Heterogeneous direct bonding technology based on pyroelectric effect

Abstract

The present invention discloses a heterogeneous direct bonding technology based on the pyroelectric effect. The invention discloses that the experimental method for direct bonding includes the following steps: providing a first wafer and a second wafer, wherein the first wafer and the second wafer each have at least one smooth surface, and the first wafer has a pyroelectric effect; placing the smooth surface of the first wafer on the smooth surface of the second wafer, so that the first wafer and the second wafer form a pre-bonded body; applying pressure to the upper surface and / or lower surface of the pre-bonded body, and at the same time, heating the pre-bonded body; releasing the pressure on the pre-bonded body, and cooling the pre-bonded body. This method can be used with simple equipment and simple steps, without the need for an intermediate layer, and can utilize the characteristics of the first wafer itself to bond the first wafer to the second wafer.

Description

Technical Field

[0001] The present application relates to the technical field of processing optoelectronic devices, and in particular to a heterogeneous direct bonding technology based on the pyroelectric effect, which belongs to the technical field of processing optoelectronic devices. Background Art

[0002] Bonding technology is a processing technique that emerged with the development of integrated circuits and microelectromechanical systems (MEMS). The ability to integrate numerous electrical, optical, and electro-optical components on a single platform reduces costs, increases throughput, and adds device functionality not available on standalone platforms. Fabricating optoelectronic devices using multilayer heterostructures has become a key to improving MEMS performance. Commonly used bonding techniques include anodic bonding, eutectic bonding, adhesive bonding, and direct bonding.

[0003] Anodic bonding is bonding assisted by an applied electric field. Its advantages are that it is suitable for materials that can undergo ion diffusion and has good stability and sealing properties. However, this method is not suitable for pyroelectric materials and requires accurate equipment and complex methods. Eutectic bonding is a method in which eutectic alloy atoms diffuse into the atomic structure of the material to be bonded. Adhesive bonding technology relies on the surface wetting and self-bonding forces of the adhesive to combine two different materials. Both methods introduce an intermediate layer, such as the introduction of an intermediate layer of benzocyclobutene (BCB) with a thickness of 100nm. Compared with direct bonding, the magneto-optical effect that can be obtained is greatly reduced. Direct bonding technology generally uses high temperature and high pressure or special chemical or physical treatment of the bonding surface. For some materials, such as lithium niobate and single crystal silicon, the difference in thermal expansion coefficient between the two materials is huge and cannot withstand high temperature environments. Special physical and chemical treatments require complex steps and expensive equipment. Therefore, how to develop a simpler and more effective bonding method remains an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of this application is to provide a heterogeneous direct bonding technology based on the pyroelectric effect, which is used to solve the problem that the bonding efficiency and bonding effect in the existing bonding technology need to be improved.

[0005] To achieve the above-mentioned and other related purposes, the present invention provides a heterogeneous direct bonding technology based on the pyroelectric effect, comprising the following steps:

[0006] S1: Providing a first wafer and a second wafer, wherein each of the first wafer and the second wafer has at least one smooth surface, the first wafer has a pyroelectric effect, and the melting point of the first wafer and the second wafer is above 500° C.;

[0007] S2: placing the smooth surface of the first wafer on the smooth surface of the second wafer, so that the first wafer and the second wafer form a pre-bonded body;

[0008] S3: applying pressure to the upper surface and / or lower surface of the pre-bonded body so that the pressure between the first wafer and the second wafer is between 0.025 MPa and 0.100 MPa, and heating the pre-bonded body;

[0009] S4: releasing the pressure on the pre-bonded body and cooling the pre-bonded body.

[0010] In one embodiment, the first wafer is selected from one of lithium niobate, lithium tantalate, and piezoelectric ceramics (PZT, etc.).

[0011] In one embodiment, the second wafer is selected from one of Si, SiN, and glass.

[0012] In one embodiment, step S3 includes a heating stage and a heat preservation stage.

[0013] In one embodiment, the heating rate in the heating stage is 5°C·min -1 - 20℃·min -1 The maximum temperature in the heating stage is between 150°C and 300°C.

[0014] In one embodiment, the duration of the insulation stage is in the range of 1 hour to 3 hours.

[0015] In one embodiment, the cooling process in step S4 is performed on a carrier at room temperature.

[0016] In one embodiment, the execution time of step S4 does not exceed 1 hour.

[0017] In one embodiment, the execution time of step S4 does not exceed 5 minutes.

