JP7212833B2 - Crack detection device and method - Google Patents

Description

The present invention relates to a crack detection device and method, and more particularly to a crack detection device and method for detecting cracks formed inside a workpiece.

Conventionally, a substrate such as a silicon wafer or a glass wafer (hereinafter referred to as "workpiece") is irradiated with a laser beam along a planned cutting line with a focal point aligned inside, and the work piece is cut along the processing line. There is known a laser processing apparatus (also referred to as a laser dicing apparatus) that forms a modified region that serves as a starting point for cutting in the interior of the substrate. The workpiece on which the modified region is formed is then split along the planned cutting line by a splitting process such as expanding or breaking into individual chips.

By the way, when a modified region is formed in a workpiece by a laser processing apparatus, cracks extend from the modified region in the thickness direction of the workpiece. If the crack reaches the front surface (laser light incident surface) or the opposite back surface of the workpiece, it can be properly divided into chips in the cutting process. The reason for this is that the crack formed inside the workpiece serves as a starting point for dividing the workpiece, so the degree of extension of the crack determines the division rate of the workpiece. In addition, in the case of a thick workpiece, cracks may not reach the front or back surface of the workpiece. In some cases, it may not be possible to properly determine whether or not the

Therefore, after the modified region is formed by the laser processing apparatus and before the cutting process, whether or not the modified region that serves as the starting point for dividing the workpiece is properly formed. By detecting the crack depth of the cracks that have formed, it is possible to accurately predict the success or failure of splitting into chips in the breaking process. Then, if there is a portion where the modified region is not properly formed inside the workpiece, there are countermeasures such as reprocessing only that portion again with a laser processing device or changing the cutting method in the cutting process. It becomes possible. This eliminates chip loss in the subsequent breaking process. In addition, it is also possible to modify the processing conditions in the laser processing apparatus with reference to the occurrence of defective portions, etc., and 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 loss of time required for reprocessing can be reduced by reducing the number of defective portions.

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

In response to this, a technique for non-destructively inspecting cracks formed inside a workpiece has been proposed (see, for example, Patent Literature 1).

In the technique disclosed in Patent Document 1, light is incident from one side of a crack, light transmitted through a region containing the crack is detected, and crack inspection is performed using a decrease in the amount of detected light due to scattering of the crack. .

JP 2008-222517 A

However, in the technique disclosed in Patent Literature 1, the signal level of the light receiver does not directly indicate the crack depth, but is treated as a threshold value. Therefore, it was necessary to conduct an experiment in advance and set a threshold value. Moreover, 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 experiment. In addition, since the crack head position is confirmed using only the decrease in transmitted light (light that has passed through the region containing the crack), there is a limit to improving the detection accuracy of the crack depth of the crack.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a crack detection apparatus and method capable of non-destructively and accurately detecting the 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 has a light source unit for emitting detection light along a main optical axis, and a lens optical axis coaxial with the main optical axis. a condensing lens for condensing the detection light emitted from the part onto the workpiece; and the detection light emitted along the main optical axis is irradiated onto the workpiece to detect the first reflected light from the workpiece. and an interface detecting means for detecting the interface position indicating the front surface or the back surface of the workpiece based on the detection signal corresponding to the first reflected light, and polarizing illumination of the workpiece using 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, detect the crack depth of the crack formed inside the workpiece with reference to the interface position. and a crack detection means.

According to the first aspect, by detecting the interface position of the workpiece and detecting the crack depth based on this interface position, the crack depth of the crack formed inside the workpiece is determined. It can be detected non-destructively and accurately.

In the crack detection device according to a second aspect of the present invention, in the first aspect, the interface detection means includes a photodetector having a light receiving surface for receiving the first reflected light, and a photodetector disposed on the light receiving surface side to receive the light. and a pinhole panel for shielding part of the first reflected light incident on the surface, and the pinhole formed in the pinhole panel is optically conjugate with the position of the condensing point of the condensing lens. and the interface detection means detects the position of the interface 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 detection device according to a third aspect of the present invention is, in the first or second aspect, provided with a condensing point changing means for changing the condensing point of the condensing lens in the thickness direction of the workpiece, The detecting means detects the crack depth of the crack based on the 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. is.

A crack detection device according to a fourth aspect of the present invention is a crack detection device according to any one of the first to third aspects, wherein the light source unit is a limiting member having an opening, the limiting member blocking part of the detection light. , and by locating the opening at a position eccentric from the light source optical axis of the light source unit, the detection light is eccentric with respect to the main optical axis.

