JP7547166B2 - Laser processing equipment - Google Patents

Description

The present invention relates to a laser processing device.

Wafer surfaces are divided into ICs, LSIs, and other devices along planned dividing lines, and are then divided into individual device chips using a dicing machine or laser processing machine. These chips are then used in electrical devices such as mobile phones and personal computers.

The laser processing device comprises at least a holding means having a holding surface defined by an X-axis and a Y-axis for holding a workpiece, a laser irradiation means for irradiating a laser beam of an absorbent wavelength to the workpiece held by the holding means to perform ablation processing, a feed means for feeding the holding means and the laser irradiation means relatively in the X-axis and Y-axis directions for processing, an imaging means for imaging the processing area, and a control means. The laser irradiation means comprises an oscillator for emitting a laser beam, a condenser for condensing the laser beam oscillated by the oscillator, and a Z-axis movement means for moving the condenser in the Z-axis direction perpendicular to the holding surface, and can perform laser processing on a wafer.

In a laser processing device, the focal point of the laser beam focused by the focusing device must be accurately positioned at the desired position in the Z-axis direction. In addition, the position of the focal point shifts over time while the laser processing is performed by the laser processing device. Therefore, the position of the focal point is checked periodically or arbitrarily by the operator, and the reference position of the focal point in the Z-axis direction is corrected as necessary (see, for example, Patent Document 1).

JP 2013-78785 A

In the technology described in the above-mentioned Patent Document 1, a wafer to be inspected is held on a chuck table, a concentrator that focuses and irradiates a laser beam is moved in the Z-axis direction, and the chuck table is moved in the X-axis or Y-axis direction to irradiate the laser beam, forming a linear laser-processed groove (processing mark), and then the laser-processed groove is imaged by an imaging means and displayed on a display means, and the position in the Z-axis direction corresponding to the focal point position is detected based on the position where the laser-processed groove is narrowest.

However, with the above detection method, it is not easy to determine and pinpoint the position where the laser-processed groove is narrowest, and it takes time to pinpoint the position of the focusing point of the focusing device, resulting in poor productivity.

The present invention has been made in consideration of the above facts, and its main technical objective is to provide a highly productive laser processing device that can automatically detect the focal point position of a laser beam without spending a lot of time.

In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a laser processing apparatus comprising at least a holding means having a chuck table equipped with a holding surface defined by an X-axis and a Y-axis for holding a workpiece, a laser irradiation means for irradiating a pulsed laser beam having an absorbent wavelength to the workpiece held on the chuck table to perform ablation processing, a feeding means for relatively feeding the chuck table and the laser irradiation means in the X-axis and Y-axis directions for processing, an imaging means for imaging a processing area of the workpiece, and a control means, wherein the laser irradiation means comprises an oscillator for oscillating a pulsed laser beam, a condenser for condensing the pulsed laser beam oscillated by the oscillator, and a condenser for focusing the condenser on the holding surface of the chuck table. and Z-axis moving means for moving in the orthogonal Z-axis direction, and the control means comprises a Z-position memory section which stores the Z-axis position of the focal point positioned by the condenser, an inspection range setting section which sets an inspection range with coarse and fine intervals and an inspection range with fine intervals based on the position stored in the Z-position memory section, an image memory section which stores an image of the processing area of the workpiece imaged by the imaging means corresponding to the inspection range with coarse and fine intervals and the inspection range with fine intervals, and an image processing section which processes the image stored in the image memory section, and the control means moves the condenser in the inspection range with coarse and fine intervals set by the inspection range setting section based on the position in the Z-axis direction at which the focal point is positioned on the top surface of the workpiece for inspection held on the chuck table. a pulsed laser beam is irradiated one shot at a time in synchronization with the intermittent operation to form a plurality of discontinuous first processed marks corresponding to the one shot on the upper surface of the workpiece, the imaging means images the first processed marks and stores them in the image storage unit, the image of the first processed marks stored in the image storage unit is processed by the image processing unit to extract a first minimum processed mark that is the smallest among the first processed marks, and a first minimum processed mark Z position in the Z axis direction of the light focusing point corresponding to the first minimum processed mark is detected, and further, using the first minimum processed mark Z position that positions the light focusing point on the upper surface of the workpiece for inspection held on the chuck table as a reference, a laser processing apparatus which intermittently moves the concentrator in the Z-axis direction and intermittently moves the chuck table in the X-axis or Y-axis direction within the inspection range with precise intervals set by the inspection range setting unit, irradiates a pulsed laser beam one shot at a time, forms a plurality of discontinuous second processing marks corresponding to the one shot on the upper surface of the workpiece, images the second processing marks with the imaging means and stores them in the image storage unit, processes the image of the second processing marks stored in the image storage unit by the image processing unit to extract a second minimum processing mark that is the smallest among the second processing marks, detects a second minimum processing mark Z position in the Z-axis direction of the focusing point corresponding to the second minimum processing mark, and stores the second minimum processing mark Z position in the Z position storage unit.

