JP2020076651A - Crack detector and crack detection method - Google Patents

Abstract

To provide a crack detector and a crack detection method for non-destructively and accurately detecting the crack depth of a crack formed inside a workpiece.SOLUTION: A crack detector (10, 10A) comprises: a light source part (100) for emitting detection light along a main optical axis; a condenser lens (504) having a lens optical axis that is coaxial with the main optical axis, and condensing the detection light emitted from the light source part on a workpiece; interface detection means (500, 300) for exposing the workpiece to the detection light emitted along the main optical axis and detecting a first reflection light from the workpiece, and detecting an interface position indicating a front face or a rear face of the workpiece, on the basis of a detection signal corresponding to the first reflection light; and crack detection means (500, 400) for obliquely illuminating the workpiece with detection light decentering from the main optical axis and detecting a second reflection light from the workpiece, and detecting the crack depth of a crack formed inside the workpiece by using the interface position as a reference, on the basis of a detection signal corresponding to the second reflection light.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 detecting a crack formed inside a workpiece.

  Conventionally, a substrate such as a silicon wafer or a glass wafer (hereinafter, referred to as a "workpiece") is focused on the inside to irradiate a laser beam along a planned cutting line, and the workpiece is processed along the processing line. There is known a laser processing device (also referred to as a laser dicing device) that forms a modified region serving as a starting point of cutting inside a sheet. The workpiece on which the modified region has been formed is then cut along the planned cutting line by a cutting process such as expanding or breaking and divided into individual chips.

  By the way, when a modified region is formed on a workpiece by a laser processing apparatus, a crack extends from the modified region in the thickness direction of the workpiece. If the crack reaches the front surface (laser light incident surface) of the workpiece or the back surface on the opposite side, it is possible to appropriately divide the chip into chips in the cutting process. The reason is that the crack formed inside the workpiece serves as a starting point when the workpiece is divided, and thus the degree of extension of the crack affects the division rate of the workpiece. Further, in the case of a thick work piece, the crack may not reach the front surface or the back surface of the work piece. Therefore, the modified region is not always appropriate depending on whether the crack reaches the front surface or the back surface of the work piece. In some cases, it may not be possible to properly determine whether or not it has been formed.

  Therefore, after the modified region is formed by the laser processing device and before the cutting process, whether or not the modified region serving as the starting point when the workpiece is divided is properly formed, that is, inside the workpiece. By detecting the crack depth of the formed crack, it becomes possible to accurately predict the quality of the cutting into chips in the cutting process. Then, if there is a part where the modified region is not properly formed inside the work piece, it is possible to reprocess only that part with the laser processing device or change the cutting method in the cutting process. It will be possible. This makes it possible to eliminate chip loss in the subsequent cleaving process. Further, it is possible to correct the processing conditions in the laser processing apparatus with reference to the occurrence status of defective portions, and it is possible to reduce the occurrence of defective portions in the modified region in the workpiece to be processed thereafter. When the modified region of the defective portion is reprocessed, the defective portion can be reduced, so that the loss of time required for the reprocessing can be reduced.

  On the other hand, the evaluation of the cracks generated inside the workpiece has conventionally been performed by cutting and polishing the sample or observing under limited conditions. Therefore, it was difficult to apply it to a processing process using a laser processing device.

  On the other hand, a technique of nondestructively inspecting a crack formed inside a workpiece has been proposed (for example, see Patent Document 1).

  In the technique disclosed in Patent Document 1, light is incident from one of the cracks, the light transmitted through a region including the crack is detected, and the crack is inspected by utilizing the decrease in the detected light amount due to the scattering of the crack. ..

JP, 2008-222517, A

  However, in the technique disclosed in Patent Document 1, the signal level of the light receiver does not directly indicate the crack depth but is treated as a threshold value. Therefore, it is necessary to perform an experiment in advance and set the threshold value. Further, in order to detect the crack length (crack depth), it was necessary to set a plurality of threshold values in advance according to the crack length by experiments. In addition, since the crack head position is confirmed by using only the reduction of transmitted light (light transmitted through a region including a crack), there is a limit to improving the detection accuracy of the crack depth of the crack.

  The present invention has been made in view of such circumstances, and provides a crack detection device and method capable of nondestructively and accurately detecting the crack depth of a crack formed inside a workpiece. With the goal.

