JP2009113068A - Laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect the position of an edge of a workpiece with satisfactory accuracy. <P>SOLUTION: A voltage signal is inputted to a drive unit to drive a lens along an optical axis direction by moving a laser beam for AF along a direction complying with an edge detection line 15a so as to step over the edge x1 of a workpiece 1 while irradiating the workpiece 1 with the laser beam via the lens and to determine a displacement signal by photodetecting the reflected light of the laser beam for AF and to maintain the displacement signal constant. Then, the position of the edge x1 is detected based on a change in the voltage signal. Here, when the laser beam for AF runs on the workpiece 1 from the upside of a tape 211, a reflection surface is a laser beam irradiation surface 3 from the tape surface 211a and, therefore, the position of the reflection surface changes drastically, and consequently, the voltage signal changes significantly. Also, the displacement signal is normalized by the total quantity of the light of the photodetected reflected light as the relative value of the total quantity of the light of the reflected light, and therefore, the voltage signal is eventually unaffected by the quantity of the light of the reflected light. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser processing method for cutting a workpiece.

As a conventional laser processing method, a region for cutting a processing target is formed along a planned cutting line by irradiating a plate-shaped processing target with a condensing point and irradiating a first laser beam. In such a laser processing method, the second laser beam is applied so as to straddle the edge of the workpiece while irradiating the second laser beam. The reflected light of the second laser beam is received along with the movement in one direction intersecting the thickness direction of the workpiece. And based on the change of the total light quantity of the reflected light of a 2nd laser beam, the position of the edge part of a workpiece is detected.
JP 2007-167918 A

  Here, in the laser processing method as described above, for example, a thin film such as an oxide film or a nitride film may be formed on the laser light irradiation surface of the workpiece. The transmittance of the thin film depends on the wavelength of the laser beam and the film pressure of the thin film, and is known to change periodically with respect to the film thickness. When the film thickness becomes small, the reflectance of the second laser beam on the laser beam irradiation surface is decreased. Therefore, in this case, the difference between the total amount of reflected light reflected from the laser light irradiation surface and the total amount of reflected light reflected from other than the workpiece is reduced, and the position of the edge of the workpiece is accurately detected. There is a risk that it cannot be done.

  Then, this invention makes it a subject to provide the laser processing method which can detect the position of the edge of a process target object accurately.

  In order to solve the above-described problem, a laser processing method according to the present invention includes a region for cutting a processing target by irradiating a plate-shaped processing target with a first laser beam with a focusing point aligned. Is formed along the planned cutting line, and the second laser beam is applied to the workpiece so as to straddle the edge of the workpiece while irradiating the second laser beam through the lens. A displacement signal related to the displacement of the reflecting surface reflected by the second laser beam is received by receiving the reflected light of the second laser beam in conjunction with moving in one direction intersecting the thickness direction of the first laser beam. Normalizing with the total amount of reflected light and inputting the drive signal to the drive means so that the obtained displacement signal is constant, and driving the lens along the optical axis direction, and the change of the displacement signal Detecting the position of the edge based on And it said to contain a.

  According to this laser processing method, the irradiated second laser light is moved in one direction so as to straddle the edge of the object to be processed, and at the same time, the reflected light of the second laser light is received. A displacement signal is obtained, and the lens is driven by the driving means along the optical axis direction so that the displacement signal becomes constant. Accordingly, when the second laser light is moved in one direction, the lens is driven so as to follow the displacement of the reflecting surface on which the second laser light is reflected outside and on the workpiece. It will be. Here, for example, when the second laser beam rides on the object to be processed, the position of the reflecting surface changes greatly, so that the drive signal input to the drive means changes greatly. Furthermore, since the displacement signal is normalized by the total amount of reflected light received and obtained as a relative value of the total amount of reflected light, the drive signal is sent to the drive means even when the total amount of reflected light is small. The lens is driven so as to follow the displacement of the reflecting surface. That is, the drive signal does not depend on the amount of reflected light. Therefore, by detecting the position of the edge of the workpiece based on the change in the drive signal, the position of the edge can be accurately detected even when the total amount of reflected light is small.

  In addition, when the second laser light is moved in one direction, it is preferable that the moving speed of the second laser light in a predetermined region including the edge portion is slower than the moving speed in a region other than the predetermined region. In this case, in the predetermined area including the edge, the change in the drive signal is detected finely, and the position of the edge of the workpiece can be detected with higher accuracy.

  Moreover, it is preferable that the area | region for cut | disconnecting a workpiece is a modified area | region used as the starting point of a cutting | disconnection. Thereby, a process target object can be cut | disconnected accurately.

  Further, in order to achieve the above-described effects, the lens focus is preferably adjusted to the laser light irradiation surface of the workpiece, and the drive signal input to the drive means in this state is used as a reference. When detecting the position of the edge including the step of obtaining it as a drive signal, there is a case where the position in one direction of the optical axis when the drive signal becomes the reference drive signal is detected as the position of the edge. .

