A multi-source heterogeneous material wafer and wafer synchronous bonding method
By thinning and adjusting the pressure to achieve coplanarization of heterogeneous material wafers, the problems of low bonding efficiency and high damage risk of multiple heterogeneous material wafers on the same target wafer are solved, realizing efficient and low-damage synchronous bonding.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- PENG CHENG LAB
- Filing Date
- 2026-06-23
- Publication Date
- 2026-07-21
AI Technical Summary
In existing technologies, bonding multiple heterogeneous material wafers on the same target wafer suffers from low efficiency, poor coplanarity, and high risk of damage, especially in batch bonding and plasma activation processes, which are difficult to meet the needs of large-scale production.
By thinning the substrate of the wafer to be bonded, adjusting the placement pressure of the heterogeneous material wafers, and using a temporary bonding adhesive layer, multiple heterogeneous material wafers can be made coplanar and simultaneously bonded to the target wafer in a vacuum environment, reducing the number of plasma activation processes.
It improves bonding efficiency, reduces damage risk, and ensures close contact and uniformity between multiple heterogeneous material wafers and the target wafer, meeting the needs of large-scale production.
Smart Images
Figure CN122438599A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the semiconductor field, and in particular to a method for synchronous bonding of multi-source heterogeneous material wafers and wafers. Background Technology
[0002] Bonding technology is the main technique for heterogeneous integration of non-silicon heteromaterials with silicon wafers. For example, various non-silicon materials with excellent optoelectronic properties, such as III-V epitaxial wafers, lithium niobate, lithium tantalate, and germanium, can be heterogeneously integrated with silicon wafers to construct functionally rich heterogeneous integrated silicon photonic chips. However, in the fabrication of heterogeneous integrated silicon photonic chips, non-silicon material wafers are small in size and expensive. If wafer-to-wafer direct bonding is performed with large-size silicon wafers, significant size mismatch problems will be encountered, resulting in low wafer utilization and serious cost waste.
[0003] Wafer-level die-to-wafer bonding dicing of non-silicon wafers into small wafers, attaching them to a carrier wafer using temporary bonding adhesive, and then directly bonding the carrier wafer with the wafers to the target silicon wafer, selectively transferring the non-silicon wafers to areas requiring bonding. This die-to-wafer bonding significantly improves the utilization rate of expensive non-silicon materials. Currently, this bonding method can only bond one type of heteromaterial wafer to a silicon wafer at a time. If multiple heteromaterial wafers need to be directly bonded to the same silicon wafer, multiple batch bonding operations are required. However, this batch bonding process has the following problems: First, batch bonding is time-consuming and inefficient, making it difficult to meet the needs of large-scale production; Second, there are thickness differences between different wafers, and even wafers made of the same material can have uneven thickness, inconsistent placement, and poor coplanarity due to process fluctuations, which makes it impossible to achieve tight contact between the surface of all wafers and the target silicon wafer during bonding; Third, when using plasma-activated hydrophilic direct bonding technology, the bonding of each type of wafer in different batches requires a plasma activation treatment of the target silicon wafer. Each treatment will damage the target silicon wafer, and the accumulated damage from multiple treatments will increase the risk of bonding interface failure, thereby affecting device performance.
[0004] To address the challenge of packaging multiple heterogeneous materials, an existing solution proposes a wafer-level global planarization method. This method controls chip thickness to ensure that the top surfaces of multiple chips placed in rigid grooves on a carrier wafer achieve global coplanarity. However, this solution has significant limitations: the groove height is fixed, requiring chemical mechanical polishing (CMP) for planarization, which is complex and sensitive to material systems. Especially for non-silicon materials with insulating layers (such as thin-film lithium niobate, thin-film lithium tantalate, and III-V epitaxial wafers), this solution necessitates the growth of an intermediate layer for protection. Therefore, this groove-assisted coplanarization solution has poor applicability in direct bonding without an intermediate layer and struggles to meet the practical requirements of multi-material integration for coplanarity accuracy and material compatibility.
[0005] How to achieve efficient, low-damage, and coplanar synchronous bonding of multiple heterogeneous material wafers on the same target wafer while ensuring bonding quality has become a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0006] The purpose of this application is to provide a method for simultaneous bonding of multi-source heterogeneous material wafers and wafers to improve bonding efficiency, increase bonding power, and reduce damage to the bonding interface.
[0007] To address the aforementioned technical problems, this application provides a wafer synchronous bonding method, comprising: When the thickness difference between wafers to be bonded made of different materials is greater than or equal to a preset difference threshold, the substrate of the wafer to be bonded is thinned so that the thickness difference between the wafers to be bonded made of different materials is less than the preset difference threshold. Each of the wafers to be bonded is cut to obtain multiple heteromaterial wafers; the multiple heteromaterial wafers include at least two heteromaterial wafers with different thicknesses; A temporary bonding adhesive layer is formed on one side surface of the carrier wafer; Soften the temporary bonding adhesive layer; The plurality of heterogeneous material wafers are placed on the softened temporary bonding adhesive layer, and the placement pressure is adjusted according to the target parameters of the plurality of heterogeneous material wafers to make the plurality of heterogeneous material wafers coplanar, and the plurality of heterogeneous material wafers are fixed to one side surface of the carrier wafer; the target parameters include at least one of the size, thickness and mass of the heterogeneous material wafers; Prepare the target wafer; The carrier wafer, on which the plurality of heteromaterial wafers are fixed, is aligned with the target wafer, and the plurality of heteromaterial wafers are simultaneously bonded to the target wafer in one step through a bonding process.
