JP2003088978A - 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 process for placing a work 1 on the placing table 107 of a laser beam machining apparatus 100, a process for forming an intended cutting part based on a reformed region in the inside of a work 1 along the intended cutting line 5 of the work 1 by adjusting a converging point P in the inside of the work 1 and by irradiating the work 1 with a laser beam L, a process for transporting the work 1 in which the intended cutting part based on the reformed region is formed and placing it on the placing plate of an absorptive laser irradiation apparatus, and a process for cutting the work 1 by irradiating the surface of the work 1 with an absorptive laser beam and making a crack arrive at the surface of the work 1 from the internal reformed region of the work 1 as a starting point.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor material substrate,
The present invention relates to a laser processing method used for cutting a workpiece such as a piezoelectric material substrate or a glass substrate. 2. Description of the Related Art Cutting is one of laser applications, and general cutting with a laser is as follows. For example, a portion to be cut of a workpiece such as a semiconductor wafer or a glass substrate is irradiated with laser light having a wavelength that is absorbed by the workpiece, and the portion to be cut by the absorption of the laser light is directed from the front surface to the back surface of the workpiece. The workpiece is cut by advancing heating and melting. However, in this method, the periphery of the region to be cut out of 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, there is a possibility that the semiconductor elements located around the region are melted. [0003] As a method for preventing melting of the surface of a workpiece, for example, Japanese Patent 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 part to be cut of the workpiece is heated by laser light, and the workpiece is cooled,
A thermal shock is generated at a portion of the workpiece to be cut to cut the workpiece. However, in the cutting methods of these publications, if the thermal shock generated on the workpiece is large, the surface of the workpiece will be cracked off the line to be cut or cracked to the previous part not irradiated with laser. Unnecessary cracks such as the above may occur. Therefore, these cutting methods cannot perform precision cutting. 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 and a glass substrate on which an electrode pattern is formed, this unnecessary crack may damage the semiconductor chip, the liquid crystal display device, and the electrode pattern. Moreover, since these cutting methods have a large average input energy, the thermal damage given to the semiconductor chip or the like is also large. An object of the present invention is to provide a laser processing method in which unnecessary cracks are not generated on the surface of an object to be processed and the surface does not melt. [0006] A laser processing method according to the present invention includes a step of placing a processing object on a mounting table of a laser processing apparatus, and a condensing point within the processing object. Irradiate laser beam to form a planned cutting part by the modified region inside the processing object along the planned cutting line of the processing object, and processing by which the planned cutting part by the modified region is formed inside The process of transporting the object and placing it on the mounting table of the absorptive laser irradiation device, and irradiating the surface of the object to be processed with the absorptive laser beam, starting from the modified region inside the object to be processed And a step of cutting the object to be processed by causing a crack to reach the surface of the object. According to the laser processing method of the present invention, the laser beam is irradiated with the focusing point inside the object to be processed,
A modified region is formed inside the workpiece. If there is any starting point at the location where the workpiece is to be cut, the workpiece can be cut with a relatively small force. According to the laser processing method of the present invention, the processing object can be cut by breaking the processing object along the scheduled cutting line starting from the modified region. Therefore, the workpiece can be cut with a relatively small force,
The workpiece can be cut without causing unnecessary cracks that are off the cutting line on the surface of the workpiece. Also, according to the laser processing method of the present invention, the modified region is locally formed inside the object to be processed. Therefore, since the laser beam is hardly absorbed on the surface of the processing object, the surface of the processing object does not melt. In addition, a condensing point is a location which the laser beam condensed. The line to be cut may be a line actually drawn on the surface or inside of the workpiece, or may be a virtual line. DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 very high. First, multiphoton absorption will be briefly described. [0010] 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 beam is determined by the peak power density (W / cm ² ) at the condensing point of the laser beam. For example, the multiphoton is obtained under the condition that the peak power density is 1 × 10 ⁸ (W / cm ² ) or more. Absorption occurs. The peak power density is determined by (energy per pulse of laser light at the condensing point) / (laser beam cross-sectional area of laser light × pulse width). In the case of a continuous wave, the intensity of the laser beam is determined by the electric field intensity (W / cm ² ) at the condensing point of the laser beam. 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 workpiece 1 during laser processing, FIG. 2 is a cross-sectional view taken along line II-II of the workpiece 1 shown in FIG. 1, and FIG. 3 is a workpiece after laser processing. Thing 1
FIG. 4 is a plan view of the workpiece 1 shown in FIG.
