KR20230086587A - Inspection method - Google Patents

Abstract

The inspection method performed by the laser processing apparatus includes a first step of attaching a holding member to the back surface of a wafer on which a modified region is formed, and setting the mounting surface of the holding member on a suction table; Based on the second step of outputting light having transparency from the mounted wafer by the imaging unit and detecting the light having transparency passing through the wafer, and the captured image output from the imaging unit that detected the light having transparency , and a third step of specifying the state of the modified region of the wafer. In the first step, a holding member whose thickness is set according to the modified region distance is attached to the back surface.

Description

Inspection method {INSPECTION METHOD}

One aspect of the present invention relates to a test method.

In addition to providing a semiconductor substrate, a plurality of lines are formed by irradiating the wafer with a laser beam from the surface side of the semiconductor substrate to cut along each of the plurality of lines of the wafer having the functional element layer formed on the semiconductor substrate as the back surface. An inspection apparatus is known which forms a plurality of rows of modified regions inside a semiconductor substrate along each of them. The inspection apparatus described in Japanese Patent Laid-Open No. 2017-64746 is equipped with an infrared camera and is capable of observing modified regions formed inside the semiconductor substrate, processing damage formed in the functional element layer, and the like from the surface side of the semiconductor substrate. is supposed to In the inspection device, for example, based on such an internal observation result, the crack state of the wafer after processing is estimated, and based on the crack state estimation result, whether or not the processing passes (processing desired under the set processing conditions) is estimated. can be performed) is determined.

In the internal observation as described above, in addition to direct observation in which imaging is performed by moving the focal point from the front surface side toward the rear surface side, a region on the opposite side to the front surface is focused from the front side with respect to the rear surface, and the light reflected from the rear surface is captured In some cases, the backside reflection observation is performed. In internal observation, usually, a holding member is attached to the back side of the wafer, and the above-described direct observation and back surface reflection observation are performed in a state where the holding member is attached to the suction table. Here, about the holding member, embossing process is given to the surface which contact|connects with an adsorption|suction table in some cases. Also, in the adsorption table, the surface on which the holding member is attached has a porous structure, and there are cases in which minute concavities and convexities made of a porous material are formed. In the case where such a retaining member and/or adsorption table is used and observation of back surface reflection is performed, the pattern of the embossed surface of the holding member and the porous structure of the adsorption table are captured images. There are cases where it is stamped on and thrown away. In this case, there is a risk that the estimation accuracy of the state of dents or cracks in the modified region deteriorates (a misjudgment of the state of the modified region occurs).

One aspect of the present invention has been made in view of the above circumstances, and relates to an inspection method capable of suppressing erroneous judgment in observing the inside of a wafer after laser processing.

In an inspection method according to one aspect of the present invention, a holding member is attached to a second surface opposite to a first surface to which a laser beam is irradiated with respect to a wafer having a modified region formed therein by irradiation with a laser beam ( ), and the first step of installing the surface opposite to the surface to be attached to the wafer in the holding member to the suction table, and the wafer placed on the suction table via the holding member, the imaging unit has transparency Based on the second step of outputting light and detecting light having transparency that has propagated through the wafer, and a captured image output from the imaging unit that has detected the light having transparency, the state of the modified region of the wafer is determined. A third step for specifying is provided, and in the first step, the holding member whose thickness is set according to the modified region distance, which is the distance from the second surface of the wafer to the modified region most separated from the second surface. is attached to the second surface.

In the inspection method according to one aspect of the present invention, a holding member is attached to the second surface, which is the back side of a wafer having a modified region formed therein, and the holding member is installed on a suction table. Then, the inside of the wafer is observed by outputting light having transparency to the wafer placed on the suction table through the holding member, and the state of the modified region of the wafer is specified based on the captured image there is. Here, in the case where internal observation is performed with such a configuration, the area on the opposite side to the first surface, which is the surface, is focused from the side of the first surface with respect to the second surface, which is the back surface, and the light reflected from the second surface is imaged. When observation of the back surface reflection is performed, the pattern of the embossed surface of the holding member or the pattern of the porous structure of the suction table may be captured in the captured image. In this case, there is a possibility that the accuracy of estimating the state of the modified region of the wafer based on the captured image may deteriorate. In this regard, in the inspection method according to one aspect of the present invention, a holding member whose thickness is set according to the modified region distance, which is the distance from the second surface to the modified region most separated from the second surface, is placed on the second surface of the wafer. are attached In this way, by setting the thickness of the holding member in consideration of the distance of the modified region, setting the thickness of the holding member so as to prevent the pattern of the holding member or the like from being reflected in the captured image in the observation of the rear surface reflection of the modified region. It becomes possible. This can suppress erroneous judgment in internal observation of the wafer after laser processing.

In the first step, a holding member whose thickness is set to be greater than the distance between the modified regions may be attached to the second surface. This suppresses the appearance of the pattern of the retaining member or the like in the picked-up image in the backside reflection observation of the modified region. This can suppress erroneous judgment in internal observation of the wafer after laser processing.

In the first step, a holding member whose thickness is set to be larger than a value obtained by multiplying the modified region distance by the refractive index ratio of the holding member to the wafer may be attached to the second surface. By multiplying the modified region distance with the refractive index ratio, the modified region distance is converted to an approximate distance in the holding member taking the refractive index into consideration, so that a holding member having a thickness greater than the value after conversion is attached to the second surface, thereby modifying It is suppressed that the pattern of the retaining member or the like is captured in the picked-up image in the observation of the backside reflection related to the area. This can suppress erroneous judgment in internal observation of the wafer after laser processing. In addition, by setting the thickness of the holding member according to the value obtained by multiplying the modified region distance by the refractive index ratio, the thickness of the holding member can be reduced, compared to the case where the thickness of the holding member is simply set to be larger than the modified region distance, for example. can be made small That is, erroneous judgment in observation of the inside of the wafer after laser processing can be suppressed while avoiding an excessive increase in the thickness of the holding member.

In the first step, a holding member whose thickness is set to be larger than a value obtained by multiplying the modified region distance by the dz rate ratio of the holding member to the wafer may be attached to the second surface. By multiplying the modified region distance with the dz rate ratio, the modified region distance is converted into an approximate distance in the holding member taking into account the refractive index and NA (Numerical Aperture) of the objective lens of the imaging unit, so that the thickness is larger than the value after conversion By attaching the member to the second surface, it is suppressed that the pattern of the retaining member or the like is captured in the captured image in the backside reflection observation of the modified region. This can suppress erroneous judgment in internal observation of the wafer after laser processing. In addition, by setting the thickness of the holding member according to the value obtained by multiplying the modified region distance by the dz rate ratio, for example, when the thickness of the holding member is simply set to be larger than the modified region distance, only the refractive index ratio is considered and maintained Compared with the case where the thickness of the member is set, the thickness of the holding member can be reduced. That is, erroneous judgment in observation of the inside of the wafer after laser processing can be suppressed while avoiding an excessive increase in the thickness of the holding member.

In an inspection method according to one aspect of the present invention, a holding member is attached to a second surface opposite to a first surface to which a laser beam is irradiated with respect to a wafer having a modified region formed therein by irradiation with a laser beam, , the first step of installing the surface opposite to the surface attached to the wafer in the holding member to the suction table, and outputting light having transparency by the imaging unit to the wafer placed on the suction table through the holding member and a second step of detecting the light having transmission through the wafer, and a third step of specifying the state of the modified region of the wafer based on the captured image output from the imaging unit that detects the light having transmission. And, in the first step, a holding member having transmittance of 50% or less of light transmittance is attached to the second surface.

