JP2002192371A - Laser beam machining method and laser beam machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining method capable of cutting a machining object without developing a crack, deviating from the predetermined line for welding or cutting on the surface of the machining object, and accurately. SOLUTION: A reforming area is formed in the machining object by radiating a pulse laser beam L onto the predetermined line 5 for cutting under the condition of causing multiple photon absorbtion, and making a condensing point P agree with the inside of the machining object 1. By splitting the machining object 1 along the determined line 5 for cutting, the machining object 1 can be cut with a comperatively small force. Since in the irradiation of the laser beam L, the pulse laser beam L is scarcely absorbed on the surface 3 of the machining object 1, the surface 3 is not melted, caused by the formation of the reforming area. By adjusting the position of the condensing point P of the pulse laser beam L in the thickness direction of the machining object 1, the position of the reforming area in the thickness direction of the machining object is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a semiconductor material substrate,
The present invention relates to a laser processing method and a laser processing apparatus used for cutting an object to be processed such as a piezoelectric material substrate or a glass substrate.

[0002]

2. Description of the Related Art One of laser applications is cutting. A general cutting by a laser is as follows. For example, a portion to be cut of a processing object such as a semiconductor wafer or a glass substrate is irradiated with laser light having a wavelength that is absorbed by the processing object, and is directed from the front surface to the back surface of the processing object at a position where the cutting is performed by absorbing the laser light. The workpiece is cut by heating and melting. However, in this method, the periphery of a region to be cut on the surface of the workpiece is also melted. Therefore, when the object to be processed is a semiconductor wafer, of the semiconductor elements formed on the surface of the semiconductor wafer, there is a possibility that a semiconductor element located near the above-described region may be melted.

[0003]

As a method for preventing the surface of a workpiece from melting, for example, Japanese Patent Laid-Open No. 2000-21
There is a cutting method using a laser disclosed in JP-A-9528 and JP-A-2000-15467. In the cutting methods disclosed in these publications, a portion to be cut of a processing object is heated by a laser beam, and the processing object is cooled,
The object to be processed is cut by generating a thermal shock at a position where the object to be processed is cut.

However, according to the cutting methods disclosed in these publications, if the thermal shock generated on the object to be processed is large, the surface of the object to be processed may have cracks that deviate from the line to be cut or cracks up to a point not irradiated with laser. Unnecessary cracks such as may occur. Therefore, precision cutting cannot be performed by these cutting methods. In particular, the processing object is a semiconductor wafer,
In the case of a glass substrate on which a liquid crystal display device is formed or a glass substrate on which an electrode pattern is formed, the unnecessary chip may damage the semiconductor chip, the liquid crystal display device, or the electrode pattern. In addition, since these cutting methods have a large average input energy, thermal damage to semiconductor chips and the like is also large.

An object of the present invention is to provide a laser processing method and a laser processing apparatus which do not cause unnecessary cracks on the surface of a processing object and do not melt the surface.

[0006]

According to the laser processing method of the present invention, the focal point of the laser light is adjusted to be inside the processing object beyond the laser light incident surface of the processing object, and the thickness of the processing object is adjusted. By adjusting the position closer to or farther from the incident surface than the half-thickness position in the direction, and irradiating the processing object with laser light, a large number of Forming a modified region by photon absorption.

[0007] According to the laser processing method of the present invention, a laser beam is radiated while focusing on the inside of the object to be processed, and a phenomenon called multiphoton absorption is used to convert the inside of the object to be processed. Quality region. If there is any starting point at the cutting position of the object, the object can be cut by relatively small force. ADVANTAGE OF THE INVENTION According to the laser processing method which concerns on this invention, a to-be-processed object can be cut | disconnected by breaking a to-be-processed object along a line to cut from a modified area as a starting point. Therefore, since the object to be processed can be cut with a relatively small force, it is possible to cut the object to be processed without generating unnecessary cracks off the cutting line on the surface of the object to be processed. Note that the focal point is a point where the laser light is focused.
The line to be cut may be a line actually drawn on the surface or inside of the object to be processed, or a virtual line.

Further, according to the laser processing method of the present invention, the modified region is formed by locally generating multiphoton absorption inside the object to be processed. Therefore, since the laser light is hardly absorbed on the surface of the processing object, the surface of the processing object does not melt. The above can be said for the laser processing method according to the present invention described below.

Further, according to the laser processing method of the present invention, when the focal point of the laser beam is adjusted to a position closer to the incident surface than a position of half the thickness in the thickness direction of the processing object, the modified region becomes the processing object. The modified region is formed on the incident surface (for example, the front surface) in the interior of the object, while the modified region is formed on the surface (for example, the back surface) opposite to the incident surface in the interior of the workpiece when adjusted to a position far from the incident surface. Is done. When a crack along the line to be cut is generated on the front or back surface of the object, the object can be easily cut. According to the laser processing method according to the present invention, the modified region can be formed on the front side or the back side inside the object to be processed. Therefore, a crack along the line to be cut can be easily formed on the front surface or the back surface, so that the workpiece can be easily cut.

In the laser processing method according to the present invention, at least one of an electronic device and an electrode pattern is formed on the incident surface, and the focal point of the laser light irradiated on the object to be processed is the thickness in the thickness direction. Is adjusted to a position closer to the entrance surface than a half position of the incident surface. According to the laser processing method of the present invention, cracks are grown from the modified region in the direction of the incident surface (for example, the front surface) and the opposite surface (for example, the back surface) of the processing object,
The workpiece is cut. When the modified region is formed on the incident surface side, the distance between the modified region and the incident surface is relatively short, so that the shift in the crack growth direction can be reduced. Therefore, when an electronic device or an electrode pattern is formed on the incident surface of the object to be processed, cutting can be performed without damaging the electronic device or the like. Note that the electronic device means a semiconductor element, a display device such as a liquid crystal, a piezoelectric element, or the like. The laser processing method according to the present invention is to irradiate the laser beam to the processing object by adjusting the focal point of the laser light to the inside of the processing object, thereby cutting the processing object along the line to cut the processing object. A first step of forming a modified region by multiphoton absorption therein; and, after the first step, the laser light converging point is located at a position different from the laser light converging position in the first step in the thickness direction of the workpiece. By irradiating the laser beam to the processing object according to the inside of the processing object, the other modified area due to multiphoton absorption is modified inside the processing object along other planned cutting lines of the processing object And a second step of forming a three-dimensional intersection with the region.

According to the laser processing method of the present invention, in the cutting where the cut surfaces of the processing object intersect, the modified region and the other modified regions do not overlap each other at the intersection between the cut surfaces. Therefore, it is possible to prevent a decrease in cutting accuracy at a location that becomes an intersection.

