JP7809012B2 - Joining system and joining method - Google Patents

Description

This disclosure relates to a joining system and a joining method.

To meet the demand for higher integration of semiconductor devices, three-dimensional integration technology has been proposed, which stacks semiconductor devices in three dimensions. A known example of semiconductor manufacturing equipment used in this three-dimensional integration technology is a bonding system that bonds substrates such as semiconductor wafers together.

Patent Document 1 discloses a bonding system in which the surfaces of substrates to be bonded are modified, the modified substrate surfaces are made hydrophilic, and the hydrophilized substrates are bonded together using van der Waals forces and hydrogen bonds (intermolecular forces).

Japanese Patent Application Laid-Open No. 2017-073455

This disclosure provides technology that can improve the bonding quality of laminated substrates.

A bonding system according to one aspect of the present disclosure includes a surface modification device, a bonding device, and a control unit. The surface modification device performs a surface modification process that modifies the insulating film of the insulating film and metal wiring located on the surface of the substrate using plasma from a processing gas. The bonding device performs a bonding process that uses intermolecular forces to bond two substrates whose insulating films have been modified by the surface modification process. The control unit acquires information regarding the thickness of the metal oxide film on the surface of the substrate before the surface modification process, and determines the processing conditions for the surface modification process based on the acquired information.

This disclosure makes it possible to improve the bonding quality of laminated substrates.

FIG. 1 is a schematic plan view showing the configuration of a joining system according to a first embodiment. FIG. 2 is a schematic side view of the same. FIG. 3 is a schematic side view of the upper wafer and the lower wafer according to the embodiment. FIG. 4 is a schematic cross-sectional view showing the configuration of the surface modification device. FIG. 5 is a schematic plan view showing the configuration of the joining device according to the embodiment. FIG. 6 is a schematic side view showing the configuration of the joining device according to the embodiment. FIG. 7 is a schematic diagram showing an upper chuck and a lower chuck according to the embodiment. FIG. 8 is a flowchart illustrating a procedure of a process executed by the joint system according to the embodiment. FIG. 9 is a graph showing an example of the relationship between the processing time of the surface modification processing and the bonding strength. FIG. 10 is a graph showing an example of the relationship between the processing time of the surface modification process and the thickness of the metal oxide film when the power applied from the high frequency power source to the stage is relatively low. FIG. 11 is a graph showing an example of the relationship between the processing time of the surface modification process and the thickness of the metal oxide film when the power applied from the high frequency power source to the stage is relatively high. FIG. 12 is a graph showing an example of a process window of a surface modification process taking into consideration both the modification threshold and the film thickness threshold. FIG. 13 is a flowchart showing an example of a procedure for determining processing conditions for a surface modification process. FIG. 14 is a flowchart illustrating an example of a procedure for determining whether or not joining processing is executable. FIG. 15 is a diagram showing another example of the configuration of the processing station included in the bonding system. FIG. 16 is a diagram showing another example of the configuration of the joining system. FIG. 17 is a schematic plan view showing the configuration of a joining system according to the second embodiment. FIG. 18 is a schematic diagram showing the configuration of a removal device according to the second embodiment. FIG. 19 is a graph showing the relationship between the plasma power applied in the plasma treatment and the proportion of metal oxide films and metal nitride films present on the Cu substrate after the plasma treatment. FIG. 20 is a graph showing the relationship between the plasma irradiation time in the plasma treatment and the proportion of metal oxide films and metal nitride films present on the Cu substrate after the plasma treatment. FIG. 21 is a graph showing the relationship between the plasma applied power and the proportion of metal nitride film present after plasma treatment on a Cu substrate having a metal oxide film on its surface. FIG. 22 is a graph showing the relationship between the plasma applied power and the proportion of metal nitride film present after plasma treatment on a Cu substrate on the surface of which no metal oxide film exists.

Below, a detailed description will be given of a form (hereinafter referred to as an "embodiment") for implementing the bonding system and bonding method according to the present disclosure, with reference to the drawings. Note that the present disclosure is not limited to this embodiment. Furthermore, the embodiments can be combined as appropriate to the extent that the processing content is not contradictory. Furthermore, the same components in the following embodiments will be assigned the same reference numerals, and duplicate explanations will be omitted.

Furthermore, in the embodiments described below, expressions such as "constant," "orthogonal," "perpendicular," or "parallel" may be used, but these expressions do not necessarily mean "constant," "orthogonal," "perpendicular," or "parallel" in the strict sense. In other words, the above expressions allow for deviations due to, for example, manufacturing accuracy, installation accuracy, etc.

In addition, for ease of understanding, the drawings referenced below may show an orthogonal coordinate system in which the X-axis, Y-axis, and Z-axis directions are defined as being orthogonal to each other, with the positive Z-axis direction being the vertically upward direction. Furthermore, the direction of rotation around the vertical axis may be referred to as the θ direction.

Please note that the drawings are schematic and the dimensional relationships and proportions of each element may differ from reality. Furthermore, there may be parts in the drawings where the dimensional relationships and proportions differ.

A conventional method for bonding substrates such as semiconductor wafers involves modifying the surfaces of the substrates to be bonded, making the modified substrate surfaces hydrophilic, and then bonding the hydrophilized substrates together using van der Waals forces and hydrogen bonds (intermolecular forces).

Substrate surface modification is a process in which the surface of a substrate is modified using plasma from a processing gas. Specifically, surface modification is a process in which the insulating film located on the surface of the substrate is activated by plasma.

In some cases, the surface of a substrate contains not only an insulating film but also metal wiring. When a surface modification process is performed on a substrate with an insulating film and metal wiring on its surface, the native oxide film on the metal wiring (hereinafter referred to as "metal oxide film") is removed by the plasma and then re-deposited on the metal wiring. In other words, the thickness of the metal oxide film on the metal wiring is temporarily thinned by the surface modification process, and then thickens again. Note that this phenomenon does not always occur, and it is known to occur more easily when plasma is generated with relatively high power. On the other hand, it is also known that when plasma is generated with relatively low power, the metal oxide film itself is not removed (or is barely removed).

If the metal oxide film on the metal wiring of a substrate after surface modification treatment is too thick, there is a risk of poor bonding between the metal wiring of one substrate and the metal wiring of the other substrate when the substrates are bonded together.

The thickness of the metal oxide film formed on the metal wiring varies from substrate to substrate due to factors such as the manufacturing process and environment. Therefore, if surface modification is performed under fixed processing conditions (applied power, processing time, etc.), it may not be possible to properly control the thickness of the metal oxide film. For example, if a surface modification process is performed on a substrate with a thick metal oxide film using low-power plasma, the metal oxide film may not be removed, and the metal oxide film may proceed to the bonding process while remaining thicker than the critical thickness. Furthermore, if a surface modification process is performed on a substrate with a thick metal oxide film using high-power plasma, the metal oxide film may be removed by the plasma, but depending on the processing time, the metal oxide film may re-deposit and become thicker than the critical thickness. The critical thickness is a predetermined thickness that prevents poor bonding between metal wiring.

Therefore, there is a need to develop technology that can overcome the above-mentioned problems and improve the bonding quality of laminated substrates. Specifically, there is a need to develop technology that can improve the bonding quality of laminated substrates by activating the insulating film during surface modification while keeping the thickness of the metal oxide film on the metal wiring below the critical film thickness.

(First embodiment)
<Configuration of the joining system>
First, the configuration of a bonding system 1 according to a first embodiment will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a schematic plan view showing the configuration of the bonding system 1 according to the first embodiment, and Fig. 2 is a schematic side view of the same. Also, Fig. 3 is a schematic side view of the upper wafer W1 and the lower wafer W2 according to the first embodiment.

The bonding system 1 shown in Figure 1 forms a laminated wafer T by bonding a first substrate W1 and a second substrate W2.

The first substrate W1 and the second substrate W2 are semiconductor substrates such as silicon wafers or compound semiconductor wafers. The first substrate W1 and the second substrate W2 have approximately the same diameter.

Hereinafter, the first substrate W1 will be referred to as the "upper wafer W1," and the second substrate W2 will be referred to as the "lower wafer W2." In other words, the upper wafer W1 is an example of a first substrate, and the lower wafer W2 is an example of a second substrate. Furthermore, when referring collectively to the upper wafer W1 and the lower wafer W2, they may be referred to as "wafer W."

Furthermore, as shown in FIG. 3, of the surfaces of the upper wafer W1, the surface that is bonded to the lower wafer W2 will be referred to as the "bonding surface W1j," and the surface opposite the bonding surface W1j will be referred to as the "non-bonding surface W1n." Furthermore, of the surfaces of the lower wafer W2, the surface that is bonded to the upper wafer W1 will be referred to as the "bonding surface W2j," and the surface opposite the bonding surface W2j will be referred to as the "non-bonding surface W2n."