In the inspection method according to one aspect of the present invention, since a holding member (holding member having a light-shielding property) having a transmittance of 50% or less of light transmittance is attached to the second surface, in the observation of the reflection of the back surface, the light-blocking property has An image of a thing disposed below the holding member (at the suction table side) is difficult to be captured in the captured image. Specifically, the pattern of the embossed surface of the holding member and the pattern of the porous structure of the adsorption table are difficult to be captured in the captured image. This suppresses the pattern of the holding member or the like from being reflected in the captured image in the observation of the back surface reflection, and suppresses erroneous judgment in the observation of the inside of the wafer after laser processing.

In the first step, a holding member having a transmissive light transmittance of 30% or less may be attached to the second surface. By setting the transmittance of light having transmittance in the holding member to 30% or less, it is more appropriate to suppress the pattern of the holding member or the like from being reflected in the captured image in the backside reflection observation, and to observe the inside of the wafer after laser processing Misjudgment in can be suppressed.

In the first step, a holding member made of a transmissive light absorbing material may be applied to the second surface. According to such a structure, the transmittance|permeability of the light which has permeability in a holding member can be moderately suppressed.

In the first step, a holding member made of a transmissive material that reflects light may be attached to the second surface. According to such a structure, the transmittance|permeability of the light which has permeability in a holding member can be moderately suppressed.

In the second step, while changing the imaging area along the Z direction, which is the vertical direction, light having transmittance is detected for each imaging area, and in the third step, the captured image for each imaging area along the Z direction The feature point and the feature amount of the feature point may be detected, and the position of the feature point having a relatively large feature amount may be specified as the formation position of the modified region. In this way, by specifying the formation position of the modified region from the feature amount of the feature point in the captured image, the precision and efficiency of the inside observation of the wafer after laser processing can be improved.

According to the inspection method according to one aspect of the present invention, erroneous judgment in internal observation of a wafer after laser processing can be suppressed.

1 is a configuration diagram of a laser processing apparatus according to an embodiment.
2 is a plan view of a wafer in one embodiment.
3 is a cross-sectional view of a portion of the wafer shown in FIG. 2;
FIG. 4 is a configuration diagram of a laser irradiation unit shown in FIG. 1 .
FIG. 5 is a configuration diagram of an imaging unit for inspection shown in FIG. 1 .
FIG. 6 is a configuration diagram of an imaging unit for alignment correction shown in FIG. 1 .
FIG. 7 is a cross-sectional view of a wafer for explaining the principle of imaging by the imaging unit for inspection shown in FIG. 5 and images at each location by the imaging unit for inspection.
FIG. 8 is a cross-sectional view of a wafer for explaining the principle of imaging by the imaging unit for inspection shown in FIG. 5 and images at each location by the imaging unit for inspection.
Fig. 9 is a SEM image of modified regions and cracks formed inside the semiconductor substrate.
Fig. 10 is a SEM image of modified regions and cracks formed inside the semiconductor substrate.
FIG. 11 is a schematic diagram showing an optical path for explaining the principle of imaging by the imaging unit for inspection shown in FIG. 5 and an image at a focus by the imaging unit for inspection.
FIG. 12 is a schematic diagram showing an optical path for explaining the principle of imaging by the imaging unit for inspection shown in FIG. 5 and an image at a focus by the imaging unit for inspection.
13 is a diagram explaining crack detection.
14 is a diagram explaining crack detection.
15 is a diagram explaining dent detection.
16 is a diagram explaining dent detection.
17 is a diagram explaining dent detection.
Fig. 18 is a diagram explaining detailed configurations of a holding member and an adsorption table.
Fig. 19 is a view explaining problems in observing the reflection of the back side of the inside observation.
Fig. 20 is a diagram for explaining an example of a holding member suitable for observation of back surface reflection.
Fig. 21 is a diagram for explaining an example of a holding member suitable for observation of back surface reflection.
Fig. 22 is a diagram showing the determination result according to the combination of the thickness and the transmittance of the holding member.
23 is a diagram for explaining an example of the distance to a modified region for each processing type.
24 is a flowchart according to an example of an inspection method.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings. In addition, in each figure, the same code|symbol is attached|subjected to the same or equivalent part, and overlapping description is abbreviate|omitted.

[Configuration of laser processing equipment]

As shown in FIG. 1, the laser processing apparatus 1 includes a suction table 2, a laser irradiation unit 3, a plurality of imaging units (imaging units) 4, 5, 6, and a drive unit ( 7) (drive unit), control unit 8, and display 150 are provided. The laser processing device 1 is a device that forms a modified region 12 on an object 11 by irradiating the object 11 with a laser beam L.

The suction table 2 supports the target object 11 by adsorbing, for example, a film applied to the target object 11 . In addition, although illustration is omitted in FIG. 1, as shown in FIG. 18 and the like, a holding member 300 holding the wafer 20 between the wafer 20 serving as the target object 11 and the suction table 2. ) is provided (details will be described later). The suction table 2 is movable along each of the X and Y directions, and is rotatable about an axis parallel to the Z direction as a center line. Further, the X direction and the Y direction are the first horizontal direction and the second horizontal direction perpendicular to each other, and the Z direction is the vertical direction.

The laser irradiation unit 3 condenses the laser beam L having transparency to the object 11 and irradiates the object 11 with it. When the laser beam L is condensed inside the target object 11 supported by the adsorption table 2, the laser beam L is particularly absorbed in a portion corresponding to the convergence point C of the laser beam L. , the modified region 12 is formed inside the object 11.

The modified region 12 is a region different from the surrounding unmodified region in density, refractive index, mechanical strength, and other physical properties. Examples of the modified region 12 include a melted region, a crack region, a dielectric breakdown region, and a refractive index change region. The modified region 12 has a characteristic that cracks tend to extend from the modified region 12 to the incident side of the laser beam L and to the opposite side. Such properties of the modified region 12 are used for cutting the object 11 .

As an example, when the adsorption table 2 is moved along the X direction and the light converging point C is moved relative to the target object 11 along the X direction, a plurality of modified spots 12s are formed along the X direction. It is formed so as to line up in a row. One modified spot 12s is formed by irradiation of one pulse of laser light L. A row of modified regions 12 is a set of a plurality of modified spots 12s arranged in a row. Modified spots 12s adjacent to each other may be connected to each other or separated from each other depending on the relative moving speed of the light converging point C with respect to the object 11 and the repetition frequency of the laser beam L.

The imaging unit 4 images the modified region 12 formed in the object 11 and the tip of a crack extending from the modified region 12 .

The imaging unit 5 and the imaging unit 6 capture an image of the target object 11 supported on the suction table 2 under the control of the control unit 8 by light passing through the target object 11 . The image obtained by imaging by the imaging units 5 and 6 is provided for the alignment of the irradiation position of the laser beam L as an example.

The drive unit 7 supports the laser irradiation unit 3 and the plurality of imaging units 4, 5 and 6. The drive unit 7 moves the laser irradiation unit 3 and the plurality of imaging units 4, 5 and 6 along the Z direction.

