JP5025876B2 - Laser processing equipment - Google Patents

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]
  A laser processing apparatus according to the present invention is a laser processing apparatus that forms a modified region that is a starting point of cutting only inside a wafer-shaped processing object, and a mounting table on which the processing object is mounted; An observation light source that emits illumination light;Permeability to the workpieceThe laser light source that emits the laser light, and the illumination light is condensed on the surface of the workpiece mounted on the mounting table, and at the position of the laser light condensing pointWithout melting the surface of the workpieceA condensing lens that condenses the laser light inside the workpiece mounted on the mounting table and a reflected light of the illumination light collected on the surface of the workpiece so that the modified region is formed After moving at least one of the mounting table and the condensing lens so that the focus of the illumination light is located on the surface of the object to be processed based on the imaging data, Only a predetermined amount determined based on the thickness and refractive index of the workpiece so that the focal point of the laser beam is located inside the workpiece.,Processing objectAt which the focus of the illumination light is locatedMove at least one of the mounting table and condensing lens in the thickness direction of the object to be processed with respect to the surface, so that the condensing point of the laser light moves along the planned cutting line of the object to be processed. And a control unit having a function of moving at least one of the mounting table and the condensing lens in a direction orthogonal to the thickness direction of the object.
  Further, the laser light source emits a plurality of laser beams, and the plurality of laser beams simultaneously form a plurality of condensing points along a planned cutting line inside the workpiece.
  In addition, a plurality of laser light sources are provided, and a plurality of laser beams emitted from each of the plurality of laser light sources and applied to the workpiece from different directions form one condensing point inside the workpiece. It is characterized by doing.
[0007]
According to the laser processing method of the present invention, a laser beam is irradiated with a focusing point inside the object to be processed, and a modified region is formed inside the object to be processed. 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.
[0008]
Further, according to the laser processing method of the present invention, the modified region is locally formed inside the object to be processed. Therefore, since the laser beam is hardly absorbed on the surface of the processing object, the surface of the processing object does not melt. In addition, a condensing point is a location which the laser beam condensed. The line to be cut may be a line actually drawn on the surface or inside of the workpiece, or may be a virtual line.
[0009]
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.
[0010]
Band gap E of material absorption_GIf the photon energy hv is smaller than that, it becomes optically transparent. Therefore, the condition for absorption in the material is hν> E_GIt is. However, even if it is optically transparent, if the intensity of the laser beam is made very large, nhν> E_GUnder 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)
[0011]
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.
[0012]
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.
[0013]
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.
[0014]
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.
[0015]
In addition, the following two kinds of cutting | disconnection of the processing target object from the modification | reformation area | 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, 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.
[0016]
As modified regions formed by multiphoton absorption in this embodiment, there are the following (1) to (3).
[0017]
(1) When the modified region is a crack region including one or more cracks
Laser light can be processed (eg glass or LiTaO_ThreeThe 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”.
[0018]
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) Object to be processed: Pyrex 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: 100 kHz
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 placed: 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.
[0019]
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.
[0020]
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. 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.
[0021]
(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 strength at the focus is 1 × 10.⁸(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.
[0022]
The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.
(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
[0023]
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.
[0024]
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.
[0025]
For example, when the thickness of the silicon substrate is 500 μm or less at the wavelength of 1064 nm of the Nd: YAG laser, it can be seen that the laser light is transmitted by 80% or more 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). Are listed.
[0026]
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. 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 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, since the unnecessary cracks that are off the planned cutting line are not easily generated at the time of cleaving, cleaving control is facilitated.
[0027]
(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 changing region by multiphoton absorption is described in, for example, “The Femtosecond Laser Irradiation to the Inside of Glass” on pages 105 to 111 of the 42nd Laser Thermal Processing Research Institute Proceedings (November 1997). Photo-induced structure formation ”.
[0028]
Next, a specific example of this embodiment will be described.
[0029]
[First example]
A laser processing method according to the first example of this embodiment will be described. FIG. 14 is a schematic configuration diagram of a laser processing apparatus 100 that can be used in this method. 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.
[0030]
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. 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 a moving unit.
[0031]
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._FourThere are lasers, Nd: YLF lasers, and titanium sapphire lasers. Nd: YAG laser, Nd: YVO when forming a crack region or a melt processing region_FourIt 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.
[0032]
In the first example, pulsed laser light is used for processing the workpiece 1, but continuous wave laser light may be used as long as multiphoton absorption can be caused. In the present invention, the laser light includes a laser beam. The condensing lens 105 is an example of a condensing unit. The Z-axis stage 113 is an example of means for aligning the laser beam condensing point with the inside of the workpiece. By moving the condensing lens 105 in the Z-axis direction, the condensing point of the laser light can be adjusted to the inside of the object to be processed.
[0033]
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
[0034]
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.
[0035]
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 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.
[0036]
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.
[0037]
Next, the laser processing method according to the first example of the present embodiment will be described with reference to FIGS. FIG. 15 is a flowchart for explaining this laser processing method. The workpiece 1 is a silicon wafer.
[0038]
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 of the workpiece 1 in the Z-axis direction is determined (S103). 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. This movement amount is input to the overall control unit 127.
[0039]
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).
[0040]
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. 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.
[0041]
The movement amount data determined in advance 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).
