Copper-copper hybrid bonding method and its application in packaging structures

Abstract

A copper-copper hybrid bonding method for bonding a plurality of copper pillars to a plurality of copper contacts on a substrate, comprising performing a thermo-press bonding process to bond the copper pillars to the copper contacts, characterized in that: each copper pillar has a mesh pattern on a bonding surface corresponding to a copper contact, and the mesh pattern is formed by a surface microstructure forming process.

Description

Copper-copper hybrid bonding method and its application in packaging structures This invention relates to packaging technology, and more particularly to a copper-copper hybrid bonding method. The chip manufacturing process includes packaging and testing. As the functional requirements of chips continue to increase, the size of the contact pads and the gaps between the contact pads have become very small. Therefore, when testing chips, the bottom surface of a test card must be used to contact the numerous contact pads of the chip, and three-dimensional traces are used to connect these contact pads to the top surface of the test card to provide numerous test contacts with larger sizes and gaps on the top surface of the test card. Typically, multiple copper pillars must be soldered to the bottom surface of the test card to contact the contact pads of the chip. Traditional soldering methods involve first using an adhesive (tin, silver paste, copper paste, etc.) to bond the copper pillar to the pad, followed by a soldering cycle. However, adhesives can cause contamination. To address the aforementioned issues, some companies have proposed a thermoforming bonding process, which joins two metals by heating and applying pressure. For example, a thermoforming bonding process can be used to join multiple copper contacts to multiple copper pillars on a chip, wherein the dimensions of these copper contacts, i.e., their diameter or diagonal length, are generally less than 10 μm. However, in some applications, the size of these copper contacts is much larger than 10um, for example, between 60um and 500um. In this case, copper-copper bonding becomes difficult due to the much larger bonding area. To address the aforementioned problems, a novel copper-copper hybrid bonding method is urgently needed in this field. One objective of this invention is to provide a copper-copper hybrid bonding method, which can effectively enhance the bonding force between the copper pillar and the corresponding copper junction by forming a mesh pattern on the bonding surface of the copper pillar. Another objective of this invention is to provide a copper-copper hybrid bonding method, which can effectively reduce the temperature and time required for bonding between the copper pillar and the corresponding copper junction by forming a mesh pattern on the bonding surface of the copper pillar. Another object of the present invention is to provide a copper-copper hybrid bonding method, which can absorb the height deviation of the copper pillars when multiple copper pillars are bonded to multiple copper contacts of a substrate by forming a mesh pattern on the bonding surface of the copper pillars. Another object of the present invention is to provide a packaging structure that can effectively improve the bonding force between the copper pillar and the copper contact of a substrate by the aforementioned method. Another objective of this invention is to provide a packaging structure that can effectively reduce the temperature and time required for bonding between the copper pillar and the corresponding copper contact using the aforementioned method. Another object of the present invention is to provide a packaging structure that can absorb the height deviation of the copper pillars when the aforementioned method is used to bond the copper pillars to the copper contacts of a substrate. To achieve the above objectives, a copper-copper hybrid bonding method is proposed for bonding a plurality of copper pillars to a plurality of copper contacts on a substrate. The method includes performing a thermoforming bonding process to bond the copper pillars to the copper contacts, and is characterized in that: each copper pillar has a mesh pattern on a bonding surface corresponding to a copper contact, and the mesh pattern is formed by a surface microstructure forming process. In one embodiment, the surface microstructure forming process includes a laser engraving operation to form a first network microstructure on the bonding surface. In one embodiment, the laser engraving operation is performed under atmospheric conditions. In one embodiment, the surface microstructure forming process includes an etching process to form a first network microstructure on the bonding surface. In one embodiment, the surface microstructure forming process further includes an electroplating process to coat a nano-bicrystalline copper layer on the first network microstructure, and a metal coating process to coat a metal plating layer on the nano-bicrystalline copper layer to form the network texture. In possible embodiments, the metal coating may comprise titanium, palladium, or gold. In possible embodiments, the metal coating process may include processes such as electroplating, chemical vapor deposition, or metal sputtering. In one embodiment, the substrate is a substrate for a chip. In one embodiment, the substrate is a printed circuit board. To achieve the above objectives, the present invention further proposes a packaging structure having a plurality of copper pillars and a substrate. The copper pillars are