[0018] In one embodiment, the contact area between the first wafer and the second wafer is no greater than 40 mm×40 mm.

[0019] This application proposes a heterogeneous direct bonding technology for pyroelectric materials. This bonding process primarily occurs during a rapid cooling phase. During this rapid cooling process, the pyroelectric effect of the first wafer releases a large amount of charge, forming an electrostatic attraction between the first wafer and the second wafer, causing the two wafers to bond. Compared to other methods, this method utilizes simple materials, does not require complex steps or expensive equipment for experimental testing, and is low-cost, simple to operate, and has easily adjustable process parameters. Ultimately, it can produce heterogeneous bonded pairs with high bonding rates and bond strengths that meet application standards. This high bonding rate has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings:

[0021] Figure 1 This is a flow chart of the heterogeneous direct bonding method based on the pyroelectric effect of the present invention;

[0022] Figure 2 Schematic diagram of the structure of the heterogeneous direct bonding method based on the pyroelectric effect of the present invention;

[0023] Figure 3 Schematic diagram of the heating structure of the bonding system in Example 1;

[0024] Figure 4 This is a schematic diagram of the cooling structure of the bonding system in the embodiment of the present application;

[0025] Figure 5 The natural cooling curve of the sample in Example 1 of the present application from 250°C to room temperature is shown;

[0026] Figure 6 Sample photos of Example 1;

[0027] Figure 7 is a comparison diagram between Example 1 and Example 2, wherein Figure 7 (a)(b)(c)(d) are photos of samples with the highest temperatures of 150℃, 200℃, 250℃ and 300℃ respectively. Figure 7 (e) shows the bonding rate and shear strength curve results, Figure 7 (e) Curve 1 is the bonding rate data, and curve 2 is the shear strength data;

[0028] Figure 8 is a comparison diagram between Example 1 and Example 3, as shown in Figure 8 Figures (f), (g), and (h) are photos of samples with insulation time of 1h, 2h, and 3h, respectively. Figure 8 (i) shows the bonding rate and shear strength curve results, Figure 8 (i) Curve 3 is the bonding rate data, and curve 4 is the shear strength data;

[0029] Figure 9 For comparison between Example 1 and Example 4, Figure 9 Figures (j), (k), and (l) are photos of samples with pressures of 0.025 MPa, 0.050 MPa, and 0.100 MPa between the first wafer 101 and the second wafer 102, respectively. Figure 9 (m) shows the bonding rate and shear strength curve results, Figure 9 (m) Curve 5 is the bonding rate data, and curve 6 is the shear strength data.

[0030] Reference numerals:

[0031] 101 First Wafer

[0032] 101a First wafer surface to be bonded

[0033] 101b First wafer non-bonding surface

[0034] 102 Second Wafer

[0035] 102a Second wafer surface to be bonded

[0036] 201 upper gasket

[0037] 202 lower gasket

[0038] 301 Heating device

[0039] 302 Room temperature carrier DETAILED DESCRIPTION

[0040] In order to illustrate the present invention in more detail, the technical solution of the present invention is further described below in conjunction with preferred embodiments and drawings.

[0041] refer to Figure 1-9 In this application, a heterogeneous direct bonding technology based on the pyroelectric effect is proposed, including the following steps:

[0042] S1: Providing a first wafer 101 and a second wafer 102, wherein each of the first wafer 101 and the second wafer 102 has at least one smooth surface, the first wafer 101 has a pyroelectric effect, and the melting point of the first wafer 101 and the second wafer 102 is above 500°C;

[0043] S2: placing the first wafer surface 101a to be bonded on the second wafer surface 102a to be bonded, so that the first wafer 101 and the second wafer 102 form a pre-bonded body, and both the first wafer surface 101a to be bonded and the second wafer surface 102a to be bonded are smooth surfaces;

[0044] S3: applying pressure to the upper surface and / or lower surface of the pre-bonded body so that the pressure between the first wafer 101 and the second wafer 102 is between 0.025 MPa and 0.100 MPa, and heating the pre-bonded body;

[0045] S4: releasing the pressure on the pre-bonded body and cooling the pre-bonded body.

[0046] The bonding process of the above-mentioned preparation method mainly occurs in the cooling stage of step S4. During the rapid cooling process, a large amount of charge is released due to the pyroelectric effect of the first wafer 101, forming an electrostatic attraction between the first wafer 101 and the second wafer 102, ultimately forming a heterogeneous bonded pair with a high bonding rate and a shear strength that meets the application standards. By regulating the maximum temperature of the heating stage in step S3, the length of the heat preservation stage, and the cooling execution time in step S4, the problem of heterogeneous materials cracking during the bonding process due to differences in thermal expansion coefficients can be avoided. In addition, the preparation method has simple steps, low equipment requirements, does not require a special annealing atmosphere, and the process parameters are easy to control.

