JP2003088973A - Laser beam machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining method by which an unnecessary cleavage is not caused on the surface of a work and the surface is not melted. SOLUTION: The laser beam machining method comprises a first process for forming a reformed region 7 based on multiphoton absorption in the inside of the work 1 along the intended cutting line of the work 1 by adjusting the focus of a converging point P in the work 1 and by irradiating the work 1 with a laser beam L, and a second process, after the first process, for causing stress at places where the work 1 is cut along the intended cutting line by cooling the work 1 so that the temperature of the work 1 becomes lower than that of the work 1 when the reformed region 7 is formed.

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 an object to be processed such as a piezoelectric material substrate and a glass substrate.

[0002]

2. Description of the Related Art Cutting is one of laser applications, and general cutting by laser is as follows. For example, a laser beam having a wavelength absorbed by the object to be processed is irradiated to a point where the object to be processed such as a semiconductor wafer or a glass substrate is cut, and the surface of the object to be processed is directed from the front surface to the back surface at the position to be cut by absorbing the laser light. The heating and melting are advanced to cut the object to be processed. However, according to this method, the periphery of the area to be cut on the surface of the workpiece is also melted. Therefore, when the object to be processed is a semiconductor wafer, among the semiconductor elements formed on the surface of the semiconductor wafer, the semiconductor elements located in the periphery of the region may melt.

[0003]

As a method of preventing melting of the surface of an object to be processed, for example, Japanese Patent Application Laid-Open No. 2000-21.
There are laser cutting methods disclosed in Japanese Patent No. 9528 and Japanese Patent Laid-Open No. 2000-15467. In the cutting methods of these publications, the cutting point of the workpiece is heated by laser light, and the workpiece is cooled,
The object to be processed is cut by causing a thermal shock at the place where the object to be processed is cut.

However, in the cutting methods disclosed in these publications, when the thermal shock generated on the object to be processed is large, the surface of the object to be processed is cracked off the planned cutting line or to a point before laser irradiation. Unnecessary cracks may occur. Therefore, precision cutting cannot be performed by these cutting methods. In particular, the object to be processed 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 cracks may damage the semiconductor chip, the liquid crystal display device, and the electrode pattern. Further, since the average input energy is large in these cutting methods, thermal damage to the semiconductor chip or 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 an object to be processed and does not melt the surface.

[0006]

A laser processing method according to the present invention irradiates a laser beam with a converging point inside an object to be processed, and the object is processed along a line to cut the object. First to form a modified region by multiphoton absorption inside
After the step 1 and the first step, the workpiece is cooled such that the temperature of the workpiece becomes lower than the temperature of the workpiece when the modified region is formed, and the workpiece is cut along the planned cutting line. And a second step of causing stress at the cut point.

According to the laser processing method of the present invention, in the first step, the inside of the object to be processed is irradiated with the laser beam with the converging point aligned and the phenomenon of multiphoton absorption is utilized to perform the processing. A modified region is formed inside the object. If there is some starting point at the point where the object to be machined is cut, the object to be machined can be cut with a relatively small force.

According to the above laser processing method, when the volume of the object to be processed shrinks in the second step due to cooling, the modified region formed in the first step causes Stress such as thermal stress due to a temperature difference is generated at the location where the workpiece is cut. This stress allows cracks to grow in the thickness direction of the object to be processed starting from the modified region, and the object to be processed can be broken and cut.

Therefore, the object to be machined can be cut with a relatively small force such as a thermal stress due to a temperature difference, so that unnecessary cracks deviating from the planned cutting line are generated on the surface of the object to be machined. Without this, it is possible to cut the object to be processed.

According to the laser processing method of the present invention, the modified region is formed by locally causing multiphoton absorption inside the object to be processed. Therefore, the laser beam is hardly absorbed on the surface of the object to be processed, so that the surface of the object to be processed is not melted. The converging point is a place where the laser light is condensed. 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.

In the laser processing method according to the present invention, a converging point is set inside the object to be processed, and the peak power density at the converging point is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1.
A first step of irradiating a laser beam under the condition of μs or less to form a modified region including a crack region inside the object to be processed along a line to cut the object to be processed, and after the first step,
The workpiece is cooled so that the temperature of the workpiece becomes lower than the temperature of the workpiece when the modified region is formed, and stress is generated at the location where the workpiece is cut along the planned cutting line. And a second step.

