Method for wafer bonding

Abstract

A method for bonding wafers includes performing a cleaning process on a first surface of a first wafer, and performing a surface activation process on the first surface. The surface activation process is selected from the group consisting of: a plasma surface activation process comprising generating a plasma from the process gas, in which ions in the plasma are removed using a filter, and in which the first surface is treated using a remaining uncharged portion of the plasma; a laser surface activation process using a laser beam; an acid surface activation process using an acid; and an alkali surface activation process using an alkali. After the surface activation process, a rinsing process is performed on the first surface. The first surface of the first wafer is bonded to the second surface of the second wafer.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to methods for wafer bonding. Background Art

[0002] Wafer bonding processes are commonly used in the manufacture of integrated circuits. To achieve wafer bonding, the surfaces of the wafers to be bonded may be activated by a plasma activation process. Summary of the invention

[0003] Some embodiments of the present disclosure provide a method for bonding wafers, the method comprising: performing a cleaning process on a first surface of a first wafer; performing a surface activation process on the first surface, wherein the surface activation process is selected from the following group consisting of: a plasma surface activation process, comprising generating plasma from a process gas, wherein a filter is used to remove ions in the plasma, and wherein the first surface is treated with a remaining uncharged portion of the plasma; a laser surface activation process, using a laser beam; an acid surface activation process, using an acid; and an alkaline surface activation process, using an alkaline; after the surface activation process, performing a rinsing process on the first surface; and bonding the first surface of the first wafer to the second surface of the second wafer.

[0004] Other embodiments of the present disclosure provide a method for bonding wafers, the method comprising: generating plasma from a process gas; removing charged particles from the plasma using a filter; performing a surface activation process on a first wafer using an uncharged portion of a remaining portion of the plasma; after the surface activation process, performing a rinsing process on the first wafer; and bonding the first wafer to a second wafer.

[0005] Yet another embodiment of the present disclosure provides a method for bonding wafers, the method comprising: placing a first wafer into a process chamber; introducing a process gas into the process chamber; generating plasma from the process gas, wherein a filter is located between the first wafer and the plasma, and wherein an uncharged portion of the plasma passes through the filter to reach the first wafer; and bonding the first wafer to a second wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] When read in conjunction with the accompanying drawings, aspects of the present disclosure can be best understood from the following detailed description. It should be noted that, in accordance with standard practice in the industry, the various components are not drawn to scale. In fact, the dimensions of the various components may be arbitrarily increased or reduced for clarity of discussion.

[0007] Figure 1 An apparatus for wafer bonding according to some embodiments is shown.

[0008] Figure 2 A cleaning process using a cleaning module according to some embodiments is shown.

[0009] Figure 3 A surface activation module including a plasma ion filter using metastable species is shown according to some embodiments.

[0010] Figure 4 A top view of a plasma ion filter is shown according to some embodiments.

[0011] Figures 5 to 7 Two plasma ion filters are shown used in combination according to some embodiments.

[0012] Figure 8 A surface activation module is shown according to some embodiments, the surface activation module including a plasma ion filter for filtering plasma generated by a reaction gas.

[0013] Fig. 9 A surface activation module including a plasma ion filter for generating high-energy molecules is shown according to some embodiments.

[0014] Fig.10 A laser surface activation process according to some embodiments is shown.

[0015] Fig.11 A table showing some materials used for laser surface activation processes and corresponding laser wavelengths and powers according to some embodiments.

[0016] Fig.12 A surface activation process by spraying acid or base according to some embodiments is shown.

[0017] Fig.13 A surface activation process by acid or base bathing is shown according to some embodiments.

[0018] Figures 14 to 17 Flushing and alignment for bonding two wafers are shown in accordance with some embodiments.

[0019] Figures 18 to 21 The formation of a bond for joining two wafers is shown in accordance with some embodiments.

[0020] Figure 22 to Figure 26 A process for bonding two wafers is shown in accordance with some embodiments.

[0021] Fig. 27 A process flow for bonding two wafers according to some embodiments is shown. DETAILED DESCRIPTION

[0022] The following disclosure provides many different embodiments or examples for implementing the different components of the present application. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first component above or on a second component may include an embodiment in which the first component and the second component are directly in contact with each other, and may also include an embodiment in which an additional component may be formed between the first component and the second component so that the first component and the second component may not be in direct contact. As used herein, forming a first component on a second component means that the first component is directly in contact with the second component. In addition, the present disclosure may repeat reference numerals and / or characters in various examples. This repetition is for the purpose of clarity and simplicity, and does not itself indicate the relationship between the individual embodiments and / or configurations discussed.

[0023] Additionally, for ease of description, spatially relative terms such as "below," "beneath," "lower," "above," and "upper" may be used herein to describe the relationship of one element or component to another element or component as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein should likewise be interpreted accordingly.

[0024] A wafer bonding process and an apparatus for performing the wafer bonding process are provided. According to some embodiments of the present disclosure, the apparatus includes a surface activation module for activating the surface of the wafer to be bonded. When the surface activation module is used, the surface activation module can avoid damage to the wafer circuit (the damage is caused by plasma). Surface activation can use a filter to filter out ions when generating plasma, or through an ion-free activation process, such as a laser activation process, an acid activation process, an alkali activation process, etc.

