JP3626442B2 - Laser processing method - Google Patents

Laser processing method Download PDF

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Publication number
JP3626442B2
JP3626442B2 JP2001278663A JP2001278663A JP3626442B2 JP 3626442 B2 JP3626442 B2 JP 3626442B2 JP 2001278663 A JP2001278663 A JP 2001278663A JP 2001278663 A JP2001278663 A JP 2001278663A JP 3626442 B2 JP3626442 B2 JP 3626442B2
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workpiece
region
laser
formed
processing
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JP2002205180A (en
JP2002205180A5 (en
Inventor
直己 内山
敏光 和久田
文嗣 福世
憲志 福満
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浜松ホトニクス株式会社
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36Removing material
    • B23K26/40Removing material taking account of the properties of the material involved
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50Working by transmitting the laser beam through or within the workpiece
    • B23K26/53Working by transmitting the laser beam through or within the workpiece for modifying or reforming the material inside the workpiece, e.g. for producing break initiation cracks
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2101/00Articles made by soldering, welding or cutting
    • B23K2101/36Electric or electronic devices
    • B23K2101/40Semiconductor devices
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00Materials to be soldered, welded or cut
    • B23K2103/50Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laser processing method used for cutting an object to be processed such as a semiconductor material substrate, a piezoelectric material substrate or a glass substrate.
[0002]
[Prior art]
One of laser applications is cutting, and general cutting by 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, the semiconductor elements located in the vicinity of the region may be melted.
[0003]
[Problems to be solved by the invention]
As a method for preventing melting of the surface of the workpiece, for example, there is a laser cutting method disclosed in Japanese Patent Application Laid-Open No. 2000-219528 and Japanese Patent Application Laid-Open No. 2000-15467. In the cutting methods of these publications, a part to be processed is heated by a laser beam, and the object to be processed is cooled to cause a thermal shock at the part to be processed to cut the object to be processed. Disconnect.
[0004]
However, in the cutting methods of these publications, if the thermal shock generated on the workpiece is large, the surface of the workpiece is not cracked, such as a crack that is off the planned cutting line, or a crack that is not irradiated with laser. Necessary cracks may occur. Therefore, these cutting methods cannot perform precision cutting. In particular, when the object to be processed is a semiconductor wafer, a glass substrate on which a liquid crystal display device is formed, or a glass substrate on which an electrode pattern is formed, this unnecessary crack may damage the semiconductor chip, the liquid crystal display device, or the electrode pattern. is there. 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.
[0005]
An object of the present invention is to provide a laser processing method in which unnecessary cracks are not generated on the surface of a workpiece and the surface does not melt.
[0006]
[Means for Solving the Problems]
In the laser processing method according to the present invention, a multiphoton is formed inside a processing object along a scheduled cutting line of the processing object by irradiating a laser beam with a focusing point inside the wafer-shaped processing object. A modified region is formed by absorption, and a plurality of modified regions are formed so as to be aligned along the incident direction by changing the position of the condensing point of the laser beam in the incident direction of the laser beam incident on the workpiece. Then, a plurality of modified regions are formed, and a region that is a starting point of cutting is formed at a predetermined distance inside the laser light incident surface of the processing object along a planned cutting line of the processing object. .
[0007]
According to the laser processing method of the present invention, the modified region is formed inside the workpiece by using the phenomenon of multi-photon absorption by irradiating the laser beam with the condensing point inside the workpiece. Forming. 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, since the workpiece can be cut with a relatively small force, it is possible to cut the workpiece without generating unnecessary cracks off the planned cutting line on the surface of the workpiece. 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.
[0008]
In addition, according to the laser processing method of the present invention, the modified region is formed by generating multiphoton absorption locally 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.
[0009]
Further, according to the laser processing method of the present invention, the modified region is changed in the incident direction by changing the position of the condensing point of the laser light in the incident direction of the laser light irradiated to the processed object. A plurality are formed so as to line up along the line. For this reason, the location used as a starting point when cutting a workpiece can be increased. In addition, as an incident direction, there exists the direction orthogonal to the thickness direction and thickness direction of a workpiece, for example.
