JP2008012542A - Laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining method capable of forming a first modified area closest to a first surface and a second modified area closest to a second surface when forming a plurality of rows of modified areas along a cut scheduled line in the thickness direction of an object to be machined. <P>SOLUTION: In the laser beam machining method, laser beams are applied to an object 1 to be machined with their condensed spot focused on the inside of the object to form modified areas M1-M6 forming cut-starting points along a cut scheduled line 5 of the object 1 in the thickness direction of the object 1. The modified area M6 closest to a rear side 21 out of the modified areas M1-M6 is formed with the position of the back side 21 as a reference, and the modified area M1 closest to a face side 11a is formed with the position of the face side 11a as a reference. Thus, even when the thickness of the object 1 is dispersed and changed, deviation of the position of the modified area M6 and the position of the modified area M1 attributable to the change in thickness of the object 1 is suppressed thereby. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser processing method for cutting a plate-like workpiece along a planned cutting line.

As a conventional laser processing method, by aligning a condensing point inside a plate-like workpiece and irradiating laser light, a modified region that becomes a starting point of cutting along the planned cutting line of the workpiece is obtained. A method of forming a plurality of rows in the thickness direction of a workpiece is known (for example, see Patent Document 1). In such a laser processing method, the position of the first surface where the laser beam is incident on the object to be processed is detected, and the position of the condensing point of the laser light is controlled in accordance with this detection signal, whereby the object to be processed is detected. In general, each modified region is formed at a predetermined distance from the first surface in the interior.
JP 2005-150537 A

  By the way, when a plurality of modified regions are formed in the heat direction of the workpiece and the workpieces are cut, the modified region closest to the first surface and the second surface facing the first surface In particular, a high precision is required in terms of the quality of the cut surface at the formation position of the modified region closest to. This is because, if these modified regions are not accurately formed at predetermined distances from the first surface and the second surface, respectively, for example, when the cut surface is cut in the thickness direction of the workpiece. This is because a so-called skirt phenomenon may occur in which the end portion is greatly deviated from the planned cutting line.

  However, in the laser processing method as described above, since the modified region is formed in a plurality of rows in the thickness direction of the processing object based only on the position of the first surface, the thickness of the processing object is, for example, a grinding lot. The second surface when there is a variation between a plurality of workpieces due to the difference between them or when a part of the workpiece is thick or thin (that is, when the thickness of the workpiece changes). There is a possibility that the modified region closest to the position cannot be accurately formed at a predetermined distance from the second surface.

  Therefore, the present invention provides a first modified region closest to the first surface and a second surface when the modified regions are formed in a plurality of rows in the thickness direction of the workpiece along the cutting line. It is an object of the present invention to provide a laser processing method capable of accurately forming the second modified region closest to.

  In order to achieve the above object, a laser processing method according to the present invention irradiates a laser beam with a condensing point inside a plate-like processing object, thereby along the planned cutting line of the processing object. A laser processing method for forming a plurality of modified regions as starting points for cutting in the thickness direction, wherein the first region of the modified regions is based on the position of the first surface on which laser light is incident on the workpiece. Forming the first modified region closest to the first surface and the position of the second surface facing the first surface in the object to be processed as a reference, the second surface of the modified region being the closest to the second surface Forming a near second modified region.

  According to this laser processing method, the first modified region closest to the first surface in the modified region is formed on the basis of the position of the first surface, and the second modified surface is the most in the modified surface. A near second modified region is formed with reference to the position of the second surface. As described above, since the positions of both the first surface and the second surface are used as a reference, even if the thickness of the workpiece is changed, the first surface of the modified region is changed to the first surface. The position of the first modified region closest to the position of the second modified region closest to the second surface can be prevented from shifting due to the change in the thickness of the workpiece. That is, when a plurality of modified regions are formed in the thickness direction of the workpiece along the planned cutting line, the first modified region closest to the first surface and the first closest to the second surface It becomes possible to form the two modified regions with high accuracy. As a result, the high quality of the cut surface can be maintained. Each modified region is formed by causing multi-photon absorption or other light absorption inside the processing object by irradiating the processing object with a laser beam with the focusing point aligned.

