JP2003001473A - Laser beam machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining device which is capable of cutting an object for machining without the occurrence of melting and a crack deviating from a planned cutting line on the surface of the object for machining. SOLUTION: This laser beam amchining device 100 has a laser beam source 101 which emits a laser beam L below 1 μs in pulse width, frequency adjusting means 102 which adjusts the magnitude of the repeating frequencies of the laser beam, condensing means 105 which condenses the laser beam in such a manner that the peak power density of the condensing point P of the emitted laser beam attains >=1×10<8> (w/cm<2> ), means 113 which aligns the condensing point of the laser to the inside of the object 1 for machining, means 109 and 111 which relatively move the condensing point along the planned cutting line 5 and frequency computing means 127 which computes the magnitude of the repeating frequencies of the laser beam in order to adjust the distance between he adjacent reforming spots to the input value. The frequency adjusting means adjusts the magnitude of the repeating frequencies of the laser beam in such a manner that the computed magnitude of the frequencies is attained.

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 apparatus 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, the semiconductor elements located in the vicinity of the region may be melted. [0003] As a method for preventing melting of the surface of a workpiece, for example, JP 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 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. 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 apparatus that does not cause unnecessary cracks on the surface of a workpiece and does not melt the surface. A laser processing apparatus according to the present invention includes a laser light source that emits a pulse laser beam having a pulse width of 1 μs or less, and a repetition frequency of the pulse laser beam emitted from the laser light source. The pulse laser beam is focused so that the peak power density at the focusing point of the pulse laser beam emitted from the laser light source and the frequency adjusting means for adjusting the size is 1 × 10 ⁸ (W / cm ² ) or more. The focusing means, the means for aligning the focusing point of the pulsed laser beam focused by the focusing means with the inside of the object to be processed, and the focusing point of the pulsed laser beam along the planned cutting line of the processing object And a moving means for moving the target, and by aligning a condensing point inside the processing target and irradiating the processing target with one pulsed laser beam, one modified spot is formed inside the processing target. Formed By aligning the focal point inside the workpiece and moving the focal point relatively along the planned cutting line and irradiating the workpiece with multiple pulses of pulsed laser light, A plurality of modified spots are formed inside the workpiece along the line, and the distance between the adjacent modified spots is set to this size based on the input of the magnitude of the distance between the adjacent modified spots. And a frequency calculating means for calculating the repetition frequency of the pulsed laser light emitted from the laser light source, and the frequency adjusting means is emitted from the laser light source so as to have the frequency calculated by the frequency calculating means. The repetition frequency of the pulse laser beam is adjusted. According to the laser processing apparatus of the present invention, the inside of the object to be processed is modified by using the phenomenon of multi-photon absorption by irradiating the laser beam with the focusing point inside the object to be processed. Forming a quality region. 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 apparatus according to the present invention, the workpiece can be cut by breaking the workpiece 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. Also, according to the laser processing apparatus of the present invention, the modified region is formed by locally generating multiphoton absorption 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. Further, according to the present inventor, when the relative moving speed of the condensing point of the pulsed laser beam is constant, if the repetition frequency of the pulsed laser beam is reduced, the modified laser beam formed by one pulsed laser beam is used. Quality part (called reforming spot)
It was found that the distance between the modified spot formed by the next pulse laser beam of 1 pulse can be controlled to be large. Conversely, it has been found that the distance can be controlled to be small when the repetition frequency of the pulse laser beam is increased. In this specification, this distance is expressed as a distance or pitch between adjacent modified spots. Therefore, the distance between the adjacent modified spots can be controlled by adjusting the repetition frequency of the pulse laser beam to be larger or smaller. By changing this distance according to the type, thickness, etc. of the workpiece, cutting according to the workpiece can be performed. The modified region is defined by forming a plurality of modified spots inside the workpiece along the planned cutting line. According to the laser processing apparatus of the present invention, in order to make the distance between the adjacent modified spots based on the input of the magnitude of the distance between the adjacent modified spots, The magnitude of the repetition frequency of the pulse laser beam emitted from the laser light source is calculated. The frequency adjusting means adjusts the magnitude of the repetition frequency of the pulsed laser light emitted from the laser light source so as to be the magnitude of the frequency calculated by the frequency calculating means. Therefore,
The distance between adjacent modification spots can be set to a desired size. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The laser processing apparatus according to the present embodiment forms the modified region 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. [0013] 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 light L along the planned cutting line 5 (that is, along the direction of 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 part 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. Note that 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. 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 in the thickness direction, and when the thickness of the workpiece is large, a plurality of modified regions are formed in the thickness direction. Is possible. 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. 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 cracks, the laser beam is focused on the inside of the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ). The electric field intensity at the light spot is 1 × 10 ⁸ (W / cm ² ) or more and the pulse width is 1.
