Method for laser beam machining of transparent brittle materials and apparatus for carrying out said method

Abstract

The present invention relates to a laser tool, particularly a pulsed scanning laser used to cut brittle substrates. The authors propose a method and apparatus for forming a stressed edge in a substrate for cutting the substrate, whereby a cavity track is formed in the body of the material through optically induced fracture during irradiation with a focused laser beam having a fixed focal length during angled scanning of the laser beam with longitudinal movement along the length of the substrate. The technical results are improved product strength parameters, better quality straight and beveled edges formed during substrate cutting, the absence of chips and microcracks, and faster formation of the stressed cleaved edge, which means faster laser cutting.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates to the field of laser technology, and in particular to pulsed scanning lasers used to cut brittle substrates.

[0002] Background of the Invention Pulsed lasers are widely used in the semiconductor industry to scribe substrates made of silicon, germanium, gallium arsenide, and other semiconductors, as well as ceramic and glass substrates, up to 1 mm thick. The prior art describes various methods for creating cleavage lines, ranging from V-shaped grooves during laser scribing to ablation or melting of the material on its top or bottom surface (see U.S. Patent Application Publication No. 2019 / 0169062). However, after this operation, it becomes necessary to apply mechanical force to the laser-treated material or to create a thermal deformation wave by heating (or locally cooling) the material. None of these actions necessarily produces good results, i.e., cleavage without chips, microcracks, or defects.

[0003] Femtosecond and picosecond lasers are used to prepare substrates, including thick glass substrates, for cutting. Prior art (U.S. Pat. No. 10,233,112) describes a method for drilling thin glass substrates used for smartphones and display screens using a picosecond laser. The method involves drilling holes in the glass and then heating the perforation line with a second laser, a high-power CO2 laser, to induce cracks and cut the glass. This method is not applicable to thick glass. At the same time, the use of an additional high-power laser complicates the process. Such cutting problems arise during the machining of thick commercial window panes, laminated and tempered car windows, protectively coated glass, and protective glass.

[0004] The prior art teaches methods for cutting glass by forming a grid of filaments (tracks) as a result of self-focusing of a laser beam due to the presence of nonlinear effects in glass. During beam filamentation, hollow tracks several hundred micrometers long are formed within the body of the substrate (as in Russian Patent Application Publication No. 2013102422 or International Patent Application Publication No. 2012 / 006736 and U.S. Patent No. 9757815), allowing a series of tracks to be formed, including near the back surface, to prepare the substrate for breaking. The filament method also imposes limitations on cutting thick glass. Due to the geometry of the optical system, it cannot be applied to glass with a thickness of 6 mm or more (this requires microlenses with a short focal length or specialized optical systems that can ensure a long focus and an interference pattern within the glass body, i.e., a Bessel beam). To eliminate breakage in the near-surface region, the laser beam waist must be formed relatively deep within the body of the substrate. In light of the fact that the track array is not continuous, certain fundamental limitations apply during track formation. During focusing and self-focusing, there must be no boundary interference from nearby irregularities and filaments. Restrictions on glass thickness also apply. To fill the substrate body with filaments that are far apart (due to the filament formation conditions), multiple passes along the substrate surface are required, which limits the alignment accuracy of the filament grid array. The contour accuracy should be at least 4 micrometers. This method requires the use of complex and highly accurate systems for tracking and reproducibility of the movement trajectory. During multi-pass cutting, this negatively impacts the quality of the cut, which can lead to chipping during the inevitable final separation of the glass substrate after cutting using the filament method. All of this makes it impossible to break the material without applying mechanical force, limiting the industrial applicability of this method.

[0005] Disclosure of the Invention The present invention proposes a method for cleaving brittle substrate materials that are transparent to the laser beam and do not excessively absorb it, along a substantially continuously stressed edge within the body of the substrate, which is formed as a result of laser-induced material fracture. The operation of this method can be easily illustrated using the example of cutting thick glass with a thickness of 20 mm or more and up to 30 mm. This cleavage, i.e., the substantially continuously stressed edge, consists of a plurality of microcavities. These are formed as a result of induced fracture caused by a laser beam focused within the body of the substrate. The laser beam is incident on the surface of the body at a predetermined angle while moving incrementally along the surface. Simultaneously with this incremental movement, the beam is continuously and rapidly oscillated in the same plane along which it is moving incrementally. This ensures continuous scanning of the entire substrate section by the beam. This method is independent of the direction of beam movement in the substrate section from the top or bottom surface of the substrate. Importantly, the focused laser beam periodically penetrates the entire thickness of the substrate body, which is particularly important considering the long focal length (150-350 mm) of the single-selection lens in the optical system, which remains constant throughout the process, forming the edge that, once complete, is stressed for fracture of the substrate.