  Here, in the step of forming the first modified region, the first position information regarding the position of the first surface is acquired by detecting the reflected light reflected by the first surface, and the first In the step of forming the first modified region on the inner side by a predetermined distance from the first surface and forming the second modified region based on the positional information, the reflection reflected by the second surface By detecting light, second position information related to the position of the second surface is obtained, and based on the second position information, the second modified region is located on the inner side by a predetermined distance from the second surface. May form.

  Further, in the step of forming the first modified region, the first position information relating to the position of the first surface is obtained by detecting the reflected light reflected by the first surface, and the first modified region is obtained. In the step of forming the first modified region on the inner side by a predetermined distance from the first surface and forming the second modified region based on the position information, the first position information and the workpiece to be processed are formed. In some cases, the second modified region is formed on the inner side by a predetermined distance from the second surface based on the thickness information regarding the thickness.

  Further, in the step of forming the second modified region, second position information relating to the position of the second surface is obtained by detecting reflected light reflected by the second surface, and the second modified region is obtained. In the step of forming the second modified region on the inner side by a predetermined distance from the second surface based on the position information, and forming the first modified region, the second position information and the processing object The first modified region may be formed on the inner side by a predetermined distance from the first surface based on the thickness information regarding the thickness.

  In some cases, the object to be processed includes a semiconductor substrate, and the modified region includes a melt processing region.

  Moreover, it is preferable to include the process of cut | disconnecting a process target object along a scheduled cutting line by making a modification | reformation area | region into the starting point of cutting | disconnection. As a result, the workpiece can be accurately cut along the scheduled cutting line.

  According to the present invention, when a plurality of modified regions are formed in the thickness direction of the object to be processed along the planned cutting line, the first modified region closest to the first surface and the second surface It is possible to accurately form the second modified region closest to.

  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 of the present embodiment, a phenomenon called multiphoton absorption is used in order to form a modified region inside the workpiece. Therefore, first, a laser processing method for forming a modified region by multiphoton absorption will be described.

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 pulsed waves, the intensity of laser light is determined by the peak power density of the focus point of the laser beam (W / cm ^2), for example, the peak power density multiphoton at ^{1 × 10 8 (W / cm} 2) or more conditions Absorption occurs. The peak power density is obtained by (energy per one pulse of laser light at a 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 the laser processing method according to this embodiment using such multiphoton absorption will be described with reference to FIGS. As shown in FIG. 1, there is a planned cutting line 5 for cutting the workpiece 1 on the surface 3 of the wafer-like (plate-like) workpiece 1. The planned cutting line 5 is a virtual line extending linearly. In the laser processing method according to the present embodiment, as shown in FIG. 2, the modified region 7 is formed by irradiating the laser beam L with the focusing point P inside the processing object 1 under the condition that multiphoton absorption occurs. Form. In addition, the condensing point P is a location where the laser light L is condensed. Further, the planned cutting line 5 is not limited to a straight line but may be a curved line, or may be a line actually drawn on the workpiece 1 without being limited to a virtual line.

  Then, 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, in the direction of arrow A in FIG. 1). Thereby, as shown in FIGS. 3 to 5, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5, and this modified region 7 becomes the cutting start region 8. Here, the cutting starting point region 8 means a region that becomes a starting point of cutting (cracking) when the workpiece 1 is cut. The cutting starting point region 8 may be formed by continuously forming the modified region 7 or may be formed by intermittently forming the modified region 7.

  The laser processing method according to the present embodiment does not form the modified region 7 by causing the workpiece 1 to generate heat when the workpiece 1 absorbs the laser beam 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.

  If the cutting start region 8 is formed inside the processing target 1, cracks are likely to occur from the cutting start region 8, so that the processing target 1 is cut with a relatively small force as shown in FIG. 6. be able to. Therefore, the processing object 1 can be cut with high accuracy without causing unnecessary cracks on the surface 3 of the processing object 1.