[0042]
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 a melt processing region inside the workpiece 1 along the planned cutting line 5 (S113). Then, the workpiece 1 is cut by bending the workpiece 1 along the planned cutting line 5 (S115). Thereby, the workpiece 1 is divided into silicon chips.
[0043]
The effect of the first example will be described. According to this, the pulsed laser light L is irradiated on the planned cutting line 5 under the 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.
[0044]
Further, according to the first example, the cutting laser beam L is irradiated to the cutting line 5 under the condition that causes the multi-photon absorption in the processing target 1 and the focusing point P is set inside the processing target 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.
[0045]
As described above, according to the first example, it is possible to cut the workpiece 1 without causing unnecessary cracks or melting off the planned cutting line 5 on the surface 3 of the workpiece 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 first example, 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.
[0046]
In addition, according to the first example, the cutting line 5 on the surface 3 of the workpiece 1 is not melted, so the width of the cutting line 5 (this width is, for example, in the case of a semiconductor wafer, between the 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.
[0047]
Further, according to the first example, since laser light is used for cutting the workpiece 1, more complicated processing than dicing using a diamond cutter becomes possible. For example, as shown in FIG. 16, even if the planned cutting line 5 has a complicated shape, the cutting process is possible according to the first example. These effects are the same in the examples described later.
[0048]
The number of laser light sources is not limited to one, and a plurality of laser light sources may be used. For example, FIG. 17 is a schematic diagram for explaining a laser processing method according to the first example of the present embodiment in which a plurality of laser light sources are used. This irradiates three laser beams emitted from the three laser light sources 15, 17, 19 from different directions with the converging point P inside the workpiece 1. Each laser beam from the laser light sources 15 and 17 is incident from the surface 3 of the workpiece 1. Laser light from the laser light source 19 enters from the back surface 3 of the workpiece 1. According to this, since a plurality of laser light sources are used, even if the laser light is continuous wave laser light whose power is smaller than that of the pulsed laser light, the electric field intensity at the focal point is set to a magnitude that causes multiphoton absorption. It becomes possible. For the same reason, multiphoton absorption can be generated without a condensing lens. In this example, the condensing point P is formed by the three laser light sources 15, 17, and 19. However, the present invention is not limited to this, and a plurality of laser light sources may be used.
[0049]
FIG. 18 is a schematic diagram for explaining another laser processing method according to the first example of the present embodiment in which a plurality of laser light sources are used. This example includes three array light source units 25, 27, and 29 in which a plurality of laser light sources 23 are arranged in a line along the planned cutting line 5. Laser light emitted from the laser light sources 23 arranged in the same row in each of the array light source units 25, 27, and 29 is a single condensing point (for example, a condensing point P).₁). According to this example, a plurality of condensing points P along the planned cutting line 5₁, P₂,... Can be formed simultaneously, so that the processing speed can be improved. In this example, it is also possible to simultaneously form a plurality of modified regions by laser scanning on the surface 3 in a direction perpendicular to the planned cutting line 5.
[0050]
[Second example]
Next, a second example of this embodiment will be described. This example is a cutting method and a cutting apparatus for a light transmissive material. The light transmissive material is an example of an object to be processed. In this example, LiTaO is used as the light transmissive material._ThreeA piezoelectric element wafer (substrate) having a thickness of about 400 μm is used.
[0051]
The cutting device according to the second example includes the laser processing device 100 shown in FIG. 14 and the devices shown in FIGS. 19 and 20. The apparatus shown in FIGS. 19 and 20 will be described. The piezoelectric element wafer 31 is held by a wafer sheet (film) 33 as holding means. The wafer sheet 33 is made of an adhesive resin tape or the like on the surface holding the piezoelectric element wafer 31 and has elasticity. The wafer sheet 33 is sandwiched between the sample holders 35 and set on the mounting table 107. The piezoelectric element wafer 31 includes a large number of piezoelectric device chips 37 that are cut and separated later, as shown in FIG. Each piezoelectric device chip 37 has a circuit portion 39. The circuit portion 39 is formed on the surface of the piezoelectric element wafer 31 for each piezoelectric device chip 37, and a predetermined gap α (about 80 μm) is formed between adjacent circuit portions 39. FIG. 20 shows a state in which a minute crack region 9 as a modified portion is formed only inside the piezoelectric element wafer 31.
[0052]
Next, based on FIG. 21, the cutting method of the light transmissive material according to the second example will be described. First, a light transmissive material to be cut (in the second example, LiTaO_ThreeA light absorption characteristic of the piezoelectric element wafer 31) is measured (S201). The light absorption characteristic can be measured by using a spectrophotometer or the like. When the light absorption characteristics are measured, the laser light source 101 that emits the laser light L having a wavelength that is transparent or less absorbed by the material to be cut is selected based on the measurement result (S203). In the second example, a pulse wave (PW) type YAG laser having a fundamental wavelength of 1064 nm is selected. This YAG laser has a pulse repetition frequency of 20 Hz, a pulse width of 6 ns, and a pulse energy of 300 μJ. The spot diameter of the laser light L emitted from the YAG laser is about 20 μm.
[0053]
Next, the thickness of the material to be cut is measured (S205). When the thickness of the cutting target material is measured, based on the measurement result, the cutting target material in the optical axis direction of the laser light L is positioned so that the condensing point of the laser light L is located inside the cutting target material. The amount of displacement (movement amount) of the condensing point of the laser beam L from the surface (incident surface of the laser beam L) is determined (S207). The amount of displacement (movement amount) of the condensing point of the laser light L is set to, for example, an amount that is ½ of the thickness of the material to be cut corresponding to the thickness and refractive index of the material to be cut.