[0010]
In the laser processing method according to the present invention, the laser beam is irradiated with a focusing point inside the wafer-like workpiece, and modified inside the workpiece along the planned cutting line of the workpiece. By forming the region and changing the position of the condensing point of the laser beam in the incident direction of the laser beam incident on the workpiece, a plurality of modified regions are formed to be aligned along the incident direction. By the modified region thus formed, a region serving as a starting point of cutting is formed on the inner side of a predetermined distance from the laser light incident surface of the processing object along the planned cutting line of the processing object. In the laser processing method according to the present invention, the condensing point is set inside the wafer-like workpiece, and the peak power density at the condensing point is 1 × 108(W / cm2) By irradiating with laser light under the above conditions with a pulse width of 1 μs or less, a modified region is formed inside the workpiece along the planned cutting line of the workpiece and is incident on the workpiece. By changing the position of the condensing point of the laser beam in the incident direction of the laser beam, a plurality of modified regions are formed so as to be aligned along the incident direction, and the workpiece is cut by the plurality of modified regions formed A region serving as a starting point of cutting is formed on the inner side by a predetermined distance from the laser light incident surface of the workpiece along the planned line.
[0011]
These laser processing methods according to the present invention can perform laser processing that does not cause unnecessary cracks on the surface of the workpiece and does not melt for the same reason as the laser processing method according to the present invention. And the location used as the starting point when cutting a process target object can be increased. However, the formation of the modified region may be caused by multiphoton absorption or may be caused by other reasons.
[0012]
The laser processing method according to the present invention has the following modes. First, a plurality of modified regions may be sequentially formed one by one.
[0013]
Further, a plurality of modified regions can be formed in order from the far side from the laser light incident surface. According to this, a plurality of modified regions can be formed in a state where there is no modified region between the incident surface and the condensing point of the laser beam. Therefore, since the laser beam is not scattered by the already formed modified region, each modified region can be formed uniformly.
[0014]
The modified region includes a crack region in which a crack is generated inside the workpiece, a melt-processed region that is a melt-processed region inside, and a refractive-index changing region that is a region in which the refractive index has changed inside. Including at least one of them.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described 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.
[0016]
Band gap E of material absorptionGIf the photon energy hv is smaller than that, it becomes optically transparent. Therefore, the condition for absorption in the material is hν> EGIt is. However, even if it is optically transparent, if the intensity of the laser beam is made very large, nhν> EGUnder these conditions (n = 2, 3, 4,...), Absorption occurs in the material. This phenomenon is called multiphoton absorption. In the case of a pulse wave, the intensity of the laser beam is the peak power density (W / cm at the condensing point of the laser beam).2), For example, the peak power density is 1 × 108(W / cm2) Multiphoton absorption occurs under the above conditions. 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 the electric field intensity (W / cm at the focal point of the laser beam).2)
[0017]
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. 4 is a plan view of the object 1, FIG. 4 is a cross-sectional view taken along line IV-IV of the object 1 shown in FIG. 3, and FIG. 5 is taken along line VV of the object 1 shown in FIG. FIG. 6 is a plan view of the cut workpiece 1.
[0018]
As shown in FIGS. 1 and 2, the surface 3 of the workpiece 1 has a planned 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.
[0019]
The condensing point P is moved along the planned cutting line 5 by relatively moving the laser light L along the planned cutting line 5 (that is, along the direction of the arrow A). Thereby, as shown in FIGS. 3 to 5, the modified region 7 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 workpiece 1 to generate heat by causing the workpiece 1 to absorb the laser light L. The modified region 7 is formed by transmitting the laser beam L through 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.
[0020]
In the cutting of the workpiece 1, if there is a starting point at the location to be cut, the workpiece 1 is broken from the starting point, so that the workpiece 1 can be cut with a relatively small force as shown in FIG. 6. Therefore, the processing object 1 can be cut without causing unnecessary cracks on the surface 3 of the processing object 1.
[0021]
In addition, the following two kinds of cutting | disconnection of the processing target object from the modification | reformation area | region are 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. It is to let you. 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. . In addition, even when this breaks naturally, on the surface of the portion to be cut, the crack does not run to the part where the modified region is not formed, and only the part where the modified part is formed can be cleaved, The cleaving can be controlled well. In recent years, since the thickness of a semiconductor wafer such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.
