Wafer bonding method
By employing multiple annealing processes and testing feedback, bubbles at the wafer bonding interface are gradually eliminated, resolving issues such as decreased bonding strength and the risk of wafer cracking, thereby improving the reliability and yield of wafer bonding.
Patent Information
- Application Number
- CN202511340753.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-18
- Publication Date
- 2025-12-30
AI Technical Summary
In existing technologies, bubbles generated after wafer bonding lead to a decrease in bonding strength and even the risk of wafer cracking. Existing methods are difficult to effectively eliminate micro and deep bubbles.
A multi-stage annealing process is employed, with different temperatures and times for each annealing stage, to gradually promote gas diffusion at the bonding interface. The number and size of bubbles are then assessed using detection equipment to determine if the conditions are met, and the bubbles are gradually eliminated.
It achieves efficient bubble elimination, improves bonding strength, avoids wafer damage, is applicable to a variety of material systems, and significantly improves yield.
Smart Images
Figure CN121237663A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to a wafer bonding method. Background Technology
[0002] Wafer bonding is a key process in advanced semiconductor packaging, 3D integrated circuit (3D IC) manufacturing, and MEMS device fabrication. It achieves electrical connections or structural integration by directly bonding the surfaces of two or more wafers, such as through direct bonding or adhesive bonding. However, bubbles are easily generated at the interface during bonding, primarily composed of air, moisture, organic residues, or reactive gases. These bubbles can lead to decreased bond strength, deterioration of interface insulation performance, and even the risk of wafer cracking during subsequent dicing and packaging processes, severely impacting device yield.
[0003] Existing methods for eliminating bonding bubbles mainly include: The first method is to optimize the single annealing process: by increasing the annealing temperature or extending the holding time, the gas inside the bubble is promoted to diffuse out. However, excessively high temperatures may cause wafer deformation or excessive interface reaction, such as metal diffusion contamination. The second method is surface treatment before bonding, such as plasma cleaning and megasonic cleaning, which reduces surface contaminants and reduces bubble formation, but cannot solve the problem of bubbles that have already formed after bonding. The third method is stepwise pressure bonding: gradually increasing the pressure during the bonding process to squeeze out the bubbles, but it has limited effect on microbubbles with a diameter of less than 5μm or deep bubbles located below structures with high aspect ratios.
[0004] Therefore, there is an urgent need to design a process method that can efficiently eliminate bubbles after bonding without damaging wafer performance. Summary of the Invention
[0005] One objective of this invention is to provide a wafer bonding method that solves the technical problem in the prior art where bubbles generated after wafer bonding lead to a decrease in bonding strength and even the risk of wafer cracking.
[0006] A further objective of this invention is to improve the bubble removal effect.
[0007] Specifically, the present invention provides a wafer bonding method, comprising the following steps: Provide the first wafer and the second wafer; The first wafer and the second wafer are aligned and bonded together using a bonding process to obtain a preliminary bonding structure; The initial bonded structure is subjected to multiple annealing processes to obtain the final bonded structure. During each annealing process, the annealing temperature and the holding time are different.
[0008] Optionally, in the step of performing multiple annealing processes on the preliminary bonded structure to obtain the final bonded structure, the annealing temperature and the holding time of each annealing process are increased sequentially.
[0009] Optionally, during multiple annealing processes, the final annealing temperature is less than or equal to a first preset temperature, where the first preset temperature is the highest temperature that the bonding material can withstand.
[0010] Optionally, during multiple annealing processes, the holding time for each annealing process ranges from 10 min to 120 min.
[0011] Optionally, in the step of aligning the first wafer and the second wafer and bonding the first wafer and the second wafer through a bonding process to obtain a preliminary bonded structure, the first wafer and the second wafer are bonded in a vacuum environment and bonded at a second preset temperature and preset pressure. The second preset temperature range is 20℃-100℃; The preset pressure range is 0.1MPa-5MPa.
[0012] Optionally, during multiple annealing processes, a stepped cooling process is performed after each annealing holding period. The stepped cooling process is as follows: first, the temperature is lowered to below a third preset temperature at a preset rate, and then naturally cooled to room temperature; the preset rate ranges from 5℃ / min to 20℃ / min, and the third preset temperature ranges from 90℃ to 110℃.
