JP2021000645A - Laser processing device - Google Patents

Abstract

To provide a laser processing device capable of avoiding reduction in processing quality and reduction in condensation accuracy.SOLUTION: A laser processing device 2 includes: holding means 4 for holding a workpiece; laser beam irradiation means 6 for irradiating the workpiece held by the holding means 4 with a laser beam LB; X-axis feeding means 8 for relatively processing and feeding the holding means 4 and the laser beam irradiation means 6 in an X-axis direction; and Y-axis feeding means 10 for relatively indexing and feeding the holding means 4 and the laser beam irradiation means 6 in a Y-axis direction orthogonal to the X-axis direction. The laser beam irradiation means 6 includes: an oscillator 30 for oscillating the laser beam LB; a condenser 32 for applying the laser beam LB oscillated by the oscillator 30 while positioning a condensation point FP inside the workpiece held by the holding means 4; and a detector 34 arranged between the oscillator 30 and the condenser 32 and detecting abrasion light AL which is emitted when the condensation point FP of the laser beam LB is positioned on an upper surface of the workpiece.SELECTED DRAWING: Figure 2

Description

In the present invention, the focusing point of the laser beam having a wavelength that is transparent to the workpiece is positioned inside the workpiece, and the laser beam is irradiated to the workpiece to form a modified layer inside the workpiece. Regarding laser processing equipment.

A wafer in which a plurality of devices such as ICs and LSIs are partitioned by a scheduled division line and formed on the surface is divided into individual device chips by irradiating the scheduled division line with a laser beam by a laser processing device to form a modified layer. It is used for electric devices such as mobile phones and personal computers.

The laser processing apparatus includes a holding means for holding the work piece (waiha), a laser beam irradiation means for irradiating the work piece held by the holding means with a laser beam having a wavelength having a transmittance, and a holding means and a laser beam irradiation. It is provided with an X-axis feed means for processing and feeding the means relatively in the X-axis direction, and a Y-axis feed means for indexing and feeding the holding means and the laser beam irradiation means in the Y-axis direction relatively orthogonal to the X-axis direction. A modified layer serving as a starting point of division is formed inside the scheduled division line by irradiating the wafer with a laser beam by locating a condensing point of a laser beam inside the planned division line of the wafer (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2012-2604

However, when the height of the upper surface of the wafer irradiated with the laser beam is detected to control the vertical position of the focusing point of the laser beam, but there is a swell above the allowable value on the upper surface of the wafer. There is a problem that the focusing point of the laser beam is positioned on the upper surface of the wafer and ablation processing is performed to deteriorate the processing quality.

In addition, when forming a modified layer inside the wafer, the distance between the lower surface of the objective lens of the condenser and the upper surface of the wafer is relatively narrow, about 2 mm, so debris will occur if ablation processing is applied. There is a problem that the light is scattered and adheres to the objective lens, and the light collection accuracy is lowered.

An object of the present invention made in view of the above facts is to provide a laser processing apparatus capable of avoiding a decrease in processing quality and a decrease in light collection accuracy.

The present invention provides the following laser processing apparatus in order to solve the above problems. That is, laser processing in which a condensing point of a laser beam having a wavelength that is transparent to the workpiece is positioned inside the workpiece and the laser beam is irradiated to the workpiece to form a modified layer inside the workpiece. A device that holds a workpiece, a laser beam irradiating means that irradiates a workpiece held by the holding means with a laser beam, and the holding means and the laser beam irradiating means relative to each other on the X-axis. The laser beam irradiating means includes an X-axis feeding means for processing and feeding in a direction, and a Y-axis feeding means for indexing and feeding the holding means and the laser beam irradiating means in the Y-axis direction relatively orthogonal to the X-axis direction. , An oscillator that oscillates a laser beam, a concentrator that irradiates the laser beam oscillated by the oscillator by positioning a condensing point inside the workpiece held by the holding means, and the oscillator and the concentrator. The present invention provides a laser processing apparatus including a detector arranged between them and detecting ablation light emitted when a condensing point of a laser beam is positioned on the upper surface of a work piece.

Preferably, when the detector detects the ablation light, the oscillation of the laser beam is stopped. The detector includes a dichroic mirror that reflects a laser beam of a wavelength oscillated by the oscillator and guides it to the condenser and transmits ablation light, and a sensor that detects ablation light transmitted through the dichroic mirror. Suitable. The detector includes a dichroic mirror that transmits a laser beam of a wavelength oscillated by the oscillator and guides it to the concentrator and reflects ablation light, and a sensor that detects the ablation light reflected by the dichroic mirror. It is convenient. The sensor preferably comprises a photodiode or an image sensor.

