Bonding packaging method of lithium niobate / lithium tantalate single crystal cavity structure and application of bonding packaging method

Abstract

The invention discloses a bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure and application of the bonding packaging method, and belongs to the technical field of semiconductor bonding packaging. The method comprises the steps that a cavity structure layer is provided, and at least one concave cavity is formed in the surface of one side of the cavity structure layer; providing a slide glass, and preparing a bonding glue layer on the surface of one side of the slide glass; one of the cavity structure layer and the slide glass is made of a lithium niobate single crystal or a lithium tantalate single crystal; carrying out pre-curing treatment on the bonding glue layer so as to form a pre-curing area in an area corresponding to the concave cavity in the bonding glue layer; and aligning and bonding the slide glass and the cavity structure layer to enable the pre-curing area to cover the opening end of the corresponding concave cavity, and then performing complete curing treatment on the bonding glue layer with the pre-curing area to form a bonding layer. According to the method, the bonding strength is ensured while the cavity is kept, cavity blockage caused by overflow of the bonding glue in the pressurized bonding process is effectively prevented, and the packaging requirement of a micro electro mechanical system device with a complex cavity structure can be met.

Description

TECHNICAL FIELD

[0001] The application relates to a bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure and application thereof, and belongs to the technical field of semiconductor bonding packaging. BACKGROUND

[0002] In the field of semiconductor manufacturing and advanced packaging, the bonding technology of cavity structure is crucial for protecting sensitive components such as Micro-Electro-Mechanical System (MEMS) sensors, radio frequency devices and optical elements, which can effectively isolate external humidity and particle pollution, and provide necessary mechanical freedom for movable structures. With the development of technologies such as Internet of Things, 5G communication and autonomous driving, the market demand for high reliability and high airtightness cavity packaging is increasing.

[0003] At present, common cavity bonding methods include anodic bonding, eutectic bonding, direct bonding and polymer adhesion, etc. Anodic bonding is suitable for bonding of glass and silicon, and has the advantages of high airtightness and good mechanical strength, but is limited by material combination, and high temperature (300-450℃) and high voltage electric field may cause damage to heat-sensitive devices. Eutectic bonding uses low-melting-point alloys (such as Au-Si and Sn-Ag) to achieve bonding, which has high bonding strength and is suitable for various metalized surfaces, but the difference in thermal expansion coefficient of the metal layer may introduce stress, affecting the long-term stability of the cavity structure, and the process temperature (usually 200-400℃) is still relatively high. Direct bonding (such as silicon fusion bonding) can achieve a high-strength bonding interface without the need for an intermediate layer, and has excellent airtightness and thermal stability, but it has very high requirements for surface roughness and cleanliness, and usually requires high-temperature (>800℃) annealing, which limits its application in low-temperature sensitive devices. These limitations make it difficult for existing technologies to balance low temperature and high compatibility while ensuring bonding quality. In contrast, polymer adhesion (such as benzocyclobutene resin (BCB) and epoxy resin) has a low process temperature (<250℃), is compatible with a variety of materials and has relatively low requirements for surface flatness, but due to the flowability of the adhesive, the polymer can easily penetrate into the channel during pressure bonding, causing the cavity to be blocked and affecting the performance of the device. SUMMARY

[0004] In order to solve the problem that the existing bonding technology of cavity structure in the field of semiconductor manufacturing and advanced packaging cannot balance low temperature and high compatibility while ensuring bonding quality and maintaining the integrity of the cavity, the application provides a bonding packaging technology of a lithium niobate / lithium tantalate single crystal cavity structure, which forms a pre-solidification area capable of covering the concave cavity by pre-solidifying the bonding adhesive, and then performs global secondary solidification after bonding, to solve the above technical problems.

[0005] The application adopts the following technical solutions:

[0006] According to a first aspect of this application, a bonding and encapsulation method for a cavity structure is provided, comprising:

[0007] A cavity structure layer is provided, wherein at least one cavity is formed on one side surface of the cavity structure layer;

[0008] A carrier is provided, and a bonding adhesive layer is prepared on one side of the carrier.

