CN117690869A - A copper-copper low-temperature direct bonding method in air environment - Google Patents

Abstract

The invention belongs to the technical field of three-dimensional packaging, and discloses a copper-copper low-temperature direct bonding method in an air environment, which comprises the following steps: firstly, pretreating a copper plating surface of a clean copper plating bonding body by utilizing glycerol in an air environment to obtain the copper plating bonding body to be bonded; then, the copper-plated bonded body to be bonded is pressure bonded in an air atmosphere. The bonding method provided by the invention has the advantages that the gas atmosphere is normal, no protective gas is needed, the process is simple, the process cost is low, the industrial production is facilitated, and the obtained copper-copper bonding surface has high shearing strength.

Description

A copper-copper low-temperature direct bonding method in air environment

Technical field

The invention belongs to the field of three-dimensional packaging technology, and specifically relates to a copper-copper low-temperature direct bonding method in an air environment.

Background technique

Over the past few decades, the miniaturization of integrated circuits has been controlled by the reduction in transistor size following Moore's Law, with the characteristic size of transistors approaching physical limits. At the same time, the continuous expansion of transistors has led to an explosion in the density of metal layers, resulting in a significant increase in connection delays. In recent years, shrinking transistor size to improve IC performance has been a challenge due to physical limitations and interconnect bottlenecks. Therefore, three-dimensional integrated circuits (3D IC), as an important alternative technology to solve the above problems, have attracted widespread attention and research. By vertically integrating multiple IC layers in the same package, 3D IC technology promises to provide short interconnect line lengths, small form factors, low power consumption and heterogeneous integration capabilities.

Bonding is key to the vertical stacking of chips or wafers in three-dimensional integrated circuits, and solder interconnects are the most commonly used bonding technology due to their low cost and high throughput. However, solder interconnects are difficult to meet the extremely high requirements for I/O density and reliability due to the rise of emerging industries such as artificial intelligence, autonomous driving, the Internet of Things, and 5G networks. Therefore, the exploration of bonding solutions continues, and Cu-Cu direct bonding is considered to be a more promising connection method with higher density and reliability. Cu has excellent properties, including excellent electromigration resistance, high electrical and thermal conductivity, low cost and high compatibility with packaging manufacturing, and has always been the most popular bonding medium.

Although Cu-Cu direct bonding has many advantages, the high thermal budget of the direct bonding process limits the scope of applications in this industry. In particular, copper will be oxidized during the bonding process, hindering copper diffusion at the copper-copper bonding interface. At present, the common method to solve the oxidation problem of copper is to bond in a protective atmosphere or reducing atmosphere. This method not only requires the device to have good air tightness, but also uses protective or reducing gases, which increases process complexity and bonding costs.

Contents of the invention

In view of this, the object of the present invention is to provide a low-temperature direct bonding method of copper-copper in an air environment. The bonding method provided by the present invention can realize direct bonding of copper-copper at a lower temperature in the air. Obtain a bonded body with higher bonding strength.

In order to achieve the purpose, the present invention adopts the following technical solutions:

A copper-copper low-temperature direct bonding method in an air environment, including the following steps:

First, use glycerol to pretreat the copper-plated surface of the clean copper-plated bonded body in an air environment to obtain a copper-plated bonded body to be bonded;

Then, the copper-plated bonded bodies to be bonded are pressure bonded in an air environment.

Preferably, the pretreatment method is: adding glycerol dropwise to the copper-plated surface of the first copper-plated bonded body, and allowing the glycerol to evenly cover the copper-plated surface; and then using the plating method of the first copper-plated bonded body. The copper surface and the copper-plated surface of the second copper-plated bonded body are opposite. The second copper-plated bonded body is stacked on top of the first copper-plated bonded body and the centers of the two are aligned. Treat at 150~250°C for 5 minutes to obtain the desired result. Bonded copper-plated bond body.

Preferably, the volume concentration of glycerol is not less than 99%.

