TWI890793B - Wafer inspection device and wafer inspection method - Google Patents

Abstract

[Topic] Precisely determine the formation state of a modified layer within a wafer. [Solution] A wafer inspection device comprises: a holding table capable of holding a wafer with its back side exposed upward; a point light source emitting light that is irradiated onto the back side of the wafer held on the holding table; and an imaging unit that captures reflected light emitted from the point light source and irradiated onto the back side of the wafer, the imaging unit comprising: an imaging lens facing the wafer held on the holding table. A beam splitter is positioned at the imaging point of the imaging lens; and a camera is disposed on the path branched by the beam splitter. The point light source is disposed on a second optical path branched by the beam splitter. Disposed on the second optical path are: a collimating lens for generating parallel light from the light emitted from the point light source; and a focusing lens for focusing the parallel light generated by the collimating lens onto the beam splitter.

Description

Wafer inspection device and wafer inspection method

The present invention relates to a wafer inspection device and a wafer inspection method for inspecting the shape of a modified layer formed inside a wafer.

In the manufacturing process for device chips used in electronic devices such as mobile phones and personal computers, a plurality of intersecting predetermined dividing lines are first set on the surface of a wafer made of materials such as semiconductors. Devices such as ICs (Integrated Circuits) and LSIs (Large Scale Integration) are then formed in the areas divided by these predetermined dividing lines. The wafer is then thinned to a specific thickness and then divided along the predetermined dividing lines to form device chips.

When separating a wafer, a laser beam with a wavelength that is transparent to the wafer (a wavelength that the wafer can transmit) is focused inside the wafer along the predetermined separation line, forming a modified layer that serves as the starting point for separation. Subsequently, when external force is applied to the wafer, cracks extend from the modified layer to the front and back sides of the wafer, separating the wafer along the predetermined separation line (see, for example, Patent Documents 1 and 2).

If the modified layer is not properly formed inside the wafer, the wafer may not be properly divided, resulting in damage. Therefore, the presence of these irregularities is detected by illuminating the back of the wafer with light and capturing an image of the reflected light. This image, which is illuminated by the reflected light, emphasizes the irregularities. This phenomenon is called a magic mirror, and a technique for detecting the presence of a modified layer using this magic mirror has been developed (see Patent Document 3). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent No. 3408805 [Patent Document 2] Japanese Patent No. 4358762 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-220480

[The problem that the invention aims to solve]

To accurately detect the formation of a modified layer, it is necessary to capture sharp photographic images. However, since the contrast of images taken with reflected light tends to decrease, accurately determining the presence of a modified layer is not easy.

The present invention was developed in light of these problems. Its purpose is to provide a wafer inspection device and wafer inspection method that can produce images of reflected light with high contrast and clarity, allowing precise determination of the formation state of a modified layer within the wafer. [Means for Solving the Problem]

According to one embodiment of the present invention, a wafer inspection device is provided for inspecting a wafer having a modified layer formed therein. The wafer inspection device is characterized in that it comprises: a holding table capable of holding the wafer with its back side exposed upward; a point light source for emitting light that is irradiated onto the back side of the wafer held on the holding table; and an imaging unit for capturing reflected light emitted from the point light source and irradiated onto the back side of the wafer. The imaging unit includes an imaging lens facing the wafer held on the holding table, a spectrometer positioned at the imaging point of the imaging lens, and a camera arranged on a first optical path branched by the spectrometer. The point light source is arranged on a second optical path branched by the spectrometer. In the second optical path, a collimating lens is arranged to generate parallel light from light emitted from the point light source, and a focusing lens is arranged to focus the parallel light generated by the collimating lens on the spectrometer.

It is preferable to further provide a moving unit that enables the holding platform and the imaging unit to move relative to each other.

Furthermore, it is preferred that the light emitted by the point light source is a laser beam.

