Laser processing device

Abstract

Laser processing device (1) with: a clamping table (36) for holding a workpiece, a laser beam application means (5) for applying a laser beam to the workpiece which is held on the clamping table (36), wherein the laser beam application means (5) comprises a laser beam oscillator (6) for oscillating a laser beam, a focusing means (7) for concentrating the laser beam which has been set into oscillation by the laser beam oscillator (6) and for applying the concentrated laser beam to the workpiece which is held on the clamping table (36), and a laser beam branching mechanism (8) which is provided between the laser beam oscillator (6) and the focusing means (7) for branching the laser beam which has been set into oscillation by the laser beam oscillator (6) into a plurality of laser beams, and a feeding means (37) for moving the clamping table (36) and the laser beam application means (5) relative to each other in a feeding direction, wherein the laser beam branching mechanism (8) comprises a branching unit (90a, 90b, 90c) for branching the laser beam, which has been set into oscillation by the laser beam oscillator (6), into a plurality of laser beams, wherein the branching unit (90a, 90b, 90c) a half-wave plate (91) for rotating the polarization plane of the laser beam, which was set into oscillation by the laser beam oscillator (6), a first polarization beam splitter (92) for splitting the laser beam that has passed through the half-wave plate (91) into P-polarized light and S-polarized light, a first mirror (93) for reflecting the P-polarized light obtained by the first polarization beam splitter (92), a second mirror (94) for reflecting the S-polarized light obtained by the first polarization beam splitter (92), a second polarization beam splitter (95) for guiding the P-polarized light reflected by the first mirror (93) and the S-polarized light reflected by the second mirror (94) to different optical paths extending in the same direction,and an angle-adjusting means (930, 940) for adjusting the reflection angle of the P polarized light and / or the S polarized light to be reflected by the first and second mirrors (93, 94), wherein , The reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors (93, 94) is adjusted by the angle-adjusting means (930, 940) to adjust the distance between the focal points of the plurality of laser beams formed by the P-polarized light and the S-polarized light and to be concentrated by the focusing means (7), wherein the laser beam branching mechanism (8) has a plurality of branching units (90a to 90c), wherein the P-polarized light and the S-polarized light that has passed through the upstream portion of the plurality of branching units (90a to 90c) is rotated by 45° in the plane of polarization by the half-wave plate of the next of the plurality of branching units, and the P-polarized light is further branched into P-polarized light and S-polarized light in the next branching unit.that is to be introduced into the focusing medium (7), and the S polarized light is further branched in the next branching unit into P polarized light and S polarized light, which is to be introduced into the focusing medium (7).

Description

BACKGROUND OF THE INVENTION Technical field

[0001] The present invention relates to a laser processing device suitable for forming a laser-machined groove by applying a laser beam along a path formed on the front of a workpiece, such as a semiconductor wafer. Technical field

[0002] In a semiconductor device fabrication process, a multilayer layer, comprising an insulating layer and a functional layer, is formed on the front face of a semiconductor substrate, for example, a silicon substrate. From this multilayer layer, a multitude of devices, such as ICs and LSIs, are formed in a matrix, resulting in a semiconductor wafer containing these devices. The multiple devices are separated from each other by a multitude of partition lines, called roads, formed on the front face of the semiconductor wafer. The semiconductor wafer is then split along these roads to obtain the individual devices.

[0003] The sectioning of the semiconductor wafer along its length is typically performed using a cutting device known as a saw. This cutting device comprises a clamping table for holding the semiconductor wafer as a workpiece, a cutting element for cutting the semiconductor wafer held by the clamping table, and a motion device for moving the clamping table and the cutting element relative to each other. The cutting element includes a spindle configured to rotate at high speeds and a cutting blade attached to the spindle. The cutting blade consists of a disc-shaped base and an annular cutting edge attached to a side surface of the base along its outer circumference. The cutting edge is formed by bonding diamond abrasive grains with a grain size of approximately 3 µm through electroforming, resulting in a cutting edge thickness of, for example, 20 to 30 µm.

[0004] In recent years, a semiconductor wafer has been used to improve the processing efficiency of devices such as ICs and LSIs. This semiconductor wafer comprises a semiconductor substrate, such as a silicon substrate, and a multilayer layer formed on the front side of the semiconductor substrate. The multilayer layer features a low-permittivity insulating layer (low-k layer) and a functional layer formed on top of the low-k layer, with the functional layer forming a variety of circuits. Thus, the semiconductor devices are formed from the multilayer layer. The low-k layer is formed, for example, from an inorganic layer of SiOF, BSG (SiOB), etc., or from an organic layer, such as a polymer layer of polyimide, parylene, etc.A semiconductor wafer is also used in practice which has a design in which a large number of metal grids, a so-called test element group (TEG), are partially provided on the roads of the semiconductor wafer to test the function of the circuits through the metal grids before the semiconductor wafer is split.

