Crack measuring instrument

Abstract

This crack measuring instrument is for detecting a crack generated inside a workpiece, and comprises: a light source unit that emits detection light along a light source optical axis which is parallel to a main optical axis and is eccentric with respect to the main optical axis; a condenser lens that condenses the detection light emitted from the light source unit within the workpiece; a condensing point changing unit that changes the condensing point of the condenser lens in the thickness direction of the workpiece; a bifurcation unit that is disposed at a position conjugate with the condensing point of the condenser lens and bifurcates light passing through a specific region; a detector that detects one of light components, of the detection light, that have been bifurcated by the bifurcation unit after the detection light is reflected at the interface of the workpiece, and that outputs a detection signal on the basis of the detection result; and a control unit that detects the position of the interface and the depth of the crack on the basis of the position of the condensing point of the condenser lens and the detection signal.

Description

Crack Measuring Instrument

[0001] This application claims priority to Japanese Patent Application No. 2024-055379, filed on March 29, 2024, the contents of which are incorporated herein by reference.

[0002] Conventionally, laser processing devices have been known that focus light inside a substrate (hereinafter also referred to as "workpiece") such as a silicon wafer or a glass wafer, irradiate the laser light along a planned cutting line, and form a laser processing area that serves as a starting point for cutting inside the workpiece along the planned cutting line. When the laser processing area is formed inside the workpiece by the laser processing device, a crack is generated from the laser processing area in the thickness direction of the workpiece.

[0003] Crack measuring devices that are attached to a laser processing device and measure cracks generated inside a workpiece are known. For example, a crack measuring device such as that disclosed in Patent Document 1 is known. The crack measuring device measures the interfaces (front and back surfaces) of the workpiece as a preliminary measurement for the crack measuring device.

[0004] Japanese Patent Application Publication No. 2017-133997

[0005] In the conventional technology, the interface measurement and the crack measurement are performed sequentially, which results in a long measurement time from the preliminary interface measurement to the completion of the crack measurement.

[0006] An object of the present invention is to provide a crack measuring instrument that can shorten the measurement time from the preliminary measurement of the interface to the completion of the crack measurement.

[0007] In order to solve the above problems, the crack measuring device of the present invention is a crack measuring device that detects cracks generated inside a workpiece, and is equipped with a light source unit that emits detection light along a light source optical axis that is parallel to the main optical axis and eccentric to the main optical axis, a focusing lens that has a lens optical axis coaxial with the main optical axis and focuses the detection light emitted from the light source unit inside the workpiece, a focusing point changing unit that changes the focusing point of the focusing lens in the thickness direction of the workpiece, a branching unit that is positioned conjugate to the focusing point of the focusing lens and branches light that passes through a specific area, a detector that is positioned downstream along the main optical axis from the branching unit and detects one of the detection light beams that is reflected at the interface of the workpiece and then branched by the branching unit, and outputs a detection signal based on the detection result, and a control unit that detects the position of the interface and the crack depth of the crack based on the position of the focusing point of the focusing lens and the detection signal.

[0008] According to the present invention, it is possible to provide a crack measuring instrument that can shorten the measurement time from the preliminary measurement of the interface to the completion of the crack measurement.

[0009] 1 is a schematic diagram showing an outline of a crack measurement device; FIG. 2 is a diagram showing an optical system and an optical path of a first detection light in the crack measurement device; FIG. 3 is a diagram showing an optical system and an optical path of a second detection light in the crack measurement device; FIG. 4 is a schematic optical path diagram showing reflected light when a first focal plane is located below the back surface of a workpiece; FIG. 5 is a diagram summarizing the light receiving positions of reflected light when the first focal plane is located below the back surface of a workpiece; FIG. 6 is a schematic optical path diagram showing reflected light when the first focal plane is located at the back surface of a workpiece; FIG. 7 is a diagram summarizing the light receiving positions of reflected light when the first focal plane is located at the back surface of a workpiece; FIG. 8 is a schematic optical path diagram showing reflected light when the first focal plane is located at an internal position of a workpiece; FIG. 9 is a diagram summarizing the light receiving positions of reflected light when the first focal plane is located at an internal position of a workpiece; FIG. 10 is a schematic optical path diagram showing reflected light when the first focal plane is located at the surface of a workpiece; FIG. 11 is a diagram summarizing the light receiving positions of reflected light when the first focal plane is located at the surface of a workpiece; 16 is a diagram summarizing the light receiving positions of reflected light when the first focal plane is located above the surface of the workpiece. FIG. 17 is a diagram showing how detection light is irradiated inside the workpiece. FIG. 18 is a diagram showing a measurement graph in which the output from the photodetector when the lens is scanned is plotted. FIG. 19 is a diagram showing a graph obtained by smoothing the measurement graph of FIG. 15 by first-order differentiation. FIG. 19 is a diagram showing an application example of the calculation function configuration of the control unit. FIG. 20 is a flowchart showing an application example of a laser processing device equipped with a crack measurement device.

[0010] Hereinafter, a crack measurement device according to an embodiment will be described with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted.

[0011] The crack measurement device 100 will be described with reference to Figures 1 to 18. First, the overall configuration of the crack measurement device 100 will be described. However, the crack measurement device 100 does not need to have all of the components described below, and some components may be omitted as appropriate.

[0012] FIG. 1 is a schematic diagram showing the configuration of the crack measurement instrument 100. FIG. 2 is a diagram showing the optical system and the optical path of the first detection light La in the crack measurement instrument 100. FIG. 3 is a diagram showing the optical system and the optical path of the second detection light Lb in the crack measurement instrument 100. Note that in FIGS. 2 and 3, some optical components such as the dichroic mirror 32 and the focus adjustment mechanism 71 are omitted to simplify the optical system. The crack measurement instrument 100 is a crack measurement instrument that can shorten the measurement time from the preliminary measurement of the interface to the completion of the crack measurement.

[0013] The crack measurement device 100 is a crack measurement device that is attached to a laser processing device (not shown) that generates cracks K inside a substrate such as a silicon wafer or a glass wafer (hereinafter also referred to as "workpiece W"). However, to avoid complicating the drawing, FIG. 1 only illustrates the components related to the crack measurement device 100 that are necessary for explaining the present invention. In this specification, of the surfaces that make up the workpiece W, the surface onto which the detection light L is incident is referred to as the surface s, and the surface spaced apart from the surface s is referred to as the back surface t, with the surface s and the back surface t collectively defined as the interface u. Furthermore, the side of the workpiece W onto which the detection light L is incident is defined as the upper side, and the side on which the workpiece W is placed on the stage is defined as the lower side.

[0014] 1, the crack measurement instrument 100 includes a light source unit 1, an illumination optical system 2, a half mirror 31, a dichroic mirror 32, a condenser lens 4, a detection optical system 5, a photodetector 6, a focus adjustment mechanism 71, an alignment mechanism 72, and a control unit 8. The workpiece W is placed on a stage (not shown).

