TW202323771A - Inspection method which can avoid false determination for modified regions of a wafer machined by a laser processing device - Google Patents

Abstract

The inspection method implemented by a laser processing device includes: a first process of attaching a holding member to the back surface of a wafer on which modified regions are formed, and setting the mounting surface of the holding member on a suction table; a second process of outputting light having permeability to the wafer set on the suction table and detecting the light propagating through the wafer by using an image capture unit; a third process of determining the state of the modified region of the wafer based on the photographed image output from the image capture unit that detects the light having permeability. In the first process, a holding member whose thickness is set according to the distance between the modified regions is attached to the back surface.

Description

Inspection Method

One aspect of the present invention relates to an inspection method.

There is known an inspection apparatus for cutting a wafer having a semiconductor substrate and having a surface having a functional element layer as the back surface along each of a plurality of lines by moving from the surface side of the semiconductor substrate to the wafer. Laser light is irradiated circularly to form a plurality of columns of modified regions inside the semiconductor substrate along each of the plurality of lines. The inspection device described in JP-A-2017-64746 includes an infrared camera, and can observe a modified region formed inside a semiconductor substrate, processing damage formed in a functional element layer, and the like from the surface side of the semiconductor substrate. In this inspection device, for example, based on such internal observation results, the crack state of the wafer after processing is estimated, and whether the processing is qualified or not (whether the desired processing is performed under the set processing conditions) is determined based on the estimated result of the crack state. processing).

[Problem to be solved by the invention]

In the internal observation as described above, in addition to the direct observation in which the focus is shifted from the front side to the back side and photographed, there are also cases where the focus is aligned from the front side to the area on the opposite side to the front side and photographed from the back side. Reflected light is observed by back reflection. When internal observation is performed, a holding member is usually attached to the back side of the wafer, and the above-mentioned direct observation and rear reflection observation are performed with the holding member set on the suction table. Here, the holding member may be embossed on the surface in contact with the suction table. In addition, in the adsorption table, the surface on which the holding member is provided may have a porous structure, and fine unevenness may be formed by the porous material. When performing back reflection observation using such a holding member and/or suction table, the pattern of the embossed surface of the holding member and the pattern of the porous structure of the suction table may be reflected in the captured image. . In this case, there is a possibility that the accuracy of estimating the state of dents or cracks in the modified region may be deteriorated (misjudgment of the state related to the modified region may occur). [Technical means to solve the problem]

One aspect of the present invention has been developed in view of the above-mentioned actual situation, and relates to an inspection method capable of suppressing erroneous judgments in internal observation of a laser-processed wafer.

An inspection method according to an aspect of the present invention includes: a first step, for a wafer having a modified region formed inside by irradiating laser light, the second wafer on the opposite side of the first surface irradiated by laser light The holding member is attached to the surface, and the surface of the holding member opposite to the surface attached to the wafer is set on the suction table; in the second process, the wafer that is set on the suction table through the holding member is output by the imaging unit. penetrating light and detecting the penetrating light propagating in the wafer; and the third process, determining the wafer In the first process, a holding member whose thickness is set according to the distance of the modified region is attached to the second surface. The distance of the modified region refers to the distance from the second surface of the wafer to the second surface. The distance of the furthest modified region.

In the inspection method according to one aspect of the present invention, the holding member is attached to the second surface, which is the back surface of the wafer in which the modified region is formed, and the holding member is placed on the suction table. Furthermore, the inside of the wafer is observed by outputting penetrating light to the wafer mounted on the suction table through the holding member, and the state related to the modified region of the wafer is determined from the captured image. Here, in the case of internal observation with such a configuration, if the focus is aligned from the surface, that is, the first surface side, to the rear surface, that is, the area on the opposite side of the second surface from the first surface, and the image reflected by the second surface is photographed The pattern of the embossed surface of the holding member and the pattern of the porous structure of the adsorption table may be reflected in the captured image when observed by back reflection of light. In this case, there is a possibility that the estimation accuracy of the state related to the modified region of the wafer from the captured image may be deteriorated. In this regard, according to the inspection method of one aspect of the present invention, the holding member whose thickness is set according to the distance from the second surface to the modified region farthest from the second surface, that is, the modified region distance, is attached to the second side. By setting the thickness of the holding member in consideration of the modified region distance in this way, it is possible to set the thickness of the holding member so as to prevent the pattern of the holding member or the like from appearing in the captured image in the rear reflection observation of the modified region. In this way, it is possible to suppress erroneous judgments in the internal observation of the laser-processed wafer.

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. Thereby, it is possible to suppress the pattern of the holding member or the like from appearing on the captured image in the rear reflection observation of the modified region. In this way, it is possible to suppress erroneous judgments in the internal observation of the laser-processed wafer.

In the first step, the holding member whose thickness is set to be greater than the 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 by the above-mentioned refractive index ratio, the modified region distance is converted into an approximate distance in the holding member in consideration of the refractive index, and by attaching the holding member having a thickness larger than the converted value On the other hand, in the rear reflection observation of the modified region, it is possible to suppress the pattern of the holding member or the like from appearing on the captured image. In this way, it is possible to suppress erroneous judgments in the internal observation of the laser-processed wafer. In addition, by setting the thickness of the holding member based on the value obtained by multiplying the distance of the modified region by the refractive index ratio, the thickness of the holding member can be reduced compared to, for example, only setting the thickness of the holding member larger than the distance of the modified region. thickness. That is, it is possible to avoid excessive thickness of the holding member, and to suppress erroneous determination in internal observation of the laser-processed wafer.

In the first step, the holding member whose thickness is set to be greater than a value obtained by multiplying the modified region distance by the dz ratio of the holding member to the wafer may be attached to the second surface. By multiplying the distance of the modified region by the dz ratio, the distance of the modified region is converted into an approximate distance in the holding member in consideration of the refractive index and the NA (Numerical Aperture) of the objective lens of the imaging unit. Attaching a holding member having a thickness larger than the converted value to the second surface can suppress the pattern of the holding member or the like from appearing in the captured image in rear reflection observation of the modified region. In this way, it is possible to suppress erroneous judgments in the internal observation of the laser-processed wafer. In addition, setting the thickness of the holding member by multiplying the value obtained by multiplying the distance of the modified region by the dz rate ratio is different from, for example, setting the thickness of the holding member to be larger than the distance of the modified region, or setting only in consideration of the refractive index ratio. Compared with the case where the thickness of the holding member is maintained, the thickness of the holding member can be reduced. That is, it is possible to avoid excessive thickness of the holding member, and to suppress erroneous determination in internal observation of the laser-processed wafer.