[0009] The cavity structure layer and the carrier are both made of lithium niobate single crystal or lithium tantalate single crystal.

[0010] The bonding adhesive layer is pre-cured so that at least a portion of the bonding adhesive layer forms a pre-cured area;

[0011] The carrier is aligned and bonded to the cavity structure layer so that the pre-cured area covers the opening end of the corresponding cavity, and the bonding adhesive layer with the pre-cured area is fully cured to form a bonding layer.

[0012] Optionally, the pre-curing treatment of the bonding adhesive layer includes:

[0013] The bonding adhesive layer is pre-cured either as a whole or selectively.

[0014] Optionally, the bonding adhesive layer is made of a photocurable adhesive.

[0015] Optionally, the selective pre-curing includes:

[0016] The area corresponding to the cavity in the bonding adhesive layer is pre-cured by using mask exposure or laser direct writing to form a pre-cured area.

[0017] Optionally, the thickness of the bonding layer is 0.5-10 μm.

[0018] Optionally, the bonding adhesive layer is further dispersed and filled with photochromic powder.

[0019] Optionally, the material of the cavity structure layer and the other of the carrier wafers is selected from monocrystalline silicon, polycrystalline silicon, and glass.

[0020] Optionally, at least one of the cavity structure layer and the carrier is a wafer or a thin film.

[0021] Optionally, at least one of the cavity structure layer and the carrier is subjected to double-sided polishing.

[0022] According to a second aspect of this application, an application of the above-described cavity structure bonding and packaging method in the fabrication or packaging of microelectromechanical system devices is provided.

[0023] The beneficial effects of this application include:

[0024] The bonding and encapsulation method for lithium niobate / lithium tantalate single-crystal cavity structures provided in this application establishes a protective barrier for the cavity region during the bonding process through pre-curing treatment, ensuring the bonding strength of the device and effectively preventing cavity blockage caused by bonding adhesive overflow during pressure bonding. Furthermore, selective curing is employed for pre-curing treatment to ensure the bonding strength of the remaining bonding adhesive, maintaining the integrity of the cavity while guaranteeing the overall bonding strength of the device. The bonding and encapsulation method for lithium niobate / lithium tantalate single-crystal cavity structures provided in this application is suitable for the packaging requirements of microelectromechanical systems (MEMS) devices with complex cavity structures, providing a new technical approach for the reliable packaging of high-precision micro / nano devices. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the bonding and packaging method for the lithium niobate / lithium tantalate single-crystal cavity structure of this application;

[0026] Figure 2 This is a cross-sectional schematic diagram of the bonded lithium niobate / lithium tantalate single-crystal cavity structure in Comparative Example 1 of this application;

[0027] Figure 3 This is a cross-sectional schematic diagram of the bonded lithium niobate / lithium tantalate single-crystal cavity structure in Embodiment 1 of this application;

[0028] Figure 4 This is a schematic flowchart of the bonding and encapsulation method for the lithium niobate / lithium tantalate single-crystal cavity structure in Embodiment 2 of this application;

[0029] Figure 5 This is a cross-sectional schematic diagram of the substrate with a pre-cured bonding layer before bonding in Embodiment 2 of this application;

[0030] Figure 6 This is a cross-sectional schematic diagram of the bonded lithium niobate / lithium tantalate single-crystal cavity structure in Embodiment 2 of this application. Detailed Implementation

[0031] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0032] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0033] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0034] Currently, common cavity bonding methods include anodic bonding, eutectic bonding, direct bonding, and polymer bonding, but these technologies all have certain limitations. For example, anodic bonding is only suitable for specific material combinations, and high-temperature processes may affect device performance; while eutectic bonding can achieve high strength, the thermal stress of the metal layer may reduce the airtightness of the cavity; direct bonding requires extremely high surface flatness and cleanliness, and usually requires high-temperature annealing, resulting in high process costs; although polymer bonding has a lower process temperature, the fluidity of the bonding adhesive during pressure bonding can easily cause cavity blockage. These limitations make it difficult for existing technologies to simultaneously ensure bonding quality while meeting the requirements of low temperature, high compatibility, and maintaining cavity integrity.

