JP2010188370A - Laser beam machining apparatus and laser beam machining method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam machining apparatus having high flatness in a cut face and fast machining speed, and to provide a machining method. <P>SOLUTION: The laser beam machining apparatus includes: a laser beam source 1 for emitting a laser beam LB; an optical element 3 that utilizes diffraction for diffracting the laser beam LB in a direction parallel to a planned cutting line SL; and a condensing lens 4 that condenses, inside a workpiece 10, the laser beam LB diffracted by the optical element 3 utilizing diffraction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser processing method and a laser processing apparatus for forming a modified region which is a starting point of cleaving by condensing and irradiating laser light along a cleaving line of a processing object.

  Conventionally, when cutting a hard and brittle material plate such as a semiconductor substrate, a piezoelectric ceramic substrate, a glass substrate, etc., a short optical pulse laser having a wavelength transparent to the plate along the line to be cut inside the plate to be processed Light is focused and irradiated to generate a fine melt mark (modified region) in which micro cracks are clustered inside, and then stress is applied, and cracks are generated in the thickness direction of the plate starting from the fine melt mark. (For example, refer to Patent Document 1).

  Also known is a processing method in which the beam diameter of the laser beam is enlarged with an inverse telescope to enhance directivity, and a sheet-like beam parallel to the line to be cleaved is shaped with a slit and condensed with a condenser lens ( For example, see Patent Document 2.)

JP 2005-271563 A JP 2007-75886 A

  However, in this conventional laser processing method, since the laser beam is focused on a circular spot, the internal stress that causes cracks to grow isotropically works. For this reason, cracks are generated and grow in directions other than the direction along the planned cutting line, and the generation and growth of cracks cannot be concentrated in the direction of the planned cutting line. As a result, the flatness of the fractured surface is impaired. Moreover, when irradiating a circular spot along the planned cutting line, there is a problem that the number of irradiation spots per unit length increases and the processing speed is slow.

  Further, in the conventional method of condensing and irradiating a sheet beam parallel to the planned cutting line, the cross-sectional shape of the laser beam at the focal point is set so that the maximum length in the direction perpendicular to the planned cutting line is parallel to the planned cutting line. The shape is shorter than the maximum length in the direction. For this reason, it is possible to suppress the appearance of twist hackles on the fractured surface and improve the flatness of the fractured surface. However, the maximum length in the direction parallel to the planned cutting line of the cross-sectional shape at the condensing point by this method is the same as the diameter of the circular focused spot when a normal circular beam is collected, and it is still the unit length. The number of irradiation spots per hit must be increased. As a result, the problem that the processing speed is slow still remains.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a laser processing apparatus and a processing method having a high flatness of a fractured surface and a high processing speed.

  The laser processing apparatus according to the present invention, which has been made to solve the above-described problems, is a modification that becomes the starting point of cleaving along the planned cutting line of the processing object by condensing and irradiating the processing object with laser light. A laser processing apparatus for forming a quality region inside the object to be processed, the laser light source emitting the laser light, and diffracting the laser light emitted from the laser light source in a direction parallel to the cleaved line And an optical element that uses diffraction, and a condensing lens that condenses the laser light diffracted by the optical element that uses diffraction inside the object to be processed.

  In the above laser processing apparatus, it is preferable to have a polarizing element that polarizes the laser light in a direction orthogonal to the plane including the cleaving line and the optical axis.

  The optical element using diffraction may include a pair of knife edges that form slits extending in a direction orthogonal to the plane including the cleaved line and the optical axis.

  Further, when the diffraction angle of the optical element using the diffraction is θx and the entrance pupil diameter of the condenser lens is D, a distance between the optical element using the diffraction and the condenser lens is D / 2θx or less. It is good to be.

  The laser processing method of the present invention, which has been made to solve the above-mentioned problems, is a modification that becomes the starting point of cleaving along the planned cutting line of the processing object by condensing and irradiating the processing object with laser light. A laser processing method for forming a quality region inside the workpiece, a diffraction step for diffracting the laser light in a direction parallel to the cleaved line by an optical element using diffraction, and diffraction by the diffraction step And a condensing irradiation step of condensing and irradiating the processed laser beam inside the object to be processed with a condensing lens.

  The laser processing method may further include a polarization step of polarizing the laser light in a direction perpendicular to the plane including the cleaved line and the optical axis.