The control unit 8 controls the operation of the suction table 2, the laser irradiation unit 3, the plurality of imaging units 4, 5 and 6, and the driving unit 7. The control unit 8 is configured as a computer device including a processor, memory, storage and communication device and the like. In the control unit 8, a processor executes software (program) read into a memory or the like, and controls reading and writing of data in the memory and storage, and communication by the communication device.

The display 150 has a function as an input unit that accepts input of information from the user and a function as a display unit that displays information to the user.

[Construction of object]

The object 11 of this embodiment is a wafer 20 as shown in FIGS. 2 and 3 . The wafer 20 includes a semiconductor substrate 21 and a functional element layer 22 . In this embodiment, the wafer 20 is described as having the functional element layer 22, but the wafer 20 may or may not have the functional element layer 22, and may be a bare wafer. The semiconductor substrate 21 has a back surface 21a and a surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The functional element layer 22 is formed on the back surface 21a of the semiconductor substrate 21 . The functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the back surface 21a. The functional element 22a is, for example, a light-receiving element such as a photodiode, a light-emitting element such as a laser diode, or a circuit element such as a memory. In some cases, the functional element 22a is configured three-dimensionally by stacking a plurality of layers. In addition, the semiconductor substrate 21 is provided with a notch 21c indicating the crystal orientation, but an orientation flat may be provided instead of the notch 21c.

The wafer 20 is cut into functional elements 22a along each of the plurality of lines 15 . The plurality of lines 15 pass between each of the plurality of functional elements 22a when viewed from the thickness direction of the wafer 20 . More specifically, the line 15 passes through the center of the street area 23 (the center in the width direction) when viewed from the thickness direction of the wafer 20 . The street region 23 extends in the functional element layer 22 so as to pass between neighboring functional elements 22a. In this embodiment, the plurality of functional elements 22a are arranged in a matrix shape along the back surface 21a, and the plurality of lines 15 are set in a grid pattern. In addition, although the line 15 is a virtual line, it may be a line actually drawn.

[Configuration of the laser irradiation unit]

As shown in FIG. 4 , the laser irradiation unit 3 has a light source 31 , a spatial light modulator 32 , and a condensing lens 33 . The light source 31 outputs the laser light L by, for example, a pulse oscillation method. The spatial light modulator 32 modulates the laser light L output from the light source 31 . The spatial light modulator 32 is, for example, a spatial light modulator (SLM) of liquid crystal on silicon (LCOS). The condensing lens 33 condenses the laser light L modulated by the spatial light modulator 32 . In addition, the condensing lens 33 may be a correction ring lens.

In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with the laser beam L from the surface 21b side of the semiconductor substrate 21 along each of the plurality of lines 15, Two rows of modified regions 12a and 12b are formed inside the semiconductor substrate 21 along each of the lines 15 of . The modified region 12a is a modified region closest to the back surface 21a among the two rows of modified regions 12a and 12b. The modified region 12b is a modified region closest to the modified region 12a among the two rows of modified regions 12a and 12b, and is a modified region closest to the surface 21b.

The two rows of modified regions 12a and 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20 . The two rows of modified regions 12a and 12b are formed by relatively moving the two converging points C1 and C2 along the line 15 with respect to the semiconductor substrate 21 . The laser light L is modulated by the spatial light modulator 32 so that, for example, the light-converging point C2 is located on the rear side of the traveling direction and on the incident side of the laser light L with respect to the light-converging point C1. . Regarding the formation of the modified region, either a single focal point or a multi focal point may be used, and either one pass or multiple passes may be used.

The laser irradiation unit 3 irradiates the wafer 20 with a laser beam L from the surface 21b side of the semiconductor substrate 21 along each of a plurality of lines 15 . As an example, with respect to the semiconductor substrate 21, which is a single crystal silicon <100> substrate with a thickness of 400 μm, two light converging points C1 and C2 are aligned at positions of 54 μm and 128 μm from the back surface 21a, respectively, The laser beam L is irradiated to the wafer 20 from the surface 21b side of the semiconductor substrate 21 along each of the plurality of lines 15 . At this time, for example, in the case where the cracks 14 spanning two rows of modified regions 12a and 12b reach the back surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm and the pulse width is is 700 n seconds, and the repetition frequency is 120 kHz. In addition, the output of the laser light L at the light-converging point C1 is 2.7 W, and the output of the laser light L at the light-converging point C2 is 2.7 W, so that 2 for the semiconductor substrate 21 The relative moving speed of the dog's light converging points C1 and C2 is 800 mm/sec. Further, for example, when the number of processing passes is 5, with respect to the wafer 20 described above, for example, ZH80 (position 328 μm from the back surface 21a), ZH69 (position 283 μm from the back surface 21a) ), ZH57 (position 234 μm from the back surface 21a), ZH26 (position 107 μm from the back surface 21a), ZH12 (position 49.2 μm from the back surface 21a) may be the processing position. In this case, for example, the wavelength of the laser light L may be 1080 nm, the pulse width may be 400 nsec, the repetition frequency may be 100 kHz, and the moving speed may be 490 mm/sec.

[Configuration of imaging unit for inspection]

As shown in FIG. 5 , the imaging unit 4 (imaging unit) includes a light source 41 , a mirror 42 , an objective lens 43 , and an optical detection unit 44 . The imaging unit 4 captures an image of the inside of the wafer 20 by outputting light having transparency to the wafer 20 and detecting the light propagating through the wafer 20 . The light source 41 outputs light l1 having transparency to the semiconductor substrate 21 . The light source 41 is constituted by, for example, a halogen lamp and a filter, and outputs light 11 in the near infrared region. The light l1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated to the wafer 20 from the surface 21b side of the semiconductor substrate 21. At this time, the suction table 2 supports the wafer 20 on which two rows of modified regions 12a and 12b are formed as described above.

The objective lens 43 passes the light 11 reflected from the back surface 21a of the semiconductor substrate 21 . That is, the objective lens 43 passes the light l1 propagated through the semiconductor substrate 21 . The numerical aperture NA of the objective lens 43 is, for example, 0.45 or more. The objective lens 43 has a correction ring 43a. The correction ring 43a corrects the aberration occurring in the light 11 in the semiconductor substrate 21 by, for example, adjusting the distance between a plurality of lenses constituting the objective lens 43 . Also, the means for correcting the aberration is not limited to the correction ring 43a, and other means for correcting such as a spatial light modulator may be used. The light detector 44 detects the light 11 transmitted through the objective lens 43 and the mirror 42 . The photodetector 44 is constituted by, for example, an InGaAs camera, and detects the light 11 in the near infrared region. The means for detecting (imaging) the light 11 in the near-infrared region is not limited to the InGaAs camera, and may be any other imaging means, such as a transmission type confocal microscope, as long as it performs transmission type imaging.

The imaging unit 4 can image each of the two rows of modified regions 12a and 12b and the tips of each of the plurality of cracks 14a, 14b, 14c and 14d (details will be described later). The crack 14a is a crack extending from the modified region 12a to the side of the back surface 21a. The crack 14b is a crack extending from the modified region 12a to the surface 21b side. The crack 14c is a crack extending from the modified region 12b to the back surface 21a side. The crack 14d is a crack extending from the modified region 12b to the surface 21b side.

