METHOD FOR MACHINING A WORKPIECE

Description

Technical field

[0001] The present invention relates to a method for processing a workpiece, in particular for introducing at least one recess or opening into the workpiece, by means of laser etching. State of the art

[0002] Laser etching involves modifying a material transparent to the laser radiation used by means of one or more ultrashort laser pulses. Nonlinearly induced absorption processes, such as multiphoton absorption or tunnel ionization, occur at the focus of these pulses. This modifies the chemical and / or physical properties of the material, making it more susceptible to etching. In a subsequent step, the modified material is selectively removed using an etching process.

[0003] The selectivity of the etching process is understood as the ratio between the etch rate for modified material and the etch rate for unmodified material.

[0004] If the unmodified material is also removed during the etching process (albeit more slowly), it is not possible to create precise contours of varying sizes in a single workpiece solely and directly through the geometry of the applied modifications. This is particularly true with a long, continuous modification spanning the entire material thickness, as in... Fig. 1aDepending on the etching process, different cavities can be created in transparent materials. In a selective etching step with high selectivity, for example, predominantly only the modified material is attacked, while the unmodified material remains largely resistant. In this way, for example, through-holes with a constant diameter can be created across the entire thickness of transparent material (see Fig. 1b If a low-selectivity etching step is performed after modification instead of a high-selectivity etching step, both modified and (to a lesser extent) unmodified material can be etched. In this way, hourglass-shaped through-holes can be created from elongated laser modifications (see Fig. 1cThe ratio of the inlet / outlet diameter to the waist diameter can be adjusted using this method via the etching time. However, at longer etching times, a reduction in material thickness Δh can occur in a less selective etching step. Furthermore, the minimum near-surface diameter of the through-holes, through which etching occurs, is therefore dependent on the material thickness.

[0005] WO 2018 / 162385 A1 describes a laser etching process in which different modifications are introduced into the transparent material by changing the laser parameters. This allows for different selectivities to be achieved in the subsequent etching step, depending on the type of modification.

[0006] Document US 2018 / 029924 A1 discloses a method which, by combined etching and the formation of a modified part of the substrate by means of UV laser irradiation, makes it possible to produce a hole with a circular outline and a smooth inner wall. Description of the invention

[0007] Starting from the known prior art, it is an object of the present invention to provide an improved method for processing workpieces by means of laser etching. This object is achieved by a method with the features of claim 1. Advantageous further developments will become apparent from the dependent claims, the description, and the figures.

[0008] Accordingly, a method for processing a workpiece is proposed, comprising the steps of introducing a plurality of adjacent modifications into the material of the workpiece by means of laser radiation, then etching the material of the workpiece in a first etching process with a first selectivity in order to predominantly remove the material modified by the laser radiation, and then, after completion of the first etching process, etching the material of the workpiece (1) in a second etching process with a second selectivity different from the first selectivity in order to remove the bridges remaining between the removed modified material.

[0009] The modification can alter the material's behavior towards an etching agent. To enable the modification not only on the surface but also in deeper layers of the workpiece, the workpiece material is preferably transparent, at least to the wavelength of the laser radiation used. To avoid or minimize losses during laser radiation penetration into the material, the surface should be as smooth and free of contaminants as possible. The material can be, for example, glass, transparent ceramic, glass-ceramic, or sapphire.

[0010] The modification of the workpiece material can be achieved, in particular, by means of a laser beam in the form of a Bessel beam, especially a quasi-Bessel beam (hereinafter also simply referred to as a Bessel beam) with an elongated focal zone. This elongated focal zone has a substantially constant beam profile over the processing length (e.g., over the thickness of the workpiece). In practice, elongated focal zones with a length of more than 10 mm can already be generated. The generation of such quasi-Bessel beams is described, for example, in DE 10 2014 116 958 B4 and in WO 2016 / 079062 A1.

[0011] The modification of the workpiece material can also be carried out using a laser beam in the form of a focused Gaussian beam, whereby the modification of the material essentially takes place in the focus of the laser beam.

[0012] The laser source can be movably positioned relative to the workpiece, in particular in at least two spatial directions perpendicular to the direction of propagation of the laser beam, but also displaceable in all spatial directions. If displaceable in three spatial directions, the focus of the laser beam can be moved as desired parallel and perpendicular to the surface of the workpiece.

[0013] Several modifications can be applied sequentially to the workpiece material separately, so that they do not overlap. This reduces the stress on the workpiece and the risk of cracks or other damage within the workpiece. Alternatively, sequentially applied modifications can overlap, thus forming a single, continuous modification. Such overlapping modifications are considered a single modification here and in the following. A combination of overlapping and non-overlapping modifications is also possible.

[0014] A modification can extend, for example, from the workpiece's working surface (i.e., the surface through which the laser beam enters the workpiece) to a defined depth (viewed from the working surface) of the workpiece, particularly linearly and along the propagation direction of the laser beam. For this purpose, a Bessel beam with a focal zone shorter than the material thickness can be used, or a Bessel beam with a longer focal zone can be positioned so that the modification does not extend across the entire material thickness. Modifications can also be introduced inside the workpiece using a Bessel beam with a focal zone shorter than the material thickness, without having a direct connection to any surface of the workpiece. A modification can also extend across the entire thickness of the workpiece, i.e.,extend from the working surface to the opposite surface of the workpiece.

[0015] After the introduction of at least one modification, the workpiece is subjected to an etching process with varying selectivity. The selectivity of the etching process is defined as the ratio between the etch rate for the modified material and the etch rate for the unmodified material. The selectivity of the etching process can be adjusted, in particular, by the chemical composition, temperature, and / or concentration of the etchant.

[0016] The etching process can be liquid etching, dry etching, or vapor-phase etching. For example, an aqueous solution of KOH can be used as the etchant in a liquid etching process. Alternatively, the etching process can be carried out in an ultrasonic bath. In this case, the selectivity of the etching process can also be adjusted via the applied ultrasonic power.

[0017] To vary the selectivity of the etching process, one or more of the parameters determining selectivity can be changed during the etching process. For example, the temperature can be increased or decreased. This changes the selectivity during the etching process.

