Thin-film lithium niobate strip electrode fine alignment method for high-speed modulator

Abstract

A thin-film lithium niobate strip electrode fine alignment method for a high-speed modulator comprises the following steps: acquiring a pixel coordinate of a target waveguide to be measured, and determining a physical coordinate of each sampling point according to an equipment calibration parameter to generate a waveguide continuous offset curve; and dividing the target waveguide into a plurality of waveguide intervals, and calculating target offset coordinates of each waveguide interval to construct a segmented reference frame. And based on the segmented reference frame, electrode segmented photoetching alignment is performed in each waveguide interval, and an electrode pre-alignment center line is generated. And determining segmented deposition windows according to the electrode pre-alignment center line, and carrying out continuous splicing correction on the segmented deposition windows to obtain an electrode center line. And outputting an alignment structure when the center line of the electrode is consistent with the waveguide length of the target waveguide. According to the method, the local two-point alignment precision can reach the standard, and the situation that the center line of the electrode is not strictly parallel to the waveguide in a long distance is further avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-speed modulators, and more particularly to a thin-film lithium niobate strip electrode fine alignment method for high-speed modulators. BACKGROUND

[0002] In the scenario of "ultra-long row wave electrodes (> 20mm)", although the local alignment meets the requirements, the overall alignment linearity cannot be maintained. In actual high-speed modulators, the length of the row wave electrode often exceeds 20mm, and some devices even reach 30-40mm. In this "ultra-long electrode" scenario, the waveguide itself has a very weak but actually observable linear drift or arc-shaped deviation (caused by local warping of the wafer, light etching focal length compensation), and the drift amount accumulates along the length direction.

[0003] At present, in the traditional technical solution, although the local two-point alignment accuracy can meet the requirements, the electrode center line and the waveguide may not remain strictly parallel over a long distance. This problem is essentially a geometric inconsistency of the reference line along the length direction, which is difficult to solve by single-point optimization or adding local markers. SUMMARY

[0004] To solve the problems in the prior art, the purpose of the present application is to solve the above-mentioned defects, and further to provide a thin-film lithium niobate strip electrode fine alignment method for high-speed modulators.

[0005] The application adopts the following technical solutions.

[0006] The first aspect of the application discloses a thin-film lithium niobate strip electrode fine alignment method for high-speed modulators, which comprises: obtaining the pixel coordinates of the target waveguide to be measured, and determining the physical coordinates of each sampling point according to the device calibration parameters to generate a waveguide continuous offset curve; dividing the target waveguide into a plurality of waveguide intervals, and calculating the target offset coordinates of each waveguide interval to construct a segmented reference framework; based on the segmented reference framework, performing electrode segmented photolithography alignment in each waveguide interval to generate an electrode pre-alignment center line; determining a segmented deposition window according to the electrode pre-alignment center line, and continuously splicing and correcting the segmented deposition window to obtain an electrode center line; outputting an alignment structure when the electrode center line is consistent with the waveguide length of the target waveguide.

[0007] Further, the obtaining of the pixel coordinates of the target waveguide to be measured and the determination of the physical coordinates of each sampling point according to the device calibration parameters to generate a waveguide continuous offset curve comprises: A target waveguide to be tested is selected on a thin-film lithium niobate waveguide sample, and the waveguide length of the target waveguide in the layout is determined so as to divide the waveguide length into multiple sampling intervals; Using the propagation direction of the target waveguide as the X-axis and the direction perpendicular to the waveguide propagation as the Y-axis, a rectangular coordinate system is established in the measurement software, and a reference pixel is selected at the center of the field of view to determine the theoretical axial position of each sampling point based on the reference pixel.

[0008] Furthermore, the step of obtaining the pixel coordinates of the target waveguide under test and determining the physical coordinates of each sampling point according to the device calibration parameters to generate a continuous waveguide offset curve also includes: Based on the theoretical axial position, multiple imaging measurements are performed on the same cross section for each sampling point, and the results of the multiple imaging measurements are averaged to obtain the average pixel coordinates of each sampling point. The average pixel coordinates are converted into physical coordinates using the calibrated pixel scale constant, and the waveguide continuous offset curve is generated by first-order linear fitting using the physical coordinates as discrete points.

[0009] Furthermore, the step of dividing the target waveguide into multiple waveguide intervals and calculating the target offset coordinates for each waveguide interval to construct a segmented reference frame includes: The number of segments of the target waveguide is determined according to the preset single segment length, and the target waveguide is divided into multiple waveguide intervals according to the number of segments, while the axial length of each waveguide interval is determined. The midpoint position of the waveguide interval is determined based on the axial length, and the midpoint position is substituted into the waveguide continuous offset curve to obtain the target offset corresponding to the center position.

[0010] Furthermore, the step of dividing the target waveguide into multiple waveguide intervals and calculating the target offset coordinates for each waveguide interval to construct a segmented reference frame further includes: An alignment mark and its minimum side length are set at the center position, and the actual mark side length and mark geometric parameters of the waveguide interval are determined based on the safe distance between the alignment mark and the target waveguide. The midpoint position is transformed to the wafer layout coordinate system, and the center coordinates of the alignment mark in the wafer layout coordinate system are determined according to the set global coordinate offset. In the layout editing software, the alignment marks are drawn according to the electrode plate layer identifier, and the alignment marks are merged according to the center coordinates to obtain the segmented reference frame.

