Wafer inspection apparatus and wafer inspection method

Abstract

The present application provides wafer inspection device and wafer inspection method, precisely determine the formation state of the modified layer in the wafer. Wafer inspection device has: holding workbench, which can be held in the state of exposing the back side of wafer to the upper side; Point light source, which emits light irradiated to the back side of the wafer held by the holding workbench; And the shooting unit, the reflection of the light emitted from the point light source and irradiated to the back of the wafer is shot, the shooting unit contains: imaging lens, facing the wafer held by the holding workbench; Spectrometer, which is positioned at the imaging point of the imaging lens; And camera, which is arranged on the first light path branched by the spectrometer, the point light source is arranged on the second light path branched by the spectrometer, the collimating lens and the condenser lens are arranged on the second light path, the collimating lens generates the light emitted from the point light source into parallel light, and the condenser lens condenses the parallel light generated by the collimating lens on the spectrometer.

Description

Technical Field

[0001] The present invention relates to a wafer inspection apparatus and a wafer inspection method for inspecting the shape and condition of a modified layer formed inside a wafer. Background Technology

[0002] In the manufacturing process of device chips used in electronic devices such as mobile phones or personal computers, firstly, multiple intersecting predetermined dicing lines are formed on the front side of a wafer made of a semiconductor or other material. Then, devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed in the regions divided by these predetermined dicing lines. Furthermore, by thinning the wafer to a predetermined thickness and then dicing the wafer along these predetermined dicing lines, device chips can be formed.

[0003] When dicing a wafer, a laser beam of wavelength that is transparent to the wafer (the wavelength that can pass through the wafer) is focused along a predetermined dicing line into the interior of the wafer to form a modified layer that serves as the starting point for dicing. Then, when an external force is applied to the wafer, cracks extend from the modified layer toward the front and back sides of the wafer, and the wafer is diced along the predetermined dicing line (see, for example, Patent Documents 1 and 2).

[0004] Here, if a modifier layer is not properly formed inside the wafer, the wafer may sometimes be damaged due to improper dicing. Therefore, by utilizing the fact that tiny irregularities appear on the back side of the wafer when a modifier layer is formed, light is shone onto the back side of the wafer and the reflected light is captured to detect the presence or absence of these irregularities. The irregularities are highlighted in the image reflecting this reflected light. This phenomenon is called a "magic mirror," and a technique for detecting the presence or absence of a modifier layer using this magic mirror has been developed (see Patent Document 3).

[0005] Patent Document 1: Japanese Patent No. 3408805

[0006] Patent Document 2: Japanese Patent No. 4358762

[0007] Patent Document 3: Japanese Patent Application Publication No. 2017-220480

[0008] Here, in order to detect the formation state of the modified layer with high precision, clear images are required. However, since the contrast of images with reflected light tends to be low, it is not easy to accurately determine whether a modified layer is present. Summary of the Invention

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a wafer inspection apparatus and a wafer inspection method, which can obtain images of reflected light with good contrast and clarity, and can accurately determine the formation state of the modified layer inside the wafer.

[0010] According to one aspect of the present invention, a wafer inspection apparatus is provided for inspecting wafers with a modified layer formed therein. The wafer inspection apparatus comprises: a holding stage capable of holding the wafer with its back side exposed upwards; a point light source emitting light that illuminates the back side of the wafer held by the holding stage; and an imaging unit that captures the reflected light from the point light source illuminating the back side of the wafer. The imaging unit includes: an imaging lens facing the wafer held by the holding stage; a beam splitter positioned at the imaging point of the imaging lens; and a camera disposed on a first optical path branched by the beam splitter. The point light source is disposed on a second optical path branched by the beam splitter. A collimating lens and a condenser lens are disposed on the second optical path. The collimating lens generates parallel light from the light emitted by the point light source, and the condenser lens focuses the parallel light generated by the collimating lens onto the beam splitter.