  Further, when forming a region for cutting the workpiece by irradiating the first laser beam along the planned cutting line, from a position away from the workpiece to a position on the workpiece. In addition to moving the lens along the planned cutting line, the driving of the lens by the driving means is stopped until it is determined that the optical axis of the lens is at the detected edge position. After it is determined that the axis is at the detected edge position, it is preferable to drive the lens along the optical axis direction by inputting a drive signal to the drive means so that the displacement signal becomes constant. . Further, when forming the region for cutting the workpiece by irradiating the first laser beam along the planned cutting line, from the position on the workpiece to a position away from the workpiece. In addition to moving the lens along the planned cutting line, the driving means is driven so that the displacement signal is constant until it is determined that the optical axis of the lens is at the detected edge position. It is preferable to stop driving the lens by the driving means after inputting a signal to drive the lens along the optical axis direction and determining that the optical axis of the lens is at the detected edge position. . In these cases, the lens is suitably followed by the laser light irradiation surface, and the region for cutting the workpiece can be accurately formed along the planned cutting line.

  Further, when forming a region for cutting the workpiece by irradiating the first laser beam along the planned cutting line, from a position away from the workpiece to a position on the workpiece. In addition to moving the lens along the planned cutting line, the irradiation of the first laser beam is stopped until it is determined that the optical axis of the lens is at the detected edge position. After it is determined that the optical axis is at the detected edge position, it is preferable to form the region along the planned cutting line by irradiating the first laser beam. Further, when forming the region for cutting the workpiece by irradiating the first laser beam along the planned cutting line, from the position on the workpiece to a position away from the workpiece. In addition to moving the lens along the planned cutting line, the region is cut by irradiating the first laser beam until it is determined that the optical axis of the lens is at the detected edge position. It is preferable to stop the irradiation of the first laser light after it is determined that the optical axis of the lens is located at the detected edge position along the planned line. In these cases, irradiation of the first laser beam is started and stopped based on the detected position of the edge, and a region for cutting the workpiece is formed more accurately along the planned cutting line. can do. Note that “stopping the irradiation of the first laser beam” not only means stopping the oscillation of the first laser beam or physically blocking the first laser beam with a shutter or the like, for example. For example, the laser intensity is set to be less than a processing threshold value (a lower limit value of the laser intensity sufficient to form a region for cutting an object to be processed). Including cases.

  According to the present invention, it is possible to accurately detect the position of the edge of the workpiece.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent element in each figure, and the overlapping description is abbreviate | omitted.

  In the laser processing method according to the present embodiment, a modified region is formed on the processing object along the planned cutting line by irradiating the first laser beam with the focusing point on the plate-shaped processing object. To do. First, the formation of the modified region in the laser processing method according to this embodiment will be described with reference to FIGS.

  As shown in FIG. 1, the laser processing apparatus 100 is arranged to change the direction of the optical axis of the laser light L by 90 ° and the laser light source 101 that pulsates the laser light (first laser light) L. A dichroic mirror 103 and a condensing lens 105 for condensing the laser light L are provided. The laser processing apparatus 100 also includes a support 107 for supporting the workpiece 1 irradiated with the laser light L collected by the condensing lens 105, and the support 107 in the X, Y, and Z axis directions. A stage 111 for moving the light source, a laser light source control unit 102 for controlling the laser light source 101 to adjust the output and pulse width of the laser light L, and a stage control unit 115 for controlling the movement of the stage 111. I have.

  In this laser processing apparatus 100, the laser light L emitted from the laser light source 101 has its optical axis changed by 90 ° by the dichroic mirror 103, and the inside of the processing object 1 placed on the support base 107. The light is condensed by the condensing lens 105. At the same time, the stage 111 is moved, and the workpiece 1 is moved relative to the laser beam L along the planned cutting line 5. As a result, a modified region serving as a starting point for cutting is formed on the workpiece 1 along the planned cutting line 5. Hereinafter, the modified region will be described in detail.

  As shown in FIG. 2, a scheduled cutting line 5 for cutting the workpiece 1 is set on the plate-like workpiece 1. The planned cutting line 5 is a virtual line extending linearly. When forming a modified region inside the workpiece 1, as shown in FIG. 3, the laser beam L is projected along the planned cutting line 5 in a state where the focused point P is aligned with the inside of the workpiece 1. It moves relatively (that is, in the direction of arrow A in FIG. 2). Thereby, as shown in FIGS. 4 to 6, the modified region 7 is formed inside the workpiece 1 along the planned cutting line 5, and the modified region 7 formed along the planned cutting line 5 is formed. It becomes the cutting start area 8.

  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 surface 3 of the workpiece 1 without being limited to a virtual line. In addition, the modified region 7 may be formed continuously or intermittently. Moreover, the modified area | region 7 should just be formed in the inside of the workpiece 1 at least. In addition, a crack may be formed starting from the modified region 7, and the crack and modified region 7 may be exposed on the outer surface (front surface, back surface, or outer peripheral surface) of the workpiece 1.

  Incidentally, here, the laser beam L passes through the workpiece 1 and is particularly absorbed in the vicinity of the condensing point inside the workpiece 1, whereby a modified region 7 is formed in the workpiece 1. (Ie, internal absorption laser processing). 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 general, when a removed portion such as a hole or a groove is formed by being melted and removed from the front surface 3 (surface absorption laser processing), the processing region gradually proceeds from the front surface 3 side to the back surface side.

  By the way, the modified region formed by the laser processing method and the laser processing apparatus according to the present embodiment refers to a region in which the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings. . For example, there are (1) a melt treatment region, (2) a crack region, a dielectric breakdown region, and (3) a refractive index change region, and there are regions where these are mixed.