An inspection method according to an aspect of the present invention includes: a first step, for a wafer having a modified region formed inside by irradiating laser light, the second wafer on the opposite side of the first surface irradiated by laser light Attach the holding member on the surface, and set the surface of the holding member opposite to the surface attached to the wafer on the suction table; in the second process, the wafer that is set on the suction table through the holding member is output by the imaging unit penetrating light and detecting the penetrating light propagating in the wafer; and in the third process, determining the wafer The state related to the circular modified region; in the first step, a holding member having a transmissive light transmittance of 50% or less is attached to the second surface.

In the inspection method of one aspect of the present invention, since the holding member (holding member having light-shielding properties) having a transparent light transmittance of 50% or less is attached to the second surface, in back reflection observation, It is difficult for an image of an object disposed below (on the side of the suction table) than the holding member having the light-shielding property to appear on 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 appear in the captured image. In this way, the pattern of the holding member or the like is suppressed from being reflected on the captured image during back reflection observation, and it is possible to suppress erroneous determination in internal observation of a laser-processed wafer.

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 transparent light transmittance of the holding member to 30% or less, it is more appropriate to suppress the pattern of the holding member and the like from being reflected in the captured image in back reflection observation, and it is possible to suppress the occurrence of laser-processed wafers. Misjudgments in internal observations of .

In the first step, a holding member made of a material that absorbs penetrating light may be attached to the second surface. According to such a configuration, the transmittance of the holding member to transmit light can be appropriately suppressed.

In the first step, a holding member made of a material that reflects transparent light may be attached to the second surface. According to such a configuration, the transmittance of the holding member to transmit light can be appropriately suppressed.

It is also possible that in the second process, while changing the shooting area along the Z direction, which is the vertical direction, the penetrating light is detected for each shooting area; in the third process, for each shooting area along the Z direction The region-related captured image detects the feature point and the feature value of the feature point, and determines the position of the feature point with a relatively large feature value as the formation position of the modified region. In this way, by determining the formation position of the modified region based on the feature value of the feature point in the captured image, the accuracy and efficiency of internal observation of the laser-processed wafer can be improved.

According to the inspection method of one aspect of the present invention, erroneous judgments in internal observation of a laser-processed wafer can be suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code|symbol is attached|subjected to the same or corresponding part, and overlapping description is abbreviate|omitted.

[Structure of Laser Processing Device] As shown in FIG. 1 , a laser processing device 1 includes an adsorption table 2, a laser irradiation unit 3, a plurality of imaging units 4 (imaging units), 5, 6, a driving unit 7 (driving unit), a control unit 8, and a display. 150. The laser processing apparatus 1 is an apparatus for forming a modified region 12 on an object 11 by irradiating the object 11 with laser light L.

The suction table 2 supports the object 11 by, for example, suctioning a film attached to the object 11 . Although not shown in FIG. 1 , as shown in FIG. 18 and the like, a holding member 300 (details will be described later) for holding wafer 20 is provided between wafer 20 as object 11 and suction table 2 . The suction table 2 is movable in each of the X direction and the Y direction, and is rotatable about an axis parallel to the Z direction as a center line. In addition, 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 laser light L penetrating the object 11 and irradiates the object 11 . When the laser light L is condensed inside the object 11 supported by the adsorption stage 2, the laser light L is particularly absorbed at a part corresponding to the condensing point C of the laser light L, and a modified surface is formed inside the object 11. Area 12.

The modified region 12 is a region different in density, refractive index, mechanical strength, and other physical properties from the surrounding non-modified region. As the modified region 12, there are, for example, a melt-processed region, a crack region, a dielectric breakdown region, a refractive index change region, and the like. The modified region 12 has a characteristic of making it easy for cracks to extend from the modified region 12 to the incident side of the laser light L and the opposite side. Such properties of the modified region 12 are utilized for cutting the object 11 .

As an example, if the adsorption table 2 is moved along the X direction and the light-converging point C is moved relative to the object 11 along the X direction, a plurality of modified spots 12 s are formed in a row along the X direction. One modified spot 12s is formed by irradiation with one pulsed laser light L. A row of modified regions 12 is a collection of a plurality of modified spots 12s arranged in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the relative moving speed of the focused spot C with respect to the object 11 and the repetition frequency of the laser light 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 image the object 11 supported by the suction table 2 with light passing through the object 11 based on the control of the control unit 8 . As an example, images captured by the imaging units 5 and 6 are used for alignment of the irradiation position of the laser light L. FIG.

The drive unit 7 supports the laser irradiation unit 3 and the plurality of imaging units 4 , 5 , and 6 . The driving unit 7 moves the laser irradiation unit 3 and the plurality of imaging units 4, 5, 6 in 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 , 6 and the driving unit 7 . The control unit 8 is configured as a computer device including a processor, memory, storage, communication equipment, and the like. In the control unit 8, the processor executes software (program) loaded in the memory or the like, and controls reading and writing of data in the memory and storage, and communication by communication devices.

The display 150 has a function as an input unit for receiving an input of information from a user and a function as a display unit for displaying information to the user.

[constitution of object] As shown in FIGS. 2 and 3 , the object 11 of this embodiment is a wafer 20 . The wafer 20 includes a semiconductor substrate 21 and a functional element layer 22 . In addition, although the wafer 20 described in this embodiment has the functional element layer 22, the wafer 20 may have the functional element layer 22 or not have the functional element layer 22, and may be a bare wafer. The semiconductor substrate 21 has a back surface 21a and a front surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The functional element layer 22 is formed on the back surface 21 a of the semiconductor substrate 21 . The functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the rear 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. The functional element 22a may also have a three-dimensional structure 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 along each of the plurality of lines 15 for each functional element 22a. When viewed from the thickness direction of the wafer 20 , the plurality of lines 15 pass between the plurality of functional elements 22 a. More specifically, the wire 15 passes through the center (the center in the width direction) of the street region 23 when viewed from the thickness direction of the wafer 20 . The track region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, a plurality of functional elements 22a are arranged in a matrix along the back surface 21a, and a plurality of lines 15 are set in a grid. In addition, the line 15 is an imaginary line, but may be actually drawn. [Configuration of 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 condenser lens 33 . The light source 31 outputs laser light L by, for example, pulse oscillation. 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 reflective liquid crystal (LCOS: Liquid Crystal on Silicon, liquid crystal on silicon) spatial light modulator (SLM: Spatial Light Modulator). 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 lens with a correction ring.