  In order to achieve the above object, a crack detection device according to a first aspect of the present invention includes a light source unit that emits detection light along a main optical axis and a lens optical axis that is coaxial with the main optical axis. Condensing lens for condensing the detection light emitted from the part to the work piece and the detection light emitted along the main optical axis to the work piece to detect the first reflected light from the work piece. Then, based on the detection signal corresponding to the first reflected light, the interface detection means for detecting the interface position indicating the front surface or the back surface of the workpiece, and the obliquely illuminating the workpiece with the detection light decentered from the main optical axis. Then, the second reflected light from the workpiece is detected, and the crack depth of the crack formed inside the workpiece is detected based on the interface position based on the detection signal corresponding to the second reflected light. And a crack detecting means for performing the crack detection.

  According to the first aspect, the crack depth of the crack formed inside the workpiece is detected by detecting the interface position of the workpiece and detecting the crack depth with reference to this interface position. Non-destructive and accurate detection is possible.

  A crack detecting device according to a second aspect of the present invention is the crack detecting device according to the first aspect, wherein the interface detecting means is arranged on the light receiving surface side and a photodetector having a light receiving surface for receiving the first reflected light, A pinhole panel for blocking a part of the first reflected light incident on the surface, and the pinhole formed in the pinhole panel has an optically conjugate relationship with the position of the condensing point of the condensing lens. The interface detection means is configured to detect the interface position based on the first reflected light that has passed through the pinhole.

  According to the second aspect, it is possible to detect the interface position of the workpiece based on the reflected light that is condensed at a position that is optically conjugate with the position of the condensing point of the condensing lens. Become.

  A crack detecting apparatus according to a third aspect of the present invention is the crack detecting apparatus according to the first or second aspect, which includes a condensing point changing unit that changes a condensing point of a condensing lens in a thickness direction of a workpiece. The detecting means detects the crack depth of the crack based on the change of the detection signal when the condensing point of the condensing lens is changed in the thickness direction of the workpiece by the condensing point changing means. Is.

  A crack detecting device according to a fourth aspect of the present invention is the crack detecting device according to any one of the first to third aspects, wherein the light source unit is a limiting member that has an opening and that blocks a part of the detection light. And the detection light is decentered with respect to the main optical axis by arranging the opening at a position decentered from the light source optical axis of the light source section.

  According to the fourth aspect, by arranging the position of the opening of the limiting member away from the main optical axis, it becomes possible to easily perform the polarized illumination.

  A crack detecting apparatus according to a fifth aspect of the present invention is the crack detecting device according to any one of the first to fourth aspects, wherein the crack detecting unit detects a crack depth a plurality of times by switching a method of incident illumination of detection light. The average value of the crack depth detection results obtained a plurality of times is calculated.

  According to the fifth aspect, even if the accuracy of alignment between the condenser lens and the workpiece is not sufficient by switching the method of oblique illumination and detecting the crack depth and using the average value of the results. It is possible to accurately and stably detect the crack depth of the crack formed inside the workpiece.

  A crack detection method according to a sixth aspect of the present invention irradiates a workpiece with detection light emitted from a light source unit along a main optical axis to detect first reflected light from the workpiece, Based on the detection signal corresponding to the first reflected light, the interface detection step of detecting the interface position indicating the front surface or the back surface of the workpiece, and the detection light emitted from the light source unit and decentered from the main optical axis The second reflected light from the work piece by irradiating the object with partial illumination, and based on a detection signal corresponding to the second reflected light, a crack of a crack formed inside the work piece with the interface position as a reference. A crack detection step of detecting a depth.

  According to the present invention, the interfacial position of the workpiece is detected, and the crack depth is detected based on this interfacial position, thereby non-destructing the crack depth of the crack formed inside the workpiece. And it can be detected with high accuracy.

FIG. 1 is a block diagram showing a crack detection device according to the first embodiment of the present invention. FIG. 2 is a diagram showing a state when the workpiece is illuminated with the detection light in a partial direction. FIG. 3 is a diagram showing a state in which the object to be processed is subjected to the polarized illumination of the detection light. FIG. 4 is a diagram showing a state in which the workpiece is subjected to the polarized illumination of the detection light. FIG. 5 is a diagram showing a state of reflected light received by the photodetector. FIG. 6 is a diagram showing a state of reflected light received by the photodetector. FIG. 7 is a diagram showing a state of reflected light received by the photodetector. FIG. 8 is a diagram for explaining a path through which reflected light from the workpiece reaches the condenser lens pupil. FIG. 9 is a flowchart showing the crack detection method according to the first embodiment of the present invention. FIG. 10: is a block diagram which shows the crack detection apparatus which concerns on the 2nd Embodiment of this invention. FIG. 11 is a flowchart showing a crack detection method according to the second embodiment of the present invention.