[0018] Depending on the selectivity of the etching process or the respective section of the etching process, predominantly or almost exclusively the modified material is removed, and only to a lesser extent or hardly at all the unmodified material.

[0019] It is also envisaged that the etching process with varying selectivity comprises two or more etching processes, each with a fixed selectivity. For example, the workpiece can first be subjected to an initial etching process with a first selectivity and—after completion of the first etching process—to a second etching process with a second selectivity. In particular, a different etchant can be used in each of the two etching processes.

[0020] In this process, the modified material of the workpiece is removed during the first etching step. This first etching step has a first selectivity, meaning the ratio between the etch rate for modified material and the etch rate for unmodified material has a first value. The modified material is etched faster than the unmodified material, so the material of the workpiece is predominantly removed along the modification.

[0021] During the initial etching process, the workpiece is immersed for a period of time in a bath of an initial etching solution with a specific concentration and temperature. Preferably, this bath is an ultrasonic bath, meaning that an initial ultrasonic power is introduced into the bath.

[0022] After the first etching process is complete, the workpiece undergoes a second etching process. In this second process, material is removed from the workpiece. The second etching process has a second selectivity, meaning the ratio between the etch rate for modified material and the etch rate for unmodified material has a second value.

[0023] Accordingly, a first etching process with high selectivity can primarily remove the material modified by the laser radiation. A second etching process with lower selectivity then removes the remaining ridges of unmodified material between the removed modified material. The channels formed during the first etching process provide access for the second etching solution, allowing it to attack the ridges along their entire length. This enables rapid removal of the ridges and minimizes the impact of the second etching process on the rest of the workpiece. This method is particularly useful for creating recesses of any desired shape in the workpiece.

[0024] The first and second selectivities differ in magnitude. Here too, the modified material is etched faster than the unmodified material, so that the workpiece material is predominantly removed along the modification; however, the ratio of the etch rates in the second etching process differs from the ratio in the first etching process.

[0025] During the second etching process, the workpiece is immersed for a second time, for example, in a bath of a second etching solution with a second concentration and temperature. Preferably, the bath is an ultrasonic bath, meaning that a second ultrasonic power is introduced into the bath. Alternatively, the workpiece can remain in the first bath for the second etching process, and the selectivity-determining parameters of the bath can be changed, for example, the temperature and / or the ultrasonic power can be increased or decreased.

[0026] The first and second etching processes can differ in the chemical composition, temperature, and / or concentration of the etching solutions and / or the ultrasonic power applied in an ultrasonic bath. These parameters allow the selectivity of the two etching processes to be adjusted.

[0027] In particular, the first selectivity and the second selectivity can differ by at least a factor of 2, preferably by a factor of 100, and more preferably by a factor of 10000.

[0028] In some embodiments of the process, the first selectivity is greater than the second selectivity. This means that during the first etching process, the modified material is removed more quickly relative to the unmodified material than during the second etching process.

[0029] This makes it possible, for example, to remove essentially only the modified material during the first etching process (high selectivity, for example, a selectivity of at least 1000). This creates a channel into which the second etching solution can penetrate during the second etching process, and along which the second etching solution can then also remove the unmodified material (lower selectivity, for example, a selectivity of at most 100). The second etching solution can then act inside the channel from the beginning of the second etching process and expand the channel more quickly to the desired diameter, thus minimizing the change in the workpiece thickness.

[0030] In a further embodiment, the introduction of at least one modification comprises the introduction of a plurality of adjacent modifications into the material by means of laser radiation. The modifications can be introduced, for example, linearly, along a contour, or in a two- or three-dimensional arrangement (regularly in the form of a grid or irregularly). Modifications are considered adjacent, in particular, if the distance between them is no more than five times, preferably one, the diameter of the respective modifications.

[0031] The majority of modifications can be arranged, in particular, within a desired area for a recess in the workpiece, for example within a circle or a polygon, or within another, even irregular, area.

[0032] All modifications of the plurality of modifications can have the same length. At least some of the modifications can also have different lengths. All or at least some of the modifications can have the same orientation, i.e., be parallel to each other. All or at least some of the modifications can have a starting point in a common plane; for example, all or at least some of the modifications can extend from the work surface into the workpiece.

[0033] If the modifications are arranged within a surface, the angle of the side wall of a recess can be shaped by appropriately selecting the lengths of the modifications. For example, one or more modifications with the greatest length can be arranged in the center of the recess, and the length of the modifications can decrease towards the edge of the recess.

[0034] The lengths of the modifications introduced into the material of the workpiece are preferably different in the propagation direction of the laser beam used.

[0035] In another embodiment, a plurality of modifications are arranged sequentially along a contour and incorporated into the material. Here, a contour is understood to be a predefined path, corresponding, for example, to the perimeter of a geometric figure (e.g., circle, ellipse, polygon, etc.), but which can also be irregularly shaped. As long as the path does not intersect itself or at least come very close to itself, most of the modifications will only have two adjacent modifications. Even if, in a grid-like arrangement over a surface, the modifications are incorporated into the material one after the other and thus also along a path, such an arrangement is not considered "along a contour" here.

[0036] In another embodiment, the contour along which the modifications are introduced into the material is closed, i.e., it completely encloses an area (with, of course, a gap between each adjacent modification). Such a contour can, in particular, correspond to the perimeter of a geometric figure (e.g., circle, ellipse, polygon, etc.). All modifications along this contour extend across the thickness of the workpiece, i.e., from the working surface to the opposite surface of the workpiece. Etching the material in a first, highly selective etching process predominantly removes the material modified by the laser radiation, so that the area enclosed by the contour and the area outside the contour are still connected by ridges of unmodified material.Etching the material in a second etching process then removes the remaining bridges between the removed modified material, so that the area of ​​material enclosed by the contour is separated from the area outside and can be removed.

[0037] In some embodiments of the process, the first selectivity is lower than the second selectivity. This means that during the first etching process, the modified material is removed more slowly relative to the unmodified material than during the second etching process.

