Laser processing method and device combining dynamic oscillation micro-scanning and frost layer assistance

Abstract

A laser processing method combining dynamic oscillation micro-scanning and frost layer assistance comprises the steps that a to-be-processed sample is lowered to be below the freezing point, and it is ensured that a frost layer is formed on the surface of the to-be-processed sample; focusing a laser beam on the surface of the processed sample on which the frosted layer is formed; enabling the focused micro focal spots to carry out small-range high-speed oscillation scanning around a central point by utilizing a scanning device; the sample is driven to move through the motion platform, the laser is made to conduct direct writing and scribing on the surface of the sample according to a preset track, and a synchronous composite scanning strategy is formed through laser focus high-speed scanning and motion platform low-speed direct writing. Heat concentration is reduced through high-speed oscillation of focusing light spots, generation of a recast layer and adhesion of surface scraps are restrained through a frost layer, the efficiency and quality of microgroove milling and precise cutting machining are improved, the device is suitable for precise cutting and slotting machining of hard and brittle materials, and the machining efficiency and quality are improved. And the section shape of the microgroove is regulated and controlled by changing the proportion of the laser irradiation time in different areas in the dynamic oscillation scanning path.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser processing, and specifically relates to a laser processing method and device combining dynamic oscillation micro-scanning and frost layer assistance, which is suitable for precision milling and precision cutting of micro-grooves on the surfaces of various brittle and hard materials. Background Art

[0002] Ultrafast lasers, with their extremely short pulse width and high peak power, can directly ionize the material in the laser irradiated area, achieve precise removal or modification of the material on a microscopic scale, and achieve the effect of "cold processing" without thermal melting, greatly reducing the thermal effect of the laser. However, when the laser works at a high repetition frequency or high power mode, although its processing efficiency is improved, the problem of heat accumulation also becomes prominent. Heat accumulation will not only lead to the formation of microcracks, the appearance of recast layers, and the accumulation of debris, but will also seriously affect the processing efficiency and the quality of the finished product.

[0003] In order to deal with the problem of heat accumulation in high repetition frequency or high power laser processing, there are usually two solutions. The first strategy is to optimize the laser scanning method and achieve uniform energy dispersion through high-speed scanning, thereby alleviating the heat accumulation phenomenon. The research on scanning strategies has also begun to receive great attention in recent years. Studies have found that changes in the scanning path will have a very large impact on laser energy deposition, heat transfer, and thermal stress and strain distribution, thereby significantly affecting the processing quality and processing efficiency. Wlodarczyk et al. significantly improved the laser processing quality of glass by changing the scanning strategy from "sequential processing" to "interlaced processing" (Journal of Materials Processing Technology, 2020, 285: 116807.). However, conventional laser scanning methods are limited by the large spot area caused by the focusing of long focal length lenses, which limits the processing accuracy. In addition, a large amount of molten debris generated during rapid scanning is easy to adhere to the surface of the material, increasing the difficulty of subsequent cleaning.

[0004] The second strategy is to absorb the heat generated during laser processing through some auxiliary cooling methods. For example, the method of immersion water jet assisted laser processing can be used to process micropores with small heat-affected zones and no recast layer on metal workpieces, and effectively reduce the taper angle of the micropores. Using water-assisted femtosecond laser ablation technology, high-precision and smooth SiC ceramic microgrooves can be obtained under low pulse energy, low repetition rate and low scanning speed conditions (Journal of Materials Processing Technology, 2018, 262: 290-298.). Thanks to the convection, explosive evaporation and bubble movement of water induced by laser, water-assisted laser ablation can effectively reduce the debris and recast layer during laser ablation, thereby obtaining a high-precision processing effect. However, the liquid-assisted cooling strategy also faces challenges: the incident laser is easily affected by deflection and scattering when passing through liquid, cavitation bubbles and suspended ablation debris, resulting in a decrease in processing accuracy. More importantly, these methods are still difficult to completely eliminate the problem of heat accumulation under extreme processing conditions of high repetition rate and high power.

