Bidirectional and bifocal inscribing focal plane focusing method and device for laser direct writing

Abstract

The invention discloses a bidirectional and bifocal inscribing focal plane focus fixing method and device for laser direct writing, and belongs to the field of optical precision detection.The method comprises the steps that a first auxiliary focus fixing laser beam and a second auxiliary focus fixing laser beam are arranged at the front and back symmetrical positions of an inscribing focusing laser beam respectively in the laser direct writing scanning path direction; the reflected signal intensity of the two auxiliary fixed-focus laser beams is detected through the two detection modules respectively; the method comprises the following steps: when laser direct writing carries out preset pattern inscribing in a specific scanning mode, according to different scanning path directions, dividing the scanning direction into forward scanning and reverse scanning, and when forward scanning and reverse scanning are carried out, detecting the reflected signal intensity of an auxiliary fixed-focus laser beam at the front side position of an inscribing focusing laser beam in the direction; and locking the focal plane of the inscribing laser beam. The bidirectional scanning technology is adopted, the machining speed is effectively increased, the overall efficiency is effectively improved, and the precision is improved by combining the double-auxiliary fixed-focus laser beam and the differential confocal detection technology.

Description

Technical Field

[0001] The present invention relates to the field of optical precision detection, and in particular to a method and device for fixing the focus of a bidirectional and dual-focus writing focal plane for laser direct writing. Background Art

[0002] Laser direct writing technology uses the photo-chemical or photo-physical interaction between a focused laser beam with adjustable intensity and photoresist to prepare pre-set micro-nano structures. With its high processing flexibility and arbitrary three-dimensional graphics processing capabilities, this technology has been widely used in the printing and manufacturing of high-precision complex micro-nano devices such as meta-lenses and microfluidic chips. In the laser direct writing process, positioning the focal plane of the focused laser beam and maintaining a stable action distance between the focal plane and the photoresist are key factors in determining the resolution of micro-nano graphics. However, due to mechanical and environmental instability, system disturbances such as mechanical vibration and axial drift often occur during the processing process, resulting in defocusing of the direct writing process, thereby reducing the resolution of the processed graphics and causing inconsistent writing line width.

[0003] In order to improve the writing resolution of laser direct writing and ensure the consistency of processing line width, it is usually necessary to integrate an auxiliary focusing system into the laser direct writing system. The system monitors the focal plane position of the focused laser beam in real time, and feeds back the position offset to the translation stage to adjust and maintain the focal plane position, thereby eliminating the writing error caused by system disturbance. Traditional auxiliary focusing systems mostly use a single-point focusing method, using a weak auxiliary focusing beam with a wavelength located in the transparent window of photoresist absorption, and locking the focal plane of the writing focused laser beam by positioning the focal plane position of the auxiliary focusing laser beam, so as to achieve high-precision and long-term laser direct writing processing. However, laser direct writing technology often uses raster scanning to perform arbitrary graphic processing. During the reciprocating scanning process, single-point focus tracking relies on a single focus point to accurately focus on a specific area. This focusing method is difficult to quickly refocus in fast-moving or multi-target scenarios because it needs to switch from a single focus to another focus, and the process takes a long time. At the same time, the single-point focusing method cannot adjust the focus prediction amount according to the change of the scanning direction, which can easily lead to focus errors related to the scanning direction, which is not conducive to stable and high-precision processing of large-area laser direct writing.

