MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy

Abstract

The invention belongs to the technical field of optical measurement, and relates to an MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy, which comprises a red light super-radiation light-emitting diode light source, a wire grid type beam splitter, an objective lens and a CCD, and is characterized in that a linear polarizer, a half-wave plate and the wire grid type beam splitter are fixedly arranged on a light path emitted by a red light super-radiation light-emitting diode; a half-wave plate, a beam expanding lens group, a plano-convex lens, a beam splitter prism, an objective lens and a sample table are fixedly arranged on an object light path in sequence, a reflector is arranged on a vertical light path, and an optical delay line, the beam expanding lens group and the plano-convex lens are fixedly arranged on a reference light path; after the reference light passes through the reflector and the beam splitter prism, the reference light interferes with the object light reflected by the beam splitter prism on the CCD and is observed. According to the invention, the hologram of the MEMS device under high-frequency vibration can be acquired, and the surface topography of the MEMS device is obtained through computer rapid phase unwrapping, so that the purpose of observing fatigue evolution of the MEMS structure in real time is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical measurement, and particularly relates to a MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy. BACKGROUND

[0002] With the continuous development of micro-nano scale processing technology, especially the development of micro-electro-mechanical system (MEMS), the position of micro-nano measurement becomes more and more important. MEMS has micro-nano scale electronic structure and mechanical structure, and many MEMS structures have high force sensitivity. Traditional contact measurement is easy to cause damage to the structure of the MEMS to a certain extent, thereby affecting the performance of the MEMS. Digital holographic microscopy as a non-contact optical interference measurement method can quantitatively obtain the phase distribution of the surface of the MEMS device by using the reflected light of the surface of the MEMS device, thereby avoiding damage to the MEMS device. The off-axis digital holographic microscopy can reproduce the object wave front of the measured MEMS device by using one interference hologram, so that the purpose of fast and real-time measurement is achieved.

[0003] In real-time observation of the fatigue evolution law of the MEMS structure, the measured MEMS device is usually in a periodic vibration or reciprocating motion state under the fatigue test excitation, and the motion frequency may be from several hertz to several thousand hertz. In the prior art, the off-axis digital holographic collection is usually carried out by using conventional continuous light illumination. However, this method will cause obvious motion blur in the exposure time due to the dynamic displacement of the MEMS structure, thereby causing the contrast of the hologram to decrease, and seriously affecting the quantitative measurement accuracy of the micro deformation in the fatigue evolution process. SUMMARY

[0004] The application aims at overcoming the defects in the prior art, and provides a MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy.

[0005] The application solves the technical problem by the following technical scheme:

[0006] The MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy comprises a red light super-radiation light-emitting diode light source, a line grating type beam splitter, an objective lens and a CCD camera.

[0007] A linear polarizer and a first half-wave plate are sequentially fixed on a red light path of the red superluminescent light emitting diode light source, so that the red light emitted by the red superluminescent light emitting diode light source is converted into linearly polarized light in a certain direction after passing through the linear polarizer and the first half-wave plate, the linear grating beam splitter is fixed behind the first half-wave plate and used for splitting the linearly polarized light into a horizontal light beam and a vertical light beam, a second half-wave plate is fixed on the vertical light beam and used for rotating the polarization direction of the vertical light beam by 90° and forming a first light path, a first plano-concave lens, a first plano-convex lens, a second plano-convex lens, a light splitting prism, an objective lens, an environmental cavity and a sample are sequentially fixed on the first light path, so that the first light path passing through the first plano-concave lens and the first plano-convex lens to form an expansion lens group is focused into a spherical wave by the second plano-convex lens, then is incident on the objective lens and is collimated to the surface of the sample placed in the environmental cavity, the surface of the sample reflects the light, the reflected light is magnified by the objective lens and is reflected by the light splitting prism, and then the light path perpendicular to the first light path is the object light;

[0008] A first mirror is installed on the light path of the horizontal light beam and used for reflecting the light path of the horizontal light beam by 90° and forming a second light path, a knife-edge right-angle prism, a displacement table and a right-angle prism are sequentially fixed on the second light path to form an optical delay line, which is used for adjusting the optical path difference between the second light path and the first light path, a second plano-concave lens, a third plano-convex lens, a fourth plano-convex lens and a second mirror are sequentially fixed behind the optical delay line, the second light path passes through the second plano-concave lens and the third plano-convex lens to form an expansion lens group, is expanded and is focused into a spherical wave by the fourth plano-convex lens, and then is reflected by 90° by the second mirror and is incident on the light splitting prism, and the light path transmitted by the light splitting prism is the reference light;

[0009] The CCD camera is used for receiving the light intensity after the object light and the reference light interfere with each other.

