CN112518110A - Laser processing method and laser processing apparatus - Google Patents

Laser processing method and laser processing apparatus Download PDF

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Publication number
CN112518110A
CN112518110A CN202010978979.5A CN202010978979A CN112518110A CN 112518110 A CN112518110 A CN 112518110A CN 202010978979 A CN202010978979 A CN 202010978979A CN 112518110 A CN112518110 A CN 112518110A
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China
Prior art keywords
workpiece
laser beam
processing
imaging
laser
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CN202010978979.5A
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Chinese (zh)
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小田中健太郎
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Disco Corp
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Disco Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/77—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate
    • H01L21/78—Manufacture or treatment of devices consisting of a plurality of solid state components or integrated circuits formed in, or on, a common substrate with subsequent division of the substrate into plural individual devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0648—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/36—Removing material
    • B23K26/38—Removing material by boring or cutting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/70—Auxiliary operations or equipment
    • B23K26/702—Auxiliary equipment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67011—Apparatus for manufacture or treatment
    • H01L21/67092—Apparatus for mechanical treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
    • H01L21/67005—Apparatus not specifically provided for elsewhere
    • H01L21/67242—Apparatus for monitoring, sorting or marking
    • H01L21/67259—Position monitoring, e.g. misposition detection or presence detection
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
    • B23K2103/56—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26 semiconducting

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Power Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Plasma & Fusion (AREA)
  • Laser Beam Processing (AREA)
  • Dicing (AREA)

Abstract

Provided are a laser processing method and a laser processing apparatus, which are easy to notice non-temporary abnormality in laser processing. The laser processing method comprises the following steps: a processing step of processing a workpiece by irradiating the workpiece with a laser beam on an upper surface side thereof; an imaging step of imaging an upper surface side of the workpiece at a predetermined timing in the processing step, and acquiring an image of an irradiated region irradiated with the laser beam on the upper surface side; a detection step of detecting at least one of a size and a position of an irradiated region, which is a region brighter than other regions, in the image acquired in the imaging step; and a calculation step of repeating the imaging step and the detection step in the processing step for a plurality of different regions of the workpiece, or performing the imaging step and the detection step in the processing step for each of the plurality of workpieces, and calculating a deviation of at least one of the size and the position of the irradiated region detected in each detection step.

Description

Laser processing method and laser processing apparatus
Technical Field
The present invention relates to a laser processing method and a laser processing apparatus for processing a workpiece by irradiating the workpiece with a laser beam.
Background
For processing and dividing a workpiece such as a semiconductor wafer, for example, a laser processing apparatus is used. The laser processing apparatus includes, for example: a laser oscillator that emits a pulsed laser beam; a condenser for condensing the laser beam emitted from the laser oscillator on the workpiece; and a chuck table disposed below the condenser.
For example, when a workpiece is processed by a pulse-shaped laser beam having a wavelength absorbed by the workpiece, the workpiece is first held by a chuck table. Next, the converging point of the laser beam is positioned on a line to divide the workpiece (i.e., a street), and the converging point and the chuck table are relatively moved along the line to divide the workpiece. Thereby, the object to be processed is ablated along the moving path, and a laser processing groove is formed.
During the ablation process, it was checked whether the laser processing groove was formed as designed. For example, it is checked whether or not the position of the converging point of the laser beam is deviated from a predetermined processing position (for example, see patent document 1). In ablation processing, it is also sometimes checked whether the width of the laser-processed groove deviates from a set value (see, for example, patent document 2).
Further, there is a case where a pulsed laser beam having a wavelength absorbed by the workpiece is irradiated to the workpiece, and a plasma beam generated in an irradiated region of the laser beam is confirmed (for example, see patent document 3). An image of the machining region is obtained by imaging the plasma beam, and a deviation between the irradiation position of the laser beam and a predetermined machining position is measured from the image.
Further, there is a case where a pulsed laser beam having a wavelength absorbed by the workpiece is irradiated to the workpiece, and a light emitting region generated in the irradiated region of the laser beam is confirmed (for example, see patent document 4). An image of the processing region is acquired by imaging the light emitting region, and it is determined whether or not the shape of the light emitting region deviates from a predetermined shape.
In an image obtained by imaging an irradiated region to which a laser beam is irradiated, the irradiated region is a region brighter than other regions, and is used for observing laser processing in real time.
However, even when there is no particular abnormality in the laser processing apparatus, the shape of the irradiated region in the image may suddenly change. In addition, the position of the irradiated region may suddenly deviate from the irradiation position of the laser beam.
