JP2022117055A - Device and method for detecting cracks - Google Patents

Abstract

To provide a device and a method for detecting cracks which can suppress an influence of unevenness in reflection rates that is generated by a surface property of a workpiece and accurately detect a position of a crack formed inside the workpiece.SOLUTION: A device for detecting cracks comprises: a light source part for emitting detection light along a main optical axis; an objective lens that has a lens optical axis coaxial to the main optical axis and condenses the detection light emitted from the light source part to an inside of a workpiece by making the detection light incident from an upper surface side of the workpiece; prior measurement means that detects reflected light from an undersurface of the workpiece by obliquely illuminating the workpiece before a crack is formed inside the workpiece and obtains a prior measurement value of the reflected light; main measurement means that detects reflected light from the workpiece by obliquely illuminating the workpiece after the crack is formed inside the workpiece and obtains a main measurement value of the reflected light; and crack detection means that corrects the main measurement value using the prior measurement value and detects depth of the crack formed inside the workpiece.SELECTED DRAWING: Figure 1

Description

The present invention relates to a crack detection device and method, and more particularly to a crack detection device and method for non-destructively detecting the crack depth of a crack formed inside a workpiece.

Conventionally, a laser beam is irradiated along a planned division line with a focal point aligned inside a workpiece such as a semiconductor wafer, and a laser processing area that serves as a starting point for cutting is formed inside the workpiece along the planned division line. A laser processing apparatus (also referred to as a laser dicing apparatus) for forming is known. The workpiece on which the laser-processed region is formed is then split along splitting lines by a splitting process such as expanding or breaking into individual chips (see, for example, Patent Document 1).

By the way, when a laser processing area is formed in a workpiece by a laser processing apparatus, a crack extends from the laser processing area in the thickness direction of the workpiece. A crack formed inside the workpiece serves as a starting point for cutting the workpiece, and therefore the degree of extension of the crack affects the quality of chips after cutting the workpiece.

For this reason, after forming a laser processing region with a laser processing device and before the cutting process, by detecting the crack depth of the crack formed inside the workpiece, the quality of the division into chips in the cutting process can be determined. can be predicted.

In Patent Document 1, the depth of a crack formed inside the workpiece is detected by illuminating the workpiece with polarized detection light and receiving the reflected light from the workpiece. A crack detection device is disclosed.

JP 2017-133997 A

The crack detection device described in Patent Literature 1 irradiates a workpiece with detection light and detects reflected light reflected from the front and back surfaces of the workpiece. More specifically, the crack detection device described in Patent Document 1 irradiates the back surface (upper surface) of the workpiece with detection light, and the reflected light reflected from the front surface (lower surface) of the workpiece is detected by the crack. The depth of the crack is detected by utilizing the fact that the reflected light is blocked and the amount of reflected light is reduced.

By the way, depending on the properties of the surface of the workpiece, unevenness in reflectance may occur when the detection light for crack detection is applied and the reflected light is detected. For example, when the object to be processed is a semiconductor wafer, since devices are formed on the surface of the semiconductor wafer, uneven reflectance occurs due to the influence of the pattern of the devices on the surface of the semiconductor wafer. Even in the case of workpieces other than semiconductor wafers, irregularities in reflectance occur due to structures formed on the surface of the workpiece. In this case, the reflected light detection signal includes not only information on cracks (information on changes in the amount of reflected light caused by cracks) but also information on reflectance irregularities caused by the surface properties of the workpiece (reflectance information on changes in the amount of reflected light caused by unevenness) is included.

As described above, when detecting the depth position of a crack formed inside the workpiece by irradiating the back surface of the workpiece with the detection light, uneven reflectance caused by the properties of the surface of the workpiece However, there is a problem that the detection accuracy of the crack depth position is lowered.

The present invention has been made in view of such circumstances, and is capable of accurately detecting the position of a crack formed inside a workpiece by suppressing the influence of uneven reflectance caused by the properties of the surface of the workpiece. It is an object of the present invention to provide a crack detection device and method capable of

In order to solve the above problems, a crack detection device according to a first aspect of the present invention has a light source unit that emits detection light along a main optical axis, a lens optical axis coaxial with the main optical axis, An objective lens that causes the detection light emitted from the light source to enter from the upper surface side of the workpiece and converge the light inside the workpiece, and an objective lens that is eccentric from the main optical axis before forming a crack inside the workpiece. Preliminary measurement means for illuminating the workpiece with the detection light in an oblique direction, detecting the reflected light from the lower surface of the workpiece to obtain a preliminary measurement value of the reflected light, and forming a crack inside the workpiece. After that, the work piece is illuminated with the detection light decentered from the main optical axis, the reflected light from the work piece is detected, and the main measurement means acquires the main measurement value of the reflected light; and a crack detection means for correcting this measured value using the crack detection means to detect the crack depth of the crack formed inside the workpiece.

In the crack detection device according to the second aspect of the present invention, in the first aspect, the crack detection means has a pre-measured value V ₀ , a main measured value V, k a positive coefficient, M=V/V ₀ , the measured value I after correction is calculated by the following formula.

