White light interferometry apparatus and method using a virtual reference surface

Abstract

The application discloses a white light interference measuring device and method using a virtual reference surface, which comprises a white light illumination unit for generating illumination required for measurement, a reference light path for constructing a virtual reference surface and generating reference light, a test light path for obtaining test light with surface topography information of a measured object, and an imaging light path for imaging the virtual reference surface and the surface of the measured object to form white light interference fringes. The application can realize high-precision measurement of surface roughness of an object and topography measurement of a large-aperture high-depth object.

Description

Technical Field

[0001] This invention belongs to the field of optical interferometric measurement technology, specifically a white light interferometric measurement device and method utilizing a virtual reference surface. Background Technology

[0002] White light interferometry is an important method for measuring the surface topography of objects. Its principle lies in changing the optical path of the reference or test light through scanning motion to achieve optical path matching between the measured area and the reference surface. The surface topography distribution is then obtained by calculating the white light interference fringes captured by the camera. However, due to limitations in manufacturing processes, reference mirrors often inherently contain waviness and roughness errors. The resulting reference light also carries information about these surface errors and interferes with the test light. Consequently, the calculated topography distribution incorporates high-frequency information from these errors, an unavoidable surface error when using a solid reference surface. To obtain a high-precision roughness distribution of the measured surface, it is necessary to suppress the mid-to-high frequency components in the reference light caused by these errors. Currently, there is no relevant research in this area. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the current technology by providing a white light interferometry method that uses a virtual reference surface to suppress high-frequency errors in the reference light.

[0004] The technical solution to achieve the purpose of this invention is as follows: On the one hand, a white light interferometry measurement device using a virtual reference surface is provided, the device including a white light illumination unit, a reference optical path, a test optical path and a white light interferometry imaging unit;

[0005] The white light illumination unit is used to generate the illumination light required for measurement;

[0006] The reference optical path is used to construct a virtual reference surface to suppress mid-to-high frequency information, and the reference light required for interference is generated by the virtual reference surface;

[0007] The test optical path is used to generate test light containing information about the surface of the object under test;

[0008] The white light interferometric imaging unit is used to receive white light interference signals and to image the object under test.

[0009] Furthermore, the white light illumination unit includes a white light source, a first converging mirror, and a second converging mirror arranged sequentially along the vertical optical axis;

[0010] The reference optical path includes a first beam splitter arranged along the vertical optical axis, a second beam splitter arranged along the direction of transmitted light from the first beam splitter, and a first reflector and a virtual reference surface arranged sequentially along the direction of reflected light from the second beam splitter. It also includes a displacement control module for controlling the movement of the first reflector. The virtual reference surface is formed by superimposing light of different angles and wavelengths contained in the white light source surface light source.

[0011] The test optical path includes a first beam splitter, a third beam splitter arranged along the direction of reflected light from the first beam splitter, a fourth beam splitter arranged sequentially along the direction of reflected light from the third beam splitter, and the object to be tested.

[0012] The white light interferometric imaging unit includes an imaging lens and an area array detector arranged sequentially along the direction of the reference light emitted from the reference light path and transmitted through the fourth beam splitter.

[0013] Furthermore, in the reference optical path, the distance from the first beam splitter through the second beam splitter and the first reflecting mirror to the virtual reference surface is equal to the distance from the first beam splitter through the third beam splitter and the fourth beam splitter to the object under test in the test optical path.

[0014] Furthermore, the virtual reference surface and the position of the object under test are conjugate with respect to the target surface position of the array detector.

[0015] Furthermore, the distance between the first beam splitter and the second beam splitter is equal to the distance between the third beam splitter and the fourth beam splitter.

[0016] Furthermore, the distance between the first beam splitter and the third beam splitter is equal to the distance between the second beam splitter and the fourth beam splitter.

[0017] Furthermore, the distance from the second beam splitter to the first reflecting mirror is equal to the distance from the fourth beam splitter to the object under test.

[0018] Furthermore, the displacement control module is a long-stroke displacement module, and the imaging lens is a dual telecentric imaging lens, enabling the device to measure the morphology of large-diameter, high-depth objects.

