CN110270769B - non-destructive testing method - Google Patents

Abstract

To provide a non-destructive inspection method capable of efficiently confirming the depth position and length of a modified layer formed on a workpiece by laser processing, and setting appropriate laser processing conditions promptly. The interior of the workpiece is intermittently photographed at predetermined intervals (H) in the Z-axis direction perpendicular to the X-axis and Y-axis planes, and multiple X-axis and Y-axis plane images are obtained. image (101), calculate the clear three-dimensional clear image after removing the blur by deconvolution, cut the three-dimensional clear image parallel to the Z axis, and analyze the modified layer according to the two-dimensional image of the cross-section of the modified layer The Z-axis coordinate value and the length of the modified layer are detected. The laser processing and the state detection of the modified layer can be repeated rapidly, and the most suitable laser processing conditions for the formation of the modified layer can be found as soon as possible.

Description

non-destructive testing method

technical field

The present invention relates to a method of detecting the state of a modified layer formed inside a workpiece by laser processing.

Background technique

There is a method of irradiating laser light having a wavelength that is transparent to the wafer from the back surface of a wafer in which devices are formed in a region divided by the planned dividing line on the front surface, and converging the laser light on the wafer along the planned dividing line. Internally, a modified layer is formed at the converging point, and an external force is applied to the modified layer to split the wafer starting from the modified layer (for example, refer to Patent Document 1).

In this dividing method, the depth position and length of the modified layer in the thickness direction of the wafer are related to the ease of dividing the wafer. Therefore, by knowing the depth position and length of the modified layer, it is possible to determine whether a modified layer suitable for division is formed.

Therefore, a method has also been proposed in which the edge of the wafer is cut in advance to form a modified layer inside the wafer, and then the cut surface of the wafer is photographed to observe the state of the modified layer (for example, refer to Patent Document 2). .

Patent Document 1: Japanese Patent No. 3408805

Patent Document 2: Japanese Patent Laid-Open No. 2017-166961

However, in order to determine whether the depth position and length of the modified layer are most suitable for the division of the workpiece, it is necessary to alternately repeat the formation of the modified layer and the observation of the formed modified layer. In this method, it is necessary to cut the wafer to observe the modified layer, and thus there is a problem that it takes time to set the optimum laser processing conditions.

Contents of the invention

The present invention was made in view of the above problems, and its object is to efficiently confirm the depth position and length of the modified layer formed on the workpiece by laser processing, and to quickly set appropriate laser processing conditions. .

The present invention is a non-destructive detection method, which detects the modified layer in a non-destructive manner, and the modified layer is obtained by positioning the laser beam with a wavelength that is transparent to the processed object at the inside of the processed object and Formed by irradiating laser light, the workpiece has a first surface and a second surface opposite to the first surface, wherein the non-destructive inspection method has the following steps: a preparation step, preparing the following inspection device: the The inspection device has a photographing unit, a light source, a drive unit, and a storage unit, wherein the photographing unit has an objective lens and photographs the inside of the workpiece from the first surface side, and the light source illuminates the object from the first surface side. With light in a transparent wavelength band, the driving unit makes the objective lens approach or move away from the first surface, and the storage unit stores the image captured by the shooting unit; When the parallel surface is set as the X-axis Y-axis plane, the objective lens is intermittently approached to the first surface at a predetermined interval H in the Z-axis direction perpendicular to the X-axis Y-axis plane. The refractive index locates the focal point at the Z-axis coordinate position in the processed object, and acquires multiple X-axis Y-axis plane images inside the processed object according to each Z-axis coordinate value and stores them in the storage unit; the storage process is for Based on the three-dimensional image generated by the plurality of X-axis and Y-axis plane images for each Z-axis coordinate value stored in the acquisition process, a clear three-dimensional clear image after deconvolution and deblurring is calculated and stored in the a storage unit; and a detection step of cutting the three-dimensional clear image stored in the storage step parallel to the Z axis, and detecting the Z-axis coordinate value of the modified layer and the Z-axis coordinate value of the modified layer from the two-dimensional image of the cross section of the modified layer. length.

Preferably, the deconvolution is: dividing the Fourier transform of the three-dimensional image generated according to the X-axis and Y-axis plane images of each Z-axis coordinate value stored in the acquisition process by the Fourier transform of the three-dimensional point spread function Leaf transform, followed by inverse Fourier transform to calculate a clear three-dimensional clear image, wherein the three-dimensional point spread function represents the blur effect caused by the optical system of the focal point of the shooting unit positioned in the modified layer.