[0005] The low-k layer, or the previously mentioned test element group (TEG), is composed of a different material than the semiconductor substrate, making it difficult to cut the semiconductor substrate along with the low-k layer or TEG using a cutting blade. Specifically, the low-k layer is very brittle, similar to mica. Therefore, when the semiconductor wafer containing the low-k layer is cut along its edges using a cutting blade, the problem arises that the low-k layer can be chipped off, and this chipping can reach the equipment, potentially causing catastrophic damage. Furthermore, the TEG is made of metal. Cutting the semiconductor wafer containing the TEG along its edges can therefore create burrs.To solve these problems, a processing method has been proposed in which a pulsed laser beam is applied along the roads on the semiconductor wafer to remove the low-k layer which forms the roads or the test element group (TEG) provided on the roads, and then the area where the low-k layer or test element group (TEG) is no longer present is cut using the cutting blade (see, for example, Japanese application JP 2005-142 398 A).

[0006] In the case where the low-k layer or test element group (TEG) is removed by applying a pulsed laser beam along the paths of the semiconductor wafer, as in the processing method disclosed in Japanese application JP 2005-142 398 A, it is necessary to form a laser processing groove along each path with a width greater than the thickness of the cutting blade. Accordingly, if the concentrated spot diameter of the laser beam is approximately 10 µm, a laser beam application step must be performed multiple times to apply the laser beam along each path, causing the concentrated spot to shift along the width of each path, resulting in a reduction in productivity.

[0007] To solve this problem, a laser processing device was proposed, as described in Japanese application JP 2011-156 551 A. This laser processing device has an embodiment in which a laser beam is branched into a plurality of laser beams to form a plurality of concentrated spots (focus points) arranged along the width of each road such that they can form a wide laser processing groove in one stroke, enabling the efficient removal of the low-k layer or test element group (TEG).

[0008] KR 10 2012 0 016 456 A discloses a laser processing device with a light source, a first beam splitter, and a path difference generation device. The light source emits laser light at a fixed frequency, which is split into first and second laser light by means of the first beam splitter. The path difference generation device comprises a first and a second reflecting mirror and a second beam splitter. The first reflecting mirror reflects the second laser light, which is directed to the second reflecting mirror. The second reflecting mirror reflects the second laser light, which originates from the first reflecting mirror, towards the second beam splitter. The first laser light passes through the second beam splitter, and the second laser light is reflected by the second beam splitter.The first and second laser lights emerge from the second beam splitter with a path difference that can be adjusted using the path difference generation device.

[0009] US 2010 / 0317172A1 discloses a laser processing device comprising a clamping table, a laser beam application means, a means for moving the clamping table, and a laser beam branching mechanism with a branching unit for branching a laser beam.

[0010] US 2011 / 0 186 555 A1 discloses a laser processing device with a laser beam branching mechanism, which includes a branching unit for branching a laser beam. The branching unit comprises a beam splitter and a beam combiner, wherein each of the two beams split by the beam splitter is directed by a mirror onto the beam combiner. To split the laser beam into more than two beams, switches with additional optical elements are provided between the beam splitter and the mirrors. PRESENTATION OF THE INVENTION

[0011] In contrast, in the method described in the Japanese application JP 2011-156 551 A, it is difficult to adjust the distance between the multitude of concentrated spots (focus points) to the multitude of laser beams, so that the multitude of concentrated spots (focus points) cannot be arranged in such a way that they fall within the area corresponding to the width of each road.

[0012] It is therefore an object of the present invention to provide a laser processing device with which the distance between the plurality of concentrated spots (focus points) of the plurality of laser beams can be easily adjusted.

[0013] According to one aspect of the present invention, a laser processing device is provided comprising a clamping table for holding a workpiece; a laser beam application means for applying a laser beam to the workpiece which is held on the clamping table, wherein the laser beam application means comprises a laser beam oscillator for oscillating a laser beam, a focusing means for concentrating the laser beam which has been set into oscillation by the laser beam oscillator and for applying the concentrated laser beam to the workpiece which is held on the clamping table, and a laser beam branching mechanism which is provided between the laser beam oscillator and the focusing means for branching the laser beam which has been set into oscillation by the laser beam oscillator into a plurality of laser beams.comprising; and a feed means for moving the clamping table and the laser beam application means relative to each other in a feed direction; wherein the laser beam branching mechanism comprises a branching unit for branching the laser beam, which has been set into oscillation by the laser beam oscillator, into a plurality of laser beams; and the branching unit comprises a half-wave plate for rotating the polarization plane of the laser beam, which has been set into oscillation by the laser beam oscillator, by 45°, a first polarization beam splitter for splitting the laser beam, which has passed through the half-wave plate, into P-polarized light and S-polarized light, a first mirror for reflecting the P-polarized light obtained by the first polarization beam splitter, a second mirror for reflecting the S-polarized light obtained by the first polarization beam splitter,a second polarization beam splitter for guiding the P-polarized light reflected by the first mirror and the S-polarized light reflected by the second mirror to different optical paths extending in the same direction, and an angle-adjusting device for adjusting the reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors; wherein the reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors is adjusted by the angle-adjusting device in order to adjust the distance between the focal points of the plurality of laser beams formed by the P-polarized light and the S-polarized light and to be concentrated by the focusing device.

