Joining method

Abstract

In a first joining method, a second joining object is superposed on a first joining object in an atmosphere having an atmospheric pressure lower than a prescribed atmospheric pressure, and then a fixing part for fixing the second joining object to the first joining object is annularly formed along the outer peripheral edge of the first joining object while the aforementioned atmosphere is maintained, whereby the interior of the annular shape is sealed. In a second joining method, a second joining object is superposed on a first joining object having a plurality of device regions in an atmosphere having an atmospheric pressure lower than a prescribed atmospheric pressure, and then a fixing part for fixing the second joining object to the first joining object is formed so as to have an annular shape surrounding the plurality of device regions while the aforementioned atmosphere is maintained, whereby the interior of the annular shape is sealed.

Description

Joining method

[0001] The present invention relates to a joining technique using laser light.

[0002] In devices such as MEMS (Micro Electro Mechanical Systems), elements such as sensors (such as acceleration sensors and gyro sensors), micromachines (such as actuators), and electronic circuits may be sealed in cavities (see, for example, Patent Document 1). In the manufacturing process of such devices, two joining objects (one having a recess that serves as the cavity, and another that closes the recess) are used, and after the element is placed in the recess, the two joining objects are joined to form a cavity, thereby simultaneously sealing the element in the cavity.

[0003] On the other hand, depending on the type of element sealed in the cavity, maintaining the internal pressure of the cavity at an appropriate value is important to improve the performance of the element. For example, if the element is an acceleration sensor, it is preferable that the internal pressure of the cavity be set to a moderately low value so that air resistance can cause damping of the acceleration sensor. For another example, if the element is a gyro sensor, it is preferable that the internal pressure of the cavity be set as low as possible (in other words, the degree of vacuum should be as high as possible).

[0004] Conventionally, the following methods have been used to set the internal pressure of a cavity to a target internal pressure (an appropriate value depending on the elements): (1) first, align and overlap the two objects to be joined; (2) then, perform a temporary joining to maintain the adjusted positional relationship; (3) then, place the two objects to be joined in a chamber, and reduce the internal pressure of the chamber until it becomes approximately the same as the internal pressure of the target cavity; and (4) then, perform actual joining in the chamber to seal the cavity.

[0005] JP 2013-251743 A

[0006] In the conventional method described above, the differential pressure generated by reducing the internal pressure of the chamber is used to force the air in the cavity to flow out through the gap between the joining surfaces (the area other than the temporarily joined area) that is created when the two objects to be joined are placed on top of each other, thereby reducing the internal pressure of the cavity to the target internal pressure.

[0007] The inventors have found that it is difficult to reduce the internal pressure of the cavity to a target internal pressure with conventional methods, or even if it is possible, it takes an extremely long time to reduce the internal pressure to the target. The inventors believe that the reason for this is that after the two objects to be joined are overlapped, even if a pressure difference is generated, the flow resistance in the gap between the joining surfaces becomes large, making it difficult for air to flow out through the gap between the joining surfaces.

[0008] SUMMARY OF THE INVENTION An object of the present invention is to efficiently create a state in which the internal pressure of the cavity is reduced to a target internal pressure in a bonding method in which two objects to be bonded are bonded to form a cavity.

[0009] A first bonding method according to the present invention includes a laminating step and a fixing portion forming step (aspect 1). In the laminating step, a second object to be bonded is placed on a first object to be bonded in an atmosphere lower than a predetermined pressure. After the laminating step, in the fixing portion forming step, a fixing portion for fixing the second object to the first object to be bonded is formed in an annular shape along the outer periphery of the first object to be bonded while maintaining the atmosphere, thereby sealing the inside of the annular shape.

[0010] A second bonding method according to the present invention includes a laminating step and a fixing portion forming step (aspect 2). In the laminating step, a second bonding object having a plurality of device regions is placed on a first bonding object in an atmosphere lower than a predetermined pressure. After the laminating step, in the fixing portion forming step, while maintaining the atmosphere, a fixing portion for fixing the second bonding object to the first bonding object is formed in an annular shape surrounding the plurality of device regions, thereby sealing the inside of the annular shape.

[0011] In the bonding method according to the above aspect 2, a recess that will become a cavity may be formed in each device region of the first bonding target, and in the stacking step, an atmosphere whose air pressure has been reduced to a value equal to or close to the target internal pressure value of the cavity (the target internal pressure in the cavity after sealing) may be used (aspect 3).

[0012] According to the above-described aspects 1 to 3, in the lamination step, the pressure inside the cavity formed before sealing can be made the same as the atmospheric pressure at that time by a simple method of overlapping two objects to be joined in an atmosphere lower than a predetermined pressure. Moreover, by simply adjusting the atmospheric pressure during the lamination step to a pressure similar to the target internal pressure of the cavity after sealing, it is possible to reduce the pressure inside the cavity before sealing to the same level as the target internal pressure. Then, in the subsequent fixing portion formation step, by forming a fixing portion in an annular shape and sealing the annular area while maintaining the above-described atmosphere, it is possible to maintain the pressure inside the annular area at the target internal pressure even when the objects to be joined are exposed to an atmosphere of a predetermined pressure (e.g., atmospheric pressure) or a higher pressure.

