Method for finely modifying and processing interior of crystal based on double-beam focus interference

Abstract

The invention discloses a method for finely modifying the interior of a crystal based on double-beam laser focus interference, and belongs to the field of laser precision machining. The implementation method comprises the step of adjusting a double-beam divergence angle by using the laser shaping device to realize the overlapping of the focus A and the focus B. The double focuses are overlapped and interfered, and the interference phenomenon that the energy intensity is alternately changed occurs in a focus overlapping area; under the interference effect, most energy of the laser can be concentrated to an interference enhancement part, and the energy peak value of the laser can exceed a modification threshold value in the material so as to be modified; the size of the double-focus overlapping area is compressed relative to that of a conventional single-focus area, interference modification only occupies a part of the overlapping area, and the size of the modified area can be further compressed. Compared with a conventional single-focus modification area, the longitudinal size modified by the method can be compressed by at least 50%, so that the precision of the internal micro-nano structure of the processed crystal is higher. Laser parameters are selected according to the characteristics of a crystal material, mobile scanning is performed according to a preset track, modification points form modification lines, and then high-precision machining of a complex micro-nano structure in the crystal can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser precision processing and relates to a method for finely modifying and processing the interior of a crystal based on double-beam focal interference. Background Art

[0002] Crystal materials have excellent optical, electrical, and mechanical properties, and are therefore widely used in aerospace, new energy, electronic information, and other fields. Semiconductor materials, such as silicon, silicon carbide, gallium arsenide, and diamond, in particular, play an irreplaceable role in the field of microelectronics and are in huge demand. During the application process, the interior of the crystal material needs to be precisely processed, including waveguides, microchannels, sensors, etc. Among the internal processing techniques, the two-photon polymerization process is relatively mature, but the two-photon polymerization process is generally used for 3D printing of polymer materials, and the use of conventional laser processing technology limits the internal processing accuracy of crystal materials.

[0003] At present, conventional laser internal modification methods cause self-focusing due to the aberrations and nonlinear effects caused by laser processing inside the crystal, so that the formed modified area has a large longitudinal extension, resulting in limited processing accuracy inside the crystal. Summary of the invention

[0004] In order to further improve the processing accuracy of micro-nano structures inside crystal materials, the purpose of the present invention is to provide a method for fine modification and processing of the interior of a crystal based on double-beam focal interference, wherein the double beams are focused to the same position inside the crystal and interfere there; modification occurs through interference, thereby reducing the aberration of the laser inside the crystal and the influence of self-focusing modification on processing accuracy; the scanning is moved along a preset trajectory, and the modified points form modified lines to achieve fine modification of the interior of the crystal.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention discloses a method for finely modifying and processing the interior of a crystal based on double-beam focal interference, comprising the following steps:

[0007] Step 1: Ultrafast laser is spatially shaped and divided into two beams;

[0008] Step 2: Irradiate the interior of the crystal vertically along the same longitudinal axis and focus at a certain depth. By adjusting the laser parameters, the single laser beam focus will not cause any modification effect on the crystal;

[0009] Step 3: After spatial shaping, beam 1 forms focus A at a determined position. After spatial shaping, beam 2 is reflected by the bottom surface of the crystal and returns to form focus B at the same position, overlapping and interfering with focus A to form a fine modified area;

[0010] Step 4: Move and scan along the set trajectory, and the modified points form modified lines to achieve the processing of the micro-nano structure inside the crystal.

[0011] The specific implementation method of step three is: using laser shaping devices to adjust the divergence angle to achieve the overlap of focus A and focus B in time and space. The two focal points overlap and interfere, and the overlapping area of ​​the focal points will experience interference with alternating energy intensity; under the interference effect, the laser will concentrate most of the energy at the interference enhancement point, and its energy peak can exceed the modification threshold inside the material and then undergo modification; the size of the overlapping area of ​​the two focal points is compressed compared to the conventional single-focus modification, and the interference modification only occupies a part of the overlapping area. The modified area will be further compressed to form a fine modified area, making the micro-nano structure inside the processed crystal more accurate.

[0012] Dual-beam interference is achieved through beam splitting, shaping, modulation and focusing of the same laser system, or through synchronous focusing of two laser systems.

[0013] The crystal has properties such as high hardness and high brittleness; the crystal can be penetrated by lasers of corresponding wavelengths to achieve ultrafast laser internal modification. The high hardness means that the Mohs hardness is higher than 7, and the high brittleness means that the elongation of the fracture under the action of external force is lower than 1%.

[0014] The crystals include silicon, silicon carbide, sapphire, gallium nitride, gallium arsenide and diamond.

[0015] There is no restriction on setting the trajectory, and the required micro-nano structure can be processed according to actual needs.

[0016] Ultrafast laser refers to laser pulse width in femtoseconds (10 -15 seconds) to picoseconds (10 -12 Seconds) of laser light.

