Inspection equipment

Abstract

The present invention provides an inspection device that inspects the internal condition of an object being measured from its back surface. [Solution] The inspection device comprises a holding means, an ultrasonic vibration generating means 40, an ultrasonic vibration capturing means 70, and an image generating means 110. The ultrasonic vibration generating means comprises an oscillator 41 that emits a pulsed laser beam LB1, and a fiber bundle 43 composed of multiple rings in which multiple optical fibers are arranged in multiple rings of different diameters that form concentric circles. The length of the optical fibers constituting the fiber bundle is formed to increase from the configuration of a large ring with a large diameter that forms the concentric circles to the configuration of a small ring with a small diameter that forms the concentric circles. The pulsed laser beam is first irradiated onto the upper surface of the object to be measured from the optical fibers constituting the large ring, and then the pulsed laser beam is gradually irradiated onto the upper surface of the object to be measured from the optical fibers constituting the small ring with a time difference, thereby focusing the ultrasonic vibration at a desired internal position of the object to be measured.

Description

[Technical Field]

[0001] This invention relates to an inspection device for inspecting the internal state of an object to be measured. [Background technology]

[0002] A wafer, on which multiple devices such as ICs and LSIs are divided along planned division lines and formed on its surface, is then divided into individual device chips using dicing equipment and laser processing equipment, and used in electrical devices such as mobile phones and personal computers.

[0003] Furthermore, when dividing a wafer on which devices sensitive to contamination, such as MEMS, CCDs, and CMOS, are formed on the surface into individual device chips, the surface of the wafer is held in place with protective tape, and the division lines formed on the surface are detected from the back side of the wafer using an infrared camera, and dicing or laser processing is performed from the back side (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-075955 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in wafers where a metal film is coated on the back surface, infrared light does not penetrate, and there is a problem in that infrared cameras cannot detect the planned division lines formed on the front surface from the back surface of the wafer.

[0006] Furthermore, in the case of bonded wafers, where two wafers are joined together by siloxane bonding or the like to improve the functionality of the device chip, there is a problem in that minute voids are formed at the bonding surface due to bonding defects, resulting in unstable device chip quality.

[0007] The present invention has been made in view of the above facts, and its main technical problem is to provide an inspection device that can inspect the condition of the inside and surface of an object to be measured from the back surface, for example, the division line formed on the surface, or in the case of a bonded wafer, the condition of the bonded surface, regardless of whether or not a metal film is coated on the back surface of the object to be measured. [Means for solving the problem]

[0008] To solve the above-mentioned main technical problems, the present invention provides an inspection device for inspecting the internal state of an object to be measured, comprising: a holding means for holding the object to be measured and having a holding surface defined by X and Y coordinates; an ultrasonic vibration generating means for irradiating the upper surface of the object to be measured held by the holding means with a pulsed laser beam to generate ultrasonic vibrations inside the object to be measured; an ultrasonic vibration capturing means for capturing the ultrasonic vibrations that appear on the upper surface of the object to be measured; and an image generating means for generating an image based on the information captured by the ultrasonic vibration capturing means, wherein the ultrasonic vibration generating means comprises an oscillator that emits a pulsed laser beam and the pulsed laser beam emitted by the oscillator irradiated onto the object to be measured held by the holding means An inspection device is provided, comprising a fiber bundle composed of multiple rings, in which multiple optical fibers leading to the upper surface of a target object are arranged in multiple rings of different diameters that form concentric circles, wherein the length of the optical fibers constituting the fiber bundle is formed to increase from the configuration of the large ring with a large diameter that forms the concentric circle to the configuration of the small ring with a small diameter that forms the concentric circle, and pulsed laser beams are first irradiated onto the upper surface of the object to be measured from the optical fibers constituting the large ring, and then pulsed laser beams are gradually irradiated onto the upper surface of the object to be measured from the optical fibers constituting the small ring with a time difference, thereby focusing ultrasonic vibrations at a desired internal position of the object to be measured.

[0009] Let point P be the desired internal position where ultrasonic vibrations generated by pulsed laser beams irradiated onto the upper surface of the object under test in a ring shape with a time difference from the optical fibers constituting the fiber bundle converge directly below the center of the concentric circles. Let H1 be the distance from the large ring light irradiated onto the object under test from the optical fibers constituting the large ring to point P. Let Hx be the distance from the small ring light irradiated onto the object under test from the optical fibers constituting the small ring to point P. Let V be the speed at which the vibrations propagate through the object under test. (H1-Hx) / V=t It is preferable to generate a time difference t, defined by the length of the optical fiber, and focus the ultrasonic vibrations to point P.

[0010] Furthermore, if L is the length of the optical fiber constituting the large ring, c is the speed of light, and n is the refractive index of the optical fiber, then the length Lx of the optical fiber constituting the small ring corresponding to Hx is: Lx = L + c × t ÷ n It can be determined by this method.