[0025] The embodiments discussed herein are intended to provide examples to enable the manufacture or use of the subject matter of the present disclosure, and those of ordinary skill in the art will readily appreciate the modifications that may be made while remaining within the intended scope of the different embodiments. Throughout the various views and illustrative embodiments, the same reference numerals are used to represent the same elements. Although the method embodiments may be discussed as being performed in a particular order, other method embodiments may be performed in any logical order.

[0026] Figure 1A system diagram of an apparatus 20 is shown, which, according to some embodiments, is referred to as a wafer bonding module 20. According to some embodiments, the wafer bonding module 20 is used to bond wafers that may include integrated circuits. The wafer bonding module 20 also includes a load port 22, a transfer module 24, a wafer cleaning module 26, a surface activation module 28, a transfer module 30, a rinse module 32, and a wafer bonding (pre-bonding) and annealing module 34.

[0027] The load port 22 is configured to load a wafer (wafer to be bonded) into the wafer bonding module 20 , and is configured to take the wafer out of the wafer bonding module 20 after completing a wafer bonding process.

[0028] To start the wafer bonding process, the wafer to be bonded is transferred to the wafer cleaning module 26 through the transfer module 24. The wafer cleaning module 26 is configured to clean the surface of the wafer. The corresponding process is shown as follows Fig. 27 Process 202 of process flow 200 is shown. The cleaning process may include removing metal oxides, chemicals, particles, etc. from the surface of the wafer.

[0029] Figure 2 A view of a portion of a wafer cleaning module 26 is shown in accordance with some embodiments. The wafer cleaning module 26 may include a dispensing head 46 connected to a reservoir (not shown). The reservoir stores a cleaning agent 44 or multiple types of cleaning agents, which may include deionized (DI) water and chemicals such as NH 3 , H 2 O 2 , citric acid, etc., or a combination thereof. According to some embodiments, the wafer cleaning module 26 is configured to dispense the cleaning agent 44 onto the wafer 42 or 142 (hereinafter referred to as 42 / 142), and the wafer rotates when the cleaning agent 44 is dispensed. The cleaning agent 44 spins off the wafer 42 / 142 and is collected by the wafer slot 40.

[0030] After cleaning the wafer 42 / 142, the wafer 42 / 142 is transferred to the surface activation module 28, such as Figure 1 As shown. A surface activation process is then performed to form dangling bonds on the surface of the wafer 42 / 142. The corresponding process is shown as Fig. 27 Process 204 in process flow 200 is shown.

[0031] Figure 3 Surface activation module 28A is shown according to some embodiments. Surface activation module 28A is Figure 1. The surface activation module 28A may include a vacuum chamber 48, which is configured to be evacuated. An input port 50 is connected to the vacuum chamber 48, and a process gas 52 can be introduced into the vacuum chamber 48 through the input port 50. The surface activation module 28A is also configured to generate a plasma from the process gas, such as by a built-in RF generator and by a coil (not shown) surrounding the area where the plasma is generated. The coil can be placed inside or outside the process chamber 48. The wafer 42 / 142 is placed on a wafer support 58, which can be, for example, an electrostatic chuck.

[0032] A plasma ion filter 56 is also built into the vacuum chamber 48 and is located between the wafer 42 / 142 and the area where the plasma is generated. According to some embodiments, the plasma ion filter 56 is used to filter ions in the generated plasma and leave free radicals to treat the wafer 42 / 142. According to some embodiments, the plasma ion filter 56 is electrically grounded. According to optional embodiments, the plasma ion filter 56 is not electrically grounded and can be, for example, electrically floating or connected to a voltage (such as a positive voltage such as 1V, 2V, 5V, 10V, etc.). Accordingly, in Figure 3 In FIG. 5 , the electrical ground connected to the plasma ion filter 56 is shown as a dashed line to indicate that the plasma ion filter 56 may or may not be electrically grounded.

[0033] The plasma ion filter 56 may be formed of a conductive material (e.g., a metal such as copper, aluminum, nickel, tungsten, etc.), a semiconductor material (e.g., silicon), a dielectric material (e.g., quartz, silicon oxide, silicon nitride, silicon carbide), a metal-containing dielectric (e.g., a metal oxide (e.g., CuO, AlO), a metal nitride (e.g., AlN)), etc.

[0034] According to some embodiments, a surface activation process is performed on the wafer 42 / 142, during which a process gas is introduced into the process chamber 48. The process gas may include an inert gas such as He, Ne, Ar, Kr, Xe, etc., or a combination thereof. Other process gases such as N 2 , O 2 In the following discussion, it is assumed that He is used as the process gas, but the discussion is also applicable to other types of process gases.

[0035] like Figure 3 As shown, plasma 54 is generated, for example, by applying RF source power to a coil surrounding the location where plasma 54 is generated. The chamber pressure is controlled to be low (less than Fig. 9The plasma 54 may be formed by the process gas and the plasma may be formed by the process gas. For example, when the process gas includes He (helium), the plasma 54 may include free radicals such as He* and free radicals such as He*. + ions.

