Method for bonding substrates and substrate bonding apparatus

Abstract

To provide a method for bonding substrates capable of bonding two substrates in a state where copper oxide is removed from a surface of copper pads.SOLUTION: The method for bonding substrates includes: a plasma treatment step of treating bonding surfaces (111, 211) of substrates (W) with a rare gas plasma, which is a plasma of a rare gas; treating the bonding surfaces (111, 211) of the substrates (W) that were treated with the rare gas plasma with a hydrogen plasma, which is a plasma of hydrogen, and treating the bonding surfaces (111, 211) of the substrates (W) that were treated with the hydrogen plasma with a nitrogen plasma, which is a plasma of nitrogen; and a substrate bonding step of bonding the two substrates (W) by bringing the bonding surfaces (111, 211) of the two substrates (W) into contact with each other so that the copper pads (112, 212) of the two substrates face each other and the insulating films of the two substrates W face each other.SELECTED DRAWING: Figure 4A-F

Description

[Technical Field]

[0001] The present invention relates to a substrate bonding method and a substrate bonding apparatus for bonding two substrates. [Background technology]

[0002] Patent Document 1 discloses a semiconductor device including a first substrate and a second substrate that are bonded together. Paragraph 0061 of Patent Document 1 states, "A second substrate 2 having a second connection wiring layer 22 formed thereon is bonded to the first substrate 3. In this state, O of copper oxide (CuO, Cu2O, etc.) is present on the bonding surface X between the first electrode 33 and the second electrode 23." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-6789 Summary of the Invention [Problem to be solved by the invention]

[0004] At least one embodiment of the present invention provides a substrate bonding method and substrate bonding apparatus that can bond two substrates in a state where copper oxide has been removed from the surfaces of the copper pads. [Means for solving the problem]

[0005] One embodiment of the present invention provides a substrate bonding method for bonding two substrates, each having a bonding surface where copper oxide of a copper pad and an insulating film are exposed, including: a plasma treatment step of treating the bonding surface of each substrate with a rare gas plasma that is a rare gas plasma, treating the bonding surface of each substrate that has been treated with the rare gas plasma with a hydrogen plasma that is a hydrogen plasma, and treating the bonding surface of each substrate that has been treated with the hydrogen plasma with a nitrogen plasma that is a nitrogen plasma; and a substrate bonding step of bonding the two substrates by bringing the bonding surfaces of the two substrates into contact with each other so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other after the plasma treatment step.

[0006] In the above embodiment, at least one of the following features may be added to the substrate bonding method.

[0007] The plasma treatment process is a process in which the following steps are performed on each of the two substrates: a rare gas plasma treatment process in which the bonding surface is treated with plasma containing the rare gas plasma but not containing the nitrogen plasma; a nitrogen plasma treatment process in which the bonding surface is treated with the nitrogen plasma; and a hydrogen plasma treatment process in which the bonding surface is treated with the hydrogen plasma simultaneously with at least one of the rare gas plasma treatment process and the nitrogen plasma treatment process, or after the rare gas plasma treatment process and before the nitrogen plasma treatment process.

[0008] The plasma treatment process is a process in which a first plasma treatment process is performed on each of the two substrates, in which a first reactive gas containing the rare gas and hydrogen but not the nitrogen is supplied into a sealed container that houses the substrates, and the bonding surface is treated with a first plasma generated from the first reactive gas, and a second plasma treatment process is performed on each of the two substrates, in which a second reactive gas containing the nitrogen is supplied into the sealed container, and the bonding surface is treated with a second plasma generated from the second reactive gas.

[0009] The substrate bonding method further includes an oxygen contacting step of contacting the bonding surfaces of the substrates with at least one of oxygen in the air and oxygen in a liquid after the plasma treatment step.

[0010] The oxygen contact step includes a cleaning step of cleaning each of the two substrates with a cleaning liquid and drying the cleaning liquid after the plasma treatment step and before the substrate bonding step.

[0011] The substrate bonding method further includes a heat treatment step of heating the two bonded substrates to directly bond the copper contained in the copper pad of one of the two substrates to the copper contained in the copper pad of the other of the two substrates.

[0012] The plasma treatment process is a process of treating the bonding surfaces of each of the substrates with the rare gas plasma, the hydrogen plasma, and the nitrogen plasma by generating the rare gas plasma, the hydrogen plasma, and the nitrogen plasma in a plasma treatment unit of a substrate bonding apparatus; the substrate bonding process is a process of bonding the two substrates by contacting the bonding surfaces of the two substrates in a bonding unit of the substrate bonding apparatus so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other; and the heat treatment process is a process of directly bonding the copper contained in the copper pad of one of the two substrates to the copper contained in the copper pad of the other of the two substrates by heating the bonded substrates in a heat treatment unit of the substrate bonding apparatus.

[0013] The plasma treatment process is a process of generating an inductively coupled plasma of at least one of the rare gas, hydrogen, and nitrogen by supplying a high-frequency current to an antenna arranged in the space between an inner plate that covers a hole opened on the inner surface of the outer wall of a sealed container containing the substrate and an outer plate that covers a hole opened on the outer surface of the outer wall.

[0014] Another embodiment of the present invention provides a substrate bonding apparatus for bonding two substrates, each having a bonding surface where copper oxide of a copper pad and an insulating film are exposed, including: a plasma processing unit that treats the bonding surface of each substrate with a rare gas plasma, treats the bonding surface of each substrate treated with the rare gas plasma with a hydrogen plasma, and treats the bonding surface of each substrate treated with the hydrogen plasma with a nitrogen plasma; and a bonding unit that, after the plasma processing step, bonds the two substrates by bringing the bonding surfaces of the two substrates into contact with each other so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other. At least one of the features described above regarding the substrate bonding method may be added to the substrate bonding apparatus. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing two substrates before they are bonded together. [Figure 2A-B] 1 is a schematic diagram showing the cross sections of two substrates before and after bonding. [Figure 3A-F] FIG. 1 is a schematic diagram for explaining an example of a flow from treating substrates with plasma to heating two bonded substrates. [Figure 4A-F] 1 is a schematic diagram for explaining an example of a change that is expected to occur on the surface of a copper pad when a substrate is being treated with plasma or heated. [Figure 5] 1 is a schematic diagram of a substrate bonding apparatus according to an embodiment of the present invention. [Figure 6] 1 is a schematic diagram showing a vertical cross section of a plasma processing unit. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] First, the two substrates W to be bonded will be described. When distinguishing between the two substrates W, they will be referred to as a first substrate W1 and a second substrate W2. Bonding is synonymous with joining.