In the present embodiment, the laser irradiation unit 3 irradiates the laser light L from the surface 21b side of the semiconductor substrate 21 to the wafer 20 along each of the plurality of lines 15, whereby along each of the plurality of lines 15 Inside the semiconductor substrate 21, two rows of modified regions 12a, 12b are formed. The modified region 12a is the modified region closest to the rear surface 21a among the two rows of modified regions 12a, 12b. The modified region 12b is the modified region closest to the modified region 12a among the two rows of modified regions 12a, 12b, and is the modified region closest to the surface 21b.

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

The laser irradiation unit 3 irradiates laser light L from the surface 21 b side of the semiconductor substrate 21 to the wafer 20 along each of the plurality of lines 15 . As an example, for a semiconductor substrate 21 which is a single-crystal silicon <100> substrate with a thickness of 400 μm, the two light-converging points C1 and C2 are respectively aligned at positions 54 μm and 128 μm away from the back surface 21 a, along a plurality of lines. Each of 15 irradiates laser light L toward the wafer 20 from the surface 21 b side of the semiconductor substrate 21 . At this time, for example, under the condition that the cracks 14 straddling the two rows of modified regions 12a, 12b reach the back surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099nm, the pulse width is 700nsec, and repeated The frequency is 120kHz. In addition, the output of the laser light L at the condensing point C1 is set to 2.7 W, the output of the laser light L at the condensing point C2 is set to 2.7 W, and the output of the two condensing points C1 and C2 to the semiconductor substrate 21 is The relative moving speed was set at 800 mm/sec. In addition, for example, when the number of processing passes is set to 5, ZH80 (position 328 μm away from the back surface 21a), ZH69 (position 283 μm away from the back surface 21a), ZH57 ( A position separated by 234 μm from the back surface 21 a), ZH26 (a position separated by 107 μm from the back surface 21 a), and ZH12 (a position separated by 49.2 μm from the back surface 21 a) were set as processing positions. 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.

[Structure of the imaging unit for inspection] As shown in FIG. 5 , the imaging unit 4 (imaging unit) has a light source 41 , a reflecting mirror 42 , an objective lens 43 , and a light detecting unit 44 . The photographing unit 4 photographs the interior of the wafer 20 by outputting penetrating light to the wafer 20 and detecting the light propagating in the wafer 20 . The light source 41 outputs the light 11 with penetrability to the semiconductor substrate 21 . The light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light 11 in the near-infrared region. The light 11 output from the light source 41 is reflected by the mirror 42 , passes through the objective lens 43 , and is irradiated toward the wafer 20 from the side surface 21 b of the semiconductor substrate 21 . At this time, the adsorption table 2 supports the wafer 20 on which the two rows of modified regions 12a, 12b are formed as described above.

The objective lens 43 passes the light 11 reflected by the back surface 21 a of the semiconductor substrate 21 . That is, the objective lens 43 passes the light 11 that has propagated through the semiconductor substrate 21 . The numerical aperture (NA) of the objective lens 43 is 0.45 or more, for example. The objective lens 43 has a correction ring 43a. The correction ring 43 a adjusts, for example, the distance between a plurality of lenses constituting the objective lens 43 , thereby correcting aberrations caused by the light 11 in the semiconductor substrate 21 . In addition, the means for correcting aberrations is not limited to the correction ring 43a, and other correction means such as a spatial light modulator may also be used. The light detection unit 44 detects the light 11 that has passed through the objective lens 43 and the reflection mirror 42 . The photodetector 44 is composed of, for example, an InGaAs camera, and detects the light 11 in the near-infrared region. In addition, the means of detecting (photographing) the light 11 in the near-infrared region is not limited to an InGaAs camera, as long as it is a penetrating confocal microscope or the like, and other photographing means may be used.

The imaging unit 4 is capable of imaging each of the two rows of modified regions 12a, 12b and the respective front ends 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 toward the rear 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 rear surface 21a side. The crack 14d is a crack extending from the modified region 12b to the surface 21b side.

[Structure of the imaging unit for alignment correction] As shown in FIG. 6 , the photographing unit 5 has a light source 51 , a mirror 52 , a lens 53 and a photodetector 54 . The light source 51 outputs the light I2 having penetrability 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 also be shared with the light source 41 of the photographing unit 4 . The light I2 output from the light source 51 is reflected by the reflector 52 , passes through the lens 53 , and is irradiated toward the wafer 20 from the side of the surface 21 b of the semiconductor substrate 21 .

The lens 53 passes the light I2 reflected by the back surface 21 a 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 detection unit 54 detects the light I2 passing through the lens 53 and the mirror 52 . The photodetector 54 is composed of, for example, an InGaAs camera, and detects the light I2 in the near-infrared region.

The imaging unit 5 irradiates light I2 from the surface 21b side to the wafer 20 based on the control of the control unit 8 and detects the light I2 returned from the back surface 21a (functional element layer 22 ), thereby photographing the functional element layer 22 . In addition, similarly, the imaging unit 5 irradiates the light I2 from the surface 21b side to the wafer 20 based on the control of the control unit 8, and detects the light I2 returning from the formation positions of the modified regions 12a, 12b in the semiconductor substrate 21, Thereby, an image of a region including the modified regions 12a and 12b is acquired. These images are used for alignment of the irradiation position of the laser light L. FIG. The imaging unit 6 has the same configuration as the imaging unit 5 except that the lens 53 has a lower magnification (for example, 6 times in the imaging unit 5 and 1.5 times in the imaging unit 6), and has the same structure as the imaging unit 5. ground for alignment.

[Based on the imaging principle of the imaging unit for inspection] Using the photographing unit 4 shown in FIG. 5, as shown in FIG. 7, for the crack 14 that straddles the two rows of modified regions 12a, 12b to reach the semiconductor substrate 21 of the back surface 21a, let the focal point F (the focal point of the objective lens 43) from the surface The 21b side moves toward the rear 21a side. In this case, when the focal point F is aligned with the front end 14e of the crack 14 extending from the modified region 12b to the surface 21b side from the surface 21b side, the front end 14e can be confirmed (the image on the right in FIG. 7 ). . However, even if the focal point F is aligned with the fissure 14 itself and the front end 14e of the fissure 14 reaching the back surface 21a from the front surface 21b side, they cannot be confirmed (left image in FIG. 7 ). Moreover, the functional element layer 22 can be confirmed by aligning the focal point F with the back surface 21a of the semiconductor substrate 21 from the front surface 21b side.

