LASER CUTTING METHOD AND ASSOCIATED LASER CUTTING DEVICE

Abstract

A laser cutting method cuts a planar material using an associated laser cutting device. In a first step the material to be cut is weakened along a provided cutting line by irradiation by a pulsed first laser beam. In a second step, the material to be cut is locally heated by irradiation by a second laser beam in the region of the cutting line in order to produce material stress. In the second step, the material to be cut is heated only in one place or in a plurality of spaced apart places on the cutting line.

Claims

1. A laser cutting method for cutting a planar material, which comprises: performing a first step of weakening the planar material to be cut by irradiation with a pulsed first laser beam along a provided cutting line; and performing a second step of locally heating the planar material to be cut by irradiation via a second laser beam in a region of the cutting line to produce a material stress, wherein the planar material to be cut is heated only at one point or at a plurality of mutually spaced apart points on the cutting line.

2. The method according to claim 1, wherein, in the second step, the planar material to be cut is heated only at exactly two mutually spaced apart points on the cutting line.

3. The method according to claim 1, which further comprises performing a third step, in which the planar material to be cut is separated by mechanical loading.

4. The method according to claim 1, which further comprises focusing the first laser beam using an axicon to form a Bessel beam, and in a focus region of the Bessel beam the planar material to be cut is disposed.

5. The method according to claim 1, which further comprises emitting the second laser beam in a weakly focused or unfocused fashion onto the planar material to be cut.

6. The method according to claim 1, wherein the planar material to be cut is transparent to the pulsed first laser beam.

7. The method according to claim 1, wherein the planar material to be cut is nontransparent or semitransparent to the second laser beam.

8. The method according to claim 1, which further comprises emitting the pulsed first laser beam in pulses having a pulse length of between 300 femtoseconds and 30 picoseconds onto the planar material to be cut.

9. The method according to claim 1, which further comprises providing a glass plate as the planar material to be cut, wherein the pulsed first laser beam has a wavelength of approximately 1 micrometer, and wherein the second laser beam has a wavelength of approximately 10 micrometers.

10. The method according to claim 1, which further comprises providing a plate composed of silicon as the planar material to be cut, wherein the pulsed first laser beam has a wavelength of approximately 2 micrometers, and wherein the second laser beam has a wavelength of approximately 1 micrometer.

11. The method according to claim 1, which further comprises performing the first step by perforating the planar material.

12. The method according to claim 3, which further comprises performing the mechanical loading by bending, shearing and/or pulling apart the planar material to be cut at the cutting line.

13. The method according to claim 9, which further comprises forming the glass plate from non-tempered glass.

14. A laser cutting device for cutting planar material, the laser cutting device configured for carrying out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0035] FIG. 1 is a perspective view showing a laser cutting device for cutting a planar material, here a glass plate, containing a workpiece receptacle for mounting the material to be cut, having a first laser for generating the first laser beam, having a second laser for generating the second laser beam, having a feed mechanism for moving the workpiece receptacle relative to the first and second laser beams, and also having a controller for the feed mechanism and the two lasers;

[0036] FIG. 2 is a schematic illustration of a beam path of the first laser beam and also an axicon positioned in the beam path;

[0037] FIG. 3 is a plan view showing the glass plate after a first step of a method carried out by means of the laser cutting device, in which the glass plate is weakened in a series of burning points along a cutting line by means of the first laser beam;

[0038] FIG. 4 is a plan view showing in accordance with FIG. 3, the glass plate after a second step of the method, in which the glass plate is locally heated by means of the second laser beam at a point on the cutting line in order to produce a material stress;

[0039] FIG. 5 is a plan view showing in accordance with FIG. 3, the glass plate after a third step of the method, in which the glass plate is separated by mechanical loading, here bending, along the cutting line;

[0040] FIG. 6 is an illustration showing in accordance with FIG. 3, as a further example of a material to be cut, a silicon wafer after the first step of the method, in which the silicon wafer is weakened in a series of burning points along the cutting line by means of the first laser beam;

[0041] FIG. 7 is an illustration showing in accordance with FIG. 3, the silicon wafer after the second step of the method, in which the silicon wafer is locally heated by means of the second laser beam at two opposite points on the cutting line in order to produce a material stress; and

[0042] FIG. 8 is an illustration showing in accordance with FIG. 3, the silicon wafer after the third step of the method, in which the silicon wafer is separated by mechanical loading, here pulling apart, along the cutting line.

DETAILED DESCRIPTION OF THE INVENTION

[0043] Mutually corresponding parts and structures are always provided with identical reference signs in all the figures.

[0044] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown, in a roughly schematically simplified perspective illustration, a (laser cutting) device 1 for cutting a planar material, which is a glass plate 2 composed of untempered glass in the example shown here. The glass plate 2 has a thickness of 1 millimeter, for example.