Although the Debris (Debris) generated by the ablation process adheres to the glass cover provided below the condenser, when the amount of adhesion of the Debris increases as the process proceeds, the variation in the shape and position of the irradiated region increases.
Patent document 1: japanese patent laid-open publication No. 2016-104491
Patent document 2: japanese patent laid-open publication No. 2017-28030
Patent document 3: japanese patent laid-open publication No. 2017-120820
Patent document 4: japanese patent laid-open publication No. 2018-202468
When the shape of the irradiated region in the image deviates from a predetermined shape, there is a possibility that the processing cannot be performed according to the design. In addition, when the position of the irradiated region in the image is deviated from a predetermined processing position, a device formed on the workpiece may be damaged.
Disclosure of Invention
However, since the shape and position of the irradiated region in the image may change due to a sudden change, it is difficult to know whether the abnormality is a temporary abnormality or a non-temporary abnormality. The present invention has been made in view of the above problems, and an object of the present invention is to easily notice a non-temporary abnormality in laser processing.
According to one aspect of the present invention, there is provided a laser processing method for processing a workpiece by irradiating the workpiece with a pulsed laser beam having a wavelength absorbed by the workpiece, the laser processing method including: a holding step of holding the workpiece by a holding table; a processing step of processing the workpiece by irradiating the laser beam onto an upper surface side of the workpiece held by the holding table; an imaging step of imaging the upper surface side of the workpiece at a predetermined timing in the processing step, and acquiring an image of an irradiated area irradiated with the laser beam on the upper surface side; a detection step of detecting at least one of a size and a position of the irradiated region, which is a region brighter than other regions, in the image acquired in the imaging step; and a calculation step of repeating the imaging step and the detection step in the processing step for a plurality of different regions of the workpiece, or performing the imaging step and the detection step in the processing step for each of the plurality of workpieces, and calculating a deviation of at least one of a size and a position of the irradiated region detected in each detection step.
Preferably, the laser processing method further has a warning step of: and a warning is issued when the deviation of at least one of the size and the position of the irradiated region calculated in the calculating step exceeds a preset threshold.
According to another aspect of the present invention, there is provided a laser processing apparatus for processing a workpiece by irradiating the workpiece with a pulsed laser beam having a wavelength absorbed by the workpiece, the laser processing apparatus including: a holding table for holding the workpiece; an imaging unit that images the workpiece held by the holding table; a laser beam irradiation unit that irradiates the laser beam; a detection unit that detects at least one of a size and a position of an irradiated region, which is a region brighter than other regions, in an image obtained by imaging the irradiated region on the upper surface side irradiated with the laser beam by the imaging unit at a predetermined timing when the workpiece is processed by irradiating the laser beam from the laser beam irradiation unit onto the upper surface side of the workpiece held by the holding table; and a calculation unit that calculates a deviation of at least one of the size and the position of the irradiated region detected by the detection unit.
In the laser processing method according to one aspect of the present invention, the upper surface side of the workpiece is imaged at a predetermined timing in the processing step, and an image of the irradiated region irradiated with the laser beam on the upper surface side is acquired (imaging step). Then, in the image obtained in the capturing step, at least one of the size and the position of the irradiated region, which is a region brighter than the other regions, is detected (detecting step).
Further, the imaging step and the detection step in the processing step are repeatedly performed for a plurality of different regions of the workpiece, or the imaging step and the detection step in the processing step are performed for each of a plurality of workpieces. Then, a deviation of at least one of the size and the position of the irradiated region detected in each detection step is calculated (calculation step).
In the calculation step, since the deviation of at least one of the shape and the position of the irradiation target region is quantitatively evaluated, the operator is likely to notice a non-temporary abnormality in the laser processing. This prevents the abnormality of laser processing from being overlooked, thereby preventing the deterioration of processing quality.
Drawings
Fig. 1 is a perspective view of a laser processing apparatus.
Fig. 2 is a diagram showing a configuration example of the laser beam irradiation unit.
Fig. 3 is a timing chart for explaining the wafer imaging.
Fig. 4 is a flowchart of a laser processing method.
Fig. 5 is a partial sectional side view of the wafer or the like showing the holding step.
Fig. 6 is a partial cross-sectional side view of a wafer or the like showing a processing step.
Fig. 7 is an example of an image obtained in the photographing step.
Fig. 8 is a graph showing a variation in the size of the irradiated region.