The modified region in the laser processing method and laser processing apparatus according to the present embodiment is formed by a phenomenon of local absorption of laser light or multiphoton absorption. The multiphoton absorption, since the energy hv of photons than the band gap E _G of absorption of the material is small becomes optically transparent, but a condition under which absorption occurs in the material is hv> E _G, optically transparent But, when a very large intensity of the laser beam L nhν> of _{E G} condition (n = 2,3,4, ···) refers to a phenomenon in which absorption occurs in the material. 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.

Also, D. Du, X. Liu, G. Korn, J. Squier, and G. Mourou, “Laser Induced Breakdown by Impact Ionization in SiO ₂ with Pulse Widths from 7ns to 150fs”, Appl Phys Lett64 (23), Jun As described in .6, 1994, a modified region formed by using an ultrashort pulse laser beam having a pulse width of several picoseconds to femtoseconds may be used.

(1) When the modified region includes 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 the laser beam L is performed under the conditions of the above and the pulse width of 1 μs or less. As a result, the laser beam L is absorbed in the vicinity of the condensing point, and the inside of the processing object is locally heated, and a melting treatment region is formed inside the processing object by this heating.

  The melt treatment region is a region once solidified after being melted, a region in a molten state, a region in which the material is resolidified 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.

  FIG. 7 is a view showing a photograph of a cross section of a part of a silicon wafer (semiconductor substrate) irradiated with laser light. As shown in FIG. 7, a melt processing region 13 is formed inside the semiconductor substrate 11.

  It will be described that the melt processing region 13 is formed inside a material that is transparent to the wavelength of the incident laser beam. FIG. 8 is a diagram 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 1064 nm of the Nd: YAG laser, it can be seen that the laser light L is transmitted by 80% or more inside the silicon substrate. Since the thickness of the semiconductor substrate 11 shown in FIG. 7 is 350 μm, the melt processing region 13 is formed near the center of the semiconductor substrate 11, that is, at a portion of 175 μm from the surface. The transmittance in this case is 90% or more with reference to a silicon wafer having a thickness of 200 μm, so that the laser light L is hardly absorbed inside the semiconductor substrate 11 and is almost transmitted. However, by condensing the laser beam L inside the silicon wafer under the conditions of 1 × 10 ⁸ (W / cm ² ) or more and a pulse width of 1 μs or less, the laser beam is absorbed locally at and near the focal point. Then, the melt processing region 13 is formed inside the semiconductor substrate 11.

  Note that cracks may occur in the silicon wafer starting from the melt processing region. In some cases, cracks are included in the melt treatment region. In this case, the cracks are formed over the entire surface in the melt treatment region, or are formed in only a part or a plurality of parts. Sometimes. Furthermore, the crack may grow naturally or may grow by applying a force to the silicon wafer. When the crack grows naturally from the melt-processed area, either the case where the melt-processed area grows from the melted state or the case where the melt-processed area grows when re-solidified from the melted state There is also. However, in both cases, the melt processing region is formed inside the silicon wafer, and the melt processing region is formed inside the cut surface as shown in FIG.

(2) When the modified region includes a crack region The focusing point is set inside a workpiece (for example, a piezoelectric material made of glass or LiTaO ₃ ), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / The laser light L is irradiated under the conditions of cm ² ) or more and a pulse width of 1 μs or less. The magnitude of the pulse width is a condition that the laser beam L is absorbed inside the workpiece and a crack region is formed. As a result, a phenomenon called optical damage occurs inside the workpiece. This optical damage induces thermal strain inside the workpiece, thereby forming a crack region containing one or more cracks inside the workpiece. It can be said that the crack region is a dielectric breakdown region.

FIG. 9 is a diagram showing the experimental results of the relationship between the electric field strength and the crack size. The horizontal axis represents the peak power density. Since the laser beam L is a pulse laser beam, the electric field strength is represented by the peak power density. The vertical axis indicates the size of a crack portion (crack spot) formed inside the workpiece by one pulse of laser light L. 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.

(3) When the modified region includes a refractive index changing region The focusing point is set inside the object to be processed (for example, glass), and the electric field strength at the focusing point is 1 × 10 ⁸ (W / cm ² ) or more. In addition, the laser beam L is irradiated under the condition that the pulse width is 1 ns or less. Thus, when the laser beam L is absorbed inside the object to be processed in a state where the pulse width is extremely short, the energy is not converted into thermal energy, and the ion valence change, crystallization occurs inside the object to be processed. Alternatively, a permanent structural change such as a polarization orientation is induced, and a refractive index change region is formed.

  Note that the modified region includes the melt-processed region, the dielectric breakdown region, the refractive index change region, etc., and the mixed region thereof, and the density of the modified region in the material is compared with the density of the non-modified region. It may be a changed region or a region where lattice defects are formed. These can be collectively referred to as a high-density transition region.

  In addition, the area where the density of the melt-processed area, the refractive index changing area, the modified area is changed compared to the density of the non-modified area, and the area where lattice defects are formed are further divided into these areas and the modified area. In some cases, cracks (cracks, microcracks) are included in the interface with the non-modified region. The included crack may be formed over the entire surface of the modified region, or may be formed in only a part or a plurality of parts.

