A flying-shot three-dimensional white-light interferometry profile measurement system

Abstract

The present invention belongs to the technical field related to nanoscale three-dimensional shape measurement, and discloses a flying-type three-dimensional white light interferometric shape measurement system, comprising a linear translation stage (13), a Kohler illumination system (100), a Linnik-type interference objective lens (200), an imaging lens (11), and a high-speed camera (12); the Linnik-type interference objective lens (200) comprises an objective lens 1 (8), a beam splitter (7), a reflector (10), and an objective lens 2 (9); the Kohler illumination system (100), the beam splitter (7), the objective lens 2 (9), and the reflector (10) are sequentially arranged on a horizontal illumination light path (14); the objective lens 1 (8), the beam splitter (7), the imaging lens (11), and the high-speed camera (12) are sequentially arranged on a vertical imaging light path (15). The system can realize high-speed, high-precision, large-field-of-view, and large-measurement-range three-dimensional shape measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field related to three-dimensional profile measurement, and more specifically, relates to a flying-type three-dimensional white-light interferometry profile measurement system. Background Art

[0002] White-light interferometry (WLI) originated in the 1980s and is one of the most commonly used optical surface measurement methods for 3D surface reconstruction of microstructures in modern manufacturing processes. This method utilizes a broadband light source, such as white light, whose extremely short coherence length produces a distinct intensity peak in its interference signal, which can be detected by vertical scanning. Light intensity reaches maximum when the optical path difference (OPD) between the measurement and reference light paths is zero. Profile depth can be determined by demodulating and peak-identifying the interference signal for each pixel along the Z-axis scan. White-light interferometry (WLI) has attracted industry attention due to its advantages, including high vertical resolution, wide field of view (FOV), and non-contact measurement. Unlike laser interferometry, which utilizes a coherent light source, WLI utilizes an incoherent light source with a short coherence length to resolve the 2π phase height ambiguity in regions with large step heights. These characteristics make WLI feasible for integration with other precision measurement equipment, such as atomic force microscopes, during semiconductor device manufacturing. However, due to its limited field of view, WLI has limitations in wafer-level manufacturing process monitoring. Image stitching has emerged as a solution, as it allows for a larger field of view. However, this approach suffers from issues such as pixel misalignment and unpatterned intersections. Consequently, vertical scanning interferometry (VSI) using traditional white-light interferometers suffers from low measurement efficiency, making it difficult to measure large samples.

[0003] To overcome the problem of image stitching, traditional lateral scanning interferometry (LSI) technology measures interference signals through the off-axis motion of a laterally moving linear stage, and measures morphologies with a wide field of view by laterally moving the sample without the need for image stitching. Despite the technical importance of LSI, when the camera frame rate is fixed, the speed of the linear stage must be selected within the limits of the camera frame rate, and research on LSI that increases speed is relatively limited. Moreover, white light interferometry requires ensuring that the sampling intervals of the interference signal are equal during the lateral scanning measurement process to better restore the measured morphology. Traditional LSI is very sensitive to environmental vibrations, and errors in the horizontality, straightness, and speed uniformity of the linear translation stage can seriously affect the spacing stability of the interference pattern, and can also cause the interference fringes to tilt and the interference signal to deform, resulting in insufficient measurement accuracy of the three-dimensional morphology. Therefore, it is urgent to propose a measurement system to achieve high-speed, high-precision, large-field-of-view, and large-measurement-range three-dimensional morphology measurement. Summary of the Invention

[0004] In response to the above defects or improvement needs of the existing technology, the present invention provides a flying-type three-dimensional white-light interferometry profile measurement system, thereby solving the technical problems of low measurement efficiency and low accuracy of traditional vertical scanning interferometry (VSI) and lateral scanning interferometry (LSI).

[0005] To achieve the above-mentioned objectives, according to one aspect of the present invention, a flying-type three-dimensional white-light interferometric profilometry system is provided, comprising a linear translation stage 13, a Köhler illumination system 100, a Linnik-type interference objective lens 200, an imaging lens 11, and a high-speed camera 12; the Linnik-type interference objective lens 200 comprises an objective lens 1 8, a beam splitter 7, a reflector 10, and an objective lens 2 9; the Köhler illumination system 100, the beam splitter 7, the objective lens 2 9, and the reflector 10 are sequentially arranged on a horizontal illumination optical path 14; the objective lens 1 8, the beam splitter 7, the imaging lens 11, and the high-speed camera 12 are sequentially arranged on a vertical imaging optical path 15.

