Detection device

Abstract

The present invention provides a detection device that can detect a dicing predetermined line formed on the front surface from the back surface of a wafer even when it is impossible to detect the dicing predetermined line formed on the front surface from the back surface of the wafer using an infrared camera. A detection mechanism for detecting the inside of a workpiece includes: a wavelength-division delay unit that causes the pulsed laser light of each pulse emitted from a laser oscillator to have a time difference for each wavelength; and a ring generation unit that generates the pulsed laser light having a time difference for each wavelength into a ring shape and splits the small-ring light into large-ring light for each wavelength. When the workpiece is irradiated with the pulsed laser light having a time difference for each wavelength in a ring shape, an interference wave of ultrasonic waves is generated inside the workpiece, and vibration is generated at the position where the ultrasonic waves converge. Laser light is irradiated from a laser light irradiator onto the upper surface of the workpiece corresponding to the center of the vibration.

Description

Technical Field

[0001] The present invention relates to an inspection device having an inspection mechanism for inspecting the inside of a workpiece held by a chuck table. Background Art

[0002] A wafer divided by a plurality of intersecting dividing predetermined lines and having a plurality of devices such as ICs and LSIs formed on the front surface is divided into individual device chips by a cutting device or a laser processing device, and the divided device chips are used in electronic devices such as mobile phones or personal computers.

[0003] In addition, in the case of dividing a wafer having devices such as MEMS, CCD, and CMOS, which are not suitable for contamination, formed on the front surface into individual device chips, the front surface of the wafer is held by a protective tape, and the dividing predetermined line formed on the front surface is detected from the back surface of the wafer by an infrared camera, and cutting processing or laser processing is performed from the back surface side.

[0004] Patent Document 1: Japanese Patent Laid-Open No. 07-75955

[0005] However, in a wafer having a metal film covering the back surface, there is a problem that infrared rays cannot pass through and the dividing predetermined line formed on the front surface cannot be detected from the back surface of the wafer by an infrared camera. Summary of the Invention

[0006] Therefore, an object of the present invention is to provide an inspection device that can detect the dividing predetermined line on the front surface from the back surface of the workpiece even when the dividing predetermined line formed on the front surface cannot be detected from the back surface of the workpiece by an infrared camera.

[0007] According to the present invention, a detection device is provided, which includes a chuck table and a detection mechanism. The chuck table has a holding surface defined by an X-axis coordinate and a Y-axis coordinate, and the holding surface holds a workpiece. The detection mechanism detects the inside of the workpiece held by the chuck table. The detection mechanism includes: a laser oscillator that oscillates pulsed laser light with a broadband wavelength; a wavelength discrimination delay unit that causes the pulsed laser light rays of each pulse emitted from the laser oscillator to have a time difference according to each wavelength; a ring generation unit that generates the pulsed laser light rays having a time difference according to each wavelength into a ring shape, and splits the pulsed laser light rays from a small ring-shaped light into a large ring-shaped light according to each wavelength; a beam splitter that branches the pulsed laser light rays split from the small ring-shaped light into the large ring-shaped light; a raster scanner that scans the pulsed laser light rays branched in a first direction by the beam splitter according to the X-axis coordinate; a pitch scanner that pitches the pulsed laser light rays according to the Y-axis coordinate; an fθ lens that irradiates the pulsed laser light rays split from the small ring-shaped light into the large ring-shaped light onto the upper surface of the workpiece held by the chuck table determined by the X-axis coordinate and the Y-axis coordinate; a laser light irradiator that is disposed in a second direction branched by the beam splitter and irradiates detection laser light; a half mirror that is disposed between the laser light irradiator and the beam splitter; a retroreflector that is disposed in such a manner as to sandwich the beam splitter with the half mirror and returns the detection laser light that has passed through the half mirror to the half mirror; a light detector that receives the light reflected by the half mirror; and an image generation unit that generates an image based on the intensity of the light received by the light detector and the X-axis coordinate and the Y-axis coordinate of the upper surface of the measured portion irradiated with the pulsed laser light rays. The interference wave of the ultrasonic waves generated by irradiating the upper surface of the workpiece held by the chuck table with the pulsed laser light rays split from the small ring-shaped light into the large ring-shaped light with a time difference converges at a specified Z-axis coordinate inside the workpiece to generate vibration. The interference light of the first return light that captures the modulation of the vibration and is reflected by irradiating the detection laser light onto the upper surface of the workpiece corresponding to the position where the vibration occurs and the second return light generated by the detection laser light returned through the retroreflector is guided to the light detector through the half mirror, and the image generation unit generates an image representing the state near the point where the interference wave of the ultrasonic waves converges.

