Device and method for testing resolution of optical thickness gauge

Abstract

The invention provides a resolution testing device and method for an optical thickness gauge, and belongs to the technical field of optical precision measurement. The resolution testing device comprises a displacement table, a movable lens base, a movable lens, an angle adjusting device, a fixed lens base and a fixed lens; the displacement table comprises a displacement table main body structure and a displacement table movement structure, and the displacement table movement structure moves on the displacement table main body structure; the moving mirror base is installed on a displacement table moving structure, and the moving lens is installed on the moving mirror base through the angle adjusting device. The fixed lens is clamped on a fixed lens base, and the fixed lens base is installed on a displacement table main body structure or other static objects. Different types of thickness sheets are simulated by selecting the moving lens and the fixed lens which are made of different materials and have different coating films; the displacement table drives the moving lens to move, so that continuous and precise thickness change can be equivalently realized; the resolution test is realized by analyzing the measurement results of the optical thickness gauge when the moving lens is at different positions.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, specifically relating to an optical thickness gauge resolution testing device and method. Background Technology

[0002] Resolution is one of the key performance parameters for optical thickness gauges, directly representing the smallest difference in film thickness that the instrument can resolve. It is the most important system performance parameter for detecting the limits of thickness variation. Therefore, accurately verifying the resolution of a thickness gauge is of great significance for research on performance testing and evaluation techniques for thickness gauges.

[0003] Patent No.: 202310371338.7, Patent Name: A Measurement Method Based on a Linear Displacement Sensor Resolution Testing Device. This patent discloses a method for generating minute displacements by heating a linear expansion rod to calculate the resolution of the linear displacement sensor. However, this method is only applicable to the field of linear displacement measurement technology and cannot test the resolution of optical thickness gauges. In 2021, Guo Tong et al. from Tianjin University proposed a method for simultaneously measuring surface profile and film thickness (Guo T, Zhao G, Tang D, et al. High-accuracy simultaneous measurement of surface profile and film thickness using line-field white-light dispersive interferometer[J]. Optics and Lasers in Engineering, 2021, 137: 106388). This method indirectly characterizes the vertical resolution of the system by the noise level of the data points, but it lacks direct testing of the resolution for thickness measurement. In 2023, Kong Shuaishuai et al. from Shanghai University of Science and Technology designed a standard with adjustable quartz glass plate spacing (Kong Shuaishuai. Research on film thickness measurement during liquid film evaporation and flow of R1233zd[D]. Shanghai University of Science and Technology, 2022), which achieved controllable change of liquid film thickness. Theoretically, it can be used for thickness resolution measurement. However, this device is only suitable for liquid thin films, and the upper limit of thickness control accuracy is difficult to adapt to high-precision optical thickness gauges. In addition, the standard lacks an angle adjustment structure, which makes the lower limit of measurable liquid film thickness relatively low. Furthermore, this paper only used the device to verify the thickness measurement accuracy and did not propose an effective resolution testing method. Summary of the Invention

[0004] The purpose of this invention is to provide an optical thickness gauge resolution testing device and method, which can achieve resolution testing by analyzing the measurement results of the optical thickness gauge when the moving lens is in different positions.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An optical thickness gauge resolution testing device includes: a displacement stage, a motion mirror base, a motion lens, an angle adjustment device, a fixed mirror base, and a fixed lens;

[0007] The displacement stage includes a main structure and a moving structure, wherein the moving structure moves on the main structure.

[0008] The motion mirror mount is mounted on the displacement stage moving structure, and the motion lens is mounted on the motion mirror mount via the angle adjustment device;

[0009] The fixed lens is clamped on the fixed lens mount, which is mounted on the main structure of the displacement stage or other stationary object.

[0010] Furthermore, the motion lens and the fixed lens constitute an opaque sample without a substrate, a transparent sample without a substrate, and a transparent sample with a substrate.

[0011] Furthermore, when the motion lens and the fixed lens constitute an opaque sample without a substrate, the motion lens and the fixed lens are respectively selected as transparent lenses. Each transparent lens is coated with an anti-reflection film on one side and a high-reflection film on the other side, and the high-reflection film-coated sides of the two transparent lenses are installed facing each other.

[0012] Furthermore, when the motion lens and the fixed lens constitute a transparent sample without a substrate, the motion lens and the fixed lens are respectively selected as transparent lenses, each of the transparent lenses has an anti-reflective coating on one side and no coating on the other side, and the uncoated sides of the two transparent lenses are mounted facing each other.

