JP2002205180A - Method for laser beam machining - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for laser beam machining, by which a molten point or a crack deviant from a planned cutting line on a surface of the work to be machined is not generated and the work to be machined is accurately cut. SOLUTION: A property modification zone is formed inside the work 1 to be machined by irradiating the planned cutting line 5 with a pulse laser beam L by placing the focal point inside the work 1 to be machined under a condition that a multiphoton absorption takes place. By cutting the work 1 to be machined along the planned cutting line 5 originated at the property modification zone, the work 1 to be machined is cut with a comparatively small force. When irradiated with the laser beam L, the pulse laser beam L is scarcely absorbed on the surface 3 of the work 1 to be machined, thus the surface 3 is never melted due to the formation of the property modification zone. By changing the location of the focal point of the laser beam L in the incident direction of the work 1 to be machined, a plurality of the property modification zones are formed along a line in the direction of the thickness of the work 1 to be machined.

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 used for cutting a processing target 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 which does not cause unnecessary cracks on the surface of a workpiece and does not melt the surface.

[0006]

SUMMARY OF THE INVENTION A laser processing method according to the present invention is characterized in that a laser beam is radiated to a processing object so that a focal point of the laser light is set inside the processing object, thereby cutting the processing object. Forming a modified region by multiphoton absorption inside the object along the scheduled line, and the position of the focal point of the laser beam in the direction of incidence of the laser beam irradiated on the object to be processed And forming a plurality of modified regions so as to be arranged in the incident direction.

[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.

Further, according to the laser processing method of the present invention, by changing the position of the focal point of the laser light in the direction of incidence of the laser light irradiated on the processing object to the processing object, the modified region Are formed so as to be arranged along the incident direction. Therefore, it is possible to increase the number of starting points when cutting the workpiece. The incident direction includes, for example, the thickness direction of the object to be processed and a direction orthogonal to the thickness direction.

A laser processing method according to the present invention is characterized in that a laser beam is irradiated on a processing object by adjusting a focal point of the laser light to the inside of the processing object, thereby processing the processing object along a cutting line. The modified region is formed by forming a modified region inside the object, and changing the position of the laser light focusing point in the incident direction of the laser light irradiated on the object to be processed. A step of forming a plurality of cells so as to be arranged in a direction. In addition, the laser processing method according to the present invention provides a method for condensing laser light under the condition that the peak power density at the focal point of the laser light is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1 μs or less. By irradiating the laser beam to the processing object with the point aligned with the inside of the processing object, a modified area is formed inside the processing object along a line to cut the processing object, and the processing object is formed. By changing the position of the focal point of the laser light in the direction of incidence of the laser light irradiated on the object to be processed, thereby forming a plurality of modified regions so as to be arranged along the direction of incidence. And

[0011] The laser processing method according to the present invention comprises:
For the same reason as the laser processing method according to the present invention,
Laser processing can be performed without causing unnecessary cracks on the surface of the processing object and without melting the surface, and the number of starting points when cutting the processing object can be increased. However, the formation of the modified region may be caused by multiphoton absorption or by other causes.

The laser processing method according to the present invention has the following aspects.

[0013] The plurality of modified regions can be formed in order from the farthest from the incident surface of the object on which the laser light irradiated to the object is incident. According to this, a plurality of modified regions can be formed without any modified region between the incident surface and the focal point of the laser beam. Therefore, since the laser light is not scattered by the already formed modified regions, each modified region can be formed uniformly.

The modified region is a crack region where a crack has occurred inside the object to be processed, a melt-processed region where the inside has been melt-processed, and a refractive index where the refractive index has changed inside. At least one of the change regions is included.

[0015]

Preferred embodiments of the present invention will be described below with reference to the drawings. In the laser processing method 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.

[0016] 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 object 1, if the starting point is located at a position to be cut, the object 1 is broken from the starting point. Therefore, as shown in FIG. 6, the 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.

The 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 the present 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 The laser beam is focused on the inside of the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ) by focusing. The electric field intensity at the light spot is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1
Irradiate under the condition of μs or less. The magnitude of this pulse width is
This 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, for example, 1 ns to 2
00 ns is preferred. The formation of a crack region by multiphoton absorption is described in, for example, “Inside a Glass Substrate by Solid-State Laser Harmonics” on page 23 to page 28 of the 45th Meeting of the Laser Thermal Processing Society of Japan (December 1998). marking"
It is described in.