bonded to a plurality of copper contacts on the substrate by a copper-copper hybrid bonding method. The method includes performing a thermoforming bonding process to bond the copper pillars to the copper contacts. The invention is characterized in that each copper pillar has a mesh pattern on a bonding surface corresponding to a copper contact, and the mesh pattern is formed by a surface microstructure forming process. To enable your review committee to further understand the structure, features and purpose of this invention, detailed descriptions of the drawings and preferred embodiments are attached below. Please refer to Figure 1, which illustrates a schematic diagram of a hot pressing apparatus used to produce the packaging structure of the present invention. As shown in Figure 1, a hot pressing apparatus 100 has a pressurizing device 110, a tooling component 120, and a heating seat 130 for performing a hot pressing bonding process. The pressurizing device 110 is located above the tooling component 120, and the heating seat 130 is used to support a substrate 10 and is located below the tooling component 120. The tooling 120 has a first surface 121 (top surface) for abutting against the pressure device 110, and a second surface 122 (bottom surface) for fixing a plurality of copper pillars 20, wherein the copper pillars 20 are aligned with a plurality of copper contacts 11 of the substrate 10, and each copper pillar 20 has a mesh pattern on a bonding surface corresponding to a copper contact 11. Please refer to Figure 2, which is a schematic diagram of one embodiment of the copper pillar 20 of the present invention. As shown in Figure 2, a bonding surface of the copper pillar 20 has a mesh pattern 20a. In detail, the hot-press bonding process includes: (a) To make the bonding surfaces of the copper pillars 20 on the second surface 122 of the tooling 120 abut against the copper contacts 11 on the substrate 10; and (ii) The pressurizing device 110 applies longitudinal pressure to the first surface 121 of the tooling 120 and the heating seat 130 heats the substrate 10, thereby bonding the copper pillars 20 to the copper contacts 11 together. Furthermore, the mesh pattern 20a is formed by a surface microstructure formation process. Specifically, this surface microstructure formation process may include a laser engraving operation to form a first mesh microstructure on the bonding surface, wherein the laser engraving operation can be performed under predetermined atmospheric conditions; or the surface microstructure formation process may include an etching process to form a first mesh microstructure on the bonding surface. Please refer to Figure 3a, which is a schematic diagram of the formation of a first mesh microstructure 20a1 on the bonding surface of the copper pillar 20 using a laser engraving operation or an etching process according to the present invention. Furthermore, the surface microstructure formation process may further include an electroplating process to coat a nano-bicrystalline copper layer on the first network microstructure 20a1, and a metal coating process to coat a metal plating layer on the nano-bicrystalline copper layer to form a mesh pattern 20a. The metal plating layer may contain titanium, palladium, or gold. The metal coating process may include processes such as electroplating, chemical vapor deposition, or metal sputtering. Please refer to Figures 3b and 3c together. Figure 3b is a schematic diagram of coating a nano-bicrystalline copper layer 20a2 on the first network microstructure 20a1 of the copper pillar 20 using an electroplating process according to the present invention; and Figure 3c is a schematic diagram of coating a metal plating layer 20a3 on the nano-bicrystalline copper layer 20a2 using a metal coating process according to the present invention to form a mesh pattern 20a. Alternatively, the substrate 10 may be a substrate for a chip or a printed circuit board. In addition, the pressurizing device 110 may also have a heating function to assist in the bonding of the copper pillars 20 and the copper contacts 11. It is worth mentioning that the mesh pattern 20a has the following functions: (i) In this hot-press bonding process, the diffusion bonding flux of copper atoms on the bonding surface is increased to enhance the copper-copper bonding force; (ii) Effectively reduces the temperature and time required for bonding between the copper pillar 20 and the corresponding copper contact 11; and (iii) The height deviation of the copper pillars 20 can be absorbed when the copper pillars 20 are bonded to the copper contacts 11. That is, the present invention can provide a buffer depth in the hot-press bonding process by means of the mesh pattern 20a to absorb the height deviation of the copper pillars 20. As described above, this invention discloses a copper-copper hybrid bonding method. Referring to Figure 4, which illustrates a flowchart of one embodiment of the copper-copper hybrid bonding method of this invention, the method is used to bond multiple copper pillars to multiple copper contacts of a substrate. The method includes: fixing multiple copper pillars to a second surface of a tooling (step a); contacting the bonding surfaces of the copper pillars to the copper contacts of the substrate (step b); applying longitudinal pressure to a first surface of the tooling using a pressure device; and heating the substrate using a heating seat abutting the bottom surface of the substrate, thereby bonding the copper pillars to the copper contacts together. Each copper pillar has a mesh pattern on its bonding surface, and the mesh