Low-temperature bonding method for reducing surface damage and bonding sheet thereof

Abstract

The invention provides a low-temperature bonding method for reducing surface damage and a bonding sheet thereof, and relates to the technical field of wafer bonding. In a high vacuum environment, the bonding surfaces of a first wafer and a second wafer which are to be bonded are subjected to first irradiation treatment by using a first atomic beam to obtain a first activation layer; s2, carrying out at least one second irradiation treatment on the bonding surface after the first irradiation treatment in the step S1 by adopting a second atomic beam to obtain a second activation layer; and carrying out ballasting bonding to obtain a bonding sheet. According to the low-temperature bonding method for reducing the surface damage, the bonding surface is activated in a gradient manner, so that the damage to the surface of the wafer caused by single activation can be reduced, the surface roughness is reduced, the probability of bubbles after bonding is reduced, and the bonding strength is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wafer bonding, and in particular to a low-temperature bonding method for reducing surface damage. Background Art

[0002] Direct wafer bonding technology combines dissimilar wafer materials through strong covalent bonds formed by atomic contact. Compared to traditional bonding methods, direct bonding can complete wafer bonding at low temperatures, overcoming the problems of thermal expansion coefficient and lattice constant mismatch, making it a key technology for heterogeneous integration.

[0003] At present, the mainstream direct bonding technologies mainly include surface activated bonding (Surface Activated Bonding), which uses Ar atomic beam to activate the bonding surface of the wafer and then completes direct bonding of the wafer under low temperature conditions; and plasma activated bonding (Plasma Activated Bonding), which uses O2, N2, and Ar plasma to activate the bonding surface of the wafer and then pre-bond and anneal under low temperature conditions.

[0004] Chinese invention patent publication number CN116005269A discloses a method and wafer for bonding gallium oxide to diamond based on ultra-high vacuum surface activation. The diamond-based gallium oxide wafer produced by this method has two structures: a gallium oxide layer / amorphous gallium oxide layer / nano-bonding layer / amorphous carbon layer / diamond substrate, and a gallium oxide layer / amorphous gallium oxide layer / amorphous carbon layer / diamond substrate. The main preparation steps are: fine polishing the gallium oxide and diamond surfaces; activating the polished gallium oxide and diamond surfaces using a fast argon atomic beam; and depositing a nano-bonding layer on each of the activated gallium oxide and diamond surfaces. Alternatively, the activated gallium oxide and diamond can be directly bonded without depositing a nano-bonding layer. This patent uses a single argon atomic beam to activate the wafer surface and deposit the intermediate layer. However, prolonged irradiation can exacerbate surface damage and increase wafer surface roughness. Furthermore, the patent does not address the issue of solving the problems of bonding surface damage and rough bonding surface during wafer bonding. Summary of the Invention

[0005] To address the above issues, the present invention provides a low-temperature bonding method that reduces surface damage. This method uses a decreasing mass gradient of an atomic beam to sequentially activate the surface of the wafer to be bonded, achieving a graded activation process of "deep activation-surface cleaning-fine finishing." The use of an atomic beam neutral particle stream avoids bombardment by charged particles in the plasma, enabling a gentler surface treatment. The graded activation process can reduce the damage caused by a single activation to the wafer surface, lowering surface roughness, thereby reducing the probability of bubbles appearing after bonding and improving the bond strength of the bonded wafer.

[0006] A first aspect of the present invention provides a low-temperature bonding method for reducing surface damage, the low-temperature bonding method comprising the following steps: S1: Under a high vacuum environment, irradiating the bonding surfaces of the first wafer and the second wafer to be bonded with a first atomic beam for the first time to obtain a first activation layer; S2: subjecting the bonding surface (first activation layer) after the first irradiation treatment in step S1 to at least one second irradiation treatment using a second atomic beam to obtain a second activation layer; S3: The bonding surfaces (second activation layer) of the first wafer and the second wafer after the second irradiation are pressed and bonded to obtain a bonding wafer; Figure 1 As shown, Figure 1 A process flow chart of the low temperature bonding method is shown.

[0007] Wherein, the first atomic beam and the second atomic beam are both inert gas atomic beams; The relative atomic mass of the second atomic beam is smaller than the relative atomic mass of the first atomic beam.