In the laser processing method according to the present invention, another modified region can be formed closer to the laser light incident surface of the object to be processed than the modified region. According to this, since the laser beam irradiated at the time of forming another modified region at the intersection is not scattered by the modified region, the other modified region can be formed uniformly.

The laser processing method according to the present invention described above has the following aspects. The conditions for irradiating the laser beam to the object to be processed are such that the peak power density at the focal point of the laser beam is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. A modified region including a crack region can be formed inside the substrate. According to this, a phenomenon called optical damage due to multiphoton absorption occurs inside the object to be processed. This optical damage induces thermal strain inside the object, thereby forming a crack region inside the object. This crack region is an example of the modified region. As an object to be processed by this laser processing method, for example, there is a member containing glass.
Note that the peak power density means the electric field intensity at the focal point of the pulsed laser light.

The conditions for irradiating the object to be processed with laser light are as follows:
The peak power density at the focal point of the laser beam is 1 × 10
By setting the pulse width to ⁸ (W / cm ² ) or more and the pulse width to 1 μs or less, it is possible to form a modified region including a melt-processed region inside the object to be processed. According to this, the inside of the object to be processed is locally heated by multiphoton absorption. By this heating, a melt processing area is formed inside the object to be processed. This melt processing region is an example of the modified region.
An object to be processed by this laser processing method includes, for example, a member containing a semiconductor material.

The conditions for irradiating the object to be processed with laser light are as follows:
The peak power density at the focal point of the laser beam is 1 × 10
By setting the pulse width to ⁸ (W / cm ² ) or more and the pulse width to 1 ns or less, it is possible to form a modified region including a refractive index change region which is a region where the refractive index has changed inside the object to be processed. . When the pulse width is extremely short and multiphoton absorption occurs inside the object, the energy due to multiphoton absorption does not convert to thermal energy, and the ionic valence changes inside the object. A permanent structural change such as crystallization or polarization orientation is induced to form a refractive index change region. This refractive index change region is an example of the modified region.
An object to be processed by this laser processing method is, for example, a member containing glass.

The adjustment of the position in the thickness direction of the focal point of the laser beam irradiated on the object to be processed is performed by setting a desired position in the thickness direction of the focal point of the laser beam irradiated on the object from the incident surface to the inside. And a calculation step of calculating data of a relative movement amount of the processing object in the thickness direction by dividing the distance by a refractive index of the processing object with respect to the laser beam irradiated on the processing object, Another calculation step of calculating data of another relative movement amount in the thickness direction required to position the focal point of the laser beam irradiated on the processing object on the incident surface; A moving step of relatively moving the workpiece in the thickness direction based on the data of the target moving amount, and, after the moving step, moving the workpiece relatively in the thickness direction based on the data of the relative moving amount. Moving process, It can be made to contain. According to this, the position of the focal point of the laser beam in the thickness direction of the processing object is adjusted to a predetermined position inside the processing object with reference to the incident surface. That is, when the incident surface is used as a reference, the product of the relative movement amount of the processing object in the thickness direction of the processing object and the refractive index of the processing object with respect to the laser light applied to the processing object is the laser from the incident surface. This is the distance to the light focusing point. Therefore, if the processing object is moved by a relative movement amount obtained by dividing the distance from the incident surface to the inside of the processing object by the above-mentioned refractive index, the focal point of the laser light can be adjusted. Can be adjusted to a desired position in the thickness direction.

In the laser processing apparatus according to the present invention, a laser light source that emits a pulse laser beam having a pulse width of 1 μs or less, and a peak power density of a focal point of the pulse laser beam emitted from the laser light source is 1 × 10 ⁸ (W / cm ² ) Focusing means for focusing the pulsed laser light so that it is greater than or equal to the focus point of the pulsed laser light focused by the focusing means along the line to cut the workpiece Means for moving the object in a vertical direction, and data of the relative movement amount of the object in the thickness direction for adjusting the focal point of the pulsed laser beam condensed by the light condensing means to a desired position inside the object. The desired position is the distance from the incident surface where the pulse laser light emitted from the laser light source enters the object to be processed, and this distance is the distance of the object to be processed with respect to the pulse laser light emitted from the laser light source. Storage means for storing data of the relative movement amount obtained by dividing by the folding ratio, and a thickness direction necessary for adjusting the focal point of the pulsed laser light focused by the focusing means to the incident surface. Calculating means for calculating data of another relative movement amount of the object to be processed; processing based on the data of the relative movement amount stored by the storage means and the data of the other relative movement amount calculated by the calculating means And other moving means for relatively moving the object in the thickness direction.

Further, in the laser processing apparatus according to the present invention, a laser light source for emitting a pulse laser beam having a pulse width of 1 μs or less, and a peak power density of a focal point of the pulse laser light emitted from the laser light source is 1 × A condensing means for condensing the pulsed laser light so as to be 10 ⁸ (W / cm ² ) or more; and a means for adjusting the condensing point of the pulsed laser light condensed by the condensing means to the inside of the object to be processed. Means for adjusting the position of the focal point of the pulsed laser light condensed by the condensing means within the range of the thickness of the object to be processed, and a focal point of the pulsed laser light along a line to cut the object to be processed. And moving means for relatively moving.

According to the laser processing apparatus of the present invention, for the same reason as that of the laser processing method of the present invention, unnecessary cracks are generated on the surface of the object to be melted or deviate from the line to be cut. It is possible to perform laser processing without performing the laser processing or to control the position of the focal point of the pulsed laser light in the thickness direction of the processing object inside the processing object.

[0020]

Preferred embodiments of the present invention will be described below with reference to the drawings. In the laser processing method and the laser processing apparatus according to the present embodiment, the modified region is formed by multiphoton absorption. Multiphoton absorption is a phenomenon that occurs when the intensity of laser light is extremely increased. First, multiphoton absorption will be briefly described.

[0021] a band gap E photon energy hν than _G of absorption of the material is less optically clear. Therefore, a condition under which absorption occurs in the material is hv> E _G. However, even when optically transparent, increasing the intensity of the laser beam very Nhnyu> of E _G condition (n = 2, 3, 4, a, ...) absorbed in the material occurs. This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser light is determined by the peak power density (W / cm ² ) at the focal point of the laser light. For example, when the peak power density is 1 × 10 ⁸ (W / cm ² ) or more, multiphoton Absorption occurs. The peak power density is obtained by (energy per pulse of laser light at a focal point) / (beam spot cross-sectional area of laser light × pulse width). In the case of a continuous wave, the intensity of the laser light is determined by the electric field intensity (W / cm ² ) at the focal point of the laser light.

