Laser working system

Abstract

The invention relates to a laser working system (10) for laser working a workpiece (36).

Description

[0001] LASER PROCESSING SYSTEM

[0002] The present invention relates to a system for laser processing of a workpiece, in particular for ablative laser processing of a workpiece, and preferably a system for laser cutting of a workpiece. The system according to the invention can be used in particular for cutting wafers.

[0003] Laser processing methods and systems are generally well-known. A laser beam is directed onto the workpiece using a focusing unit. The focused laser radiation heats the workpiece locally, causing the locally heated material to melt or vaporize, depending on the amount of heat applied. Laser processing offers significant advantages compared to conventional material processing methods. For example, laser cutting places less stress on the workpiece than mechanical cutting processes. Furthermore, the use of laser radiation allows for particularly precise cuts.

[0004] One challenge in laser material processing is that the workpiece is subjected to thermal stress during the process. Oxidation of the material being processed can also occur during the machining process. Therefore, a special variant of laser material processing has proven effective in some applications, in which the laser processing is carried out in a liquid (for example, water). The use of the liquid serves, on the one hand, to cool the workpiece during the laser processing. On the other hand, the use of suitable liquids can also suppress the oxidation effect described above.

[0005] According to the state of the art, laser material processing in liquid is carried out primarily in closed process chambers. In this process, the chamber is completely or partially filled with liquid, so that the workpiece is completely submerged. An additional advantage of processing in a liquid-filled chamber is that particles released during laser material processing, particularly those resulting from material vaporization, are contained within the liquid and thus cannot spread towards the focusing optics, preventing contamination.

[0006] In some applications, open process chambers are used, formed by a processing unit and a holding element. These process chambers are open on the sides, allowing liquid to be introduced from one side and flow out from a second side, usually opposite the first. The process chamber is often bounded by a transparent window in the processing unit (also called a process window), which can be wet and dirty after the laser processing. Therefore, the window must be dried and / or cleaned after the laser processing. Currently, this drying and cleaning is done manually and is time-consuming.

[0007] Based on the problem described above, the object of the present invention is to provide a laser processing system that allows efficient cleaning and / or drying of the process window.

[0008] To solve the described problem, the present invention proposes a laser processing system for laser processing of a workpiece, in particular for ablative laser processing of a workpiece and preferably for laser cutting of a workpiece, comprising: a laser beam source for generating pulsed laser radiation; a focusing unit for focusing the pulsed laser radiation onto the workpiece to be processed; a holding unit designed to accommodate the workpiece to be processed; a processing unit arranged between the holding unit and the laser beam source, the processing unit comprising: a first side with a first opening designed to allow the laser radiation into the processing unit; a second side arranged opposite the first side with a second opening; a chamber wall surrounding an interior space of the processing unit; and a transparent window.a flow generator for generating a flow on a surface of the workpiece; a movable positioning unit designed to accommodate the holding unit and to adjust the position of the holding unit; and a cleaning unit comprising at least one first nozzle, the nozzle being designed to provide a fluid jet on the transparent window.

[0009] The system according to the invention allows for particularly efficient cleaning of the transparent window using the additional cleaning unit. The cleaning unit allows a liquid jet or a gas jet to be applied to the transparent window, or to a surface of the transparent window. This enables the window to be cleaned and / or dried efficiently and automatically, ensuring a reproducible cleaning or drying process.

[0010] The system according to the invention can be used in particular for laser cutting of workpieces and preferably for laser cutting of wafers.

[0011] The first nozzle can, in particular, have a circular cross-section. However, the present invention is not limited to such round nozzles, as will be explained in detail below. The first side of the processing unit faces the laser beam source, while the second side of the processing unit faces the workpiece. In other words, the processing unit faces the laser radiation incident from the laser beam source.

[0012] The transparent window can be arranged, in particular, on the second side of the processing unit, on the first side of the processing unit, between the first and second sides of the processing unit, or in the chamber wall. Preferably, the transparent window can be arranged on the second side of the processing unit. The transparent window, together with the holding element, can define a laterally open processing space (also referred to as a process chamber or open process chamber) in which the workpiece can be received and processed. The flow generator can be configured, in particular, to generate a flow within the process chamber in which the workpiece is received.

[0013] As mentioned earlier, the processing unit is located between the holding unit and the laser beam source. In other words, the processing unit is positioned within the beam path or optical path between the laser beam source and the holding unit.

[0014] The cleaning unit can be used to provide a fluid jet on the transparent window, thereby removing dirt, particles or liquid from the transparent window.

