Bonding method for substrates

Abstract

To provide a bonding method for substrates capable of bonding a first substrate and a second substrate more accurately than the prior arts.SOLUTION: Provided is a bonding method for substrates including: an adhesive layer forming step of forming an adhesive layer in one of or both a first substrate and a second substrate; a temporary bonding step of disposing the first substrate and the second substrate in such a manner that the first substrate and the second substrate are opposed via the adhesive layer after the adhesive layer forming step and pressing one of or both the first substrate and the second substrate under a first air pressure lower than an atmospheric pressure in a direction in which the substrates are close to each other relatively, thereby forming a temporarily bonded substrate in which the first substrate and the second substrate are integrated via the adhesive layer; and a main bonding step of heating the temporarily bonded substrate under a second air pressure higher than the first air pressure after the temporary bonding step, thereby bonding the first substrate and the second substrate.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] The device chip manufacturing process uses a substrate (semiconductor wafer) on which semiconductor devices are formed in multiple regions defined by multiple streets (planned division lines) arranged in a grid pattern. By dividing this substrate along the streets, multiple device chips, each equipped with a semiconductor device, are obtained. The device chips are incorporated into various electronic devices, such as mobile phones and personal computers.

[0003] In recent years, techniques for manufacturing device chips including a plurality of stacked semiconductor devices (stacked device chips) have been put to practical use. For example, a method called WoW (Wafer on Wafer) has been proposed as a method for manufacturing stacked device chips.

[0004] In this method, two substrates (first and second substrates) are joined and stacked, and the semiconductor devices on each substrate are connected to each other using electrodes (TSV: Through-Silicon Via) formed to penetrate the stacked substrates, thereby forming a stacked substrate. Stacked device chips are manufactured by dividing this stacked substrate along the streets.

[0005] One known method for joining two substrates as described above is to use an adhesive (adhesive layer) made of a thermoplastic resin. In this method, the first and second substrates are bonded together via the adhesive while heating the adhesive to a temperature at which the adhesive softens in a reduced pressure environment (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-100349 Summary of the Invention [Problem to be solved by the invention]

[0007] High bonding accuracy is required when bonding the first substrate and the second substrate. However, when bonding the first substrate and the second substrate while heating the adhesive to a temperature at which the adhesive softens, as described above, it can be difficult to bond the first substrate and the second substrate with high accuracy.

[0008] For example, if the arrangement (angle) of the first substrate and the second substrate is not precisely adjusted so that they are parallel to each other, the first substrate and the second substrate will be joined with adhesive while remaining non-parallel, reducing the joining accuracy.

[0009] Therefore, a dedicated bonding device is sometimes used to bond the first and second substrates. The bonding device is equipped with a pair of stages that can hold the first and second substrates facing each other, and the positions (angles) of the pair of stages are precisely adjusted so that the first and second substrates are held parallel to each other.

[0010] The bonding device then brings the first substrate and the second substrate close together while holding them parallel to each other using a pair of stages, thereby improving the bonding accuracy of the first substrate and the second substrate.

[0011] The alignment of the pair of stages in a bonding device is usually adjusted at room temperature while the bonding device is not operating. However, bonding a first substrate and a second substrate with an adhesive requires a heat treatment, during which the pair of stages are also heated. As a result, distortion occurs in the pair of stages due to heating, causing a misalignment of the pair of stages that had been precisely adjusted at room temperature.

[0012] The distortion caused in the pair of stages by the heat treatment during bonding is so large that it affects the precision of bonding the first and second substrates. Therefore, even when a bonding device with an adjusted position of the pair of stages is used, the first and second substrates are bonded while being affected by the distortion of the stages, as long as the heat treatment is performed to bond the first and second substrates with an adhesive, and this poses a problem of reduced precision in bonding the substrates.

[0013] In view of the above circumstances, an object of the present invention is to provide a method for bonding substrates that can bond a first substrate and a second substrate with higher accuracy than conventional methods. [Means for solving the problem]

[0014] According to one aspect of the present invention, there is provided a method for bonding a first substrate and a second substrate via an adhesive layer, the method including: an adhesive layer formation step of forming the adhesive layer on one or both of the first substrate and the second substrate; a temporary bonding step of, after the adhesive layer formation step, arranging the first substrate and the second substrate so that they face each other with the adhesive layer interposed therebetween, and pressing one or both of the first substrate and the second substrate in a direction that brings the first substrate and the second substrate closer together under a first atmosphere that is lower than atmospheric pressure, thereby forming a temporary bonded substrate in which the first substrate and the second substrate are integrated via the adhesive layer; and a main bonding step of, after the temporary bonding step, heating the temporary bonded substrate under a second atmosphere that is higher than the first atmosphere, thereby bonding the first substrate and the second substrate.

[0015] Preferably, in the temporary bonding step, the adhesive layer is heated to a first temperature, and in the main bonding step, the adhesive layer is heated to a second temperature, the first temperature being lower than the second temperature, at which the adhesive layer softens.

[0016] Preferably, in the temporary bonding step, a region including the periphery of the first substrate and a region including the periphery of the second substrate are adhered to each other via the adhesive layer. [Effects of the Invention]

[0017] In the bonding method according to the present invention, the bonding of a first substrate and a second substrate is carried out in two steps: a temporary bonding step and a main bonding step. In the temporary bonding step, the first substrate and the second substrate are integrated together via an adhesive layer under a first atmospheric pressure to form a temporary bonded substrate. In the main bonding step, the first substrate and the second substrate are bonded together by heating the temporary bonded substrate under a second atmospheric pressure higher than the first atmospheric pressure.

