it is the most suitable choice to adopt a blue laser in the range between 400 nm and 500 nm.

[0021] In the initial stage of the development of blue semiconductor lasers, there were limitations in materials and manufacturing technologies. The power of one blue diode was limited by the area of the light-emitting source, and it could only output at low power. However, with the progress of materials and development technologies, currently, blue laser diodes mainly use gallium nitride (GaN) as a semiconductor material and benefit from the maturity of optical microlens optical coupling technology. Further, the applicant has been continuously researching and developing an integrated laser output module system for blue laser diodes for many years, and has created a blue laser light source that outputs with a high-power optical fiber suitable for industrial applications. In addition, the inventor has continuously conducted tests, and in the processing of colored metal (gold, silver, copper, aluminum) materials, the blue laser has achieved extremely high stable absorption characteristics of the molten pool, and its absorption rate has reached 65% or more. Therefore, as shown in FIG. 5, the present invention enables the formation of the molten pool 31 at the bonding position by applying a blue laser, using energy in the range between 200 and 300 W (watts), and heating a part of the substrate 30 for about 2 to 3 ms (ms).

[0022] In this embodiment, the melting pool 31 presents an arc-shaped recess, the maximum diameter (D) of which ranges between 330 μm and 360 μm, and the maximum depth (H) of the arc-shaped recess ranges between 67 μm and 77 μm, but the present invention is not limited thereto.

[0023] In step e, finally, wire bonding is used to fuse and join the wire 40 and the substrate 30, and then a sphere 50 higher than the substrate 30 is formed, and the bonding end 41 of the wire 40 is completely covered in the melting pool 31.

[0024] FIG. 6, FIGS. 7A and 7B are schematic diagrams showing photos of observing the wire bonding of the melting pool using an optical microscope (OM) according to the present invention, and cross-sectional views using a scanning electron microscope (SEM). As shown in the above figures, the present invention can surely achieve the expected wire bonding state.

[0025] Based on the above new process, the present invention uses a blue laser to first clean the surface of the substrate 30. Next, after generating the melting pool 31 on the surface, wire bonding is performed on the melting pool 31. The present invention is different from the conventional flowchart in that the size of the melting pool 31 is preset in advance based on the bondable depth and size of the substrate 30. In this way, the entire bonding end 41 of the wire 40 is completely fused and covered by the melting pool 31, which is different from only a part of the conventional surface being bonded to the base material. Therefore, the new process of the present invention can completely cover the bonding end 41 of the wire 40 with the melting pool 31 and enhance the bondability between the wire 40 and the substrate 30. Since there is no need to forcibly bond the wire 40 and the substrate 30, the probability of the occurrence of IMC is significantly reduced.

[0026] With the above technical means, in the prior art, there were few methods to enhance the bondability and strength of wire bonding using an infrared (IR) laser. However, all of them were applied during the wire bonding process. However, the method of the present invention is completely different from the prior art. The present invention first forms a suitable molten pool 31 on the substrate 30 and then performs wire bonding. Moreover, the blue laser has extremely high stable absorption characteristics of the molten pool in the processing of colored metal (gold, silver, copper, aluminum) materials, making it easier to melt the metal, reducing the electrical resistance value after bonding, and increasing the conductivity. In particular, it is applied to wire bonding with copper wires, has the advantages of low cost, suitable electrical conductivity, heat conductivity, and mechanical strength, and the wire diameter of the copper wire can be designed to be thinner, providing suitable heat dissipation efficiency.

[0027] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope indicated in the claims. Embodiments obtained by appropriately combining the technical means devised in different embodiments are also included in the technical scope of the present invention.

Explanation of Reference Numerals

[0028] 20 Laser light source 30 Substrate 31 Molten pool 40 Wire 41 Bonding end 50 Sphere (D) Diameter (H) Depth (L) Laser beam

Claims

1. A substrate, on a bonding position where the surface is cleaned, a melting pool is formed by a blue laser in a wavelength range between 400 nm and 500 nm, the melting pool presents an arc-shaped recess, the maximum diameter of the arc-shaped recess is in the range between 330 μm and 360 μm, and the maximum depth is in the range between 67 μm and 77 μm, and a wire, by wire bonding, the wire and the substrate are fused, in the joined state, a sphere higher than the substrate is formed, and the bonding end is completely covered in the melting pool, and a wire characterized by comprising a laser wire bonding configuration for a semiconductor device.

2. The laser wire bonding configuration for a semiconductor device according to claim 1, wherein the blue laser includes a fiber laser or a free space laser.

3. The laser wire bonding configuration for a semiconductor device according to claim 1, wherein the wire is a copper wire.

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