Preferably said three-dimensional point spread function is a formulation of the Gibson-Lanni model.

Preferably, the clear three-dimensional clear image stored in the storing step is obtained by: including clear multiple X In the three-dimensional clear image of the Y-axis clear plane image, the linear interpolation method is used to calculate the relative The pixel value of the object pixel between the two X-axis Y-axis clear plane images is interpolated to interpolate the pixel values of the plurality of pixels between the separated X-axis Y-axis clear plane images.

In the present invention, the three-dimensional clear image is obtained in the storage process, and the three-dimensional clear image is cut parallel to the Z axis in the detection process, and the Z-axis coordinate value of the modified layer and the modified The length of the modified layer is detected, so the position and length of the modified layer can be grasped without destroying the workpiece. Therefore, the laser processing and the state detection of the modified layer can be repeatedly performed rapidly, and the most suitable laser processing conditions for forming the modified layer can be quickly found.

Description of drawings

FIG. 1 is a perspective view showing the configuration of an example of an inspection device.

2 is a cross-sectional view showing a state where a modified layer is formed inside a workpiece.

Fig. 3 is a cross-sectional view illustrating an image acquisition process.

FIG. 4 is an explanatory diagram showing the correlation between the refractive index of the workpiece and the focal point of the objective lens.

FIG. 5 is an explanatory diagram illustrating a state in which the objective lens is intermittently moved at a predetermined interval H in the acquisition step.

FIG. 6 is an image diagram showing a plurality of X-axis Y-axis plane images acquired in the acquisition process.

FIG. 7 is an image diagram showing an example of an observed three-dimensional image.

FIG. 8 is a perspective view showing an example of obtaining pixel values by linear interpolation.

9 is an image diagram showing an example of a Z-axis X-axis clear planar image obtained by cutting a three-dimensional image parallel to the Z-axis.

(a) to (c) of FIG. 10 are image diagrams showing examples of X-axis Y-axis clear planar images obtained by cutting a three-dimensional image parallel to the XY plane.

Label description

W: workpiece; Wa: first side; S: planned dividing line; D: device; Wb: second side; M: modified layer; C: crack; T: belt; F: frame; 1: inspection Device; 2a, 2b, 2c, 2d, 2e, 2f, 2g: X-axis and Y-axis plane images; 10: device base; 11: column; 12: holding table; 12a: holding surface; 13: cover table; 130: opening part; 14; rotation unit; 15: frame holding unit; 20: moving unit in X-axis direction; 21: ball screw; 22: motor; 23: guide rail; 24: bearing part; 25: moving base; 30 : Y-axis moving unit; 31: ball screw; 32: motor; 33: guide rail; 34: bearing; 35: moving base; 40: laser processing unit; 41: laser processing head; 42: condenser lens; 43: laser light; 50: shooting unit; 51: camera; 52: objective lens; 53: half mirror; 60: light source; 61: infrared; 70: drive unit; 80: storage unit; 90: control unit; 91: image Processing unit; 100: monitor; 101: three-dimensional image; 102: three-dimensional point spread function; 400: ZX clear plane image; 501a, 501b, 501c: XY clear plane image.

detailed description

The workpiece W shown in FIG. 1 has, for example, a circular plate-shaped substrate, and is formed on its front surface (the first surface Wa in the illustrated example) in areas divided by a plurality of grid-like dividing lines S. There are multiple devices D. The dividing line S extends along the X-axis direction and the Y-axis direction.

The tape T is pasted on the second surface Wb on the opposite side to the first surface Wa. The workpiece W is integrated with the ring-shaped frame F via the belt T. As shown in FIG. Hereinafter, a non-destructive inspection method for non-destructively inspecting a modified layer that passes through a laser beam having a wavelength that is transparent to the workpiece W will be described with reference to the accompanying drawings. It is formed by converging and irradiating the inside of the workpiece W having the first surface Wa and the second surface Wb on the opposite side.

(1) Preparation process

As shown in FIG. 1 , for example, an inspection device 1 capable of forming a modified layer inside a workpiece W and capable of imaging the inside of the workpiece W is prepared. The inspection device 1 has a device base 10 , and a column 11 with a substantially L-shaped cross section is erected on the upper surface of the device base 10 on the rear side in the Y-axis direction. The device base 10 has: a holding table 12, which holds the workpiece W integrated with the frame F; a frame holding unit 15, which is arranged around the holding table 12, and holds the frame F; An X-axis direction moving unit 20 moves the holding table 12 in the X-axis direction; and a Y-axis direction moving unit 30 moves the holding table 12 in the Y-axis direction. The front end of the column 11 extends to the upper side of the path in the moving direction (X-axis direction) of the holding table 12 .