[0018] FIG. 1 is a schematic diagram showing two substrates W before being bonded. The first substrate W1 and the second substrate W2 are flat, circular substrates W with the same diameter. The diameters of the first substrate W1 and the second substrate W2 may be 300 mm or other. The first substrate W1 includes a first bonding surface 111 and a first non-bonding surface 131, which are two parallel circular flat surfaces, and an annular first end surface connecting the outer edges of the first bonding surface 111 and the first non-bonding surface 131. Similarly, the second substrate W2 includes a second bonding surface 211 and a second non-bonding surface 231, which are two parallel circular flat surfaces, and an annular second end surface connecting the outer edges of the second bonding surface 211 and the second non-bonding surface 231. The first substrate W1 and the second substrate W2 are bonded together so that the first bonding surface 111 and the second bonding surface 211 face each other.

[0019] 2A and 2B are schematic diagrams showing cross sections of two substrates W before and after bonding. 2A and 2B show cross sections cut along a plane perpendicular to the two substrates W. 2A shows the cross section of the two substrates W before bonding. 2B shows the cross section of the two substrates W after bonding. 2A shows the cross section of the two substrates W after polishing has been performed to flatten the first bonding surface 111 and the second bonding surface 211. The proportions of the elements shown in 2A and 2B may not be the same as the actual proportions.

[0020] 2A, the first substrate W1 includes a plurality of disk-shaped layers stacked in the thickness direction of the first substrate W1 and a disk-shaped first base material 130 that supports the plurality of layers. The plurality of layers includes a disk-shaped first device layer 120 formed on the first base material 130 and a disk-shaped first bonding layer 110 formed on the first device layer 120. Similarly, the second substrate W2 includes a plurality of disk-shaped layers stacked in the thickness direction of the second substrate W2 and a disk-shaped second base material 230 that supports the plurality of layers. The plurality of layers includes a disk-shaped second device layer 220 formed on the second base material 230 and a disk-shaped second bonding layer 210 formed on the second device layer 220.

[0021] The first substrate 130 and the second substrate 230 are made of a semiconductor such as single crystal silicon. The first substrate 130 may be made of a material other than a semiconductor. The same applies to the second substrate 230. The surface of the first substrate 130 opposite the first device layer 120 corresponds to the first non-bonding surface 131 (see FIG. 1). The surface of the first bonding layer 110 opposite the first device layer 120 corresponds to the first bonding surface 111. Similarly, the surface of the second substrate 230 opposite the second device layer 220 corresponds to the second non-bonding surface 231 (see FIG. 1). The surface of the second bonding layer 210 opposite the second device layer 220 corresponds to the second bonding surface 211.

[0022] Semiconductor devices such as transistors and diodes are arranged in a first device layer 120 and a second device layer 220. The first device layer 120 includes a plurality of first semiconductor devices 121 that form an electronic circuit and a first insulating film 122 that electrically insulates the plurality of first semiconductor devices 121. Similarly, the second device layer 220 includes a plurality of second semiconductor devices 221 that form an electronic circuit and a second insulating film 222 that electrically insulates the plurality of second semiconductor devices 221. The function of the electronic circuit of the first substrate W1 may be the same as or different from the function of the electronic circuit of the second substrate W2.

[0023] The first bonding layer 110 includes a plurality of first copper pads 112 electrically connected to a plurality of first semiconductor devices 121 in the first device layer 120, and a first insulating film 113 that electrically insulates the plurality of first copper pads 112. Similarly, the second bonding layer 210 includes a plurality of second copper pads 212 electrically connected to a plurality of second semiconductor devices 221 in the second device layer 220, and a second insulating film 213 that electrically insulates the plurality of second copper pads 212.

[0024] The first copper pad 112 and the second copper pad 212 are both made of copper (Cu). The first copper pad 112 is electrically insulated from the other first copper pads 112 by a first insulating film 113. Similarly, the second copper pad 212 is electrically insulated from the other second copper pads 212 by a second insulating film 213. The first insulating film 113 is made of silicon oxide (SiO2). The second insulating film 213 is also made of silicon oxide. The first insulating film 113 and the second insulating film 213 may be silicon oxide films made using TEOS (tetraethoxysilane), or may be other silicon oxide films. The first insulating film 113 and the second insulating film 213 may be made of an insulating material containing silicon other than silicon oxide, such as silicon nitride (SiN), or may be made of other insulating materials.

[0025] The first copper pad 112 and the first insulating film 113 are exposed at the first bonding surface 111. In other words, the first copper pad 112 and the first insulating film 113 constitute the first bonding surface 111. The first copper pad 112 and the first insulating film 113 may constitute the entire first bonding surface 111, or may constitute only a portion of the first bonding surface 111. Similarly, the second copper pad 212 and the second insulating film 213 are exposed at the second bonding surface 211. In other words, the second copper pad 212 and the second insulating film 213 constitute the second bonding surface 211. The second copper pad 212 and the second insulating film 213 may constitute the entire second bonding surface 211, or may constitute only a portion of the second bonding surface 211.

[0026] 2B, the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 are stacked so that the multiple first copper pads 112 face the multiple second copper pads 212 and the first insulating film 113 faces the second insulating film 213. The first substrate W1 and the second substrate W2 are then heated. As a result, one first copper pad 112 is electrically connected to one second copper pad 212, and the first semiconductor device 121 and the second semiconductor device 221 are electrically connected via the first copper pad 112 and the second copper pad 212.

[0027] Next, an example of the flow from treating the substrates W with plasma to heating the two bonded substrates W will be described.

[0028] Figures 3A to 3F are schematic diagrams for explaining the same example. Figures 4A to 4D are schematic diagrams for explaining an example of changes that are expected to occur on the surfaces of the copper pads 112, 212 when the substrate W is processed with plasma. Figures 4E to 4F are schematic diagrams for explaining an example of changes that are expected to occur on the surfaces of the copper pads 112, 212 when the substrate W is heated.

[0029] When bonding the first substrate W1 and the second substrate W2, the first substrate W1 and the second substrate W2 are treated with plasma. Specifically, as shown in Fig. 3A, the first substrate W1 is carried into a sealed container 12 and supported by a substrate holder 11 arranged inside the sealed container 12. Fig. 3A shows an example in which the first substrate W1 is supported horizontally inside the sealed container 12 by the substrate holder 11 with the first bonding surface 111 of the first substrate W1 facing upward.