  The following two types of cutting of the workpiece 1 starting from the cutting start region 8 are conceivable. First, after the cutting start region 8 is formed, when the artificial force is applied to the processing target 1, the processing target 1 is broken starting from the cutting start region 8 and the processing target 1 is cut. It is. This is, for example, cutting when the workpiece 1 is thick. The artificial force is applied by, for example, applying bending stress or shear stress to the workpiece 1 along the cutting start region 8 of the workpiece 1 or giving a temperature difference to the workpiece 1. It is to generate thermal stress. The other one forms the cutting start region 8 so that it is naturally cracked from the cutting start region 8 in the cross-sectional direction (thickness direction) of the processing target 1, and as a result, the processing target 1 is formed. This is the case when it is disconnected. For example, when the thickness of the workpiece 1 is small, the cutting start region 8 is formed by the one row of the modified region 7, and when the thickness of the workpiece 1 is large, for example. This is made possible by forming the cutting start region 8 by the modified region 7 formed in a plurality of rows in the thickness direction. Even in the case of natural cracking, cracks do not run on the surface 3 of the portion corresponding to the portion where the cutting start region 8 is not formed at the portion to be cut, and the portion where the cutting start region 8 is formed. Since only the corresponding part can be cleaved, the cleaving can be controlled well. In recent years, since the thickness of the workpiece 1 such as a silicon wafer tends to be thin, such a cleaving method with good controllability is very effective.

  In the laser processing method according to the present embodiment, the modified regions formed by multiphoton absorption include the following cases (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, the mechanism of cutting the workpiece by forming the crack region will be described with reference to FIGS. As shown in FIG. 8, the laser beam L is irradiated with the focusing point P inside the workpiece 1 under the condition that multiphoton absorption occurs, and a crack region 9 is formed inside along the planned cutting line. The crack region 9 is a region including one or more cracks. The crack region 9 thus formed becomes a cutting start region. As shown in FIG. 9, the crack further grows from the crack region 9 (that is, from the cutting start region), and the crack is formed on 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 broken and the workpiece 1 is cut. A crack that reaches the front surface 3 and the back surface 21 of the workpiece 1 may grow naturally, or may grow when a force is applied to the workpiece 1.

(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 processing region is a region once solidified after melting, a region in a molten state, a region in which the material is 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 referred to as 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, and 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 (semiconductor substrate). 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 11, 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-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.

  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. And 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. In this way, when the cutting start region is formed by the melt processing region inside the workpiece, unnecessary cracking off the cutting start region line is unlikely to occur during cleaving, so that cleaving control is facilitated. Incidentally, the melt processing region may include not only multiphoton absorption but also other absorption effects.

(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, and still more accurately.

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 preferred embodiment of the present invention will be described.
[First Embodiment]

  As shown in FIGS. 14 and 15, the workpiece 1 is formed on the surface (hereinafter also simply referred to as “surface”) 11 a of the silicon wafer 11 including the silicon wafer 11 and the plurality of functional elements 15. And a functional element layer 16 having a thickness of about 300 μm. The functional element 15 is, for example, a semiconductor operation layer formed by crystal growth, a light receiving element such as a photodiode, a light emitting element such as a laser diode, or a circuit element formed as a circuit, and the orientation flat 6 of the silicon wafer 11. Are formed in a matrix form in a direction parallel to and perpendicular to. Such a workpiece 1 is cut along a scheduled cutting line 5 (see a broken line in FIG. 14) set in a lattice shape so as to pass between adjacent functional elements 15, and is a discrete device or the like that is a microchip. It will be.

  When the workpiece 1 is cut, first, a protective tape is applied to the surface of the functional element layer 16, and the functional element layer 16 is protected by the protective tape, and then the workpiece 1 is placed on the stage of the laser processing apparatus. Secure the masking tape that is held. Subsequently, the laser beam is irradiated from the back surface (hereinafter also simply referred to as “back surface”) 21 of the workpiece 1 to the inside of the silicon wafer 11 under the condition that multi-photon absorption occurs by aligning the condensing point, and each cutting is scheduled. A modified region serving as a starting point for cutting is formed along the line 5 (backside incident processing). Here, six rows of modified regions are formed in the thickness direction of the workpiece 1 along the respective scheduled cutting lines 5. Subsequently, the protective tape fixed to the stage is separated from the workpiece 1. Then, an expand tape is attached to the back surface 21 of the silicon wafer 11, and the protective tape is peeled off from the surface of the functional element layer 16, and then the expand tape is expanded. As a result, the workpiece 1 is accurately cut for each functional element 15 along the scheduled cutting line 5 using the modified region as a starting point of cutting, and the plurality of semiconductor chips are separated from each other. Note that the modified region may include a crack region or the like in addition to the melt processing region.

