JP6425368B2 - Laser processing apparatus and laser processing method - Google Patents

Laser processing apparatus and laser processing method Download PDF

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JP6425368B2
JP6425368B2 JP2012102507A JP2012102507A JP6425368B2 JP 6425368 B2 JP6425368 B2 JP 6425368B2 JP 2012102507 A JP2012102507 A JP 2012102507A JP 2012102507 A JP2012102507 A JP 2012102507A JP 6425368 B2 JP6425368 B2 JP 6425368B2
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laser
processing
reflected light
workpiece
light amount
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JP2013230477A (en
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信守 生越
信守 生越
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株式会社ディスコ
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/50Working by transmitting the laser beam through or within the workpiece
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03Observing, e.g. monitoring, the workpiece
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/0648Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms comprising lenses
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/067Dividing the beam into multiple beams, e.g. multifocusing
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B23MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K37/00Auxiliary devices or processes, not specially adapted to a procedure covered by only one of the preceding main groups
    • B23K37/04Auxiliary devices or processes, not specially adapted to a procedure covered by only one of the preceding main groups for holding or positioning work
    • B23K37/0461Welding tables

Description

  The present invention relates to a laser processing apparatus and a laser processing method for performing laser processing on a workpiece such as a semiconductor wafer.

  A wafer such as a silicon wafer or sapphire wafer on which a plurality of devices such as IC, LSI and LED are partitioned by dividing lines and formed on the surface is divided into individual devices by a processing device, and the divided devices are mobile phones, It is widely used in various electronic devices such as personal computers.

  A dicing method using a cutting device called a dicer is widely adopted for dividing the wafer. In the dicing method, the wafer is cut by cutting a cutting blade with a thickness of about 30 μm while solidifying abrasive particles such as diamond with metal or resin at a high speed of about 30,000 rpm, and cutting the wafer into individual devices. Divide into chips.

  On the other hand, in recent years, a method of dividing a wafer into individual device chips using a laser beam has been developed and put to practical use. First and second processing methods described below are known as methods for dividing a wafer into individual device chips using a laser beam.

  In the first processing method, the focal point of a laser beam of a wavelength (for example, 1064 nm) having transparency to the wafer is positioned inside the wafer corresponding to the dividing line, and the laser beam is along the dividing line. In this method, a modified layer is formed inside the wafer by irradiation, and then an external force is applied to the wafer by a dividing device to divide the wafer into individual device chips using the modified layer as a division starting point (for example, Japanese Patent No. 3408805). reference).

  In the second processing method, a focused spot of a laser beam of a wavelength (for example, 355 nm) having absorbency to the wafer is irradiated to a region corresponding to the planned dividing line to form a processing groove by ablation processing, and then external force To divide the wafer into individual device chips with the processing groove as the dividing starting point (see, for example, JP-A-10-305420).

  The processing method using a laser beam can increase the processing speed as compared to the dicing method using a dicer, and can relatively easily process even a wafer made of a high-hardness material such as sapphire or SiC. .

  In addition, since the modified layer or the processed groove can be made as narrow as, for example, 10 μm or less, it has an advantage that the amount of devices taken per wafer can be increased compared to the case of processing by dicing method. ing.

  By the way, an oxide film or a nitride film remains on the back surface of the semiconductor wafer before the back surface grinding by the grinding apparatus. In addition, there are also semiconductor wafers in which a low-k film is formed on the front surface and wafers in which a metal film is formed on the back surface.

  When a laser beam is irradiated to the workpiece with the film to perform laser processing, a part of the laser beam irradiated by the film is reflected. The reflectance varies depending on the type, thickness and the like of the film, and there are some in which the reflectance differs for each workpiece, and in which there is variation in reflectance even within one workpiece.

  A first processing method for forming a modified layer inside a workpiece using a wavelength having transparency to the workpiece, and a workpiece using a wavelength having an absorptivity for the workpiece In the case of the second processing method in which the laser beam is ablated, the amount of the transmitted or absorbed laser beam is reduced if the reflectance of the workpiece is high. It is necessary to increase the power of the beam.