[0022]
As modified regions formed by multiphoton absorption in this embodiment, there are the following (1) to (3).
[0023]
(1) When the modified region is a crack region including one or more cracks
Laser light can be processed (eg glass or LiTaO3The electric field strength at the condensing point is 1 × 108(W / cm2) Irradiation is performed under the above conditions with a pulse width of 1 μs or less. The magnitude of the pulse width is a condition that a crack region can be formed only inside the workpiece without causing extra damage to the workpiece surface 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 × 1012(W / cm2). The pulse width is preferably 1 ns to 200 ns, for example. The formation of the crack region by multiphoton absorption is described in, for example, “Inside of glass substrate by solid-state laser harmonics” on pages 23-28 of the 45th Laser Thermal Processing Research Papers (December 1998). It is described in “Marking”.
[0024]
The inventor obtained the relationship between the electric field strength and the size of the cracks by experiment. The experimental conditions are as follows.
(A) Workpiece: Pyrex (registered trademark) glass (thickness 700 μm)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser beam spot cross-sectional area: 3.14 × 10-8cm2
Oscillation form: Q switch pulse
Repeat frequency: 100kHz
Pulse width: 30ns
Output: Output <1mJ / pulse
Laser light quality: TEM00
Polarization characteristics: linearly polarized light
(C) Condensing lens
Transmittance to laser light wavelength: 60 percent
(D) Moving speed of the mounting table on which the workpiece is mounted: 100 mm / second
The laser beam quality is TEM00The term “highly condensing” means that light can be condensed up to the wavelength of laser light.
[0025]
FIG. 7 is a graph showing the results of the 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 represents the size of a crack portion (crack spot) formed inside the workpiece by one pulse of laser light. Crack spots gather to form a crack region. The size of the crack spot is the size of the portion having the maximum length in the shape of the crack spot. Data indicated by black circles in the graph is for the case where the magnification of the condenser lens (C) is 100 times and the numerical aperture (NA) is 0.80. On the other hand, the data indicated by the 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. Peak power density is 1011(W / cm2From the above, it can be seen that crack spots are generated inside the workpiece, and the crack spots increase as the peak power density increases.
[0026]
Next, in the laser processing according to the present embodiment, a mechanism for cutting a workpiece by forming a crack region will be described with reference to FIGS. As shown in FIG. 8, the laser beam L is irradiated to 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 along the planned cutting line. 9 is formed. The crack region 9 is a region including one or a plurality of cracks. 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. The workpiece 1 is cut by cracking. Cracks that reach the front and back surfaces of the workpiece may grow naturally or may grow when a force is applied to the workpiece.
[0027]
(2) When the reforming region is a melt processing 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 focus is 1 × 108(W / cm2) Irradiation is performed under the above conditions with a pulse width of 1 μs or less. 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 melting treatment region means at least one of a region once solidified after melting, a region in a molten state, and a region in a state of being resolidified from melting. Further, it can be said that the melt-processed region is a phase-changed region or a region where the crystal structure is 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 × 1012(W / cm2). The pulse width is preferably 1 ns to 200 ns, for example.
[0028]
The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.
[0029]
(A) Workpiece: silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser beam spot cross-sectional area: 3.14 × 10-8cm2
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: 20μJ / pulse
Laser light quality: TEM00
Polarization characteristics: linearly polarized light
(C) Condensing lens
Magnification: 50 times
NA: 0.55
Transmittance to laser light wavelength: 60 percent
(D) Moving speed of the mounting table on which the workpiece is placed: 100 mm / second
[0030]
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. In addition, the size in the thickness direction of the melt processing region formed under the above conditions is about 100 μm.
[0031]
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 above relationship was shown for each of the silicon substrate thicknesses t of 50 μm, 100 μm, 200 μm, 500 μm, and 1000 μm.