In the laser processing apparatus of the present invention, the holding means for holding the workpiece, the laser beam irradiating means for irradiating the workpiece held by the holding means with a laser beam, and the holding means and the laser beam irradiating means are relative to each other. The laser beam is provided with an X-axis feed means for processing and feeding in the X-axis direction, and a Y-axis feed means for indexing and feeding the holding means and the laser beam irradiating means in the Y-axis direction relatively orthogonal to the X-axis direction. The irradiating means includes an oscillator that oscillates a laser beam, a concentrator that irradiates the laser beam oscillated by the oscillator by positioning a condensing point inside the workpiece held by the holding means, and the oscillator and the condensing. Since it includes a detector that is arranged between the device and detects the ablation light emitted when the focusing point of the laser beam is positioned on the upper surface of the workpiece, it avoids deterioration of processing quality and focusing accuracy. can do.

The perspective view of the laser processing apparatus configured according to this invention. The block diagram which shows the structure of the laser beam irradiation means. (A) A perspective view showing a state in which the back surface of the wafer is attached to an adhesive tape whose peripheral edge is fixed to an annular frame, and (b) a front surface of the wafer is attached to an adhesive tape whose peripheral edge is fixed to an annular frame. The perspective view which shows the state which is. The schematic diagram which shows the state which positions the condensing point in the wafer and irradiates the wafer with a laser beam to form a modified layer. The schematic diagram which shows the state which the condensing point is positioned on the upper surface of a wafer and ablation processing is applied. The block diagram which shows the structure of the modification of the laser beam irradiation means.

Hereinafter, preferred embodiments of a laser processing apparatus configured according to the present invention will be described with reference to the drawings.

The laser processing apparatus 2 shown in FIG. 1 includes a holding means 4 for holding a work piece, a laser beam irradiating means 6 for irradiating a work piece held by the holding means 4 with a laser beam, and a holding means 4 and a laser beam irradiating means 6. The X-axis feeding means 8 for processing and feeding the laser beam in the X-axis direction, and the Y-axis feeding means 10 for indexing and feeding the holding means 4 and the laser beam irradiating means 6 in the Y-axis direction are provided. The X-axis direction is the direction indicated by the arrow X in FIG. 1, and the Y-axis direction is the direction indicated by the arrow Y in FIG. 1 and is orthogonal to the X-axis direction. Further, the XY plane defined by the X-axis direction and the Y-axis direction is substantially horizontal.

As shown in FIG. 1, the holding means 4 has an X-axis movable plate 14 mounted on the base 12 so as to be movable in the X-axis direction and a Y-axis mounted on the X-axis movable plate 14 so as to be movable in the Y-axis direction. It includes a movable plate 16, a support column 18 fixed to the upper surface of the Y-axis movable plate 16, and a cover plate 20 fixed to the upper end of the support column 18. An elongated hole 20a extending in the Y-axis direction is formed in the cover plate 20, and a chuck table 22 extending upward through the elongated hole 20a is rotatably mounted on the upper end of the support column 18. The chuck table 22 is rotated by a chuck table motor (not shown) built in the support column 18. A porous circular suction chuck 24 connected to a suction means (not shown) is arranged at the upper end portion of the chuck table 22, and in the chuck table 22, suction is performed on the upper surface of the suction chuck 24 by the suction means. By generating a force, the work piece placed on the upper surface of the suction chuck 24 is sucked and held. Further, a plurality of clamps 26 are arranged on the peripheral edge of the chuck table 22 at intervals in the circumferential direction.

The laser beam irradiation means 6 will be described with reference to FIGS. 1 and 2. As shown in FIG. 1, the laser beam irradiating means 6 includes a housing 28 extending upward from the upper surface of the base 12 and then extending substantially horizontally. As shown in FIG. 2, the housing 28 is a collection in which an oscillator 30 that oscillates a laser beam LB and a laser beam LB oscillated by the oscillator 30 are irradiated by positioning a condensing point inside a work piece held by the holding means 4. The optical device 32 is provided with a detector 34 that is arranged between the oscillator 30 and the concentrator 32 and detects the ablation light AL emitted when the condensing point of the laser beam LB is positioned on the upper surface of the workpiece. Has been done.