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

In a crack detection device according to a fifth aspect of the present invention, in any one of the first to fourth aspects, the crack detection means detects the crack depth a plurality of times by switching the polarized illumination method of the detection light. , to calculate the average value of the detection results of the crack depth a plurality of times.

According to the fifth aspect, by switching the polarized illumination method to detect the crack depth and using the average value of the results, even if the alignment accuracy between the condenser lens and the workpiece is not sufficient, 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 includes irradiating a workpiece with detection light emitted from a light source along a main optical axis to detect a first reflected light from the workpiece, an interface detection step of detecting the interface position indicating the front surface or the back surface of the workpiece based on the detection signal corresponding to the first reflected light; to detect the second reflected light from the workpiece, and based on the detection signal corresponding to the second reflected light, the crack of the crack formed inside the workpiece with reference to the interface position and a crack detection step for detecting depth.

According to the present invention, by detecting the interface position of the workpiece and detecting the crack depth based on this interface position, the crack depth of the crack formed inside the workpiece can be measured in a non-destructive manner. Moreover, it can be detected with high accuracy.

FIG. 1 is a block diagram showing a crack detection device according to a first embodiment of the invention. FIG. 2 is a diagram showing a state when a workpiece is illuminated with polarized detection light. FIG. 3 is a diagram showing a state when polarized illumination of the detection light is performed on the workpiece. FIG. 4 is a diagram showing a state when polarized illumination of the detection light is performed on the workpiece. FIG. 5 is a diagram showing how reflected light is received by the photodetector. FIG. 6 is a diagram showing how reflected light is received by the photodetector. FIG. 7 is a diagram showing how reflected light is received by the photodetector. FIG. 8 is a diagram for explaining a path along which reflected light from a workpiece reaches a condenser lens pupil. FIG. 9 is a flow chart showing a crack detection method according to the first embodiment of the invention. FIG. 10 is a block diagram showing a crack detection device according to a second embodiment of the invention. FIG. 11 is a flow chart showing a crack detection method according to a second 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.

[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 a first embodiment of the invention.

The crack detection device 10 according to the present embodiment irradiates the workpiece W with the detection light L1 and detects the reflected light L2 from the workpiece W, so that the crack detection device 10 formed inside the workpiece W The crack depth of crack K is detected. 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. In the following description, the components of the crack detection device 10 , and the description of the configuration of the laser dicing apparatus is omitted.

In the following description, a three-dimensional orthogonal coordinate system in which the stage 510 on which the workpiece W is placed is a plane parallel to the XY plane and 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, It includes a condenser lens 504 , an operation section 506 and a display section 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. As shown in FIG. Here, when the workpiece W is a silicon wafer, it is desirable to use infrared light with a wavelength of 1060 nm or more as the detection light L1.

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

The light source 102 emits 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 so that it becomes parallel light.

The restricting member 106 is formed with an opening 106A. The limiting member 106 is a light blocking member that blocks part of the detection light L1 from the collimator lens 104 . The restricting member 106 can appear and disappear with respect to the optical path of the detection light L1 by a driving mechanism (not shown). The control unit 500 controls the appearance and retraction of the restricting member 106 by controlling an actuator (not shown). When the crack detection optical system 400 detects the crack K, the limiting member 106 shields part of the detection light L1 and decenters the detection light L1 with respect to the main optical axis AX. The restricting member 106 will be described later.

The illumination optical system 200 guides the detection light L1 emitted from the light source section 100 to the condenser lens 504 . Illumination optics 200 includes relay lenses 202 and 206 and mirror 204 . 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. Here, as the mirror 204, for example, a dichroic mirror that selectively reflects infrared light with 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 is transmitted through the relay lens 206 and emitted toward the condenser lens 504 .

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

The focus adjustment mechanism 502 adjusts the condensing position of the detection light L1 on the workpiece W. As shown in FIG. The focus adjustment mechanism 502 includes a driving section that moves at least one of a condenser lens 504 and a stage 510 on which the workpiece W is placed. The focus adjustment mechanism 502 adjusts the relative position in the XYZ directions between the condenser lens 504 and the stage 510, thereby moving the condensing position of the detection light L1 in the XYZ directions.

The reflected light L2 that is 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 to detect the interface of the workpiece W and the crack detection optical system 400, respectively. Used for crack detection.