Furthermore, when one of the other aspects of the present invention is used, a wafer inspection method is provided, which is to inspect a wafer having a plurality of predetermined dividing lines intersecting each other set on the surface, and a device formed in each area divided by the predetermined dividing lines on the surface, by positioning the focal point inside the wafer and irradiating the wafer with a laser beam of a wavelength that is penetrating, thereby forming a modified layer on the wafer along the plurality of predetermined dividing lines, the wafer inspection method having: a holding step, which is to turn the surface of the wafer toward the holding table The wafer is held on the holding stage with the back side exposed upward; an irradiation step is performed, wherein the back side of the wafer is irradiated with the light emitted from the point light source via the collimating lens, the focusing lens, the beam splitter, and the imaging lens; an imaging step is performed, wherein the reflected light of the light irradiated onto the back side of the wafer in the irradiation step, reflected from the back side, and reaching the camera via the imaging lens and the beam splitter is captured to form a photographic image; and a determination step is performed, based on the photographic image obtained in the imaging step, to determine the formation state of the modified layer formed inside the wafer. [Effects of the Invention]

In a wafer inspection apparatus and method according to one aspect of the present invention, light emitted from a point light source is focused by a focusing lens onto a beam splitter, where it is then irradiated onto the backside of the wafer. The reflected light is then focused onto the beam splitter and captured by a camera. In this case, light scattering is suppressed from the point light source, through reflection from the wafer, and on to the camera. As a result, the camera produces sharp images, enabling more precise assessment of the state of the modified layer within the wafer.

Therefore, the present invention provides a wafer inspection device and a wafer inspection method that can obtain a clear image of reflected light with good contrast and accurately determine the formation state of the modified layer inside the wafer.

The embodiments of the present invention are described with reference to the attached drawings. First, the wafer that serves as the inspection target in the wafer inspection apparatus and wafer inspection method according to this embodiment will be described. FIG1(A) schematically shows a perspective view of the surface 1a side of a wafer 1, wherein a plurality of intersecting predetermined dividing lines 3 are set on the surface 1a, and a device 5 is formed in each area of the surface 1a divided by the predetermined dividing lines 3. FIG1(B) schematically shows a perspective view of the back side 1b side of the wafer 1.

Wafer 1 is formed of, for example, silicon (Si), silicon carbide (SiC), gallium nitride (GaN), or other semiconductor materials. Alternatively, wafer 1 is formed of a material such as a complex oxide of lithium tantalum (LT) and lithium niobate (LN).

On the surface 1a of wafer 1, a plurality of intersecting predetermined dividing lines 3 are provided. Devices 5, such as ICs (Integrated Circuits) and LSIs (Large Scale Integrations), are formed in the areas demarcated by the predetermined dividing lines 3. Furthermore, when wafer 1 is divided along the predetermined dividing lines 3, individual device chips are formed.

When wafer 1 is cut, wafer 1 is brought into a laser processing device that focuses a laser beam of a wavelength that is penetrating to wafer 1 (a wavelength that penetrates wafer 1) inside wafer 1. FIG2(A) is a perspective view schematically showing wafer 1 being laser processed in laser processing device 2.

As shown in Figure 2(A), wafer 1 is integrated with sheet 9 and frame 7 before laser processing. This forms a frame unit 11 containing wafer 1, sheet 9, and frame 7. Sheet 9 is positioned on the front surface 1a of wafer 1, leaving the back surface 1b exposed. The individual device chips formed by dividing wafer 1 are supported on sheet 9. Later, by expanding sheet 9 to widen the gap between the device chips, the device chips can be easily picked up.

The ring-shaped frame 7 is formed of a material such as metal, and has an opening having a diameter larger than that of the wafer 1. When the frame unit 11 is formed, the wafer 1 is positioned in the opening of the frame 7 and is received in the opening.

Sheet 9 has a diameter larger than the opening of frame 7. Sheet 9 comprises, for example, a base layer and an adhesive layer formed on the base layer, such as a tape called dicing tape. If sheet 9 is dicing tape, the adhesive layer adheres sheet 9 to frame 7 and surface 1a of wafer 1. Alternatively, sheet 9 may be a resin sheet without an adhesive layer, such as a polyolefin sheet or polyester sheet. In this case, sheet 9 is heat-pressed to wafer 1.

Laser processing apparatus 2 includes a holding stage (not shown) that holds wafer 1 via a sheet 9, and a laser processing unit 4 that irradiates wafer 1 held on the holding stage with a laser beam. Laser processing unit 4 includes a processing head 4a that focuses a laser beam 6 having a wavelength that is penetrating enough to penetrate wafer 1 onto the interior of wafer 1. Laser processing unit 4 includes a laser oscillator made of a medium such as Nd:YAG, which pulses and oscillates a laser beam having a wavelength of, for example, 1064 nm.