[0005] Although existing strategies have alleviated the problem of heat accumulation in ultrafast laser processing to a certain extent, there are still technical difficulties that cannot be ignored in terms of processing accuracy, debris handling and laser beam stability. Although frost-assisted processing has attracted widespread attention because it can effectively reduce the temperature of the processing area and reduce thermal effects, how to combine frost-assisted with efficient laser scanning strategies to achieve high-quality micro-nano processing is still a hot topic and difficulty in current research. Summary of the invention

[0006] In order to solve the deficiencies of the prior art, the present invention provides a laser processing method and device that combines dynamic oscillation micro-scanning and frost layer assistance. While the high-speed scanning system allows the tightly focused laser to oscillate and scan at high speed, the semiconductor refrigeration module with refrigeration function can drive the sample to be processed to move along a predetermined trajectory. The tightly focused femtosecond laser is used to perform dynamic oscillation writing on the surface of the material covered with frost layer. The melted frost layer can absorb the laser heat to achieve high-precision and high-quality laser processing. At the same time, the unmelted frost layer on the surface of the material can protect the unprocessed area to prevent debris from adhering.

[0007] To achieve the above purpose, the technical solution of the present invention is as follows:

[0008] First, the present invention provides a laser time shaping method based on galvanometer oscillation scanning, which is characterized by comprising:

[0009] The high-speed scanning system includes but is not limited to a high-speed scanning galvanometer, a high-speed scanning rotating mirror, and a high-speed acousto-optic scanning device. Lenses or reflectors can be added as needed to adjust the optical path for practical application.

[0010] The microscopic imaging system usually includes a CMOS camera, a tube lens, and an objective lens, and can realize real-time observation of processing.

[0011] Second, the present invention provides a frosting control method based on a semiconductor refrigeration module, which is characterized in that the semiconductor refrigeration module is usually composed of multiple semiconductor thermoelectric coolers, which can achieve precise control of the thickness of the frost layer on the surface of the material.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1) Through the combination of frost layer assistance and dynamic oscillation micro-scanning, the temperature of the processing area is effectively reduced, the heat affected zone is reduced, and the processing accuracy and surface quality are improved.

[0014] 2) Through the closed-loop temperature control strategy, the thickness of the frost layer can be accurately adjusted to meet different processing requirements.

[0015] 3) The precise processing of complex patterns or structures is achieved through the synchronous composite scanning strategy of high-speed scanning of the laser focus and slow direct writing of the motion platform.

[0016] 4) By changing the proportion of laser irradiation time in different areas of the dynamic oscillation micro-scanning path, the cross-sectional shape of the micro-groove can be regulated, thereby improving the processing flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic diagram of a laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to the present invention;

[0018] Figure 2 It is a laser processing device combining dynamic oscillation micro-scanning and frost layer assistance adopted in an embodiment of the present invention;

[0019] In the figure: 1. Laser; 2. Laser beam; 3. Beam expansion collimator; 4. Half wave plate; 5. Polarization beam splitter; 6. Quarter wave plate; 7. First reflector; 8. Scanning galvanometer; 9. 4f system; 10. Second reflector; 11. CMOS camera; 12. Tube lens; 13. Dichroic mirror; 14. Microscope objective; 15. Processing sample; 16. Semiconductor refrigeration module; 17. Displacement platform.

[0020] Figure 3 This is an embodiment diagram of the present invention combining dynamic oscillation micro-scanning and frost layer assistance, in which: (a) a sample without frost layer assistance processing; (b) a sample with frost layer assistance processing.

[0021] Figure 4This is a diagram of an implementation example of the dynamic oscillation scanning path used in the present invention, in which: (a) the middle area is a vertical scanning path, and the areas on both sides are cross scanning paths; (b) a bow-shaped scanning path.