[0035] To address the aforementioned technical issues, this application proposes a bonding and packaging technology for lithium niobate / lithium tantalate single-crystal cavity structures. This technology aims to reduce process complexity while maintaining bonding strength to meet the application requirements of advanced semiconductor cavity structure bonding and packaging. The technology first pre-cures the bonding adhesive to reduce its flowability and prevent it from blocking the cavity structure during subsequent bonding. Alternatively, photomask technology can be used to selectively cure and cover the periphery of the via, forming a precise pre-cured area. After bonding is completed, a global secondary curing process is performed. These two step-by-step processes have the following significant advantages: (1) they maintain the cavity while ensuring bonding strength; (2) they effectively prevent cavity blockage caused by bonding adhesive overflow during pressure bonding; and (3) they are particularly suitable for the packaging needs of microelectromechanical systems (MEMS) devices with complex cavity structures, providing a new technical approach for reliable packaging of high-precision micro / nano devices.

[0036] According to one embodiment of this application, a bonding and encapsulation method for a lithium niobate / lithium tantalate single-crystal cavity structure is provided, such as... Figure 1 As shown, it includes:

[0037] S1. A cavity structure layer is provided, wherein at least one cavity is formed on one side surface of the cavity structure layer;

[0038] S2. Provide a carrier sheet, and prepare a bonding adhesive layer on one side of the carrier sheet;

[0039] The cavity structure layer and the carrier are made of lithium niobate single crystal or lithium tantalate single crystal, with the lithium niobate single crystal or lithium tantalate single crystal serving as the functional layer.

[0040] S3. The bonding adhesive layer is pre-cured so that at least a portion of the area in the bonding adhesive layer corresponding to the cavity forms a pre-cured area;

[0041] S4. Align and bond the carrier with the cavity structure layer so that the pre-cured area covers the opening end of the corresponding cavity, and fully cure the bonding adhesive layer with the pre-cured area to form a bonding layer.

[0042] In one embodiment, the pre-curing treatment of the bonding adhesive layer includes:

[0043] The bonding adhesive layer is pre-cured either entirely or selectively. The pre-curing process aims to reduce the flowability of the bonding layer. Selective curing covers the periphery of the cavity, creating a precise pre-cured area to facilitate alignment and bonding of the substrate with the cavity structure layer. Simultaneously, selective pre-curing ensures the bonding strength of the remaining bonding layer material, maintaining the integrity of the cavity while guaranteeing the overall bonding strength of the device.

[0044] In one embodiment, the bonding adhesive layer is made of a photocurable adhesive. Using a photocurable adhesive, combined with a photomask, allows for selective pre-curing of specific areas. In contrast, thermocurable adhesives typically require heating the entire single crystal, making precise pre-curing of specific areas on the single crystal difficult.

[0045] In one embodiment, the material of the bonding layer is selected from debonded photocurable adhesive or non-debonded photocurable adhesive.

[0046] In one embodiment, the selective pre-curing includes:

[0047] The area corresponding to the cavity in the bonding adhesive layer is pre-cured using either mask exposure or laser direct writing to form a pre-cured region. Parameters such as laser intensity and exposure time are used to control the curing degree of the pre-cured region. When the pre-curing process is selective, a mask can be used for exposure.

[0048] In one embodiment, the thickness of the bonding layer is 0.5-10 μm. A suitable bonding layer thickness ensures bonding quality; an excessively thin layer may result in uneven adhesive coverage, insufficient bonding strength, or unbonded areas. Conversely, an excessively thick layer may cause the adhesive cohesion to be lower than the interfacial adhesion, leading to cohesive failure and increased curing shrinkage stress. The bonding layer can be obtained by spin-coating the bonding adhesive onto the cleaned substrate surface using a spin-coating method, followed by curing. The thickness of the bonding adhesive layer can be controlled by the spin-coating speed.

[0049] In one embodiment, the bonding adhesive layer is further dispersed and filled with photochromic powder. The bonding adhesive is typically transparent, making it difficult to distinguish the pre-cured and uncured areas under a microscope. By mixing a small amount of photochromic powder into the bonding adhesive, the color distinction between the pre-cured and uncured areas can be effectively achieved.

