Bonding method

Abstract

The invention provides a bonding method, and the method comprises the steps: enabling the surface of a first substrate and the surface of a second substrate to be opposite, and enabling the first substrate and the second substrate to be pre-bonded at a preset temperature; and carrying out heat treatment on the pre-bonded first substrate and second substrate, wherein the heat treatment temperature is higher than 1000 DEG C and / or the heat treatment time is longer than 2 hours. According to the method and the device, bubbles on the bonding interface can be effectively reduced.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a bonding method. Background Art

[0002] Bonding is a technology that combines two or more materials (or structures) into one, and is an indispensable and important part of the semiconductor manufacturing process. Wafer Direct Bonding is a technology that directly completes bonding without an intermediate layer of dielectric, voltage, or pressure. It is widely used in wafer-level packaging (WLP), 3D stacking, silicon on insulator (SOI), etc. in the design and manufacture of micro-electromechanical systems (MEMS), and plays an irreplaceable role in achieving the complexity and three-dimensionality of the structure.

[0003] The direct bonding process includes two steps: pre-bonding and heat treatment. Improper handling of these two steps may cause bubbles on the bonding surface, which will have a great impact on the bonding quality. At the least, it will affect the product yield, and at the worst, it will cause the product to be scrapped. According to the causes of bubbles, they can be roughly divided into the following categories: bubbles caused by particles, bubbles caused by insufficient surface flatness or defects, bubbles trapped inside due to abnormal bonding, bubbles generated during the annealing process, bubbles caused by organic contamination on the bonding surface, etc. Appropriate heat treatment after bonding will reduce bubbles.

[0004] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0005] The inventor of the present application found that in the prior art, the highest temperature of the heat treatment stage of direct bonding does not exceed 1000°C. In theory, such a heat treatment temperature can eliminate all bubbles at the bonding interface. However, the results of a large number of experiments show that a considerable number of bubbles still exist. Therefore, how to further reduce the bubbles at the bonding interface is a problem that needs to be solved.

[0006] An embodiment of the present application provides a bonding method, in which the heat treatment temperature after pre-bonding is higher than 1000° C. and / or the heat treatment time is greater than 2 hours, thereby effectively improving the bubble condition of the bonding interface.

[0007] According to one aspect of an embodiment of the present application, a bonding method is provided, the method comprising:

[0008] placing a surface of a first substrate and a surface of a second substrate opposite to each other, and pre-bonding the first substrate and the second substrate at a predetermined temperature; and

[0009] The pre-bonded first substrate and the second substrate are subjected to heat treatment, wherein the heat treatment temperature is higher than 1000° C. and / or the heat treatment time is greater than 2 hours.

[0010] In at least one embodiment, the temperature of the heat treatment is higher than 1000°C and less than or equal to 1200°C.

[0011] In at least one embodiment, the heat treatment time is greater than 2 hours and less than or equal to 4 hours.

[0012] In at least one embodiment, a surface of at least one of the first substrate and the second substrate has an oxide layer.

[0013] In the case where the thickness of the oxide layer is less than a predetermined thickness, the smaller the thickness of the oxide layer, the higher the temperature of the heat treatment and / or the longer the time of the heat treatment.

[0014] In at least one embodiment, a surface of one of the first substrate and the second substrate is silicon oxide, and a surface of the other substrate is silicon.

[0015] In at least one embodiment, the method further comprises:

[0016] The surface of at least one of the first substrate and the second substrate is cleaned to remove the oxide layer on the surface.

[0017] The beneficial effect of the present application is that the heat treatment temperature after pre-bonding is higher than 1000° C. and / or the heat treatment time is greater than 2 hours, thereby being able to effectively improve the bubble condition at the bonding interface.

[0018] With reference to the following description and accompanying drawings, the specific embodiments of the present application are disclosed in detail, indicating the way in which the principles of the present application can be adopted. It should be understood that the embodiments of the present application are not limited in scope. Within the scope of the spirit and clauses of the appended claims, the embodiments of the present application include many changes, modifications and equivalents.

