Error compensation and correction method for femtosecond laser galvanometer 4F machining system

Abstract

The invention discloses an error compensation correction method for a femtosecond laser galvanometer 4F machining system, and belongs to the technical field of high-precision machining. Leveling the processing system; processing and characterization of the square block are calibrated; deflection correction of a scanning galvanometer of the femtosecond laser processing system and deflection correction of a scanning plane of the scanning galvanometer of the femtosecond laser processing system; according to the method, the length and width data of the calibration square block are collected, pre-compensation operation is carried out on an original structure machining file, and the size error of a machining structure caused by deflection of laser through a scanning galvanometer reflector is eliminated; by collecting the angle difference value of the scanning plane of the scanning galvanometer control laser and the plane of the substrate, plane deflection correction operation is carried out on an original structure processing file, the problem that the scanning plane does not coincide with the plane of the substrate is solved, and the consistency of all areas of a scanning structure is extremely high; the preparation of a high-precision and large-size true three-dimensional structure can be realized through the galvanometer-based femtosecond laser two-photon polymerization processing system, and the processing capability of the galvanometer-based femtosecond laser processing system is successfully optimized; the method has the outstanding advantages of being universal, high in operability and wide in applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of high-precision machining, and in particular relates to an error compensation and correction method for a femtosecond laser galvanometer 4F machining system. Background Art

[0002] With the rapid development of modern manufacturing and high-tech industries, higher and higher requirements are placed on the precision, quality and efficiency of material processing. Femtosecond laser processing technology has been widely used in many fields such as micro-nano manufacturing, biomedicine, and electronic information due to its unique ultra-short pulse characteristics. However, in many high-precision processing fields such as laser marking, welding, 3D printing, and precision cutting, the requirements for processing accuracy are extremely stringent due to the extremely high precision of the processed devices. For example, in the manufacture of ultra-fine semiconductor chip circuits, micro-optical components, and micro-electromechanical systems (MEMS), the requirements for processing accuracy have reached sub-micron or even nanometer levels. Based on this, improving the processing accuracy of femtosecond laser processing systems is extremely important in many fields such as micro-nano manufacturing, biomedicine, and electronic information.

[0003] The galvanometer-based femtosecond laser processing system has attracted great attention due to its advantages such as large processing range and true three-dimensional processing. The principle is that the scanning galvanometer system in the femtosecond laser processing system can control the laser beam by adjusting the deflection of two reflectors, so that the laser focus spot scans along the preset path. This greatly improves the processing freedom of the processing system on the X and Y planes. However, in the actual scanning process of the galvanometer system, affected by multiple factors such as optical and physical properties, there is a nonlinear error between the preset processing size and the deflection angle of the laser controlled by the scanning galvanometer. At the same time, as a packaged integrated optical element, the scanning galvanometer has the problem of difficulty in aligning its specific position in the optical path with the direction of laser incidence. It may also cause the XY plane of the emitted laser scanning to be not the same plane as the bottom surface of the substrate after leveling. When processing large-area, high-precision structures, problems such as uneven energy on both sides and poor processing quality are prone to occur. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides an error compensation correction method for a femtosecond laser galvanometer 4F processing system. The present invention adopts a correction method based on pre-compensation to correct the laser processing sample from the following two aspects: first, the correction of the deflection error of the scanning galvanometer; in the experiment, when the size of the sample to be processed is small, that is, the deflection angle of the scanning galvanometer is small, the error between the actual scanning size and the theoretical size is very small; when the deflection angle of the scanning galvanometer is large, there is an obvious error between the actual scanning size and the theoretical size. By preparing objects with different size parameters for many times, a relationship curve of the ratio of the deflection distance to the theoretical deflection distance in the experiment is obtained at different deflection distances, and then the original data of the processed sample is pre-compensated to realize the correction of the deflection angle of the scanning galvanometer. Second, the offset correction of the laser focus deflection plane and the substrate plane; in the experiment, it is found that after the substrate is leveled, the substrate plane and the laser focus deflection plane often do not coincide. After the substrate is leveled, the galvanometer is deflected to focus the laser on three points that are not on the same straight line, and the Z-axis position is adjusted to make the laser spot intensity at the three points the same. The three points determine a plane, and the position information of the Z-axis is adjusted to make the three-point spot intensity the same. The original data of the processed sample is mapped and transformed to achieve the coincidence of the laser scanning plane and the substrate plane, and finally the correction of the size error and plane offset of the processed sample is realized.