According to the laser processing method of the present invention, in the first step, the focus point is aligned inside the object to be processed, and the peak power density at the focus point is 1 × 10 ⁸ (W / c).
Laser light is emitted under the condition that the pulse width is m ² ) or more and the pulse width is 1 μs or less. Therefore, 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 to be processed, thereby forming a crack region inside the object to be processed. This crack area is an example of the modified area and the second step is the same as that described above. Therefore, according to the laser processing method of the present invention, the surface of the object to be processed is melted or cut from a planned cutting line. Laser processing is possible without causing unnecessary cracks that come off. An object to be processed by this laser processing method is, for example, a member containing glass. The peak power density means the electric field strength at the condensing point of the pulsed laser light.

In the laser processing method according to the present invention, a converging point is set inside the object to be processed, the peak power density at the converging point is 1 × 10 ⁸ (W / cm ² ) or more, and the pulse width is 1
A first step of irradiating a laser beam under a condition of μs or less, and forming a modified region including a melt processing region inside the object to be processed along a planned cutting line of the object, and after the first step,
The workpiece is cooled so that the temperature of the workpiece becomes lower than the temperature of the workpiece when the modified region is formed, and stress is generated at the location where the workpiece is cut along the planned cutting line. And a second step.

According to the laser processing method of the present invention, in the first step, the focus point is aligned inside the object to be processed, and the peak power density at the focus point is 1 × 10 ⁸ (W / c).
Laser light is emitted under the condition that the pulse width is m ² ) or more and the pulse width is 1 μs or less. Therefore, the inside of the object to be processed is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the object to be processed. This melting treatment area is an example of the above modification area and the second step is the same as that described above. Therefore, according to the laser processing method of the present invention, a melting or cutting line is planned on the surface of the object to be processed. Laser processing can be performed without causing unnecessary cracks that are not formed. An object to be processed by this laser processing method is, for example, a member containing a semiconductor material.

In the laser processing method according to the present invention, the focusing point is set inside the object to be processed, the peak power density at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more, and the pulse width is 1
Laser light is irradiated under a condition of ns or less to form a modified region including a refractive index changing region, which is a region where the refractive index has changed, inside the processing target along the planned cutting line of the processing target. After the step and the first step, the object to be processed is cooled so that the temperature of the object to be processed becomes lower than the temperature of the object to be processed when the modified region is formed, and the object to be processed is cut along the planned cutting line. And a second step of causing stress at a cut portion.

According to the laser processing method of the present invention, in the first step, the focus point is aligned inside the object to be processed, and the peak power density at the focus point is 1 × 10 ⁸ (W / c).
m ²⁾ or more and a pulse width is irradiated with laser light under the following conditions 1 ns. When the pulse width is made extremely short as in the present invention and multiphoton absorption is caused inside the object to be processed, the energy due to the multiphoton absorption is not converted into thermal energy, and the ion value inside the object to be processed is increased. A permanent structural change such as a number change, 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 and the second step is the same as that described above. Therefore, according to the laser processing method of the present invention, it is planned to melt or cut the surface of the object to be processed. Laser processing is possible without causing unnecessary cracks off the line.
The object to be processed by this laser processing method is, for example, a member containing glass.

As a mode applicable to the laser processing method according to the present invention, the modified region may be formed in the heated object in the first step. Further, in the second step, the cooling of the object to be processed may be natural cooling or forced cooling.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to the drawings. In the laser processing method according to this embodiment, the modified region is formed by multiphoton absorption. Multiphoton absorption is a phenomenon that occurs when the intensity of laser light is made extremely high. First, the multiphoton absorption will be briefly described.

When the photon energy hν is smaller than the absorption band gap E _G of the material, it becomes optically transparent. Therefore, the condition for absorption in the material is hν> E _G. However, even if it is optically transparent, if the intensity of the laser light is made extremely large, absorption occurs in the material under the condition of nhν> E _G (n = 2, 3, 4, ...). This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of laser light is determined by the peak power density (W / cm ² ) at the focus point of the laser light. For example, multiphoton is used under the condition that the peak power density is 1 × 10 ⁸ (W / cm ² ) or more. Absorption occurs. The peak power density is obtained by (energy per pulse of laser light at the converging point) / (beam spot cross-sectional area of laser light × pulse width). Further, in the case of a continuous wave, the intensity of 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 this embodiment using such multiphoton absorption will be described with reference to FIGS. FIG. 1 is a plan view of a processing object 1 during laser processing, FIG. 2 is a cross-sectional view taken along line II-II of the processing object 1 shown in FIG. 1, and FIG. 3 is a processing object after laser processing. Thing 1
4 is a plan view of FIG. 4, and FIG.
5 is a cross-sectional view taken along line IV, FIG. 5 is a cross-sectional view taken along line VV of the processing object 1 shown in FIG. 3, and FIG. 6 is a plan view of the cut processing object 1.