[0006] Preferably, the Kohler illumination system 100 includes an illumination light source 1, a focusing lens 2, an aperture stop 3, a first lens 4, a field stop 5, and a second lens 6, which are sequentially arranged on a horizontal illumination light path 14.

[0007] Preferably, the inclination angle α of the reflector 10 is adjustable, and the inclination angle α is expressed as:

[0008] α=arcsin(λ(8Δx))

[0009] Wherein, Δx is the sampling interval, and λ / 8 is the optical path difference of a single pixel in each frame image.

[0010] Preferably, the lens 1 4 and the lens 2 6 conjugate the light filtered by the aperture stop 3 to the back focal plane of the objective lens 1 8 .

[0011] Preferably, the light from the field stop 5 is conjugated to the sample plane through the second lens 6 and the first objective lens 8.

[0012] Preferably, the models and magnification parameters of the objective lens 1 8 and the objective lens 2 9 are the same, and the objective lens 1 8 and the objective lens 2 9 are placed perpendicular to each other.

[0013] Preferably, the linear translation stage 13 is configured as an electric translation stage with a stroke of 25 mm.

[0014] Preferably, the moving speed V of the linear translation stage 13 is expressed as:

[0015] V=FS / M

[0016] Where F is the frame rate of the high-speed camera, M is the magnification of the measurement system, and S is the interval between adjacent pixels.

[0017] Preferably, the high-speed camera 12 is a high-speed camera with a resolution of 1280×800, a pixel size of 9 um / pixel, and a maximum frame rate of 22500 fps.

[0018] Preferably, the lighting source 1 is configured as an LED lighting source.

[0019] In general, the above technical solutions conceived by the present invention, compared with the prior art, provide a flying-type three-dimensional white-light interferometry profilometry system, which has the following beneficial effects:

[0020] 1. The flying-shot 3D white-light interferometry profiling system proposed in this paper replaces the inefficient PZT vertical stepping scanning and stitching method. By leveraging the horizontal movement of the sample, the wide field of view of the high-speed camera, the system's continuous scanning capability, and the camera's image acquisition for processing and calculation, the system can cover a larger measurement area and obtain complete 3D topography information without image stitching, significantly improving the field of view and measurement efficiency.

[0021] 2. Compared with traditional lateral scanning interferometry (LSI) technology, the present invention adopts Linnik interferometer objective lens. The advantage of Linnik interferometer objective lens is that it can use objective lenses with magnification of 100 times or above. At the same time, the mirror tilt angle α is adjustable. The mirror tilt angle α is not a random value, but is determined by the scanning interval Δx and the optical path difference between two adjacent images. Then, a phase compensation algorithm is introduced to ensure the stability and accuracy of the interference signal during high-speed scanning, thereby making the three-dimensional shape measurement more accurate and the measurement range larger.

[0022] 3. Unlike traditional LSI technology, where the linear platform speed is generally in the order of μm / s, the flying-type 3D white-light interferometric profile measurement system proposed in this invention uses a 10,000-frame-level high-speed camera, and the speed of the linear translation stage can reach the order of mm / s. This can meet the needs of high-speed moving samples without stopping, and can capture images and perform processing calculations in a flying-type manner, effectively improving image acquisition efficiency, improving 3D profile measurement efficiency, and reducing environmental interference and errors that may be introduced by long-term scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of the flying-type three-dimensional white-light interferometry profiling measurement system provided by the present invention;

[0024] Figure 2 Schematic diagram of the Linnik type white light interference objective lens provided by the present invention;

[0025] Figure 3 This is a schematic diagram of the sample plane interference signal provided by the present invention;

[0026] Figure 4 This is a schematic diagram of the relationship between the tilt angle of the reflector and the sampling interval provided by the present invention;

[0027] Figure 5 Schematic diagram of the deviation of the peak point of the interference signal provided by the present invention;

[0028] Figure 6 This is the sample three-dimensional morphology restoration result diagram provided by the present invention;

[0029] Figure 7 This is a comparison chart of the measurement results of the measurement system provided by the present invention and the white light interferometer;

