Wafer inspection method and inspection device

Abstract

To provide a wafer inspection method and inspection device which can inspect a void formed on an interface of a laminated wafer without contamination of the wafer.SOLUTION: A wafer inspection method comprises: a laminated wafer formation step 101 of laminating a plurality of wafers to form a laminated wafer; an irradiation step 102 of irradiating the surface of the laminated wafer with light at a prescribed incident angle from a light source; an imaging step 103 of imaging reflection light of light with which the surface of the laminated wafer is irradiated in the irradiation step 102 to form a photographed image in which irregularities generated on the surface of the laminated wafer is reflected; and a determination step 104 of determining the state of a void on an interface of wafers of the laminated wafer from the photographed image obtained in the imaging step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wafer inspection method and an inspection apparatus. [Background technology]

[0002] In recent years, as semiconductor devices have become smaller and thinner, technologies have been developed to bond semiconductor devices together without using bonding wires to increase integration in three dimensions. Among these, the WoW (Wafer on Wafer) method, which stacks multiple wafers via an adhesive layer, has the advantage of being highly productive because it allows wafers to be processed in one go. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-302967 [Patent Document 2] Japanese Patent Application Publication No. 05-288732 Summary of the Invention [Problem to be solved by the invention]

[0004] When wafers are bonded together, so-called voids, such as the inclusion of air bubbles or particles, may occur (see Patent Document 1). Devices in areas where voids occur are deemed defective, so inspection is required after bonding. However, inspection using SAT (Scanning Acoustic Tomography) requires observation underwater, which raises concerns about wafer contamination (see Patent Document 2).

[0005] The present invention has been made in consideration of the above problems, and its object is to provide a wafer inspection method and inspection apparatus that can inspect voids formed at the interface of a bonded wafer without contaminating the wafer. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a wafer inspection method of the present invention includes a bonded wafer forming step of bonding a plurality of wafers together to form a bonded wafer, and exposed an irradiation step of irradiating a surface of the bonded wafer with light from a light source at a predetermined angle of incidence; exposed The reflected light of the light irradiated onto the surface is imaged, and the bonded wafer exposed an imaging step of forming an image in which unevenness occurring on the surface is reflected; The exposed surface of the bonded wafer and a determining step of determining a state of voids at the interface between the wafers of the bonded wafer from the captured image. The bonded wafer is formed by bonding at least three wafers together, and in the determining step, the layer in which the void occurs is determined based on at least one of brightness, contrast, and blur amount of an uneven area corresponding to the void in the captured image. It is characterized by the following.

[0007] Wafer inspection method of the present invention teeth , The method comprises a bonded wafer forming step of bonding a plurality of wafers together to form a bonded wafer; an irradiation step of irradiating an exposed surface of the bonded wafer with light from a light source at a predetermined angle of incidence; an imaging step of imaging reflected light of the light irradiated onto the exposed surface of the bonded wafer in the irradiation step to form an image that reflects irregularities generated on the exposed surface of the bonded wafer; and a determination step of determining a state of voids at an interface between wafers of the bonded wafer from the image of the exposed surface of the bonded wafer obtained in the imaging step, The bonded wafer is formed by bonding at least three wafers together, and in the determining step, the captured image This is a trained model constructed by machine learning so that when input is made, it outputs the layer where the void occurs. The layer in which the void occurs may be determined.

[0008] In the wafer inspection method of the present invention, the bonded wafer forming step includes: exposed A grinding step may be included to thin the surface to a finish thickness.

[0009] The inspection device of the present invention also includes: At least threeAn inspection apparatus for inspecting a bonded wafer formed by bonding a plurality of wafers together, the apparatus comprising: a mounting table for mounting the bonded wafer; a light source for irradiating an exposed surface of the bonded wafer mounted on the mounting table with light at a predetermined angle of incidence; an imaging unit for capturing an image including light reflected from the exposed surface of the bonded wafer from the light source; and a control unit having a determination unit for detecting irregularities generated on the exposed surface of the bonded wafer from the captured image and determining a state of voids at an interface between wafers of the bonded wafer based on the irregularities on the exposed surface. The determining unit determines the layer in which the void occurs based on at least one of brightness, contrast, and blur amount of the concave-convex region corresponding to the void in the captured image. It is characterized by the following.