[0008] Preferably, the time difference of the pulsed laser light rays split from the small ring-shaped light into the large ring-shaped light by the ring generation unit according to each wavelength is adjusted by the wavelength discrimination delay unit, so as to adjust the Z-axis coordinate of the point where the ultrasonic waves converge inside the workpiece.

[0009] Preferably, inside the workpiece, the distance from the point where the ultrasonic waves converge to the upper surface of the workpiece for the large annular light is set as H1, the distance from the point where the ultrasonic waves converge to the annular light adjacent to the large annular light is set as H2, and the velocity of the ultrasonic waves propagating inside the workpiece is set as V. In this case,

[0010] The wavelength discrimination delay unit delays the time t calculated by

[0011] (H1 - H2) / V = t

[0012] to adjust the Z-axis coordinate of the point where the ultrasonic waves converge. Preferably, the ring generation unit is an axicon lens assembly or a diffractive optical element, and the axicon lens assembly has a pair of axicon lenses and a diffraction grating.

[0013] According to the present invention, even when the back side of the workpiece is covered with a metal film or the like and infrared rays cannot pass through, so that the front side cannot be detected from the back side by an infrared camera, it is possible to detect, for example, a dicing predetermined line formed on the front side from the back side. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is an overall perspective view of a laser processing apparatus having the detection apparatus according to an embodiment of the present invention.

[0015] Figure 2 shows Figure 1 a block diagram of the structure of the detection mechanism of the detection apparatus shown.

[0016] Figure 3 is a conceptual diagram showing a method of detecting the state of a wafer by generating ultrasonic waves according to a plurality of annular lights irradiated onto the wafer.

[0017] REFERENCE SIGNS

[0018] 1: Laser processing apparatus; 2: Base; 4: Frame; 4a: Vertical wall portion; 4b: Horizontal wall portion; 10: Wafer; 10a: Front side; 10b: Back side; 12: Device; 14: Dicing predetermined line; 20: Holding unit; 25: Chuck table; 25a: Holding surface; 30: Moving mechanism; 40: Laser beam irradiation unit; 50: Display unit; 60: Detection mechanism; 61: Laser oscillator; 62: Wavelength discrimination delay unit; 620, 621: Optical fiber; 64: Ring generation unit; 65: Beam splitter; 65a: Reflecting surface; 67: Indexing scanner; 68: Scanning scanner; 69: Condensing lens for detection; 691: fθ lens; 71: Laser beam irradiator; 72: Half mirror; 73: Retroreflector; 74: Photodetector; 75: Image generation unit. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the inspection device according to the embodiment of the present invention will be described in detail with reference to the accompanying drawings.

[0020] Figure 1 FIG. 1 is an overall perspective view of a laser processing device 1 shown as an example of a device provided with the inspection device according to the present embodiment.

[0021] Figure 1 The shown laser processing device 1 includes: a holding unit 20 that holds a workpiece; a moving mechanism 30 that moves the holding unit 20; a laser beam irradiation unit 40 that irradiates a laser beam onto the workpiece held by the holding unit 20; a display unit 50; and an inspection mechanism 60 that, together with the holding unit 20, constitutes the inspection device according to the present embodiment.

