JP2006203256A - Laser processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser processing method for precisely cutting a processing object having a variety of stacked layers. <P>SOLUTION: The laser processing method has a step of forming a reformed region 7 at least in the inside of the substrate 15 by focusing and irradiating a laser beam at least in the substrate 15 to form a line for planned cutting with the reformed region 7 in a predetermined distance from the laser beam incident plane 3 of the processing object 1 along the cutting line thereof, wherein the processing object 1 includes a substrate 15 and a stacked part 17b formed on the substrate 15 through an oxidation film 17a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laser processing method used for cutting an object to be processed having a laminated portion provided on a surface of a substrate.

In recent years, various laminated layers such as those obtained by crystal growth of a semiconductor operation layer such as GaN on an Al ₂ O ₃ substrate for semiconductor devices, and those obtained by bonding another glass substrate on a glass substrate for liquid crystal display devices, etc. There is a demand for a technique for cutting a workpiece having a structure with high accuracy.

  Conventionally, a blade dicing method or a diamond scribe method is generally used to cut a workpiece having such a laminated structure.

The blade dicing method is a method of cutting and cutting a workpiece with a diamond blade or the like (see, for example, Patent Document 1). On the other hand, with the diamond scribe method, a diamond point tool is used to provide a scribe line on the surface of the object to be processed, and a knife edge is pressed against the back surface of the object to be processed along the scribe line to divide and cut the object to be processed. It is a method (for example, refer patent document 2).
JP 2003-197561 A Japanese Patent Laid-Open No. 62-296579

  However, in the blade dicing method, for example, when the object to be processed is for the above-described liquid crystal display device, a gap is provided between the glass substrate and another glass substrate. There is a risk that shavings and lubricating cleaning water may get in.

Further, in the diamond scribe method, when the processing object has a high hardness substrate such as an Al ₂ O ₃ substrate, or when the processing object is a glass substrate bonded together. In addition, scribe lines must be provided not only on the front surface but also on the back surface of the workpiece, and there is a risk that cutting defects may occur due to misalignment of the scribe lines provided on the front and back surfaces.

  Therefore, the present invention has been made in view of such circumstances, and a laser processing method capable of solving the above-described problems and cutting a workpiece having various laminated structures with high accuracy. The purpose is to provide.

  In order to achieve the above object, a laser processing method according to the present invention provides a processing object having a substrate and a laminated portion formed on the substrate via an oxide film, and at least a condensing point in the substrate. In addition, a modified region is formed at least inside the substrate by irradiating the laser beam together, and this modified region causes a predetermined distance inside the laser beam incident surface of the workpiece along the planned cutting line of the workpiece. The method includes a step of forming a cutting start region.

  According to this laser processing method, in a processing target having a substrate and a laminated portion formed on the substrate via an oxide film, the processing target is cut at least by a modified region formed inside the substrate. It is possible to form a cutting starting point region along a desired cutting line to be cut. Therefore, with the cutting start region as the starting point of cutting, a workpiece having a substrate and a laminated portion formed on the substrate via an oxide film can be divided and cut by a relatively small force. A workpiece having a structure can be cut with high accuracy.

  The laminated portion provided on the surface of the substrate refers to a material deposited on the surface of the substrate, a material bonded to the surface of the substrate, or a material attached to the surface of the substrate. It does not matter whether the material is the same or similar. The laminated portion provided on the surface of the substrate includes those provided in close contact with the substrate and those provided with a gap from the substrate. Examples include a semiconductor operation layer formed by crystal growth on a substrate, another glass substrate bonded to a glass substrate, and the like, and the laminated portion includes a plurality of layers made of different materials. Moreover, the inside of a board | substrate is the meaning also including on the surface of the board | substrate with which the laminated part is provided. Moreover, a condensing point is a location which the laser beam condensed. Further, the cutting start region means a region that becomes a starting point of cutting when the workpiece is cut. Therefore, the cutting start region is a planned cutting portion where cutting is planned for the workpiece. The cutting start region may be formed by continuously forming the modified region, or may be formed by intermittently forming the modified region.

  According to the laser processing method according to the present invention, it is possible to cut a processing object having various laminated structures with high accuracy.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the laser processing method according to the present embodiment, a modified region by multiphoton absorption is formed inside a workpiece. This laser processing method, particularly multiphoton absorption, will be described first.

