A method for calibrating optical axis attitude and an overlay measurement device

Abstract

This invention belongs to the field of semiconductor testing technology, specifically relating to an optical axis attitude calibration method and an overlay measurement device. The overlay measurement device includes a reference plate with reference marks sensitive to changes in the optical axis attitude. The reference plate is positioned outside the workpiece stage. The optical axis attitude calibration method includes: acquiring a first set of overlay measurements of the reference marks at the initial optical axis attitude, using these as reference overlay measurements, and determining a preset sensitivity of the reference marks to the initial optical axis attitude; periodically acquiring a second set of overlay measurements of the reference marks, and determining the overlay measurement change based on the second set of measurements and the reference overlay measurements; calculating the attitude change of the current optical axis attitude relative to the initial optical axis attitude based on the overlay measurement change and the preset sensitivity; and adjusting the optical axis attitude back to the initial optical axis attitude according to the attitude change to compensate for overlay errors caused by changes in the optical axis attitude.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor testing technology, specifically relating to an optical axis attitude calibration method and an overlay measurement device. Background Technology

[0002] In the semiconductor manufacturing industry, overlay accuracy is a key indicator for measuring the alignment of patterns between two layers, directly affecting chip yield and performance. As process precision continues to advance towards advanced processes such as 5nm and 3nm, the allowable range of overlay errors has been reduced to the nanometer level, which places extremely stringent requirements on overlay measurement equipment and related measurement technologies.

[0003] Currently, commonly used measurement technologies for overlay measurement equipment mainly include image-based overlay (IBO) and diffraction-based overlay measurement. IBO technology, which uses a camera to image the overlay marks and employs image recognition algorithms to calculate the overlay error, is widely used.

[0004] In the aforementioned overlay measurement techniques, total measurement uncertainty is used to comprehensively describe the overall error of lithography measurement and is a key indicator for measuring the accuracy of lithography measurement. Factors affecting total measurement uncertainty include measurement repeatability and asymmetry. However, during long-term use, environmental changes, stress release after equipment debugging, and positional drift of optomechanical components can cause optical axis attitude shifts, thus affecting total measurement uncertainty. Specifically, the existing literature "Machine learning for Tool Induced Shift (TIS) reduction: an HVM case study" points out that TIS is a measurement error that measures the accuracy of metrology tools. Its error originates from component asymmetry, with common causes including lens aberrations, lens alignment, and illumination alignment, and changes in optical axis attitude directly affect these factors. Another literature, "Overlay Error Compensation Method and Lithography Exposure Method," proposes that overlay measurement techniques based on imaging and image recognition can generate machine errors due to optical deviations, which are closely related to optical axis attitude.

[0005] In summary, precise control and effective compensation for deviations in optical axis attitude are crucial for improving chip manufacturing yield and ensuring the performance of advanced process chips, and have become a key technical challenge that needs to be overcome by those skilled in the art. Summary of the Invention

[0006] This invention provides an optical axis attitude calibration method and an overlay measurement device to solve the technical problem of overlay error caused by optical axis attitude deviation.

[0007] The technical solution adopted in this invention is as follows: This invention provides an optical axis attitude calibration method applied to an overlay measurement device. The overlay measurement device includes a workpiece stage and an optical system. The optical system has an optical axis for transmitting a light beam. The workpiece stage is used to support a wafer. The overlay measurement device also includes a reference plate. The reference plate is provided with a reference mark sensitive to changes in the attitude of the optical axis. The reference plate is located outside the workpiece stage. The optical axis attitude calibration method includes the following steps: at an initial optical axis attitude, acquiring a first set of overlay measurements of the reference mark as a reference overlay measurement value, and determining a preset sensitivity of the reference mark to the initial optical axis attitude; periodically acquiring a second set of overlay measurements of the reference mark, and determining the change in the overlay measurement value; based on the change in the overlay measurement value and the preset sensitivity, calculating the attitude change of the current optical axis attitude relative to the initial optical axis attitude; and adjusting the optical axis attitude to the initial optical axis attitude according to the attitude change to compensate for overlay errors caused by changes in the optical axis attitude.