[0013] Furthermore, when the motion lens and the fixed lens constitute a transparent sample containing a substrate, the motion lens and the fixed lens are respectively selected as transparent lenses, one of which is coated with an anti-reflective film on one side and uncoated on the other side, and the other lens is smooth on both sides and uncoated, with the uncoated side mounted on the lens that is smooth on both sides and uncoated.

[0014] Furthermore, the angle adjustment device includes a motion lens base, which is connected to a deformable rubber ring via a set of screws, and the deformable rubber ring is connected to the motion lens base.

[0015] Furthermore, the motion lens mount has a circular through hole one, which is smaller than the area of ​​the motion lens.

[0016] Furthermore, the fixed lens mount has a second circular through hole, which is smaller in area than the fixed lens.

[0017] The present invention may also include:

[0018] A method for testing the resolution of an optical thickness gauge, using the aforementioned optical thickness gauge resolution testing device, the method comprising:

[0019] (1) Perform power-on, preheating, and calibration operations;

[0020] (2) Adjust the angle of the moving lens by means of the angle adjustment device so that the moving lens is parallel to the fixed lens;

[0021] (3) Use an optical thickness gauge to measure the equivalent thickness of the moving lens and the fixed lens, set the displacement stage step distance ΔL, and measure at different displacement values ​​to obtain the thickness measurement value with the theoretical step distance ΔL.

[0022] (4) Determine the resolution of the optical thickness gauge:

[0023] When the thickness change information output by the optical thickness gauge presents a step signal with the same theoretical trend, it indicates that the resolution of the optical thickness gauge reaches ΔL.

[0024] Alternatively, the thickness measurement resolution can be calculated based on the output of the optical thickness gauge.

[0025] The displacement stage (1) has undergone n displacements of magnitude ΔL in a single direction. First, the thickness observation value is reduced to zero, and the average value D0 of the reduced value is calculated:

[0026]

[0027] In the formula: D i These are the measured thickness values; d i It is the thickness value that changes from zero on the displacement stage, i.e., d. i = (i-1)ΔL; i is the measurement sequence number 1, 2, ..., n;

[0028] Resolution m 分 The calculation formula is as follows:

[0029]

[0030] Among them, the difference between the measured value and the recalculated value:

[0031] v i =D i -D0-d i (3).

[0032] The beneficial effects of this invention are as follows:

[0033] This invention has a wide range of applications and can directly provide quantitative results for the resolution of an optical thickness gauge through experimental testing. It features a simple structure, compact size, and ease of operation; the theoretical upper limit of resolution testing is determined solely by the movement accuracy of the displacement stage, meeting the resolution testing accuracy requirements of numerous optical thickness gauges; it can be used to measure various common types of samples; and by precisely controlling the parallelism between the two lenses through an angle adjustment device, resolution testing can be achieved at even smaller thicknesses.

[0034] This invention verifies the resolution of an instrument by measuring the equivalent thickness change caused by displacement, thus solving the problem that the manufacturing process cannot produce a series of standard thickness sheets with minimal thickness differences and good uniformity.

[0035] This invention can simulate different types of thickness sheets by selecting moving and fixed lenses with different materials and coatings; the displacement stage drives the moving lenses to move, which can achieve continuous and precise thickness changes; by analyzing the measurement results of the optical thickness gauge when the moving lenses are in different positions, resolution testing can be achieved. Attached Figure Description

[0036] Appendix Figure 1 This is a schematic diagram of the structure of the present invention;

[0037] Appendix Figure 2 This is a schematic diagram of the structure of an equivalent opaque sample without a substrate according to the present invention;

[0038] Appendix Figure 3 This is a schematic diagram of the structure of an equivalent transparent sample without a substrate according to the present invention;

[0039] Appendix Figure 4 This is a schematic diagram of the structure of the equivalent transparent sample containing the substrate according to the present invention.

[0040] In the attached diagram: 1. Displacement stage; 1-1. Main structure of displacement stage; 1-2. Moving structure of displacement stage; 2. Moving mirror base; 3. Moving lens; 4. Angle adjustment device; 5. Fixed mirror base; 6. Fixed lens. Detailed Implementation

[0041] The present invention will now be further described with reference to the accompanying drawings.