In the crack detection method according to the third aspect of the present invention, before a crack is formed inside the work piece, the work piece is polarized and illuminated from the upper surface side with detection light eccentric from the main optical axis of the objective lens. A pre-measurement step of detecting the reflected light from the lower surface of the workpiece and acquiring a pre-measured value of the reflected light, and after forming a crack inside the workpiece, the A main measurement step of illuminating the work piece with polarized light, detecting reflected light from the work piece, and obtaining a main measurement value of the reflected light; and a crack detection step of detecting a crack depth of a crack formed inside the object.

ADVANTAGE OF THE INVENTION According to this invention, the depth of the crack formed inside the to-be-processed object can be detected accurately.

FIG. 1 is a block diagram showing a crack detection device according to one embodiment of the invention. FIG. 2 is an explanatory diagram showing a state when the workpiece is polarized and illuminated with the detection light. FIG. 3 is an explanatory diagram showing a state when the object to be processed is polarized and illuminated with the detection light. FIG. 4 is an explanatory diagram showing a state when the object to be processed is polarized and illuminated with the detection light. FIG. 5 is a diagram showing how reflected light is received by the photodetector (corresponding to FIG. 2). FIG. 6 is a diagram showing how reflected light is received by the photodetector (corresponding to FIG. 3). FIG. 7 is a diagram showing how reflected light is received by the photodetector (corresponding to FIG. 4). FIG. 8 is a diagram for explaining the path along which the light reflected from the workpiece reaches the objective lens pupil. FIG. 9 is a diagram schematically showing optical paths of detection light and reflected light inside the wafer. FIG. 10 is a table showing a comparison of crack detection results based on this measurement data and corrected data. FIG. 11 is a block diagram showing the measurement value correction calculation function of the crack detection device according to this embodiment. FIG. 12 is a flowchart illustrating a crack detection method according to one embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a crack detection device and method according to the present invention will be described below with reference to the accompanying drawings.

[Crack detector]
FIG. 1 is a block diagram showing a crack detection device according to one embodiment of the present invention.

The crack detection device 10 is a device that is used in combination with a laser processing device (not shown) that forms a laser processing region inside a wafer W that is a workpiece. provided movably to the In the following description, the constituent elements of the crack detection device 10 will be described, and the description of the configuration of the laser processing device will be omitted.

The crack detection device 10 according to the present embodiment irradiates a wafer W such as a silicon wafer with detection light L1 and detects a reflected light L2 from the wafer W, thereby detecting a crack K formed inside the wafer W. to detect the crack depth of In the following description, a three-dimensional orthogonal coordinate system in which the stage 510 on which the wafer W is placed is a plane parallel to the XY plane and the Z direction is the thickness direction of the wafer W is used.

As shown in FIG. 1, the crack detection device 10 according to the present embodiment includes a light source unit 100, an illumination optical system 200, an interface detection optical system 300, a crack detection optical system 400, a control unit 500, and a condensing point position movement. It includes a mechanism 502 , an objective lens 504 , an operation section 506 and a display section 508 .

The light source unit 100 emits detection light L1. The detection light L1 is used for detecting the interface position of the wafer W and detecting the crack K formed inside the wafer W. FIG. Here, when the wafer W is a silicon wafer, as the detection light L1, light having transparency to the wafer W, for example, infrared light having a wavelength of 1,000 nm or more is used.

The light source section 100 includes light sources 102A, 102B and 102C and a half mirror 104. As shown in FIG. Light sources 102A, 102B and 102C and half mirror 104 are arranged along main optical axis AX coaxial with the lens optical axis of objective lens 504 .

Light sources 102A, 102B, and 102C emit detection light L1 along main optical axis AX. As the light sources 102A, 102B and 102C, for example, laser light sources (infrared laser light sources, laser diodes) or LED (Light Emitting Diode) light sources can be used.

The light source 102A has a laser aperture capable of illuminating substantially the entire surface of the objective lens pupil 504a of the objective lens 504. FIG. The light source 102A is used for interface detection, which will be described later.

The light sources 102B and 102C each have a laser aperture capable of illuminating only a part of the objective lens pupil 504a of the objective lens 504 decentered from the main optical axis AX (lens optical axis). Light sources 102B and 102C are used for crack detection, which will be described later.

Although the interface detection opening (light source 102A) and the crack detection openings (light sources 102B and 102C) are provided separately in this embodiment, the present invention is not limited to this. For example, one aperture may be used in common, and a light blocking means may be used to switch between the interface detection aperture and the crack detection aperture.

Half mirror 104 reflects detection light L1 emitted from light source 102A for interface detection, and transmits detection light L1 emitted from light sources 102B and 102C for crack detection. Hereinafter, although illustration is omitted, the detection light beams L1 emitted from the light sources 102A, 102B and 102C are assumed to be L1(A), L1(B) and L1(C), respectively.

Incidentally, in this embodiment, instead of the half mirror 104, a total reflection mirror or a dichroic mirror can also be used. In this case, a mirror may be inserted at the position of the half mirror 104 on the optical path when the interface is detected, and the mirror may be retracted from the optical path when the crack is detected.

The light sources 102A, 102B, and 102C are each connected to a control unit 500, and the control unit 500 controls emission of the light sources 102A, 102B, and 102C.

