TW201816864A - Inspection wafer, and use method thereof capable of finding processing conditions for well cutting a wafer while suppressing the influence of light leakage on the devices of the wafer during laser processing - Google Patents

Abstract

To find processing conditions that can well cut a wafer while suppressing the influence of light leakage on the devices during laser processing. An inspection wafer (WA) is used to replace a wafer and is used in a laser processing apparatus (1) to examine light leakage during laser processing when forming a modified layer (M) on the inside of a wafer (W) by laser processing. The inspection wafer includes a substrate for inspection (41), an underlayer (42) with a predetermined thickness formed entirely on the surface of the substrate for inspection, and a metal foil (43) laminated on the underlayer. This invention is characterized in that the thickness of the underlayer is formed in such a way that the influence of the light leakage on the devices of the wafer is the same as that on the metal foil of the inspection wafer.

Description

Inspection wafer and usage method of inspection wafer

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

[0002] As a method of dividing a wafer, a method of dividing a wafer with a reformed layer as a starting point after forming a reformed layer inside a substrate of the wafer along a predetermined dividing line is known (for example, refer to Patent Literature) 1). In the division method described in Patent Document 1, laser light having a transmissive wavelength is irradiated to the wafer from the back side of the wafer, and a modified layer is formed inside the wafer along a predetermined division line. Then, an external force is applied to the wafer by breaking or expanding, so that the modified layer having a reduced strength will form a division starting point, and the wafer will be divided into individual device wafers. [Preceding Technical Documents] [Patent Documents] [0003] [Patent Document 1] Japanese Patent No. 3408805

(Problems to be Solved by the Invention) [0004] However, the laser light radiated from the back side of the wafer is usually condensed near the device, and the laser light that does not contribute to the formation of the reforming layer is collected from the light condensing point. Diffusion toward the device on the surface side of the wafer. Leakage of laser light from the light-condensing point is irradiated under the device, resulting in a problem that the device is damaged due to heat. On the other hand, by reducing the output of the laser light or moving the position of the light collecting 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 by modifying the layer as a starting point. [0005] The present invention has been developed in view of such a point, in order to provide an inspection wafer and an inspection wafer that can satisfactorily divide the processing conditions of the wafer while suppressing the influence of light leakage on the device during laser processing. The use of inspection wafers is one of the purposes. (Means to Solve the Problem) [0006] An inspection wafer according to one aspect of the present invention is used in a laser processing apparatus, and inspects laser light condensing without changing the laser light from forming a modified layer. The laser processing device irradiates the substrate constituting the wafer with laser light having a transmissive wavelength from the back of the wafer on the surface of which a plurality of devices are formed by dividing a predetermined line by dividing the light leakage that affects the device with a mass layer. Condensed on the inside of the substrate, along the predetermined dividing line, a modified layer is formed inside the substrate. Its characteristics are: The inspection substrate and the bottom layer formed with a predetermined thickness on the entire surface of the inspection substrate, The bottom layer is made of metal foil on the bottom layer. The bottom layer is formed on the metal foil to a thickness that can only detect light leakage that affects the device. [0007] According to this configuration, by the thickness of the bottom layer of the inspection wafer, the influence of the leakage of laser light on the device of the wafer and the influence of the leakage of laser light on the metal foil of the inspection wafer can be achieved. Consistent. Therefore, there is no case where light leakage that has no effect on the device is detected in the metal foil, and only light leakage that has an effect on the device is detected in the metal foil. By replacing the wafer and using the inspection wafer, it is possible to find the processing conditions most suitable for the laser processing of the wafer while suppressing the influence of light leakage on the device. Therefore, there is no case where a wafer to be a product is wasted, and the optimum processing conditions can be found using the inspection wafer. [0008] A method for using an inspection wafer according to an aspect of the present invention is the above-mentioned method for using an inspection wafer, and is characterized by comprising: (1) a reforming layer forming process, which is performed from a back surface of the inspection wafer; The inspection substrate is irradiated with laser light of a transmissive wavelength, and the light-condensing point condensed inside the inspection substrate is moved linearly in the plane direction of the inspection wafer to form a linear modified layer. ； Width measurement process, which After the reforming layer forming 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 deformation of the metal foil measured in the width measurement process. The laser beam is adjusted so that the maximum width is within the width of the predetermined line. [Effects of the Invention] [0009] According to the present invention, by using a wafer for inspection that can detect only light leakage that affects the device with a metal foil, it is possible to suppress the influence of the light leakage of laser light on the device, Find out the processing conditions that can well divide the wafer.