[0045] The device 1 contains a workpiece receptacle 3 for mounting the glass plate 2. In this case, the workpiece receptacle 3 is formed by a carrier plate 4 composed of glass, on which a diffusing layer 5 composed of polytetrafluoroethylene is applied on the workpiece side (i.e. on the side on which the glass plate 2 to be cut is placed as intended during operation of the device 1).

[0046] The carrier plate 4 has a thickness of 5 centimeters, for example, and the diffusing layer 5 has a thickness of 0.2 millimeter, for example.

[0047] The workpiece receptacle 3 is embodied as an X-Y table, in which, by means of a feed mechanism 6 (merely indicated in FIG. 1), the carrier plate 4 is displaceable in directions identified by arrows 7 within a plane parallel to the area of the carrier plate 4. The feed mechanism 6 contains for example two linear motors coupled to the carrier plate 4 in terms of drive technology.

[0048] The device 1 furthermore contains first laser 10 for generating a first laser beam 11 and a second laser 12 for generating a second laser beam 13. The two lasers 10 and 12 are mounted above the workpiece receptacle 3 in such a way that the laser beams 11 and 13 respectively emitted by them are aligned in each case perpendicular to the carrier plate 4 on the workpiece-side area thereof. The lasers 10 and 12 are mounted in stationary fashion, such that in the event of an adjustment of the carrier plate 4 by the feed mechanism 6, the glass plate 2 mounted on the carrier plate 4 is moved relative to the laser beams 11 and 13.

[0049] The first laser 10 is a mode-locked MOPA ultrashort pulse laser, which generates the first laser beam 11 in the form of laser pulses in the example in accordance with FIG. 1. In this case, the first laser beam 11 has a light wavelength of approximately 1 micrometer, specifically 1064 nanometers, for example. It is thus in the near infrared range of the electromagnetic spectrum, such that the glass plate 2 to be cut is transparent to the first laser beam 11.

[0050] An axicon 14 as optical unit is disposed in front of the first laser 10 and focuses the first laser beam 11 to form a Bessel beam 15 with a thin and elongated focus region 16. In an exemplary dimensioning, an axicon 14 forms the focus region 16 of the first laser beam 11 with a width (measured transversely with respect to the beam direction) of 2 to 5 micrometers and a length (measured in the beam direction) of approximately 2 millimeters. The axicon 14, the Bessel beam 15 produced by it and the focus region 16 of the Bessel beam are illustrated in a roughly schematically simplified manner in FIG. 2. In the context of the device 1, the axicon 14 is aligned in relation to the workpiece receptacle 3 in such a way that the focus region 16 of the Bessel beam 15 passes through the glass plate 2 mounted on the carrier plate 4 over the entire thickness of the glass plate.

[0051] In the embodiment in accordance with FIG. 1, the second laser 12 is a CO.sub.2 laser, which generates the second laser beam 13 as a continuous (i.e. unpulsed) laser beam having a light waves of approximately 10 micrometers, specifically for example 10.6 micrometers, and a power/intensity of e.g. 100 watts. The light of the second laser beam 13 is thus in the mid-infrared range of the electromagnetic spectrum, such that the glass plate 2 to be cut is semitransparent or even nontransparent to the second laser beam 13, depending on the type of glass. The second laser beam 13 is emitted in unfocused fashion onto the carrier plate 4 and the glass plate 2 mounted thereon.

[0052] Finally, the device 1 contains a control computer 17 as controller. A control program 18 is implemented in the control computer 17, according to which control program the control computer 17 controls the feed mechanism 6 and the two lasers 10 and 12 during operation of the device 1.

[0053] A laser cutting method is carried out as intended by means of the device 1, the laser cutting method having three steps in its application to the cutting of untempered glass. The state of the glass plate 2 after the first and second and third steps is illustrated here in FIGS. 3 to 5, respectively.

[0054] In a first step of this method, the first laser beam 11 is guided along a provided cutting line 20 (FIG. 3) over the glass plate 2 to be cut by the carrier plate—under the control of the control program 18 executed in the control computer 17 and in a manner driven by the feed mechanism 6—being moved relative to the first laser 10. In this case, the highly focused, pulsed laser beam 11 produces a series of burning points 21 (FIG. 3) in the glass plate 2 along the cutting line 20, at which points the material of the glass plate 2 is weakened or destroyed by nonlinear absorption of the pulse energy. Owing to the transparency of the glass plate 2 to the light of the first laser beam 11 and the long axial extent of the focus region 16, each burning point 21 extends over the entire thickness of the glass plate 2 with a width of 2 to 5 micrometers. The burning points 21 are produced on the cutting line 20 for example with a spacing of 1 to 10 micrometers, in particular 4 to 5 micrometers. The laser beam 11 emerging from the glass plate 2 is diffused in the diffusion layer 5 in a manner free of absorption, such that the energy density is decreased in the further course of the beam path of the laser beam. As a result, the first laser beam 11 is transmitted through the carrier plate 4 without damaging the latter.