Patent No. 3408805 JP 10-305420 A JP, 2009-021476, A JP, 2010-245172, A

  When the reflectance is different for each workpiece, when laser processing is performed on a plurality of workpieces under a single processing condition, the depths of the laser-processed grooves formed by the laser beam irradiation among the workpieces vary. There is a problem in that there is a variation in the reformed layer formed by the laser beam irradiation.

  In addition, in the case where the reflectance varies in one workpiece, if laser processing is performed under a single processing condition, the depth of the laser processed groove formed by the irradiation of the laser beam varies depending on the region. In addition, there is a problem that variation occurs in the modified layer formed by the irradiation of the laser beam.

  The present invention has been made in view of these points, and the object of the present invention is to provide a laser processing apparatus and a laser processing capable of performing uniform laser processing regardless of the laser irradiation surface state of the workpiece. It is to provide a method.

According to the first aspect of the present invention, there is provided a laser processing apparatus for performing laser processing on a workpiece divided by a plurality of planned dividing lines, and a chuck table for holding the workpiece, and processing feed of the chuck table. Laser beam irradiating means including a processing feed means, a laser oscillator, and a processing head having a condensing lens for condensing a laser beam oscillated from the laser oscillator, and held from the laser beam irradiating means to the chuck table Reflection light amount detection means for detecting the reflection light amount of the laser beam irradiated to the processed workpiece, the reflectance calculated from the reflection light amount detected by the reflection light amount detection means, the appropriate energy of the laser beam and the reflection Power regulation for adjusting the power of the laser beam oscillated from the laser oscillator based on the correlation with the And means, a stage number calculating means for the number of stages for performing laser processing a plurality of stages, calculated on the basis of the amount of reflected light detected by the reflected light amount detecting means across the thickness direction of the workpiece by the laser beam irradiation means, the While the processing table feeds the chuck table with the processing feed means, the laser beam is irradiated to any planned dividing line, plural planned dividing lines, or all planned dividing lines of the workpiece held by the chuck table. The laser beam is irradiated from the means, and the reflected light amount of the reflected light reflected on the upper surface of the workpiece is detected by the reflected light amount detecting means, and then the output of the laser beam irradiated by the laser beam irradiating means is set. The arbitrary planned dividing line of the workpiece held by the chuck table while processing feeding the chuck table by the processing feed means, the plurality of divided Line, or the all the dividing lines by irradiating a laser beam from the laser beam irradiation means, a laser machining apparatus characterized by performing laser processing on a workpiece is provided.

According to the second aspect of the present invention, there is provided a laser processing method for performing laser processing on a workpiece, wherein a holding step of holding the workpiece by a chuck table, and the chuck table being processed and fed while being processed. A laser beam irradiation step for reflected light amount detection which irradiates a laser beam from the laser beam irradiation means to a predetermined dividing line, a plurality of dividing lines, or all dividing lines of the held object under the first condition A reflected light amount detecting step of detecting a reflected light amount of reflected light reflected by the upper surface of the workpiece from the laser beam irradiated to the workpiece in the reflected light amount detecting laser beam irradiation step; and detected by the reflected light amount detecting step Step number calculation to calculate the number of steps to apply multiple steps of laser processing in the thickness direction of the workpiece based on the reflected light amount Steps and, after performing the laser beam irradiation step and said reflected light detecting step for the amount of reflected light detected, the reflectance is calculated from the detected amount of reflected light in the reflected light amount detecting step, and a laser beam of appropriate energy and the The power of the laser beam irradiated by the laser beam irradiation means is set based on the correlation with the reflectance, and the arbitrary division of the workpiece held by the chuck table is performed while the chuck table is processed and fed. A laser processing step of applying a laser beam to the planned line, the plurality of divided planned lines, or all the divided planned lines from the laser beam irradiating means under the second condition to perform the laser processing on the workpiece comprising, in the laser processing step, it passed to the thickness direction of the workpiece based on the number calculated by the stepped number calculation step Laser processing method characterized by performing laser processing a plurality of stages of Te is provided.

  The laser processing apparatus according to the present invention comprises: a reflected light amount detecting means for detecting the light amount of the reflected light reflected by the upper surface of the workpiece; and an output adjusting means for optimally adjusting the output of the laser beam based on the detected reflected light amount. Since it has, it becomes possible to perform uniform laser processing irrespective of the laser irradiation surface state of a to-be-processed object.