[0013] A third bonding method according to the present invention includes a replacing step, a stacking step, and a fixing portion forming step (Aspect 4). In the replacing step, a chamber in which a first object to be bonded and a second object to be bonded are placed is evacuated, and then a predetermined gas is injected to replace the atmosphere with the predetermined gas. In the stacking step, the second object to be bonded is placed on the first object to be bonded in the atmosphere filled with the predetermined gas. After the stacking step, in the fixing portion forming step, while maintaining the atmosphere, a fixing portion for fixing the second object to the first object to be bonded is formed in an annular shape along the outer periphery of the first object to be bonded, thereby sealing the annular interior.

[0014] A fourth bonding method according to the present invention includes a replacement step, a stacking step, and a fixing portion forming step (Aspect 5). In the replacement step, a chamber in which a first bonding object and a second bonding object having a plurality of device regions are placed is evacuated, and then a predetermined gas is injected to replace the atmosphere with the predetermined gas. In the stacking step, the second bonding object is placed on the first bonding object in the atmosphere filled with the predetermined gas. After the stacking step, in the fixing portion forming step, while maintaining the atmosphere, a fixing portion for fixing the second bonding object to the first bonding object is formed in an annular shape surrounding the plurality of device regions, thereby sealing the annular space.

[0015] According to the above-mentioned aspects 4 and 5, by evacuating the chamber and then injecting a predetermined gas in the substitution step, the chamber can be easily substituted with an atmosphere mainly composed of the predetermined gas. Then, in the stacking step, by simply stacking two objects to be joined in an atmosphere filled with the predetermined gas, the cavity formed therebefore sealing can be filled with the same gas as the atmosphere at that time. Moreover, by simply selecting the type of gas to fill the chamber, the cavity before sealing can be filled with the desired gas. Then, in the subsequent fixing portion formation step, by forming a fixing portion in an annular shape and sealing the annular portion while maintaining the above-mentioned atmosphere, the annular portion can be kept filled with the desired gas even when the objects to be joined are exposed to air.

[0016] In the bonding method according to any one of the above aspects 2, 3, and 5, the second bonding object may have a device region corresponding to the device region of the first bonding object, and in the stacking step, the positions of at least one of the first bonding object and the second bonding object may be aligned so that the positions of the corresponding device regions coincide with each other, and after the alignment, the second bonding object may be stacked on the first bonding object (aspect 6).

[0017] According to the above-mentioned aspect 6, when wiring, electrodes, etc. are formed in both of the two corresponding device regions, it is possible to adjust the positional relationship between them so that they are electrically connected correctly when bonded.

[0018] The joining method according to any one of Aspects 1 to 6 above may have the following configuration (Aspect 7). The joining method may further include, as a step performed before the laminating step, a metal layer forming step of forming a metal layer on at least one of the joining surfaces of the first object to be joined and the second object to be joined. Then, in the fixing portion forming step, a laser beam may be locally irradiated onto the metal layer interposed between the first object to be joined and the second object to be joined, thereby locally heating the irradiated portion of the laser beam and forming an annular fixing portion.

[0019] According to the seventh aspect, the metal layer can be melted together with the first and second objects to be joined at the laser beam irradiation location (the location where the bonded portion is to be formed), or the metal that is the main component of the metal layer can be diffused into the first and second objects to be joined. As a result, compounds (e.g., metal silicides) or alloys (e.g., metal-Si alloys) of the main components (e.g., semiconductors) of the first and second objects to be joined and the metal are formed at the interfaces between the first and second objects to be joined and the metal layer, respectively. In other words, a bonded portion that firmly bonds the first and second objects to be joined can be formed. Furthermore, by forming such a bonded portion in an annular shape in an atmosphere at a pressure lower than a predetermined pressure, the inside of the annular portion can be reliably sealed while maintaining a pressure lower than the predetermined pressure.

[0020] A fifth joining method according to the present invention includes a temporary joining step and a main joining step (Aspect 8). In the temporary joining step, a first object to be joined and a second object to be joined are temporarily joined using the joining method according to any one of Aspects 1 to 7. After the temporary joining step, in the main joining step, the first object to be joined and the second object to be joined are further joined in a region inside the annular joining portion. At this time, the main joining step is performed using a chamber different from the chamber used for performing the temporary joining step.

[0021] As described above, the temporary bonding step efficiently creates a state in which the internal pressure in the cavity (cavity before sealing) is reduced to the target internal pressure. Therefore, in the main bonding step, simply by performing bonding to seal the cavity (cavity before sealing), it is possible to easily create a cavity (cavity after sealing) in which the internal pressure is maintained at an appropriate value (target internal pressure).

[0022] Furthermore, according to the above-mentioned Aspect 8, the main bonding step is performed using a chamber different from the chamber used for performing the temporary bonding step, thereby making it possible to shorten the cycle time required for processing (temporary bonding + main bonding) one set of objects to be bonded (first object to be bonded and second object to be bonded).

[0023] The lamination step of the temporary bonding step (a step that requires creating an atmosphere at a lower pressure than a predetermined pressure (e.g., an atmosphere with a high degree of vacuum)) and the main bonding step are both time-consuming processes. If the temporary bonding step and the main bonding step were performed sequentially in one chamber, the chamber would not be able to move on to processing the next set of objects to be bonded until processing of one set of objects to be bonded was completed, which would lengthen the cycle time required to process one set of objects to be bonded (temporary bonding + main bonding).