[0011] The holding means comprises an X-axis moving part that moves in the X-axis direction and a Y-axis moving part that moves in the Y-axis direction, and the ultrasonic vibration capturing means comprises a capturing oscillator that emits a capturing laser beam for capturing ultrasonic vibrations, a half mirror that splits the capturing laser beam emitted by the capturing oscillator into a first direction and a second direction, a return mirror that is arranged in the first direction straight ahead from the half mirror and generates a reference laser beam by reflecting the capturing laser beam back to the half mirror, an ultrasonic capturing optical fiber arranged in the center of the fiber bundle that guides the capturing laser beam guided in the second direction by the half mirror to the upper surface of the object to be measured, and a light-receiving element that receives interference light between the return light of the capturing laser beam guided by the ultrasonic capturing optical fiber that has captured ultrasonic vibrations and the reference laser beam, and preferably the image generation means generates an image using the intensity of the interference light received by the light-receiving element as the information captured by the ultrasonic vibration capturing means. Furthermore, the fiber handle is preferably equipped with a fiber length adjustment section and can be replaced as appropriate depending on the position in which ultrasonic vibrations are focused inside the object being measured. Moreover, the object being measured is a bonded wafer in which two wafers are joined together, and the bonded surface of the bonded wafer can be inspected. [Effects of the Invention]

[0012] The inspection apparatus of the present invention comprises: a holding means for holding an object to be measured and having a holding surface defined by X and Y coordinates; an ultrasonic vibration generating means for irradiating the upper surface of the object to be measured held by the holding means with a pulsed laser beam to generate ultrasonic vibrations inside the object to be measured; an ultrasonic vibration capturing means for capturing the ultrasonic vibrations that appear on the upper surface of the object to be measured; and an image generating means for generating an image based on the information captured by the ultrasonic vibration capturing means, wherein the ultrasonic vibration generating means comprises an oscillator that emits a pulsed laser beam, and a fiber bundle composed of multiple rings in which a plurality of optical fibers that guide the pulsed laser beam emitted by the oscillator to the upper surface of the object to be measured held by the holding means are arranged in a plurality of rings of different diameters that form concentric circles, the length of the optical fibers constituting the fiber bundle is such that the larger diameter ring constituting the concentric circles The configuration is formed to be longer from the large ring to the small ring with a smaller diameter that makes up the concentric circles. A pulsed laser beam is first irradiated onto the top surface of the object to be measured from the optical fiber making up the large ring, and then pulsed laser beams are gradually irradiated onto the top surface of the object to be measured from the optical fiber making up the small ring with a time difference, focusing ultrasonic vibrations at a desired position inside the object to be measured. This makes it possible to position the point where the ultrasonic vibrations are focused at the location inside the object to be inspected and inspect the internal state. Even when infrared light does not penetrate due to a metal film coating on the back side of the object to be measured, and the state of the surface cannot be detected from the back side with an infrared camera, it becomes possible to detect the object to be measured, such as division lines formed on the surface of a wafer, or voids formed on the bonding surface of a bonded wafer. Furthermore, the present invention is applicable not only when a metal film is coated on the top surface of the object to be measured, but also when there is no metal film coating, and it becomes possible to inspect the internal state of the object to be measured without irradiating it with infrared light. [Brief explanation of the drawing]

[0013] [Figure 1] This is an overall perspective view of the inspection apparatus of this embodiment. [Figure 2] This is a perspective view showing a bonded wafer being inspected by the inspection device shown in Figure 1. [Figure 3] It is a perspective view showing a state in which the bonded wafer shown in FIG. 2 is supported by a frame. [Figure 4] It is a block diagram showing the configuration of an ultrasonic vibration generation means and an ultrasonic vibration capture means disposed in the inspection apparatus shown in FIG. 1. [Figure 5] It is a bottom view showing the end face of the fiber bundle of the ultrasonic vibration generation means attached to the inspection apparatus shown in FIG. 1. [Figure 6] It is a perspective view and a side view showing a state in which the object to be measured is irradiated with a pulsed laser beam from the ultrasonic vibration generation means and a capture laser beam from the ultrasonic vibration capture means.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of an inspection apparatus configured based on the present invention will be described in detail with reference to the accompanying drawings.

[0015] FIG. 1 shows an overall perspective view of an inspection apparatus 1 of the present embodiment. The inspection apparatus 1 shown in FIG. 1 includes a holding means 20 having a holding surface 25a that holds an object to be measured and is defined by X and Y coordinates, an ultrasonic vibration generation means 40 that irradiates a pulsed laser beam onto the upper surface of the object to be measured held by the holding means 20 to generate ultrasonic vibration inside the object to be measured, an ultrasonic vibration capture means 70 (to be described in detail later based on FIG. 4) that captures the ultrasonic vibration appearing on the upper surface of the object to be measured, and an image generation means 110 (to be described in detail later) that generates an image based on the information captured by the ultrasonic vibration capture means 70.

[0016] Figure 2 shows a bonded wafer W, which is an example of an object to be measured whose internal state is inspected by the inspection apparatus 1 described above. The bonded wafer W is a wafer formed by bonding a first wafer 10A and a second wafer 10B together, as shown in the figure. The first wafer 10A is, for example, a silicon (Si) wafer with a diameter of 200 mm and a thickness of 700 μm, with multiple devices 12A formed on the surface 10Aa, demarcated by division lines 14A, and notches 10Ac indicating the crystal orientation formed on the outer circumference. The first wafer 10A has a surface 10Aa and a back surface 10Ab.