[0038] In an embodiment where the first selectivity is lower than the second selectivity, the second etching process, with high selectivity, separates two parts of the workpiece. This can be achieved, in particular, by introducing a series of adjacent modifications into the workpiece material, all extending across the thickness of the workpiece, i.e., from the working surface to the opposite surface, and then removing the modified material by the second etching process with high selectivity. Adjacent modifications may overlap or be separated. If the distance between non-overlapping modifications is sufficiently small (e.g., less than five times the diameter of the modification), the two parts of the workpiece can be mechanically separated after the second etching process, e.g., by pulling them apart.Depending on the process parameters, the two parts may separate from each other even during the second etching process, as microcracks can occur and spread in unmodified areas between the modifications due to the modifications.

[0039] In the initial etching process with low selectivity, both the modified material and (depending on the level of low selectivity, possibly at a lower rate) the unmodified material are removed along the series of modifications, potentially creating a rounded edge on both sides of the modification series. After the two parts of the workpiece are separated as described above, these rounded edges result in a rounded edge (also called a chamfer) on each of the two parts.

[0040] A further third etching process with low selectivity or even with selectivity 1 (i.e., modified and unmodified material are etched at the same speed, so no selectivity) can be carried out, in particular to smooth the parting lines.

[0041] In further embodiments of the method, after completion of the etching of the material in the second etching process, one or more further etching processes with different selectivities can be carried out; that is, the selectivity of each further etching process can differ from the selectivity of the preceding etching process. The selectivities of the further etching processes can be the same as, or different from, the selectivities of the first two etching processes. For example, after completion of the etching of the material in the second etching process, one or more further etching processes with first and second selectivities can be carried out alternately.Thus, particularly when continuous modification of the material across the thickness of the workpiece is not possible, etching processes with high selectivity can essentially remove only the modified material, while etching processes with low selectivity can also remove the unmodified material. This, in turn, allows access to further areas containing modified material that were previously inaccessible to the etching solution. These further areas with modified material can then be removed again by means of a high-selectivity etching process without removing any significant amount of the unmodified material in the process.

[0042] With the help of multispot modifications, i.e. modifications with several modified areas in the longitudinal as well as in the transverse direction, complex structures (e.g. lenses) can also be introduced into transparent materials when using etching solutions of different selectivities.

[0043] Preferably, the material of the workpiece is transparent to the wavelength of the laser radiation.

[0044] The modifications are preferably introduced into the workpiece material using ultrashort laser pulses.

[0045] The proposed method has the advantage over other material processing methods (such as laser drilling) that it introduces no or only minimal stresses into the material, which could lead to cracking under load or over time. This is particularly true when adjacent modifications do not overlap, leaving an unmodified area between them.

[0046] Furthermore, a workpiece with a plurality of elongated holes produced by a method according to the invention is disclosed herein. Such a workpiece can, in particular, be a sieve made of glass, transparent ceramic, glass-ceramic, or sapphire with a plurality of through-holes from one surface to an opposite surface. Preferably, the through-holes have a substantially constant diameter along their length. In one embodiment, the through-holes have a diameter of less than 1 µm, for example, about 500 nm ("nanosieve"). Brief description of the characters

[0047] Preferred further embodiments of the invention are explained in more detail by the following description of the figures. These show: Figure 1 is a schematic representation of a known laser etching method; Figure 2 is a schematic representation of a first embodiment of a laser etching method according to the invention; Figure 3 is a schematic representation of a second embodiment of a laser etching method according to the invention; Figure 4 is a schematic representation of a third embodiment of a laser etching method according to the invention; Figure 5 is a schematic representation of a fourth embodiment of a laser etching method according to the invention; Figure 6 is a schematic representation of a fifth embodiment of a laser etching method according to the invention; Figure 7 is a schematic representation of a workpiece produced using a method according to the invention; Figure 8 is a schematic representation of a sixth embodiment of a laser etching method according to the invention;Figure 9 is a schematic representation of a seventh embodiment of a laser etching method according to the invention; Figure 10 is a schematic representation of an eighth embodiment of a laser etching method according to the invention; Figure 11 is a schematic representation of a ninth embodiment of a laser etching method according to the invention; and Figure 12 is a schematic representation of a laser processing device for modifying the material of a workpiece. Detailed description of preferred embodiments

[0048] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are designated with identical reference numerals, and repeated descriptions of these elements are sometimes omitted to avoid redundancy.

[0049] In the Figures 1-6 , 7a , as well as 9-11Each section shows a cross-section through a workpiece 1 along the beam propagation direction S of a laser beam used to introduce the modifications 2. Figures 7b and 8 show a top view of the respective workpiece 1.

[0050] In Figure 1 The diagram schematically depicts a well-known laser etching process. Fig. 1a Figure 1 shows a section of a workpiece 1 with a thickness h. An elongated, continuous modification 2 was introduced into the material of the workpiece 1 using laser radiation, to which the material of the workpiece 1 is transparent. This modification extends from one surface 3 to another, opposite surface 3'. Fig. 1bThe workpiece 1 is shown after the modified material was attacked and removed by the etching solution in a highly selective etching step. Due to the high selectivity of the etching step, the unmodified material was not affected or only minimally affected. This resulted in a through-hole 4 with a substantially constant diameter d1 in workpiece 1.

[0051] In Fig. 1cThe workpiece 1 is shown after a low-selectivity etching step, instead of a high-selectivity etching step, in which both the modified material and, to a lesser extent, the unmodified material were attacked and removed by the etching solution. Because the unmodified material near surfaces 3, 3' is exposed to the etching solution for a longer period during the etching process until the modified material is completely removed, an hourglass-shaped through-hole 5 with an outer diameter d2 and a smaller diameter d3 at the waist is formed. The waist diameter d3 can be adjusted by varying the etching time using this method.

[0052] However, with long etching times (e.g., to achieve a large waist diameter d3), a reduction in material thickness can occur in a less selective etching step where the unmodified material is attacked along the entire surface of the workpiece 1. This is shown schematically in Fig. 1d shown, in which the thickness of workpiece 1 is reduced by 2Δh after a long etching process with low selectivity compared to the thickness of workpiece 1 after a short etching process with low selectivity.