[0054]
As shown in FIG. 22, the position of the condensing point P of the actual laser beam L depends on the difference between the refractive index in the cutting target material atmosphere (for example, air) and the refractive index of the cutting target material. The laser beam L condensed by the lens 105 is positioned deeper from the surface of the material to be cut (piezoelectric element wafer 31) than the position of the condensing point Q of the laser beam L. That is, in the air, the relationship “the amount of movement of the Z-axis stage 113 in the optical axis direction of the laser light L × the refractive index of the material to be cut = the amount of movement of the condensing point of the actual laser light L” holds. Become. The displacement amount (movement amount) of the condensing point of the laser light L is set in consideration of the above-described relationship (the thickness and refractive index of the material to be cut). Thereafter, the wafer sheet 33 is placed on the mounting table 107 arranged on the XYZ-axis stage (in the present embodiment, constituted by the X-axis stage 109, the Y-axis stage 111, and the Z-axis stage 113). The held material to be cut is placed (S209). When the placement of the cutting target material is finished, light is emitted from the observation light source 117, and the emitted light is irradiated to the cutting target material. Based on the imaging result of the imaging device 121, the Z axis stage 113 is moved so that the condensing point of the laser light L is located on the surface of the material to be cut, and focus adjustment is performed (S211). Here, a surface observation image of the piezoelectric element wafer 31 obtained by the observation light source 117 is picked up by the image pickup device 121, and the image pickup data processing unit 125 cuts the light emitted from the observation light source 117 based on the image pickup result. The movement position of the Z-axis stage 113 is determined so as to focus on the surface of the target material, and is output to the stage control unit 115. Based on the output signal from the imaging data processing unit 125, the stage control unit 115 moves the Z-axis stage 113 so that the light emitted from the observation light source 117 focuses on the surface of the material to be cut. The Z-axis stage 113 is controlled so that the condensing point of the laser light L is positioned on the surface of the material to be cut.
[0055]
When the focus adjustment of the light emitted from the observation light source 117 is completed, the condensing point of the laser light L is moved to a condensing point corresponding to the thickness and refractive index of the material to be cut (S213). Here, the entire Z-axis stage 113 is moved in the optical axis direction of the laser beam L by the amount of displacement of the condensing point of the laser beam L determined corresponding to the thickness and refractive index of the material to be cut. The control unit 127 sends an output signal to the stage control unit 115, and the stage control unit 115 that receives the output signal controls the movement position of the Z-axis stage 113. As described above, the Z-axis stage 113 is moved in the optical axis direction of the laser beam L by the amount of displacement of the condensing point of the laser beam L determined in accordance with the thickness and refractive index of the material to be cut. Then, the arrangement of the condensing point of the laser beam L inside the material to be cut is completed (S215).
[0056]
When the arrangement of the condensing point of the laser beam L inside the material to be cut is completed, the laser beam L is irradiated onto the material to be cut and the X-axis stage 109 and the Y-axis stage 111 are moved according to a desired cutting pattern. (S217). The laser light L emitted from the laser light source 101 is, as shown in FIG. 22, a predetermined gap α (80 μm as described above) formed between the adjacent circuit portions 39 by the condensing lens 105. The light is condensed so that the light condensing point P is located inside the piezoelectric element wafer 31 facing the surface. The desired cutting pattern described above is set so that the laser beam L is irradiated to the gap formed between the adjacent circuit portions 39 in order to separate the plurality of piezoelectric device chips 37 from the piezoelectric element wafer 31. Therefore, the laser beam L is irradiated while confirming the irradiation state of the laser beam L on the monitor 129.
[0057]
Here, the laser light L applied to the material to be cut is a circuit formed on the surface of the piezoelectric element wafer 31 (the surface on which the laser light L is incident), as shown in FIG. The part 39 is condensed at an angle at which the laser beam L is not irradiated. In this way, by condensing the laser light L at an angle at which the laser light L is not irradiated onto the circuit unit 39, the laser light L can be prevented from entering the circuit unit 39, and the circuit unit 39 can be prevented from entering the laser light L. Can be protected from.
[0058]
The laser light L emitted from the laser light source 101 is condensed so that the condensing point P is located inside the piezoelectric element wafer 31, and the energy density of the laser light L at the condensing point P is the optical value of the material to be cut. When the threshold value of the mechanical damage or optical dielectric breakdown is exceeded, a minute crack region 9 is formed only at the condensing point P and its vicinity inside the piezoelectric element wafer 31 as a material to be cut. At this time, the front and back surfaces of the material to be cut (piezoelectric element wafer 31) are not damaged.
[0059]
Next, based on FIGS. 23 to 27, the point of forming a crack by moving the condensing point of the laser light L will be described. By irradiating the cutting target material 32 (light transmissive material) having a substantially rectangular parallelepiped shape shown in FIG. 23 with the laser light L so that the condensing point of the laser light L is located inside the cutting target material 32. 24 and FIG. 25, the minute crack region 9 is formed only at the condensing point inside the material to be cut 32 and in the vicinity thereof. Further, the scanning of the laser light L or the movement of the cutting target material 32 is controlled so that the condensing point of the laser light L moves in the longitudinal direction D of the cutting target material 32 intersecting the optical axis of the laser light L. .
