JP2014079791A - Laser processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing method for performing stable laser processing even to a work piece having warpage.SOLUTION: There is provided a laser processing method for performing laser processing on a work piece having warpage in which an irradiation scheduled line of a laser beam is set, the method comprising: a holding step of holding the work piece by holding means; a laser processing step of performing the laser processing on the work piece along the laser beam irradiation scheduled line by irradiating the work piece held by the holding means with the laser beam by laser beam irradiation means and relatively moving the holding means and the laser beam irradiation means. In the laser processing step, irradiation with the laser beam is executed while a pressing member arranged on both sides of the laser beam irradiation scheduled line of the work piece presses the work piece under processing.

Description

  The present invention relates to a laser processing method for performing laser processing on a workpiece having warpage.

  A street in which a semiconductor layer (epitaxial layer) such as gallium nitride (GaN) is formed on the surface of a sapphire substrate, SiC substrate, etc., and a plurality of optical devices such as LEDs are formed in a lattice shape on the semiconductor layer (division planned line) Since the optical device wafer formed by dividing the optical device wafer has a relatively high Mohs hardness and is difficult to divide by a cutting blade, the optical device wafer is divided into individual optical devices by laser beam irradiation. Used in electrical equipment such as personal computers.

  As methods for dividing an optical device wafer into individual optical devices using a laser beam, first and second processing methods described below are known. In the first processing method, a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the substrate is irradiated to a region corresponding to the planned split line to form a split starting groove serving as a split starting point by ablation processing, Thereafter, an external force is applied to divide the optical device wafer into individual optical devices (see, for example, Japanese Patent Application Laid-Open No. 2008-311404).

  In the second processing method, a condensing point of a laser beam having a wavelength that is transparent to the substrate (for example, 1064 nm) is positioned inside the substrate corresponding to the division line, and the laser beam is moved along the division line. In this method, a modified layer is formed by irradiation, and then an external force is applied to divide the optical device wafer into individual optical devices using the modified layer as a starting point (see, for example, JP-A-2011-35253). In any processing method, the optical device wafer can be surely divided into individual optical devices.

JP 2008-311404 A JP 2011-35253 A

  However, when a gallium nitride layer is epitaxially grown on a sapphire substrate, warpage occurs in the sapphire substrate after film formation due to a difference in thermal expansion coefficient and a lattice constant between gallium nitride and sapphire. The amount of warpage increases as the diameter of the sapphire substrate increases.

  Even if you try to form an ablation or modified layer by irradiating a warped workpiece with a laser beam, the depth of the laser processing groove due to ablation does not become constant, the modified layer has a constant height inside the workpiece. There is a problem that it is not formed with a certain width at the position, and there is a problem that stable laser processing cannot be performed.

  The present invention has been made in view of these points, and an object of the present invention is to provide a laser processing method capable of performing stable laser processing even on a workpiece having warpage.

  According to the present invention, there is provided a laser processing method for performing laser processing on a workpiece having a warp in which a laser beam irradiation scheduled line is set, the holding step of holding the workpiece by the holding means, and the holding means. Laser processing is performed on the workpiece along the planned laser beam irradiation line by irradiating the held workpiece with a laser beam by means of laser beam irradiation means and relatively moving the holding means and the laser beam irradiation means. A laser processing step for applying a laser beam in the laser processing step, while pressing members arranged across the laser beam irradiation planned line of the workpiece press the workpiece being processed. A laser processing method is provided.

  In the laser processing method of the present invention, laser beam irradiation is performed while a pressing member disposed across a laser beam irradiation scheduled line of the workpiece presses the workpiece being processed. Therefore, even if the workpiece is warped, the workpiece is flat at the processing point of the workpiece irradiated with the laser beam, that is, the lower surface of the workpiece is in close contact with the holding surface of the holding means. Since it is held in a state, the distance from the laser beam irradiation port to the upper surface of the workpiece can be made uniform.

  Therefore, the laser processing groove depth does not become constant, and the problem that stable laser processing cannot be performed, such as the modified layer not being formed with a constant width at a constant height position inside the workpiece, is stable. Laser processing can be performed.

It is a surface side perspective view of an optical device wafer. It is a disassembled perspective view which shows a mode that the outer peripheral part sticks the surface side of an optical device wafer to the dicing tape with which the annular frame was mounted | worn. It is a partial cross section side view which shows a holding | maintenance step. It is a front view of a laser head. It is a schematic block diagram of the laser beam irradiation unit which shows a laser processing step. It is a partial cross section side view which shows a laser processing step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a perspective view of the surface side of an optical device wafer 11 to be processed by the laser processing method of the present invention is shown.