[0008] This invention provides a method for calibrating the optical axis posture. A reference plate is added outside the workpiece stage of the overlay measurement device. The reference plate is equipped with reference marks sensitive to changes in the optical axis posture. Under the initial optical axis posture, the first set of overlay measurements of the reference marks is acquired as the reference overlay measurement value, and a preset sensitivity of the reference marks to the initial optical axis posture is determined, providing basic data for subsequent calculations of optical axis posture changes. Notably, this application is the first to propose obtaining overlay measurement changes based on reference marks, combining this with a preset calculation function, and using the preset sensitivity and the overlay measurement change value to infer the deviation of the optical axis posture, thus accurately calculating the posture change and adjusting the optical axis back to its initial posture. This direct calculation method based on physical sensitivity does not rely on complex image recognition algorithms, has simpler calculation logic, and higher computational efficiency. More importantly, it can fundamentally avoid overlay measurement accuracy errors caused by changes in optical axis posture, preventing measurement lag and significantly improving the long-term stability and accuracy of the overlay measurement device. Furthermore, since the reference plate is located outside the workpiece stage, meaning it remains in place without interference from the workpiece stage's movement, the monitoring of the optical axis orientation can be performed periodically and rapidly before and after each wafer loading, or during the intervals between wafer processing batches. This high-frequency monitoring does not require interruption of the normal wafer transport path, effectively hiding the time spent on optical axis orientation detection and calibration within the wafer production cycle. It can instantly capture minute optical axis offsets caused by environmental changes and compensate in real time through a feedback system, ensuring the continuous stability of measurement accuracy during long-term continuous production. It also avoids large-scale rework caused by accumulated errors, guaranteeing the measurement accuracy and long-term operational stability of the overlay measurement equipment, and meeting the increasingly stringent requirements for overlay accuracy in current advanced semiconductor manufacturing processes.

[0009] In a preferred embodiment, the step of determining the preset sensitivity corresponding to the reference mark includes: by changing the angle of the beam incident on the reference mark, measuring different overlay measurements corresponding to the change in optical axis attitude along a single direction, establishing a linear function relationship between the change in optical axis attitude along the single direction and the change in overlay measurements, and determining the slope of the linear function relationship as the preset sensitivity in the single direction.

[0010] By measuring the overlay measurement values ​​corresponding to the change in optical axis attitude in a single direction and constructing a linear function relationship, the preset sensitivity is determined by the slope of the function. This decouples the attitude change of the optical axis in multiple degrees of freedom (such as X / Y translation directions). By using the preset sensitivity in different directions and the measured overlay deviation, the attitude change in each direction can be accurately calculated, ensuring the objectivity and uniqueness of the sensitivity characterization. This provides stable and reliable parameter support for subsequent overlay measurement and optical alignment operations, thereby enabling fine calibration of the optical axis attitude along different directions.

[0011] In a preferred embodiment, the single direction is the X direction or the Y direction perpendicular to the X direction.

[0012] By setting a single direction as either the X direction or the Y direction perpendicular to the X direction, specifically, firstly, while keeping the optical axis orientation in the Y direction constant, the optical axis orientation in the X direction is changed, and different overlay measurements are taken in the corresponding X direction. A linear relationship is established between the change in the optical axis orientation in the X direction and the change in the overlay measurement. The preset sensitivity in the X direction is determined based on the slope of this linear relationship. Similarly, while keeping the optical axis orientation in the X direction constant, the optical axis orientation in the Y direction is changed, and different overlay measurements are taken in the corresponding Y direction. A linear relationship is established between the change in the optical axis orientation in the Y direction and the change in the overlay measurement. The preset sensitivity in the Y direction is determined based on the slope of this linear relationship. Accurately calculating the orientation changes in each direction provides stable and reliable parameter support for subsequent overlay measurements and optical alignment operations.

[0013] In a preferred embodiment, the step of calculating the attitude change of the current optical axis attitude relative to the initial attitude of the optical axis specifically includes: calculating the change in overlay measurement value ΔT=T1. T, where T is the reference set measurement value and T1 is the second set measurement value; the attitude change ΔX is calculated according to the formula ΔX=ΔT / S, where S is the preset sensitivity.

[0014] By directly calculating the change in overlay measurement ΔT and combining it with a preset sensitivity S to solve for the attitude change ΔX, the minute offset of the optical axis attitude can be accurately quantified. Since the preset sensitivity S is predetermined under the initial attitude, it can reflect the inherent response characteristics of the reference mark to changes in the optical axis. Therefore, the calculation of ΔX does not need to rely on complex image recognition or iterative approximation algorithms, which reduces the computational complexity. It also fundamentally eliminates the computational delay and uncertainty caused by the complexity of algorithms in traditional methods, realizes real-time capture and instant compensation of attitude changes, avoids measurement lag and reduced signal-to-noise ratio caused by processing a large amount of image data, and avoids the continuous accumulation of overlay errors.