[0042] This invention provides an optical thickness gauge resolution testing device, as shown in the attached figure. Figure 1 As shown, it includes: a displacement stage 1, a motion mirror base 2, a motion lens 3, an angle adjustment device 4, a fixed mirror base 5, and a fixed lens 6;

[0043] The displacement stage 1 includes a main displacement stage structure 1-1 and a moving displacement stage structure 1-2, wherein the moving displacement stage structure 1-2 moves on the main displacement stage structure 1-1.

[0044] The motion lens mount 2 is mounted on the displacement stage motion structure 1-2, and the motion lens 3 is mounted on the motion lens mount 2 through the angle adjustment device 4. The angle adjustment device can adjust the angle of the motion lens.

[0045] The fixed lens 6 is clamped on the fixed lens base 5, which is mounted on the main structure 1-1 of the displacement stage or other stationary objects.

[0046] The fixed lens 6 is connected to the fixed lens mount 5, and the fixed lens 6 and the moving lens 3 together constitute an equivalent thickness sample.

[0047] The relative displacement between the main structure 1-1 of the displacement stage and the moving structure 1-2 of the displacement stage is adjustable, and the moving structure 1-2 of the displacement stage can move up and down, forward and backward, and left and right.

[0048] A control line is connected to the side of the main structure 1-1 of the displacement stage, which is connected to a controller. The motion state of the moving parts can be precisely controlled according to the input voltage of the controller.

[0049] The motion lens 3 can be replaced with different types of lenses, and the motion lens 3 is connected to the motion lens mount through an angle adjustment device.

[0050] Furthermore, the motion lens 3 and the fixed lens 6 constitute an opaque sample without a substrate, a transparent sample without a substrate, and a transparent sample with a substrate.

[0051] As attached Figure 2 As shown, when the motion lens 3 and the fixed lens 6 constitute an opaque sample without a substrate, the motion lens 3 and the fixed lens 6 are respectively selected as transparent lenses. Each of the transparent lenses is coated with an anti-reflection film on one side and a high-reflection film on the other side. The high-reflection film-coated sides of the two transparent lenses are installed facing each other.

[0052] As attached Figure 3 As shown, when the motion lens 3 and the fixed lens 6 constitute a transparent sample without a substrate, the motion lens 3 and the fixed lens 6 are respectively selected as transparent lenses. Each transparent lens has an anti-reflective coating on one side and no coating on the other side. The uncoated sides of the two transparent lenses are installed facing each other.

[0053] Alternatively, both the fixed lens 6 and the moving lens 3 are coated with an anti-reflective coating on one side and an anti-reflective coating on the other side, with the two anti-reflective coatings placed facing each other to form an opaque sample without substrate with a smaller equivalent thickness (or they can be placed in opposite directions to form an opaque sample without substrate with a larger equivalent thickness).

[0054] As attached Figure 4As shown, when the motion lens 3 and the fixed lens 6 constitute a transparent sample containing a substrate, the motion lens 3 and the fixed lens 6 are respectively selected as transparent lenses. One of the lenses is coated with an anti-reflective film on one side and uncoated on the other side, while the other lens is smooth on both sides and uncoated. The uncoated side is mounted on the lens with smooth and uncoated sides.

[0055] In this embodiment, the angle adjustment device 4 includes a motion lens base, which is connected to a deformable rubber ring via a set of screws. The deformable rubber ring is connected to the motion lens base 2.

[0056] The motion mirror mount 2 has a circular through-hole, which is smaller than the area of ​​the motion lens 3. In order to allow the measuring light to pass through the motion mirror mount and illuminate the motion lens, the motion mirror mount 2 has a circular opening that is slightly smaller than that of the motion lens 3.

[0057] Example 1:

[0058] This embodiment provides a method for testing the resolution of an optical thickness gauge, implemented using the aforementioned optical thickness gauge resolution testing device, and includes the following steps:

[0059] When the optical thickness gauge is powered on, the resolution testing device is not placed in the measurement optical path. The distance L between the two probes of the optical thickness gauge under test is measured as a reference value for subsequent thickness measurement.

[0060] The resolution testing device described above is placed in the measuring optical path of the optical thickness gauge to be tested;

[0061] By turning the screw in the angle adjustment device 4, the rubber ring is deformed, thereby adjusting the angle of the moving lens and making the fixed lens parallel to the moving lens.

[0062] The two probes of the optical thickness gauge under test are perpendicularly aligned with the outer surfaces of the moving lens 3 and the fixed lens 6, respectively. At this time, the two probes will receive reflected light from the two anti-reflection films respectively.