  The optical device wafer 11 is configured by laminating an epitaxial layer (semiconductor layer) 15 such as gallium nitride (GaN) on a sapphire substrate 13. The optical device wafer 11 has a front surface 11a on which an epitaxial layer 15 is stacked and a back surface 11b on which the sapphire substrate 13 is exposed.

  The sapphire substrate 13 has a thickness of 100 μm, for example, and the epitaxial layer 15 has a thickness of 5 μm, for example. A plurality of optical devices 19 such as LEDs are formed in the epitaxial layer 15 by being partitioned by division lines (streets) 17 formed in a lattice pattern.

  When the epitaxial layer 15 made of gallium nitride (GaN) is grown on the sapphire substrate 13 in this way, the sapphire substrate 13 after film formation is caused by the difference in thermal expansion coefficient and lattice constant between gallium nitride and sapphire. Warping occurs. The laser processing method of the present invention is particularly suitable for a workpiece such as an optical device wafer 11 having warpage.

  Here, the workpiece is not limited to the optical device wafer 11, and the workpiece or thinned plate-like material in which different materials are laminated, such as WL-CSP (Wafer Level-Chip Size Package). Is also included. A workpiece having warpage includes warpage, undulation, deflection, and the like.

  As a preparation step of the laser processing method of the optical device wafer 11, the surface 11a side of the optical device wafer 11 is attached to a dicing tape T, which is an adhesive tape having an outer peripheral portion attached to an annular frame F, as shown in FIG. . Thereby, a laser beam is irradiated from the back surface 11b side of the optical device wafer 11 at the time of laser processing for forming a modified layer inside the wafer.

  In carrying out laser processing of the optical device wafer 11, as shown in FIG. 3, the optical device wafer 11 having warpage is sucked and held through the dicing tape T by the chuck table 10 of the laser processing apparatus, and the annular frame F is clamped. Clamp with 12 and fix. The back surface 11b of the optical device wafer 11 is an exposed surface.

  As shown in FIG. 5, the laser beam irradiation unit (laser beam irradiation means) 14 of the laser processing apparatus includes a laser beam generation unit 16 and a laser head (condenser) 18.

  The laser beam generating unit 16 includes a laser oscillator 20 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 22, a pulse width adjusting unit 24, and a power adjusting unit 26.

  As shown in FIG. 4, mounting members 32 are fixed to both sides of the laser beam irradiated from the laser head 18 in the casing 18 a of the laser head 18, and an air cylinder 34 is fixed to each mounting member 32. ing. A roller support member 38 is fixed to the tip of the piston rod 36 of the air cylinder 34, and a pressure roller 40 is rotatably attached to the roller support member 38.

  The pressing roller 40 is made of, for example, rubber or silicone coated with a fluorine resin. In addition to pressing by the pressing roller 40, the optical device wafer 11 may be pressed by an annular member surrounding the laser beam. In this case, since the annular member slides with the back surface 11b of the optical device wafer 11, the surface thereof is preferably coated with a fluorine-based resin or the like.

  As another embodiment, a pair of bar-shaped members sandwiching the laser beam irradiation scheduled line 40 is arranged on the chuck table 10 so that the optical device wafer 11 is pressed by the bar-shaped members and the laser beam is irradiated. It may be. Of course, the pair of bar-shaped members are arranged to be movable in the indexing and feeding direction.

  In the embodiment shown in FIG. 5, the pair of pressing rollers 40 are arranged on both sides of the laser beam irradiation scheduled line 42. However, the pressing rollers 40 extend in the extending direction of the laser beam irradiation scheduled line 40, that is, before and after the laser head 18. 40 may be provided.

  In performing laser processing on the optical device wafer 11, first, the imaging unit picks up an image of the optical device wafer 11 from the back surface 11b side, and aligns the region corresponding to the planned division line 17 with the laser head 18 in the processing feed direction. To implement.

  For this alignment, well-known image processing such as pattern matching is used. Since the sapphire substrate 13 is transparent to the laser beam to be used, the division line 17 can be detected from the back surface 11b side with a normal imaging device.

  After performing the alignment of the division line 17 extending in the first direction, the chuck table 10 is rotated 90 degrees, and then the division line 17 extending in the second direction orthogonal to the first direction is aligned. .