The upper surface of the holding table 12 serves as a holding surface 12a for holding the workpiece W. As shown in FIG. The holding table 12 is fixed to the cover table 13 having the opening 130 , and the rotation unit 14 is connected to the lower part of the holding table 12 . The rotation unit 14 can rotate the holding table 12 by a predetermined angle.

The X-axis direction moving unit 20 has: a ball screw 21 extending in the X-axis direction; a motor 22 connected to one end of the ball screw 21; a pair of guide rails 23 extending parallel to the ball screw 21; The other end of which is rotatably supported by a bearing part 24 ; One surface of the moving base 25 is in sliding contact with the pair of guide rails 23 , and the ball screw 21 is screwed into a nut formed at the center of the moving base 25 . When the motor 22 rotates the ball screw 21 , the moving base 25 can be moved in the X-axis direction along the guide rail 23 , thereby moving the holding table 12 in the X-axis direction.

The Y-axis direction moving unit 30 has: a ball screw 31 extending in the Y-axis direction; a motor 32 connected to one end of the ball screw 31; a pair of guide rails 33 extending parallel to the ball screw 31; The other end of 31 is rotatably supported by a bearing portion 34 ; and a moving base 35 that supports the holding table 12 . One surface of the moving base 35 is in sliding contact with the pair of guide rails 33 , and the ball screw 31 is screwed into a nut formed at the center of the moving base 35 . When the motor 32 rotates the ball screw 31 , the moving base 35 can be moved in the Y-axis direction along the guide rail 33 to adjust the position of the holding table 12 in the Y-axis direction.

The inspection device 1 has a laser processing unit 40 that performs laser processing on the first surface Wa of the workpiece W held by the holding table 12 . The laser processing unit 40 has a laser processing head 41 disposed below the front end of the column 11 and irradiates laser light 43 of a wavelength transparent to the workpiece W shown in FIG. 2 downward. An oscillator that oscillates the laser beam 43 and an output adjuster that adjusts the output of the laser beam 43 are connected to the laser processing head 41 . As shown in FIG. 2 , a condenser lens 42 for converging laser beams 43 oscillated from an oscillator is incorporated in the laser processing head 41 . The laser machining head 41 can move in the vertical direction, and can adjust the focusing position of the laser beam 43 .

Here, an example in which a modified layer is formed inside the workpiece W by the laser processing unit 40 will be described. In the present embodiment, for example, the following laser processing conditions are set and implemented. In addition, the workpiece W is, for example, a silicon wafer.

[Laser processing conditions]

As shown in FIG. 2 , after the workpiece W is sucked and held by the holding surface 12 a of the holding table 12 with the tape T side facing down, the holding table 12 is moved below the laser processing unit 40 . Next, the holding table 12 is processed at the above-mentioned processing feed rate (500 mm/s), for example, in the X-axis direction, and the laser beam having a wavelength that is transparent to the workpiece W is collected by the condenser lens 42. The converging point of 43 is positioned inside the workpiece W. In this state, the laser light 43 is irradiated from the first surface Wa side of the workpiece W along the planned dividing line S shown in FIG. A modified layer M with reduced strength is formed inside W.

In order to inspect the modified layer M formed inside the workpiece W in a non-destructive manner, as shown in FIG. 3 , the inspection device 1 shown in FIG. The first surface Wa of the object W is photographed; the light source 60 irradiates light in a wavelength band that is transparent to the workpiece W from the side of the first surface Wa; approach and distance. In addition, as shown in FIG. 1 , the inspection device 1 has: a storage unit 80 that stores images captured by the imaging unit 50; a control unit 90 that can perform image processing based on the images stored in the storage unit 80; 100, which displays various data (images, processing conditions, etc.).