[0004] Traditional writing technology usually adopts a unidirectional scanning strategy, that is, the laser only performs direct writing or printing operations in a single moving direction, and does not actively print in the return stroke. Under the unidirectional scanning strategy, the laser beam moves in a fixed direction, which helps to reduce errors caused by direction changes, improve writing accuracy, and facilitate synchronization and control, reducing system complexity. However, unidirectional scanning is less efficient when writing large areas or complex structures, because it needs to return to the starting point after each scan, increasing non-productive time, resulting in only half of the movement being used for writing, reducing overall efficiency. In contrast, bidirectional scanning can write in both directions, significantly improving processing efficiency. Bidirectional scanning provides higher processing flexibility and adapts to more complex graphics and structures, especially for large-area processing. However, in bidirectional scanning, maintaining writing accuracy is more challenging, and the movement and focus of the laser beam in both directions must be precisely controlled. Therefore, unidirectional scanning and bidirectional scanning each have their own advantages and disadvantages in laser direct writing technology. Unidirectional scanning is more suitable in some applications due to its simplicity and accuracy, especially for occasions requiring high accuracy and repeatability, but its efficiency and processing speed may be limited. Bidirectional scanning provides higher processing efficiency and flexibility and is suitable for processing large areas and complex structures, but it may require a more complex control system and higher costs. Summary of the invention

[0005] The present invention aims to address the deficiencies of the prior art and to provide a method and device for laser direct writing with a bidirectional and dual-focus writing focal plane.

[0006] The object of the present invention is achieved through the following technical scheme: a two-way, dual-focus writing focal plane focusing method for laser direct writing, the method comprising:

[0007] Along the laser direct writing scanning path direction, a first auxiliary fixed-focus laser beam and a second auxiliary fixed-focus laser beam are respectively arranged at symmetrical positions in front and behind the writing focused laser beam;

[0008] Respectively detecting the reflected signal intensities of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam by two differential confocal detection modules;

[0009] When laser direct writing performs preset graphics engraving through a specific scanning method, the scanning direction is divided into forward scanning and reverse scanning according to the different directions of the scanning path. When performing forward scanning and reverse scanning, the reflection signal intensity of the auxiliary fixed-focus laser beam at the front side of the writing focused laser beam in this direction is detected to lock the focal plane of the writing laser beam.

[0010] Furthermore, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are generated by emitting laser light from a laser and then splitting the laser light through a Wollaston prism, wherein the first auxiliary fixed-focus laser beam is ordinary light and the second auxiliary fixed-focus laser beam is extraordinary light.

[0011] Furthermore, after being split by the Wollaston prism, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam will enter the D-type mirror, and after being reflected by the D-type mirror respectively, enter the writing objective lens through the beam splitting cube and focus on the front and rear sides of the writing focused laser beam.

[0012] Furthermore, the specific scanning mode includes raster scanning and vector scanning.

[0013] Furthermore, the laser wavelengths of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are different from the laser wavelength of the writing focused laser beam, and are located in the transparent absorption window of the photoresist.

[0014] Furthermore, the detection of the reflected signal intensity of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam includes: using a differential confocal detection method, focusing the reflected signal using an imaging lens and dividing it into two paths, detecting the reflected signals of the two paths at the position before the lens focus and the position after the focus, respectively, and determining the difference curve of the reflected signal intensity through the difference of the detectors, taking the linear change segment therein as the feedback fixed-focus signal to determine the focal position of the displacement stage.

[0015] According to another aspect of the specification, there is also provided a bidirectional, dual-focus writing focal plane focusing device for laser direct writing, the device comprising: a laser, a Wollaston prism, a D-type reflector group, a first beam splitter, an objective lens, a first differential confocal detection module and a second differential confocal detection module;

[0016] The laser is used as an auxiliary fixed-focus laser. The emitted laser is divided into two laser beams with mutually perpendicular polarization directions at a certain angle by the Wollaston prism. After being respectively reflected by the D-type reflector group, the two laser beams are transmitted through the beam splitter and incident along the objective lens at a certain angle respectively. After being focused by the objective lens, the surface of the writing sample is irradiated. The focused light spot corresponds to the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam, which are respectively located on the front and back sides of the focused writing beam. The detection signal reflected by the wafer surface is separated from the main beam by the beam splitter. The first differential confocal detection module and the second differential confocal detection module are used to respectively receive the detection signals after the reflection of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam to perform confocal measurement.