[0017] Beneficial effects:

[0018] 1. The present invention discloses a method for finely modifying a crystal based on double-beam laser focal interference, which uses double beams to focus on the inside of the crystal to interfere and modify it. Compared with the conventional single laser focal modification method, it can reduce the influence of laser aberration inside the crystal and self-focusing on the processing accuracy, achieve fine modification inside the crystal material, and facilitate high-precision processing of micro-nano structures inside the crystal.

[0019] 2. The present invention discloses a method for finely modifying crystals based on dual-beam laser focus interference, which uses a laser shaping device to flexibly adjust the divergence angle to achieve dual-beam synchronous focusing at any depth inside the crystal, and the dual-beam focus overlaps and interferes. Under the interference effect, the laser will concentrate most of the energy at the interference enhancement point, and its energy peak exceeds the modification threshold inside the material, thereby causing modification, and finally achieving fine processing at different depths inside the crystal material.

[0020] 3. The present invention discloses a method for finely modifying a crystal based on double-beam laser focal interference. The size of the double-focal overlap area is compressed relative to the conventional single-focal area, and the interference modification only occupies a part of the overlap area, and the modified area is further compressed. The longitudinal size of the area modified by the method of the present invention can be compressed by at least 50%, which improves the refinement of the modification and can greatly improve the accuracy of the micro-nano structure inside the processed crystal.

[0021] 4. The present invention discloses a method for finely modifying crystals based on dual-beam laser focal interference, which selects corresponding laser parameters for modification according to the characteristics of the crystal material. The method is suitable for internal processing of various types of crystal materials and has a wide range of applications.

[0022] 4. The present invention discloses a method for finely modifying crystals based on dual-beam laser focal interference. The method moves and scans along a preset trajectory, and the modified points form modified lines. By adjusting the laser parameters, flexible modification is achieved, which facilitates the processing of complex micro-nano structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic flow chart of a method for finely modifying crystals based on double-beam laser focal interference of the present invention;

[0024] Figure 2 It is a schematic diagram of forming a fine modified region inside a SiC ingot by using the method of the present invention;

[0025] Among them: 1—laser beam splitter A, 2—laser beam splitter B, 3—objective lens, 4—SiC crystal ingot, 5—dual-focus interference modified area, 6—single-focus modified area, 7—reflector, 8—infrared camera, 9—ultrafast laser, 10—spatial light modulator.

[0026] Figure 3 Schematic diagram of forming a fine modified surface inside a SiC ingot by using the method of the present invention in an embodiment;

[0027] Among them: 1—laser beam splitter A, 2—laser beam splitter B, 3—objective lens, 4—SiC crystal ingot, 5—double-focus interference modification area.

[0028] Figure 4 It is a side view of an experiment comparing the modification inside a crystal using a conventional method and the method of the present invention. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below in conjunction with the accompanying drawings and examples. The following embodiment is only one of the embodiments of the present invention, not all. The drawings of the present invention are only for illustration, and their specific proportions can be adjusted according to design requirements.

[0030] This embodiment discloses using femtosecond laser to perform fine internal modification on SiC ingot as a specific embodiment of the method of the present invention. The sample used in the embodiment is a semi-insulating SiC ingot, and the laser used in the embodiment is a femtosecond laser with a wavelength of 1030nm.

[0031] like Figure 1 As shown, the present embodiment discloses a method for finely modifying a crystal based on double-beam laser focal interference, and the specific implementation steps are as follows:

[0032] Step 1: The femtosecond laser is spatially shaped by a spatial light modulator (SLM) and divided into two independent beams. The divergence angle, intensity distribution, phase and polarization state of the laser beam are dynamically adjusted to meet actual processing requirements.

[0033] Step 2: Irradiate the interior of the crystal vertically along the same longitudinal axis and focus at a depth of 200 μm. By adjusting the laser parameters, the energy at the focus of the single laser beam does not exceed the modification threshold of SiC, and the SiC ingot is not modified.

[0034] In the step 2, the pulse width range of the laser is 200fs-20ps, the wavelength range is 355nm-1100nm, and the laser power is adjustable from 0 to 20W.

[0035] Step 3: After spatial shaping, beam 1 forms a focus A at a certain position 200μm away from the surface of the SiC ingot. After spatial shaping, beam 2 is reflected by the bottom surface of the crystal and returns to form a focus B at the same position, overlapping and interfering with focus A to form a fine modified point area.

[0036] In step 3, the divergence angle is adjusted by a spatial shaper to achieve the temporal and spatial overlap of focus A and focus B. Under the interference effect, the overlapping area of ​​the focus will undergo an interference phenomenon in which the energy intensity alternates, and the laser will concentrate most of the energy at the interference enhancement point, generating an interference peak and undergoing modification.

[0037] Step 4: By precisely controlling the femtosecond laser beam to move and scan along a preset trajectory, multiple modified points can be generated inside the SiC ingot. These modified points are connected to form modified lines, thereby accurately manufacturing a variety of micro-nano structures inside the SiC ingot.