[0011] Preferably, the wafer inspection apparatus also has a moving unit that allows the holding stage and the imaging unit to move relative to each other.

[0012] In addition, preferably, the light emitted by the point light source is a laser beam.

[0013] Furthermore, according to another aspect of the present invention, a wafer inspection method is provided, which uses the wafer inspection apparatus described in any one of technical solutions 1 to 3 to inspect a wafer having multiple intersecting predetermined dividing lines on its front side, and having devices formed in each region divided by the predetermined dividing lines on the front side. A modified layer is formed in the wafer along the multiple predetermined dividing lines by positioning a focusing point inside the wafer and irradiating it with a laser beam of a wavelength transparent to the wafer. The wafer inspection method is characterized by the following step: a holding step, in which the wafer is held using a holding stage. The wafer is held with its front side facing the holding table and its back side exposed upwards; in the illumination step, light emitted from the point light source is irradiated onto the back side of the wafer through the collimating lens, the condenser lens, the beam splitter, and the imaging lens; in the imaging step, the reflected light irradiated onto the back side of the wafer through the illumination step, reflected by the back side, and reaching the camera through the imaging lens and the beam splitter is photographed to form an image; and in the determination step, the formation state of the modified layer formed inside the wafer is determined based on the image obtained through the imaging step.

[0014] In one aspect of the wafer inspection apparatus and method of the present invention, a condenser lens focuses light emitted from a point light source onto a beam splitter, causing the light to illuminate the back side of the wafer. Reflected light is then focused onto the beam splitter, and a camera captures the reflected light. In this case, light scattering is suppressed from the time the light originates from the point light source until it is reflected from the wafer and reaches the camera. Therefore, the image formed by the camera is clear, allowing for a more precise determination of the formation state of the modified layer inside the wafer.

[0015] Therefore, according to the present invention, a wafer inspection apparatus and a wafer inspection method are provided, which can obtain images of reflected light with good contrast and clarity, and can accurately determine the formation state of the modified layer inside the wafer. Attached Figure Description

[0016] Figure 1 (A) is a schematic perspective view of the front side of the wafer. Figure 1 (B) is a schematic perspective view of the back side of the wafer.

[0017] Figure 2 (A) is a perspective view schematically showing the formation of a modified layer inside a wafer. Figure 2 (B) is a cross-sectional view schematically showing the formation of a modified layer inside a wafer.

[0018] Figure 3 This is a schematic perspective view of a wafer inspection apparatus.

[0019] Figure 4 This is a schematic side view of the optical system of a wafer inspection apparatus.

[0020] Figure 5 It is a three-dimensional diagram that schematically illustrates the illumination and photographing steps.

[0021] Figure 6 This is a top view schematically showing an example of a captured image.

[0022] Figure 7 This is a flowchart illustrating the steps of the wafer inspection method.

[0023] Figure 8 It is a side view schematically showing the path of light focused on the beam splitter.

[0024] Label Explanation

[0025] 1: Wafer; 1a: Front side; 1b: Back side; 3: Pre-defined dividing line; 3a: Modified layer; 5: Device; 7: Frame; 9: Wafer; 11: Frame unit; 13: Image capture; 15: Line; 2: Laser processing device; 4: Laser processing unit; 4a: Processing head; 4b: Focusing point; 6: Laser beam; 8: Wafer inspection device; 10: Base; 12, 22: Moving unit; 14, 24: Guide rail; 16, 26: Moving worktable; 18, 28: Ball screw; 20, 30: Pulse 32: Electric motor; 34: Holding table; 34a: Upper surface; 34b: Fixture; 36: Support; 38: Imaging unit; 40: Display unit; 42: Imaging lens; 44: Beam splitter; 44a, 44b: Interface; 46: Imaging point; 48: Camera; 50, 62: Optical path; 52: Light source; 54: Optical fiber; 56: Point light source; 58: Collimating lens; 60: Condensing lens; 64: Light; 66, 68a, 68b: Reflected light; 66a, 66b: Light. Detailed Implementation

[0026] Embodiments of the present invention will be described with reference to the accompanying drawings. First, the wafer inspection apparatus of this embodiment and the wafer that is the object of inspection in the wafer inspection method will be described. Figure 1 (A) is a perspective view of the front 1a side of a wafer 1 with multiple intersecting predetermined dividing lines 3 set on the front 1a and the device 5 formed in each region of the front 1a divided by the predetermined dividing lines 3. Figure 1 (B) is a perspective view schematically showing the back side 1b of the wafer 1.