[0017] The second wafer 10B has a similar configuration to the first wafer 10A. Although not shown in the figure, on the surface 10Ba facing downwards in the figure, multiple devices corresponding to the device 12A of the first wafer 10A are formed and partitioned by predetermined division lines. It is a silicon wafer with a diameter of 200 mm and a thickness of 700 μm. The second wafer 10B also has notches 10Bc that indicate the crystal orientation.

[0018] In this embodiment, the first wafer 10A and the second wafer 10B of the bonded wafer W are joined together, for example, as shown in the figure, by aligning the notches 10Ac and 10Bc of the first wafer 10A and the surface 10Ba of the second wafer 10B, and forming a bonded surface 16 by siloxane bonding. Siloxane bonding is a Si-O-Si bond in which silicon (Si) and oxygen (O) are alternately bonded. Since the first wafer 10A and the second wafer 10B are joined by bonding them together and subjecting them to heat treatment, a strong bond is maintained even at high temperatures.

[0019] When inspecting the internal state of the bonded wafer W described above using the inspection device 1 shown in Figure 1, for example, an annular frame F having an opening Fa capable of accommodating the bonded wafer W, as shown in Figure 3, is prepared. The bonded wafer W, with the back surface 10Ab of the first wafer 10A facing upwards, is positioned in the center of the opening Fa, and the frame F and the second wafer 10B side of the bonded wafer W are attached together with adhesive tape T to form a single unit. If the bonding is not properly performed on the bonding surface 16 of the bonded wafer W, voids (cavities) may occur, which degrades the quality of the resulting device chip. Therefore, the inspection device 1 of this embodiment is used to perform an inspection and detect the presence or absence of such voids. The inspection device 1 of this embodiment also detects the planned division line 14A formed on the surface 10Aa of the first wafer 10A and the planned division line (not shown) formed on the surface 10Ba of the second wafer 10B that are facing each other on the bonding surface 16.

[0020] Furthermore, the object to be inspected by the inspection device 1 of this embodiment is not limited to the bonded wafer W described above, but may be a single wafer, and the inspection device 1 of this embodiment can also be used to detect the division line formed from the back side to the front side of the single wafer. In addition, even if a metal film is coated on the surface of the object to be inspected, for example, although it is not formed on the bonded wafer W described above, the inspection device 1 of this embodiment can be used to inspect the internal state of the object to be inspected.

[0021] Returning to Figure 1, the description of the inspection device 1 continues. The holding means 20 includes a rectangular X-axis movable plate 21 mounted on the base 2 so as to be movable in the X-axis direction indicated by arrow X in the figure, a rectangular Y-axis movable plate 22 mounted on the X-axis movable plate 21 so as to be movable in the Y-axis direction perpendicular to the X-axis direction indicated by arrow Y in the figure, a cylindrical support column 23 fixed to the upper surface of the Y-axis movable plate 22, and a rectangular cover plate 26 fixed to the upper end of the support column 23. A circular chuck table 25 is provided on the cover plate 26, extending upward through an elongated hole formed on the cover plate 26. The chuck table 25 is configured to be rotatable by a rotational drive means (not shown).

[0022] The holding surface 25a, defined by the X and Y coordinates that constitute the upper surface of the chuck table 25, is formed from a porous material and is permeable, and is connected to a suction means (not shown) by a channel passing through the inside of the support column 23. The chuck table 25 is also provided with a plurality of clamps 27 (four in the illustrated embodiment) for gripping an annular frame F that supports the bonded wafer W, which is the object to be measured, via adhesive tape T.

[0023] The moving mechanism 30 is disposed on the base 2 and includes an X-axis moving unit 31 that feeds the holding mechanism 20 in the X-axis direction and a Y-axis moving unit 32 that indexes and feeds the Y-axis movable plate 22 in the Y-axis direction. The X-axis moving unit 31 converts the rotational motion of the pulse motor 33 into linear motion via a ball screw 34 and transmits it to the X-axis movable plate 21, causing the X-axis movable plate 21 to move back and forth in the X-axis direction along the guide rails 2a, 2a on the base 2. The Y-axis moving unit 32 converts the rotational motion of the pulse motor 35 into linear motion via a ball screw 36 and transmits it to the Y-axis movable plate 22, causing the Y-axis movable plate 22 to move back and forth in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. Although not shown in the diagram, the X-axis moving unit 31, the Y-axis moving unit 32, and the chuck table 25 are equipped with position detection means (not shown), which accurately detect the X coordinate, Y coordinate, and circumferential rotation angle position of the chuck table 25, and this position information is sent to the control means 100 (shown in the diagram). Based on this position information, the control means 100 issues instruction signals which control the rotation drive means of the X-axis moving unit 31, the Y-axis moving unit 32, and the chuck table 25 (not shown), thereby positioning the chuck table 25 at a desired position on the base 2.

