Bonding strength inspection method

Abstract

To provide an inspecting method for bonding strength of a bonded wafer in which a condition when bonding is appropriately set in order to improve a yield of divided device chips.SOLUTION: A method includes: a preparation step of preparing a three-point bending tester; a chip generation step of generating individual chips by dividing a bonded wafer; a peeling starting point formation step of forming, in one chip 10Ac corresponding to one wafer supported by a pair of supporting points 9a of the three-point bending tester, a pair of grooves 110 that do not reach the other chip corresponding to the other wafer at intervals smaller than an interval between the pair of supporting points, as peeling starting points between the one chip and the other chip 10Bc; a mounting step of mounting one chip surface so that the peeling starting point is positioned inside the pair of supporting points 9a; and a load measuring step of positioning and pressing an indenter 7a on the other chip surface to raise the load, and measuring the maximum load when the load rapidly falls from the rise. The maximum load measured in the load measuring step is used as the bonding strength.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a bond strength inspection method for inspecting the bond strength of a bonded wafer in which one wafer and another wafer are bonded together. [Background technology]

[0002] A wafer with multiple devices such as ICs and LSIs formed on its surface along dividing lines is then divided into individual device chips by a dicing machine and used in electrical equipment such as mobile phones and personal computers.

[0003] Furthermore, two wafers are bonded together to form a bonded wafer, and the bonded wafer is then divided into individual device chips, thereby improving the functionality of the device chips (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-077203 Summary of the Invention [Problem to be solved by the invention]

[0005] When performing a bonding process to bond two wafers to form a bonded wafer, various methods can be selected, such as room-temperature bonding using surface activation or bonding using siloxane bonding. However, if the bonding conditions are not appropriate, the two wafers may not be properly bonded across the entire surface, resulting in partial delamination. If a bonded wafer with such delamination is divided into individual device chips, chips that do not have the desired functionality are produced, resulting in a low yield. To prevent such delamination, the conditions for performing the bonding process to form the bonded wafer must be properly set. To this end, it is necessary to inspect the bonded wafers bonded under the specified conditions and evaluate whether the bond strength is appropriate.

[0006] The present invention has been made in consideration of the above-mentioned facts, and its main technical object is to provide a bonding strength inspection method that can properly inspect the bonding strength of a bonded wafer obtained by bonding two wafers. [Means for solving the problem]

[0007] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a bond strength inspection method for inspecting the bond strength of a bonded wafer obtained by bonding one wafer to another wafer, the bonded wafer including: a preparation step of preparing a three-point bending tester including a pair of fulcrums and an indenter positioned at the center of the pair of fulcrums and pressing against the center of a chip supported by the pair of fulcrums; a chip production step of dividing the bonded wafer to generate individual chips; a peeling start point formation step of forming a groove or division trigger in one chip corresponding to one of the wafers supported by the pair of fulcrums, the groove or division trigger not reaching the other chip corresponding to the other wafer, thereby forming a peeling start point between the one chip and the other chip; a placement step of placing a surface of one of the chips so that the peeling start point is positioned inside the pair of fulcrums; a load measurement step of positioning the indenter on the surface of the other chip and pressing against it to increase the load and measure the maximum load when the load suddenly drops from the increase; and the bond strength inspection method using the maximum load measured in the load measurement step as the bond strength.

[0008] In the peel start point forming step, it is preferable to form a pair of grooves or a pair of dividing triggers in one chip corresponding to one wafer supported by the pair of fulcrums, at a distance smaller than the distance between the pair of fulcrums, so as not to reach the other chip corresponding to the other wafer, thereby forming peel start points between the one chip and the other chip.Furthermore, it is preferable to inspect the bonding strength of any chip among the chips generated in the chip generating step in the load measuring step. [Effects of the Invention]

