A large range focusing system with two-dimensional angular measurement adjustment

Abstract

A large range focusing system with two-dimensional angle measurement adjustment relates to the field of optical precision measurement technology. A two-dimensional electric rotary displacement table is installed above the experiment table, a measurement sensor is installed on the two-dimensional electric rotary displacement table, a laser emits parallel polarized light, the parallel polarized light passes through a beam expander and a beam splitter to be divided into an eccentric light beam and a coaxial light beam, the coaxial light beam is reflected by a polarization beam splitter, passes through a 1 / 4 wave plate, and is focused on the surface of a measured object together with the eccentric light beam through a main objective lens, the eccentric light beam is reflected by a mirror after being reflected by a mirror, and then is focused on a CCD area array detector through a detection objective lens, the coaxial light beam is reflected in the original path after passing through the main objective lens, and then is transmitted through the 1 / 4 wave plate and the polarization beam splitter to act on a four-quadrant detector. The angle measurement adjustment and the measurement of Z-axis displacement change can be carried out at the same time, the number of components is reduced by multiple utilization of the optical path, the size of the control system is conducive to control, and better integration is realized.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement technology, specifically a large-range focusing system with two-dimensional angle measurement and adjustment. Background Technology

[0002] Optical inspection of wafer defects has long been an engineering problem that has accompanied the development of IC manufacturing. Wafer defect inspection requires accurate identification of defects on the wafer, such as voids, dents, scratches, etc., and requires obtaining specific information about the defects to meet the speed and capacity requirements of large-scale industrial production and achieve rapid inspection.

[0003] Automated optical inspection systems are a common method for wafer inspection. However, the imaging system within these systems achieves higher resolution only at the focal point. The wafer under inspection, due to variations in its surface microstructure, is never perfectly flat. Furthermore, the imaging system may encounter vibrations and structural thermal effects during operation, making it difficult to maintain optimal focus on the wafer. Therefore, the imaging system must possess a certain depth of field. However, for most imaging systems, a greater depth of field results in lower resolution. Additionally, the wafer is subjected to stress during various processes, and residual stress can cause the wafer surface to warp at a certain angle, resulting in a non-perpendicular relationship between the wafer surface and the optical axis of the imaging system, which can also interfere with wafer defect detection.

[0004] With the increasing demand for precise measurement of changes in object surface morphology, a wide-range, high-precision, multi-degree-of-freedom positioning measurement device is needed in more and more applications. However, traditional contact measurement methods have limitations in these applications, such as potential damage to the object surface, interference from surface coatings, and the inability to achieve high-precision measurements, or the inability to simultaneously achieve rapid, high-precision displacement measurement and positioning adjustment. Non-contact measurement often uses multiple sensors in combination to meet these requirements, which can lead to Abbe errors and other influences during the measurement and positioning process, reducing the accuracy of the measurement and positioning.

[0005] Therefore, in response to the key issue of automatic focusing in automatic optical inspection systems, which is to meet the requirements of large-range, high-precision, and multi-degree-of-freedom measurement, and to solve the problem of measuring and adjusting the angle changes of the measured surface of the object during the measurement process, thereby improving the positioning accuracy and range of Z-axis displacement, there is an urgent need for a large-range focusing system that can measure the measured surface of the object and perform two-dimensional angle measurement and adjustment. Summary of the Invention