[0008] Optionally, after placing the plurality of heterogeneous material wafers on the softened temporary bonding adhesive layer, and adjusting the placement pressure according to the target parameters of the plurality of heterogeneous material wafers to achieve coplanarization of the plurality of heterogeneous material wafers, and fixing the plurality of heterogeneous material wafers to one side surface of the carrier wafer, the method further includes: Soften the temporary bonding adhesive layer; An ultra-flat wafer is placed over the surface of the multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers.
[0009] Optionally, covering the surfaces of the plurality of heterogeneous material wafers with an ultra-flat wafer and applying uniform pressure to the ultra-flat wafer to further achieve coplanarization of the plurality of heterogeneous material wafers includes: The ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed are placed in a vacuum environment; Heat to the transition temperature of the temporary bonded adhesive layer; An ultra-flat wafer is placed over the surface of the multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers; The temperature was cooled to room temperature, and the vacuum environment was restored to normal atmospheric pressure.
[0010] Optionally, applying uniform pressure to the ultra-flat wafer includes: Based on the target parameters and material types of the plurality of heterogeneous material wafers, the pressure resistance rating of the plurality of heterogeneous material wafers is determined; The applied pressure is determined according to the pressure rating, and the pressure is applied uniformly to the ultra-flat wafer.
[0011] Optionally, before covering the surfaces of the plurality of heterogeneous material wafers with an ultra-flat wafer and applying uniform pressure to the ultra-flat wafer to further achieve coplanarization of the plurality of heterogeneous material wafers, the method further includes: Clean the ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed.
[0012] Optionally, cleaning the ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed includes: The ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed are cleaned by inorganic and organic cleaning.
[0013] Optionally, the pressure applied to the ultra-flat wafer is in the range of 0.05 MPa to 0.5 MPa.
[0014] Optionally, aligning the carrier wafer on which the plurality of heteromaterial wafers are fixed with the target wafer, and simultaneously bonding the plurality of heteromaterial wafers to the target wafer in one step using a bonding process includes: The surfaces of the target wafer and the plurality of heteromaterial wafers are subjected to plasma activation treatment and water washing treatment; Align the carrier wafer, on which the plurality of heterogeneous material wafers are fixed, with the target wafer; In a vacuum environment, the plurality of heterogeneous material wafers are brought into contact with the target wafer, and pre-bonding is performed at room temperature. Heating and pressurizing are performed under in-situ conditions to allow the plurality of heteromaterial wafers to continue bonding with the target wafer; Annealing process is performed to complete the one-time synchronous bonding of the multiple heterogeneous material wafers to the target wafer; The carrier wafer is separated from the plurality of heterogeneous material wafers.
[0015] Optionally, when the plurality of heteromaterial wafers are fixed to the carrier wafer by a temporary bonding adhesive layer, separating the carrier wafer from the plurality of heteromaterial wafers includes: The bonded composite structure after heat annealing has a heating temperature higher than the transition temperature of the temporary bonding adhesive layer. The temporary bonding between the carrier wafer and the plurality of heteromaterial wafers is released by a pyrolysis slip process or a thermal peeling process.
[0016] Optionally, aligning the carrier wafer on which the plurality of heterogeneous material wafers are fixed with the target wafer includes: The carrier wafer, on which the plurality of heterogeneous material wafers are fixed, is aligned with the target wafer by means of alignment marks pre-set on the carrier wafer and the target wafer.
[0017] The method for simultaneous bonding of multi-source heteromaterial wafers to a wafer provided in this application involves thinning the wafer to be diced and compensating for the thickness of multiple heteromaterial wafers by softening a temporary bonding adhesive layer and adjusting the placement pressure of the heteromaterial wafers. This eliminates the need for an intermediate layer, improves thickness differences, and makes the surfaces of heteromaterial wafers with varying thicknesses tend to be coplanar, thus fixing multiple heteromaterial wafers to one side of a carrier wafer. When multiple heteromaterial wafers are bonded to a target wafer, the contact tightness and uniformity between the wafers and the target wafer are improved. This application transfers and bonds multiple heteromaterial wafers to the target wafer simultaneously in the same bonding process, eliminating the need for batch bonding, shortening process time, and improving bonding efficiency, meeting the needs of large-scale production. Furthermore, since this application transfers and bonds multiple heteromaterial wafers to the target wafer in one go, when using hydrophilic bonding technology, only one plasma activation treatment is required, reducing damage to the target wafer and thus lowering the risk of bonding interface failure. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 A flowchart illustrating a method for synchronous bonding of multi-source heterogeneous material wafers and wafers provided in this application embodiment; Figures 2 to 13 This is a process flow diagram of a method for synchronous bonding of multi-source heterogeneous material wafers and wafers provided in an embodiment of this application.
[0020] Reference numerals: 1. First wafer to be bonded; 11. First heteromaterial wafer; 2. Second wafer to be bonded; 21. Second heteromaterial wafer; 3. Carrier wafer; 4. Temporary bonding adhesive layer; 5. Ultra-flat wafer; 6. Target silicon photonics wafer; 7. Covalent bond. Detailed Implementation
[0021] To enable those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0023] As described in the background section, in the prior art, when bonding wafers of different materials to the same target wafer, multiple batch bonding processes are required, which results in low bonding efficiency and a high risk of bonding interface failure.
[0024] In view of this, this application provides a method for simultaneous bonding of multi-source heterogeneous material wafers and wafers. Please refer to [the relevant documentation]. Figure 1 The method may include: Step S101: When the thickness difference between wafers to be bonded made of different materials is greater than or equal to a preset difference threshold, the substrate of the wafer to be bonded is thinned so that the thickness difference between wafers to be bonded made of different materials is less than the preset difference threshold.