[0011] A laser processing apparatus according to this embodiment will be described below with reference to the drawings. 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 for laser processing in a comparative example. The laser processing apparatus may have a configuration that can be carried out by using an inspection wafer according to 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 that irradiates laser light and the holding table 21 holding the wafer W relatively, and the laser processing the wafer W. On the surface of the wafer W, a plurality of planned division lines L are arranged in a grid shape, and a plurality of devices are formed in each area divided by the planned division line L. The wafer W is supported by the ring frame F via a dicing tape T. In addition, the wafer W is not particularly limited, but as long as a semiconductor wafer, an optical device wafer, or the like, a device may be formed on the surface. [0013] The base 10 of the laser processing apparatus 1 is provided with a stage moving means 11 that moves the holding stage 21 in the X-axis direction and the Y-axis direction with respect to the laser processing means 31. The platform moving means 11 includes a pair of guide rails 12 arranged on the base 10 and parallel to the X-axis direction, and a motor-driven X-axis platform 14 slidably provided on the pair of guide rails 12. The platform moving means 11 includes a pair of guide rails 13 arranged parallel to the Y-axis direction on the upper surface of the X-axis platform 14 and a motor-driven Y-axis platform 15 slidably provided on the pair of guide rails 13. . [0014] A nut portion (not shown) is formed on the back side of the X-axis stage 14 and the Y-axis stage 15, respectively, and ball screws 16, 17 are screwed into the nut portions. Then, by the drive motors 18 and 19 connected to one end portions of the ball screws 16 and 17, the holding platform 21 moves along the guide rails 12 and 13 in the X-axis direction and the Y-axis direction. Further, a holding table 21 holding a wafer W is provided on the Y-axis table 15. A holding surface 22 is formed on the upper surface of the holding table 21, and a clamping portion 23 of a ring frame F for holding and fixing the periphery of the wafer W is provided around the holding table 21. [0015] The standing wall portion 25 behind the holding platform 21 is provided with an arm portion 26 in a protruding manner, and at the front end of the arm portion 26 is a laser processing means 31 provided with a wafer W on the laser processing holding platform 21. The laser processing means 31 irradiates a laser beam having a transmissive wavelength from the back surface side of the wafer W to the substrate constituting the wafer W. When the stage 21 is relatively moved in the X-axis direction and the Y-axis direction with respect to the laser processing means 31, the laser light is focused inside the substrate, and is formed along the predetermined division line L inside the wafer W Modified layer M (see FIG. 2A). The wafer W is divided into individual device wafers using the modified layer M having a reduced strength as a starting point for division. [0016] An imaging means 32 for aligning the wafer W is provided beside the laser processing means 31. The imaging means 32 captures the surface of the wafer W and generates a photographed image. In addition to the alignment of the wafer W, an inspection method using an inspection wafer WA (see FIG. 3) described later is used. In addition, the modified layer M (see FIG. 2A) is irradiated with laser light, and the density, refractive index, mechanical strength, or other physical characteristics of the wafer W will be different from the surroundings, meaning Areas that have a lower intensity than the surroundings. The modified layer M is, for example, a melt processing field, a crack field, an insulation breakdown field, or a refractive index change field, and may be a mixed field. [0017] Further, the laser processing apparatus 1 is provided with a control means 33 which integrates each section of the control apparatus. The control means 33 is constituted by a processor, a memory, or the like that performs various processes. The memory is composed of one or a plurality of memory media such as a ROM (Read Only Memory), a RAM (Random Access Memory), and the like according to the purpose. In the memory, in addition to the control program of each unit of the control device, the processing conditions of laser processing, the programs of each process performed by the method of using the inspection wafer WA (refer to FIG. 3), and the like are stored. The details of the inspection wafer WA will be described later. [0018] Moreover, the processing conditions for laser processing are set based on actual processing results for wafer W, but when the processing conditions are reset, etc., in addition to the effect of laser light leakage on the device, it must also be considered. The slicing of the wafer W is easy. In the laser processing apparatus 1, once the laser light is condensed inside the substrate of the wafer W, there is a fear that the apparatus may be exposed to heat due to light leakage diffused from the light-condensing point. On the other hand, if the output of the laser light or the position of the light-condensing point is adjusted so as to reduce the influence of heat and the like on the device, it is difficult to form a modified layer M having an appropriate intensity at an appropriate position on the wafer W (see Figure 2A). [0019] Specifically, as shown in FIG. 2A, during the laser processing of the wafer W, the leakage of the laser light will not be collected within the width of the division line L, and