5 is a cross-sectional view taken along line IV, FIG. 5 is a cross-sectional view taken along line VV of the workpiece 1 shown in FIG. 3, and FIG. 6 is a plan view of the cut workpiece 1. As shown in FIG. 1 and FIG.
The surface 3 has a cutting line 5. The planned cutting line 5 is a virtual 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 beam L by aligning the condensing point P inside the processing object 1 under the condition that multiphoton absorption occurs. In addition, a condensing point is a location where the laser beam L is condensed. The condensing point P is moved along the planned cutting line 5 by relatively moving the laser beam L along the planned cutting line 5 (that is, along the direction of the arrow A). As a result, as shown in FIGS.
Is formed only inside the workpiece 1 along the planned cutting line 5. The laser processing method according to the present embodiment does not form the modified region 7 by causing the processing object 1 to generate heat when the processing object 1 absorbs the laser light L, thereby forming the modified region 7. The modified region 7 is formed by transmitting the laser beam L to the workpiece 1 and generating multiphoton absorption inside the workpiece 1. Therefore, since the laser beam L is hardly absorbed by the surface 3 of the workpiece 1, the surface 3 of the workpiece 1 is not melted. In cutting the workpiece 1, if there is a starting point at the location to be cut, the workpiece 1 is cracked from the starting point, so that the workpiece 1 can be cut with a relatively small force as shown in FIG. 6. it can. Therefore, the surface 3 of the workpiece 1
The workpiece 1 can be cut without causing unnecessary cracks. The following two types of cutting of the object to be processed starting from the modified region can be considered. One is a case where, after the modified region is formed, an artificial force is applied to the workpiece, so that the workpiece is cracked and the workpiece is cut from the modified region as a starting point. This is, for example, cutting when the thickness of the workpiece is large. When artificial force is applied, for example, bending stress or shear stress is applied to the workpiece along the planned cutting line of the workpiece, or thermal stress is generated by giving a temperature difference to the workpiece. (Laser processing method according to this embodiment). The other is that when the modified region is formed, the modified region starts as a starting point, and naturally breaks in the cross-sectional direction (thickness direction) of the workpiece, resulting in the workpiece being cut. It is. For example, when the thickness of the workpiece is small, even one modified region is possible, and when the workpiece is large, a plurality of modified regions can be formed in the thickness direction. . Even in the case of natural cracking, it is possible to cleave only the surface on the portion where the modified region is formed, without causing cracks to advance to the surface on the portion where the modified region is not formed at the location to be cut. Since it is possible, the cleaving can be controlled well. In recent years, since the thickness of semiconductor wafers such as silicon wafers tends to be thin, such a cleaving method with good controllability is very effective. Now, the modified regions formed by multiphoton absorption in this embodiment include the following (1) to (3). (1) When the modified region is a crack region including one or a plurality of crack spots, a laser beam is focused on the inside of a workpiece (for example, a 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
This is a condition in which a crack region can be formed inside the processing target without causing extra damage to the processing target while causing multiphoton absorption. As a result, a phenomenon of optical damage due to multiphoton absorption occurs inside the workpiece. This optical damage induces thermal strain inside the workpiece, thereby forming a crack region inside the workpiece. As an upper limit value of the electric field strength, for example, 1 × 10 ¹²
(W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example. The formation of the crack region by multiphoton absorption is, for example, the 45th Laser Thermal Processing Society Proceedings (19
1998. (December), page 23 to page 28, "Internal marking of glass substrate by solid laser harmonics". The inventor of the present invention obtained the relationship between the electric field strength and the crack size by experiment. The experimental conditions are as follows. (A) Workpiece: Pyrex (registered trademark) glass (thickness 700 μm, outer diameter 4 inches) (B) Laser light source: Semiconductor laser excitation 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 with respect to laser light wavelength Transmittance: 60% (D) Moving speed of mounting table on which workpiece is mounted: 10
0 mm / sec. Note that the laser beam quality TEM ₀₀ means that the condensing property is high and the laser beam 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 beam is a pulsed laser beam, the electric field strength is represented by the peak power density. The vertical axis indicates the size of a crack spot formed inside the workpiece 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 black circles in the graph shows that the magnification of the condenser lens (C) is 10