[0025] The thickness compensation method in this embodiment can be applied to both non-single-material wafers and single-material wafers. A non-single-material wafer refers to a wafer formed from a non-silicon material wafer (e.g., a group III-V epitaxial material, a lithium niobate thin film wafer on a silicon substrate, etc.) whose structure is asymmetrical along the Z-direction (perpendicular to the top surface of the wafer). A single-material wafer refers to a wafer formed from a non-silicon material wafer (e.g., a group III-V substrate, a lithium niobate wafer, etc.) whose structure is symmetrical along the Z-direction (perpendicular to the top surface of the wafer).
[0026] The thickness of each wafer to be bonded is measured, and the difference in thickness between the wafers is compared. When the difference in thickness is greater than or equal to a preset difference threshold, it indicates that the thickness difference between the wafers to be bonded is too large. The thickness of the temporary bonding adhesive layer is limited, and its ability to balance heterogeneous material wafers of different thicknesses is also limited. Therefore, the thickness difference is reduced first by thinning the layer to make it easier to achieve coplanarization when multiple heterogeneous material wafers are placed.
[0027] It should be noted that this application does not limit the preset difference threshold, which can be set by the user. For example, the preset difference threshold can be 0~50μm, preferably less than 10μm.
[0028] After one thinning step, if the thickness difference between different wafers to be bonded is not less than a preset difference threshold, thinning is performed again until the thickness difference is less than the preset difference threshold.
[0029] Understandably, when the thickness difference between different wafers to be bonded is less than a preset difference threshold, it is not necessary to thin them and they can be cut directly.
[0030] Step S102: Cut each wafer to be bonded to obtain multiple heteromaterial wafers; the multiple heteromaterial wafers include at least two heteromaterial wafers with different thicknesses.
[0031] Different heterogeneous material wafers can be the same size or different sizes, and this application does not limit them.
[0032] This application does not limit the materials of different heterogeneous material wafers; it depends on the specific circumstances.
[0033] Step S103: A temporary bonding adhesive layer is formed on one side surface of the carrier wafer.
[0034] The carrier wafer can be a silicon wafer.
[0035] Temporary bonding adhesive is spin-coated onto one side of the carrier wafer. Heating causes the solvent in the temporary bonding adhesive to evaporate. After cooling and pre-curing, a temporary bonding adhesive layer of a certain thickness is formed.
[0036] Step S104: Soften the temporary bonding adhesive layer.
[0037] Heating the carrier wafer to the elastic state temperature (100℃~180℃) of the temporary bonding adhesive softens the temporary bonding adhesive layer. At this point, the viscosity of the temporary bonding adhesive layer decreases, which can reduce the impact on multiple heterogeneous material wafers when in contact with the temporary bond.
[0038] Step S105: Place multiple heterogeneous material wafers on a softened temporary bonding adhesive layer, and adjust the placement pressure according to the target parameters of the multiple heterogeneous material wafers to make the multiple heterogeneous material wafers coplanar; the target parameters include at least one of the size, thickness and mass of the heterogeneous material wafers.
[0039] The placement positions of multiple heterogeneous material wafers are arranged according to their positions on the target wafer.
[0040] The dimensions of a heterogeneous material wafer refer to its length and width.
[0041] After the heterogeneous material wafer is placed, the temperature returns to room temperature, and the temporary bonding adhesive layer is cured again.
[0042] The adjustment of the placement pressure of multiple heterogeneous material wafers in this step is a coarse adjustment process. Applying different placement pressures to different heterogeneous material wafers is a thickness compensation process, which makes the surfaces of multiple heterogeneous material wafers tend to be coplanar.
[0043] For example, for heterogeneous material wafers that are small in size, light in weight, and thin in thickness, the placement pressure can be lower, while for heterogeneous material wafers that are large in size, heavy in weight, and thick in thickness, the placement pressure can be higher.
[0044] Step S106: Prepare the target wafer.
[0045] The type of target wafer is not limited in this application and depends on the specific circumstances. For example, the target wafer can be a silicon wafer or a silicon photonics wafer.
[0046] The target wafer and the carrier wafer are the same size.
[0047] Step S107: Align the carrier wafer with multiple heterogeneous material wafers fixed on it with the target wafer, and bond the multiple heterogeneous material wafers to the target wafer simultaneously in one go through a bonding process.
[0048] It should be noted that this application does not limit the bonding method and you can choose it yourself.
[0049] As one possible implementation, aligning a carrier wafer with multiple heterogeneous material wafers fixed thereon with a target wafer, and then simultaneously bonding the multiple heterogeneous material wafers to the target wafer in one step using a bonding process includes: Step S1071: Perform plasma activation treatment and water washing treatment on the surface of the target wafer and multiple heterogeneous material wafers.
[0050] The process of activating surface dangling bonds through plasma activation and water washing can be as follows: During plasma activation, the target wafer and a carrier wafer with multiple heterogeneous material wafers fixed are placed in a plasma processing chamber. A suitable plasma activation process is selected according to the different material systems. The chamber is evacuated and activated gas is introduced. The gas is selected from oxygen (O2), nitrogen (N2), argon (Ar) or a mixture thereof, with a flow rate of 50 sccm (Standard Cubic Centimeter per Minute) to 300 sccm. The radio frequency power is set to 30W to 150W, the processing time is 10 seconds to 180 seconds, and the chamber pressure is maintained at 0.1 mBar to 1 mBar. Immediately immerse the plasma-activated target wafer and the carrier wafer with multiple heterogeneous material wafers fixed in it (transfer time < 5 minutes) into a high-purity deionized water bath for overflow rinsing for 1 to 3 minutes, or use a single-wafer spray water wash (rotation speed 300 rpm (Revolutions Per Minute) to 500 rpm, deionized water flow rate 0.5 L / min to 2 L / min, rinsing for 30 to 60 seconds), and use a low rotation speed (< 500 rpm) to spin dry to remove excess water droplets without completely drying, so as to prevent the surface from being contaminated or deactivated again.