[0008] Optionally, the first atomic beam is one or two of Ar, Kr, and Xe atomic beams, and the second atomic beam is one or two of Ne or He atomic beams.

[0009] For example, in one embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: providing a clean first wafer 100 and a second wafer 200 to be bonded, and subjecting the bonding surfaces of the first wafer 100 and the second wafer 200 to be bonded to a first irradiation treatment with an Ar atomic beam in a high vacuum environment, thereby forming a first activation layer 110 corresponding to the first wafer and a first activation layer 210 corresponding to the second wafer, respectively; S2: performing a second irradiation treatment on the first activation layer 110 and the first activation layer 210 after the first irradiation treatment in step S1 using Ne or He atomic beams, respectively, to obtain a second activation layer 110' corresponding to the first wafer and a second activation layer 210' corresponding to the second wafer, respectively; S3: The second activation layer 110' and the second activation layer 210' after the second irradiation treatment in step S2 are subjected to pressure bonding to obtain a bonding sheet. Figure 2 As shown, Figure 2 A schematic diagram showing the low-temperature bonding method.

[0010] In an exemplary embodiment of the present invention, in step S2, the bonding surface after the first irradiation treatment is subjected to two second irradiation treatments using a second atomic beam, including the following steps: firstly subjecting the bonding surface after the first irradiation treatment in step S1 to the first second irradiation treatment using a Ne atomic beam, and then subjecting the bonding surface to the second second irradiation treatment using a He atomic beam. In this embodiment, a graded activation process of "deep activation-surface cleaning-fine finishing" is implemented using Ar (heavy) → Ne (medium) → He (light). By controlling the graded activation parameters, a high-kinetic energy argon atomic beam is first used to irradiate the bonding surface, achieving rapid activation and removing contaminants, organic matter, and the natural surface oxide layer. This also produces a certain degree of nanoscale roughness and some defects caused by the bombardment of the Ar atomic beam. A medium-kinetic energy neon atomic beam is then used. Since neon has a small relative atomic mass, it activates the wafer surface more uniformly, smoothing rough bumps caused by argon and repairing damage to the wafer surface caused by the original or Ar atomic beam. This further increases the thickness of the activated amorphous layer, reduces surface roughness, and increases the contact area between the two wafers. Finally, a low-kinetic energy helium atomic beam is used to irradiate the bonding surface to further generate a high-density dangling bonds, further reducing the depth of the activation layer, reducing surface roughness, and increasing the contact area between the two wafers. During the subsequent bonding process, the dangling bonds interact with the dangling bonds of the other wafer to form covalent bonds, thereby completing the bonding, further enhancing the bond strength and reducing the probability of defects.

[0011] Optionally, the voltage of the first irradiation treatment is 100-2000V, and the irradiation time is 10-200s. Optionally, the voltage of the first irradiation treatment is 1000-1500V, and the irradiation time is 30-100s.

[0012] Optionally, the current of the first irradiation treatment is 50-300 mA, and the irradiation angle between the first atomic beam and the bonding surface is 50°-80°. Optionally, the current of the first irradiation treatment is 80-200 mA, and the irradiation angle between the first atomic beam and the bonding surface is 60°-70°.

[0013] Optionally, the voltage of the second irradiation treatment is 500-2000V, and the irradiation time is 10-200s. Optionally, the voltage of the second irradiation treatment is 1000-1500V, and the irradiation time is 30-100s.

[0014] Optionally, the current of the second irradiation treatment is 10-300 mA, and the irradiation angle is 50°-80°. Optionally, the current of the second irradiation treatment is 80-200 mA, and the irradiation angle is 60°-70°.

[0015] Optionally, the vacuum degree of the high vacuum environment is not higher than 1×10 -6 Pa, the temperature is not higher than 30 ° C. The low-temperature bonding method of the present invention directly applies high pressure after activation to achieve bonding, without annealing, and can be performed at low temperature. There is no need to involve heat treatment of the bonded wafer, and there will be no thermal mismatch phenomenon. There will also be no phenomenon such as wafer fragmentation, chipping, warping, etc. caused by thermal mismatch.

[0016] Optionally, the surface root mean square roughness of the first wafer and the second wafer is both within the range of 0.1-0.5 nm. Optionally, the surface root mean square roughness of the first wafer and the second wafer is both within the range of 0.2-0.4 nm.