[0022] The holding unit 20 includes: a rectangular X-axis direction movable plate 21 that is movably placed on a base 2 in the X-axis direction shown by an arrow X in the figure; a rectangular Y-axis direction movable plate 22 that is movably placed on the X-axis direction movable plate 21 in the Y-axis direction shown by an arrow Y in the figure; a cylindrical support column 23 that is fixed to the upper surface of the Y-axis direction movable plate 22; and a rectangular cover plate 26 that is fixed to the upper end of the support column 23. A circular chuck table 25 is provided on the cover plate 26, and the chuck table 25 extends upward through a long hole formed in the cover plate 26. The chuck table 25 is configured to be rotatable by a rotation drive unit (not shown). A holding surface 25a defined by an X-axis coordinate and a Y-axis coordinate perpendicular to the X-axis coordinate on the upper surface of the chuck table 25 is formed of a porous material and has air permeability, and is connected to an attracting unit (not shown) through a flow path passing through the inside of the support column 23. A jig 27 is provided on the chuck table 25, and the jig 27 is used to fix a ring-shaped frame F that supports the workpiece with a protective tape T interposed therebetween. In addition, for example, as Figure 1 shown, the workpiece according to the present embodiment is a wafer 10 divided by a dicing line 14 on a silicon substrate and having a device 12 formed on a front surface 10a. In order to protect the front surface 10a, the wafer 10 is turned over so that the back surface 10b side faces upward, and the front surface 10a side is adhered to the protective tape T and held by the ring-shaped frame F. A metal film is formed on the back surface 10b, and it is impossible to detect the front surface 10a side by irradiating infrared rays.

[0023] The moving mechanism 30 is disposed on the base 2 and includes an X-axis feed mechanism 31 that feeds the holding unit 20 in the X-axis direction for machining and a Y-axis feed mechanism 32 that indexes and feeds the Y-axis movable plate 22 in the Y-axis direction. The X-axis feed mechanism 31 converts the rotational motion of the pulse motor 33 into a linear motion via the ball screw 34 and transmits it to the X-axis movable plate 21, causing the X-axis movable plate 21 to move forward and backward in the X-axis direction along the guide rails 2a, 2a on the base 2. The Y-axis feed mechanism 32 converts the rotational motion of the pulse motor 35 into a linear motion via the ball screw 36 and transmits it to the Y-axis movable plate 22, causing the Y-axis movable plate 22 to move forward and backward in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. In addition, although not shown in the figure, position detection units are provided on the X-axis feed mechanism 31, the Y-axis feed mechanism 32, and the chuck table 25 to accurately detect the X-axis coordinate, Y-axis coordinate, and circumferential rotational position of the chuck table 25, and this position information is sent to a control unit (not shown). Then, according to the instruction signal indicated from the control unit based on this position information, the X-axis feed mechanism 31, the Y-axis feed mechanism 32, and the rotational drive unit of the chuck table 25 (not shown) are driven, and the chuck table 25 can be positioned at a desired position on the base 2.

[0024] As Figure 1 shown, a frame 4 is erected on the side of the moving mechanism 30. The frame 4 has a vertical wall portion 4a disposed on the base 2 and a horizontal wall portion 4b extending horizontally from the upper end portion of the vertical wall portion 4a. An optical system (not shown) including a laser beam irradiation unit 40 is housed inside the horizontal wall portion 4b of the frame 4, and a condenser 42 that forms a part of this optical system is disposed on the lower surface of the front end portion of the horizontal wall portion 4b.

[0025] Inside the horizontal wall portion 4b of the frame 4 of the laser processing apparatus 1, in addition to the above-mentioned laser beam irradiation unit 40, a detection mechanism 60 for detecting the inside of the wafer 10 held by the holding unit 20 is also provided, and the detection mechanism 60 and the above-mentioned holding unit 20 constitute the detection device of this embodiment.