  In the laser processing method of the present invention, the output of the laser beam is set based on the reflected light amount detected in the reflected light amount detection laser beam irradiation step, the reflected light amount detection step for detecting the reflected light amount, and the reflected light amount detection step. Since the laser processing step of subjecting the workpiece to laser processing is provided, uniform laser processing can be applied to the workpiece regardless of the laser irradiation surface state of the workpiece.

It is a perspective view of a laser processing apparatus. It is a block diagram of the optical system of a laser beam irradiation unit. It is a surface side perspective view of a semiconductor wafer. It is a disassembled perspective view which shows a mode that the surface side of a semiconductor wafer is stuck to the adhesive tape with which the outer peripheral part was mounted | worn with the cyclic | annular flame | frame. It is a partial cross section side view which shows a holding | maintenance step. It is a partial cross section side view which shows the laser beam irradiation step for reflected light amount detection. It is a figure which shows the correlation of the reflectance of a workpiece, and appropriate pulse energy. It is a partial cross section side view which shows the laser processing step which forms a modification layer inside a wafer. It is a partial cross section side view which shows the laser beam irradiation step for reflected light amount detection implemented to the surface side of a wafer. It is a partial cross section side view which shows embodiment which gives a laser processing, detecting a reflected light quantity. It is a perspective view which shows a back surface grinding step.

  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 the stationary base 4 so as to be movable in the X-axis direction.

  The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by machining feed means 12 composed of a ball screw 8 and a 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 in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing and feeding means 22 composed of the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26. The chuck table 28 is movable in the X-axis direction and the Y-axis direction by the processing feed means 12 and the indexing feed means 22. . The chuck table 28 is provided with a clamp 30 for clamping a semiconductor wafer held by suction on the chuck table 28.

  A column 32 is erected on the stationary base 4, and a laser beam irradiation unit 34 is attached to the column 32. The laser beam irradiation unit 34 includes a laser oscillation unit 62 shown in FIG. 2 housed in a casing 35, and a processing head 36 attached to the tip of the casing 35.

  As shown in FIG. 2, the laser oscillation unit 62 includes a laser oscillator 64 that oscillates a YAG laser or a YVO 4 laser, and a repetition frequency setting unit 66. Although not shown in particular, the laser oscillator 64 has a Brewster window, and the laser beam emitted from the laser oscillator 64 is a linearly polarized laser beam.

  At the tip of the casing 35, an imaging unit 38 is disposed in alignment with the processing head 36 in the X-axis direction to detect a processing area to be laser-processed. The imaging unit 38 includes an imaging element such as a normal CCD for imaging the processing area of the semiconductor wafer by visible light.

  The imaging unit 38 further includes an infrared irradiating means for irradiating the semiconductor wafer with infrared rays, an optical system for capturing infrared rays emitted by the infrared irradiating means, and an infrared CCD for outputting an electrical signal corresponding to the infrared rays captured by the optical system. And the like, and the captured image signal is transmitted to the controller (control means) 40.

  The controller 40 is constituted by a computer, and a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read only memory (ROM) 44 that stores control programs and the like, and random readable / writable random numbers that store arithmetic results and the like. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Denoted at 56 is a processing feed amount detecting means comprising a linear scale 54 disposed along the guide rails 14 and a reading head (not shown) disposed on the first slide block 6. The detected signal is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes indexing feed amount detecting means comprising a linear scale 58 disposed along the guide rail 24 and a reading head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal captured by the imaging unit 38 is also input to the input interface 50 of the controller 40. On the other hand, control signals are output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  Referring to FIG. 2, an optical system of the laser beam irradiation unit 34 according to the embodiment of the present invention is shown. In a casing 70 of the processing head 36, a reflection mirror 76 and a condenser lens 74 are accommodated. Furthermore, a half mirror (beam splitter) 76 is disposed between the reflection mirror 72 and the focusing lens 74.

  The laser beam 69 oscillated from the laser beam oscillation unit 62 and further adjusted to a predetermined power by the output adjustment unit 68 is reflected by the reflection mirror 72 of the processing head 36, and a part thereof is transmitted through the half mirror 76 to be collected. By the step 74, the wafer 11, which is a workpiece, is irradiated.