[0006] The technical result is a better quality of straight, curved or angled edges of the substrate cleavage, free from uncontrolled chipping and microcracks, and a faster formation of the stressed cleavage edge, which means faster laser cutting. Reconfiguration of the optical system to focus the laser beam while scanning through the entire depth of the substrate body Interruption of the process to reconstruct the depth of the stressed edge layer formation within the substrate body, regardless of the direction of beam movement from the top or bottom surface of the substrate. Furthermore, This generally improves the strength properties of products made from substrates fractured using the proposed method, by ensuring that the maximum possible number of optically induced fracture cavities are present within the material of the body of the substrate while the scanning system moves incrementally and continuously along the length of the substrate.

[0007] The relative displacement between the beam and the substrate is not limited to linear or curved paths. The scope of the present invention includes relative rotational displacement between the beam and the substrate, which can be combined with linear displacement to form holes in the substrate. Furthermore, as disclosed above, the system according to the present invention can form 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" that separates the cut substrate pieces with their respective smooth edges.

[0008] Other advantages and salient features of the proposed invention will become apparent from the following detailed description of its nature, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a process for forming a stressed fracture edge in the body of a substrate by a laser beam positioned at an angle, viewed from the front.

[0010] Embodiments of the invention The essence of the claimed invention is reflected in the following features and details.

[0011] The general details of the invention are illustrated by the drawings and relate to a method according to the invention and to an apparatus (100) for carrying out the method according to the invention. 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 on the substrate (2) during a process of angled scanning of the beam. The relative linear movement of the beam and the substrate (2) results in the formation of cavity tracks in the substrate body through localized optically induced material destruction during the irradiation. When the substrate is irradiated by the beam in the manner disclosed above, the following occurs: In one pass of the beam (3) in a direction from one surface of the substrate to the opposite surface, a substantially linear chain (4) of closely spaced cavities (at least one cavity per pulse) is formed in the body of material; and During other (successive) passes of the beam, the relative incremental longitudinal movement of the beam and the substrate results in the formation of the next chain of closely spaced cavities. The net result of the incremental longitudinal movement and angled periodic scanning of the beam in the plane of this movement is a substantially continuous track of optically induced cavities in the form of an internal bubbly stressed edge (1) along which the substrate is fractured, where no chipping defects occur along the entire length of the substrate (2) upon completion of the process of longitudinal movement of the beam.

[0012] The apparatus for carrying out the method of the present invention disclosed above comprises a pulsed laser source (5), which may be selected from a solid-state laser or a fiber laser. The emitted laser beam is collimated in a collimator (6) and then enters a beam deflection system or scanner (7). The scanner (7) ensures the 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 backward) is irrelevant). An optical focusing system (8) ensures beam focusing and has settings that remain unchanged throughout the machining process. During this process, the angle of incidence of the laser beam on the surface varies from 90° to approximately 40.5° relative to the normal to the substrate surface, depending on the desired shape of the cleavage. For example, when forming a linear cleavage, this angle can be slightly smaller than 60°. If the cleavage is to be oblique or chamfered, a smaller angle of incidence of up to 45° is required. It should be noted that as the angle of incidence increases, so does the optical loss due to deflection at larger angles. It has been found that the angle at which the cut is made relative to the surface of the substrate should preferably be limited to the range of 45° to 90°. The desired angle is set along spatial axes X, Y, and Z relative to the surface of the substrate by a beam spatial orientation system (9). The longitudinal gradual movement of the beam (3) along the surface of the substrate (2) is ensured by an actuator (10), which is responsible for the unidirectional gradual movement along axis X across the fixed substrate, with a lead in front of the area where the stressed edge is to be formed. It should be noted that the scanner (7) and the optical focusing system (8) may be arranged at a different angle relative to the surface of the workpiece compared to the angle shown.

[0013] It is important to note that for fast scanning of the beam (3) transversely to the substrate (2), the deflection system (7) for uniaxial scanning in at least one plane can be implemented based on both galvanometer scanners and polygon scanners, with polygon scanners being the preferred solution since they guarantee a uniform distribution of the optically induced destruction cavities.

[0014] In particular, stressed edges (up to 30 mm thick) are formed substantially throughout the entire body of the thick substrate, with the distance between optically induced fracture cavities in the micrometer range, determined by the cavity dimensions and the speed of scanning in both the angled transverse and longitudinal directions.