[0063] The measurement begins by measuring the distance L1 between the left probe and the high-reflectivity film side of the fixed lens 6, and the distance L2 between the right probe and the anti-reflective film side of the moving lens 3. Here, L1 and L2 include the optical thickness of the glass. Therefore, the equivalent thickness of the opaque sample due to the air gap is: d = L - L1 - L2 + 2ΔD, where ΔD is the difference between the pre-measured optical thickness and physical thickness of the glass sheet (assuming the two lenses are identical in size and material). During the test, L and ΔD remain constant.

[0064] Start the displacement stage 1 and set its step distance to ΔL. After each movement of the displacement stage 1, the optical thickness gauge immediately takes a measurement. Assuming the moving part of the displacement stage 1 moves ΔL to the right, this is equivalent to a reduction of ΔL in the distance between the moving lens 3 and the right probe of the optical thickness gauge. At this point, d' = L - L1 - (L2 - ΔL) + 2ΔD = d + ΔL + 2ΔD, where d' is the thickness measurement value after the movement. From the formula, it can be deduced that each rightward movement of the displacement stage 1 by ΔL is equivalent to an increase of ΔL in the thickness of the air gap, i.e., the equivalent thickness of the opaque sample without a substrate.

[0065] After obtaining ten displacement measurements, the resolution of an optical thickness gauge can be determined in the following two ways:

[0066] a. If the thickness change information output by the optical thickness gauge presents a step signal with the same theoretical trend, it indicates that the resolution of the optical thickness gauge reaches ΔL;

[0067] b. Calculate the thickness measurement resolution based on the output of the optical thickness gauge. Since the displacement stage 1 has undergone n displacements of magnitude ΔL in a single direction, first reduce the thickness observations to zero and calculate the average value D0 of the reduced values:

[0068]

[0069] In the formula: D i These are the measured thickness values; d i It is the thickness value that changes from zero on the displacement stage, i.e., d. i = (i-1)ΔL; i is the measurement sequence number 1, 2, ..., n;

[0070] Resolution m 分 The calculation formula is as follows:

[0071]

[0072] Among them, the difference between the measured value and the recalculated value:

[0073] v i =D i -D0-d i (3).

[0074] Example 2:

[0075] The difference between this embodiment and Embodiment 1 is that both the fixed lens 6 and the moving lens 3 have an anti-reflective coating on one side and no coating on the other, thus representing an equivalent transparent sample without a substrate. Figure 3 As shown, the optical thickness gauge under test was changed from a dual-probe type to a single-probe type.

[0076] After the thickness gauge is turned on, the measurement can be started directly. The optical path difference of the reflected light from the two uncoated surfaces is the equivalent thickness d of the transparent sample without the substrate.

[0077] Start the displacement stage 1 and set its step distance to ΔL. The optical thickness gauge will immediately take a measurement after each movement of the displacement stage 1. Assuming the displacement stage moves ΔL to the right, this is equivalent to an increase of ΔL in the thickness of the air gap, i.e., the equivalent thickness of the transparent sample without a substrate. In this case, d' = d + ΔL, where d' is the thickness measurement value after the movement.

[0078] The method for determining the instrument's resolution is the same as in Example 1.

[0079] Example 3:

[0080] The difference between this embodiment and Embodiment 1 is that the fixed lens 6 has an anti-reflective coating on one side and no coating on the other, while the moving lens 3 is a double-polished silicon wafer, using a transparent sample with an equivalent silicon substrate, such as... Figure 4 As shown, the optical thickness gauge under test was changed from a dual-probe type to a single-probe type.

[0081] After the thickness gauge is powered on, measurement can begin directly. The optical path difference between the reflected light from the two surfaces of the air gap between the fixed lens 6 and the moving lens 3 is calculated, which is the equivalent thickness d of the transparent silicon substrate sample. If the silicon substrate is transparent at this wavelength, the probe will receive reflected light from three parts: the uncoated surface of the fixed lens 6 and the two surfaces of the double-polished silicon wafer of the moving lens 3, as well as multiple reflections. Stray light interference can be eliminated through optical path analysis, or the thickness of the double-polished silicon wafer of the moving lens 3 can be demodulated simultaneously using the known silicon refractive index.

[0082] Start the displacement stage 1 and set its step distance to ΔL. The optical thickness gauge will immediately take a measurement after each movement of the displacement stage 1. Assuming the displacement stage moves ΔL to the right, this is equivalent to an increase of ΔL in the thickness of the transparent sample on the equivalent silicon substrate within the air gap. In this case, d' = d + ΔL, where d' is the measured thickness after the movement.

