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

Abstract

The application provides a low-temperature bonding method for reducing surface damage and a bonded wafer, 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 to be bonded are subjected to first irradiation treatment by using a first atomic beam, so that a first activated layer is obtained; the bonding surfaces after the first irradiation treatment in step S1 are subjected to at least one second irradiation treatment by using a second atomic beam, so that a second activated layer is obtained; and pressure bonding is performed, so that a bonded wafer is obtained. The low-temperature bonding method for reducing surface damage adopts gradient-activated bonding surfaces, can reduce the damage to the wafer surface caused by single activation, reduce the surface roughness, thereby reducing the probability of the occurrence of air bubbles after bonding, and improving the bonding strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wafer bonding technology, in particular to a low-temperature bonding method for reducing surface damage. BACKGROUND

[0002] Wafer direct bonding technology can combine wafer materials of different materials through atomic contact to form strong covalent bonds. Compared with traditional bonding methods, direct bonding technology can complete wafer bonding at low temperature, overcoming the problems of thermal expansion coefficient and lattice constant mismatch, and is an important technology for heterogeneous integration.

[0003] Currently, the mainstream direct bonding technology mainly includes surface activated bonding (Surface Activated Bonding) which uses Ar atomic beam to activate the bonding surface of the wafer and then completes the direct bonding of the wafer at low temperature; and plasma activated bonding (Plasma Activated Bonding) which uses O2, N2, Ar plasma to activate the bonding surface of the wafer and then pre-bonds at low temperature and anneals.

[0004] The Chinese invention patent with patent publication number CN116005269A discloses a gallium oxide and diamond bonding method based on ultra-high vacuum surface activation and wafer. The diamond-based gallium oxide wafer prepared by the method has two structures of gallium oxide layer / amorphous gallium oxide layer / nano adhesive layer / amorphous carbon layer / diamond substrate and gallium oxide layer / amorphous gallium oxide layer / amorphous carbon layer / diamond substrate. The main preparation steps are: finely polishing the surfaces of gallium oxide and diamond; activating the surfaces of the polished gallium oxide and diamond using a fast argon atomic beam; depositing a nano adhesive layer on the surfaces of the activated gallium oxide and diamond, respectively; and contacting the gallium oxide and diamond with the deposited nano adhesive layer for indirect bonding, or directly bonding the activated gallium oxide and diamond without depositing a nano adhesive layer. In the patent, a single argon atomic beam is used to activate the wafer surface and deposit an intermediate layer. However, long-time irradiation will exacerbate wafer surface damage and increase wafer surface roughness. Moreover, the patent does not address the problems of bonding surface damage and roughness during wafer bonding. SUMMARY

[0005] To solve the above problems, the application provides a low-temperature bonding method for reducing surface damage, which adopts atomic beams with gradually decreasing mass to sequentially perform surface activation treatment on the bonding surfaces of wafers, realizes graded activation treatment of "deep activation-surface cleaning-fine trimming", and adopts neutral particle flow in the atomic beams to avoid bombardment of charged particles in plasma and realize more gentle surface treatment. The graded activation process can reduce damage to the wafer surface caused by single activation, reduce surface roughness, thereby reducing the probability of bubble occurrence after bonding, and improving the bonding strength of the bonded wafer.

[0006] The application provides a low-temperature bonding method for reducing surface damage, which comprises the following steps:

[0007] S1: In a high-vacuum environment, the bonding surfaces of the first wafer and the second wafer to be bonded are respectively subjected to first irradiation treatment by a first atomic beam to obtain first activation layers;

[0008] S2: The bonding surfaces (the first activation layers) after the first irradiation treatment in step S1 are subjected to at least one second irradiation treatment by a second atomic beam to obtain second activation layers;

[0009] S3: The bonding surfaces (the second activation layers) of the first wafer and the second wafer after the second irradiation are subjected to pressure bonding to obtain a bonded wafer; reference Figure 1 is shown, Figure 1 The process flow diagram of the low-temperature bonding method is shown.

