JP2013230478A - Laser machining apparatus and laser machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser machining apparatus and a laser machining method capable of applying uniform laser machining without depending on a laser irradiation surface state of a workpiece.SOLUTION: A laser machining apparatus is for applying laser machining to a workpiece, and includes a laser beam irradiation means that includes a chuck table for holding the workpiece, a laser oscillator, and a machining head having a condensing lens for collecting laser beam oscillated from the laser oscillator, a reflection light quantity detection means that detects the reflection light quantity of the laser beam irradiated to the workpiece held on the chuck table from the laser beam irradiation means, and a step number calculating means that calculates the number of the steps where a plurality of the steps of laser machining are applied over the thickness direction of the workpiece by the laser beam irradiation means based on the reflection light quantity detected by the reflection light quantity detection means.

Description

  The present invention relates to a laser processing apparatus and a laser processing method for performing laser processing on a workpiece such as a semiconductor wafer.

  A wafer such as a silicon wafer or a sapphire wafer formed on the surface by dividing a plurality of devices such as IC, LSI, LED, etc. by dividing lines is divided into individual devices by a processing apparatus, and the divided devices are mobile phones, Widely used in various electronic devices such as personal computers.

  A dicing method using a cutting device called a dicer is widely used for dividing the wafer. In the dicing method, a wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or a resin at a high speed of about 30000 rpm. Divide into chips.

  On the other hand, in recent years, a method of dividing a wafer into individual device chips using a laser beam has been developed and put into practical use. As methods for dividing a wafer into individual device chips using a laser beam, first and second processing methods described below are known.

  In the first processing method, a condensing point of a laser beam having a wavelength transparent to the wafer (for example, 1064 nm) is positioned inside the wafer corresponding to the division line, and the laser beam is aligned along the division line. This is a method in which a modified layer is formed inside the wafer by irradiation, and then an external force is applied to the wafer by a dividing device to divide the wafer into individual device chips using the modified layer as a starting point (for example, Japanese Patent No. 3408805). reference).

  In the second processing method, a processing groove is formed by ablation processing by irradiating a condensing point of a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to a wafer to an area corresponding to a division-scheduled line. Is used to divide the wafer into individual device chips with the processing groove as a starting point (see, for example, JP-A-10-305420).

  The processing method using a laser beam can increase the processing speed as compared with a dicing method using a dicer, and can relatively easily process even a wafer made of a material having high hardness such as sapphire or SiC. .

  In addition, since the modified layer or the processed groove can be made to have a narrow width of, for example, 10 μm or less, there is an advantage that the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method. ing.

  Incidentally, an oxide film or a nitride film remains on the back surface of the semiconductor wafer before the back surface grinding by the grinding apparatus. There are also semiconductor wafers having a low-k film formed on the front surface and wafers having a metal film formed on the back surface.

  When laser processing is performed by irradiating a workpiece with these films with a laser beam, a part of the laser beams irradiated by the film is reflected. The reflectivity varies depending on the type and thickness of the film, and the reflectivity varies depending on the workpiece, and there are variations in reflectivity even within one workpiece.

  A first processing method for forming a modified layer inside a workpiece using a wavelength that is transmissive to the workpiece, and a workpiece using a wavelength that is absorptive for the workpiece Also in the case of the second processing method in which ablation processing is performed on the workpiece, if the reflectance of the workpiece is large, the amount of transmitted or absorbed laser beam is reduced. It is necessary to increase the beam output.

Japanese Patent No. 3408805 JP-A-10-305420 JP 2009-021476 A JP 2010-245172 A

  If the workpieces have different reflectivities, and laser processing is performed on multiple workpieces under a single processing condition, the depth of the laser processing grooves formed by laser beam irradiation varies between workpieces. Or a variation occurs in the modified layer formed by laser beam irradiation.

  Also, in the case where the reflectance varies within one workpiece, when laser processing is performed under a single processing condition, the depth of the laser processing groove formed by laser beam irradiation varies depending on the region. Or the modified layer formed by the laser beam irradiation has a problem.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a laser processing apparatus and laser processing capable of performing uniform laser processing regardless of the state of the laser irradiation surface of the workpiece. Is to provide a method.

  According to the first aspect of the present invention, there is provided a laser processing apparatus for performing laser processing on a workpiece, a chuck table for holding the workpiece, a laser oscillator, and a laser beam oscillated from the laser oscillator. A laser beam irradiating unit including a processing head having a condenser lens, and a reflected light amount detecting unit for detecting a reflected light amount of the laser beam irradiated to the workpiece held on the chuck table from the laser beam irradiating unit And a stage number calculating means for calculating the number of stages for performing laser processing of a plurality of stages in the thickness direction of the workpiece by the laser beam irradiation means based on the reflected light quantity detected by the reflected light quantity detecting means. There is provided a laser processing apparatus characterized by the above.