[0014] The laser beam branching mechanism comprises a plurality of branching units, wherein the P polarized light and the S polarized light that has passed through the upstream portion of the plurality of branching units is rotated by 45° in the plane of polarization by the half-wave plate of the following plurality of branching units, and the P polarized light is further branched in the following branching unit into P polarized light and S polarized light, which is to be directed to the focusing means, wherein the S polarized light is further branched in the following branching unit into P polarized light and S polarized light, which is to be directed to the focusing means.

[0015] In the laser processing device according to the present invention, the laser beam branching mechanism, which is provided between the laser beam oscillator and the focusing means for branching the laser beam, which has been set into oscillation by the laser beam oscillator, into a plurality of laser beams, comprises the branching unit for branching the laser beam, which has been set into oscillation by the laser beam oscillator, into the plurality of laser beams. The branching unit comprises the half-wave plate for rotating the polarization plane of the laser beam, which has been set into oscillation by the laser beam oscillator, by 45°, the first polarization beam splitter for splitting the laser beam, which has passed through the half-wave plate, into P-polarized light and S-polarized light, and the first mirror for reflecting the P-polarized light.which was obtained by the first polarization beam splitter, the second mirror for reflecting the S-polarized light obtained by the first polarization beam splitter, the second polarization beam splitter for guiding the P-polarized light reflected by the first mirror and the S-polarized light reflected by the second mirror to different optical paths extending in the same direction, and the angle-adjusting device for adjusting the reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors. The reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors is adjusted by the angle-adjusting device to determine the distance between the focal points of the plurality of laser beams.which are formed by P-polarized and S-polarized light and must be concentrated by the focusing device. Accordingly, the distance between the concentrated spots (focus points) of the multitude of laser beams can be easily adjusted.

[0016] The above and further tasks, features and advantages of the present invention and the way in which they are realized will become clearer, and the invention itself is best understood by studying the following description and the attached claim with reference to the accompanying drawings, which show a preferred embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a perspective view of a laser processing device according to the present invention; Fig. Figure 2 is a block diagram showing the design of a laser beam application device that performs the function described in Figure 2. Fig. 1 laser processing device shown; Fig. 3 is a schematic diagram to show a branching unit that divides the in Fig. 2 laser beam application means shown; Fig. Figure 4 is a schematic diagram showing a variety of laser beams emitted by the one in Fig. The laser beam application means shown in the 2 are to be applied; Fig. 5 is a block diagram showing the design of a control device which is used in the Fig. The laser processing device shown in 1 is included; Fig. 6A is a perspective view of a semiconductor wafer as a workpiece; Fig. Figure 6B is an enlarged cross-sectional view of a substantial portion of the semiconductor wafer that is in Fig. 6A is shown; Fig. 7A and Fig. Figure 7B shows perspective views of a semiconductor wafer placement step, which is performed in Fig. 6A shows a protective strap that is supported by a ring-shaped frame; Fig. Figures 8A to 8C are views showing a laser beam application step for forming a laser-machined groove along each road of the semiconductor wafer, which is in Fig. Figure 6A shows the laser processing device, which is located in Fig. 1 is shown, is used; and Fig. Figure 9 is an enlarged cross-sectional view of the laser-machined groove, which is created on the semiconductor wafer by performing the process described in Fig. The laser beam application step shown in 8A to 8C is formed. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0017] A preferred embodiment of the laser processing device according to the present invention will now be described with reference to the accompanying drawings. Fig. Figure 1 is a perspective view of a laser processing device 1 according to a preferred embodiment of the present invention. The laser processing device 1, which is shown in Fig. Figure 1, comprising a stationary base 2, a clamping table mechanism 3 for holding a workpiece, wherein the clamping table mechanism 3 is provided on the stationary base 2 such that it is movable in a feed direction (X-direction) indicated by an arrow X, a laser beam application unit support mechanism 4, which is provided on the stationary base 2 such that it is movable in an adjustment direction (Y-direction) indicated by an arrow Y and arranged perpendicular to the X-direction, and a laser beam application unit 5, which is provided on the laser beam application unit support mechanism 4 such that it is movable in a focus position adjustment direction (Z-direction) indicated by an arrow Z.