[0013] Optionally, the step of performing multiple annealing processes on the preliminary bonding structure to obtain the final bonding structure specifically includes the following steps: After each annealing process, the number and size of bubbles at the bonding interface between the first wafer and the second wafer are obtained by a detection device; Determine whether the number and size of the bubbles at the bonding interface meet preset conditions; If not, proceed with the next annealing process; if yes, end the process.
[0014] Optionally, the preset condition is that the number of bubbles is less than 5, and the size of each bubble is less than 1000um.
[0015] Optionally, the step of aligning the first wafer and the second wafer, and bonding the first wafer and the second wafer through a bonding process to obtain a preliminary bonded structure, further includes the following steps beforehand: The first wafer and the second wafer are sequentially cleaned and activated.
[0016] Optionally, the materials of the first wafer and the second wafer are any one of silicon, glass, or III-V compound semiconductors.
[0017] This invention first provides a first wafer and a second wafer, then aligns the first wafer and the second wafer, and bonds them together using a bonding process to obtain a preliminary bonded structure. Finally, the preliminary bonded structure is subjected to multiple annealing processes to obtain the final bonded structure. During each of the multiple annealing processes, the annealing temperature and holding time are different. This technical solution, by subjecting the initial bonded structure to multiple annealing processes, promotes the phased diffusion and escape of gas within bubbles at the bonding interface, gradually reducing bubble density and size, achieving efficient bubble elimination. This avoids damage to the wafer from a single high-temperature process, is applicable to bonding processes of various materials, and has advantages such as strong process compatibility and significantly improved yield.
[0018] Furthermore, in this invention, after each annealing process, the number and size of bubbles at the bonding interface between the first and second wafers are first obtained using a detection device. Then, it is determined whether the number and size of bubbles at the bonding interface meet preset conditions. If not, the next annealing process is performed; if so, the process ends. The above technical solution can avoid incomplete bubble removal by making multiple judgments, thereby improving the bubble removal effect.
[0019] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description
[0020] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of a wafer bonding method according to an embodiment of the present invention; Figure 2 This is a schematic flowchart of a wafer bonding method according to another embodiment of the present invention; Figure 3 (a) is a schematic diagram of bubbles after the first annealing treatment according to an embodiment of the present invention; Figure 3 (b) is a schematic diagram of bubbles after the second annealing treatment according to an embodiment of the present invention. Detailed Implementation
[0021] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0022] Figure 1 This is a schematic flowchart of a wafer bonding method according to an embodiment of the present invention. Figure 1 As shown, in a specific embodiment, the wafer bonding method includes the following steps: Step S100: Provide a first wafer and a second wafer; Step S200: Align the first wafer and the second wafer, and bond the first wafer and the second wafer together using a bonding process to obtain a preliminary bonding structure; In step S300, the preliminary bonded structure is subjected to multiple annealing processes to obtain the final bonded structure. During the multiple annealing processes, the annealing temperature and the holding time are different each time.
[0023] In this embodiment, by performing multiple annealing processes on the initial bonding structure, the gas inside the bubbles at the bonding interface is promoted to diffuse out in stages, gradually reducing the bubble density and size, thereby achieving efficient bubble elimination. This avoids damage to the wafer caused by a single high temperature, is applicable to bonding processes of various materials, and has advantages such as strong process compatibility and significant yield improvement.
[0024] In step S100, the first wafer and the second wafer are made of silicon, glass, or a III-V compound semiconductor. The materials of the first wafer and the second wafer can be the same or different. Furthermore, the sizes of the first wafer and the second wafer can be the same or different; for example, both can be 8-inch silicon wafers. It can be understood that this embodiment is applicable to various material systems without requiring additional equipment modifications.
[0025] In step S200, the bonding type can be various, such as silicon-silicon, silicon-silicon oxide, etc., offering strong process compatibility. Furthermore, alignment and bonding are performed in a vacuum bonding machine.
[0026] In step S300, during the multiple annealing processes, the annealing temperature increases sequentially, and the holding time for each annealing process increases sequentially.
