METHOD FOR PROCESSING A SUBSTRATE AND OPTICAL DEVICE

Description

BE2025 / 5079 -2- and a lower face, the process comprising the supply of a substrate, a laser source and a spherical aberration compensation plate, the activation of the laser source to emit a laser beam in the direction of the upper face of the substrate to be treated, the compensation plate being interposed between the laser source and the upper face of the substrate to be treated, the treatment of the substrate by focusing the laser beam in the thickness of the substrate and then by focusing the laser beam in the direction of the upper face. According to one variant, the treatment of the substrate is by focusing the beam through the thickness at a point on the lower face of the substrate and then by focusing the laser beam towards the upper face.10 According to another variant, the treatment of the substrate is carried out on a part of the thickness or especially the entire thickness of the substrate between the lower and upper faces of the substrate.According to one variant, the process also includes the provision of one or more converging lenses, the lens(es) being between the compensation plate and the upper surface of the substrate to be treated. According to another variant, the compensation plate is chosen according to the wavelength of the laser beam. According to another variant, the laser source emits the laser beam with a wavelength between 350 and 2200 nm. According to another variant, the laser source is ultra-short pulsed, preferably with a pulse duration of 10 fs to 10 ps. According to another variant, the pulses of the laser source are high-power, preferably with a power greater than 2 W, preferably even greater than 20 W. According to another variant, the repetition rate of the laser beam is between 1 and 5 GHz. According to one variant, the substrate is a translucent or even transparent material, preferably a polymer or glass. According to another variant, the substrate has a thickness between the lower and upper faces of between 50µm and 15mm.2025 / 5079 BE2025 / 5079 -3- According to one variant, the treatment consists of machining, ablation, engraving, cutting, drilling, structuring, marking or internal marking of the substrate / or welding of two substrates together, a TGV treatment. According to one variant, the focal point of the laser beam is controlled by imposing a burst mode on said laser source so as to generate a laser beam comprising a pulse train comprising sets of laser pulses, the sets of pulses being repeated in time. The invention also relates to an optical device for implementing the process as described above.10 According to one variant, the device comprises a laser source and a spherical aberration compensation plate, the laser source being capable of emitting a laser beam in the direction of the upper surface of a substrate, through the spherical aberration compensation plate.According to one variant, the device is capable of focusing the laser beam into the thickness of the substrate, for example at a point on a lower surface of the substrate, and then capable of focusing the laser beam towards the upper surface. The use, in this document, of the verb "comprendre" (to understand), its variants, as well as its conjugations, cannot in any way exclude the presence of elements other than those mentioned. The use, in this document, of the indefinite article "un" (a), "une" (an), or the definite article "le" (the), "la" (the), or "l'" (an) to introduce an element does not exclude the presence of a plurality of these elements. The terms "first", "second", "third", etc., are used in this document exclusively to differentiate between different elements, without implying any order between these elements. All the preferred embodiments and all the advantages of the processing method according to the invention are transferred mutatis mutandis to the present optical device. The different embodiments can be considered individually or in combination.2025 / 5079 BE2025 / 5079 -4- Brief description of the figures Other features and advantages of the present invention will become apparent from the reading of the detailed description which follows, for the understanding of which reference should be made to the attached figures which show: - Figure 1, a schematic view of an example of an optical device; - Figure 2, a schematic view of the treatment of a substrate; - Figure 3, a schematic view of the elongation of the focal points of the laser beam; - Figure 4, a schematic view of the stabilization of the focal point of the laser beam with the process of the invention; - Figure 5, a comparison of the effect of increasing the power on the treatment of the substrate according to the application of the process of the invention or without; -Figure 6, a comparison of the ablation depth as a function of the number of laser passes according to the application of the process of the invention or without.15 The drawings of the figures are not to scale. Similar elements are generally denoted by similar reference numerals in the figures.Within the framework of this document, identical or analogous elements may bear the same references. Furthermore, the presence of numbers or letters of reference to the drawings cannot be considered as limiting, including when these numbers or letters are indicated in the claims. Detailed description of embodiments of the invention: The invention relates to a method for treating a substrate with a laser beam emitted by a laser source, the substrate having an upper and a lower face. The method comprises the provision of a substrate, a laser source, and a spherical aberration compensation plate. The laser source is activated to emit a laser beam in the direction of the upper face of the substrate to be treated, the compensation plate being interposed between the laser source and the upper face of the substrate to be treated. The substrate is treated by focusing the laser