[0018] The clamping table mechanism 3 comprises a pair of guide rails 31, which are arranged on the stationary base such that they extend parallel to each other in the X-direction, a first sliding block 32, which is arranged on the guide rails 31 so that it can move in the X-axis direction, a second sliding block 33, which is arranged on the first sliding block 32 so that it can move in the Y-direction, a support table 35, which is supported by a cylindrical element 34 that stands on the second sliding block 33, and a clamping table 36 as a workpiece holding device. The clamping table 36 includes a workpiece holding surface 361, which is formed from a porous material. A workpiece, such as a disk-shaped semiconductor wafer, is arranged to be held by suction on the workpiece holding surface 361 during operation by a suction device (not shown).The clamping table 36 is rotatable by means of an actuator (not shown) which is provided in the cylinder element 34. Furthermore, clamps 362 are provided on the clamping table 36 to fix an annular frame which, as described later, supports the wafer.

[0019] The lower surface of the first sliding block 32 is provided with a pair of guide grooves 321 to engage slidably with the aforementioned pair of guide rods 31. A pair of guide rods 322 is provided on the upper surface of the first sliding block 32 such that they extend parallel to each other in the Y-direction. Accordingly, the first sliding block 32 is movable in the X-direction along the guide rods 31 by means of the slidable engagement of the guide grooves 321 with the guide rods 31. The clamping table mechanism 3 further comprises a feeder 37 for moving the first sliding block 32 in the X-direction along the guide rods 31. The feeder 37 includes an external threaded rod 371, which extends parallel to the guide rods 31 so that it is inserted between them, and an actuator 372 as a drive source for rotating the external threaded rod 371.The external threaded rod 371 is rotatably mounted at one end in a bearing block 373, which is attached to the stationary base 2, and at the other end is connected to the output shaft of the actuator 372 to receive the torque. The external threaded rod 371 engages with a threaded through-bore in an internal threaded block (not shown) that projects from the lower surface of the first sliding block 32 in a central region. Accordingly, the first sliding block 32 is moved in the X-direction, as the feed direction, along the guide rods 31 by operating the actuator 372 to rotate the external threaded rod 371 normally or in reverse.

[0020] The lower surface of the second sliding block 33 is provided with a pair of guide grooves 331 for sliding engagement with the pair of guide rods 322 provided on the upper surface of the first sliding block 32, as previously mentioned. Accordingly, the second sliding block 33 is movable in the Y-direction along the guide rods 322 by means of the sliding engagement of the guide grooves 331 with the guide rods 322. The clamping table mechanism 3 further comprises a first adjusting means 38 for moving the second sliding block 33 in the Y-direction along the guide rods 322. The first adjusting means 38 comprises an externally threaded rod 381, which extends parallel to the guide rods 322 such that it is inserted between them, and an actuator 382 as a drive source for rotaryally driving the externally threaded rod 381.The external threaded rod 381 is rotatably mounted at one end in a bearing block 383, which is attached to the upper surface of the first sliding block 32, and at the other end is connected to the output shaft of the actuator 382 to absorb its torque. The external threaded rod 381 engages with a threaded through-hole formed in an internal threaded block (not shown) that projects from the lower surface of the second sliding block 33 in a central region thereof. Accordingly, the second sliding block 33 is moved in the Y-direction as the adjustment direction along the guide rods 322 by operating the pulse motor 382 to rotate the external threaded rod 381 normally or in reverse.

[0021] The laser beam application unit support mechanism 4 comprises a pair of guide rods 41 mounted on the stationary base 2 such that they extend parallel to each other in the Y-direction, and a movable support base 42 mounted on the guide rods 41 such that it is movable in the Y-direction. The movable support base 42 comprises a horizontal section 421, which is slidably supported on the guide rods 41, and a vertical section 422, which extends vertically upward from the upper surface of the horizontal section 421. Furthermore, a pair of guide rods 423 is mounted on a side surface of the vertical section 422 such that they extend parallel to each other in the Z-direction. The laser beam application unit support mechanism 4 also comprises a second adjustment means 43 for moving the movable support base 42 along the guide rods 41 in the Y-direction.The second adjusting means 43 comprises an external threaded rod 431, which extends parallel to the guide rods 41 such that it is inserted between them, and an actuator 432 as a drive source for rotating the external threaded rod 431. The external threaded rod 431 is rotatably supported at one end by a bearing block (not shown) attached to the stationary base 2, and at the other end is connected to the output shaft of the actuator 432 to receive the torque. The external threaded rod 431 engages with a threaded through-hole formed in an internal threaded block (not shown) that projects from the lower surface of the horizontal area 421 in a central region thereof.Accordingly, the movable support base 42 is moved in the Y direction as the adjustment direction along the guide rods 41 by operating the actuator 432 to drive the external threaded rod 431 normally or backwards.

[0022] The laser beam application unit 5 comprises a unit holder 51 and a laser beam application device 52, which is attached to the unit holder 51. The unit holder 51 is provided with a pair of guide grooves 511 for sliding engagement with the pair of guide rods 423, which are provided on the vertical section 422 of the movable support base 42. Accordingly, the unit holder 51 is supported by the movable support base 42 such that the base is movable in the Z-direction by the sliding engagement of the guide grooves 511 with the guide rods 423.

