KR102086168B1 - Laser machining apparatus and laser machining method - Google Patents

Laser machining apparatus and laser machining method Download PDF

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Publication number
KR102086168B1
KR102086168B1 KR1020130042293A KR20130042293A KR102086168B1 KR 102086168 B1 KR102086168 B1 KR 102086168B1 KR 1020130042293 A KR1020130042293 A KR 1020130042293A KR 20130042293 A KR20130042293 A KR 20130042293A KR 102086168 B1 KR102086168 B1 KR 102086168B1
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South Korea
Prior art keywords
laser
reflected light
light amount
irradiation
workpiece
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KR1020130042293A
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Korean (ko)
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KR20130121719A (en
Inventor
노부모리 오고시
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가부시기가이샤 디스코
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Priority to JP2012102507A priority Critical patent/JP6425368B2/en
Priority to JPJP-P-2012-102507 priority
Application filed by 가부시기가이샤 디스코 filed Critical 가부시기가이샤 디스코
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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

Abstract

An object of the present invention is to provide a laser processing apparatus and a laser processing method capable of performing uniform laser processing irrespective of the state of the laser irradiation surface of the workpiece.
A laser processing apparatus for laser processing a workpiece, comprising: a laser beam irradiation means comprising a chuck table for holding a workpiece, a laser oscillator, and a processing head for condensing a laser beam oscillated from the laser oscillator And the reflected light amount detecting means for detecting the reflected light amount of the laser beam irradiated from the laser beam irradiation means to the workpiece held on the chuck table, and the laser oscillator based on the reflected light amount detected by the reflected light amount detecting means. And output adjustment means for adjusting the output of the laser beam oscillated from the laser beam.

Description

LASER MACHINING APPARATUS AND LASER MACHINING METHOD}

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

A plurality of devices such as ICs, LSIs, LEDs, etc. are partitioned by lines to be divided, and wafers such as silicon wafers and sapphire wafers formed on the surface are divided into individual devices by a processing apparatus. It is widely used in various electronic devices.

For dividing the wafer, a dicing method using a cutting device called a dicer is widely adopted. In the dicing method, the wafer is cut by dividing the abrasive grains such as diamond into metal or resin and cutting the wafer while rotating the cutting blade having a thickness of about 30 μm at a high speed of about 30000 rpm, and the wafer is cut into individual device 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 into practical use. As a method of dividing a wafer into individual device chips using a laser beam, first and second processing methods described below are known.

In the first processing method, a light converging point of a laser beam having a wavelength (for example, 1064 nm) that is transparent to a wafer is positioned inside the wafer corresponding to the dividing line, and the laser beam is irradiated along the dividing line so as to be inside the wafer. The modified layer is formed on the wafer, and then the external device is applied to the wafer by a dividing device, and the wafer is divided into individual device chips with the modified layer as the starting point of division (see Japanese Patent No. 3408805, for example).

The second processing method irradiates an area corresponding to a division scheduled line with a light-converging point of a laser beam having a wavelength (for example, 355 nm) having an absorptance with respect to a wafer to form a processing groove by ablation processing, and then applies an external force. It is a method of dividing a wafer into individual device chips by making a process groove into a division origin (for example, refer Unexamined-Japanese-Patent No. 10-305420).

The processing method using a laser beam can make processing speed faster than the dicing method by a dicer, and can process it easily even with the wafer which consists of materials with high hardness, such as sapphire and SiC.

In addition, since the modified layer or the processing groove can be made narrow, for example, 10 µm or less, there is an advantage that the amount of the device per wafer can be increased compared with the case of processing by the dicing method.

By the way, an oxide film and a nitride film remain | survive on the back surface of the semiconductor wafer before back surface grinding by a grinding apparatus. There are also semiconductor wafers in which a low-k film is formed on the surface and a wafer on which a metal film is formed on the back surface.

When a laser beam is irradiated to a workpiece | work which has such a film | membrane and laser processing, a part of laser beam irradiated by the film | membrane will be reflected. The reflectance is different depending on the kind, thickness, etc. of the film, and the reflectance may be different for each workpiece, or the reflectance may be uneven within one workpiece.