Figure 2(B) schematically illustrates a cross-section of wafer 1 undergoing laser processing. Focusing point 4b is positioned at a specific depth within wafer 1. Laser beam 6 is focused on focusing point 4b while wafer 1 and laser beam 6 are moved relative to each other. This irradiates wafer 1 along predetermined separation lines 3, forming a modified layer 3a along predetermined separation lines 3 within wafer 1.

Furthermore, even when the modified layer 3a is formed, cracks may extend from the modified layer 3a toward the front surface 1a and back surface 1b of the wafer 1. Furthermore, even when external force is applied to the wafer 1 with the modified layer 3a formed therein, cracks may not extend from the modified layer 3a. When the modified layer 3a is formed on the wafer 1 and cracks extend from the modified layer 3a, the wafer 1 is separated along the predetermined separation line 3. In other words, the modified layer 3a functions as the starting point for separation when the wafer 1 is separated.

However, if the wafer 1 is not properly laser processed and 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, resulting in damage to the wafer 1. In other words, cracks may deviate from the predetermined direction and reach the device 5, or the ends of the wafers formed by dividing the wafer 1 may be rough, resulting in reduced wafer quality.

Therefore, it is possible to inspect a laser-processed wafer 1 to see if the modified layer 3a has been formed as intended within the wafer 1. However, the formed modified layer 3a cannot be identified from the outside of the wafer 1. Therefore, the presence of minute irregularities on the back surface 1b of the wafer 1 when the modified layer 3a is formed is exploited.

Specifically, light is irradiated onto the back surface 1b of the wafer 1 and the reflected light is captured, forming a photographic image. The state of the modified layer 3a is determined based on this photographic image. In the image of the reflected light, the concave and convex shapes are emphasized. This phenomenon is called a magic mirror, and it is used to determine the state of the modified layer 3a.

To accurately detect the state of formation of the modified layer 3a, it is necessary to obtain a photographic image of reflected light in which the unevenness is clearly reflected. However, since photographic images of reflected light tend to have low contrast, it is not easy to accurately determine the state of formation of the modified layer 3a based on these photographic images.

Therefore, the wafer inspection apparatus according to this embodiment is configured as described below to obtain high-contrast, sharp images of reflected light and accurately determine the formation state of the modified layer 3a within the wafer 1. Next, the wafer inspection apparatus according to this embodiment will be described. Figure 3 is a perspective view schematically illustrating an example configuration of a wafer inspection apparatus 8 according to this embodiment.

The wafer inspection apparatus 8 includes a base 10 that supports the various components. Disposed on the base 10 are an X-axis movement unit 12 that moves a holding table 34 holding the wafer 1 in the X-axis direction, and a Y-axis movement unit 22 that moves the holding table 34 in the Y-axis direction, which is perpendicular to the X-axis direction.

The X-axis motion unit 12 is equipped with a pair of X-axis guide rails 14 on the base 10, running along the X-axis. An X-axis motion stage 16 is slidably mounted on the pair of X-axis guide rails 14. A nut (not shown) is provided on the back side of the X-axis motion stage 16, into which an X-axis ball screw 18, which is approximately parallel to the X-axis guide rails 14, is threaded.

One end of the X-axis ball screw 18 is connected to the X-axis pulse motor 20. When the X-axis pulse motor 20 rotates the X-axis ball screw 18, the X-axis moving stage 16 moves in the X-axis direction along the X-axis guide rail 14.

The X-axis motion unit 22 is equipped with a pair of Y-axis guide rails 24 along the Y-axis on the X-axis motion stage 16. The Y-axis motion stage 26 is slidably mounted on the pair of Y-axis guide rails 24. A nut (not shown) is provided on the back side of the Y-axis motion stage 26, which screws into a Y-axis ball screw 28 that is approximately parallel to the Y-axis guide rails 24.

