JP2018176212A - Laser beam machining apparatus and laser beam machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus and a laser beam machining method which enable a workpiece to precisely be machined without being influenced by a surface shape of the workpiece.SOLUTION: The laser beam machining apparatus comprises: a laser beam head 20 which irradiates a workpiece W with a machining laser beam L1 via a condenser lens 24 to machine the workpiece W; an AF device 30 which irradiates the workpiece W with a detection laser bean L2 with a wavelength having a transparency to the workpiece W and detects a reflected beam reflected on the back face (opposite face on the opposite side to a laser beam irradiation face) thereby detecting positional information related to a position of the back face of the workpiece W in a thickness direction of the workpiece W; and a first actuator 25 which adjusts a focal point of the condensed machining laser beam L1 focused by a condenser lens 24, with a position of the back face of the workpiece W as the reference, on the basis of positional information detected by the AF device 30.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a laser processing apparatus and a laser processing method for processing a workpiece by irradiating the workpiece with a laser beam through a condenser lens.

  Conventionally, there has been known a laser processing apparatus which processes a workpiece by irradiating the workpiece with a laser beam through a condenser lens (see, for example, Patent Document 1).

  In the laser processing apparatus disclosed in Patent Document 1, the inside of the object to be processed is aligned with the condensing point and the laser beam is irradiated to form the modified region serving as the starting point of cutting on the inside of the object . In this laser processing apparatus, a processing laser beam and a detection laser beam are condensed toward a workpiece by a condenser lens, and the reflected light reflected on the surface (laser beam irradiation surface) of the workpiece is detected. By this, the position of the focusing point of the processing laser beam is controlled. Thereby, the condensing point of the processing laser beam can be located at a predetermined distance from the surface of the workpiece, and the modified region can be formed at a desired position inside the workpiece.

JP 2007-167918 A

  However, depending on the type of a workpiece such as a wafer and the processing state, there are also workpieces in which the thickness of the workpiece is uneven, and the surface shape of the workpiece may be unstable. In such a case, the laser processing apparatus disclosed in Patent Document 1 is easily affected by the surface shape of the workpiece. Therefore, the position information of the surface of the workpiece can not be obtained with high accuracy, and there is a problem that the modified region can not be formed with high accuracy inside the wafer.

  The present invention has been made in view of such circumstances, and provides a laser processing apparatus and a laser processing method that can precisely process a workpiece without being affected by the surface shape of the workpiece. The purpose is

  In order to achieve the above object, the following invention is provided.

  A laser processing apparatus according to a first aspect of the present invention comprises a laser processing means for processing a workpiece by irradiating the workpiece with a processing laser beam through a condenser lens, and a permeability to the workpiece By irradiating the workpiece with a detection laser beam having a wavelength having a wavelength of 100 nm, and detecting the reflected light reflected by the opposite surface of the workpiece opposite to the laser beam irradiated surface in the thickness direction of the workpiece Based on the position information detection means for detecting position information on the position of the opposite surface of the workpiece and the position information detected by the position information detection device, the light is collected by the condenser lens with reference to the position on the opposite surface of the workpiece And first focusing point position adjusting means for adjusting the focusing point position of the processing laser light to be emitted.

  In the laser processing apparatus according to the second aspect of the present invention, in the first aspect, the position information detection means irradiates the detection laser beam to the workpiece through the focusing lens, and the focusing point of the processing laser beam In a state where the position is fixed, a second focusing point position adjustment unit that adjusts the focusing point position of the detection laser beam is provided.

  In the laser processing apparatus according to the third aspect of the present invention, the second focusing point position adjusting means includes, in order from the workpiece side, a first lens group provided immovably along the optical path of the detection laser beam. And a second lens group movably provided along the optical path of the detection laser beam.

  In a laser processing apparatus according to a fourth aspect of the present invention, in the first aspect, the first lens group has positive refractive power.

  A laser processing apparatus according to a fifth aspect of the present invention is the laser processing device according to any one of the first to fourth aspects, wherein the laser processing means condenses the processing laser light into the interior of the workpiece by the condensing lens. Forming a reformed region which becomes a starting point of cutting inside the workpiece.

  A laser processing method according to a sixth aspect of the present invention comprises a laser processing step of processing a workpiece by irradiating the workpiece with a processing laser beam through a condenser lens, and permeability to the workpiece By irradiating the workpiece with a detection laser beam having a wavelength having a wavelength of 100 nm, and detecting the reflected light reflected by the opposite surface of the workpiece opposite to the laser beam irradiated surface in the thickness direction of the workpiece Based on the position information detection step of detecting position information regarding the position of the opposite surface of the workpiece, and the position information detected by the position information detection means, the light is collected by the condenser lens with reference to the position of the opposite surface of the workpiece And a first focusing point position adjustment step of adjusting a focusing point position of the processing laser light to be emitted.

  The laser processing method according to the seventh aspect of the present invention is the laser processing method according to the sixth aspect, wherein in the position information detecting step, the laser beam for detection is irradiated to the workpiece through the condenser lens, and the focusing point of the laser beam for processing In a state where the position is fixed, a second focusing point position adjustment step of adjusting the focusing point position of the detection laser beam is provided.

  In the laser processing method according to the eighth aspect of the present invention, in the sixth aspect or the seventh aspect, in the laser processing step, a processing laser beam is condensed by a condensing lens inside a workpiece, Form a reformed region as a starting point of cutting inside.

  According to the present invention, the workpiece can be machined with high accuracy without being affected by the surface shape of the workpiece.