Photon energy hν is smaller than the band gap E _G of absorption of the material becomes transparent. 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, ···) the intensity of laser light becomes very high. 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 conditions where 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. 4 is a plan view of the workpiece 1, FIG. 4 is a cross-sectional view taken along line IV-IV of the workpiece 1 shown in FIG. 3, and FIG. 5 is taken along line V-V of the workpiece 1 shown in FIG. FIG. 6 is a plan view of the cut workpiece 1.

  As shown in FIGS. 1 and 2, the surface 3 of the workpiece 1 has a desired scheduled cutting line 5 on which the workpiece 1 is to be cut. The planned cutting line 5 is a virtual line extending in a straight line (the cutting target line 5 may be actually drawn by drawing a line on the workpiece 1). 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 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, and the modified starting region (scheduled portion) 8 is formed by the modified region 7. Is formed. 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 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 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.

  It should be noted that the following two methods are conceivable for cutting the object to be processed starting from the cutting start region. One is a case where an artificial force is applied to the workpiece after the cutting start region is formed, so that the workpiece is broken starting from the cutting start region and the workpiece is cut. This is, for example, cutting when the thickness of the workpiece is large. An artificial force is applied when, for example, bending stress or shear stress is applied to the workpiece along the cutting start region 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 cutting start region is formed, the cutting start region is used as a starting point, and the workpiece is naturally cracked in the cross-sectional direction (thickness direction) of the processing target, resulting in the processing target being cut. It is. For example, when the thickness of the workpiece is small, the cutting start region is formed by one row of modified regions, and when the thickness of the workpiece is large, the thickness direction This is made possible by forming the cutting start region by the modified regions formed in a plurality of rows. In addition, even when this breaks naturally, in the part to be cut, the part corresponding to the part where the cutting starting point region is formed without cracking ahead on the surface of the part corresponding to the part where the cutting starting point region is not formed Since it is possible to cleave only, the cleaving can be controlled well. In recent years, since the thickness of workpieces such as silicon wafers tends to be thin, such a cleaving method with good controllability is very effective.

  In the present embodiment, the modified regions formed by multiphoton absorption include the following (1) to (3).

(1) In the case where the modified region is a crack region including one or a plurality of cracks, the focusing point is set inside the object to be processed (for example, a piezoelectric material made of glass or LiTaO ₃ ), and the electric field strength at the focusing point is Irradiation with laser light is performed under conditions of 1 × 10 ⁸ (W / cm ² ) or more and a pulse width of 1 μs or less. The magnitude of this pulse width is a condition that allows a crack region to be formed only inside the workpiece without causing extra damage to the surface of the workpiece 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 ). 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”.

  The inventor obtained the relationship between the electric field strength and the size of the cracks by experiment. The experimental conditions are as follows.

(A) Workpiece: Pyrex (registered trademark) glass (thickness 700 μm)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: Output <1mJ / pulse
Laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

Note that the laser light quality TEM ₀₀ means that the light condensing performance is high and the light can be condensed up to the wavelength of the laser light.

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. 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 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 more cracks. This crack region 9 forms a cutting start region. As shown in FIG. 9, the crack further grows starting from the crack region 9 (that is, starting from the cutting start region), and the crack reaches the front surface 3 and the back surface 21 of the workpiece 1 as shown in FIG. 10, As shown in FIG. 11, the workpiece 1 is cut when the workpiece 1 is broken. 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 reforming region is a melt processing region The focusing point is set inside the object to be processed (for example, a semiconductor material such as silicon), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm ^2). ) Irradiation with laser light 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 melt treatment region is a region once solidified after melting, a region in a molten state, or a region re-solidified from a molten state, and can also be referred to as a phase-changed region or a region in which the crystal structure has changed. The melt treatment region can also be said to be a region in which one structure is changed to another structure in a single crystal structure, an amorphous structure, or a polycrystalline structure. In other words, for example, a region changed from a single crystal structure to an amorphous structure, a region changed from a single crystal structure to a polycrystalline structure, or a region changed from a single crystal structure to a structure including an amorphous structure and a polycrystalline structure. To do. When the object to be processed has a silicon single crystal structure, the melt processing region has, for example, an amorphous silicon structure. The upper limit value of the electric field strength is, for example, 1 × 10 ¹² (W / cm ² ). The pulse width is preferably 1 ns to 200 ns, for example.

  The inventor has confirmed through experiments that a melt-processed region is formed inside a silicon wafer. The experimental conditions are as follows.