[0027] This embodiment employs multiple progressive annealing processes on the initial bonded structure, with each annealing cycle involving progressively increasing and extending temperature and time. This effectively promotes the staged escape of gases such as air and water vapor from bubbles within the bonding interface, achieving an elimination rate of over 95%, particularly effective for microbubbles and deep bubbles, resulting in more thorough bubble removal. Furthermore, this embodiment avoids wafer deformation or excessive interfacial reactions caused by a single high-temperature treatment. The progressive processing from low to high temperatures reduces thermal stress damage to the initial bonded structure, maintaining interfacial stability. Repeated annealing also promotes interfacial atomic diffusion, and the bond strength after multiple annealing cycles can reach 1.5-2 times the initial bond strength, thus significantly improving the bond strength of the initial bonded structure.
[0028] In some embodiments, during multiple annealing processes, the final annealing temperature is less than or equal to a first preset temperature, which is the highest temperature that the bonding material can withstand.
[0029] In some embodiments, during multiple annealing processes, the holding time for each annealing process ranges from 10 min to 120 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.
[0030] In other words, when the number of annealing processes is n, n≥2; the process parameters for each annealing process must meet the following conditions: The annealing temperature Ti for the i-th time must satisfy: T1≤T2≤……≤Tn≤Tmax, where Tmax is the first preset temperature, which is the highest temperature that the bonding material can withstand. For example, for silicon-silicon bonding, Tmax=1150℃.
[0031] The holding time ti for the i-th annealing must satisfy: 10min≤ti≤120min, and t1≤t2≤……≤tn.
[0032] In some embodiments, in step S300, the annealing atmosphere is an inert gas or a vacuum, such as N2 or Ar, and the vacuum degree is less than 1 Pa, which can prevent oxidation of the bonding interface.
[0033] In some embodiments, in step S200, the first wafer and the second wafer are bonded together in a vacuum environment at a second preset temperature and a preset pressure. The second preset temperature ranges from 20°C to 100°C, for example, it can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C. The preset pressure ranges from 0.1MPa to 5MPa, for example, it can be 0.1MPa, 0.5MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, or 5MPa. Here, the applied temperature and pressure are maintained for 10 minutes to complete the initial bonding.
[0034] In some embodiments, during multiple annealing processes, a stepped cooling process is performed after each annealing holding period. The stepped cooling process involves first cooling to below a third preset temperature at a preset rate, and then allowing it to cool naturally to room temperature.
[0035] This embodiment can avoid incomplete bubble removal by making multiple judgments, thereby improving the bubble removal effect.
[0036] In some embodiments, the preset rate ranges from 5°C / min to 20°C / min, for example, it can be 5°C / min, 10°C / min, 15°C / min, or 20°C / min, etc., and the third preset temperature ranges from 90°C to 110°C, for example, it can be 90°C, 100°C, or 110°C, etc. In other embodiments, the preset rate and the third preset temperature can also be determined according to specific design requirements.
[0037] Figure 2 This is a schematic flowchart of a wafer bonding method according to another embodiment of the present invention. Figure 2 As shown, in some embodiments, step S300 specifically includes the following steps: Step S310: After each annealing process, the number and size of bubbles at the bonding interface between the first wafer and the second wafer are obtained by a detection device. Step S320: Determine whether the number and size of the bubbles on the bonding interface meet the preset conditions; if yes, proceed to step S330; otherwise, end.
[0038] Step S330: Perform the next annealing process, then return to step S310.
[0039] In step S310, the detection device is an infrared imaging device or an ultrasonic scanning device.
[0040] In some embodiments, the preset condition is that the number of bubbles is less than 5, and the size of each bubble is less than 1000 μm. For example, the number of bubbles needs to be less than 5, 4, or 3, etc. In other embodiments, the preset condition can also be determined according to specific design requirements.
[0041] In some embodiments, the following steps are included before step S200: The first and second wafers were sequentially cleaned and activated.
[0042] Here, cleaning can be RCA cleaning or megasonic cleaning, and activation treatment can be plasma activation or chemical cleaning activation, thereby removing contaminants from the wafer surface and increasing surface chemical energy, controlling the surface roughness Ra of the wafer to ≤1nm.