The block diagram which showed the outline of the laser processing apparatus which concerns on one Embodiment of this invention A perspective view showing a workpiece mounted on a frame through a tape A conceptual diagram for explaining the reforming area formed in the vicinity of the condensing point inside the workpiece Schematic showing an example of the configuration of the AF device A diagram showing the appearance of a light collection image formed on the light receiving surface of a two-part photodiode Graph showing output characteristics of AF signal The figure which showed a mode that the condensing point of the laser beam for detection changes to the thickness direction of the to-be-processed object W A flowchart showing the flow of a laser processing method using the laser processing apparatus of the present embodiment A flowchart showing the detailed flow of the calibration operation shown in FIG. The figure which showed an example of the output characteristic of AF signal measured by calibration operation A flowchart showing the detailed flow of the real-time machining operation shown in FIG. 8 A schematic diagram showing another configuration example of the AF device Figure showing the light receiving surface of a 4-split photodiode A schematic diagram showing yet another configuration example of the AF device

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

  FIG. 1 is a schematic view showing a laser processing apparatus 10 according to an embodiment of the present invention. As shown in the figure, the laser processing apparatus 10 includes a stage 12 for moving the workpiece W, a laser head 20 for irradiating the workpiece W with laser light, and a control unit for controlling each part of the laser processing apparatus 10 And 50.

  The workpiece W is not particularly limited. For example, a semiconductor substrate such as a silicon wafer, a glass substrate, a piezoelectric ceramic substrate, a glass substrate, or the like can be used.

  The stage 12 is configured to be movable in the XYZθ direction, and holds the workpiece W by suction. As shown in FIG. 2, the workpiece W is mounted on the stage 12 in a state in which a dicing sheet S having an adhesive material is attached to one surface and integrated with the frame F via the dicing sheet S. Ru.

  The laser head 20 is disposed at a position facing the workpiece W, and the processing laser light L1 for forming a modified region by multiphoton absorption inside the workpiece W is applied to the workpiece W. Irradiate. The laser head 20 is an example of a laser processing unit.

  The control unit 50 includes a CPU, a memory, an input / output circuit unit, and the like, and stores data necessary for the operation and processing of each unit of the laser processing apparatus 10.

  In addition, the laser processing apparatus 10 is composed of a not-shown workpiece conveyance means, an operation plate, a television monitor, a display lamp, and the like.

  Switches and a display device for operating the operation of each part of the laser processing apparatus 10 are attached to the operation plate. The television monitor displays an image of a workpiece taken by a CCD camera (not shown), or displays program contents, various messages, and the like. The indicator light indicates the operation status such as processing end, emergency stop, etc. during processing of the laser processing apparatus 10.

  Next, the detailed configuration of the laser head 20 will be described.

  As shown in FIG. 1, the laser head 20 includes a processing laser light source 21, a dichroic mirror 23, a condensing lens 24, a first actuator 25, and an AF device (autofocus device) 30.

The processing laser light source 21 emits processing laser light L1 for forming a modified region inside the workpiece W. For example, the processing laser light source 21 emits a laser beam having a pulse width of 1 μs or less and a peak power density at a focusing point of 1 × 10 ⁸ (W / cm ² ) or more.

  On the first optical path of the processing laser beam L1, a dichroic mirror 23 and a condensing lens 24 are disposed in order from the processing laser light source 21 side. The dichroic mirror 23 transmits the processing laser light L1 and reflects the detection laser light L2 emitted from an AF device 30 described later. The second light path of the detection laser light L2 is bent by the dichroic mirror 23 so as to share a part of the light path with the first light path of the processing laser light L1, and the condenser lens 24 is disposed on the common light path. Ru.

  The processing laser light L1 emitted from the processing laser light source 21 passes through the dichroic mirror 23, and is then condensed on the inside of the workpiece W by the condensing lens 24. The position in the Z direction (the position in the thickness direction of the workpiece W) of the focusing point of the processing laser beam L1 is adjusted by minutely moving the focusing lens 24 in the Z direction by the first actuator 25. The first actuator 25 is an example of a first focusing point position adjustment unit.

  FIG. 3 is a conceptual view for explaining a reforming region formed in the vicinity of a light condensing point inside the workpiece W. As shown in FIG. FIG. 3 (a) shows a state in which the modified region P is formed at the focusing point of the processing laser beam L1 incident on the inside of the workpiece W, and FIG. 3 (b) is an intermittent pulse processing The workpiece W is moved in the horizontal direction under the for-use laser beam L1, and the state where the discontinuous modified regions P, P,... Are formed side by side is shown. FIG. 3C shows a state in which the modified region P is formed in multiple layers inside the workpiece W.

  As shown in FIG. 3A, when the condensing point of the processing laser beam L1 incident from the surface (laser beam irradiation surface) of the workpiece W is set in the thickness direction of the workpiece W The energy of the processing laser light L1 transmitted through the surface of the workpiece W is concentrated at the focusing point inside the workpiece W, and a crack due to multiphoton absorption near the focusing point inside the workpiece W Modified regions such as a region, a melting region, and a refractive index change region are formed. As shown in FIG. 3B, the workpiece W is irradiated with intermittent pulse-like processing laser light L1 to form a plurality of modified regions P, P,... Along the lines to be cut. The workpiece W loses its balance of intermolecular force, and is naturally cut from the modified regions P, P,... As a starting point, or cut by applying a slight external force.

  Further, in the case of a thick workpiece W, the layer in the modified region P can not be cut in one layer, so as shown in FIG. 3C, the processing laser light in the thickness direction of the workpiece W The focusing point of L1 is moved to form and modify the modified region P in multiple layers.