[0019] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0020] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps or components. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation methods of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0022] Figure 1 It is a schematic diagram of hydrophilic bonding;

[0023] Figure 2 is a schematic diagram of hydrophobic bonding;

[0024] Figure 3 is a schematic diagram of a bonding method according to an embodiment of the present application;

[0025] Figure 4 It is a schematic diagram of the test results of ultrasonic scanning test on the bonding interface after heat treatment in three groups of experiments. DETAILED DESCRIPTION

[0026] With reference to the accompanying drawings, the above and other features of the present application will become apparent through the following description. In the description and the accompanying drawings, specific embodiments of the present application are specifically disclosed, which show some embodiments in which the principles of the present application can be adopted. It should be understood that the present application is not limited to the described embodiments. On the contrary, the present application includes all modifications, variations and equivalents falling within the scope of the attached claims.

[0027] In the description of each embodiment of the present application, for the convenience of description, the direction parallel to the surface of the first substrate is called "lateral", and the direction perpendicular to the surface of the first substrate is called "longitudinal".

[0028] Example 1

[0029] According to the bonding mechanism, it can be divided into hydrophilic bonding and hydrophobic bonding according to the different bonding states.

[0030] Figure 1 is a schematic diagram of hydrophilic bonding. Figure 1 As shown, hydrophilic bonding is a surface with a high hydroxyl concentration formed after the wafer surface is treated (such as RCA cleaning, plasma treatment, etc.). This surface easily absorbs water from the air or solution to form a layer of water film. At room temperature (for example, Figure 1The pre-bonding is completed at RT (shown in Figure 1) and then heat treated. As the heat treatment temperature increases, Si-O-Si covalent bonds begin to form at the bonding interface when the temperature exceeds 200°C. As the temperature continues to rise, Si and H 2 O reacts to form Si-O-Si covalent bonds, while expelling H 2 As the reaction accelerates, the excess H 2 O and H 2 Unable to diffuse effectively, they aggregate to form bubbles. At 700°C, most of the H 2 O has completed the reaction, the hydrogen on the bonding surface above 900℃ diffuses and disappears, and the H atoms at the bonding interface at 1000℃ are completely reacted.

[0031] Figure 2 is a schematic diagram of hydrophobic bonding. Figure 2 As shown, hydrophobic bonding is to remove the natural oxide layer on the wafer surface with hydrofluoric acid (HF) to form a hydrophobic Si-H bond on the exposed wafer surface at room temperature (e.g., Figure 2 The pre-bonding is completed at RT shown in the figure. During the subsequent heating process, Si-H precipitates H 2 The Si-Si covalent bond is formed. This reaction mainly occurs at 400-700°C. The H 2 has diffused completely through the bonding surface.

[0032] Based on the above heat treatment theory for hydrophilic bonding and hydrophobic bonding, conventional heat treatment conditions are: temperature is less than or equal to 1000° C., and heat treatment time is less than or equal to 2 hours. In theory, such heat treatment can eliminate bubbles at the bonding interface.

[0033] However, based on a large number of experiments, the inventors found that this was not the case. In some cases, there were still a considerable number of bubbles at the bonding interface. After a large number of analyses, the inventors found that the type or thickness of the bonding interface film layer would affect the H generated by the heat treatment. 2 O or H 2 The diffusion of bubbles will be affected, thus affecting the elimination of bubbles; in addition, different pre-bonding cleaning treatments will also have a great impact on the movement of bubbles.

[0034] In order to solve the above problems, an embodiment of the present application provides a bonding method.

[0035] Figure 3 FIG. 1 is a schematic diagram of a bonding method according to an embodiment of the present application. Figure 3 As shown, the bonding method includes:

[0036] Operation 301, placing a surface of a first substrate and a surface of a second substrate opposite to each other, and pre-bonding the first substrate and the second substrate at a predetermined temperature; and

[0037] Operation 302 : performing a heat treatment on the pre-bonded first substrate and the second substrate, wherein the heat treatment temperature is higher than 1000° C. and / or the heat treatment time is greater than 2 hours.

[0038] In the present application, the first substrate and the second substrate may be substrates used in the semiconductor field, for example, a silicon wafer, a silicon on insulator (SOI) wafer, a germanium silicon wafer, and the like.