[0060]
Since the laser light L is emitted in a pulse form from the laser light source 101, when the scanning of the laser light L or the movement of the material 32 to be cut is performed, the crack region 9 is to be cut as shown in FIG. A plurality of crack regions 9 are formed along the longitudinal direction D of the material 32 with an interval corresponding to the scanning speed of the laser light L or the moving speed of the material 32 to be cut. By reducing the scanning speed of the laser beam L or the moving speed of the material to be cut 32, as shown in FIG. 26, the interval between the crack areas 9 is shortened and the number of crack areas 9 to be formed is increased. Is also possible. Further, by further lowering the scanning speed of the laser beam L or the moving speed of the material to be cut, as shown in FIG. 27, the crack region 9 is moved in the scanning direction of the laser light L or the moving direction of the cutting target material 32, That is, it is continuously formed along the moving direction of the condensing point of the laser beam L. Adjustment of the space between the crack regions 9 (the number of crack regions 9 to be formed) can also be achieved by changing the relationship between the repetition frequency of the laser light L and the moving speed of the material to be cut 32 (X-axis stage or Y-axis stage). It is feasible. Further, the throughput can be improved by increasing the repetition frequency of the laser light L and the moving speed of the material 32 to be cut.
[0061]
When the crack region 9 is formed along the above-described desired cutting pattern (S219), stress is generated in the material to be cut, particularly the portion where the crack region 9 is formed, by applying physical external force or changing the environment. Then, the crack region 9 formed only inside the material to be cut (the condensing point and its vicinity) is grown, and the material to be cut is cut at the position where the crack region 9 is formed (S221).
[0062]
Next, with reference to FIGS. 28 to 32, the cutting of the material to be cut by applying physical external force will be described. First, the material to be cut (piezoelectric element wafer 31) in which the crack region 9 is formed along the desired cutting pattern is placed in the cutting device while being held by the wafer sheet 33 held between the sample holders 35. The cutting device includes a suction chuck 34 as will be described later, a suction pump (not shown) to which the suction chuck 34 is connected, a pressure needle 36 (pressing member), and a pressure needle drive for moving the pressure needle 36. Means (not shown) and the like. As the pressurizing needle driving means, an electric or hydraulic actuator can be used. 28 to 32, the circuit unit 39 is not shown.
[0063]
When the piezoelectric element wafer 31 is arranged in the cutting device, as shown in FIG. 28, the suction chuck 34 is moved closer to the position corresponding to the piezoelectric device chip 37 to be separated. As shown in FIG. 29, by operating the suction pump device in a state in which the suction chuck 34 is separated from or in contact with the piezoelectric device chip 37 that separates, the piezoelectric device chip 37 (piezoelectric element wafer) that is separated into the suction chuck 34 is obtained. 31) is adsorbed. When the separated piezoelectric device chip 37 (piezoelectric element wafer 31) is attracted to the suction chuck 34, as shown in FIG. 30, the wafer sheet 33 is separated from the back surface (the back surface of the surface holding the piezoelectric element wafer 31). The pressure needle 36 is moved to a position corresponding to the piezoelectric device chip 37 to be moved.
[0064]
When the pressure needle 36 is further moved after the pressure needle 36 contacts the back surface of the wafer sheet 33, the wafer sheet 33 is deformed and stress is applied to the piezoelectric element wafer 31 from the outside by the pressure needle 36. Stress is generated in the wafer portion where the crack region 9 is formed, and the crack region 9 grows. As the crack region 9 grows to the front and back surfaces of the piezoelectric element wafer 31, the piezoelectric element wafer 31 is cut at the end of the piezoelectric device chip 37 to be separated as shown in FIG. Is separated from the piezoelectric element wafer 31. Since the wafer sheet 33 has adhesiveness as described above, the cut and separated piezoelectric device chip 37 can be prevented from scattering.
[0065]
When the piezoelectric device chip 37 is separated from the piezoelectric element wafer 31, the suction chuck 34 and the pressure needle 36 are moved away from the wafer sheet 33. When the suction chuck 34 and the pressurizing needle 36 are moved, the separated piezoelectric device chip 37 is attracted to the suction chuck 34 and thus separated from the wafer sheet 33 as shown in FIG. At this time, ion air is sent in the direction of arrow B in FIG. 32 using an ion air blower (not shown), and is held by the wafer sheet 33 and the piezoelectric device chip 37 separated and adsorbed by the suction chuck 34. The piezoelectric element wafer 31 (surface) is cleaned with ion air. Instead of ion air cleaning, a suction device may be provided to clean the piezoelectric device chip 37 and the piezoelectric element wafer 31 that have been cut and separated by sucking dust or the like. As a method of cutting the material to be cut by environmental change, there is a method of giving a temperature change to the material to be cut in which the crack region 9 is formed only inside. In this way, by applying a temperature change to the material to be cut, thermal stress is generated in the material portion where the crack region 9 is formed, and the crack region 9 is grown to cut the material to be cut. it can.