  In the examples shown in FIGS. 3B and 3C, the discontinuous reformed regions P, P,... Are formed by the intermittent pulsed laser beam L1 for processing. A continuous reformed area P may be formed under the continuous wave of the laser light L1. In the case where the discontinuous modified region P is formed, cutting is more difficult than in the case where the continuous modified region P is formed. Therefore, depending on the thickness of the workpiece W, safety during transport, etc., the processing laser Whether to use the continuous wave or the intermittent wave of the light L1 is appropriately selected.

  The AF device 30 emits a detection laser beam L2 for detecting position information related to the position of the back surface (opposite surface) opposite to the surface (laser beam incident surface) of the workpiece W, and the workpiece W The reflected light of the detection laser beam L2 reflected by the back surface of the object is received, and the displacement of the back surface of the workpiece W from the reference position in the Z direction is detected based on the received reflected light.

  FIG. 4 is a schematic view showing a configuration example of the AF device 30. As shown in FIG. The AF device 30 shown in FIG. 4 detects the displacement in the Z direction from the reference position of the back surface of the workpiece W using a knife edge method.

  The AF device 30 includes a light source for detection 31, a condenser lens 32, a pinhole 33, a knife edge 34, an illumination system lens 35, a half mirror 36, a focusing optical system 37, and an imaging lens 38. A detector 39, an AF signal processor 40, and a second actuator 41 are provided.

  The light source 31 for detection includes, for example, an LD (Laser Diode) light source, an SLD (Super Luminescent Diode) light source, and the like, and has a wavelength different from that of the processing laser light L1 and having a transparency to the object W The detection laser beam L2 is emitted.

  The detection laser beam L2 emitted from the detection light source 31 passes through the condenser lens 32 and the pinhole 33 and is partially shielded by the knife edge 34, and shielded by the knife edge 34. After passing through the illumination system lens 35, the light which has not traveled is reflected by the half mirror 36 and guided to the dichroic mirror 23 through the focusing optical system 37. The detection laser beam L2 reflected by the dichroic mirror 23 travels along an optical path shared with the processing laser beam L1, is condensed by the condenser lens 24, and is irradiated onto the workpiece W. The knife edge 34 may be provided between the pinhole 33 and the half mirror 36, and the same effect can be obtained even after the illumination system lens 35 is disposed.

  The detection laser beam L2 irradiated to the workpiece W is incident on the inside of the workpiece W and is reflected by the back surface of the workpiece W. Then, the reflected light of the detection laser light L2 reflected by the back surface of the workpiece W returns to the condensing lens 24, travels along the shared optical path, and is reflected by the dichroic mirror 23. The reflected light of the detection laser light L2 reflected by the dichroic mirror 23 sequentially passes through the focusing optical system 37 and the half mirror 36. The reflected light of the detection laser light L2 that has passed through the half mirror 36 is condensed by the imaging lens 38 and irradiated onto the detector 39 to form a condensed image on the light receiving surface of the detector 39.

  The detector 39 is composed of a 2-divided photodiode having a 2-divided light receiving element (photoelectric conversion element), and divides and receives the condensed image of the reflected light of the detection laser beam L2, and outputs according to the respective light amounts A signal (electrical signal) is output to the AF signal processing unit 40.

  The AF signal processing unit 40 detects position information on the position of the back surface of the workpiece W in the Z direction (the thickness direction of the workpiece W) based on the output signals output from the light receiving elements of the detector 39. Specifically, an AF signal (autofocus signal) indicating the displacement (defocus distance) in the Z direction from the reference position of the back surface of the workpiece W is generated as position information on the position of the back surface of the workpiece W Output to the control unit 50.

  Here, the detection principle of the displacement of the back surface of the workpiece W will be described.

  FIG. 5 is a view showing a state of a condensed image formed on the light receiving surface of the two-divided photodiode 42 constituting the detector 39. As shown in FIG. 5 (a) to 5 (c) are formed on the light receiving surface of the two-divided photodiode 42 when the back surface of the workpiece W in FIG. 4 is at the positions indicated by h1, h2 and h3, respectively. It shows the appearance of the light image.

  First, as shown in FIG. 5B, when the back surface of the workpiece W is at the position of h2, that is, when the back surface of the workpiece W and the focusing point of the detection laser beam L2 coincide with each other. On the light receiving surface of the two-divided photodiode 42, a sharp image (perfect circle) is formed in the middle. At this time, it is understood that the amounts of light received by the light receiving elements 42A and 42B of the two-divided photodiode 42 are both equal, and the back surface of the workpiece W is at the in-focus position.

  On the other hand, when the back surface of the workpiece W is at the position h1, that is, when the back surface of the workpiece W is closer to the focusing lens 24 than the focusing point of the detection laser beam L2, as shown in FIG. As shown in a), a semicircular condensed image is formed on the light receiving element 42A side on the light receiving surface of the two-divided photodiode 42, and the size (the amount of blurring) is the workpiece W and the condensing lens It changes according to the distance with 24.

  Further, when the back surface of the workpiece W is at the position h3, that is, when the back surface of the workpiece W is at a position farther from the focusing lens 24 than the focusing point of the detection laser beam L2, as shown in FIG. As shown in c), on the light receiving surface of the two-divided photodiode 42, a semicircular condensed image is formed on the light receiving element 42B side, and the size (the amount of blurring) is the workpiece W and the condensing lens It changes according to the distance with 24.

  Thus, the amount of light received by the light receiving elements 42A and 42B of the two-divided photodiode 42 changes according to the displacement of the back surface of the workpiece W. Therefore, position information on the position of the back surface of the workpiece W, that is, the displacement of the back surface of the workpiece W can be detected using such properties.