[Configuration of Imaging Unit for Alignment Correction]

As shown in FIG. 6 , the imaging unit 5 has a light source 51 , a mirror 52 , a lens 53 , and a light detection unit 54 . The light source 51 outputs light I2 having transparency to the semiconductor substrate 21 . The light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near infrared region. The light source 51 may be common with the light source 41 of the imaging unit 4 . The light I2 output from the light source 51 is reflected by the mirror 52, passes through the lens 53, and is irradiated to the wafer 20 from the surface 21b side of the semiconductor substrate 21.

The lens 53 passes the light I2 reflected from the back surface 21a of the semiconductor substrate 21 . That is, the lens 53 passes the light I2 that has propagated through the semiconductor substrate 21 . The numerical aperture of the lens 53 is 0.3 or less. That is, the numerical aperture of the objective lens 43 of the imaging unit 4 is larger than the numerical aperture of the lens 53 . The light detector 54 detects the light I2 passing through the lens 53 and the mirror 52 . The photodetector 54 is constituted by, for example, an InGaAs camera, and detects light I2 in the near infrared region.

The imaging unit 5 irradiates the wafer 20 with light I2 from the front surface 21b side under the control of the control unit 8, and also from the rear surface 21a (functional element layer 22) side. By detecting the returning light I2, the functional element layer 22 is imaged. In addition, the imaging unit 5 similarly irradiates the wafer 20 with the light I2 from the surface 21b side under the control of the control unit 8, and the modified region in the semiconductor substrate 21 By detecting the light I2 returning from the formation position of (12a, 12b), an image of the region including the modified regions 12a, 12b is acquired. These images are used for alignment of the irradiation position of the laser beam L. The imaging unit 6 is the same as the imaging unit 5 except that the lens 53 has a lower magnification (eg, 6x for the imaging unit 5 and 1.5x for the imaging unit 6). It has the same configuration as the above, and is used for alignment like the imaging unit 5.

[Principle of imaging by imaging unit for inspection]

Using the imaging unit 4 shown in FIG. 5 , as shown in FIG. 7 , a semiconductor substrate 21 in which cracks 14 spanning two rows of modified regions 12a and 12b reach the back surface 21a , the focal point F (focal point of the objective lens 43) is moved from the front surface 21b side toward the rear surface 21a side. In this case, when the focus F is set on the tip 14e of the crack 14 extending from the modified region 12b to the surface 21b side from the surface 21b side, the tip 14e can be confirmed (Fig. image on the right in 7). However, even if the focus F is set on the crack 14 itself and the front end 14e of the crack 14 reaching the back surface 21a from the surface 21b side, they cannot be confirmed (in FIG. 7 image on the left side of ). Further, if the focus F is set on the back surface 21a of the semiconductor substrate 21 from the front surface 21b side, the functional element layer 22 can be confirmed.

Further, using the imaging unit 4 shown in FIG. 5 , as shown in FIG. 8 , a semiconductor substrate in which cracks 14 spanning two rows of modified regions 12a and 12b do not reach the back surface 21a. Regarding (21), the focal point F is moved from the front surface 21b side toward the back surface 21a side. In this case, even if the focus F is focused on the front end 14e of the crack 14 extending from the modified region 12a to the back side 21a side from the front surface 21b side, the front end 14e cannot be confirmed ( image on the left in Fig. 8). However, the area on the opposite side of the back surface 21a to the surface 21b (i.e., the area on the functional element layer 22 side with respect to the back surface 21a) is focused F from the surface 21b side, When the virtual focal point Fv, which is symmetrical to the focal point F with respect to the back surface 21a, is positioned at the tip 14e, the tip 14e can be confirmed (image on the right in Fig. 8). In addition, the virtual focal point Fv is a point symmetrical with respect to the focal point F considering the refractive index of the semiconductor substrate 21 and the back surface 21a.

As described above, it is assumed that the reason why the crack 14 itself cannot be confirmed is because the width of the crack 14 is smaller than the wavelength of the light 11 as the illumination light. 9 and 10 are SEM (Scanning Electron Microscope) images of a modified region 12 and a crack 14 formed inside a semiconductor substrate 21 that is a silicon substrate. Fig. 9(b) is an enlarged image of region A1 shown in Fig. 9(a), Fig. 10(a) is an enlarged image of region A2 shown in Fig. 9(b), Fig. 10(b) is an enlarged image of the region A3 shown in Fig. 10(a). In this way, the width of the crack 14 is about 120 nm, and is smaller than the wavelength of the light l1 in the near infrared region (for example, 1.1 to 1.2 μm).

Based on the above, the assumed imaging principle is as follows. As shown in Fig. 11(a), when the focal point F is placed in the air, since the light l1 does not return, a black image is obtained (image on the right in Fig. 11(a)). . As shown in (b) of FIG. 11, when the focal point F is placed inside the semiconductor substrate 21, the light l1 reflected from the back surface 21a returns, so that a white image is obtained ( image on the right in Fig. 11(b)). As shown in (c) of FIG. 11 , when the focus F is focused on the modified region 12 from the front surface 21b side, the light l1 reflected from the back surface 21a by the modified region 12 and returned ), an image in which the modified region 12 is reflected in black is obtained in a white background (right image in FIG. 11(c)).

As shown in (a) and (b) of FIG. 12 , when the focus F is focused on the tip 14e of the crack 14 from the surface 21b side, for example, the crack 14 is formed near the tip 14e. Due to optical singularity (stress concentration, deformation, discontinuity of atomic density, etc.), confinement of light generated near the tip 14e, etc., a part of the light l1 reflected from the back surface 21a and returned is scattered, reflected, interfered, and absorbed Because of this, an image in which the tip 14e is reflected in black in a white background is obtained (images on the right in Fig. 12 (a) and (b)). As shown in Fig. 12(c), when the focus F is focused from the surface 21b side on a part other than the vicinity of the tip 14e of the crack 14, the light l1 reflected from the back surface 21a Since at least a part of is returned, a white image is obtained (the image on the right in Fig. 12(c)).

[Detection algorithm in internal observation]

Regarding the above-described internal observation of the wafer 20, an algorithm for detecting (specifying) cracks 14 and an algorithm for detecting (specifying) dents related to modified regions will be described in detail. The detection of such cracks 14 and the detection of dents related to the modified region may be performed after being judged by AI.

13 and 14 are views explaining crack detection. In Fig. 13, internal observation results (images inside the wafer 20) are shown. The controller 8 first detects a group of straight lines 140 in the image inside the wafer 20 as shown in FIG. 13(a). For detection of the group of straight lines 140, an algorithm such as Hough transform or LSD (Line Segment Detector) is used, for example. The Hough transform is a method of detecting straight lines for a point on an image by detecting all straight lines passing through that point and giving weight to straight lines passing more feature points. LSD is a method of estimating an area that becomes a line segment by calculating the gradient and angle of luminance values in an image, and detecting a straight line by approximating the area to a rectangle.

Next, as shown in FIG. 14 , the control unit 8 detects the crack 14 from the group of straight lines 140 by calculating the degree of similarity with the crack line for the group of straight lines 140 . As shown in the upper drawing of Fig. 14, the fracture line has a feature that the front and back are very bright in the Y direction with respect to the luminance value on the line. For this reason, the control unit 8 compares, for example, the luminance values of all the pixels of the detected straight line group 140 with the front and back in the Y direction, and determines the number of pixels whose difference is equal to or greater than a threshold value with the front and back as well. to score Then, among the plurality of straight line groups 140 detected, the one having the highest score of the degree of similarity with the fracture line is taken as the representative value in the image. The higher the representative value, the higher the probability that cracks 14 exist. The control unit 8 sets a relatively high score as a crack image candidate by comparing representative values in a plurality of images.