[0018] By carrying out the temporary bonding step and the main bonding step in this order, the first substrate and the second substrate are bonded together while reducing the influence of distortion of the bonding device, which makes it possible to bond the first substrate and the second substrate together more accurately than before. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1(A) is a perspective view of the first substrate, and FIG. 1(B) is a cross-sectional view of the first substrate. [Figure 2] FIG. 2 is a flow diagram of the substrate bonding method according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view of the adhesive layer forming apparatus and the first substrate when the adhesive layer forming step is performed. [Figure 4] FIG. 4 is a cross-sectional view of the first substrate on which the adhesive layer is formed. [Figure 5] FIG. 5 is a partial cross-sectional side view of the temporary bonding device, the first substrate, and the second substrate when the temporary bonding step is performed. [Figure 6] FIG. 6 is a cross-sectional view of the temporarily bonded substrate formed by the temporary bonding step. [Figure 7] FIG. 7 is a cross-sectional view of the permanent bonding apparatus and the temporarily bonded substrate when the permanent bonding step is performed, and an enlarged view of a part thereof. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. First, a first substrate and a second substrate to be bonded by a substrate bonding method according to this embodiment will be described. Fig. 1(A) is a perspective view of the first substrate 11, and Fig. 1(B) is a cross-sectional view of the first substrate 11.

[0021] As shown in FIGS. 1A and 1B, the first substrate 11 is disc-shaped and has a circular first surface 11a and a circular second surface 11b opposite the first surface 11a. Similarly to the first substrate 11, the second substrate 13 is disc-shaped and has a circular first surface 13a and a circular second surface 13b opposite the first surface 13a (see FIG. 5). For example, the first substrate 11 and the second substrate 13 are semiconductor wafers. In this case, the material of the first substrate 11 and the second substrate 13 is, for example, silicon. However, the material of the first substrate 11 and the second substrate 13 is not limited thereto. For example, glass may also be used for the first substrate 11 and the second substrate 13. Furthermore, the material of the first substrate 11 and the second substrate 13 may be different. For example, the material of the first substrate 11 may be silicon, and the material of the second substrate 13 may be glass.

[0022] The substrate bonding method according to this embodiment bonds the first surface 11a of the first substrate 11 to the first surface 13a of the second substrate 13. Hereinafter, the first surfaces 11a and 13a bonded to each other will also be referred to as bonding surfaces. A device such as an IC (Integrated Circuit) may be formed on the bonding surface.

[0023] However, the shapes, materials, structures, etc. of the first substrate 11 and the second substrate 13 are not limited to those described above. For example, one of the first substrate 11 and the second substrate 13 may be a wafer on which a device is formed, and the other of the first substrate 11 and the second substrate 13 may be a support substrate that supports the wafer. In this case, the wafer and the support substrate are bonded together, and the wafer is supported by the support substrate.

[0024] There are also no particular limitations on the diameter (width) and thickness of the first substrate 11 and the second substrate 13, as long as they fit into an adhesive layer forming device (see FIG. 3) described below and can be held by a holding table (see FIG. 5) of a temporary bonding device and a stage (see FIG. 7) of a main bonding device. Furthermore, the first substrate 11 may have a shape, material, diameter (width), and thickness different from those of the second substrate 13.

[0025] Furthermore, the first substrate 11 and the second substrate 13 may be supported by a support frame for ease of handling, such as transportation. The support frame is, for example, a ring frame made of metal such as SUS (stainless steel) and having an opening in the center. A film is attached to one surface of the support frame so as to cover the opening of the support frame. For example, with the first substrate 11 placed in the opening, a film is attached to the second surface 11b of the first substrate 11 and one surface of the support frame. This forms a frame unit in which the support frame, the film, and the first substrate 11 are integrated.

[0026] In this way, the second surface 11b of the first substrate 11 may be attached to a film, so that the first substrate 11 is supported by the support frame. Similarly, the second surface 13b of the second substrate 13 may be attached to a film, so that the second substrate 13 is supported by the support frame. Furthermore, both the first substrate 11 and the second substrate 13 may be supported by the support frame.

[0027] Next, a substrate bonding method used to bond the above-described first substrate 11 and second substrate 13 will be described. Fig. 2 is a flow diagram of the substrate bonding method according to this embodiment. As shown in Fig. 2, the substrate bonding method according to this embodiment includes an adhesive layer forming step S1, a temporary bonding step S2, and a main bonding step S3.

[0028] In the adhesive layer forming step S1, an adhesive layer is formed on one or both of the first substrate 11 and the second substrate 13. The following describes an example in which an adhesive layer is formed on the first substrate 11. FIG. 3 is a cross-sectional view showing the adhesive layer forming apparatus 2 and the first substrate 11 when the adhesive layer forming step S1 is performed. In this embodiment, the adhesive layer forming apparatus 2 is a spin coater that forms an adhesive layer by spin coating. In the adhesive layer forming step S1, an adhesive layer is formed on the first surface 11a side of the first substrate 11 by spin coating using the adhesive layer forming apparatus 2.