  The reflected light 71 reflected on the upper surface of the wafer 11 is condensed by a condensing lens 74, a part of which is reflected by a half mirror 76, and a reflected light amount detector 78 including a light receiving element such as a photodiode detects the reflected light amount. Ru. Based on the reflected light quantity, the controller 40 controls the laser beam oscillation unit 62 and the power adjustment unit 68 as will be described in detail later.

  The half mirror 76 may be disposed between the condensing lens 74 and the workpiece (wafer) 11. However, when the half mirror 76 is disposed on the upstream side of the condensing lens 74, the upper surface of the wafer 11 is Such an arrangement is preferable for detecting the amount of reflected light because only the reflected light that has been reflected can be condensed by the condensing lens 74 and be incident on the half mirror 76.

Referring to FIG. 3, a front side perspective view of a semiconductor wafer 11, which is one of the workpieces of the laser processing method of the present invention, is shown. The semiconductor wafer 11 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of planned dividing lines 13 are formed in a lattice shape on the surface 11 a and in each area partitioned by the plurality of planned dividing lines 13. Devices 15 such as IC and LSI are respectively formed. As shown in FIG. 4, an oxide film 17 made of SiO 2 is formed on the back surface 11 b of the semiconductor wafer 11.

  In the laser processing method of the present invention, the workpiece is not limited to the semiconductor wafer 11 shown in FIG. 3 and has a film such as an oxide film, a nitride film, a metal film or a low-k film on the front or back surface. It contains a workpiece.

  In carrying out the laser processing method of the present invention, as shown in FIG. 4, the surface 11a side of the semiconductor wafer 11 is adhered to the adhesive tape T whose outer peripheral portion is attached to the annular frame F, and the back surface 11b is the upper side Become.

  Then, as shown in FIG. 5, the semiconductor wafer 11 is held by suction via the adhesive tape T by the chuck table 28 of the laser processing apparatus 2, and the annular frame F is clamped and fixed by the clamp 30.

  Then, as shown in FIG. 6, the laser beam irradiation step for reflected light amount detection is performed to irradiate the laser beam 69 under the first condition from the processing head 36 of the laser beam irradiation unit 34 to the wafer 11 held by the chuck table 28. Do.

  Before carrying out the laser beam irradiation step for reflected light amount detection, alignment is carried out to detect the planned dividing line 13 to be laser processed. That is, the wafer 11 is imaged from the back surface 11b side by the infrared camera of the imaging unit 38, and the planned division line 13 and the direction orthogonal to the first direction extend in the first direction using well known image processing such as pattern matching. The division planned line 13 extending in the second direction is detected.

  As another embodiment, the holding surface of the chuck table 28 may be formed of a transparent member, and the wafer 11 may be imaged by a camera disposed below the chuck table 28 to perform alignment.

  Furthermore, in the present invention, before detecting the amount of light reflected from the wafer 11, one or more reference works having a known reflectance are prepared in advance, the amount of light reflected is detected by the reference work, and the amount of light reflected at that time is calculated. It is stored in the RAM 46 of the controller 40 as reference data.

  In this reflected light amount detection laser beam irradiation step, as shown in FIG. 6, while processing and feeding the chuck table 28 in the direction of the arrow X1, a laser beam is applied from the processing head 36 to the back surface 11b of the wafer 11 on which the oxide film 17 is formed. The reflected light 71 is detected by a reflected light amount detector 78.

  For example, the reflected light amount is detected by irradiating a laser beam for reflected light amount detection on an arbitrary divided planned line 13, a plurality of divided planned lines 13, or all the divided planned lines 13 of the wafer 11.

  The irradiation conditions of the laser beam for reflected light amount detection in the case of forming a modified layer inside the wafer 11 by the irradiation of the laser beam 69 are, for example, as shown below.