there is a fear of scattering to the division line L. Tolerance may cause device D to break. If the light leakage can be confined within the width of the division line L, the output of the laser light is reduced, or the position of the light collecting point is separated from the device D, the modified layer M formed on the wafer W will not be formed. A case where the starting point is appropriately divided. That is, although the influence of light leakage on the device D can be suppressed, it is difficult to modify the layer M as a starting point for dividing the wafer W. [0020] Therefore, as shown in FIG. 2B, the wafer W for inspection is generally used instead of the wafer W, and the influence of light leakage on the device D (see FIG. 2A) is confirmed, and the crystal can be appropriately divided while being set. Processing conditions for circle W. In the inspection wafer WB of the comparative example, a metal foil 53 is laminated on the front surface 55 side of the substrate 51 with a bottom layer 52 interposed therebetween, and thermal deformation (splash) S is likely to occur in the metal foil 53 due to light leakage. The inspection wafer WB is irradiated with laser light from the back surface 56 side, and the device is found by observing the thermal deformation S of the metal foil 53 at a position corresponding to the device D of the wafer W (outside the planned division line L). 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 is thermally deformed even if the light leakage does not affect the device D (see FIG. 2A). That is, even if the light leakage scattered on the wafer W (refer to FIG. 2A) to the outside of the planned division line L is a light leakage with sufficient power reduction, it will not affect the device D. However, such a light leakage with reduced power is also in the metal All the foils 53 were detected. Therefore, it is unknown whether there is light leakage that affects the device D. Therefore, there may be a disadvantage that the processing conditions for which the influence of the light leakage on the device D is excessively set are set. [0022] Therefore, the inspection wafer WA (refer to FIG. 3) of this embodiment can change the thickness of the bottom layer 42 to which the metal foil 43 is attached to the inspection substrate 41, and enable the light leakage of the metal foil 43 to be adjusted. Detection sensitivity. The detection sensitivity of the metal foil 43 is passivated by thickening the bottom layer 42, so that the metal foil 43 detects only the light leakage affected by the device D (see FIG. 2A). Therefore, the inspection wafer WA can be used to change the processing conditions to various types, and the influence of the light leakage on the device D can be detected by detecting the thermal deformation S of the metal foil 43. Optimal processing conditions. [0023] Hereinafter, an inspection wafer according to this embodiment will be described with reference to FIG. 3. FIG. 3 is an exploded perspective view of an inspection wafer according to this embodiment. FIG. 4 is an explanatory diagram of a method for adjusting the thickness of the underlayer in the present embodiment. In addition, although the planned division line is not formed in the inspection wafer, in FIG. 4B and FIG. 4C, the planned division line is indicated by a dotted line for convenience of description. [0024] As shown in FIG. 3, when determining the processing conditions of the laser processing apparatus 1 (see FIG. 1), an inspection wafer WA is used instead of the wafer W. The inspection wafer WA is formed for inspection. When the laser light is focused, the laser light that does not contribute to the formation of the reforming layer affects the device D (see FIG. 2A) of the wafer W and is a light leak. The inspection substrate 41 on the inspection wafer WA is formed by laminating a metal foil 43 with a bottom layer 42 having a predetermined thickness. The metal foil 43 is thermally deformed by being irradiated with light leakage transmitted through the bottom layer 42. The thermal deformation of the metal foil 43 is used to check the light leakage that affects the device D. [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 focused. Although various materials can be selected, it is usually the same as the wafer during actual production. W substrates of the same material and thickness will be selected. For example, when the wafer W (see FIG. 4A) in actual production is a semiconductor wafer, a semiconductor substrate is selected as the inspection substrate 41. When the wafer W in actual production is an optical device wafer, an inorganic material substrate is selected as Inspection substrate 41. The inspection substrate 41 may be, for example, silicon (Si), silicon carbide (SiC), sapphire (Al ₂ O ₃ ), or gallium nitride (GaN). [0026] The bottom layer 42 having a predetermined thickness over the entire surface of the inspection substrate 41 is formed by vapor deposition. Although the bottom layer 42 can be selected from various materials, a material that allows the metal foil 43 to adhere to the inspection substrate 41 satisfactorily is selected. The bottom layer 42 may be made of, for example, titanium (Ti) or chromium (Cr). In addition, the thickness of the bottom layer 42 is formed such that, as described above, when laser processing the wafer W (see FIG. 2A), the metal foil 43 can detect only the thickness of light leakage that affects the device D. The details of the adjustment of the thickness of the bottom layer 42 will be described later. [0027] A metal foil 43 is formed on the surface of the bottom layer 42 instead of the device D (see FIG. 4A) by vapor deposition. Although various materials