[0030] After the first substrate W1 is supported by the substrate holder 11 and the door 12d of the sealed container 12 is closed, the gas inside the sealed container 12 is discharged and the pressure inside the sealed container 12 is reduced to a value lower than atmospheric pressure. Then, a first plasma processing step is performed to process the first bonding surface 111 of the first substrate W1 with a first plasma P1 generated from a first reactive gas. Specifically, with the pressure inside the sealed container 12 lower than atmospheric pressure, the first reactive gas, i.e., a mixed gas of argon gas and hydrogen gas, is supplied into the sealed container 12, and then the plasma source 14 ionizes the first reactive gas inside the sealed container 12. This converts the first reactive gas inside the sealed container 12 into the first plasma P1, i.e., a plasma of argon and hydrogen, and the first bonding surface 111 of the first substrate W1 is exposed to the first plasma P1.

[0031] The plasma generated in the first plasma treatment step may be inductively coupled plasma, or may be a plasma other than inductively coupled plasma, such as capacitively coupled plasma or surface wave plasma. This also applies to the second plasma treatment step and the third plasma treatment step described below. When treating the first substrate W1 and the second substrate W2 with inductively coupled plasma, inductively coupled plasma may be generated from the reaction gas in the sealed container 12 by supplying a high-frequency current to at least one antenna disposed in the sealed container 12 or at least one antenna disposed in the space within the outer wall 12w of the sealed container 12 (see FIG. 6).

[0032] As described above, the first bonding surface 111 of the first substrate W1 is composed of the first copper pad 112 and the first insulating film 113. As shown in FIG. 4A, the surface of the first copper pad 112, which is part of the first bonding surface 111, is composed of copper oxide such as copper(I) oxide (cuprous oxide: CuO) or copper(II) oxide (cupric oxide: CuO). In other words, the surface of the first copper pad 112 is terminated with oxygen atoms. The surface of the second copper pad 212 is also terminated with oxygen atoms. This is because the copper atoms that constitute the surfaces of the first copper pad 112 and the second copper pad 212 are oxidized by oxygen in the air or the liquid.

[0033] As shown in Figure 4B, the plasma of argon, an example of a rare gas (a group 18 element), removes oxygen atoms from the copper oxide that constitutes the surface of the first copper pad 112, converting at least one of CuO and CuO to Cu. As shown in Figure 4C, the hydrogen atoms (strictly speaking, hydrogen atom radicals or excited hydrogen atoms; the same applies below) contained in the hydrogen plasma bond to the copper that constitutes the surface of the first copper pad 112, forming Cu-H bonds on the surface of the first copper pad 112. In other words, the surface of the first copper pad 112 is terminated with hydrogen atoms. As a result, oxygen atoms exposed on the surface of the first copper pad 112 are replaced with hydrogen atoms.

[0034] After the oxygen atoms exposed on the first bonding surface 111 of the first substrate W1 are replaced with hydrogen atoms, a second plasma treatment process is performed to treat the first bonding surface 111 of the first substrate W1 with a second plasma P2 generated from a second reactive gas. Specifically, as shown in FIG. 3B , the second reactive gas, i.e., a mixed gas of argon gas, hydrogen gas, and nitrogen gas, is supplied into the sealed container 12 while the pressure inside the sealed container 12 is lower than atmospheric pressure, and then the plasma source 14 ionizes the second reactive gas inside the sealed container 12. This converts the second reactive gas inside the sealed container 12 into the second plasma P2, i.e., a plasma of argon, hydrogen, and nitrogen, and the first bonding surface 111 of the first substrate W1 is exposed to the second plasma P2.

[0035] When supplying the second reactive gas into the sealed container 12, the supply of the second reactive gas may be started after all of the first reactive gas has been exhausted from the sealed container 12, or the supply of the second reactive gas may be started while the first reactive gas remains in the sealed container 12. In the above example, the first reactive gas is a mixture of argon gas and hydrogen gas, and the second reactive gas is a mixture of argon gas, hydrogen gas, and nitrogen gas. Therefore, nitrogen gas may be supplied into the sealed container 12 to mix with the argon gas and hydrogen gas remaining in the sealed container 12. The supply of the second reactive gas may be started while the plasma source 14 is ionizing the first reactive gas in the sealed container 12, or the supply of the second reactive gas may be started after the plasma source 14 stops ionizing the first reactive gas.

[0036] As described above, oxygen atoms exposed on the first bonding surface 111 of the first substrate W1 are replaced with hydrogen atoms. As shown in FIG. 4D, the nitrogen plasma replaces the hydrogen atoms exposed on the surface of the first copper pad 112 with nitrogen atoms, forming Cu-N bonds on the surface of the first copper pad 112. Immediately after the hydrogen atoms are replaced with nitrogen atoms (when the nitrogen atoms are highly active), at least one of the hydrogen atoms cleaved from the first copper pad 112 and the like and the hydrogen atoms contained in the hydrogen plasma is bonded to the nitrogen atoms bonded to the copper atoms. As a result, Cu-NH2 bonds are formed on the surface of the first copper pad 112, as shown in FIG. 4D. In other words, the surface of the first copper pad 112 is terminated with amino groups (NH2).

[0037] After the surface of the first copper pad 112 is terminated with an amino group, the plasma source 14 stops ionizing the first reactive gas in the sealed container 12. This stops the generation of plasma of argon, hydrogen, and nitrogen. Then, while supplying an inert gas (such as nitrogen gas or argon gas) into the sealed container 12, the exhaust of gas from the sealed container 12 is stopped. This causes the first reactive gas and first plasma P1 in the sealed container 12 to be exhausted, and the pressure inside the sealed container 12 to rise to atmospheric pressure or close to it. Then, the door 12d of the sealed container 12 is opened, and the first substrate W1 is carried out of the sealed container 12.

[0038] The second bonding surface 211 of the second substrate W2 is also subjected to the first plasma treatment step and the second plasma treatment step, similar to the first bonding surface 111 of the first substrate W1. Specifically, the second bonding surface 211 of the second substrate W2 is treated with a first plasma P1, which is a plasma of argon and hydrogen, and then the second bonding surface 211 of the second substrate W2 is treated with a second plasma P2, which is a plasma of argon, hydrogen, and nitrogen. This terminates the surface of the second copper pad 212 with amino groups. Then, the second reactive gas and the second plasma P2 are discharged from the sealed container 12, and the pressure inside the sealed container 12 is increased to atmospheric pressure or nearby. Then, the door 12d of the sealed container 12 is opened, and the second substrate W2 is removed from the sealed container 12.