[0010] The first atomic beam and the second atomic beam are both inert gas atomic beams.

[0011] The relative atomic mass of the second atomic beam is smaller than that of the first atomic beam.

[0012] 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.

[0013] For example, in an embodiment of the application, the low-temperature bonding method for reducing surface damage comprises the following steps:

[0014] S1: Provide clean first wafer 100 and second wafer 200 to be bonded after cleaning, and in a high-vacuum environment, the bonding surfaces of the first wafer 100 and the second wafer 200 to be bonded are respectively subjected to first irradiation treatment by an Ar atomic beam to obtain a first activation layer 110 corresponding to the first wafer and a first activation layer 210 corresponding to the second wafer, respectively;

[0015] S2: the first activated layer 110 and the first activated layer 210 after the first irradiation treatment in step S1 are respectively subjected to second irradiation treatment by using Ne or He atom beams, and the second activated layer 110' corresponding to the first wafer and the second activated layer 210' corresponding to the second wafer are respectively obtained;

[0016] S3: the second activated layer 110' and the second activated layer 210' after the second irradiation treatment in step S2 are subjected to pressure bonding, and a bonded wafer is obtained. Figure 2 As shown in the figure, Figure 2 A schematic diagram of the low-temperature bonding method is shown.

[0017] In an exemplary embodiment of the present application, in step S2, the bonding surface after the first irradiation treatment is subjected to 2 times of second irradiation treatment by using a second atom 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 by using a Ne atom beam, and then subjected to the second second irradiation treatment by using a He atom beam. In this embodiment, Ar (heavy) -> Ne (medium) -> He (light) is used to realize the hierarchical activation treatment of "deep activation-surface cleaning-fine trimming", by controlling the hierarchical activation parameters, the bonding surface is first irradiated by using a high-energy argon atom beam, which can achieve the purpose of rapid activation and remove contaminants, organic matter and surface natural oxide layer, and at the same time, a certain degree of nanoscale roughness and some defects caused by Ar atom beam bombardment will also be generated; then a medium-energy neon atom beam is used, the relative atomic mass of neon is small, the surface activation of the wafer is more uniform, the rough protrusions caused by argon can be smoothed, the original damage to the wafer surface or the damage to the wafer surface caused by the Ar atom beam can be repaired, the thickness of the activated amorphous layer is further increased, the surface roughness is reduced, and the contact area of the two wafers is increased; then a low-energy helium atom beam is used to irradiate the bonding surface, further generating high-density dangling bonds, further reducing the depth of the activated layer, reducing the surface roughness, and increasing the contact area of the two wafers, the dangling bonds interact with the dangling bonds of the other wafer in the subsequent bonding process to form covalent bonds, thereby completing the bonding, which can further enhance the bonding strength and reduce the probability of defect occurrence.

[0018] 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.

[0019] Optionally, the current of the first irradiation treatment is 50-300mA, and the irradiation angle of the first atom beam to the bonding surface is 50°-80°. Optionally, the current of the first irradiation treatment is 80-200mA, and the irradiation angle of the first atom beam to the bonding surface is 60°-70°.

[0020] Optionally, the voltage of the second irradiation treatment is 500-2000V, and the irradiation time is 10-200s.

[0021] Optionally, the current of the second irradiation treatment is 10-300mA, and the irradiation angle is 50°-80°. Optionally, the current of the second irradiation treatment is 80-200mA, and the irradiation angle is 60°-70°.

[0022] Optionally, the vacuum degree of the high-vacuum environment is not higher than 1×10 -6 Pa, and the temperature is not higher than 30℃. The low-temperature bonding method of the present application directly applies high pressure to realize bonding after activation, without annealing. The bonding can be performed at low temperature, without involving thermal treatment of the bonded wafer, without the phenomenon of thermal mismatch, and without the phenomenon of wafer cracking, chipping, warping, etc. caused by thermal mismatch.

[0023] Optionally, the root mean square roughness of the surface of the first wafer and the second wafer is in the range of 0.1-0.5nm. Optionally, the root mean square roughness of the surface of the first wafer and the second wafer is in the range of 0.2-0.4nm.