[0009] The bonding strength inspection method of the present invention is a bonding strength inspection method for inspecting the bonding strength of a bonded wafer obtained by bonding one wafer to another wafer, and includes the following steps: a preparation step of preparing a three-point bending tester including a pair of fulcrums and an indenter positioned at the center of the pair of fulcrums and pressing the center of a chip supported by the pair of fulcrums; a chip production step of dividing the bonded wafer to generate individual chips; and a peeling start step of forming a groove or a dividing trigger in one chip corresponding to one of the wafers supported by the pair of fulcrums, the groove or dividing trigger not reaching the other chip corresponding to the other wafer, thereby forming a peeling start point between one chip and the other chip. The bonding strength measurement method includes a forming step, a mounting step in which the surface of one chip is mounted so that the peeling start point is positioned inside the pair of fulcrums, a load measurement step in which the indenter is positioned on the surface of the other chip and pressed to increase the load and measure the maximum load when the load suddenly drops from the increased load, and the maximum load measured in the load measurement step is used as the bonding strength. This allows the internal bonding strength of the bonded wafer to be detected and highly accurate bonding strength data to be generated that can be fed back to the bonding step in which two wafers are bonded to form a bonded wafer, and bonding conditions can be found under which the entire surfaces of the wafers are bonded with an appropriate bonding strength. As a result, the problem of inadequate bonding of the entire surfaces of the wafers, resulting in partial peeling and the production of non-functional device chips when the bonded wafer is divided, can be solved. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an overall perspective view of a three-point bending tester. [Figure 2] 1 is a perspective view illustrating an embodiment of a bonding process to produce a bonded wafer. [Figure 3] 1 is a perspective view illustrating an embodiment of a chip production process. FIG. [Figure 4] (a) is a perspective view showing an example in which the peel start point formation process is performed using a cutting device; (b) is a partially enlarged cross-sectional view showing an example of a groove formed by the peel start point formation process shown in (a); (c) is a partially enlarged cross-sectional view showing another example of a groove formed by the peel start point formation process shown in (a). [Figure 5] 1(b) is a perspective view showing an example in which the peeling start point forming step is carried out by a laser processing device, and FIG. 1(a) is a partially enlarged cross-sectional view showing the peeling start points (modified layers) formed by the laser processing device shown in FIG. [Figure 6] FIG. 10 is a perspective view showing an embodiment of a placing step. [Figure 7] FIG. 10 is a perspective view showing an embodiment of a load measuring step. [Figure 8] 8(a) to 8(d) are partially enlarged side views showing the change in the shape of the tip in the load measurement process shown in FIG. 7. [Figure 9] FIG. 1 is a conceptual diagram showing the Z position of the indenter and the change in load measured by a load measuring instrument. [Figure 10] FIG. 2 is a plan view of a bonded wafer divided by a chip generating process. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a bonding strength inspection method configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0012] (preparation process) 1 shows a three-point bending tester 1 prepared in a preparation step in the bonding strength testing method of this embodiment. The three-point bending tester 1 shown in the figure is a tester for measuring the three-point bending strength of a chip to be tested, which will be described later, and includes a fulcrum block 9 having fulcrum rails 9b extending in the Y direction that support the underside of the chip at two fulcrums 9a spaced apart in the X direction indicated by the arrow X in the figure, and an indenter 7a extending in the Y direction that is positioned at the center of the fulcrum block 9, more specifically, midway between the two fulcrums 9a, and moves from above to below (in the Z direction) to apply a load to the chip supported by the fulcrum block 9. The device includes an indenter block 7, a moving means 8 that moves the indenter 7a in the Z direction to bring it into contact with and away from a tip supported by a fulcrum block 9, a load measuring instrument 4 that measures the load generated when the indenter 7a comes into contact with the tip supported by the fulcrum block 9, and a position measuring instrument 5 that measures the movement position of the indenter 7a in the Z direction (Z position), and the load measured by the load measuring instrument 4 and the Z position of the indenter 7a measured by the position measuring instrument 5 are transmitted to and stored in control means 20 constituted by a computer. The indenter 7a has a tip that forms an acute angle when viewed in cross section, and the indenter block 7 including the indenter 7a and the fulcrum block 9 are both made of a material having high hardness (cemented carbide, SUS, etc.).

[0013] The three-point bending tester 1 is supported so as to be movable up and down relative to a support wall 2 disposed vertically on an apparatus frame (not shown). A pair of guide rails 2a, 2a extending in the Z direction (up and down direction) are provided on the inner surface of the support wall 2. A movable base 3 including a load measuring instrument 4 and a position measuring instrument 5 is attached to the guide rails 2a, 2a.