The first processing method of forming a modified layer inside the workpiece using a wavelength having a transmittance with respect to the workpiece, and the second processing method of ablating the workpiece with a wavelength having absorption with the workpiece. Even in this case, when the reflectance of the workpiece is large, the amount of light of the laser beam that is transmitted or absorbed is reduced. Therefore, in order to perform desired laser processing, it is necessary to increase the output of the irradiated laser beam.

Japanese Patent No. 3408805 Japanese Patent Laid-Open No. 10-305420 Japanese Patent Publication No. 2009-021476 Japanese Patent Laid-Open No. 2010-245172

When the reflectance is different for each workpiece, when a plurality of workpieces are subjected to laser processing under a single processing condition, the depth of the laser processing groove formed by the irradiation of the laser beam between the workpieces becomes uneven or the laser beam is irradiated. There exists a problem that a nonuniformity arises in the modified layer formed by this.

Moreover, in the case where the reflectance is nonuniform in one workpiece, if the laser processing is performed under a single processing condition, the depth of the laser processing groove formed by the irradiation of the laser beam depending on the area becomes uneven or the laser beam There exists a problem that a nonuniformity arises in the modified layer formed by irradiation.

This invention is made | formed in view of such a point, Comprising: It aims at providing the laser processing apparatus and laser processing method which can perform uniform laser processing irrespective of the state of the laser irradiation surface of a to-be-processed object.

According to the invention of claim 1, there is provided a laser processing apparatus for performing laser processing on a workpiece, comprising: a chuck table for holding the workpiece, a laser oscillator, and a condenser lens for condensing the laser beam oscillated from the laser oscillator Laser beam irradiation means including a head, reflected light amount detecting means for detecting the reflected light amount of the laser beam irradiated from the laser beam irradiation means to the workpiece held on the chuck table, and the reflection detected by the reflected light amount detecting means The laser processing apparatus provided with the output adjusting means which adjusts the output of the laser beam oscillated from the said laser oscillator based on the light quantity.

Preferably, the laser processing apparatus calculates the number of stages in which the laser beam irradiation means performs a plurality of stages of laser processing over the thickness direction of the workpiece based on the amount of reflected light detected by the reflected light amount detection means. Further means is provided.

According to the invention of claim 3, there is provided a laser processing method for performing laser processing on a workpiece, comprising: a holding step of holding the workpiece on a chuck table, and a first condition from a laser beam irradiation means on the workpiece held on the chuck table; A laser beam irradiation step of detecting a reflected light amount to irradiate a laser beam and detecting a reflected light amount of reflected light reflected from an upper surface of a workpiece by a laser beam irradiated to a workpiece in the reflected beam amount detecting laser beam irradiation step After performing the reflected light amount detecting step and the reflected light amount detecting step, based on the reflected light amount detected in the reflected light amount detecting step, the output of the laser beam irradiated by the laser beam irradiation means is set and held in the chuck table. The workpiece to be irradiated with a laser beam under a second condition from the laser beam irradiation means. This laser processing method is provided which is characterized in that it comprises a laser processing method comprising: performing laser processing.

Preferably, the laser processing method further includes a stage calculating step of calculating a stage for performing a plurality of stages of laser processing over the thickness direction of the workpiece, based on the amount of reflected light detected in the reflected light amount detecting step, In the laser processing step, a plurality of stages of laser processing are performed over the thickness direction of the workpiece on the basis of the stage calculated in the stage calculation.

The laser processing apparatus of the present invention includes reflected light amount detecting means for detecting the light amount of the reflected light reflected from the upper surface of the workpiece and output adjusting means for optimally adjusting the output of the laser beam based on the detected reflected light amount. It becomes possible to perform uniform laser processing irrespective of the state of the laser irradiation surface of a workpiece.

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

1 is a perspective view of a laser processing apparatus.
2 is a block diagram of an optical system of a laser beam irradiation unit.
3 is a perspective view of the surface side of a semiconductor wafer.
It is an exploded perspective view which shows the aspect which adhere | attaches the surface side of a semiconductor wafer to the adhesive tape with which the outer peripheral part was attached to the annular frame.
5 is a partial cross-sectional side view showing the holding step.
6 is a partial cross-sectional side view showing the laser beam irradiation step for detecting the reflected light amount.
7 is a diagram showing a correlation between reflectance of a workpiece and an appropriate pulse energy.
8 is a partial cross-sectional side view illustrating a laser processing step of forming a modified layer inside a wafer.
9 is a partial cross-sectional side view showing a laser beam irradiation step for detecting a reflected light amount on a surface side of a wafer.
It is a partial cross-sectional side view which shows embodiment which performs laser processing, detecting the amount of reflected light.
It is a perspective view which shows a back surface grinding step.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1, there is shown an external perspective view of a laser processing apparatus according to an embodiment of the present invention. 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, in the X-axis direction by the machining feed means 12 constituted by the ball screw 8 and the pulse motor 10. do.