can be selected for the metal foil 43, the same material or a material close to the melting point as the metal wiring of the device to be processed during actual production is selected. The metal foil 43 may be made of, for example, aluminum (Al), tin (Sn), platinum (Pt), gold (Au), silver (Ag), indium (In), lead (Pb), copper (Cu), or chromium ( Cr). In addition, although the thickness of the metal foil 43 is not particularly limited, the thickness of the metal foil 43 is likely to be caused by thermal deformation of light leakage caused by laser light. [0028] The inspection wafer WA adjusts the thickness of the bottom layer 42 so that the light leakage affects the device D of the wafer W (see FIG. 2A) used in actual production and the metal foil 43 of the inspection wafer WA. Accordingly, when the metal foil 43 is thermally deformed during the inspection using the inspection wafer WA, it can be considered that the device D of the wafer W used in actual production is damaged due to thermal influence. By testing various processing conditions using the wafer WA for inspection, the processing conditions of the device D that are not affected by light leakage can be set. Although the bottom layer 42 and the metal foil 43 are formed by vapor deposition, any method may be used as long as the bottom layer 42 and the metal foil 43 can be formed in a suitable thickness for the inspection wafer WA. [0029] As shown in FIG. 4A, when adjusting the thickness of the bottom layer 42 (see FIG. 4B), first, the actual laser processing is used for the wafer W that is actually produced, and a reference processing condition that does not affect the device D is found. . In addition, it is only necessary to determine the processing conditions that do not affect the device D here. 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, or the like. Calculations etc. theoretically determine the processing conditions. The presence or absence of the influence on the device D can also 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 wafer WA for inspection is picked up by the imaging means 32 (see FIG. 1), and the thermal deformation S is detected in the metal foil 43 that leaks the laser light. Since the reference processing conditions are set so as not to affect the device D (see FIG. 4A), as long as the influence of light leakage on the wafer W and the inspection wafer WA is consistent, the device D corresponding to the wafer W is formed. In the inspection wafer WA, that is, outside the line width of the division line L, the metal foil 43 should not be thermally deformed. [0031] Outside of the line width of the division line L, when the metal foil 43 is thermally deformed, even if light leakage does not affect the device D, it is determined that the metal foil 43 is detected. 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 so that the thermal deformation point S of the metal foil 43 can be within the line width of the division line L. Conversely, on the inner side of the line width of the division line L, when the metal foil 43 is not thermally deformed, the bottom layer 42 is thick and the detection sensitivity is too low. The extent within the width is reduced to form the bottom layer 42. [0032] By performing the laser processing under the reference processing conditions as described above, the thickness of the bottom layer 42 is formed such that the thermal deformation S of the metal foil 43 is within the width of the predetermined division line L, and light leakage can be prevented for the wafer W (see 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, light leakage that affects only the device D is detected as the thermal deformation S of the metal foil 43. Therefore, the light leakage that has no effect on the device D can be ignored, and the thermal deformation S of the metal foil 43 can be contained within the width of the predetermined division line L, and the optimum processing conditions for the wafer W can be found. [0033] Next, a method of using the inspection wafer will be described with reference to FIG. 5. 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 a method of using the inspection wafer, and can be appropriately changed. [0034] As shown in FIG. 5A, a modified layer forming process is first performed. In the modified layer forming process, in the laser processing apparatus 1 (see FIG. 1), the metal foil 43 side of the surface of the inspection wafer WA faces downward, and the inspection wafer WA is held by the dicing tape T. The ring frame F around the stage 21 and the inspection wafer WA is held by the clamp portion 23. In addition, the emission opening of the laser processing means 31 is positioned directly above the inspection wafer WA, and the laser processing means 31 irradiates laser light from the back surface of the inspection wafer WA. The laser light is a wavelength that is transmissive to the inspection substrate 41 and is adjusted to be focused on the inside of the inspection substrate 41. [0035] Then, the laser processing means 31 relatively moves the inspection wafer WA, and the condensing point moves linearly in the plane direction of the inspection wafer WA, thereby forming a linear modification inside the inspection substrate 41. Layer M. At this time, the light leakage of the laser light diffuses from the light-condensing point toward the metal foil 43 of the inspection wafer WA, and the light leakage after passing through the bottom layer 42 causes the metal foil 43 to be thermally deformed. Since the thickness of the bottom layer 42 of the inspection wafer WA is formed on the metal foil 43, only the light leakage that affects the device D (see FIG. 4A) can be detected, so there is no weak