[0066]
As described above, in the second example, the condensing point of the laser light L emitted from the laser light source 101 by the condensing lens 105 is positioned inside the light transmitting material (piezoelectric element wafer 31). The energy density of the laser beam L at the condensing point exceeds the threshold value for optical damage or optical breakdown of the light transmissive material, and the light condensing point inside the light transmissive material and its A minute crack region 9 is formed only in the vicinity. Since the light transmissive material is cut at the position of the formed crack region 9, the amount of dust generation is extremely low, and the possibility of occurrence of dicing scratches, chipping, cracks on the material surface, and the like is extremely low. Further, since the light transmissive material is cut along the crack region 9 formed by optical damage or optical breakdown of the light transmissive material, the stability of the cutting direction is improved and the cutting direction is controlled. It can be done easily. In addition, the dicing width can be reduced as compared with dicing with a diamond cutter, and the number of light transmissive materials cut from one light transmissive material can be increased. As a result, according to the second example, the light transmissive material can be cut very easily and appropriately.
[0067]
In addition, by forming stress in the material to be cut by applying physical external force or changing the environment, the formed crack region 9 is grown and the light transmissive material (piezoelectric element wafer 31) is cut. The light transmissive material can be reliably cut at the position of the crack region 9.
[0068]
Moreover, since the crack region 9 is grown by applying stress to the light transmissive material (piezoelectric element wafer 31) using the pressurizing needle 36 and the light transmissive material is cut, the formed crack region 9 The light transmissive material can be cut even more reliably at the position.
[0069]
Further, when the piezoelectric element wafer 31 (light transmissive material) on which a plurality of circuit portions 39 are formed is cut and separated for each piezoelectric device chip 37, it is formed between adjacent circuit portions 39 by the condensing lens 105. Since the laser beam L is condensed so that the condensing point is located inside the wafer portion facing the formed gap and the crack region 9 is formed, at the position of the gap formed between the adjacent circuit portions 39, The piezoelectric element wafer 31 can be cut reliably.
[0070]
Further, by moving the light transmitting material (piezoelectric element wafer 31) or scanning the laser beam L and moving the condensing point in a direction crossing the optical axis of the laser beam L, for example, a direction orthogonal to the crack region 9 Will be formed continuously along the moving direction of the condensing point, the cutting direction stability will be further improved, and the cutting direction can be controlled more easily.
[0071]
Further, in the second example, since there is almost no dust generating powder, lubricating cleaning water for preventing the dust generating powder from being scattered is unnecessary, and a dry process can be realized in the cutting process.
[0072]
Further, in the second example, the formation of the modified portion (crack region 9) is realized by non-contact processing with the laser beam L, and thus problems such as blade durability and replacement frequency in dicing with a diamond cutter occur. There is nothing. In the second example, as described above, since the formation of the modified portion (crack region 9) is realized by non-contact processing using the laser beam L, the light transmitting material is not cut completely. It is possible to cut the light transmissive material along a cutting pattern in which the transparent material is cut out. The present invention is not limited to the second example described above. For example, the light transmissive material is not limited to the piezoelectric element wafer 31 and may be a semiconductor wafer, a glass substrate, or the like. The laser light source 101 can also be appropriately selected according to the light absorption characteristics of the light transmissive material to be cut. Further, in the second example, the minute crack region 9 is formed by irradiating the laser beam L as the modified portion, but is not limited thereto. For example, by using an ultrashort pulse laser light source (for example, a femtosecond (fs) laser) as the laser light source 101, a modified portion due to a refractive index change (high refractive index) can be formed. The light transmissive material can be cut without using the change in characteristics to generate the crack region 9.
[0073]
In the laser processing apparatus 100, the focus adjustment of the laser beam L is performed by moving the Z-axis stage 113. However, the present invention is not limited to this, and the condensing lens 105 is moved to the optical axis of the laser beam L. Focus adjustment may be performed by moving in the direction.
[0074]
In the laser processing apparatus 100, the X-axis stage 109 and the Y-axis stage 111 are moved according to a desired cutting pattern. However, the present invention is not limited to this, and the laser light L is scanned according to the desired cutting pattern. You may make it do.
[0075]
Further, after the piezoelectric element wafer 31 is attracted to the suction chuck 34, the piezoelectric element wafer 31 is cut by the pressurizing needle 36. However, the present invention is not limited to this, and the piezoelectric element wafer 31 is not limited to this. After cutting, the piezoelectric device chip 37 cut and separated may be adsorbed to the suction chuck 34. In addition, after the piezoelectric element wafer 31 is attracted to the suction chuck 34, the piezoelectric element wafer 31 is cut by the pressurizing needle 36, so that the surface of the cut and separated piezoelectric device chip 37 is covered with the suction chuck 34. Thus, it is possible to prevent dust and the like from adhering to the surface of the piezoelectric device chip 37.
[0076]
Further, by using an infrared sensor as the image sensor 121, the focus adjustment can be performed using the reflected light of the laser light L. In this case, it is necessary to use a half mirror instead of using the dichroic mirror 103, and to arrange an optical element that suppresses the return light to the laser light source 101 between the half mirror and the laser light source 101. At this time, the output of the laser light L emitted from the laser light source 101 at the time of focus adjustment is more than the output for crack formation so that the material to be cut is not damaged by the laser light L for focus adjustment. Is preferably set to a low energy value.
[0077]
The features of the present invention will be described below from the viewpoint of the second example.
[0078]
The light transmissive material cutting method according to the present invention condenses the laser light emitted from the laser light source so that the condensing point is located inside the light transmissive material, and collects the light within the light transmissive material. It is characterized by comprising a reforming part forming step for forming the reforming part only at the light spot and its vicinity, and a cutting step for cutting the light transmissive material at the position of the formed reforming part. .