The inspection range for the coarse/fine spacing is preferably 50 μm or more in the Z-axis direction and an inspection range of ±2.0 mm or more, and the inspection range for the fine spacing is preferably 5 μm or less in the Z-axis direction and an inspection range of ±0.2 mm or less. The laser processing device is also preferably equipped with a display means, which displays an image of the processing mark captured by the imaging means and also displays the Z coordinate position of the focal point corresponding to the processing mark.

The laser irradiation means of the laser processing apparatus of the present invention includes an oscillator that oscillates a pulsed laser beam, a condenser that condenses the pulsed laser beam oscillated by the oscillator, and a Z-axis movement means that moves the condenser in a Z-axis direction perpendicular to the holding surface of the chuck table, and the control means includes a Z-position memory section that stores the Z-axis position of the focal point positioned by the condenser, an inspection range setting section that sets an inspection range with coarse and fine intervals and an inspection range with fine intervals based on the position stored in the Z-position memory section, and an image of the processing area of the workpiece imaged by the imaging means that corresponds to the inspection range with coarse and fine intervals and the inspection range with fine intervals. and an image processing unit that processes the image stored in the image storage unit, and the control means, based on the position in the Z-axis direction at which a focal point is positioned on the upper surface of the workpiece for inspection held on the chuck table, intermittently moves the condenser in the Z-axis direction within the inspection range with coarse and fine intervals set by the inspection range setting unit, and intermittently moves the chuck table in the X-axis direction or the Y-axis direction to irradiate a pulsed laser beam one shot at a time in synchronization with the intermittent operation , thereby forming a plurality of discontinuous first processed marks corresponding to the one shot on the upper surface of the workpiece, and image the first processed marks by the imaging means. and storing the image in the image storage unit, processing the image of the first machining mark stored in the image storage unit by the image processing unit to extract a first minimum machining mark that is the smallest among the first machining marks, detecting a first minimum machining mark Z position in the Z-axis direction of the light focusing point corresponding to the first minimum machining mark, and further, using the first minimum machining mark Z position that positions the light focusing point on the upper surface of the workpiece for inspection held on the chuck table as a reference, intermittently moving the condenser in the Z-axis direction and intermittently moving the chuck table in the X-axis direction or the Y-axis direction in the inspection range of the precise interval set by the inspection range setting unit to obtain a pulse. a laser beam is irradiated one shot at a time to form a plurality of discontinuous second processing marks corresponding to each shot on the upper surface of the workpiece, the second processing marks are imaged by the imaging means and stored in the image memory unit, the image of the second processing marks stored in the image memory unit is processed by the image processing unit to extract a second minimum processing mark that is the smallest among the second processing marks, a Z position of the second minimum processing mark in the Z axis direction of the focal point corresponding to the second minimum processing mark is detected, and the Z position of the second minimum processing mark is stored in the Z position memory unit, so that the Z coordinate position of the focal point where the processing mark is smallest can be automatically determined, improving productivity.

FIG. 2 is an overall perspective view of the laser processing device. 2 is a block diagram showing an optical system of a laser irradiation means arranged in the laser processing apparatus of FIG. 1. FIG. 2 is a perspective view showing an embodiment of laser processing for forming a first processing mark. 1A is a perspective view showing an embodiment in which a first processing mark is imaged by an imaging means, and FIG. 1B is an enlarged view of the first processing mark imaged in the embodiment shown in FIG. FIG. 11 is a perspective view showing an embodiment of laser processing for forming a second processing mark. 1A is a perspective view showing an embodiment in which a second processing mark is imaged by an imaging means, and FIG. 1B is an enlarged view of the second processing mark imaged in the embodiment shown in FIG.