15 to 17 are diagrams explaining dent detection. In Fig. 15, internal observation results (images inside the wafer 20) are shown. For the image inside the wafer 20 as shown in FIG. Thus, the feature point 250 is detected. As methods for detecting feature points in this way, Eigen, Harris, Fast, SIFT, SURF, STAR, MSER, ORB, AKAZE and the like are known.

Here, as shown in FIG. 16, since forms, such as a circle and a rectangle, line up at regular intervals, the dent 280 has strong characteristics as a corner. For this reason, it becomes possible to detect the dent 280 with high precision by counting the feature amount of the feature point 250 in an image. As shown in Fig. 17, when the sum of feature values for each image shifted in the depth direction is compared, it is possible to confirm a change in the peak representing the amount of cracking heat for each modified layer. The controller 8 estimates the peak of the change as the position of the dent 280 . By counting the feature amount in this way, it becomes possible to estimate not only the dent position but also the pulse pitch.

[Details of internal observation method (inspection method)]

Internal observation is performed on the wafer 20 (wafer 20 after laser processing) on which modified regions are formed for the purpose of cutting the wafer 20 or the like. The internal observation method (inspection method) according to the present embodiment includes a first step, a second step, and a third step.

As shown in FIG. 18(a), in the first step, the laser beam is irradiated on the surface of the wafer 20 having modified regions SD1 and SD2 formed therein by irradiation with the laser beam. (21b) The holding member 300 is attached to the back surface 21a (second surface) opposite to the (first surface), and the surface of the holding member 300 to be adhered to the wafer 20 This is a step of attaching the mounting surface 300x, which is the opposite side of the surface, to the support surface 2x of the adsorption table 2.

The holding member 300 is, for example, a tape such as dicing tape or back grind tape. As shown in (b) of FIG. 18, the mounting surface 300x of the holding member 300 is embossed. In addition, the support surface 2x of the adsorption table 2 has a porous structure, and minute concavities and convexities made of a porous material are formed. In the case where the holding member 300 and/or the adsorption table 2 is used and internal observation is performed, the shape and adsorption of the mounting surface 300x of the holding member 300 are observed at the time of observation of the back surface reflection. The pattern of the support surface 2x of the table 2 may be reflected in the captured image (details will be described later). Therefore, as will be described later, in the internal observation method according to the present embodiment, the holding member 300 is installed so that the patterns of the holding member 300 and the adsorption table 2 do not appear in the captured image during observation of the back surface reflection. Optimization is performed, and the optimized holding member 300 is attached to the wafer 20 (details will be described later).

In the second step, the imaging unit 4 transmits light 11 (see Fig. 18(a)) to the wafer 20 installed on the suction table 2 via the holding member 300. ) and detecting the light l1 having transmittance passing through the wafer 20. In the second step, detection of the light 11 having transmittance (i.e., imaging) is performed for each imaging area while changing the imaging area along the Z direction, which is the vertical direction. Specifically, in the second step, the control unit 8 sequentially moves the imaging unit 4 to a position where imaging of each imaging area along the Z direction in the predetermined imaging range of the wafer 20 becomes possible. In addition to controlling the drive unit 7 to do so, the imaging unit 4 is controlled so that each imaging area is imaged while changing the imaging area along the Z direction. In the imaging range here, a direct observation area imaged by shifting the focus from the front surface 21b side toward the back surface 21a side, and the surface 21b in the area opposite to the front surface 21b with respect to the back surface 21a. A back surface reflection area in which light reflected from the back surface 21a by focusing from the side is imaged is included. That is, in the internal observation according to the present embodiment, in addition to direct observation in which imaging is performed by moving the focus from the front surface 21b side toward the rear surface 21a side, the rear surface 21a on the opposite side to the front surface 21b is observed. Back side reflection observation is performed in which the area is focused from the front side and the light 11 reflected from the back side is imaged.

The third step is a step of specifying the state of the modified region of the wafer 20 based on the captured image output from the imaging unit 4 that has detected the light 11 having transmission. In the third step, the control unit 8 detects dents and cracks in the modified region based on the feature amount of the feature point shown in the captured image of each captured region, and based on the detected information, the modified region Determine whether or not the state regarding is appropriate. The control unit 8 detects feature points and feature amounts of the feature points for the captured image of each captured region along the Z direction, and takes, for example, the position of a feature point having a relatively large feature amount as a formation position of a modified region. be specific As the detection algorithm in such internal observation, the above detection algorithm described with reference to Figs. 13 to 17 is used, for example.

Here, as described above, at the time of the backside reflection observation of the inside observation, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the suction table 2 are captured in the captured image. There is a task to throw away. Fig. 19 is a view explaining problems in observing the reflection of the back side of the inside observation. As shown in (a) of FIG. 19 , in the back surface reflection observation, in the area on the opposite side of the surface 21 b with respect to the back surface 21 a, that is, in the area on the holding member 300 and suction table 2 side, The light l1 having transparency is focused. Therefore, when the light l1 reflected by the back surface 21a is captured by the imaging unit 4, the shape of the mounting surface 300x of the holding member 300 in the captured image (see Fig. 19(b)) However, there are cases where the pattern of the support surface 2x of the adsorption table 2 (see FIG. 19(c)) is imprinted. In this case, there is a possibility that the accuracy of determination of the state of the modified region by the control unit 8, specifically, the estimation accuracy of the dent or crack state of the modified region may deteriorate.

Fig. 19(d) is a diagram showing an example of internal observation results in the case where the pattern of the holding member 300 or the like is captured in the captured image. In (d) of FIG. 19, the horizontal axis represents the feature amount, and the vertical axis represents the imaging depth. In the example of (d) of FIG. 19 , in the direct observation region, feature data 901 of the modified region SD1 on the back surface 21a side and feature data of the modified region SD2 on the surface 21b side (902), feature data 910 of the phase crack tip is detected, and feature data 903 of the modified region SD1 on the back surface 21a side is detected in the back surface reflection region. Further, in the rear reflection area, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the suction table 2 are detected as feature data 1900. Due to the influence of the feature data 1900, the feature data 1904 of the modified region SD2 on the surface 21b side is detected in a state where the feature amount is smaller than in the case where the feature data 1900 is not detected. has been In this way, by detecting the feature data 1900 related to the shape of the holding member 300 or the like, it affects at least the detection of the modified region SD2 on the surface 21b side, and thereby, There is a possibility that the accuracy of determining the state of the modified region deteriorates.

In order to solve the above-described problem, in the internal observation method according to the present embodiment, in the first step, the patterns of the holding member 300 and the suction table 2 are not captured in the captured image during observation of the back surface reflection. The holding member 300 is optimized so as not to fall, and the optimized holding member 300 is attached to the wafer 20 . Specifically, optimization of the thickness of the holding member 300 and/or optimization of the material of the holding member 300 is performed. Optimization of the thickness of the holding member 300 and optimization of the material of the holding member 300 will be described below, respectively.