[0029] As shown in Fig. 3, the adhesive layer forming apparatus 2 has a holding table 4. The holding table 4 includes a disk-shaped frame 6 made of, for example, ceramics or metal. A recess 6a with a circular opening at the top end is formed on the upper surface of the frame 6. A disk-shaped holding plate 8 that matches the shape of the recess 6a is fixed to the recess 6a of the frame 6.

[0030] The holding plate 8 is made of a porous material such as ceramics, and holds the first substrate 11 placed on its upper surface (holding surface) 8a by suction from the second surface 11b side. The upper surface 8a of the holding plate 8 is configured to be roughly parallel to the X-axis and Y-axis when the holding plate 8 is fixed in the recess 6a. The X-axis and Y-axis indicate horizontal directions that are perpendicular to each other.

[0031] A flow path (not shown) having one end open to the bottom of the recess 6a is provided inside the frame 6. The other end of the flow path is connected to a suction source (not shown) such as an ejector via a valve (not shown) or the like. Therefore, when the valve is opened, negative pressure generated by the suction source acts on the upper surface 8a of the holding plate 8 through the flow path, the recess 6a, etc.

[0032] For example, first substrate 11 is placed on holding table 4, and with second surface 11b of first substrate 11 in contact with upper surface 8a of holding plate 8, negative pressure from a suction source is applied to first substrate 11 through upper surface 8a. Then, first substrate 11 is sucked through upper surface 8a of holding plate 8. As a result, first substrate 11 is held on holding table 4 with first surface 11a side exposed upward.

[0033] As shown in Fig. 3, one end of a cylindrical spindle 10 is connected to the lower part of the frame 6 of the holding table 4. A rotary drive source (not shown), such as a motor, is connected to the other end of the spindle 10. Therefore, the power generated by this rotary drive source causes the holding table 4 to rotate around an axis (rotation axis) 12 of the spindle 10, which is generally parallel to the Z axis. The Z axis is aligned in a direction (vertical direction) perpendicular to the X axis and the Y axis.

[0034] The adhesive layer forming apparatus 2 has a coating liquid supply unit 14 provided near the holding table 4. The coating liquid supply unit 14 includes a shaft 14a provided along the Z axis on the outside of the holding table 4, an arm 14b extending from the upper end of the shaft 14a in a direction parallel to the upper surface 8a of the holding plate 8, and a nozzle (coating liquid supply nozzle) 14c provided at the tip of the arm 14b.

[0035] The shaft 14a and the arms 14b are pipe-shaped members each having a flow path (not shown) through which a liquid flows. The nozzle 14c is connected to a liquid supply source (not shown) via the flow path provided inside the shaft 14a and the arms 14b. The liquid supply source supplies the coating liquid 17, which contains the adhesive that forms the adhesive layer, to the nozzle 14c via the flow path in the shaft 14a and the arms 14b.

[0036] The adhesive layer forming device 2 also includes a rotary drive source (not shown), such as a motor, that rotates the shaft portion 14a around the Z-axis direction. By operating the rotary drive source, the nozzle 14c can be swung above the holding table 4. By operating the liquid supply source and the rotary drive source, the nozzle 14c is swung above the holding table 4, and the coating liquid 17 is supplied from the nozzle 14c toward the first surface 11a of the first substrate 11 held on the holding table 4.

[0037] The coating liquid 17 contains an adhesive that forms an adhesive layer, which will be described later. The adhesive is a thermoplastic resin that softens when heated and hardens when cooled. Specific examples of the thermoplastic resin include 1,3,5-trimethylbenzene, divinylsiloxane-bisbenzocyclobutene partial polymer, 1,2-dihydro-2,2,4-trimethylquinoline polymer, 1,2,4-trimethylbenzene, methyl isobutyl ketone, antimony compounds, 4-acetoxyphenyldimethylsulfonium hexafluoroantimonate, and cyclohexane. The coating liquid 17 also contains a dispersion medium that provides the adhesive with sufficient fluidity to be sprayed from the nozzle 14c. Examples of the dispersion medium that can be used include water, alcohol, 1,3,5-trimethylbenzene, methyl isobutyl ketone, cyclohexanone, 2-methoxy-1-methylethyl acetate, and propylene glycol monoethyl ether.

[0038] In the adhesive layer forming step S1, the first substrate 11 placed on the upper surface 8a of the holding plate 8 is held by the holding table 4 in the above-described procedure. Thereafter, the rotation of the holding table 4 is started by the rotation drive source connected to the spindle 10. Then, while the holding table 4 is rotating, the above-described coating liquid 17 is supplied from the nozzle 14c toward the first surface 11a of the first substrate 11.

[0039] As a result, the coating liquid 17 is applied to the first surface 11a of the first substrate 11. At this time, due to centrifugal force generated by the rotation of the holding table 4, the coating liquid 17 dropped onto a portion of the first surface 11a of the first substrate 11 spreads over the first surface 11a toward the outer periphery of the holding table 4. As a result, an adhesive layer 15 of approximately uniform thickness is formed on the first surface 11a.

[0040] After a predetermined amount of coating liquid 17 is supplied from nozzle 14c toward first surface 11a of first substrate 11, the rotation of holding table 4 continues, causing the dispersion medium to volatilize. As a result, an adhesive layer 15 is formed on first surface 11a of first substrate 11. Figure 4 is a cross-sectional view of first substrate 11 on which adhesive layer 15 has been formed.