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

[0006] A femtosecond laser galvanometer 4F processing system error compensation correction method specifically comprises the following steps:

[0007] (1) Sample preparation;

[0008] The specific steps are as follows: dropping the optical resin on a substrate; wherein the substrate is a clean substrate that has been wiped with an alcohol cotton ball, rinsed with deionized water and dried in advance; placing the substrate on a hot table for preheating to form a polymer film, and then cooling it naturally at room temperature;

[0009] (2) Leveling processing system;

[0010] Specific steps: First, place the prepared substrate in the galvanometer-based femtosecond laser processing system, adjust the laser energy to the reference value, and focus the laser beam on the interface between the polymer film and the substrate; rotate the stage support screw until the spot energy is always constant when the substrate moves left and right and forward and backward, and it is judged that the substrate has been leveled; then, focus the laser again to the interface between the polymer film and the substrate;

[0011] (3) Processing and characterization of calibration blocks;

[0012] Specific steps: prepare calibration blocks with different lengths X and widths Y according to measurement needs; generate point data files for each calibration block and import them into processing software; set the laser processing power and perform point-by-point scanning processing; develop, dry and ultraviolet-expose the scanned substrate sheet to finally prepare an uncalibrated calibration block; measure the actual processing area of ​​the uncalibrated calibration block; characterize the uncalibrated calibration block using a scanning electron microscope and collect the length X' and width Y' of the uncalibrated calibration block;

[0013] (4) Deflection correction of the scanning galvanometer of the femtosecond laser processing system;

[0014] The specific steps are as follows: the length X' of the uncorrected calibration block is compared with the designed length X to obtain k1=X' / X, the width Y' of the uncorrected calibration block is compared with the designed width Y to obtain k2=Y' / Y, and a machining error curve is drawn with X and Y as the horizontal coordinates and k as the vertical coordinate, and the original machining point data is pre-compensated according to the corresponding relationship between the length and width data of the uncorrected calibration block and the length and width data of the calibration block in the machining error curve;

[0015] (5) Deflection correction of the scanning plane of the scanning galvanometer of the femtosecond laser processing system;

[0016] Place a pre-prepared substrate in the galvanometer-based femtosecond laser processing system, adjust the laser energy to a reference value, focus the laser on the interface between the polymer film and the substrate, and rotate the stage support screws to ensure that the laser focus spot energy remains unchanged when the substrate moves left and right and forward and backward. At this time, it is determined that the substrate has been leveled.

[0017] The laser focus point at the interface between the polymer film and the substrate is set as the coordinate origin (0,0,0). When the laser focus is located at (0,0,0), the laser energy is set as a reference value. At this time, the gray value of the spot formed by the laser focus is P, which is set as the spot energy reference value. The deflection angle of the scanning galvanometer is adjusted so that the laser focus is located on the substrate plane, and the horizontal and vertical coordinates are (Xa, Ya), (Xb, Yb) and (Xc, Yc) respectively. The Z-axis height is adjusted so that the gray value of the spot formed by the laser focus is P, and the Z-axis change heights △Za, △Zb and △Zc in this process are recorded, where upward is positive and downward is negative; then the coordinates of the three points on the laser scanning plane are determined to be (Xa, Ya, △Za), (Xb, Yb, △Zb) and (Xc, Yc, △Zc); projection mapping is performed on the horizontal plane according to the coordinate plane where the three points are located, so that the plane to be processed overlaps with the interface between the polymer film and the substrate, and the processing point data corrected by the Z coordinate is obtained, and the corrected processing point data is imported into the processing software for processing.