The following describes in detail an embodiment of a laser processing device constructed according to the present invention, with reference to the attached drawings.

Figure 1 shows a laser processing device 1 of this embodiment. The laser processing device 1 includes a holding means 2 for holding the workpiece, a base 3 on which the holding means 2 is disposed, a laser irradiation means 6, a moving means 30 disposed as a feed means for feeding the holding means 2 and the laser irradiation means 6 relatively in the X-axis and Y-axis directions for processing, an imaging means 7, a display means 9, and a control means (indicated by 100 in Figure 2) described later.

The holding means 2 includes a rectangular X-axis direction movable plate 21 mounted on the base 3 so as to be movable in the X-axis direction indicated by the arrow X in the figure, a rectangular Y-axis direction movable plate 22 mounted on the X-axis direction movable plate 21 so as to be movable in the Y-axis direction indicated by the arrow Y in the figure perpendicular to the X-axis direction, a cylindrical support 23 fixed to the upper surface of the Y-axis direction movable plate 22, and a rectangular cover plate 26 fixed to the upper end of the support 23. A chuck table 25 is disposed on the cover plate 26, which extends upward through a long hole and has a holding surface 25a defined by the X-axis and the Y-axis, and the chuck table 25 is configured to be rotatable by a rotation drive means not shown. The holding surface 25a is formed of a porous material having air permeability and is connected to a suction source not shown by a flow path passing through the inside of the support 23. In addition, in the upper left of Figure 1, an inspection wafer 10 is shown, which is prepared as a workpiece to be laser processed by the laser processing device 1 of this embodiment. The inspection wafer 10 is, for example, a silicon wafer with nothing formed on the front or back surface, and has a thickness of 700 μm. The inspection wafer 10 is supported by an annular frame F via an adhesive tape T.

The moving means 30 is provided on the base 3 with an X-axis feed means 31 for feeding the holding means 2 in the X-axis direction for processing, and a Y-axis feed means 32 for indexing and feeding the Y-axis movable plate 22 in the Y-axis direction. The X-axis feed means 31 converts the rotational motion of the pulse motor 33 into linear motion via a ball screw 34 and transmits it to the X-axis movable plate 21, and moves the X-axis movable plate 21 forward and backward in the X-axis direction along the guide rails 3a, 3a on the base 3. The Y-axis feed means 32 converts the rotational motion of the pulse motor 35 into linear motion via a ball screw 36 and transmits it to the Y-axis movable plate 22, and moves the Y-axis movable plate 22 forward and backward in the Y-axis direction along the guide rails 21a, 21a on the X-axis movable plate 21. Although not shown, the X-axis feed means 31, the Y-axis feed means 32, and the chuck table 25 are provided with position detection means, which accurately detect the X-axis coordinate, the Y-axis coordinate, and the circumferential rotational position of the chuck table 25, and the position information is sent to the control means of the laser processing device 1. Then, the control means issues an instruction signal based on the position information to drive the X-axis feed means 31, the Y-axis feed means 32, and the rotation drive means of the chuck table 25 (not shown), so that the chuck table 25 can be positioned at the desired position on the base 3.

As shown in FIG. 1, a frame 37 is erected on the side of the holding means 2. The frame 37 is provided with a vertical wall 37a disposed on the base 3 along the Z-axis direction (up and down direction) perpendicular to the X-axis direction and the Y-axis direction, and a horizontal wall 37b extending horizontally from the upper end of the vertical wall 37a. The optical system of the laser irradiation means 6 is housed inside the horizontal wall 37b of the frame 37, and a condenser 64 constituting a part of the optical system is disposed on the underside of the tip of the horizontal wall 37b.

The imaging means 7 is used primarily for alignment purposes to image the processing area, and is disposed on the underside of the tip of the horizontal wall portion 37b, at a position spaced apart in the X-axis direction from the condenser 64 of the laser irradiation means 6. The imaging means 7 includes a normal imaging element (CCD) that captures images using visible light, and an illumination means that irradiates visible light. The image captured by the imaging means 7 is sent to the control means.

