Flying-patting type three-dimensional white light interference morphology measurement system

Abstract

The invention belongs to the related technical field of nanoscale three-dimensional shape measurement, and discloses a flying shooting type three-dimensional white light interference shape measurement system, which comprises a linear displacement table (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 I (8), a spectroscope (7), a reflector (10) and an objective lens II (9); the Kohler illumination system (100), the spectroscope (7), the objective lens II (9) and the reflector (10) are sequentially arranged on a horizontal illumination light path (14); and the objective lens I (8), the spectroscope (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-view-field and large-measurement-range three-dimensional shape measurement.

Description

Technical Field

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

[0002] White light interferometry originated in the 1980s. White light interferometry is one of the most commonly used optical surface measurement methods for microstructure 3D surface reconstruction in modern manufacturing processes. This method uses a broadband light source, such as white light, whose extremely short coherence length produces a unique intensity peak in its interference signal, which can be detected by vertical scanning. The light intensity is maximum when the optical path difference (OPD) between the measurement light path and the reference light path is zero. The profile depth can be obtained by demodulating and peak identifying the interference signal for each pixel along the Z-axis scanning direction. White light interferometry (WLI) has attracted the attention of the industry due to its multiple advantages such as high-precision vertical resolution, wide field of view (FOV) and non-contact measurement. Unlike laser interferometry using coherent light sources, WLI uses incoherent light sources with short coherence lengths to solve the 2π phase height ambiguity problem in large step height areas. These characteristics make it possible to integrate WLI with other precision measurement equipment (such as atomic force microscopes) in the manufacturing process of semiconductor devices. However, due to the limited field of view, WLI has limitations in wafer-level manufacturing process monitoring. Therefore, the image stitching method has emerged as one of the solutions because it can obtain a larger field of view. However, the image stitching method has the following problems, such as pixel misalignment and patternless cross-regions. Therefore, the vertical scanning interferometry (VSI) measurement efficiency of the traditional white light interferometer is low and it is difficult to meet the measurement needs of large-area samples.

[0003] To overcome the problem of image stitching, the traditional lateral scanning interferometry (LSI) technology measures the interference signal through the off-axis motion of the laterally moving linear stage, and measures the morphology with a wide field of view by moving the sample laterally without stitching the image. Although LSI is technically important, the speed of the linear stage must be selected within the limit of the camera frame rate when the camera frame rate is fixed, and the research on LSI to increase the speed is relatively limited. Moreover, white light interferometry measurement needs to ensure that the sampling interval of the interference signal is equal during the lateral scanning measurement process in order to better restore the morphology to be measured. Traditional LSI is very sensitive to environmental vibrations. The horizontality, straightness and speed uniformity errors of the linear translation stage will seriously affect the spacing stability of the interference pattern, and will also cause the inclination of the interference fringes and the deformation of the interference signal, 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 view of the above defects or improvement needs of the prior art, the present invention provides a flying-shot three-dimensional white-light interferometry profile measurement system, thereby solving the technical problems of low measurement efficiency and low accuracy of lateral scanning interferometry (LSI) in traditional vertical scanning interferometry (VSI).

[0005] To achieve the above-mentioned purpose, according to one aspect of the present invention, a flying-type three-dimensional white-light interferometric profile measurement system is provided, 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 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 comprises an illumination light source 1, a focusing lens 2, an aperture stop 3, a lens 1 4, a field stop 5, and a lens 2 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 rear focal plane of the objective lens 1 8 .

[0011] Preferably, the light from the field aperture 5 is conjugated to the sample plane through lens 2 6 and objective lens 1 8 .

[0012] Preferably, the objective lens 1 8 and the objective lens 2 9 have the same model and magnification parameter settings, 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, compared with the prior art, the above technical solution conceived by the present invention provides a flying three-dimensional white light interferometry topography measurement system, which mainly has the following beneficial effects:

[0020] 1. The flying-shot three-dimensional white-light interferometric topography measurement system proposed in the present invention replaces the inefficient method of PZT vertical stepping scanning and splicing. Through the horizontal movement of the sample, the wide field of view of the high-speed camera, the continuous scanning capability of the system, and the camera collecting images for processing and calculation, the system can cover a larger measurement area and obtain complete three-dimensional topography information without image splicing, which greatly improves the field of view and measurement efficiency.