The control unit 500 is implemented by, for example, a personal computer or workstation. The control unit 500 includes a CPU (Central Processing Unit) for controlling the operation of each part of the crack detection device 10, a ROM (Read Only Memory), a storage device (reference numeral 512 in FIG. 11) for storing the control program. Drive) or SSD (Solid State Drive), etc.) and SDRAM (Synchronous Dynamic Random Access Memory) that can be used as a work area for the CPU. The control unit 500 receives an operation input from the operator via the operation unit 506 and transmits a control signal corresponding to the operation input to each unit of the crack detection device 10 to control the operation of each unit.

An operation unit 506 is means for receiving operation input by an operator, and includes, for example, a keyboard, mouse, or touch panel.

The display unit 508 is a device that displays an operation GUI (Graphical User Interface) for operating the crack detection device 10 and images (for example, crack detection results, etc.). As the display unit 508, for example, a liquid crystal display can be used.

The illumination optical system 200 guides the detection light L1 emitted from the light source section 100 to the objective lens 504 . Illumination optics 200 includes relay lenses 202 and 206 and mirror 204 (eg, a total reflection mirror).

The detection light L1 emitted from the light source unit 100 is transmitted through the relay lens 202, reflected by the mirror 204, and the optical path is bent. The detection light L<b>1 reflected by the mirror 204 passes through the relay lens 206 , is sequentially reflected by the half mirrors 304 and 302 , and is emitted toward the objective lens 504 .

Return light (observation light) that has been reflected by the wafer W and returned after passing through the half mirror 302 can be observed using an observation optical system 600 (for example, a photodetector or the like). Note that when the observation optical system 600 is not used, a dichroic mirror or a total reflection mirror can be used in place of the half mirror 302 .

The objective lens 504 converges (focuses) the detection light L1 emitted from the illumination optical system 200 onto the wafer W. As shown in FIG. The objective lens 504 is arranged at a position facing the wafer W and arranged coaxially with the main optical axis AX.

The condensing point position moving mechanism 502 changes the position of the condensing point of the detection light L1 in the Z direction (optical axis direction of the objective lens 504). The focal point position moving mechanism 502 includes an actuator (for example, a piezo actuator, not shown) that moves the objective lens 504 in the Z direction. A focal point position moving mechanism 502 moves an objective lens 504 in the Z direction by driving a piezo actuator under the control of the control unit 500 . Thereby, the relative distance in the Z direction between the objective lens 504 and the wafer W can be changed to adjust (finely adjust) the position in the Z direction of the focal point of the detection light L1.

Further, the focal point position moving mechanism 502 may include a Z drive mechanism that moves the crack detection device 10 in the Z direction with respect to the stage 510 . By moving the crack detection device 10 in the Z direction, the Z drive mechanism aligns (coarsely adjusts) the objective lens 504 and the wafer W in the Z direction with an adjustment width larger than that of the piezo actuator.

As described above, when combining the position adjustment (coarse adjustment) of the focal point by the Z drive mechanism and the position adjustment (fine adjustment) of the focal point by the piezo actuator, the detection light The degree of freedom (adjustment range) for adjusting the position of the focal point of L1 in the Z direction is increased. This enables detection of cracks and the like for wafers W having various thicknesses.

The Z drive mechanism may be a mechanism that drives the stage 510 in the Z direction, or may be a mechanism that drives both the crack detection device 10 and the stage 510 in the Z direction. Moreover, the Z drive mechanism may also serve as a drive mechanism for moving the processing head of the laser processing apparatus.

The reflected light L2 collected by the objective lens 504 and reflected by the wafer W is guided to the interface detection optical system 300 and the crack detection optical system 400, and used for interface detection and crack detection of the wafer W, respectively. be done.

[Crack detection procedure]
In this embodiment, the interface of the surface Wa of the wafer W (the surface in contact with the stage 510 and on which the device is formed) is detected, and then the crack depth is measured with the interface position of the surface Wa of the wafer W as a reference. An example of detecting is described.

In this embodiment, the crack depth is detected using the surface Wa of the wafer W as a reference, but the present invention is not limited to this. For example, the crack depth may be detected using the back surface Wb of the wafer W as a reference, or the average value of the crack depths detected using the interface positions of both the front surface Wa and the back surface Wb of the wafer W as a reference. It is also possible to

[Optical system for interface detection]
First, detection of the interface of the wafer W will be described.

The interface detection optical system 300 is an optical system for detecting the interface (front surface Wa or rear surface Wb) of the wafer W, and includes a half mirror 302, a half mirror 304, a relay lens 306, a half mirror 308, and a photodetector 310. contains.

When detecting the front surface Wa of the wafer W as the interface of the wafer W, the control unit 500 causes the light source 102A to emit the detection light L1(A) to irradiate the rear surface (upper surface) Wb side of the wafer W with the detection light beam L1(A).

The detection light L1(A) from the light source 102A is a laser beam having an opening approximately the same size as the objective lens pupil 504a of the objective lens 504, and is sequentially reflected by the half mirrors 304 and 302 to the objective lens 504. be guided. The detection light L1(A) is applied to substantially the entire surface of the objective lens pupil 504a of the objective lens 504. FIG.

