KR20130121718A - Laser machining apparatus and laser machining method - Google Patents

Abstract

The present invention relates to a laser processing device and a laser processing method capable of performing an even laser processing regardless of the conditions of the surface irradiated with a laser. The laser processing device comprises: a chuck table maintaining objects; a laser oscillator; a laser beam irradiation member including a processing head having a condensing lens condensing laser beams oscillated from the laser oscillator; a reflection light amount detection member detecting the reflection light amount of the laser beams with which the object is irradiated from the laser beam irradiation member; and a singular number calculating member calculating the singular numbers performing the laser processing towards the thickness direction of the object from the laser beam irradiation member based on the reflection light amount detected from the reflection light amount detection member. [Reference numerals] (12) Processing transporting unit;(22) Indexing transporting unit;(64) Laser oscillator;(66) Repetition frequency setting unit;(68) Output adjusting unit;(78) Reflex light amount detector;(80) Singular calculating unit;(81) Concentrating light point changing unit

Description

LASER MACHINING APPARATUS AND LASER MACHINING METHOD}

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 plurality of devices such as ICs, LSIs, LEDs, etc. are partitioned by lines to be divided, and wafers such as silicon wafers and sapphire wafers formed on the surface are divided into individual devices by a processing apparatus, and the divided devices are divided into mobile phones, PCs, and the like. It is widely used in various electronic devices.

For dividing the wafer, a dicing method using a cutting device called a dicer is widely adopted. In the dicing method, a wafer is cut by dividing a grain such as diamond into metal or resin and cutting the wafer while rotating the cutting blade having a thickness of about 30 μm at a high speed of about 30000 rpm to cut the wafer into individual device 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 a method of dividing a wafer into individual device chips using a laser beam, first and second processing methods described below are known.

In a first processing method, a light converging point of a laser beam having a transmittance with respect to a wafer (for example, 1064 nm) is positioned inside a wafer corresponding to a dividing scheduled line, and the laser beam is irradiated along the dividing scheduled line, thereby A modified layer is formed on the substrate, and then, an external force is applied to the wafer by a dividing apparatus, and the wafer is divided into individual device chips with the modified layer as the starting point of division (see Japanese Patent No. 3408805, for example).

The second processing method irradiates a region corresponding to a division scheduled line with a light-converging point of a laser beam having a wavelength (for example, 355 nm) having an absorptance with respect to a wafer to form a processing groove by ablation processing, and then applies external force. It is a method of dividing a wafer into individual device chips by making a process groove into a division origin (for example, refer Unexamined-Japanese-Patent No. 10-305420).

The processing method using a laser beam can make processing speed faster than the dicing method by a dicer, and can process it easily even with the wafer which consists of materials with high hardness, such as sapphire and SiC.

Moreover, since a modified layer or a process groove can be made into narrow width, such as 10 micrometers or less, it has the advantage that the quantity which can take a device per wafer can be increased compared with the case of processing by the dicing method.

By the way, an oxide film and a nitride film remain | survive on the back surface of the semiconductor wafer before back surface grinding by a grinding apparatus. There are also semiconductor wafers in which a low-k film is formed on the surface and a wafer on which a metal film is formed on the back surface.

When a laser beam is irradiated to the workpiece | work which has such a film | membrane, a part of the laser beam irradiated by the film | membrane will be reflected. The reflectance is different depending on the kind, thickness, etc. of the film, and the reflectance is different for each workpiece, or the reflectance is uneven even in one workpiece.

A first processing method for forming a modified layer inside a workpiece by using a wavelength having a transmittance with respect to the workpiece and a second processing method for ablating the workpiece with a wavelength having absorption with the workpiece. Even in this case, when the reflectance of the workpiece is large, the amount of light of the laser beam that is transmitted or absorbed is reduced. Therefore, in order to perform desired laser processing, it is necessary to increase the output of the irradiated laser beam.

Japanese Patent No. 3408805 Japanese Patent Laid-Open No. 10-305420 Japanese Patent Publication No. 2009-021476 Japanese Patent Laid-Open No. 2010-245172

When the reflectance is different for each workpiece, when a plurality of workpieces are subjected to laser processing under a single processing condition, the depth of the laser processing groove formed by the irradiation of the laser beam between the workpieces becomes uneven or the laser beam is irradiated. There exists a problem that a nonuniformity arises in the modified layer formed by this.

