LASER PROCESSING DEVICE

Abstract

Laser processing device (40) comprising: a clamping table (54) which holds a wafer (10) having a front side (10a) and a back side (10b); a laser beam application means (44) that applies a laser beam to the wafer (10) which is held by the clamping table (54); and a processing feed means (43) that performs a relative processing feed of the clamping table (54) and the application means (44) for a laser beam, wherein the application means for a laser beam comprises a laser oscillator (44b) which oscillates a pulsed laser beam, and a focusing device (44a) which focuses the pulsed laser beam oscillated by the laser oscillator (44b) in order to apply the pulsed laser beam to the wafer (10) which is held by the clamping table (54), and The pulsed laser beam, oscillated by the laser oscillator (44b), includes burst pulses (BP), each of which has several subpulses that are gradually amplified stepwise from a lower energy to a high energy, and the burst pulses (BP) are applied to the wafer (10) to form shielding tunnels (100), each containing a small hole (102) and an amorphous phase (104) surrounding the small hole, wherein the application means (44) is configured for a laser beam to form a circular small hole (102) and a circular amorphous phase (104), each extending from the front side (10a) to the rear side (10b) of the wafer (10), wherein the focusing device (44a) is movable in the direction of the optical axis and configured such that the focal point is positioned at a predetermined position in the wafer (10). is.

Description

BACKGROUND OF THE INVENTION Technical field

[0001] The present invention relates to a laser processing device for performing laser processing to form division start points along division lines of a wafer. Description of the state of the art

[0002] A wafer containing multiple components such as integrated circuits (ICs), large-scale integrations (LSIs), light-emitting diodes (LEDs), surface acoustic wave (SAW) devices, and power devices, formed in areas of a front surface divided by dividing lines, is divided into individual component chips by a laser processing device, and the chips thus divided are used in electronic devices such as mobile phones, personal computers, and lighting devices (see, for example, Japanese patent application JP H10-305 420 A).

[0003] The laser processing device generally includes a clamping table for holding a workpiece, a laser beam delivery device which includes a focusing unit for applying a laser beam to the workpiece held on the clamping table, and a processing feeder for performing a relative processing feed of the laser beam between the clamping table and the delivery device. The laser processing device enables the laser beam to be applied with high accuracy along any parting line of a wafer to process the wafer for sectioning.

[0004] The laser processing devices are classified into a type in which a laser beam having a wavelength that is absorbed in the workpiece is applied to the workpiece to subject the workpiece to surface ablation, as disclosed in Japanese patent application JP H10-305 420 A, and into a type in which a laser beam having a wavelength that is transmitted in the workpiece is applied with a focal point positioned in the workpiece to form modified layers in the workpiece, as described, for example, in Japanese patent JP 3 408 805 B2.

[0005] However, both types of laser processing devices suffer from the problem of low productivity, as the laser beam must be applied multiple times along the parting lines to cut the wafer while maintaining good quality. Addressing this problem, the present inventor has developed and proposed a technology for forming shielding tunnels extending from the front surface to the rear surface of a wafer along the parting lines, each shielding tunnel consisting of a small hole and an amorphous phase surrounding the small hole (see, for example, Japanese patent application JP 2014-221 483 A).

[0006] JP 2014 - 221 483 A concerns the laser processing of single crystal substrates.

[0007] DE 10 2014 213 775 A1 relates to a method for laser-based processing of a planar, crystalline substrate.

[0008] JP 2015 - 207 664 A relates to a method for processing a single crystal substrate.

[0009] JP 2010-82645A relates to a laser marking method. JP 2013-132664A relates to a method for laser processing with double pulses.

[0010] EP 2 965 853 A1 discloses a treatment of a material using asymmetric laser beams, which results in the material being cut. Ultrashort laser pulses are generated, with each emitted laser pulse causing a crack within the material. Each laser pulse is shaped with respect to its beam profile such that a cross-sectional shape, defined by a cross-section of the laser pulse at its focal position perpendicular to the application direction, is asymmetric with respect to its shape and defines a principal propagation axis according to its asymmetric propagation.

[0011] EP 2 859 983 A2 discloses a system for processing a transparent material using a laser, wherein it is generally stated that a control and processing unit can make different settings, which, for example, can vary the pulse energy of the individual pulses within a range from the laser source. However, the focus of the laser beam is set as lying outside the material.

[0012] EP 2 868 421 A1 discloses a method and a device for processing diamonds and gemstones by filamentation using ultrashort laser pulses of a burst. According to the technical teaching of the publication, a focus for the laser pulses is selected that lies outside the material.

