CN111085773B - Metal film assisted laser drilling device and method for brittle materials - Google Patents

Abstract

The present invention discloses a method and device for laser drilling of brittle materials assisted by metal films. The laser drilling device includes a laser processing system and a sample motion system; the laser processing system includes a laser, a beam expander, a mechanical shutter, a laser energy controller, a reflector and a focusing objective lens, and the laser generated by the laser passes through the beam expander, the mechanical shutter, the laser energy controller, the reflector and the focusing objective lens in sequence to be focused; the sample motion system includes a three-dimensional displacement stage and a brittle material substrate coated with a metal film placed on the three-dimensional displacement stage; the laser of the laser processing system is focused on the upper surface of the brittle material substrate coated with a metal film to write a microhole pattern. It has the following advantages: it can not only improve the surface quality of the microholes, but also increase the hole depth of the laser drilling, and finally realize high-quality, high-aspect-ratio drilling on brittle materials.

Description

Metal film assisted laser drilling device and method for brittle materials

Technical Field

The invention relates to the technical field of laser processing, and in particular to a method and a device for laser drilling of brittle materials assisted by a metal film.

Background Art

Microporous structure patterns are widely used in optics, machinery, aerospace and other fields. Traditional mechanical processing methods are difficult to process and inefficient in the production of microporous patterns on brittle materials. Problems such as edge collapse and cracks are prone to occur around the holes. With the vigorous development of laser manufacturing technology, laser processing technology has been widely used in the field of microporous manufacturing. Laser drilling has the advantages of flexible processing methods, no tool loss, high processing efficiency, and environmental friendliness. However, the disadvantages of brittle materials themselves, such as low plasticity, brittle failure, easy microcracks and easy surface damage, lead to edge collapse when drilling holes on brittle materials with laser direct writing technology, and thermal cracks are prone to occur inside and around the processing area. A layer of molten recondensate will adhere to the processing area, which seriously reduces the processing quality of micropores. In addition, for transparent brittle materials, the absorption rate of laser energy is relatively low, and the depth of drilling is limited. Therefore, how to increase the depth of laser drilling of brittle materials is also a problem that needs to be considered.

The Chinese patent database has disclosed the invention application 200910300654.5, a method for laser marking on the surface of a wafer. The method requires the preparation of a marking sheet. The substrate of the marking sheet is a glass sheet that is transparent to lasers. A metal film is coated on one side of the glass sheet. The surface of the metal film layer on the marking sheet fits the position on the wafer surface that needs to be marked. The laser is incident from the side of the surface without the metal film layer on the marking sheet and converges to the position on the wafer that needs to be marked. The converged laser is blocked by the metal film layer and accumulates at the metal film layer. The accumulated laser melts the metal film layer to ablate the wafer surface and form a mark on the crystal surface. Since the metal film layer is coated on the marking sheet instead of on the wafer to be processed, and the role of the metal film layer is only to increase the wafer's absorption rate of the laser, the technical solution of the invention application cannot improve the quality of laser marking on the wafer surface.

The Chinese Patent Database has published the invention application 201711077427.1, a femtosecond laser micromachining method and device. This method solves the technical problem that heat-affected zones, recast layers, thermal deformations and cracks exist near the processing area during femtosecond laser processing, which affect the processing quality and processing accuracy, by coating a metal film or a dielectric film on the substrate material. However, this method is specifically proposed to improve the quality of femtosecond laser micromachining. The coating plays a protective and heat-conducting role to avoid the appearance of heat-affected zones, recast layers, thermal deformations and cracks. It does not increase the depth of laser drilling in brittle materials.

Summary of the invention

The present invention provides a metal film assisted laser drilling method and device for brittle materials, which overcomes the shortcomings of the metal film assisted laser drilling method for brittle materials in the background technology.