3, an insulating film WL and metal wiring WM are located on the bonding surface W1j of the first substrate W1 and the bonding surface W2j of the second substrate W2. The insulating film WL is, for example, a _SiO2 (silicon dioxide) film or a SiCN (silicon carbonitride) film. The metal wiring WM is, for example, a Cu (copper) wiring.

As shown in FIG. 1, the bonding system 1 includes a loading/unloading station 2 and a processing station 3. The loading/unloading station 2 and the processing station 3 are arranged in the positive direction of the X-axis in the order loading/unloading station 2 and processing station 3. The loading/unloading station 2 and the processing station 3 are also integrally connected.

The loading/unloading station 2 comprises a mounting table 10 and a transfer area 20. The mounting table 10 comprises multiple mounting plates 11. Each mounting plate 11 is loaded with a cassette C1, C2, or C3, which holds multiple substrates (e.g., 25 substrates) in a horizontal position. For example, cassette C1 is a cassette that holds upper wafers W1, cassette C2 is a cassette that holds lower wafers W2, and cassette C3 is a cassette that holds overlapping wafers T.

The transport area 20 is located adjacent to the mounting table 10 on the positive side of the X axis. This transport area 20 is provided with a transport path 21 extending in the Y axis direction and a transport device 22 that can move along this transport path 21.

The transfer device 22 is capable of moving not only in the Y-axis direction but also in the X-axis direction and of rotating around the Z-axis. The transfer device 22 transfers the upper wafer W1, lower wafer W2, and overlapping wafer T between cassettes C1 to C3 placed on the mounting plate 11 and the third processing block G3 of processing station 3, which will be described later.

Note that the number of cassettes C1 to C3 placed on the placement plate 11 is not limited to that shown in the figure. Furthermore, in addition to cassettes C1, C2, and C3, cassettes for recovering defective substrates may also be placed on the placement plate 11.

Processing station 3 is equipped with multiple processing blocks, such as three processing blocks G1, G2, and G3, each equipped with various devices. For example, a first processing block G1 is provided on the front side of processing station 3 (negative Y-axis side in Figure 1), and a second processing block G2 is provided on the rear side of processing station 3 (positive Y-axis side in Figure 1). Furthermore, a third processing block G3 is provided on the loading/unloading station 2 side of processing station 3 (negative X-axis side in Figure 1).

The first processing block G1 is equipped with a surface modification device 30 that modifies the bonding surfaces W1j, W2j of the upper wafer W1 and the lower wafer W2 using plasma from a processing gas. In the surface modification device 30, for example, a given processing gas is excited into plasma, ionized, or radicalized in a reduced-pressure atmosphere. The ions (radicals) of elements contained in the processing gas are then irradiated onto the bonding surfaces W1j, W2j of the upper wafer W1 and the lower wafer W2, activating the insulating film WL located on the bonding surfaces W1j, W2j.

For example, when nitrogen gas is used as the processing gas, the surface modification apparatus 30 can form dangling bonds on the bonding surfaces W1j and W2j of the upper wafer W1 and lower wafer W2 by irradiating plasma. In this case, the surface modification apparatus 30 can activate the insulating film WL located on the bonding surfaces W1j and W2j so that they are more likely to be subsequently rendered hydrophilic.

The first processing block G1 also includes a surface hydrophilization device 40. The surface hydrophilization device 40 hydrophilizes the bonding surfaces W1j and W2j of the upper wafer W1 and the lower wafer W2 using, for example, pure water, and cleans the bonding surfaces W1j and W2j.

In the surface hydrophilization device 40, pure water is supplied onto the upper wafer W1 or lower wafer W2 while the upper wafer W1 or lower wafer W2 is rotated, for example, while being held by a spin chuck. As a result, the pure water supplied onto the upper wafer W1 or lower wafer W2 spreads over the bonding surfaces W1j, W2j of the upper wafer W1 or lower wafer W2, making the bonding surfaces W1j, W2j hydrophilic.

A film thickness measuring device 35 is disposed in the second processing block G2. The film thickness measuring device 35 measures the film thickness of the metal oxide film on the metal wiring WM located on the bonding surface W1j of the upper wafer W1. Similarly, the film thickness measuring device 35 measures the film thickness of the metal oxide film on the metal wiring WM located on the bonding surface W2j of the lower wafer W2. The film thickness measuring device 35 can be, for example, an ellipsometer or an optical interferometer (e.g., a UV interferometer).

The optical axis of the film thickness measuring device 35 is preferably perpendicular to the bonding surfaces W1j and W2j, which are the surfaces to be measured. This configuration allows the incident light to be irradiated onto a narrower area than when the optical axis is angled relative to the bonding surfaces W1j and W2j. Therefore, even if the pattern of the metal wiring WM is fine, it is easy to irradiate only the metal wiring WM with the incident light, eliminating the influence of layers other than the metal wiring WM (i.e., the insulating film WL) on the measurement results. This means that the accuracy of measuring the thickness of the metal oxide film can be improved.

Note that the optical axis of the film thickness measuring instrument 35 does not necessarily have to be perpendicular to the bonding surfaces W1j and W2j. The optical axis of the film thickness measuring instrument 35 may be oblique to the bonding surfaces W1j and W2j.

The second processing block G2 also includes a bonding device 41. The bonding device 41 bonds the upper wafer W1 and the lower wafer W2. Details of the bonding device 41 will be described later.

As shown in FIG. 2, the third processing block G3 is equipped with transition (TRS) devices 50 and 51 for the upper wafer W1, lower wafer W2, and overlapping wafer T, which are arranged in two stages from bottom to top.

As shown in FIG. 1, a transfer region 60 is formed in the area surrounded by the first processing block G1, the second processing block G2, and the third processing block G3. A transfer device 61 is disposed in the transfer region 60. The transfer device 61 has a transfer arm that can move, for example, vertically, horizontally, and around a vertical axis.

The transfer device 61 moves within the transfer area 60 and transfers the upper wafer W1, lower wafer W2, and overlapped wafer T to designated devices within the first processing block G1, second processing block G2, and third processing block G3 adjacent to the transfer area 60.

The bonding system 1 also includes a control device 4. The control device 4 controls the operation of the bonding system 1. The control device 4 is, for example, a computer, and includes a control unit 5 and a memory unit 6. The memory unit 6 stores programs that control various processes, such as the bonding process. The control unit 5 controls the operation of the bonding system 1 by reading and executing the programs stored in the memory unit 6.

The program may be recorded on a computer-readable recording medium and installed from that recording medium into the memory unit 6 of the control device 4. Examples of computer-readable recording media include hard disks (HDs), flexible disks (FDs), compact disks (CDs), magnetic optical disks (MOs), and memory cards.

<Configuration of Surface Modification Device>
Next, the configuration of the surface modification device 30 will be described with reference to Fig. 4. Fig. 4 is a schematic cross-sectional view showing the configuration of the surface modification device 30.

As shown in FIG. 4, the surface modification apparatus 30 has a processing vessel 70 whose interior can be sealed. A loading/unloading port 71 for the upper wafer W1 or the lower wafer W2 is formed on the side of the processing vessel 70 facing the transfer area 60 (see FIG. 1), and a gate valve 72 is provided at the loading/unloading port 71.

A stage 80 is disposed inside the processing vessel 70. The stage 80 is, for example, a lower electrode and is made of a conductive material such as aluminum. Pin through-holes (not shown) are formed in the stage 80, and lifter pins (not shown) are housed in these pin through-holes. The lifter pins are configured to be able to be raised and lowered in the vertical direction by a lifting mechanism (not shown).

An exhaust ring 103 with multiple baffle holes is placed between the stage 80 and the inner wall of the processing vessel 70. The exhaust ring 103 allows the atmosphere inside the processing vessel 70 to be uniformly exhausted from within the processing vessel 70.

A power feed rod 104 made of a conductor is connected to the underside of the stage 80. A high-frequency power supply 106 is connected to the power feed rod 104 via a matching device 105, such as a blocking capacitor. During plasma processing, a given high-frequency power is applied to the stage 80 from the high-frequency power supply 106.

An upper electrode 110 is disposed inside the processing vessel 70. The upper surface of the stage 80 and the lower surface of the upper electrode 110 are disposed parallel to each other and facing each other with a given distance between them. The distance between the upper surface of the stage 80 and the lower surface of the upper electrode 110 is adjusted by an elevation mechanism (not shown).

