TWI729205B - Inspection wafer and how to use inspection wafer - Google Patents

Abstract

The subject of the present invention is to suppress the influence of light leakage on the device during laser processing, and to find processing conditions that can divide wafers well. The solution is to use an inspection wafer (WA) to replace the wafer. It is used in a laser processing device (1) for forming the modified layer (M) inside the wafer (W) by laser processing. ), inspection of light leakage during laser processing, 　　 is provided with: an inspection substrate (41), an underlayer (42) formed with a predetermined thickness on the entire surface of the inspection substrate, and a metal foil (43) laminated on the underlayer, The thickness of the bottom layer is formed so that the influence of light leakage on the device of the wafer and the metal foil of the inspection wafer is consistent.

Description

Inspection wafer and how to use inspection wafer

[0001] The present invention relates to an inspection wafer used in a laser processing device and a method of using the inspection wafer.

[0002] As a method of dividing a wafer, there is a known method of dividing the wafer with the modified layer as a starting point after forming a modified layer inside the substrate of the wafer along the planned dividing line (for example, refer to Patent Literature). 1). In the dividing method described in Patent Document 1, a laser beam having a transparent wavelength is irradiated on the wafer from the back side of the wafer, and a modified layer is formed inside the wafer along the planned dividing line. Then, an external force is applied to the wafer by breaking or expanding, whereby the modified layer with reduced strength will form a starting point for division, and the wafer will be divided into individual device chips. [Prior Art Document] [Patent Document] 　　[0003] 　　 [Patent Document 1] Japanese Patent No. 3408805

(Problem to be solved by the invention) 　　[0004] However, usually the laser light irradiated from the back side of the wafer is condensed near the device, and the laser light that does not contribute to the formation of the reforming layer will come from the condensing point Diffusion toward the device on the surface side of the wafer. The leakage of the laser light from this condensing point is irradiated under the device, causing the device to be damaged by heating. On the other hand, by reducing the output of the laser light or moving the focus point away from the device, although the influence of light leakage on the device can be suppressed, there is a problem that it is difficult to divide the wafer with the modified layer as a starting point. [0005] The present invention was developed in view of such points to provide an inspection wafer and a wafer that can suppress the influence of light leakage on the device during laser processing and find processing conditions that can divide the wafer well. One of the purposes is the use of wafers for inspection. (Means to Solve the Problem) 　　[0006] The inspection wafer of one aspect of the present invention is used in a laser processing device, and the inspection laser light is concentrated without changing the laser light that does not contribute to the formation of the modified layer. For light leakage that affects the device due to the quality layer, the laser processing device irradiates the substrate constituting the wafer with the laser light of the transmissive wavelength from the back surface of the wafer on which plural devices are formed by dividing the predetermined line on the surface. Focusing on the inside of the substrate, along the planned dividing line, a modified layer is formed inside the substrate. 　　 is characterized by: 　　 consists of an inspection substrate and an underlayer formed with a predetermined thickness on the entire surface of the inspection substrate, and laminated The bottom layer is composed of metal foil, and the bottom layer is formed on the metal foil. Only the thickness of the light leakage that affects the device can be detected. [0007] According to this configuration, by the thickness of the bottom layer of the inspection wafer, the influence of the light leakage of the laser light on the device of the wafer and the influence of the light leakage of the laser light on the metal foil of the inspection wafer can be made Unanimous. Therefore, light leakage that does not affect the device is detected in the metal foil, and only light leakage that affects the device is detected in the metal foil. By replacing wafers and using inspection wafers, it is possible to find the most suitable processing conditions for the laser processing of the wafer while suppressing the influence of light leakage on the device. Therefore, there is no waste of the wafers used as products, and the inspection wafers can be used to find the most suitable processing conditions. [0008] A method of using an inspection wafer according to one aspect of the present invention is the above-mentioned method of using an inspection wafer, and is characterized by having: a "modified layer formation process" which is made from the back of the inspection wafer The inspection substrate is irradiated with a laser beam of a transparent wavelength, and the condensed spot focused on the interior of the inspection substrate is moved linearly in the direction of the surface of the inspection wafer to form a straight modified layer; 　　 width measurement process, which After the reforming layer formation process, the metal foil of the inspection wafer is taken, and the maximum width of the metal foil deformation that appears on the surface of the metal foil is measured; and the adjustment process is based on the metal foil deformation measured in the width measurement process The laser beam is adjusted in such a way that the maximum width is within the width of the predetermined dividing line. [Effects of the invention] 　　[0009] According to the present invention, by using a metal foil to detect only the light leakage that affects the device, it is possible to suppress the effect of the light leakage of the laser light on the device. At the same time, find the processing conditions that can divide the wafer well.