[0014] The movable base 3 is provided with guided grooves that slidably engage with the guide rails 2a, 2a arranged on the support wall 2, and is equipped with a moving means 8 that moves the movable base 3 in the up and down direction. The moving means 8 is equipped with a male threaded rod 8b that is arranged in the Z direction parallel to the guide rails 2a, 2a and rotatably supported on the support wall 2, a pulse motor 8a for rotating the male threaded rod 8b, and a female threaded block (not shown) that is attached to the movable base 3 and threadedly engages with the male threaded rod 8b. The male threaded rod 8b is driven in the forward and reverse directions by the pulse motor 8a to move the movable base 3 in the Z direction, and the indenter 7a is brought into contact with and separated from the tip supported by the fulcrum block 9.

[0015] A fixed block 6, to which an indenter block 7 is attached, is disposed at the lower end of the load measuring instrument 4, which is disposed below the movable base 3. The fixed block 6 includes a support portion 6a into which the plate-shaped indenter block 7, which has an indenter 7a extending in the Y direction, is inserted, a rotation shaft 6b, which extends in the X direction and is inserted into a through-hole (not shown) in the indenter block 7, to rotatably attach the indenter block 7 within the support portion 6a, and set bolts 6c, 6c, disposed on both sides of the rotation shaft 6b and screwed into the fixed block 6 to fix the indenter block 7. The indenter block 7 is fixed by rotating the set bolts 6c, 6c forward so that their tips abut against the side surface of the indenter block 7 within the support portion 6a. The set bolts 6c, 6c are rotated forward to loosen the set bolts 6c, 6c to release the fixation of the indenter block 7, allowing the indenter block 7 to be rotated about the rotation shaft 6a, thereby allowing fine adjustment of the angle of the tip of the indenter 7a.

[0016] The position measuring device 5 is equipped with a linear scale 5a arranged along the Z-axis direction on the support wall 2, and a read head 5b arranged on the movable base 3 side for reading the graduations of the linear scale 5a. The position measuring device 5 can measure the position (Z position) of the indenter 7a when the moving means 8 is operated to move the movable base 3 in the Z-axis direction, and transmits this to the control means 20.

[0017] The above-described three-point bending tester 1 is merely one example of a three-point bending tester that can be used in the present invention. For example, unlike the position measuring device 5 described above, which is configured with a linear scale 5a disposed on the support wall 2 and a read head 5b disposed on the movable base 3, the position of the indenter 7a can be measured by counting the number of drive pulses of the pulse motor 8a constituting the moving means 8 using the control means when the movable base 3 is moved. Alternatively, a light irradiating means for irradiating light in the Z direction can be disposed on the movable base 3, which moves in the Z direction, and the light can be reflected in the Z direction on the support wall 2 or on the device frame (not shown) to generate reflected light. A light receiving unit for receiving the reflected light can be disposed to measure the optical path length, thereby measuring the moving position of the indenter 7a disposed on the movable base 3. This can serve as the position measuring device in the three-point bending tester 1 of this embodiment.

[0018] As described above, according to the preparation process of this embodiment, a three-point bending tester 1 is prepared, which includes a pair of fulcrums 9a, 9a and an indenter 7a positioned at the center of the pair of fulcrums 9a, 9a and pressing against the center of the chip supported by the pair of fulcrums 9a, 9a.

[0019] (Chip production process) A chip producing step is carried out in which the bonded wafer obtained by bonding two wafers by a desired bonding method and under desired bonding conditions is divided to produce individual chips that will be test pieces. Note that the chip producing step described below may be carried out before the above preparation step is carried out.

[0020] In the chip production process described below, to divide the bonded wafer into individual chips to be inspected, a bonding process is first performed to prepare a bonded wafer W by bonding two wafers together. To perform the bonding process, a first wafer 10A and a second wafer 10B are first prepared, as shown in FIG. 2. The first wafer 10A is, for example, a silicon (Si) wafer having a diameter of 300 mm and a thickness of 300 μm. The first wafer 10A has a front surface 10Aa and a back surface 10Ab. A plurality of devices 12A are formed on the front surface 10Aa, partitioned by planned division lines 14A. The second wafer 10B also has a similar configuration to the first wafer 10A. Although not shown, the second wafer 10B is a silicon wafer having a front surface 10Ba, facing downward in the figure, on which a plurality of devices are formed, partitioned by planned division lines. The bonding step of bonding the first wafer 10A and the second wafer 10B is carried out using a predetermined bonding method and under predetermined bonding conditions, and an example of the bonding step will be described below.