[0022] Figure 5 It is a schematic diagram of the dynamic oscillation scanning processing results adopted by the present invention, in which: (a) the middle area is the processing result of the vertical scanning path, and the areas on both sides are the processing result of the cross scanning path; (b) the processing result of the bow-shaped scanning path. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. The technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0024] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods without specific conditions in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0025] Unless otherwise specified, the reagents and raw materials used in the examples and comparative examples of the present invention can be obtained through commercial channels.

[0026] A laser processing method combining dynamic oscillation micro-scanning and frost layer assistance, the method comprising the following steps:

[0027] (1) Use semiconductor refrigeration module to cool the sample to be processed to below freezing point, so that a uniform and stable frost layer forms on the sample surface. This provides a protective layer during the processing and reduces the thermal impact caused by direct contact between the laser and the material.

[0028] (2) The laser beam is focused on the sample surface with a high numerical aperture objective lens, and a scanning galvanometer or other beam scanning device is used to make the micro-focus spot perform a small-range high-speed oscillation scan around the center point. Through high-speed oscillation scanning, the uniform distribution of laser energy is achieved, avoiding the degradation of processing quality caused by excessive energy concentration.

[0029] (3) The motion platform drives the sample to be processed so that the laser directly writes and scribes the sample surface along a predetermined trajectory.

[0030] In addition, the present invention also adopts a closed-loop temperature control strategy to accurately adjust the thickness of the frost layer on the surface of the processed material to meet different processing requirements.

[0031] Build a laser processing device combining dynamic oscillation micro-scanning and frost layer assistance, such as Figure 2 As shown, it includes: a laser for emitting ultrafast laser pulses, a beam expansion collimator for expanding and collimating the laser beam, a half wave plate and a polarization beam splitter prism for adjusting the laser energy, a quarter wave plate for adjusting the polarization direction of the laser, a scanning galvanometer for beam oscillation scanning, a 4f system for adjusting the spot size to match the entrance pupil of the microscope objective, a second reflector and a dichroic mirror for fine-tuning the laser beam so that the laser beam is vertically injected into the microscope objective, a microscope objective for focusing the laser, a CMOS camera and a tube lens for real-time imaging observation, a semiconductor refrigeration module for cooling and frosting, and a displacement platform for adjusting the sample position to move the laser focus relative to the sample. Among them, the number of reflectors can be increased or the reflector angle can be adjusted according to the needs, and the optical path can be adjusted to facilitate practical application. During operation, the laser beam 2 emitted by the laser 1 is collimated by the beam expander collimator 3 and then the laser beam power is adjusted by the power regulation system composed of the half wave plate 4 and the polarization beam splitter prism 5. The laser polarization direction is then adjusted by the quarter wave plate 6. The laser oscillation scanning is controlled by the scanning galvanometer 8. The spot size is then adjusted by the 4f system 9. Finally, the laser is focused by the microscope objective 14.

[0032] Example 1

[0033] A femtosecond laser with a central wavelength of 1030nm, a pulse width of 300fs, a maximum power of 10W, and a repetition rate of 50-1000kHz was used. The experimental material was a single-sided polished single crystal silicon wafer (20mm×20mm×0.5mm).

[0034] The single crystal silicon wafer is cleaned to remove pollutants and impurities on the surface. The cleaned single crystal silicon wafer is placed on the semiconductor refrigeration module.

[0035] To compare the effects of different oscillation scanning paths on the cross-sectional shape, other processing parameters were kept unchanged: laser power 3.6W, repetition frequency 50kHz, focal spot diameter 6.6μm, platform movement speed 0.2mm / s, galvanometer scanning speed 600mm / s, and only the dynamic oscillation scanning path was changed to compare the effects of different scanning paths on the cross-sectional shape. The scanning path is as follows Figure 3 shown.

[0036] The first scanning path: the middle area is vertical scanning (line spacing 2μm), and the two side areas are cross scanning (line spacing 0.1μm), such as Figure 3(a) This scanning method uses different scanning densities in the middle area and the two side areas, resulting in changes in the spatial distribution of laser pulses.

[0037] The second scanning path: all vertical scanning (line spacing 1.5μm), such as Figure 3 (b) This scanning method uses a uniform scanning density throughout the rectangular area.