  By the way, the thickness of the workpiece 1 varies among a plurality of workpieces 1 due to differences in grinding lots, for example, or a portion of the workpiece 1 becomes thick or thin due to unevenness during grinding. In some cases (when the thickness of the workpiece 1 changes). Specifically, in the processing object 1 having a thickness of 300 μm, the thickness may vary between the plurality of processing objects 1 by ± 10 μm or more. May vary by more than ± 5μm.

  However, in a general autofocus function, the thickness of the workpiece 1 is regarded as constant, and only the amount of displacement of the back surface 21 that is the laser light incident surface is measured, so that the condensing point position of the laser light is set to the back surface 21. To a predetermined position. Therefore, conventionally, as shown in FIG. 20, the modified region closest to the surface 11 a in the formed modified region M is formed so as to protrude from the processed object 1 in a portion where the processed object 1 is thick. In a portion where the processing object 1 is thin, the processing object 1 may be formed near the back surface 21 without reaching the deep position of the processing object 1.

  Therefore, in the laser processing method of the present embodiment, the modified region formed in a plurality of rows in the thickness direction along the planned cutting line 5 of the workpiece 1 is closest to the back surface (first surface) 21. The first modified region is formed with reference to the position of the back surface 21, and the second modified region closest to the front surface (second surface) 11a is formed with reference to the position of the front surface 11a. Hereinafter, the formation of the modified region will be described in more detail.

[Height set]
First, in a state where, for example, a reticle image projected onto the back surface 21 of the workpiece 1 is in focus, the distance measuring laser beam is irradiated, and the reflected light of the distance measuring laser beam reflected on the back surface 21 is detected as a voltage value. Then, the detected voltage value is stored in memory (S1 in FIG. 16).

[trace]
Subsequently, while the reflected light of the distance measuring laser light irradiated with the distance measuring laser light and reflected by the back surface 21 is detected as a voltage value, the line 5 to be cut is maintained so that this voltage value maintains the voltage value by the height set. The displacement of the back surface 21 along the scheduled cutting line 5 is acquired, and the displacement of the back surface 21 is stored as back surface position information (first position information). That is, the back surface position information is obtained as a relative distance in the thickness direction from the back surface 21 to the position of the back surface 21 that has been height set.
Back surface position information = displacement of the back surface 21
= Relative distance in the thickness direction from the back surface 21 to the position of the back surface 21 set at height

  At this time, the distance measuring laser beam is scanned, and at the same time, the thickness (thickness information) of the workpiece 1 is optically measured and calculated along the planned cutting line 5 by the thickness measuring instrument. Specifically, as shown in FIG. 17A, along the planned cutting line 5, the reflected light L1 from the back surface 21 and the reflected light L2 that passes through the inside of the workpiece 1 and is reflected by the front surface 11a. The line sensor 50 receives light. Then, the distance from the front surface 11a to the back surface 21, that is, the thickness of the workpiece 1 is calculated based on the light receiving positions of the reflected lights L1 and L2 in the line sensor 50 and the refractive index of the workpiece 1 obtained in advance. To do.