  Embodiments of a crack detection device and method according to the present invention will be described below with reference to the accompanying drawings.

[First Embodiment]
First, a first embodiment of the present invention will be described. FIG. 1 is a block diagram showing a crack detection device according to the first embodiment of the present invention.

  The crack detecting apparatus 10 according to the present embodiment is formed inside the workpiece W by irradiating the workpiece W with the detection light L1 and detecting the reflected light L2 from the workpiece W. The crack depth of the crack K is detected. Note that the crack detection device 10 is used in combination with a laser dicing device (not shown) that forms a modified region inside the workpiece W, but in the following description, components related to the crack detection device 10 will be described. The description will be omitted for the configuration of the laser dicing device.

  In the following description, the stage 510 on which the workpiece W is placed is a plane parallel to the XY plane, and a three-dimensional orthogonal coordinate system in which the Z direction is the thickness direction of the workpiece 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, a focus adjustment mechanism 502, and It includes a condenser lens 504, an operation unit 506, and a display unit 508.

  The light source unit 100 emits detection light L1 used for detecting the interface of the workpiece W and detecting the crack K formed inside the workpiece W. Here, when the workpiece W is a silicon wafer, it is desirable to use infrared light having a wavelength of 1060 nm or more as the detection light L1.

  The light source unit 100 includes a light source 102, a collimator lens 104, and a limiting member 106. The light source 102, the collimator lens 104, and the limiting member 106 are arranged along the main optical axis AX that is coaxial with the lens optical axis of the condenser lens 504.

  The light source 102 emits the detection light L1 along the main optical axis AX. As the light source 102, for example, an LD (Laser Diode) light source can be used. The light source 102 is connected to the control unit 500, and the control unit 500 controls emission of the light source 102.

  The collimator lens 104 adjusts the detection light L1 emitted from the light source 102 to be parallel light.

  An opening 106A is formed in the limiting member 106. The limiting member 106 is a light blocking member that blocks a part of the detection light L1 from the collimator lens 104. The limiting member 106 can be moved in and out of the optical path of the detection light L1 by a drive mechanism (not shown). The control unit 500 controls an actuator (not shown) to control whether the limiting member 106 appears or disappears. When the crack K is detected by the crack detecting optical system 400, the limiting member 106 blocks a part of the detection light L1 and decenters the detection light L1 with respect to the main optical axis AX. The limiting member 106 will be described later.

  The illumination optical system 200 guides the detection light L1 emitted from the light source unit 100 to the condenser lens 504. The illumination optical system 200 includes relay lenses 202 and 206 and a mirror 204. The detection light L1 emitted from the light source unit 100 passes through the relay lens 202, is reflected by the mirror 204, and the optical path is bent. Here, as the mirror 204, for example, a dichroic mirror that selectively reflects infrared light having a wavelength of 1060 nm or more and transmits light in other wavelength bands can be used. The detection light L1 reflected by the mirror 204 passes through the relay lens 206 and is emitted toward the condenser lens 504.

  The condenser lens 504 condenses (focuses) the detection light L1 emitted from the illumination optical system 200 onto the workpiece W. The condenser lens 504 is arranged at a position facing the workpiece W, and is arranged coaxially with the main optical axis AX.

  The focus adjustment mechanism 502 adjusts the focus position of the detection light L1 on the workpiece W. The focus adjustment mechanism 502 includes a drive unit that moves at least one of the condenser lens 504 and the stage 510 on which the workpiece W is placed. The focus adjustment mechanism 502 can move the focus position of the detection light L1 in the XYZ directions by adjusting the relative position between the focus lens 504 and the stage 510 in the XYZ directions.

  The reflected light L2 collected by the condenser lens 504 and reflected by the workpiece W is guided to the interface detection optical system 300 and the crack detection optical system 400, and the interface detection and the crack detection optical system 400, respectively. Used to detect cracks.