[0015] In particular, optically induced breakdown is achieved by a pulsed femto- or pico- or nano-second focused laser beam source with sufficient pulse energy for optically induced breakdown of the material, with wavelengths in the ultraviolet to infrared range, provided that the material being machined has a weak absorption of this wavelength.

[0016] Importantly, the material transparent to the laser beam can comprise one or more layers and can be selected from glass, quartz, semiconductors, dielectrics, polymeric materials, crystals, sapphire and / or diamond-like films. In engineering, substrates made of transparent materials are chosen for the purpose of making information display devices (flat screens or TV screens) or for cutting window panes, mirrors, laminated glass for car windows, protective window glass or transparent ceramics.

[0017] The present invention has been successfully tested using the YLPP-50-10-100-R picosecond Fibre-by-Terbium laser (IRE-Polys, https: / / www.ipgphotonics.com / ru_) to cut glass, including laminated glass, with thicknesses ranging from 4 to 20 mm.

[0018] The pulse length was 10-20 ps, the pulse energy was up to 100 μJ, and the pulse repetition rate was up to 2 MHz. A 20 mm thick glass was cut using a scanning system based on a galvanometer scanner. The beam incidence angle was 40.5°, the deflection angle was ±4.5°, the focal length of the focusing system based on an F-theta lens was 260 mm, the reflection coefficient from the glass surface was in the range of 4.6-5.2%, and the longitudinal movement speed was up to 40 mm / s. However, other configurations or modifications of the above-mentioned setup, particularly with regard to wavelength, pulse energy, pulse repetition rate, and / or pulse duration, may be selected by those skilled in the art, as described, for example, in U.S. Pat. No. 9,296,066 or U.S. Pat. No. 10,399,184.

[0019] The laser beam and the substrate can be rotated relative to one another to drill holes in the substrate. Additionally, the disclosed system can produce curved edges. If the processed substrate is not completely cleaved, a thulium (Tm) laser, preferably, but not necessarily, a Tm fiber laser, can be used to provide the final "touch" that separates the cut substrate pieces with smooth edges.

[0020] It is clear to those skilled in the art that the present invention is not limited to the above-mentioned embodiment options, but can be modified within the scope of the claims of the present invention. Several distinctive features shown in the description together with other distinctive features can also be used separately from each other if necessary.

Claims

1. 1. A method for forming a stressed edge for breaking a substrate made of a material transparent to a laser beam, the method comprising the steps of: forming a track of cavities in the body of the substrate through localized optically induced destruction of the material during irradiation with a focused laser beam having a fixed focal length during a process of scanning the laser beam at an angle relative to the surface of the substrate, with oscillation in a direction from one surface of the substrate to the opposite surface and gradual longitudinal movement along the length of the substrate, whereby a substantially angular linear chain of closely spaced cavities (at least one cavity per pulse) is formed within the body of material in a single pass of the beam in a direction from one surface of the substrate to the opposite surface; and During another pass of the beam, the relative incremental longitudinal movement of the beam and the substrate results in the formation of the next chain of closely spaced cavities; the final result of said process of incremental longitudinal movement and angular periodic scanning of said beam in the same plane is a substantially continuous track of optically induced cavities in the form of internally bubble-stressed edges along which said substrate is fractured without chipping defects; using a pulsed femtosecond or picosecond or nanosecond focused laser beam source with sufficient pulse energy for optically induced destruction of the material, said laser beam source being based on a solid-state laser or a fiber laser; method.

2. 2. The method of claim 1, wherein the other passes of the beam are reverse or return passes of the beam during successive incremental longitudinal movements of the beam in the same direction across a substrate fixed in place, with a leading edge to the region where the stressed edge is formed.

3. 3. The method of claim 1, wherein the track of stressed edges is formed substantially over the entire body of the substrate, with the distance between optically induced fracture cavities in the micrometer range, the distance being determined by the cavity dimensions and the speed of scanning in both the angled transverse and longitudinal directions.

4. 4. The method of claim 1, wherein the plane along which the breaking edge is formed is perpendicular to the surface or is inclined at an angle of at least 45 degrees to form an oblique breaking edge.

5. 5. The method of claim 1, wherein the material transparent to the laser beam comprises one or more layers of a material selected from glass, quartz, a semiconductor, a dielectric, a polymer material, a crystal, sapphire, a diamond-like film.

6. 6. The method according to claim 5, wherein the substrate made of a transparent material is selected for the purpose of producing information display devices, in particular flat screens or TV screens, or for cutting window panes, mirrors, laminated car windows, protective glass or transparent ceramics.

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