[0010] The inspection device of the present invention is an inspection device for inspecting a bonded wafer formed by bonding at least three wafers together, comprising: a mounting table for mounting the bonded wafer; a light source for irradiating light at a predetermined angle of incidence onto the exposed surface of the bonded wafer mounted on the mounting table; an imaging unit for capturing an image including light reflected from the exposed surface of the bonded wafer from the light source irradiated onto the exposed surface of the bonded wafer; and a control unit having a determination unit for detecting irregularities generated on the exposed surface of the bonded wafer from the captured image and determining the state of voids at the interface between the wafers of the bonded wafer based on the irregularities on the exposed surface, wherein the determination unit determines the layer in which the voids occur using a trained model configured by machine learning so as to output the layer in which the voids occur when the captured image is input.

[0011] In addition, in the inspection device of the present invention, The control unit further includes a moving unit that moves the imaging unit and the mounting table relatively, and the control unit has a memory section that stores a plurality of captured images of a predetermined region of the bonded wafer while moving the imaging unit and the bonded wafer relatively, and an image forming section that combines the plurality of captured images stored in the memory section to form an entire image of the entire surface of the bonded wafer. You may do so.

[0013] In addition, in the inspection device of the present invention, the judgment unit may judge the cause of the void using a trained model constructed by machine learning so as to output the cause of the void when the captured image is input. [Effects of the Invention]

[0014] The present invention makes it possible to inspect for voids formed at the interface of bonded wafers without contaminating the wafers. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a flowchart showing the flow of a wafer inspection method according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing one state of the wafer forming step shown in FIG. [Figure 3] FIG. 3 is a schematic diagram showing a state after FIG. 2 in the wafer forming step shown in FIG. [Figure 4]FIG. 4 is a schematic diagram showing a state after FIG. 3 in the wafer forming step shown in FIG. [Figure 5] FIG. 5 is a cross-sectional view showing a state of the bonded wafer after the wafer forming step shown in FIG. [Figure 6] FIG. 6 is a partially enlarged view of FIG. [Figure 7] FIG. 7 is a schematic diagram showing an example of the configuration of an inspection device that performs the irradiation step, the imaging step, and the determination step shown in FIG. [Figure 8] FIG. 8 is a diagram showing an example of a captured image captured in the imaging step shown in FIG. [Figure 9] FIG. 9 is a diagram showing an example of an entire image formed from a plurality of captured images captured in the imaging step shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made within the scope of the gist of the present invention.

[0017] [Embodiment] A wafer inspection method according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flow chart showing the flow of the wafer inspection method according to the embodiment. The wafer inspection method according to the embodiment includes a wafer formation step 101, an irradiation step 102, an imaging step 103, and a determination step 104.

[0018] (Wafer Formation Step 101) FIG. 2 is a schematic diagram showing one state of the wafer forming step 101 shown in FIG. 1. FIG. 3 is a schematic diagram showing one state of the wafer forming step 101 shown in FIG. 1 after FIG. 2. FIG. 4 is a schematic diagram showing one state of the wafer forming step 101 shown in FIG. 1 after FIG. 3. FIG. 5 is a cross-sectional view showing the state of the bonded wafer 2 after the wafer forming step 101 shown in FIG. 1. FIG. 6 is a partially enlarged view of FIG. 5. FIG. 6 is an enlarged view of the inside of the frame in FIG. 5.

[0019] The wafer formation step 101 is a step in which a plurality of wafers 10 are bonded together to form bonded wafers 1 and 2. The wafer 10 is a disk-shaped semiconductor wafer, an optical device wafer, or the like, whose substrate is made of silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like. The wafer 10 has a plurality of devices formed thereon, each of which has electrode pads and through-electrodes connected to the electrode pads, in regions defined by a plurality of intersecting planned division lines.

[0020] 2 to 4, one wafer 10 is bonded to another wafer 10-1 to form a bonded wafer 1 consisting of the two wafers 10 and 10-1. In the wafer formation step 101, wafers 10-2, 10-3, 10-4, and 10-5 may be further bonded to the bonded wafer 1 in sequence to form a multi-layered bonded wafer 2 as shown in FIGS.