[0024] On the other hand, according to the above-mentioned aspect 8, by performing the main bonding step using a chamber different from the chamber used to execute the temporary bonding step, it becomes possible to process these steps in parallel using multiple chambers, and as a result, it becomes possible to shorten the cycle time required to process one set of bonding objects (temporary bonding + main bonding).

[0025] According to the present invention, it is possible to efficiently create a state in which the internal pressure of the cavity is reduced to a target internal pressure.

[0026] FIG. 1 is a conceptual diagram showing the temporary bonding step executed in the embodiment in processing order. FIG. 2 is a conceptual diagram showing the temporary bonding step, continuing from FIG. 1 in processing order. FIGS. 3A and 3B are plan views illustrating a first bonding target and a second bonding target prepared in the preparation step, respectively. FIG. 4 is a plan view illustrating a planned formation pattern of a fixing portion used in the temporary bonding step. FIG. 5 is a conceptual diagram showing the main bonding step executed in the embodiment in processing order. FIG. 6 is a plan view illustrating a planned formation pattern of a fixing portion used in the main bonding step. FIGS. 7A and 7B are plan views showing two examples of a planned formation pattern of a fixing portion used in the temporary bonding step of the first modified example. FIGS. 8A and 8B are plan views showing other two examples of a planned formation pattern of a fixing portion used in the temporary bonding step of the first modified example. FIG. 9 is a conceptual diagram showing the temporary bonding step executed in the second modified example in processing order. FIG. 10 is a conceptual diagram showing the temporary bonding step, continuing from FIG. 9 in processing order. FIG. 11 is a conceptual diagram showing the order of the main joining steps executed in the second modified example.

[0027] The bonding method according to the present invention is a method for bonding two objects to be bonded (such as semiconductor wafers, hereinafter referred to as a "first object to be bonded W1" and a "second object to be bonded W2"). ​​Hereinafter, embodiments and modifications of the bonding method according to the present invention will be specifically described. Note that the bonding method described below can be realized using various well-known devices.

[0028] [1] Embodiment In the joining method of this embodiment, the steps for joining the first object to be welded W1 and the second object to be welded W2 are roughly divided into two joining steps that are performed in sequence. Specifically, a temporary joining step S1 is performed as the first joining step, and then a main joining step S2 is performed as the second joining step. Details of these joining steps will be described below.

[0029] 1 and 2 are conceptual diagrams showing the order of the temporary joining step S1 performed in this embodiment. In the temporary joining step S1, a preparation step S10, a lamination step S11, and a fixing portion formation step S12 are performed in this order.

[0030] <Preparation Step S10> In preparation step S10, a first object to be welded W1 and a second object to be welded W2 are prepared. Figures 3A and 3B are plan views illustrating the first object to be welded W1 and the second object to be welded W2, respectively, prepared in preparation step S10. Note that the first object to be welded W1 and the second object to be welded W2 shown in Figures 1 and 2 are shown in cross section along the A1-A1 line and the A2-A2 line, respectively, shown in Figures 3A and 3B. The same applies to the other figures showing various steps.

[0031] In this embodiment, the first welding target W1 has a plurality of device regions Rd1 that are cut along cutting lines Ct to be separated into individual pieces (see FIG. 3A), and the second welding target W2 has device regions Rd2 that correspond to each device region Rd1 of the first welding target W1 (see FIG. 3B). Then, a corresponding pair of device regions Rd1 and Rd2 are cut along cutting lines Ct after bonding to be separated into individual pieces, thereby constituting one device.

[0032] Specifically, each device region Rd1 of the first welding target W1 is a portion that serves as the base of a device, and each device region Rd1 has a recess 10 formed therein that serves as an enclosed space (cavity) for sealing an element Ge that performs the function of the device. Here, the element Ge is a sensor (such as an acceleration sensor or a gyro sensor), a micromachine (such as an actuator), an electronic circuit, etc. In this embodiment, the element Ge is an element for which it is important to maintain the internal pressure of the cavity at an appropriate value in order to improve its performance.

[0033] Furthermore, each device region Rd2 of the second object to be welded W2 is a region that closes the corresponding recess 10 of the device region Rd1 of the first object to be welded W1, and is a portion that becomes a lid portion in the device.

[0034] Furthermore, wiring, electrodes, and the like (not shown) that are to be connected to each other are formed in the device regions Rd1 and Rd2, and it is required that they are electrically connected correctly when they are joined.

[0035] <Laminating Step S11> In the laminating step S11, using the first object to be welded W1 and the second object to be welded W2 prepared in the preparation step S10, the second object to be welded W2 is stacked on the first object to be welded W1 in an atmosphere at a pressure lower than a predetermined pressure Pt. Here, the predetermined pressure Pt is the pressure of the atmosphere used in the main welding step S2 described below, and is not particularly limited to, but is, for example, atmospheric pressure.

[0036] Specifically, first, the first welding object W1 and the second welding object W2 are placed in a chamber 30 whose internal pressure can be adjusted. At this time, the first welding object W1 and the second welding object W2 are placed in the chamber 30 with their welding surfaces 11s and 21s facing each other and spaced apart (see the upper diagram of S11 in FIG. 1 ). Here, the welding surfaces 11s and 21s are surfaces that will be bonded in the temporary bonding step S1 and the main bonding step S2, respectively, and are surfaces on which the recess 10 and the wiring and electrodes that will be connected to each other are exposed.