Then, the above-described back surface position information is added to the calculated thickness of the workpiece 1 and stored as surface position information (second position information) along the scheduled cutting line 5. That is, the front surface position information is obtained as a relative distance in the thickness direction from the front surface 11a to the height 21 back surface position (S2 in FIG. 16).
Front surface position information = Back surface position information + Thickness of workpiece 1
= Relative distance in the thickness direction from the front surface 11a to the position of the back surface 21 that has been height set

  Here, the measurement system for the back surface 21 and the measurement system for the thickness of the workpiece 1 are constituted by two axes. Further, the displacement of the back surface 21 and the thickness of the workpiece 1 are acquired in association with the coordinates in the direction along the planned cutting line 5. Therefore, the measurement system of the back surface 21 and the thickness measurement system of the workpiece 1 are configured with two axes, and the back surface position information and the surface position information are synthesized on the coordinates from the distance D1 between the measurement systems, and the back surface position Information and surface position information are required with high accuracy.

  Or as shown in FIG.17 (b), the thickness of the workpiece 1 may be measured by making the reflected light L3 from the back surface 21 and the reflected light L4 from the surface 11a interfere. Even in this case, the measurement system of the back surface 21 and the thickness measurement system of the workpiece 1 are configured by two axes, and the displacement of the back surface 21 and the thickness of the workpiece 1 are in the cutting line 5. Acquired in association with the coordinates of the direction along. Therefore, the back surface position information and the front surface position information are synthesized on the coordinates from the distance D2 between the measurement systems, and the back surface position information and the front surface position information are obtained with high accuracy.

[Formation of modified region]
Subsequently, as shown in FIG. 18A, inside the workpiece 1, a laser beam is irradiated with a focusing point aligned to the inner side (upper side in the drawing) by 10 μm from the surface 11 a, and along the planned cutting line 5. Scan. Specifically, inside the workpiece 1, the focal point is moved to the position on the back surface 21 side by 10 μm from the surface position information, and laser light is emitted at an output of 0.72 W, and the stored surface position information is displayed. The scanning is performed along the planned cutting line 5 while being reproduced by a position adjusting element (actuator using a piezo element in the present embodiment) and controlling the focal point position. Thereby, the modified region (second modified layer) M1 is formed along the planned cutting line 5 by 10 μm inside from the surface 11a with reference to the surface 11a (S3 in FIG. 16). . Specifically, the modified region M1 along the planned cutting line 5 is formed at a position on the back surface 21 side by 10 μm from the surface position information.

  Subsequently, as shown in FIG. 18 (b), within the workpiece 1, a laser beam is irradiated with a condensing point on the inner side (upper side in the drawing) by 25 μm from the surface 11 a, and along the planned cutting line 5. Scan. Specifically, inside the workpiece 1, the condensing point is moved to the position on the back surface 21 side by 25 μm from the surface position information, and laser light is emitted at an output of 1.20 W. Scanning along the planned cutting line 5 while reproducing the position by the piezo element and controlling the focal point position. As a result, the modified region M2 is formed along the planned cutting line 5 inward by 25 μm from the surface 11a with respect to the surface 11a (S4 in FIG. 16). Specifically, the modified region M2 along the planned cutting line 5 is formed at a position on the back surface 21 side by 25 μm from the surface position information.

  Subsequently, inside the workpiece 1, the laser beam is irradiated with the focusing point on the inner side (upper side in the drawing) of 35 μm from the surface 11 a, and scanning is performed along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved to a position on the back surface 21 side by 35 μm from the surface position information, and laser light is irradiated at an output of 1.20 W, and the stored surface position information is displayed. Scanning along the planned cutting line 5 while reproducing the position by the piezo element and controlling the focal point position. Thereby, the modified region M3 is formed along the planned cutting line 5 by 35 μm inside from the surface 11a with reference to the surface 11a (S5 in FIG. 16). Specifically, the modified region M3 along the planned cutting line 5 is formed at a position on the back surface 21 side by 35 μm from the surface position information.

  Subsequently, inside the workpiece 1, the laser beam is irradiated with the focusing point on the inner side (upper side in the drawing) of 45 μm from the surface 11 a, and scanning is performed along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved by 45 μm from the surface position information to the position on the back surface 21 side, the laser beam is irradiated at an output of 1.20 W, and the stored surface position information is displayed. Scanning along the planned cutting line 5 while reproducing the position by the piezo element and controlling the focal point position. As a result, the modified region M4 is formed along the planned cutting line 5 within 45 μm from the surface 11a with respect to the surface 11a (S6 in FIG. 16). Specifically, the modified region M4 along the planned cutting line 5 is formed at a position on the back surface 21 side by 45 μm from the surface position information.