[0018] Furthermore, in step (1), the optical resin includes epoxy resin SU-8, organic and inorganic hybrid photoresist IP-DIP, SZ2080 and UV optical curing glue NOA61, NOA63; the optical resin is dripped onto the substrate through a rubber-tipped dropper, and the liquid dosage is set to 1 drop; the heating temperature of the substrate in the pre-baking stage is maintained at 80 to 110°C, and the heating time is 80 to 100 minutes; in order to prevent the photoresist from failing due to exposure, both the photoresist dripping step and the heating step must be carried out under a yellow light environment; the size of the substrate is 24×24×0.14 mm.

[0019] Furthermore, in step (2), the galvanometer-based femtosecond laser processing system includes an optical fiber femtosecond laser oscillator, an attenuation plate, an optical gate, a reflector, a beam expansion system, a scanning galvanometer, a 4F optical system and an oil-immersed objective lens; the femtosecond pulse laser is generated by the femtosecond laser oscillator, and the transmission path is the attenuation plate and the optical gate in sequence, and enters the beam expansion system after being reflected by the reflector. The deflection angle of the laser beam after beam expansion is controlled by the scanning galvanometer, and then the laser beam is projected to the entrance pupil position of the objective lens with the help of the 4F optical system. After passing through the oil-immersed objective lens, the laser beam is focused inside the processed sample and cooperates with the movement of the translation stage to achieve a three-dimensional scanning function; a real-time monitoring system composed of an illumination light source, a filter and an imaging CCD is used to observe and record the status in real time during the sample processing process, so as to accurately grasp the processing progress and effect, and provide a reliable visualization basis for subsequent research and analysis and process optimization.

[0020] Furthermore, the femtosecond laser center wavelength of the galvanometer-based femtosecond laser processing system is 780nm, the pulse width is 80-180fs, and the repetition frequency is 85-100MHz; the attenuation plate is a gradient density filter with an operating wavelength of 400-1100nm; and the reflector is a dielectric film reflector with an operating wavelength of 800nm.

[0021] Furthermore, in step (3), the laser processing power is 15-35mw, and the single-point exposure time is 200-2000μs; after the scanning is completed, the substrate is removed and placed in a beaker with the side with the polymer film facing downward; a developer is poured along the wall of the beaker to cover the polymer film for development; the photoresist development time is 20-90min; the above operations are all carried out under a yellow light environment; the wavelength of the ultraviolet lamp used for ultraviolet exposure is 300-450nm, the power of the ultraviolet lamp is 5-10W, and the exposure time is 3-60min.

[0022] Furthermore, the minimum intervals between the length X and the width Y of the calibration block are 20 μm and 10 μm, respectively.

[0023] Furthermore, in step (5), three points on different straight lines determine a plane, i.e., the plane on which the scanning galvanometer controls the laser deflection. By moving the Z-axis position, the energy of the laser spot at the three points is made the same, and the Z-axis variables of each point are recorded. A model is established to obtain the mapping of the laser deflection plane to the substrate plane through the variables. Based on this result, the original structure processing data is deflected to realize the leveling of the galvanometer scanning plane and the substrate plane in the femtosecond laser processing system, as follows:

[0024] Assume that the plane equation of the scanning galvanometer controlling the laser deflection is Ax+By+Cz+D=0, where A, B, C are the plane normal vector components and D is a constant; any point on the plane satisfies the above equation; the normal vector of the plane of laser deflection is (A, B, C); by rotating the coordinate system, the plane normal vector of the laser deflection points to the Z axis, that is, the new normal vector is (0, 0, 1); calculate the rotation matrix between the normal vector (A, B, C) and (0, 0, 1) The coordinates of all points on the plane where the laser is deflected are transformed through the rotation matrix The transformation is performed to obtain a new point (X", Y", Z"), where Z" is a constant. The Z" of the bottom processing point data is translated to 0 by up and down translation, thus completing the leveling of the laser scanning plane and the substrate plane.

[0025] Furthermore, the reference point coordinates Xa, Xb, Xc and Ya, Yb, Yc in the scanning plane calibration range from 40 μm to 60 μm. If the reference point distance is too small, the calibration result will be affected and inaccurate. If the value exceeds 60 μm, it is beyond the observable range of this machining system and data cannot be obtained.