The optical system of the laser irradiation means 6 housed in the horizontal wall portion 37b of the laser processing device 1 will be described with reference to FIG. 2. As shown in FIG. 2, the laser irradiation means 6 includes an oscillator 61 that oscillates a pulsed laser beam LB having a wavelength that is absorbed by the inspection wafer 10 held on the chuck table 25, an attenuator 62 that adjusts the pulsed laser beam LB oscillated by the oscillator 61 to a desired output, a reflecting mirror 63 that changes the optical path direction of the pulsed laser beam LB whose output has been adjusted by the attenuator 62 to an arbitrary direction, and a condenser 64 that condenses the pulsed laser beam LB whose optical path direction has been changed by the reflecting mirror 63. The condenser 64 is provided with a condensing lens 641 that positions the focal point P on the inspection wafer 10 held on the chuck table 25.

The laser irradiation means 6 includes a Z-axis moving means 5 that moves the condenser 64 along the Z-axis direction perpendicular to the holding surface 25a of the chuck table 25 to adjust the position of the focal point, and a Z-position detection means 8 that detects the Z-axis position of the focal point formed by focusing the light by the condenser 64. The Z-axis moving means 5 includes a pulse motor 51 driven by a drive pulse of the control means 100 shown in the figure, and a ball screw 52 connected to the output shaft of the pulse motor 51. The ball screw 52 is driven by the forward and reverse rotation of the pulse motor 51, and the condenser 64 is moved in the Z-axis direction. The Z-position detection means 8 includes a Z-axis scale 81 whose position is fixed relative to the base 3, and a Z-position reading unit 82 that is attached to the condenser 64 and moves in the Z-axis direction together with the condenser 64 to read the memory of the Z-axis scale 81. The distance from the holding surface 25a to the Z-position reading unit 82 is detected based on the holding surface 25a of the chuck table 25. The Z-axis moving means 5 and the Z-position detecting means 8 are connected to the control means 100 as shown in the figure. Furthermore, the control means 100 is connected to the imaging means 7 and the display means 9, which are disposed adjacent to the condenser 64 in the X-axis direction, and the image captured by the imaging means 7 is sent to the control means 100 and displayed on the display means 9.

The control means 100 is composed of a computer and includes a Z position memory unit 110 that stores the position in the Z axis direction of the focusing point P of the collector 64, an inspection range setting unit 120 that sets an inspection range with coarse and fine spacing and an inspection range with fine spacing in order to inspect the deviation of the focusing point P based on a predetermined position stored in the Z position memory unit 110, an image memory unit 130 that stores images captured by the imaging means 7 corresponding to the inspection range with coarse and fine spacing and the inspection range with fine spacing, and an image processing unit 140 that processes the images stored in the image memory unit 130.

The laser processing device 1 of this embodiment has a configuration generally as described above, and the functions and actions of this embodiment will be described below with reference to Figures 2 to 6 in addition to Figure 1.

When carrying out this embodiment, first prepare the inspection wafer 10 shown in FIG. 1 and place it on the holding surface 25a of the chuck table 25. Then, activate the suction source (not shown) to hold and fix the wafer by suction via the adhesive tape T and the annular frame F.

Once the inspection wafer 10 is fixed to the chuck table 25, the actual position of the focal point of the laser processing device 1 is detected based on the control program stored in the control means 100 described above, in order to correct the Z position of the focal point P stored in the Z position memory unit 110 of the control means 100. More specifically, as shown in FIG. 2, the moving means 30 described above is first operated to move the chuck table 25 in the X-axis direction and the Y-axis direction, and a predetermined processing start position on the inspection wafer 10 is positioned directly below the condenser 64 of the laser irradiation means 6.

Here, the Z-position memory unit 110 of the control means 100 of this embodiment stores in advance the Z-axis position Z0 before correction when the focal point P of the pulsed laser beam LB focused by the condenser 64 is positioned on the surface 10a forming the upper surface of the inspection wafer 10. Then, based on the position Z0, the Z-axis moving means 5 is operated and the focal point P is positioned near the surface 10a of the inspection wafer 10. The focal length Za of the focusing lens 641 arranged in the condenser 64 of this embodiment is, for example, 50 mm, and the designed distance from the focal point P to the Z-position reading unit 82 is 100 mm. In this embodiment, since the thickness of the inspection wafer 10 is 700 μm (= 0.7 mm), the Z-axis position Z0 of the focal point P before correction stored in the Z-position memory unit 110 is 100.7 mm. In this embodiment, the laser processing is repeatedly performed in the laser processing device 1, so the following explanation will assume that the focal point P, which is positioned based on the position Z0 stored in the Z position memory unit 110, is shifted a certain amount in the Z-axis direction from the front surface 10a of the inspection wafer 10.