[0041] In this embodiment, the adhesive layer 15 is formed by spin coating, but the adhesive layer 15 may also be formed by spray coating. In spray coating, for example, high pressure is applied to the above-mentioned coating liquid 17, and the coating liquid 17 is sprayed in a mist form from a nozzle to apply it to the first surface 11a of the first substrate 11. The adhesive layer 15 may also be provided on the second substrate 13, or on both the first substrate 11 and the second substrate 13.

[0042] Next, the temporary bonding step S2 is performed. Figure 5 is a partial cross-sectional side view of the temporary bonding device (pressure device) 16, the first substrate 11, and the second substrate 13 when the temporary bonding step S2 is performed. In the temporary bonding step S2, the temporary bonding device 16 shown in Figure 5 is used. Note that Figure 5 shows a side view of part of the configuration of the temporary bonding device 16. However, in Figure 5, a chamber 18, which will be described later, is shown in cross section. Note that in Figure 5, the X-axis and Y-axis are perpendicular to each other. Furthermore, the Z-axis is perpendicular to the X-axis and Y-axis.

[0043] The temporary bonding apparatus 16 has a chamber 18. The chamber 18 is connected to a vacuum pump 34 via a first pipe 30 provided with a first valve 32. One end of a second pipe 36 provided with a second valve 38 is also connected to the chamber 18. The other end of the second pipe 36 reaches the space outside the chamber 18 and is open to the atmosphere. Furthermore, the chamber 18 has an opening 18a and an opening / closing door 28 provided to cover the opening 18a.

[0044] When the first valve 32, the second valve 38 and the opening / closing door 28 are closed, the internal space of the chamber 18 is isolated from the outside and becomes a sealed space.

[0045] A first stage 20 that holds a first substrate 11, which is the object to be bonded, is provided at the bottom (floor side) of the internal space of the chamber 18. In this embodiment, the first substrate 11 is held by the first stage 20. The first stage 20 is configured in a generally cylindrical shape having a generally circular first surface (holding surface) 20a and a generally circular second surface 20b opposite the first surface 20a. The first surface 20a of the first stage 20 has a diameter (width) that is slightly larger than that of the first substrate 11 so that it can hold the first substrate 11 by contacting the entire second surface 11b of the first substrate 11.

[0046] A second stage 22 that holds the substrates to be bonded is provided at the top (ceiling side) of the internal space of the chamber 18. In this embodiment, the second substrate 13 is held by the second stage 22. The second stage 22 is configured in a generally cylindrical shape having a generally circular first surface (holding surface) 22a and a generally circular second surface 22b opposite the first surface 22a. The first surface 22a of the second stage 22 has a diameter (width) slightly larger than that of the second substrate 13 so that it can hold the second substrate 13 by contacting the entire second surface 13b of the second substrate 13.

[0047] For example, electrostatic chucks can be used as the first stage 20 and the second stage 22. The first stage 20 is equipped with a holding mechanism (not shown) that can attract and hold the first substrate 11. For example, an electrode (not shown) is provided inside the first stage 20, and the first stage 20 is configured to attract and hold the first substrate 11 by electrostatic force generated by supplying power to this electrode.

[0048] Similarly, the second stage 22 is equipped with a holding mechanism (not shown) that can attract and hold the second substrate 13. For example, an electrode (not shown) is provided inside the second stage 22, and the second stage 22 is configured to be able to attract and hold the second substrate 13 by electrostatic force generated by supplying power to this electrode.

[0049] The first stage 20 is connected to a first moving unit 24, and the second stage 22 is connected to and supported by a second moving unit 26. The first moving unit 24 and the second moving unit 26 move the first stage 20 and the second stage 22 relatively along the Z-axis direction so that the first surface 20a of the first stage 20 and the first surface 22a of the second stage 22 move closer to or farther away from each other.

[0050] For example, the first moving unit 24 and the second moving unit 26 can each be configured with a drive mechanism using a ball screw mechanism and a servo motor. Specifically, the drive mechanism includes a moving member (not shown) connected to the first stage 20 or the second stage 22, and the moving member has a nut portion (not shown). A ball screw (not shown) arranged in a direction along the Z axis is threadedly engaged with this nut portion. Furthermore, a servo motor (not shown) that rotates the ball screw is connected to the end of the ball screw.

[0051] When the ball screw is rotated by the servo motor, the moving member moves in a direction along the Z axis, and the first stage 20 or the second stage 22 moves up and down along the Z axis direction. In this way, by using a ball screw type drive mechanism as the first moving unit 24 and the second moving unit 26, it becomes possible to precisely adjust the distance between the first surface 20a of the first stage 20 and the first surface 22a of the second stage 22, and the relative moving speed between the first stage 20 and the second stage 22. However, the moving mechanism is not limited to the above-mentioned configuration.

[0052] In the temporary bonding step S2, first, the opening / closing door 28 is opened to expose the opening 18a of the chamber 18. Then, the first substrate 11 held by a transport device such as a robot arm is carried into the chamber 18 through the opening 18a and placed on the first surface 20a of the first stage 20. Then, the holding mechanism of the first stage 20 is activated, and the first substrate 11 is held by the first stage 20. In this embodiment, the second surface 11b side of the first substrate 11 is held by the first stage 20 so that the first surface 11a side of the first substrate 11, on which the adhesive layer 15 is formed, is exposed upward.