[0037] Next, by lowering the internal pressure of the chamber 30, an atmosphere (an atmosphere with a lower pressure than the predetermined pressure Pt) is created within the chamber 30, in which the pressure has been lowered to a value equal to or close to the internal pressure target value Px of the above-mentioned cavity (an enclosed space for sealing the element Ge).

[0038] Furthermore, in this embodiment, in the stacking step S11, the positions of at least one of the first welding target W1 and the second welding target W2 are aligned so that the positions of the corresponding device regions Rd1 and Rd2 coincide with each other. Specifically, the alignment adjusts the positional relationship of wiring, electrodes, and the like formed in the corresponding device regions Rd1 and Rd2 so that they can be properly electrically connected during bonding.

[0039] Thereafter, the second object to be welded W2 is placed on the first object to be welded W1 while maintaining the positional relationship after alignment (see the lower diagram of S11 in FIG. 1).

[0040] According to this stacking step S11, by simply stacking two objects to be joined (the first object to be joined W1 and the second object to be joined W2) under an atmosphere lower than the predetermined pressure Pt, the pressure inside the cavity before sealing formed there can be made the same as the atmospheric pressure at that time. Moreover, simply by adjusting the atmospheric pressure during the stacking step S11 to a pressure equivalent to the target internal pressure value Px of the cavity after sealing, it is possible to reduce the pressure inside the cavity before sealing to the same level as the target internal pressure value Px. This makes it possible to efficiently create a state in which the internal pressure of the cavity (here, the cavity before sealing) is reduced to the target internal pressure (target internal pressure value Px). In this way, according to the stacking step S11, it is possible to efficiently control the internal pressure of the cavity before sealing.

[0041] Furthermore, the positional relationship of the wiring, electrodes, etc. formed in the two corresponding device regions Rd1 and Rd2 is adjusted by the alignment described above, so that when the second joining object W2 is placed on top of the first joining object W1, they are electrically connected correctly.

[0042] <Fixing portion forming step S12> In the fixing portion forming step S12, while the atmosphere in the chamber 30 is maintained as it is (in other words, the air pressure remains the same as that adjusted in the stacking step S11), a fixing portion Qs for fixing the second object to be welded W2 to the first object to be welded W1 is formed in a ring shape (closed ring) along the outer peripheral edge 11t of the first object to be welded W1, thereby sealing the inside of the ring shape.

[0043] Specifically, by locally irradiating the interface (contact surface) between the bonding surfaces 11s and 21s with laser light (see the upper diagram of S12 in FIG. 2), the irradiated area of ​​the laser light is locally heated and melted or altered, thereby bonding the bonding surfaces 11s and 21s together at that localized location (see the lower diagram of S12 in FIG. 2). At this time, the first bonding object W1 and the second bonding object W2 may be clamped between quartz plates or the like to enhance the adhesion between the bonding surfaces 11s and 21s. Then, by scanning the laser light along a closed annular pattern (a pattern Xs for forming the bonding portion Qs; see FIG. 4), the bonding surfaces 11s and 21s are bonded together along the pattern. In this manner, the closed annular bonding portion Qs is formed.

[0044] 4 is a plan view illustrating an example of a to-be-formed pattern Xs of the fixing portion Qs. In the example of FIG. 4, the first welding target W1 is disk-shaped, and the to-be-formed pattern Xs is set to have an annular shape along the outer circumferential edge 11t at its peripheral portion Re. With this shape, the to-be-formed pattern Xs is set to have an annular shape that surrounds all of the device regions Rd1 of the first welding target W1.

[0045] According to this fixing portion forming step S12, by forming the fixing portion Qs in a ring shape (closed ring) and sealing the inside of the ring while maintaining the atmosphere inside the chamber 30 (in other words, while maintaining the air pressure adjusted in the stacking step S11), it becomes possible to maintain the air pressure inside the ring at the internal pressure target value Px even if the first joining object W1 and the second joining object W2 after temporary joining are exposed to an atmosphere of a predetermined air pressure Pt (such as atmospheric pressure) or an atmosphere of a higher air pressure.

[0046] [1-2] Main Bonding Step Fig. 5 is a conceptual diagram showing the processing order of the main bonding step S2 performed in this embodiment. In this embodiment, the first object to be bonded W1 and the second object to be bonded W2 are removed from the chamber 30 after temporary bonding, and the main bonding step S2, which will be described below, is performed on these objects at atmospheric pressure. In this embodiment, the main bonding step S2 is performed using a chamber other than the chamber 30 used to perform the main bonding step S1. These chambers may be constructed in the same apparatus, or may be constructed in separate apparatuses.

[0047] According to the above-described temporary bonding step S1, the annular space within the bonded portion Qs is sealed at an air pressure equal to or approximately equal to the target internal pressure value Px. Therefore, by exposing the first and second bonded objects W1 and W2 to atmospheric pressure after temporary bonding, a pressure difference is generated between the air pressure inside the annular space (internal pressure) and the air pressure outside the annular space (external pressure). This pressure difference allows the first and second bonded objects W1 and W2 to be clamped from their rear surfaces in a region inside the annular bonded portion Qs. This clamping pressure, utilizing the pressure difference, allows the bonded surfaces 11s and 21s to be tightly attached to each other in a region inside the annular bonded portion Qs. The actual bonding step S2 is performed with the bonded surfaces 11s and 21s tightly attached to each other.