The principle of laser processing according to the present embodiment utilizing such multiphoton absorption will be described with reference to FIGS. 1 is a plan view of the processing target 1 during laser processing, FIG. 2 is a cross-sectional view of the processing target 1 shown in FIG. 1 along line II-II, and FIG. 3 is a processing target after laser processing. Thing 1
FIG. 4 is a plan view of the workpiece 1 shown in FIG.
5 is a cross-sectional view of the processing target 1 shown in FIG. 3 along the line V-V, and FIG. 6 is a plan view of the processing target 1 shown in FIG.

As shown in FIG. 1 and FIG.
The surface 3 has a line 5 to be cut. The scheduled cutting line 5 is a virtual line extending linearly. In the laser processing according to the present embodiment, the laser light L is irradiated on the processing target 1 while adjusting the focal point P inside the processing target 1 under the condition where multiphoton absorption occurs, thereby forming the modified region 7. Note that the focal point is a point where the laser light L is focused.

The laser beam L is relatively moved along the line 5 to be cut (that is, along the direction of arrow A), so that the focal point P is moved along the line 5 to be cut. As a result, as shown in FIGS.
Are formed only inside the object 1 along the line 5 to be cut. The laser processing method according to the present embodiment does not form the modified region 7 by causing the processing target 1 to generate heat by absorbing the laser light L by the processing target 1. The modified region 7 is formed by transmitting the laser beam L to the processing target 1 and generating multiphoton absorption inside the processing target 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the processing target 1, the surface 3 of the processing target 1 is not melted.

In the cutting of the processing object 1, if the starting point is located at a position to be cut, the processing object 1 is broken from the starting point. Therefore, as shown in FIG. 6, the processing object 1 can be cut with a relatively small force. it can. Therefore, the surface 3 of the workpiece 1
The workpiece 1 can be cut without causing unnecessary cracks.

It should be noted that cutting of the object to be processed starting from the modified region can be considered in the following two ways. One is a case where an artificial force is applied to the object to be processed after the modified area is formed, whereby the object to be processed is cracked starting from the modified area and the object to be processed is cut. This is, for example, cutting when the thickness of the processing target is large. An artificial force is applied when, for example, a bending stress or a shear stress is applied to a workpiece along a line to cut the workpiece, or a thermal stress is generated by giving a temperature difference to the workpiece. Or let them do that. The other is that, by forming the modified region, the fracture is naturally caused in the cross-sectional direction (thickness direction) of the object to be processed from the modified region as a starting point, resulting in the cutting of the object to be processed. It is. This is possible, for example, when the thickness of the object to be processed is small, even one modified area is provided,
When the thickness of the object to be processed is large, it becomes possible by forming a plurality of modified regions in the thickness direction. In addition, even if this cracks naturally, on the surface of the cut portion, the crack does not advance to the portion where the modified region is not formed,
Since only the portion where the reformed portion is formed can be cut, the cut can be controlled well. In recent years, the thickness of a semiconductor wafer such as a silicon wafer tends to be reduced, and thus such a controllable cutting method is very effective.

The modified regions formed by multiphoton absorption in this embodiment include the following (1) to (3). (1) In the case where the modified region is a crack region including one or a plurality of cracks, such as a piezoelectric material made of glass or LiTaO ₃ ), the electric field intensity at the light condensing point is 1 × 10 ⁸ (W / c
Irradiation is performed under the condition of m ² ) or more and pulse width of 1 μs or less. The magnitude of the pulse width is a condition under which a crack region can be formed only inside the object to be processed without causing unnecessary damage to the surface of the object to be processed while causing multiphoton absorption. As a result, a phenomenon called optical damage occurs due to multiphoton absorption inside the object to be processed. This optical damage induces thermal strain inside the object, thereby forming a crack region inside the object. The upper limit of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is preferably, for example, 1 ns to 200 ns. The formation of a crack region by multiphoton absorption is performed, for example,
Proceedings of the 45th Workshop on Laser Thermal Processing (1998.12
Mon.), pages 23 to 28, "Internal Marking of Glass Substrate by Solid-State Laser Harmonics".

The present inventor has experimentally determined the relationship between the electric field strength and the crack size. The experimental conditions are as follows. (A) Object to be processed: Pyrex (registered trademark) glass (thickness: 700 μm) (B) Laser light source: Nd: YAG laser excited by a semiconductor laser Wavelength: 1064 nm Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ² oscillation Form: Q switch pulse Repetition frequency: 100 kHz Pulse width: 30 ns Output: Output <1 mJ / pulse Laser beam quality: TEM ₀₀ Polarization characteristics: Linear polarization (C) Condensing lens Transmittance to laser beam wavelength: 60% (D) Moving speed of the mounting table on which the workpiece is mounted: 10
0 mm / sec The laser beam quality of TEM ₀₀ means that the laser beam has a high light-collecting property and can be focused to the wavelength of the laser beam.

FIG. 7 is a graph showing the results of the above experiment. The horizontal axis represents the peak power density. Since the laser light is a pulsed laser light, the electric field intensity is represented by the peak power density. The vertical axis indicates the size of a crack portion (crack spot) formed inside the object by one pulse of laser light. Crack spots gather to form a crack area. The size of the crack spot is the size of the portion having the maximum length in the shape of the crack spot. The data indicated by the black circles in the graph is the condenser lens (C)
Is 100 times and the numerical aperture (NA) is 0.80. On the other hand, data indicated by white circles in the graph are obtained when the magnification of the condenser lens (C) is 50 times and the numerical aperture (NA) is 0.55. From the peak power density of about 10 ¹¹ (W / cm ² ), it can be seen that a crack spot occurs inside the object to be processed, and the crack spot increases as the peak power density increases.

Next, in the laser processing according to the present embodiment, a mechanism of cutting an object to be processed by forming a crack region will be described with reference to FIGS. As shown in FIG. 8, the laser light L is irradiated on the processing target 1 by aligning the converging point P inside the processing target 1 under the condition where multiphoton absorption occurs, and a crack region is formed inside along the line to be cut. 9 is formed. The crack region 9 is a region including one or a plurality of cracks. Cracks further grow from the crack region 9 as shown in FIG. 9, and the cracks reach the front surface 3 and the back surface 21 of the processing object 1 as shown in FIG. 10, and as shown in FIG. The workpiece 1 is cut by breaking. Cracks that reach the front and back surfaces of the processing object may grow naturally, or may grow when a force is applied to the processing object.