The oscillator 30 oscillates a pulsed laser beam LB having a wavelength that is transparent to the workpiece. For example, when the workpiece is a silicon wafer, the oscillator 30 oscillates a pulsed laser beam LB having a wavelength of about 1300 to 1400 nm, which is a wavelength that is transparent to silicon. As shown in FIG. 1, the condenser 32 that collects the pulsed laser beam LB oscillated by the oscillator 30 is mounted on the lower surface of the tip of the housing 28. The condenser 32 has a focusing point position adjusting means (not shown) for adjusting the vertical position of the focusing point of the pulsed laser beam LB, and the focusing point position adjusting means is a voice coil motor or a linear motor. Can be composed of. In FIG. 2, the condenser 32 is represented by a lens for convenience.

In the illustrated embodiment, as shown in FIG. 2, the detector 34 reflects the pulsed laser beam LB having the wavelength oscillated by the oscillator 30 and guides it to the condenser 32, and the dichroic mirror 36 and the dichroic mirror that transmit the ablation light AL. It includes a sensor 38 that detects the ablation light AL that has passed through 36. For example, when the workpiece is a silicon wafer, the dichroic mirror 36 reflects light having a wavelength in the range of 1300 to 1400 nm and transmits light having a wavelength other than the range of 1300 to 1400 nm.

The sensor 38 may consist of a photodiode or an image sensor. When the sensor 38 detects light, it outputs an electric signal according to the detected amount of light. Further, the sensor 38 preferably detects the ablation light AL in synchronization with the oscillation interval of the pulsed laser beam LB, which improves the detection accuracy of the ablation light AL.

The pulsed laser beam LB oscillated by the oscillator 30 is reflected by the dichroic mirror 36, guided to the condenser 32, condensed by the condenser 32, and irradiated to the workpiece. When the focusing point of the pulsed laser beam LB is positioned on the upper surface of the workpiece, the upper surface of the workpiece is ablated and visible light ablation light AL is generated. The ablation light AL passes through the condenser 32 and the dichroic mirror 36 and is detected by the sensor 38.

Explaining with reference to FIG. 1, the X-axis feeding means 8 has a ball screw 40 extending in the X-axis direction along the upper surface of the base 12, and a motor 42 for rotating the ball screw 40. The nut portion (not shown) of the ball screw 40 is connected to the X-axis movable plate 14. Then, the X-axis feeding means 8 converts the rotational motion of the motor 42 into a linear motion by the ball screw 40 and transmits it to the X-axis movable plate 14, and the X-axis movable plate 14 is transmitted along the guide rail 12a on the base 12. Is processed and fed in the X-axis direction relative to the laser beam irradiating means 6.

As shown in FIG. 1, the Y-axis feeding means 10 has a ball screw 44 extending in the Y-axis direction along the upper surface of the X-axis movable plate 14, and a motor 46 for rotating the ball screw 44. The nut portion (not shown) of the ball screw 44 is connected to the Y-axis movable plate 16. Then, the Y-axis feeding means 10 converts the rotational motion of the motor 46 into a linear motion by the ball screw 44 and transmits it to the Y-axis movable plate 16 so that the Y-axis feed means 10 can move along the guide rail 14a on the X-axis movable plate 14. The plate 16 is indexed and fed in the Y-axis direction relative to the laser beam irradiating means 6.

In the illustrated embodiment, as shown in FIG. 2, the laser processing apparatus 2 further includes a control means 48 for controlling the operation of the laser processing apparatus 2. The control means 48 composed of a computer includes a central processing unit 50 (CPU) that performs arithmetic processing according to a control program, a read-only memory 52 (ROM) that stores a control program and the like, and a readable and writable random that stores the arithmetic results and the like. Includes access memory 54 (RAM).

The control means 48 is electrically connected to an operation panel (not shown) for operating the laser processing device 2, a laser beam irradiation means 6, and the like, and is a laser beam based on an instruction input to the operation panel. Controls the operation of the irradiation stage 6 and the like. Further, as shown in FIG. 2, the sensor 38 of the detector 34 is electrically connected to the control means 48, and the electric signal output from the sensor 38 is sent to the control means 48.

Then, in the control means 48 of the illustrated embodiment, when the electric signal sent from the sensor 38 is equal to or more than the above-mentioned predetermined value, the operation of the oscillator 30 of the laser beam irradiation means 6 is stopped, and the pulse laser beam LB It is designed to stop the oscillation.