[0032]
For example, at a Nd: YAG laser wavelength of 1064 nm, when the thickness of the silicon substrate is 500 μm or less, it can be seen that 80% or more of the laser light is transmitted inside the silicon substrate. Since the thickness of the silicon wafer 11 shown in FIG. 12 is 350 μm, the melt processing region by multiphoton absorption is formed near the center of the silicon wafer, that is, at a portion of 175 μm from the surface. In this case, the transmittance is 90% or more with reference to a silicon wafer having a thickness of 200 μm. Therefore, 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 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 processing region is formed by multiphoton absorption. The formation of the melt-processed region by multiphoton absorption is described in, for example, “Evaluation of processing characteristics of silicon by picosecond pulse laser” on pages 72 to 73 of the 66th Annual Meeting of the Japan Welding Society (April 2000). Has been described.
[0033]
In addition, a silicon wafer is cut | disconnected as a result by generating a crack toward a cross-sectional direction starting from the melt processing region and 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. Note that cracks grow naturally from the melted region to the front and back surfaces of the silicon wafer when cracks grow from a region once melted and resolidified, or when cracks grow from a melted region. And at least one of the cases where cracks grow from a region in a state of being solidified from melting. In either case, the cut surface after cutting is formed with a melt treatment region only inside as shown in FIG. In the case where the melt processing region is formed inside the object to be processed, it is difficult to cause unnecessary cracks that are off the planned cutting line at the time of cleaving, so that cleaving control is facilitated.
[0034]
(3) When the modified region is a refractive index changing region
A laser beam is focused on the inside of an object to be processed (for example, glass), and the electric field strength at the beam focusing point is 1 × 10.8(W / cm2) Irradiation is performed under the above conditions with 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. As an upper limit value of the electric field strength, for example, 1 × 1012(W / cm2). For example, the pulse width is preferably 1 ns or less, and more preferably 1 ps or less. The formation of the refractive index change region by multiphoton absorption is described in, for example, “The Femtosecond Laser Irradiation to the Inside of the Glass” on pages 105 to 111 of the 42nd Laser Thermal Processing Workshop Papers (November 1997). Photo-induced structure formation ”.
[0035]
As described above, according to the present embodiment, the modified region is formed by multiphoton absorption. In this embodiment, a plurality of modified regions are arranged along the incident direction by changing the position of the condensing point of the laser light in the incident direction of the laser light irradiated to the processed object. Forming.
[0036]
The formation of a plurality of modified regions will be described using a crack region as an example. FIG. 14 is a perspective view of the workpiece 1 in which two crack regions 9 are formed inside the workpiece 1 using the laser machining method according to the present embodiment.
[0037]
A method for forming the two crack regions 9 will be briefly described. First, the focused point of the pulse laser beam L is aligned with the vicinity of the back surface 21 inside the workpiece 1, and the workpiece 1 is irradiated with the pulsed laser beam L while moving the focused point along the planned cutting line 5. . Thereby, the crack region 9 (9A) is formed in the vicinity of the back surface 21 inside the workpiece 1 along the planned cutting line 5. Next, the focused point of the pulse laser beam L is aligned with the vicinity of the inner surface 3 of the workpiece 1, and the workpiece 1 is irradiated with the pulsed laser beam L while moving the focused point along the planned cutting line 5. To do. By this irradiation, a crack region 9 (9B) is formed in the vicinity of the surface 3 inside the workpiece 1 along the planned cutting line 5.
[0038]
And as shown in FIG. 15, the crack 91 grows naturally from the crack area | region 9A, 9B. Specifically, the crack 91 naturally grows from the crack region 9A to the back surface 21 direction, from the crack region 9A (9B) to the crack region 9B (9A) direction, and from the crack region 9B to the front surface 3 direction. Thereby, the crack 9 extended long in the thickness direction of the workpiece 1 can be formed on the surface of the workpiece 1 along the planned cutting line 5, that is, the surface to be cut. Therefore, it is possible to naturally cut the workpiece 1 along the planned cutting line 5 with or without applying a relatively small force artificially.
[0039]
As described above, according to the present embodiment, a plurality of crack regions 9 are formed to increase the number of locations that serve as starting points when cutting the workpiece 1. Therefore, according to the present embodiment, the workpiece 1 is cut even when the thickness of the workpiece 1 is relatively large, or when the material of the workpiece 1 is difficult to grow the crack 91 after the crack region 9 is formed. Is possible.