[0010] In the above technical solution, the full width at half maximum of the red superluminescent light emitting diode light source is .

[0011] In the above technical solution, the red superluminescent light emitting diode light source can perform stroboscopic illumination, the stroboscopic frequency is , and the minimum stroboscopic pulse width is .

[0012] In the above technical solution, the first mirror and the second mirror are the same and are mirrors for visible light.

[0013] In the above technical solution, the first half-wave plate and the second half-wave plate are the same, and the applicable wavelength range of the first half-wave plate is .

[0014] In the above technical solution, the applicable wavelength range of the linear grating beam splitter is , extinction ratio .

[0015] In the above technical solution, the stroke of the displacement table is .

[0016] In the above technical solution, the first plano-concave lens is same as the second plano-concave lens.

[0017] In the above technical solution, the first plano-convex lens is same as the third plano-convex lens.

[0018] In the above technical solution, the second plano-convex lens is same as the fourth plano-convex lens.

[0019] In the above technical solution, the objective lens is an infinite far correction objective lens for visible light, and the magnification is times.

[0020] In the above technical solution, the CCD camera is a black and white CCD camera sensor for visible light.

[0021] In the above technical solution, the included angle between the object light and the reference light is , .

[0022] The advantages and beneficial effects of the present application are:

[0023] 1. Based on off-axis digital holographic microscopy, the MEMS structure fatigue evolution law real-time observation device can collect off-axis holograms of MEMS devices, reconstruct the object wave front through a computer, and obtain the surface topography information of the MEMS device through fast phase unwrapping, so as to achieve the purpose of real-time observation.

[0024] 2. Based on the stroboscopic vibration measurement technology, the MEMS structure fatigue evolution law real-time observation device can use periodic pulse illumination of the light source, and the light source pulse and the motion period of the MEMS structure are strictly synchronized, and only when the MEMS structure moves to a specific phase, the exposure is triggered to obtain a clear hologram equivalent to static observation. By adjusting the synchronization phase successively, the purpose of continuously collecting holographic data of the MEMS structure at different times during the fatigue cycle can be achieved.

[0025] 3. The MEMS structure fatigue evolution law real-time observation device realizes the combination of off-axis digital holographic microscopy and stroboscopic vibration measurement technology, which can not only measure the surface topography of the static MEMS device in real time, but also measure the fatigue evolution of the MEMS device under test excitation in real time. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the MEMS structure fatigue evolution law real-time observation device.

[0027] Figure 2 The off-axis hologram of the 44nm standard step (VLSI, SHS-440-QC) collected by the real-time observation device for fatigue evolution law of the MEMS structure of the application;

[0028] Figure 3 The off-axis hologram of the 44nm standard step (VLSI, SHS-440-QC) collected by the real-time observation device for fatigue evolution law of the MEMS structure of the application;

[0029] Figure 4 The off-axis hologram of the 44nm standard step (VLSI, SHS-440-QC) collected by the real-time observation device for fatigue evolution law of the MEMS structure of the application;

[0030] Figure 5 The gray scale image of the surface topography of the measured 44nm step;

[0031] Figure 6 The three-dimensional image of the surface topography of the measured 44nm step;

[0032] Figure 7 The off-axis hologram of the 44nm standard step (VLSI, SHS-440-QC) collected by the real-time observation device for fatigue evolution law of the MEMS structure of the application;

[0033] Figure 8 The motion law time sequence diagram of the ROI area of the measured AFM probe in a vibration cycle.