[0053] Next, the second substrate 13 held by a transfer device such as a robot arm is carried into the chamber 18 through the opening 18a and placed on the first surface 22a of the second stage 22. Then, the holding mechanism of the second stage 22 is activated, and the second substrate 13 is held by the second stage 22. In this embodiment, the second surface 13b side of the second substrate 13 is held by the second stage 22 so that the first surface 13a side of the second substrate 13 is exposed downward.

[0054] As a result, the first substrate 11 and the second substrate 13 are arranged to face each other via the adhesive layer 15. It does not matter which of the first substrate 11 and the second substrate 13 is carried into the chamber 18 first. The first substrate 11 and the second substrate 13 may be carried into the chamber 18 manually by an operator.

[0055] Once the first substrate 11 and the second substrate 13 have been loaded, the door 28 is closed. After the second valve 38 is closed, the vacuum pump 34 is activated and the first valve 32 is opened. This reduces the pressure in the interior space of the chamber 18. The vacuum pump 34 reduces the pressure in the interior space of the chamber 18 to a first atmospheric pressure, which is lower than atmospheric pressure. The first atmospheric pressure may be, for example, 10 -5 Pa or more 10 -1 Pa or less.

[0056] Thereafter, the first stage 20 is raised along the Z axis by the first moving unit 24. Furthermore, the second stage 22 is lowered along the Z axis by the second moving unit 26. That is, the first substrate 11 and the second substrate 13 move in directions that bring them relatively closer to each other. Then, the adhesive layer 15 provided on the first substrate 11 and the first surface 13a of the second substrate 13 come into contact with each other.

[0057] After the adhesive layer 15 and the first surface 13a of the second substrate 13 come into contact, the first stage 20 is further raised along the Z axis by the first moving unit 24, and the second stage 22 is lowered along the Z axis by the second moving unit 26. As a result, the first substrate 11 and the second substrate 13 are pressed in a direction in which they approach each other. At this time, the first substrate 11 and the second substrate 13 are pressed so that a load of 5 kN or more and 30 kN or less (e.g., 10 kN) is applied, for example. However, the load applied to the first substrate 11 and the second substrate 13 is not limited to this range and can be set appropriately depending on the types of the first substrate 11 and the second substrate 13, the bonding conditions, etc.

[0058] In this way, by applying pressure to first substrate 11 and second substrate 13 under the first atmospheric pressure, first substrate 11 and second substrate 13 are pressed together, and a region including the outer periphery of first substrate 11 and a region including the outer periphery of second substrate 13 are tightly attached to each other. As a result, first substrate 11 and second substrate 13 are temporarily bonded to form temporary bonded substrate 19. At this time, if there are minute irregularities on first surface 13a of second substrate 13, voids due to these irregularities may occur at the interface between first surface 13a of second substrate 13 and adhesive layer 15.

[0059] Fig. 6 is a cross-sectional view of the temporary bonded substrate 19 formed in the temporary bonding step S2. Note that in Fig. 6, the voids described above are not shown.

[0060] If the first substrate 11 and the second substrate 13 were bonded at high temperatures as in the past, the first stage 20 and the second stage 22 would also be heated to high temperatures and expand, causing distortion in the first surface 20a of the first stage 20 and the first surface 22a of the second stage 22. As a result, it would be difficult to maintain the first substrate 11 and the second substrate 13, which are held by the first surface 20a and the first surface 22a, respectively, in a strictly parallel state, which would be a factor in reducing the accuracy of bonding the first substrate 11 and the second substrate 13 together.

[0061] Therefore, in the temporary bonding step S2 in this embodiment, the first substrate 11 and the second substrate 13 are temporarily bonded via the adhesive layer 15 at a temperature (first temperature) that is lower than the heating temperature during main bonding, which will be described later. This suppresses distortion caused by heating in the temporary bonding device 16, and makes it difficult for the parallelism of the first substrate 11 and the second substrate 13 held by the first stage 20 and the second stage 22 to be disturbed. As a result, a decrease in the accuracy of bonding the first substrate 11 and the second substrate 13 is suppressed.

[0062] For example, in the temporary bonding step S2, when the first substrate 11 and the second substrate 13 are pressed together, the adhesive layer 15 is not heated. This avoids heating the first stage 20 and the second stage 22, and also prevents distortion of the temporary bonding device 16. If the adhesive layer 15 is not heated, the adhesive layer 15 will not exhibit sufficient adhesiveness. Therefore, the first substrate 11 and the second substrate 13 will not be completely bonded, but will remain in a temporary bonded state.

[0063] However, in the temporary bonding step S2, the adhesive layer 15 may be heated within an allowable range for distortion of the temporary bonding device 16. For example, the first stage 20 may be equipped with a heater, and the first substrate 11 and the second substrate 13 may be pressed together while the first substrate 11 is heated to a first temperature by the heater. As a result, the heat applied to the first substrate 11 is conducted to the adhesive layer 15, and the adhesive layer 15 is heated.

[0064] When adhesive layer 15 is heated as described above, adhesive layer 15 softens to a certain extent. Then, after first substrate 11 and second substrate 13 are bonded together, adhesive layer 15 is cooled and hardened, whereby first substrate 11 and second substrate 13 are temporarily bonded together. At this time, the bonding strength between first substrate 11 and second substrate 13 is higher than when adhesive layer 15 is not heated.