[0024] Optionally, the size of the first wafer and the second wafer is any one of 1-12 inches. For example, the size of the first wafer and the second wafer can be one of 4 inches, 6 inches, 8 inches, and 10 inches.

[0025] Optionally, the first wafer and the second wafer can be selected from one of silicon dioxide, monocrystalline silicon, silicon carbide, aluminum nitride, gallium oxide, diamond, lithium niobate, lithium tantalate, zirconium oxide, aluminum oxide, and boron nitride. The material of the first wafer and the second wafer can be the same or different during the bonding process.

[0026] Optionally, the vacuum degree of the high-vacuum environment is 1×10 -6 -10 -8 Pa, and the temperature is 10-25℃.

[0027] Optionally, the pressure of the pressure-weighted bonding is 1-50kN. Optionally, the pressure of the pressure-weighted bonding is 5-20kN.

[0028] The second aspect of the present application provides a bonded wafer prepared by the above low-temperature bonding method for reducing surface damage, and the bonding energy of the bonded wafer is not less than 1.5 J / m 2 .

[0029] Optionally, the probability of defects of the bonded wafer is not higher than 16%.

[0030] Compared with the prior art, the present application at least has one of the following beneficial effects:

[0031] (1) The low-temperature bonding method for reducing surface damage of the present application adopts gradient activation of the bonding surface, which can reduce the damage to the wafer surface caused by single activation, reduce the surface roughness, thereby reducing the probability of defects after bonding, and improving the bonding strength.

[0032] (2) The low-temperature bonding method for reducing surface damage of the present application directly applies high pressure to realize bonding after activation, without annealing, and can bond at low temperature, without involving heat treatment of the bonded wafer, and without the phenomena of thermal mismatch, wafer cracking, chipping, warping, etc. caused by thermal mismatch. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings described herein are used to provide further understanding of the present application, and form a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 An exemplary embodiment of a process flow diagram of the low-temperature bonding method for reducing surface damage of the present application is shown;

[0035] Figure 2 An exemplary embodiment of a schematic diagram of the low-temperature bonding method for reducing surface damage of the present application is shown;

[0036] Figure 3 A characterization test diagram of the roughness of the lithium niobate bonding surface after the second irradiation of the embodiment 1 of the present application is shown;

[0037] Figure 4 An exemplary embodiment of a bonding wafer defect comparison diagram of the present application is shown;

[0038] Figure 5 An exemplary embodiment of a characterization test diagram of the crack length of the bonding wafer of the embodiment 1 of the present application is shown.

[0039] Explanation of reference signs:

[0040] 100 - first wafer; 200 - second wafer; 110 - first activation layer corresponding to the first wafer; 210 - first activation layer corresponding to the second wafer; 110' - second activation layer corresponding to the first wafer; 210' - second activation layer corresponding to the second wafer 210'. DETAILED DESCRIPTION

[0041] In order to more clearly explain the overall concept of the present application, the following will be described in detail with reference to the drawings.

[0042] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure aspects of the present application.

[0043] Example 1

[0044] In one exemplary embodiment of the present application, the low temperature bonding method for reducing surface damage includes the following steps:

[0045] S1: Provide a clean single-side polished 6-inch lithium niobate (LN) piezoelectric single crystal wafer, with a surface root mean square roughness of 0.2 nm and a thickness of 250 μm; provide a clean single-side polished 6-inch single crystal silicon sample, with a surface root mean square roughness of 0.2 nm and a thickness of 500 μm; and provide a clean single-side polished 6-inch single crystal Si with a 300 nm thick SiO2 film layer. In this embodiment, the following roughness characterization and bonding energy characterization use the LN and single crystal Si wafer without the SiO2 film layer, and the etching depth characterization uses the single crystal Si wafer with the 300 nm thick SiO2 film layer.