[0039] When the first bonding surface 111 of the first substrate W1 is sequentially treated with the first plasma P1 and the second plasma P2, the surface of the first insulating film 113, which is part of the first bonding surface 111, is also sequentially treated with the first plasma P1 and the second plasma P2. Similarly, when the second bonding surface 211 of the second substrate W2 is sequentially treated with the second plasma P2 and the second plasma P2, the surface of the second insulating film 213, which is part of the second bonding surface 211, is also sequentially treated with the first plasma P1 and the second plasma P2. Both the first insulating film 113 and the second insulating film 213 are made of silicon oxide. Oxygen atoms contained in the silicon oxide are substituted with amino groups. As a result, the surfaces of the first insulating film 113 and the second insulating film 213 are terminated with amino groups.

[0040] When the first substrate W1 is removed from the sealed container 12, air comes into contact with the first bonding surface 111 of the first substrate W1. Similarly, when the second substrate W2 is removed from the sealed container 12, air comes into contact with the second bonding surface 211 of the second substrate W2. Therefore, oxygen in the air comes into contact with the surface of the first copper pad 112. Because the surface of the first copper pad 112 is terminated with amino groups, even when air comes into contact with the first bonding surface 111 of the first substrate W1, the copper atoms constituting the surface of the first copper pad 112 do not change to copper oxide. The copper atoms constituting the surface of the second copper pad 212 also do not change to copper oxide. Therefore, even when air comes into contact with the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2, the surfaces of the first copper pad 112 and the second copper pad 212 remain terminated with amino groups.

[0041] Although not shown, the first substrate W1 includes at least one alignment mark that serves as a reference for adjusting the alignment between the first substrate W1 and the second substrate W2. The same applies to the second substrate W2. After the first substrate W1 and the second substrate W2 are treated with plasma generated from the first and second reactive gases, as shown in FIG. 3D , an alignment confirmation process is performed to confirm the alignment, which indicates the magnitude and direction of misalignment between the first substrate W1 and the second substrate W2, while the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 are facing each other with a gap therebetween. Then, an alignment adjustment process is performed to reduce the amount of misalignment between the first substrate W1 and the second substrate W2 by moving the first substrate W1 and the second substrate W2 relative to each other based on the confirmed alignment. FIG. 3D shows an example of checking and adjusting the alignment of the first substrate W1 and the second substrate W2 based on images generated by a camera 34 that photographs a first mask M1 and a second mask M2, which are respectively provided on a first chuck 31A that holds the first substrate W1 and a second chuck 31B that holds the second substrate W2.

[0042] After the second plasma treatment step and before the alignment confirmation step, a cleaning step may be performed in which the first substrate W1 and the second substrate W2 are each washed with a cleaning solution such as pure water and dried, as shown in FIG. 3C. This allows particles (such as copper particles) generated when the first substrate W1 and the second substrate W2 are treated with plasma to be removed from the first substrate W1 and the second substrate W2. Furthermore, even if oxygen in the air or the cleaning solution comes into contact with the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2, the surfaces of the first copper pad 112 and the second copper pad 212 can remain terminated with amino groups, as described above.

[0043] After adjusting the alignment of the first substrate W1 and the second substrate W2, a substrate bonding process is performed in which the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 are brought into direct contact under atmospheric pressure, as shown in FIG. 3E. Then, as shown in FIG. 3F, a heat treatment process is performed in which the bonded first substrate W1 and second substrate W2 are heated. FIG. 3F shows an example in which multiple pairs of first substrates W1 and second substrates W2 are heated simultaneously. This heating process is also called annealing.

[0044] The first copper pad 112 of the first substrate W1 and the second copper pad 212 of the second substrate W2 may be separated before the first substrate W1 and the second substrate W2 are heated, as long as they are in contact after the first substrate W1 and the second substrate W2 are heated. In this case, when the first substrate W1 and the second substrate W2 are heated, the first copper pad 112 and the second copper pad 212 expand and come into contact with each other. As a result, the first substrate W1 and the second substrate W2 are heated with the first copper pad 112 and the second copper pad 212 in contact with each other.

[0045] As shown in FIG. 4E, the surface of the first copper pad 112 is terminated with an amino group, and the surface of the second copper pad 212 is terminated with an amino group. When the first substrate W1 and the second substrate W2 are heated while the first copper pad 112 and the second copper pad 212 are in contact with each other, two amino groups are desorbed from the surfaces of the first copper pad 112 and the second copper pad 212. This causes the reaction "Cu-NH2 + Cu-NH2 → Cu-Cu + N2 + 2H2" ("-" represents the bond between two atoms), and as shown in FIG. 4F, the copper atoms constituting the surface of the first copper pad 112 and the copper atoms constituting the surface of the second copper pad 212 are directly bonded. As shown in this chemical reaction formula, the two desorbed amino groups are converted into one nitrogen molecule (gas) and two hydrogen molecules (gas). Such nitrogen molecules and hydrogen molecules are discharged from between the first substrate W1 and the second substrate W2, or are absorbed into the first insulating film 113 or the second insulating film 213.

[0046] The amino group bonded to the copper atom is believed to be released at 200°C or higher. Therefore, the first substrate W1 and the second substrate W2 may be heated to 200°C or higher in the heat treatment process. Specifically, the first substrate W1 and the second substrate W2 may be heated at a temperature of 200°C or higher but less than 350°C, or at a temperature of 200°C or higher but less than 250°C. If only one nitrogen atom, rather than an amino group, is bonded to one copper atom, the nitrogen atom will be released when the first substrate W1 and the second substrate W2 are heated at a temperature higher than the temperature at which the amino group is released. Therefore, when releasing the amino group, the heating temperature of the first substrate W1 and the second substrate W2 can be lower than when releasing the nitrogen atom.

[0047] On the other hand, when the first substrate W1 and the second substrate W2 are heated while the first insulating film 113 and the second insulating film 213 are in contact with each other, four hydrogen atoms are released from two amino groups, i.e., one amino group constituting the surface of the first insulating film 113 and one amino group constituting the surface of the second insulating film 213. This causes a reaction of "Si-NH2 + Si-NH2 → Si-NN-Si + 2H2" (where "-" represents a bond between two atoms), and silicon atoms constituting the surface of the first insulating film 113 and silicon atoms constituting the surface of the second insulating film 213 are bonded via two nitrogen atoms. As shown in this chemical reaction formula, the four released hydrogen atoms change into two hydrogen molecules (gas). These hydrogen molecules are either discharged from between the first substrate W1 and the second substrate W2 or absorbed into the first insulating film 113 or the second insulating film 213.

[0048] When the first substrate W1 and the second substrate W2 are heated while the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 are in direct contact with each other, the above-mentioned reaction occurs at every location at the interface between the first substrate W1 and the second substrate W2. This increases the bonding strength between the first substrate W1 and the second substrate W2. Furthermore, because two copper atoms are directly bonded at the interface between the first copper pad 112 and the second copper pad 212, electrical resistance can be reduced compared to when copper oxide is present between the two copper atoms.