pattern is formed by a surface microstructure formation process (step c). In the above steps, the surface microstructure formation process may include a laser engraving operation to form a first network microstructure on the bonding surface, and the laser engraving operation may be performed under a predetermined atmosphere; or the surface microstructure formation process may include an etching process to form a first network microstructure on the bonding surface. In addition, the surface microstructure forming process may further include an electroplating process to coat a nano-bicrystalline copper layer on the first network microstructure, and a metal coating process to coat a metal coating on the nano-bicrystalline copper layer to form a network pattern, wherein the metal coating may contain titanium, palladium or gold. In addition, the metal coating process may include processes such as electroplating, chemical vapor deposition, or metal sputtering. Alternatively, the substrate can be a chip substrate or a printed circuit board. Based on the above description, the present invention can provide the following advantages: (1) The copper-copper hybrid bonding method of the present invention can effectively enhance the bonding force between the copper pillar and the corresponding copper junction by forming a mesh pattern on the bonding surface of the copper pillar; (2) The copper-copper hybrid bonding method of the present invention can effectively reduce the temperature and time required for bonding between the copper pillar and the corresponding copper junction by forming a mesh pattern on the bonding surface of the copper pillar. (3) The copper-copper hybrid bonding method of the present invention can absorb the height deviation of the copper pillars when multiple copper pillars are bonded to multiple copper contacts of a substrate by forming a mesh pattern on the bonding surface of the copper pillars. (4) The packaging structure of the present invention can effectively improve the bonding force of the copper pillar and the copper contact of a substrate by means of the aforementioned method; (5) The packaging structure of the present invention can effectively reduce the temperature and time required for bonding between the copper pillar and the corresponding copper contact by means of the aforementioned method; and (6) The packaging structure of the present invention can absorb the height deviation of the copper pillars when the multiple copper pillars are bonded to the multiple copper contacts of a substrate by the aforementioned method. The embodiments disclosed in this case are preferred embodiments. Any partial changes or modifications that originate from the technical ideas of this case and can be easily deduced by those skilled in the art are within the scope of the patent rights of this case. In conclusion, this case demonstrates a significant difference from conventional technology in terms of purpose, means, and effectiveness. Furthermore, its invention is practical and meets the patent requirements for an invention. We earnestly request that your esteemed examiner carefully review the case and grant a patent as soon as possible to benefit society. This is our sincere prayer. 10: Substrate; 11: Copper contact; 20: Copper pillar; 20a: Mesh pattern; 20a1: First mesh microstructure; 20a2: Nano bicrystalline copper layer; 20a3: Metal plating; 100: Hot pressing equipment; 110: Pressurizing device; 120: Tooling; 130: Heating seat. Step a: Fix multiple copper pillars to the second surface of one of the tooling components. Step b: Make the bonding surfaces of the copper pillars abut against the copper contacts of the substrate. Step c: Apply longitudinal pressure to the first surface of one of the tooling components using a pressurizing device, and heat the substrate using a heating seat abutting the bottom surface of the substrate, thereby bonding the copper pillars and the copper contacts together. Each copper pillar has a mesh pattern on its bonding surface, and the mesh pattern is formed by a surface microstructure forming process. Figure 1 illustrates a schematic diagram of a hot-pressing apparatus used to produce the packaging structure of the present invention; Figure 2 is a schematic diagram of an embodiment of the copper pillar structure used in the present invention; Figure 3a is a schematic diagram of the present invention forming a first network microstructure on the bonding surface of the copper pillar using a laser engraving operation or an etching process; Figure 3b is a schematic diagram of the present invention coating a nano-bicrystalline copper layer on the first network microstructure shown in Figure 3a using an electroplating process; Figure 3c is a schematic diagram of the present invention coating a metal layer on the nano-bicrystalline copper layer shown in Figure 3b using a metal coating process to form the network texture shown in Figure 2; and Figure 4 illustrates a flowchart of an embodiment of the copper-copper hybrid bonding method of the present invention. Step a: Fix multiple copper pillars to the second side of one of the tooling components. Step b: Make the bonding faces of the copper pillars abut against the copper contacts of the substrate. Step c: Apply longitudinal pressure to one of the tooling components using a pressurizing device, and heat the substrate using a heating seat abutting the bottom surface of the substrate, thereby bonding the copper pillars and copper contacts together. Each copper pillar has a mesh pattern on the bonding surface, and the mesh pattern is formed by a surface microstructure forming process.