  When light that has passed through an optical element that uses diffraction having a diffraction angle in a direction along the planned cutting line is collected by a lens, a Fraunhofer diffraction pattern is formed on the focal plane of the lens. The diffraction pattern is that the laser beam is diffracted in a direction parallel to the planned cleaving line, so that the maximum length in the direction parallel to the planned cleaving line is the diameter of the circular focused spot when a normal circular beam is collected. Can be larger. As a result, the number of irradiation spots per unit length can be reduced, and the processing speed can be increased.

  If the laser light is polarized in a direction perpendicular to the plane including the cleaved line and the optical axis, many cracks are generated in a direction (thickness direction) parallel to the plane including the cleaved line and the optical axis. As a result, it can be cleaved with a small cleaving load.

  If the diffraction angle of the optical element using diffraction is θx and the entrance pupil diameter of the condenser lens is D, the distance between the optical element using diffraction and the condenser lens is D / 2θx or less. Thus, the laser beam is not deviated from the entrance pupil diameter and can be condensed efficiently.

1 is an xz plan view of a laser processing apparatus according to the present invention. It is a principal part perspective view of FIG. It is a principal part enlarged view of FIG. It is xy plane view of a condensing area | region. 2 is a burn pattern observation photograph of Example 1. FIG. 2 is a burn pattern observation photograph of Comparative Example 1. It is a schematic diagram of a braking device.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is an xz plan view of a laser processing apparatus according to the present invention, and FIG. 2 is a perspective view of a main part of FIG. 3 is an enlarged view of the main part of FIG. 1, and FIG. 4 is an xy plan view of the light condensing region.

  As shown in FIG. 1, the laser processing apparatus of the present invention includes a laser light source 1 that emits a short pulse laser beam, an optical axis OA that is parallel to the cleaved line SL of the workpiece 10 and the z axis. A polarizing element 2 that polarizes in a direction perpendicular to the plane including the surface (y-axis direction), an optical element 3 that uses diffraction to diffract a short pulse laser beam in the x-axis direction parallel to the cleaving line SL, and uses diffraction And a condensing lens 4 that condenses the short pulse laser light diffracted by the optical element 3 inside the workpiece 10.

  The laser light source 1 is, for example, a mode-locked fiber laser (Imura, USA, model D1000), and specifications and performance are as follows.

Center wavelength λ: 1045 nm
Beam diameter d0: 4 mm
Mode: Single (Gaussian)
Pulse width: 700 fs
Pulse energy: 10μJ
Repeat frequency: 100 kHz
Average power: 1000mW
The short pulse laser beam emitted from the laser light source 1 travels toward the workpiece 10 when the shutter 5 is opened.

  The laser light that has passed through the shutter 5 is attenuated to a predetermined power by the next attenuator 6. The attenuator 6 includes a half-wave plate 6a and a polarizing beam splitter 6b.

  The laser beam that has passed through the attenuator 6 is bent by the optical path bending mirror 7 from the x-axis direction to the z-axis direction.

  The polarizing element 2 is a half-wave plate, and the laser light that has passed through the polarizing element 2 is polarized in a direction (y-axis direction) orthogonal to the plane including the optical axis OA parallel to the cleaved line SL and the z-axis. Linearly polarized light.

  As shown in FIG. 2, the optical element 3 using diffraction includes a pair of knives that form a slit having a width w extending in a direction (y-axis direction) perpendicular to the plane including the cleaving line SL and the optical axis OA. It is an edge. In this embodiment, the sides 31a and 32a of the rectangular stainless steel plates 31 and 32 having a thickness of 0.1 mm are arranged opposite to each other so that the sides are parallel to the y-axis direction and the gap (slit width) is w = 1 mm. A slit is formed.

  The laser beam diffracted by the optical element 3 using diffraction is a processing target line in which the long axis of the condensing spot is processed inside the processing target 10 by the condenser lens 4 which is L = 300 mm away from the optical element 3 using diffraction. Condensed along SL.

  The condenser lens 3 is, for example, a microscope objective lens (Mitutoyo model M Plan Apo NIR HR50 × / 0.65), and the specifications and performance are as follows.

Target light: Near infrared light Magnification: 50 × (focal length: 4 mm)
Numerical aperture: 0.65 (incident pupil diameter: 5.2 mm)
The workpiece 10 is placed on the xyz axis moving stage 20.

  Next, how the laser light diffracted by the optical element 3 using diffraction is condensed by the condenser lens 4 will be described with reference to FIGS. 3 and 4.

Since the laser beam having the wavelength λ incident on the optical element 3 utilizing diffraction is a single mode, if the beam diameter is d0, the spread angle θ is θ≈2λ / πd0 (1)
It is expressed.