  According to a second aspect of the present invention, there is provided a laser processing method for performing laser processing on a workpiece, a holding step for holding the workpiece with a chuck table, and a laser beam applied to the workpiece held on the chuck table. A laser beam irradiation step for detecting a reflected light amount that irradiates a laser beam under the first condition from the irradiation means, and the laser beam irradiated to the workpiece in the laser beam irradiation step for detecting the reflected light amount is reflected on the upper surface of the workpiece. A reflected light amount detecting step for detecting the amount of reflected light, and a number of steps for calculating the number of steps for performing laser processing of a plurality of steps in the thickness direction of the workpiece based on the reflected light amount detected in the reflected light amount detecting step After performing the calculating step and the step number calculating step, the laser beam irradiation means is applied to the workpiece held on the chuck table. A laser processing step of irradiating a laser beam under the second condition and performing laser processing of the number of steps calculated in the step number calculating step in the thickness direction of the workpiece. A method is provided.

  The laser processing apparatus of the present invention includes a reflected light amount detecting unit that detects the amount of reflected light reflected from the upper surface of the workpiece, and a step number calculating unit that calculates an optimum number of steps for performing laser processing based on the detected reflected light amount. Therefore, uniform laser processing can be performed regardless of the laser irradiation surface state of the workpiece.

  The laser processing method of the present invention includes a laser beam irradiation step for detecting a reflected light amount, a reflected light amount detecting step for detecting the reflected light amount, and a thickness of the workpiece based on the reflected light amount detected in the reflected light amount detecting step. Therefore, a uniform laser processing can be performed on the workpiece regardless of the state of the laser irradiation surface of the workpiece.

It is a perspective view of a laser processing apparatus. It is a block diagram of the optical system of a laser beam irradiation unit. It is a surface side perspective view of a semiconductor wafer. It is a disassembled perspective view which shows a mode that the outer peripheral part adheres the surface side of a semiconductor wafer to the adhesive tape with which the annular frame was mounted | worn. It is a partial cross section side view showing a holding step. It is a partial cross section side view which shows the laser beam irradiation step for reflected light amount detection. It is a figure which shows the correlation with the reflectance of a to-be-processed object, and the appropriate number of process steps. It is a partial cross section side view which shows the laser processing step which forms a modified layer inside a wafer. It is sectional drawing explaining the number of steps of laser processing. It is a partial cross section side view which shows the laser beam irradiation step for the reflected light amount detection implemented on the surface side of a wafer. It is a partial cross section side view which shows embodiment which performs laser processing, detecting the reflected light quantity. It is a perspective view which shows a back surface grinding step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an external perspective view of a laser processing apparatus according to an embodiment of the present invention is shown. The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by a machining feed means (machining feed unit) 12 including a ball screw 8 and a pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means (indexing feeding unit) 22 composed of the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 for clamping the semiconductor wafer sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a laser beam irradiation unit 34 is attached to the column 32. The laser beam irradiation unit 34 includes a laser oscillation unit 62 shown in FIG. 2 housed in a casing 35 and a processing head 36 attached to the tip of the casing 35.

  As shown in FIG. 2, the laser oscillation unit 62 includes a laser oscillator 64 that oscillates a YAG laser or a YVO4 laser, and a repetition frequency setting unit 66. Although not particularly illustrated, the laser oscillator 64 has a Brewster window, and the laser beam emitted from the laser oscillator 64 is a linearly polarized laser beam.

  At the tip of the casing 35, an imaging unit 38 that detects the machining area to be laser machined in alignment with the machining head 36 in the X-axis direction is disposed. The image pickup unit 38 includes an image pickup device such as a normal CCD that picks up an image of a processing region of a semiconductor wafer with visible light.

  The imaging unit 38 further includes an infrared irradiation unit that irradiates the semiconductor wafer with infrared rays, an optical system that captures the infrared rays irradiated by the infrared irradiation unit, and an infrared CCD that outputs an electrical signal corresponding to the infrared rays captured by the optical system. Infrared imaging means composed of an infrared imaging element such as the above is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal captured by the imaging unit 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  Referring to FIG. 2, an optical system of the laser beam irradiation unit 34 according to the embodiment of the present invention is shown. A reflection mirror 76 and a condenser lens 74 are accommodated in a casing 70 of the processing head 36. Further, a half mirror (beam splitter) 76 is disposed between the reflection mirror 72 and the condenser lens 74.