[0011] Hereinafter, the laser processing apparatus according to this embodiment will be described with reference to the drawings. Fig. 1 is a perspective view of the laser processing apparatus of the present embodiment. Fig. 2 is an explanatory diagram of a method of setting processing conditions of laser processing in a comparative example. In addition, the laser processing apparatus has only a configuration that can be performed using the inspection wafer of this embodiment, and is not limited to the configuration shown in FIG. 1. [0012] As shown in FIG. 1, the laser processing apparatus 1 is configured to move the laser processing means 31 for irradiating laser light and the holding platform 21 holding the wafer W relative to each other, and the wafer W is processed by laser. On the surface of the wafer W, a plurality of planned dividing lines L are arranged in a grid pattern, and plural devices are formed in each area divided by the planned dividing line L. The wafer W is supported by the ring frame F via the dicing tape T. In addition, the wafer W is not particularly limited, but as long as the device is formed on the surface like a semiconductor wafer or an optical device wafer. [0013] The base 10 of the laser processing apparatus 1 is provided with a platform moving means 11 that moves the holding platform 21 in the X-axis direction and the Y-axis direction with respect to the laser processing means 31. The platform moving means 11 has a pair of guide rails 12 arranged on the base 10 in parallel to the X-axis direction, and a motor-driven X-axis platform 14 slidably provided on the pair of guide rails 12. In addition, the stage moving means 11 has a pair of guide rails 13 arranged on the upper surface of the X-axis stage 14 parallel to the Y-axis direction, and a motor-driven Y-axis stage 15 slidably provided on the pair of guide rails 13 . [0014] On the back side of the X-axis stage 14 and the Y-axis stage 15 are respectively formed nut portions not shown, and the ball screws 16, 17 are screwed to the nut portions. Then, by the drive motors 18 and 19 connected to one end of the ball screws 16 and 17 to rotate and drive, the holding platform 21 moves along the guide rails 12 and 13 in the X-axis direction and the Y-axis direction. In addition, a holding platform 21 for holding the wafer W is provided on the Y-axis platform 15. A holding surface 22 is formed on the upper surface of the holding platform 21, and a clamping portion 23 for holding and fixing the periphery of the wafer W is provided around the holding platform 21. [0015] An arm portion 26 is protrudingly provided on the upright wall portion 25 behind the holding platform 21, and a laser processing means 31 for laser processing the wafer W on the holding platform 21 is provided at the front end of the arm portion 26. The laser processing means 31 irradiates a laser beam of a transmissive wavelength from the back side of the wafer W to the substrate constituting the wafer W. By moving the holding platform 21 in the X-axis direction and the Y-axis direction relative to the laser processing means 31, the laser light is condensed inside the substrate, and a line L along the planned dividing line is formed inside the wafer W. The modified layer M (refer to Figure 2A). The wafer W is divided into individual device wafers by using the modified layer M whose strength has been reduced as the starting point of division. [0016] In addition, an imaging means 32 for alignment of the wafer W is provided beside the laser processing means 31. The imaging means 32 captures the surface of the wafer W to generate an imaging image. In addition to the alignment of the wafer W, it is also used in an inspection method using an inspection wafer WA (see FIG. 3) described later. In addition, the modified layer M (refer to FIG. 2A) is irradiated with laser light, and the density, refractive index, mechanical strength, or other physical properties of the inside of the wafer W will be in a different state from the surroundings, which means Areas where the intensity is lower than the surrounding area. The modified layer M is, for example, a melting processing area, a cracking area, a dielectric breakdown area, and a refractive index change area, and it may also be an area where these are mixed. [0017] In addition, the laser processing apparatus 1 is provided with a control means 33 that collectively controls each part of the apparatus. The control means 33 is constituted by a processor or memory that executes various processes. The memory is composed of one or more storage media such as ROM (Read Only Memory) and RAM (Random Access Memory) according to the purpose. In the memory, in addition to the control program of each part of the control device, the processing conditions of the laser processing, the program of each process executed by the use method of the inspection wafer WA (refer to FIG. 3), etc. are stored. In addition, the details of the inspection wafer WA will be described later. [0018] Moreover, the processing conditions of the laser processing are set based on the actual processing results of the wafer W, etc. However, in the case of resetting the processing conditions, etc., in addition to the effect of the leakage of the laser light on the device, it must also be considered Ease of division of wafer W. In the laser processing apparatus 1, once the laser light is condensed inside the substrate of the wafer W, there is a possibility that the apparatus may be heated due to the light leakage diffused from the condensing point. On the other hand, if the output of the laser light or the position of the condensing point is adjusted in a way to reduce the influence of heat on the device, it is difficult to form a modified layer M of suitable strength at a suitable position for the wafer W (refer to Figure 2A). [0019] Specifically, as shown in FIG. 2A, during the laser processing of the wafer W, the leakage light of the laser light will not be collected within the width of the planned dividing line L, and may be scattered to the planned dividing line L. It is too wide to cause damage to the device D. If the light leakage can be