Light source: LD excitation Q switch Nd: YVO4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100kHz
Average power: 0.1 W
Processing feed rate: 400 mm / s

When the back surface 11b of the wafer 11 is irradiated with the laser beam 69 in the reflected light amount detection laser beam irradiation step, the reflected light 71 reflected by the back surface 11b on which the oxide film 17 is formed is condensed by the condenser lens 74 shown in FIG. A part of the light is reflected by the half mirror 76 and enters the reflected light amount detector 78 composed of a light receiving element, and the reflected light amount reflected by the back surface 11 b of the wafer 11 is detected. The reflectance of the back surface 11 b of the wafer 11 is calculated from the detected amount of reflected light and the amount of reflected light of the reference work whose reflectance is stored in the RAM 46 and known.

  A plurality of correlation diagrams as shown in FIG. 7 are stored in the ROM 44 of the controller 40, which show the correlation 73 between the reflectance and the appropriate pulse energy for each type of film or film type. Therefore, appropriate pulse energy for the reflectance can be obtained from these correlation diagrams.

The average power and repetition frequency of the laser beam oscillated from the laser oscillator 64 are adjusted based on appropriate pulse energy. For example, when the reflectance is 50%, it is determined from the correlation diagram of FIG. 7 that the appropriate pulse energy is 20 μJ. Therefore, based on pulse energy (J) = average output (W) / repetition frequency (Hz), for example, a repetition frequency of 100 kHz and an average output of 2 W are set.

  Depending on the reflectance, the maximum power of the laser oscillator 64 is insufficient, so that a single reformed layer can not be formed inside the wafer 11 by one laser beam irradiation. Therefore, based on the amount of reflected light detected in the step of detecting the amount of reflected light, a plurality of modified layers are formed in the thickness direction of the wafer 11. The stage number calculation means for calculating the required number of stages based on the reflected light amount is stored in the ROM 44 of the controller 40.

  After performing the reflected light amount detection step, the output of the laser beam to be irradiated by the laser beam irradiation unit 34 is set based on the reflected light amount detected in the reflected light amount detection step, and the laser beam is set to the wafer 11 held by the chuck table 28 A laser beam is irradiated from the processing head 36 of the irradiation unit 34 under the second condition to perform a laser processing step of forming the modified layer 19 inside the wafer 11.

  In this laser processing step, as shown in FIG. 8, while processing and feeding the chuck table 28 in the direction of the arrow X1, the laser beam 69 is irradiated under the second condition from the processing head 36 of the laser beam irradiation unit 34. 11 form the modified layer 19 inside.

  Similar reforming layers 19 are formed one after another along the planned dividing line 13 extending in the first direction while indexing and feeding the chuck table 28 in the Y-axis direction. Next, after rotating the chuck table 28 by 90 degrees, the same modified layer 19 is formed along the planned dividing line 13 extending in the second direction.

  If the dividability is low due to the thickness and the material of the wafer 11, the modified layers 19 in multiple stages are formed inside the wafer. In addition, when the reflectance of the wafer 11 is high and the maximum power of the laser beam oscillator 64 is too low, a plurality of modified layers 19 can not be formed inside the wafer 11 by one laser beam irradiation. The reformed layer 19 of the stage is formed inside the wafer 11.

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser Wavelength: 1064 nm
Repetition frequency: 100kHz
Average power: 2.0W
Processing feed rate: 400 mm / s

  Referring to FIG. 9, there is shown a partial cross-sectional side view for explaining a laser beam irradiation step for reflected light amount detection in the case where the wafer 11 is subjected to ablation processing. For example, when the low-k film formed on the surface 11 a of the wafer 11 is subjected to ablation processing, the laser beam 69 is incident on the surface 11 a side of the wafer 11. Then, the amount of light of the reflected light 71 reflected by the surface 11 a is detected by a reflected light amount detector 78.

  In the case of the ablation processing, as in the modification layer forming processing described above, the laser beam for detecting the amount of reflected light is irradiated to the predetermined dividing line 13 of the wafer 11, the plural dividing lines 13 or all the dividing lines 13 And the amount of reflected light is detected.

  The laser beam irradiation conditions in the case of ablation processing are set, for example, as follows.