  The laser beam 69 oscillated from the laser beam oscillation unit 62 and further adjusted to a predetermined power by the output adjustment unit 68 is reflected by the reflection mirror 72 of the processing head 36, and a part of the laser beam 69 passes through the half mirror 76 and passes through the condenser lens. The wafer 11 which is a workpiece is irradiated by 74.

  The reflected light 71 reflected from the upper surface of the wafer 11 is collected by a condenser lens 74, a part of which is reflected by a half mirror 76, and a reflected light amount detector 78 comprising a light receiving element such as a photodiode detects the reflected light amount. The

  Based on the amount of reflected light, the stage number calculation unit 80 calculates the number of stages to be subjected to a plurality of stages of laser processing in the thickness direction of the workpiece (wafer). The step number calculation unit 80 is connected to the machining feed unit 12, the index feed unit 22, and the condensing point position changing unit 81, and the controller 40 determines whether the step 40 is calculated according to the calculated number of steps. The light spot position changing unit 81 is controlled.

  The half mirror 76 may be disposed between the condensing lens 74 and the workpiece (wafer) 11, but the half mirror 76 disposed on the upstream side of the condensing lens 74 on the upper surface of the wafer 11. Since only the reflected reflected light can be condensed by the condenser lens 74 and incident on the half mirror 76, such an arrangement is preferable for detecting the amount of reflected light.

Referring to FIG. 3, there is shown a front perspective view of a semiconductor wafer 11 which is one of the workpieces of the laser processing method of the present invention. The semiconductor wafer 11 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of division lines 13 are formed in a lattice shape on the surface 11 a and each region divided by the plurality of division lines 13 is formed in each region. A device 15 such as an IC or LSI is formed. An oxide film 17 made of SiO ₂ is formed on the back surface 11b of the semiconductor wafer 11 as shown in FIG.

  In the laser processing method of the present invention, the workpiece is not limited to the semiconductor wafer 11 shown in FIG. 3, but has a film such as an oxide film, a nitride film, a metal film, or a low-k film on the front surface or the back surface. Includes workpieces.

  In carrying out the laser processing method of the present invention, the front surface 11a side of the semiconductor wafer 11 is adhered to the adhesive tape T attached to the annular frame F as shown in FIG. Become.

  Then, as shown in FIG. 5, the semiconductor wafer 11 is sucked and held by the chuck table 28 of the laser processing apparatus 2 via the adhesive tape T, and the annular frame F is clamped and fixed by the clamp 30.

  Next, as shown in FIG. 6, a reflected light amount detection laser beam irradiation step is performed in which the wafer 11 held on the chuck table 28 is irradiated with the laser beam 69 from the processing head 36 of the laser beam irradiation unit 34 under the first condition. To do.

  Prior to performing the laser beam irradiation step for detecting the reflected light amount, alignment for detecting the division line 13 to be laser processed is performed. That is, the wafer 11 is imaged from the back surface 11b side by the infrared camera of the image pickup unit 38, and is orthogonal to the planned dividing line 13 and the first direction extending in the first direction by using well-known image processing such as pattern matching. The division planned line 13 extending in the second direction is detected.

  As another embodiment, the holding surface of the chuck table 28 may be formed of a transparent member, and the wafer 11 may be imaged with a camera disposed under the chuck table 28 to perform alignment.

  Further, in the present invention, before detecting the reflected light amount of the wafer 11, one or a plurality of reference workpieces having a known reflectance are prepared in advance, the reflected light amount is detected by the reference workpiece, and the reflected light amount at that time is determined. It is stored in the RAM 46 of the controller 40 as reference data.

  In this reflected light amount detection laser beam irradiation step, as shown in FIG. 6, the laser beam is applied from the processing head 36 to the back surface 11b of the wafer 11 on which the oxide film 17 is formed while processing the chuck table 28 in the direction of the arrow X1. 69 and the reflected light 71 is detected by a reflected light amount detector 78.

  For example, the amount of reflected light is detected by irradiating an arbitrary scheduled division line 13, a plurality of scheduled division lines 13, or all the planned division lines 13 of the wafer 11 with a reflected light amount detection laser beam.

  The irradiation conditions of the reflected light amount detection laser beam when the modified layer is formed inside the wafer 11 by irradiation with the laser beam 69 are as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100 kHz
Average output: 0.1W
Processing feed rate: 400 mm / s

  When the laser beam 69 is irradiated on the back surface 11b of the wafer 11 in the reflected light amount detection laser beam irradiation step, the reflected light 71 reflected by the back surface 11b on which the oxide film 17 is formed is condensed by the condenser lens 74 shown in FIG. Then, a part of the light is reflected by the half mirror 76 and enters the reflected light amount detector 78 including a light receiving element, and the reflected light amount reflected by the back surface 11 b of the wafer 11 is detected. The reflectance of the back surface 11b of the wafer 11 is calculated from the detected reflected light amount and the reflected light amount of the reference workpiece whose reflectance stored in the RAM 46 is known.