Moreover, in the case where the reflectance is nonuniform in one workpiece, when the laser processing is performed under a single processing condition, the depth of the laser processing groove formed by the irradiation of the laser beam depending on the area becomes uneven or the laser beam There exists a problem that a nonuniformity arises in the modified layer formed by irradiation.

This invention is made | formed in view of such a point, Comprising: It aims at providing the laser processing apparatus and laser processing method which can perform uniform laser processing irrespective of the state of the laser irradiation surface of a to-be-processed object.

According to the invention of claim 1, there is provided a laser processing apparatus for performing laser processing on a workpiece, which has a chuck table for holding the workpiece, a laser oscillator, and a condenser lens for condensing the laser beam oscillated from the laser oscillator. Laser beam irradiation means including a head, reflected light amount detection means for detecting the reflected light amount of the laser beam irradiated from the laser beam irradiation means to the workpiece held on the chuck table, and the reflection detected by the reflected light amount detection means On the basis of the amount of light, the laser processing apparatus is provided with the number calculating means which calculates the number of stages which perform a plurality of steps of laser processing in the thickness direction of a to-be-processed object by the said laser beam irradiation means.

According to the invention of claim 2, there is provided a laser processing method for performing laser processing on a workpiece, comprising: a holding step of holding the workpiece on a chuck table, and a first condition from a laser beam irradiation means on the workpiece held on the chuck table; A laser beam irradiation step of detecting a reflected light amount to irradiate a laser beam and a reflection of detecting a light amount of reflected light reflected from an upper surface of the workpiece by a laser beam irradiated to the workpiece in the reflected beam amount detecting laser beam irradiation step After the step of calculating the number of steps for performing the laser processing of a plurality of stages over the thickness direction of the workpiece based on the amount of light detection step and the reflected light amount detected in the reflected light amount detection step, and after the step And a laser beam under the second condition from the laser beam irradiation means to the workpiece held on the chuck table. There is provided a laser processing method comprising a laser processing step of irradiating and performing a single laser processing calculated in the above-mentioned stage calculation step over the thickness direction of the workpiece.

Since the laser processing apparatus of the present invention has a reflected light amount detecting means for detecting the light amount of the reflected light reflected from the upper surface of the workpiece, and a singular calculating means for calculating the optimum number of steps for laser processing based on the detected reflected light amount. It becomes possible to perform uniform laser processing irrespective of the state of the laser irradiation surface of a to-be-processed object.

The laser processing method of the present invention comprises a plurality of stages over the thickness direction of the workpiece based on the laser beam irradiation step for detecting the reflected light amount, the reflected light amount detecting step for detecting the reflected light amount, and the reflected light amount detected in the reflected light amount detecting step. Since it includes the stage calculating step of calculating the stage which performs the laser processing of the workpiece | work, a uniform laser processing can be performed to a to-be-processed object irrespective of the state of the laser irradiation surface of a to-be-processed object.

1 is a perspective view of a laser processing apparatus.
2 is a block diagram of an optical system of a laser beam irradiation unit.
3 is a perspective view of the surface side of a semiconductor wafer.
It is an exploded perspective view which shows the aspect which adhere | attaches the surface side of a semiconductor wafer to the adhesive tape with which the outer peripheral part was attached to the annular frame.
5 is a partial cross-sectional side view showing the holding step.
6 is a partial cross-sectional side view showing the laser beam irradiation step for detecting the reflected light amount.
7 is a diagram showing a correlation between reflectance of a workpiece and an appropriate pulse energy.
8 is a partial cross-sectional side view illustrating a laser processing step of forming a modified layer inside a wafer.
9 is a cross-sectional view illustrating the number of stages of laser processing.
10 is a partial cross-sectional side view showing a laser beam irradiation step for detecting a reflected light amount on a surface side of a wafer.
It is a partial cross-sectional side view which shows embodiment which performs laser processing, detecting the amount of reflected light.
12 is a perspective view illustrating the back grinding step.

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

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

The 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 indexed in the indexing direction along the pair of guide rails 24 by the indexing conveying means (indexing conveying unit) 22 composed of the ball screw 18 and the pulse motor 20. That is, it moves in the Y-axis direction.