The upper electrode 110 is grounded and connected to ground potential. Because the upper electrode 110 is grounded in this way, damage to the underside of the upper electrode 110 during plasma processing can be suppressed.

In this way, plasma is generated inside the processing vessel 70 by applying high-frequency power from the high-frequency power supply 106 to the stage 80, which serves as the lower electrode.

In this embodiment, the stage 80, power feed rod 104, matching box 105, high-frequency power supply 106, upper electrode 110, and matching box are an example of a plasma generation mechanism that generates plasma of the processing gas within the processing vessel 70. The high-frequency power supply 106 is controlled by the control unit 5 of the control device 4 described above.

A hollow portion 120 is formed inside the upper electrode 110. A gas supply pipe 121 is connected to the hollow portion 120. The gas supply pipe 121 is connected to a gas supply source 122 that stores a processing gas and a static elimination gas inside. The gas supply pipe 121 is also provided with a group of supply devices 123, including valves and flow rate regulators that control the flow of the processing gas and the static elimination gas.

The processing gas and static elimination gas supplied from the gas supply source 122 are flow-controlled by a supply device group 123 and introduced into the hollow portion 120 of the upper electrode 110 via a gas supply pipe 121. Examples of processing gases that can be used include oxygen gas, nitrogen gas, and argon gas. Examples of static elimination gases that can be used include inert gases such as nitrogen gas and argon gas.

A baffle plate 124 is provided inside the hollow portion 120 to promote uniform diffusion of the processing gas and static elimination gas. The baffle plate 124 has a large number of small holes. The lower surface of the upper electrode 110 has a large number of gas outlets 125 formed therein, which eject the processing gas and static elimination gas from the hollow portion 120 into the processing vessel 70.

The processing vessel 70 is formed with an intake port 130. The intake port 130 is connected to an intake pipe 132 that communicates with a vacuum pump 131 that reduces the atmosphere inside the processing vessel 70 to a given vacuum level.

The upper surface of the stage 80, i.e., the surface facing the upper electrode 110, is a horizontal surface that is circular in plan view and has a diameter larger than the diameters of the upper wafer W1 and lower wafer W2. A stage cover 90 is placed on the upper surface of the stage 80, and the upper wafer W1 or lower wafer W2 is placed on the placement portion 91 of the stage cover 90.

<Configuration of the joining device>
Next, the configuration of the joining device 41 will be described with reference to Fig. 5 and Fig. 6. Fig. 5 is a schematic plan view showing the configuration of the joining device 41 according to the embodiment, and Fig. 6 is a schematic side view showing the configuration of the joining device 41 according to the embodiment.

As shown in FIG. 5, the bonding apparatus 41 has a processing vessel 190 whose interior can be sealed. A loading/unloading port 191 for the upper wafer W1, the lower wafer W2, and the overlapped wafer T is formed on the side of the processing vessel 190 facing the transfer area 60, and the loading/unloading port 191 is provided with an opening/closing shutter 192.

The interior of the processing vessel 190 is divided into a transfer region T1 and a processing region T2 by an inner wall 193. The above-mentioned loading/unloading port 191 is formed on the side of the processing vessel 190 in the transfer region T1. In addition, loading/unloading ports 194 for the upper wafer W1, lower wafer W2, and overlapping wafer T are also formed in the inner wall 193.

In the transport area T1, a transition 200, a substrate transport mechanism 201, an inversion mechanism 220, and a position adjustment mechanism 210 are arranged, for example, in this order from the loading/unloading port 191 side.

The transition 200 temporarily holds the upper wafer W1, the lower wafer W2, and the overlapped wafer T. The transition 200 may be formed, for example, in two stages, allowing any two of the upper wafer W1, the lower wafer W2, and the overlapped wafer T to be held simultaneously.

The substrate transfer mechanism 201 has a transfer arm that can move freely, for example, in the vertical direction (Z-axis direction), horizontal direction (Y-axis direction, X-axis direction), and direction around the vertical axis (θ direction). The substrate transfer mechanism 201 can transfer the upper wafer W1, lower wafer W2, and overlapping wafer T within the transfer region T1 or between the transfer region T1 and processing region T2.

The position adjustment mechanism 210 adjusts the horizontal orientation of the upper wafer W1 and the lower wafer W2. Specifically, the position adjustment mechanism 210 has a base 211 equipped with a holding unit (not shown) that holds and rotates the upper wafer W1 and the lower wafer W2, and a detection unit 212 that detects the position of the notch portion of the upper wafer W1 and the lower wafer W2. The position adjustment mechanism 210 adjusts the position of the notch portion by detecting the position of the notch portion of the upper wafer W1 and the lower wafer W2 using the detection unit 212 while rotating the upper wafer W1 and the lower wafer W2 held on the base 211. This adjusts the horizontal orientation of the upper wafer W1 and the lower wafer W2.

The inversion mechanism 220 inverts the upper wafer W1. Specifically, the inversion mechanism 220 has a holding arm 221 that holds the upper wafer W1. The holding arm 221 extends horizontally (in the X-axis direction). The holding arm 221 also has holding members 222, for example, at four locations, that hold the upper wafer W1.

The holding arm 221 is supported by a drive unit 223 equipped with, for example, a motor. The drive unit 223 allows the holding arm 221 to rotate freely around a horizontal axis. The holding arm 221 is also rotatable around the drive unit 223 and is also movable horizontally (in the X-axis direction). Below the drive unit 223, another drive unit (not shown) equipped with, for example, a motor is provided. This other drive unit allows the drive unit 223 to move vertically along a support column 224 extending vertically.

In this way, the upper wafer W1 held by the holding member 222 can be rotated around a horizontal axis by the drive unit 223 and moved vertically and horizontally. Furthermore, the upper wafer W1 held by the holding member 222 can rotate around the drive unit 223 and move between the position adjustment mechanism 210 and the upper chuck 230, which will be described later.

The processing region T2 is provided with an upper chuck 230 that suction-holds the upper surface (non-bonding surface W1n) of the upper wafer W1 from above, and a lower chuck 231 that suction-holds the lower surface (non-bonding surface W2n) of the lower wafer W2 from below. The lower chuck 231 is provided below the upper chuck 230 and is configured to be able to be positioned opposite the upper chuck 230. The upper chuck 230 and the lower chuck 231 are, for example, vacuum chucks.

As shown in FIG. 6 , the upper chuck 230 is supported by a support member 270 provided above the upper chuck 230. The support member 270 is fixed to the ceiling surface of the processing vessel 190 via, for example, multiple support columns 271.

An upper imaging unit 235 is provided to the side of the upper chuck 230 to capture an image of the upper surface (bonding surface W2j) of the lower wafer W2 held by the lower chuck 231. The upper imaging unit 235 may be, for example, a CCD camera.

The lower chuck 231 is supported by a first moving unit 250 provided below the lower chuck 231. As described below, the first moving unit 250 moves the lower chuck 231 in the horizontal direction (X-axis direction). The first moving unit 250 is also configured to be able to move the lower chuck 231 vertically and rotate it around a vertical axis.

The first moving section 250 is provided with a lower imaging section 236 that captures an image of the lower surface (bonding surface W1j) of the first substrate W1 held by the upper chuck 230. The lower imaging section 236 is, for example, a CCD camera.

The first moving unit 250 is attached to a pair of rails 252, 252. The pair of rails 252, 252 are provided on the underside of the first moving unit 250 and extend horizontally (in the X-axis direction). The first moving unit 250 is configured to be freely movable along the rails 252.

The pair of rails 252, 252 are arranged on the second moving part 253. The second moving part 253 is attached to a pair of rails 254, 254. The pair of rails 254, 254 are arranged on the underside of the second moving part 253 and extend horizontally (in the Y-axis direction). The second moving part 253 is configured to be movable horizontally (in the Y-axis direction) along the rails 254. The pair of rails 254, 254 are arranged on a mounting table 255 provided on the bottom surface of the processing vessel 190.

The first moving unit 250, second moving unit 253, etc. constitute the alignment unit 256. The alignment unit 256 moves the lower chuck 231 in the X-axis direction, Y-axis direction, and θ direction to horizontally align the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231. The alignment unit 256 also moves the lower chuck 231 in the Z-axis direction to vertically align the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231.

Note that, although the lower chuck 231 is moved in the X-axis direction, Y-axis direction, and θ direction here, the alignment unit 256 may, for example, move the lower chuck 231 in the X-axis direction and Y-axis direction, and move the upper chuck 230 in the θ direction. Note that, although the lower chuck 231 is moved in the Z-axis direction here, the alignment unit 256 may, for example, move the upper chuck 230 in the Z-axis direction.