[0021] First, the surface 10Aa of the first wafer 10A and the surface 10Ba of the second wafer 10B are wet-cleaned to form hydroxyl (OH) groups on the surfaces, thereby adhering them together. This creates an interface between the first and second wafers 10A and 10B via Si-OH-OH-Si bonds, resulting in a temporary bond between the two wafers. The bonded wafers W are then heated to a predetermined temperature (e.g., approximately 1000°C) for a certain period of time to convert the bond at the interface between the first and second wafers 10A and 10B into Si-O-Si bonds (siloxane bonds), thereby increasing the bonding strength of the bonded wafers W. This completes the bonding process. The planned dividing line 14A of the first wafer 10A and the planned dividing line (not shown) of the second wafer 10B are bonded so that they coincide with each other when facing each other.

[0022] The bonded wafer W obtained by carrying out the above-described bonding process is divided into individual chips by a cutting device 30 (only a portion of which is shown) shown in FIG. 3. The cutting device 30 includes a chuck table (not shown) that suction-holds the bonded wafer W, and cutting means 32 that cuts the bonded wafer W held on the chuck table. The chuck table is rotatable and includes an X-axis moving means (not shown) that feeds the chuck table in the direction indicated by the arrow X in the figure. The cutting means 32 includes a spindle housing 33 that rotatably holds a spindle 34 disposed in the Y-axis direction indicated by the arrow Y in the figure, an annular cutting blade 35 held at the tip of the spindle 34, and a blade cover 36 that covers the cutting blade 35. The cutting means 32 also includes a Y-axis moving means (not shown) that indexes and feeds the cutting blade 35 in the Y-axis direction. The spindle 34 is rotationally driven by a spindle motor (not shown), causing the cutting blade 35 to rotate in the direction indicated by the arrow R1.

[0023] To divide the bonded wafer W into individual chips, first, the bonded wafer W is placed on a chuck table of the cutting device 30 with one wafer (the first wafer 10A in this embodiment) facing upward and the other wafer (the second wafer 10B in this embodiment) facing downward, and held by suction. In this embodiment, the bonded wafer W is positioned in advance in an opening Fa of an annular frame F that has the opening Fa capable of accommodating the bonded wafer W, and the frame F and the second wafer 10B side of the bonded wafer W are attached with protective tape T, so that the bonded wafer W is supported by the frame F. Next, an image of the bonded wafer W held on the chuck table is captured by an alignment means including an infrared camera equipped with an infrared irradiation means and an infrared receiving element (not shown), and the predetermined dividing line 14A of one of the wafers (first wafer 10A) is aligned in the X-axis direction, and the cutting blade 35 is aligned with the dividing line 14A.

[0024] Next, the cutting blade 35, rotated at high speed in the direction indicated by arrow R1, is positioned at a position corresponding to the division line 14A aligned in the X-axis direction, and is caused to cut from the side of one wafer (first wafer 10A). At the same time, the chuck table is processed and fed in the X-axis direction to cut the division line of the other wafer (second wafer 10B) as well, thereby forming division grooves 100 for dividing the bonded wafer W. Furthermore, the cutting blade 35 of the cutting means 32 is indexed and fed to a position adjacent in the Y-axis direction to the division groove 100 formed as described above and corresponding to the division line 14A where no division groove 100 has been formed, and is caused to cut from above in the same manner as described above, thereby forming division grooves 100. By repeating these steps, division grooves 100 for dividing the bonded wafer W are formed along all of the division lines 14A along the X-axis direction.

[0025] Next, the chuck table is rotated 90 degrees, and the direction perpendicular to the direction in which the division grooves 100 were previously formed is aligned with the X-axis direction. The cutting process described above is then performed on the positions corresponding to all of the division lines 14A newly aligned with the X-axis direction, forming division grooves 100 along all of the division lines 14A of one wafer (first wafer 10A) of the bonded wafers W. As a result, as shown enlarged at the bottom of FIG. 3, the bonded wafer W is divided into chips 12W, each of which is formed by bonding one chip 10Ac corresponding to one wafer (first wafer 10A) and another chip 10Bc corresponding to the other wafer (second wafer 10B). The chip 12W has a rectangular shape with sides measuring 15 mm x 15 mm in plan view, for example. This completes the chip production process.