As shown in FIG. 1 and FIG.
The surface 3 has a planned cutting line 5. The planned cutting line 5 is an imaginary line extending linearly. In the laser processing according to the present embodiment, the modified region 7 is formed by irradiating the processing object 1 with the laser light L by aligning the converging point P inside the processing object 1 under the condition that multiphoton absorption occurs. The converging point is a position where the laser light L is condensed.

By moving the laser beam L relatively along the planned cutting line 5 (that is, along the direction of arrow A), the focal point P is moved along the planned cutting line 5. As a result, as shown in FIG. 3 to FIG.
Are formed only inside the object 1 along the planned cutting line 5. The laser processing method according to the present embodiment does not generate the modified region 7 by causing the processing target 1 to absorb the laser light L to cause the processing target 1 to generate heat. The laser light L is transmitted to the processing target 1 to cause multiphoton absorption inside the processing target 1 to form the modified region 7. Therefore, since the laser beam L is hardly absorbed on the surface 3 of the processing object 1, the surface 3 of the processing object 1 is not melted.

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

There are two possible ways of cutting the object to be processed starting from the modified region. One is a case where an artificial force is applied to the object to be processed after forming the modified region, so that the object to be processed is cracked and the object to be processed is cut from the modified region as a starting point. This is, for example, cutting when the thickness of the object to be processed is large. The application of artificial force means that thermal stress is generated by, for example, applying bending stress or shear stress to the workpiece along the planned cutting line of the workpiece or by giving a temperature difference to the workpiece. Or (the laser processing method according to the present embodiment). The other is when the modified region is formed, so that the modified region is the starting point and is naturally cracked in the cross-sectional direction (thickness direction) of the workpiece, resulting in cutting of the workpiece. Is. For example, when the thickness of the processing target is small, even one modified region is possible, and when the thickness of the processing target is large, it is possible to form a plurality of modified regions in the thickness direction. . Even in the case of spontaneous cracking, it is possible to cut only the surface on the part where the modified region is formed without cracks precipitating to the surface on the part where the modified region is not formed. Therefore, the cleaving can be controlled better. In recent years, the thickness of semiconductor wafers such as silicon wafers has tended to be thin, and such a cleaving method with good controllability 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 crack spots: The laser light is focused on the inside of the object to be processed (eg, piezoelectric material made of glass or LiTaO ₃ ), The electric field strength at the focal point is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1
Irradiate under conditions of μs or less. The magnitude of this pulse width is
It is a condition that a crack region can be formed inside the object to be processed without causing extra damage to the object to be processed while causing multiphoton absorption. As a result, 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 to be processed, thereby forming a crack region inside the object to be processed. The upper limit of the electric field strength is, for example, 1 × 10 ¹²
(W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example. The formation of crack regions by multiphoton absorption is described in, for example, the 45th Laser Thermal Processing Research Group Proceedings (19
1998. Dec., pp. 23-28, "Internal marking of glass substrates by solid-state laser harmonics".

The inventor of the present invention 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 (thickness 700 μm, outer diameter 4 inches) (B) Laser light source: semiconductor laser pumped 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: Output <1 mJ / pulse Laser light quality: TEM ₀₀ Polarization characteristics: Linearly polarized light (C) Condensing lens Laser light transmittance: 60 Percent (D) Moving speed of the mounting table on which the processing target is mounted: 10
0 mm / sec. The laser beam quality of TEM ₀₀ means that the laser beam quality is high and the laser beam can be focused up 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 pulsed laser light, the electric field strength is represented by the peak power density. The vertical axis represents the size of the crack spot formed inside the object to be processed by one pulse of laser light.
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 indicate that the condensing lens (C) has a magnification of 10
The case is 0 times and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by white circles in the graph are when the magnification of the condenser lens (C) is 50 and the numerical aperture (NA) is 0.55. It can be seen that when the peak power density is about 10 ¹¹ (W / cm ² ), crack spots occur inside the object to be processed, and the crack spot also increases as the peak power density increases.