In addition, using the imaging unit 4 shown in FIG. 5, as shown in FIG. The back side 21a moves sideways. In this case, even if the focal point F is aligned from the surface 21b side to the front end 14e of the crack 14 extending from the modified region 12a to the rear surface 21a side, the front end 14e cannot be confirmed (the left image in FIG. 8 ). However, if the focal point F is aligned from the surface 21b side to the area on the opposite side of the back surface 21a from the surface 21b (that is, the area on the functional element layer 22 side of the back surface 21a), and a hypothetical symmetry with the focus F is made with respect to the back surface 21a When the focal point Fv is positioned at the front end 14e, the front end 14e can be confirmed (the image on the right in FIG. 8 ). In addition, the virtual focal point Fv is a point symmetrical to the focal point F with respect to the back surface 21a in consideration of the refractive index of the semiconductor substrate 21 .

The reason why the crack 14 itself cannot be confirmed as described above is that 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, scanning electron microscope) images of modified regions 12 and cracks 14 formed inside semiconductor substrate 21 which is a silicon substrate. Fig. 9 (b) is an enlarged image of the region A1 shown in Fig. 9 (a), Fig. 10 (a) is an enlarged image of the region A2 shown in Fig. 9 (b), and Fig. 10 (b) is an enlarged image of Fig. 10 (a) ) is an enlarged image of the area A3 shown. In this way, the width of the fissure 14 is about 120 nm, which is smaller than the wavelength of the light 11 in the near-infrared region (for example, 1.1 to 1.2 μm).

The imaging principle assumed from the above description is as follows. As shown in FIG. 11( a ), if the focal point F is placed in the air, a black image (image on the right in FIG. 11( a )) is obtained because the light 11 does not return. As shown in FIG. 11( b ), if the focal point F is positioned inside the semiconductor substrate 21 , a white image (right image in FIG. 11( b )) is obtained because the light 11 reflected on the back surface 21 a returns. As shown in FIG. 11(c), if the focal point F is aligned with the modified region 12 from the surface 21b side, the modified region 12 will absorb, scatter, etc. a part of the light 11 reflected and returned from the back surface 21a. An image in which the modified region 12 appears in black on a white background was obtained (the right image in FIG. 11( c )).

As shown in Fig. 12(a) and (b), if the focal point F is aligned with the front end 14e of the crack 14 from the surface 21b side, for example, due to the optical specificity (stress concentration, strain, atomic density) generated near the front end 14e discontinuity, etc.), the confinement of light generated near the front end 14e, etc., cause scattering, reflection, interference, absorption, etc., to a part of the light 11 that is reflected and returned from the back surface 21a, so that it appears black on a white background An image of the front end 14e (images on the right side in Fig. 12(a) and (b)). As shown in FIG. 12( c), if the focal point F is aligned with the portion other than the vicinity of the front end 14e of the crack 14 from the surface 21b side, at least part of the light 11 reflected by the back surface 21a returns, and a white image is obtained ( Image on the right in Figure 12(c)).

[Detection Algorithm in Internal Observation] Regarding the above-mentioned internal observation of the wafer 20 , the algorithm for detecting (determining) the crack 14 and the algorithm for detecting (determining) the dent in the modified region will be described in detail. The detection of such cracks 14 and the detection of dents in the modified region can also be judged and implemented by AI.

13 and 14 are diagrams illustrating crack detection. FIG. 13 shows the internal observation results (images of the inside of the wafer 20). The control unit 8 first detects the straight line group 140 for the image inside the wafer 20 as shown in FIG. 13( a ). The detection of the straight line group 140 uses algorithms such as Hough transform or LSD (Line Segment Detector, straight line segment detection algorithm). Hough transform refers to the following algorithm: detect all straight lines passing through the point on the image, and detect the straight lines while weighting the straight lines passing through more feature points. LSD refers to an algorithm that estimates a region to be a line segment by calculating the gradient and angle of luminance values within an image, and detects a straight line by approximating the region to a rectangle.

Next, as shown in FIG. 14 , the control unit 8 calculates the degree of similarity between the straight line group 140 and the crack line, thereby detecting the crack 14 based on the straight line group 140 . As shown in the upper diagram of FIG. 14 , the crack line is characterized by being very bright in the front and back in the Y direction with respect to the brightness value on the line. Therefore, the control unit 8 compares, for example, the brightness values of all pixels in the detected straight line group 140 with the front and back in the Y direction, and uses the number of pixels whose differences are both above the threshold as the similarity score. Moreover, the one with the highest similarity score to the crack line among the multiple detected straight line groups 140 is used as the representative value in the image. The higher the representative value, the higher the probability that the crack 14 exists is an index. The control unit 8 compares the representative values of the plurality of images, and selects those with relatively higher scores as crack image candidates.

15 to 17 are diagrams illustrating dent detection. FIG. 15 shows the internal observation results (images of the inside of the wafer 20). The control unit 8 detects the corner (concentration of edges) in the image of the inside of the wafer 20 as shown in FIG. 15( a) as a key point, and detects its position, size, direction to detect feature points 250 . As methods for detecting feature points in this way, Eigen, Harris, Fast, SIFT, SURF, STAR, MSER, ORB, AKAZE, etc. are known.

Here, as shown in FIG. 16 , since the dimples 280 are arranged at regular intervals in a shape such as a circle or a rectangle, they have strong characteristics as corners. Therefore, by adding up the feature quantities of the feature points 250 in the image, the dent 280 can be detected with high precision. As shown in FIG. 17 , by comparing the totals of the feature values for each image captured while shifting in the depth direction, changes in peaks indicating the amount of crack rows for each modified layer can be confirmed. The control unit 8 estimates the peak value of this change as the position of the dent 280 . By summing up the feature quantities in this way, not only the dent position but also the pulse pitch can be estimated.

[details of internal observation method (inspection method)] The internal observation is carried out on the wafer 20 (laser processed wafer 20 ) in which the modified region is formed for the purpose of cutting the wafer 20 or the like. The internal observation method (inspection method) of this embodiment includes a first step, a second step, and a third step.

As shown in FIG. 18(a), in the first step, for the wafer 20 having modified regions SD1, SD2 formed inside by irradiation with laser light, the surface 21b (first surface) irradiated with laser light The holding member 300 is attached to the back surface 21a (second surface) on the opposite side, and the surface of the holding member 300 opposite to the surface attached to the wafer 20, that is, the mounting surface 300x is provided on the supporting surface 2x of the suction table 2. .

The holding member 300 is a tape such as dicing tape or back grinding tape. As shown in FIG.18(b), 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 irregularities made of a porous material are formed. In the case of using such a holding member 300 and/or the adsorption table 2 for internal observation, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the adsorption table 2 will appear when the back reflection observation is performed. Shows the current situation of captured images (details will be described later). Therefore, as described below, in the internal observation method of the present embodiment, the holding member 300 is optimized so that the patterns of the holding member 300 and the suction table 2 are not reflected in the captured image during back reflection observation, and the optimal The optimized holding member 300 is attached to the wafer 20 (details will be described later).