  In the AF signal processing unit 40, when the output signals output from the light receiving elements 42A and 42B of the two-divided photodiode 42 are A and B, respectively, the AF signal E is obtained according to the following equation (1).

E = (A−B) / (A + B) (1)
FIG. 6 is a graph showing the output characteristics of the AF signal. The horizontal axis shows the displacement (defocus distance) in the Z direction from the reference position on the back surface of the workpiece W, and the vertical axis shows the output value of the AF signal. It shows. It is assumed that the focal point of the detection laser beam L2 is adjusted in advance so as to coincide with the reference position (origin) of the back surface of the workpiece W.

  As shown in FIG. 6, the output characteristic of the AF signal is an S-shaped curve with the reference position (origin) on the back surface of the workpiece W as the zero cross point. Further, when the position of the back surface of the workpiece W is in the range indicated by the arrow in the figure, that is, within the measurement range (focus pull-in range) in which the displacement of the back surface of the workpiece W can be detected The relationship between the displacement of the back surface of W and the output of the AF signal is a monotonous curve passing through the origin. That is, if the output of the AF signal is zero, it is known that the back surface of the workpiece W is at the in-focus position coincident with the focusing point of the detection laser beam L2, and if the output of the AF signal is not zero, The displacement direction and displacement amount of the back surface of the workpiece W can be known.

  The AF signal having such output characteristics is used as the position information on the position of the back surface of the workpiece W (that is, information indicating the displacement in the Z direction from the reference position on the back surface of the workpiece W) by the AF signal processing unit 40 It is generated and output to the control unit 50.

  The control unit 50 controls the driving of the first actuator 25 based on the AF signal output from the AF signal processing unit 40 so that the distance between the condensing lens 24 and the back surface of the workpiece W becomes constant. . Thereby, the condenser lens 24 is minutely moved in the Z direction (thickness direction of the workpiece W) so as to follow the displacement of the back surface of the workpiece W, and for processing at a constant distance from the back surface of the workpiece W Since the condensing point of the laser beam L1 comes to be located, the modified region can be formed at a desired position inside the workpiece W.

  In the configuration in which the condensing lens 24 is disposed on the shared optical path between the first optical path of the processing laser light L1 and the second optical path of the detection laser light L2 as in the present embodiment, When the relative distance between the focusing lens 24 and the workpiece W changes to change the processing depth, the focusing point of the detection laser beam L2 is also the workpiece W together with the focusing point of the processing laser beam L1. Position in the direction of Z changes. In the present specification, “the processing depth of the modified region” refers to the distance (depth) from the surface of the workpiece W to the position where the modified region is formed.

  For example, as shown in FIG. 7A, when forming the modified region at a position shallow from the surface of the workpiece W, the light condensing point of the detection laser beam L2 coincides with the back surface of the workpiece W It is assumed that In such a case, as shown in FIG. 7B, the relative distance between the condensing lens 24 and the workpiece W is set to form a modified region at a position deep from the surface of the workpiece W. When changed, the condensing point of the detection laser beam L2 largely deviates from the back surface of the workpiece W in the Z direction (the thickness direction of the workpiece W). Then, when the distance between the focusing point of the detection laser light L2 and the back surface of the workpiece W exceeds the measurement range (focus pull-in range), the displacement of the back surface of the workpiece W can not be detected. It will In particular, since the condenser lens 24 uses a high NA lens, the measurement range in which the displacement of the back surface of the workpiece W can be detected is limited to the vicinity of the focusing point (focusing position) of the detection laser beam L2. The above problems become more prominent.

  Therefore, the AF device 30 according to the present embodiment adjusts the position of the focusing point of the detection laser beam L2 in the Z direction (the thickness direction of the workpiece W) independently of the focusing point of the processing laser beam L1. The focusing optical system 37 is provided. The focusing optical system 37 is an example of a component of the second focusing point position adjusting means together with a second actuator 41 described later.

  The focusing optical system 37 is disposed on the second optical path of the detection laser beam L2 and at a position independent of the shared optical path with the first optical path of the processing laser beam L1. Specifically, it is disposed between the dichroic mirror 23 and the half mirror 36.

  The focusing optical system 37 comprises a plurality of lenses including at least a movable lens configured to be movable along the second optical path, and in this example, from the object side (workpiece W side) to the image side (detector 39 side) The first lens group 37A and the second lens group 37B are provided in this order.

  The first lens group 37A is a fixed lens group provided immovably along the second optical path, and has positive refractive power. The second lens group 37B is a movable lens group provided movable along the second optical path, and has positive refractive power.

  The second actuator 41 moves the second lens group 37B along the second optical path. When the second lens group 37B moves along the second optical path, detection is performed according to the movement direction and movement amount of the second lens group 37B while the Z direction position of the focusing point of the processing laser light L1 is fixed. Position in the Z direction of the focusing point of the laser light L2 changes. That is, the relative distance between the focusing point of the processing laser beam L1 and the focusing point of the detection laser beam L2 changes.

  Based on the AF signal output from the AF signal processing unit 40, the control unit 50 causes the focusing point of the detection laser beam L2 to coincide with the back surface of the workpiece W (specifically, the AF signal of the AF signal processing unit). The drive of the second actuator 41 is controlled so that the output value becomes zero).

  As described above, the control unit 50 controls the drive of the second actuator 41 based on the AF signal output from the AF signal processing unit 40, so that the control point 50 independently of the condensing point of the processing laser light L1. It is possible to make the condensing point of the detection laser beam L2 coincide with the back surface of the workpiece W.