The imaging unit 50 is disposed close to the laser processing unit 40 on the lower side of the front end of the column 11 . As shown in FIG. 3 , the photographing unit 50 has: a camera 51, which photographs the workpiece W from above; an objective lens 52, which is arranged at the bottom of the camera 51; and a half mirror 53, which is arranged between the camera 51 and the objective lens. 52, the light emitted from the light source 60 is reflected downward. The camera 51 is an infrared camera incorporating an imaging element such as a CCD image sensor or a CMOS image sensor. The light source 60 is constituted by, for example, an infrared LED, and can emit infrared rays 61 in a wavelength band transparent to the workpiece W. FIG. In the imaging unit 50, the reflected light of the infrared rays 61 emitted from the light source 60 and reflected inside the workpiece W is captured by the imaging element, so that the X-axis coordinates and the Y-axis coordinates of the workpiece W can be obtained. X-axis Y-axis plane image. The X-axis and Y-axis plane images captured by the photographing unit 50 are stored in the storage unit 80 .

A drive unit 70 is connected to the objective lens 52 . The drive unit 70 is an actuator capable of vertically moving the objective lens 52 in the Z-axis direction. The driving unit 70 is, for example, a piezoelectric motor composed of a piezoelectric element that expands and contracts in the vertical direction with respect to the workpiece W held by the holding table 12 by applying a voltage. In the drive unit 70 , by adjusting the voltage applied to the piezoelectric element, the objective lens 52 can be moved in the vertical direction, thereby finely adjusting the position of the objective lens 52 . Therefore, the position of the objective lens 52 can be moved for each desired Z-axis coordinate value by the driving unit 70, and the X-axis Y inside the workpiece W can be photographed by the imaging unit 50 for each Z-axis coordinate value. axis plane image. In addition, the drive unit 70 is not limited to a piezoelectric motor, and may be constituted by a voice coil motor capable of linear movement, for example.

The control unit 90 has at least: a CPU that performs arithmetic processing according to a control program; a ROM that stores the control program, etc.; a readable and writable RAM that stores arithmetic processing results, etc.; and an input interface and an output interface. The control unit 90 controls the rotation unit 14 , the X-axis direction movement unit 20 , the Y-axis direction movement unit 30 , and the drive unit 70 . In addition, the control unit 90 has an image processing unit 91 that processes the image formed by the imaging unit 50 and the image stored in the storage unit 80 .

In addition, in the image processing unit 91, a three-dimensional image may be generated from a plurality of captured two-dimensional images, or a cross-sectional image of a modified layer formed inside the workpiece W may be obtained from the generated three-dimensional image. (An image cut in a direction parallel to the Z-axis direction) is cut out and formed. By displaying the two-dimensional planar image and the three-dimensional image acquired in this way on the monitor 100, the state of the modified layer can be observed.

(2) Acquisition process

After preparing the inspection device 1 and forming the modified layer M inside the workpiece W, as shown in FIG. The state of the inside of the workpiece W is photographed on the first surface Wa side of the workpiece W. FIG. In the image acquisition step described in this embodiment, a plurality of X-axis Y-axis plane images parallel to the first surface Wa of the workpiece W are captured. In this embodiment, a case where an image acquisition step is performed immediately after forming the modified layer M along a row of planned dividing lines S facing the X-axis direction will be described.

Here, when the infrared rays 61 emitted from the light source 60 shown in FIG. The angle of refraction changes. That is, the refractive index (N) differs depending on the type of material of the workpiece W. FIG. FIG. 4 shows the correlation between the refractive index (N) of the workpiece W and the focal point at which the infrared rays 61 are converged by the objective lens 52 . For convenience of description, the angle α with respect to the optical axis O shown in the illustrated example represents the case where the infrared rays 61 passing through the objective lens 52 are incident linearly without being refracted on the first surface Wa of the workpiece W. In this case, the distance from the first surface Wa to the focal point P is set to the distance h1.

Generally, when the infrared rays 61 passing through the objective lens 52 enter the inside from the first surface Wa of the workpiece W, they are refracted at, for example, an angle β from the angle α when the infrared rays 61 are not refracted, and converged to the focal point P'. The angle β with respect to the optical axis O corresponds to the refraction angle, and the refractive index (N) of the workpiece W in this case can be calculated based on the following formula (1) according to Snell's law.

N=sinα/sinβ formula (1)

In addition, the distance h2 from the first surface Wa of the workpiece W to the focal point P' can be calculated by substituting the refractive index (N) calculated by the above formula (1) into the following formula (2).

h2＝N×cosβ/cosα×h1 Formula (2)

The distance h2 is longer than the distance h1, and it can be confirmed that the focal point is far from the objective lens.