[0026] Compared with the prior art, the advantages of the present invention are as follows:

[0027] (1) The calibration of the scanning galvanometer of a femtosecond laser processing system of the present invention collects the length and width data of the calibration block and performs pre-compensation operation on the original structure processing file, thereby eliminating the error of the processing structure size caused by the deflection of the laser through the scanning galvanometer reflector;

[0028] (2) By collecting the angle difference between the scanning plane of the scanning galvanometer laser and the substrate plane, the original structure processing file is subjected to a plane deflection correction operation, thereby eliminating the problem of misalignment between the scanning plane and the substrate plane, and making each area of ​​the scanned structure highly consistent;

[0029] (3) The galvanometer-based femtosecond laser two-photon polymerization processing system can realize the preparation of high-precision, large-size true three-dimensional structures, successfully optimizing the processing capabilities of the galvanometer-based femtosecond laser processing system;

[0030] (4) It has the outstanding advantages of universal method, strong operability and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0032] Figure 1 This is a calibration flow chart for the scanning galvanometer of a femtosecond laser processing system;

[0033] Figure 2 The schematic diagram of the femtosecond laser deflection error caused by the complex optical transformation relationship between the scanning galvanometer reflection and the 4F system;

[0034] Figure 3 It is a schematic diagram of the position relationship between the laser scanning plane and the substrate plane after leveling;

[0035] Figure 4 This is a schematic diagram of the optical path of the galvanometer-based femtosecond laser processing system;

[0036] Figure 5 This is a physical diagram of the optical path of the galvanometer-based femtosecond laser processing system;

[0037] Figure 6 The scanning electron microscopy characterization images of squares of different sizes are not corrected for size;

[0038] Figure 7 Scanning electron microscope characterization images of blocks of different sizes that have been size-corrected for the present invention;

[0039] Figure 8 It is a schematic diagram of the relationship between the deflection correction coefficient and the deflection distance in the X and Y directions;

[0040] Fig. 9 This is a scanning electron microscope characterization image of a large-area grid structure prepared without correction of the deflection plane and the substrate sheet plane of the present invention;

[0041] Fig.10 This is a scanning electron microscope characterization image of the large-area grid structure prepared through scanning galvanometer correction and pre-compensation of the present invention. DETAILED DESCRIPTION

[0042] In order to clearly and completely describe the technical solution and its specific working process of the present invention, the specific implementation methods of the present invention are as follows in conjunction with the accompanying drawings of the specification:

[0043] Example 1

[0044] like Figure 1As shown, this embodiment adopts an error compensation correction method for a femtosecond laser galvanometer 4F processing system, which specifically includes the following steps:

[0045] Step 1: Place the substrate in an ultrasonic machine for ultrasonic cleaning for 5 minutes to remove large debris and dust particles on its surface. Then wipe the substrate with a cotton ball soaked in anhydrous ethanol, rinse its surface with deionized water to remove residual ethanol, and then place it in a vacuum drying oven at 70°C to dry for 6 minutes. Use a rubber-tipped dropper to take 1 drop of SZ2080 photoresist and drop it on the clean substrate; place the substrate on a hot plate and heat it at a temperature of 100°C to form a polymer film, and then cool it at room temperature;

[0046] Step 2: Level the processing system, insert the prepared substrate, accurately adjust the laser energy to the reference value, and focus the laser beam on the interface between the polymer film and the substrate. By rotating the stage support screw, the laser spot intensity remains unchanged when the substrate moves left and right and forward and backward; then, focus the laser again to the interface between the polymer film and the substrate. At this time, the laser focus does not deflect during the leveling process, but the spot energy remains unchanged when the substrate moves horizontally, which may also cause the subsequent laser scanning plane to not coincide with the substrate plane;

[0047] Step 3: According to the existing femtosecond laser processing system, five calibration blocks of different sizes are processed, and the length and width are respectively X1=20μm, Y1=10μm; X2=40μm, Y2=20μm; X3=60μm, Y3=30μm; X4=80μm, Y4=40μm; X5=150μm, Y5=60μm; and the length and width (X' and Y') data are obtained by characterizing them using a scanning electron microscope, X1'=20μm, Y1'=10μm; X2'=39.6μm, Y2'=19.8μm; X3'=59.3μm, Y3'=29.5μm; X4'=79μm, Y4'=39.4μm; X5'=147.3μm, Y5'=58.5μm;

[0048] Step 4: Establish the processing error curve of the femtosecond laser processing system, and obtain the nonlinear relationship between the ratio k of the length (X'), width (Y') of the collected calibration block and the designed length (X) and width (Y) and X and Y respectively; obtain the error from the relationship curve and perform pre-compensation correction in the point processing data.