Optimization of the thickness of the holding member 300 will be described. In the first step, the holding member 300A, the thickness of which is set according to the distance to the modified region most separated from the back surface 21a of the wafer 20 (hereinafter sometimes referred to as "modified region distance") (300) is attached to the back surface (21a) of the wafer (20). Specifically, in the first step, the holding member 300A (300), the thickness of which is set to be larger than the value obtained by multiplying the modified region distance by the refractive index ratio of the holding member 300 with respect to the wafer 20, is placed on the wafer 20 ) You may stick it on the back surface 21a. For example, in the example shown in (a) of FIG. 20, the modified region distance is the distance from the back surface 21a to the end (upper end) of the modified region SD2 on the front surface 21b side. When the thickness of the holding member 300A is T1, the modified region distance is D, the refractive index of the holding member 300A is R1, and the refractive index of the wafer 20 is R2, the holding member 300A is satisfied with the following expression (1). The thickness T1 of 300A is set. For example, in the case of D = 350 µm, R1 = 1.5, and R2 = 3.5, the thickness T1 of the holding member 300A is calculated as > 150 µm based on the lower formula (1).

T1>D×R1/R2 . . . (One)

When such a holding member 300A is used, the thickness of the holding member 300A is larger than the distance obtained by converting the modified region distance into an approximate distance in the holding member 300A, so in FIG. 20(a) As shown, the light 11 does not reach the mounting surface 300x of the holding member 300A and the supporting surface 2x of the suction table 2 at the time of observing the rear surface of the modified regions SD1 and SD2. . Therefore, at the time of rear surface observation, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the suction table 2 are not captured in the captured image. Fig. 20(b) is a diagram showing an example of internal observation results when the holding member 300A is used. In Fig. 20(b), the horizontal axis represents the feature amount, and the vertical axis represents the imaging depth. In the example of (b) of FIG. 20 , in the rear reflection region, in addition to the feature amount data 903 of the modified region SD1 on the back surface 21a side, the characteristics of the modified region SD2 on the front surface 21b side Quantity data 904 is properly detected. And, in the back reflection area, feature data relating to the shape of the mounting surface 300x of the holding member 300A and the shape of the support surface 2x of the suction table 2 is not detected. Thereby, the position of the dent of each modified area|region SD1, SD2 etc. can be detected with high precision, without being influenced by the characteristic quantity data regarding the shape of holding member 300A grade|etc.,.

Regarding the thickness of the holding member 300A, the dz rate calculated from the refractive index for each observation wavelength and NA (Numerical Aperture) of the objective lens 43 may be considered and determined. That is, in the first step, the holding member 300 whose thickness is set to be greater than the value obtained by multiplying the modified region distance by the dz rate ratio of the holding member 300 to the wafer 20 is placed on the back surface 21a of the wafer 20. ) may be attached to The dz rate is the rate between the amount of Z-axis movement of the objective lens in the air and the light-converging position in the object to be observed. For example, when the wavelength of the light l1 is 1100 nm and the objective lens 43 moves 1 μm, in the case of moving 4 μm in the silicon constituting the wafer 20, the dz rate of the wafer 20 is It becomes 4.0. In the first step, a holding member 300A having a thickness set to be greater than a value obtained by multiplying the modified region distance by the dz rate ratio of the holding member 300A with respect to the wafer 20 is applied to the back surface 21a of the wafer 20. can be attached Now, for example, when the modified region distance D = 350 μm, the dz rate of the holding member 300A = 1.6, and the dz rate of the wafer 20 = 4.0, the thickness T1 of the holding member 300A It is calculated as >350 × 1.6/4.0 = 140 μm. Further, the thickness of the holding member 300 may simply be greater than the distance between the modified regions. That is, in the first step, the holding member 300 whose thickness is set to be greater than the distance between the modified regions may be simply attached to the back surface 21a of the wafer 20 . However, since the holding member 300 becomes too thick in this case, it is preferable that the thickness of the holding member 300 be calculated from the above-described formula (1) or a calculation formula taking the dz rate ratio into account. That is, the thickness of the holding member 300 is calculated by considering the wafer thickness, laser processing conditions, the wavelength of observation light, the refractive index of the wafer 20 and the holding member 300, and the NA of the objective lens 43. desirable.

Next, optimization of the material of the holding member 300 will be described. In the first step, as shown in (a) of FIG. 21 , the holding member 300B having a transmittance of 50% or less of the transmittance light 11 output from the imaging unit 4 is placed on the back surface of the wafer 20. You may stick it to (21a). More preferably, in the first step, the holding member 300B having a transmittance of light 11 having transmittance of 30% or less may be attached to the back surface 21a of the wafer 20 . The holding member 300B has, for example, a transmittance of 50% or less (preferably 30%) when the wafer 20 is a silicon wafer, and the wavelength range of the light 11 having transparency is 950 nm to 1700 nm. below) may be

When such a holding member 300B having a certain light-blocking property for the light 11 having transparency is used, as shown in FIG. At this time, the light 11 does not reach the mounting surface 300x of the holding member 300B and the support surface 2x of the suction table 2. Therefore, at the time of rear surface observation, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the suction table 2 are not captured in the captured image. Fig. 21(b) is a diagram showing an example of internal observation results when the holding member 300B is used. In Fig. 21(b), the horizontal axis represents the feature amount, and the vertical axis represents the imaging depth. In the example of (b) of FIG. 21 , in the rear reflection region, in addition to the feature amount data 903 of the modified region SD1 on the back surface 21a side, the characteristics of the modified region SD2 on the front surface 21b side Quantity data 904 is properly detected. And, in the back reflection area, feature data relating to the shape of the mounting surface 300x of the holding member 300B and the shape of the support surface 2x of the suction table 2 is not detected. Thereby, the position of the dent of each modified area|region SD1, SD2 etc. can be detected with high precision, without being influenced by the characteristic quantity data concerning the shape of holding member 300B grade|etc.,.

In the first step, the holding member 300B made of a material that absorbs the light l1 having transparency may be attached to the back surface 21a of the wafer 20 . Alternatively, in the first step, the holding member 300B made of a material that reflects the light 11 having transparency may be attached to the back surface 21a of the wafer 20 .

Optimization of the thickness of the holding member 300 and optimization of the material of the holding member 300 described above may be performed in combination of both. The thickness of the holding member 300 is sufficiently thick and the holding member 300 is made of a material having high light-shielding properties, so that the shape of the mounting surface 300x of the holding member 300 and the suction table 2 ) can be suppressed more effectively that the pattern of the support surface 2x is captured in the captured image.

22 is a diagram showing an example of the determination result according to the combination of the thickness and the transmittance of the holding member 300 . As a result of the determination here, “○” indicates that the design of the holding member 300 or the like is not stamped in, indicating that erroneous judgment is suppressed, and “Δ” indicates that the design of the holding member 300 or the like is not stamped in generally and erroneous determination is made. It shows that this is generally suppressed, and "x" shows that the design of the holding member 300 etc. was imprinted and misjudgment occurred. 23 is a diagram for explaining an example of the distance to a modified region for each processing type. As shown in (a) of FIG. 23 , when SDBG (Stealth Dicing Before Grinding) processing is performed as laser processing, if the thickness of the wafer 20 is 775 μm, the modified region distance is, for example, 230 μm. becomes μm. In addition, as shown in (b) of FIG. 23 , as laser processing, when FC (full cut) processing in which cracks reach the surface 21b after laser processing is performed, the thickness of the wafer 20 is Assuming that it is 775 μm, the modified region distance becomes, for example, 730 μm. In this way, depending on the processing type, the modified region distance is different.