[0021] 2. Compared with the traditional lateral scanning interferometry (LSI) technology, the present invention adopts the Linnik interferometer objective lens. The advantage of the Linnik interferometer objective lens is that it can use an objective lens with a magnification of 100 times or more, and the tilt angle α of the reflector is adjustable. The tilt angle α of the reflector 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 morphology measurement more accurate and having a larger measurement range.

[0022] 3. Different from the traditional LSI technology, whose linear platform speed is generally in the order of um / s, the flying-type three-dimensional white-light interferometric profile measurement system proposed in the present invention adopts a high-speed camera of 10,000 frames, and the speed of the linear translation stage can reach the order of mm / s. It can meet the needs of high-speed moving samples without stopping, and can collect images and perform processing and calculations in a flying-type manner, effectively improving the image acquisition efficiency, improving the efficiency of three-dimensional profile measurement, and reducing environmental interference and errors that may be introduced by long-term scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the flying-shot three-dimensional white-light interferometric profile 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 It is a schematic diagram of the sample plane interference signal provided by the present invention;

[0026] Figure 4 It 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 It is a schematic diagram of the deviation of the peak point of the interference signal provided by the present invention;

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

[0029] Figure 7 It is a comparison diagram 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 lens, 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-reflector, 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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 interferometric profiling system, which can achieve high-speed, high-precision, large field of view and large measurement range three-dimensional profiling measurement, and is suitable for continuous and 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 Kohler illumination system 100, a Linnik interference objective lens 200, an imaging lens 11 and a high-speed camera 12; the Linnik interference objective lens 200 includes 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 Kohler 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 light path 14.

[0034] Lens 1 4 and lens 2 6 conjugate the light filtered by aperture diaphragm 3 to the rear focal plane of objective lens 1 8, and the light of field diaphragm 5 is conjugate to the sample plane through lens 2 6 and objective lens 1 8; 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 by 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 light source 1 uses an LED illumination light source with a wavelength of 455nm and a bandwidth of 18nm, and the model is ThorlabsM455L4. The objective lens 1 8 and the objective lens 2 9 use an objective lens with a NA of 0.5 and a magnification of 50, and the model is Olympus LMPLFLN 50X. The linear displacement stage 13 uses an electric displacement stage with a stroke of 25mm, and the model is Thorlabs PT3 / M-Z9. The moving speed V of the linear displacement 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 high-speed camera with a resolution of 1280×800, a pixel size of 9um / pixel, and a maximum frame rate of 22500fps, and the model is Revealer GR220M. The series of images collected by the high-speed camera 12 are saved on the computer, and then the three-dimensional morphology of the sample is restored through image processing and algorithm calculation.

[0036] like Figure 3 As shown, 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). The height information (h1-h2) of the measured surface is calculated by identifying and extracting the coordinates of the peak point, and the height information of each point on the measured surface is extracted to integrate the three-dimensional morphology distribution of the measured surface. Therefore, the three-dimensional morphology 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 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 the measured peak point (envelope peak point) has a deviation of Δz from 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 of the image. When the sample moves horizontally, the relationship between the sampling interval Δx and the tilt angle α of the reflector 10 is as shown in Figure 5 shown.

[0038] In order to verify the feasibility of the 3D profile 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 profile measurement system proposed in the present invention obtained a 3D profile 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 measurement system proposed by the present invention is compared with the three-dimensional morphology measurement results of the commercial white light interferometer, the same feature of the sample is measured and the height information of the same section is extracted. It can be concluded that the measurement system provided by the present invention is close to the measurement results 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 the traditional LSI technology (tens of nanometers). Therefore, the measurement accuracy of the measurement system provided by the present invention is significantly improved compared with the traditional LSI technology, and the measurement efficiency is also higher than that of the commercial white light interferometer. The system can realize continuous and non-stop rapid scanning and high-precision three-dimensional morphology measurement of the surface of large-area micro-nano products, 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 only 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 protection scope of the present invention.

Claims

1. A flying three-dimensional white light interferometry profile measurement system, characterized in that: The invention comprises a linear displacement stage (13), a Kohler illumination system (100), a Linnik interference objective lens (200), an imaging lens (11) and a high-speed camera (12); the Linnik 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. A flying-type three-dimensional white-light interferometry profilometry system as claimed in claim 1, characterized in that: The Kohler illumination system (100) comprises an illumination light source (1), a condenser 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. A flying-type three-dimensional white-light interferometry profilometry system as claimed in 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. A flying-type three-dimensional white-light interferometry profilometry system as claimed in 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 rear 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 diaphragm (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 model and magnification parameter settings 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 vertically 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 displacement 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 um / 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.

Images