[0015] In a preferred embodiment, the step of periodically acquiring the second set of calibrated measurements of the reference mark is performed by guiding the light beam to the reference plate without unloading or moving the wafer on the workpiece stage; or, the step of periodically acquiring the second set of calibrated measurements of the reference mark is performed during an idle period when the calibrated measurement equipment is in a non-photolithography measurement period, the idle period including a wafer loading period, a wafer unloading period, or a stepping movement period of the workpiece stage between measurement points.

[0016] By employing the above method, the second set of calibration measurements of the reference mark is cleverly embedded in the wafer processing gap, eliminating the need for dedicated equipment downtime. This ensures close integration with the wafer processing process, guaranteeing the accuracy of calibration measurements in the next wafer processing step, and achieving high-precision and high-efficiency wafer processing.

[0017] In a preferred embodiment, the adjustment of the optical axis attitude to the initial optical axis attitude is achieved by adjusting a movable or rotatable optical element in the optical system, the optical element including a mirror, a lens or a beam splitter.

[0018] In a preferred embodiment, the overlay measurement device includes a dual aperture device, and the adjustment of the optical axis attitude to the initial optical axis attitude is achieved by controlling the dual aperture device to change the incident direction of the illumination beam.

[0019] Whether adjusting the optical axis attitude through optical elements or through a dual aperture device, high sensitivity and low inertia adjustment and correction of the optical axis attitude can be achieved. This allows the attitude change calculated based on the preset sensitivity to be quickly and accurately converted into actual adjustment of the beam path. Using a dual aperture device can avoid the introduction of additional vibration and positioning errors by mechanical movement, resulting in higher accuracy. Moreover, the control is direct, achieving fast response and making it easier to adjust in one step, with high control precision.

[0020] In a preferred embodiment, before the step of calculating the change in attitude of the current optical axis relative to the initial attitude of the optical axis, the method further includes: determining whether the change in the overlay measurement exceeds a preset threshold; if it exceeds the preset threshold, then performing the step of calculating the change in attitude.

[0021] In special circumstances, changes in overlay measurements may not be caused by optical axis misalignment, such as momentary reading anomalies due to equipment micro-vibrations. Forcing optical axis compensation under these conditions would disrupt the originally accurate optical path. Therefore, a threshold judgment step is added before calculating the attitude change. The attitude change calculation and optical axis adjustment process is only initiated when the accumulated optical axis attitude misalignment is sufficient to affect overlay accuracy. This reduces the impact of unnecessary noise interference or momentary fluctuations, prevents invalid responses and invalid optical axis attitude compensation, and improves the long-term testing stability of the overlay measurement equipment.

[0022] In a preferred embodiment, the reference plate is further provided with a reference mark, the sensitivity of the reference mark to changes in optical axis attitude is different from that of the reference mark; the optical axis attitude calibration method further includes: obtaining the change in the overlay measurement value of the reference mark; determining whether the ratio of the change in the overlay measurement value of the reference mark and the reference mark is within a preset ratio range, if it does not meet the preset ratio range, then determining that the reference mark is abnormal and issuing an alarm signal.

[0023] By adding a reference mark on the base plate that has a different sensitivity to changes in optical axis attitude than the base mark, complementary verification can be formed. This can accurately identify abnormal states of the base mark, issue alarm signals in a timely manner to avoid erroneous calibration and invalid calibration, avoid generating unpredictable secondary errors, improve the accuracy of overlay measurement and wafer processing yield, and ensure the measurement accuracy and long-term operational stability of the overlay measurement equipment.

[0024] The present invention also provides a semiconductor overlay measurement device, including a workpiece stage, an optical system, a memory, and a processor. The semiconductor overlay measurement device further includes a reference plate containing reference marks, the reference plate being disposed in an area outside the workpiece stage. The memory stores a computer program, and the processor executes the computer program to implement the above-described optical axis attitude calibration method.