[0011] Furthermore, the step of performing segmented photolithographic alignment of electrodes in each waveguide section based on the segmented reference frame to generate electrode pre-alignment centerlines includes: The segmented reference frame is imported into the photolithography equipment, and the photolithography equipment is used as the coordinate system reference to determine the alignment reference point, so as to control the photolithography equipment to perform alignment according to the alignment reference point. After the photolithography equipment is aligned, the coordinates of the pattern center are scanned in real time to calculate the lateral offset between the pattern center coordinates and the alignment reference point. Lateral offset compensation and smoothing are performed on the lateral offset of each waveguide interval based on the nominal centerline of the electrode layout to obtain the corrected centerline position. The corrected centerline position is then connected by piecewise linear interpolation to obtain the electrode pre-alignment centerline.

[0012] Furthermore, the step of determining segmented deposition windows based on the electrode pre-alignment centerline and continuously splicing and correcting the segmented deposition windows to obtain the electrode centerline includes: Based on the electrode pre-alignment centerline and the axial center position of each waveguide interval, the initial deposition window, as well as the window length and centerline position of the initial deposition window, are determined. Calculate the axial distance difference between the end center points of adjacent waveguide intervals and set an overlap length for the adjacent waveguide intervals to update the initial deposition window based on the axial distance difference and the overlap length; Define the lateral expansion of the waveguide interval, and correct the window length and centerline position after metal deposition based on the lateral expansion to obtain the electrode centerline when the centerline error does not exceed a set threshold.

[0013] Furthermore, the output alignment structure, wherein the centerline of the electrode coincides with the waveguide length of the target waveguide, includes: The electrode centerline is compared point by point with the actual waveguide trajectory, and a lateral error threshold between the electrode centerline and the actual waveguide trajectory is set in the high-speed modulator to filter out multiple over-limit error intervals that exceed the lateral error threshold. When the maximum error value in the over-limit error range does not exceed the set maximum correction capability value for a single segment, the electrode centerline in the over-limit error range is finely adjusted.

[0014] A second aspect of the present invention discloses a fine alignment apparatus for thin-film lithium niobate strip electrodes for high-speed modulators, used to implement the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators as described in any one of the first aspects, the apparatus comprising: The offset curve generation module is used to obtain the pixel coordinates of the target waveguide under test and determine the physical coordinates of each sampling point according to the device calibration parameters in order to generate a continuous waveguide offset curve. The reference frame construction module is used to divide the target waveguide into multiple waveguide intervals and calculate the target offset coordinates of each waveguide interval to construct a segmented reference frame. The centerline generation module is used to perform segmented photolithographic alignment of electrodes in each waveguide interval based on the segmented reference frame, and generate electrode pre-alignment centerlines. The window splicing correction module is used to determine the segmented deposition windows based on the electrode pre-alignment center line, and to continuously splice and correct the segmented deposition windows to obtain the electrode center line. The alignment structure verification module is used to output the alignment structure when the center line of the electrode is consistent with the waveguide length of the target waveguide.

[0015] A third aspect of the present invention discloses a terminal, including a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method described in the first aspect.

[0016] A fourth aspect of the present invention discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0017] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages: (1) This invention reduces the impact of random measurement errors and slight changes in the focal plane on the results of a single measurement by establishing a unified coordinate system and sampling point layout at the engineering level, collecting pixel coordinates multiple times at the same physical location and averaging them. At the same time, the pixel values ​​in the device imaging coordinate system are converted into physically meaningful length units, and the overall translation error is eliminated by zero-point correction, so that the physical coordinates can be directly used to represent the true offset of the waveguide center relative to the reference line. Then, the discrete physical coordinate data are converted into a continuous offset curve, which numerically represents the linear drift trend of the entire waveguide length, thus essentially avoiding the geometric inconsistency of the baseline along the length direction.

[0018] (2) This invention converts abstract marker parameters into actual manufacturable layout data and establishes a correspondence with the wafer global coordinates and electrode layers to generate a segmented alignment reference frame that can be directly used by lithography equipment. This allows the electrode pattern to be aligned with the markers in the frame in each segment, thus ensuring overall linear consistency in the ultra-long traveling wave electrode scenario. Then, the corrected center values ​​of each segment are spliced ​​together to form a complete electrode centerline, enabling the electrode pre-alignment pattern to continuously fit along the waveguide drift curve. At the same time, based on the width and center compensation of the metal deposition window, the continuity of the joints between segments is quantitatively checked and corrected, ultimately forming a final electrode centerline that meets the overall linear requirements of the ultra-long traveling wave electrode. This not only ensures that the local two-point alignment accuracy meets the standard, but also further avoids the situation where the electrode centerline and the waveguide are not strictly parallel over long distances. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention.

[0020] Figure 2 This is a schematic diagram of the fine alignment device for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention. Detailed Implementation

[0021] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0022] like Figure 1 As shown, in one embodiment, a method for fine alignment of a thin-film lithium niobate strip electrode for a high-speed modulator includes the following steps: Step S110: Obtain the pixel coordinates of the target waveguide under test, and determine the physical coordinates of each sampling point according to the device calibration parameters to generate a continuous waveguide offset curve.