This is a case of 0 times and a numerical aperture (NA) of 0.80. On the other hand, the data indicated by white circles in the graph is when the magnification of the condenser lens (C) is 50 times 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 ), a crack spot is generated inside the workpiece, and the crack spot increases as the peak power density increases. Next, the mechanism of cutting the workpiece by forming the crack region will be described with reference to FIGS. As shown in FIG. 8, the laser beam L is irradiated on the workpiece 1 by aligning the condensing point P inside the workpiece 1 under the condition that multiphoton absorption occurs, and a crack region is formed inside along the planned cutting line. 9 is formed. The crack region 9 is a region including one or a plurality of crack spots. As shown in FIG. 9, the crack further grows starting from the crack region 9, and 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. 11. The workpiece 1 is cut by cracking. A crack that reaches the front surface and the back surface of the workpiece may grow naturally, or grows when a force is applied to the workpiece (laser machining method according to this embodiment).
There is also. (2) When the modified region is a melted region The laser beam is focused on the inside of a workpiece (for example, a semiconductor material such as silicon), and the electric field strength at the focused point is 1 × 10. ⁸ (W / cm ² ) or more and pulse width 1μs
Irradiate under the following conditions. As a result, the inside of the workpiece is locally heated by multiphoton absorption. By this heating, a melt processing region is formed inside the workpiece. The melt treatment region is a region once solidified after melting, a region in a molten state, or a region re-solidified from a molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure has changed. The melt treatment region can also be said to be a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, or a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. To 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 value 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 inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows. (A) Processing object: silicon wafer (thickness 350 μm, outer diameter 4 inches) (B) Laser light source: semiconductor laser excitation 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 with respect to light wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 10
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 in the thickness direction of the melt processing region 13 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 to show the transmittance 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 is used.
When the thickness of the silicon substrate is 4 μm or less at 4 nm, it can be seen that 80% or more of the laser light is transmitted inside the silicon substrate. Silicon wafer 11 shown in FIG.
Since the thickness of is melted by 350 μm, the melt-processed region 13 by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. The transmittance in this case is as follows with reference to a silicon wafer having a thickness of 200 μm.
Since it is 90% or more, the laser beam is hardly absorbed inside the silicon wafer 11 and almost all is transmitted.
This is not because the laser beam is absorbed inside the silicon wafer 11 and the melt processing region 13 is formed inside the silicon wafer 11 (that is, the melt processing region is formed by normal heating with laser light) It means that the melt processing region 13 is formed by multiphoton absorption. The formation of the melt processing region by multiphoton absorption is, for example, from page 72 of the 66th Annual Meeting of the Japan Welding Society (April 2000).
It is described in “Evaluation of processing characteristics of silicon by picosecond pulse laser” on page 73. The silicon wafer is cracked as a result of cracking in the cross-sectional direction starting from the melting treatment region, and the crack reaching the front and back surfaces of the silicon wafer. The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the workpiece. When cracks grow naturally from the melt processing area to the front and back surfaces of the wafer, the crack grows when the melt processing area grows from the molten state or resolidifies from the molten state None of them. However, also in these cases, the melt processing region is formed only inside the wafer, and the cut surface after cutting is formed only inside as shown in FIG. In the case where the melt processing region is formed inside the object to be processed, since the unnecessary cracks that are off the planned cutting line are not easily generated at the time of cleaving, cleaving control is facilitated. (3) When the modified region is a refractive index changing region The laser beam is focused on the inside of the object to be processed (for example, glass), and the electric field intensity at the focused point is 1 × 10 ⁸ (W / c
Irradiation is performed under conditions of m ² ) or more and a pulse width of 1 ns or less.