  Incidentally, if the modified region is formed as follows in consideration of the crystal structure of the object to be processed and its cleavage property, the object to be processed can be accurately cut.

That is, in the case of a substrate made of a single crystal semiconductor having a diamond structure such as silicon, the modified region is formed in a direction along the (111) plane (first cleavage plane) or the (110) plane (second cleavage plane). Is preferred. Further, 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 modified region in the direction along the (110) plane. Furthermore, 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 modified region in a direction along the (M plane).

  In addition, the orientation flat on the substrate along the direction in which the modified 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 modified region is to be formed. If this is formed, the modified region can be easily and accurately formed on the substrate by using the orientation flat as a reference.

  Next, a laser processing method according to an embodiment of the present invention will be described.

  FIG. 10 is a schematic configuration diagram of a laser processing apparatus according to the present embodiment. As shown in FIG. 10, the laser processing apparatus 200 includes a stage 201, a laser light source 202, a lens 203, an AF (autofocus) unit 204, a control unit 205, and a drive unit (drive means) 206.

  The stage 201 is configured to be capable of translational movement in the XYZ directions, and supports the workpiece 1. The processing object 1 is a semiconductor substrate made of silicon and having a thickness of 300 μm, for example, and has a substantially circular shape when viewed from above, as shown in FIG. On the surface of the semiconductor substrate, a plurality of functional elements (for example, light receiving elements) arranged in a matrix in a direction parallel to and perpendicular to the orientation flat 6 are formed. In such a workpiece 1, a grid-like cutting scheduled line 5 is set so as to pass between adjacent functional elements.

  Returning to FIG. 10, the laser light source 202 emits laser light (first laser light) L that is transmitted by the beam splitter 210 and collected by the lens 203. The lens 203 is a lens group that includes a plurality of lenses.

  The AF unit 204 emits AF laser light (second laser light) LB that is reflected by the beam splitter 210 and collected by the lens 203. Further, the AF unit 204 receives the reflected light of the AF laser light LB, thereby receiving a displacement signal related to the displacement (swell) of the reflective surface (hereinafter simply referred to as “reflecting surface”) of the AF laser light LB. Obtained by normalizing the total amount of reflected light. Here, for example, an astigmatism method is used to obtain an astigmatism signal corresponding to the condensed image of the reflected light, a total light quantity signal corresponding to the total light quantity of the received reflected light is obtained, and the astigmatism signal is calculated. The displacement signal is obtained by dividing by the total light quantity signal. Further, the AF unit 204 outputs the acquired displacement signal to the control unit 205.

  The control unit 205 includes, for example, a CPU, a ROM, a RAM, and the like. The control unit 205 inputs a voltage signal (drive signal) to the drive unit 206 so that the displacement signal becomes constant, and moves the lens 203 along the optical axis direction. Drive. Thereby, the lens 203 is driven so as to follow the displacement of the reflecting surface.

  The drive unit 206 drives the lens 203 along the optical axis direction according to the voltage signal input from the control unit 205. As the drive unit 206 here, for example, a piezo is used, and a voltage signal within a range of 2.5 V ± 2.5 V is input, and the lens 203 is moved along the optical axis direction within a stroke range of 20 μm ± 20 μm. Drive.

  Next, a case where the workpiece 1 is cut using the laser processing apparatus 200 will be described.

  First, a tape 211 such as an expanded tape is attached to the back surface 21 of the workpiece 1, and the workpiece 1 is placed on the stage 201. Subsequently, the surface 3 that is the laser light irradiation surface of the workpiece 1 is imaged via the lens 203 by an imaging means (not shown) such as a CCD camera. Then, the lens 203 is moved in the Z-axis direction so that the contrast of the projected reticle pattern is maximized (height set).

  During the height setting, the AF laser beam LB is irradiated, the reflected light reflected by the laser beam irradiation surface 3 is received, and a displacement signal is acquired. The displacement signal is stored in the control unit 205 as a reference displacement signal. Thereby, the laser beam irradiation surface 3 at the time of height setting is set to zero displacement in the displacement signal. Further, the voltage signal input to the drive unit 206 at the time of height setting is stored in the control unit 205 as a reference voltage signal (in this case, 2.5 V).

  Next, the position of the edge (edge) of the workpiece 1 is detected. First, the approximate position of the workpiece 1 is calculated under known conditions. Here, the approximate position of the workpiece 1 is calculated on the basis of the size of the workpiece 1 and the condition that the workpiece 1 is placed at the center of the suction table (not shown) of the stage 201. .

  Subsequently, as shown in FIG. 12A, the lens is positioned in the vicinity of the edge x1 on one side of the edge detection line 15a (see FIG. 18) in the workpiece 1 (for example, several mm before the approximate position of the edge x1). The workpiece 1 is moved so that the optical axis G 203 is located. The speed of the stage 201 at this time is 600 mm / second, for example.

  Subsequently, as shown in FIGS. 12B to 13B, the arrow A1 along the edge detection line 15a while irradiating the AF laser beam LB through the lens 203 in a predetermined region including the edge. The workpiece 1 is moved in the direction at, for example, 10 mm / second, and the AF laser beam LB is relatively moved in the direction of the arrow B1 so as to straddle the edge x1 of the workpiece 1. The edge detection line 15a is one direction orthogonal to the thickness direction of the workpiece 1 and is set here with reference to an alignment mark formed on the workpiece 1. Note that the planned cutting line 5 may be used as the edge detection line 15a.