(2) In the case where the reformed region is a melt-processed region:
The focusing point inside the material) and the electric field at the focusing point
1 × 10 strength⁸(W / cm^Two) Or more and the pulse width is 1μs
Irradiation is performed under the following conditions. This allows the inside of the workpiece
Local heating due to multiphoton absorption. Due to this heating
A melt processing region is formed inside the workpiece. Melting
The treatment area is an area that has been melted and then re-solidified,
Less of the area and the area in the state of resolidification from melting
Means either one. Also, the melting process area is
It may be a changed area or a changed crystal structure.
Wear. In addition, the melt processing region is a single crystal structure or an amorphous structure.
In a polycrystalline structure, one structure changes to another
Area. That is, for example, a single crystal structure
From amorphous structure to amorphous structure, single crystal structure to polycrystalline
Region changed from single crystal structure to amorphous structure and
A region changed to a structure including a polycrystalline structure is meant. processing
When the object has a silicon single crystal structure, the melt processing area is an example
An example is an amorphous silicon structure. The upper limit of the electric field strength
The value is, for example, 1 × 10¹²(W / cm ^Two). Pal
The width is preferably, for example, 1 ns to 200 ns.

The present inventor has confirmed through experiments that a melt processing region is formed inside a silicon wafer. The experimental conditions are as follows. (A) Object to be processed: Silicon wafer (thickness: 350 μm, outer diameter: 4 inches) (B) Laser light source: Semiconductor laser-excited Nd: YAG laser Wavelength: 1064 nm Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ² Oscillation form: Q switch pulse Repetition frequency: 100 kHz Pulse width: 30 ns Output: 20 μJ / pulse Laser beam quality: TEM ₀₀ Polarization characteristics: linearly polarized light (C) Condensing lens Magnification: 50 times NA: 0.55 with respect to laser beam wavelength Transmittance: 60% (D) Moving speed of the mounting table on which the workpiece is mounted: 10
0mm / sec

FIG. 12 is a view showing a photograph of a cross section of a part of a silicon wafer cut by laser processing under the above conditions. A melt processing area 13 is formed inside the silicon wafer 11. The size in the thickness direction of the melt processing region formed under the above conditions is about 100 μm.

The fact that the melt processing region 13 is formed by multiphoton absorption will be described. FIG. 13 is a graph showing the relationship between the wavelength of the laser beam and the transmittance inside the silicon substrate. However, the reflection components on the front side and the back side of the silicon substrate are removed, and the transmittance is shown only inside. The thickness t of the silicon substrate is 50 μm, 100 μm, 200 μm,
The above relationship was shown for each of 500 μm and 1000 μm.

For example, the wavelength 106 of the Nd: YAG laser
At 4 nm, when the thickness of the silicon substrate is 500 μm or less, 80% or more of the laser light is transmitted inside the silicon substrate. Silicon wafer 11 shown in FIG.
Has a thickness of 350 μm, so that the melted region by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion 175 μm from the surface. The transmittance in this case is
Referring to a silicon wafer having a thickness of 200 μm, 90
% Or more, the laser light is slightly absorbed inside the silicon wafer 11 and almost all is transmitted. This means that the laser beam is absorbed inside the silicon wafer 11 and the melting region is not formed inside the silicon wafer 11 (that is, the melting region is formed by normal heating by the laser beam). It means that the processing region was formed by multiphoton absorption. The formation of the melt processing region by multiphoton absorption is described in, for example, “Evaluation of Silicon Processing Characteristics by Picosecond Pulsed Laser” on pages 72 to 73 of the 66th Annual Meeting of the Japan Welding Society (April 2000).
It is described in.

It should be noted that the silicon wafer is cracked in the cross-section direction starting from the melt processing region, and the crack reaches the front and back surfaces of the silicon wafer, resulting in cutting. The cracks reaching the front and back surfaces of the silicon wafer may grow spontaneously or may grow when a force is applied to the workpiece. The cracks naturally grow on the front and back surfaces of the silicon wafer from the melt processing area when the cracks grow from the area once re-solidified after melting, or when the cracks grow from the melted area. And at least one of the cases where cracks grow from a region in a state of being re-solidified from melting. In each case, the cut surface after cutting is shown in FIG.
As shown in FIG. 2, a melt processing region is formed only inside.
In the case of forming a melt-processed area inside the object to be processed, at the time of cutting, unnecessary cracks deviating from the line to be cut hardly occur, so that the cutting control is facilitated.

(3) When the Modified Region is a Refractive Index Change Region The laser beam is focused on the inside of the object to be processed (eg, glass) and the electric field intensity at the focused point is 1 × 10 ⁸ (W / c
Irradiation is performed under the condition of not less than m ² ) and a pulse width of 1 ns or less.
When the pulse width is extremely short and multi-photon absorption occurs inside the object, the energy due to multi-photon absorption does not convert to heat energy. Alternatively, a permanent structural change such as polarization orientation is induced to form a refractive index change region. The upper limit of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is, for example, preferably 1 ns or less, and more preferably 1 ps or less. The formation of the refractive index change region by multiphoton absorption is
For example, the 42nd Laser Thermal Processing Research Group Transactions (1997)
Year. (November), pp. 105-111, "Formation of Photo-Induced Structure Inside Glass by Femtosecond Laser Irradiation". As described above, according to the present embodiment, the modified region is formed by multiphoton absorption. In the present embodiment, the position of the modified region in the thickness direction of the object is controlled by adjusting the position of the focal point of the laser beam in the thickness direction of the object.

The position control will be described by taking a crack area as an example. FIG. 14 is a perspective view of the processing target 1 in which a crack region 9 is formed inside the processing target 1 using the laser processing method according to the present embodiment. The focal point of the pulse laser light L is adjusted to the inside of the processing object 1 via the surface (incident surface) 3 of the pulse laser light L of the processing object 1. The focal point is adjusted to a position approximately half the thickness in the thickness direction of the processing target 1. Under these conditions, the pulse laser beam L is applied to the workpiece 1 along the line 5 to be cut.
Is irradiated, a crack region 9 is formed along the line 5 to be cut and at a position at and near a half of the thickness of the workpiece 1.

FIG. 15 is a partial sectional view of the object 1 shown in FIG. After the formation of the crack region 9, the crack region 9 is formed.
Cracks 91 grow naturally from the front surface 3 and the back surface 21. When the crack region 9 is formed at and near a half of the thickness in the thickness direction of the processing object 1, for example, when the processing object 1 has a relatively large thickness, the crack 91 grows naturally and the front surface 3 (the back surface 21). Can be made relatively long. Therefore, the portion to be cut along the line to be cut 5 of the workpiece 1 has a certain strength. Therefore, when performing the cutting step of the processing target 1 after the end of the laser processing, handling of the processing target becomes easy.

FIG. 16 is a perspective view of the processing object 1 including the crack region 9 formed by using the laser processing method according to the present embodiment, similarly to FIG. In the crack region 9 shown in FIG.
It is formed by adjusting to a position close to 3. The crack region 9 is formed on the surface 3 side inside the object 1. FIG. 17 is a partial sectional view of the object 1 shown in FIG. Since the crack region 9 is formed on the surface 3 side, the crack 91 that grows naturally reaches the surface 3 or its vicinity. Therefore, cracks along the scheduled cutting line 5 are likely to occur on the surface 3, so that the workpiece 1 can be easily cut.