Next, the mechanism of cutting the object to be processed by forming the crack region will be described with reference to FIGS. As shown in FIG. 8, a laser beam L is irradiated to the processing target 1 by aligning the converging point P inside the processing target 1 under the condition that multiphoton absorption occurs, and a crack region is generated inside along the planned cutting line. 9 is formed. The crack area 9 is an area including one or a plurality of crack spots. As shown in FIG. 9, the crack further grows from the crack region 9 as a starting point, the crack reaches the front surface 3 and the back surface 21 of the workpiece 1 as shown in FIG. 10, and the workpiece 1 as shown in FIG. The object 1 to be processed is cut by cracking. In some cases, the cracks reaching the front surface and the back surface of the object to be processed may naturally grow, or when a force is applied to the object to be processed (the laser processing method according to this embodiment).
There is also.

(2) When 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 of 1 μs
Irradiate under the following conditions. As a result, the inside of the object to be processed is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the object to be processed. The melt-processed region is a region that has been once melted and then re-solidified, a region that is just in a molten state, or a region that is in a state where it is re-solidified from the molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure is changed. The 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 in which a single crystal structure is changed to an amorphous structure, a region in which a single crystal structure is changed to a polycrystalline structure, or a region in which a single crystal structure is changed to a structure including an amorphous structure and a polycrystalline structure is meant. To do.
When the object to be processed has a silicon single crystal structure, the melt-processed 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 1 ns to 200 ns, for example.

The present inventor has confirmed by experiments that a melt-processed 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-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 light quality: TEM ₀₀ Polarization characteristics: Linearly polarized light (C) Condensing lens Magnification: 50 times NA: 0.55 laser Transmittance for light wavelength: 60% (D) Moving speed of the mounting table on which the processing target is mounted: 10
0 mm / 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 region 13 is formed inside the silicon wafer 11. The size of the melt-processed region 13 formed under the above conditions in the thickness direction is about 100 μm.

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

For example, 106 which is the wavelength of the Nd: YAG laser.
At 4 nm, it can be seen that 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, the melt-processed region 13 by multiphoton absorption is formed in the vicinity of the center of the silicon wafer, that is, 175 μm from the surface. For the transmittance in this case, referring to a 200 μm thick silicon wafer,
Since it is 90% or more, the laser light is hardly absorbed inside the silicon wafer 11, and most of it is transmitted.
This does not mean that the laser light is absorbed inside the silicon wafer 11 and the melt-processed region 13 is formed inside the silicon wafer 11 (that is, the melt-processed region is formed by normal heating with laser light). This means that the melt-processed region 13 is formed by multiphoton absorption. The formation of the melt-processed region by multiphoton absorption is described in, for example, the Welding Society National Conference Lecture Summary 66th Collection (April 2000), pp. 72-.
It is described in "Evaluation of Silicon Processing Characteristics by Picosecond Pulse Laser" on page 73.

The silicon wafer is cracked in the cross-sectional direction starting from the melt-processed region and reaches the front surface and the back surface of the silicon wafer, whereby the silicon wafer is eventually cut. The crack reaching the front surface and the back surface of the silicon wafer may grow naturally, or may grow when a force is applied to the object to be processed. When cracks naturally grow from the melt processing area to the front and back surfaces of the wafer, when the melt processing area grows from the molten state or the crack grows when resolidifying from the molten state. There are both. However, in these cases as well, the melt-processed region is formed only inside the wafer, and the cut surface after cutting has the melt-processed region formed only inside as shown in FIG. When forming the melt-processed region inside the object to be processed, it is difficult to cause unnecessary cracks that deviate from the planned cutting line at the time of cutting, so that the cutting control becomes easy.

(3) When the modified region is the refractive index changing region The laser beam is focused on the inside of the object to be processed (eg glass), and the electric field strength at the focused point is 1 × 10 ⁸ (W / c
Irradiation is performed under the condition of m ² ) or more and pulse width of 1 ns or less.
When the pulse width is made extremely short and multiphoton absorption is caused inside the object to be processed, the energy due to multiphoton absorption is not converted into thermal energy, and the ion valence change and crystallization occur inside the object to be processed. 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 preferably 1 ns or less, 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 Proceedings (1997
Year. (November), pp. 105-111, "Photo-induced structure formation inside glass by femtosecond laser irradiation".

Next, a specific example of this embodiment will be described. The laser processing method according to the present embodiment includes a modified region forming step (first step) of forming a modified region by multiphoton absorption inside a processing target, and a temperature of the processing target forming the modified region. And a stress step (second step) of forcibly cooling the object to be processed so that the object to be processed is subjected to a stress such as a thermal stress due to a temperature difference at a position where the object is cut. In the modified region forming step, the temperature of the object to be processed is equal to the room temperature of the room in which the laser processing apparatus described later is installed, and in the stress step, the object to be processed is placed on the Peltier cooler and is higher than the room temperature. Forced cooling to low temperature.