Here, the reflected light L2(A) is the light reflected by the wafer W from the detection light L1(A). The reflected light L2(A) is reflected by the half mirror 302 and guided to the relay lens 306 after passing through the half mirror 304 . Reflected light L2(A) transmitted through relay lens 306 is reflected by half mirror 308 and guided to photodetector 310 .

The photodetector 310 is a device for receiving reflected light L2(A) from the wafer W to detect the interface of the wafer W, and includes a detector body 310A and a pinhole panel 310B.

As the detector main body 310A, a photodetector (for example, a photodiode) that converts received light into an electric signal and outputs the electric signal to the control unit 500, an infrared camera, or the like can be used.

A pinhole is formed in the pinhole panel 310B for transmitting part of the incident light. The pinhole panel 310B is arranged upstream with respect to the light receiving surface of the detector main body 310A, and arranged so that the pinhole of the pinhole panel 310B is positioned on the optical axis of the reflected light L2(A). there is The position of the pinhole of the pinhole panel 310B is optically conjugate with the focal point (front focal position) of the objective lens 504 (confocal pinhole). Also, the size of the pinholes of the pinhole panel 310B is adjusted to about the diffraction limit of the objective lens 504 .

The reflected light L2(A) reflected by the wafer W is condensed at the position of the pinhole of the pinhole panel 310B, which is optically conjugate with the focal point of the objective lens 504. FIG. When the focal point of the objective lens 504 coincides with the surface Wa of the wafer W, which serves as a reflecting surface, the light flux of the detection light L1(A) is reflected by the surface Wa of the wafer W and becomes a parallel light flux through the objective lens. It passes through 504 and returns. Therefore, the signal D (see FIG. 10) output from the detector main body 310A has a sharp peak when the focal point of the objective lens 504 coincides with the position of the surface Wa of the wafer W serving as the reflecting surface. .

The control unit 500 changes the relative distance between the objective lens 504 and the wafer W by means of the focal point position moving mechanism 502 while irradiating the wafer W with the detection light L1(A) from the light source 102A. The position of the focal point of L1(A) (that is, the front focal position of the objective lens 504) is moved in the Z direction. Thereby, the focal point of the detection light L1(A) is scanned in the Z direction. The control unit 500 detects the reflected light L2 (A) from the wafer W when the focal point of the detection light L1 (A) is scanned in the Z direction by the photodetector 310, and the light from the photodetector 310 detects The interface position Z(0) on the front surface Wa of the wafer W is detected by detecting the peak of the signal.

In this embodiment, the confocal method is used to detect the interface of the wafer W, but the present invention is not limited to this. For example, other focus detection methods such as an astigmatism method, white light interferometry, etc. may be used.

[Optical system for crack detection]
Next, detection of the crack K formed inside the wafer W will be described.

Crack detection optics 400 includes a relay lens 402 and photodetectors 404 and 406 .

When detecting the crack K formed inside the wafer W, the control unit 500 causes the light sources 102B and 102C to emit light to irradiate the wafer W with detection light (probe light) L1(B) and L1(C). . Here, the control unit 500 and the optical system for crack detection 400 function as a part of pre-measurement means, main measurement means, and crack detection means, respectively. The light sources 102B and 102C each have a laser aperture at a position shifted from the main optical axis AX. As a result, the wafer W is irradiated with detection lights L1(B) and L1(C) that are eccentric with respect to the main optical axis AX.

Reflected lights L2(B) and L2(C), which are the detection lights L1(B) and L1(C) reflected by the wafer W, respectively, are reflected by the half mirror 302, then reflected by the half mirror 304, the relay lens 306, and the half mirror 306. The light sequentially passes through the mirror 308 and enters the relay lens 402 . Reflected lights L2(B) and L2(C) transmitted through relay lens 402 are received by photodetectors 404 and 406, respectively.

Incidentally, in the interface detection optical system 300, instead of the half mirror 308, a total reflection mirror, a dichroic mirror, or the like can be used. In this case, a mirror may be inserted at the position of the half mirror 308 on the optical path when the interface is detected, and the mirror may be retracted from the optical path when the crack is detected.

The photodetectors 404 and 406 are devices for receiving reflected light L2(B) and L2(C) from the wafer W to detect cracks K inside the wafer W. FIG. As the photodetectors 404 and 406, a photodetector (for example, a photodiode) that converts received light into an electrical signal and outputs the electrical signal to the control unit 500, an infrared camera, or the like can be used.

Photodetectors 404 and 406 are positioned conjugate with objective lens pupil 504a, and are positioned offset from the optical axis of objective lens 504 so as to receive detected light beams L1(B) and L1(C). .

FIGS. 2 to 4 are explanatory diagrams showing the state when the wafer W is illuminated with the detection light L1 in polarized light. 2 shows the case where the crack K exists at the focal point of the objective lens 504, FIG. 3 shows the case where the crack K does not exist at the focal point of the objective lens 504, and FIG. Each shows a case where the crack depth (crack bottom end position) matches.

5 to 7 are diagrams showing states of the reflected light L2 received by the photodetectors 404 and 406, corresponding to the cases shown in FIGS. 2 to 4, respectively.