[0050] In one embodiment, the cavity structure layer and the other of the carrier wafers are made of a material selected from monocrystalline silicon, polycrystalline silicon, and glass, serving as a support layer. The combination of the carrier wafer and the cavity structure layer can be lithium tantalate monocrystalline / silicon wafer, lithium niobate monocrystalline / silicon wafer, lithium niobate monocrystalline / glass wafer, silicon wafer / lithium tantalate monocrystalline, silicon wafer / lithium niobate monocrystalline, etc.

[0051] Since the cavity structure is mostly used in piezoelectric MEMS device structures, at least one layer of the carrier and cavity structure layer must be a lithium niobate / lithium tantalate single crystal with good piezoelectric properties. In addition, the lithium niobate / lithium tantalate single crystal has good light transmittance, which can meet the requirements for subsequent photopolymerization.

[0052] In one embodiment, at least one of the cavity structure layer and the carrier is a wafer or a thin film. The wafer or thin film form makes it suitable for the fabrication of specific devices, such as microfluidics, mechano-ultrasonic transducers, and surface acoustic wave devices.

[0053] In one embodiment, at least one of the cavity structure layer and the substrate is subjected to double-sided polishing. The purpose of double-sided polishing is twofold: to improve permeability and to ensure better bonding after polishing. The polishing process also includes ultrasonic cleaning of the substrate sequentially with acetone, alcohol, and water after polishing.

[0054] In one embodiment, the horizontal cross-sectional shape of the cavity is selected according to the function to be achieved by the device. For example, it can be selected from circular, square, or interdigitated shapes. For microfluidic devices, a square cavity structure layer is usually adopted, while for planar piezoelectric MEMS devices, an interdigitated shape may be adopted.

[0055] This application also provides an application of the aforementioned cavity structure bonding and packaging method in the fabrication and packaging of microelectromechanical system (MEMS) devices. The cavity structure bonding and packaging method of this application is suitable for the packaging needs of MEMS devices with complex cavity structures.

[0056] Comparative Example 1

[0057] The typical bonding and packaging method for cavity structures in the prior art involves the following steps:

[0058] Step S1: Using a lithium tantalate single crystal as a carrier, the 500-micrometer-thick lithium tantalate single crystal is ultrasonically cleaned for 5-15 minutes using acetone, alcohol, and deionized water, respectively, and then dried with a nitrogen gun. A layer of resin adhesive is spin-coated onto the surface of the carrier as a bonding layer using a spin coater. The thickness of the bonding layer is controlled within the range of 0.5-10 μm. The material of the bonding layer is selected from organic adhesives, resin adhesives, etc.

[0059] Step S2: After aligning the carrier wafer with the cavity structure layer, place it in a bonding machine for bonding. Due to the fluidity of the bonding adhesive, some adhesive may inevitably overflow into the cavity structure during the pressure bonding process. The bonded wafer is then exposed to achieve complete curing of the bonding adhesive. A cross-sectional schematic diagram of the bonded cavity structure is shown below. Figure 1 As shown, because the bonding adhesive has a certain fluidity, it is easily squeezed into the cavity structure when it is bonded under pressure with the cavity structure layer, which can block the cavity and affect the device performance.

[0060] Example 1

[0061] Step S1: Using a lithium tantalate single crystal as a carrier, the double-sided polished lithium niobate single crystal is ultrasonically cleaned for 5-15 minutes using acetone, alcohol, and deionized water, respectively, followed by drying with a nitrogen gun. A layer of resin adhesive is spin-coated onto the carrier surface as a bonding layer using a spin coater. The thickness of the bonding layer is controlled within the range of 0.5-10 μm. The material of the bonding layer is selected from photocurable adhesives such as organic glue and resin adhesive.