In particular, when an electronic device or an electrode pattern is formed on the surface 3 of the object 1, if the crack region 9 is formed near the surface 3, damage to the electronic device or the like is prevented when the object 1 is cut. be able to. That is, the workpiece 1 is cut by growing the cracks 91 from the crack region 9 in the direction of the front surface 3 and the back surface 21 of the workpiece 1. In some cases, cutting can be performed only by the natural growth of the crack 91, and in other cases, the crack 91 can be artificially grown and cut in addition to the natural growth of the crack 91. If the distance between the crack region 9 and the surface 3 is relatively long,
The shift in the growth direction of the crack 91 on the front surface 3 side becomes large. As a result, the crack 91 may reach a formation region of the electronic device or the like, and the electronic device or the like is damaged by the arrival. When the crack region 9 is formed in the vicinity of the surface 3, the distance between the crack region 9 and the surface 3 is relatively short, so that the shift of the crack 91 in the growth direction can be reduced.
Therefore, cutting can be performed without damaging the electronic device or the like. However, if the crack region 9 is formed at a location too close to the surface 3, the crack region 9 is formed on the surface 3.
For this reason, a random shape of the crack region 9 itself appears on the surface 3, causing chipping of the surface 3, resulting in poor cutting accuracy.

Note that the focal point of the pulse laser beam L is shifted from the position of half the thickness in the thickness direction of the object 1 to the surface 3.
The crack region 9 can be formed by adjusting the position to a position far from In this case, the crack region 9 is formed on the back surface 21 side inside the object 1. FIG. 18 is a perspective view of the processing target 1 including the crack region 9 formed by using the laser processing method according to the present embodiment, similarly to FIG. The crack region 9 in the X-axis direction shown in FIG. 18 is formed by adjusting the focal point of the pulsed laser beam L to a position farther from the surface (incident surface) 3 than a position at half the thickness in the thickness direction of the processing object 1. It was done. On the other hand, the crack region 9 in the Y-axis direction is formed by adjusting the focal point to a position closer to the surface 3 than a position at half the thickness. The crack region 9 in the X-axis direction and the crack region 9 in the Y-axis direction cross three-dimensionally.

When the object 1 is a semiconductor wafer, for example, a plurality of crack regions 9 are formed in parallel in the X-axis direction and the Y-axis direction. As a result, the crack regions 9 are formed in the semiconductor wafer in a lattice shape, and are divided into individual chips starting from the lattice-like crack regions. If both the crack region 9 in the X-axis direction and the crack region 9 in the Y-axis direction have the same position in the thickness direction of the workpiece 1, the crack region 9 in the X-axis direction and the crack region 9 in the Y-axis direction are formed. There are orthogonal locations. The crack area 9 at the orthogonal position
Are superimposed on each other, so that it is difficult to accurately orthogonalize the cut surface in the X-axis direction and the cut surface in the Y-axis direction. This allows
Precise cutting of the processing target 1 is hindered at the orthogonal position.

On the other hand, as shown in FIG. 18, when the position of the crack region 9 in the X-axis direction is different from the position of the crack region 9 in the Y-axis direction in the thickness direction of the workpiece 1, The crack region 9 in the axial direction and the crack region 9 in the Y-axis direction can be prevented from overlapping. Therefore, the workpiece 1 can be cut precisely.

The crack region 9 formed after the crack region 9 in the X-axis direction and the crack region 9 in the Y-axis direction is formed closer to the front surface (incident surface) 3 than the crack region 9 formed earlier. Is preferred. If the crack region 9 formed later is formed closer to the back surface 21 than the crack region 9 formed earlier, the crack region 9 formed later is formed at a location where the cut surface in the X-axis direction and the cut surface in the Y-axis direction are orthogonal to each other. Laser light L irradiated when forming the crack region 9 to be formed
Are scattered by the crack region 9 formed earlier. As a result, in the crack region 9 to be formed later, the size of a portion formed in the above-described orthogonal portion and the size of a portion formed in another portion are varied. Therefore, the crack region 9 formed later cannot be formed uniformly.

On the other hand, if the crack region 9 to be formed later is formed closer to the surface 3 than the crack region 9 to be formed first, scattering of the pulsed laser light L does not occur at the above-mentioned orthogonal position. Therefore, a crack region 9 to be formed later can be formed uniformly.

As described above, according to the present embodiment, by adjusting the position of the focal point of the laser beam in the thickness direction of the object, the position of the modified region in the thickness direction of the object is adjusted. Can control. By changing the position of the focal point in consideration of the thickness, material, and the like of the processing target, laser processing according to the processing target can be performed.

The position control of the modified region has been described in the case of the crack region, but the same can be said for the melted region and the refractive index change region. Although the pulse laser beam has been described, the same can be said for a continuous wave laser beam. Next, a laser processing apparatus according to the present embodiment will be described. FIG. 19 is a schematic configuration diagram of the laser processing apparatus 100. Laser processing device 10
0 denotes a laser light source that generates the laser light L, a laser light source control unit 102 that controls the laser light source 101 to adjust the output and the pulse width of the laser light L, and a laser light
It has the function of reflecting L and the direction of the optical axis of laser light L is 90 °
Dichroic mirror 103 arranged to change
And the laser light reflected by the dichroic mirror 103
The condensing lens 105 for condensing L and the condensing lens 10
A mounting table 107 on which the workpiece 1 to be irradiated with the laser light L condensed by 5 is mounted, an X-axis stage 109 for moving the mounting table 107 in the X-axis direction, and a mounting table 107
A Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis stage 113 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions.
And a stage control unit 115 for controlling the movement of these three stages 109, 111, 113.

The laser light source 101 is an Nd: YAG laser that generates a pulse laser beam. Other lasers that can be used for the laser light source 101 include Nd: YVO ₄ laser and Nd:
There are YLF laser and titanium sapphire laser. When forming a crack region or a melt processing region, an Nd: YAG laser, N
It is preferable to use a d: YVO ₄ laser and a Nd: YLF laser.
When forming the refractive index change region, it is preferable to use a titanium sapphire laser. The movement of the focal point P in the X (Y) axis direction is performed by moving the workpiece 1 to the X (Y) axis stage 109 (111).
By moving in the X (Y) axis direction. Since the Z-axis direction is a direction orthogonal to the surface 3 of the processing target 1, it is the direction of the depth of focus of the laser light L incident on the processing target 1. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the focal point P of the laser light L is
Can be combined. That is, the Z-axis stage 113
As a result, the position of the focal point P in the thickness direction of the processing target 1 is adjusted. Thereby, for example, the focal point P is adjusted to a position closer to or farther from the incident surface (surface 3) than a position of half the thickness in the thickness direction of the processing target 1, or to a position substantially half the thickness. Or you can. In addition,
By moving the condenser lens 105 in the Z-axis direction, these adjustments and the focal point of the laser beam can be adjusted to the inside of the object to be processed. Therefore, in the present invention, since the processing object 1 may move in the thickness direction of the processing object 1 and the condensing lens 105 may move in the thickness direction of the processing object 1, the processing object in the thickness direction of the processing object 1 may be used. 1
Is the relative movement amount or another relative movement amount.