[0027] The wafer 1 is formed, for example, of silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or other semiconductor materials. Alternatively, the wafer 1 is formed of materials such as a composite oxide of lithium tantalate (LT) and lithium niobate (LN).

[0028] Multiple intersecting segmentation lines 3 are provided on the front side 1a of the wafer 1. Devices 5 such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations) are formed in the regions divided by the segmentation lines 3. Moreover, when the wafer 1 is segmented along the segmentation lines 3, individual device chips can be formed.

[0029] When the wafer 1 is disconnected, the wafer 1 is moved into a laser processing apparatus that can focus a laser beam of wavelength that is transparent to the wafer 1 onto the interior of the wafer 1. Figure 2 (A) is a schematic perspective view of a wafer 1 being laser-processed using a laser processing apparatus 2.

[0030] like Figure 2 As shown in (A), the wafer 1 is integrated with the wafer 9 and the frame 7 before laser processing. Furthermore, a frame unit 11 is formed, comprising the wafer 1, the wafer 9, and the frame 7. At this time, the wafer 9 is disposed on the front side 1a of the wafer 1, and the back side 1b is exposed to the outside. The individual device chips formed by dividing the wafer 1 are supported by the wafer 9. Subsequently, when the spacing between the device chips is increased by expanding the wafer 9, the picking up of the device chips becomes easier.

[0031] The annular frame 7 is formed of a material such as metal and has an opening with a diameter larger than that of the wafer 1. When forming the frame unit 11, the wafer 1 is positioned within the opening of the frame 7 and housed within the opening.

[0032] The sheet 9 has a diameter larger than the opening of the frame 7. The sheet 9 is, for example, a strip called a dicing strip, having a substrate layer and an adhesive layer formed on the substrate layer. When the sheet 9 is a dicing strip, the sheet 9 is adhered to the frame 7 and the front side 1a of the wafer 1 by the adhesive force exhibited by the adhesive layer. Alternatively, the sheet 9 may also be a resin-based sheet without an adhesive layer, such as a polyolefin sheet or a polyester sheet, in which case the sheet 9 is thermo-pressed to the wafer 1.

[0033] The laser processing apparatus 2 includes: a holding stage (not shown) that holds a wafer 1 with a spacer 9; and a laser processing unit 4 that irradiates the wafer 1 held by the holding stage with a laser beam. The laser processing unit 4 has a processing head 4a that focuses a laser beam 6 of a wavelength that is transparent to the wafer 1 into the interior of the wafer 1. The laser processing unit 4 includes, for example, a laser oscillator using a medium such as Nd:YAG that pulses to emit a laser beam with a wavelength of 1064 nm.

[0034] Figure 2 (B) is a schematic cross-sectional view of a wafer 1 being laser-processed. A focal point 4b is positioned at a predetermined depth within the wafer 1, and a laser beam 6 is focused onto the focal point 4b while the wafer 1 and the laser beam 6 are moved relative to each other. Thus, the laser beam 6 irradiates the wafer 1 along a predetermined dividing line 3, forming a modified layer 3a along the predetermined dividing line 3 within the wafer 1.

[0035] Furthermore, during the formation of the modified layer 3a, cracks extending from the modified layer 3a toward the front side 1a and back side 1b of the wafer 1 can also be formed. Alternatively, cracks can be caused to extend from the modified layer 3a by applying an external force to the wafer 1 in which the modified layer 3a is formed internally. When the modified layer 3a and the cracks extending from it are formed on the wafer 1, the wafer 1 is divided along the predetermined dividing line 3. That is, the modified layer 3a functions as the dividing starting point when dividing the wafer 1.