  At the same time, the reflected light of the AF laser beam LB is received, and a displacement signal related to the displacement of the reflecting surface is obtained by normalizing with the total light amount of the received reflected light. Then, a voltage signal is input to the drive unit 206 so that the displacement signal becomes the reference displacement signal, and the lens 203 is driven along the optical axis G direction. As a result, the lens 203 is driven so as to follow the displacement of the reflecting surface, and the distance between the lens 203 and the reflecting surface is the distance between the lens 203 and the laser light irradiation surface 3 during height setting. To be controlled.

  Specifically, as shown in FIG. 12B, the tape surface 211a which is the surface of the tape 211 on the side irradiated with the AF laser light LB while relatively moving the AF laser light LB in the direction of the arrow B1. The reflected light reflected at is received and a displacement signal is obtained. At the same time, a voltage signal is input to the drive unit 206 so that the displacement signal becomes a reference displacement signal, and the lens 203 is driven along the optical axis G direction. At this time, since the displacement signal becomes approximately 0V, as shown in FIG. 14, the voltage signal input to the drive unit 206 is constant at the maximum value of 5V. This is because of the following reason.

  FIG. 15 is a graph showing the characteristics of the displacement signal. In the figure, the horizontal axis indicates the displacement of the reflecting surface, and the vertical axis indicates the value of the displacement signal. An arrow R indicates a length measurement range that is a range in which the displacement of the reflecting surface can be measured. As shown in FIG. 15, the center of the displacement sensor is shifted in such a direction that the lens 203 approaches the workpiece 1 so as to expand the length measurement range R. The displacement signal value is a negative value. Therefore, when the displacement signal is approximately 0 V, the drive unit 206 is reduced so that the displacement signal becomes the reference displacement signal (the displacement signal moves to the right in the figure), and the lens 203 is moved to the workpiece. Move away from 1. On the other hand, the thickness of the workpiece 1 exceeds the stroke range of the drive unit 206. Therefore, when the AF laser beam LB is reflected by the tape surface 211a, the drive unit 206 is in a reduction limit state with a full stroke, and the voltage signal becomes the maximum value of 5V.

  When the AF laser beam LB rides on the edge x1 of the workpiece 1 (the state shown in FIG. 13A), the reflection surface of the AF laser beam LB changes from the tape surface 211a to the laser beam irradiation surface. Change to 3. Further, as described above, a voltage signal of 2.5 V is input to the drive unit 206 at the time of height setting. Therefore, as shown in FIG. 14, it can be determined that the AF laser beam LB rides on the workpiece 1 when the voltage signal changes from 5V to 2.5V. Therefore, the coordinates when the voltage signal becomes 2.5 V (reference voltage signal) (circle mark in the figure) are acquired as the position of the edge x1 and stored in the control unit 205.

  Subsequently, as shown in FIG. 13B, while the AF laser beam LB is continuously moved in the direction of the arrow B1, the reflected light reflected by the laser beam irradiation surface 3 of the workpiece 1 is received and displaced. A signal is obtained, and a voltage signal is input to the drive unit 206 so that the displacement signal becomes a reference displacement signal, the lens 203 is driven along the optical axis G direction, and the lens 203 follows the laser light irradiation surface 3. .

  Next, as illustrated in FIG. 16A, the stage 201 is arranged such that the optical axis G of the lens 203 is positioned in the vicinity of the edge x2 on the other side of the edge detection line 15a (see FIG. 18) in the workpiece 1. To move the workpiece 1. As shown in FIGS. 16B to 17B, in a predetermined region including the edge, processing is performed in the direction of arrow A2 along the edge detection line 15a while irradiating the AF laser beam LB through the lens 203. The object 1 is moved, and the AF laser beam LB is relatively moved in the arrow B2 direction so as to straddle the edge x2 of the object 1 to be processed. At the same time, the reflected light of the AF laser beam LB is received to obtain a displacement signal, and a voltage signal is input to the drive unit 206 so that the displacement signal becomes the reference displacement signal, and the lens 203 is moved to the optical axis G. Drive along the direction.

  Similarly to the case where the AF laser beam LB rides on the edge x1, the coordinates when the voltage signal becomes 2.5 V are acquired as the position of the edge x2, and are stored in the control unit 205.

  Next, similarly to the acquisition of the positions of the edges x1 and x2, the positions of the edges x3 and x4 along the edge detection line 15b (see FIG. 18) of the workpiece 1 are acquired, and these are acquired by the control unit 205. Each memory. Subsequently, as shown in FIG. 18, at the intersection of the perpendicular bisector 16a obtained from the stored positions of the edges x1 and x2 and the vertical bisector 16b obtained from the positions of the stored edges x3 and x4. Based on this, the position of the center point o of the workpiece 1 is calculated. Then, the position of the edge over the entire circumference of the workpiece 1 is derived from the position of the center point o and the diameter of the workpiece 1, and the detection of the position of the edge in the workpiece 1 is completed. .

  In addition, the diameter of the workpiece 1 may be obtained from the size of the workpiece 1 or may be obtained from a formula of a circle passing through the edges x1 to x4. In the above, for convenience of explanation, the orientation flat 6 is omitted.