Here, the adjustment of the position of the focal point P in the thickness direction of the object to be processed by the Z-axis stage is shown in FIG.
This will be described with reference to FIG. In this embodiment, the position of the focal point of the laser beam in the thickness direction of the processing target is adjusted to a desired position inside the processing target with reference to the surface (incident surface) of the processing target. FIG. 20 shows a state in which the focal point P of the laser light L is located on the surface 3 of the processing object 1. As shown in FIG. 21, when the Z-axis stage is moved z toward the condenser lens 105, the focal point P
From the workpiece 1 to the inside of the workpiece 1. The amount of movement of the focal point P inside the object 1 is Nz (where N is the laser light L
Is the refractive index of the object 1 to be processed). Therefore, by moving the Z-axis stage in consideration of the refractive index of the processing target 1 with respect to the laser light L, the position of the focal point P in the thickness direction of the processing target 1 can be controlled. That is, a desired position of the light condensing point P in the thickness direction of the processing target 1 is defined as a distance (Nz) from the surface (incident surface) 3 to the inside of the processing target 1. This distance (Nz) is the refractive index (N)
The workpiece 1 is moved in the thickness direction by the movement amount (z) obtained by dividing by. Thereby, the focal point P can be adjusted to the desired position. The laser processing apparatus 100 further includes an observation light source 117 that generates visible light to illuminate the processing target 1 mounted on the mounting table 107 with visible light, and a dichroic mirror 103.
And a beam splitter 119 for visible light arranged on the same optical axis as the condensing lens 105. The dichroic mirror 103 is arranged between the beam splitter 119 and the condenser lens 105. The beam splitter 119 has a function of reflecting about half of visible light and transmitting the other half, and is arranged so as to change the direction of the optical axis of visible light by 90 °. About half of the visible light generated from the observation light source 117 is reflected by the beam splitter 119, and the reflected visible light passes through the dichroic mirror 103 and the condensing lens 105, and
The surface 3 including the line 5 to be cut is illuminated.

The laser processing apparatus 100 further includes an image sensor 12 arranged on the same optical axis as the beam splitter 119, the dichroic mirror 103, and the condenser lens 105.
1 and an imaging lens 123. As the imaging element 121, for example, there is a charge-coupled device (CCD) camera.
The reflected light of visible light illuminating the surface 3 including the line to be cut 5 and the like passes through the condenser lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the image sensor 121. And becomes image pickup data.

The laser processing apparatus 100 further includes an imaging data processing unit 125 to which the imaging data output from the imaging element 121 is input, an overall control unit 127 for controlling the entire laser processing apparatus 100, and a monitor 129. . The imaging data processing unit 125 calculates focus data for adjusting the focus of the visible light generated by the observation light source 117 on the surface 3 based on the imaging data. The stage controller 115 controls the movement of the Z-axis stage 113 based on the focus data so that the visible light is focused on the surface 3. Therefore, the imaging data processing unit 125 functions as an autofocus unit. Focus on visible light is surface 3
The laser processing apparatus 1 is adjusted so that the focal point P of the laser beam L is also located on the surface 3 at the position of the Z-axis stage 113 located at. Therefore, the focus data is
7 is an example of another relative movement amount of the processing object 1 in the thickness direction of the processing object 1 required to position the processing object 1 on the front surface (incident surface) 3. The imaging data processing unit 125 has a function of calculating another relative movement amount. The imaging data processing unit 125 calculates image data such as an enlarged image of the front surface 3 based on the imaging data. The image data is sent to the overall control unit 127, where various processes are performed, and the image data is sent to the monitor 129. As a result, an enlarged image or the like is displayed on the monitor 129.

The overall control unit 127 includes the stage control unit 1
15 and the image data from the imaging data processing unit 125, and the laser processing apparatus controls the laser light source control unit 102, the observation light source 117, and the stage control unit 115 based on these data. 100 overall control. Therefore, the overall control unit 127 functions as a computer unit. Also, the overall control unit 127
The data of the movement amount (z) described with reference to FIGS. 20 and 21 is input and stored. That is, the overall control unit 127
Has a function of storing data of the relative movement amount of the processing object 1 in the thickness direction of the processing object 1. Overall control unit 127, stage control unit 115, and Z-axis stage 113
As a result, the position of the focal point of the pulse laser beam focused by the focusing lens 105 is adjusted within the range of the thickness of the processing target 1. Next, a laser processing method according to the present embodiment will be described with reference to FIGS. FIG. 22 is a flowchart for explaining this laser processing method. The processing object 1 is a silicon wafer.

First, the light absorption characteristics of the object 1 are measured by a spectrophotometer (not shown) or the like. Based on the measurement result, a laser light source 101 that generates a laser beam L having a wavelength that is transparent or has a small absorption with respect to the workpiece 1 is selected (S101). Next, the thickness of the workpiece 1 is measured. The movement amount (z) of the processing object 1 in the Z-axis direction is determined based on the thickness measurement result and the refractive index of the processing object 1 (S103). This is because the focal point P of the laser beam L is located inside the object 1, so that the surface 3 of the object 1
Is the amount of movement of the processing target 1 in the Z-axis direction with respect to the focal point of the laser beam L located at. That is, the position of the focal point P in the thickness direction of the workpiece 1 is determined. The movement amount (z) in the Z-axis direction is an example of data of the relative movement amount of the processing target 1 in the thickness direction of the processing target 1. Focus point
The position of P is determined in consideration of the thickness, material, processing effect (for example, easy handling and easy cutting of the processing object 1) of the processing object 1, and the like. The data of the movement amount is input to the overall control unit 127.

The workpiece 1 is mounted on the mounting table 107 of the laser processing apparatus 100. Then, the processing target 1 is illuminated by generating visible light from the observation light source 117 (S10).
5). Workpiece 1 including illuminated scheduled cutting line 5
Is imaged by the image sensor 121. This imaging data is sent to the imaging data processing unit 125. On the basis of the image data, the image data processor 125 sets the observation light source 1
The focus data is calculated such that the focus of the visible light 17 is located on the surface 3 (S107). The focus data is data of another relative movement amount of the workpiece 1 in the Z-axis direction.