[0047] The heterogeneous direct bonding process of the present invention will be described in detail below with reference to the accompanying drawings.

[0048] During the preparation process, preferably, Figure 1 In step S1, the first wafer 101 and the second wafer 102 both have at least one smooth surface as a surface to be bonded. Figure 2 The first wafer surface to be bonded 101a and the second wafer surface to be bonded 102a are shown. The first wafer 101 exhibits the pyroelectric effect, which refers to the charge release phenomenon manifested by changes in polarization intensity with temperature. When the temperature is constant, the free charges in the dielectric form a dynamic equilibrium with external conditions, resulting in a neutral state. However, once the temperature changes, the previously free charges can no longer completely shield the bound charges, and free charges appear on the surface. These free charges form an electric field in the surrounding space, attracting or repelling charged particles, creating a potential difference between the upper and lower surfaces of the crystal. If connected to an external electric field, a current can be observed in the circuit, with the current direction being opposite under heating and cooling conditions.

[0049] Specifically, first wafer 101 can be lithium niobate, lithium tantalate, or piezoelectric ceramic; second wafer 102 can be single crystal silicon, SiN, or a glass wafer. As described in the background, differences in thermal expansion coefficients between heterogeneous materials can lead to cracking at high temperatures. Currently, a low-temperature direct bonding process is used to overcome this problem, producing a complete heterostructure. To ensure that first wafer 101 and second wafer 102 do not melt during the low-temperature bonding process, the melting points of first wafer 101 and second wafer 102 are above 500°C.

[0050] In addition, the first wafer 101 can be made of any pyroelectric material known to those skilled in the art, and is not limited to the above materials.

[0051] Then, if Figure 1 In step S2, the first wafer 101 and the second wafer 102 both have smooth and clean polished surfaces, so that the first wafer surface 101a to be bonded is placed on the second wafer surface 102a to be bonded, so that the first wafer 101 and the second wafer 102 form a pre-bonded body. Figure 2 Specifically, the surface roughness of the first wafer surface 101a and the second wafer surface 102a is less than 3 nm. Microscopically, there is an air gap between the first wafer 101 and the second wafer 102 in the pre-bonded body, and its length is x.

[0052] In addition, the cleaning process before bonding is crucial. Foreign contamination particles on the bonding surface will cause the bonding surface to be uneven. On the other hand, the presence of contaminants will increase the air gap distance x between the first wafer 101 and the second wafer 102. Specifically, step S1 includes the following cleaning steps for the first wafer 101 and the second wafer 102:

[0053] S101: ultrasonically cleaning the first wafer 101 and the second wafer 102 alternately using ethanol and acetone;

[0054] S102 : Rinse the first wafer 101 and the second wafer 102 after ultrasonic treatment with deionized water, and then dry the first wafer 101 and the second wafer 102 with inert gas.

[0055] After the above cleaning steps, their surface roughness can be reduced to less than 3 nm.

[0056] In some instances, such as Figure 2 As shown, there is an air gap between the first wafer 101 and the second wafer 102. The length x of the air gap is the distance between the two wafers. The potential difference between the relative positions of the air gap is V gap , the attraction per unit bonding interface area is the electrostatic attraction P, Among them E gap is the local electrostatic field in the air gap, ε0 is the dielectric constant of vacuum (8.854187817×10 -12 F·m -1 ). Assume that the voltage V gap is 200V, and the air gap length x is 2μm, then the electrostatic field strength E in the air gap is gap 100 MV·m -1 , the electrostatic attraction force is about 0.045MPa.

[0057] This formula shows that the electrostatic attraction pulling the first wafer 101 and the second wafer 102 closer together is proportional to the square of the potential difference between their relative positions in the air gap, and inversely proportional to the square of the air gap length. Therefore, the cleaning process before bonding is crucial. The presence of foreign contaminants on the bonding surface increases the air gap distance x between the first wafer 101 and the second wafer 102, significantly weakening the electrostatic attraction within a certain area and leading to the formation of a large bonding void.