[0021] As shown in FIG. 2, in the wafer formation step 101, first, the top surface 11-1 of the wafer 10-1 is attached to one surface of the support wafer 30 via a temporary adhesive 31. The temporary adhesive 31 is an adhesive whose adhesive strength decreases when an external stimulus is applied. The external stimulus includes, for example, ultraviolet light irradiation or heating. The temporary adhesive 31 may be a liquid resin adhesive applied to one surface of the support wafer 30, or may be a resin sheet adhesive having adhesive layers on both sides.

[0022] Next, in the wafer formation step 101, an adhesive layer 20-1 made of an adhesive is formed on the lower surface 12-1 of the wafer 10-2 supported on the support wafer 30. The adhesive layer 20-1 may be a liquid resin adhesive applied to the lower surface 12-1 of the wafer 10-1, or may be a resin sheet adhesive having adhesive layers on both sides.

[0023] In the wafer formation step 101, the adhesive layer 20-1 formed on the lower surface 12-1 of the wafer 10-1 is then faced downward, facing the upper surface 11 of the wafer 10 with a gap therebetween. Next, as shown in Fig. 3, the wafer 10-1 is bonded to the wafer 10 via the adhesive layer 20-1 so that the adhesive layer 20-1 formed on the lower surface 12-1 of the wafer 10-1 is in close contact with the upper surface 11 of the wafer 10. As a result, the upper surface 11 of the wafer 10 and the lower surface 12-1 of the wafer 10-2 are bonded together via the adhesive layer 20-1, and a bonded wafer 1 consisting of the two wafers 10 and 10-1 is formed.

[0024] 4, in the wafer formation step 101, an external stimulus is applied to the temporary adhesive 31 to reduce the adhesive strength of the temporary adhesive 31, and the support wafer 30 is removed from the wafer 10-1. Next, the exposed surface (upper surface 11-1) of the wafer 10-1 of the bonded wafer 1 is ground to thin it to a finishing thickness. That is, the wafer formation step 101 may include a grinding step.

[0025] In the grinding step, a grinding device 35 grinds the exposed surface (upper surface 11-1) of the uppermost wafer (wafer 10-1) of the bonded wafer 1 held on the holding surface of a chuck table 36. In the example shown in FIG. 4 , the grinding device 35 includes a chuck table 36, a spindle 37 which is a rotating shaft member, a grinding wheel 38 attached to the lower end of the spindle 37, and a grinding stone 39 attached to the lower surface of the grinding wheel 38. The grinding wheel 38 rotates on an axis of rotation parallel to the axis of the chuck table 36.

[0026] In the grinding step, first, the lower surface 12 of the bottom wafer 10 of the bonded wafer stack 1 is suction-held on the holding surface of the chuck table 36. Next, while the chuck table 36 is rotated about its axis, the grinding wheel 38 is rotated about its axis. Next, grinding water is supplied to the processing point, and the grinding stone 39 of the grinding wheel 38 is brought closer to the chuck table 36 at a predetermined feed rate. As a result, the exposed surface (top surface 11-1) of the top wafer (wafer 10-1) of the bonded wafer stack 1 is ground by the grinding stone 39, thinning it down to a predetermined finishing thickness.

[0027] 5, when forming a multi-layered bonded wafer 2, wafers 10-2, 10-3, 10-4, and 10-5 are bonded one after another via adhesive layers 20-2, 20-3, 20-4, and 20-5, respectively. Specifically, an adhesive layer 20-2 is formed on the lower surface 12-2 of wafer 10-2, and wafer 10-2 is bonded to wafer 10-1 via adhesive layer 20-2 so that adhesive layer 20-2 is in close contact with upper surface 11-1 of wafer 10-1. An adhesive layer 20-3 is formed on the lower surface 12-3 of wafer 10-3, and wafer 10-3 is bonded to wafer 10-2 via adhesive layer 20-3 so that adhesive layer 20-3 is in close contact with upper surface 11-2 of wafer 10-2. An adhesive layer 20-4 is formed on the lower surface 12-4 of the wafer 10-4, and the wafer 10-4 is bonded to the wafer 10-3 via the adhesive layer 20-4 so that the adhesive layer 20-4 is in close contact with the upper surface 11-3 of the wafer 10-3. An adhesive layer 20-5 is formed on the lower surface 12-5 of the wafer 10-5, and the wafer 10-5 is bonded to the wafer 10-4 via the adhesive layer 20-5 so that the adhesive layer 20-5 is in close contact with the upper surface 11-4 of the wafer 10-4. As a result, wafers 10-1, 10-2, 10-3, 10-4 and 10-5 are stacked in five stages on the wafer 10, and a bonded wafer 2 is formed consisting of six wafers 10, 10-1, 10-2, 10-3, 10-4 and 10-5 with the top surface 11-5 of the wafer 10-5 exposed.