[0026] (Peeling starting point formation process) As described above, after the chip generating step is performed to generate the chip 12W, a peel start point forming step is performed in which a pair of grooves or a pair of dividing triggers are formed in one chip 10Ac supported by a pair of supports 9a, 9a formed on the support block 9 of the three-point bending tester 1, the pair of grooves being spaced apart from the other chip 10Bc at a distance smaller than the distance between the pair of supports 9a, 9a, thereby forming peel start points between the one chip 10Ac and the other chip 10Bc. The peel start point forming step of this embodiment will be described in more detail below.

[0027] The chips 12W produced by the above-described chip production process are transferred to a cutting device 40 (only a portion of which is shown) shown in FIG. 4(a). A holding device (not shown) holds one of the chips 10Ac corresponding to one of the wafers with the chips facing upward, and a cutting device 41 is positioned above the chips 12W. The cutting device 41 has a cutting blade 44 attached to the tip of a rotary shaft 42 driven by a spindle motor (not shown). To form the peeling start points, two planned cutting positions are set at intervals (e.g., 9 mm) smaller than the interval (e.g., 12 mm) between the pair of fulcrums 9a, 9a of the fulcrum block 9. Next, the cutting blade 44 of the cutting device 40 is rotated in the direction indicated by arrow R2, positioned at the planned cutting positions, and cut and fed from above, moving the chips 12W in the direction indicated by arrow R3. As a result, as shown in FIG. 4(b), a groove 110 having a depth of, for example, 200 μm is formed, which does not reach the other chip 10Bc corresponding to the other wafer (second wafer 10B). Note that the "groove that does not reach the other chip 10Bc corresponding to the other wafer (second wafer 10B)" also includes a groove 112 formed by cutting to remove substantially all of the planned processing position of one chip 10Ac, as shown in FIG. 4(c). When forming such a groove 112, the cutting is also performed so as not to reach the other chip 10Bc. Note that the above-mentioned peeling start point forming step may be performed by a cutting device 30 shown in FIG. 3.

[0028] In the peeling start point forming step of the present invention, instead of forming grooves 110 or 112 in the chip 12W using the above-described cutting device 40, a laser processing device 50 (only a portion of which is shown) shown in FIG. 5(a) may be used to irradiate a laser beam LB onto one chip 10Ac of the chip 12W to form a pair of dividing triggers. To form the dividing triggers, the chip 12W is first transferred to the illustrated laser processing device 50, and one chip 10Ac corresponding to one wafer is held facing upward by a holding means (not shown). In the laser processing device 50, two planned processing positions for laser processing are set on the chip 12W at a distance (e.g., 9 mm) smaller than the distance (12 mm) between the pair of fulcrums 9a, 9a of the fulcrum block 9. Next, laser beam application means 52, which applies a laser beam LB having a wavelength that is transparent to one of the chips 10Ac, is positioned above the chip 12W, and the focal point is positioned inside the intended processing position on one of the chips 10Ac, and the laser beam is applied, and the chip 12W is moved in the direction shown by arrow R4 to form a modified layer 120. In this way, laser processing is performed to form the modified layer 120 along the two intended processing positions, and as shown in Figure 5(b), a modified layer 120 that will trigger division is formed inside one of the chips 10Ac.

[0029] The method for forming a pair of grooves spaced apart by a distance smaller than the distance between the pair of fulcrums 9a, 9a of the fulcrum block 9 and not reaching the other chip 10Bc is not limited to the form of formation by the cutting device 40 described above. For example, grooves equivalent to the grooves 110, 112 shown in Figures 4(b) and 4(c) can be formed by setting the wavelength of the laser beam LB irradiated by the laser beam application means 52 to a wavelength that is absorbed by one chip 10Ac, positioning the focal point on the surface of one chip 10Ac, and irradiating the laser beam LB along the two planned processing positions. In the steps described below, it is assumed that a pair of grooves 110, 110 that serve as peel start points are formed in the chip 12W in the peel start point forming step.