[0024] As shown in Figure 1, a frame 4 is erected to the side of the moving means 30. The frame 4 comprises a vertical wall portion 4a disposed on the base 2, and a horizontal wall portion 4b extending horizontally from the upper end of the vertical wall portion 4a. Inside the horizontal wall portion 4b of the frame 4 is an optical system including an ultrasonic vibration generating means 40, the ultrasonic vibration capturing means 70 (not shown in Figure 1) described above, and an alignment means. The end face 43d of the fiber bundle 43 constituting the ultrasonic vibration generating means 40 and the imaging camera 60 constituting the alignment means are exposed on the lower surface of the tip of the horizontal wall portion 4b.

[0025] In addition to the ultrasonic vibration generating means 40, ultrasonic vibration capturing means 70, and alignment means described above, a laser beam irradiation means may also be provided inside the tip of the horizontal wall portion 4b of the frame 4 of the inspection device 1. This means irradiates the bonded wafer W held by the holding means 20 with a laser beam of, for example, an absorbing wavelength to perform laser processing that forms a modified layer inside. Details regarding the laser beam irradiation means are omitted.

[0026] Figure 4 shows a block diagram illustrating the optical systems of the ultrasonic vibration generation means 40 and the ultrasonic vibration capture means 70. The ultrasonic vibration generation means 40 includes an oscillator 41 that emits a pulsed laser beam LB1 of a predetermined wavelength (e.g., 532 nm), and a fiber bundle 43 in which multiple optical fibers that guide the pulsed laser beam LB1 emitted by the oscillator 41 to the upper surface of the object to be measured (bonded wafer W) held by the holding means 20 are arranged in multiple rings of different diameters that form concentric circles, thereby forming a multi-ring structure.

[0027] The fiber bundle 43 includes an optical fiber length adjustment unit 42b that adjusts the length of each optical fiber constituting multiple rings of different diameters in the multiple ring (this will be described in detail later). The pulsed laser beam LB1 emitted from the oscillator 41 is received by a first connector 42a that receives the pulsed laser beam LB1 and is spectrally separated into multiple optical fibers constituting the fiber bundle 43. A first fiber bundle cable 43a that introduces the pulsed laser beam LB1 to the optical fiber length adjustment unit 42b is connected to the first connector 42a. The pulsed laser beam LB1 introduced into the optical fiber length adjustment unit 42b via the first connector 42a and the first fiber bundle cable 43a is introduced into the third fiber bundle cable 43c via the second fiber bundle cable 43b and the second connector 42c connected to the optical fiber length adjustment unit 42b, and is irradiated from the end face 43d of the third fiber bundle cable 43c to the back surface 10Ab of the bonded wafer W held on the chuck table 25 of the holding means 20. The gap between the end face 43d and the back surface 10Ab of the first wafer 10A of the bonded wafer W is set to, for example, 100 μm.

[0028] Figure 5 shows the end face 43d of the third fiber bundle cable 43c facing the object to be measured, which is held by the holding means 20. As shown in the figure, the end face 43d exposes the ends of a plurality of first optical fibers 441 (30 in the illustrated embodiment) that constitute the largest diameter ring (large ring) in the multi-ring described above, the ends of a plurality of second optical fibers 442 (24 in the illustrated embodiment) that are arranged inside the first optical fibers 441 and constitute the second largest diameter ring, the ends of a plurality of third optical fibers 443 (18 in the illustrated embodiment) that are arranged inside the second optical fibers 442 and constitute the third largest diameter ring, the ends of a plurality of fourth optical fibers 444 (12 in the illustrated embodiment) that are arranged inside the third optical fibers 443 and constitute the fourth largest diameter ring, and the ends of a plurality of fifth optical fibers 445 (6 in the illustrated embodiment) that are arranged inside the fourth optical fibers 444 and constitute the smallest diameter ring (small ring). Furthermore, the end of the capturing laser optical fiber 75, which constitutes the ultrasonic vibration capturing means 70 described later, is also exposed at the center of the end face 43d (this will be explained later).

[0029] As described above, the pulsed laser beam LB1 emitted from the oscillator 41 is spectrally separated into optical fibers 441 to 445 that constitute multiple rings (multi-rings) of different diameters. As shown in Figure 6, the pulsed laser beam LB1a transmitted by the first optical fiber 441, the pulsed laser beam LB1b transmitted by the second optical fiber 442, the pulsed laser beam LB1c transmitted by the third optical fiber 443, the pulsed laser beam LB1d transmitted by the fourth optical fiber 444, and the pulsed laser beam LB1e transmitted by the fifth optical fiber 445 are irradiated onto the back surface 10Ab of the first wafer 10A of the bonded wafer W, forming ring beams R1 to R5 corresponding to the diameters of the multiple rings that constitute the fiber handle 43 described above.