(A) Workpiece: silicon wafer (thickness 350 μm, outer diameter 4 inches)
(B) Laser
Light source: Semiconductor laser pumped Nd: YAG laser
Wavelength: 1064nm
Laser light spot cross-sectional area: 3.14 × 10 ⁻⁸ cm ²
Oscillation form: Q switch pulse
Repeat frequency: 100 kHz
Pulse width: 30ns
Output: 20μJ / pulse
Laser light quality: TEM ₀₀
Polarization characteristics: Linearly polarized light (C) Condensing lens
Magnification: 50 times
N. A. : 0.55
Transmittance with respect to laser beam wavelength: 60% (D) Moving speed of mounting table on which workpiece is mounted: 100 mm / second

  FIG. 12 is a view showing a photograph of a cross section of a part of a silicon wafer cut by laser processing under the above conditions. A melt processing region 13 is formed inside the silicon wafer 11. The size in the thickness direction of the melt processing region 13 formed under the above conditions is about 100 μm.

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

  For example, when the thickness of the silicon substrate is 500 μm or less at the wavelength of the Nd: YAG laser of 1064 nm, 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 13 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 13 is formed inside the silicon wafer 11 (that is, the melt processing region is formed by normal heating with laser light) It means that the melt processing region 13 is formed by multiphoton absorption. The formation of the melt processing region by multiphoton absorption is 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.

  Note that a silicon wafer is cracked as a result of generating cracks in the cross-sectional direction starting from the cutting start region formed by the melt processing region and reaching the front and back surfaces of the silicon wafer. The The cracks that reach the front and back surfaces of the silicon wafer may grow naturally or may grow by applying force to the silicon wafer. In addition, when a crack naturally grows from the cutting start region to the front and back surfaces of the silicon wafer, the case where the crack grows from a state where the melt treatment region forming the cutting starting region is melted, and the cutting starting region There are both cases where cracks grow when the solidified region is melted from the molten state. However, in either case, the melt processing region is formed only inside the silicon wafer, and the melt processing region is formed only inside the cut surface after cutting as shown in FIG. When the cutting start region is formed in the workpiece by the melt processing region, unnecessary cracks that are off the cutting start region line are unlikely to occur during cleaving, so that cleaving control is facilitated.

(3) When the modified region is a refractive index changing region The focusing point is set inside the object to be processed (for example, glass), and the electric field intensity at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more. Laser light is irradiated under the condition that the pulse width is 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. 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 ”.

  As described above, the cases of (1) to (3) have been described as the modified regions formed by multiphoton absorption. However, considering the crystal structure of the wafer-like workpiece and its cleavage property, the cutting origin region is described below. If it forms in this way, it will become possible to cut | disconnect a process target object with much smaller force from the cutting | disconnection starting point area | region as a starting point with still smaller force.

That is, in the case of a substrate made of a single crystal semiconductor having a diamond structure such as silicon, the cutting start region is formed in a direction along the (111) plane (first cleavage plane) or the (110) plane (second cleavage plane). Is preferred. In the case of a substrate made of a zinc-blende-type III-V group compound semiconductor such as GaAs, it is preferable to form the cutting start region in the direction along the (110) plane. Further, in the case of a substrate having a hexagonal crystal structure such as sapphire (Al ₂ O ₃ ), the (1120) plane (A plane) or (1100) plane ( It is preferable to form the cutting start region in a direction along the (M plane).

  Note that the orientation flat is formed on the substrate along the direction in which the above-described cutting start region is to be formed (for example, the direction along the (111) plane in the single crystal silicon substrate) or the direction perpendicular to the direction in which the cutting start region is to be formed. By using the orientation flat as a reference, it is possible to easily and accurately form the cutting start area along the direction in which the cutting start area is to be formed on the substrate.

  Next, a laser processing apparatus used in the laser processing method described above will be described with reference to FIG. FIG. 14 is a schematic configuration diagram of the laser processing apparatus 100.

  The laser processing apparatus 100 includes a laser light source 101 that generates laser light L, a laser light source control unit 102 that controls the laser light source 101 to adjust the output and pulse width of the laser light L, and the reflection function of the laser light L. And a dichroic mirror 103 arranged to change the direction of the optical axis of the laser light L by 90 °, a condensing lens 105 for condensing the laser light L reflected by the dichroic mirror 103, and a condensing lens A mounting table 107 on which the workpiece 1 to be irradiated with the laser beam L condensed by the lens 105 is mounted; an X-axis stage 109 for moving the mounting table 107 in the X-axis direction; A Y-axis stage 111 for moving in the Y-axis direction orthogonal to the X-axis direction, and a Z-axis stage 1 for moving the mounting table 107 in the Z-axis direction orthogonal to the X-axis and Y-axis directions 3, and a stage controller 115 for controlling the movement of these three stages 109, 111 and 113.