[0049] In the above example, the first reactive gas is a mixed gas of argon gas and hydrogen gas, and the second reactive gas is a mixed gas of argon gas, hydrogen gas, and nitrogen gas, but the compositions of the first reactive gas and the second reactive gas are not limited to this as long as the terminal oxygen atoms can be substituted with amino groups. The number of times that the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 are treated with plasma (the number of plasma treatment steps) may be one or three times.

[0050] For example, in the above example, the second plasma treatment step may be omitted, and the first bonding surface 111 of the first substrate W1 and the second bonding surface 211 of the second substrate W2 may be treated with plasma of argon, hydrogen, and nitrogen.

[0051] In the above example, the first reactant gas may be a mixture of argon gas and hydrogen gas, and the second reactant gas may be nitrogen gas. Alternatively, the first reactant gas may be argon gas, and the second reactant gas may be a mixture of argon gas, hydrogen gas, and nitrogen gas.

[0052] In the above example, after the first plasma treatment step and the second plasma treatment step and before the heat treatment step, a third plasma treatment step may be performed in which the first bonding surface 111 of the first substrate W1 or the second bonding surface 211 of the second substrate W2 is treated with a third plasma generated from a third reactive gas. In this case, the first reactive gas may be argon gas, the second reactive gas may be hydrogen gas or a mixed gas of argon gas and hydrogen gas, and the third reactive gas may be nitrogen gas, a mixed gas of hydrogen gas and nitrogen gas, or a mixed gas of argon gas, hydrogen gas, and nitrogen gas.

[0053] Next, the substrate bonding apparatus 1 that performs the above-mentioned steps will be described.

[0054] Fig. 5 is a schematic diagram of a substrate bonding apparatus 1 according to one embodiment of the present invention. Fig. 6 is a schematic diagram showing a vertical cross section of a plasma processing unit 2a.

[0055] The substrate bonding apparatus 1 is an apparatus for bonding two disk-shaped substrates W, such as semiconductor wafers. As shown in Fig. 5, the substrate bonding apparatus 1 includes a plurality of load ports LP on each of which is placed one carrier CA, each carrier CA accommodating a plurality of substrates W, such as a FOUP (Front-Opening Unified Pod), a plurality of processing units 2 for processing the substrates W transferred from the plurality of load ports LP, a transfer system TS for transferring the substrates W between the plurality of load ports LP and the plurality of processing units 2, and an outer wall 1a forming an enclosed space accommodating the plurality of processing units 2 and the transfer system TS. The substrate bonding apparatus 1 further includes a control device 3 for controlling the substrate bonding apparatus 1.

[0056] 5 shows an example in which three load ports LP are provided. The three load ports LP include a first load port LP1 on which a carrier CA accommodating a first substrate W1 is placed, a second load port LP2 on which a carrier CA accommodating a second substrate W2 is placed, and a third load port LP3 on which a carrier CA accommodating the bonded first substrate W1 and second substrate W2 is placed. The first load port LP1 and the second load port LP2 are load ports on which carriers CA accommodating substrates W to be bonded in the substrate bonding apparatus 1 are placed. The third load port LP3 is an unload port on which carriers CA accommodating two substrates W bonded in the substrate bonding apparatus 1 are placed.

[0057] The transfer system TS transfers substrates W from the first load port LP1 and the second load port LP2 to the plurality of processing units 2, and transfers substrates W from the plurality of processing units 2 to the third load port LP3. The transfer system TS further transfers substrates W between the plurality of processing units 2. The transfer system TS may include at least one transfer robot TR that transfers one or more substrates W in a horizontal position on a transfer path TP indicated by a thick line in FIG.

[0058] The transport robot TR includes at least one hand TH that holds one substrate W in a horizontal position. The transport robot TR moves along the transport path TP while holding the substrate W horizontally with the hand TH. Figure 5 shows an example in which the transport path TP extends from each of the first load port LP1 and the second load port LP2 to multiple processing units 2, and returns from the multiple processing units 2 to the third load port LP3.

[0059] The processing units 2 include a plasma processing unit 2a, a cleaning unit 2b, a bonding unit 2c, and a heat-treating unit 2d. Figure 5 shows an example in which two plasma processing units 2a and two cleaning units 2b are provided. Unless otherwise specified, the bonding unit 2c described in this specification bonds substrates W under atmospheric pressure.

[0060] The plasma processing unit 2a is a unit that performs plasma processing steps such as the first plasma processing step, the second plasma processing step, and the third plasma processing step described above. The cleaning unit 2b is a unit that cleans the substrate W with a cleaning liquid such as pure water and then dries the substrate W. The bonding unit 2c is a unit that brings two substrates W into contact with each other to bond the two substrates W. The heat processing unit 2d is a unit that performs the heat processing step described above.

[0061] The plasma processing unit 2a, cleaning unit 2b, and bonding unit 2c are single-wafer type units that process substrates W one by one (however, for bonding unit 2c, a pair of first substrate W1 and second substrate W2 is considered to be one substrate W). The heat-treating unit 2d may be a single-wafer type unit that processes bonded substrates W one by one, or may be a batch type unit that processes multiple bonded substrates W all at once. One bonded substrate W is a bonded pair of first substrate W1 and second substrate W2.

[0062] The cleaning unit 2b includes a spin chuck 21 that holds one substrate W horizontally and rotates the substrate W around a vertical line passing through the center of the substrate W, a chamber 22 that accommodates the substrate W held on the spin chuck 21, and a cleaning liquid nozzle 23 that ejects a cleaning liquid toward the substrate W held on the spin chuck 21.

[0063] The bonding unit 2c includes a first chuck 31A that holds the first substrate W1, a second chuck 31B that holds the second substrate W2, and a chamber 32 that accommodates the first substrate W1 and the second substrate W2 held by the first chuck 31A and the second chuck 31B. The first chuck 31A includes a first mask M1, and the second chuck 31B includes a second mask M2. The first mask M1 and the second mask M2 are made of a material that transmits visible light, such as glass. The bonding unit 2c also includes at least one actuator 33 that moves the first chuck 31A and the second chuck 31B relative to each other, and a camera 34 that confirms the alignment of the first substrate W1 and the second substrate W2 by photographing the first mask M1 and the second mask M2. The positional relationship between the first mask M1 and the first substrate W1, and the positional relationship between the second mask M2 and the second substrate W2 may be detected separately by a camera not shown, or may be determined based on positioning members (positioning pins, etc.) provided on the first mask M1 and the second mask M2.