Preferably, the pressure bonding temperature is 150-250°C, the pressure is 300-1000N, and the heat and pressure holding time is 15-30 minutes.

Preferably, the method for obtaining the clean copper-plated bonded body includes: subjecting the copper-plated bonded body to ultrasonic cleaning. The ultrasonic cleaning includes sequentially performing ultrasonic cleaning with acetone, ultrasonic cleaning with absolute ethanol, ultrasonic cleaning with 0.1 mol/L dilute hydrochloric acid, and ultrasonic cleaning with deionized water.

The above-mentioned copper-copper low-temperature direct bonding method of the present invention is suitable for a variety of copper-plated bonding bodies, including but not limited to copper-plated silicon, copper-plated germanium, copper-plated silicon carbide, copper-plated gallium arsenide, copper-plated gallium nitride, A series of semiconductor materials such as copper-plated indium phosphide.

The beneficial effects of the present invention are reflected in:

The invention provides a copper-copper low-temperature direct bonding method in an air environment, which includes two steps of glycerol pretreatment and pressure bonding. The invention utilizes the reaction between glycerol and the surface of the copper-plated bonded body. On the one hand, the glycerol isolates the contact between oxygen and the copper-plated surface. On the other hand, the glycerol can reduce the oxides on the copper-plated surface. Then under a certain temperature and pressure, , so that the copper atoms on the two pre-treated copper-plated surfaces can mutually diffuse at the interface to achieve bonding. The bonding method of the present invention does not require the use of lead-free solder for interconnection, and directly diffuses the reduced copper-plated surfaces into pairs and connects them through atomic contact. When bonding using an intermediate layer of solder, the solder has a low melting point and is prone to desoldering at high temperatures. However, the bonding method of the present invention can improve the high temperature resistance of the device. Moreover, the shear strength of the copper-copper bonding surface obtained by the bonding method provided by the present invention can reach more than 19 MPa. In addition, the gas atmosphere in the bonding process of the present invention is a normal atmospheric environment, and no protective gas is required. The process of the invention is simple, the process cost is low, and it is beneficial to industrial production.

Description of the drawings

Figure 1 is a schematic diagram of the bonding process of the present invention. The numbers in the figure: 11 is the substrate of the second copper-plated bonded body; 12 is the substrate of the first copper-plated bonded body; 21 is the copper layer of the second copper-plated bonded body. ; 22 is the copper layer of the first copper-plated bonded body; 31 is the surface oxide layer of the copper layer of the second copper-plated bonded body; 32 is the surface oxide layer of the copper layer of the first copper-plated bonded body; 4 is glycerol.

Figure 2 is a physical picture of the copper-plated bonded body before glycerol treatment in Example 1.

Figure 3 is a physical picture of the copper-plated bonded body after glycerol treatment in Example 1.

Figure 4 is an SEM image of the bonding interface of the copper-plated silicon bonded body that has been bonded in Example 1.

Figure 5 is a comparison diagram of the bonding strength of the bonded products of Examples 1 to 5.

Detailed ways

As shown in Figure 1, the present invention provides a copper-copper low-temperature direct bonding method in an air environment, which includes the following steps:

First, use glycerol to pretreat the copper-plated surface of the clean copper-plated bonded body in an air environment to obtain a copper-plated bonded body to be bonded;

Then, the copper-plated bonded bodies to be bonded are pressure bonded in an air environment.

In a preferred embodiment, the pretreatment method is: adding glycerol dropwise to the copper-plated surface of the first copper-plated bonded body, and allowing the glycerol to evenly cover the copper-plated surface; and then using the first copper-plated bonding body to The copper-plated surface of the bonded body is opposite to the copper-plated surface of the second copper-plated bonded body. The second copper-plated bonded body is stacked on top of the first copper-plated bonded body and the centers of the two are aligned. Treat at 150~250℃ for 5 minutes. , to obtain the copper-plated bonded body to be bonded.

In a preferred embodiment, the volume concentration of glycerol is not less than 99%.