[0040]
If it is difficult to cut with only two crack regions 9, three or more crack regions 9 are formed. For example, as shown in FIG. 16, a crack region 9C is formed between the crack region 9A and the crack region 9B. Moreover, if it is the incident direction of a laser beam, it can cut | disconnect also in the direction orthogonal to the thickness direction of the workpiece 1 as shown in FIG.
[0041]
In this embodiment, it is preferable to form the plurality of crack regions 9 in order from the far side with respect to the incident surface (for example, the surface 3) of the workpiece on which the pulse laser beam L is incident. For example, in FIG. 14, the crack region 9A is formed first, and then the crack region 9B is formed. When the crack region 9 is formed in order from the side closer to the incident surface, the pulse laser beam L irradiated when the crack region 9 to be formed later is formed is scattered by the crack region 9 formed first. As a result, the size of the crack portion (crack spot) formed by one shot of the pulsed laser light L constituting the crack region 9 to be formed later varies. Therefore, the crack region 9 to be formed later cannot be formed uniformly. On the other hand, when the crack region 9 is formed in order from the far side with respect to the incident surface, the above-mentioned scattering does not occur, so that the crack region 9 to be formed later can be formed uniformly.
[0042]
However, in the present embodiment, the order of forming the plurality of crack regions 9 is not limited to the above, and may be formed in order from the side closer to the incident surface of the workpiece, or may be formed randomly. . Random formation means, for example, in FIG. 16 that the crack region 9C is first formed, then the crack region 9B is formed, and the crack region 9A is finally formed with the laser light incident direction being reversed.
[0043]
The formation of the plurality of modified regions has been described in the case of the crack region, but the same can be said for the melt-treated region and the refractive index change region. Further, the pulse laser beam has been described, but the same can be said for the continuous wave laser beam.
[0044]
Next, an example of a laser processing apparatus used in the laser processing method according to this embodiment will be described. FIG. 18 is a schematic configuration diagram of the laser processing apparatus 100. The laser processing apparatus 100 includes a laser light source 101 that generates laser light L, a laser light source control unit 102 that controls the laser light source 101 to adjust the output and pulse width of the laser light L, and the reflection function of the laser light L. And a dichroic mirror 103 arranged to change the direction of the optical axis of the laser light L by 90 °, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a condensing lens A mounting table 107 on which the workpiece 1 to be irradiated with the laser beam L condensed by the lens 105 is mounted; an X-axis stage 109 for moving the mounting table 107 in the X-axis direction; A Y-axis stage 111 for moving in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis stage 1 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions Comprising a 3, and a stage controller 115 for controlling the movement of these three stages 109, 111 and 113, a.
[0045]
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.4There are lasers, Nd: YLF lasers, and titanium sapphire lasers. Nd: YAG laser, Nd: YVO when forming a crack region or a melt processing region4It is preferable to use a laser, Nd: YLF laser. When forming the refractive index changing region, it is preferable to use a titanium sapphire laser.
[0046]
The converging point P is moved in the X (Y) axis direction by moving the workpiece 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111). Since the Z-axis direction is a direction perpendicular to the surface 3 of the workpiece 1, the Z-axis direction is the direction of the focal depth of the laser light 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. That is, the position of the condensing point P in the thickness direction of the workpiece 1 is adjusted by the Z-axis stage 113. Thereby, for example, the condensing point P is adjusted to a position closer to or farther from the incident surface (surface 3) than the half position of the thickness in the thickness direction of the workpiece 1 or to a position approximately half the thickness. Can be. In addition, by moving the condensing lens 105 in the Z-axis direction, these adjustments and the condensing point of the laser beam can be adjusted to the inside of the object to be processed.