The laser processing apparatus of this embodiment will be described. FIG. 14 is a schematic configuration diagram of the laser processing apparatus 100 used in the modified region forming step. As shown in the figure, the laser processing apparatus 100 includes a laser light source 101 that generates a laser light L, and a laser light source control unit 1 that controls the laser light source 101 to adjust the output and pulse width of the laser light L.
02, a dichroic mirror 103 which has a function of reflecting the laser light L and is arranged so as to change the direction of the optical axis of the laser light L by 90 °, and a collection unit which collects the laser light L reflected by the dichroic mirror 103. The light lens 105, the mounting table 107 on which the processing object 1 irradiated with the laser beam L condensed by the condensing lens 105 is mounted, and the mounting table 10.
An X-axis stage 109 for moving 7 in the X-axis direction,
The Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and the mounting table 107 for the X-axis and Y-axis.
The Z-axis stage 113 for moving in the Z-axis direction orthogonal to the axial direction, and these three stages 109, 111, 11
3 of the stage control unit 115 for controlling the movement.

The object 1 to be processed is a LiTaO ₃ wafer (thickness: 350).
μm, outer diameter 4 inches), and a plurality of circuit portions are formed on the surface 3. The back surface 21 of the object 1 to be processed
A dicing film is attached to the.

Since the Z-axis direction is the direction orthogonal to the surface 3 of the object 1 to be processed, it is the direction of the depth of focus of the laser light L incident on the object 1 to be processed. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the focus point P of the laser light L can be aligned inside the object to be processed 1. Further, the movement of the condensing 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).

The laser light source 101 is an Nd: YAG laser which generates pulsed laser light. Other lasers that can be used for the laser light source 101 are Nd: YVO ₄ laser and Nd: YVO ₄ laser.
There is a YLF laser. When forming a crack region and a melt-processed region, it is preferable to use the above-mentioned laser light source,
When forming the refractive index changing region, it is preferable to use a titanium sapphire laser. In the present embodiment, pulsed laser light is used for processing the object to be processed 1, but continuous wave laser light may be used as long as it can cause multiphoton absorption.

The laser processing apparatus 100 further includes a mounting table 1
For observing light source 117 for generating visible light for illuminating the object 1 placed on 07 with visible light, and for dichroic mirror 103 and condensing lens 105 arranged on the same optical axis 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 approximately 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 emitted from the observation light source 117 is reflected by the beam splitter 119, and the reflected visible light is reflected by the dichroic mirror 103 and the condenser lens 105.
And illuminates the surface 3 of the object 1 including the planned cutting line 5 and the like. Since the workpiece 1 is cut into a plurality of circuit portions formed on the surface 3, the planned cutting line 5 is set in the gap between the adjacent circuit portions.

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 condenser lens 105.
1 and the imaging lens 123. The image pickup device 121 is, for example, a CCD (charge-coupled device) camera.
The reflected light of visible light that illuminates the surface 3 including the planned cutting line 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 imaging element 121. And becomes imaging data.

The laser processing apparatus 100 further includes an imaging data processing unit 125 to which the imaging data output from the image sensor 121 is input, an overall control unit 127 that controls the entire laser processing apparatus 100, and a monitor 129. . The imaging data processing unit 125 calculates focus data for focusing the visible light generated by the observation light source 117 on the surface 3 based on the imaging data. Based on this focus data, the stage controller 115 controls the movement of the Z-axis stage 113 so that the visible light is focused on the surface 3. Therefore, the imaging data processing unit 125 functions as an autofocus unit. Note that the focus of visible light coincides with the focal point of the laser light L. Further, the imaging data processing unit 125 calculates image data such as an enlarged image of the surface 3 based on the imaging data. This image data is sent to the overall control unit 127, where various processing is performed in the overall control unit 127.
Sent to monitor 129. As a result, an enlarged image or the like is displayed on the monitor 129.

The overall controller 127 includes the stage controller 1
Data from the image pickup device 15, image data from the image pickup data processing unit 125, and the like are input, and the laser light source control unit 102, the observation light source 117, and the stage control unit 115 are controlled based on these data, thereby the laser processing apparatus. 100
Control the whole thing. Therefore, the overall control unit 127 functions as a computer unit.

Next, the laser processing method according to this embodiment will be described with reference to FIGS. Figure 15
3 is a flow chart for explaining a laser processing method.

