Source: https://patents.google.com/patent/EP1804280B1/en
Timestamp: 2020-02-22 17:19:13
Document Index: 430757549

Matched Legal Cases: ['art 51', 'art 51', 'art 51', 'art 51', 'art 51', 'art 51', 'art 51']

EP1804280B1 - Laser beam machining method - Google Patents
EP1804280B1
EP1804280B1 EP05790460.9A EP05790460A EP1804280B1 EP 1804280 B1 EP1804280 B1 EP 1804280B1 EP 05790460 A EP05790460 A EP 05790460A EP 1804280 B1 EP1804280 B1 EP 1804280B1
EP05790460.9A
EP1804280A4 (en
EP1804280A1 (en
2005-10-05 Application filed by Hamamatsu Photonics KK filed Critical Hamamatsu Photonics KK
2005-10-05 Priority to PCT/JP2005/018464 priority patent/WO2006040984A1/en
2007-07-04 Publication of EP1804280A1 publication Critical patent/EP1804280A1/en
2009-09-23 Publication of EP1804280A4 publication Critical patent/EP1804280A4/en
2015-09-30 Publication of EP1804280B1 publication Critical patent/EP1804280B1/en
230000000994 depressed Effects 0 claims description 48
238000003672 processing method Methods 0 claims description 37
The present invention relates to a laser processing method according to the preamble of claim 1. JP 2002 219591 discloses such a method.
Known as a method of cutting an object to be processed by laser processing is one disclosed in the following Nonpatent Document 1. The laser processing method disclosed in Nonpatent Document 1 is one for cutting a silicon wafer, which uses laser light having a wavelength near 1 µm transmittable through silicon and converges this laser light within the wafer, so as to continuously form a modified layer, from which the wafer is cut.
Nonpatent Document 1: Arai, Kazuhisa, "Laser dicing process for Si wafer", Journal of the Japan Society for Abrasive Technology, Vol. 47, No. 5, May, 2003, 229-231.
JP 2002 219591 A relates to a laser beam irradiation device comprising a laser device, an optical fiber, a focus position driving mechanism and a measurement control means. >
For overcoming the problem mentioned above, the present invention provides a laser processing method according to claim 1.
At the time of irradiation with the processing laser light along a part on the depressed area surface on the line to cut in the first step, the position of light-converging point of processing laser light can follow the displacement of the entrance surface (e.g., irregularities and undulations in the entrance surface) in the thickness direction of the object. Also, at the time of irradiation with the processing laser light along a part on the protruded area surface in the line to cut in the first step, the light-converging point of the processing laser light can reliably be positioned outside the object. Similarly, at the time of irradiation with the processing laser light along a part on the protruded area surface in the line to cut in the second step, the position of light-converging point of processing laser light can follow the displacement of the entrance surface (e.g., irregularities and undulations in the entrance surface) in the thickness direction of the object. Also, at the time of irradiation with the processing laser light along a part on the depressed area surface in the line to cut in the second step, the light-converging point of the processing laser light can reliably be positioned outside the object.
1...object to be processed; 5...line to cut; 51a...part on a protruded area surface in lines to cut; 51b...part on a depressed area surface in lines to cut; 7...modified region; 71...first modified region; 72...second modified region; r...entrance surface; r1...protruded area surface of the entrance surface; r2...depressed area surface of the entrance surface; L...processing laser light; P...light-converging point.
An object to be processed (e.g., glass or a piezoelectric material made of LiTaO3) is irradiated with laser light while locating a light-converging point therewithin under a condition with a field intensity of at least 1x108 (W/cm2) at the light-converging point and a pulse width of 1 µs or less. This magnitude of pulse width is a condition under which a crack region can be formed only within the object while generating multiphoton absorption without causing unnecessary damages on the front face of the object. This generates a phenomenon of optical damage by multiphoton absorption within the object. This optical damage induces a thermal distortion within the object, thereby forming a crack region therewithin. The upper limit of field intensity is 1 x 1012 (W/cm2), for example. The pulse width is preferably 1 ns to 200 ns, for example. The forming of a crack region by multiphoton absorption is disclosed, for example, in "Internal Marking of Glass Substrate with Solid-state Laser", Proceedings of the 45th Laser Materials Processing Conference (December, 1998), pp. 23-28.