This focus data is sent to the stage control unit 115. The stage control unit 115 moves the Z-axis stage 113 in the Z-axis direction based on the focus data (S
109). Thereby, the focus of the visible light of the observation light source 117 is located on the surface 3. At this position of the Z-axis stage 113, the focal point P of the pulsed laser light L is located on the front surface 3. In addition, the imaging data processing unit 125 processes the processing target 1 including the planned cutting line 5 based on the imaging data.
The enlarged image data of the surface 3 is calculated. The enlarged image data is sent to the monitor 129 via the overall control unit 127, and the enlarged image near the cut line 5 is displayed on the monitor 129.

Step S10 is performed in advance by the overall control unit 127.
The relative movement amount data determined in 3 is input,
This movement amount data is sent to the stage control unit 115.
The stage control unit 115 determines, based on the movement amount data,
The object 1 is moved in the Z-axis direction by the Z-axis stage 113 to a position where the focal point P of the laser light L is inside the object 1 (S111). Next, a laser light L is generated from the laser light source 101, and the laser light L is applied to the line 5 to be cut on the surface 3 of the workpiece 1. Since the focal point P of the laser beam L is located inside the processing target 1, the melt processing region is formed only inside the processing target 1. Then, the X-axis stage 109 is moved along the line 5 to be cut.
The Y-axis stage 111 is moved to form a melt processing area inside the processing target object 1 along the planned cutting line 5 (S113). Then, the object 1 is cut by bending the object 1 along the line 5 to be cut (S115). As a result, the workpiece 1 is divided into silicon chips.

The effect of this embodiment will be described. According to the present embodiment, the pulse laser beam L is applied to the line 5 to be cut under the condition that multiphoton absorption occurs and the focusing point P is set inside the object 1 to be processed. And X axis stage 1
09 and the Y-axis stage 111 are moved to move the focal point P along the line 5 to be cut. As a result, a modified region (for example, a crack region, a melt processing region, a refractive index change region) is formed inside the processing target object 1 along the line 5 to be cut. If there is any starting point at the cutting position of the object, the object can be cut by relatively small force. Therefore, the work 1 can be cut with a relatively small force by breaking the work 1 along the scheduled cutting line 5 with the modified region as a starting point. Thereby, the object 1 can be cut without generating unnecessary cracks off the cutting line 5 on the surface 3 of the object 1.

According to the present embodiment, the object to be processed 1
The pulse laser beam L is applied to the line 5 to be cut under the condition that multi-photon absorption occurs and the focal point P is set inside the object 1 to be processed. Therefore, the pulse laser beam L is transmitted through the object 1 and the pulse laser beam L is hardly absorbed on the surface 3 of the object 1. Therefore, the surface 3 may be damaged such as melting due to the formation of the modified region. There is no.

As described above, according to the present embodiment,
The processing object 1 can be cut without causing unnecessary cracks or melting off the cutting line 5 on the surface 3 of the processing object 1. Therefore, when the processing target 1 is, for example, a semiconductor wafer, the semiconductor chip can be cut out of the semiconductor wafer without causing unnecessary cracks or melting of the semiconductor chip off the line to be cut. The same applies to a processing object having an electrode pattern formed on the surface, or a processing object having an electronic device formed on the surface, such as a glass substrate on which a display device such as a piezoelectric element wafer or a liquid crystal is formed. Therefore, according to the present embodiment, the yield of products (for example, display devices such as semiconductor chips, piezoelectric device chips, and liquid crystals) manufactured by cutting a processing target can be improved.

According to the present embodiment, the object to be processed 1
Since the line 5 to be cut on the surface 3 does not melt, the width of the line 5 to be cut (for example, in the case of a semiconductor wafer, is the interval between regions to be semiconductor chips) can be reduced. Thereby, the number of products manufactured from one processing target object 1 increases, and the productivity of the products can be improved.

According to the present embodiment, the object to be processed 1
Since a laser beam is used for the cutting process, more complicated processing can be performed than dicing using a diamond cutter.
For example, as shown in FIG. 23, according to the present embodiment, cutting can be performed even if the line 5 to be cut has a complicated shape. Further, according to the present embodiment, the position of the focal point P in the thickness direction of the processing target 1 is adjusted to irradiate the processing target 1 with the pulse laser beam L to form the modified region.
Thereby, the position of the modified region in the thickness direction of the workpiece 1 can be controlled. Therefore, the processing target 1
By changing the position of the modified region in the thickness direction of the processing target 1 according to the material, thickness, processing effect, and the like of the processing target 1, cutting processing according to the processing target 1 can be performed.

[0063]

According to the laser processing method and the laser processing apparatus according to the present invention, the object can be cut without melting or cracking off the cutting line on the surface of the object. Therefore, the yield and productivity of a product (for example, a display device such as a semiconductor chip, a piezoelectric device chip, or a liquid crystal) manufactured by cutting an object to be processed can be improved.

Further, according to the laser processing method and the laser processing apparatus according to the present invention, the modified region can be formed on the front side or the back side inside the object to be processed. As a result, the object to be processed can be easily cut, so that efficient cutting can be performed.

Further, according to the laser processing method and the laser processing apparatus according to the present invention, the modified region and the other modified region can be formed so as to three-dimensionally intersect. Therefore, since the modified region and the other modified region do not overlap each other at the intersection between the cut surfaces, it is possible to prevent a decrease in cutting accuracy at the intersection. This enables accurate cutting.

[Brief description of the drawings]

FIG. 1 is a plan view of an object to be processed during laser processing by a laser processing method according to an embodiment.

FIG. 2 is a cross-sectional view of the object illustrated in FIG. 1 taken along the line II-II.

FIG. 3 is a plan view of a processing target after laser processing by the laser processing method according to the embodiment.

FIG. 4 is a cross-sectional view of the object shown in FIG. 3, taken along line IV-IV.

FIG. 5 is a cross-sectional view of the processing target object shown in FIG. 3 taken along line VV.

FIG. 6 is a plan view of a processing object cut by the laser processing method according to the embodiment.

FIG. 7 is a graph showing a relationship between electric field intensity and crack size in the laser processing method according to the embodiment.

FIG. 8 is a sectional view of an object to be processed in a first step of the laser processing method according to the embodiment.

FIG. 9 is a cross-sectional view of a processing target in a second step of the laser processing method according to the embodiment.

FIG. 10 is a sectional view of an object to be processed in a third step of the laser processing method according to the embodiment.

FIG. 11 is a sectional view of an object to be processed in a fourth step of the laser processing method according to the embodiment.

FIG. 12 is a diagram showing a photograph of a cross section of a part of the silicon wafer cut by the laser processing method according to the embodiment.