[0017] Optionally, the sizes of the first wafer and the second wafer are any one of 1-12 inches. For example, the sizes of the first wafer and the second wafer can be one of 4 inches, 6 inches, 8 inches, and 10 inches.

[0018] Optionally, the first wafer and the second wafer can both be selected from one of silicon dioxide, single crystal silicon, silicon carbide, aluminum nitride, gallium oxide, diamond, lithium niobate, lithium tantalate, zirconium oxide, aluminum oxide, and boron nitride. During the bonding process, the materials of the first wafer and the second wafer can be the same or different.

[0019] Optional, high vacuum environment with a vacuum degree of 1×10 -6 -10 -8 Pa, temperature is 10-25℃.

[0020] Optionally, the pressure for the heavy bonding is 1-50 kN. Optionally, the pressure for the heavy bonding is 5-20 kN.

[0021] The second aspect of the present invention provides a bonding sheet prepared by the above-mentioned low-temperature bonding method for reducing surface damage, wherein the bonding sheet has a bonding energy of not less than 1.5 J / m 2 .

[0022] Optionally, the probability of defects in the bonding wafer is no more than 16%.

[0023] Compared with the prior art, the present invention achieves at least one of the following beneficial effects: (1) The low-temperature bonding method of the present invention for reducing surface damage adopts gradient activation of the bonding surface, which can reduce the damage caused to the wafer surface by a single activation, reduce the surface roughness, thereby reducing the probability of defects after bonding, and improve the bonding strength.

[0024] (2) The low-temperature bonding method of the present invention for reducing surface damage directly applies high pressure after activation to achieve bonding. No annealing is required and bonding can be performed at low temperatures. There is no need to involve heat treatment of the bonded wafers, and no thermal mismatch will occur. There will also be no wafer fragmentation, chipping, warping, etc. caused by thermal mismatch. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 An exemplary embodiment of a process flow chart of a low-temperature bonding method for reducing surface damage according to the present invention is shown; Figure 2 An exemplary embodiment of a schematic diagram of a low-temperature bonding method for reducing surface damage according to the present invention is shown; Figure 3 A roughness characterization test diagram of the lithium niobate bonding surface after the second irradiation in Example 1 of the present invention is shown; Figure 4 An exemplary embodiment of a bonding wafer defect comparison diagram of the present invention is shown; Figure 5 An exemplary embodiment of a bonding wafer crack length characterization test diagram according to Example 1 of the present invention is shown.

[0026] Description of reference numerals: 100 - first chip; 200 - second chip; 110 - first activation layer corresponding to the first chip; 210 - first activation layer corresponding to the second chip; 110' - second activation layer corresponding to the first chip; 210' - second activation layer 210' corresponding to the second chip. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0029] Example 1 In an exemplary embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: Provide a clean, single-side polished, 6-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface RMS roughness of 0.2nm and a thickness of 250μm; provide a clean, single-side polished, 6-inch single crystal silicon sample with a surface RMS roughness of 0.2nm and a thickness of 500μm; and provide a clean, single-side polished, 6-inch single crystal Si with a 300nm thick SiO2 thin film layer. In this example, the roughness characterization and bonding energy characterization described below use LN and single crystal Si wafers without a silicon dioxide layer, while the etch depth characterization uses a single crystal Si wafer with a 300nm thick SiO2 thin film layer.

[0030] At room temperature (25°C), the above-mentioned single crystal silicon sample and LN piezoelectric single crystal wafer were respectively transported to the transfer chamber by a robot. The vacuum degree of the transfer chamber was 1.7×10 -3 Pa; After alignment is completed, the two wafers are moved to the bonding chamber by the robot, and the vacuum degree of the bonding chamber is 2×10 -6 Pa.

[0031] Then, ultrapure argon gas (>99.9999%) was introduced with an argon flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid Ar atomic beam bombardment was performed with a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 45 seconds to complete the first activation treatment.

[0032] The wafer that completed the first irradiation was carried out by the robotic arm, and the roughness of the bonding surface after the first irradiation was characterized. The root mean square roughness of the LN surface increased to 0.372nm / rms; the root mean square roughness of the single crystal silicon Si surface increased to 0.391nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 2.3nm.