[0023] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following steps in step S110: Step S111: Select the target waveguide to be tested on the thin-film lithium niobate waveguide sample and determine the waveguide length of the target waveguide in the layout so as to divide the waveguide length into multiple sampling intervals.

[0024] Step S112: Using the propagation direction of the target waveguide as the X-axis and the direction perpendicular to the waveguide propagation as the Y-axis, establish a rectangular coordinate system in the measurement software, and select a reference pixel at the center of the field of view to determine the theoretical axial position of each sampling point based on the reference pixel.

[0025] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention further includes the following steps in step S110: Step S113: Based on the theoretical axial position, perform multiple imaging measurements on the same cross section for each sampling point, and average the results of the multiple imaging measurements to obtain the average pixel coordinates of each sampling point.

[0026] Step S114: Convert the average pixel coordinates into physical coordinates using the calibrated pixel scale constant, and use the physical coordinates as discrete points to generate a waveguide continuous offset curve through first-order linear fitting.

[0027] In a specific embodiment, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes steps 1 to 5: Step 1: Obtain the full-length geometric trajectory of the waveguide and quantize the continuous offset curve.

[0028] Includes the following sub-steps: Sub-step 1.1: Establish the waveguide measurement coordinate system and determine the distribution of sampling points.

[0029] Specifically, firstly, the target waveguide to be measured is selected on the fabricated thin-film lithium niobate waveguide sample, and its nominal length in the layout is determined, typically ranging from 20 mm to 40 mm. Depending on the engineering accuracy requirements, the number of sampling points along the length is set, for example, between 50 and 200, prioritizing that the distance between adjacent sampling points is no greater than 1 mm. Then, the theoretical axial sampling interval is equal to the ratio of the nominal length of the waveguide in the layout (numerator) to the difference between the number of sampling points minus 1 (denominator). This theoretical axial sampling interval characterizes the theoretical distance between two adjacent sampling points in the axial direction, expressed in millimeters.

[0030] Next, a Cartesian coordinate system is established in the measurement software: the X-axis is along the waveguide propagation direction, and the Y-axis is perpendicular to the waveguide propagation direction. A reference pixel is selected near the center of the field of view and defined as the pixel position corresponding to the origin of the coordinate system. For any sampling point, its theoretical axial position is equal to the product of the sampling point number minus 1 and the corresponding theoretical axial sampling interval.

[0031] Sub-step 1.2: Collect the discrete pixel coordinates of the waveguide center and perform multiple measurements to average them.

[0032] Specifically, in a microscopic imaging or interferometry system, the field of view is moved sequentially along the waveguide direction so that the cross-section at each theoretical axial position is within the clear imaging region. For any sampling point, multiple imaging measurements are performed on the same cross-section; for example, three measurements are taken to reduce random errors, resulting in three sets of pixel coordinates. Then, the pixel coordinates of each sampling point are arithmetically averaged to obtain the final average pixel coordinates used for geometric fitting. The x-coordinate of the average pixel coordinates is the average of the x-coordinates of the three measurements at that sampling point, and the y-coordinate is similarly calculated, with the unit being pixels.

[0033] Sub-step 1.3 converts pixel coordinates to physical coordinates and performs zero-point correction.

[0034] Specifically, pixel coordinates are converted into physical length using a pre-calibrated pixel scale constant. For any sampling point, the horizontal coordinate of its physical coordinates is equal to the horizontal pixel scale constant (typically ranging from 0.1 μm / pixel to 1 μm / pixel) multiplied by the difference between the average pixel horizontal coordinate of that sampling point and the pixel coordinates corresponding to the origin.

[0035] It should be noted that in some devices, the pixel coordinates corresponding to the origin of the coordinate system correspond to the physical X and Y axes of the device, respectively. The specific correspondence is determined during calibration. To eliminate the overall zero-point offset, a reference point (e.g., the first sampling point) is selected at one end of the waveguide, and the ordinate corresponding to this reference point is used as the zero-point reference (e.g., the initial lateral physical coordinate of the first sampling point, in micrometers). Longitudinal zero-point correction is performed, and the reassigned value represents the relative lateral offset relative to the starting point of the waveguide, which is more convenient to reflect the arc-shaped or linear drift trend along the length direction.

[0036] Sub-step 1.4: Fit the waveguide continuous offset curve and generate offset parameters.

[0037] Specifically, to obtain the continuous geometric trajectory of the waveguide centerline over its entire length, the aforementioned physical coordinates are used as discrete points, and a first-order linear fitting is employed to obtain an approximate offset curve, expressed as: ; In the formula, In axial position The theoretical lateral offset at the center of the waveguide, in micrometers; The slope of the waveguide longitudinal drift is expressed in micrometers per micrometer (dimensionless). For when The initial offset when it equals 0, in micrometers.

[0038] To obtain the above formula and First, calculate the average of the axial position and theoretical lateral offset of all sampling points, then obtain the slope using the least squares method. ,intercept From the slope The above formula is derived from this.

[0039] Finally, the geometric residual for each sampling point can be calculated based on the approximate offset curve described above. This residual represents the difference between the actual offset of any sampling point and the fitted curve, expressed in micrometers. The maximum residual and the mean square residual can be statistically analyzed to determine the applicability of the linear model to the current waveguide.

