Chip bonding interconnection method

Abstract

The present application provides a chip bonding interconnection method, comprising: providing a first structure to be bonded and a second structure to be bonded, each of the first structure to be bonded and the second structure to be bonded comprising a gold layer and a tin layer arranged in a ladder shape; stacking the first structure to be bonded and the second structure to be bonded so that the tin layer of the first structure to be bonded and the tin layer of the second structure to be bonded are arranged opposite each other; applying pressure to both sides of the stacked first structure to be bonded and the second structure to be bonded facing away from the tin layer, and heating one side so that the tin layer and the gold layer form a gold-tin compound to complete the bonding. The ladder-shaped structure of the gold and tin layers in the present application can ensure the effect of directional migration and effectively guarantee the bonding quality.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor integration applications, and in particular to a chip bonding interconnection method. Background Art

[0002] Microelectronics have continued to advance over the past few decades, following Moore's Law. However, with the continuous development of the microelectronics industry, the reduction in device size and the increase in IC integration, traditional microelectronics processes have reached their physical limits. As Moore's Law, the driving force behind chip technology development, faces the severe challenge of approaching its own physical limits, achieving "More Than Moore" through system packaging and integration at the packaging level has become a development trend and a major demand in the field of microelectronics. Solid-liquid-inter-diffusion bonding (SLID), with its unique advantages, has become a promising method for chip interconnection. However, high-temperature, long-term SLID cannot reduce the scale of multi-chip interconnections and increases the overall time for three-dimensional integration. The high bonding temperature can cause low-melting-point metals such as tin to overflow. Summary of the Invention

[0003] In view of the above problems existing in the prior art, the present application proposes a chip bonding interconnection method, which mainly solves the problems that tin surface oxidation affects the bonding quality and continuous high temperature affects the bonding quality effect.

[0004] In order to achieve the above-mentioned and other purposes, the technical solutions adopted by the present invention are as follows.

[0005] The present application provides a chip bonding interconnection method, comprising:

[0006] Providing a first structure to be bonded and a second structure to be bonded, wherein the first structure to be bonded and the second structure to be bonded both comprise a gold layer and a tin layer arranged in a ladder shape;

[0007] stacking the first structure to be bonded and the second structure to be bonded so that the tin layer of the first structure to be bonded is arranged opposite to the tin layer of the second structure to be bonded;

[0008] Pressure is applied to both sides of the stacked first structure to be bonded and the second structure to be bonded, which are away from the tin layer, and one side is heated to form a gold-tin compound between the tin layer and the gold layer, thereby completing bonding.

[0009] In one embodiment of the present application, the steps of manufacturing the first structure to be bonded include:

[0010] providing a first substrate;

[0011] providing an adhesive layer on the first substrate, and bonding the initial gold layer to one side of the first substrate via the adhesive layer;

[0012] The initial gold layer is thickened by electroplating to obtain the gold layer, and a tin layer is formed by evaporation deposition on the side of the gold layer away from the first substrate, and the outer edge of the tin layer shrinks inward relative to the outer edge of the gold layer to form the ladder-like arrangement.

[0013] In one embodiment of the present application, the adhesion layer includes a titanium layer.

[0014] In one embodiment of the present application, after the tin layer is provided on the side of the gold layer facing away from the first substrate, the method further includes: providing a heat insulation layer on the first substrate, the heat insulation layer covering the gold layer and the tin layer, and the heat insulation layer having a trapezoidal structure.

[0015] In one embodiment of the present application, the structural arrangement of the second structure to be bonded is the same as that of the first structure to be bonded, and the insulation layer of the second structure to be bonded uses an insulation material different from that of the insulation layer of the first structure to be bonded.

[0016] In one embodiment of the present application, the thickness of the gold layer is 2-3 microns.

[0017] In one embodiment of the present application, the thermal insulation material includes: polypropylene carbonate, cyclic polyphthalaldehyde, carboxyethylphenyl hypophosphite, acrylonitrile-butadiene-styrene copolymer

[0018] In one embodiment of the present application, before providing the heat insulation layer on the first substrate, the method further includes: providing an anti-oxidation layer on the surface of the tin layer facing away from the gold layer.

[0019] In one embodiment of the present application, the material of the anti-oxidation layer includes gold.