[0026] Figure 2A block diagram showing the optical system of the detection mechanism 60 is shown. The detection mechanism 60 includes: a laser oscillator 61 that oscillates pulsed laser light with a broadband wavelength (e.g., 400 nm to 800 nm); a wavelength division delay unit 62 that causes the pulsed laser light rays PL0 emitted from the laser oscillator 61 to have a time difference for each wavelength and outputs them as pulsed laser light rays PL1; a ring generation unit 64 that generates the pulsed laser light rays PL1 as annular light, and splits the small annular light into large annular light for each wavelength, and generates and outputs pulsed laser light rays PL2; a beam splitter 65 that has a function of branching the transmitted light in an appropriate direction; a pitch scanner 67 that is composed of, for example, an electric scanner, and pitches the pulsed laser light rays PL2 branched in the first direction D1 by the beam splitter 65 along the Y-axis coordinate direction on the chuck table 25 of the holding unit 20; a scan scanner 68 that is composed of, for example, a resonant scanner, and scans the pulsed laser light rays PL2 along the X-axis coordinate on the chuck table 25; and a detection condenser 69 that includes an fθ lens 691, and the fθ lens 691 condenses the pulsed laser light rays PL2 split from the small annular light into large annular light onto the upper surface, i.e., the back surface 10b, of the wafer 10 held by the chuck table 25 at a position determined by the X-axis coordinate and the Y-axis coordinate for irradiation.

[0027] The pulsed laser light rays PL0 emitted from the laser oscillator 61 are guided to the wavelength division delay unit 62 via an optical fiber 620. The wavelength division delay unit 62 can be realized, for example, by using an optical fiber that generates wavelength dispersion. More specifically, for example, it is realized by the following wavelength division delay unit 62: In an optical fiber (not shown) included inside the wavelength division delay unit 62, a diffraction grating is formed such that the reflection position is different for each wavelength. For example, it is set such that the reflection distance of long-wavelength light is short and the reflection distance of short-wavelength light is long. Thus, via Figure 2 the optical fiber 621 provided on the output side of the wavelength division delay unit 62 as shown, each pulse has a prescribed time difference in the order of wavelengths from long to short. For example, pulsed laser light rays PL1 that output red light PL1a, yellow light PL1b, green light PL1c, and blue light PL1d with a prescribed time difference are generated.

[0028] The pulsed laser beam PL1, which has a time difference for each wavelength by differentiating the delay unit 62 by wavelength, becomes parallel light through a collimating lens 63 set as needed, and is introduced into a ring generation unit 64. The ring generation unit 64 is implemented by, for example, an axicon lens assembly that includes a pair of axicon lenses 641, 642 and a diffraction grating 643 that is symmetric in the radial direction in a doughnut shape. The pulsed laser beam PL1 passes through the pair of axicon lenses 641, 642 to become a ring-shaped light, and then passes through the diffraction grating 643 to generate a pulsed laser beam PL2 that is spectrally split from a small ring-shaped light to a large ring-shaped light for each wavelength. By adjusting the interval between the pair of axicon lenses 641, 642, the size of the ring-shaped light that makes up the pulsed laser beam PL2 can be adjusted. In addition, in the present embodiment, an example of using the above-described axicon lens body as a member that spectrally splits the pulsed laser beam PL1 from a small ring-shaped light to a large ring-shaped light for each wavelength is shown, but the present invention is not limited thereto. For example, a diffractive optical element (DOE) may also be used.

[0029] The pulsed laser beam PL2, which is spectrally split from a small ring-shaped light to a large ring-shaped light for each wavelength, is introduced into a beam splitter 65. The pulsed laser beam PL2 introduced into the beam splitter 65 passes through the reflection surface 65a and is guided in the first direction D1. The optical path is changed by a mirror 66 set as needed, and the pulsed laser beam PL2 is guided to a dividing scanner 67 that performs indexing on the Y-axis coordinate. The dividing scanner 67 controls the angle of the reflection surface 67a by a control unit (not shown), and precisely controls the position where the pulsed laser beam PL2 is irradiated on the chuck table 25 in the indexing feed direction (Y-axis direction) perpendicular to the drawing. Further, the pulsed laser beam PL2 reflected by the dividing scanner 67 is guided to a raster scanner 68. The raster scanner 68 controls the angle of the reflection surface 68a by a control unit (not shown), and precisely controls the position where the pulsed laser beam PL2 is irradiated on the chuck table 25 in the scanning direction (X-axis direction) set in the left-right direction with respect to the drawing. The pulsed laser beam PL2, whose irradiation direction is controlled by the dividing scanner 67 and the raster scanner 68, is guided to an fθ lens 691 and condensed, and is irradiated onto a predetermined X-axis coordinate and Y-axis coordinate position on the upper surface (back surface 10b) of the wafer 10.