[0053] The ratio of the inlet / outlet diameter d2 to the waist diameter d3 can only be adjusted via selectivity using this method. Such a method with fixed selectivity is therefore very inflexible.

[0054] In Figure 2Figure 1 schematically illustrates a first embodiment of a laser etching method according to the invention. In this embodiment, hourglass-shaped through-holes are produced with minimal material loss along the surfaces and thus minimal reduction in thickness by separate etching processes with different selectivities. For this purpose, as in Figure 2, the following are used: Fig. 2aAs shown, several elongated modifications 2 are initially introduced into the material of the workpiece 1. The modifications 2 each extend from a surface 3, 3' to a desired depth, or continuously from one surface 3 to the opposite surface 3'. The modifications 2 are essentially distributed over the volume that is to be removed in the subsequent etching steps to create the hourglass-shaped through-hole 5. In this figure, as in all other figures, a section through the workpiece 1 along the beam propagation direction S is shown, and the modifications 2 lie in the plane of the section. It is understood that the modifications 2 can be distributed not only in a plane but also in a volume (i.e., arranged in front of and / or behind the plane of the drawing).

[0055] In Fig. 2bThe workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not affected or only minimally affected. This resulted in through holes 4 and blind holes 6 with essentially uniform diameters in workpiece 1. Between the through holes 4 and the blind holes 6, the unmodified material not removed in the first etching process remains in the form of ridges 7.

[0056] These bridges 7 are attacked and removed in a second etching process with low selectivity. The resulting workpiece 1 is in Fig. 2cAs shown, the removal of the modified material and the ridges 7 creates hourglass-shaped through-holes 6. Thus, hourglass-shaped through-holes 6 with different diameters can be produced in a single workpiece 1 within the same process, since the diameter of the holes is determined by the number of modifications 2 and not by the duration of the etching process. Therefore, the resulting thickness of the workpiece is also independent of the diameter to be achieved.

[0057] Selective etching, as in the other embodiments, creates an etching access point for the less selective etching solution. This allows the less selective etching process to occur along the entire length of the modifications removed in the first etching process, without having to work its way inwards from the surface of workpiece 1. The exposure time of the less selective solution is therefore so short that no significant material loss occurs, in particular no significant reduction in material thickness, nor does unavoidable near-surface etching occur outside the modified area. This makes it possible to create well-defined recesses and through-holes by combining consecutive modifications. There are no limitations regarding the angle or geometry of the recesses and through-holes.

[0058] In Figure 3A second embodiment of a laser etching method according to the invention is schematically shown. Here, elongated modifications 2 extend only to a certain depth into the workpiece 1, as in Fig. 3a shown. Further adjacent modifications, which also extend only to this depth into the workpiece, are provided in front of and / or behind the drawing plane. The adjacent modifications can be spaced apart from each other, preferably by a distance of up to five times the diameter of the individual modifications. In Fig. 3bThe workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not affected or only minimally affected. As a result, blind holes 6 with essentially constant diameters were formed in workpiece 1, between which webs (not shown) of unmodified material remain.

[0059] In a second etching process with low selectivity, the blind holes 6 created in the first etching process can then be widened so that the bridges between them are removed. Thus, grooves 8 can be created in the workpiece 1 as shown in Fig. 3c As shown. By arranging the modifications 2 along arbitrary geometries, arbitrary geometries of grooves in the workpiece can be created by combining selective and less selective etching.

[0060] In Figure 4 A third embodiment of a laser etching method according to the invention is schematically shown. In this embodiment, recesses 9 are created on one of the surfaces 3 of the workpiece 1 by separate etching processes with different selectivities. For this purpose, as in Fig. 4aAs shown, several elongated modifications 2 are initially introduced into the material of the workpiece 1. Each modification 2 extends from a surface 3 to a desired depth. The modifications 2 for a recess 9 can have different lengths (see left and center) or the same length (see right). The modifications 2 are essentially arranged over the volume that is to be removed in the subsequent etching steps to create the recess 9. In this figure, as in all other figures, a section through the workpiece 1 is shown, and the modifications 2 lie in the plane of the section. It is understood that the modifications 2 can be arranged not only in a plane but also distributed throughout a volume.

[0061] In Fig. 4bThe workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not attacked or only minimally affected. This resulted in blind holes 6 with essentially constant diameters in workpiece 1. The unmodified material not removed in the first etching process remains between the blind holes 6 in the form of ridges 7.

[0062] These bridges 7 are attacked and removed in a second etching process with low selectivity. The resulting workpiece 1 is in Fig. 4cAs shown, by removing the modified material and the webs 7, recesses 9 were created (in the example shown with triangular (left and center) and rectangular (right) cross-sections, i.e., for example, conical and cuboid shapes). Thus, recesses 9 with different shapes can be produced in a workpiece 1 within the same process.

[0063] In Figure 5 A fourth embodiment of a laser etching method according to the invention is schematically shown. In this embodiment, through holes 4 with a constant diameter are produced through the workpiece 1 by separate etching processes with different selectivities. For this purpose, as in Fig. 5a As shown, an elongated modification 2 is introduced into the material of the workpiece 1. The modification 2 extends continuously from one surface 3 to the opposite surface 3'.

[0064] In Fig. 5bThe workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not affected or only minimally affected. This resulted in a through-hole 6 in workpiece 1 with a substantially constant diameter (corresponding to the diameter of the modification, for example, less than 500 nm).

[0065] In a subsequent second etching process with low selectivity, the diameter of the through-hole 4 is enlarged to the desired diameter as shown in Fig. 5cAs shown, because the etching solution can attack the entire thickness of the workpiece 1 from the beginning of the second etching process, the widening of the through-hole 4 occurs uniformly along its length. The widening of the through-hole 4 can be controlled by the duration of the attack of the less selective etching solution. Here too, an excessively long etching attack can lead to a reduction in material thickness, as shown in Fig. 5d shown.

