Method for processing transparent brittle materials with laser beams and device for implementing the method

Abstract

The present invention relates to a laser device, in particular a pulsed scanning laser for cutting brittle substrates. The inventors propose a method and a device for forming a stressed edge in a substrate for cleaving the substrate, for which purpose the trajectory of the cavity is formed by light-induced breakdown in the body of the material during irradiation of the material with a focused laser beam with a fixed focal length during an angled scanning process of the laser beam, the focused laser beam moving longitudinally along the length of the substrate. The technical effects of the invention are: improved strength parameters of the product, better quality of the straight and inclined edges formed during substrate cleaving, without chipping and microcracks, high formation rate of stressed cleaved edges, which means faster laser cutting speed.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to a pulse scanning laser for cutting a brittle substrate. Background Art

[0002] Pulsed lasers are widely used in the semiconductor industry for scribing thin substrates, up to 1 mm, made of silicon, germanium, gallium arsenide and other semiconductors, as well as ceramic and glass substrates. The prior art describes various methods of forming cleave lines, ranging from V-shaped grooves during laser scribing to ablation or melting of the material on its top or bottom surface (US20190169062A1). However, after this operation, it is necessary to apply mechanical forces to the laser-treated material, or to generate thermal deformation waves by heating (or locally cooling) the material. None of these actions always has a favorable result - cleavage without chipping, microcracks and defects.

[0003] Femtosecond and picosecond lasers are used to prepare substrates for cleavage, including thick substrates made of glass. Prior art (US10233112B2) describes a method of perforating thin glass substrates used as smartphones and display screens using a picosecond laser, which is performed by perforating the glass and then heating the perforation line with a second laser - a high-power CO2 laser - to cause glass cracking and cleavage. This method is not suitable for thick glass. At the same time, the use of additional high-power lasers complicates the process. This cutting problem occurs during the processing of thick window glass, laminated and strengthened car windows, glass with protective coatings, and tempered glass.

[0004] The prior art teaches a method for cutting glass by creating a grid of filaments (tracks) as a result of the self-focusing of the laser beam due to the nonlinear effects present in the glass. During the beam filamentation, hollow tracks several hundred micrometers long are created in the bulk of the substrate (RU2013102422A or international publications WO2012006736A2 and US9757815B2), making it possible to create a series of tracks including one close to the back side to prepare the substrate for cleaving. This filamentation method also imposes limitations on the cutting of thick glass: it cannot be applied to glass with a thickness of 6 mm or more due to the geometry of the optics (which requires microlenses with short focal lengths or dedicated optics capable of ensuring long focal lengths and interference patterns within the bulk of the glass - Bessel beams). In order to eliminate breakdown in the near-surface area, the laser beam waist must be formed deeper into the bulk of the substrate. Given the fact that the array of tracks is discontinuous, certain fundamental limitations are applied during its formation: during focusing and self-focusing, there must be no boundary interference from nearby irregularities and filaments. Limitations regarding glass thickness also apply: multiple passes are required along the substrate surface in order to fill the substrate body with filaments that are far from each other (due to the conditions in which they are formed), which imposes limitations on the alignment accuracy of the array of filament grids. The profile accuracy should be at least 4 microns. The method requires the use of complex and high-precision systems to track the trajectory and trajectory repeatability; this can have an adverse effect on the cutting quality during multiple cuts and can cause chipping during the inevitable final splitting of the glass substrate after cutting using the filamentation method. All of this makes it impossible to split the material without applying mechanical forces and imposes limitations on the industrial applicability of the method. Summary of the invention

[0005] The present invention proposes a method for cleaving the brittle material of a substrate along a practically continuous stressed edge formed in the body of the substrate due to laser-induced breakdown of the material, the substrate being transparent to the laser beam and not very absorbing of the laser beam. The effect of the method can be easily illustrated using an example of cutting thick glass having a thickness of 20 mm or more - up to 30 mm. This cleaved, substantially continuous stressed edge consists of microcavities. The latter are formed due to the induced breakdown, which in turn is caused by the laser beam focused in the body of the substrate. The laser beam strikes the surface of the body at a certain angle while it moves progressively along this surface. While moving progressively, the beam oscillates continuously and rapidly in the same plane in which it moves progressively. This ensures a continuous scanning of the beam over the entire substrate cross section. The method is insensitive to the direction in which the beam moves in the substrate cross section, from the top or bottom surface of the substrate. It is important that the focused laser beam cyclically penetrates the entire thickness of the substrate body, especially considering the once selected long focal length (150-350mm) of the lenses of the optical system, which is maintained throughout the process of forming the stressed edge for cleaving the substrate at its completion.