[0033] S2: The wafer that has completed the first irradiation is sent back to the bonding machine and the above steps are repeated. The wafer is moved to the bonding chamber and ultrapure neon gas (>99.9999%) is introduced with a neon flow rate of 90 sccm. After pre-ventilation for 10 seconds, a rapid neon atomic beam bombardment is performed with a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 40 seconds to complete the second activation treatment.

[0034] The wafer that completed the second irradiation was carried out by the robotic arm, and the roughness of the bonding surface after the second irradiation was characterized again. The root mean square roughness of the LN surface decreased from 0.372nm / rms to 0.314nm / rms, and the root mean square roughness of the Si surface decreased from 0.391nm / rms to 0.332nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 3.3nm.

[0035] S3: Take multiple groups of LN and Si wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 5 kN and a time of 60 s to obtain bonded wafers.

[0036] Example 2 In an exemplary embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: Provide a clean, single-side polished, 6-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface RMS roughness of 0.231nm and a thickness of 250μm; provide a clean, single-side polished, 6-inch single crystal silicon sample with a surface RMS roughness of 0.203nm and a thickness of 500μm; and provide a clean, single-side polished, 6-inch single crystal Si with a 300nm thick SiO2 thin film layer. In this example, the roughness characterization and bonding energy characterization described below use LN and single crystal Si wafers without a SiO2 layer, while the etch depth characterization uses a single crystal Si wafer with a 300nm thick SiO2 thin film layer.

[0037] At room temperature (25°C), the single crystal silicon sample and the LN piezoelectric single crystal wafer were transported to the transfer chamber by a robot. The vacuum degree of the transfer chamber was 1.7×10 -3 Pa; After alignment is completed, the two wafers are moved to the bonding chamber by the robot, and the vacuum degree of the bonding chamber is 2×10 -6 Pa.

[0038] Then, ultrapure argon gas (>99.9999%) was introduced with a flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid Ar atomic beam bombardment was performed with a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 45 seconds to complete the first activation treatment.

[0039] The wafer that completed the first irradiation was carried out by the robotic arm, and the roughness of the bonding surface after the first irradiation was characterized. The root mean square roughness of the LN surface increased from 0.231nm / rms to 0.372nm / rms; the root mean square roughness of the single crystal silicon Si surface increased from 0.203nm / rms to 0.391nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 2.3nm.

[0040] S2: The wafer that has been irradiated for the first time is sent back to the bonding machine and the above steps are repeated. The wafer is moved to the bonding chamber and ultrapure neon gas (>99.9999%) is introduced at a neon flow rate of 90 sccm. After pre-gassing for 10 seconds, a rapid Ne atomic beam bombardment is performed at a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 40 seconds. The irradiated wafer was carried out by the robotic arm, and the roughness of the irradiated bonding surface was characterized again. The root mean square roughness of the LN surface decreased from 0.372nm / rms to 0.314nm / rms, and the root mean square roughness of the Si surface decreased from 0.391nm / rms to 0.322nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 3.3nm.

[0041] The irradiated wafer is sent to the bonding machine for the third time and the above steps are repeated to move it to the bonding chamber. Ultrapure helium (>99.9999%) is introduced with a helium flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid He atomic beam bombardment is performed with a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 80 seconds.

[0042] The irradiated wafer was carried out by the robotic arm, and the roughness of the irradiated bonding surface was characterized again. The root mean square roughness of the LN surface decreased from 0.314nm / rms to 0.303nm / rms, and the root mean square roughness of the Si surface decreased from 0.322nm / rms to 0.31nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was still 3.3nm.

[0043] S3: Take multiple groups of LN and Si wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 5 kN and a time of 60 s to obtain bonded wafers.

[0044] Example 3 In an exemplary embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: Provide a clean, single-side polished, 6-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface RMS roughness of 0.2nm and a thickness of 250μm; provide a clean, single-side polished, 6-inch single crystal silicon sample with a surface RMS roughness of 0.2nm and a thickness of 500μm; and provide a clean, single-side polished, 6-inch single crystal Si wafer with a 300nm thick SiO2 thin film layer. In this example, the roughness characterization and bond energy characterization described below use LN and Si wafers, while the etch depth characterization uses a single crystal Si wafer with a 300nm thick SiO2 thin film layer.