  Subsequently, as shown in FIG. 18 (c), within the workpiece 1, a laser beam is irradiated with a focusing point on the inner side (lower side in the drawing) by 25 μm from the back surface 21, and the line 5 to be cut is irradiated. Scan along. Specifically, inside the processing object 1, the condensing point is moved to the position on the front surface 11a side by 25 μm from the back surface position information, and laser light is emitted at an output of 1.20 W. Scanning along the planned cutting line 5 while reproducing the position by the piezo element and controlling the focal point position. Accordingly, the modified region M5 is formed along the planned cutting line 5 on the inner side by 25 μm from the rear surface 21 with respect to the rear surface 21 (S7 in FIG. 16). Specifically, the modified region M5 along the planned cutting line 5 is formed at a position on the front surface 11a side by 25 μm from the back surface position information.

  Finally, within the object 1 to be processed, the laser beam is irradiated with the condensing point aligned with the inner side (lower side in the drawing) by 15 μm from the back surface 21, and scanning is performed along the planned cutting line 5. Specifically, inside the workpiece 1, the focal point is moved to the position on the front surface 11 a side by 10 μm from the back surface position information, and laser light is emitted at an output of 0.68 W, and the stored back surface position information is stored. It reproduces with a piezo element and scans along the scheduled cutting line 5 while controlling the focal point position. Thereby, the modified region (second modified layer) M6 is formed along the planned cutting line 5 by 15 μm inside from the back surface 21 with reference to the back surface 21 (S8 in FIG. 16). Specifically, the modified region M6 along the scheduled cutting line 5 is formed at a position on the front surface 11a side by 15 μm from the back surface position information.

  Here, among the modified regions M1 to M6 formed in a plurality of rows in the thickness direction inside the workpiece 1, the modified regions M5 and M6 are modified regions for forming a half cut on the upper surface. This is called a so-called half cut SD. This half cut ensures separation by expanding the expanded tape, and therefore the half cut SD is a very important factor. Of the modified regions M1 to M6 formed in a plurality of rows, the modified region M1 closest to the surface 11a is a modified region that particularly affects the quality of the cut surface after cutting, and is referred to as so-called quality SD. The The quality SD is for cutting the functional element layer 16 with high accuracy, and is a very important factor for maintaining the quality when cutting the workpiece 1.

  Therefore, in the present embodiment, as described above, inside the workpiece 1, the modified regions M <b> 5 and M <b> 6 are cut along the planned cutting line 5 inwardly by a predetermined distance from the back surface 21 with respect to the back surface 21. At the same time, the modified region M1 is formed along the planned cutting line 5 inwardly by a predetermined distance from the surface 11a with respect to the surface 11a. As described above, since the positions of both the back surface 21 and the front surface 11a are used as references, even if the thickness of the workpiece 1 varies and changes, the positions of the modified regions M5 and M6 and the modified regions M6 are changed. It is possible to prevent the position from being shifted due to a change in the thickness of the workpiece 1. Therefore, according to the present embodiment, when a plurality of modified regions are formed in the thickness direction of the workpiece 1 along the scheduled cutting line 5, the modified regions M6 and M6 that are closest to the back surface 21 are formed. It is possible to accurately form the modified region M5 adjacent to and the modified region M1 closest to the surface 11a.

  Furthermore, in this embodiment, since the modified regions M5 and M6 are formed with high accuracy, the following effects can be obtained. That is, since the modified regions M5 and M6 are too close to the back surface 21, the half cut meanders and the quality is prevented from deteriorating. Furthermore, since the modified regions M5 and M6 are too far from the back surface 21, the elongation of cracks generated from the modified regions M5 and M6 becomes insufficient, and it is possible to prevent the half-cut from being formed well.