[0046] At room temperature (25 °C), the single crystal silicon sample and the LN piezoelectric single crystal wafer are respectively carried by a mechanical hand to a transfer cavity, and the transfer cavity has a vacuum degree of 1.7 x 10 -3 Pa; after alignment, the two wafers are carried by the mechanical hand to a bonding cavity, and the bonding cavity has a vacuum degree of 2 x 10 -6 Pa.

[0047] Subsequently, ultra-pure argon gas (>99.9999%) is introduced, the argon gas flow is 90 sccm, and after pre-ventilation for 10 s, rapid Ar 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 45 s, to complete the first activation treatment.

[0048] The wafer after the first irradiation is carried out by a mechanical arm, and the roughness of the bonding surface after the first irradiation is characterized. The LN surface root mean square roughness increases to 0.372 nm / rms; the single crystal silicon Si surface root mean square roughness increases to 0.391 nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same conditions is about 2.3 nm.

[0049] S2: The wafer after the first irradiation is again sent to the bonding machine to repeat the above operation to be carried to the bonding cavity, ultra-pure neon gas (>99.9999%) is introduced, the neon gas flow is 90 sccm, and after pre-ventilation for 10 s, 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 s, to complete the second activation treatment.

[0050] The wafer after the second irradiation is carried out by a mechanical arm, and the roughness of the bonding surface after the second irradiation is characterized again. The LN surface root mean square roughness is reduced from 0.372 nm / rms to 0.314 nm / rms, and the Si surface root mean square roughness is reduced from 0.391 nm / rms to 0.332 nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions is about 3.3 nm.

[0051] S3: Take multiple sets of LN and Si wafers of the same specification to perform the above process again and directly perform pressure bonding. The pressure is 5 kN, and the time is 60 s. A bonded wafer is obtained.

[0052] Example 2

[0053] In an exemplary embodiment of the present application, the low-temperature bonding method for reducing surface damage includes the following steps:

[0054] S1: Provide a clean single-side polished 6-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface root mean square roughness of 0.231 nm and a thickness of 250 μm. Provide a clean single-side polished 6-inch single crystal silicon sample with a surface root mean square roughness of 0.203 nm and a thickness of 500 μm. Provide a clean single-side polished 6-inch single crystal Si with a 300 nm thick SiO2 thin film layer. In this embodiment, the following roughness characterization and bonding energy characterization use LN and single crystal Si wafers without a SiO2 layer, and the etching depth characterization uses single crystal Si with a 300 nm thick SiO2 thin film layer.

[0055] At room temperature (25°C), the single crystal silicon sample and the LN piezoelectric single crystal wafer are carried into the transmission cavity by a mechanical hand. The transmission cavity has a vacuum degree of 1.7 x 10 -3 Pa. After alignment, the two wafers are carried into the bonding cavity by the mechanical hand. The bonding cavity has a vacuum degree of 2 x 10 -6 Pa.

[0056] Then, ultra-pure argon gas (>99.9999%) is introduced, and the argon gas flow is 90 sccm. After 10 s of pre-bleeding, rapid Ar atomic beam bombardment is performed at a voltage of 1500 V and a current of 100 mA, an irradiation angle of 70°, and an irradiation time of 45 s. The first activation treatment is completed.

[0057] The wafer after the first irradiation is carried out by a mechanical arm, and the roughness of the bonding surface after the first irradiation is characterized. The LN surface root mean square roughness is increased from 0.231 nm / rms to 0.372 nm / rms, and the single crystal silicon Si surface root mean square roughness is increased from 0.203 nm / rms to 0.391 nm / rms. At this time, the etching depth of the SiO2 layer activated under the same conditions is about 2.3 nm.

[0058] S2: The wafer after the first irradiation is sent into the bonder again to repeat the above operation to carry to the bonding cavity, and ultra-pure neon gas (>99.9999%) is introduced, the neon gas flow is 90sccm, after pre-ventilation for 10s, fast Ne atomic beam bombardment is performed, the voltage is 1500V, the current is 100mA, the irradiation angle is 70°, and the irradiation time is 40s.