[0013] EP 2 910 532 A1 discloses a system for processing a workpiece using a laser, wherein, inter alia, a focus for the laser beam is selected which is arranged outside the workpiece. PRESENTATION OF THE INVENTION

[0014] According to the technology disclosed in Japanese patent application JP 2014 - 221 483 A, shielding tunnels extending from the front surface to the rear surface of a wafer along each of the division lines, each consisting of a small hole and an amorphous phase surrounding the small hole, can be formed in which wafers are formed, with brittle sections serving as division start points being formed.It was found that this technology has a problem in that, when the laser beam is applied from the rear surface of the wafer to form the shielding tunnels, part of the laser beam applied by the laser beam application device reaches a layer (epitaxial layer) in which the components are formed on the front surface of the wafer, thereby damaging the components formed on the front surface, leading to a reduction in the quality of the components.

[0015] Accordingly, an objective of the present invention is to provide a laser processing device by which shielding tunnels extending from the front surface to the rear surface of a wafer along parting lines, each consisting of a small hole and an amorphous phase surrounding the small hole, can be formed by laser processing without damaging the components formed on the wafer.

[0016] In accordance with one aspect of the present invention, a laser processing device according to claim 1 has been provided, comprising a clamping table holding a wafer, a laser beam application means for applying a laser beam to the wafer held by the clamping table, and a processing feed means for performing a relative processing feed of the clamping table and the laser beam application means. The laser beam application means comprises a laser oscillator for oscillating a pulsed laser beam and a focusing device for focusing the pulsed laser beam oscillated by the laser oscillator to apply the pulsed laser beam to the wafer held by the clamping table.The pulsed laser beam, which is oscillated by the laser oscillator, includes burst pulses, each of which has several subpulses, and the burst pulses are applied to the wafer to form shielding tunnels, each containing a small hole and an amorphous phase surrounding the small hole.

[0017] The laser oscillator generates the multiple subpulses that make up the burst pulse in such a way that the energy of the subpulses changes sequentially from a low energy to a higher energy. The pulsed laser beam, which contains the burst pulses thus generated, is applied to the wafer, effectively forming shielding tunnels that extend from the front surface to the back surface of the wafer, each containing a small hole and an amorphous phase surrounding the small hole.

[0018] According to the laser processing device of the present invention, the pulsed laser beam, oscillated by the laser oscillator, comprises burst pulses, each containing several subpulses. This pulsed laser beam, containing the burst pulses, is applied to the wafer to form shielding tunnels, each containing the small hole and the amorphous phase surrounding the small hole. Therefore, the energy per pulse applied to the wafer is dispersed into several subpulses, and nearly all the energy emitted by the laser beam is used to form the shielding tunnels, thus suppressing light leakage. Consequently, damage to the devices formed on the wafer is prevented, and the problem of device quality degradation is solved.

[0019] Additionally, at the moment the laser beam is applied, the laser oscillator generates the subpulses that make up the burst pulse in such a way that the energy of the subpulses changes sequentially from low to high energy. When the pulsed laser beam, which contains the burst pulses—each with subpulses that change from low to high energy—is applied to the wafer, each shielding tunnel is formed gradually. Therefore, almost all the energy of the pulsed laser beam is effectively used to form the shielding tunnels, and light leakage can be reduced. Consequently, the problem of device quality degradation can be solved more reliably.

[0020] The above and other aims, features and advantages of the present invention and the manner of realizing them will become clearer and the invention itself best understood by studying the following description and attached claims with reference to the attached figures, which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1 is a perspective view of a laser processing device showing an application means for a laser beam according to an embodiment of the present invention; Fig. Figure 2A shows a block diagram representing the application means for a laser beam; Fig. 2B is a graph showing the time variation of a burst pulse formed from several subpulses; Fig. 3 is a perspective view showing a holding step to hold a wafer through a frame, which is processed by the laser processing device. Fig. 1 is being processed, shows; Fig. 4A is a perspective view showing a laser processing step; Fig. 4B is a sectional view of a wafer in which several shielding tunnels are formed; and Fig. 4C is a schematic perspective view of a shielding tunnel. DETAILED DESCRIPTION OF THE PREFERRED VERSION

[0021] A laser processing device according to the present invention and an actuation thereof are described in detail below with reference to the attached figures. Fig. Figure 1 shows a general perspective view of a laser processing device 40 for laser processing, designed based on the present invention. The laser processing device 40 shown in the figures includes a base 41, a holding mechanism 42 for holding a wafer, a movement means 43 for moving the holding mechanism 42, a laser beam application means 44 for applying a laser beam to the wafer 10, which is held by the holding mechanism 42, an imaging means 45, and a control 20 (see Figure 1). Fig. 2), which is designed from a computer which will be described later, wherein each of the means is controlled by the control 20.