[0015] The light source unit 1 emits detection light L for detecting the depth of a crack K formed inside the workpiece W. Detecting the crack depth means detecting the upper and lower end positions of the crack K. Here, when the workpiece W is a silicon wafer, it is desirable to use infrared light with a wavelength of 1000 nm or more as the detection light L. The detection light L includes a first detection light La and a second detection light Lb. The first light source optical axis Pa is parallel to the main optical axis P but is eccentric with respect to the main optical axis P, and in this embodiment, is eccentric in the +Y direction. The second light source optical axis Pb is parallel to the main optical axis P but is eccentric with respect to the main optical axis P on the opposite side to the first light source optical axis Pa, and in this embodiment, is eccentric in the -Y direction. The light source unit 1 emits a first detection light La along the first light source optical axis Pa. The light source unit 1 emits a second detection light Lb along the second light source optical axis Pb. The light source unit 1 is connected to a control unit 8, and the control unit 8 controls the emission of the light from the light source unit 1. In this specification, the direction in which the main optical axis P extends is defined as the Z direction, the direction perpendicular to the Z direction is defined as the X direction, and the direction perpendicular to the Z and X directions is defined as the Y direction. Furthermore, the Y direction when facing the direction in which light travels within the Z direction is defined as the left-right direction, with the left direction being defined as the +Y direction and the right direction being defined as the -Y direction. In the drawings, the direction perpendicular to the paper surface is the X direction, and the direction parallel to the paper surface is the Y direction.

[0016] As shown in FIGS. 2 and 3, the light source unit 1 includes a light source 11 and a polarizing beam splitter 12 .

[0017] The light source 11 is disposed on the second light source optical axis Pb, and emits the detection light L0 along the second light source optical axis Pb.

[0018] The polarizing beam splitter 12 is formed by bonding a total reflection prism 13 and a polarizing beam splitter 14 together. The total reflection prism 13 is arranged on the first light source optical axis Pa. The polarizing beam splitter 14 is a cube type formed by bonding two right-angle prisms together. The polarizing beam splitter 14 is arranged on the second light source optical axis Pb. The total reflection prism 13 and the polarizing beam splitter 14 do not need to be bonded together, and the total reflection prism 13 and the polarizing beam splitter 14 may be separate. It is also possible to use a total reflection mirror or the like instead of the total reflection prism 13.

[0019] In this embodiment, the polarizing beam splitter 12 is provided, so that the polarization directions of the first detection light La and the second detection light Lb are orthogonal to each other. The first detection light La is polarized in the X direction, and the second detection light Lb is polarized in the Y direction. The light source unit 1 is not limited to the above example. For example, the light source unit 1 may have different numbers, structures, and arrangements of light sources and polarizing beam splitters from the above example. Furthermore, the crack measurement instrument 100 of this embodiment may be configured so that the detection light is emitted along two optical axes, the first light source optical axis Pa and the second light source optical axis Pb. For example, the crack measurement instrument 100 may be configured to use two light sources, or may be configured to split one light source into two using a mask or a shutter.

[0020] As shown in FIG. 1 , the illumination optical system 2 includes a pair of relay lenses 21 and 22 and a field stop 23. The pair of relay lenses 21 and 22 constitute a telecentric afocal optical system and project the first detection light La and the second detection light Lb onto the lens pupil position of the condenser lens 4. The field stop 23 limits the range of the detection light L irradiated from the light source unit 1 toward the workpiece W. The field stop 23 is positioned conjugate with the focal point of the condenser lens 4. Note that, in this specification, the focal point of the condenser lens 4 refers to the focal point of the detection light L condensed by the condenser lens 4. This allows the detection light L to be focused toward a point on the image plane of the condenser lens 4 inside the workpiece W to form a light spot, thereby reducing unnecessary reflected light and scattered light and improving the accuracy of detecting the crack depth of a crack K formed inside the workpiece W. Note that, if the detection light L emitted from the light source unit 1 is collimated light, the field stop 23 may be omitted.

[0021] The half mirror 31 is disposed between the illumination optical system 2 and the dichroic mirror 32, and transmits and reflects a portion of the incident light. That is, the half mirror 31 transmits a portion of the detection light L incident from the light source unit 1 via the illumination optical system 2, and guides the transmitted detection light L to the condenser lens 4 via the dichroic mirror 32, and also reflects a portion of the reflected light M from the workpiece W and guides the reflected light M to the detection optical system 5.

[0022] The dichroic mirror 32 bends the main optical axis P by 90 degrees. That is, the dichroic mirror 32 reflects the detection light L from the light source unit 1 at a right angle and guides it to the condenser lens 4, and also reflects the reflected light M from the workpiece W at a right angle and guides it to the half mirror 31. The dichroic mirror 32 is provided to separate the processing light and the detection light L when the condenser lens 4 is shared by the processing optical system of the laser processing device and the detection optical system 5 for detecting the interface u and the crack K. Note that if the processing light does not need to be taken into consideration, a total reflection mirror or the like may be provided instead of the dichroic mirror 32.

[0023] The condenser lens 4 is positioned opposite the workpiece W and condenses the detection light L incident from the light source unit 1 via the illumination optical system 2, the half mirror 31, and the dichroic mirror 32 into the workpiece W. The optical axis of the condenser lens 4 is coaxial with the main optical axis P. The condenser lens 4 has a first focal plane F1 and a second focal plane F2. Since light incident on the condenser lens 4 is condensed on the first focal plane F1, the condensing point of the condenser lens 4 is on the first focal plane F1. The first focal plane F1 and the second focal plane F2 are conjugate to each other. The first focal plane F1 is divided into a first positive region F1+ and a first negative region F1- in the Y direction with the main optical axis P as the boundary. Within the first focal plane F1, the region on the +Y side of the boundary where the main optical axis P is located is the first positive region F1+, and the region on the -Y side of the boundary where the main optical axis P is located is the first negative region F1-. The second focal plane F2 is divided into a second positive region F2+ and a second negative region F2- in the Y direction with the main optical axis P as a boundary. Within the second focal plane F2, the region on the +Y side of the boundary where the main optical axis P is located is the second positive region F2+, and the region on the -Y side of the boundary where the main optical axis P is located is the second negative region F2-. The condenser lens 4 is arranged so that the position of the first focal plane F1 is located inside the workpiece W or in its vicinity. When the detection light L is condensed inside the workpiece W by the condenser lens 4, the detection light L is reflected inside the workpiece W. Reflected light M from inside the workpiece W passes through the condenser lens 4 and the dichroic mirror 32, is reflected by the half mirror 31, and is guided to the detection optical system 5.

[0024] 2 and 3, the detection optical system 5 has a pair of relay lenses 51 and 52 and a branching mirror (branching portion) 54. The detection optical system 5 guides the reflected light M reflected by the half mirror 31 to the photodetector 6.