  The control unit 500 includes a CPU (Central Processing Unit) that controls the operation of each unit of the crack detection device 10, a ROM (Read Only Memory) that stores a control program, and an SDRAM (Synchronous Dynamic Random Access) that can be used as a work area of the CPU. Memory) is included. The control unit 500 receives an operation input by an operator via the operation unit 506 (for example, a keyboard and a pointing device such as a mouse and a touch panel) and transmits a control signal corresponding to the operation input to each unit of the crack detection device 10. Control the operation of each part.

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

(Optical system for interface detection)
Next, the interface detection of the workpiece W will be described. In the following description, the case where the interface of the back surface of the workpiece W (the surface in contact with the stage 510) is detected and the crack depth is detected with the interface position of the back surface of the workpiece W as a reference will be described. In the crack depth detection, the surface of the workpiece W may be used as a reference, or the average of the crack depths detected with reference to both the front and back surfaces of the workpiece W may be used. Is.

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

  When detecting the interface of the workpiece W, the control unit 500 irradiates the workpiece W with the detection light L1 with the limiting member 106 retracted from the optical path of the detection light L1. Here, the control unit 500 and the interface detection optical system 300 each function as a part of interface detection means.

  The half mirror 302 transmits the detection light L1 from the illumination optical system 200 to the condenser lens 504 side and reflects the reflection light L2 (first reflection light) from the workpiece W. The reflected light L2 from the workpiece W is reflected by the half mirror 302, the optical path is bent, and is guided to the relay lens 304. The reflected light L2 that has passed through the relay lens 304 is reflected by the half mirror 306 and guided to the photodetector 308.

  The photodetector 308 is a device for receiving the reflected light L2 from the workpiece W and detecting the interface of the workpiece W, and includes a detector main body 308A and a pinhole panel 308B.

  As the detector main body 308A, a photodetector (for example, a photodiode) that converts received light into an electric signal and outputs the electric signal to the control unit 500 can be used.

  The pinhole panel 308B is formed with pinholes for passing a part of incident light. The pinhole panel 308B is arranged on the light receiving surface side of the detector body 308A so that the pinhole is on the optical axis of the reflected light L2.

  The interface detection optical system 300 is an optical system in which the position of the pinhole of the pinhole panel 308B is optically conjugate with the position of the condensing point of the condensing lens 504.

  The controller 500 moves the condensing lens 504 and the stage 510 relatively in the Z direction while retracting the limiting member 106 from the optical path of the detection light L1 and irradiating the workpiece W with the detection light L1. The control unit 500 detects the reflected light L2 when the detection light L1 is focused on the interface (front surface or back surface) of the workpiece W, and detects the Z of the interface of the workpiece W from the position of the converging point at that time. Calculate the directional position.

(Optical system for crack detection)
Next, the detection of the crack K formed inside the workpiece W will be described.

  The crack detection optical system 400 includes a relay lens 402, a half mirror 404, and photodetectors 406 and 408.

  When detecting the crack K formed inside the workpiece W, the control unit 500 inserts the limiting member 106 into the optical path of the detection light L1. Here, the control unit 500, the limiting member 106, and the crack detection optical system 400 each function as a part of a crack detection unit. The limiting member 106 is provided with an opening 106A at a position deviated from the main optical axis AX, and light of the detection light L1 that has passed through the opening 106A is applied to the workpiece W. Thereby, the workpiece W is irradiated with the detection light L1 that is decentered with respect to the main optical axis AX.

  The reflected light L2 (second reflected light) from the workpiece W is reflected by the half mirror 302, then sequentially passes through the relay lens 304 and the half mirror 306, and enters the relay lens 402. The reflected light L2 that has passed through the relay lens 402 is received by the photodetectors 406 and 408 via the half mirror 404. Here, the transmittance and the reflectance of the light incident on the half mirror 404 are each about 50%.

  The photodetectors 406 and 408 are devices for receiving the reflected light L2 from the workpiece W and detecting the crack K inside the workpiece W. The photodetector 406 includes a detector body 406A and a pinhole panel 406B, and the photodetector 408 includes a detector body 408A and a pinhole panel 408B.

  As the detector bodies 406A and 408A, photodetectors (for example, photodiodes) that convert the received light into an electric signal and output the electric signal to the control unit 500 can be used.

  Pinhole panels 406B and 408B are provided with pinholes for passing a part of incident light. The pinhole panels 406B and 408B are arranged on the light receiving surface sides of the detector bodies 406A and 408A, respectively. The pinhole panels 406B and 408B are arranged so that the pinholes are displaced from the optical axis of the reflected light L2.