[0030] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0031] 100-Köhler illumination system, 200-Linnik interference objective, 1-illumination light source, 2-condensing lens, 3-aperture diaphragm, 4-lens one, 5-field diaphragm, 6-lens two, 7-beam splitter, 8-objective lens one, 9-objective lens two, 10-reflecting mirror, 11-imaging lens, 12-high-speed camera, 13-linear translation stage, 14-horizontal illumination light path, 15-vertical imaging light path. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] This embodiment provides a flying three-dimensional white light interferometry profiling system that can achieve high-speed, high-precision, large-field-of-view, and large-measurement-range three-dimensional profiling measurement. It is suitable for continuous, non-stop rapid scanning and high-precision three-dimensional profiling measurement of large-area micro-nano product surfaces. Figure 1 As shown, the system includes a linear translation stage 13, a Köhler illumination system 100, a Linnik-type interference objective lens 200, an imaging lens 11, and a high-speed camera 12. The Linnik-type interference objective lens 200 includes an objective lens 1 8, a beam splitter 7, a reflector 10, and an objective lens 2 9. The Köhler illumination system 100, the beam splitter 7, the objective lens 2 9, and the reflector 10 are sequentially arranged on a horizontal illumination optical path 14. The objective lens 1 8, the beam splitter 7, the imaging lens 11, and the high-speed camera 12 are sequentially arranged on a vertical imaging optical path 15. The Köhler illumination system 100 includes an illumination light source 1, a condenser lens 2, an aperture stop 3, a lens 1 4, a field stop 5, and a lens 2 6, which are sequentially arranged on the horizontal illumination optical path 14.

[0034] Lens 1 4 and lens 2 6 conjugate the light filtered by aperture diaphragm 3 to the back focal plane of objective lens 1 8, and the light of field diaphragm 5 passes through lens 2 6 and objective lens 1 8 conjugate to the sample plane; Figure 2 As shown, the Linnik interference objective lens 200 includes a beam splitter 7, an objective lens 1 8, an objective lens 2 9, and a reflector 10. The objective lens 1 8 and the objective lens 2 9 have the same model and magnification parameter settings and are placed perpendicular to each other to ensure that the object light path and the reference light path have equal optical path lengths. The light reflected from the reflector 10 and the sample passes through the imaging lens 11 and forms an interference pattern on the high-speed camera 12.

[0035] In this embodiment, the illumination source 1 uses a Thorlabs M455L4 LED with a wavelength of 455 nm and a bandwidth of 18 nm. Objective lenses 1 and 2, 9, use Olympus LMPLFLN 50X lenses with a NA of 0.5 and a magnification of 50. The linear translation stage 13 uses a Thorlabs PT3 / M-Z9 motorized translation stage with a travel of 25 mm. The movement speed V of the linear translation stage 13 is expressed as: V = FS / M, where F is the frame rate of the high-speed camera, M is the magnification of the measurement system, and S is the interval between adjacent pixels. The high-speed camera 12 uses a Revealer GR220M high-speed camera with a resolution of 1280 × 800, a pixel size of 9 μm / pixel, and a maximum frame rate of 22,500 fps. The series of images captured by the high-speed camera 12 are stored on a computer and then processed and calculated using algorithms to restore the three-dimensional morphology of the sample.

[0036] like Figure 3 As shown in the figure, when the measured surface of the sample enters the coherent region, the measured surface has different heights, and the corresponding interference signal peak points appear at different positions (h1, h2). By identifying and extracting the coordinates of this peak point, the height information of the measured surface (h1-h2) is calculated, and the height information of each point on the measured surface is extracted to integrate the three-dimensional topography distribution of the measured surface. Therefore, the three-dimensional topography measurement system provided in this embodiment can immediately reconstruct the surface cross-section through horizontal scanning, without the need for vertical scanning operations, and can achieve the same effect as vertical scanning in traditional VSI.

[0037] Since the stability of interference fringes during horizontal scanning is easily affected by the horizontality, straightness, speed uniformity errors of the linear translation stage and the low-frequency vibration of the environment, the peak point of the interference signal will produce positioning errors, and the position of the peak point may offset the position of zero optical path difference. The envelope is the actual measured signal, and there is a deviation of Δz between the measured peak point (envelope peak point) and the theoretical peak point (zero optical path difference point), such as Figure 4As shown. Therefore, in order to improve the positioning accuracy of the peak point of the interference signal, it is also necessary to introduce phase compensation to accurately locate the position closest to the peak point. Due to the introduction of the phase compensation algorithm, the tilt angle α of the reflector is not a random value, but is determined by the sampling interval Δx and the optical path difference. The tilt angle α of the reflector 10 is expressed as α=arcsin(λ(8Δx)), where Δx is the sampling interval and λ / 8 is the optical path difference of a single pixel point in each frame image. When the sample moves horizontally, the relationship between the sampling interval Δx and the tilt angle α of the reflector 10 is as follows Figure 5 shown.