beam into the thickness of the substrate and then by focusing the laser beam in the direction of the upper face.This allows for precise processing of the substrate and therefore a higher quality treatment. Figure 1 shows a schematic view of an example of an optical device 10 enabling the implementation of the substrate processing method. More particularly, the device 10 is an example of an optical device for processing 5 of the substrate 16. By processing, we mean any type of action on the substrate, such as machining, ablation, engraving, cutting, drilling, structuring, marking or internal marking of the substrate or even welding two substrates together. Also, the invention makes it possible to implement a TGV treatment (for "Through Glass Via" or drilling through glass). The substrate 16 may be a translucent, transparent material. It may be a glass or polymer substrate. The substrate 16 has a lower face 161 and an upper face 162. Between the two faces 161, 162, the substrate has a thickness 163. The thickness 163 is, for example, greater than 300µm. The thickness 163 may be up to 15mm (or more).The device 10 may include a laser source 12 that emits a laser beam 14. The laser source may be ultrashort pulsed, preferably with a pulse duration of 10 fs (10 x 10⁻¹⁵ s) to 15 ps (15 x 10⁻¹² s). The device 10 may include an optical path 18 that shapes the laser beam 14. The optical path 18 may include various optical elements, for example, at least one mirror, one or more lenses, a beam expander / collimator, an attenuator, a polarizer, etc. The optical path 18 may direct the laser beam 14 along its principal propagation direction (optical axis 30) towards a scanner head 20. The scanner head 20 may include, for example, mirrors 25. tiltable, an ocular lens. It may be a galvanometric scanner head. After scanning, the laser beam 14 may pass through one or more focusing lenses 26. The focusing lens 26 allows the laser beam 14 to be focused at a focal point in or on the substrate 16 to ensure its processing.The laser beam 14 is then directed towards the substrate 16.30 More specifically, the laser beam 14 is directed towards the upper face 162. The upper face 162 is turned towards the scanner head 20 and the focusing lens 26. The lower face 161 is turned away from the scanner head 20 and the focusing lens 26. The upper face 162 is the first of the two faces 161, 162 reached by the laser beam 14. The optical device 10 also includes at least one compensation plate 24. We will refer to one plate hereafter, but the invention also applies to several plates 24. The plate 24 is interposed between the laser source 12 and the upper face 162 of the substrate 16. More specifically, the laser beam 14 passes through the plate 24 before reaching the upper face 162 of the substrate 16. More specifically still, before passing through the scanner head 20, the laser beam 14 passes through the compensation plate 24 and then, at the exit of the scanner head 20, the beam passes through the focusing lens 26 before reaching the upper face 162 of the substrate 16.The compensating plate 24 is positioned along the laser beam at a location where the laser is collimated. It is also possible to position the plate 24 downstream of the focusing lens 26. The upper face 15 162 is facing the arrival of the beam (the lower face 161 being opposite the arrival of the beam). According to Figure 1, the compensating plate 24 is upstream of the scanner head 20. The compensating plate 24 is a blade with a pre-established compensating structure. Once the laser source 12 is activated, the laser beam is emitted and propagates 20 towards the upper face 162 of the substrate 16, the compensating plate 24 being interposed between the laser source 12 and the upper face 162 of the substrate to be treated. The substrate 16 is treated by focusing the laser beam 14 into the thickness of the substrate. In other words, the laser beam 14 penetrates the substrate 16 through the upper face 162 and is focused at a certain height within the thickness. 25 The waist of the laser beam is not external to the substrate.The treatment of the substrate 16 is then continued by focusing the laser beam towards the upper surface 162 of the substrate. The focusing occurs progressively as it moves upwards through the thickness of the substrate. The treatment is carried out by progressive focusing from a height within the thickness, in the direction 30 of the upper surface. The treatment is performed in successive layers within the thickness, in the direction of the upper surface. The advantage is that the laser beam focuses at points in the thickness where focusing has not yet occurred, unlike focusing that would occur while moving downwards through the substrate. This allows for precise treatment of the substrate and therefore a higher quality treatment. In particular, the focusing of the laser beam in the thickness of the substrate 5 can take place on the lower face 161 before taking place in the direction of the upper surface.In other words, the treatment of substrate 16 is by focusing the laser beam within the thickness of substrate 16 at a point on the lower face, and then by focusing the laser beam towards the upper face. This is visible in Figure 2, which shows a schematic view of substrate treatment, in a particular example where the laser beam 14 is focused at the bottom of the thickness, namely, on the lower face 161. The Z-axis shows the propagation direction of the laser beam 14. On the right-hand side, the laser beam 14 passes through the compensating plate 24; the focusing lens 26 is reached by the substrate 16 via the upper face 162. The laser beam 14 is first focused at a point 15 point of the lower face 161. The treatment in thickness begins from the lower face 161, opposite the upper face 162 through which the laser beam 14 reaches the substrate 16. In other words, the substrate is treated from below. The debris (or particles or debris