[0036] However, if the wafer 1 is not properly laser-processed or the modified layer 3a is not properly formed inside the wafer 1 along the predetermined dividing line 3, the wafer 1 cannot be properly divided, which will damage the wafer 1. That is, there may be cases where cracks deviate from the predetermined direction and travel to the device 5, or the ends of the chip formed by dividing the wafer 1 are rough and the quality of the chip is reduced.

[0037] Therefore, it is considered to inspect the laser-processed wafer 1 to confirm whether the modified layer 3a has been formed inside the wafer 1 as intended. However, the formed modified layer 3a cannot be visually confirmed from the outside of the wafer 1. Therefore, the fact that a small uneven shape appears on the back side 1b of the wafer 1 when the modified layer 3a is formed is utilized.

[0038] That is, light is shone onto the back surface 1b of wafer 1 and the reflected light is captured to form an image, and the formation state of the modified layer is determined based on the captured image. The uneven shape is highlighted in the image reflecting the reflected light. This phenomenon is called a magic mirror, and the formation state of the modified layer 3a is determined using this magic mirror.

[0039] Here, in order to detect the formation state of the modified layer 3a with high precision, it is necessary to obtain an image of reflected light that clearly reflects the uneven shape. However, since the contrast of the image of reflected light tends to be low, it is not easy to accurately determine the formation state of the modified layer 3a based on the image.

[0040] Therefore, the wafer inspection apparatus of this embodiment is configured as described below to obtain high-contrast and clear images of reflected light, thereby enabling precise determination of the formation state of the modified layer 3a inside the wafer 1. Next, the wafer inspection apparatus of this embodiment will be described. Figure 3 This is a perspective view schematically showing the wafer inspection apparatus 8 of this embodiment.

[0041] The wafer inspection apparatus 8 has a base 10 that supports various structural elements. An X-axis moving unit 12 and a Y-axis moving unit 22 are provided on the upper surface of the base 10. The X-axis moving unit 12 moves the holding stage 34 that holds the wafer 1 along the X-axis direction, and the Y-axis moving unit 22 moves the holding stage 34 along the Y-axis direction that is perpendicular to the X-axis direction.

[0042] The X-axis moving unit 12 has a pair of X-axis guide rails 14 along the X-axis direction on the upper surface of the base 10. An X-axis moving stage 16 is slidably mounted on the pair of X-axis guide rails 14. A nut portion (not shown) is provided on the back side of the X-axis moving stage 16, in which an X-axis ball screw 18, which is substantially parallel to the X-axis guide rails 14, is screwed.

[0043] An X-axis pulse motor 20 is connected to one end of the X-axis ball screw 18. The X-axis pulse motor 20 rotates the X-axis ball screw 18, thereby moving the X-axis moving table 16 along the X-axis guide rail 14 in the X-axis direction.

[0044] The Y-axis moving unit 22 has a pair of Y-axis guide rails 24 along the Y-axis direction on the upper surface of the X-axis moving stage 16. The Y-axis moving stage 26 is slidably mounted on the pair of Y-axis guide rails 24. A nut portion (not shown) is provided on the back side of the Y-axis moving stage 26, in which a Y-axis ball screw 28, which is substantially parallel to the Y-axis guide rails 24, is screwed.

[0045] A Y-axis pulse motor 30 is connected to one end of the Y-axis ball screw 28. The Y-axis pulse motor 30 rotates the Y-axis ball screw 28, thereby moving the Y-axis moving stage 26 along the Y-axis guide rail 24 in the Y-axis direction. A cover 32 covering the X-axis moving unit 12 and the Y-axis moving unit 22, and a holding stage 34 for holding the wafer 1 are provided on the upper surface of the Y-axis moving stage 26.