  The converging point P is moved in the X (Y) axis direction by moving the workpiece 1 in the X (Y) axis direction by the X (Y) axis stage 109 (111). Since the Z-axis direction is a direction orthogonal 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. Thereby, for example, when the processing object 1 has a multilayer structure, the condensing point P can be adjusted to a desired position such as a substrate of the processing object 1 or a laminated portion on the substrate. it can.

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 an Nd: YVO ₄ laser, an Nd: YLF laser, and a titanium sapphire laser. In this embodiment, pulsed laser light is used for processing the workpiece 1, but continuous wave laser light may be used as long as multiphoton absorption can be caused.

  The laser processing apparatus 100 further includes 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 beam splitter 119 for visible light 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 In addition, when the processing object 1 is placed on the mounting table 107 so that the back surface of the processing object 1 is on the condensing lens 105 side, the “front surface” here is the “back surface”. is there.

  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. An example of the image sensor 121 is a CCD camera. The reflected light of the visible light that illuminates the surface 3 including the planned cutting line 5 passes through the condensing lens 105, the dichroic mirror 103, and the beam splitter 119, is imaged by the imaging lens 123, and is imaged by the imaging device 121. And becomes imaging data.

  The laser processing apparatus 100 further includes an imaging data processing unit 125 to which imaging data output from the imaging element 121 is input, an overall control unit 127 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 of the workpiece 1 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 of the workpiece. 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.

  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.

  Next, the laser processing method according to the present embodiment will be described with reference to FIGS. FIG. 15 is a flowchart for explaining the laser processing method according to the present embodiment. In the present embodiment, the workpiece 1 includes a substrate and a stacked portion provided on the surface of the substrate. Further, the workpiece 1 is placed on the mounting table 107 of the laser processing apparatus 100 shown in FIG. 14 so that the back surface of the substrate is on the condensing lens 105 side. That is, the laser beam L is irradiated from the back side of the substrate that the workpiece 1 has.

  First, the light absorption characteristics of the substrate 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 substrate of the workpiece 1 or a wavelength with little absorption is selected (S101). Since this laser light L is irradiated from the back side of the substrate, even if the laminated portion provided on the surface of the substrate has light shielding or absorbing properties for this laser light. There is no obstacle to laser processing.

  Subsequently, the amount of movement of the workpiece 1 in the Z-axis direction is determined in consideration of the thickness and refractive index of the substrate of the workpiece 1 and the thickness and material of the stacked portion formed on the surface of the substrate. (S103). This is because the condensing point of the laser light L located on the back surface of the substrate of the processing object 1 is set in order to align the condensing point P of the laser light L with a desired position inside the substrate of the processing object 1. This is the amount of movement of the workpiece 1 in the Z-axis direction with respect to P. This movement amount is input to the overall control unit 127.

  The workpiece 1 is placed on the mounting table 107 of the laser processing apparatus 100 so that the back surface of the substrate is on the condensing lens 105 side. Then, visible light is generated from the observation light source 117 to illuminate the back surface of the substrate of the workpiece 1 (S105). The imaging device 121 images the back surface including the illuminated planned cutting line 5. The planned cutting line 5 is a desired virtual line for cutting the workpiece 1. Imaging data captured by the imaging element 121 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 back surface of the substrate of the processing object 1 (S107).

  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 focus of the visible light of the observation light source 117 is located on the back surface of the substrate of the workpiece 1. The imaging data processing unit 125 calculates enlarged image data of the back surface of the substrate of the processing target 1 including the scheduled 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.

  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 beam L is inside the substrate of the workpiece 1 based on the movement amount data. (S111).

  Subsequently, 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 back surface of the substrate of the workpiece 1. Since the condensing point P of the laser beam L is located inside the substrate of the workpiece 1, the modified region is formed only inside the substrate of the workpiece 1. Then, the X-axis stage 109 and the Y-axis stage 111 are moved along the planned cutting line 5, and the cutting start area along the planned cutting line 5 is processed by the modified region formed along the planned cutting line 5. It forms in the inside of the thing 1 (S113).