[0030] The detection mechanism 60 of the present embodiment further includes: a laser light irradiator 71 disposed in the second direction D2 branched by the beam splitter 65 to irradiate a detection laser light LB0; a half mirror 72 disposed between the laser light irradiator 71 and the beam splitter 65; a retroreflector 73 disposed on the opposite side with the beam splitter 65 sandwiched between it and the half mirror 72; a light detector 74 that receives the light that returns via the beam splitter 65 and is guided to the half mirror 72 and is reflected; and an image generation unit 75 (analyzer) that generates an image based on the intensity of the light received by the light detector 74 and the information on the X-axis coordinate and Y-axis coordinate on the chuck table 25 irradiated with the pulsed laser light PL2.

[0031] The laser light irradiator 71 is constituted by, for example, a laser diode (LD). The detection laser light LB0 irradiated from the laser light irradiator 71 passes through the half mirror 72 and is introduced into the beam splitter 65, and is branched into a branched light LB1 that is reflected by the reflection surface 65a of the beam splitter 65 and advances along the first direction D1 and a branched light LB2 that passes through the reflection surface 65a. The branched light LB1 reflected by the reflection surface 65a advances along the center of the pulsed laser light PL2, is scanned by the indexing scanner 67 and the raster scanner 68, and is irradiated to the specified X-axis coordinate and Y-axis coordinate on the back surface 10b of the wafer 10 through the fθ lens 691.

[0032] The branched light LB1 irradiated to the back surface 10b of the wafer 10 is reflected by the upper surface (back surface 10b) of the wafer 10 to become a first return light LB1', passes through the raster scanner 68, the indexing scanner 67, and the mirror 66, is reflected by the reflection surface 65a of the beam splitter 65, advances along the second direction D2, and is guided to the half mirror 72. On the other hand, the branched light LB2 of the detection laser light LB0 irradiated from the laser light irradiator 71 and passing through the beam splitter 65 is reflected by the retroreflector 73 and then passes through the reflection surface 65a of the beam splitter 65 to become a second return light LB2'. At this time, the optical path of the first return light LB1' is set to be the same as the optical path of the second return light LB2'. Therefore, interference light is generated from the first return light LB1' that captures the vibration modulation of the back surface 10b of the wafer 10 and the second return light LB2' that functions as a reference light not affected by the wafer 10. This interference light is reflected by the half mirror 72 and guided to the light detector 74. The image generation unit 75 generates image information based on the intensity of the light received by the light detector 74 (the interference light of the first return light LB1' + the second return light LB2') and the X-axis coordinate and Y-axis coordinate indicating the position on the back surface 10b of the wafer 10 irradiated by the detection laser light LB1, and outputs this image to the display unit 50.

[0033] The detection mechanism 60 generally has the structure as described above. Hereinafter, with reference to Figure 3Describe the functions and roles of the inspection institution 60.

[0034] As Figure 1 shown, after preparing the wafer 10 as the workpiece, the wafer 10 is attracted and held on the chuck table 25 of the holding unit 20 and fixed by the clamp 27. After fixing the wafer 10 to the chuck table 25, the moving mechanism 30 is actuated to move the chuck table 25, positioning a specified inspection area of the wafer 10 directly below the inspection condenser 69 having an fθ lens 691. Next, the laser oscillator 61 is actuated to oscillate pulsed laser light, and a pulsed laser beam PL2 is generated and output that has a time difference for each wavelength and includes a plurality of annular light beams that are split from small annular light to large annular light for each wavelength by means of the wavelength-division delay unit 62 and the ring generation unit 64. The pulsed laser beam PL2 passes through the beam splitter 65 and branches in the first direction D1, and is irradiated to specified X-axis coordinate and Y-axis coordinate positions in the inspection area on the back surface 10b of the wafer 10 via the indexing scanner 67, the raster scanner 68, and the fθ lens 691 that are controlled by a control unit (not shown).