[0017] Further, the first differential confocal detection module and the second differential confocal detection module each include: an imaging lens, a second beam splitter, a first detector and a second detector;

[0018] The optical path is as follows: after the reflected signal is focused by an imaging lens, it is divided into two paths by a second beam splitter, in which the first detector is used to detect the signal in front of the lens focus in one path, and the second detector is used to detect the signal in the position behind the lens focus in the other path, wherein the distances before and after the focus are the same from the focus.

[0019] Beneficial effects of the present invention: The present invention reduces the time it takes for the laser head to return to the starting point after each scan by adopting a bidirectional scanning technology, thereby effectively improving the processing speed and overall efficiency. This improvement makes the engraving process of large areas and complex structures more efficient. Secondly, the present invention greatly improves the engraving accuracy. The use of a dual auxiliary fixed-focus laser beam combined with differential confocal detection technology ensures accurate positioning of the focus during the bidirectional scanning process, effectively ensures the consistency of the line width during the writing process, and reduces errors caused by changes in direction. Finally, the present invention has real-time focusing capabilities, and can achieve real-time focus tracking by detecting changes in the focal plane position in advance, ensuring that the substrate is always engraved at the best focus quality, further reducing processing errors. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a dual-focus focusing device according to an embodiment of the present invention.

[0021] Figure 2 Write line graphics for the out-of-focus moments.

[0022] Figure 3 Write line graphics for dual focus two-way fixed focus moments.

[0023] Figure 4 Schematic diagram of a differential confocal detection module in an embodiment.

[0024] Figure 5 The collected signal is from the differential confocal detection module.

[0025] Figure 6 Schematic diagram of dual-focus focusing method under different scanning modes. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0027] It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and thus the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0028] The embodiment of the present invention first provides a method for setting the focus of a bidirectional and dual-focus writing focal plane for laser direct writing, the method comprising the following steps:

[0029] Along the direction of the laser direct writing scanning path, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are respectively arranged at symmetrical positions in front and behind the writing focused laser beam; the reflection signal strengths of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are respectively detected confocally by two differential confocal detection modules to lock the focal plane of the writing laser beam; when the laser direct writing performs preset graphics engraving through a specific scanning method, the scanning direction is divided into forward scanning and reverse scanning according to the different directions of the scanning path, wherein the first auxiliary fixed-focus laser beam is located in front of the writing focused laser beam during forward scanning, and the second auxiliary fixed-focus laser beam is located in front of the writing focused laser beam during reverse scanning; during forward scanning writing, the first differential confocal detection module is used to detect the reflection signal strength of the first auxiliary fixed-focus laser beam to lock the focal plane of the writing laser beam; during reverse scanning writing, the second differential confocal detection module is used to detect the reflection signal strength of the second auxiliary fixed-focus laser beam to lock the focal plane of the writing laser beam.

[0030] In the above method, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are obtained by splitting the laser emitted by the laser through a Wollaston prism, wherein the first auxiliary fixed-focus laser beam is ordinary light (o light), and the second auxiliary fixed-focus laser beam is extraordinary light (e light), and the two beams of light will form a certain angle of separation after leaving the Wollaston prism, and the angle can be determined by the wedge angle of the prism and the wavelength of the laser.

[0031] After the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are split by the Wollaston prism, they will enter the D-type mirror. Since the D-type mirror is mainly used to change the diameter or direction of the beam, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam will be reflected by the D-type mirror respectively. Subsequently, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam pass through the beam splitting cube and enter the writing objective lens, and are focused on the front and rear sides of the writing focused laser beam.

[0032] The first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam do not need to be strictly located at symmetrical positions before and after the writing focused laser beam, but only need to be located before and after the writing focused laser beam. The distance between this position and the writing focused laser beam will be divided by the writing speed to obtain the delay time, which will be fed back to the computer to ensure real-time focus tracking. Specifically, since the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are located in front of and behind the writing focused laser beam, respectively, they can detect changes in the focal plane position in advance. Therefore, when the writing focused laser beam reaches the target position for writing, the system has completed the focusing operation, thereby ensuring the precise locking of the focal plane position and realizing the real-time focus tracking function.