A mechanism by which the objet to be processed is cut by forming a crack region will now be explained with reference to Figs. 8 to 11. As shown in Fig. 8, the object 1 is irradiated with laser light L while the light-converging point P is located within the object 1 under a condition where multiphoton absorption occurs, so as to form a crack region 9 therewithin along a line to cut. The crack region 9 is a region containing one crack or a plurality of cracks. Thus formed crack region 9 yields a starting point region for cutting. A crack further grows from the crack region 9 acting as a start point (i.e., from the starting point region for cutting acting as a start point) as shown in Fig. 9, and reaches the front face 3 and rear face 21 of the object 1 as shown in Fig. 10, whereby the object 1 fractures and is consequently cut as shown in Fig. 11. The crack reaching the front face 3 and rear face 21 of the object 1 may grow naturally or as a force is applied to the object 1.
An object to be processed (e.g., semiconductor material such as silicon) is irradiated with laser light while locating a light-converging point within the object under a condition with a field intensity of at least 1x108 (W/cm2) at the light-converging point and a pulse width of 1 µs or less. As a consequence, the inside of the object is locally heated by multiphoton absorption. This heating forms a molten processed region within the object. The molten processed region encompasses regions once molten and then re-solidified, regions just in a molten state, and regions in the process of being re-solidified from the molten state, and can also be referred to as a region whose phase has changed or a region whose crystal structure has changed. The molten processed region may also be referred to as a region in which a certain structure has changed to another structure among monocrystal, amorphous, and polycrystal structures. For example, it means a region having changed from the monocrystal structure to the amorphous structure, a region having changed from the monocrystal structure to the polycrystal structure, or a region having changed from the monocrystal structure to a structure containing amorphous and polycrystal structures. When the object to be processed is of a silicon monocrystal structure, the molten processed region is an amorphous silicon structure, for example. The upper limit of field intensity is 1 x 1012 (W/cm2), for example. The pulse width is preferably 1 ns to 200 ns, for example.
In this embodiment, the object to be processed 1 is constituted by a substrate 4 comprising protrusions 4a and depressions 4b positioned between the protrusions 4a, 4a. Examples of the object 1 include MEMS (Micro-Electro-Mechanical Systems). The thickness d of the substrate 4 is 300 µm, for example, at positions where the protrusions 4a exist, and 100 µm, for example, at positions where the depressions 4b exist. An example of the substrate 4 is a silicon wafer. In the object 1, the surface of the substrate 4 on the side of the projections 4a and depressions 4b is an entrance surface r for laser light L (processing laser light). The entrance surface r is an irregular surface comprising a protruded area surface r1 which is the top face of the projections 4a and a depressed area surface r2 which is the bottom face of the depressions 4b. The protruded area surface r1 corresponds to the top face of the protrusion 4a having a rectangular cross section, for example. The depressed area surface r2 corresponds to the bottom face of the depression 4b having a rectangular cross section, for example. A bump r3 extending in the thickness direction of the object 1 is provided between the depressed area surface r2 and projected area surface r1. The height ΔH of the protrusion (the height of the bump r3) is 200 µm, for example.
Here, at the time of irradiation with the laser light L along the part 51 a on the protruded area surface r1 in the lines to cut 5 as shown in Fig. 16(a), it will be preferred if an irradiation condition of the laser light L is fixed. At the time of irradiation with the laser light L along the part 51b on the depressed area surface r2 in the lines to cut 5 as shown in Fig. 16(b), it will be preferred if the irradiation condition of the laser light L is changed so as to position the light-converging point P of laser light L inside by the distance d1 from the depressed area surface r2. An example of the irradiation condition of the laser light L is the position of the objective lens 30 in the thickness direction of the object 1. The position of the objective lens 30 is adjusted when the amount of expansion/contraction of the actuator 32 is regulated by the controller 39.
Specifically, at the time of irradiation with the laser light L along the part 51a on the protruded area surface r1 in the lines to cut 5 as shown in Fig. 16(a), for example, the actuator 32 is stopped expanding/contracting, so as to fix the objective lens 30 at a predetermined position in the thickness direction of the object 1, thereby reliably positioning the light-converging point P of laser light on the outside of the object 1. At the time of irradiation with the laser light L along the part 51b on the depressed area surface r2 in the lines to cut 5 as shown in Fig. 16(b), for example, the position of the objective lens 30 is displaced so as to follow fine irregularities and undulations (each being several to several tens of micrometers). This can form the modified region 71 at a fixed position inside by the distance d1 from the depressed area surface r2 along the part 51 b on the depressed area surface r2 in the lines to cut 5. Namely, the modified region 71 is formed on the inside of the depressed area surface r2 so as to follow the displacement of the entrance surface r in the thickness direction of the object 1.