  The ROM 44 of the controller 40 stores a plurality of correlation diagrams as shown in FIG. 7, for example, showing a correlation 73 between the reflectance of the workpiece and the appropriate number of machining steps for each type of workpiece and each machining condition. Keep it. In the present invention, it is assumed that the laser beam power oscillated by the laser oscillator 64 adjusted by the output adjustment unit 68 cannot be processed sufficiently by a single laser processing.

  After performing the reflected light amount detection step, the step number calculation unit 80 calculates the number of processing steps based on the reflected light amount detected in the reflected light amount detection step, and the laser beam irradiation unit 34 is applied to the wafer 11 held on the chuck table 28. A laser processing step of forming the modified layer 19 inside the wafer 11 by irradiating a laser beam from the processing head 36 under the second condition is performed.

  In this laser processing step, as shown in FIG. 8, while the chuck table 28 is processed and fed in the direction of the arrow X1, the laser beam 69 is irradiated from the processing head 36 of the laser beam irradiation unit 34 under the second condition, and the wafer is processed. 11, a modified layer 19 is formed inside.

  While indexing and feeding the chuck table 28 in the Y-axis direction, similar modified layers 19 are successively formed in the wafer 11 along the scheduled division line 13 extending in the first direction. Next, after the chuck table 28 is rotated by 90 degrees, a similar modified layer 19 is formed along the planned dividing line 13 extending in the second direction.

  When the number of processing steps calculated by the step number calculating unit 80 is two, as shown in FIG. 9, the first modified layer 19a and the second modified layer 19a and the second modified layer are changed while the condensing point position is changed by the condensing point position changing unit 81. The modified layer 19b is formed inside the wafer.

  The laser processing conditions in this modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100 kHz
Average output: 2.0W
Processing feed rate: 400 mm / s

  Referring to FIG. 10, there is shown a partial cross-sectional side view for explaining a reflected light amount detecting laser beam irradiation step when the wafer 11 is ablated. For example, when ablation processing is performed on the Low-k film formed on the surface 11 a of the wafer 11, the laser beam 69 is incident on the surface 11 a side of the wafer 11. Then, the amount of reflected light 71 reflected by the surface 11 a is detected by a reflected light amount detector 78.

  Also in the case of ablation processing, similarly to the above-described modified layer forming processing, a laser beam for detecting the amount of reflected light is irradiated on an arbitrary division line 13, a plurality of division division lines 13, or all the division division lines 13 of the wafer 11. The amount of reflected light is detected.

  The laser beam irradiation conditions in the case of ablation processing are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 355 nm (third harmonic of YVO 4 pulse laser)
Repetition frequency: 200 kHz
Average output: 0.1W
Processing feed rate: 200 mm / s

  In the ablation processing, after performing the reflected light amount detection step, the step number calculation unit 80 calculates the processing step number based on the reflected light amount detected in the reflected light amount detection step, and the surface 11a of the wafer 11 held by the chuck table 28. Next, a laser processing step is performed in which a laser beam is irradiated from the processing head 36 of the laser beam irradiation unit 34 under the second condition to ablate the division planned line 13 of the wafer 11 to form a laser processing groove.

  The laser processing conditions in this ablation processing are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 355 nm (third harmonic of YVO 4 pulse laser)
Repetition frequency: 200 kHz
Average output: 1W
Processing feed rate: 200 mm / s

  When the number of processing steps calculated by the step number calculation unit 80 is two, the focal point position is set on the surface 11a of the wafer 11 in the first laser processing, and the first in the second laser processing. A condensing point position is set near the bottom surface of the laser processing groove formed by the second ablation processing.

  In the second embodiment of the laser processing method of the present invention, the laser processing step may be performed while performing the reflected light amount detection step. That is, as shown in FIG. 11, a laser beam 69 is irradiated from the processing head 36 of the laser beam irradiation unit 34 while processing and feeding the chuck table 28 in the direction of the arrow X1, and the reflected light 71 reflected by the back surface 11b of the wafer 11 is reflected. The reflected light amount is detected by a reflected light amount detector 78.