Irradiate under conditions of μs or less. The magnitude of this pulse width is
This is a condition in which 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. The upper limit value of the electric field strength is, for example, 1
× 10 ¹² (W / cm ² ) For example, the pulse width is 1 ns to 2
00 ns is preferred. 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). marking"
It is described in. 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) Processing object: Pyrex (registered trademark) glass (thickness 700 μm) (B) Laser light source: Semiconductor laser excitation Nd: YAG laser wavelength: 1064 nm Laser light spot cross section: 3.14 × 10 ⁻⁸ cm ² oscillation Form: Q switch pulse repetition frequency: 100 kHz Pulse width: 30 ns Output: Output <1 mJ / pulse Laser light quality: TEM ₀₀ Polarization characteristics: Linearly polarized (C) Condensation lens Transmittance to wavelength of laser light: 60 percent (D) Moving speed of the mounting table on which the workpiece is placed: 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 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. The data indicated by black circles in the graph is the condensing lens (C)
The magnification is 100 times and the numerical aperture (NA) is 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. From the peak power density of about 10 ¹¹ (W / cm ² ), it can be seen that a crack spot is generated inside the workpiece, and the crack spot increases as the peak power density increases. Next, in the laser processing according to this embodiment, 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 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. 11. 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. (2) When the modified 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 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 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, the melting treatment region is a region once solidified after being melted, and can also be referred to as a phase-changed region or a region where 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 ). For example, the pulse width is 1 ns
200 ns is preferred. 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. In addition, the size in the thickness direction of the melt processing region formed under the above conditions is about 100 μm. It will be described that the melt processing region 13 is formed by multiphoton absorption. 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 the film is 350 μm, the melted region 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
When referring to a silicon wafer with a thickness of 200 μm, 90
% Or more, the laser beam is hardly absorbed inside the silicon wafer 11 and is almost 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 processing region by multiphoton absorption is, 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).
It is described in. The silicon wafer is cracked in the direction of the cross section starting from the melt processing region, and the crack reaches the front and back surfaces of the silicon wafer, resulting in cutting. 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. In addition, the crack grows naturally from the melt processing area to the front and back surfaces of the silicon wafer when the crack grows from the area once solidified after being melted, or when the crack grows from the melted area. And at least one of the cases where cracks grow from a region in a state of being resolidified from melting. In either case, the cut surface after cutting is shown in FIG.
As shown in FIG. 2, a melt processing region is formed only inside.
In the case 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 (eg, glass), and the electric field strength 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". As described above, according to the present embodiment, the modified region is formed by multiphoton absorption. And this embodiment adjusts the magnitude | size of the repetition frequency of a pulse laser beam, and the magnitude | size of the relative moving speed of the condensing point of a pulse laser beam, and the modification spot formed with a pulse laser beam of 1 pulse. And the modified spot formed by the next pulse laser beam of one pulse is controlled. That is, the distance between adjacent reforming spots is controlled. Hereinafter, this distance will be described as the pitch p. The control of the pitch p will be described taking a crack region as an example. The repetition frequency of the pulse laser beam is f (H
z) Let the moving speed of the X-axis stage or Y-axis stage of the workpiece be v (mm / sec). The moving speed of these stages is an example of the relative moving speed of the condensing point of the pulse laser beam. A crack portion formed by one shot of pulsed laser light is called a crack spot. Therefore, the number n of crack spots formed per unit length of the planned cutting line 5 is as follows. n = f / v The inverse of the number n of crack spots formed per unit length corresponds to the pitch p. Therefore, the pitch p is controlled by adjusting at least one of the repetition frequency of the pulse laser beam and the relative moving speed of the focused point of the pulse laser beam. be able to. In other words, increase the repetition frequency f (Hz) and the stage moving speed v
By reducing (mm / sec), the pitch p can be controlled to be small. Conversely, the pitch p can be largely controlled by decreasing the repetition frequency f (Hz) and increasing the stage moving speed v (mm / sec). By the way, the relationship between the pitch p and the crack spot dimension d in the direction of the cutting line 5 is shown in FIG.