[0046] A plurality of clamps 34b are arranged around the holding stage 34 to hold the frame 7 of the frame unit 11. The holding stage 34 has: a porous component exposed on the upper surface 34a of the holding stage 34; a suction path connected at one end to the porous component; and a suction source connected to the other end of the suction path. When the suction source is activated, the wafer 1 placed on the holding stage 34 is attracted and held.

[0047] An imaging unit 38 is disposed above the holding stage 34 for imaging the wafer 1 held by the holding stage 34. The imaging unit 38 is supported by a support portion 36, which has a column extending upward from the rear upper surface of the base 10 and an arm extending upward from the upper end of the column toward the holding stage 34. A display unit 40, such as a liquid crystal display capable of displaying various information, may also be disposed on the support portion 36.

[0048] Figure 4 This is a schematic side view of the optical system of the wafer inspection apparatus 8. The optical system is housed, for example, in the support portion 36. The wafer inspection apparatus 8 includes: a point light source 56 that emits light that illuminates the back surface 1b of the wafer 1 held by the holding stage 34; and an imaging unit 38 that captures the reflected light from the point light source 56 that illuminates the back surface 1b of the wafer 1.

[0049] The imaging unit 38 includes: an imaging lens 42 facing the wafer 1 held by the holding stage 34; a beam splitter 44 positioned at the imaging point 46 of the imaging lens 42; and a camera 48 disposed on a first optical path 50 branched by the beam splitter 44. The camera 48 has an image sensor such as a CCD sensor or a CMOS sensor and is capable of capturing light arriving at the camera 48 to form an image.

[0050] A point light source 56 is provided in the second optical path 62 branched by the beam splitter 44. The point light source 56 is, for example, formed by the other end of an optical fiber 54 connected at one end to the light source 52, serving as the starting point for light emitted from the light source 52 and traveling in the optical fiber 54 towards the second optical path 62. Furthermore, the light source 52 is, for example, a laser oscillator that oscillates to produce laser light, and the point light source 56 emits a laser beam as that light. However, the light source 52 is not limited to this; it can also be an LED, etc.

[0051] A collimating lens 58 and a condenser lens 60 are provided on the second optical path 62. The collimating lens 58 generates parallel light from the light 64 emitted from the point light source 56, and the condenser lens 60 focuses the parallel light generated by the collimating lens 58 onto the beam splitter 44. The focusing point of the condenser lens 60 coincides with the imaging point 46 of the imaging lens 42, which is positioned on the beam splitter 44. Furthermore, in... Figure 4 In the image, the diffusion of light 64 emitted from point light source 56 is emphasized.

[0052] When inspecting a wafer 1 with a modified layer 3a formed inside it using the wafer inspection apparatus 8, the wafer 1 is first held using the holding stage 34. At this time, the back side 1b of the wafer 1 is exposed upwards. Then, the area of ​​the wafer 1 to be observed is positioned below the imaging lens 42. Furthermore, in Figure 4 In the text, parts 9 and frame 7 are omitted.

[0053] Next, when the light source 52 is activated, the light 64 emitted from the point light source 56 travels along the second optical path 62. That is, the light 64 enters the collimating lens 58, where it is generated into parallel light. Then, the light 64 enters the condenser lens 60 and is focused onto the beam splitter 44, and is reflected by the beam splitter 44 before traveling to the imaging lens 42. The light 64, again generated into parallel light by the imaging lens 42, illuminates the back surface 1b side of the wafer 1 and is reflected by the wafer 1.

[0054] The reflected light 66 from light 64 travels towards the imaging lens 42 and is focused at the imaging point 46 positioned at the beam splitter 44. Then, the reflected light 66 travels along the first optical path 50 and reaches the camera 48. The camera 48 captures the arriving reflected light 66 to form an image.

[0055] like Figure 5As shown, when the wafer 1 held by the holding stage 34 and the imaging unit 38 are moved along the X-axis and Y-axis directions, and the light 64 is irradiated along the predetermined dividing line 3 and the reflected light 66 is photographed by the camera 48, the entire area of ​​the back surface 1b of the wafer 1 can be inspected.