[0048] Then, in the main joining step S2, the first object to be welded W1 and the second object to be welded W2 are further joined together in a region inside the annular joining portion Qs formed in the temporary joining step S1.

[0049] Specifically, for each pair of corresponding device regions Rd1 and Rd2 (device regions Rd1 and Rd2 whose positions coincide with each other through alignment), a fixing portion Qt is formed to seal the cavity (cavity before sealing) formed in that pair of regions. At this time, the fixing portion Qt is formed to have a ring shape (closed ring) surrounding the recess 10 that constitutes each cavity.

[0050] More specifically, by locally irradiating the interface (contact surface) between the bonding surfaces 11s and 21s in a region inside the fixing portion Qs with laser light (see the upper diagram of S2 in FIG. 5 ), the irradiated area of ​​the laser light is locally heated and melted or altered, thereby bonding the bonding surfaces 11s and 21s together at that localized location (see the lower diagram of S2 in FIG. 5 ). At this time, the first bonding target W1 and the second bonding target W2 may be clamped between quartz plates or the like to further increase the adhesion between the bonding surfaces 11s and 21s. Then, by scanning the laser light along a closed annular pattern (a pattern Xt for forming the fixing portion Qt; see FIG. 6 ) for each corresponding device region Rd1 and Rd2, the bonding surfaces 11s and 21s are bonded together along the pattern. In this way, a closed annular fixing portion Qt is formed for each corresponding device region Rd1 and Rd2.

[0051] 6 is a plan view illustrating an example of a to-be-formed pattern Xt of the fixing portion Qt. In the example of FIG. 6, the shape of each device region Rd1 is rectangular (the corresponding device region Rd2 is also rectangular), and the to-be-formed pattern Xt is set so as to be a rectangular ring along the periphery of the device region Rd1 and surround the recess 10. Note that the shape of the to-be-formed pattern Xt is not limited to a rectangular ring, and can be changed as appropriate to another ring shape (such as a circle or a polygon) depending on the peripheral shape of each device region Rd1 and the opening shape of the recess 10.

[0052] As described above, the temporary bonding step S1 efficiently creates a state in which the internal pressure inside the cavity (cavity before sealing) is reduced to the internal pressure target value Px. Therefore, in the main bonding step S2, simply by performing bonding to seal the cavity (cavity before sealing) as described above, it is possible to easily create a cavity (cavity after sealing) in which the internal pressure is maintained at an appropriate value (internal pressure target value Px).

[0053] Furthermore, in this embodiment, the main bonding step S2 is performed using a chamber different from the chamber 30 used to perform the temporary bonding step S1, which makes it possible to shorten the cycle time required for processing (temporary bonding and main bonding) one set of objects to be bonded (the first object to be bonded W1 and the second object to be bonded W2).

[0054] The lamination step S11 of the temporary bonding step S1 (a step that requires creating an atmosphere at a lower pressure than the predetermined pressure Pt (for example, an atmosphere with a higher degree of vacuum)) and the main bonding step S2 are both time-consuming processes. If the temporary bonding step S1 and the main bonding step S2 were performed sequentially in one chamber, the chamber would not be able to move on to processing the next set of objects to be bonded until processing of one set of objects to be bonded was completed, which would lengthen the cycle time required to process one set of objects to be bonded (temporary bonding + main bonding).

[0055] On the other hand, according to the manufacturing method of this embodiment, by performing the main bonding step S2 using a chamber other than the chamber 30 used to perform the temporary bonding step S1, these steps can be processed in parallel using multiple chambers, and as a result, it is possible to shorten the cycle time required to process one set of bonding objects (temporary bonding + main bonding).

[0056] [2] Modified Examples [2-1] First Modified Example The pattern Xs to be formed of the fixing portion Qs used in the temporary bonding step S1 may be appropriately changed to a different ring shape that is not limited to the shape illustrated in FIG. 4 (a ring shape along the outer peripheral edge 11t), as long as it is a ring shape that can surround multiple device regions Rd1.

[0057] 7A and 7B are plan views showing two examples of the planned formation pattern Xs of the fixed portions Qs used in the first modified example. Figures 8A and 8B are plan views showing two other examples of the planned formation pattern Xs of the fixed portions Qs used in the first modified example.

[0058] In FIG. 7A, the pattern to be formed Xs is set to be annular in shape surrounding all the device regions Rd1 of the first target to be welded W1 along their outermost edges.

[0059] On the other hand, in Figures 7(B) to 8(B), multiple device regions Rd1 are divided into several groups, and the to-be-formed pattern Xs is set for each group so as to be a ring that surrounds all of the device regions Rd1 in that group. In Figure 7(B), the to-be-formed pattern Xs is set so as to be an independent ring for each group. In contrast, in Figures 8(A) and 8(B), the to-be-formed pattern Xs is set by combining a circular pattern Xs1 and a linear pattern Xs2 so that part of the ring can be shared between groups. Specifically, this is as follows.

[0060] 8A, the pattern Xs to be formed is composed of a circular pattern Xs1 set in a ring shape along the outer circumferential edge 11t and one straight line pattern Xs2 that crosses the inside of the circular pattern Xs1. In this case, the straight line pattern Xs2 portion of the pattern Xs to be formed is shared between the groups, and as a result, the pattern Xs to be formed includes two semicircular rings for each group that can surround all of the device regions Rd1 in the group.