[0065] The first temperature in the temporary bonding step S2 may be determined taking into consideration the type of adhesive constituting the adhesive layer 15 and the heat resistance of the temporary bonding device 16. For example, the difference between the first temperature and the heating temperature (second temperature) in the main bonding step S3 described below is set to 10°C or more, preferably 50°C or more, and more preferably 100°C or more. This maintains the temporary bonding device 16 at a low temperature, effectively suppressing distortion of the temporary bonding device 16. For example, the first temperature can be set to 10°C or more and less than 130°C, preferably 10°C or more and less than 80°C, and more preferably 25°C or more and less than 80°C. However, the first temperature is not limited to this.

[0066] Furthermore, if adhesive layer 15 has a softening point, the first temperature may be set based on the softening point of adhesive layer 15. Specifically, the first temperature can be set to a value lower than the softening point of adhesive layer 15. In this case, even if adhesive layer 15 is heated at the first temperature in temporary bonding step S2, adhesive layer 15 does not soften sufficiently, and first substrate 11 and second substrate 13 remain in a temporarily bonded state even after adhesive layer 15 is cooled thereafter.

[0067] After the first substrate 11 and the second substrate 13 are pressed together, the second stage 22 releases its hold on the second substrate 13. Then, the first stage 20 is lowered along the Z axis by the first moving unit 24, and the second stage 22 is raised along the Z axis by the second moving unit 26. As a result, the first stage 20 and the second stage 22 are separated from each other, and the temporarily bonded substrate 19 is left on the first stage 20.

[0068] Up to this point, an example has been described in which both the first stage 20 and the second stage 22 are raised and lowered. However, the temporary bonding step S2 and the temporary bonding device 16 are not limited to this. For example, the temporary bonding device 16 does not have to include either the first moving unit 24 that raises and lowers the first stage 20 or the second moving unit 26 that raises and lowers the second stage 22. Furthermore, in the temporary bonding step S2, one of the first stage 20 and the second stage 22 may be fixed, and only the other may be raised and lowered.

[0069] After the temporary bonding of the first substrate 11 and the second substrate 13 is completed, the temporarily bonded substrate 19 is carried out of the chamber 18 of the temporary bonding apparatus 16. Specifically, the first valve 32 is closed and the vacuum pump 34 is stopped. Next, the second valve 38 is opened. This allows air to be introduced into the chamber 18 through the second pipe 36, increasing the pressure inside the chamber 18. After the pressure inside the chamber 18 has been increased to atmospheric pressure, the opening / closing door 28 is opened and the temporarily bonded substrate 19 is carried out from inside the chamber 18 to outside by a transfer device (not shown). After the temporarily bonded substrate 19 is carried out, the opening / closing door 28 is closed.

[0070] As described above, temporary bonding step S2 is performed, and first substrate 11 and second substrate 13 are temporarily bonded together. As described above, in temporary bonding step S2, the thermoplastic resin that constitutes adhesive layer 15 is not sufficiently heated and softened, and therefore adhesive layer 15 does not exhibit sufficient adhesiveness. As a result, bonding between first substrate 11 and second substrate 13 is incomplete.

[0071] Furthermore, as described above, voids may occur at the interface between first surface 13a of second substrate 13 and adhesive layer 15. If adhesive layer 15 is not heated sufficiently, the fluidity of adhesive layer 15 will not be increased, and voids will remain at the interface between adhesive layer 15 and first surface 13a of second substrate 13, which will cause the adhesive layer 15 and second substrate 13 to not adhere closely to each other. Therefore, in order to sufficiently increase the adhesiveness of adhesive layer 15 and to increase the fluidity of adhesive layer 15, a main bonding step S3 is then performed.

[0072] Fig. 7 is a cross-sectional view of the main bonding apparatus (heating apparatus) 40 and the temporary bonded substrate 19 when the main bonding step S3 is performed. Fig. 7 also shows an enlarged view of a portion of the temporary bonded substrate 19 in the main bonding step S3. As shown in Fig. 7, the main bonding apparatus 40 has a stage 42 that holds the temporary bonded substrate 19.

[0073] The stage 42 is made of a thermally conductive metal or the like and has a generally cylindrical shape. A first surface (upper surface) 42a of the stage 42 corresponds to a holding surface that holds the temporary bonded substrate 19. Specifically, the stage 42 holds the second surface 11b side of the first substrate 11 or the second surface 13b side of the second substrate 13 with the first surface 42a. For example, when the second surface 11b side of the first substrate 11 is held with the first surface 42a, the first surface 42a has a diameter (width) that is slightly larger than the second surface 11b of the first substrate 11 so that the first surface 42a can contact the entire second surface 11b of the first substrate 11 included in the temporary bonded substrate 19 and hold the first substrate 11.

[0074] The stage 42 may be provided with a holding mechanism (not shown) that can attract and hold the first substrate 11. For example, an electrode (not shown) is provided inside the stage 42, and the stage 42 is configured so that the first substrate 11 can be attracted and held by electrostatic force generated by applying a voltage to this electrode.

[0075] The stage 42 also includes a heater 44 therein. The heater 44 is configured, for example, by an electric heating wire made of ceramics or the like. When power is supplied to the heater 44, the heater 44 generates heat, and the heat emitted from the heater 44 is conducted to the temporary bonding substrate 19 via the stage 42. This allows the adhesive layer 15 to be heated and softened.