[0079]
In the method for cutting a light transmissive material according to the present invention, in the modified part forming step, the light transmissive property is obtained by condensing the laser light so that the condensing point of the laser light is located inside the light transmissive material. The reforming part is formed only at the condensing point in the material and in the vicinity thereof. In the cutting process, the light-transmitting material is cut at the position of the formed reforming portion, the amount of dust generation is extremely low, and there is a possibility that dicing scratches, chipping, cracks on the material surface, etc. may occur. Extremely low. Further, since the light transmissive material is cut at the position of the formed reforming portion, the cutting direction stability is improved, and the cutting direction can be easily controlled. In addition, the dicing width can be reduced as compared with dicing with a diamond cutter, and the number of light transmissive materials cut from one light transmissive material can be increased. As a result, according to the present invention, the light transmissive material can be cut very easily and appropriately.
[0080]
In addition, in the method for cutting a light transmissive material according to the present invention, since there is almost no dust generation powder, lubricating cleaning water for preventing the dust generation powder from scattering is unnecessary, and a dry process can be realized in the cutting process. Can be realized.
[0081]
Further, in the method for cutting a light transmissive material according to the present invention, since the modified portion is formed by non-contact processing using laser light, the durability of the blade in dicing with a diamond cutter as in the prior art There will be no problems such as replacement frequency. Further, in the method for cutting a light transmissive material according to the present invention, as described above, since the modified portion is formed by non-contact processing using laser light, the light transmissive material is not cut completely. The light transmissive material can be cut along a cutting pattern that cuts out the transmissive material.
[0082]
Further, the light transmissive material has a plurality of circuit portions. In the reforming portion forming step, a light condensing point is formed inside the light transmissive material portion facing the gap formed between adjacent circuit portions. It is preferable to focus the laser beam so that is positioned and form the modified portion. In such a configuration, the light transmissive material can be reliably cut at the position of the gap formed between the adjacent circuit portions.
[0083]
In addition, in the modified portion forming step, when the light transmissive material is irradiated with laser light, it is preferable to focus the laser light at an angle at which the circuit portion is not irradiated with laser light. As described above, in the modified part forming step, when the light transmissive material is irradiated with the laser beam, the laser beam is incident on the circuit unit by condensing the laser beam at an angle at which the circuit unit is not irradiated with the laser beam. The circuit portion can be protected from the laser beam.
[0084]
Further, in the modified part forming step, it is preferable to continuously form the modified part along the moving direction of the condensing point by moving the condensing point in a direction crossing the optical axis of the laser beam. In this way, in the reforming part forming step, the condensing point is moved in the direction intersecting the optical axis of the laser beam, thereby forming the reforming part continuously along the moving direction of the condensing point. The cutting direction stability is further improved, and the cutting direction can be controlled more easily.
[0085]
The light transmissive material cutting method according to the present invention condenses the laser light emitted from the laser light source so that the condensing point is located inside the light transmissive material, and collects the light within the light transmissive material. A crack forming step for forming a crack only at the light spot and its vicinity, and a cutting step for cutting the light-transmitting material at the position of the formed crack are provided.
[0086]
In the method for cutting a light transmissive material according to the present invention, in the crack formation step, the laser light is condensed so that the laser light condensing point is located inside the light transmissive material, so that the laser at the light condensing point is obtained. The energy density of light exceeds the threshold value for optical damage or optical breakdown of the light transmissive material, and cracks are formed only at and near the focal point inside the light transmissive material. In the cutting process, the light-transmitting material is cut at the position of the formed crack, the amount of dust generation is extremely low, and the possibility of occurrence of dicing scratches, chipping, cracks on the material surface, etc. is extremely low. Become. Further, since the light transmissive material is cut along a crack formed by optical damage or optical breakdown of the light transmissive material, the cutting direction stability is improved and the cutting direction can be easily controlled. It can be carried out. In addition, the dicing width can be reduced as compared with dicing with a diamond cutter, and the number of light transmissive materials cut from one light transmissive material can be increased. As a result, according to the present invention, the light transmissive material can be cut very easily and appropriately.
[0087]
In addition, in the method for cutting a light transmissive material according to the present invention, since there is almost no dust generation powder, lubricating cleaning water for preventing the dust generation powder from scattering is unnecessary, and a dry process can be realized in the cutting process. Can be realized.
[0088]
Further, in the method for cutting a light transmissive material according to the present invention, since the formation of cracks is realized by non-contact processing with a laser beam, the durability and replacement of the blade in dicing with a diamond cutter as in the conventional technique There is no problem with frequency. In the method for cutting a light transmissive material according to the present invention, as described above, since the formation of cracks is realized by non-contact processing using laser light, the light transmissive material does not cut completely. The light transmissive material can be cut along a cutting pattern that cuts through the material.
[0089]
In the cutting step, it is preferable to cut the light transmissive material by growing the formed cracks. Thus, in the cutting step, the light transmitting material can be cut at the position of the formed crack by reliably cutting the light transmitting material by growing the formed crack.
[0090]
In the cutting step, it is preferable that the light transmitting material is cut by growing a crack by applying stress to the light transmitting material using a pressing member. In this way, in the cutting process, by using the pressing member and applying stress to the light transmissive material, the light transmissive material is further cut at the position of the crack by growing the crack and cutting the light transmissive material. It can cut more reliably.