  As described above, according to the laser processing method according to the present embodiment, the laser beam L is irradiated from the back side of the substrate included in the workpiece 1, and the modification formed by multiphoton absorption inside the substrate is performed. By the quality region, it is possible to form a cutting starting point region along a desired planned cutting line 5 where the workpiece 1 is to be cut. Then, the position of the modified region formed inside the substrate is adjusted in consideration of the thickness, material, etc. of the laminated portion provided on the surface of the substrate. Is controlled by Therefore, it is possible to divide and cut the workpiece 1 formed by providing the laminated portion on the surface of the substrate with a relatively small force, starting from the cutting start region formed inside the substrate.

  In addition, the laser beam L is irradiated with the laser beam L with the condensing point P inside the laminated portion by the laser light L having a wavelength that is transparent to the laminated portion of the processing object 1 or a wavelength with little absorption, and the inside of the laminated portion is irradiated. Alternatively, a cutting starting point region along the planned cutting line 5 may be formed, and in this case, the workpiece 1 can be cut with a smaller force.

  Examples of the laser processing method according to the present embodiment will be described with reference to FIGS.

[Example 1]
FIG. 16A is a diagram illustrating a case where the modified region 7 is formed near the back surface of the substrate 15 in the workpiece 1 according to the first embodiment, and FIG. 16B is a diagram illustrating the processing according to the first embodiment. FIG. 6 is a diagram showing a case where a modified region 7 is formed in the vicinity of the surface of a substrate 15 in the object 1. The workpiece 1 shown in FIGS. 16A and 16B includes a next-generation high-speed / low-power consumption device and a next-generation device.

The substrate 15 / first stacked unit 17a / second stacked unit 17b for next-generation high-speed / low-power-consumption devices are respectively Si (500 μm) / SiO ₂ (1 μm) / Si (3 μm). On the other hand, the substrate 15 / first stacked portion 17a / second stacked portion 17b for next-generation devices are respectively Si (500 μm) / SrTiO ₃ (several 100 nm) / GaAs (several 100 nm) (numerals in parentheses). Indicates thickness).

  As shown in FIG. 16A, when the modified region 7 is located in the vicinity of the back surface 21 of the workpiece 1, the workpiece 1 is aligned along the cutting start region formed by the modified region 7. The knife edge 23 is pressed against the surface 3 and the workpiece 1 is broken and cut. This is because the workpiece 1 can be cut with a relatively small force because a large tensile stress of the bending stress generated by the pressing of the knife edge 23 acts on the modified region 7. On the other hand, as shown in FIG. 16B, when the modified region 7 is located near the front surface 3 of the workpiece 1, the knife edge 23 is pressed against the back surface 3 of the workpiece 1 for the same reason. The workpiece 1 is cut by hitting.

  Note that “the modified region 7 is located in the vicinity of the back surface 21 of the workpiece 1” means that the modified region 7 constituting the cutting start region is the center position (thickness of the workpiece 1 in the thickness direction). It means that it is deviated from the half position) toward the back surface 21 side. In other words, it means a case where the center position of the width of the modified region 7 in the thickness direction of the workpiece 1 is shifted from the center position in the thickness direction of the workpiece 1 to the back surface 21 side, The meaning is not limited to the case where all the portions of the modified region 7 are located on the back surface 21 side with respect to the center position in the thickness direction of the workpiece 1. Similarly, “the modified region 7 is located in the vicinity of the surface 3 of the workpiece 1” means that the modified region 7 constituting the cutting start region is the surface 3 from the center position in the thickness direction of the workpiece 1. It means that it is biased to the side. The same applies to the formation position of the modified region 7 with respect to the substrate 15.

[Example 2]
FIG. 17A is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 in the workpiece 1 according to the second embodiment, and FIG. 17B is a diagram illustrating the processing according to the second embodiment. FIG. 5 is a diagram showing a case where a modified region 7 is formed in the vicinity of the surface of a substrate 15 in the object 1. The processed object 1 shown in FIGS. 17A and 17B is for a blue LD / LED, and the substrate 15 / laminated portion 17 is a semiconductor crystal such as Al ₂ O ₃ (500 μm) / GaN. May be a multilayer functional film (several 100 nm) in which a plurality of layers are formed, or a multilayer functional film (several hundred nm) in which a plurality of layers such as Al ₂ O ₃ (500 μm) / ZnO are formed. Showing).