One end of the Y-axis ball screw 28 is connected to the Y-axis pulse motor 30. When the Y-axis pulse motor 30 rotates the Y-axis ball screw 28, the Y-axis moving stage 26 moves in the Y-axis direction along the Y-axis guide rail 24. A cover 32 covering the X-axis moving unit 12 and the Y-axis moving unit 22, as well as a holding stage 34 for holding the wafer 1, are located on the Y-axis moving stage 26.

Multiple clamps 34b are installed around the holding platform 34 to hold the frame 7 of the frame unit 11. The holding platform 34 includes a porous member exposed on its upper surface 34a, a suction device connected to one end of the porous member, 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 platform 34 is sucked and held.

Above the holding platform 34, an imaging unit 38 is provided to capture images of the wafer 1 held by suction on the holding platform 34. The imaging unit 38 is supported by a support 36 comprising a column extending generally upward from the rear upper surface of the base 10 and an arm extending from the upper end of the column toward the top of the holding platform 34. A display unit 40, such as a liquid crystal display capable of displaying various information, may also be provided above the support 36.

Figure 4 is a side view schematically showing the optical system of wafer inspection apparatus 8. This optical system is housed in, for example, support portion 36. Wafer inspection apparatus 8 includes a point light source 56 that emits light that is directed toward the back surface 1b of wafer 1 held on holding table 34, and an imaging unit 38 that captures reflected light emitted from point light source 56 and directed toward back surface 1b of wafer 1.

The imaging unit 38 includes an imaging lens 42 facing the wafer 1 held on the holding stage 34, a beam splitter 44 positioned at an imaging point 46 of the imaging lens 42, and a camera 48 disposed on the first optical path 50 branched by the beam splitter 44. The camera 48 includes an image sensor such as a CDD camera or a CMOS sensor, and can capture light reaching the camera 48 to form a photographic image.

A point light source 56 is provided in the second optical path 62 branched by the beam splitter 44. Point light source 56 is located on the other end of an optical fiber 54 connected to the light source 52. It is emitted from the light source 52 and serves as the point of departure for light traveling along the optical fiber 54 as it travels toward the second optical path 62. While light source 52 is, for example, a laser oscillator that oscillates a laser, point light source 56 emits a laser beam as the light. However, light source 52 is not limited to this; an LED or the like may also be used as the light source.

In the second optical path 62, there are provided a collimating lens 58 for generating parallel light from the light 64 emitted from the point light source 56, and a focusing lens 60 for focusing the parallel light generated by the collimating lens 58 onto the beam splitter 44. The focusing point of the focusing lens 60 coincides with the imaging point 46 of the beam splitter 44 positioned in the imaging lens 42. Furthermore, FIG4 emphasizes the diffusion of the light 64 emitted from the point light source 56.

When inspecting wafer 1 with modified layer 3a formed therein using wafer inspection apparatus 8, wafer 1 is first held by holding table 34. At this point, back surface 1b of wafer 1 is exposed upward. Furthermore, the area of wafer 1 to be inspected is positioned below imaging lens 42. In FIG4 , sheet 9 and frame 7 are omitted.

Next, when light source 52 is activated, light 64 emitted from point light source 56 travels along second optical path 62. Specifically, light 64 passes through collimating lens 58, where it is converted into parallel light. Light 64 then passes through focusing lens 60, where it is focused onto beam splitter 44. It is then reflected by beam splitter 44 and passes through imaging lens 42. Light 64, once again converted into parallel light by imaging lens 42, is then irradiated onto back surface 1b of wafer 1 and reflected back onto wafer 1.

Reflected light 66 of light 64 travels to imaging lens 42 and is focused onto imaging point 46 located on beam splitter 44. Reflected light 66 then travels along first optical path 50 and reaches camera 48. Camera 48 captures the reflected light 66 to form a photographic image.

As shown in FIG5 , while the wafer 1 held by the holding stage 34 and the imaging unit 38 are moved along the X-axis and Y-axis directions, 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 side 1b of the wafer 1 can be inspected.

When modified layer 3a forms inside wafer 1, minute irregularities appear on back surface 1b of wafer 1, reflecting the state of the modified layer 3a. Furthermore, because light 64 is scattered in the areas where the irregularities appear, the areas where the irregularities appear bright in the image captured by reflected light 66. This phenomenon is called a magic mirror.