Fig. 22(a) shows the determination result according to the combination of the thickness and the transmittance of the holding member 300 in SDBG processing. In the example shown in (a) of FIG. 22, under the conditions that the thickness of the wafer 20 is 775 μm and the distance between the modified regions is 230 μm, when the thickness of the holding member 300 is greater than 101 μm, Regardless of the transmittance of the holding member 300, the judgment result was "○". In addition, when the transmittance|permeability of the holding member 300 became 10 % or less, regardless of the thickness of the holding member 300, the judgment result became "(circle)". In addition, when the thickness of the holding member 300 is 51 to 100 μm, and when the thickness of the holding member 300 is 50 μm or less, and the transmittance of the holding member 300 is greater than 85%, the judgment result is “ x”, and when the transmittance of the holding member 300 was 30%, the judgment result was “Δ”. In this way, by making the thickness of the holding member 300 sufficiently thick or making the transmittance of the holding member 300 sufficiently small, regardless of the combination of the thickness and transmittance of the holding member 300, the determination result is " ○” was able to do it. In addition, even when the judgment result does not become "○" only with the thickness of the holding member 300 or only the transmittance of the holding member 300, by combining the thickness and the transmittance, the judgment result is set to "Δ". Could.

Fig. 22(b) shows the determination result according to the combination of the thickness and the transmittance of the holding member 300 in FC processing. In the example shown in (b) of FIG. 22, under the conditions that the thickness of the wafer 20 is 775 μm and the distance between the modified regions is 730 μm, when the thickness of the holding member 300 is greater than 301 μm, Regardless of the transmittance of the holding member 300, the judgment result was "○". In addition, when the transmittance|permeability of the holding member 300 became 10 % or less, regardless of the thickness of the holding member 300, the judgment result became "(circle)". In addition, when the thickness of the holding member 300 is 201 to 300 μm, 51 to 200 μm, and 50 μm or less, and the transmittance of the holding member 300 is greater than 85%, the judgment result is “× ”, and when the transmittance of the holding member 300 was 30%, the judgment result was “Δ”. In this way, by making the thickness of the holding member 300 sufficiently thick or making the transmittance of the holding member 300 sufficiently small, regardless of the combination of the thickness and transmittance of the holding member 300, the determination result is " ○” was able to do it. In addition, even when the judgment result does not become "○" only with the thickness of the holding member 300 or only the transmittance of the holding member 300, by combining the thickness and the transmittance, the judgment result is set to "Δ". Could.

24 is a flowchart according to an example of the above-described internal observation method (inspection method). As shown in FIG. 23 , in this inspection method, first, the opposite side of the surface 21b to which the laser beam is irradiated with respect to the wafer 20 in which the modified region is formed by being irradiated with the laser beam. The holding member 300 is attached to the back surface 21a, and the mounting surface 300x, which is opposite to the surface attached to the wafer 20 in the holding member 300, is installed on the suction table 2 (step S1, 1st process).

In step S1, the holding member 300, the thickness of which is set to be larger than the value obtained by multiplying the modified region distance by the refractive index ratio of the holding member 300 to the wafer 20, for example, is placed on the surface 21b of the wafer 20. ) is attached to Alternatively, in step S1, the holding member 300 having a transmittance of light 11 having transmittance of 50% (preferably 30%) or less may be attached to the surface 21b of the wafer 20.

Subsequently, light l1 having transparency is output by the imaging unit 4 to the wafer 20 installed on the adsorption table 2 via the holding member 300, and the transmittance that propagates through the wafer 20 is The light l1 having is detected, and imaging of the wafer 20 is performed (step S2, second process).

Finally, the state of the modified region of the wafer 20 is specified based on the captured image output from the imaging unit 4 that has detected the light 11 having transparency (step S3, third process).

Next, the effect of the internal observation method (inspection method) performed by the laser processing apparatus 1 according to the present embodiment will be described.

The internal observation method (inspection method) performed by the laser processing apparatus 1 according to the present embodiment is applied to the back surface 21a of the wafer 20 having a modified region formed therein by being irradiated with a laser beam. The first step of attaching the holding member 300 and attaching the mounting surface 300x of the holding member 300 to the adsorption table 2, and the adsorption table 2 via the holding member 300 A second step of outputting, by the imaging unit 4, light 11 having transparency to the wafer 20 installed thereon and detecting the light 11 having transparency passing through the wafer 20; A third step of specifying the state of the modified region of the wafer 20 based on a captured image output from the imaging unit 4 that detects the light l1 having A holding member 300 whose thickness is set according to the distance is attached to the back surface 21a.

In the inspection method according to the present embodiment, a holding member 300 is attached to the rear surface 21a of the wafer 20 having a modified region formed therein, and the holding member 300 is installed on the suction table 2 has been Then, the inside of the wafer 20 is observed by outputting the light l1 having transparency to the wafer 20 placed on the adsorption table 2 through the holding member 300, and based on the captured image Thus, the state of the modified region of the wafer 20 is specified. Here, in the case where internal observation is performed with such a configuration, the area on the opposite side of the front surface 21b with respect to the rear surface 21a is focused from the front surface 21b side, and the light reflected from the rear surface 21a is captured. When observation of the back surface reflection is performed, the pattern of the embossed surface of the holding member 300 and the pattern of the porous structure of the adsorption table 2 may be captured in the captured image. In this case, there is a possibility that the accuracy of estimating the state of the modified region of the wafer 20 based on the captured image may deteriorate. In this respect, in the inspection method according to the present embodiment, the holding member whose thickness is set according to the modified region distance, which is the distance from the back surface 21a of the wafer 20 to the modified region most separated from the back surface 21a 300 is attached to the back surface 21a of the wafer 20 . In this way, by setting the thickness of the holding member 300 in consideration of the distance of the modified region, the shape of the holding member 300 or the like is prevented from being captured in the captured image in the observation of the rear reflection of the modified region. It becomes possible to set the thickness of (300). This makes it possible to suppress erroneous judgment in internal observation of the wafer 20 after laser processing.

In addition, as a method of avoiding erroneous determination of internal observation due to the influence of the shape of the holding member 300 or the like, for example, all captured images in the Z direction (depth direction) to be imaged are acquired before laser processing, When internal observation is performed after laser processing, the captured image captured before laser processing is subtracted from the captured image after laser processing, and only the information on the modified region formed after laser processing is included in the angle of view (pattern by filtering avoidance method). However, in such a method, since it is necessary to acquire all images in the Z direction to be imaged before laser processing, the tact deteriorates. In addition, in the captured image before and after laser processing, if the imaging conditions such as the amount of light and the luminance value change even slightly, the filtering function (subtraction function) does not function normally, and the accuracy of internal observation deteriorates. In this respect, the internal observation method (inspection method) performed by the laser processing apparatus 1 according to the present embodiment does not require image pickup before laser processing, so that tact-up can be achieved, and filtering is not Since this is not the case, the above-mentioned decrease in accuracy of internal observation is not a problem. That is, the internal observation method (inspection method) performed by the laser processing apparatus 1 according to the present embodiment can suppress erroneous judgment in internal observation of the wafer 20 after laser processing while achieving a tact-up. there is.