[0020] In one embodiment of the present application, applying pressure to both sides of the stacked first structure to be bonded and the second structure to be bonded, which are away from the tin layer, and heating one side thereof so that the tin layer and the gold layer form a gold-tin compound, includes:

[0021] The applied pressure is between 1-2 MPa and the pressurization time is 4-6 minutes;

[0022] The temperature of the heated side reaches 300°C and the temperature of the other side reaches 150°C.

[0023] As described above, the chip bonding interconnection method provided in this application has the following beneficial effects.

[0024] In this application, metal atoms are directed to migrate from a high-temperature region to a low-temperature region through unilateral heating. The trapezoidal structure of the gold layer and the tin layer is designed to ensure the effect of the directed migration and effectively guarantee the bonding quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process of chip bonding interconnection method in one embodiment of the present invention.

[0026] Figure 2 Schematic diagram of the structure of the first structure to be bonded.

[0027] Figure 3 Schematic diagram of the structure after the first structure to be bonded and the second structure to be bonded are stacked in one embodiment of the present application. DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other unless they conflict.

[0029] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0030] See also Figure 1 , the present application provides a chip bonding interconnection method, which includes the following steps.

[0031] Step S100 : providing a first structure to be bonded and a second structure to be bonded, wherein the first structure to be bonded and the second structure to be bonded both comprise a gold layer and a tin layer arranged in a ladder shape.

[0032] See also Figure 2 , Figure 2 Schematic diagram of the structure of the first structure to be bonded. The steps of making the first structure to be bonded include:

[0033] Provide a first substrate; a silicon wafer can be selected as the first substrate, clean the surface of the silicon wafer to be bonded, and remove organic compounds on the surface.

[0034] An adhesion layer is provided on the first substrate, and the initial gold layer is bonded to one side of the first substrate through the adhesion layer; specifically, a 50nm thick Ti layer and a 100nm thick Au layer can be sputtered on the surface of one side of the first substrate by sputtering, wherein Ti serves as the adhesion layer to obtain good adhesion performance between gold and silicon.

[0035] The initial gold layer is thickened by electroplating to obtain the gold layer. A tin layer is then formed by evaporation deposition on the side of the gold layer facing away from the first substrate, with the outer edge of the tin layer contracting inward relative to the outer edge of the gold layer to form the ladder-like arrangement. The Au film is electroplated to a thickness of 2-3 μm to obtain the gold layer. A 2 μm Sn layer is then deposited by evaporation. The gold and tin layers are designed to form a ladder-like shape, with the outer edge of the tin layer contracting inward relative to the outer edge of the gold layer, forming a two-layer ladder structure.

[0036] In one embodiment, the second structure to be bonded and the first structure to be bonded may adopt the same stacking structure, that is, the second structure to be bonded may include a second substrate, a gold layer is made on the second substrate, and a tin layer is made on the gold layer, and the gold layer and tin layer in the second structure to be bonded are also arranged in a trapezoidal shape.

[0037] In one embodiment, a thermal insulation layer can be coated on the first structure to be bonded, and the gold layer and the tin layer are covered by the thermal insulation layer. The thermal insulation layer can use PPA (phenyl-propanolamine) thermal insulation material, and the thickness can be set to 2 microns. The thermal insulation layer can prevent the surface oxidation of the tin layer, and at the same time, it is convenient to form a temperature difference between the first structure to be bonded and the second structure to be bonded during the heating process, thereby ensuring the bonding effect. Similarly, a thermal insulation layer can also be coated on the second structure to be bonded. The material of the thermal insulation layer of the second structure to be bonded can be different from that of the first structure to be bonded, and the different thermal insulation coefficients can ensure that the temperature difference is more controllable.

[0038] In one embodiment, before coating the heat-insulating layer, an anti-oxidation layer may be coated on the surface of the tin layer to further enhance the anti-oxidation performance, wherein the anti-oxidation layer may be an Au film.

[0039] Step S101 : stacking the first structure to be bonded and the second structure to be bonded, so that the tin layer of the first structure to be bonded is arranged opposite to the tin layer of the second structure to be bonded.

[0040] See 3, Figure 3 Schematic diagram of the structure after stacking the first structure to be bonded and the second structure to be bonded in one embodiment of the present application. After stacking, the tin layer of the first structure to be bonded and the tin layer of the second structure to be bonded are arranged opposite to each other.

[0041] Step 102 : applying pressure to both sides of the stacked first and second structures facing away from the tin layer, and heating one side thereof to form a gold-tin compound between the tin layer and the gold layer, thereby completing bonding.