When the pulse width is made extremely short and multiphoton absorption occurs inside the workpiece, the energy due to the multiphoton absorption is not converted into thermal energy, and the ion valence change and crystallization occur inside the workpiece. Alternatively, a permanent structural change such as polarization orientation is induced to form a refractive index change region. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). For example, the pulse width is preferably 1 ns or less, and more preferably 1 ps or less. Formation of the refractive index change region by multiphoton absorption is
For example, the 42nd Laser Thermal Processing Workshop Proceedings (1997)
Year. (November), page 105 to page 111, "Photo-induced structure formation in 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 for forming a modified region by multiphoton absorption inside a workpiece, and a stress step for causing stress at a location where the workpiece is cut. I have. The laser processing apparatus of this embodiment will be described. FIG. 14 is a schematic configuration diagram of a laser processing apparatus 100 used in the modified region forming step. As illustrated, a laser processing apparatus 100 includes a laser light source 101 that generates laser light L, and a laser light source control unit 1 that controls the laser light source 101 in order to adjust the output, pulse width, and the like of the laser light L.
02, a dichroic mirror 103 having a function of reflecting the laser light L and arranged so as to change the direction of the optical axis of the laser light L by 90 °, and a collector for condensing the laser light L reflected by the dichroic mirror 103 The mounting lens 107 on which the processing object 1 irradiated with the lens 105 for light, the laser beam L condensed with the condensing lens 105 is mounted, and the mounting table 10
X-axis stage 109 for moving 7 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 the mounting table 107 as the X-axis and Y-axis
A Z-axis stage 113 for moving in the Z-axis direction orthogonal to the axial direction, and these three stages 109, 111, 11
And a stage control unit 115 for controlling the movement of 3. In the present embodiment, the workpiece 1 is a Pyrex glass wafer. Since the Z-axis direction is a direction orthogonal to the surface 3 of the workpiece 1, it is the direction of the focal depth of the laser beam L incident on the workpiece 1. Therefore, by moving the Z-axis stage 113 in the Z-axis direction, the condensing point P of the laser light L can be adjusted inside the workpiece 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 that generates pulsed laser light. Other lasers that can be used for the laser light source 101 include Nd: YVO ₄ laser and Nd:
There is a YLF laser. As the laser light source, the above-described laser light source is preferably used when forming the crack region and the melting treatment region, and when forming the refractive index changing region, it is preferable to use the titanium sapphire laser. In this embodiment, pulsed laser light is used for processing the workpiece 1, but continuous wave laser light may be used as long as multiphoton absorption can be caused. The laser processing apparatus 100 further includes a mounting table 1.
The observation light source 117 that generates visible light to illuminate the workpiece 1 placed on 07 with visible light, and the visible light disposed on the same optical axis as the dichroic mirror 103 and the condensing lens 105. Beam splitter 119
And comprising. A dichroic mirror 103 is disposed between the beam splitter 119 and the condensing 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 reflected by the dichroic mirror 103 and the condensing lens 105.
, And the surface 3 including the planned cutting line 5 of the workpiece 1 is illuminated. The laser processing apparatus 100 further includes an image sensor 12 disposed 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. An example of the image sensor 121 is a CCD (charge-coupled device) camera.
The reflected light of the visible light that illuminates the surface 3 including the planned cutting line 5 passes through the condensing lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the imaging device 121. And becomes imaging data. The laser processing apparatus 100 further includes an imaging data processing unit 125 to which 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 focusing the visible light generated by the observation light source 117 on the surface 3 based on the imaging data. The stage control unit 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. The focal point of visible light coincides with the condensing point of the laser light L. 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 processes are performed.