One of the technical solutions adopted by the present invention to solve its technical problem is:

A metal film-assisted laser drilling device for brittle materials comprises a laser processing system and a sample motion system; the laser processing system comprises a laser (1), a beam expander (2), a mechanical shutter (3), a laser energy controller (4), a reflector (5) and a focusing lens (6); the laser (1), the beam expander (2), the mechanical shutter (3), the laser energy controller (4), the reflector (5) and the focusing lens (6) are arranged in sequence so that the laser light generated by the laser (1) passes through the beam expander (2), the mechanical shutter (3), the laser energy controller (4), the reflector (5) and the focusing lens (6) in sequence to be focused; the sample motion system comprises a three-dimensional displacement stage (8) and a brittle material substrate (71) coated with a metal film (72) placed on the three-dimensional displacement stage (8); the laser light of the laser processing system is focused on the upper surface of the brittle material substrate (71) coated with the metal film (72) to write a microhole pattern.

In one embodiment, the invention further comprises a control part (9), wherein the control part (9) is connected to the laser (1), the mechanical shutter (3) and the three-dimensional displacement stage (8) to write a micro-hole pattern on the upper surface of the brittle material substrate (71).

In one embodiment, the laser energy controller is a neutral density filter, or a combination of a half-wave plate and a thin-film polarizer, so as to control the laser pulse energy acting on the brittle material substrate (71).

The second technical solution adopted by the present invention to solve its technical problem is:

The laser drilling method of the above-mentioned metal film-assisted laser drilling device for brittle materials comprises:

Step 1: a metal film (72) is plated on the upper surface of a brittle material substrate (71);

Step 2: placing a brittle material substrate (71) coated with a metal film (72) on a three-dimensional displacement stage (8);

Step 3: The laser light emitted by the laser (1) passes through a beam expander (2), a mechanical shutter (3), a laser energy controller (4), a reflector (5) and a focusing lens (6) in sequence and is then focused onto the upper surface of a brittle material substrate (71) coated with a metal film (72);

Step 4: focusing laser to write the desired micro-hole pattern on the upper surface of the brittle material substrate (71) coated with the metal film (72);

Step 5: placing the brittle material substrate (71) processed with a microporous pattern into a reaction solution until the metal film (72) material remaining on the surface of the brittle material substrate (71) is completely reacted and removed;

Step 6: Take out the brittle material substrate (71) from which the metal film (72) has been washed away from the reaction solution, wash it, and blow it dry, thereby obtaining a brittle material substrate (71) having a microporous pattern.

In one embodiment: in step 6, the reaction solution is a mixed solution of I ₂ and KI, or a mixed solution of HF acid and H ₂ O ₂ .

In one embodiment: In step six, the brittle material substrate (71) with the metal film (72) washed away is taken out from the reaction solution, and then ultrasonically cleaned with acetone, alcohol, and deionized water respectively, and finally dried with nitrogen, thereby obtaining a brittle material substrate (71) with a microporous pattern.

In one embodiment: in the step 1, a metal film (72) is plated on the upper surface of a brittle material substrate (71) using magnetron sputtering technology, electron beam evaporation technology, thermal evaporation technology or laser pulse deposition technology.

In one embodiment, the material of the metal film (72) is one of gold, silver, copper, aluminum, platinum, titanium or an alloy thereof, and the thickness of the metal film (72) is between 10 nanometers and 500 nanometers.

In one embodiment, the metal film (72) includes a layer of the same metal material or a layer of metal alloy material or multiple layers of different metal materials.

In one embodiment, the brittle material substrate (71) is at least one of glass, sapphire, silicon carbide, silicon, gallium arsenide, gallium nitride, diamond, ceramic and stone.

Compared with the background technology, this technical solution has the following advantages:

The laser drilling device and method of the technical solution can not only improve the surface quality of micro-holes, but also increase the hole depth of laser drilling, and finally realize high-quality, high-aspect ratio drilling on brittle materials. It can provide a higher quality and drilling depth than various pulsed lasers in the background technology for drilling holes on brittle materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

FIG1 is a schematic structural diagram of a laser drilling device according to this specific embodiment;

Figure 2(a) is a scanning electron microscope image of a sapphire substrate coated with a 12 nm thick metal film processed by femtosecond laser according to this specific embodiment. The corresponding laser processing parameters are: laser center wavelength 800 nm, pulse width 160 fs, laser energy density 14.32 J/cm ² , pulse number N=50;