[0040] Step S120: Divide the target waveguide into multiple waveguide intervals and calculate the target offset coordinates for each waveguide interval to construct a segmented reference frame.

[0041] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following steps in step S120: Step S121: Determine the number of segments of the target waveguide according to the preset single segment length, divide the target waveguide into multiple waveguide intervals according to the number of segments, and determine the axial length of each waveguide interval.

[0042] Step S122: Determine the midpoint position of the waveguide interval based on the axial length, and substitute the midpoint position into the waveguide continuous offset curve to obtain the target offset corresponding to the center position.

[0043] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention further includes the following steps in step S120: Step S123: Set an alignment mark and the minimum side length of the alignment mark at the center position, and determine the actual mark side length and mark geometric parameters of the waveguide section based on the safe distance between the alignment mark and the target waveguide.

[0044] Step S124: Transform the midpoint position to the wafer layout coordinate system, and determine the center coordinates of the alignment mark in the wafer layout coordinate system according to the set global coordinate offset.

[0045] Step S125: Draw alignment marks in the layout editing software according to the electrode plate layer identifier, and merge the alignment marks according to the center coordinates to obtain a segmented reference frame.

[0046] In a specific embodiment, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following sub-steps: Step 2, constructing a segmented alignment reference frame based on the offset curve. Sub-step 2.1: Determine the number of segments and divide the waveguide length interval.

[0047] Specifically, firstly, based on the overall linearity requirements of the ultra-long traveling wave electrode, the maximum allowable length of a single segment is set, typically ranging from 2 mm to 5 mm, determined jointly by process experience and alignment equipment capabilities. The required number of segments is then calculated based on the total waveguide length and the maximum allowable length of a single segment; that is, the total waveguide length is the ratio of the numerator to the maximum allowable length of a single segment, rounded up.

[0048] Then, the total length of the waveguide is evenly divided into multiple waveguide intervals according to the obtained number of segments. The theoretical axial length of each segment is the ratio of the total length of the waveguide to the number of segments. The starting position of each segment is the product of the segment number minus 1 and the theoretical axial length, and the ending position is the product of the segment number and the theoretical axial length. The starting position and the ending position together constitute a waveguide interval.

[0049] Sub-step 2.2: Calculate the center position of each segment and the target offset coordinates.

[0050] Specifically, for any waveguide segment, the midpoint within its axial range is taken as the center position of that segment. The axial center coordinates of this center position are equal to the average of the starting and ending positions of that segment. Then, the axial center coordinates of this midpoint are used as... Substituting the offset curve obtained in step 1, the lateral offset of the waveguide target corresponding to the center position of the corresponding waveguide segment is calculated, in micrometers. Finally, by integrating the lateral offsets of the waveguide target corresponding to the center positions of all waveguide segments, a set of discrete target reference points is obtained.

[0051] Sub-step 2.3: Design a local alignment mark structure around the target reference point.

[0052] Specifically, to achieve reliable alignment near each target reference point, square or cross-shaped photolithographic alignment marks of appropriate size, maintaining a safe distance from the waveguide, need to be designed. The nominal minimum side length of the mark is set, typically ranging from 5 to 20 micrometers, and the safe distance between the waveguide and the mark is typically ranging from 2 to 10 micrometers. Considering the local process environment of different segments, the actual mark side length for the corresponding waveguide segment is obtained by summing the aforementioned nominal minimum side length and the safe distance between the waveguide and the mark.

[0053] Subsequently, for each waveguide segment, the designed marker center is aligned with the target reference point to obtain the marker center coordinates. In the specific layout design, the marker can be made into a cross or a rectangle, but its geometric center must coincide with the marker center coordinates. To ensure that the marker as a whole does not interfere with the waveguide's dominant mode field, the actual waveguide core and the marker can be kept at a minimum distance greater than the safety margin in the layout. Therefore, the marker geometric parameters of each waveguide segment are composed of its marker center coordinates and the actual marker side length.

[0054] Sub-step 2.4 generates a segmented reference frame layout that can be used for photolithographic alignment.

[0055] Specifically, since the process design layout typically uses a fixed point on the wafer as its origin, its coordinate system may be offset from the measurement coordinate system. Therefore, it is necessary to transform the marker center coordinates in sub-step 2.3 to the wafer layout coordinate system. Simultaneously, a global coordinate offset is set (consisting of horizontal and vertical offsets, generally within the range of -5 mm to 5 mm in process design). Then, the final center coordinates of each marker in the wafer coordinate system are: the horizontal coordinate of the marker center coordinates plus the corresponding horizontal offset of the global coordinate offset; and the vertical coordinate is the sum of the vertical coordinate of the marker center coordinates and the corresponding vertical offset of the global coordinate offset.

[0056] Subsequently, in the layout editing software, the markers for each segment are drawn on the layer specified by the electrode layer identifier, using a rectangle or cross structure with sides equal to the actual marker side length, and its geometric center is set to the final center coordinates in the aforementioned wafer coordinate system. All the markers for each segment are then combined to form a complete segmented alignment reference frame. This frame contains both spatial coordinate information and layer attributes, and can be automatically recognized and used during subsequent electrode pattern photolithography.

[0057] Step S130: Based on the segmented reference frame, perform segmented photolithographic alignment of electrodes in each waveguide section to generate electrode pre-alignment center lines.