The control unit 500 includes a CPU (Central Processing Unit) that controls the operation of each part of the crack detection device 10, a ROM (Read Only Memory) that stores a control program, and an SDRAM (Synchronous Dynamic Random Access Memory) that can be used as a work area for the CPU. Memory). The control unit 500 receives an operation input by an operator via an 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. to control the operation of each part.

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

(Interface detection optical system)
Next, 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 detecting the crack depth, the surface of the workpiece W may be used as a reference, or both the front and back surfaces of the workpiece W may be used as a reference to obtain the average value of the crack depths detected. 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 controller 500 irradiates the workpiece W with the detection light L1 while the limiting member 106 is retracted from the optical path of the detection light L1. Here, the controller 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 reflected light L2 from the workpiece W (first reflected light). The reflected light L2 from the workpiece W is reflected by the half mirror 302 to bend the optical path and is guided to the relay lens 304 . Reflected light L2 transmitted through relay lens 304 is reflected by half mirror 306 and guided to photodetector 308 .

The photodetector 308 is a device for receiving the reflected light L2 from the workpiece W to detect the interface of the workpiece W, and includes a detector 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.

A pinhole is formed in the pinhole panel 308B to allow part of the incident light to pass therethrough. The pinhole panel 308B is arranged on the light receiving surface side of the detector main 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 and the position of the condensing point of the condensing lens 504 are in an optically conjugate relationship.

The control unit 500 moves the condensing lens 504 and the stage 510 relatively in the Z direction while irradiating the workpiece W with the detection light L1 by retracting the limiting member 106 from the optical path of 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 Calculate the position of the direction.

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

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

When detecting a 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 crack detection means. The restricting member 106 is provided with an opening 106A at a position shifted from the main optical axis AX, and the workpiece W is irradiated with the light transmitted through the opening 106A out of the detection light L1. As a result, the workpiece W is irradiated with the detection light L1 decentered with respect to the main optical axis AX.

Reflected light L<b>2 (second reflected light) from the workpiece W is reflected by the half mirror 302 , sequentially passes through the relay lens 304 and the half mirror 306 , and enters the relay lens 402 . Reflected light L2 transmitted through relay lens 402 is received by photodetectors 406 and 408 via half mirror 404 . Here, the transmittance and reflectance of the light incident on the half mirror 404 are assumed to be approximately 50%, respectively.

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

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

Pinhole panels 406B and 408B are formed with pinholes for passing a portion of the incident light. Pinhole panels 406B and 408B are arranged on the light receiving surface side of detector bodies 406A and 408A, respectively. The pinhole panels 406B and 408B are arranged such that the pinholes are positioned off the optical axis of the reflected light L2.

FIGS. 2 to 4 are explanatory diagrams showing the state when the workpiece W is subjected to 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. Each of these shows a case where the crack depth (crack bottom position) of the crack K matches. 5 to 7 are diagrams showing states of the reflected light L2 received by the photodetectors 406 and 408, 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 workpiece W reaches the condenser lens pupil 504a. Here, a case will be described in which 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 workpiece W is subjected to polarized illumination. do.

As shown in FIG. 2, when there is a crack K 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 is a component that follows the path on the same side as the optical path of the light L1 and reaches the area on the same side as the detection light L1 of the condenser lens pupil 504a. That is, as shown in FIG. 8, when the detection light L1 from the light source 102 irradiates the workpiece W through the condenser lens 504, the path of the detection light L1 is R1. The reflected light L2 totally reflected by the internal crack K 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 travels to the first light of the condenser lens pupil 504a. It passes through area G1.

As shown in FIG. 3, when there is no crack K at the condensing point of the condensing lens 504, the detection light L1 is reflected by the back surface of the workpiece W, and the reflected light L2 is reflected by the condensing lens pupil 504a. It becomes 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 by the back surface of the workpiece W travels along a path R3 on the opposite side (the left side in FIG. 8) of the main optical axis AX from the path R1 of the detection light L1. It passes through the second region G2 of the condenser lens pupil 504a.