[0049] like Figure 2The figure shows the principle diagram of the error between the deflection size of the femtosecond laser and the calibrated size. Due to the limitation of the combination of multiple lenses in the system, a deflection error will occur when the scanning galvanometer controls the laser deflection. When the deflection angle of the scanning galvanometer is small, the error between the two is small when the size of the processed sample is small. When the deflection angle of the scanning galvanometer is large, there is an obvious error with the size of the processed sample. The figure describes that when the galvanometer controls the laser to deflect at a large angle, the actual deflection distance is smaller than the theoretical deflection distance, resulting in an error in the size of the processed structure.

[0050] like Figure 3 As shown in the figure, there is a schematic diagram of the position relationship between the laser scanning plane and the plane of the substrate sheet after leveling. During the experiment, in the process of leveling the substrate sheet, the support screws of the stage are rotated so that the energy of the laser spot remains unchanged when the substrate sheet moves forward, backward, left and right. However, at this time, it cannot be guaranteed that the scanning plane during laser deflection coincides with the plane of the substrate sheet after leveling. Affected by the lens alignment error in the optical system, the laser scanning plane and the plane of the substrate sheet after leveling often do not coincide, which also results in the sample not having good uniformity during processing.

[0051] like Figure 4 and Figure 5 As shown in the figure, in the processing system, the femtosecond pulse laser generated by the femtosecond laser oscillator first passes through the attenuation plate and the light gate, and then is transmitted through the reflector and enters the beam expansion system. After the beam expansion, the laser beam with a beam size increased five times is deflected by the scanning galvanometer to adjust its deflection angle, and then the laser beam is projected to the entrance pupil position of the objective lens with the help of the 4F optical system. This laser beam is further focused on the inside of the processing sample through the oil-immersed objective lens, and the three-dimensional scanning function is realized by coordinating with the movement of the translation stage.

[0052] like Figure 6 and Figure 7 As shown in the figure, the length and width of the squares of different sizes that have not been size-corrected have obvious errors compared with the theoretical length and width, while the length and width of the squares of different sizes that have been size-corrected are basically consistent with the theoretical length and width, where the red frame range represents the theoretical size of the square; this shows that we have achieved the correction of the deflection angle of the scanning galvanometer by performing pre-compensation operations on the processing point data file.

[0053] like Figure 8 As shown in the figure, when the calibration block length X is 20μm, its correction coefficient is 1, that is, the actual scanned block length X' is also 20μm. When the calibration block length X is 150μm, its correction coefficient is 0.982, that is, the actual scanned block length X' is 147.3μm. When the calibration block width Y is 10μm, its correction coefficient is 1, that is, the actual scanned block width Y' is also 10μm. When the calibration block width Y is 60μm, its correction coefficient is 0.975, that is, the actual scanned block width Y' is 58.5μm.

[0054] Example 2

[0055] This embodiment provides a method for leveling a scanning plane of a femtosecond laser galvanometer 4F processing system and a substrate plane, and the specific steps are as follows:

[0056] (1) Sample preparation and system leveling;

[0057] Specific steps: First, carry out preliminary pretreatment work on the substrate sheet. Place the substrate sheet in an ultrasonic machine for ultrasonic cleaning for 5 minutes to remove large debris and dust particles on its surface. Subsequently, wipe the substrate sheet with a cotton ball soaked in anhydrous ethanol, rinse its surface with deionized water to remove residual ethanol, and then place it in a vacuum drying oven at 70°C for 6 minutes. Next, use a rubber-tipped dropper to take a drop of optical resin SZ2080 and drop it on the surface of the above-treated substrate sheet. After that, place the substrate sheet in front of the heating table for baking, the pre-baking temperature is set to 90°C, the pre-baking time is 100 minutes, and the pre-baking is completed. Cooling treatment is carried out at room temperature. Then, the pre-prepared substrate sheet is placed in the galvanometer-based femtosecond laser direct writing processing system, the laser energy is accurately adjusted to the reference value, and the laser beam is focused on the interface between the polymer film and the substrate sheet. By rotating the stage support screws, the light spot energy can be kept constant when the substrate moves left and right and forward and backward. At this moment, the substrate is determined to be leveled, and the laser is focused on the interface between the polymer film and the substrate. At this time, the focal position is set as the origin of the coordinate axis.