Figure 6 is a top view schematically showing an example of photographic image 13. As shown in Figure 6, photographic image 13 captures a bright line 15 reflecting the state of formation of the modified layer 3a. Therefore, the state of formation of the modified layer 3a within the wafer 1 can be determined based on photographic image 13. For example, if bright line 15 captured by photographic image 13 has a notch, it can be confirmed that the modified layer 3a has not been properly formed in the region where the notch is detected.

Here, when a linear or planar light source of a specific size is installed in wafer inspection apparatus 8 instead of point light source 56, the difference in the path of light 64 emitted from the center of the light source and the peripheral light emitted from the edge causes blurring in photographic image 13. This is because when light 64 and the peripheral light are ultimately incident on back surface 1b of wafer 1, the peripheral light enters from an unintended direction due to the uneven shape and is reflected in an unintended direction.

Therefore, in the wafer inspection apparatus 8 according to this embodiment, to prevent the generation of peripheral light that blurs the photographic image 13, the optical fiber 54 forming the point light source 56 can be set to a diameter of 20 μm or less. Furthermore, when a laser oscillator is used as the light source 52, the laser oscillator can oscillate laser light within a wavelength range of, for example, 600 nm to 700 nm. Because laser beams are monochromatic, have a small diameter, and exhibit excellent linearity, using a laser beam as light 64 results in a sharp photographic image 13 with improved contrast.

Furthermore, in the wafer inspection apparatus 8 according to this embodiment, light 64 is focused by the focusing lens 60 onto the beam splitter 44, and reflected light 66 is focused by the imaging lens 42 onto the beam splitter 44. Therefore, compared to a case where the light incident on the beam splitter is not focused onto the beam splitter 44, light scattering in the beam splitter 44 is suppressed. Consequently, the captured image 13 becomes sharper and has improved contrast.

FIG8 is a side view schematically illustrating the path of reflected light 66 focused on beam splitter 44. Reflected light 66 enters beam splitter 44 from interface 44a on the imaging lens 42 side of beam splitter 44, is focused within beam splitter 44, and travels outside beam splitter 44 from interface 44b on the camera 48 side of beam splitter 44. At this point, a portion of reflected light 66 is reflected at interfaces 44a and 44b.

Figure 8 shows the paths of light beams 66a and 66b traveling along the outer edge of reflected light 66. As shown in Figure 8, light beams 66a and 66b are partially reflected at interface 44b, and reflected light beams 68a and 68b are also reflected at interface 44a. When reflected light beams 68a and 68b reach camera 48 and are simultaneously reflected on camera image 13 along with light beams 66a and 66b, camera image 13 becomes blurred.

However, when imaging point 46 of imaging lens 42 is positioned within beam splitter 44, the incident and reflection angles of light beams 66a and 66b at interface 44b, and the incident and reflection angles of light beams 68a and 68b at interface 44a, become relatively large. Consequently, reflected light beams 68a and 68b travel a great distance from camera 48 and are less likely to reach camera 48.

On the other hand, if the beam splitter 44 is not positioned at the imaging point 46 of the imaging lens 42, the incident and reflected angles of light at the interfaces 44a and 44b become smaller. In this case, the light reflected at the interfaces 44a and 44b easily reaches the camera 48, which is a major factor causing the captured image 13 to become unclear.

Therefore, the photographic image 13 obtained using the wafer inspection apparatus 8 according to this embodiment has high contrast and high precision. Based on the photographic image 13, more precise analysis and more detailed information can be obtained regarding the formation state of the modified layer 3a inside the wafer 1.

Next, the wafer inspection method according to this embodiment, which inspects wafer 1 using the wafer inspection apparatus 8 described above, will be described. FIG7 is a flow chart illustrating the flow of each step of the wafer inspection method according to this embodiment. This wafer inspection method is implemented using wafer inspection apparatus 8 schematically shown in FIG3 and other figures. Below, the wafer 1 inspected using the wafer inspection method according to this embodiment and each step will be described.

The wafer 1 inspected using this inspection method has a plurality of intersecting predetermined dividing lines 3 defined on its surface 1a, as shown in FIG1(A). Devices 5 are formed in the respective areas of the surface 1a demarcated by the predetermined dividing lines 3. Furthermore, as shown in FIG2(A) and FIG2(B), a laser beam 6 having a wavelength penetrating the wafer 1 is irradiated with the laser beam 6, with a focal point 4b positioned within the wafer 1, to form a modified layer 3a along the plurality of predetermined dividing lines 3.