[0030] (Placement process) Once the grooves 110, 110 that will serve as peel start points have been formed in the chip 12W as described above, the chip 12W is transferred to the three-point bending tester 1, and as shown in FIG. 6, the chip 12W is placed with the surface on one chip 10Ac side facing downward and the grooves 110, 110 positioned inside and in the direction along the pair of fulcrums 9a, 9a of the fulcrum block 9. At this time, the fulcrum block 9 is placed so that the midpoint between the pair of fulcrums 9a, 9a of the fulcrum block 9 coincides with the midpoint of the grooves 110, 110 that will form the peel start points. This completes the placement process.

[0031] (Load measurement process) After the above-described placement step is performed, the moving means 8 of the three-point bending tester 1 described with reference to Fig. 1 is operated to lower the fixed block 6 at a slow, constant speed in the direction indicated by arrow R5 as shown in Fig. 7, positioning and pressing the indenter 7a of the indenter block 7 against the other tip 10Bc, and measuring the Z position of the indenter 7a with the position measuring instrument 5 and the load with the load measuring instrument 4. Figs. 8(a) to 8(d) show the state from when the indenter 7a of the indenter block 7 contacts the other tip 10Bc of the tip 12W until one tip 10Ac is peeled off from the groove 110 described above as the peel starting point, and Fig. 9 shows the change in load corresponding to the Z position, with the horizontal axis representing the measurement value of the position measuring instrument 5 corresponding to the Z position of the indenter 7a shown in Figs. 8(a) to 8(d) and the vertical axis representing the measurement value of the load measured by the load measuring instrument 4.

[0032] By lowering the indenter 7a as described above, the indenter 7a comes into contact with the other tip 10Bc of the tip 12W as shown in Fig. 8(a), and from that position, the load begins to be measured by the load measuring instrument 4 as shown in Fig. 9(a). After the indenter 7a comes into contact with the tip 12W, the indenter 7a is lowered in the direction shown by arrow R5 in Fig. 8(b) to press the tip 12W, which causes the tip 12W to begin to deform as shown. Until peeling occurs starting from the groove 110, the loads of both the one tip 10Ac and the other tip 10Bc are applied to the indenter 7a, and the load measured by the load measuring instrument 4 increases in proportion to the amount of descent of the Z position of the indenter 7a as shown in Fig. 9(b).

[0033] In the state shown in FIG. 8(b), if the indenter 7a is further lowered in the direction indicated by arrow R5 to press and deform the chip 12W, the bond strength between the chip 10Ac and the other chip 10Bc constituting the chip 12W reaches its limit. As shown in FIG. 8(c), a crack 130 occurs in one groove 110, which is the starting point of the peeling. Peeling of the one chip 10Ac begins from the groove 110 where the crack 130 occurred. The position shown in FIG. 9(c) is the Z position of the indenter 7a where this peeling began. In the illustrated embodiment, the load measured at this Z position is 31 N, which is the maximum load measured in this test. Then, by further lowering the indenter 7a, the area of ​​the peeled portion 132 of the one chip 10Ac expands as shown in FIG. 8(d), and the measured load value decreases as the peeling progresses as shown in FIG. 9(d). After the peeling has progressed to a certain extent, the load applied to the indenter 7a by the other tip 10Bc increases, the load measured by the load measuring instrument 4 starts to increase, and the load measurement in the load measurement step is completed.

[0034] The control means 20 measures the maximum load of the load measured at the start of peeling based on the Z position of the indenter 7a and the load measurement value measured in the load measurement process. In the embodiment described above, the Z position of the indenter 7a reaches 148 μm, and a maximum load of 31 N is measured at the position where peeling starts from the groove 110. This 31 N is recorded as an index indicating the bonding strength of the currently inspected chip 12W. Note that substantially similar results can be obtained even when the load measurement process is performed using a chip 12W on which the groove 112 shown in FIG. 4(c) and the modified layer 120 shown in FIG. 5(b) are formed as the peeling start point in the peeling start point formation process.