[0006] To address the current limitations of separate angle measurement and Z-axis displacement measurement required for the measured object during the measurement process, and the fact that confocal measurement is affected by changes in the pose of the measured object's surface or whether it is horizontal, this invention provides a large-range focusing system with two-dimensional angle measurement and adjustment to achieve simultaneous angle measurement and better Z-axis displacement measurement. This system splits parallel polarized light into an eccentric beam and a coaxial beam. The eccentric beam is used for Z-axis displacement measurement based on the confocal principle and triangulation principle, while the coaxial beam is used for two-dimensional angle and attitude measurement based on the self-collimation principle. This allows for simultaneous attitude measurement and adjustment of the measured object's surface and high-precision Z-axis displacement measurement. The multiple uses of the optical path reduce the number of components, contributing to the size and better integration of the control system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a large-range focusing system with two-dimensional angle measurement and adjustment, comprising an experimental stage, a two-dimensional electric rotary displacement stage, and a measuring sensor. The two-dimensional electric rotary displacement stage is mounted above the experimental stage and is capable of two-dimensional rotation around the X and Y axes. The measuring sensor is mounted on the two-dimensional electric rotary displacement stage and includes a beam splitter, a laser, a beam expander, a main objective lens, a detector objective lens, a CCD array detector, a reflector, a quarter-wave plate, a polarizing beam splitter, and a four-quadrant detector. The laser emits parallel polarized light that first passes through the... After beam expansion by the beam expander, the beam is split into an eccentric beam and a coaxial beam by the beam splitter. The coaxial beam is further reflected by the polarizing beam splitter and then passes through the quarter-wave plate. Together with the eccentric beam, it passes through the main objective lens and is focused onto the surface of the object under test. The eccentric beam is reflected by the mirror of the object under test as an eccentric reflected beam, passes through the main objective lens again, and is reflected by the reflecting mirror. Then, it is focused onto the CCD array detector by the detection objective lens. The coaxial beam is reflected by the object under test along the original path, passes through the main objective lens again, passes through the quarter-wave plate, and is transmitted through the polarizing beam splitter before acting on the four-quadrant detector.

[0008] Furthermore, during the measurement process, the rotation angles RX and RY of the surface of the object being measured are measured by the measuring sensor, and the two-dimensional electric rotary displacement stage is controlled to rotate so that the Z-axis direction of the measuring sensor is perpendicular to the surface of the object being measured.

[0009] Furthermore, during the measurement process, the displacement change of the surface of the object being measured in the Z-axis direction is calculated using the light intensity and position information of the CCD array detector.

[0010] Furthermore, during the measurement process, the rotation angle RX around the X-axis and the rotation angle RY around the Y-axis of the surface of the object under test are calculated by using the two-dimensional position change of the light spot obtained on the four-quadrant detector.

[0011] Furthermore, displacement in the Z-axis direction is measured during the measurement process, and error compensation is performed on the rotation angles RX and RY.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] 1. This invention cleverly combines the principles of differential confocal focusing, triangulation, and laser self-collimation. It splits parallel polarized light into an eccentric beam and a coaxial beam. The eccentric beam is used to measure the displacement change in the Z-axis direction. The differential confocal principle can be used to perform high-precision measurement of the Z-axis, and the triangulation principle can be used to perform large-range measurement of the Z-axis. The coaxial beam is used to measure the rotation angle changes RX and RY around the X-axis and Y-axis. By measuring the angular displacement of the surface of the object being measured by the sensor, i.e., RX and RY, the two-dimensional electric rotary displacement stage is controlled to rotate, so that the Z-axis direction of the measuring sensor is perpendicular to the measuring surface, thereby improving the measurement accuracy of the Z-axis displacement.

[0014] 2. The measurement sensor designed in this invention uses optical components, which can be more easily integrated. In the process of optical path design, the optical path is reused multiple times, the optical path structure is simplified, the number of components is greatly reduced, and the size of the control system is made smaller.

[0015] 3. The measurement sensor designed in this invention has an absolute zero point position, which can be used in some situations where focal position detection and angle measurement are required at the same time, or it can be used for free-form surface measurement through subsequent processing of the measurement results. The application scenarios of the measurement are more extensive.

[0016] 4. The measurement sensor designed in this invention adopts non-contact optical measurement, which can avoid the problem of damaging the object being measured by contact with the surface of the object being measured in some precision equipment measurements. In addition, the confocal measurement technology also has relatively high measurement accuracy. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the large-range focusing system of the present invention;

[0018] Figure 2 This is a schematic diagram of the structure of the measuring sensor in this invention;

[0019] Figure 3 This is a schematic diagram of the optical path of the differential confocal measurement section of the measurement sensor in this invention;

[0020] Figure 4This is a differential confocal response curve of the CCD array detector in this invention;

[0021] Figure 5 This is a schematic diagram of the optical path of the triangular light measurement part of the measurement sensor in this invention;

[0022] Figure 6 This is a schematic diagram of the principle of the self-collimation angle measurement part of the measuring sensor in this invention.