[0047]
Here, adjustment of the position of the condensing point P in the thickness direction of the workpiece by the Z-axis stage will be described with reference to FIGS. 19 and 20. In this embodiment, the position of the condensing point of the laser beam in the thickness direction of the workpiece is adjusted to a desired position inside the workpiece with reference to the surface (incident surface) of the workpiece. FIG. 19 shows a state where the condensing point P of the laser beam L is located on the surface 3 of the workpiece 1. As shown in FIG. 20, when the Z-axis stage is moved z toward the condensing lens 105, the condensing point P moves from the surface 3 to the inside of the workpiece 1. The amount of movement of the condensing point P inside the workpiece 1 is Nz (N is the refractive index of the workpiece 1 with respect to the laser beam L). Therefore, by moving the Z-axis stage in consideration of the refractive index of the workpiece 1 with respect to the laser light L, the position of the condensing point P in the thickness direction of the workpiece 1 can be controlled. That is, a desired position in the thickness direction of the processing target 1 of the condensing point P is defined as a distance (Nz) from the surface 3 to the inside of the processing target 1. The workpiece 1 is moved in the thickness direction by the movement amount (z) obtained by dividing the distance (Nz) by the refractive index (N). Thereby, the condensing point P can be adjusted to the desired position.
[0048]
The laser processing apparatus 100 further includes an observation light source 117 that generates visible light to illuminate the workpiece 1 placed on the mounting table 107 with visible light, and the same light as the dichroic mirror 103 and the condensing lens 105. A visible light beam splitter 119 disposed on the axis. 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 passes through the dichroic mirror 103 and the condensing lens 105, and the line 5 to be cut of the workpiece 1 or the like. Illuminate the surface 3 containing
[0049]
The laser processing apparatus 100 further includes an imaging element 121 and an imaging lens 123 disposed on the same optical axis as the beam splitter 119, the dichroic mirror 103, and the condensing lens 105. As the image sensor 121, for example, there 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.
[0050]
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 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. 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 laser processing apparatus 1 is adjusted so that the focal point P of the laser light L is also located on the surface 3 at the position of the Z-axis stage 113 where the focus of visible light is located on the surface 3. 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 by the overall control unit, and sent to the monitor 129. Thereby, an enlarged image or the like is displayed on the monitor 129.
[0051]
Data from the stage controller 115, image data from the imaging data processor 125, and the like are input to the overall controller 127. Based on these data, the laser light source controller 102, the observation light source 117, and the stage controller By controlling 115, the entire laser processing apparatus 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit. The overall control unit 127 receives and stores the data of the movement amount (z) described with reference to FIGS. 19 and 20.
[0052]
Next, the laser processing method according to the present embodiment will be described with reference to FIGS. FIG. 21 is a flowchart for explaining this laser processing method. The workpiece 1 is a silicon wafer.
[0053]
First, the light absorption characteristics of the workpiece 1 are measured with 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 workpiece 1 or a wavelength with little absorption is selected (S101). 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 (z) in the Z-axis direction of the workpiece 1 is determined (S 103). This is because the focusing point P of the laser beam L positioned on the surface 3 of the workpiece 1 in order to position the focusing point P of the laser beam L inside the workpiece 1, This is the amount of movement in the Z-axis direction. That is, the position of the condensing point P in the thickness direction of the workpiece 1 is determined. The position of the condensing point P is determined in consideration of the thickness, material, etc. of the workpiece 1. In the present embodiment, the first movement amount data for positioning the focusing point P near the back surface inside the workpiece 1 and the second movement amount data for positioning the focusing point P near the front surface 3 are provided. used. The melting processing region to be formed first is formed using the first movement amount data. The melt processing region to be formed next is formed using the second movement amount data. These movement amount data are input to the overall control unit 127.
[0054]
The workpiece 1 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 (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 this 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).
[0055]
This focus data is sent to the stage controller 115. The stage controller 115 moves the Z-axis stage 113 in the Z-axis direction based on the focus data (S109). Thereby, the focal point of the visible light of the observation light source 117 is located on the surface 3. At this position of the Z-axis stage 113, the condensing point P of the pulse laser beam L is located on the surface 3. The imaging data processing unit 125 calculates 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, whereby an enlarged image near the planned cutting line 5 is displayed on the monitor 129.
[0056]
Data of the first movement amount previously determined in step S <b> 103 is input to the overall control unit 127, 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). This internal position is near the back surface of the workpiece 1.