[0045] At room temperature (25°C), the single crystal silicon sample and the LN piezoelectric single crystal wafer were transported to the transfer chamber by a robot. The vacuum degree of the transfer chamber was 1.7×10 -3 Pa; After alignment is completed, the two wafers are moved to the bonding chamber by the robot, and the vacuum degree of the bonding chamber is 2×10 -7 Pa.

[0046] Then, ultrapure argon gas (>99.9999%) was introduced with an argon flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid Ar atomic beam bombardment was performed with a voltage of 2000 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 38 seconds to complete the first activation treatment.

[0047] The wafer that completed the first irradiation was carried out by the robotic arm, and the roughness of the irradiated bonding surface was characterized. The root mean square roughness of the LN surface increased to 0.386nm / rms; the root mean square roughness of the Si surface increased to 0.401nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 2.4nm.

[0048] S2: The wafer that has been irradiated for the first time is sent back into the bonding machine and the above steps are repeated to move it to the bonding chamber. Ultrapure neon gas (>99.9999%) is introduced with a neon flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid Ne atomic beam bombardment is performed with a voltage of 2000 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 30 seconds to complete the second activation treatment.

[0049] The irradiated wafer was carried out by the robotic arm, and the roughness of the bonding surface after irradiation was characterized again. The root mean square roughness of the LN surface decreased from 0.386nm / rms to 0.337nm / rms, and the root mean square roughness of the Si surface decreased from 0.401nm / rms to 0.344nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 3.5nm.

[0050] S3: Take multiple groups of LN and Si wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 5 kN and a time of 60 s to obtain bonded wafers.

[0051] Example 4 In an exemplary embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: The same as step S1 of Example 1, except that after irradiation, the root mean square roughness of the LN surface increased to 0.375 nm / rms; the root mean square roughness of the Si surface increased to 0.387 nm / rms.

[0052] S2: The same as step S2 of Example 1, after irradiation, the root mean square roughness of the LN surface decreased from 0.375 nm / rms to 0.324 nm / rms, and the root mean square roughness of the Si surface decreased from 0.387 nm / rms to 0.329 nm / rms.

[0053] S3: Take multiple groups of LN and Si wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 10 kN and a time of 60 s to obtain bonded wafers.

[0054] Example 5 In an exemplary embodiment of the present invention, a low-temperature bonding method for reducing surface damage includes the following steps: S1: Provide a clean, double-sided polished, 4-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface RMS roughness of 0.2nm and a thickness of 250μm; provide a clean, double-sided polished, 4-inch silicon carbide (SiC) sample with a surface RMS roughness of 0.2nm and a thickness of 500μm; and provide a clean, single-sided polished, 4-inch single crystal Si with a 300nm thick SiO2 film layer. In this example, the roughness and bond energy characterizations described below are performed using LN and SiC wafers, while the etch depth characterization uses a single crystal Si wafer with a 300nm thick SiO2 film layer.

[0055] At room temperature (25°C), the SiC sample, LN piezoelectric single crystal wafer, and single crystal silicon were transported to the transfer chamber by a robot. The vacuum degree of the transfer chamber was 1.7×10 -3 Pa; after alignment is completed, the two wafers are moved to the bonding chamber by the robot, and the vacuum degree of the bonding chamber is 1×10 -8 Pa.

[0056] Then, ultrapure argon gas (>99.9999%) was introduced with an argon flow rate of 90 sccm. After pre-ventilation for 10 seconds, rapid Ar atomic beam bombardment was carried out with a voltage of 1500 V, a current of 150 mA, an irradiation angle of 70°, and an irradiation time of 45 seconds to complete the first activation treatment.

[0057] The irradiated wafers were carried out by a robotic arm, and the roughness of the bonding surfaces after irradiation was characterized. The root mean square roughness of the LN surface increased to 0.372nm / rms; the root mean square roughness of the SiC surface increased to 0.391nm / rms.

[0058] S2: The wafer that has been irradiated for the first time is sent back to the bonding machine and the above steps are repeated. The wafer is moved to the bonding chamber and ultrapure neon gas (>99.9999%) is introduced at a neon flow rate of 90 sccm. After pre-gassing for 10 seconds, a rapid Ne atomic beam bombardment is performed with a voltage of 1500 V, a current of 150 mA, an irradiation angle of 70°, and an irradiation time of 40 seconds. The irradiated wafer was carried out by the robotic arm, and the roughness of the bonding surface after irradiation was characterized again. The root mean square roughness of the LN surface decreased from 0.372nm / rms to 0.318nm / rms, and the root mean square roughness of the SiC surface decreased from 0.391nm / rms to 0.323nm / rms. At this time, the etching depth of SiO2 activated under the same conditions was about 3.3nm.