[0064] At least one actuator 33 of the bonding unit 2c adjusts the alignment of the first substrate W1 and the second substrate W2 by moving the first chuck 31A and the second chuck 31B relative to each other. The at least one actuator 33 further bonds the first substrate W1 and the second substrate W2 by moving the first chuck 31A and the second chuck 31B relative to each other. An actuator is a device that converts driving energy, such as electrical, fluid, magnetic, thermal, or chemical energy, into mechanical work, that is, the movement of a tangible object. Actuators include electric motors (rotary motors), linear motors, air cylinders, and other devices.

[0065] 5 shows an example in which the heat-treating unit 2d is a batch type. Whether the heat-treating unit 2d is a single-wafer type or a batch type, the heat-treating unit 2d includes a substrate holder 41 that holds two bonded substrates W, a heat-treating furnace 42 that houses the two substrates W held by the substrate holder 41, and a heater 43 that raises the temperature inside the heat-treating furnace 42.

[0066] 6, the plasma processing unit 2a includes a substrate holder 11 that supports a first substrate W1 or a second substrate W2, and a sealed container 12 that houses the first substrate W1 or the second substrate W2 supported by the substrate holder 11. The plasma processing unit 2a further includes an exhaust pipe 13d that guides gas exhausted from the sealed container 12, a gas supply pipe 13s that guides gas to be supplied to the sealed container 12, such as a reactive gas, and a plasma source 14 that generates plasma from the reactive gas in the sealed container 12. The sealed container 12 includes an outer wall 12w that forms an internal space that houses the first substrate W1 or the second substrate W2 and a passage port through which the first substrate W1 or the second substrate W2 passes to enter and exit the internal space, and a door 12d that opens and closes the passage port.

[0067] Fig. 6 shows an example in which plasma source 14 generates inductively coupled plasma. Plasma source 14 includes at least one antenna 15 equivalent to a coil and a high-frequency power supply 16 that supplies high-frequency current to at least one antenna 15. Fig. 6 shows an example in which two antennas 15 are arranged in two spaces within outer wall 12w. In this example, antenna 15 is arranged in the space between inner plate 17 that covers a hole opened on the inner surface of outer wall 12w and outer plate 18 that covers a hole opened on the outer surface of outer wall 12w.

[0068] The high-frequency power supply 16 supplies high-frequency current to the antenna 15 while the air pressure in the space between the inner plate 17 and the outer plate 18 is lowered to a value lower than atmospheric pressure. When the high-frequency current is supplied to the antenna 15, an induced electric field is generated in the sealed container 12, ionizing the reactive gas in the sealed container 12. This generates plasma. The embedded antenna 15, which is disposed in the outer wall 12w of the sealed container 12, is electrically insulated from the plasma by the inner plate 17, which is a dielectric.

[0069] FIG. 6 shows an example in which a U-shaped antenna 15 is arranged in a vertical plane with its opening facing upward. The U-shaped antenna 15 includes two parallel portions that are parallel or nearly parallel to each other and a connecting portion (the portion extending left and right in FIG. 6) that connects the two parallel portions. The connecting portion of the antenna 15 is arranged in the space within the outer wall 12w. The area of ​​the space inside the antenna 15 corresponds to the area of ​​the antenna 15. The area of ​​the antenna 15 is smaller than the area of ​​the first bonding surface 111 of the first substrate W. The inductance of the antenna 15 decreases as the area of ​​the antenna 15 decreases. The area of ​​the antenna 15 may be equal to or greater than the area of ​​the first bonding surface 111. The antenna 15 may be maintained in a horizontal position. The antenna 15 may be arranged inside or outside the sealed container 12. The number of turns of the coil-shaped antenna 15 may be one or more.

[0070] The control device 3 (see FIG. 5) controls the electrical and electronic devices provided in the substrate bonding apparatus 1. The control device 3 includes a processor 3a that processes information, such as executing a program, and a memory 3b that stores information, such as the program to be executed by the processor 3a. The control device 3 controls the substrate bonding apparatus 1 to transport and process the substrate W as described above. In other words, the control device 3 is programmed to transport and process the substrate W as described above. The control device 3 controls the substrate bonding apparatus 1 to perform each of the processes from the plasma treatment process to the heat treatment process described with reference to FIGS. 1 to 4F. The processor 3a may be any one of a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), a digital signal processor (DSP), or a combination of these. Alternatively, the processor 3a may be configured to include a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC).

[0071] Next, the effects of this embodiment will be described.

[0072] In this embodiment, the bonding surfaces 111, 211, where the copper oxide and insulating films 113, 213 of the copper pads 112, 212 are exposed, are treated with a rare gas plasma (rare gas plasma), a hydrogen plasma (hydrogen plasma), and a nitrogen plasma (nitrogen plasma). Argon is an example of a rare gas (Group 18 element). The rare gas plasma removes oxygen atoms from the copper oxide of the copper pads 112, 212, converting the copper oxide into copper atoms. The hydrogen plasma bonds hydrogen atoms to the copper atoms of the copper pads 112, 212. The nitrogen plasma replaces hydrogen atoms bonded to the copper atoms of the copper pads 112, 212 with nitrogen atoms, bonding the nitrogen atoms to the copper atoms. Because the nitrogen atoms are highly active immediately after bonding with the copper atoms, hydrogen atoms on the bonding surfaces 111, 211, such as hydrogen atoms separated from the copper atoms, bond to the nitrogen atoms. As a result, amino groups bond to the copper atoms, and the surfaces of the copper pads 112, 212 are terminated with amino groups.

[0073] After treating the bonding surfaces 111 and 211 of each substrate W with plasma, the bonding surfaces 111 and 211 of the two substrates W are brought into contact with each other. This causes the copper pads 112 and 212 of the two substrates W to face each other, and the insulating films 113 and 213 of the two substrates W to face each other. As described above, the surfaces of the copper pads 112 and 212 are terminated with amino groups. Therefore, the two amino groups are located between the two copper atoms. When the two bonded substrates W are heated, the amino groups are released from the interface between the two copper pads 112 and 212, and the copper atoms of the two copper pads 112 and 212 are directly bonded to each other. Therefore, the electrical resistance at the interface between the two bonded copper pads 112 and 212 can be reduced compared to when copper oxide is present at the interface.

[0074] In this embodiment, the bonding surfaces 111, 211 of each substrate W are treated with plasma that contains a rare gas plasma but does not contain nitrogen plasma. Thereafter, the bonding surfaces 111, 211 of each substrate W are treated with nitrogen plasma. The hydrogen plasma treatment, which is treatment of the bonding surfaces 111, 211 with hydrogen plasma, may be performed before or simultaneously with the nitrogen plasma treatment, which is treatment of the bonding surfaces 111, 211 with nitrogen plasma. In the former case, the hydrogen plasma treatment may be performed simultaneously with the rare gas plasma treatment, which is treatment of the bonding surfaces 111, 211 with rare gas plasma.