[0076] In the main bonding step S3, first, a transfer device such as a robot arm places the temporary bonded substrate 19 on the first surface 42a of the stage 42. In this embodiment, the temporary bonded substrate 19 is placed on the stage 42 so that the second surface 11b of the first substrate 11 constituting the temporary bonded substrate 19 contacts the first surface 42a of the stage 42. Then, a holding mechanism provided on the stage 42 is activated, thereby holding the temporary bonded substrate 19 on the stage 42. Note that the temporary bonded substrate 19 may also be placed on the stage 42 manually by an operator.

[0077] In the main bonding step S3, the temporarily bonded substrate 19 is held by the stage 42 under a second atmospheric pressure higher than the first atmospheric pressure (the pressure during temporary bonding in the temporary bonding step S2). For example, the stage 42 is placed in the atmosphere. In this case, the second atmospheric pressure is atmospheric pressure. As shown in the enlarged view of FIG. 7, the second atmospheric pressure applies pressure from the second surface 13b of the second substrate 13 constituting the temporarily bonded substrate 19 toward the first surface 42a of the stage 42 (in the direction of the arrow in FIG. 7). This pressure of the second atmospheric pressure causes the first substrate 11 and the second substrate 13 to be pressure-bonded to each other via the adhesive layer 15, and thus to be fixed to a certain extent. However, at this stage, the adhesive layer 15 has not yet been heated by the heater 44, and the adhesive layer 15 has not yet exhibited sufficient adhesiveness.

[0078] Next, the temporarily bonded substrate 19 is heated by the heater 44 provided on the stage 42. At this time, the temporarily bonded substrate 19 is heated to the second temperature. The second temperature is higher than the temperature (first temperature) used when temporarily bonding the first substrate 11 and the second substrate 13 in the temporary bonding step S2, and is a temperature at which the adhesive layer 15 softens. More specifically, the second temperature corresponds to the temperature required to completely bond the first substrate 11 and the second substrate 13 with the adhesive layer 15. The preferable value of the difference between the first temperature and the second temperature is as described above.

[0079] The second temperature is set, for example, to a temperature between 80°C and 350°C, preferably between 130°C and 250°C, and more preferably between 200°C and 250°C. The second temperature is set appropriately depending on the type of adhesive that constitutes the adhesive layer 15. Specifically, a heating temperature suitable for bonding with an adhesive is specified in advance depending on the adhesive material, and that temperature is set as the second temperature. For example, when the adhesive that constitutes the adhesive layer 15 is divinylsiloxane-bisbenzocyclobutene, the second temperature can be set to a temperature between 150°C and 350°C.

[0080] Furthermore, particularly when adhesive layer 15 has a softening point, the second temperature may be set based on the softening point of adhesive layer 15. Specifically, the second temperature can be set to a temperature equal to or higher than the softening point of adhesive layer 15. This allows adhesive layer 15 to be sufficiently softened, and the adhesiveness of adhesive layer 15 to be effectively exhibited.

[0081] Here, the voids 21 remaining between the first surface 13a of the second substrate 13 and the adhesive layer 15 are formed under reduced pressure in the temporary bonding step S2 described above. Then, when a heat treatment is performed in the main bonding step S3, the adhesive layer 15 softens and the fluidity of the adhesive layer 15 increases. As a result, the softened adhesive layer 15 flows and enters the voids 21, thereby reducing the size of the voids 21. The enlarged partial view of FIG. 7 shows how the adhesive layer 15 flows in a direction that fills the voids 21 (the direction of the white arrow in FIG. 7), thereby filling the voids 21 present at the interface between the second substrate 13 and the adhesive layer 15 with the softened adhesive layer 15 and reducing the size of the voids 21. This improves the adhesion between the second substrate 13 and the adhesive layer 15.

[0082] Temporarily bonded substrate 19 is heated by heater 44, and after a sufficient amount of time has passed, heater 44 stops generating heat and temporarily bonded substrate 19 is cooled. As a result, adhesive layer 15 is cooled and hardened, and first substrate 11 and second substrate 13 are firmly bonded via adhesive layer 15. In this way, first substrate 11 and second substrate 13 are permanently bonded together.

[0083] In the main bonding step S3, the first substrate 11 is held by the stage 42, but unlike the temporary bonding step S2 (see FIG. 5), the second substrate 13 is not directly held by another stage. Therefore, even if heating at the second temperature causes distortion in the first surface 42a of the stage 42 and displaces the first substrate 11, the second substrate 13 can also displace along with the first substrate 11. As a result, even if distortion occurs in the first surface 42a of the stage 42, the parallelism between the first substrate 11 and the second substrate 13 is maintained.

[0084] Furthermore, in the main bonding step S3, a second atmospheric pressure (e.g., atmospheric pressure) higher than the first atmospheric pressure (the atmospheric pressure during temporary bonding in the temporary bonding step S2) acts uniformly on the entire second substrate 13. This causes the entire second substrate 13 to be pressed uniformly toward the first substrate 11. As a result, the first substrate 11 and the second substrate 13 are bonded uniformly while maintaining a high degree of parallelism, and a decrease in the accuracy of bonding the first substrate 11 and the second substrate 13 is suppressed.