Figure 2(b) is a scanning electron microscope image of a hole ablated on a sapphire substrate without metal film by femtosecond laser processing according to this specific embodiment. The corresponding laser processing parameters are: laser center wavelength 800nm, pulse width 160fs, laser energy density 14.32J/ ^cm2 , pulse number N=50;

FIG3 is a curve showing the variation of the depth of the ablated holes on the sapphire substrate coated with a 12 nm thick metal film and the sapphire substrate without the metal film by femtosecond laser processing according to the specific embodiment of the present invention with the energy of the single laser pulse, wherein the number of pulses acting on the sapphire substrate is N=50;

FIG4 is a curve showing the change of the volume of the ablated hole on the sapphire substrate coated with a 12 nm thick metal film and the sapphire substrate without the metal film by femtosecond laser processing according to the specific embodiment of the present invention as a function of the energy of the single laser pulse, wherein the number of pulses acting on the sapphire substrate is N=50;

Explanation of the numbers in the figure: 1-laser, 2-beam expander, 3-mechanical shutter, 4-laser energy controller, 5-reflector, 6-focusing lens, 71-brittle material substrate, 72-metal film, 8-three-dimensional displacement platform, 9-control part.

DETAILED DESCRIPTION

A metal film-assisted laser drilling device for brittle materials, as shown in FIG1, includes a laser processing system and a sample motion system; the laser processing system includes a laser 1, a beam expander 2, a mechanical shutter 3, a laser energy controller 4, a reflector 5 and a focusing objective 6; the sample motion system includes a three-dimensional displacement stage 8 and a control part 9, and a brittle material substrate 71 coated with a metal film 72 is placed on the three-dimensional displacement stage 8. The control part 9 is connected to the mechanical shutter 3 to control the opening or closing time of the mechanical shutter 3 to control the number of laser pulses acting on the brittle material substrate 71. The control part 9 is connected to the three-dimensional displacement stage 8, and the control part 9 controls the movement of the three-dimensional displacement stage 8 to realize the micro-hole spacing control. The control part 9 is such as a computer or a PLC. The laser energy controller is a neutral density filter, or a combination of a half-wave plate and a thin film polarizer to control the laser pulse energy acting on the brittle material substrate 71.

The laser 1, the beam expander 2, the mechanical shutter 3, the laser energy controller 4, the reflector 5 and the focusing lens 6 are arranged in sequence so that the laser generated by the laser 1 passes through the beam expander 2, the mechanical shutter 3, the laser energy controller 4, the reflector 5 and the focusing lens 6 in sequence to be focused; the laser of the laser processing system is focused on the upper surface of the brittle material substrate 71 coated with the metal film 72 to write the micro-hole pattern. The control part 9 connects the laser 1, the mechanical shutter 3 and the three-dimensional displacement stage 8 to write the micro-hole pattern on the upper surface of the brittle material substrate 71.

In order to more clearly explain the purpose, technical solution and advantages of the specific implementation of the present invention, the laser drilling method of the brittle material assisted by the above-mentioned metal film is described in detail below. In this specific implementation, the laser adopts a femtosecond laser with a wavelength of 800nm, a pulse width of 160fs, and a repetition frequency of 1-1kHz adjustable; the processed brittle material is a non-metallic material, such as a sapphire substrate, with a size of 10mm´10mm and a thickness of 0.5mm. The laser drilling method includes:

Step 1: A 12 nm thick metal film 72 is plated on the surface of a flaky brittle material substrate 71 using magnetron sputtering technology. The brittle material substrate 71 is a non-metallic material. In this specific implementation, a sapphire substrate is used as an example for illustration. The thickness of the metal film 72 can be set to other sizes as needed, and the material of the metal film 72 can be gold or other types of metals.

Step 2: placing the brittle material substrate 71 coated with the metal film 72 on the three-dimensional displacement stage 8 .

Step 3: The laser emitted by the femtosecond laser 1 is controlled by the control part 9 to sequentially pass through the beam expander 2, the mechanical shutter 3, the laser energy controller 4, the reflector 5 and the focusing lens 6 and then focus on the surface of the brittle material substrate 71 (sapphire substrate) coated with the metal film 72. The present invention uses a femtosecond laser, but is not limited thereto, and other various pulse lasers are applicable.