[0066] Another embodiment of a method according to the invention, with which through holes 4 with a constant diameter can be produced, is shown schematically in Figure 6 This embodiment offers greater flexibility regarding the diameter of the through holes 4 without excessive material loss and thus without excessive thickness reduction of the workpiece 1. For this purpose, as shown in Fig. 6aAs shown, several elongated modifications 2 are initially introduced into the material of the workpiece 1. The modifications 2 each extend continuously from one surface 3 to the opposite surface 3'. The modifications 2 are essentially arranged over the volume that is to be removed in the subsequent etching steps to create the through-hole 4. In this figure, as in all other figures, a section through the workpiece 1 is shown, and the modifications 2 lie in the plane of the section. It is understood that the modifications 2 can be arranged not only in a plane but also distributed throughout a volume.

[0067] In Fig. 6bThe workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not affected or only minimally affected. This resulted in through-holes 4 with essentially constant diameters (corresponding to the diameter of the modification, for example, less than 500 nm, often around 1 µm in glass) being formed in workpiece 1. The unmodified material not removed in the first etching process remains between the through-holes 4 in the form of ridges 7.

[0068] These bridges 7 are attacked and removed in a second etching process with low selectivity. The resulting workpiece 1 is in Fig. 6cAs shown, the removal of the modified material and the webs 7 creates through holes 4 with a constant diameter. Thus, multiple through holes 4 with different diameters can be produced in a single workpiece 1 within the same process, since the diameter of the holes is determined by the number of modifications 2 and not by the duration of the etching process. Therefore, the resulting thickness of the workpiece is also independent of the diameter to be achieved.

[0069] A schematic representation of a workpiece produced using a method according to the invention is shown in Fig. 7 shown. Several through holes 4 of constant diameter were drilled along the length of the workpiece 1, which consists of, for example, glass or sapphire. A cross-section through the workpiece 1 in a plane A, in which several through holes 4 are located, is shown in Fig. 7aThe figure shows that the through-holes extend from one surface 3 of the workpiece 1 to the opposite surface 3'. By the inventive method, comprising a first etching step with high selectivity and a second etching step with low selectivity, the through-holes can be produced with any desired diameter that remains essentially constant along their length. A top view of the workpiece 1 is shown in Fig. 7bAs shown, workpiece 1 has through holes 4 not only in plane A, but also in planes parallel to plane A. The spacing, number, arrangement, and diameter of the through holes 4 can be adjusted as desired. Such a tool can be used, for example, as a nanosieve or microsieve. The dimensions of workpiece 1 in this and the other illustrations are not to scale. In particular, the workpiece can have a thickness that is much smaller than its other dimensions, such as length and width.

[0070] In Figure 8 Figure 1 schematically illustrates a sixth embodiment of a laser etching method according to the invention. The method is explained here with reference to a top view of workpiece 1. In this embodiment, a portion of workpiece 1 is separated from the rest of the workpiece by means of separate etching processes with different selectivities. For this purpose, as described in Figure 1, the following steps are taken: Fig. 8aFirst, several elongated modifications 2 are introduced into the material of the workpiece 1. The modifications 2 extend continuously from one surface 3 to the opposite surface 3'. The modifications 2 are arranged along a contour 10, which is shown here as a circle. The section D is cut into the Figures 8b, 8c and 8d Shown enlarged.

[0071] In Fig. 8b The workpiece 1 is shown in section after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not attacked or only minimally affected. As a result, through-holes 4 are formed in workpiece 1. Between the through-holes 4, the unmodified material not removed in the first etching process remains in the form of ridges 7.

[0072] These bridges 7 are attacked and removed in a second etching process with low selectivity, as shown in the section in Fig. 8c shown. Depending on the duration of the second etching process, the width of the gap 11 created between the part of workpiece 1 to be separated and the remainder of workpiece 1 can be adjusted. During the low-selectivity etching process, the diameter of the through holes 4 created in the first etching process is also normally increased. This is not shown in the present schematic drawing. Furthermore, depending, for example, on the distance between each pair of modifications, microcracks can form between these modifications during the etching of the modified material, through which the second low-selectivity etching process preferentially proceeds along the contour 10. Fig. 8d Is the workpiece 1 partially visible after a longer exposure time of the second etching process than in Fig. 8cThe through holes 4 created in the first etching process serve as access for the etching solution of the second etching process, which can thus act from the beginning over the entire thickness of the workpiece 1, so that the gap 11 has an essentially straight shape over the thickness of the workpiece 1.

[0073] Workpiece 1, after the removal of the separated part, is in Fig. 8e The present method thus also allows for the separation or extraction of parts of a workpiece from its interior.

[0074] In Figure 9 A seventh embodiment of a laser etching method according to the invention is schematically shown. In this embodiment, a workpiece 1 is divided into two parts with rounded edges 12. For this purpose, as in Fig. 9a The illustration initially shows several elongated modifications 2 being introduced into the material of workpiece 1 across the entire thickness of workpiece 1. Fig. 9aOnly one modification 2 is shown; the other modifications are arranged adjacently in planes parallel to the drawing plane. Adjacent modifications can be overlapping or non-overlapping, as shown above with reference to Fig. 3 described. In one embodiment, the modifications have a diameter of about 1 µm and a distance of at least 1 µm, so that adjacent modifications do not overlap, but at most just touch.

[0075] In Fig. 9bThe workpiece 1 is shown after a first etching process with low selectivity in which both the modified material (partially) and the unmodified material were attacked and removed by the etching solution. This creates a trench 8 or (depending on the spacing of the modifications and the duration of the first etching process) a sequence of funnel-shaped depressions on both surfaces 3, 3' along the series of modifications 2. Since even in a low-selectivity etching process the modified material is preferentially attacked, the trench 8 runs along the series of modifications 2. If adjacent modifications are non-overlapping (i.e., spaced apart), in a further embodiment (not shown) an additional continuous modification can be introduced along the contour, which, for example, extends only to the depth of the desired edge rounding into the workpiece material.During the first etching process, a trench with rounded edges is created along this continuous modification.

[0076] In a subsequent second etching process with high selectivity, (predominantly) only the modified material is removed, so that the two parts of the workpiece can be separated from each other, as in Fig. 9c shown. The round walls of the trench 8 now each result in rounded edges 12 of the two parts of the workpiece 1.