[0028] As shown in FIG. 6, in the bonded wafer 2, voids 21 and 22 occur in adhesive layers 20-1, 20-2, 20-3, 20-4, and 20-5 (hereinafter referred to as adhesive layer 20 unless otherwise specified). The voids 21 and 22 include a nucleated void 22 containing a particle 23. In the portion shown in FIG. 6, specifically, voids 21-2 and 21-3 occur in the adhesive layer 20-2 between the wafers 10-1 and 10-2 and the adhesive layer 20-3 between the wafers 10-2 and 10-3. In addition, a nucleated void 22-5 containing a particle 23 occurs in the adhesive layer 20-5 between the wafers 10-4 and 10-5.

[0029] (Inspection device 50) Here, a description will be given of the configuration of the inspection device 50 that performs the irradiation step 102, the imaging step 103, and the determination step 104 in the embodiment. Fig. 7 is a schematic diagram showing an example of the configuration of the inspection device 50 that performs the irradiation step 102, the imaging step 103, and the determination step 104 shown in Fig. 1.

[0030] 7 shows an example in which an inspection apparatus 50 inspects a bonded wafer 3 formed by bonding three wafers 10, 10-1, and 10-2 together and stacking them in three layers. The following description of the irradiation step 102, the imaging step 103, and the determination step 104 will be given using the bonded wafer 3 stacked in three layers as an example. The bonded wafer 3 has an annular frame 40 attached thereto, and a tape 41 having a diameter larger than the outer diameter of the bonded wafer 3 is attached to the lower surface 12 of the wafer 10, and is supported within an opening of the frame 40. The inspection apparatus 50 includes a mounting table 51, a light source 60, an imaging unit 70, a moving unit 80, and a control unit 90.

[0031] The mounting table 51 has a mounting surface 52 on which the bonded wafer 3 is mounted. The mounting surface 52 has a disk shape made of, for example, porous ceramic or the like. In the embodiment, the mounting surface 52 is a flat surface parallel to the horizontal direction. The mounting surface 52 is connected to a vacuum suction source, for example, via a vacuum suction path. The mounting table 51 suction-holds the bonded wafer 3 mounted on the mounting surface 52.

[0032] A plurality of clamps 53 are arranged around the periphery of the mounting table 51 to clamp the frame 40 that supports the bonded wafer 3. The mounting table 51 is rotated by a rotation unit 54 about an axis parallel to the Z-axis direction. The mounting table 51 is supported by a movement unit 80, which will be described later, so as to be movable in the X-axis direction and the Y-axis direction. The mounting table 51 may be supported by the movement unit 80 via the rotation unit 54 so as to be movable in the X-axis direction and the Y-axis direction. The mounting table 51 may be supported by the movement unit 80 so as to be movable in the Z-axis direction. The mounting table 51 may be supported by the movement unit 80 via the rotation unit 54 so as to be movable in the Z-axis direction.

[0033] The light source 60 irradiates the exposed surface of the bonded wafer 3 placed on the mounting table 51 with light 61. The light source 60 irradiates the bonded wafer 3 with the light 61 at a predetermined angle of incidence 62. In the example shown in FIG. 7 , the exposed surface of the bonded wafer 3 is the top surface 11-2 of the wafer 10-2. The light 61 incident on the bonded wafer 3 at the predetermined angle of incidence 62 is reflected by the top surface 11-2 and enters the imaging unit 70 as reflected light 63.