[0034] 1: red light super radiation light emitting diode light source, 2: linear polarizer, 3: first half-wave plate, 4: linear grating beam splitter, 5: first mirror, 6: displacement table, 7: right-angle prism, 8: knife-edge right-angle prism, 9: second half-wave plate, 10: first plano-concave lens, 11: first plano-convex lens, 12: second plano-convex lens, 13: second plano-concave lens, 14: third plano-convex lens, 15: fourth plano-convex lens, 16: second mirror, 17: beam splitter prism, 18: objective lens, 19: sample, 20: CCD camera, 21: environmental chamber. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below in combination with the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0036] The specific implementation of the application will be described in detail below in combination with specific embodiments.

[0037] Embodiment 1

[0038] The application discloses a MEMS fatigue evolution law observation device based on off-axis digital holographic microscopy.

[0039] A linear polarizer 2 and a first half-wave plate 3 are sequentially fixed on a red light path of the red super radiation light emitting diode light source 1, so that the red light emitted from the red super radiation light emitting diode light source 1 is converted into linearly polarized light along a certain direction after passing through the linear polarizer 2 and the first half-wave plate 3.

[0040] The linearly polarized light is split into a horizontal light beam and a vertical light beam by the linear grating beam splitter 4 fixed behind the first half-wave plate 3, a second half-wave plate 9 is fixed on the vertical light path, the second half-wave plate 9 is used for rotating the polarization direction of the vertical light beam by 90° and forming a first light path, a first plano-concave lens 10, a first plano-convex lens 11, a second plano-convex lens 12, a light splitting prism 17, an objective lens 18, an environmental cavity 21 and a sample 19 are sequentially fixed on the first light path, so that the first light path passing through the first plano-concave lens 10 and the first plano-convex lens 11 to form an expansion lens group is focused into a spherical wave by the second plano-convex lens 12, and then is incident on the objective lens 18 and is collimated to be emitted onto the surface of the sample 19 placed in the environmental cavity 21, the surface of the sample 19 is reflected, the reflected light is magnified by the objective lens 18, and then is reflected by the light splitting prism 17 and is perpendicular to the first light path.

[0041] A first reflector 5 is installed on the light path of the horizontal light beam, the first reflector 5 is used for reflecting the light path of the horizontal light beam by 90° and forming a second light path, a knife-edge right-angle prism 8, a displacement table 6 and a right-angle prism 7 are fixed on the second light path to form an optical delay line, the optical delay line is used for adjusting the optical path difference between the second light path and the first light path, a second plano-concave lens 13, a third plano-convex lens 14, a fourth plano-convex lens 15 and a second reflector 16 are sequentially fixed behind the optical delay line, the second light path is expanded by an expansion lens group formed by the second plano-concave lens 13 and the third plano-convex lens 14, and then is focused into a spherical wave by the fourth plano-convex lens 15 and is reflected by the second reflector 16 by 90° to be incident on the light splitting prism 17, and a light path transmitted by the light splitting prism 17 is reference light; the CCD camera 20 is used for receiving the light intensity after the interference of the object light and the reference light.

[0042] Embodiment 2

[0043] On the basis of the embodiment 1, the full width at half maximum of the red super radiation light emitting diode light source 1 is The red super radiation light emitting diode light source 1 can perform stroboscopic illumination, the stroboscopic frequency is , and the minimum stroboscopic pulse width is ; the first reflector 5 and the second reflector 16 are the same, and are visible light reflectors; the first half-wave plate and the second half-wave plate are the same, and the applicable wavelength range of the first half-wave plate is The applicable wavelength range of the wire grid beam splitter 4 is , the extinction ratio is ; the stroke of the displacement stage 6 is ; the first plano-concave lens 10 is the same as the second plano-concave lens 13; the first plano-convex lens 11 is the same as the third plano-convex lens 14; the second plano-convex lens 12 is the same as the fourth plano-convex lens 15; the objective lens 18 is an infinite far correction objective lens for visible light, and the magnification is times; and the CCD camera is a black and white CCD camera sensor for visible light.