[0006] The technical effect is a better quality of the straight, curved or angled cleaved edge of the substrate without uncontrolled chipping and micro cracking, a high rate of formation of the stressed cleaved edge, which means faster laser cutting due to the absence of:

[0007] - reconfiguration of the optical system to focus the laser beam during its scanning over the entire depth of the substrate body,

[0008] - the depth of formation of the layer where the process is interrupted to reconfigure the stress edge within the bulk of the substrate, regardless of the direction in which the beam is moved, from the top or bottom surface of the substrate,

[0009] - and it generally improves the strength properties of products made from substrates cleaved using the proposed method, due to the presence of a maximum possible number of light-induced breakdown cavities in the bulk of the substrate material during the progressive continuous movement of the scanning system along the length of the substrate.

[0010] The displacement of the beam and substrate relative to each other is not limited to linear or curved paths. The scope of the present invention includes rotational displacement of the beam and substrate relative to each other, which combined with the linear displacement produces a hole in the substrate. In addition, as disclosed above, the system of the present invention can produce angled or curved edges. If the processed substrate is not completely separated, a thulium (Tm) laser, preferably but not necessarily a Tm fiber laser, can be used to provide the final "touch" to cause the cut substrate pieces to be separated with corresponding smooth edges.

[0011] Other advantages and distinctive features of the proposed invention will become apparent from the following detailed description of its elements with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The sole figure is a schematic diagram of the process of forming a stressed cleaved edge in a substrate body, wherein the laser beam is positioned at an angle, the figure being a front view. DETAILED DESCRIPTION

[0013] The elements of the claimed invention are reflected in the following features and details.

[0014] The general details of the invention are illustrated by the accompanying drawings and relate to an inventive method and a device (100) for implementing the same. In order to provide a stressed edge (1) in a substrate (2) made of a material transparent to the laser beam, a focused laser beam with a fixed focal length is incident thereon during an angled scanning process of the beam. When the beam and the substrate (2) are linearly moved relative to each other, a track of cavities is formed in the bulk of the substrate by localized photoinduced breakdown of the material during the irradiation of the material. When the beam irradiates the substrate in the manner disclosed above, the following occurs:

[0015] - forming a substantially linear chain of narrowly spaced cavities (4) (at least one cavity per pulse) in the bulk of the material in a single pass of the beam (3) in a direction from one surface of the substrate to the opposite surface, and

[0016] - During another (continuous) pass of the beam, a relative progressive longitudinal movement of the beam and substrate results in the formation of the next chain of narrowly spaced cavities.

[0017] The net result of the progressive longitudinal movement and the angled cyclic scanning of the light beam in the plane of this movement is a substantially continuous trajectory of the light-induced cavity in the form of an internal bubble stress edge (1), along which the substrate is cleaved without fragmentation defects at the completion of the process of longitudinal movement of the light beam along the entire length of the substrate (2).

[0018] The device for implementing the above disclosed inventive method is constructed with a pulsed laser source (5). The latter can be selected from a solid-state laser or a fiber laser. The emitted laser beam is collimated in a collimator (6) and then it strikes a beam scanner (7). The scanner (7) ensures a cyclic scanning of the beam through the thickness of the substrate from the top surface to the opposite surface or vice versa, since the direction - forward or reverse - is unimportant. The optical focusing system (8) ensures the beam focusing and has a setting that does not change during the entire processing process. During this process, the angle of incidence of the laser beam onto the surface varies between 90° and about 40.5°, depending on the desired shape of the cleavage relative to the normal of the surface of the substrate. For example, when forming a straight cleavage, the angle can be slightly less than 60°. If the cleavage is inclined or beveled, a smaller angle of incidence of up to 45° is required. Note that with increasing angle of incidence, light losses also increase due to deflection at higher angles. It has been determined that the angle formed by the cut relative to the substrate surface should preferably be limited to a range of 45-90°. The desired angle is set relative to the substrate surface along the spatial axis XYZ by the beam spatial orientation system (9). The longitudinal progressive movement of the beam (3) along the surface of the substrate (2) is ensured by the actuator (10), which is responsible for the unidirectional progressive movement of the beam along the axis X on the fixed substrate and with a lead before the area where the stress edge is formed. Note that the scanner (7) and the optical focusing system (8) can also be positioned at another angle relative to the workpiece surface than shown in the figure.

[0019] It is important to note that a scanner (7) that scans in one plane and is at least uniaxial can be implemented based on a galvano scanner and a polygon for high-speed scanning of the light beam (3) in a lateral direction relative to the substrate (2), the polygon being the preferred solution because it ensures a uniform distribution of the light-induced breakdown cavities.

[0020] Notably, the stress edge (up to 30 mm thick) is formed essentially over the entire body of the thick substrate, with the distance between the light-induced breakdown cavities being in the micrometer range, determined by the size of the cavities and the scan rate in the lateral angled direction and in the longitudinal direction.

[0021] It is noteworthy that photoinduced breakdown is achieved by pulsed femtosecond or picosecond or nanosecond focused laser beam sources with sufficient pulse energy for photoinduced breakdown of materials, with wavelengths ranging from ultraviolet to infrared waves, subject to their weak absorption in the processed material.