[0083] The method for determining the instrument's resolution is the same as in Example 1.

[0084] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical thickness gauge resolution testing device, characterized in that, include: Displacement stage (1), motion mirror base (2), motion lens (3), angle adjustment device (4), fixed mirror base (5), fixed lens (6); The displacement stage (1) includes a main displacement stage structure (1-1) and a displacement stage motion structure (1-2), wherein the displacement stage motion structure (1-2) moves on the main displacement stage structure (1-1); The motion mirror mount (2) is mounted on the displacement stage motion structure (1-2), and the motion lens (3) is mounted on the motion mirror mount (2) through the angle adjustment device (4); The fixed lens (6) is clamped on the fixed lens mount (5), which is mounted on the main structure (1-1) of the displacement stage or other stationary objects.

2. The optical thickness gauge resolution testing device according to claim 1, characterized in that, The motion lens (3) and the fixed lens (6) constitute an opaque sample without a substrate, a transparent sample without a substrate, and a transparent sample with a substrate.

3. The optical thickness gauge resolution testing device according to claim 2, characterized in that, When the motion lens (3) and the fixed lens (6) constitute an opaque sample without a substrate, the motion lens (3) and the fixed lens (6) are respectively selected as transparent lenses. Each of the transparent lenses is coated with an anti-reflection film on one side and a high-reflection film on the other side. The high-reflection film coated on the two transparent lenses are installed facing each other.

4. The optical thickness gauge resolution testing device according to claim 2, characterized in that, When the motion lens (3) and the fixed lens (6) constitute a transparent sample without a substrate, the motion lens (3) and the fixed lens (6) are respectively selected as transparent lenses. Each transparent lens has an anti-reflective coating on one side and no coating on the other side. The uncoated sides of the two transparent lenses are installed facing each other.

5. The optical thickness gauge resolution testing device according to claim 2, characterized in that, When the motion lens (3) and the fixed lens (6) constitute a transparent sample containing a substrate, the motion lens (3) and the fixed lens (6) are respectively selected as transparent lenses. One of the lenses is coated with an anti-reflective film on one side and uncoated on the other side, while the other lens is smooth on both sides and uncoated. The uncoated side is mounted on the lens with smooth and uncoated sides.

6. The optical thickness gauge resolution testing device according to claim 3, 4, or 5, characterized in that, The angle adjustment device (4) includes a motion lens base, which is connected to a deformable rubber ring by a set of screws, and the deformable rubber ring is connected to the motion lens base (2).

7. The optical thickness gauge resolution testing device according to claim 3, 4, or 5, characterized in that, The motion lens mount (2) has a circular through hole, which is smaller than the area of ​​the motion lens (3).

8. The optical thickness gauge resolution testing device according to claim 3, 4, or 5, characterized in that, The fixed lens mount (5) has a circular through hole II, which is smaller in area than the fixed lens (6).

9. A method for testing the resolution of an optical thickness gauge, characterized in that, The method of using the optical thickness gauge resolution testing apparatus according to any one of claims 1-8 includes: (1) Perform power-on, preheating, and calibration operations; (2) Adjust the angle of the moving lens (3) by means of the angle adjustment device (4) so ​​that the moving lens (3) is parallel to the fixed lens (6); (3) Use an optical thickness gauge to measure the equivalent thickness of the moving lens (3) and the fixed lens (6), set the displacement stage (1) step distance ΔL, measure at different displacement values, and obtain the thickness measurement value with the theoretical step distance ΔL. (4) Determine the resolution of the optical thickness gauge: When the thickness change information output by the optical thickness gauge presents a step signal with the same theoretical trend, it indicates that the resolution of the optical thickness gauge reaches ΔL. Alternatively, the thickness measurement resolution can be calculated based on the output of the optical thickness gauge. The displacement stage (1) has undergone n displacements of magnitude ΔL in a single direction. First, the thickness observation value is reduced to zero, and the average value D0 of the reduced value is calculated: In the formula: D i These are the measured thickness values; d i It is the thickness value that changes from zero on the displacement stage, i.e., d. i = (i-1)ΔL; i is the measurement sequence number 1, 2, ..., n; Resolution m 分 The calculation formula is as follows: Among them, the difference between the measured value and the recalculated value: v i =D i -D0-d i (3)。

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