The 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 indexed along the pair of guide rails 24 in the indexing direction, that is, the Y-axis direction by the indexing conveying means 22 constituted by the ball screw 18 and the pulse motor 20. Move.

The chuck table 28 is mounted on the 2nd slide block 16 via the cylindrical support member 26, and the chuck table 28 is an X-axis direction by the process feed means 12 and the indexing feed means 22. As shown in FIG. And move in the Y-axis direction. The chuck table 28 is provided with a clamp 30 for clamping the semiconductor wafer attracted and held by 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 accommodated in the casing 35 and a processing head 36 attached to the tip of the casing 35.

The laser oscillation unit 62 includes the laser oscillator 64 which oscillates a YAG laser or a YVO4 laser, and the repetition frequency setting unit 66, as shown in FIG. Although not particularly shown, 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 distal end of the casing 35, an imaging unit 38 is arranged that detects a machining region to be laser-processed in alignment with the machining head 36 in the X-axis direction. The imaging unit 38 includes an imaging device such as a normal CCD for imaging the processing region of the semiconductor wafer with visible light.

The imaging unit 38 includes infrared irradiation means for irradiating infrared rays onto a semiconductor wafer, an optical system for capturing infrared rays irradiated by the infrared irradiation means, an infrared CCD for outputting an electric signal corresponding to the infrared rays captured by the optical system, and the like. Infrared imaging means constituted by an infrared imaging element, wherein the captured image signal is transmitted to a controller (control means) 40.

The controller 40 is configured by a computer, and includes a central processing unit (CPU) 42 that performs arithmetic processing in accordance with a control program, a read-only memory (ROM) 44 that stores a control program, and the like, arithmetic results, and the like. And a recordable / readable random access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 for storing the data.

Reference numeral 56 denotes a machining feed amount detecting means comprising a linear scale 54 arranged along the guide rail 14 and a readhead (not shown) disposed on the first slide block 6, and the machining feed amount detecting means 56 ) Is input to the input interface 50 of the controller 40.

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

The image signal picked up by the imaging unit 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is 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.

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

The laser beam 69 oscillated from the laser beam oscillation unit 62 and adjusted to the power determined in the output adjustment unit 68 is reflected by the reflection mirror 72 of the processing head 36, and part of the half mirror ( It penetrates 76 and is irradiated to the wafer 11 which is a workpiece by the condensing lens 74.

The reflected light 71 reflected from the upper surface of the wafer 11 is collected by the condenser lens 74, and part of the reflected light is reflected by the half mirror 76 to the reflected light amount detector 78 including a light receiving element such as a photodiode. The amount of reflected light is detected. Based on this reflected light amount, the controller 40 controls the laser beam oscillation unit 62 and the output adjustment unit 68 as described later in detail.

Although the half mirror 76 may be arrange | positioned between the condensing lens 74 and the to-be-processed object (wafer) 11, the half mirror 76 is arrange | positioned more upstream than the condensing lens 74, but the wafer 11 Since only the reflected light reflected from the upper surface of the light can be collected by the condenser lens 74 and incident on the half mirror 76, such arrangement is preferable for the detection of the reflected light amount.

Referring to Fig. 3, there is shown a perspective view of the surface side of a semiconductor wafer 11, which is one of the workpieces of the laser processing method of the present invention. The semiconductor wafer 11 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of division scheduled lines 13 are formed in a lattice shape on the surface 11 a, and divided by a plurality of division scheduled lines 13. In each of the regions, devices 15 such as IC and LSI are formed. There is (11b) of the semiconductor wafer 11, the oxide film 17 made of SiO 2 is formed, as shown in FIG.