[0051] As one possible implementation, before plasma activation treatment, the target wafer and multiple heterogeneous material wafers can be subjected to inorganic and organic cleaning to remove inorganic and organic contaminants and improve bonding strength. The inorganic and organic cleaning processes can be referred to in the following embodiments for the inorganic and organic cleaning process of the ultra-flat wafer and multiple heterogeneous material wafers.
[0052] Step S1072: Align the carrier wafer, on which multiple heterogeneous material wafers are fixed, with the target wafer.
[0053] Alignment can be achieved by using alignment marks on the bonding machine or by using alignment marks pre-set on the carrier wafer and the target wafer to align the carrier wafer with the target wafer, thereby improving alignment accuracy.
[0054] Step S1073: In a vacuum environment, multiple heterogeneous material wafers are brought into contact with the target wafer, and pre-bonding is performed at room temperature.
[0055] After plasma activation and water washing, surface molecular dangling bonds are generated on the surface of the target wafer and the surfaces of multiple heteromaterial wafers. At room temperature, the surface of the target wafer and the surfaces of multiple heteromaterial wafers are closely bonded to achieve pre-bonding based on van der Waals forces and hydrogen bonds, which provides the prerequisite for subsequent heating and pressure increase to generate covalent bonds and improve the final bonding strength.
[0056] Step S1074: Heating and pressurizing are performed in situ to allow multiple heterogeneous material wafers to continue bonding with the target wafer.
[0057] In-situ conditions refer to the conditions under which the target wafer and multiple heterogeneous material wafers are pre-bonded in a vacuum environment, avoiding contamination or alignment misalignment caused by intermediate transfer, and ensuring process stability and repeatability.
[0058] The temperature range for heating can be 150℃ to 180℃, and the pressure range for pressurization can be 0.5MPa to 1.5MPa, maintained for a certain period of time. The specific temperature, pressure, and holding time depend on the actual situation. In this step, hydrogen bonds are converted into high-strength covalent bonds, significantly improving the bond strength.
[0059] Step S1075: Annealing process to complete the one-time synchronous bonding of multiple heterogeneous material wafers to the target wafer.
[0060] The purpose of annealing is to further improve the stability of covalent bonds. Annealing temperatures below 300℃ and temperatures above or equal to 300℃ can lead to the temporary bonding adhesive layer failing. Furthermore, excessively high temperatures increase the coefficient of thermal expansion, resulting in greater thermal stress between the target wafer and multiple heterogeneous material wafers, which can easily lead to bonding failure.
[0061] This embodiment employs a plasma-activated hydrophilic direct bonding technique to bond the target wafer and multiple heterogeneous material wafers, which has advantages such as low bonding temperature and no intermediate bonding layer. Step S1076: Separate the carrier wafer from multiple heterogeneous material wafers.
[0062] It should be noted that the separation process is not limited in this application, as long as the effect of separating the carrier wafer from multiple heterogeneous material wafers can be achieved.
[0063] As one possible implementation, when multiple heterogeneous material wafers are fixed to a carrier wafer by a temporary bonding adhesive layer, separating the carrier wafer from the multiple heterogeneous material wafers includes: The bonded composite structure after heat annealing has a heating temperature higher than the transition temperature of the temporary bonding adhesive layer. Temporary bonding between a carrier wafer and multiple heterogeneous material wafers is removed by pyrolysis slip process or thermal peeling process.
[0064] The heating temperature of the bonded composite structure after annealing can be 150℃~200℃, which is higher than the transition temperature of the temporary bonding adhesive layer, so as to facilitate debonding.
[0065] The specific operational procedures of the pyrolysis slip process and the thermal stripping process are well known to those skilled in the art and will not be described in detail here. After separation, multiple heterogeneous material wafers are transferred onto the target wafer in one go.
[0066] The multi-source heterogeneous material wafer-to-wafer synchronous bonding method provided in this embodiment thins the substrate of the wafer to be diced and compensates for the thickness difference of multiple heterogeneous material wafers by softening the temporary bonding adhesive layer and adjusting the placement pressure of the heterogeneous material wafers. This improves the surface coplanarity of the heterogeneous material wafers with different thicknesses, thus fixing multiple heterogeneous material wafers to one side of the carrier wafer. When multiple heterogeneous material wafers are bonded to the target wafer, the contact tightness and uniformity between the multiple heterogeneous material wafers and the target wafer can be improved. In this embodiment, multiple heterogeneous material wafers are transferred and bonded to the target wafer simultaneously in the same bonding process, eliminating the need for batch bonding, shortening the process time, improving bonding efficiency, and meeting the needs of large-scale production. At the same time, since multiple heterogeneous material wafers are transferred and bonded to the target wafer in one go in this embodiment, when using hydrophilic bonding technology, only one plasma activation treatment is required, which can reduce damage to the target wafer and reduce the risk of bonding interface failure.
[0067] Based on the above embodiments, in one embodiment of this application, multiple heterogeneous material wafers are placed on a softened temporary bonding adhesive layer, and the placement pressure is adjusted according to the target parameters of the multiple heterogeneous material wafers to achieve coplanarization of the multiple heterogeneous material wafers. After fixing the multiple heterogeneous material wafers to one side surface of the carrier wafer, the method may further include: Soften the temporary bonding adhesive layer; An ultra-flat wafer is placed over the surface of multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers.
[0068] This implementation includes two coplanarization processes. The placement pressure is adjusted according to the target parameters of multiple heterogeneous material wafers to achieve coplanarization of the multiple heterogeneous material wafers, which can be regarded as pre-coplanarization, where multiple heterogeneous material wafers achieve initial coplanarization. Softening the temporary bonding adhesive layer and applying pressure uniformly to the ultra-flat wafers can further achieve more stringent coplanarization of the multiple heterogeneous material wafers that have achieved initial coplanarization.