The chuck table 28 is mounted on the 2nd slide block 16 via the cylindrical support member 26, and the chuck table 28 is an X-axis direction by the process feed means 12 and the indexing feed means 22. As shown in FIG. And move in the Y-axis direction. The chuck table 28 is provided with a clamp 30 for clamping the semiconductor wafer attracted 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 accommodated in the 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 for oscillating a YAG laser or a YVO4 laser, and a repetition frequency setting unit 66. Although not particularly shown, 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 distal end of the casing 35, an imaging unit 38 is arranged that detects a machining region to be laser-processed by aligning the machining head 36 in the X-axis direction. The imaging unit 38 includes an imaging device such as a normal CCD for imaging a processing region of a semiconductor wafer with visible light.

The imaging unit 38 includes infrared irradiation means for irradiating infrared rays to a semiconductor wafer, an optical system for capturing infrared rays irradiated by the infrared irradiation means, an infrared CCD for outputting an electric signal corresponding to the infrared rays captured by the optical system, and the like. Infrared imaging means constituted by an infrared imaging element, wherein the captured image signal is transmitted to a controller (control means) 40.

The controller 40 is configured by a computer, and includes a central processing unit (CPU) 42 for arithmetic processing in accordance with a control program, a read-only memory (ROM) 44 for storing a control program and the like, arithmetic results, and the like. A read / write random access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52.

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

Reference numeral 60 is an indexing feed amount detecting means composed of a linear scale 58 arranged along the guide rail 24 and a read head (not shown) arranged on the second slide block 16, and the indexing feed amount detecting means 60. The detection signal of is input to the input interface 50 of the controller 40.

The image signal picked up 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.

2, an optical system of a laser beam irradiation unit 34 according to an embodiment of the present invention is shown. The reflective mirror 76 and the condenser lens 74 are accommodated in the casing 70 of the processing head 36. In addition, 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 adjusted to the power determined in the output adjustment unit 68 is reflected by the reflection mirror 72 of the processing head 36, and part of the half mirror ( It penetrates 76 and is irradiated to the wafer 11 which is a workpiece by the condensing lens 74.

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

Based on this reflected light quantity, the number of stages which perform a laser processing of multiple stages in the thickness direction of a to-be-processed object (wafer) in the stage calculation unit 80 is calculated. The stage calculating unit 80 is connected to the machining transfer unit 12, the indexing transfer unit 22, and the condensing point position changing unit 81, and the controller 40 controls the machining transfer unit 12 in accordance with the calculated stage. , The indexing transfer unit 22 and the condensing point position changing unit 81 are controlled.

Although the half mirror 76 may be arrange | positioned between the condensing lens 74 and the to-be-processed object (wafer) 11, the half mirror 76 is arrange | positioned upstream rather than the condensing lens 74, The wafer 11 Since only the reflected light reflected from the upper surface of the light can be collected by the condenser lens 74 and incident on the half mirror 76, such an arrangement is preferable for the detection of the reflected light amount.

Referring to Fig. 3, there is shown a perspective view of the surface side 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 scheduled lines 13 are formed in a lattice shape on the surface 11 a, and divided by a plurality of division scheduled lines 13. In each of the regions, devices 15 such as IC and LSI are formed. On the back surface 11b of the semiconductor wafer 11, an oxide film 17 made of SiO ₂ is formed, 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, and includes a workpiece having a film such as an oxide film, a nitride film, a metal film, a Low-k film or the like on the front or back surface. It is.

In performing the laser processing method of this invention, as shown in FIG. 4, the surface 11a side of the semiconductor wafer 11 adhere | attaches the adhesive tape T by which the outer periphery was attached to the annular frame F. As shown in FIG. The back surface 11b becomes an upper side.

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

6, the reflection which irradiates the laser beam 69 to a 1st condition from the processing head 36 of the laser beam irradiation unit 34 to the wafer 11 hold | maintained at the chuck table 28 as shown in FIG. A laser beam irradiation step for detecting the amount of light is performed.

Before performing the laser beam irradiation step for detecting the reflected light amount, alignment is performed to detect the division scheduled line 13 to be laser processed. That is, the division scheduled line 13 extending in the first direction by imaging the wafer 11 from the back surface 11b side with an infrared camera of the imaging unit 38 and using well-known image processing such as pattern matching. And the division scheduled line 13 extending in the second direction orthogonal to the first direction.

As another embodiment, the holding surface of the chuck table 28 may be formed of a transparent member, and the wafer 11 may be picked up by the camera disposed below the chuck table 28 to perform alignment.

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

In this laser beam irradiation step for detecting the reflected light amount, as illustrated in FIG. 6, the wafer 11 on which the oxide film 17 is formed from the processing head 36 is processed while transferring the chuck table 28 in the direction of arrow X1. The laser beam 69 is irradiated to the rear surface 11b to detect the reflected light 71 by the reflected light amount detector 78.