[0033] Specific scanning modes of laser direct writing technology generally include raster scanning and vector scanning, and this method is applicable to both scanning modes.

[0034] The laser wavelengths of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are usually different from the laser wavelength of the writing focused laser beam, and the laser wavelengths of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are often located in the transparent absorption window of the photoresist.

[0035] After reaching the wafer surface, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam will carry the wafer information and reflect back to the original path, and continue to pass through the beam splitter cube. The reason for choosing the beam splitter cube is that in differential confocal detection, the detector used has an extremely high amplification gain for the incident light intensity. Excessive light intensity may damage the cathode, thereby increasing noise, reducing the sensitivity of the detector and shortening its service life. Therefore, the beam splitter cube is introduced in the optical path to weaken the intensity of the laser beam. In theory, each time the laser beam passes through the beam splitter cube, its light intensity will be weakened by 50%; after passing through the beam splitter cube twice, the laser can operate at the middle power end, thereby effectively reducing the influence of the dark noise of the laser itself on the light intensity stability.

[0036] The differential confocal detection method uses two detectors symmetrically arranged on both sides of the focal plane to collect the defocus light intensity signal. When the substrate interface and the focal plane of the objective lens coincide precisely, the light intensity signals recorded by the two detectors are equal, which is the measurement benchmark. Once the substrate is displaced and defocused, the signals of the two detectors will show an increase and decrease trend, and the change direction is opposite. In addition, by scanning with the help of the Z-axis translation stage, the normalized axial light intensity response curves of the two detectors can be obtained, and then the differential axial response curve can be constructed. The curve shows a linear relationship in a specific area, and the functional relationship between the differential response signal and the defocus amount can be established through linear fitting. Based on this, the system can calculate the defocus amount in real time, realize the automatic focus tracking function, and ensure that the substrate is always engraved with the best focus quality.

[0037] In order to further reduce noise interference, this method strictly shields and seals the entire optical path system. Especially at the signal receiving end of the differential confocal detection method, since its impact on signal quality is particularly significant, we installed a special sleeve in front of the detector to effectively reduce the impact of factors such as ambient light and airflow disturbance on the measurement results.

[0038] By implementing bidirectional writing, this method can be combined with more flexible writing strategies. For example, in traditional unidirectional writing, the laser head needs to return to the starting point after completing one line of writing before starting the next line of writing; with bidirectional writing, the laser head can directly start writing the next line without pausing, thus significantly improving processing speed and efficiency.

[0039] This method is of great significance in the field of laser direct writing technology. First, it significantly improves the efficiency and accuracy of laser direct writing, solves the problem of poor focusing accuracy in traditional bidirectional scanning, and is suitable for high-precision laser engraving applications such as micro-nano processing and optoelectronic device manufacturing. Secondly, through dual-focus and differential confocal detection technology, real-time focus tracking is achieved during the engraving process, which reduces processing errors and improves product quality. In addition, this method solves the problem of low processing efficiency in traditional unidirectional scanning by reducing pauses and adjustment time, improves productivity and reduces production costs. Finally, this invention is expected to promote the development of laser direct writing technology, open up new application areas, and has important academic and industrial value.

[0040] According to the above method embodiment, this specification also provides a device embodiment for implementing the method, specifically:

[0041] like Figure 1 The dual focus fixed focus device shown here includes the following optical elements:

[0042] The laser 1 is used as an auxiliary fixed-focus laser. The emitted laser is divided into two laser beams with mutually perpendicular polarization directions at a certain angle by the Wollaston prism 2. The two laser beams are respectively reflected by the D-type reflector group 3, transmitted through the beam splitter 4, and then focused by the objective lens 5 to irradiate the surface of the writing sample wafer 10. Since the two laser beams are incident along the objective lens at a certain angle, the focused spots correspond to the first auxiliary fixed-focus laser beam 7 and the second auxiliary fixed-focus laser beam 8, which are respectively located on the front and back sides of the focused writing beam 9.