particles) from the treatment of the substrate are ejected by gravity.This prevents debris from falling back down onto the substrate 20 by gravity (which would be the case if the treatment started on the upper surface 162). This avoids damaging the substrate treatment. Furthermore, treatment on the lower surface 161 also reduces, or even eliminates, the corresponding "feather" effect. During laser beam treatment of a substrate, a plasma feather forms. This plasma contains electrons, atoms, and ions from the evaporated substrate 25. During the laser pulse, this feather risks absorbing a large part of the laser beam's energy 14, thus reducing the amount of laser radiation reaching the substrate. Thanks to the focusing of the laser beam on the lower surface 161 of the substrate, through the substrate, and therefore through the face opposite to the direction of propagation of the laser beam, the consequences of the feather effect are reduced. The 30 treatment of the substrate 16 is then continued by focusing the laser beam 2025 / 5079 BE2025 / 5079 -8- in the direction of the upper face 162 of the substrate, going upwards.In other words, the point in the thickness of the substrate where the focusing of the laser beam14 begins is on the lower surface161, through the substrate, then the focusing takes place at points in the substrate, approaching the upper surface162. This is a bottom-up treatment of the substrate, or rather, a treatment from the lower face to the upper face. This is a "bottom-up" treatment. This avoids hindering the laser's treatment of the substrate due to breaks and the feathering effect. The substrate treatment is more precise and of better quality. Thus, on the right side of Figure 2, the laser beam first treats the lower face of the substrate, which is opposite the upper face of the substrate, through which the laser beam will reach the substrate. Then, the treatment is carried out progressively towards the upper face. The treatment is carried out progressively, moving upwards towards the upper face. is done by progressive focusing from the lower face, towards the upper face.The treatment is carried out in successive layers, from the lower surface 15 towards the upper face. The treatment is from bottom to top. Furthermore, the interposition of the compensating plate 24 allows for better control of the laser beam's focal point. The plate allows for better control of the substrate treatment, and therefore results in higher-quality substrate treatment. The plate 24 further improves the substrate treatment carried out 20 towards the upper surface, particularly from the lower surface. The left part of Figure 2 and Figure 3 show the treatment process without the compensating plate 24, and the right part of Figure 2 and Figure 4 show the treatment process with the compensating plate 24 (from a point on the lower surface). In Figure 2, two beams are given as examples. In 25, the plate 24 is upstream of the lens 26, without representation of the scanner head 20. According to the left part of figure 2, focusing through the focusing lens 26 introduces spherical aberrations.The rays closest to the optical axis 30 of the laser beam 14 focus on a focal point 3230, while the rays furthest from the optical axis 30 focus on a focal point 34 different from point 32. Thus, each ray focuses on a point (32 and 34 as examples), the set of focal points of all the rays extending along the Z-axis. Figure 3 shows the set of focal points of the laser beam, corresponding to the left part of Figure 2. The focal points are shown at three different depths. The depth increases from left to right. Not only does the extension of the focal points (32 and 34 for example) generate a focusing filament 35 but in addition, the filament 35 stretches over a greater length as the depth increases. The deeper the desired laser beam focusing is in the substrate, the further apart the focal points become and the longer the filament 35 becomes.10 Also, the deeper the desired focus is in the substrate, the lower the energy-per-pulse density. According to the left part of Figure 2 and Figure 3, there are no sufficient controls of the energy-per-pulse at depth. The treatment of a substrate from base to top is therefore not controlled, which leads to poor quality treatment.15 Thanks to the invention, according to the right-hand part of Figure 2, focusing through the focusing lens 26 introduces a spherical aberration, which is compensated by the compensating plate 24. The rays (whether they are close to or far from the optical axis 30 of the laser beam 14) focus (approximately) on the same focal point 36. Figure 4 shows the stabilization of the focal point 20 36 of the laser beam, corresponding to the right-hand part of Figure 2. The focal point 36 is shown at three different depths. The depth increases from left to right. The formation of a focusing filament 37 is not completely avoided. However, the filament 37 is stretched over a shorter length in Figure 4 than in Figure 3.The compensation plate 24 of 25 introduces a spherical aberration in the opposite direction to the spherical aberration introduced by the focusing lens 26. The invention allows focusing at different depths during the process, while keeping a filament 37 (if necessary) of the same length (but reduced) from one depth to another. Thus, whatever the desired depth of focusing in the substrate, the focal point is constant. Also, whatever the desired depth of focusing in the substrate, the pulse energy density is stable. According to the invention of the right-hand side of Figure 2 and Figure 4, there is control of the pulse energy with depth. The treatment of a substrate from the base to the top is therefore controlled, which leads to a good quality treatment. Thanks to the invention, it is possible to perform a treatment by working upwards through the thickness, while reducing and controlling the elongation of the focal point regardless of the