For example, the reflected light amount detection laser beam is irradiated to an arbitrary division scheduled line 13, a plurality of division scheduled lines 13, or all the division scheduled lines 13 of the wafer 11 to detect the reflected light amount.

Irradiation conditions of the laser beam for detecting the reflected light amount when the modified layer is formed inside the wafer 11 by irradiation of the laser beam 69 are as described below, for example.

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 1064 nm

Repetition frequency: 100 ㎑

Average power: 0.1 W

Machining feed rate: 400 mm / s

When the laser beam 69 is irradiated to the back surface 11b of the wafer 11 in the laser beam irradiation step for detecting the reflected light amount, the reflected light 71 reflected from the back surface 11b on which the oxide film 17 is formed is shown in FIG. 2. The amount of reflected light reflected by the condensing lens 74, a part of which is reflected by the half mirror 76, is incident on the reflected light amount detector 78 including the light receiving element, and is reflected on the back surface 11b of the wafer 11. Is detected. The reflectance of the back surface 11b of the wafer 11 is calculated from the amount of reflected light detected and the amount of reflected light of the reference workpiece whose reflectance stored in the RAM 46 is known.

The ROM 44 of the controller 40 stores, for example, a plurality of correlations as shown in FIG. 7 showing the correlation 73 between the reflectance of the workpiece and the appropriate number of cutting stages for each kind of workpiece or processing conditions. . In the present invention, the case where the power of the laser beam oscillated by the laser oscillator 64 adjusted by the output adjustment unit 68 cannot fully process by one laser processing is assumed.

After performing the reflected light amount detection step, based on the reflected light amount detected in the reflected light amount detection step, the singularity calculating unit 80 calculates the number of processed pieces and irradiates a laser beam to the wafer 11 held on the chuck table 28. The laser beam is irradiated under the second condition from the processing head 36 of the unit 34 to perform the laser processing step of forming the modified layer 19 inside the wafer 11.

In this laser machining step, as shown in FIG. 8, the laser beam 69 is subjected to the second condition from the machining head 36 of the laser beam irradiation unit 34 while processing the chuck table 28 in the direction of arrow X1. ), And the modified layer 19 is formed inside the wafer 11.

While indexing and conveying the chuck table 28 in the Y-axis direction, the same reformed layer 19 is sequentially formed inside the wafer 11 along the division scheduled line 13 extending in the first direction. Subsequently, the chuck table 28 is rotated 90 degrees, and then the same modified layer 19 is formed along the dividing line 13 extending in the second direction.

In the case where the number of processing stages calculated by the stage calculating unit 80 is two stages, as shown in FIG. 9, the first modified layer 19a and the position of the focusing point are changed by the focusing point position changing unit 81. The second reformed 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: YVO4 pulse laser

Wavelength: 1064 nm

Repetition frequency: 100 ㎑

Average power: 2.0 W

Machining feed rate: 400 mm / s

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

In the case of ablation processing, the amount of reflected light is detected on any of the scheduled division lines 13, the plurality of scheduled division lines 13, or all the scheduled division lines 13 of the wafer 11, similarly to the modified layer forming process described above. The amount of reflected light is detected by irradiating the laser beam.

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 355 nm (third harmonic of the YVO4 pulsed laser)

Repetition frequency: 200 ㎑

Average power: 0.1 W

Machining feed rate: 200 mm / s

In the ablation processing, after the reflected light amount detection step is performed, the number of stages calculating unit 80 calculates the number of processed steps based on the reflected light amount detected in the reflected light amount detection step, and the wafer 11 held in the chuck table 28 is provided. Irradiates the laser beam to the surface 11a of the laser beam under the second condition from the processing head 36 of the laser beam irradiation unit 34, and performs ablation processing on the division scheduled line 13 of the wafer 11, A laser machining step is performed to form a processing groove.

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 355 nm (third harmonic of the YVO4 pulsed laser)

Repetition frequency: 200 ㎑

Average power: 1 W

Machining feed rate: 200 mm / s

In the case of the first laser processing, in the case of the first laser processing, the focusing point position is set on the surface 11a of the wafer 11 in the case of the second laser processing, and in the case of the second laser processing Sets the light collection point position in the vicinity of the bottom surface of the laser processing groove formed by the first ablation processing.