[0015] In some embodiments of the invention, the processing unit can have a first transparent window arranged on the second side of the processing unit and, additionally, a second transparent window arranged in the chamber wall. As already explained in connection with the exemplary embodiment described above, the first window can adjoin the processing chamber in which the workpiece can be received and processed. Within the scope of the present invention, the first window is also referred to as the process window. The second window can serve to monitor the interior of the processing unit, for example, by means of a camera. Within the scope of the present invention, the second window is also referred to as the measuring window or monitoring window.

[0016] The cleaning unit can be connected to at least one fluid reservoir via one or more supply lines. The fluid reservoir can contain a liquid or gas that is supplied to the cleaning unit as needed. In some embodiments, a supply line may connect the cleaning unit to the processing chamber. This allows the fluid present in the processing chamber to be used for cleaning the transparent window.

[0017] In the system according to the invention, the holding element can in particular be designed as a vacuum clamping device (also referred to as a vacuum chuck) which is designed to receive a wafer and fix it within the process chamber.

[0018] The processing unit can be designed in such a way that its chamber wall surrounds the interior of the processing unit in a ring shape.

[0019] In the system according to the invention, it can be provided that the cleaning unit has a second nozzle, wherein the first nozzle is designed to provide a liquid jet on the transparent window, and the second nozzle is designed to provide a gas jet on the transparent window.

[0020] The liquid jet can consist of water (especially ultrapure water) or a cleaning solution. The cleaning solution can consist of, or contain, an alcohol, especially isopropanol. The gas jet can consist of, in particular, compressed air, nitrogen, or argon, or at least contain one of these gases. The cleaning unit can optionally comprise a first cleaning element with a first nozzle and a second cleaning element with a second nozzle. Alternatively, the cleaning unit can comprise a single cleaning element with two separate nozzles, one nozzle being configured to provide a liquid jet and the other nozzle to provide a gas jet.

[0021] The system according to the invention can also be provided in that the cleaning unit has a first supply line and a second supply line, wherein the first supply line is designed to supply a liquid to the cleaning unit; and the second supply line is designed to supply a gas to the cleaning unit.

[0022] In the system according to the invention, the cleaning unit can have a single nozzle through which either a liquid or a gas flows. Alternatively, the cleaning unit can have two separate nozzles, the first nozzle being supplied by the first supply line and the second nozzle by the second supply line.

[0023] The cleaning unit can have a first cleaning element with one or two nozzles. Alternatively, the cleaning unit can have a first cleaning element with a first nozzle and a second cleaning element with a second nozzle, as will be explained in more detail below in connection with the figures.

[0024] In some embodiments of the present invention, the first nozzle and / or the second nozzle may be designed to provide a fluid jet on the transparent window at an angle of incidence of 15° < 0 < 55°, preferably 20° < 0 < 45°, and particularly preferably 25° < 0 < 35°, where 0 describes the angle between the surface normal of the transparent window and the jet axis of the fluid provided by the first and / or second nozzle. Initial practical investigations have shown that the selection of the aforementioned angles of incidence enables particularly efficient cleaning of the transparent window. Furthermore, the selection of these angles prevents the fluid dispensed by a nozzle from settling on the nozzle after the cleaning process and thus clogging the nozzle.

[0025] It may also be provided that the tilt angle of the first and / or second nozzle is set so that the supplied fluid jet has a jet propagation direction that has a component directed away from the workpiece.

[0026] According to the present invention, the first nozzle and / or the second nozzle may have a slotted cross-section. Providing a slotted opening enables particularly efficient cleaning and drying of the transparent window. The slotted opening delivers a fluid jet with an elongated cross-sectional profile, suitable for cleaning and drying a larger area of ​​the transparent window. The first nozzle may have a slotted cross-section, while the second nozzle has a circular cross-section. This allows for the provision of a slotted fluid jet for cleaning the window, followed by drying through the second nozzle with the circular cross-section.Alternatively, the second nozzle can have a slotted cross-section and the first nozzle a circular cross-section. This allows a circular jet of liquid to be used for cleaning the window, with drying then taking place through the second nozzle with the slotted cross-section.

[0027] In some embodiments of the invention, the first and second nozzles may have a slotted cross-section. Furthermore, in the system according to the invention, the cleaning unit may be arranged on or attached to the positioning unit. This has the advantage that, when the positioning unit extends, the first and / or second nozzle of the cleaning unit can pass directly by the window to be cleaned, thus enabling efficient cleaning of the transparent window during the extension of the positioning unit. It is also possible for the cleaning unit to be integrated into the positioning unit.