As mentioned above, it will be preferred if the irradiation condition of the laser light L is switched from the fixed state to the changed state or vice versa between the depressed area surface r2 and the protruded area surface r1, i.e., at the position of the bump r3. This makes it easier to reliably locate the light-converging point P on the outside of the object 1 at the time of irradiation with the laser light L along the part 51a on the protruded area surface r1in the lines to cut 5. This is particularly effective when the protrusion 4a has a large height, i.e., a height ΔH of 100 µm or greater. When the entrance surface r has fine irregularities and undulations (each being several to several tens of micrometers), the position of the objective lens 30 can be adjusted (by an autofocus mechanism) in conformity to the displacement of the entrance surface r such that the modified region is formed at a position inside by a predetermined distance from the entrance surface r. When the height ΔH of the protrusion 4a is large, however, the driving amount and driving time for the actuator 32 increase so that it becomes harder to drive the objective lens 30 so as to make it follow the bump r3. In the first step of this embodiment, by contrast, the position of the objective lens 30 is set such that the light-converging point P is positioned within the object 1 (more preferably in the vicinity of the position where the modified region 71 is formed) in the depressed area surface r2, and such that the light-converging point P is positioned on the outside of the object 1 in the protruded area surface r1. This position is the fixed position of the objective lens 30 when the laser light L passes the protruded area surface r1, and is a reference position for driving the objective lens 30 by the actuator 32 so as to form the modified region 71 at a position inside by a fixed distance from the depressed area surface r2 following fine irregularities and undulations of the entrance surface r. Therefore, when moving the objective lens 30 from the depressed area surface r2 to the protruded area surface r1 or vice versa, it is not necessary for the objective lens 30 to move its position greatly for changing the objective lens 30 from a variable state to a fixed state or vice versa at the position of the bump r3 even if ΔH is large. Consequently, the objective lens 30 can smoothly move when passing over the bump r3, whereby the modified region 71 can be formed at an accurate position within the object 1.
As mentioned above, it will be preferred if the irradiation condition of the laser light L is switched from the fixed state to the changed state or vice versa between the depressed area surface r2 and the protruded area surface r1, i.e., at the position of the bump r3. This makes it easier to reliably locate the light-converging point P on the outside of the object 1 at the time of irradiation with the laser light L along the part 51b on the depressed area surface r2 in the lines to cut 5. This is particularly effective when the protrusion 4a has a large height, i.e., a height ΔH of 100 µm or greater. When the entrance surface r has fine irregularities and undulations (each being several to several tens of micrometers), the position of the objective lens 30 can be adjusted (by an autofocus mechanism) in conformity to the displacement of the entrance surface r such that the modified region is formed at a position inside by a predetermined distance from the entrance surface r. When the height ΔH of the protrusion 4a is large, however, the driving amount and driving time for the actuator 32 increase so that it becomes harder to drive the objective lens 30 so as to make it follow the bump r3. In the second step of this embodiment, by contrast, the position of the objective lens 30 is set such that the light-converging point P is positioned within the object 1 (more preferably in the vicinity of the position where the modified region 72 is formed) in the protruded area surface r1, and such that the light-converging point P is positioned on the outside of the object 1 in the depressed area surface r2. This position is the fixed position of the objective lens 30 when the laser light L passes the depressed area surface r2, and is a reference position for driving the objective lens 30 by the actuator 32 so as to form the modified region 72 at a position inside by a fixed distance from the protruded area surface r1 following fine irregularities and undulations of the entrance surface r. Therefore, when moving the objective lens 30 from the depressed area surface r2 to the protruded area surface r1 or vice versa, it is not necessary for the objective lens 30 to move its position greatly for changing the objective lens 30 from a variable state to a fixed state or vice versa at the position of the bump r3 even if ΔH is large. Consequently, the objective lens 30 can smoothly move when passing over the bump r3, whereby the modified region 72 can be formed at an accurate position within the object 1.