In the first step, the holding member 300 whose thickness is set to be greater than the distance of the modified region may be attached to the back surface 21a. This suppresses the appearance of the pattern of the holding member 300 or the like in the picked-up image in the observation of the rear surface reflection with respect to the modified region. This makes it possible to suppress erroneous judgment in internal observation of the wafer 20 after laser processing.

In the first step, the holding member 300 having a thickness set to be greater than the value obtained by multiplying the modified region distance by the refractive index ratio of the holding member 300 to the wafer 20 may be attached to the back surface 21a. By multiplying the modified region distance with the refractive index ratio, the modified region distance is converted into an approximate distance in the holding member 300 taking the refractive index into consideration, so that the holding member 300 having a thickness greater than the value after conversion is placed on the back surface 21a. By being affixed, it is suppressed that the pattern of the holding member 300 or the like is captured in the captured image in the backside reflection observation of the modified region. This makes it possible to suppress erroneous judgment in internal observation of the wafer 20 after laser processing. In addition, by setting the thickness of the holding member 300 according to the value obtained by multiplying the modified region distance by the refractive index ratio, compared to the case where the thickness of the holding member 300 is simply set to be greater than the modified region distance, for example. , the thickness of the holding member 300 can be reduced. That is, erroneous judgment in internal observation of the wafer 20 after laser processing can be suppressed while avoiding an excessive increase in the thickness of the holding member 300 .

In the first step, the holding member 300 whose thickness is set to be larger than the value obtained by multiplying the modified region distance by the dz rate ratio of the holding member 300 to the wafer 20 may be attached to the back surface 21a. By multiplying the modified region distance by the dz rate ratio, the modified region distance is converted into an approximate distance in the holding member 300 considering the refractive index and NA (Numerical Aperture) of the objective lens 43 of the imaging unit 4 Therefore, by attaching the holding member 300 having a thickness larger than the value after conversion to the back surface 21a, the design of the holding member 300 or the like is prevented from being captured in the captured image in the back surface reflection observation of the modified region. do. This makes it possible to suppress erroneous judgment in internal observation of the wafer 20 after laser processing. In addition, when the thickness of the holding member 300 is set according to the value obtained by multiplying the modified region distance by the dz rate ratio, for example, the thickness of the holding member 300 is simply set to be greater than the modified region distance; Compared to the case where the thickness of the holding member 300 is set considering only the refractive index ratio, the thickness of the holding member 300 can be reduced. That is, erroneous judgment in internal observation of the wafer 20 after laser processing can be suppressed while avoiding an excessive increase in the thickness of the holding member 300 .

In the internal observation method (inspection method) performed by the laser processing apparatus 1 according to the present embodiment, in the first step, the holding member 300 having a transmittance of light l1 having transmittance of 50% or less is placed on the back surface ( 21a) may be attached. In this way, by attaching the holding member 300 having a light-shielding property to the back surface 21a, in the back-side reflection observation, it is below the holding member 300 having the light-shielding property (on the suction table 2 side). It becomes difficult for the image of the arranged thing to be captured in the captured image. Specifically, the pattern of the embossed surface of the holding member 300 and the pattern of the porous structure of the suction table 2 are difficult to be captured in the captured image. This suppresses the pattern of the holding member 300 or the like from being reflected in the captured image in the observation of the back surface reflection, and suppresses erroneous judgment in the observation of the inside of the wafer 20 after laser processing.

In the first step, the holding member 300 having a transmittance of light 11 having transmittance of 30% or less may be attached to the back surface 21a. By setting the transmittance of light 11 having transmittance through the holding member 300 to 30% or less, the design of the holding member 300 or the like is suppressed from appearing in the captured image more appropriately in the backside reflection observation. Therefore, misjudgment in the observation of the inside of the wafer 20 after laser processing can be suppressed.

In the first step, the holding member 300 made of a material that absorbs the light 11 having transmissivity may be attached to the back surface 21a. According to such a configuration, the transmittance of light 11 having transmittance in the holding member 300 can be appropriately suppressed.

In the first step, the holding member 300 made of a material that reflects the light 11 having transparency may be attached to the back surface 21a. According to such a configuration, the transmittance of light 11 having transmittance in the holding member 300 can be appropriately suppressed.

In the second step, while changing the imaging area along the Z direction, which is the vertical direction, the light 11 having transparency is detected for each imaging area, and in the third step, the captured image for each imaging area along the Z direction , the feature point and the feature amount of the feature point may be detected, and the position of the feature point having a relatively large feature amount may be specified as the formation position of the modified region. In this way, by specifying the formation position of the modified region from the feature amount of the feature point in the captured image, the accuracy and efficiency of observing the inside of the wafer 20 after laser processing can be improved.

2… adsorption table 4 . . . imaging unit
20... Wafer 21a... Back (side 2)
21b... surface (first surface) 300... absence of maintenance
L... Laser light l1... light that transmits

Claims (9)

A holding member is attached to a second surface opposite to the first surface to which the laser beam is irradiated, with respect to a wafer having a modified region formed therein by irradiation with the laser beam, and A first step of installing a surface opposite to the surface to be attached to the wafer to a suction table;
A second step of outputting, by an imaging unit, light having transparency to the wafer placed on the adsorption table via the holding member and detecting the light having transparency that has propagated through the wafer;
a third step of specifying a state of the modified region of the wafer based on a captured image output from the imaging unit that has detected the light having the transmission property;
In the first step, the holding member, the thickness of which is set according to the modified region distance, which is the distance from the second surface of the wafer to the modified region most separated from the second surface, is placed on the second surface. Inspection method to stick. The method of claim 1,
In the first step, the holding member, the thickness of which is set to be larger than the modified region distance, is attached to the second surface. The method of claim 1,
In the first step, the holding member, the thickness of which is set to be greater than a value obtained by multiplying the modified region distance by the refractive index ratio of the holding member to the wafer, is attached to the second surface. The method of claim 1,
In the first step, the holding member, the thickness of which is set to be greater than a value obtained by multiplying the modified region distance by a dz rate ratio of the holding member to the wafer, is attached to the second surface. A holding member is attached to a second surface opposite to the first surface to which the laser beam is irradiated, with respect to a wafer having a modified region formed therein by being irradiated with a laser beam, and to the wafer in the holding member A first step of installing the surface opposite to the surface to be affixed on an adsorption table;
A second step of outputting, by an imaging unit, light having transparency to the wafer placed on the adsorption table via the holding member and detecting the light having transparency that has propagated through the wafer;
a third step of specifying a state of the modified region of the wafer based on a captured image output from the imaging unit that has detected the light having the transmission property;
In the first step, the holding member having a light transmittance of 50% or less is attached to the second surface. The method of claim 5,
In the first step, the holding member having a light transmittance of 30% or less is attached to the second surface. According to claim 5 or claim 6,
In the first step, the holding member made of a light-absorbing material having the transmittance is attached to the second surface. According to claim 5 or claim 6,
In the first step, the holding member made of a light-reflecting material having transparency is attached to the second surface. The method according to any one of claims 1 to 6,
In the second step, light having the transmittance is detected for each imaging area while changing the imaging area along the Z direction, which is a vertical direction;
In the third step, a feature point and a feature amount of the feature point are detected for the captured image of each captured region along the Z direction, and the position of the feature point having a relatively large feature amount is used as the formation position of the modified region. A specific inspection method.

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