Sent to the monitor 129. Thereby, an enlarged image or the like is displayed on the monitor 129. The overall controller 127 includes a stage controller 1
15, image data from the imaging data processing unit 125, and the like are input. Based on these data, the laser light source control unit 102, the observation light source 117, and the stage control unit 115 are controlled, thereby the laser processing apparatus. 100
Control the whole. Therefore, the overall control unit 127 functions as a computer unit. Further, the absorptive laser irradiation apparatus used in the stress process is different from the above-described laser processing apparatus 100 only in the laser light source and the dichroic mirror. As a laser light source of the absorptive laser irradiation apparatus, a wavelength of 10.4 that generates continuous wave laser light is generated.
A 6 μm CO ₂ laser was used. This is because the workpiece 1 is a Pyrex glass wafer and has an absorptivity. Hereinafter, laser light generated by this laser light source is referred to as “absorbing laser light”. The beam quality is TEM ₀₀ , and the polarization characteristic is linearly polarized light. Further, the output of the laser light source is set to 10 W or less so that the workpiece 1 is heated and is not melted. The dichroic mirror of the absorptive laser irradiation apparatus has a function of reflecting the absorptive laser beam and is arranged so as to change the direction of the optical axis of the absorptive laser beam by 90 °. Next, the laser processing method according to this embodiment will be described with reference to FIGS. FIG.
These are the flowcharts for demonstrating the laser processing method. First, the light absorption characteristic of the workpiece 1 is measured by a spectrophotometer or the like (not shown). Based on the measurement result, a laser light source 101 that generates a laser beam L having a wavelength that is transparent or less absorbed with respect to the workpiece 1, and an absorptive laser beam having an absorptive wavelength with respect to the workpiece 1. The laser light source to be generated is selected, and each laser processing apparatus 1
00 and an absorptive laser irradiation device (S10
1). Next, the thickness of the workpiece 1 is measured. Based on the measurement result of the thickness and the refractive index of the workpiece 1, the amount of movement of the workpiece 1 in the Z-axis direction in the laser machining apparatus 100 is determined (S 103). This is the condensing point P of the laser beam L
Is the amount of movement in the Z-axis direction of the workpiece 1 with reference to the condensing point of the laser beam L located on the surface 3 of the workpiece 1. This movement amount is determined by the laser processing apparatus 10 used in the modified region forming process.
0 is input to the overall control unit 127. The workpiece 1 is placed on the mounting table 107 of the laser processing apparatus 100 (S104). Then, visible light is generated from the observation light source 117 to illuminate the workpiece 1 (S105). The imaging device 121 images the surface 3 of the workpiece 1 including the illuminated cutting line 5.
This imaging data is sent to the imaging data processing unit 125.
Based on the imaging data, the imaging data processing unit 125 calculates focus data such that the visible light focus of the observation light source 117 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 the focus data (S
109). Thereby, the focal point of the 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 workpiece 1 including the planned cutting line 5 based on the imaging data. This enlarged image data is sent to the monitor 129 via the overall control unit 127.
This causes the monitor 129 to send a cut line 5
A nearby enlarged image is displayed. The overall control unit 127 is previously provided with step S10.
The movement amount data determined in 3 is input, and this movement amount data is sent to the stage control unit 115. The stage control unit 115 moves the workpiece 1 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 workpiece 1 based on the movement amount data ( S111). Next, a laser beam L is generated from the laser light source 101, and the laser beam L is irradiated onto the planned cutting line 5 on the surface 3 of the workpiece 1. FIG. 16 is a cross-sectional view of the workpiece 1 including the crack region 9 during laser processing in the modified region forming step. As shown in the drawing, since the condensing point P of the laser beam L is located inside the workpiece 1, the crack region 9 is formed only inside the workpiece 1. Then, the X-axis stage 10 is aligned along the planned cutting line 5.
9 and the Y-axis stage 111 are moved so that the crack region 9
Is formed inside the workpiece 1 along the planned cutting line 5 (S113). After the modified region is formed by the laser processing apparatus 100, the object to be processed 1 is transferred to the mounting table 107 of the absorptive laser irradiation apparatus and mounted (S115). Since the crack region 9 in the modified region forming step is formed only inside the workpiece 1, the workpiece 1 is not separated, and thus the workpiece 1 can be easily conveyed. In step 117, the object 1 is illuminated, and in step 119, focus data is calculated so that the visible light focus of the observation light source is located on the surface 3 of the object 1. In step 121, the focus data is calculated. The processing object 1 is placed so that the focal point is located on the surface 3 of the processing object 1.