  Next, based on the detected edge position, the lens 203 is driven along the direction of the optical axis G by the drive unit 206, and the processing object 1 is irradiated with the laser light L with the focusing point P aligned with the object to be processed. A modified region 7 for cutting the object 1 is formed along the planned cutting line 5. Specifically, a predetermined distance with respect to the workpiece 1 on the other end side of the extension line of the planned cutting line 5 from a position away from the workpiece 1 by a predetermined distance on one end side of the extension line of the planned cutting line 5. The lens 203 is relatively moved along the scheduled cutting line 5 up to a position separated by a distance. At the same time, when it is determined that the optical axis G of the lens 203 is on the tape 211 based on the detected edge position, the lens 203 does not follow the tape surface 211a and the laser beam L Irradiation is turned off. On the other hand, when it is determined that the optical axis G of the lens 203 is on the laser light irradiation surface 3 based on the detected edge position, the lens 203 is made to follow the displacement of the laser light irradiation surface 3 and the laser Light L irradiation is turned on. More specifically, the following operation is executed.

  That is, first, the lens 203 is moved along the scheduled cutting line 5 from a position that is a predetermined distance away from the processing object 1 to a position on the processing object 1. Here, until it is determined that the optical axis G of the lens 203 is at the position of the detected edge, the driving unit 206 is deactivated so that the lens 203 is not driven, and the irradiation of the laser light L is stopped. To do. The position of the lens 203 in this state in the direction of the optical axis G is such that the focus of the lens 203 is aligned with the laser light irradiation surface 3. Incidentally, “stopping the irradiation of the laser beam L” not only stops the oscillation of the laser beam L and physically shuts off the laser beam L toward the workpiece 1 using a shutter or the like, For example, by driving the laser light source 101 CW, setting the laser output low, etc., the laser intensity becomes less than the processing threshold (the lower limit value of the laser intensity sufficient to form the modified region 7). This includes the case where the irradiation of the laser beam L is substantially stopped (the same applies in the following description).

  After determining that the optical axis G of the lens 203 is at the detected edge position, the AF laser beam LB is irradiated from the AF unit 204 to obtain a displacement signal, and this displacement signal becomes constant. As described above, the lens 203 is driven by inputting a voltage signal to the drive unit 206, thereby causing the lens 203 to follow the displacement of the laser light irradiation surface 3. At the same time, the modified region 7 is formed along the planned cutting line 5 by irradiating the laser beam L. As a result, the modified region 7 is accurately formed at a desired position inside the workpiece 1. Note that “irradiate laser beam L” means that the laser beam L is oscillated to irradiate the workpiece 1 with the laser beam L, and the laser beam L physically blocked by a shutter or the like is processed. In addition to releasing the cut-off state so that the object 1 is irradiated, the laser intensity of the laser light L already irradiated may be set to be equal to or higher than the processing threshold by, for example, pulse driving the laser light source 101. Included (same in the following description).

  Subsequently, the lens 203 is moved along the scheduled cutting line 5 from a position on the processing object 1 to a position away from the processing object 1 by a predetermined distance. Here, until it is determined that the optical axis G of the lens 203 is at the position of the detected edge, the voltage signal is continuously input to the drive unit 206 to drive the lens 203, and the lens 203 is moved to the laser light irradiation surface 3. Then, the modified region 7 is formed along the planned cutting line 5 by continuously irradiating the laser beam L.

  Then, after it is determined again that the optical axis G of the lens 203 is at the detected edge position, the irradiation of the AF laser beam LB is stopped, the drive unit 206 is deactivated, and the lens 203 is not driven. And the irradiation of the laser beam L is stopped.

  Thereafter, similarly to the above, the modified region 7 is formed along the other scheduled cutting lines 5. By repeating this along each planned cutting line 5, the modified region 7 is formed along each planned cutting line 5.

  Finally, the tape 211 is expanded, the workpiece 1 is divided along the scheduled cutting line 5 using the modified region 7 as a starting point of cutting, and separated from each other as a plurality of semiconductor chips.

  As described above, according to the present embodiment, the irradiated AF laser light LB is moved along the edge detection lines 15 a and 15 b so as to straddle the edges x 1, x 2, x 3, and x 4 of the workpiece 1. At the same time, the reflected light of the AF laser beam LB is received to obtain the displacement signal, and the lens 203 is driven along the optical axis G direction by the drive unit 206 so that the displacement signal becomes constant. Therefore, when the AF laser beam LB is moved along the edge detection lines 15 a and 15 b, the tape surface 211 a on which the AF laser beam LB is reflected on the tape 211 and the workpiece 1, and the laser beam irradiation surface 3. The lens 203 is driven so as to follow the displacement.

  Here, when the AF laser beam LB rides on the workpiece 1 from the tape 211, the reflection surface changes from the tape surface 211a to the laser beam irradiation surface 3, so that the position of the reflection surface changes greatly. The voltage signal input to 206 changes greatly. Further, the displacement signal is normalized by the total light amount of the received reflected light and obtained as a relative value of the total light amount of the reflected light. Therefore, even when the total amount of reflected light is small, a voltage signal is input to the drive unit 206, and the lens 203 is driven so as to follow the displacement of the reflecting surface. That is, the voltage signal does not depend on the amount of reflected light. Therefore, by detecting the positions of the edges x1 to x4 of the workpiece 1 based on the change of the voltage signal, the positions of the edges x1 to x4 can be detected with high accuracy even when the total amount of reflected light is small. . As a result, it is possible to accurately detect the positions of the edges x1 to x4 even with respect to the workpiece 1 having a variation in film thickness such as an oxide film or a nitride film formed on the laser light irradiation surface 3.