[0039] The surface of the first substrate and / or the surface of the second substrate may have a circuit structure and / or a micro-electromechanical structure. The circuit structure may be used to realize the transmission or amplification of electrical signals. The circuit structure may be electrically connected to or isolated from the electromechanical structure. The micro-electromechanical structure may be a beam, a membrane, a depression, a protrusion, etc., and the micro-electromechanical structure may be movable or fixed.

[0040] The predetermined temperature of the pre-bonding in operation 301 is, for example, room temperature (RT). In addition, the predetermined temperature of the pre-bonding may be other temperatures.

[0041] Through operation 301, a surface of a first substrate and a surface of a second substrate are bonded together.

[0042] In operation 302, the first substrate and the second substrate pre-bonded together are subjected to a heat treatment, wherein the temperature of the heat treatment is higher than 1000° C. and / or the time of the heat treatment is greater than 2 hours. That is, compared with the heat treatment conditions of the prior art (temperature lower than or equal to 1000° C. and heat treatment time less than or equal to 2 hours), the heat treatment temperature of the present application is higher and / or the heat treatment time is longer.

[0043] The inventors of this application believe that: for hydrophilic bonding, when the heat treatment temperature reaches about 800°C, the SiO 2 Plastic deformation, solid diffusion and viscous flow begin to occur. As the heat treatment temperature and / or heat treatment time increase, SiO 2 The fluidity of the gas is increased, and bubbles generated by the uneven bonding surface can be effectively eliminated. In addition, with the increase of heat treatment temperature and / or heat treatment time, the intermolecular gaps at the bonding interface increase, and the gas diffusion rate increases, which can make the gas generated at the bonding interface diffuse more effectively, thereby reducing or eliminating bubbles during the heat treatment process; for hydrophobic bonding, with the increase of heat treatment temperature and / or heat treatment time, the Si atom gaps at the bonding interface can be increased, thereby increasing the gas diffusion rate, and can also significantly reduce or eliminate bubbles during the heat treatment process.

[0044] In the present application: the temperature of the heat treatment is lower than or equal to 1000°C, and the time of the heat treatment is greater than 2 hours; or, the temperature of the heat treatment is higher than 1000°C, and the time of the heat treatment is less than or equal to 2 hours; or, the temperature of the heat treatment is higher than 1000°C, and the time of the heat treatment is greater than 2 hours.

[0045] Wherein, when the temperature of the heat treatment of the present application is higher than 1000° C., the temperature of the heat treatment may be less than or equal to 1200° C. For example, the temperature of the heat treatment is 1020° C., 1050° C., 1080° C., 1100° C., 1120° C., 1150° C., 1180° C. or 1200° C.

[0046] When the heat treatment time of the present application is greater than 2 hours, the heat treatment time may be less than or equal to 4 hours. For example, the heat treatment time is 2.25 hours, 2.5 hours, 2.75 hours, 3 hours, 3.25 hours, 3.5 hours, 3.75 hours or 4 hours.

[0047] In the present application, at least one of the first substrate and the second substrate has an oxide layer (e.g., SiO 2 ). For example, the surface of one of the first substrate and the second substrate is silicon oxide, and the surface of the other substrate is silicon (for example, single crystal silicon, polycrystalline silicon or amorphous silicon, etc.); for another example, the surface of the first substrate is silicon oxide, and the surface of the second substrate is also silicon oxide.

[0048] The conditions of the heat treatment in operation 302 are related to the thickness of the oxide layer. For example, when the thickness of the oxide layer is less than a predetermined thickness (for example, the predetermined thickness is 500 nm), the smaller the thickness of the oxide layer, the higher the temperature of the heat treatment and / or the longer the time of the heat treatment. Specifically, when at least one of the first substrate and the second substrate has an oxide layer on its surface, the bonding between the first substrate and the second substrate is a hydrophilic bonding, and the oxide layer (for example, SiO 2 )The thicker it is, the better it is for heat treatment. 2 O and H 2 The discharge of the oxide layer (e.g. SiO 2 ) is small (for example, the thickness of the oxide layer is less than 500 nm), it is necessary to improve the H by increasing the heat treatment temperature and / or extending the heat treatment time. 2 O and H 2 The discharge effect.