Next, the configuration of the upper chuck 230 and the lower chuck 231 will be described with reference to Figure 7. Figure 7 is a schematic diagram showing the upper chuck 230 and the lower chuck 231 according to the embodiment.

As shown in FIG. 7 , the upper chuck 230 has a main body 260. The main body 260 is supported by a support member 270. A through-hole 266 is formed in the support member 270 and the main body 260, penetrating the support member 270 and the main body 260 in the vertical direction. The position of the through-hole 266 corresponds to the center of the upper wafer W1 held by suction on the upper chuck 230. A pressing pin 281 of a striker 280 is inserted into the through-hole 266.

The striker 280 is disposed on the upper surface of the support member 270 and comprises a pressure pin 281, an actuator unit 282, and a linear motion mechanism 283. The pressure pin 281 is a cylindrical member extending vertically and is supported by the actuator unit 282.

The actuator unit 282 generates a constant pressure in a certain direction (vertically downward in this case) using air supplied from, for example, an electropneumatic regulator (not shown). The actuator unit 282 contacts the center of the upper wafer W1 using air supplied from the electropneumatic regulator, allowing it to control the pressure load applied to the center of the upper wafer W1. In addition, the tip of the actuator unit 282 is movable vertically through the through-hole 266 using air from the electropneumatic regulator.

The actuator unit 282 is supported by a linear motion mechanism 283. The linear motion mechanism 283 moves the actuator unit 282 vertically using, for example, a drive unit incorporating a motor.

The striker 280 is configured as described above, with the linear motion mechanism 283 controlling the movement of the actuator unit 282, and the actuator unit 282 controlling the pressing load on the upper wafer W1 by the pressing pin 281. As a result, the striker 280 presses the center of the upper wafer W1, which is held by suction on the upper chuck 230, to bring it into contact with the lower wafer W2.

The underside of the main body 260 is provided with multiple pins 261 that contact the upper surface (non-bonding surface W1n) of the upper wafer W1. The multiple pins 261 have a diameter of, for example, 0.1 mm to 1 mm and a height of several tens to several hundred μm. The multiple pins 261 are evenly spaced, for example, at intervals of 2 mm.

The upper chuck 230 has a plurality of suction portions that suction the upper wafer W1 in a portion of the area where the plurality of pins 261 are provided. Specifically, the lower surface of the main body 260 of the upper chuck 230 is provided with a plurality of outer suction portions 391 and a plurality of inner suction portions 392 that suction the upper wafer W1 by vacuuming. The plurality of outer suction portions 391 and the plurality of inner suction portions 392 have suction areas that are arc-shaped in plan view. The plurality of outer suction portions 391 and the plurality of inner suction portions 392 have the same height as the pins 261.

The multiple outer suction portions 391 are arranged on the outer periphery of the main body 260. The multiple outer suction portions 391 are connected to a suction device (not shown), such as a vacuum pump, and suck the outer periphery of the upper wafer W1 by vacuuming.

The multiple inner suction portions 392 are arranged in a row along the circumferential direction, radially inward of the multiple outer suction portions 391 in the main body portion 260. The multiple inner suction portions 392 are connected to a suction device (not shown), such as a vacuum pump, and suck the area between the outer periphery and center of the upper wafer W1 by vacuuming.

The lower chuck 231 has a main body 290 with a diameter equal to or larger than that of the lower wafer W2. Here, the lower chuck 231 is shown with a diameter larger than that of the lower wafer W2. The upper surface of the main body 290 is the opposing surface that faces the lower surface (non-bonding surface W2n) of the lower wafer W2.

The upper surface of the main body 290 is provided with multiple pins 291 that contact the lower surface (non-bonding surface W2n) of the lower wafer W2. The multiple pins 291 have a diameter of, for example, 0.1 mm to 1 mm and a height of several tens to several hundred μm. The multiple pins 291 are evenly spaced, for example, at intervals of 2 mm.

In addition, a lower rib 292 is provided in an annular shape on the upper surface of the main body 290, outside the multiple pins 291. The lower rib 292 is formed in an annular shape and supports the outer periphery of the lower wafer W2 around the entire circumference.

The main body 290 also has a plurality of lower suction ports 293. The plurality of lower suction ports 293 are provided in the suction area surrounded by the lower ribs 292. The plurality of lower suction ports 293 are connected to a suction device (not shown), such as a vacuum pump, via a suction pipe (not shown).

The lower chuck 231 depressurizes the suction area surrounded by the lower ribs 292 by vacuuming it through multiple lower suction ports 293. As a result, the lower wafer W2 placed in the suction area is suction-held by the lower chuck 231.

Because the lower ribs 292 support the entire outer periphery of the lower surface of the lower wafer W2, the lower wafer W2 is properly vacuumed up to its outer periphery. This allows the entire surface of the lower wafer W2 to be suction-held. Furthermore, because the lower surface of the lower wafer W2 is supported by multiple pins 291, the lower wafer W2 is easily released from the lower chuck 231 when the vacuum on the lower wafer W2 is released.

<Specific operation of the joining system>
Next, a specific operation of the bonding system 1 according to the embodiment will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the procedure of processing executed by the bonding system 1 according to the embodiment. The various processing shown in Fig. 8 is executed based on control by the control unit 5 of the control device 4.

First, cassette C1 containing multiple upper wafers W1, cassette C2 containing multiple lower wafers W2, and empty cassette C3 are placed on a predetermined loading plate 11 in the load/unload station 2. Then, the upper wafer W1 in cassette C1 is removed by the transfer device 22 and transferred to the transition device 50 located in the third processing block G3.

Next, the upper wafer W1 is transferred to the film thickness measuring device 35 by the transfer device 61. The film thickness measuring device 35 measures the film thickness of the upper wafer W1 (step S101). Specifically, the film thickness measuring device 35 measures the film thickness of the metal oxide film on the metal wiring WM located on the bonding surface W1j of the upper wafer W1. The measurement results from the film thickness measuring device 35 are input to the control unit 5.

Next, the upper wafer W1 is transferred by the transfer device 61 to the surface modification device 30 in the first processing block G1. In the surface modification device 30, the bonding surface W1j of the upper wafer W1 is surface modified (step S102). Specifically, dangling bonds are formed by removing terminal groups from the insulating film WL located on the bonding surface W1j of the upper wafer W1, and the dangling bonds are terminated with OH groups.

Next, the upper wafer W1 is transferred by the transfer device 61 to the surface hydrophilization device 40 in the first processing block G1. In the surface hydrophilization device 40, pure water is supplied onto the upper wafer W1 while the upper wafer W1 held by the spin chuck is rotated. This makes the bonding surface W1j of the upper wafer W1 hydrophilic. The bonding surface W1j of the upper wafer W1 is also cleaned with the pure water (step S103).

Next, the upper wafer W1 is transferred by the transfer device 61 to the bonding device 41 in the second processing block G2. After being transferred to the bonding device 41, the upper wafer W1 is transferred via the transition 200 to the position adjustment mechanism 210, where its horizontal orientation is adjusted by the position adjustment mechanism 210 (step S104).

Then, the upper wafer W1 is transferred from the position adjustment mechanism 210 to the reversing mechanism 220, which then reverses the upper wafer W1 upside down (step S105). Specifically, the bonding surface W1j of the upper wafer W1 faces downward.

Next, the upper wafer W1 is transferred from the reversing mechanism 220 to the upper chuck 230, and the upper wafer W1 is held by suction by the upper chuck 230 (step S106).

The processing of the lower wafer W2 overlaps with the processing of steps S101 to S106 for the upper wafer W1. First, the transfer device 22 removes the lower wafer W2 from the cassette C2 and transfers it to the transition device 50 located in the third processing block G3.

Next, the lower wafer W2 is transferred by the transfer device 61 to the film thickness measuring device 35. The film thickness measuring device 35 measures the film thickness of the lower wafer W2 (step S107). Specifically, the film thickness measuring device 35 measures the film thickness of the metal oxide film on the metal wiring WM located on the bonding surface W2j of the lower wafer W2. The measurement results from the film thickness measuring device 35 are input to the control unit 5.

Next, the lower wafer W2 is transferred by the transfer device 61 to the surface modification device 30, where the bonding surface W2j of the lower wafer W2 is modified (step S108).

Then, the lower wafer W2 is transferred by the transfer device 61 to the surface hydrophilization device 40, where the bonding surface W2j of the lower wafer W2 is hydrophilized and cleaned (step S109).