First, the light absorption characteristics of the object 1 to be processed are measured by a spectrophotometer or the like not shown. Based on the measurement result, the laser light source 101 that generates the laser light L having a wavelength transparent to the object 1 or a wavelength with little absorption is selected. (S101). Next, the thickness of the processing object 1 is measured. Based on the measurement result of the thickness and the refractive index of the processing object 1, the Z of the processing object 1 in the laser processing apparatus 100.
The amount of movement in the axial direction is determined (S103). In order to position the condensing point P of the laser light L inside the machining target 1, the machining point 1 of the machining target 1 based on the condensing point of the laser light L located on the surface 3 of the machining target 1 is used. This is the amount of movement in the Z-axis direction. This movement amount is input to the overall control unit 127 of the laser processing apparatus 100 used in the modified region forming step.

The object 1 to be processed is mounted on the mounting table 107 of the laser processing apparatus 100. Then, visible light is generated from the observation light source 117 to illuminate the workpiece 1 (S10).
5). Workpiece 1 including illuminated cutting line 5
The surface 3 of the image is imaged by the image sensor 121. The image pickup data is sent to the image pickup data processing unit 125. Based on this imaged data, the imaged data processing unit 125 determines that the observation light source 1
The focus data is calculated such that the focus of visible light 17 is located on the surface 3 (S107).

This focus data is sent to the stage controller 115. The stage control unit 115 moves the Z-axis stage 113 in the Z-axis direction based on this focus data (S
109). As a result, the focus of visible light of the observation light source 117 is located on the surface 3. The imaging data processing unit 125
Calculates the enlarged image data of the surface 3 of the object 1 including the planned cutting line 5 based on the imaged data. This enlarged image data is sent to the monitor 129 via the overall control unit 127.
To the monitor 129 and the planned cutting line 5
An enlarged image of the vicinity is displayed.

In step S10, the overall control unit 127 is set in advance.
The movement amount data determined in 3 is input, and the movement amount data is sent to the stage control unit 115. Based on this movement amount data, the stage control unit 115 moves the object 1 to be processed in the Z-axis direction by the Z-axis stage 113 to a position where the condensing point P of the laser light L is inside the object 1 ( S111).

Next, laser light L is generated from the laser light source 101, and the laser light L is applied to the planned cutting line 5 on the surface 3 of the object 1 to be processed. Since the focal point P of the laser light L is located inside the processing object 1, the crack region 9 is formed only inside the processing object 1. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the planned cutting line 5 to form the crack region 9 inside the processing object 1 along the planned cutting line 5 (S11).
3). At this time, the temperature of the processing target 1 is equal to the room temperature of the room in which the laser processing apparatus 1 is installed.

After forming the modified region, the workpiece 1 is conveyed to the cooling device 131 (S115). Since the crack region 9 in the modified region forming step is formed only inside the processing object 1, the processing object 1 does not fall apart,
Therefore, the workpiece 1 can be easily transported.
As shown in FIG. 16, the workpiece 1 is a chamber 133.
1 Peltier cooler placed in a dry nitrogen atmosphere
35. The Peltier cooler 135 is set to a temperature lower than the room temperature of the room in which the laser processing apparatus 1 is installed by the cooling temperature control device 137. As a result, the workpiece 1 is forcibly cooled so that its temperature becomes lower than the room temperature, and its volume shrinks. At this time, the crack area 9 causes the temperature of the workpiece to be cut. Stress such as thermal stress due to the difference occurs (S11
7). Due to this stress, a crack is generated in the crack area 9
The surface 3 and the back surface 21 of the object 1 to be grown.
And the workpiece 1 is cut into each of the plurality of circuits formed on the surface 3 (S119).

In the present embodiment, the case where the crack region is formed as the modified region has been described. However, the same applies to the case where the above-described melt-treated region or the refractive index changing region is formed as the modified region. Is. in this case,
In the stress process, when the workpiece is forcibly cooled so that the temperature of the workpiece becomes lower than that when the modified region is formed, and the volume shrinks, the melt processing region and the refractive index change region cause As a result, stress such as thermal stress due to a temperature difference is generated at a position where the object to be processed is cut, and the object to be processed can be cut by causing a crack to start and grow from the melting processing region or the refractive index change region.

Even when the thickness of the object to be processed is large, even when cracks grown from the modified region as a starting point in the stress process do not reach the front and back surfaces of the object to be processed, bending stress and shear By applying an artificial force such as stress, the object to be processed can be broken and cut. Since this artificial force is sufficient with a smaller force, it is possible to prevent the occurrence of unnecessary cracks that deviate from the planned cutting line on the surface of the workpiece.