[0036] When the plasma ion filter 56 is electrically grounded, the plasma ion filter 56 attracts ions such as He + ) and the charge of the electron. Radicals such as He* are uncharged and can pass through the opening 57 in the plasma ion filter 56 to impinge on the wafer 42 / 142. When the plasma ion filter 56 is not electrically grounded (such as electrically floating), the properties of the plasma 54 can cause an electric field to be generated at a nearby interface (such as the surface of the plasma ion filter 56). Therefore, even if the plasma ion filter 56 is not electrically grounded, free radicals such as electrons e- and ions He* can pass through the opening 57 in the plasma ion filter 56 to impinge on the wafer 42 / 142. + The charges will still be captured by the plasma ion filter 56.

[0037] According to some embodiments, by adjusting process conditions (such as RF source power), metastable radicals (e.g., He*) may be generated. The metastable radical He* is in a high energy state (because the high energy state is not very stable, and therefore the high energy state is metastable). For example, in a metastable state, the radical He* may have an energy of about 20 eV. If Ne is used as a process gas, the Ne radical in a metastable state may have an energy of about 16 eV. If Ar is used as a process gas, the Ar radical in a metastable state may have an energy of about 12 eV.

[0038] After passing through the through opening 57, the metastable radicals will collide with the surface of the wafer 42 / 142, release energy and return to the ground state. For example, the surface material of the wafer 42 / 142 may include a silicon-containing material (the silicon-containing material may include silicon, silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride), diamond, AlN, etc. The energy causes the bonds of the surface material of the wafer 42 / 142 to break, thereby forming dangling bonds on the silicon, which can form OH bonds in a subsequent rinsing process and / or when the wafer 42 / 142 is exposed to air (with moisture).

[0039] Figures 4 to 7 A plasma ion filter 56 is shown according to some embodiments. Figure 4 The plasma ion filter 56 may be a plate including a plurality of densely distributed through openings 57. The through openings 57 may be arranged to have a repeating pattern, such as an array, a honeycomb pattern, or the like.

[0040] Figure 5 and Figure 6 Two assemblies 56A and 56B are shown, and according to an alternative embodiment, the two assemblies 56A and 56B are used together as a plasma ion filter 56. Figure 5 , the plasma ion filter 56A includes a plurality of elongated through openings 57A parallel to each other. Figure 6 , the plasma ion filter 56B includes a plurality of elongated through openings 57B parallel to each other. When placed in the vacuum chamber 48, the plasma ion filter 56B is stacked above the plasma ion filter 56A, such as Figure 7 As shown, to form a plasma ion filter 56.

[0041] According to some embodiments, Figure 7 As shown, when the plasma ion filters 56A and 56B are installed in the vacuum chamber 48, the plasma ion filter 56A can be electrically interconnected or electrically disconnected. One or both of the plasma ion filters 56A and 56B can be electrically floating or electrically grounded. The length directions of the through openings 57A and 57B can be parallel to each other. The through opening 57A can be slightly offset from the corresponding upper opening 57B. According to some embodiments, the through opening 57A is completely offset from the lower through opening 57B, which means that when the plasma ion filters 56A and 56B are observed from the top, the material of the plasma ion filter 56A will be observed through the through opening 57B, and the wafer 42 / 142 below will not be seen due to the obstruction of the plasma ion filter 56A. Figure 3 ).

[0042] By completely offsetting through opening 57A from through opening 57B, the efficiency of collecting ions will be improved, and ions will be less likely to pass through both through openings 57A and 57B at the same time. For example, any ions moving downward will collide with plasma ion filter 56A if they pass through opening 57B. On the other hand, some radicals may move through both openings 57B and 57A at the same time and reach wafer 42 / 142.

[0043] In order to maximize the effect of trapping ions and also maximize the passage of free radicals, the through opening 57A only deviates from the nearest through opening 57B above the corresponding one, and does not deviate further. Figure 7 As shown, plasma ion filter 56B includes a left edge 56E2 facing opening 57B1 , and plasma ion filter 56A includes a right edge 56E1 facing opening 57A1 , wherein edges 57E1 and 57E2 are vertically aligned to the same vertical line 59 .

[0044] According to an alternative embodiment, when the plasma ion filters 56A and 56B are installed in the vacuum chamber 48, the length direction of the through opening 57A can be rotated, for example, as shown in FIG. Figure 6 As shown by arrow 60 in FIG. 1 . The rotation angle can be any angle between 0 and 90 degrees. When the rotation angle is 90 degrees, the length direction of opening 57A is perpendicular to the length direction of opening 57B. Accordingly, when viewed from the top of the stacked plasma ion filters 56A and 56B, the overlapping portions of openings 57A and 57B form a plurality of openings arranged in an array. This is equivalent to Figure 4 The openings 57 shown are different in that the portion of opening 57A that does not overlap with opening 57B can increase the chance of free radicals passing through, and the portion of opening 57B that does not overlap with opening 57A can increase the chance of free radicals passing through.