Also, the diffraction angle θx in the x-axis direction (direction parallel to the cleaving line SL) by the optical element 3 using diffraction with a slit width of w is:
θx ≒ 0.688λ / w (2)
It is expressed.

Since the laser light is not diffracted in the y-axis direction by the optical element 3 using diffraction, the diameter of the condensed spot in the y-axis direction (the length of the short axis) when condensed by the condenser lens 4 having the focal length f. Ds is
ds≈2fθ≈4λf / πd0 (3)
It is expressed.

On the other hand, since the laser light is diffracted in the x-axis direction by an optical element using diffraction, the diameter (long-axis length) dl of the focused spot in the x-axis direction is:
dl≈2fθx≈1.376λf / w (4)
It is expressed.

To increase the processing speed,
dl> ds (5)
It is necessary to satisfy. From (3) to (5), in order to increase the processing speed,
w <0.344πd0
It is necessary to satisfy. That is, it can be seen that if the slit width w is made smaller than the value obtained by multiplying the beam diameter d0 of the laser beam by 0.344π, the processing speed is increased.

  For example, as described above, in the case of laser light with do = 4 mm, w <4.3 mm, and the slit width w needs to be less than 4.3 mm.

  In this embodiment, since d0 = 4 mm, λ = 1045 nm, f = 4 mm, and w = 1 mm, ds = 1.3 μm from the expression (3) and dl = 5.8 μm from the expression (4) (short diameter) The ellipticity, which is the ratio of the major axis and the major axis, is 0.22). That is, according to the present invention, the condensed spot when the laser beam is condensed without being diffracted is equivalent to the case where six condensed spots are arranged in the cleaved line SL, and the processing speed is increased six times. I understand that.

In FIG. 3, when the diffraction angle θx is large or when the distance between the optical element 3 using the diffraction and the condenser lens 4 is large, all of the diffracted light cannot pass through the entrance pupil 4a of the condenser lens 3, and the laser The power of light is lost. If the distance from the optical element 3 utilizing diffraction to the entrance pupil 4a is L and the diameter of the entrance pupil is D, the diffracted light spreads to 2Ltanθx≈2Lθx at a position L away from the optical element 3 utilizing diffraction. If it is smaller than the entrance pupil diameter D, no power loss occurs. Therefore, to avoid power loss,
2Lθx <D
L <D / 2θx
It is necessary to satisfy. In this embodiment, since D = 5.2 mm and θx = 0.719 mrad, power loss is avoided if L is less than 3600 mm. In this embodiment, since L = 300 mm, there is no power loss due to kicking at the entrance pupil.

  A converging spot verification experiment was performed using the laser processing apparatus shown in FIG. The processing target 10 is a silicon plate having a thickness of 300 μm. The focus of the condensing lens 4 was focused on the surface of the silicon plate, and the burn pattern corresponding to the condensing spot was observed. Note that the power of the laser light incident on the optical element 3 using diffraction at this time was adjusted to 5 mW by the attenuator 6. Moreover, the x-axis moving speed of the moving stage 20 was 500 mm / s.

  FIG. 5 shows a burn pattern observation photograph. FIG. 5a is a case where the observation magnification is low, and FIG. 5b is a photograph observed with a high observation magnification. From FIG. 5a, it can be seen that the focused spot is continuous along the cleaving line SL. Moreover, it turns out that one condensing spot is an ellipse whose major axis coincides with the planned cutting line SL. From this photograph, the major axis dl≈5 μm, the minor axis ds≈1.4 μm, and the ellipticity was 0.28. From this, it can be seen that this measured value agrees with the calculated value in the error range.

[Comparative Example 1]
The burn pattern was observed under the same conditions as in Example 1 except that the optical element 3 utilizing diffraction in FIG. 1 was removed.

  FIG. 6 shows a burn pattern observation photograph. From this, it can be seen that the condensing spot is circular, and is positioned so as to jump along the planned cutting line SL.

  A cleaving experiment was conducted with the laser processing apparatus shown in FIG. The processing target 10 is a sapphire plate having a thickness of 100 μm. The sapphire plate was placed on the xyz axis moving stage 20 and the focusing lens 4 was focused on the surface of the sapphire plate, and then the stage 20 was moved 8 μm in the z axis direction (upward in FIG. 1). The focal position at a depth of 8 μm from the surface is a focal position at a depth of 20 μm from the effective magnification (1.89) of the condensing lens 3 in consideration of the refractive index (1.75) for the wavelength of sapphire of 1045 nm. It corresponds to.