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 glass (700μ thick)
m) (B) Laser Light source: Semiconductor laser pumped Nd: YAG laser Wavelength: 1064 nm Laser beam cross section: 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: linearly polarized light (C) Condensing lens Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which 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 a processing object 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 modified region is a melt-processed region The laser beam is focused on the inside of the object to be processed (for example, a semiconductor material such as silicon), and the electric field intensity at the focused point is 1 × 10 ⁸ (W / cm ² ) or more and pulse width 1 μs
Irradiation is performed under the following conditions. Thereby, 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. The melt-processed region means at least one of a region that has once been melted and re-solidified, a region in a molten state, and a region in a state of being re-solidified from melting. Further, the melt-processed region can also be referred to as a region where the phase has changed or a region where the crystal structure has changed. In addition, a melt-processed region can also be referred to as a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. That is, for example, a region that has changed from a single crystal structure to an amorphous structure, a region that has changed from a single crystal structure to a polycrystalline structure, and a region that has changed from a single crystal structure to a structure that includes an amorphous structure and a polycrystalline structure. I do. When the object to be processed has a silicon single crystal structure, the melt processing region has, for example, an amorphous silicon structure. 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 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 pumped Nd: YAG laser Wavelength: 1064 nm Laser light spot cross section: 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 Laser Transmittance with respect to light wavelength: 60% (D) Moving speed of mounting table on which object to be processed is mounted: 10
0mm / sec

FIG. 12 is a diagram 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.

Note that the silicon wafer is cracked in the cross-section direction starting from the melt processing area, 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 Area is a Refractive Index Change Area When the laser light is focused on the inside of the object to be processed (eg, glass), 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 this embodiment, the modified region is formed by multiphoton absorption. In this embodiment, by changing the position of the focal point of the laser light in the direction of incidence of the laser beam irradiated on the object to be processed, a plurality of modified regions are arranged so as to be aligned along the direction of incidence. Has formed.

The formation of a plurality of modified regions will be described using a crack region as an example. FIG. 14 is a perspective view of the processing target 1 in which two crack regions 9 are formed inside the processing target 1 using the laser processing method according to the present embodiment.

The method for forming the two crack regions 9 will be briefly described. First, the focal point of the pulse laser light L is matched with the vicinity of the back surface 21 inside the processing object 1, and the processing object 1 is irradiated with the pulse laser light L while moving the focal point along the line 5 to be cut. . Thereby, the crack area 9
(9A) is formed near the back surface 21 inside the processing target object 1 along the line 5 to be cut. Next, pulsed laser light
The focal point of L is adjusted to the vicinity of the surface 3 inside the object 1, and the object 1 is irradiated with the pulse laser beam L while moving the focal point along the line 5 to be cut. By this irradiation, a crack region 9 (9B) is formed near the surface 3 inside the processing target object 1 along the line 5 to be cut.

Then, as shown in FIG. 15, cracks 91 grow naturally from the crack regions 9A and 9B. Specifically, the crack 91 is formed from the crack region 9A toward the back surface 21 and from the crack region 9A (9B) to the crack region 9B (9
A), and naturally grows from the crack region 9B in the surface 3 direction. Thereby, on the surface of the processing object 1 along the line 5 to be cut, that is, the surface to be the cut surface,
Cracks 9 extending long in the thickness direction of the workpiece 1 can be formed. Therefore, the workpiece 1 is naturally applied only by applying a relatively small force or without applying it.
Can be cut along the line 5 to be cut.

As described above, according to the present embodiment, a plurality of crack regions 9 are formed to increase the number of starting points for cutting the workpiece 1. Therefore, according to the present embodiment, even when the thickness of the processing object 1 is relatively large, or when the material of the processing object 1 is difficult to grow the crack 91 after the formation of the crack region 9, the processing object 1 can be used.
Can be cut.

When it is difficult to cut only the two crack regions 9, three or more crack regions 9 are formed.
For example, as shown in FIG. 16, a crack region 9C is formed between the crack region 9A and the crack region 9B. Further, as shown in FIG. 17, the laser beam can be cut in a direction orthogonal to the thickness direction of the processing target 1 as long as the laser light is incident.

In the present embodiment, the plurality of crack regions 9 are preferably formed in order from the farthest from the incident surface (for example, the surface 3) of the object on which the pulsed laser light L is incident. For example, in FIG.
A is formed, and then a crack region 9B is formed. When the crack regions 9 are formed in order from the one closer to the incident surface, the pulsed laser light L irradiated when the crack regions 9 are formed later is scattered by the crack regions 9 formed earlier. As a result, the size of a crack portion (crack spot) formed by one shot of the pulse laser beam L constituting the crack region 9 formed later varies. Therefore, the crack region 9 formed later cannot be formed uniformly. On the other hand, when the crack regions 9 are formed in order from the farthest from the incident surface, the scattering does not occur.
Can be formed uniformly.

