JP2013010123A - Laser processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser processing device wherein an objective lens of a condenser is not polluted even if smoke occurs by irradiation of a laser beam.SOLUTION: This laser processing device includes: a chuck table holding an object to be processed; a laser beam irradiation means irradiating the laser beam of a wavelength having transmissivity to the object to be processed held by the chuck table; and a processing-feeding means performing relative processing-feeding of the chuck table and the laser beam irradiation means. The laser beam irradiation means includes: a laser oscillator; and the condenser condensing the laser beam oscillated by the laser oscillator, positioning a condensing point inside the object to be processed, and forming a reformed layer inside the object to be processed. The laser processing device includes a gas jet means disposed adjacently to the condenser, and having a nozzle jetting gas toward a region of the object to be processed, irradiated by the laser beam.

Description

  The present invention relates to a laser processing apparatus for irradiating a workpiece such as a wafer with a laser beam to form a modified layer therein.

  In a semiconductor device manufacturing process, a plurality of regions are partitioned by dividing lines called streets formed in a lattice shape on the surface of a semiconductor wafer having a substantially disk shape, and devices such as ICs and LSIs are divided into these partitioned regions. Form. Each semiconductor device is manufactured by dicing the semiconductor wafer along a street with a cutting blade.

  In recent years, as a method of dividing a plate-like workpiece such as a semiconductor wafer, a condensing point of a laser beam having a wavelength (for example, 1064 nm) having transparency to the workpiece is set inside the substrate corresponding to the planned division line. A method is proposed in which a modified layer is formed inside a workpiece by irradiating a laser beam along a planned dividing line, and then the workpiece is cleaved by a mechanical braking device (Japanese Patent No. 3408805). No. publication).

  In this laser processing method, an epitaxial layer (semiconductor layer) such as gallium nitride (GaN) is formed on the surface of a sapphire substrate, a SiC substrate, etc., and a plurality of optical devices such as LEDs are formed in a lattice shape on the epitaxial layer. It is also actively used to divide optical device wafers that are defined by dividing lines (streets).

  When the focused point of the pulse laser beam having a wavelength that is transparent to the wafer is positioned inside the planned split line and irradiated with the laser beam, a fragile modified layer is formed inside the wafer without scattering debris, By applying an external force, the wafer can be divided into individual devices along the planned division line using the modified layer as a division starting point.

  Therefore, as compared with a method in which a laser beam having a wavelength (for example, 355 nm) having an absorptivity with respect to the wafer is irradiated to a region corresponding to the line to be divided and a laser processing groove serving as a starting point of the division is formed by ablation. The debris is not scattered and the quality of the device is not deteriorated, and there is an advantage that it is not necessary to cover the processing surface with a protective film.

Japanese Patent No. 3408805 JP 2004-188475 A

  However, the outer periphery of the wafer is arc-shaped chamfered from the front surface to the back surface, and when the condensing point of the laser beam positioned inside the wafer is irradiated to the chamfered region, the laser beam is However, it has a problem that it is absorbed in the chamfered region and smoke is generated by ablation processing, and the objective lens of the condenser is contaminated by the generated smoke.

  A similar problem is that even if foreign matter such as dust adheres to the surface of the wafer corresponding to the division line, the foreign matter is instantaneously heated by the laser beam and burned to generate smoke. It happens even if the objective lens is contaminated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a laser processing apparatus in which the objective lens of the condenser is not contaminated even if smoke is generated by laser beam irradiation. Is to provide.

  According to the present invention, a chuck table for holding a workpiece, laser beam irradiation means for irradiating a laser beam having a wavelength that is transparent to the workpiece held on the chuck table, the chuck table, and the chuck table A laser processing apparatus comprising a processing feed means for relatively processing and feeding a laser beam irradiation means, wherein the laser beam irradiation means collects a laser oscillator and a laser beam oscillated by the laser oscillator. A concentrator for positioning a condensing point inside the workpiece and forming a modified layer inside the workpiece, and disposed adjacent to the concentrator and held on the chuck table. There is provided a laser processing apparatus comprising gas injection means having a nozzle for injecting a gas toward a region irradiated with a laser beam of a workpiece.