There are three ways shown in FIG. 14-16 is a top view of the part along the cutting scheduled line 5 of the process target object in which the crack area | region was formed by the laser processing which concerns on this embodiment. The crack spot 90 is formed by one pulsed laser beam. A crack region 9 is formed by forming a plurality of crack spots 90 so as to line up along the planned cutting line 5. FIG. 14 shows a case where the pitch p is larger than the dimension d. The crack region 9 is intermittently formed inside the workpiece along the planned cutting line 5. FIG.
5 shows a case where the pitch p is substantially equal to the dimension d. The crack region 9 is continuously formed along the planned cutting line 5 inside the workpiece. FIG. 16 shows a case where the pitch p is smaller than the dimension d. The crack region 9 is continuously formed along the planned cutting line 5 inside the workpiece. According to FIG. 14, since the crack region 9 is not continuous along the planned cutting line 5, the portion of the planned cutting line 5 maintains a certain level of strength. Therefore,
When performing the cutting process of the workpiece after laser processing is finished,
Handling of the workpiece is easy. According to FIG.15 and FIG.16, since the crack area | region 9 is continuously formed along the cutting scheduled line 5, the cutting | disconnection of the workpiece from the crack area | region 9 becomes easy. According to FIG. 14, the pitch p is larger than the dimension d, and according to FIG. 15, the pitch p is substantially equal to the dimension d. Already formed crack spot 90
Can be prevented from overlapping. As a result, the variation in the size of the crack spot can be reduced. That is, according to the present inventors, when a region where multiphoton absorption occurs due to irradiation with pulsed laser light overlaps with a crack spot 90 that has already been formed, variation in the size of the crack spot 90 formed in this region increases. I understood that. If the variation in the size of the crack spot 90 becomes large, it becomes difficult to precisely cut the workpiece along the line to be cut, and the flatness of the cut surface also deteriorates. According to FIGS. 14 and 15, since the variation in the size of the crack spot can be reduced, the workpiece can be precisely cut along the planned cutting line, and the cut surface can be flattened. As described above, according to this embodiment, the pitch p is controlled by adjusting the repetition frequency of the pulse laser beam and the relative moving speed of the focused point of the pulse laser beam. can do. As a result, by changing the pitch p in consideration of the thickness and material of the workpiece, laser processing according to the workpiece can be performed. Although the control of the pitch p has been described in the case of a crack spot, the same can be said for a melting treatment spot and a refractive index change spot.
However, there is no problem even if the melt processing spot and the refractive index change spot overlap with the already formed melt processing spot and the refractive index change spot. The relative movement of the focused point of the pulsed laser beam may be a case where the focused object of the pulsed laser beam is fixed and the object to be processed is moved, or the focused object of the pulsed laser beam is collected while the processed object is fixed. The light spot may be moved, the object to be processed and the focused point of the pulse laser light may be moved in opposite directions, or the speed of the processed object and the focused point of the pulse laser light may be different. And may be moved in the same direction. Next, the laser processing apparatus according to this embodiment will be described. FIG. 17 is a schematic configuration diagram of the laser processing apparatus 100. The laser processing apparatus 100 is a laser beam
A laser light source 101 for generating L, a laser light source control unit 102 for controlling the laser light source 101 to adjust the output, pulse width, etc. of the laser light L; A dichroic mirror 103 arranged to change the direction of the optical axis by 90 °, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a laser condensed by the condensing lens 105 A mounting table 107 on which the workpiece 1 irradiated with the light L is mounted, and X for moving the mounting table 107 in the X-axis direction.