FIG. 8 is a diagram for explaining the path along which the reflected light L2 from the wafer W reaches the objective lens pupil 504a. Here, the case where the detection light L1 passes through the first region G1 on one side (the right side in FIG. 8) of the objective lens pupil 504a and the wafer W is subjected to polarized illumination will be described.

As shown in FIG. 2, when there is a crack K at the focal point of the objective lens 504, the detection light L1 is totally reflected by the crack K, and the reflected light L2 becomes the detection light with respect to the main optical axis AX. It is a component that follows the path on the same side as the optical path of L1 and reaches the area on the same side as the detection light L1 of the objective lens pupil 504a. That is, as shown in FIG. 8, when the detection light L1 from the light source unit 100 is irradiated onto the wafer W through the objective lens 504 and the path of the detection light L1 is R1, the crack K inside the wafer W is defined as R1. The reflected light L2 totally reflected at , follows the path R2 on the same side (the right side in FIG. 8) with respect to the main optical axis AX as the path R1 of the detection light L1, and passes through the first region G1 of the objective lens pupil 504a. .

As shown in FIG. 3, when there is no crack K at the focal point of the objective lens 504, the detection light L1 is reflected by the surface Wa of the wafer W, and the reflected light L2 becomes the detection light L1 of the objective lens pupil 504a. is the component that reaches the area on the opposite side of the That is, as shown in FIG. 8, the reflected light L2 reflected by the surface Wa of the wafer W follows a path R3 on the opposite side (left side in FIG. 8) of the main optical axis AX from the path R1 of the detection light L1. passes through the second region G2 of the objective lens pupil 504a.

As shown in FIG. 4, when the focal point of the objective lens 504 and the lower end position of the crack K match, the detection light L1 is split into a reflected light component L2a and a non-reflected light component L2b. The reflected light component L2a is totally reflected by the crack K, then reflected by the surface Wa, and reaches the area of the objective lens pupil 504a on the same side as the detection light L1. The light is reflected by the surface Wa of the wafer W without being exposed, and reaches the area of the objective lens pupil 504a on the opposite side of the detection light L1. That is, as shown in FIG. 8, of the reflected light L2, the reflected light component L2a totally reflected by the crack K inside the wafer W is on the same side of the main optical axis AX as the path R1 of the detection light L1 ( The non-reflected light component L2b, which passes through the first region G1 of the objective lens pupil 504a along the path R2 on the right side of FIG. It passes through the second region G2 of the objective lens pupil 504a following the path R3 on the opposite side (the left side in FIG. 8) of the main optical axis AX from the path R1 of L1.

The photodetectors 404 and 406 are arranged so as to be optically conjugate with the first region G1 and the second region G2 of the objective lens pupil 504a, respectively. As a result, the photodetectors 404 and 406 can selectively receive light that has passed through the first region G1 and the second region G2 of the objective lens pupil 504a.

Here, in the example shown in FIG. 2 (when there is a crack K at the condensing point of the objective lens 504), the reflected light L2 is incident on the light receiving surface 404C of the photodetector 404 of the photodetectors 404 and 406. . Therefore, the level of the detection signal output from the light receiving surface 404C of the photodetector 404 is higher than the level of the detection signal output from the light receiving surface 406C of the photodetector 406, as shown in FIG.

On the other hand, in the example shown in FIG. 3 (when there is no crack K at the condensing point of the objective lens 504), the reflected light is incident on the light receiving surface 406C of the photodetector 406 out of the photodetectors 404 and 406. FIG. Therefore, the level of the detection signal output from the light receiving surface 406C of the photodetector 406 is higher than the level of the detection signal output from the light receiving surface 404C of the photodetector 404, as shown in FIG.

In the example shown in FIG. 4 (when the focal point of the objective lens 504 coincides with the lower end position of the crack K), the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 receive the respective components L2a and L2a of the reflected light L2. L2b respectively enter. Therefore, as shown in FIG. 7, the levels of the detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 are substantially equal.

Thus, the amount of light received by the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 changes depending on whether or not there is a crack K at the focal point of the objective lens 504. FIG. In the present embodiment, using such properties, the crack depth of the crack K formed inside the wafer W (crack end position indicating the crack bottom end position or the crack top end position) can be detected.

Specifically, when D1 and D2 are the outputs of the detection signals output from the light receiving surfaces 404C and 406C of the photodetectors 404 and 406, respectively, to determine the existence of the crack K at the focal point of the objective lens 504. can be expressed by the following equation.

S = (D1-D2)/(D1+D2)
In the above formula, when the condition of S=0, that is, when the amounts of light received by the light receiving surfaces 404C and 406C of the photodetectors 404 and 406 match, the condensing point of the objective lens 504 and the bottom end position of the crack ( or crack top position).

The control unit 500 (see FIG. 1) controls the focal point position moving mechanism 502 to move the focal point of the detection light L1 in the Z direction, and moves the focal point of the detection light L1 from the interface position on the surface Wa of the wafer W to the thickness direction of the wafer W. Detection signals output from the light-receiving surfaces 404C and 406C of the photodetectors 404 and 406 are sequentially acquired while sequentially changing (in the Z direction), and the evaluation value S represented by the above formula is calculated based on the detection signals. Then, by evaluating the evaluation value S and the focal point position information, the crack depth (crack bottom position or crack top position) of the crack K can be detected.