By moving in the Z-axis direction, the condensing point of the absorptive laser beam is adjusted to the surface 3 of the workpiece 1. Note that the details of the operations in Step 117, Step 119, and Step 121 are Step 105, Step 107, and Step 10 in the laser processing apparatus 100 described above.
The same as 9. Next, an absorptive laser beam is generated from the laser light source of the absorptive laser irradiation device, and the absorptive laser beam is irradiated onto the planned cutting line 5 on the surface 3 of the workpiece 1. This irradiation may be irradiation to the vicinity of the cutting scheduled line 5. Then, by moving the X-axis stage or Y-axis stage of the absorptive laser irradiation device along the planned cutting line 5 and heating the workpiece 1 along the planned cutting line 5, A stress such as a thermal stress due to a temperature difference is generated at a location along which the workpiece 1 is cut (S123). At this time, since the intensity of the absorptive laser is such that the workpiece 1 is not heated and melted,
The surface of the workpiece is not melted. FIG. 17 is a sectional view of the workpiece 1 including the crack region 9 during laser processing in the stress process. As shown in the figure, by the absorption laser beam irradiation, the crack further grows starting from the crack region 9 and the crack reaches the front surface 3 and the back surface 21 of the workpiece 1,
The cut surface 10 is formed on the workpiece 1 and the workpiece 1 is cut (S125). Thereby, the workpiece 1 is divided into silicon chips. In the present embodiment, the case where the crack region is formed as the modified region has been described. However, the case where the melting treatment region or the refractive index changing region as described above is formed as the modified region is also described. It is the same, causing stress by the irradiation of the absorbing laser beam, generating cracks starting from the melt processing region and the refractive index change region,
The workpiece can be cut by growth. Further, even when the thickness of the workpiece is large, etc., even if the crack grown from the modified region as a starting point by the stress process does not reach the front and back surfaces of the workpiece, bending stress or shear By applying an artificial force such as stress, the workpiece 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 line to be cut on the surface of the workpiece. The effect of this embodiment will be described. According to this, in the modified region forming step, the line 5 to be cut is irradiated with the pulsed laser light L under conditions that cause multiphoton absorption and the focused point P is set inside the workpiece 1. . Then, by moving the X-axis stage 109 and the Y-axis stage 111, the condensing point P is moved along the scheduled cutting line 5. As a result, a modified region (for example, a crack region, a melt processing region, a refractive index change region) is formed inside the workpiece 1 along the planned cutting line 5. If there is any starting point at the location where the workpiece is to be cut, the workpiece can be cut with a relatively small force. According to the present embodiment, in the stress process, the workpiece 1 is irradiated with the absorptive laser light along the planned cutting line 5 to generate a stress such as a thermal stress due to a temperature difference. Therefore, the workpiece 1 can be cut with a relatively small force such as a thermal stress due to a temperature difference. Thereby, the processing target object 1 can be cut | disconnected, without generating the unnecessary crack which remove | deviated from the cutting scheduled line 5 to the surface 3 of the processing target object 1. FIG. Further, according to the present embodiment, in the modified region forming step, the pulse laser is formed by aligning the condensing point P inside the processing object 1 under the condition that the processing object 1 causes multiphoton absorption. Since the light L is irradiated, the pulse laser beam L
Passes through the workpiece 1, and the pulse laser beam L is hardly absorbed by the surface 3 of the workpiece 1. In the stress process, the intensity of the absorptive laser beam is such that the workpiece 1 is not heated and melted. Therefore,
The surface 3 is not damaged such as melting due to the irradiation of the laser beam. As described above, according to this embodiment,
The processing object 1 can be cut without causing unnecessary cracks and melting off the cutting line 5 on the surface 3 of the processing object 1. Therefore, when the workpiece 1 is, for example, a semiconductor wafer, the semiconductor chip can be cut out from the semiconductor wafer without causing unnecessary cracking or melting of the semiconductor chip off the line to be cut. The same applies to a workpiece on which an electrode pattern is formed on the surface, and a workpiece on which an electronic device is 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 the present embodiment, the yield of a product (for example, a display device such as a semiconductor chip, a piezoelectric device chip, or a liquid crystal) manufactured by cutting the workpiece can be improved. Further, according to the present embodiment, the processing object 1
Since the planned cutting line 5 on the surface 3 of the surface is not melted, the width of the planned cutting line 5 (this width is, for example, the interval between the regions to be semiconductor chips in the case of a semiconductor wafer) can be reduced. Thereby, the number of products produced from one piece of processing object 1 increases, and productivity of a product can be improved. Further, according to the present embodiment, the processing object 1
Since laser light is used for the cutting process, it is possible to perform more complicated processing than dicing using a diamond cutter.