Step 4: The control unit 9 controls the laser 1, the mechanical shutter 3 and the three-dimensional displacement stage 8, so that the femtosecond pulse laser writes the desired micro-hole pattern on the upper surface of the sapphire substrate coated with the metal film 72. In this specific embodiment, the number of laser pulses is set to 50, and the laser energy density is 14.32 J/cm ² . Other laser parameters can also be used as needed.

Step 5: Place the sapphire substrate processed with the micropore pattern into the reaction solution until the remaining metal film 72 material on the surface of the sapphire substrate is completely reacted and removed.

Step 6: Take out the sapphire substrate with the metal film 72 washed off from the reaction solution, then ultrasonically clean it with acetone, alcohol and deionized water respectively, and finally blow dry it with nitrogen to obtain a sapphire substrate with a microporous pattern.

Figure 2 (a) and Figure 2 (b) are scanning electron microscope images of the micropore morphology on the sapphire substrate with and without metal film coating. By comparison, it is found that after a metal film is coated on the sapphire surface, the shape of the ablation hole is more regular, and there are fewer molten recondensates around the ablation hole. There are no thermal cracks in and around the ablation hole, which shows that the metal film can improve the surface quality of the micropore. Comparing the depth of the ablation hole coated with a metal film and the one without a metal film under the same laser parameters, as shown in Figure 3, it is found that after a metal film is coated on the sapphire surface, the depth of the ablation hole increases significantly, which shows that the metal film is conducive to laser processing of micropores with a higher aspect ratio on the brittle material substrate. Comparing the ablation volume of the metal film coated with and the one without a metal film under the same laser parameters, as shown in Figure 4, it is found that after a metal film is coated on the sapphire surface, its ablation volume is also significantly larger than the volume of the ablation hole without a film coating, which shows that the metal film can significantly increase the ablation rate of the material.

The present invention discloses a device and method for laser drilling of brittle materials assisted by metal film. Experimental results show that after the metal film is plated on the surface of the brittle material substrate, the shape of the ablated hole is more regular, the melt recondensate around the hole is less, the thermal cracks in and around the hole are less, and the depth of the hole is deeper. The method and device have important guiding significance for processing high-quality, high-aspect-ratio microholes on brittle materials. In the present invention, the metal film plated on the brittle material substrate not only plays a role in protection and heat conduction, but also more importantly provides a high-density free electron on the surface of the brittle material. These free electrons can not only make the laser energy evenly deposited on the surface of the brittle material, thereby making the shape of the hole more regular, but also increase the energy coupling between the incident laser and the brittle material, thereby increasing the depth of the drilling. In the present invention, a metal film is plated on the surface of a brittle material substrate, which can not only improve the surface quality of the micropores, specifically including more regular shapes of the micropores, less melt recondensation around the micropores, less thermal cracks in and around the holes, and obtain more regular micropores, but also increase the ablation rate of laser drilling, increase the absorption of laser energy by brittle materials, increase the depth of laser drilling, and obtain micropores with a higher aspect ratio. High-quality, high aspect ratio micropores are processed.

The present invention provides a metal film-assisted laser drilling method for brittle materials, which solves the problems that the laser directly drills holes on the surface of brittle materials, the edges are prone to collapse, the inside and around the processing area are prone to thermal cracks, and a layer of molten recondensate adheres around the processing area. The physical mechanism includes: first, the metal film has a high thermal conductivity, which can effectively reduce the thermal effect and thermal stress during the drilling process, so that there are fewer molten recondensate on the hole surface and fewer thermal cracks inside and around the hole; second, there are a large number of free electrons in the metal film, which will quickly diffuse to the metal film-brittle material substrate interface after absorbing the energy of the incident photon, resulting in the free electron density on the surface of the brittle material coated with the metal film under laser irradiation is much higher than the free electron density on the surface of the brittle material without the film. The high-density free electrons on the metal film-brittle material substrate interface can enhance the energy transfer between the incident laser and the brittle material, thereby improving the absorption of laser energy by the brittle material and increasing the laser ablation rate of the brittle material. In addition, the high-density free electrons provided by the metal film are conducive to the uniform deposition of laser energy on the surface of the brittle material, which makes the shape of the ablation hole more regular.