[0057]
Next, the laser light L is generated from the laser light source 101, and the laser light L is irradiated onto the planned cutting line 5 on the surface 3 of the workpiece 1. Since the condensing point P of the laser beam L is located inside the workpiece 1, the melting region is formed only inside the workpiece 1. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the planned cutting line 5 to form the melt processing region inside the workpiece 1 along the planned cutting line 5 (S113). The melt processing region is formed in the vicinity of the back surface inside the workpiece 1.
[0058]
Next, in the same manner as in step S111, based on the second movement amount data, the processing target is processed by the Z-axis stage 113 at a position where the condensing point P of the laser light L is near the inner surface 3 of the processing target 1. The object 1 is moved in the Z-axis direction (S115). Then, in the same manner as in step S113, a melting processing region is formed inside the workpiece 1 (S117). In this step, a melt processing region is formed near the inner surface 3 of the workpiece 1.
[0059]
Finally, the workpiece 1 is cut by bending the workpiece 1 along the planned cutting line 5 (S119). Thereby, the workpiece 1 is divided into silicon chips.
[0060]
The effect of this embodiment will be described. According to the present embodiment, the pulsed laser light L is applied to the planned cutting line 5 under conditions that cause multiphoton absorption and the focusing point P is aligned 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. Therefore, the workpiece 1 can be cut with a relatively small force by dividing the workpiece 1 along the scheduled cutting line 5 starting from the modified region. Thereby, the processing target object 1 can be cut | disconnected without generating the unnecessary crack which remove | deviated from the cutting planned line 5 on the surface 3 of the processing target object 1. FIG.
[0061]
Further, according to the present embodiment, the cutting laser beam L is irradiated on the planned cutting line 5 under conditions that cause multi-photon absorption in the workpiece 1 and the focusing point P is set inside the workpiece 1. ing. Therefore, 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, so that the surface 3 is damaged by melting due to the formation of the modified region. There is no.
[0062]
As described above, according to the present 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, it is possible to improve the yield of products (for example, display devices such as semiconductor chips, piezoelectric device chips, and liquid crystals) manufactured by cutting the workpiece.
[0063]
Further, according to the present embodiment, since the planned cutting line 5 on the surface 3 of the workpiece 1 is not melted, the width of the planned cutting line 5 (this width is, for example, in the case of a semiconductor wafer, between regions to be semiconductor chips) (This is the interval.) Thereby, the number of products produced from one piece of processing object 1 increases, and productivity of a product can be improved.
[0064]
Further, according to the present embodiment, since laser light is used for cutting the workpiece 1, more complicated processing than dicing using a diamond cutter becomes possible. For example, even if the planned cutting line 5 has a complicated shape as shown in FIG. 23, the cutting process can be performed according to this embodiment.
[0065]
In addition, according to the present embodiment, a plurality of modified regions are formed so as to be aligned in the incident direction, thereby increasing the number of locations that are the starting points when cutting the workpiece 1. For example, when the dimension of the laser beam incident direction of the workpiece 1 is relatively large, or when the workpiece 1 is made of a material in which cracks hardly grow from the modified region, the modified region along the planned cutting line 5 is formed. It is difficult to cut the workpiece 1 with only one piece. Therefore, in such a case, the workpiece 1 can be easily cut by forming a plurality of modified regions as in this embodiment.
[0066]
【The invention's effect】
According to the laser processing method according to the present invention, it is possible to cut the processing object without causing melting or cracks that are out of the planned cutting line on the surface of the processing object. Therefore, the yield and productivity of a product (for example, a display device such as a semiconductor chip, a piezoelectric device chip, and a liquid crystal) manufactured by cutting the workpiece can be improved.
[0067]
In addition, according to the laser processing method of the present invention, the number of locations serving as starting points when cutting the workpiece is increased by forming a plurality of modified regions. Therefore, even when the thickness of the workpiece is relatively large, the workpiece can be cut.
[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.
2 is a cross-sectional view taken along 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.
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 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 perspective view of an example of a processing object in which a crack region is formed inside the processing object using the laser processing method according to the present embodiment.
15 is a perspective view of a workpiece on which a crack extending from the crack region shown in FIG. 14 is formed.
FIG. 16 is a perspective view of another example of the processing target in which a crack region is formed inside the processing target using the laser processing method according to the present embodiment.