[0023] The laser beam application unit 5 further comprises a focus position adjustment device 54 for moving the unit holder 51 along the guide rods 423 in the Z-direction. The focus position adjustment device 54 includes an external threaded rod (not shown) extending parallel to the guide rods 423 such that it is inserted between them, and an actuator 542 as a drive source for rotating this external threaded rod. Accordingly, the unit holder 51 and the laser beam application device 52 are moved in the Z-direction as the focus position adjustment direction along the guide rods 423 by operating the actuator 542 to drive this external threaded rod normally or backwards.In this preferred embodiment, the laser beam application means 52 is moved upwards when the actuator 542 is operated normally, and the laser beam application means 52 is moved downwards when the actuator 542 is operated in reverse.

[0024] As in Fig. As shown in Figure 1, the laser beam application means 52 comprises a cylindrical housing 521, which is attached to the unit holder 51 such that the latter extends in a substantially horizontal direction. As shown in Fig. As shown in Figure 2, the laser beam application means 52 comprises a pulsed laser beam oscillator 6 provided in the housing 521, a focusing means 7 for concentrating the pulsed laser beam, which has been set into oscillation by the pulsed laser beam oscillator 6, and for applying the pulsed laser beam to a workpiece W held on the clamping table 36, and a laser beam branching mechanism 8 provided between the pulsed laser beam oscillator 6 and the focusing means 7 to branch the pulsed laser beam, which has been set into oscillation by the pulsed laser beam oscillator 6, into a plurality of laser beams. The focusing means 7 has a focusing objective lens 71. As shown in Fig. As shown in Figure 1, the focusing means 7 is provided at a front end of the housing 521.

[0025] The pulsed laser beam oscillator 6 comprises a pulsed laser oscillator 61, such as a YAG laser oscillator or a YVO4 laser oscillator, and a repetition rate setting device 62, which is connected to the pulsed laser oscillator 61. The pulsed laser oscillator 61 oscillates a pulsed laser beam (LB) at a predetermined frequency, which is set by the repetition rate setting device 62. The repetition rate setting device 62 sets the repetition frequency of the pulsed laser beam to be set into oscillation by the pulsed laser oscillator 61. The pulsed laser oscillator 61 and the repetition rate setting device 62 of the pulsed laser beam oscillator 6 are controlled by the control device, which is described below.

[0026] Referring again to Fig. 2, the laser beam branching mechanism 8 comprises a first branching unit 90a, a second branching unit 90b, and a third branching unit 90c, all of which have the same configuration. That is, each of the first, second, and third branching units 90a, 90b, and 90c includes a half-wave plate 91, a first polarization beam splitter 92, a first mirror 93, a second mirror 94, and a second polarization beam splitter 95. The operation of the first to third branching units 90a to 90c is now described with reference to Fig. 3. The polarization plane of the laser beam incident on the half-wave plate 91 is rotated by 45° by the half-wave plate 91. Subsequently, the laser beam passing through the half-wave plate 91 is split into P-polarized light and S-polarized light by the first polarization beam splitter 92. The P-polarized light obtained by the first polarization beam splitter 92 is reflected by the first mirror 93 to fall onto the second polarization beam splitter 95. On the other side, the S-polarized light obtained by the first polarization beam splitter 92 is reflected by the second mirror 94 to fall onto the second polarization beam splitter 95.The P-polarized light and the S-polarized light incident on the second polarization beam splitter 95 are thus parallelized by the second polarization beam splitter 95 to propagate along different optical paths extending in the same direction.

[0027] The first to third branching units 90a to 90c are configured as previously described. Accordingly, the laser beam, which has been set into oscillation by pulsed laser beam oscillators 6, is first branched into P-polarized light and S-polarized light by the first branching unit 90a. The P-polarized light propagating from the first branching unit 90a is further branched into P-polarized light and S-polarized light by the second branching unit 90b, and the S-polarized light propagating from the first branching unit 90a is further branched into P-polarized light and S-polarized light by the second branching unit 90b.Each P-polarized light propagating from the second branching unit 90b is further branched into P-polarized light and S-polarized light by the third branching unit 90c, and each S-polarized light propagating from the second branching unit 90b is further branched into P-polarized light and S-polarized light by the third branching unit 90c. In this manner, the laser beam, which has been set into oscillation by the pulsed laser beam oscillator 6, is branched into a beam of P-polarized light and a beam of S-polarized light by the first branching unit 90a, then into two beams of P-polarized light and two beams of S-polarized light by the second branching unit 90b, and finally into four beams of P-polarized light and four beams of S-polarized light by the third branching unit 90c.Thus, the laser beam, which has been set into oscillation by the pulsed laser beam oscillator 6, is split into eight laser beams by the first to third branching units 90a to 90c, and these eight laser beams are concentrated by the focusing objective lens 71 of the focusing unit 7. Each of the first to third branching units 90a to 90c, which form the laser beam branching mechanism, further comprises a first angle-adjusting device 930 for adjusting the reflection angle of the P-polarized light to be reflected by the first mirror 93, and a second angle-adjusting device 940 for adjusting the reflection angle of the S-polarized light to be reflected by the second mirror 94. In this preferred embodiment, each of the first and second angle-adjusting devices 930 and 940 comprises a servo motor and is controlled by a control device described below.