An axis stage 109, a Y-axis stage 111 for moving the mounting table 107 in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis direction for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions A Z-axis stage 113 and a stage control unit 115 that controls the movement of these three stages 109, 111, 113 are provided. 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 are YLF laser and titanium sapphire laser. Nd: YAG laser, N
It is preferable to use a d: YVO ₄ laser or an Nd: YLF laser.
When forming the refractive index changing region, it is preferable to use a titanium sapphire laser. The laser light source 101 is a Q switch laser. FIG. 18 is a schematic configuration diagram of a Q switch laser provided in the laser light source 101. The Q-switched laser has mirrors 51 and 53 arranged at a predetermined interval, and a laser medium 55 arranged between the mirror 51 and the mirror 53.
And an excitation source 5 for applying an excitation input to the laser medium 55
7. Q placed between the laser medium 55 and the mirror 51
A switch 59. The material of the laser medium 55 is Nd: YAG, for example. The excitation input from the excitation source 57 is applied to the laser medium 5 with the loss of the resonator increased by using the Q switch 59.
By adding to 5, the inversion distribution of the laser medium 55 is raised to a predetermined value. After that, by using the Q switch 59 to reduce the loss of the resonator, the accumulated energy is instantly oscillated to generate the pulsed laser light L. The Q switch 59 is controlled to be in a high state by a signal S from the laser light source control unit 102 (for example, a change in the repetition frequency of the ultrasonic pulse). Therefore, the repetition frequency of the pulsed laser light L emitted from the laser light source 101 can be adjusted by the signal S from the laser light source control unit 102. Laser light source controller 1
02 is an example of the frequency adjusting means. The repetition frequency is adjusted by the operator of the laser processing apparatus inputting the repetition frequency using a keyboard or the like to the overall control unit 127 described later. The details of the laser light source 101 have been described above. During laser processing, the workpiece 1 is moved in the X-axis direction or Y direction.
By moving in the axial direction, the modified region is formed along the planned cutting line. Therefore, for example, when the modified region is formed in the X-axis direction, the relative movement speed of the focused point of the pulse laser beam can be adjusted by adjusting the movement speed of the X-axis stage 109. Further, when the modified region is formed in the Y-axis direction, the relative movement speed of the focused point of the pulse laser beam can be adjusted by adjusting the movement speed of the Y-axis stage 111. Adjustment of the moving speed of these stages is controlled by the stage controller 115. The stage control unit 115 is an example of a speed adjustment unit. The speed is adjusted by the operator of the laser processing apparatus inputting the magnitude of the speed using a keyboard or the like to the overall control unit 127 described later. Note that the speed of relative movement of the focused point of the pulse laser beam can be adjusted by making the focused point P movable and adjusting the moving speed. 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 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. 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 X (Y) axis stage 109 (111) is an example of the moving means. The condensing lens 105 is an example of a condensing means. The Z-axis stage 113 is an example of means for aligning the laser beam condensing point with the inside of the workpiece. Condensing lens 1
By moving 05 in the Z-axis direction, the condensing point of the laser beam can be adjusted to the inside of the workpiece. 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 image data processing unit 125 to which the image data output from the image sensor 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 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. The overall control unit 127 includes a stage control unit 1.
15, image data from the imaging data processing unit 125, and the like are input, and the laser processing apparatus is controlled by controlling the laser light source control unit 102, the observation light source 117 and the stage control unit 115 based on these data. The entire 100 is controlled. Therefore, the overall control unit 127 functions as a computer unit. FIG. 19 is a block diagram showing a part of an example of the overall control unit 127. The overall control unit 127 includes a distance calculation unit 141, a dimension storage unit 143, and an image creation unit 145. The distance calculation unit 141 receives the magnitude of the repetition frequency of the pulse laser beam and the magnitude of the moving speed of the stages 109 and 111. These inputs are performed by the operator of the laser processing apparatus using a keyboard or the like. The distance calculation unit 141 receives the above equation (n = f / v,
p = 1 / n) is used to calculate the distance (pitch) between adjacent reforming spots. The distance calculation unit 141 sends this distance data to the monitor 129. As a result, the monitor 12
9 shows the distance between the reforming spots formed under the inputted frequency and speed. The distance data is stored in the image creation unit 145.