The second process is the photographing process. For the wafer 20 set on the suction table 2 through the holding member 300, the photographing unit 4 outputs the penetrating light 11 (refer to FIG. 18(a)) and detects the wafer 20 The penetrating light l1 propagated in the medium. In the second step, the penetrating light 11 is detected (that is, photographed) for each imaging area while changing the imaging area along the Z direction which is the vertical direction. Specifically, in the second process, the control unit 8 controls the driving unit 7 so that the imaging unit 4 moves sequentially to the position where each imaging area along the Z direction within the predetermined imaging range of the wafer 20 can be imaged. , and the imaging unit 4 is controlled so as to capture each imaging area while changing the imaging area along the Z direction. The photographing range here includes: the direct observation area that is photographed by moving the focus from the surface 21b side to the rear surface 21a side; 21a reflects light from the back reflective area. That is, in the internal observation in this embodiment, not only the direct observation is performed by moving the focus from the surface 21b side to the back surface 21a side and photographing, but also the focus is aligned from the surface side to the area on the opposite side of the surface 21b of the back surface 21a. And photograph the back reflection observation of the light l1 reflected by the back.

The third step is to determine the state of the modified region of the wafer 20 according to the captured image output from the photographing unit 4 that detects the penetrating light 11 . In the third process, the control unit 8 detects dents and cracks in the modified region based on the feature values of the feature points displayed in the captured images of each captured region, and determines the modified state based on the detected information. Whether the zone-related state is appropriate. The control unit 8 detects feature points and feature quantities of the captured images related to each shot area along the Z direction, for example, determines the position of a feature point with a relatively large feature value as the formation position of the modified area. The detection algorithm in such internal observation, for example, uses the above-mentioned detection algorithm described with reference to FIGS. 13 to 17 .

Here, as described above, there is a problem in that the pattern of the mounting surface 300x of the holding member 300 and the pattern of the support surface 2x of the adsorption table 2 appear in the captured image during the rear reflection observation of the internal observation. FIG. 19 is a diagram explaining problems in back reflection observation of internal observation. As shown in FIG. 19( a ), when observed by back reflection, the penetrating light 11 is focused on the area on the side opposite to the surface 21b of the back surface 21a, that is, the area on the side of the holding member 300 and the adsorption table 2 . Therefore, if the light 11 reflected by the back surface 21a is photographed by the imaging unit 4, there will be a pattern on the mounting surface 300x of the holding member 300 (see FIG. 19(c)) reflects the situation where the image is captured. In this case, the accuracy of determination of the state of the modified region by the control unit 8 (specifically, the estimation accuracy of the state of dents or cracks in the modified region) may deteriorate.

FIG. 19( d ) is a diagram showing an example of an internal observation result in which patterns of the holding member 300 and the like are reflected when an image is captured. In FIG. 19( d ), the horizontal axis represents the feature value, and the vertical axis represents the imaging depth. In the example of FIG. 19( d ), the feature data 901 of the modified region SD1 on the rear surface 21a side, the feature data 902 of the modified region SD2 on the surface 21b side, and the front end of the upper crack were detected in the direct observation region. The feature data 910 is the feature data 903 of the modified region SD1 on the rear surface 21a side detected in the rear reflection region. Furthermore, in the back reflection area, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the supporting 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 with a smaller feature value than when the feature data 1900 is not detected. In this way, detection of the feature data 1900 of the pattern of the holding member 300 etc. affects at least the detection of the modified region SD2 on the surface 21b side, and the accuracy of determination of the state related to the modified region may deteriorate.

In order to solve the above-mentioned problems, in the internal observation method of this embodiment, in the first step, the holding member 300 is optimized so that the pattern of the holding member 300 and the adsorption table 2 will not be reflected in the photographed image during back reflection observation. image, and attach the optimized holding member 300 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 are performed. Hereinafter, optimization of the thickness of the holding member 300 and optimization of the material of the holding member 300 will be described respectively.

Optimization of the thickness of the holding member 300 will be described. In the first step, the holding member 300A ( 300 ) whose thickness is set according to the distance of the modified region farthest from the back surface 21 a in the wafer 20 (hereinafter, may be referred to as “modified region distance”) is pasted. attached to the backside 21a of the wafer 20. Specifically, in the first step, the holding member 300A ( 300 ) whose thickness 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 may be attached. on the backside 21a of the wafer 20 . For example, in the example shown in FIG. 20( a ), the modified region distance is the distance from the back surface 21 a to the end (upper end) of the modified region SD2 on the front 21 b 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 following (1 ) formula to set the thickness T1 of the holding member 300A. For example, in the case of D=350 μm, R1=1.5, and R2=3.5, the thickness T1 of the holding member 300A>150 μm is calculated from the following formula (1). T1＞D×R1/R2 (1)

In the case of using such a holding member 300A, since the thickness of the holding member 300A is thicker than the distance for converting the modified region distance into the approximate distance in the holding member 300A, as shown in FIG. 20( a ), When the rear surface of the modified regions SD1 and SD2 is observed, the light 11 does not reach the mounting surface 300x of the holding member 300A and the support surface 2x of the adsorption table 2 . Therefore, when observing the back side, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the supporting surface 2x of the suction table 2 are not reflected in the captured image. FIG. 20( b ) is a diagram showing an example of an internal observation result when the holding member 300A is used. In FIG. 20( b ), the horizontal axis represents the feature value, and the vertical axis represents the imaging depth. In the example of FIG. 20(b), in the back reflective region, in addition to the feature quantity data 903 of the modified region SD1 on the back surface 21a side, the modified region SD2 on the surface 21b side is also appropriately detected. Feature quantity data 904 . Furthermore, in the back reflection area, the feature quantity data of the pattern of the mounting surface 300x of the holding member 300A and the pattern of the support surface 2x of the suction table 2 were not detected. Thereby, it is possible to detect the positions of the dents in the modified regions SD1 and SD2 with high precision without being affected by the feature amount data of the pattern of the holding member 300A or the like.