[0025] This invention provides a calibration measurement device that adds a reference plate outside the workpiece stage. The reference plate is equipped with reference marks sensitive to changes in the optical axis posture. This allows for the acquisition of the first calibration measurement value of the reference marks as the reference calibration measurement value at the initial optical axis posture, and the determination of a preset sensitivity of the reference marks to the initial optical axis posture, providing basic data for subsequent calculations of optical axis posture changes. By acquiring the calibration measurement change through the reference marks on the reference plate and combining it with a preset calculation function, the deviation of the optical axis posture can be inferred based on the preset sensitivity, allowing for accurate calculation of the posture change and adjustment of the optical axis back to its initial posture. This direct calculation method using physical sensitivity eliminates the need for complex image recognition algorithms, resulting in simpler calculation logic, higher computational efficiency, and, more importantly, avoids calibration measurement accuracy errors caused by changes in optical axis posture at the source. It prevents measurement lag and significantly improves the long-term stability and calibration measurement accuracy of the calibration measurement device. Furthermore, since the reference plate is located outside the workpiece stage, meaning it remains in place without interference from the workpiece stage's movement, the monitoring of the optical axis orientation can be performed periodically and rapidly before and after each wafer loading, or during the intervals between wafer processing batches. This high-frequency monitoring does not require interruption of the normal wafer transport path, effectively hiding the time spent on optical axis orientation detection and calibration within the wafer production cycle. It can instantly capture minute optical axis offsets caused by environmental changes and compensate in real time through a feedback system, ensuring the continuous stability of measurement accuracy during long-term continuous production. It also avoids large-scale rework caused by accumulated errors, guaranteeing the measurement accuracy and long-term operational stability of the overlay measurement equipment, and meeting the increasingly stringent requirements for overlay accuracy in current advanced semiconductor manufacturing processes. Attached Figure Description

[0026] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a flowchart of an optical axis attitude calibration method according to one embodiment of the present invention; Figure 2 This is a schematic diagram of the overlay measurement device in one embodiment of the present invention; Figure 3 This is a schematic diagram showing the positional relationship between the workpiece stage and the reference plate in one embodiment of the present invention; Figure 4 This is a schematic diagram of the overlay measurement results when the optical axis attitude shifts in one embodiment of the present invention; Figure 5 This is a schematic diagram of the overlay measurement results after adjusting the optical axis attitude to the initial optical axis attitude in one embodiment of the present invention; Figure 6This is a graph showing the experimental results of the relationship between the optical axis orientation and overlay measurement accuracy of a process piece in one embodiment of the present invention.

[0027] Component and drawing reference numerals: 100. Working platform; 200. Optical mechanism; 300. Optical axis; 400. Beam splitter; 101. Workpiece stage; 102. Reference plate stage; 103. Reference mark; 104. Outer frame center point; 105. Inner frame center point. Detailed Implementation

[0028] One or more embodiments of the present invention provide a method for automatically creating chip bumps for prescriptions. This method can be executed by a chip bump detection device for automatically creating prescriptions provided by one or more embodiments of the present invention. Certain input parameters or intermediate results in the detection method can be manually adjusted to help improve accuracy.

[0029] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0030] Among the existing technologies for reducing overlay errors in overlay measurement, for example, patent CN114428444B discloses a correction method for an overlay measurement system, which corrects the measurement error caused by the tilted surface by moving the wafer along the optical axis. This method introduces additional positional deviations due to the physical movement of the wafer, which in turn exacerbates the error risk of overlay measurement. At the same time, the wafer movement operation process also increases the measurement time and reduces the overall work efficiency, making it difficult to adapt to the high-precision and high-timeliness requirements of overlay measurement. To avoid the drawbacks caused by wafer movement, patent CN106154765B also discloses an overlay measurement device that achieves overlay measurement without moving the wafer by moving the aperture and integrating multiple measurement units. Patent CN103365107B discloses a multi-off-axis alignment system matching and calibration method that unifies the measurement results of multiple systems through offline measurement and online coordinate transformation. Although both avoid the additional deviation caused by wafer movement, the existing technologies can only achieve accurate detection of overlay offset or post-measurement compensation of measurement results. They are still passive responses to measurement deviations and cannot solve the overlay error at the core root cause of optical axis attitude offset, which affects the accuracy of overlay measurement.

[0031] Based on this, the applicant has creatively proposed an optical axis attitude calibration method and an overlay measurement device after exploration, which provides a solution to the problems in the prior art where the optical axis attitude is easily affected by environmental changes, stress release after equipment debugging, and position drift of optomechanical components, which leads to continuous aggravation of overlay measurement errors, decline in wafer processing quality, and difficulty in controlling accuracy.