As shown in FIG. 4, when the condensing point of the condensing lens 504 and the lower end position of the crack K coincide, the detection light L1 is totally reflected by the crack K, and the detection light L1 of the condensing lens pupil 504a and a reflected light component L2a that reaches the area on the same side as the non-reflected light component L2a that is not totally reflected by the crack K and is reflected on the back surface of the workpiece W and reaches the area on the opposite side of the detection light L1 of the condenser lens pupil 504a. and the reflected light component L2b. 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 workpiece W is the same as the path R1 of the detection light L1 with respect to the main optical axis AX. The non-reflected light component L2b reflected on the back surface of the workpiece W without being totally reflected by the crack K while following the path R2 on the side (right side in FIG. 8) and passing through the first region G1 of the condenser lens pupil 504a. passes through the second region G2 of the condenser lens pupil 504a following the path R3 on the opposite side (left side in FIG. 8) with respect to the main optical axis AX from the path R1 of the detection light L1.

The pinhole panels 406B and 408B are arranged such that the pinholes are optically conjugate with the first region G1 and the second region G2 of the condenser lens pupil 504a, respectively. As a result, the detector main body 406A and the detector main 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 a crack K exists at the condensing point of the condensing lens 504), as shown in FIG. Reflected light L2 is received by 406C, and the level of the detection signal output from light receiving surface 406C becomes higher than the level of the detection signal output from light receiving surface 408C of detector body 408A.

On the other hand, in the example shown in FIG. 3 (when there is no crack K at the condensing point of the condensing lens 504), as shown in FIG. 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 coincides with the lower end position of the crack K), as shown in FIG. , and L2b respectively, and the levels of the detection signals output from the light receiving surfaces 406C and 408C become substantially equal.

Thus, the amount of light received by the light receiving surfaces 406C and 408C changes depending on whether or not there is a crack K at the condensing point of the condensing lens 504. FIG. In the present embodiment, using such properties, the crack depth (crack bottom position or crack top position) of the crack K formed inside the workpiece W can be detected.

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 that indicates the relationship between the condensing point of the condensing 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 equation (1), when the condition of S=0 is satisfied, that is, when the amounts of light received by the light receiving surfaces 406C and 408C are the same, the condensing point of the condenser lens 504 and the crack bottom end position (or crack top end position) indicates a match.

The control unit 500 controls the focus adjustment mechanism 502 (condensing point changing means) to change the condensing point of the condensing lens 504 from the interface position Z(0) on the back surface to the thickness direction of the workpiece W (Z direction), the detection signals output from the light-receiving surfaces 406C and 408C are sequentially acquired, and based on these detection signals, an evaluation value S represented by Equation (1) is calculated, and this evaluation value S is evaluated. By doing so, the crack depth of the crack K (crack bottom end position or crack top end position) can be detected.

In this embodiment, photodetectors are used as the detector main 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 photodetector.

Further, 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, a dichroic mirror, or the like.

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

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

First, the control unit 500 irradiates the workpiece W with the detection light L1 while the restricting member 106 is 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 ) is detected (step S10: interface detection step).

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

Next, the control unit 500 inserts the limiting member 106 into 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 acquired from the photodetectors 406 and 408 (step S18), and the evaluation value S is calculated by Equation (1) (step S20).

Next, the controller 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 an integer that satisfies the condition n≧T/dZ−1, for example. Thus, an 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 is calculated from the back surface of the workpiece W at the lower end position and the upper end position of (step S26). For example, when the condensing position of the condensing lens 504 is sequentially moved from the interface position Z(0) on the back surface of the workpiece W, the control unit 500 controls the position Z where S(i)=0 first. (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. FIG. Further, if there is no position where S(i)=0, the control unit 500 controls positions Z(i−1) and Z(i) where the sign of S(i) is inverted, and an evaluation value at that position. From S(i−1) and S(i), the Z coordinate of the position where S=0 may be obtained 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. FIG.

According to this embodiment, the crack depth of the crack K formed inside the workpiece W can be detected non-destructively and accurately. Further, according to this embodiment, it is possible to detect the absolute position of the interface of the wafer, which is the workpiece W, and detect the crack depth with reference to the interface. 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 there is an adherent such as a back grind tape, the position of the interface of the wafer can be accurately shifted from the position of the stage 510 or the like. Even if it is difficult to obtain, it is possible to accurately detect the crack depth.

[Second embodiment]
Next, a second embodiment of the invention will be described with reference to FIGS. 10 and 11. FIG. In the present embodiment, when performing crack detection, the method of oblique illumination (hereinafter also referred to as 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. Calculated as crack depth. Here, switching the illumination method means switching the eccentricity of the detection light L1 (for example, the distance and position between the opening through which the detection light L1 is emitted and the main optical axis).

FIG. 10 is a block diagram showing a crack detection device according to a second embodiment of the invention. In addition, in the following description, the same reference numerals are given to the same configurations as in the first embodiment, and the description thereof is omitted.