[0069] In this embodiment, the specific process of using an ultra-flat wafer to make multiple heterogeneous material wafers coplanar is not limited, as long as coplanarization can be achieved.
[0070] During softening, a carrier wafer with multiple heterogeneous material wafers mounted can be placed on a heating stage and heated to the high elasticity temperature (i.e., transition temperature, 100℃~180℃) of the temporary bonding adhesive, causing the temporary bonding adhesive layer to soften again. At this temperature, the viscosity of the temporary bonding adhesive layer decreases significantly, but it still maintains a certain elastic modulus. The temporary bonding adhesive layer undergoes controllable flow, allowing multiple heterogeneous material wafers to undergo controlled vertical displacement and angular adjustment within it.
[0071] An ultra-flat wafer refers to a wafer with a total thickness variation (TTV) of less than 1.5 μm, preferably less than 500 nm, and a surface roughness (Ra) of less than 0.5 nm on the bonding surface. The ultra-flat wafer serves as a reference plane for coplanar imprinting. By applying uniform pressure, the upper surfaces of multiple heterogeneous material wafers are pressed to conform to this reference plane, thereby achieving high-precision compensation for thickness and placement differences among the multiple heterogeneous material wafers.
[0072] The pressure applied to the ultra-flat wafer can range from 0.05 MPa to 0.5 MPa, and the holding time of the applied pressure depends on the specific circumstances. After the pressure is applied, the wafer should be cooled to room temperature and the pressure released.
[0073] In this embodiment, the control process for applying pressure is not limited. Pressure can be applied at a fixed pressure or in stages according to the wafer type.
[0074] As one possible implementation, applying uniform pressure to an ultra-flat wafer includes: Based on the target parameters and material types of multiple heterogeneous material wafers, the pressure resistance rating of multiple heterogeneous material wafers is determined; The applied pressure is determined according to the pressure rating, and uniform pressure is applied to the ultra-flat wafer.
[0075] Materials can be, for example, InP, GaAs, LiNbO3, LiTaO3, Si, etc.
[0076] In this embodiment, the target parameters and material types of multiple heterogeneous material wafers are matched with a preset pressure rating table. For example, the pressure rating table can be: Level 1 pressure bearing (low pressure): suitable for brittle wafers with small size (2mm×2mm~5mm×5mm) and thickness ≤350μm (materials such as InP, GaAs and other III-V group materials). Level 2 pressure bearing (medium pressure): suitable for tough wafers of medium size (5mm×5mm~10mm×10mm) and thickness of 350μm~600μm (materials such as lithium niobate, lithium tantalate, etc.). Level 3 pressure bearing (higher pressure): suitable for large-size (10mm×10mm~15mm×15mm) high-toughness wafers (such as silicon wafers) with a thickness >600μm.
[0077] The corresponding applied pressure range is determined according to the pressure rating: Level 1 pressure rating: 0.05~0.2 MPa; Level 2 pressure rating: 0.1~0.3 MPa; Level 3 pressure rating: 0.2~0.5 MPa.
[0078] Since uniform pressure is applied to the ultra-flat wafer in this application, the global pressure value is determined by the lowest pressure rating (i.e., the most fragile heteromaterial wafer) among all heteromaterial wafers.
[0079] In this embodiment, the pressure level is set according to the target parameters and material type of the heterogeneous material wafer, and the applied pressure is adjusted accordingly. While ensuring coplanarization, this effectively prevents brittle wafers (such as InP and GaAs) from shattering due to excessive pressure, significantly reducing the risk of process damage. Meanwhile, for heterogeneous material wafers with better toughness, although a lower pressure is used, the long-term pressure holding of the ultra-flat wafer and the high elasticity of the temporary bonding adhesive still allow for sufficient sinking and coplanarization. This adaptive pressure strategy balances safety and coplanar accuracy, and is particularly suitable for heterogeneous integration scenarios involving multiple materials (such as brittle III-V group silicon and tough silicon, lithium niobate).
[0080] When multiple heterogeneous material wafers are placed on temporary bonding adhesive, misalignment is highly likely to occur in the direction perpendicular to the carrier wafer surface. Furthermore, the temporary bonding adhesive layer may also have varying thickness distribution due to the spin-coating process, leading to inconsistent surface heights among the multiple heterogeneous material wafers. In this embodiment, an ultra-flat wafer is introduced as a reference plane. While the temporary bonding adhesive layer is in a softened state, the ultra-flat wafer is used to uniformly press down on the multiple heterogeneous material wafers, redistributing and adjusting their angles in the vertical direction until the upper surfaces of all heterogeneous material wafers are pressed into complete contact with the ultra-flat wafer surface, achieving strict coplanarity. In this embodiment, applying uniform pressure to the ultra-flat wafer eliminates residual minor height differences from the preceding pre-coplanarization process, as well as issues such as uneven placement (e.g., tilting) of multiple heteromaterial wafers and variations in the thickness of the temporary bonding adhesive layer. This ensures that the upper surfaces of all heteromaterial wafers are on the same horizontal plane, providing ideal contact conditions for subsequent room-temperature pre-bonding with the target wafer. Specifically, all heteromaterial wafers can simultaneously achieve effective contact with the target wafer surface through van der Waals forces and hydrogen bonds, thereby generating high-density and uniformly distributed covalent bonds and significantly improving bonding success. Simultaneously, the high flatness and low roughness of the ultra-flat wafer prevent localized stress concentration, protecting the brittle heteromaterial wafers.