[0022] The holding mechanism 42 comprises a rectangular plate 51, which can be moved in the X-direction and is mounted on the base 41 in such a way that it is movable in the X-direction; a rectangular movable plate 53, which is movable in the Y-direction and is mounted on the plate 51, which is movable in the X-direction, in such a way that it is movable in the Y-direction; a hollow, cylindrical support column 50, which is fixed to a surface of the plate 53, which is movable in the Y-direction; and a rectangular cover plate 52, which is fixed to an upper end of the support column 50. The cover plate 52 is formed with a slot 52a that extends in the Y-direction.A clamping table 54, extending upwards through the slot 52a, is configured as a holding means for a circular workpiece, and a circular suction clamp 56, formed by a gas-permeable porous material and extending substantially horizontally, is provided on the upper surface of the clamping table 54. The suction clamp 56 is connected to the suction means (not shown) by a passage extending through the support column 50. Several clamps 58 are arranged at intervals along the circumference of the clamping table 54. Note that the X-direction is the direction indicated by an arrow X in the figure. Fig. 1 is indicated, and the Y direction is the direction indicated by an arrow Y in Fig. 1 is indicated and orthogonal to the X-direction. A plane formed by the X-direction and the Y-direction is essentially horizontal.

[0023] The motion element 43 comprises a motion element 60 for an X-direction, a motion element 65 for a Y-direction, and a rotary element (not shown). The motion element 60 for an X-direction comprises a ball screw 60b extending in the X-direction over the base 41, and a motor 60a connected to an end section of the ball screw 60b. A nut section (not shown) of the ball screw 60b is fixed to a lower surface of the plate 51, which is movable in the X-direction. The X-movement means 60 converts a rotary motion of the motor 60a into a linear motion and transmits the linear motion to the plate 51, which is movable in the X direction, through the ball screw 60b, thereby advancing or retracting the plate 51, which is movable in the X direction, along guide rails 43a at the base 41 in the X direction.The motion device 65 for a Y-direction comprises a ball screw 65b extending in the Y-direction over the plate 51, which is movable in the X-direction, and a motor 65a connected to an end section of the ball screw 65b. A nut section (not shown) of the ball screw 65b is fixed to a lower surface of the plate 53, which is movable in the Y-direction. The motion element 65 for a Y-direction converts a rotary motion of the motor 65a into a linear motion and transmits the linear motion to the plate 53, which is movable in the Y-direction, via the ball screw 65b. This causes the plate 53, which is movable in the Y-direction, to be advanced and retracted in the Y-direction along the guide rails 51a on the plate 51, which is movable in the X-direction. The rotary element is integrated into the support column 50 and rotates the clamping table 56 relative to the support column 50.

[0024] As described above, the laser processing device 40 in this embodiment has a control unit 20, which is designed as a computer and includes a central processing unit (CPU) for performing arithmetic operations according to a control program, a read-only memory (ROM) for storing the control program, etc., a read / write memory (RAM) for temporarily storing detection values ​​obtained through detection, results of arithmetic processes, etc., an input interface, and an output interface (details omitted from the figures). In addition to an image signal from the imaging device 45, signals from the detection device for a position in the X and Y directions (not shown) of the holding mechanism 52, etc., are inputted to the input interface of the control unit.In addition, actuation signals are output from the output interface to the application means 44 for a laser beam, which will be described later, the motion means 60 for an X direction, the motion means 65 for a Y direction, and the like.

[0025] The laser beam delivery device 44 is integrated into a frame body 46 that extends upwards from an upper surface of the base 41 and thereafter extends substantially horizontally. The laser beam delivery device 44 includes a configuration for forming shielding tunnels along the parting lines of the wafer 10, which serves as a workpiece, each shielding tunnel including a small hole and an amorphous phase surrounding the small hole. In particular, as shown in Fig. As shown in Figure 2A, the application means 44 for a laser beam in the present invention comprises a laser oscillator 44b, a reflector 44c for reflecting a pulsed laser beam emitted by the laser oscillator 44b, and a focusing device 44a comprising a focusing lens 446 through which the pulsed laser beam, the optical path of which is modified by the reflector 44c, is focused and applied to the wafer 10.