When imaging the inside of the workpiece W, the drive unit 70 intermittently moves the objective lens 52 at a predetermined interval H in the Z-axis direction perpendicular to the X-axis and Y-axis planes. To move the objective lens 52 intermittently means to move the position of the objective lens 52 by the movement amount V in the Z-axis direction with a fixed interval. That is, interval H=movement amount V. The predetermined interval HR shown in the example of FIG. 5 can be changed according to the refractive index (N) of the workpiece W to be inspected and the movement amount (V) of the objective lens 52 in the Z-axis direction, and can be obtained by using the above formula ( 1) Calculated by multiplying the calculated refractive index (N) by the movement amount (V) (HR=N×V).

When the workpiece W described in this embodiment is, for example, a silicon wafer, its refractive index (N) is 3.6. When the movement amount (V) of the drive unit 70 is set to 1 μm, for example, the predetermined interval HR can be calculated as 3.6 μm by multiplying the movement amount (1 μm) by the refractive index (3.6) of the workpiece W. That is, the distance HR between the focal points extending inside the workpiece W (the distance between the Z-axis coordinate value z1 and the Z-axis coordinate value z2 ) is at least 3.6.

The drive unit 70 lowers the objective lens 52 toward the first surface Wa of the workpiece W to position the focal point P1 at the Z-axis coordinate value z1. When the inside of the workpiece W is photographed by the camera 51 shown in FIG. 3 , for example, an X-axis and Y-axis plane image 2 a shown in FIG. 6 can be acquired. Next, the driving unit 70 intermittently moves the objective lens 52 toward the first surface Wa side according to the setting of the above-mentioned predetermined interval H (1 μm), and positions the focal point P2 so that the focal point P1 extends at intervals according to the above-mentioned refractive index (N). The final Z-axis coordinate value z2. When the inside of the workpiece W is photographed by the camera 51, for example, an X-axis and Y-axis plane image 2b can be acquired. In this way, the drive unit 70 intermittently moves the position of the objective lens 52 at a predetermined interval H, and the camera 51 photographs the inside of the workpiece W according to the Z-axis coordinate values z1, z2 . Images 2a, 2b, 2c, 2d, 2e, 2f and 2g. And, the acquired X-axis and Y-axis plane images 2 a to 2 g are stored in the storage unit 80 shown in FIG. 1 .

(3) Storage process

In this process, the X-axis and Y-axis plane images 2 a - 2 g of each Z-axis coordinate value acquired in the acquisition process are first superimposed to obtain a three-dimensional image 101 as shown in FIG. 7 . The three-dimensional image 101 formed in this way is formed based on the actually observed X-axis and Y-axis plane images, so there is blurring. Hereinafter, this image is referred to as a three-dimensional observation image.

In the acquisition step, the modified layer M shown in FIG. 3 is observed while shifting the focus of the imaging unit 50 , so the modified layer M can be considered as a collection of many point light sources. Moreover, since there is blur in the three-dimensional observation image, it is necessary to remove the blur through deconvolution to calculate a three-dimensional clear image. As shown in FIG. 7 , this blurring can be represented by a point spread function PSF(x, y, z) representing three-dimensional diffusion of light from a point light source. PSF(x, y, z) is obtained by estimating how one point light source is seen, and by removing the blur from the three-dimensional observation image, a three-dimensional clear image can be obtained. The obtained three-dimensional clear image is stored in the storage unit 80 . In this step, a three-dimensional sharp image is obtained by the method shown below. As this method, there are, for example, the progressive method and the inverse filtering method.

(A) Progressive method

In the asymptotic method, the estimated value O _k (x, y, z) of the luminance distribution of the three-dimensional sharp image is asymptotically approximated to the actual luminance distribution O(x, y, z) as in Equation (3).

O _k (x, y, z)×OTF(x, y, z)-I(x, y, z)-→0·····Formula (3)

Here, OTF(x, y, z) is an optical transfer function obtained by Fourier transforming a point spread function PSF(x, y, z).

According to the following formula (4), the estimated value O _k+1 (x, y, z) is updated so as to be asymptotic to the real luminance distribution O _k (x, y, z).