[0025] The pair of relay lenses 51 and 52 constitute a telecentric afocal optical system, and project the pupil of the condenser lens 4 onto the photodetector 6 .

[0026] The branching mirror 54 limits the range of the reflected light M from the workpiece. The branching mirror 54 is disposed so as to be conjugate with the focal point of the condensing lens 4. That is, the branching mirror 54 is disposed at the position of the second focal plane F2. The branching mirror 54 branches the optical path by blocking and bending light that passes through a specific region. In this embodiment, the branching mirror 54 is fixed to the second negative region F2-, and one end of the branching mirror 54 is disposed near the main optical axis P. Therefore, light that passes through the second positive region F2+ is not blocked by the branching mirror 54. On the other hand, light that passes through the second negative region F2- is blocked by the branching mirror 54 and branched.

[0027] The branching mirror 54 is, for example, a total reflection mirror. Note that the branching mirror 54 may be replaced by any branching unit that branches the optical path by blocking and bending light that passes through a specific region. The branching mirror 54 may be, for example, a prism or a lens.

[0028] The photodetector 6 includes a first photodetector (first detector) 6a and a second photodetector (second detector) 6b.

[0029] The first photodetector 6a is arranged downstream along the main optical axis P with respect to the branching mirror 54. The first photodetector 6a detects the light of the first detection light La that is not blocked by the branching mirror 54 after being reflected at the interface u of the workpiece W. In other words, the first photodetector 6a receives the reflected light Ma of the first detection light La from the workpiece W. The first photodetector 6a outputs a first detection signal 62a to the control unit 8 based on the detection result. The first detection signal 62a is a detection signal corresponding to the amount of light received by the first photodetector 6a. A relay lens 52 is arranged between the first photodetector 6a and the branching mirror 54. A first polarizer 61a is arranged between the first photodetector 6a and the relay lens 52.

[0030] The first polarizer 61a is disposed downstream of the splitting mirror 54 along the main optical axis P, and the first photodetector 6a is disposed downstream of the first polarizer 61a. The first polarizer 61a has the same polarization direction as the first detection light La. In this embodiment, the first polarizer 61a transmits only linearly polarized light polarized in the X direction. That is, the first polarizer 61a transmits the first detection light La and the reflected light Ma of the first detection light La but does not transmit the second detection light Lb and the reflected light Mb of the second detection light Lb. The first polarizer 61a is, for example, a polarizing filter. The polarization direction of the first polarizer 61a may be changed in accordance with the polarization directions of the first detection light La and the second detection light Lb. The first polarizer 61a may not be provided if the polarization directions of the first detection light La and the second detection light Lb are not orthogonal to each other.

[0031] The second photodetector 6b is disposed downstream of the optical path branched by the branching mirror 54. The second photodetector 6b detects the light of the second detection light Lb that is reflected by the interface u of the workpiece W and then branched by the branching mirror 54. That is, the second photodetector 6b receives the reflected light Mb of the second detection light Lb from the workpiece W. The second photodetector 6b outputs a second detection signal 62b to the control unit 8 based on the detection result. The second detection signal 62b is a detection signal corresponding to the amount of light received. A relay lens 53 is disposed between the second photodetector 6b and the branching mirror 54. The pair of relay lenses 51 and 53 constitute a telecentric afocal optical system. A second polarizer 61b is disposed between the second photodetector 6b and the relay lens 53.

[0032] The second polarizer 61b is disposed downstream of the optical path branched by the branching mirror 54, and the second photodetector 6b is disposed downstream of the second polarizer 61b. The second polarizer 61b has the same polarization direction as the second detection light Lb. In this embodiment, the second polarizer 61b transmits only linearly polarized light polarized in the Y direction. That is, the second polarizer 61b transmits the second detection light Lb and the reflected light Mb of the second detection light Lb but does not transmit the first detection light La and the reflected light Ma of the first detection light La. The second polarizer 61b is, for example, a polarizing filter. The polarization direction of the second polarizer 61b may be changed in accordance with the polarization directions of the first detection light La and the second detection light Lb. The second polarizer 61b may not be provided if the polarization directions of the first detection light La and the second detection light Lb are not orthogonal to each other.

[0033] The focus adjustment mechanism 71 is an example of a focal point changing unit, and changes the focal point of the condensing lens 4 in the thickness direction of the workpiece W. That is, the focus adjustment mechanism 71 changes the first focal plane F1. This focus adjustment mechanism 71 includes a lens driving unit (not shown) that moves the condensing lens 4 in a direction along the main optical axis P. The lens driving unit (not shown) is, for example, a piezoelectric actuator. The lens driving unit (not shown) moves the condensing lens 4 in a direction along the main optical axis P, thereby changing the distance between the condensing lens 4 and the workpiece W, thereby changing the first focal plane F1 in the thickness direction of the workpiece W. The focus adjustment mechanism 71 is connected to the control unit 8, and the first focal plane F1 is controlled by the control unit 8.

[0034] If the condenser lens 4 is configured to be movable in the Z direction together with the processing head (not shown) of the laser processing device, the focus adjustment mechanism 71 may include a driving mechanism for the processing head. In this case, it becomes possible to combine the adjustment of the position of the focal point (coarse adjustment) by the driving mechanism for the processing head and the adjustment of the focal point (fine adjustment) by the piezo actuator.

[0035] The alignment mechanism 72 is an example of an alignment unit, and performs relative positioning (alignment) between the condenser lens 4 and the workpiece W in the horizontal direction (X direction and Y direction). The alignment mechanism 72 has a lens driving unit (not shown) that slightly moves the condenser lens 4 in the horizontal direction perpendicular to the lens optical axis. The lens driving unit is connected to the control unit 8, and the control unit 8 controls the lens driving unit to perform relative positioning between the condenser lens 4 and the workpiece W in the horizontal direction. Note that instead of the alignment mechanism 72, a configuration may be adopted in which a stage (not shown) on which the workpiece W is placed is moved relative to the condenser lens 4.

[0036] The control unit 8 is a programmable computer including a processor such as a CPU (Central Processing Unit), a memory, a storage unit capable of storing programs and data, and an input / output control unit. The functions of the control unit 8 are realized by the processor executing the programs. At least some of the functions of the control unit 8 may be realized by a dedicated logic circuit. The control unit 8 controls the operation of each unit of the crack measurement instrument 100. Specifically, the control unit 8 sequentially acquires detection signals output from the photodetector 6 while changing the focal point of the focusing lens 4 in the thickness direction (Z direction) of the workpiece W using the focus adjustment mechanism 71. The control unit 8 then performs crack detection processing and interface detection processing based on the acquired detection signals.

[0037] The crack detection process is a process for detecting the crack depth of a crack K generated inside the workpiece W. The interface detection process is a process for detecting an interface u of the workpiece W.