[0030] The length of each optical fiber constituting the multiple rings of the fiber bundle 43 is adjusted by the optical fiber length adjustment unit 42b described above, and is adjusted so that the length increases from the first optical fiber 441 which constitutes the largest ring with the largest diameter constituting the concentric circles, to the fifth optical fiber 445 which constitutes the smallest ring with the smallest diameter constituting the concentric circles. Specifically, the lengths of the optical fibers are adjusted to increase in the following order on the back surface 10Ab of the first wafer W: multiple first optical fibers 441 forming the largest diameter large ring light R1, multiple second optical fibers 442 forming the second largest diameter ring light R2, multiple third optical fibers 443 forming the third largest diameter ring light R3, multiple fourth optical fibers 444 forming the fourth largest diameter ring light R4, and multiple fifth optical fibers 445 forming the smallest diameter small ring light R5. The pulsed laser beam LB1a is first irradiated onto the upper surface of the object to be measured from the first optical fibers 441 forming the large ring light R1, and then the pulsed laser beam LB1e is irradiated from the fifth optical fibers 445 forming the small ring light R5, with the irradiation timing gradually delayed and irradiating the back surface 10Ab of the first wafer W with a time difference. The pulse width of the pulsed laser beam LB1 emitted by the ultrasonic vibration generation means 40 described above is, for example, 10 ns, the repetition frequency is 1 MHz, and the average output is 1 W.

[0031] The ultrasonic vibration capture means 70 of this embodiment is arranged to capture ultrasonic vibrations appearing on the back surface 10Ab of the first wafer 10A of the bonded wafer W, which is the object to be measured. As can be seen from Figure 4, the ultrasonic vibration capture means 70 of this embodiment includes a capture oscillator 71 that emits a capture laser beam LB2 for capturing ultrasonic vibrations, a half mirror 72 that splits the capture laser beam LB2 emitted by the capture oscillator 71 into a first direction D1 and a second direction D2, and a return ray that is arranged in the first direction D1, which is straight ahead from the half mirror 72, and generates a reference laser beam LB3 by reflecting the capture laser beam LB2 back to the half mirror 72. The ultrasonic vibration capture means 70 of this embodiment includes a mirror 73, an ultrasonic vibration capture optical fiber 75 that guides the capture laser beam LB4, which is branched by the half mirror 72 and guided in the second direction D2, to the back surface 10Ab of the first wafer 10A of the bonded wafer W, and a light-receiving element 76 that receives interference light LB6 between the return light LB5 of the capture laser beam LB4 guided by the ultrasonic vibration capture optical fiber 75 that has captured ultrasonic vibrations and the reference laser beam LB3. In this embodiment, a focusing lens 74 is disposed between the half mirror 72 and the ultrasonic vibration capture optical fiber 75. The ultrasonic vibration capturing optical fiber 75 is positioned in the center of the third fiber bundle cable 43c that constitutes the fiber bundle 43, and as described with reference to Figure 5, the end of the ultrasonic capturing fiber 75 on the chuck table 25 side is exposed at the center of the concentric circles of the multiple rings on the end face 43d of the fiber bundle cable 43c. The capturing oscillator 71 is, for example, a laser diode, and the wavelength of the capturing laser beam LB2 is, for example, 1550 nm, and the average output is set lower than that of the pulsed laser beam LB1, for example, 10 mW.

[0032] The image generation means 110 of this embodiment has an analyzer function that generates an image from the intensity of the interference light LB6 received by the light receiving element 76 and the X and Y coordinate information on the chuck table 25 irradiated by the capturing laser beam LB4, and displays it on the display means 50, and is configured as a control means 100 that controls each operating part of the inspection device 1 of this embodiment.

[0033] The inspection device 1 of this embodiment has a configuration that is generally as described above, and the functions and operation of the inspection device 1 will be described below with reference to the above-described figures.

[0034] Once the bonded wafer W, which is the object to be measured as shown in Figure 3, is prepared, it is placed on the chuck table 25 of the holding means 20, and the suction means (not shown) is activated to suck it in, and the frame F is held in place by the clamp 27. Once the bonded wafer W is held on the chuck table 25, the moving means 30 is activated to move the chuck table 25 to position it directly below the imaging camera 60 of the alignment means. Next, the imaging camera 60 images the bonded wafer W and detects the X and Y coordinates of a predetermined detection area on the bonded wafer W. Then, based on the information of the X and Y coordinates of the detection area, the chuck table 25 is moved to position the detection area of ​​the bonded wafer W directly below the end face 43d of the fiber bundle 43. Then, the oscillator 41 of the ultrasonic vibration generation means 40 described above is activated to generate a pulsed laser beam LB1, and as explained with reference to Figure 6, pulsed laser beams LB1a to LB1e are irradiated onto the detection area of ​​the first wafer 10A of the bonded wafer W, forming a plurality of ring lights R1 to R5.

[0035] In this embodiment, the fiber bundle 43 spectrally separates the pulsed laser beam LB1, and as shown in Figure 6, ring light R1 formed by the pulsed laser beam LB1a, ring light R2 formed by the pulsed laser beam LB1b, ring light R3 formed by the pulsed laser beam LB1c, ring light R4 formed by the pulsed laser beam LB1d, and ring light R5 formed by the pulsed laser beam LB1e are formed concentrically on the back surface 10Ab of the first wafer 10A with center C. The pulsed laser beam LB1a, which forms the largest ring light R1, is the first to reach the back surface 10Ab of the wafer 10 held on the chuck table 25. Subsequently, in order of the size of the formed ring light, the pulsed laser beam LB1b arrives with a time difference t1, then the pulsed laser beam LB1c arrives with a time difference t2, then the pulsed laser beam LB1d arrives with a time difference t3, and finally the pulsed laser beam LB1e arrives with a time difference t4. The time differences t1 to t4 (seconds) mentioned above are based on the arrival time of the first pulsed laser beam LB1a. In this embodiment, for the sake of explanation, the explanation is based on an example in which the pulsed laser beam LB1 is spectrally separated to correspond to ring light with five diameters, but the present invention is not limited to this, and spectral separation may be used to generate multiple ring light with even more diameters.