[0035] In the present embodiment, as Figure 3 shown, the pulsed laser beam PL2 includes, in order of decreasing diameter, the annular light PL2a generated from the red light PL1a, the annular light PL2b generated from the yellow light PL1b, the annular light PL2c generated from the green light PL1c, and the annular light PL2d generated from the blue light PL1d, and is irradiated onto the back surface 10b of the wafer 10 in a concentric circle shape with the center set to C. The annular light PL2a with the largest diameter is the first to reach the back surface 10b of the wafer 10 held by the chuck table 25, and then, in order of decreasing diameter, the annular light PL2b reaches with a time difference t1, followed by the annular light PL2c reaching with a time difference t2, and finally the annular light PL2d reaches with a time difference t3. In addition, in the present embodiment, for ease of explanation, an example of splitting according to four wavelength regions is described, but actually splitting is performed corresponding to 10 to 20 wavelength regions.

[0036] A metal film is formed on the back surface 10b of the wafer 10 in the present embodiment, and the pulsed laser light PL2 composed of the above-described annular lights PL2a to PL2d cannot pass through the wafer 10. However, each of the annular lights PL2a to PL2d reaches the back surface 10b, thereby generating ultrasonic waves that propagate within the wafer 10 from each arrival point. By appropriately setting the time differences t1 to t3 when each of the annular lights PL2a to PL2d reaches the back surface 10b of the wafer 10, the interference wave of the ultrasonic waves can be converged at the position P of the desired Z-axis coordinate Pz in the thickness direction of the wafer 10 at the center C of each of the annular lights PL2a to PL2d irradiated on the back surface 10b of the wafer 10. In addition, in the present embodiment, in order to detect the state near the front surface 10a of the wafer 10, the position P is set near the front surface 10a.

[0037] The steps for appropriately setting the time differences t1 to t3 are as follows. The diameters of the annular lights PL2a to PL2d irradiated on the back surface 10b of the wafer 10 are values set by the diffraction grating 643 included in the above-described ring generation unit 64. For example, as Figure 3 shown, they are set to a1 to a4. Moreover, if the Z-axis coordinate (depth) from the center C of the annular lights PL2a to PL2d to the desired position P where the operator wants the ultrasonic waves generated by each of the annular lights PL2a to PL2d to converge in the thickness direction of the wafer 10 is Pz, the distances H1 to H4 from the points where each of the annular lights PL2a to PL2d on the back surface 10b of the wafer 10 arrives to the position P are calculated by the following formulas.

[0038] H1 = (a1 2 + Pz 2 ) 1 / 2

[0039] H2 = (a2 2 + Pz 2 ) 1 / 2

[0040] H3 = (a3 2 + Pz 2 ) 1 / 2

[0041] H4 = (a4 2 + Pz 2 ) 1 / 2

[0042] Here, as described above, when the annular lights PL2a to PL2d reach the back surface 10b of the wafer 10 with time differences t1 to t3 and ultrasonic waves that propagate inside the wafer 10 are generated by the respective annular lights, in order to converge the interference wave composed of the respective ultrasonic waves at the position P, it is only necessary to set the time differences t1 to t3 that satisfy the following expressions. In addition, V is the velocity (m / s) at which the ultrasonic wave propagates inside the wafer 10, and is the velocity determined by the material of the wafer 10.

[0043] (H1 - H2) / V = t1

[0044] (H2 - H3) / V = t2

[0045] (H3 - H4) / V = t3

[0046] The above time differences t1 to t3 can be adjusted by the wavelength division delay unit 62. In the above wavelength division delay unit 62, it is only necessary to change the positions of the diffraction gratings (not shown) disposed corresponding to the wavelengths in the optical fiber constituting the wavelength division delay unit 62 in such a manner as to generate the above time differences t1 to t3.