[0026] The laser oscillator 54b includes a seeder 441 for oscillating a pulsed laser beam with high frequency and low power as a seed light, an acousto-optic modulator (hereinafter referred to as "AOM") 442, onto which the pulsed laser beam with high frequency, oscillated by the seeder 441, impinges, a beam trap 443 for absorbing the pulsed laser beam, which is thinned by a diffraction grating of the AOM 442, and an amplifier 444 for amplifying the power of the high-frequency pulse, which is transmitted by the AOM 442 in such a way as to enable the formation of shielding tunnels.The AOM 442 thins the incident laser beam by a predetermined number of pulses at a predetermined repetition frequency through the action of a diffraction grating to output a pulsed laser beam consisting of a pulse (hereinafter referred to as a "burst pulse") comprising several high-frequency pulses (in this embodiment five pulses, hereinafter referred to as "subpulses") as a unit.

[0027] The AOM 442 comprises an acousto-optic medium, for example, made of tellurite-based glass, and a piezoelectric element (not shown) is attached to the acousto-optic medium. The acousto-optic medium acts as a diffraction grating due to a photoelastic effect when an ultrasonic vibration is transmitted to it by the piezoelectric element. An AOM controller 445 for generating an arbitrary ultrasonic vibration is connected to the piezoelectric element of the AOM 442. By controlling the AOM controller 445, it is possible to generate an arbitrary number of subpulses that are transmitted by the AOM 442. Furthermore, in this embodiment, as shown in Fig. As shown in Figure 2B, the effect of the amplifier 444, in addition to the effect of the AOM 442, is to gradually increase the power (B) of each of the five subpulses forming a burst pulse (BP) from low energy to high energy at the time of output, thereby producing a pulsed laser beam suitable for forming shielding tunnels, with a repetition frequency equal to the burst pulse. The seeder 441, the AOM 442, and the amplifier 444, as described above, are suitably controlled by a controller 20 provided in the laser processing device 40.

[0028] An operation of the laser processing device 40, which is designed based on the present invention, is described in the corresponding sequence. First, as in Fig. As shown in Figure 3, a wafer 10, containing, for example, lithium niobate (LiNbO3), is prepared as a substrate. Several areas on a front side 10a of the wafer 10 are divided by several intersecting division lines 12, and SAW devices 14 are formed in the divided areas. In this embodiment, so that a laser beam for forming division start points in the wafer 10 is applied from the rear side 10b of the wafer 10, the wafer 10 rests against an opening section of an annular frame 11 with the rear surface 10b of the wafer 10 facing upwards, the front surface 10a of the wafer 10 is attached to an adhesion-promoting band T, and a circumferential section of the adhesion-promoting band T is attached to the annular frame F, whereby the wafer 10 is supported by the frame 11 via the adhesion-promoting band T.The wafer 10 is supported on the suction clamping device 56 of the clamping table 54 of the laser processing device 40, wherein the side with the adhesion-promoting band T is on the lower side, namely with the front surface side 10a on the lower side, the annular frame 22 is held by the clamps 58 and the suction means (not shown) is actuated to cause a negative pressure to act on the suction clamping device 56, thereby holding the wafer 10 by suction.

[0029] After the wafer 10 is held on the clamping table 56 by suction, the motion device 60 is actuated for an X-direction and the motion device 65 for a Y-direction to move the clamping table 54, thereby positioning the wafer 10 directly under the imaging device 45. When the clamping table 54 is positioned directly under the imaging device 45, an alignment step is performed by the imaging device 45 and the controller 20 to detect the area of ​​the wafer 10 to be processed with the laser.In particular, the imaging means 45 and the control 20 perform image processing, such as pattern recognition, to align the position between the division line 12, which is formed in a predetermined direction on the wafer 10, and the focusing device 44a of the application means 44 for a laser beam, in order to apply the laser beam along the positions of the corresponding division lines 12, thereby aligning the application position for a laser beam. A similar alignment step is also performed along the division line 12 that is formed in a direction orthogonal to the predetermined direction.

[0030] After the alignment step as described above has been performed, the clamping table 54 is moved into the laser beam training area in which the focusing device 44a is positioned, and such positioning is carried out that one end of a predetermined division line 12, formed in the first direction, is positioned immediately below the focusing device 44a. Thereafter, the focusing point positioning device (not shown) is actuated to move the focusing device 44a in the optical axis direction, thereby positioning the focusing point at a predetermined position in the lithium tantalate substrate that forms the wafer 10.