  Based on the amount of reflected light, the number of processing steps required by the step number calculation unit 80 is calculated, and the modified layer 19 having the calculated number of steps is formed inside the wafer 11. Also in the case of ablation processing, the number of processing steps required by the step number calculation unit 80 is calculated according to the amount of reflected light, and ablation processing is performed for the calculated number of steps. After the modified layer 19 and the laser processing groove are formed on the wafer 11, a dividing step is performed in which an external force is applied to the wafer 11 to divide the wafer into individual chips.

  In the present embodiment, after the modified layer 19 is formed inside the wafer 11 along all the planned division lines 13, a back surface grinding step for grinding the back surface 11b of the wafer 11 is performed. In this back surface grinding step, as shown in FIG. 12, the back surface 11b of the wafer 11 held by the chuck table 96 of the grinding device is ground with a grinding wheel 94, and the wafer 11 is divided into individual chips by the pressing force during grinding. To divide.

  In FIG. 12, the grinding unit 82 includes a spindle 84, a wheel mount 86 fixed to the tip of the spindle 84, and a grinding wheel 88 detachably attached to the wheel mount 86 with a plurality of screws 90. The grinding wheel 88 is configured by fixing a plurality of grinding wheels 94 to the outer periphery of the lower end portion of the annular base 92.

  In this back surface grinding step, the grinding unit feed mechanism is operated while the chuck table 96 is rotated in the direction of arrow a at 300 rpm, for example, and the grinding wheel 88 is rotated in the direction of arrow b at 6000 rpm, for example. It is made to contact the back surface 11b.

  Then, the back surface 11b of the wafer 11 is ground while the grinding wheel 88 is ground and fed downward at a predetermined grinding feed rate. While measuring the thickness of the wafer 11 with a contact-type or non-contact-type thickness measurement gauge, the wafer 11 is finished to a desired thickness, for example, 50 μm.

  In the middle of this grinding, the modified layer 19 is formed along the scheduled division line 13 inside the wafer 11, so that the wafer 11 is separated into individual chips from the modified layer 19 by the pressing force during grinding. Divided into

  Here, in the case of a work piece with low splittability, a splitting step for splitting by applying an external force to the work piece is performed before performing back surface grinding. Alternatively, after performing the back surface grinding, a dividing step is performed in which an external force is applied to the workpiece to divide the workpiece.

  In the embodiment described above, after the modified layer 19 is formed on the thick (700 μm) wafer, the back surface 11b of the wafer 11 is ground to thin the wafer, and at the same time, the modified layer is applied by the pressing force during grinding. 19 is divided into individual chips, but the modified layer 19 and the laser processing groove may be formed on the wafer 11 that has been thinned by grinding the back surface 11b in advance.

11 Semiconductor wafer 13 Scheduled division line 15 Device 17 Oxide film 19, 19a, 19b Modified layer 28 Chuck table 34 Laser beam irradiation unit 36 Processing head 38 Imaging unit 62 Laser oscillation unit 64 Laser oscillator 66 Repetitive frequency setting unit 68 Output adjustment unit 69 Laser beam 71 Reflected light 74 Condensing lens 76 Half mirror 78 Reflected light quantity detector 80 Stage number calculation unit

Claims (2)

A laser processing apparatus for performing laser processing on a workpiece,
A chuck table for holding the workpiece;
A laser beam irradiation means comprising: a laser oscillator; and a processing head having a condenser lens for condensing a laser beam oscillated from the laser oscillator;
A reflected light amount detecting means for detecting a reflected light amount of a laser beam irradiated on the workpiece held on the chuck table from the laser beam irradiation means;
Based on the reflected light amount detected by the reflected light amount detecting means, a stage number calculating means for calculating the number of stages for performing laser processing of a plurality of stages over the thickness direction of the workpiece by the laser beam irradiation means;
A laser processing apparatus comprising: A laser processing method for performing laser processing on a workpiece,
A holding step for holding the workpiece on the chuck table;
A laser beam irradiation step for detecting the amount of reflected light for irradiating the workpiece held on the chuck table with a laser beam from the laser beam irradiation means under a first condition;
A reflected light amount detecting step for detecting a light amount of reflected light that is reflected on the workpiece upper surface by the laser beam irradiated on the workpiece in the reflected light amount detecting laser beam irradiation step;
Based on the amount of reflected light detected in the reflected light amount detection step, a step number calculating step for calculating the number of steps to perform a plurality of steps of laser processing in the thickness direction of the workpiece;
After performing the step number calculating step, the workpiece held on the chuck table is irradiated with a laser beam under the second condition from the laser beam irradiation means, and the step number is calculated in the thickness direction of the workpiece. A laser processing step for performing laser processing of the number of steps calculated in the step;
A laser processing method comprising:

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