[0056] When a modified layer 3a is formed inside wafer 1, tiny uneven shapes reflecting the formation state of the modified layer 3a appear on the back surface 1b of wafer 1. Furthermore, since light 64 is scattered in the areas where the uneven shapes appear, the locations where the uneven shapes occur are brightly reflected in the image obtained by photographing the reflected light 66. This phenomenon is called a magic mirror.

[0057] Figure 6 This is a top view schematically showing an example of a captured image 13. (See image 13.) Figure 6 As shown, bright lines 15 reflecting the formation state of the modified layer 3a are displayed in the captured image 13. Therefore, the formation state of the modified layer 3a inside the wafer 1 can be determined based on the captured image 13. For example, if there is a defect in the bright lines 15 displayed in the captured image 13, it can be confirmed that the modified layer 3a has not been properly formed in the area where the defect was found.

[0058] Here, when a linear or planar light source of a specific size is placed in the wafer inspection apparatus 8 instead of a point light source 56, blurring occurs in the captured image 13 due to the difference in the travel paths of the light 64 emitted from the center of the light source and the peripheral light emitted from the ends. This is because when the peripheral light finally enters the back surface 1b of the wafer 1 along with the light 64, the peripheral light is incident from an unpredictable direction due to the uneven shape, resulting in the peripheral light being reflected in an unpredictable direction.

[0059] Therefore, in the wafer inspection apparatus 8 of this embodiment, in order to prevent the generation of peripheral light that blurs the captured image 13, the optical fiber 54 forming the point light source 56 can be 20. μ The diameter is less than m. Furthermore, when a laser oscillator is used as the light source 52, this oscillator can, for example, oscillate laser light with a wavelength in the range of 600 nm to 700 nm. Because the laser beam is monochromatic, has a small diameter, and excellent linearity, when the light 64 is a laser beam, the resulting image 13 is clear and has improved contrast.

[0060] Furthermore, in the wafer inspection apparatus 8 of this embodiment, the light 64 is focused onto the beam splitter 44 by the condenser lens 60, and the reflected light 66 is focused onto the beam splitter 44 by the imaging lens 42. Therefore, compared to the case where the light incident on the beam splitter 44 is not focused onto the beam splitter 44, the scattering of light in the beam splitter 44 is suppressed. As a result, the captured image 13 is clearer and the contrast is improved.

[0061] Figure 8 This is a side view schematically showing the travel path of the reflected light 66 focused on the beam splitter 44. The reflected light 66 enters the beam splitter 44 from the interface 44a on the imaging lens 42 side, is focused inside the beam splitter 44, and travels out of the beam splitter 44 from the interface 44b on the camera 48 side. At this time, a portion of the reflected light 66 is reflected at interfaces 44a and 44b.

[0062] Figure 8 The travel paths of light 66a and light 66b, which advance along the outer edge of reflected light 66, are shown. (As shown) Figure 8 As shown, on interface 44b, a portion of light 66a and light 66b is reflected, and consequently, the reflected light 68a and 68b are reflected by interface 44a. When the reflected light 68a and 68b reach camera 48 and are simultaneously reflected into the captured image 13 along with light 66a and 66b, the captured image 13 is blurry.

[0063] However, when the imaging point 46 of the imaging lens 42 is positioned inside the beam splitter 44, the incident and reflection angles of the light 66a and 66b on the interface 44b, as well as the incident and reflection angles of the reflected light 68a and 68b on the interface 44a, are relatively large. Therefore, the reflected light 68a and 68b travels far away from the camera 48, making it difficult for them to reach the camera 48.

[0064] Conversely, when the imaging point 46 of the imaging lens 42 is not positioned on the beam splitter 44, the incident angle and reflection angle of light on interfaces 44a and 44b become smaller. In this case, the light reflected by interfaces 44a and 44b easily reaches the camera 48, becoming the main reason for the blurriness of the captured image 13.