In a preferred embodiment, the pressure bonding temperature is 150-250°C, the pressure is 300-1000N, and the heat and pressure holding time is 15-30 minutes.

In a preferred embodiment, the copper-plated bonded body includes but is not limited to a series of copper-plated silicon, copper-plated germanium, copper-plated silicon carbide, copper-plated gallium arsenide, copper-plated gallium nitride, copper-plated indium phosphide, etc. Semiconductor material. In the present invention, the size of the copper-plated bonded body is not specifically limited.

In a preferred embodiment, the method for obtaining a clean copper-plated bonded body includes: subjecting the copper-plated bonded body to ultrasonic cleaning. The frequency of ultrasonic cleaning is preferably 20 to 50 KHz, and more preferably 40 KHz. The ultrasonic cleaning preferably includes sequentially performing ultrasonic cleaning with acetone, ultrasonic cleaning with absolute ethanol, ultrasonic cleaning with 0.1 mol/L dilute hydrochloric acid, and ultrasonic cleaning with deionized water. The acetone ultrasonic cleaning time is preferably 4 to 6 min, more preferably 5 min, and the frequency is preferably 2 to 3 times; the absolute ethanol ultrasonic cleaning time is preferably 4 to 6 min, more preferably 5 min, and the frequency is preferably 2 ~3 times; the time of ultrasonic cleaning with dilute hydrochloric acid is preferably 4~6min, more preferably 5min, and the frequency is preferably 2~3 times; the time of ultrasonic cleaning with deionized water is preferably 4~6min, more preferably 5min , the number of times is preferably 2 to 3 times.

In a preferred embodiment, after the ultrasonic cleaning, the method further includes blowing the cleaned copper-plated bonded body with argon gas.

In a preferred embodiment, both the pretreatment and the pressure bonding are performed in a bonding cavity of a chip bonding machine.

In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the examples, but they should not be understood as limiting the protection scope of the present invention.

Example 1

In this embodiment, two pieces of copper-plated bonded bodies are processed as follows (the size of the second copper-plated bonded body is 6mm×6mm, the size of the first copper-plated bonded body is 10mm×10mm, and the substrates of the two copper-plated bonded bodies are both silicon, A copper layer is formed on the silicon) for bonding:

1. Ultrasonic cleaning

The two copper-plated bonded bodies were subjected to ultrasonic cleaning with acetone, ultrasonic cleaning with absolute ethanol, ultrasonic cleaning with 0.1 mol/L dilute hydrochloric acid, and ultrasonic cleaning with deionized water. The ultrasonic frequency is 40KHz, each cleaning time is 5 minutes, and the number of cleanings with each solvent is 2 times. Blow dry the cleaned copper-plated bonded body with argon gas.

2. Preprocessing

Add 0.2 mL of glycerol dropwise to the copper-plated surface of the first copper-plated bonded body, and make the glycerol evenly cover the copper-plated surface; then use the copper-plated surface of the first copper-plated bonded body and the second copper-plated bonded body The copper-plated surfaces are opposite to each other, stack the second copper-plated bonded body on top of the first copper-plated bonded body and align the centers of the two, and treat it at 150°C for 5 minutes in a normal air environment to obtain the copper-plated bonded body to be bonded. . Glycerol reacts with the surface of the copper-plated bonded body, which can not only protect the copper-plated surface from being oxidized, but also reduce the original oxide layer on the surface of the copper layer.

3. Pressure bonding

Continue to heat the copper-plated bonded body to be bonded to the bonding temperature of 150°C in the air environment, keep the temperature constant and apply a pressure of 360N, and keep the bonding for 30 minutes to achieve the bonding of two copper-plated silicon bonded bodies.

Figures 2 and 3 are physical pictures of the copper-plated bonded body before and after glycerol treatment. It can be seen from the figure that glycerol can effectively reduce the oxide layer on the surface of the copper layer of the copper-plated bonded body.

Figure 4 is an SEM image of the bonding interface of the copper-plated silicon bonded body that has been bonded. It can be seen from the picture that the copper bonding condition is very good, with a continuous bonding interface and almost no holes.