[0043] The detection signal reflected by the surface of the wafer 10 is separated from the main light beam by the beam splitter 4, and the reflection signals of the two auxiliary fixed-focus laser beams are confocally measured by the first differential confocal detection module 11 and the second differential confocal detection module 12, respectively, wherein the first differential confocal detection module 11 and the second differential confocal detection module 12 both include imaging lenses and detectors; according to different scanning directions, the reflection signal intensity is measured by the differential confocal detection modules 11, 12 respectively, and the intensity change information is fed back to the translation stage for axial position adjustment, so as to realize high-precision focusing of the real-time system.

[0044] Graphic differences when writing dual focus fixed focus

[0045] like Figure 2 and Figure 3 The following shows the difference in the engraved lines when using dual focus or not. Figure 2 As shown in the figure, when dual-focus fixed focus is not used, due to the lack of a real-time fixed focus feedback system, the focal plane changes dramatically during the line writing process, and the consistency of the position of the written pattern cannot be guaranteed. As a result, the width of the written lines varies too much, resulting in the fall-off of the written long lines. When dual-focus fixed focus is used, as shown in the figure, Figure 3 As shown, the focal plane can be kept stable during the writing process, the line width of the written pattern is consistent, and the line uniformity is much better than Figure 2 In medium cases, the dual-focus fixed-focus method can effectively ensure the stability of the long-term lithography line width.

[0046] like Figure 4 As shown, the basic structure of each differential confocal detection module is as follows: the signal of the first auxiliary fixed-focus laser beam 7 or the second auxiliary fixed-focus laser beam 8 reflected by the wafer 10 is focused by the imaging lens 13, and then divided into two paths by the beam splitter 14. At the same time, the reflected signal is detected by the first detector 15 and the second detector 16 at the front and rear symmetrical positions of the focus of the lens 13, and the difference between the two detectors is used to determine the focus position of the translation stage, which effectively improves the positioning accuracy.

[0047] The reflection signals measured by the first detector 15 and the second detector 16 are as follows: Figure 5 As shown, I 1 , I 2 The reflected signal intensity curves corresponding to the first detector 15 and the second detector 16, I d =I 1 -I 2 It is the difference curve of the reflected signal intensity, and the linear change segment is taken as the feedback focusing signal. At the same time, the difference change is more obvious. The differential focusing method effectively improves the positioning accuracy and is more compatible with the dual-focus focusing method.

[0048] Based on the methods and devices provided in the above embodiments, this embodiment also provides a method for using the device in different scanning modes.

[0049] like Figure 6 As shown, in the grating scanning mode, when the laser moves to the vertex along the positive direction of X, it moves a certain distance in the Y direction, and then moves back to the starting point along the negative direction of X, and this cycle is repeated, and the corresponding pattern can be engraved by switching the laser on and off at the corresponding position. Therefore, when the laser moves along the positive direction of X, the differential confocal detection module is used to detect the reflection signal intensity of the auxiliary focusing grating scanning first auxiliary fixed focus laser beam 17, which is used to feedback the signal to adjust the axial position of the displacement stage in real time; when the laser moves along the negative direction of X, the differential confocal detection module is used to detect the reflection signal intensity of the auxiliary grating scanning focusing and the auxiliary fixed focus laser beam 18, which is used to feedback the signal to adjust the axial position of the displacement stage in real time.

[0050] In the vector scanning method, the laser scans along the path of the engraved pattern, so the direction of the scanning path must be determined first, such as Figure 6 As shown in the schematic diagram of vector scanning, when the scanning path of the laser beam is from left to right, the differential confocal detection module is used to detect the reflected signal intensity of the first auxiliary fixed-focus laser beam 19 of the auxiliary focusing vector scanning, and is used to feedback the signal to adjust the axial position of the displacement stage in real time; when the scanning path of the laser beam is from right to left, the differential confocal detection module is used to detect the reflected signal intensity of the second auxiliary fixed-focus laser beam 20 of the auxiliary focusing vector scanning, and is used to feedback the signal to adjust the axial position of the displacement stage in real time. Therefore, for different scanning modes, whether raster scanning or vector scanning, the dual-focus focusing method can achieve efficient focusing and ensure the stability of the line width of long-term writing.