  2 to 4 are explanatory diagrams showing a state when the workpiece W is subjected to the polarized illumination of the detection light L1. 2 shows the case where the crack K exists at the condensing point of the condensing lens 504, FIG. 3 shows the case where the crack K does not exist at the condensing point of the condensing lens 504, and FIG. 4 shows the condensing point of the condensing lens 504. The case where the crack depth of crack K (the crack lower end position) corresponds is shown, respectively. FIGS. 5 to 7 are diagrams showing the state of the reflected light L2 received by the photodetectors 406 and 408, and correspond to the cases shown in FIGS. 2 to 4, respectively. FIG. 8 is a diagram for explaining the path of the reflected light L2 from the workpiece W reaching the condenser lens pupil 504a. Note that, 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 condenser lens pupil 504a and the incident illumination is performed on the workpiece W will be described. To do.

  As shown in FIG. 2, when the crack K exists at the condensing point of the condenser lens 504, the detection light L1 is totally reflected by the crack K, and the reflected light L2 is detected with respect to the main optical axis AX. It becomes a component that follows the path on the same side as the optical path of the light L1 and reaches the region on the same side as the detection light L1 of the condenser lens pupil 504a. That is, as shown in FIG. 8, when the path of the detection light L1 when the detection light L1 from the light source 102 is applied to the work W through the condenser lens 504 is R1, the work W The reflected light L2 totally reflected by the internal crack K follows a path R2 on the same side (right side in FIG. 8) as the path R1 of the detection light L1 with respect to the main optical axis AX, and reaches the first position of the condenser lens pupil 504a. It passes through the area G1.

  As shown in FIG. 3, when the crack K does not exist at the focal point of the condenser lens 504, the detection light L1 is reflected on the back surface of the workpiece W, and the reflected light L2 is reflected by the condenser lens pupil 504a. It is a component that reaches the area on the opposite side of the detection light L1. That is, as shown in FIG. 8, the reflected light L2 reflected on the back surface of the workpiece W travels along 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. Traces and passes through the second region G2 of the condenser lens pupil 504a.

  As shown in FIG. 4, when the focal point of the condenser lens 504 and the lower end position of the crack K coincide with each other, the detection light L1 is totally reflected by the crack K and is detected by the condenser lens pupil 504a. The reflected light component L2a reaching the region on the same side as the non-reflected light component L2a that is not totally reflected by the crack K but is reflected on the back surface of the workpiece W and reaches the region on the opposite side of the detection light L1 of the condenser lens pupil 504a. It is divided into a reflected light component L2b. That is, as shown in FIG. 8, the reflected light component L2a of the reflected light L2 that is totally reflected by the crack K inside the workpiece W is the same as the main optical axis AX with the path R1 of the detection light L1. The non-reflected light component L2b which passes through the first region G1 of the condenser lens pupil 504a along the path R2 on the side (the right side in FIG. 8) and is reflected by the back surface of the workpiece W without being totally reflected by the crack K. Passes through the second region G2 of the condenser lens pupil 504a following a path R3 on the opposite side (left side in FIG. 8) to the main optical axis AX of the path R1 of the detection light L1.

  The pinhole panels 406B and 408B are arranged such that the pinholes are at positions optically conjugate with the first region G1 and the second region G2 of the condenser lens pupil 504a. As a result, the detector body 406A and the detector body 408A can selectively receive light that has passed through the first region G1 and the second region G2 of the condenser lens pupil 504a, respectively.

  In the example shown in FIG. 2 (when the crack K exists at the condensing point of the condensing lens 504), as shown in FIG. 5, of the detector main body 406A and the detector main body 408A, the light receiving surface of the detector main body 406A. The reflected light L2 is received by 406C, and the level of the detection signal output from the light receiving surface 406C becomes higher than the level of the detection signal output from the light receiving surface 408C of the detector body 408A.

  On the other hand, in the example shown in FIG. 3 (when the crack K does not exist at the condensing point of the condensing lens 504), as shown in FIG. 6, of the detector main body 406A and the detector main body 408A, The reflected light is received by the light receiving surface 408C, and the level of the detection signal output from the light receiving surface 408C becomes higher than the level of the detection signal output from the light receiving surface 406C.