In this inspection method, first, a holding step S10 is performed in which the wafer 1 is held by the holding stage 34 with the surface 1a of the wafer 1 facing the holding stage 34 and the back side 1b exposed upward.

Next, as shown in FIG4 and other figures, an irradiation step S20 is performed, in which light 64 emitted from point light source 56 is directed through collimating lens 58, focusing lens 60, beam splitter 44, and imaging lens 42 to the back surface 1b of wafer 1. Light 64 can be, for example, a laser beam having a wavelength of 600 nm to 700 nm. However, light 64 is not limited to a laser beam. In particular, when light 64 is a laser beam, although the linearity of light 64 is excellent, FIG4 emphasizes the diffusion of light 64 emitted from point light source 56 for ease of illustration.

Light 64 emitted from point light source 56 first travels to collimating lens 58, where it is converted into parallel light. This parallel light 64 is then focused by focusing lens 60 onto beam splitter 44 and reflected toward imaging lens 42. Since imaging point 46 of imaging lens 42 is positioned at beam splitter 44, light 64 is further converted into parallel light by imaging lens 42 and irradiated onto back surface 1b of wafer 1.

Next, the imaging step S30 is performed, where the light 64 irradiated onto the back surface 1b of the wafer 1 in the irradiation step S20 and reflected from the back surface 1b, passing through the imaging lens 42 and the beam splitter 44 and reaching the camera 48, thereby forming the photographic image 13. Specifically, the reflected light 66 of the light 64 reflected from the back surface 1b of the wafer 1 is focused by the imaging lens 42 onto the beam splitter 44. Furthermore, a portion of the reflected light 66 travels along the first optical path 50 and reaches the camera 48, where it is detected by the image sensor of the camera 48.

Next, a determination step S40 is performed to determine the formation state of the modified layer 3a formed inside the wafer 1 based on the photographic image 13 obtained in the imaging step S30. Figure 6 is a schematic top view of an example of the photographic image 13. Bright lines 15 are captured in the photographic image 13 by the magic mirror phenomenon. Bright lines 15 appear in the photographic image 13 due to the reflection of light 64 from the uneven surface of the back surface 1b of the wafer 1 caused by the formation of the modified layer 3a inside the wafer 1. These lines 15 are reflected in the photographic image 13, reflecting the formation state of the modified layer 3a.

For example, if it is not possible to irradiate the entire back surface 1b of the wafer 1 with light 64 at once, after performing step S20 and imaging step S30, the irradiation step S20 and imaging step S30 can be repeated while the wafer 1 and imaging unit 38 are moved relative to each other. Furthermore, when the photographic image 13 is obtained for the entire back surface 1b of the wafer 1, step S40 is performed to determine the state of formation of the modified layer 3a over the entire area of the wafer 1.

In particular, in the wafer inspection method according to this embodiment, since light 64 is emitted from a point light source 56, when it strikes the back surface 1b of the wafer 1, it does not contain any peripheral light components that travel in a direction that deviates from the direction of travel of the deflected light 64. Consequently, the photographic image 13 has a high contrast, and the bright lines 15 are captured with high precision. Therefore, the formation status of the modified layer 3a can be determined more precisely and in detail based on the photographic image 13.

For example, in photographic image 13, if bright line 15 is interrupted, modified layer 3a is not formed within wafer 1 at the location corresponding to the interruption of bright line 15. Furthermore, this suggests that if bright line 15 snakes significantly, modified layer 3a also snakes. Furthermore, the size and depth of modified layer 3a can be determined from the thickness or color of bright line 15.

Therefore, when it is determined that the modified layer 3a is not sufficiently formed inside the wafer 1, laser processing can be performed again to form a sufficient modified layer 3a on the wafer 1, or the processing conditions when laser processing a new wafer 1 are improved.

Furthermore, the present invention is not limited to the above-described embodiment and can be implemented with various modifications. For example, in the above-described embodiment, the wafer 1 and the imaging unit 38 are moved relative to each other by moving the holding stage 34. However, one aspect of the present invention is not limited to this. Specifically, the imaging unit 38 may be movable in one or both of the X-axis and Y-axis directions.