[0038] (Optical Path) The optical path of the detection light L in the crack measurement instrument 100 will be described with reference to FIGS. 1, 2 and 3. FIG.

[0039] The crack measurement instrument 100 simultaneously emits the first detection light La and the second detection light Lb and detects the reflected light M obtained, thereby detecting the crack K generated inside the workpiece W and the interface u of the workpiece W. In this embodiment, the first detection light La and the second detection light Lb are linearly polarized light whose polarization directions are orthogonal to each other.

[0040] Of the detection light L0 emitted from the light source 11, the component polarized in the X direction (first detection light La) is reflected sequentially by the reflecting surfaces of the polarizing beam splitter 14 and the total reflection prism 13, and then travels along the first light source optical axis Pa.

[0041] Of the detection light L0 emitted from the light source 11, the component polarized in the Y direction (second detection light Lb) passes through the reflecting surface of the polarizing beam splitter 14 and travels along the second light source optical axis Pb.

[0042] (First Detection Light La) First, the optical path of the first detection light La (Y direction component) when the first focal plane F1 of the condenser lens 4 is located inside the workpiece W will be described with reference to FIGS. 1 and 2. FIG.

[0043] As shown in FIG. 2, the first detection light La is guided to the condenser lens 4 via the relay lens 21 , the relay lens 22 , the field stop 23 , the half mirror 31 , and the dichroic mirror 32 .

[0044] After the first detection light La is guided to the focusing lens 4, a portion of the light is reflected by the surface s of the workpiece W, and a portion of the light is focused on a first focal plane F1 of the workpiece W. Of the first detection light La, the light reflected by the surface s of the workpiece W is referred to as surface reflected light Ma1. Of the light focused on the first focal plane F1 of the workpiece W, the light that does not hit the crack K travels to the back surface t of the workpiece W, and a portion of the light is reflected by the back surface t of the workpiece W. Of the light reflected by the back surface t of the workpiece W, the light that travels from the back surface t of the workpiece W toward the surface s of the workpiece W and then proceeds to the detection optical system 5 without being reflected by the surface s of the workpiece W is referred to as back surface reflected light Ma2. Of the first detection light La focused on the first focal plane F1, the light that hits the crack K is totally reflected by the crack K. Of the light totally reflected by the crack K, the light that proceeds to the detection optical system 5 is referred to as crack reflected light Ma3. The reflected light Ma of the first detection light La is not limited to the above, and may be, for example, multiple reflected light. However, since the light intensity is low, the optical path of the multiple-reflected light is not shown in order to avoid complicating the drawing. The multiple-reflected light is light that travels to the detection optical system 5 after being reflected multiple times by the back surface t and the front surface s of the workpiece W.

[0045] An imaginary extension line of the surface reflected light Ma1 toward the second focal plane F2 intersects with the second focal plane F2 at the second negative region F2-, so the surface reflected light Ma1 behaves as a light beam emitted from the first negative region F1- of the first focal plane F1. Therefore, after intersecting the main optical axis P, the surface reflected light Ma1 passes through the condenser lens 4 again and is guided as a diverging light beam to the detection optical system 5. After passing through the relay lens 51, the surface reflected light Ma1 travels toward the second negative region F2- of the second focal plane F2 and becomes a light beam that intersects with the main optical axis P downstream of the second focal plane F2.

[0046] A branching mirror 54 is disposed in the region of the second focal plane F2 where the surface reflected light Ma1 reaches, blocking the path of the surface reflected light Ma1 to the first photodetector 6a. Therefore, the surface reflected light Ma1 is reflected by the branching mirror 54 and guided by the relay lens 53 to a region on the opposite side of the main optical axis P from the second photodetector 6b.

[0047] A second polarizer 61b that transmits only the component polarized in the Y direction is disposed upstream of the second photodetector 6b. The surface reflected light Ma1 is linearly polarized light polarized in the X direction and is therefore blocked by the second polarizer 61b.

[0048] The back-surface reflected light Ma2 is reflected by the back surface t of the workpiece W, then passes through the condenser lens 4 again and is guided as a condensed light beam to the detection optical system 5. After passing through the relay lens 51, the back-surface reflected light Ma2 intersects with the main optical axis P upstream of the second focal plane F2 and passes through the second positive region F2+ at the second focal plane F2. The back-surface reflected light Ma2 then travels through the relay lens 52 toward the first photodetector 6a.

[0049] A first polarizer 61a that transmits only linearly polarized light polarized in the X direction is disposed upstream of the first photodetector 6a. The back-surface reflected light Ma2 is linearly polarized in the X direction, and therefore passes through the first polarizer 61a to reach the first photodetector 6a.

[0050] The crack-reflected light Ma3 is reflected by the back surface t of the workpiece W, then passes through the condenser lens 4 again and is guided as a convergent light beam to the detection optical system 5. After passing through the relay lens 51, the crack-reflected light Ma3 intersects with the main optical axis P upstream of the second focal plane F2 and travels toward the second negative region F2- of the second focal plane F2. The crack-reflected light Ma3 is then reflected by the branching mirror 54 and travels toward the second photodetector 6b via the relay lens 53.

[0051] A second polarizer 61b that transmits only the linear component polarized in the Y direction is disposed upstream of the second photodetector 6b. The crack-reflected light Ma3 is linearly polarized in the X direction and is therefore blocked by the second polarizer 61b.

[0052] (Second Detection Light Lb) Next, the optical path of the second detection light Lb (Y direction component) when the first focal plane F1 of the condenser lens 4 is located inside the workpiece W will be described with reference to FIGS. 1 and 3. FIG.

[0053] As shown in FIG. 3 , the second detection light Lb is guided to the condenser lens 4 via the relay lens 21 , the relay lens 22 , the field stop 23 , the half mirror 31 , and the dichroic mirror 32 .

[0054] After the second detection light Lb is guided to the focusing lens 4, a portion of the light is reflected by the surface s of the workpiece W, and a portion of the light is focused on the first focal plane F1 of the workpiece W. Of the second detection light Lb, the light reflected by the surface s of the workpiece W is referred to as surface reflected light Mb1. Of the light focused on the first focal plane F1 of the workpiece W, the light that does not hit the crack K travels to the back surface t of the workpiece W, and a portion of the light is reflected by the back surface t of the workpiece W. Of the light reflected by the back surface t of the workpiece W, the light that travels from the back surface t of the workpiece W toward the surface s of the workpiece W and then proceeds to the detection optical system 5 without being reflected by the surface s of the workpiece W is referred to as back surface reflected light Mb2. Of the second detection light Lb focused on the first focal plane F1, the light that hits the crack K is totally reflected by the crack K. Of the light totally reflected by the crack K, the light that proceeds to the detection optical system 5 is referred to as crack reflected light Mb3. The reflected light Mb of the second detection light Lb is not limited to the above, and may be, for example, multiple reflected light. However, since the light intensity is low, the optical path of the multiple-reflected light is not shown in order to avoid complicating the drawing. The multiple-reflected light is light that travels to the detection optical system 5 after being reflected multiple times by the back surface t and the front surface s of the workpiece W.