  Thereby, as shown in FIG. 7 (b) from the state shown in FIG. 7 (a), the relative position between the condenser lens 24 and the workpiece W to change the processing depth of the modified region Even when the dynamic distance changes, processing is performed as shown in FIG. 7C by moving the second lens group 37B of the focusing optical system 37 along the second optical path as described above. It is possible to make the focusing point of the detection laser beam L2 coincide with the back surface of the workpiece W in a state where the Z-direction position of the focusing point of the for-use laser beam L1 is fixed.

  The reason why such a configuration of the focusing optical system 37 is preferable will be described.

  When control is performed so that the focusing point of the detection laser beam L2 coincides with the back surface of the workpiece W, the reflected light reflected by the back surface of the workpiece W is a focusing lens as shown in FIG. After leaving 24, it is emitted as convergent light. At this time, as the processing position (the position of the light condensing point of the processing laser light L1) in the interior of the workpiece W is separated from the back surface of the workpiece W, the degree of convergence in the convergent light becomes stronger.

  Since the light emitted from the condensing lens 24 is a convergent light beam, it may be considered that the first lens group 37A is configured as a concave lens as the focusing optical system 37. However, when the first lens group 37A is configured as a concave lens, the light emitted from the condensing lens 24 converges to the front focal position of the first lens group 37A (concave lens) in a state where the convergence of the light is weak. Limits become stricter.

  On the other hand, when the first lens group 37A is configured by a convex lens, the light emitted from the condensing lens 24 does not converge to the front focal position of the first lens group 37A until the convergence of the light converges more strongly. The restriction on the processing depth is more relaxed than when the lens 37A is configured with a concave lens.

  Therefore, in the focusing optical system 37 in the present embodiment, a configuration in which the first lens group 37A disposed on the object side has a positive refractive index is preferably adopted.

  Next, a laser processing method using the laser processing apparatus 10 of the present embodiment will be described. FIG. 8 is a flowchart showing a flow of a laser processing method using the laser processing apparatus 10 of the present embodiment. In addition, as shown in FIG. 3, the dicing sheet S which has an adhesive material is stuck on one surface, and the workpiece W is adsorbed on the stage 12 in the state integrated with the flame | frame F through this dicing sheet S. It shall be held. Further, it is assumed that the workpiece W suction-held on the stage 12 is appropriately aligned by alignment means (not shown) having an image processing apparatus.

  As shown in FIG. 8, the laser processing apparatus 10 executes a calibration operation for measuring the output characteristic of the auto AF signal prior to the real time processing operation described later (step S10).

  After the calibration operation is completed, the laser processing apparatus 10 adjusts the position in the Z direction of the focusing point of the processing laser beam L1 so as to follow the displacement of the back surface of the workpiece W, and the inside of the workpiece W In step S12, a real-time processing operation for forming a reformed region is performed.

  FIG. 9 is a flowchart showing the detailed flow of the calibration operation shown in FIG.

  First, the control unit 50 controls the drive of the second actuator 41 to move the second lens group 37B of the focusing optical system 37 to a position according to the processing depth of the modified region (step S20). The memory unit (not shown) of the control unit 50 holds the correspondence between the processing depth of the modified region and the position of the second lens group 37B of the focusing optical system 37.

  Subsequently, the control unit 50 controls the movement of the stage 12 to move the reference position on the back surface of the workpiece W directly below the condensing lens 24 (step S22). The reference position on the back surface of the workpiece W is a position at which the focal point of the detection laser beam L2 is made to coincide, and is a reference position for displacement of the Z direction position on the back surface of the workpiece W. It is desirable that the back surface of the workpiece W has a small level difference (smooth surface). For example, a predetermined position of a central portion excluding the outer peripheral portion of the workpiece W is set as a reference position.

  Subsequently, the control unit 50 controls the driving of the second actuator 41 so that the second lens group 37B of the focusing optical system 37 is secondly operated so that the AF signal output from the AF signal processing unit 40 becomes zero. It is moved along the optical path (step S24). Thereby, as shown in FIG. 7 (b), even when there is a deviation between the focusing point of the detection laser beam L2 and the reference position on the back surface of the workpiece W, as shown in FIG. 7 (c), Focusing point adjustment is performed so that the focusing point of the detection laser beam L2 coincides with the reference position on the back surface of the workpiece W. Note that the control unit 50 sets the position of the second lens group 37B of the focusing optical system 37 held in the memory unit (not shown) to the position (correction position) of the second lens group 37B after the focusing point adjustment. rewrite.

  Subsequently, the control unit 50 controls the driving of the first actuator 25 to move the condensing lens 24 along the Z direction over the entire movable range, and outputs the AF signal output from the AF signal processing unit 40. The output characteristics are measured, and the output characteristics are stored as a lookup table in a memory unit (not shown) (step S26).

  In the case where a plurality of layers of the modified region are formed inside the workpiece W, the processing from step S20 to step S26 is performed for each processing depth of the modified region.

  By the above processing, in the real-time processing operation of step S12 of FIG. 8, the control unit 50 refers to the look-up table stored in the memory unit (not shown) to output the AF output from the AF signal processing unit 40. Since the displacement (defocus distance) in the Z direction from the reference position of the back surface of the workpiece W from the reference value of the signal can be easily obtained, it is possible to improve the processing efficiency (throughput) in the real time processing operation Become.

  FIG. 10 is a view showing an example of the output characteristic of the AF signal measured by the calibration operation, and shows the output characteristic when the processing depth of the modified region is changed in the range of 500 to 800 μm. .

  In the present embodiment, the Z-direction position of the focusing point of the detection laser beam L2 is adjusted to coincide with the reference position on the back surface of the workpiece W according to the processing depth of the modified region. As shown in FIG. 5, the output characteristics of the AF signal corresponding to each processing depth are substantially uniform, and both become S-shaped curves with the reference position (origin) on the back surface of the workpiece W as the zero cross point. . Therefore, by executing the real-time machining operation using the AF signal having such output characteristics, the displacement of the back surface of the workpiece W can be stabilized stably without being affected by the change in the machining depth of the modified region. It becomes possible to detect with high accuracy.