The Z-axis moving means 5 is operated based on the inspection range of the coarse and fine intervals set by the inspection range setting unit 120 of the control means 100, with the position Z0 stored in the Z position memory unit 110 as a reference. Then, the Z-axis moving means 5 intermittently moves the condenser 64 in the Z-axis direction and the chuck table 25 in the X-axis direction to irradiate the pulsed laser beam LB. More specifically, the coarse and fine intervals set by the inspection range setting unit 120 are, for example, 50 μm, and the deviation amount of the focus in the Z-axis direction from the above-mentioned position Z0 is empirically less than ±1.0 mm, so the inspection range is set to, for example, ±1.0 mm. Then, first, the Z-axis moving means 5 is operated to move the condenser 64 to a position (lower side in the figure) where the Z position detected by the Z position detection means 8 is Z0-1 mm, and the first pulsed laser beam LB is irradiated to form the processing mark shown by R1 in FIG. 3. Following this, the Z-axis moving means 5 is operated to intermittently move the condenser 64 upward by 50 μm, which is the coarse/fine interval, and the moving means 30 is operated in synchronization therewith to intermittently move the chuck table 25 in the X-axis direction, for example, by 5 mm, and the pulsed laser beam LB is irradiated one shot at a time in synchronization with this intermittent operation. In this manner, the condenser 64 and the moving means 30 are intermittently operated, and the pulsed laser beam LB is irradiated one shot at a time, until the position in the Z-axis direction detected by the Z-position detecting means 8 becomes Z0+1 mm. When the pulsed laser beam LB is irradiated, the position in the Z-axis direction of the condensing point P detected by the Z-position detecting means 8 is stored in the control means 100 in correspondence with the X-coordinate and Y-coordinate of the position irradiated with the pulsed laser beam LB. As a result, as shown in Figure 3, ablation processing is performed intermittently at 5 mm intervals on the front surface 10a of the inspection wafer 10, and 41 first processing marks Rn are formed along the X-axis direction. Note that in Figure 3, for convenience of explanation, the first processing marks Rn are shown larger than their actual dimensions, and the number of first processing marks Rn is shown smaller than the actual number.

The laser processing conditions in the above-mentioned laser processing are set, for example, as follows.
Wavelength: 355 nm
Repetition frequency: 50kHz
Average power output: 3W
Focal length: 50mm
Processing feed speed: 200 mm/sec

After the 41 first processing marks Rn are formed as described above, as shown in FIG. 4(a), the inspection wafer 10 is positioned directly under the imaging means 7, and the imaging means 7 images the first processing marks Rn formed on the surface 10a of the inspection wafer 10. More specifically, the X-axis feed means 31 of the moving means 30 is operated to move the chuck table 25 in the X-axis direction while sequentially imaging the 41 first processing marks Rn one by one, starting from R1. The images of the first processing marks Rn imaged by the imaging means 7 in this manner are stored in the image storage unit 130 of the control means 100 for each processing mark. The images imaged by the imaging means 7 can be displayed on the display means 9 via the control means 100. Also, as described above, the Z-axis position where the focal point P was located when each processing mark was formed is stored in the control means 100 for each processing mark, so when the image is displayed on the display means 9, the Z coordinate position detected by the Z position detection means 8 for each processing mark can be displayed together with each processing mark.

Next, the image processing unit 140 performs image processing on the first machining mark Rn stored in the image storage unit 130. This image processing is a process of analyzing the images of the individual machining marks stored in the image storage unit 130, calculating the area of each machining mark, and extracting the smallest machining mark. Through the action of this image processing unit 140, as shown in FIG. 4(b), the smallest first minimum machining mark Ra is extracted from among the machining marks included in the first machining mark Rn. Once the first minimum machining mark Ra has been extracted, the position in the Z-axis direction corresponding to the first minimum machining mark Ra and detected by the Z-position detection means 8 is stored in the Z-position storage unit 110 as the first minimum machining mark Z position Z1.