[0045] Figure 8 A surface activation module 28A is shown according to some embodiments. The surface activation module 28A also includes a vacuum chamber 48, which is configured to be evacuated. An input port 50 is connected to the vacuum chamber 48, and a process gas 52 can be input into the vacuum chamber 48 through the input port 50. According to some embodiments, the input port 50 is connected to a reservoir 53, which stores a gas capable of etching the bonding layer of the wafer 42 / 142. When the bonding layer of the wafer 42 / 142 includes silicon, silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride, diamond, AlN, etc., the etching gas may include a fluorine-containing etching gas (such as XeF 2 BrF 3 IF 5 , ClF 3 、F 2 CF 4 , CHF 3 , CH 2 F 2 , CH 3 F, etc.), gases containing halogens and carbon (such as fluorocarbons, for example C 4 F 8 ), chlorine-containing gases (such as ClF 3 , Cl 2 , HCl, etc.), etc. or a combination of the above gases.

[0046] A plasma ion filter 56 is also built into the vacuum chamber 48. According to some embodiments, the plasma ion filter 56 is used to filter ions in the generated plasma and leave radicals to etch the wafer 42 / 142 placed in the vacuum chamber 48. According to some embodiments, the plasma ion filter 56 is electrically grounded, electrically floating, or connected to a positive voltage. According to some embodiments, the plasma ion filter 56 can be as described in reference Figures 4 to 7As discussed.

[0047] The surface activation module 28A is also configured to generate a plasma from the etching gas, for example, by a built-in RF source generator. The plasma may contain ions and free radicals of the etching gas as well as electrons. For example, when the etching gas is or includes a fluorine-containing gas, a plasma such as F is generated. + The charges of ions and electrons and free radicals such as F* radicals.

[0048] Through the plasma ion filter 56, ions and electrons are filtered, and free radicals of etching substances, such as F* radicals, pass through the through opening 57 of the plasma ion filter 56 to collide with the bonding layer of the wafer 42 / 142. Therefore, the free radicals etch away some surface materials of the wafer 42 / 142 to activate surface reactions. For example, some silicon-containing dielectric materials are etched to generate dangling bonds, thereby making it easy to form OH bonds in the subsequent rinsing process.

[0049] As will be discussed in subsequent processes, in addition to the gas used for etching, the reservoir 53 may also store a non-etching gas that is not used for etching the wafer 42 / 142, and also introduce the gas into the process chamber 48 to generate plasma. According to some embodiments, the reservoir 53 stores an inert gas such as He, Ne, Ar, Kr, Xe, etc. According to some embodiments, the reservoir 53 stores another gas that can be used to generate plasma, such as O 2 、N 2 , H 2 etc., or a combination thereof. Non-etching gases can also be obtained by referring to Figure 3 Mechanism or reference discussed Fig. 9 The mechanisms discussed help to generate dangling bonds. Accordingly, according to these embodiments, two mechanisms including etching and bombardment can work simultaneously to generate dangling bonds.

[0050] Fig. 9 Surface activation module 28A according to some embodiments is shown. Surface activation module 28A may include vacuum chamber 48, which is configured to be evacuated. Input port 50 is connected to vacuum chamber 48, and process gas 52 may be input into vacuum chamber 48 through input port 50. Process gas 52 may be supplied from a vacuum chamber 48 having a surface activation module 28A. Figure 3 The gaseous molecules may be selected from the same group of candidate gases discussed in the embodiments of the present invention, and may include He, Ne, Ar, Kr, Xe, etc., or combinations thereof. There may also be molecules formed from more than one atom, such as N 2 , O 2 , H 2 Etc. The gas may include a combination of the above gases.

[0051] like Fig. 9As shown, plasma 54 is generated, for example, by applying RF source power. The chamber pressure is controlled to be high, for example, above about 1 mTorr, and may be in a range between about 1 mTorr and about 10 Torr. Ions and radicals are generated from the process gas. Plasma 54 may include radicals (such as He*) and ions 62 (such as He + ), depending on the type of gas.

[0052] According to some embodiments, due to the high pressure in the vacuum chamber 48, the ions 62 bombard the molecules 64 in the process chamber, such as N 2 , O 2 , H 2 The impacted molecules 64 are accelerated downward. Since the molecules 64 are not charged, they can pass through the through openings 57 and collide with the wafers 42 / 142. On the other hand, the ions 62 and electrons are still captured by the plasma ion filter 56. Free radicals can also be generated in the process gas, and these free radicals can also pass through the through openings 57 and collide with the wafers 42 / 142.

[0053] According to these embodiments, the surface material of the wafer 42 / 142 may include a silicon-containing material (the silicon-containing material may include silicon, silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon oxycarbide, silicon oxycarbonitride), diamond, AlN, etc. The kinetic energy of the molecules 64 causes the bonds of the surface material of the wafer 42 / 142 to break, thereby forming dangling bonds on the silicon, which can form OH bonds in subsequent rinsing or when exposed to moisture. Accordingly, according to these embodiments, the kinetic energy of the high-pressure inert gas is used to drive the molecules to activate the bonding surface.

[0054] Understandably, Figure 3 , Figure 8 and Fig. 9 The mechanisms in can be combined. For example, in the above Fig. 9 In the embodiment of FIG. 5 , when the process gas 52 includes an inert gas, the first mechanism using metastable free radicals (see FIG. 5 ) is used. Figure 3 mechanism discussed) and a second mechanism using accelerating molecules (ref. Fig. 9 The first mechanism and the second mechanism discussed above can coexist simultaneously. When the chamber pressure is in an intermediate range (such as in a range between about 0.1 mTorr and about 1 mTorr), the first mechanism and the second mechanism are balanced and have similar effects. As the chamber pressure decreases, the first mechanism begins to dominate until the second mechanism can eventually be ignored. As the chamber pressure increases, the second mechanism begins to dominate until the first mechanism can eventually be ignored.