  After the alignment, as shown in FIGS. 5 and 6, the piston rod 36 of the air cylinder 34 is extended and the back surface 11 b of the optical device wafer 11 is pressed by the pressing roller 40. The pulse laser beam adjusted to a predetermined bar by the power adjusting means 26 of the laser beam generating unit 16 is reflected by the mirror 28 of the laser head (condenser) 18 and further held on the chuck table 10 by the objective lens 30 for condensing. The light is condensed and irradiated on a light condensing point P inside the optical device wafer 11. Reference numeral 42 denotes a laser beam irradiation scheduled line corresponding to the division planned line 17.

  In the laser processing step, as shown in FIG. 5, the condensing point P of the laser beam is positioned inside the optical device wafer 11, and the laser beam is irradiated from the back surface 11b side of the optical device wafer 11 along the laser beam irradiation planned line 42. Irradiation is performed to form a modified layer serving as a division starting point inside the optical device wafer 11.

  In the laser processing step of this embodiment, as shown in FIG. 6, while the chuck table 10 is processed and fed in the direction of arrow A, the laser beam irradiation scheduled line 42 of the optical device wafer 11 is sandwiched as shown in FIG. Laser beam irradiation is performed while the pair of pressing rollers 40 disposed presses the optical device wafer 11 being processed.

  While the chuck table 10 is indexed in the indexing feed direction orthogonal to the machining feed direction indicated by the arrow A, it is reformed inside the optical device wafer 11 corresponding to all the division lines 17 that extend in the first direction. Form a layer.

  Next, after the chuck table 10 is rotated by 90 degrees, a similar modified layer is formed inside the optical device wafer 11 corresponding to all the planned division lines 17 extending in the second direction orthogonal to the first direction. To do.

  When this modified layer is formed, laser beam irradiation is performed while pressing the optical device wafer 11 with a pair of pressing rollers 40 arranged with a laser beam irradiation scheduled line 42 corresponding to the division planned line 17 interposed therebetween. Even if the optical device wafer 11 is warped, the optical device wafer 11 is held flat at the processing point of the optical device wafer 11 irradiated with the laser beam. The distance to the upper surface (back surface) 11b of the optical device wafer 11 can be made uniform.

  Therefore, the modified layer is formed at a constant height position inside the optical device wafer 11 with a constant width without causing the problem that the modified layer is not formed at a constant height position inside the optical device wafer 11 as in the prior art. And stable laser processing can be performed.

  The laser processing conditions in the modified layer forming step are set as follows, for example.

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100 kHz
Pulse output: 10μJ
Condensing spot diameter: φ1μm
Processing feed rate: 100 mm / sec After forming a modified layer serving as a division starting point inside the optical device wafer 11, an external force is applied to the optical device wafer 11, and each of the optical device wafers 11 is separated from the modified layer as a starting point. The device chip 19 is divided.

  In the embodiment described above, a modified layer is formed inside the optical device wafer 11 by irradiating the optical device wafer 11 with a laser beam having a wavelength that is transmissive. The gist of the present invention that is pressed by the pressing roller 40 can also be applied to the case where a laser processing groove is formed on the optical device wafer 11 by ablation by irradiating a laser beam having a characteristic wavelength.

  When forming a laser processed groove by ablation, a laser beam is irradiated from the surface 11a side of the optical device wafer 11. In the case of this laser processing, as shown in FIG. 5, by arranging a pair of pressing rollers 40 with the laser beam irradiation planned line 42 sandwiched in a direction orthogonal to the extending direction of the laser beam irradiation planned line 42, Since the laser processing groove is not pressed by the pressing roller 40, it is possible to prevent the edge of the laser processing groove from being chipped due to the pressing.

10 Chuck Table 11 Optical Device Wafer 13 Sapphire Substrate 14 Laser Beam Irradiation Unit 16 Laser Beam Generation Unit 17 Scheduled Line 18 Laser Head (Condenser)
19 Optical device 30 Condensing objective lens 34 Air cylinder 40 Press roller 42 Laser beam irradiation scheduled line

Claims (1)

A laser processing method for performing laser processing on a workpiece having a warp in which a laser beam irradiation scheduled line is set,
A holding step for holding the workpiece by holding means;
The workpiece held by the holding means is irradiated with a laser beam by the laser beam irradiation means, and the workpiece is processed along the laser beam irradiation scheduled line by relatively moving the holding means and the laser beam irradiation means. A laser processing step for applying laser processing to an object,
In the laser processing step, laser beam irradiation is performed while a pressing member arranged across the laser beam irradiation scheduled line of the workpiece presses the workpiece being processed. Processing method.

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