[0091]
The light-transmitting material cutting device according to the present invention includes a laser light source, a holding means for holding the light-transmitting material, and a laser beam emitted from the laser light source. An optical element that condenses the light so as to be positioned, and a cutting means that cuts the light transmissive material at the position of the modified portion formed only at and near the condensing point of the laser light inside the light transmissive material, It is characterized by having.
[0092]
In the light transmissive material cutting device according to the present invention, the optical element condenses the laser light so that the condensing point of the laser light is located inside the light transmissive material. The reforming part is formed only at the condensing point and the vicinity thereof. The cutting means cuts the light transmissive material at the position of the modified portion formed only in the vicinity of the condensing point of the laser beam in the light transmissive material and in the vicinity thereof, so that the light transmissive material is formed. Therefore, the amount of dust generation is extremely low, and the possibility of occurrence of dicing scratches, chipping, cracks on the material surface, and the like is extremely low. Further, since the light transmissive material is cut along the modified portion, the cutting direction stability is improved and the cutting direction can be easily controlled. In addition, the dicing width can be reduced as compared with dicing with a diamond cutter, and the number of light transmissive materials cut from one light transmissive material can be increased. As a result, according to the present invention, the light transmissive material can be cut very easily and appropriately.
[0093]
Further, in the light transmissive material cutting device according to the present invention, since there is almost no dust generation powder, there is no need for lubricating cleaning water for preventing the dust generation powder from scattering, and a dry process in the cutting process can be realized. Can be realized.
[0094]
Further, in the light transmissive material cutting device according to the present invention, since the modified portion is formed by non-contact processing with laser light, the durability and replacement of the blade in dicing with a diamond cutter as in the prior art There is no problem with frequency. Further, in the light transmissive material cutting device according to the present invention, since the modified portion is formed by non-contact processing using laser light as described above, the light transmissive material does not completely cut the light transmissive material. The light transmissive material can be cut along a cutting pattern that cuts through the material.
[0095]
The light-transmitting material cutting device according to the present invention includes a laser light source, a holding means for holding the light-transmitting material, and a laser beam emitted from the laser light source. An optical element that focuses light so as to be positioned, and a cutting means that cuts the light transmissive material by growing a crack formed only at and near the laser light condensing point inside the light transmissive material. It is characterized by that.
[0096]
In the light transmissive material cutting device according to the present invention, the laser light is condensed by the optical element so that the light condensing point of the laser light is located inside the light transmissive material. The energy density of light exceeds the threshold value for optical damage or optical breakdown of the light transmissive material, and cracks are formed only at and near the focal point inside the light transmissive material. And since the cutting means grows the crack formed only in the condensing point of the laser beam inside the light transmissive material and the vicinity thereof, the light transmissive material cuts the light transmissive material. The material is surely cut along the cracks formed by optical damage or optical breakdown of the material, and the amount of dust generation is extremely low. Dicing scratches, chipping, or cracks on the material surface may occur. Is also extremely low. Further, since the light transmissive material is cut along the cracks, the cutting direction stability is improved, and the cutting direction can be easily controlled. In addition, the dicing width can be reduced as compared with dicing with a diamond cutter, and the number of light transmissive materials cut from one light transmissive material can be increased. As a result, according to the present invention, the light transmissive material can be cut very easily and appropriately.
[0097]
Further, in the light transmissive material cutting device according to the present invention, since there is almost no dust generation powder, there is no need for lubricating cleaning water for preventing the dust generation powder from scattering, and a dry process in the cutting process can be realized. Can be realized.
[0098]
Further, in the light transmissive material cutting device according to the present invention, since the crack is formed by non-contact processing with laser light, the durability of the blade in dicing with a diamond cutter, the replacement frequency, etc. as in the prior art The problem does not occur. Further, in the light transmissive material cutting device according to the present invention, since the cracks are formed by non-contact processing using laser light as described above, a light transmissive material that does not completely cut the light transmissive material is used. The light-transmitting material can be cut along a cutting pattern that cuts out.
[0099]
Moreover, it is preferable that the cutting | disconnection means has a press member for applying a stress to a light transmissive material. Thus, since the cutting means has a pressing member for applying stress to the light transmissive material, it becomes possible to apply the stress to the light transmissive material by this pressing member and grow a crack. The light transmissive material can be more reliably cut at the position of the crack.
[0100]
Further, the light transmissive material is a light transmissive material having a plurality of circuit portions formed on the surface thereof, and the optical element is a light transmissive material portion facing a gap formed between adjacent circuit portions. It is preferable to focus the laser beam so that the focusing point is located inside. When configured in this manner, the light transmissive material can be reliably cut at the position of the gap formed between adjacent circuit portions.
[0101]
The optical element preferably condenses the laser beam at an angle at which the circuit unit is not irradiated with the laser beam. In this way, the optical element condenses the laser beam at an angle at which the circuit unit is not irradiated with the laser beam, thereby preventing the laser beam from entering the circuit unit and protecting the circuit unit from the laser beam. Can do.
[0102]
Moreover, it is preferable to further include a condensing point moving means for moving the condensing point in a direction crossing the optical axis of the laser beam. As described above, by further providing a condensing point moving means for moving the condensing point in a direction intersecting the optical axis of the laser beam, the cracks are continuously formed along the moving direction of the condensing point. Therefore, the cutting direction stability can be further improved, and the cutting direction can be controlled more easily.