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

In performing the laser processing method of this invention, as shown in FIG. 4, the surface 11a side of the semiconductor wafer 11 adhere | attaches the adhesive tape T by which the outer peripheral part was attached to the annular frame F. In FIG. The back surface 11b becomes the upper side.

As shown in FIG. 5, the semiconductor wafer 11 is sucked and held by the adhesive tape T on the chuck table 28 of the laser processing apparatus 2, and the annular frame F is clamped 30. It is clamped and fixed by.

6, the reflection which irradiates the laser beam 69 to a 1st condition from the processing head 36 of the laser beam irradiation unit 34 to the wafer 11 hold | maintained at the chuck table 28 as shown in FIG. A laser beam irradiation step for detecting the amount of light is performed.

Before performing this laser beam irradiation step for detecting the reflected light amount, alignment is performed to detect the division scheduled line 13 to be laser processed. That is, the division scheduled line 13 extending in the first direction by imaging the wafer 11 from the back surface 11b side with an infrared camera of the imaging unit 38 and using well-known image processing such as pattern matching. And the division scheduled line 13 extending in the second direction orthogonal to the first direction.

As another embodiment, the holding surface of the chuck table 28 may be formed of a transparent member, and the alignment of the wafer 11 may be performed by imaging a camera disposed under the chuck table 28.

In the present invention, before detecting the amount of reflected light of the wafer 11, one or a plurality of reference workpieces having a predetermined reflectance are prepared in advance, the amount of reflected light is detected by the reference workpiece, and the amount of reflected light at that time is referenced. The data is stored in the RAM 46 of the controller 40 as data.

In this laser beam irradiation step for detecting the reflected light amount, as shown in FIG. 6, the wafer 11 on which the oxide film 17 is formed from the processing head 36 is processed while transferring the chuck table 28 in the direction of arrow X1. The laser beam 69 is irradiated to the rear surface 11b to detect the reflected light 71 with the reflected light amount detector 78.

For example, the reflected light amount detection laser beam is irradiated to an arbitrary division scheduled line 13, a plurality of division scheduled lines 13, or all the division scheduled lines 13 of the wafer 11 to detect the reflected light amount.

Irradiation conditions of the laser beam for detecting the reflected light amount when the modified layer is formed inside the wafer 11 by irradiation of the laser beam 69 are as described below, for example.

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 1064 nm

Repetition frequency: 100 ㎑

Average power: 0.1 W

Machining feed rate: 400 mm / s

When the laser beam 69 is irradiated to the back surface 11b of the wafer 11 in the laser beam irradiation step for detecting the reflected light amount, the reflected light 71 reflected from the back surface 11b on which the oxide film 17 is formed is shown in FIG. 2. The amount of reflected light reflected by the condenser lens 74, a part of which is reflected by the half mirror 76, is incident on the reflected light amount detector 78 including the light receiving element, and is reflected by the back surface 11b of the wafer 11 Is detected. The reflectance of the back surface 11b of the wafer 11 is calculated from the amount of reflected light detected and the amount of reflected light of the reference workpiece whose reflectance stored in the RAM 46 is known.

The ROM 44 of the controller 40 stores a plurality of correlations as shown in FIG. 7, which shows the correlation 73 between the reflectance and the appropriate pulse energy for each type of workpiece or film type. Therefore, appropriate pulse energy for the reflectance can be obtained from these correlations.

Based on the appropriate pulse energy, the average power and repetition frequency of the laser beam oscillated from the laser oscillator 64 are adjusted. For example, when the reflectance is 50%, an appropriate pulse energy is determined to be 20 mu J from the correlation diagram of FIG. Therefore, from pulse energy J = average output W / repetition frequency Hz, it sets to repetition frequency 100kHz and average output 2W, for example.

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

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

In this laser machining step, as shown in FIG. 8, the laser beam 69 is subjected to the second condition from the machining head 36 of the laser beam irradiation unit 34 while the chuck table 28 is processed and transferred in the direction of the arrow X1. ) To form a modified layer 19 inside the wafer 11.

While indexing and conveying the chuck table 28 in the Y-axis direction, the same modified layer 19 is sequentially formed inside the wafer 11 along the division scheduled line 13 extending in the first direction. Subsequently, after rotating the chuck table 28 by 90 degrees, the same modified layer 19 is formed along the dividing line 13 extending in a 2nd direction.