[0058] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following steps in step S130: Step S131: Import the segmented reference frame into the photolithography equipment, use the photolithography equipment as the coordinate system reference, determine the alignment reference point, and control the photolithography equipment to perform alignment according to the alignment reference point.

[0059] Step S132: After the photolithography equipment is aligned, the coordinates of the pattern center are scanned in real time to calculate the lateral offset between the pattern center coordinates and the alignment reference point.

[0060] Step S133: Based on the nominal centerline of the electrode layout, perform lateral offset compensation and smoothing on the lateral offset of each waveguide interval to obtain the corrected centerline position. Then, connect the corrected centerline positions through piecewise linear interpolation to obtain the electrode pre-alignment centerline.

[0061] In a specific embodiment, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following sub-steps: Step 3, performing segmented photolithographic alignment of the electrodes and generating electrode pre-alignment center lines. Sub-step 3.1: Read the segmented alignment marks and establish the lithographic alignment coordinates.

[0062] Specifically, the segmented alignment reference frame file obtained in step 2 is imported into the lithography equipment, and the geometric center coordinates of each segment mark are read through layout analysis. The lithography machine uses its own coordinate system as a reference and converts each mark point into an alignment reference point for the exposure system according to the waveguide interval sequence. To ensure the accuracy of the exposure system's recognition of the mark positions, the pixel accuracy requirements for lithography alignment need to be calculated. Let the pixel resolution of the lithography machine be the lithography pixel resolution (unit: micrometers / pixel, typical range 0.02–0.1 micrometers / pixel), while controlling the alignment error to not exceed the maximum allowable alignment error (set as 30–50 nanometers). Therefore, the maximum allowable alignment error is equal to the product of the lithography pixel resolution and the maximum allowable number of pixels for offset (a positive integer, generally 1 to 3). If the lithography pixel resolution is 0.05 micrometers / pixel, then the maximum allowable number of pixels for offset must not exceed 1, and the equipment can lock the imaging magnification accordingly.

[0063] Sub-step 3.2: Measure the center position of each exposure pattern segment and calculate the local offset.

[0064] Specifically, an electrode pattern is loaded into the lithography machine. The electrode pattern has a nominal center position in each waveguide segment (composed of horizontal and vertical nominal coordinates). After the lithography equipment is aligned, the actual scanned center coordinates of the pattern are obtained using the pre-exposure measurement function. The center error (composed of axial error and lateral offset error) is calculated. The axial error is automatically corrected by the equipment. The lateral offset error is equal to the difference between the lateral position of the electrode centerline measured by the lithography equipment and the lateral coordinates of the alignment reference point provided in sub-step 3.1.

[0065] In this example, the electrode centerline coordinates measured by the lithography equipment are obtained through CCD imaging. The actual sources of error include projection distortion and focal plane deviation. The lateral offset is a key parameter for subsequent correction of the exposure centerline. To verify whether the lateral offset is within the allowable range, it is necessary to check whether it meets the following requirements: the absolute value of the lateral offset does not exceed the maximum allowable deviation of the process (typically ranging from 0.05 to 0.10 micrometers).

[0066] Sub-step 3.3 applies exposure bias compensation to each segment of the electrode pattern and generates a correction center line within the segment.

[0067] Specifically, in order to align the nominal center position of the electrode pattern with the lateral offset in each waveguide segment, lateral offset compensation needs to be applied to each waveguide segment. The compensated centerline position is equal to the lateral position of the nominal electrode centerline of that segment minus the lateral offset of that segment, which means that the pattern is pushed back to the reference line position by offsetting in the opposite direction.

[0068] Next, in order to ensure a smooth transition between segments, it is necessary to define an inter-segment smoothing coefficient (typically ranging from 0.1 to 0.3) to correct for possible broken lines at segment boundaries, ultimately forming a set of segmented corrected centerline positions.

[0069] Sub-step 3.4 generates the pre-alignment centerline function for the entire electrode segment.

[0070] Specifically, to establish a complete centerline, piecewise linear interpolation is used to connect the corrected center coordinates of each segment, indicating that the centerline remains constant within each segment. However, to better reflect the continuity of the actual electrode, a linear interpolation formula can be used between segments, expressed as: ; In the formula, For the first The center value of the segment waveguide interval; For the first The center value of the segment waveguide interval; For any position within the waveguide interval; , The first The starting and ending points of the segment waveguide interval.

[0071] Finally, a complete electrode pre-alignment centerline is obtained, and the consistency error between its full-length shape and the reference curve obtained in step 2 can generally be controlled within ±0.05 micrometers.

[0072] Step S140: Determine the segmented deposition window based on the electrode pre-alignment centerline, and continuously splice and correct the segmented deposition window to obtain the electrode centerline.

[0073] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following steps in step S140: Step S141: Based on the electrode pre-alignment centerline and the axial center position of each waveguide interval, determine the initial deposition window, as well as the window length and centerline position of the initial deposition window.

[0074] Step S142: Calculate the axial distance difference between the end center points of adjacent waveguide intervals and set the overlap length for adjacent waveguide intervals to update the initial deposition window based on the axial distance difference and the overlap length.

[0075] Step S143: Define the lateral expansion of the waveguide interval, and correct the window length and centerline position after metal deposition based on the lateral expansion, so as to obtain the electrode centerline when the centerline error does not exceed the set threshold.