contained within the width of the predetermined dividing line L, the output of the laser light is weakened, or the position of the condensing point is moved away from the device D, the modified layer M formed on the wafer W will not be formed Appropriate starting point for segmentation. That is, although the influence of light leakage on the device D can be suppressed, it is difficult to divide the wafer W by using the modified layer M as a starting point for division. [0020] Therefore, as shown in FIG. 2B, usually instead of wafer W, the inspection wafer WB of the comparative example is used, and while confirming the influence of light leakage on the device D (see FIG. 2A), the setting can be appropriately divided. Processing conditions of circle W. In the inspection wafer WB of the comparative example, the metal foil 53 is laminated on the surface 55 side of the substrate 51 with the base layer 52 interposed therebetween, and thermal deformation (splash) S is easily generated in the metal foil 53 due to light leakage. For this inspection wafer WB, laser light is irradiated from the back side 56 side, and the thermal deformation S of the metal foil 53 is observed at the position corresponding to the device D of the wafer W (outside the planned dividing line L) to find the device D Processing conditions that are not affected by light leakage. [0021] However, in the inspection wafer WB of the comparative example, if the sensitivity of the metal foil 53 is too high, the metal foil 53 will be thermally deformed even if the light leakage does not affect the device D (see FIG. 2A). In other words, even if the leaked light scattered outside the planned dividing line L on the wafer W (see FIG. 2A), as long as the leaked light with a sufficiently reduced power does not affect the device D, the leaked light with such reduced power is also caused by the metal. The foil 53 is all detected. Therefore, it is not known whether it is the light leakage that affects the device D, so there is a problem that the processing conditions are set that excessively consider the effect of the light leakage on the device D. [0022] Therefore, the inspection wafer WA (see FIG. 3) of the present embodiment is for the inspection substrate 41, the thickness of the base layer 42 for attaching the metal foil 43 can be changed, and the light leakage of the metal foil 43 can be adjusted. Detection sensitivity. By thickening the bottom layer 42 to passivate the detection sensitivity of the metal foil 43, the metal foil 43 only detects the light leakage affected by the device D (refer to FIG. 2A). Therefore, the inspection wafer WA can be used to change the processing conditions into various types. While the effect of light leakage on the device D is detected as the thermal deformation S of the metal foil 43, it is possible to find out where the wafer W is divided. Optimal processing conditions. [0023] Hereinafter, the inspection wafer according to this embodiment will be described with reference to FIG. 3. Fig. 3 is an exploded perspective view of the inspection wafer of the present embodiment. Fig. 4 is an explanatory diagram of the method of adjusting the thickness of the base layer of the present embodiment. In addition, in the wafer for inspection, the planned dividing line is not formed. However, in FIGS. 4B and C, the planned dividing line is indicated by a broken line for convenience of explanation. [0024] As shown in FIG. 3, when determining the processing conditions of the laser processing apparatus 1 (see FIG. 1), instead of the wafer W, the inspection wafer WA is used. The inspection wafer WA is formed and inspected, and when the laser light is condensed, the laser light that does not contribute to the formation of the modified layer affects the light leakage of the device D (see FIG. 2A) of the wafer W. On the inspection substrate 41 of the inspection wafer WA, a metal foil 43 is laminated with a base layer 42 of a predetermined thickness therebetween. The metal foil 43 is irradiated with light leakage through the bottom layer 42 and thermally deformed, and the light leakage that affects the device D is inspected by the thermal deformation of the metal foil 43. [0025] The inspection substrate 41 is formed with a modified layer M (see FIG. 4B) that becomes the starting point of division when the laser light is condensed. Although various materials can be selected, it is usually the same as the actual production wafer. A substrate with the same material and thickness will be selected. For example, when the actual production wafer W (refer to FIG. 4A) is a semiconductor wafer, a semiconductor substrate is selected as the inspection substrate 41, and when the actual production wafer W is an optical device wafer, an inorganic material substrate is selected as Board 41 for inspection. For the inspection substrate 41, for example, silicon (Si), silicon carbide (SiC), sapphire (Al ₂ O ₃ ), or gallium nitride (GaN) may be used. [0026] The base layer 42 having a predetermined thickness on the entire surface of the inspection substrate 41 is formed by vapor deposition. Although various materials can be selected for the bottom layer 42, a material that allows the metal foil 43 to be well attached to the inspection substrate 41 is selected. For the underlayer 42, for example, titanium (Ti) or chromium (Cr) may also be used. In addition, the thickness of the bottom layer 42 is formed: as described above, when the wafer W (see FIG. 2A) is processed by laser, the metal foil 43 can only detect the thickness of the light leakage that affects the device D. In addition, the details of the adjustment of the thickness of the base layer 42 will be described later. [0027] On the surface of the bottom layer 42, instead of the device D (see FIG. 4A), the metal foil 43 is formed by vapor deposition. Although various materials can be selected for the metal foil 43, the same material or a material with a melting point close to that of the metal wiring of the device to be processed at the time of actual production is selected. The metal foil 43 can also be used, for example, aluminum (Al), tin (Sn), platinum (Pt), gold (Au), silver (Ag), indium (In), lead (Pb), copper (Cu), chromium ( Cr). In addition, although the thickness of the metal foil 43 is not particularly limited, it is a thickness that is likely to occur due to thermal deformation of the light leakage of the laser light. [0028] In the inspection wafer WA, the thickness of the base layer 42 is adjusted so that the influence of light leakage on the device D of the wafer W (see FIG. 2A) used in actual production and the metal foil 43 of the inspection wafer WA is consistent. Thereby, when the metal foil 43 is thermally deformed in the inspection using the inspection wafer WA, it can be regarded that the device D of the wafer W used in actual production is damaged due to the influence of heat. By using the inspection wafer WA to try various processing conditions, it is possible to set the processing conditions for the device D not to be affected by light leakage. In addition, the bottom layer 42 and the metal foil 43 are formed by vapor deposition. However, the bottom layer 42 and the metal foil 43 may be formed by any method as long as they can be formed into an appropriate thickness for the inspection wafer WA. [0029] As shown in FIG. 4A, when adjusting the thickness of the bottom layer 42 (refer to FIG. 4B), first, actual laser processing is used on the actually produced wafer W, and the standard processing conditions that have no effect on the device D are found. . In addition, here, it is sufficient to determine the processing conditions that do not affect the device D. Instead of the actual laser processing wafer W, the processing conditions may be determined, or the processing conditions may be determined empirically based on past processing performance, etc. Calculations etc. theoretically determine the processing conditions. In addition, the presence or absence of the influence on the device D may be determined by, for example, checking the resistance of the wiring in the device D by an inspection unit (not shown). [0030] As shown in FIG. 4B, once the reference processing conditions are determined, laser processing is performed on the inspection wafer WA under the reference processing conditions. Then, the metal foil 43 of the inspection wafer WA is picked up by the imaging means 32 (refer to FIG. 1), and the thermal deformation S is detected in the metal foil 43 of the light leakage of the laser light. Since the reference processing conditions are set to conditions that do not affect the device D (refer to FIG. 4A), as long as the light leakage has the same effect on the wafer W and the inspection wafer WA, the device D corresponding to the wafer W is formed. In the inspection wafer WA, that is, outside the line width of the planned dividing line L, the metal foil 43 should not be thermally deformed. [0031] When the metal foil 43 is thermally deformed outside the line width of the planned dividing line L, even light leakage that does not affect the device D is determined to be detected in the metal foil 43. Therefore, the bottom layer 42 is thin and the detection sensitivity is too high. As shown in FIG. 4C, the bottom layer 42 is thickened in such a way that the thermally deformed part S of the metal foil 43 can be contained within the line width of the predetermined dividing line L. Conversely, on the inner side of the line width of the planned dividing line L, when the metal foil 43 is not thermally deformed, the bottom layer 42 is thick, and the detection sensitivity is too low, then the thermal deformation point S of the metal foil 43 is closed to the planned dividing line L The thickness within the width is reduced to form the bottom layer 42. [0032] By laser processing under the standard processing conditions in this way, the thermal deformation S of the metal foil 43 is contained within the width of the planned dividing line L to form the thickness of the bottom layer 42, so that light leakage can be made to the wafer W (refer to FIG. The device D of 4A) corresponds to the influence of the metal foil 43 of the inspection wafer WA. In such an inspection wafer WA, only light leakage that affects the device D is detected as the thermal deformation S of the metal foil 43. Therefore, light leakage that does not affect the device D can be ignored, and the thermal deformation S of the metal foil 43 can be contained within the width of the planned dividing line L, and the most suitable processing conditions for the wafer W can be found. [0033] Next, referring to FIG. 5, a method of using the inspection wafer will be described. Fig. 5 is an explanatory diagram of a method of using the inspection wafer according to the present embodiment. In addition, FIG. 5 shows an example of the usage method of the wafer for inspection, which can be changed as appropriate. [0034] As shown in FIG. 5A, first, the reforming layer formation process is performed. In the reforming layer formation process, in the laser processing device 1 (refer to FIG. 1), the metal foil 43 side of the surface of the inspection wafer WA will face downward, and the inspection wafer WA will be held by the dicing tape T. The stage 21 and the ring frame F around the inspection wafer WA are held by the clamp part 23. In addition, the ejection port of the laser processing means 31 is positioned directly above the inspection wafer WA, and the laser processing means 31 irradiates the laser light from the back surface of the inspection wafer WA. The laser light has a wavelength that is transparent to the inspection substrate 41 and is adjusted to be focused on the inside of the inspection substrate 41. [0035] Then, by relatively moving the inspection wafer WA by the laser processing means 31, the condensing point moves linearly in the surface direction of the inspection wafer WA, and a linear modification is formed inside the inspection substrate 41. Layer M. At this time, the light leakage of the laser light diffuses from the condensing point toward the metal foil 43 of the inspection wafer WA, and the metal foil 43 is thermally deformed by the light leakage after passing through the bottom layer 42. Since the thickness of the bottom layer 42 of the inspection wafer WA is