The thickness of the holding member 300A may also be determined in consideration of the dz ratio calculated from the refractive index for each observation wavelength and the NA (Numerical Aperture) of the objective lens 43 . 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 may be attached to the wafer 20. Back 21a. The dz rate is the ratio of the Z-axis movement amount of the objective lens in the air to the light-converging position in the object to be observed. For example, when the wavelength of the light 11 is 1100 nm and the objective lens 43 is moved by 1 μm, and the light moves by 4 μm in the silicon constituting the wafer 20 , the dz ratio of the wafer 20 is 4.0. Alternatively, in the first step, the holding member 300A 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 300A to the wafer 20 may be attached to the wafer 20 . Back 21a. Here, for example, in the case where the modified region distance D=350 μm, the dz ratio of the holding member 300A=1.6, and the dz ratio of the wafer 20=4.0, it is calculated that the thickness T1 of the holding member 300A>350×1.6/4.0= 140 μm. In addition, the thickness of the holding member 300 may be set to be only larger than the modified region distance. That is, in the first step, the holding member 300 whose thickness is set to be greater than the modified region distance may be attached to the back surface 21 a of the wafer 20 . However, in this case, the holding member 300 becomes too thick, so it is preferable to calculate the thickness of the holding member 300 according to the above formula (1) or a calculation formula considering the dz rate ratio. That is, it is preferable to calculate the thickness of the holding member 300 in consideration of 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 .

Next, optimization of the material of the holding member 300 will be described. In the first step, as shown in FIG. 21( a), a holding member 300B having a transmittance of 50% or less of the transmissive light 11 output from the imaging unit 4 may be attached to the wafer 20. Back 21a. More preferably, in the first step, a holding member 300B having a transmissive light 11 transmittance of 30% or less may be attached to the back surface 21 a of the wafer 20 . For example, when the wafer 20 is a silicon wafer and the wavelength band of the transparent light 11 is 950 nm to 1700 nm, the transmittance of the holding member 300B may be 50% or less (preferably 30% or less).

In the case of using such a holding member 300B that has a certain light-shielding property to penetrating light 11, as shown in FIG. It reaches the placement surface 300x of the holding member 300B and the support surface 2x of the suction table 2 . Therefore, when viewing the back side, the pattern of the mounting surface 300x of the holding member 300 and the pattern of the supporting surface 2x of the suction table 2 are not reflected in the captured image. FIG. 21( b ) is a diagram showing an example of an internal observation result when the holding member 300B is used. In FIG. 21( b ), the horizontal axis represents the feature value, and the vertical axis represents the imaging depth. In the example of FIG. 21(b), in the back reflective region, in addition to the feature quantity data 903 of the modified region SD1 on the back surface 21a side, the characteristics of the modified region SD2 on the surface 21b side are also appropriately detected. Quantitative data 904. In addition, in the back reflection area, the feature quantity data of the pattern of the mounting surface 300x of the holding member 300B and the pattern of the support surface 2x of the suction table 2 were not detected. Accordingly, it is possible to detect the positions of the dents in the modified regions SD1 and SD2 with high precision without being affected by the feature amount data of the pattern of the holding member 300B or the like.

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

The above-mentioned optimization of the thickness of the holding member 300 and optimization of the material of the holding member 300 may be implemented in combination. By making the thickness of the holding member 300 sufficiently thick, and the holding member 300 is made of a material with high light-shielding properties, it is possible to more effectively suppress the pattern on the mounting surface 300x of the holding member 300 and the pattern on the supporting surface 2x of the suction table 2 from being reflected in the photographing. image.

FIG. 22 is a diagram showing an example of determination results corresponding to combinations of the thickness and transmittance of the holding member 300 . Here, the judgment result "○" indicates that the patterns of the holding member 300 and the like are not reflected and misjudgment is suppressed, "△" represents the situation that the patterns of the holding member 300 and the like are almost not reflected and misjudgment is suppressed, and "×" It shows that the pattern of the holding member 300 and the like is reflected and an erroneous determination occurs. FIG. 23 is a diagram illustrating an example of the distance to the modified region for each processing category. As shown in Figure 23 (a), in the case of performing SDBG (Stealth Dicing Before Grinding, Stealth Dicing Before Grinding) processing as the laser processing, if the thickness of the wafer 20 is set to 775 μm, the modified The area distance is set to, for example, 230 μm. In addition, as shown in FIG. 23( b ), in the case of performing FC (full cutting) processing in which cracks reach the surface 21b after laser processing as laser processing, if the thickness of the wafer 20 is set to 775 μm, Then, the modified region distance is set to 730 μm, for example. In this way, the modified region distance varies depending on the type of processing.

FIG. 22( a ) shows the determination results corresponding to the combinations of the thickness and transmittance of the holding member 300 in SDBG processing. In the example shown in FIG. 22( a ), when the thickness of the wafer 20 is 775 μm and the distance between the modified regions is 230 μm, if the thickness of the holding member 300 is made larger than 101 μm, regardless of the transmittance of the holding member 300 In any case, the judgment result becomes "○". In addition, when the transmittance of the holding member 300 was set to 10% or less, the determination result was "◯" regardless of the thickness of the holding member 300 . 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, when the transmittance of the holding member 300 exceeds 85%, the judgment result becomes “×”, when the holding member 300 When the transmittance is 30%, the judgment result becomes "△". 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, the determination result can be “◯” regardless of the combination of the thickness and transmittance of the holding member 300 . In addition, even when the determination result cannot be "○" only by the thickness of the holding member 300 or only by the transmittance of the holding member 300, the determination result can be made to be "△".

FIG. 22( b ) shows determination results corresponding to combinations of the thickness and transmittance of the holding member 300 in FC processing. In the example shown in FIG. 22( b ), under the condition that the thickness of the wafer 20 is 775 μm and the distance between the modified regions is 730 μm, if the thickness of the holding member 300 is made larger than 301 μm, regardless of the transmittance of the holding member 300 In any case, the judgment result becomes "○". In addition, when the transmittance of the holding member 300 was set to 10% or less, the determination result was "◯" regardless of the thickness of the holding member 300 . In addition, when the thickness of the holding member 300 is 201 to 300 μm, 51 to 200 μm, and 50 μm or less, when the transmittance of the holding member 300 is greater than 85%, the judgment result becomes “×”, when the holding member 300 The judgment result becomes "△" when the transmittance is 30%. 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, the determination result can be “◯” regardless of the combination of the thickness and transmittance of the holding member 300 . In addition, even when the determination result cannot be "○" only by the thickness of the holding member 300 or only by the transmittance of the holding member 300, it is possible to make the determination result by combining the thickness and the transmittance. become "△".

FIG. 24 is a flowchart of an example of the above internal observation method (inspection method). As shown in FIG. 23, in this inspection method, first, for a wafer 20 having a modified region formed inside by irradiation of laser light, stick and hold the wafer on the back surface 21a opposite to the surface 21b irradiated with laser light. The mounting surface 300x of the member 300 opposite to the surface attached to the wafer 20 in the holding member 300 is provided on the suction table 2 (step S1, first process).