[0061] 8B, the pattern Xs to be formed is composed of a circular pattern Xs1 set in a ring shape along the outer peripheral edge 11t and two straight line patterns Xs2 that cross the inside of the circular pattern Xs1 and intersect with each other (orthogonal in the example of FIG. 8B). In this case, the straight line pattern Xs2 portion of the pattern Xs to be formed is also shared between groups, and as a result, the pattern Xs to be formed for each group includes four fan-shaped rings that can surround all of the device regions Rd1 in that group.

[0062] 9 and 10 are conceptual diagrams showing the order of the temporary joining step S1 performed in the second modified example, and FIG. 11 is a conceptual diagram showing the order of the main joining step S2 performed in the second modified example.

[0063] 9 , in the preparation step S10, a metal layer Lm may be formed on at least one of the joining surface 11 s of the first object to be welded W1 and the joining surface 21 s of the second object to be welded W2 (metal layer formation step). The example of FIG. 9 shows a case where the metal layer Lm is formed only at the locations of the joining surface 21 s on the second object to be welded W2 where the fixing portions Qs and Qt are formed (see FIGS. 10 and 11 ). More specifically, the metal layer Lm is formed at locations that avoid electrodes, wiring, etc. that are electrically connected when the first object to be welded W1 and the second object to be welded W2 are joined (locations where the metal layer Lm can be formed in a state of electrical non-contact with electrodes, wiring, etc.).

[0064] Although not particularly limited, the metal layer Lm is formed to a thickness of 1 μm or less using a film formation method such as a vapor deposition method, and the main component of the metal layer Lm can be a metal such as Cu, Al, Cr, Ti, Ta, or Au.

[0065] The metal layer Lm may be formed on the joining surface 11s on the side of the first joining object W1. The metal layer Lm may also be formed on both the joining surfaces 11s and 21s. In this case, two types of metal layers Lm having different main components may be formed on the joining surfaces 11s and 21s. If there is no need to electrically connect electrodes, wiring, or the like when joining the first joining object W1 and the second joining object W2, the metal layer Lm may be formed on the entirety of at least one of the joining surfaces 11s and 21s.

[0066] In this modification, the metal layer Lm is used to form the fixed portions Qs and Qt in the fixed portion forming step S12 (see FIG. 10) and the main welding step S2 (see FIG. 11). Specifically, by locally irradiating the metal layer Lm interposed between the first object to be welded W1 and the second object to be welded W2 with laser light, the irradiated portion of the laser light is locally heated, and the annular fixed portions Qs and Qt are formed.

[0067] More specifically, by irradiating the metal layer Lm with laser light (see the upper diagrams of S12 and S2 in FIGS. 10 and 11 , respectively), the metal layer Lm can be melted together with the first object W1 to be welded and the second object W2 to be welded at the irradiated locations of the laser light (locations where the fixed portions Qs and Qt are to be formed; patterns Xs and Xt to be formed), or the metal that is the main component of the metal layer Lm can be diffused into the first object W1 to be welded and the second object W2 to be welded. As a result, compounds (such as metal silicides) or alloys (such as metal-Si alloys) of the main components (such as semiconductors) of the first object W1 to be welded and the second object W2 to be welded are formed at the interfaces between the first object W1 to be welded and the second object W2 to be welded and the metal layer Lm, respectively. In other words, fixed portions Qs and Qt that firmly bond the first object W1 to the second object W2 to be welded can be formed (see the lower diagrams of S12 and S2 in FIGS. 10 and 11 , respectively).

[0068] In the temporary joining step S1, such a fixing portion Qs is formed in a ring shape (closed ring shape) under an atmosphere with a lower pressure than the predetermined pressure Pt, thereby making it possible to reliably seal the inside of the ring shape while maintaining a state of lower pressure than the predetermined pressure Pt.

[0069] [2-3] Third Modification The main welding step S2 is not limited to being performed at atmospheric pressure, but may also be performed in a pressurized atmosphere in a chamber. This configuration increases the pressure difference between the air pressure inside the annular groove (internal pressure) and the air pressure outside the annular groove (external pressure). As a result, the first object to be welded W1 and the second object to be welded W2 can be clamped with greater force in the region inside the annular fixing portion Qs. This makes it possible to correct any distortion in the first object to be welded W1 or the second object to be welded W2 and bring the welded surfaces 11s and 21s into close contact with each other.

[0070] [2-4] Fourth Modification The above-described bonding method is not limited to bonding two objects to be bonded (a first object to be bonded W1 and a second object to be bonded W2) to form a cavity, but can also be applied to bonding two objects to be bonded for various other purposes. In this case, too, the pressure difference between the air pressure inside the annulus (internal pressure) and the air pressure outside the annulus (external pressure) can be utilized to bring the first object to be bonded W1 and the second object to be bonded W2 into close contact with each other. Furthermore, by performing the main bonding step S2 in a chamber separate from the chamber 30 used to perform the temporary bonding step S1, the cycle time required to process one pair of objects to be bonded (temporary bonding + main bonding) can be shortened.

[0071] Furthermore, the above-described joining method can also be applied to the case where two joining targets are joined together without device regions Rd1 and Rd2. In this case as well, it is possible to bring the two joining targets into close contact with each other and shorten the cycle time.