[0075] If the bonding surfaces 111, 211 of the substrates W are treated with a plasma containing a rare gas plasma and nitrogen plasma but not hydrogen plasma before removing oxygen atoms from the copper oxide, nitrogen atoms may become stable in a bonded state with copper atoms after the oxygen atoms are removed from the copper oxide. In other words, copper nitride (CuN) may be generated on the surfaces of the copper pads 112, 212. Even if the bonding surfaces 111, 211 of the substrates W are treated with hydrogen plasma after the bonds between the nitrogen atoms and copper atoms have stabilized, the nitrogen atoms do not change to amino groups or remain almost unchanged. Furthermore, the nitrogen atoms contained in the copper nitride do not desorb from the interface between the two copper pads 112, 212 unless the two substrates W are heated at a higher temperature than when amino groups are desorbed.

[0076] As described above, treating the bonding surfaces 111, 211 of each substrate W with rare gas plasma, hydrogen plasma, and nitrogen plasma increases the probability that hydrogen atoms will bond to copper atoms before nitrogen atoms bond to copper atoms. If hydrogen atoms bond to copper atoms first, the surfaces of the copper pads 112, 212 can be terminated with amino groups. This can prevent copper nitride from forming on the surfaces of the copper pads 112, 212, or reduce the amount of copper nitride that forms on the surfaces of the copper pads 112, 212.

[0077] In this embodiment, a first reactive gas containing a rare gas and hydrogen but not nitrogen is supplied into the sealed container 12 containing the substrate W, and a first plasma P1 containing a rare gas and hydrogen but not nitrogen is generated from the first reactive gas. This replaces oxygen atoms contained in copper oxide with hydrogen atoms. Then, a second reactive gas containing at least nitrogen is supplied into the sealed container 12, and a second plasma P2 containing at least nitrogen is generated from the second reactive gas. This replaces amino groups with copper atoms constituting the surfaces of the copper pads 112 and 212. The second reactive gas may be a gas containing no rare gas and hydrogen (nitrogen gas), or a gas containing nitrogen and one or both of a rare gas and hydrogen. In the latter case, if copper oxide remains on the surfaces of the copper pads 112 and 212, the oxygen atoms contained in the copper oxide are replaced with hydrogen atoms, and then these hydrogen atoms are replaced with amino groups.

[0078] The first reactive gas differs from the second reactive gas in that it does not contain nitrogen. Therefore, the second reactive gas can be supplied into the sealed container 12 by adding nitrogen gas to the first reactive gas in the sealed container 12, without supplying a mixture of a rare gas, hydrogen gas, and nitrogen gas into the sealed container 12. Therefore, it is not necessary to exhaust the first reactive gas from the sealed container 12 before starting the supply of the second reactive gas. Furthermore, by adding nitrogen gas to the first reactive gas in the sealed container 12 while ionizing the gas in the sealed container 12 with the plasma source 14, it is possible to continuously switch from the first plasma treatment process to the second plasma treatment process.

[0079] In this embodiment, oxygen is brought into contact with the bonding surfaces 111, 211 of the plasma-treated substrates W. Specifically, an oxygen-containing gas, such as air, is brought into contact with the substrate W, or a liquid containing dissolved oxygen is brought into contact with the substrate W. Even if copper oxide is removed from the surfaces of the copper pads 112, 212, if oxygen atoms or oxygen molecules come into contact with the surfaces of the copper pads 112, 212, copper atoms on the surfaces of the copper pads 112, 212 will be oxidized before the two substrates W are bonded. If the surfaces of the copper pads 112, 212 are terminated with amino groups, such oxidation can be prevented or reduced. Therefore, it is not necessary to bond the two substrates W in a vacuum or to transport each substrate W in a vacuum using a transfer robot TR.

[0080] In this embodiment, the bonding surfaces 111, 211 of the substrates W that have been treated with plasma are washed with a cleaning solution and then dried. Even if oxygen is dissolved in the cleaning solution, the surfaces of the copper pads 112, 212 are terminated with amino groups, which can suppress or prevent copper atoms on the surfaces of the copper pads 112, 212 from being oxidized by oxygen in the cleaning solution. Furthermore, since the cleaning solution is supplied to the bonding surfaces 111, 211 of the substrates W, it is possible to reduce particles that are generated when the bonding surfaces 111, 211 of the substrates W are treated with plasma. This reduces the number of particles that remain at the interface between the two bonded substrates W.

[0081] In this embodiment, two bonded substrates W are heated. This heating causes amino groups to be released from the interface between the two copper pads 112 and 212, and the copper atoms of the two copper pads 112 and 212 are directly bonded to each other. Therefore, the electrical resistance at the interface between the two bonded copper pads 112 and 212 can be reduced compared to when copper oxide is present at the interface. Furthermore, the heating temperature of the two bonded substrates W can be reduced compared to when copper oxide is removed from the interface between the two copper pads 112 and 212 by heating the two bonded substrates W.

[0082] In this embodiment, plasma processing and bonding of substrates W are performed in a single substrate bonding apparatus 1. Specifically, the plasma processing unit 2a of the substrate bonding apparatus 1 performs plasma processing on each of two substrates W, and then the bonding unit 2c of the substrate bonding apparatus 1 bonds the two substrates W. After the two substrates W are bonded, the heat processing unit 2d of the substrate bonding apparatus 1 heats the two substrates W. This heating causes amino groups to desorb from the interfaces between the two copper pads 112, 212. Because not only the plasma processing and bonding of the substrates W but also the heat treatment are performed in a single substrate bonding apparatus 1, the time between performing plasma processing and performing heat treatment can be shortened. This reduces the number of amino groups that are altered or lost during this time.

[0083] In this embodiment, an inductive electric field is generated in the sealed container 12 containing the substrate W by supplying a high-frequency current to the antenna 15. This ionizes the gas in the sealed container 12, generating inductively coupled plasma of at least one of a rare gas, hydrogen, and nitrogen. This inductively coupled plasma comes into contact with the bonding surfaces 111, 211 of the substrate W in the sealed container 12, thereby processing the bonding surfaces 111, 211. The inductively coupled plasma is a high-density plasma with a high density of electrons, ions, radicals, and the like. Therefore, the bonding surfaces 111, 211 of the substrate W can be processed uniformly.