[0032] like Figure 1 As shown, in one embodiment of the present invention, a method for calibrating the optical axis attitude is proposed and applied to an overlay measurement device, such as... Figure 2 , 3 As shown, the overlay measurement equipment includes a working platform 100 and an optical system. The optical system includes an optomechanical system 200, an optical axis 300 for transmitting the light beam, and a beam splitter 400. The working platform 100 includes a workpiece stage 101 and a reference stage 102. The workpiece stage 101 is used to hold the wafer, and a reference plate is mounted on the reference stage 102. The reference plate has reference marks 103 that are sensitive to changes in the orientation of the optical axis. (Combined with...) Figure 3 As shown, the reference plate is set in an area outside the workpiece stage. (Refer to...) Figure 1 The optical axis attitude calibration method includes the following steps: S1, under the initial optical axis attitude, acquire the first set of calibration measurements of the reference mark as the reference calibration measurements, and determine the preset sensitivity of the reference mark to the initial optical axis attitude; S2, periodically acquire the second set of calibration measurements of the reference mark, and determine the amount of change in the calibration measurements; S3, based on the amount of change in the calibration measurements and the preset sensitivity, calculate the attitude change of the current optical axis attitude relative to the initial optical axis attitude; S4, adjust the optical axis attitude to the initial optical axis attitude according to the attitude change, so as to compensate for the calibration error caused by the change in optical axis attitude.

[0033] Those skilled in the art will understand that the inner and outer frames of the selected reference mark have a height difference. Combined with Figure 4 and Figure 5 , Figure 4 This diagram illustrates the overlay measurement results before adjustment when the optical axis attitude shifts in step S4, where there is a deviation between the outer frame center point 104 and the inner frame center point 105 of the reference mark. Figure 5 The diagram illustrates the overlay measurement results after adjusting the optical axis attitude to the initial optical axis attitude in step S4, where the center point 104 of the outer frame of the reference mark and the center point 105 of the inner frame coincide.

[0034] Based on this, the present invention provides an optical axis attitude calibration method. A reference plate is added to the area outside the workpiece stage of the overlay measurement device. The reference plate is equipped with reference marks sensitive to changes in the optical axis attitude. Under the initial optical axis attitude, the first set of overlay measurements of the reference marks is obtained as the reference overlay measurement values, and the preset sensitivity of the reference marks to the initial optical axis attitude is determined, providing basic data for subsequent calculations of optical axis attitude changes. It is particularly important to note that this application is the first to propose obtaining overlay measurement changes based on reference marks, combining this with a preset calculation function, and using the preset sensitivity and the overlay measurement change values ​​to infer the deviation of the optical axis attitude, thus accurately calculating the attitude change and adjusting the optical axis back to its initial attitude. This direct calculation method based on physical sensitivity does not rely on complex image recognition algorithms, has simpler calculation logic, and higher computational efficiency. More importantly, it can fundamentally avoid overlay measurement accuracy errors caused by changes in optical axis attitude, preventing measurement lag and significantly improving the long-term stability and accuracy of the overlay measurement device. Furthermore, since the reference plate is located outside the workpiece stage, meaning it remains in place without interference from the workpiece stage's movement, the monitoring of the optical axis orientation can be performed periodically and rapidly before and after each wafer loading, or during the intervals between wafer processing batches. This high-frequency monitoring does not require interruption of the normal wafer transport path, effectively hiding the time spent on optical axis orientation detection and calibration within the wafer production cycle. It can instantly capture minute optical axis offsets caused by environmental changes and compensate in real time through a feedback system, ensuring the continuous stability of measurement accuracy during long-term continuous production. It also avoids large-scale rework caused by accumulated errors, guaranteeing the measurement accuracy and long-term operational stability of the overlay measurement equipment, and meeting the increasingly stringent requirements for overlay accuracy in current advanced semiconductor manufacturing processes.

[0035] It should be noted that, as Figure 6 As shown, the applicant conducted multiple experiments, using different process wafers. By changing the optical axis orientation and measuring the change in overlay accuracy, it was found that the optical axis orientation of the same process wafer mark is linearly related to the overlay measurement accuracy, and the sensitivity of the overlay accuracy of different process wafer marks to the optical axis orientation is not the same.

[0036] In a preferred embodiment, step S1 above, determining the preset sensitivity corresponding to the reference mark, includes: by changing the angle of the beam incident on the reference mark, measuring different overlay measurements corresponding to changes in the optical axis attitude along a single direction, establishing a linear functional relationship between the change in optical axis attitude along a single direction and the change in overlay measurements, and determining the slope of this linear functional relationship as the preset sensitivity in the single direction. Here, the single direction is the X direction or the Y direction perpendicular to the X direction.