Fig. 9 (a) is an example of an image in a case where the center line of the line to divide coincides with the center line of the region to be irradiated, and fig. 9 (B) is an example of an image in a case where the center line of the line to divide does not coincide with the center line of the region to be irradiated.
Fig. 10 is an example of an image having two irradiated regions according to embodiment 2.
Description of the reference symbols
11: a wafer (workpiece); 11 a: front side (upper surface); 11 b: a back side; 13: dividing the predetermined line; 13 a: a centerline; 15: a device; 17: a frame; 19: protecting the belt; 21: a wafer unit; 23: machining a mark; 25: an irradiated area; 25 a: a centerline; 27: a key pattern; 2: a laser processing device; 4: a base station; 6: a chuck table (holding table); 6 a: a holding surface; 6 b: a clamp unit; 8: a horizontal moving mechanism (a processing feeding member, an indexing feeding member); 10: an X-axis guide rail; 12: an X-axis moving table; 14: an X-axis ball screw; 16: an X-axis pulse motor; 18: a Y-axis guide rail; 20: a Y-axis moving table; 22: a Y-axis ball screw; 24: a Y-axis pulse motor; 26: a workbench mounting base; 28: a cover; 30: a support structure; 30 a: a pillar portion; 30 b: an arm portion; 32: a laser beam irradiation unit; 32 a: a condenser; 32 b: a condenser lens; 34: a 1 st camera unit; 36: a laser beam generating section; 38: a laser oscillator; 40: a repetition frequency setting unit; 42: a dichroic mirror; 50: a strobe light irradiation section; 52: a stroboscopic light source; 54: an aperture; 56: a collimating lens; 58: a mirror; 60: a beam splitter; 62: a 2 nd camera unit (photographing unit); 64: a lens group; 64 a: an aberration correcting lens; 64 b: an imaging lens; 66: an imaging element; 70: a control unit; 72: a detection unit; 74: a calculation section; l: a laser beam; d: distance.
Detailed Description
An embodiment of one embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view of a laser processing apparatus 2. In fig. 1, a part of the components of the laser processing apparatus 2 is shown by functional blocks.
By using the laser processing apparatus 2, a wafer (object to be processed) 11 mainly made of a semiconductor material such as silicon is processed. The wafer 11 has a disk shape, and the thickness from the front surface 11a to the back surface 11b is, for example, about 10 μm to 800 μm.
The material, shape, structure, size, and the like of the workpiece are not limited. For example, the workpiece may be made of a semiconductor material other than silicon such as gallium arsenide (GaAs) or silicon carbide (SiC), glass, resin, or ceramics, or may not be circular.
A plurality of lines to divide (streets) 13 are set on the wafer 11 (see fig. 5 and the like). Devices 15 such as an IC (Integrated Circuit) and an LSI (large-scale Integrated Circuit) are provided in each region on the front surface 11a side defined by the plurality of lines to divide 13. A critical pattern 27 (see fig. 9) (also referred to as a target pattern or alignment mark) is included on the front-most surface of each device 15.
A metal ring-shaped frame 17 is disposed around the wafer 11, and the frame 17 has an opening with a diameter larger than that of the wafer 11. A substantially circular protective tape 19 having a diameter larger than that of the opening of the frame 17 is bonded to one surface of the frame 17 and the back surface 11b of the wafer 11.
The protective tape 19 is a resin film and has a laminated structure including an adhesive layer (not shown) having adhesive properties and a base material layer (not shown) having no adhesive properties. The adhesive layer is, for example, an ultraviolet-curable resin layer, and is provided on the entire surface of the resin base layer.
The wafer unit 21 in which the wafer 11 is supported by the frame 17 via the protective tape 19 is formed by closely adhering the adhesive layer side of the protective tape 19 to the back surface 11b side of the wafer 11 and the outer peripheral portion of the frame 17.
The laser processing apparatus 2 includes a substantially rectangular parallelepiped base 4 on which each component is mounted. A chuck table (holding table) 6 for holding the wafer unit 21 is provided on the upper surface side of the base 4.
A horizontal movement mechanism (a machining feed member, an indexing feed member) 8 is provided below the chuck table 6, and the horizontal movement mechanism 8 moves the chuck table 6 in the X-axis direction (a machining feed direction) and the Y-axis direction (an indexing feed direction).
The horizontal movement mechanism 8 includes a pair of X-axis guide rails 10, and the pair of X-axis guide rails 10 are fixed to the upper surface of the base 4 and are substantially parallel to the X-axis direction. An X-axis moving table 12 is slidably attached to the X-axis guide rail 10.