[0077] In an embodiment not shown, a method according to the invention can be used in accordance with the method of Fig. 9 Rounding of the opening of through holes and blind holes or of the edges of trenches can also be achieved by preceding the corresponding methods described above with an etching process with low selectivity, in which a funnel-shaped depression is created around the modification.

[0078] The edges can be further straightened and thus polished by another short etching process with low selectivity.

[0079] In Fig. 10 Figure 1 schematically illustrates an eighth embodiment of a laser etching method according to the invention. In this embodiment, a workpiece 1 is divided into two parts. For this purpose, as in Figure 1, the following steps are taken: Fig. 10a The illustration initially shows several elongated modifications 2 being introduced obliquely through the workpiece 1, across its entire thickness, into the material of the workpiece 1. Fig. 10a Only one modification 2 is shown; the other modifications are arranged adjacently in planes parallel to the drawing plane. Adjacent modifications can be overlapping or non-overlapping, as shown above with reference to Fig. 3As described. In one embodiment, the modifications have a diameter of approximately 1 µm and a spacing of at least 1 µm, such that adjacent modifications do not overlap but at most just touch. Each of the elongated modifications 2 can be generated either by means of a laser beam with a longitudinally extended intensity profile (e.g., a Bessel beam with an elongated focus zone) incident obliquely on the surface 3 of the workpiece 1, or by arranging several modifications in a step-like fashion. The latter can be particularly advantageous at larger angles.

[0080] Several modifications arranged in a step-like sequence can be generated sequentially, for example, by a Bessel beam with a short focal zone at varying distances from the surface 3 of the workpiece 1 (or correspondingly by a Gaussian beam with a focal point at varying distances from the surface 3 of the workpiece 1). The varying distance of the focal zone from the workpiece surface can be achieved, for example, by adjusting the distance between the laser and the workpiece or by shaping the laser beam differently. Several modifications arranged in a step-like sequence can also be generated by a so-called multispot laser beam, which, through beam shaping, is designed, for example, to have an extension in a direction perpendicular to the beam direction, with the focal position varying along this direction.Such a beam can also be viewed as several parallel beams, each with a different focus position. The in . Fig. 10a The specified beam direction S corresponds to the variant with an angled Bessel beam.

[0081] In Fig. 10b The workpiece 1 is shown after a first etching process with high selectivity in which the modified material was attacked and removed by the etching solution. Due to the high selectivity of the etching process, the unmodified material was not affected or only minimally affected. As a result, through-holes 4 are formed in workpiece 1. Between the through-holes 4, the unmodified material not removed in the first etching process remains in the form of ridges (not shown).

[0082] These bridges are attacked and removed in a second etching process with low selectivity, as in Fig. 10cThis is shown. This divides the workpiece 1 into two parts 1', 1". During the low-selectivity etching process, the through holes 4 created in the first etching process are enlarged and the bridges between them are removed. Depending, for example, on the distance between each modification, microcracks can also form between these modifications during the modification of the material, through which the second low-selectivity etching process preferentially passes through the bridges.

[0083] In Fig. 10d The workpiece 1 is shown after the separated part 1" has been removed.

[0084] In Figure 11A ninth embodiment of a laser etching method according to the invention is schematically depicted. Depending on the process and / or material parameters, a wide variety of material modifications can occur. If continuously modified areas across the thickness of the workpiece are not possible or desired, continuous etching cannot be selectively performed. For example, round or elongated material modifications can be arranged in a chain-like fashion in the beam propagation direction (longitudinal multispots) as shown in [reference missing]. Fig. 11a As illustrated. Especially when stresses during modification need to be kept to a minimum, multispot modifications can be advantageous compared to long, continuous modifications.

[0085] In order to still be able to create a through-hole 4 through the workpiece 1, especially with a diameter that is as constant as possible, in such cases, the etching process can be alternated several times between etching with high selectivity and etching with low selectivity. During the etching processes with high selectivity, the modified material accessible to the etching solution from the outside is removed (see Fig. 11b and Fig. 11d Due to the high selectivity of the etching process, the unmodified material is not affected, or only minimally so. This largely prevents unwanted diameter expansion.

[0086] During etching processes with low selectivity, the unmodified material is also removed, so that the modified material is accessible again afterwards (see Fig. 11c and Fig. 11eIn the next etching process with high selectivity, the modified material accessible to the etching solution is again removed. After repeatedly alternating between etching processes with high and low selectivity, a through-hole 4 is created through the workpiece 1 as shown in Fig. 11f shown.

[0087] Such alternating etching, i.e., alternating etching processes with high and low selectivity, ensures that through holes as well as blind holes have the desired length, even if the modification in the longitudinal direction is not perfectly homogeneous.

[0088] The methods presented here can be used to create through holes and recesses with any diameter from a few hundred nanometers to several millimeters. Since material loss due to etching with low selectivity can be kept to a minimum, the achievable dimensions are not dependent on the workpiece thickness.

[0089] In the Fig. 12 In the laser processing system 21 shown, an optical system 31 can be used, for example, for modifying the material of a workpiece 1. The laser processing system 21 has a support system 23 and a workpiece storage unit 25. The support system 23 spans the workpiece storage unit 25 and carries a laser system which is located in Fig. 12For example, the optical system 31 is integrated into an upper crossbeam 23A of the support system 23. Furthermore, the optical system 31 is mounted on the crossbeam 23A so that it can be moved in the X-direction, allowing both components to be positioned close to each other. In alternative embodiments, the laser system can, for example, be provided as a separate external unit, the laser beam of which is guided to the optical system 31 by means of optical fibers or as a free beam.

[0090] The workpiece support unit 25 carries a workpiece 1 extending in the XY plane, for example, a glass disc or a disc made of ceramic or crystalline material such as sapphire or silicon that is largely transparent at the laser wavelength used. The workpiece support unit 25 allows the workpiece to be moved in the Y direction relative to the support system 23, so that, in combination with the mobility of the optical system 31, a processing area extending in the XY plane is available.