[0062] Step S2: Subsequently, the bonding adhesive on the substrate surface is pre-cured using exposure or laser direct writing. The degree of pre-curing of the bonding adhesive is adjusted and controlled by parameters such as the laser intensity and exposure time used for exposure, thereby reducing the fluidity of the bonding adhesive. In the pre-cured state, the fluidity of the bonding adhesive is reduced, making it less likely to block gaps during subsequent bonding processes;

[0063] Step S3: After aligning the pre-cavity structure layer of the carrier wafer, place it in the bonding machine for bonding. Subsequently, expose the bonded wafer to achieve complete curing of the bonding adhesive. A cross-sectional schematic diagram of the bonded cavity structure is shown below. Figure 3 As shown, because the bonding adhesive was pre-cured to reduce its fluidity, it was able to maintain its shape and was not pressed into the cavity structure when it was pressure bonded to the cavity structure layer.

[0064] Example 2

[0065] To further improve the bonding strength of the bonded sheets, bonding can be performed using a zone curing method, as shown in the flowchart below. Figure 4 As shown, the specific implementation steps are as follows:

[0066] Step S1: The bonding adhesive is usually transparent, making it difficult to distinguish the pre-cured and uncured areas under a microscope. By mixing a small amount of photochromic powder into the bonding adhesive, the color distinction between the pre-cured and uncured areas can be effectively achieved. A layer of photochromic bonding adhesive is spin-coated onto the surface of a double-sided polished substrate using a spin coater. The substrate is then patterned using mask exposure or laser direct writing to prepare the pre-cured area. The substrate can be a double-sided polished transparent sample such as lithium tantalate single crystal or lithium niobate single crystal. The shape of the pre-cured area can be consistent with the shape of the cavity structure and slightly larger than the cavity structure layer. It can also be any shape, such as rectangle or circle, with an area larger than the cavity structure area. A cross-sectional diagram of the substrate with the pre-cured bonding layer before bonding is shown below. Figure 4 As shown, a pre-cured area is formed in the bonding layer;

[0067] Step S2: Since the selected substrate is transparent, the pattern of the pre-cured area can be observed from the side of the substrate that is not coated with adhesive. Cover it on the cavity structure layer and align the device structure under a yellow light microscope.

[0068] Step S3: After alignment, place the bonded sheet in the bonding machine for bonding. After bonding, expose the bonded sheet to achieve complete curing of the bonding adhesive. A cross-sectional schematic diagram of the bonded cavity structure is shown below. Figure 6 As shown, the pre-planned area covers the concave cavity opening end of the cavity structure layer.

[0069] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A bonding encapsulation method of a lithium niobate / lithium tantalate single crystal cavity structure, characterized by, The application relates to a bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure. Providing a cavity structure layer, at least one concave cavity being formed on one side of the cavity structure layer; Providing a slide and preparing a bonding glue layer on one side of the slide; One of the cavity structure layer and the slide is made of lithium niobate single crystal or lithium tantalate single crystal; Pre-solidifying the bonding glue layer to form a pre-solidification area in at least part of the bonding glue layer; Aligning and bonding the slide and the cavity structure layer to cover the opening end of the concave cavity with the pre-solidification area, and completely solidifying the bonding glue layer to form a bonding layer.

2. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, The pre-solidification of the bonding glue layer comprises: The bonding glue layer is pre-solidified as a whole or is selectively pre-solidified.

3. The bonded package method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 2, characterized by, The bonding glue layer is made of light-curing glue.

4. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 2, characterized in that, The selective pre-solidification comprises: The bonding glue layer is pre-solidified in the area corresponding to the concave cavity by using a mask exposure or a laser direct writing method to form a pre-solidification area.

5. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, The thickness of the bonding layer is 0.5-10 mu m.

6. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, The bonding glue layer is also filled with photochromic powder.

7. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, The other of the cavity structure layer and the slide is made of one of single crystal silicon, polycrystalline silicon and glass.

8. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, At least one of the cavity structure layer and the slide is a wafer or a film.

9. The bonding packaging method of a lithium niobate / lithium tantalate single crystal cavity structure according to claim 1, characterized in that, At least one of the cavity structure layer and the slide is subjected to double-side polishing treatment.

10. Application of the bonding packaging method of the lithium niobate / lithium tantalate single crystal cavity structure in claim 1 to 9 in the preparation or packaging of a micro-electro-mechanical system device.

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