  FIG. 11 is a flowchart showing the detailed flow of the real-time machining operation shown in FIG.

  First, the control unit 50 controls the drive of the second actuator 41 to set the second lens group 37B of the focusing optical system 37 at a position according to the processing depth of the reforming area, as in step S20 of FIG. It is moved (Step S30, an example of the second focusing point position adjustment process). At this time, the control unit 50 moves the position (correction position) of the second lens group 37B held in the memory unit (not shown). Thereby, the condensing point of the detection laser beam L2 coincides with the reference position of the back surface of the workpiece W, and the AF device 30 detects the displacement in the Z direction based on the reference position of the back surface of the workpiece W It is possible to

  Subsequently, the control unit 50 controls the movement of the stage 12 to move the workpiece W suction-held on the stage 12 to a predetermined processing start position (step S32).

  Subsequently, after turning on the processing laser light source 21, the control unit 50 moves the workpiece W in the horizontal direction (XY direction), and the processing laser light L 1 emitted from the processing laser light source 21. A reformed region is formed inside the workpiece W along the line to cut (step S34).

  At this time, the control unit 50 turns on the detection light source 31 at a timing substantially simultaneously with or before the timing at which the processing laser light source 21 is turned on. Thus, the processing laser beam L1 and the detection laser beam L2 are condensed toward the workpiece W by the condensing lens 24. The detection laser beam L2 emitted from the detection light source 31 enters the inside of the workpiece W, is reflected by the back surface of the workpiece W, and the reflected light forms a condensed image on the light receiving surface of the detector 39. . The AF signal processing unit 40 generates an AF signal indicating the displacement in the Z direction from the reference position of the back surface of the workpiece W based on the output signal output from the detector 39 and outputs it to the control unit 50 (position An example of the information detection process).

  Then, the control unit 50 controls the drive of the first actuator 25 based on the AF signal output from the AF signal processing unit 40, thereby adjusting the Z direction position of the focusing point of the processing laser beam L1. While (an example of a 1st condensing point position adjustment process), a modification | reformation area | region is formed in the inside of the to-be-processed object W (an example of a laser processing process).

  Subsequently, the control unit 50 determines whether the formation of the modified region is completed for all the lines to be cut of the workpiece W (step S36). If formation of the modified region is not completed for all the planned cutting lines (in the case of No), the processing moves to the next planned cutting line (step S38), and steps S34 to S36 are performed for the planned cutting lines. Repeat the process. On the other hand, if the formation of the modified region is completed for all the planned cutting lines (in the case of Yes), the process proceeds to the next step S40.

  Subsequently, the control unit 50 determines whether the formation of the modified region is completed for all the processing depths (step S40). If the formation of the modified region is not completed for all the processing depths, the processing moves to the next processing depth (step S42), and the processing from step S30 to step S36 is repeated. On the other hand, when the formation of the modified region is completed for all the processing depths, the real-time processing operation is ended.

  In this manner, by forming the modified region that becomes the starting point of cutting at a desired position inside the workpiece W, the processing region W is divided into a plurality of chips with the modified region as the starting point of cutting. Is possible.

  Here, verification simulation performed to confirm the effect of the present embodiment will be described.

  In this verification simulation, a model substantially equivalent to that of the laser processing apparatus 10 of this embodiment is set, and when the thickness of the silicon wafer as the workpiece W changes, the focus position from the back surface of the silicon wafer It was confirmed how much (the Z direction position of the condensing point of the processing laser light L1) fluctuates.

  As a condition of the verification simulation, the thickness of the silicon wafer is 400 μm, and the state (focusing laser light L1 for processing) is focused to a position of 200 μm from the back surface (the opposite surface opposite to the laser light irradiation surface) State)) as the reference state. Then, assuming that the thickness of the silicon wafer fluctuates by ± 10 μm, position information regarding the position of the back surface of the silicon wafer is acquired using the reflected light from the back surface of the silicon wafer, and the focus position is determined based on the position information. It resets and calculates | requires the distance of a focus position and the back surface of a silicon wafer. Ideally, the focus position from the back surface of the silicon wafer is always constant even if the thickness of the silicon wafer changes.

  The results of the verification simulation are shown in Table 1. In Table 1, the working distance is the distance between the condenser lens 24 and the silicon wafer (the workpiece W). Further, the shift of the focus position has a positive value in the direction away from the back surface of the silicon wafer.

  As shown in Table 1, according to the results of the verification simulation, although a slight shift of about ± 0.4 μm was observed in the shift of the focus position, it is within an acceptable range for practical use, and sufficient performance can be obtained. It was confirmed.

  As described above, according to the present embodiment, the workpiece W is irradiated with the detection laser beam L2 having a wavelength having transparency to the workpiece W, and the back surface of the workpiece W (laser beam irradiation surface) The position information about the position of the back surface of the workpiece W can be obtained by detecting the reflected light reflected on the opposite surface opposite to the surface of the object W). And since the Z direction position of the condensing point of the processing laser beam L1 is adjusted based on the position information, the workpiece W can be precisely measured without being affected by the surface shape of the workpiece W. It becomes possible to process.