A nut portion (not shown) is provided on the back surface side (lower surface side) of the X-axis moving table 12, and an X-axis ball screw 14 substantially parallel to the X-axis guide rail 10 is rotatably coupled to the nut portion.
An X-axis pulse motor 16 is connected to one end of the X-axis ball screw 14. The X-axis moving table 12 is moved in the X-axis direction along the X-axis guide rail 10 by rotating the X-axis ball screw 14 by the X-axis pulse motor 16.
A pair of Y-axis guide rails 18 substantially parallel to the Y-axis direction are fixed to the front surface (upper surface) of the X-axis moving table 12. A Y-axis moving table 20 is slidably attached to the Y-axis guide rail 18.
A nut portion (not shown) is provided on the back surface side (lower surface side) of the Y-axis moving table 20, and a Y-axis ball screw 22 substantially parallel to the Y-axis guide rail 18 is rotatably coupled to the nut portion.
A Y-axis pulse motor 24 is connected to one end of the Y-axis ball screw 22. The Y-axis moving table 20 is moved in the Y-axis direction along the Y-axis guide 18 by rotating the Y-axis ball screw 22 by the Y-axis pulse motor 24.
A table mounting base 26 is provided on the front surface (upper surface) of the Y-axis moving table 20, and the chuck table 6 is disposed on the table mounting base 26 via a cover 28.
The upper surface of the chuck table 6 serves as a holding surface 6a for holding the wafer 11. The holding surface 6a is partially formed of a disk-shaped porous member, and the porous member is connected to a suction source (not shown) such as an injector via a suction passage (not shown) formed inside the chuck table 6.
When the suction source is operated, a negative pressure is generated on the upper surface (a part of the holding surface 6 a) of the porous member. When the wafer unit 21 is placed on the holding surface 6a so that the protective tape 19 side is in contact with the holding surface 6a, the back surface 11b side of the wafer 11 is sucked and held by the holding surface 6a when negative pressure is generated.
Four clamp units 6b for fixing the frame 17 from the periphery are provided around the holding surface 6 a. A rotation drive source (not shown) is connected to the table attachment base 26, and the chuck table 6 is rotated by the rotation drive source about a rotation axis substantially parallel to the Z-axis direction (vertical direction).
A support structure 30 is provided in a region different from the horizontal movement mechanism 8 in the upper surface of the base 4. The support structure 30 has a columnar pillar portion 30 a. An arm portion 30b extending in the Y-axis direction is provided at the upper end of the column portion 30a so as to protrude toward the horizontal movement mechanism 8.
The arm 30b is provided with a laser beam irradiation unit 32. The laser beam irradiation unit 32 has a condenser 32a for irradiating the wafer 11 attracted and held by the chuck table 6 with a laser beam. The condenser 32a is located on the front end side of the arm 30 b.
A 1 st camera unit 34 for taking an image of the wafer 11 or the like held by the chuck table 6 is provided at a position adjacent to the condenser 32 a. The 1 st camera unit 34 is used for, for example, adjustment (i.e., alignment) of the positions of the wafer 11 and the laser beam irradiation unit 32.
Here, details of the laser beam irradiation unit 32 will be described with reference to fig. 2. Fig. 2 is a diagram showing a configuration example of the laser beam irradiation unit 32. In fig. 2, a part of the components of the laser beam irradiation unit 32 is shown by functional blocks.
In fig. 2, although the frame 17 and the protective tape 19 are omitted, the wafer 11 is held by the holding surface 6a via the protective tape 19 on the back surface 11b side of the wafer 11 so that the front surface 11a is exposed.
The laser beam irradiation unit 32 has a laser beam generation section 36. The laser beam generating section 36 includes a laser oscillator 38 that emits a pulsed laser beam. The laser oscillator 38 contains Nd: YAG, Nd: YVO4Etc. laser media.
The laser oscillator 38 is connected to a repetition frequency setting unit 40 that sets the repetition frequency of the pulses of the laser beam. The laser beam L emitted from the laser beam generator 36 has a wavelength absorbed by the wafer 11, for example.
In the case where the wafer 11 is mainly formed of silicon, the wavelength absorbed by the wafer 11 is 355nm, for example. In addition, the repetition frequency of the laser beam L used is, for example, 50kHz, and the average output of the laser beam L is, for example, 3.0W.
The laser beam generator 36 further includes a wavelength converter for converting the wavelength of the laser beam emitted from the laser oscillator 38, a pulse width adjuster for adjusting the pulse width of the laser beam, a power adjuster (not shown) for adjusting the output of the laser beam, and the like.