[0037] First, while keeping the optical axis orientation in the Y direction constant, the optical axis orientation in the X direction can be changed, and different overlay measurements can be taken in the corresponding X direction. A linear relationship can be established between the change in the optical axis orientation in the X direction and the change in the overlay measurement. The preset sensitivity in the X direction can be determined based on the slope of this linear relationship. Similarly, while keeping the optical axis orientation in the X direction constant, the optical axis orientation in the Y direction can be changed, and different overlay measurements can be taken in the corresponding Y direction. A linear relationship can be established between the change in the optical axis orientation in the Y direction and the change in the overlay measurement. The preset sensitivity in the Y direction can be determined based on the slope of this linear relationship.

[0038] By measuring the overlay measurements corresponding to changes in the optical axis attitude in a single direction and constructing a linear function relationship, the preset sensitivity is determined by the function slope. This decouples the optical axis attitude changes in multiple degrees of freedom (such as X / Y translation directions). Using preset sensitivities in different directions and measured overlay deviations, the attitude change in each direction is accurately calculated, ensuring the objectivity and uniqueness of the sensitivity characterization. This provides stable and reliable parameter support for subsequent overlay measurements and optical alignment, enabling fine calibration of the optical axis attitude along different directions. By setting the single direction to the X direction or the Y direction perpendicular to the X direction, the attitude change in each direction is accurately calculated, providing stable and reliable parameter support for subsequent overlay measurements and optical alignment.

[0039] In a preferred embodiment, step S3, calculating the attitude change of the current optical axis attitude relative to the initial attitude, specifically includes: calculating the change in overlay measurement value ΔT=T1. T, where T is the baseline scale measurement value and T1 is the second scale measurement value; the attitude change ΔX is calculated according to the formula ΔX=ΔT / S, where S is the preset sensitivity.

[0040] Understandably, the attitude change ΔX includes the attitude change along the X direction and the attitude change along the Y direction.

[0041] By directly calculating the change in overlay measurement ΔT and combining it with a preset sensitivity S to solve for the attitude change ΔX, the minute offset of the optical axis attitude can be accurately quantified. Since the preset sensitivity S is predetermined under the initial attitude, it can reflect the inherent response characteristics of the reference mark to changes in the optical axis. Therefore, the calculation of ΔX does not need to rely on complex image recognition or iterative approximation algorithms, which reduces the computational complexity. It also fundamentally eliminates the computational delay and uncertainty caused by the complexity of algorithms in traditional methods, realizes real-time capture and instant compensation of attitude changes, avoids measurement lag and reduced signal-to-noise ratio caused by processing a large amount of image data, and avoids the continuous accumulation of overlay errors.

[0042] In a preferred embodiment, the step of periodically acquiring the second set of calibration measurements of the reference mark is performed by guiding the beam to the reference plate without unloading or moving the wafer on the workpiece stage; or, the step of periodically acquiring the second set of calibration measurements of the reference mark is performed during the idle period when the calibration measurement equipment is in non-photolithography measurement, including the wafer loading period, the wafer unloading period, or the stepping movement period of the workpiece stage between measurement points.

[0043] By employing the above method, the second set of calibration measurements of the reference mark is cleverly embedded in the wafer processing gap, eliminating the need for dedicated equipment downtime. This ensures close integration with the wafer processing process, guaranteeing the accuracy of calibration measurements in the next wafer processing step, and achieving high-precision and high-efficiency wafer processing.

[0044] In step S4 of this invention, the specific method of adjusting the optical axis attitude is not limited. In a preferred embodiment, adjusting the optical axis attitude to the initial optical axis attitude is achieved by adjusting movable or rotatable optical elements in the optical system, including mirrors, lenses, or beam splitters. In another preferred embodiment, the overlay measurement device includes a double aperture device, and adjusting the optical axis attitude to the initial optical axis attitude is achieved by controlling the double aperture device to change the incident direction of the illumination beam.

[0045] Whether adjusting the optical axis attitude through optical elements or through a dual aperture device, high sensitivity and low inertia adjustment and correction of the optical axis attitude can be achieved. This allows the attitude change calculated based on the preset sensitivity to be quickly and accurately converted into actual adjustment of the beam path. Using a dual aperture device can avoid the introduction of additional vibration and positioning errors by mechanical movement, resulting in higher accuracy. Moreover, the control is direct, achieving fast response and making it easier to adjust in one step, with high control precision.