[0044] Example 3

[0045] On the basis of Example 2, the linear polarizer 1 is rotated to maximize the intensity of the outgoing light passing through the linear polarizer 1, the first half-wave plate 3 is rotated to make the intensities of the object light and the reference light substantially the same, the second half-wave plate 9 is rotated to make the polarization directions of the object light and the reference light consistent, the distance between the first plano-concave lens 10 and the first plano-convex lens 11 is 100 mm, the second plano-convex lens 12 is focused on the back focal plane of the objective lens, the distance between the second plano-concave lens 13 and the third plano-convex lens 14 is 100 mm, the focal point of the first light path passing through the second plano-convex lens 12 and reflected by the beam splitter is on the same plane as the focal point of the second light path passing through the fourth plano-convex lens 15 and reflected by the second mirror 16, the second mirror 16 is adjusted so that the included angle between the object light and the reference light is , , and the displacement stage 6 is adjusted to an appropriate distance so that the interference fringes are clear.

[0046] The following describes the test of a standard 44 nm step (VLSI, SHS-440-QC) as an example. The specific models and specifications of the components used in the following test are as follows:

[0047]

[0048] Test results:

[0049] The hologram of the measured sample is collected by the CCD camera 20, and the sample surface topography information is calculated by digital holographic phase unwrapping by a computer combined with the relationship between the phase and the sample surface topography. The specific operation steps are as follows:

[0050] First, the distance between the sample surface and the objective lens is adjusted to the working distance of the objective lens, so that the objective lens can clearly image the sample surface. At this time, the displacement stage is adjusted so that the interference fringes are clear and cover the whole field. The off-axis image plane hologram of the measured sample is collected (as shown in Figure 2 ), and the intensity distribution of the hologram collected by the sample is

[0051]

[0052] Among them, is the complex conjugate of the complex amplitude of the object light, is the complex conjugate of the complex amplitude of the reference light, is the complex conjugate of the complex amplitude of the object light, is the complex conjugate of the complex amplitude of the reference light.

[0053] Since the reconstruction plane of the image plane hologram is the image plane, the diffraction propagation calculation of the light wave is not required, and the interference term is directly separated , that is, the object light wave front can be reproduced. The specific method is to perform Fourier transform on the off-axis image plane hologram of the measured sample, filter it with a circular filter window (as shown in Figure 3 , the red selected area is the position of the circular filter window), and then perform inverse Fourier transform to obtain the interference term.

[0054] Record the hologram of the smooth part of the measured sample (as shown in Figure 4 ), and the light intensity distribution of the hologram of the smooth part is

[0055]

[0056] wherein, is the complex amplitude of the object light of the smooth area, is the complex conjugate of the complex amplitude of the object light of the smooth area, and the interference term is obtained by using the same circular filter window according to the above steps.

[0057] By multiplying the interference term of the hologram of the measured sample with the complex conjugate of the interference term of the hologram of the smooth part of the measured sample, the purpose of correcting the phase distortion of the holographic plane can be achieved, that is:

[0058]

[0059] wherein, is the sample phase, and the unwrapping phase is obtained by performing phase unwrapping operation on the sample phase. The specific steps of this step can be found in the reference: Wang Fei. Research on the theory and algorithm of digital holographic microscopy[D]. Tianjin University, 2012.

[0060] The surface topography of the final sample is . Wherein, is the center wavelength of the red super radiation light emitting diode (650 nm), Figure 5 and Figure 6 are the surface topography gray scale diagram (Fig. Figure 5 ) and the surface topography three-dimensional diagram (Fig. Figure 6 ) of the measured sample, respectively. The specific steps of this step can be found in the reference: Zeng Yanan. Research on micro-nano geometric measurement method based on digital holographic microscopy[D]. Tianjin University, 2016.

[0061] Example 4

[0062] On the basis of Embodiment 3, the red superluminescent diode light source is driven by a stroboscopic signal with a stroboscopic frequency of 1 kHz and a stroboscopic pulse width of 1 us, a piezoelectric ceramic is used to apply a 1 kHz sinusoidal excitation signal to the measured AFM probe, and the excitation signal is strictly synchronized with the stroboscopic driving signal. The duration of the low level stage of the working trigger signal of the CCD camera is not less than 170 us, and the stroboscopic driving signal illuminates the same phase of the excitation signal multiple times within the exposure time of the camera until the imaging requirements are met. Figure 7 A certain phase off-axis hologram of the measured AFM probe collected under stroboscopic illumination (the red area is the ROI area), Figure 8 A time sequence diagram of the motion law of the ROI area of the measured AFM probe within one vibration period.