[0059] The wafer after the irradiation is carried out by the mechanical arm, the roughness of the bonding surface after the irradiation is characterized again, the LN surface root mean square roughness is reduced from 0.314nm / rms to 0.303nm / rms, and the Si surface root mean square roughness is reduced from 0.322nm / rms to 0.31nm / rms, at this time, the etching depth of the SiO2 layer activated under the same condition is still 3.3nm.

[0060] The wafer after the irradiation is carried out by the mechanical arm, the roughness of the bonding surface after the irradiation is characterized again, the LN surface root mean square roughness is reduced from 0.314nm / rms to 0.303nm / rms, and the Si surface root mean square roughness is reduced from 0.322nm / rms to 0.31nm / rms, at this time, the etching depth of the SiO2 layer activated under the same condition is still 3.3nm.

[0061] The wafer after the irradiation is carried out by the mechanical arm, the roughness of the bonding surface after the irradiation is characterized again, the LN surface root mean square roughness is reduced from 0.314nm / rms to 0.303nm / rms, and the Si surface root mean square roughness is reduced from 0.322nm / rms to 0.31nm / rms, at this time, the etching depth of the SiO2 layer activated under the same condition is still 3.3nm.

[0062] S3: A plurality of groups of LN and Si wafers of the same specification are taken to repeat the above process and direct pressure bonding is performed, the pressure is 5kN, and the time is 60s, to obtain a bonded wafer.

[0063] Example 3

[0064] In one exemplary embodiment of the present application, the low-temperature bonding method for reducing surface damage comprises the following steps:

[0065] S1: A clean single-side polished 6-inch lithium niobate (LN) piezoelectric single crystal wafer is provided, the surface root mean square roughness is 0.2nm, and the thickness is 250μm; a clean single-side polished 6-inch single crystal silicon sample is provided, the surface root mean square roughness is 0.2nm, and the thickness is 500μm; and a clean single-side polished 6-inch single crystal Si with a 300nm-thick SiO2 thin film layer is provided. In this embodiment, the LN and Si wafers are used for the following roughness characterization and bonding energy characterization, and the single crystal Si wafer with a 300nm-thick SiO2 thin film layer is used for the etching depth characterization.

[0066] The single crystal silicon sample and the LN piezoelectric single crystal wafer are respectively carried by a mechanical hand to a transmission cavity under room temperature (25°C), and the vacuum degree of the transmission cavity is 1.7*10 -3 Pa; after alignment, the two wafers are carried by the mechanical hand to a bonding cavity, and the vacuum degree of the bonding cavity is 2*10 -7 Pa.

[0067] Subsequently, ultra-pure argon gas (>99.9999%) is introduced, the argon gas flow is 90sccm, and after pre-bleeding for 10s, rapid Ar atomic beam bombardment is performed, the voltage is 2000V, the current is 100mA, the irradiation angle is 70°, and the irradiation time is 38s, so as to complete the first activation treatment.

[0068] The wafer after the first irradiation is carried out by the mechanical arm, the roughness of the bonded surface after irradiation is characterized, the LN surface root mean square roughness is increased to 0.386nm / rms; the Si surface root mean square roughness is increased to 0.401nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same condition is about 2.4nm.

[0069] S2: the wafer after the first irradiation is carried into the bonding machine again to repeat the above operation to carry to the bonding cavity, ultra-pure neon gas (>99.9999%) is introduced, the neon gas flow is 90sccm, and after pre-bleeding for 10s, rapid Ne atomic beam bombardment is performed, the voltage is 2000V, the current is 100mA, the irradiation angle is 70°, and the irradiation time is 30s; the second activation treatment is completed.

[0070] The wafer after irradiation is carried out by the mechanical arm, and the roughness of the bonded surface after irradiation is characterized again, the LN surface root mean square roughness is reduced from 0.386nm / rms to 0.337nm / rms, the Si surface root mean square roughness is reduced from 0.401nm / rms to 0.344nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same condition is about 3.5nm.