The effects of this embodiment will be described. According to this, in the modified region forming step, the converging point P is aligned with the inside of the object to be processed 1 under the condition of causing multiphoton absorption, and the pulse laser beam L is irradiated to the planned cutting line 5. . Then, by moving the X-axis stage 109 and the Y-axis stage 111, the condensing point P is moved along the planned cutting line 5. As a result, a modified region (for example, a crack region, a melting treatment region, a refractive index change region) is formed inside the object 1 to be processed along the planned cutting line 5. If there is some starting point at the point where the object to be machined is cut, the object to be machined can be cut with a relatively small force. According to the present embodiment, in the stress process, the processing target is forcibly cooled so that the temperature of the processing target becomes lower than that at the time of forming the modified region, and heat is generated at a location where the processing target is cut due to a temperature difference. It causes stress such as stress. Therefore, the workpiece 1 can be cut with a relatively small force such as thermal stress due to a temperature difference. As a result, the processing target 1 can be cut without causing unnecessary cracks on the surface 3 of the processing target 1 that deviate from the planned cutting line 5.

Further, according to the present embodiment, in the modified region forming step, a pulsed laser beam is obtained by adjusting the converging point P inside the object 1 to be processed under the condition of causing multiphoton absorption in the object 1. Since the pulsed laser light L is transmitted through the object to be processed 1 and the surface 3 of the object to be processed 1 hardly absorbs the pulsed laser light L, the surface 3 is affected by the formation of the modified region. There is no damage such as melting.

As described above, according to this embodiment,
It is possible to cut the processing target 1 without causing unnecessary cracks or melting off the planned cutting line 5 on the surface 3 of the processing target 1. Therefore, when the processing target 1 is, for example, a semiconductor wafer, the semiconductor chip can be cut out from the semiconductor wafer without causing unnecessary cracking or melting off the planned cutting line. The same applies to a processed object having an electrode pattern formed on the surface and a processed 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 liquid crystal is formed. Therefore, according to this embodiment, it is possible to improve the yield of a product (for example, a semiconductor chip, a piezoelectric device chip, a display device such as a liquid crystal) manufactured by cutting a processing target.

Further, according to this embodiment, the object to be processed 1
Since the planned cutting line 5 on the surface 3 is not melted, the width of the planned cutting line 5 (this width is, for example, in the case of a semiconductor wafer, the interval between regions to be semiconductor chips) can be reduced. As a result, the number of products manufactured from one processing object 1 is increased, and the productivity of the products can be improved.

Further, according to this embodiment, the object to be processed 1
Since a laser beam is used for the cutting process, a more complicated process can be performed than dicing using a diamond cutter.
For example, even if the planned cutting line 5 has a complicated shape as shown in FIG. 17, the cutting process can be performed.

Although one embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited to the above embodiment.

For example, in the present embodiment, the temperature of the object to be processed at the time of forming the modified region is the room temperature of the room in which the laser processing apparatus is arranged. However, in the present invention, the object to be heated is heated. A modified region may be formed in the. And
In this case, the cooling of the object to be processed may be natural cooling or forced cooling. This is because the volume of the object to be processed at the time of forming the modified region is expanded by heating, so that the volume of the object to be processed contracts even if the object to be cooled is, for example, natural cooling to room temperature. As a result, due to the modified region, stress such as thermal stress due to a temperature difference is generated at the location where the workpiece is cut, and the workpiece can be cut. The same applies to the case where the cooling of the object to be processed is forced cooling, but the forced cooling can cut the object to be processed in a shorter time than the natural cooling.

As the heating device for heating the object to be processed, for example, the heating device 139 shown in FIG.
There is a heating device 141 shown in FIG. As shown in FIG. 18, the heating device 139 includes a constant temperature bath 143 in which the workpiece 1 is placed, and a heating temperature control device 145 that controls the temperature in the constant temperature bath 143. The heating temperature control device 145 uses the temperature sensor 149 having the temperature measuring unit 147 installed in the vicinity of the workpiece 1 to control the constant temperature bath 1.
The temperature inside 43 is controlled. Further, as shown in FIG. 19, the heating device 141 includes a heater plate 151 on which the workpiece 1 is placed, and a heating temperature control device 153 that controls the temperature of the heater plate 151. The object 1 to be processed may be preheated using these heating devices, or, for example, the heater plate 151 of the heating device 141 is provided on the mounting table 107 of the laser processing device 100 described above, and the reforming region is provided. The object to be processed 1 may be heated at the time of forming.