  While moving the sapphire plate 10 in the x-axis direction (scheduled cutting line SL direction) with the moving stage 20 at a speed of 500 mm / s, a 150 mW laser beam is focused and irradiated to form a minute melt mark (in which minute cracks are clustered) Modified region).

  Next, as schematically shown in FIG. 7, using a breaking device (Daitron model DBR-301R), cracks generated in the thickness direction of the sapphire plate 10 starting from the fine melt mark 10a are used. And then cleaved.

  As shown in FIG. 7, first, both sides (parts indicated by white arrows 17 in FIG. 8) of the fine melt mark 10 a formed inside along the planned cutting line SL of the sapphire plate 10 are held from the back surface. Next, a blade (not shown) is pressed against a portion corresponding to the fine melt mark 10a on the surface of the sapphire plate 10 (a portion indicated by a white arrow 18 in FIG. 7), and the blade is pushed into the fine melt mark 10a. The stress was concentrated and cleaved.

  It was 30 micrometers as a result of calculating | requiring the minimum pushing amount of the braid | blade which can be cleaved.

[Comparative Example 2]
The sapphire plate was cleaved under the same conditions as in Example 2 except that the optical element 3 utilizing diffraction in FIG. 1 was removed. The minimum pushing amount of the blade that can be cut was 60 μm. Moreover, the flatness of the cut surface was also low.

  Compared to Example 2, the amount of pushing of the blade is doubled to 60 μm, and the flatness is lowered. That is, compared to the present invention, it becomes difficult to cleave as follows from the burn pattern observation photograph of Comparative Example 1 (FIG. 6). Since there is no optical element 3 using diffraction, the fine melt mark 10a formed inside the sapphire plate 10 is not connected in the direction of the planned cutting line SL. As a result, it is difficult to cleave, and it is considered that the flatness is lowered because of cleaving.

  If the moving speed of the moving stage 20 is reduced so that the fine melt mark 10a is connected in the direction of the planned cutting line SL, the cutting speed can be reduced with a small amount of pushing of the blade, so that the processing speed is slower than that of the present invention. This means that the present invention has a high processing speed and a high flatness of the fractured surface.

[Comparative Example 3]
The sapphire plate was cleaved under the same conditions as in Example 2 except that the half-wave plate 2 in FIG. 1 was removed. The minimum push amount of the blade that can be cut was 40 μm. That is, it was hard to cleave compared with Example 2.

1 .... Laser light source 2 .... Polarizing element 3 .... Optical element using diffraction (knife edge)
4 .... Condensing lens 10 ... Workpiece 10a ... Modified region (fine melt marks)
30 ... Transmission diffraction grating
LB ・ ・ ・ ・ ・ ・ Laser beam
SL ・ ・ ・ ・ Scheduled line

Claims (6)

A laser processing apparatus that forms a modified region, which is a starting point of cleaving, along the planned cleaving line of the processing object by condensing and irradiating the processing object with laser light. ,
A laser light source for emitting the laser light;
An optical element utilizing diffraction that diffracts the laser light emitted from the laser light source in a direction parallel to the cleaving line;
A laser processing apparatus comprising: a condensing lens that condenses the laser light diffracted by the optical element using the diffraction inside the object to be processed.   The laser processing apparatus according to claim 1, further comprising a polarizing element that polarizes the laser light in a direction orthogonal to a plane including the cleaving line and an optical axis.   The laser processing apparatus according to claim 1, wherein the optical element using diffraction includes a pair of knife edges that form slits extending in a direction perpendicular to the plane including the cleaving line and the optical axis.   When the diffraction angle of the optical element using the diffraction is θx and the entrance pupil diameter of the condenser lens is D, the distance between the optical element using the diffraction and the condenser lens is D / 2θx or less. The laser processing apparatus of any one of Claim 1 thru | or 3. A laser processing method for forming a modified region, which is a starting point of cleaving, along a planned cutting line of the processing object by condensing and irradiating the processing object with laser light. ,
A diffraction step of diffracting the laser beam in a direction parallel to the cleaved line with an optical element using diffraction;
And a condensing irradiation step of condensing and irradiating the laser beam diffracted in the diffraction step into the object to be processed with a condensing lens.   The laser processing method according to claim 5, further comprising a polarization step of polarizing the laser light in a direction perpendicular to a plane including the cleaved line and an optical axis.