[0023] In the diagram: 1. Experimental stage; 2. Two-dimensional electric rotary displacement stage; 3. Measurement sensor; 4. Object under test; 5. Beam splitter; 6. Laser; 7. Beam expander; 8. Eccentric beam; 9. Coaxial beam; 10. Main objective lens; 11. Probe objective lens; 12. CCD array detector; 13. Mirror; 14. Quarter wave plate; 15. Polarizing beam splitter; 16. Four-quadrant detector; 17. Eccentric reflected beam. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] like Figures 1-6 As shown, a large-range focusing system with two-dimensional angle measurement and adjustment includes an experimental stage 1, a two-dimensional electric rotary displacement stage 2, a measurement sensor 3, a measured object 4, a beam splitter 5, a laser 6, a beam expander 7, an eccentric beam 8, a coaxial beam 9, a main objective lens 10, a probe objective lens 11, a CCD array detector 12, a reflector 13, a quarter-wave plate 14, a polarizing beam splitter 15, a four-quadrant detector 16, and an eccentric reflected beam 17.

[0026] Combination Figure 1 As shown, a two-dimensional electric rotary displacement stage 2 is installed above the experimental platform 1. The two-dimensional electric rotary displacement stage 2 is capable of two-dimensional rotation around the X-axis and Y-axis. The measuring sensor 3 is installed on the two-dimensional electric rotary displacement stage 2. By measuring the angular displacements RX and RY of the surface of the object 4 being measured by the measuring sensor 3, the two-dimensional electric rotary displacement stage 2 is controlled to rotate, so that the Z-axis direction of the measuring sensor 3 is perpendicular to the measuring surface, thereby improving the measurement accuracy of the Z-axis displacement.

[0027] Combination Figure 2 As shown, the specific form of the measuring sensor 3 is as follows: the laser 6 emits parallel polarized light, which is first expanded to a suitable beam diameter by the beam expander 7, and then split into an eccentric beam 8 and a coaxial beam 9 by the beam splitter 5.

[0028] Combination Figure 3 As shown, the eccentric beam 8 is focused onto the surface of the object under test 4 by the main objective lens 10. After specular reflection on the surface of the object under test 4, it becomes an eccentrically reflected beam 17. The eccentrically reflected beam 17 passes through the main objective lens 10 again and is reflected by the reflecting mirror 13. The reflected eccentrically reflected beam 17 is focused onto the CCD array detector 12 by the detection objective lens 11. The displacement change of the surface of the object under test 4 in the Z-axis direction can be calculated by using the light intensity information and position information of the CCD array detector 12. Specifically, a linear relationship between light intensity and displacement change can be established by using the light intensity information of the array CCD, thereby calculating the high-precision displacement change of the surface of the object under test 4 in the Z-axis direction. The displacement change of the laser spot on the array CCD is obtained by extracting the centroid of the array CCD, and then the large-range displacement change of the surface of the object under test 4 can be calculated.

[0029] Combination Figure 4 As shown, the CCD area array detector 12 forms a circular light spot. Two symmetrical circular micro-regions, C and D, are set as detection areas with the center B of the light spot as the symmetrical point in the Z-axis direction. When the surface of the object being measured 4 moves axially, the total gray value of the two detection areas, C and D, will change. This is equivalent to two pinhole positions in a normal differential confocal optical path, which is equivalent to two bell-shaped response curves. After differentially subtracting the sum of the gray values ​​of the two detection areas, a response curve with an absolute zero point is obtained. The linear range in the middle of the curve can be extracted for displacement measurement in the Z-axis direction.

[0030] According to coherent imaging theory, the amplitude point spread function of the eccentric beam 8 and the amplitude point spread function of the eccentric reflected beam 17 are respectively h i (x,y,z) and h c (x,y,z,v M ), can be represented as:

[0031]

[0032] The differential response curve is the subtraction of the intensity responses in regions C and D, and can be expressed as:

[0033] I idff (x,y,z,v M ) = I B (x,y,v,z M )-I F (x,y,z,-v M )

[0034] In the formula, x, y, and z are the coordinates in the mirror space of the principal object, and v x v x vx P represents the normalized coordinates of x, y, and z, respectively. i (ρ,θ,u) is the defocusing pupil function of the eccentric beam, P c (ρ,θ,u) is the defocusing pupil function of the eccentrically reflected beam, u = 8πzsin 2 2(α o / 2) / λ,v M To detect the lateral normalized offset of the region, v M =2πMsinα M / λ, M is the physical offset between the detection regions C and D, λ is the laser wavelength, sinα o ρ is the effective numerical aperture of the primary objective lens, and θ is the normalized pupil coordinate in polar coordinates.