[0059] S3: Take multiple groups of LN and SiC wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 5 kN and a time of 60 s to obtain bonded wafers.

[0060] Comparative Example 1 In an exemplary embodiment of the present invention, the low temperature bonding method comprises the following steps: A clean, single-side polished, 6-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface RMS roughness of 0.2 nm and a thickness of 250 μm was provided. A clean, single-side polished, 6-inch single crystal silicon sample with a surface RMS roughness of 0.2 nm and a thickness of 500 μm was provided. A clean, single-side polished, 6-inch single crystal Si wafer with a 300 nm thick SiO2 thin film layer was provided. In this embodiment, the roughness characterization and bonding energy characterization described below were performed using LN and single crystal Si wafers, while the etch depth characterization was performed using a single crystal Si wafer with a 300 nm thick SiO2 thin film layer.

[0061] At room temperature (25°C), the single crystal silicon sample and the LN piezoelectric single crystal wafer were transported to the transfer chamber by a robot. The vacuum degree of the transfer chamber was 1.7×10 -3 Pa; After alignment is completed, the two wafers are moved to the bonding chamber by the robot, and the vacuum degree of the bonding chamber is 2×10 -6 Pa.

[0062] Then, ultrapure argon gas (>99.9999%) was introduced at a flow rate of 90 sccm. After pre-gassing for 10 seconds, rapid Ar atomic beam bombardment was performed with a voltage of 1500 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 65 seconds. The irradiated wafer was carried out by the robotic arm, and the roughness of the bonding surface after irradiation was characterized. The root mean square roughness of the LN surface increased to 0.39nm / rms; the root mean square roughness of the Si surface increased to 0.386nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 3.3nm.

[0063] Take multiple groups of LN and Si wafers of the same specifications and perform the above process again and perform direct pressure bonding with a pressure of 5 kN and a time of 60 s to obtain bonded wafers.

[0064] Comparative Example 2 In an exemplary embodiment of the present invention, the low temperature bonding method comprises the following steps: S1: The same as step S1 in Example 1.

[0065] The irradiated wafers were carried out by a robotic arm, and the roughness of the bonding surfaces after irradiation was characterized. The root mean square roughness of the LN surface increased to 0.391nm / rms; the root mean square roughness of the Si surface increased to 0.382nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 2.3nm.

[0066] S2: The wafer that has been irradiated for the first time is sent back to the bonding machine and the above steps are repeated. The wafer is moved to the bonding chamber and ultrapure neon gas (>99.9999%) is introduced at a neon flow rate of 90 sccm. After pre-gassing for 10 seconds, a rapid Ne atomic beam bombardment is performed with a voltage of 3000 V, a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 20 seconds. The irradiated wafer was carried out by the robotic arm, and the roughness of the irradiated bonding surface was characterized again. The root mean square roughness of the LN surface increased to 0.601nm / rms, and the root mean square roughness of the Si surface increased to 0.622nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions was about 3.5nm.

[0067] S3: The same as step S3 in Example 1.

[0068] Comparative Example 3 The main difference from Example 1 is that, S3: multiple sets of LN and Si wafers of the same specifications are subjected to the above process again and direct press-rebonded with a pressure of 100 N and a time of 60 seconds. The other steps are the same as in Example 1.

[0069] Test Case After bonding was completed in the above examples and comparative examples, the bonding wafers were transported out of the chamber by a robotic arm and exposed to the atmosphere. The surfaces were visually inspected for defects such as bubbles and debonding. Bond energy was measured using a blade insertion method, with the average value calculated for five test points. The test results for roughness, bonding energy, and defect probability are shown in Table 1.

[0070] The calculation formula of bond energy is as follows: , Where, E1, E2 are Young's moduli of the first and second wafers, respectively (Pa); t1, t2 – wafer thickness of the first and second wafer, respectively (m); t b ——Blade thickness (m), the thickness of the blade used in the test t b =0.0001m; γ——bonding energy (J / m 2 ); L——crack length (mm); Among them, reference Figure 4 , Figure 4 A defect comparison diagram of the bonding wafer of the present invention is shown. The bonding interface of the bonding wafer is observed by naked eye to determine whether there are defects such as bubbles and debonding. Multiple groups of bonding wafers are taken to calculate the probability of defects in the bonding wafers.