For example, as shown in FIG. 18, even if the planned cutting line 5 has a complicated shape, cutting can be performed. According to the laser processing method of the present invention,
The object to be processed can be cut without melting or cracking off the line to be cut on the surface of the object to be processed. Therefore, products manufactured by cutting a workpiece (for example, semiconductor chips, piezoelectric device chips,
Yield and productivity of a display device such as a liquid crystal display can be improved. Further, since the portion to be cut by the modified region is formed only inside the workpiece, the workpiece does not fall apart, so that the workpiece can be transported. And, without giving a special external force, because it is possible to cut and separate the processing object by irradiating the surface of the processing object formed inside the portion to be cut by the modified region with the absorbing laser light, It is possible to cleanly cut the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an object to be processed during laser processing by the laser processing method according to the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of the workpiece 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. 4 is a cross-sectional view taken along line IV-IV of the workpiece shown in FIG. FIG. 5 is a cross-sectional view taken along line VV of the workpiece shown in FIG. FIG. 6 is a plan view of a processing object cut by the laser processing method according to the present embodiment. FIG. 7 is a graph showing the relationship between electric field strength and crack spot size in the laser processing method according to the present embodiment. FIG. 8 is a cross-sectional view of an object to be processed in a first step of the laser processing method according to the present embodiment. FIG. 9 is a cross-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 cross-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 cross-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 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 the embodiment; FIG. 16 is a cross-sectional view of a workpiece including a crack region during laser processing in a modified region forming step according to the present embodiment. FIG. 17 is a cross-sectional view of an object to be processed including a crack region during laser processing in the stress process according to the present embodiment. FIG. 18 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. [Explanation of Symbols] 1 ... work object, 3 ... surface, 5 ... scheduled line, 7 ...
Modified region, 9 ... crack region, 100 ... laser processing apparatus, 101 ... laser light source, 105 ... condensing lens, 10
9 ... X axis stage, 111 ... Y axis stage, 113 ... Z axis stage, L ... laser beam, P ... condensing point.

──────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme code (reference) // H01L 21/301 B23K 101: 40 B23K 101: 40 H01L 21/78 B (72) Inventor Naoki Uchiyama Shizuoka No. 1126, Nomachi, Hamamatsu City, Prefecture Hamamatsu Photonics Co., Ltd. (72) Inventor Toshimitsu Wakuda No. 1 1126, Nomachi, Hamamatsu City, Shizuoka Prefecture F Reference Term, Hamamatsu Photonics Co., Ltd. AA05 AD01 AE01 CA11 CE11 DA10 DA11 4G015 FA01 FA06 FB01 FB02 FC14

Claims (1)

Claims: 1. A step of placing a processing object on a mounting table of a laser processing apparatus; and a laser beam with a focusing point inside the processing object and irradiating a laser beam, A step of forming a portion to be cut by the modified region inside the object to be processed along a line to be cut of the object, and transporting the object to be cut having the portion to be cut by the modified region formed therein, A step of placing on a mounting table of an absorptive laser irradiation device; and irradiating the surface of the workpiece with an absorptive laser beam, and starting from a modified region inside the workpiece, the surface of the workpiece And a step of causing the crack to reach and cutting the workpiece.