[0034] In the embodiment, the light source 60 is an LD (laser diode) with a wavelength of 635 nm, but the present invention is not limited to a specific type or position, and may include, for example, an incandescent light bulb or an LED. The light 61 emitted from the light source 60 may be parallel or non-parallel. When the light 61 is parallel, it is preferable to combine the light source 60 with an optical element such as a lens. When the light 61 is non-parallel, it is preferable that the light source 60 has a small light-emitting area and can be regarded as a point light source.

[0035] The imaging unit 70 captures an image (such as the captured image 71 shown in FIG. 8 ) including light 61 irradiated from the light source 60 onto the exposed surface (upper surface 11-2) of the bonded wafer 3, and reflected light 63 from the exposed surface. The imaging unit 70 includes, for example, a digital camera that combines an imaging element such as a CMOS (Complementary Metal Oxide Semiconductor) with an optical element such as a lens. In the embodiment, the imaging area captured by the imaging unit 70 is approximately 20 mm × 20 mm or 15 mm × 15 mm. The imaging unit 70 outputs the captured image to the control unit 90. The imaging unit 70 receives reflected light 63 of the light 61 incident on the bonded wafer 3 placed on the mounting table 51, and therefore the position of the imaging unit 70 relative to the light source 60 can be fixed.

[0036] The moving unit 80 moves the imaging unit 70 and the mounting table 51 relatively. More specifically, the moving unit 80 moves the mounting table 51 and an area where the light source 60 irradiates the bonded wafer 3 mounted on the mounting table 51 and where the area is imaged by the imaging unit 70, relative to each other. The moving unit 80 includes, for example, an X-axis direction moving unit and a Y-axis direction moving unit that move the mounting table 51 in the X-axis direction and the Y-axis direction. The moving unit 80 may include, for example, a Z-axis direction moving unit that moves the mounting table 51 in the Z-axis direction. The moving unit 80 may include, for example, an X-axis direction moving unit, a Y-axis direction moving unit, and a Z-axis direction moving unit that move both the light source 60 and the imaging unit 70 in the X-axis direction, the Y-axis direction, and the Z-axis direction.

[0037] The control unit 90 controls each of the above-mentioned components of the inspection device 50, causing the inspection device 50 to perform an inspection operation on the bonded wafer 3. The control unit 90 is a computer including an arithmetic processing device as a calculation means, a storage device as a storage means, and an input / output interface device as a communication means.

[0038] The arithmetic processing device includes, for example, a microprocessor such as a CPU (Central Processing Unit). The storage device has a memory such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The arithmetic processing device performs various calculations based on predetermined programs stored in the storage device. The arithmetic processing device outputs various control signals to the above-mentioned components via the input / output interface device according to the calculation results, thereby controlling the inspection device 50. The control unit 90 has a determination unit 91, a storage unit 92, and an image forming unit 93.

[0039] The determination unit 91 detects irregularities occurring on the exposed surface (upper surface 11-2) of the bonded wafer 3 from a captured image (see, for example, captured image 71 shown in FIG. 8 ) captured by the imaging unit 70. Based on the detected irregularities on the exposed surface, the determination unit 91 determines the state of voids 21 and 22 at the interface between the wafers 10, 10-1, and 10-2 of the bonded wafer 3. That is, the determination unit 91 detects the voids 21 and 22 from the upper surface 11-2 side of the bonded wafer 3 by the so-called magic mirror principle.

[0040] The determination unit 91 determines the layer in which the voids 21 and 22 occur based on at least one of the brightness, contrast, and blur amount of the uneven areas in the captured image that correspond to the voids 21 and 22. The layer in which the voids 21 and 22 occur refers to the adhesive layers 20-1 and 20-2 between the wafers 10 and 10-1 and the wafers 10-1 and 10-2 in which the voids 21 and 22 occur.

[0041] The determination unit 91 may determine the layer in which the voids 21, 22 occur using a trained model configured by machine learning so as to output the layer in which the voids 21, 22 occur when a captured image is input. The determination unit 91 may determine the cause of the voids 21, 22 occurrence using a trained model configured by machine learning so as to output the cause of the voids 21, 22 when a captured image is input. The cause of the voids 21, 22 occurrence includes, for example, particles 23 or air entrapment, i.e., causes caused by inappropriate bonding conditions, etc.