  Further, in the example shown in FIG. 4 (when the condensing point of the condensing lens 504 and the lower end position of the crack K coincide with each other), as shown in FIG. 8, each component L2a of the reflected light L2 is reflected on the light receiving surfaces 406C and 408C. , L2b respectively receive the light and the levels of the detection signals output from the light receiving surfaces 406C and 408C become substantially equal.

  As described above, the amount of light received by the light-receiving surfaces 406C and 408C changes depending on whether or not the crack K exists at the condensing point of the condensing lens 504. In this embodiment, the crack depth (the crack lower end position or the crack upper end position) of the crack K formed inside the workpiece W can be detected by utilizing such a property.

  Specifically, when the outputs of the detection signals output from the light receiving surfaces 406C and 408C are D1 and D2, respectively, the evaluation value S indicating the relationship between the focal point of the condenser lens 504 and the crack depth of the crack K is , Can be expressed by the following equation.

S = (D1-D2) / (D1 + D2) (1)
In the formula (1), when the condition of S = 0 is satisfied, that is, when the light amounts received by the light receiving surfaces 406C and 408C match, the converging point of the condenser lens 504 and the crack lower end position (or the crack upper end position). Indicates that the and match.

  The control unit 500 controls the focus adjusting mechanism 502 (focusing point changing unit) to move the focusing point of the focusing lens 504 from the back surface interface position Z (0) to the thickness direction (Z) of the workpiece W. Direction)), the detection signals output from the light receiving surfaces 406C and 408C are sequentially acquired, the evaluation value S represented by the equation (1) is calculated based on the detection signals, and the evaluation value S is evaluated. By doing so, the crack depth of the crack K (the crack lower end position or the crack upper end position) can be detected.

  In this embodiment, photodetectors are used as the detector bodies 308A, 406A, and 408A, but the present invention is not limited to this. For example, an infrared camera or the like may be used instead of the photo detector.

  When detecting the crack K, the half mirror 306 may be retracted from the optical path of the reflected light L2. In this case, the half mirror 306 of the interface detection optical system 300 may be replaced with a total reflection mirror or a dichroic mirror.

  Further, in the present embodiment, the transmittance and the reflectance of the light incident on the half mirror 404 are each set to about 50%, but the present invention is not limited to this. When the transmittance and the reflectance of the half mirror 404 are different, when calculating the evaluation value S, the outputs D1 and D2 of the detection signals from the photodetectors 406 and 408 are determined according to the transmittance and the reflectance of the half mirror 404. It may be multiplied by a weighting factor.

(Crack detection method)
Next, the crack detection method according to this embodiment will be described with reference to FIG. FIG. 9 is a flowchart showing the crack detection method according to the first embodiment of the present invention.

  First, the control unit 500 irradiates the workpiece W with the detection light L1 with the limiting member 106 retracted from the optical path of the detection light L1. Then, the control unit 500 detects the reflected light L2 from the workpiece W by the photodetector 308, and based on the detection signal from the photodetector 308, the interface position Z (0) of the back surface of the workpiece W. ) Is detected (step S10: interface detection step).

  Next, in steps S12 to S26 (crack detection step), the depth of the crack inside the workpiece W is detected. The controller 500 sets i = 1 (step S12), and moves the condensing position of the condensing lens to the inside of the workpiece W (+ Z side in FIG. 1) by dZ (step S14). At this time, Z (i) = Z (i-1) + dZ.

  Next, the control unit 500 inserts the limiting member 106 on the optical path of the detection light L1 and illuminates the workpiece W with the detection light L1 decentered with respect to the main optical axis AX (step S16). Then, the detection signals D1 and D2 are obtained from the photodetectors 406 and 408 (step S18), and the evaluation value S is calculated by the equation (1) (step S20).

  Next, the control unit 500 sets i = i + 1 (step S24) and repeats steps S14 to S24 until i = n (Yes in step S22). Here, n is a parameter determined based on the thickness T of the workpiece W and dZ, and is, for example, an integer satisfying the condition of n ≧ T / dZ−1. As a result, the evaluation value S (i) for each condensing position Z (i) is calculated.