O _k+1 (x,y,z)=O _k (x,y,z)-γ{O _k (x,y,z)×OTF(x,y,z)-I(x,y,z )}·····Formula (4)

In formula (4), the difference between the value of O _k (x, y, z)×OTF(x, y, z) and the Fourier transform I(x, y, z) of the three-dimensional observation image is obtained first. This difference is a fuzzy component contained in the estimated value _Ok (x, y, z). This difference is subtracted from O _k (x, y, z) to obtain the next estimated value O _k+1 (x, y, z). The obtained _Ok+1 (x, y, z) is substituted into _Ok (x, y, z) in formula (4), and the next _Ok+1 (x, y, z) is obtained. Such calculations are repeated until the above-mentioned difference becomes 0, that is, until the blur component becomes 0. In addition, in the first calculation based on the formula (4), I(x, y, z) is substituted into the estimated value _Ok (x, y, z). The calculation of formula (4) is repeated, and when the fuzzy component is 0, _Ok+1 (x, y, z) is a three-dimensional clear image.

When the calculation of the above formula (4) is repeated, by using the maximum likelihood method to reduce the number of calculations of the formula (4), a clear three-dimensional clear image can be obtained even in the case of a lot of noise in the three-dimensional observation image.

In addition, a three-dimensional sharp image can also be obtained by a blind deconvolution method using a maximum likelihood method for estimation of OTF (x, y, z). In the blind deconvolution method, OTF(x, y, z) is also updated every time the calculation is repeated.

(B) Inverse filtering method

In the inverse filtering method, first, the Fourier transform O(x, y, z) of the luminance distribution of the three-dimensional observation image is obtained by the following equation (5).

Here, I(x, y, z) is the Fourier transform of the three-dimensional observation image, OTF (x, y, z) is obtained by performing Fourier transform on the point spread function PSF (x, y, z), In the above formula (5), the Fourier transform of the three-dimensional observation image is divided by the Fourier transform of the point spread function. In addition, inverse Fourier transform is performed on the obtained O(x, y, z) to obtain the luminance distribution o(x, y, z) of the three-dimensional clear image.

In addition, in the Wienner (Wiener) method, as shown in the following formula (6), a constant w is added to the denominator of the above formula (5), and a constant w is added to a frequency band where the S/N ratio is relatively high. Reconstruction of signal components after larger weights. The constant w added to the denominator functions as a low-pass filter that removes high-frequency components.

In addition, the point spread function PSF (x, y, z) in the above-mentioned asymptotic method and inverse filtering method can be obtained by the following formula (7) according to the Gibson-Lanni (Gibson-Lanni) model.

Here, variables and constants in Equation (7) are as follows.

k0: wave number (=2π/wavelength)

Λ: Optical path difference

x, y: the x-coordinate and y-coordinate of the observation position

x0, y0: the x-coordinate and y-coordinate of the position of the point light source

NA: Numerical aperture of the objective lens

ρ: The distance from the center of the objective lens when the center of the objective lens is ρ=0 and the outermost circumference of the objective lens is ρ=1

In addition, the optical path difference Λ can be calculated using the following formula (8).

Here, variables and constants in Equation (8) are as follows.

z: the Z coordinate of the observation position

z0: The z coordinate of the position of the point light source

ns: Refractive index of the workpiece

NA: Numerical aperture of the objective lens

ρ: The distance from the center of the objective lens when the center of the objective lens is ρ=0 and the outermost circumference of the objective lens is ρ=1

In addition, in the formula (8), the following formula (9) is the optical path difference when there is a workpiece and when there is no workpiece.

In addition, the following equation (10) is a defocus component derived from a point light source.

(4) Detection process

Next, the three-dimensional clear image stored in the storage unit 80 is cut parallel to the Z axis to obtain a plurality of two-dimensional clear images. For example, the Z-axis X-axis clear plane image 400 shown in FIG. 9 is one example. Here, it is considered that the three-dimensional PSF 102 expands in diameter toward the first surface Wa and the second surface Wb around the converging point P0.

In the Z-axis X-axis clear planar image 400 shown in FIG. 9, the two scales on the vertical axis are the interval H×refractive index shown in FIG. Length L. In addition, the Z coordinates of the upper end and the lower end of the modified layer M can also be obtained (first detection step).

On the other hand, as shown in (a) to (c) of FIG. 10, the three-dimensional clear image stored in the storage unit 80 can also be cut perpendicular to the Z axis (that is, parallel to the X axis and Y axis plane) to obtain A plurality of X-axis Y-axis clear plane images 501a, 501b, 501c.

However, the X-axis Y-axis clear planar images facing each other in the Z-axis direction are spaced apart by an interval HR. Therefore, it is necessary to use an interpolation method (linear interpolation) to obtain the pixel value of the target pixel between the opposing X-axis and Y-axis clear planar images.