[0055] Since a virtual extension line of the surface reflected light Mb1 toward the second focal plane F2 intersects with the second focal plane F2 at the second positive region F2+, the surface reflected light Mb1 behaves as a light beam emitted from the first positive region F1+ of the first focal plane F1. Therefore, after intersecting the main optical axis P, the surface reflected light Mb1 passes through the condenser lens 4 again and is guided to the detection optical system 5 as a diverging light beam. After passing through the relay lens 51, the surface reflected light Mb1 passes toward the second positive region F2+ at the second focal plane F2 and becomes a light beam that intersects with the main optical axis P downstream of the second focal plane F2. The surface reflected light Mb1 is then guided to a region on the opposite side of the first photodetector 6a with respect to the main optical axis P.

[0056] A first polarizer 61a that transmits only linear components of light polarized in the X direction is disposed upstream of the first photodetector 6a. The surface reflected light Mb1 is linearly polarized light polarized in the Y direction and is therefore blocked by the first polarizer 61a.

[0057] The back-surface reflected light Mb2 is reflected by the back surface t of the workpiece W, then passes through the condenser lens 4 again and is guided as a condensed light beam to the detection optical system 5. After passing through the relay lens 51, the back-surface reflected light Mb2 intersects with the main optical axis P upstream of the second focal plane F2 and passes through the second negative region F2- at the second focal plane F2. The back-surface reflected light Ma2 is then reflected by the branching mirror 54 and travels toward the second photodetector 6b via the relay lens 53.

[0058] A second polarizer 61b that transmits only light polarized in the Y direction is disposed upstream of the second photodetector 6b. The back-surface reflected light Mb2 is linearly polarized light polarized in the Y direction, and therefore passes through the second polarizer 61b to reach the second photodetector 6b.

[0059] The crack-reflected light Mb3 is reflected by the back surface t of the workpiece W, then passes through the condenser lens 4 again and is guided as a convergent light beam to the detection optical system 5. After passing through the relay lens 51, the crack-reflected light Mb3 intersects with the main optical axis P upstream of the second focal plane F2 and travels toward the second positive region F2+ of the second focal plane F2. The crack-reflected light Mb3 then travels toward the first photodetector 6a via the relay lens 52.

[0060] A first polarizer 61a that transmits only linear components polarized in the X direction is disposed upstream of the first photodetector 6a. The crack-reflected light Mb3 is linearly polarized in the Y direction and is therefore blocked by the first polarizer 61a.

[0061] (Appearance of reflected light Ma of first detection light La when first focal plane F1 is moved) Next, a description will be given of an appearance of reflected light Ma of the first detection light La when the focusing lens 4 is scanned by the focus adjustment mechanism 71 and the first focal plane F1 of the focusing lens 4 is moved. Here, a case where a crack K is not generated inside the workpiece W will be described. For convenience, a virtual third photodetector 6c that receives light from an area on the opposite side of the main optical axis P from the first photodetector 6a, and a virtual fourth photodetector 6d that receives light from an area on the opposite side of the main optical axis P from the second photodetector 6b will be provided.

[0062] (When the first focal plane F1 is located below the back surface t of the workpiece W) First, a description will be given of a case where the first focal plane F1 is located below the back surface t of the workpiece W. Fig. 4 is a schematic diagram of an optical path showing the reflected light Ma when the first focal plane F1 is located below the back surface t of the workpiece W. Fig. 5 is a diagram summarizing the light receiving positions of the reflected light Ma when the first focal plane F1 is located below the back surface t of the workpiece W.

[0063] As shown in FIG. 5, the surface-reflected light Ma1 is received by the fourth photodetector 6d, the back-reflected light Ma2 is received by the fourth photodetector 6d, and the multiple-reflected light is received by the first photodetector 6a. Regarding FIG. 4, since light has retrograde properties, the light reflected by the surface s or back surface t of the workpiece W can be considered to have a light source at a position where the light path is extended, and the reflected light Ma can each be considered to have a light source at the first focal plane F1. Because the first focal plane F1 and the second focal plane F2 are in a conjugate relationship, the splitting mirror 54 can be considered to be in the first negative region F1- of the first focal plane F1. As shown in FIG. 4, the surface-reflected light Ma1 and the back-reflected light Ma2 are blocked by the splitting mirror 54 and are therefore received by the fourth photodetector 6d.

[0064] (When the first focal plane F1 is located at the position of the back surface t of the workpiece W) Next, a description will be given of a case where the first focal plane F1 is located at the position of the back surface t of the workpiece W. Fig. 6 is a schematic diagram of an optical path showing reflected light Ma when the first focal plane F1 is located at the position of the back surface t of the workpiece W. Fig. 7 is a diagram summarizing the light receiving positions of reflected light Ma when the first focal plane F1 is located at the position of the back surface t of the workpiece W.

[0065] As shown in Fig. 7, the front-surface reflected light Ma1 is received by the fourth photodetector 6d, the back-surface reflected light Ma2 is received by the first photodetector 6a and the fourth photodetector 6d, and the multiple-reflected light is received by the first photodetector 6a. As shown in Fig. 6, the front-surface reflected light Ma1 is blocked by the branching mirror 54 and is therefore received by the fourth photodetector 6d. As shown in Fig. 6, the back-surface reflected light Ma2 hits the edge of the branching mirror 54 and is split into light directed toward the first photodetector 6a and light directed toward the fourth photodetector 6d. Therefore, the back-surface reflected light Ma2 is received by the first photodetector 6a and the fourth photodetector 6d. However, because the back-surface reflected light Ma2 is split into two, the intensity of the received light is also split into two.

[0066] (When the first focal plane F1 is located inside the workpiece W) Next, a case where the first focal plane F1 is located inside the workpiece W will be described. Fig. 8 is a schematic diagram of an optical path showing reflected light Ma when the first focal plane F1 is located inside the workpiece W. Fig. 9 is a diagram summarizing the light receiving positions of reflected light Ma when the first focal plane F1 is located inside the workpiece W.

[0067] As shown in Fig. 9, the front surface reflected light Ma1 is received by the fourth photodetector 6d, the back surface reflected light Ma2 is received by the first photodetector 6a, and the multiple reflected light is received by the first photodetector 6a. As shown in Fig. 8, the front surface reflected light Ma1 is blocked by the branching mirror 54 and is therefore received by the fourth photodetector 6d. The back surface reflected light Ma2 is not blocked by the branching mirror 54 and is therefore received by the first photodetector 6a.