  Further, in the present embodiment, since the focusing optical system 37 capable of adjusting the position in the Z direction of the focusing point of the detection laser beam L2 independently of the focusing point of the processing laser beam L1 is provided, the processing laser The relative distance between the focusing point of the light L1 and the focusing point of the detection laser beam L2 can be adjusted. As a result, it becomes possible to align the focusing point of the detection laser beam L2 in the vicinity of the back surface of the workpiece W according to the processing depth of the modified region, and the displacement of the back surface of the workpiece W is stable and accurate Can be detected. Therefore, the degree of freedom with respect to the change in the processing depth of the modified region is high, and the modified region can be accurately formed at a desired position inside the workpiece W.

  In the present embodiment, the detector 39 as means for receiving the reflected light of the detection laser beam L2 is an example composed of a two-split photodiode, but the present invention is not limited to this, and the light amount balance can be measured ( For example, a four-split photodiode, a two-dimensional imaging device, or the like may be used.

  Moreover, in this embodiment, although the knife edge method was used as a method of detecting the displacement of the back surface of the to-be-processed object W, it is also possible to use not only this but an astigmatic method etc., for example.

  FIG. 12 is a schematic view showing another configuration example of the AF device 30. As shown in FIG. 12, the same or similar components as or to FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted.

  The AF device 30 shown in FIG. 12 detects the displacement of the back surface of the workpiece W using an astigmatism method. The AF device 30 is provided as astigmatism applying means for applying astigmatism to the reflected light of the detection laser beam L2 between the imaging lens 38 and the detector 39, instead of the knife edge 34 shown in FIG. A cylindrical lens 43 is disposed. Also, the detector 39 is configured by a 4-divided photodiode.

  Here, the detection principle of the displacement of the back surface of the workpiece W by the astigmatism method will be described.

  The condensed image of the reflected light of the detection laser beam L2 formed on the light receiving surface of the four-divided photodiode constituting the detector 39 is such that the back surface of the workpiece W matches the focus of the detection laser beam L2. If it is, it will be a true circle. On the other hand, when the back surface of the workpiece W and the condensing point of the detection laser beam L2 are shifted, the condensed image is stretched in the longitudinal direction or the lateral direction according to the displacement direction of the back surface of the workpiece W The size is dependent on the amount of displacement of the back surface of the workpiece W. Therefore, the displacement of the back surface of the workpiece W can be detected by utilizing this property.

  FIG. 13 is a view showing the light receiving surface of the four-divided photodiode. As shown in the figure, the four-divided photodiode 44 has four light receiving elements (photoelectric conversion elements) 44A to 44D, and each of the light receiving elements 44A to 44D is a focused image of the reflected light of the detection laser light L2. Is divided and received, and an output signal corresponding to each light amount is output to the AF signal processing unit 40.

  When the output signals respectively output from the light receiving elements 44A to 44D are A to D, the AF signal processing unit 40 obtains an AF signal E according to the following equation (2).

E = {(A + C)-(B + D)} / {(A + C) + (B + D)} (2)
The control unit 50 controls the driving of the first actuator 25 and the second actuator 41 based on the AF signal output from the AF signal processing unit 40, as in the above-described embodiment, to thereby obtain the workpiece W. Controlling the focusing point of the processing laser beam L1 with high precision so as to follow the displacement of the back surface of the workpiece W without being affected by the influence of the surface shape or the change of the processing depth of the modified region It is possible to form the modified region at a desired position inside the workpiece W with high precision.

  FIG. 14 is a schematic view showing still another configuration example of the AF device 30. As shown in FIG. In FIG. 14, the same or similar components as or to FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted.

  The AF device 30 shown in FIG. 14 detects the displacement of the back surface of the workpiece W using the light amount ratio of the reflected light received by the two detectors. The AF device 30 has a half mirror 45, a condenser lens 46, a mask (light shielding plate) 47, a first detector 48, and a second detector 49 in place of the knife edge 34, the imaging lens 38 and the detector 39 shown in FIG. It is configured with.

  The detection laser beam L2 emitted from the detection light source 31 is reflected by the half mirror 36 via the condenser lens 32, the pinhole 33, and the illumination system lens 35. Further, the detection laser beam L2 is reflected by the dichroic mirror 23 via the focusing optical system 37, travels along the shared optical path with the processing laser beam L1, and is condensed by the condensing lens 24. The workpiece W is irradiated.

  The detection laser beam L2 irradiated to the workpiece W is incident on the inside of the workpiece W, and is reflected on the back surface of the workpiece W. Then, the reflected light reflected by the back surface of the workpiece W is refracted by the condenser lens 24, reflected by the dichroic mirror 23, and transmitted through the half mirror 36 via the focusing optical system 37. Further, the reflected light is branched by the half mirror 45 into two branch paths. The reflected light branched into one branch path is condensed 100% by the condenser lens 46 and imaged on the light receiving surface of the first detector 48. Then, the first detector 48 outputs an output signal according to the received light amount to the AF signal processing unit 40. The reflected light branched into the other branch path passes through the hole of the mask 47 (the light receiving area is limited) and is imaged on the light receiving surface of the second detector 49. Then, the second detector 49 outputs an output signal corresponding to the received light amount to the AF signal processing unit 40.

  The AF signal processing unit 40, based on the output signals output from the first detector 48 and the second detector 49, indicates an AF signal indicating the displacement (defocus distance) in the Z direction from the reference position of the back surface of the workpiece W Are generated and output to the control unit 50.

  Here, the detection principle of the displacement of the back surface of the workpiece W will be described.