Next, the moving means 30 is operated to index and feed the chuck table 25 in the Y-axis direction shown by the arrow Y in FIG. 5, and the X-axis direction feed means 31 is operated to position the condenser 64 at the irradiation start position of the pulsed laser beam LB (the position shown by S1 in the figure), and the Z-axis moving means 5 is operated based on the inspection range of the precise interval set in the inspection range setting unit 120 of the control means 100, and the condenser 64 is intermittently moved in the Z-axis direction and the chuck table 25 is intermittently moved in the X-axis direction to irradiate the pulsed laser beam LB. More specifically, the precise interval set by the inspection range setting unit 120 is, for example, 5 μm, and the inspection range is set to, for example, ±50 μm. This inspection range is set with a margin to ensure that even smaller processing marks are included. Then, the position of the condenser 64 in the Z-axis direction is moved to a position (lower side in the figure) where the position detected by the Z-position detection means 8 is the first minimum processing mark Z position, Z1-50 μm, and the first pulsed laser beam LB is irradiated to form the processing mark shown by S1 in FIG. 5. Following this, the Z-axis moving means 5 is operated to intermittently move the condenser 64 upward by a precision interval of 5 μm, and the moving means 30 is operated to intermittently move the chuck table 25 in the X-axis direction, for example, by 5 mm, while irradiating the pulsed laser beam LB one shot at a time. In this way, the condenser 64 is intermittently raised in the Z-axis direction until the position in the Z-axis direction detected by the Z-position detection means 8 is Z1+50 μm on the upper side in the figure, and the pulsed laser beam LB is intermittently irradiated one shot at a time, to form 21 second processing marks Sn on the front surface 10a of the inspection wafer 10. In FIG. 5, for ease of explanation, the second processing marks Sn are shown larger than their actual dimensions and in fewer numbers than the actual number.

If the second processing marks Sn are formed as described above, as shown in FIG. 6(a), the inspection wafer 10 is moved along the X-axis direction together with the chuck table 25 and positioned directly under the imaging means 7, and the second processing marks Sn formed on the surface 10a of the inspection wafer 10 are imaged by the imaging means 7. More specifically, in the same manner as in the imaging of the first processing marks Rn described above, the X-axis feed means 31 of the moving means 30 is operated to move the chuck table 25 in the X-axis direction while sequentially imaging the 21 second processing marks Sn one by one starting from S1. The images of the second processing marks Sn thus imaged by the imaging means 7 are stored in the image storage unit 130 of the control means 100 for each processing mark. In this case, as in the case of the first processing marks Rn described above, the images imaged by the imaging means 7 can be displayed on the display means 9 via the control means 100. In addition, since the Z-axis position detected by the Z-position detection means 8 when each processing mark was formed is stored in the control means 100 in correspondence with each processing mark, when the image is displayed on the display means 9, the Z-coordinate position of the focal point P corresponding to each processing mark can be displayed together with each processing mark.

Next, the second machining marks Sn stored in the image storage unit 130 are processed by the image processing unit 140, and in the same manner as the first machining marks Rn are processed, the smallest second minimum machining mark Sa is extracted from among the machining marks included in the second machining marks Sn, as shown in FIG. 6(b). Once the second minimum machining mark Sa is extracted, the second minimum machining mark Z position Z2 in the Z-axis direction corresponding to the second minimum machining mark Sa is detected, and the second minimum machining mark Z position Z2 is stored in the Z position storage unit 110.

According to the above embodiment, by executing the control program provided in the control means 100, it is possible to automatically and accurately determine the position of the focal point P where the machining mark is smallest on the front surface 10a of the inspection wafer 10 (second minimum machining mark position Z2), thereby improving productivity. Then, based on the second minimum machining mark Z position Z2 for forming the focal point P where the machining mark is smallest detected in this manner, it is possible to properly position the focal point P with respect to the workpiece (wafer) held on the chuck table 25.

In the above embodiment, the chuck table 25 is fed in the X-axis direction to form the first machining mark Rn and the second machining mark Sn, but the present invention is not limited to this. For example, the chuck table 25 may be fed in the Y-axis direction to form the first machining mark Rn and the second machining mark Sn by intermittently irradiating the pulsed laser beam LB.