[0036] When the pulsed laser beams LB1a to LB1e that form the respective ring lights R1 to R5 reach the back surface 10Ab of the first wafer 10A, ultrasonic vibrations that propagate within the first wafer 10A are generated from each arrival point. By appropriately setting the time differences t1 to t4 when the respective pulsed laser beams LB1a to LB1e reach the back surface 10Ab of the first wafer 10A, as shown in FIG. 6, the ultrasonic vibrations that propagate within the first wafer 10A can be focused on the position P of the desired Z-axis coordinate Pz in the thickness direction of the first wafer 10A at the center C of each of the ring lights R1 to R5 formed on the back surface 10Ab of the first wafer 10A. In the present embodiment, in order to inspect the state near the bonding surface 16 between the first wafer 10A and the second wafer 10B, the position P is set to be near the bonding surface 16.

[0037] The procedure for appropriately setting the above-described time differences t1 to t4 is as follows, for example. The radii of the respective ring lights R1 to R5 formed on the back surface 10Ab of the first wafer 10A are values set by the arrangement of the optical fibers 441 to 445 that form the multi-ring of the fiber bundle 43 described above, and are set to be radii a1 to a5, for example, as shown in FIG. 6. Then, in the thickness direction of the first wafer 10A from the center C of the ring lights R1 to R5, when the Z-axis coordinate (depth) from the center C of the ring lights R1 to R5 on the back surface 10Ab of the first wafer 10A to the desired position P where the operator wants to focus the ultrasonic vibrations generated by the pulsed laser beams LB1a to LB1e is Pz, the distances H1 to H5 (m) from each of the ring lights R1 to R5 on the back surface 10Ab of the first wafer 10A to the position P are calculated by the following equations. H1=(a1 2 +Pz 2 ) 1 / 2 H2=(a2 2 +Pz 2 ) 1 / 2 H3=(a3 2 +Pz 2 ) 1 / 2 H4=(a4 2 +Pz 2 ) 1 / 2 H5=(a5 2 +Pz 2 ) 1 / 2

[0038] Here, as described above, when pulsed laser beams LB1a to LB1e reach the back surface 10Ab of the first wafer 10A with a time difference of t1 to t4 (seconds) and generate ultrasonic vibrations that propagate inside the wafer 10, in order to focus each ultrasonic vibration to position P, a time difference (delay time) t1 to t4 that satisfies the following equation should be set. Note that V is the speed (m / s) at which the ultrasonic vibrations propagate inside the wafer 10, and is a speed determined by the material of the wafer 10. (H1-H2) / V=t1 (H1-H3) / V=t2 (H1-H4) / V=t3 (H1-H5) / V=t4

[0039] The above-mentioned time differences t1 to t4 can be achieved by adjusting the lengths of the optical fibers 441 to 445 that constitute the multiple rings using the optical fiber length adjustment unit 42b provided in the fiber bundle 43. The optical fiber length adjustment unit 42b should be used to change the lengths of the optical fibers 441 to 445 so that the above-mentioned time differences t1 to t4 occur. More specifically, if the length from the first connector 42a of the first optical fiber 441 that constitutes the largest ring in the multiple rings to the end face 43d of the third fiber bundle cable 43c is L1 (m), the speed of light is c (m / sec), and the refractive index of the optical fibers 441 to 445 is n, then the length L2 (m) of the second optical fiber 442 is: L2 = L1 + c × t1 ÷ n It is set as follows. Similarly, the length L3(m) of the third optical fiber 443, the length L4(m) of the fourth optical fiber 444, and the length L5(m) of the fifth optical fiber 445 are, L3 = L1 + c × t2 ÷ n L4 = L1 + c × t3 ÷ n L5 = L1 + c × t4 ÷ n This is set. This length adjustment is performed by the optical fiber length adjustment unit 42b. Since this optical fiber length adjustment unit 42b is attached via the first connector 42a and the second connector 42c described above, it can be replaced according to changes in the thickness of the object to be measured or the depth (Pz) of the desired position P to be measured.

[0040] When pulsed laser beams LB1a to LB1e are irradiated onto the back surface 10b of wafer 10 with a time difference t1 to t4 that satisfies the above conditions, the ultrasonic vibrations propagating within the first wafer 10A are focused at position P, generating strong ultrasonic vibrations. A portion of these vibrations are reflected near position P and propagate within the first wafer 10A, reaching the center C of the ring light R1 to R5 formed on the surface directly above position P where the ultrasonic vibrations were generated, i.e., on the back surface 10Ab of the first wafer 10A, causing the back surface 10Ab to vibrate. These vibrations correspond to the state near position P where the above-mentioned ultrasonic vibrations were focused.