[0076] In a specific embodiment, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following sub-steps: Step 4 involves performing continuous splicing correction of the deposition window and forming the overall electrode centerline. Sub-step 4.1: Generate initial segmented deposition window parameters based on the pre-aligned centerline.

[0077] Specifically, firstly, the center position of each waveguide segment is reconfirmed, similarly, the axial center positions of the start and end points are also reconfirmed. Within each segment, the centerline position of the segment is calculated using the pre-alignment centerline obtained in step 3, yielding the initial lateral center position of the deposition window for each segment, in micrometers. Then, based on the nominal length requirements of the electrode design, the initial deposition window length for each segment is given, in millimeters. The initial opening width of the window is determined according to the process safety margin of the nominal width of the designed electrode. The initial opening width of the window is equal to the sum of the target metal width of the electrode (typically ranging from 3 to 10 micrometers) and the allowance after considering lithography and deposition shrinkage (generally 0.2 to 0.5 micrometers). Therefore, the window parameters for each deposition window segment include the axial center position, the initial lateral center position, the axial opening length of the deposition window, and the initial opening width of the window.

[0078] Sub-step 4.2: Calculate the inter-segment seam error and determine the axial overlap length.

[0079] Specifically, for two adjacent segments, segment k and segment (k+1), their theoretical splicing position is located at the end point of segment k and the starting point of segment (k+1). Since there may be slight axial length or step errors in the preceding segments, it is necessary to calculate the inter-segment seam error. To simplify engineering implementation, the axial seam error can be defined as the difference in axial distance between the center points of the two segment ends, equal to the difference between the starting point of segment (k+1) and the center point of the end of segment k. Subsequently, to avoid gaps at the seam after metal deposition, and to prevent excessive overlap in the exposure repetition area, an overlap length needs to be set for each pair of adjacent segments. This overlap length can be determined based on the basic overlap amount and the absolute value of the seam error, equal to the product of an adjustment factor (typically ranging from 0.5 to 1.0, used to amplify or reduce the impact of the seam error on the overlap length) and the absolute value of the seam error, plus the basic overlap amount. Finally, the axial boundary of the window of each adjacent segment is redefined according to the overlap length set for each pair of adjacent segments, so that there is an overlap area with an overlap length between the two windows in the axial direction. Thus, the physical continuity of the electrode is achieved through the continuous growth of the metal itself after deposition, and the updated window parameters are obtained.

[0080] Sub-step 4.3 considers the compensation of metal growth and lateral expansion on the window width and center.

[0081] Specifically, during evaporation or sputtering, the metal undergoes a certain lateral expansion, the extent of which is related to the metal thickness and growth method. To ensure that the final electrode metal width still meets the design target width, the window width needs to be "shrunken" in advance during the window design stage. First, define the lateral expansion coefficient (typically ranging from 0.05 to 0.2, in micrometers per micrometer, indicating that every 1-micrometer increase in thickness results in a lateral expansion of 0.05 to 0.2 micrometers). Then, the lateral expansion of a certain waveguide segment on each side is equal to the product of the lateral expansion coefficient of that segment and the target metal thickness (in micrometers, typically in the range of 1 to 3 micrometers).

[0082] To achieve the target width after metal deposition, the window opening width should be equal to the target width minus twice the lateral expansion factor. Since the metal expands outwards on both sides, a reduction of twice the expansion amount is necessary. In overlapping regions, because two metal segments may grow superimposed within the overlap area, a small lateral offset compensation can be made to the center of the overlapping region to avoid obvious "bulges" or unnecessary widening in the middle. An upper limit for the allowable overlap width deviation needs to be set, typically between 0.1 and 0.3 micrometers. If the calculation results show that the corrected window width plus twice the expansion amount exceeds the target width plus the set upper limit for the allowable overlap width deviation, the local window in the overlapping region is appropriately narrowed in the layout so that the corrected window width plus twice the expansion amount does not exceed the target width plus the set upper limit for the allowable overlap width deviation. After correction, the updated parameters for each segment are obtained, including the corrected centerline position (if a slight offset is made to the overlapping region) and the corrected window width. Integrating the updated parameters of all segments yields the corrected window parameter set.

[0083] Sub-step 4.4 generates the overall electrode centerline from the corrected window parameters and completes the continuity verification.

[0084] Specifically, based on the set of correction window parameters, the corrected centerline position is used as the reference value for the electrode centerline within each interval, and linear interpolation is used to smooth the transition between segments. In the overlapping area of ​​adjacent segments, the centerline continuity error is defined by the difference between the centerlines of the two segments at the joint location. This error must not exceed the upper limit of the allowable centerline continuity error, typically between 0.05 and 0.10 micrometers. If the absolute value of the centerline continuity error at a joint exceeds this range, a small window segment near the joint is fine-tuned so that the two centerlines in the overlapping area meet the above constraints again through linear interpolation.

[0085] Step S150: When the center line of the electrode is aligned with the waveguide length of the target waveguide, the alignment structure is output.

[0086] In some embodiments, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following steps in step S150: Step S151: The electrode centerline is compared point by point with the actual waveguide trajectory, and a lateral error threshold between the electrode centerline and the actual waveguide trajectory is set in the high-speed modulator to filter out multiple over-limit error intervals that exceed the lateral error threshold.