[0072] [2-5] Fifth Modification In the bonding method of the above-described embodiment, in order to efficiently create a state in which the internal pressure of the cavity has decreased to the target internal pressure (target internal pressure value Px), the lamination step S11 involves overlapping the two bonding objects (first bonding object W1 and second bonding object W2) in an atmosphere with a lower pressure than the predetermined pressure Pt. Instead of this, in this modification, in order to efficiently create a state in which the cavity is filled with a desired gas (mainly an inert gas such as nitrogen gas, neon gas, or argon gas), the following processing is performed in the temporary bonding step S1.

[0073] In the temporary joining step S1 of this modified example, the same preparation step S10 as in the above embodiment is performed, and then the replacement step S31, the stacking step S32, and the fixed portion forming step S33 are performed in this order.

[0074] <Replacing Step S31> In the replacing step S31, first, the first welding object W1 and the second welding object W2 are placed in a chamber 30 in which gas can be injected and the internal pressure can be adjusted. At this time, the first welding object W1 and the second welding object W2 are placed in the chamber 30 with their welding surfaces 11s and 21s facing each other and spaced apart from each other (see the upper diagram of S11 in FIG. 1 ).

[0075] Next, the internal pressure of the chamber 30 is reduced to create a vacuum inside the chamber 30 (a state in which the air pressure has been reduced to a desired degree of vacuum). Thereafter, a gas of the same type (hereinafter, this gas will be referred to as a "predetermined gas") as the desired gas (mainly an inert gas such as nitrogen gas, neon gas, or argon gas) to fill the cavity is injected into the chamber 30, thereby replacing the atmosphere inside the chamber 30 with the predetermined gas. The internal pressure of the chamber 30 at this time can be adjusted, and may be adjusted to a negative pressure lower than atmospheric pressure or a positive pressure higher than atmospheric pressure.

[0076] According to such a replacement step S31, by creating a vacuum inside the chamber 30 and then injecting a predetermined gas, it becomes easy to replace the atmosphere inside the chamber 30 with an atmosphere mainly composed of the predetermined gas.

[0077] <Stacking Step S32> In the stacking step S32, the second welding target W2 is stacked on the first welding target W1 in an atmosphere filled with a predetermined gas. Furthermore, as in the above embodiment, the positions of at least one of the first welding target W1 and the second welding target W2 are aligned so that the positions of the corresponding device regions Rd1 and Rd2 coincide with each other. Thereafter, the second welding target W2 is stacked on the first welding target W1 while maintaining the aligned positional relationship (see the lower diagram of S11 in FIG. 1 ).

[0078] Here, conventionally, the following methods have been used to fill the cavity with the desired gas: (1) first, two objects to be joined are aligned and then superimposed; (2) then, a temporary joining is performed to maintain the adjusted positional relationship; (3) then, the two objects to be joined are placed in a chamber, and the chamber is evacuated; (4) then, the chamber is filled with the same type of gas as the desired gas (a specified gas); and (5) finally, a final joining is performed in the chamber to seal the cavity.

[0079] In this conventional method, the chamber is evacuated in (3), and the resulting pressure difference (internal pressure greater than external pressure) is used to force the air in the cavity to flow out through the gap between the joining surfaces of the two objects to be joined (a portion other than the temporarily joined portion), thereby creating a vacuum inside the cavity. However, as mentioned above, after the two objects to be joined are superimposed, even if a pressure difference is generated, the flow resistance in the gap between the joining surfaces increases, which is thought to make it difficult to force the air to flow out through the gap between the joining surfaces.

[0080] In addition, by filling the chamber with a predetermined gas in (4), the resulting pressure difference (external pressure greater than internal pressure) is utilized to cause the gas in the chamber to flow into the interior through the gap between the joining surfaces of the two objects to be joined (a portion other than the temporarily joined portion), thereby filling the cavity with the predetermined gas. However, even in this case, it is thought that it will be difficult to cause the gas to flow into the interior through the gap between the joining surfaces due to the large flow resistance in the gap between the joining surfaces.

[0081] In contrast, according to the stacking step S32 of this modified example, by using a simple method in which two objects to be joined (the first object to be joined W1 and the second object to be joined W2) are stacked in an atmosphere filled with a predetermined gas, the pre-sealed cavity formed there can be filled with the same gas as the atmosphere at that time. Moreover, by simply selecting the type of gas to fill the chamber 30 appropriately, the pre-sealed cavity can be filled with the desired gas. This makes it possible to efficiently create a state in which the cavity (here, the pre-sealed cavity) is filled with the desired gas. In this way, according to the stacking step S32, it is possible to efficiently control the internal state of the pre-sealed cavity.

[0082] <Fixed portion forming step S33> In the fixed portion forming step S33, while the atmosphere inside the chamber 30 is maintained as it is (in other words, the atmosphere remains filled with a predetermined gas), the fixed portion Qs for fixing the second object to be welded W2 to the first object to be welded W1 is formed in an annular shape (closed annular shape) along the outer peripheral edge 11t of the first object to be welded W1, as in the above embodiment, thereby sealing the inside of the annular shape (see the lower diagram of S12 in FIG. 2 and FIG. 4).