  Further, according to the present embodiment, as described above, when the AF laser light LB is moved along the edge detection lines 15a and 15b, the moving speed of the AF laser light LB in the vicinity of the edges x1 to x4. However, it is slower than the movement speed except in the vicinity of the edges x1 to x4. Therefore, in the vicinity of the edges x1 to x4, changes in the voltage signal can be detected finely (with high resolution), and the positions of the edges x1 to x4 of the workpiece 1 can be detected with higher accuracy.

  In the present embodiment, as described above, when the modified region 7 is formed along the planned cutting line 5 by irradiating the laser beam L, the lens 203 is adapted to follow the displacement of the laser beam irradiation surface 3. Are driven along the optical axis G. Therefore, the modified region 7 is accurately formed at a desired position inside the workpiece 1. Here, in the conventional laser processing method, when the optical axis G of the lens 203 gets on the processing object 1 or gets on or off the processing object 1, the position of the reflecting surface changes greatly as described above, and the voltage is increased. The signal changes greatly (here, the voltage signal changes between 5V and 2.5V). Therefore, the driving amount of the lens 203 is increased. Therefore, for example, when the optical axis G rides on the object 1 to be processed, the lens 203 is largely driven, so that the lens 203 may be delayed in following the edge.

  In this respect, the present embodiment has the following effects. That is, as described above, the optical axis G is moved to the edge position as the lens 203 is moved along the planned cutting line 5 from a position away from the processing object 1 to a position on the processing object 1. Until it is determined that there is, the driving of the lens 203 is stopped, and after it is determined that the optical axis G is at the edge position, the lens 203 is made to follow the displacement of the laser light irradiation surface 3. Therefore, when the optical axis G of the lens 203 rides on the object to be processed, the lens 203 is prevented from being greatly driven, and the lens 203 can be made to follow the edge suitably. Further, as described above, since the lens 203 is not driven, the position of the lens 203 in the direction of the optical axis G is set so that the focal point thereof is aligned with the laser light irradiation surface 3. And the lens 203 can follow the edge more preferably.

  Further, as described above, in addition to moving the lens 203 along the planned cutting line 5 from a position on the processing object 1 to a position away from the processing object 1, the optical axis G is set to the edge position. Until it is determined that the lens 203 is present, the lens 203 is made to follow the displacement of the laser light irradiation surface 3, and after it is determined that the optical axis G is at the edge position, the driving of the lens 203 is stopped. Therefore, even after the optical axis G of the lens 203 gets on and off the workpiece 1, the position of the lens 203 in the direction of the optical axis G remains at a position where the focus of the lens 203 matches the laser light irradiation surface 3. can do. As a result, for example, when the modified region 7 is subsequently formed along the other scheduled cutting line 5, when the optical axis G of the lens 203 rides on the workpiece 1, the lens 203 preferably follows the edge. Can be made. Therefore, in the present embodiment, the lens 203 can be suitably followed by the laser light irradiation surface 3, and the modified region 7 can be accurately formed along the planned cutting line 5.

  Further, in the present embodiment, as described above, when the modified region 7 is formed along the planned cutting line 5 by irradiating the laser beam L, the processing object 1 is located away from the processing object 1. As the lens 203 is moved to the upper position along the planned cutting line 5, the irradiation of the laser beam L is stopped until it is determined that the optical axis G is at the edge position. Is determined to be at the edge position, the modified region 7 is formed along the planned cutting line 5 by irradiating the laser beam L. Then, it is determined that the optical axis G is at the edge position as the lens 203 is moved along the planned cutting line 5 from the position on the processing object 1 to a position away from the processing object 1. Until then, the laser beam L is irradiated to form the modified region 7 along the planned cutting line 5, and after it is determined that the optical axis G is at the edge position, the irradiation of the laser beam L is stopped. ing. Accordingly, the irradiation of the laser beam L is started and stopped based on the detected edge position, and the modified region 7 can be formed along the scheduled cutting line 5 with higher accuracy.

  With respect to the laser processing method described above, comparison verification with the edge position detected by the image using the high magnification camera was performed. As a result, the edge position detected by the present embodiment, the edge position detected from the image, and the average error were 0.0085 mm. Thereby, the said effect that the position of the edge of the workpiece 1 can be detected accurately was able to be confirmed.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, the modified region 7 including the melt processing region is formed on the workpiece 1 made of a semiconductor material, but the crack region is formed inside the workpiece made of another material such as glass or a piezoelectric material. Alternatively, other modified regions such as a refractive index changing region may be formed. Further, the present invention is more suitable for accurately forming a modified region inside a workpiece, but is also applicable to a laser machining method using a laser ablation method for cutting a workpiece. The present invention can also be applied when a groove or the like is formed as a region.