However, in the present embodiment, the order of forming the plurality of crack regions 9 is not limited to the above, and the plurality of crack regions 9 may be formed in order from the one closer to the incident surface of the workpiece, or may be formed randomly. You may. The term “random formation” means, for example, in FIG. 16, a crack region 9C is formed first, a crack region 9B is formed next, and a crack region 9A is formed last with the laser light incident direction reversed.

Although the formation of the plurality of modified regions has been described in the case of the crack region, the same can be said for the melt-processed 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, an example of a laser processing apparatus used in the laser processing method according to the present embodiment will be described. FIG. 18 is a schematic configuration diagram of the laser processing apparatus 100.
The laser processing apparatus 100 includes a laser light source 101 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 reflection function of the laser light L. And a dichroic mirror 103 arranged so as to change the direction of the optical axis of the laser light L by 90 °; a condenser lens 105 for condensing the laser light L reflected by the dichroic mirror 103;
A mounting table 107 on which the processing target 1 to be irradiated with the laser light L condensed by the condensing lens 105 is mounted;
Axis stage 109 for moving 07 in the X axis direction
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 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions. 113 and these three stages 109, 111,
And a stage control unit 115 that controls the movement of the 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 in the X (Y) axis direction by the X (Y) axis stage 109 (111). 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 beam L can be adjusted inside the object 1 to be processed. That is, the position of the focal point P in the thickness direction of the workpiece 1 is adjusted by the Z-axis stage 113. 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. The condensing lens 10
By moving 5 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.

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. 19 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. 20, 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, the desired position of the light-converging point P in the thickness direction of the processing target 1 is determined by the distance (Nz) from the surface 3 to the inside of the processing target 1.
And The workpiece 1 is moved in the thickness direction by a movement amount (z) obtained by dividing the distance (Nz) by the refractive index (N). Thereby, the focal point P can be adjusted to the desired position.

The laser processing apparatus 100 further includes a mounting table 1
07, an observation light source 117 that generates visible light to illuminate the processing target 1 with visible light, and a visible light arranged on the same optical axis as the dichroic mirror 103 and the condenser lens 105. Beam splitter 119
And. 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 is converted to the dichroic mirror 103 and the condenser lens 105.
To illuminate the surface 3 of the object 1 including the line 5 to be cut.

The laser processing apparatus 100 further includes an image pickup device 12 arranged on the same optical axis as the beam splitter 119, the dichroic mirror 103, and the condensing 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. Further, the imaging data processing unit 125
Calculates image data such as an enlarged image of the front surface 3 based on the imaging data. This image data is sent to the overall control unit 127, where various processes are performed, and the monitor 129
Sent to 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. 19 and 20 is input and stored.

Next, a laser processing method according to this embodiment will be described with reference to FIGS. FIG. 21 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. Focus point P
Is determined in consideration of the thickness, material, and the like of the workpiece 1. In the present embodiment, the data of the first movement amount and the front surface 3 for positioning the focal point P near the back surface inside the object 1
The data of the second movement amount for positioning the focal point P in the vicinity is used. The first melt processing region is formed using the data of the first movement amount. The melt processing area to be formed next is formed using the data of the second movement amount. The data of these movement amounts 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 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.

The general control unit 127 has a step S10 in advance.
The data of the first movement amount determined in 3 is input,
The data of the movement amount is sent to the stage control unit 115. The stage control unit 115 moves the processing target 1 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 processing target 1 based on the data of the movement amount. (S111). This internal position is near the back surface of the object 1.

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 and the Y-axis stage 1 are arranged along the line 5 to be cut.
11 is moved to form a melt-processed area inside the object 1 along the line 5 to be cut (S11).
3). The melt processing area is formed near the back surface inside the processing target object 1.

Next, the same as in step S111, the second
Based on the data of the movement amount, the processing target 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 beam L is near the surface 3 inside the processing target 1 (S
115). Then, similarly to step S113, a melt processing area is formed inside the processing target object 1 (S11).
7). In this step, a melt processing region is formed in the vicinity of the surface 3 inside the workpiece 1.