[0055] exist Figure 8 In the embodiment shown, the etching mechanism can also be combined with the bombardment mechanism ( Figure 3 and Fig. 9). For example, when an inert gas is introduced into the vacuum chamber 48, when the chamber pressure is low, metastable free radicals of the inert gas may also be generated to bombard the surface of the wafer 42 / 142. Conversely or simultaneously, when the chamber pressure is high, and both the inert gas and the molecules are also introduced into the chamber 48, in addition to etching the wafer 42 / 142, the molecules may be accelerated to bombard the surface of the wafer 42 / 142. Thus, more dangling bonds may be generated.

[0056] In the above-described embodiments, plasma is generated by different mechanisms to generate dangling bonds on the surface of the wafer 42 / 142. The plasma ion filter 56 is used to filter charges including ions and electrons so that the charges do not reach the wafer 42 / 142. If the ions and electrons reach the wafer 42 / 142, the charges may damage the devices in the wafer 42 / 142, and this effect is called plasma-induced damage. For example, the charges may flow through the metal interconnect structure in the wafer 42 / 142 to the gate dielectric of the transistor and be collected by the gate dielectric, and the charges may damage the gate dielectric. According to some embodiments of the present disclosure, since the charges are filtered and do not reach the wafer activated by the plasma activation process, damage is avoided.

[0057] Fig.10 Surface activation module 28B according to alternative embodiments is shown. According to these embodiments, surface activation module 28B implements the following Figure 1 The surface activation module 28 is shown. The surface activation module 28B includes a laser module 68, which includes a laser beam generator and a laser beam projector for projecting a generated laser beam 70 onto the wafer 42 / 142.

[0058] According to some embodiments, the laser module 68 scans the wafer 42 / 142 line by line using a laser beam 70. According to an optional embodiment, the projection area of ​​the laser beam is enlarged to cover the entire wafer 42 / 142 or a portion of the wafer 42 / 142. The laser beam 70 is projected to the intended area of ​​the wafer 42 / 142 until the projected wafer 42 / 142 is activated and dangling bonds have been generated. Then, the laser beam 70 is moved to another area of ​​the wafer 42 / 142 (when the projection area is a portion of the wafer 42 / 142 but not all) to perform activation. Repeat this process until the entire wafer 42 / 142 is projected and activated by the laser beam 70. When the laser beam 70 is projected to the entire wafer 42 / 142, the projection is performed until the desired activation is achieved. The laser energy causes the bonds on the bonding layer to break, thereby enabling the formation of OH bonds.

[0059] In order to fully activate the surface of the wafer 42 / 142, the laser beam 70 may need to be within a certain wavelength range and have a certain power density. The wavelength range and the required power density are also related to the surface material of the wafer 42 / 142 to be activated. Fig.11 A table showing some materials, corresponding wavelength ranges, and corresponding power densities according to some embodiments.

[0060] According to some embodiments, when the surface layer (e.g. Fig.23 When the layer 94 or 194 in the substrate includes silicon oxide, the wavelength may be in the range of about 100 nm to about 300 nm, or in the range of about 3 μm to about 20 μm. When the surface layer includes SiCN, the wavelength may be in the range of about 100 nm to about 600 nm. When the surface layer includes diamond, the wavelength may be in the range of about 100 nm to about 400 nm. When the surface layer includes AlN, the wavelength may be in the range of about 100 nm to about 400 nm.

[0061] The power density of laser beam 70 also needs to be within a certain range. When the power density is too high, wafer 42 / 142 may be damaged. When the power density is too low, the surface of wafer 42 / 142 may not be fully activated. According to some embodiments, when the surface layer includes silicon oxide, SiCN, diamond or AlN, the power density may be about 1 mJ / cm 2 About 1J / cm 2 Since laser activation does not involve plasma, plasma-induced damage is avoided.

[0062] Fig.12 FIG. 2 shows a surface activation module 28C according to some embodiments. According to these embodiments, the surface activation module 28C implements Figure 1 The surface activation module 28 is shown. The surface activation module 28C includes a wet surface activation module 73, which includes a sprayer 74 and a reservoir 78 for storing an activation solution 76. The sprayer 74 is configured to spray the activation solution 76 onto the wafer 42 / 142.

[0063] According to some embodiments, the activation solution 76 is an acid, and the pH value of the activation solution 76 may be in the range of about 1 to about 6. For example, the activation solution 76 may include carbon dioxide (CO 2 ) solution. The surface activation process may include spraying the activation solution 76 on the wafer 42 / 142 for a period of time ranging from about 1 minute to about 2 hours. Due to the spraying, the acid destroys the bonds at the surface of the wafer 42 / 142 and thus generates dangling bonds. Because the activation using the acid solution does not involve plasma, it does not cause plasma-induced damage.