[Detection of cracks in consideration of the properties of the surface of the wafer W]
Next, crack detection for suppressing the influence of reflectance unevenness caused by the surface properties of the wafer W in the crack detection apparatus 10 will be described.

In the present embodiment, in order to suppress the influence of reflectance unevenness caused by the properties (device surface) of the front surface (lower surface) Wa of the wafer W, the crack upper end position _KT and the crack lower end of the crack K are controlled by the following procedure. _Calculate the position KB.

First, before the crack K is formed inside the wafer W (before laser processing), a preliminary measurement is performed, and when the converging point positions of the detection lights L1a and L1b irradiated to the wafer W are scanned in the Z direction, Preliminary measurement data showing changes in detection signals of the resulting reflected lights L2a and L2b are obtained (see FIG. 9). Next, after the crack K is formed inside the wafer W (after laser processing), the reflected lights L2a and L2b from the wafer W are measured and the wafer W is irradiated in the same manner as in the pre-measurement. Main measurement data showing changes in the detection signals of the reflected lights L2a and L2b obtained when the positions of the focal points of the detection lights L1a and L1b are scanned in the Z direction are obtained. Then, the pre _- measured data is regarded as reflectance data, the main measurement data is corrected, and the crack upper end position _KT and the crack lower end position KB of the crack K are obtained from the corrected main measurement data (hereinafter referred to as corrected data). Calculate

Next, an overview of the crack detection procedure according to this embodiment will be described with reference to FIG. FIG. 9 is a diagram schematically showing the optical paths of the detection lights L1a and L1b and the reflected lights L2a and L2b inside the wafer W. As shown in FIG. In addition, in FIG. 9, hatching of the back surface Wb of the wafer W and the cross section of the wafer W is omitted for simplification of the drawing. Also, the objective lens 504 is shown in a simplified manner.

In addition, in the example shown in FIG. 9, detection light incident from the right side in the figure (hereinafter referred to as side a) and from the left side in the figure (hereinafter referred to as side b) are L1a (first detection light) and L1b, respectively. (second detection light), and the reflection lights of the detection lights L1a and L1b reflected by the surface Wa of the wafer W are L2a (first reflection light) and L2b (second reflection light), respectively. Here, the a side and the b side correspond to the first region G1 and the second region G2 in FIG. 8, respectively.

The detection light L1a incident on the wafer W from the side a in FIG. 9 (the side of the first region G1 in FIG. 8) is reflected by the surface Wa of the wafer W, and then becomes reflected light L2a from the side b in FIG. It returns to the objective lens 504 side on the second area G2 side) and is detected by the photodetector 406 . On the other hand, the detection light L1b incident on the wafer W from the side b in FIG. 9 is reflected by the surface Wa of the wafer W, returns to the side a in FIG.

In the preliminary measurement, since the crack K is not formed inside the wafer W, the crack K does not block the detection lights L1a and L1b and the reflected lights L2a and L2b. When the focal points of the detection lights L1a and L1b are scanned in the Z direction, the positions of the reflection points where the detection lights L1a and L1b are reflected on the surface Wa of the wafer W move along arrows Aa and Ab along the Y direction, respectively. . Since the pre-measurement data is data showing changes in the detection signals of the reflected lights L2a and L2b when the focal points of the detection lights L1a and L1b are scanned in the Z direction, the properties of the surface Wa of the wafer W (device surface). It contains information about the non-uniformity of reflectance in the Y direction caused by .

In the present embodiment, this pre-measured data is used to correct the actual measured data, and the post-correction data is used to detect the depth position of the crack. Suppress. That is, when the amount of reflected light L2a and L2b is reduced in the pre-measured data due to unevenness in reflectance, correction is performed to compensate for the decrease in the amount of reflected light L2a and L2b.

More specifically, when the sensor value (preliminary measurement value) in the pre-measurement data is V ₀ and the sensor value (main measurement value) in the main measurement data is V, the sensor value I in the post-correction data is expressed by the following formula ( 1).

但し、Ｍは、事前測定値Ｖ_０と本測定値Ｖとの比（Ｖ／Ｖ_０）を示す。

However, M indicates the ratio (V/V ₀ ) between the pre-measured value V ₀ and the actual measured value V.

Here, k is an arbitrary coefficient (positive coefficient). This is because (V/V ₀ ) becomes 1 when the reflectance of Wa on the surface of the wafer W is equal between the pre-measured data and the actual measured data (the sensor values are equal), so depending on the range of the graph to be displayed , it becomes difficult to see the difference between the corrected data and the actual measurement data. In other words, the coefficient k is a coefficient for making the graph of corrected data easier to see. For example, when the 10-0V range is adopted as the range of the graph, correction calculation is performed with k=8 as an example.

According to the formula (1), the sensor value V in the main measurement data is multiplied by the ratio of the sensor value V in the main measurement data and the sensor value V ₀ in the pre-measurement data to obtain the sensor value V ₀ in the pre-measurement data can be corrected to compensate for the decrease in the amount of reflected light L2a and L2b.