[0028] While the first and second angle-adjusting means 930 and 940 are used to adjust the reflection angles of the P-polarized light and the S-polarized light to be reflected by the first and second mirrors, respectively, in this preferred embodiment the reflection angle of at least one of the P-polarized light and the S-polarized light to be reflected by the first and second mirrors 93 and 94 can be adjusted. In this way, the first and second angle-adjusting means 930 and 940, each comprising an actuating motor in this preferred embodiment, are used to adjust the reflection angles of the P-polarized light and the S-polarized light, respectively.to adapt the S polarized light, which is to be reflected by the first second mirror 93 and 94, so that the eight laser beams which propagate from the third branching unit 90c are concentrated at different focal points P1 to P8 by the focusing objective lens 71, as in . Fig. Figure 4 shows that in this preferred embodiment, the focal points P1 to P8 of the laser beam, which is to be concentrated by the focusing objective lens 71, are arranged at given intervals in the Y direction. The intervals of the focal points P1 to P8 of the laser beams, which are to be concentrated by the focusing objective lens 71, can be adjusted by operating the first and second angle-adjusting means 930 and 940 in order to change the reflection angles of the P-polarized light and the S-polarized light, which is to be reflected by the first and second mirrors 93 and 94, respectively.

[0029] Referring again to Fig. 2. The laser processing device 1 has a focus spot interval monitor unit 11 for checking the intervals of the focus points P1 to P8 of the laser beam, which is to be concentrated by the focusing objective lens 71. The focus spot interval monitor unit 11 comprises a semi-transparent mirror 111, which is provided on an optical path between the third branching unit 90c and the focusing means 7, a bandpass filter 112 for transmitting light with a wavelength corresponding to the wavelength of the laser beam reflected by the semi-transparent mirror 111, an imaging lens 113 for imaging the laser beam that has passed through the bandpass filter 112, and a CCD camera 114 for detecting the focus points (concentrated spots) of the laser beam that have been imaged by the imaging lens 113. The focus spot interval monitor unit 11 is operated in the following manner.The eight laser beams, consisting of four beams of P-polarized light and four beams of S-polarized light, and obtained by the first to third branching units 90a to 90c, are reflected by the semi-transparent mirror 111 and passed through the bandpass filter 112 to enter the imaging lens 113. The eight laser beams incident on the imaging lens 113 are thus imaged as focal points P1 to P8 by the imaging lens 113, just as by the focusing lens 71. The focal points P1 to P8, which are thus imaged, are detected by the CCD camera 114. Subsequently, the focal points P1 to P8 detected by the CCD camera 114 are sent to control devices (not shown) and then displayed by indicator devices (not shown), both of which are subsequently written to.The semi-transparent mirror 111 is preferably designed to optionally assume an operating position which is arranged on the optical path and a retraction position which is withdrawn from the optical path.

[0030] Referring again to Fig. 1. The imaging device 12 is provided for detecting an area of ​​the workpiece, which is to be laser-processed by the laser beam application device 52, at the front end region of the housing 521, which forms the laser beam application device 52. The imaging device 12 comprises an illumination device for illuminating the workpiece, an optical system for detecting an area illuminated by the illumination device, and an imaging device (CCD) for imaging the area detected by the optical system. An imaging signal output by the imaging device 12 is transmitted to the control device 10, which is located in Fig. 6 is shown, transmitted.

[0031] The laser processing device 1 comprises the in Fig. The control device 10 shown comprises a central processing unit (CPU) 101 for executing operational processes according to a control program, a read-only memory (ROM) 102 that temporarily stores the control program, a random-access memory (RAM) 103 for storing the calculation results, etc., an input interface 104, and an output interface 105. Detection signals from the CCD camera 114, the focus spot interval monitor unit 11, and the imaging device 12 are input into the input interface 104 of the control device 10.On the other hand, control signals are sent from the output interface 105 of the control device 10 to the actuator 372 of the feed device 37, the actuator 382 of the first adjustment device 38, the actuator 432 of the second adjustment device 43, the actuator 542 of the focus position adjustment device 54, the pulsed laser beam oscillation device 6 of the laser beam application device 52, an actuator 89 of a spread angle adjustment device 80 (. Fig. 2), and a display medium 15 was issued.