  Next, when i = n (Yes in step S22), the control unit 500 determines the depth position of the crack K, that is, the crack K, based on the evaluation value S (i) for each condensing position Z (i). The distances from the back surface of the workpiece W at the lower end position and the upper end position are calculated (step S26). For example, when the control unit 500 sequentially moves the condensing position of the condensing lens 504 from the interface position Z (0) on the back surface of the workpiece W, the position Z where S (i) = 0 is first obtained. (I) is detected as the lower end position of the crack K, and then the position Z (i) where S (i) = 0 is detected as the upper end position of the crack K. Further, when there is no position where S (i) = 0, the control unit 500 positions Z (i-1) and Z (i) at which the sign of S (i) is reversed and the evaluation value at that position. The Z coordinate of the position where S = 0 may be obtained from S (i-1) and S (i) by interpolation. The depth position of the crack K calculated in step S26 is displayed on the display unit 508 and stored in the storage device provided in the control unit 500.

  According to this embodiment, the crack depth of the crack K formed inside the workpiece W can be detected nondestructively and accurately. Further, according to the present embodiment, it is possible to detect the absolute position of the interface of the wafer that is the workpiece W and detect the crack depth with the interface as a reference. As a result, for example, when a mechanical error occurs in the position control of the stage 510 or the like by the control unit 500, or when an adhered matter such as a back grind tape is present, the position of the interface of the wafer is accurately determined from the position of the stage 510 or the like. Even if it is difficult to obtain the crack depth, it is possible to accurately detect the crack depth.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, when performing crack detection, the method of oblique illumination (hereinafter, also referred to as an illumination method) is switched, the crack depth is detected a plurality of times, and the average value of the detection results of the plurality of times is calculated. Calculate as crack depth. Here, switching the illumination method means switching the mode of eccentricity of the detection light L1 (for example, the distance and position between the opening and the main optical axis from which the detection light L1 is emitted).

  FIG. 10: is a block diagram which shows the crack detection apparatus which concerns on the 2nd Embodiment of this invention. In the following description, the same components as those in the first embodiment will be designated by the same reference numerals and description thereof will be omitted.

  As shown in FIG. 10, the crack detection device 10A according to the present embodiment includes a limiting member 108 instead of the limiting member 106.

  The restricting member 108 has openings 108A and 108B that can be opened and closed, respectively. In the present embodiment, when the object W is subjected to the polarized illumination, the mode of eccentricity of the detection light L1 is changed by opening either one of the openings 108A and 108B of the limiting member 108.

  Next, the crack detection method according to this embodiment will be described with reference to FIG. FIG. 11 is a flowchart showing a crack detection method according to the second embodiment of the present invention.

  First, the control unit 500 irradiates the workpiece W with the detection light L1 with the limiting member 106 retracted from the optical path of the detection light L1. Then, the control unit 500 detects the reflected light L2 from the workpiece W by the photodetector 308, and based on the detection signal from the photodetector 308, the interface position Z (0) of the back surface of the workpiece W. ) Is detected (step S30: interface detection step).

  Next, the control unit 500 sets k = 1 (step S32) and sets the illumination method k (k = 1) (step S34). Here, the illumination method 1 is a method of opening the opening 108A of the limiting member 108 to perform the partial illumination, and the illumination method 2 is a method of opening the opening 108B of the limiting member 108 to perform the partial illumination. To do.

  Next, the control unit 500 detects the crack depth under the illumination method 1 as in the first embodiment (steps S36 to S50: crack detection step). Since steps S36 to S50 are the same as steps S12 to S26 of FIG. 9, description thereof will be omitted.

  Next, the control unit 500 switches the lighting method to the lighting method 2 (No in step S52, steps S54 and S34). Then, the control unit 500 moves the position of the condensing point of the condensing lens 504 to the interface position Z (0) on the back surface of the workpiece W, and detects the crack depth under the illumination method 2 (step). From S36 to step S50).

  Next, the control unit 500 calculates the average value of the crack depths calculated under each lighting method (step S56). The depth position of the crack K calculated in step S56 is displayed on the display unit 508 and stored in the storage device provided in the control unit 500.

  According to the present embodiment, even if the alignment accuracy between the condenser lens 504 and the workpiece W is not sufficient by switching the method of oblique illumination and detecting the crack depth and using the average value of the results. The crack depth of the crack K formed inside the workpiece W can be detected accurately and stably.

  In this embodiment, the two openings 108A and 108B that can be opened and closed are provided, but the configuration for the polarized illumination is not limited to the above. For example, three or more openings may be formed in the limiting member 108, and the method of polarized illumination may be three or more. Further, for example, the limiting member may be provided with only one opening, and the limiting member may be rotated around the main optical axis AX to change the method of the polarized illumination.