FIG. 10 is a table showing a comparison of crack detection results based on this measurement data and corrected data. FIG. 10 shows graphs of pre-measurement data, main measurement data, and post-correction data in order from the top, and graphs Da and Db of each data show detection signals of reflected lights L2a and L2b, respectively. The horizontal axis of each graph is the piezo movement amount of the focusing point position moving mechanism 502 indicating the positions of the focusing points of the detection lights L1a and L1b, and the vertical axis is the sensor value of the detection signal.

The dashed line D _Ref in the graph of the pre-measurement data in FIG. ) shows the output value. When the amounts of the detected lights L1a and L1b are equal, the D _Refs of the reflected lights L2a and L2b are the same.

In the graphs Da and Db of the pre-measurement data, portions below the line D _Ref (reflectance is low) are considered to be affected by the properties of the surface of the wafer W (device surface).

Corrected data is obtained by correcting the main measurement data using the pre-measurement data using equation (1). Note that the post-correction data have different coefficients k used for correction, so the maximum values of the sensor values in the graphs Da and Db are different from each other.

The graph of FIG. 10 shows the positions (detected values) of the crack upper end position K _T and the crack lower end position K _B obtained using the actual measurement data and the corrected data. The numerical values in the rightmost column of the table in FIG. 10 are the visually measured values of the _crack upper end position _KT and the crack lower end position KB when the wafer W is cut and the crack K is visually observed with a microscope (hereinafter referred to as visual values). , and the result of comparison with each detected value.

As shown in FIG. 10, the differences between the detected _crack top position _KT and the crack bottom position KB obtained using this measurement data (without correction) and the visual values are 10 μm and 8.4 μm, respectively. On the other hand, the difference between the detected values of the crack top position K _T and the crack bottom position K _B obtained using the post-correction data and the visual values are 5.3 μm and 6.3 μm, respectively. Based on the above results, the detected values obtained using the post-correction data are better than the detected values obtained using the actual measurement data (without correction) compared to the visual values at both the upper and lower ends. It can be seen that the difference is small. That is, from the above results, it is possible to improve the accuracy of crack detection by removing the influence of the surface Wa of the wafer W using the pre-measured data.

FIG. 11 is a block diagram showing the measurement value correction calculation function of the crack detection device according to this embodiment.

As shown in FIG. 11, the control unit 500 of the crack detection device 10 has a measurement value correction calculation function 700 for correcting the measurement values of the _crack upper end position _KT and the crack lower end position KB of the crack K.

The control unit 500 acquires the pre-measured data Data1 after pre-measurement before laser processing, and stores it in the storage device 512 . As shown in FIG. 11, the pre-measured data Data1 is a detection signal obtained from the detection light L1a incident from the side a (a-side pre-measurement value; corresponding to the graph Da) and from the detection light L1b incident from the side b. and the obtained detection signal (preliminary measurement value on the b side, corresponding to graph Db).

Next, the control unit 500 performs main measurement after laser processing and acquires main measurement data Data2. Similar to the pre-measured data Data1, the main measurement data Data2 includes a detection signal (a-side measurement value (main measurement value), corresponding to the graph Da) obtained from the detection light L1a incident from the a-side, and a detection light L1a incident from the b-side. and a detection signal obtained from the detection light L1b (measured value on the b side (main measured value), corresponding to the graph Db). After completing the main measurement, the control unit 500 inputs the main measurement data Data2 to the measurement value correction calculation function 700 .

The measured value correction calculation function 700 reads the pre-measured data Data1 from the storage device 512 and corrects the main measured data Data2. That is, according to equation (1), the a-side pre-measured value is used to correct the a-side measured value, and the b-side pre-measured value is used to correct the b-side measured value, thereby generating corrected data Data3. The control unit 500 performs crack detection using the post-correction data Data3. As described above, by using the pre-measured data Data1 to suppress the influence of the properties of the surface Wa of the wafer W, it is possible to improve the crack depth detection accuracy.

Note that the pre-measurement may be performed for each wafer W, which is a workpiece, or may be performed only for some of the wafers W. For example, when performing laser processing on a plurality of wafers W of the same type, one or some of the wafers W are extracted as samples, and only the sample wafers W are processed. Then, the pre-measured data Data1 obtained from the sample wafer W or its average value data may be used to correct the actual measured data Data2 obtained from the wafer W other than the sample. Further, pre-measurement data Data1 is prepared in advance for each type of wafer W (for example, the size, thickness, material, type of device formed on the surface Wa of the wafer W, etc.), and the operation unit 506 By specifying the type of wafer W using , the pre-measurement data Data1 may be called from the storage device 512 .

In the present embodiment, crack detection is performed using two detection lights, the detection light L1a on the a side and the detection light L1b on the b side, but crack detection may be performed using only one of the detection lights. is also possible.

[Crack detection method]
FIG. 12 is a flowchart illustrating a crack detection method according to one embodiment of the invention.