[0035] Since a virtual pinhole is used, the position and size of the detection areas C and D can be arbitrarily set by the software. This allows for the comprehensive consideration of the relationship between resolution, measurement range, and other factors according to different needs. By changing the position and size of the detection areas C and D, a suitable curve can be obtained, and by selecting a suitable line segment, the correspondence between grayscale light intensity and axial position can be obtained.

[0036] Combination Figure 5 As shown, simultaneously, for the circular light spot formed by the CCD area array detector 12, when the surface of the object being measured 4 is displaced along the Z-axis, the light spot on the CCD area array detector 12 will shift. By extracting the centroid coordinates of the light spot using an image processing algorithm, a displacement relationship can be established, which can be expressed as:

[0037]

[0038] In the formula, ΔZ is the Z-axis displacement change of the surface of the object being measured, f1 is the focal length of the main objective lens, f2 is the focal length of the detector objective lens, s is the offset between the eccentric beam and the optical axis, and Δd is the displacement change of the light spot on the CCD array detector.

[0039] Combination Figure 6 As shown, the coaxial beam 9 needs to be reflected by the polarizing beam splitter 15, and after reflection, it passes through the quarter-wave plate 14 and is focused onto the surface of the object under test 4 by the main objective lens 10. The coaxial beam 9 is reflected along the original path by the surface of the object under test 4, and after reflection, it passes through the main objective lens 10 again, then its polarization state is changed by the quarter-wave plate 14, and then it is transmitted through the polarizing beam splitter 15 and acts on the four-quadrant detector 16 to form a light spot. By obtaining the two-dimensional position change of the light spot on the four-quadrant detector 16, the rotation angle RX of the surface of the object under test 4 about the X-axis and the rotation angle RY about the Y-axis can be calculated. Specifically:

[0040] The origin of the light spot is E. When the surface of the object being measured 4 undergoes an RX angle change, that is, after moving from O to O(1), the light spot on the four-quadrant detector 16 will also move accordingly, moving from E to point F. The X-axis angle measurement calculation formula is:

[0041] f1*tan(2a)=ΔX

[0042] In the formula, a is the rotation angle of the surface of the object being measured around the X-axis, and ΔX is the distance the light spot moves along the X-axis on the four-quadrant detector.

[0043] Similarly, the principle for measuring the angle of the Y-axis is the same as that for the X-axis, as shown below:

[0044] f1*tan(2β)=ΔY

[0045] In the formula, β is the rotation angle of the surface of the object being measured around the Y-axis, and ΔY is the distance the light spot moves along the Y-axis on the four-quadrant detector.

[0046] During the measurement process, the displacement measurement range in the Z-axis direction is generally within ±1mm. When the displacement change is small, the displacement in the Z-axis direction has little impact on the measurement of angles RX and RY. The measurement algorithm can compensate for the error caused by the displacement measurement of angles RX and RY, thereby improving the measurement accuracy.

[0047] One workflow in the measurement process is as follows: At the start of the measurement, the experimental stage 1 moves up and down along the Z-axis for scanning. Since the absolute zero point position of the differential confocal sensor is not affected by the change in the surface angle of the object being measured 4, the measurement stops when the object being measured 4 moves to the absolute zero point calibrated by the measuring sensor 3. Then, the measuring sensor 3 starts to measure the two-dimensional angles RX and RY on the surface of the object being measured 4 and feeds the measured angles back to the two-dimensional electric rotary stage 2. The two-dimensional electric rotary stage 2 rotates to adjust the posture of the measuring sensor 3 so that the Z-axis direction of the measuring sensor 3 is perpendicular to the surface of the object being measured 4. Finally, the displacement in the Z-axis direction is measured to improve the measurement accuracy of the Z-axis.