Example 2

The only difference between this embodiment and Embodiment 1 is that the pretreatment temperature and bonding temperature are 175°C.

Example 3

The only difference from Example 1 is that the pretreatment temperature and bonding temperature are 200°C.

Example 4

The only difference from Example 1 is that the pretreatment temperature and bonding temperature are 225°C.

Example 5

The only difference from Example 1 is that the pretreatment temperature and bonding temperature are 250°C.

Example 6

The only difference from Embodiment 1 is that the silicon substrate of the copper bonding body is replaced with a silicon carbide substrate.

The present invention uses a shear force tester to conduct a bonding strength (shear strength) test on the copper-plated silicon bonded bodies after bonding in Examples 1 to 5. The test results are shown in Figure 5. From Figure 5, it can be seen that: according to Example 1 (The bonding temperature is 150°C) The bonding strength of the bonded product is 14.8MPa, according to Example 2 (The bonding temperature is 175°C) The bonding strength of the bonded product is 17.1MPa, according to Example 3 (The bonding temperature is 200°C) The bonding strength of the bonded product is 18.7MPa, according to Example 4 (The bonding temperature is 225°C) The bonding strength of the bonded product is 19.9MPa, according to Example 5 (Bonding temperature is 250°C) The bonding strength of the bonded product is 18.5 MPa. As the bonding temperature increases, the bonding strength gradually increases, but the reason why the bonding strength decreases after 250°C is that glycerol is consumed too quickly as the temperature increases, and the copper-plated silicon wafer is subject to secondary oxidation. The bonding strength of the bonded product in Example 6 is 17.5MPa.

Note: The bonding strength obtained by the test of the present invention is the average value obtained by testing three samples bonded under the same process conditions in each embodiment. In fact, the location of the break in the shear force test is often the silicon wafer. Non-bonded interface, so the actual bonding force is greater than the measured shear force.

The above are only preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications can also be made. should be regarded as the protection scope of the present invention.

Claims (6)

1. A method for copper-copper low temperature direct bonding in an air environment, comprising the steps of:

firstly, pretreating a copper plating surface of a clean copper plating bonding body by utilizing glycerol in an air environment to obtain the copper plating bonding body to be bonded;

then, the copper-plated bonded body to be bonded is pressure bonded in an air atmosphere.

2. A copper-copper low temperature direct bonding method in an air environment according to claim 1, wherein the pretreatment method is as follows: dripping glycerol to the copper plating surface of the first copper plating bonding body, and enabling the glycerol to uniformly cover the copper plating surface; and then stacking the second copper plating bonding body above the first copper plating bonding body by using the copper plating surface of the first copper plating bonding body and the copper plating surface of the second copper plating bonding body to be opposite, aligning the centers of the first copper plating bonding body and the second copper plating bonding body, and processing for 5 minutes at 150-250 ℃ to obtain the copper plating bonding body to be bonded.

3. A method of copper-copper low temperature direct bonding in an air environment according to claim 1 or 2, characterized in that: the volume concentration of the glycerol is not less than 99%.

4. A method of copper-copper low temperature direct bonding in an air environment according to claim 1 or 2, characterized in that: the temperature of the pressurizing bonding is 150-250 ℃, the pressure is 300-1000N, and the heat preservation and pressure maintaining time is 15-30 min.

5. A method of copper-copper low temperature direct bonding in an air environment according to claim 1 or 2, characterized in that: the method for obtaining the clean copper-plated bonding body comprises the following steps: and (5) carrying out ultrasonic cleaning on the copper-plated bonding body.

6. A method of copper-copper low temperature direct bonding in an air environment according to claim 5, wherein: the ultrasonic cleaning comprises the steps of sequentially performing acetone ultrasonic cleaning, absolute ethyl alcohol ultrasonic cleaning, dilute hydrochloric acid ultrasonic cleaning and deionized water ultrasonic cleaning.