[0028] Furthermore, the present invention may provide that the cleaning unit is arranged on a separate positioning unit (also referred to as a second positioning unit), the separate positioning unit preferably being designed as a positioning arm. This allows for flexible positioning of the cleaning unit, whereby the position of the cleaning unit can be determined independently of the positioning unit (also referred to as the first positioning unit) that receives the holding element. Alternatively, the cleaning unit may be arranged on a stationary positioning unit, and the processing unit can be moved close to the cleaning unit for cleaning or drying the transparent window.

[0029] Furthermore, the system according to the invention can include an additional protective device, wherein the protective device comprises at least one wall element extending between the first nozzle or the second nozzle and the holding unit, the wall element preferably being substantially vertical. The protective device serves to protect the workpiece being processed from splashes caused by the liquid supplied at the first nozzle and / or the second nozzle. These splashes occur because the liquid jet is typically supplied at a relatively high propagation velocity through the first and / or second nozzle.At the same time, the cleaning unit and in particular the first and / or second nozzle are protected from the liquid that can spread from the processing room towards the cleaning unit (especially when the holding unit is moved out of the processing position after the laser processing process has ended) and that can contaminate the first or second nozzle.

[0030] Finally, the system according to the invention may include a detection unit designed to evaluate light propagating through the transparent window. The detection unit may, in particular, comprise a camera. The camera can generate images of the transparent window, which can then be evaluated using software. This allows for the reliable detection of contamination of the transparent window. Alternatively, spectroscopic methods can also be used to analyze the contamination of the transparent window. The detection unit may also be designed to perform power measurement. This allows the optical power after passing through the transparent window to be measured. For this purpose, a photodetector arranged on the other side of the processing unit can be used.Low optical performance can serve as an indication of a contaminated process window.

[0031] The present invention is now specified in more detail with reference to the figures. The figures show...

[0032] Fig. 1 shows an embodiment of the system according to the invention comprising a cleaning unit with a cleaning element,

[0033] Fig. 2 shows a further embodiment of the system according to the invention comprising a cleaning unit with two cleaning elements,

[0034] Fig. 3 shows the cleaning unit shown in Fig. 2 during the cleaning process.

[0035] Fig. 4 shows a further embodiment of the cleaning unit according to the invention, and

[0036] Fig. 5 shows a further embodiment of the cleaning unit according to the invention, comprising a protective device. Fig. 1 schematically illustrates an embodiment of the laser processing system 10 according to the invention. The laser processing system 10 has a laser beam source 12, which is designed to generate preferably pulsed laser radiation 14. The laser radiation 14 is directed onto a focusing unit 18 by means of a beam deflection unit 16, which in this case is designed as a deflection mirror. In the embodiment shown in Fig. 1, the focusing unit 18 is designed as a focusing lens and is configured to focus the laser radiation 14 onto the surface of a workpiece 36, which is arranged on a holding unit 38. The focused laser radiation 14 propagates through a transparent window 48 (also referred to in this case as the process window).In the illustrated embodiment, the transparent window 48 is housed in a processing unit 20. The processing unit has a first side 22 facing the laser beam source 12 and a second side 24 facing the holding unit 38. The holding unit 38 and the second side 24 of the processing unit 20 together form a processing chamber 39 (also referred to here as a process chamber or open process chamber). In the illustrated embodiment, the focusing unit 18 is also arranged in the processing unit 20. Alternatively, the focusing unit 18 can also be arranged outside the processing unit (for example, above the processing unit 20). The processing unit 20 also has a chamber wall 26 that defines an interior space 28 of the processing unit.Furthermore, in the illustrated embodiment, the processing unit 20 includes a flow generator 30 designed to supply a liquid 35, which is directed onto the surface of the workpiece 36 via a liquid inlet channel 32. A liquid outlet channel 34 is provided on the opposite side of the chamber wall, through which the introduced liquid 35 can be discharged from the processing chamber 39. The liquid 35 can also flow laterally out of the processing chamber 39. The use of the flow generator 30 ensures that particles and bubbles present in the processing chamber, which could negatively affect the laser process, are removed. The supplied liquid also cools the workpiece. The holding unit 38 can be designed, in particular, as a vacuum chuck, which is configured to fix the workpiece (especially a wafer).In the illustrated embodiment, the holding unit 38 is arranged on a positioning unit 40, which is designed to position the holding unit 38 and the workpiece 36 mounted on it. The laser processing system 10 also includes a cleaning unit 42, which comprises a first cleaning element 50 with a first nozzle 44. The first nozzle is designed to provide a fluid jet onto the transparent window 48 during a cleaning process. The fluid jet removes dirt or liquid from the surface of the transparent window 48. This prevents deposits from accumulating on the surface of the transparent window 48, thus preventing a deterioration in laser processing quality over time.