When the dividing property is low depending on the thickness and the material of the wafer 11, a plurality of stages of the reformed layer 19 are formed inside the wafer. Moreover, when the reflectance of the wafer 11 is high and the maximum power of the laser oscillator 64 is too low, sufficient modification layer 19 cannot be formed inside the wafer 11 by one laser beam irradiation. A plurality of stages of the reformed layer 19 are formed inside the wafer 11.

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 1064 nm

Repetition frequency: 100 ㎑

Average power: 2.0 W

Machining feed rate: 400 mm / s

With reference to FIG. 9, a partial cross-sectional side view for explaining the laser beam irradiation step for detecting the reflected light amount when the ablation process is performed on the wafer 11 is shown. For example, when performing ablation processing on the Low-k film formed on the surface 11a of the wafer 11, the laser beam 69 is incident on the surface 11a side of the wafer 11. The light amount of the reflected light 71 reflected from the surface 11a is detected by the reflected light amount detector 78.

In the case of ablation processing, the amount of reflected light is detected on any of the scheduled division lines 13, the plurality of scheduled division lines 13, or all the scheduled division lines 13 of the wafer 11, similarly to the modified layer forming process described above. The amount of reflected light is detected by irradiating the laser beam.

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 355 nm (third harmonic of the YVO4 pulsed laser)

Repetition frequency: 200 ㎑

Average power: 0.1 W

Machining feed rate: 200 mm / s

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

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

Light source: LD excitation Q switch Nd: YVO4 pulse laser

Wavelength: 355 nm (third harmonic of the YVO4 pulsed laser)

Repetition frequency: 200 ㎑

Average power: 1 W

Machining 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, in the case of ablation processing, the focusing point by the condenser lens 74 is changed in the thickness direction of the wafer 11. A plurality of stages of laser processing grooves are formed. The number of stages in this case is calculated by the stage calculating means stored in the ROM in accordance with the reflectance detected in the reflectance detection step.

In the second embodiment of the laser machining method of the present invention, the laser machining step may be performed while the reflected light amount detection step is performed. 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, processing the chuck table 28 in the direction of arrow X1, and the wafer 11 A reflected light amount detector 78 detects the reflected light amount of the reflected light 71 reflected from the back surface 11b of the.

Based on this reflected light amount, the controller 40 feedback-controls the output adjustment unit 68, and forms the modified layer 19 inside the wafer 11 with the laser beam 69 of the optimal output based on the reflected light amount. do.

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

In this embodiment, after the modification layer 19 is formed in the inside of the wafer 11 along all the division planned lines 13, the back surface grinding step which grinds the back surface 11b of the wafer 11 is performed. In this back surface grinding step, as shown in FIG. 11, the back surface 11b of the wafer 11 hold | maintained at the chuck table 96 of a grinding apparatus is ground by the grinding grindstone 94, and a wafer is pressed by the pressure applied during grinding. (11) is divided into individual chips.

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

In this back grinding step, the chuck table 96 rotates at 300 rpm in the direction of arrow a, for example, and the grinding wheel 88 operates the grinding unit feed mechanism while rotating at 6000 rpm in the direction of arrow b, thereby grinding the grinding wheel 94 ) Is brought into contact with the back surface 11b of the wafer 11.

Then, the grinding wheel 88 is ground to the lower side at the predetermined grinding feed speed, while grinding the back surface 11b of the wafer 11. While measuring the thickness of the wafer 11 with a contact or non-contact thickness measuring gauge, the wafer 11 is finished to a desired thickness, such as 50 μm.

During this grinding process, the reformed layer 19 is formed inside the wafer 11 along the dividing line 13, so that the wafer 11 is divided with the pressing force during grinding as the starting point for the division. It is divided into individual chips.

Here, in the case of a work piece having a low dividing property, a dividing step of applying and dividing an external force to the work piece is performed before performing back surface grinding. Or after a back grinding operation, the division | segmentation step of applying and dividing an external force to a workpiece is performed.