[0041] In this embodiment, a capture laser beam LB2 is emitted from the capture oscillator 71 of the ultrasonic vibration capture means 70, and a capture laser beam LB4, which is branched at the half mirror 72 and guided via the ultrasonic vibration capture optical fiber 75, is irradiated onto the center C of the ring light R1~R5 formed on the back surface 10Ab of the first wafer 10A (see Figure 6). When the capture laser beam LB4 reaches the center C on the back surface 10Ab and is reflected, it becomes a return light LB5 that captures the ultrasonic vibration that reached the center C on the back surface 10Ab. The return light LB5 is focused through the focusing lens 74 and reaches the half mirror 72. At the same time, a reference laser beam LB3, which is emitted from the capture oscillator 71, passes through the half mirror 72 and is reflected by the return mirror 73, also reaches the half mirror 72. Then, interference light LB6 is generated by the reflected light LB5 that has passed through the half mirror 72 and the reference laser beam LB3 that has been reflected by the half mirror 72 and is not affected by the vibration of the back surface 10Ab of the first wafer 10A, and its light intensity is detected by the photodetector 76. The detected light intensity of interference light LB6 is transmitted to the image generation means 110 configured in the control means 100, along with the X and Y coordinates in which the center C on the back surface 10Ab of the first wafer 10A is positioned.

[0042] In this embodiment, the X-axis moving unit 31 and the Y-axis moving unit 32 are operated to sequentially irradiate the entire predetermined detection area on the chuck table 25, defined by the X and Y coordinates, with pulsed laser beams LB1a to LB1e that form the ring light R1 to R5 and a capturing laser beam LB4. Each time, the light intensity of the interference light LB6 is detected by the light receiving element 76 and transmitted to the image generation means 110 along with the position information of the X and Y coordinates of the center C of the ring light R1 to R5 irradiated by the capturing laser beam LB4.

[0043] The image generation means 110 generates an image showing the state of the vicinity of the bonding surface 16 of the bonded wafer W in the detection region, as shown in the display means 50 of Figure 4, based on the interference light LB6 affected by the reflected light LB5. For example, if there are voids B1 and B2, as shown in the display means 50 of Figure 4, near a position P set near the bonding surface 16, the ultrasonic vibrations focused at position P are reflected by the voids B1 and B2, and these vibrations reach the center C of the ring light R1 to R5 on the back surface 10Ab of the first wafer 10A. As a result, the intensity of the interference light LB6 detected by the photodetector 76 changes significantly compared to when position P is located in a region where there are no voids B1 and B2 nearby, allowing the state of the vicinity of position P, i.e., the state of the bonding surface 16, to be inspected.

[0044] As described above, the image information showing the state of the detected joint surface 16, along with its position information, is displayed on the display means 50 as shown in Figure 4. The image information of the detected area displayed on the display means 50, along with the corresponding X and Y coordinate information, is stored in a control means (not shown).

[0045] Furthermore, according to the inspection apparatus 1 of this embodiment, it is possible to detect not only the voids B1 and B2 described above, but also the division line 14A formed on the surface 10Aa of the first wafer 10A. The method for detecting the division line 14A is the same as the procedure for detecting the voids B1 and B2 described above. The moving means 30 described above is operated to move the chuck table 25 directly below the imaging camera 60 to identify the X and Y coordinates of the detection area, and based on this position information, the chuck table 25 is positioned directly below the end face 43d of the fiber bundle 43 of the ultrasonic vibration generating means 40. Then, using the same procedure as described above, the boundary between the device 12A on the surface 10Aa of the first wafer 10A and the division line 14A can be detected and stored. If the inspection apparatus 1 of this embodiment is equipped with a laser beam irradiation means for processing, laser processing can be performed based on the position information of the division line 14A on the surface 10Aa side of the first wafer 10A detected in this way.

[0046] Although not specifically mentioned in the description of the above embodiment, according to this embodiment, even if a metal film is coated on the back surface 10Ab side of the first wafer 10A of the bonded wafer W which is the object to be measured, the state of the bonding surface 16 and the division line 14 formed on the surface 10Aa of the first wafer 10A can be detected from the back surface 10Ab side of the first wafer 10A by the procedure described above.

[0047] In the embodiment described above, the ultrasonic vibration capturing optical fiber 75 is introduced inside the fiber bundle 43, and the end of the ultrasonic vibration capturing optical fiber 75 is positioned in the center of the end face 43d of the fiber bundle 43, so that the capturing laser beam LB4 is irradiated onto the back surface 10Ab of the first wafer 10A of the bonded wafer W. However, the present invention is not limited to this. Instead of introducing the ultrasonic vibration capturing optical fiber 75 inside the fiber bundle 43 as described above, for example, a focusing lens may be placed between the end face 43d of the fiber bundle 43 and the upper surface of the part to be measured, and a dichroic mirror (or beam splitter) may be placed between the end face 43d of the fiber bundle 43 and the focusing lens. The ultrasonic vibration capturing means 70 is connected from the side of the dichroic mirror, the capturing laser beam LB4 is guided to the object to be measured via the dichroic mirror, and the reflected light LB5 from the object to be measured is guided to the ultrasonic vibration capturing means 70 by the dichroic mirror. This configuration also makes it possible to obtain the same effects and advantages as those of the embodiment described above. [Explanation of Symbols]