[0084] The antenna 15 is disposed in the space between an inner plate 17 that closes a hole opened on the inner surface of the outer wall 12w of the sealed container 12, and an outer plate 18 that closes a hole opened on the outer surface of the outer wall 12w of the sealed container 12. The size of the antenna 15 is limited to the size that can be placed in the space inside the outer wall 12w. This allows the antenna 15 to be miniaturized and the inductance of the antenna 15 to be reduced. If the inductance of the antenna 15 is low, the voltage applied to the antenna 15 when a high-frequency current is supplied to the antenna 15 decreases, thereby reducing damage to the substrate W caused by the plasma. Therefore, the bonding surfaces 111, 211 can be uniformly processed with the plasma while reducing damage.

[0085] Next, another embodiment will be described.

[0086] The rare gas (group 18 element) contained in the reactive gas for generating plasma may be a rare gas other than argon, such as helium or neon.

[0087] At least one of the plasma processing unit 2a and the heat-treating unit 2d may be an apparatus separate from the substrate bonding apparatus 1. That is, at least one of the plasma processing unit 2a and the heat-treating unit 2d may be disposed outside the outer wall 1a of the substrate bonding apparatus 1.

[0088] Any two or more of the above-mentioned features may be combined. Any two or more of the above-mentioned steps may be combined.

[0089] Although the embodiments of the present invention have been described in detail, these are merely examples used to clarify the technical contents of the present invention, and the present invention should not be construed as being limited to these examples. The spirit and scope of the present invention are limited only by the appended claims. [Explanation of symbols]

[0090] 1: substrate bonding device, 2a: plasma processing unit, 2b: cleaning unit, 2c: bonding unit, 2d: heat treatment unit, 11: substrate holder, 12: sealed container, 12d: door, 12w: outer wall, 13d: exhaust pipe, 13s: gas supply pipe, 14: plasma source, 15: antenna, 16: high frequency power source, 17: inner plate, 18: outer plate, 31A: first chuck, 31B: second chuck, 32: chamber, 33: actuator, 34: camera, 41: substrate holder, 42: heat treatment furnace, 43: heater, 110: First bonding layer, 111: first bonding surface, 112: first copper pad, 113: first insulating film, 120: first device layer, 121: first semiconductor device, 122: first insulating film, 130: first substrate, 131: first non-bonding surface, 210: second bonding layer, 211: second bonding surface, 212: second copper pad, 213: second insulating film, 220: second device layer, 221: second semiconductor device, 222: second insulating film, 230: second substrate, 231: second non-bonding surface, P1: first plasma, P2: second plasma, W: substrate, W1: first substrate, W2: second substrate

Claims

1. A substrate bonding method for bonding two substrates, each having a bonding surface where copper oxide of a copper pad and an insulating film are exposed, comprising the steps of: a plasma treatment step of treating the bonding surfaces of each substrate with rare gas plasma, treating the bonding surfaces of each substrate treated with the rare gas plasma with hydrogen plasma, and treating the bonding surfaces of each substrate treated with the hydrogen plasma with nitrogen plasma; and a substrate bonding step of bonding the two substrates by bringing the bonding surfaces of the two substrates into contact with each other so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other after the plasma treatment step.

2. 2. The substrate bonding method according to claim 1, wherein the plasma treatment step is a step of treating the bonding surface with plasma containing the rare gas plasma but not containing the nitrogen plasma, a nitrogen plasma treatment step of treating the bonding surface with the nitrogen plasma, and a hydrogen plasma treatment step of treating the bonding surface with the hydrogen plasma simultaneously with at least one of the rare gas plasma treatment step and the nitrogen plasma treatment step, or after the rare gas plasma treatment step and before the nitrogen plasma treatment step, for each of the two substrates.

3. 3. The substrate bonding method according to claim 2, wherein the plasma treatment step comprises: a first plasma treatment step of supplying a first reactive gas containing the rare gas and hydrogen but not containing nitrogen into a sealed container that houses the substrates, and treating the bonding surface with a first plasma generated from the first reactive gas; and a second plasma treatment step of supplying a second reactive gas containing the nitrogen into the sealed container, and treating the bonding surface with a second plasma generated from the second reactive gas, for each of the two substrates.

4. 4. The substrate bonding method according to claim 1, further comprising an oxygen contacting step of contacting the bonding surfaces of the substrates with at least one of oxygen in air and oxygen in a liquid after the plasma treatment step.

5. 5. The substrate bonding method according to claim 4, wherein the oxygen contact step includes a cleaning step of cleaning each of the two substrates with a cleaning liquid and drying the cleaning liquid after the plasma treatment step and before the substrate bonding step.

6. 4. The substrate bonding method according to claim 1, further comprising a heat treatment step of heating the two bonded substrates to directly bond the copper contained in the copper pad of one of the two substrates to the copper contained in the copper pad of the other of the two substrates.

7. the plasma treatment step is a step of treating the bonding surfaces of the substrates with the rare gas plasma, the hydrogen plasma, and the nitrogen plasma by generating the rare gas plasma, the hydrogen plasma, and the nitrogen plasma in a plasma treatment unit of a substrate bonding apparatus; the substrate bonding step is a step of bonding the two substrates by bringing the bonding surfaces of the two substrates into contact with a bonding unit of the substrate bonding apparatus so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other; 7. The substrate bonding method according to claim 6, wherein the heat treatment step is a step of directly bonding the copper contained in the copper pad of one of the two substrates to the copper contained in the copper pad of the other of the two substrates by heating the two bonded substrates in a heat treatment unit of the substrate bonding apparatus.

8. 4. The substrate bonding method according to claim 1, wherein the plasma treatment step is a step of generating inductively coupled plasma of at least one of the rare gas, hydrogen, and nitrogen by supplying a high-frequency current to an antenna disposed in a space between an inner plate that closes a hole opened on the inner surface of an outer wall of a sealed container that houses the substrates, and an outer plate that closes a hole opened on the outer surface of the outer wall.

9. A substrate bonding apparatus for bonding two substrates, each having a bonding surface where copper oxide of a copper pad and an insulating film are exposed, comprising: a plasma processing unit that processes the bonding surfaces of each substrate with rare gas plasma, which is a plasma of a rare gas, processes the bonding surfaces of each substrate that have been processed with the rare gas plasma with hydrogen plasma, which is a plasma of hydrogen, and processes the bonding surfaces of each substrate that have been processed with the hydrogen plasma with nitrogen plasma, which is a plasma of nitrogen; a bonding unit that bonds the two substrates after the plasma treatment step by bringing the bonding surfaces of the two substrates into contact so that the copper pads of the two substrates face each other and the insulating films of the two substrates face each other.

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