Though a semiconductor wafer made of silicon is used as the object 1 in this embodiment, the material of the semiconductor wafer is not limited thereto. Examples of the semiconductor wafer include group IV element semiconductors other than silicon, compound semiconductors containing group IV elements such as SiC, compound semiconductors containing group III-V elements, compound semiconductors containing group II-VI elements, and semiconductors doped with various dopants (impurities). The object 1 may also be an SOI (silicon-on-insulator) in which an insulating layer is provided between a semiconductor device and a support substrate.
A laser processing method of irradiating a planar object (1) to be processed with processing laser light(L) while locating a light-converging point (P) within the object (1) so as to form a modified region to become a starting point region for cutting within the object along a line to cut (5) the object;
the method comprising, when an entrance surface (r) of the processing laser light (L) in the object (1) is an irregular surface while the line to cut extends over a depressed area surface (r2) and a protruded area surface (r1) in the entrance surface (r):
a first step of forming a first modified region (71) inside by a predetermined distance from the depressed area surface (r2) along the line to cut (5); and
a second step of forming a second modified region (72) inside by a predetermined distance from the protruded area surface (r1) along the line to cut (5);
wherein, in the first step, the light-converging point (P) is located outside the object (1) at the time of irradiation with the processing laser light (L) along a part (51 a) on the protruded area surface (r1) in the line to cut (5); and
wherein, in the second step, the light-converging point (P) is located outside the object at the time of irradiation with the processing laser light along a part (51 b) on the depressed area surface (r2) in the line to cut (5).
wherein, in the first step, an irradiation condition of the processing laser light (L) is changed so as to position the light-converging point (P) of the processing laser light inside by a predetermined distance from the depressed area surface (r2) at the time of irradiation with the processing laser light along a part (51 b) on the depressed area surface (r2) in the line to cut, and is fixed at the time of irradiation with the processing laser light along a part (51 a) on the protruded area surface (r1) in the line to cut; and wherein, in the second step, the irradiation condition of the processing laser light (L) is changed so as to position the light-converging point (P) of the processing laser light inside by a predetermined distance from the protruded area surface (r1) at the time of irradiation with the processing laser light along a part (51 a) on the protruded area surface (51a) in the line to cut, and is fixed at the time of irradiation with the processing laser light along a part (51 b) on the depressed area surface (r2) in the line to cut.
A laser processing method according to claim 1, wherein, after forming the first and second modified regions, the object (1) is cut along the line to cut (5).
A laser processing method according to claim 1 or 2,
wherein, in the first step, at the time of irradiation with the processing laser light (L) along the part (51a) on the protruded area surface (r1) in the lines to cut (5), the position of an objective lens (30) converging the laser light (L) is fixed and at the time of irradiation with the processing laser light (L) along the part (51b) on the depressed area surface (r2) in the lines to cut (5), the position of the objective lens (30) follows fine irregularities and undulations of the depressed area surface (r2); and
wherein, in the second step, at the time of irradiation with the processing laser light (L) along the part (51a) on the protruded area surface (r1) in the lines to cut (5), the position of the objective lens (30) follows fine irregularities and undulations of the protruded area surface (r1) and at the time of irradiation with the processing laser light (L) along the part (51b) on the depressed area surface (r2) in the lines to cut (5), the position of the objective lens (30) is fixed.
EP05790460.9A 2004-10-13 2005-10-05 Laser beam machining method Active EP1804280B1 (en)
EP1804280A1 EP1804280A1 (en) 2007-07-04
EP1804280A4 EP1804280A4 (en) 2009-09-23
EP1804280B1 true EP1804280B1 (en) 2015-09-30
EP05790460.9A Active EP1804280B1 (en) 2004-10-13 2005-10-05 Laser beam machining method
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Ipc: B23K 101/40 20060101ALN20090818BHEP
Ipc: H01L 21/301 20060101AFI20060829BHEP
Ipc: B23K 26/06 20060101ALI20090818BHEP
Ipc: H01L 21/78 20060101ALI20090818BHEP
Ipc: H01L 21/302 20060101ALI20090818BHEP
Ipc: B28D 5/00 20060101ALI20090818BHEP
Ipc: B23K 26/40 20060101ALI20090818BHEP
Ipc: B23K 26/00 20060101ALI20090818BHEP
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