[0103]
【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.
[0104]
Further, the processing object is placed on the mounting table of the laser processing apparatus, the surface of the processing object is irradiated with illumination light emitted from the observation light source of the laser processing apparatus, and the reflected light is irradiated on the laser processing apparatus. After capturing the image by the imaging means to acquire the imaging data, and moving the mounting table so that the focus of the illumination light emitted from the observation light source is located on the surface of the processing object based on the imaging data, the laser beam In order to move the mounting table by a predetermined amount so that the focal point of the laser beam is located inside the workpiece, and to adjust the focal point to the inside of the workpiece, the laser beam is focused on the workpiece. It becomes easy.
[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 schematic configuration diagram of a laser processing apparatus that can be used in the laser processing method according to the first example of the embodiment;
FIG. 15 is a flowchart for explaining a laser processing method according to the first example of the embodiment;
FIG. 16 is a plan view of a processing object for explaining a pattern that can be cut by the laser processing method according to the first example of the embodiment;
FIG. 17 is a schematic diagram for explaining a laser processing method according to the first example of the present embodiment regarding a plurality of laser light sources.
FIG. 18 is a schematic diagram for explaining another laser processing method according to the first example of the present embodiment with respect to a plurality of laser light sources.
FIG. 19 is a schematic plan view showing a piezoelectric element wafer held on a wafer sheet in a second example of the present embodiment.
FIG. 20 is a schematic cross-sectional view showing a piezoelectric element wafer held by a wafer sheet in a second example of the embodiment.
FIG. 21 is a flowchart for explaining a cutting method according to a second example of the embodiment;
FIG. 22 is a cross-sectional view of a light transmissive material irradiated with laser light by a cutting method according to a second example of the present embodiment.
FIG. 23 is a plan view of a light transmissive material irradiated with laser light by a cutting method according to a second example of the present embodiment.
24 is a cross-sectional view of the light transmissive material shown in FIG. 23 taken along line XXIV-XXIV.
25 is a cross-sectional view of the light transmissive material shown in FIG. 23 taken along line XXV-XXV.
26 is a cross-sectional view taken along line XXV-XXV of the light transmissive material shown in FIG. 23 when the moving speed of the condensing point is slowed.
27 is a cross-sectional view of the light transmissive material shown in FIG. 23 taken along line XXV-XXV when the moving speed of the condensing point is further decreased.
FIG. 28 is a cross-sectional view of a piezoelectric element wafer and the like showing a first step of a cutting method according to the second example of the embodiment.
29 is a cross-sectional view of a piezoelectric element wafer and the like showing a second step of the cutting method according to the second example of the embodiment. FIG.
30 is a cross-sectional view of a piezoelectric element wafer and the like showing a third step of the cutting method according to the second example of the embodiment. FIG.
31 is a cross-sectional view of a piezoelectric element wafer and the like showing a fourth step in the cutting method according to the second example of the embodiment. FIG.
32 is a cross-sectional view of a piezoelectric element wafer and the like showing a fifth step of the cutting method according to the second example of the embodiment. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Work object, 3 ... Surface, 5 ... Planned cutting line, 7 ... Modified area | region, 9 ... Crack area | region, 11 ... Silicon wafer, 13 ... Melting process Area, 15, 17, 19, 23 ... laser light source, 25, 27, 29 ... array light source unit, 31 ... piezoelectric element wafer, 37 ... piezoelectric device chip, 100 ... laser processing apparatus 101 ... Laser light source, 105 ... Condensing lens, 109 ... X-axis stage, 111 ... Y-axis stage, 113 ... Z-axis stage, P ... Condensing point

Claims (3)

A laser processing apparatus that forms a modified region that is a starting point of cutting only inside a wafer-like workpiece,
A mounting table on which the workpiece is mounted;
An observation light source that emits illumination light;
A laser light source that emits a laser beam having transparency to the workpiece ;
The modified region is formed without condensing the illumination light on the surface of the processing object placed on the mounting table and melting the surface of the processing object at the position of the condensing point of the laser light. A condensing lens for condensing the laser beam inside the workpiece placed on the mounting table as described above;
Imaging means for capturing imaging data by imaging reflected light of the illumination light collected on the surface of the workpiece;
After moving at least one of the mounting table and the condensing lens so that the focus of the illumination light is located on the surface of the object to be processed based on the imaging data, a condensing point of the laser light is said to be located within the object, the predetermined amount determined on the basis of the thickness and refractive index of the object only, the said surface of the focal point of the illumination light in said workpiece is positioned as a reference The processing is performed such that at least one of the mounting table and the condensing lens is moved in the thickness direction of the processing object, and the condensing point of the laser light is moved along a scheduled cutting line of the processing object. A laser processing apparatus comprising: a control unit having a function of moving at least one of the mounting table and the condensing lens in a direction orthogonal to a thickness direction of an object. The laser light source emits a plurality of the laser beams,
The laser processing apparatus according to claim 1, wherein the plurality of laser beams simultaneously form a plurality of the condensing points along the planned cutting line inside the object to be processed. A plurality of the laser light sources are provided,
The plurality of laser beams emitted from each of the plurality of laser light sources and irradiated on the workpiece from different directions form one condensing point inside the workpiece. Item 3. A laser processing apparatus according to Item 2.

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