FIG. 17 is a perspective view of still another example of a processing object in which a crack region is formed inside the processing object using the laser processing method according to the present embodiment.
FIG. 18 is a schematic configuration diagram of an example of a laser processing apparatus that can be used in the laser processing method according to the present embodiment.
FIG. 19 is a diagram showing a state where a condensing point of laser light is located on the surface of the workpiece.
FIG. 20 is a diagram showing a state in which a condensing point of laser light is located inside a workpiece.
FIG. 21 is a flowchart for explaining a laser processing method according to the present embodiment;
FIG. 22 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]
DESCRIPTION OF SYMBOLS 1 ... Processing object, 3 ... Surface, 5 ... Planned cutting line, 7 ... Modified area | region, 9, 9A, 9B, 9C ... Crack area | region, 11 ... Silicon wafer, DESCRIPTION OF SYMBOLS 13 ... Melting process area, 100 ... Laser processing apparatus, 101 ... Laser light source, 105 ... Condensing lens, 109 ... X-axis stage, 111 ... Y-axis stage, 113 ..Z axis stage, P ... Focusing point

Claims (10)

  1. Forming a modified region by multiphoton absorption inside the processing object along the planned cutting line of the processing object by irradiating a laser beam with a focusing point inside the wafer-shaped processing object And
    By changing the position of the condensing point of the laser light in the incident direction of the laser light incident on the workpiece, a plurality of the modified regions are formed so as to be aligned along the incident direction,
    A laser processing method, wherein a plurality of the modified regions are formed to form a cutting start region on a predetermined distance inward from a laser light incident surface of the processing target along a planned cutting line of the processing target.
  2. By irradiating a laser beam with a focusing point inside the wafer-like workpiece, a modified region is formed inside the workpiece along the planned cutting line of the workpiece, and
    By changing the position of the condensing point of the laser light in the incident direction of the laser light incident on the workpiece, a plurality of the modified regions are formed so as to be aligned along the incident direction,
    A laser processing method, wherein a plurality of the modified regions are formed to form a cutting start region on a predetermined distance inward from a laser light incident surface of the processing target along a planned cutting line of the processing target.
  3. A condensing point is aligned inside the wafer-like workpiece, and laser light is irradiated under conditions where the peak power density at the condensing point is 1 × 10 8 (W / cm 2 ) or more and the pulse width is 1 μs or less. By forming a modified region in the processing object along the planned cutting line of the processing object, and
    By changing the position of the condensing point of the laser light in the incident direction of the laser light incident on the workpiece, a plurality of the modified regions are formed so as to be aligned along the incident direction,
    A laser processing method, wherein a plurality of the modified regions are formed to form a cutting start region on a predetermined distance inward from a laser light incident surface of the processing target along a planned cutting line of the processing target.
  4. The laser processing method according to claim 1, wherein a plurality of the modified regions are sequentially formed one by one.
  5. The laser processing method according to claim 1, wherein a plurality of the modified regions are formed in order from a distance from the laser light incident surface.
  6. The modified region is a crack region that is a region where a crack is generated in the inside of the workpiece, a melt-processed region that is a melt-processed region in the interior, and a refractive index that is a region in which the refractive index is changed in the interior. The laser processing method according to claim 1, comprising at least one of the change regions.
  7. A fusion processing region is formed inside the processing object along the scheduled cutting line of the processing object by irradiating a laser beam with a focusing point inside the processing object of a wafer shape made of a semiconductor material. And
    By changing the position of the condensing point of the laser beam in the incident direction of the laser beam incident on the object to be processed, a plurality of the melting treatment regions are formed so as to be aligned along the incident direction,
    A laser processing method for forming a region serving as a starting point of cutting inside a predetermined distance from a laser light incident surface of the processing object along a planned cutting line of the processing object by a plurality of the melt processing regions formed.
  8. The laser processing method according to claim 7, wherein a plurality of the melt processing regions to be formed are sequentially formed one by one.
  9. 9. The laser processing method according to claim 7, wherein a plurality of the melt processing regions are formed in order from a distance from the laser light incident surface.
  10. The laser processing method according to any one of claims 1 to 9, wherein the processing object is cut along the scheduled cutting line after forming a region to be the starting point of the cutting.
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