[0071] S3: a plurality of groups of LN and Si wafers of the same specification are taken to perform the above process again and direct pressure bonding is performed, the pressure is 5kN, and the time is 60s, so as to obtain a bonded wafer.

[0072] Example 4

[0073] In an exemplary embodiment of the present application, the low-temperature bonding method for reducing surface damage comprises the following steps:

[0074] S1: the same as the S1 step of example 1, the LN surface root mean square roughness after irradiation is increased to 0.375nm / rms; and the Si surface root mean square roughness is increased to 0.387nm / rms.

[0075] S2: Same as S2 of Example 1, after irradiation, the LN surface root mean square roughness is reduced from 0.375 nm / rms to 0.324 nm / rms, and the Si surface root mean square roughness is reduced from 0.387 nm / rms to 0.329 nm / rms.

[0076] S3: Take multiple sets of LN and Si wafers of the same specifications and perform the above process again and directly perform pressure bonding, the pressure is 10 kN, and the time is 60 s, to obtain a bonded wafer.

[0077] Example 5

[0078] In one exemplary embodiment of the present application, the low-temperature bonding method for reducing surface damage includes the following steps:

[0079] S1: Provide a clean double-side polished 4-inch lithium niobate (LN) piezoelectric single crystal wafer with a surface root mean square roughness of 0.2 nm and a thickness of 250 μm; provide a clean double-side polished 4-inch silicon carbide (SiC) sample with a surface root mean square roughness of 0.2 nm and a thickness of 500 μm; and provide a clean single-side polished 4-inch single crystal Si with a 300 nm thick SiO2 film layer. In this embodiment, the following roughness characterization and bonding energy characterization are performed using the LN and SiC wafers, and the etching depth characterization is performed using the single crystal Si wafer with a 300 nm thick SiO2 film layer.

[0080] At room temperature (25°C), the SiC sample, the LN piezoelectric single crystal wafer, and the single crystal Si are respectively transported by a mechanical hand to a transmission cavity, and the transmission cavity has a vacuum degree of 1.7 x 10 -3 Pa; after alignment, the two wafers are transported by the mechanical hand to a bonding cavity, and the bonding cavity has a vacuum degree of 1 x 10 -8 Pa.

[0081] Subsequently, ultra-pure argon gas (>99.9999%) is introduced, the argon gas flow is 90 sccm, and after pre-flowing for 10 s, rapid Ar atomic beam bombardment is performed, the voltage is 1500 V, the current is 150 mA, the irradiation angle is 70°, and the irradiation time is 45 s, to complete the first activation treatment.

[0082] The irradiated wafer is transported out by the mechanical arm, and the roughness of the irradiated bonding surface is characterized, the LN surface root mean square roughness is increased to 0.372 nm / rms, and the SiC surface root mean square roughness is increased to 0.391 nm / rms.

[0083] S2: The wafer after the first irradiation is sent into the bonder again to repeat the above operation to carry to the bonding cavity, and ultra-pure neon gas (>99.9999%) is introduced, the neon gas flow is 90sccm, and after pre-ventilation for 10s, fast Ne atomic beam bombardment is carried out, the voltage is 1500V, the current is 150mA, the irradiation angle is 70°, and the irradiation time is 40s;

[0084] The wafer after irradiation is carried out by the mechanical arm, and the roughness of the bonding surface after irradiation is characterized again, the LN surface root mean square roughness is reduced from 0.372nm / rms to 0.318nm / rms, and the SiC surface root mean square roughness is reduced from 0.391nm / rms to 0.323nm / rms, at this time, the etching depth of SiO2 activated under the same condition is about 3.3nm.

[0085] S3: A plurality of groups of LN and SiC wafers of the same specification are taken to repeat the above process and direct pressure bonding is carried out, the pressure is 5kN, and the time is 60s, to obtain a bonded wafer.