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

Openings 108A and 108B that can be opened and closed are formed in the restricting member 108, respectively. In the present embodiment, when the workpiece W is subjected to polarized illumination, one of the openings 108A and 108B of the limiting member 108 is opened to change the eccentricity of the detection light L1.

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

First, the control unit 500 irradiates the workpiece W with the detection light L1 while the restricting member 106 is 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 ) is detected (step S30: interface detection step).

Next, the controller 500 sets k=1 (step S32) and sets the lighting method k (k=1) (step S34). Here, the illumination method 1 is a method of performing polarized illumination by opening the opening 108A of the limiting member 108, and the illumination method 2 is a method of performing polarized illumination by opening the opening 108B of the limiting member 108. do.

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

Next, the control unit 500 switches the illumination method to illumination 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 S36 to step S50).

Next, the control unit 500 calculates the average value of crack depths calculated under each illumination 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. FIG.

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

Although two openings 108A and 108B that can be opened and closed are provided in this embodiment, the configuration for polarized illumination is not limited to the above. For example, three or more openings may be formed in the restricting member 108 to provide three or more oblique illumination methods. Also, for example, the limiting member may have only one opening, and the polarized illumination method may be changed by rotating the limiting member around the main optical axis AX.

Further, in each of the above-described embodiments, the limiting member 106 is used to block part of the detection light L1 for polarized illumination, but the present invention is not limited to this. For example, polarized illumination may be performed by displacing the light source 102 of the light source unit 100 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. Also, in the second embodiment, the light sources 102 may be provided at a plurality of positions shifted from the main optical axis AX.

In each of the above-described embodiments, two photodetectors are provided in the crack detection optical system 400, 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. Also, a photodetector having a light receiving surface divided into a number corresponding to the type of illumination method may be used.

Also, the configuration for guiding the detection light L1 and the reflected light L2 is merely an example, and 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.

DESCRIPTION OF SYMBOLS 10, 10A... Crack detection apparatus 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 Interface detection optical system 302 Half mirror 304 Relay lens 306 Half mirror 308 Photodetector 400 Crack detection optical system 402 Relay lens 404 Half mirror 406, 408 Photodetector 500 Control unit 502 Focus adjustment mechanism 504 Collecting lens 506 Operation unit 508 Display unit

Claims (6)

a light source unit that emits detection light along a main optical axis;
a condensing lens having a lens optical axis coaxial with the main optical axis and condensing the detection light emitted from the light source unit onto a workpiece;
irradiating the workpiece with detection light emitted along the main optical axis to detect a first reflected light from the workpiece; 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;
detecting second reflected light from the workpiece by illuminating the workpiece with detection light decentered from the main optical axis; crack detection means for detecting a crack depth of a crack formed inside the workpiece with reference to the interface position;
A crack detection device comprising: The interface detection means is
a photodetector having a light receiving surface that receives the first reflected light;
a pinhole panel arranged on the light receiving surface side and shielding part of the first reflected light incident on the light receiving surface;
The pinholes formed in the pinhole panel are arranged so as to be in an optically conjugate relationship with the position of the condensing point of the condensing lens,
The interface detection means detects the interface position based on the first reflected light that has passed through the pinhole.
A crack detection device according to claim 1. Condensing point changing means for changing the condensing point of the condensing lens in the thickness direction of the workpiece,
The crack detection means detects the crack depth of the crack based on the 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
The crack detection device according to claim 1 or 2. The light source unit has an opening and includes a limiting member that blocks part of the detection light,
The detection light is decentered with respect to the main optical axis by positioning the opening at a position decentered from the light source optical axis of the light source unit;
A crack detection device according to any one of claims 1 to 3. The crack detection means detects the crack depth multiple times by switching the method of polarized illumination of the detection light, and calculates the average value of the detection results of the multiple crack depths.
A crack detection device according to any one of claims 1 to 4. detecting the first reflected light from the workpiece by irradiating the workpiece with the detection light emitted along the main optical axis from the light source, and detecting the first reflected light from the workpiece, 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;
A second reflected light from the workpiece is detected by detecting the second reflected light from the workpiece by polarizing illumination of the workpiece with detection light that is emitted from the light source unit and decentered from the main optical axis, and corresponds to the second reflected light. a crack detection step of detecting a crack depth of a crack formed inside the workpiece with reference to the interface position based on the detection signal;
A crack detection method comprising:

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