[0032] The operation of the laser processing device, which is designed as described above, will now be described. Fig. Figure 6A is a perspective view of a semiconductor wafer 20 as a workpiece, and Fig. Figure 6B is an enlarged cross-sectional view of a substantial part of the semiconductor wafer 20, which is located in Fig. 6A is shown. As in Fig. 6A and Fig. As shown in Figure 6B, the semiconductor wafer 20 is formed from a semiconductor substrate 21, such as a silicon substrate, and a multilayer layer 22 formed on the front face of the semiconductor substrate 21. The multilayer layer 22 has an insulating layer and a functional layer formed on the insulating layer, the functional layer forming a plurality of circuits. A plurality of devices 23, such as ICs and LSIs, are formed in a grid pattern through the multilayer layer 22. These devices 23 are separated by a plurality of intersecting roads 24 formed on the multilayer layer 22. In this preferred embodiment, the insulating layer forming the multilayer layer 22 is formed by a SiO2 layer or a low-permittivity insulating layer (low-k layer).Examples of the low-k layer include an inorganic layer on SiOF, BSG (SiOB), etc., and an organic layer, such as a polymer layer of polyimide, parylene, etc. A method for forming a laser-machined groove on the multilayer layer 22 along a road 24 of the semiconductor wafer 20 is now described.

[0033] Before the semiconductor wafer 20 is divided along each road 24, the semiconductor wafer 20 is attached to a protective belt T, which is mounted on an annular frame F, as shown in Fig. 7A and Fig. 7B shown, supported, attached. More precisely, the back side 20b of the semiconductor wafer 20 is attached to the protective band T in the state where the front side 20a of the semiconductor wafer 20 is oriented upwards. Subsequently, a laser beam application step is performed such that a laser beam is applied along each roadway 24 of the semiconductor wafer 20 to remove the multilayer layer 22 present on each roadway 24. First, the semiconductor wafer 20, which is supported by the protective band T on the annular frame F, is placed on the clamping table 36 of the laser processing device 1, which is in Fig. As shown in Figure 1, the semiconductor wafer 20 is arranged in the state where the front face 20a is oriented upwards. In this state, the suction device (not shown) is operated to hold the semiconductor wafer 20 under suction by the protective band T on the clamping table 36. Accordingly, the semiconductor wafer 20 is held on the clamping table 36 in the state where the front face 20a of the semiconductor wafer 20 is oriented upwards. Furthermore, the annular frame F, which supports the semiconductor wafer 20 by the protective band T, is fixed by the clamps 362.

[0034] The feeder 37 is then operated to move the clamping table 36, which holds the semiconductor wafer 20 under suction, to a position directly below the imaging device 12. In this state, where the clamping table 36 is positioned directly below the imaging device 12, the control device 10 operates the imaging device 12 to perform an alignment operation in order to detect the area of ​​the semiconductor wafer 20 to be laser-processed. More precisely, the imaging device 12 and the control device 10 perform an image processing operation, such as raster matching, to align the roads 24 extending in a first direction on the semiconductor wafer 20, and the focusing device 7 of the laser beam application device 52 to apply the laser beam along the roads 24, thereby aligning a laser beam application position.The imaging device 12 and the control device 10 perform the alignment operation for the other roads 24, which extend in a second direction perpendicular to the previously mentioned first direction, in a similar manner.

[0035] After executing the alignment operation to detect all roads 24 on the semiconductor wafer 20, which is held on the clamping table 36, the clamping table 36 is moved in the X-direction and the Y-direction so that one end (left end in Fig. 8A) one of the predetermined roads 24 extending in the first direction, directly below the focusing means 7, as in Fig. 8A is shown, arranged. Fig. Figure 8B is a magnified top view showing this state, with S1 to S8 showing eight concentrated spots at the focal points P1 to P8 of the eight laser beams to be applied by the focusing means 7. As in Fig. As shown in Figure 8B, these concentrated spots S1 to S8 are arranged along the width of this predetermined road 24. Subsequently, the focus position adjustment means 54 is operated to adjust the height of the laser beam application means 52 so that the concentrated spots S1 to S8 of the eight laser beams are formed on the front (top surface) of this predetermined road 24.

[0036] The laser beam application device 52 is then operated to apply the eight laser beams with an absorption wavelength onto the semiconductor wafer 20 from the focusing device 7, and the clamping table 36 is moved in the direction indicated by an arrow X1. Fig. As shown in 8A, the laser beam is moved at a predetermined feed rate (laser beam application step). Once the other end (right end in 8A) is reached, the laser beam is moved at a predetermined feed rate (laser beam application step). Fig. 8C) of the predetermined road 24 reaches the position directly below the focusing medium 7, as in Fig. As shown in Figure 8C, the application of the laser beam is stopped by the focusing means 7 and the movement of the clamping table 36 is also stopped.