  Moreover, since the modified region M1 is formed with high accuracy as described above, the following effects are obtained. That is, since the modified region M1 is too close to the surface 11a, the irradiated laser beam protrudes from the workpiece 1 and a hole is made in the surface 11a, so that the bending strength of the workpiece 1 is weakened. Suppress. Furthermore, since the modified region M1 is too far from the surface 11a, the so-called skirt phenomenon in which the end on the surface 11a side greatly deviates from the planned cutting line 5 on the cut surface is prevented. In the present embodiment, the functional element 15 is formed on the surface 11a, which is the surface opposite to the surface on which the laser light is incident, for back-surface incident processing, and thus the above effect of preventing the occurrence of the skirt phenomenon. Is particularly prominent.

  Further, according to the present embodiment, it is possible to correct the shift of the position of the modified region due to the thickness variation or unevenness of the workpiece 1, and to the distance from the front surface 11 a and the distance from the back surface 21. It becomes possible to perform multi-stage processing that optimizes the quality of the modified region that depends on it and optimizes the cut surface quality after cutting.

  The thickness of the workpiece 1 may be measured with a contact-type thickness measuring instrument. In this case, there is a foreign object between the workpiece 1 and the stage, or the expanded tape When pasted, air may be mixed between the expanded tape and the workpiece 1, and the position of the workpiece 1 that is in contact does not necessarily indicate the thickness of the workpiece 1. Therefore, in this embodiment, a measuring instrument using a transmission type laser is used, and the thickness of the workpiece 1 is measured with high accuracy.

Incidentally, in the present embodiment, as described above, the modified regions M2, M3, and M4 are formed on the basis of the surface 11a. However, the modified regions M2, M3 are not limited to the present embodiment. , M4 may be formed using the back surface 21 as a reference.
[Second Embodiment]

  Next, a laser processing method according to the second embodiment of the present invention will be described. The laser processing method according to the second embodiment is different from the laser processing method according to the first embodiment in that an autofocus function is used as shown in FIG. This is a point where the reflected light L5 on the back surface 21 and the reflected light L6 on the front surface 11a are detected using the optical system.

Specifically, in the laser processing method according to the present embodiment, the reflected light L5 reflected by the back surface 21 and the reflected light L6 transmitted through the workpiece 1 and reflected by the front surface 11a are detected, respectively, and the displacement of the front surface 11a and the back surface are detected. By directly acquiring the displacements 21, the back surface position information and the front surface position information are directly obtained.
Back surface position information = displacement of the back surface 21
= Relative distance in the thickness direction from the back surface 21 to the position of the back surface 21 that has been height set Surface position information = displacement of the surface 11a
= Relative distance in the thickness direction from the front surface 11a to the position of the back surface 21 that has been height set

  As described above, even in the laser processing method of the present embodiment, the same effects as those of the above-described embodiment, that is, the positions of the modified regions M5 and M6 even if the thickness of the workpiece 1 varies and changes. And the effect of suppressing that the position of the modification | reformation area | region M6 shifts | deviates due to the change of the thickness of the workpiece 1 is produced. As a result, when a plurality of modified regions are formed in the thickness direction of the workpiece 1 along the planned cutting line 5, the modified region M6 closest to the back surface 21 and the modified region adjacent to the modified region M6. M5 and the modified region M1 closest to the surface 11a can be formed with high accuracy.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  For example, in the above-described embodiment, the so-called trace processing is performed in which the modified region is formed by scanning the laser beam after measuring the displacement or the like of the surface 11 a of the workpiece 1. So-called real-time processing for forming a quality region may be used.

  Further, when irradiating the distance measuring laser light that passes through the object to be processed and the distance measuring laser light that is reflected without being transmitted, a plurality of laser light sources may be used, and the wavelength is changed from one laser light source. It may be irradiated.

  Moreover, in the said embodiment, although it is set as the back surface incident process which injects a laser beam from the back surface 21 side which opposes the surface 11a in which the functional element 15 was formed, of course, it is a process which injects a laser beam from the surface 11a side. good.

  Moreover, although the processing target object 1 provided with the silicon wafer 11 is used as the processing target object, it has crystallinity such as a semiconductor compound material such as gallium arsenide, a piezoelectric material, and sapphire, for example. It may be a material.