[0081] Based on the above embodiments, in one embodiment of this application, an ultra-flat wafer is covered on the surface of multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers, including: Step S201: Place the ultra-flat wafer and the carrier wafer with multiple heterogeneous material wafers fixed in a vacuum environment.
[0082] The ultra-flat wafer and the carrier wafer with multiple heterogeneous material wafers fixed on it are placed together in a vacuum chamber and a vacuum is drawn to remove air bubbles and increase the density of covalent bond formation during bonding.
[0083] Step S202: Heat to the transition temperature of the temporary bonding adhesive layer.
[0084] Heating is performed in a vacuum environment at a temperature of 100℃~180℃, and the temporary bonded adhesive layer reaches a highly elastic state.
[0085] Step S203: Cover the surface of multiple heterogeneous material wafers with an ultra-flat wafer and apply uniform pressure to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers.
[0086] An ultra-flat wafer is placed on the surface of multiple heterogeneous material wafers, so that the reference surface of the ultra-flat wafer is in contact with the upper surface of the multiple heterogeneous material wafers. A pressure device (such as an airbag or mechanical pressure head) is used to apply uniform pressure to the ultra-flat wafer and maintain it for a certain period of time. During this process, the multiple heterogeneous material wafers slowly sink or adjust their angle in the temporary bonding adhesive layer until the upper surface of all heterogeneous material wafers is completely attached to the reference surface of the ultra-flat wafer.
[0087] Step S204: Cool the temperature to room temperature and restore the vacuum environment to normal atmospheric pressure.
[0088] Turn off the heating, allow it to cool naturally or through a program to room temperature, and then restore it to normal pressure. Remove the carrier wafer, which has multiple heterogeneous material wafers fixed in it, from the vacuum chamber to obtain a coplanarized array of multiple heterogeneous material wafers and a carrier wafer composite structure.
[0089] In this embodiment, the heating and pressurizing coplanarization process is performed under vacuum, which prevents air bubbles from being trapped at the interface between the multiple heterogeneous material wafers and the temporary bonding adhesive layer, thus preventing bonding defects caused by bubble expansion during subsequent bonding. Simultaneously, the vacuum conditions ensure the cleanliness of the surfaces of the multiple heterogeneous material wafers at high temperatures, avoiding oxidation or particle adsorption. By precisely controlling the temperature, pressure, and time parameters, the flow behavior of the temporary bonding adhesive is controllable, and the redistribution process of the multiple heterogeneous material wafers is stable and repeatable. After cooling, the temporary bonding adhesive layer solidifies and locks in the coplanar state of the multiple heterogeneous material wafers, providing a stable and high-quality coplanar interface for subsequent bonding with the target wafer.
[0090] Based on the above embodiments, in one embodiment of this application, before covering the surfaces of multiple heterogeneous material wafers with an ultra-flat wafer and applying uniform pressure to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers, the method further includes: Clean ultra-flat wafers and carrier wafers with multiple heterogeneous material wafers fixed on them.
[0091] This application does not specify the specific cleaning method; you may choose your own method.
[0092] As one possible implementation, cleaning the ultra-flat wafer and the carrier wafer on which multiple heterogeneous material wafers are fixed includes: cleaning the ultra-flat wafer and the carrier wafer on which multiple heterogeneous material wafers are fixed by inorganic cleaning and organic cleaning.
[0093] After cleaning, the ultra-flat wafer and the carrier wafer with multiple heterogeneous material wafers fixed on it are sent into the vacuum chamber to avoid secondary contamination, in preparation for the subsequent process of re-coplanarizing the ultra-flat wafer.
[0094] The purpose of organic cleaning is to remove organic impurities such as grease, photoresist residue, and silicone contaminants from the surface of the ultra-flat wafer and multiple heterogeneous material wafers, preventing subsequent chemical cleaning solutions from being blocked by the organic contamination layer and becoming ineffective. A single-wafer spray cleaning method is used, where organic cleaning solution is sequentially sprayed onto the surface of the ultra-flat wafer and the carrier wafer containing the array of multiple heterogeneous material wafers. The organic cleaning solution includes, but is not limited to, one or more mixed solvents selected from acetone, isopropanol, anhydrous ethanol, or N-methylpyrrolidone. The cleaning process is carried out at room temperature, utilizing the principle of "like dissolves like" to dissolve and remove organic contaminants, and then removing the chemical cleaning solution by spin drying or nitrogen purging. Alternatively, the ultra-flat wafer and the carrier wafer with multiple heterogeneous material wafers fixed on it can be placed in an organic cleaning tank for cleaning.
[0095] The purpose of inorganic cleaning is to remove particulate contaminants and residual metal ions from the surfaces of ultra-flat wafers and multiple heterogeneous material wafers. Inorganic cleaning employs a two-fluid rinsing process, mixing high-purity nitrogen gas with deionized water to form a high-speed mist-like two-fluid (gas-liquid two-phase flow) that is sprayed onto the surfaces of the ultra-flat wafers and multiple heterogeneous material wafers. Utilizing the high-speed impact and cavitation effect of the gas-liquid mixture, submicron-sized particles are effectively stripped and removed. Simultaneously, due to the small liquid volume and controllable impact force, there is no mechanical damage to the surfaces of the ultra-flat wafers and multiple heterogeneous material wafers. Alternatively, megasonic waves can be used to perform the inorganic cleaning step. The above inorganic cleaning steps can be carried out under normal or reduced pressure. After cleaning, the wafers are dried by blowing with high-purity nitrogen gas or by high-speed spin drying (speed range 1000 rpm~2500 rpm) to ensure that the surfaces of the ultra-flat wafers and multiple heterogeneous material wafers are dry and free of residue.