[0058] Among them, the femtosecond pulse laser (with a central wavelength of 800nm, a pulse width of 100fs, and a repetition frequency of 80MHz) generated by the femtosecond laser oscillator passes through the attenuation plate and the optical gate in turn, and then passes through the reflector and the beam expansion system, causing the laser beam to increase its beam size five times. The laser beam uses the scanning galvanometer to adjust its deflection angle, and then the 4F optical system deflects the angle of the laser beam and projects it to the entrance pupil position of the objective lens. The oil-immersed objective lens with a numerical aperture of 1.35 and a magnification of 60 times produced by Olybus is used to focus the incident light tightly inside the processed sample, thereby realizing three-dimensional scanning processing. At the same time, the real-time monitoring system composed of the illumination light source, the filter and the CCD can monitor the status of the sample in real time during the processing. Among them, the illumination light source uses a white LED light source; the filter uses a band-selective absorption filter with a transmission range of 580-2300nm; the real-time observation system CCD is a domestic high-definition driver-free industrial camera.

[0059] (2) Scanning galvanometer controls the acquisition of laser deflection plane data;

[0060] Specific steps: Control the scanning galvanometer to deflect and move the horizontal and vertical coordinates of the laser spot to three points that are not on the same straight line. The horizontal and vertical coordinates of these three points are (0,40), (0,-40), and (40,0), respectively; adjust the laser spot energy to the reference value at the horizontal and vertical coordinates (0,0), and the gray value of the spot formed by the laser focus is 70; deflect the laser to the horizontal and vertical coordinates (0,40), adjust the laser spot energy to the reference value by moving the Z axis, and record the moving height as -2μm; Deflect the laser to the horizontal and vertical coordinates (0, -40), adjust the laser spot energy to the reference value by moving the Z axis and record the moving height as 0μm; deflect the laser to the horizontal and vertical coordinates (40, 0), adjust the laser spot energy to the reference value by moving the Z axis and record the moving height as -13μm; so the laser deflection plane is on the plane determined by the three points (0, 40, 2), (0, -40, 0) and (40, 0, -13); the above coordinate units are all microns. After the substrate is leveled, it is considered to be a horizontal plane. Through plane mapping, the above laser scanning plane is mapped to the horizontal plane, and the original processing data is pre-compensated. From the coordinates of the above three points, it is known that the normal vector of the laser scanning plane is right Normalize it to become a unit vector The rotation axis is the cross product of the normal vector and the Z-axis vector (0,0,1), which is (-0.024,-0.330,0). The calculated rotation angle is about θ=8.1°. Construct the rotation matrix in is the identity matrix, is the antisymmetric matrix about the rotation axis.

[0061] After coordinate transformation Then, the coordinates are translated to make the Z" of the bottom processing point data translate to 0. After the above operation, the xyz correction of all processing point file data is realized, and the leveling of the laser scanning plane and the substrate plane is completed.

[0062] (3) Sample preparation and characterization;

[0063] Specific steps: After the above-mentioned leveling and pre-compensation of the original data of the processed structure, open the processed point cloud file of the processed structure in the processing software. Adjust the attenuation plate so that the laser power in front of the objective lens is 20.0mw, set the single point exposure time to 200μs, and start point-by-point scanning processing.

[0064] The processed structure is a large-area grid structure of 200μm*200μm*500nm;

[0065] Development and drying of the device: Place the processed substrate in the photoresist developer n-propanol and soak for 50 minutes. After the development is completed, take the substrate out of the developer and dry it naturally.