  Further, in each of the above-described embodiments, the partial illumination is performed by blocking a part of the detection light L1 using the limiting member 106, but the present invention is not limited to this. For example, the oblique illumination may be performed by arranging the light source 102 of the light source unit 100 so as to be displaced from the main optical axis AX. In this case, the optical axis of the light source 102 is preferably parallel to the main optical axis AX. Further, in the second embodiment, the light sources 102 may be provided at a plurality of positions deviated from the main optical axis AX.

  Further, in each of the above-described embodiments, the crack detecting optical system 400 is provided with two photodetectors, but the present invention is not limited to this. For example, instead of the half mirror 404 and the photodetectors 406 and 408, one split photodetector whose light receiving surface is divided into two may be provided, and the evaluation value S may be calculated from the output of each light receiving surface. Moreover, you may use the photodetector whose light-receiving surface is divided into the number according to the kind of illumination method.

  Further, the configuration for guiding the detection light L1 and the reflected light L2 is merely an example, and the present invention is not limited to the above embodiments. For example, without providing the mirror 204, the light source 102, the condenser lens 504, and the stage 510 on which the workpiece W is placed can be arranged in a straight line.

  10, 10A ... Crack detection device, 100 ... Light source part, 102 ... Light source, 104 ... Collimating lens, 106, 108 ... Limiting member, 200 ... Illumination optical system, 202 ... Relay lens, 204 ... Mirror, 206 ... Relay lens, 300 ... optical system for interface detection, 302 ... half mirror, 304 ... relay lens, 306 ... half mirror, 308 ... photodetector, 400 ... optical system for crack detection, 402 ... relay lens, 404 ... half mirror, 406, 408 ... Photodetector, 500 ... Control unit, 502 ... Focus adjustment mechanism, 504 ... Condensing lens, 506 ... Operation unit, 508 ... Display unit

Claims (6)

A light source unit that emits detection light along the main optical axis,
A condensing lens that has a lens optical axis coaxial with the main optical axis, and condenses the detection light emitted from the light source unit on a workpiece.
Detecting the first reflected light from the workpiece by irradiating the workpiece with the detection light emitted along the main optical axis, based on a detection signal corresponding to the first reflected light, Interface detection means for detecting an interface position indicating the front surface or the back surface of the workpiece,
The workpiece is eccentrically illuminated by the detection light decentered from the main optical axis to detect the second reflected light from the workpiece, and based on the detection signal corresponding to the second reflected light, Crack detection means for detecting the crack depth of the crack formed inside the workpiece on the basis of the interface position,
A crack detection device comprising. The interface detection means,
A photodetector having a light receiving surface for receiving the first reflected light;
A pinhole panel disposed on the light-receiving surface side for blocking a part of the first reflected light incident on the light-receiving surface,
The pinhole formed in the pinhole panel is arranged so as to have an optically conjugate relationship with the position of the condensing point of the condensing lens,
The interface detecting means detects the interface position based on the first reflected light that has passed through the pinhole.
The crack detection device according to claim 1. A condensing point changing means for changing the condensing point of the condensing lens in the thickness direction of the workpiece,
The crack detection means is a crack depth of the crack based on a change in the detection signal when the condensing point of the condensing lens is changed in the thickness direction of the workpiece by the condensing point changing means. To detect,
The crack detection device according to claim 1. The light source unit has an opening and includes a limiting member that shields a part of the detection light.
By locating the opening at a position decentered from the light source optical axis of the light source unit, the detection light is decentered with respect to the main optical axis.
The crack detection device according to any one of claims 1 to 3. The crack detecting means detects the crack depth a plurality of times by switching the method of oblique illumination of the detection light, and calculates an average value of the detection results of the crack depth of the plurality of times.
The crack detection device according to any one of claims 1 to 4. The workpiece is irradiated with the detection light emitted from the light source unit along the main optical axis to detect the first reflected light from the workpiece, and based on the detection signal corresponding to the first reflected light. An interface detection step of detecting an interface position indicating the front surface or the back surface of the workpiece,
Corresponding to the second reflected light by detecting the second reflected light from the workpiece by irradiating the workpiece with the detection light emitted from the light source unit and decentered from the main optical axis. Based on the detection signal to do, a crack detection step of detecting the crack depth of the crack formed inside the workpiece with reference to the interface position,
A crack detection method comprising:

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