[0048] Another workflow in the measurement process is as follows: First, the measurement sensor 3 measures the angles of RX and RY. The effect of displacement in the Z-axis direction on the angle measurement is compensated by the compensation algorithm. The measured angle is fed back to the two-dimensional electric rotary stage 2. The two-dimensional electric rotary stage 2 rotates and adjusts the position of the measurement sensor 3. Finally, the displacement in the Z-axis direction is measured.

[0049] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0050] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A large-range focusing system with two-dimensional angle measurement and adjustment, characterized in that: The experimental setup includes an experimental platform (1), a two-dimensional electric rotary stage (2), and a measuring sensor (3). The two-dimensional electric rotary stage (2) is mounted on top of the experimental platform (1). The two-dimensional electric rotary stage (2) is capable of two-dimensional rotation around the X-axis and Y-axis. The measuring sensor (3) is mounted on the two-dimensional electric rotary stage (2). The measuring sensor (3) includes a beam splitter (5), a laser (6), a beam expander (7), a main objective lens (10), a probe objective lens (11), a CCD array detector (12), a reflector (13), a quarter-wave plate (14), a polarizing beam splitter (15), and a four-quadrant detector (16). 16) The laser (6) emits parallel polarized light, which is first expanded by the beam expander (7) and then split into an eccentric beam (8) and a coaxial beam (9) by the beam splitter (5). The coaxial beam (9) is further reflected by the polarizing beam splitter (15) and then passes through the quarter-wave plate (14). Together with the eccentric beam (8), it passes through the main objective lens (10) and is focused onto the surface of the object under test (4). The eccentric beam (8) is reflected by the mirror of the object under test (4) into an eccentric reflected beam (17), which passes through the main objective lens (10) again and is reflected by the reflecting mirror (13). After that, it passes through the main objective lens (10) and then through the reflecting mirror (13). The detection objective (11) is focused on the CCD array detector (12), which forms a circular spot. Two symmetrical circular micro-regions are set as detection areas along the Z-axis with the center of the spot as the symmetrical point. When the surface of the object under test (4) moves axially, the sum of the gray values ​​of the two detection areas is differentially subtracted to obtain a response curve with an absolute zero point. The high-precision displacement change of the object under test (4) is obtained through the linear range in the middle of the curve. At the same time, the centroid position coordinates of the spot are extracted by the image processing algorithm to establish the displacement relationship and obtain the large range displacement change of the object under test (4). After the beam (9) is reflected by the object under test (4) and passes through the main objective lens (10) again, it is transmitted through the quarter wave plate (14) and then through the polarizing beam splitter (15) before acting on the four-quadrant detector (16). The two-dimensional position change of the light spot obtained by the four-quadrant detector (16) is used to calculate the rotation angle RX of the surface of the object under test (4) around the X axis and the rotation angle RY around the Y axis. The two-dimensional electric rotary displacement stage (2) rotates according to the feedback measurement angle to adjust the posture of the measuring sensor (3) so that the Z-axis direction of the measuring sensor (3) is perpendicular to the surface of the object under test (4) to eliminate the error of the angle on the Z-axis displacement measurement.

2. The large-range focusing system with two-dimensional angle measurement and adjustment according to claim 1, characterized in that: During the measurement process, the rotation angles RX and RY of the surface of the object under test (4) measured by the measuring sensor (3) are used to control the two-dimensional electric rotary displacement stage (2) to rotate, so that the Z-axis direction of the measuring sensor (3) is perpendicular to the surface of the object under test (4).

3. A large-range focusing system with two-dimensional angle measurement and adjustment according to claim 1, characterized in that: During the measurement process, the displacement change of the surface of the object under test (4) in the Z-axis direction is calculated using the light intensity information and position information of the CCD array detector (12).

4. A large-range focusing system with two-dimensional angle measurement and adjustment according to claim 1, characterized in that: During the measurement process, the two-dimensional position change of the light spot obtained by the four-quadrant detector (16) is used to calculate the rotation angle RX around the X-axis and the rotation angle RY around the Y-axis of the surface of the object under test (4).

5. A large-range focusing system with two-dimensional angle measurement and adjustment according to claim 4, characterized in that: During the measurement process, displacement in the Z-axis direction is measured, and error compensation is performed on the rotation angles RX and RY.

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