Claims

1. A copper-copper hybrid bonding method for bonding a plurality of copper pillars to a plurality of copper contacts on a substrate, comprising performing a thermoforming bonding process using a pressurizing device and a heating seat to bond the copper pillars to the copper contacts, wherein the copper pillars are fixed on a fixture and exposed on the bottom surface of the fixture, the top surface of the fixture abuts against the pressurizing device, and the heating seat supports the substrate, characterized in that: each copper pillar has a mesh pattern on a bonding surface corresponding to a copper contact, and the mesh pattern is formed by a surface microstructure forming process; wherein, The mesh pattern is used to provide a buffer depth in the hot-press bonding process to absorb height deviations of the copper pillars.

2. The copper-copper hybrid bonding method as described in claim 1, wherein, The surface microstructure formation process includes a laser engraving operation to form a first network microstructure on the bonding surface.

3. The copper-copper hybrid bonding method as described in claim 2, wherein, The laser engraving operation is performed under specific atmospheric conditions.

4. The copper-copper hybrid bonding method as described in claim 1, wherein, The surface microstructure formation process includes an etching process to form a first network microstructure on the bonding surface.

5. The copper-copper hybrid bonding method as described in claim 2 or 4, wherein, The surface microstructure forming process further includes an electroplating process to coat a nano-bicrystalline copper layer on the first network microstructure, and a metal coating process to coat a metal plating layer on the nano-bicrystalline copper layer to form the network texture.

6. The copper-copper hybrid bonding method as described in claim 5, wherein, The metal coating comprises a metal coating selected from the group consisting of titanium, palladium and gold.

7. The copper-copper hybrid bonding method as described in claim 5, wherein, The metal coating process includes one selected process from a group consisting of electroplating, chemical vapor deposition, and metal sputtering.

8. The copper-copper hybrid bonding method as described in claim 1, wherein, The substrate is the base material for a chip.

9. The copper-copper hybrid bonding method as described in claim 1, wherein, The substrate is a printed circuit board.

10. A packaging structure having a plurality of copper pillars and a substrate, the copper pillars being bonded to a plurality of copper contacts on the substrate by a copper-copper hybrid bonding method, the method comprising performing a thermocompression bonding process using a pressurizing device and a heating seat to bond the copper pillars to the copper contacts together, the copper pillars being fixed on a fixture and exposed on the bottom surface of the fixture, the top surface of the fixture abutting against the pressurizing device, and the heating seat supporting the substrate, characterized in that: each copper pillar has a mesh pattern on a bonding surface corresponding to a copper contact, and the mesh pattern is formed by a surface microstructure forming process; wherein, The mesh pattern is used to provide a buffer depth in the hot-press bonding process to absorb height deviations of the copper pillars.

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