[0049] In the present application, the surface of at least one of the first substrate and the second substrate may be cleaned before the pre-bonding in operation 301 to remove the oxide layer on the surface (for example, the oxide layer may be a natural oxide layer). Thus, a hydrophobic bond is formed between the first substrate and the second substrate. For the hydrophobic bond, the heat treatment in operation 302 of the present application can also play an effect of reducing bubbles at the bonding interface. In addition, for the hydrophobic bond, H generated during the heat treatment 2 Increasing the heat treatment temperature and / or extending the heat treatment time can increase the atomic spacing of the bonding interface, which is more conducive to H 2 diffusion, thereby reducing bubbles.

[0050] The technical effects of the present application are explained below with reference to specific examples.

[0051] In this example, the surface of the first substrate has a 150 nm thick SiO 2 The surface of the second substrate has 250nm thick polysilicon, and the surfaces of the first substrate and the second substrate are polished. This example is divided into three groups of experiments. After the pre-bonding is completed, ultrasonic scanning (CSAM) is performed to test the bubbles in the bonding interface. The pre-bonding conditions of the three groups of experiments are the same, and the heat treatment conditions are different.

[0052] The heat treatment conditions for the first group of experiments were 1000°C for 2 hours; the heat treatment conditions for the second group of experiments were 1000°C for 4 hours; and the heat treatment conditions for the third group of experiments were 1150°C for 2 hours.

[0053] Figure 4 It is a schematic diagram of the test results of ultrasonic scanning test on the bonding interface after heat treatment in three groups of experiments.

[0054] like Figure 4 As shown in 401 , for the first set of experiments, after heat treatment, obvious bubbles 400 are generated at the edge, and several small bubbles 400 with diameters of hundreds of micrometers are also generated inside;

[0055] like Figure 4 As shown in 402 , for the second set of experiments, the edge bubbles 400 are significantly reduced after heat treatment;

[0056] like Figure 4 As shown in 403, for the third group of experiments, when the heat treatment temperature reaches 1150°C, after 2 hours of heat treatment, there are no bubbles on the bonding interface.

[0057] In the bonding method of the embodiment of the present application, the heat treatment temperature after pre-bonding is higher than 1000° C. and / or the heat treatment time is greater than 2 hours, thereby effectively improving the bubble condition at the bonding interface.

[0058] The present application is described above in conjunction with specific implementation methods, but it should be clear to those skilled in the art that these descriptions are exemplary and are not intended to limit the scope of protection of the present application. Those skilled in the art can make various modifications and variations to the present application based on the spirit and principles of the present application, and these modifications and variations are also within the scope of the present application.

Claims

1. A bonding method, It is characterized in that The method comprises: placing a surface of a first substrate and a surface of a second substrate opposite to each other, and pre-bonding the first substrate and the second substrate at a predetermined temperature; and The pre-bonded first substrate and the second substrate are subjected to heat treatment, wherein the heat treatment temperature is higher than 1000° C. and / or the heat treatment time is greater than 2 hours.

2. The bonding method according to claim 1, It is characterized in that The temperature of the heat treatment is higher than 1000°C and lower than or equal to 1200°C.

3. The bonding method according to claim 2, It is characterized in that The heat treatment time is greater than 2 hours and less than or equal to 4 hours.

4. The bonding method according to claim 1, It is characterized in that A surface of at least one of the first substrate and the second substrate has an oxide layer, In the case where the thickness of the oxide layer is less than a predetermined thickness, the smaller the thickness of the oxide layer, the higher the temperature of the heat treatment and / or the longer the time of the heat treatment.

5. The bonding method according to claim 1, It is characterized in that A surface of one of the first substrate and the second substrate is silicon oxide, and a surface of the other substrate is silicon.

6. The bonding method according to claim 1, It is characterized in that The method further comprises: The surface of at least one of the first substrate and the second substrate is cleaned to remove the oxide layer on the surface.

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