light leakage to the extent that it does not affect the device D. A situation in which the metal foil 43 is thermally deformed. [0036] As shown in FIG. 5B, a width measurement process is performed after the modified layer formation process. In the width measurement process, after the dicing tape T (see FIG. 5A) is peeled off from the inspection wafer WA, the metal foil 43 of the inspection wafer WA is directed upward, and the inspection wafer 32 is used to pick up the inspection wafer WA. Metal foil 43. In the imaging means 32, the maximum width d of the metal foil deformation S occurring on the surface of the metal foil 43 is measured based on the photographed image of the metal foil 43. At this time, the thermal deformation of the metal foil 43 is detected by performing various image processings on the photographed image, and measurement is made between two points of the deformation of the metal foil 43 that are most separated from each other in a direction orthogonal to the extending direction of the modified layer M. Distance d. [0037] As shown in FIG. 5C, the adjustment process is performed after the width measurement process. In the adjustment process, the processing conditions of the laser light are adjusted so that the maximum width d of the deformation of the metal foil can be within the width of the division line L. Since the light leakage affects the metal foil 43 of the inspection wafer WA and the device D of the wafer W (see FIG. 4A), the light leakage deviating from the width of the division line L may damage the device D of the wafer W. 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 within the width of the predetermined division line L, thereby setting processing conditions that do not cause damage to the device D of the wafer W. [0038] In the adjustment process, for example, the wavelength of the laser light, the shape of the spot, the average output, the repetition frequency, the pulse width, the numerical aperture (NA) of the condenser lens, the position of the condenser spot, the processing feed rate, etc. At least one of the processing conditions will be adjusted. In this way, the processing conditions are adjusted in the range of the device D that does not damage the wafer W, and the optimum processing conditions for forming a good modified layer M on the wafer W can be found. Although the line width of the planned division line L is used as a data memory in advance, the planned division 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 according to this embodiment, the leakage of laser light can be made to the apparatus D and inspection for the wafer W by the thickness of the bottom layer 42 of the inspection wafer WA. The influence of the metal foil 43 on the wafer WA is the same. Therefore, the light leakage of the laser light which has no influence on the device D is not detected on the metal foil 43, and only the light leakage of the laser light which has an influence on the device D is detected on the metal foil 43. By replacing the wafer W and using the inspection wafer WA, it is possible to find the processing conditions most suitable 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 case where the wafer W to be a product is wasted, and the wafer WA for inspection can be used to find the optimum processing conditions. [0040] In this embodiment, the metal foil is formed on the entire surface of the bottom layer of the inspection wafer, but the configuration is not limited to this. The metal foil is only required to detect the effect of light leakage on the device, and may be partially formed on the bottom layer. [0041] Furthermore, in this embodiment, an oxidation preventing 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 may be used to prevent oxidation of the metal foil. [0042] Furthermore, in this embodiment, a configuration is implemented in which a laser processing device is used to perform a modified layer formation process, a width measurement process, and an adjustment process, but it is not limited to this. The modified layer forming process, the width measuring process, and the adjustment process may be implemented by dedicated devices, respectively. [0043] Although this embodiment and the modification have been described, as another embodiment of the present invention, the above-mentioned embodiment and the modification may be combined in whole or in part. [0044] In addition, the embodiments and modifications of the present invention are not limited to those described above, and various changes, substitutions, and modifications may be made without departing from the scope of the technical idea of the present invention. Moreover, with the advancement of technology or another technology derived, as long as the technical idea of the present invention can be realized by other methods, this method can also be used for implementation. Therefore, the scope of the patent claim is to cover all embodiments included in the scope of the technical idea of the present invention. [0045] In the present embodiment, the configuration in which the present invention is applied to an inspection wafer is described. However, the present embodiment is applicable to a process that can find processing conditions that can be well divided by a modified layer. Processed. [Industrial Applicability] As explained above, the present invention has the effect of finding the processing conditions that can well divide the wafer while suppressing the effect of light leakage on the device during laser processing, particularly The method is useful for an inspection wafer and a method of using the inspection wafer for finding processing conditions of a semiconductor wafer or an optical device wafer.