[0038] Compared with the single-focus modified area, the modified area processed by the method of the present invention has a longitudinal modified size compressed by at least 50%, which indicates that under the same processing conditions, the processing accuracy is significantly improved.

[0039] like Figure 2As shown, a fine modified region is formed inside the SiC crystal ingot 4 using the method of the present invention. The ultrafast laser 9 is split by the spatial light modulator 10 into laser beam A and laser beam B. The laser beam A and laser beam B are spatially shaped by the spatial light modulator 10 to achieve aberration correction. There is a pulse delay between the two laser beams, and they can reach a depth of 200μm inside the crystal at the same time. The laser beam A is vertically irradiated inside the crystal through the reflector 7 and the objective lens 3 and forms a focus A at a depth of 200μm. The laser beam B is vertically irradiated inside the crystal ingot through the reflector 7 and the objective lens 3, and then returns to the original path after being reflected by the bottom surface of the crystal and forms a focus B at the same position. The processing process is observed by the infrared camera 8 to accurately measure the distance of the laser focus. After spatial shaping, the focus A and the focus B overlap and interfere along the same longitudinal axis direction to form a dual-focus interference modified region 5. Compared with the single-focus modified region 6, the dual-focus interference modified region 5 has a smaller longitudinal dimension.

[0040] like Figure 3 As shown, laser beam A and laser beam B are focused on the inside of the semi-insulating SiC ingot 4 through the objective lens 3, respectively, with a focusing depth of 200μm. After the dual-focus interference modified area 5 is formed by the method of the present invention, scanning modification is performed along the scanning track at a scanning speed of 2000μm / s. The scanning track is composed of a plurality of modified lines, and microcracks will be generated around the modified lines. The lines are spaced 50μm apart, so that the microcracks extend and achieve full coverage to form a modified surface. Subsequently, the method of the present invention can be used to modify SiC ingots of larger sizes and apply equal and opposite forces to the upper and lower surfaces of the modified SiC ingot, so that the SiC wafer is peeled off from the ingot.

[0041] like Figure 4 This is a side view of the experiment comparing the modification inside the crystal using the conventional method and the method of the present invention. Since there is still room for optimization of the laser parameters, the longitudinal dimensional accuracy of the modification using the method of the present invention is not the best effect. The modified area sizes of the two methods under the same laser parameters are compared. The longitudinal size of the modification using the method of the present invention is compressed by 50% compared to the single focus modification, and the modified area is finer.

[0042] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference, characterized in that: The following steps are included: Step 1: Ultrafast laser is spatially shaped and divided into two beams; Step 2: irradiate the interior of the crystal vertically along the same longitudinal axis and focus at a certain depth; by adjusting the laser parameters, the focus of the single laser beam does not cause any modification effect on the crystal; Step 3: After the beam 1 is shaped in the spatial domain, it forms a focus A at a determined position; after the beam 2 is shaped in the spatial domain, it is reflected by the bottom surface of the crystal and returns to form a focus B, which overlaps with the focus A and interferes to form a fine modified area; Step 4: Move and scan along the set trajectory, and the modified points form modified lines to achieve the processing of the micro-nano structure inside the crystal.

2. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1, characterized in that: The specific implementation method of step three is to use a laser shaping device to adjust the divergence angle to achieve the overlap of focus A and focus B in time and space; the two focal points overlap and interfere, and an interference phenomenon of alternating energy strength will occur in the focus overlapping area; under the interference effect, the laser will concentrate most of the energy at the interference enhancement point, and its energy peak exceeds the modification threshold inside the material and thus modification will occur; the size of the dual-focus overlapping area is compressed relative to the conventional single-focus area, and the interference modification only occupies a part of the overlapping area. The modified area will be further compressed to form a fine modified area, so that the micro-nano structure inside the processed crystal is more accurate.

3. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1 or 2, characterized in that: Dual-beam interference is achieved through beam splitting, shaping, modulation and focusing of the same laser system.

4. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1 or 2, characterized in that: Dual-beam interference is achieved by synchronous focusing of two laser systems.

5. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1 or 2, characterized in that: The crystal has the properties of high hardness and high brittleness, and can be penetrated by laser of corresponding wavelength to achieve ultrafast laser internal modification; the high hardness refers to a Mohs hardness greater than 7, and the high brittleness refers to an elongation of less than 1% when destroyed and fractured under external force.

6. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1 or 2, characterized in that: The crystals include silicon, silicon carbide, sapphire, gallium nitride, gallium arsenide and diamond.

7. A method for finely modifying and processing the interior of a crystal based on double-beam focal interference as claimed in claim 1 or 2, characterized in that: The laser pulse width ranges from 200fs to 20ps, the wavelength ranges from 355nm to 1100nm, and the laser power ranges from 0 to 20W.

Images