In the above embodiment, the inspection range with coarse and fine intervals and the inspection range with fine intervals are set to detect the second minimum machining mark Z position Z2 corresponding to the second minimum machining mark Sa, and the second minimum machining mark Z position Z2 is stored in the Z position memory unit. However, if it is desired to detect the position of the focal point P in the Z axis direction more precisely, it is also possible to add a setting of an inspection range with an ultra-precise interval of 0.5 μm, which is even narrower than the inspection range with fine intervals, of ±5 μm, and after detecting the above-mentioned second minimum machining mark Z position Z2, to newly form 21 third machining marks, detect the smallest third minimum machining mark from among the third machining marks, and obtain the third minimum machining mark Z position corresponding to the third minimum machining mark.

1: Laser processing device 2: Holding means 25: Chuck table 25a: Holding surface 3: Base 4: Holding means 5: Z-axis moving means 51: Pulse motor 52: Ball screw 6: Laser irradiation means 61: Oscillator 64: Condenser 7: Imaging means 8: Z-position detection means 81: Z-axis scale 82: Z-position reading unit 9: Display means 10: Inspection wafer 30: Moving means (feeding means)
31: X-axis direction feed means 32: Y-axis direction feed means 37: Frame 37a: Vertical wall portion 37b: Horizontal wall portion 100: Control means 110: Z-position storage unit 120: Inspection range setting unit 130: Image storage unit 140: Image processing unit

Claims (3)

A laser processing apparatus comprising at least a holding means having a chuck table with a holding surface defined by an X-axis and a Y-axis for holding a workpiece, a laser irradiation means for irradiating a pulsed laser beam having an absorbent wavelength to the workpiece held on the chuck table to perform ablation processing, a feeding means for feeding the chuck table and the laser irradiation means relatively in the X-axis and Y-axis directions for processing, an imaging means for imaging a processing area of the workpiece, and a control means,
the laser irradiation means includes an oscillator that oscillates a pulsed laser beam, a condenser that condenses the pulsed laser beam oscillated by the oscillator, and a Z-axis movement means that moves the condenser in a Z-axis direction perpendicular to the holding surface of the chuck table;
the control means comprises a Z-position memory section which stores a Z-axis position of the focusing point positioned by the focusing device, an inspection range setting section which sets an inspection range with coarse and fine intervals and an inspection range with fine intervals based on the position stored in the Z-position memory section, an image memory section which stores an image of the processing area of the workpiece imaged by the imaging means in correspondence with the inspection range with coarse and fine intervals and the inspection range with fine intervals, and an image processing section which processes the image stored in the image memory section;
The control means, based on the position in the Z-axis direction at which a focal point is located on the upper surface of the workpiece to be inspected held on the chuck table, intermittently moves the condenser in the Z-axis direction within the inspection range with coarse and fine intervals set by the inspection range setting unit, and intermittently moves the chuck table in the X-axis or Y-axis direction to irradiate the pulse laser beam one shot at a time in synchronization with the intermittent operation, thereby forming a plurality of discontinuous first processed marks corresponding to one shot on the upper surface of the workpiece, images of the first processed marks by the imaging means and stores them in the image storage unit, processes the image of the first processed marks stored in the image storage unit by the image processing unit, extracts a first minimum processed mark that is smallest among the first processed marks, detects a first minimum processed mark Z position in the Z-axis direction of the focal point corresponding to the first minimum processed mark, and further, a first minimum machining mark Z position for positioning a focal point on the upper surface of an inspection workpiece held on a chuck table as a reference, and the condenser is intermittently moved in the Z-axis direction and the chuck table is intermittently moved in the X-axis or Y-axis directions within the inspection range of the precise interval set by the inspection range setting unit to irradiate a pulsed laser beam one shot at a time to form a plurality of discontinuous second machining marks corresponding to one shot on the upper surface of the workpiece, the second machining marks are imaged by the imaging means and stored in the image storage unit, the image of the second machining marks stored in the image storage unit is processed by the image processing unit to extract a second minimum machining mark that is the smallest among the second machining marks, the second minimum machining mark Z position in the Z-axis direction of the focal point corresponding to the second minimum machining mark is detected, and the second minimum machining mark Z position is stored in the Z position storage unit. The laser processing device according to claim 1, wherein the inspection range for the coarse and fine spacing is 50 μm or more in the Z-axis direction and the inspection range is ±1.0 mm or more, and the inspection range for the fine spacing is 5 μm or less in the Z-axis direction and the inspection range is ±0.05 mm or less. The laser processing device according to claim 1 or 2, further comprising a display means for displaying an image of the processing mark captured by the imaging means and displaying the Z coordinate position of the focal point corresponding to the processing mark.