[0083] According to this fixing portion forming step S33, by forming the fixing portion Qs in a ring shape (closed ring) and sealing the inside of the ring while maintaining the atmosphere inside the chamber 30 (in other words, while maintaining an atmosphere filled with a predetermined gas), it is possible to keep the inside of the ring filled with the desired gas even when the first joining object W1 and the second joining object W2 are exposed to air after temporary joining.

[0084] The configurations of the first to fourth modified examples described above can also be applied to this modified example.

[0085] [2-6] Other Modifications The metal layer forming step, which is part of the preparation step S10, may be performed in the chamber 30 where the lamination step S11 is performed.

[0086] In cases where there is no need to shorten the cycle time or where there is a high need to complete the processing (temporary bonding + main bonding) within one chamber, the main bonding step S2 may be performed within the same chamber 30 used to perform the temporary bonding step S1.

[0087] In cases where high precision is not required for the positional relationship between the two objects to be joined during bonding, such as when wiring or electrodes to be connected during bonding are not formed on the objects to be joined, or when device regions Rd1 and Rd2 are not set, the above-mentioned bonding method may be appropriately changed to one in which bonding is performed without alignment in the stacking step S11.

[0088] The above-described embodiments and modifications should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined not by the above-described embodiments and modifications, but by the claims. Furthermore, the scope of the present invention is intended to include all modifications that are equivalent to the scope of the claims and fall within the scope thereof.

[0089] Furthermore, from the above-described embodiments and modifications, some steps constituting the joining method may be partially extracted as the subject of the invention, or each step may be extracted individually. For example, the temporary joining step S1 and the main joining step S2 may be extracted individually as the subject of the invention.

[0090] 10 Recess 11s, 21s Bonding surface 11t Outer periphery 30 Chamber Ct Cutting line Ge Element Lm Metal layer Pt Predetermined atmospheric pressure Px Internal pressure target value Rd1, Rd2 Device region Qs, Qt Fixing portion Re Peripheral portion W1 First bonding object W2 Second bonding object Xs, Xt Pattern to be formed Xs1 Circular pattern Xs2 Linear pattern S1 Temporary bonding step S2 Main bonding step S10 Preparation step S11 Laminating step S12 Fixing portion forming step S31 Replacement step S32 Laminating step S33 Fixing portion forming step

Claims

1. A bonding method comprising: a stacking step of stacking a second bonding target on a first bonding target in an atmosphere of a pressure lower than a predetermined pressure; and a fixing portion forming step of, after the stacking step, forming an annular fixing portion along an outer peripheral edge of the first bonding target to fix the second bonding target to the first bonding target while maintaining the atmosphere, thereby sealing the inside of the annulus.

2. A bonding method comprising: a stacking step of stacking a second bonding target on a first bonding target having a plurality of device regions in an atmosphere of a pressure lower than a predetermined pressure; and a fixing portion forming step of, after the stacking step, forming an annular fixing portion that surrounds the plurality of device regions to fix the second bonding target to the first bonding target while maintaining the atmosphere, thereby sealing the inside of the annulus.

3. In each device region of the first bonding target, a recess serving as a cavity is formed. In the stacking step of claim 2, the atmosphere used is an atmosphere in which the pressure is reduced until it reaches a value equal to or near the target internal pressure value of the cavity.

4. A bonding method comprising: a replacement step of evacuating a chamber in which a first bonding target and a second bonding target are disposed and then replacing the chamber with an atmosphere filled with a predetermined gas by injecting the predetermined gas; a stacking step of stacking the second bonding target on the first bonding target in the atmosphere filled with the predetermined gas; and a fixing portion forming step of, after the stacking step, forming an annular fixing portion along an outer peripheral edge of the first bonding target to fix the second bonding target to the first bonding target while maintaining the atmosphere filled with the predetermined gas, thereby sealing the inside of the annulus.

5. A replacement step of evacuating a chamber in which a first object to be joined and a second object to be joined having a plurality of device regions are disposed, and then injecting a predetermined gas to replace the atmosphere with the predetermined gas; a stacking step of stacking the second object to be joined on the first object to be joined in the atmosphere filled with the predetermined gas; and a fixing portion forming step of forming a fixing portion that surrounds the plurality of device regions in an annular shape so as to seal the inside of the annular shape while maintaining the atmosphere filled with the predetermined gas after the stacking step, and fixing the second object to be joined to the first object to be joined. A joining method comprising the steps of:

6. The second object to be joined has a device region corresponding to the device region of the first object to be joined. In the stacking step, alignment of at least one of the positions of the first object to be joined and the second object to be joined is performed so that the positions of the corresponding device regions coincide with each other, and after the alignment, the second object to be joined is stacked on the first object to be joined. The joining method according to any one of claims 2, 3, and 5.

7. Further comprising a metal layer forming step of forming a metal layer on at least one of the joining surfaces of the first object to be joined and the second object to be joined before the stacking step. In the fixing portion forming step, a laser beam is locally irradiated onto the metal layer interposed between the first object to be joined and the second object to be joined to locally heat the irradiated portion of the laser beam to form the annular fixing portion. The joining method according to any one of claims 1 to 6.

8. A temporary joining step of temporarily joining a first object to be joined and a second object to be joined using the joining method according to any one of claims 1 to 7; and a main joining step of further fixing the first object to be joined and the second object to be joined in a region inside the annular fixing portion after the temporary joining step. The joining method is performed using a chamber different from the chamber used for the execution of the temporary joining step.

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