[0051] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. A method for laser direct writing with two-way and dual-focus writing focal plane focusing, characterized in that: The method includes: Along the laser direct writing scanning path direction, a first auxiliary fixed-focus laser beam and a second auxiliary fixed-focus laser beam are respectively arranged at symmetrical positions in front and behind the writing focused laser beam; Respectively detecting the reflected signal intensities of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam by two differential confocal detection modules; When laser direct writing performs preset graphics engraving through a specific scanning method, the scanning direction is divided into forward scanning and reverse scanning according to the different directions of the scanning path. When performing forward scanning and reverse scanning, the reflection signal intensity of the auxiliary fixed-focus laser beam at the front side of the writing focused laser beam in this direction is detected to lock the focal plane of the writing laser beam.

2. A method for determining the focus of a bidirectional, dual-focus laser direct writing focal plane according to claim 1, characterized in that: The first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are generated by emitting laser light from a laser and then splitting the laser light through a Wollaston prism, wherein the first auxiliary fixed-focus laser beam is ordinary light and the second auxiliary fixed-focus laser beam is extraordinary light.

3. A method for determining the focus of a bidirectional and dual-focus laser direct writing focal plane according to claim 2, characterized in that: After being split by the Wollaston prism, the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam will enter the D-type mirror, and after being reflected by the D-type mirror respectively, enter the writing objective lens through the beam splitting cube and focus on the front and rear sides of the writing focused laser beam.

4. A method for determining the focus of a bidirectional and dual-focus laser direct writing focal plane according to claim 1, characterized in that: The specific scanning mode includes raster scanning and vector scanning.

5. A method for determining the focus of a bidirectional and dual-focus laser direct writing focal plane according to claim 1, characterized in that: The laser wavelengths of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam are different from the laser wavelength of the writing focused laser beam and are located in the transparent absorption window of the photoresist.

6. A method for determining the focus of a bidirectional and dual-focus laser direct writing focal plane according to claim 1, characterized in that: The detection of the reflected signal intensity of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam includes: using a differential confocal detection method, focusing the reflected signal using an imaging lens and dividing it into two paths, detecting the reflected signals of the two paths at the position before the lens focus and the position after the focus, respectively, and determining the difference curve of the reflected signal intensity through the difference of the detector, taking the linear change segment therein as the feedback fixed-focus signal to determine the focal position of the displacement stage.

7. A bidirectional, dual-focus writing focal plane focusing device for laser direct writing, characterized in that: The device comprises: a laser, a Wollaston prism, a D-type reflector group, a first beam splitter, an objective lens, a first differential confocal detection module and a second differential confocal detection module; The laser is used as an auxiliary fixed-focus laser. The emitted laser is divided into two laser beams with mutually perpendicular polarization directions at an angle by the Wollaston prism. After being reflected by the D-type reflector group, the two laser beams are transmitted through the beam splitter and incident along the objective lens at an angle respectively. After being focused by the objective lens, the surface of the writing sample is irradiated. The focused light spot corresponds to the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam, which are respectively located on the front and back sides of the focused writing beam. The detection signal reflected by the wafer surface is separated from the main beam by the beam splitter. The first differential confocal detection module and the second differential confocal detection module are used to receive the detection signals after the reflection of the first auxiliary fixed-focus laser beam and the second auxiliary fixed-focus laser beam respectively, and perform confocal measurement.

8. A bidirectional, dual-focus writing focal plane focusing device for laser direct writing according to claim 7, characterized in that: The first differential confocal detection module and the second differential confocal detection module both include: an imaging lens, a second beam splitter, a first detector and a second detector; The optical path is as follows: after the reflected signal is focused by an imaging lens, it is divided into two paths by a second beam splitter, in which the first detector is used to detect the signal in front of the lens focus in one path, and the second detector is used to detect the signal in the position behind the lens focus in the other path, wherein the distances before and after the focus are the same from the focus.

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