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

Based on this reflected light amount, the number of stages of processing required by the stage calculating unit 80 is calculated, and the number of stages of modified layers 19 calculated inside the wafer 11 are formed. In the case of ablation processing, the number of processing stages required by the stage calculating unit 80 is calculated according to the amount of reflected light, and the calculated number of stages of ablation processing is performed. After the modified layer 19 and the laser processing groove are formed on the wafer 11, the division step of applying an external force to the wafer 11 and dividing it into individual chips is performed.

In this embodiment, after the modified layer 19 is formed in the inside of the wafer 11 along all the division scheduled lines 13, the back surface grinding step which grinds 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 hold | maintained by the chuck table 96 of a grinding apparatus is ground by the grinding grindstone 94, and a wafer is pressed by the pressing force during grinding. (11) is divided into individual chips.

In FIG. 12, the grinding unit 82 is detachably mounted with a spindle 84, a wheel mount 86 fixed to the tip of the spindle 84, and a plurality of screws 90 to the wheel mount 86. It consists of a grinding wheel 88. The grinding wheel 88 is configured by fixing a plurality of grinding grindstones 94 around the outside of the lower end of the annular base 92.

In this back grinding step, the chuck table 96 is rotated at, for example, 300 rpm in the direction of arrow a, and the grinding wheel 88 is operated at the grinding unit feed mechanism while rotating at, for example, 6000 rpm in the direction of arrow b, thereby grinding the grinding wheel 94 ) Is brought into contact with the back surface 11b of the wafer 11.

And the grinding | polishing wheel 88 is grind | pulverized and conveyed downward at the predetermined grinding | polishing conveyance speed, grinding the back surface 11b of the wafer 11 is performed. While measuring the thickness of the wafer 11 with a contact or non-contact thickness measuring gauge, the wafer 11 is finished to a desired thickness, such as 50 μm.

During this grinding process, since the modified layer 19 is formed inside the wafer 11 along the dividing line 13, the wafer 11 is divided by the pressing force during grinding as the starting point. It is divided into individual chips.

Here, in the case of a workpiece having a low dividing property, a division step of dividing the workpiece by applying an external force to the workpiece before back grinding is performed. Or after a back grinding operation, the division | segmentation step of applying and dividing an external force to a to-be-processed object is implemented.

In the above-described embodiment, 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 modified by the pressing force at the time of grinding. Although the layer 19 is divided into individual chips as the starting point of division, the modified back surface 11b may be ground in advance to form the modified layer 19 or the laser processing groove in the thinned wafer 11.

11: semiconductor wafer 13: line to be divided
15 device 17 oxide film
19, 19a, 19b: modified layer 28: chuck table
34 laser beam irradiation unit 36 machining head
38: imaging unit 62: laser oscillation unit
64: laser oscillator 66: repetition frequency setting unit
68: output adjustment unit 69: laser beam
71: reflected light 74: condensing lens
76: half mirror 78: reflected light amount detector
80: singular calculation unit

Claims (2)

In the laser processing apparatus which performs a laser processing on a to-be-processed object,
A chuck table for holding the workpiece,
Laser beam irradiation means comprising a laser oscillator and a processing head having a condenser lens for condensing the laser beam oscillated from the laser oscillator;
Reflected light amount detecting means for detecting the reflected light amount of the laser beam irradiated from the laser beam irradiation means to the workpiece held on the chuck table;
Number of stages calculating means for calculating the number of stages of laser processing of a plurality of stages in the thickness direction of a workpiece by the said laser beam irradiation means based on the amount of reflected light detected by the said reflected light quantity detection means.
Laser processing apparatus comprising a. In the laser processing method which performs a laser processing on a to-be-processed object,
A holding step of holding the workpiece on the chuck table;
A laser beam irradiation step for detecting a reflected light amount for irradiating a workpiece held on the chuck table to a workpiece under a first condition from a laser beam irradiation means;
A reflected light amount detecting step of detecting a light amount of reflected light reflected from the upper surface of the workpiece by the laser beam irradiated to the workpiece in the laser beam irradiation step for detecting the reflected light amount;
A stage calculating step of calculating a stage for performing a plurality of stages of laser processing over the thickness direction of the workpiece, based on the amount of reflected light detected in the reflected light amount detecting step;
After performing the number calculating step, the laser beam is irradiated to the workpiece held on the chuck table under a second condition from the laser beam irradiation means, and the number of lasers calculated in the number calculating step in the thickness direction of the workpiece is Laser processing step to perform processing
Wherein the laser processing method comprises the steps of:

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