Finally, a line 5 for cutting the object 1
The object 1 is cut by bending along (S119). As a result, the workpiece 1 is divided into silicon chips.

The effect of the present 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 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, a plurality of modified regions are formed so as to be arranged in the incident direction, so that the number of starting points when cutting the workpiece 1 is increased. For example, when the dimension of the processing target 1 in the direction of incidence of the laser beam is relatively large, or when the processing target 1 is made of a material in which cracks are unlikely to grow from the reformed region, the modified region along the planned cutting line 5 is It is difficult to cut the workpiece 1 with only one piece. Therefore, in such a case, by forming a plurality of modified regions as in the present embodiment, the workpiece 1
Can be easily cut.

[0066]

According to the laser processing method of the present invention,
The object to be processed can be cut without causing melting or cracking on the surface of the object to be cut out of the line to be cut. Therefore, products (eg, semiconductor chips, piezoelectric device chips,
The yield and productivity of display devices such as liquid crystal) can be improved.

Further, according to the laser processing method of the present invention, a plurality of modified regions are formed to increase the number of starting points when cutting a workpiece. Therefore,
Even when the thickness of the processing target is relatively large, the processing target can be cut.

[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 perspective view of a workpiece on which a crack extending from the crack region shown in FIG. 14 is formed.

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.

FIG. 17 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 embodiment.

FIG. 18 is a schematic configuration diagram of an example of a laser processing apparatus that can be used in the laser processing method according to the present embodiment.

FIG. 19 is a diagram illustrating a state in which a focal point of a laser beam is located on a surface of a processing object.

FIG. 20 is a diagram illustrating a state in which a focal point of a laser beam is located inside a processing target object.

FIG. 21 is a flowchart for explaining a laser processing method according to the embodiment.

FIG. 22 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.

[Description of Signs] 1 ... workpiece, 3 ... surface, 5 ... cutting line, 7 ... modification area, 9,9A, 9B, 9C ... crack area, 11 ..Silicon wafer, 13 ... Molten processing area, 100 ... Laser processing apparatus, 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) G03F 7/20 505 G03F 7/20 505 // H01L 21/301 B23K 101: 40 B23K 101: 40 H01L 21 / 78 B (72) Inventor Naoki Uchiyama 1126-1, Hachimatsu-cho, Hamamatsu-shi, Shizuoka Pref. Inside Hamamatsu Photonics Co., Ltd. (Reference) 2H097 AA03 BA01 BB01 CA17 LA10 LA20 3C069 AA03 BA08 CA05 CA11 EA02 4E068 AE01 CA02 CA03 DA10 DA11 4G015 FA06 FB01 FB02 FC14

Claims (5)

[Claims] A laser light is irradiated onto the object to be processed by aligning a focal point of the laser light with the inside of the object, and thereby the inside of the object is cut along a line to cut the object. Forming a modified region by multiphoton absorption, and changing the position of the focal point of the laser light in the direction of incidence of the laser light applied to the processing object to the processing object, thereby performing the modification. A laser processing method, comprising a step of forming a plurality of regions so as to be arranged in the incident direction. 2. A method according to claim 1, further comprising: irradiating the processing object with the laser light while adjusting a focal point of the laser light to the inside of the processing object, thereby forming an inner portion of the processing object along a cutting line of the processing object. Forming a modified region on the object, and changing the position of the laser light converging point in the direction of incidence of the laser light applied to the object to be processed to the object, thereby allowing the incident area to enter the modified region. A laser processing method, comprising: forming a plurality of lasers so as to be arranged in a direction. 3. A laser beam having a peak power density at a focal point of 1 × 10 ⁸ (W / cm ² ) or more and a pulse width of 1 μm.
s Under the following conditions, by irradiating the laser beam to the processing object by adjusting the focal point of the laser light to the inside of the processing object, along the line to cut the processing object, By forming a modified region inside, and by changing the position of the focal point of the laser light in the direction of incidence of the laser light applied to the processing object to the processing object, the modified region is the A laser processing method including a step of forming a plurality of lasers so as to be arranged along an incident direction. 4. The processing apparatus according to claim 1, wherein the plurality of modified regions are formed in order from a farther side with respect to an incident surface of the object on which the laser light irradiated to the object is incident. The laser processing method according to any one of the above. 5. The modified region has a crack region in which a crack has occurred in the inside of the object to be processed, a melt-processed region in which the inside has been melt-processed, and a refractive index changed in the inside. Including at least one of the refractive index change regions that are regions,
The laser processing method according to claim 1.