In the above-described embodiment, after the modified layer 19 is formed on the thick (700 µm) wafer, the back surface 11b of the wafer 11 is ground to thin the wafer and modified by the pressing force at the time of grinding. Although the layer 19 is divided into individual chips as the starting point of division, the modified back surface 11b may be ground in advance to form the modified layer 19 or the laser processing groove in the thinned wafer 11. In addition, the wafer 11 may be irradiated with a laser beam having a wavelength having absorbance to full cut the wafer 11.

11: semiconductor wafer 13: line to be divided
15 device 17 oxide film
19: modified layer 28: chuck table
34 laser beam irradiation unit 36 machining 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 (4)

  1. In the laser processing apparatus which laser-processes the to-be-processed object divided by the some dividing plan line,
    A chuck table for holding the workpiece,
    A processing feed means for processing and conveying the chuck table;
    Laser beam irradiation means including a laser oscillator and a processing head having a condenser lens for condensing a laser beam oscillated from the laser oscillator;
    Reflected light amount detecting means for detecting the reflected light amount of the laser beam irradiated from the laser beam irradiation means to the workpiece held on the chuck table;
    Output adjusting means for adjusting the output of the laser beam oscillated from the laser oscillator based on the reflectance calculated from the reflected light amount detected by the reflected light amount detecting means, and the correlation between the appropriate energy of the laser beam and the reflectance;
    In consideration of the reflected light amount detected by the reflected light amount detecting means and the maximum power of the laser beam that can be irradiated by the laser beam irradiation means, it is determined whether or not the workpiece can be processed by one laser beam irradiation. When it is determined that the workpiece is impossible to be processed by the irradiation of the laser beam, the number of stages for performing laser processing of a plurality of stages in the thickness direction of the workpiece by the laser beam irradiation means is detected by the reflected light amount detecting means. And a singular calculating means for calculating based on the amount of reflected light,
    Irradiating a laser beam from the laser beam irradiation means to any division scheduled line, a plurality of division scheduled lines, or all division scheduled lines of the workpiece held in the chuck table while processing the chuck table by the machining transfer means. After detecting the reflected light amount of the reflected light reflected from the upper surface of the workpiece by the reflected light amount detecting means,
    An arbitrary division schedule line of the workpiece held in the chuck table, the plurality of division schedules, while setting the output of the laser beam irradiated from the laser beam irradiation means and processing the chuck table with the machining transfer means; A laser processing apparatus is subjected to laser processing on a workpiece by irradiating a line or all the division scheduled lines with a laser beam from the laser beam irradiation means based on the stage calculated by the stage calculation unit.
  2. In the laser processing method which performs a laser processing on the to-be-processed object partitioned by several division plan line,
    A holding step of holding the workpiece on the chuck table;
    Reflection which irradiates a laser beam to a 1st condition from a laser beam irradiation means to arbitrary division schedule lines, several division schedule lines, or all division division lines of a workpiece hold | maintained by the chuck table, while processing and conveying the said chuck table. Laser beam irradiation step for detecting light quantity;
    A reflected light amount detecting step of detecting the reflected light amount of the reflected light reflected from the upper surface of the workpiece by the laser beam irradiated to the workpiece in the laser beam irradiation step for detecting the reflected light amount;
    Considering the reflected light amount detected in the reflected light amount detecting step and the maximum power of the laser beam that can be irradiated by the laser beam irradiation means, it is determined whether or not the workpiece can be processed by one laser beam irradiation. When it is determined that the workpiece is impossible to be processed by the irradiation of a single laser beam, the number of stages for performing laser processing of a plurality of stages over the thickness direction of the workpiece is calculated based on the amount of reflected light detected in the reflected light amount detection step. And singular output stage made,
    Based on the reflected light amount calculated from the reflected light amount detected in the reflected light amount detecting step and the correlation between the appropriate energy of the laser beam and the reflectance after performing the laser beam irradiation step and the reflected light amount detecting step, The arbitrary division schedule lines, the plurality of division schedule lines, or all the division scheduled lines of the workpiece held on the chuck table while setting the output of the laser beam radiated by the laser beam irradiation means and processing the chuck table. A laser processing step of irradiating a laser beam to a workpiece to be split under a second condition from the laser beam irradiation means, and subjecting the workpiece to laser processing.
    Including,
    In the said laser processing step, the laser processing method of multiple stages is performed over the thickness direction of a to-be-processed object based on the number of stages computed by the said stage calculation.
  3. delete
  4. delete
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