[0065] Therefore, the image 13 obtained using the wafer inspection apparatus 8 of this embodiment is high-contrast and high-resolution. Based on this image 13, the formation state of the modified layer 3a inside the wafer 1 can be analyzed in more detail to obtain more detailed information.

[0066] Next, the wafer inspection method of this embodiment, which uses the wafer inspection apparatus 8 described above to inspect the wafer 1, will be described. Figure 7This is a flowchart illustrating the steps of the wafer inspection method according to this embodiment. The wafer inspection method... Figure 3 The wafer inspection apparatus 8, shown schematically, is used for implementation. Hereinafter, the wafer 1 inspected by the wafer inspection method of this embodiment and each step will be described.

[0067] like Figure 1 As shown in (A), the wafer 1 inspected by this inspection method has multiple intersecting predetermined dividing lines 3 on its front side 1a, and the wafer 1 in which the device 5 is formed in each region divided by the predetermined dividing lines 3 on the front side 1a. Furthermore, as... Figure 2 (A) and Figure 2 As shown in (B), a modified layer 3a is formed on the wafer 1 along multiple predetermined dividing lines 3 by irradiating a laser beam 6 of a wavelength that is transparent to the wafer 1 with the focus point 4b positioned inside the wafer 1.

[0068] In this inspection method, firstly, the following holding step S10 is performed: with the front side 1a of the wafer 1 facing the holding stage 34 and the back side 1b exposed sideways upward, the wafer 1 is held using the holding stage 34.

[0069] Next, as Figure 4 As shown, the following illumination step S20 is performed: light 64 emitted from point light source 56 is passed through collimating lens 58, condenser lens 60, beam splitter 44, and imaging lens 42 to illuminate the back surface 1b of wafer 1. Light 64 can be, for example, a laser beam with a wavelength of 600 nm to 700 nm. However, light 64 is not limited to a laser beam. Especially when light 64 is a laser beam, its linearity is excellent, but... Figure 4 In the illustration, for ease of explanation, the diffusion of light 64 emitted from point light source 56 is emphasized.

[0070] The light 64 emitted from the point light source 56 first enters the collimating lens 58 and is generated as parallel light. Then, the parallel light 64 is focused by the condenser lens 60 onto the beam splitter 44 and reflected towards the imaging lens 42. Moreover, since the imaging point 46 of the imaging lens 42 is positioned at the beam splitter 44, the light 64 is regenerated as parallel light through the imaging lens 42 and illuminates the back surface 1b of the wafer 1.

[0071] Next, the following imaging step S30 is performed: the reflected light 66 of the light 64, which is irradiated by the back surface 1b of the wafer 1 through the illumination step S20, is reflected by the back surface 1b, and reaches the camera 48 after passing through the imaging lens 42 and the beam splitter 44, is captured to form an image 13. That is, the reflected light 66, after the light 64 is reflected by the back surface 1b of the wafer 1, is focused by the imaging lens 42 onto the beam splitter 44. Then, a portion of the reflected light 66 travels along the first optical path 50 and reaches the camera 48, where it is received by the image sensor of the camera 48.

[0072] Next, the following determination step S40 is performed: the formation state of the modified layer 3a formed inside the wafer 1 is determined based on the captured image 13 obtained by the capturing step S30. Figure 6 This is a top view schematically showing an example of an image 13. Bright lines 15 are reflected in image 13 due to the magic mirror effect. These bright lines 15 appear in image 13 because light 64 is reflected by the uneven shape on the back surface 1b of wafer 1, which is formed inside wafer 1 due to the presence of a modified layer 3a, reflecting the formation state of the modified layer 3a.