[0022] Importantly, the material transparent to the laser beam may comprise one or more layers and may be selected from glass, quartz, semiconductors, dielectrics, polymer materials, crystals, sapphire and / or diamond-like films. In engineering, substrates made of transparent materials are selected for the manufacture of information display devices - flat screens or TV screens, or for cutting window glass, mirrors, laminated car windows, armored window glass or transparent ceramics.

[0023] The present invention has been successfully tested in cutting 4 to 20 mm thick glass (including laminated glass) using a YLPP-50-10-100-R picosecond fiber ytterbium laser (IRE-Polys, https: / / www.ipgphotonics.com / ru_).

[0024] The pulse length is 10-20 ps; the pulse energy is at most 100 μJ; and the pulse repetition rate is at most 2 MHz. Glass of 20 mm thickness has been cut using a scanning system based on a galvano scanner; the beam incidence angle is 40.5 degrees; the deflection angle is ±4.5 degrees; the focal length of the focusing system based on an F-Theta lens is 260 mm; the reflectivity of the glass surface is in the range of 4.6 to 5.2%; and the rate of longitudinal movement is at most 40 mm / s. However, other configurations or modifications of the above settings, especially with respect to wavelength, pulse energy, pulse repetition rate and / or pulse duration, may also be selected by a person skilled in the art, for example as described in U.S. Patents 9,296,066 or 10,399,184.

[0025] The laser beam and substrate can be rotated relative to each other to drill holes in the substrate. In addition, the disclosed system can produce curved edges. If the processed substrate is not completely cleaved, a thulium (Tm) laser can be used, preferably but not necessarily, a Tm fiber laser can be used to provide the final "touch" to cause the cut substrate piece to be separated with a corresponding smooth edge.

[0026] It should be obvious to those skilled in the art that the invention is not limited to the implementation options described above and that modifications can be made within the scope of the claims of the invention. If necessary, the distinctive features shown in the description as well as other distinctive features can also be used separately from each other.

Claims

1. A method for forming a stressed edge for cleaving a substrate made of a material transparent to a laser beam, for which purpose a track of a cavity is formed in the bulk of the substrate by local photoinduced breakdown of the material during irradiation of the material with a focused laser beam having a fixed focal length during an angled scanning process of the laser beam, wherein The focused laser beam is moved longitudinally along the length of the substrate, wherein: - forming an angular, linear chain of narrowly spaced cavities in the bulk of the material in a single pass of the beam in a direction from one surface of the substrate to an opposite surface, and - During another pass of the beam, the relative progressive longitudinal movement of the beam and the substrate results in the formation of the next chain of narrowly spaced cavities, and the end result of this process of progressive longitudinal movement and angled cyclic scanning of the beam in the same plane is a continuous trajectory of light-induced cavities in the form of internal bubble stress edges, wherein the substrate is cleaved along the trajectory without fragmentation defects.

2. The method according to claim 1, characterized in that Another pass of the beam is a reverse or return pass of the beam during the progressive longitudinal movement of the beam, the other pass of the beam continuing in the same direction over the substrate held in place with an advance relative to the region where the stress edge is formed.

3. The method according to claim 1 or 2, characterized in that: The tracks of stressed edges are formed over the entire body of the substrate, with the distance between light-induced breakdown cavities being in the micrometer range and determined by the size of the cavities and the scanning rate in the lateral angled direction and in the longitudinal direction.

4. The method according to claim 1 or 2, characterized in that: The plane in which the cleave edge is formed is normal or inclined at an angle of at least 45 degrees relative to the surface to form an inclined cleave edge.

5. The method according to claim 1 or 2, characterized in that: A pulsed femtosecond or picosecond or nanosecond focused laser beam source is used with sufficient pulse energy for photoinduced breakdown of the material, and wherein the laser beam source is based on a solid-state laser or a fiber laser.

6. The method according to claim 1 or 2, characterized in that: The material transparent to the laser beam comprises one or more layers of material selected from the following group: glass, semiconductor, dielectric, polymer material, crystal, diamond-like film.

7. The method according to claim 6, characterized in that The crystal includes quartz or sapphire.

8. The method according to claim 6, characterized in that The substrate made of a transparent material is selected for use in manufacturing information display devices, or for cutting window glass, mirrors, laminated vehicle windows, armored glass or transparent ceramics.

9. The method according to claim 8, characterized in that The information display device is a flat screen or a television screen.

10. An apparatus for forming a stress edge in a given plane in a body of a transparent material to be cleaved using the method of any one of claims 1 to 9, comprising: - Pulsed laser source with collimated beam emitter, - systems for beam orientation in space relative to the substrate surface, - an angled scanning system for high-speed beam scanning in a single plane in a lateral direction relative to the substrate, - an actuator for unidirectional progressive movement of the angled light beam along the surface of the substrate, - Optical focusing system.

11. The device according to claim 10, characterized in that The optical focusing system does not change the beam focus when forming a stressed edge up to 30 mm thick.

12. The device according to claim 10 or 11, characterized in that During creation of the stress edge, the angle of incidence of the light beam relative to the surface normal can be less than 60 degrees in an orthogonal plane, or an angle of up to 45 degrees in any other angled plane.

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