The lower wafer W2 is then transferred to the bonding device 41 by the transfer device 61. After being transferred to the bonding device 41, the lower wafer W2 is transferred to the position adjustment mechanism 210 via the transition 200. The position adjustment mechanism 210 then adjusts the horizontal orientation of the lower wafer W2 (step S110).

The lower wafer W2 is then transferred to the lower chuck 231 and held by suction on the lower chuck 231 with the notch facing in a predetermined direction (step S111).

Next, the horizontal positions of the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231 are adjusted (step S112).

Next, the vertical positions of the upper wafer W1 held by the upper chuck 230 and the lower wafer W2 held by the lower chuck 231 are adjusted (step S113). Specifically, the first moving part 250 moves the lower chuck 231 vertically upward, thereby bringing the lower wafer W2 closer to the upper wafer W1.

Next, the upper wafer W1 is released from suction by the multiple inner suction portions 392 (step S114), and the pressure pin 281 of the striker 280 is lowered to press down the center of the upper wafer W1 (step S115).

When the center of the upper wafer W1 comes into contact with the center of the lower wafer W2 and the striker 280 presses the centers of the upper wafer W1 and lower wafer W2 together with a predetermined force, bonding begins between the pressed centers of the upper wafer W1 and lower wafer W2. That is, because the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 have been modified, van der Waals forces (intermolecular forces) are first generated between the bonding surfaces W1j and W2j, bonding the bonding surfaces W1j and W2j together. Furthermore, because the bonding surface W1j of the upper wafer W1 and the bonding surface W2j of the lower wafer W2 have been hydrophilized, the hydrophilic groups between the bonding surfaces W1j and W2j form hydrogen bonds, firmly bonding the bonding surfaces W1j and W2j together. In this way, a bonded region is formed.

After that, a bonding wave is generated between the upper wafer W1 and the lower wafer W2, expanding the bonding area from the center of the upper wafer W1 and the lower wafer W2 toward their outer peripheries. Then, the upper wafer W1 is released from suction and hold by the multiple outer suction members 391 (step S116). This causes the outer periphery of the upper wafer W1, which had been suction-held by the outer suction members 391, to fall. As a result, the entire bonding surface W1j of the upper wafer W1 and the entire bonding surface W2j of the lower wafer W2 come into contact, forming the overlapped wafer T.

Then, the pressure pin 281 is raised to the upper chuck 230, and the lower chuck 231 releases the lower wafer W2 from suction. The overlapped wafer T is then removed from the bonding device 41 by the transfer device 61. This completes the series of bonding processes.

Next, the surface modification process in steps S102 and S108 will be described. First, the relationship between the processing time of the surface modification process and the bonding strength will be described with reference to Figure 9. Figure 9 is a graph showing an example of the relationship between the processing time of the surface modification process and the bonding strength.

As shown in Figure 9, there is a correlation between the processing time of the surface modification process and the bond strength. Specifically, the longer the processing time of the surface modification process, the higher the bond strength tends to be. To obtain the desired bond strength, in other words, to obtain a bond strength equal to or greater than the modification threshold, a processing time of at least t0 is required. Although not shown in Figure 9, it is known that if the processing time of the surface modification process is too long, the bond strength will actually decrease.

Next, the relationship between the processing time of the surface modification process and the thickness of the metal oxide film on the metal wiring WM (hereinafter referred to as "metal oxide film thickness") will be described with reference to Figures 10 and 11. Figure 10 is a graph showing an example of the relationship between the processing time of the surface modification process and the thickness of the metal oxide film when the power applied from the high-frequency power supply 106 to the stage 80 is relatively low (e.g., 30 W). Figure 11 is a graph showing an example of the relationship between the processing time of the surface modification process and the thickness of the metal oxide film when the power applied from the high-frequency power supply 106 to the stage 80 is relatively high (e.g., 150 W).

As shown in Figure 10, metal oxide films are not removed (or are removed very little) by plasma generated with a relatively low applied power. Therefore, for example, if the metal oxide film thickness T1 is below the film thickness threshold (the upper limit of film thickness at which poor bonding does not occur, or the critical film thickness), there is no problem. However, if the film thickness T2 exceeds the film thickness threshold, there is a risk of poor bonding because the film thickness does not change even after surface modification treatment.

Note that "almost no abrasion" means that the amount of abrasion of the metal oxide film is negligibly small when taking into account the typical processing time for the surface modification process. Furthermore, "relatively low applied power" refers to the applied power (equivalent to an example of the first power) that generates plasma that does not (or hardly) abrade the metal oxide film.

On the other hand, as shown in Figure 11, when plasma is generated with a relatively high applied power, the metal oxide film is eroded by the plasma. In other words, the metal oxide film thickness becomes thinner as the processing time of the surface modification process elapses. Therefore, for example, if the metal oxide film thickness is T2, when the processing time of the surface modification process exceeds t1, the metal oxide film thickness will fall below the film thickness threshold at which bonding failure does not occur.

However, when plasma is generated with a relatively high applied power, the metal oxide film is first removed and then begins to deposit again on the metal wiring WM. For example, if the metal oxide film thickness is T2, the metal oxide film will exceed the film thickness threshold if the surface modification treatment time exceeds t3. Also, even if the metal oxide film thickness is originally T1, which is below the film thickness threshold, the metal oxide film will exceed the film thickness threshold if the surface modification treatment time exceeds t2.

Note that "relatively high applied power" refers to the applied power (equivalent to an example of the second power) required to generate plasma that removes the metal oxide film.

Figure 12 is a graph showing an example of the process window for a surface modification process that takes into account both the modification threshold and the film thickness threshold.

As mentioned above, in order to obtain a bonding strength equal to or greater than the modification threshold, the processing time for the surface modification process must be set to t0 or greater. Furthermore, when the metal oxide film thickness is T1, in order to keep the metal oxide film thickness below the film thickness threshold, the processing time for the surface modification process must be set to t2 or less. Furthermore, when the metal oxide film thickness is T2, in order to keep the metal oxide film thickness below the film thickness threshold, the processing time for the surface modification process must be set to t1 or greater and t3 or less.

Therefore, taking into account both the modification threshold and the film thickness threshold, the processing time for the surface modification process must be set within the range of t0 to t2 (range P1 shown in Figure 12) when the metal oxide film thickness is T1. Furthermore, the processing time for the surface modification process must be set within the range of t1 to t3 (range P2 shown in Figure 12) when the metal oxide film thickness is T2.

In the bonding system 1 according to the first embodiment, the control unit 5 acquires the measurement results from the film thickness measuring device 35 before performing the surface modification process. Then, based on the acquired measurement results, the control unit 5 determines the processing conditions for the surface modification process so as to satisfy both the modification threshold and the film thickness threshold.

Figure 13 is a flowchart showing an example of the procedure for determining processing conditions for surface modification processing. The processing condition determination process shown in Figure 13 is executed between steps S101 and S102, or between steps S107 and S108, shown in Figure 8.

As shown in FIG. 13, the control unit 5 first acquires the measurement results of the metal oxide film thickness from the film thickness measuring device 35 (step S201). Next, the control unit 5 determines whether the metal oxide film thickness is equal to or less than the film thickness threshold (step S202).

In step S202, if the metal oxide film thickness is equal to or less than the film thickness threshold (step S202, Yes), the control unit 5 determines the power to be applied from the high-frequency power supply 106 to the stage 80 to be the first power (step S203). As described above, the first power is a power that is preset as the applied power for generating plasma that does not (or hardly does) remove the metal oxide film.

The control unit 5 also determines the processing time as the first processing time (step S204). Specifically, if the applied power is determined to be the first power, the control unit 5 determines the first processing time to be the time predetermined as the processing time for the surface modification process at which the bonding strength becomes equal to or greater than the modification threshold.

On the other hand, if the metal oxide film thickness exceeds the film thickness threshold in step S202 (step S202, No), the control unit 5 determines the power to be applied from the high-frequency power supply 106 to the stage 80 to be the second power (step S205). As described above, the second power is a power that is preset as the power to be applied to generate plasma that removes the metal oxide film.

The control unit 5 also determines the processing time as the second processing time (step S206). Specifically, if the applied power is determined to be the second power, the control unit 5 determines the processing time of the surface modification process at which the bonding strength becomes equal to or greater than the modification threshold and the metal oxide film thickness becomes equal to or less than the film thickness threshold as the second processing time.

Here, the "processing time for the surface modification process at which the metal oxide film thickness becomes equal to or less than the film thickness threshold" may be determined, for example, based on information (hereinafter referred to as "film thickness change information") previously stored in the memory unit 6 as information indicating the relationship between the metal oxide film thickness and the processing time for the surface modification process.