[0019] On the other hand, a white light interferometry method utilizing a virtual reference surface is provided, the method comprising the following steps:

[0020] Step 1: White light is emitted from the white light source and passes through the first converging mirror and the second converging mirror to obtain the white light illumination beam required for measurement;

[0021] Step 2: After the white light illumination beam passes through the first beam splitter, it generates a pair of beams with orthogonal propagation directions. The transmitted white light is reflected by the second beam splitter, then reflected by the first reflecting mirror, and then passes through the virtual reference surface to generate reference light. The reference light is then transmitted through the second beam splitter to the fourth beam splitter to form a reference optical path. The virtual reference surface is formed by superimposing light of different angles and wavelengths contained in the white light source surface. After passing through the white light illumination unit, the light of each angle converges at the conjugate position in the reference optical path. Several wavefronts are superimposed at this point, and the mid-to-high frequency information they carry is suppressed. The wavefronts serve as the reference wavefronts required for interferometry, and the conjugate position is equivalent to the reference surface required for interferometry, serving as the virtual reference surface.

[0022] Step 3: After the white light illumination beam passes through the first beam splitter, the reflected white light is reflected by the third beam splitter, and then transmitted through the fourth beam splitter to the surface of the object under test, generating test light, which is then reflected into the fourth beam splitter to form the test light path.

[0023] Step 4: The test light and the reference light enter the white light interferometric imaging unit, and after passing through the imaging lens, they form white light interference fringes at the target surface of the array detector, thus imaging the object under test.

[0024] Step 5: Control the first reflecting mirror to perform phase-shifting scanning measurement through the displacement control module;

[0025] Step 6: Based on Step 4 and Step 5, calculate the phase distribution of the object under test by using the white light interference fringes obtained by the white light interference imaging unit, thereby calculating the surface morphology distribution of the object under test.

[0026] Furthermore, during the phase-shifting scanning measurement in step 5, the virtual reference surface always maintains a conjugate position relationship with the target surface of the array detector.

[0027] Compared with the prior art, the present invention has the following significant advantages: 1) By superimposing the anisotropic multi-wavelength wavefronts emitted from the light source, a reference wavefront that effectively suppresses mid-to-high frequency errors is generated in the reference optical path, constructing a virtual reference surface without a physical structure. This greatly reduces the mid-to-high frequency errors of the reference light in the interference between the reference light and the test light, thus improving the measurement accuracy; 2) A modified Mach-Zehnder interference structure (reference optical path and test optical path) is adopted in the interference optical path, which facilitates the phase-shifting scanning measurement process and makes it convenient to perform optical path matching, optical path alignment, and other operations. It can achieve high-precision measurement of the surface roughness of objects through a precision displacement control module, and can also achieve morphological measurement of large-aperture, high-depth objects by combining a long-stroke displacement control module and a dual telecentric imaging lens; 3) The device has low system complexity, fast measurement speed, low cost, and high practicality.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the optical path structure of the white light interferometry device utilizing a virtual reference surface according to the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0031] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0032] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0033] In one embodiment, combined Figure 1 A white light interferometric measurement device utilizing a virtual reference surface is provided. The device includes a white light illumination unit 14, a reference optical path 15, a test optical path 16, and a white light interferometric imaging unit 17.

[0034] The white light illumination unit 14 is used to generate the illumination light required for measurement;

[0035] The reference optical path 15 is used to construct a virtual reference surface 8 to suppress mid-to-high frequency information, and the reference light required for interference is generated by the virtual reference surface 8;

[0036] The test optical path 16 is used to generate test light containing surface information of the object under test 11;

[0037] The white light interference imaging unit 17 is used to receive white light interference signals and image the object 11 under test.

[0038] The white light illumination unit 14 includes a white light source 1, a first converging mirror 2, and a second converging mirror 3 arranged sequentially along the vertical optical axis;

[0039] The reference optical path 15 includes a first beam splitter 4 arranged along the vertical optical axis, a second beam splitter 5 arranged along the direction of transmitted light from the first beam splitter 4, and a first reflector 6 and a virtual reference surface 8 arranged sequentially along the direction of reflected light from the second beam splitter 5. It also includes a displacement control module 7 for controlling the movement of the first reflector 6. The virtual reference surface 8 is formed by superimposing light of different angles and wavelengths contained in the white light source 1.

[0040] The test optical path 16 includes a first beam splitter 4, a third beam splitter 9 arranged along the direction of reflected light from the first beam splitter 4, a fourth beam splitter 10 arranged sequentially along the direction of reflected light from the third beam splitter 9, and an object to be tested 11.