[0037] Figure 2 schematically illustrates another embodiment of the laser processing system 10 according to the invention. Compared to the embodiment shown in Figure 1, the system 10 shown in Figure 2 has a cleaning unit 42 with a first cleaning element 50 and a second cleaning element 52. The first cleaning element 50 has a first nozzle 44, while the second cleaning element 52 has a second nozzle 46. The first nozzle 44 is designed to provide a jet of liquid onto the transparent window 48 during a cleaning process. In contrast, the second nozzle 46 is designed to provide a jet of gas onto the transparent window 48.This makes it possible to first clean the transparent window 48 with a cleaning agent (or with ultrapure water) when the positioning unit 40 is extended, and then immediately dry the transparent window 48 using the gas jet. This ensures a particularly efficient cleaning and drying process.

[0038] Figure 3 schematically depicts the cleaning unit 42 shown in Figure 2 during the cleaning process. After the laser processing process is complete, the positioning unit 40 can be moved out of the processing position (to the right in Figure 3) so that the processed workpiece can be removed from the holding unit (the workpiece and holding unit are not shown in Figure 3). As the positioning unit 40 moves out, the first cleaning element 50 of the cleaning unit 42 is guided under the transparent window 48. The transparent window 48 has a first side 48a (also referred to as the underside of the transparent window) facing the cleaning unit 42 and a second side 48b facing the laser beam source.Once the first cleaning element 50 is positioned below the transparent window 48, a liquid jet 54 is directed onto the transparent window 48 (or its underside 48a) by the first nozzle 44. The liquid jet 54 can consist of, in particular, ultrapure water or isopropanol. Subsequently, the second cleaning element 52 of the cleaning unit 42 is moved below the transparent window 48 by further extending the positioning unit 40. Once the second cleaning element 52 is positioned below the transparent window 48, a gas jet 56 is directed onto the transparent window 48 (or its underside 48a) by the second nozzle 46. The gas jet 56 can consist of, in particular, compressed air, nitrogen, or argon.By using the cleaning unit 42 with the two cleaning elements 50, 52, the liquid supplied by the first nozzle 44 can be removed promptly, thus preventing any residue from forming on the underside 48a of the transparent window 48. The cleaning unit shown in Fig. 3 enables particularly efficient and easy cleaning of the transparent window 48.

[0039] Figure 4 schematically illustrates another embodiment of the cleaning unit 42 according to the invention. In the embodiment shown here, the cleaning unit 42 has a first cleaning element 50, which is connected to the positioning unit 40 via a retaining arm 58. More precisely, the first cleaning element 50 is connected to a first side 40a (underside) of the positioning unit 40. The first cleaning element 50 is preferably designed to be pivotable relative to the positioning unit 40. The first cleaning element 50 is arranged such that an angle of incidence 60° (0) is not equal to zero between the jet axis 64 of the liquid jet 54 and the surface normal 62 of the transparent window 48. This ensures that the liquid supplied to the transparent window 48 by the first nozzle 44 does not reach the first nozzle 44 and settle there after the cleaning process.Consequently, the risk of contamination or clogging of the first nozzle 44 is significantly reduced. Initial investigations have shown that an angle of incidence of 15° < 0 < 55°, preferably 20° < 0 < 45°, and particularly preferably 25° < 0 < 35° can contribute to a significant reduction in the risk of contamination of the first nozzle 44. In some embodiments of the invention, the holding arm 58 may be provided with a motor unit designed to adjust the angle of incidence 60.

[0040] Figure 5 schematically illustrates another embodiment of the cleaning unit 42 according to the invention. As in the embodiment shown in Figure 4, the cleaning unit 42 shown in Figure 5 is also pivotably arranged relative to the positioning unit 40. Additionally, the embodiment shown in Figure 5 includes a protective device 66 comprising a wall element 68 located between the first nozzle 44 of the first cleaning element 50 and the holding unit 40. The wall element 68 can, for example, be ring-shaped. In the embodiment shown in Figure 5, the wall element 68 extends vertically. Alternatively, the wall element 68 can also be inclined relative to the vertical axis.The protective element 66 serves to protect the first nozzle 44 from the fluid located within the open process chamber above the positioning unit 40 during the laser processing process. In particular, when the positioning unit 40 is moved out of the processing position, the fluid supplied for laser processing can come into contact with the first nozzle 44 and contaminate it. The risk of such contamination and a resulting blockage of the first nozzle 44 can be significantly reduced by using the protective device 66 described above. (See reference numeral list.)