[0047] The annular lights PL2a to PL2d are irradiated onto the back surface 10b of the wafer 10 with the time differences t1 to t3 that satisfy the above conditions. The interference wave of the ultrasonic waves generated by the annular lights PL2a to PL2d and propagating inside the wafer 10 converges at the position P to generate a strong vibration. A part of the interference wave of the ultrasonic wave is reflected near the position P and propagates inside the wafer 10, and reaches the center C of the annular lights PL2a to PL2d on the upper surface of the wafer 10 (i.e., the back surface 10b of the wafer 10) corresponding to the position P where the vibration is generated, causing the back surface 10b to vibrate. This vibration corresponds to the state near the position P where the above ultrasonic wave is converged.

[0048] Here, in the present embodiment, the detection laser beam LB0 is irradiated from the laser beam irradiator 71, and the branched light LB1 branched by the beam splitter 65 is irradiated onto the center C of the annular lights PL2a to PL2d on the back surface 10b of the wafer 10. When the branched light LB1 reaches the center C of the back surface 10b and is reflected, the first return light LB1' that captures the modulation of the vibration of the back surface 10b is formed. The first return light LB1' that is reflected by the back surface 10b of the wafer 10 and captures the modulation passes through the raster scanner 68, the indexing scanner 67, the mirror 66, and the reflecting surface 65a of the beam splitter 65 and reaches the half mirror 72. At the same time, the branched light LB2 of the detection laser beam LB0 that is irradiated from the laser beam irradiator 71 and passes through the beam splitter 65 is also reflected by the retroreflector 73 to become the second return light LB2', and becomes integrated with the first return light LB1' on the reflecting surface 65a of the beam splitter 65 and reaches the half mirror 72. The interference light is generated by the first return light LB1' reflected by the half mirror 72 and the second return light LB2' that functions as a reference light not affected by the wafer 10, and the light intensity thereof is detected by the photodetector 74. The detected light intensity is transmitted to the image generation unit 75 together with the X-axis coordinate and Y-axis coordinate of the center C on the back surface 10b of the wafer 10.

[0049] As described above, in the present embodiment, there are a raster scanner 68 and an indexing scanner 67. The raster scanner 68 and the indexing scanner 67 are operated so that the annular lights PL2a to PL2d and the branched light LB1 are sequentially irradiated onto the entire specified detection region specified by the X-axis coordinate and Y-axis coordinate. Each time, the light intensity is detected by the photodetector 74, and the light intensity is transmitted to the image generation unit 75 together with the information on the position where the pulsed laser beam PL2 and the branched light LB1 are irradiated (i.e., the position information of the X-axis coordinate and Y-axis coordinate of the center C of the annular lights PL2a to PL2d).

[0050] The image generation unit 75 generates an image on the front surface 10a side corresponding to the position of the branched light LB1 of the detection laser beam irradiated in the detection region based on the change in the light intensity of the first return light LB1' clearly grasped by generating the interference wave from the first return light LB1' and the second return light LB2'. For example, in the wafer 10, when there is a device 12 near the position P where the ultrasonic waves converge, the converged ultrasonic waves are reflected by the device 12, and the vibration reaches the center C of the back surface 10b. Therefore, a strong interference waveform is detected by the photodetector 74. In contrast, when the position P is located near the dicing predetermined line 14, the ultrasonic waves are hardly reflected, and no modulation occurs on the back surface 10b of the wafer 10. Therefore, almost no interference waveform is detected by the photodetector 74.

[0051] As described above, the image information including the position information of the detected front surface 10a of the device 12 and the dicing predetermined line 14 is displayed on the display unit 50 as shown in Figure 2 and the image information of the detection area displayed on the display unit 50 is stored together with the information of the corresponding X-axis coordinates and Y-axis coordinates in a control unit (not shown). The moving mechanism 30 is operated to move the chuck table 25, and the area of the wafer 10 is sequentially positioned at the detection area detected by the detection mechanism 60, and the device 12 and the dicing predetermined line 14 on the front surface 10a of the wafer 10 are detected and stored through the above steps. In this way, after the state of the front surface 10a side of the wafer 10 is detected, the chuck table 25 is positioned directly below the condenser 42 of the laser beam irradiation unit 40, and laser processing is performed using this position information.