[0042] The storage unit 92 stores the captured images of the predetermined region of the bonded wafer 3. At this time, the control unit 90 causes the imaging unit 70 to capture a plurality of captured images of the predetermined region of the bonded wafer 3 while causing the moving unit 80 to move the imaging unit 70 and the bonded wafer 3 placed on the mounting table 51 relatively.

[0043] At this time, the control unit 90 controls the imaging unit 70 and the moving unit 80 so that there is no blank space between the imaging area of ​​a captured image and the imaging area of ​​an adjacent captured image. The storage unit 92 stores a plurality of captured images captured by the imaging unit 70. The storage unit 92 stores the captured images, for example, by linking the captured images with coordinate information indicating the imaging area of ​​the captured image.

[0044] The image forming unit 93 combines the plurality of captured images stored in the storage unit 92 to form an entire image (for example, see the entire image 72 shown in FIG. 9 ) of the entire surface of the bonded wafer 3. The image forming unit 93 combines the plurality of captured images based on, for example, the coordinate information of each of the plurality of captured images stored in the storage unit 92.

[0045] (Irradiation step 102) The irradiation step 102 is a step in which light 61 is irradiated from the light source 60 onto the upper surface 11-2 of the bonded wafer 3 at a predetermined incident angle 62. In the irradiation step 102 of the embodiment, the control unit 90 shown in FIG. 7 causes the light source 60 to irradiate the light 61. The light 61 irradiated from the light source 60 is reflected by the upper surface 11-1 of the bonded wafer 3 placed on the mounting table 51, and enters the imaging unit 70.

[0046] (Image capture step 103) Fig. 8 is a diagram showing an example of a captured image 71 captured in the imaging step 103 shown in Fig. 1. The imaging step 103 is a step of capturing an image of reflected light 63 of light 61 irradiated onto the upper surface 11-2 of the bonded wafer 3 in the irradiation step 102, and forming a captured image 71 that reflects the unevenness generated on the upper surface 11-2 of the bonded wafer 3.

[0047] 7 causes the imaging unit 70 to capture an image of reflected light 63 of light 61 reflected by the upper surface 11-2 of the bonded wafer 3. The captured image 71 captured by the imaging unit 70 is an image 71 that reflects irregularities occurring on the upper surface 11-2 of the bonded wafer 3. As shown in FIG. 8, voids 21-1, 21-2, 22-1, 22-2, etc. are captured in the captured image 71.

[0048] 9 is a diagram showing an example of an entire image 72 formed from a plurality of captured images 71 captured in the imaging step 103 shown in Fig. 1. In the imaging step 103, the control unit 90 causes the imaging unit 70 to capture a plurality of captured images 71 of a predetermined region of the bonded wafer 3 while causing the moving unit 80 to relatively move the imaging unit 70 and the bonded wafer 3 placed on the mounting table 51. Next, the storage unit 92 of the control unit 90 stores the captured images 71 of the predetermined region of the bonded wafer 3. Next, the image forming unit 93 of the control unit 90 combines the plurality of captured images 71 stored in the storage unit 92 to form an entire image 72 of the entire surface of the bonded wafer 3.

[0049] (Decision step 104) The determining step 104 is a step of determining the state of the voids 21 and 22 at the interface (adhesive layers 20-1 and 20-2) between the wafers 10, 10-1 and 10-2 of the bonded wafer 3 from the captured image 71 obtained in the imaging step 103. In the determining step 104 of the embodiment, the determining unit 91 of the control unit 90 shown in Fig. 7 detects irregularities generated on the exposed surface (upper surface 11-2) of the bonded wafer 3 from the captured image 71. The determining unit 91 determines the state of the voids 21 and 22 at the interface between the wafers 10, 10-1 and 10-2 of the bonded wafer 3 based on the detected irregularities on the exposed surface.

[0050] In the determination step 104, the layer in which the voids 21 and 22 occur is determined based on, for example, at least one of the brightness, contrast, and blur amount of the uneven areas corresponding to the voids 21 and 22 in the captured image 71. That is, the voids 21 and 22 occurring in the upper layer of the bonded wafer 3 have a large contrast, and the voids 21 and 22 occurring in the lower layer have a small contrast.