[0086] Comparative Example 1

[0087] In an exemplary embodiment of the present application, the low-temperature bonding method comprises the following steps:

[0088] A clean single-side polished 6-inch lithium niobate (LN) piezoelectric single crystal wafer is provided, with a surface root mean square roughness of 0.2nm and a thickness of 250μm; a clean single-side polished 6-inch single crystal silicon sample is provided, with a surface root mean square roughness of 0.2nm and a thickness of 500μm; and a clean single-side polished 6-inch single crystal Si with a 300nm-thick SiO2 film layer is provided. In this embodiment, the following roughness characterization and bonding energy characterization use LN and single crystal Si wafers, and the etching depth characterization uses the single crystal Si wafer with a 300nm-thick SiO2 film layer.

[0089] At room temperature (25℃), the single crystal silicon sample and the LN piezoelectric single crystal wafer are carried to the transmission cavity by the mechanical hand, the transmission cavity has a vacuum degree of 1.7×10 -3 Pa; after alignment, the two wafers are carried to the bonding cavity by the mechanical hand, and the bonding cavity has a vacuum degree of 2×10 -6 Pa.

[0090] Subsequently, ultra-pure argon gas (>99.9999%) is introduced, the argon gas flow is 90sccm, and after pre-ventilation for 10s, fast Ar atomic beam bombardment is carried out, the voltage is 1500V, the current is 100mA, the irradiation angle is 70°, and the irradiation time is 65s;

[0091] The irradiated wafer is carried out by a mechanical arm, and the roughness of the bonded surface after irradiation is characterized. The LN surface root mean square roughness is increased to 0.39 nm / rms; the Si surface root mean square roughness is increased to 0.386 nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same conditions is about 3.3 nm.

[0092] A plurality of groups of LN and Si wafers of the same specification are taken again to perform the above process and direct pressure bonding, the pressure is 5 kN, and the time is 60 s, to obtain a bonded wafer.

[0093] Comparative Example 2

[0094] In an exemplary embodiment of the present application, the low-temperature bonding method comprises the following steps:

[0095] S1: the same as the S1 step of Example 1.

[0096] The irradiated wafer is carried out by a mechanical arm, and the roughness of the bonded surface after irradiation is characterized. The LN surface root mean square roughness is increased to 0.391 nm / rms; the Si surface root mean square roughness is increased to 0.382 nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same conditions is about 2.3 nm.

[0097] S2: the wafer irradiated for the first time is sent into the bonder again to repeat the above operation and carried to the bonding cavity, and ultra-pure neon gas is introduced (>99.9999%), the neon gas flow is 90 sccm, the gas is pre-introduced for 10 s, and then rapid Ne atomic beam bombardment is performed, the voltage is 3000 V, the current is 100 mA, the irradiation angle is 70°, and the irradiation time is 20 s.

[0098] The irradiated wafer is carried out by a mechanical arm, and the roughness of the bonded surface after irradiation is characterized. The LN surface root mean square roughness is increased to 0.391 nm / rms; the Si surface root mean square roughness is increased to 0.382 nm / rms, and at this time, the etching depth of the SiO2 layer activated under the same conditions is about 2.3 nm.

[0099] S3: the same as the S3 step of Example 1.

[0100] Comparative Example 3

[0101] Based on Example 1, the main difference is that S3: a plurality of groups of LN and Si wafers of the same specification are taken again to perform the above process and direct pressure bonding, the pressure is 100 N, and the time is 60 s. The other steps are the same as those of Example 1.

[0102] Test Example

[0103] After bonding in the above embodiments and comparative examples, the bonded sheets were transported out of the chamber and into the atmospheric environment by a robotic arm. The surface was visually inspected for defects such as bubbles and debonding. The bonding energy was tested using a blade insertion method, with five test points used as the average value. The test results for roughness, bonding energy, and the probability of defects are shown in Table 1.

[0104] The formula for calculating the bond energy is as follows:

[0105] ,

[0106] Wherein, E1 and E2 are the Young's modulus (Pa) of the first and second wafers, respectively.

[0107] t1 and t2 are the wafer thicknesses (m) of the first and second wafers, respectively.