The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of the present invention. That is, equivalent changes and modifications made according to the patent scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims (10)

1. A metal film-assisted laser drilling device for brittle materials, characterized in that it comprises a laser processing system and a sample motion system; the laser processing system comprises a laser (1), a beam expander (2), a mechanical shutter (3), a laser energy controller (4), a reflector (5) and a focusing lens (6); the laser (1), the beam expander (2), the mechanical shutter (3), the laser energy controller (4), the reflector (5) and the focusing lens (6) are arranged in sequence so that the laser light generated by the laser (1) passes through the beam expander (2), the mechanical shutter (3), the laser energy controller (4), the reflector (5) and the focusing lens (6) in sequence to be focused; the sample motion system comprises a three-dimensional displacement stage (8) and a brittle material substrate (71) coated with a metal film (72) placed on the three-dimensional displacement stage (8); the laser light of the laser processing system is focused on the upper surface of the brittle material substrate (71) coated with the metal film (72) to write a microhole pattern. 2. The metal film-assisted laser drilling device for brittle materials according to claim 1 is characterized in that it also includes a control part (9), wherein the control part (9) connects the laser (1), the mechanical shutter (3) and the three-dimensional displacement stage (8) to write a microhole pattern on the upper surface of the brittle material substrate (71). 3. The metal film-assisted laser drilling device for brittle materials according to claim 1 is characterized in that the laser energy controller is a neutral density filter, or a combination of a half-wave plate and a thin-film polarizer, so as to control the laser pulse energy acting on the brittle material substrate (71). 4. The laser drilling method of the metal film-assisted laser drilling device for brittle materials according to claim 1, characterized in that it comprises: Step 1: a metal film (72) is plated on the upper surface of a brittle material substrate (71); Step 2: placing a brittle material substrate (71) coated with a metal film (72) on a three-dimensional displacement stage (8); Step 3: The laser light emitted by the laser (1) passes through a beam expander (2), a mechanical shutter (3), a laser energy controller (4), a reflector (5) and a focusing lens (6) in sequence and is then focused onto the upper surface of a brittle material substrate (71) coated with a metal film (72); Step 4: focusing laser to write the desired micro-hole pattern on the upper surface of the brittle material substrate (71) coated with the metal film (72); Step 5: placing the brittle material substrate (71) processed with a microporous pattern into a reaction solution until the metal film (72) material remaining on the surface of the brittle material substrate (71) is completely reacted and removed; Step 6: Take out the brittle material substrate (71) from which the metal film (72) has been washed away from the reaction solution, wash it, and blow it dry, thereby obtaining a brittle material substrate (71) having a microporous pattern. 5. The metal film-assisted laser drilling method for brittle materials according to claim 4, characterized in that: in the step 6, the reaction solution is _a mixed solution of _I2 and KI, or a mixed solution of HF acid and _H2O2 . 6. The metal film-assisted laser drilling method for brittle materials according to claim 4 is characterized in that: in the step six, the brittle material substrate (71) with the metal film (72) washed away is taken out from the reaction solution, and then ultrasonically cleaned with acetone, alcohol, and deionized water respectively, and finally dried with nitrogen to obtain a brittle material substrate (71) with a microporous pattern. 7. The metal film-assisted laser drilling method for brittle materials according to claim 4 is characterized in that: in the step 1, a metal film (72) is plated on the upper surface of the brittle material substrate (71) using magnetron sputtering technology, electron beam evaporation technology, thermal evaporation technology or laser pulse deposition technology. 8. The metal film-assisted laser drilling method for brittle materials according to claim 4 is characterized in that: the material of the metal film (72) is one of gold, silver, copper, aluminum, platinum, titanium or their alloys, and the thickness of the metal film (72) is between 10 nanometers and 500 nanometers. 9. The metal film-assisted laser drilling method for brittle materials according to claim 4, characterized in that the metal film (72) comprises a layer of the same metal material or a layer of metal alloy material or multiple layers of different metal materials. 10. The metal film-assisted laser drilling method for brittle materials according to claim 4, characterized in that the brittle material substrate (71) is at least one of glass, sapphire, silicon carbide, silicon, gallium arsenide, gallium nitride, diamond, ceramic and stone.