[0046] It should be noted that, in this invention, the two optical axis attitude adjustment methods described above can still be applied to the process of determining the preset sensitivity.

[0047] In a preferred embodiment, before calculating the change in attitude of the current optical axis relative to the initial attitude of the optical axis, the method further includes: determining whether the change in the overlay measurement exceeds a preset threshold; if it exceeds the preset threshold, then performing the step of calculating the change in attitude.

[0048] In special circumstances, changes in overlay measurements may not be caused by optical axis misalignment, such as momentary reading anomalies due to equipment micro-vibrations. Forcing optical axis compensation under these conditions would disrupt the originally accurate optical path. Therefore, a threshold judgment step is added before calculating the attitude change. The attitude change calculation and optical axis adjustment process is only initiated when the accumulated optical axis attitude misalignment is sufficient to affect overlay accuracy. This reduces the impact of unnecessary noise interference or momentary fluctuations, prevents invalid responses and invalid optical axis attitude compensation, and improves the long-term testing stability of the overlay measurement equipment.

[0049] In a preferred embodiment, a reference mark is further provided on the reference plate, and the sensitivity of the reference mark to changes in the optical axis attitude is different from that of the reference mark; the optical axis attitude calibration method further includes: obtaining the change in the overlay measurement value of the reference mark; determining whether the ratio of the change in the overlay measurement value of the reference mark and the reference mark is within a preset ratio range; if it does not meet the preset ratio range, it is determined that the reference mark is abnormal and an alarm signal is issued.

[0050] By adding a reference mark on the base plate that has a different sensitivity to changes in optical axis attitude than the base mark, complementary verification can be formed. This can accurately identify abnormal states of the base mark, issue alarm signals in a timely manner to avoid erroneous calibration and invalid calibration, avoid generating unpredictable secondary errors, improve the accuracy of overlay measurement and wafer processing yield, and ensure the measurement accuracy and long-term operational stability of the overlay measurement equipment.

[0051] like Figure 2 , 3 As shown, in one embodiment of the present invention, an overlay measurement device is provided, including a working platform 100 and an optical system. The optical system includes an optomechanical system 200, an optical axis 300 for transmitting a light beam, and a beam splitter 400. The working platform 100 includes a workpiece stage 101 and a reference stage 102. The workpiece stage 101 is used to support a wafer. A reference plate is disposed on the reference stage 102. The reference plate is provided with a reference mark 103 that is sensitive to changes in the attitude of the optical axis. The reference plate is disposed in an area outside the workpiece stage (i.e., the reference plate and the workpiece stage do not overlap in the horizontal direction, thereby avoiding interference with wafer loading and unloading). The memory stores a computer program, and when the processor executes the computer program, it implements the above-mentioned optical axis attitude calibration method.

[0052] This invention provides a calibration measurement device that adds a reference plate outside the workpiece stage. The reference plate is equipped with reference marks sensitive to changes in the optical axis posture. This allows for the acquisition of the first calibration measurement value of the reference marks at the initial optical axis posture, serving as the baseline calibration measurement value. A preset sensitivity of the reference marks to the initial optical axis posture is also determined, providing fundamental data for subsequent calculations of optical axis posture changes. By acquiring the calibration measurement change through the reference marks on the reference plate and combining it with a preset calculation function, the deviation of the optical axis posture can be inferred based on the preset sensitivity, allowing for accurate calculation of the posture change and subsequent adjustment of the optical axis back to its initial posture. This direct calculation method using physical sensitivity eliminates the need for complex image recognition algorithms, resulting in simpler calculation logic, higher computational efficiency, and, most importantly, fundamentally avoiding calibration measurement accuracy errors caused by changes in optical axis posture. This prevents measurement lag and significantly improves the long-term stability and accuracy of the calibration measurement device. Furthermore, since the reference plate is located outside the workpiece stage, meaning it remains in place without interference from the workpiece stage's movement, the monitoring of the optical axis orientation can be performed periodically and rapidly before and after each wafer loading, or during the intervals between wafer processing batches. This high-frequency monitoring does not require interruption of the normal wafer transport path, effectively hiding the time spent on optical axis orientation detection and calibration within the wafer production cycle. It can instantly capture minute optical axis offsets caused by environmental changes and compensate in real time through a feedback system, ensuring the continuous stability of measurement accuracy during long-term continuous production. It also avoids large-scale rework caused by accumulated errors, guaranteeing the measurement accuracy and long-term operational stability of the overlay measurement equipment, and meeting the increasingly stringent requirements for overlay accuracy in current advanced semiconductor manufacturing processes.