FIG. 13 is a graph showing the relationship between the wavelength of laser light and the transmittance inside a silicon substrate in the laser processing method according to the present embodiment.

FIG. 14 is a perspective view of an example of a processing object in which a crack region is formed inside the processing object using the laser processing method according to the present embodiment.

FIG. 15 is a partial sectional view of the object shown in FIG. 14;

FIG. 16 is a perspective view of another example of the processing object in which a crack region is formed inside the processing object using the laser processing method according to the present embodiment.

17 is a partial cross-sectional view of the object shown in FIG.

FIG. 18 is a perspective view of still another example of the processing object in which a crack region is formed inside the processing object using the laser processing method according to the present embodiment.

FIG. 19 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment.

FIG. 20 is a diagram showing a state in which a focal point of a laser beam is located on the surface of a processing object.

FIG. 21 is a diagram illustrating a state in which a focal point of a laser beam is located inside a processing target object.

FIG. 22 is a flowchart illustrating a laser processing method according to the embodiment.

FIG. 23 is a plan view of a processing object for explaining a pattern that can be cut by the laser processing method according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Processing object, 3 ... Surface, 5 ... Cut line, 7 ... Modification area, 9 ... Crack area, 1
1 ... silicon wafer, 13 ... melt processing area, 1
00: laser processing device, 101: laser light source,
105: Condensing lens, 109: X-axis stage, 111: Y-axis stage, 113: Z-axis stage, P: Focus point

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 101: 40 H01L 21/78 B (72) Inventor Naoki Uchiyama 1126 Nomachi, Hamamatsu City, Shizuoka Prefecture 1 Hamamatsu In Photonics Co., Ltd. (72) Inventor Toshimitsu Wakuda 1126 Nomachi, Hamamatsu City, Shizuoka Prefecture 1 Hamamatsu Photonics Co., Ltd. F-term (reference)

Claims (10)

[Claims] 1. A laser beam converging point is set inside the processing object beyond a laser light incident surface of the processing object, and the incident surface is positioned at a position of half the thickness in the thickness direction of the processing object. By adjusting to a position close to or far from, and irradiating the processing object with a laser beam, a modified region by multiphoton absorption inside the processing object along a line to cut the processing object. Comprising a step of forming
Laser processing method. 2. An incident surface on which at least one of an electronic device and an electrode pattern is formed, wherein a focal point of a laser beam applied to the object to be processed is positioned at a half of the thickness in the thickness direction. The laser processing method according to claim 1, wherein the laser processing method is adjusted to a position closer to the incident surface. 3. The processing object is irradiated with laser light by adjusting the focal point of the laser light to the inside of the processing object, so that the inside of the processing object is cut along a line to cut the processing object. A first step of forming a modified region by multiphoton absorption, and after the first step, a focal point of the laser beam is different from a focal position of the laser beam in the first step in a thickness direction of the workpiece. By irradiating the processing object with laser light in accordance with the position of the inside of the processing object, another multi-photon absorption inside the processing object along another cutting line of the processing object. A second step of forming the modified region so as to three-dimensionally cross the modified region. 4. The laser processing method according to claim 3, wherein the other modified region is formed closer to the laser light incident surface of the processing target than the modified region. 5. A condition for irradiating a laser beam to the object to be processed is set so that a peak power density at a focal point of the laser beam is 1
The laser according to any one of claims 1 to 4, wherein the modified region including a crack region is formed in the inside thereof by setting the pulse width to 1 × 10 ⁸ (W / cm ² ) or more and 1 μs or less. Processing method. 6. A condition for irradiating a laser beam to the object to be processed is such that a peak power density at a focal point of the laser beam is one.
5. The modified region according to claim 1, wherein the modified region including the melt-processed region is formed therein by setting the pulse width to 1 × 10 ⁸ (W / cm ² ) or more and 1 μs or less. 6. Laser processing method. 7. A condition for irradiating a laser beam to the object to be processed is such that a peak power density at a laser beam converging point is one.
The modified region including a refractive index change region, which is a region where the refractive index has changed, is formed in the inside by setting the pulse width to 1 × 10 ⁸ (W / cm ² ) or more and the pulse width to 1 ns or less. The laser processing method according to any one of claims 1 to 4. 8. Adjustment of the position in the thickness direction of the focal point of the laser beam applied to the processing object may be performed by adjusting the position of the focal point of the laser beam applied to the processing object in the thickness direction. A position is defined as a distance from the incident surface to the inside, and the distance is divided by a refractive index of the processing object with respect to a laser beam applied to the processing object, so that a relative position of the processing object in the thickness direction is obtained. Calculating the data of the target movement amount, and the other relative position of the processing object in the thickness direction necessary to position the focal point of the laser beam irradiated on the processing object on the incident surface. Another operation step of calculating data of a movement amount; a movement step of relatively moving the workpiece in the thickness direction based on the data of the other relative movement amount; Target Including with other moving step of relatively moving the workpiece in the thickness direction based on the rotation amount of data, the laser processing method according to any one of claims 1 to 7. 9. A laser light source for emitting a pulse laser beam having a pulse width of 1 μs or less, and a peak power density of a focal point of the pulse laser beam emitted from the laser light source is 1 × 10 ⁸ (W / cm ² ). A focusing means for focusing the pulsed laser light as described above, and a movement for relatively moving the focal point of the pulsed laser light focused by the focusing means along a line to cut the object to be processed. Means, and data of a relative movement amount of the processing object in the thickness direction for adjusting a focal point of the pulsed laser light focused by the focusing means to a desired position inside the processing object. Wherein the desired position is a distance from the incident surface where the pulsed laser light emitted from the laser light source is incident on the object to the inside, and the distance is a pulsed laser light emitted from the laser light source. Storage means for storing data of the relative movement amount obtained by dividing by the refractive index of the object to be processed; and a light-receiving point of the pulse laser light collected by the light-collecting means. Calculating means for calculating data of another relative movement amount of the object in the thickness direction necessary to match the relative movement amount data calculated by the relative movement amount data stored by the storage means; And another moving means for relatively moving the object to be processed in the thickness direction based on the data of the other relative movement amount obtained. 10. A laser light source that emits a pulse laser beam having a pulse width of 1 μs or less, and a peak power density of a focal point of the pulse laser beam emitted from the laser light source is 1 × 10 ⁸ (W / cm ² ). Focusing means for focusing the pulsed laser light as described above; means for adjusting the focusing point of the pulsed laser light focused by the focusing means to the inside of the processing object; and focusing by the focusing means. Means for adjusting the position of the focal point of the emitted pulsed laser light within the range of the thickness of the object to be processed, and relatively the focal point of the pulsed laser light along a line to be cut of the object to be processed. A laser processing apparatus comprising: a moving means for moving;