[0066] like Fig. 9 It can be seen from the scanning electron microscope photo of the large-area grid structure that was prepared without leveling the scanning plane and the substrate sheet plane; because the laser scanning plane and the substrate sheet plane do not coincide, the right side of the grid shows that the structure is not scanned, the processing effect is not ideal, and the consistency of the structure under the same parameters is poor.

[0067] like Fig.10 It can be seen that the scanning electron microscope photos of the large-area grid structure prepared after scanning galvanometer correction and pre-compensation; after correction, the grids are scanned and the processing effect is good.

[0068] Traditional galvanometer-based femtosecond laser processing systems have nonlinear deviations between the galvanometer deflection angle and the preset scanning position, and the scanning plane may be inconsistent with the substrate plane, which causes errors in the length and width of the processed structure and deviations in the processing height. The femtosecond laser processing system scanning galvanometer correction scheme proposed in this embodiment enables the size of the processed structure to be accurately controlled and also provides a high degree of consistency in large-area preparation.

[0069] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0070] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0071] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A femtosecond laser galvanometer 4F processing system error compensation correction method, characterized in that: The specific steps include: (1) Sample preparation; The specific steps are as follows: dropping the optical resin on a substrate; wherein the substrate is a clean substrate that has been wiped with an alcohol cotton ball, rinsed with deionized water and dried in advance; placing the substrate on a hot table for preheating to form a polymer film, and then cooling it naturally at room temperature; (2) Leveling processing system; Specific steps: First, place the prepared substrate in the galvanometer-based femtosecond laser processing system, adjust the laser energy to the reference value, and focus the laser beam on the interface between the polymer film and the substrate; rotate the stage support screw until the spot energy is always constant when the substrate moves left and right and forward and backward, and it is judged that the substrate has been leveled; then, focus the laser again to the interface between the polymer film and the substrate; (3) Processing and characterization of calibration blocks; Specific steps: prepare calibration blocks with different lengths X and widths Y according to measurement needs; generate point data files for each calibration block and import them into processing software; set the laser processing power and perform point-by-point scanning processing; develop, dry and ultraviolet-expose the scanned substrate sheet to finally prepare an uncalibrated calibration block; measure the actual processing area of ​​the uncalibrated calibration block; characterize the uncalibrated calibration block using a scanning electron microscope and collect the length X' and width Y' of the uncalibrated calibration block; (4) Deflection correction of the scanning galvanometer of the femtosecond laser processing system; The specific steps are as follows: the length X' of the uncorrected calibration block is compared with the designed length X to obtain k1=X' / X, the width Y' of the uncorrected calibration block is compared with the designed width Y to obtain k2=Y' / Y, and a machining error curve is drawn with X and Y as the horizontal coordinates and k as the vertical coordinate, and the original machining point data is pre-compensated according to the corresponding relationship between the length and width data of the uncorrected calibration block and the length and width data of the calibration block in the machining error curve; (5) Deflection correction of the scanning plane of the scanning galvanometer of the femtosecond laser processing system; Place a pre-prepared substrate in the galvanometer-based femtosecond laser processing system, adjust the laser energy to a reference value, focus the laser on the interface between the polymer film and the substrate, and rotate the stage support screws to ensure that the laser focus spot energy remains unchanged when the substrate moves left and right and forward and backward. At this time, it is determined that the substrate has been leveled. The laser focus point at the interface between the polymer film and the substrate is set as the coordinate origin (0,0,0). When the laser focus is located at (0,0,0), the laser energy is set as a reference value. At this time, the gray value of the spot formed by the laser focus is P, which is set as the spot energy reference value. The deflection angle of the scanning galvanometer is adjusted so that the laser focus is located on the substrate plane, and the horizontal and vertical coordinates are (Xa, Ya), (Xb, Yb) and (Xc, Yc) respectively. The Z-axis height is adjusted so that the gray value of the spot formed by the laser focus is P, and the Z-axis change heights △Za, △Zb and △Zc in this process are recorded, where upward is positive and downward is negative; then the coordinates of the three points on the laser scanning plane are determined to be (Xa, Ya, △Za), (Xb, Yb, △Zb) and (Xc, Yc, △Zc); projection mapping is performed on the horizontal plane according to the coordinate plane where the three points are located, so that the plane to be processed overlaps with the interface between the polymer film and the substrate, and the processing point data corrected by the Z coordinate is obtained, and the corrected processing point data is imported into the processing software for processing.