The film thickness change information may be stored in the memory unit 6 for each of multiple second powers. For example, the memory unit 6 may store film thickness change information when the second power is 100 W, film thickness change information when the second power is 120 W, and film thickness change information when the second power is 150 W. In this case, the control unit 5 can use the film thickness change information corresponding to the second power determined in step S205 and the metal oxide film thickness obtained in step S201 to determine the processing time for the surface modification process at which the metal oxide film thickness will be equal to or less than the film thickness threshold.

After completing step S204 or step S206, the control unit 5 ends the processing condition determination process for the surface modification process. The control unit 5 then proceeds to step S102 or step S108, where it performs the surface modification process under the processing conditions determined in the processing condition determination process.

(First Modification of the First Embodiment)
In the first embodiment described above, an example in which thickness measurement of a metal oxide film is performed before a surface modification process has been described. However, the bonding system 1 according to the first embodiment may also perform thickness measurement of a metal oxide film after a surface modification process. This example will be described with reference to FIG. 14 . FIG. 14 is a flowchart showing an example of the procedure for a bonding process execution feasibility determination process. The bonding process execution feasibility determination process shown in FIG. 14 is performed after a surface modification process is performed on a wafer W and before a surface hydrophilization process is performed.

As shown in FIG. 14, the control unit 5 loads the wafer W after the surface modification process into the film thickness measuring device 35 (step S301), and the film thickness measuring device 35 performs a measurement process of the metal oxide film thickness (step S302). Then, the control unit 5 obtains the measurement results of the metal oxide film thickness measured by the film thickness measuring device 35 (step S303).

Next, the control unit 5 determines whether the metal oxide film thickness is equal to or less than the film thickness threshold based on the measurement results obtained in step S303 (step S304).

In step S304, if the metal oxide film thickness is equal to or less than the film thickness threshold (step S304, Yes), the control unit 5 permits the execution of the bonding process (step S305). Specifically, if the wafer is the upper wafer W1, the control unit 5 proceeds to step S103 shown in FIG. 8, and if the wafer is the lower wafer W2, the control unit 5 proceeds to step S109 shown in FIG. 8.

On the other hand, in step S304, if the metal oxide film thickness exceeds the film thickness threshold (step S304, No), the control unit 5 prohibits the execution of the bonding process (step S306). That is, if the wafer is the upper wafer W1, the control unit 5 does not perform the process proceeding to step S103 shown in FIG. 8, and if the wafer is the lower wafer W2, the control unit 5 does not perform the process proceeding to step S109 shown in FIG. 8.

The control unit 5 also performs abnormality response processing on wafers W whose metal oxide film thickness exceeds the threshold (step S307).

For example, as an abnormality response process, the control unit 5 may return a wafer W whose metal oxide film thickness exceeds a threshold to the transfer station 2 (an example of a transfer unit) in order to transfer it from the bonding system 1. In this case, a cassette (not shown) for recovering defective wafers may be placed on the mounting table 10. The control unit 5 may control the transfer device 61 and the transfer device 22 to remove the wafer W whose metal oxide film thickness exceeds a threshold from the film thickness measuring device 35 and store it in the recovery cassette.

Furthermore, as an abnormality response process, the control unit 5 may load a wafer W whose metal oxide film thickness exceeds the threshold into the surface modification apparatus 30 and perform the surface modification process again in the surface modification apparatus 30. In this case, the control unit 5 may set different process conditions for the first surface modification process and the second surface modification process. For example, if the first surface modification process is performed at a first power, the control unit 5 may perform the second surface modification process at a second power. Furthermore, if the first surface modification process and the second surface modification process are performed at a second power, the control unit 5 may set the processing time for the second surface modification process to be shorter than the processing time for the first surface modification process. Note that if the surface modification process is to be performed again in step S307, the control unit 5 may return the process to step S301 and perform the process from step S301 again.

When step S306 or step S307 is completed, the control unit 5 ends the joining process execution feasibility determination process.

In this way, the bonding system 1 according to the first embodiment may measure the thickness of the metal oxide film after the surface modification treatment.

(Second Modification)
15 is a diagram showing another example of the configuration of the processing station 3 included in the bonding system 1. In the first embodiment described above, an example has been described in which the film thickness measuring device 35 is disposed in the second processing block G2 of the processing station 3, but the location of the film thickness measuring device 35 is not limited to this example.

For example, as shown in FIG. 15, the film thickness measuring device 35 may be built into the surface modification device 30. This configuration can shorten the time required for a series of processes in the bonding system 1. In addition, the increase in the footprint of the bonding system 1 due to the incorporation of the film thickness measuring device 35 can be suppressed.

(Third Modification)
16 is a diagram showing another example of the configuration of the bonding system 1. As shown in FIG. 16, the film thickness measuring device 35 may be provided separately from the bonding system 1. That is, the bonding system 1 does not necessarily need to include the film thickness measuring device 35. In this case, the control device 4 may obtain information on the metal oxide film thickness from the film thickness measuring device 35 via a network such as a LAN (Local Area Network). In this case, the wafer W whose film thickness has already been measured by the film thickness measuring device 35 is loaded into the bonding system 1.

As described above, the bonding system (for example, bonding system 1) according to the first embodiment includes a surface modification device (for example, surface modification device 30), a bonding device (for example, bonding device 41), and a control unit (for example, control unit 5). The surface modification device performs a surface modification process using plasma from a processing gas to modify the insulating film (for example, insulating film WL) and metal wiring (for example, metal wiring WM) located on the surfaces of substrates (for example, upper wafer W1 and lower wafer W2). The bonding device performs a bonding process using intermolecular forces to bond two substrates whose insulating films have been modified by the surface modification process. The control unit acquires information about the thickness of the metal oxide film on the surfaces of the substrates before the surface modification process and determines the processing conditions for the surface modification process based on the acquired information.

This bonding system can activate the insulating film while suppressing bonding defects caused by metal oxide films. Therefore, the bonding system according to the first embodiment can improve the bonding quality of laminated substrates.

The bonding system according to the first embodiment (for example, bonding system 1) includes a surface modification device (for example, surface modification device 30), a bonding device (for example, bonding device 41), and a control unit (for example, control unit 5). The surface modification device performs a surface modification process using plasma from a processing gas to modify the insulating film (for example, insulating film WL) and metal wiring (for example, metal wiring WM) located on the surfaces of substrates (for example, upper wafer W1 and lower wafer W2). The bonding device performs a bonding process using intermolecular forces to bond two substrates whose insulating films have been modified by the surface modification process. The control unit acquires information regarding the thickness of the metal oxide film on the surfaces of the substrates after the surface modification process, and determines whether or not to perform a bonding process on the substrates after the surface modification process based on the acquired information.

In this way, by determining whether or not to perform the bonding process beforehand based on information about the thickness of the metal oxide film, the bonding quality of the laminated substrate can be improved.

For example, the bonding system according to the first embodiment can suppress yield by prohibiting the execution of the bonding process when the thickness of the metal oxide film is thicker than the critical thickness. In other words, two substrates bonded by a bonding process cannot be separated and then re-bonded. In contrast, if the substrate has not yet been bonded, it can be salvaged as a product substrate by, for example, temporarily removing it from the bonding system, subjecting it to CMP (chemical mechanical polishing), and then loading it back into the bonding system.

Second Embodiment
The bonding system may perform a process of removing the metal oxide film from the substrate before measuring the thickness of the metal oxide film. Therefore, in the second embodiment, an example will be described in which the thickness measurement process of the metal oxide film is performed after at least a part of the metal oxide film on the substrate is removed using a removal device.

Figure 17 is a schematic plan view showing the configuration of a joint system 1A according to the second embodiment. In the following explanation, parts that are similar to parts already explained will be assigned the same reference numerals as those already explained, and duplicate explanations will be omitted.

As shown in FIG. 17, the bonding system 1A according to the second embodiment differs from the bonding system 1 according to the first embodiment in that a removal device 300 is disposed in the second processing block G2. The removal device 300 removes at least a portion of the metal oxide film on the metal wiring WM located on the bonding surface W1j of the upper wafer W1. Similarly, the removal device 300 removes at least a portion of the metal oxide film on the metal wiring WM located on the bonding surface W2j of the lower wafer W2.

An example of the configuration of such a removal device 300 will be described with reference to Figure 18. Figure 18 is a schematic diagram showing the configuration of a removal device 300 according to the second embodiment.

As shown in FIG. 18, the removal device 300 includes a chamber 320, a substrate holding mechanism 330, a liquid supply unit 340, and a collection cup 350.