  The reflected light received by the first detector 48 is condensed 100% by the condensing lens 46, so the amount of received light is constant, and the output of the first detector 48 is constant. On the other hand, the reflected light received by the second detector 49 is limited to the central portion by the mask 47 in the light receiving area, so that the distance from the condenser lens 24 to the back surface of the workpiece W, ie, the workpiece W The amount of light received by the second detector 49 changes depending on the position (Z direction position) of the back surface of the workpiece W in the thickness direction. Therefore, the output of the second detector 49 changes depending on the position of the back surface of the workpiece W to which the detection laser beam is irradiated. Therefore, displacement of the back surface of the workpiece W can be detected by utilizing such a property.

  When the output signals from the first detector 48 and the second detector 49 are S1 and S2, respectively, the AF signal processing unit 40 obtains the AF signal E according to the following equation (3).

E = S1 / S2 (3)
The control unit 50 controls the drive of the first actuator 25 and the second actuator 41 based on the AF signal output from the AF signal processing unit 40 as in the above-described embodiment, thereby processing the modified region. The focusing point of the processing laser beam L1 can be controlled with high accuracy so as to follow the displacement of the back surface of the workpiece W without being affected by the change to the depth, and the inside of the workpiece W can be It is possible to form the modified region at a desired position with high accuracy.

  The detector 39 is not limited to the 4-divided photodiode, and any detector capable of measuring the light amount balance may be used. For example, a two-dimensional imaging device or the like may be used.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above examples, and it goes without saying that various improvements and modifications may be made without departing from the scope of the present invention. . Hereinafter, some modifications will be described.

<Modification 1>
In the embodiment described above, as a preferable mode, a configuration is shown in which the processing laser beam L1 and the detection laser beam L2 are condensed by the same condensing lens 24, but the present invention is not limited to this mode. The condensing lens which condenses the light L1 and the condensing lens which condenses the laser light L2 for detection may be respectively configured by different condensing lenses.

<Modification 2>
In the embodiment described above, as a preferable aspect, the aspect in which the first lens group 37A constituting the focusing optical system 37 has a positive refractive index has been described, but the present invention is not limited thereto. It may have the In this case, the restriction of the processing depth is stricter than that of the present embodiment, but the present invention is applicable to the case where the thickness of the workpiece W is thin.

<Modification 3>
In the embodiment described above, as a preferable mode, the laser processing apparatus 10 aligns the focusing point to the inside of the workpiece W and irradiates the processing laser light L1 to become the starting point of the cutting inside the workpiece W. Although the aspect which forms a modification | reformation area | region was demonstrated, you may apply not only to this but the laser processing apparatus etc. which form a laser processing groove | channel in the to-be-processed object W, for example.

  DESCRIPTION OF SYMBOLS 10 ... Laser processing apparatus, 12 ... Stage, 20 ... Laser head, 21 ... Laser light source, 23 ... Dichroic mirror, 24 ... Condensing lens, 25 ... 1st actuator, 30 ... AF apparatus, 31 ... Light source for AF, 32 ... Condenser lens 33 Pinhole 34 Knife edge 35 Illumination system lens 36 Half mirror 37 Focusing optical system 37A Fixed lens 37B Moving lens 38 Imaging lens 39 Detector , 40: AF signal processing unit, 41: second actuator, 42: two split photodetector, 43: cylindrical lens, 44: four split photodiode, 45: half mirror, 46: focusing lens, 47: mask, 48: 48 1 detector, 49: second detector, 50: control unit, L1: processing laser light, L2: for detection Za light

Claims (8)

Laser processing means for processing the workpiece by irradiating the workpiece with a processing laser beam through a condenser lens;
The processing object is irradiated with a detection laser beam of a wavelength having transparency to the processing object, and the reflected light reflected on the opposite surface of the processing object opposite to the laser light irradiation surface is detected Position information detecting means for detecting position information related to the position of the opposite surface of the workpiece in the thickness direction of the workpiece;
Based on the position information detected by the position information detecting means, adjust the focusing point position of the processing laser beam collected by the condensing lens based on the position of the opposite surface of the workpiece First focusing point position adjusting means,
Laser processing equipment. The position information detection means irradiates the detection laser beam to the workpiece through the condenser lens,
A second focusing point position adjustment unit configured to adjust a focusing point position of the detection laser beam in a state where the focusing point position of the processing laser beam is fixed;
The laser processing apparatus according to claim 1. The second focusing point position adjusting means includes, in order from the workpiece side, a first lens group provided immovably along the optical path of the detection laser beam, and an optical path of the detection laser beam. And a second lens group movably provided,
The laser processing apparatus according to claim 2. The first lens group has a positive refractive power,
The laser processing apparatus according to claim 3. The laser processing means condenses the processing laser beam with the condenser lens inside the workpiece, and forms a modified region which becomes a starting point of cutting inside the workpiece.
The laser processing apparatus of any one of Claim 1 to 4. A laser processing step of processing the workpiece by irradiating the workpiece with a processing laser beam through a condenser lens;
The processing object is irradiated with a detection laser beam of a wavelength having transparency to the processing object, and the reflected light reflected on the opposite surface of the processing object opposite to the laser light irradiation surface is detected Position information detecting step of detecting position information related to the position of the opposite surface of the workpiece in the thickness direction of the workpiece;
Based on the position information detected by the position information detecting means, adjust the focusing point position of the processing laser beam collected by the condensing lens based on the position of the opposite surface of the workpiece Adjusting the first focusing point position;
Laser processing method equipped with In the positional information detection step, the laser beam for detection is irradiated to the workpiece through the condenser lens,
A second focusing point position adjusting step of adjusting the focusing point position of the detection laser beam in a state where the focusing point position of the processing laser beam is fixed;
The laser processing method according to claim 6. In the laser processing step, the processing laser beam is condensed by the condenser lens inside the workpiece, and a modified region which becomes a starting point of cutting is formed inside the workpiece.
The laser processing method of Claim 6 or 7.

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