[0064] According to an optional embodiment, the activation solution 76 is a base, and the pH value of the activation solution 76 may be greater than 7 and may be in the range of about 8 to about 12. For example, the activation solution 76 may include ammonia (NH 3 ) solution, and thus includes NH 4 OH. The surface activation process may include spraying the activation solution 76 on the wafer 42 / 142 for a period of time ranging between about 1 minute and about 2 hours. Due to the spraying, the base destroys the bonds at the surface of the wafer 42 / 142 and thus generates dangling bonds. Because activation using an alkaline solution does not involve plasma, it does not cause plasma-induced damage.

[0065] Fig.13 Surface activation module 28D according to some embodiments is shown. According to these embodiments, surface activation module 28D implements Figure 1 The surface activation module 28 shown. The surface activation module 28D includes an activation solution tank 80, in which a wet surface activation solution 76 is stored. The wafers 42 and / or 142 (also referred to as wafers 42 / 142) are immersed and soaked in the activation solution 76, so that the surfaces of the wafers 42 / 142 are activated.

[0066] The wet surface activation solution 76 can be obtained from reference Fig.12 The activation process includes immersing the wafer 42 / 142 in the activation solution 76 for a period of time ranging between about 1 minute to about 2 hours. Due to immersing the wafer in the acid or base, the acid or base will destroy the bonds at the surface of the wafer 42 / 142, and thus generate dangling bonds. Because the activation by immersing the wafer in the acid or base does not involve plasma, no plasma-induced damage will be caused.

[0067] According to some embodiments, after the wafer 42 / 142 is sprayed or immersed in the acid or base, the wafer 42 / 142 is rinsed with deionized water to remove the residual acid or base from the wafer 42 / 142. The rinsing may be performed in an activation module.

[0068] According to some embodiments, the surface activation module 28 includes a single one of the activation modules 28A, 28B, 28C, and 28D. According to an optional embodiment, the surface activation module 28 includes two or more of the activation modules 28A, 28B, 28C, and 28D. Therefore, two or more surface activation processes can be performed to improve activation.

[0069] Return to reference Figure 1 , in the surface activation process 28 (reference Figures 3 to 13After the activation of the wafer 42 / 142, the activated wafer 42 / 142 is transferred from the transfer module 30 to the rinse module 32, where a rinse process is performed. The corresponding process is shown as follows Fig. 27 Process 206 in process flow 200 is shown. Fig.14 The surface activated wafer 42 / 142 is shown. In order to provide sufficient H between the wafers 2 To improve subsequent wafer bonding, the wafer 42 / 142 may be immersed in water. Optionally, a water sprayer may be used to distribute water onto the bonding surface of the wafer 42 / 142. The relative humidity in the bonding area is controlled within a range between about 20% and about 70% to provide a sufficient amount of water to form hydrogen bonds and establish a connection between the wafers. Water 81 on the surface of the wafer 42 / 142 is shown in the figure.

[0070] In the rinsing process, water (H 2 O) reacts with dangling bonds on the surface of the wafer 42 / 142, which are generated during the surface activation process. Thus, a high density of Si-OH bonds is formed. These OH bonds are Fig.18 shown.

[0071] Fig.15 FIG. 4 shows a rough pre-alignment process of wafer 142 and wafer 42. The misalignment value may be greater than about 200 μm. Next, as shown in FIG. Fig.16 As shown, a fine alignment process is performed until the misalignment value is reduced to about 400 nm or less. In a subsequent process, an annealing process is performed so that water 81 between the wafers 42 and 142 evaporates and Si-O-Si bonds are formed to bond the wafers 42 and 142, as shown in FIG. Fig.17 shown.

[0072] Figures 18 to 21 The chemical structure between the stages and wafers 42 and 142 is shown according to some embodiments. Fig.18 , wafer 142 is pre-bonded to wafer 42 (also shown in Fig.15 and Fig.16 The corresponding process is shown as Fig. 27 Process 208 in process flow 200 is shown. Fig.18 Shows Fig.16 Water 81 is shown. In pre-bonding, a force is applied to the center of wafer 142 so that the center of wafer 142 contacts the center of wafer 42. The contact propagates from the center to the edge of wafer 142 and wafer 42, and a bonding wave is generated and propagated. As the bonding wave propagates, air and moisture between wafer 142 and wafer 42 are squeezed out. Schematically, the resulting structure is as shown in FIG. Fig.19 As shown, the OH bonds at the surface of wafer 142 are close to the OH bonds at the surface of wafer 42 .

[0073] Then, for example, an annealing process is performed at a temperature ranging from about 150° C. to about 200° C. The corresponding process is shown as follows. Fig. 27 The annealing time may be in the range of about 1 hour to 2.5 hours. During the annealing, H atoms are formed due to the cleavage of the OH bonds and due to the reaction of the OH bonds with the H atoms cleaved from the OH bonds. 2 O. The O atom bonded to the Si atom bonds to another oxygen atom generated by the cleavage of the OH bond. Thus, a Si-O-Si bond is formed. Finally, the wafers 142 and 42 are bonded together. Fig. 20 and Fig.21 shown.

[0074] Return to reference Figure 1 The wafer bonding module 20 includes a control unit 150 , which is connected to and controls the operation of all the above-mentioned processes, including the operations of the wafer cleaning module 26 , the surface activation module 28 , the transfer modules 24 and 30 , the rinsing module 32 , and the pre-bonding and annealing module 34 .