[0085] As described above, according to the substrate bonding method of this embodiment, the temporary bonding step S2 and the main bonding step S3 are performed in this order. Here, in a conventional bonding process, a bonding apparatus having a configuration similar to the temporary bonding apparatus 16 (see FIG. 5 ) is used, and the first substrate 11 and the second substrate 13 are bonded together while fixed to a stage, while the adhesive layer 15 is heated to a temperature required for main bonding (corresponding to the second temperature in this embodiment), thereby bonding the first substrate 11 and the second substrate 13 in a single step. Therefore, when bonding the first substrate 11 and the second substrate 13, the stage of the bonding apparatus is heated to a high temperature (the second temperature), causing distortion of the stage, which causes a problem of reducing the parallelism between the first substrate 11 and the second substrate 13.

[0086] On the other hand, in this embodiment, first, the first substrate 11 and the second substrate 13 are heated at a first temperature lower than the second temperature while being pressed together via the adhesive layer 15 in the temporary bonding device 16 (temporary bonding step S2). Then, while holding the first substrate 11 and applying a second pressure to the second substrate 13, the adhesive layer 15 is heated at the second temperature to permanently bond the first substrate 11 and the second substrate 13 (permanent bonding step S3). This allows the heating temperature when the first substrate 11 and the second substrate 13 are fixed by the first stage 20 and the second stage 22 (see FIG. 5), respectively, to be lower than in the past, thereby reducing distortion of the first stage 20 and the second stage 22. As a result, the first substrate 11 and the second substrate 13 are maintained in high parallelism, and the first substrate 11 and the second substrate 13 can be bonded more precisely than in the past.

[0087] The second atmospheric pressure when the main bonding step S3 is performed may be any pressure higher than the first atmospheric pressure, and may not be atmospheric pressure. In other words, the second atmospheric pressure may be higher than the first atmospheric pressure and lower than atmospheric pressure.

[0088] In the above embodiment, the case has been described in which the temporary bonding step S2 is performed using the temporary bonding apparatus 16, and the main bonding step S3 is performed using the main bonding apparatus 40. However, the temporary bonding step S2 and the main bonding step S3 may also be performed using the temporary bonding apparatus 16.

[0089] When the temporary bonding step S2 and the main bonding step S3 are performed by the temporary bonding apparatus 16, a heater for heating the first substrate 11 is provided on the first stage 20 of the temporary bonding apparatus 16. The heater has the same configuration as the heater 44 of the main bonding apparatus 40 (see FIG. 7). Then, after the temporary bonding step S2 is performed as described above, the second stage 22 releases the second substrate 13 from its hold, and the second stage 22 rises. This results in the temporarily bonded substrate 19 (see FIG. 6) being placed on the first stage 20. At this time, the first substrate 11 is fixed to the first stage 20, but the second substrate 13 is not fixed to the second stage 22.

[0090] Next, the chamber 18 of the temporary bonding apparatus 16 is opened to the atmosphere. This increases the pressure inside the chamber 18 to a second pressure (atmospheric pressure). Furthermore, the first stage 20 is heated by a heater until the adhesive layer 15 reaches a temperature (second temperature) required for permanent bonding. As a result, with the adhesive layer 15 softened, the second pressure acts uniformly on the second substrate 13 side of the temporary bonded substrate 19 held by the first stage 20, and the permanent bonding step S3 is performed.

[0091] In addition, the structures, methods, etc. according to the above-described embodiments and modifications may be modified and implemented without departing from the scope of the present invention. [Explanation of symbols]

[0092] 11: First board 11a: 1st surface (joint surface) 11b: 2nd side 13: Second board 13a: 1st surface (joint surface) 13b: 2nd side 15: Adhesive layer 17: Coating liquid 19: Temporary bonded substrate 21 :Void 2: Adhesive layer forming device 4: Holding table 6: Frame 6a: Recess 8: Holding plate 8a:Top surface (holding surface) 10: Spindle 12: Axis center (rotating axis) 14: Coating liquid supply unit 14a:Shaft part 14b: Arm 14c: Nozzle 16: Temporary bonding device (pressure device) 18: Chamber 20: First Stage 20a: Side 1 20b: 2nd side 22: Second Stage 22a: 1st page 22b: 2nd side 24: 1st movement mechanism 26:Second movement mechanism 28: Opening and closing door 30: First piping 32: First valve 34: Vacuum pump 36: Second piping 38: Second valve 40: Main bonding device (heating device) 42: Stage 42a: 1st page 44: Heater

Claims

1. A method for bonding a first substrate and a second substrate via an adhesive layer, comprising: an adhesive layer forming step of forming the adhesive layer on one or both of the first substrate and the second substrate; a temporary bonding step of, after the adhesive layer forming step, arranging the first substrate and the second substrate so that they face each other with the adhesive layer interposed therebetween, and pressing one or both of the first substrate and the second substrate in a direction in which the first substrate and the second substrate approach each other relatively under a first atmospheric pressure that is lower than atmospheric pressure, thereby forming a temporary bonded substrate in which the first substrate and the second substrate are integrated together via the adhesive layer; a main bonding step of bonding the first substrate and the second substrate together by heating the temporarily bonded substrate under a second atmosphere higher than the first atmosphere after the temporary bonding step.

2. In the temporary bonding step, the adhesive layer is heated to a first temperature; In the bonding step, the adhesive layer is heated to a second temperature; the first temperature is lower than the second temperature; 2. The method for bonding substrates according to claim 1, wherein the adhesive layer softens at the second temperature.

3. 3. The method for bonding substrates according to claim 1, wherein in the temporary bonding step, a region including the periphery of the first substrate and a region including the periphery of the second substrate are adhered to each other via the adhesive layer.

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