A dichroic mirror 42 is provided in the vicinity of the laser beam generating section 36. The dichroic mirror 42 reflects light having a wavelength of the laser beam L (for example, 355nm), but transmits light having other wavelength bands.
A condenser 32a is provided below the dichroic mirror 42. The condenser 32a is provided with a condenser lens 32b for condensing the laser beam L on the front surface (upper surface) 11a side of the wafer 11.
The laser beam L emitted from the laser beam generator 36 is reflected by the dichroic mirror 42, and then passes through the condenser lens 32b to be condensed on the front surface 11a side of the wafer 11. The wafer 11 is, for example, processed by ablation by the focal point of the laser beam L irradiated on the wafer 11.
The laser beam irradiation unit 32 of the present example includes a strobe light irradiation section 50 in addition to the laser beam generation section 36. The strobe light irradiation section 50 includes a strobe light source 52 that instantaneously emits white light. The strobe light source 52 is, for example, a xenon flash lamp.
The strobe light source 52 emits light periodically at intervals of, for example, 100 μ s, and emits white light. Light emitted from the strobe light source 52 is incident on the collimator lens 56 through the aperture 54. The diaphragm 54 adjusts the amount of light incident on the collimator lens 56 from the strobe light source 52, and the collimator lens 56 collimates the light passing through the diaphragm 54.
A mirror 58 is provided on the side opposite to the diaphragm 54 with respect to the collimator lens 56. The light emitted from the collimator lens 56 is reflected by the mirror 58 and travels toward the dichroic mirror 42.
A beam splitter 60 is provided between the mirror 58 and the dichroic mirror 42. As described above, the beam splitter 60 transmits a part of the light reflected by the mirror 58 to the dichroic mirror 42. The light transmitted through the dichroic mirror 42 is irradiated toward the front surface 11a of the wafer 11 through the condenser lens 32 b.
The light reflected from the front surface 11a side of the wafer 11 passes through the dichroic mirror 42, and a part thereof is reflected by the beam splitter 60 and guided to the 2 nd camera unit (imaging unit) 62.
The 2 nd camera unit 62 includes a lens group 64, and the lens group 64 has an aberration correcting lens 64a and an imaging lens 64 b. The lens group 64 guides incident light from the beam splitter 60 to an imaging element 66 formed of a CMOS (Complementary Metal Oxide Semiconductor) image sensor, a CCD (Charge Coupled Device) image sensor, or the like.
Then, information (electric signal) for constituting an image is formed through photoelectric conversion in the imaging element 66. The information constituting the image is output to a control unit 70 described later. Here, light received by the imaging element 66 will be described with reference to fig. 3.
Fig. 3 is a timing chart for explaining the imaging of the wafer 11. The horizontal axis represents time (μ s). As described above, in the case where the repetition frequency of the laser beam irradiation unit 32 is 50kHz, the laser beam L is irradiated to the wafer 11 one pulse every 20 μ s. In fig. 3, a pulse representing the laser beam L is denoted by Ls.
The strobe light source 52 irradiates the wafer 11 at a timing different from the irradiation timing of the laser beam L. The strobe light of this example irradiates the wafer 11 at a predetermined timing (time 50 μ s in fig. 3), and then irradiates the wafer 11 at every 100 μ s. In fig. 3, pulses representing a strobe light are labeled St.
The 2 nd camera unit 62 is provided with a shutter (not shown), and the timing of shooting, shooting time, and the like are adjusted by appropriately controlling the opening/closing timing of the shutter. In this example, the shutter is opened immediately before the strobe light emits at a predetermined timing, and the shutter is opened for a predetermined time of 50 μ s to 70 μ s, for example, to take light into the image sensor 66 and perform imaging. In fig. 3, the shooting time is represented by t.
An image including light (plasma light) generated in an irradiated region of the laser beam L by ablation processing of a part of the wafer 11 by the laser beam L is acquired by the 2 nd camera unit 62. The image also includes the line to be divided 13 irradiated with the strobe light and its surroundings (for example, a key pattern described later). In this way, an image including the light emission of the laser beam L in the irradiation region, the reflected light of the strobe light, and the like is acquired at a predetermined timing during the processing of the wafer 11.
Here, returning to fig. 1, other components of the laser processing apparatus 2 will be described. The laser processing apparatus 2 has a control unit 70. The control unit 70 controls the operations of the respective components such as the horizontal movement mechanism 8, the laser beam irradiation unit 32, and the 1 st camera unit 34 so as to appropriately process the wafer 11.