[0043] In one specific embodiment, two 8-inch silicon wafers are used for bonding. One of the wafers has a 1µm thick oxide layer grown on it. The wafers are then cleaned sequentially using SPM and SC1 to remove organic residues and metallic impurities. The parameters for SPM are: H2SO4:H2O2 = 4:1 at 125°C, and the parameters for SC1 are: NH4OH:H2O2:DIW = 1:4:20 at 70°C. The wafers are then activated with N2 plasma at a power of 60W for 15 seconds to remove surface contaminants and increase the bonding chemical energy.
[0044] During the first annealing process, the temperature T1 = 1000℃, the holding time t1 = 120 min, under a N2 atmosphere, the heating rate was 10℃ / min, and the cooling rate was 10℃ / min to 80℃. During the second annealing process, the temperature T2 = 1100℃, the holding time t2 = 120 min, under a N2 atmosphere, the heating rate was 10℃ / min, and the cooling rate was 10℃ / min to 80℃.
[0045] Figure 3 (a) is a schematic diagram of bubbles after the first annealing treatment according to an embodiment of the present invention, as shown in the figure. Figure 3 As shown in (a), after the first annealing treatment, there are many large-area strip-shaped bubbles at the edge of the preliminary bond structure, with a maximum width of 0.82 mm, which does not meet the preset conditions, so a second annealing treatment is required.
[0046] Figure 3 (b) is a schematic diagram of bubbles after the second annealing treatment according to an embodiment of the present invention. Figure 3 As shown in (b), after the second annealing treatment, the large area of bubbles disappeared, and only a few small area bubbles remained, with a maximum diameter of 0.4 μm, which met the process requirements, and the annealing treatment was stopped.
[0047] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.
Claims
1. A wafer bonding method, characterized in that, Includes the following steps: Provide the first wafer and the second wafer; The first wafer and the second wafer are aligned and bonded together using a bonding process to obtain a preliminary bonding structure; The initial bonded structure is subjected to multiple annealing processes to obtain the final bonded structure. During each annealing process, the annealing temperature and the holding time are different.
2. The wafer bonding method according to claim 1, characterized in that, In the step of performing multiple annealing processes on the preliminary bonded structure to obtain the final bonded structure, the annealing temperature and the holding time of each annealing process increase sequentially.
3. The wafer bonding method according to claim 2, characterized in that, During multiple annealing processes, the final annealing temperature is less than or equal to a first preset temperature, which is the highest temperature that the bonding material can withstand.
4. The wafer bonding method according to claim 3, characterized in that, During multiple annealing processes, the holding time for each annealing process ranges from 10 min to 120 min.
5. The wafer bonding method according to any one of claims 1-4, characterized in that, In the step of aligning the first wafer and the second wafer and bonding the first wafer and the second wafer through a bonding process to obtain a preliminary bonded structure, the first wafer and the second wafer are bonded in a vacuum environment and bonded at a second preset temperature and preset pressure. The second preset temperature range is 20℃-100℃; The preset pressure range is 0.1MPa-5MPa.
6. The wafer bonding method according to any one of claims 1-4, characterized in that, During the multiple annealing processes, a stepped cooling process is performed after each annealing heat treatment and holding period. The stepped cooling process is as follows: first, the temperature is lowered to below a third preset temperature at a preset rate, and then naturally cooled to room temperature; the preset rate ranges from 5℃ / min to 20℃ / min, and the third preset temperature ranges from 90℃ to 110℃.
7. The wafer bonding method according to any one of claims 1-4, characterized in that, The step of performing multiple annealing processes on the preliminary bond structure to obtain the final bond structure specifically includes the following steps: After each annealing process, the number and size of bubbles at the bonding interface between the first wafer and the second wafer are obtained by a detection device; Determine whether the number and size of the bubbles at the bonding interface meet preset conditions; If not, proceed with the next annealing process; if yes, end the process.
8. The wafer bonding method according to claim 7, characterized in that, The preset condition is that the number of bubbles is less than 5, and the size of each bubble is less than 1000um.
9. The wafer bonding method according to any one of claims 1-4, characterized in that, The step of aligning the first wafer and the second wafer, and bonding the first wafer and the second wafer together using a bonding process to obtain a preliminary bonded structure, also includes the following steps before the initial bonding structure: The first wafer and the second wafer are sequentially cleaned and activated.
10. The wafer bonding method according to any one of claims 1-4, characterized in that, The first wafer and the second wafer are made of any one of silicon, glass or III-V compound semiconductors.