[0051] For example, the voids 21-1 and 22-1 in the captured image 71 have low contrast and can therefore be determined to be voids 21 and 22 generated in the adhesive layer 20-1 between the wafer 10 and wafer 10-1, which is the lower layer. Also, for example, the voids 21-2 and 22-2 in the captured image 71 have high contrast and can therefore be determined to be voids 21 and 22 generated in the adhesive layer 20-2 between the wafer 10-1 and wafer 10-2, which is the upper layer.

[0052] In the determination step 104, the layer in which the voids 21 and 22 occur and the cause of their occurrence may be determined using a trained model constructed by machine learning. This allows for accurate determination even when the number of layers in the bonded wafer 3 is large.

[0053] As described above, the wafer inspection method and inspection device 50 according to the embodiment irradiates the surface (upper surface 11-2) of the bonded wafer 3 with light 61, captures an image of the reflected light 63, and determines the state of the voids 21, 22 at the interface between the wafers based on the surface irregularities reflected in the captured image 71. That is, irregularities are formed on the surface of the bonded wafer 3 corresponding to the positions where the voids 21, 22 have occurred at the interface. Based on the brightness, contrast, or blur of the captured image, the surface irregularities, i.e., the planar positions of the voids 21, 22, are detected and the layer in which they occur is determined.

[0054] According to the embodiment, the voids 21, 22 formed at the interface of the wafer can be confirmed without immersion in water, and therefore, the voids 21, 22 can be inspected without contaminating the wafer. Furthermore, even in the multilayer laminated bonded wafers 2, 3, it is possible to confirm in which layer the voids 21, 22 exist by a single observation, which eliminates the need to inspect each time lamination is performed, and thus has the advantage of reducing the number of inspection steps.

[0055] 5 and 6, the wafer inspection method of the embodiment can be performed when the thicknesses of the thinned wafers 10-1, 10-2, 10-3, 10-4, and 10-5 are 5 μm or less and the thicknesses of the adhesive layers 20-1, 20-2, 20-3, 20-4, and 20-5 are 5 μm or less. The wafer inspection method of the embodiment can be performed on a bonded wafer having a thickness of 100 μm or less.

[0056] The present invention is not limited to the above-described embodiment, and can be implemented in various modifications without departing from the gist of the present invention.

[0057] For example, in the wafer formation step 101, in the embodiment, after the wafers are bonded together, the exposed surface of the bonded wafer is ground to thin it, but in the present invention, the wafers may or may not be thinned before bonding.

[0058] Furthermore, although the imaging unit 70 directly receives the reflected light 63 in the embodiment, in the present invention it may also capture a projected image of the reflected light 63 projected onto a screen.

[0059] In the embodiment, light 61 from light source 60 is irradiated onto the upper surface of the bonded wafer, the lower surface of which is placed on mounting table 51. However, for example, when the surface of the wafer on which no pattern is formed is located on the lower surface, the outer periphery of the bonded wafer may be supported, the lower surface may be exposed, and light 61 from light source 60 may be irradiated onto the lower surface. In this case, reflected light 63 reflected on the lower surface is imaged, and the state of voids 21, 22 is determined from the image that reflects the unevenness generated on the lower surface. That is, in the present invention, the target on which light 61 is irradiated and the reflected light 63 is imaged may be the exposed surface of the bonded wafer, i.e., the surface of the wafer. In this specification, the "surface" of the wafer refers to the surface that faces outward relative to the interior, and is not affected by whether or not a pattern is formed. [Explanation of symbols]

[0060] 1, 2, 3 Bonded wafer 10 wafers 11 Top surface (surface, exposed surface) 12 Bottom side 20 Adhesive layer 21, 22 Void 23 Particles 10-1, 10-2, 10-3, 10-4, 10-5 wafers 11-1, 11-2, 11-3, 11-4, 11-5 Top 12-1, 12-2, 12-3, 12-4, 12-5 Bottom side 20-1, 20-2, 20-3, 20-4, 20-5 Adhesive layer (interface) 21-1, 21-2, 21-3, 22-1, 22-2, 22-5 Void 50 Inspection equipment 51 Loading table 60 light source 61 light 62 angle of incidence 63 Reflected light 70 Imaging unit 71 Captured images 72 Full image 80 Mobile Units 90 Control Unit 91 Judgment Department 92 Memory Department 93 Image Formation Department