For example, as shown in FIG. 8 , when it is desired to obtain the pixel value of the pixel 300 between the X-axis and Y-axis plane image 2 a and the X-axis and Y-axis plane image 2 b, the value in the X-axis and Y-axis plane image 2 a is obtained. The pixel value of the pixel 201a directly above the pixel 300 and the pixel value of the pixel 201b directly below the pixel 300 in the X-axis and Y-axis plane image 2b. In addition, the distance Z11 in the Z-axis direction from the pixel 300 to the pixel 201 a and the distance Z12 in the Z-axis direction from the pixel 300 to the pixel 201 b are respectively obtained. Then, a weight corresponding to each distance is performed, and the weighted average of the pixel value of the pixel 201 a and the pixel value of the pixel 201 b is obtained using the weight, and the value of the weighted average is used as the pixel value of the pixel 300 . Similarly, for example, the pixel value of the pixel 202a directly above the pixel 301 in the X-axis and Y-axis plane image 2a and the pixel value of the pixel 202b directly below the pixel 301 in the X-axis and Y-axis plane image 2b are obtained, and respectively Calculate the distance Z21 from the pixel 301 to the pixel 202a in the Z-axis direction and the distance Z22 from the pixel 301 to the pixel 202b in the Z-axis direction, perform weighting corresponding to each distance, and use the weights to obtain the pixel value of the pixel 202a and The weighted average of the pixel values of the pixel 202 b is used as the pixel value of the pixel 301 . In this way, the pixel value of each pixel constituting the XY plane image 2ab located between the X-axis and Y-axis plane image 2a and the X-axis and Y-axis plane image 2b is obtained. Then, the pixel values of all pixels that may exist between adjacent X-axis and Y-axis plane images are calculated to determine the pixel values of all pixels in the three-dimensional space to form a three-dimensional image (pixel value calculation step). In addition, in the pixel value calculation step, interpolation methods such as bilinear interpolation, nearest neighbor method, and bicubic method can be used. The X-axis Y-axis clear planar image 501a shown in (a) of FIG. 10 is an enlarged image of a part of the cross-sectional image farther from the modified layer M to the first surface Wa side in the three-dimensional clear image after linear interpolation. , it can be understood from the image that the first crack C1 continuous in the X-axis direction is formed above the modified layer M.

The X-axis Y-axis clear planar image 501b shown in (b) of FIG. state. In addition, it can also be ascertained that a crack C extending in the X-axis direction is formed between adjacent modified layers M, and that the modified layers M are connected via the crack C (second detection step).

The X-axis Y-axis clear plane image 501c shown in (c) of FIG. 10 is an enlarged image of a part of the cross-sectional image closer to the second surface Wb than the converging point P0. The second crack C2 continuous in the X-axis direction is formed below the layer M. By detecting in this way that the first crack C1 shown in (a) of FIG. 10 and the second crack C2 shown in (c) of FIG. The crack C shown in FIG. 10 (b) connecting the layers M extends along the X-axis direction, and it can be seen that the processing conditions at this time are processing conditions that can reliably divide the workpiece by applying an external force later (the second detection process).

In this way, by acquiring a three-dimensional clear image, cross-sectional images obtained by cutting out the image from various directions can be formed, so the positions and states of the modified layer M and the cracks C can be confirmed from various angles. In addition, the X-axis Y-axis cross-sectional image 501 ab shown in FIG. 9 is an image obtained by linear interpolation, and can also be confirmed in this cross-sectional image.

In addition, the XY clear planar images 501a, 501b, and 501c acquired in this way are cross-sectional images of three-dimensional clear images after the blurring has been removed in the storage process, and therefore are clearer than the X-axis Y-axis planar images 2a-2g acquired in the acquisition process. clear. Therefore, the positions and states of the modified layer M and the cracks C can be grasped more reliably. Since there is a correlation between the depth position and length of the modified layer M in the thickness direction of the workpiece and the ease of division of the workpiece, by grasping the depth position and length of the modified layer M, it is possible to judge whether the modified layer M is It is formed so that the workpiece can be easily divided. In addition, since the depth position and length of the modified layer formed on the workpiece by laser processing can be checked efficiently, appropriate laser processing conditions can be quickly set.