[0071] Table 1

[0072] As shown in Table 1, the low-temperature bonding method for reducing surface damage of the present invention adopts a gradient activation bonding surface. After activation, the roughness of the bonding surface is not higher than 0.35nm / rms, the etching depth is not higher than 3.5nm, and the average bonding energy is not lower than 1.5J / m 2 , the probability of defects on the bonding surface is no more than 16%.

[0073] refer to Figure 3 As shown, Figure 3 The roughness characterization test diagram of the lithium niobate bonding surface after the second irradiation of Example 1 of the present invention is shown. Figure 5 , Figure 5 An exemplary embodiment of the crack length characterization test diagram of the bonding sheet in Example 1 of the present invention is shown. According to the crack length, the bonding energy of the bonding sheet can be calculated according to the above formula.

[0074] Referring to Comparative Example 1, when a single argon atomic beam is used to irradiate the wafer, the surface roughness of the wafer bonding surface is significantly increased, with the surface roughness increase exceeding 90%. However, after the graded activation method in the present application, the surface roughness increase of the bonded wafer is no more than 75%. This demonstrates to some extent that the present invention's use of graded activation of the bonding surface can reduce the damage to the wafer surface caused by a single activation method and reduce surface roughness.

[0075] Compared with Example 1, the main difference between Comparative Example 2 is that increasing the second irradiation voltage will damage the wafer surface and increase the surface roughness, thereby increasing the probability of bubbles appearing after bonding and reducing the bonding strength.

[0076] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A low-temperature bonding method for reducing surface damage, characterized in that: The low temperature bonding method comprises the following steps: S1: Under a high vacuum environment, irradiating the bonding surfaces of the first wafer and the second wafer to be bonded with a first atomic beam for the first time to obtain a first activation layer; S2: subjecting the bonding surface after the first irradiation treatment in step S1 to at least one second irradiation treatment using a second atomic beam to obtain a second activation layer; S3: performing pressure-rebonding on the bonding surfaces of the first wafer and the second wafer after the second irradiation to obtain a bonded wafer; Wherein, the first atomic beam and the second atomic beam are both inert gas atomic beams; The relative atomic mass of the second atomic beam is smaller than the relative atomic mass of the first atomic beam.

2. The low-temperature bonding method according to claim 1, characterized in that The first atomic beam is one or two of Ar, Kr, and Xe atomic beams, and the second atomic beam is one or two of Ne or He atomic beams.

3. The low-temperature bonding method according to claim 2, characterized in that: In step S2, the bonding surface after the first irradiation treatment is subjected to two second irradiation treatments using a second atomic beam, including the following steps: the bonding surface after the first irradiation treatment in step S1 is first subjected to the first second irradiation treatment using a Ne atomic beam, and then subjected to the second second irradiation treatment using a He atomic beam.

4. The low-temperature bonding method according to claim 1, characterized in that The voltage of the first irradiation treatment is 100-2000V, and the irradiation time is 10-200s.

5. The low-temperature bonding method according to claim 1, characterized in that The voltage of the second irradiation treatment is 500-2000V, and the irradiation time is 10-200s.

6. The low-temperature bonding method according to claim 1, characterized in that The vacuum degree of high vacuum environment is not higher than 1×10 -6 Pa, temperature not higher than 30℃.

7. The low-temperature bonding method according to claim 1, characterized in that: The sizes of the first wafer and the second wafer are both selected from any one of 1-12 inches.

8. The low-temperature bonding method according to claim 1, characterized in that The surface root mean square roughness of the first wafer and the second wafer are both within the range of 0.1-0.5 nm.

9. The low-temperature bonding method according to claim 1, characterized in that: The pressure for rebonding is 1-50kN.

10. A bonding sheet prepared by the low-temperature bonding method for reducing surface damage according to any one of claims 1 to 9, characterized in that: The bonding energy of the bonding sheet is not less than 1.5 J / m 2 ; The probability of defects in the wafer and / or bonding pad is no more than 16%.

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