Claims

1. A wafer inspection method, comprising: a bonded wafer forming step of bonding a plurality of wafers together to form a bonded wafer; an irradiation step of irradiating the exposed surface of the bonded wafer with light from a light source at a predetermined incident angle; an imaging step of imaging reflected light of the light irradiated onto the exposed surface of the bonded wafer in the irradiation step, and forming an image reflecting unevenness generated on the exposed surface of the bonded wafer; a determining step of determining a state of voids at an interface between wafers of the bonded wafer from a captured image of the exposed surface of the bonded wafer obtained in the imaging step; Equipped with The bonded wafer is formed by bonding at least three wafers together, In the determination step, A wafer inspection method, characterized in that a layer in which the void occurs is determined based on at least one of brightness, contrast, and blur amount of an uneven area corresponding to the void in the captured image.

2. A wafer inspection method, comprising: a bonded wafer forming step of bonding a plurality of wafers together to form a bonded wafer; an irradiation step of irradiating the exposed surface of the bonded wafer with light from a light source at a predetermined incident angle; an imaging step of imaging reflected light of the light irradiated onto the exposed surface of the bonded wafer in the irradiation step, and forming an image reflecting unevenness generated on the exposed surface of the bonded wafer; a determining step of determining a state of voids at an interface between wafers of the bonded wafer from a captured image of the exposed surface of the bonded wafer obtained in the imaging step; Equipped with The bonded wafer is formed by bonding at least three wafers together, In the determination step, A wafer inspection method characterized by determining the layer in which the void occurs using a trained model constructed by machine learning so as to output the layer in which the void occurs when the captured image is input.

3. The bonded wafer forming step includes: a grinding step of grinding the exposed surfaces of the wafers to a finishing thickness before or after bonding the plurality of wafers together; 3. The wafer inspection method according to claim 1 or 2.

4. An inspection device for inspecting a bonded wafer formed by bonding together at least three wafers, comprising: a mounting table on which the bonded wafer is placed; a light source that irradiates light onto the exposed surface of the bonded wafer placed on the placement table at a predetermined angle of incidence; an imaging unit that captures an image including light irradiated from the light source onto the exposed surface of the bonded wafer and reflected by the exposed surface; a control unit having a determination unit that detects irregularities occurring on the exposed surface of the bonded wafer from the captured image and determines a state of voids at the interface between the wafers of the bonded wafer based on the irregularities on the exposed surface; Equipped with The determination unit An inspection apparatus that determines a layer in which the void occurs based on at least one of brightness, contrast, and blur amount of an uneven area corresponding to the void in the captured image.

5. An inspection device for inspecting a bonded wafer formed by bonding together at least three wafers, comprising: a mounting table on which the bonded wafer is placed; a light source that irradiates light onto the exposed surface of the bonded wafer placed on the placement table at a predetermined angle of incidence; an imaging unit that captures an image including light irradiated from the light source onto the exposed surface of the bonded wafer and reflected by the exposed surface; a control unit having a determination unit that detects irregularities occurring on the exposed surface of the bonded wafer from the captured image and determines a state of voids at the interface between the wafers of the bonded wafer based on the irregularities on the exposed surface; Equipped with The determination unit An inspection device characterized in that when the captured image is input, the layer in which the void occurs is determined using a trained model constructed by machine learning so as to output the layer in which the void occurs.

6. a moving unit that moves the imaging unit and the mounting table relative to each other; The control unit a storage unit that stores a plurality of captured images of a predetermined region of the bonded wafer while moving the imaging unit and the bonded wafer relatively; an image forming unit that combines the plurality of captured images stored in the storage unit to form an entire image of the entire surface of the bonded wafer; characterized in that it has 6. The inspection device according to claim 4 or 5.

7. The determination unit The cause of the void is determined using a trained model configured by machine learning so as to output the cause of the void when the captured image is input. The inspection device according to any one of claims 4 to 6.

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