[0042] In one embodiment, the stacked first structure to be bonded and the second structure to be bonded are placed on a hot plate, the hot plate is docked with the substrate of the first structure to be bonded or with the substrate of the second structure to be bonded, and is electrically heated to 330°C. The bonding temperature is maintained under this condition for 20 minutes, and a pressure of 1.0-2.0 MPa is applied to the stacked first structure to be bonded and the second structure to be bonded by a clamp. The pressurization time is 4-6 minutes. Because of the insulation layer, the temperatures of the silicon substrate and the silicon cap layer are ensured to reach 300°C and 150°C, respectively, thereby forming a thermal gradient bonding structure. After cooling, a gold-tin eutectic bonding sheet can be formed.

[0043] In traditional packaging technology, template printing and solder ball placement are used to form Au / Sn solder. The disadvantage of these two technologies is that the bonding spacing is quite large, always greater than 100 microns. Since Au / Sn solder is pre-formed, it usually has a high oxide content, which is detrimental to bonding and the barrier to reducing the bonding spacing to tens of microns. Electroplating has the advantages of low cost and high roughness that can be obtained by vacuum evaporation. Therefore, the present application adopts the method of electroplating to form the Au layer and evaporating the Sn layer, so that the Au / Sn bumps not only have a lower oxide content, but also have a lower roughness surface, which is conducive to improving the subsequent bonding quality. The melting point of tin is 235°C, while the melting point of gold is much higher than that of tin. When the temperature of the heating plate is higher than that of the low-melting-point metal, the tin atoms migrate directionally from the high-temperature area to the low-temperature area, and form a metal compound (IMC, intermetallic compound) with the gold layer through diffusion, thereby achieving a bonding effect. However, continuous high-temperature solid-liquid bonding will hinder the proportional reduction of chip interconnection and cannot achieve a short-time bonding effect. The above two disadvantages can be effectively avoided by using thermal gradient bonding. However, the present application is different from the traditional thermal gradient bonding method. The present design adopts a trapezoidal pad structure, and the pad of the gold layer is larger than the pad of the tin layer. This structure is conducive to the diffusion of tin atoms and reduces the overflow of tin caused by excessive pressure. By heating the silicon substrate, the gold layer and the tin layer are coated with a recyclable metastable polymer and composite material cyclic polyphthalaldehyde (PPA) for thermal insulation, and the silicon substrate is coated with polypropylene carbonate (PPC, Polypropyl Carbonate) creates a temperature difference between the upper and lower ends of the bond. The cyclic polyphthalaldehyde (PPA) coated with the gold and tin layers is a fully recyclable metastable polymer and composite material that depolymerizes at temperatures reaching 150°C. Similarly, polypropylene carbonate (PPC), a thermoplastic organic binder that can withstand temperatures up to 260°C and has a depolymerization temperature of approximately 260°C, is coated on the silicon substrate. In addition to the aforementioned PPA and PPC pair of thermal insulation materials, other alternative thermal insulation materials can also be used to achieve the same effect. For example, thermal insulation materials may include carboxyethyl phenylphosphinic acid (CPPA) and acrylonitrile-butadiene-styrene (ABS) plastic. ABS is a terpolymer of acrylonitrile (A), butadiene (B), and styrene (S). This material has excellent bonding properties and a decomposition temperature of approximately 250°C, making it a good alternative to PPC, achieving the same thermal insulation effect as PPC. CPPA and PPA belong to the same category of substances and can also replace each other well.This application further improves the traditional bonding structure. This improvement not only prevents tin oxidation and thus improves the bonding effect, but also because the trapezoidal structure of the thermal insulation layer design allows the polymer to be more fully in contact with the air present in the bonding structure when the bonding structure is heated, the depolymerization process can better consume the oxygen in the environment, thereby preventing tin (Sn) from being oxidized and achieving a better bonding effect. In addition, compared with the traditional structure, more materials are saved. The specific structure is as follows. Figure 3 As shown in the figure, the expected target is to set the hot end temperature to 300°C, the cold end temperature to 150°C, and the bonding pressure to 1.0-2.0 MPa. The bonding conditions are maintained for 20 minutes to achieve thermal gradient bonding (TGB).