Also sent to. The dimension storage unit 143 stores in advance the dimensions of the modified spots formed by this laser processing apparatus. Based on the distance data and the dimension data stored in the dimension storage unit 143, the image creation unit 145 creates image data of the modified region formed by the distance and the dimension and sends it to the monitor 129. Thereby, the image of the modified region is also displayed on the monitor 129. Therefore, it is possible to know the distance between adjacent modified spots and the shape of the modified region before laser processing. The distance calculation unit 141 uses the formula (n = f / v, p = 1 /
The distance between the reforming spots is calculated using n), but may be as follows. First, a table in which the relationship between the magnitude of the repetition frequency, the moving speed of the stages 109 and 111, and the distance between the reforming spots is registered in advance is stored in the distance calculation unit 141. When the magnitude of the repetition frequency and the magnitude of the moving speed of the stages 109 and 111 are input to the distance computing unit 141, the distance computing unit 141 is reformed that is formed from the above table under the conditions of these sizes. Read the distance between the modified spots in the spot. Note that the magnitude of the repetition frequency may be fixed and the magnitude of the stage moving speed may be variable. vice versa,
The stage moving speed may be fixed and the repetition frequency may be variable. Also in these cases, the distance calculation unit 141 uses the above-described formulas and tables to monitor the distance between the modified spots and the image of the modified region on the monitor 1.
The processing for displaying on the screen 29 is performed. As described above, the overall control unit 12 shown in FIG.
In step 7, the distance between adjacent reforming spots is calculated by inputting the magnitude of the repetition frequency and the magnitude of the moving speed of the stage. A desired distance between adjacent reforming spots may be input to control the repetition frequency and the stage moving speed. This will be described below. FIG. 20 is a block diagram showing a part of another example of the overall control unit 127. The overall control unit 127 includes a frequency calculation unit 147. The operator of the laser processing apparatus inputs the magnitude of the distance between the modified spots adjacent to the frequency calculation unit 147 using a keyboard or the like. The magnitude of this distance is determined in consideration of the thickness and material of the workpiece.
Based on this input, the frequency calculation unit 147 calculates a frequency for achieving the distance based on the above formula and table. In this example, the moving speed of the stage is fixed.
The frequency calculation unit 147 sends the calculated data to the laser light source control unit 102. The distance between adjacent modified spots can be set to a desired size by laser processing a workpiece with a laser processing apparatus adjusted to the frequency size. This frequency magnitude data is also sent to the monitor 129, and the frequency magnitude is displayed. FIG. 21 is a block diagram showing a part of still another example of the overall control unit 127. The overall control unit 127 includes a speed calculation unit 149. Similarly to the above, the magnitude of the distance between adjacent reforming spots is input to the speed calculation unit 149. Based on this input, the speed calculation unit 149 calculates the stage moving speed for achieving the distance based on the above formula and table. In this example, the repetition frequency is fixed. The speed calculation unit 149 sends the calculated data to the stage control unit 115. The distance between adjacent modified spots can be set to a desired size by laser processing the workpiece with the laser processing apparatus adjusted to the magnitude of the stage moving speed. The data on the magnitude of the stage moving speed is also sent to the monitor 129, and the magnitude of the stage moving speed is displayed. FIG. 22 is a block diagram showing a part of still another example of the overall control unit 127. The overall control unit 127 includes a combination calculation unit 151. A difference from the cases of FIGS. 20 and 21 is that both the repetition frequency and the stage moving speed are calculated. Similar to the above, the calculation unit 1 combines the magnitudes of the distances between adjacent reforming spots.
Input to 51. The combination calculation unit 151 calculates a repetition frequency and a stage moving speed for achieving the distance based on the above formula and table. The combination calculation unit 151 outputs the calculated data to the laser light source control unit 102 and the stage control unit 115.