Light source: LD pumped Q switch Nd: YVO4 pulse laser Wavelength: 355 nm (third harmonic of YVO4 pulse laser)
Repetition frequency: 200 kHz
Average power: 0.1 W
Processing feed rate: 200 mm / s

  In the ablation processing, after the reflected light amount detection step is performed, the output of the laser beam to be irradiated by the laser beam irradiation unit 34 is set based on the reflected light amount detected in the reflected light amount detection step and held by the chuck table 28 A laser processing step of forming a laser processing groove by performing ablation processing on the planned dividing line 13 of the wafer 11 by irradiating the surface 11a of the wafer 11 with the laser beam under the second condition from the processing head 36 of the laser beam irradiation unit 34 Conduct.

  The laser processing conditions in this ablation processing are set, for example, as follows.

Light source: LD pumped Q switch Nd: YVO4 pulse laser Wavelength: 355 nm (third harmonic of YVO4 pulse laser)
Repetition frequency: 200 kHz
Average power: 1 W
Processing feed rate: 200 mm / s

  Depending on the reflectance of the surface 11a of the wafer 11 and the maximum power of the laser oscillator 64, even in the case of ablation processing, the light condensing point by the condenser lens 74 is changed in the thickness direction of the wafer 11 to form multiple steps of laser processing grooves. . The number of stages in this case is calculated by the stage number calculation means stored in the ROM according to the reflectance detected in the reflectance detection step.

  In the second embodiment of the laser processing method of the present invention, the laser processing step may be performed while performing the reflected light amount detection step. That is, as shown in FIG. 10, the laser beam 69 is irradiated from the processing head 36 of the laser beam irradiation unit 34 while processing and feeding the chuck table 28 in the direction of arrow X1, and the reflected light 71 reflected on the back surface 11b of the wafer 11 The reflected light amount is detected by the reflected light amount detector 78.

  The controller 40 feedback-controls the output adjusting unit 68 based on the reflected light quantity, and forms the modified layer 19 inside the wafer 11 with the laser beam 69 of the optimum output based on the reflected light quantity.

  Also in the case of ablation processing, the power adjustment unit 68 may be controlled according to the amount of reflected light so that ablation processing may be performed while irradiating the laser beam 69 of optimum power from the processing head 36. After forming the modified layer 19 and the laser processing groove on the wafer 11, an external force is applied to the wafer 11 to perform a dividing step of dividing into individual chips.

  In the present embodiment, after forming the modified layer 19 inside the wafer 11 along all the planned dividing lines 13, a back surface grinding step is performed to grind the back surface 11b of the wafer 11. In this back surface grinding step, as shown in FIG. 11, the back surface 11b of the wafer 11 held by the chuck table 96 of the grinding apparatus is ground by the grinding wheel 94, and the pressure during grinding makes the wafer 11 into individual chips. To divide.

  In FIG. 11, the grinding unit 82 comprises a spindle 84, a wheel mount 86 fixed to the tip of the spindle 84, and a grinding wheel 88 detachably mounted on the wheel mount 86 with a plurality of screws 90. The grinding wheel 88 is configured by fixing a plurality of grinding wheels 94 around the outer periphery of the lower end portion of the annular base 92.

  In this back surface grinding step, while rotating the chuck table 96 in the direction of arrow a at, for example, 300 rpm, the grinding wheel 88 is rotated at the direction of arrow b, for example The back surface 11b is brought into contact.

  Then, the grinding of the back surface 11 b of the wafer 11 is performed while grinding-feeding the grinding wheel 88 downward at a predetermined grinding feed rate. The wafer 11 is finished to a desired thickness, for example 50 μm, while measuring the thickness of the wafer 11 with a contact or non-contact thickness measurement gauge.

  In the middle of this grinding, since the modified layer 19 is formed along the planned dividing line 13 inside the wafer 11, the wafer 11 is an individual chip starting from the modified layer 19 as a dividing start point by the pressing force during grinding. Divided into

  Here, in the case of a workpiece having low dividability, a division step is performed in which an external force is applied to the workpiece to perform division before the back surface grinding is performed. Alternatively, after the back surface grinding is performed, a dividing step of dividing the workpiece by applying an external force to the workpiece is performed.