[0108] t b — Blade thickness (m), blade thickness t used for testing b =0.0001m;

[0109] γ — Bonding energy (J / m) 2 );

[0110] L—Crack length (mm);

[0111] Among them, reference Figure 4 , Figure 4 The diagram shows a comparison of defects in the bonded sheets of the present invention. By visually observing whether there are defects such as bubbles or debonding at the bonding interface of the bonded sheets, multiple sets of bonded sheets are taken and the probability of defects in the bonded sheets is calculated.

[0112] Table 1

[0113]

[0114] Referring to Table 1, the low-temperature bonding method for reducing surface damage in this invention employs gradient activation of the bonding surface. After activation, the surface roughness is no higher than 0.35 nm / rms, the etching depth is no higher than 3.5 nm, and the average bonding energy is no lower than 1.5 J / m. 2 The probability of defects on the bonding surface is no higher than 16%.

[0115] refer to Figure 3 As shown, Figure 3 The image shows a roughness characterization test result of the lithium niobate bonding surface after the second irradiation in Example 1 of the present invention. (Reference) Figure 5 , Figure 5 An exemplary embodiment of the test diagram for characterizing the crack length of the bonded sheet in Embodiment 1 of the present invention is provided. Based on the crack length, the bonding energy of the bonded sheet can be calculated according to the above formula.

[0116] Compared with the reference example 1, the surface roughness of the wafer bonding surface is greatly increased when the wafer is irradiated by a single argon atom beam, and the surface roughness increase rate is greater than 90%. The surface roughness increase rate of the wafer bonding surface after the graded activation of the present application is not greater than 75%, which to some extent proves that the graded activation of the wafer bonding surface can reduce the damage to the wafer surface caused by single activation and reduce the surface roughness.

[0117] Compared with the example 1, the main difference of the reference example 2 is that the second irradiation voltage is increased, which can cause damage to the wafer surface, increase the surface roughness, increase the probability of bubble occurrence after bonding, and reduce the bonding strength.

[0118] The above only describes the embodiments of the present application and is not used to limit the present application. The present application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A low temperature bonding method for reducing surface damage, characterized by, The low-temperature bonding method comprises the following steps: S1: under a high-vacuum environment, bonding surfaces of a first wafer and a second wafer to be bonded are subjected to first irradiation treatment by a first atomic beam, to obtain first activation layers; S2: the bonding surfaces subjected to the first irradiation treatment in step S1 are subjected to at least one second irradiation treatment by a second atomic beam, to obtain second activation layers; S3: the bonding surfaces of the first wafer and the second wafer subjected to the second irradiation are subjected to pressure bonding, to obtain a bonded wafer; 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 less than that of the first atomic beam; 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; The voltage of the first irradiation treatment is 100-2000V, the current of the first irradiation treatment is 50-300mA, and the irradiation time is 10-200s; The voltage of the second irradiation treatment is 500-2000V, the current of the second irradiation treatment is 10-300mA, and the irradiation time is 10-200s; The vacuum degree of the high vacuum environment is not higher than 1×10 -6 Pa, and the temperature is not higher than 30℃. In step S2, the bonding surfaces subjected to the first irradiation treatment are subjected to two second irradiation treatments by the second atomic beam, which comprises the following steps: the bonding surfaces subjected to the first irradiation treatment in step S1 are first subjected to a first second irradiation treatment by a Ne atomic beam, and then subjected to a second second irradiation treatment by a He atomic beam.

2. The cryogenic bonding method according to claim 1, wherein The sizes of the first wafer and the second wafer are both selected from any one of 1-12 inches.

3. The cryogenic bonding method according to claim 1, wherein The surface root mean square roughness of the first wafer and the second wafer is both within the range of 0.1-0.5nm.

4. The cryogenic bonding method of claim 1, wherein The pressure of the pressure bonding is 1-50kN.

5. A bonded wafer prepared by the low-temperature bonding method for reducing surface damage according to any one of claims 1 to 4, characterized by The bonding sheet bonding energy can be not less than 1.5 J / m 2 ; The probability of defects of the bonded wafer is not higher than 16%.

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