[0096] Cleaning before coplanarization with ultra-flat wafers removes contaminants such as particles, oil, and metal ions from the carrier wafer, the surfaces of multiple heteromaterial wafers, and the ultra-flat wafer itself. This ensures flawless contact between the ultra-flat wafer and the multiple heteromaterial wafers, resulting in uniform pressure transmission. It also improves the covalent bond density when the thickness of the multiple heteromaterial wafers is bonded to the target wafer. By combining cleaning with a vacuum environment, interface defects can be minimized.
[0097] The bonding method in this application will be described below using two heterogeneous material wafers as an example, where they are not single-material wafers.
[0098] Step 1: Measure the thickness of the wafers to be bonded using two different materials and determine whether the thickness difference is less than 10 μm.
[0099] Step 2: When the thickness difference between wafers made of different materials is not less than 10 μm, mechanically grind the substrate of the wafer with the larger thickness until the thickness difference is less than 10 μm.
[0100] Step 3: When the thickness difference between wafers of different materials to be bonded is less than 10μm, the wafers to be bonded are diced and cut into multiple heterogeneous material wafers of suitable size.
[0101] For ease of description, the two types of wafers to be bonded will be referred to as the first wafer to be bonded (1) and the second wafer to be bonded (2), respectively. Figure 2 As shown, the first wafer to be bonded 1 can be diced to obtain the first heteromaterial wafer 11, as follows: Figure 3 As shown, the second heteromaterial wafer 2 can be obtained by dicing the second wafer to be bonded 2.
[0102] Step 4: Spin-coat a temporary bonding adhesive onto one side of the carrier wafer 3, heat it to evaporate the solvent in the temporary bonding adhesive, and after cooling and pre-curing, form a temporary bonding adhesive layer 4 of a certain thickness.
[0103] like Figure 4 As shown, the temporary bonding adhesive layer 4 is located on the upper surface of the carrier wafer 3.
[0104] Step 5: Reheat the carrier wafer to the high elasticity temperature of the temporary bonding adhesive to soften the temporary bonding adhesive layer.
[0105] Step 6: Place multiple heterogeneous material wafers on a softened temporary bonding adhesive layer, and adjust the placement pressure according to the target parameters of the multiple heterogeneous material wafers to achieve pre-coplanarization of the multiple heterogeneous material wafers; the target parameters include the size, thickness and mass of the heterogeneous material wafers.
[0106] like Figure 5 As shown, the first heteromaterial wafer 11 and the second heteromaterial wafer 21 are placed on the softened temporary bonding adhesive layer 4 in the required order. During the placement process, corresponding placement pressures are applied according to the different properties of the first heteromaterial wafer 11 and the second heteromaterial wafer 21. The placement pressure of the first heteromaterial wafer 11 is F. A The placement pressure of the second heteromaterial wafer 21 is F. B .
[0107] like Figure 6 As shown, after pre-coplanarization, the upper surfaces of the first heteromaterial wafer 11 and the second heteromaterial wafer 21 may still not achieve strict coplanarization and may have a certain degree of tilt.
[0108] Step 7: Perform inorganic cleaning and organic cleaning sequentially on the carrier wafer and the ultra-flat wafer on which multiple heterogeneous material wafers are fixed.
[0109] Step 8: Place the cleaned ultra-flat wafer and the carrier wafer with multiple heterogeneous material wafers fixed in a vacuum environment.
[0110] Step 9: Heat the material in a vacuum environment to the transition temperature of the temporary bonding adhesive layer.
[0111] Step 10: Flip the ultra-flat wafer upside down onto the surface of multiple heterogeneous material wafers, and apply uniform pressure to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers.
[0112] like Figure 7 As shown, the ultra-flat wafer 5 is flipped and inverted onto the surfaces of the first heteromaterial wafer 11 and the second heteromaterial wafer 21. After a certain uniform pressure F is applied to the surface of the ultra-flat wafer 5, the upper surfaces of the first heteromaterial wafer 11 and the second heteromaterial wafer 21 are made coplanar.
[0113] Step 11: Cool the temperature to room temperature and restore the vacuum environment to normal atmospheric pressure to obtain a composite structure of multiple heterogeneous material wafers and carrier wafers.
[0114] Step 12: Clean the composite structure of multiple heterogeneous material wafers and carrier wafers and the target silicon photonic wafer.
[0115] like Figure 8 and Figure 9 As shown, when passive devices are required, the bonding surface of the target silicon photonics wafer 6 can be etched to form a patterned target silicon photonics wafer 6. Figure 8 This is a graphical top view of the target silicon photonics wafer. Figure 9 This is a graphical schematic diagram of the cross-section of the target silicon photonics wafer.
[0116] Step 13: The surfaces of multiple heterogeneous material wafers in the cleaned composite structure and the surface of the target silicon photonic wafer are sequentially subjected to plasma activation treatment and water washing treatment.
[0117] Step 14: Place the cleaned and activated target silicon photonic wafer upside down on top of the composite structure and align it. In a vacuum environment, multiple heterogeneous material wafers are brought into contact with the target silicon photonic wafer and pre-bonded at room temperature.
[0118] like Figure 10 and Figure 11 As shown, the target silicon photonic wafer 6 is flipped onto the surface of multiple heteromaterial wafers and prebonded at room temperature, forming a large number of covalent bonds 7 between the target silicon photonic wafer 6 and the multiple heteromaterial wafers.
[0119] Step 15: Heating and pressurizing are performed in situ to allow multiple heterogeneous material wafers to continue bonding with the target wafer.
[0120] Step 16: Annealing process to complete the one-time synchronous bonding of multiple heterogeneous material wafers to the target wafer.
[0121] Step 17: The bonded composite structure after heat annealing is heated at a temperature higher than the transition temperature of the temporary bonding adhesive layer.