[0041] The white light interferometric imaging unit 17 includes an imaging lens 12 and an area array detector 13 arranged sequentially along the direction of the reference light emitted from the reference light path 15 and transmitted through the fourth beam splitter 10.

[0042] More preferably, in one embodiment, the distance from the first beam splitter 4 through the second beam splitter 5 and the first reflector 6 to the virtual reference surface 8 in the reference optical path 15 is equal to the distance from the first beam splitter 4 through the third beam splitter 9 and the fourth beam splitter 10 to the object under test 11 in the test optical path 16.

[0043] More preferably, in one embodiment, the positions of the virtual reference surface 8 and the object under test 11 are conjugate with respect to the target surface position of the array detector 13.

[0044] More preferably, in one embodiment, the distance between the first beam splitter 4 and the second beam splitter 5 is equal to the distance between the third beam splitter 9 and the fourth beam splitter 10.

[0045] More preferably, in one embodiment, the distance between the first beam splitter 4 and the third beam splitter 9 is equal to the distance between the second beam splitter 5 and the fourth beam splitter 10.

[0046] More preferably, in one embodiment, the distance from the second beam splitter 5 to the first reflecting mirror 6 is equal to the distance from the fourth beam splitter 10 to the object to be measured 11.

[0047] More preferably, in one embodiment, the displacement control module 7 is a long-stroke displacement module, and the imaging lens 12 is a dual telecentric imaging lens, enabling the device to achieve morphological measurement of large-diameter, high-depth objects.

[0048] In one embodiment, a white light interferometry method utilizing a virtual reference surface is provided, the method comprising the following steps:

[0049] Step 1: White light source 1 emits white light, which passes through the first converging mirror 2 and the second converging mirror 3 to obtain the white light illumination beam required for measurement;

[0050] Step 2: After the white light illumination beam passes through the first beam splitter 4, it generates a pair of beams with orthogonal propagation directions. The transmitted white light is reflected by the second beam splitter 5, then reflected by the first reflecting mirror 6, and then passes through the virtual reference surface 8 to generate reference light. The reference light is then transmitted through the second beam splitter 5 to the fourth beam splitter 10 to form a reference optical path. The virtual reference surface 8 is formed by superimposing light of different angles and wavelengths contained in the white light source 1. After passing through the white light illumination unit 14, the light of each angle converges at the conjugate position in the reference optical path 15. Several wavefronts are superimposed at this point, and the mid-to-high frequency information they carry is suppressed. The wavefronts serve as the reference wavefronts required for interferometric measurement, and the conjugate position is equivalent to the reference surface required for interferometric measurement, serving as the virtual reference surface 8.

[0051] Step 3: After the white light illumination beam passes through the first beam splitter 4, the reflected white light is reflected by the third beam splitter 9, and transmitted through the fourth beam splitter 10 to the surface of the object under test 11 to generate test light, which is then reflected into the fourth beam splitter 10 to form the test light path.

[0052] Step 4: The test light and the reference light enter the white light interferometric imaging unit 17, and after passing through the imaging lens 12, they form white light interference fringes at the target surface position of the array detector 13, and image the object under test 11.

[0053] Step 5: The first reflecting mirror 6 is controlled by the displacement control module 7 to perform phase-shifting scanning measurement;

[0054] During this process, the virtual reference surface 8 always maintains a conjugate position relationship with the target surface of the array detector 13.

[0055] Step 6: Based on steps 4 and 5, the phase distribution of the object under test 11 is calculated by using the white light interference fringes obtained by the white light interference imaging unit 17, thereby calculating the surface morphology distribution of the object under test 11.

[0056] This invention can achieve both high-precision measurement of surface roughness and morphological measurement of large-diameter, deep-penetrating objects.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention without departing from its spirit and scope should be included within the protection scope of the present invention.