The control unit 70 is, for example, a computer, and has a CPU, a ROM, a RAM, a hard disk drive, an input/output device, and the like connected to each other via a main controller. The CPU performs arithmetic processing and the like based on programs, data and the like stored in a storage section such as a ROM, a RAM, a hard disk drive and the like.
The control unit 70 functions as a specific means in which software and hardware resources cooperate by the CPU reading in the program stored in the storage portion. The control unit 70 has a detection section 72. The detection unit 72 is constituted by a program stored in a storage unit, for example.
The detection unit 72 is, for example, an image processing unit that performs edge detection processing on the image acquired by the 2 nd camera unit 62. The detection unit 72 measures the length of the measurement object in a predetermined direction, and calculates the coordinates of the edge of the measurement object. Therefore, at least one of the size and the position of the irradiated region 25 (see fig. 7) of the laser beam L in the image is detected by the detection unit 72.
The illuminated region 25 is a region brighter than other regions in the image acquired by the 2 nd camera unit 62. In addition, even when the brightness of the acquired image is reversed, the irradiated region 25 may be displayed darkly, but in this case, the determination of the irradiated region 25 is not prevented.
The control unit 70 also has a calculation section 74. The calculation unit 74 is constituted by a program stored in a storage unit, for example. The calculation unit 74 calculates a deviation of at least one of the size and the position of the irradiated region 25 detected by the detection unit 72 for a plurality of different regions of the wafer 11 according to a predetermined function.
The laser processing apparatus 2 is provided with a monitor (not shown). The monitor is, for example, a touch panel type monitor. The monitor functions as an input unit for receiving an input from an operator and a display unit for displaying machining conditions, machining results, and the like.
The monitor is set to display a warning of occurrence of an abnormality or the like when the laser processing apparatus 2 is in an abnormal state. The laser processing apparatus 2 is provided with a speaker and a warning lamp (both not shown), and the warning lamp is set to emit a warning sound and to blink when an abnormality occurs in the laser processing apparatus 2.
Next, a laser processing method for performing ablation processing on the wafer 11 by using the laser processing apparatus 2 will be described. Fig. 4 is a flowchart of a laser processing method. In the laser processing method according to embodiment 1, first, the wafer unit 21 is placed on the holding surface 6a so that the front surface 11a side is exposed.
Next, the suction source is operated to hold the back surface 11b side by the holding surface 6a (holding step (S10)). Fig. 5 is a partial cross-sectional side view showing the wafer 11 and the like in the holding step (S10).
Next, the chuck table 6 is positioned directly below the condenser 32a, alignment is performed using the 1 st camera unit 34, the rotation drive source and the horizontal movement mechanism 8 are operated, and one line to divide 13 is positioned parallel to the X axis.
Then, the chuck table 6 is moved in the X-axis direction at a predetermined processing feed speed (for example, 100mm/s) while positioning the converging point of the laser beam L on one line 13 on the front surface 11a side.
Thereby, the laser beam L is irradiated to the front surface 11a side along the path of movement of the converging point, and the wafer 11 is ablated along one line to divide 13 (processing step (S20)). Fig. 6 is a partial cross-sectional side view of the wafer 11 and the like showing the processing step (S20).
In the present embodiment, at a predetermined timing in the processing step (S20), the 2 nd camera unit 62 is used to capture an image of the front surface 11a side. For example, the front surface 11a side is imaged once for one line to divide 13. Thus, the irradiation target region 25 on the front surface 11a side to which the laser beam L is irradiated is imaged to acquire an image (imaging step (S30)).
Fig. 7 is an example of the image obtained in the capturing step (S30). In this example, the machining mark 23 corresponding to the movement path of the converging point is displayed, but the machining mark 23 may not necessarily be displayed according to the imaging method.
An irradiated region 25 of the laser beam L which is displayed relatively brightly exists in the substantial center of the image. The range of the light emitting region of the plasma generated by the irradiation of the laser beam L corresponds to the range of the irradiated region 25 of the laser beam L.
The irradiated region 25 of this example has a longer width in the Y-axis direction than in the X-axis direction (i.e., is an elongated region). In the present embodiment, the detection unit 72 detects at least one of the size and the position of the irradiation target area 25 (detection step (S40)).
After the laser beam L is irradiated along one line to divide 13, the chuck table 6 is moved in the Y-axis direction by the horizontal movement mechanism 8. Thus, the condenser 32a is positioned directly above the other line 13 adjacent to the one line 13 in the Y-axis direction.