[0087] Step S152: When the maximum error value in the error range does not exceed the set maximum correction capability value for a single segment, the electrode centerline in the error range is finely adjusted.

[0088] In a specific embodiment, the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention includes the following sub-steps: Step 5 verifies the consistency between the final electrode centerline and the entire waveguide length, and outputs the final alignment structure. Sub-step 5.1: Calculate the full-length offset function between the final electrode centerline and the waveguide trajectory.

[0089] Specifically, the final electrode centerline is compared point-by-point with the waveguide trajectory to obtain the full-length offset function. This full-length offset function is equal to the difference between the final electrode centerline obtained in step 4 and the actual waveguide trajectory curve obtained in step 1. Discrete sampling is performed over the entire electrode length range, for example, at equal intervals of 0.1 mm to 0.5 mm, to calculate the discrete point sequence of the full-length offset function.

[0090] Sub-step 5.2 checks the total error based on the offset threshold and identifies the out-of-range areas.

[0091] Specifically, in high-speed modulators, the lateral error of the electrode centerline relative to the waveguide trajectory must be below a predetermined threshold, typically 0.05–0.20 micrometers. The absolute value of the full-length offset function result for each sampling point is checked to see if it exceeds this predetermined threshold. All sampling points exceeding the threshold are integrated into an error interval set. Simultaneously, the maximum offset value of each error interval is calculated to determine the continuity of the error interval; for example, at least two consecutive sampling points must exceed the limit for it to be considered a valid error segment.

[0092] Sub-step 5.3 determines whether the alignment offset can be eliminated through local correction based on the error range.

[0093] Specifically, for each error segment, it is necessary to determine whether the offset is caused by inter-segment splicing and can still be corrected through local compensation. A maximum permissible correction capability value for a single segment is set, typically 0.03–0.08 micrometers, representing the maximum offset that can be compensated for by local photolithography eccentricity or linewidth fine-tuning after metal forming. If the maximum offset value of the above error interval does not exceed this maximum correction capability value for a single segment, then the corresponding error interval is determined to be correctable, and the correction direction of the error interval is recorded. If the total offset function result of the error interval is greater than 0, then the electrode center needs to be offset negatively in the Y-axis direction; if it is less than 0, it needs to be offset positively in the Y-axis direction. Finally, the corrected offset is equal to half the negative value of the maximum offset value of the segment, in micrometers. Taking half is to avoid over-correction leading to reverse offset.

[0094] Sub-step 5.4 involves reconstructing the window for the correctable interval and generating the final alignment structure.

[0095] Specifically, for each correctable interval, the electrode centerline is locally adjusted, and the new centerline is defined as the sum of the offset compensation to be performed on that segment and the original electrode centerline. For uncorrectable intervals, the original electrode centerline remains unchanged, but process markings are added to the final structure so that the backend can evaluate whether to replan the waveguide layout or electrode path. Finally, the output alignment structure is represented by the electrode centerline along the entire length of the waveguide, and includes the inter-segment splicing, local corrections, and uncorrectable markings for the waveguide intervals.

[0096] Sub-step 5.5: Perform a final consistency comparison and output the consistency conclusion of the entire electrode length.

[0097] Specifically, based on the final output alignment structure, the final offset function is recalculated and its maximum offset is taken. If the preset requirements are met, the final consistency verification is determined to be "passed" and marked; otherwise, it is determined to be "failed" and marked.

[0098] The fine alignment device for thin-film lithium niobate strip electrodes for high-speed modulators provided by the present invention is described below. The fine alignment device for thin-film lithium niobate strip electrodes for high-speed modulators described below can be referred to in correspondence with the fine alignment method for thin-film lithium niobate strip electrodes for high-speed modulators described above.

[0099] like Figure 2 As shown, in one embodiment, a fine alignment device for thin-film lithium niobate strip electrodes for high-speed modulators includes an offset curve generation module, a reference frame construction module, a centerline generation module, a window splicing correction module, and an alignment structure verification module.

[0100] The offset curve generation module is used to obtain the pixel coordinates of the target waveguide under test and determine the physical coordinates of each sampling point according to the device calibration parameters in order to generate a continuous offset curve of the waveguide.

[0101] The reference frame construction module is used to divide the target waveguide into multiple waveguide intervals and calculate the target offset coordinates of each waveguide interval in order to construct a segmented reference frame.

[0102] The centerline generation module is used to perform segmented photolithographic alignment of electrodes in each waveguide section based on a segmented reference frame, and generate electrode pre-alignment centerlines.

[0103] The window splicing correction module is used to determine the segmented deposition windows based on the electrode pre-alignment centerline, and to continuously splice and correct the segmented deposition windows to obtain the electrode centerline.

[0104] The alignment structure verification module is used to output the alignment structure when the electrode centerline is consistent with the waveguide length of the target waveguide.

[0105] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for fine alignment of thin-film lithium niobate strip electrodes for high-speed modulators, characterized in that, The method comprises: acquiring pixel coordinates of a target waveguide to be measured, and determining physical coordinates of each sampling point according to device calibration parameters to generate a waveguide continuous offset curve; dividing the target waveguide into multiple waveguide intervals, and calculating target offset coordinates of each waveguide interval to construct a segmented reference framework; based on the segmented reference framework, performing electrode segmented photolithography alignment in each waveguide interval to generate an electrode pre-alignment center line; determining a segmented deposition window according to the electrode pre-alignment center line, and continuously splicing and correcting the segmented deposition window to obtain an electrode center line; when the electrode center line is consistent with the waveguide length of the target waveguide, outputting an alignment structure.