[0064]

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

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view taken along line II-II of the object to be processed shown in FIG.

FIG. 3 is a plan view of an object to be processed after laser processing by the laser processing method according to the present embodiment.

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

5 is a sectional view taken along line VV of the object to be processed shown in FIG.

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

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

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

FIG. 9 is a sectional view of an object to be processed in a second step of the laser processing method according to the present 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 present 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 present embodiment.

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

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

FIG. 14 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment.

FIG. 15 is a flowchart for explaining a laser processing method according to this embodiment.

FIG. 16 is a schematic configuration diagram of a cooling device according to the present embodiment.

FIG. 17 is a plan view of an object to be processed for explaining a pattern that can be cut by the laser processing method according to the present embodiment.

FIG. 18 is a schematic configuration diagram of a heating device including a constant temperature bath according to the present embodiment.

FIG. 19 is a schematic configuration diagram of a heating device including a heater plate according to the present embodiment.

[Explanation of Codes] 1 ... Object, 3 ... Surface, 5 ... Planned cutting line, 7 ...
Modified region, 9 ... Crack region, 100 ... Laser processing device, 101 ... Laser light source, 105 ... Focusing lens, 10
9 ... X-axis stage, 111 ... Y-axis stage, 113 ... Z-axis stage, 131 ... Cooling device, L ... Laser light, P ... Focusing point.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B23K 101: 40 H01L 21/78 B (72) Inventor Naoki Uchiyama 1126 Hamamatsu City, Hamamatsu City, Shizuoka Prefecture 1126 Hamamatsu Photonics Co., Ltd. (72) Inventor Toshimitsu Wakuda 1 126-1, Nono-cho, Hamamatsu-shi, Shizuoka Prefecture 1 Hamamatsu Photonics Co., Ltd. F-term (reference) 3C069 AA01 BA08 BB03 BB04 CA05 CA11 EA01 EA02 EA04 EA05 4E068 AE01 CA02 CA03 CA11 CB06 DA10 DB13 4G015 FA06 FB01 FC10

Claims (7)

[Claims] 1. A modified region by multiphoton absorption is formed inside the object to be processed along a line to cut the object by irradiating the inside of the object to be focused with a laser beam. And a first step of cooling the object to be processed such that the temperature of the object to be processed is lower than the temperature of the object to be processed when the modified region is formed, A second step of applying stress to a position where the object to be processed is cut along the planned cutting line. 2. A converging point is set inside the object to be processed,
Peak power density at condensing point is 1 × 10 ⁸ (W / cm ² )
The first step of irradiating a laser beam under the condition that the pulse width is 1 μs or less, and forming a modified region including a crack region inside the object to be processed along a line to cut the object to be processed. After the first step, the processing object is cooled so that the temperature of the processing object becomes lower than the temperature of the processing object at the time of forming the modified region, and along the cutting planned line. A second step of causing stress in a portion where the object to be processed is cut. 3. A light converging point is set inside the object to be processed,
Peak power density at condensing point is 1 × 10 ⁸ (W / cm ² )
The first step of irradiating a laser beam under the above condition and a pulse width of 1 μs or less to form a modified region including a melting treatment region inside the object to be processed along a line to cut the object to be processed. And, after the first step, cooling the processing target object such that the temperature of the processing target object becomes lower than the temperature of the processing target object at the time of forming the modified region, and along the planned cutting line. And a second step of applying stress to a portion where the object to be processed is cut. 4. A converging point is set inside the object to be processed,
Peak power density at condensing point is 1 × 10 ⁸ (W / cm ² )
The laser light is irradiated under the condition that the pulse width is 1 ns or less, and a modified area including a refractive index change area, which is an area in which the refractive index is changed inside the processing object along the planned cutting line of the processing object. A first step of forming a quality region, and the first step
After the step of, the object to be processed is cooled so that the temperature of the object to be processed becomes lower than the temperature of the object to be processed when the modified region is formed, and the object to be processed along the planned cutting line. And a second step of causing stress to occur at a portion to be cut. 5. The laser processing method according to claim 1, wherein in the first step, the modified region is formed on the heated object to be processed. 6. The cooling of the object to be processed in the second step is natural cooling.
4. The laser processing method according to any one of 4 above. 7. The cooling of the object to be processed in the second step is forced cooling.
4. The laser processing method according to any one of 4 above.