[0068] (When the first focal plane F1 is located at the surface s of the workpiece W) Next, a description will be given of a case where the first focal plane F1 is located at the surface s of the workpiece W. Fig. 10 is a schematic diagram of the optical path showing the reflected light Ma when the first focal plane F1 is located at the surface s of the workpiece W. Fig. 11 is a diagram summarizing the light receiving positions of the reflected light Ma when the first focal plane F1 is located at the surface s of the workpiece W.

[0069] As shown in Figure 11, the surface reflected light Ma1 is received by the first photodetector 6a and the fourth photodetector 6d, the back surface reflected light Ma2 is received by the first photodetector 6a, and the multiple reflected light is received by the first photodetector 6a. As shown in Figure 10, the surface reflected light Ma1 hits the edge of the splitting mirror 54 and is split into two light beams, one directed toward the first photodetector 6a and the other directed toward the fourth photodetector 6d. Therefore, the surface reflected light Ma1 is received by the first photodetector 6a and the fourth photodetector 6d. However, because the surface reflected light Ma1 is split into two beams, the intensity of the received light is also split into two. As shown in Figure 10, the back surface reflected light Ma2 is not blocked by the splitting mirror 54 and is received by the first photodetector 6a.

[0070] (When the first focal plane F1 is located above the surface s of the workpiece W) Next, a case where the first focal plane F1 is located above the surface s of the workpiece W will be described. Fig. 12 is a schematic diagram of the optical path showing the reflected light Ma when the first focal plane F1 is located above the surface s of the workpiece W. Fig. 13 is a diagram summarizing the light receiving positions of the reflected light Ma when the first focal plane F1 is located above the surface s of the workpiece W.

[0071] 13, the front surface reflected light Ma1 is received by the first photodetector 6a, the back surface reflected light Ma2 is received by the first photodetector 6a, and the multiple reflected light is received by the first photodetector 6a. As shown in FIG. 12, the front surface reflected light Ma1 and the back surface reflected light Ma2 are not blocked by the branching mirror 54 and are therefore received by the first photodetector 6a.

[0072] (Appearance of reflected light Mb of second detection light Lb when first focal plane F1 is moved) Next, a description will be given of an appearance of reflected light Mb of second detection light Lb when the focusing lens 4 is scanned by the focus adjustment mechanism 71 and the first focal plane F1 of the focusing lens 4 is moved. Here, a case will be described in which a crack K is not generated inside the workpiece W. For convenience, the description will be given by installing a virtual third photodetector 6c that receives light from an area on the opposite side of the main optical axis P from the first photodetector 6a, and a virtual fourth photodetector 6d that receives light from an area on the opposite side of the main optical axis P from the second photodetector 6b.

[0073] (When the first focal plane F1 is located below the back surface t of the workpiece W) First, a description will be given of the case where the first focal plane F1 is located below the back surface t of the workpiece W. The front surface reflected light Mb1 is received by the third photodetector 6c, the back surface reflected light Mb2 is received by the third photodetector 6c, and the multiple reflected light is received by the second photodetector 6b. The front surface reflected light Ma1 and the back surface reflected light Ma2 are not blocked by the branching mirror 54, and are therefore received by the third photodetector 6c.

[0074] (When the first focal plane F1 is located at the rear surface t of the workpiece W) Next, a case where the first focal plane F1 is located at the rear surface t of the workpiece W will be described. The front surface reflected light Mb1 is received by the third photodetector 6c, the rear surface reflected light Mb2 is received by the second photodetector 6b and the third photodetector 6c, and the multiple reflected light is received by the second photodetector 6b. The front surface reflected light Ma1 is not blocked by the branching mirror 54 and is therefore received by the third photodetector 6c. The rear surface reflected light Ma2 hits the edge of the branching mirror 54 and is split into light directed toward the second photodetector 6b and light directed toward the third photodetector 6c. Therefore, the rear surface reflected light Mb2 is received by the second photodetector 6b and the third photodetector 6c. However, because the rear surface reflected light Mb2 is split into two, the intensity of the received light is also split into two.

[0075] (When the first focal plane F1 is located inside the workpiece W) Next, a case where the first focal plane F1 is located inside the workpiece W will be described. The surface reflected light Mb1 is received by the third photodetector 6c, the back surface reflected light Mb2 is received by the second photodetector 6b, and the multiple reflected light is received by the second photodetector 6b. The surface reflected light Ma1 is not blocked by the branching mirror 54, so it is received by the third photodetector 6c. The back surface reflected light Mb2 is blocked by the branching mirror 54, so it is received by the second photodetector 6b.

[0076] (When the first focal plane F1 is located at the surface s of the workpiece W) Next, a description will be given of the case where the first focal plane F1 is located at the surface s of the workpiece W. The surface reflected light Mb1 is received by the second photodetector 6b and the third photodetector 6c, the back surface reflected light Mb2 is received by the second photodetector 6b, and the multiple reflected light is received by the second photodetector 6b. The surface reflected light Ma1 hits the edge of the branching mirror 54 and is split into light directed toward the second photodetector 6b and light directed toward the third photodetector 6c. Therefore, the surface reflected light Mb1 is received by the second photodetector 6b and the third photodetector 6c. However, because the surface reflected light Mb1 is split into two, the intensity of the received light is also split into two. The back surface reflected light Mb2 is blocked by the branching mirror 54 and is received by the second photodetector 6b.

[0077] (When the first focal plane F1 is located above the surface s of the workpiece W) Next, a case where the first focal plane F1 is located above the surface s of the workpiece W will be described. The surface reflected light Mb1 is received by the second photodetector 6b, the back surface reflected light Mb2 is received by the second photodetector 6b, and the multiple reflected light is received by the second photodetector 6b. The surface reflected light Mb1 and the back surface reflected light Mb2 are blocked by the branching mirror 54 and are therefore received by the second photodetector 6b.

[0078] (Crack Detection Process) Next, a description will be given of a crack detection process that uses the back-surface reflected light Ma2 and the back-surface reflected light Mb2 to detect the crack depth of the crack K generated inside the workpiece W. Fig. 14 is a diagram showing how the detection light L is irradiated inside the workpiece W.

[0079] 2, when no crack K is present at the focal point of the focusing lens 4, the first detection light La does not hit a crack but is reflected by the back surface t of the workpiece W, and is then detected by the first photodetector 6a as back surface reflected light Ma2. In this case, the amount of light detected by the first photodetector 6a is maximized, and the signal level of the first detection signal 62a is maximized.

[0080] On the other hand, if a crack K is present at the focal point of the focusing lens 4, as shown in Figure 2, the first detection light La is totally reflected by the crack K, so the amount of light detected by the first photodetector 6a becomes zero and the signal level of the first detection signal 62a becomes zero.