[0038] The third scanning path: a scanning path composed of ellipses of different sizes (overall length 150μm, width 30μm), the scanning direction is from inside to outside, such as Figure 3 (c) This scanning method can increase the cutting efficiency in the middle area and improve the processing depth. On the other hand, it can reduce the laser's residence time in the edge area and reduce thermal damage to the material.

[0039] like Figure 4 As shown, the cross-sectional shapes corresponding to the two oscillation scanning paths are completely different:

[0040] The cross-sectional shape produced by the first scanning path is a conventional V-shaped cross-section. This is because uniform vertical scanning is used in the entire rectangular area, and the laser energy is evenly distributed inside the material, forming a typical V-shaped cross-section.

[0041] The cross-sectional shape produced by the second scanning path is a U-shaped cross-sectional shape with a flat bottom. Due to the combination of vertical scanning in the middle area and cross scanning in the two side areas, the laser energy is more concentrated in the bottom area, thus forming a flat bottom.

[0042] The cross-sectional shape produced by the third scanning path is a deeper V-shaped cross-section. Since this scanning path improves the efficiency of chip removal, a higher processing depth can be obtained.

[0043] Therefore, by changing the proportion of irradiation time of the oscillation scanning path at different positions, the spatial distribution of the laser pulse can be changed, thereby achieving the regulation of the cross-sectional shape of the microgroove.

[0044] Example 2

[0045] Based on Example 1, the processing effect can be optimized by adjusting the thickness of the frost layer.

[0046] A femtosecond laser with a central wavelength of 1030nm, a pulse width of 300fs, a maximum power of 10W, and a repetition rate of 50-1000kHz was used. The experimental material was a single-sided polished single crystal silicon wafer (20mm×20mm×0.5mm).

[0047] The single crystal silicon wafer is cleaned to remove pollutants and impurities on the surface. The cleaned single crystal silicon wafer is placed on the semiconductor refrigeration module.

[0048] In order to compare the influence of frost layer thickness on processing quality, the same laser processing parameters are used, which are as follows: laser power 3.4W, repetition frequency 300kHz, focal spot diameter 8μm, platform movement speed 1mm / s, galvanometer scanning speed 600mm / s, and the scanning path is the third scanning path described in Example 1.

[0049] The three processing methods are:

[0050] 1) Frost-free oscillation scanning processing: In this processing method, there is no frost layer on the surface of the silicon wafer, and the laser beam acts directly on the surface of the material. Due to the lack of cooling effect of the frost layer, the heat generated by the laser may be more easily diffused inside the material, resulting in increased thermal damage.

[0051] 2) Thin frost layer assisted oscillation scanning processing: In this processing method, the surface of the silicon wafer is covered with a uniform frost layer with a thickness of less than 20μm. When the laser is focused on the surface of the silicon wafer, the frost layer can quickly melt to form a water film, absorbing most of the heat, reducing the heat accumulation between the laser and the silicon wafer, thereby reducing thermal damage. At the same time, the presence of the frost layer also helps to reduce surface debris generated during the processing process.

[0052] 3) Thick frost layer assisted oscillation scanning processing: In this processing method, the surface of the silicon wafer is covered with a uniform frost layer with a thickness greater than 50μm. When the laser is focused on the surface of the silicon wafer, the frost layer melts slowly and easily blocks the propagation of the laser beam, resulting in rough groove edges and poor processing quality.

[0053] Processing results such as Figure 5 As shown in the figure, the silicon wafer surface processed by frost layer assisted oscillation scanning with appropriate thickness shows lower thermal damage and less surface debris. This result verifies the effectiveness of frost layer assisted processing in improving processing quality. Frost layer assisted oscillation scanning processing can reduce laser thermal damage and reduce surface debris in the processing area.

[0054] It should be pointed out that the above embodiments are intended to facilitate understanding of the technical solutions of the present invention rather than to limit them; any modification, equivalent substitution and improvement of the present invention are within the protection scope of the present invention.