[0053] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the device embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0054] Those skilled in the art will recognize that the modules and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0055] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The aforementioned units can be implemented in hardware or software.

[0056] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for calibrating an optical axis attitude, applied to an overlay measurement device, the overlay measurement device comprising a workpiece stage and an optical system, the optical system having an optical axis for transmitting a light beam, the workpiece stage for supporting a wafer, characterized in that, The overlay measurement device also includes a reference plate, on which reference marks sensitive to changes in the optical axis attitude are set. The reference plate is located outside the workpiece stage. The optical axis attitude calibration method includes the following steps: Under the initial orientation of the optical axis, the first set of scale measurements of the reference mark is obtained as the reference set scale measurements, and the preset sensitivity of the reference mark to the initial orientation of the optical axis is determined. The second set of scale measurements of the reference mark is periodically acquired, and the change in scale measurement is determined based on the second set of scale measurements and the reference scale measurements. Based on the change in the overlay measurement and the preset sensitivity, calculate the change in the current optical axis attitude relative to the initial optical axis attitude; Based on the change in attitude, the optical axis attitude is adjusted back to the initial optical axis attitude to compensate for the overlay error caused by the change in optical axis attitude.

2. The optical axis attitude calibration method according to claim 1, characterized in that, The step of determining the preset sensitivity corresponding to the reference mark includes: By changing the angle of the beam incident on the reference mark, different overlay measurements are measured corresponding to the change in optical axis attitude along a single direction. A linear functional relationship is established between the change in optical axis attitude along the single direction and the change in overlay measurement. The slope of this linear functional relationship is determined as the preset sensitivity of the single direction.

3. The optical axis attitude calibration method according to claim 2, characterized in that, The single direction is the X direction or the Y direction perpendicular to the X direction.

4. The optical axis attitude calibration method according to claim 1 or 2, characterized in that, The step of calculating the attitude change of the current optical axis attitude relative to the initial optical axis attitude specifically includes: Calculate the change in overlay measurement value ΔT=T1 T, where T is the reference set measurement value and T1 is the second set measurement value; the attitude change ΔX is calculated according to the formula ΔX=ΔT / S, where S is the preset sensitivity.

5. The optical axis attitude calibration method according to claim 1, characterized in that, The step of periodically acquiring the second set of calibrated measurements of the reference mark is performed by guiding the beam to the reference plate without unloading or moving the wafer on the workpiece stage; Alternatively, the step of periodically acquiring the second set of calibrated measurements of the reference mark is performed during a non-photolithography measurement idle period of the calibrated measurement equipment, which includes a wafer loading period, a wafer unloading period, or a period of stepping movement of the workpiece stage between measurement points.

6. The optical axis attitude calibration method according to claim 1, characterized in that, The adjustment of the optical axis attitude to the initial optical axis attitude is achieved by adjusting movable or rotatable optical elements in the optical system, including mirrors, lenses or beam splitters.

7. The optical axis attitude calibration method according to claim 1, characterized in that, The overlay measurement device includes a dual aperture device, and the adjustment of the optical axis attitude to the initial optical axis attitude is achieved by controlling the dual aperture device to change the incident direction of the illumination beam.

8. The optical axis attitude calibration method according to claim 1, characterized in that, Before the step of calculating the change in attitude of the current optical axis relative to the initial attitude of the optical axis, the method further includes: determining whether the change in the overlay measurement exceeds a preset threshold; if it exceeds the preset threshold, then performing the step of calculating the change in attitude.

9. The optical axis attitude calibration method according to claim 1, characterized in that, The reference plate is also provided with a reference mark, and the sensitivity of the reference mark to changes in the optical axis attitude is different from that of the reference mark. The optical axis attitude calibration method further includes: obtaining the change in the overlay measurement of the reference mark; determining whether the ratio of the change in the overlay measurement of the reference mark to that of the benchmark mark is within a preset ratio range; if it does not meet the preset ratio range, it is determined that the benchmark mark is abnormal and an alarm signal is issued.

10. A measuring device for overlay, comprising a workpiece stage, an optical system, a memory, and a processor, characterized in that, The semiconductor overlay measurement device further includes a reference plate, on which a reference mark sensitive to changes in the optical axis attitude is provided. The reference plate is located in an area outside the workpiece stage. The memory stores a computer program, and when the processor executes the computer program, it implements the optical axis attitude calibration method as described in claim 1.

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