[0081] Furthermore, when the focal point of the focusing lens 4 coincides with the lower end position or the upper end position of the crack K, the first detection light La is split into back-reflected light Ma2 that does not hit the crack K and is reflected by the back surface t of the workpiece W, and crack-reflected light Ma3 that is totally reflected by the crack K and then reflected by the back surface t of the workpiece W. The back-reflected light Ma2 of the first detection light La then enters the first photodetector 6a along the path shown in FIG. 2. At this time, the amount of light detected by the first photodetector 6a is lower than when a crack K is not present at the focal point of the focusing lens 4. Furthermore, the signal level of the first detection signal 62a is lower than when a crack K is not present at the focal point of the focusing lens 4.

[0082] Similarly, in the case of the second detection light Lb, the signal level of the second detection signal 62b output by the second photodetector 6b is maximum when there is no crack K at the focal point of the focusing lens 4, decreases when the focal point of the focusing lens 4 coincides with the lower end position or upper end position of the crack K, and becomes zero when there is a crack K at the focal point of the focusing lens 4.

[0083] The control unit 8 sequentially acquires the first detection signal 62a output from the first photodetector 6a and the second detection signal 62b output from the second photodetector 6b while controlling the focus adjustment mechanism 71 to change the focal point of the condenser lens 4 in the thickness direction (Z direction) of the workpiece W. This allows the control unit 8 to detect the crack depth of the crack K.

[0084] (Interface Detection Process) Next, a description will be given of the interface detection process for detecting the position of the interface u of the workpiece W. The interface detection process is performed as a preliminary measurement for detecting the crack depth of the crack K.

[0085] 15 is a measurement graph plotting the outputs from the first photodetector 6a and the second photodetector 6b when the condenser lens 4 is scanned when no crack K is present inside the workpiece W. The movement amount of the condenser lens 4 is the movement amount of the condenser lens 4 in the Z direction, and the greater the movement amount, the closer the condenser lens 4 is to the workpiece W. In other words, the greater the movement amount, the further downward the first focal plane F1 of the condenser lens 4 moves.

[0086] 15, channel A (Ch-A) indicates the output of the first photodetector 6a when irradiated with the first detection light La. In FIG. 15, channel B (Ch-B) indicates the output of the second photodetector 6b when irradiated with the second detection light Lb.

[0087] In the graph of FIG. 15, regions p, q, and r are calculated. Region p is a region where the first photodetector 6a and the second photodetector 6b receive multiple reflected light, but do not receive surface reflected light or back surface reflected light. Region p corresponds to a case where the first focal plane F1 is located below the back surface of the workpiece W. Region q is a region where the first photodetector 6a and the second photodetector 6b receive multiple reflected light and back surface reflected light, but do not receive surface reflected light. Region q corresponds to a case where the first focal plane F1 is located inside the workpiece W. Region r is a region where the first photodetector 6a and the second photodetector 6b receive multiple reflected light, back surface reflected light, and surface reflected light. Region r corresponds to a case where the first focal plane F1 is located above the surface of the workpiece W. The detection intensity of region q is greater than the detection intensity of region p. The detection intensity of region r is greater than the detection intensity of region q.

[0088] FIG. 16 is a graph obtained by smoothing the measurement graph of FIG. 15 through first-order differentiation. In the graph of FIG. 16, peak position Sa (first interface position), peak position Ta (first interface position), peak position Sb (second interface position), and peak position Tb (second interface position) are calculated. Peak position Sa is a peak located between region q and region r in channel A. Peak position Sa corresponds to the case where the first focal plane F1 is located at the surface s of the workpiece W. In other words, peak position Sa is the position of surface s detected based on the first detection signal 62a. Peak position Ta is a peak located between region p and region q in channel A. Peak position Ta corresponds to the case where the first focal plane F1 is located at the back surface t of the workpiece W. In other words, peak position Ta is the position of back surface t detected based on the first detection signal 62a. Peak position Sb is a peak located between region q and region r in channel B. Peak position Sb corresponds to the case where the first focal plane F1 is located at the surface s of the workpiece W. That is, peak position Sb is the position of the surface s detected based on the second detection signal 62b. Peak position Tb is a peak located between region p and region q in channel B. Peak position Tb corresponds to the case where the first focal plane F1 is located at the position of the back surface t of the workpiece W. That is, peak position Tb is the position of the back surface t detected based on the second detection signal 62b. That is, the control unit 8 can detect the position of the interface u of the workpiece W by detecting peak position Sa, peak position Ta, peak position Sb, and peak position Tb.

[0089] The control unit 8 calculates the average value of the first interface position and the second interface position as the position of the interface u of the workpiece W. The control unit 8 can calculate a more accurate position of the surface s of the workpiece W by averaging the detected peak positions Sa and Sb. The control unit 8 can calculate a more accurate position of the back surface t of the workpiece W by averaging the detected peak positions Ta and Tb. Note that if the branching mirror 54 is not misaligned in the Y direction, the control unit 8 may detect the position of the interface u of the workpiece W using the detection results of only the A channel or the B channel without calculating the average value.

[0090] 15 and 16 are examples in which there is no crack K inside the workpiece W, but even if there is a crack inside the workpiece W, the surface reflected light is not affected by the crack K, and so the control unit 8 is able to detect the peak positions Sa and Sb. In other words, even if there is a crack K inside the workpiece W, the control unit 8 is able to calculate the position of the surface s of the workpiece W. On the other hand, if there is a crack K inside the workpiece W, the light that hits the crack K is totally reflected, and so it is difficult for the control unit 8 to detect the peak positions Ta and Tb.

[0091] The position of the back surface t of the workpiece W can be calculated using the position of the front surface s. The control unit 8 can calculate the position of the back surface t of the workpiece W from the position of the front surface s of the workpiece W and the thickness and real refractive index of the workpiece W measured in advance.

[0092] When the thickness of the workpiece W is D, the position of the surface s of the workpiece is S, and the value of the effective refractive index is n, the position T of the back surface t of the workpiece W is calculated by the following formula (1): T = S + D / n (1)

[0093] In other words, if a crack K has been generated inside the workpiece W, the control unit 8 detects the position of the surface s of the workpiece W based on the detection results of the first photodetector 6a and the second photodetector 6b, and measures the interface position of the workpiece W by calculating the position of the back surface t of the workpiece W using the position of the surface s.

[0094] Next, the operation of the crack measuring device 100 will be described.

[0095] Before measuring the crack depth of the crack K, the user adjusts the relative positions of the workpiece W and the condenser lens 4. At this time, for example, the condenser lens 4 is installed so that the first focal plane F1 of the condenser lens 4 is located inside the workpiece W. However, it is sufficient that the condenser lens 4 can move from below the back surface t of the workpiece W to above the front surface s.

[0096] Before measuring the crack depth of the crack K, the user measures the thickness and real refractive index of the workpiece W. By measuring the thickness and real refractive index of the workpiece W, the position of the back surface t of the workpiece W can be calculated even if a crack K has formed inside the workpiece W.