[0063] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. This application is intended to cover any variations, uses or adaptations of the disclosure other than those expressly disclosed herein and including combinations of the disclosed features with other present or future technologies that are within the scope of the general inventive concepts. The specification and examples are to be regarded as illustrative only, and the true scope and spirit of the disclosure are indicated by the claims.

Claims

1. A MEMS fatigue evolution observation device based on off-axis digital holographic microscopy, characterized in that: It includes a red superluminescent diode light source (1), a wire-grid beam splitter (4), an objective lens (18), and a CCD (20), among which, A linear polarizer (2) and a first half-wave plate (3) are sequentially fixed in the red light path emitted by the red light superluminescent diode light source (1). The red light emitted by the red light superluminescent diode light source (1) is converted into linearly polarized light along a certain direction after passing through the linear polarizer (2) and the first half-wave plate (3). The wire grating beam splitter (4) is fixed after the first half-wave plate (3) and is used to split the linearly polarized light into a horizontal beam and a vertical beam. The second half-wave plate (9) is fixed on the vertical beam and is used to rotate the polarization direction of the vertical beam by 90° to form a first optical path. The first plano-concave lens (10), the first plano-convex lens (11), the second plano-convex lens (12), the beam splitter (17), the objective lens (18), the ambient cavity (21), and the sample (19) are fixed in sequence on the first optical path so that the first optical path formed by the first plano-concave lens (10) and the first plano-convex lens (11) is focused into a spherical wave by the second plano-convex lens (12). The spherical wave is incident on the objective lens (18) and collimated and exited onto the surface of the sample (19) placed in the ambient cavity (21). After being reflected by the surface of the sample (19), the light path is magnified by the objective lens (18) and reflected by the beam splitter (17) and is perpendicular to the first optical path, which is the object beam. A first reflecting mirror (5) is installed on the optical path of the horizontal beam to reflect the optical path of the horizontal beam by 90° to form a second optical path. An optical delay line composed of a knife-edge right-angle prism (8), a displacement stage (6), and a right-angle prism (7) is fixed on the second optical path. The optical delay line is used to adjust the optical path difference between the second optical path and the first optical path. A second plano-concave lens (13), a third plano-convex lens (14), a fourth plano-convex lens (15), and a second reflecting mirror (16) are fixed in sequence after the optical delay line. The second optical path is expanded by a beam-expanding lens group composed of the second plano-concave lens (13) and the third plano-convex lens (14), and is focused into a spherical wave by the fourth plano-convex lens (15) and then reflected by the second reflecting mirror (16) by 90° to be incident on a beam-splitting prism (17). The optical path transmitted by the beam-splitting prism (17) is the reference light. The CCD (20) is used to receive the light intensity after the interference of the object light and the reference light.

2. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The full width at half maximum (FWHM) of the red superluminescent diode light source (1) is .

3. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The red-light superluminescent diode light source (1) can provide strobe illumination with a flicker frequency of [frequency value missing]. The minimum flicker pulse width is .

4. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The first reflector (5) is the same as the second reflector (16), and is a visible light reflector; The first half-wave plate (3) is the same as the second half-wave plate (9), and the applicable wavelength range of the first half-wave plate (3) is... ; The applicable wavelength range of the linear beam splitter (4) is: Extinction ratio ; The stroke of the displacement stage (6) is ; The first plano-concave lens (10) is the same as the second plano-concave lens (13); The first plano-convex lens (11) is the same as the third plano-convex lens (14); The second plano-convex lens (12) is the same as the fourth plano-convex lens (15).

5. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The objective lens (18) is a visible light infinity-corrected objective lens with a magnification of [missing information]. times.

6. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The CCD (20) is a black and white CCD sensor for visible light.

7. The MEMS fatigue evolution observation device based on off-axis digital holographic microscopy according to claim 1, characterized in that: The angle between the object beam and the reference beam is , .

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