formed on the metal foil 43, only light leakage that affects the device D (see FIG. 4A) can be detected, so there will be no weak light leakage that does not affect the device D. This causes the metal foil 43 to be thermally deformed. [0036] As shown in FIG. 5B, the width measurement process is performed after the reforming layer formation process. In the width measurement process, after peeling off the dicing tape T (refer to FIG. 5A) from the inspection wafer WA, the metal foil 43 of the inspection wafer WA is directed upward, and the imaging means 32 picks up the inspection wafer WA. Metal foil 43. In the imaging means 32, the maximum width d of the metal foil deformation S that appears on the surface of the metal foil 43 is measured based on the image taken of the metal foil 43. At this time, various image processing is performed on the captured image to detect the thermal deformation S of the metal foil 43, and the difference between the two points of the deformation of the metal foil 43 that is the most separated in the direction perpendicular to the extending direction of the modified layer M is measured. Distance d. [0037] As shown in FIG. 5C, the adjustment process is implemented after the width measurement process. In the adjustment process, the laser beam processing conditions are adjusted in such a way that the maximum width d of the deformation of the metal foil can form the width of the predetermined dividing line L. Since light leakage has the same influence on the metal foil 43 of the inspection wafer WA and the device D of the wafer W (see FIG. 4A), the light leakage that deviates from the width of the planned dividing line L may damage the device D of the wafer W The fear. Therefore, the processing conditions are adjusted so that the maximum width d of the thermal deformation S of the metal foil 43 can be contained within the width of the planned dividing line L, thereby setting the processing conditions that do not damage the device D of the wafer W. [0038] In the adjustment process, for example, the wavelength of the laser light, the spot shape, the average output, the repetition rate, the pulse width, the numerical aperture (NA) of the condenser lens, the position of the condenser point, the processing feed speed, etc. At least one of the processing conditions will be adjusted. In this way, by adjusting the processing conditions within the range of the device D that does not damage the wafer W, it is possible to find the most suitable processing conditions for the wafer W to form a good modified layer M. In addition, the line width of the planned dividing line L is previously memorized as a data, but the planned dividing line may be actually formed on the metal foil 43 of the inspection wafer WA. [0039] As described above, according to the inspection wafer WA of the present embodiment, the thickness of the bottom layer 42 of the inspection wafer WA can cause the leakage of laser light to the device D and the inspection wafer W. The influence of the metal foil 43 of the wafer WA is the same. Therefore, the leakage of the laser light that does not affect the device D will not be detected in the metal foil 43, and the leakage of the laser light that only affects the device D will be detected in the metal foil 43. By replacing the wafer W and using the inspection wafer WA, it is possible to find the most suitable processing conditions for the laser processing of the wafer W while suppressing the influence of the light leakage of the laser light on the device D. Therefore, there is no waste of the wafer W as a product, and the inspection wafer WA can be used to find the most suitable processing conditions. [0040] In addition, in this embodiment, the metal foil is formed on the entire surface of the bottom layer of the inspection wafer, but it is not limited to this configuration. The metal foil only needs to be able to detect the effect of light leakage on the device, and it may be partially formed on the bottom layer. [0041] Furthermore, in this embodiment, an anti-oxidation film may be formed on the metal foil of the inspection wafer. The oxidation prevention film can prevent the oxidation of the metal foil. In addition, a protective tape can also be used to prevent oxidation of the metal foil. [0042] In addition, in this embodiment, a laser processing device is used to perform the reforming layer forming process, the width measurement process, and the adjustment process, but it is not limited to this. The modified layer formation process, the width measurement process, and the adjustment process can also be implemented with dedicated devices. [0043] In addition, although the present embodiment and modification examples have been described, as another embodiment of the present invention, the above-mentioned embodiment and modification examples may be combined in whole or in part. [0044] In addition, the embodiments and modifications of the present invention are not limited to the above-mentioned embodiments, and various changes, substitutions, and modifications may be implemented without departing from the scope of the technical idea of the present invention. Moreover, through technological progress or other derived technologies, as long as the technical idea of the present invention can be realized by other methods, this method can also be used to implement it. Therefore, the scope of the patent request covers all the embodiments included in the scope of the technical idea of the present invention. [0045] In addition, in the present embodiment, the present invention is applied to the structure of the inspection wafer, but it can be applied to a substrate that can find processing conditions that can be well divided by a modified layer. Processed objects. [Industrial Applicability] [0046] As explained above, the present invention has the effect of suppressing the effect of light leakage on the device during laser processing and finding the processing conditions that can divide the wafer well, especially It is useful in the use of inspection wafers and inspection wafers to find out the processing conditions of semiconductor wafers or optical device wafers.