Claims

1. A white-light interferometry device utilizing a virtual reference surface, characterized in that, The device includes a white light illumination unit (14), a reference optical path (15), a test optical path (16), and a white light interference imaging unit (17). The white light illumination unit (14) is used to generate the illumination light required for measurement; The reference optical path (15) is used to construct a virtual reference surface (8) for suppressing mid-to-high frequency information, and the reference light required for interference is generated by the virtual reference surface (8); The test optical path (16) is used to generate test light containing surface information of the object under test (11); The white light interference imaging unit (17) is used to receive white light interference signals and to image the object under test (11); The white light illumination unit (14) includes a white light source (1), a first converging mirror (2), and a second converging mirror (3) arranged sequentially along the vertical optical axis. The reference optical path (15) includes a first beam splitter (4) arranged along the vertical optical axis, a second beam splitter (5) arranged along the direction of transmitted light from the first beam splitter (4), a first reflector (6) and a virtual reference surface (8) arranged sequentially along the direction of reflected light from the second beam splitter (5), and also includes a displacement control module (7) for controlling the movement of the first reflector (6); the virtual reference surface (8) is formed by superimposing light of different angles and wavelengths contained in the surface light source of the white light source (1); The test optical path (16) includes the first beam splitter (4), the third beam splitter (9) arranged along the direction of reflected light from the first beam splitter (4), the fourth beam splitter (10) arranged sequentially along the direction of reflected light from the third beam splitter (9), and the object to be tested (11). The white light interferometric imaging unit (17) includes an imaging lens (12) and an area array detector (13) arranged sequentially along the direction of the transmission of the reference light emitted from the reference light path (15) through the fourth beam splitter (10). In the reference optical path (15), the distance from the first beam splitter (4) through the second beam splitter (5) and the first reflector (6) to the virtual reference surface (8) is equal to the distance from the first beam splitter (4) through the third beam splitter (9) and the fourth beam splitter (10) to the object under test (11) in the test optical path (16). The positions of the virtual reference surface (8) and the object under test (11) are conjugate with respect to the target surface position of the array detector (13); The distance from the first beam splitter (4) to the second beam splitter (5) is equal to the distance from the third beam splitter (9) to the fourth beam splitter (10); The distance between the first beam splitter (4) and the third beam splitter (9) is equal to the distance between the second beam splitter (5) and the fourth beam splitter (10); The distance from the second beam splitter (5) to the first reflecting mirror (6) is equal to the distance from the fourth beam splitter (10) to the object to be measured (11).

2. The white light interferometry apparatus utilizing a virtual reference surface according to claim 1, characterized in that, The displacement control module (7) is a long-stroke displacement module, and the imaging lens (12) is a dual telecentric imaging lens, enabling the device to measure the morphology of large-diameter, high-depth objects.

3. A white-light interferometry method using a virtual reference plane based on the apparatus of any one of claims 1 to 2, characterized in that, The method includes the following steps: Step 1: White light is emitted from the white light source (1), and the white light illumination beam required for measurement is obtained through the first converging mirror (2) and the second converging mirror (3); Step 2: After the white light illumination beam passes through the first beam splitter (4), a pair of beams with orthogonal propagation directions are generated. The transmitted white light is reflected by the second beam splitter (5), then reflected by the first reflector (6) and then passes through the virtual reference surface (8) to generate reference light. The reference light is then transmitted through the second beam splitter (5) to the fourth beam splitter (10) to form a reference optical path. The virtual reference surface (8) is formed by superimposing light of different angles and wavelengths contained in the white light source (1). After passing through the white light illumination unit (14), the light of each angle converges at the conjugate position in the reference optical path (15). Several wavefronts are superimposed here, and the mid-to-high frequency information they carry is suppressed. The wavefront is used as the reference wavefront required for interferometric measurement. The conjugate position is equivalent to the reference surface required for interferometric measurement and serves as the virtual reference surface (8). Step 3: After the white light illumination beam passes through the first beam splitter (4), the reflected white light is reflected by the third beam splitter (9), and transmitted through the fourth beam splitter (10) to the surface of the object to be tested (11), generating test light, and reflecting into the fourth beam splitter (10) to form a test light path; Step 4: The test light and the reference light enter the white light interference imaging unit (17), and after passing through the imaging lens (12), they form white light interference fringes at the target surface position of the array detector (13) and image the object under test (11). Step 5: Control the first reflector (6) to perform phase-shifting scanning measurement through the displacement control module (7); Step 6: Based on Step 4 and Step 5, the phase distribution of the object under test (11) is calculated by obtaining the white light interference fringes through the white light interference imaging unit (17), thereby calculating the surface morphology distribution of the object under test (11).

4. The white light interferometry method using a virtual reference surface according to claim 3, characterized in that, During the phase-shifting scanning measurement in step 5, the virtual reference surface (8) always maintains a conjugate position relationship with the target surface of the array detector (13).

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