[0058] Continuing, in some embodiments, the bonded body is heated in step S3, and the heating is divided into a heating stage and a heat preservation stage. The heating rate in the heating stage is 5°C·min -1 -20℃·min -1 When the first wafer 101 is heated or cooled, the polarization electric field strength of the crystal will change. At this time, the current density J on the surface of the first wafer 101 satisfies the relationship This means that the faster the temperature changes per unit time, the higher the surface current density of the first wafer 101, that is, the greater the amount of charge released per unit time. Specifically, during the heating stage, the first wafer surface 101a to be bonded is negatively charged, and the first wafer non-bonding surface 101b is positively charged. When the heating rate is low, the surface current density of the induced charge generated by the first wafer surface 101a to be bonded and the second wafer surface 102a to be bonded is low, so the voltage V between the first wafer surface 101a to be bonded and the second wafer surface 102a to be bonded is gap The electrostatic attraction is also small, and the bonding is not sufficient during the heating process. Preferably, the heating rate of the pre-bonded body is 10℃·min -1 .

[0059] In some embodiments, the temperature is raised to between 150°C and 300°C during the heating phase in step S3. When the pre-bonded body is heated or cooled, the change in the polarization intensity ΔPs of the first wafer 101 is proportional to the temperature, satisfying the relationship ΔPs = γΔT, where γ is the pyroelectric coefficient of the first wafer 101. This means that the greater the temperature change ΔT, the greater the change in polarization intensity, that is, the greater the amount of charge released. When the temperature change amplitude is a constant value, the change in polarization intensity is a constant value, and the amount of charge released is the same. The maximum temperature to which the temperature is raised must ensure that sufficient charge can be released during the subsequent cooling phase in step S4 to facilitate bonding. Further preferably, the temperature is raised to 250°C during the heating phase.

[0060] In some embodiments, during the heating phase in step S3, pressure is applied to the upper and / or lower surfaces of the pre-bonded structure, such that the preferred pressure between the first wafer 101 and the second wafer 102 is between 0.025 MPa and 0.100 MPa. Using an appropriate pressure, the air gap distance x between the first wafer 101 and the second wafer 102 is moderate, thereby moderately affecting the electrostatic force between the two wafers, thereby forming a complete, high-bonding-ratio bonded structure. In the present application, the preferred pressure between the first wafer 101 and the second wafer 102 is between 0.040 MPa and 0.070 MPa, and more preferably, the pressure is 0.050 MPa.

[0061] In some embodiments, the holding period during the heating phase in step S3 is maintained for 1-3 hours. The longer the holding period, the shorter the air gap distance x between the first wafer 101 and the second wafer 102 under pressure, i.e., the holding period must be maintained at a moderate duration. More preferably, the holding period is 2 hours.

[0062] Finally, in some embodiments, during the cooling process described in step S4, when the pressure between the first wafer 101 and the second wafer 102 is released, bonding has not yet occurred between the pre-bonded bodies. After the pressure is released, the pre-bonded bodies are cooled, and the bonding effect occurs during the cooling stage. Preferably, the cooling process is performed on a support 302 at room temperature, that is, the pre-bonded bodies are transferred to the support 302 at room temperature. When the temperature drops to near room temperature, a good bonding effect is achieved. Typically, the cooling process lasts less than 1 hour. Under normal room temperature conditions, the temperature of the pre-bonded bodies can be reduced to near room temperature within 5 minutes to obtain a bonded body. In this embodiment, the support 302 should be clean and have good electrical and thermal conductivity.

[0063] Specifically, during the cooling process described in step S4, the longer the execution time, the smaller the temperature change rate. Conversely, the shorter the execution time, the higher the temperature change rate, the greater the current density on the first wafer surface 101a to be bonded, the greater the current density of the induced charge generated on the second wafer surface 102a to be bonded, and the greater the electrostatic attraction between the first wafer 101 and the second wafer 102. However, excessive electrostatic attraction may cause the bonded pair to break.

[0064] In summary, the execution time of the cooling process does not exceed 1 hour. More preferably, the execution time of the cooling process does not exceed 5 minutes.

[0065] In addition, during the cooling process, positive charges are generated near the bonding surface 101a of the first wafer, and negative charges are generated near the non-bonding surface 101b, which are exactly opposite in polarity to the charges generated during the heating process in step S3. During the entire bonding process, the temperature must start from room temperature and eventually return to room temperature. If bonding is achieved in step S3, the charges of opposite polarity released by the first wafer 101 in step S4 will inevitably have a counter-effect on the bonding, or even cause debonding. Therefore, a slow heating and rapid cooling method is adopted, so that the bonding process occurs primarily during the cooling process in step S4.