[0035] By performing the above-described peel start point forming step, placement step, and load measurement step on all chips 12W generated by the above-described chip generation step, it is possible to accurately inspect the bonding strength of the entire bonded wafer W. However, the above-described bonding strength inspection method does not necessarily have to be performed on all chips 12W generated by the chip generation step. In that case, for example, as shown in FIG. 10 , among the chips formed by dividing the bonded wafer W in the chip generation step, chip (1) at the center of the bonded wafer W, chips (2) to (5) at the periphery, and chips (6) to (9) at intermediate positions between the central chip (1) and the peripheral chips (2) to (5) may be selected, and the bonding strength inspection method including the above-described peel start point forming step, placement step, and load measurement step may be performed. In this way, chips to be inspected for bonding strength are selected from the entire bonded wafer W, allowing for appropriate evaluation of the bonding strength.

[0036] The peeling initiation points formed by the present invention are not necessarily limited to a pair as described above, but may be a single groove or a single dividing trigger. In this case, for example, only one of the pair of grooves 110, 110 (or 112, 112) described with reference to FIG. 4 may be formed, or only one of the modified layers 120, 120 formed as a pair of dividing triggers described with reference to FIG. 5 may be formed. However, when forming the above-mentioned groove or dividing trigger as a peeling initiation point, forming it in a pair as described with reference to FIGS. 4 and 5 allows the stress from the indenter 7a to be applied uniformly to the tip 12W, which is preferable for measuring the load using the three-point bending tester 1.

[0037] According to the above-described embodiment, it is possible to detect the internal bond strength of a bonded wafer, generate highly accurate data on the bond strength that can be fed back to the bonding process of bonding two wafers to form a bonded wafer, and find bonding conditions under which the entire surfaces of the wafers are bonded with an appropriate bond strength. As a result, it is possible to solve the problem of inadequate bonding of the entire surfaces of the wafers, resulting in partial peeling, which, when the bonded wafer is divided into individual device chips, results in the production of non-functional device chips and low yields. [Explanation of symbols]

[0038] 1: 3-point bending tester 2: Support wall 3: Mobile base 4: Load measuring instrument 5: Position measuring instrument 5a: Linear scale 5b: Read head 6: Fixed block 6a: Support part 6b: Rotation axis 6c: Set bolt (fixing device) 7: Indenter block 7a:Indenter 8. Transportation 8a: Pulse motor 8b: Male threaded rod 9: Support block 9a:Fulcrum 9b: Support rail 10A: First wafer (one wafer) 10Aa: Surface 10Ab: Back 10Ac: One chip 12A:Device 12W: Chip 14A: Planned division line 10B: Second wafer 10 (the other wafer) 10Ba: Surface 10Bb: Back side 10Bc: The other chip 20: Control means 30: Cutting equipment 32: Cutting means 35: Cutting blade 40: Cutting equipment 44: Cutting blade 50: Laser processing equipment 52: Laser beam irradiation means 100: Dividing groove 110, 112: Groove 120: Modified layer 130: Crack 132: Peeling part

Claims

1. A bonding strength inspection method for inspecting a bonding strength of a bonded wafer obtained by bonding one wafer to another wafer, comprising: a preparation step of preparing a three-point bending tester including a pair of fulcrums and an indenter positioned at the center of the pair of fulcrums and pressing against the center of the chip supported by the pair of fulcrums; a chip producing step of dividing the bonded wafer into individual chips; a separation starting point forming step of forming a groove or a dividing trigger in one chip corresponding to one of the wafers supported by the pair of fulcrums, the groove or dividing trigger not reaching the other chip corresponding to the other wafer, to form a separation starting point between the one chip and the other chip; a placing step of placing a surface of one of the chips so that the peeling start point is positioned inside the pair of fulcrums; a load measuring step of positioning the indenter on the surface of the other tip, pressing the indenter against the surface of the other tip, increasing the load, and measuring the maximum load when the load suddenly decreases from the increased load; In the load measuring step, the maximum load measured is used as the bond strength.

2. In the peeling starting point forming step, 2. A bonding strength inspection method as described in claim 1, wherein a pair of grooves or a pair of dividing triggers are formed in one chip corresponding to one wafer supported by the pair of fulcrums, at a distance smaller than the distance between the pair of fulcrums, and do not reach the other chip corresponding to the other wafer, thereby forming a peeling starting point between one chip and the other chip.

3. 2. The bonding strength inspection method according to claim 1, wherein the bonding strength of any one of the chips produced in the chip production step is inspected in the load measurement step.

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