Claims

1. A laser processing method combining dynamic oscillation micro-scanning and frost layer assistance, characterized in that: include: Step 1. Lower the sample to be processed to below the freezing point to ensure that a uniform frost layer is formed on the surface of the sample to be processed; Step 2. Focusing the laser beam on the surface of the processed sample with a frost layer formed; Step 3. Using a scanning device, the focused micro-focus spot performs a small-range high-speed oscillation scan around the center point; Step 4. The sample is moved by the motion platform so that the laser performs direct writing and engraving on the sample surface along a predetermined trajectory, wherein the high-speed scanning of the laser focus and the slow direct writing of the motion platform form a synchronous composite scanning strategy.

2. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1, characterized in that: Before step 2., the method also includes emitting ultrafast laser pulses using a laser, expanding and collimating the ultrafast laser pulses using a beam expansion and collimation system, and adjusting the power of the laser beam using a power regulation system.

3. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1 or 2, characterized in that: It also includes the use of closed-loop temperature control to adjust the thickness of the frost layer on the sample surface according to processing requirements.

4. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1 or 3, characterized in that: The thickness of the frost layer is within the range of 0.5-100 microns, and the diameter of the focus spot is within the range of 0.5-10 microns.

5. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1, characterized in that: A synchronous composite scanning strategy of high-speed scanning of the laser focus and slow direct writing of the moving platform is adopted: while the moving platform realizes the predetermined trajectory engraving, the laser focus continuously oscillates and scans under the control of the high-speed scanning device to prevent the laser energy from being too concentrated and affecting the processing quality.

6. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1, characterized in that: By changing the proportion of laser irradiation time in different areas of the dynamic oscillation micro-scanning path, the cross-sectional shape of the microgroove can be controlled.

7. The laser processing method combining dynamic oscillation micro-scanning and frost layer assistance according to claim 1, characterized in that: The scanning path includes a concentric circle path, an arc-shaped path, a curved path or a complex path formed by combining multiple simple paths, wherein the scanning times and scanning speeds of each path formed by combining multiple simple paths may be different.

8. A laser processing device combining dynamic oscillation micro-scanning and frost layer assistance for implementing the method according to any one of claims 1 to 7, characterized in that: include: A laser emitting device configured to emit an ultrafast laser beam, and to expand, collimate and power-regulate the laser beam to form a focused laser beam; A scanning device, used to control the laser beam to oscillate and scan the sample surface at high speed; The motion platform is used to drive the sample to move so that the laser beam can scratch the sample surface along a predetermined trajectory; Semiconductor refrigeration module, used to cool the processed material, so as to form a uniform frost layer on the surface of the material; Coaxial imaging equipment for real-time monitoring of processing status; and, The control unit is used to control the above-mentioned devices to work in coordination.

9. The laser processing device combining dynamic oscillation micro-scanning and frost layer assistance according to claim 8, characterized in that: The laser emitting device comprises a laser, and a beam expander collimator, a half-wave plate, a polarization beam splitter, a quarter-wave plate, a first reflector, a scanning galvanometer, a 4f system, a second reflector, a dichroic mirror and a microscope objective lens which are sequentially arranged along the laser output direction of the laser. The incident laser is time-shaped to form an oscillating scanning beam, and is focused onto the sample surface through the microscope objective lens.

10. The laser processing device combining dynamic oscillation micro-scanning and frost layer assistance according to claim 8, characterized in that: The coaxial imaging device includes a CMOS camera and a tube lens, and is used to image the processing area to monitor the processing effect in real time.

11. The laser processing device combining dynamic oscillation micro-scanning and frost layer assistance according to claim 8, characterized in that: It also includes ultrasonic cleaning equipment for cleaning the processed materials after processing.

12. The laser processing device combining dynamic oscillation micro-scanning and frost layer assistance according to claim 8, characterized in that: It also includes a closed-loop temperature control system to adjust the thickness of the frost layer on the sample surface according to processing requirements.

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