[0066] In some embodiments, the contact area between the first wafer 101 and the second wafer 102 is arbitrary. Preferably, the contact area between the first wafer 101 and the second wafer 102 is at most 40 mm × 40 mm. Excessive contact area will cause air to be trapped in the air gap during wafer bonding, resulting in a decrease in bonding rate. Preferably, the contact area between the first wafer 101 and the second wafer 102 is 20 mm × 20 mm. In this application, there is no restriction on the shape of the first wafer 101 and the second wafer 102. They can be circular, elliptical, rectangular or other curved shapes and polygons.

[0067] The technical solution of the present invention is further described below with reference to the embodiments:

[0068] Example 1

[0069] A 128° YX-cut lithium niobate wafer is used as the first wafer 101, with a P-type orientation of <100> The double-polished silicon wafer is used as the second wafer 102, and its thickness is 500 μm. The wafer is cut into regular 20 mm × 20 mm pieces using a dicing machine;

[0070] A first wafer 101 and a second wafer 102 of 20 mm x 20 mm size were ultrasonically treated in acetone for 15 minutes to remove organic contaminants, and then ultrasonically treated in anhydrous ethanol for 15 minutes to remove inorganic contaminants on the bonding surface. The wafers were then rinsed with deionized water and dried with nitrogen. The cleaned first wafer surface 101a and the second wafer surface 102a were placed opposite each other to form a pre-bonded body.

[0071] like Figure 3 As shown, a 4-inch silicon wafer is placed on the top of the pre-bonded body as an upper gasket 201, and a 2kg weight is added to the upper gasket 201 to make the pressure between the pre-bonded bodies at 0.050 MPa. The purpose of the upper gasket 201 is to make the pre-bonded body bear the force evenly. In order to ensure the cleanliness of the pre-bonded body, a 4-inch silicon wafer is placed under the pre-bonded body as a lower gasket 202. At the same time, the pre-bonded body is heated using a heating device 301 at a heating rate of 10°C min -1 , raise the temperature to 250°C and maintain at this temperature for 2 hours;

[0072] like Figure 4 As shown, the pressure on the pre-bonded body is released, and the pre-bonded body is transferred to a table covered with aluminum foil, that is, a room temperature carrier 302 for rapid cooling. The cooling process takes a total of 2 minutes. During the cooling process, bonding is completed. The real-time temperature is recorded using an infrared camera. The cooling curve is as follows: Figure 5 As shown, it is the real-time temperature curve from 250℃ to room temperature.

[0073] Example 2

[0074] The only difference between Example 2 and Example 1 is that the maximum temperature of the pre-bonded body is 150° C., 200° C., and 300° C., respectively. Other bonding conditions are the same as those in Example 1.

[0075] Example 3

[0076] The only difference between Example 3 and Example 1 is that the duration of the pre-bonding body heat preservation stage is 1 hour and 3 hours. Other bonding conditions are the same as those in Example 1.

[0077] Example 4

[0078] The only difference between Example 4 and Example 1 is that the pressures between the first wafer 101 and the second wafer 102 in the pre-bonded body are 0.025 MPa and 0.100 MPa respectively. Other bonding conditions are the same as those in Example 1.

[0079] The bonding rate was calculated for each example, using shear strength as a criterion for bonding strength.

[0080] refer to Figure 6 , is a photo of the sample after bonding. After testing, the bonding rate is 97.73% and the shear strength is 2.09MPa.

[0081] Figure 7 For the comparison between Example 1 and Example 2, Figure 7 (a)(b)(c)(d) are photos of samples with the highest temperatures of 150℃, 200℃, 250℃ and 300℃ respectively. Figure 7 (e) shows the bonding rate and shear strength curve results, Figure 7 (e) Curve 1 shows the bonding rate data, and Curve 2 shows the shear strength data. When the heating time is 2 hours and the pressure is 2 kg, the shear strength is directly proportional to the maximum temperature. However, the bonding rate decreases significantly when the temperature increases from 250°C to 300°C. This is because the electrostatic pulses are not generated uniformly but are randomly distributed at any position on the plane. During the bonding process, the excessively large electrostatic pulses shatter the first wafer 101, allowing air to enter the gap between the first wafer 101 and the second wafer 102, resulting in voids.