As shown in FIG. 1, on the lower surface of the tip of the housing 28, an imaging means 56 for imaging a work piece held by the holding means 4 and detecting a region to be laser-processed is provided in the X-axis direction with the condenser 32. It is installed at intervals. The imaging means 56 includes a normal imaging element (CCD) that images the work piece with visible light, an infrared irradiation means that irradiates the work piece with infrared rays, and an optical system that captures the infrared rays that are irradiated by the infrared irradiation means. It includes an image pickup element (infrared CCD) that outputs an electric signal corresponding to the infrared rays captured by the optical system (neither is shown).

FIG. 3 shows a disk-shaped wafer 60 as a work piece in which a modified layer is formed by the laser processing apparatus 2. The wafer 60 can be formed from silicon. As shown in FIG. 3A, the surface 60a of the wafer 60 is divided into a plurality of rectangular regions by a grid-like division schedule line 62, and devices 64 such as ICs and LSIs are formed in each of the plurality of rectangular regions. ing. The wafer 60 is attached to an adhesive tape 68 whose peripheral edge is fixed to the annular frame 66, and is supported by the annular frame 66 via the adhesive tape 68. As shown in FIG. 3A, the back surface 60b of the wafer 60 may be attached to the adhesive tape 68, or as shown in FIG. 3B, the front surface 60a of the wafer 60 is attached to the adhesive tape 68. May be.

When forming the modified layer inside the wafer 60 along the planned division line 62 by using the above-mentioned laser processing apparatus 2, first, the annular frame is interposed via the adhesive tape 68 with the wafer 60 side facing upward. The wafer 60 supported by 66 is sucked and held on the upper surface of the chuck table 22. Further, the annular frame 66 is fixed by a plurality of clamps 26.

Next, the wafer 60 is imaged from above by the imaging means 56, and the X-axis feeding means 8, the Y-axis feeding means 10 and the chuck table motor are operated based on the image of the wafer 60 imaged by the imaging means 56 to divide the wafer 60. The scheduled line 62 is aligned in the X-axis direction, and the scheduled split line 62 aligned in the X-axis direction is positioned below the condenser 32. Even when the back surface 60b of the wafer 60 is facing upward, as described above, the image pickup means 56 includes an infrared irradiation means, an optical system that captures infrared rays, and an image pickup that outputs an electric signal corresponding to infrared rays. Since the element (infrared CCD) is included, the scheduled division line 62 of the front surface 60a can be imaged through the back surface 60b of the wafer 60.

Next, the focusing point FP (see FIG. 4) is positioned inside the wafer 60 corresponding to the scheduled division line 62 by the focusing point position adjusting means. Next, as shown in FIG. 4, while the chuck table 22 is processed and fed by the X-axis feeding means 8 in the X-axis direction at a relatively predetermined feeding speed with respect to the condenser 32, the transparency to the wafer 60 is increased. By irradiating the pulsed laser beam LB having the pulse laser beam LB from the condenser 32, a modified layer 70 having a lower intensity than the surroundings is formed inside the wafer 60 along the planned division line 62.

Next, the chuck table 22 is indexed and fed by the Y-axis feeding means 10 in the Y-axis direction relative to the condenser 32 by the distance in the Y-axis direction of the scheduled division line 62. Then, by alternately repeating the irradiation of the pulsed laser beam LB and the indexing feed, the modified layer 70 is formed inside the wafer 60 along all of the scheduled division lines 62 aligned in the X-axis direction. Further, after rotating the chuck table 22 by 90 degrees with the chuck table motor, irradiation of the pulsed laser beam LB and indexing feed are alternately repeated, so that the modified layer 70 is formed at right angles to the planned division line 62. A modified layer 70 is formed inside the wafer 60 along all of the planned division lines 62. In this way, the modified layer 70 is formed in a grid pattern inside the wafer 60 along all of the grid-shaped scheduled division lines 62. The modified layer 70 can be formed, for example, under the following processing conditions.
Wavelength of pulsed laser beam: 1342 nm
Repeat frequency: 90kHz
Average output: 1.2W
Feed rate: 700 mm / s

When the condensing point FP of the pulsed laser beam LB is positioned on the upper surface of the wafer 60 when the modified layer 70 is formed as described above, the condensing point FP is positioned as shown in FIG. The upper surface of the wafer 60 is subjected to ablation processing. Then, the debris 72 is scattered from the upper surface of the wafer 60, and the visible light ablation light AL is generated. As shown in FIG. 2, the ablation light AL generated by the ablation process passes through the condenser 32 and the dichroic mirror 36 and is detected by the sensor 38.