[0047]1‧‧‧Laser processing device 41‧‧‧Inspection substrate 42‧‧‧Bottom layer 43‧‧‧Metal foil D‧‧‧Device F‧‧‧Ring frame L‧‧‧Preparation line M‧‧ ‧Modified layer T‧‧‧Dicing tape W‧‧‧Wafer WA‧‧‧Wafer for inspection

[0010] 　　 FIG. 1 is a perspective view of a laser processing apparatus according to this embodiment.　　 FIG. 2 is an explanatory diagram of a method of setting processing conditions of laser processing in a comparative example.　　 FIG. 3 is an exploded perspective view of the inspection wafer of this embodiment.　　 FIG. 4 is an explanatory diagram of the method of adjusting the thickness of the base layer in this embodiment.　　 FIG. 5 is an explanatory diagram of the method of using the inspection wafer of the present embodiment.

41‧‧‧Substrate for inspection

42‧‧‧Bottom

43‧‧‧Metal foil

D‧‧‧device

L‧‧‧Divide line

M‧‧‧Modified layer

W‧‧‧wafer

WA‧‧‧Inspection Wafer

Claims (2)

A wafer for inspection is used in a laser processing device to inspect the light leakage of the laser light that is condensed and does not contribute to the formation of a modified layer from the modified layer and affects the device of the wafer. The laser The processing device irradiates the substrate constituting the wafer with laser light having a transmissive wavelength from the back surface of the wafer on which a plurality of devices are formed by dividing the predetermined line on the surface, and focuses the light on the inside of the substrate, A modified layer is formed inside the substrate along the planned dividing line, which is characterized by: an inspection substrate, an underlayer formed with a predetermined thickness on the entire surface of the inspection substrate, and a metal layer laminated on the underlayer The bottom layer is formed by the foil, and the metal foil can only detect the thickness of the light leakage that affects the device. A method of using inspection wafers is the method of using inspection wafers as described in item 1 of the scope of patent application. The inspection substrate is irradiated with laser light of a transmissive wavelength, and the condensing point condensed inside the inspection substrate is moved linearly in the surface direction of the inspection wafer to form a straight modified layer; width measurement The process is to take the metal foil of the inspection wafer after the reforming layer formation process, and measure the maximum width of the metal foil deformation that appears on the surface of the metal foil; and The adjustment process is to adjust the laser beam so that the maximum width of the deformation of the metal foil measured in the width measurement process falls within the width of the planned dividing line.

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