[0091] According to Fig. 12 Furthermore, a Z-direction shift capability is provided for, e.g., of the optical system 31 or the crossbeam 23A, in order to adjust the distance to the workpiece. For a modification extending in the Z direction, the laser beam is usually also directed in the Z direction (i.e., normal) towards the workpiece. However, additional machining axes can be provided, as shown in Fig. 12This is exemplified by a boom arrangement 27 and the additional axes of rotation 29. Accordingly, the boom arrangement 27 is designed as shown in the following. Fig. 12 Optional. Furthermore, redundant additional axes can be provided for higher dynamics by, for example, accelerating not the workpiece or the optical system, but more compact and appropriately designed components.

[0092] The laser processing system 21 also includes a control system (not explicitly shown), which is integrated, for example, into the carrier system 23 and, in particular, has an interface for the input of operating parameters by a user. In general, the control system comprises elements for controlling electrical, mechanical, and optical components of the laser processing system 21, for example, by controlling corresponding operating parameters such as pump laser power, cooling power, direction and speed of the laser system and / or the workpiece holder, electrical parameters for adjusting an optical element (for example, an SLM), and the spatial orientation of an optical element (for example, for rotating it).

[0093] Further arrangements for laser processing systems with various degrees of freedom are disclosed, for example, in EP 1 688 807 A1. Generally, for small workpieces, often only the workpiece is moved, and for larger workpieces, only the laser beam is moved, or – as in Fig. 12 - the workpiece and the laser beam. Furthermore, two or more optical systems, and thus focus zones, can be supplied by one laser system.

[0094] The modifications to the material produced by laser processing systems can be used for selective laser etching. Accordingly, it is important to be able to adequately control both the geometry and the type of modification. In addition to parameters such as laser wavelength, pulse shape, number of pulses, energy and time interval of the pulses in a pulse group generating a single modification, as well as pulse energy or pulse group energy, the beam shape plays a crucial role.

[0095] In particular, an elongated volume modification allows machining over a large volume region in the beam propagation direction in a single machining step. Specifically, machining over a large area at a single location in the feed direction can be performed in just one modification machining step.

[0096] Furthermore, an elongated focus zone can be helpful when processing uneven materials, since essentially identical laser processing conditions prevail along the elongated focus zone, so that in such embodiments, corresponding tracking in the direction of propagation is not necessary or only becomes necessary if the position of the material to be processed deviates more than the length of the elongated focus area (taking into account the required processing / penetration depth).

[0097] In general, when processing transparent materials using extended volume absorption, it is true that as soon as absorption occurs, this absorption itself, or the resulting change in the material properties, can influence the propagation of the laser beam. Therefore, it is advantageous if beam components intended to cause modifications deeper within the workpiece, i.e., downwards in the beam propagation direction, are not directed through areas of significant absorption.

[0098] In other words, it is advantageous to supply the beam components used for modification further down the beam at an angle to the interaction zone. An example of this is the quasi-Bessel beam, which has a ring-shaped far-field distribution with a ring width that is typically small compared to its radius. The beam components of the interaction zone are supplied at this angle in a rotationally symmetric manner. The same applies to the inverse quasi-Bessel beam or to modifications and additions of the same, such as the homogenized or modulated inverse quasi-Bessel beam. Another example is the inverse accelerated "quasi-Airy-beam-like" beam, in which the beam components of the modification are supplied at an offset angle. This is intuitively tangential to the curved modification zone and—unlike the pure quasi-Bessel beam, which is rotationally symmetric—not to it.like a curved inverse quasi-Bessel beam.

[0099] Furthermore, it is desirable to significantly exceed the threshold for nonlinear absorption only in the targeted volume region and to select the geometry of this volume region such that it is suitable for the desired application while also not significantly interfering with propagation to volume regions further downstream. For example, it may be advantageous to keep secondary maxima of an apodized Bessel beam profile below the threshold intensity required for nonlinear absorption.

[0100] With regard to successive modifications in the feed direction, the geometry of the modified volume can also be chosen such that, in the case of a series of several modifications in the feed direction, a previously introduced modification has only an insignificant influence on the formation of the subsequent modifications.

[0101] For fast processing, the generation of a single modification can be done with only a single laser pulse / a single laser pulse group, so that a position on the workpiece is only approached once in this case.

[0102] Ultrashort pulse lasers can provide intensities (power densities) sufficient to induce substantial material modification in correspondingly long interaction zones. The geometric extent of the modification is defined by beam shaping, resulting in a long, high free electron density through nonlinear absorption within the material. Energy is delivered laterally to deeper regions, thus preventing the shielding effect caused by upstream plasma interaction, unlike Gaussian focusing. For example, a uniformly distributed electron density in the longitudinal direction or a spatially high-frequency modulated electron density can be generated.

[0103] At sufficiently high intensities, an explosive expansion of the material can occur in regions with a sufficiently high free electron density, with the resulting shock wave potentially generating nanoscopic holes (nanovoids). Further examples of modifications (modification zones) include changes in refractive index, compressed and / or tensile stress-inducing regions, microcrystallites, and local stoichiometry changes.

[0104] The modification geometry is primarily determined by beam shaping (and not by nonlinear propagation such as filamentation). Spatial gradients can be generated by the optical systems, while temporal gradients can be generated by pulse trains or pulse shaping.

[0105] In general, the intensity distribution of a beam shape can be scaled by the imaging ratio of the system, particularly by the focal length and the numerical aperture of the near-field optics of the imaging system. Further scaling possibilities arise from the use of an additional lens, as well as from the displacement of the beam shaping element and / or the far-field optics. This allows the lateral and longitudinal extent of the beam profile within the workpiece to be influenced. Furthermore, spatial filters and apertures can be used in the beam path to condition the beam.