[0037] For example, the laser beam application step is performed with the following processing states.

[0038] Laser beam light source: YVO4 laser or YAG laser Wavelength: 355 nm Power: 10 W Repetition rate: 100kHz Pulse width: 1 ns Concentrated spot diameter: 5 µm Processing feed speed: 100 mm / s

[0039] By specifying the condition that the concentrated spots S1 to S8, each having a concentrated spot diameter of 5 µm as previously mentioned, are in contact with each other, as in Fig. Figure 8B shows a laser-machined groove 210 with a width (E) of 40 µm and a depth greater than the thickness of the multilayer layer 22 present on the predetermined road 24, along this road 24 by the eight laser beams, as shown in Fig.The intervals of the concentrated spots S1 to S8 can be easily adjusted by operating the first and second angle-adjusting devices 930 and 940 to adjust the reflection angle of the P-polarized light and the S-polarized light, which is to be reflected by the first and second mirrors 93 and 94, respectively, and incident on the second polarization beam splitter 95. The laser beam application step mentioned previously is performed similarly for all other roads 24 formed on the semiconductor wafer 20. After forming the laser-machined groove 210 along each road 24, the semiconductor wafer 20 is transported to a cutting device for a splitting step.

[0040] In this preferred embodiment, the laser processing device 1 is used to apply laser beams with an absorption wavelength to the workpiece, thereby performing ablation to form the laser-processed groove 210 along each road 24. However, the laser processing device according to the present invention can also be used in the case where the laser beams with a transmission wavelength are applied to the workpiece in such a way that the focal points of the laser beams are fixed within the workpiece, thereby forming a modified layer within the workpiece.

[0041] Furthermore, while the focal points P1 to P8 of the laser beams are arranged in the Y direction perpendicular to the feed direction (X direction) in this preferred embodiment, the focal points P1 to P8 of the laser beams can also be arranged in the feed direction (X direction) depending on the processing states.

[0042] In the case where the maximum distance between the first and last focal points forming the plurality of focal points of the laser beams is approximately 150 µm, a general convex lens can be used as the focusing objective lens 71 of the focusing means 7. In the case where the maximum distance is 1 mm or more, however, an fθ lens or an image-side telecentric lens can preferably be used.

Claims

[1] Laser processing device (1) with: a clamping table (36) for holding a workpiece, a laser beam application means (5) for applying a laser beam to the workpiece which is held on the clamping table (36), wherein the laser beam application means (5) comprises a laser beam oscillator (6) for oscillating a laser beam, a focusing means (7) for concentrating the laser beam which has been set into oscillation by the laser beam oscillator (6) and for applying the concentrated laser beam to the workpiece which is held on the clamping table (36), and a laser beam branching mechanism (8) which is provided between the laser beam oscillator (6) and the focusing means (7) for branching the laser beam which has been set into oscillation by the laser beam oscillator (6) into a plurality of laser beams, and a feeding means (37) for moving the clamping table (36) and the laser beam application means (5) relative to each other in a feeding direction, wherein the laser beam branching mechanism (8) comprises a branching unit (90a, 90b, 90c) for branching the laser beam, which has been set into oscillation by the laser beam oscillator (6), into a plurality of laser beams, wherein the branching unit (90a, 90b, 90c) a half-wave plate (91) for rotating the polarization plane of the laser beam, which was set into oscillation by the laser beam oscillator (6), a first polarization beam splitter (92) for splitting the laser beam that has passed through the half-wave plate (91) into P-polarized light and S-polarized light, a first mirror (93) for reflecting the P-polarized light obtained by the first polarization beam splitter (92), a second mirror (94) for reflecting the S-polarized light obtained by the first polarization beam splitter (92), a second polarization beam splitter (95) for guiding the P-polarized light reflected by the first mirror (93) and the S-polarized light reflected by the second mirror (94) to different optical paths extending in the same direction,and an angle-adjusting means (930, 940) for adjusting the reflection angle of the P polarized light and / or the S polarized light to be reflected by the first and second mirrors (93, 94), wherein, The reflection angle of the P-polarized light and / or the S-polarized light to be reflected by the first and second mirrors (93, 94) is adjusted by the angle-adjusting means (930, 940) to adjust the distance between the focal points of the plurality of laser beams formed by the P-polarized light and the S-polarized light and to be concentrated by the focusing means (7), wherein the laser beam branching mechanism (8) has a plurality of branching units (90a to 90c), wherein the P-polarized light and the S-polarized light that has passed through the upstream portion of the plurality of branching units (90a to 90c) is rotated by 45° in the plane of polarization by the half-wave plate of the next of the plurality of branching units, and the P-polarized light is further branched into P-polarized light and S-polarized light in the next branching unit.that is to be introduced into the focusing medium (7), and the S polarized light is further branched in the next branching unit into P polarized light and S polarized light, which is to be introduced into the focusing medium (7).

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