[0097] The control unit 8 controls the light source unit 1 to emit the first detection light La along the first light source optical axis Pa (detection light emission step).

[0098] The control unit 8 controls the light source unit 1 to emit the second detection light Lb along the second light source optical axis Pb.

[0099] The condenser lens 4 condenses the first detection light La and the second detection light Lb inside the workpiece W (condensing process).

[0100] The control unit 8 controls the focus adjustment mechanism 71 to change the focal point of the condenser lens 4 in the thickness direction of the workpiece W (focal point changing step).

[0101] The branching mirror 54 blocks and bends the light passing through the second negative region F2- at the second focal plane F2, thereby branching the optical path (branching step).

[0102] The first photodetector 6a detects the reflected light M of the first detection light La that is reflected at the interface u of the workpiece W and then not branched by the branching mirror 54, and outputs a first detection signal 62a to the control unit 8 based on the detection result (detection process).

[0103] The second photodetector 6b detects the reflected light M of the second detection light Lb that is reflected at the interface u of the workpiece W and then branched by the branching mirror 54, and outputs a second detection signal 62b to the control unit 8 based on the detection result.

[0104] The control unit 8 detects the position of the interface u of the workpiece W and the crack depth of the crack K based on the position of the focal point of the focusing lens 4 and the first detection signal 62a (crack detection process).

[0105] The control unit 8 can simultaneously perform the interface detection process and the crack detection process by irradiating the detection light L from the light source unit 1. Here, simultaneously performing the interface detection process and the crack detection process means performing the interface detection process and the crack detection process based on the same detection signal, and the calculations and other processes may be performed separately. At this time, the condenser lens 4 is moved in the Z direction by the focus adjustment mechanism 71, and a change in the detection signal corresponding to the amount of movement of the condenser lens 4 is sent to the control unit 8.

[0106] The control unit 8 calculates the position of the interface u of the workpiece W based on the changes in the first detection signal 62 a and the second detection signal 62 b according to the amount of movement of the condenser lens 4 .

[0107] According to this embodiment, the crack measuring device 100 can be attached to a laser processing device, so that the position of the interface u of the workpiece W and the crack depth of the crack K can be detected during the production of the crack K.

[0108] According to this embodiment, the detection of the crack depth of the crack K and the detection of the interface u are performed based on the detection signals of the first photodetector 6a and the second photodetector 6b. Therefore, the control unit 8 can simultaneously detect the crack depth of the crack K and the detection of the interface u. Here, simultaneously performing the interface detection process and the crack detection process means performing the interface detection process and the crack detection process based on the same detection signal, and the calculation and other processes may be performed separately. Therefore, the measurement time from the preliminary measurement of the interface u to the completion of the measurement of the crack depth of the crack K is shortened.

[0109] According to this embodiment, the first polarizer 61a and the second polarizer 61b are arranged upstream of the first photodetector 6a and the second photodetector 6b, thereby reducing the amount of extraneous light, such as noise, that enters the first photodetector 6a and the second photodetector 6b.

[0110] (Application Example) Next, an application example using the crack measurement device 100 will be described. Fig. 17 is a diagram showing an application example of the calculation function configuration of the control unit. Fig. 18 is a flowchart showing an application example of a laser processing device equipped with the crack measurement device 100.

[0111] A user performs a preliminary measurement before processing the workpiece W with a laser processing device. The preliminary measurement includes measurement of the position of the interface u of the workpiece W and measurement of the workpiece properties. When measuring the position of the interface u of the workpiece W as the preliminary measurement, an interface detection process is performed by the crack measurement device 100 of this embodiment.

[0112] The user can further shorten the measurement time of the crack measurement device 100 by checking whether the workpiece properties (reflectance) at the measurement point are uniform during preliminary measurement. For example, if the workpiece properties (reflectance) at the measurement point are uniform, workpiece property measurement, including measurement of the position of the interface u of the workpiece W, can be omitted. If the workpiece properties are not uniform, the measured value will be affected by the workpiece properties when detecting the crack depth of crack K. If the workpiece properties are not uniform, the accurate crack depth of crack K can be calculated by performing a calculation process corresponding to the workpiece properties on the measured crack depth of crack K. On the other hand, if the workpiece properties are uniform, the measured crack depth of crack K is not affected by the workpiece properties, and therefore, there is no need to perform a calculation process corresponding to the workpiece properties. Therefore, if the workpiece properties are uniform, there is no need to perform a workpiece property measurement, including measurement of the position of the interface u of the workpiece W, thereby shortening the measurement time. Whether the workpiece properties are uniform can be confirmed, for example, using a camera.

[0113] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

[0114] 100...crack measuring instrument, 1...light source unit, 2...illumination optical system, 31...half mirror, 32...dichroic mirror, 4...condensing lens, 5...detection optical system, 6...photodetector, 71...focus adjustment mechanism, 72...alignment mechanism, 8...control unit, 54...branching mirror, 6a...first photodetector, 6b...second photodetector, 61a...first polarizer, 61b...second polarizer, 62a...first detection signal, 62b...second detection signal, P...main optical axis, Pa...first light source optical axis, Pb...second light source optical axis, L...detection light, La...first detection light, Lb...second detection light, M...reflected light, W...workpiece, u...interface, K...crack

Claims

1. A crack measuring device for detecting cracks generated inside a workpiece, comprising: a light source unit that emits detection light along a light source optical axis that is parallel to a main optical axis and eccentric to the main optical axis; a focusing lens that has a lens optical axis coaxial with the main optical axis and focuses the detection light emitted from the light source unit inside the workpiece; a focusing point changing unit that changes the focusing point of the focusing lens in the thickness direction of the workpiece; a branching unit that is positioned conjugate to the focusing point of the focusing lens and branches light that passes through a specific region; a detector that is positioned downstream of the branching unit along the main optical axis and detects one of the light beams of the detection light that is reflected by the interface of the workpiece and then branched by the branching unit, and outputs a detection signal based on the detection result; and a control unit that detects the position of the interface and the crack depth of the crack based on the position of the focusing point of the focusing lens and the detection signal.

2. The crack measuring instrument according to claim 1, wherein the control unit calculates the position of the interface using a differential value of the detection signal.

3. A crack detection method for detecting the crack depth of a crack generated inside a workpiece, comprising: a detection light emitting step of emitting detection light along a light source optical axis that is parallel to a main optical axis and eccentric to the main optical axis; a focusing step of focusing the detection light inside the workpiece using a focusing lens having a lens optical axis coaxial with the main optical axis; a branching step of branching the optical path by branching light that passes through a specific region at a position conjugate to the focusing point of the focusing lens; a detection step of detecting light of the detection light that is branched by the branching step after being reflected at an interface of the workpiece and outputting a detection signal based on the detection result; and a crack detection step of detecting the position of the interface and the crack depth of the crack based on the position of the focusing point of the focusing lens and the detection signal.

Images