[0038] In order to verify the feasibility of the 3D topography measurement system, a microscopic sample was measured. A silicon wafer with a pattern depth of 200 nm was selected as the sample. Without using the image stitching method of a commercial white-light interferometer, the flying-shot 3D white-light interferometry topography measurement system proposed in this invention obtained the 3D topography restoration result of a pattern with a length of 0.1 mm in the scanning direction. Figure 6 In addition, Figure 7 As shown, the three-dimensional morphology measurement results of the measurement system proposed in the present invention are compared with those of a commercial white light interferometer. The same feature of the sample is measured and the height information of the same cross section is extracted. It can be concluded that the measurement results of the measurement system provided by the present invention are close to those of the white light interferometer, and the measurement error is less than 10nm, which is within the confidence interval. The repeatability of the system measurement is evaluated by repeating the measurement of the same sample feature 20 times. The repeatability error is less than 3nm, which is better than the repeatability measurement accuracy of traditional LSI technology (tens of nanometers). Therefore, the measurement accuracy of the measurement system provided by the present invention is significantly improved compared with traditional LSI technology, and the measurement efficiency is also higher than that of commercial white light interferometers. The system can realize continuous, non-stop rapid scanning and high-precision three-dimensional morphology measurement of large-area micro-nano product surfaces, and is expected to play an important role in semiconductor manufacturing measurement fields such as semiconductor wafer surface roughness measurement, chemical mechanical polishing (CMP) process wafer polishing result monitoring, and back-end packaging optical measurement.

[0039] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A flying three-dimensional white light interferometry profilometry system, characterized by: The invention comprises a linear translation stage (13), a Kohler illumination system (100), a Linnik-type interference objective lens (200), an imaging lens (11) and a high-speed camera (12); the Linnik-type interference objective lens (200) comprises an objective lens 1 (8), a beam splitter (7), a reflector (10) and an objective lens 2 (9); the Kohler illumination system (100), the beam splitter (7), the objective lens 2 (9) and the reflector (10) are sequentially arranged on a horizontal illumination light path (14); the objective lens 1 (8), the beam splitter (7), the imaging lens (11) and the high-speed camera (12) are sequentially arranged on a vertical imaging light path (15).

2. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The Kohler illumination system (100) comprises an illumination light source (1), a focusing lens (2), an aperture stop (3), a first lens (4), a field stop (5), and a second lens (6), which are sequentially arranged on a horizontal illumination light path (14).

3. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The inclination angle α of the reflector (10) is adjustable, and the inclination angle α is expressed as: α=arcsin(λ(8Δx)) Wherein, Δx is the sampling interval, and λ / 8 is the optical path difference of a single pixel in each frame image.

4. The flying-type three-dimensional white-light interferometry profilometry system according to claim 2, characterized in that: The lens 1 (4) and the lens 2 (6) conjugate the light filtered by the aperture stop (3) to the back focal plane of the objective lens 1 (8).

5. The flying-type three-dimensional white-light interferometry profilometry system according to claim 2, characterized in that: The light from the field stop (5) is conjugated to the sample plane through lens 2 (6) and objective lens 1 (8).

6. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The models and magnification parameters of the objective lens 1 (8) and the objective lens 2 (9) are the same, and the objective lens 1 (8) and the objective lens 2 (9) are placed perpendicular to each other.

7. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The linear displacement stage (13) is configured as an electric displacement stage with a stroke of 25 mm.

8. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The moving speed V of the linear translation stage (13) is expressed as: V=FS / M Where F is the frame rate of the high-speed camera, M is the magnification of the measurement system, and S is the interval between adjacent pixels.

9. The flying-type three-dimensional white-light interferometry profilometry system according to claim 1, characterized in that: The high-speed camera (12) is a high-speed camera with a resolution of 1280×800, a pixel size of 9 μm / pixel, and a maximum frame rate of 22500 fps.

10. The flying-type three-dimensional white-light interferometry profilometry system according to claim 2, characterized in that: The lighting light source (1) is configured as an LED lighting light source.

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