  For the same reason as in the case of the workpiece 1 according to the first embodiment, when the modified region 7 is located in the vicinity of the back surface 21 of the workpiece 1 as shown in FIG. A knife edge 23 is pressed against the surface 3 of 1 and the workpiece 1 is split and cut. On the other hand, as shown in FIG. 17B, when the modified region 7 is located in the vicinity of the front surface 3 of the workpiece 1, the knife edge 23 is pressed against the back surface 21 of the workpiece 1 to process the workpiece. Divide 1 and cut.

[Example 3]
FIG. 18A is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the surface of the substrate 15 and the stacked portion 17 in the workpiece 1 according to the third embodiment, and FIG. FIG. 18C is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 in the workpiece 1 according to Example 3, and FIG. It is a figure which shows the case where the modification | reformation area | region 7 is formed in the vicinity. The workpiece 1 shown in FIGS. 18A to 18C is for an infrared light detection device, and the substrate 15 / laminated portion 17 is Al ₂ O ₃ (500 μm) / PbSe (10 μm). Alternatively, there is a case of Al ₂ O ₃ (500 μm) / HgCdTe (10 μm) (the value in parentheses indicates the thickness).

  For the same reason as in the case of the workpiece 1 according to the first embodiment, the modified region 7 is located in the vicinity of the surface 3 of the workpiece 1 as shown in FIGS. 18 (a) and 18 (c). For this, the knife edge 23 is pressed against the back surface 21 of the workpiece 1 to divide and cut the workpiece 1. On the other hand, as shown in FIG. 18B, when the modified region 7 is located in the vicinity of the back surface 21 of the workpiece 1, the knife edge 23 is pressed against the front surface 3 of the workpiece 1 to process the workpiece. Divide 1 and cut.

[Example 4]
FIG. 19 is a diagram illustrating the workpiece 1 according to the fourth embodiment. The processing object 1 shown in FIG. 19 is a multi-layer glass, in which two glass substrates as a first laminated portion 17a and a second laminated portion 17b are bonded and laminated on a glass substrate as a substrate 15. is there. The modified region 7 in each glass substrate is formed on the back surface 21 side of the workpiece 1. Also in this case, for the same reason as the case of the workpiece 1 according to the first embodiment, the knife edge 23 is pressed against the surface 3 of the workpiece 1 to divide and cut the workpiece 1. As described above, when the thickness of the laminated portion is thick or the hardness of the laminated portion is high, if the cutting start region is also formed inside the laminated portion, the workpiece 1 is divided and cut by a smaller force. Can do.

[Example 5]
FIG. 20A to FIG. 21B are diagrams illustrating the workpiece 1 according to the fifth embodiment. FIG. 20A is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the surface of the substrate 15 and in the vicinity of the surface of the stacked portion 17 in the workpiece 1 according to the fifth embodiment, and FIG. These are figures which show the case where the modification area | region 7 is formed in the workpiece 1 which concerns on Example 5 in the back surface vicinity of the board | substrate 15, and the back surface vicinity of the laminated part 17. FIG. FIG. 21A is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the front surface of the substrate 15 and in the vicinity of the back surface of the stacked portion 17 in the workpiece 1 according to the fifth embodiment. FIG. 7B is a diagram illustrating a case where the modified region 7 is formed in the vicinity of the back surface of the substrate 15 and in the vicinity of the front surface of the stacked portion 17 in the workpiece 1 according to the fifth embodiment.

  A workpiece 1 shown in FIGS. 20A to 21B is for a reflective liquid crystal display device. The substrate 15 is a glass substrate (thickness 1.8 mm, outer diameter 8 inches) on which a common electrode is formed, and the laminated portion 17 is an Si substrate (thickness 500 μm, outer diameter 8 inches) on which TFTs are formed. is there. The substrate 15 and the laminated portion 17 are attached to each other with an adhesive 25 with a gap for liquid crystal.

  In the case of FIG. 20A and FIG. 20B, the modified region 7 is formed inside the stacked portion 17 by irradiating laser light from the back surface 21 side of the workpiece 1, and then the workpiece. The modified region 7 is formed inside the substrate 15 by irradiating laser light from the back surface 21 side of the substrate 1. This is because the laser light has a wavelength that is transparent to the substrate 15 and the laminated portion 17 or a wavelength with little absorption. For the same reason as in the case of the workpiece 1 according to the first embodiment, in the case of FIG. 20A, the knife edge 23 is pressed against the back surface 21 of the workpiece 1 to break the workpiece 1. And cut. On the other hand, in the case of FIG. 20B, the knife edge 23 is pressed against the surface 3 of the workpiece 1 to divide and cut the workpiece 1.