[0075] Figure 22 to Figure 26 1 shows a view of an intermediate stage in bonding wafers, where wafers 42 and 142 include gate-all-around (GAA) transistors, and hybrid bonding is performed, according to some embodiments. Fig. 22 , wafer 42 includes GAA transistor 90. Bonding pad 92 and bonding layer 94 are formed on the surface of wafer 42. Wafer 142 includes GAA transistor 190. Bonding pad 192 and bonding layer 194 are formed on the surface of wafer 142.

[0076] Next, if Fig.23 As shown, a surface activation process 130 is performed on wafers 42 and 142. Figure 1 The surface activation module 28 shown performs the surface activation process 130. The surface activation module 28 may be a Figures 3 to 13 Any of the activation modules 28A-28D shown. The surface activation process 130 causes dangling bonds to be generated on the surface of the bonding layers 94 and 194.

[0077] After the subsequent rinsing process, a high density of OH bonds is formed on the surfaces of the wafers 42 and 142 , such as Fig.24 Wafer 142 is then placed on top of wafer 42, as shown. Fig.25 As shown. Wafer 142 is then bonded to wafer 42 by pre-bonding and annealing. The resulting bonded wafers are as shown. Fig.26 shown.

[0078] Embodiments of the present disclosure have several advantageous features. By performing the activation process without allowing the plasma to contact the wafer, plasma-induced damage is not caused. The activation process may involve filtered plasma, a laser beam, or a spray or bath process using an acid or base.

[0079] According to some embodiments of the present disclosure, a method includes performing a cleaning process on a first surface of a first wafer; performing a surface activation process on the first surface, wherein the surface activation process is selected from the following group consisting of: a plasma surface activation process, including generating plasma from a process gas, wherein a filter is used to remove ions in the plasma, and wherein the remaining uncharged portion of the plasma is used to treat the first surface; a laser surface activation process using a laser beam; an acid surface activation process using an acid; and an alkaline surface activation process using an alkali; after the surface activation process, performing a rinsing process on the first surface; and bonding the first surface of the first wafer to the second surface of the second wafer.

[0080] In an embodiment, the surface activation process includes a plasma surface activation process, and wherein a filter including a plurality of openings is used to filter ions in the plasma. In an embodiment, an electrically grounded filter is used to remove ions. In an embodiment, an electrically floating filter is used to remove ions. In an embodiment, free radicals remain in the filtered plasma, and the free radicals are used to process the first wafer. In an embodiment, ions in the plasma are used to collide with molecules in the process gas and accelerate the molecules, and the accelerated molecules pass through the openings in the filter to reach the first wafer.

[0081] In an embodiment, the process gas comprises an etching gas, and wherein the radicals remaining in the plasma are used to etch the first wafer. In an embodiment, the etching gas comprises fluorine, and wherein the radicals remaining in the plasma comprise fluorine radicals. In an embodiment, the surface activation process comprises a laser surface activation process, and the laser surface activation process comprises using a laser beam to project onto the first surface of the first wafer. In an embodiment, the surface activation process comprises an acid surface activation process, and wherein the acid surface activation process comprises using an acid to etch a surface portion of the first wafer.

[0082] In an embodiment, the acid surface activation process comprises spraying the first surface of the first wafer with a solution of an acid. In an embodiment, the acid surface activation process comprises soaking the first wafer with a solution of an acid. In an embodiment, the surface activation process comprises an alkaline surface activation process, and wherein the alkaline surface activation process comprises spraying the first surface of the first wafer with a solution of an alkaline.

[0083] According to some embodiments of the present disclosure, a method includes generating plasma from a process gas; removing charged particles from the plasma using a filter; performing a surface activation process on a first wafer using an uncharged portion of a remaining portion of the plasma; performing a rinsing process on the first wafer after the surface activation process; and bonding the first wafer to a second wafer.

[0084] In an embodiment, the uncharged portion for the surface activation process includes free radicals, and wherein the first wafer is etched by the free radicals. In an embodiment, the uncharged portion includes metastable free radicals, and the metastable free radicals release energy to the first wafer. In an embodiment, the uncharged portion for the surface activation process includes molecules accelerated by ions in the plasma.

[0085] According to some embodiments of the present disclosure, a method includes placing a first wafer into a process chamber; introducing a process gas into the process chamber; generating a plasma from the process gas, wherein a filter is located between the first wafer and the plasma, and wherein an uncharged portion of the plasma passes through the filter to reach the first wafer; and bonding the first wafer to a second wafer. In an embodiment, the process gas includes an etching gas. In an embodiment, the process gas further includes an inert gas, the inert gas being selected from the group consisting of He, Ne, Ar, Kr, Xe, and combinations thereof.