[0106] Exemplary laser beam parameters for, e.g., ultrashort pulse laser systems and parameters of the optical system and the elongated focus zone that can be used within the scope of this disclosure are: Pulse energy Ep: 1 µJ to 10 mJ (e.g., 20 µJ to 1000 µJ), energy of a pulse group Eg: 1 µJ to 10 mJ. Wavelength ranges: IR, VIS, UV (e.g., 2 µm > λ > 200 nm; e.g., 1550 nm, 1064 nm, 1030 nm, 515 nm, 343 nm). Pulse duration (FWHM): 10 fs to 50 ns (e.g., 200 fs to 20 ns). Exposure time (dependent on feed rate): less than 100 ns (e.g., 5 ps - 15 ns). Duty cycle (exposure time to the repetition time of the laser pulse / pulse group): less than or equal to 5%, e.g., less than or equal to 1%. Raw beam diameter D (1 / e2) at entry into optical System: e.g., in the range of 1 mm to 25 mm; focal length of the near-field optics: 3 mm to 100 mm (e.g., 10 mm to 20 mm); Numerical aperture NA of the near-field optics: 0.15 ≤ NA ≤ 0.5; Length of the beam profile in the material: greater than 20 µm; Maximum lateral extent of the beam profile in the material, if applicable.In the short direction: less than 20 λ Aspect ratio: greater than 20 Modulation in the propagation direction: greater than 10 Periods across the focal zone Feed rate dv between two adjacent modifications e.g. for separating applications: 100 nm < dv < 10 * lateral extent in feed direction Feed rate during exposure time: e.g. less than 5% of the lateral extent in feed direction.

[0107] The pulse duration refers to a single laser pulse, while the exposure time refers to the time interval in which, for example, a group of laser pulses interacts with the material to create a single modification at a specific location. The exposure time is short relative to the current feed rate, ensuring that all laser pulses in a group contribute to the modification at that location.

[0108] If the workpiece is thinner than the focal zone is long, the focal zone lies partially outside the workpiece, resulting in modifications that are shorter than the focal zone. This situation can be advantageously exploited to make the machining process robust even when the distance between the optics and the workpiece varies. In some embodiments, a modification that does not extend through the entire workpiece can be advantageous. In particular, the length of the focal zone and / or its position within the workpiece can be adjusted. It should be noted in general that, due to different thresholds for nonlinear absorption, a focal zone with assumed identical intensity will cause modifications of varying sizes in different materials.

[0109] The aspect ratio relates to the geometry of the beam profile (the focal zone) in the material being processed, as well as the geometry of the modification produced by a beam profile. For asymmetric or laterally modulated (e.g., non-rotationally symmetric or annular) beam profiles, the aspect ratio is determined by the ratio of the length of the modification to a maximum lateral extent occurring within this length range in the shortest direction. If the beam profile exhibits modulation in the lateral direction, e.g., in the case of annular beam profiles, the aspect ratio refers to the width of a maximum, for example, the ring thickness in the case of an annular beam profile. When multiple laterally spaced modification volumes are formed, the aspect ratio refers to the lateral extent of each individual modification. For a beam profile modulated in the direction of propagation (e.g.,(due to interference) the aspect ratio is related to the overall length.

[0110] Starting from a distance d between beam shaping element and focusing lens (near-field optics), which is in particular larger than the focal length f N of the near-field optics, and an NA of the near-field optics relative to air > 0.15, the used angular spectrum α of the beam shaping element can lie in the range tan(α) < f * NA / d < NA / 2, and preferably tan(α) > f * NA / (d * 4).

[0111] Where applicable, all individual features shown in the exemplary embodiments can be combined and / or exchanged without leaving the scope of the invention. Reference symbol list

[0112] 1 Workpiece 2 Modifications 3, 3' Surfaces 4 Through holes 5 Hourglass-shaped through hole 6 Blind holes 7 Webs 8 Trenches 9 Recesses 10 Contour 11 Gap 12 Rounded edge 21 Laser processing system 23 Support system 23A Crossbeam 25 Workpiece support unit 27 Cantilever arrangement 29 Rotation axes 31 Optical system

Claims

1. A method for machining a workpiece (1), comprising the steps of: - introducing a plurality of adjacent modifications (2) into the material of the workpiece (1) by means of laser radiation, - etching the material of the workpiece (1) in a first etching operation with a first selectivity in order to remove most of the material modified by the laser radiation, characterized by, - after completion of the first etching operation, in a second etching operation with a second selectivity different from the first selectivity, etching the material of the workpiece (1) in order to remove the webs that remain behind between the removed modified material.

2. The method according to claim 1, characterized in that the first etching operation and the second etching operation differ by the chemical composition, the temperature and / or the concentration of the etching solutions and / or by the ultrasonic power introduced in an ultrasonic bath.

3. The method according to claim 1 or 2, characterized in that the first selectivity and the second selectivity differ by at least the factor of 2, preferably by the factor of 100, more preferably by the factor of 10,000.

4. The method according to any one of the preceding claims, characterized in that the first selectivity is greater than the second selectivity.

5. The method according to any one of the preceding claims, characterized in that at least some of the modifications (2) introduced into the material of the workpiece (1) have different lengths.

6. The method according to claim 5, characterized in that the modifications (2) have different lengths in the direction of propagation of the laser radiation.

7. The method according to any one of the preceding claims, characterized in that a plurality of modifications (2) are introduced into the material of the workpiece (1) lined up together along a contour.

8. The method according to claim 6, characterized in that each modification extends over the thickness of the workpiece (1), wherein the contour is closed and wherein the etching in the first and second etching operations removes the region of the material enclosed by the contour.

9. The method according to claims 1 to 3, characterized in that the first selectivity is less than the second selectivity.

10. The method according to claim 8, characterized in that two parts of the workpiece (1) are separated from one another by the second etching operation with high selectivity, wherein a rounding of the separating edge created during the second etching operation is brought about by the first etching operation with low selectivity.

11. The method according to any one of the preceding claims, characterized in that after completion of the etching of the material, one or more further etching operations take place in the second etching operation, each with a different selectivity.

12. The method according to any one of the preceding claims, characterized in that the material of the workpiece (1) is transparent to the wavelength of the laser radiation.

13. The method according to any one of the preceding claims, characterized in that the modifications (2) are introduced into the material of the workpiece (1) by ultrashort laser pulses.