The structures and methods related to the above-mentioned embodiments may be implemented with appropriate modifications as long as they do not depart from the scope of the purpose of the present invention.

1: Wafer 1a: Surface 1b: Backside 3: Predetermined dividing line 3a: Modified layer 5: Device 7: Frame 9: Sheet 11: Frame unit 13: Camera image 15: Line 2: Laser processing device 4: Laser processing unit 4a: Processing head 4b: Converging point 6: Laser beam 8: Wafer inspection device 10: Base 12, 22: Moving unit 14, 24: Guide rails 16, 26: Moving stage 18, 28: Ball screw 20, 30: Pulse motor 32: Cover 34: Holding platform 34a: Top surface 34b: Clamp 36: Support unit 38: Imaging unit 40: Display unit 42: Imaging lens 44: Beam splitter 44a, 44b: End face 46: Imaging point 48: Camera 50, 62: Optical path 52: Light source 54: Optical fiber 56: Point light source 58: Collimating lens 60: Focusing lens 64: Light 66, 68a, 68b: Reflected light 66a, 66b: Light

Figure 1(A) is a perspective view schematically showing the front surface of a wafer, and Figure 1(B) is a perspective view schematically showing the back surface of a wafer. Figure 2(A) is a perspective view schematically showing a modified layer formed inside a wafer, and Figure 2(B) is a cross-sectional view schematically showing a modified layer formed inside a wafer. Figure 3 is a perspective view schematically showing a wafer inspection apparatus. Figure 4 is a side view schematically showing the optical system of the wafer inspection apparatus. Figure 5 is a perspective view schematically showing the irradiation step and the imaging step. Figure 6 is a top view schematically showing an example of a photographed image. Figure 7 is a flow chart illustrating the flow of each step of the wafer inspection method. Figure 8 is a side view schematically showing the path of light focused by the spectrometer.

1: Wafer

1a: Surface

1b: Back

34: Holding Station

34a: Above

38: Camera unit

42: Imaging lens

44: Optical Splitter

46: Imaging point

48: Camera

50,62: Light path

52: Light Source

54: Fiber Optic

56: Point Light Source

58: Collimating lens

60: Focusing lens

64: Light

66: Reflected Light

Claims (3)

A wafer inspection device for inspecting a wafer having a modified layer formed therein is characterized in that it comprises: a holding table capable of holding the wafer with its back side exposed upward; a point light source for emitting light that is irradiated onto the back side of the wafer held on the holding table; and an imaging unit for capturing reflected light emitted from the point light source and irradiated onto the back side of the wafer, the imaging unit comprising a wafer held on the holding table. An imaging lens facing the wafer, 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. The light emitted by the point light source is a laser beam. A collimating lens is disposed on the second optical path to generate parallel light from the light emitted from the point light source, and a focusing lens is disposed to focus the parallel light generated by the collimating lens onto the beam splitter. The wafer inspection apparatus as recited in claim 1 further comprises a moving unit for moving the holding stage and the imaging unit relative to each other. A wafer inspection method, wherein a wafer having a plurality of intersecting predetermined dividing lines defined on its surface and having devices formed in respective regions of the surface divided by the predetermined dividing lines is inspected using the wafer inspection apparatus of claim 1 or 2. A laser beam having a wavelength penetrating the wafer is irradiated with a focal point positioned within the wafer, thereby forming a modified layer along the plurality of predetermined dividing lines. The wafer inspection method comprises: a holding step of placing the wafer with its surface facing the holding table, with its back side exposed upward, and holding the wafer with the holding table. The wafer is held on a stage; an irradiation step is performed, wherein the light emitted from the point light source is irradiated onto the back surface of the wafer via the collimating lens, the focusing lens, the beam splitter, and the imaging lens; an imaging step is performed, wherein the reflected light of the light irradiated onto the back surface of the wafer in the irradiation step and reflected from the back surface, then reaching the camera via the imaging lens and the beam splitter, is captured to form a photographic image; and a determination step is performed, wherein the state of the modified layer formed inside the wafer is determined based on the photographic image obtained in the imaging step. The light emitted by the point light source is a laser beam.