[0082] Figure 8 For the comparison between Example 1 and Example 3, Figure 8 Figures (f), (g), and (h) are photos of samples with insulation time of 1h, 2h, and 3h, respectively. Figure 8 (i) shows the bonding rate and shear strength curve results, Figure 8 (i) Curve 3 shows the bonding rate data, and Curve 4 shows the shear strength data. Both the bonding rate and shear strength reached their maximum values at a holding time of 2 hours. At a holding time of 1 hour, the negative charge generated on the polished surface of first wafer 101 had not fully dissipated, and the distance between first wafer 101 and second wafer 102 was relatively large. As a result, after the holding temperature was increased, the positive charge on the bonding surface 101a of the first wafer was first neutralized by the existing negative charge during the cooling process. This then interacted with the image charge generated on the bonding surface 102a of the second wafer, generating an electrostatic pulse that brought them closer together. Consequently, both the bonding rate and shear strength improved to a certain extent. However, when the holding time was increased from 2 hours to 3 hours, the distance between first wafer 101 and second wafer 102 became too small under the current temperature conditions. The lithium niobate in first wafer 101 could not withstand the gravitational force of the electrostatic pulse, resulting in fragmentation. This fragmentation, in turn, caused bonding failure in some areas.

[0083] Figure 9 For the comparison between Example 1 and Example 4, Figure 9 Figures (j), (k), and (l) are photos of samples with pressures of 0.025 MPa, 0.050 MPa, and 0.100 MPa between the first wafer 101 and the second wafer 102, respectively. Figure 9 (m) shows the bonding rate and shear strength curve results, Figure 9 (m) Curve 5 is the bonding rate data, and curve 6 is the shear strength data. When the pressure is 0.025MPa, lithium niobate as the first wafer 101 can show clear stress waves, which is the result of electrostatic attraction during the bonding process. When the temperature and heating time are consistent, lithium niobate and silicon cannot bond, and only a few stress ripples are shown, indicating that the large air gap spacing caused by too little pressure during the heating process is one of the factors that determine whether the subsequent bonding can be successful. The highest bonding rate is 100%. In this group of experiments, when the pressure was 0.050MPa and 0.100MPa, the bonding rate reached more than 97%. In the absence of an intermediate layer between the two substances, it is a very high bonding rate. After the pressure is increased, the bonding rate remains at the same level, and the shear strength has a limited improvement.

[0084] Finally, it should be noted that the above-described embodiments are merely preferred examples for clearly illustrating the present invention, but this does not limit the implementation scheme of the present invention. Those skilled in the art should understand that the technical features in the above schemes can be arbitrarily combined, and other different forms of modifications or equivalent replacements of some technical features can be made on the basis of the above-mentioned specific implementation schemes. It is impossible to enumerate all implementation schemes here. Therefore, all modifications, improvements, equivalent replacements, etc. derived from the technical scheme of the present invention within the spirit and principles of the present invention should be within the technical scope of the present invention.

Claims

1. A heterogeneous direct bonding technology based on pyroelectric effect, characterized by The following steps are involved: S1: Providing a first wafer and a second wafer, wherein each of the first wafer and the second wafer has at least one smooth surface, the first wafer has a pyroelectric effect, and the melting point of the first wafer and the second wafer is above 500° C.; S2: placing the smooth surface of the first wafer on the smooth surface of the second wafer, so that the first wafer and the second wafer form a pre-bonded body; S3: applying pressure to the upper surface and / or lower surface of the pre-bonded body so that the pressure between the first wafer and the second wafer is between 0.025 MPa and 0.100 MPa, and heating the pre-bonded body; S4: releasing the pressure on the pre-bonded body and cooling the pre-bonded body, wherein the cooling time does not exceed 1 hour.

2. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 1, characterized in that: The first wafer is selected from one of lithium niobate, lithium tantalate, and piezoelectric ceramics.

3. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 1, characterized in that: The second wafer is selected from one of Si, SiN and glass.

4. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 1, characterized in that: The step S3 includes a heating stage and a heat preservation stage.

5. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 4, characterized in that: The heating rate in the heating stage is between 5°C·min-1 and 20°C·min-1, and the maximum temperature in the heating stage is between 150°C and 300°C.

6. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 5, characterized in that: The duration of the insulation stage is within the range of 1 hour to 3 hours.

7. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 1, characterized in that: The cooling process in step S4 is performed on the support at room temperature.

8. The heterogeneous direct bonding technology based on pyroelectric effect according to claim 1, characterized in that: The contact area between the first wafer and the second wafer is no greater than 40 mm×40 mm.

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