In step S1 , for example, 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 holding member 300 to wafer 20 is attached to surface 21 b of wafer 20 . Alternatively, in step S1 , the holding member 300 having a transmissive light 11 transmittance of 50% (preferably 30%) or less is attached to the surface 21b of the wafer 20 .

Next, for the wafer 20 set on the suction table 2 through the holding member 300, the imaging unit 4 outputs the penetrating light 11 and detects the penetrating light 11 propagating in the wafer 20 to perform Photographing of the wafer 20 (step S2, second process).

Finally, according to the photographed image output from the photographing unit 4 that detected the penetrating light 11 , the state of the modified region of the wafer 20 is determined (step S3 , third process).

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

The internal observation method (inspection method) implemented by the laser processing apparatus 1 of the present embodiment includes a first step of attaching a wafer 20 on the back surface 21a of the wafer 20 in which a modified region is formed by irradiating laser light. The holding member 300 is set on the adsorption table 2 on the mounting surface 300x of the holding member 300; the second process is to output the penetrating wafer 20 through the holding member 300 and set on the adsorption table 2 through the imaging unit 4. light l1 and detect the penetrative light l1 propagating in the wafer 20; in the third process, determine the wafer The state related to the modified region of 20; in the first step, the holding member 300 whose thickness is set according to the distance of the modified region is attached to the back surface 21a.

In the inspection method of this embodiment, the holding member 300 is attached to the rear surface 21 a of the wafer 20 in which the modified region is formed, and the holding member 300 is installed on the suction table 2 . Furthermore, by outputting the penetrating light 11 to the wafer 20 mounted on the adsorption table 2 through the holding member 300, the inside of the wafer 20 is observed, and the modified region of the wafer 20 is determined from the captured image. state. Here, in the case of internal observation in this way, if the focus is aligned from the surface 21b side to the area on the opposite side of the surface 21b of the back surface 21a, and the back reflection observation is performed to capture the light reflected from the back surface 21a, the The pattern of the embossed surface of the holding member 300 and the pattern of the porous structure of the adsorption table 2 may appear in the captured image. In this case, the estimation accuracy of the state of the modified region of the wafer 20 from the captured image may deteriorate. In this regard, in the inspection method of the present embodiment, the holding member 300 whose thickness is set according to the distance from the rear surface 21a of the wafer 20 to the modified region farthest from the rear surface 21a, that is, the modified region distance, is attached. on the backside 21a of the wafer 20 . In this way, by setting the thickness of the holding member 300 in consideration of the modified region distance, it is possible to set the thickness of the holding member 300 so as to prevent the patterns of the holding member 300 and the like from appearing in the captured image in the rear reflection observation of the modified region. . In this way, it is possible to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 .

In addition, as a method of avoiding erroneous determination of internal observation based on the influence of the pattern of the holding member 300, etc., for example, a method may be considered in which all captured images in the Z direction (depth direction) that are planned to be captured are acquired before laser processing, and in the When internal observation is performed after laser processing, the photographed image taken before laser processing is removed from the photographed image after laser processing so that only the information of the modified region formed after laser processing is within the viewing angle (based on filter pattern avoidance method). However, since such a method needs to acquire all the images in the Z direction taken in advance before the laser processing, the tact is deteriorated. In addition, if the imaging conditions such as light intensity or brightness value change slightly in the captured images before and after laser processing, the filter function (subtraction function) will not work properly, and the accuracy of internal observation will decrease. In this regard, the internal observation method (inspection method) implemented by the laser processing device 1 of the present embodiment does not require photographing before laser processing, so it is possible to improve the tact, and because no filtering is required, the above-mentioned The reduced precision of internal observations will not be a problem. That is, the internal observation method (inspection method) implemented by the laser processing apparatus 1 of the present embodiment can improve the tact and suppress erroneous judgments in the internal observation of the laser processed wafer 20 .

Alternatively, in the first step, the holding member 300 whose thickness is set to be greater than the modified region distance may be attached to the back surface 21a. Thereby, it is possible to suppress the pattern of the holding member 300 and the like from appearing on the captured image in the rear reflection observation of the modified region. In this way, it is possible to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 .

Alternatively, 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 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 by the above-mentioned refractive index ratio, the modified region distance is converted into an approximate distance in the holding member 300 in consideration of the refractive index, by attaching the holding member 300 having a thickness larger than the converted value on the The rear surface 21a can suppress the pattern of the holding member 300 and the like from appearing in the captured image in the rear reflection observation of the modified region. In this way, it is possible to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 . In addition, by setting the thickness of the holding member 300 according to the value of the modified region distance multiplied by the refractive index ratio, it is possible to reduce the size of the holding member 300 compared to, for example, only setting the thickness of the holding member 300 larger than the modified region distance. 300 thickness. In other words, it is possible to avoid excessive thickness of the holding member 300 and to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 .

Alternatively, 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 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 above-mentioned dz rate ratio, the modified region distance is converted into an approximate distance in the holding member 300 in consideration of the refractive index and the NA (Numerical Aperture, Numerical Aperture) of the objective lens 43 of the imaging unit 4, By attaching the holding member 300 having a thickness larger than the converted value to the back surface 21a, it is possible to suppress the patterns of the holding member 300 and the like from appearing on the captured image in the rear reflection observation of the modified region. In this way, it is possible to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 . In addition, setting the thickness of the holding member 300 by multiplying the value obtained by multiplying the modified region distance by the dz rate ratio is different from, for example, setting the thickness of the holding member 300 to be larger than the modified region distance, or considering only the refractive index ratio. Compared with the case where the thickness of the holding member 300 is set, the thickness of the holding member 300 can be reduced. In other words, it is possible to avoid excessive thickness of the holding member 300 and to suppress erroneous determinations in the internal observation of the laser-processed wafer 20 .

In the internal observation method (inspection method) implemented by the laser processing apparatus 1 of this embodiment, in the first step, the holding member 300 having a transmissive light 11 transmittance of 50% or less may be pasted Attached to the back 21a. In this way, by attaching the light-shielding holding member 300 to the back surface 21a, the image of an object placed below the light-shielding holding member 300 (on the suction table 2 side) is difficult to be reflected in rear reflection observation. Take an image. Specifically, the pattern of the embossed surface of the holding member 300 and the pattern of the porous structure of the adsorption table 2 are difficult to appear in the captured image. In this way, the patterns of the holding member 300 and the like are suppressed from being reflected in the captured image during back reflection observation, and it is possible to suppress erroneous determination in the internal observation of the wafer 20 after laser processing.