The chamber 320 houses the substrate holding mechanism 330, the liquid supply unit 340, and the collection cup 350. An FFU (Fan Filter Unit) 321 is provided on the ceiling of the chamber 320. The FFU 321 creates a downflow within the chamber 320.

FFU 321 is connected to downflow gas supply source 323 via valve 322. FFU 321 discharges downflow gas (e.g., dry air) supplied from downflow gas supply source 323 into chamber 320.

The substrate holding mechanism 330 includes a rotating holder 331, a support column 332, and a drive unit 333. The rotating holder 331 is located approximately in the center of the chamber 320. A holding member 311 that holds the wafer W from the side is provided on the upper surface of the rotating holder 331. The wafer W is held horizontally by the holding member 311, slightly spaced from the upper surface of the rotating holder 331.

The support column 332 is a member extending vertically, its base end is rotatably supported by the drive unit 333, and its tip end supports the rotation holder 331 horizontally. The drive unit 333 rotates the support column 332 around the vertical axis.

The substrate holding mechanism 330 rotates the support column 332 using the drive unit 333, thereby rotating the rotary holder 331 supported by the support column 332, thereby rotating the wafer W held by the rotary holder 331.

The liquid supply unit 340 supplies various processing liquids to the wafer W held by the substrate holding mechanism 330. The liquid supply unit 340 includes a nozzle 341, an arm 342 that horizontally supports the nozzle 341, and a pivoting and lifting mechanism 343 that pivots and raises and lowers the arm 342.

Nozzle 341 is connected to citric acid supply source 345a via valve 344a. Nozzle 341 is also connected to rinse liquid supply source 345b via valve 344b. Citric acid supply source 345a supplies citric acid (citric acid aqueous solution) to nozzle 341 via valve 344a. Rinse liquid supply source 345b supplies rinse liquid to nozzle 341 via valve 344b. The rinse liquid is, for example, pure water (deionized water) at room temperature (approximately 23 to 25 degrees). While Figure 18 shows an example in which liquid supply unit 340 has one nozzle 341, liquid supply unit 340 may also have a total of two nozzles: one for supplying citric acid and one for supplying rinse liquid.

The liquid supply unit 340 is configured as described above and supplies the citric acid aqueous solution or rinse liquid to the wafer W.

Citric acid is an example of a removal processing liquid that removes at least a portion of a metal oxide film from the surface of the wafer W. Note that, instead of citric acid, oxalic acid, sulfuric acid, or the like may also be used as the removal processing liquid. The rinse liquid is a processing liquid used to wash away citric acid remaining on the wafer W.

The collection cup 350 is disposed to surround the rotating holder 331 and collects the processing liquid scattered from the wafer W due to the rotation of the rotating holder 331. A drain port 351 is formed in the bottom of the collection cup 350, and the processing liquid collected by the collection cup 350 is discharged from the drain port 351 to the outside of the removal device 300. In addition, an exhaust port 352 is formed in the bottom of the collection cup 350, which discharges the downflow gas supplied from the FFU 321 to the outside of the removal device 300.

Next, the specific operation of the removal apparatus 300 according to the second embodiment will be described. Processing by the removal apparatus 300 may be performed, for example, before the film thickness measurement of the metal oxide film in the first embodiment. In this case, processing by the removal apparatus 300 may be performed on the upper wafer W1 and the lower wafer W2, respectively, before steps S101 and S107 in FIG. 8. Hereinafter, the upper wafer W1 and the lower wafer W2 will be collectively referred to as "wafer W." Similarly, below, the bonding surfaces W1j and W2j will be collectively referred to as "bonding surfaces."

First, a substrate loading process is performed in the removal apparatus 300. During this substrate loading process, the wafer W loaded into the chamber 320 by the substrate transfer device is held by the holding member 311 of the substrate holding mechanism 330. At this time, the wafer W is held by the holding member 311 with its bonding surface facing upward. The rotating holder 331 is then rotated by the drive unit 333. As a result, the wafer W rotates together with the rotating holder 331 while being held horizontally by the rotating holder 331.

Next, in the removal device 300, a metal oxide film removal process is performed. During this metal oxide film removal process, the nozzle 341 of the liquid supply unit 340 is positioned above the center of the wafer W. Then, citric acid, a metal oxide film removal process liquid, is supplied to the bonding surface of the wafer W. The citric acid supplied to the wafer W spreads over the bonding surface of the wafer W due to centrifugal force generated by the rotation of the wafer W. This removes at least a portion of the metal oxide film from the bonding surface of the wafer W. For example, the removal device 300 may remove almost all of the metal oxide film from the bonding surface of the wafer W using citric acid. The metal oxide film removal rate can be controlled, for example, by the concentration of citric acid, the supply time of citric acid, the supply flow rate, etc.

Next, a rinse process is performed in the removal device 300. During this rinse process, a rinse liquid is supplied to the rotating wafer W, thereby cleaning the bonding surface of the wafer W.

Next, a drying process is performed in the removal device 300. In this drying process, for example, the rotation speed of the wafer W is increased for a predetermined period of time to shake off any rinsing liquid remaining on the surface of the wafer W and dry the wafer W. Thereafter, the rotation of the wafer W is stopped.

The drying process may also be a process of reducing the humidity inside the chamber 320 using downflow gas supplied from the FFU 321.

Next, the removal apparatus 300 performs a substrate unloading process. During this substrate unloading process, the transfer device 61 (see FIG. 1) removes the wafer W from the chamber 320 of the removal apparatus 300. The wafer W is then transferred to the film thickness measuring device 35 by the transfer device 61. Once this substrate unloading process is complete, the metal oxide film removal process for one wafer W is complete.

The inventors of the present application have experimentally discovered that when plasma processing is performed on a substrate having a metal oxide film on its surface, a metal nitride film is formed on the surface of the substrate.

The experiment was carried out as follows. First, the inventors prepared a plurality of Cu substrates each having a metal oxide film (Cu ₂ O) formed on its surface, and irradiated these Cu substrates with plasma generated by applying different powers. Specifically, plasma was irradiated to four Cu substrates at applied powers of 50 W, 100 W, 200 W, and 400 W, respectively. The proportions of the metal oxide film (Cu 2 O) and the metal nitride film (CuxOyN) were then examined for a total of five Cu substrates, including the four Cu substrates that had been subjected to plasma treatment and a Cu substrate that had not been subjected to plasma treatment (i.e., a Cu substrate with _an applied power of _{0 W} ). The results are shown in FIG. 19 .

19 is a graph showing the relationship between the applied plasma power in plasma treatment and the abundance ratio of metal oxide film (Cu ₂ O) and metal nitride film (Cu _x O _y N) on Cu substrates after plasma treatment. As shown in FIG. 19, no metal nitride film (Cu _x O _y N) was detected from the Cu substrate that was not subjected to plasma treatment (Cu substrate with applied power of 0 W). In contrast, metal nitride film (Cu _x O _y N) was detected from the four Cu substrates that were subjected to plasma treatment. Furthermore, the abundance ratio of metal nitride film (Cu _x O _y N) tended to be higher for Cu substrates that were subjected to plasma treatment with higher applied power, i.e., Cu substrates from which a larger amount of metal oxide film (Cu ₂ O) was removed.

The inventors of the present invention also irradiated a plurality of Cu substrates having metal oxide films formed on their surfaces with plasma generated by the same applied power for different irradiation times. Then, the inventors investigated the abundance ratios of the metal oxide film (Cu 2 O) and the metal nitride film (Cu _x O _y N) for each of the Cu substrates that had been subjected to plasma treatment and for a Cu substrate that had not been subjected to plasma treatment (i.e., a Cu _substrate with an irradiation time of 0 seconds). The results are shown in Figure 20.

FIG. 20 is a graph showing the relationship between the plasma irradiation time in the plasma treatment and the proportion of the metal oxide film (Cu ₂ O) and the metal nitride film (Cu _x O _y N) on the Cu substrate after the plasma treatment.

As shown in FIG. 20, the abundance ratio of the metal nitride film (Cu _x O _y N) tended to be higher for Cu substrates exposed to plasma for a longer period of time, i.e., for Cu substrates from which a larger amount of the metal oxide film (Cu ₂ O) was removed.

From the results shown in FIGS. 19 and 20, it can be seen that when a plasma treatment is performed on a substrate on which a metal oxide film (Cu ₂ O) exists, a metal nitride film (Cu _x O _y N) is produced on the substrate.

The mechanism by which the metal nitride film is produced by plasma processing may be, for example, that nitrogen used in the plasma processing combines with the metal oxide film (Cu ₂ O) during the plasma processing to produce the metal nitride film (Cu _x O _y N).