[0048] 1: Inspection device 2: Base 4:Frame body 10A: First wafer 10Aa: Surface 10Ab: Reverse side 10Ac: Notch 12A: Device 14A: Planned division line 10B: Second wafer 10Ba: Surface 10Bb: Back side 10Bc: Notch 20: Holding means 21:X-axis movable plate 22: Y-axis movable plate 23: Post 25: Chuck Table 25a: Holding surface 26: Cover board 27: Clamp 30: Means of transportation 31:X-axis moving part 32:Y-axis moving part 40: Ultrasonic vibration generation means 41: Oscillator 42a: First connector 42b: Optical fiber length adjustment section 42c: Second connector 421: First Optical Fiber 422: Second Optical Fiber 423: The third optical fiber 424: The fourth optical fiber 425: The fifth optical fiber 43: Fiber Bundle 43a: First fiber bundle cable 43b: Second fiber bundle cable 43c: Third fiber bundle cable 43d: End face 50:Display means 60: Imaging camera 70: Ultrasonic vibration capture means 71: Capture Oscillator 72: Half-mirror 73: Return Mirror 74: Focusing lens 75: Optical fiber for ultrasonic vibration capture 76: Photodetector 100: Control means 110: Image generation means D1: First direction D2: Second direction LB1: Pulsed laser beam LB2: Capture laser beam LB3: Reference laser beam LB4: Capture laser beam LB5: Reflected light LB6: Interferential light

Claims

1. An inspection device for inspecting the internal state of an object to be measured, The system comprises: a holding means for holding an object to be measured and having a holding surface defined by X and Y coordinates; an ultrasonic vibration generating means for irradiating the upper surface of the object to be measured held by the holding means with a pulsed laser beam to generate ultrasonic vibrations inside the object to be measured; an ultrasonic vibration capturing means for capturing the ultrasonic vibrations that appear on the upper surface of the object to be measured; and an image generating means for generating an image based on the information captured by the ultrasonic vibration capturing means. The ultrasonic vibration generating means comprises an oscillator that emits a pulsed laser beam, and a fiber bundle composed of multiple rings, in which multiple optical fibers that guide the pulsed laser beam emitted by the oscillator to the upper surface of an object to be measured held by the holding means are arranged in multiple rings of different diameters that form concentric circles, and the bundle is composed of multiple rings. The length of the optical fibers constituting the fiber bundle is formed to increase from the configuration of large rings with larger diameters that constitute the concentric circles to the configuration of small rings with smaller diameters that constitute the concentric circles. An inspection device in which a pulsed laser beam is first irradiated onto the upper surface of the object to be measured from the optical fiber constituting the large ring, and then pulsed laser beams are gradually irradiated onto the upper surface of the object to be measured from the optical fiber constituting the small ring with a time difference, thereby focusing ultrasonic vibrations at a desired internal position of the object to be measured.

2. Let point P be the desired internal position where ultrasonic vibrations generated by pulsed laser beams irradiated onto the upper surface of the object under test in a ring shape with a time difference from the optical fibers constituting the fiber bundle converge directly below the center of the concentric circles. Let H1 be the distance from the large ring light irradiated onto the object under test from the optical fibers constituting the large ring to point P. Let Hx be the distance from the small ring light irradiated onto the object under test from the optical fibers constituting the small ring to point P. Let V be the speed at which the vibrations propagate through the object under test. (H1-Hx) / V=t The inspection apparatus according to claim 1, which generates a time difference t defined by the length of the optical fiber and focuses the ultrasonic vibrations to point P.

3. If L is the length of the optical fiber constituting the large ring, c is the speed of light, and n is the refractive index of the optical fiber, then the length Lx of the optical fiber constituting the small ring corresponding to Hx is: Lx = L + c × t ÷ n The inspection apparatus according to claim 2, which is determined by...

4. The holding means comprises an X-axis moving part that moves in the X-axis direction and a Y-axis moving part that moves in the Y-axis direction. The ultrasonic vibration capture means comprises a capture oscillator that emits a capture laser beam for capturing ultrasonic vibrations, a half-mirror that splits the capture laser beam emitted by the capture oscillator into a first direction and a second direction, a return mirror positioned in the first direction straight ahead from the half-mirror and reflecting the capture laser beam back to the half-mirror to generate a reference laser beam, an ultrasonic vibration capture optical fiber positioned in the center of the fiber bundle that guides the capture laser beam, which has been guided in the second direction by the half-mirror, to the upper surface of the object to be measured, and a light-receiving element that receives interference light between the return light of the capture laser beam guided by the ultrasonic vibration capture optical fiber that has captured ultrasonic vibrations and the reference laser beam. The inspection apparatus according to claim 1, wherein the image generation means generates an image using the intensity of the interference light received by the light receiving element as information captured by the ultrasonic vibration capturing means.

5. The inspection apparatus according to claim 1, wherein the fiber handle is equipped with a fiber length adjustment unit and is appropriately replaced according to the position in which ultrasonic vibrations are focused inside the object to be measured.

6. The inspection apparatus according to any one of claims 1 to 5, wherein the object to be measured is a bonded wafer formed by joining two wafers, and the joint surface of the bonded wafer is inspected.

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