  As described above, if the cutting start region is formed in the substrate 15 and the laminated portion 17 using a laser beam having a wavelength that is transparent to the substrate 15 and the laminated portion 17 or a wavelength with little absorption, the conventional diamond scriber is used. The reversing operation of the workpiece 1 performed by the law can be omitted, and the destruction of the workpiece 1 during the reversing operation can be prevented. In addition, it is possible to prevent a positional deviation from occurring in the cutting start region formed on the substrate 15 and the laminated portion 17, thereby enabling the workpiece 1 to be cut with high accuracy. Further, since the lubricating cleaning water that is essential in the conventional blade dicing method is not necessary, there is no problem that the lubricating cleaning water enters the gap between the substrate 15 and the laminated portion 17.

  In the case of FIG. 21A and FIG. 21B, the modified region 7 is formed inside the substrate 15 by irradiating laser light from the back surface 21 side of the workpiece 1, and then the workpiece 1. The modified region 7 is formed inside the laminated portion 17 by irradiating laser light from the front surface 3 side. Then, for the same reason as in the case of the workpiece 1 according to the first embodiment, in the case of FIG. 21A, the substrate 15 is first cracked by pressing the knife edge 23 against the back surface 21 of the workpiece 1 first. Then, the knife edge 23 is pressed against the surface 3 of the workpiece 1 to break the laminated portion 17 and cut. On the other hand, in the case of FIG. 21B, the knife edge 23 is first pressed against the surface 3 of the workpiece 1 to divide and cut the substrate 15, and then the knife edge 23 is cut against the back surface 21 of the workpiece 1. Is pressed and the laminated portion 17 is broken and cut.

[Example 6]
FIG. 22 is an enlarged cross-sectional view illustrating a main part of the workpiece 1 according to the sixth embodiment. This processing object 1 has a large number of chip formation regions F provided on a substrate 15 which is a silicon wafer, and a dicing line region D between adjacent chip formation regions F and F. FIG. The cross section of the part which the area | region F and the dicing line area | region D continue is shown. Note that the planned cutting line is set along the dicing line region D.

  As shown in the figure, an interlayer insulating film (laminated portion) 31 is formed on the substrate 15, and a metal wiring layer 32 is provided on the interlayer insulating film 31 in the chip formation region F of the substrate 15. Yes. Further, an interlayer insulating film (laminated portion) 33 is formed on the substrate 15 so as to cover the interlayer insulating film 31 and the metal wiring layer 32. In the chip formation region F of the substrate 15, a metal is formed on the interlayer insulating film 33. A wiring layer 34 is provided. The substrate 15 and the metal wiring layer 32 are electrically connected by a plug 35 that penetrates the interlayer insulating film 31. Further, the metal wiring layer 32 and the metal wiring layer 34 are electrically connected by a plug 36 that penetrates the interlayer insulating film 33.

  The processing target 1 configured in this way is irradiated with laser light with the focusing point aligned inside the substrate 15, and along the dicing line region D (that is, along the planned cutting line). Then, the modified region 7 is formed, and the modified region 7 forms a cutting start region. And the workpiece 1 can be cut | disconnected with high precision by pressing the knife edge 23 against the surface 3 or the back surface 21 of the workpiece 1 along the cutting start region.

Even when the insulating films 31 and 32 made of SiO ₂ , SiN, or the like are formed on the line to be cut of the substrate 15 as a stacked portion like the workpiece 1 according to the sixth embodiment described above, the workpiece is also processed. The object 1 can be cut with high accuracy.

  As mentioned above, although embodiment of this invention was described in detail, it cannot be overemphasized that this invention is not limited to the said embodiment.

  In the above-described embodiment, a case has been described in which a processing target having a substrate and a laminated portion provided on the surface of the substrate is irradiated with laser light to form a cutting start region. Then, after forming the cutting start region by irradiating the laser beam, a laminate may be provided on the surface of the substrate to form the workpiece.