  In the laser processing apparatus of the present invention, gas injection means having a nozzle for injecting gas toward a region irradiated with a laser beam of a workpiece held on a chuck table is disposed adjacent to a condenser. Therefore, even if smoke is generated by irradiation with the laser beam, the smoke is immediately removed by the gas jetting means, so that the objective lens of the condenser is not contaminated.

It is a schematic perspective view of a laser processing apparatus. It is a block diagram of a laser beam generation unit. It is a surface side perspective view of an optical device wafer. It is a perspective view of the optical device wafer supported by the annular frame via the dicing tape. 5A is a partially broken side view showing a chamfered portion of the optical device wafer, and FIG. 5B is a partially broken plan view showing an outer peripheral portion of the optical device wafer. It is a side view which shows the principal part of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, an external perspective view of a laser processing apparatus according to an embodiment of the present invention is shown. The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved in the machining feed direction, that is, the X-axis direction along the pair of guide rails 14 by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved along the pair of guide rails 24 by the index feed means 22 constituted by the ball screw 18 and the pulse motor 20 in the index feed direction, that is, the Y-axis direction.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. At the same time, it is rotated by a motor accommodated in the cylindrical support member 26.

  The chuck table 28 is provided with a clamp 30 that clamps a frame that supports the semiconductor wafer sucked and held by the chuck table 28. 32 is a cover, and a bellows (not shown) is connected to the cover 32 to protect the processing feeding means 12 and the index feeding means 22 from dust and the like.

  A column 34 is erected on the stationary base 4, and a laser beam irradiation mechanism (laser beam irradiation means) 36 is attached to the column 34. The laser beam irradiation mechanism 36 includes a laser beam generation unit 38 housed in the casing 40 and a condenser 42 attached to the tip of the casing 40. An imaging unit 52 is attached to the tip of the casing 40 so as to align with the condenser 42 in the X-axis direction.

  As shown in FIG. 2, the laser beam generating unit 38 includes a laser oscillator 44 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 46, a pulse width adjusting unit 48, and a power adjusting unit 50. . Although not particularly shown, the laser oscillator 44 has a Brewster window, and the laser beam emitted from the laser oscillator 44 is a linearly polarized laser beam.

  Referring to FIG. 3, there is shown a front side perspective view of an optical device wafer 11 which is a processing target of the laser processing apparatus of the present invention. 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, for example, 100 μm, the epitaxial layer 15 has a thickness of, for example, 5 μm, and the division planned line in which a plurality of optical devices 19 such as LEDs are formed in a lattice shape on the epitaxial layer 15. It is partitioned and formed by (street) 17.

  In performing laser processing on the optical device wafer 11, as shown in FIG. 4, the back surface 11 b of the optical device wafer 11 is attached to a dicing tape T that is an adhesive tape, and the outer peripheral portion of the dicing tape T is attached to an annular frame F. Worn.

  As a result, the optical device wafer 11 is supported by the annular frame F via the dicing tape T. At the time of laser processing, the optical device wafer 11 is sucked and held by the chuck table 28 via the dicing tape T and is clamped by the clamp 30. The annular frame F is clamped and fixed.

  After the optical device wafer 11 is sucked and held by the chuck table 28, the area to be imaged of the optical device wafer 11 is positioned immediately below the imaging unit 52, and the target pattern is detected by well-known pattern matching or the like.

  The target pattern is detected at two points separated in the X-axis direction along the same division line 17 and the chuck table 28 is rotated by θ so that the straight line connecting these two points is parallel to the X-axis direction. Then, the chuck table 28 is moved in the Y-axis direction by the distance between the center of the planned division line 17 and the Y coordinate of the target pattern, and alignment for aligning the planned division line 17 with the condenser 42 is performed.

  Next, after the chuck table 28 is rotated 90 degrees, the same alignment is performed on the planned division line 17 extending in the second direction orthogonal to the planned division line 17 extending in the first direction.