In the first step, the holding member 300 having a transmissive light 11 transmittance of 30% or less may be attached to the back surface 21a. By setting the transmittance of the penetrating light 11 of the holding member 300 to 30% or less, it is more appropriate to suppress the pattern of the holding member 300 and the like from being reflected in the captured image in the back reflection observation, and it is possible to suppress the damage after laser processing. Misjudgment during internal observation of wafer 20.

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

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

It is also possible that in the second process, the penetrating light 11 is detected for each shooting area while changing the shooting area along the Z direction which is the vertical direction; in the third process, for each shooting area along the Z direction A feature point and a feature value of the feature point are detected in the shot image related to the shot area, and the position of the feature point with a relatively large feature value is determined as the formation position of the modified area. In this way, by determining the formation position of the modified region based on the feature value of the feature point in the captured image, the accuracy and efficiency of internal observation of the laser-processed wafer 20 can be improved.

2: adsorption table 4: Shooting unit 20: Wafer 21a: Back (second side) 21b: Surface (first side) 300: keep the components L: laser light l1: penetrating light

[ Fig. 1 ] is a configuration diagram of a laser processing apparatus according to an embodiment. [ Fig. 2 ] is a plan view of a wafer according to an embodiment. [ Fig. 3 ] is a cross-sectional view of a part of the wafer shown in Fig. 2 . [ Fig. 4 ] is a configuration diagram of the laser irradiation unit shown in Fig. 1 . [ Fig. 5 ] is a configuration diagram of the imaging unit for inspection shown in Fig. 1 . [FIG. 6] It is a block diagram of the imaging unit for alignment correction shown in FIG. 1. [FIG. [ Fig. 7] Fig. 7 is a cross-sectional view of a wafer for explaining the principle of imaging by the inspection imaging unit shown in Fig. 5 , and images of various parts by the inspection imaging unit. [ Fig. 8] Fig. 8 is a cross-sectional view of a wafer for explaining the principle of imaging by the inspection imaging unit shown in Fig. 5 , and images of various parts by the inspection imaging unit. [FIG. 9(a), (b)] are SEM images of modified regions and cracks formed inside a semiconductor substrate. [FIG. 10(a), (b)] are SEM images of modified regions and cracks formed inside a semiconductor substrate. [FIGS. 11(a) to (c)] are optical path diagrams for explaining the principle of imaging by the inspection imaging unit shown in FIG. 5, and schematic diagrams showing images at focus by the inspection imaging unit. [FIG. 12(a) to (c)] are optical path diagrams for explaining the principle of imaging by the inspection imaging unit shown in FIG. 5, and schematic diagrams showing images at focus by the inspection imaging unit. [FIG. 13(a), (b)] is a figure explaining crack detection. [ Fig. 14 ] is a diagram illustrating crack detection. [FIG. 15(a), (b)] are diagrams explaining dent detection. [ Fig. 16 ] is a diagram illustrating dent detection. [ Fig. 17 ] is a diagram illustrating dent detection. [FIG. 18(a), (b)] is a figure explaining the detailed structure of a holding member and an adsorption table. [FIG. 19(a)-(d)] It is a figure explaining the problem in the back reflection observation of internal observation. [FIG. 20 (a), (b)] is a figure explaining an example of the holding member suitable for back reflection observation. [FIG. 21(a), (b)] is a figure explaining an example of the holding member suitable for back reflection observation. [FIG. 22 (a), (b)] is a figure which shows the determination result corresponding to the combination of the thickness of a holding member, and a transmittance. [FIG. 23 (a), (b)] is a figure explaining an example of the distance to a modified area for each processing type. [ Fig. 24 ] It is a flowchart of an example of the inspection method.

Claims (9)

A method of inspection, the system has: The first step is to attach a holding member to the second surface opposite to the first surface irradiated with the laser light, and attach the holding member to a wafer having a modified region formed inside by irradiating laser light. The surface on the opposite side to the surface attached to the aforementioned wafer is set on the suction table; In the second process, for the aforementioned wafer set on the aforementioned suction table through the aforementioned holding member, the imaging unit outputs penetrating light and detects the aforementioned penetrating light after propagating in the aforementioned wafer; and The third step is to determine the state related to the modified region of the wafer according to the photographed image output from the photographing unit that detects the penetrating light, In the aforementioned first process, the aforementioned holding member whose thickness is set according to the modified region distance is attached to the aforementioned second surface. The distance of the far aforementioned modified region. The inspection method as described in Claim 1, wherein, In the first step, the holding member whose thickness is set to be greater than the distance between the modified regions is attached to the second surface. The inspection method as described in Claim 1, wherein, In the first step, the holding member having a thickness set to be greater than a value obtained by multiplying the modified region distance by a refractive index ratio of the holding member to the wafer is attached to the second surface. The inspection method as described in Claim 1, wherein, In the first step, the holding member having a thickness set to be greater than a value obtained by multiplying the modified region distance by a dz ratio of the holding member to the wafer is attached to the second surface. A method of inspection, the system has: The first step is to stick a holding member on the second surface opposite to the first surface irradiated with laser light on the wafer having a modified region formed inside by irradiating laser light, and attach a holding member to the wafer in the holding member. The surface on the opposite side to the surface attached to the aforementioned wafer is arranged on the suction table; In the second process, for the aforementioned wafer set on the aforementioned suction table through the aforementioned holding member, the imaging unit outputs penetrating light and detects the aforementioned penetrating light after propagating in the aforementioned wafer; and The third step is to determine the state related to the modified region of the wafer according to the photographed image output from the photographing unit that detects the penetrating light, In the first step, the holding member having a transmissive light transmittance of 50% or less is attached to the second surface. The inspection method as described in Claim 5, wherein, In the first step, the holding member having a transmissive light transmittance of 30% or less is attached to the second surface. The inspection method as described in Claim 5 or 6, wherein, In the first step, the holding member including a material that absorbs the penetrating light is attached to the second surface. The inspection method as described in Claim 5 or 6, wherein, In the first step, the holding member including a material that reflects the penetrating light is attached to the second surface. The inspection method according to any one of Claims 1 to 6, wherein, In the aforementioned second process, the aforementioned penetrating light is detected for each imaging area while changing the imaging area along the Z direction which is the vertical direction, In the aforementioned third process, the feature points and the feature values of the feature points are detected for the aforementioned shot images related to each shot area along the aforementioned Z direction, and the position of the feature point with a relatively large feature amount is determined as the aforementioned modification. The location where the region is formed.

Images