Then, the processing step (S20), the photographing step (S30), and the detecting step (S40) are similarly performed. In this way, after the processing step (S20), the imaging step (S30), and the detection step (S40) are performed on all the lines to divide 13 along the X-axis direction, the rotation driving source is operated to rotate the chuck table 6 by 90 degrees.
Then, the processing step (S20), the imaging step (S30), and the detection step (S40) are similarly performed on all the lines to divide 13 along the X-axis direction. In this way, the photographing step (S30) and the detecting step (S40) in the processing step (S20) are repeatedly performed for different plural regions of the wafer 11.
The calculation unit 74 calculates the deviation of at least one of the size and the position of the irradiation target area 25 detected in each detection step (S40) (calculation step (S50)). The timing for performing the calculation step (S50) is appropriately set according to the type of the workpiece, the machining conditions, and the like. First, an example of calculating the variation in the size of the irradiation target region 25 in the calculation step (S50) will be described.
Fig. 8 is a graph showing the variation in the size of the irradiated region 25. The horizontal axis represents the order of acquiring the irradiated region 25, and corresponds to the elapsed time from the start of processing. The vertical axis represents a dimension (μm) in the longitudinal direction of the irradiation target region 25 in a direction perpendicular to the longitudinal direction of the line to divide 13 during processing (i.e., the Y-axis direction).
In this example, the standard deviation s is calculated for 20 irradiation target regions 25 each time the size of the irradiation target region 25 in the longitudinal direction (hereinafter, the size of the irradiation target region 25) is measured. The standard deviation s is expressed by the following mathematical formula 1.
[ mathematical formula 1 ]
Figure BDA0002686830210000111
Here, i and n are natural numbers, i represents the order of the acquired irradiation regions 25, and n represents the total number of the acquired irradiation regions 25. x is the number ofiIs the size of the irradiated region 25 acquired at the ith time. In addition, the character with the horizontal line on the upper part of the x is from the x1To xnAverage value of (a).
In this example, when n is 20, s is 0.19. In addition, when n is equal to 40, s is equal to 0.21, and when n is equal to 60, s is equal to 0.28. Thus, the standard deviation s in this example gradually increases as the measurement advances. That is, as the processing time elapses, the variation in the size of the irradiated region 25 becomes large.
In the calculation step (S50), since the shape of the irradiation target region 25 is quantitatively evaluated, the operator is likely to notice a non-temporary abnormality in the laser processing. This prevents the abnormality of laser processing from being overlooked, thereby preventing the deterioration of processing quality. In addition, the variation in the size of the irradiated region 25 (i.e., the graph shown in fig. 8) may be displayed on the monitor of the laser processing apparatus 2.
Since the variation in the size of the irradiation target region 25 tends to increase with the elapse of the processing time, a threshold value for the variation may be set in advance. In this case, when the variation in the size of the irradiated region 25 calculated in the calculation step (S50) exceeds a preset threshold, the laser processing device 2 issues a warning such as a warning display, a warning sound, or a lamp blinking (warning step (S60)).
This enables the operator to clearly recognize the occurrence of an abnormality in the laser processing apparatus 2. When a warning is issued from the laser processing apparatus 2, the operator stops the operation of the laser processing apparatus 2 and performs emergency processing (for example, removing debris adhering to the condenser 32 a). Further, it is preferable to identify the cause of the occurrence of the abnormality.
Next, an example of calculating the deviation of the position of the irradiation target region 25 in the calculation step (S50) will be described. Fig. 9 (a) is an example of an image in a case where the center line 13a of the line to divide 13 coincides with the center line 25a of the irradiation target region 25.
The center line 13a of the line to divide 13 is detected by the detection unit 72 based on, for example, a pattern of metal or the like having a predetermined geometric shape (i.e., the key pattern 27) provided at a corner of the device 15 when the device 15 is viewed in plan.
Fig. 9 (B) is an example of an image in a case where the center line 13a of the line to divide 13 does not coincide with the center line 25a of the irradiation target region 25. The Y coordinate of the center line 25a shown in fig. 9 (B) is shifted from the Y coordinate of the center line 13a by a distance d in the Y-axis direction.
The calculation unit 74 also calculates the standard deviation s using equation 1 for the Y coordinate of the center line 25 a. However, Y representing the Y coordinate of the center line 25a is usediInstead of x of math figure 1iUsing from y1To ynInstead of from x1To xnAverage value of (a).