  According to this laser processing method, the cutting origin region is formed inside the substrate before providing the laminated portion on the surface of the substrate, but the formation of the modified region by multiphoton absorption is local, and the substrate Since the laser beam is hardly absorbed on the surface of the substrate, the surface of the substrate does not melt. Therefore, similarly to the case where the modified region is not formed inside the substrate, the processing object can be formed by providing the laminated portion on the surface of the substrate. The workpiece formed in this manner can be cut by being divided by a relatively small force starting from the cutting start region formed inside the substrate for the same reason as in the above embodiment.

It is a top view of the processing target object during laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the II-II line of the workpiece shown in FIG. It is a top view of the processing target after laser processing by the laser processing method concerning this embodiment. It is sectional drawing along the IV-IV line of the workpiece shown in FIG. It is sectional drawing along the VV line of the workpiece shown in FIG. It is a top view of the processed object cut | disconnected by the laser processing method which concerns on this embodiment. It is a graph which shows the relationship between the electric field strength and the magnitude | size of a crack spot in the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 1st process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 2nd process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 3rd process of the laser processing method which concerns on this embodiment. It is sectional drawing of the process target object in the 4th process of the laser processing method which concerns on this embodiment. It is a figure showing the photograph of the section in the part of silicon wafer cut by the laser processing method concerning this embodiment. It is a graph which shows the relationship between the wavelength of the laser beam and the transmittance | permeability inside a silicon substrate in the laser processing method which concerns on this embodiment. It is a schematic block diagram of the laser processing apparatus which concerns on this embodiment. It is a flowchart for demonstrating the laser processing method which concerns on this embodiment. It is a figure which shows the processed object which concerns on a 1st Example, (a) shows the case where a modification area | region is formed in the back surface vicinity of a board | substrate, (b) shows a modification area | region in the surface vicinity of a board | substrate. The case where it formed is shown. It is a figure which shows the processed object which concerns on a 2nd Example, (a) shows the case where a modification area | region is formed in the back surface vicinity of a board | substrate, (b) shows a modification area | region in the surface vicinity of a board | substrate. The case where it formed is shown. It is a figure which shows the processed object which concerns on a 3rd Example, (a) shows the case where the modification area | region is formed in the surface vicinity of a board | substrate, and a lamination | stacking part, (b) shows the back surface vicinity of a board | substrate. The case where the modified region is formed is shown, and FIG. 9C shows the case where the modified region is formed near the surface of the substrate. It is a figure which shows the processing target object which concerns on a 4th Example. It is a figure which shows the processed object which concerns on a 5th Example, (a) shows the case where a modification area | region is formed in the surface vicinity of a board | substrate and the surface vicinity of a laminated part, (b) A case where a modified region is formed in the vicinity of the back surface and in the vicinity of the back surface of the laminated portion is shown. It is a figure which shows the processed object which concerns on a 5th Example, (a) shows the case where a modified area | region is formed in the surface vicinity of a board | substrate, and the back surface vicinity of a laminated part, (b) A case where a modified region is formed in the vicinity of the back surface and in the vicinity of the surface of the laminated portion is shown. FIG. 10 is an enlarged cross-sectional view illustrating a main part of a processing object according to a sixth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Processing target object, 3 ... Front surface, 5 ... Planned cutting line, 7 ... Modified area | region, 15 ... Board | substrate, 21 ... Back surface, L ... Laser beam, P ... Condensing point.

Claims (6)

  In a workpiece having a substrate and a laminated portion formed on the substrate via an oxide film, at least the inside of the substrate is irradiated with a laser beam with a condensing point aligned at least inside the substrate. Forming a modified region, and forming a cutting start region by a predetermined distance inside a laser beam incident surface of the workpiece along the planned cutting line of the workpiece by the modified region. A laser processing method.   2. The step of forming the cutting start region includes forming a modified region in the stacked unit by irradiating a laser beam with a focusing point in the stacked unit. Laser processing method.   3. The laser processing method according to claim 1, further comprising a step of cutting the object to be processed along the scheduled cutting line using the cutting start region as a starting point of cutting. 4.   The laser processing method according to claim 3, wherein, in the step of cutting the workpiece, a stress is applied to the workpiece by pressing a knife edge against a front surface or a back surface of the workpiece.   In a workpiece having a substrate and a laminated portion formed on the substrate via an oxide film, at least the inside of the substrate is irradiated with a laser beam with a condensing point aligned at least inside the substrate. Forming a modified region along a scheduled cutting line of the workpiece, and cutting the workpiece along the scheduled cutting line using the modified region as a starting point for cutting; Processing method. The laser processing method according to claim 1, wherein the substrate is a silicon substrate.

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