[0047]

1‧‧‧laser processing device

41‧‧‧Inspection substrate

42‧‧‧ ground floor

43‧‧‧metal foil

D‧‧‧device

F‧‧‧ ring frame

L‧‧‧ divided scheduled line

M‧‧‧Modified layer

T‧‧‧Cutting Tape

W‧‧‧ Wafer

WA‧‧‧ Inspection Wafer

[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 for laser processing of a comparative example. 3 is an exploded perspective view of an inspection wafer according to this embodiment. FIG. 4 is an explanatory diagram of a method for adjusting the thickness of the bottom layer in the present embodiment. 5 is an explanatory diagram of a method of using the inspection wafer according to this embodiment.

Claims (2)

An inspection wafer is used in a laser processing device. The laser processing device is used for inspecting the laser light to collect light, but does not help to form a modified layer. The laser light leaks from the modified layer and affects the device. The substrate constituting the wafer is irradiated with laser light of a transmissive wavelength from the back surface of the wafer on which a plurality of devices are divided by a predetermined division line on the surface, so that it is condensed inside the substrate, along the division line, A modified layer is formed inside the substrate. 特征 It is characterized by: It is composed of an inspection substrate, a bottom layer formed on the entire surface of the inspection substrate with a predetermined thickness, and a metal foil laminated on the bottom layer. The thickness formed on the metal foil can only detect light leakage that affects the device. A method for using an inspection wafer is the method for using an inspection wafer as described in item 1 of the scope of patent application, which is characterized by: (1) a reforming layer forming process, which is performed from the back of the inspection wafer; The inspection substrate is irradiated with laser light of a transmissive wavelength, and the light-condensing point condensed inside the inspection substrate is moved linearly in the plane direction of the inspection wafer to form a linear modified layer; Width measurement A process for taking the metal foil of the inspection wafer after the reforming layer forming process and measuring the maximum width of the metal foil deformation that appears on the surface of the metal foil; and an adjustment process for making the metal foil at the width The laser beam is adjusted so that the maximum width of the metal foil deformation measured by the measurement process is within the width of the division line.