Send to. The laser light source control unit 102 adjusts the laser light source 101 so as to have the calculated repetition frequency. The stage control unit 115 adjusts the stages 109 and 111 so that the calculated stage moving speed is obtained. The distance between adjacent modified spots can be set to a desired size by laser processing a workpiece with the laser processing apparatus in which these adjustments have been made. Data of the calculated repetition frequency magnitude and stage movement speed magnitude is also sent to the monitor 129, and these calculated values are displayed. Next, a laser processing method using the laser processing apparatus according to this embodiment will be described with reference to FIGS. FIG. 23 is a flowchart for explaining this laser processing method. The workpiece 1 is a silicon wafer. 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 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 thickness measurement result and the refractive index of the workpiece 1, the amount of movement of the workpiece 1 in the Z-axis direction is determined (S10).
3). This is because the converging point P of the laser light L is located inside the processing object 1, so that the processing object 1 is based on the condensing point of the laser light L positioned on the surface 3 of the processing object 1. This is the amount of movement in the Z-axis direction. This movement amount is input to the overall control unit 127. The object 1 to be processed is placed on the mounting table 107 of the laser processing apparatus 100. Then, visible light is generated from the observation light source 117 to illuminate the workpiece 1 (S10).
5). Work object 1 including illuminated cutting line 5
The surface 3 is imaged by the image sensor 121. This imaging data is sent to the imaging data processing unit 125. Based on this imaging data, the imaging data processing unit 125 uses the observation light source 1.
Focus data is calculated such that the focus of the visible light 17 is located on the surface 3 (S107). This focus data is sent to the stage controller 115. The stage control unit 115 moves the Z-axis stage 113 in the Z-axis direction based on 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, the distance between adjacent melt processing spots in the melt processing spot formed by one pulse laser, that is, the size of the pitch p is determined (S11).
2). The pitch p is determined in consideration of the thickness and material of the workpiece 1. The magnitude of the pitch p is input to the overall control unit 127 shown in FIG. Next, a laser beam L is generated from the laser light source 101, and the laser beam L is irradiated to the 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 melted region is formed only inside the workpiece 1. Then, the X-axis stage 109 and the Y-axis stage 1 are aligned along the scheduled cutting line 5.
11 is moved, and the melt processing region is formed inside the workpiece 1 along the planned cutting line 5 (S11).
3). Then, the workpiece 1 is cut by bending the workpiece 1 along the planned cutting line 5 (S11).
5). Thereby, the workpiece 1 is divided into silicon chips. The effect of this embodiment will be described. According to this, the pulse laser beam L is irradiated on the planned cutting line 5 under the condition that causes multiphoton absorption and the focusing point P is set inside the workpiece 1. And the X axis stage 109
Or by moving the Y axis stage 111, the focal point P
Is moved along the planned 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 scheduled line 5 to the surface 3 of the processing target object 1. FIG. Further, according to the present embodiment, the processing object 1
The laser beam L is irradiated on the planned cutting line 5 under the conditions that cause multiphoton absorption at the same time and the focusing point P is set inside the workpiece 1. 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. 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. 24, even if the planned cutting line 5 has a complicated shape, the cutting process is possible according to this embodiment. These effects are the same in the examples described later. Further, according to the present embodiment, the magnitude of the repetition frequency of the pulsed laser beam is adjusted, and the X-axis stage 1 is adjusted.