[0122] Step 18: Remove the temporary bonding between the carrier wafer and multiple heterogeneous material wafers by pyrolysis slip process or thermal peeling process.
[0123] like Figure 12 As shown, the carrier wafer 3, the first heteromaterial wafer 11, and the second heteromaterial wafer 21 are debonded to obtain multiple bonding structures between the heteromaterial wafers and the target silicon photonic wafer 6. Figure 13 As shown.
[0124] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.
[0125] The above provides a detailed description of the method for simultaneous bonding of multi-source heterogeneous material wafers and piezoelectric materials provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the solution and core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of this application.
Claims
1. A method for simultaneous bonding of multi-source heterogeneous material wafers and wafers, characterized in that, include: When the thickness difference between wafers to be bonded made of different materials is greater than or equal to a preset difference threshold, the substrate of the wafer to be bonded is thinned so that the thickness difference between the wafers to be bonded made of different materials is less than the preset difference threshold. Each of the wafers to be bonded is cut to obtain multiple heteromaterial wafers; the multiple heteromaterial wafers include at least two heteromaterial wafers with different thicknesses; A temporary bonding adhesive layer is formed on one side surface of the carrier wafer; Soften the temporary bonding adhesive layer; The plurality of heterogeneous material wafers are placed on the softened temporary bonding adhesive layer, and the placement pressure is adjusted according to the target parameters of the plurality of heterogeneous material wafers to make the plurality of heterogeneous material wafers coplanar, and the plurality of heterogeneous material wafers are fixed to one side surface of the carrier wafer; the target parameters include at least one of the size, thickness and mass of the heterogeneous material wafers; Prepare the target wafer; The carrier wafer, on which the plurality of heteromaterial wafers are fixed, is aligned with the target wafer, and the plurality of heteromaterial wafers are simultaneously bonded to the target wafer in one step through a bonding process.
2. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 1, characterized in that, After placing the plurality of heterogeneous material wafers onto the softened temporary bonding adhesive layer, and adjusting the placement pressure according to the target parameters of the plurality of heterogeneous material wafers to achieve coplanarization of the plurality of heterogeneous material wafers, and fixing the plurality of heterogeneous material wafers to one side surface of the carrier wafer, the process further includes: Soften the temporary bonding adhesive layer; An ultra-flat wafer is placed over the surface of the multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers.
3. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 2, characterized in that, Covering the surfaces of the plurality of heterogeneous material wafers with an ultra-flat wafer and applying uniform pressure to the ultra-flat wafer to further achieve coplanarization of the plurality of heterogeneous material wafers includes: The ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed are placed in a vacuum environment; Heat to the transition temperature of the temporary bonded adhesive layer; An ultra-flat wafer is placed over the surface of the multiple heterogeneous material wafers, and uniform pressure is applied to the ultra-flat wafer to further achieve coplanarization of the multiple heterogeneous material wafers; The temperature was cooled to room temperature, and the vacuum environment was restored to normal atmospheric pressure.
4. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 2, characterized in that, Applying uniform pressure to the ultra-flat wafer includes: Based on the target parameters and material types of the plurality of heterogeneous material wafers, the pressure resistance rating of the plurality of heterogeneous material wafers is determined; The applied pressure is determined according to the pressure rating, and the pressure is applied uniformly to the ultra-flat wafer.
5. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 2, characterized in that, Before covering the surfaces of the plurality of heterogeneous material wafers with an ultra-flat wafer and applying uniform pressure to the ultra-flat wafer to further achieve coplanarization of the plurality of heterogeneous material wafers, the process further includes: Clean the ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed.
6. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 5, characterized in that, Cleaning the ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed includes: The ultra-flat wafer and the carrier wafer on which the plurality of heterogeneous material wafers are fixed are cleaned by inorganic and organic cleaning.
7. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 2, characterized in that, The pressure applied to the ultra-flat wafer ranges from 0.05 MPa to 0.5 MPa.
8. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in any one of claims 1 to 7, characterized in that, Aligning the carrier wafer, on which the plurality of heteromaterial wafers are fixed, with the target wafer, and simultaneously bonding the plurality of heteromaterial wafers to the target wafer in one step using a bonding process includes: The surfaces of the target wafer and the plurality of heteromaterial wafers are subjected to plasma activation treatment and water washing treatment; Align the carrier wafer, on which the plurality of heterogeneous material wafers are fixed, with the target wafer; In a vacuum environment, the plurality of heterogeneous material wafers are brought into contact with the target wafer, and pre-bonding is performed at room temperature. Heating and pressurizing are performed under in-situ conditions to allow the plurality of heteromaterial wafers to continue bonding with the target wafer; Annealing process is performed to complete the one-time synchronous bonding of the multiple heterogeneous material wafers to the target wafer; The carrier wafer is separated from the plurality of heterogeneous material wafers.
9. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 8, characterized in that, When the plurality of heterogeneous material wafers are fixed to the carrier wafer by a temporary bonding adhesive layer, separating the carrier wafer from the plurality of heterogeneous material wafers includes: The bonded composite structure after heat annealing has a heating temperature higher than the transition temperature of the temporary bonding adhesive layer. The temporary bonding between the carrier wafer and the plurality of heteromaterial wafers is released by a pyrolysis slip process or a thermal peeling process.
10. The method for simultaneous bonding of multi-source heterogeneous material wafers and wafers as described in claim 8, characterized in that, Aligning the carrier wafer, on which the plurality of heterogeneous material wafers are fixed, with the target wafer includes: The carrier wafer, on which the plurality of heterogeneous material wafers are fixed, is aligned with the target wafer by means of alignment marks pre-set on the carrier wafer and the target wafer.