Even if the pixel values of the pixels between the X-axis and Y-axis plane images are obtained by interpolation immediately after the three-dimensional observation images are formed from the X-axis and Y-axis plane images 2a to 2g, blurring is included in the three-dimensional observation images. It is also difficult to obtain the appropriate pixel value, but after removing the blur of the three-dimensional observation image by deconvolution, the pixel value of the pixel between the X-axis and Y-axis plane images is obtained by interpolation, so that a clear image can be finally obtained. three-dimensional clear images. In addition, linear interpolation is performed by dividing adjacent X-axis and Y-axis plane images 100 times, for example.

In the above manner, various images are obtained to grasp the position and length of the modified layer and the connection of cracks. For example, when the cracks are not connected in the X-axis direction, it is considered that it cannot be properly divided even if an external force is applied. Therefore, the modified layer was formed again by changing the processing conditions, and each image was acquired again to perform the same analysis. When judging whether the processing conditions are appropriate or not, it is not necessary to cut the workpiece, so adjustment of the processing conditions and confirmation of the states of the modified layer and cracks can be quickly repeated.

In addition, the inspection device 1 shown in this embodiment has a structure that functions as a laser processing device that forms the modified layer M inside the workpiece W, but the inspection device 1 is not limited to the device configuration shown in this embodiment. , can also be a separate device structure independent from the laser processing device.

Claims (4)

1. A non-destructive detection method, which detects the modified layer in a non-destructive manner, and the modified layer is positioned on the surface of the processed object by the focus point of the laser light having a wavelength that is transparent to the processed object The inside is formed by irradiating laser light along the X-axis direction to be separately arranged in the X-axis direction, and the workpiece has a first surface and a second surface on the opposite side of the first surface, wherein the The non-destructive testing method has the following steps: In the preparatory process, the following inspection device is prepared: the inspection device has an imaging unit, a light source, a driving unit, and a storage unit, wherein the imaging unit has an objective lens and photographs the inside of the workpiece from the first surface side, and the light source is from The first surface is irradiated with light of a wavelength band that is transparent to the processed object, the driving unit makes the objective lens approach or move away from the first surface, and the storage unit stores the image captured by the shooting unit; In the obtaining step, when the surface parallel to the first surface is defined as the X-axis Y-axis plane, the objective lens is intermittently separated by a predetermined interval (H) in the Z-axis direction perpendicular to the X-axis Y-axis plane. And close to the first surface, the focal point is positioned in the Z-axis direction according to the Z-axis movement of the objective lens multiplied by the refractive index of the workpiece to be processed at intervals to form the modified object. The Z-axis coordinate position of the modified layer, and according to each Z-axis coordinate value, a plurality of X-axis Y-axis plane images containing the modified layer inside the processed object are obtained and stored in the storage unit; a storing step of calculating a clear three-dimensional clear image from which blurring has been removed by deconvolution with respect to the three-dimensional image generated from the plurality of X-axis and Y-axis plane images for each Z-axis coordinate value stored in the acquiring step and stored in the storage unit; and a detection step of obtaining the Z-axis coordinate value and the Z-axis direction of the modified layer from the two-dimensional image of the cross-section of the modified layer obtained by cutting the three-dimensional sharp image stored in the storing step parallel to the Z axis; The length of the modified layer is determined, and cracks extending from the modified layer in the X-axis direction are detected from a two-dimensional image of a cross section obtained by cutting the three-dimensional clear image perpendicular to the Z axis. 2. The non-destructive testing method according to claim 1, wherein, The deconvolution is: dividing the Fourier transform of the three-dimensional image generated according to the X-axis and Y-axis plane images of each Z-axis coordinate value stored in the acquisition process by the Fourier transform of the three-dimensional point spread function transformation, followed by inverse Fourier transformation to calculate a clear three-dimensional clear image, wherein the three-dimensional point spread function represents the blur effect caused by the optical system of the focal point of the shooting unit positioned in the modified layer. 3. The non-destructive testing method according to claim 2, wherein, The three-dimensional point spread function is a formula of the Gibson-Lanni model. 4. The non-destructive testing method according to claim 1, wherein, The clear three-dimensional clear image stored in the storage process is obtained as follows: In the three-dimensional clear image including a plurality of clear X-axis Y-axis clear planar images for each of the Z-axis coordinate values after the blurring has just been removed by the deconvolution, according to The pixel value and the distance of the pixels of the two adjacent X-axis Y-axis clear plane images, using linear interpolation to calculate the pixel value of the object pixel between the two opposite X-axis Y-axis clear plane images, thereby Interpolate the pixel values of multiple pixels between the separated x-axis y-axis sharp plane images.

Images