The inventors of the present invention prepared Cu substrates with and without a metal oxide film on their surfaces, and performed plasma treatment on each Cu substrate at applied powers of 100 W and 400 W. After the plasma treatment, the inventors investigated the proportions of metal oxide film (Cu ₂ O) and metal _{nitride film (CuxOyN )} on each Cu substrate. The results are shown in Figures 21 and 22.

Fig. 21 is a graph showing the relationship between the applied plasma power and the abundance ratio of a metal nitride film (Cu _x O _y N) after plasma treatment for a Cu substrate having a metal oxide film on its surface. Fig. 22 is a graph showing the relationship between the applied plasma power and the abundance ratio of a metal nitride film (Cu _x O _y N) after plasma treatment for a Cu substrate having no metal oxide film on its surface.

As shown in Figure 21, when a plasma treatment is performed on a Cu substrate having a metal oxide film (Cu ₂ O) on its surface, a metal nitride film (Cu _x O _y N) is generated on the surface of the Cu substrate. In contrast, as shown in Figure 22, when a plasma treatment is performed on a Cu substrate having a metal oxide film (Cu ₂ O) on its surface, a metal nitride film (Cu _x O _y N) is not generated on the surface of the Cu substrate. These results show that removing the metal oxide film from the surface of the Cu substrate suppresses the generation of a metal nitride film due to plasma treatment (surface modification treatment).

Because metal nitride films are relatively difficult to reduce, their presence on the substrates can have adverse effects, such as reduced bonding strength, during the subsequent bonding process. In contrast, in the second embodiment, a process for removing the metal oxide film from the substrate is performed before measuring the thickness of the metal oxide film, specifically before the surface modification process, thereby preventing the formation of a metal nitride film on the substrate during the surface modification process. Therefore, the bonding system 1A according to the second embodiment can prevent the metal nitride film on the substrate from adversely affecting the bonding process.

(Modification of the second embodiment)
In the second embodiment described above, the metal oxide film removal process is performed using citric acid. However, the metal oxide film removal process is not limited to a wet process using a processing liquid, and may be a dry process. For example, the metal oxide film may be removed by supplying hydrogen (H ₂ ) gas to the bonding surface of the wafer W. The hydrogen gas reduces and removes the metal oxide film. The hydrogen gas may be heated to a high temperature to promote a chemical reaction. The hydrogen gas may also be converted into plasma to promote the chemical reaction.

As described above, in the bonding system 1A according to the second embodiment, a process for removing at least a portion of the metal oxide film is performed before measuring the thickness of the metal oxide film. As described above, in the flowchart of FIG. 8 according to the first embodiment, the metal oxide film removal process is performed on each of the upper wafer W1 and the lower wafer W2 before steps S101 and S107. The control unit 5 then determines the process conditions for the surface modification process based on information about the thickness of the metal oxide film after the removal process. This process reduces the thickness of the metal oxide film, so step S202 in FIG. 13 described in the first embodiment is answered Yes, and the surface modification process can be performed using plasma generated by applying a relatively low power.

When performing the metal oxide film removal process in the first modified example of the first embodiment, the removal process is performed, for example, before step S301 in the flowchart of FIG. 14, specifically, before the surface modification process, on each of the upper wafer W1 and the lower wafer W2. Thereafter, the surface modification process is performed on the wafer W, and the process of step S301 is initiated.

This metal oxide film removal process reduces the thickness of the metal oxide film, allowing surface modification processing to be performed using plasma generated by applying a relatively low amount of power. Furthermore, this metal oxide film removal process reduces the thickness of the metal oxide film, resulting in a Yes result in step S304, and the bonding process is performed. In other words, in the first modified example, performing the metal oxide film removal process can reduce the number of substrates that are subject to abnormality response processing.

Furthermore, as shown in Figure 12 described in the first embodiment, the thin metal oxide film allows for a reduction in the processing time for surface modification.

Furthermore, by performing the metal oxide film removal process, it is possible to suppress the formation of a metal nitride film on the metal wiring due to the surface modification process, thereby preventing adverse effects on the subsequent bonding process.

Therefore, with the bonding system 1A according to the second embodiment, surface modification processing can be performed more efficiently, and bonding defects caused by metal oxide films can be suppressed.

(Other embodiments)
The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

REFERENCE SIGNS LIST 1 Bonding system 2 Loading/unloading station 3 Processing station 4 Control device 5 Control unit 6 Memory unit 10 Mounting table 30 Surface modification device 35 Film thickness measuring device 40 Surface hydrophilization device 41 Bonding device 80 Stage 106 High frequency power supply 110 Upper electrode 230 Upper chuck 231 Lower chuck 280 Striker T Overlapped wafer W1 Upper wafer W2 Lower wafer WL Insulating film WM Metal wiring

Claims (15)

a surface modification device for performing a surface modification process to modify the insulating film of the insulating film and the metal wiring located on the surface of the substrate by plasma of a processing gas;
a bonding apparatus for performing a bonding process by which the two substrates, the insulating films of which have been modified by the surface modification process, are bonded together by intermolecular forces;
a control unit that acquires information about the thickness of the metal oxide film on the surface of the substrate before the surface modification treatment, and determines treatment conditions for the surface modification treatment based on the acquired information. The bonding system of claim 1, further comprising a film thickness measuring device that measures the film thickness of the metal oxide film on the surface of the substrate. The bonding system described in claim 2, wherein the surface modification device is equipped with the film thickness measuring device. The bonding system of claim 2, wherein the optical axis of the film thickness gauge is perpendicular to the surface of the substrate. The bonding system described in claim 1, wherein the control unit generates plasma at a first power when the thickness of the metal oxide film is equal to or less than a threshold value, and generates plasma at a second power greater than the first power when the thickness of the metal oxide film exceeds the threshold value. The bonding system described in claim 5, wherein the control unit varies the processing time of the surface modification treatment depending on whether the thickness of the metal oxide film is equal to or less than the threshold value or whether the thickness of the metal oxide film exceeds the threshold value. The bonding system described in claim 6, wherein the control unit determines the processing time of the surface modification treatment within a predetermined range as a processing time range in which the thickness of the metal oxide film does not exceed the threshold value when the thickness of the metal oxide film exceeds the threshold value due to the surface modification treatment. a removal device that performs a removal process to remove at least a part of the metal oxide film from the surface of the substrate before the surface modification process,
The bonding system according to claim 1 , wherein the control unit acquires information about a thickness of the metal oxide film after the removal process. a surface modification device for performing a surface modification process to modify the insulating film of the insulating film and the metal wiring located on the surface of the substrate by plasma of a processing gas;
a bonding apparatus for performing a bonding process by which the two substrates, the insulating films of which have been modified by the surface modification process, are bonded together by intermolecular forces;
and a control unit that acquires information about the thickness of a metal oxide film on the surface of the substrate after the surface modification treatment, and determines whether or not to perform the bonding treatment on the substrate after the surface modification treatment based on the acquired information. The bonding system of claim 9, wherein the control unit permits the execution of the bonding process on the substrate after the surface modification process when the thickness of the metal oxide film is equal to or less than a threshold value, and prohibits the execution of the bonding process on the substrate after the surface modification process when the thickness of the metal oxide film exceeds the threshold value. a loading/unloading unit for loading/unloading the substrate into/from the bonding system,
The bonding system according to claim 10 , wherein the control unit returns the substrate for which the execution of the bonding process has been prohibited to the carry-in/out unit. The bonding system described in claim 10, wherein the control unit loads the substrate for which the bonding process has been prohibited into the surface modification device and performs the surface modification process on the substrate again. a removal device that performs a removal process to remove at least a part of the metal oxide film from the surface of the substrate before the surface modification process,
The bonding system according to claim 9 , wherein the control unit acquires information about a thickness of the metal oxide film after the removal process. a step of performing a surface modification process in which the insulating film and the metal wiring located on the surface of the substrate are modified by plasma of a processing gas;
a step of performing a bonding process of bonding the two substrates, the insulating films of which have been modified by the surface modification process, by intermolecular forces;
acquiring information about the thickness of the metal oxide film on the surface of the substrate before the surface modification treatment, and determining treatment conditions for the surface modification treatment based on the acquired information. a step of performing a surface modification process in which the insulating film and the metal wiring located on the surface of the substrate are modified by plasma of a processing gas;
a step of performing a bonding process of bonding the two substrates, the insulating films of which have been modified by the surface modification process, by intermolecular forces;
acquiring information about the thickness of a metal oxide film on the surface of the substrate after the surface modification treatment, and determining whether or not to perform the bonding treatment on the substrate after the surface modification treatment based on the acquired information.