treatment depth in the substrate.In particular, it is possible to perform bottom-to-top treatment of the substrate (from the lower face 161 to the upper face 162), with debris removal by gravity and reduction of the feathering effect, while reducing and controlling the elongation of the focal point 10 regardless of the treatment depth in the substrate. The substrate treatment is of better quality. Moreover, when a translucent (or even transparent) substrate is treated, the substrate itself introduces additional spherical aberrations. The compensating plate 24 compensates for these additional spherical aberrations. The compensating plate 24 is determined according to the focusing lens 26 and the substrate to be treated. This accentuates the advantages described in connection with the invention. Furthermore, the 24-compensation plate allows for quality treatment while simplifying the focusing of the optical device. Indeed, the 20-24-compensation plate allows the laser beam wavefront to be fixed, which facilitates the adjustment of the optical device.The interposition of the plate 24 is made along the optical axis 30 of the laser beam, without adjusting the angle of incidence. This facilitates the adjustment of the focal point. Also, the use of the compensating plate 24 reduces the cost of substrate treatment, as a compensating plate 25 is inexpensive. The pulses from the laser source can be high-power, preferably with a power greater than 2W, and even more preferably with a power greater than 20W. A power of 100W, 300W, or even 500W can be applied. Figure 5 shows the effect of increasing the power 30 on the substrate treatment according to the application of the method of the invention or without. 2025 / 5079 BE2025 / 5079 -11- The two parts are a top view of the substrate, along the direction Z perpendicular to the upper face 162 of the substrate. The upper part of figure 5 shows the substrate 16 treated without the compensation plate 24. The lower part of figure 5 shows the substrate 16 treated with the compensation plate 24, according to the method of the invention.For a desired focusing depth, the pulse power 5 is increased from P1 to P4. The substrate begins to be damaged on its upper surface 162 from power P2 in the absence of a compensating plate 24, while the substrate begins to be damaged on its upper surface 162 from power P4, which is higher than P2. For example, the power P1 can be approximately 28W, P2 approximately 29W, P3 approximately 30W, and P4 approximately 31W. The damage threshold power is increased according to the method of the invention. With the method, the stresses in the substrates are reduced, which allows the substrate to be treated with higher powers. Thus, with a fixed power, the method makes it possible to increase The thickness of the substrate to be treated. Furthermore, the optical device 10 is more resistant to high powers because the compensating plate 24 offers greater power resistance. The plate 24 is a simple, untreated blade, therefore more resistant to high powers. The laser beam repetition rate remains between 1 and 20 GHz.Within the context of this document, the "repetition rate" of a pulsed laser beam is the number of laser beam pulses per unit of time. The laser source 12 is capable of generating the laser beam in burst mode or in single-pulse mode. Burst mode can be characterized by a pulse train comprising sets of laser pulses. The sets of pulses are separated from each other by a time interval. As an example 25, the time interval can be between 100 ns and 1 ms, preferably between 500 ns and 20 µs. The choice may depend on the material being treated; the greater the material's sensitivity to heat, the larger the interval. The laser source can be configured in burst mode. Burst mode allows for the delivery of a high energy dose. The same energy dose is delivered in burst mode 30 as with a single-pulse mode, but distributed over several pulses. 2025 / 5079 BE2025 / 5079 -12- moderafale allows energy to be used more efficiently than with a single pulse.The substrate treatment can be carried out on part of the thickness (in particular from the lower face 161) of the substrate. Alternatively, the substrate treatment can be carried out over the entire thickness (from the lower face 5 161) of the substrate. This allows for internal marking and / or engraving or structuring of the lower face 161 or machining from part to part of the substrate. The substrate16 has, for example, a thickness between the lower and upper faces of 50µm, greater than or equal to 100µm, or even greater than or equal to 300µm, for example 700µm. The thickness can be less than or equal to 5mm, or less than or equal to 10mm, or even less than or equal to 15mm. These values ​​are indicative; the substrate can be even thinner or thicker. The compensation plate 24 is chosen according to the wavelength 15 of the laser beam. More specifically, the compensation plate 24 is chosen according to the wavelength at the wavefront of the laser beam. The laser source 12 can emit the laser beam 14 with a wavelength between 340-2200nm.The wavelength used can be on the order of the visible spectrum, between 340 nm and 780 nm. Advantageously, the wavelengths are 343, 355, 515, and 532 nm. The advantage of these wavelengths on the order of the visible spectrum is that substrate processing is faster. In particular, with a wavelength of 515 nm, a pulse duration between 10 fs and 15 ps, and a repetition rate of 1 to 15 GHz, it is possible to perform processing (such as, but not limited to, hole processing) through a substrate between 300 µm and 15 mm rapidly, on the order of a few minutes, or even a few seconds, or even a few tens of milliseconds. A wavelength of 1.030 nm and 1.064 nm is also advantageous, with the same benefits. For example, in a basic treatment at the top of a substrate in the form of a 700µm thick boroflaot® plate, l.

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