  In the above embodiment, the AF laser light LB is emitted with the optical axis coaxial with the optical axis of the laser light L, but may be emitted non-coaxial. Further, in the above embodiment, when detecting the position of the edge, the irradiated AF laser light LB is moved so as to ride on the workpiece 1. However, the AF laser light moves so as to get on and off the workpiece. In short, the AF laser light may be moved so as to straddle the edge of the object to be processed.

It is a schematic block diagram of the laser processing apparatus used for formation of a modification area | region. It is a top view of the processing target object used as the object of formation of a modification field. It is sectional drawing along the III-III line of the workpiece of FIG. It is a top view of the processing target after laser processing. It is sectional drawing along the VV line of the workpiece of FIG. It is sectional drawing along the VI-VI line of the processing target object of FIG. It is the figure showing the photograph of the cut surface of the silicon wafer after laser processing. It is a graph which shows the relationship between the wavelength of a laser beam, and the transmittance | permeability inside a silicon substrate. It is a graph which shows the relationship between the peak power density of a laser beam, and the magnitude | size of a crack spot. It is a schematic block diagram of the laser processing apparatus which concerns on this embodiment. It is a top view of the processing target used as the object of the laser processing method concerning this embodiment. It is explanatory drawing about the laser processing method which concerns on this embodiment. FIG. 13 is an explanatory diagram subsequent to FIG. 12. It is a figure which shows the voltage signal in the laser processing method which concerns on this embodiment. It is a graph which shows the characteristic of the displacement signal in the laser processing method concerning this embodiment. FIG. 14 is an explanatory diagram subsequent to FIG. 13. FIG. 17 is an explanatory diagram subsequent to FIG. 16. It is explanatory drawing of the process of calculating the center point position of the workpiece in the laser processing method which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Processing object, 3 ... Laser beam irradiation surface (reflection surface), 5 ... Planned cutting line, 7 ... Modified area | region (area | region), 203 ... Lens, 206 ... Drive unit (drive means), 211 ... Tape surface ( Reflection surface), L ... laser light (first laser light), LB ... AF laser light (second laser light), P ... condensing point, x1, x2, x3, x4 ... edge (edge), G: Optical axis of the lens.

Claims (8)

A laser processing method for forming an area for cutting the processing object along a planned cutting line by irradiating a first laser beam with a focusing point on a plate-shaped processing object,
While moving the second laser beam through the lens, the second laser beam is moved in one direction intersecting the thickness direction of the workpiece so as to straddle the edge of the workpiece. together,
By receiving the reflected light of the second laser light, a displacement signal related to the displacement of the reflecting surface reflected by the second laser light is obtained by normalizing with the total light amount of the received reflected light,
A step of inputting a driving signal to a driving means so as to drive the lens along the optical axis direction so that the obtained displacement signal is constant;
And a step of detecting the position of the edge based on the change of the displacement signal. When moving the second laser light in the one direction,
2. The laser processing method according to claim 1, wherein a moving speed of the second laser light in a predetermined region including the edge is made slower than a moving speed in a region other than the predetermined region.   The laser processing method according to claim 1, wherein the region for cutting the workpiece is a modified region serving as a starting point of cutting. A state in which the focus of the lens matches the laser light irradiation surface of the workpiece, and the driving signal input to the driving means in this state is obtained as a reference driving signal,
When detecting the position of the edge,
The position in the said one direction of the said optical axis when the said drive signal turns into the said reference drive signal is detected as the said position of the said edge part, The Claim 1 characterized by the above-mentioned. Laser processing method. When forming the region for cutting the workpiece by irradiating the first laser light along the planned cutting line,
In addition to moving the lens along the planned cutting line from a position away from the processing object to a position on the processing object,
Until the optical axis of the lens is determined to be at the detected position of the edge, the driving of the lens by the driving means is stopped,
After it is determined that the optical axis of the lens is at the detected position of the edge, the driving signal is input to the driving means so that the displacement signal becomes constant, and the lens is moved to the optical axis. It drives along a direction, The laser processing method as described in any one of Claims 1-4 characterized by the above-mentioned. When forming the region for cutting the workpiece by irradiating the first laser light along the planned cutting line,
In addition to moving the lens along the planned cutting line from a position on the processing object to a position away from the processing object,
Until the optical axis of the lens is determined to be at the detected position of the edge, the drive signal is input to the driving means so that the displacement signal is constant, and the lens is moved to the optical axis. Drive along the direction,
6. The driving of the lens by the driving unit is stopped after it is determined that the optical axis of the lens is at the detected position of the edge. 6. Laser processing method. When forming the region for cutting the workpiece by irradiating the first laser light along the planned cutting line,
In addition to moving the lens along the planned cutting line from a position away from the processing object to a position on the processing object,
Until it is determined that the optical axis of the lens is at the detected edge position, the irradiation of the first laser beam is stopped,
After it is determined that the optical axis of the lens is at the detected position of the edge, the region is formed along the planned cutting line by irradiating the first laser beam. The laser processing method according to any one of claims 1 to 6. When forming the region for cutting the workpiece by irradiating the first laser light along the planned cutting line,
In addition to moving the lens along the planned cutting line from a position on the processing object to a position away from the processing object,
Until the optical axis of the lens is determined to be at the detected edge position, the region is formed along the planned cutting line by irradiating the first laser beam,
8. The irradiation of the first laser light is stopped after it is determined that the optical axis of the lens is at the detected position of the edge portion. 8. Laser processing method.

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