09, by adjusting the magnitude of the moving speed of the Y-axis stage 111, the distance between adjacent melting processing spots can be controlled. By changing the distance in consideration of the thickness and material of the workpiece 1, processing according to the purpose can be performed. According to the laser processing apparatus 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.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an object to be processed during laser processing by laser processing 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 laser processing 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 laser processing according to the present embodiment. FIG. 7 is a graph showing the relationship between electric field strength and crack size in laser processing according to the present embodiment. FIG. 8 is a cross-sectional view of an object to be processed in a first step of laser processing according to the present embodiment. FIG. 9 is a cross-sectional view of an object to be processed in a second step of laser processing according to the present embodiment. FIG. 10 is a cross-sectional view of an object to be processed in a third step of laser processing according to the present embodiment. FIG. 11 is a cross-sectional view of an object to be processed in a fourth step of laser processing 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 laser processing according to the present embodiment. FIG. 13 is a graph showing the relationship between the wavelength of laser light and the transmittance inside a silicon substrate in laser processing according to the present embodiment. FIG. 14 is a plan view of a first example of a portion along a planned cutting line of a workpiece on which a crack region is formed by laser processing according to the present embodiment; FIG. 15 is a plan view of a second example of a portion along a planned cutting line of a workpiece on which a crack region is formed by laser processing according to the present embodiment; FIG. 16 is a plan view of a third example of a portion along a planned cutting line of a workpiece on which a crack region is formed by laser processing according to the present embodiment; FIG. 17 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment. FIG. 18 is a schematic configuration diagram of a Q-switched laser provided in a laser light source of the laser processing apparatus according to the present embodiment. FIG. 19 is a block diagram illustrating a part of an example of an overall control unit of the laser processing apparatus according to the present embodiment. FIG. 20 is a block diagram illustrating a part of another example of the overall control unit of the laser processing apparatus according to the present embodiment. FIG. 21 is a block diagram showing a part of still another example of the overall control unit of the laser processing apparatus according to the present embodiment. FIG. 22 is a block diagram showing a part of still another example of the overall control unit of the laser processing apparatus according to the present embodiment. FIG. 23 is a flowchart for explaining laser processing according to the present embodiment. FIG. 24 is a plan view of a processing object for explaining a pattern that can be cut by laser processing according to the present embodiment. [Explanation of Symbols] 1 ... workpiece, 3 ... surface, 5 ... scheduled line, 7 ... modified region, 9 ... crack region, 1
DESCRIPTION OF SYMBOLS 1 ... Silicon wafer, 13 ... Melting process area, 9
DESCRIPTION OF SYMBOLS 0 ... Crack spot, 100 ... Laser processing apparatus, 101 ... Laser light source, 105 ... Condensing lens, 109 ... X-axis stage, 111 ... Y-axis stage, 113 ...・ Z axis stage, 141... Distance calculation unit, 143... Dimension storage unit, 145... Image creation unit, 147... Frequency calculation unit, 149. Arithmetic unit, P ... Condensing point, p
... Pitch of crack spots, d ... Dimensions of crack spots

Front page continuation (51) Int.Cl. ⁷ Identification symbol FI Theme code (reference) B28D 5/00 B28D 5/00 Z H01L 21/301 C03B 33/09 // C03B 33/09 B23K 101: 40 B23K 101: 40 H01L 21/78 B (72) Inventor Naomi Uchiyama 1 1126 Nomachi, Hamamatsu City, Shizuoka Prefecture 1 Hamamatsu Photonics Co., Ltd. (72) Inventor Toshimitsu Wakuda 1126 Nomachi, Hamamatsu City Shizuoka Prefecture 1 Hamamatsu Photonics Stock Internal F-term (Reference) 3C069 AA01 BA08 BB01 BB02 BC01 CA05 CA11 EA02 EA05 4E068 AA01 AD00 AE00 CA03 CA04 CA09 CA11 CC06 CD01 CD05 CE04 DA10 DA11 4G015 FA06 FB01 FC14

Claims (1)

1. A laser light source that emits pulsed laser light having a pulse width of 1 μs or less, and a frequency adjusting means that adjusts the repetition frequency of the pulsed laser light emitted from the laser light source; Condensing means for condensing the pulsed laser light so that the peak power density of the condensing point of the pulsed laser light emitted from the laser light source is 1 × 10 ⁸ (W / cm ² ) or more; Means for aligning the focal point of the pulsed laser beam focused by the means with the inside of the workpiece, and moving means for relatively moving the focal point of the pulsed laser beam along the planned cutting line of the workpiece. And irradiating the object to be processed with a pulse laser beam of one pulse with the converging point inside.
Two modified spots are formed, and the object to be processed is irradiated with a plurality of pulsed laser beams by aligning the condensing point in the interior and relatively moving the condensing point along the planned cutting line. A plurality of the modified spots are formed in the interior along the planned cutting line, and the distance between the adjacent modified spots is determined based on the input of the magnitude of the distance between the adjacent modified spots. In order to achieve this size, it comprises frequency calculating means for calculating the magnitude of the repetition frequency of the pulsed laser light emitted from the laser light source, and the frequency adjusting means is the magnitude of the frequency calculated by the frequency calculating means. The laser processing apparatus which adjusts the magnitude | size of the repetition frequency of the pulse laser beam radiate | emitted from the said laser light source so that it may become.