  In the embodiment described above, after the modified layer 19 is formed on a thick (700 μm) wafer, the back surface 11 b of the wafer 11 is ground to thin the wafer, and at the same time the modified layer is formed by the pressing force during grinding. The division 19 is used as a division start point to divide into individual chips, but the modified layer 19 and the laser processing groove may be formed on the wafer 11 which is thinned by grinding the back surface 11 b in advance. Alternatively, the wafer 11 may be fully cut by irradiating the wafer 11 with a laser beam of an absorbing wavelength.

11 semiconductor wafer 13 division scheduled line 15 device 17 oxide film 19 modified layer 28 chuck table 34 laser beam irradiation unit 36 processing head 38 imaging unit 62 laser oscillation unit 64 laser oscillator 66 repetition frequency setting unit 68 output adjustment unit 69 laser beam 71 Reflected light 74 Condensing lens 76 Half mirror 78 Reflected light amount detector

Claims (2)

  1. A laser processing apparatus for performing laser processing on a workpiece partitioned by a plurality of planned dividing lines,
    A chuck table for holding a workpiece;
    A processing feed means for processing and feeding the chuck table;
    A laser beam irradiation means including a laser oscillator and a processing head having a condensing lens for condensing a laser beam oscillated from the laser oscillator;
    Reflected light amount detecting means for detecting a reflected light amount of the laser beam emitted from the laser beam irradiating means to the workpiece held on the chuck table;
    An output for adjusting an output of a laser beam oscillated from the laser oscillator based on a reflectance calculated from a reflected light amount detected by the reflected light amount detecting means and a correlation between an appropriate energy of the laser beam and the reflectance. Adjustment means,
    Number-of-stages calculating means for calculating the number of stages of laser processing in a plurality of stages across the thickness direction of the workpiece by the laser beam irradiation means based on the reflected light amount detected by the reflected light amount detection means;
    Equipped with
    While processing feeding the chuck table by the processing feed means, the laser beam irradiation means to any planned dividing line, a plurality of planned dividing lines, or all the planned dividing lines of the workpiece held by the chuck table. After irradiating a laser beam and detecting the amount of reflected light of the reflected light reflected on the upper surface of the workpiece by the reflected light detection means,
    The output of the laser beam to be irradiated is set by the laser beam irradiation means, and the arbitrary division scheduled line of the workpiece held by the chuck table while the processing of the chuck table is performed by the processing feed means, the plurality A laser processing apparatus characterized in that a laser beam is irradiated from the laser beam irradiation means to the dividing planned line of or all the dividing planned lines to perform laser processing on a workpiece.
  2. A laser processing method for performing laser processing on a workpiece divided by a plurality of planned dividing lines,
    A holding step for holding the workpiece on a chuck table;
    While processing feeding the chuck table, a laser is applied to a predetermined dividing line, a plurality of dividing lines, or all dividing lines of the workpiece held by the chuck table under the first condition from the laser beam irradiating means A laser beam irradiation step for reflected light amount detection which irradiates a beam;
    A reflected light amount detection step of detecting a reflected light amount of reflected light of the laser beam irradiated to the workpiece in the reflected light amount detection laser beam irradiation step reflected on the upper surface of the workpiece;
    A step number calculation step of calculating the number of steps for performing a plurality of laser processing steps in the thickness direction of the workpiece based on the reflected light amount detected in the reflected light amount detection step;
    After performing the laser beam irradiation step for reflected light amount detection and the reflected light amount detection step, the reflectance calculated from the reflected light amount detected in the reflected light amount detection step, the appropriate energy of the laser beam, and the reflectance Setting the output of the laser beam to be irradiated by the laser beam irradiation means based on the correlation of the laser beam irradiation means, and processing and feeding the chuck table, the predetermined dividing planned line of the workpiece held by the chuck table; A laser processing step of applying a laser beam to the plurality of division planned lines or all the division planned lines from the laser beam irradiation unit under a second condition to perform laser processing on a workpiece;
    Equipped with
    In the laser processing step, a plurality of steps of laser processing are performed in the thickness direction of the workpiece based on the number of steps calculated in the step number calculation step .
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CN201310128509.XA CN103372720B (en) 2012-04-27 2013-04-15 Laser processing device and laser processing
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CN103372720B (en) 2016-07-13
CN103372720A (en) 2013-10-30

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