[0073] For example, if it is not possible to illuminate the entire area of ​​the back surface 1b of the wafer 1 with light 64 at once, after performing the illumination step S20 and the imaging step S30, the wafer 1 and the imaging unit 38 can be moved relative to each other and the illumination step S20 and the imaging step S30 can be repeated. Then, when an image 13 can be obtained over the entire area of ​​the back surface 1b of the wafer 1, the determination step S40 is performed to determine the formation state of the modified layer 3a in the entire area of ​​the wafer 1.

[0074] In particular, in the wafer inspection method of this embodiment, the light 64 is emitted from the point light source 56, and therefore does not have the component of peripheral light that travels in a direction deviating from the direction of travel of the light 64 when it is irradiated onto the back surface 1b of the wafer 1. Therefore, the captured image 13 has high contrast, and the bright lines 15 are reflected in high detail in the captured image 13, so the formation state of the modified layer 3a can be determined in more detail and with greater precision based on the captured image 13.

[0075] For example, in image 13, if the bright line 15 is interrupted, it is determined that the modified layer 3a has not been formed inside the wafer 1 at the location corresponding to the interruption of the bright line 15. Furthermore, if the bright line 15 exhibits significant meandering, it indicates that the modified layer 3a is also meandering. In addition, the size and formation depth of the modified layer 3a can be determined based on the thickness and color of the bright line 15.

[0076] Therefore, if it is determined that the modified layer 3a has not been sufficiently formed inside the wafer 1, in order to form a sufficient modified layer 3a in the wafer 1, laser processing can be performed again or the processing conditions when laser processing a new wafer 1 can be improved.

[0077] Furthermore, the present invention is not limited to the embodiments described above, and various modifications can be made to implement it. For example, in the above embodiments, the wafer 1 and the imaging unit 38 are moved relative to each other by moving the holding stage 34, but one aspect of the present invention is not limited to this. That is, the imaging unit 38 may also be able to move along one or both of the X-axis and Y-axis directions.

[0078] The structure and method of the above embodiments can be implemented with appropriate modifications without departing from the purpose of the present invention.

Claims

1. A wafer inspection apparatus for inspecting wafers with an internal modified layer, characterized in that, This wafer inspection device has the following features: A stage that holds the wafer with its back side facing upwards; A point light source that emits light that illuminates the back side of the wafer held by the holding stage; and The imaging unit captures the reflected light emitted from the point light source and illuminating the back surface of the chip. This camera unit includes: An imaging lens that faces the wafer held by the holding stage; A beam splitter, positioned at the imaging point of the imaging lens; and A camera is mounted on the first optical path branched off by the beam splitter. The point light source is positioned on the second optical path branched off from the beam splitter. The light emitted by this point light source is a laser beam. A collimating lens and a condensing lens are provided in the second optical path. The collimating lens generates parallel light from the point source, and the condensing lens focuses the parallel light generated by the collimating lens onto the beam splitter.

2. The wafer inspection apparatus according to claim 1, characterized in that, The wafer inspection device also has a moving unit that allows the holding stage and the imaging unit to move relative to each other.

3. A wafer inspection method, comprising inspecting a wafer using the wafer inspection apparatus of claim 1 or 2, wherein the wafer has multiple intersecting predetermined dividing lines on its front side, and devices are formed in each region on the front side divided by the predetermined dividing lines, and a modified layer is formed in the wafer along the multiple predetermined dividing lines by positioning a focusing point inside the wafer and irradiating it with a laser beam of a wavelength that is transparent to the wafer, characterized in that, The wafer inspection method comprises the following steps: The holding step involves holding the wafer with its front side facing the holding stage and its back side exposed upwards using the holding stage. In the illumination step, the light emitted from the point light source is passed through the collimating lens, the condensing lens, the beam splitter, and the imaging lens to illuminate the back side of the wafer; The imaging step involves capturing the reflected light—light that has been irradiated onto the back surface of the wafer by the illumination step, reflected by the back surface, and then passed through the imaging lens and the beam splitter to reach the camera—to form an image; and The determination step involves using the image obtained through the imaging step to determine the formation state of the modified layer formed inside the wafer. The light emitted by this point light source is a laser beam.

Images