[0086] Some embodiments of the present application provide a method, comprising: performing a cleaning process on a first surface of a first wafer; performing a surface activation process on the first surface, wherein the surface activation process is selected from the group consisting of: a plasma surface activation process, comprising generating a plasma from a process gas, wherein a filter is used to remove ions in the plasma, and wherein the remaining uncharged portion of the plasma is used to treat the first surface; a laser surface activation process, using a laser beam; an acid surface activation process, using an acid; and an alkaline surface activation process, using an alkali; after the surface activation process, performing a rinsing process on the first surface; and bonding the first surface of the first wafer to the second surface of a second wafer. In some embodiments, the surface activation process includes the plasma surface activation process, and wherein the filter including a plurality of openings is used to filter the ions in the plasma. In some embodiments, the electrically grounded filter is used to remove the ions. In some embodiments, the electrically floating filter is used to remove the ions. In some embodiments, free radicals remain in the filtered plasma, and the free radicals are used to treat the first wafer. In some embodiments, the ions in the plasma are used to collide with and accelerate molecules in the process gas, and the accelerated molecules pass through the openings in the filter to reach the first wafer. In some embodiments, the process gas comprises an etching gas, and wherein the radicals remaining in the plasma are used to etch the first wafer. In some embodiments, the etching gas comprises fluorine, and wherein the radicals remaining in the plasma comprise fluorine radicals. In some embodiments, the surface activation process comprises the laser surface activation process, and the laser surface activation process comprises using the laser beam to project onto the first surface of the first wafer. In some embodiments, the surface activation process comprises the acid surface activation process, and wherein the acid surface activation process comprises using the acid to etch a surface portion of the first wafer. In some embodiments, the acid surface activation process comprises spraying the first surface of the first wafer with a solution of the acid. In some embodiments, the acid surface activation process comprises soaking the first wafer with a solution of the acid. In some embodiments, the surface activation process comprises the alkali surface activation process, and wherein the alkali surface activation process comprises spraying the first surface of the first wafer with a solution of the alkali.

[0087] Other embodiments of the present application provide a method, comprising: generating a plasma from a process gas; removing charged particles from the plasma using a filter; performing a surface activation process on a first wafer using an uncharged portion of a remaining portion of the plasma; performing a rinsing process on the first wafer after the surface activation process; and bonding the first wafer to a second wafer. In some embodiments, the uncharged portion used for the surface activation process includes free radicals, and wherein the first wafer is etched by the free radicals. In some embodiments, the uncharged portion includes metastable free radicals, and the metastable free radicals release energy to the first wafer. In some embodiments, the uncharged portion used for the surface activation process includes molecules accelerated by ions in the plasma.

[0088] Some other embodiments of the present application provide a method, comprising: placing a first wafer into a process chamber; introducing a process gas into the process chamber; generating a plasma from the process gas, wherein a filter is located between the first wafer and the plasma, and wherein an uncharged portion of the plasma passes through the filter to reach the first wafer; and bonding the first wafer to a second wafer. In some embodiments, the process gas comprises an etching gas. In some embodiments, the process gas further comprises an inert gas, and the inert gas is selected from the group consisting of He, Ne, Ar, Kr, Xe, and combinations thereof.

[0089] The features of several embodiments are summarized above so that those skilled in the art can better understand aspects of the present disclosure. Those skilled in the art should understand that they can easily use the present disclosure as a basis to design or modify other processes and structures for implementing the same purpose and / or achieving the same advantages as the embodiments introduced herein. Those skilled in the art should also appreciate that such equivalent constructions do not deviate from the spirit and scope of the present disclosure, and that they can make various changes, substitutions, and modifications herein without departing from the spirit and scope of the present disclosure.

Claims

1. A method for bonding wafers, comprising: performing a cleaning process on a first surface of a first wafer; Performing a surface activation process on the first surface, wherein the surface activation process is selected from the group consisting of: a plasma surface activation process comprising generating a plasma from a process gas, wherein a filter is used to remove ions in the plasma, and wherein a remaining uncharged portion of the plasma is used to treat the first surface; Laser surface activation process, using a laser beam; Acid surface activation processes, using acids; and Alkali surface activation process, using alkali; After the surface activation process, performing a rinsing process on the first surface; and The first surface of the first wafer is bonded to a second surface of a second wafer.

2. The method according to claim 1, wherein: The surface activation process includes the plasma surface activation process, and wherein the ions in the plasma are filtered using the filter including a plurality of openings.

3. The method according to claim 2, wherein: The filter, which is electrically grounded, is used to remove the ions.

4. The method according to claim 2, wherein: The filter is electrically floated to remove the ions.

5. The method according to claim 2, wherein: Free radicals remain in the filtered plasma, and the free radicals are used to process the first wafer.

6. The method according to claim 1, wherein: Ions in the plasma are used to collide with and accelerate molecules in the process gas, and the accelerated molecules pass through openings in the filter to reach the first wafer.

7. The method according to claim 1, wherein: The process gas includes an etching gas, and wherein radicals remaining in the plasma are used to etch the first wafer.

8. The method according to claim 7, wherein: The etching gas includes fluorine, and wherein the radicals remaining in the plasma include fluorine radicals.

9. A method for bonding wafers, comprising: generating a plasma from a process gas; removing charged particles from the plasma using a filter; performing a surface activation process on the first wafer using an uncharged portion of a remaining portion of the plasma; After the surface activation process, performing a rinsing process on the first wafer; as well as The first wafer is bonded to a second wafer.

10. A method for bonding wafers, comprising: placing a first wafer into a process chamber; introducing a process gas into the process chamber; generating a plasma from the process gas, wherein a filter is located between the first wafer and the plasma, and wherein an uncharged portion of the plasma passes through the filter to reach the first wafer; and The first wafer is bonded to a second wafer.

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