It is a top view of the processing target object during the laser processing by the laser processing device 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 device 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 apparatus 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 apparatus which concerns on this embodiment. It is sectional drawing of the process target object in the 1st process of the laser processing apparatus which concerns on this embodiment. It is sectional drawing of the process target object in the 2nd process of the laser processing apparatus which concerns on this embodiment. It is sectional drawing of the process target object in the 3rd process of the laser processing apparatus which concerns on this embodiment. It is sectional drawing of the processing target object in the 4th process of the laser processing apparatus which concerns on this embodiment. It is a figure showing the photograph of the cross section in a part of silicon wafer cut | disconnected by the laser processing apparatus which concerns on this embodiment. It is a graph which shows the relationship between the wavelength of the laser beam in the laser processing apparatus which concerns on this embodiment, and the transmittance | permeability inside a silicon substrate. It is a front view which shows the process target object used as the object of the laser processing method which concerns on 1st Embodiment of this invention. It is a fragmentary sectional view in alignment with the XV-XV line | wire in FIG. It is a flowchart which shows the laser processing method which concerns on 1st Embodiment of this invention. It is a figure for demonstrating calculation of the back surface position information and surface position information in the laser processing method shown in FIG. It is a fragmentary sectional view along the XVIII-XVIII line in FIG. 14 for demonstrating the laser processing method shown in FIG. It is a figure for demonstrating calculation of the back surface position information and surface position information in the laser processing method which concerns on 2nd Embodiment of this invention. It is the fragmentary sectional view in alignment with the XVIII-XVIII line in FIG. 14 in the laser processing method by the conventional autofocus function.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Processing target object, 5 ... Planned cutting line, 11a ... Front surface (2nd surface), 21 ... Back surface (1st surface), L ... Laser beam, L1, L3, L5 ... Reflected light (1st surface) , Reflected light (reflected light reflected by the second surface), M1, M2, M3, M4, M5, M6 ... modified region, P ... condensing point .

Claims (6)

By aligning a condensing point inside the plate-like workpiece and irradiating the laser beam, a modified region serving as a starting point of cutting along the planned cutting line of the workpiece is set to the thickness of the workpiece. A laser processing method for forming a plurality of rows in the vertical direction,
Forming a first modified region closest to the first surface among the modified regions with reference to a position of a first surface on which laser light is incident on the workpiece;
Forming a second modified region closest to the second surface among the modified regions, based on the position of the second surface facing the first surface in the workpiece. A laser processing method comprising: In the step of forming the first modified region, first position information relating to the position of the first surface is acquired by detecting reflected light reflected by the first surface, and the first Based on the positional information, the first modified region is formed on the inner side by a predetermined distance from the first surface,
In the step of forming the second modified region, second position information regarding the position of the second surface is obtained by detecting reflected light reflected by the second surface, and the second 2. The laser processing method according to claim 1, wherein the second modified region is formed on the inner side by a predetermined distance from the second surface based on the position information. In the step of forming the first modified region, first position information relating to the position of the first surface is acquired by detecting reflected light reflected by the first surface, and the first Based on the positional information, the first modified region is formed on the inner side by a predetermined distance from the first surface,
In the step of forming the second modified region, on the basis of the first position information and the thickness information related to the thickness of the workpiece, the inner side is a predetermined distance from the second surface. The laser processing method according to claim 1, wherein a second modified region is formed. In the step of forming the second modified region, second position information regarding the position of the second surface is obtained by detecting reflected light reflected by the second surface, and the second Based on the positional information, the second modified region is formed on the inner side by a predetermined distance from the second surface,
In the step of forming the first modified region, on the basis of the second position information and the thickness information related to the thickness of the workpiece, the inner side is a predetermined distance from the first surface. The laser processing method according to claim 1, wherein the first modified region is formed.   The laser processing method according to claim 1, wherein the object to be processed includes a semiconductor substrate, and the modified region includes a melt processing region. The laser processing method according to any one of claims 1 to 5, further comprising a step of cutting the object to be processed along the scheduled cutting line with the modified region as a starting point for cutting.

Images