2. The error compensation correction method of a femtosecond laser galvanometer 4F processing system according to claim 1, characterized in that: In step (1), the optical resin includes epoxy resin SU-8, organic and inorganic hybrid photoresist IP-DIP, SZ2080 and UV optical curing glue NOA61, NOA63; the optical resin is dripped onto the substrate through a rubber-tipped dropper, and the liquid dosage is set to 1 drop; the heating temperature of the substrate in the pre-baking stage is maintained at 80 to 110°C, and the heating time is 80 to 100 minutes; the size of the substrate is 24×24×0.14 mm.

3. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: In step (2), the galvanometer-based femtosecond laser processing system includes an optical fiber femtosecond laser oscillator, an attenuation plate, an optical gate, a reflector, a beam expansion system, a scanning galvanometer, a 4F optical system and an oil-immersed objective lens; the femtosecond pulse laser is generated by the femtosecond laser oscillator, and the transmission path is the attenuation plate and the optical gate in sequence, and enters the beam expansion system after being reflected by the reflector. The deflection angle of the laser beam after beam expansion is controlled by the scanning galvanometer, and then the laser beam is projected to the entrance pupil position of the objective lens with the help of the 4F optical system. After passing through the oil-immersed objective lens, the laser beam is focused inside the processed sample and cooperates with the movement of the translation stage to achieve the function of three-dimensional scanning; the real-time monitoring system composed of the illumination light source, the filter and the imaging CCD is used to observe and record the status in real time during the sample processing process.

4. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: The femtosecond laser center wavelength of the galvanometer-based femtosecond laser processing system is 780nm, the pulse width is 80-180fs, and the repetition frequency is 85-100MHz; the attenuation plate is a gradient density filter with an operating wavelength of 400-1100nm; the reflector is a dielectric film reflector with an operating wavelength of 800nm.

5. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: In step (3), the laser processing power is 15-35mw, and the single-point exposure time is 200-2000μs; after the scanning is completed, the substrate is removed and placed in a beaker with the side with the polymer film downward; a developer is poured along the wall of the beaker to cover the polymer film for development; the photoresist development time is 20-90min; the above operations are all performed under a yellow light environment; the wavelength of the ultraviolet lamp used for ultraviolet exposure is 300-450nm, the power of the ultraviolet lamp is 5-10W, and the exposure time is 3-60min.

6. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: The minimum intervals between the length X and width Y of the calibration block are 20 μm and 10 μm respectively.

7. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: In step (5), three points on different straight lines determine a plane, i.e., the plane on which the scanning galvanometer controls the laser deflection. By moving the Z-axis position, the laser spot energy of the three points is made the same, and the Z-axis variables of each point are recorded. A model is established to obtain the mapping of the laser deflection plane to the substrate plane through the variables. Based on this result, the original structure processing data is deflected to realize the leveling of the galvanometer scanning plane and the substrate plane in the femtosecond laser processing system, as follows: Assume that the plane equation of the scanning galvanometer controlling the laser deflection is Ax+By+Cz+D=0, where A, B, C are the plane normal vector components and D is a constant; any point on the plane satisfies the above equation; the normal vector of the plane of laser deflection is (A, B, C); by rotating the coordinate system, the plane normal vector of the laser deflection points to the Z axis, that is, the new normal vector is (0, 0, 1); calculate the rotation matrix between the normal vector (A, B, C) and (0, 0, 1) The coordinates of all points on the plane where the laser is deflected are transformed through the rotation matrix The transformation is performed to obtain a new point (X", Y", Z"), where Z" is a constant. The Z" of the bottom processing point data is translated to 0 by up and down translation, thus completing the leveling of the laser scanning plane and the substrate plane.

8. The error compensation correction method of a femtosecond laser galvanometer 4F processing system as claimed in claim 1, characterized in that: The value range of the reference point coordinates Xa, Xb, Xc and Ya, Yb, Yc in the scanning plane correction is 40μm-60μm.

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