[0052] According to the present embodiment, even when the back surface 10b side of the wafer 10 as the workpiece is covered with a metal film or the like and infrared rays cannot pass through, so that the dicing predetermined line 14 formed on the front surface 10a cannot be detected from the back surface 10b of the wafer 10 by an infrared camera, the dicing predetermined line 14 formed on the front surface 10a can be detected from the back surface 10b side of the wafer 10.

[0053] In addition, the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, an example is shown in which the pulsed laser beam PL0 is split into four annular lights PL2a to PL2d with a time difference in accordance with four wavelength regions, but the present invention is not limited thereto, and as long as it is split into a plurality of annular lights and irradiated, the number of annular lights is not limited.

Claims

1. A detection device, comprising a chuck table and a detection mechanism. The chuck table has a holding surface defined by an X-axis coordinate and a Y-axis coordinate, and the holding surface holds a workpiece. The detection mechanism detects the interior of the workpiece held by the chuck table. Wherein, The detection mechanism includes: A laser oscillator that oscillates pulsed laser light with a broadband wavelength; A wavelength-division delay unit that causes the pulsed laser light rays of each pulse emitted from the laser oscillator to have a time difference for each wavelength; A ring generation unit that generates the pulsed laser light rays having a time difference for each wavelength into a ring shape, and splits the pulsed laser light rays from a small ring light into a large ring light for each wavelength; A beam splitter that branches the pulsed laser light rays split from the small ring light into the large ring light; A raster scanner that scans the pulsed laser light rays branched in a first direction by the beam splitter according to the X-axis coordinate; A pitch scanner that pitches the pulsed laser light rays according to the Y-axis coordinate; An fθ lens that irradiates the upper surface of the workpiece held by the chuck table, which is determined by the X-axis coordinate and the Y-axis coordinate, with the pulsed laser light rays split from the small ring light into the large ring light; A laser light irradiator that is disposed in a second direction branched by the beam splitter and irradiates detection laser light; A half mirror that is disposed between the laser light irradiator and the beam splitter; A retroreflector that is disposed in such a manner as to sandwich the beam splitter with the half mirror, and returns the detection laser light that has passed through the half mirror to the half mirror; A light detector that receives the light reflected by the half mirror; And An image generation unit that generates an image based on the intensity of the light received by the light detector and the X-axis coordinate and the Y-axis coordinate of the upper surface of the measured part irradiated with the pulsed laser light rays. The interference wave of the ultrasonic waves generated by irradiating the upper surface of the workpiece held by the chuck table with the pulsed laser light rays split from the small ring light into the large ring light with a time difference converges at a prescribed Z-axis coordinate inside the workpiece to generate vibration. The interference light of the first return light that captures the modulation of the vibration and is reflected by irradiating the upper surface of the workpiece corresponding to the position where the vibration has occurred with the detection laser light and the second return light generated by the detection laser light returned through the retroreflector is guided to the light detector through the half mirror, and the image generation unit generates an image representing the state near the point where the interference wave of the ultrasonic waves converges.

2. The detection device according to claim 1, Wherein, The time difference of the pulsed laser light rays split from the small ring light into the large ring light for each wavelength by the ring generation unit is adjusted by the wavelength-division delay unit, so as to adjust the Z-axis coordinate of the point where the ultrasonic waves converge inside the workpiece.

3. The detection device according to claim 2, Wherein, Inside the workpiece, the distance from the point where the ultrasonic waves converge to the upper surface of the workpiece for the large annular light is set as H1, the distance from the point where the ultrasonic waves converge to the annular light adjacent to the large annular light is set as H2, and the velocity of the ultrasonic waves propagating inside the workpiece is set as V. In this case, The time t calculated by (H1 - H2) / V = t is delayed by the wavelength discrimination delay unit, thereby adjusting the Z-axis coordinate of the point where the ultrasonic waves converge.

4. The detection device according to claim 1, wherein, the ring generation unit is an axicon lens assembly or a diffractive optical element, and the axicon lens assembly has a pair of axicon lenses and a diffraction grating.

5. The detection device according to claim 1, wherein, the detection mechanism further has a display unit, and the image generated by the image generation unit is displayed on the display unit.

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