[0031] After positioning the focal point as described above, the application means 44 is actuated for a laser beam, a pulsed laser beam for forming shielding tunnels 100 in the wafer 10 by the laser oscillator 44b, because Fig. 4A shows how to apply the laser beam. The pulsed laser beam is focused by the focusing device 44a to be applied to an end section of the division line 12 on the wafer 10. Once the laser beam application has started, the motion device 60 is actuated in an X direction to move the clamping table 54 in a direction indicated by arrow X1. Fig. 4A and Fig. 4B is indicated, relative to a base, whereby the laser beam is applied along the division lines 12. This results in the shielding tunnels 100, each consisting of a small hole 102 extending vertically from the front surface 10a to the rear surface 10b of the wafer 10, and an amorphous phase 104 shielding the small hole 102, being successively formed along the division line 12 (see Fig. 4B) trained.

[0032] The laser beam application means 44, the clamping table 54, the X-direction movement means 60, and the Y-direction movement means 65 are actuated according to the control program in the controller 20, thereby forming the shielding tunnels 100, which are the same as above, along all the division lines 12 on the wafer 10. After the shielding tunnel formation step 100 is completed in this way, the wafer 10 is moved to a separation step to separate the wafer 10 into individual components 14 by applying an external force. Note that the separation step is not an essential part of the present invention and can be performed using known division means (see, for example, Fig. 8 and the description in Japanese patent application no. 2014-221483, mentioned above) and therefore a detailed description of the separation step has been omitted.

[0033] Note that the conditions for laser processing when forming shielding tunnels are set as follows, for example. Note that the "wavelength of a pulsed laser beam" in the following refers to the wavelength of a pulsed laser beam, where a burst pulse formed from several subpulses is a pulse.

[0034] Wavelength of a pulsed laser beam: 1030 nm Oscillator frequency of the seeder: 10 MHz Number of subpulses forming a burst pulse: 5 Repetition rate of a pulsed laser beam: 50 kHz Average power after amplification: 3 W Spot diameter: 10 µm (numerical aperture of the focusing lens) / (refractive index of the wafer): 0.05–0.20 Processing Feed rate in the X direction: 500 mm / second Shielding tunnel size: 1 µm for small hole, 10 µm for amorphous phase

[0035] The present invention is designed as described above, such that a shielding tunnel is formed by a burst pulse composed of several subpulses. Therefore, damage to components formed using an epitaxial layer, caused by light leakage or the like, is suppressed compared to the case where the shielding tunnel is formed by applying a high energy pulse. In particular, in the embodiment described above, the multiple subpulses forming a burst pulse are configured such that the energy of the subpulses changes from low to high energy, and the pulsed laser beam containing the burst pulses is applied to the wafer, thus reliably preventing damage to the epitaxial layer.

[0036] Note that the present invention is not limited to the embodiment described above, but may include various modifications. While an example in which lithium tantalate is adapted as the wafer substrate for processing has been shown in the above embodiment, this is not limiting and any material that allows the formation of shielding tunnels within it, such as lithium niobate and silicon carbide (SiC), may be adapted.Additionally, the acousto-optic modulator (AOM) was used to extract multiple pulses from high-frequency pulses oscillated by the seeder, so that the generated burst pulses each form multiple subpulses; this is not limited; for example, an electro-optic modulator (EOM), a laser switch, or a similar known method can be adapted as a means of thinning pulses with a specific repetition frequency from high-frequency pulses oscillated by the seeder.

Claims

[1] Laser processing device (40) comprising: a clamping table (54) which holds a wafer (10) having a front side (10a) and a back side (10b); a laser beam application means (44) that applies a laser beam to the wafer (10) which is held by the clamping table (54); and a processing feed means (43) that performs a relative processing feed of the clamping table (54) and the application means (44) for a laser beam, wherein the application means for a laser beam comprises a laser oscillator (44b) which oscillates a pulsed laser beam, and a focusing device (44a) which focuses the pulsed laser beam oscillated by the laser oscillator (44b) in order to apply the pulsed laser beam to the wafer (10) which is held by the clamping table (54), and The pulsed laser beam, oscillated by the laser oscillator (44b), includes burst pulses (BP), each of which has several subpulses that are gradually amplified stepwise from a lower energy to a high energy, and the burst pulses (BP) are applied to the wafer (10) to form shielding tunnels (100), each containing a small hole (102) and an amorphous phase (104) surrounding the small hole, wherein the application means (44) is configured for a laser beam to form a circular small hole (102) and a circular amorphous phase (104), each extending from the front side (10a) to the rear side (10b) of the wafer (10), wherein the focusing device (44a) is movable in the direction of the optical axis and configured such that the focal point is positioned at a predetermined position in the wafer (10). is.

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