The sensor 38 that has detected the ablation light AL outputs an electric signal to the control means 48. The control means 48 determines whether or not the received electric signal is equal to or higher than a predetermined threshold value (for example, 3 V), and if the electric signal is equal to or higher than the threshold value, the operation of the oscillator 30 of the laser beam irradiation means 6 is stopped. The oscillation of the pulsed laser beam LB is stopped. This prevents the formation of the modified layer 70 from continuing while the debris 72 is attached to the objective lens of the condenser 32. Therefore, in the laser processing apparatus 2 of the illustrated embodiment, it is possible to avoid a decrease in processing quality and a decrease in light collection accuracy.

The detector of the laser beam irradiating means 6 is not limited to the above-described form, and may be, for example, the form shown in FIG. The detector 74 shown in FIG. 6 is a dichroic mirror 76 that transmits the pulsed laser beam LB of the wavelength oscillated by the oscillator 30 and guides it to the condenser 32 and reflects the ablation light AL, and the ablation light AL reflected by the dichroic mirror 76. Includes a sensor 78 to detect. For example, when the workpiece is a silicon wafer, the dichroic mirror 76 transmits light having a wavelength in the range of 1300 to 1400 nm and reflects light having a wavelength other than the range of 1300 to 1400 nm. Further, the sensor 78, which may be composed of a photodiode or an image sensor, outputs an electric signal when it detects light. In the example shown in FIG. 6, a reflection mirror 80 is provided that reflects the pulsed laser beam LB oscillated by the oscillator 30 and guides it to the dichroic mirror 76.

In the example shown in FIG. 6, the pulsed laser beam LB oscillated by the oscillator 30 is reflected by the reflection mirror 80, then passes through the dichroic mirror 76, is guided to the condenser 32, is condensed by the condenser 32, and is covered. The work piece is irradiated. When the condensing point FP of the pulsed laser beam LB is positioned on the upper surface of the workpiece, the upper surface of the workpiece is ablated and visible light ablation light AL is generated. The ablation light AL is transmitted by the condenser 32, then reflected by the dichroic mirror 76, and then detected by the sensor 78. Then, when an electric signal is sent from the sensor 78 to the control means 48 and the electric signal sent to the control means 48 is equal to or higher than a predetermined threshold value (for example, 3 V), the oscillation of the pulsed laser beam LB is stopped by the control means 48. To. This prevents the formation of the modified layer 70 from continuing while the debris 72 is attached to the objective lens of the condenser 32. Therefore, deterioration of processing quality and reduction of light collection accuracy are avoided.

2: Laser processing device 4: Holding means 6: Laser beam irradiation means 8: X-axis feeding means 10: Y-axis feeding means 30: Oscillator 32: Condenser 34: Detector 36: Dichroic mirror 38: Sensor LB: Laser beam FP: Focus point AL: Ablation light

Claims (5)

A laser machining device that positions the focusing point of a laser beam with a wavelength that is transparent to the work piece inside the work piece and irradiates the work piece with the laser beam to form a modified layer inside the work piece. There,
The holding means for holding the workpiece, the laser beam irradiating means for irradiating the workpiece held by the holding means with a laser beam, and the holding means and the laser beam irradiating means are relatively processed and fed in the X-axis direction. The X-axis feeding means and the Y-axis feeding means for indexing and feeding the holding means and the laser beam irradiating means in the Y-axis direction relatively orthogonal to the X-axis direction are provided.
The laser beam irradiating means includes an oscillator that oscillates a laser beam, a condenser that irradiates the laser beam oscillated by the oscillator by positioning a condensing point inside a work piece held by the holding means, and the oscillator. A laser processing apparatus including a detector disposed between the concentrator and detecting ablation light emitted when a condensing point of a laser beam is positioned on the upper surface of a work piece. The laser processing apparatus according to claim 1, wherein when the detector detects ablation light, the oscillation of the laser beam is stopped. A claim that the detector includes a dichroic mirror that reflects a laser beam of a wavelength oscillated by the oscillator and guides it to the concentrator and transmits ablation light, and a sensor that detects ablation light transmitted through the dichroic mirror. The laser processing apparatus according to 1. A claim that the detector includes a dichroic mirror that transmits a laser beam of a wavelength oscillated by the oscillator and guides it to the condenser and reflects ablation light, and a sensor that detects the ablation light reflected by the dichroic mirror. The laser processing apparatus according to 1. The laser processing apparatus according to claim 3 or 4, wherein the sensor includes a photodiode or an image sensor.