In this way, in the calculation step (S50), since the deviation of the position of the irradiation target region 25 (i.e., the Y-coordinate of the center line 25 a) is quantitatively evaluated, the operator easily notices a non-temporary abnormality in the laser processing. This prevents the abnormality of laser processing from being overlooked, thereby preventing the deterioration of processing quality. The deviation of the position of the irradiation target area 25 obtained in the calculation step (S50) may be displayed on a monitor of the laser processing apparatus 2.
In addition, a threshold value for the positional deviation of the irradiation target region 25 may be set in advance. In this case, when the deviation of the position of the irradiated region 25 calculated in the calculation step (S50) exceeds a preset threshold, the laser processing device 2 issues a warning such as a warning display, a warning sound, or a lamp blinking (warning step (S60)).
This enables the operator to clearly recognize the occurrence of an abnormality in the laser processing apparatus 2. In the calculation step (S50) and the warning step (S60), both or either one of the variation in the size of the irradiation target region 25 and the variation in the position of the irradiation target region 25 may be used.
In the above-described embodiment 1, one shot is performed for one line to divide 13, and one irradiation target region 25 is detected. However, it is also possible to perform imaging once for one line to divide 13 and detect a plurality of irradiation regions 25 for one line to divide 13. Fig. 10 is an example of an image having two irradiated regions 25 according to embodiment 2.
In embodiment 2, two irradiation regions 25 are detected by simultaneously irradiating two different portions on one line 13 with the laser beam L. For example, by branching the laser beam L emitted from the laser beam irradiation unit 32 into two, two different portions of one line to divide 13 can be laser-processed at the same time.
In embodiment 2, the deviation in at least one of the size and the position of the irradiation target region 25 is also quantitatively evaluated by performing the holding step (S10) to the warning step (S60). Therefore, the operator is likely to notice a non-temporary abnormality in the laser processing. This prevents the abnormality of laser processing from being overlooked, thereby preventing the deterioration of processing quality.
Next, embodiment 3 will be explained. In embodiment 3, the photographing step (S30) and the inspection step (S40) in the processing step (S20) are performed once for one wafer 11. However, by performing the imaging step (S30) and the detection step (S40) in the processing step (S20) on the plurality of wafers 11, the deviation of at least one of the size and the position of the irradiated region 25 is calculated in the calculation step (S50).
In embodiment 3, the operator can easily notice a non-temporary abnormality in the laser processing. This prevents the abnormality of laser processing from being overlooked, thereby preventing the deterioration of processing quality.
In addition, the structure, method, and the like of the above embodiments can be modified as appropriate without departing from the object of the present invention. For example, the index of deviation used in the calculation step (S50) is not limited to the standard deviation S. A variance or other index obtained by squaring the standard deviation s may also be used.

Claims (3)

1. A laser processing method for processing a workpiece by irradiating the workpiece with a pulsed laser beam having a wavelength absorbed by the workpiece,
the laser processing method comprises the following steps:
a holding step of holding the workpiece by a holding table;
a processing step of processing the workpiece by irradiating the laser beam onto an upper surface side of the workpiece held by the holding table;
an imaging step of imaging the upper surface side of the workpiece at a predetermined timing in the processing step, and acquiring an image of an irradiated area irradiated with the laser beam on the upper surface side;
a detection step of detecting at least one of a size and a position of the irradiated region, which is a region brighter than other regions, in the image acquired in the imaging step; and
and a calculation step of repeating the imaging step and the detection step in the processing step for a plurality of different regions of the workpiece, or performing the imaging step and the detection step in the processing step for each of the plurality of workpieces, and calculating a deviation of at least one of a size and a position of the irradiated region detected in each detection step.
2. The laser processing method according to claim 1,
the laser processing method also has the following warning steps: and a warning is issued when the deviation of at least one of the size and the position of the irradiated region calculated in the calculating step exceeds a preset threshold.
3. A laser processing apparatus for processing a workpiece by irradiating the workpiece with a pulsed laser beam having a wavelength absorbed by the workpiece,
the laser processing device comprises:
a holding table for holding the workpiece;
an imaging unit that images the workpiece held by the holding table;
a laser beam irradiation unit that irradiates the laser beam;
a detection unit that detects at least one of a size and a position of an irradiated region, which is a region brighter than other regions, in an image obtained by imaging the irradiated region on the upper surface side irradiated with the laser beam by the imaging unit at a predetermined timing when the workpiece is processed by irradiating the laser beam from the laser beam irradiation unit onto the upper surface side of the workpiece held by the holding table; and
and a calculation unit that calculates a deviation of at least one of the size and the position of the irradiated region detected by the detection unit.
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