[0055] In the subsequent second step of the method, the glass plate 2 to be cut is moved together with the workpiece receptacle 3 in such a way that the second laser beam 13 impinges at a predefined point 22 (FIG. 4) on the cutting line 20. The material of the glass plate 2 is then locally heated at the point 22 by the glass plate 2 being irradiated with the second laser beam 13 for a duration of 5 to 2000 milliseconds, for example. A material stress is produced in the glass plate 2 as a result of this thermal treatment, the material stress supporting the subsequent separation of the glass plate 2 at the cutting line 20.

[0056] For this purpose, the third step involves introducing mechanical loading into the glass plate 2, such that the latter breaks at the cutting line 20 pretreated by the preceding steps. As a result of this mechanical loading, after the third step, in accordance with FIG. 5, the glass plate 2 is present in two pieces 23 separated at the cutting line 20. In the exemplary embodiment illustrated here, the mechanical loading is effected by bending of the glass plate 2 by means of a separation device, not explicitly illustrated, which is preferably embodied as an integral mechanism that is automatically actuated by the control computer 17. In this case, the separation device is a lifting mechanism, for example, which locally raises the glass plate 2 and in this way causes bending of the glass plate 2 under the action of its own weight. Alternatively, a separation device detached from the device 1 can also be used for bending the glass plate 2. As yet another alternative, the glass plate 2 can also be manually bent or loaded in some other way.

[0057] In a further application illustrated with reference to FIGS. 6 to 8, the laser cutting method is used for singulating chips 30 (for example integrated electronic circuits) from a wafer 31 composed of silicon. Analogously to the sequence in FIGS. 3 to 5, FIGS. 6 to 9 show the wafer 31 after the first and second and third steps, respectively, of the method. The method steps are repeated taking different cutting edges 20 as a basis until all chips 30 are present in singulated form.

[0058] The variant of the laser cutting method described with reference to FIGS. 6 to 8 is carried out by an embodiment of the device 1 which—apart from the differences described below—corresponds to the device 1 in accordance with FIG. 1. In contrast to the latter embodiment, however, for the purpose of cutting the wafer 31 the first laser 10 and the second laser 12 are configured in such a way that the first laser beam 11 is generated with a light wavelength of 2 micrometers, and the second laser beam 13 is generated with a light wavelength of 1 micrometer. This choice of the light wavelengths ensures that the wafer 31 is transparent to the light of the first laser beam 11 and is semitransparent or nontransparent to the light of the second laser beam 13. Instead of a CO.sub.2 laser, here it is also possible to use a neodymium-YAG laser as second laser 12.

[0059] A further difference with respect to the method variant in accordance with FIGS. 3 to 5 is that in the second step, in accordance with FIG. 7, the wafer 31 is heated at two points 22 arranged at opposite ends of the cutting line 20.

[0060] Finally, the separation of the wafer 31 in accordance with FIG. 8 is effected by the pieces 23 of the wafer 31 that are delimited by the cutting line 20 being pulled apart. For this purpose, the wafer 31 is preferably adhesively bonded areally on a flexible carrier film, not illustrated, which is stretched in order to separate the pieces 23.

[0061] As an alternative to the method sequence illustrated in FIGS. 6 to 8, first all cutting lines 20 required for singulating the chips 30 are pretreated by the first and second steps being repeatedly carried out in succession, without initially dividing the wafer 31. Afterward, by means of the third step being carried out once, namely by means of the carrier film being stretched once, all chips 31 of the wafer 30 are separated from one another simultaneously.

[0062] The invention becomes particularly clear from the exemplary embodiments above. Nevertheless, it is not restricted to these exemplary embodiments, however. Rather, numerous further embodiments of the invention can be derived from the claims and the description above. In particular, individual features of the exemplary embodiments described above can also be combined in other ways, without departing from the invention.

[0063] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0064] 1 (Laser cutting) device [0065] 2 Glass plate [0066] 3 Workpiece receptacle [0067] 4 Carrier plate [0068] 5 Diffusing layer [0069] 6 Feed mechanism [0070] 7 Arrow [0071] 10 (First) laser [0072] 11 (First) laser beam [0073] 12 (Second) laser [0074] 13 (Second) laser beam [0075] 14 Axicon [0076] 15 Bessel beam [0077] 16 Focus region [0078] 17 Control computer [0079] 18 Control program [0080] 20 Cutting line [0081] 21 Burning point [0082] 22 Point [0083] 23 Piece [0084] 30 Chip [0085] 31 Wafer