2. The method of claim 1, wherein the method is performed on a thin-film lithium niobate strip electrode for a high-speed modulator. The acquisition of the pixel coordinates of the target waveguide to be measured, and the determination of the physical coordinates of each sampling point according to the device calibration parameters to generate the waveguide continuous offset curve comprises: selecting a target waveguide to be measured on a thin-film lithium niobate waveguide sample, and determining a waveguide length of the target waveguide in a layout to divide the waveguide length into multiple sampling intervals; taking the propagation direction of the target waveguide as the X-axis and the direction perpendicular to the waveguide propagation direction as the Y-axis, establishing a rectangular coordinate system in the measurement software, and selecting a reference pixel point at the center of the field of view to determine the theoretical axial position of each sampling point based on the reference pixel point.

3. The method of claim 2, wherein the method further comprises: The acquisition of the pixel coordinates of the target waveguide to be measured, and the determination of the physical coordinates of each sampling point according to the device calibration parameters to generate the waveguide continuous offset curve further comprises: based on the theoretical axial position, performing multiple imaging measurements of each sampling point on the same cross section, and averaging the multiple imaging measurement results to obtain the average pixel coordinates of each sampling point; converting the average pixel coordinates into physical coordinates through the calibrated pixel scale constant, and taking the physical coordinates as discrete points to generate the waveguide continuous offset curve through first-order linear fitting.

4. The method of claim 1, wherein the method is used for fine alignment of thin film lithium niobate strip electrodes for high speed modulators. The division of the target waveguide into multiple waveguide intervals, and the calculation of the target offset coordinates of each waveguide interval to construct a segmented reference framework comprises: determining the number of segments of the target waveguide according to a preset waveguide single-segment length, and dividing the target waveguide into multiple waveguide intervals according to the number of segments, while determining the axial length of each waveguide interval; determining the midpoint position of the waveguide interval according to the axial length, and substituting the midpoint position into the waveguide continuous offset curve to obtain the target offset corresponding to the center position.

5. The method of claim 4, wherein the method further comprises: The division of the target waveguide into multiple waveguide intervals, and the calculation of the target offset coordinates of each waveguide interval to construct a segmented reference framework further comprises: setting an alignment mark and the minimum side length of the alignment mark at the center position, and determining the actual mark side length and mark geometric parameters of the waveguide interval according to the safety distance between the alignment mark and the target waveguide; converting the midpoint position to a wafer layout coordinate system, and determining the center coordinates of the alignment mark in the wafer layout coordinate system according to the set global coordinate offset; The alignment marks are drawn according to the electrode layout layer identification in the layout editing software, and each alignment mark is fused according to the center coordinates to obtain the segmented reference frame.

6. The method for fine alignment of thin film lithium niobate strip electrodes for high speed modulators as claimed in claim 1, wherein, The segmented reference frame is used to perform electrode segmentation photolithography alignment in each waveguide section to generate an electrode pre-alignment center line, including: The segmented reference frame is imported into a photolithography device, and the photolithography device is used as a coordinate system reference to determine an alignment reference point, so that the photolithography device is controlled to align according to the alignment reference point; After the photolithography device is aligned, the pattern center coordinates are scanned in real time to calculate the lateral offset between the pattern center coordinates and the alignment reference point; The lateral offset of each waveguide section is compensated and smoothed according to the nominal center line of the electrode layout to obtain a corrected center line position, and the corrected center line position is connected through segmented linear interpolation to obtain the electrode pre-alignment center line.

7. The method for fine alignment of thin film lithium niobate strip electrodes for high speed modulators as claimed in claim 1, wherein, The electrode pre-alignment center line is used to determine a segmented deposition window, and the segmented deposition window is continuously spliced and corrected to obtain an electrode center line, including: Based on the electrode pre-alignment center line and the axial center position of each waveguide section, an initial deposition window and the window length and center line position of the initial deposition window are determined; The axial distance difference between the end center points of adjacent waveguide sections is calculated, and an overlap length is set for the adjacent waveguide sections, so that the initial deposition window is updated according to the axial distance difference and the overlap length; The lateral outward expansion amount of the waveguide section is defined, and the window length and center line position after metal deposition are corrected based on the lateral outward expansion amount, so that the electrode center line is obtained when the center line error does not exceed a set threshold.

8. The method for fine alignment of thin film lithium niobate strip electrodes for high speed modulators as claimed in claim 1, wherein, When the electrode center line is consistent with the waveguide length of the target waveguide, an alignment structure is output, including: The electrode center line is compared with the waveguide actual trajectory point by point, and a lateral error threshold of the electrode center line and the waveguide actual trajectory is set in a high-speed modulator to screen out a plurality of over-limit error sections that exceed the lateral error threshold; When the maximum error value in the over-limit error section does not exceed a set single-section maximum correction capability value, the electrode center line in the over-limit error section is fine-tuned.

9. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is used to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the steps of the method according to any one of claims 1-8.

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