[0041] Laser processing system

[0042] Laser beam source

[0043] Laser radiation

[0044] Beam deflection unit

[0045] Focusing unit

[0046] Processing unit first side of the processing unit second side of the processing unit

[0047] chamber wall

[0048] Interior of the processing unit

[0049] Flow generator

[0050] fluid inlet channel

[0051] Liquid outlet channel

[0052] liquid

[0053] workpiece

[0054] Holding unit

[0055] Processing room

[0056] Positioning unit a first side of the positioning unit

[0057] Cleaning unit first nozzle second nozzle transparent window a first side of the transparent window b second side of the transparent window first cleaning element second cleaning element

[0058] liquid jet

[0059] gas jet

[0060] Support arm

[0061] angle of incidence

[0062] Surface normal of the transparent window 64 Beam axis

[0063] 66 Protective device

[0064] 68 Wandelement

Claims

Claims 1. Laser processing system (10) for laser processing of a workpiece (36), in particular for laser cutting of a workpiece (36), comprising: a laser beam source (12) for generating pulsed laser radiation (14); a focusing unit (18) for focusing the pulsed laser radiation (14) onto the workpiece (36) to be processed; a holding unit (38) designed to hold the workpiece (36) to be processed; a processing unit (20) arranged between the holding unit (38) and the laser beam source (12), the processing unit (20) comprising: a first side (22) with a first opening designed to allow the laser radiation (14) into the processing unit (20); a second side (24) arranged opposite the first side (22) with a second opening designed to allow the laser radiation (14) out of the processing unit (20);a chamber wall (26) surrounding an interior space (28) of the processing unit (20); and a transparent window (48); a flow generator (30) for generating a flow on a surface of the workpiece (36); a movable positioning unit (40) designed to accommodate the holding unit (38) and to adjust the position of the holding unit (38); and a cleaning unit (42) comprising at least one first nozzle (44), the nozzle being designed to provide a fluid jet on the transparent window (48).

2. Laser processing system (10) according to claim 1, characterized in that the cleaning unit (42) has a second nozzle (46), wherein the first nozzle (44) is designed to provide a liquid jet (54) on the transparent window (48); and the second nozzle (46) is designed to provide a gas jet (56) on the transparent window (48).

3. Laser treatment system (10) according to claim 1 or 2, characterized in that the cleaning unit (42) has a first supply line and a second supply line, wherein the first supply line is designed to supply the cleaning unit (42) with a liquid (35); and the second supply line is designed to supply the cleaning unit (42) with a gas.

4. Laser processing system (10) according to one of claims 1 to 3, characterized in that the first nozzle (44) and / or the second nozzle (46) is designed to provide a fluid jet (54, 56) on the transparent window (48) at an angle of incidence (60) 15° < 0 < 55°, preferably at 20° < 0 < 45°, and particularly preferably at 25° < 0 < 35°, wherein 0 describes the angle between the surface normal (62) of the transparent window (48) and the jet axis (64) of the fluid provided by the first (44) and / or second nozzle (46).

5. Laser processing system (10) according to one of claims 1 to 4, characterized in that the first nozzle (44) and / or the second nozzle (46) has a slotted cross-section.

6. Laser processing system (10) according to one of claims 1 to 5, characterized in that the cleaning unit (42) is arranged on or at the positioning unit (40).

7. Laser processing system (10) according to one of claims 1 to 6, characterized in that the cleaning unit (42) is arranged on a separate positioning unit, wherein the separate positioning unit is preferably designed as a positioning arm.

8. Laser processing system (10) according to one of claims 1 to 7, characterized by a protective device (66), wherein the protective device (66) has at least one wall element (68) which extends between the first nozzle (44) or the second nozzle (46) and the holder unit (38), wherein the wall element (68) is preferably formed substantially vertically.

9. Laser processing system (10) according to one of claims 1 to 8, characterized by a detection unit designed to evaluate light that propagates through the transparent window (48) or is reflected at the transparent window (48).

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