First, the relative positions of the wafer W, which is the object to be processed, and the objective lens 504 are adjusted (step S10), and preliminary measurement is performed (step S12: preliminary measurement step). In the pre-measurement step, the detection lights L1a and L1b are reflected by the surface Wa of the wafer W by scanning the focal point of the detection lights L1a and L1b in the Z direction while the crack K is not formed inside the wafer W. The positions of the reflected points to be reflected are moved along arrows Aa and Ab along the Y direction, respectively. As a result, it is possible to obtain pre-measured data including information on non-uniformity in reflectance in the Y direction caused by the properties of the front surface Wa of the wafer W (device surface). Here, when performing the preliminary measurement, the relative positions of the wafer W and the objective lens 504 are adjusted so that both the peak of the front surface (lower surface) Wa and the peak of the back surface (upper surface) Wb of the wafer W can be confirmed. (step S14).

Next, laser processing is performed to form a crack K inside the wafer W (step S16), and then the main measurement is performed (step S18: main measurement step). In the main measurement process, with the crack K formed inside the wafer W, main measurement data is obtained by scanning the focal points of the detection lights L1a and L1b in the Z direction as in the pre-measurement process.

Next, the measured value correction calculation function 700 corrects the main measured data Data2 of step S18 using the pre-measured data Data1 of the measured value step S12 to generate post-correction data Data3. Then, the crack K is detected using the corrected data Data3 (step S20: crack detection step).

[Another embodiment]
In the above embodiment, the corrected data _Data3 is generated using the ratio of the sensor value V of the main measurement data Data2 after laser processing and the sensor value V0 of the pre-measurement data Data1 before laser processing. is not limited to this. For example, it is also possible to detect the crack K by subtracting the pre-measured data Data1 before laser processing from the main measurement data Data2 after laser processing and using the difference (I=V−V ₀ ) as post-correction data Data3.

Note that when the pre-measurement data Data1 is prepared in advance, the pre-measurement and the main measurement are performed separately. In this case, between data measured at different times, light quantity fluctuations such as fluctuations in the light source intensity of the light source unit 100 may occur at the time of data acquisition.

Therefore, when the post-correction data Data3 is generated using the difference as in another embodiment, it is necessary to consider the influence of light source variation. For example, if the amount of light from the light source unit 100 at the time of the main measurement is lower than that at the time of the preliminary measurement, the amount of reflected light L2a and L2b at the time of the main measurement is reduced. Alternatively, it is conceivable to add a function for lowering the sensor value of the pre-measured data Data1, or apply such a coefficient.

On the other hand, as in the above embodiment, the corrected data _Data3 is generated using the ratio of the sensor value V of the main measurement data Data2 after laser processing and the sensor value V0 of the pre-measured data Data1 before laser processing. In this case, it is not necessary to consider variations in the amount of light from the light source unit 100 when each data is acquired. Therefore, according to the above-described embodiment, it is possible to suppress the influence of the properties of the surface Wa of the wafer W on the crack depth detection accuracy with simpler calculations.

DESCRIPTION OF SYMBOLS 10... Crack detection apparatus, 100... Light source part, 102A, 102B, 102C... Light source, 104... Half mirror, 200... Illumination optical system, 202... Relay lens, 204... Mirror, 206... Relay lens, 300... Optics for interface detection System 302 Half mirror 304 Half mirror 306 Relay lens 308 Half mirror 310 Photodetector 400 Crack detection optical system 402 Relay lens 404, 406 Photodetector 500 ... control section 502 ... focal point position moving mechanism 504 ... objective lens 506 ... operation section 508 ... display section 510 ... stage 512 ... storage device 700 ... measurement value correction calculation function

Claims (3)

a light source unit that emits detection light along a main optical axis;
an objective lens having a lens optical axis coaxial with the main optical axis, and configured to allow the detection light emitted from the light source unit to enter from the upper surface side of the workpiece and focus the light inside the workpiece;
before forming a crack inside the workpiece, illuminating the workpiece with the detection light eccentric from the main optical axis to detect reflected light from the lower surface of the workpiece; pre-measurement means for obtaining a pre-measurement of reflected light;
After forming a crack inside the workpiece, illuminating the workpiece with the detection light eccentric from the main optical axis, detecting the reflected light from the workpiece, and detecting the reflected light. a main measurement means for obtaining a main measurement value;
a crack detection means for correcting the actual measured value using the pre-measured value and detecting a crack depth of a crack formed inside the workpiece;
A crack detection device comprising: The crack detection means calculates the measured value I after correction by the following formula when the pre-measured value is V ₀ , the actual measured value is V, k is a positive coefficient, and M = V / V ₀ The crack detection device of claim 1, wherein:

Before a crack is formed inside the work piece, the work piece is obliquely illuminated from the top side with detection light decentered from the main optical axis of the objective lens, and reflected light from the bottom surface of the work piece is detected. and obtaining a pre-measured value of the reflected light;
After forming a crack inside the workpiece, illuminating the workpiece with the detection light eccentric from the main optical axis, detecting the reflected light from the workpiece, and detecting the reflected light. a main measurement step of obtaining a main measurement value;
a crack detection step of correcting the actual measured value using the pre-measured value and detecting a crack depth of a crack formed inside the workpiece;
A crack detection method comprising:

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