[0044] Generally speaking, a certain time interval is required in the process of preparing the bonding, because the bonding process is carried out in an environment filled with air. In order to prevent the tin from being oxidized during the bonding process, the present application plates a gold film of a certain thickness on the surface of the tin, which can prevent the oxidation of the tin to a certain extent during the short-time heating bonding process. The present application achieves the requirements of thermal gradient bonding by coating the bonding structure with heat-insulating substances of different materials, and by adjusting the depolymerization temperature of different substances to make the upper and lower ends of the structure reach the expected temperature, thereby realizing Au / Sn solid-liquid low-temperature rapid bonding. The method of coating the bonding structure with an organic layer can also prevent the tin layer, which is extremely easy to oxidize, from oxidizing during bonding in an air environment. The bonding structure has been further improved on the traditional bonding process. The use of gold-tin pads with trapezoidal structures of different sizes can avoid the overflow of tin caused by excessive bonding pressure. At the same time, such a structure also effectively reduces the cost of bonding materials, and the bonding method at different gradient temperatures makes it easier to achieve the bonding effect. In addition, in order to control the gradient temperature required by this application, this application coats a certain thickness of thermal insulation layer on the bonding structure. These are metastable polymers and composite materials that are stable at ambient temperature, easy to depolymerize under specific conditions, and fully recyclable. PPA depolymerizes in just 14 minutes at 150°C. PPC is a thermoplastic organic binder that can withstand high temperatures of up to 260°C, and its depolymerization temperature is around 260°C. These two materials have a good thermal insulation effect. In addition, the depolymerization of the two materials can expel the air between the bonding structures, thereby reducing the appearance of metal oxides. Because the time required for the depolymerization of the thermal insulation layer is very short, the bonding time can also be shortened, which has the advantages of fast bonding speed and low production cost.

[0045] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A chip bonding interconnection method, characterized in that: include: Providing a first structure to be bonded and a second structure to be bonded, wherein the first structure to be bonded and the second structure to be bonded both comprise a gold layer and a tin layer arranged in a ladder shape; The manufacturing steps of the first structure to be bonded include: providing a first substrate; disposing an adhesion layer on the first substrate, and bonding an initial gold layer to one side of the first substrate via the adhesion layer; thickening the initial gold layer by electroplating to obtain the gold layer, and forming a tin layer by evaporation deposition on the side of the gold layer facing away from the first substrate, wherein the outer edge of the tin layer shrinks inward relative to the outer edge of the gold layer to form the ladder-like arrangement; after disposing the tin layer on the side of the gold layer facing away from the first substrate, further comprising: disposing a thermal insulation layer on the first substrate, wherein the thermal insulation layer covers the gold layer and the tin layer, and the thermal insulation layer has a ladder-like structure; the structural arrangement of the second structure to be bonded is the same as that of the first structure to be bonded, and the thermal insulation layer of the second structure to be bonded is made of a different thermal insulation material than that of the thermal insulation layer of the first structure to be bonded; stacking the first structure to be bonded and the second structure to be bonded so that the tin layer of the first structure to be bonded is arranged opposite to the tin layer of the second structure to be bonded; Pressure is applied to both sides of the stacked first structure to be bonded and the second structure to be bonded, which are away from the tin layer, and one side is heated to form a gold-tin compound between the tin layer and the gold layer, thereby completing bonding.

2. The chip bonding interconnection method according to claim 1, characterized in that: The adhesion layer includes a titanium layer.

3. The chip bonding interconnection method according to claim 1 or 2, characterized in that: The thickness of the gold layer is 2-3 microns.

4. The chip bonding interconnection method according to claim 1, characterized in that: The heat insulating material comprises: polypropylene carbonate, cyclic poly-o-phthalaldehyde, carboxyethylphenyl hypophosphite, and acrylonitrile-butadiene-styrene copolymer.

5. The chip bonding interconnection method according to claim 1, characterized in that: Before providing the heat-insulating layer on the first substrate, the method further includes: providing an anti-oxidation layer on the surface of the tin layer facing away from the gold layer.

6. The chip bonding interconnection method according to claim 5, characterized in that: The material of the anti-oxidation layer includes gold.

7. The chip bonding interconnection method according to claim 1, characterized in that: Applying pressure on both sides of the stacked first structure to be bonded and the second structure to be bonded, which are away from the tin layer, and heating one side thereof so that the tin layer and the gold layer form a gold-tin compound, comprising: The applied pressure is between 1-2 MPa and the pressurization time is 4-6 minutes; The temperature of the heated side reaches 300°C and the temperature of the other side reaches 150°C.

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