  After the alignment is performed, a laser beam having a wavelength that is transmissive to the optical device wafer 11 is focused by the collector 42 while irradiating the optical device wafer 11 corresponding to the planned division line 17 with a focusing point positioned. A modified layer is formed inside the optical device wafer 11 along the scheduled division line 17 while processing and feeding the table 28 in the X-axis direction.

  The modified layer refers to a region where the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings. The modified layer is formed as a melt rehardened layer.

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

Light source: LD excitation Q switch Nd: YVO 4 pulse laser Wavelength: 1064 nm
Pulse energy: 40μJ
Condensing spot diameter: φ1μm
Pulse width: 25 ms
Repetition frequency: 100 kHz
Processing feed rate: 100 mm / s

  After this modified layer forming step is performed along all the division lines 17 extending in the first direction, the chuck table 28 is rotated 90 degrees, and then the second direction orthogonal to the first direction. The process is carried out along all the planned division lines 17 that extend to (1).

  By the way, when the pulsed laser beam is irradiated along the division line 17, the focal point of the laser beam coincides with one point P of the chamfer 21 formed on the outer periphery of the optical device wafer 11 as shown in FIG. There is.

  Then, this point P is ablated by the absorption component of the laser beam with respect to the wafer 11, and smoke is generated. This ablation processing occurs at the intersection P between the laser beam condensing point locus 23 and the outer periphery of the wafer 11 along all the division lines 17.

  In the laser processing apparatus 2 of the present embodiment, as shown in FIG. 6, gas injection means 54 for blowing off smoke generated by ablation processing of the chamfered portion 21 is disposed adjacent to the condenser 42. The gas injection means 54 includes an injection nozzle 56 attached to the condenser 42 and a high-pressure air source 58 connected to the injection nozzle 56.

  Preferably, the diameter of the outlet of the injection nozzle 56 is 0.4 to 0.6 mm, more preferably about 0.5 mm, and the gas injection amount is preferably 20 to 30 liters / minute. As the gas, high-pressure air is generally used, but it is not limited to air.

  According to the laser processing apparatus 2 of the present invention, since the injection nozzle 56 for injecting high-pressure air toward the region irradiated with the laser beam of the optical device wafer 11 is provided, smoke is generated by ablation processing by irradiation of the laser beam. Even if it occurs, since the generated smoke is immediately removed by the high-pressure air from the injection nozzle 56, the objective lens of the condenser 42 is prevented from being contaminated by the smoke.

  This smoke is generated even when a foreign matter such as dust attached to the surface of the optical device wafer 11 is irradiated with the laser beam, but this smoke is also immediately removed by the high-pressure air jetted from the jet nozzle 56. The 42 objective lens is not contaminated by smoke.

  In the above-described embodiment, the example in which the laser processing apparatus 2 of the present invention is applied to the optical device wafer 11 as the workpiece has been described. However, the workpiece is not limited to the optical device wafer 11 and is a normal semiconductor. The same can be applied to a wafer such as a wafer.

2 Laser processing apparatus 11 Optical device wafer 21 Chamfer 23 Laser beam condensing point locus 28 Chuck table 36 Laser beam irradiation mechanism 38 Laser beam generating unit 42 Condenser 54 Gas injection means 56 Injection nozzle

Claims (2)

A chuck table for holding a workpiece, a laser beam irradiation means for irradiating a laser beam having a wavelength that is transmissive to the workpiece held on the chuck table, the chuck table, and the laser beam irradiation means, A laser processing apparatus comprising a processing feed means for processing and relatively processing,
The laser beam irradiation means includes a laser oscillator and a condenser for condensing the laser beam oscillated by the laser oscillator and positioning a condensing point inside the workpiece to form a modified layer inside the workpiece. Including
A gas injection means having a nozzle arranged adjacent to the condenser and for injecting a gas toward a region irradiated with a laser beam of a workpiece held on the chuck table is provided. Laser processing equipment.   2. The laser processing apparatus according to claim 1, wherein the nozzle has a diameter of 0.4 to 0.6 mm and a gas injection amount of 20 to 30 liters / minute.

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